Light-synchronized acoustic ToA measurement system for mobile smart nodes

We describe a novel time-synchronization technique for mobile smart nodes. We capture modulated LED light with a video camera, which is usually built into a smart node. The CMOS image sensor of a video camera does not take a snapshot at a certain time. Instead, the sensor captures data on a line-byline basis and the sensor output consists of lines taken at slightly different times. Therefore, we can extract time information from the image. This can be used for time synchronization for time-of-arrival (ToA) measurements. In this paper, we describe the fundamentals and an experiment using light-synchronized acoustic ToA measurements with mobile smart nodes. The acknowledged precision of the obtained time information is equivalent to 5.8 mm with an airborne sound wave.