Beamforming in Wireless Sensor Networks

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Beamforming in Wireless Sensor Networks

• Omar Bakr
• ombakr_at_cs.berkeley.edu

R. Mudumbai, J. Hespanha, U. Madhow, Scalable
Feedback Control for Distributed Beamforming in
Sensor Networks, Proc. 2005 IEEE International
Symposium on Information Theory (ISIT 2005),
Adelaide, Australia, September 2005.
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Advantages of Beamforming

• More coverage for less power
• Less interference gt improved capacity
• Basic idea use a cluster of nodes to emulate
  elements of a phased array
• Challenges relative locations of the different
  nodes are unknown and clocks are not synchronized
• Beamforming has to be done in a distributed and
  scalable fashion

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Beamforming Scenario
Sender
Beamformers
Receiver
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Randomized Beamforming Algorithm

• Each node needs to apply the proper phase shift
  to the signal in order to maximize the signal in
  strength in a particular direction
• How to choose the right phase delay? Use feedback
• Each node independently adjusts its phase delay
  by ? or -? with equal probability at each time
  slot
• If an SNR improvement is detected, then the new
  delays are used otherwise revert to the previous
  delays

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Performance Evaluation (100 nodes)
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Weaknesses of this approach

• Works well only when the channel is time
  invariant
• May not converge if the channel varies at high
  rates
• Requires a noiseless feedback channel
• Not clear what beam pattern gets produced with
  the random weight assignment