lte

LTE tutorial- Looking forward beyond HSPA+

[email protected] System Engineer

All rights reserved @ 2009

Outline

Beyond HSPA+ LTE: motivation and expectations E-UTRAN overview & initial performance evaluation OFDMA and SC-FDMA fundamentals LTE physical layer LTE transmission procedures


Beyond HSPA evolution 3GPP path

Rel-99WCDMA

Rel-7

HSPA+ (HSPA Evolution)

DL: 14.4 MbpsUL: 5.76Mbps

HSDPA/HSUPA

DL: 28 MbpsUL: 11 Mbps



DL: 100+ MbpsUL: 23+ Mbps

Rel-8 Rel-9 Beyond Rel-9

LTE specification process ~ 2007Q4

E-UTRAN

UTRAN

Rel-6Rel-5

LTE-A

DL:300 MbpsUL: 75 Mbps

DL: 1 GbpsUL: 100 Mbps

deployment& service

enhancement


LTE - background Motivation:

Based on HSPA success story(274* commercial HSPA networks worldwide)

Uptake of mobile data traffic upon cellular networks enforces:

Reduced latency Higher user data rate Improved system capacity and coverage Cost-reduction per bit

Expectation: Detailed requirements captured

in 3GPP TR 25.913 NGMN formally released requirements

on next generation RAN in late 2006**

*source: www.gsacom.com mobile broadband evolution: roadmap from HSPA to LTE UMTS forum White paper**http://www.ngmn.org/nc/de/downloads/techdownloads.html


LTE feature overview

Flexible and expandable spectrum bandwidth

Simplified network architecture

High data throughput (Macro eNodeB & Home eNodeB)

Support for multi-antenna scheme (up to 4x4 MIMO in Rel-8)

Time-frequency scheduling on shared-channel

Soft(fractional) frequency reuse

Self-Organizing Network (SON)


LTE spectrum flexibility

FDD Pair

uplink downlink

5 MHz20 MHz

Operating bands Flexible carriers: from 700MHz to

2600MHz Extensible bandwidth: from 5MHz to

20MHz

active RBs

Transmission bandwidth configuration(RBs)

Channel bandwidth (MHz)


LTE basic parameters

Frequency range UMTS FDD bands and TDD bands defined in 36.101(v860) Table 5.5.1

channel bandwidth (MHz)1.4 3 5 10 15 20

Transmission bandwidth NRB:(1 resource block = 180kHz in 1ms TTI)

6 15 25 50 75 100

Downlink: QPSK, 16QAM, 64QAMModulation Schemes:

Uplink: QPSK, 16QAM, 64QAM(optional)

downlink: OFDMA (Orthogonal Frequency Division Multiple Access)Multiple Access:

uplink: SC-FDMA (Single Carrier Frequency Division Multiple Access)

downlink: TxAA, spatial multiplexing, CDD ,max 4x4 arrayMulti-Antenna Technology

Uplink: Multi-user collaborative MIMO

Downlink: 150Mbps(UE Category 4, 2x2 MIMO, 20MHz bandwidth)300Mbps(UE category 5, 4x4 MIMO, 20MHz bandwidth)Peak data rate

Uplink: 75Mbps(20MHz bandwidth)


LTE Peak throughput w.r.t UE categories

UE Category Maximum number of DL-SCH transport block bits received

within a TTI

Maximum number of bits of a DL-SCH transport

block received within a TTI

Total number of soft

channel bits

Maximum number of supported layers for spatial multiplexing

in DL

Category 1 10296 10296 250368 1

Category 2 51024 51024 1237248 2

Category 3 102048 75376 1237248 2

Category 4 150752 75376 1827072 2

Category 5 299552 149776 3667200 4

3GPP TS 36.306 v850 User Equipment (UE) radio access capabilities

Table 4.1-1: Downlink physical layer parameter values set by the field ue-Category

Table 4.1-2: Uplink physical layer parameter values set by the field ue-CategoryUE

Category

Maximum number of bits of an UL-SCH transport block transmitted within a TTI

Support for 64QAM in

UL

Category 1 5160 No

Category 2 25456 No

Category 3 51024 No

Category 4 51024 No

Category 5 75376 Yes

Peak rate 150Mbps with

2x2 MIMO

Peak rate 300Mbps with 4x4 MIMO

Peak rate 75Mbps


LTE UE category

UE Category 1 2 3 4 5

DL 10 50 100 150 300

UL 5 25 50 50 75

RF bandwidth 20 MHz

DL QPSK, 16QAM, 64QAM

UL QPSK, 16QAMQPSK,

16QAM,64QAM

2 Rx Diversity Assumed in performance requirements

2x2 MIMO Optional Mandatory

4x4 MIMO Not supported Mandatory

Modulation

Peak rate(Mbps)

3GPP TS 36.306 v850 User Equipment (UE) radio access capabilities


Channel dependent scheduling

Time-frequency scheduling

UE #1

UE #2


Soft (fractional) frequency reuse Soft Frequency Reuse(SFR):

inner part of cell uses all subbands with less power; Outer part of cell uses pre-served subbands with higher power;

MS 21

MS 11BS 1

BS 3

BS 2

Power density

sub-

carri

er

power density

Powe

r den

sity

Sub-carriers

sub-

carrie

r

MS 31MS 12

MS 22

MS 32

3GPP R1-050841 Further Analysis of Soft Frequency Reuse Scheme


E-UTRAN overview


E-UTRAN architecture

S1 S1

S1 S1X2

X2


E-UTRAN architecture


E-UTRAN radio protocol

Paging System informationDedicated Control

and information transfer

PCCH

SRB0 SRB1 SRB2 DRB1 DRB2

PCH

BCCH

BCH

CCCH

RACH

DCCH 1 DCCH 2 DTCH 1 DTCH 2

DL-SCH UL-SCH

PBCH PRACH PDSCH PUSCH

PHY layer functions

Multiplexing and HARQ control

Integrity and ciphering

ARQ

Integrity and ciphering

ARQ

ciphering and ROHC

ARQ

ciphering and ROHC

ARQ

PDCP

RLC

MAC

RRC

radiobearers

logicalchannels

transportchannels

physicalchannels

notifications common dedicated


E-UTRAN radio channels

PCCH BCCH CCCH DCCH DTCH MCCH MTCH

PCH BCH DL-SCH MCH

PDCCH PBCH PDSCH PMCH

CCCH DCCH DTCH

RACH

PRACH

UL-SCH

PUCCH PUSCH

downlinkLogical

channels

Transport channels

Physical channels

uplink

Logical ChannelsDefine what type of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc.

Transport Channels no per-user dedicated channels!Define how is something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data

Physical ChannelsDefine where is something transmitted over the air, e.g. first N symbols in the DL frame


E-UTRAN bearersMA

CRL

CLT

E L

1

PDCP

RRC

IP

NAS

UDP

RTP

TCP

HTTP

UE

MAC

RLC

LTE

L1

PDCP

RRC

PHY

Layer

2IP

S1 AP

SCTP

GTP-u

UDP

eNodeB

L2

PHY

IPSC

TPS1

AP

MME

NAS L2

PHY

IPUD

PGT

P-u

S-GW

L2

PHY

IPUD

PGT

P-uIP

P-GW

L2

PHY

IPUD

PGT

P-u

SRB: internal E-UTRAN signalings such as RRC signalings, RB management signalings

NAS signalings: such as tracking area update and mobility management messagesdata traffic: E-UTRAN radio bearer + S1 bearer +S5/S8 bearer

E-UTRAN radio bearer S1 bearerS5/S8 bearer

EPS bearer

L1/L2 control channel


E-UTRAN Control plane stack

RRC

PDCP

RLC

MAC

PHY

RRC

PDCP

RLC

MAC

PHY

S1APX2AP

SCTP

L2

L1

IP

S1APX2AP

SCTP

L2

L1

IP

NAS NAS

UE

eNodeB

MME/eNodeB

24.301

36.331

36.323

36.322

36.321

36.211~36.214

36.41336.423

36.41236.422

S1-MME/X2-CLTE-Uu


E-UTRAN User Plane Stack

IP

PDCP

RLC

MAC

PHY

PDCP

RLC

MAC

PHY

GTP-u

UDP

L2

L1

IP

GTP-u

UDP

L2

L1

IP

Application

UE

eNodeB

PDN/S-GWeNodeB

36.323

36.322

36.321

36.211~36.214

S1-U/X2-uLTE-Uu

IP

29.274


Radio resource management

RLC

MAC

RRC

PHY

PDCP

QoS managementAdmission

control Semi-persistentscheduling

Hybrid ARQmanager

Dynamicscheduling Link adaptation

PDCCH adaptation CQI manager

Interferencemanagement

Loadcontrol

L2

L1

L3 mobilitymanagement

An overview of downlink radio resource management for LTE, Klaus Ingemann Pedersen, et al, IEEE communication magazine, 2009 July


E-UTRAN mobility Simplified RRC states Idle-mode mobility (similar as HSPA) Connected-mode mobility

handover controlled by network

RRC-connectedRRC-idle

Cell reselection decided by UE Based on UE measurements Controlled by broadcasted parameters Different priorities assigned to frequency

layers

Network controlled handovers Based on UE measurements

MME/SGW

Target cell signal quality meets

reporting threshold

SourceeNodeB

HO decision

targeteNodeB

Call Admission

Mobility difference between UTRAN and E-UTRAN UTRAN E-UTRAN

Location area (CS core) Not relevant since no CS connections

Routing area Tracking area

SHO No SHO

Cell_FACH, Cell_PCH,URA_PCH No similar RRC states

RNC hides most of mobility Core network sees every handover

Neighbour cell list requiredNo need to provide cell-specific

information, only carrier-frequency is required.


Overview of a PS call control plane UE activities after power-on

Initialcell search

Derive system information

RandomAccess Data Tx/Rx

Power up

PDCCH

PDSCH

PCFICH

/PHICH

PSS/SS

S

BCH

Rnadom

Access

PUSCH

/PUCCH

UE E-UTRAN

Radom Access procedure

Security procedures

paging

RRC Connection Request

RRC Connection Setup

RRC Connection Setup Complete

RRC Connection Reconfiguration

RRC Connection Reconfiguration Complete

Connection establishment

Radio bearer establishment


Overview of a PS call control plane UE activities after power-on

Initialcell search

Derive system information

RandomAccess Data Tx/Rx

Power up

DL da

ta tran

smissio

n

ACK &

channe

l status

report

UL data

transmi

ssion

ACK & u

plink sc

hedulin

g grant

UE E-UTRAN

Radom Access procedure

Security procedures

paging

RRC Connection Request

RRC Connection Setup

RRC Connection Setup Complete

RRC Connection Reconfiguration

RRC Connection Reconfiguration Complete

Connection establishment

Radio bearer establishment


Overview of a PS call user plane

1 resource block:180 kHz = 12 subcarriers

1 resource block pair1 TTI = 1ms = 2 slots

PS data via S1 interface

Multiplexingper user

scheduling

RLC(Segmentation, ARQ)

PDCP(Ciphering

Header Compression,)

HARQ

OFDM SignalGeneration

coding

data modulator

resourcemapping

eNodeB

Tx

to RF

UE


Overview of a PS call user plane


1 resource block pair1 TTI = 1ms = 2 slots

PS data via S1 interface

Multiplexingper user

scheduling

RLC(Segmentation, ARQ)

PDCP(Ciphering

Header Compression,)

HARQ

OFDM SignalGeneration

coding

data modulator

resourcemapping

eNodeB

Tx

to RF

UEOccupying different radio resources across TTIsadapts to time-varying radio channel condition!


LTE initial deployment scenario

Similar coverage as 3G HSPA on existing 3G frequency bands LTE radio transmission technology itself does not provide coverage boost. Lower frequency (e.g, 900MHz) provides better coverage but demands large-

size antennas.

Over-layed initial deployment on hot-spot area Spectrum availability Backhaul capacity Handset maturity (multi-mode)

urban(0.6 ~ 1.2km)

sub-urban(1.5 ~ 3.4km)

Rural(26 ~ 50 km)


LTE initial trial performance LTE data rates

Peak rate measured in lab and trial align with3GPP performance targets

In reality, user throughputs are impacted by RF conditions & UE speed Inter-cell interference & multiple users sharing the capacity Application overhead

Source: www.lstiforum.org

Active users per cell

Peak rate measured with a single user in unloaded, optimal radio condition

Top 5%, loaded

Average

Cell edge

Active users per cell

Average: 10 active users with 3Mbps

throughput per user

1Mpbs throughput at cell edge


Macro Cellular network: peak rate Vs average rate Unlike circuit-switched network design, live network throughput

is not fixed any more, being dependent on many environmental factors such as CQI,Tx buffer status,etc.

In macro cellular network, network average throughput falls behind peak rate by 10x.

Cellular booster for Mobile broadband Ubiquitous coverage High capacity & data rate Low cost>> FemtoCell Home eNodeB!

Tput (Mbps)

0

8

4

2

-3

2

10

25

15

G-factor (dB)HSPA cell throughput

3GPP TS 25.101 Table 9.8D3, 9.8D4, 9.8F3 for PA3


LTE initial trial performance

User plane latency 3GPP RTT target is 10ms for short IP packet Field trial results:

10~13ms with pre-scheduled uplink


OFDMA and SC-FDMA rationale


OFDM fundamentals frequency spectrum

f

FDM

f

OFDM

No Inter-Carrier Interference!

fff 2 0 f2

)sin(ff

fTu =

1

Time domain

frequency domain


OFDM fundamentals multicarrier modulation

+1

+1

-1

f1

f2

f3

+

Modulatedsubcarriers

110 ,...,, cNaaa

0a

S/P 1a

1Nca

tfje 02

tfje 12

tfj Nce 12

)(0 tx

)(1 tx

)(1 txNc

+)(tx

110 ,...,, cNaaa0a

S/P

1a

1Nca

IFFT

0

0

P/S

X0

X1

XN-1

=

===

1

0

21

0)()(

Nc

k

ftkjk

Nc

kk eatxtx

Specifying system sampling rate: fNTf ss == /1We get:

=

=

=

==

==1

0

1

0

22

1

0

2)(

Nc

k

N

k

Nnkj

kNnkj

k

Nc

k

fnTskjkn

eaea

eanTsxx


OFDM fundamentals- Cyclic Prefix

1ka 1+ka

uT

Integration interval of direct path

directed path:

reflected path:

guard time FFT integration time=1/Carrier spacing

OFDM symbol time

ka

>cpT

directed path:

reflected path:

Guard time: Cyclic Prefix Vs Padding Zeroes


OFDM fundamentals- Cyclic Prefix

1ka 1+ka

uT

Integration interval of direct path

directed path:

reflected path:

guard time FFT integration time=1/Carrier spacing

OFDM symbol time

ka

>cpT

directed path:

reflected path:

Guard time: Cyclic Prefix Vs Padding Zeroes

IFFT

0a1a

1Nca

addCyclicPrefixTu Tu+Tcp

an OFDM symbol

P/S


OFDM fundamentals general link level chains

Digital communications: fundamentals and applications by Bernard Sklar, Prentice Hall, 1998. ISBN: 0-13-212713-xOFDM for Wireless Multimedia Communications by Richard van Nee & Ramjee Prasad, Artech house,2000, ISBN: 0-89006-530-6

3GPP TR 25892-600 feasibility study for OFDM in UTRAN

Coding Interleaving QAM mappingPilot

Insertion S/P IFFT P/S add CP

Pulse shapingDACRF Tx

Timing andfrequency SyncADCRF Rx

de-coding de-interleavingQAM

de-mapping Equalizer P/S FFT S/PCP

removal

Binary input data

Binary output data

Sub-carriersFFT

Time

Symbols

5 MHz Bandwidth

Guard Intervals

Frequency


OFDM fundamentals frequency domain equalizer

)(h)(tS

transmitter

)(w+

)(tn

)(tr )(~ ts

receiverChannel model

)()( * = hw1)()( = wh

})()({ 2tstsE =

D D D

W0 W1 WL-1

+

nr

nsDFT

0R0W

0S

1NR 1 NS1NW IDFT

)(tr )( ts

MRC filter:Zero Forcing:MMSE:

Time domain frequency domain

Frequency domain equalization for single carrier broadband wireless systems, David Falconer , et.al,IEEE Communication magazine, 2002 April

Frequency domain equalizer outperforms with much less complexity!


OFDM fundamentals Advantages:

OFDM itself does not provide processing gains, but provides a degree of freedom in frequency domain by partitioning the wideband channel intomultiple narrow flat-fading sub-channels.

Channel coding is mandatory for OFDM to combat frequency-selective fading.

Efficiently combating multi-path propagation in term of cyclic prefix OFDM receiver (frequency domain equalizer) has less complexity than that of

Rake receiver on wideband channels. OFDM characterizes flexible spectrum expansion for cellular systems.

Drawbacks: high peak-to-average ratio. Sensitive to frequency offset, hence to Doppler-shift as well

f

f


OFDM fundamentals downlink OFDMA

f


1 slot = 0.5 ms

PDSCH

PDCCH

OFDMA provides flexible scheduling in time-frequency domain. In case of multi-carrier transmission, OFDMA has larger PAPR than traditional

single carrier transmission. Fortunately this is less concerned with downlink. Does OFDMA suits for uplink transmission?

Uplink being sensitive to PAPR due to UE implementation requirements With wider bandwidth in operation, OFDMA in uplink will have lower power per pilot

symbol which in turn leads to deterioration of demodulation performance.


Wideband single carrier transmission -frequency domain equalizer (SC-FDE)

While time-domain discrete equalizer has effect of linear convolution on channel response; frequency domain equalizer actually serves as cyclic convolution thereof.

The difference will make first L-1 symbols incorrect at the output of FDE.

Solution could be either overlapped processing or cyclic prefixadded in transmitter.

Adaptive Frequency-Domain Equalization and Diversity Combining for Broadband Wireless Communications, M. V. Clark, IEEE J. Sel. Areas Commun., vol. 16, no. 8, Oct. 1998Linear Time and Frequency Domain Turbo Equalization, M. Tchler et al., Proc. IEEE 53rd Veh. Technol. Conf. (VTC), vol. 2,

May 2001Block Channel Equalization in the Frequency Domain, F. Pancaldi et al., IEEE Trans. Commun., vol. 53, no. 3, Mar. 2005

CPinsertionN samples N+Ncp samples

Single carriersignal

generation

PulseShaping

x(t)

block-wise generation

transmitter


SC-FDMA multiple access with FDE

Introduction to Single Carrier FDMA, Hyung G Myung, 2007 EURASIP

Coding Interleaving QAM mapping add CP

Pulse shapingDACRF Tx

Timing andfrequency SyncADCRF Rx

de-coding de-interleavingQAM

de-mappingFreq Domain

EqualizerCP

removal

DFT (size M)

IFFT(size N) P/S

Subcarriermapping

IDFT(Size M) P/S

FFT(size N) S/P

Binary input data

Binary output data

Single Carrier: sequential transmission of the symbolsover a single frequency carrier

FDMA: user multiplexing in frequency domain


SC-FDMA multiple access with SC-FDE

Multiple access in LTE uplink

DFT OFDM

0

Pulse Shaping

data stream

DFT OFDM

0Pulse

Shapingdata stream

Terminal B

Terminal A

f

f

Orthogonal uplink design in frequency domain!


SC-FDMA multiple access with FDE

block-wisesignals

DFT(M)

IFFT(N)

CPinsertion

D/A conversion/pulse shaping

RF

Also called DFT-Spread OFDM!

Adopted by LTE uplink!

DFT(M)

IFFT(N)A B C D

DFT(M)

A B C D

IFFT(N)

Distributed FDMA:Localized FDMA:

A B C D A B C D A B C D A B C D

Upsampling in freq domain makesrepeated sequence at time domain output

A * * * B * * * C * * * D * * *

OverSampling in freq domain results in interpolation at time domain output

time domain:

frequency domain:


OFDMA Vs SC-FDMA

ttime domain

ffrequency domain

Input data symbols

OFDM symbol

SC-FDMA symbol *

* Assuming bandwidth expansion factor Q=4 in distributed FDMA.

Time domain: Frequency domain- OFDM symbol is a sum of all data symbols by IFFT- SC-FDMA symbol is repeated sequence of data chips

- OFDM modulates each subcarrier with one data symbol- SC-FDMA distributes all data symbols on each subcarrier.


OFDMA Vs SC-FDMA Similarities

Block-wise data processing and use of Cyclic Prefix Divides transmission bandwidth into smaller sub-carriers Channel inversion/equalization is done in frequency domain SC-FDMA is regarded as DFT-Precoded or DFT-Spread OFDMA

Difference Signal structure: In OFDMA each sub-carrier only carries information related

to only one data symbol while in SC-FDMA, each sub-carrier contains information of all data symbols.

Equalization: Equalization for OFDMA is done on per-subcarrier basis while for SC-FDMA, equalization is done over the group of sub-carriers used by transmitter.

PAPR: SC-FDMA presents much lower PAPR than OFDMA does. Sensitivity to freq offset: yes for OFDMA but tolerable to SC-FDMA.


LTE Physical layer and transmission procedures


LTE physical layer a vertical view What kind of information is transmitted?

Upper layer SDUs plus additional L1 control information in transmission, e.gReference Signals, Sync signals,CQI, HARQ,etc

How is it transmitted? Downlink OFDMA and uplink SC-FDMA Channel dependent scheduling, HARQ,etc multiple antenna support

Related L1 procedures random access, power control, time alignment, etc

coding Scrambling multiplexmodulation

reference signals

control information

time

frequency

PDCP

RLC

MAC

Transport blocks

control informationor user data

signals from other channels


LTE physical layer - a horizontal view

PBCH: carries system broadcast information PCFICH: indicates resources used for PDCCH PHICH: carries ACK/NACK for HARQ operation. PDCCH: carriers scheduling assignments and other control information PDSCH: conveys data or control information PMCH: for MBMS data transmission Reference signal Synchronization signal (PSS,SSS) PUCCH: carries control information

PRACH: to obtain uplink synchronization PUSCH: for data or control information Reference Signals (Demod RS & SRS)

data transmissionPDCCH notifies how to demodulate data

Feedback CQIs,


Fundamental Downlink transmission scheme

1 resourrc block = 12 sub-carriers = 180KHz

1 slot = 0.5 ms =7 OFDM symbols

1 sub-frame = 1 ms1 resource

element

1 radio frame = 10 ms

1 radio frame = 10 sub-frames = 10 ms

1 sub-frame = 2 slot = 14 OFDM symbols*

*An alternative slot structure for MBMS is 6 OFDM symbols per slot where extended CP is in use.

=

,7.4,2.5

ss

Tcp

66.7 us

66.7 us

Tcp

Tcp-e

for first OFDM symbol

for remaining symbols

seTcp 7.16_ =


System information broadcast System information

MIB: transmitted on PBCH (40msTTI) information about downlink bandwidth PHICH configuration SFN

SIB: transmitted on PDSCH(DL-SCH) SIB1: operator infor & access restriction infor SIB2: uplink cell bandwidth, random access parameters SIB3: cell-reselection SIB4~SIB8: neighbor cell infor

Synchronization signal

PBCH: the first 4 OFDM symbol in 2nd Slot per

10ms frame

10MHz600 subcarriers

10ms frame

1.08 MHz

10ms frame

CRC insertion

scrambling

modulation

antennamapping

De-multiplexing

1/3 conv. coding

One BCH transportation block


Downlink control channels PCFICH,PHICH PCFICH:

tells about the size of the control region. Locates in the first OFDM symbol for each sub-frame.

PHICH: acknowledges uplink data transfer Locates in 1st OFDM symbol for each sub-frame

inferior to PCFICH allocation

1/16 block code Scrambling QPSK mod

2 bits 32 bits 32 bits16 symbols

PCFICH-to-resource-element mapping depends on cell identity so as to avoid inter-cell interference.

3xrepetition BPSK mod

1 bit 3 bits

scrambling3x

repetition BPSK mod1 bit 3 bits

Orthogonal code

Orthogonal code

I

Q

12 symbols

One PHICH group contains 8 PHICHs


Downlink control channels - PDCCH

Downlink control information (DCIs) Downlink scheduling assignments Uplink scheduling assignments Power control commands

Control region size indicated by PCFICH Blind decoded by UE in its search space and common search

space allows UEs micro-sleep even in active state QPSK always used but channel coding rate is variable

R1-073373 Search space definition ofr L1/L2 control channels.Downlink control channel design for 3GPP LTE, Robert Love, Amitava Ghosh, et,al. IEEE WCNC 2008.

reference signals

control information

1 sub-frame = 1 ms

control region


Downlink control channels PDCCH

How to map DCIs to physical resource elements Control Channel Elements(CCEs), consisting of 36 REs, are used to

construct control channels. CCE aggregated at pre-defined level(1,2,4,8) to ease blind detections.

Usually 5MHz bandwidth system renders 6 UL/DL scheduling assignments within a sub-frame.

Control Channel Element 0






Control channel candidates on which the UE attempts to decode the information

(10 decoding attempts in this example)

Control channel candidate set Or search space

C

C

H

c

a

n

d

i

d

a

t

e

1

C

C

H

c

a

n

d

i

d

a

t

e

2

C

C

H

c

a

n

d

i

d

a

t

e

3

C

C

H

c

a

n

d

i

d

a

t

e

4

C

C

H

c

a

n

d

i

d

a

t

e

5

C

C

H

c

a

n

d

i

d

a

t

e

6

C

C

H

c

a

n

d

i

d

a

t

e

7

C

C

H

c

a

n

d

i

d

a

t

e

8

C

C

H

c

a

n

d

i

d

a

t

e

9

C

C

H

c

a

n

d

i

d

a

t

e

1

0

R1-070787 Downlink L1/L2 CCH design


Downlink control channels - PDCCH Each PDCCH carries one DCI message.

CRC attachment

1/3 Conv Coding

Rate mattching

Control information

RNTI CRC attachment

1/3 Conv Coding

Rate mattching

Control information

RNTI

CRC attachment

1/3 Conv Coding

Rate mattching

Control information

RNTI

CCE aggragation and PDCCH multiplexing

Scrambling

QPSK

Interleaving

Cell specific Cyclic shift


Downlink shared channel: PDSCH

Support up to 4 Tx antennas* Resource block allocation:

Localized: with less signaling overheads Distributed: benefits from frequency diversity

Channelization (location):

reference signals

control information

1 sub-frame = 1 ms

User A

User B

User C

unused

CRC

Segmentation

FEC

RM+HARQ

Scrambling

Modulation

CRC

Segmentation

FEC

RM+HARQ

Scrambling

Modulation

Antenna mapping

Transport blockfrom MAC

Transport blockfrom MAC

RB mapping

To OFDM modulation for each antenna

data region

Cell-specific, bit-level scrambling for interference

randomization **

* For MBSFN, antenna diversity scheme does not apply. ** For MBSFN, its MBSFN-area-specific scrambling.


Downlink reference signals Cell-specific reference signals are length-31 Gold sequence,

initialized based on cell ID and OFDM symbol location. Each antenna has a specific reference signal pattern, e.g 2

antennas frequency domain spacing is 6 sub-carriers Time domain spacing is 4 OFDM symbols That is, 4 reference symbols per Resource Block per antenna

time

frequency

Antenna 0 Antenna 1

3GPP TS 36.211 physical channels and modulation section 6.10.1.1


LTE Multiple antenna scheme

3210 ,,, SSSSSTTD UE

3210 ,,, SSSS

*2

*3

*0

*1 ,,, SSSS

NodeB transmitter

OFDM modulation

0a1a2a3a

OFDM modulation

*1a

*0a

*2a

*3a

UE

eNodeB transmitter

OFDM modulation

0a1a2a3a

OFDM modulation

tfjea 21

UE

eNodeB transmitter

0a

tfjea 222

tfjea 323

WCDMA STTD scheme:

LTE SFBC (space frequency block coding): LTE CDD (cyclic delay diversity):


LTE Multiple antenna scheme Downlink SU-MIMO

Transmission of different data streams simultaneously over multiple antennas Codebook based pre-coding: signal is pre-coded at eNodeB before transmission

while optimum pre-coding matrix is selected from pre-defined codebook based on UE feedback.

Open-loop mode possible for high speed

Uplink MU-MIMO: collaborative MIMO Simultaneous transmission from 2UEs on

same time-frequency resource Each UE with one Tx antenna Uplink reference signals are coordinated

between UEs

Pre-coding

SICreceiver

S1

S2

Sr

r1

r2

r

H

eNodeB UEPMI, RI, CQI


LTE Multiple antenna schemeLTE channels Multiple Antenna Schemes comments

open-loop spatial multiplexing large delay CDD/ SFBC

closed-loop spatical multiplexing SU-MIMO

multi-user MIMO MU-MIMO

UE specific RS beam-forming Applicable > 4 Antennas

PDCCH SFBC

PHICH SFBC

PCFICH SFBC

PBCH SFBC

Sync Signals PVS

receiver diversity MRC/IRC

multi-user MIMO MU-MIMO

PUCCH receiver diversity MRC

PRACH receiver diversity MRCUL control channel

UL data channel PUSCH

open-loop transmit diversityDL control channel

DL data channel PDSCH


Synchronization and Cell Search LTE synchronization design considerations:

high PSR (Peak to side-lobe ratio: the ratio between the peak to the side-lobes of its aperiodic autocorrelation function) to ease time-domain processing

low PAPR for coverage Generalized Chirp Like (GCL) sequences overwhelm Golay and Gold sequences!

Synchronization signals PSS: length-63 Zadoff-Chu sequences

Auto-correlation/cross-correlation/hybrid correlation based detection SSS: an interleaved concatenation of two length-31 binary sequences

Alternative transmission (SSS1 and SSS2) in one radio frame

0 1 2 3 4 5 6 7 8 91 radio frame = 10 ms SSS

PSS

3GPP TS 36.211 physical channels and modulation Cell search in 3GPP LTE systems, by Yingming Tsai etal, JUNE 2007 | IEEE VEHICULAR TECHNOLOGY MAGAZINE


Synchronization and Cell Search LTE synchronization design considerations:

high PSR (Peak to side-lobe ratio: the ratio between the peak to the side-lobes of its aperiodic autocorrelation function) to ease time-domain processing

low PAPR for coverage Generalized Chirp Like (GCL) sequences overwhelm Golay and Gold sequences!

Synchronization signals PSS: length-63 Zadoff-Chu sequences

Auto-correlation/cross-correlation/hybrid correlation based detection SSS: an interleaved concatenation of two length-31 binary sequences

Alternative transmission (SSS1 and SSS2) in one radio frame

0 1 2 3 4 5 6 7 8 91 radio frame = 10 ms SSS

PSS

62 CentralSub-carriers

3GPP TS 36.211 physical channels and modulation Cell search in 3GPP LTE systems, by Yingming Tsai etal, JUNE 2007 | IEEE VEHICULAR TECHNOLOGY MAGAZINE


Synchronization and Cell Search Hierarchical cell ID(1 out of 504):

Cell ID = 3* Cell group ID + PHY ID :

PSS structure

SSS structure

)2()1(3 IDIDCELLID NNN +=

=== ++

+

61,...,32,31

30,...,1,0)(63

)2)(1(

63)1(

ne

nend nnuj

nunj

u

25=29=34=

0)2( =IDN1)2( =IDN2)2( =IDN

IFFT

0pssx1pssx62pssx

CPinsertion

PSS sequences f

62 sub-carriers excluding DC carrier

f

slot 0 slot 10

odd sub-carriers

even sub-carriers

+

)0(0mS

0C

1SSC

+

)1(1mS

1C

2SSC

+

)0(1mZ

+

)1(1mS

0C

1SSC

+

)0(0mS

1C

2SSC

+

)1(1mZ

The indices (m0, m1) define the cell group identity.


LTE Cell Search Vs WCDMA cell search PSS detection

Slot timing Physical layer ID (1 of 3)

SSS detection Radio frame timing Cell group ID (1 of 168) CP length

PBCH decoding PBCH timing System information access

P-SCH detection Slot boundary

S-SCH detection frame timing code group ID

CPICH detection Cell-specific scrambling code

identified

BCH reading

cell searching in WCDMA,Sanat Kamal Bahl, IEEE Potential 2003;


LTE uplink SC-FDMA: fundamental uplink radio parameters are aligned with

downlink scheme, e.g frame structure, sub-carrier spacing, RB size.

Multiplexing of uplink data and control information Combination of FDM and TDM are adopted in LTE uplink

Uplink transmission are well time-aligned to maintain orthogonality (no intra-cell interference)

PRACH will not convey user data like WCDMA does, but serve to obtain uplink synchronization


Fundamental uplink transmission scheme

Uplink transmission frame aligned with downlink parameterizationto ease UE implementation.

f

1 radio frame = 10 ms

=

,7.4,2.5

ss

Tcp

66.7 us

66.7 us

Tcp

Tcp-e

for first OFDM symbol

for remaining symbols

seTcp 7.16_ =

1 slot = 0.5 ms =7 OFDM symbols

1 sub-frame = 1 ms

under eNodeB scheduling


Uplink reference signal Uplink reference signals

Mostly based on Zadoff-Chu sequences (cyclic extensions) Pre-defined QPSK sequences for small RB allocation

Demodulation Reference Signal (DRS) in a cell Each cell is assigned 1 out of 30 sequence groups Each sequence group contains 1(for less than 5 RB case) or 2 (6RB+ case) RS

sequence across all possible RB allocations Sequence-group hopping is configurable in term of broadcasting information where the

hopping pattern is decided by Cell ID Cyclic time shift hopping applies to both control channel and data channel

DRS on PUSCH

DFT(size M)

OFDMmodulator add CP

block of data symbols

00

00

One DFTS-OFDM symbol

Instantaneous bandwidth

(M sub-carriers)

interference randomization

across intra-cell and inter-cells

R

S sequence3GPP TS 36.101 physical channels and modulation section 5.5.1


Uplink reference signal DRS on PUCCH

See next slides

Sounding Reference Signal (SRS) Not regularly but allows eNodeB to estimate uplink channel quality at alternative

frequencies UEs SRS transmission is subject to network configuration Location: always on last OFDM symbol of a sub-frame if available

one sub-frame

wideband, non-frequency hopping SRS narrowband, frequency hopping SRS


Uplink control channel transmission - PUCCH Uplink control signaling

Data associated: transport format, new data indicator, MIMO parameters Non-data associated: ACK/NACK, CQI, MIMO codeword feedback

Channelization In the absence of uplink data transmission: in reserved frequency region on

band edge In the presence of uplink data transmission: see multiplexing with data on

PUSCH

f

downlinkdata transmission

downlinkdata transmission

Uplink control TDM

with data

standaloneuplink control

no explicit tranmissionfrom UE as it follows eNodeB scheduling!

..

1 ms sub-frame

Control region 1 Control region 2

total uplink system bandwidth


Uplink control channel transmission - PUCCH

To cater for multiple downlink transmission mode, while preserving single-carrier property in uplink, multiple PUCCH formats exist.

PUCCH is thus mainly classified by PUCCH format 1 & 2 PUCCH format 1/1a/1b: 1 or 2 bits transmitted per 1ms, for ACK/NACK/SR PUCCH format 2/2a/2b: up to 20 bits transmitted per 1ms, for CQI/PMI/RI

..

1 ms sub-frame

CQI referencesignal

..

1 ms sub-frame

ACK/NACK referencesignal


Multiuser transmission on PUCCH In PUCCH format 1, multiple PUCCHs are distinguished by cyclic

shift of ZACAC sequences plus orthogonal cover sequence In PUCCH format 2, multiple PUCCHs are distinguished by cyclic

shift of ZACAC sequences.

IFFT IFFT IFFT IFFT

RS RS RS

ACK/NACK bit

BPSK/QPSK

Length-12 phaserotated sequence

IFFT IFFT IFFT IFFT

RS RS

channel status report

QPSK

Length-12 phaserotated sequence

IFFTLength-4 Walsh sequence

1 slot = 0.5 ms 1 slot = 0.5 ms


Uplink data transmission - PUSCH In case of PUSCH available, control signaling is multiplexed with

data on PUSCH. To cater for radio channel variation, link adaptation applies to data part Control signaling does not adopt adaptive modulation but the size of REs

(resource elements) can change w.r.t varying radio condition

Turbocoding

Ratematching

MUXConv

codingRate

matching

Blockcoding

Ratematching

basebandmodulation IFFTDFT

QPSKBlockcoding

DFTS-OFDMmodulation

UL-SCH

CQI,/PMI

RI

ACK/NACK

CQI/PMI

RSACK/NACK

RIPUSCH data

t


Uplink data transmission - PUSCH UL-SCH processing chain

No Tx diversity/spatial multiplexing as downlink does PUSCH frequency hopping (on slot basis)

Subband-based hopping according to cell-specific hopping patterns Hopping based on explicit hopping information in scheduling grant

Transport blockfrom MAC @UE

CRC

Segmentation

FEC

RM+HARQ

Scrambling

ModulationUE-specific,

bit-level scrambling To DFTS-OFDM and map to

assigned frequency resorurce


Random Access LTE random access serves to obtain uplink synchronization, not

to carry data. Contention-based random access: preambles based on ZC sequences Contention-free random access: faster with reserved preambles (e.g, for

handover)

Random access resources 64 preambles classified into 3 parts:

RA area: 1 in every 1~20 ms(configurable)

UE eNodeB

RA preambles

RA response (timing adjustment, UL grant)

UE terminal ID

Contention resolution

Preamble set #0 Preamble set #1 reserved

10 ms frame

1ms

6 RBs random access area

NAS UE ID RRC

Connection Request

temporary C-RNTI; timing advance;

initial uplink grant

early contention resolution


Random Access PRACH structure

Preamble sequence: cyclic shifted sequences from multiple root ZC sequences CP: facilitates frequency-domain prcoessing at eNodeB Guard time: to handle timing uncertainty

PRACH format options

Other users CP Preamble Sequence Guard time Other usersnear user

Other users CP Preamble Sequence Other users

timinguncertainty

far user

preamble format RA window (ms) Tcp length (ms) Tseq length (ms) Typical usage

0 1 0.1 0.8 for small~medium cells (up to ~ 14 km)

1 2 0.68 0.8 for larget cells(up to ~ 77km) without link budget problem

2 2 0.2 1.6 for medium cells(up to ~ 29km) supporting low data rates

3 3 0.68 1.6 for very large cells(up to ~ 100km)


Layer 1 procedures power control

Uplink power control WCDMA power control is continuous at 1500Hz; while LTE runs power control

slower at 200Hz Based on open-loop setting while assisted by close-loop adjustment Independent power control on PUCCH and PUSCH respectively

PUCCH power control

PUSCH power control Independent of PUCCH power control UE Power Headroom in use to indicate the true desired Tx power

To increase uplink data rate, LTE would increase users bandwidth rather than increase Tx power!{ }+++= formatDLT PLPPP 0max ,min

{ } ++++= MCSDLT MPLPPP )(log10,min 100max


Layer 1 procedures Timing Alignment To maintain uplink intra-cell orthogonality, timing alignment is

necessary. The further away from eNodeB, the earlier the UE transmits. Configurable by eNodeB at granularity of 0.52us from 0 ~0.67 ms

(corresponding to max cell radius of 100km)

Tp1

Ta1

Tp2

Ta2

Timing aligned uplink reception at eNodeB for

different users

Tx

Rx

Tx

Tx

Rx

Rx


Backup - OFDMA Vs SC-FDMA

Channel equalizer: OFDMA: divides wideband into multiple narrow flat-fading sub-

bands hence equalization done on each sub-band is sufficient. SC-FDMA: frequency domain equalization on the whole group

bandwidth of sub-carriers in use.

DFT Sub-carrierde-mapping

equalizer

equalizer

equalizer

Detect

Detect

Detect

DFT Sub-carrierde-mapping

equalizer IDFT detect

OFDMA:

SC-FDMA:


Backup - OFDMA Vs SC-FDMA

PAPR: CM: a better measure of UE PA back-off

3G evolution, HSPA and LTE for mobile broadband(2nd edition), ISBN: 978-0-12-374538-5, page.118,

))((

)(2

2

tsE

tsPAPR =

85.15237.1)(log20)(

)(log203

103

3

10 =

= rmsnrmsrefrmsn

vF

vv

CM

SC-FDMA has around 2dB CM gain against OFDMA!


Backup - Zadoff-Chu sequence characteristics

Zadoff-Chu sequences

Property of ZC sequences: Constant amplitude, even after Nzc-point DFT. Ideal cyclic auto-correlation Constant cross-correlation[=sqrt(1/Nzc)], assuming Nzc is a prime number

=== ++

+

61,...,32,31

30,...,1,0)(63

)2)(1(

63)1(

ne

nend nnuj

nunj

u

Polyphase codes with good periodic correlation properties, J.D.C.Chu, IEEE trans on Informaiton theory, ,vol.18, pp.531-532, July 1972Phase shift pulse codes with good periodic correlation properties, R.Frank,S.Zadoff and R.Heimiller, IEEE Trans on Information Theory, Vol 8, pp 381-382, Oct 1962.


Backup mobility: intra-MME handover

UE Source eNodeB Target eNodeB EPC

Measurement reporting

Handoverdecision

Handover requestAdmission

control

Handover request Ack

RRC Connection ReconfigurationDetach from

old cellDeliver packets

to target eNodeB

Data forwardingbuffer packets

From source eNodeB

RRC Connection Reconfiguration completePath switch procedure

UE context releaseFlush buffer

Release resource

LTE tutorial - Looking forward beyond HSPA+ OutlineBeyond HSPA evolution 3GPP pathLTE - backgroundLTE - backgroundLTE feature overviewLTE spectrum flexibilityLTE basic parametersLTE Peak throughput w.r.t UE categoriesLTE UE categoryChannel dependent schedulingSoft (fractional) frequency reuseE-UTRAN overviewE-UTRAN architectureE-UTRAN architectureE-UTRAN radio protocolE-UTRAN radio channelsE-UTRAN bearersE-UTRAN Control plane stackE-UTRAN User Plane StackRadio resource managementE-UTRAN mobilityOverview of a PS call control planeOverview of a PS call control planeOverview of a PS call user planeOverview of a PS call user planeLTE initial deployment scenarioLTE initial trial performanceMacro Cellular network: peak rate Vs average rateLTE initial trial performanceOFDMA and SC-FDMA rationaleOFDM fundamentals frequency spectrumOFDM fundamentals multicarrier modulationOFDM fundamentals- Cyclic PrefixOFDM fundamentals- Cyclic PrefixOFDM fundamentals general link level chainsOFDM fundamentals frequency domain equalizerOFDM fundamentalsOFDM fundamentals downlink OFDMAWideband single carrier transmission - frequency domain equalizer (SC-FDE)SC-FDMA multiple access with FDESC-FDMA multiple access with SC-FDESC-FDMA multiple access with SC-FDESC-FDMA multiple access with FDEOFDMA Vs SC-FDMAOFDMA Vs SC-FDMALTE Physical layer and transmission proceduresLTE physical layer a vertical viewLTE physical layer - a horizontal viewFundamental Downlink transmission schemeSystem information broadcastDownlink control channels PCFICH,PHICHDownlink control channels - PDCCHDownlink control channels PDCCHDownlink control channels - PDCCHDownlink shared channel: PDSCHDownlink reference signalsLTE Multiple antenna scheme LTE Multiple antenna schemeLTE Multiple antenna schemeSynchronization and Cell SearchSynchronization and Cell SearchSynchronization and Cell SearchLTE Cell Search Vs WCDMA cell searchLTE uplink Fundamental uplink transmission schemeUplink reference signalUplink reference signalUplink control channel transmission - PUCCHUplink control channel transmission - PUCCHMultiuser transmission on PUCCHUplink data transmission - PUSCH Uplink data transmission - PUSCHRandom AccessRandom AccessLayer 1 procedures power controlLayer 1 procedures Timing AlignmentBackup - OFDMA Vs SC-FDMABackup - OFDMA Vs SC-FDMABackup - Zadoff-Chu sequence characteristicsBackup mobility: intra-MME handover

lte

Documents

hspa lte

hspa hspa evolutiondl

lte tutorial

lte background motivation

lte specification process

hspa success story274

lte feature overview

lte umts forum white