Relay Channel for Mobile Communications

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Relay Channel for Mobile
Communications

• Presenter Rohit Kumar

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Wireless Network
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Outline

• Relay Channel
• Transmission Strategies
• Diversity
• Cooperative Communication Virtual Antenna Array
• Model Analysis
• Few points about the Model
• Cooperative Diversity
• Concluding Remarks

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Relay Channel
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Transmission Strategies

• Fixed Relaying
• Decode and forward (Limited by Tx-R link)
• Observe and forward (effec. when R-Rx is good)
• Amplify and forward (Not as good as others )
• Adaptive forwarding
• Selective Relaying (Selects based on channel)
• Incremental Relaying (Uses feedback to improve
  spectral efficiency)
• Linear Relaying

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Diversity

• Diversity Gain
• Diversity mitigates effect of multipath fading.
• One method is to use multiple transmit and
  receive antennas.
• Transmit diversity may not be practical
• - most handsets (size)
• - wireless sensor network (size, power)

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Idea of Cooperative Communication
MIMO System
MIMO using relays
DIVERSITY
Potential increase of
CAPACITY
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Idea of cooperative communication
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Channel Model
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Capacity of the system

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Statistical Equivalent Channel to BS
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Different Channels Towards BS
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Probability of Outage
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Deduction of the scheme

• Higher data rates for given power or reduced
  power requirements for same rate increased
  battery life.
• Increase in receiver complexity.
• Significant reduction in outage probability.
• Increase in cellular region.

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So can we celebrate????
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All that glitters is not gold!!
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Issues with proposed model

• It can be generalized to M-users. Complexity
  incurred would be tremendous.
• Which users would should cooperate and what/who
  is deciding factor?
• Model uses phase information at Tx, and Laneman
  et al. proved that without CSI at Tx, there is no
  gain from cooperation in fast fading environment.
• Laneman also proved that in slow fading
  condition, cooperative diversity can be achieved.

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Contd.

• Good news Diversity gain would be equal to the
  number of cooperating terminals.
• With orthogonal users, SNR losses due to
  bandwidth inefficiency is very low
• With Space time coding, SNR loss is linear in
  nature.

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References

• A Sendonaris, E. Erkip, and Aazhang, User
  Cooperative diversity part I system
  description, IEEE Trans. on Comm.
• T. M. Cover, and A. A. E. Gamal, Capacity
  theorems for relay channels IEEE Trans. On
  Information Theory.
• S. Zahedi, On reliable communication over relay
  channels, PhD dissertation, Stanford University,
  CA, August 2005.
• J. Nicholas Laneman, Cooperative Diversity in
  Wireless Networks Algorithms and Architectures,
  MIT, September 2002.

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• Questions?????

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The Process