02 LTE Air Interface and Physical Layer

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

47pt

www.huawei.com

LTE Air Interface and

Physical Layer

Contents

• Key LTE PHY Technologies

• LTE PHY Structure Overview

• Downlink Physical Channels and Signals

• Uplink Physical Channels and Signals

HUAWEI TECHNOLOGIES CO., LTD. Page 3Huawei Confidential

Key LTE PHY Technologies

Single Carrier Sub-frame

Frequency

Time

Time frequency resource for User 1



System Bandwidth Sub-carriers

Sub-frame

Frequency

Time




System Bandwidth

MIMO

OFDMA

LTE

SC-FDMA

64QAMMultiple-Input Multiple-Output Adaptive Modulation and Coding (AMC)

up to 64QAM

Orthogonal Frequency

Division Multiple AccessSingle-Carrier Frequency

Division Multiple Access


OFDM Theory

• Serial data stream mapped onto many parallel sub-carriers� Lower symbol rate and longer symbols vs. single-carrier

• The sub-carriers are orthogonal� At each sub-carrier center, neighboring sub-carriers ideally have zero amplitude

� This removes need for inter-sub-carrier guard bands

• OFDM leverages the Discrete Fourier Transform (DFT) to synthesize and recover the signal� Fast Fourier Transformation (FFT/IFFT) algorithm reduces computational complexity

Frequency

OFDM Sub-Carriers


OFDM Tx/Rx Structure

Serial to

Parallel …

s[n] IFFT

....

....

....

… …

Parallel

to Serial

Add

Cyclic

Prefix

s(t)

Constellation Mapping

Parallel

to Serial …

s[n] FFT

....

....

....… …

Serial to

Parallel

Remove

Cyclic

Prefix

s(t)

Symbol Detection

Transmitter

Receiver

bit-stream in

bit-stream out

OFDM signal out

OFDM signal in


OFDM Cyclic Prefix (CP)

TTCP

τmax

ISI-free symbol

start region

T

Multi-path arrivals

T – FFT interval

TCP – cyclic prefix guard period

T + TCP – OFDM symbol period

τmax – max multi-path delay

• CP adds overhead but provides inter-symbol interference (ISI) mitigation

• LTE defines normal CP of 4.7µs and extended CP of 16.7µs


Wireless Technology PHY Comparison

Channel or Subcarrier

SpacingSymbol PeriodTechnology

66.7 µs

0.26 µs

(1/3.84Mcps)

15 kHzLTE

5 MHzUMTS WCDMA

• Symbol period is roughly 1/(channel spacing) for single-carrier

systems, 1/(subcarrier spacing) for OFDM

• LTE: Long OFDM symbol periods and CP mitigate ISI without

equalization

• UMTS: Short symbol periods relative to delay spread requires

channel equalization (i.e. rake receiver) to mitigate ISI

• Rake receiver adds cost/complexity


OFDM Advantages

• Low-complexity UE receiver design

� Efficient IFFT/FFT processing

� Traditional equalizer not needed

• Robust fading channel performance

� Long symbol time with cyclic prefix provides tolerance to multi-

path delay spread without equalization

• Each sub-carrier modulated independently

� Allows MCS adjustment across frequency to match channel

conditions

• Improved MIMO performance due to flat frequency

response per subcarrier


OFDM Limitations

• Peak Power Problem

� The OFDM signal has a large peak to average power ratio (PAPR)

� Higher power amplifiers are needed leading to increased cost and

linearization requirements and decreased power efficiency

� Low noise receiver amplifiers need larger dynamic range

• Inter-Carrier-Interference (ICI)

� Due to narrow subcarrier spacing, frequency offsets, phase noise,

and Doppler spread destroy orthogonality and create ICI

� OFDM design parameters trade off robustness to fading (delay

spread) and Doppler (velocity)

• Capacity and Power Loss Due to Cyclic Prefix

� Cyclic prefix consumes bandwidth and transmit power


Downlink based on OFDMA

• Users are multiplexed onto time and frequency OFDM resources

• Frequency-diverse scheduling helps maximize spectral efficiency from a

system perspective

Sub-carriers

TTI： 1ms

Frequency

Tim e




System Bandwidth

Sub-band： 12Sub-carriers

Sub-frames

Groups of subcarriers


SC-FDMA

Serial toParallel

Converter

Incoming BitStream

m1 bitsBit to

ConstellationMapping

Bit toConstellation

Mapping

Bit toConstellation

Mapping

m2 bits

mMbits

x(0,n)

x(1,n)

x(M- 1,n)

Serial toParallel

Converter

Incoming BitStream

m1 bitsBit to

ConstellationMapping

Bit toConstellation

Mapping

Bit toConstellation

Mapping

m2 bits

mMbits

x(0,n)

x(1,n)

x(M- 1,n)

N-point

IFFTAdd cyclic

prefix

Parallel to

Serialconverter

M-point

FFT

of

1f

1−Mf

2−Mf

12/ −Mf

2/Mf

00

0

0

0

0

00

0

0

Channel BW

Additional step

• Single Carrier Frequency Division Multiple Access (SC-FDMA) is a form of DFT Spread-OFDM with adjacent subcarrier mapping� An additional DFT spreads information across all subcarriers� Contiguous subcarrier allocation for IFFT results in single-carrier signal

• Advantage: The single-carrier signal has generally lower peak-to-average power ratio (PAPR) which allows use of lower cost UE power amplifier (PA) and reduces UE power consumption

• Disadvantage: Single-carrier modulation results in ISI and requires equalization

DFT


Uplink based on SC-FDMA

Single Carrier Sub-frame

Frequency

Time




System Bandwidth

• SC-FDMA is used for uplink in LTE

• As with OFDMA DL,

• Users are multiplexed onto time and frequency OFDM resources

• Frequency-diverse scheduling helps maximize spectral efficiency

from a system perspective

Sub-frames


Flexible Scheduler

FrequencyFrequencyFrequencyFrequency

TimeTimeTimeTime

Benefits: Increased radio link reliability, cell capacity and coverage

• Different users experience different fading in time-frequency domain

• OFDMA and SC-FDMA in LTE support flexible DL/UL scheduling to

achieve frequency-selective scheduling gain

SINRUser 1

User 2Optimal allocation


MIMO

• MIMO adds spatial dimension to the wireless PHY interface

• Beamforming (BF) and Transmit Diversity (TD)

� Single-stream: improves SINR

� Mainly for improving coverage through the parallel transmission of

differently weighted (BF) or coded (TD) versions of a single stream

• Spatial Multiplexing (SM)

� Multiple-streams: power is shared (lower SINR per stream)

� Improves capacity through the parallel transmission of multiple

spatial streams on the same time-frequency resources


MIMO Mode Selection

SINR

Throughput

SINR-limited

(best to use beamforming

or transmit diversity)

Bandwidth-limited(best to use spatial-multiplexing)

• Low SINR: increasing SINR via BF or TD provides improved

range and/or throughput gain at the cell edge

• High SINR: throughput saturates so SM provides best

throughput gain despite lower SINR per stream

Shannon Channel Capacity Theorem

)/1(log2 NSBC +=


MIMO Impact on Throughput and Coverage

• Channel rank dictates the number of simultaneous streams

that the channel can support

� Rank-1 transmission via BF or TD improves coverage

� Spatial Multiplexing (rank > 1) increases peak rate

Throughput vs. Coverage with 4x4 MIMO


DL MIMO

codeword

S

F

B

C

Mod

Rank = 1

Rank > 1

UE

UE

UE

Pre-coder

(3) Precoding matrix indication (PMI),rank indication (RI)

(1) Reference symbols

(2) U

Es

dete

rmin

e b

est p

reco

din

gm

atrix

Transmit Diversity via SFBC

Open-Loop Spatial Multiplexing Closed-Loop Spatial Multiplexing

(Single or Multi-User)

Pre-codercodeword Mod

Beamforming

(codebook or non-codebook-based)

codeword Mod

codeword Mod

Layer 1, CW1

Layer 2, CW2

codeword Mod

codeword Mod

Layer 1, CW1

Layer 2, CW2

• LTE eNB has up to 4 Tx chains• LTE UE has up to 4 Rx chains

SU

MU

UE Feedback


UL MIMO

1x2 SIMO MRC Rx Diversity 1x2 MU MIMO (with UE pairing)

• Single-Layer transmission at UE

� Optional switched Tx-Diversity

• Maximum ratio combining

(MRC) at eNB increases uplink

range/sensitivity

• “Virtual” MIMO on UL with single-transmitter UEs

• UEs with orthogonal channels are paired

• Allows resource reuse in highly-loaded scenarios

• Degrades single-user performance due to interference

•LTE UE has 1 Tx chain• With optional switched Tx diversity

•LTE eNB has up to 4 Rx chains


Key LTE-Advanced PHY Technologies

CoMP

CA

LTE-A

Relay

Coordinated Multi-Point Transmission and Reception

In-Band Relay

Carrier Aggregation

High-Order (8x8) MIMO Support

RF

/IF

RF

/IF

RF

/IF

RF

/IF

RF

/IF

RF

/IF

RF

/IF

RF

/IF

Base Band

LT E C a rrier 1 f

LT E C a rrier 2 LT E C a rrier 3

f

B and 1

C o m bine d LT E C ar r ie r 1 a nd LT E C a rr ier 2

LT E -A C a rrier LT E C a rrier 3

f

O p era to r 2

LT E C a rr ier 2

f

B a n d 1

C o m b in e d LT E C a r rier 1 a n d LT E C a r rier 3

O p era to r 1

LT E C a rr ier 1

O p e ra t or 1

LT E C a r rie r 3

O p era to r 2

LT E C a rr ier 2

O p era to r 1

LT E -A C a rr ie r

O p era tor 1

LT E - A C a rr ier

LT E C a r r ie r 1 f

LT E

C a r r ie r 2

f

B a n d 1 B a n d 2

LT E - A

C a r r ie r

LT E -A

C a r r ie r

LT E C a r r ier 1 in b a n d 1 C o m b in e d w it h LT E ca r r ier 2 in ba n d 2

Enhanced MIMO

Improved MU-MIMO UL SM-MIMO


LTE-A Benefits

• CoMP

� DL: Controlled/canceled interference – better signal quality

� UL: Higher order diversity and aperture gain (soft combining)

• Relay

� Improved coverage and data rates, especially at edge

• Carrier Aggregation

� Higher throughput and peak data rates

� Asymmetric UL/DL

� Better utilization of discontinuous or multi-band spectrum resources

• Enhanced MIMO

� Up to 8x8 MIMO for higher throughput and enhanced coverage

� Improved DL MU-MIMO performance by addressing R8 limitations

� UL SM-MIMO for higher UL data rates


Section Review – Key Takeaways

• OFDM

� Data multiplexed onto many narrow subcarriers

� CP and long symbol time mitigate ISI

� Good MIMO performance due to flat frequency response per subcarrier

• OFDMA DL

� Low-complexity UE receiver design with robust fading channel performance, especially with MIMO

� Flexible MCS adjustment and UE allocation across time and frequency (sub-carriers) enhances spectral efficiency

• SC-FDMA UL

� Similar benefits as OFDMA but lower PAPR allows lower cost UE power amplifier and reduces UE power consumption

� Some additional receiver complexity required at eNB

• MIMO

� Spatial multiplexing at high SINR increases capacity

� Transmit diversity or beamforming at low SINR enhances range

Contents






LTE OFDM Parameters

4.7 or 16.7 µsCyclic Prefix Time

71.4 or 83.4 µsTotal Symbol Time

LTETheoryParameter

1.4, 3, 5, 10, 15, 20 MHzTotal Bandwidth

72-1200Number of Subcarriers

15 kHz (k=1)Subcarrier Spacing

66.7 µsUseful Symbol Time uT

uTkf /=∆

fNB ∆⋅=

N

CPT

CPutotal TTT +=

. . .

. . .

time

fre

qu

en

cy

totalTf∆

1

2

3

. . .

N


Frame Structure

#0 #1 #2 #3 #19

One slot, Tslot = 15360×Ts = 0.5 ms

One radio frame, Tf = 307200×Ts=10 ms

#18

One subframe

=×= slotsubframe TT 2 1 ms

• One subframe (1 ms) is an LTE transmission time interval (TTI)


Resource Grid One downlink slot, Tslot

Resource element

OFDM symbolsDLsymbN OFDM symbolsDLsymbN

Nsc

subca

rrie

rsR

B

Resource block

RBsc

DLsymb NN × resource elements

NR

BDL

subcar

riers

NscR

B×fr

eq

uen

cy

time

(RB)


UL/DL Resource Block

• A physical resource block is defined as consecutive

OFDM symbols in the time domain and consecutive

subcarriers in the frequency domain

• Multi-Media Broadcast over a Single Frequency Network

(MBSFN) combines 7.5kHz subchannel spacing with

double length symbol time and CP to handle greater delay

spread (DL only)

symbNRBscN

324

6Extended cyclic prefix

712

Normal cyclic prefix

ConfigurationDLsymbN

kHz 15=∆f

kHz 5.7=∆f

RBscN

kHz 15=∆f

MBSFN-

dedicated

cell

UL

symbN

-

6

7


LTE Numerology

120090060030018072Number of

Subcarriers

100755025156Number of

Resource Blocks

204815361024512256128FFT Size

201510531.4Transmission BW

(MHz)



• LTE frame structure

� 0.5ms slot

� 1ms subframe

� 10ms frame

• Resource allocation

� RB is the minimum resource allocation

� Typically 7 symbols (in time) x 12 subcarriers (in frequency)

• Supported system bandwidths

� 1.4, 3, 5, 10, 15, and 20MHz

Contents






DL Physical Channels and Signals

• Physical channels

� PDSCH: Physical Downlink Shared Channel

� PBCH: Physical broadcast channel

� PMCH: Physical multicast channel

� PDCCH: Physical Downlink Control Channel

� PCFICH: Physical control format indicator channel

� PHICH: Physical Hybrid ARQ Indicator Channel

• Reference Signal (RS)

� Cell specific RS

� UE-specific RS

� MBSFN RS

• Synchronization Signal (SCH)

� Primary Synchronization Signal (P-SCH)

� Secondary Synchronization Signal (S-SCH)


Synchronization and System Information

• SCH used for:

� Symbol synchronization

� Frame synchronization

� Cell-ID determination

• BCH indicates:

� Basic L1/L2 system parameters

� Downlink system bandwidth

� Reference-signal transmit power

� Multi-media Broadcast over a Single Frequency Network

(MBSFN)-related parameters

� Number of transmit antennas

� HARQ resource allocation

SCH

10-MHz bandwidth

20-MHz bandwidth

5-MHz bandwidth

1.25-MHz bandwidth

2.5-MHz bandwidth

1.4 MHz bandwidth

3 MHz bandwidth

5 MHz bandwidth

10 MHz bandwidth

20 MHz bandwidth

SCH / BCHSCH

10-MHz bandwidth

20-MHz bandwidth

5-MHz bandwidth

1.25-MHz bandwidth

2.5-MHz bandwidth

1.4 MHz bandwidth

3 MHz bandwidth

5 MHz bandwidth

10 MHz bandwidth

20 MHz bandwidth

SCH / BCH

SCH/BCH each occupy 72 center subcarriers

regardless of system bandwidth


Time Structure of SCH/BCH

• Primary and secondary SCH (P-SCH, S-SCH) are transmitted in

consecutive OFDM symbols in the 1st and 6th subframes (every

5ms) of each frame

• BCH is transmitted in four consecutive OFDM symbols in the

first subframe of every frame, but it is only updated every 40ms

BCH


DL Reference Signals

• Downlink reference signals are used for estimation of

channel gain (for symbol demodulation) and channel

quality (for channel quality feedback to eNB)

• Ports 0-3:

� Cell-specific reference signals

� Associated with non-MBSFN (i.e. unicast) transmission

� Support for one, two, or four antenna port configuration

• Port 4: MBSFN reference signals

• Port 5: UE-specific reference signals used for beamforming


Cell-Specific Reference Signals

0=l

0R

0R

0R

0R

6=l 0=l

0R

0R

0R

0R

6=l

0=l

0R

0R

0R

0R

6=l 0=l

0R

0R

0R

0R

6=l 0=l

1R

1R

1R

6=l 0=l

1R

1R

1R

1R

6=l

0=l

0R

0R

0R

0R

6=l 0=l

0R

0R

0R

0R

6=l 0=l

1R

1R

1R

1R

6=l 0=l

1R

1R

1R

1R

6=l 0=l 6=l 0=l

2R

6=l 0=l 6=l 0=l 6=l

2R

2R

2R

3R

3R

3R

3R

� Example RS mapping for normal CP

� Other antenna ports silent during RS

transmission

� Reduced RS density on ports 2 and 3On

e a

nte

nn

a p

ort

Tw

o a

nte

nn

a p

ort

sF

ou

r a

nte

nna

port

s

l=0 l=6 l=0 l=6

l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6

l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6

Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3

Resource element (k,l)

Not used for transmission on this antenna port

Reference symbols on this antenna port

even numbered slots

odd numbered slots


Cell-Specific RS Frequency Shift

f

Cell specific frequency shift

Cell 0 Cell 1 Cell 5

6modcell

IDshift Nv =

• RS mapping to resource elements

� To reduce RS interference between adjacent cells, a cell specific frequency shift is applied

� There are 6 shift values since the frequency interval of RS is 6 subcarriers

…


DL Control Signaling

• Control region is 1-4 OFDM symbols at the beginning of each subframe

• PCFICH – Physical Control Format Indicator Channel

� # of OFDM symbols of control region

• PHICH – Physical Hybrid ARQ Channel

� ACK/NACK signalling

• PDCCH – Physical Downlink Control Channel

� Scheduling

� UL power control

freq time

Control Region Data Region

OFDM symbols1 2 3 4 5 6 7 8 9 10 11 12 13 14

- PCFICH mini-CE

t2 t4 t1 t2 t3 t1

Mini-CE Boundary - A/N mini-CE

(symbol 1,2)

t1 t3 t2 t1 t4 t2 - Data symbols

RB1

t2 t4 t1 t2 t3 t1 - mini-CE for CCE1

- mini-CE for CCE2

RB Boundary t1 t3 t2 t1 t4 t2 - mini-CE for CCE3

t2 t4 t1 t2 t3 t1 - mini-CE for CCE4

Mini-CE Boundary

(symbol 3) - Unassigned mini-CE

t1 t3 t2 t1 t4 t2

RB2 t1 - RS for TX antenna 1

t2 t4 t1 t2 t3 t1

t2 - RS for TX antenna 2

t1 t3 t2 t1 t4 t2 t3 - RS for TX antenna 3

t4 - RS for TX antenna 4. .. .. .

1

t2 t4 t1 t2 t3 t1 2

3

4

t1 t3 t2 t1 t4 t2 5

RB6 6 12 subcarriers

7

t2 t4 t1 t2 t3 t1 8

9

10

t1 t3 t2 t1 t4 t2 11

12

PCFICH

PHICH

Data

REG for CCE1

REG for CCE2

REG for CCE3

REG for CCE4

Unassigned REG

Port 1 RS

Port 2 RS

Port 3 RS

Port 4 RS

1 RB = 12 sub-carriers

REG Boundary

REG Boundary

PDCCH


PDCCH CCE Aggregation

…

…

…

…

1 CCE

2 CCE

4 CCE

8 CCE

1 2 3 4 5 6 7 8 10 11 12 13 14 150 9

• CCE aggregation is a form of repetition coding

• The same PDCCH information is coded across 1, 2, 4, or 8 CCEs

• eNB adjusts CCE aggregation based on DL SINR operating point

• Tree-based aggregation supports blind decoding search

� 1-CCE aggregation can start on any CCE position (i=0,1,2,3,4,...)

� 2-CCE can start only on even numbered locations (i=0,2,4,6,...)

� 4-CCE on every fourth (i=0, 4, 8, ...)

� 8-CCE on every eight position (i=0, 8, ...)

frequency



• SCH

� Symbol synchronization

� Frame synchronization

� Cell-ID determination

• BCH

� Basic L1/L2 system parameters such as: system bandwidth, reference-

signal transmit power, and number of transmit antennas

• RS

� Ports 0-3: Cell-specific, support MIMO, unique time/frequency location

per antenna port

� Ports 4 and 5: MBSFN and UE-specific for beamforming

• Control Signaling

� Control region in first 1-4 OFDM symbols per subframe

� Carries ACK/NACK, UL/DL data/paging scheduling, UL power control

� PDCCH variable aggregation based on UE SINR operating point

Contents






UL Physical Channels and Signals

• Physical channels

� PUSCH: Physical Uplink Shared Channel

� PUCCH: Physical Uplink Control Channel

� PRACH: Physical Random Access Channel

• Reference signals

� Demodulation Reference Signal (DM RS)

� Sounding Reference Signal (SRS)


UL Reference Signals

• Demodulation (DM) RS used for estimation of UL channel

gain and channel quality from active UEs

• DM RS are transmitted with data in the 4th and 11th SC-

FDMA symbols of the subframe

• DM RS are code division multiplexed (CDM) to support MU-

MIMO and inter-sector interference

0.5 ms slot

RB 1

RB 2

RB N

• Sounding Reference Signals (SRS) used to evaluate UL

channel quality for idle/lightly loaded UEs

• SRS is in the 7th SC-FDMA symbol of the subframe and is

typically wideband (on contiguous or periodic REs)

• SRS is also CDM

…

0.5 ms slot

UE1 DM RS

UE2 DM RS

UE3 DM RS

UE4 SRS

1 ms subframe

… …UE2 allocation

UE1 allocation

UE3 allocation


Uplink Control Signaling• Channel measurement indications from UE

� Channel quality indicator (CQI) – Value that points to a modulation/coding index in a 4-bit CQI table (implies SINR)

� Precoding matrix indicator (PMI) – Value that corresponds to the suggested precoding matrix codebook index

� Rank indication (RI) – Indicates the rank (# of layers) the channel can support

• Measurement indications are transmitted

� Periodically on PUCCH (alone) or PUSCH (multiplexed with data)

� Aperiodically on PUSCH (alone or multiplexed with data)

• Other signaling:

� HARQ acknowledgement (ACK/NACK) from higher layers

� Scheduling request indication (SRI) from higher layers

Wideband-onlyWideband-onlyRI

Wideband or subbandWideband-onlyPMI

Wideband or subbandWideband or subbandCQI

PUSCHPUCCH


Physical Resources for Control Signaling

• Control signaling uses reserved frequency regions at edges of BW

• A “control channel resource” is defined as N=12 subcarriers (an RB) in two consecutive 0.5ms slots located at opposite ends of the BW for frequency diversity

• Control signaling is CDM with multiple users sharing the resources via orthogonal

spreading codes

• PUCCH can cause and suffer from adjacent channel interference issues

� Especially in 700MHz band (shared with DTV, public safety, and MediaFLO)

� One solution is over-provisioning to push PUCCH allocation towards inner

subcarriers, but this hurts capacity

N=12 subcarriers

0.5ms slot 0.5ms slot

Another control channel resource

Spectr

um

allo

cation:

Mre

sourc

e b

locks

One control channel resource

… …

Slot structure for ACK/NAK

RS RS RS

0.5ms slot

RS locations for control signals

(transmitted on PUCCH)

Slot structure for CQI

RS RS

0.5ms slot



• UL Reference Signals

� Code division multiplexed (CDM) for orthogonality between users

� DM RS – For estimation of UL channel gain and channel quality from active UEs

� SRS – Used to evaluate UL channel quality for idle/lightly loaded UEs

• Channel measurement indications from UE

� Channel quality indicator (CQI) – Indicates the channel quality observed by the UE

� Precoding matrix indicator (PMI) – Indicates the precoding matrix suggested by the UE

� Rank indication (RI) – Indicates the rank, or # of layers, the channel can support

• Physical Uplink Control Channel (PUCCH)

� Located at upper and lower edges of bandwidth

� Shared between multiple users via CDM

� Susceptible to adjacent channel interference issues (e.g. DTV, public safety, and MediaFLO) in 700MHz band

Thank youwww.huawei.com


Backup Slides


DL OFDM/MIMO Signal Generation

• Scrambling of coded bits for each codeword

� Up to two codewords transmitted at a time

• Modulation of scrambled bits to modulated symbols (e.g. QPSK,

16 QAM, 64 QAM)

• Multi-antenna blocks

� Mapping of modulated symbols to one or more transmission layers

� Precoding of symbols on each layer onto antenna ports

• Mapping of symbols on each port to resource elements

• Generation of time domain OFDM signal on each antenna port

Multi-antenna blocks


UL SC-FDMA Signal Generation

• Similar structure as for DL OFDM signal synthesis

• Additional DFT process creates single-carrier property

Modulation

mapper

DFT

precoderScrambling

SC-FDMA

signal gen.

Resource

element mapperOFDM signal generation

New element for SC-FDMA


Transport Block SizesPRBN

TBSI 1 2 3 4 5 6 7 8 9 10

0 16 32 56 88 120 152 176 208 224 256

1 24 56 88 144 176 208 224 256 328 344

2 32 72 144 176 208 256 296 328 376 424

3 40 104 176 208 256 328 392 440 504 568

4 56 120 208 256 328 408 488 552 632 696

5 72 144 224 328 424 504 600 680 776 872

6 328 176 256 392 504 600 712 808 936 1032

7 104 224 328 472 584 712 840 968 1096 1224

8 120 256 392 536 680 808 968 1096 1256 1384

9 136 296 456 616 776 936 1096 1256 1416 1544

10 144 328 504 680 872 1032 1224 1384 1544 1736

11 176 376 584 776 1000 1192 1384 1608 1800 2024

12 208 440 680 904 1128 1352 1608 1800 2024 2280

13 224 488 744 1000 1256 1544 1800 2024 2280 2536

14 256 552 840 1128 1416 1736 1992 2280 2600 2856

15 280 600 904 1224 1544 1800 2152 2472 2728 3112

16 328 632 968 1288 1608 1928 2280 2600 2984 3240

17 336 696 1064 1416 1800 2152 2536 2856 3240 3624

18 376 776 1160 1544 1992 2344 2792 3112 3624 4008

19 408 840 1288 1736 2152 2600 2984 3496 3880 4264

20 440 904 1384 1864 2344 2792 3240 3752 4136 4584

21 488 1000 1480 1992 2472 2984 3496 4008 4584 4968

22 520 1064 1608 2152 2664 3240 3752 4264 4776 5352

23 552 1128 1736 2280 2856 3496 4008 4584 5160 5736

24 584 1192 1800 2408 2984 3624 4264 4968 5544 5992

25 616 1256 1864 2536 3112 3752 4392 5160 5736 6200

26 712 1480 2216 2984 3752 4392 5160 5992 6712 7480

# bits per transport

block (TB)

Data Rate (bits/sec) = (# bits per TB) x (# of TB/TTI)

(# of RB pairs)

QPSK

16QAM

64QAM


Cell search procedure

• Step 1: OFDM symbol synchronization

and determination of cell ID� UE uses the primary synchronization sequence to

� acquire the symbol synchronization

� identify (one of three possible) cell IDs within a cell ID group

� This is done by continuously correlating three local primary

synchronization sequences with the received signal

� Symbol synchronization is obtained by detecting a time-domain

correlation peak, and the sequence corresponding to the

correlation peak indicates one of three IDs within a cell ID group


Cell search procedure (continued)

• Step 2: Radio frame synchronization and

cell ID group detection� UE uses the secondary synchronization sequence to determine

� radio frame timing

� cell ID group index of the cell detected in the first step

� The UE correlates the received S-SCH signal with each of the

secondary candidate sequences based on the symbol

synchronization acquired in the first step to determine the cell ID

group

� During the detection of secondary synchronization channel, the

CP length may also be obtained by blind detection


DL Control Signaling (2)

• PCFICH

� Indicates size (i.e. number of OFDM symbols) of control region

• PHICH

� ACK/NACK in response to uplink transmission

• PDCCH

� Scheduling grant for uplink data transmission

� Scheduling information for downlink data transmission

� Scheduling information for paging message transmission

� Scheduling information for RACH response transmission in UL

� UL power control signaling

� Each PDCCH is made up of 1, 2, 4, or 8 control channel

elements (CCEs)


PDCCH Blind Decoding

• Common and UE-specific search spaces defined

• UE blindly attempts to decode with different aggregation

assumptions

• In early 3GPP discussions, it was agreed that a maximum

of ~40 PDCCH decoding attempts by the UE would be

acceptable

� ~10 for common search space

� ~30 for UE-specific search space


MBSFN and UE-Specific Reference Signals

0=l 5=l 0=l 5=l

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

4R

0=l

5R

5R

5R

5R

5R

5R

5R

5R

5R

5R

5R

5R

0=l 6=l6=l

MBSFN RS

(Extended CP, ) UE-Specific RS

kHz 15=∆f

02 LTE Air Interface and Physical Layer

Documents

uechannel

loop spatial

flat frequency

cell id group

ul channel

consecutive

specific reference

single frequency