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Little Wireless and Smart Antennas Jack H. Winters jwinters@motia.com 2/26/04. OUTLINE. Smart antennas Implementation issues Appliqué Conclusions. Smart Antennas for WLANs. Smart Antenna. Smart Antenna. AP. AP. Interference.

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little wireless and smart antennas jack h winters jwinters@motia com 2 26 04
Little Wireless and Smart AntennasJack H. Wintersjwinters@motia.com2/26/04
outline
OUTLINE
  • Smart antennas
  • Implementation issues
  • Appliqué
  • Conclusions
slide3

Smart Antennas for WLANs

Smart

Antenna

Smart

Antenna

AP

AP

Interference

Smart Antennas can significantly improve the performance of WLANs

  • TDD operation (only need smart antenna at access point or terminal for performance improvement in both directions)
  • Interference suppression  Improve system capacity and throughput
    • Supports aggressive frequency re-use for higher spectrum efficiency, robustness in the ISM band (microwave ovens, outdoor lights)
  • Higher antenna gain  Extend range (outdoor coverage)
  • Multipath diversity gain  Improve reliability
  • MIMO (multiple antennas at AP and laptop)  Increase data rates
slide4

Implementation Issues

SIGNAL

SIGNAL

BEAM SELECT

SIGNAL OUTPUT

BEAMFORMER

INTERFERENCE

BEAMFORMER WEIGHTS

INTERFERENCE

Adaptive Antenna Array

Switched Multibeam Antenna

SIGNAL OUTPUT

  • Smart antenna is a multibeam or adaptive antenna array that tracks the wireless environment to significantly improve the performance of wireless systems
  • Adaptive arrays in any environment provide:
  • Antenna gain of M
  • Suppression of M-1 interferers
  • In a multipath environment, they also provide:
  • M-fold multipath diversity gain
  • With M Tx antennas (MIMO), M-fold data rate increase in same channel with same total transmit power
multiple input multiple output mimo radio
Multiple-Input Multiple-Output (MIMO) Radio
  • With M transmit and M receive antennas, can provide M independent channels, to increase data rate M-fold with no increase in total transmit power (with sufficient multipath) – only an increase in DSP
    • Indoors – up to 150-fold increase in theory
    • Outdoors – 8-12-fold increase typical
  • Measurements (e.g., AT&T) show 4x data rate & capacity increase in all mobile & indoor/outdoor environments (4 Tx and 4 Rx antennas)
    • 216 Mbps 802.11a (4X 54 Mbps)
    • 1.5 Mbps EDGE
    • 19 Mbps WCDMA
slide6

Weight Generation

WEIGHT GENERATION TECHNIQUES

For Smart Antenna: Need to identify desired signal and distinguish it from interference

Blind (no demod): MRC – Maximize output power

Interference suppression – CMA, power inversion, power

out-of-band

Non-Blind (demod): Training sequence/decision directed reference signal

MIMO needs non-blind, with additional sequences

digital vs analog implementation
Digital vs. Analog Implementation
  • Analog Advantages:
    • Digital requires M complete RF chains, including M A/D and D/A's, versus 1 A/D and D/A for analog, plus substantial digital signal processing
    • The cost is much higher for digital
    • An appliqué approach is possible - digital requires a complete baseband
  • Digital Advantages:
    • Slightly higher gain in Rayleigh fading (as more accurate weights can be generated)
    • Temporal processing can be added to each antenna branch much easier than with analog, for higher gain with delay spread
    • Modification for MIMO (802.11n) is easier than with analog
slide8

Appliqué

Wireless Transceiver

RF

Processor

Baseband/MAC

Processor,

Host Interface

RF Appliqué

(Spatial processing only)

  • Conforms to 802.11 standard (blind beamforming with MRC)
  • Appliqué configuration requires minimal modifications to legacy designs
smart antenna wifi pcmcia reference design

Legacy Transceiver

Baseband/MAC

Processor

RF

Processor

Smart Antenna WiFi (PCMCIA Reference Design)

Appliqué Architecture Plug-and-Play to legacy designs

PCMCIA - CARDBUS Interface

Motia Smart Antenna RF Chip

Partners: Intersil/Globespan, Maxim/TI, RFMD, Atmel

802 11b packet structure

20 µs

192 symbol Long Preamble

MPDU

Preamble

SFD

PHY H

Data from MAC

128 Barker

BPSK

16 Barker

BPSK

48 Barker

BPSK

Barker BPSK/QPSK

(CCK 5.5/11Mbps)

802.11b Packet Structure

Time permits weight generation

96 symbol Short Preamble

MPDU

Preamble

SFD

PHY H

Data from MAC

56 Barker

BPSK

16 Barker

BPSK

24 Barker

QPSK

Barker BPSK/QPSK

CCK 5.5/11Mbps

802 11b performance with fading
802.11b Performance with Fading

Achieves a 12 to 14 dB gain over a single antenna

802 11b beamforming gains with 4 antennas
802.11b Beamforming Gains with 4 Antennas

Performance Gain over a Single Antenna in a Rayleigh Fading Channel

2X to 3X Range + Uniform Coverage

3X to 4X Range + Uniform Coverage

802 11n
802.11n
  • Requirements for 802.11n:
    • >100 Mbps in MAC
    • >3 bits/sec/Hz
    • Backward compatible with all 802.11 standards
  • Requires MAC changes and may require MIMO:
    • 4X4 system (?)
  • Next standards meeting in Orlando
summary and conclusions
Summary and Conclusions
  • Current research is finding ways to implement smart antennas in a variety of commercial systems:
    • Reusing same silicon where possible to reduce cost
    • Minimizing modifications to existing systems
    • Staying within the standards
    • Meeting each system’s unique requirements