On energy efficient secure routing in multi-hop underlay D2D communications for IoT applications

In this paper, a physical layer security based secure routing problem in a multi-hop cognitive radio enabled device-to-device (CRD2D) communication, under the threat of multiple randomly distributed eavesdroppers (EVEs), is studied. Delivery of confidential packets between a given legitimate D2D transmitter-receiver pair is targeted with the aid of multiple intermediate legitimate D2D nodes that share spectrum of a predefined licensed/primary user for their transmissions as unlicensed/secondary users and operate on the principle of randomized-and-forward relaying. In view of the energy limitations of the D2D nodes engaged in IoT applications, the secure routing problem aims to maximize the secrecy energy efficiency (SEE) under the constraints of - (i) minimum secrecy rate (ii) minimum signal-to-interference plus noise ratio at any D2D receiver (iii) maximum primary user outage loss in presence of the D2D transmission (iv) maximum retransmission attempts by any D2D nodes. Based on our analysis, an optimal routing algorithm is proposed. Simulation results illustrate the dependence of SEE on various critical system parameters. Further, complexity analysis and implementation issues are also presented for the proposed routing algorithm.