Cognitive relay network with several primary receivers and outdated CSI: a new spectrum sharing constraint

This paper introduces a new spectrum sharing constraint which facilitates outage analysis for the cognitive relay networks with multiple primary receivers (PR)s and under outdated channel state information (CSI). The pivotal idea in spectrum sharing paradigm is controlling the interference generated due to the coexistence of primary and secondary users. In a realistic scenario, interference management is hampered by several parameters. In this context, this paper targets the influence of the CSI accuracy and the number of PRs. In a cognitive network with multiple PRs, the best approach to shielding the receivers from intolerable interference is to limit the maximum inflicted interference. Although being effective, this strategy has two drawbacks. First: it measurably affects mathematical tractability of the outage analysis. Second: it requires substantial resources to find the strongest interference channel which may be unaffordable in certain applications, especially when there are many PRs. In this paper, we propose the total interference (TI) constraint as the spectrum sharing criterion and investigate the outage behavior of the secondary network. A simple back-off power control method is adopted so as to mitigate the harmful effect of the outdated CSI. Considering decode-and-forward relays and partial relay selection strategy, we derive exact expressions for the end-to-end outage probability. Monte-Carlo simulations are made and results corroborate correctness of the mathematical derivations. The findings suggest that: first, outage assessment under the TI constraint is more tractable than under the maximum interference (MI) constraint as it leads to simple closed-form expressions. Second, the secondary network under the TI constraint is more resilient against the outdated CSI because the interference probability arising from the outdated CSI is smaller under the TI constraint than MI.