HAP-assisted LEO satellite downlink transmission: An energy harvesting perspective

In this work, we consider a low-earth orbit (LEO) satellite communication system with a high-altitude platform (HAP) as a relay on the downlink. Both the satellite and the HAP are assumed to harvest solar energy to power their operations. The aim is to minimize the energy usage over one orbit, while delivering a given amount of information from the satellite. We first assume that the channel gains as well as the amount of harvested energy in each time slot are completely known at the beginning of each orbit. The associated energy-minimization problem for this non-causal case is formulated and solved. For the causal case where the amount of harvested energy is assumed to be known only up to the present transmission slot, a greedy algorithm for on-line scheduling is presented. Finally, we present numerical results to evaluate the performance of the proposed schemes.