MIMO Technology for Advanced Wireless Local Area Networks

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MIMO Technology for Advanced Wireless Local Area
Networks Dr. Won-Joon ChoiDr. Qinfang Sun Dr.
Jeffrey M. Gilbert Atheros Communications MIMO
RAKE Antenna Technology for Advanced MIMO
Wireless WAN and LAN Pr. Jean-Claude
Ducasse Hypercable Telecommunications
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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

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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

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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!

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Conventional (SISO) Wireless Systems
DSP
Bits
DSP
Radio
Radio
Bits
TX
RX

• 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

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MIMO Wireless Systems
Radio
Radio
DSP
DSP
Bits
Bits
Radio
Radio
TX
RX

• 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

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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

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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 / combining boosts reception
  of standard 802.11 signals

DSP
Radio
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Bits
Radio
TX
Radio
RX

• Phased array transmit beamforming to focus energy
  to each receiver

DSP
Radio
Bits
Bits
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Radio
RX
TX
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Benefits of Beamforming

• Benefits
• Power gain (applicable only to transmit
  beamforming)
• Power from multiple PAs 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

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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

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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
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DSP
BitMerge
BitSplit
Bits
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Radio
DSP
Radio
DSP
RX
TX
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MIMO RAKE Antenna Concept

• Dual Circular Polarization Diversity
• Spatial Multiplexing
• Multipath Mitigation
• Space diversity
• Beamforming

Radio
Radio
Radio
Radio
DSP
DSP
DSP
DSP
BitSplit
BitSplit
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TX
TX
GIGABIT I/O POE
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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
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DSP
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DSP
RX
TX
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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
Radio
DSP
Radio
RX
TX
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MIMO RAKE Antenna Solution

• Dual Circular Polarization Diversity
• Spatial Multiplexing
• Multipath Mitigation
• Space diversity
• Beamforming

Radio
Radio
Radio
Radio
DSP
DSP
DSP
DSP
BitSplit
BitSplit
Bits
TX
TX
GIGABIT I/O POE
Bits
Bits
Bits
Bits
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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

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MIMO Scalability

• Data Rates
• R Es Bw Ns -gt Scales with bandwidth and the
  number of spatial streams
• Example
• 11a/g Es 2.7 Bw 20MHz Ns1 R 54Mbps
• Spatial multiplexing MIMO
• Es 3.75 Bw40MHzNs 2 R 300Mbps
• Number of Tx/Rx chains
• At least as many chains as Ns
• Ns min(NR, NT)

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MIMO Hardware Requirements

• MIMO Transmitter (parallelism and data rate
  scaling)

IFFT
MOD
RF
Stream Split
Spatial Mapping
FEC
RF
IFFT
MOD
1 O(BwEsNs)
Ns O(BwEs)
1 O(BwEsNsNT)
NT O(BwEs)
NT Analog RF
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MIMO Hardware Requirements

• MIMO Receiver (parallelism and data rate scaling)

Demod
RF
Stream Merge
MIMO Equalizer
RF
Demod
1 O(BwEsNs)
NR Analog RF
1 O(BwEsNRNs2)
NR O(BwEs)
Ns O(BwEs)
Ns O(BwEs)
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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 Moores
  law to deliver higher performance wireless
  systems