HARQ Soft Combining Using Bidirectional LSTMs

Abstract

Hybrid Automatic Repeat reQuest is used in modern wireless data communication to integrate both Automatic Repeat reQuest and high-rate Forward Error Correction mechanisms to enhance the reliability of data transmission. Unlike traditional ARQ, where an error-ridden frame is discarded upon reception, HARQ temporarily stores the erroneous frame in a buffer. When the re-transmission of the same frame occurs, these two frames are combined to generate a new frame, trying to minimize errors. This is HARQ with Soft Combining. Existing methods like Chase Combining (Type-I) and Incremental Redundancy (Type-II and Type-III) implement Log-Likelihood Ratio and Maximum Ratio Combining to combine two erroneous frames. This paper uses a Bidirectional Long Short-Term Memory model to combine two frames with high channel noise errors. This paper introduces the BiLSTM model, which aims to reduce the Bit Error Rate and provides an approach for integrating this model into the existing HARQ structure. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.