E-MiLi: Energy-Minimizing Idle Listening in Wireless Networks

WiFi interface is known to be a primary energy consumer in mo-bile devices, and idle listening (IL) is the dominant source of en-ergy consumption in WiFi. Most existing protocols, such as the 802.11 power-saving mode (PSM), attempt to reduce the time spent in IL by sleep scheduling. However, through an extensive analysis of real-world traffic, we found more than 60 % of energy is con-sumed in IL, even with PSM enabled. To remedy this problem, we propose E-MiLi (Energy-Minimizing idle Listening) that re-duces the power consumption in IL, given that the time spent in IL has already been optimized by sleep scheduling. Observing that ra-dio power consumption decreases proportionally to its clock-rate, E-MiLi adaptively downclocks the radio during IL, and reverts to full clock-rate when an incoming packet is detected or a packet has to be transmitted. E-MiLi incorporates sampling rate invariant detection, ensuring accurate packet detection and address filtering even when the receiver’s sampling clock-rate is much lower than the signal bandwidth. Further, it employs an opportunistic down-clocking mechanism to optimize the efficiency of switching clock-rate, based on a simple interface to existing MAC-layer scheduling protocols. We have implemented E-MiLi on the USRP software radio platform. Our experimental evaluation shows that E-MiLi can detect packets with close to 100 % accuracy even with down-clocking by a factor of 16. When integrated with 802.11, E-MiLi can reduce energy consumption by around 44 % for 92 % of users in real-world wireless networks