On the performance of hybrid ARQ schemes for uplink information transmission with wireless power transfer in the downlink

We investigate a form of energy harvesting consisting of gathering energy from the radio frequency (RF) electromagnetic waves, also know as wireless power transfer. We employ a time switching (TS) protocol to coordinate the harvesting process, which separates a time slot into two parts, one devoted to wireless energy transfer and the other to wireless information transmission. The fraction of time devoted to each task, the TS parameter, has great impact on the overall performance. This paper presents an investigation on the usage of the TS protocol, including the numerical optimization of the TS parameter, when hybrid automatic retransmission (HARQ) schemes are used for information transmission. Our results demonstrate that HARQ schemes can improve the system performance for high SNR. This improvement is even better if if the destination applies Chase combining among the previously received copies of a frame.