Ground-to-air FSO communications: when high data rate communication meets efficient energy harvesting with simple designs.

The capability of free-space optical (FSO) communications in delivering very high data rates and the agility of unmanned aerial vehicle (UAV) flying platforms render FSO-UAV-based solutions attractive for delivering 5G wireless communication services. In parallel, research on simultaneous information and power transfer, whether in the context of radio frequency (RF) networks or indoor optical wireless communication (OWC) networks, is on the rise. Even though the operation of a UAV is limited by its battery lifetime, the concept of energy harvesting (EH) from the information-carrying FSO signals was not deeply investigated in the literature. This paper highlights the inherent EH capabilities in FSO transmissions and investigates novel signal design methodologies for boosting the EH efficiency. We focus on the ground-to-air communications where the ground-based FSO transmitter is connected to the power grid and, hence, is governed by a peak-power constraint and not an average-power constraint. For this setup, simulations carried out under different weather conditions demonstrate that high data rates can be associated with significant amounts of harvested energy using simple transceiver architectures.

Exploiting the relays' backup RF antennas for enhanced FSO cooperative communications.

This paper investigates a novel method for boosting the performance of parallel-relaying decode-and-forward (DF) cooperative free space optical (FSO) networks. The proposed solution takes advantage from the presence of the radio frequency (RF) links that are often established to backup the FSO links in practical systems. In this context, the low speed RF links are used for carrying the information packets that have not been delivered along the direct FSO link for the sake of sharing these packets among the relays in a simple and efficient manner. This packet sharing enhances the chances for correct detection at the relays thus increasing the number of relays that will participate in the relay-destination transmission phase. An exact outage probability analysis is carried out in the case of gamma-gamma FSO fading channels with pointing errors and of Rician/Rayleigh RF fading channels. At a second time, the cut-set method is applied for deriving a simple and tractable upper-bound that is useful for evaluating the asymptotic performance and diversity gain.