Why low-power millimeter wave radar is better than ultrasonic in parking assistance applications

Today's parking systems primarily use ultrasonic sensors , a low-cost solution that can sense nearby objects. While this technology has matured, original equipment manufacturers (OEMs) must meet the evolving requirements of park assist and autonomous parking applications in cost-sensitive markets, while Tier 1 manufacturers are finding it necessary to squeeze more performance out of ultrasonic sensing. The returns are diminishing.

Whether it is next-generation parking assist, autonomous parking or valet parking assist systems, they will require higher and longer resolution, accuracy and distance than ultrasonic sensing to detect the vehicle's surroundings.

Current status of ultrasonic sensors

Depending on the level of autonomy, ultrasonic parking systems can alert the driver to sensed objects and can also steer the vehicle into a parking space using camera sensing. As shown in Figure 1, these systems use 8 to 12 ultrasonic cameras installed on the car to achieve complete coverage, with typical sensing distances of 10cm to 5m.

Figure 1 : Comparison of parking configurations with ultrasonic sensor (left) and AWRL1432 sensor (right)

Ultrasonic sensors sense objects by emitting sound waves and receiving the sound waves reflected by objects in their path. They calculate the distance of nearby objects by measuring the time difference between emitting a sound wave and receiving an echo. Today, these sensors typically send the entire waveform of the received signal on a high-speed Distributed Systems Interface (DSI3) channel to a central sensor fusion electronic control unit (ECU).

Compared to ultrasonic sensors that emit sound waves, millimeter-wave radar sensors sense objects by emitting electromagnetic waves whose frequency increases over time. Such signals are reflected from surfaces along a given path. Millimeter wave sensors measure changes in the properties of a sensed object to calculate its distance, velocity and angle of arrival.

77GHz millimeter-wave radar has a wide radio frequency bandwidth that enables precise distance and velocity measurements, making it increasingly popular for advanced driver assistance systems and automotive body applications. Devices such as Texas Instruments'  AWRL1432 single-chip radar sensor can also accurately sense objects at ranges from 4cm to 10m and beyond, depending on antenna configuration. This expanded range enables obstacles to be sensed in advance, giving the driver more time to react and drive safely.

Advantages of radar sensors for parking assistance

Ultrasonic sensors are optimized for the propagation of sound waves in a medium such as air (environmental conditions such as mud, rain and fog can limit their performance). In contrast, millimeter-wave radar uses electromagnetic waves that require no propagation medium and provide precise object sensing under any external conditions. Radar sensors are also generally less prone to false readings than ultrasonic sensors, providing a reliable solution for parking assistance functions.

In addition, since ultrasonic sensors are affected by the sound wave propagation medium, when installing an ultrasonic parking system on a car, different drilling and painting processes are required on the bumper, which will bring huge costs to the OEM. In contrast, millimeter-wave radar sensors can be installed on car bumpers (as shown in Figure 2), simplifying installation while maintaining aesthetics.

Texas Instruments' AWRL1432 mmWave radar sensor integrates an analog front end with a digital processing back end to transmit processed output data over a cost-effective controller area network flexible data rate channel for central ECU decision-making. In comparison, the DSI3 cables required to transmit waveform data from ultrasonic sensors to a central ECU are expensive. You can also combine the AWRL1432 sensor with an existing angle radar in a car (a configuration that is becoming increasingly common), allowing multipurpose sensors to be reused in increasingly space-constrained sensing systems.

Figure 2 : Multi-mode angular radar system with AWRL1432

Conclusion

The AWRL1432 sensor delivers greater range, resolution and accuracy to help meet the requirements of today's future applications with higher levels of autonomy, such as parking assistance, entry-level blind spot detection and valet parking. Its low-power architecture requires less active power and offers idle and deep-sleep modes, providing radar advantages in kick-open and door-sensing applications that require battery power.

The AWRL1432 sensor not only enables OEMs and Tier 1 manufacturers to improve radar performance in parking systems, but also enables implementation in external applications that were previously limited by cost and power consumption. These capabilities enable the development of software-defined, multi-purpose radars that can reuse the same hardware and shorten engineering cycles for next-generation near-field sensing applications.