Abstract:

To improve the transmission rate of cognitive radio multiple input single output(CRMISO) system, a cognitive user (CU) selection algorithm based on beamforming is proposed. The channel state information is assumed to be perfectly known, the proposed algorithm uses null space method to eliminate interference to primary users (PU) and zeroforcing beamforming (ZFBF) optimization technique to reduce cognitive interuser interference. When the transmit power control is considered, the CUs are sequentially selected to allocate waterfilling power so that CRMISO system can achieve maximum transmission rate. Moreover, orthogonal triangular decomposition (LQ) decomposition is adopted to reduce the complexit〖JP+3〗y of the proposed algorithm in iteration steps. Numerical simulation results show that, for CRMISO system, the system’s transmission rate of adopting the proposed algorithm is 4~6 bps/Hz more than that of the system adopting approximate orthogonal user selection algorithm, which is irrelevant with PU’s interference threshold. Moreover, when the transmit power control is 10 dB, the system’s transmission rate based on the optimal ZFBF is 1 bps/Hz greater than that based on ZFBF under the same conditions.