Outage performance of decode‐and‐forward (DF)‐based multiuser spectrum sharing relay system with direct link in the presence of primary users’ power

Abstract

This study investigates outage probability (OP) of a generalised decode-and-forward-based multiuser spectrum sharing relay system. In practice, the secondary users are exposed to the primary transmitters’ signals which can measurably affect the OP in the secondary system. In this context, analytical and asymptotic outage analysis are presented for two different relay selection techniques, namely partial relay selection (PRS) and opportunistic relay selection (ORS). In terms of the ORS, deriving an exact analytical expression for the end-to-end (e-t-e) OP is contingent upon solving a very complicated integral. To resolve this problem, they propose a simple modification under which the OP can be obtained with preferable accuracy. Numerical simulations are presented where the excellent agreement of the simulation results with the analytical results validates the mathematical derivations and confirms that the proposed simplification is accurate. Findings suggest that the ORS has three main advantages over the PRS. First, it is more robust against the primary interference. Second, it achieves the full diversity order, whereas the PRS limits the diversity order to the number of secondary destinations plus one. Third, the gain of enhancement achieved by increasing the number of relays is significantly larger.