3G Long-Term Evolution (LTE) and System Architecture ... · PDF file3G Long-Term Evolution (LTE) and System Architecture Evolution ... and “System Architecture Evolution” (SAE)

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


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


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


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


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)


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


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 !


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


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


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)


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


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


LTE Frequency Bands

u LTE will support all band classes currently specified for UMTS as well asadditional bands


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


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


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


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


OFDM symbol


OFDM symbol

OFDM Symbol OFDM Symbol OFDM Symbol

TG TG


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


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


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


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


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


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


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


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


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


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)


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


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


20 MHz: 2048 pt IFFT10 MHz: 1024 pt IFFT5 MHz: 512 pt IFFT


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


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


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


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


.. DFT

..

.

.. Subcarrier

mapping


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


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


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


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





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


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


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


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


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


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


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)


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


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


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


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


LTE Handover: Execution Phase

UEUE SourceeNB

SourceeNB

TargeteNB


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


LTE Handover: Completion Phase

UEUE SourceeNB

TargeteNB


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


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


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


EPS Bearer Service Architecture


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


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


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


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


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.


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


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


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


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


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


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


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


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


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”


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

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