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

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