Performance enhancement for underlay cognitive radio with partial relay selection methods under impact of hardware impairment

In this paper, we investigate two partial relay selection (PRS) protocols in underlay cognitive radio under impact of hardware impairment. In particular, the re-active and pro-active PRS schemes are proposed to compensate the performance loss due to the hardware noises and the interference constraints required by multiple primary users (PUs). Moreover, incremental relaying technique is also used to enhance spectrum efficiency. For performance evaluation and comparison, we drive exact and asymptotic closed-form expressions of outage probability over Rayleigh fading channel. Finally, Monte Carlo simulations are presented to verify the analytical derivations.

I. Introduction

In recent decades, telecommunication has promptly growth rate about the number of users and transmission rate. As a result, spectrum scarcity problem becomes more and more critical. For a realizable solution of spectrum scarce situation, Mitola [1] introduced cognitive radio (CR) concept, in which the unlicensed network (secondary network) can operate on the same frequency band licensed to the licensed network (primary network). However, to access these bands, the secondary operations must be not harmful to quality of service (QoS) of the primary network [2].