Using ANT communications for node synchronization and timing in a wireless ultrasonic ranging system

Indoor localization and tracking of persons and assets for gaming, augmented reality, medical monitoring, train- ing, security, and inventory is an emerging technology. Localization can be computed from multiple distance measurements between reference beacons and sensors. Low cost, small, light, tiny-battery, or even batteryless operated sensors are required. Ranging can be carried out by measuring the time of flight of an ultrasonic chirp traveling from an emitting beacon to receiving sensors. That requires a tight synchronization between the beacon and the sensors. In this article, we present a ranging system based on miniature commercial modules featuring ANT wireless personal area network communication plus onboard microprocessor. A protocol is developed for microseconds synchronization and accurate onboard ranging computations are carried out through ultrasonic signal cross correlation. The sensor privately computes its own range. The ranging system is composed of a synchronizing unit, a beacon emitting ultrasonic chirps, and a battery-operated distance sensor. The sensor shows low average power consumption (less than 22 mW) and a ranging accuracy of about 1.8 mm for distances up to 2.5 m, under stable environmental conditions.