Feedback Enhances Simultaneous Wireless Information and Energy Transmission in Multiple Access Channels

TL;DR

This paper fully characterizes the limits of simultaneous information and energy transmission in a two-user Gaussian multiple access channel, showing how feedback can significantly enhance energy transfer rates at high SNRs.

Contribution

It provides the first complete characterization of achievable rates for simultaneous information and energy transmission in G-MACs with and without feedback, including optimal schemes.

Findings

Feedback can double energy transmission rates at high SNRs.

Optimal schemes based on power-splitting and interference cancellation are identified.

Feedback has negligible effect on energy transmission at very low SNRs.

Abstract

In this report, the fundamental limits of simultaneous information and energy transmission in the two-user Gaussian multiple access channel (G-MAC) with and without feedback are fully characterized. More specifically, all the achievable information and energy transmission rates (in bits per channel use and energy-units per channel use, respectively) are identified. Furthermore, the fundamental limits on the individual and sum- rates given a minimum energy rate ensured at an energy harvester are also characterized. In the case without feedback, an achievability scheme based on power-splitting and successive interference cancellation is shown to be optimal. Alternatively, in the case with feedback (G-MAC-F), a simple yet optimal achievability scheme based on power-splitting and Ozarow's capacity achieving scheme is presented. Finally, the energy transmission enhancement induced by the use of feedback is quantified. Feedback can at most double the energy transmission rate at high SNRs when the information transmission sum-rate is kept fixed at the sum-capacity of the G-MAC, but it has no effect at very low SNRs.