3g long-term evolution (lte) and system architecture evolution (sae)
TRANSCRIPT
3G Long-term Evolution (LTE) andSystem Architecture Evolution (SAE)
BackgroundEvolved Packet System ArchitectureLTE Radio InterfaceRadio Resource ManagementLTE-Advanced
UMTS Networks 2Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
3GPP Evolution – Background
Discussion started in Dec 2004State of the art then:The combination of HSDPA and E-DCH provides very efficient packet data transmission capabilities, but UMTS should continue to be evolved to meet the ever increasing demand of new applications and user expectations.10 years have passed since the initiation of the 3G programme and it is time to initiate a new programme to evolve 3G which will lead to a 4G technology.From the application/user perspectives, the UMTS evolution should target at significantly higher data rates and throughput, lower network latency,and support of always-on connectivity.From the operator perspectives, an evolved UMTS will make business sense if it:
Provide significantly improved power and bandwidth efficiencies Facilitate the convergence with other networks/technologiesReduce transport network costLimit additional complexity
Evolved-UTRA is a packet only network - there is no support of circuit switched services (no MSC)Evolved-UTRA starts on a clean state - everything is up for discussion including the system architecture and the split of functionality between RAN and CNLed to 3GPP Study Item (Study Phase: 2005-4Q2006) „3G Long-term Evolution (LTE)” for new Radio Access and “System Architecture Evolution” (SAE) for Evolved Network
UMTS Networks 3Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Requirements and Performance Targets
High Peak Data Rates
100 Mbps DL (20 MHz, 2x2 MIMO)
50 Mbps UL (20 MHz, 1x2)
Improved Spectrum Efficiency
3-4x HSPA Rel’6 in DL*
2-3x HSPA Rel’6 in UL
1 bps/Hz broadcast
Improved Cell Edge Rates
2-3x HSPA Rel’6 in DL*
2-3x HSPA Rel’6 in UL
Full broadband coverage
Support Scalable BW
1.4, 3, 5, 10, 15, 20 MHz
Low Latency
< 5ms user plane (UE to RAN edge)
<100ms camped to active
< 50ms dormant to active
Packet Domain Only
High VoIP capacity
Simplified network architecture
* Assumes 2x2 in DL for LTE,
but 1x2 for HSPA Rel’6
UMTS Networks 4Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Key Features of LTE to Meet Requirements
Selection of OFDM for the air interfaceLess receiver complexityRobust to frequency selective fading and inter-symbol interference (ISI)Access to both time and frequency domain allows additional flexibility in scheduling (including interference coordination)Scalable OFDM makes it straightforward to extend to different transmission bandwidths
Integration of MIMO techniquesPilot structure to support 1, 2, or 4 Tx antennas in the DL and MU-MIMO in the UL
Simplified network architectureReduction in number of logical nodes flatter architectureClean separation of user and control plane
UMTS Networks 5Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
3GPP / LTE R7/R8 specifications timeline
After Study Phase: Two Lines in 3GPPEVOLUTION of HSPA to HSPA+ (enhanced W-CDMA incl. MIMO)REVOLUTION towards LTE/SAE (OFDM based)
Stage 2 (Principles) completed in March 07Stage 3 (Specifications) completed in Dec 07Test specifications completed in Dec 08
RAN 32 March 06WI agreed, concepts
approved
LTERAN 35 March 07Stage 2 Technical
Specs
RAN 37 Sept 07 Stage 3 Technical Specs- L1 & L2
Corrections Phase (2008 and beyond)
RAN 34 Dec 06NEW WI (64/16 QAM)
RAN 35 Mar 07WI Completion (inc 64QAM)
RAN 36 Jun 07WI Completion 16QAM UL
RAN 37 Sept 07WI Completion (performance)
2006 2007 2008
R7 HSPA+Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
RAN 38 Dec 07 Stage 3 Technical
Specs – L3
RAN 42 Dec 08Test Specs
UMTS Networks 6Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Terminology: LTE + SAE = EPS
From set of requirements it was clear that evolution work would be required for both, the radio access network as well as the core network
LTE would not be backward compatible with UMTS/ HSPA !RAN working groups would focus on the air interface and radio access network aspectsSystem Architecture (SA) working groups would develop the Evolved Packet Core (EPC)
Note on terminologyIn the RAN working groups term Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and Long Term Evolution (LTE) are used interchangeably.In the SA working groups the term System Architecture Evolution (SAE) was used to signify the broad framework for the architectureFor some time the term LTE/SAE was used to describe the new evolved system, but now this has become known as the Evolved Packet System (EPS)
UMTS Networks 7Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Network Simplification: From 3GPP to 3GPP LTE
3GPP architecture4 functional entities on the control plane and user plane3 standardized user plane & control plane interfaces
3GPP LTE architecture2 functional entities on the user plane: eNodeB and S-GWSGSN control plane functions
S-GW & MMELess interfaces, some functions will disappear
4 layers into 2 layersEvolve GGSN integrated S-GW Moving SGSN functionalities to S-GW. RNC evolutions to RRM on a IP distributed network for enhancing mobility management.Part of RNC mobility function being moved to S-GW & eNodeB
GGSN
SGSN
RNC
NodeB
ASGW
eNodeB
MMFGGSN
SGSN
RNC
NodeB
Control plane User plane
ASGW
eNodeB
MMF
S-GW
eNodeB
MME
Control plane User plane
S-GW: Serving GatewayMME: Mobility Management Entity
eNodeB: Evolved NodeB
UMTS Networks 8Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Evolved UTRAN Architecture
eNB
eNB
eNB
MME/S-GW MME/S-GW
X2
EPCE-U
TRAN
S1
S1
S1S1
S1S1
X2
X2
EPC = Evolved Packet Core
Key elements of network architectureNo more RNCRNC layers/functionalities moves in eNBX2 interface for seamless mobility (i.e. data/ context forwarding) and interference management
Note: Standard only defines logical structure/ Nodes !
UMTS Networks 9Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Architecture – Functional description of the Nodes
eNodeB contains all radio access functions
Admission ControlScheduling of UL & DL
dataScheduling and
transmission of paging and system broadcast
IP header compressionOuter ARQ (RLC)
Serving GatewayLocal mobility anchor for inter-eNB handoversMobility anchor for inter-3GPP handoversIdle mode DL packet bufferingLawful interceptionPacket routing and forwarding
PDN GatewayUE IP address allocationMobility anchor between 3GPP and non-3GPP
accessConnectivity to Packet Data Network
MME control plane functionsIdle mode UE reachabilityTracking area list managementS-GW/P-GW selectionInter core network node signaling
for mobility bw. 2G/3G and LTENAS signalingAuthenticationBearer management functions
UMTS Networks 10Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Architecture – Control Plane Layout over S1
UE eNode-B MME
RRC sub-layer performs: BroadcastingPagingConnection MgtRadio bearer controlMobility functionsUE measurement reporting & control
PDCP sub-layer performs: Integrity protection & ciphering
NAS sub-layer performs: AuthenticationSecurity controlIdle mode mobility handlingIdle mode paging origination
UMTS Networks 11Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Architecture – User Plane Layout over S1
UE eNode-B MME
S-Gateway
RLC sub-layer performs: Transferring upper layer PDUsIn-sequence delivery of PDUsError correction through ARQDuplicate detectionFlow controlSegmentation/ Concatenation of SDUs
PDCP sub-layer performs: Header compressionCiphering
MAC sub-layer performs: SchedulingError correction through HARQPriority handling across UEs & logical
channelsMultiplexing/de-multiplexing of RLC
radio bearers into/from PhCHs on TrCHs
Physical sub-layer performs: DL: OFDMA, UL: SC-FDMAFECUL power controlMulti-stream transmission & reception (i.e. MIMO)
UMTS Networks 12Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Architecture – Interworking for 3GPP and non-3GPP Access
Serving GW anchors mobility for intra-LTE handover between eNBs as well as mobility between 3GPP access systems HSPA/EDGE uses EPS core for access to packet data networksPDN GW is the mobility anchor between 3GPP and non-3GPP access systems (SAE anchor function); handles IP address allocationS3 interface connects MME directly to SGSN for signaling to support mobility across LTE and UTRAN/GERAN; S4 allows direction of user plane between LTE and GERAN/ UTRAN (uses GTP)
GERAN
UTRAN
E-UTRAN
SGSN
MME
non-3GPP Access
Serving GW PDN GWS1-U
S1-MME S11
S3
S4
S5
Internet
EPS Core
S12
SGi
HSSS6a
S10
PCRF
Gx
UMTS Networks 13Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Key Radio Features (Release 8)
Multiple access schemeDL: OFDMA with CPUL: Single Carrier FDMA (SC-FDMA) with CP
Adaptive modulation and codingDL modulations: QPSK, 16QAM, and 64QAMUL modulations: QPSK, 16QAM, and 64QAM (optional for UE)Rel-6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders, and a contention-free internal interleaver.
ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer. Advanced MIMO spatial multiplexing techniques
(2 or 4)x(2 or 4) downlink and 1x(2 or 4) uplink supported.Multi-layer transmission with up to four streams.Multi-user MIMO also supported.
Implicit support for interference coordinationSupport for both FDD and TDD
UMTS Networks 14Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Frequency Bands
LTE will support all band classes currently specified for UMTS as well as additional bands
UMTS Networks 15Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
OFDM Basics – Overlapping Orthogonal
OFDM: Orthogonal Frequency Division MultiplexingOFDMA: Orthogonal Frequency Division Multiple-AccessFDM/ FDMA is nothing new: carriers are separated sufficiently in frequency so that there is minimal overlap to prevent cross-talk.
OFDM: still FDM but carriers can actually be orthogonal (no cross-talk) while actually overlapping, if specially designed saved bandwidth !
conventional FDM
frequency
OFDM
frequency
saved bandwidth
UMTS Networks 16Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
OFDM Basics – Waveforms
Frequency domain: overlapping sinc functions
Referred to as subcarriersTypically quite narrow, e.g. 15 kHz
Time domain: simple gated sinusoid functions
For orthogonality: each symbol has an integer number of cycles over the symbol timefundamental frequency f0 = 1/TOther sinusoids with fk = k • f0
4 5 6 7 8 9
x 105
-0.2
0
0.2
0.4
0.6
0.8
1
freq
f = 1/T
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
time
T = symbol time
UMTS Networks 17Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
OFDM Basics – The Full OFDM Transceiver
Modulating the symbols onto subcarriers can be done verry efficiently in baseband using the FFT algorithm
Serial to Parallel
. . . IFFT
bit stream . . .
Parallel to Serial
D/A
A/DSerial to Parallel
. . .FFT
. . .
OFDM Transmitter
OFDM Receiver
Parallel to Serial
add CP
RF Tx
RF Rx
remove CP
Encoding + Interleaving + Modulation
Demod + de-interleave +
decode
Estimated bit stream
Channel estimation & compensation
UMTS Networks 18Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
OFDM Basics – Cyclic Prefix
ISI (between OFDM symbols) eliminated almost completely by inserting a guard time
Within an OFDM symbol, the data symbols modulated onto the subcarriers are only orthogonal if there are an integer number of sinusoidal cycles within the receiver window
Filling the guard time with a cyclic prefix (CP) ensures orthogonality of subcarriers even in the presence of multipath elimination of same cell interference
CP Useful OFDM symbol time
OFDM symbol
CP Useful OFDM symbol time
OFDM symbol
CP Useful OFDM symbol time
OFDM symbol
OFDM Symbol OFDM Symbol OFDM Symbol
TG TG
UMTS Networks 19Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Comparison with CDMA – Principle
OFDM: particular modulation symbol is carried over a relatively long symbol time and narrow bandwidth
LTE: 66.6 µsec symbol time and 15 kHz bandwidthFor higher data rates send more symbols by using more sub-carriers increases bandwidth occupancy
CDMA: particular modulation symbol is carried over a relatively short symbol time and a wide bandwidth
UMTS HSPA: 4.17 µsec symbol time and 3.84 Mhz bandwidthTo get higher data rates use more spreading codes
frequency
time
symbol 0symbol 1symbol 2symbol 3
frequency
time
sym
bol 0
sym
bol 1
sym
bol 2
sym
bol 3CDMA OFDM
UMTS Networks 20Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Comparison with CDMA – Time Domain Perspective
Short symbol times in CDMA lead to ISI in the presence of multipath
Long symbol times in OFDM together with CP prevent ISI from multipath
1 2 3 4
1 2 3 4
1 2 3 4
CDMA symbols
Multipath reflections from one symbol significantly overlap subsequent symbols ISI
1 2CPCP
1 2CPCP
1 2CPCP
Little to no overlap in symbols from multipath
UMTS Networks 21Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Comparison with CDMA – Frequency Domain Perspective
In CDMA each symbol is spread over a large bandwidth, hence it will experience both good and bad parts of the channel response in frequency domainIn OFDM each symbol is carried by a subcarrier over a narrow part of the band can avoid send symbols where channel frequency response is poor based on frequency selective channel knowledge frequency selective scheduling gain in OFDM systems
Frequency
ChannelResponse
f = 15 kHz
5 MHz
UMTS Networks 22Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
OFDM Basics – Choosing the Symbol Time for LTE
Two competing factors in determining the right OFDM symbol time:CP length should be longer than worst case multipath delay spread, and the OFDM symbol time should be much larger than CP length to avoid significant overhead from the CPOn the other hand, the OFDM symbol time should be much smaller than the shortest expected coherence time of the channel to avoid channel variability within the symbol time
LTE is designed to operate in delay spreads up to ~5 s and for speeds up to 350 km/h (1.2ms coherence time @ 2.6GHz). As such, the following was decided:
CP length = 4.7 sOFDM symbol time = 66.6 s(= 1/20 the worst case coherence time)
f = 15 kHz
CP
~4.7 µs ~66.7 µs
UMTS Networks 23Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Scalable OFDM for Different Operating Bandwidths
With Scalable OFDM, the subcarrier spacing stays fixed at 15 kHz (hence symbol time is fixed to 66.6 µs) regardless of the operating bandwidth (1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz)
The total number of subcarriers is varied in order to operate in different bandwidths
This is done by specifying different FFT sizes (i.e. 512 point FFT for 5 MHz, 2048 point FFT for 20 MHz)
Influence of delay spread, Doppler due to user mobility, timing accuracy, etc. remain the same as the system bandwidth is changed robust design
common channels
10 MHz bandwidth
20 MHz bandwidth
5 MHz bandwidth
1.4 MHz bandwidth
3 MHz bandwidth
centre frequency
UMTS Networks 24Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Downlink Frame Format
Subframe length is 1ms consists of two 0.5ms slots
7 OFDM symbols per 0.5ms slot 14 OFDM symbols per 1ms subframeIn UL center SC-FDMA symbol used for the data demodulation reference signal (DM-RS)
slot = 0.5ms slot = 0.5ms
subframe = 1.0ms
OFDM symbol
Radio frame = 10ms
UMTS Networks 25Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Multiple Antenna Techniques Supported in LTE
SU-MIMOMultiple data streams sent to the same user (max. 2 codewords)Significant throughput gains for UEs in high SINR conditions
MU-MIMO or BeamformingDifferent data streams sent to different users using the same time-frequency resourcesImproves throughput even in low SINR conditions (cell-edge)Works even for single antenna mobiles
Transmit diversity (TxDiv)Improves reliability on a single data streamFall back scheme if channel conditions do not allow SMUseful to improve reliability on common control channels
UMTS Networks 26Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
MIMO Support is Different in Downlink and Uplink
DownlinkSupports SU-MIMO, MU-MIMO, TxDiv
UplinkInitial release of LTE does only support MU-MIMO with a single transmit antenna at the UE Desire to avoid multiple power amplifiers at UE
UMTS Networks 27Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Duplexing Modes
LTE supports both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) to provide flexible operation in a variety of spectrum allocations around the world.
Unlike UMTS TDD there is a high commonality between LTE TDD & LTE FDD
Slot length (0.5 ms) and subframe length (1 ms) is the same than LTE FDD with the same numerology (OFDM symbol times, CP length, FFT sizes, sample rates, etc.)
UL/ DL switching pointsdesigned to allow co-existance with UMTS-TDD(TD-CDMA, TD-SCDMA)
UMTS Networks 28Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Half-Duplex FDD
In addition to FDD & TDD, LTE supports also Half-Duplex FDD (HD-FDD)
HD-FDD is like FDD, only the UE cannot transmit and receive at the same time
Note, that the eNodeB can still transmit and receive at the same time to different UEs; half-duplex is enforced by the eNodeB scheduler
Reasons for HD-FDDHandsets are cheaper, as no duplexer is requiredMore commonality between TDD and HD-FDD than compared to full duplex FDDCertain FDD spectrum allocations have small duplex space; HD-FDD leads to duplex desense in UE
UMTS Networks 29Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Downlink
The LTE downlink uses scalable OFDMAFixed subcarrier spacing of 15 kHz for unicast
Symbol time fixed at T = 1/15 kHz = 66.67 µs
Different UEs are assigned different sets of subcarriers so that they remain orthogonal to each other (except MU-MIMO)
Serial to Parallel
. . .
IFFTbit
stream . . .
Parallel to Serial
add CP
Encoding + Interleaving + Modulation
20 MHz: 2048 pt IFFT10 MHz: 1024 pt IFFT5 MHz: 512 pt IFFT
UMTS Networks 30Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Physical Channels to Support LTE Downlink
eNode-B
Carries DL traffic
DL resource allocation
HARQ feedback for DL
CQI reporting
MIMO reporting
Time span of PDCCH
Carries basic system broadcast information
Allows mobile to get timing and frequency sync with the cell
UMTS Networks 31Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Mapping between DL Logical, Transport and Physical Channels
LTE makes heavy use of shared channels common control, paging, and part of broadcast information carried on PDSCHPCCH: paging control channel
BCCH: broadcast control channel
CCCH: common control channel
DCCH: dedicated control channel
DTCH: dedicated traffic channel
PCH: paging channel
BCH: broadcast channel
DL-SCH: DL shared channel
UMTS Networks 32Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Uplink Transmission Scheme (1/2)
To facilitate efficient power amplifier design in the UE, 3GPP chose single carrier frequency domain multiple access (SC-FDMA) in favor of OFDMA for uplink multiple access.
SC-FDMA results in better PAPRReduced PA back-off improved coverage
SC-FDMA is still an orthogonalmultiple access scheme
UEs are orthogonal in frequencySynchronous in the time domain through the use of timing advance(TA) signaling
Only need to be synchronous within a fraction of the CP length0.52 s timing advance resolution
Node BUE C
UE B
UE A
UE A Transmit Timing
UE B Transmit Timing
UE C Transmit Timing
UMTS Networks 33Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Uplink Transmission Scheme (2/2)
SC-FDMA implemented using an OFDMA front-end and a DFT pre-coder, this is referred to as either DFT-pre-coded OFDMA or DFT-spread OFDMA (DFT-SOFDMA)
Advantage is that numerology (subcarrier spacing, symbol times, FFT sizes, etc.) can be shared between uplink and downlinkCan still allocate variable bandwidth in units of 12 sub-carriersEach modulation symbol sees a wider bandwidth
+1 -1 -1 +
1 -1 -1 -1 +1 +
1 +1 -
1
DFT pre-coding
Serial to Parallel IFFT
bit stream . . .
Parallel to Serial
add CP
Encoding + Interleaving + Modulation
. . DFT
. . .
. . Subcarrier mapping
UMTS Networks 34Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Physical Channels to Support LTE Uplink
eNode-B
Random access for initial access and UL timing
alignment
UL scheduling grant
Carries UL Traffic
UL scheduling request for time synchronized IEs
HARQ feedback for UL
UMTS Networks 35Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Mapping between UL Logical, Transport and Physical Channels
CCCH: common control channel
DCCH: dedicated control channel
DTCH: dedicated traffic channel
RACH: random access channel
UL-SCH: UL shared channel
PUSCH: physical UL shared channel
PUCCH: physical UL control channel
PRACH: physical random access channel
UMTS Networks 36Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Downlink Peak Rates
bandwidth# of parallel streams supported
1 2 4
1.4 MHz 5.4 MBps 10.4 MBps 19.6 MBps
3 MHz 13.5 MBps 25.9 MBps 50 MBps
5 MHz 22.5 MBps 43.2 MBps 81.6 MBps
10 MHz 45 MBps 86.4 MBps 163.2 MBps
15 MHz 67.5 MBps 129.6 MBps 244.8 MBps
20 MHz 90 MBps 172.8 MBps 326.4 MBps
assumptions: 64QAM, code rate =1, 1OFDM symbol for L1/L2, ignores subframes with P-BCH, SCH
UMTS Networks 37Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Uplink Peak Rates
bandwidthHighest Modulation
16 QAM 64QAM
1.4 MHz 2.9 MBps 4.3 MBps
3 MHz 6.9 MBps 10.4 MBps
5 MHz 11.5 MBps 17.3 MBps
10 MHz 27.6 MBps 41.5 MBps
15 MHz 41.5 MBps 62.2 MBps
20 MHz 55.3 MBps 82.9 MBps
assumptions: code rate =1, 2PRBs reserved for PUCCH (1 for 1.4MHz), no SRS, ignores subframes with PRACH,takes into account highest prime-factor restriction
UMTS Networks 38Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Release 8 System Parameters
Access Scheme UL DFTS-OFDMDL OFDMA
Bandwidth 1.4, 3, 5, 10, 15, 20MHzMinimum TTI 1msecSub-carrier spacing 15kHzCyclic prefix length Short 4.7µsec
Long 16.7µsecModulation QPSK, 16QAM, 64QAMSpatial multiplexing Single layer for UL per UE
Up to 4 layers for DL per UEMU-MIMO supported for UL and DL
UMTS Networks 39Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE-Release 8 User Equipment Categories
Category 1 2 3 4 5
Peak rate Mbps
DL 10 50 100 150 300
UL 5 25 50 50 75
Capability for physical functionalities
RF bandwidth 20MHz
Modulation DL QPSK, 16QAM, 64QAM
UL QPSK, 16QAM QPSK,16QAM,64QAM
Multi-antenna
2 Rx diversity Assumed in performance requirements.
2x2 MIMO Not supported
Mandatory
4x4 MIMO Not supported Mandatory
UMTS Networks 40Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Scheduling and Resource Allocation (1/2)
Basic unit of allocation is called a Resource Block (RB)12 subcarriers in frequency (= 180 kHz) 1 timeslot in time (= 0.5 ms, = 7 OFDM symbols)Multiple resource blocks can be allocated to a user in a given subframe
The total number of RBs available depends on the operating bandwidth
12 sub-carriers(180 kHz)
Bandwidth (MHz) 1.4 3.0 5.0 10.0 15.0 20.0
Number of available resource blocks
6 15 25 50 75 100
UMTS Networks 41Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Scheduling and Resource Allocation (2/2)
LTE uses a scheduled, shared channel on both the uplink (UL-SCH) and the downlink (DL-SCH)Normally, there is no concept of an autonomous transmission; all transmissions in both uplink and downlink must be explicitly scheduled
LTE allows "semi-persistent" (periodical) allocation of resources, e.g. for VoIP
14 OFDM symbols
12 subcarriers
Slot = 0.5ms
Slot = 0.5ms
UE A
UE B
UE C
Time
Freq
uenc
y<=3 OFDM symbols for PDCCH
Downlink Scheduling
UMTS Networks 42Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Interference Coordination with Flexible Frequency Reuse
Cell edge users with frequency reuse > 1,
eNB transmits with higher power
Improved SINR conditions
Cell centre users can use whole frequency band
eNB transmits with reduced power
Less interference to other cells
Flexible frequency reuse realized through intelligent scheduling and power allocation
Cell edge
Reuse > 1
Cell centre
Reuse = 1
Scheduler can place restriction on which PRBs can be used in which sectors
Achieves frequency reuse > 1
Reduced inter-cell interference leads to improved SINR, especially at cell-edge
Reduction in available transmission bandwidth leads to poor overall spectral efficiency
UMTS Networks 43Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Random-Access Procedure
RACH only used for Random Access PreambleResponse/ Data are sent over SCH
Non-contention based RA to improve access time, e.g. for HO
UE eNB
Random Access Preamble1
Random Access Response 2
Scheduled Transmission3
Contention Resolution 4
Contention based RA Non-Contention based RA
UMTS Networks 44Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Handover
LTE uses UE-assisted network controlled handoverUE reports measurements; network decides when handover and to which cellRelies on UE to detect neighbor cells no need to maintain and broadcast neighbor lists
Allows "plug-and-play" capability; saves BCH resources
For search and measurement of inter-frequency neighboring cells only carrier frequency need to be indicated
X2 interface used for handover preparation and forwarding of user dataTarget eNB prepares handover by sending required information to UE transparently through source eNB as part of the Handover Request Acknowledge message
New configuration information needed from system broadcastAccelerates handover as UE does not need to read BCH on target cell
Buffered and new data is transferred from source to target eNB until path switch prevents data lossUE uses contention-free random access to accelerate handover
UMTS Networks 45Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Handover: Preparation Phase
UEUE Source eNB
Source Source eNB
Measurement Control
Target eNB
Target eNB MMEMME sGWsGW
Packet Data Packet Data
UL allocation
Measurement Reports
HO decision
Admission Control
HO Request
HO Request AckDL allocation
RRC Connection Reconfig.
L1/L2 signaling
L3 signaling
User data
HO decision is made by source eNB based on UE measurement report
Target eNB prepares HO by sending relevant info to UE through source eNB as part of HO request ACK command, so that UE does not need to read target cell BCH
SN Status Transfer
UMTS Networks 46Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Handover: Execution Phase
UEUE Source eNB
SourceeNB
Target eNB
TargeteNB MMEMME sGWsGW
Detach from old cell, sync with new cell
Deliver buffered packets and forward new packets to target eNB
DL data forwarding via X2
Synchronisation
UL allocation and Timing Advance
RRC Connection Reconfig. Complete
L1/L2 signaling
L3 signaling
User dataBuffer packets from source eNB
Packet Data
Packet Data
RACH is used here only so target eNB can estimate UE timing and provide timing advance for synchronization; RACH timing agreements ensure UE does not need to read target cell P-BCH to obtain SFN (radio frame timing from SCH is sufficient to know PRACH locations)
UL Packet Data
UMTS Networks 47Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Handover: Completion Phase
UEUE SourceeNB
Target eNB
TargeteNB MMEMME sGWsGW
DL Packet Data
Path switch req
User plane update req
Switch DL path
User plane update responsePath switch req ACK
Release resources
Packet Data Packet Data
L1/L2 signaling
L3 signaling
User data
DL data forwarding
Flush DL buffer, continue delivering in-transit packets
End Marker
Release resources
Packet Data
End Marker
UMTS Networks 48Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE Handover: Illustration of Interruption Period
UL
U- plane active
U-plane active
UEUE Source eNB
Source eNB
Target eNB
Target eNB
UL
U- plane active
U-plane active
UEs stops
Rx/Tx on the old cell
DL sync
+ RACH (no contention)
+ Timing Adv
+ UL Resource Req and Grant
ACK
HO Request
HO Confirm
HandoverLatency
(approx 55 ms)approx 20 ms
Measurement Report
HO Command
HO Complete
HandoverInterruption
(approx 35 ms)
Handover Preparation
UMTS Networks 49Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Tracking Area
BCCHTAI 1
BCCHTAI 1
BCCHTAI 1
BCCHTAI 1
BCCHTAI 1
BCCHTAI 2
BCCHTAI 2
BCCHTAI 2
BCCHTAI 2
BCCHTAI 2
BCCHTAI 2
BCCHTAI 3
BCCHTAI 3
BCCHTAI 3
BCCHTAI 3
Tracking Area 1
Tracking Area 2 Tracking Area 3
• Tracking Area Identifier (TAI) sent over Broadcast Channel BCCH• Tracking Areas can be shared by multiple MMEs• One UE can be allocated to multiple tracking areas
UMTS Networks 50Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Bearer Service Architecture
UMTS Networks 51Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE RRC States
No RRC connection, no context in eNodeB (but EPS bearers are retained)UE controls mobility through cell selectionUE specific paging DRX cycle controlled by upper layersUE acquires system information from BCHUE monitors paging channel to detect incoming calls
RRC connection and context in eNodeBNetwork controlled mobilityTransfer of unicast and broadcast data to and from UEUE monitors control channels associated with the shared data channelsUE provides channel quality and feedback informationConnected mode DRX can be configured by eNodeB according to UE activity level
RRC_IDLE RRC_Connected
Release RRC connection
Establish RRC connection
UMTS Networks 52Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Connection Management States
No signaling connection between UE and core network (no S1-U/ S1-MME)No RRC connection (i.e. RRC_IDLE)UE performs cell selection and tracking area updates (TAU)
Signaling connection established between UE and MME, consists of two components
RRC connectionS1-MME connection
UE location is known to accuracy of Cell-IDMobility via handover procedure
ECM_IDLE ECM_Connected
Signaling connection released
Signaling connection established
UMTS Networks 53Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EPS Mobility Management States
EMM context holds no valid location or routing information for UEUE is not reachable by MME as UE location is not known
UE successfully registers with MME with Attach procedure or Tracking Area Update (TAU)UE location known within tracking areaMME can page to UEUE always has at least one PDN connection
EMM_Deregistered
Detach
AttachEMM_Registered
UMTS Networks 54Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE – Summary
LTE is a new air interface with no backward compatibility to WCDMACombination of OFDM, MIMO and HOM
SAE/ EPS realizes a flatter IP-based network architecture with less complexityeNodeB, S-GW, P-GW
Some procedures/protocols are being re-used from UMTSProtocol stackConcept of Logical/ Transport/ Physical Channels
Complexity is significantly reducedReduced UE state spaceMost transmission uses SCH
LTE standard (Rel. 8) is stableRel. 9: technical enhancements/ E-MBMSRel. 10: LTE-Advanced (cf. next slides)
UMTS Networks 55Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE-Advanced
The evolution of LTECorresponding to LTE Release 10 and beyond
Motivation of LTE-AdvancedIMT-Advanced standardisation process in ITU-RAdditional IMT spectrum band identified in WRC07Further evolution of LTE Release 8 and 9 to meet:
Requirements for IMT-Advanced of ITU-RFuture operator and end-user requirements
Work Item phaseStudy Item phase
First submission
Final submissionLTE release 10 (”LTE-Advanced”)
2009 20102008Proposals
Circular Letter
3GPP WSIMT-Advanced
Specification
IMT-Advanced recommendation
Evaluation
3GPP
ITU
UMTS Networks 56Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Evolution from IMT-2000 to IMT-Advanced
Interconnection
IMT-2000
Mobility
Low
High
1 10 100 1000Peak useful data rate (Mbit/s)
EnhancedIMT-2000
Enhancement
IMT-2000
Mobility
Low
High
1 10 100 1000
Area Wireless Access
EnhancedIMT-2000
Enhancement
Digital Broadcast SystemsNomadic / Local Area Access Systems
New Nomadic / Local
IMT-Advanced will encompass the
capabilities of previous systems
New capabilities of IMT-Advanced
New Mobile Access
• 56
UMTS Networks 57Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Peak data rate1 Gbps data rate will be achieved by 4-by-4 MIMO and transmission bandwidth wider than approximately 70 MHz
Peak spectrum efficiencyDL: Rel. 8 LTE satisfies IMT-Advanced requirementUL: Need to double from Release 8 to satisfy IMT-Advanced requirement
Rel. 8 LTE LTE-Advanced IMT-Advanced
Peak data rateDL 300 Mbps 1 Gbps
1 Gbps(*)
UL 75 Mbps 500 Mbps
Peak spectrum efficiency [bps/Hz]
DL 15 30 15
UL 3.75 15 6.75
*“100 Mbps for high mobility and 1 Gbps for low mobility” is one of the key features as written in Circular Letter (CL)
System Performance Requirements
UMTS Networks 58Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Technical Outline to Achieve LTE-Advanced Requirements
Support wider bandwidthCarrier aggregation to achieve wider bandwidthSupport of spectrum aggregationPeak data rate, spectrum flexibility
Advanced MIMO techniquesExtension to up to 8-layer transmission in downlinkIntroduction of single-user MIMO up to 4-layer transmission in uplinkPeak data rate, capacity, cell-edge user throughput
Coordinated multipoint transmission and reception (CoMP)CoMP transmission in downlinkCoMP reception in uplinkCell-edge user throughput, coverage, deployment flexibility
RelayingType 1 relays create a separate cell and appear as Rel. 8 LTE eNB to Rel. 8 LTE UEsCoverage, cost effective deployment
Further reduction of delayAS/NAS parallel processing for reduction of C-Plane delay
UMTS Networks 59Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Frequency
System bandwidth, e.g., 100 MHz
CC, e.g., 20 MHz
UE capabilities• 100-MHz case
• 40-MHz case
• 20-MHz case (Rel. 8 LTE)
Carrier Aggregation
Wider bandwidth transmission using carrier aggregationEntire system bandwidth up to, e.g., 100 MHz, comprises multiple basic frequency blocks called component carriers (CCs)
Each CC is backward compatible with Rel. 8 LTE
Carrier aggregation supports both contiguous and non-contiguous spectrums, and asymmetric bandwidth for FDD
UMTS Networks 60Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Advanced MIMO Techniques
Extension up to 8-stream transmission for single-user (SU) MIMO in downlink
improve downlink peak spectrum efficiency
Enhanced multi-user (MU) MIMO in downlink
Specify additional reference signals (RS)
Introduction of single-user (SU)-MIMO up to 4-stream transmission in uplink
Satisfy IMT requirement for uplink peak spectrum efficiency
Max. 8 streams
Higher-order MIMO up to 8 streams
Enhanced MU-MIMO
CSI feedback
Max. 4 streams
SU-MIMO up to 4 streams
UMTS Networks 61Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Coordinated Multipoint Transmission/ Reception (CoMP)
Enhanced service provisioning, especially for cell-edge usersCoMP transmission schemes in downlink
Joint processing (JP) from multiple geographically separated points
Coordinated scheduling/beamforming (CS/CB) between cell sites
Similar for the uplinkDynamic coordination in uplink schedulingJoint reception at multiple sites
Coherent combining or dynamic cell selection
Joint transmission/dynamic cell selection
Coordinated scheduling/beamforming
Receiver signal processing at central eNB (e.g., MRC, MMSEC)
Multipoint reception
UMTS Networks 62Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
eNB RNUE
Cell ID #x Cell ID #y
Higher node
Relaying
Type 1 relayRelay node (RN) creates a separate cell distinct from the donor cellUE receives/transmits control signals for scheduling and HARQ from/to RN RN appears as a Rel. 8 LTE eNB to Rel. 8 LTE UEs
Deploy cells in the areas where wired backhaul is not available or very expensive
UMTS Networks 63Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EASY-C Overview
EASY C Project topics / objectivesBMBF project3 year project: 2007 – 2010Preparation of a new Standard: “LTE Advanced”Focus on improved spectral efficiency, cell border throughput, fairness, and latency
Working groupsWG1: Algorithms and ConceptsWG2: Technology Test BedsWG3: Hardware Architecture
Web page: http://www.easy-c.de
Project partners:
UMTS Networks 64Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
EASY-C Testbeds in Dresden and Berlin
Dresden: testbed focussed on physical layer aspects
Berlin: focus on new algorithms, services and applications
UMTS Networks 65Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
LTE References
Literature:H. Holma/ A. Toskala (Ed.): “LTE for UMTS - OFDMA and SC-FDMA Based Radio Access,” 2nd edition, Wiley 2011E. Dahlman et al: “3G Evolution, HSPA and LTE for Mobile Broadband,” 3rd edition, Academic Press 2011S. Sesia et al: “LTE, The UMTS Long Term Evolution: From Theory to Practice,” Wiley 2011T. Nakamura (RAN chairman): “Proposal for Candidate Radio Interface Technologies for IMT-Advanced Based on LTE Release 10 and Beyond LTE-Advanced),” ITU-R WP 5D 3rd Workshop on IMT-Advanced, October 2009
StandardsTS 36.xxx series: RAN AspectsTS 36.300 “E-UTRAN; Overall description; Stage 2”TR 25.912 “Feasibility study for evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access Network (UTRAN)”TR 25.814 “Physical layer aspect for evolved UTRA”TR 23.882 “3GPP System Architecture Evolution: Report on Technical Options and Conclusions”TR 36.912 “Feasibility study for Further Advancements for E-UTRA (LTE-Advanced)”TR 36.814 “Further Advancements for E-UTRA - Physical Layer Aspects”
UMTS Networks 66Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011
Abbreviations
CP Cyclic PrefixDFT Discrete Fourier TransformationDRX Discontinuous ReceptionECM EPS Connection ManagementEMM EPS Mobility ManagementeNodeB/eNB Evolved NodeBEPC Evolved Packet CoreEPS Evolved Packet SystemE-UTRAN Evolved UMTS Terrestrial Radio Access
NetworkFDD Frequency-Division DuplexFDM Frequency-Division MultiplexingFFT Fast Fourier TransformationHD-FDD Half-Duplex FDDHO HandoverHOM Higher Order ModulationHSS Home Subscriber ServerIFFT Inverse FFTISI Inter-Symbol InterferenceLTE Long Term EvolutionMIMO Multiple-Input Multiple-OutputMME Mobility Management EntityMU Multi-User
OFDM Orthogonal Frequency-Division Multiplexing
OFDMA Orthogonal Frequency-Division Multiple-Access
PCRF Policy & Charging FunctionPDN Packet Data NetworkP-GW PDN GatewayRA Random AccessRB Resource BlockRRC Radio Resource ControlSAE System Architecture EvolutionSCH Shared ChannelS-GW Serving GatewaySC-FDMA Single Carrier FDMASU Single UserTDD Time-Division DuplexTA Timing Advance/ Tracking AreaTAI Tracking Area IndicatorTAU Tracking Area UpdateUE User Equipment