LTE MIMO Schemes

  • View
    234

  • Download
    6

Embed Size (px)

DESCRIPTION

MIMO Schemes in 3GPP LTE

Text of LTE MIMO Schemes

MIMO schemes in 3GPP-LTE

(Dec. 2007)

Jacob Scheim, Ph.D.

MIMO schemes in 3GPP-LTEDownlinkBackground Infrastructure for MIMO over LTE SU-MIMO MU-MIMO Transmit diversity

Uplink

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

2

Background

Max. code words - 2 Max. Tx. Antennas 4Potentially up to four layers

Pre-coding16 elements, unitary, for SU-MIMO

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

3

0000000000000000

000000000000000000

000000000000000000

000000000000000000000000000000000000R3

0000000000000000

0000000000000000000000000000000000R2

0000000000000000

0000000000000000

000000000000000000000000000000000000R1

000000000000000000000000000000000000R1

0000000000000000R0

0000000000000000

0000000000000000R0

0000000000000000

000000000000R1

00000000000000R1

0000 00000000R0

0000 00000000R0

000000000000 0000 00000000 000000000000

000000000000000000000000000 00000 000000000 000000000000000000000000000R3

00000000000000 00000 000000000 00000000000000

00000000000000 000000000 000000000000000000 00000000000000R3

000000000000 0000 00000000 000000000000

000000000000 00000000 00000000000000000 000000000000R2

000000000000 0000 00000000 000000000000

000000000000000000000000 0000 00000000 000000000000000000000000R2

000000000000

00000000000000 000000000 000000000000000000 00000000000000R1

00000000000000

00000000000000 000000000 000000000000000000 00000000000000R1

000000000000000000000000 0000 00000000 000000000000000000000000R0

000000000000000000000000 0000 00000000 000000000000000000000000R0

00000000000000R1

00000000000000R1

000000000000R0

000000000000R0

000000000000R1

00000000000000R1

000000000000R0

000000000000R0

000000000000000000R1

000000000000000000R1

0000000000000000R0

0000000000000000R0

000000000000l =6

00000000000000l =0

000000000000

000000000000l =0

Pilot patterns for spatial multiplexing

R0

R0

R0

One antenna port

R0

e ve n-nu mbere d slot s

R0

R0

Antenna port 0

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reservedR0 R0 R0 R0 od d-nu mbere d sl ot s R0 R0

l= 6

eve n-numbered s lots

R1

R1

Antenna port 1

o dd-n umb ered slot s

R1

R1

Two antenna ports

Reference symbols on this antenna port

Not used for transmission on this antenna port

e ven-numbe re d sl ot s

R2

Antenna port 2

odd-numbe red sl ots

eve n-numbered s lots

Ant enna port 3

o dd-n umb ere d slot s

R3

4

Four antenna ports

Pilot patterns for spatial multiplexing180 [KHz] 0.5 [msec]

Antenna port #0 Antenna port #1 Antenna port #2

Antenna port #3 (C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

5

Comments on reference signalIs not affected by applying pre-coding Is not affected by applying transmit diversity Reference signals density reduces with number of antennas:Higher layer MIMO for lower mobility

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

6

Multi layer data transmission (SU-MIMO)

Rank 2 MIMO Space

Rank 4 MIMO

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

7

Data/Control partitioning1 msec

Increased diversity region => 150 Mbps >300 Mbps antenna)

SISO: 11*12*6*110*1000 MIMO (2x2, 4x2) doubles the rate MIMO (4x4) quadruples the rare= High class UEs category 5 (with 4 Rx may exceed 300 Mbps

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

9

InfrastructurePre-coding for what:Increasing SNR (Beam-forming) Decreasing intra-cell interference Decreasing inter-cell interference

Code book designUnitary matrices (Householder based) 16 matrices for 4x(1:4) scheme Feedback:Wideband Narrowband

Channel quality indicationPer layer FeedbackWideband Narrowband

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

10

Comments on MU-MIMORequires standard adaptation for SDMA:Optimizing the pre-coding codebook Changing the CQI feedback structure

(SDMA)

User A

User C

User B

User D

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

11

DL transmit diversity modesTransmit diversity 1 stream to 2 antennae port - Alamouti scheme 1 stream to 4 antennae port Alamouti alike schemeTwo parallel Alamouti schemes

Cyclic delay diversity (CDD) Zero/small delay diversity Large delay diversity

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

12

Transmit diversityTwo transmit antennasBasic assumptions:Two transmit chains Channel doesnt change along the retransmission

Origin*: Antenna

LTE: Antenna

Time

x0 x* 1

x1 x* 0

Freq.

x0 x1

x x

* 1 * 0

Rate 1 code Diversity order = 2S.M. Alamouti "A simple transmit diversity technique for wireless communications," IEEE JSAC vol. 16 (8), pp. 14511458(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved 13*

Transmit diversityFour transmit antennasLTE: Antenna

cont

Alternative*: Antenna

x0Freq.

0 0 x2 x3

* x1 * x0 0

0 0 * x3* x2

x0Time* x1 * x2

x1* x0 * x3

x2* x3 * x0

x3* x2 * x1

x1 0 0

0

x3

x2

x1

x0

Rate 1 code Diversity order = 2

(spatial)

Rate 1 code Diversity order < 4 Biased scheme (Ch. Est.)

Unbiased scheme (Ch. Est.)*

Hamid Jafarkhani "A quasi-orthogonal spacetime block code," IEEE Trans. Comm. Vol. 49 (1): pp. 14(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved 14

Transmit diversitySummary:STBC => SFBC For 4 transmit antennasDiversity order equals 2 Unbiased channel estimates

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

15

Cyclic delay diversityx0 xd x1 Xd+1 x2

xN-2 xN-1

FFT FFT

x0 x1 x2

Modulator Modulator

1st Tx. antenna 2nd Tx. antenna

xN-2 Xd-2 xN-1 Xd-1

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

16

Cyclic delay diversityProblemThe pilots are processed also

SolutionProject the processing backwards prior the FFTCDD requires extra processing for channel estimation Pilots remain orthogonal

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

17

UplinkRequirementsOpen loop Tx diversity: SxBC, CDD 2x2 MU-MIMOVirtual MIMO

2x2 SU-MIMO

StandardPreliminary stages The TS 36.211 doesnt reflect currently any decision taken

TechnicallyThe same as DL Reference signals are orthogonal by time divisionBetween antennas orthogonal sequences may be used

Two transmit antennasA single RF chain?(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

18

www.comsysmobile.com

(C) 2007 Comsys communication and Signal Processing Ltd. All rights reserved

19