AU-APSD: Adaptive IEEE 802.11e Unscheduled Automatic Power Save Delivery

The integration of the wireless LAN technology in mobile devices such as cellular phones or PDAs has become a user need due to its popularity for providing high speed wireless Internet access at a low cost. Such devices though should meet users´ expectations with regard to QoS, e.g., guarantee a reasonable voice quality when VoIP is used, and power saving efficiency, e.g., standby and calling times should be similar to the ones of cellular phones. IEEE 802.11e defines QoS and power saving enhancements that should allow the wireless LAN technology address users´ wishes in such specific devices. Our focus is the study of the distributed power saving mechanism of 802.11e, i.e., U-APSD, as compared to the legacy 802.11 power saving mode in order to assess its suitability for solving the challenges of the upcoming mobile devices requirements. Our contributions are as follows. We provide first an overview of the U-APSD functionality. Then, we describe in detail our proposed implementation of the U-APSD mechanism, Adaptive U-APSD (AU-APSD), a generic solution that requires only information available at the MAC layer. Finally, we quantify the performance improvements that are obtained with our proposed AU-APSD implementation as compared to the legacy 802.11 power save mode.