On the Achievable Transmission Capacity of Secrecy-Based D2D Cellular Networks

Device-to-Device (D2D) communication is one of the key technologies to get to very high data rates in future 5G networks through offloading part of the cellular traffic onto D2D networks. While extensive research is targeted on addressing the many challenges D2D brings along in cellular networks, security issues have not gained much attention, especially that the direct connections between proximity devices are more vulnerable to security threats, which in turn deteriorate users' experience. In this paper, we consider a D2D communication overheard by eavesdroppers in an underlay cellular network, where D2D users access a proportion of the spectrum occupied by cellular users. To mitigate the potential security threats, we turn towards a lightweight low-complexity approach by exploiting the physical characteristics of the wireless channels. Using tools from stochastic geometry, we derive the D2D transmission region and the average transmit power that guarantee a minimum secrecy rate and a target outage probability. Results reveal that when offloading less cellular traffic onto D2D links, the large cellular interference can be exploited to protect D2D links from eavesdroppers. On the other hand, with aggressive D2D offloading, D2D users can achieve a much higher secrecy capacity due to significantly reducing the distances between them.