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Cooperative Beamforming in Relay Assisted MIMO-OFDMA Cognitive Radio Systems

In this paper, a new algorithm is proposed for cooperative beamforming, power allocation and relay selection in the multiple input multiple output (MIMO) Orthogonal Frequency Division Multiple Access (OFDMA) CR systems where a pair of SU communicates with each other assisted by some single antenna relay nodes. The objective is to maximize signal to interference plus noise ratio (SINR) of SU subject to guarantee the PU's quality of service and power constraints of SU and relay nodes over all subchannels. The transmitter and receiver beamforming vectors of PU and SU are estimated by the proposed twostep iterative algorithm. Simulation results show that the proposed algorithm is able to increase the spectrum usage efficiency and, further, guarantee the required QOS at the PU.