Distance measurement by an ultrasonic system based on a digital polarity correlator

Ultrasonic systems based on a pulse time-of-flight estimation have been widely used for determining the two-dimensional position and orientation of mobile robots inside a room. The problems with existing systems, that use constant-frequency emissions, are mainly related to potential confusion of echoes from previous or subsequent pulses, those of other systems, or from other objects. This paper presents an ultrasonic system combining frequency-modulated emissions and correlation detection for time-of-flight estimation from the noisy echoes in real-time based on a digital polarity correlator where both input signals are infinitely clipped and converted to binary representations before correlation. The digital signal processing system is integrated into a single programmable logic device. Some experimental results are presented, and an analysis of the performance of distance measurement is carried out. The system can be easily adapted for sonar systems for robot navigation.