Interference Reduction and Cancellation by Beamforming in Cognitive Radios

Gavili Gilan, Adnan | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42279 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Nasiri Kenari, Masoumeh
  7. Abstract:
  8. Cognitive Radio (CR), as a new concept to efficiently utilize a licensed spectrum, and this has received intensive attension in recent years. By applying the cognitive technique, an unlicensed user (the secondary user (SU)) is allowed to transmit at the Primary User’s (PU) spectrum band under some conditions. Different approaches have been introduced to be utilized by the SU in order to be able to efficiently transmit at the PR’s spectrum without any sustainsial destructive effects on PR transmission and reception, which one of them is using multiple antenna in the cognitive transmitter. Hereby, CR is able to increase its throughput without substansial harmfull effect on PR’ transmission by desining a pattern of wave (Beamforming) at the direction of its Receiver. In this thesis, we consider the optimum design of beamforming vectors in CR system. In contrast to the previous works we assume that CR receiver has multiple antennas. We consider two different methods for designing the optimum transmit and receive beamforming vectors. At first method, the two beamforming vectors are designed separately; while in the second method, they are designed jointly. In our design, we consider the effect of PR transmitter on CR receiver as well as imperfect channel state information. We show that our both design approaches outperform the conventional design in which the effect of the PR transmission is not taken into account. The beamforming vectors are designed for two commonly used models for channel estimation errors, namely Normbounded Error and Statistical Error. At the last part of the thesis, we consider multi user CR system and design beamforming vectors for two different cases: A) CRs transmit in different orthogonal sub bands each dedicated to one PR. B) CRs transmit simultaneously on whole PR bands. For the first case, we derive an optimum closed form solution. For the second case, as the optimum solution is very complicated, we provide a sub optimum solution based on linear programming which its performance is slightely less than the optimum solution
  9. Keywords:
  10. Cognitive Radio ; Multiple Antenna System ; Beamforming ; Estimation Error

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