An Efficient Switching Threshold-Based Scheduling Protocol for Multiuser Cognitive AF Relay Networks with Primary Users Using Orthogonal Spectrums

Abstract

In this paper, we propose and evaluate the performance of multiuser switched diversity (MUSwiD) cognitive amplify-and-forward (AF) relay networks with multiple primary receivers using orthogonal spectrums. Using orthogonal spectrum bands aims to mitigate the interference between users in wireless networks. The spectrum of primary receiver whose channel results in the best performance for the secondary system is shared with secondary users. To reduce the channel estimation load in the secondary cell, the MUSwiD selection scheme is used to select among secondary users. In this scheme, the user whose end-to-end (e2e) signal-to-noise ratio (SNR) satisfies a predetermined switching threshold is scheduled to receive data from the source instead of the best user. In the analysis, an upper bound on the e2e SNR of a user is used in deriving of analytical approximations of the outage probability and average symbol error probability (ASEP). The performance is also studied at the high SNR regime where the diversity order and coding gain are derived. The derived expressions are verified by Monte-Carlo simulations. Results illustrate that the diversity order of the studied MUSwiD cognitive AF relaying network is the same as its non-cognitive counterpart. Unlike the existing papers where the same spectrum band is assumed to be shared by the primary receivers, our findings demonstrate that increasing the number of primary receivers in the proposed scenario enhances the system performancevia improving the coding gain.