无人机中继通信是实现远距离无线通信的一种重要技术手段，无人机的飞行航迹对无人机中继通信系统的链路传输可靠性存在显著的影响，在频率选择性衰落信道环境下研究了基于直序列码分多址（DS-CDMA）的无人机中继通信系统的航迹优化的问题。首先，给出了基于DS-CDMA的译码转发无人机中继通信系统的模型，并理论分析给出无人机中继通信系统的链路中断概率及平均误码率计算公式，以此为基础，基于链路中断概率最小化准则提出了中继无人机的航迹规划方法，最后通过仿真验证了所提出方法的正确性与有效性。研究表明：最大比值合并DS-CDMA无人机中继通信系统可充分获取频率选择性衰落信道提供的分集增益，显著改善链路传输的可靠性。
Unmanned Aerial Vehicle (UAV) relay communication is an important technique for long-range wireless communications. However, the link reliability of a UAV relay communication system is severely influenced by its flying path. This paper investigates the path planning issue of relaying UAV with the Direct Sequence Code Division Multiple Access (DS-CDMA) transmission scheme over frequency selective fading channel. Firstly, the model of UAV relay communication system using decode-and-forward protocol is given. Both the outage probability and the average symbol error probability of the relaying link are derived. Then, a path planning method based on the criterion of minimizing the outage probability is proposed. Finally, computer simulations are provided to verify the correctness of the theoretical results. Our study shows that the proposed system can obtain the diversity gain provided by the frequency selective fading channel, greatly improving the link reliability of the system.
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