Average spectral efficiency of CSI-assisted multi-relay amplify-and-forward cooperative communication scheme

This paper studies the multiple relays amplify-and-forward (AF) cooperative communication system with adaptive continuous (ACR) and discrete rate (ADR) M-QAM modulation in Rayleigh fading channel. The average spectral efficiency of the fixed ACR, ADR M-QAM schemes with various number of relays are researched and analyzed. We first obtain quantitative spectral efficiency loss for the fixed rate M-QAM scheme resulting from the increasing number of the relay nodes. It is verified that under certain BER level, the adaptive M-QAM scheme achieves significant efficiency gains over the non-adaptive one. And, the more constellation size is available in ADR M-QAM, the closer the BER approaches to the target level and the more potentialities of the spectral efficiency can be realized.