Implementation of an ultrasonic distance measuring system with kalman filtering in wireless sensor networks for transport logistics

In this paper an empirical study about distance measurements with ultrasonic sensors within an intermodal container is presented. In a previous work the Received Signal Strength Indicator (RSSI) was used for measuring the distance between two nodes in a Wireless Sensor Network (WSN). Since RSSI revealed a huge distance measurement error (52 cm) and standard deviation (47 cm) a Time-of-Flight (ToF) approach is applied. For this purpose self-developed ultrasonic sensor boards are equipped on the sensor nodes and a Time-Difference-of-Arrival (TDoA) algorithm is implemented. Afterwards, the system is tested and calibrated to decrease the distance error. Then a multi stage filter, including Kalman filtering , is implemented to enhance the measurement stability. The following tests in the container reach a measuring accuracy around 1.5 cm with a standard deviation of 0.4 cm under the same environmental conditions.