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SMART ANTENNAS FOR WIRELESS COMMUNICATIONS JACK H. WINTERS

SMART ANTENNAS FOR WIRELESS COMMUNICATIONS JACK H. WINTERS. AT&T Labs - Research Red Bank, NJ 07701-7033 jhw@research.att.com September 9, 1999. AGENDA. Background Use of adaptive antennas Key research issues Conclusions. Smart Antennas. SIGNAL. SIGNAL. BEAM SELECT.

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SMART ANTENNAS FOR WIRELESS COMMUNICATIONS JACK H. WINTERS

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  1. SMART ANTENNAS FOR WIRELESS COMMUNICATIONS JACK H. WINTERS AT&T Labs - Research Red Bank, NJ 07701-7033 jhw@research.att.com September 9, 1999

  2. AGENDA • Background • Use of adaptive antennas • Key research issues • Conclusions

  3. Smart Antennas SIGNAL SIGNAL BEAM SELECT SIGNAL OUTPUT BEAMFORMER INTERFERENCE BEAMFORMER WEIGHTS INTERFERENCE Phased Array Adaptive Antenna Array SIGNAL OUTPUT Smart Antenna Definition: Phased array or adaptive array antenna which adjusts to the environment. From site visits: “Smart antenna technology is the most (or one of the most) important technology for 4G cellular systems” (speakers at NTT, Filtronics, etc.).

  4. Future Systems Will Need Greater: • Power: • Higher data rates need higher power for the adequate reliability and perhaps higher frequencies (which have higher propagation and circuit losses) • Interference suppression: • For higher capacity with frequency reuse • Multipath mitigation: • For more reliable and robust communications

  5. Smart Antennas Provide: • Power: • Phased arrays provide narrow pencil beams with higher gain, particularly at higher frequencies, as do adaptive arrays • Interference suppression: • Phased arrays reduce probability of interference, and adaptive arrays suppress interference • Multipath mitigation: • Diversity (spatial, polarization, and angle)

  6. Smart Antennas Use: • From site visits, phased arrays and adaptive arrays are considered and researched about equally • Phased arrays: • Point-to-point • Some macrocellular base stations (e.g., GSM) • On satellites and on satellite terminals • Adaptive arrays: • Indoor systems • Microcells • Some cellular base stations (e.g., ANSI-136) • Terminals

  7. Key Research Issues: • Cost: • Power • 50% of power is in RF electronics, adding more antennas increases power usage (decreases terminal battery life) • RF electronics and A/D are expensive • Low cost phased array • Cost limits the number of antenna elements that can be used • Solutions being studied: • Optical beamforming for large phased arrays • Integrated antennas • Limited introduction • Size: • Antenna on a chip • “Antenna-less” terminals

  8. Key Research Issues: • Diversity: • Multiple antennas for diversity • Spatial (separation) • Difficult on handset • Difficult for point-to-point or base stations with small angular spread • Polarization (dual diversity only) • Angle (direction/pattern) • Multibeam antennas (depends on angular spread) • Antennas on handset where hand placement is critical • Minimize headloss

  9. Key Research Issues: • Tracking • Angle-of-arrival with phased arrays • Weights with adaptive arrays • Signal processing horsepower is not considered a significant research issue for tracking in most future systems • Better algorithms required: • AOA with MUSIC/ESPRIT today, but need to be robust with angular spread, obtain higher resolution • Adaptive array needs better subspace tracking methods: • higher data rates => longer equalizers => longer training sequences => greater overhead

  10. Key Research Issues: • Spatial-Temporal Processing: • Equalization of intersymbol interference (delay spread at high data rates) with cochannel interference suppression • Better architectures needed • Space-Time coding • interference suppression • tracking • BLAST/MIMO technology • M-fold increase in capacity with M antennas without increase in power or bandwidth • Extension to outdoors with tracking and multipath richness issues • Cochannel interference suppression

  11. Key Research Issues: • Hooks in standards (interdisciplinary research - protocols): • Incorporate features so that smart antennas are possible • 2G system problems: • ANSI-136: continuous downlink • IS-95: common downlink pilot • 3G hooks: • WCDMA: Downlink pilots dedicated to each user • EDGE: Signals from base stations that need to be broadcast to all users restrict smart antenna usage • 4G: Any packet/multimedia access to all users is a critical issue for smart antennas

  12. Key Research Issues: • Vertical Integration/Interdisciplinary Approach • Protocols for smart antennas - pilots and broadcast signals • Interaction with frequency hopping, power control, discontinuous transmission, adaptive channel assignment • RF matching (multiband antennas) • Adaptation to hand position • Limited introduction with nonuniform traffic • Ad hoc networks • Channel characterization • Base versus terminal antenna (complexity) tradeoffs • Transmit diversity with space-time coding

  13. Conclusions • Future system needs: higher data rates/better coverage/ubiquitous users and systems • Smart antennas are seen as a critical component to satisfy these needs - significant research in nearly all wireless companies visited • Substantial research to reduce cost, develop technologies, and integrate into future systems is required to achieve these goals

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