UWB Coexistence and Cognitive Radio

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UWB Coexistence and Cognitive Radio

• Dr. Jim Lansford, CTO
• Alereon, Inc
• jim.lansford_at_alereon.com
• 1 512 345 4200 x 2166
• February 13, 2004

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Agenda

• What is UWB?
• What is Cognitive Radio?
• Whats interference temperature?
• What are methods for coexistence?
• Are there coexistence problems unique to UWB?
• Why is this interesting and significant?
• What has been done to date?
• What direction is this going?
• Are there opportunities for bright and creative
  researchers?

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What is UWB?

• FCC definition
• B/Fc gt 0.20 or
• B gt 500MHz
• Why is this good?
• Shannon
• CB log(1SNR) bits/sec
• Capacity scales linearly with bandwidth, but
  logarithmically with powerHOWEVER recall SNR is
  a function of B

Claude Shannon
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Whats UWB? (2)

• OriginallyMarconis spark gap generator!
• Until 2002impulse radio
• Todaymulti-band OFDM

Impulse radio signal
Marconis spark gap generator in 1901
Multiband-OFDM signal
http//www.localhistory.scit.wlv.ac.uk/Museum/Engi
neering/Electronics/history/radiohistory.htm
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What is Cognitive Radio?

• A radio that is aware of its environment and
  adapts its behavior
• Multi-protocol
• Interference management
• Software defined

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Whats interference temperature?

• FCC term to attempt to quantify link degradation
  due to interference
• Analogous to kTB

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What are methods for coexistence?

• Power - Use no more than needed for the link
• Frequency Channelization is the classical
  method, but has limits (FDMA)
• Time Transmit at different times (TDMA)
• Code Use FH or DS techniques to manage
  interference (CDMA)
• Space Use antenna characteristics (smart or
  not) to enhance the channel (SDMA)

The goal? To make every transmission from A to B
reliable (meets performance criteria)
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Coexistence methods (2)

• The best answer? COLLABORATION
• A collaboration technique allows dissimilar
  systems to negotiate optimal access to the
  medium, and thus spectrum utilization
• Frequency Coordination
• Time Scheduling
• Some interference management can be done without
  collaboration
• Spectrum adaptation
• Antenna beamforming
• Power control
• Error/multiple access coding

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Are there coexistence problems unique to UWB?

• You bet!
• Cant use traditional filtering techniques
• Spectrum is wide
• Meant to be an underlay

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Why is this interesting and significant?

• Spectral reuse
• Spectrum management based on local environment,
  not national policies
• Better reliability (throughput, QoS)
• Wireless is a noisy, unreliable, expensive,
  insecure piece of wire.
• Optimized capacity
• Bits/sec/Hz/m3
• And of course, lots of research topics

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What has been done to date?

• Several technologies that have been combined into
  a systems approach for interference management
• Uses Time and Frequency coordination, along with
  RF signal processing
• SimOp-D (called PTA in IEEE) intelligent traffic
  management based on prioritized scheduling
• SimOp-A RF signal cancellation
• Reduces dynamic range requirements at A/Ds
• Reduces burden on filters to remove adjacent
  channel signals
• Reduces need for antenna isolation
• Antenna isolation
• A systems approach maximizes performance vs.
  piecemeal approaches.

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What direction is this going?

• Optimizes
• Cost of connection
• Data rate
• Error rate/QoS
• By controlling
• Protocol (if multiple available)
• Power levels
• Antenna beamforming
• Frequency
• Coding
• Timing

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Research areas?

• Variable BW, Fc preselector filters (MEMS?)
• Flexible, low power A/D
• Scalable, reconfigurable BB/MAC designs
• Tradeoffs between power and flexibility
• Optimization policies
• What is the objective function and what are the
  constraint functions? (see prev slide)
• UWB specific
• OFDM has large dynamic range
• Signal excision prior to A/D
• Efficient OFDM Tx shaping (closed loop?)
• Fill the interference temperature gaps
• Improved mesh networking techniques
• Improved coding
• Smarter Viterbi decoders