A Low Sample Rate Real Time Advanced Sonar Ring

This paper describes an advanced sonar ring that employs a low receiver sample rate to achieve processing of 48 receiver channels at near real time repetition rates of 15 Hz. The sonar ring sensing covers 360 degrees around the robot with simultaneously firing of 24 transmitters. The receiver sampling frequency is 250 kHz, compared to previous work at 1 MHz, firstly to maximize the speed of processing and secondly to avoid memory limitations of the DSPs. The processing to produce accurate distance and bearing measurements is performed on 6 DSPs using template matching of echoes with short duration. This paper presents a summary of the hardware architecture, software architecture and sensing theory of the advanced sonar ring. The use of a reference point and offset table is introduced and experimentally verified to improve the sensor accuracy and robustness. The problem and solution to cycle hopping, caused by the low sampling rate, are described in the paper.