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Click to enter your title. MIMO Technology for Advanced Wireless Local Area Networks Dr. Won-Joon Choi Dr. Qinfang Sun Dr. Jeffrey M. Gilbert Atheros Communications 2005 Design Automation Conference – June 15, 2005. Agenda.

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MIMO Technology for Advanced Wireless Local Area NetworksDr. Won-Joon ChoiDr. Qinfang Sun Dr. Jeffrey M. Gilbert Atheros Communications2005 Design Automation Conference – June 15, 2005


Agenda
Agenda

  • This presentation will give an overview of MIMO technology and its future in Wireless LAN:

  • Wireless Local Area Networks (WLAN)

    • Current standards (11a/b/g)

    • Next-generation 11n overview and status

  • MIMO fundamentals

    • Beamforming

    • Spatial Multiplexing

  • MIMO scalability

    • Bandwidth

    • Number of spatial streams


  • The wireless lan explosion

    Email / Info anywhereVoice over IP

    Internet everywhereMultimedia

    Hot-spot coverageMetro-Area Networks

    The Wireless LAN Explosion

    The Wireless LAN / Wi-Fi market has exploded!

    New technology is enabling new applications:

    Office

    Home

    “Hot-spots”


    Wireless lan technology advances
    Wireless LAN Technology Advances

    Wireless LAN technology has seen rapid advancements

    • Standards:

    • Data rates:

    • Range / coverage:

    • Integration:

    • Cost:

    802.11  .11b  .11a  .11g

    2Mbps  100+ Mbps

    Meters  kilometers

    Multiple discretes  single chip solutions

    $100’s  $10’s (sometimes free w/rebates!)

    • How can this growth continue?

      • Previous advances have been limited to a single transmitting and receiving radio

      • The next generation exploits multiple parallel radios using revolutionary class of techniques called MIMO (Multiple Input Multiple Output) to send information farther and faster



    What is being proposed for 802 11n
    What Is Being Proposed for 802.11n?

    Main Features

    • PHY

      • MIMO-OFDM

        • Beamforming

        • Spatial Multiplexing

      • Extended bandwidth (40MHz)

      • Advanced coding

    • MAC

      • Aggregation

      • Block ACK

      • Coexistence

      • Power saving


    Wireless fundamentals i
    Wireless Fundamentals I

    In order to successfully decode data, signal strength needs to be greater than noise + interference by a certain amount

    • Higher data rates require higher SINR (Signal to Noise and Interference Ratio)

    • Signal strength decreases with increased range in a wireless environment


    Wireless fundamentals ii
    Wireless Fundamentals II

    Ways to increase data rate:

    • Conventional single tx and rx radio systems

      • Increase transmit power

        • Subject to power amplifier and regulatory limits

        • Increases interference to other devices

        • Reduces battery life

      • Use high gain directional antennas

        • Fixed direction(s) limit coverage to given sector(s)

      • Use more frequency spectrum

        • Subject to FCC / regulatory domain constraints

    • Advanced MIMO: Use multiple tx and / or rx radios!


    Conventional siso wireless systems

    channel

    Conventional (SISO) Wireless Systems

    Conventional “Single Input Single Output” (SISO) systems were favored for simplicity and low-cost but have some shortcomings:

    • Outage occurs if antennas fall into null

      • Switching between different antennas can help

    • Energy is wasted by sending in all directions

      • Can cause additional interference to others

    • Sensitive to interference from all directions

    • Output power limited by single power amplifier

    Bits

    DSP

    DSP

    Radio

    Radio

    Bits

    TX

    RX


    Mimo wireless systems

    channel

    MIMO Wireless Systems

    Multiple Input Multiple Output (MIMO) systems with multiple parallel radios improve the following:

    • Outages reduced by using information from multiple antennas

    • Transmit power can be increased via multiple power amplifiers

    • Higher throughputs possible

    • Transmit and receive interference limited by some techniques

    Radio

    Radio

    DSP

    DSP

    Bits

    Bits

    Radio

    Radio

    TX

    RX


    Mimo alternatives
    MIMO Alternatives

    There are two basic types of MIMO technology:

    • Beamforming MIMO

      • Standards-compatible techniques to improve the range of existing data rates using transmit and receive beamforming

      • Also reduces transmit interference and improves receive interference tolerance

    • Spatial-multiplexing MIMO

      • Allows even higher data rates by transmitting parallel data streams in the same frequency spectrum

      • Fundamentally changes the on-air format of signals

        • Requires new standard (11n) for standards-based operation

        • Proprietary modes possible but cannot help legacy devices


    Beamforming mimo overview
    Beamforming MIMO Overview

    Consists of two parts to make standard 802.11 signals “better

    Uses multiple transmit and/or receive radios to form coherent 802.11a/b/g compatible signals

    • Receive beamforming / combiningboosts reception of standard 802.11 signals

    Radio

    DSP

    Bits

    Bits

    Radio

    TX

    Radio

    RX

    • Phased array transmit beamforming to focus energy to each receiver

    DSP

    Radio

    Bits

    Bits

    Radio

    Radio

    RX

    TX


    Benefits of beamforming
    Benefits of Beamforming

    Benefits

    • Power gain (applicable only to transmit beamforming)

      • Power from multiple PA’s simultaneously (up to regulatory limits)

      • Relaxes PA requirements, increases total output power delivered

    • Array gain: “dynamic high-gain antenna”

    • Interference reduction

      • Reduce co-channel inter-cell interference

    • Diversity gain: combats fading effects

    • Multipath mitigation

      • Per- subcarrier beamforming to reduce spectral nulls


    Multipath mitigation
    Multipath Mitigation

    • Multiple transmit and receive radios allow compensation of notches on one channel by non-notches in the other

    • Same performance gains with either multiple tx or rx radios and greater gains with both multiple tx and rx radios


    Spatial multiplexing mimo concept
    Spatial Multiplexing MIMO Concept

    Spatial multiplexing concept:

    • Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates

    Radio

    DSP

    Radio

    DSP

    BitMerge

    BitSplit

    Bits

    Bits

    DSP

    Radio

    DSP

    Radio

    RX

    TX


    Spatial multiplexing mimo difficulties
    Spatial Multiplexing MIMO Difficulties

    Spatial multiplexing concept:

    • Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates

    • However, there are cross-paths between antennas

    Radio

    DSP

    Radio

    DSP

    BitMerge

    BitSplit

    Garbage

    Bits

    DSP

    Radio

    DSP

    Radio

    RX

    TX


    Spatial multiplexing mimo reality
    Spatial Multiplexing MIMO Reality

    Spatial multiplexing concept:

    • Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates

    • However, there are cross-paths between antennas

    • The correlation must be decoupled by digital signal processing algorithms

    DSP

    Radio

    DSP

    Radio

    BitMerge

    BitSplit

    Bits

    Bits

    DSP

    Radio

    Radio

    RX

    TX


    Spatial multiplexing mimo theory
    Spatial Multiplexing MIMO Theory

    • High data rate

      • Data rate increases by the minimum of number of transmit and receive antennas

      • Detection is conceptually solving equations

        Example of 2-by-2 system:

        • Transmitted signal is unknown,

        • Received signal is known,

        • Related by the channel coefficients,

        • Need more equations than unknowns to succeed

    • High spectral efficiency

      • Higher data rate in the same bandwidth


    Mimo scalability
    MIMO Scalability

    • Moore’s law

      • Doubling transistors every couple of years

    • MIMO

      • Increases number of streams

      • Higher performance/speed

      • Higher complexity

        MIMO is the bridge to allow us to exploit Moore’s law to get higher performance


    Mimo scalability1
    MIMO Scalability

    • Notation

      • R: data rates (Mbps)

      • Es: spectral efficiency (bps/Hz)

      • Bw: bandwidth (MHz)

      • Ns: number of spatial streams

      • NR: number of Rx chains

      • NT: number of Tx chains


    Mimo scalability2
    MIMO Scalability

    • Data Rates

      • R = Es * Bw * Ns -> Scales with bandwidth and the number of spatial streams

      • Example

        • 11a/g: Es = 2.7; Bw = 20MHz; Ns=1; R = 54Mbps

        • Spatial multiplexing MIMO

          Es = 3.75; Bw=40MHz;Ns = 2; R = 300Mbps

    • Number of Tx/Rx chains

      • At least as many chains as Ns

        Ns = min(NR, NT)


    Mimo hardware requirements
    MIMO Hardware Requirements

    MIMO Transmitter (parallelism and data rate scaling)

    IFFT

    MOD

    RF

    Stream

    Split

    Spatial

    Mapping

    FEC

    RF

    IFFT

    MOD

    1 *O(Bw*Es*Ns)

    Ns *O(Bw*Es)

    1*

    O(Bw*Es*Ns*NT)

    NT*

    O(Bw*Es)

    NT*

    Analog RF


    Mimo hardware requirements1

    DEC

    FFT

    FFT

    MIMO Hardware Requirements

    MIMO Receiver (parallelism and data rate scaling)

    Demod

    RF

    Stream

    Merge

    MIMO

    Equalizer

    RF

    Demod

    NR*

    Analog RF

    NR*

    O(Bw*Es)

    1*

    O(Bw*Es*NR*Ns2)

    Ns*

    O(Bw*Es)

    Ns*

    O(Bw*Es)

    1*

    O(Bw*Es*Ns)


    Conclusions
    Conclusions

    • The next generation WLAN uses MIMO technology

      • Beamforming MIMO technology

        • Extends range of existing data rates by transmit and receive beamforming

      • Spatial-multiplexing MIMO technology

        • Increases data rates by transmitting parallel data streams

    • MIMO allows system designers to leverage Moore’s law to deliver higher performance wireless systems


    Circuit implications of mimo
    Circuit Implications of MIMO

    • Crystal

      • Common crystal is required

    • Synthesizer

      • Common synthesizer is preferred

    • PA

      • Allow additional flexibility

        • With total power limit, PA requirements relaxed

        • With PA limit, total power increased.

    • Cross-talk/ Coupling

      • Need to minimize coupling between antennas


    Circuit impairments corrections
    Circuit Impairments/Corrections

    • Timing offset

      • Common across multiple chains

    • Frequency offset

      • Common across multiple chains

    • Phase noise

      • Common with common synthesizer

      • With independent synthesizers, a new tracking algorithm may be needed.

    • Other impairments

      • 1/f noise, I/Q mismatch, spurs, etc.

      • Estimated and corrected for each chain


    Backup slides
    Backup Slides

    • 0.18um standard digital CMOS

    • 7.2x7.2 mm2 die size

    • 15x15mm2 BGA with 261 balls

    • Ref: ISSCC’05




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