Transcript No Slide Title

SMART ANTENNAS FOR WIRELESS
COMMUNICATIONS
JACK H. WINTERS
AT&T Labs - Research
Red Bank, NJ 07701-7033
[email protected]
September 9, 1999
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AGENDA
• Background
• Use of adaptive antennas
• Key research issues
• Conclusions
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Smart Antennas
Phased Array
Adaptive Antenna Array
SIGNAL
BEAMFORMER
SIGNAL
BEAM
SELECT
SIGNAL
OUTPUT
SIGNAL
OUTPUT
INTERFERENCE
INTERFERENCE
BEAMFORMER
WEIGHTS
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.).
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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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