LTE MIMO System Level Design

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LTE MIMO Explained

Text of LTE MIMO System Level Design

  • 1Copyright Agilent Technologies 2009Agilent Restricted

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    LTE MIMO System-Level Design(Preliminary)

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    Agenda

    MIMO OverviewMIMO Transmitter Case StudyMIMO Receiver Case StudyEarly R&D LTE Hardware Testing

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    Basic channel access modesTransmitAntennas

    ReceiveAntennas

    SISO

    The Radio Channel

    MISO

    Single Input Single Output

    Multiple Input Single Output(Transmit diversity)

    ReceiveAntennas

    TransmitAntennas

    MIMO

    The Radio Channel

    SIMO

    Single Input Multiple Output(Receive diversity)

    Multiple Input Multiple Output(Multiple stream)

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    Advantages of multiple antennas

    MISO (Tx diversity) increases the robustness of the signal to poor channel conditions. It does not increase data rates but increases coverage and therefore cell capacity.

    SIMO (Rx diversity) improves the received SNR by combining multiple copies of the same signal. Like MISO it does not increase data rates but extends coverage and hence cell capacity.

    MIMO uses multiple data streams to increase cell capacity. The data streams can be allocated to one user to increase single-user data rates.

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    Multiple antenna techniques

    Multiple antenna techniques are fundamental to LTE and an appreciation of the different methods and their relative advantages and disadvantages is important

    There are three main multi-antenna techniques used in LTE1. Transmit/receive diversity2. Spatial multiplexing

    Single User MIMO (SU-MIMO) Multi-user MIMO (MU-MIMO)

    3. Beamforming

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    Transmit/receive diversity

    This is the same as what already exists for UMTS Transmit diversity has been specified for W-CDMA since R99. Receive

    diversity was introduced in Rel-6 for HSDPA.

    The same data is sent on two antennas which provides better SNRImproves performance in low SNR conditions and with fadingSimple combining is used in the receiver

    eNB UE

    Stream 1

    Stream 1

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    Single user MIMO

    This is an example of downlink 2x2 single user MIMO with precoding. Two data streams are mixed (precoded) to best match the channel

    conditions.The receiver reconstructs the original streams resulting in increased single-

    user data rates and corresponding increase in cell capacity. 2x2 SU-MIMO is mandatory for the downlink and optional for the uplink

    SU-MIMO

    eNB 1 UE 1

    = data stream 1

    = data stream 2

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    Multiple user MIMO

    UE 2

    UE 1

    eNB 1

    MU-MIMO

    Example of uplink 2x2 MU-MIMO.In multiple user MIMO the data streams come from different UE.There is no possibility to do precoding since the UE are not connected but

    the wider TX antenna spacing gives better de-correlation in the channel.Cell capacity increases but not the single user data rate.The key advantage of MU-MIMO over SU-MIMO is that the cell capacity

    increase can be had without the increased cost and battery drain of two UE transmitters.

    MU-MIMO is more complicated to schedule than SU-MIMO

    = data stream 1

    = data stream 2

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    SystemVue MIMO Source

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    SystemVue MIMO Channel Model

    Simulated Spectrum with MIMO Fading

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    SystemVue MIMO Receiver

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    Agenda

    MIMO OverviewMIMO Transmitter Case StudyMIMO Receiver Case StudyEarly R&D LTE Hardware Testing

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    Mixed-Signal Challenges: System Design Tradeoffs

    Tx RxCodingAlgorithms

    D/ABits In Decoding

    Algorithms Bits Out

    ChannelA/D

    GainLinearityOutput Power

    GainNFPhase Noise

    Considerations: Key Algorithms Baseband Implementation/ Fixed-Point Effects RF Design Impairments/Non-Linearities Phase Noise, ADC Jitter Channel Impairments

    FPGA HDL Code

    Fixed Point Baseband Designs

    Math Algorithms

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    System-Level Architecture DesignPartition Design Requirements to Meet LTE Specifications without Over-Designing

    ADC and DACImpairments

    RF Transmitter/PA Nonlinarities

    Baseband Fixed-PointMixed-Signal

    Receiver

    Tx RxCodingAlgorithms

    D/A

    Bits In DecodingAlgorithms Bits Out

    RF ChannelA/D

    Coding/Decoding

    Algorithms

    With LTE having such high performance targets every part of the transmit and receive chain becomes critical to the link budgetSo how to decide the optimum balance, without over-designing?How are design requirements impacted going from QPSK to 16QAM to 64QAM?

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    Baseband Libraries Algorithm Test Vectors for FPGA Development

    (Preliminary)

    Coding/Decoding

    Algorithms

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    Configurable References

    (Preliminary)

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    Diff

    FPGA HDL CoSim Output

    SystemVueScrambler

    Output

    HDL (Actual Scrambler Code Not Shown)

    Switch between C++ model and math algorithm model

    FPGA Scrambler Example

    (Preliminary)

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    Diff

    FPGA HDL CoSim Output

    SystemVueScrambler

    Output

    HDL (Actual Scrambler Code Not Shown)

    Switch between C++ model and math algorithm model

    FPGA Scrambler Example

    (Preliminary)

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    Transmitter Design Start with SystemVue Pre-Configured Template

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    I in

    Q in

    4XUpSample

    4XUpSample

    FIR RRC

    FIR RRC

    Fs/4 Carrier Multiplexing

    I(t)*CosWc(t)

    Q(t)*SinWc(t)

    I(t)*CosWc(t)-Q(t)*SinWc(t)

    Design Fixed Point IQ Modulator andReplace Ideal IQ Modulator

    Baseband Fixed-Point

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    64QAM EVM Results with FIR Wordlength =10 for Fixed Point IQ Modulator Design

    EVM = 0.5 %

    (Preliminary)

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    64QAM EVM Results with FIR Wordlength =8 forFixed Point IQ Modulator Design

    EVM = 1.3 %

    (Preliminary)

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    64QAM EVM Results with FIR Wordlength =6 & 7 for Fixed Point IQ Modulator Design

    EVM = 2.9 % EVM = 46 % !

    FIR Wordlength = 7 bits FIR Wordlength = 6 bits

    (Preliminary)

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    Enable HDL Code Gen to Target an FPGA

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    Add RF Design: Transmitter and Antenna Cross Talk

    Specify LO Phase Noise dBc/Hz @ Freq. Offset RF Transmitter/

    PA Nonlinarities

    Specify 1dBComp. Pt.

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    -80 dBc/Hz Phase Noise @ 10kHz with -30 dB CrossTalk

    Specify Phase Noise in

    dBc/Hz vs. Frequency

    Offset

    RS EVM = 1.3 % RS EVM = 1.3 %

    QPSK 64 QAM(Preliminary)

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    -70 dBc/Hz Phase Noise @ 10kHz with -30 dB CrossTalk

    Specify Phase Noise in

    dBc/Hz vs. Frequency

    Offset

    RS EVM = 3.5 % RS EVM = 3.5 %

    QPSK 64 QAM(Preliminary)

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    -60 dBc/Hz Phase Noise @ 10kHz with -30 dB CrossTalk

    RS EVM = 11.2 %

    QPSK

    Specify Phase Noise in

    dBc/Hz vs. Frequency

    Offset

    RS EVM = 11.2 % ,but composite EVM is 85%

    64 QAM

    Phase noise is introducing significant ICI , which is impacting OFDMA subcarrier orthogonality

    (Preliminary)

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    LTE MIMO Downlink BER with ADI A/D Converter

    MIMO SourceMIMO Receiver

    Sweep SNR

    ADI A/D Converter

    MIMO Channel

    ADC and DACImpairments

    Mixed-SignalReceiver

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    QPSK BER Results with Swept ADI A/D Converter Jitter

    2% Jitter

    4% Jitter

    6% Jitter

    (Preliminary)

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    QPSK , 16QAM, 64QAM Results vs. Swept ADI ADC Jitter

    QPSK 16 QAM 64 QAM

    2% Jitter4% Jitter

    6% Jitter

    2% Jitter

    4% Jitter

    6% Jitter

    2% Jitter4% Jitter

    6% Jitter

    (Preliminary)

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    QPSK , 16QAM, 64QAM Results vs. Swept LO Phase Noise

    QPSK 16 QAM 64 QAM

    -70 dBc/Hz

    -65 dBc/Hz

    -60 dBc/Hz

    (Preliminary)

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