On distributed power saving mechanisms of wireless LANs 802.11e U-APSD vs 802.11 power save mode

The integration of wireless LAN technology in mobile devices such as cellular phones, PDAs or laptops has become a user need due to its popularity in providing high speed wireless Internet access at a low cost. Such devices though should meet users' expectations with regard to QoS, i.e., guarantee a reasonable voice quality when VoIP is used, and power saving efficiency, i.e., standby and calling times should be similar to the ones of cellular phones. The IEEE 802.11e standard, which extends the 802.11 wireless LAN MAC layer with QoS and power saving enhancements, should be the most appropriate solution to address users' wishes in those devices. In this paper, we focus on the 802.11e functionality likely to be included in mobile devices in the short-term, EDCA for QoS and U-APSD for power saving, and evaluate the performance improvements and associated costs of two possible configurations of U-APSD as compared to the 802.11 power save mode. In addition, the dependency between the QoS and power saving enhancements obtained with U-APSD and the available channel capacity is analyzed considering three different scenarios: 802.11b, 802.11b+g and 802.11g. The evaluation is based on our proposed implementation of U-APSD: Static U-APSD (SU-APSD). The main conclusions that can be drawn from our results are that U-APSD significantly outperforms the 802.11 power save mode in all considered performance metrics and that the performance enhancements obtained with U-APSD are independent of the available channel capacity.