Security--Reliability Tradeoff for Untrusted and Selfish Relay-Assisted D2D Communications in Heterogeneous Cellular Networks for IoT

This paper investigates security-reliability tradeoff for untrusted and selfish two-way relay-assisted device-to-device (D2D) communications in heterogeneous cellular networks for the Internet of Things (IoT). On one hand, the relay is untrusted and may try to extract useful information during the relaying process. On the other hand, the relay is selfish and is only willing to use the harvesting energy from the sources' signals for relaying. Both instantaneous and statistical security-reliability tradeoffs are taken into consideration. For instantaneous model, the security and the reliability are characterized by the secrecy rate and the data rate, respectively. We aim at maximizing the tradeoff function of a tradeoff factor subject to a total transmit power constraint. For statistical model, the security and the reliability are characterized by the secrecy outage probability (SOP) and the data outage probability (DOP), respectively. An SOP optimization problem is developed with a DOP constraint and a total transmit power constraint. For both the problems, closed-form solutions are achieved. Simulation results show that both instantaneous and statistical security-reliability tradeoffs can achieve the Pareto optimal front.