Evaluation of cross layer QoS aproachs for improving voice quality over multi-rate WLANs

Voice over IP (VoIP) applications over wireless local area networks (WLANs) has become increasingly popular in recent years. However, due to some performance related topics like existence of multi-rate transmission or channel conditions, it has to be placed under control continuously to prevent possible performance losses. In case of any deterioration on the wireless link conditions, IEEE 802.11 PHY/MAC specifications allow mobile nodes to select a proper transmission rate to optimize bit transmission. However, if a node selects lower transmission rate, packet losses and delays increase due to multi-rate effect. Therefore, all active calls have a general degradation. Besides, Jitter buffering is also one of the most important performance metrics of VoIP over WLANs and has to be taken into account to maximize the perceived voice quality. In this paper, we propose and evaluate our cross layer based Adaptive Codec and Frame size Modification algorithm (ACFM) with related algorithms for the optimization of maximum throughput and voice quality on multi-rate WLANs.