In this paper, we propose a novel derivation approach to obtain the exact closed form expression of ergodic capacity for cognitive underlay amplify-and-forward (AF) relay networks over Rayleigh fading channels. Simulation results are performed to verify the analysis results. | Research and Development on Information and Communication Technology Exact Ergodic Capacity Analysis for Cognitive Underlay Amplify-and-Forward Relay Networks over Rayleigh Fading Channels Vo Nguyen Quoc Bao and Vu Van San Posts and Telecommunications Institute of Technology, Ho Chi Minh City, Vietnam E-mail: baovnq@, sanvv@ Correspondence: Vo Nguyen Quoc Bao Communication: received 20 August 2017, revised 1 September 2017, accepted 1 September 2017 bound expression due to the complicated form of the endto-end signal-to-noise ratio (SNR) of dual-hop amplifyand-forward (AF) relaying [12]. As an alternative, ergodic capacity of underlay decode-and-forward (DF) systems is usually employed to estimate that of underlay AF systems at high SNR regime leading to the fact that we cannot understand the performance gap between AF and DF. Abstract: In this paper, we propose a novel derivation approach to obtain the exact closed form expression of ergodic capacity for cognitive underlay amplify-and-forward (AF) relay networks over Rayleigh fading channels. Simulation results are performed to verify the analysis results. Numerical results are provided to compare the system performance of cognitive underlay amplify-and-forward relay networks under both cases of AF and decode-and-forward (DF) confirming that the system with DF provides better performance as compared with that with AF. To the best knowledge of the authors, exact and general ergodic capacity analysis of cognitive underlay dual-hop relaying over Rayleigh fading channels remains an open problem. This paper is to fill this important gap, ., providing the exact closed-form expression of the system ergodic capacity in terms of dilogarithm functions [13, 14]. All analytical results developed in this paper are corroborated by MATLAB-based simulation results, verifying the accuracy of the proposed derivation approach and the provided results. Numerical results are provided to investigate the
