This paper exploits the multi-antenna technique to enhance the covert communication performance in a relay system, where a source S conducts covert communication with a destination D via a relay R, subjecting to the detections of transmissions in the two hops from a single-antenna warden W. To demonstrate the performance gain from adopting the multi-antenna technique, we first consider the scenario when S, R and D all adopt single antenna, and apply hypothesis testing and statistics theories to develop a theoretical framework for the covert performance modeling in terms of detection error probability (DEP) and covert throughput. We then consider the scenario when S, R and D all adopt multiple antennas, and apply the hypothesis testing, statistics and matrix theories to develop corresponding theoretical framework for performance modeling. We further explore the optimal designs of the target rate and transmit power for covert throughput maximization under above both scenarios, subjecting to the constraints of covertness, reliability and transmit power. To solve the optimization problems, we employ Karushi-Kuhn-Tucker (KKT) conditions method in the single antenna scenario and a search algorithm in the multi-antenna scenario. Finally, we provide extensive numerical results to illustrate how the multi-antenna technique can enhance the covert performance in two-hop relay systems.

翻译：本文利用多天线技术来增强中继系统中的隐蔽通信性能。在该系统中，源节点S通过中继节点R与目的节点D进行隐蔽通信，并受到一个单天线看守节点W对两跳传输的检测。为了展示采用多天线技术所带来的性能增益，我们首先考虑S、R和D均采用单天线的情况，并应用假设检验和统计学理论，构建了一个基于检测错误概率和隐蔽吞吐量的隐蔽性能建模理论框架。随后，我们考虑S、R和D均采用多天线的情况，并应用假设检验、统计学和矩阵理论，构建了相应的性能建模理论框架。我们进一步探讨了在上述两种场景下，如何在隐蔽性、可靠性和发射功率的约束下，对目标速率和发射功率进行优化设计，以实现隐蔽吞吐量的最大化。为了解决这些优化问题，我们在单天线场景中采用了Karush-Kuhn-Tucker条件方法，在多天线场景中采用了一种搜索算法。最后，我们提供了大量的数值结果，以说明多天线技术如何能够增强两跳中继系统中的隐蔽性能。