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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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