中文摘要：

选择中继已被证明是一种有效和实用的协作分集方法。但是，现有的分析主要集中在渐进高信噪比（SNR）区域，因此，研究认知选择协同分集系统任意信噪比的中断概率具有现实意义。推导了瑞利衰落信道选择中继协议的中断概率解析式，并进行了仿真。仿真结果表明，选择中继协议在任意信噪比情况下，增加中继节点可降低中断概率，而解码中继协议（DF）在低、中信噪比情况下不一定降低中断概率；同时，选择中继协议的中断性能和分集增益随频谱空穴检测能力的提高而增强。

英文摘要：

Selection cooperation has been shown to be an effective and practical method of implementing cooperative diversity. However, the available analysis has largely focused on the asymptotically high signal to noise ratio （SNR） regimes. It is of practical significance to investigate the outage performance of a cog- nitive selection cooperation at arbitrary SNR. Closed - form expressions are obtained for independent Ray- leigh fading channels, and simulation is performed. The simulation results show that DF does not necessarily decrease the probability of outage using more relays from the low SNR regime to the middle SNR regime. On the other hand, increasing relays in selection cooperation always improve the outage performance in the all SNR regime. At the same time, the outage performance and diversity gain of selection cooperation will improve with the increasing of spectrum hole detection ability.