The multiuser switched diversity (MUSwiD) selection schemes are useful in reducing the required channel estimation\nload in wireless networks. In this paper, we propose and evaluate the performance of cognitive amplify-and-forward\n(AF) MUSwiD relay networks where a cognitive user is selected among a set of users for data reception. The selection\nprocess is performed such that the end-to-end (e2e) signal-to-noise ratio (SNR) of the selected user satisfies a\npredetermined switching threshold. Such a user that satisfies this threshold is scheduled instead of the best user to\nreceive its message from the secondary source. In the proposed system, we consider a cognitive source, a cognitive\nrelay, a set of cognitive users, and a primary user. In this paper, an upper bound on the e2e SNR of a user is used in\nderiving of closed-form approximations for the outage probability and average symbol error probability (ASEP) of the\nstudied system in addition to deriving the ergodic channel capacity. To get more about system insights, the\nperformance is studied at the high SNR regime where approximate expressions for the outage probability, SEP,\ndiversity order, and coding gain are derived. The derived analytical and asymptotic expressions are verified by\nMonte-Carlo simulations, and some numerical examples are provided to illustrate the effect of some parameters such\nas number of users and switching threshold on the system performance. Findings illustrate that the diversity order of\nthe studied cognitive AF multiuser switched diversity relaying network is the same as its non-cognitive counterpart.\nAlso, results show that the asymptotic results tightly converge to the exact ones, and the analytical bounds are indeed\nvery tight, validating the accuracy of our approach of analysis. Furthermore, findings illustrate that the proposed\nMUSwiD user selection schemes are efficient in the range of low SNR values, which makes them attractive options for\npractical implementation in emerging mobile broadband communication systems. In contrast, these selection\nschemes are shown to be inefficient in the range of high SNR values where the multiuser diversity gain is noticeably\ndegraded when they are implemented.
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