An efficient secondary user selection scheme for cognitive networks with imperfect channel estimation and multiple primary users

In this paper, we study the performance of multiuser cognitive generalized order user scheduling networks with multiple primary users and imperfect channel estimation. The utilized generalized order user selection scheme is efficient in situations where a user other than the best user is erroneously selected by the scheduling unit for data reception as in imperfect channel estimation or outdated channel information conditions. In this scheme, the secondary user with the second or even the Nth best signal-to-noise ratio (SNR) is assigned the system resources in a downlink channel. In our paper, closed-form expressions are derived for the outage probability, average symbol error probability (ASEP), and ergodic channel capacity assuming Rayleigh fading channels. Also, to get more insights about the system performance, the behavior is studied at the high SNR regime where the diversity order and coding gain are derived and analyzed. The achieved results are verified by Monte- Carlo simulations. Main results illustrate that the number of primary users affects the secondary system performance through affecting only the coding gain. Also, findings illustrate that a zero diversity gain is achieved by the system and a noise floor appears in the results when the secondary user channels are imperfectly estimated. Finally, results show that the generalized order user scheduling in cognitive networks has exactly the same diversity order as when implemented in the noncognitive counterparts.