MIMO-AF协作中继网络中发送预编码器的优化

本文首先利用中继节点和目标节点在第一时隙中的接收信噪比之和最大准则，推导出优化问题并解得优化的预编码器矢量。然后又利用目标节点最大比合并后的接收信号信噪比最大准则，推导出性能更佳的预编码器优化问题，但由于表达式复杂不能得到闭式解。为此本文提出了两种次优解决方法，分别是梯度下降迭代法和近似求解法。仿真结果表明，提出的两种准则优化预编码器方法都能有效改进系统性能，且因后者更能直接反映接收端情况，效果更好。两种次优的解优化方法能够获得几乎相同的系统性能，但梯度下降法采用迭代运算，计算量比较大，而近似求解法在性能不损失的情况下大大降低了计算复杂度。 

Optimization of precoder for MIMO-AF cooperative relay networks

The optimal precoder vector at a source node is designed for MIMO cooperative relay networks with an amplify-and-forward (AF) strategy. Firstly, this paper derive the optimum solution of the precoder vector with the criterion of maximizing the sum of SNR observed at both destination and relay nodes in the first time slot. Meanwhile, the precoder optimization with the criterion of maximizing SNR after MRC at the destination node is also devised, but its analytical solution is unavailable. In order to reduce the complexity, two suboptimal methods are proposed, namely, the gradient descent iterative method and the approximate solution method. The simulation results show that the proposed optimal precoders using two criterions can also improve the system performance, and the case of maximizing SNR at the destination node is more effective because it can describe the status of the receiver directly. The performance of the gradient descent method is almost the same as the one of the approximate solution method, but the former method is more complex due to iterations. The approximate solution method achieves low complexity with no performance reduction.