Feedback enhances simultaneous energy and information transmission in multiple access channels

In this paper, the fundamental limits of simultaneous information and energy transmission in the two-user Gaussian multiple access channel with feedback are fully characterized. A simple achievability scheme based on power-splitting and Ozarow's scheme is shown to be optimal. Finally, the maximum individual information rates and the information sum-capacity that are achievable given a minimum energy rate constraint of b energy-units per channel use at the input of the energy harvester are identified. An interesting conclusion is that for a fixed information transmission rate, feedback can at most double the energy transmission rate with respect to the case without feedback.