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WCDMA OverviewWCDMA Overview
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OutlineOutline
IntroductionWhat is different from GSMBasic Concept of 3G (UTRAN)WCDMA Coverage & CapacityCore network Architecture and EvolutionHSDPA Basics
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Introduction
Mobile networks established in mid 80’s
It is widely recognized that there are three different generations as far as Mobile communications is concerned.
• The first generation, 1G – Speech • The Second generation, 2G – Speech+ Data• The Third Generation, 3G – Speech+ High Data Speed
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Evolution from 2G to 3G
Basic GSM and VAS are basically meant to produce “mass services for mass people” but due to requirements raised from end-users, more individual type of services is required.
3G introduces the new radio access method, WCDMA. 3G introduces the new radio access method, WCDMA. WCDMA and its variants are global. WCDMA and its variants are global.
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Evolution from 2G to 3G
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GSM and WCDMA Comparison
Separate users through different codes
Continuous transmission and reception
Code planning – No Frequency Planning
Variable Cell Radius: Cell Breathing
Radio Link: 1 UE <-> Many Node-B’s
Power is Capacity
Scrambling Code Planning
Hard/Soft/Softer Handover
Orthogonal in time within a cell
Time Slot Synchronization in time
Frequency planning
“Fixed” Cell Radius
Radio Link: 1 MS <-> 1 RBS
# of Frequencies limit capacity
BSIC Planning
Hard Handover
GSM WCDMABTS NodeB
BSC RNCMS UE
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GSM Radio Access Network
Core Network
BSC
BSC
A/Gb
Abis
UmBTS BTS
BTS
MS
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WCDMA Radio Access Network
Iu= Iu PS - GbIu CS - A
Core Network
RNC
RNC
Iu
Iur
Iub
UuNodeB NodeB
NodeB
UE
UTRANCore Network
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Development process for 3G
The third generation, 3G, is expected to complete the globalization process of the mobile communication. Again there are national and regional interests involved and difficulties can be foreseen.
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What is WCDMA.....
Wide Band Code Division Multiple Access is a third generation mobile communication system. It’s a wireless system where the telecommunication, datacom & media industry converge and is based on a Layered Architecture.
Convergence:Convergence:
1. User Service convergence
2. Device convergence
3. Network convergence
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YesterdaySingle-Service networks
Da
ta/I
P N
etw
ork
sD
ata
/IP
Ne
two
rks
PL
MN
PL
MN
PS
TN
/IS
DN
PS
TN
/IS
DN
Services
Access Transport & Switching Networks
Servers
Clients
IP Network
AccessAccess
TomorrowMulti-Service networks
From Single- to Multi-Service Networks
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Layered Architecture
The architecture of telecommunication networks, whether wireless or wire line has changed and they are now split into several horizontal layers that are more or less independent of each other.
Applications Layer
Control Layer
MSC-S HLR
GGSN
GMSC/TransitSG
Connectivity Layer
GSM/ EDGEAccess
WCDMAAccess
M-MGW M-MGW
InternetIntranet
PSTNISDN
SGSN
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Multiple Access
The cellular concept approaches the capacity limitation in terms of system coverage. Therefore, it does not alone help the per-cell capacity limitation as far as the simultaneous users are in question. From radio spectrum standpoint, it is extremely important how the radio resources are allocated to the simultaneous users.
Numbers of multiple accesses have been developed to combat the problem of simultaneous radio access allocation to the access requesters.
The main aspect of any multiple access scheme is the strategy how the available frequency band is allocated.
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Different Approaches
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WCDMA Band
From 3G point of view, it has been decided (in mid-1999 by OHG) that therewill be three CDMA variants in use. Those are:
DS-WCDMA-FDD: Direct Sequence- Wideband Code Division Multiple Access - Frequency Division Duplex
Uplink: 1920 -1980 MHzDownlink: 2110 -2170 MHzDuplex Distance: 190 MHz
DS-WCDMA-TDD: Direct Sequence- Wideband Code Division Multiple Access – Time Division Duplex
Lower Band: 1900 -1920 MHzUpper Band: 2010 -2025 MHz
MC-CDMA: Multi Carrier - Code Division Multiple Access
It was chosen for private indoor services
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WCDMA Bandwidth
In WCDMA, the data stream of the base station transmitter handles in downlink direction represents the traffic from the network to the terminal. This traffic uses several channels in the Uu interface. In the Uu interface the effective bandwidth for WCDMA is 3.84 MHz and with guard bands the required bandwidth is 5 MHz.
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WCDMA at a glance
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WCDMA Frequency allocations
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Basic Concept
The principles of WCDMA technique are based on Spread Spectrum.
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Spread Spectrum
The main advantages of the spread spectrum are:
– Its resistance to radio interference and jamming.
– It lowers the probability of intercept by an adversary.
– Its resistance to signal interference from multiple transmission signal branches.
– It providing multiple access facility with a reuse factor equal to one.
– It supporting means for measuring range, or the distance between two points.
– It yields the possibility of utilising diversity techniques, including multi-path diversity, as well as frequency and time diversity.
– It provides user access at any time without waiting for a free channel as far as the level of interference meets the system's tolerance.
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WCDMA Network
The WCDMA network is a multi-service “network of networks”, providing both traditional telecommunications services and new internet based services over the same network with support for high bit rates.
Network Architecture:3GPP (Third Generation Project Partnership) Reference Model:
Based on 3GPP reference network model, the WCDMA network can be considered to consists of four major components:
1. User Equipment (UE)
2. Access Network (AN)
3. Core Network (CN)
4. Network External to WCDMA
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3GPP Release 1999 Reference Architecture
Co-operatingNetworksUser Equipment Radio Access Network Core Network
Note: Not all interfaces areshown and named
BSCBTSBTS
Um
Abis
BSS
F
HLRHLR
D C
EIR
AU
C
EA
GMSCGMSC
Gf
Gn
SGSNSGSN
Gb Gr
Gn
SGSNSGSN
GGSNGGSN
Gs
Gc
Gi
Gd
IuCS
MSC/VLR
MSC/VLR
G
H
Gp
IuPS
RNCNode B
Uu
Iur
Iub
RNCNode BIub
RNS
RNS
UTRANIur
ME
Cu
or
SIM-ME i/f
USIM
SIMMS
ISDNPSTNPSPDNCSPDNPDN:- Intranet- Extranet- Internet- X.25
SMS
MSC/VLR
MSC/VLR SCFSCF
ME
SIM-ME i/f
SIM
MS
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WCDMA Channels
The WCDMA radio access allocates bandwidth for users and the allocated bandwidth and its controlling functions are handled with term ‘Channel’.
WCDMA uses 3 Layers:WCDMA uses 3 Layers:
1. Logical Channels: Describe the types of information to be transmitted
2. Transport Channels: Describe how the Logical Channels are to be transferred.
3. Physical Channels: These are the “transmission media” providing the radio platform through which the information is actually transferred.
In GSM the Physical Channels and their structure is recognised by the BSC but in WCDMA the Physical Channels really exist in the Uu interface and the RNC is not necessarily aware their structure at all. Instead of Physical Channels the RNC “sees” Transport Channels.
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Channel Architecture
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UTRAN
The main task of UTRAN is to create and maintain Radio Access Bearers (RAB) for communication between UEs and Core Network.
With RAB the Core Network elements are given an illusion about a fixed communication path to the UEs thus releasing them from the need to take care of radio communication aspects.
UTRAN is located between two open interfaces being Uu and Iu.
From the bearer architecture point of view the main task of UTRAN is to provide Bearer service over these interfaces.
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What is Radio Access Bearer (RAB) ?
RAB The Radio Access Bearer (RAB) is the entity responsible for transporting The Radio Access Bearer (RAB) is the entity responsible for transporting
radio frames of an application over the access network in UMTS.radio frames of an application over the access network in UMTS.
• Controlled by the core network (CN)
• CN determines traffic class and QoS
• Real-Time Applications– Streaming Class: Preserve time relation between entities
(packets) in a data stream
– Conversational Class: Preserve time relation between entities within a certain delay
• Non-Real Time Applications– Background Class: Destination is not expecting data.
Preserve Payload
– Interactive Class: Request / Response Pattern with preserved payload
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Conversational Speech 12.2 kbps Circuit switched
Conversational CS Data 64 kbps Circuit switched
Streaming 128/128 PS
Interactive Variable rate Packet switched
Multi-RABCombination of Conversational Speech and Interactive 64/64
RAB Examples
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RAB Attributes
• Transfer delay
RAB Service Attributes
• Traffic Class
• Maximum bit rate [kbps]
• Delivery order
• Maximum SDU size
• SDU format information
• SDU error ratio
• Residual bit error ratio
• Delivery of erroneous SDUs
• Guaranteed bit rate
• Traffic handling priority
• Allocation/retention priority
• Source statistics descriptor
• Relocation requirement
•RAB asymmetry indicator
RAB
UE RBS RNC CN
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UTRAN Architecture
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UTRAN & Interfaces
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NODE B
The BS is located between the Uu and Iub interfaces. Its main tasks are to establish the physical implementation of the Uu interface and, towards the network, the implementation of the Iub interface by utilising the protocol stacks specified for these interfaces.
Realization of the Uu interface means that the BS implements WCDMA radio access physical channels and transfers information from transport channels to the physical channels based on the arrangement determined by the RNC.
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Modulation Method
WCDMA uses Quadrature Phase Shift Keying (QPSK) as its modulation method in downlink direction and the Offset Quadrature Phase Shift Keying (OQPSK) in uplink direction.
The result is that the spectrum used for QPSK and OQPSK is the same but OQPSK has smoother signal. This allows the amplifiers to operate also on their non-linear operating area without problems.
The conventional QPSK could be used in both directions but then the UE would suffer power consumption problems and high prices.
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Receiver Technique
The WCDMA utilises multipath propagation.
On the other hand, to gain better capacity in the radio network, the transmit powers of the UEs (and BSs) should be relatively small. This decreases interference in the radio interface and gives more space for other transmissions and it is very useful that both the UE and the BS are able to “collect” many weak level signals.
This requires special type of receiver. One example of this kind of arrangement is called RAKE.
The purpose of the RAKE receiver is to improve the received signal level by exploiting the multi-path propagation characteristics of the radio wave.
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Diversity Technique
In general, diversity techniques are efficient means to overcome the radio signal deterioration due to shadowing and fading.
In addition to that utilizing diversity technique is a prerequisite for providing soft handover feature in the cellular systems.
In WCDMA technology, typically polarisation diversity is utilized both for uplink and down transmission.
The purpose of multipath diversity is to resolve individual multipath components and combine them to obtain a sum signal component with better quality.
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RNC (Radio Network Controller)
The RNC is switching and controlling element of the UTRAN. RNC is located
between the Iub and Iu interface. It also has the third interface called Iur for inter-RNS connections.
Referring to the Bearers, the RNC is a switching point between the Iu Bearer
and Radio Bearer(s).
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RNC Function
The whole functionality of RNC can be classified into two parts:
• UTRAN Radio Resource Management
• UTRAN Control Functions
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Radio Resource Management
The RRM is a collection of algorithms used to guarantee the stability of the radio path and the QoS of radio connection by efficient sharing and managing of the radio resources.
The RRM algorithms to be shortly presented here are:
Handover ControlPower ControlAdmission Control and Packet SchedulingCode Management
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Handovers
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WCDMA Handover Scenarios
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Soft Handover
In WCDMA system, the majority of handovers are intra-frequency soft handovers
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Concept of Soft/Softer Handover
Cell A
Cell B
Cell C
Single Link
The UE measured the CPICH Signal strenght (RSCP) and quality (Ec/No) to determine which cell to add in the active set
Add and remove from active set is based on relative measurments
Softer handover-two cells within the same RBS in Active Set
Soft handover-two cells from different RBS in Active Set
Soft/Softer handover-three cells in Active Set
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WCDMA Coverage GSM Coverage
Road
Using the WCDMA Frequency
Using the GSM Frequency
Inter RAT Handover
Inter Radio Access Technology (IRAT) handover
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Hand over from/to GSM
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POWER CONTROL
Power control is an essential feature of any CDMA based cellular system.
In WCDMA, power control is employed in both uplink and downlink.
Downlink power control is basically for minimising the interference to other cells and compensating for other cells' interference as well as achieving acceptable SIR.
To manage the power control properly in WCDMA, the system uses different two defined power control: Open Loop Power Control Closed Loop Power Control (CLPC), including Inner and Outer Loop Power Control mechanisms
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Types of Power Control
Open Loop Power Control (OLPC): Basically used for uplink power adjusting, the UE adjusts its transmission power based on estimate of the received signal level from the BS Common Pilot Channel (CPICH) when the UE is in idle mode and prior to Physical Random Access Channel (PRACH) transmission.
Closed-Loop Power Control (CLPC): Utilised for adjusting the transmission power when the radio connection has already been established. Its main target is to compensate the effect of rapid changes in the radio signal strength and hence it should be fast enough to respond to those changes.
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Admission Control and Packet Scheduling
WCDMA Radio Access has several limiting factors, but the most difficult to control is the interference occurring in the radio path. When the WCDMA cellular network is planned, one of the basic criteria for planning is to define the acceptable interference level with which the network is expected to function correctly. The main task of Admission Control is to estimate whether a The main task of Admission Control is to estimate whether a new call can have access to the system without sacrificing the new call can have access to the system without sacrificing the bearer requirements of existing calls. bearer requirements of existing calls.
Also responsible to handle packet connections with bursty Also responsible to handle packet connections with bursty traffic, having a very random arrival time, number of packet call traffic, having a very random arrival time, number of packet call per session, reading time, as well as number of packets per session, reading time, as well as number of packets within a call.within a call.
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Code ManagementRNC manages both Channelisation and Scrambling Codes used in the Uu interface connections.
In principle, the BS could manage them, but then the system may behave unstable when the RNC is otherwise controlling the radio resources.
The Uu interface requires two kinds of codes for proper functionality:
Every Cell uses 1 Scrambling Code, the UE is able to make separation between cells by recognising this code.
Under every Scrambling Code the RNC has a set of Channelisation Codes.
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Control Functions
In order for the UTRAN to control and manage the radio bearers, which is essential to provide the Radio Access Bearer (RAB) service, it should perform other functions in addition to the RRM algorithms.
These can be classified as:
System Information BroadcastingSystem Information BroadcastingRandom Access and Signalling Bearer SetupRandom Access and Signalling Bearer SetupRadio Bearer ManagementRadio Bearer ManagementUTRAN Security FunctionsUTRAN Security FunctionsUTRAN level mobility managementUTRAN level mobility managementDatabase HandlingDatabase HandlingUE positioningUE positioning
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WCDMA in nutshell
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What is Coverage in WCDMA
Signal does not mean “Coverage” in WCDMA
Pilot Signal - RSCPPilot Ec/NoService Coverage
Pilot RSCP
Pilot Ec/No
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Capacity Considerations Effect of different user distribution
High power usageLow capacity
Low power usageHigh code usage
Code limited scenario
Power limited scenario
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CELL CAPACITY
In GSM the TRX capacity calculation is very straightforward procedure but because In GSM the TRX capacity calculation is very straightforward procedure but because in WCDMA the radio interface is handled differently and the system capacity is limited in WCDMA the radio interface is handled differently and the system capacity is limited by variable factors, the capacity of the WCDMA TRX is not very easy to be by variable factors, the capacity of the WCDMA TRX is not very easy to be determined.determined.
The capacity of a cell depends on the downlink Scrambling Code amount assigned for the cell (minimum is 1). Every downlink Scrambling Code then has a set of Channelisation Codes under it and every call/transaction requires one Channelisation Code to operate.
In WCDMA technology, all the users share the common physical resource, being frequency band in 5 MHz slices. All users of the WCDMA TRX co-exist on the frequency band at the same moment of time and different transactions are for the people is the capacity of the WCDMA TRX.
Some assumptions: All the subscribers under the TRX coverage area are equally distributed so that they have equal distances to the TRX antenna. The Power level they use is the same and thus the interference they cause is on the same level. Subscribers under the TRX use the same baseband bit rate, i.e. also the same Symbol Rates.
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CALCULATIONS
Under these circumstances:Under these circumstances:
A value called Processing Gain (Gp) - Its a relative indicator informing what is the relationship between the whole bandwidth available (BRF) and the Baseband bit rate (B Information).
G G p = p = B B RFRF// B B InformationInformation
or
G G p = p = Chip rateChip rate// Data rateData rate
The system chip rate is constant; 3.84 Mcps (3840000 chips per second). Hence, as an example the Bearer having the bit rate 30 kb/s will have the Spreading Factor 128:
Assume that SNR = Eb/No is 3 dB, then
Users per TRX will be : 128/2 = 64Users per TRX will be : 128/2 = 64
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Designing for Load
RAB Coverage Unloaded
RAB Coverage High Load
Coverage shrinks with load due to cell breathing.
Coverage and capacity evaluation should be performed early in the design.
Capacity per sector is specified, then coverage is evaluated under corresponding load.
Coverage and capacity can be traded off.
• Large coverage footprint, low capacity.
• Smaller coverage footprint, high capacity.
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Transport Design
Design Criteria:Design Criteria:Up to 6 Node-Bs grouped into one cluster of a Sub-hubUp to 4 Sub-Hub clusters grouped into 1 hub.
STM-1 from Hub/Sub-Hub to RNC through media
Interfaces:Interfaces:End node-B: E1 interface.Sub-Hub: E1 interface southbound and STM-1 interface northbound.Hub: STM-1 interface.
RNC
Node
HubHub
Node Node
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3GPP (3rd Generation Partnership Project) release outline
3GPP Releases
• 3GPP Release 1999
• Release 4
• Release 5
• Future evolution with R6, R7..
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3GPP Releases - Time Schedule
1998 20011999 2000
3GPP Release 4
3GPP Release 1999
Q2Q1Q3 Q2 Q3Q4 Q4 Q1Q1 Q2 Q3 Q4Q4 Q3 Q1
1097 8542 3 11 121
3GPP TSGsPlenary Meetings
6
Q2
2002
1817 1916151413 222120 23
Q3 Q4 Q1 Q2 Q3 Q4 Q1
2003
3GPP Release 5
Versions of3GPP Release 1999
Versions of 3GPP Release 4
3GPP Release 6
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Core Network - Architecture and EvolutionCore Network - Architecture and Evolution
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How Does My Network Topology Look Today ?
SGSN
IP BackboneGGSN
SGSNGGSN
Internet
GPRS - Network Baseline
GSM - Network Baseline
BSC
BSC
GSM RAN
BSC
BSC
GSM RAN
TDM BackboneMSC MSC
HLR/AUC
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TDM/IP/ATM
How Would this look with WCDMA
SGSN
WCDMA Introduction
BSC
BSC
GSM RAN
BSC
BSC
GSM RAN
MSC MSC
GGSNSGSN
GGSN
Internet
MGw MGw
MSC-S MSC-S
RNC
RNC
WCDMA RAN
RNC
RNC
WCDMA RAN
HLR/AUC
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Soft switch Concept
Centralization & pooling of network control functions.
Payload uses shortest path & most efficient coding.
Free choice of Transport technologies.
Separate complex control & execution functions from service payload transport.
Layered Architecturenetwork
End-userapplications
Control
MSC-S HLR
GGSN
GMSC/Transit
SG
Connectivity
GSM/ EDGEAccess
WCDMAAccess
M-MGW M-MGW
InternetIntranet
PSTNISDN
SGSN
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What is Mobile Softswitch?
Classic MSC(control and switching)
MSC Server(Control)
Mobile Media Gateway (Switching)
Mobile Softswitch Solution Classic MSC Solution
MSC-S
MGW
MSC
TDM IP/ATM
Control Layer
Connectivity Layer
Classic circuit-switched network Layered Architecture network
MSC-S
MGW
MGW MGW
MGW
MGW
MSC MSC
MSC
MSCMSC
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Distributed switching, Local Switching
Main Site
Remote Site
MS12PSTN
BSC
PSTN
MS1
MS2
BSC
BSC
MS11
BSC
TDM
IP
M-MGw
MSC-S
M-MGw
MSS approach:Main Site
Remote Site
MS1
MS2
MS11
MS12PSTN
TDM
BSC
BSC
PSTN
Classical MSC approach:
BSC
BSC
MSC
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MSC Server
ApplicationServers
ApplicationService enablers
Services/applications
Control
Servers
Control
MSC HLR/AuC/FNR GMSC/Transit
ConnectivityMGWMGW
ServerServer
PSTN/ISDN
InternetIntranetsGGSNSGSN
SGW
User data
Main MSC Server functions
Service control
Mobility management
Charging control and CDR generation
Can control more than one MGWGSMEDGE
WCDMA
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Media Gateway
ApplicationServers
ApplicationService enablers
Services/applications
Control
Servers
Control
MSC HLR/AuC/FNR GMSC/Transit
ConnectivityMGWMGW
ServerServer
PSTN/ISDN
InternetIntranetsGGSNSGSN
SGW
User dataGSM
EDGEWCDMA
Main Media Gateway functions
Speech & media processing
Setup/release of user data bearers
Interfacing between different transport standards
Boundary between different networks
Can be controlled by several MSC Servers
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M-MGw Interfaces
MGW
HTTP, FTP,S-FTP, IIOP,
SSH,TELNET
ATM ATM IuUP, AAL2)
TDM Q.AAL2Q.AAL2
RANAP, 3GPP 24.008 BICC
O&M
ISUP
IP (NbUP, RTP)
BSSAP
TDM (A)
GCP
(GPS)Synch
M-MGw
-
(NbUP, I.trunk, AAL2)(
MSC/TSC Server
BSC
RNC
PSTNother networks
M-MGw
(Mc)
ATM, IP
IP
Positioning the M-MGw in the Network
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What is High Speed Downlink Packet Access (HSDPA)
STANDARDIZED Integral part of WCDMA (3GPP Release 5)
REDUCED DELAY Reduced round trip time
CAPACITY 2 – 3 times improved system throughput
SPEED Higher bit rates: up to 14 Mbps
Smooth Upgrade Short time to market with existing sites
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HSDPA Basic Principles
Shared Channel TransmissionDynamically shared in time & code
domain
Higher-order Modulation16QAM in complement to QPSK for
higher peak bit rates
2 ms
Short TTI (2 ms)Reduced round trip delay
Fast Hybrid ARQ with Soft Combining
Reduced round trip delay
Fast Radio Channel Dependent Scheduling
Scheduling of users on 2 ms time basis
Fast Link AdaptationData rate adapted to radio
conditions on 2 ms time basis
t
P
Dynamic Power AllocationEfficient power &
spectrum utilisation
Let´s be ready….Let´s be ready….