Performance of Hybrid-ARQ in Block-Fading Channels: A Fixed Outage Probability Analysis

TL;DR

This paper analyzes the performance of hybrid-ARQ in Rayleigh block fading channels, showing that even limited H-ARQ rounds significantly improve transmission rates and approach ergodic capacity under outage constraints.

Contribution

It provides a theoretical analysis of H-ARQ performance in block-fading channels with outage probability constraints, highlighting its advantages over non-H-ARQ systems.

Findings

Few H-ARQ rounds close the gap to ergodic capacity.

H-ARQ significantly outperforms non-H-ARQ rate adaptation.

Performance depends on outage probability and maximum H-ARQ rounds.

Abstract

This paper studies the performance of hybrid-ARQ (automatic repeat request) in Rayleigh block fading channels. The long-term average transmitted rate is analyzed in a fast-fading scenario where the transmitter only has knowledge of channel statistics, and, consistent with contemporary wireless systems, rate adaptation is performed such that a target outage probability (after a maximum number of H-ARQ rounds) is maintained. H-ARQ allows for early termination once decoding is possible, and thus is a coarse, and implicit, mechanism for rate adaptation to the instantaneous channel quality. Although the rate with H-ARQ is not as large as the ergodic capacity, which is achievable with rate adaptation to the instantaneous channel conditions, even a few rounds of H-ARQ make the gap to ergodic capacity reasonably small for operating points of interest. Furthermore, the rate with H-ARQ provides a significant advantage compared to systems that do not use H-ARQ and only adapt rate based on the channel statistics.