Relay Performance in D2D Communications Overlaying Multi-Antenna Cellular Networks

This paper reports the outage performance of different relaying mechanisms, namely amplify-and-forward (AF), decode-and-forward (DF) and their hybrid mode, in a multi-antenna cooperative cognitive radio network (CCRN). The proposed CCRN model supports two-way device-to-device (D2D) communications through spectrum sharing of the existing cellular network. In this architecture, cellular nodes are considered as primary users (PUs) and the associated devices in D2D communications act as secondary users (SUs). Furthermore, it is also considered that the SU devices are able to harvest energy from PUs’ radio frequency signals, using simultaneous wireless information and power transfer (SWIPT) protocol. Closed form expressions of outage probability for both cellular and D2D communications are derived and the analytical results are validated through simulation results. Numerical values show that performance of the proposed system is about ∼ 92% and ∼ 47% better in terms spectrum efficiency (SE) and energy efficiency (EE), respectively over the existing system using DF relaying mechanism. The study also reports the various relaying options at different SU nodes and their relative performance comparison. Based on the exhaustive simulation results, it is found that hybrid relaying is the best option over all other single relaying techniques. It is also observed that about ∼ 12% SE improvement is achieved using multiple antenna over the single antenna communications.