MIMO-AF协作系统中继发射矩阵的优化及性能分析

Performance Analysis and Optimization of Relay Transmit Matrix in MIMO-AF Cooperative System

为了提高MIMO放大前传(AF)协作中继系统的性能,文中提出在中继节点向目标节点发送信号之前,加入优化的发射矩阵。中继节点采用空时码,在发射功率受限的条件下,首先针对目标节点的接收信号运用最小均分误差MMSE准则,定义推导了求解最佳发射矩阵和接收端均衡器系数的优化问题。接着,为了降低解优化问题的计算复杂度,提出了梯度下降的迭代算法。然后通过推导误码率上限,从理论上证明了文中算法的有效性。仿真结果表明,在中继节点设置发射矩阵能够降低误码率上限,用文中方法对发射矩阵进行优化以后,与现有空时码相比,可以有效提高系统性能,且优化算法收敛性好,计算复杂度低。

The optimal transmit matrix is designed at MIM0 relay node with an amplify-and-forward（AF） cooperation strategy before the amplified data are forwarded to the destination node. It can improve the performance of the system with the STC at relay node. The MMSE expressions for the received signal at the destination node are devised to compute the parameters of the transmit matrix subject to a power constraint. Then, a gradient descent algorithm to simplify the optimization is proposed. Finally, the upper bound on the pairwise error probability is derived and the advantage of the transmit matrix is indicated. Simulation results show that the relay transmit matrix can reduce the upper bound of the error probability and the proposed optimization can obtain performance gains compared with existing STC schemes. Thus, the proposed algorithm has a fast convergence and low computational complexity.