LTE Phy Engineering - additional slides

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OFDM Processing Chain (From Bits to Carrier Frequency)

101010011101….. Modulator

QPSK/16QAM/64QAM S/P IFFT P/S

CP D/A Upconverter

(Local Oscillator)

X1 X2 X3 X4 … XN

X1

X2

X3

X4

…

XN

x1

x2

x3

x4

…

xN

xN … x4 x3 x2 x1

t I

Q

xN … x4 x3 x2 x1 xN xN-1

t

t

t

fc

t

f 0MHz

BW

f fc

BW

0MHz


1 Radio Frame (10 ms)

1 subframe (1 ms)

1 slot (0.5 ms)

Slot =

7 OFDM symbols

(Normal CP)

CP CP CP CP CP CP Useful Part

CP Useful Part CP Useful Part CP Useful Part CP Useful Part CP Useful Part CP Useful Part CP Useful Part

1 OFDM symbol (83μs)

1 OFDM symbol (71μs)

Frame =

10 subframes

Subframe =

2 slots

Slot =

6 OFDM symbols

(Extended CP)

or

Useful Part Useful Part Useful Part Useful Part Useful Part

Radio Frame Time Structure


1 Symbol in the frequency domain

Subcarrier (SC)

BW: 1.4MHz = 128 SC (72 useful SC)

3MHz = 256 SC (180 useful SC)





Smallest allocation

12 SCs (180kHz)

Guardband

(not used SCs) Guardband

(not used SCs)

DC subcarrier

(not used in DL)

Pilot subcarrier

(QPSK symbol)

Data Subcarrier

(QPSK/16QAM/64QAM symbol)

Useful Subcarriers

Radio Frame Frequency Structure


TDD E-UTRA Radio Frame Downlink Frame Parts (e.g. Configuration 1)

1 slot (0.5 ms)

Control Region:

First 1-3 OFDM Symbols in subframe (for DwPTS 1-2 Symbols)

PCFICH – OFDM symbol 0,

PHICH – OFDM symbol 0

PDCCH – the rest

PBCH – 4 OFDM symbols (0-3)

in slot 1 in subframe 0

Synchronization Signals:

P-SS – OFDM symbol 2 in subframe 1 and 6

S-SS – OFDM symbol 13 in subframe 0 and 5

BW

PDSCH – rest REs

DC

1 subframe (1 ms)

62

SCs

72

SCs


12 SC

7 OFDM Symbols

RS RE

2 PRB

OFDM Subcarrier

OFDM Symbol

Guard Band

for S-SS or P-SS

UL T

ransm

issio

n

UL T

ransm

issio

n

DwPTS


TDD E-UTRA Radio Frame Uplink Parts (e.g. Configuration 1)

DL T

ransm

issio

n

PUCCH – firsts and last PRB

alternatively

SRS – on demand

last SCFDMA symbol in subframe

every second subcarrier (also in UpPTS)

12 SC

1 slot (0.5 ms)

2 PRB

PUSCH – rest REs


1 subframe (1 ms)

BW

PRACH – 72 subcarriers x 1 subframe

May appear several times within a frame, up to 6 RACHs in subframe

(also shorter RACH 72 subcarriers x 2 symbols in UpPTS)

DRS

7 SCFDMA Symbols

PUSCH – can include:

• User data multiplexed with feedback:

CQI/PMI/RI/HARQ-ACK

• Only feedback:

CQI/PMI/RI/HARQ-ACK

UpPTS UpPTS

DL T

ransm

issio

n

DL T

ransm

issio

n


TDD E-UTRA Radio Frame DL and UL Subframe Configuration 1

1 slot (0.5 ms)

BW

DC

1 subframe (1 ms)

62

SCs

72

SCs


DwPTS

Downlink

SF

UpPTS GP

Special

SF Uplink

SF

Uplink

SF Downlink

SF

Downlink

SF Special

SF

Uplink

SF

Uplink

SF Downlink

SF


LTE Rel. 8 Duplex Types

Frequency Division Duplex

Half-duplex FDD

DL: fC

UL: fC

DL: fC

UL: fC

Time Division Duplex

DL/UL: fC

FDD for

reduced

UE complexity

t

f

t

f

t

f

UL and DL

selected from

different

frequency

bands

UL and DL

use the same

frequency

band divided

in time


LTE Rel. 8 Radio Frame Differences Between FDD and TDD

DL

U

L

FDD frame 10ms frame

TDD frame (example configuration)

DL

/UL

One half frame (5ms)

10ms frame

1ms subframe

1ms subframe

Control Region (CR)

DL resource allocation ptr

UL resource allocation ptr

Special Subframe

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

DL/UL Switch

FDD DL/UL resource allocations:

single allocation PDCCH – single PDSCH/PUSCH

TDD DL resource allocation:

single allocation PDCCH – single PDSCH

TDD UL resource allocation

possible single allocation PDCCH – for multiple PUSCHs (for UL heavy conf)

DL:D

CI s

ubfra

me n

, allo

c s

ubfra

me n

UL: D

CI s

ubfra

me n

, allo

c s

ubfra

me n

+4

D

L:D

CI s

ubfra

me n

, allo

c s

ubfra

me n

UL: D

CI s

ubfra

me n

, allo

c s

ubfra

me n

+k (k

=4

-7)

P-SS

S-SS

Different placement of sync signals

After synchronization UE knows

already if this is TDD or FDD system


E-UTRA TDD Radio Frame Configurations

DL/UL configuration is broadcasted in SIB 1 (subframe #5)

Configuration 0

DL:UL 2:3 (UL HEAVY)

Configuration 1

DL:UL 3:2

Configuration 2

DL:UL 4:1

5ms half frame

10ms frame

Configuration 3

DL:UL 7:3

Configuration 4

DL:UL 8:2

Configuration 5

DL:UL 9:1 (DL HEAVY)

Configuration 6

DL:UL 5:5

5 ms switch periodicity configurations

10 ms switch periodicity configurations Guard period

Downlink

Uplink

1ms subframe

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

Special Subframe Special Subframe


Special Subframe Structure and Configurations

Special switching subframes #1 and #6

UpPTS DwPTS GP

Subframe (1ms), 14 OFDM Symbols

Downlink Pilot Time Slot

Guard Period

Uplink Pilot Time Slot

DLUL switch time (no transmission)

To allow UE to switch from Rx to Tx

To support coexistence with other systems

Normal, but shorter DL subframe includes:

* Control region – 1 to 2 symbols

* P-SS

* PDSCH and RSs – 1 to 10 symbols

Possible Configurations (normal CP)

0 1 2 3 4 5 6 7 8 9 10 11 12 13

0 1 2 3 4 5 6 7 8

Symbol number

Configuration

PDCCH

PCFICH

PHICH

PDCCH or

PDSCH

P-SS

PDSCH

SRS or

PRACH

PDSCH


E-UTRA Rel.8 MIMO Processing

OFDMA

Mod

OFDMA

Mod

FEC/

Mod FEC/

Mod

Layer Mapping

MIMO Precoding

Resource

Mapping

Resource

Mapping

Channel

Matrix

BS Tx UE Rx

OFDMA

deMod

OFDMA

deMod

deFEC/

deMod deFEC/

deMod

Layer deMapping

MIMO dePrecoding

Resource

deMapping

Resource

deMapping

Data bits Data bits Data bits Data bits

1 or 2

transport blocks

1 or 2 codewords

1 to 4 layers

1 to 4

antennas

MIMO Processing

Selection of

predefined Matrix

Selection of

technique

(SISO/

SM/TxDiv)

Channel

estimation

Synchronization

Channel

correction

CQI, ACK/NACK

PMI/RI

CQI

Feedback

Indicates

preferred

matrix

Indicates

number

of layers

Different RSs

placement

for accurate

channel estimation

mapping of symbols

into the transmit

antenna port

independently encoded

data block

Indicates good part

of the spectrum

Indicates achievable

spectral efficiency


EUTRA MIMO MIMO Operation for SFBC

Layer Mapping

One codeword 2 Layers

MIMO Precoding

2 antennas

Matrix for 2 antennas Matrix for 4 antennas

Alamouti

with antennas switch

x4x3x2x1

x4 x3 x2 x1

x*3 -x*4 x*1 -x

* 2

x3 x1

x4 x2

Towards

Resource Mapping

Mapped to different SCs

2 antennas are used

in a single symbol

transmission


EUTRA MIMO MIMO Operation for SM (1/2)

Precoding for CL SM (low speed scenario) Precoding for OL SM with large CDD (high speed scenario)

Precoding

matrix Large CDD

matrix

For CL UE indicates PMI – index of matrix W

Layer Mapping

2 codewords 3 Layers

MIMO Precoding

(W)

4 antennas

x2x1 z21 z11 x2 x1

y2 y1 Towards

Resource Mapping

y4y3y2y1 y4 y3

z22 z12

z23 z13

z24 z14

z1=Wv1

z2=Wv2

v1 v2

BS may or may not to use it


LTE MIMO

- Large delay CDD

- Cyclically assigned precoding matrices

- For high mobile users

- SU-MIMO: 2x2, 4x2, 4x4

- UE feedbacks the CQI, PMI

(codebook selection) with Rank adaptation

- 1 or 2 codewords applies

- Pair of UE uses the same TF resources

with Rank=1 transmission

- MU-MIMO precoding vector uses

a subset of SU-MIMO codebook

Open-loop Spatial Multiplexing

Closed-loop Spatial Multiplexing

Multi-User MIMO

MCS

eNB

Code

books

Channel

UE

Channel

estimation

Code

books

MCS

eNB

Code

books

MCS

Feedback

processing

UE 1

Channel 1

estimation

Code

books

UE 2

Channel 2

estimation

Code

books

MCS

eNB

Code

books

Channel

UE

Channel

estimation UEs are semistatically

assigned to MU-MIMO

mode. UE is not

allowed to be scheduled

in MU-Mode in one

subframe and SU

MIMO in the next one

Only one stream can be

allocated to a UE operating in a

MU-Mode

MIMO Operation for SM (2/2)


LTE MIMO MIMO Operation for BF

Eigenbeamforming

Suitable precoding is chosen as a form of

eigenbeamforming for 1layer-1codeword

the same matrices as for SVD SM

Based on UE specific RS. UE sends in UL

then BS adjust RF parts.

Phased array appears at UE as a single

transmission, for UEs at cell edge

Layer Mapping

1 codeword 1 Layer

MIMO Precoding

(W)

4 antennas

z21 z11

x4x3x2 x1 Towards

Resource Mapping

z22 z12

z23 z13

z24 z14

z1=Wx1

z2=Wx2

x4x3x2 x1

DoA based beamforming

2 Types of BF

Specs don’t include exact definition of operation for these


LTE MIMO Feedback Reporting

UE

eNB

UE

Rank Indication

Good uncorrelation

of spatial channels

(3 streams are transmitted)

Worse uncorrelation

of spatial channels

(2 streams can be transmitted)

Rank indication informs base station

how many layers/streams can it transmit

RI = 2

RI = 3

Precoding Matrix Indication

UE

eNB

UE

PMI = 0

PMI = 2

10

010P

11

112P

.

.

.

Channel realization 1

Matrix P2 applied

Channel realization 2

(conditions has changed)

Matrix P0 applied

Precoding matrix indication is used by the UE for pointing to the

selected codebook index for 2 and 4 antennas (only for SM)

Single RI per UE allocation Single PMI per UE allocation if allocated RB < 12,

per 5RB if allocated RB > 12

Minimum periodicity of the reports = 1subframe (1ms)

Examples

Examples


LTE MIMO Spatial Mode Switching

Transmission mode Multi-antenna mode of PDSCH

1 Single-antenna port, port 0

2 Transmit diversity

3 Transmit diversity if the associated

rank indicator is 1, otherwise large

delay CDD

4 Closed-loop spatial multiplexing

5 Multi-user MIMO

6 Closed-loop spatial multiplexing

with a single transmission layer

7 If the number of PBCH antenna

ports is one, Single-antenna port,

port 0; otherwise Transmit diversity

FEC/

Modulator

SD

encoder

Tx Mode

Resource

Mapper

SM

Encoder

Resource

Mapper

IFFT

IFFT

Tx mode

selection

SD

layer mapper

SM

layer mapper

SNIR

Spectr

al E

ffic

iency

Switching point

(10dB – rule of thumb)

SM

SD


LTE MIMO Rel. 8 Scenarios

eNB UE

eNB

UE

UE

eNB

UE

UE

eNB

UE

Space Diversity

DL: 2x1, 2x2, 4x1, 4x2, UL: 1x2, 1x4

Used for: PHICH, PCFICH, PDCCH, PBCH, PDSCH, PUSCH

Uncorrelated Channels (rich scattering)

Poor Channel (Fast variations)

Precoded 2 copies of the same signal

SFBC rank-1 transmission

Improved Link Reliability

SU-MIMO (Spatial Multiplexing) DL: 2x2, 4x2, 4x4

Used for: PDSCH (traffic)


Good Channel (slow variations)

Precoded 2 different streams

Increase in throughput

MU-MIMO (Spatial Multiplexing) DL: 2x1, UL: 1x2

Used for: PDSCH(traffic)


Good Channels

Precoded 2 different streams for 2 users

Increase in system capacity

Beamforming DL: 2x1, 4x1, 8x1

Used for: PDSCH, PUSCH (traffic)

Uncorrelated Channels (between users)

Poor/Good channels (for each user)

Increase in coverage

Less interference

Detailed operation

not described in specs

Technology

LTE Phy Engineering - additional slides