在差分协作分集系统中，传统的差分最大比合并器( MRC) 需要各链路的二阶统计量作为合并器的权． 选择合并器( SC) 可以直接根据接收信号构造决策变量，接收机根据决策变量选择接收链路并进行非相关检测． 文中分析了使用 SC 的差分放大转发( AF)系统在 Nakagami-m 衰落信道模型下的性能，应用矩生成函数的方法推导出系统误比特率的精确解析表达式和中断概率，并给出了最优功率分配． 理论分析和仿真结果表明: 使用SC、MRC 方案的差分 AF 系统性能均优于直接传输; 与 MRC 方案相比，SC 方案不需要任何信道状态信息，在降低复杂度的同时可以获得近似于 MRC 方案的性能．

In differential cooperative diversity systems，the traditional maximal ratio combiner (MRC) needs the
second-order statistics of all channels as the weights of the combiner． Meanwhile，a selection combiner (SC) can form a decision variable based on the received signals，and the link with the maximum magnitude of the decision variable is chosen for non-coherent detection． In this paper，the performance of a differential amplify-and-forward system employing a SC is analyzed． Then，an exact analytical expression of the average bit error rate (BER) and the outage probability are derived by means of the moment generating function (MGF) method and the optimal power allocation point is put forward． Theoretical analysis and simulation results demonstrate that the performance of the differential amplify-and-forward system employing the SC and the MRC is better than that of direct transmission， and in comparison with the MRC scheme，the SC scheme without any channel state information reduces the complexity and achieves a similar performance．