$\mu$Nap: Practical Micro-Sleeps for 802.11 WLANs

TL;DR

This paper introduces $5$Nap, a practical, standards-compliant micro-sleep mechanism for 802.11 WLANs that significantly reduces overhearing time and saves energy without hardware modifications.

Contribution

We design and evaluate a practical micro-sleep scheme for 802.11 WLANs that is compatible with existing hardware and standards, achieving substantial energy savings.

Findings

57% reduction in overhearing time

15.8% energy savings in activity time

Backwards compatible and incrementally deployable scheme

Abstract

In this paper, we revisit the idea of putting interfaces to sleep during 'packet overhearing' (i.e., when there are ongoing transmissions addressed to other stations) from a practical standpoint. To this aim, we perform a robust experimental characterisation of the timing and consumption behaviour of a commercial 802.11 card. We design $\mu$Nap, a local standard-compliant energy-saving mechanism that leverages micro-sleep opportunities inherent to the CSMA operation of 802.11 WLANs. This mechanism is backwards compatible and incrementally deployable, and takes into account the timing limitations of existing hardware, as well as practical CSMA-related issues (e.g., capture effect). According to the performance assessment carried out through trace-based simulation, the use of our scheme would result in a 57% reduction in the time spent in overhearing, thus leading to an energy saving of 15.8% of the activity time.