Energy efficiency analysis in relay assisted hybrid-ARQ communications

This paper studies the energy efficiency (bits/joule) in relay assisted networks using Chase combining hybrid-ARQ (HARQ-CC) retransmission technique. As energy efficiency depends on the average delay and the packet error probability (PER), we start by deriving an approximation of the PER for HARQ-CC retransmission scheme. This approximation is really simple compared to the existing expressions in the literature and is proved to be tight enough to address the energy efficiency study. In particular, the energy efficiency is investigated in terms of destination position and in terms of transmission power of the source and the relay. The results give some insights on the optimal transmission power according to the maximum number of retransmissions maximizing the energy efficiency.