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 μNap, 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.
Since its conception, 802.11 has attempted to minimise idle listening with the introduction of the PS mode, and some previous work followed this path. For instance, Liu and Zhong @cite_25 proposed @math PM to exploit short idle intervals ( @math 100 ms) without buffering or cooperation. @math PM predicts the arrival time of the next frame and puts the interface in PS mode while no arrivals are expected. This mechanism demonstrated poor granularity (tens of ms) on existing hardware and leads to performance degradation due to frame loss. Therefore, it is only suitable for low-traffic scenarios.
@cite_25
2044993311
Wireless interfaces are major power consumers on mobile systems. Considerable research has improved the energy efficiency of elongated idle periods or created more elongated idle periods in wireless interfaces, often requiring cooperation from applications or the network infrastructure. With increasing wireless mobile data, it has become critical to improve the energy efficiency of active wireless interfaces. In this work, we present micro power management (μPM), a solution inspired by the mismatch between the high performance of state-of-the-art 802.11 interfaces and the modest data rate requirements by many popular network applications. μPM enables an 802.11 interface to enter unreachable power-saving modes even between MAC frames, without noticeable impact on the traffic flow. To control data loss, μPM leverages the retransmission mechanism in 802.11 and controls frame delay to adapt to demanded network throughput with minimal cooperation from the access point. Based on a theoretical framework, we employ simulation to systematically investigate an effective and efficient implementation of μPM. We have built a prototype μPM on an open-access wireless hardware platform. Measurements show that more than 30 power reduction for the wireless transceiver can be achieved with μPM for various applications without perceptible quality degradation.