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On the Achievable Rate Region Improvement in Information Networks Utilizing Cognition and Cooperative Strategies

Emadi, Mohammad Javad | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44501 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Aref, Mohammad Reza
  7. Abstract:
  8. User cooperation is an important concept in wireless networks to achieve best performance subject to low cost. Dynamic and broadcast natures of wireless networks are two indispensable characteristics of these networks. Therefore, when a user transmits his signal to the receiver, other users in his neighborhood may receive the signal as well. Hence, these neighbors can decide to cooperate with each other in transmitting their messages to the receiver. On the other hand, due to the dynamic nature of the wireless networks, one can assume that each user has some knowledge about the interference signals or the fading coefficient that are not known to the other users. Therefore by utilizing user cooperation, they can combat interference signals, too.
    In the thesis, a two-user uplink channel is assumed in which some random processes control statistics of the channel. These random processes are partly known at each user. Moreover, it is assumed that each user can ideally overhear the transmitted signal of the other user in a strictly causal manner. For a given channel model, upper and lower bounds on the capacity region are derived that are reduced to a channel capacity region for a special case in which only one user can receive the transmitted signal and knows the channel state completely. Then a general state-dependent multiple access channel with generalized feedback is introduced in which each user partly knows the channel state information noncausally. By proposing a coding strategy, an achievable rate region is derived that reduces to several known special cases. In the proposed scheme, besides using message cooperation between users, each user tries to describe its knowledge about the channel state information to the other user and the receiver. By analyzing Gaussian channel models, the effect of the state and message cooperation on the enlargement of the achievable rate region is discussed. Moreover, it is proved that if at least one of the encoders knows the channel state information completely, then an achievable rate region is derived which is independent of the power of interference signal. Finally, a fading relay channel with decode-and-forward relaying strategy under individual average power constraints at the source and the relay is introduced. It is proved that the problem of deriving optimal power allocation for the given channel model, is a convex optimization problem and optimal solutions are derived. By numerical examples, optimal power allocations are derived for a fading channel and its performance is compared without optimal power allocation and other scenarios
  9. Keywords:
  10. Relay Channel ; Multiple Access Channel With Feedback ; Channel State Description ; Cooperation Strategies ; Channel State ; Optimal Power Allocation

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