基于定向天线和机会中继的DF协作通信系统性能分析

定向天线(directional antenna,DA)的电磁波波束具有较小的成型角度,仅能覆盖某一方向上的通信节点,相比全向天线(omni-directional antenna, ODA),具有方向性好、功率增益大、传输距离远以及满足军事通信射频隐身等优点。协作通信技术通过节点间的相互辅助,对抗信道衰落,实现协作分集。为了实现有限节点间如车间、船间且需要采用定向天线的可靠通信,提出了将定向天线和采用解码转发型最佳中继选择的机会中继协作策略(opportunistic relaying,OR)相结合的解决方案,在此基础上推导出相应的通信系统中断概率理论公式,并对中断概率和信噪比、中继节点数、天线增益以及信道衰落系数之间的关系进行了数值仿真分析,以及和全向天线系统进行了比较分析。理论分析和仿真结果表明：在有限节点间定向通信中,采用定向天线的协作通信系统性能与各节点定向天线增益、信道质量和功率分配方式密切相关,适合在小信噪比及深衰落信道环境下采用。最后,进一步分析得出最优功率分配(Optimal power allocation, OPA)比平均功率分配(average power allocation,APA)性能更优。

Cooperative Communication System with Directional Antennae and Opportunistic DF Strategy

The electromagnetic beam of directional antenna with small forming angle can only cover the nodes in a certain direction. Comparing with omnidirectional antenna, directional antenna has the advantages of good directivity, high gain, far transmission distance and meeting the requirements of the RF stealth in military communications, etc. Cooperative communication technology through the auxiliary to each other between nodes, achieve cooperative diversity, against channel fading. Firstly, the opportunistic decode-and-forward relaying (opportunistic DF) multi-node cooperative communication system model and the cooperation strategy with the directional antennas are presented. Secondly, the theoretical formula of outage probability is derived. Numerical and simulation results of the cooperative communication systems operating in two kinds of antenna pattern are presented to verify our analysis. These findings reveal that excellent performance of cooperative communication system with directional antennas could be achieved and closely related to the conditions of relaying nodes number, SNR, channel quality and gain of the antennas. The findings further reveal that the performance of the cooperative communication system can be further improved by using the unequal power allocation scheme compared with the equal power allocation scheme and suggested to be used under the condition of smaller SNR and deep fading channel environment.