Finite Block-length Analysis of the Incremental Redundancy HARQ

TL;DR

This paper analyzes the power-limited throughput of INR HARQ systems with finite-length codes, deriving outage probabilities and evaluating feedback delay effects to optimize throughput in practical scenarios.

Contribution

It provides closed-form outage probability expressions and conditions for the effectiveness of INR HARQ with finite-length codes considering feedback delays.

Findings

Finite-length coding improves throughput with proper sub-codeword length adaptation.

Feedback delay impacts the throughput gains of INR HARQ.

Optimal sub-codeword length adaptation enhances system performance.

Abstract

This letter studies the power-limited throughput of a communication system utilizing incremental redundancy (INR) hybrid automatic repeat request (HARQ). We use some recent results on the achievable rates of finite-length codes to analyze the system performance. With codewords of finite length, we derive closed-form expressions for the outage probabilities of INR HARQ and study the throughput in the cases with variable-length coding. Moreover, we evaluate the effect of feedback delay on the throughput and derive sufficient conditions for the usefulness of the HARQ protocols, in terms of power-limited throughput. The results show that, for a large range of HARQ feedback delays, the throughput is increased by finite-length coding INR HARQ, if the sub-codeword lengths are properly adapted.