Footprint

Recently commercial mobile phones have been shipped with integrated Wi-Fi NIC (Network Interface Card), while a fundamental barrier for easily using such Wi-Fi is its high energy cost for phone. We profile two integrated mobile phone Wi-Fi NICs and observe that the energy cost on PSM (Power Saving Mode) is greatly reduced, yet the scan state still costs most of the energy when it's not connected on discovering potential AP (Access Point). In this paper, we propose footprint, leveraging the cellular information such as the overheard cellular tower IDs and signal strength, to guild the Wi-Fi scan and thus greatly reduce the number of unnecessary scans through the changes and history logs of the mobile user's locations. Our experiments and implementation demonstrate that our scheme effectively saves energy for mobile phone integrated with Wi-Fi.