29618940 umts overview book
TRANSCRIPT
UMTS OVERVIEW
Contents
CHAPTER 1: UMTS, THE DEFINITION OF A NEW ERA.............................................................................1
1.1 INTRODUCTION ..................................................................................................................................................1
1.2 BACKGROUND AND STANDARDISATION...................................................................................................................1
1.2.1 Background in Europe...........................................................................................................................1
1.2.2 Background in Japan.............................................................................................................................3
1.2.3 Background in China.............................................................................................................................4
1.2.4 Creation of 3GPP...................................................................................................................................4
1.2.5 Creation of 3GPP2.................................................................................................................................5
1.3 IMT-2000 AND UMTS ...................................................................................................................................6
1.3.1 IMT-2000 Process in ITU......................................................................................................................6
1.3.2 UMTS ....................................................................................................................................................8
1.4 UMTS AS THE 3RD GENERATION SYSTEM..........................................................................................................12
1.4.1 Main Service Differences Between 2G and 3G....................................................................................12
1.4.2 New Roles and Relationships for UMTS..............................................................................................13
1.4.3 Work Regulations.................................................................................................................................14
1.4.4 UMTS Services and Applications.........................................................................................................14
1.4.5 UMTS Advanced Concepts...................................................................................................................15
1.4.6 Network Operators’ Functions...........................................................................................................15
1.4.7 Technological Progress Impact...........................................................................................................16
CHAPTER 2: ARCHITECTURE OVERVIEW................................................................................................17
2.1 GENERAL OVERVIEW OF THE SYSTEM..................................................................................................................17
2.2 USER EQUIPMENT (UE)....................................................................................................................................17
2.2.1 Schematic of the Receiver for UTRAN - Outdoor................................................................................19
2.3 THE ACCESS NETWORK: UTRAN.....................................................................................................................20
2.3.1 RNS Architecture..................................................................................................................................20
2.3.2 UTRAN Architecture............................................................................................................................21
2.4 CORE NETWORK...............................................................................................................................................22
2.4.1 Serving Network...................................................................................................................................23
2.4.2 Home Network......................................................................................................................................23
2.4.3 Transit Network....................................................................................................................................23
2.4.4 Interfaces and Their Function..............................................................................................................24
2.5 MOBILITY........................................................................................................................................................24
CHAPTER 3: CDMA TECHNIQUE..................................................................................................................27
3.1 INTRODUCTION.................................................................................................................................................27
3.2 ACCESS METHODS FDMA, TDMA, CDMA, FDD VS. TDD...........................................................................27
3.2.1 Frequency Division Multiple Access (FDMA).....................................................................................27
3.2.2 Time Division Multiple Access (TDMA)..............................................................................................28
3.2.3 Code Division Multiple Access (CDMA).............................................................................................29
3.2.4 FDD vs. TDD.......................................................................................................................................30
3.3 INTRODUCTION TO SPREADING AND MODULATION.................................................................................................30
3.3.1 Orthogonal Codes................................................................................................................................32
3.3.2 RAKE Receiver.....................................................................................................................................35
3.3.3 Spread Spectrum Goals........................................................................................................................37
3.3.4 Code Properties...................................................................................................................................37
3.4 SOFT AND HARD HANDOVER..............................................................................................................................38
3.4.1 Handover..............................................................................................................................................38
3.4.2 Soft Handover......................................................................................................................................38
3.4.3 Softer Handover...................................................................................................................................39
3.5 POWER CONTROL..............................................................................................................................................39
3.5.1 Inner Loop Power Control - Uplink.....................................................................................................42
3.5.2 Outer Loop Power Control (SIR target adjustment) -Uplink..............................................................43
3.5.3 Open Loop Power Control - Uplink.....................................................................................................43
3.5.4 Inner Loop Power Control - Downlink................................................................................................44
3.5.5 Outer Loop Power Control - Downlink...............................................................................................44
3.5.6 Open Loop Power Control - Downlink................................................................................................45
CHAPTER 4: AIR INTERFACE........................................................................................................................46
4.1 RADIO TRANSMISSION AND RECEPTION................................................................................................................46
4.1.1 Frequency Band...................................................................................................................................46
4.1.2 Channel Arrangement .........................................................................................................................46
4.1.3 Tx-Rx Frequency Separation ..............................................................................................................46
4.1.4 Terminal Service Classes ....................................................................................................................47
4.1.5 Receiver Requirements.........................................................................................................................47
4.1.6 Diversity Characteristics......................................................................................................................47
4.2 LOGICAL, PHYSICAL AND TRANSPORT CHANNELS..................................................................................................48
4.2.1 Transport Channels:............................................................................................................................49
4.2.2 Physical Channels:...............................................................................................................................50
4.2.3 Mapping of Transport Channels to Physical Channels.......................................................................57
4.3 SPREADING, SCRAMBLING AND MODULATION.......................................................................................................58
4.3.1 Uplink Spreading, Scrambling and Modulation..................................................................................58
4.3.2 Downlink Spreading, Scrambling and Modulation.............................................................................61
4.4 TRANSPORT CHANNEL CODING AND MULTIPLEXING CHAIN....................................................................................62
4.4.1 Channel Coding...................................................................................................................................64
4.4.2 Inner Inter-Frame Interleaving...........................................................................................................66
4.4.3 Rate Matching......................................................................................................................................66
4.4.4 Transport-Channel Multiplexing.........................................................................................................67
4.4.5 Inner Intra-Frame Interleaving...........................................................................................................67
4.5 SERVICE MULTIPLEXING....................................................................................................................................67
4.6 TRAFFIC CASES (EXAMPLES).............................................................................................................................69
4.6.1 Continuous Transmission in Uplink with Variable Rate......................................................................69
4.6.2 Discontinuous Transmission (DTx) in Downlink with Variable Rate (1)............................................69
4.6.3 Discontinuous Transmission (DTx) in Downlink with Variable Rate (2)............................................70
4.7 INITIAL CELL SEARCH.......................................................................................................................................70
4.7.1 Step 1: Slot Synchronisation................................................................................................................71
4.7.2 Step 2: Frame Synchronisation and Code Group Identification.........................................................71
4.7.3 Step 3: Scrambling Code Identification...............................................................................................72
4.7.4 Idle Mode Cell Search..........................................................................................................................72
4.7.5 Active Mode Cell Search......................................................................................................................73
4.8 PACKET ACCESS...............................................................................................................................................73
4.8.1 Common Channel Packet Access.........................................................................................................73
4.8.2 Dedicated Channel Single Packet Transmission.................................................................................74
4.8.3 Dedicated Channel Multi-Packet Transmission..................................................................................74
CHAPTER 5: RADIO THEORY........................................................................................................................75
5.1 INTRODUCTION.................................................................................................................................................75
5.1.1 Radio Waves and Modulations............................................................................................................75
5.1.2 Access Methods....................................................................................................................................77
5.2 RADIO TRANSMISSION PROPERTIES AND PROBLEMS...............................................................................................78
5.2.1 Needed vs. Available Capacity ............................................................................................................78
5.2.2 Path Loss..............................................................................................................................................79
5.2.3 Shadowing............................................................................................................................................79
5.2.4 Multi-Path Propagation.......................................................................................................................80
5.2.5 Time Dispersion...................................................................................................................................81
5.3 RADIO TRANSMISSION OPTIMISATIOIN TECHNIQUES...............................................................................................81
5.3.1 Access Methods: Capacity vs Interference..........................................................................................81
5.3.2 Diversity...............................................................................................................................................83
5.3.3 Error Detection and Correction...........................................................................................................84
CHAPTER 6: USER EQUIPMENT (UE)...........................................................................................................88
6.1 TERMINALS IN THE GENERAL UMTS SYSTEM.....................................................................................................88
6.1.1 User Equipment Domain......................................................................................................................89
6.2 APPLICATIONS OF THE UE.................................................................................................................................90
6.3 MULTIMEDIA USER EQUIPMENT..........................................................................................................................91
6.4 UMTS SUBSCRIBER IDENTITY MODULE (USIM)................................................................................................93
6.5 TECHNOLOGY OF THE TERMINALS.......................................................................................................................95
CHAPTER 7: UMTS TERRESTRIAL RADIO ACCES NETWORK (UTRAN)..........................................98
7.1 INTRODUCTION.................................................................................................................................................98
7.2 UTRAN MAIN ASPECTS..................................................................................................................................98
7.2.1 General Principles ..............................................................................................................................98
7.2.2 Capabilities .........................................................................................................................................99
7.2.3 UTRAN and GSM BSS (GSM Base Station Subsystem).....................................................................100
7.3 UTRAN SYSTEM ARCHITECTURE....................................................................................................................100
7.3.1 UMTS General System Architecture .................................................................................................100
7.3.2 UTRAN Architecture..........................................................................................................................100
7.4 UTRAN NODES ..........................................................................................................................................101
7.4.1 Node B................................................................................................................................................101
7.4.2 The Radio Network Controller (RNC)...............................................................................................103
7.5 UTRAN INTERFACES ....................................................................................................................................103
7.5.1 General Principles for UTRAN Interfaces.........................................................................................104
7.5.2 Iu Interface.........................................................................................................................................104
7.5.3 Iur Interface.......................................................................................................................................106
7.5.4 Iub Interface.......................................................................................................................................109
7.5.5 UTRAN Internal Bearers....................................................................................................................110
7.6 UTRAN FUNCTIONS .....................................................................................................................................112
7.6.1 System Access Control.......................................................................................................................112
7.6.2 Radio Channel Ciphering / Deciphering...........................................................................................113
7.6.3 Mobility..............................................................................................................................................113
7.6.4 Radio Resource Management and Control........................................................................................116
7.7 IDENTIFIERS...................................................................................................................................................120
7.7.1 UTRAN identifiers .............................................................................................................................120
7.7.2 UE Identifiers ....................................................................................................................................120
7.8 UMTS QOS AND RAB.................................................................................................................................121
7.8.1 Quality of Service (QoS) ..................................................................................................................121
7.8.2 Radio Access Bearers (RAB)..............................................................................................................122
CHAPTER 8: CORE NETWORK....................................................................................................................124
8.1 INTRODUCTION...............................................................................................................................................124
8.2 GPRS, AN IMPORTANT STEPPING STONE TOWARDS A UMTS CORE NETWORK.....................................................124
8.3 UPGRADING THE GSM CORE FOR GPRS.........................................................................................................126
8.3.1 New Nodes for Packet Data...............................................................................................................126
8.3.2 Upgrades to Existing GSM Nodes......................................................................................................127
8.4 MOVING TO UMTS IN THE GSM/GPRS CORE...............................................................................................127
8.4.1 Cell-Based Transport Network...........................................................................................................130
8.5 UMTS CORE NETWORK PHASE 1 (RELEASE 99) REQUIREMENTS........................................................................130
CHAPTER 9: HANDOVER (DOWNLINK CASE EXAMPLE)...................................................................133
9.1 POSITION 1....................................................................................................................................................133
9.2 POSITION 2....................................................................................................................................................133
9.3 POSITION 3....................................................................................................................................................133
9.4 POSITION 4....................................................................................................................................................134
9.5 POSITION 5....................................................................................................................................................134
9.6 POSITION 6....................................................................................................................................................134
9.7 POSITION 7....................................................................................................................................................134
9.8 POSITION 8....................................................................................................................................................135
9.9 POSITION 9....................................................................................................................................................135
9.10 POSITION 10................................................................................................................................................135
CHAPTER 10: CELL PLANING......................................................................................................................136
10.1 INTRODUCTION TO CELL PLANNING.................................................................................................................136
10.2 DIFFERENT CELL TYPES................................................................................................................................136
10.3 STEPS IN THE CELL PLANNING PROCESS..........................................................................................................138
10.3.1 System Requirements:......................................................................................................................139
10.3.2 Define Radio Planning Guidelines:.................................................................................................139
10.3.3 Initial Cell Plan:..............................................................................................................................139
10.3.4 Surveys:............................................................................................................................................140
10.3.5 Individual Site Design and Parameter Setting:...............................................................................140
10.3.6 Implementation:...............................................................................................................................140
10.3.7 Launch of Commercial Service:.......................................................................................................140
10.3.8 On-going Testing, Analyses and Optimisation:...............................................................................141
10.3.9 System Growth.................................................................................................................................141
10.4 DIFFERENCES WITH 2G TDMA SYSTEMS - DEPLOYMENTS..............................................................................141
10.4.1 Exploiting Existing Networks...........................................................................................................141
10.4.2 Multi Service....................................................................................................................................141
10.4.3 New Air Interface.............................................................................................................................142
10.5 CALCULATION OF COVERAGE AND CAPACITY....................................................................................................142
10.5.1 Needed Input Parameters.................................................................................................................142
10.5.2 Uplink Design...................................................................................................................................143
10.5.3 Downlink Design..............................................................................................................................143
10.5.4 Co-Siting With GSM Case................................................................................................................144
CHAPTER 11: WORLD-WIDE CONSENSUS ON ADDITIONAL SPECTRUM FOR 3RD
GENERATION....................................................................................................................................................145
Glossary
Active Set:Set of radio links simultaneously involved in a specific communication service between an MS and aUTRAN.
Air Interface: The radio interface between a mobile communications handset and the base station.
Bandwidth: The information capacity of a communications resource, usually measured in bits per second. Alsosee Narrowband, Wideband and Broadband.
Broadband: A classification of the information capacity or bandwidth of a communication channel. Broadbandis generally taken to mean a bandwidth higher than 2 Mbit/s.
CDMA: Code Division Multiple Access. A multiple access technique used for CdmaOne and WCDMA airinterfaces.
Cell: The basic geographical unit of a cellular communications system.
Service coverage of a given area is based on an interlocking network of cells, each with a radio base station(transmitter/receiver) at its centre. The size of each cell is determined by the terrain and the number of users.
Geographical area served from one UTRAN Access Point. A cell is defined by a cell identity broadcast from theUTRAN Access Point.
Chiprate: Chiprate is the bit rate of the code/codes used for spreading. This is for helping us distinguishbetween user data or control data which is expressed in bit rate.
Coded Composite Transport Channel (CCTrCH): A data stream resulting from encoding and multiplexing ofone or several transport channels.
Drift RNS: The role an RNS can take with respect to a specific connection between an UE and UTRAN. AnRNS that supports the Serving RNS with radio resources when the connection between the UTRAN and the UEneed to use cell (s) controlled by this RNS is referred to as Drift RNS.
ETSI: European Telecommunications Standards Institute. A body formed by the European Commission in 1988to take over most of the standardisation work previously undertaken by CEPT. ETSI´s purpose is to definestandards that will enable the European market for telecommunications to function as a single market.
Fixed Wireless (or Fixed Cellular) Network: This apparent contradiction in terms signifies a cellular networkthat is set up to support fixed rather than mobile subscribers. Increasingly being used as a fast and economic wayto roll out modern telephone services, since it avoids the need for major cable-laying.
GPRS: GSM General Packet Radio Services. A data transmission technique that does not set up a continuouschannel from a portable terminal for the transmission and reception of data, but transmits and receives data inpackets. It makes very efficient use of available radio spectrum, and users may pay only for the volume of datasent and received.
GSM: Global System for Mobile Communications. Originally defined as a pan-European standard for a digitalcellular telephone network, to support cross-border roaming, GSM is now one of the world’s main digitalwireless standards. Uses TDMA air interface. Can be implemented in 900 MHz, 1800 MHz or 1900 MHzfrequency bands.
IMT-2000: The term used by the International Telecommunications Union for the specification for the projectedthird-generation wireless services.
Intelligent Network (IN): A capability in the public telecom network environment that allows new servicessuch as Free-phone and tele-voting to be developed quickly and introduced on any scale, from a local trial tonetwork-wide. Also implies a suitable network infrastructure.
Internet: The name given to the world-wide collection of networks and gateways using the TCP/IP protocol,that functions as a single, virtual network.
IP: Internet Protocol. (See also TCP/IP).
ISDN: Integrated Services Digital Network. A digital public telecommunications network in which multipleservices (voice, data, images and video) can be provided via standard terminal interfaces.
ITU: International Telecommunications Union.
Iu: The interconnection point (interface) between the RNS and the Core Network. It is also considered as areference point.
Iub: Interface between the RNC and the Node B.
Iur: Interface between two RNSs.
Logical Channel: A logical channel is a radio bearer, or part of it, dedicated for exclusive use of a specificcommunication process. Different types of logical channel are defined according to the type of informationtransferred on the radio interface.
MexE: Mobile station Execution Environment
Narrowband: A classification of the information capacity or bandwidth of a communication channel.Narrowband is generally taken to mean a bandwidth of 64 Kbit/s or lower.
Node B: A logical node responsible for radio transmission/reception in one or more cells to/from the UE.Terminates the Iub interface towards the RNC.
PCS: Personal Communications Service. A generic term for a mass-market mobile personal communicationsservice, independent of the technology used to provide it.
Physical Channel: In FDD mode, a physical channel is defined by code, frequency and, in the uplink, relativephase (I/Q). In TDD mode, code, frequency, and time-slot define a physical channel.
Physical Channel Data Stream: In the uplink, a data stream that is transmitted on one physical channel.
In the downlink, a data stream that is transmitted on one physical channel in each cell of the active set.
PSTN: Public Switched Telephone Network. The ordinary, wired, analogue telephone network.
Radio Access Bearer: The service that the access stratum provides to the non-access stratum for transfer of userdata between MS and CN.
Radio Access Network Application Part: Radio Network Signalling over the Iu.
Radio Cell: The area served by a radio base station in a cellular or cordless communications system. This iswhere the term "cellular" came from. Cell sizes range from a few tens of meters to several kilometres.
Radio Frame: A radio frame is a numbered time interval of 10ms duration used for data transmission on theradio physical channel. A radio frame is divided into 16 slots of 0.625 ms duration. The unit of data that ismapped to a radio frame (10ms time interval) may also be referred to as radio frame.
Radio Link: A set of (radio) physical channels that link an MS to a UTRAN access point.
Radio Link Addition: A [soft handover] procedure whereby a branch through a new [sector of a cell] is addedin case some of the already existing branches were using [sectors] of the same cell.
Radio Link Removal: A [soft handover] procedure whereby a branch through a new [sector of a cell] isremoved in case some of the remaining existing branches use [sectors of] that cell.
Radio Network Controller: This equipment in the RNS is in charge of controlling the use and the integrity ofthe radio resources.
Radio Network Subsystem: Either a full network or only the access part of a UMTS network offering theallocation and the release of specific radio resources to establish means of connection in between an UE and theUTRAN.
A Radio Network Subsystem is responsible for the resources and transmission/reception in a set of cells.
Radio Network Subsystem Application Part: Radio Network Signalling over the Iur.
Roaming: Ability of a cordless or mobile phone user to travel from location to location, with completecommunications continuity. Supported by a cellular network of radio base stations.
RLL/WLL: Radio in the Local Loop/Wireless Local Loop. The use of a radio access technology to linksubscribers into the fixed public telecom network. The radio link replaces the traditional wired local loop.
RRC Connection: A point-to-point bi-directional connection between RRC peer entities on the UE and theUTRAN sides, respectively. An UE has either zero or one RRC connection.
Serving RNS: A role an RNS can take with respect to a specific connection between an UE and UTRAN.There is one Serving RNS for each UE that has a connection between a UE and the UTRAN. The serving RNSterminates the Iu for this UE.
Signalling Connection: An assured-mode link between the user equipment and the core network to transferhigher layer information between peer entities in the non-access stratum.
Signalling Link: Provides an assured-mode link layer to transfer the MS_UTRAN signalling messages as wellas MS-Core Network signalling messages (using the signalling connection)
TCP/IP: Transmission Control Protocol/Internet Protocol. The data protocol used in the Internet.
TDMA: Time Division Multiple Access. A technique used for GSM, D-AMPS (IS-136) and PDC air interfaces.
TIA: Telecommunications Industry Association. The US telecom standars body.
Transport Channel:The channels that are offered by the physical layer to Layer 2 for data transport betweenpeer L1 entities are denoted as Transport Channels. Different types of transport channels are defined by how andwith which characteristics data is transferred on the physical layer, e.g. whether using dedicated or commonphysical channels are employed.
Transport Format: A combination of encoding, interleaving, bit rate and mapping onto physical channels.
Transport Format Indicator (TFI): A label for a specific Transport Format within a Transport Format Set.
Transport Format Set: A set of Transports Formats. For example, a variable rate DCH has a Transport FormatSet (one Transport Format for each rate), whereas a fixed rate DCH has a single Transport Format.
UMTS: Universal Mobile Telecommunications System. The European third-generation system, underdevelopment, under the auspices of ETSI.
UTRAN Access Point: The UTRAN-side end point of a radio link. A UTRAN access point is a cell.
User Equipment: A mobile Equipment with one several UMTS Subscriber Identity Module(s).
Wideband: A classification of the information capacity or bandwidth of a communication channel. Wideband isgenerally taken to mean a bandwidth between 64 Kbit/s and 2 Mbit/s.
Wideband CDMA (WCDMA): The air interface technology selected by the major Japanese mobilecommunications operators, and in January 1998 by ETSI, for wideband wireless access to support third-generation services. This technology is optimised to allow very high-speed multimedia services such as full-motion video, Internet access and videoconferencing.
World Wide Web (WWW): Name commonly applied to the global Internet for multimedia, graphics, sound,etc...
Abbreviations
ARQ Automatic Repeat Request
AAL Application Adaptation Layer
ATM Asynchronous Transfer Mode
BCCH Broadcast Control Channel
BER Bit Error Ratio
BLER Block Error Ratio
BS Base Station
BSS Base Station System
BPSK Binary Phase Shift Keying
CA Capacity Allocation
CAA Capacity Allocation Acknowledgement
CBR Constant Bit Rate
C- Control-CC Call Control
CCCH Common Control Channel
CCPCH Common Control Physical Channel
CCTrCH Coded Composite Transport Channel
CD Capacity De-allocation
CDA Capacity De-allocation Acknowledgement
CDMA Code Division Multiple Access
CN Core Network
CTDMA Code Time Division Multiple Access
CRC Cyclic Redundancy Check
DCA Dynamic Channel Allocation
DCH Dedicated Channel
DCCH Dedicated Control Channel
DC-SAP Dedicated Connection Service Access Point
DL Downlink
DPCH Dedicated Physical Channel
DPCCH Dedicated Physical Control Channel
DPDCH Dedicated Physical Data Channel
DRNS Drift RNS
DRX Discontinuous Reception
DTX Discontinuous Transmission
DS-CDMA Direct-Sequence Code Division Multiple Access
FACH Forward Access Channel
FDD Frequency Division Duplex
FDMA Frequency Division Multiple Access
FEC Forward Error Correction
FER Frame Error Ratio
HCS Hierarchical Cellular Structures
HO Handover
GMSK Gaussian Minimum Shift Keying
GSM Global System for Mobile Communication
ITU International Telecommunication Union
JD Joint Detection
kbps kilo-bits per second
L1 Layer 1 (physical layer)
L2 Layer 2 (data link layer)
L3 Layer 3 (network layer)
LAC Link Access Control
LLC Logical Link Layer
MA Multiple Access
MAC Medium Access Control
MAHO Mobile Assisted Handover
Mcps Mega Chip Per Second
ME Mobile Equipment
MM Mobility Management
MO Mobile Originated
MOHO Mobile Originated Handover
MS Mobile Station
MT Mobile Terminated
NRT Non-Real Time
ODMA Opportunity Driven Multiple Access
OVSF Orthogonal Variable Spreading Factor (codes)
PC Power Control
PCH Paging Channel
PDU Protocol Data Unit
PHY Physical layer
PhyCH Physical Channel
QoS Quality of Service
QPSK Quaternary Phase Shift Keying
PG Processing Gain
PRACH Physical Random Access Channel
PUF Power Up Function
RACH Random Access Channel
RANAP Radio Access Network Application Part
RF Radio Frequency
RLC Radio Link Control
RLCP Radio Link Control Protocol
RNC Radio Network Controller
RNS Radio Network Subsystem
RNSAP Radio Network Subsystem Application Part
RR Radio Resource
RRC Radio Resource Control
RRM Radio Resource Management
RT Real Time
RU Resource Unit
RX Receive
SAP Service Access Point
SCH Synchronisation Channel
SDCCH Stand-alone Dedicated Control Channel
SDU Service Data Unit
SF Spreading Factor
SIR Signal-to-Interference Ratio
SMS Short message Service
SP Switching Point
SRNS Serving RNS
TCH Traffic Channel
TDD Time Division Duplex
TDMA ime Division Multiple Access
TFI Transport Format Indicator
TPC Transmit Power Control
TX Transmit
U- User-UE User Equipment
UL Uplink
UMTS Universal Mobile Telecommunications System
USIM UMTS Subscriber Identity Module
UTRA UMTS Terrestrial Radio Access
UTRAN UMTS Terrestrial Radio Access Network
VA Voice Activity
VBR Variable Bit Rate
1 UMTS, the Definition of a New Era
Chapter 1: UMTS, the Definition of a New Era
1.1 Introduction
In 1992 the International Telecommunication Union (ITU) defined in World Administrative
Radio Conference (WAPC) global frequency bands for Future Public Land Mobile
Telecommunications Systems (FPLMTS). FPLMTS is standardised by the
Telecommunications Standardisation Sector (ITU-T) and the Radio-communications Sector
(ITU-R), formerly known as the CCITT and the CCIR. These FPLMTS bands were
identified as 1885-2025 MHz and 1980- 2010 MHz which included a special band identified
for satellite communication of 2170-2200 MHz.
1.2 Background and Standardisation
1.2.1 Background in Europe
1.2.1.1 ETSI
The European Telecommunications Standards Institute (ETSI) is a non-profit organisation in
charge to determine and produce the telecommunications standards. It is an open forum
made of Administrations, network operators, manufacturers, service providers, and users. In
total, 490 members from 34 countries are represented.
The members of ETSI are in charge to fix the work program standards in function of market
needs. ETSI produces voluntary standards; which are requested by those who subsequently
implement them, as the standards remain practical.
ETSIs work program is based upon, and is co-phased with, the activities of international
standardisation bodies, and mainly with ITU.
1 UMTS, the Definition of a New Era
ETSI consists of a General Assembly, a Board, a Technical Organisation and a Secretariat.
The technical standards are produced and approved by the Technical Organisation. It
encompasses ETSI Projects (EPs), Technical Committees (TCs) and Special Committees.
More than 3500 experts, in over 200 groups, are at present working for ETSI.
The central Secretariat of ETSI is located in Sophia Antipolis, a high tech research park in
the south of France.
1.2.1.2 ITU
The ITU is an international organisation (United Nations) within which governments and the
private sector co-ordinate global telecom networks and services. The ITU has its
headquarters in Geneva, Switzerland.
Samuel Morse did the first usher in the communications era on 24 May 1844, by sending the
first public message over a telegraph line between Washington and Baltimore. Barely ten
years later, telegraphy had become available to the general public. However, at this period
telegraph lines did not cross national frontiers because each country used a different system
and what is more, each had its own telegraph code to preserve the secrecy of its military and
political telegraph messages. Therefore, before being retransmitted over the telegraph
network of a neighbouring country, messages had to be transcribed, translated and handed
over the frontiers.
It is not surprising then, that agreements were made between countries to interconnect their
national networks together. But for each link numerous agreements were required. As a
conclusion, 20 European States decided to work together on a framework agreement,
deciding on common rules to standardise equipment to guarantee generalised
interconnection. They adopted a set of uniform operating instructions and came along to
common international tariff and accounting rules, which by the past were different from one
country to another.
The first International Telegraph Convention was signed by the 20 participating countries on
the 17 May of 1865 after two and a half months of negotiations, and the International
Telegraph Union was born.
1 UMTS, the Definition of a New Era
Since that time, the telecommunications progression has continued and advances have been
made.
With the invention in 1896 of wireless it was decided to convene on a preliminary radio
conference. In 1903 the conference would be held to study the question of international
regulations for radiotelegraph communications.
In 1920 sound was broadcasted at the studios of the Marconi Company. In 1927, the Union
allocated frequency bands to the various radio services existing at the time: fixed, maritime
and aeronautical mobile, broadcasting, amateur and experimental.
At the 1932 Madrid Conference the name was changed to the International
Telecommunication Union to reaffirm the whole scope of its responsibilities: wire, radio,
optical system or other electromagnetic system communications.
In 1959, the ITU set up a Study Group for the study of space radio communication.
In the changing world of telecommunications today new players constantly appear on the
international scene.
In the area of telecommunications, new trends are emerging: globalisation, deregulation,
restructuring, value added network services, convergence (of services as well as
technologies), intelligent networks and regional arrangements. Telecommunications have
become a key ingredient in many non-telecommunication services such as banking, tourism,
transportation and information services of various types.
The traditional role of telecommunications is being transformed every day with new service
dimensions.
1.2.2 Background in Japan
In Japan, the development of internationalisation, the integration of telecommunications and
broadcasting, and the promotion of businesses using radio waves required the need for an
organisation. In response to this need, on May 15, 1995, the Association of Radio Industries
and Businesses (ARIB) was established as a public service corporation with the support of
the Minister of Posts and Telecommunications.
1 UMTS, the Definition of a New Era
This organisation would proclaim the research & development of new radio systems and the
international standardisation of technical standards in the fields of telecommunications and
broadcasting.
1.2.3 Background in China
China Wireless Telecommunication Standard is the standard development organisation
responsible for wireless standardisation in China as approved by the Ministry of Information
Industry.
1.2.4 Creation of 3GPP
In November 1998, the standardisation organisations (ARIB, ETSI, T1, TTA and TTC)
involved in the creation of the 3rd Generation Partnership Project known as 3GPP. They all
agreed to co-operate for the production of technical specifications for a 3rd Generation
Mobile System based on the evolved GSM core networks and the radio access technologies
that they support (both FDD and TDD). In 1999 China Wireless Telecommunication
Standard (CWTS) joined the project.
At a meeting in July 1999, the Third Generation Partnership Project agreed to make
standards for the FDD and TDD modes following the recommendations from ITU IMT-
2000. According to the agreement, 3GPP will cover the technical issues related to the
development of FDD and TDD modes. The work will also include the inter-working
between the evolved ANSI-41 and GSM MAP platforms.
For a global harmonisation, 3GPP changed the chip to rate to 3.84 Mcps and adopted a new
downlink pilot structure. The complete 3G standards will enable global roaming and
seamless provisional.
The 3GPP have established a schedule of annual releases for the development of the
standards. Release 1999 will be completed by 31 December 1999 and will be first deployed
in early 2001 in Japan. Release 2000 will include Internet Protocol based networks and will
be rolled out in 2002. Further enhancements will be included in later releases.
1 UMTS, the Definition of a New Era
For more information about 3GPP see: www.3GPP.org .
The six standards development organisations are:
ARIB, www.arib.or.jp .
CWTS.
ETSI, www.etsi.org .
T1, www.t1.org .
TTA, www.tta.or.kr .
TTC, www.ttc.or.jp .
The tree market representations partners are:
The GSM Association represents 347 members which is comprised of GSM Network
Operators and Regulators with more than 165 million GSM subscribers in 133 countries. See
www.gsmworld.com .
The Global Mobile Suppliers Association, GSA, has a cross industry representation world-
wide of GSM infrastructure, terminals, customer care and billing suppliers. See
www.GSAssociation.org .
UMTS Forum represents 182 members from over 30 countries and content representing
operators, regulators, manufacturers, IT providers. See www.UMTS-Forum.org .
1.2.5 Creation of 3GPP2
Members of the ANSI board were concerned that the ETSI proposal was too limiting, and as
a result, established a 3G ad hoc committee to examine how all standards development
organisations (SDOs) could be involved. In June 1999, a meeting was held between this
ANSI ad hoc group and a delegation from ETSI in Seattle to further discuss how the 3GPP
could accommodate all industry participants.
3GPP 2 is an effort spearheaded by the International Committee of the American National
Standards Institute's (ANSI) board of director to establish a 3G Partnership Project (3GPP)
1 UMTS, the Definition of a New Era
for evolved ANSI/TIA/EIA-41, "Cellular Radio-telecommunication Intersystem Operations"
networks and related radio transmission technologies (RTTs).
This co-operation may result in either complete specifications or in agreed technical
elements, which the participating SDOs may submit to the ITU through their normal national
or regional processes.
The proposed 3G partnership is structured into two projects:
3GPP 1: Global specifications for GSM/MAP network evolution to 3G and the UTRA RTT.
3GPP 2: Global specifications for ANSI/TIA/EIA-41 network evolution to 3G and global
specifications for the RTTs supported by ANSI/TIA/EIA-41.
1.3 IMT-2000 and UMTS
1.3.1 IMT-2000 Process in ITU
In 1986, the ITU began its studies on International Mobile Telecommunications-2000 (IMT-
2000), when the availability of hand-held cellular phones offered the potential for global,
rather than National/Regional, land mobile systems.
IMT-2000 is an initiative of the ITU.
It will provide wireless access to the global telecommunication infrastructure through both
satellite and terrestrial systems, serving fixed and mobile users in public and private
networks.
With close to 5 million new mobile users a month, million a month in Japan alone, wireless
access will likely blast fixed access to global telecommunications very early in the 21st
century.
Future public land mobile telecommunication systems (FPLMTS) are aimed at providing
global wireless access around the year 2000, based primarily on the 2 GHz spectrum
identified at the 1992 World Administrative Radio Conference (WARC-92). Standardisation
of FPLMTS is one of the strategic priorities of the ITU.
1 UMTS, the Definition of a New Era
The acronym FPLMTS where changed to IMT-2000.
The International Mobile Telecommunication vision encompasses complementary satellite
and terrestrial components. Satellite systems have limited capacity due to power and radio
spectrum. Terrestrial macro, micro and pico cells complement global satellite coverage and
provide the frequency reuse necessary to serve a global market estimated to be of the order
of one billion wireless access users early in the 21st century.
IMT-2000 represents the satellite and terrestrial portion of IMT that will be available around
the year 2000 primarily based on the spectrum identified at 2 GHz.
The satellite component of IMT-2000, together with earlier global satellite systems in other
bands, will likely provide the first telephone in many rural villages. The terrestrial
infrastructure will then follow as demand increases.
There are two major areas of technological innovation that may impact on future wireless
systems: the first is multimedia, the second is software radio technology. What this really
means is that more and more is being done by software rather than by hardware.
The impact of microprocessors and chip will allow greatly increased flexibility in radio
equipment which is going to have a dramatic effect on what should, and what should not, be
standardised. In the past, radio standards were developed to a certain level of detail based on
channel, modulation and coding structures over the radio path because ¡t was difficult to
build flexible radios.
One of the key benefits of IMT-2000, as a true third generation system, will be its ability to
deal efficiently with audio-visual multimedia communications In the future the users
application will control how the negotiated radio bearer is used, which will require a very
different radio and control infrastructure.
IMT-2000 covers a very wide range of radio operating environments, all the way from the
satellite to indoor pico cells. An adaptive radio interface is envisaged for IMT-2000 to
optimise performance in these widely differing propagation conditions. This adaptation will
be controlled by software using digital signal processing technology.
1 UMTS, the Definition of a New Era
Multi-mode and multiband mobile terminals will be a common mechanism to link IMT-
2000 to earlier systems. The ITU standardisation work on IMT-2000 encourages
convergence of the many diverse satellite and terrestrial mobile systems towards the ITU
vision for third generation global mobile communications, i.e. IMT-2000. However, with the
rapid changes in technology, particularly in the digital processing area, new standards must
not be restrictive, but should enable future telecommunication enhancements. In other words
the standardisation must be in such away that it can be efficiently controlled by future
applications that we do not even dream about today.
1.3.2 UMTS
1.3.2.1 ETSIs Projects on GSM and UMTS
The task of SMG, Special Mobile Group, is to develop and maintain the specifications of the
digital cellular telecommunications system operating in the 900 MHz band known as GSM
900 and of its variation in the 1800 MHz band, known as DCS 1800.
Moreover it is responsible for maintaining the integrity of the GSM platform by close co-
operation with ANSI T1P1, who are responsible for the 1900 MHz version, known as PCS
1900.
SMG is also responsible for studying, and defining all aspects of third generation mobile
systems based on the concept of Universal Mobile Telecommunications System (UMTS), in
co-operation with studies by the International Telecommunication Union (ITU) regarding a
global system known as the International Mobile Telecommunications 2000 System (IMT-
2000).
UMTS Terrestrial Radio Access (UTRA) is the ETSI candidate for IMT-2000 Radio
Transmission Technology (RTT).
SMG maintains close-working relations with the UMTS FORUM based on the co-operation
agreement between ETSI and the FORUM.
1 UMTS, the Definition of a New Era
The scope of the work is focused to the GSM family. It includes the definition of the GSM
services offered and the selection and specification of the most efficient radio techniques and
speech coding algorithms.
SMG is also responsible for the elaboration of the GSM network architecture, signalling-
protocols and conditions of interworking with other networks. In addition SMG is charged
with the application of the Telecommunications Management Network (TMN) concept to
the GSM network entities regarding operation and maintenance.
The goal for the future work in SMG2 is to provide the standard for the radio access network
part of UMTS. In addition, to this goal SMG2 is to provide UTRA as a candidate for IMT-
2000 to ITU.
For the work towards the UMTS standard it proposed that this work should consist of the
following, events and phases:
Finalise the SMG2 proposal of the radio access part of IMT-2000 and present this
(submission from SMG to ITU June 30, 1998).
A first phase is to elaborate technical descriptions and evaluate performance of the final
solutions of UTRA. This phase is concluded with a detailed description of UTRA including
the mobile station. This includes all radio protocols terminated in UTRA, the UTRA internal
protocols and the Iu interface as well as descriptions of the functionality's required of the
network nodes and in terminal.
A second phase that could be initiated during phase 1 would be to write the actual
specifications/standards based on the material elaborated in the first phase. It should he the
goal to freeze the specifications/standard in December 1999.
The third phase is the iterative correction phase, where the specification/standard is
corrected based on the experience gained with the standard during development and
implementation of UMTS. This phase in principle never ends, but should considered done in
2001. The fourth part would further development of UMTS towards the UMTS phase 2 to be
introduced 2005.
Figure 1.1.1. Spectrum Allocation UMTS/IMT-2000.
1 UMTS, the Definition of a New Era
Spectrum consists of one paired band (1920-1980 MHz + 2110-2170 MHz) and one
unpaired band (1910-1920 MHz + 2010-2025 MHz). Same spectrum allocation in Europe
and Japan.
ETSI decision on UTRA in January 1998:
-WCDMA to be used in the paired band
-TD/CDMA to be used in the unpaired band
It is also stated that it should fit into 2*5 MHz spectrum allocations and that the two modes
FDD/TDD should have harmonised parameters.
UTRA FDD UTRA TDD
Multiple-Access scheme W-CDMA W-TDMA/CDMA
Duplex scheme FDD TDD
Chip Rate 3.84 Mcps (7.68 Mcps, 15.36 Mcps)
Carrier spacing (3.84 Mcps) 4.2-5 MHz (200 kHz carrier raster)
Frame length 10 ms
Inter-BS synchronisation Not required Required
Max. Spreading factor 256 16
Table 1.1.1. UTRA Basic Parameters
1.3.2.2 UMTS Harmonisation Phase
UMTS Phase 1
- GSM GPRS Release 99 with UMTS
Sat.IMT-2000
MSSS-PCN(UL)
MSSS-PCN(UL)
MSSS-PCN(DL)
IMT-2000
IMT-2000
UMTS FDD
220021502100205020001950190018501800
IMT-2000Sat.
IMT-2000
IMT-2000MSS
S-PCN(UL)
TDD
PHS
UMTS FDDMSS
S-PCN(UL)
TDD
DECT
TDD
GSM 1800(DL)
PCS (DL)MSS
S-PCN(DL)
PCSUn.Lic.
MHz
PCS (UL)USA
Europe
Japan
ITU
1 UMTS, the Definition of a New Era
UMTS Phase 2
- Higher bitrates (2 Mbit/s)
UMTS Phase 3
-?
1.3.2.3 UMTS Releases
December 1999: Standardisation freezes. First operator licences for UMTS. Release 99
completed by 31 December.
2000 –2001: Vendors development of network elements. Iterative experimental
process that might effect the standards. First launch of UMTS in Japan
2001 based on Release 99.
January 2002: UMTS in Europe. Release 2000 including Internet Protocol based
networks.
2005: Availability of all core bands for UMTS.
2008-2010: Additional spectrum for terrestrial and satellite use.
To meet the need of higher bitrates and packet data for the user UMTS will include other
enhancements in the network. In order to reach higher bitrates High Speed Circuit Switched
Data, HSCSD will let the users use more than one timeslot in the TDMA air interface. GSM
Packet Radio Switching will add the ability to send and receive packet data. It will also be
the backbone in the UMTS/GSM network. EDGE will be a complement to UMTS that might
give the operators without UMTS frequencies the possibility to present high bitrates for the
customer.
Figure 1.1.2. Bit Rate and Coverage
1 UMTS, the Definition of a New Era
1.4 UMTS as the 3rd Generation System
1.4.1 Main Service Differences Between 2G and 3G
Three main criteria characterise the services in 2G systems :
A variety standardised services are provided by 2G network operators.
The system restricts Roaming where provided.
Designed primarily for speech, 2G mobile networks are usually restricted to relatively
low bit rate services.
In contrast, the following main features characterise 3G systems:
Under the conditions of a still growing mass market, 3G system shall meet the individual
communication requirements of a customer with his personalised service profile and user
interface.
Instead of individual services the tools for service creation will be standardised.
Access to and invocation of the users' own personalised services should be possible
regardless of the operating environment and access system, thus supporting intersystem
roaming.
GSM
HSCSD, GPRS10 kbps
144 kbps
384 kbps
2 Mbps
EDGE
UMTS
Wide area/High mobilityFixed/Low mobility
User bit rate
1 UMTS, the Definition of a New Era
3G system can offer spectrum efficient access to multimedia services of higher, flexible
bandwidth to mobile users, in addition to services already offered within 2G system.
The user of today expects a variety of services to be offered by various providers and for
these services to be flexible enough to meet his individual demands.
In pre-3G mobile systems like GSM but also in ISDN, the user has already a broad choice of
services, in particular supplementary services. This variety of services has led to complex
instructions on how to use these services. Ordinary users will not accept an increase in
complexity of service handling. Instead they will prefer a simpler 'personal assistant type'
man-machine interface.
1.4.2 New Roles and Relationships for UMTS
Traditionally, in most models, the following actors play a role:
Network Operator
Service Provider
Subscriber
User.
However, a new business environment such as Value Added Service Provider, Content
Providers, Service Brokers and others, may create new categories. Between the roles various
relationships can appear. These will be used to identify interfaces that may require
standardisation and make relations more clear.
While maintaining a single identity, a user may subscribe to services at different service
providers. In addition, services offered by a provider may be offered to more than one
network.
In consequence, definitions of the home "network" or visited "network" used by second
generation’s system are no longer valid. The term "home environment", is proposed as a
replacement.
1 UMTS, the Definition of a New Era
1.4.3 Work Regulations
In recent years, we have been seeing the telecommunication services deregulation. Today
service definition is not a matter for regulators, except for emergency services.
Commercial network operators/service providers may agree on some items such as a
minimum set of services and the respective specifications, but the decision is left to the
market demand.
As a consequence, IMT-2000 is expected to exist in various forms and aspects.
In the area of licensing, the position of regulators is also changing, with a tendency to giving
licenses for frequency use rather than to complete systems. As a result it increases the
complexity of interworking or interoperation of networks for global roaming.
1.4.4 UMTS Services and Applications
3G service capabilities for these services should take account of their discontinuous and
asymmetric nature in order to make efficient use of network resources. Basic services
provided in 3G networks are audio, video, facsimile transfer, data communication, Internet
services, e-mail/voice mail, paging, messaging, and combinations of these i.e. multimedia.
They can be divided in several classes.
1.4.4.1 UMTS Service Classes
1.4.4.1.1 Conversational Class
3G must provide the capabilities for high quality speech conversation.
1.4.4.1.2 Streaming Class
It is assumed that video communications will become a mass service after ordinary
telephony.
1.4.4.1.3 Multimedia Class
3G systems will support multimedia services and provide the necessary service capabilities.
1 UMTS, the Definition of a New Era
1.4.5 UMTS Advanced Concepts
1.4.5.1 Service Portability
Roaming between different 3G environments shall he possible without limiting the user in
his personal service set and accustomed user-interface.
1.4.5.2 VHE Concept
Virtual home environment (VHE) is a system concept for service portability in the Third
Generation across network borders. In this concept, the serving network emulates for a
particular user the behaviour of his home environment.
1.4.5.3 Relationship Between Mobile and Fixed Networks
Any future system should be designed with the concept of a new type of network. Future
network operators and service providers will have to offer both wired and wireless access for
terminals.
Mobile Fixed Convergence, MFC, is a technological trend in telecommunications. in it
distinction between fixed and mobile networks is continuously blurring through increased
singularities of network functions in both network types.
1.4.6 Network Operators’ Functions
In GSM networks, operators agreed on a set of services to be provided by each operator.
This simplifies the service management considerably but should no longer be sufficient to
satisfy user demand.
Service providers may request from the network operator that it enable roaming in other
environments for all or some of his customers. Third generation systems must provide the
necessary tools.
It is proposed that in future the networks should only provide service capabilities, which
may differ slightly or fundamentally between different networks (e.g. cordless, cellular,
1 UMTS, the Definition of a New Era
satellite networks). These service capabilities are used by other parties to compose services
for the market.
1.4.7 Technological Progress Impact
Latest achievements in modern technologies as information and entertainment technologies,
transparency between fixed and mobile network concepts, multimedia presentation, transfer
of application support software packages (e.g. Java applets), high-capacity chips and
memories, has to be taken into account in the design of any third generation mobile system.
The use of Internet service is already today very common and well accepted by the user. The
3G system should cope with Internet and Intranet services, putting high demands on
bandwidth requirements.
3G systems capabilities need to be built upon standardisation of the following services:
Definition for flexible service.
Personal mobility in mobile and fixed networks.
Support for multi-system terminals.
Support of multi-mode operation
Capability for international roaming and inter network roaming
Flexible charging, including pre-payment and electronic purse systems
Comprehensive real time charging information to the user.
Integrated mailbox-service for voice, fax, text and other formats (in mobile and fixed
networks, accessible via both networks).
Personal Assistant and intelligent agent suppor.
2 Architecture Overview
Chapter 2: Architecture Overview
2.1 General Overview of the System
Figure 2.2.1. UMTS Architecture
2.2 User Equipment (UE)
The UMTS behaviour will be much faster than the GSM one. The progressive change from
one system to the other will give us a whole new world of possibilities in terminals for the
user, with all the new technology that it involves.
We have different kinds of equipment, with different technologies as well. We will speak
about the terminal as the UE (user equipment). The idea is that this terminal will be
compatible with the old system, such GSM, and will be able to connect to both networks,
UMTS-GSM. In addition, the user equipment may include a removable smart card that may
be used in every UE. In this card we the user will have all the data and the private
passwords.
UMTS GSM
Core Network, CN
IWNInter Working
Unit
IWNInter Working
Unit
RNS 2Radio Network
SubsystemRNS 2Iur
Iu Iu
Terminal Terminal
Uu
GSM CN HLR
MSC GMSC MSC
BSSBase StationSubsystem
BSS 2
A A
MSMS
Um
2 Architecture Overview
The terminal is sub-divided into the Mobile Equipment (ME) and the UMTS Subscriber
Identity Module (USIM).
The terminal of the user develops the radio connection with different software capabilities.
Furthermore, the ME can be divided into several parts. We have the MT (Mobile
Termination), that performs the transmission and some related capabilities, and we also have
the TE (Terminal Equipment), the part that contains the end-to-end applications. The
references that can be found in the specifications are not clear in this point, leaving the
design to the several providers.
We have the identification properties inside of the USIM, based on several kinds of data and
procedures that will identify the user with no error. The electronic technology of the VLSI
gives us a very high power of integration so that the smart cards can have a lot of capabilities
of identification. The smart card will identify a user in such a way that it does not matter
which kind of ME he is using.
Inside the UMTS terminals Rake reception in used to generate soft decisions that are fed into
the channel decoder. The channel decoding also develops jobs of setting the target for the
power control, as well as the obvious functions of decoding the channels. If the power
control is bad implemented, the capacity of the network will decrease, as it will be seen in
some following chapters.
Rake Channel decoding
Searcher
Power control
Inputsamples
Decoded bits
PowerControlrequest
2 Architecture Overview
2.2.1 Schematic of the Receiver for UTRAN - Outdoor
Figure 2.2.2. Receiver Method
2.2.1.1 Rake Receiver:
When the data acquisition has been already made, the RAKE receiver will use the several re-
echoed signals that arrive to the antenna of the UE to improve the final signal quality. This
can be made because of the properties of the codes used in the system, because they are
orthogonal. We can de-spread the signal whether it is received delayed from a initial one or
not. Once we have the several echoes de-spread, we can combine the signals obtained
through different ways to increase the final SNR, the final quality at the end. We will add the
signals coherently. We can find fast fading in some signals, but this fading is independent
from one signal to the other, so combining correctly the signals, the final SNR will be
increased. This process is known as micro-diversity.
We can also find macro-diversity in the SOHO (soft handover), and the rake way to avoid
the problems in this case is basically the same. Now we have just to consider that the signals
come from different Node B, not from several reflections of the same antenna.
2.2.1.2 Searcher:
Sometimes we want to know the offset and the magnitude of the echoes and the power of the
signals coming from different base stations. This can be made with the scrambling codes and
the primary and secondary synchronisation channels.
2 Architecture Overview
Although this will be seen much deeper in following chapters, we can say the PSCH
(Primary Synchronisation Channels) are used to identify the power of the signals coming
from different near base stations, in the cell search process. We can identify the one that will
be the server Node B with this channel. The SSCH (Secondary Synchronisation Channel)
allows us to know the specific Node B and the downlink scrambling code group used by this
station. Once we know the scrambling code, the UE, through the searcher, can identify
different echoes from the scrambled pilot symbol. The echo profile is highly correlated from
one power control period to the next. We can use this characteristic to decrease the
complexity of the design of the UE.
2.2.1.3 Power Control:
The interface in the downlink is reduced minimising the transmission power at the base
station for a particular user, in such a way that the characteristics of the link performance
(throughput and error rate) are fulfilled. The UE will ask the base station to increase or to
decrease the transmission power every power control period (0.625 ms), trying in every
moment to keep the SIR as close as possible to a reference value. This SIR target is re-
evaluated every 10 ms depending on the status of the channel that is being decoded.
2.2.1.4 Channel Decoding:
As well as supporting a more powerful version of the convolutional channel decoding used
in GSM, UMTS terminals are likely to employ high performance turbo decoders.
2.3 The Access Network: UTRAN
By Access Network it is known the several physical entities that control the resources of the
access network, and gives the user the chance to access to the Core Network.
2.3.1 RNS Architecture
The Radio Network Subsystem basically is made of the RNC and other objects that at the
moment are called Node B. This Node B has the same function as the Base Station in GSM
2 Architecture Overview
systems. We have several interfaces, but here we can introduce the Iub, between the RNC
and the Node B.
Figure 2.2.3. RNS Architecture
2.3.1.1 Radio Network Controller, RNC
This part is the responsible of the handover decisions that need signalling to the UE. The
RNC comprises a combining/splitting function to support macro diversity between different
Node B. This part of the UMTS system will need much more intelligence than its partner in
the GSM system. These extra capabilities will increase the speed of the system, and
therefore, the yield.
2.3.1.2 Node B
The Node B will also be more intelligent than the Base Station in GSM. It will develop
functions of combining/splitting to allow macro diversity. The communication among
several Node B will allow the terminal to change from one cell to an adjacent one without
losing connection in the process.
2.3.2 UTRAN Architecture
At the end, the UTRAN is made of an amount of several Radio Network Subsystems that
represent an interface between the UE and the Core Network. For these functions, we have
2 Architecture Overview
several interfaces among the different parts that compose the Access Network that allows the
system to work properly.
Figure 2.2.4. UTRAN Architecture
It is a hierarchical structure, so every RNS will have a certain group of cells to serve, as it
can be seen in the picture.
We can see two different RNS very easily. First, we have the Serving RNS, which is the one
that gives the service at a certain moment. If it is needed, the Drift RNSs can help the
Serving RNS to give radio resources. The role of an RNS (Serving or Drift) is on a per
connection basis between a UE and the UTRAN.
Figure 2.2.5. Serving and Drift RNS
2.4 Core Network
We must have a fixed network in this system to provide support for the different capabilities
and features that we will find. The system cannot be all-wireless. With the Core Network
2 Architecture Overview
(CN), we will support the several functionality of the system, as for example the
management of the location of the user, or to provide a mechanism for transferring the signal
(switching and transmission).
The characteristics of the CN should allow it to handle circuit switched data ? 64 kbits/s,
packet data ? Mbits/s. To have the strictest control of several service parameters (maximum
delay or bandwidth). To support the Virtual Home Environment VHE, that makes the user
think that he is always using the same interface, always "at home".
We can see different parts in the Core. We can find the Serving Network, The Home
Network and the Transit Network. Probably, in later versions of the specification than the
release '99 it will be possible to find different versions and characteristics of the division.
2.4.1 Serving Network
This part of the core is the responsible of giving connection between the access network (to
which the user is connected) and the core itself. The local functions of the CN are
represented by this section. It is also responsible for the routing calls and transport user
data/information from source to destination.
2.4.2 Home Network
This part of the network represents all the functions that are related to a fixed location,
regardless of the place that the user made the connection to the network.
The USIM is related by subscription to the home network. The home network therefore
contains at least permanently user specific data and is responsible for management of
subscription information.
2.4.3 Transit Network
This part of the CN is located between the serving network (home network), and the remote
party.
2 Architecture Overview
2.4.4 Interfaces and Their Function
The Inter Working Function (IWF) has the role of interconnecting the Access Network to the
Core Networks, mainly through the Iu interface. This IWF is a logical unit (and a virtual
one) that will allow the CN to work with different protocols, due to the number of vendors
that will work on this technology.
2.5 Mobility
Logically, we can see two domains in the Core. We can find a IP domain and a PSTN/ISDN
domain. It shall be possible to connect the UTRAN either to both these CN or to one of the
CN domains.
It shall be possible to interconnect the GSM network and the UMTS one, from the point of
view of roaming and handover. At the beginning of the deployment, the coverage of the
UMTS network won't be absolute at all, and it will be necessary the compatibility between
the two networks. This implies that International Mobile Subscriber Identity, IMSI, shall be
used as the common user identity in the two CN. Common MAP signalling will be applied to
both GSM and UMTS. The GSM MAP mobile service operations shall be evolved and re-
used as fast as possible.
The UTRAN will store all the capabilities of the radio connection and all the radio network
parameters.
We have two service domains the Circuit Switched service domain (PSTN/ISDN) and the
Packet Switched service domain (IP). We have one service state machine for each service
domain. A terminal that is supporting both CS and PS services, has a CS service state
machine and a PS service state machine. They work independently to each other, although
associated to the same terminal (or UE). The UE-CN signalling aims to keep the peer entities
synchronised.
The UTRAN will try to offer a unified set of radio bearers, in such a way that they will bi
able to be used for bursty packet traffic and for traditional telephony traffic. The radio
2 Architecture Overview
resource handling is UTRAN internal functionality and the CN does not define the type of
radio resource allocated.
Once we decide to connect the UE, an initial connection is already set up, in such a way that
the radio resource has two modes, Connected and Idle mode. The UE will be identified by
the different modes. In Idle mode the UE is identified by a CN associated identity. In
Connected mode the UE is assigned a Radio Network Temporary Identity to be used as UE
identity on common transport channels. When we are transmitting via a dedicated channel,
the UE uses an inherent addressing (code a frequency), provided by these transport channels.
We can see four areas for different concepts, about the mobility functionality. Location
Areas (related to CS services) and Routing Areas (related to PS services) are used in the
Core Network. In the UTRAN the UTRAN Registration Areas and Cell Areas will be used.
Location Area for CS services: The CN manages one Location Area. This means that the
terminal (UE) is registered in the CN node responsible for handling this specific location
area. The 3G_MSC/VLR for paging the terminal use LA.
Routing Area for PS services: They are managed by the CN. In parallel, this means that the
UE is registered in the CN node responsible for handling this specific routing area. The
3G_SGSN for paging the terminal use RA.
Registration Areas and Cell Areas in URAN are only visible in the Access Network and
used when the UE is in connected mode. UTRAN internal areas are used when the terminal
is in connected mode. These areas are used at e.g. UTRAN initiated paging. The UTRAN
internal area structure should not be visible from outside the UTRAN, because the internal
area updating is a radio network procedure. In connected mode, the UE position is known on
cell level or on UTRAN Registration Area (URA) level.
For the relation between LA and RA it shall be possible for the operator to have a LA and a
RA equal (same cell) or a RA as part of a LA, or a LA as a part of RA, and LA and RA
independently. A more clear specification shall be defined in this point if an area consists of
both UMTS cells and GSM cells.
2 Architecture Overview
An CS-IDLE terminal will initiate Location Update towards the CN when crossing LA
border. In Idle mode it is the broadcasted system information, e. g. information about the
present LA and RA, that determines when the UE initiates a location registration procedure
towards the CN. A PS-IDLE terminal will initiate Routing Area update towards the CN
when crossing RA border.
When the UE is connected, the terminal receives the system information on the established
connection. A UE in CS-IDLE will initiate Location Area update towards the CN when
receiving information about a new LA, in connected mode. A UE in PS-IDLE will initiate
Routing Area update towards the CN when receiving information about new RA in
connected mode. The UE in CS-CONNECTED mode will not initiate Location Area update
and a UE in PS-CONNECTED mode will not initiate Routing Area update towards CN.
If we use separately PS and CS mobility mechanisms within the UE and within the CN we
may not obtain non-optimal usage of the radio resource. The use of combined updated may
be used to avoid this. It should be possible to use combined mechanisms for location
management purposes as well as for attach/detach status purposes. UMTS Phase 1 R99
terminals should support the use of both combined and separate mechanisms.
The radio access network will not co-ordinate mobility management procedures that are
logically between the CN and the UE, as it is seen in the UMTS specifications R99. This
includes several capabilities, as location management, authentication, temporary identity
management and equipment identity check.
3 CDMA Technique
Chapter 3: CDMA Technique
3.1 Introduction
CDMA (Code Division Multiple Access), is an access system based on spread spectrum
communication in which multiple users share the same frequency band. This part contains
the CDMA concepts.
3.2 Access Methods FDMA, TDMA, CDMA, FDD vs. TDD
3.2.1 Frequency Division Multiple Access (FDMA)
In FDMA system, all the stations use a diffent band, within the available range of frequency,
so in this access technique each user has a continuous access in a given frequency band. It´s
no necesary a co-ordination or synchronisation among stations and each station doesn´t
interfere in the other bands. It´s not possible a station transmits in a bandwidth used by
stations are idle, this can be a problem when the load is high and more resources are needed.
Also, FDMA is not a flexible system because of adding a new user requires some
modifications in the equipment.
Figure 3.3.1. FDMA
Advantages: FDMA uses a symple technique that has been proved.
Code
Time
Frequency
3 CDMA Technique
Disadvantages: Reconfiguration of the system in case of capacity variation is difficult, due
to flexibility.
3.2.2 Time Division Multiple Access (TDMA)
In TDMA the resource is the time which is divided into slots. Each station uses a pre-
assigned slot. The station is allowed to transmit freely into its assigned slot, and the entire
system resources are devoted to the station. Slots are repeated periodically in a cycle called
frame. A station could be assigned to one or more time slots during a cycle. Each station
knows when trasmit because all are synchronised.
Figure 3.3.2.. TDMA
The most important disvantage of TDMA is the fixed time slot allocation, whether or not it
has data to transmit. For applications with bursty transmission requirements a fixed time
allocation could be a bad use of the resources.
Advantages: High transmission throughput for a large number of stations. A single station
occupies all of channel bandwidth at each instant. Digital processing leads to operational
simplicity. It´s no necessary to control the transmitting power of the users. The tuning is
easier because all stations transmit and receive on the same frequency.
Disadvantages: TDMA need synchronisation. A high throughput is needed to dimension the
station transmits. A better channel and hence better throughput can compensate a big cost of
the equipments.
Code
Time
Frequency
3 CDMA Technique
3.2.3 Code Division Multiple Access (CDMA)
As we have show neither FDMA nor TDMA allow any time overlap of the stations
transmissions. Code Division Multiple Access (CDMA) is a conflict-free protocol that
allows overlap transmission, both in frequency and time.
Using quasi-orthogonal signals in conjunction with matching filters at the receiving stations
CDMA achieves the conflict-free property. The multiple orthogonal signals (information
that does not interfere with each other) increases the bandwidth required for transmission.
Several systems can coexist in the same frequency bands using different signals, but the
transmission of the code requires a much greater radio-frequency bandwidth. This is the
reason for calling it Spread Spectrum transmission. The code, in CDMA, is modulated on the
carrier with the digital data on the top of it and each station is assigned a particular code
sequence.
There are different ways: 1) phase-coded in which the carrier is phased-modulated by the
digital data sequence and the code sequence and, 2) frequency-hopped in which according to
some known pattern the frequency is periodically changing.
The ability of the receiver to lock onto packet while all other overlapping packets appear as
noise (capture effect), minimizes the effect of interference when several stations employ the
same code.
Figure 3.3.3. CDMA
Advantages: Since it does not require any transmission synchronisation between the mobile
stations, it is simple to operate. Against other interference systems it offers protection.
Code
Time
Frequency
3 CDMA Technique
Disadvantages: The low throughput is the main disadvantage.
3.2.4 FDD vs. TDD
In FDD (Frequency Division Duplex) mode, separate frequencies are used in the uplink and
downlink for the connection between a mobile and a base station. This means that the mobile
will receive on one frequency and then transmit on another frequency. The FDD mode doesn
´t imply any specific accesses method.
In TDD (Time Division Duplex) the uplink and downlink will be on the same frequency.
The TDD mode doesn´t imply any specific accesses method.
Figure 3.3.4. FDD vs. TDD
3.3 Introduction to Spreading and Modulation
There are two categories in which spread spectrum, generally, falls into: Frequency Hopping
(FH) or Direct Sequence (DS). It is required, in both cases, synchronisation of transmitter
and receiver. It can be considered the use of a pseudo-random carrier in the two forms, but
they generate the carrier in different ways.
Is typically implement a frequency hopping system by rapid switching frequency in a
pseudo-random pattern.
In the technique for spread spectrum DS-CDMA, the total power is spreaded over the entire
transmission bandwidth. Before the modulation and transmission over the air, the base-band
binary data is spread by means of a high speed pseudo-noise (PN) code called chip rate,
creating a composite data.
Time
FrequencyFDD
TDD
Time
Time
FrequencyTDD
3 CDMA Technique
By means of increasing the frequency of the time signal spectrum spreading can be
accomplished. Consider a waveform with an amplitude of V and frequency f (where f = 1/T
and T is the bit duration), if we increase the frequency by a factor n, T is now reduced by n.
Figure 3.3.5. Power Spectrum for n = 1 and n =2
The total energy remains the same after spreading. The total area under the curve gives the
total energy delivered and if the spreading bandwidth is high the amplitude of the signal will
be reduced. This is called process gain, Gp.
The definition of process gain is Gp = 10 log (transmission bandwidth/bit rate). For example
if the transmission bandwidth is 2,5 MHz and the bit rate is 1 MHz the processing gain
would be 3,98 dB. If we increase the bandwidth to 5 MHz the process gain would be 6,99
dB. This would provide as with an additional margin of 3 dB to help as suppress
interference.
When more and more users enter the system, the margin described above is reduced since
there will be a processing loss for every new user (interferer) that enters the system. For k
users this loss can be described as Process loss = 10 log (k).
The overall system gain is described by CDMA gain = Process gain - Process loss due to k
users. The formula would become:
CDMA gain = 10 log (bandwidth/k * bit rate)
where the bandwidth is as described a function of the chip rate.
After spreading the amplitude of the signal will be reduced, so energy are independent of the
frequency and that the amplitude of the signal will be reduced. If we consider the Gaussian
n=1
n=2
Amplitude
Baseband
3 CDMA Technique
"white noise" that we always have around us, the bandwidth is enough the amplitude will be
close to the noise level.
In CDMA each user will have its own code, therefore multiple users use the same frequency.
The code is made by means of an m-bit pseudo random, PR, generator that provides 2^(m-1)
different codes.
Figure 3.3.6. Uplink DS-CDMA
3.3.1 Orthogonal Codes
A pair of codes is said to be orthogonal if the cross-correlation is zero. This means that for
two m-bit codes: x1, x2, ..., xm and y1, y2, ..., ym the sum of all m from 1 to m shall be 0.
For example, the cross-correlation between two 4-bits codes:
X = 0 0 1 1
Y = 0 1 1 0 will be
_________
1-1+1-1=0 (assigning +1 for xm = ym and -1 xm ym).
In the transmitter, Direct Sequence is multiplication of more conventional communication
waveform by a pseudo noise (PN) 1 binary sequence.
M1M2
M3
M1 PN1
M2 PN2
M3 PN3
PN1 SpreadingPN2
PN3
3 CDMA Technique
Spreading is entirely done in the binary domain and the transmitted signals are carefully
band limited. It takes prior to any modulation,
In the receiver a second multiplication by a replica of the same 1 sequence recovers the
original signal.
When the signals reach the detector, the noise and interference, being uncorrelated with the
PN sequence, become noise-like and increase in bandwidth. The most of the interference
power can be rejected with a narrow band filtering that can enhance the signal-to-noise ratio,
SNR.
The data signal (user information) is multiplied by a PN-code in DS-CDMA. The period of a
PN-code is called the period, so the code is a sequence of chips. PN-codes, M-sequences,
Gold-codes and Kasami-codes are different classes of PN-code. In the simplest case a
complete PN-code is multiplied with a single data bit and the signal is now multiplied by a
factor N, the processing gain.
Figure 3.3.7.. Chips and bits
In the receiver squeme, the signal is multiplied by the same PN-Code which removes the
PN-code and recovers the desired data signal.
At the modulator/demodulator the transmitted signal (data information) is spreaded and de-
spreaded with a binary value sequence seudo random (PR) that a sequence generator
produces. The basic system design parameters are transmitted power and channel
bandwidth.
1 bit period
Data signal
PN-code
1 chip period
Coded signal
3 CDMA Technique
We increase (spread) the bandwidth of the data signal to overcome the problem of
interference, that will lead to a bandwidth expansion factor, process gain, g = W/R where W
is the spread code bandwidth (chip-rate) and R is the data bandwidth (bit-rate).
Figure 3.3.8. Different PN-Sequences
It is possible to use the same transmission bandwidth for more than one user by means of
using different PR-sequences for each user.
Figure 3.3.9. Different PN-Sequences for Each User
If the spreading is done by a different PN-sequence for many users then it is called direct
sequence code division multiple access, DS-CDMA.
Figure 3.3.10. DS-CDMA Principle
User 1
User 2
User N
Spread code 1
Spread code 2
Spread code N
channel receiver
Output 1
Output 2
Output N
.
.
.
.
.
.
PN1
PN2
PN3
M1
M2
M3
PN3
PN2
PN1
3 CDMA Technique
DS-CDMA uses PN codes to detect each multipath signal and to pick up the signals from the
desired base station. Orthogonal code is used for spreading and channelisation.
We get a similar signal as thermal noise (white noise) if the random code pattern is nearly
Gaussian distributed. Thus the interference of the other users is noise, and the problem can
be simplified.
DS-CDMA spreads the original information over wide bandwidth by using much higher rate
spreading codes, and makes use of frequency diversity to combat frequency selective deep
fading. The filtering is essential in DS-CDMA to reduce the required bandwidth and FIR
digital filters are usually used for sharp response.
3.3.2 RAKE Receiver
Transmissions arriving causes deep multipath fading at the receiver that have followed
different propagation paths. CDMA is less prone to this effect. In fact, one approach in
common use with CDMA system, the Rake receiver, takes advantages of multipath,
normally a major source of interference and signal degradation in other systems. In a Rake
receiver, the signals of several correlation receivers belonging to the strongest multipath
components are combined to provide an enhanced signal with better quality.
Data signal
PN-code
Spread datasequence
t
3 CDMA Technique
The users in a CDMA cellular environment simultaneously share the same radio frequency
band and can be separated at the receiver end with the knowledge of their unique code using
a Rake receiver.
Figure 3.3.11. RAKE Receiver
An optimum receiver contains several detection channels with different code delays, which
are adjusted to match the major components of the impulse response. The timing accuracy to
obtain full processing gain is approximately one chip time, i. e. the inverse of the channel
bandwidth. The fingers in the rake collect together the contributions of the total signal
energy from several multipath components. The impulse response is measured continuously
in order to set the delay and phase of the different rake fingers. Thus the output from the
channels can be added coherently giving diversity combining.
Both the right coding and the right timing must be done to be able to despread the wanted
signal in the receiver. An optimum receiver contains several detection channels with
different code delays, which are adjusted to match the major components of the impulse
response.
In the Rake receiver the contribution from several multipath components are combined. It is
necessary to measure continuously the impulse response of the propagation channel in order
to set the delay and phase on the different rake branches. The output from the channels can
then be added giving diversity combining.
1
2
3
Micro diversity
Macrodiversity
PNgenerator
PNgenerator
PNgenerator
1
2
3
3 fingers
adaptivechanneldelay
Linearcombiner
data
3 CDMA Technique
3.3.3 Spread Spectrum Goals
"Spread" the radio signal over a wide frequency range by modulating it with a code word
unique to the radio.
Techniques known since 1940s and used in military communications system since 1950s.
Receiver's correlator distinguishes sender's signal from other signals by examining the wide
spectrum band with a time-synchronised duplicate of the spreading code word.
A spreading process at the Receiver recovers the sent signal.
Spread spectrum waveform is more resistant to multipath effects and more tolerant of
interference.
Figure 3.3.12. Interference Averaging
Spread spectrum systems are power rather than bandwidth limited.
With a wider band the interference will have an averaging effect in such a way that all user
will share the problem.With a narrow bandwidth a user channel might receive severe fading
dips.
3.3.4 Code Properties
The code should have good Auto Correlation (Time Relation) and Cross Correlation
(suppress other users) properties.
f f
Channel Quality Channel Quality
3 CDMA Technique
3.3.4.1 Short Codes:
Code sequence length = bit (bit = 1 bit user data).
Code sequence repeated for each new data bit.
+ Orthogonal codes if perfect synchronisation.
+ Good synchronisation properties.
- Code planning needed since limited number of good short codes.
3.3.4.2 Long Codes:
Code sequence length >> bit
+ No code planning needed since low probability that users might have same code.
- Non orthogonal codes.
- Bad synchronisation properties since long repetition cycle.
3.4 Soft and Hard Handover
3.4.1 Handover
In general the change of physical channels allocated to a call while maintaining this call is
considered as handover. In a hard handover the mobile station will instructed to move from
one channel to another and only be receiving from one base station at a time (break before
make). In a soft handover the mobile belongs to two base stations during the time it moves
between the cells (make before brake).
3.4.2 Soft Handover
The mobile station continuously searches for new base stations on the current carrier
frequency when is in active mode. During the search, the mobile station monitors the
received signal level from neighbouring base stations, compares them to a set of thresholds,
and reports them accordingly back to the base station. The active set is defined as the set of
3 CDMA Technique
base stations from which the same user information is sent simultaneously. Based on this
information the network orders the mobile station to add or remove base stations links from
its active set.
3.4.3 Softer Handover
Conceptually, a softer handover is initiated and executed in the same way as an ordinary soft
handover. Softer handover is the special case of a soft handover between sectors/cells
belonging to the same base station site. The main differences are on the implementation
level within the network.
The inter-frequency handover is always performed as a hard handover.
Intra-frequency handover is an handover between cells using the same (single) radio
frequency whereas inter-frequency handover is a handover between cells using different
radio frequencies.
3.5 Power Control
Since there are several users in the same frequency band the received signal strength will be
different for different mobiles, resulting in a near-far interference problem. Near-far refers to
the ratio of the signal strength from a near mobile to a mobile far away. This problem will
give lower performance and reduce capacity in the system.
Many simultaneous connections share a common transmission channel in an interference-
limited system, like CDMA. While in FDMA each connection has its one frequency and in
TDMA each connection has one time slot, this will permit high isolation between the
connections (orthogonality).
Figure 3.3.13. Near-far Problem
3 CDMA Technique
If the mobiles would transmit the same power the ratio of the received signal would be:
RS1/RS2 = (d2/d1)^ where lambda is the path loss or propagation environment. If d1 is not
equal to d2 then the received signal strength from mobile 1 might be much stronger than the
mobile 2 and the receiver would not be able to detect and recover mobile 2. This means that
the transmitting power of each mobile has to be controlled so that the received power is
constant irrespective of the distance.
Figure 3.3.14. Controlled Transmitting Power
A specific code is assigned to each connection in interference limited system. This will help
us to discriminate between the wanted signal C and interference I from all other users.
M1M2
SS1=
SS2=
d2
SS2
d1
SS1
M1M2
SS1=SS2=
d2
SS2
d1
SS1
3 CDMA Technique
There will be a point when the C/I becomes to low when the total interference level is
increased (more users). This is called anti-jamming margin, AJ, which is the maximum value
for I/C. This gives us an interference limited system for CDMA compared to FDMA and
TDMA who are channel limited system.
The Gp determines how much the receiver can suppress the interference.
To get an acceptable isolation between the connections a large bandwidth is needed to
increase the AJ. The processing gain, Gp, is a related parameter, also related to the
bandwidth.
It is then very important with power regulation so that all signals have the same level at the
receiver input.
Commercially available SS systems typically implement processing gains in the 10-100
range.
Information can be transmitted at power levels below ambient noise for high values of Gp
(>1000),. This means low probability of "intercept/detect" and narrowband jamming or
interference.
To illustrate the problem and advantages with an interference limited system, the
"International Cocktail Party" analogy can be used. Picture a large room with a number of
people, in pairs, who would like to hold conversations.
The people in each pair only want to talk and listen to each other, and have no interest in
what is being said in other pairs. In order for these conversations to keep place, however, it
is necessary to define the environment for each conversation.
Gp is high and it is easier to distinguish individual speakers, if people speak in different
languages. Now if a Band is playing a "random noise" is got and the Gp will be lower, I/C
increases, and it will be more difficult to extract the conversation from the background.
Now imagine that the Band starts playing even louder! Speakers try to talk more loudly,
increasing the noise and if more and more people enter the room each conversation will be
louder and louder to cope with the interferers.
3 CDMA Technique
The solution is to minimise the interference level at the base station receiver is only effective
for terminals assigned to this base station. Interference from terminals in other cells is still a
problem. To minimise this interference the use of soft handover and careful selection of
which base station shall be involved in macro diversity are needed.
3.5.1 Inner Loop Power Control - Uplink
The uplink inner loop power control adjusts the mobile station transmit power in order to
keep the received uplink Signal-to-Interference Ratio (SIR) at a given SIR target. The base
station should estimate the received uplink power after RAKE combining of the connection
to be power controlled. Simultaneously, the base station should estimate the total uplink
received interference in the current frequency band and generates a SIR estimate. The base
station then generates TPC (Transmit Power Control) commands.
Figure 3.3.15. Forward and ReverseLink
Upon the reception of TPC command, the mobile station should adjust the transmit power of
the uplink in the given direction with a step of TPC dB. The step size TPC is a parameter
that may differ between different cells, in the region [0.25-1.5] dB.
In case of receiver diversity (e.g., space diversity) or softer handover at the base station, the
TPC command should be generated after diversity combining.
In case of soft handover, the following procedure is considered:
In the base station a quality measurement is performed on the received signals; in case
the quality measurement indicated a value below a given threshold, an increase
Forward Link
Reverse Link
3 CDMA Technique
command is sent to the mobile, otherwise a decrease command is transmitted; all the
base stations in the active set send power commands to the mobile;
The mobile compares the commands received from different base stations and increases
its power only if all the commands indicate an increase value (this means that all the
receivers are below the threshold);
In case one command indicates a decrease step (that is, at least one receiver is operating
in good conditions), the mobile reduces its power; in case more than one decrease
commands are received by the mobile, the mobile station should adjust the power with
the largest step in the "down" direction ordered by the TPC commands received from
each base station in the active set;
The quality threshold for the base stations in the active set should be adjusted by the
outer loop power control (to be implemented in the network node were soft handover
combining is performed).
3.5.2 Outer Loop Power Control (SIR target adjustment)
-Uplink
The outer loop adjusts the SIR target used by the inner-loop power control. The SIR target is
independently adjusted for each connection based on the estimated quality of the connection.
In addition, the power offset between the uplink may be adjusted.
3.5.3 Open Loop Power Control - Uplink
Open-loop power control is used to adjust the transmit power of the physical access channel.
Before the transmission of the access burst, the mobile station should measure the received
power of the downlink. From the power estimate and knowledge of the transmitted power
from the base station (broadcast from the base station) the downlink path-loss including
shadow fading can be found. From this path loss estimate and knowledge of the uplink
interference level and the required received SIR, the transmit power of the physical access
channel can be determined.
3 CDMA Technique
The uplink interference level as well as the required received SIR are broadcast from the
base station.
3.5.4 Inner Loop Power Control - Downlink
The downlink inner loop power control adjusts the base station transmit power in order to
keep the received downlink SIR at a given SIR target.
The mobile station should estimate the received downlink power after RAKE combining of
the connection of the connection to be power controlled. Simultaneously, the mobile station
should estimate the total downlink received interference in the current frequency band. The
mobile station then generates TPC commands.
Upon the reception of a TPC command, the base station should adjust the transmit power in
the given direction with a step of TPC dB. The step size TPC is a parameter that may
differ between different cells, in the region [0.25-1.5] dB.
In case of receiver diversity (e.g., space diversity) at the mobile station, the TPC command
should be generated after diversity combining.
3.5.5 Outer Loop Power Control - Downlink
The downlink outer loop power control sets the target quality value for the downlink inner
loop power control. It receives input from quality estimates of the transport channel,
measured in the UE. The downlink outer loop power control is mainly used for a long-term
quality control of the radio channel.
This function is located mainly in the UE, but some control parameters are set by the
UTRAN.
The SRNC, regularly (or under some algorithms), sends the target down link power range
based on the measurement report from UE.
3 CDMA Technique
3.5.6 Open Loop Power Control - Downlink
The downlink open loop power control sets the initial power of downlink channels. It
receives downlink measurement reports from the UE.
This function is located in both the UTRAN and the UE.
4 Air Interface
Chapter 4: Air Interface
4.1 Radio Transmission and Reception
4.1.1 Frequency Band
UTRA is designed to operate in the following paired band:
1920-1980 MHz
UP-LINK
Mobile transmit; basereceive
2110-2170 MHz
DOWN-LINK
Base transmit; mobilereceive
Table 4.4.1. Proposed Frequency Band for UTRA
4.1.2 Channel Arrangement
The nominal channel spacing is 5 MHz, but this can be adjusted to optimise performance in
a particular deployment scenario. The channel raster is 200 KHz, so the centre frequency
must be a integer multiple of 200 KHz.
4.1.3 Tx-Rx Frequency Separation
The minimum transmit to receive frequency separation is 134.8 MHz and the maximum
value is 245.2 MHz and all UE(s) shall support a Tx-Rx frequency separation of 190 MHz
when operating in the paired band defined in 4.1.1. UTRA can support both fixed and
variable transmit to receive frequency separation.
4 Air Interface
4.1.4 Terminal Service Classes
Different service classes will be used to define the data rate and code allocation for a
UTRA/FDD terminal. Data rates of 144 kbps, 384 kbps and 2048 kbps are possible service
profile types.
Output power dynamics: Both the uplink and the downlink use the following power
control mechanism:
Fast closed-loop Carrier/Interference based power control.
Slow quality-based power control.
Uplink (UL) Downlink (DL)
Power control steps Variable 0.25-1.5 dB Variable 0.25-1.5 dB
Minimum transmit power -50 dBm [ ] dBm
Power control cycles per second 1.5 kHz 1.6 kHz
Power control dynamic 80 dB 30 dB
Table 4.4.2. Output Power Dynamics for UL and DL
4.1.5 Receiver Requirements
A suitable receiver structure must use coherent reception in channel impulse response
estimation and in code tracking mechanisms. A Rake receiver satisfies these reception
characteristics.
4.1.6 Diversity Characteristics
The following diversity possibilities are considered to be available in UTRA:
Time diversity Channel coding and interleaving in both uplink and downlink.
Multi-path diversityRake receiver or other suitable receiver structure with maximumcombining. Additional processing elements can increase the delay-spread performance due to increased capture of signal energy.
Antenna diversityAntenna diversity with maximum ratio combining in the base stationand optionally in the mobile stations. Possibility for downlinktransmit diversity in the base station.
4 Air Interface
Table 4.4.3. Diversity Characteristics for UTRA
4.2 Logical, Physical and Transport Channels
Logical Channel: A logical channel is a radio bearer or part of it, dedicated for exclusive
use of a specific communication process. Depending on the type of information transferred
on the radio interface, different types of logical channel are defined.
Physical Channel: A physical channel is defined by code, frequency and, in the uplink,
relative phase (I/Q). In TDD mode, code, frequency, and time-slot define a physical channel.
Physical Channel Data Stream: In the uplink, a data stream that is transmitted on one
physical channel.
In the downlink, a data stream that is transmitted on one physical channel in each cell of the
active set.
Active Set: Set of radio links simultaneously involved in a specific communication service
between an MS and a UTRAN.
Transport Channel: Transport Channels are those that are offered by the physical layer for
data transport between peer L1 entities. Different types of transport channels are defined by
how and with which characteristics data is transferred on the physical layer, e.g. whether
using dedicated or common physical channels are employed.
Transport Format: The Transport Format is a combination of encoding, interleaving, bit
rate and mapping onto physical channels.
Transport Format Combination Indicator (TFCI): The TFCI is a label for a specific
Transport Format within a Transport Format Set.
Transport Format Set: A set of Transport Formats. For example, a variable rate DCH
(Dedicated Channel) has a Transport Format Set (one Transport Format for each rate),
whereas a fixed rate DCH (Dedicated Channel) has a single Transport Format.
UTRAN
Iu
UE
Uu
UTRAN UMTS Terrestrial Radio Access NetworkCN Core NetworkUE User Equipment
CN
4 Air Interface
4.2.1 Transport Channels:
4.2.1.1 Dedicated Transport Channel
DCH - Dedicated Channel: Both user data and control information between the network
and a mobile station is carried in the Dedicated Channel (DCH), which is a downlink or
uplink transport channel transmitted over the entire cell or over only a part of the cell, using
lobe-forming antennas.
4.2.1.2 Common Transport Channels
4.2.1.2.1 BCH - Broadcast Channel
A base station uses the Broadcast Channel (BCH) to broadcast system and cell-specific
information. The BCH is a downlink transport channel that is always transmitted over the
entire cell.
4.2.1.2.2 FACH - Forward Access Channel
When the system knows the location cell of the mobile station, the Forward Access Channel
(FACH) is used to carry control information to the mobile. The FACH is a downlink
transport channel that is transmitted over the entire cell or over only a part of the cell using
lobe-forming antennas. The FACH may also carry short user packets.
4.2.1.2.3 PCH - Paging Channel
When the system does not know the location cell of the mobile, the Paging Channel (PCH) is
used to carry control information to a the mobile station. The PCH is a downlink transport
channel that is always transmitted over the entire cell.
4.2.1.2.4 RACH - Random Access Channel
Control information from a mobile station is transmitted into the Random Access Channel
(RACH). The RACH is an uplink transport channel that is always received from the entire
cell. It may also carry short user packets.
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4.2.1.2.5 DSCH - Downlink Shared Channel
The downlink shared channel (DSCH) is a downlink transport channel shared by several
UEs carrying dedicated control or traffic data.
4.2.2 Physical Channels:
A physical channel is defined by a specific carrier frequency, code, and relative phase (on
the uplink, 0 or /2).
4.2.2.1 Dedicated Uplink Physical Channels
There are two types of uplink dedicated physical channels, the uplink Dedicated Physical
Data Channel (uplink DPDCH) and the uplink Dedicated Physical Control Channel
(DPCCH).
Dedicated data generated for the dedicated transport channel are transmitted into the uplink
DPDCH. Each connection may support zero, one, or several uplink DPDCHs. Control
information is transmitted into the DPCCH. The control information consists of:
Pilot bits to allow channel estimation for coherent detection.
Transmit power control (TPC) commands.
Optional transport-format indicator (TFI).
The transport-format indicator informs the receiver about the instantaneous parameters of
the different transport channels multiplexed on the uplink DPDCH. There is only one uplink
DPCCH on each connection.
4.2.2.1.1 Frame Structure
Each frame of length 10 ms is divided into 15 slots, each of length Tslot = 0,666 ms,
corresponding to one power-control period (see Figure 4.4.1). A super frame corresponds to
72 consecutive frames, i.e. the super-frame length is 720 ms.
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Figure 4.4.1. Frame Structure for Uplink DPDCH/DPCCH
The parameter k is related to SF, the spreading factor of the physical channel, as SF =
256/2k. SF may thus range from 4 up to 256. The parameter k determines the number of bits
per uplink DPDCH/DPCCH slot. But the same connection usually carry an uplink DPDCH
and uplink DPCCH which have different rates, i.e. have different spreading factors and
different values of k.
The exact number of bits of the different uplink DPCCH is yet to be determined.
4.2.2.2 Common Uplink Physical Channel
4.2.2.2.1 Physical Random Access Channel
The RACH is transmitted into the Physical Random Access Channel (PRACH). The access
control is based on a Slotted Aloha approach, which means that a mobile station can start the
transmission of the PRACH at a number of well-defined time offsets, relative to the frame
boundary of the received BCCH of the current cell. The different time slots, the access slots,
are spaced 1.5 ms (see Figure 4.4.2). The BCCH broadcasts information about available
access slots in the current cell.
PilotN pilot bits
TFI N TFI bits
DataN data bits
Slot #1 Slot #2 Slot # i Slot #15
Frame #1 Frame #2 Frame # i Frame #72
0.666 ms, 10*2 k bits (k=0..6)
T f = 10 ms
T super = 720 ms
DPDCH
DPCCHTPC
N TPC bits
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Figure 4.4.2. Access Slot
The random access burst consists of two parts:
A preamble part (length 1 ms)
A message part (length 10 ms)
Between the preamble and the message part there is an idle time period of length 1.5 ms
(preliminary value), which allows for detection of the preamble part and subsequent on-line
processing of the message part.
Preamble Part: The preamble part of the random-access burst consists of a signature. There
are a total of 16 different signatures.
Message Part: The structure of the message part of the random-access burst is the same as
the uplink DPH. It has a data part, corresponding to the uplink DPDCH, and a control part,
corresponding to the uplink DPCCH. The data and control parts are transmitted in parallel.
The data part carries the random access request or small user packets, using a channel bit
rate of 16, 32, 64 or 128 kbps, which corresponds to a spreading factor (SF) of 256, 128, 64
and 32, respectively. The control part uses a spreading factor of 256, and carries pilot bits
and rate information. The rate information indicates which channelisation code (or rather the
spreading factor of the channelisation code) is used on the data part.
The random-access burst consists of the fields shown in Figure 4.4.3 and listed below (the
values in brackets are preliminary values):
Random-access burstAccess slot #1
Access slot #2
1.5 ms
Offset of access slot #i
Frame boundary
Access slot #i
Access slot #8
Random-access burst
Random-access burst
Random-access burst
Random-access burstRandom-access burstAccess slot #1
Access slot #2
1.5 ms
Offset of access slot #i
Frame boundary
Access slot #i
Access slot #8
Random-access burstRandom-access burst
Random-access burstRandom-access burst
Random-access burstRandom-access burst
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Mobile station identification. The MS ID is chosen at random by the mobile station at the
time of each random-access attempt.
Required Service. This field informs the base station what type of service is required
(short packet transmission, dedicated-channel setup, etc.)
An optional user packet
A CRC to detect errors in the data part of the random-access burst
Figure 4.4.3. Structure of Random - Access Burst Data Part
4.2.2.3 Downlink Physical Channels
4.2.2.3.1 Dedicated Physical Channels
The Downlink Dedicated Physical Channel (dowlink DPCH) is the only type of downlink
dedicated physical channel. It carries dedicated data for the dedicated transport channel
(DPH) and control information (known pilot bits, TPC commands, and an optional TFCI).
4.2.2.3.2 Frame Structure
Figure 4.4.4 shows the frame structure of the downlink DPCH. Each frame of length 10 ms
is split into 15 slots, each of length Tslot = 0,666 ms, corresponding to one power-control
period. A super frame corresponds to 72 consecutive frames, i.e. the super-frame length is
720 ms.
MS IDReq.ServOptional user packet CRCMS IDRe.ServOptional user packet CRC
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Figure 4.4.4. Frame Structure for Downlink DPCH
The parameter k is related to SF, the spreading factor of the physical channel, as SF =
256/2k. SF may thus range from 4 up to 256. The parameter k determines the number of bits
per downlink DPCH slot. But the same connection usually carry an uplink DPDCH and
uplink DPCCH which have different rates, i.e. have different spreading factors and different
values of k.
The exact number of bits of the different downlink DPCH fields is yet to be determined.
In order to support the use of downlink adaptive antennas, connection-dedicated pilot bits
are transmitted also for the downlink.
Multi-code transmission is employed when the total bit rate to be transmitted on one
downlink connection exceeds the maximum bit rate for a downlink physical channel: several
parallel downlink DPCHs are transmitted for one connection using the same spreading
factor.
In this case, the control information is put on only the first downlink DPCH, while the
additional downlink DPCHs belonging to the connection do not transmit any data during the
corresponding time period.
Pilot Datos
Slot #1 Slot #2 Slot #i Slot #15
Frame #1 Frame #2 Frame #i Frame #72
0.666 ms, 20*2 k bits (k=0..6)
T f = 10 ms
T super = 720 ms
TPC TFCI
DPCCH DPDCH
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4.2.2.4 Common Physical Channels
4.2.2.4.1 Primary Common Control Physical Channel
The Primary CCPCH is a fixed rate (32 kbps, SF=256) downlink physical channel used to
carry the BCCH.
The Figure 4.4.5 shows the frame structure of the Primary CCPCH. It differs from the
downlink DPCH in that no TPC commands or TFCI is transmitted. The only control
information is the common pilot bits, needed for coherent detection.
Figure 4.4.5. Frame Structure for Primary Common Control Physical Channel
4.2.2.4.2 Secondary Common Control Physical Channel
The secondary CCPCH is used to carry the FACH and PCH. As the Primary CCPCH, it is of
constant rate, but the difference between them is that in the Secondary CCPCH the rate may
be different for different secondary CCPCHs within one cell and between cells. This is done
in order to be able to allocate different amount of FACH and PCH capacity to a cell (see
Figure 4.4.6). The BCCH broadcasts the rate and spreading factor of each secondary
CCPCH. The set of possible rates is the same as for the downlink DPCH.
The FACH and PCH are mapped to separate Secondary CCPCHs. A CCPCH is not power
controlled, and this is the main difference between a CCPCH and a downlink dedicated
physical channel. The main difference between the Primary and Secondary CCPCH is that
the Primary CCPCH has a fixed predefined rate while the Secondary CCPCH has a constant
Pilot Data
Slot #1 Slot #2 Slot #i Slot #15
Frame #1 Frame #2 Frame # i Frame #72
0.666 ms, 20 bits
T f = 10 ms
T super = 720 ms
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rate that may be different for different cells, depending on the capacity needed for FACH
and PCH.
Figure 4.4.6. Frame Structure for Secondary Common Control Physical Channel
Furthermore, a Primary CCPCH is continuously transmitted over the entire cell while a
Secondary CCPCH is only transmitted when there is data available and may be transmitted
in a narrow lobe in the same way as a DPH (only valid for a Secondary CCPCH carrying the
FACH).
4.2.2.4.3 Synchronisation Channel
The Synchronisation Channel (SCH) is a downlink signal used for cell search. It consists of
two sub channels, the Primary and Secondary SCH, as shown in Figure 4.4.7.
The Primary SCH transmits the Primary Synchronisation Code, which is an unmodulated
orthogonal code of length 256, the same for every base station in the system.
The Secondary SCH repeatedly transmits the Secondary Synchronisation Codes, a sequence
of 16 unmodulated orthogonal codes of length 256 chips. These are transmitted in parallel
with the Primary Synchronisation channel.
The sequence on the Secondary SCH identifies a group of scrambling codes among 32
possibilities. The base station downlink scrambling code belongs to the indicated group. 32
Pilot Data
Slot #1 Slot #2 Slot #i Slot #15
Frame #1 Frame #2 Frame #i Frame #72
0.666 ms, 20*2k bits (k=0..6)
T f = 10 ms
T super = 720 ms
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sequences are used to encode the 32 different code groups each containing 16 scrambling
codes. It is used to uniquely determine both the long code group and the frame timing.
Figure 4.4.7. Structure of Synchronisation Channel (SCH)
4.2.3 Mapping of Transport Channels to Physical Channels
The Figure 4.4.8 summarises the mapping of transport channels to physical channels.
Figure 4.4.8. Transport-Channel to Physical-Channel Mapping
Cp
i
Csi,1
Cp
Csi,2
Cp
Csi,15
Tframe=15*Tslot
Tslot=2560 chips
256 chips
Primary SCH
Secondary SCH
Cp: Primary Synchronisation CodeCsi,k: One of 16 possible Secondary Synchronisation Codes(Csi,1, Csi,2,...,Csi,15) encode cell specific long scrambling code group i
Transport Channels
BCCH
FACH
PCH
RACH
CPCH
DCH
DSCH
Physical Channels
Primary Common Control Physical Channel (Primary CCPCH)
Secondary Common Control Physical Channel (Secondary CCPCH)
Physical Random Access Channel (PRACH)
Physical Common Packet Channel (PCPCH)
Dedicated Physical Data Channel (DPDCH)
Synchronisation Channel (SCH)
Physical Sownlink Shared Channel (PDSCH)
Transport Channels
BCCH
FACH
PCH
RACH
CPCH
DCH
DSCH
Physical Channels
Primary Common Control Physical Channel (Primary CCPCH)
Secondary Common Control Physical Channel (Secondary CCPCH)
Physical Random Access Channel (PRACH)
Physical Common Packet Channel (PCPCH)
Dedicated Physical Data Channel (DPDCH)
Synchronisation Channel (SCH)
Physical Sownlink Shared Channel (PDSCH)
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4.3 Spreading, Scrambling and Modulation
The basic spreading (and scrambling) chip rate is 3.84 Mcps, which can be extended to 7.68
or 15.36 Mcps.
4.3.1 Uplink Spreading, Scrambling and Modulation
4.3.1.1 Modulation
4.3.1.1.1 Uplink Dedicated Physical Channels (Uplink DPDCH/DPCCH)
The uplink DPDCH and DPCCH are mapped to the I and Q branch respectively. Two
different channelisation codes cD and cC are then used to spread both branches to the chip
rate, and subsequently they are coded by a complex scrambling code associated to the
mobile terminal.
In the case of multi-code transmission, both the I and Q branches may be used to transmit a
new uplink DPDCH, which must be assigned its own channelisation code. However, uplink
DPDCHs transmitted on different branches may use the same channelisation code.
4.3.1.2 PRACH
The message part of the random-access channel uses the same coding/modulation procedure
as the uplink dedicated physical channels, described previously. The data part is similar to
the uplink DPDCH and the control part is similar to the uplink DPCCH. In order to
guarantee that two simultaneous random-access attempts using different preamble codes
and/or sequences will not collide during the message part, the selection of the scrambling
code for the data part is based on:
The randomly chosen preamble sequence,
The preamble code associated to the base station, and
The randomly chosen access slot (random-access time-offset).
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4.3.1.3 Spreading: Channelisation Codes
The uplink uses the same type of channelisation codes as the downlink. In the case of the
uplink, the limitations on the allocation of these codes are only valid within one mobile
station.
Each connection is allocated at least one uplink channelisation code, to be used for the
uplink DPCCH. Usually at least one additional uplink channelisation code is allocated for an
additional uplink DPDCH. If more than one uplink DPDCH is necessary, further uplink
channelisation codes may be allocated.
As different mobile stations use different uplink scrambling codes, the uplink channelisation
codes may be allocated without any co-ordination between different connections. So the
uplink channelisation codes are always allocated in a pre-established order. Once the mobile
station and network reach an agreement on the number and length (spreading factor) of the
uplink channelisation codes, the exact codes to be used are implicitly given.
4.3.1.4 Scrambling: Scrambling Codes
Either short or long scrambling codes should be used on uplink.
4.3.1.4.1 Short Scrambling Code
The short scrambling code is a complex code c scramb = cI + jcQ, where cI and cQ are two
different codes of length 256.
It’s the network who decides the uplink short scrambling code. After an uplink Random
Access Request, the base-station emits a downlink Access Grant message, which tells the
mobile station the short scrambling to use.
The short scrambling code may, only in rare cases, be changed during the duration of a
connection.
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4.3.1.4.2 Long Scrambling Codes
The long uplink scrambling code is typically used in cells without multi-user detection in the
base station. The mobile station is informed if a long scrambling code should be used in the
Access Grant Message following a random-access request and in the handover message.
4.3.1.5 Random Access Codes (Spreading & Scrambling)
4.3.1.5.1 Preamble Spreading Code
The base station broadcasts the spreading code for the preamble part, which is specific of the
cell. If the traffic load is high, the base station can use more than preamble code.
Since two neighbouring cells must not use the same preamble code, these codes have to be
planned.
The code used is a 256 chip code, and the system uses all 256 codes.
4.3.1.5.2 Preamble Signature
The preamble part carries one of 16 different signatures of length 16, <P0, P1,..., P15>. The
base station broadcasts which signatures are allowed to be used in a cell.
4.3.1.5.3 Channelisation Codes for the Data Part
The signature in the preamble specifies one of the 16 possibilities for the channelisation
code. The control part is always spread with a known channelisation code of length 256, so it
can be detected by the base station. The base station obtains the spreading factor used on the
message part from the rate information field of control part. The base station gets the
channelisation code used in the data part either with the help of the preamble signature and
the rate information.
In this way, simultaneous detection of multiple random access messages arriving in the same
access slot is allowed by the use of different signatures.
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4.3.1.5.4 Scrambling Code for the Data Part
In addition to spreading, the message part is also subject to scrambling with a 10 ms
complex code. The scrambling code is cell-specific and has a one-to-one correspondence to
the spreading code used for the preamble part. Note that although the scrambling code is the
same for every access slot, there is no scrambling-code collision problems between different
access slots due to the 1.25 ms time shift between the access slots.
4.3.2 Downlink Spreading, Scrambling and Modulation
4.3.2.1 Modulation
The modulation scheme used for the data part is QPSK; each pair of two bits are first
converted from serial to parallel and then mapped to the I and Q branch, respectively. The
channelisation code cch spreads the I and Q branch to the chip rate (real spreading), and
subsequently they are scrambled with cscramb, the cell-specific scrambling code (real
scrambling).
The spread/modulation process must also be applied to every additional downlink DPCH, in
the case of multi-code transmission. Each additional downlink DPCH should be assigned its
own channelisation code.
4.3.2.2 Spreading: Channelisation Codes
The number of available channelisation codes is not fixed but depends on the rate and
spreading factor of each physical channel.
The BCCH uses a predefined channelisation code, which is the same for all the cells within
the system.
The BCCH broadcasts the channelisarion code(s) used in the Secondary Common Control
Physical Channel.
The channelisation codes for the downlink dedicated physical channels are decided by the
network. After an uplink Random Access request, the base station responds with a downlink
Access Grant message, informing the mobile station about the downlink channelisation
Coding /interleaving
Coding /interleaving
Coding /interleaving
Parallel services
Service 1
Service 2
Service N
Coding /interleaving
Coding /interleaving
Coding /interleaving
Coding /interleaving
Coding /interleaving
Coding /interleaving
Parallel services
Service 1
Service 2
Service N
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codes to receive. If a change of service or an inter-cell handover occurs, the set of
channelisation codes may be changed during the duration of the connection. This change of
downlink channelisarion codes is negotiated over a DCH.
4.3.2.3 Srambling: Scrambling Codes
There are 512 available scrambling codes, grouped into 32 code sets with 16 codes in each
set. The grouping facilitates the process of fast cell search. In the initial deployment a
downlink scrambling code is assigned to every cell, and the mobile knows the scrambling
code in the cell search process.
The scrambling codes are repeated for every 20 ms radio frame.
4.3.2.4 Synchronisation Codes
The Primary and Secondary code words, cp and {c1 ,... , c17} respectively, consist of pair wise
mutually orthogonal codes of length 256.
4.4 Transport Channel Coding and Multiplexing Chain
The following steps can be identified in the Figure 4.4.9, which describes the overall concept
of transport-channel coding and multiplexing:
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Figure 4.4.9. Coding and Multiplexing of Transport Channels
Channel coding, including optional transport-channel multiplexing
Static rate matching
Inter-frame interleaving
Transport-channel multiplexing
Dynamic rate matching
Intra-frame interleaving
The different steps are described in detail below.
The output of the inner interleaving block is usually mapped to one DPDCH. In the case of
multi-code transmission, with very high bit rates, the output is split onto several DPDCHs.
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Transport channels are coded and multiplexed as described above, i.e. into one data stream
mapped on one or several physical channels.
4.4.1 Channel Coding
Every transport channel is coded before transport-channel multiplexing, i.e. channel coding
is done on a per-transport-channel basis. Figure 4.4.10 illustrates this concept.
Figure 4.4.10. Channel Coding in UTRA/FDD
4.4.1.1 Convolutional Coding
If the service requires a BER in the order of 10-3 then is typical to apply convolutional
coding. If the service requires a BER in the order of 10-6 then convolutional coding is
applied in concatenation with RS coding and outer interleaving.
Dedicated transport channels (DCHs) in normal (non-slotted) mode typically use a 1/3-rate
convolutional coding, while DCHs in slotted mode are usually coded with a ½-rate
convolutional coding.
4.4.1.2 Turbo Coding
ETSI is currently investigating the use of Turbo coding for high quality services, which
require data rates above 32 kbps (see Figure 4.4.11). Turbo codes of rate 1/3 and ½ (for the
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highest data rates), have been proposed to replace the concatenation of convolutional and
Reed-Solomon codes. ETSI is awaiting further results of simulations illustrating the
performance of Turbo Codes.
Figure 4.4.11. Block Diagram of a Turbo code encoder
Figure 4.4.12 shows the basic FEC coding structure for the UTRA, which will be employed
in case Turbo codes give an improved FEC for high quality services, compared to the
existing proposals.
Figure 4.4.12. FEC Coding for UTRA/FDD When Turbo Codes are Used
4.4.1.3 Service Specific Coding
The service-specific-coding option allows supplementary coding schemes, in addition to the
standard coding schemes listed above, increasing in this way the flexibility of the UTRA
Layer 1. One example is the use of unequal-error-protection coding schemes for certain
speech-codecs.
4 Air Interface
4.4.2 Inner Inter-Frame Interleaving
Those transport-channels that can allow for and require interleaving over more than one
radio frame (10 ms) use inner inter-frame bit interleaving, carried out on a per-transport-
channel basis. The span of the inner inter-frame interleaving can vary in the range 20 ms to
150 ms.
4.4.3 Rate Matching
Rate matching is carried out according to the following procedures:
Static rate matching: carried out on a slow basis, typically every time a transport channel
is added or removed from the connection.
Dynamic rate matching: carried out on a frame-by-frame 810 ms) basis
4.4.3.1 Static Rate Matching
Two different reasons lead to the use of static rate matching:
To adjust the coded transport channel bit rate to a level where minimum transmission
quality requirements of each transport channel is fulfilled with the smallest differences in
channel bit energy
To adjust the coded transport channel bit rate so that the maximum total bit rate after
transport channel multiplexing is matched to the channel bit rate of the uplink and
downlink dedicated physical channel.
The static rate matching is based on code puncturing and unequal repetition.
It is important to note that the rate matching must be co-ordinated between different
transport channels, although it is carried out prior to transport-channel multiplexing.
4.4.3.2 Dynamic Rate Matching
After the multiplexing of the parallel coded transport channels, it is necessary to match the
total instantaneous rate of the multiplexed transport channels to the channel bit rate of the
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uplink DPDCH, which is done by the dynamic rate matching. It uses unequal repetition and
is only applied to the uplink. On the downlink, discontinuous transmission (DTX) is used
when the total instantaneous rate of the multiplexed transport channels does not match the
channel bit rate.
4.4.4 Transport-Channel Multiplexing
The coded transport channels are serially multiplexed within one radio frame. The output
after the multiplexer (before the inner interleaving) will thus be according to the .
Figure 4.4.13. Transport Channel Multiplexing
Another option is transport-channel multiplexing within the channel-coding unit, usually
after outer RS coding but before outer interleaving.
4.4.5 Inner Intra-Frame Interleaving
Inner intra-frame interleaving over one radio frame (10 ms) is applied to the multiplexed set
of transport channels.
4.5 Service Multiplexing
Service multiplexing allows the separate and independent control of QoS. This is done by
treating multiple services in the same connection with separate channel coding/interleaving
and mapping to different basic physical channels (slot/code) (see Figure 4.4.14).
Figure 4.4.14. Service Multiplexing (a)
Another option is time multiplexing at different points of the channel coding scheme (see
Figure 4.4.15).
Figure 4.4.15. Service Multiplexing (b)
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After service multiplexing and channel coding, the multi-service data stream is mapped to
one or, if the total rate exceeds the upper limit for single-code transmission, several resource
units.
Time Mux
Time Mux
Outer
Coding/interf.Inner
Coding/interf.
Time Mux
Time Mux
Outer
Coding/interf.Inner
Coding/interf.
Time Mux
Service 1
Service 2
...
Service n
Parallel services
Time Mux
Time Mux
Outer
Coding/interf.
Outer
Coding/interf.Inner
Coding/interf.
Inner
Coding/interf.
Time MuxTime Mux
Time Mux
Outer
Coding/interf.Inner
Coding/interf.
Time Mux
Time MuxTime Mux
Outer
Coding/interf.
Outer
Coding/interf.Inner
Coding/interf.
Inner
Coding/interf.
Time MuxTime Mux
Service 1
Service 2
...
Service n
Parallel services
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4.6 Traffic Cases (Examples)
4.6.1 Continuous Transmission in Uplink with Variable Rate
Figure 4.4.16. Uplink Variable Rate (no DTX)
4.6.2 Discontinuous Transmission (DTx) in Downlink with
Variable Rate (1)
Figure 4.4.17. Downlink Variable Rate (DTX)
0,666 ms
1-rate
¼-rate
½-rate
0-rate
: DPCCH-part (Pilot+TPC+RI)
: DPDCH-part (Data)
0,666 ms
1-rate
¼-rate
½-rate
0-rate
: DPCCH-part (Pilot+TPC+RI)
: DPDCH-part (Data)
10 ms
1 rate
¼- rate
½- rate
0- rate
Variable rate
R = 1 R = 1/2 R = 0 R = 0 R = 1/2
: DPCCH (Pilot+TPC+RI)
: DPDCH (Data)
10 ms
1 rate
¼- rate
½- rate
0- rate
Variable rate
R = 1 R = 1/2 R = 0 R = 0 R = 1/2
: DPCCH (Pilot+TPC+RI)
: DPDCH (Data)
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4.6.3 Discontinuous Transmission (DTx) in Downlink with
Variable Rate (2)
Figure 4.4.18. Downlink Variable Rate (DTX)
4.7 Initial Cell Search
The initial cell search is the process of searching for the base station to which the mobile has
the lowest path loss. Subsequently, the mobile determines the downlink scrambling code and
frame synchronisation of that base station. The initial cell search is carried out using the
synchronisation channel (SCH), see Figure 4.4.19.
Figure 4.4.19. Structure of Synchronisation Channel (SCH)
This initial cell search is carried out in three steps:
Cp
i
Csi,1
Cp
Csi,2
Cp
Csi,15
Tframe=15*Tslot
Tslot=2560 chips
256 chips
Primary SCH
Secondary SCH
Cp: Primary Synchronisation CodeCsi,k: One of 16 possible Secondary Synchronisation Codes(Csi,1, Csi,2,...,Csi,15) encode cell specific long scrambling code group i
10 ms
1-rate
½-rate
0-rate
: DPCCH (Pilot+TPC+RI)
: DPDCH (Data)
R = 1 R = 0 R = 1/2 R = 0R = 1
Variable rate
10 ms
1-rate
½-rate
0-rate
: DPCCH (Pilot+TPC+RI)
: DPDCH (Data)
R = 1 R = 0 R = 1/2 R = 0R = 1
Variable rate
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4.7.1 Step 1: Slot Synchronisation
During the first step of the initial cell search procedure the mobile station uses the primary
SCH to acquire slot synchronisation to the strongest base station.
This is done with a single matched filter (or any similar device) matched to the primary
synchronisation code cp which is common to all base stations (see Figure 4.4.20). The output
of the matched filter will have peaks for each ray of each base station within range of the
mobile station. Detecting the position of the strongest peak gives the timing of the strongest
base station modulo the slot length. For better reliability, the matched-filter output should be
non-coherently accumulated over a number of slots.
Figure 4.4.20. Matched-Filter for Primary Synchronisation Code to Slot Synchronisation
4.7.2 Step 2: Frame Synchronisation and Code Group
Identification
During the second step of the initial cell search procedure, the mobile station uses the
secondary SCH to find frame synchronisation and identify the code group of the base station
found in the first step. This is done by correlating the received signal at the positions of the
Secondary Synchronisation Code with all possible (16) Secondary Synchronisation Codes.
Note that the position of the Secondary Synchronisation Code is known after the first step.
The outputs of all the 17 correlators for 16 consecutive secondary SCH locations are used to
form the decision variables.
The decision variables are obtained by non-coherently summing of the correlators outputs
corresponding to each 16 length sequence out of the 32 possible sequences and its 16 cyclic
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shifts giving a total of 512 decision variables. Note that the cyclic shifts of the sequences are
unique. Thus, by identifying the sequence/shift pair that gives the maximum correlation
values, the code group as well as the frame synchronisation is determined.
4.7.3 Step 3: Scrambling Code Identification
During the third and last step of the initial cell search procedure, the mobile station
determines the exact scrambling code used by the found base station. The scrambling code is
identifies through symbol-by-symbol correlation over the Primary CCPCH with all the
scrambling codes within the code group identified in the second step. Note that, from step 2,
the frame boundary and consequently the start of the scrambling code is known. Correlation
must be carried out symbol-wise, due to the unknown data of the primary CCPCH. Also, in
order to reduce the probability of wrong/false acquisition, due to combat background
noise/interference, averaging the correlator outputs over a sequence of symbols 8diversity)
might be required before using the outputs to determine the exact scrambling code.
After the scrambling code has been identified, the Primary CCPCH can be detected, super-
frame synchronisation can be acquired and the system- and cell specific BCCH information
ca be read.
4.7.4 Idle Mode Cell Search
When in idle mode, the mobile station continuously searches for new base stations on the
current and other carrier frequencies. The cell search is done basically the same way as the
initial cell search. The main difference compared to the initial cell search is that an idle
mobile station has received a priority list from the network. This priority list describes in
which order the downlink scrambling codes should be searched for and does thus
significantly reduce the time and effort needed for the scrambling-code search (step 3). Also
the complexity in the second step may be reduced if the priority list only includes
scrambling codes belonging to a subset of the total set of code groups. The priority list is
continuously updated to reflect the changing neighbourhood of a moving mobile station.
4 Air Interface
4.7.5 Active Mode Cell Search
When in active mode, the mobile station continuously searches for new base station on the
current carrier frequency. This cell search is carried out in basically the same way as the idle
mode cell search. The mobile station may also search for new base stations on other carrier
frequencies using the slotted mode.
4.8 Packet Access
The requirements for packet access are:
Fast access
Efficient use of the radio resources
In order to satisfy these requirements, the connection set-up should be fast and closed loop
power control for large packets, and a small overhead for small packets. Moreover, the
possibility of packet scheduling should be included. Small frequently sent packets are sent
on the common channels, while frequently or large packets should use the dedicated
channels.
4.8.1 Common Channel Packet Access
The common channel RACH/FACH would be used for transmitting small packets and
medium data rates. During the time there are no packets to transmit there will be no link
maintenance (see Figure 4.4.21). Open loop power control would be used.
Figure 4.4.21. Common Channel Packet Access
Access Request
User Packet
Access Request
User Packet
Arbitrary TimeAccess Request
User Packet
Access Request
User Packet
Access Request
User Packet
Arbitrary Time
4 Air Interface
4.8.2 Dedicated Channel Single Packet Transmission
Each new packet in a single and scheduled packet transmission is preceded with a random
access request, as shows Figure 4.4.22 During the packet transmission closed-loop power
control is used.
Figure 4.4.22. Dedicated Channel Single Packet Transmission
4.8.3 Dedicated Channel Multi-Packet Transmission
In the case of scheduled and non-scheduled packet transmission, the link will be maintained,
and closed–loop power control will be used during the transmission (Figure 4.4.23). The
link will be released after a defined time-out period.
Figure 4.4.23. Dedicated Channel Multi-Packet Transmissio
Access Request
User Packet
Access Reques
t
User Packet
User Packet
Dedicated Channel (DTCH)
Link maintenance (pilot, TPC)
Scheduled packets
Non-scheduled packets
Access Request
User Packet
Access Reques
t
Access Reques
t
User PacketUser
PacketUser
PacketUser
Packet
Dedicated Channel (DTCH)
Link maintenance (pilot, TPC)
Scheduled packets
Non-scheduled packets
Access Request
Access Request
Arbitrary Time
Common Channel (RACH/FACH)
User Packet
User Packet
Dedicated Channel (DTCH)
Access Request
Access Request
Arbitrary Time
Common Channel (RACH/FACH)
User Packet
User Packet
Dedicated Channel (DTCH)
5 Radio Theory
Chapter 5: Radio Theory
5.1 Introduction
The content of this chapter deals with some selected radio properties and their effects on a
mobile system. In a mobile network the connection between the mobile phone and the
network is done via the air interface with the help of radio waves. The area in which the
mobile and the network can stay in contact with some acceptable quality is called the
coverage area. This area is served by a transmitter/receiver that will transmit towards the
mobile and receive from the mobile. The serving area is called a cell.
5.1.1 Radio Waves and Modulations
A radio wave is an electromagnetic wave of a frequency lower than 3000 GHz. The
electromagnetic wave is produced by the interaction of time varying electric and magnetic
fields. The number of cycles or events per time unit is the frequency, which is expressed in
Hertz, Hz (see Figure 5.5.1).
Figure 5.5.1. Wave Form
There are many different types of electromagnetic waves including radio waves, light,
infrared rays and x-rays. Radio waves are one example of what we refer to as
electromagnetic radiation. They are generally generated by oscillating charges on a
transmitting antenna.
1 cycle
Time
1 cycle
Time
5 Radio Theory
To be able to use the radio waves for transfer of information such as speech or data a
modulation technique is used. Modulation is the process where the amplitude, frequency or
phase of a radio wave (or light wave) is changed.
Figure 5.5.2. Digital Modulation Techniques
There are different ways to modulate a radio signal. We could change the amplitude, the
frequency, the phase or use pulse modulation (see Figure 5.5.2).
In Amplitude Modulation the carrier’s amplitude changes in accordance with the modulated
user signal, while the carrier’s frequency is fixed (shown in Figure 5.5.3).
Figure 5.5.3. Amplitude Modulation
Frequency modulation occurs when the carrier’s frequency is changed according to the
input signal, while the amplitude is unchanged (see Figure 5.5.4). FM modulation is more
immune to noise than AM and improves the overall signal-to-noise ratio. The signal-to-noise
ratio is the ratio between the signal maximum peak-to-peak signal and what remains when
the signal is removed, that is, the ratio of the wanted signal to that of the noise.
Phase Modulation is similar to FM but instead of changing the frequency of the carrier wave,
the phase of the carrier changes (see Figure 5.5.5 and Figure 5.5.6).
M
M = magnitude
= phase
Quadrature component
Q =M sin
In-phase component
I =M cos
M
M = magnitude
= phase
Quadrature component
Q =M sin
In-phase component
I =M cos
Time
Amplitude
Time
Amplitude
5 Radio Theory
Pulse Modulation is a sample of the waveform taken at regular intervals. There exit a variety
of Pulse Modulation schemes not covered here.
Figure 5.5.4. Frequency Modulation
Figure 5.5.5. Binary Phase Shift Keying Figure 5.5.6. Quadrature Phase Shift
Keying
To be able to use analogue signals for digital information they have to be processed by an
intermediate stage before transmission. This is done by a modem (modulator/demodulator)
in a process known as a modulation/demodulation.
5.1.2 Access Methods
In a cellular network we have a mobile phone or terminal connected to the network via a
base station that transmits towards the mobile phone and receives signals from the mobile
phone. This connection is wireless, it uses radio waves in the air interface to set up the
connection. The way we utilise these radio waves in the air is called Access Method and
there exist a number of them with different properties.
Time
Amplitude
Time
Amplitude
Q
I0 state 1 state
Phases separated by 180º ( radians)
Binary Phase Shift Keying (BPSK)
Q
I0 state 1 state
Phases separated by 180º ( radians)
Binary Phase Shift Keying (BPSK)
Q
I
01 state
Phase of carrier: /4, 3/4, 5/4, 7/4
2x bandwidth efficiency of BPSK
Quadrature Phase Shift Keying (QPSK)
11 state
00 state 10 state
Q
I
01 state
Phase of carrier: /4, 3/4, 5/4, 7/4
2x bandwidth efficiency of BPSK
Quadrature Phase Shift Keying (QPSK)
11 state
00 state 10 state
5 Radio Theory
Commonly use access methods in radio networks are Frequency Division Multiple Access
(FDMA), Time Division Multiple Access (TDMA) y Code Division Multiple Access
(CDMA).
FDMA is used for standard analogue mobile telephony. Each user is assigned a discrete part
of the RF spectrum. FDMA permits only one user per channel since it allows the user to use
the channel 100% of the time.
In TDMA the users are still assigned a discrete part of the RF spectrum, but multiple users
now share that RF carrier on a time slot basis. Each of the users alternates their use of the RF
channel. Frequency division is still used, but these carriers are now further sub-divided into
some number of time slots per carrier (3 for TDMA-AMPS, 8 for full rate GSM, 16 for half
rate GSM).
In CDMA there is no time division, and all users use the entire carrier, all of the time.
CDMA is a spread-spectrum communication system in which multiple users have access to
the same frequency band. The allocated frequency segment for that one carrier is
considerably larger than that used in FDMA or TDMA. To distinguish the different users
occupying the same frequency band simultaneously, each user is assigned a binary code.
5.2 Radio Transmission Properties and Problems
5.2.1 Needed vs. Available Capacity
One problem encountered with radio is that the available spectrum is limited. The fewer
spectrums needed per subscriber the more subscribers that can be accommodated on the
network. Since there is no way to create new frequencies we need good modulation
techniques and efficient access methods to use the air interface properly.
Normally, the capacity available is a compromise between needed capacity and the
interference (more interference involve less quality in our connection) that the use of the
same medium by different users produces.
5 Radio Theory
5.2.2 Path Loss
Path loss or attenuation of the signal causes the received signal at the receiver to get weaker
the further away from the transmitter we are (see Figure 5.5.7).
Path loss can be a problem, making it difficult to get sufficient signal strength levels, but it
results also in a lower interference from non wanted transmitters far away from the receiver.
If there would be no path loss the interference from all transmitters around us would be very
high.
Figure 5.5.7. Path Loss
For a given frequency, path loss depends on the distance between the receiver and the
transmitter. One way to estimate this is to use the free space formula. According to this
formula, the path loss varies proximally in the following way:
Pathloss distance 2 x frequency 2
This formula assumes a line of sight condition between the transmitting and receiving
antennas. It also assumes that there are no reflections interacting with the direct radio wave.
Also, as indicated buy the formula, the higher the frequency used, the higher the path loss.
Since the pathloss will increase with an increasing frequency it is beneficial if the weakest
part, according to transmitting power, is using the lowest frequency. By this it will gain
some dB.
5.2.3 Shadowing
If the radio path does not have free line of sight between transmitter and receiver, the
obstacles will cause shadowing. Shadowing is also called “log normal fading” or “long
dd
5 Radio Theory
term fading”. Since the mobile phone normally is located in a low position, transmission
will most likely be affected by shadowing objects, e.g. buildings, hills, the user or virtually
anything in the radio path. When the mobile phone moves around, variations in signal
strength, due to the character of the objects, can be measured in tens of meters.
5.2.4 Multi-Path Propagation
Another effect that might occur especially in an urban area with a lot of reflections objects
near the transmitter and receiver is multi-path propagation (see Figure 5.5.8). Since the
transmitter normally is not transmitting directly towards the receiver but rather in a wide
area towards him/here, there will be a lot of rays reflected by obstacles and the received by
the receiver.
Figure 5.5.8. Multi- Path Propagation
Different reflections would then mean slightly different time delays for the rays and the
reflections also will have different effects on the phase of the radio wave. Normally we
would receive not one, but several reflected radio waves and the resulting wave could be
stronger, or weaker, than the individual waves. If there is no phase difference between the
waves, the resulting wave may have considerably better signal strength, but if the phase
difference between the two signals is close to 180 degrees they may null each other out. This
cancelling out effect may cause very deep fading dips. The phenomenon is called multi-path
5 Radio Theory
or Rayleigh fading. On the other hand a receiver could with the help of some addative
procedures capture a number of different reflected rays and the take “the best” out of this
information.
In a GSM system multipath propagation can cause problems in the receiver, multipath
fading, while in another system like UMTS with a RAKE receiver structure this leads to the
possibility of diversity gain turning the multipath channel to its advantage.
5.2.5 Time Dispersion
One effect of multipath propagation is time dispersion due to varying propagation delays.
The effect is that the impulse response of the propagation channel is spread out. The amount
of time dispersion is roughly described by the delay spread (see Figure 5.5.9).
Figure 5.5.9. Channel Impulse Response (Power) / Time Delay
5.3 Radio Transmission Optimisatioin Techniques
5.3.1 Access Methods: Capacity vs Interference
Interference is the term for a non-wanted signal that the receiver experiences. In e.g. GSM
where we reuse the number of frequencies available this might mean that there is a
transmitter using the same frequency as the wanted signal (see Figure 5.5.10). Reusing an
identical carrier frequency in different cells is limited by co-channel interference or C/I. Co-
Impulse response
time1 2 3
Impulse response
time1 2 3
5 Radio Theory
channel interference is the relation between the desired signal C and the undesired re-used
signal I, both using the same carrier frequency.
Radio communication systems often separate users either by frequency channels, timeslots,
or both. This is e.g. true for GSM. Since the number of available frequencies both are limited
by physics and by regulation the frequencies then must be reused (see Figure 5.5.11).
This might cause an interference problem that will be handled by keeping the reuse
frequencies (same frequencies) as far away from each other as possible. Satisfactory
performance in these systems depends critically on control of the mutual interference arising
from this reuse pattern.
Figure 5.5.10. Interference
Another approach to this is used in CDMA. Instead of partitioning either spectrum or time
into disjoint “slots” each user is assigned a different instance of the noise carrier. While
those waveforms are nor rigorously orthogonal (they do not interfere with each other), they
are nearly so.
Figure 5.5.11. Reusing Frequencies in GSM Figure 5.5.12. In CDMA
CI
Carrier, f1 Interferer, f1
CI
Carrier, f1 Interferer, f1
A
A
AA
B
B
B
B
C
C
C
D
D
D
E
FA
A
AA
B
B
B
B
C
C
C
D
D
D
E
F A
A
AA
A
A
A
AA
AA
AA
A
A
AA
A
A
A
AA
AA
AA
5 Radio Theory
The major benefit of noise-like carriers is that the system sensitivity to interference is
fundamentally altered. Traditional time or frequency slotted systems must be designed with
a reuse ratio that satisfies the worst-case interference scenario. Use of noise-like carriers,
with all users occupying the same spectrum, makes the effective noise the sum of all other-
user signals.
The receiver correlates its input with the desired noise carrier, enhancing the signal to noise
ratio at the detector. The enhancement overcomes the summed noise enough to provide an
adequate Signal to Noise Ratio, SNR at the detector. Because the interference is summed,
the system is no longer sensitive to worst-case interference, but rather to average
interference. The reuse pattern is now the same for each (see ).
5.3.2 Diversity
One of the objectives in system optimisation is to reduce or benefit from the multipath and
shadowing effects. Some are applicable to TDMA and FDMA as well as CDMA system.
There are different combinations to diversity.
5.3.2.1 Space Diversity
By using two receiving antennas, chances are that they do not experience the same multipath
propagation at the same time. A certain distance between the antennas could be used (space
diversity) or the antennas element could be polarised (polarisation diversity). The use of
antenna diversity will improve the carrier to interference (C/I) properties of the systems as
the problem with the fading dips is reduced.
5.3.2.2 Frequency Diversity
Another effective way to fight negative effects of multi-path propagation is to change the
frequency, thus changing the positions of the dips. When frequency hopping is applied as in
GSM/DCS, each consecutive burst will be transmitted (and of course received) at a different
frequency.
5 Radio Theory
5.3.2.3 Multi-Path Diversity
Here versions of the signal arrive via separate paths and at different times and are combined
in the receiver.
5.3.2.4 Macro Diversity
Simultaneous use of links between the mobile and two or more fixed transmitters. Can for
example be used to provide a smooth transition as the mobile moves from transmitter to
another (soft handover).
5.3.2.5 Time Diversity
Obtained by using symbol interleaving and error correction coding to introduce time
correlation into the signal (described later in this chapter).
5.3.3 Error Detection and Correction
In the first and second generation mobile system like NMT and GSM the main intention and
use of the system have been foe speech communication. The 3rd generation system, like
UMTS, will need to handle more and more of data transmission and multimedia. This, in
contrast to pure speech system, adds high demands on the quality. Typical data services
require very low error rates. Over a radio channel that experiences a lot of problems we need
something to detect errors and correct them.
This could be done with the help of retransmission of information that was faulty and/or by
adding redundant information to the data. Channel coding is a way to add information to the
data so that errors could be detected and corrected. Interleaving is a technique to help the
channel coding procedure.
5.3.3.1 Channel Coding
In an analogue network the loss of some information will only decrease the quality
somewhat. The ear is able to correct the analogue signals that are slightly incorrect. In a
digital network, however, the importance of each bit of information is crucial. The symbol
5 Radio Theory
“1” interpreted as a “o” gives a totally different piece of information. The quality of the
received signal is often measured in Bit Error Rate (BER). The BER represents what
percentage of the bits that is not correctly detected.
Two different methods of channel coding are block coding and convolutional coding. The
philosophy of both of them is basically the same; adding a number of redundant bits to help
detect or correct the errors protects the bits.
5.3.3.1.1 Block coding
When block coding is used, one or several check bits are added to the information block.
The check bits only depend on the bits in that block.
A simple form of block coding is using a parity bit. The parity bit could be set to zero if the
1’s in the block equal an even number. Otherwise the parity bit is set to one, so that the
number of 1’s in the total block are always even (see Figure 5.5.13).
Block coding is mainly used for detecting errors. In the computer world block coding is
often used together with a retransmission command, demanding the transmitting part to
resend. This is not so useful when dealing with a real time application such as speech.
Figure 5.5.13. The Principle of Block Coding
5.3.3.1.2 Convolutional Coding
The convolutional code consists of a shift register into which one shifts on the information
bits. Doing logical operations on the positions of the bits in the register produces the coded
information bits. This will make several coded bits dependent on one of the information
symbols shifted into the coder. When all the information are shifted through the register we
have produced the coded bits that will be sent (see Figure 5.5.14).
If 1 then add 1
If 0 then add 0
Information Parity bits
Received Means
11 1
00 0
01 error
10 error
If 1 then add 1
If 0 then add 0
Information Parity bits
Received Means
11 1
00 0
01 error
10 error
5 Radio Theory
Convolutional coding is not good for detecting errors, but also for correcting them. The
condition for being able to correct errors is that only few errors appear at a time, with a
certain number of correct bits in between the incorrect ones.
Figure 5.5.14. The Principle of Convolutional Coding
5.3.3.2 Interleaving
The error detection and correction methods mentioned, work best when the bits lost are
spread out at a certain distance.
Interleaving is a method of spreading the potential losses, so that they can be taken care of
by “Channel Coding” thus minimising the harm longer sequences lost. An analogy of this
is, if the last 20 pages are torn out of an Agatha Christie novel, it will be more difficult to
reconstruct the plot than if every 10th page, totalling 20 pages is lost. As an example, let us
assume that each message block contains four symbols.
Figure 5.5.15. If Several Blocks Regroup the Information.
Assume also that it is likely that we loose not only one, but four consecutive symbols in a
block. If we re-arrange them so that all number one symbols are put together in one block,
all the number two symbols in another, etc., we will loose symbols from several blocks,
infoBit 3 Bit 2 Bit 1
Output A
Output B
XOR
XOR
infoBit 3 Bit 2 Bit 1
Output A
Output B
XOR
XOR
T H E YM U S TH E A RT H I S
THEY MUST HEAR THIS
T H ? YM U ? TH E ? RT H ? S
THMT HEUH IASE SRTY
TH?Y MU?T HE?R TH?S
T H E YM U S TH E A RT H I S
T H E YM U S TH E A RT H I S
THEY MUST HEAR THIS
T H ? YM U ? TH E ? RT H ? S
THMT HEUH IASE SRTY
TH?Y MU?T HE?R TH?S
5 Radio Theory
BUT not one complete block. If only parts of a block are lost, the chance of reconstructing
the information improves dramatically (see Figure 5.5.15).
6 User Equipment (UE)
Chapter 6: User Equipment (UE)
6.1 Terminals in the General UMTS System
The shown below represents the general schematic in the system, as they are explained in
this chapter.
Figure 6.6.1. UMTS Domains and Reference Points
We can divide basically between the User Equipment or Terminal (UE), and the
infrastructure. This is represented by the interface Uu. So we can have these two big
domains: the User Equipment Domain and the Infrastructure domain.
HomeNetworkDomain
Zu
YuIuUuCu
USIMDomain
MobileEquipment Domain
RANDomain
CN Domain
ServingNetwork Domain
TransitNetwork Domain
User Equipment Domain Infrastructure Domain
Cu = Reference point between USIM and ME
Iu = Reference point between Access and Serving Network domains
Uu = Reference point between User Equipment and Infrastructure domains, UMTS radio
interface
Yu = Reference point between Serving and Transit Network domains
Zu = Reference point between Serving and Home Network domain
6 User Equipment (UE)
User equipment is the terminal that the user employs to access to the UMTS service. This
equipment has a radio interface to the infrastructure.
The infrastructure is made up of the several physical nodes that develop the various
functions required to terminate the radio interface and to support the telecommunication
services requirements to the users. The infrastructure is a shared resource by all the users and
it will provide services to all these users (authorised) within its coverage area. The reference
point between the user equipment domain and the infrastructure domain is called the “Uu”
reference point (UMTS radio interface). As it has been said, it is a very important interface,
because it separates two different worlds.
6.1.1 User Equipment Domain
This part of the system stores a variety of equipment types with different levels of
functionality. These equipment types are referred to as user equipment (terminals), and they
may also be inter-connectable with one or more existing access systems, in such a way that
we can have dual mode UMTS-GSM user equipment.
As it has also been said, the terminal will include a removable smart card that may be used in
different user equipment types, as it happens in GSM. The user equipment is as well sub-
divided in to the Mobile Equipment Domain (ME) and the UMTS Subscriber Identity
Module Domain (USIM). Here we have another interesting interface, the Cu reference point
6.1.1.1 USIM Domain
The USIM, UMTS Subscriber Identity Module, contains data and procedures that
unambiguously and securely identify it. These functions are typically embedded in a stand-
alone smart card. This device is associated to a given user, and as such allows identifying
this user regardless of the ME he uses.
6.1.1.2 Mobile Equipment Domain
The Mobile Equipment contains applications and performs radio transmission. The mobile
equipment may be further sub-divided into several entities, e.g. the one which performs the
6 User Equipment (UE)
radio transmission and related functions, Mobile Termination, MT, and the one which
contains the end-to-end application or (e.g. laptop connected to a mobile phone), Terminal
Equipment, TE.
6.2 Applications of the UE
This 3 generation system wants to offer service capabilities that enable the wide variety of
services that the vendors will offer to be implemented. Such services range from simple
services like voice, to complex multimedia services containing several simultaneous media
components that place totally different requirements on the system and on the terminal
equipment.
A wide range of terminal types is likely in the UMTS environment, e.g. speech only
terminals, videophones, data terminals, wideband data terminals, fax terminals, multi-
band/multi-mode terminals and any combination of the aforementioned. By standardising
service capabilities rather than actual services, more flexibility is available for service
providers/network operators to create unique services. The same principle also applies for
UMTS terminals, i.e. the types of terminals are not standardised and are therefore not limited
in any way.
We know that no UMTS Terminal is going to be defined by the specifications, the power
classes need to be determined, for cell planning reasons. The maximum power will affect
User Equipment possibilities to support the upper range of bit services over the UMTS
coverage area. Cell planners will plan for achieving coverage for higher bit rates on the cell
border primarily for power class 1-user equipment's. The following four classes are defined:
2 W
0.5 W
0.25 W
0.125 W
6 User Equipment (UE)
We already know that no terminal types are standardised, so user equipment must indicate to
the network a set of terminal capabilities in order to be handled properly by the UTRAN and
the Core Network. The set of terminal capabilities includes radio capabilities, multimedia
capabilities and speech coders/decoders that are supported by the user equipment.
The radio parts of a user equipment can support any combination of GSM circuit switched
radio, GSM packet switched radio, UMTS FDD-mode and UMTS TDD-mode, and
additionally other radio access modes, due to the compatibility we have already talked
before.
Multimedia capabilities may include which type of display and which coders/decoders that
are supported for video and audio. Finally, GSM and UMTS networks and terminals include
a number of different speech coders:
GSM Full Rate
GSM Half Rate
GSM Enhanced Full Rate
GSM Full Rate Adaptive Multi-Rate
GSM Half Rate Adaptive Multi-Rate
UMTS Adaptive Multi-Rate
The UMTS user equipment has a default speech code, the UMTS Adaptive Multi-Rate
(AMR) code. It generates a variable rate bit-stream of bit-rates between 4.75 – 12.20 kbit/s
depending on the characteristics of input speech signal.
6.3 Multimedia User Equipment
The ITU has developed extensions to the fixed terminal standards to adapt them to mobile
communication characteristics such as higher bit error rates.
The general architecture of a H.324 multimedia terminal in UMTS user equipment is shown
in Figure 6.6.2.
6 User Equipment (UE)
Mobile multimedia terminals for UMTS are based on existing multimedia terminal standards
for the fixed networks. ITU has produced a number of such standards, the so-called H-series.
Where needed slight modification for the UMTS case is introduced by 3GPP. ITU standards
H.323 and H.324 are used for UMTS multimedia terminals. H.324 is the standard for circuit
switched multimedia over the PSTN while H.323 targets multimedia over packet switched
networks with no support of guaranteed Quality-of-Service.
Figure 6.6.2. UE Multimedia General Architecture.
The Application SW is not part of the standard. It contains the application software, e.g. the
user interface, in the terminal for multimedia application and controls the usage of the other
blocks in the Figure 6.6.2 which implement the H.324 standard components.
The H.324 components are:
A video coder/decoder that transfers analogue video into a digital bit-stream (H.263)
The audio coder/decoder that transfers analogue audio into a digital bit-stream (G.723.1)
Data protocols for end-to-end retransmissions and flow control for transfer of user data
end-to-end (e.g. LAP-D)
Control procedures for multimedia session set up and release end-to-end (H.245)
All the streams generated by the four entities above are finally multiplexed into one
single bit-stream according to the H.324 multiplex standard H.223.
Multiplex
VideoCodec
AudioCodec Data
End-to-EndControl
To Mobile Termination
Application SW
6 User Equipment (UE)
In order to have terminals that work properly the single bit-stream from the multiplexer
requires a bit-rate of at least 32 kbit/s.
The five entities in the H.324 terminal part reside in the Terminal Equipment part of the
UMTS User Equipment. The single bit-stream from the multiplexer is sent to the Mobile
Termination part of the User Equipment for transparent transport over the radio interface an
onwards. (The core network will be aware of the fact that the call is a H324 call in order to
activate specific rate adaptation functions in the so-called Interworking Function in the
MSC).
3GPP has added the ETSI AMR speech coder/decoder to the list of possible audio codecs for
the purpose of mobile-to-mobile multimedia calls. The G.723.1 speech codec has to be
supported by UMTS multimedia terminals for interworking with terminals in the fixed
network. We also have the standard MPEG-4, for video applications, introduced by the
International Standardisation Organisation. It is introduced for every kind of video
applications, i.e. not only videotelephony.
6.4 UMTS Subscriber Identity Module (USIM)
This module of the Terminal must contain information enough to identify the user and
service provider. USIM is a UMTS specific application residing on a removable IC card and
is required for service provision. The application in order to allow more versatile UMTS IC
card functionality such as access to value-added services. Authentication and ciphering
functionality may be part of USIM or some other application on the same or different IC
card.
Necessary requirements for IC Cards used for holding USIM application are related to the
need to have one USIM application on the IC card, as well as to the security issues. The
following functionality is required from the IC card holding USIM application:
The support of at least one USIM application (several USIM applications belonging to
different UMTS service providers may reside on the same IC card).
6 User Equipment (UE)
Possibility to update USIM specific information over the air, (e.g. such information as
service profile information, algorithms, etc.) in a secure and controlled manner.
The support of one or more user profile on the USIM
Physical characteristics same as used for GSM SIM (note that the standard supports
inserting a GSM SIM card into a UMTS user equipment which will enable access to the
GSM set of services, i.e. no UMTS specific service).
Possibility to update USIM specific information over the air, (e.g. such information as
service profile information, algorithms, etc.) in a secure and controlled manner.
User authentication.
The standard should support the following additional functionality for the IC Cards in
UMTS environment:
Security mechanisms to prevent USIM application specific information from
unauthorised access or alteration. Verification of the access privilege shall be performed
on the card itself and not delegated to another entity (for example the terminal).
The support for more than one simultaneous application (Multiple USIM, Ecash and/or
some other applications).
An interface allowing highly secure downloading and configuration of new functionality,
new algorithms and new applications into the IC card as well as updating the existing
applications, algorithms and data.
Possibility for some applications/files to be restricted to one or some of the subscriptions,
under user/SP control, with all applications that are shared, being done so in a secure
manner.
Possibility to have shared applications/files between multiple subscriptions including
other user and Service Provider controlled files and data, as well as for as yet undefined
applications (including downloadable applications) required by the future services.
Related security issues have to be analysed.
6 User Equipment (UE)
Inclusion of a payment method (electronic money and/or prepaid and/or subscription
details)
Support for storing and possibly executing encryption related information, such as keys
and algorithms.
The ability to accept popular value-adding IC card applications, such as digital signature
applications, EMV credit/debit card, electronic purses such as Mondex and Visacash, etc.
Dynamic addition and deletion of these applications during the lifetime of the card is
envisaged.
Possibility for one UMTS SP to block multiple subscription on the card the SP has
issued.
In multi application cards a functionality to prevent the unauthorised access and
alteration of USIM specific information by other applications residing on the card.
With all of these shared applications we can include database (e.g. telephone books), service
profiles (e.g. controlling divert information), users preferences (e.g. short dialling codes) and
SP-specific parameters inside a USIM application (e.g. call barring tables).
6.5 Technology of the Terminals
The complexity of the equipment of the 2nd generation digital cellular terminals is already
considerable. The first reason for this, cellular systems themselves require a huge amount of
functions to be fulfilled, from channel and speech coding to signalling and data protocols. In
addition to those functions, all terminals have there owned mobile system independent
features, sometimes also called as Value Adding features. Examples of these are memory
databases, speech recognition, messaging features, display functions, and different source
coding methods (e.g., JPEG).
Terminal development trends for today’s terminals are mainly towards higher integration
levels resulting in smaller size. The goal of “four 100´s” has been a rule of thumb target for
handsets, i.e., 100 hour standby, 100 cc size, 100 gram weight and also 100 MIPS
performance. The size targets have already been achieved and any requirement for smaller
6 User Equipment (UE)
terminals is questionable from the usability and physical size limitation perspective. The
other target parameters have no maximum limitations. On the other hand, we can see the
following further trends for near future terminals:
Increased number of value adding features (graphics, smart messaging, PC connectivity
and compatibility).
Support of higher number of source codecs (several speech codecs).
Application specific terminals (smart traffic, vending machine radio, etc.).
Multi-mode terminals (e.g., GSM/DECT dual-mode terminal).
Multi-band terminals (e.g., GSM in 900 MHz and DCS1800).
Dynamic SW configurability.
These trends are more than likely to continue in the future. The users would prefer multi-
band and multi-mode terminals with high integration levels. Technological development of
these terminals relies on new packaging and interconnection technologies, as well as
technological steps like SW-radio. The concept trends of mobile handheld terminals is likely
to diverge from simple speech terminals towards a variety of different types, e.g.,
communicators, were able phones, data terminals, etc. These new data- and multimedia-
oriented terminals will challenge the dominant role of speech terminals in the future.
New radio-interface and system capabilities will enable higher quality multimedia services
to be provided and therefore new terminal concepts to evolve, the variety of terminals in the
UMTS environment will evidently be large. Terminal implementation technologies, such as
digitalisation providing programmability and terminal configurability, VLSI, and display
technologies, have developed a lot recently and will undergo further development in the
future. Processing power, implementation architectures, IC and passive integration, and
memory technologies are developing rapidly and will facilitate an increase in terminal
functionality that will enable higher integration of terminals, as well as the integration of
more functionality into smaller terminals.
It can be clearly seen that the technical development of IC cards in the UMTS context.
Compared to current IC cards (e.g. GSM Phase 2 SIM cards), the amount of memory and
6 User Equipment (UE)
processing power will increase significantly. These development trends will meet the
requirements of UMTS and should be taken into account while defining the features and
functions of UMTS card.
The trend for IC cards (used form the USIM) is similar to those form terminals. The next
generation of IC cards will be multi-application cards capable of supporting several
applications simultaneously. Furthermore, applications could be downloaded to and removed
from these cards, both at the time of issuing and during the card’s lifetime. The advent of
these virtual machine cards, e.g. Java cards and Multi cards, will change the roles of the card
issuers and application providers, and will enable IC cards to be much more flexible in the
future.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Chapter 7: UMTS Terrestrial Radio Acces
Network (UTRAN)
7.1 Introduction
UTRAN (UMTS Radio Access Network) is the radio access network for UMTS, and it
provides the connection between the core network and the user equipment. In UMTS
Release 99 UTRAN is considered the only access network. UTRAN will support high bit
rate bearer services with the notion of negotiated QoS characteristics. It will also support
asymmetric and bursty traffic for single- and multi-media IP as well as N-ISDN applications.
UMTS R-99 puts interoperability requirements on both UTRAN and GSM BSS access
networks, in such a way that the evolved GSM network is compatible with UTRAN
regarding roaming and handover. It might however be the case that the advanced bearer
capabilities of UTRAN not are fully supported by the core network.
7.2 UTRAN Main Aspects
7.2.1 General Principles
The general principles for UTRAN:
Logical separation of signalling and data transport networks.
A full separation of UTRAN and CN functions from the transports functions.
Full support for macro diversity in UTRAN-FDD
The RNC connection and its mobility is fully controlled by the UTRAN.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.2.2 Capabilities
The radio access bearer (RAB) capabilities for UTRAN are specified in 22.105.
UTRAN in R-99 shall have the following capabilities:
One UTRAN is contained in one UMTS network.
The set-up, re-negotiation and clearing, of connections.
Negotiation and re-negotiation of QoS.
Supported bit rates:
At least 144 kbit/s rural outdoor.
At least 384 kbit/s urban outdoor.
At least 2048 kbit/s indoor/low range outdoor.
Support for broadcast and multicast applications.
Support for multiple simultaneous RABs.
Seamless handover within UTRAN.
Support for dual mode terminals FDD-TDD.
Support for handover TDD-FDD-GSM.
Support for positioning within 50 meters.
Support for Localised Service Area (LSA)
Optimisation of UTRAN radio interface is based on high bit rates, bursty, asymmetric,
both real time and non-real time capabilities.
Standardised operation, administration and maintenance protocols co-operating with
ETSI TMN.
USIM requirements shall be considered.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.2.3 UTRAN and GSM BSS (GSM Base Station Subsystem)
Since the evolution to UMTS will be gradually, the co-existence of UTRAN and GSM BSS
in a network is essential. This requires the following for UMTS R-99:
Support of dual mode terminals (UMTS/GSM) that can select cells to camp on from both
systems in idle mode and connected mode.
Paging and cell selection procedures shall be designed to handle the combination of
GSM and UTRAN cells.
Support of handover between UMTS and GSM BSS in both directions.
Note that some traffic flows might be re-negotiated or even released because of the different
radio access bearer capabilities of the different access networks.
7.3 UTRAN System Architecture
7.3.1 UMTS General System Architecture
UTRAN is connected to the CN over the Iu interface, and with UE over the radio interface
Uu. Over these interfaces the protocols are divided in "User plane protocols" (UPP) and
"Control plane protocols (CPP). The UPP implements the actual Radio Access Bearer (RAB)
service that carries the data through the Access Stratum (AS). The CPP controls the RAB,
but can be used to transparently transfer Non-Access Stratum (NAS) messages (i.e. CM,
MM (Mobile Management), GMM and SM messages).
Figure 7.7.1. UMTS System General Architecture
7.3.2 UTRAN Architecture
The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network
through the Iu. A RNS consists of a Radio Network Controller and one or more Node Bs. A
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Node B is connected to the RNC through the Iub interface. A Node B can support FDD
mode, TDD mode or dual-mode operation.
The RNC is responsible for the Handover decisions that require signalling to the UE. The
RNC comprises a combining/splitting function to support macro diversity between different
Node B. A RNC supporting the FDD mode may include a combining/splitting function to
support macro diversity between different Node B.
Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnected
together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over
physical direct connection between RNCs or via any suitable transport network.
Figure 7.7.2. UTRAN Architecture
7.4 UTRAN Nodes
7.4.1 Node B
Node B transmits and receives in one or more cells. There are three modes for a Node B:
TDD, FDD or a combination of TDD and FDD. The Node B interfaces the UE over the Uu
interface, and the RNC over the Iub interface. One Node B consists of the following blocks:
RNS
RNC
RNS
RNC
Core Network
Node B Node B Node B Node B
Iu Iu
Iur
Iub IubIub Iub
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.4.1.1 Control
The control function is responsible for the signalling towards the RNC and the O&M
functions. It also monitors the radio quality in the cells, and insert data in the system
information.
7.4.1.2 Signal Processing
The processing of the signal has different requirements in UL and DL:
Uplink:
SC/CC generation
Despreading
Rake receiver
Deinterleaving
Channel decoding
Combining (in softer handover)
Downlink:
Splitting (in softer handover)
Channel coding
Interleaving
CC/SC generation
Spreading
7.4.1.3 Transmitter / Receiver
The transmission/reception part handles the carrier generation and is responsible for the
output power. Here is the modulation/demodulation performed. The modulation is QPSK.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.4.2 The Radio Network Controller (RNC)
The RNC is in control of one or several Node B:s. It interfaces the MSC or SGSN in the core
network over the Iu interface, and the Node B over the Iub interface. An interface between
RNC:s is specified, and known as the Iur interface. The RNC consists of the following:
7.4.2.1 Radio Network Management
Signalling both to CN and UE is handled by radio network management functions. This
function is also responsible for the (re-)negotiation with an UE in a cell and the CN for the
QoS for a call/session. This function is also responsible for the control of system information
from CN and UTRAN.
7.4.2.2 Radio Access Bearer Management
The radio access bearer management functions is responsible for the establishment,
supervision and release of radio bearers.
Establishment: assigns and activates channels in Node B, and assigns channels to the
UE
Supervision: monitors QoS, handover decisions
Release: deactivates channels
7.4.2.3 Signal Processing
The signal processing functions handles flow control and retransmissions, as well as the
SOHO procedures combining (UL) and splitting (DL). It also handles the
ciphering/deciphering.
7.5 UTRAN Interfaces
UTRAN contain two internal interfaces (Iub, Iur) and interfaces to the UE (Uu) and the core
network (Iu).
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.5.1 General Principles for UTRAN Interfaces
As few options as possible for the functional division across the interfaces.
Interfaces should be based on a logical model of the entity controlled through this
interface.
Transport Network Control Plane is a functional plane in the interface protocol structure that
is used for the transport bearer management. The actual signalling protocol that is in use
within the Transport Network Control Plane depends on the underlying transport layer
technology. The intention is not to specify a new UTRAN specific Application Part for the
Transport Network Control Plane but to use signalling protocols standardised in other
groups (if needed) for the applied transport layer technology.
7.5.2 Iu Interface
7.5.2.1 Access Network Triggered Streamlining
One Access Network triggered function needed over the Iu interface is the function for
SRNS Relocation. SRNS Relocation needs support from the Core Network to be executed.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Figure 7.7.3. Serving RNS Relocation
7.5.2.2 Iu Interface Protocol
The Radio Network signalling over Iu consists of the Radio Access Network Application
Part (RANAP). The RANAP consists of mechanisms to handle all procedures between the
CN and UTRAN. It is also capable of conveying messages transparently between the CN
and the UE without interpretation or processing by the UTRAN.
Over the Iu interface the RANAP protocol is, e.g. used for:
Facilitate a set of general UTRAN procedures from the Core Network such as paging
-notification as defined by the general SAP.
Separate each User Equipment (UE) on the protocol level for mobile specific signalling
management as defined by the dedicated SAP.
Transfer of transparent non-access signalling as defined in the dedicated SAP.
Request of various types of UTRAN Radio Access Bearers through the dedicated SAP.
Perform the streamlining function.
SRNS
Core Network
Iu
DRNSIur
UE
RNS
Core Network
Iu
SRNS
UE
After SRNS RelocationBefore SRNS Relocation
Cells
7 UMTS Terrestrial Radio Acces Network (UTRAN)
The Access Stratum provides the Radio Access Bearers.
Various transmission possibilities exist to convey the bearers over the Iu to the Core
Network. It is therefore proposed to separate the Data Transport Resource and traffic
handling from the RANAP (Figure 7.7.4). This resource and traffic handling is controlled by
the Transport Signalling. A Signalling Bearer carries the Transport Signalling over the Iu
interface.
Figure 7.7.4. Separation of RANAP and Transport over Iu
The RANAP is terminated in the SRNS.
7.5.3 Iur Interface
The Iur interface connects a SRNS and a DRNS. This interface should be open. The
information exchanged across the Iur is categorised as below:
One or more Iur Data stream which comprises:
Radio frames
Simple, commonly agreed Quality estimate
Synchronisation information
Signalling:
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Addition of Cells in the DRNS which may lead or not to the addition of an new Iur
Data stream
Removal of Cells in the DRNS
Modify Radio bearer characteristics
From a logical stand point, the Iur interface is a point to point interface between the SRNS
and all the DRNS, i.e. there is no deeper hierarchy of RNSs than the SRNS and DRNS.
However, this point to point logical interface should be feasible even in the absence of a
physical direct connection between the two RNSs.
7.5.3.1 Functional Split over Iur Interface
7.5.3.1.1 Macro Diversity Combining/Splitting
DRNS may perform macro-diversity combining/splitting of data streams communicated via
its cells. SRNS performs macro-diversity combining/splitting of Iur data streams received
from/sent to DRNS(s), and data streams communicated via its own cells.
The internal DRNS handling of the macro-diversity combining/splitting of radio frames is
controlled by the DRNS.
7.5.3.1.2 Control of Macro Diversity Combining/Splitting Topology
When requesting the addition of a new cell for a UE-UTRAN connection, the SRNS can
explicitly request to the DRNS a new Iur data stream, in which case the macro-diversity
combining and splitting function within the DRNS is not used for that cell. Otherwise, the
DRNS takes the decision whether macro-diversity combining and splitting function is used
inside the DRNS for that cell i.e. whether a new Iur data stream shall be added or not.
7.5.3.1.3 Handling of DRNS Hardware Resources
Allocation and control of DRNS hardware resources, used for Iur data streams and radio
interface transmission/reception in DRNS, is performed by DRNS.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.5.3.1.4 Allocation of Downlink Channelisation Codes
Allocation of downlink channelisation codes of cells belonging to DRNS is performed in
DRNS.
Note that this does not imply that the signalling of the code allocation to the UE must be
done from the DRNS.
7.5.3.2 Iur Interface Protocol
The signalling information across Iur interface as identified in previous section is called
Radio Network Subsystem Application Part (RNSAP).
Figure 7.7.5. Separation of RNSAP and Transport Over Iur
The RNSAP is terminated in the SRNS and in the DRNS.
As already stated in previous section a clear separation shall exist between the Radio
Network Layer and the Transport Layer. It is therefore proposed to separate the Data
Transport resource and traffic handling from the RNSAP (Figure 7.7.5). This resource and
traffic handling is controlled by the Transport Signalling. A Signalling Bearer carries the
Transport Signalling over the Iur interface.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.5.4 Iub Interface
The Iub interface connects a RNC and a Node B.
The information transferred over the Iub reference point can be categorised as follows:
1. Radio Application Related Signalling:The Iub interface allows RNC and Node B to
negotiate about radio resources, for example to add and delete cells controlled by the
Node B to support communication of the dedicated connection between UE and SRNS.
2. Radio Frame Data Blocks:The Iub interface provides means for transport of uplink and
downlink radio frame data blocks between RNC and Node B. This transport can use pre-
defined transmission links or switched connections.
3. Quality Estimations of Uplink Radio Frames and Synchronisation Data:The macro-
diversity combining function of the RNC uses Node B quality estimations of the uplink
radio frame data blocks. There is also a need for accurate time synchronisation between
the soft handover branches.
The information in category 3 is tightly coupled to the radio frame data blocks in category 2.
Therefore, category 2 and 3 information is multiplexed on the same underlying transport
mechanism (e.g. switched connection), and is together referred to as an Iub data stream.
The Iub data stream shall follow the same specification as the Iur data stream.
Over the Iub interface between the RNC and one Node B, one or more Iub data streams are
established, each corresponding to one or more cells belonging to the Node B.
7.5.4.1 Functional Split Over Iub
7.5.4.1.1 Macro-diversity Combining of Radio Frame Data Blocks
Node B may perform macro-diversity combining/splitting of data streams communicated via
its cells. RNC performs macro-diversity combining/splitting of Iub data streams received
from/sent to several Node B(s).
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.5.4.1.2 Control of Macro Diversity Combining/Splitting Topology
When requesting the addition of a new cell for a UE to UTRAN connection, the RNC can
explicitly request to the Node B a new Iub data stream, in which case the macro-diversity
combining and splitting function within the Node B is not used for that cell. Otherwise, the
Node B takes the decision whether macro-diversity combining and splitting function is used
inside the Node B for that cell i.e. whether a new Iub data stream shall be added or not.
The Node B controls the internal Node B handling of the macro-diversity
combining/splitting.
7.5.4.1.3 Soft Handover Decision
To support mobility of the UE to UTRAN connection between cells, UTRAN uses
measurement reports from the MS (Mobile Station) and detectors at the cells.
The RNC takes the decision to add or delete cells from the connection.
7.5.4.1.4 Handling of Node B Hardware Resources
Mapping of Node B logical resources onto Node B hardware resources, used for Iub data
streams and radio interface transmission/reception, is performed by Node B.
7.5.4.1.5 Allocation of Downlink Channelisation Codes
Allocation of downlink channelisation codes of cells belonging to Node B is performed in
Node B.
Note that this does not imply that the signalling of the code allocation to the UE must be
done from Node B.
7.5.5 UTRAN Internal Bearers
For all open interfaces, one mandatory set of protocols must be specified. However, a clear
separation between the Radio Network functions and the Transport functions should allow
7 UMTS Terrestrial Radio Acces Network (UTRAN)
this Transport layer to be exchanged to another one with minimum impact on the Radio
Network functions.
7.5.5.1 User Data Bearers
ATM and AAL type 2 (ITU-T recommendations I.363.2 and I.366.1) is used as the standard
transport layer for Soft Handover data stream across the Iur interface.
7.5.5.2 Signalling Bearers
7.5.5.2.1 Signalling Bearer Requirements for Iu Interface
Over the Iu interface the RANAP protocol requires:
A connectionless transport of RANAP messages to facilitate e.g. paging.
A connection oriented transport of RANAP messages e.g. to facilitate messages
belonging to a specific User equipment (UE) during a call.
A reliable connection to make the RANAP simpler.
Support of signalling inactivity testing of a specific UE connection.
7.5.5.2.2 Signalling Bearer Requirements for Iur Interface
There exist at least two major types of soft handover over the Iur interface:
1. The case when a new physical transmission (Iur data stream) is set up over the Iur
interface to provide an additional cell.
2. The case when existing transmission (Iur data stream) is used over the Iur interface when
an additional cell is added in the DRNS. In this case the DRNS must be able to identify
the UE in order to perform the adding of the cell. Consequently a UE context must exist
in the DRNS.
Over the Iur interface the RNSAP protocol requires:
A connection oriented transport of RNSAP messages, i.e. one signalling bearer
connection for each DRNS for a particular UE.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
A reliable connection to make the RNSAP simpler.
Support of signalling inactivity testing of a specific UE connection.
7.6 UTRAN Functions
The functions of UTRAN are divided in functions for overall system control, radio channel
ciphering, mobility and radio resource handling.
7.6.1 System Access Control
System access is the means by which a UMTS user is connected to the UMTS in order to use
UMTS services and/or facilities. User system access may be initiated from either the mobile
side, e.g. a mobile originated call, or the network side, e.g. a mobile terminated call.
Admission Control.
Congestion Control.
System information broadcasting: This function provides the mobile station with the
information that is needed to camp on a cell and to set up a connection in idle mode and
to perform handover or route packets in communication mode. The tasks may include:
Access rights
Frequency bands used
Configuration of transport channels, PCH, FACH and RACH channel structure of the
cell, etc.
Network and cell identities
Information for location registration purposes
UE idle mode cell selection and cell re-selection criteria
UE transmission power control information
7 UMTS Terrestrial Radio Acces Network (UTRAN)
UE access and admission control information
Because of its close relation to the basic radio transmission and the radio channel structure,
the basic control and synchronisation of this function should be located in UTRAN.
7.6.2 Radio Channel Ciphering / Deciphering
7.6.2.1 Radio Channel Ciphering
This function is a pure computation function whereby the radio transmitted data can be
protected against an non-authorised third party. Ciphering may be based on the usage of a
session-dependent key, derived through signalling and/or session dependent information.
This function is located in the UE and in the UTRAN.
7.6.2.1.1 Radio Channel Deciphering
This function is a pure computation function that is used to restore the original information
from the ciphered information. The deciphering function is the complement function of the
ciphering function, based on the same ciphering key. This function is located in the UE and
in the UTRAN.
7.6.3 Mobility
7.6.3.1 Radio Environment Survey
This function performs measurements on radio channels (current and surrounding cells) and
translates these measurements into radio channel quality estimates. Measurements may
include:
Received signal strengths (current and surrounding cells),
Estimated bit error ratios, (current and surrounding cells),
Estimation of propagation environments (e.g. high-speed, low-speed, satellite, etc.),
Transmission range (e.g. through timing information),
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Doppler shift,
Synchronisation status,
Received interference level.
In order for these measurements and the subsequent analysis to be meaningful, some
association between the measurements and the channels to which they relate should be made
in the analysis. Such association may include the use of identifiers for the network, the base
station, the cell (base station sector) and/or the radio channel. This function is located in the
UE and in the UTRAN.
7.6.3.2 Handover Decision
This function consists of gathering estimates of the quality of the radio channels (including
estimates from surrounding cells) from the measuring entities and to assess the overall
quality of service of the call. The overall quality of service is compared with requested limits
and with estimates from surrounding cells. Depending on the outcome of this comparison,
the macro-diversity control function or the handover control function may be activated.
This function may also include functionality to assess traffic loading distribution among
radio cells and to decide on handing over traffic between cells for traffic reasons. The
location of this function is depending on the handover principle chosen:
If network only initiated handover, this function is located in the UTRAN;
If mobile only initiated handover, this function is located in the UE;
If both the mobile and the network can initiate handover, this function will be located in
both the UTRAN and the UE.
7.6.3.3 Macro Diversity Control
Upon request of the handover decision function, this function control the duplication/
replication of information streams to receive/ transmit the same information through
multiple physical channels (possibly in different cells) from/ towards a single mobile
7 UMTS Terrestrial Radio Acces Network (UTRAN)
terminal. This function also controls the combining of information streams generated by a
single source (diversity link), but conveyed via several parallel physical channels (diversity
sub-links).
Macro diversity control should interact with channel coding control in order to reduce the bit
error ratio when combining the different information streams. This function controls macro-
diversity execution which is located at the two endpoints of the connection element on which
macro-diversity is applied (diversity link), that is at the access point and also at the mobile
termination.
In some cases, depending on physical network configuration, there may be several entities
which combine the different information streams, e.g. one entity combines information
streams on radio signal basis, another combines information streams on wire-line signal
basis. This function is typically located in the UTRAN. However, depending on the physical
network architecture, some bit stream combining function within the CN may have to be
included in the control.
7.6.3.4 Handover Control
In the case of switched handover, this function is responsible for the overall control of the
handover execution process. It initiates the handover execution process in the entities
required and receives indications regarding the results. Due to the close relationship with the
radio access and the Handover Decision function, this function should be located in the
UTRAN.
7.6.3.5 Handover Execution
This function is in control of the actual handing over of the communication path. It
comprises two sub-processes: handover resource reservation and handover path new radio
and wire-line resources that are required for the handover.
When the new resources are successfully reserved and activated, the handover path
switching process will perform the final switching from the old to the new resources,
including any intermediate path combination required, e.g. handover branch addition and
7 UMTS Terrestrial Radio Acces Network (UTRAN)
handover branch deletion in the soft handover case. This function is located in the UTRAN
for UTRAN internal path switching and in the CN for CN path switching.
7.6.3.6 Handover Completion
This function will free up any resources that are no longer needed. A re-routing of the call
may also be triggered in order to optimise the new connection. This function is located both
in the UTRAN and in the CN.
7.6.3.7 SRNS Relocation
The SRNS Relocation function co-ordinates the activities when the SRNS role is to be taken
over by another RNS. SRNS relocation implies that the Iu interface connection point is
moved to the new RNS. This function is located in the UTRAN and the CN.
7.6.3.8 Inter-System Handover
The Inter-system handover function enables handover to and from e.g. GSM BSS. This
function is located in the UTRAN, the UE and the CN.
7.6.4 Radio Resource Management and Control
Radio Resource Management is concerned with the allocation and maintenance of radio
communication resources. UMTS radio resources must be shared between circuit mode
(voice and data) services and other modes of service (e.g. packet data transfer mode and
connectionless services).
7.6.4.1 Radio Bearer Connection Set-Up and Release (Radio
Bearer Control)
This function is responsible for the control of connection element set-up and release in the
radio access sub network. The purpose of this function is
To participate in the processing of the end-to-end connection set-up and release.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
And to manage and maintain the element of the end-to-end connection, which is located
in the radio access sub network.
In the former case, this function will be activated by request from other functional entities at
call set-up/release. In the latter case, i.e. when the end-to-end connection has already been
established, this function may also be invoked to cater for in-call service modification or at
handover execution. This function interacts with the reservation and release of physical
(radio) channels function. This function is located both in the UE and in the UTRAN.
7.6.4.2 Reservation and Release of Physical Radio Channels
This function consists of translating the connection element set-up or release requests into
physical radio channel requests, reserving or releasing the corresponding physical radio
channels and acknowledging this reservation/release to the requesting entity. This function
may also perform physical channel reservation and release in the case of a handover.
Moreover, the amount of radio resource required may change during a call, due to service
requests from the user or macro-diversity requests. Therefore, this function must also be
capable of dynamically assigning physical channels during a call.
This function may or may not be identical to the function reservation and release of physical
radio channels. The distinction between the two functions is required e.g. to take into
account sharing a physical radio channel by multiple users in a packet data transfer mode.
This function is located in the UTRAN.
7.6.4.3 Allocation and De-Allocation of Physical Radio Channels
This function is responsible, once physical radio channels have been reserved, for actual
physical radio channel usage, allocating or de-allocating the corresponding physical radio
channels for data transfer.
This function may or may not be identical to the function reservation and release of physical
radio channels. The distinction between the two functions is required e.g. to take into
account sharing a physical radio channel by multiple users in a packet data transfer mode.
This function is located in the UTRAN.
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.6.4.4 Packet Data Transfer Over Radio Function
This function provides packet data transfer capability across the UMTS radio interface. This
function includes procedures which:
Provide packet access control over radio channels.
Provide packet multiplexing over common physical radio channels.
Provide packet discrimination within the mobile terminal.
Provide error detection and correction.
Provide flow control procedures.
This function is located in both the UE and in the UTRAN.
7.6.4.5 RF Power Control
In order to minimise the level of interference (and thereby maximise the re-use of radio
spectrum), it is important that the radio transmission power is not higher than what is
required for the requested service quality. Based on assessments of radio channel quality,
this function controls the level of the transmitted power from the mobile station as well as
the base station. This function is located in both the UE and in the UTRAN.
7.6.4.6 RF Power Setting
This function adjusts the output power of a radio transmitter according to control
information from the RF power control function. The function forms an inherent part of any
power control scheme, whether closed or open loop. This function is located in both the UE
and in the UTRAN.
7.6.4.7 Radio Channel Coding
This function introduces redundancy into the source data flow, increasing its rate by adding
information calculated from the source data, in order to allow the detection or correction of
signal errors introduced by the transmission medium. The channel coding algorithm(s) used
7 UMTS Terrestrial Radio Acces Network (UTRAN)
and the amount of redundancy introduced may be different for the different types of
transport channels and different types of data. This function is located in both the UE and in
the UTRAN.
7.6.4.8 Radio Channel Decoding
This function tries to reconstruct the source information using the redundancy added by the
channel coding function to detect or correct possible errors in the received data flow. The
channel decoding function may also employ a priori error likelihood information generated
by the demodulation function to increase the efficiency of the decoding operation. The
channel decoding function is the complement function to the channel coding function. This
function is located in both the UE and in the UTRAN.
7.6.4.9 Channel Coding Control
This function generates control information required by the channel coding/ decoding
execution functions. This may include channel coding scheme, code rate, etc. This function
is located in both the UE and in the UTRAN.
7.6.4.10 Initial (Random) Access Detection and Handling
This function will have the ability to detect an initial access attempt from a mobile station
and will respond appropriately. The handling of the initial access may include procedures for
a possible resolution of colliding attempts, etc. The successful result will be the request for
allocation of appropriate resources for the requesting mobile station. This function is located
in the UTRAN.
7.6.4.11 Other Funtions:
Radio resource configuration and operation
[TDD - Dynamic Channel Allocation (DCA)]
Radio protocols function
[TDD - Timing Advance]
7 UMTS Terrestrial Radio Acces Network (UTRAN)
CN Distribution function for Non Access Stratum messages.
7.7 Identifiers
The following identifiers are used within UTRAN
7.7.1 UTRAN identifiers
PLMN Identifier: PLMN-Id = MCC + MNC
CN Domain Identifier: CN CS Domain-Id = PLMN-Id + LAC
CN PS Domain-Id = PLMN-Id + LAC + RAC
RNC Identifier: Global RNC-Id = PLMN-Id + RNC-Id
Service Area Identifier: SAI = PLMN-Id + LAC + SAC
Cell Identifier: UC-Id = RNC-Id + C-Id
7.7.2 UE Identifiers
When the UE is known to UTRAN is given an identity, called the Radio Network
Temporary Identity. There are four different RNTIs:
1. s-RNTI: Serving RNC RNTI
2. d-RNTI: Drift RNC RNTI
3. c-RNTI: Cell RNTI
4. u-RNTI: UTRAN RNTI
7 UMTS Terrestrial Radio Acces Network (UTRAN)
7.8 UMTS QoS and RAB
7.8.1 Quality of Service (QoS)
The general QoS approach for UMTS is that only the QoS perceived by end-user matter, that
is from one terminal equipment to another terminal equipment. To realise a certain network
QoS a Bearer Service with clearly defined characteristics and functionality is to be set up
from the source to the destination of a service.
A bearer service includes all aspects to enable the provision of a contracted QoS. These
aspects are among others the control signalling, user plane transport and QoS management
functionality. The UMTS QoS concept is describes in the specification 23.107
The QoS negotiation is a trace off between bit error rate (BER) delay and bit rate. There are
four QoS classes defined for UMTS (the same as for GPRS) responding to different
requirements for delay.
When negotiating QoS a number of service attributes are agreed (Traffic class, maximum
and guaranteed bit rate, delay and BER, etc.)
Traffic class
Conversationalclass
Conversational RT
Streaming class
Streaming RT
Interactiveclass
Interactive besteffort
Background
Background besteffort
Fundamentalcharacteristics
Preserve timerelation (variation)betweeninformationentities of stream
Conversationalpattern (stringentand low delay)
Preserve timerelation(variation)betweeninformationentities ofstream
Requestresponsepattern
Preservepayloadcontent
Destination is notexpecting the datawithin a certaintime
Preserve payloadcontent
Example ofapplication
Voice Streaming video Web browsingBackgrounddownload ofemails
Table 7.7.1. UMTS QoS Classes
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Traffic classConversationa
l classStreaming
classInteractive
classBackground
class
Maximum bitrate(kbps)
<2000 <2000<2000 –overhead
<2000 –overhead
Delivery order Yes/No Yes/No Yes/No Yes/No
Maximum SDU size(octets)
<1500 <1500 <1500 <1500
Delivery oferroneous SDUs
Yes/No/- Yes/No/- Yes/No/- Yes/No/-
Residual VER5·10-2, 10-2, 10-
3, 10-4
5·10-2, 10-2, 10-
3, 10-4 10-5, 10-6
4·10-3, 10-5,6·10-8
4·10-3, 10-5,6·10-8
SDU error ratio10-2, 10-3, 10-4,
10-5
10-2, 10-3, 10-4,10-5 10-3, 10-4, 10-6 10-3, 10-4, 10-6
Transfer delay (ms)100 –
maximumvalue
500 –maximum
value
Guaranteed bit rate(kbps)
<2000 <2000
Traffic handlingpriority
1, 2, 3
Allocation/RetentionPriority
1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3
Table 7.7.2. Value Ranges for UMTS Bearer Service Attributes
7.8.2 Radio Access Bearers (RAB)
RAB is described by:
Information quality of service
Bit rate
Bit error ratio
Maximum transfer delay
Delay variation
7 UMTS Terrestrial Radio Acces Network (UTRAN)
Traffic characteristics
Point-point, uni-directional or bi-directional (symmetric or asymmetric)
Point-to-multipoint, uni-directional (multicast and broadcast)
8 Core Network
Chapter 8: Core Network
8.1 Introduction
The UMTS core network will be based in the existing GSM core network, or GSM Network
Switching System (GSM NSS).
Keeping GSM as the core network for the provision of third-generation wireless services has
distinct commercial advantages: protecting the investment of existing GSM operators;
helping ensure the widest possible customer base from day one; and fostering supplier
competition through the continuous evolution of GSM systems.
A wide customer base from day one is achieved with the help of dual mode GSM/UMTS
mobile terminals, full roaming and hand-over from one system, and with mapping of
services between the two systems as far as possible. The use of dual mode mobiles in the
early phases of introduction of third-generation systems will ensure that UMTS subscribers
will able to enjoy roaming and interworking with the global GSM community.
The GSM standard offers a sound base for UMTS core networks, whether as evolved GSM
core networks or as newly-built pure UMTS networks (albeit with different topology and
physical implementation).
8.2 GPRS, an Important Stepping Stone Towards a UMTS
Core Network
The real point of moving to third generation systems is to give users high speed access to
wireless multimedia services and other wireless data services. Bearing this in mind it is
worth noting that today’s wireless data market is still in its infancy: among wireless
subscribers, penetration of wireless datacom services is still less than three per cent,
excluding Short Message Service (SMS).
8 Core Network
The problem is that the current wireless networks are not best equipped to deal with these
new forms of data use, and do not meet the UMTS requirements. As circuit switched
networks, they are inefficient at handling small, frequent data calls and bursty IP traffic.
General Packet Radio Service (GPRS), the packet-based data bearer service for GSM, offers
current GSM operators an opportunity to kickstart the predicted mass market for wireless
data services. And important to note, it is relatively small step from building a core network
capable of delivering GPRS services to enhancing it to meet the requirements of UMTS.
In other words, implementing GPRS will provide a core network platform for current GSM
operators not only to expand the wireless data market in preparation for the introduction of
third-generation services, but also to build upon for IMT-2000.
GPRS will provide end-to-end packet switching capability from the mobile terminal
upwards, enhancing GSM data services significantly, especially for bursty Internet/intranet
traffic. Call set-up will be almost instantaneous and users will be charged on the basis of
actual data transmitted, rather than connection time. GPRS does not require any end-to-end
connection and only uses network resources and bandwidth when data is actually being
transmitted. This make extremely efficient use of available radio bandwidth to be shared
between many users.
All the widely-used data communication protocols, including IP will be supported by GPRS,
so it will be possible to connect to any data source from anywhere in the world using a
GPRS mobile terminal. By providing seamless interconnection with existing data services,
via for example TCP/IP and X.25 interfaces, GPRS will support applications ranging from
low-speed short messages to high-speed corporate LAN communications.
The introduction of GPRS is one of the key staging posts in the evolution of GSM networks
to third-generation capabilities. GPRS can therefore help remove the network barriers to
large-scale take-up of wireless data services by allowing familiar, user-friendly interfaces
like the Internet to be used, permitting volume-based charging and providing high-speed
user data rates.
So what needs to happen in the core network to support the move to GPRS and, ultimately,
UMTS?
8 Core Network
8.3 Upgrading the GSM Core for GPRS
Compared with establishing a completely new communications system, building GSM-
UMTS infrastructure based on an existing GSM network will be a relatively fast exercise.
An intermediate move to a GSM-GPRS network will make the transition even easier.
While GPRS will require new functionality in the GSM network, with new types of
connections to external packet data networks, it will essentially be an extension of GSM.
Moving to a GSM-UMTS core network will likewise be an extension of this evolved
network.
GPRS will be implemented simply by adding new packet data nodes and upgrading existing
nodes to provide a routing path for packet data between the wireless terminal and a gateway
node. The gateway node will provide interworking with external packet data networks for
access to the Internet, intranets and databases, for example.
8.3.1 New Nodes for Packet Data
Two new logical nodes will be introduced to handle GPRS applications in the GSM:
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
The SGSN will provide packet routing, including mobility management, authentication and
ciphering to and from all GPRS subscribers located in the SGSN service area. A GPRS
subscriber may be served by any SGSN in the network, depending on location. The traffic is
routed from the SGSN to the Base Station Controller (BSC) and to the mobile terminal via
the Base Transceiver Station (BTS).
The GGSN will provide the gateway to external ISP networks, handling security and
accounting functions as web as dynamic allocation of IP addresses to serve mobile terminal.
From the external IP networks point of view, the GGSN is a host that owns all IP addresses
of all subscribers served by the GPRS network.
8 Core Network
The nodes will be interconnected by an IP backbone network. The SGSN and GGSN
functions may be combined in the same physical node, or separated, even residing in
different mobile networks.
A key requirement for these new nodes is that they are scalable, so that GSM operators can
start to offer high-speed packet data services using small nodes in selected areas cost-
effectively, and add extra capacity as it is needed. The SGSN and GGSN should also support
several radio networks (those with compliant open interfaces) at the same time.
8.3.2 Upgrades to Existing GSM Nodes
Few or no hardware upgrades will be needed in the existing GSM nodes, and the same
transmissions links will be used between BTSs and BSCs for both GSM and GPRS. A
special interface will be provided between the MSC/Visitor Location Register (VLR) and the
SGSN to co-ordinate signalling for mobile terminals that can handle both circuit-switched
and packet-switched data.
The HLR will contain GPRS subscription data and routing information, and will be
accessible from the SGSN. The HLR will also map each subscriber to one or more GGSNs.
The BSC will require new capabilities for controlling the packet channels: new hardware in
the form of a Packet Control Unit (PCU) and new software for GPRS mobility management
and paging. The BSC will also have a new traffic and signalling interface from the SGSN.
The BTS will have new protocols supporting packet data for the air interface, together with
new slot and channel resource allocation functions. The utilisation of radio channels will be
optimised through dynamic sharing between the two traffic types (circuit and packet
switched traffic), handled by the BSC.
8.4 Moving to UMTS in the GSM/GPRS Core
UMTS will have an evolved GSM core network, which will be backward compatible with
the GSM network in terms of network protocols and interfaces (MAP, ISUP, etc.). This core
network will support both GSM and UMTS, with hand-over and roaming between the two.
8 Core Network
UMTS Terrestrial Radio Access Network (UTRAN) will be connected to the GSM-UMTS
core network using a new multi-vendor interface (the Iu).
The transport protocol within the new radio network and to the core network will be ATM.
There will be a clear separation between the services provided by the UTRAN and the actual
channels used to carry these services. All radio network functions (such as resource control)
will be handled within the radio access network, and clearly separated from the service and
subscription functions in the core network.
The GSM-UMTS network will consist of three main parts:
GSM-UMTS core network
UMTS Radio Access Network (URAN)
GSM Base Station Subsystem (BSS)
Like the GSM-GPRS core network, the GSM-UMTS core network will have two different
parts: a circuit switched part (MSC) and a packet-switched part (GSN). The core network
access point for GSM circuit switched connections is the GSM MSC, and for packet
switched connections is the SGSN. GSM-defined services (up to and including GSM Phase
2+) will be supported in the dual “GSM” way. The GSM-UMTS core network will
implement supplementary services according to GSM principles (HLR-MSC/VLR).
Modifications to support UMTS will be requires in all core network nodes. MSC and SGSN
must be upgraded to handle the new signalling and traffic protocols towards UTRAN.
Furthermore, HLR and VLR must be modified to store UMTS service profiles and
subscription data. Last but not least, all nodes must be upgraded to handle the new range of
data rates and the concept of quality of service negotiation and re-negotiation.
Apart from the new range of higher data rate bearer services and more advanced QoS
procedures, the UMTS core network introduces a third major novelty – as compared to pre-
UMTS networks - in how services will be handled.
Pre-UMTS systems have largely standardised the complete sets of teleservices, applications
and supplementary services which they provide. As a consequence, substantial re-
engineering is often required to enable new services to be provided and the market for
8 Core Network
services is largely determined by operators to differentiate their services. UMTS shall
therefore standardise service capabilities and not the services themselves. Service
capabilities consist of bearers defined by QoS parameters and the mechanisms needed to
realise services.
These mechanisms include the functionality provided by various network elements., the
communication between them and the storage of associated data. It is intended that these
standardised capabilities should provide a defined platform which will enable the support of
speech, video, multi-media, messaging data, other teleservices, user applications and
supplementary services and enable the market for services to be determined by users and
home environments.
New services, beyond GSM Phase 2+, will thus no longer be standardised. Instead they will
be created using new the service capabilities (which are standardised) mentioned above.
These service capabilities may be seen as ‘building blocks’ that provide service
mechanisms in the UMTS network and UMTS mobile terminal that can be used for service
creation. They include for instance:
Bearers defined by quality of service (QoS) parameters
Intelligent network functionality
Mobile Equipment Execution Environment (MEXE)
WAP and Telephony value-added Services
SIM Application Toolkit
Location servers
Open interfaces to mobile network functions
Downloadable application software
8 Core Network
So, in addition to new services provided by the GSM-UMTS network itself, many new
services and applications will be realised using a client/server approach, with servers
residing on service LANs outside the GSM-UMTS core network. For such services, the core
network will simply act as a transparent bearer. The core network will ultimately be used for
the transfer of data between the end-points, the client and the server.
8.4.1 Cell-Based Transport Network
To make the most of the new UTRAN capabilities, and to cater for the large increase in data
traffic volume, ATM (Asynchronous Transfer Mode) will be used as the transport protocol
within the UTRAN and towards the GSM-UMTS core network. The combination of ATM
and UTRAN capabilities and the increased volume of packet data traffic over the air
interface will mean a saving of at least 50% in transmission costs, compared with the
equivalent current solutions.
ATM, with the newly-standardised AAL2 adaptation layer, provides an efficient transport
protocol, optimised for delay-sensitive speech services and packet-data services. Introducing
ATM as a transport protocol does not, however, imply a completely new transport
infrastructure: the ATM could well be run over existing STM lines.
8.5 UMTS Core Network Phase 1 (Release 99)
Requirements
In the first phase of UMTS, the UMTS core network capabilities are a superset of the phase
2+ release 99 GSM core network capabilities. The additional requirements for the phase 1
UMTS core network are the following:
The phase 1 UMTS core network shall support circuit switched data service capability of
at least 64 kbit/s per user. This shall not limit the user from choosing lower data rates.
The phase 1 UMTS core network shall support packet switched data service capability of
at least 2 Mbit/s peak bit rate per user. This shall not limit the user from choosing lower
data rates.
8 Core Network
The phase 1 UMTS core network shall enable set-up, re-negotiation and clearing of
connections (i.e. CS calls or PS sessions) with a range of traffic and performance
characteristics. The re-negotiation of QoS attributes for a bearer service may be caused
by an application or the user via an application. It shall be possible to apply traffic
policing (e.g. connection admission control, flow control, usage parameter control…) on a
connection during its set-up and lifetime.
The phase 1 UMTS core network shall support a range of traffic and performance
characteristics for connectionless (e.g. unicast, broadcast, and multicast) traffic.
The range of traffic and performance characteristics that shall be supported by the phase
1 UMTS core network shall be at least those of GPRS phase 2+ release 99. This means
that the support of the full set of bearer services defined in the UMTS specifications is
not required for the phase 1 UMTS core network.
Established bearers shall not prevent the set-up of a new bearer. These bearers can be of
any type (e.g. PS, CS). It is nevertheless expected that the terminal and network
capabilities will put some limitations on the number of bearer services that can be
handled simultaneously. It shall be possible for each bearer to have independent traffic
and performance characteristics.
In order to facilitate the development of new applications, it shall be possible to address
applications to/from a phase 1 UMTS mobile termination (e.g. the notion of Internet
port).
Operator specific services based shall be supported by the phase 1 UMTS core network.
This functionality could be provided through available toolkits (such as IN, MEXE,
WAP and SIM Toolkit).
The phase 1 UMTS core network shall support interworking with PSTN, N-ISDN, GSM,
X.25 and IP networks with their respective numbering schemes.
It shall be possible for the standardised classes of phase 1 UMTS mobile terminals
supporting the GSM BSS and UTRAN radio interfaces to roam in GSM networks and
receive GSM services.
8 Core Network
Standardised protocols shall be defined for the operation, administration and
maintenance of the UMTS phase 1 core network in co-operation with relevant groups
within ETSI.
9 Handover (Downlink Case Example)
Chapter 9: Handover (Downlink Case
Example)
In this chapter a complete case of handover is presented. A GSM macro cell and six UMTS
macro cells compose the scenario. The four RNCs and the BSC are connected through the
common Core Network.
9.1 Position 1
The UE receives information from the Node B that controls the cell with Scrambling Code 1,
SC1. All the information of the first Node B is received from the Radio Network Controller
1, RNC1.
9.2 Position 2
The UE enters in a new cell using the same frequency. This cell has a different Scrambling
Code (SC2) and is controlled by a new Node B that depends on the same RNC1.
The RNC1 is transmitting to two different Node Bs. This operation is known like combining
and splitting and is performed by the RNC Signal Processing.
In this short period a soft handover, SOHO, is performed. The handover decisions are taken
in the RAB Management of the RNC1.
9.3 Position 3
The UE is completely inside the cell number two (SC2) and is receiving from the second
Node B.
9 Handover (Downlink Case Example)
9.4 Position 4
The UE is crossing the cell border to enter in the cell number three (SC3) that is controlled
by the same Node B. Now the combining operation is realised by Node B with the RNC
supervision. In this case a softer handover is performed. This is the simplest case that can be
found.
9.5 Position 5
The UE is completely inside the cell number three (SC3) and is receiving from the second
Node B.
9.6 Position 6
The UE is crossing the cell border to enter in the cell number four (SC4) that is controlled by
the third Node B. This Node B is controlled by a second RNC, RNC2. In this case an Iur
interface is present between the two RNCs. The RNC1, that controls the Serving Radio
Network Subsystem, SRNS, is called Serving RNC and the RNC2, that controls the Drift
Radio Network Subsystem, DRNS, is called Drift RNC.
The combining and splitting operations are performed by the Serving RNC, RNC1, where
the handover decision are taken. Even SRNS relocation is realised. In this case a soft
handover is performed. The SOHO condition has the drawback that is necessary to transmit
more power.
9.7 Position 7
The UE is completely inside the cell number four (SC4) and is receiving from the third Node
B.
9 Handover (Downlink Case Example)
9.8 Position 8
The UE is crossing the cell border to enter in the GSM cell controlled by the BTS. All the
information regarding the UE in position 7 is transmitted to the BSC through the Core
Network. In this case only a hard handover (UMTS-GSM) can be performed.
9.9 Position 9
The UE is crossing the cell border to enter in a UMTS cell controlled by RNC3. The
downlink is realised to frequency f1. Even in this case only a hard handover (GSM-UMTS)
can be performed. All the information regarding the UE in position 8 is transmitted to the
RNC3 through the Core Network.
9.10 Position 10
The UE is crossing the cell border to enter in a new cell controlled by RNC4. The downlink
is realised to frequency f2. In this case only a hard handover can be performed because of the
different frequencies within the two cells. Even in this case to transmit all the information
regarding the UE in position 9 to the RNC4 the Core Network is used.
For the Uplink case the analogue considerations can be done
10 Cell Planing
Chapter 10: Cell Planing
10.1 Introduction to Cell Planning
Network planning covers two major areas: radio network planning and network
dimensioning. Radio network planning includes the calculation of the link budget,
capacities, and thus the required number of cell sites. Furthermore, radio network planning
includes detailed coverage and parameter planning for individual sites.
Planning an immature network with a limited number of subscribers is not the real problem.
The difficulty is to plan a network that allows future growth and expansion. Wise re-use of
site location in the future network structure will save money for the operator.
In this chapter we will look at different cell types, the different steps in cell planning, the
differences compared to GSM cell planning as well as some of the advantages of co-siting
with GSM.
10.2 Different Cell Types
A cellular network is created by means of placing equipment in strategic places to guarantee
a certain perceived Quality of Service. Idealistic then would be to place a base station in
every street corner, this though is not cost efficient. Which dell type to use, must be weighed
against cost and expected penetration (see Figure 10.10.1).
Figure 10.10.1. The Choice of Cell Types Affecting Several Posts on The Scale
Coverage
Capacity
Penetration
Cost
Spectrum
Quality
Coverage
Capacity
Penetration
Cost
Spectrum
Quality
10 Cell Planing
Important when designing a network is to find a balance regarding which combination of the
types of cells to use. The most common ones today are macro, micro and pico cells, but
sometimes also mini cells are mentioned. As co-siting is one key design objective for
UMTS networks, it is very likely that UMTS will have the same type of cells as today’s
second generation systems. However, it should be noted that high bit rates have lower
coverage than low bit rates. Thus, if the UMTS network is designed to handle high bit rates,
i.e. 384 kbps and above, the majority of the cells will be micro and pico cells.
Macro cells, have a typical coverage range from 1 to 35 km (several vendors offers special
high coverage solutions that will extend the coverage beyond 35 km). Normally the site
location is on a hilltop or a rooftop, guarantying good coverage. The main rays are
propagated over the rooftops.
Micro cells have a typical coverage range from o.1 to 1 km, where the major part of the
radio waves is propagated along the streets. The base station antenna placement is below the
rooftops of the surrounding buildings. A micro cell can maintain indoor coverage in the
lower levels of a building.
Pico cells supplies coverage in indoor environment (or possibly outdoors in environments
physically distinctly limited – a backyard e.g.). The base station is transmitting at low output
power and the antennas could be mounted on walls or in the ceiling. Pico cells are used
when the capacity needed is extremely high in certain hot spots.
Mini cells are between macro and micro cells, as the antenna is typically placed at the same
level as the rooftops.
HCS (Hierarchical Cell Structures) is an example of how different cell types can be
deployed in the same area. Traditionally, the different cell types, i.e. macro and micro cells
use different frequency bands. HCS offers a high capacity solution, as the micro band is
capable of handle a high load. HCS also allows for the possibility to conduct load sharing
between the different cell layers. In order to limit the amount of handovers in the system,
one may also consider the user’s velocity when deciding which cell layer to use.
10 Cell Planing
In the theoretical part of cell planing, base station coverage areas or cells are shown as
hexagons. This is so because the system is designed to let the mobile always operate on the
nearest or best base station. Thus, boundaries between the base station cells will theoretically
form straight lines, perpendicular to the connection lines between the sites, and these will
form a hexagonal cellular pattern (see ).
Figure 10.10.2. Cell Coverage Shown as a Hexagon
The use of different types of cells on the same area introduces the concept of a hierarchical
structure, leading to increasingly complex handover relations and planning.
10.3 Steps in the Cell Planning Process
Cell planning means building a network able to provide service to the customers wherever
they are. This work can be simplified and structured in certain steps (see Figure 10.10.3).
Some of these steps are performed frequently whilst other are more rare. Normally the
output from one box is the input of another. A cell planner most likely is dealing with the
content of several of these boxes at the same time.
The following describes the content of the boxes and what each step may involve. This
process is by no means complete or unbeatable, each operator has its own flowchart of
processes.
System Requirements
Define Radio Planning
Initial Cell Plan
Surveys Individual Site Design
ImplementationLaunch of Service
On-going Testing
System Growth
System Requirements
Define Radio Planning
Initial Cell Plan
Surveys Individual Site Design
ImplementationLaunch of Service
On-going Testing
System Growth
10 Cell Planing
Figure 10.10.3. Different Steps in The Cell Planning Process
This process should not be considered just as it is depicted, in a single flow of events. For
instance, the radio planning and surveying actions are interlinked in an ongoing iterative
process that should ultimately lead to the individual site design.
10.3.1 System Requirements:
Licence (available bandwidth may also set coverage requirements).
Coverage for different customers in different environments.
Traffic behaviour of customers in different regions (uplink and downlink may differ).
Quality of Service (dropping and delay) and GoS (blocking).
Phase of build out (expansion and future investments?).
10.3.2 Define Radio Planning Guidelines:
Coverage and interference: which prediction model to use, fading margins for indoor,
outdoor and in-car.
Traffic planning: choice of models and processes.
Testing and optimisation strategy.
10.3.3 Initial Cell Plan:
Idealised overview of site locations (consider GSM initially also WCDMA for
expansion).
Predicted composite coverage and interference map.
Cell configuration, parameter setting, channel loading plan (if co-siting, consider
existing site).
10 Cell Planing
10.3.4 Surveys:
Radio environment survey: Investigate path loss, interference and time dispersion.
Investigate other system’s antenna and interfering transmitters.
Sit Survey: Pinpoint exact location with GPS. The ideal planned locations have to be
searched for any suitable building, tower or vacant lot that could be leased for a
reasonable cost. Check space for antenna mounting, isolation, diversity, roof clearance
(first Fresnel zone empty).
Investigate physical necessities such as space for equipment, power and PCM links.
10.3.5 Individual Site Design and Parameter Setting:
Radio engineers need to select best site location from the options available from the site
acquisitors.
Dimensioning of node B, transport network and RNC.
Antenna type and gain, direction and tilt and ERP need to be decided.
“ Final” parameter setting (power planning, HO margin, neighbour list (GSM),
scrambling code, functionality).
10.3.6 Implementation:
Install: node B, power, termination equipment for PCM link, air-conditioning equipment,
earth bar, lightning equipment and antennas. Adjust output power, set parameters.
Commissioning tests of node B. Drive testing to detect blank spots and interference and
to confirm correct call set-up, handover, location updating and to detect missing
neighbour relationships.
10.3.7 Launch of Commercial Service:
When the network is operational a commercial launch can be made.
10 Cell Planing
10.3.8 On-going Testing, Analyses and Optimisation:
System diagnostics: collect statistics in OMC, MSC or RNC to analyse traffic behaviour,
traffic distribution, Grade of Service, call success rate, handover failures, dropped calls,
radio channels quality, access links statistics, and to study trends.
Drive testing to localise weak signal strength, interference, time dispersion or other radio
problems. Also to investigate problems reported by customers and to validate changes
undertaken.
Analysis of the results above, and
Optimisation of parameters, timers, physical implementation of antenna directions or tilts
or any other measures to counteract detected problems.
10.3.9 System Growth
More traffic, due to more users or new services.
Expansion of existing sites.
New sites added.
10.4 Differences With 2G TDMA Systems - Deployments
10.4.1 Exploiting Existing Networks
Re-use of site locations and equipment (site Co-sting).
Information about traffic and propagation conditions.
Handover to GSM (for coverage or load sharing purpose).
10.4.2 Multi Service
Load from several different types of services..
10 Cell Planing
Different services have different coverage.
Delay requirements.
10.4.3 New Air Interface
Trade-off between coverage and capacity.
Power planning instead of frequency planning.
10.5 Calculation of Coverage and Capacity
In WCDMA power is the common shared resource. Thus, in order to achieve high spectrum
efficiency WCDMA supports a fast quality based power control. The combination of these
two features together with the fact that WCDMA use a frequency re-use of one results in that
WCDMA offers a trade-off between coverage and capacity.
This means that at low load, i.e. low interference, the users can be further away from the
base station, and still supported, compared to when there is a high load, i.e. high interference
in the system.
10.5.1 Needed Input Parameters
The needed input parameters are:
Coverage requirements (indoor, probability, bit rate at cell border).
Supported services.
GoS.
Available spectrum, i.e. number of carriers.
Area to cover and which type of area it is (urban, suburban,...).
Users within the area.
Traffic that each user generates (uplink and downlink separately).
10 Cell Planing
Based on that information, the amount of traffic per carrier in a given area can be calculated.
Further, the C/I for the different services can be calculated by taking the Eb/No values from
the WCDMA RTT. The C/I = Eb/No – 10log(chip rate/bit rate)
10.5.2 Uplink Design
The first step in the uplink design is to make an initial assumption about the uplink load. The
initial assumed load usually corresponds to a low load. By using the load assumption in
combination with the coverage requirement, a link budget can be calculated. From the link
budget, the cell range can be calculated and thus also the cell area. Knowing the area, the
traffic within that area can be calculated. By using the GoS input requirement, we can
calculate how much interference we should design for.
In the next step, the assumed load is compared to the calculated design load. If the assumed
load is greater than the calculated load, the process is completed and we have found a design
that handles the traffic in the system. Otherwise, one should check if the assumed load
equals or exceeds the maximum load in the system. If it does, then the system is capacity
limited and the number of sites needed can be found from dividing the total traffic with the
traffic that one site can handle. If the system is not capacity limited, one assumes a new load
and repeats the process.
10.5.3 Downlink Design
From the uplink, one gets the cell range and the cell area. Having the cell area, traffic within
that area is calculated. By using the GoS for the different supported services, the needed
resources are calculated. Then by using the downlink plot, it can be seen whether the design
supports the downlink load or not. If the downlink load is supported, the design process is
completed. Otherwise, the cell range and the cell area must be reduced until the downlink
load is handled.
10 Cell Planing
10.5.4 Co-Siting With GSM Case
When the aim is to co-site with GSM, the process is slightly different as the site locations
already are known. By knowing the cell range, one can make an uplink link budget in order
to find out now large interference margins can be tolerated. By comparing the load that a 5
MHz carrier can handle and compare it with the uplink traffic demand within the cell area,
the needed number of frequencies can be estimated.
In the downlink, the supported load per carrier can be found from the downlink plot once the
cell range is given, i.e. the cell range used in the existing GSM network. The needed amount
of carriers can then be calculated, just as in the uplink, by dividing the traffic demand within
the cell area with the traffic that one carrier can handle.
11 WORLD-WIDE CONSENSUS ON ADDITIONAL SPECTRUM FOR 3RD GENERATION
Chapter 11: WORLD-WIDE CONSENSUS ON
ADDITIONAL SPECTRUM FOR 3RD
GENERATION
IMT-2000 IS ANOTHER GIANT LEAP FORWARD FOR EVERYONE’S MOBILE
FUTURE
June 1st 2000: The promise of tomorrow’s global information society has taken a major
step forward with the successful identification of additional radio spectrum to support the
rapid rollout of "third generation" (3G) UMTS/IMT-2000 mobile communications services
for all the world’s regions.
The historic announcement - finally approved at the WRC 2000 plenary - was made at the
conclusion of the month-long WRC-2000 (World Radiocommunication Conference)
meeting in Istanbul after four weeks of intense work by spectrum administrators
representing every government. Representatives of the UMTS Forum’s Spectrum Aspects
Group (SAG) provided support and expert inputs to the Conference, following four years
involvement in this uniquely important and complex project.
The Inter-governmental Conference reached a global consensus to identify additional bands
for the terrestrial component of UMTS/IMT-2000. Crucially, as well as providing additional
capacity to support the future mass market for mobile multimedia services - calculated by
the UMTS Forum to approach 2 billion users within the next decade - this result also paves
the way for the introduction of 3G services even in regions where the core spectrum has not
hitherto been available for IMT-2000.
This means that mobile users will be able to access their personal information services using
affordable handheld terminals wherever they travel. The additional terrestrial bands agreed
by WRC2000 for IMT-2000 cover three alternative areas of spectrum to complement the
11 WORLD-WIDE CONSENSUS ON ADDITIONAL SPECTRUM FOR 3RD GENERATION
IMT-2000 core bands (1885 - 2025 and 2110 - 2200 MHz) identified by a previous
Conference in 1992.
The new bands are:
806-960 MHz
1,710-1,885 MHz
2,500-2,690 MHz
All of these three bands meet the UMTS Forum’s call for 160 MHz of global additional
spectrum that is required to support the forecast growth of traffic and services that will
outstrip the capacity of the present IMT-2000 core band in many markets before the end of
this decade. This 160 MHz of additional spectrum in every ITU Region was calculated on
the basis of traffic forecasts and the existing available mobile bands for 2nd and 3rd
generation services.
This groundbreaking news comes at a time when the UMTS licensing process is rapidly
progressing in many countries throughout Asia and Europe in order to commence
commercial services by 2001/2002. More than 100 licenses are to be awarded to operators of
high-capacity UMTS mobile multimedia services within the next 12-18 months.
Each government will make their own decision on the choice and timescale for making these
additional bands available for IMT-2000 use. Factors influencing the availability of these
additional frequencies include the local market demand for 3rd generation services and
economic factors such as the stage of development of present 2nd generation networks.
Some existing operators may also wish to consider migrating their networks to IMT-2000 in
order to offer the benefits of lower costs and high-speed packet data services up to 2Mbit/s
and beyond.
The decision on extension band spectrum follows an earlier milestone of equal importance
reached last month when the ITU Radiocommunication Assembly unanimously approved
the formal adoption of the first release of IMT-2000 radio interface specifications.
UMTS Forum Chairman Dr Bernd Eylert said today of the decision:
11 WORLD-WIDE CONSENSUS ON ADDITIONAL SPECTRUM FOR 3RD GENERATION
"The UMTS Forum wishes to congratulate the ITU and to thank all its members for this
successful result. It’s an incredible milestone in the development of tomorrow’s mobile
networks, and a fantastic result for the entire global mobile industry which is represented by
the membership of the UMTS Forum - the world’s largest pan-industry group dedicated to
3G mobile matters."
Dr Eylert continued: "This decision is particularly welcome as it provides a solid basis for
the regional introduction of 3G services, even in territories that were effectively blocked
from the benefits of 3G in the past because of limited spectrum. The stage is now set for
UMTS/IMT-2000 to deliver on its exciting promise of immense socio-economic benefits for
all the world’s mobile users. The UMTS Forum will continue its work in this very important
field to assist the regions in their IMT-2000/UMTS deployments."