Opportunistic Energy-Aware Amplify-and-Forward Cooperative Systems With Imperfect CSI

Recently, much attention has been paid to the green design of wireless communication systems using energy efficiency (EE) metrics that should capture all energy consumption sources to deliver the required data. In this paper, we design an energy-efficient relay-assisted communication system based on estimated channel state information (CSI). It employs amplify-and-forward (AF) relaying and switches between different communication schemes, which are known as direct-transmission, two-hop, and cooperative-transmission schemes, using the estimated CSI to maximize EE. Two estimation strategies are assumed, namely, disintegrated channel estimation and cascaded channel estimation. To formulate an accurate EE metric for the proposed opportunistic AF (OAF) system, the channel estimation cost is reflected on the EE metric by including its impact in the signal-to-noise ratio (SNR) term and in the energy consumption during the channel estimation phase. Based on the formulated EE metric, we propose an adaptive power allocation algorithm to maximize the EE of the proposed OAF system with channel estimation. Furthermore, we study the impact of the estimation parameters on the proposed system via simulation examples.