How to Boost the Throughput of HARQ with Off-the-Shelf Codes

TL;DR

This paper introduces a novel coding strategy for HARQ that improves throughput over fading channels by using joint packet coding and optimized compression, outperforming conventional IR-HARQ schemes.

Contribution

The work proposes a new coding scheme combining joint packet coding with binary compression and channel coding, enhancing HARQ throughput without requiring channel state information at the transmitter.

Findings

Achieves 1-2 dB gain in high throughput regions

Outperforms conventional IR-HARQ in numerical simulations

Provides practical rate adaptation strategies

Abstract

In this work, we propose a coding strategy designed to enhance the throughput of hybrid ARQ (HARQ) transmissions over i.i.d. block-fading channels with the channel state information (CSI) unknown at the transmitter. We use a joint packet coding where the same channel block is logically shared among many packets. To reduce the complexity, we use a two-layer coding where, first, packets are first coded by the binary compressing encoders, and the results are then passed to the conventional channel encoder. We show how to optimize the compression rates on the basis of the empirical error-rate curves. We also discuss how the parameters of the practical turbo-codes may be modified to take advantage of the proposed HARQ scheme. Finally, simple and pragmatic rate adaptation strategies are developed. In numerical examples, our scheme is compared to the conventional incremental redundancy HARQ (IR-HARQ), and it yields a notable gain of 1-2 dB in the region of high throughput, where HARQ fails to provide any improvement.