Cognitive DF Generalized Order Relaying with CCI and Multiple Primary Users of Orthogonal Spectrums

In this paper, we propose and evaluate the performance of cognitive decode-and-forward (DF) generalized order relay selection network with primary receivers using orthogonal spectrums in the presence of interference. The primary receiver whose channel enhances the performance of the secondary system is used in determining the interference constraint on the secondary users power. Using orthogonal spectrum bands in wireless networks aims to reduce the interference between users as in the downlink transmission in cellular networks. The used generalized order relay selection scheme is efficient in situations where the opportunistic relaying scheme could fail due to imperfect channel-state-information, outdated channel information, or in case where the best relay is busy in some scheduling and load balancing duties in other parts of the network. In this scheme, the relay with the second or even the N^th best second hop channel forwards the source message to destination. Closed-from expression is derived for the end-to-end (e2e) outage probability assuming Rayleigh fading channels. Furthermore, the performance is studied at the high signal-to-noise ratio (SNR) regime. Monte-Carlo simulations are given to verify the achieved results. Main results show that the number of primary receivers affects the system performance through affecting the coding gain. Unlike the existing papers where the same spectrum band is assumed to be used by different primary receivers, our findings demonstrate that increasing the number of primary receivers in the proposed scenario enhances the system performance. Results illustrate that when the interference at the secondary relays or destination or at both scales with SNR, the system achieves zero diversity order and a noise floor appears in the results.