中文摘要：

针对频率选择性信道下放大转发模式的多中继协同系统的波束成形因子设计问题进行研究。以最小化接收端总误比特率（BER）为目标，提出了一种两阶段的波束成形设计方法。所提方法可以有效降低设计的难度和复杂度，并且可以使接收端的总BER最小。仿真结果表明，与现有算法相比，本算法可以显著降低接收端的误比特率。

英文摘要：

This paper addresses the transmit beamforming （BF） design problem for amplify-and-forward relay network over fre- quency-selective channels. In order to get the minimum total bit-error-ratio（BER） at receiver, we develop a two-stage method to design BF vector. The proposed method can reduce the difficulty and complexity efficiently. Moreover it can lead to the minimum BER. Simulations show that proposed algorithm significantly outperforms the existing methods in terms of BER.