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On end-to-end performance of variable gain AF relayed cognitive underlay networks

ABSTRACT The objective of this work is to analyse the performance of an underlay cognitive radio network which incorporates a variable-gain amplify-and-forward relay to enhance its performance. The system is based on extended generalised-K fading distribution and works under the constraint of interference temperature. As a result, the secondary source and the relay transmit powers will be curbed to avoid secondary signal interfering with the primary transmission when both the networks communicate simultaneously. This is the basic principle of an underlay system where both primary and secondary networks are active at the same time. The influence of fading and shadowing on the different radio links of the system is also taken into account. The analysis begins with finding the end-to-end signal-to-noise-ratio and then derives its cumulative distribution function and moment generating functions. This is followed by the derivation of the analytic closed form expressions for the outage probability, the channel capacity and the error probability of the dual-hop AF relayed underlay cognitive radio network. Numerical plots following the mathematical analysis illustrate the effects of various parameters on the system performance under the constraints of interference temperature and the secondary transmit powers.