Performance evaluation of some hybrid ARQ schemes in IEEE 802.11a networks

Abstract

This paper investigates how a type II hybrid ARQ (HARQ) scheme combined with adaptive modulation and coding (AMC) can improve the throughput on top of the MAC layer, by comparing it to the existing type I HARQ + AMC mechanism in the IEEE 802.11a context. The studied type II HARQ+AMC strategy relies on incremental redundancy (IR) by use of rate compatible punctured codes as well as chase combining. The performance of the various strategies is mainly affected by two parameters. One of these is the inaccuracy of the link quality predictor, since the SNIR inherently fluctuates due to fading and interference; the other is the MAC overhead, which is especially important in IEEE 802.11a due to the CSMA/CA protocol. From the simulation results presented in this paper, it can be observed that even when MAC overhead is taken into account, the type II HARQ+AMC strategy still provides up to 1.5 dB gain with respect to current type I HARQ + AMC scheme.