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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 42601 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Hashemi, Homayoun; Nasiri Kenari, Masoumeh
- Abstract:
- In this thesis, the effect of cognition in wireless networks is studied. In a wireless communica-tion network, cognition is the ability of a device to sense the transmissions of neighboring nodes and adapt its own transmission to the sensed environment. Cognitive radios are very attractive be-cause of the increasing need for more efficient use of frequency spectrum. The goal of this thesis is the analysis of cognitive radio networks from an information theoretic perspective and to this end statistical models of the wireless medium with a limited and tractable number of devices are uti-lized. We consider three different models in three parts of the thesis. First, we consider a new communication model consisting of two interfering broadcast chan-nels with one cognitive transmitter who knows the message transmitted by the other non-cognitive transmitter in a non-causal manner. An achievable rate region is derived for this model. The region is also evaluated for the Gaussian case and the performance improvement due to the cognition is demonstrated by some numerical examples. In the second part, we consider an extension of the classical two user interference channel in which instead of asymmetric cognition in one of the transmitters, a third node, called the cognitive relay, is added to the model which has non-causal knowledge of the messages transmitted by both transmitters and aids the communication between both source-destination pairs. We derive the ca-pacity region under conditions that include the “very strong interference” regime as a special case. Then, we obtain inner and outer bounds for a class of semi-deterministic interference channels with a cognitive relay and show that the outer bound is achievable for a special case in which the sources do not create interference at the non-intended destination. In the last part, considering a multiple access channel with one cognitive transmitter, we study the effect of partial knowledge of the channel coefficients at transmitters. We assume that the re-ceiver estimates channel coefficients using training sequences, quantizes them and sends them to the transmitters through a feedback channel. We investigate the effect of some quantization schemes on transmission rates when the cognitive transmitter uses dirty-paper coding to mitigate known interference. Through numerical evaluations, we show that few quantization bits are enough to achieve rates close to the non-quantized one
- Keywords:
- Capacity ; Cognitive Radio ; Lower Bound ; Upper Bound Method ; Dirty Paper Coding ; Channel Coefficient Quantization
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