Maximum Achievable Energy Efficiency of TXOP Power Save Mode in IEEE 802.11ac WLANs

This paper provides an analysis of energy efficiency of the Transmission Opportunity Power Save Mode (TXOP PSM) in IEEE 802.11ac Wireless Local Area Networks (WLANs). This mechanism allows a device to sleep during transmissions in the channel that are addressed to other devices. This operation is also referred to as microsleep and can significantly reduce the energy consumption of devices during overhearing periods. A key contribution of the analysis presented in this paper is the awareness of the non-negligible time and energy consumption that a device incurs when it switches between awake and sleep states. If the duration of such state transitions is longer than the transmission time, microsleep operation is not possible. This becomes a critical issue as transmission rates increase, thus reducing the transmission times. In this paper, we show that the performance dependence of TXOP PSM on the awake/sleep state transitions can be overcome by using burst transmission inherent to the TXOP operation. Results obtained through theoretical analysis and computer-based simulation show gains of up to 424% in energy efficiency when compared to legacy mechanisms.