Performance Analyses of the N-Rth Dual Best Relays Opportunistic Cooperation with Amplify-and-Forward Protocols

摘要

To overcome the loss in the outage probability and symbol error ratio (SER) caused by the Nth single relay opportunistic relaying (OR), in this paper, we present the N-Rth dual best relays OR schemes in which there are two relays selected out of the available relays to forward the received signals to destination over orthogonal channels by using amplify-and-forward protocols. For the proposed N-Rth OR schemes, we obtain firstly the closed-form expressions to the probability density function (PDF) and cumulative distribution function of the instantaneous end-to-end signal-to-noise ratio (SNR) by using the appropriate mathematical manipulations over independent and non-identically distributed Rayleigh fading channels. Then, based on the derived statistical descriptions, the outage probability, average SER, and ergodic capacity of the proposed dual relays OR schemes are investigated as well as the corresponding closed-form analytical solutions. The fair comparison analyses between the Nth schemes and the N-Rth schemes show that the proposed N-Rth schemes can improve greatly the outage probability and average SER of the considered OR schemes in medium and high power transmission regions (or SNR). Especially, the proposed dual relays OR schemes can provide more improvement on SER than outage probability. At the same time, the presented numerical results indicate clearly the improvement on the outage probability and average SER is at the price of the loss in the ergodic capacity, which is due to the constrain of diversity and multiplexing tradeoff in cooperative communications.