3G Long-term Evolution (LTE) and System …...EVOLUTION of HSPA to HSPA+ (enhanced W-CDMA incl. MIMO) REVOLUTION towards LTE/SAE (OFDM based) Stage 2 (Principles) completed in March

3G Long-term Evolution (LTE) and System Architecture Evolution (SAE)

Background

Evolved Packet System Architecture

LTE Radio Interface

Radio Resource Management

LTE-Advanced

UMTS Networks 2 Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2012

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/technologies Reduce transport network cost Limit additional complexity

Evolved-UTRA is a packet only network – there is no support of circuit switched services (no MSC)

Evolved-UTRA started on a clean state – everything was 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 06

WI agreed, concepts

approved

LTE RAN 35 March 07

Stage 2 Technical

Specs

RAN 37 Sept 07

Stage 3 Technical

Specs- L1 & L2

Corrections Phase

(2008 and

beyond)

RAN 34 Dec 06

NEW WI (64/16 QAM)

RAN 35 Mar 07

WI Completion (inc 64QAM)

RAN 36 Jun 07

WI Completion 16QAM UL

RAN 37 Sept 07

WI 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 08

Test 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

MMF

GGSN

SGSN

RNC

NodeB

Control plane User plane

ASGW

eNodeB

MMF

S-GW

eNodeB

MME

Control plane User plane

S-GW: Serving Gateway MME: Mobility Management Entity

eNodeB: Evolved NodeB


Evolved UTRAN Architecture

eNB

eNB

eNB

MME/S-GW MME/S-GW

X2

EPC

E-U

TR

AN

S1

S1

S1 S1

S1

S1

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

internet

eNB

RB Control

Connection Mobility Cont.

eNB Measurement

Configuration & Provision

Dynamic Resource

Allocation (Scheduler)

PDCP

PHY

MME

S-GW

S1

MAC

Inter Cell RRM

Radio Admission Control

RLC

E-UTRAN EPC

RRC

Mobility

Anchoring

EPS Bearer Control

Idle State Mobility

Handling

NAS Security

P-GW

UE IP address

allocation

Packet Filtering

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

eNB

PHY

UE

PHY

MAC

RLC

MAC

MME

RLC

NAS NAS

RRC RRC

PDCP PDCP

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

eNB

PHY

UE

PHY

MAC

RLC

MAC

PDCPPDCP

RLC

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

Home Subscriber Server (HSS) is the subscription data repository for permanent user data (subscriber profile).

Policy Charging Rules Function (PCRF) provides the policy and charging control (PCC) rules for controlling the QoS as well as charging the user, accordingly.

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 GW

S1-U

S1-MME S11

S3

S4

S5

Internet

EPS Core

S12

SGi

HSS

S6a

S10

PCRF

Gx

Gxc


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

Df = 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

Modulating the symbols onto subcarriers can be done verry efficiently in baseband using the FFT algorithm

Serial to Parallel

. . .

IFFT

bit

stream . . .

Parallel to Serial

D/A

A/D Serial to Parallel

. . . FFT

. . .

OFDM Transmitter

OFDM Receiver

Parallel to Serial

add CP

RF Tx

RF Rx

remove CP

Encoding + Interleaving + Modulation

Demod + De-interleave

+ Decode

Estimated

bit stream

Channel estimation & compensation


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


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 ~5 μs and for speeds up to 350 km/h (1.2 ms coherence time @ 2.6 GHz). As such, the following was decided:

CP length = 4.7 μs

OFDM symbol time = 66.6 μs(= 1/20 the worst case coherence time)

Df = 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 1 ms

consists of two 0.5 ms slots

7 OFDM symbols per 0.5 ms 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


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 points designed 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)

Serial to Parallel

. . .

IFFT

bit stream . . .

Parallel to Serial

add CP


20 MHz: 2048 pt IFFT

10 MHz: 1024 pt IFFT 5 MHz: 512 pt IFFT


Physical Channels to Support LTE Downlink

eNodeB

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 PDSCH PCCH: 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

Downlink

Logical channels

Downlink

Transport channels

Downlink

Physical ChannelsPDSCH PDCCHPBCH PHICHPCFICH PMCH


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 orthogonal multiple 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 ms timing advance resolution

Node B

UE 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)

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

Serial to Parallel IFFT

bit

stream . . .

Parallel to Serial

add CP


. . DFT . . .

. .

Subcarrier mapping


Physical Channels to Support LTE Uplink

eNodeB

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

Allows channel state

information to be

obtained by eNB


Mapping between UL Logical, Transport and Physical Channels

CCCH DCCH DTCH

RACH UL-SCH

Uplink

Logical channels

Uplink

Transport channels

Uplink

Physical ChannelsPUSCH PUCCHPRACH

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

bandwidth

Highest 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 timeslot in time (= 0.5 ms, = 7 OFDM symbols)

Multiple resource blocks can be allocated to a user in a given subframe

The total number of RBs available depends on the operating bandwidth

12 sub-carriers

(180 kHz)

Bandwidth (MHz) 1.4 3.0 5.0 10.0 15.0 20.0

Number of available resource blocks

6 15 25 50 75 100


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

subcarrie

rs

Slot = 0.5ms

Slot = 0.5ms

UE A

UE B

UE C

Time

Fre

quency

<=3 OFDM symbols for PDCCH Downlink Scheduling


Uplink Power Control

Open-loop power control is the baseline uplink power control method in LTE (compensation for path loss and fading)

Open-loop PC is needed to constrain the dynamic range between signals received from different UEs

Unlike CDMA, there is no in-cell interference to combat; rather, fading is exploited by rate control

Transmit power per PRB

TxPSD(dBm) = a·PL(dB) + P0nominal(dBm)

PLdB: pathloss, estimated from DL reference signal

P0nominal (dBm) = nominal (dB) + Itot (dBm)

Sum of SINR target nominal and total interference Itot sent on BCH

Fractional compensation factor a ≤ 1 (PUSCH) → only a fraction of the path loss is compensated

Additionally, (slow) closed loop PC can be used

June 2010 LTE – Training

© 2010 Nash Technologies GmbH – All rights reserved

Page 42

Target SINR

Target SINR on PUSCH is now a function of the UE’s path loss:

SINR(dBm) = nominal (dB) + (1–a)·PL(dB)


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

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

a

b

g

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 a Sector b Sector g

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

RA Preamble assignment0

Random Access Preamble 1

Random Access Response2

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

UE UE Source

eNB Source

eNB

Measurement Control

Target eNB

Target eNB MME MME sGW sGW

Packet Data Packet Data

UL allocation

Measurement Reports

HO decision

Admission Control

HO Request

HO Request Ack

DL 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 BCCH

SN Status Transfer


LTE Handover: Execution Phase

UE UE 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 data Buffer 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

UE UE Source

eNB

Target eNB


DL Packet Data

Path switch req

User plane update req

Switch DL path

User plane update response Path 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

UE UE 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

Handover

Latency

(approx 55 ms) approx 20 ms

Measurement Report

HO Command

HO Complete

Handover Interruption

(approx 35 ms)

Handover Preparation


Tracking Area

BCCH

TAI 1

BCCH

TAI 1

BCCH

TAI 1

BCCH

TAI 1

BCCH

TAI 1

BCCH

TAI 2

BCCH

TAI 2

BCCH

TAI 2

BCCH

TAI 2

BCCH

TAI 2

BCCH

TAI 2

BCCH

TAI 3

BCCH

TAI 3

BCCH

TAI 3

BCCH

TAI 3

Tracking Area 1

Tracking Area 2 Tracking Area 3

• Tracking Area Identifier (TAI) sent over Broadcast Channel BCCH

• Tracking Areas can be shared by multiple MMEs

• One UE can be allocated to multiple tracking areas


EPS Bearer Service Architecture

P-GWS-GW Peer

Entity

UE eNB

EPS Bearer

Radio Bearer S1 Bearer

End-to-end Service

External Bearer

Radio S5/S8

Internet

S1

E-UTRAN EPC

Gi

E-RAB 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 broadcast channel

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

Attach

EMM_Registered


LTE – Status

LTE standard (Rel. 8) is stable

Rel. 8 frozen in 2Q2009

Since 2010, LTE has been deployed worldwide

Totally new infrastructure

First target was often to provide broadband coverage for fixed users

Currently, 111 LTE networks in 52 countries are in service (Nov. 2012)*

Implemented according to Release 8/9

Mostly FDD, but also some TDD networks

Mobile packet data support with fallback to 3G/2G for CS voice service

Spectrum allocation in new frequency bands as well as existing 2G/3G bands (refarming)

3GPP continues LTE development

Rel. 9: technical enhancements/ E-MBMS

Rel. 10/11: LTE-Advanced (cf. next slides)

*http://www.4gamericas.org -> Statistics


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 phase Study Item phase

First submission

Final submission

LTE release 10 (”LTE-Advanced”)

2009 2010 2008

Proposals

Circular Letter

3GPP WS

IMT-Advanced

Specification

IMT-Advanced recommendation

Evaluation

3GPP

ITU


Evolution from IMT-2000 to IMT-Advanced

Interconnection

IMT - 2000

Mobility

Low

High

1 10 100 1000

Peak useful data rate (Mbit/s)

Enhanced IMT - 2000

Enhancement

IMT - 2000

Mobility

Low

High

1 10 100 1000

Area Wireless Access

Enhanced IMT - 2000

Enhancement

Digital Broadcast Systems Nomadic / Local Area Access Systems

New Nomadic / Local

IMT-Advanced will encompass the

capabilities of previous systems

New capabilities of IMT-Advanced

New Mobile Access

• 5

7

http://www.itu.int/imt


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 rate

DL 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 RN UE

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


Heterogenous Networks (HetNet)

Network expansion due to varying traffic demand & RF environment Cell-splitting of traditional macro deployments is complex and iterative Indoor coverage and need for site acquisition add to the challenge

Future network deployments based on Heterogeneous Networks Deployment of Macro eNBs for initial coverage only Addition of Pico, HeNBs and Relays for capacity growth & better user experience

Improved in-building coverage and flexible site acquisition with low power base stations Relays provide coverage extension with no incremental backhaul expense

eICIC is introduced in LTE Rel-10 and further enhanced in Rel-11 Time domain interference management Cell range expansion Interference cancellation receiver in the terminal


LTE References

Literature:

H. Holma/ A. Toskala (Ed.): “LTE for UMTS - OFDMA and SC-FDMA Based Radio Access,” 2nd edition, Wiley 2011

E. Dahlman et al: “3G Evolution, HSPA and LTE for Mobile Broadband,” 3rd edition, Academic Press 2011

S. Sesia et al: “LTE, The UMTS Long Term Evolution: From Theory to Practice,” Wiley 2011

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 Evolved UMTS Terrestrial Radio Access Network

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 …...EVOLUTION of HSPA to HSPA+ (enhanced W-CDMA incl. MIMO) REVOLUTION towards LTE/SAE (OFDM based) Stage 2 (Principles) completed in March