3G Long-term Evolution (LTE) and System …„3G Long-term Evolution (LTE)” for new Radio Access and “System Architecture Evolution” (SAE) for Evolved Network UMTS Networks Andreas

3G Long-term Evolution (LTE) andSystem Architecture Evolution (SAE)

Background Evolved Packet System Architecture LTE Radio Interface Radio Resource Management LTE-Advanced

UMTS Networks 2Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2010

3GPP Evolution – Background

Discussion started in Dec 2004 State 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 CN

Led 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


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


Key Features of LTE to Meet Requirements

Selection of OFDM for the air interface Less receiver complexity Robust 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 techniques Pilot structure to support 1, 2, or 4 Tx antennas in the DL and MU-MIMO

in the UL

Simplified network architecture Reduction in number of logical nodes flatter architecture Clean separation of user and control plane


3GPP / LTE R7/R8 specifications timeline

After Study Phase: Two Lines in 3GPP EVOLUTION of HSPA to HSPA+ (enhanced W-CDMA incl. MIMO) REVOLUTION towards LTE/SAE (OFDM based)

Stage 2 (Principles) completed in March 07 Stage 3 (Specifications) completed in Dec 07 Test 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


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 aspects System Architecture (SA) working groups would develop the Evolved

Packet Core (EPC)

Note on terminology In 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 architecture

For 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)


Network Simplification: From 3GPP to 3GPP LTE

3GPP architecture

4 functional entities on the control plane and user plane

3 standardized user plane & control plane interfaces

3GPP LTE architecture 2 functional entities on the

user plane: eNodeB and S-GW SGSN control plane functions S-GW & MME

Less interfaces, some functions will disappear

4 layers into 2 layers Evolve 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


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 architecture

No more RNC RNC layers/functionalities

moves in eNB X2 interface for seamless

mobility (i.e. data/ context forwarding) and interference management

Note: Standard only defines logical structure/ Nodes !


EPS Architecture – Functional description of the Nodes

eNodeB contains all radio access functions Admission Control Scheduling of UL & DL data Scheduling and transmission of paging and system 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-3GPP access 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 signaling for mobility bw. 2G/3G and LTE NAS signaling Authentication Bearer management functions


EPS Architecture – Control Plane Layout over S1

UE eNode-B MME

RRC sub-layer performs: Broadcasting Paging Connection Mgt 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 eNode-B 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 & logical channels Multiplexing/de-multiplexing of RLC radio 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

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 networks

PDN GW is the mobility anchor between 3GPP and non-3GPP access systems (SAE anchor function); handles IP address allocation

S3 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


LTE Key Radio Features (Release 8)

Multiple access scheme DL: OFDMA with CP UL: Single Carrier FDMA (SC-FDMA) with CP

Adaptive modulation and coding DL modulations: QPSK, 16QAM, and 64QAM UL 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 coordination Support for both FDD and TDD


LTE Frequency Bands

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


OFDM Basics – Overlapping Orthogonal

OFDM: Orthogonal Frequency Division Multiplexing OFDMA: Orthogonal Frequency Division Multiple-Access FDM/ 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


OFDM Basics – Waveforms

Frequency domain: overlapping sinc functions Referred to as subcarriers Typically 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 time

fundamental frequency f0 = 1/T Other 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


OFDM Basics – The Full OFDM Transceiver


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


OFDM symbol


OFDM symbol

OFDM Symbol OFDM Symbol OFDM Symbol

TG TG


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 bandwidth For 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 bandwidth To 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


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


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 domain

In 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


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 CP

On 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 ~5μs and for speeds up to 350 km/h (1.2ms coherence time @ 2.6GHz). As such, the following was decided: CP length = 4.7 μs OFDM symbol time = 66.6 μs(= 1/20 the worst case coherence time)

f = 15 kHz

CP

~4.7 µs ~66.7 µs


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


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 subframe 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


LTE Downlink Frame Structure

Spectrum allocation 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz

Slot duration 0.5 ms

Sub-frame duration 1.0 ms ( = 2 slots)

Sub-carrier spacing

15 kHz(7.5 kHz for MBMS)

Sampling frequency

1.92 MHz(1/2 3.84)

3.84 MHz 7.68 MHz(2 3.84)

15.36 MHz(4 3.84)

23.04 MHz(6 3.84)

30.72 MHz(8 3.84)

FFT size 128 256 512 1024 1536 2048

Number of sub-carriers 75 150 300 600 900 1200

OFDM symbols per slot 7 (short CP), 6 (long CP)

CP length

Short 4.69 s x 65.21 s x 1

Long 16.67 s

Sampling rates are multiples of UMTS chip rate, to ease implementation of dual mode UMTS/LTE terminals

FFT size scales to support larger bandwidth Scalable OFDM

Subframe length relevant to the latency requirement


Multiple Antenna Techniques Supported in LTE

SU-MIMO Multiple data streams sent to the same user

(max. 2 codewords) Significant throughput gains for UEs in high

SINR conditions

MU-MIMO or Beamforming Different data streams sent to different users

using the same time-frequency resources Improves throughput even in low SINR

conditions (cell-edge) Works even for single antenna mobiles

Transmit diversity (TxDiv) Improves reliability on a single data stream Fall back scheme if channel conditions do

not allow SM Useful to improve reliability on common

control channels


MIMO Support is Different in Downlink and Uplink

Downlink Supports SU-MIMO, MU-MIMO, TxDiv

Uplink Initial release of LTE does only support MU-MIMO with a single transmit

antenna at the UE Desire to avoid multiple power amplifiers at UE


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)


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-FDD Handsets are cheaper, as no duplexer is required More commonality between TDD and HD-FDD than compared to full

duplex FDD Certain FDD spectrum allocations have small duplex space; HD-FDD leads

to duplex desense in UE


LTE Downlink

The LTE downlink uses scalable OFDMA Fixed 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)


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


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

BCCHPCCH CCCH DCCH DTCH MCCH MTCH

BCHPCH DL- SCH MCH

DownlinkLogical channels

DownlinkTransport channels

DownlinkPhysical Channels

PDSCH PDCCHPBCH PHICHPCFICHSCHDL- RS PM CH


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 PAPR

Reduced PA back-off improved coverage

SC-FDMA is still an orthogonalmultiple access scheme UEs are orthogonal in frequency Synchronous in the time domain

through the use of timing advance(TA) signaling Only need to be synchronous

within a fraction of the CP length 0.52 s timing advance resolution

Node BUE C

UE B

UE A

UE A Transmit Timing

UE B Transmit Timing

UE C Transmit Timing


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 downlink Can still allocate variable bandwidth in units of 12 sub-carriers Each modulation symbol sees a wider bandwidth

+1 -1 -1 +

1 -1 -1 -1 +1 +

1 +1 -

1

DFT pre-coding


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


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 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


Scheduling and Resource Allocation (1/2)

Basic unit of allocation is called a Resource Block (RB) 12 subcarriers in frequency (= 180 kHz) 1 sub-frame in time (= 1 ms, = 14 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


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


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

0 1 2 3 4 5 6 7 8 9 10 11

Sector Sector Sector

F1 F2 F3

Full Transmission Bandwidth


Random-Access Procedure

RACH only used for Random Access Preamble Response/ 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


LTE Handover

LTE uses UE-assisted network controlled handover UE reports measurements; network decides when handover and to which

cell Relies 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 data Target 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 broadcast Accelerates 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 loss

UE uses contention-free random access to accelerate handover


LTE Handover: Preparation Phase

UEUE Source eNB

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


LTE Handover: Execution Phase

UEUE Source eNB

Source eNB

Target eNB


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


LTE Handover: Completion Phase

UEUE Source eNB

Source eNB

Target eNB


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


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


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 BCHTracking Areas can be shared by multiple MMEs


EPS Bearer Service Architecture

P-GWS-GW PeerEntity

UE eNB

EPS Bearer

Radio Bearer S1 Bearer

End-to-end Service

External Bearer

Radio S5/S8

Internet

S1

E-UTRAN EPC

Gi

S5/S8 Bearer


LTE RRC States

No RRC connection, no context in eNodeB (but EPS bearers are retained)

UE controls mobility through cell selection

UE specific paging DRX cycle controlled by upper layers

UE acquires system information from BCH

UE monitors paging channel to detect incoming calls

RRC connection and context in eNodeB Network controlled mobility Transfer of unicast and broadcast data

to and from UE UE monitors control channels

associated with the shared data channels

UE provides channel quality and feedback information

Connected mode DRX can be configured by eNodeB according to UE activity level

RRC_IDLE RRC_Connected

Release RRC connection

Establish RRC connection


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 connection S1-MME connection

UE location is known to accuracy of Cell-ID

Mobility via handover procedure

ECM_IDLE ECM_Connected

Signaling connection released

Signaling connection established


EPS Mobility Management States

EMM context holds no valid location or routing information for UE

UE 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 area MME can page to UE UE always has at least one PDN

connection

EMM_Deregistered

Detach

AttachEMM_Registered


LTE – Summary

LTE is a new air interface with no backward compatibility to WCDMA Combination of OFDM, MIMO and HOM

SAE/ EPS realizes a flatter IP-based network architecture with less complexity eNodeB, S-GW, P-GW

Some procedures/protocols are being re-used from UMTS Protocol stack Concept of Logical/ Transport/ Physical Channels

Complexity is significantly reduced Reduced UE state space Most transmission uses SCH

LTE standard (Rel. 8) is stable Rel. 9: technical enhancements/ E-MBMS Rel. 10: LTE-Advanced (cf. next slides)


LTE-Advanced

The evolution of LTE Corresponding to LTE Release 10 and beyond

Motivation of LTE-Advanced IMT-Advanced standardisation process in ITU-R Additional IMT spectrum band identified in WRC07 Further evolution of LTE Release 8 and 9 to meet:

Requirements for IMT-Advanced of ITU-R Future 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


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


Peak data rate 1 Gbps data rate will be achieved by 4-by-4 MIMO and transmission

bandwidth wider than approximately 70 MHz Peak spectrum efficiency

DL: Rel. 8 LTE satisfies IMT-Advanced requirement 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 in Circular Letter (CL)

System Performance Requirements


Technical Outline to Achieve LTE-Advanced Requirements

Support wider bandwidth Carrier aggregation to achieve wider bandwidth Support of spectrum aggregation Peak data rate, spectrum flexibility

Advanced MIMO techniques Extension to up to 8-layer transmission in downlink Introduction of single-user MIMO up to 4-layer transmission in uplink Peak data rate, capacity, cell-edge user throughput

Coordinated multipoint transmission and reception (CoMP) CoMP transmission in downlink CoMP reception in uplink Cell-edge user throughput, coverage, deployment flexibility

Relaying Type 1 relays create a separate cell and appear as Rel. 8 LTE eNB to Rel.

8 LTE UEs Coverage, cost effective deployment

Further reduction of delay AS/NAS parallel processing for reduction of C-Plane delay


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 aggregation Entire 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


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


Coordinated Multipoint Transmission/ Reception (CoMP)

Enhanced service provisioning, especially for cell-edge users

CoMP transmission schemes in downlink Joint processing (JP) from multiple

geographically separated points

Coordinated scheduling/beamforming (CS/CB) between cell sites

Similar for the uplink Dynamic coordination in uplink

scheduling Joint 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


eNB RNUE

Cell ID #x Cell ID #y

Higher node

Relaying

Type 1 relay Relay node (RN) creates a separate cell distinct from the donor cell UE 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


EASY-C Overview

EASY C Project topics / objectives BMBF project 3 year project: 2007 – 2010 Preparation of a new Standard: “LTE Advanced” Focus on improved spectral efficiency, cell border throughput, fairness,

and latency Working groups

WG1: Algorithms and Concepts WG2: Technology Test Beds WG3: Hardware Architecture

Web page: http://www.easy-c.de

Project partners:


EASY-C Testbeds in Dresden and Berlin

Dresden: testbed focussed on physical layer aspects

Berlin: focus on new algorithms, services and applications


LTE References

Literature: H. Holma/ A. Toskala (Ed.): “LTE for UMTS - OFDMA and SC-FDMA Based Radio

Access,” Wiley 2009 E. Dahlman et al: “3G Evolution, HSPA and LTE for Mobile Broadband,” 2nd

edition, Elsevier 2008 S. Sesia et al: “LTE, The UMTS Long Term Evolution: From Theory to Practice,”

Wiley 2009 Special Issue on LTE/ WIMAX, Nachrichtentechnische Zeitung, 1/2007, pp. 12–24 T. 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

Standards TS 36.xxx series: RAN Aspects TS 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”


Abbreviations

CP Cyclic Prefix

DFT Discrete Fourier Transformation

DRX Discontinuous Reception

ECM EPS Connection Management

EMM EPS Mobility Management

eNodeB/eNB Evolved NodeB

EPC Evolved Packet Core

EPS Evolved Packet System

E-UTRAN

FDD Frequency-Division Duplex

FDM Frequency-Division Multiplexing

FFT Fast Fourier Transformation

HD-FDD Half-Duplex FDD

HO Handover

HOM Higher Order Modulation

HSS Home Subscriber Server

IFFT Inverse FFT

ISI Inter-Symbol Interference

LTE Long Term Evolution

MIMO Multiple-Input Multiple-Output

MME Mobility Management Entity

MU Multi-User

OFDM Orthogonal Frequency-Division Multiplexing

OFDMA Orthogonal Frequency-Division Multiple-Access

PCRF Policy & Charging Function

PDN Packet Data Network

P-GW PDN Gateway

RA Random Access

RB Resource Block

RRC Radio Resource Control

SAE System Architecture Evolution

SCH Shared Channel

S-GW Serving Gateway

SC-FDMA Single Carrier FDMA

SU Single User

TDD Time-Division Duplex

TA Timing Advance/ Tracking Area

TAI Tracking Area Indicator

TAU Tracking Area Update

UE User Equipment

Documents

3G Long-term Evolution (LTE) and System …„3G Long-term Evolution (LTE)” for new Radio Access and “System Architecture Evolution” (SAE) for Evolved Network UMTS Networks Andreas