Posterior Matching Scheme for Gaussian Multiple Access Channel with Feedback

TL;DR

This paper extends the posterior matching scheme to the Gaussian multiple access channel with feedback, achieving capacity and sum-capacity, and generalizes known schemes like Ozarow's within this framework.

Contribution

It introduces a time-varying posterior matching scheme for Gaussian MAC with feedback, unifying and extending existing capacity-achieving schemes.

Findings

Achieves the capacity of two-user Gaussian channels.

Obtains the linear-feedback sum-capacity for symmetric multiuser Gaussian MAC.

Generalizes Ozarow's and Schalkwijk-Kailath's schemes within the posterior matching framework.

Abstract

Posterior matching is a method proposed by Ofer Shayevitz and Meir Feder to design capacity achieving coding schemes for general point-to-point memoryless channels with feedback. In this paper, we present a way to extend posterior matching based encoding and variable rate decoding ideas for the Gaussian MAC with feedback, referred to as time-varying posterior matching scheme, analyze the achievable rate region and error probabilities of the extended encoding-decoding scheme. The time-varying posterior matching scheme is a generalization of the Shayevitz and Feder's posterior matching scheme when the posterior distributions of the input messages given output are not fixed over transmission time slots. It turns out that the well-known Ozarow's encoding scheme, which obtains the capacity of two-user Gaussian channel, is a special case of our extended posterior matching framework as the Schalkwijk-Kailath's scheme is a special case of the point-to-point posterior matching mentioned above. Furthermore, our designed posterior matching also obtains the linear-feedback sum-capacity for the symmetric multiuser Gaussian MAC. Besides, the encoding scheme in this paper is designed for the real Gaussian MAC to obtain that performance, which is different from previous approaches where encoding schemes are designed for the complex Gaussian MAC. More importantly, this paper shows potential of posterior matching in designing optimal coding schemes for multiuser channels with feedback.