Performance of a Cognitive Relay Network under AF Relay Selection Scheme with Imperfect Channel Estimation

Abstract

In this paper outage performance of a secondary user (SU) is evaluated under amplify and forward (AF) relay selection scheme with an imperfect channel state information (CSI)while sharing spectrum in an underlay cognitive radio network (CRN). In underlay, the SU coexists with primary user (PU) in the same band provided the interference produced by SU at the PU receiver is below the interference threshold of PU which limits the transmission power of SU and coverage area. Relays help to improve the performance of SU in underlay. However relays are also constrained in transmit power due to interference constraint imposed by PU. Closed form expression of the outage probability of SU with maximum transmit power constraint of relay under imperfect CSI is derived. A scaling factor based power control is used for the SU transmitter and the relay in order to maintain the interference constraint at PU receiver due to imperfect CSI. The impact of different parameters viz. correlation coefficient, channel estimation error, tolerable interference threshold, number of relays and the maximum transmit power constraint of relay on SU performance is investigated. A MATLAB based test bed has also been developed to carry out simulation in order to validate the theoretical result.