Relative position of UGVs in constrained environments using low cost IMU and GPS augmented with ultrasonic sensors

This paper presents a low cost approach to improve the relative position accuracy of unmanned ground vehicles (UGV) in a constrained environment through the use of ultrasonic sensors. A low cost MEMS IMU is integrated with a low cost GPS module to estimate the absolute position of the UGVs using an Extended Kalman Filter. The inherent limitations of GPS and MEMS sensors limit the estimatepsilas utility for determining the relative position of a pair of UGVs in close proximity. The estimator is augmented with range and bearing measurements from the ultrasonic sensors to overcome these limitations. The PPS from the GPS provides a common time to the ultrasonic sensors on each of the UGVs. This approach removes the necessity to differentiate between multiple returns for measuring the distance between UGV. Experiments were performed with a pair of sensors in urban terrain to evaluate the accuracy of the relative position estimate using this method. The results display the accuracy and precision of the relative position achieved. The results are compared with estimates from a pair of navigation estimators to illustrate the performance gains.