Adaptive Cross-Packet HARQ

TL;DR

This paper proposes an adaptive coding strategy for hybrid ARQ that dynamically adjusts encoding parameters based on receiver feedback and channel state information, leading to significant throughput improvements over traditional HARQ methods.

Contribution

It introduces a novel cross-packet HARQ scheme with variable joint encoding, enhancing throughput especially when conventional HARQ fails to improve performance.

Findings

Significant throughput gains with the proposed coding strategy.

Effective implementation of the scheme using turbo codes.

Practical challenges discussed and addressed.

Abstract

In this work, we investigate a coding strategy devised to increase the throughput in hybrid ARQ (HARQ) transmission over block fading channel. In our approach, the transmitter jointly encodes a variable number of bits for each round of HARQ. The parameters (rates) of this joint coding can vary and may be based on the negative acknowledgment (NACK) provided by the receiver or, on the past (outdated) information about the channel states. These new degrees of freedom allow us to improve the match between the codebook and the channel states experienced by the receiver. The results indicate that significant gains can be obtained using the proposed coding strategy, particularly notable when the conventional HARQ fails to offer throughput improvement even if the number of transmission rounds is increased. The new cross-packet HARQ is also implemented using turbo codes where we show that the theoretically predicted throughput gains materialize in practice, and we discuss the implementation challenges.