A Power-Efficient MAC Protocol for VoIP Traffic over IEEE 802.11e WLANs

Abstract

Power saving is a critical issue for VoIP over WLANs, especially when using mobile devices. In this paper, we present an IEEE 802.11e compatible power-efficient MAC protocol to improve the on-demand polling (ODP) scheme. In the ODP scheme, if two consecutive QoS Null frames are received by a QoS AP (QAP), the corresponding QoS station (QSTA) will be removed from the polling list. The proposed Power-Efficient Polling (PEP) scheme uses both the polling-based (HCCA) and contention-based (EDCA) channel access over the hybrid coordination function (HCF) mechanism. When a QSTA sends a NULL frame with a queue size of zero and the allocated transmission opportunity (TXOP) is not used up, the QSTA will be regarded as entering the silence period. The QSTA will be removed from the polling list. In order to increase the prediction accuracy of a QSTA entering the silence period, a heuristic method to evaluate the utilization of allocated TXOP is added to the PEP scheme. Simulation results show that the PEP scheme in terms of normalized power consumption outperforms the RRP (Round-Robin Polling) and ODP schemes from 24.5% to 37.1% and 12.9% to 15.1%, without sacrificing the throughput.