lte
TRANSCRIPT
(LTE) Long Term EvolutionA new Dimension to Wireless Communication
Applications of GPRS Web browsing Corporate & Internet Email Vehicle Positioning Remote LAN Access Home Automation Document Sharing/Collaborative working
Agenda Introduction Network Architecture System Architecture Evolution LTE Physical Layer LTE Layer 2/3 LTE UE Connection management LTE Network Algorithms Downlink Transmission Scheme Uplink Transmission Scheme OFDM SF-OFDM MIMO LTE-Advanced
3G and LTE RoadmapExcellent Mobile Broadband TodayVoice and Full Range of IP Services
Enhanced User ExperienceImproved voice and data capacity
CDMA2000
1XRel. 0 Rev. A Phase I Phase II
1x Advanced
EV-DORel-99 Rel-5
EV-DO Rev. BRel-6Rel-7 Rel-8
DO AdvancedRel-9 & Beyond
WCDMA
HSPA
HSPA+ (HSPA Evolved)Rel-8 Rel-9 Rel-10
LTE Leverages new, wider and TDD spectrum
LTE2011+
LTE Advanced
2009
2010
Created 01/30/09
Specifying LTE: 3 GPP SpecificationsRelease Rel-99 Functional Freeze Dec 1999 Main UMTS feature of release CS and PS R99 Radio Bearers MMS Location Services March 2000 Basic 3.84 Mcps W-CDMA (FDD & TDD) March 2001 Enhancements 1.28 Mcps TDD (aka TD-SCDMA) June 2002 HSDPA IMS AMR-WB Speech March 2005 HSUPA (E-DCH) / Enhanced Uplink MBMS WLAN-UMTS Internetworking Dec 2007 HSPA+ (64 QAM downlink, MIMO, 16 QAM uplink) LTE and SAE Feasibility Study Dec 2008 LTE work item OFDMA / SC-FDMA air interface SAE work item new IP core network Further HSPA improvements / HSPA Evolution January 2008, Rel-8 approved/December 2008, Rel-8 frozen March 2009, ASN.1 code ready and backwards compatibility secured
Rel-4 Rel-5
Rel-6
Rel - 7 Rel 8
LTE background storythe early days
Work on LTE was initiated as a 3GPP release 7 study item Evolved UTRA and UTRAN in December 2004:With enhancements such as HSDPA and Enhanced Uplink, the 3GPP radio-access technology will be highly competitive for several years. However, to ensure competitiveness in an even longer time frame, i.e. for the next 10 years and beyond, a long term evolution of the 3GPP radio-access technology needs to be considered.
LTE background story
Basic drivers for LTE have been: Reduced latency Higher user data rates Improved system capacity and coverage Cost-reduction.
the early days
3GPP Long Term Evolution - the next generation of wireless cellular technology beyond 3G Initiative taken by the 3rd Generation Partnership Project in 2004 Introduced in Release 8 of 3GPP Mobile systems likely to be deployed by 2010
LTE Network ArchitectureUMTS 3G: UTRANEPC
GGSN SGSN
MME S-GW / P-GW
MME S-GW / P-GW
RNC
RNCeNB eNB eNB E-UTRANEPC ; Evolved Packet Core MME : Mobility Management Entity S-GC : Serving Gateway P-GW : PDN Gateway PDN : Packet Data Network eNB : E-UTRAN Node B / Evolved Node B E-UTRAN ; Evolved-UTRAN
eNB
NB
NB
NB
NB
UMTS : Universal Mobile Telecommunications System UTRAN : Universal Terrestrial Radio Access Network GGSN : Gateway GPRS Support Node GPRS: General Packet Radio Service SGSN : Serving GPRS Support Node RNC: Radio Network Controller NB: Node B
Simplified LTE network elements and interfaces3GPP TS 36.300 Figure 4: Overall ArchitectureEPC
MME S-GW / P-GW
MME S-GW / P-GW
S1
eNB = All radio interface-related functions MME = Manages mobility, UE identity, and security parameters. S-GW = Node that terminates the interface towards E-UTRAN. P-GW = Node that terminates the interface towards PDN
eNB eNB
X2eNB E-UTRAN
eNB
Simple Architecture Flat IP-Based Architecture Reduction in latency and cost Split between EPC and E-UTRAN Compatibility with 3GPP and non-3GPP technologies
EPC ; Evolved Packet Core MME : Mobility Management Entity S-GC : Serving Gateway P-GW : PDN Gateway PDN : Packet Data Network eNB : E-UTRAN Node B / Evolved Node B E-UTRAN ; Evolved-UTRAN
Specifying LTE: LTE Development Lifecycle
LTE Overview 3GPP R8 solution for the next 10 years Peaks rates: DL 100Mbps with OFDMA, UL 50Mbps with SC-FDMA Latency for Control-plane < 100ms, for User-plane < 5ms Optimised for packet switched domain, supporting VoIP Scaleable RF bandwidth between 1.25MHz to 20MHz 200 users per cell in active state Supports MBMS multimedia services Uses MIMO multiple antenna technology Optimised for 0-15km/h mobile speed and support for up-to 120-350 km/h No soft handover, Intra-RAT handovers with UTRAN Simpler E-UTRAN architecture: no RNC, no CS domain, no DCH
3GPP architecture evolution towards flat architectureRelease 6 Release 7 Direct Tunnel GGSN Release 7 Direct Tunnel and RNC in NB GGSN Release 8 SAE and LTE SAE GW
GGSN
SGSNRNC
SGSNRNC
SGSN
MME
NB
NB
RNC NBUser Plane
eNB
Control Plane
ProtocoleNBRB Cont. Connection Mobility Cont. Radio Admission Cont. eNB Measurement Configuration & Provision Dynamic Resource Allocation (Scheduler) RRC PDCP RLC MAC PHY RRM : Radio Resource Management RB : Radio Bearer RRC: Radio Resource Control PDCP : Packet Data Convergence Protocol RLC : Radio Link Control MAC : Medium Access Control NAS : Non Access Stratum EPS : Evolved Packet System UE : User Equipment IP : Internet Protocol Mobile Anchoring EPS Bearer Cont.
E-UTRAN
Inter Cell RRM
MMENAS Security
EPC
Idle State Mobility Handling
SAE GWS-GW S1 P-GWUE IP Address Allocation Packet Filtering
Internet
LTE / SAE LTE has been designed to support only packet switched services, in contrast to the circuit-switched model of previous cellular systems. LTE aims to provide seamless Internet Protocol (IP) connectivity between User Equipment (UE) and the Packet Data Network (PDN), without any disruption to the end users applications during mobility.
The term LTE encompasses the evolution of the radio access through the Evolved-UTRAN(E-UTRAN), it is accompanied by an evolution of the nonradio aspects under the term System Architecture Evolution (SAE) which includes the Evolved Packet Core (EPC) network. Together LTE and SAE comprise the Evolved Packet System (EPS).
EPS = EPC + E-UTRAN
System Architecture Evolution SAE is a study within 3GPP targeting at the evolution of the overall system architecture. Objective is to develop a framework for an evolution or migration of the 3GPP system to : a higher-data-rate, lower-latency, packet optimized system
that supports multiple radio access technologies. The focus of this work is on the PS domain with the assumption that voice services are supported in this domain". This study includes the vision of an all-IP network.
Why LTE/SAE? Packet Switched data is becoming more and more dominant VoIP is the most efficient method to transfer voice data Need for PS optimised system Amount of data is continuously growing Need for higher data rates at lower cost Users demand better quality to accept new services High quality needs to be quaranteed
> Alternative solution for non-3GPP technologies (WiMAX) needed > LTE will enhance the system to satisfy these requirements.
LTE technical objectives and architecture User throughput [/MHz]: Downlink: 3 to 4 times Release 6 HSDPA Uplink: 2 to 3 times Release 6 Enhanced Uplink
Downlink Capacity: Peak data rate of 100 Mbps in 20 MHz maximum bandwidth Uplink capacity: Peak data rate of 50 Mbps in 20 MHz maximum bandwidth Latency: Transition time less than 5 ms in ideal conditions (user plane), 100 ms control plane (fast connection setup)
Mobility: Optimised for low speed but supporting 120 km/h Most data users are less mobile!
Simplified architecture: Simpler E-UTRAN architecture: no RNC, no CS domain, no DCH Scalable bandwidth: 1.25MHz to 20MHz: Deployment possible in GSM bands.
ProtocoleNBRB Cont. Connection Mobility Cont. Radio Admission Cont. eNB Measurement Configuration & Provision Dynamic Resource Allocation (Scheduler) RRC PDCP RLC MAC PHY RRM : Radio Resource Management RB : Radio Bearer RRC: Radio Resource Control PDCP : Packet Data Convergence Protocol RLC : Radio Link Control MAC : Medium Access Control NAS : Non Access Stratum EPS : Evolved Packet System UE : User Equipment IP : Internet Protocol Mobile Anchoring EPS Bearer Cont.
E-UTRAN
Inter Cell RRM
MMENAS Security
EPC
Idle State Mobility Handling
SAE GWS-GW S1 P-GWUE IP Address Allocation Packet Filtering
Internet
EPS Network ElementsS6a S1-MME
GxMME
Rx
LTE-Uu eNB UEE-UTRAN
S1-U
S-GW
S5 / S8EPC
P-GW
SGi
Operators IP Services (e.g. IMS, PSS, etc,)
UE, E-UTRAN and EPC together represent the Internet Protocol (IP) Connectivity Layer. This part of the system is also called the Evolved Packet System (EPS). The main function of this layer is to provide IP based connectivity, and it is highly optimized for that purpose only. All services will be offered on top of IP, and circuit switched nodes and interfaces seen in earlier 3GPP architectures are not present in E-UTRAN and EPC at all. IP technologies are also dominant in the transport, where everything is designed to be operated on top of IP transport.
System architecture for E-UTRAN only network
Services The IP Multimedia Sub-System (IMS) is a good example of service machinery that can be used in the Services Connectivity Layer to provide services on top of the IP connectivity provided by the lower layers. For example, to support the voice service, IMS can provide Voice over IP (VoIP) and interconnectivity to legacy circuit switched networks PSTN and ISDN through Media Gateways it controls.
EPC Functionally the EPC is equivalent to the packet switched domain of the existing 3GPP networks. Significant changes in the arrangement of functions and most nodes and the architecture in this part should be considered to be completely new. SAE GW represents the combination of the two gateways, Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW) defined for the UP handling in EPC. Implementing them together as the SAE GW represents one possible deployment scenario, but the standards define the interface between them, and all operations have also been specified for when they are separate. The Basic System Architecture Configuration and its functionality are documented in 3GPP TS 23.401. We will learn the operation when the S5/S8 interface uses the GTP protocol. However, when the S5/S8 interface uses PMIP, the functionality for these interfaces is slightly different, and the Gxc interface also is needed between the Policy and Charging Resource Function (PCRF) and S-GW.
One of the big architectural changes in the core network area is that the EPC does not contain a circuit switched domain, and no direct connectivity to traditional circuit switched networks such as ISDN or PSTN is needed in this layer.
E-UTRAN The development in E-UTRAN is concentrated on one node, the evolved Node B (eNodeB). All radio functionality is collapsed there, i.e. the eNodeB is the termination point for all radio related protocols. As a network, E-UTRAN is simply a mesh of eNodeBs connected to neighbouring eNodeBs with the X2 interface.
User Equipment UE is the device that the end user uses for communication. Typically it is a hand held device such as a smart phone or a data card such as those used currently in 2G and 3G, or it could be embedded, e.g. to a laptop. UE also contains the Universal Subscriber Identity Module (USIM) that is a separate module from the rest of the UE, which is often called the Terminal Equipment (TE). USIM is an application placed into a removable smart card called the Universal Integrated Circuit Card (UICC). USIM is used to identify and authenticate the user and to derive security keys for protecting the radio interface transmission. Maybe most importantly, the UE provides the user interface to the end user so that applications such as a VoIP client can be used to set up a voice call.
Functionally the UE is a platform for communication applications, which signal with the network for setting up, maintaining and removing the communication links the end user needs. This includes mobility management functions such as handovers and reporting the terminals location, and in these the UE performs as instructed by the network.
Logical High Level Architecture for The Evolved SystemGERAN
GB GPRS Core
UTRAN
Iu
SGSN
S4
Rx+
S6
S7IASA
S3 MME 3GPP SAE S2b UPE S5a anchor S5b anchor EPC (SAE)Trusted non 3GPP IP Access
Operators IP Services (e.g. IMS, PSS, etc,)
eNB
eNB eNB eNB Evolved RAN (LTE)
S1
SGiWLAN 3GPP IP Access WLAN Access Network
S2a
EPDG
EPS uses the concept of EPS bearers to route IP traffic from a gateway in the PDN to the UE. A bearer is an IP packet flow with a defined Quality of Service (QoS) between the gateway and the UE. The E-UTRAN and EPC together set up and release bearers as required by applications.
SAE Bearer Model
QoS parameters for QCI
System architecture for 3GPP access networks
Interfaces and Protocols in Basic System Architecture Configuration CP protocols related to a UEs connection to a PDN. The interfaces from a single MME are shown in two parts, the one on top showing protocols towards the E-UTRAN and UE, and the bottom one showing protocols towards the gateways. Those protocols that are shown in white background are developed by 3GPP, while the protocols with light grey background are developed in IETF, and represent standard internet technologies that are used for transport in EPS. 3GPP has only defined the specific ways of how these protocols are used.
LTE Protocol Stacks (UE and eNB)RRC: Radio Resource Control
Control-Plane L3RRC
User-Plane
PDCP : Packet Data Convergence Protocol RLC : Radio Link Control MAC : Medium Access Control PHY : Physical Layer
Radio Bearers
L2
PDCP RLC
Logical ChannelsMAC
Transport Channels
L1
PHY:
Physical Channels Physical Signals
Control plane protocol stack in EPS
The topmost layer in the CP is the Non-Access Stratum (NAS), which consists of two separate protocols that are carried on direct signaling transport between the UE and the MME. The content of the NAS layer protocols is not visible to the eNodeB, and the eNodeB is not involved in these transactions by any other means, besides transporting the messages, and providing some additional transport layer indications along with the messages in some cases.
NAS layer protocolsThe NAS layer protocols are: EPS Mobility Management (EMM): The EMM protocol is responsible for handling the UE mobility within the system. It includes functions for attaching to and detaching from the network, and performing location updating in between. This is called Tracking Area Updating (TAU), and it happens in idle mode. Note that the handovers in connected mode are handled by the lower layer protocols, but the EMM layer does include functions for re-activating the UE from idle mode. The UE initiated case is called Service Request, while Paging represents the network initiated case. Authentication and protecting the UE identity, i.e. allocating the temporary identity GUTI to the UE are also part of the EMM layer, as well as the control of NAS layer security functions, encryption and integrity protection. EPS Session Management (ESM): This protocol may be used to handle the bearer management between the UE and MME, and it is used in addition for E-UTRAN bearer management procedures. Note that the intention is not to use the ESM procedures if the bearer contexts are already available in the network and EUTRAN procedures can be run immediately. This would be the case, for example, when the UE has already signaled with an operator affiliated. Application Function in the network, and the relevant information has been made available through the PCRF.
User plane protocol stack in EPS
The UP includes the layers below the end user IP, i.e. these protocols form the Layer 2 used for carrying the end user IP packets. The protocol structure is very similar to the CP. This highlights the fact that the whole system is designed for generic packet data transport, and both CP signaling and UP data are ultimately packet data. Only the volumes are different.
Summary of interfaces and protocols in Basic System Architecture configuration
LTE Physical Layer Enables exchange of data & control info between eNB and UE and also transport of data to and from higher layers Functions performed include error detection, FEC, MIMO antenna processing, synchronization, etc. It consists of Physical Signals and Physical Channels Physical Signals are used for system synchronization, cell identification and channel estimation. Physical Channels for transporting control, scheduling and user payload from the higher layers OFDMA in the DL, SC-FDMA in the UL LTE supports FDD and TDD modes of operation
Channel MappingDTCH MTCH
PCCH
BCCH
CCCH
DCCH
MCCH
Logical Channels
CCCH
DCCH
DTCH
PCH
BCH
DL-SCH
MCH
Transport Channels (MAC)
RACH
UL-SCH
PDSCH
PBCH
PMCH
PDCCH
Physical Channels (L1)
PRACH
PUSCH
PUCCH
Downlink
Uplink
LTE Physical SignalsDL SignalsPSCH Primary Synchronization Signals Used for cell search and identification by the UE. Carries part of cell ID (one of three orthogonal sequences). Used for cell search and identification by the UE. Carries the remainder of cell ID (one of 168 binary sequences). Used for DL channels estimation. Extract sequence derived from cell ID (one of 3 X 168 504 pseudo random sequences)
SSCH
Secondary Synchronization Signals
RS
Reference Signal (Pilot)
UL SignalsRS Reference Signal (Demodulation and Sounding) Used for synchronization and UP channels estimations.
LTE Physical ChannelsDL ChannelsPBCH PMCH PDCCH PDSCH Physical broadcast channel Carries cell-specific information
Physical multicast channelPhysical downlink control channel Physical downlink shared channel
Carries the MCH transport channelScheduling, ACK, NACK Payload Defines number of PDCH OFDMA symbols per subframe (1, 2, or 3) Carries HARQ ACK/NACK
PCFICH Physical channelPHICH
control format indicator
Physical hybrid ARQ indicator channel
UL ChannelsPRACH Physical random access channel Call setup Scheduling, ACK, NACK Payload
PUCCH Physical uplink control channel PUSCH Physical uplink shared channel
LTE Transport ChannelsPhysical layer transport channels offer information transfer to medium access control (MAC) and higher layers.DL ChannelsBCH DL-SCH PCH MCH Broadcast Channel Downlink Shared Channel Paging Channel Multicast Channel
UL ChannelsUL-SCH RACH Uplink Shared Channel Random Access Channel
LTE Logical ChannelsLogical channels are offered by the MAC layer.Control Channels: Control-plane informationBCCH PCCH Broadcast Control Channel Paging Control Channel
CCCHMCCH DCCH
Common Control ChannelMulticast Control Channel Dedicated Control Channel
Traffic Channels: User-plane informationDTTCH MTCH Dedicated Traffic Channel Multicast Traffic Channel
Major requirements for LTEidentified during study item phase in 3GPP Higher peak data rates: 100 Mbps (downlink) and 50 Mbps (uplink) Improved spectrum efficiency: 2-4 times better compared to 3GPP release 6 Improved latency: Radio access network latency (user plane UE RNC - UE) below 10 ms Significantly reduced control plane latency
Support of scalable bandwidth: 1.4, 3, 5, 10, 15, 20 MHz Support of paired and unpaired spectrum (FDD and TDD mode) Support for interworking with legacy networks Cost-efficiency: Reduced CApital and OPerational EXpenditures (CAPEX, OPEX) including backhaul Cost-effective migration from legacy networks
A detailed summary of requirements has been captured in 3GPP TR 25.913 Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN).
3GPP Long Term Evolution (LTE) 3GPP (LTE) is Adopting: OFDMA in DL with 64QAM All IP e2e Network Channel BWs up to 20 MHz Both TDD and FDD profiles Flexible Access Network Advanced Antenna Technologies UL: Single-Carrier FDMA (SC-FDMA), (64QAM optional)
LTE is adopting technology & features already available with Mobile WiMAX Can expect similar long-term performance benefits and trade-offs
Comparing the End-to-End NetworkLTE/SAE User Plane & Data FlowApplication
e.g. IP, PPP
Multiple layers, Many nodes and proprietary protocolsRelay GTP - U GTP - U
e.g. IP, PPP
RelayPDCP PDCP GTP - U
GTP - U
RLC MAC L1
RLC MAC L1 LTE-Uu
UDP/IP L2 L1 S1-U
UDP/IP L2 L1
UDP/IP L2 L1 S5
UDP/IP L2 L1
UE/MS
E-UTRAN
Serving GW
PDN GW
SGi
Mobile WiMAX User Plane & Data FlowBased on simple IETF protocols, Fewer nodes & fewer device requirements, Optimized for high speed data
Source: LTE/SAE: 3GPP, Mobile WiMAX: WiMAX Forum Network Specification Release 1.0
LTE: Not a Simple 3G Upgrade
LTE Represents a Major Upgrade from CDMABased HSPA (or EV-DO) No longer a simple SW upgrade: CDMA to OFDMA, represent different technologies Circuit switched to IP e2e network
Also requires new spectrum to take full advantage of wider channel BWs and Requires dual-mode user devices for seamless internetwork connectivity
LTE Key Parameters
Modulation QPSK, 16 QAM and 64
QAM used for thepayload channels (spectrally efficient) BPSK and QPSK used for the control channels (Reliability and coverage)
Adaptive modulationand coding
Requirements to be met by LTEFast, Efficient, Cheap, Simple
Peak Data Rates
Spectrum efficiency Reduced Latency Mobility Spectrum flexibility Coverage Low complexity and cost Interoperability Simple packet-oriented E-UTRAN architecture
Key LTE radio access features
LTE radio access: Multicarrier Technology Downlink: OFDM Uplink: SC-FDMAOFDMA SC-FDMA
Advanced antenna solutions: Multiple Antenna Technology Diversity Beam-forming Multi-layer transmission (MIMO)
TX
TX
Three fundamental benefits of multiple antennas: (a) diversity gain; (b) array gain; (c) spatial multiplexing gain.
Key LTE radio access features
Spectrum flexibility Flexible bandwidth New and existing bands Duplex flexibility: FDD and TDD1.4 MHz 20 MHz
Packet-Switched Radio Interface
1G
Analog
2G
Digital
3G
Packets
4G
True Broadband
User Equipment Capabilities
Key Radio Technologies to WatchSpectrum flexibility
Ultra-Wideband (UWB) range 1 meter MIMO (Multiple Input Multiple Output) Advanced Radio Chipsets for handsets and dongles that incorporate MIMO Adaptive Antenna Systems (AAS) Smart networks (sector load balancing, spatial/freq/time load balancing, selftuning, dynamic resource management) Network MIMO & Heterogeneous Deployment (Pico+Micro+Femto) Orthogonal Frequency Division Multiplex (OFDM) < [xDSL, WiMAX, WiFi 802.11a,g; LTE] Spectrum Flexibility Reconfigurable Radios (SDRs), Base stations, and CPE Cognitive radios
Flexibility in band-of-operation Flexibility in bandwidth Dynamic Spectrum Usage and Reconfigurable radios and cognitive radios? Flexibility in duplexing
TDD versus FDDSource: IDC, Ericsson
Band X
Band Y
Band Z
20 MHz
+ FDD TDD fDL/UL
fDL fUL Paired spectrum
Unpaired spectrum
An SDR is a radio that includes a transmitter in which the operating parameters of frequency range, modulation type or maximum output power (either radiated or conducted) can be altered by making a change in software without making any changes to hardware components that affect the radio frequency emissions FCC Definition
TechnologyMobile Broadband speed evolutionFuture LTE releases
LTE HSPA+ Market impact Peak rate Typical user rate downlink Typical user rate uplink 2009 42 Mbps 1-10 Mbps 0.5-4.5 Mbps 2010 ~150 Mbps 10-100 Mbps 5-50 Mbps
True Mobile Broadband~2014
~1000 MbpsOperator dependent Operator dependent
Excellent user and network experience
Evolution of UMTS FDD and TDDdriven by data rate and latency requirements
FDD Bands for 3GPP Technologies
FDD Frequency band
TDD Bands for 3GPP Technologies
LTE radio interface New radio interface modulation: SC-FDMA UL and OFDMA DL Frequency division, TTI 1 ms Scalable bandwidth 1.25-20MHz TDD and FDD modes UL/DL in either in same or in another frequncy
OFDMA has multiple orthogonal subcarries that can be shared between users quickly adjustable bandwith per user
SC-FDMA is technically similar to OFDMA but is better suited for uplink from hand-held devices Single carrier, time space multiplexing Tx consumes less power
From Ericsson, H. Djuphammar
LTE/SAE Keywords aGW Access Gateway
eNB EPC E-UTRAN
Evolved NodeBEvolved Packet Core Evolved UTRAN
IASA Inter-Access System Anchor
LTE OFDMA SC-FDMA SAE UPE
Long Term Evolution of UTRANOrtogonal Frequency Division Multiple Access Single Carrier Frequency Division Multiple Access System Architecture Evolution User Plane Entity
MME Mobility Management Entity
3GPP TR 23.401 / 25.813Network Entities:MME ID eNB ID TAI Network: PLMN EPS ID PLMN Public Land Mobile Network EPS Evolved Packet System MME Mobility Management Entity eNBE-UTRAN Node B TAI -Tracking Area ID E-UTRAN Evolved Universal Radio Access Network C-RNTI Cell Radio Network Temporary Identifier RA-RNTI Random Access RNTI UE User Equipment IMEI International Mobile Equipment Identity IMSI International Mobile Subscriber Identity S-TMSI SAE Temporary Mobile Subscriber Identity
LTE/SAE Network IdentifiersEUTRAN: E-UTRAN C-RNTI RA-RNTI UE: IMEI IMSI S-TMSI
System architecture evolution
RAN interfaces X2 interface between eNBs for handovers Handover in 10 ms No soft handovers Interfaces using IP over E1/T1/ATM/Ethernet / Load sharing in S1 S1 divided to S1-U (to UPE) and S1-C (to CPE) Single node failure has limited effects
S1eNB
aGW X2 S8 eNB aGW X2
eNB
SAE architecture [3GPP TS 23.401]GERAN Gb Iu GPRS Core HSS PCRF
UTRANX1
S6 S7 S4
Rx+
S3
eNB
S1
MME UPE aGW
S11
SAE GW
S5
PDN SAE GW
SGi
Operator IP services (including IMS, PSS, ...)
X1
X2
Evolved Packet Core
S2
eNB
Non-3GPP IP Access
Evolved RAN
SAE architechture [3GPP TS 23.401]TBD HSS S1 eNB S6a S11 S5 SAE GW IASA SGi eNB aGW TBD S11 Operator IP service, including IMS PDN SAE GW PCRF
S7
TBD X2
aGW S8
eNB
Evolved RAN
aGW = MME/UPE
Functions of eNB Terminates RRC, RLC and MAC protocols and takes care of Radio Resource Management functions Controls radio bearers Controls radio admissions Controls mobility connections Allocates radio resources dynamically (scheduling) Receives measurement reports from UE
Selects MME at UE attachment Schedules and transmits paging messages coming from MME Schedules and transmits broadcast information coming from MME & O&M Decides measurement report configuration for mobility and scheduling Does IP header compression and encryption of user data streams
Functions of aGW Takes care of Mobility Management Entity (MME) functions Manages and stores UE context Generates temporary identities and allocates them to UEs Checks authorization Distributes paging messages to eNBs Takes care of security protocol Controls idle state mobility Control SAE bearers Ciphers & integrity protects NAS signaling
Takes care of User Plane Entity (UPE) functions Terminates for idle state UEs the downlink data path and triggers/initiates paging when downlink data arrive for the UE. Manages and stores UE contexts, e.g. parameters of the IP bearer service or network internal routing information. Switches user plane for UE mobility Terminates user plane packets for paging reasons
FunctionseNBInter Cell RRM RB Cont. Connection Mobility Cont. Radio Admission Cont. eNB Measurement Configuration & Provision Dynamic Resource Allocation (Scheduler) RRC PDCP RLC MAC PHY RRM : Radio Resource Management RB : Radio Bearer RRC: Radio Resource Control PDCP : Packet Data Convergence Protocol RLC : Radio Link Control MAC : Medium Access Control
aGW
Control PlaneSAE Bearer Control MME Entity
User Plane S1PDCP User Plane
LTE Control PlaneUENAS RRC PDCP RLC MAC PHY RRC PDCP RLC MAC PHY
eNB S1
aGWNAS
LTE User PlaneUEIP PDCP RLC MAC PDCP RLC MAC
eNB S1
aGWIP
PHY
PHY
GTP-U tunnelingHeader compression & encryption
UE
X1
eNB
S1
UPE
S11
SAE GW S5
PDN SAE GW
SGi
ServerApplication
Application
TCP/UDP u
TCP/UDP
IPv6/v4
PDCP RLC
ENC PDCP GTP-U RLC MAC UDPIP L2
IPv6/v4GTP-U GTP-U GTP-U GTP-U
GTP-U
UDP IP L2 L1
UDP IP L2 L1
UDP IP L2 L1
UDP IP L2 L1
UDP IP
L2
L2
L2
MAC
L2L1
L1
L1
L1
Radio L1
Radio L1
L1
Non-3GPP access tunnelingUEWLAN
APS2
PDN SAE GW HASGi
ServerApplication
TCP/UDP
IPv4/6
IPv4/6
MIP UDP
MIP UDP
IPL2
IPv6/v4L2 L2
IP
IP
IP
IP
IP
L2 L1
L2 L1
L2 L1
L2
L1
L1
L1
L1
LTE Frame Structure (Downlink) LTE Frame Structure Type I (FDD)
LTE Frame Structure Type II (TDD)
FDD (left) and TDD (right) frequency bands defined in the 3GPP (May 2009)
Downlink Transmission Scheme The downlink transmission scheme for E-UTRA FDD and TDD modes is based on conventional OFDM. In an OFDM system, the available spectrum is divided into multiple carriers, called sub-carriers, which are orthogonal to each other. Each of these sub-carriers is independently modulated by a low rate data stream. OFDM is used as well in WLAN, WiMAX and broadcast technologies like DVB. OFDM has several benefits including its robustness against multipath fading and its efficient receiver architecture.
OFDM Single Carrier Transmission (e.g. WCDMA)
Orthogonal Frequency Division Multiplexing
OFDM signal generation chain OFDM signal generation is based on Inverse Fast Fourier Transform (IFFT) operation on transmitter side:
On receiver side, an FFT operation will be used.
Difference between OFDM and OFDMA OFDM allocates users in time domain only OFDMA allocates users in time and frequency domain
LTE downlink conventional OFDMAFrequency-Time Representation of an OFDM Signal
LTE provides QPSK, 16QAM, 64QAM as downlink modulation schemes Cyclic prefix is used as guard interval, different configurations possible: Normal cyclic prefix with 5.2 Os (first symbol) / 4.7 Os (other symbols) Extended cyclic prefix with 16.7 Os 15 kHz subcarrier spacing Scalable bandwidth
Frequency and Time Domain Representation
Frequency
Time
OFDMA time-frequency multiplexing
OFDMA transmitter and receiver
LTE spectrum flexibility LTE physical layer supports any bandwidth from 1.4 MHz to 20 MHz in steps of 180 kHz (resource block) Current LTE specification supports a subset of 6 different system bandwidths All UEs must support the maximum bandwidth of 20 MHz
Generic frame structure in E-UTRA downlink For the generic frame structure frame structure, the 10 ms radio frame is divided into 20 equally sized slots of 0.5 ms. A sub-frame consists of two consecutive slots, so one radio frame contains 10 sub-frames.
Downlink Resource Grid The available downlink bandwidth consists of NDLBW subcarriers with a spacing of f = 15 kHz. In case of multi cell MBMS transmission, a sub-carrier spacing of f = 7.5 kHz is also possible. NDLBW can vary in order to allow for scalable bandwidth operation up to 20 MHz. Initially, the bandwidths for LTE were explicitly defined within layer 1 specifications. Later on a bandwidth agnostic layer 1 was introduced, with NDLBW for the different bandwidths to be specified by 3GPP RAN4 to meet performance requirements, e.g. for out-ofband emission requirements and regulatory emission limits
The LTE downlink physical resource based on OFDM
Parameters for downlink generic frame structure
Downlink Data Transmission The user data is carried on the Physical Downlink Shared Channel (PDSCH). Downlink control signaling on the Physical Downlink Control Channel (PDCCH) is used to convey the scheduling decisions to individual UEs. The PDCCH is located in the first OFDM symbols of a slot.
Downlink Reference Signal Structure and Cell Search
The downlink reference signal structure is important for cell search, channel estimation and neighbor cell monitoring. The reference signal sequence carries the cell identity.
Downlink reference signal structure
P-SCH and S-SCH Besides the reference symbols, synchronization signals are therefore needed during cell search. E-UTRA uses a hierarchical cell search scheme similar to WCDMA. This means that the synchronization acquisition and the cell group identifier are obtained from different SCH signals. Thus, a primary synchronization signal (P-SCH) and a secondary synchronization signal (S-SCH) are defined with a pre-defined structure. They are transmitted on the 72 centre sub-carriers (around DC sub-carrier) within the same predefined slots (twice per 10 ms) on different resource elements
P-SCH and S-SCH structure
CCPCH As additional help during cell search, a Common Control Physical Channel (CCPCH) is available which carries BCH type of information, e.g. system bandwidth. It is transmitted at pre-defined time instants on the 72 subcarriers centered around DC subcarrier.
Downlink Physical Layer Procedures Cell search and synchronization: Scheduling: Scheduling is done in the base station (eNodeB). The downlink control channel PDCCH informs the users about their allocated time/frequency resources and the transmission formats to use. The scheduler evaluates different types of information, e.g. Quality of Service parameters, measurements from the UE, UE capabilities, buffer status. Link Adaptation: Link adaptation is already known from HSDPA as Adaptive Modulation and Coding. Also in E-UTRA, modulation and coding for the shared data channel is not fix, but it is adapted according to radio link quality. For this purpose, the UE regularly reports Channel Quality Indications (CQI) to the eNodeB. Hybrid ARQ (Automatic Repeat Request): Downlink Hybrid ARQ is also known from HSDPA. It is a retransmission protocol. The UE can request retransmissions of incorrectly received data packets.
DL Physical Channel Processing
LTE frame structure type 1 (FDD), downlink
LTE frame structure type 2 (TDD)
Uplink Transmission Scheme During the study item phase of LTE, alternatives for the optimum uplink transmission scheme were investigated. While OFDMA is seen optimum to fulfil the LTE requirements in downlink, OFDMA properties are less favorable for the uplink. This is mainly due to weaker peak-to-average power ratio (PAPR) properties of an OFDMA signal, resulting in worse uplink coverage.
Single-Carrier Frequency Division Multiple Access (SC-FDMA)
Thus, the LTE uplink transmission scheme for FDD and TDD mode is based on SCFDMA (Single Carrier Frequency Division Multiple Access) with cyclic prefix. SC-FDMA signals have better PAPR properties compared to an OFDMA signal. This was one of the main reasons for selecting SCFDMA as LTE uplink access scheme. The PAPR characteristics are important for cost-effective design of UE power amplifiers. Still, SC-FDMA signal processing has some similarities with OFDMA signal processing, so parameterization of downlink and uplink can be harmonized.
How to generate SC-FDMA DFT pre-coding is performed on modulated data symbols to transform them into frequency domain, Sub-carrier mapping allows flexible allocation of signal to available sub-carriers, IFFT and cyclic prefix (CP) insertion as in OFDM,
Each subcarrier carries a portion of superposed DFT spread data symbols, therefore SC-FDMA is also referred to as DFT-spread-OFDM (DFT-s-OFDM).
How does a SC-FDMA signal look likeSimilar to OFDM signal, but in OFDMA, each sub-carrier only carries information related to one specific symbol, in SC-FDMA, each sub-carrier contains information of ALL transmitted symbols.
OFDMA and SC-FDMA
Why does SC-FDMA have a low PAPR?
OFDMA Parallel Transmission Multi carrier structure Increase in M => high PAPR SC-FDMA Serial Transmission Each symbol represented by a wide signal DFT spreads symbols over all subcarriers PAPR not affected by increase in M
Both occupy the same bandwidth with same symbol durations
SC-FDMA in comparison with OFDMA and DS-CDMA/FDE
SC-FDMA signal generationLocalized vs. distributed FDMA
Uplink Slot Structure
Parameters for uplink generic structure
Uplink Data Transmission In uplink, data is allocated in multiples of one resource block. Uplink resource block size in the frequency domain is 12 subcarriers, i.e. the same as in downlink. However, not all integer multiples are allowed in order to simplify the DFT design in uplink signal processing. Only factors 2,3, and 5 are allowed. The uplink transmission time interval is 1 ms (same as downlink).
PUSCH and PUCCH User data is carried on the Physical Uplink Shared Channel (PUSCH) that is determined by the transmission bandwidth NTx and the frequency hopping pattern k0. The Physical Uplink Control Channel (PUCCH) carries uplink control information, e.g. CQI reports and ACK/NACK information related to data packets received in the downlink. The PUCCH is transmitted on a reserved frequency region in the uplink.
Uplink Reference Signal Structure Uplink reference signals are used for two different purposes: on the one hand, they are used for channel estimation in the eNodeB receiver in order to demodulate control and data channels. On the other hand, the reference signals provide channel quality information as a basis for scheduling decisions in the base station. The latter purpose is also called channel sounding. The uplink reference signals are based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequences.
UL Physical Channel Processing
Cell Search Cell search: Mobile terminal or user equipment (UE) acquires time and frequency synchronization with a cell and detects the cell ID of that cell. Based on BCH (Broadcast Channel) signal and hierarchical SCH (Synchronization Channel) signals.
P-SCH (Primary-SCH) and S-SCH (Secondary-SCH) are transmitted twice per radio frame (10 ms) for FDD.
Cell search procedure 1. 5 ms timing identified using P-SCH. 2. Radio timing and group ID found from S-SCH. 3. Full cell ID found from DL RS. 4. Decode BCH.
Spatial Multiplexing
Spatial multiplexing allows to transmit different streams of data simultaneously on the same downlink resource block(s). These data streams can belong to one single user (single user MIMO / SU-MIMO) or to different users (multi user MIMO / MU-MIMO). While SU-MIMO increases the data rate of one user, MU-MIMO allows to increase the overall capacity. Spatial multiplexing is only possible if the mobile radio channel allows it.
LTE MIMO concept
Multiple Antenna Schemes in LTE In DL : Tx diversity, Rx diversity, Spatial multiplexing (2x2,4x2 configurations SUMIMO and MU-MIMO) supported In UL : Only 1 Transmitter (antenna selection Tx diversity ), MU-MIMO possible, Rx diversity with 2 or 4 antennas at eNB supported
MIMO ConfigurationsMIMO
Single base
Multiple bases (Network MIMO)
Co-located antennasSU-MIMO, MU-MIMO
Macroscopic MIMO
Distributed antennas
Noncoherent Coherent (Magnitude only) (Magnitude/phase)Collaborative MIMO Coherent Network MIMO
MIMO ConfigurationsUsed here MU-MIMO or SU-MIMO only 4 Tx, 2 Rx Next improvement step Combination of MU-MIMO SU-MIMO and
4 Tx, 4 Rx 8 Tx (4*2 xpol.), 2 Rx 8 Tx, 4 Rx IRC receiver Sector coordination
MRC receiver No sector coord.x 10 7 6 5 4 3 2 1 01x2 2x2 SU MIMO (PARC + TxDiv) 2x2 GoB 4x2 GoB 4x2 SU MIMO 4x2 GoB + SDMA5
"spectral efficiency" vs cell border TP
5-percentile Throughput in bit/s
0
0.5
1 1.5 bit/s/Hz/sector
2
2.5
LTE Throughput in Various Modes
Downlink average bitrates2.6 GHz with 20MHz BW, 2x2 MIMO, 2 x 20W, pc cards95 Mbps
45 Mbps
9%
43%
LTE doesnt fulfill the requirements of IMT-Advanced 3GPP has also started work on LTEAdvanced, an evolution of LTE, as a proposal to ITU-R for the development of IMT Advanced. LTE Advanced is envisioned to be the first true 4G technology.The requirement is defined so that a Release 8 based LTE device can operate in the LTE-Advanced system and, respectively, the Release 10 LTE Advanced device can access the Release 8 LTE networks. Obviously a Release 9 terminal would also be similarly accommodated. This could be covered, for example, with the multicarrier type of alternative. The mobility between LTE-Advanced needs to work with LTE as well as GSM/EDGE, HSPA and cdma2000.
Requirements of Peak data rates 1Gbps in DL and 500 Mbps in UL Cell edge user data rates twice as high and average user throughput thrice as high as in LTE Peak spectrum efficiency DL: 30 bps/Hz, UL: 15 bps/Hz Operate in flexible spectrum allocations up to 100 MHz and support spectrum aggregation (as BW in DL >>20 MHz) An LTE-Advanced capable network must appear as a LTE network for the LTE UEs
Resource sharing between LTE and LTE-Advanced
Technological proposals for Larger BW can be used for high date rates and more coverage at cell edges Advanced repeater structures Relaying for adaptive coding based on link quality
Carrier aggregation and Spectrum aggregation
Support asymmetric bandwidths for LTE advanced
Specification The ITU-R process aims for early 2011 completion of the ITU-R specifications, which requires 3GPP to submit the first full set of specifications around the end of 2010. This is one of the factors shaping the Release 10 finalization schedule, though officially the Release 10 schedule has not yet been defined in 3GPP, but will be discussed further once Release 9 work has progressed further.
Conclusion 3GPP Long Term Evolution has a large amount of potential to become the technology of the future whose success will definitely guarantee that 3GPP has a significant edge over all its competitors. With LTEAdvanced also adopting SC-FDMA as the uplink technology, SC-FDMA seems to be an important future technology and it is expected that the future would see a lot of research activity in this field.
LTE and LTE Advanced together seem to be very promising in fulfilling all the requirements set forth by ITU for IMT Advanced
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