153867696 lte-tutorial-femtoforum-part2-130814004042-phpapp01

1Marius Pesavento, Willem Mulder, Femto Forum Plenary, June 2010, Reading, UK © mimoOn

LTE Tutorial part 2 Advanced topics in LTE

Marius Pesavento - [email protected] Mulder - [email protected]


Outline

Advanced topics in LTE The LTE MIMO modes Codebook-based precoding Closed loop operation CQI reporting modes Using antenna port 5 (SDMA) techniques Simulation results Outlook LTE Advanced


MIMO Channel

MIMO detector


MIMO Precoding

optimum „Eigen“ precoding requires perfect channel

knowledge (CSI) at the Transmitter


Parallel AWGN channels

Equivalent SISO channels


Tx Beam 1

Tx Beam 2

Rx Beam 1

Rx Beam 2TransmitBeamformer(s)

ReceiveBeamformer(s)

Transmit/Receive beamforming interpretation


Codebook based Spatial Multiplexing (SM)

Precoding matrix is selected from codebook Reduced signaling at cost of quantization error (lose

rate optimality) Equivalent MIMO channels no longer parallel

(decoupled), reduction in rate Receiver matrix can be designed arbitrarily.In practice interference among the streams not

completely removed: receive SINR for the k-th stream


MIMO Tx processing blocks in LTE(spatial MUX)

maximum 4 spatial streams (layers) maximum 2 TBs (codewords), each with corresponding MCS. 2Tx: Code-book with 2 precoding matrices (closed-loop)

is selected from set of 16 precoding matrices. code contains matrices of type: (and column permutated versions)

Turbo encoder

Rate Match

TB 1

TB 2

CR 1

CR 2

modulator

modulator

MS 1

MS 2

2-MUXor

1-MUX

2-MUXor

1-MUX

layer mappinglayer 0

layer 1

layer 2

layer 3

IFFTframe mapperfrequency first, thenOFDM symbol index

Tx 0

Tx 1

Tx 2

Tx 3




Precoding

; ; ;

Turbo encoder

Rate Match


MIMO schemes

Transmit diversity increase the reliability of the link,

migrate fading diversity order / diversity gain: number

of inpendent replica (fades) of the signal Spatial multiplexing

increase spectral efficiency multiplexing gain: number of spatial

streams transmitted on a time-frequency resource

upper-bounded by min(Mt,Mr) requires rich multipath environment ⇒

full channel rank Beamforming (rank 1)

Tx and Rx beamforming array gain through coherent combining

increases signal-to-noise-and-interference-ratio (SINR)

requires correlated antennas (e.g. in Line-Of-Sight transmission)

fading

multipath fading constructive or destuctive

superposition

LOS

⇒rank 1

Single streamonly!


DL-MIMO modes in LTE

Single antenna port (no MIMO) Transmit Diversity (TD), space-frequency Alamouti

code Open-loop Spatial Multiplexing (SM) Closed-loop SM Multi-User (MU) MIMO Rank 1 closed-loop SM (compressed control

signaling) Antenna port 5 beamforming, UE specific reference

signals


Cyclic (Large) Delay Diversity (CDD)

x0small delay

spread

frequency“flat”

delay spread frequencyselective

τ0

τ3

τ1

τ2

τ3

„artificial“multipath

x0τ1

τ2


Open-loop SM

Inferference „randomization“. In single layer transmission (TRI = 1) TD mode (Alamouti) is

used.

is matrix formed from permutation of vectors:

column permutation changing every k subcarriers in a pre-defined manner.

TB 1

TB 2

CR 1

CR 2

modulator

modulator

MS 1

MS 2

2-MUXor

1-MUX

2-MUXor

1-MUX

layermapping

L0

L1

L2

L3


Tx0

Tx1

Tx2

Tx3




Turbo encoder

Turbo encoder

Pre-coding

DFTMatrix

CyclicDelayMatrix


Spatial DiversitySpace-Time-Coding: Alamouti

Symbolmodulator

encoded bitstream

…,b3, b2, b1, b0,...… s1, s0,...

… s*0, -s*1,...… y1, y0,...

h0

h1

… s1, s0,...

spac

e-tim

een

code

r

spac

e-tim

ede

code

r

y*1

y0

equivalent „MIMO“ channel

„MIMO“ equalizer/detector

deco

der

s1

s0

No CSI at the transmitter

required!!!


Space-Frequency Transmit Diversity“Alamouti-zation”

Single CW transmission, i.e single MCS.

Simple receiver structure, no matrix inversion required

XS0S10

S2S3

XS50

port #0

0

00

00 0X0X

00

port #1

subcarrier index

port #2

port #3

IFFT

IFFT

IFFT

IFFT

S4

0

0000

00

000

S6S7

0

S4*

-S3*S2

*

-S1*S0

* 0000

-S7*S6

*

-S5*

000

„zeros“ as reference signal place holder

0„zeros“ from orthogonal SF code

X reference signal

S1data symbol

equivalent channelreceived

vectorequalized

symbol rather feed un-scaled „equalized symbol“ and

scaling factor to soft demodulator than perform

division at this point


Diversity order

(Symbol) error rate:

Diversity gain:Coding gain:


Multiplexing – Diversity tradeoff

LTE spatial diversity techniques achieve: diversity order (Mt£Mr):

full diversity for 2Tx half diversity for 4Tx

rate (min(Mt , Mr)): full rate only for single antenna receiver half rate for 2Tx and 2Rx ¼ rate for 4Tx and 4Rx

In LTE orthogonal space frequency block codes (OSTBC) are used that allow simple receiver structures

⇒Symbol by symbol detection rather than vector detection.


Cell-Edge Beamforming to improve coverage for cell-edge user. to reduce inter-and intra-cell interference. rank-1 assumption (LOS).

reduced signaling overhead

eNB aquires statistical information, e.g. DoDs of co-channel users at cell-edge

eNB computes optimum beamformer weights for each user and applies them in the DL transmission, no codebook and subbandrestriction.

multiple users are served on overlapping resources (MU-MIMO)

beamformer weights are explicitly signaled using user specific RS.

UE “sees” equivalent SI channel. dedicated RS of all users in a cell are

transmitted on the same RE (interference), UE correlates received signal with dedicated (RNTI-based) pseudo random sequence.

LTE-feature that is expected to not be supported at initial network rollout.

LOSLOS

LOSLOS

cell-specific frequency shift


Femtocell basestation

FU1FU2

MU1MU2

MU3

Macro basestation

Antenna port 5 downlink beamforming Space Division Multiple Access (SDMA)


Beamformer design and signaling

Beamformers can be implicitly signaled to the users of the cell using antenna port 5 reference signals.

Problem: Uncertainties in the DL channels UL-DL reciprocity (e.g. in TDD) channel feedback (requires cooperation of base

stations) Paramterer estimation, Line-Of-SightRobust designs wrt. channel mismatch can be used.

Subject to QoS constraint forfemtocell user

Maximum interferenceconstrainst for macrocell user


CQI report and 4-bit CQI table

CQIindex

modulation code rate x 1024

efficiency

0 out of range

1 QPSK 78 0.1523

2 QPSK 120 0.2344

3 QPSK 193 0.3770

4 QPSK 308 0.6016

5 QPSK 449 0.8770

6 QPSK 602 1.1758

7 16QAM 378 1.4766

8 16QAM 490 1.9141

9 16QAM 616 2.4063

10 64QAM 466 2.7305

11 64QAM 567 3.3223

12 64QAM 666 3.9023

13 64QAM 772 4.5234

14 64QAM 873 5.1152

15 64QAM 948 5.5547

subband CQI index =differential CQI + wideband CQI index

Differential CQI value Offset level

0 ≤1

1 2

2 3

3 ≥4

Spatial differential CQI value

Offset level

0 0

1 1

2 2

3 ≥3

4 ≤-4

5 -3

6 -2

7 -1

3-bit subband/wideband spatial differential CQI

2-bit subband differential CQI


Adaptive coding and modulation in DL grant

Tdoc R1-07CQI_NNSN01

MCSIndex

ModulationOrder

TBS Index

TBS for1 RB

1layer…

TBS for110 RBs 1layer

0 2 0 16 … 31121 2 1 24 … 40082 2 2 32 … 49683 2 3 40 … 64564 2 4 56 … 79925 2 5 72 … 95286 2 6 328 … 114487 2 7 104 … 135368 2 8 120 … 152649 2 9 136 … 1756810 4 9 136 … 1756811 4 10 144 … 1908012 4 11 176 … 2215213 4 12 208 … 2545614 4 13 224 … 2833615 4 14 256 … 3170416 4 15 280 … 3400817 6 15 280 … 3400818 6 16 328 … 3516019 6 17 336 … 3923220 6 18 376 … 4381621 6 19 408 … 4688822 6 20 440 … 5102423 6 21 488 … 5505624 6 22 520 … 5925625 6 23 552 … 6377626 6 24 584 … 6659227 6 25 616 … 7111228 6 26 712 … 7537629 2 reserve

d reserved … reserved30 431 6

for code rate approx 1

LTE target!!!


SINR to CQI conversionfor MMSE detector

4 x 4 MIMO, full-rank

for subcarrier k , precoding index i,and precoding matrix Pi

MMSE estimate of SINR corresponding to layer p and PMI i

subcarrierlayer

(column in PM)

PMI


Average (effective) SINREstimate for CW 0 (corresponds to averaging over layer 1 and 2)

Weighting function for average SINR computation (based on rate)

SINR

(2)

SINR

(1)

SINR

(3)

SINR

(4)

SINR

(N-2)

SINI(N

-1)

SINR

(N)

SINR

(N-3)

General: averaging over layer, subcarriers,…


MIMO transmission modes

Transmission mode Transmission scheme of PDSCH1 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

open-loop,no-PMI

feedback

closed-loop,with PMIfeedback


CQI reporting modes

No PMI Single PMI Multiple PMI

Wideband(wideband CQI) Mode 1-2

UE Selected(subband CQI) Mode 2-0 Mode 2-2

Higher Layer-configured

(suband CQI) Mode 3-0 Mode 3-1

Transmission mode 4 : Modes 1-2, 2-2, 3-1 Transmission mode 5 : Mode 3-1Transmission mode 6 : Modes 1-2, 2-2, 3-1Transmission mode 7 : Modes 2-0, 3-0

Transmission mode 1 : Modes 2-0, 3-0Transmission mode 2 : Modes 2-0, 3-0Transmission mode 3 : Modes 2-0, 3-0

PMI Feedback Type

No PMI Single PMI

Wideband Mode 1-0 Mode 1-1

(wideband CQI)

UE Selected Mode 2-0 Mode 2-1

(subband CQI)

Transmission mode 4 : Modes 1-1, 2-1Transmission mode 5 : Modes 1-1, 2-1Transmission mode 6 : Modes 1-1, 2-1Transmission mode 7 : Modes 1-0, 2-0

Transmission mode 1 : Modes 1-0, 2-0Transmission mode 2 : Modes 1-0, 2-0Transmission mode 3 : Modes 1-0, 2-0

PUSCH CQI: aperiodicFeedback Type

PUCCH CQI: periodic Feedback Type


Higher layer configured reporting modes: aperidodic reporting

#bits 2N 4

∆CQI(2)

∆CQI(1)

∆CQI(3)

∆CQI(4)

∆CQI(N-3)

∆CQI(N-2)

∆CQI(N-1)

∆CQI(N)

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)

∆CQI(2)

∆CQI(1)

∆CQI(3)

∆CQI(4)

∆CQI(N-3)

∆CQI(N-2)

∆CQI(N-1)

∆CQI(N)

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)

mode 3-0single antenna, port 5 TD and open-loop SM

mode 3-1closed-loop SM

PMI(w

ideb

and)

∆CQI(2)

∆CQI(1)

∆CQI(3)

∆CQI(4)

∆CQI(N-3)

∆CQI(N-2)

∆CQI(N-1)

∆CQI(N)

CQ

I(wid

eban

d)

CW 0 CW 1

#bits 2N 4 2N 4 2|1|4

+Rank Indicator (RI)

SINR(2)

SINR(1)

SINR(3)

SINR(4)

SINR(N-2)

SINI(N-1)

SINR(N)

SINR

SINR(N-3)


UE selected reporting: mode 2-0 for single antenna, port 5, TD and open loop SM: aperiodic reporting

report # of bits

bitmap of prefered M subband locations

widebandCQI

4

subband ∆CQI

2

L CQ

I(N-1)

CQ

I(N)

CQ

I(N-2)

CQ

I(N-3)

CQ

I(4)

CQ

I(3)

CQ

I(2)

CQ

I(1)

Frequency (subbands)

SINR

(N-1)

SINR

(N)

SINR

(N-2)

SINR

(N-3)

SINR

(4)

SINR

(3)

SINI(2)

SINR

(1)

measurements

CQI(wideband)

∆average CQI(selected subbands)

SIN

R


UE selected reporting: mode 2-2 for closed-loop SM: aperidodic reporting

report location ofpreferredsubbands

subbandCQI

subbandCQI

#bits L 4|2|8 4 2 4 2measurements per PMI required !!!select best PMI and subands

(in terms of combined data rate)

SINR SINR

CQI(2)

CQI(1)

CQI(3)

CQI(4)

CQI(N-3)

CQI(N-2)

CQI(N-1)

CQI(N)

Freq

uenc

y (s

ubba

nds)

SINR(2)

SINR(1)

SINR(3)

SINR(4)

SINR(N-3)

SINR(N-2)

SINI(N-1)

SINR(N)

SINR(2)

SINR(1)

SINR(3)

SINR(4)

SINR(N-2)

SINI(N-1)

SINR(N)

CW 0 CW 1

SINI(N-3)

CQI(2)

CQI(1)

CQI(3)

CQI(4)

CQI(N-3)

CQI(N-2)

CQI(N-1)

CQI(N)

∆av

erag

e C

QI(s

elec

ted

subb

ands

)

∆av

erag

e C

QI(s

elec

ted

subb

ands

)

CW 0 CW 1

CQI(2)

CQI(1)

CQI(3)

CQI(4)

CQI(N-3)

CQI(N-2)

CQI(N-1)

CQI(N)

PMI

CQ

I(wid

eban

d)

CQ

I(wid

eban

d)

+Rank Indicator (RI)


Wideband CQI reporting modes: aperidodic reporting

#bits 4 4 2N| N|4N

PMI(2)

PMI(1)

PMI(3)

PMI(4)

PMI(N-3)

PMI(N-2)

PMI(N-1)

PMI(N)

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)


CQ

I(wid

eban

d)

CW0 CW1+Rank Indicator (RI)

SINR(2)

SINR(1)

SINR(3)

SINR(4)

SINR(N-2)

SINI(N-1)

SINR(N)

SINR

SINR(N-3)


Higher layer configured reporting modes for perdiodic feedback: perdiodic reporting

#bits 4 2|1|4

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)

mode 1-1 (rank 1)closed-loop SM, MU-MIMO

mode 1-1 (rank 2)closed-loop SM, MU-MIMO

PMI(w

ideb

and)

diffe

rent

ial s

patia

l CQ

I(wid

eban

d)

CW 0 CW 1

#bits 4 3 2|1|4

PMI(w

ideb

and)

CW 0

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)

mode 1-0 single antenna port,open-loop SM, TD

#bits 4

CW 0

+Rank Indicator

(RI)


UE selected reporting: mode 2-0 for single antenna, port 5, TD and open loop SM: periodic reporting

report # of bits

bitmap of prefered M subband locations for

current bandwidthpart

L

widebandCQI

4

subband CQI

4

CQ

I(N-1)

CQ

I(N)

CQ

I(N-2)

CQ

I(N-3)

CQ

I(4)

CQ

I(3)

CQ

I(2)

CQ

I(1)

Frequency (subbands)

SINR

(N-1)

SINR

(N)

SINR

(N-2)

SINR

(N-3)

SINR

(4)

SINR

(3)

SINI(2)

SINR

(1)

measurements

CQI(wideband)

CQI(selected subbands)

SIN

R

N1 N2 NJ

JkNL //log DLRB2=


UE selected reporting: mode 2-1for closed-loop SM: periodic reporting

report location of preferred

subbands in Bandwidth part j

sub-bandCQI

sub-bandCQI

#bits L 2|1|4 4 4 3 3

JkNL //log DLRB2=

CQI(2)

CQI(1)

CQI(3)

CQI(4)

CQI(N-3)

CQI(N-2)

CQI(N-1)

CQI(N)

Freq

uenc

y (s

ubba

nds)

SINR(2)

SINR(1)

SINR(3)

SINR(4)

SINR(N-3)

SINR(N-2)

SINI(N-1)

SINR(N)

SINR(2)

SINR(1)

SINR(3)

SINR(4)

SINR(N-2)

SINI(N-1)

SINR(N)

CW 0 CW 1

SINI(N-3)

CQI(2)

CQI(1)

CQI(3)

CQI(4)

CQI(N-3)

CQI(N-2)

CQI(N-1)

CQI(N)

CQ

I(sel

ecte

d su

bban

ds)

diffe

rent

ial C

QI(s

elec

ted

subb

ands

)

CW 0 CW 1measurements per PMI !!!

CQI(2)

CQI(1)

CQI(3)

CQI(4)

CQI(N-3)

CQI(N-2)

CQI(N-1)

CQI(N)

PMI

select best PMI and subands(in terms of combined data rate)

diffe

rent

ial s

patia

l CQ

I(wid

eban

d)

CQ

I(wid

eban

d)

SINR SINR

N1

NJ

k = subband sizeJ = number of bandwidth parts (see also next slide) +Rank Indicator (RI)


Report timing configuration for mode 2-1: periodic reporting

report location of preferred subbands in

Bandwidth part j

PMI WBCQICW1

sub-bandCQI

WBCQICW2

sub-bandCQI

#bits L 2|1|4 4 4 3 3

RISBCQIj = 0

WBCQI

SBCQIj= 1

SBCQIj = 2

WBCQI

J = 3: SB bitmap-report is split into J bandwidth parts that are reported in consecutive intervals

SBCQIj = 0

SBCQIj= 1

SBCQIj = 2

SBCQIj = 0

SBCQIj= 1

SBCQIj = 2

SBCQIj = 0

SBCQIj= 1

SBCQIj = 2

RISBCQIj = 0

WBCQI

SBCQIj= 1

SBCQIj = 2

WBCQI

SBCQIj = 0

SBCQIj= 1

SBCQIj = 2

K = 2: SB reporting periodicity (J consecutive SB reports) with respect to WB reporting periodicity

MRI = 2: RI reporting periodicity with respect to WB reporting periodicity

NP = 2: Reporting Periodicity in TTIs

…continue…


Multi-User DL MIMO

MAC scheduler decides on users „pairing“

Maximum 2 users on same resource due to 2TB restriction

∆CQI(2)

∆CQI(1)

∆CQI(3)

∆CQI(4)

∆CQI(N-3)

∆CQI(N-2)

∆CQI(N-1)

∆CQI(N)

CQ

I(wid

eban

d)

Freq

uenc

y (s

ubba

nds)


PMI(w

ideb

and)

∆CQI(2)

∆CQI(1)

∆CQI(3)

∆CQI(4)

∆CQI(N-3)

∆CQI(N-2)

∆CQI(N-1)

∆CQI(N)

CQ

I(wid

eban

d)

CW 0 CW 1

#bits 2N 4 2N 4 2|1|4


channel „experienced“ at user 1

channel „experienced“ at user 2

No joint processing at Rx, no cooperation!

4

2

4

2

desired interfering

desiredinterfering

Pre-coding matrix selection (UE1) maximize

minimize

2

2

44

4

2

UE 1

UE 2

forUE 1

forUE 2

UE 1 UE 2

Multi-User DL MIMO


UL-MIMO UL-MIMO is not explicitly supported in LTE,

single antenna port in UL, no single-user(SU) SM in UL

demodulation UL reference signals (DRS) of different users overlap/interfere

DRS of different users are separated in TD according to „cyclic-shift“ of identical sequence (theoretical max. of 8 user, depending on delay-spread)

depends on eNB scheduler‘s flexibility and PHY support

delay spread max 12 cyclic shift

h1[t] h2[t] h3[t] h12[t]

r*PUSCH(k)

DRS demapperFFT x

h1[t]+ h2[t]+…+ h12[t]

„cyclic-shift“ zero

IFFT


Source: 3GPP self evaluation results, 3GPP TSG-RAN chair, oct 2009

Spectral efficiency 3GPP self-evaluation results


0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

-10 -5 0 5 10 15 20SNR in dB

12mimoOn34

16QAM 1/2 EVA5 50 RB 2x2 SFBC

LTE DL simulation results reported by the Top4 leading LTE vendors

Thro

ughp

ut [B

its]


LTE-Advanced: Concepts

Improved Spectrum Flexibility Bandwidth up to 100MHz Spectrum and carrier aggregation

MIMO support SM in UL Higher order MIMO in DL Coordinated Multipoint Transmissionfrom interference randomization to

interference coordination

Multihop Relays L1 repeaters to improve coverage L3 relays for self-backhauling eNB

100 MHz

20 MHz 20 MHz

eNB

relaynode

UE


LTE-Advancedadvanced MIMO receiver structure

SD-SIC for OFDMA2 codewords used,

each S/P-mapped onto 2 Tx antennas

1,kY2,kY

LMMSE / Soft IC

LLR calc. Rate matching

LLR calc.

Decoder

Decoder

Signal construction

Signal construction

Channel estimate

Channel estimate

3,kY4,kY

S/P

S/P Rate matching

Figure: NSN: R1-083732 / 2008-09-23


End of Part 2

Thank you!!!

153867696 lte-tutorial-femtoforum-part2-130814004042-phpapp01

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