Intron LTE

7/27/2019 Intron LTE

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Europe & APAC

94 Duke StreetGlasgow G4 0UWScotland UK

Tel and Fax +44 (0)141 552 8855

[email protected]

USA

200N. Westlake Blvd, #202Westlake VillageLos Angeles CA 91362, USA

Tel +1 805 413 4127

Introduction to LTEDaniel Garca-Als, Iain Stirling & Bob Stewart


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Steepest Ascent Ltd. www.steepestascent.com 2

3GPP Evolution
http://www.steepestascent.com/http://www.steepestascent.com/


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General Requirements Data rates (for a 20 MHz bandwidth):

100 Mbps in DL

50 Mbps in UL

Spectral efficiency associated to data rates shown above

5 bits/sec/Hz in DL 2.5 bits/sec/Hz in UL

Latency smaller than 5 msec for small IP packets

Voice service: at least same quality as WCDMA/HSPA


4/70 Steepest Ascent Ltd. www.steepestascent.com 4

Requirements: Mobility

Mobility :

Optimised for 0 to 15 km/h

High performance for up to 120 km/h

Should maintain a connection for up to 350 km/h (or even 500km/h for some frequency bands)



Requirements: Coverage Coverage :

Up to 5 km cell radius: meet throughput, spectral efficiency andmobility targets

Up to 30 km cell radius: slight performance degradation istolerated

Up to 100 km cell radius: operation not precluded5 km

30 km100 km



Requirements: E-MBMS Enhanced Multimedia Broadcast Multicast Service (E-MBMS):

Should provide MBMS better than Release 6;

Broadcast required spectral efficiency 1 bit/sec/Hz;

Should be possible to have MBMS only or a mixture of MBMSand non-MBMS services;

Can transmit MBMS over single frequency network (MBSFN);



Requirements: Spectrum Flexibility Duplexing modes:

FDD : Frequency Division Duplex

TDD : Time Division Duplex Example bandwidths:

1.4 MHz3 MHz5 MHz

10 MHz15 MHz20 MHz



Frame Structure FDD frame structure:

TDD frame structure:

slot (0.5ms)

0

subframe (1ms)

frame (10ms)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

subframe

frame

slot

0 2 3 4 5 7 8 9

DwPTS UpPTSGP DwPTS UpPTSGP

0 2 3 4 5 7 8 9610 msec

switch-point

5 msecswitch-point



Resource Grid Two dimensional data structure:

...

0

...

...

...

...

...

...

. . .

. . .

a slot

s u

b c a r r

i e r s

OFDM symbols

time f r e q u e n c y

0 frame1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

a resource element



Flexible Bandwidth LTE defined in a bandwidth independent way with:

resource blocks of 12 sub-carriers spaced 15 kHz

System bandwidth should be easily reconfigured

1 2

s u

b c a r r

i e r s

resourceblock

1 slot

f r e q u e n c y

time



Transmission Time Interval (TTI) TTI:

length of independently decodable transmission link

In LTE a TTI is a subframe (2 slots): 1 msec

Minimum resource that can be allocated in LTE: 1 subframe in time: 1 msec

12 subcarriers in frequency:

0 2 3 4 5 7 8 91 6

subframe: 1 msec

frame: 10 msec

180 kHz 12 15 kHz=



Multiple Access Scheme

Downlink

Orthogonal Frequency Division Multiple Access ( OFDMA ) withcyclic prefix (CP)

Uplink Single Carrier Frequency Division Multiple Access ( SC-

FDMA ) with cyclic prefix


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Adaptive Modulation and Coding Downlink modulation schemes

BPSK, QPSK, 16QAM, 64 QAM

Uplink modulation schemes

QPSK, 16QAM, 64QAM

Channel coding: Turbo coder with

coding rate of 1/3

two 8-state constituent encoders contention free internal interleaver


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MIMO Support Multiple input multiple output support (downlink only):

2 or 4 transmit antennas

2 or 4 receive antennas

Transmit diversity

Cyclic delay diversity (CDD)

Space frequency transmit diversity (transmit diversity codingapplied before IDFT)

Spatial multiplexing

Up to 4 layers or transmit streams

Codebook based precoding

Note: one antenna is used in non-MIMO mode.


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LTE Release 9 enhancements Multimedia Broadcast Multicast Service (MBMS)

completion of MBMS specification by adding related logicalchannels and clarifying physical layer details.

Home eNodeB (femtocells)

Interference scenarios such as WiFi and DECT interference;

Positioning support UE reception of satellite positioning signals (Galileo/GPS/

GLONASS)

UE reception of new downlink positioning reference signal Dual-layer UE-specific (non-codebook based) beamforming

Two new reference signals are defined (antenna ports 7 and 8)


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3GPP LTE Release 10 and beyond Has been submitted to the ITU as a candidate for IMT-Advanced;

Release 10 features:

Carrier aggregation to give up to 100MHz bandwidth;

Downlink transmission with 8 antennas and layers;

Uplink multi-antenna transmission with up to 4 antennas;

Co-ordinated Multi-Point (CoMP) transmission and reception; Relaying from Relay Nodes (RN) to eNB;

Latency improvements;

2.6GHz TDD support for USA

Self Optimising Networks (SON) enhancements


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Europe & APAC

94 Duke StreetGlasgow G4 0UWScotland UK

Tel and Fax +44 (0)141 552 8855

[email protected]

USA200N. Westlake Blvd, #202

Westlake VillageLos Angeles CA 91362, USA

Tel +1 805 413 4127

LTE UplinkDaniel Garca-Als, Iain Stirling & Bob Stewart


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Uplink Channels

Transport Channels (TrCH)

Control Information

UL-SCH Uplink - Shared ChannelRACH Random Access Channel

UCI Uplink Control Information


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Mapping to Physical Channels

Control information can be carried in PUSCH and PUCCH

UL-SCH

UCI

RACH

Uplink

PUSCH

PRACH

PUCCH


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Uplink Control Signalling Conveys L1 and L2 control information

HARQ acknowledgments for DL-SCH blocks

channel quality reports: CQI, RI and PMI

scheduling requests

Transmitted on PUCCH if no resources are allocated to UL-SCH

multiplexed with UL-SCH on to PUSCH (before SC-FDMA) if there is a valid schedule grant


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Control Information PUCCH The channel coding operations are:

codeblock

up to 11 bits

Indication (CQI) ACK / NACK

1 or 2 bits

Channel Qualityscheduling

0 bits

request

PUCCHformat 1

PUCCHformat 1a

or format 1b

PUCCHformat 2

codeblock

up to 11 bits

Indication (CQI)Channel Quality

PUCCHformat 2a

ACK / NACK

1 or 2 bits

20 bits 20 bits

or format 2b


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Channels and Signals A physical channel is defined as a set of resource elements carrying

information originating at a higher layer;

A physical signal is defined as a set of resource elements used in

support of the physical layer but not originating from a higher layer. For the uplink, the following physical channels are defined:

PUSCH : Physical Uplink Shared Channel;

PUCCH : Physical Uplink Control Channel;

PRACH : Physical Random Access Channel.

For the uplink, the following physical signals are defined: Sounding Reference Signal (SRS)

Demodulation Reference Signal (DMRS)


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Uplink Reference Signals There are two types of uplink reference signals:

Demodulation reference signal : associated with PUSCH or PUCCH

Sounding reference signal : not associated with any other transmission

They are time multiplexed with uplink data (not frequency multiplexed)

Used for channel estimation

0 1 2 3 4 5 6 0 1 2 3 4 5 6

slot slotsubframe

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

user #1

user #2

user #3

reference signal

dataf

t

PUSCH demodulation referencesignal example (normal CP)


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Demodulation Reference Signals: DRS There are two demodulation reference signals:

one for the PUSCH ;

and one for the PUCCH .

Used for channel estimation to allow for coherent demodulation

Desired attributes: small power variations in:

time: results in high power amplifier efficiency frequency: results in similar channel estimation quality for all

frequency components

DRS sequences used:

Cyclic extensions of Zadoff-Chu sequences (long sequences)

Special short QPSK sequences


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Sounding Reference Signal (SRS) I eNodeB needs channel quality information in order to assign resources

From DRS eNodeB can only get channel estimates on UE spectrum

No information available out of assigned spectrum

SRS overcome this problem

Used by base station to estimate channel quality of UEs

UE

allocatedresources

txed resource

grid

channel estimatesonly available on

rxed resourcegrid

this band

no channel estimates

available in other bands

DRS


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Sounding Reference Signal (SRS) II May cover large frequency span (not assigned to UE):

minimum of 4 resource block span

multiples of 4 resource blocks span

Can be transmitted as often as 2 msec (every 2nd subframe)

Can be transmitted as infrequently as 160 msec (every 16th frame)

Not necessarily transmitted with any physical channel (unlike DRS)

SRS modes

wideband: one transmission covers band of interest

frequency hopping: narrowband, location changes with time

subframe subframe subframe subframe subframe subframe

SRS


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SRS Transmission Transmitted on last symbol of subframe every 2nd subcarrier

Multiple UEs can transmit SRS s simultaneously

Interference is avoided by:

using different cyclic shifts (phase rotations): orthogonality

changing the comb transmission pattern

. . .

. . .

. . .

. . .

subframe

. . .

. . .

OFDM symbol

SRS subcarriers UE 1

used for SRS

SRS subcarriersUE 2

UE 3

using different

cyclic shifts for SRS


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Physical Uplink Control Channel PUCCH: Physical Uplink Control Channel

conveys uplink control information;

never transmitted simultaneously with PUSCH from the UE.

PUCCH used if UE has no valid schedule grant

Transmitted with frequency hopping (provides frequency diversity)

Transmitted on band edges: leaves contiguous bandwidth for PUSCHin the middle.

UE

uplink control

PUCCH:


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PUCCH Bandwidth One resource block (RB) allocated to each PUCCH This is too large for the amount of information transmitted

Therefore more than one PUCCH can share the same RB :

Use same base reference sequence

Use different phase rotations (cyclic shifts ) Use different orthogonal cover code (formats 1, 1a & 1b)

Inter-cell interference can be a problem Inter-cell interference is randomised by using hopping patterns in

and orthogonal codes with each symbol


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Physical Uplink Shared Channel PUSCH : Physical Uplink Shared Channel carries

data;

control information.

PUSCH processing chain:

UE

uplink data & control

PUSCH:

ScramblingModulation

mapper mapper Resource el.

modulationSC-FDMA

Precoding


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PUSCH Scrambling

Modulo 2 multiplication (XOR) with a scrambling sequence

Only applied to: coded data, channel quality coded bits, ACK codedbits

Not applied to ACK placeholders, these are set to predetermined value



modulationSC-FDMA

PrecodingPUSCH

c

1 ACK bit placeholders Q m 4=( )

... 0 0 1 0 1 1 1 X X X 0 1 1 0 1 0 ...

coded datach. quality coded bits

ACK coded bits

.0 0 1 0 1 0 1 1 1 1 0 0 1 1 1 0b

i( )

b i( )

c i( )

b

i( ) b

i 1

( )=

b

i 1+( ) b

i 2+( ) 1= =

d l


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PUSCH Modulation

Maps bits into symbols

The modulation mapping defines 3 constellations as follows:



modulationSC-FDMA

PrecodingPUSCH

Q

I

QPSK

1

100

01

10

11

Q

I1

1

16-QAM

Q

I3 5 7

3

5

7

64-QAM

0000

0001

0010

0011

1010

1011

1000

1001

3

3

0101

0100

0111

0110

1111

1110

1101

1100

1

1

101111 101101 100101 100111 000111 000101 001101 001111

101110 101100 100100 100110 000110 000100 001100 001110

101010 101000 100000 100010 000010 000000 001000 001010

101011 101001 100001 100011 000011 000001 001001 001011

111011 111001 110001 110011 010010 010001 011001 011011

111010 111000 110000 110010 010010 010000 011000 011010

111110 111100 110100 110110 010110 010100 011100 011110

111111 111101 110101 110111 010111 010101 011101 011111

PUSCHP di


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PUSCH Precoding

Not the same as downlink (multi-antenna) precoding

Produces SC-FDMA modulation;

Generation process:

Split the modulated symbols into sets; Each set (of size ) forms an SC-FDMA symbol ;

Perform a DFT (precoding part of SC-FDMA modulation);

DFT size: its prime must be a product of 2, 3 and/or 5

Smallest DFT size is 12



modulationSC-FDMA

PrecodingPUSCH

Msymb Msymb MscPUSCH

Msc

PUSCH

PUSCHP di DFTSi


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PUSCH Precoding: DFT Size DFT can be implemented with FFT for efficiency; DFT size: its prime factors are 2, 3 and/or 5

Minimum DFT size (resource block size in the frequency domain): 12

MscPUSCH

NscRB

2 2

3 3

5 5

NscRB

NRBUL

=

. . .

. . .

. . .

. . .

...

...

subframefreq

time

1 2 s

u b c a

r r i er

s

DFT

N scRB 12=

R El tM i


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Resource Element Mapping

The final stage in PUSCH processing is to map the symbols to theallocated physical resource elements

Note that allocation sizes are limited to values whose prime factors are2, 3 & 5 (imposed by precoding stage)

Map in increasing order:

first subcarriers

then the time domain (SC-FDMA) Avoid SC-FDMA symbols with

Demodulation reference signals

Sounding reference signals



modulationSC-FDMA

PrecodingPUSCH

z

PUSCHF H i g


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PUSCH Frequency Hopping Allocated spectrum to a UE can change every subframe ;

This is controlled by a frequency hopping function :

This provides for better frequency and interference diversity .

f hop .( )

frequency

time

subframeintervals

short-term narrowband interference Mobile 2

Mobile 3

Mobile 1


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Europe & APAC94 Duke Street

Glasgow G4 0UWScotland UK

Tel and Fax +44 (0)141 552 8855

[email protected]

USA200N. Westlake Blvd, #202

Westlake VillageLos Angeles CA 91362, USA

Tel +1 805 413 4127

LTE DownlinkDaniel Garca-Als, Iain Stirling & Bob Stewart

DownlinkChannels


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Downlink Channels

Transport Channels (TrCH):

Control Information:

DL-SCH Downlink - Shared ChannelBCH Broadcast ChannelPCH Paging ChannelMCH Multicast Channel

CFI Control Format Indicator

HI HARQ Indicator DCI Downlink Control Information

MappingtoPhysicalChannels


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Mapping to Physical Channels

DL-SCH

CFI

BCHPCH

MCHHI

DCI

Downlink

PDSCH

PBCH

PMCH

PCFICH

PDCCH

PHICH

DownlinkChannelsandSignals


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Downlink Channels and Signals A physical channel : set of resource elements carrying information

originating at a higher layer;

A physical signal : set of resource elements used in support of thephysical layer but not originating from a higher layer.

Reference Signals;

Synchronisation Signals;

PDSCH : Phy DL Shared Ch

PDCCH : Phy DL Control Ch.

PMCH : Phy Multicast Ch.

PBCH : Phy Broadcast Ch.

PCFICH : Phy Ctrl FormatIndicator Ch.

PHICH : Phy Hybrid ARQIndicator Ch.

Framestructure


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Frame structure

s u

b c a r r

i e r

OFDM symbol

ref. signalcontrol

PSS

SSS

BCH

unused

PCFICH

ref. signal

PDCCH

PDSCH

regions

unused

unused

SSS PSS

BCH

PCFICH

SSS PSS

DownlinkPCFICH


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Downlink PCFICH PCFICH: Downlink Physical Control Format Indicator Channel

specifies how many OFDM symbols are used for PDCCHtransmission;

Uses QPSK modulation

Transmitted in the same set of antenna ports as PBCH;

It has its own specific layer mapping, precoding and mapping to

resource elements.

UE

format of PDCCH

PCFICH:

PhysicalDownlinkControlChannel I


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Physical Downlink Control Channel I PDCCH: Physical Downlink Control Channel

carries control information including scheduling assignments;

Uses QPSK modulation

Transmitted in the same set of antenna ports as PBCH; It has its own specific layer mapping, precoding and mapping to

resource elements

UE

downlink and uplink scheduling assignmentsPDCCH:

PhysicalHybridARQIndicatorChannelI


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Physical Hybrid ARQ Indicator Channel I PHICH: Physical Hybrid ARQ Indicator Channel

hybrid-ARQ ACK and NACK indicators UEs;

Transmitted in the same set of antenna ports as PBCH;

The PHICH uses its own specific:

layer mapping; precoding;

mapping to resource elements.

UE

ACK / NACKPHICH:

PhysicalDownlinkSharedChannel


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Physical Downlink Shared Channel PDSCH: Physical Downlink Shared Channel

It is the main downlink channel;

Carries transport blocks to the mobiles ;

PDSCH uses the following antenna ports:

{0}, {0,1} or {0,1,2,3} if UE-specific reference signals are nottransmitted ;

{5} if UE-specific reference signals are transmitted .

UE

downlink data

PDSCH:

DownlinkPBCH


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Downlink PBCH PBCH: Physical Broadcast Channel

carries broadcast information (from the BCCH logical channel)

Uses a simplified and fixed transport format ; A coded block of 1920 samples for normal cyclic prefix or 1728

samples for extended cyclic prefix is produced by the channel coder

every 40ms; This block is QPSK modulated into 960 or 864 complex symbols;

Transmit diversity layer mapping and precoding is performed.

UE

UE

UEUE

UE

DownlinkReferenceSignalsI


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Downlink Reference Signals I

There are three types of downlink reference signal:

Cell-specific : its structure depends on the cell ID

MBSFN references for MBSFN transmission;

UE-specific references: used in non-codebook basedbeamforming.

Provided in support of coherent demodulation;

Used by UE to perform channel estimation and to obtain channelquality measurements.

DownlinkReferenceSignals II


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Downlink Reference Signals II References are arranged across time and frequency ; Only one reference signal is transmitted through per antenna port , this

allows for channel estimation for the different antenna ports ;

When an antenna port transmits a reference signal other ports aresilent;

time

f r e q u e n c y ANTENNA PORT 1

ANTENNA PORT 2

Antenna port 1 reference signal

Antenna port 2 reference signal

No transmission

SynchronisationSignals I


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Synchronisation Signals I There are two downlink synchronisation signals :

Primary synchronisation signal;

Secondary synchronisation signal.

This structure reduces cell search procedure complexity ;

Used to obtain:

UE

CELL

Primary/secondary synch signals

Cell identity

frame timing

Synchronisation Signals II


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y g Always transmitted in the same place regardless of bandwidth used.

first 72 carriers (around DC carrier);

OFDM symbols 5 and 6 of first slot in subframes 0 & 5.

10 msec radio frame

#0 #1 #2 #3 #4 #5 #6 #7 #8 #9

subframe

0 1 2 3 4 5 6 0 1 2 3 4 5 6

slot slot

7 2 s u

b c a

r r i e r s

OFDM symbol

0 1 2 3 4 5 6 0 1 2 3 4 5 6

slot slot

7 2 s u

b c a

r r i e r s

OFDM symbol

b a n

d w i d t h

f

t

secondary synch signal

primary synch signal

Channel Coding Procedures


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g

There are a number of procedures which are used for multipletransport channel or control information types:

CRC calculation; Code block segmentation ;

Channel coding (tail biting convolutional and turbo );

Rate matching ;

Tr. Channel & Ctrl. Information Processing


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g

Depending on the channel, a different set of processing steps occurs:

channelcoding

ratematching

code blocksegment.

bitstream e k E

b i t s

bitstream f k G

b i t s

CRCattachment

code blockconcat.

channelcoding

ratematching

CRCattachment

input bits a k A b i t s


BCHDL-SCH, PCH and MCH

G C R C 1 6

D (

)

c o n v .

G C R C 2 4 A

D (

)

t u r b o

G C R C 2 4 B

D (

)

channelcoding

bitstream b k B

b i t s

CFI or HI

CFI or HI

H I : r a

t e 1 / 3 r e p e

t i t i o n c o

d e

C F I : r a

t e 1 / 1 6 b l o c

k c o

d e

bitstream e k E

b i t s

channelcoding

ratematching

CRCattachment


DCI

G C R C 1 6

D (

)

c o n v .

Downlink Physical Channel Processing


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y g

The general structure of downlink physical channels processing is:

This structure applies to the PDSCH;

other channels have slightly different processing chains.



layers antenna ports

mapper Layer

Precoding

modulationOFDM



modulationOFDM

code words

. . .

. . .

. . .

. . .

Scrambling


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g

Produces a block of scrambled bits from the code word bits :

Modulo 2 multiplication (XOR) of the code word bits with a scrambling

sequence :




mapper

Layer

Precoding

modulationOFDM



modulationOFDM

code words

. . .

. . .

. . .

. . .

b q( ) b q( )

b q( )

i( ) bq( ) i( ) c

q( ) i( )+( ) mod 2;= i 0 Mbitq( ) 1 =

c q( )

block of bits bq( ) block of bits b

q( )

c q( )scrambling sequence

code word bits scrambled bits

Modulation


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Downlink supported modulation formats:

Physical Channel Modulation Schemes

PDSCH QPSK, 16QAM, 64QAMPMCH QPSK, 16QAM, 64QAM

PDCCH QPSK

PBCH QPSK

PCFICH QPSKPHICH BPSK




mapper

Layer Precoding

modulationOFDM



modulationOFDM

code words

. . .

. . .

. . .

. . .

Downlink Modulation Mapper


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The modulation mapping defines 4 constellations as follows:

Amplitude levels are normalised.

Q

I

QPSK

1

100

01

10

11

Q

I1

1

16-QAM

Q

I3 5 7

3

5

7

64-QAM

0000

0001

0010

0011

1010

1011

1000

1001

3

3

0101

0100

0111

0110

1111

1110

1101

1100

1

1

101111 101101 100101 100111 000111 000101 001101 001111

101110 101100 100100 100110 000110 000100 001100 001110

101010 101000 100000 100010 000010 000000 001000 001010

101011 101001 100001 100011 000011 000001 001001 001011

111011 111001 110001 110011 010010 010001 011001 011011

111010 111000 110000 110010 010010 010000 011000 011010

111110 111100 110100 110110 010110 010100 011100 011110

111111 111101 110101 110111 010111 010101 011101 011111

Q

I

QPSK

1

100

01

10

11

Q

I

BPSK

1

10

1

Multi-antenna Processing in LTE


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Includes

layer mapping : splits data sequence into a number of layers precoding

Under precoding the LTE standard can use

cyclic delay diversity (CDD)

spatial multiplexing (precoding)

transmit diversity




mapper Layer

Precoding

modulationOFDM

Scrambling Modulationmapper mapper Resource el.

modulationOFDM

code words

. . .

. . .

. . .

. . .

Transmission Schemes I


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non codebook based beamforming (single antenna, Port 5):

Single antenna port, Port 0: Transmit Diversity:

UE

UE

S F B C

2 or 4 antennas supported

b e a m

f o r m


arbitrary beamforming vector

1 layer UE

Transmission Schemes II


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Open-loop spatial multiplexing (Large Delay CDD):

Closed-loop spatial multiplexing:

p r e c o

d i n g


codebook

2, 3 or 4 layersUE

UE

p r e c o

d i n g


codebook

2, 3 or 4 layers

codebook selection suggestion (PMI)

Transmission Schemes III


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Multi-user MIMO:

codebook based beamforming (Closed-loop spatial multiplexing usinga single transmission layer):

b e a m f o r m

b e a m

f o r m


codebook

2, 3 or 4

codebook selection suggestion (PMI)

layers

codebook codebook selection suggestion (PMI)

(shared resources)

UE

UE

b e a m f o r m


codebookcodebook selection suggestion (PMI)

1 layer UE

Physical Antennas and Antenna Ports


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LTE standard refers to antenna ports

Antenna ports and physical antennas are different

Antenna port: defined by the presence of an antenna port specificreference signal

There are up to 6 antenna port specific reference signals

Number of physical antennas is

Antenna ports map to physical antennas.

1 2 4, ,{ }

Precoding for Spatial Multiplexing


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Used with the layer mapping for spatial multiplexing Supports or antennas: &

Different coding used for:

precoding without CDD or closed loop spatial multiplexing

precoding with large delay CDD or open loop spatial mux.

Codebook based precoding: 7 element codebook for the 2 antenna port case

16 element codebook for the 4 antenna port case

For spatial multiplexing the number of layers is also known as thetransmission rank

P 2= P 4= p 0 1,{ } p 0 1 2 3, , ,{ }

Spatial Mux: Precoding without CDD


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Also known as closed loop precoding

Based on downlink channel estimates

UE reports recommendations : RI (rank indication) and PMI(precoder matrix indication)

eNodeB may or may not follow these recommendations whenselecting

layer 1

layer 2

layer

IDFT CP

precoding

IDFT CP

IDFT CP

W i( )P

ant 1

ant 2

ant P

x 0( ) i( )

x 1( ) i( )

x 1 ( ) i( )

W i( )

Spatial Mux: Large Delay CDD Precoding


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Also known as open loop precoding

matrices and are applied first, then precoding

codebook matrices used are predetermined

channel quality measurements are not required

layer 2

layer

IDFT CP

precodingCDD

IDFT CP

IDFT CP

W i( )P

ant 1

ant 2

ant P

1 0 0

0 e j2 k

0

0 0 e

j2 k 1 ( )

U

D i( )

layer 1

U D W i( )

Beamforming


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Supported by LTE: precoding applied to a single layer Codebook based beamforming:

Use precoding matrix from codebook

UE is informed of precoding matrix used

Non-codebook based beamforming:

Arbitrary beamforming applied UE is not notified of precoding matrix used

UE needs to estimate channel including effect of beamforming

UE specific reference signals used (antenna port 5)

Beamforming (UE specific) is applied to this reference signal

1=

Transmit Diversity Precoding


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For 2 antennas, precoding the Alamouti scheme is used as:

Note that any two columns of the coding matrix are orthogonal;

This is space-frequency transmit diversity (coding in frequencydomain)

A similar sparse mapping applies to the case of 4 antennas.

y 0( ) 2 i( )

y 1( ) 2 i( )

y 0( ) 2 i 1+( )

y 1( ) 2 i 1+( )

12

-------

1 0 j 0

0 1 0 j0 1 0 j1 0 j 0

Re x 0( ) i( ){ }

Re x 1( ) i( ){ }

Im x 0( ) i( ){ }

Im x 1( ) i( ){ }

=

Resource Element Mapping


68/70


The final stage in the physical layer processing before OFDMmodulation is resource element mapping

Symbols are mapped to assigned resource elements

Resource elements used by reference signals are avoided




mapper Layer Precoding

modulationOFDM



modulationOFDM

code words

. . . . . . . . . . . .

OFDM Symbol Construction


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DC subcarrier is not modulated Subcarriers of resource blocks are arranged on both sides of the DC

subcarrier

For larger values of resource blocks in DL ( ) more resource blockslie to the left and right of the spectrum illustrated above.

OFDM symbols are transmitted in turn.

f

resourceblock

DC subcarrier

......

NRBDL

OFDM Modulation


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Implemented using an IFFT with 15kHz carrier spacing

Cyclic prefix also added at this stage

Each antenna port has its own OFDM modulation




mapper Layer Precoding

modulationOFDM



modulationOFDM

code words

. . . . . . . . . . . .

Intron LTE

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