3G Long-Term Evolution (LTE) andSystem Architecture Evolution (SAE)
u Backgroundu Evolved Packet System Architectureu LTE Radio Interfaceu Radio Resource Managementu LTE-Advanced
Cellular Communication Networks 2Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
3GPP Evolution – Background
u Discussion started in Dec 2004u State of the art then:
u The combination of HSDPA and E-DCH provides very efficient packet datatransmission capabilities, but UMTS should continue to be evolved to meet the everincreasing demand of new applications and user expectations.
u 10 years have passed since the initiation of the 3G programme and it is time toinitiate a new programme to evolve 3G which will lead to a 4G technology.
u From the application/user perspectives, the UMTS evolution should target atsignificantly higher data rates and throughput, lower network latency,and support of always-on connectivity.
u From the operator perspectives, an evolved UMTS will make business sense if it:u Provide significantly improved power and bandwidth efficienciesu Facilitate the convergence with other networks/technologiesu Reduce transport network costu Limit additional complexity
u Evolved-UTRA is a packet only network – there is no support of circuit switchedservices (no MSC)
u Evolved-UTRA started on a clean state – everything was up for discussion includingthe system architecture and the split of functionality between RAN and CN
u Led to 3GPP Study Item (Study Phase: 2005 – 4Q2006)„3G Long-Term Evolution (LTE)” for new Radio Accessand “System Architecture Evolution” (SAE) for Evolved Network
Cellular Communication Networks 3Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
< 5 ms user plane (UE to RAN edge)
< 100 ms camped to active
< 50 ms dormant to active
Packet Domain Only
High VoIP capacity
Simplified network architecture
* Assumes2x2 in DLfor LTE,
but 1x2 forHSPA Rel’6
Cellular Communication Networks 4Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Key Features of LTE to Meet Requirements
u Selection of OFDM for the air interfaceu Less receiver complexityu Robust to frequency selective fading and inter-symbol interference (ISI)u Access to both time and frequency domain allows additional flexibility in
scheduling (including interference coordination)u Scalable OFDM makes it straightforward to extend to different
transmission bandwidths
u Integration of MIMO techniquesu Pilot structure to support 1, 2, or 4 Tx antennas in the DL and MU-MIMO
in the UL
u Simplified network architectureu Reduction in number of logical nodes ® flatter architectureu Clean separation of user and control plane
Cellular Communication Networks 5Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
3GPP / LTE R7/R8 specifications timeline
u After Study Phase: Two Lines in 3GPPu EVOLUTION of HSPA to HSPA+ (enhanced W-CDMA incl. MIMO)u REVOLUTION towards LTE/SAE (OFDM based)
u Stage 2 (Principles) completed in March 07u Stage 3 (Specifications) completed in Dec 07u Test specifications completed in Dec 08
RAN 32 March 06WI agreed, concepts
approved
LTERAN 35 March 07Stage 2 Technical
Specs
RAN 37 Sept 07Stage 3 TechnicalSpecs- L1 & L2
Corrections Phase(2008 andbeyond)
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 07Stage 3 Technical
Specs – L3
RAN 42 Dec 08Test Specs
Cellular Communication Networks 6Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Terminology: LTE + SAE = EPS
u From set of requirements it was clear that evolution work would be requiredfor both, the radio access network as well as the core networku LTE is not backward compatible with UMTS/ HSPA !u RAN working groups focus on the air interface and radio access network
aspectsu System Architecture (SA) working groups develop the Evolved Packet
Core (EPC)
u Note on terminologyu In the RAN working groups term Evolved UMTS Terrestrial Radio
Access Network (E-UTRAN) and Long Term Evolution (LTE) areused interchangeably.
u In the SA working groups the term System Architecture Evolution(SAE) was used to signify the broad framework for the architecture
u For some time the term LTE/SAE was used to describe the new evolvedsystem, but now this has become known as the Evolved PacketSystem (EPS)
Cellular Communication Networks 7Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Network Simplification: From 3GPP to 3GPP LTE
u 3GPP architectureu 4 functional entities on the
control plane and user planeu 3 standardized user plane &
control plane interfaces
u 3GPP LTE architectureu 2 functional entities on the
user plane: eNodeB and S-GWu SGSN control plane functionsà S-GW & MME
u Less interfaces, somefunctions disappeared
u 4 layers into 2 layersu Evolved GGSN à integrated
S-GWu Moved SGSN functionalities to
S-GW.u RNC evolutions to RRM on a
IP distributed network forenhancing mobilitymanagement.
u Part of RNC mobility functionmoved 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
Cellular Communication Networks 8Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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 networkarchitecture
u No more RNCu RNC layers/functionalities
move in eNBu X2 interface for seamless
mobility (i.e. data/ contextforwarding) and interferencemanagement
Note: Standard only defineslogical structure/ Nodes !
Cellular Communication Networks 9Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Architecture – Functional description of the Nodes
eNodeB contains all radioaccess functions§Admission Control§Scheduling of UL & DLdata§Scheduling andtransmission of paging andsystem broadcast§ IP header compression§Outer ARQ (RLC)
Serving Gateway§Local mobility anchor for inter-eNB handovers§Mobility anchor for inter-3GPP handovers§ Idle mode DL packet buffering§Lawful interception§Packet routing and forwarding
PDN Gateway§UE IP address allocation§Mobility anchor between 3GPP and non-3GPPaccess§Connectivity to Packet Data Network
MME control plane functions§ Idle mode UE reachability§Tracking area list management§S-GW/P-GW selection§ Inter core network node signalingfor mobility bw. 2G/3G and LTE§NAS signaling§Authentication§Bearer management functions
Cellular Communication Networks 10Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Architecture – Control Plane Layout over S1
UE eNodeB MME
RRC sub-layer performs:§Broadcasting§Paging§Connection Management§Radio bearer control§Mobility functions§UE measurement reporting & control
PDCP sub-layer performs:§ Integrity protection & ciphering
NAS sub-layer performs:§Authentication§Security control§ Idle mode mobility handling§ Idle mode paging origination
Cellular Communication Networks 11Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Architecture – User Plane Layout over S1
UE eNodeB MME
S-Gateway
RLC sub-layer performs:§Transferring upper layer PDUs§ In-sequence delivery of PDUs§Error correction through ARQ§Duplicate detection§Flow control§Segmentation/ Concatenation of SDUs
PDCP sub-layer performs:§Header compression§Ciphering
MAC sub-layer performs:§Scheduling§Error correction through HARQ§Priority handling across UEs & logicalchannels§Multiplexing/de-multiplexing of RLCradio bearers into/from PhCHs on TrCHs
Physical sub-layer performs:§DL: OFDMA, UL: SC-FDMA§FEC§UL power control§Multi-stream transmission & reception (i.e. MIMO)
Cellular Communication Networks 12Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Architecture – Interworking for 3GPP and non-3GPP Access
uHome Subscriber Server (HSS) is the subscription data repository for permanent userdata (subscriber profile).
u Policy Charging Rules Function (PCRF) provides the policy and charging control (PCC)rules for controlling the QoS as well as charging the user, accordingly.
u S3 interface connects MME directly to SGSN for signaling to support mobility across LTEand 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
GxGxc
Cellular Communication Networks 13Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Key Radio Features (Release 8)
u Multiple access schemeu DL: OFDMA with CPu UL: Single Carrier FDMA (SC-FDMA) with CP
u Adaptive modulation and codingu DL modulations: QPSK, 16QAM, and 64QAMu UL modulations: QPSK, 16QAM, and 64QAM (optional for UE)u Rel-6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders,
and a contention-free internal interleaver.
u ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer.u Advanced MIMO spatial multiplexing techniques
u (2 or 4)x(2 or 4) downlink and 1x(2 or 4) uplink supported.u Multi-layer transmission with up to four streams.u Multi-user MIMO also supported.
u Implicit support for interference coordinationu Support for both FDD and TDD
Cellular Communication Networks 14Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Frequency Bands
u LTE will support all band classes currently specified for UMTS as well asadditional bands
Cellular Communication Networks 15Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
OFDM Basics – Overlapping Orthogonal
u OFDM: Orthogonal Frequency Division Multiplexingu OFDMA: Orthogonal Frequency Division Multiple-Accessu FDM/ FDMA is nothing new: carriers are separated sufficiently in frequency
so that there is minimal overlap to prevent cross-talk.
u 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
Cellular Communication Networks 16Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
OFDM Basics – Waveforms
u Frequency domain: overlapping sincfunctionsu Referred to as subcarriersu Typically quite narrow, e.g. 15 kHz
u Time domain: simple gated sinusoidfunctionsu For orthogonality: each symbol has
an integer number of cycles overthe symbol time
u fundamental frequency f0 = 1/Tu Other sinusoids with fk = k • f0
Df = 1/T
freq.
time
T = symbol time
0 1 2 3 4 5 6-0.2
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1-1
-0.5
0
0.5
1
Cellular Communication Networks 17Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
OFDM Basics – The Full OFDM Transceiver
u Modulating the symbols onto subcarriers can be done very efficiently inbaseband using the FFT algorithm
Serial toParallel
..
. IFFT
bitstream .
..
Parallelto Serial
D/A
A/DSerial toParallel
..
.FFT
..
.
OFDM Transmitter
OFDM Receiver
Parallelto Serial
addCP
RFTx
RFRx
removeCP
Encoding +Interleaving+ Modulation
Demod +De-interleave
+ Decode
Estimatedbit stream
Channel estimation& compensation
Cellular Communication Networks 18Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
OFDM Basics – Cyclic Prefix
u ISI (between OFDM symbols) eliminated almost completely by inserting aguard time
u Within an OFDM symbol, the data symbols modulated onto thesubcarriers are only orthogonal if there are an integer number ofsinusoidal cycles within the receiver windowu Filling the guard time with a cyclic prefix (CP) ensures orthogonality of
subcarriers even in the presence of multipath à elimination of same cellinterference
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
Cellular Communication Networks 19Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Comparison with CDMA – Principle
u OFDM: particular modulation symbol is carried over a relatively long symboltime and narrow bandwidthu LTE: 66.6 µsec symbol time and 15 kHz bandwidthu For higher data rates send more symbols by using more sub-carriers ®
increases bandwidth occupancyu CDMA: particular modulation symbol is carried over a relatively short
symbol time and a wide bandwidthu UMTS HSPA: 4.17 µsec symbol time and 3.84 Mhz bandwidthu To get higher data rates use more spreading codes
time
freq
uenc
y
symbol 0symbol 1symbol 2symbol 3
time
freq
uenc
y
sym
bol0
sym
bol1
sym
bol2
sym
bol3OFDM CDMA
Cellular Communication Networks 20Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Comparison with CDMA – Time Domain Perspective
u Short symbol times in CDMA lead to ISI in the presence of multipath
u 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 symbolsignificantly overlap subsequentsymbols ® ISI
1 2CPCP
1 2CPCP
1 2CPCP
Little to no overlap insymbols from multipath
Cellular Communication Networks 21Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Comparison with CDMA – Frequency Domain Perspective
u In CDMA each symbol is spread over a large bandwidth, hence it willexperience both good and bad parts of the channel response in frequencydomain
u In OFDM each symbol is carried by a subcarrier over a narrow part ofthe band ® can avoid send symbols where channel frequency response ispoor based on frequency selective channel knowledge ® frequencyselective scheduling gain in OFDM systems
Frequency
ChannelResponse
Δf = 15 kHz
5 MHz
Cellular Communication Networks 22Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
OFDM Basics – Choosing the Symbol Time for LTE
u Two competing factors in determining the right OFDM symbol time:u 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 significantoverhead from the CP
u On the other hand, the OFDM symbol time should be much smaller than theshortest expected coherence time of the channel to avoid channel variabilitywithin the symbol time
u LTE is designed to operate in delay spreads up to ~5 μs and for speeds up to 350 km/h(~1 ms coherence time @ 2.6 GHz). As such, the following was decided:u CP length = 4.7 μsu OFDM symbol time = 66.6 μs (~1/15 the worst case coherence time)
Df = 15 kHz
CP
~4.7 µs ~66.7 µs
Cellular Communication Networks 23Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Scalable OFDM for Different Operating Bandwidths
u With Scalable OFDM, the subcarrier spacingstays fixed at 15 kHz (hence symbol time isfixed to 66.6 µs) regardless of the operatingbandwidth (1.4 MHz, 3 MHz, 5 MHz, 10 MHz,15 MHz, 20 MHz)
u The total number of subcarriers is varied inorder to operate in different bandwidthsu This is done by specifying different FFT
sizes (i.e. 512 point FFT for 5 MHz, 2048point FFT for 20 MHz)
u Influence of delay spread, Doppler due to usermobility, timing accuracy, etc. remain the sameas the system bandwidth is changed à robustdesign
common channels
10 MHz bandwidth
20 MHz bandwidth
5 MHz bandwidth
1.4 MHz bandwidth
3 MHz bandwidth
centre frequency
Cellular Communication Networks 24Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Downlink Frame Format
u Subframe length is 1 msu consists of two 0.5 ms slots
u 7 OFDM symbols per 0.5 ms slot à 14 OFDM symbols per 1ms subframeu In 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
Cellular Communication Networks 25Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Spatial Multiplexing
u Rank of the MIMO channel determines the number of independent TX/RXchannels offered by MIMO for spatial multiplexingu Rank ≤ min(#Tx, #Rx)
u To properly adjust the transmission parameters the UE provides feedbackabout the mobile radio channel situationu Channel quality (CQI), pre-coding matrix (PMI) and rank (RI)
HVUH L=
UHV
Cellular Communication Networks 26Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Multiple Antenna Techniques Supported in LTE
u SU-MIMOu Multiple data streams sent to the same user
(max. 2 codewords)u Significant throughput gains for UEs in high
SINR conditions
u MU-MIMO or Beamformingu Different data streams sent to different users
using the same time-frequency resourcesu Improves throughput even in low SINR
conditions (cell-edge)u Works even for single antenna mobiles
u Transmit diversity (TxDiv)u Improves reliability on a single data streamu Fall back scheme if channel conditions do
not allow MIMOu Useful to improve reliability on common
control channels
Cellular Communication Networks 27Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
MIMO Support is Different in Downlink and Uplink
u Downlinku Supports SU-MIMO, MU-MIMO, TxDiv
u Uplinku Initial release of LTE does only support MU-MIMO with a single transmit
antenna at the UEà Desire to avoid multiple power amplifiers at UE
Cellular Communication Networks 28Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Duplexing Modes
u LTE supports both Frequency Division Duplex (FDD) and Time DivisionDuplex (TDD) to provide flexible operation in a variety of spectrumallocations around the world.
u Unlike UMTS TDD there is a high commonality between LTE TDD & LTE FDD
u Slot length (0.5 ms) and subframe length (1 ms) is the same than LTEFDD with the same numerology (OFDM symbol times, CP length, FFTsizes, sample rates, etc.)
u UL/ DL switching pointsdesigned to allow co-existance with UMTS-TDD(TD-SCDMA)
Cellular Communication Networks 29Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Half-Duplex FDD
u In addition to FDD & TDD, LTE supports also Half-Duplex FDD (HD-FDD)
u HD-FDD is like FDD, only the UE cannot transmit and receive at the sametime
u Note, that the eNodeB can still transmit and receive at the same time todifferent UEs; half-duplex is enforced by the eNodeB scheduler
u Reasons for HD-FDDu Handsets are cheaper, as no duplexer is requiredu More commonality between TDD and HD-FDD than compared to full
duplex FDDu Certain FDD spectrum allocations have small duplex space; HD-FDD leads
to duplex desense in UE
Cellular Communication Networks 30Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Downlink
u The LTE downlink uses scalable OFDMAu Fixed subcarrier spacing of 15 kHz for unicast
u Symbol time fixed at T = 1/15 kHz = 66.67 µs
u Different UEs are assigned different sets of subcarriers so that theyremain orthogonal to each other (except MU-MIMO)
Serial toParallel
..
.
IFFTbit
stream ..
.
Parallelto Serial
addCP
Encoding +Interleaving+ Modulation
20 MHz: 2048 pt IFFT10 MHz: 1024 pt IFFT5 MHz: 512 pt IFFT
Cellular Communication Networks 31Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Physical Channels to Support LTE Downlink
eNodeB
Carries DL traffic
DL resource allocation
HARQ feedback for DLCQI reporting
MIMO reporting
Time span of PDCCH
Carries basic systembroadcast information
Allows mobile to get timing andfrequency sync with the cell
Cellular Communication Networks 32Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Mapping between DL Logical, Transport and Physical Channels
LTE makes heavy use of sharedchannels à common control,paging, and part of broadcastinformation 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
Cellular Communication Networks 33Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Uplink Transmission Scheme (1/2)
u To facilitate efficient power amplifier design in the UE, 3GPP chose singlecarrier frequency domain multiple access (SC-FDMA) in favor of OFDMAfor uplink multiple access.u SC-FDMA results in better PAPR
u Reduced PA back-off à improved coverage
u SC-FDMA is still an orthogonalmultiple access schemeu UEs are orthogonal in frequencyu Synchronous in the time domain
through the use of timing advance(TA) signalingu Only needed to be synchronous
within a fraction of the CP lengthu 0.52 ms timing advance resolution
Node BUE C
UE B
UE A
UE A Transmit Timing
UE B Transmit Timing
UE C Transmit Timing
a
b
g
Cellular Communication Networks 34Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Uplink Transmission Scheme (2/2)
u SC-FDMA implemented using an OFDMA front-end and a DFT pre-coder, thisis referred to as either DFT-pre-coded OFDMA or DFT-spread OFDMA (DFT-SOFDMA)u Advantage is that numerology (subcarrier spacing, symbol times, FFT
sizes, etc.) can be shared between uplink and downlinku Can still allocate variable bandwidth in units of 12 sub-carriersu Each modulation symbol sees a wider bandwidth
+1-1
-1+1
-1-1
-1+1
+1+1
-1
DFT pre-coding
Serial toParallel IFFT
bitstream .
..
Parallelto Serial
addCP
Encoding +Interleaving+ Modulation
.. DFT
..
.
.. Subcarrier
mapping
Cellular Communication Networks 35Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Physical Channels to Support LTE Uplink
eNodeB
Random access for initialaccess and UL timing
alignment
UL scheduling grant
Carries UL Traffic
UL scheduling request fortime synchronized IEs
HARQ feedback for UL
Allows channel stateinformation to beobtained by eNB
Cellular Communication Networks 36Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
Cellular Communication Networks 37Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
Cellular Communication Networks 38Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
Cellular Communication Networks 39Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
Cellular Communication Networks 40Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Release 8 User Equipment Categories
Category 1 2 3 4 5
Peak rateMbps
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 Notsupported
Mandatory
4x4 MIMO Not supported Mandatory
Cellular Communication Networks 41Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Scheduling and Resource Allocation
u Basic unit of allocation is called a Resource Block (RB)u 12 subcarriers in frequency (= 180 kHz)u 1 timeslot in time (= 0.5 ms, = 7 OFDM symbols)u Multiple resource blocks can be allocated to a user in a given subframe
u 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 availableresource blocks
6 15 25 50 75 100
Cellular Communication Networks 42Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Downlink Scheduling & Resource Allocation
u Channel dependent scheduling is supported in both time and frequencydomain à enables two dimensional flexibilityu CQI feedback can provide both wideband and frequency selective
feedbacku PMI and RI feedback allow for MIMO mode selectionu Scheduler chooses bandwidth allocation, modulation and coding set
(MCS), MIMO mode, and power allocationu HARQ operation is asynchronous and adaptiveu Assigned RBs need not be contiguous for a given user in the downlink
14 OFDM symbols12
subcarriers
Slot =0.5ms
Slot =0.5ms
UE A
UE B
UE C
Time
Freq
uenc
y
<=3 OFDM symbols for L1/L2 control
Cellular Communication Networks 43Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Uplink Scheduling & Resource Allocation
u Channel dependent scheduling in both time and frequency enabled throughthe use of the sounding reference signal (SRS)u Scheduler selects bandwidth, modulation and coding set (MCS), use of
MU-MIMO, and PC parametersu HARQ operation is synchronous, and can be adaptiveu PRBs assigned for a particular UE must be contiguous in the uplink
(SC-FDMA)u To reduce UE complexity, restriction placed on # of PRBs that can be
assigned
14 SC-FDMA symbols(12 for data)
12subcarriers
Slot =0.5ms
Slot =0.5ms
UE A
UE B
UE C
Time
Freq
uenc
y
Cellular Communication Networks 44Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Uplink Power Control
u Open-loop power control is the baselineuplink power control method in LTE(compensation for path loss and fading)u Open-loop PC is needed to constrain the
dynamic range between signals received fromdifferent UEs
u Unlike CDMA, there is no in-cell interference tocombat; rather, fading is exploited by ratecontrol
u Transmit power per PRBTxPSD(dBm) = a · PL(dB) + P0nominal(dBm)
u PLdB: pathloss, estimated from DL referencesignal
u P0nominal (dBm) = Gnominal (dB) + Itot (dBm)
u Sum of SINR target Gnominal and total interferenceItot sent on BCCH
Fractional compensation factor a ≤ 1 (PUSCH)→ only a fraction of the path loss is compensated
u Additionally, (slow) closed loop PC can beused
TargetSINR
Target SINR on PUSCH is now a function ofthe UE’s path loss:
SINR(dBm) = Gnominal (dB) – (1 – a) · PL(dB)
Cellular Communication Networks 45Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Interference Coordination with Flexible Frequency Reuse
u Cell edge users with frequency reuse > 1,
u eNB transmits with higher power
u Improved SINR conditions
u Cell centre users can use whole frequency band
u eNB transmits with reduced power
u Less interference to other cells
u Flexible frequency reuse realized throughintelligent scheduling and power allocation
Cell edge
Reuse > 1
Cell centre
Reuse = 1
u Scheduler can place restriction on whichPRBs can be used in which sectors
u Achieves frequency reuse > 1
u Reduced inter-cell interference leads toimproved SINR, especially at cell-edge
u Reduction in available transmissionbandwidth leads to poor overall spectralefficiency
Cellular Communication Networks 46Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Random-Access Procedure
u RACH only used for Random Access Preambleu Response/ Data are sent over SCH
u 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
Cellular Communication Networks 47Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Handover
u LTE uses mobile-assisted & network-controlled handoveru UE reports measurements using reporting criteriau Network decides when handover and to which cellu Relies on UE to detect neighbor cells ® no need to maintain and
broadcast neighbor listsu Allows "plug-and-play" capability; saves BCH resources
u For search and measurement of inter-frequency neighboring cells onlycarrier frequency need to be indicated
u X2 interface used for handover preparation and forwarding of user datau Target eNB prepares handover by sending required information to UE
transparently through source eNB as part of the Handover RequestAcknowledge messageu New configuration information needed from system broadcastu Accelerates handover as UE does not need to read BCH on target cell
u Buffered and new data is transferred from source to target eNB until pathswitch ® prevents data loss
u UE uses contention-free random access to accelerate handover
Cellular Communication Networks 48Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Handover: Preparation Phase
UEUE SourceeNB
SourceSourceeNB
Measurement Control
TargeteNB
TargeteNB MMEMME sGWsGW
Packet Data Packet Data
UL allocation
Measurement Reports
HO decision
Admission Control
HO Request
HO Request AckDL allocation
RRC Connection Reconfig.
L1/L2signaling
L3 signaling
User data
u HO decision is made by source eNB based on UE measurement report
u Target eNB prepares HO by sending relevant info to UE through source eNB as partof HO request ACK command, so that UE does not need to read target cell BCCH
SN Status Transfer
Cellular Communication Networks 49Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Handover: Execution Phase
UEUE SourceeNB
SourceeNB
TargeteNB
TargeteNB MMEMME sGWsGW
Detach from old cell,sync with new cell
Deliver buffered packets and forwardnew packets to target eNB
DL data forwarding via X2
Synchronisation
UL allocation and Timing Advance
RRC Connection Reconfig. Complete
L1/L2signaling
L3 signaling
User dataBuffer packets fromsource eNB
Packet Data
Packet Data
u RACH is used here only, so target eNB can estimate UE timing and provide timingadvance for synchronization
u RACH timing agreements ensure UE does not need to read target cell P-BCH toobtain SFN (radio frame timing from SS is sufficient to know PRACH locations)
UL Packet Data
Cellular Communication Networks 50Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Handover: Completion Phase
UEUE SourceeNB
TargeteNB
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/L2signaling
L3 signaling
User data
DL data forwarding
Flush DL buffer,continue deliveringin-transit packets
End Marker
Release resources
Packet Data
End Marker
Cellular Communication Networks 51Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE Handover: Illustration of Interruption Period
UL
U- plane active
U-plane active
UEUE SourceeNB
SourceeNB
TargeteNB
TargeteNB
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 andGrant
ACK
HO Request
HO Confirm
HandoverLatency
(approx 55 ms)approx20 ms
MeasurementReport
HO Command
HO Complete
HandoverInterruption
(approx 35 ms)
Handover Preparation
Cellular Communication Networks 52Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
u Tracking Area Identifier (TAI) sent over Broadcast Channel BCCH
u Tracking Areas can be shared by multiple MMEs
u One UE can be allocated to multiple tracking areas
Cellular Communication Networks 53Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Bearer Service Architecture
Cellular Communication Networks 54Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE RRC States
u No RRC connection, no context ineNodeB (but EPS bearers are retained)
u UE controls mobility through cellselection
u UE specific paging DRX cycle controlledby upper layers
u UE acquires system information frombroadcast channel
u UE monitors paging channel to detectincoming calls
u RRC connection and context in eNodeBu Network controlled mobilityu Transfer of unicast and broadcast data
to and from UEu UE monitors control channels
associated with the shared datachannels
u UE provides channel quality andfeedback information
u Connected mode DRX can beconfigured by eNodeB according to UEactivity level
RRC_IDLE RRC_Connected
Release RRC connection
Establish RRC connection
Cellular Communication Networks 55Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Connection Management States
u No signaling connection between UEand core network (no S1-U/ S1-MME)
u No RRC connection (i.e. RRC_IDLE)u UE performs cell selection and tracking
area updates (TAU)
u Signaling connection establishedbetween UE and MME, consists of twocomponentsu RRC connectionu S1-MME connection
u UE location is known to accuracy ofCell-ID
u Mobility via handover procedure
ECM_IDLE ECM_Connected
Signaling connection released
Signaling connection established
Cellular Communication Networks 56Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
EPS Mobility Management States
u EMM context holds no valid location orrouting information for UE
u UE is not reachable by MME as UElocation is not known
u UE successfully registers with MME withAttach procedure or Tracking AreaUpdate (TAU)
u UE location known within tracking areau MME can page to UEu UE always has at least one PDN
connection
EMM_Deregistered
Detach
AttachEMM_Registered
Cellular Communication Networks 57Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE – Status
u LTE standards are stableu Rel. 8 frozen in 2Q2009
u Since 2010, LTE has been deployed worldwideu Totally new infrastructureu First target was often to provide broadband coverage for fixed users
u Currently, 324 LTE networks in 112 countries are in service (Oct. 2014)*
u Mostly implemented according to Release 8/9, start of LTE-Advancedu Mostly FDD, but also some TDD networksu Mobile packet data support with fallback to 3G/2G for CS voice serviceu Spectrum allocation in new frequency bands as well as existing 2G/3G
bands (refarming)u 3GPP continues LTE development
u Rel. 9: technical enhancements/ E-MBMSu Rel. 10 – 12: LTE-Advanced (cf. next slides)
*http://www.4gamericas.org -> Statistics
Cellular Communication Networks 58Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE-Advanced
u The evolution of LTEu Corresponding to LTE Release 10 and beyond
u Motivation of LTE-Advancedu IMT-Advanced standardisation process in ITU-Ru Additional IMT spectrum band identified in WRC07u Further evolution of LTE Release 8 and 9 to meet:
u Performance requirements for IMT-Advanced of ITU-R
u Future operator and end-user requirements
u Other important requirementsu LTE-Advanced to be backwards compatible with Release 8u Support for flexible deployment scenarios including downlink/uplink
asymmetric bandwidth allocation for FDD and non-contiguous spectrumallocation
u Increased deployment of indoor eNB and HNB in LTE-Advanced
Cf. T. Nakamura (RAN chairman): “Proposal for Candidate Radio Interface Technologies for IMT-Advanced Basedon LTE Release 10 and Beyond LTE-Advanced),” ITU-R WP 5D 3rd Workshop on IMT-Advanced, October 2009.
Cellular Communication Networks 59Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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 willencompass the capabilities
of previous systems
New capabilities ofIMT-Advanced
New MobileAccess
Cellular Communication Networks 60Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
u Peak data rateu 1 Gbps data rate will be achieved by 4-by-4 MIMO and transmission
bandwidth wider than approximately 70 MHzu Peak spectrum efficiency
u DL: Rel. 8 LTE satisfies IMT-Advanced requirementu UL: 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 inCircular Letter (CL)
System Performance Requirements
Cellular Communication Networks 61Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Technical Outline to Achieve LTE-Advanced Requirements
u Support wider bandwidthu Carrier aggregation to achieve wider bandwidthu Support of spectrum aggregationè Peak data rate, spectrum flexibility
u Advanced MIMO techniquesu Extension to up to 8-layer transmission in downlinku Introduction of single-user MIMO up to 4-layer transmission in uplinkè Peak data rate, capacity, cell-edge user throughput
u Coordinated multipoint transmission and reception (CoMP)u CoMP transmission in downlinku CoMP reception in uplinkè Cell-edge user throughput, coverage, deployment flexibility
u Relayingu Type 1 relays create a separate cell and appear as Rel. 8 LTE eNB to
Rel. 8 LTE UEsè Coverage, cost effective deployment
Cellular Communication Networks 62Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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
u Wider bandwidth transmission using carrier aggregationu Entire system bandwidth up to, e.g., 100 MHz, comprises multiple basic
frequency blocks called component carriers (CCs)
u Each CC is backward compatible with Rel. 8 LTE
u Carrier aggregation supports both contiguous and non-contiguousspectrums, and asymmetric bandwidth for FDD
Cellular Communication Networks 63Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Advanced MIMO Techniques
u Extension up to 8-stream transmission forsingle-user (SU) MIMO in downlinkè improve downlink peak spectrumefficiency
u Enhanced multi-user (MU) MIMO indownlinkè Specify additional reference signals (RS)
u Introduction of single-user (SU)-MIMO upto 4-stream transmission in uplinkè Satisfy IMT requirement for uplink peakspectrum efficiency
Max. 8 streams
Higher-order MIMO upto 8 streams
EnhancedMU-MIMO
CSI feedback
Max. 4 streams
SU-MIMO up to 4 streams
Cellular Communication Networks 64Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Coordinated Multipoint Transmission/ Reception (CoMP)
u Enhanced service provisioning, especiallyfor cell-edge users
u CoMP transmission schemes in downlinku Joint processing (JP) from multiple
geographically separated points
u Coordinated scheduling/beamforming(CS/CB) between cell sites
u Similar for the uplinku Dynamic coordination in uplink
schedulingu Joint reception at multiple sites
Coherent combining ordynamic cell selection
Joint transmission/dynamic cell selection
Coordinated scheduling/beamforming
Receiver signal processing atcentral eNB (e.g., MRC, MMSEC)
Multipoint reception
Cellular Communication Networks 65Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
eNB RNUE
Cell ID #x Cell ID #y
Higher node
Relaying
Type 1 relayu Relay node (RN) creates a separate cell distinct from the donor cellu UE receives/transmits control signals for scheduling and HARQ from/to RNu RN appears as a Rel. 8 LTE eNB to Rel. 8 LTE UEs
è Deploy cells in the areas where wired backhaul is not available or veryexpensive
Cellular Communication Networks 66Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
Heterogenous Networks (HetNet)
u Network expansion due to varying traffic demand & RF environmentu Cell-splitting of traditional macro deployments is complex and iterativeu Indoor coverage and need for site acquisition add to the challenge
u Future network deployments based on Heterogeneous Networksu Deployment of Macro eNBs for initial coverage onlyu Addition of Pico, HeNBs and Relays for capacity growth & better user experience
u Improved in-building coverage and flexible site acquisition with low power base stationsu Relays provide coverage extension with no incremental backhaul expense
u eICIC is introduced in LTE Rel-10 and further enhanced in Rel-11/12u Time domain interference managementu Cell range expansionu Interference cancellation receiver in the terminal
Cellular Communication Networks 67Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
LTE References
u Literature:u H. Holma/ A. Toskala (Ed.): “LTE for UMTS - Evolution to LTE-Advanced,” 2nd
edition, Wiley 2011u E. Dahlman et al: “4G: LTE/LTE-Advanced for Mobile Broadband,” 2nd edition,
Academic Press 2013u S. Sesia et al: “LTE, The UMTS Long Term Evolution: From Theory to Practice,”
Wiley 2011u H. Holma/ A. Toskala (Ed.): “LTE Advanced: 3GPP Solution for IMT-Advanced,”
Wiley 2012
u Standardsu TS 36.xxx series: RAN Aspectsu TS 36.300 “E-UTRAN; Overall description; Stage 2”u TR 25.912 “Feasibility study for evolved Universal Terrestrial Radio Access (UTRA)
and Universal Terrestrial Radio Access Network (UTRAN)”u TR 25.814 “Physical layer aspect for evolved UTRA”u TR 23.882 “3GPP System Architecture Evolution: Report on Technical Options and
Conclusions”u TR 36.912 “Feasibility study for Further Advancements for E-UTRA (LTE-
Advanced)”u TR 36.814 “Further Advancements for E-UTRA - Physical Layer Aspects”
Cellular Communication Networks 68Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014
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-DivisionMultiplexing
OFDMA Orthogonal Frequency-DivisionMultiple-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 FDMASON Self-Organizing NetworkSS Synchronization SignalSU Single UserTDD Time-Division DuplexTA Timing Advance/ Tracking AreaTAI Tracking Area IndicatorTAU Tracking Area UpdateUE User Equipment