Capacity of Cognitive Radio Network under Asymmetric Fading with QoS Constraint.

Capacity at the link layer of spectrum sharing CR with K-branch maximal ratio combiner (MRC) is analyzed, subject to interference power and quality of service (QoS) constraints. It is assumed that the channel power gains of the secondary and the primary channels are not in symmetry. The secondary channel (SC) fading is Rayleigh while the primary channel (PC) is a Nakagami-m fading channel. The numerical result is compared to two symmetrical cases. First, when both channels experience Rayleigh fading, and second, when both are Nakagami-m fading channels. The overall analysis shows that more capacity is achieved when the channels experience similar fading effects than when they encounter dissimilar fading effects. As the m-parameter of Nakagami-m fading on the PC increases, more interference is perceived by the primary user (PU), consequently, the cognitive radio (CR) capacity decreases. The advantage of MRC at the secondary receiver is also apparent.