Whether and Where to Code in the Wireless Relay Channel

TL;DR

This paper analyzes the strategic use of network coding in wireless relay channels, balancing throughput and energy consumption to determine optimal coding locations and relay participation time.

Contribution

It introduces models to optimize coding placement and relay activity considering energy constraints in wireless relay channels.

Findings

Coding at the relay alone is inefficient for throughput and energy.

Optimal relay participation time depends on system parameters.

Guidelines for where and when to code in relay channels are provided.

Abstract

The throughput benefits of random linear network codes have been studied extensively for wirelined and wireless erasure networks. It is often assumed that all nodes within a network perform coding operations. In energy-constrained systems, however, coding subgraphs should be chosen to control the number of coding nodes while maintaining throughput. In this paper, we explore the strategic use of network coding in the wireless packet erasure relay channel according to both throughput and energy metrics. In the relay channel, a single source communicates to a single sink through the aid of a half-duplex relay. The fluid flow model is used to describe the case where both the source and the relay are coding, and Markov chain models are proposed to describe packet evolution if only the source or only the relay is coding. In addition to transmission energy, we take into account coding and reception energies. We show that coding at the relay alone while operating in a rateless fashion is neither throughput nor energy efficient. Given a set of system parameters, our analysis determines the optimal amount of time the relay should participate in the transmission, and where coding should be performed.