A joint power and information transfer system using retransmissions

In this paper, we develop a green joint power and information transfer system. To guarantee reliable communication, we implement hybrid automatic repeat request (HARQ) feedback both in the power and information transmission phases. Moreover, with a limit on the packet transmission delay, we derive the optimal power allocation minimizing the energy-constrained outage probability. The simulation and analytical results indicate that the diversity gain of the joint power and information transfer system is the same as the diversity gain of the conventional non-green information transfer systems. Also, the implementation of HARQ improves the power efficiency significantly. For instance, consider a Rayleigh fading channel, outage probability 10-3, code rate 1 nats-per-channel-use and the case where the receiver requires to receive 0.1 Joule-per-channel-use energy per codeword length from the transmitter to process the information. Then, with a maximum of two retransmissions in the power and information transfer phases, the HARQ reduces the average required energy by 4 dB, compared to the open-loop communication setup.