Abstract:The incremental redundancy hybrid ARQ scheme can provide high throughput efficiency. Meanwhile, it also leads to high transmission delay. This paper presents a Low-Delay Incremental Redundancy hybrid ARQ scheme with Adaptive Modulation (AM-LD-IR). It adopts different strategy of incremental redundancy and constellation size according to the received Signal-to-Noise Ratio (SNR). The calculation and simulation results in the paper show, comparing to the ordinary incremental redundancy hybrid ARQ systems with adaptive modulation, the AM-LD-IR system can provide a little higher throughput efficiency and can reduce much transmission delay.