When Can a Relay Reduce End-to-End Communication Delay?

TL;DR

This paper analyzes when relay schemes like decode-forward and amplify-forward can reduce communication latency compared to direct point-to-point transmission, deriving conditions for latency improvements.

Contribution

It provides explicit latency expressions for relay schemes and identifies conditions where relaying reduces end-to-end delay, beyond traditional rate comparisons.

Findings

Both DF and AF can achieve lower latency than P2P under certain conditions.

Latency reduction conditions are more strict than rate improvement conditions.

Explicit latency formulas are derived for relay schemes.

Abstract

The impact of relaying on the latency of communication in a relay channel is studied. Both decode-forward (DF) and amplify-forward (AF) are considered, and are compared with the point-to-point (P2P) scheme which does not use the relay. The question as to whether DF and AF can decrease the latency of communicating a number of bits with a given reliability requirement is addressed. Latency expressions for the three schemes are derived. Although both DF and AF use a block-transmission structure which sends the information over multiple transmission blocks, they can both achieve latencies lower that P2P. Conditions under which this occurs are obtained. Interestingly, these conditions are more strict when compared to the conditions under which DF and AF achieve higher information-theoretic rates than P2P.