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With the rapid increase in new wireless technologies and services, the unlicensed frequency band have been substantially overcrowded while the licensed band are reportedly under-utilized. This spectrum scarcity has brought up the concept of cognitive radio networks. By applying distributed cooperation between users, cognitive radio can direct beam towards the intended receiver and suppress interference in unintended directions which can tackle the problem of spectrum scarcity.
In this MS thesis, first beamforming in uniform array is investigated. The effect of position displacement of antenna elements from ideal uniform array shows that there is an increase in sidelobe level. Least squares method is used for the correction of error due to position displacement. The power consumption of centralized and distributed approach to beamforming is compared. The phase-only distributed beamforming method is investigated for uniformly distributed cognitive nodes with phase synchronization errors. The proposed PODB method calculates weights by adjusting the phase of the carrier signal to form a beam towards the intended receiver. The simulation results on the average beampattern and the complementary cumulative distribution function of the PODB method bring some insights to the distributed beamforming in cognitive radio networks.
Advisor: Yaoqing (Lamar) Yang