Automotive advanced driver assistance systems (ADAS) help a person drive her/his vehicle and thereby enhance driver and road safety. A commonly used ADAS is ultrasonic park assist. When installed in a vehicle, ultrasonic park assist systems use ultrasonic distance-ranging methodologies to assist the vehicle driver with back-up parking, parking spot identification, automatic parking and detection of objects in the driver's blind spots. A key figure of merit of distance-ranging systems is the accuracy of distance measured by such systems. Many factors including object, ultrasonic transducer, electronics, and signal processing algorithms influence the accuracy of the measured distance. In this article, we focus on signal processing. Specifically, we investigate the method of triangulation as a way to improve distance measurement accuracy.
In automotive ultrasonic distance-ranging applications, ultrasonic sound wave time-of-flight (TOF) is used to calculate the distance to objects from the passenger vehicle. This distance is used to assist the driver in parking the vehicle, identifying parking spots, or detecting objects in the driver’s blind spots.
A key metric used to characterize the performance of automotive distance-measuring systems is accuracy of the measured distance.
A number of factors influence the accuracy of the distance measured. These factors include the object itself, the distance between the vehicle and the object, the transducer characteristics and the electronics used to drive the transducer and signal chain used to process the echo signals.
In this article, we investigate the use of triangulation. Specifically, we look at whether triangulation is effective in improving the accuracy of the distance measured.
Ultrasonic park assist systems
An ultrasonic park assist (UPA) system consists of an UPA ECU (electronic control unit), and multiple smart ultrasonic transducers. Ultrasonic transducers typically are installed in front and rear bumpers, and wing mirrors of an automobile. Up to four transducers can be installed in each bumper.
Measuring the distance
Figure 1 shows a passenger car with two ultrasonic transducers in the car’s rear bumper. Further, this picture also shows an object (such as a parking pole) behind the car.
Figure 1: Ultrasonic park assist system
In an ultrasonic park assist system with multiple smart ultrasonic transducers, the UPA ECU coordinates the measurement of distance. In a typical scenario, the UPA ECU first commands “ultrasonic transducer 1” to measure the distance. It then commands “ultrasonic transducer 2” to measure the distance. This sequence is cycled through as long as the park assist system is activated. An example scenario in which the transducers in the rear bumper are activated is when the driver selects reverse gear to back the vehicle into a parking spot.