60GHz Wireless System Design: Towards a 1Gbps wireless link

1
60GHz Wireless System DesignTowards a 1Gbps
wireless link

• David A. Sobel
• June 12, 2003

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Introduction Why 60GHz?

• FCC allocated 59-64 GHz of unlicensed spectrum
• 5 GHZ of bandwidth
• Few regulatory specifications
• 60 GHz spectrum well-suited to indoor
  picocellular network
• Opaqueness of building materials at 60GHz
• Small wavelength

Bandwidth and channel properties suitable for
1Gbps wireless link
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High-speed Link Key Challenges

• Friis Transmission equation Loss increases with
  fc
• Additional 22dB loss relative to 5GHz system
• Typical multipath channel issues
• Specular, (mostly) weakly reflective channel
• Baseband analog interface bottleneck
• Power-handling, linearity, and noise performance
  of CMOS circuits at 60GHz

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Shannon Limits

• With unlimited BW, Shannon AWGN capacity still
  limited by received power
• Assumptions
• NFRX10dB
• d10m
• 10dB shadowing loss
• Omni-directional antenna

Omni-directional antenna cant get 1Gbps
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Beamforming Antenna Gain

• Antenna array can create narrow, steerable beam
• Concentrate Tx power in proper direction
• Reciprocal relationship with Rx
• Allows for parallel PA implementation

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Beamforming Antenna Gain

• Antenna array can create narrow, steerable beam
• Concentrate Tx power in proper direction
• Reciprocal relationship with Rx
• Allows for parallel PA implementation

Directional Tx Antenna
Tx
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Beamforming Reduced Multipath

• Multipath caused by reflections in space
• Reducing the spatial extent of signal to LOS path
  reduces reflections

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Beamforming Reduced Multipath

• Multipath caused by reflections in space
• Reducing the spatial extent of signal reduces
  reflections

Directional Tx Antenna
h(t)
Refl 1
LOS
Tx
time
Refl 2
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60 GHz Channel Properties

• Significant characterization performed in
  literature
• Typical 60GHz indoor channel properties 1
• Omni-antenna w/ LOS TRMS 25ns, KRician
  0-5dB
• 30 horn w/ LOS TRMS lt 5ns, KRician gt 15dB
• Caveats
• Pointing accuracy
• Horn antennas vs. antenna arrays
• Conclusion Directivity reduces fading problem to
  ISI problem

• 1 M. Williamson, et al, "Investigating the
  effects of antenna directivity on wireless indoor
  communication at 6O GHz," PIMRC 1997

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Baseband Analog Bottleneck

• Targeting 1Gbps with Tx power constraint
• Must use low PAR signal for efficient PA
  utilization
• Targeting 1Gbps with low SNR signal
• Must use low-order constellation, high baud rate
• Spectral efficiency not a critical requirement
• Avoid high-resolution, oversampled DACs and ADCs

Utilize mostly-analog approach of high-speed
serial link design
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Modulation 2-CPFSK

• CPFSK (h1) vs. xPSK
• 2-CPFSK is very similar to BPSK
• Half-sine pulse shape (alternating) BPSK in
  Q-channel
• Embedded half-rate clock in I-channel
• Easy analog clock and carrier extraction

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Mostly-Analog Receiver Architecture

• 2-CPFSK modulation Embedded clock in I-channel
• Allows simple analog clock, carrier phase
  recovery
• Simple analog structures running at baud rate
• Some small overhead for low SNR environment

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Status and Future Work

• Status
• 60 GHz channel model literature search complete
• 2-FSK identified as candidate modulation
  technique
• System definition underway. Model in Simulink
• Clock and carrier recovery complete
• DFE structure to be added
• Future Work
• Analyze effects of antenna array on 60GHz channel
• Complete system definition
• Circuits