alu lte workshop

8/11/2019 ALU LTE Workshop

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LTE

Uplink

Power cont ro l

Open-loop

power control:

To constrain the dynamic

range

between signals received from different UEs

Unlike

CDMA

there is no intra-cell interference -> exploit fading by means of link

adaptation and scheduling

Classical

PC :

all users achieve the same target

SINR

Interior

users transmit at

reduced

power spectral density

Fractional

PC

more flexible :

Trade-off between spectral

efficiency

and

cell

edge

rates

Target

SINR

increases

with

decreasing

path

loss

Others, e.g.

aperiodic fas t power control

Frac t iona l PC

Interference over Thermal noise loT is a key performance criterion: open-loop

PC

params

can

be adjusted to

reach

a target loT

crucial in reuse-1 deployment to guarantee coverage and stability

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Target

SINR


3/35

loT Control Mechanism Inter-cell

Power

Control

Setting of Target_SINR_dB

determines

the loT

operating point

Especially in a reuse-1

deployment

it is critical

to

manage

the

uplink

in te r fe rence level

In LTE e-NBs

can send

uplink overload indications

to

neighbor e-NBs via the

X2 in te r f ace

Power control parameters i.e. Target SINR can be adapted based on

ove rload ind i ca to r s

Allows

control

of

the

loT level to ensure coverage

and

system

stability

Measu re

Interference

emit

over load ind ica to r

Based on overload

indicator from

neighbor cell

adapt

PC

params

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c

Fractional

Power Control

While using

the

same

target

SINR

for

each

user results in very

good fairness as

far

as

power

allocation is concerned

it

also

results in poor

spectral

efficiency

An improved

power

control

scheme

called

Fractional Power

Control adjusts the target

SINR

in relation to the UE s path loss to

its serving sector

UE_TxPSD_dBm =

PL_dB Nominal_Target_SINR_dB

ULJnterference_dBm

1a is called the fractional

compensation

factor, and is sent via cell broadcast; 0 can use radix-2.3.5 FFTfor DFT-precoding i.e.. cannot assign 7. 11. 13. 17.. .. PRBs

9 |

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DL

Scheduling

mechanism

rr ies

DL

r e sou r ce

assignment on L1/L2

control channel PDCCH)

Reported

on

PUCCH or

PUSCH: provides

channel

st te

info

nd

info to

select

MIMO mode

Channel dependent scheduling is supported in both time and frequency domain

enables two dimensional flexibility

CQI feedback can provide both wideband and frequency selective feedback

P/v .l

an d

Rl

feedback allow

fo r MIMO

mode selec t ion

Scheduler chooses bandwidth allocation modulation MIMO mode and power allocation

H RQ operation is asynchronous and adaptive

Assigned

PRBs

need not be contiguous for a given user in the downlink

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Channel Quality Indicator, Pre-coding Matrix Indicator, Rank

Indicator

ess etai led

More

et iled

Periodic Reporting

Aperiodic Reporting

Physical

Channel for

Report

PUCCH

PUSCH

Trigger

for

Report

None

Indication in scheduling

grant

PMI f eedback

for closed-loop

S

Single PMI

Single PMI

and

Multiple PMI

CQI feedback

computed

assuming

calculated PMI

1) Wideband

2) UE-selected subband

coarse

subband

sizes,

one QI

report pe r codev/ord)

1) Wideband

2) UE-selected

best-M subband

granular subband sizes, one

QI

report

pe r

codeword)

3) Higher-layer

configured

subband

one

CQI report per subband pe r

codev/ord)

Rl f eedback

Sent

in

separate

subframe

from

CQI/PMI

Sent together with CQI/PMI

PUS H

is

used here

only

when UL data

is

sent,

in

order to

maintain

single

carrier

transmission

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SC

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2

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c

Scheduler proportional fair principles

The

SINR

per

PRB

on

the

UL

or per resource block group

RBG

on

the DL

for

the

traffic

channel is estimated from the

SRS

for

the UL

and

the CQI

report for

the DL

Note that

the RBG

size is bandwidth

dependent;

for 10MHz it is 3 PRBs resulting in 17 RBGs

The prioritymetric per user is formed bymapping the SINR to an achievable rate per

PRB or

RBG

using a look up

table

and dividing by the average user rate and

multiplying by the QoS and GoS weight

13 I

Presentation Title

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This i s RBG

index fo r

th e

downlink

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Priority

t t r i e

2

LE I

1

Q LE2

0

LE 3

A l c a t e l L u c e n t


13/35


For each

PRB UL

or

RBG

DL

we find the user with the highest priority metric

In

the

downlink we are

pretty

much done here as

the

OFDM

nature

of the downlink lets

us simply assign

each

RBG to the user with th e highest priority metric which maximizes

the original sum rate metric a user is allowed to be assigned discontiguous

PRBs

- There are additional points to account for such as CCE search space constraints on the

PDCCH

^

This

is RBG

i n de x f o r

t downlink

w

14 |

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For the uplinkv/e have to account for the SC-FDMA constraint of contiguous

PRBs,

as well as the fact

that

there

are

UE

power

headroom

PH)

constraints

The PH limits the max number of

PRBs

which can be assigned while the maintains its current

transmit power spectral density Tx PSD as se t by power control

axToral ower

NumPR

Uax m

TxPS

Finding

th e

optimal solution which maximizes

the

desired sum rate metric is not feasible with

the

SC-FDMA constraint, and hence

the

Maximum Priority Envelope MPE algorithm has been developed

for uplinkuser scheduling and resource allocation which accounts for

power headroom

constraints

an d th e contiguous PRB

restriction

UE

UE2

UE3

In this oxamplo

UE2has

umPRB^xPwr=3

15 |

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We

then

go

through an iterative

procoss

of

assigning

contiguous sets of

winning

user

PRBs

called

envelope groups), oach time taking into account

CCE

soarch space constraints on

the PDCCH

m L

Example:

Assume S has

9 w highest priority

metric

make

assignment for

UE2 update PRBs not f

allocated

to

UE

in

which i t was th e winne r

CS

t i t

>

16 I Presentation

Title

| Month

2 8

c

S,

gets

assigned

to

UE3 and

~

gets

assigned to

UE1

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Frequency Non Selective Scheme

esourc e

Unit

ndex

Single

priority

metric formed and used in

th e first

stage

of th e MPE algorithm

Then MPE algorithm continues as in FSS

s cheme

The SRS

SYNC SINR

is a scalar quantity per user

that

is formed by averaging the SRS

SINR

across

PRBs

and then filtered in time; used to form a single priority metric, which is replicated and used

for all

PRBs

Tosupport a large number of UEs the SRS period needs to be reduced given the multiplexingcapabilities

max of 8

UEs

per

SRS

transmission per frequency comb

The regular

MPE

algorithm as in

the FSS

algorithm is

then

utilized, which minimizes

testing verification

to

just the new

code

introduced

Currently also investigating an intermediate solution where the resolution of the frequency

selective scheduler is reduced bya certain factor in order to retain some frequency selectivenessin

the

scheduling while reducing complexity study in progress

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LU ent


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DL MCS

t ab l e

Along with the

of

PRBs allocated an MCS

level is sent in th e scheduling grant

corresponding

to 29 different possibilities

The MCS index corresponds

to

a modulation

format and transport

block size

index

Transport block size table

gives

th e block size to

use

b as ed o n

th e

of

PRBs

a l loca ted

The code rates given in

th e

table are for 50

PRBs assuming

th e RS pattern

for 1

antenna

port

and

for 3 OFDM symbols

used

for L /L2

cont rol

Precise code rate

will depend

on th e

exact

of

PR s allocated

as

well

as of Tx antenna ports and

of OFDM

symbols

reserved for

L /L2

control

Note: 3GPP allows

th e

UE

to

skip decoding if

the

code

rate

on

the

ini t ial

transmission

exceeds

0.93

M CS

Index M odula t ion

TBS

I nde x

TBS r 5

PRBs

Approx

C o d e Ra t e

0

QPSK

0

1384

11

1

QPSK 1

1800

14

2 QPSK

2

2216

18

3 QPSK

3 2856

0 23

4

QPSK

4

3624 29

5 QPSK

5 4 3 9 2

35

6

QPSK

6 5 1 6

41

7

QPSK 7

62 49

8 QPSK

8

6 9 6 8

55

9 QPSK 9

7992 6 4

1

16QAM

9 7992

32

11

16QAM 10 876 3 5

12

16QAM 11

9 9 1 2

39

13 16QAM

12

1 1 4 4 8

46

14 1 6 Q A M

13

1 2 9 6

52

15 1 6 Q A M

14 1 4 1 1 2

56

16

16QAM

15 1 5 2 6 4

0 61

17

64QAM

15

15264 4

18

64QAM

16

16416

43

19

64QAM

17

18336 4 9

2 64QAM

18 19848 53

21

64QAM

19

21384

57

22 64QAM

2

2 2 9 2 61

23 64QAM

21 2 5 4 5 6

67

24 64QAM

22

27376

72

25

64QAM

23

28336

75

26

B4QAM

24

3 576

0 81

27

2 5

26

31704

0 84

6 4 Q A M

6696^

97

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UL MCS t ab l e

Along

with

the of PRBs

allocated an

M S

level is

sent

in

th e

scheduling grant

corresponding to 29 different possibilities

The

M S

index corresponds

to

a modulation

format

and

transport

block

size index

Transport block s ize table givos the block size to

u se b as ed o n

th e

of

PRBs

al located

The

code

rates given in

the table

are for 50

PRBs assuming no SRS allocation

Precise code

rate

will depend on

SRS allocation

U I

puncturing

as

well

as precise of PRBs

allocated and the

U category

Mote: UEs

which

are not capable of 64-QAM

ca n

continue to

use

16-QAM

for

MCS

Indices

21

and higher

in which c ase th e co de rate

will

be

higher

than

that

shown

in t he t ab le

MCS I ndex

Modu la t ion

TBS

Index

T BS f or 5

P R B s

Approx

C o d e R a te

0

QPSK

0

384 1

1

QPSK

1 1 8

1 3

2

QPSK

2

2 2 1 6

1 6

3

QPSK

3

2 8 5 6

2

4

QPSK

4

3624 2 5

5

QPSK

5 4 3 9 2

31

6

QPSK

6 5 1 6

36

7

QPSK

7

62 43

8

QPSK

8

6 9 6 8

49

9

QPSK

9

7992 56

10

QPSK

8 7 6

61

11 16QAM

8 7 6

31

2

16QAM

11

9 9 1 2

35

3 16QAM

2

1 1 4 4 8

4

4

6QAM

3 1 2 9 6

45

5

6QAM

4

1 4 1 1 2

49

6

6QAM

5 15264

53

7

6QAM 6

1 6 4 1 6

57

8 16QAM

7

8336 6 4

9

16QAM 8 9848

69

2

16QAM 9

21384

74

21

64QAM 9 2 1 3 8 4

5

22

64Q A M

2

2 2 9 2

53

23

64 QAM 21

2 5 45 6 59

24

64QAM

22 2 7 3 7 6

63

25 64QAM

23

2833 6 66

26 64QAM

24 3 5 7 6

71

27 64QAM

25 317 4

1 3

28

64 QA M 26 3 6 6 9 6

85

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Q

4

0

1

2

Q

Q

3

Q

L

A

0

A

L

A

0

L

A

0

2

A

l

R

g

s

R

v

O

A

l

c

e

L

2

2

Q

1

Q

Q

L

A

0

A

c

e

L

n

^


23/35

MIMO

in

LTE

RF Hardware

To support

MIMO

2x2

the

RF

hardware

products

must

have 2

RF

transmit

paths

the

product

name

should end

with

2x such as

RRH2y

TRDU2x

T aseband Unit RRH x

PRI

M RRH

is

MIMO

ready

with

a singl

however 2

M TRX

are

required

to s

MC RRH

supporting

LTE

2x2 MIMO

LTE BBU

module

LT

MIMO

i

-

2

Antennas

X

F

e

P o w e r

Supply

Powe r

Feeding

Optical

interface

Fibre

CPRI I

outi t i

or

Ethe rne t

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MIMO in LTE

Antenna

Design

Xpol

2

uncorrelated outputs:

good diversity gains

algorithms

supported

-

TxDiv/SFBC

- CL OL SM

up to

2 streams

- UL

MU-MIMO with

2 u s e r s

poi

closely spaced

correlation between elements with equal polarisation: array and diversity gains

algorithms

supported:

TxDiv/sfbc.

-ecommended for

balanced performances

- CL OL SM up to 2

streams

- UL MU-MIMO with 4 use r s

UL

performance

DL performance

Suitable radio

environments: large/outdoor cell/cell border

LOS

environments

pol widely spaced

4 uncorrelated outputs: good diversity gains

algorithms

supported:

- TxDiv/SFBC

- CL OL SM

up to

4 streams

27 |

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Month

20

MU-MIMO wi th

4

use r s

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X

X

X

X

X

X

1 6 cm

X

X

X

X

X

X

X

X

X

T

3 ^cm

X

>1 5m

-

1 6

cm

Alcatel-Lucent^


25/35

MIMO

in LT E

eminder

Reminder

on some defini t ions

i i

U user 2

U user

SISO

ch nnel

SIMO channel i.e.

RxDiv

MIMO ch nnel

MU MIMO

ch nnel

SU-MIMO Single UserMIMO)

Spatial Multiplexing SM): increase peak

rate

by 2 in MIMO 2x2

Transmit Diversity

TxDiv):

improve reliability of a single

data

stream

MU-MIMO Multiuser

MIMO)

Multiple data

streams

from /to

different

users sent on the

same resource

Works

even

with s ingle

antenna/PA

mobile

^ iTTthe sc^OTquent

slides,

the

fdC^efsetrrtcth^ntdr3wfllink

as

uplink

doesAITrb Lu< ent@

_J I


26/35

Generali t ies

Terminology

The relationship between codewords rank and layers is not unique and depends on the

MIMO

scheme

to

e c ons id e re d

A few important definitions:

Codeword an independently encoded data block corresponding to a single transport

block

with one

CRC

a codeword is directly

related to

the

channel

coding

operation

Codewords

< layers

ank number of non-redundant data streams

that can

be

transmitted

coded data streams may be split into different layers and how the data stream is split depends on

the

an tenna s cheme

and th e rank

of

th e channel:

- if

rank

= 1 only

one codeword

can be transmitted - if multiple

coded

data

s treams, they

carry

the

same

information

- if rank = 2 either one or two codewords

can

be transmitted while offering a spatial

multiplexing gain

of

2 -> 2 unique

coded

data streams

- if

rank

= k up to codewords while

offering

a SM gain of ->

unique coded data

streams

Layer number of streams including redundant

ones

to be transmitted

- tayers-


27/35

ener li t ies

Examples

Spatial multiplexing can be achieved with either 1 or multiple codewords

t r nsm i s s ion

SU MIMO 2x2 offers 2 possibil ities: 1 or 2

codewords

for rank 2

transmission

3GPP

LTE

V

2

codeword s

WiMAX

o ewo r

Advantage: permit Successive Interference

Cance ll a tion decod ing t the receiver

Advantage: save

signaling

overhead

as th e

H RQ

associated

signaling is

rather

expensive

30 I

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Genera l i t i es

Examples

Spatial multiplexing can be achieved with

either

1 or multiple codewords

t ransmiss ion

SU MIMO 2x2 offers 2 p os si bi li tie s: 1 or 2 codewords for rank-2 transmission

2 layers

1 codeword

2 c o d e w o r d s

\

x 2x

Y

2 layers

x 2x i

X2 X

Layer

mapping

i i

i i

i i

/ >

precoder

Advantage:

permit

Successive

Interference

Cancellation

decoding

at

th e

receiver

=>

SIC

allows significant gains

x4 x3 x2 x1

>

Layer

mapping

tV-N

n5

precoder

x 4x 3

A dv ant ag e: save

signaling

overhead as the

HARQ

associated

signaling is

rather

expensive

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Downlink Signal Structure

The

LTE

downlink signal

structure

is

general and applicable to both transmit

diversity and spatial multiplexing. LTE Rel 8 can

support:

up

to

4 layers with 4

transmit antennas

both

open loop and

closed-loop

spatial

multiplexing for 2

and

4

transmit

n t e n n s

up

to

rank 4 transmission

with 4x4 MIMO

Rank Indicator Rl and Precoding Matrix Indicator PMI

are

used

to permit

closed-loop

-

the

precoding codebook is

defined

in TS36.211

odewords

Layers

eNB

antenna

ports

Channel

coding

u w

Srrnmhling

Modulation

m ppe r

Layer

m ppe r

X

Drecoding

RE

m ppe r

CFDM signal

generation

V\

I

i

i

r

l

i t

Channel

coding

|

Scrambling

Modula t ion

m ppe r

RE

m ppe r

CFDM signal

generation

7^

\

v.*

~ y

Rl, CQI

PMI

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Codeword to

layer

mapping

2

Transm i t n t enna s

With 2

transmit antennas,

TxDiv may

be

used.

In

LTE,

SFBC

is

implemented

which is a

frequency-domain

version

of

the Alamouti code.

the transmitted diversity streams are orthogonal

SFBC/Alamouti code 2x2 :

1 single possibility:

- transmission relies

on

1 single

codeword

-

the

codeword is

duplicated

on 2 layers

(redundancy)

rank

=

symbols

/

subcarriers

the single

codeword is sent- t-wirp over

1 codeword

=> 2 unique symbols on 2 suucdii ieis = rar

ci ihrarn gjrs SC

2 layers

X2 X,

bK.-iMbi

34 |

Presentation Title

I Month 2008

Modulat ion

+ coding

x2

x,

K

I

Ll t i l lM

Layer

mapping

i

iission

SFBC

precoder

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32/35

Codeword

to layer mapping

2 Tr an smi t An t ennas

With 2

transmit antennas,

uses 2

codewords see

Fig. 2)

1 codeword

corresponds

to 1 Transport Block Size TBS

C

Rank-1 transmission is often seen as a special

case

of SU-MIMO

spatial

multiplexing. In

L U V JJ \_

I

LVJULfVUlU

U

UJV U

>

tf ouewor s =

r a r iK

ot tr nsmission

The

codeword to

layer

mapping is trivial: the

codeword

n is mapped to the layer n

^codewords

=

ttl yers

The mapping

between codewords and

layers is shown below:

layer 1

CW 1

Precoding

1x4)

Rank

Fig. 1: Rank-1 transmission

Rank 2

CW 1

CW 2

layer 1

w

layer

2

V

Precoding

2x4)

Fig. 2: Rank-2 transmission

35 |

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| Month 2008

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2008,

XXXXX

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33/35

Codeword to

layer

mapping

4 Tr an sm i t An t enn a s

Transmit

diversity schemes

with

4 transmit

antennas results

in a

combination

of

tw o

SFBC

x

Frequency Shift

Transmit

Diversity

FSTD

tr?n-rm> rwmjp ^Sbf^m

each antenna on

a

different subcarrier

X\

0 0 0

a n t e nna s

r

SFB

x 0 0

0 v. 0

0 0

x

vi

i

V

x

^

SFBC + FSTD

vi

X

U 0

x

xl

0 0

0

0

v.

X

0 0

*4

SFBC + FSTD is a suitable

transmit

diversity as no orthogonal full-rate diversity

code exists beyond 2x2 configuration

Usage in either 4x2

or

4x4

antenna

configuration

?word

36 I Presentation Title I Month 2008 All Rights Reserved 3 Alcatel-Lucent 2008,

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4 I

min i IP Symbo l s nn

A c:i ihrarr ipr


34/35

o

y

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a

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l

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35/35

Codeword

to

layer

mapping

4 Tr an sm it An t enna s

Looking

into the

details

of

rank-3

transmission:

codeword

1 is

mapped

on a single layer

1 codeword

per

layer:

the

layer size equal to

the

codeword length

(i.e.

TBS)

codeword 2 is mapped on 2 layers (layers 2 & 3)

1 codeword for two layers:

- if pr ^ 55,

the

codeword is equally split on

the

two layers

- if

A/we

> b5. the 2

layers

have^ttf^same order of magnitude (almost equal); a

* ' ' /~*'*'*:'

^

--

i c I

r> I

j f) n

fr~> t >

I~i -=

^- - -^

~

~i

~ :

r in

3( *pp

c o d ew o r d

2 :

TB S

<

l ayer 2

'

S / P c o n v er t er

38 I Presentation

Title

I

Month 2008

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2008, XXXXX

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