Low-cost synchronization for WLAN Sensors

Sensing applications with many sensors often rely on synchronized measurements in order to operate correctly. For wireless sensors connected via WLAN, the number of synchronization schemes is limited. Furthermore, the most popular method, Network Time Protocol (NTP), can often not guarantee the necessary accuracy, with errors ranging from ten to hundreds of milliseconds. Next to this method there are two major options: WizSync and Reference-Broadcast Infrastructure Synchronization (RBIS). However, these methods focus on a single access point solution. This translates into a synchronization area that is limited to the range of a single WLAN access point, which may not be sufficient in many large-scale applications. To tackle this problem, we have developed an extension to RBIS that can be used over a large range, spanning multiple access points, and with a synchronization error that is substantially smaller than that of NTP, i.e., less than 1 ms.