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Little Wireless and Smart Antennas Jack H. Winters jwinters@motia.com 2/26/04

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

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  1. Little Wireless and Smart AntennasJack H. Wintersjwinters@motia.com2/26/04

  2. OUTLINE • Smart antennas • Implementation issues • Appliqué • Conclusions

  3. 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

  4. 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

  5. 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

  6. • • • 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 802.11b Performance with Fading Achieves a 12 to 14 dB gain over a single antenna

  12. 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

  13. 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

  14. 802.11n Process

  15. 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

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