Multihop Cognitive Relaying Over Composite Multipath/Shadowing Channels

Abstract

The composite multipath/shadowing model is key to accurate modeling of real-world wireless channels, due to the combination of the effects of both fading and shadowing. However, the fundamental limits of spectrum-sharing cognitive radio have not been studied for such propagation conditions, leaving a gap in the analysis of these systems and, hence, the communication strategies that can be built upon toward improving performance. In this paper, we consider a primary/secondary spectrum-sharing network and study the performance of the secondary's multihop link by taking the composite multipath/shadowing model, which is described by the generalized- $K$ distribution, for the radio channels. In the multihop system, communication between secondary users (SUs) is assisted by intermediate relay terminals, under coexistence constraints with the primary users (PUs) . We assess the performance of the multihop system, first by deriving the moment generating function (mgf) and the probability density function (pdf) of the upper bounded end-to-end signal-to-noise ratio in closed form. The result is then used to obtain closed-form expressions of bounds on the ergodic capacity and the average bit error rate (ABER) , under the resource sharing constraints. The theoretical results are assessed with numerical analysis for different operating conditions.