In this paper, we study the underlay relay-aided Device-to-Device (D2D) communications to improve the physical layer (PHY) security of the cellular network. We propose a cooperative scheme, whereby the D2D pair, in return of being allowed to share the spectrum band of the cellular network, serves as a friendly jammer, through its multiple-input multiple-output relay, to degrade the wiretapped signal at an eavesdropper. This paper aims to show that spectrum sharing is advantageous for both D2D communications and cellular networks with respect to reliability and robustness for the former, and the physical layer security enhancement for the latter. To assess the proposed cooperative system model, closed-form expressions for the D2D outage probability, the secrecy outage probability, and the probability of non-zero secrecy capacity are derived. More importantly, the benefits due to the cooperation scheme are verified through numerical and simulation results.

中文翻译：

---

论底层中继辅助设备到设备通信的物理层安全

在本文中，我们研究了底层中继辅助的设备到设备 (D2D) 通信，以提高蜂窝网络的物理层 (PHY) 安全性。我们提出了一种合作方案，其中 D2D 对作为被允许共享蜂窝网络的频谱带的回报，作为友好的干扰器，通过其多输入多输出继电器，降低窃听者的窃听信号. 本文旨在表明频谱共享对于 D2D 通信和蜂窝网络在前者的可靠性和鲁棒性以及后者的物理层安全增强方面都是有利的。为了评估所提出的合作系统模型，导出了 D2D 中断概率、保密中断概率和非零保密容量概率的闭式表达式。