C-SCAN: Wi-Fi Scan Offloading via Collocated Low-Power Radios

Wi-Fi channel scanning-the task of searching for available channels at a given location-is a fundamental feature to maintain always-available and high-quality wireless connectivity in today's mobile devices. However, it is a challenging task to design an intelligent scanning algorithm that can discover available access points (APs) in a short time period, because the scanning station has no prior knowledge on the APs in its vicinity. Therefore, traditional scanning algorithms seek to discover available APs by scanning the full set of channels, including channels where no APs exist. This often induces unnecessary scanning latency and/or energy consumption. In this paper, we present a novel scheme, called C-SCAN, that exploits a low-power wireless personal area network interface, such as Bluetooth or ZigBee integrated into the device to offload Wi-Fi scanning overhead by suppressing unnecessary scanning of AP-free Wi-Fi channels. To this end, C-SCAN inspects channel information with a low-power Bluetooth radio and identifies which Wi-Fi channels are in use, prior to the actual channel scanning with a Wi-Fi interface. By excluding the channels determined to be empty, the Wi-Fi scanning manager can perform scanning only on available Wi-Fi channels. Thereby, a significant performance gain in terms of delay and energy is obtained. We implement a prototype of C-SCAN using a Bluetooth-compliant wireless transceiver and demonstrate its efficiency. Experimental results show that C-SCAN achieves high detection accuracy with low latency, even in dense Wi-Fi environments.