Performance analysis of variable-rate adaptive modulation for AF opportunistic relaying under outdated CSI

Abstract

The impact of outdated channel state information (CSI) on the performance of variable-rate adaptive M-ary quadrature amplitude modulation (M-QAM) in an amplify-and-forward (AF) opportunistic relaying system over Rayleigh fading channels is analyzed. Closed-form expressions are derived for the average spectral efficiency, outage probability and the average bit error rate under outdated CSI. Using numerical evaluations, the performances of different cases are compared showing the impact of outdated CSI on the performance of the considered rate-adaptive modulation scheme in AF opportunistic relaying systems.