信道为瑞利信道，S_D的距离为1米，三跳协作通信系统中S_R、R1_R1、S_D的距离均为1/3米。调制方式为BPSK,信噪比在-15dB-15dB间，接收端合并方式为ERC,迭代次数为1000(The channel is Rayleigh channel, the distance of S_D is 1 m, and the distance of S_R, R1, S_D in three-hop cooperative com