Spectrum-Sharing AF Relay Networks with Switch-and-Examine Relaying and Multiple Primary Users Using Orthogonal Spectrums

Abstract

In this paper, we propose and evaluate the behavior of a new cognitive amplify-and-forward relaying scenario where the multiple primary users utilize orthogonal spectrum bands. Using orthogonal bands aims to reduce the interference between users as in the downlink transmission in cellular networks where a base station transmits the data of different users using orthogonal frequency bands. In the proposed scenario, the spectrum of the primary user whose channel enhances the secondary system performance is shared with the secondary users. In this paper, the low-complexity switch-and-examine diversity combining relaying scheme is used to select among the secondary relays. In this scheme, the relay whose end-to-end signal-to-noise ratio (SNR) satisfies a predetermined switching threshold is selected instead of the best relay to forward the source message to destination. Approximate expressions are derived for the outage probability and average symbol error probability of the studied system assuming Rayleigh fading channels. Also, the ergodic channel capacity is numerically calculated in this paper. Furthermore, to simplify the achieved expressions and to get more insights about the system behavior, the system is studied at the high SNR values where approximate expression is derived for the outage probability in addition to the derivation of the diversity order and coding gain of the system. The achieved results are validated by Monte Carlo simulations. Main findings illustrate that the diversity order of the studied system is the same as its non-cognitive counterpart and it is independent of the primary network. In contrast to the existing systems where the same spectrum band is utilized by different primary users, increasing the number of primary users in the proposed scenario enhances the overall behavior via improving the coding gain.