Variable Length Coding over the Two-User Multiple-Access Channel

TL;DR

This paper introduces a receiver-centric variable length coding framework for two-user multiple-access channels, characterizing achievable rates and proposing schemes that attain the capacity region without transmitter coordination.

Contribution

It provides a new receiver-focused definition of variable length codes and characterizes the achievable rate region with outer bounds and practical coding schemes.

Findings

Outer bound on achievable rate region established

Coding schemes achieve the capacity region in certain settings

No transmitter agreement needed for the proposed schemes

Abstract

For discrete memoryless multiple-access channels, we propose a general definition of variable length codes with a measure of the transmission rates at the receiver side. This gives a receiver perspective on the multiple-access channel coding problem and allows us to characterize the region of achievable rates when the receiver is able to decode each transmitted message at a different instant of time.We show an outer bound on this region and derive a simple coding scheme that can achieve, in particular settings, all rates within the region delimited by the outer bound. In addition, we propose a random variable length coding scheme that achieve the direct part of the block code capacity region of a multiple-access channel without requiring any agreement between the transmitters.