基于门限判断DF协议的多无人机中继传输中断性能分析

UAV（unmanned aerial vehicle，无人机）中继系统作为远距离数据传输的一种有效手段，成为当前无线通信领域的一个研究热点。首先在考虑路径损耗等实际参数的前提下，建立了基于多个UAV的中继协作传输系统模型，得到采用门限判断 DF（decode-and-forward，译码转发）协议时系统的最大输出 SNR （signal-to-noise ratio，信噪比）表达式。接着，假设上行链路和下行链路均服从Rician分布，推导出多UAV中继传输系统的中断概率闭合表达式，并且进一步得到了高信噪比条件下中断概率的渐近表达式、系统的分集度和阵列增益，为分析系统参数对中断性能的影响提供了更加便捷的方法。最后，计算机仿真验证了理论分析的正确性，并且定量分析了无人机中继个数、配置的天线数目以及中断阈值对系统中断性能的影响，为实际的系统设计和应用提供参考。

Outage performance analysis for multi-UAV relay systems with threshold-based DF protocol

The unmanned aerial vehicle (UAV) relay system has become a hot topic as an effective method for the remote transmission in wireless communications.By taking path loss into account,a relay cooperative transmission system model based on multiple UAVs was established firstly,and the maximum output signal-to-noise ratio (SNR) of the system with threshold-based decode-and-forward (DF) protocol was obtained.Then,by assuming that both the uplink and downlink experience Rician distribution,the closed-form expression for outage probability (OP) of the considered system with multiple UAVs was derived.Furthermore,the asymptotic OP formula at high SNR was also derived to show the diversity order and array gain of the considered system,which were convenient to reveal the effects of system parameters on the outage performance.Finally,the computer simulations verify the correctness of the theoretical analysis,and reveal the effect of the relay number,antenna number and the threshold on the system outage performance,thus the proposed scheme can provide guidance for the system design and application.