An Efficient Primary Receiver Selection Scheme in Cognitive Networks with Generalized Order Secondary User Scheduling and Imperfect Channel Estimation

The underlay paradigm is among the various paradigms that have been recently proposed in cognitive radio networks. In this paradigm, the secondary users are allowed to share the spectrum with primary users only if the interference between them is below a certain interference threshold. The opportunistic scheduling is among the common selection schemes that are used to select among users in cognitive networks with multiple secondary users. In this scheme, the secondary user which has the best link is assigned the system resources and allowed for data reception. This scheduling scheme could be inefficient in various situations such as in the presence of outdated channel information, imperfect channel estimation, and in cases where a user other than the best is erroneously scheduled by the scheduling unit for data communication. As a solution for these problems, we propose in this work the generalized order user scheduling scheme to select among secondary users in cognitive networks. In this scheme, the second or even the Nth best user is assigned the system resources and allowed for data reception in case an error happens in selecting the best user. A common scenario that has been widely adopted in current cognitive networks is the scenario where the multiple primary receivers are assumed to utilize the same spectrum band. There are many applications where the primary receivers could utilize orthogonal spectrum bands, among which is the downlink transmission in cellular networks. Using orthogonal spectrum bands in cellular networks aims to reduce or mitigate the interference between users. In this work, we propose an efficient primary receiver selection scheme for multiuser cognitive networks where the multiple primary receivers utilize orthogonal spectrums. Due to its importance and its impact on the system performance, the problem of imperfect channel estimation will be considered in the analysis. In this work, we propose to derive closed-form expressions for the outage probability, average symbol error probability, and ergodic channel capacity of the proposed scenario. Furthermore, we propose to study the system performance at the high signal-to-noise ratio regime where the diversity order and coding gain will be derived and analyzed. Monte-Carlo simulations will be provided to validate the achieved results and some meaningful numerical examples will be discussed to illustrate the effect of number of primary receivers, number of secondary users, and channel estimation error on the system performance. Our proposed results will be general and very useful in studying the performance of multiuser cognitive networks with multiple primary receivers using orthogonal spectrums in the presence of imperfect channel estimation.