Lte mimo schemes

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  • MIMO schemes in 3GPPMIMO schemes in 3GPP--LTE LTE (Dec. 2007)(Dec. 2007)Jacob Scheim, Ph.D.Jacob Scheim, Ph.D.

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

    MIMO schemes in 3GPP-LTE

    Downlink

    Background

    Infrastructure for MIMO over LTE

    SU-MIMO

    MU-MIMO

    Transmit diversity

    Uplink

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

    Background

    Max. code words - 2

    Max. Tx. Antennas 4 Potentially up to four layers

    Pre-coding 16 elements, unitary, for SU-MIMO

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

    Pilot patterns for spatial multiplexing

    R0

    R0

    R0

    R0

    R0

    R0

    R0

    R0

    0=l 6=l 0=l 6=l

    R0

    R0

    R 0

    R 0

    R0

    R0

    R 0

    R 0

    R 1

    R 1

    R1

    R1

    R 1

    R 1

    R1

    R1

    eve n-numbered s lots odd-numbere d slot s

    R3

    R3

    R3

    R3

    R

    0

    R0

    R0

    R0

    e ve n-numbere d slot s odd-numbere d sl ots

    R

    0

    R0

    R0

    R0

    R1

    R1

    R1

    R1

    eve n-numbered s lots odd-numbered slot s

    R1

    R1

    R1

    R1

    e ven-numbe re d slot s odd-numbe red sl ots

    R2

    R2

    R2

    R2

    On

    e ante

    nna

    port

    Tw

    o a

    nte

    nn

    a p

    ort

    sFour

    ante

    nna

    por

    ts

    Antenna port 0 Antenna port 1 Antenna port 2 Antenna port 3

    Not used for transmission on this antenna port

    Reference symbols on this antenna port

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

    Pilot patterns for spatial multiplexing

    Antenna port #0

    Antenna port #2

    Antenna port #3

    180

    [KHz]

    0.5 [msec]

    Antenna port #1

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

    Comments on reference signal

    Is 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

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

    Multi layer data transmission (SU-MIMO)

    Space

    Rank 2

    MIMO

    Rank 4

    MIMO

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

    Data/Control partitioning

    Increased

    region

    1 msec

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

    Peak rates for LTE-MIMO

    Back of the envelope calculations:

    11x12 generic tile size (assuming max. control symbols)

    Peak rate:

    64 QAM - 6 bits/symbols

    Code rate - 1 (no FEC)

    BW - 20 MHz - 110 RBs

    Sub-frames per second - 1000

    Peak rates calculation:

    SISO: 11*12*6*110*1000 =87 Mbps

    MIMO (2x2, 4x2) doubles the rate >150 Mbps

    MIMO (4x4) quadruples the rare= >300 Mbps

    High class UEs category 5 (with 4 Rx antenna)

    may exceed 300 Mbps

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

    Infrastructure

    Pre-coding for what:

    Increasing SNR (Beam-forming)

    Decreasing intra-cell interference

    Decreasing inter-cell interference

    Code book design

    Unitary matrices (Householder based)

    16 matrices for 4x(1:4) scheme

    Feedback:

    Wideband

    Narrowband

    Channel quality indication

    Per layer

    Feedback

    Wideband

    Narrowband

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

    Comments on MU-MIMO (SDMA)

    Requires standard adaptation for SDMA:

    Optimizing the pre-coding codebook

    Changing the CQI feedback structure

    User A

    User B User D

    User C

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

    DL transmit diversity modes

    Transmit diversity

    1 stream to 2 antennae port - Alamouti scheme

    1 stream to 4 antennae port Alamouti alike scheme

    Two parallel Alamouti schemes

    Cyclic delay diversity (CDD)

    Zero/small delay diversity

    Large delay diversity

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

    Transmit diversity

    *

    0

    *

    1

    10

    xx

    xx

    Origin*:

    Antenna

    Time*

    01

    *

    10

    xx

    xx

    Antenna

    Freq.

    LTE:

    Rate 1 codeDiversity order = 2

    Two transmit antennas

    Basic assumptions:

    Two transmit chains

    Channel doesnt change along the retransmission

    * S.M. Alamouti "A simple transmit diversity technique for wireless communications," IEEE JSAC vol. 16 (8), pp. 14511458

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

    Transmit diversity cont

    *

    23

    *

    32

    *

    01

    *

    10

    00

    00

    00

    00

    xx

    xx

    xx

    xx

    Antenna

    Freq.

    0123

    *

    1

    *

    0

    *

    3

    *

    2

    *

    2

    *

    3

    *

    0

    *

    1

    3210

    xxxx

    xxxx

    xxxx

    xxxx

    Antenna

    Time

    Rate 1 code

    Diversity order = 2 (spatial)

    Rate 1 code

    Diversity order < 4

    Four transmit antennas

    LTE: Alternative*:

    * Hamid Jafarkhani "A quasi-orthogonal spacetime block code," IEEE Trans. Comm. Vol. 49 (1): pp. 14

    Unbiased scheme (Ch. Est.) Biased scheme (Ch. Est.)

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

    Transmit diversity

    Summary:

    STBC => SFBC

    For 4 transmit antennas

    Diversity order equals 2

    Unbiased channel estimates

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

    Cyclic delay diversity

    x0

    x1

    x2

    xN-2

    xN-1

    FFT Modulator 1st Tx. antenna

    FFT Modulator 2nd Tx. antenna

    Xd-1

    x0

    x1

    x2

    xN-2

    xN-1

    xd

    Xd+1

    Xd-2

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

    Problem

    The pilots are processed also

    Solution

    Project the processing backwards prior the FFT

    CDD requires extra processing for channel estimation

    Pilots remain orthogonal

    Cyclic delay diversity

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

    Uplink

    Requirements Open loop Tx diversity: SxBC, CDD

    2x2 MU-MIMO Virtual MIMO

    2x2 SU-MIMO

    Standard Preliminary stages

    The TS 36.211 doesnt reflect currently any decision taken

    Technically The same as DL

    Reference signals are orthogonal by time division Between antennas orthogonal sequences may be used

    Two transmit antennas A single RF chain?

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

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