基于优化ZFBF的认知MISO系统中的用户选择算法

为提高认知无线电多输入单输出(cognitive radio multiple input single output, CR MISO)系统传输速率，给出一种基于波束成形的用户选择算法。假设信道状态信息已知，算法采用零空间理论消除对主用户(primary user, PU)干扰和优化迫零波束成形(zero forcing beamforming, ZFBF)技术消除认知用户(cognitive user, CU)间干扰。考虑发射功率限制，依次选择CU进行注水功率分配实现最大化系统传输速率。此外，在迭代中采用正交三角分解（orthogonal triangular decomposition, LQ)减少算法复杂度。数值分析表明，本算法系统的传输速率与PU的干扰门限大小无关，且比采用近正交用户选择算法的系统传输速率高4~6bps/Hz。当发射功率限制为10 dB时，在相同条件下使用优化ZFBF的传输速率比使用ZFBF的传输速率高约1 bps/Hz。

User selection algorithm for cognitive radio MISO system based on ZFBF optimization

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.