Simple differences between automotive (ultrasonic, millimeter wave, laser) radars

Nowadays, cars are becoming more and more intelligent, and various assisted driving functions are becoming more and more advanced. However, the realization of these advanced functions is inseparable from car radar. Today I would like to share with you some issues related to radar.

Automotive radar is a radar used in cars or other ground motor vehicles. It includes various radars based on different technologies (such as laser, ultrasonic, microwave), with different functions (such as obstacle detection, collision prediction, adaptive cruise control), and using different working principles (such as pulse radar, FMCW radar, microwave impact radar).

Today I will mainly share three common types of automotive radars based on different technologies: ultrasonic radar, millimeter-wave radar, and lidar. I will find an opportunity to share the differences in other categories with you later.

Ultrasonic radar uses an ultrasonic transmitter to emit ultrasonic waves, and then uses the time difference between the reflected ultrasonic waves received by the receiver to measure the distance.

Generally speaking, the higher the frequency, the higher the sensitivity, and the smaller the detection angle in the horizontal and vertical directions (usage range: 40KHz/48KHz/58KHz).

Its detection accuracy is higher when the distance is between 0.1-3 meters. Currently, some ultrasonic radars that measure side obstacles have a ranging range of up to 7 meters. Ultrasonic radars are now mainly used in reversing radar, automatic parking and other functions.

Ultrasonic radar is easily affected by weather conditions. The propagation speed is different in different weather conditions, and the error is larger when the vehicle speed is faster. In addition, the ultrasonic scattering angle is large, which is not conducive to the transmission of recovered signals at longer distances. However, it also has the advantages of low cost, strong penetration, waterproof and dustproof.

Millimeter-wave radar is a radar that works in the millimeter-wave band (usage range: 30-300GHz frequency domain, wavelength 1-10mm). The wavelength of millimeter waves is between microwaves and centimeter waves, so millimeter-wave radar has some advantages of both microwave radar and photoelectric radar.

The principle of ranging is to transmit radio waves (radar waves/electromagnetic waves) and measure the distance data of the target position based on the time difference between receiving the echo and sending it.

The general detection distance is between 0-200 meters. Compared with optical seekers such as infrared, laser, and television, millimeter-wave seekers have a strong ability to penetrate fog, smoke, and dust. They are capable of detecting targets all day and all weather (except for heavy rainy days). The anti-interference and anti-stealth capabilities of millimeter-wave seekers are also better than other microwave seekers.

However, the attenuation of millimeter-wave radar in highly humid environments such as rain, fog and wet snow, as well as the influence of high-power devices and insertion loss will reduce the detection range of millimeter-wave radar; the ability to penetrate trees is poor, and compared with microwaves, the penetration of dense trees is low; the cost of components is high, and the processing precision is relatively high. The development of single-chip transceiver integrated circuits is relatively slow, and they need to be used in conjunction with cameras.

LiDAR is a radar system that emits laser beams to detect the position, speed and other characteristic quantities of a target. LiDAR is also called optical radar.

Its working principle is to transmit a detection signal (laser beam) to the target, and then compare the received signal reflected from the target (target echo) with the transmitted signal. After appropriate processing, relevant information about the target can be obtained, such as target distance, direction, altitude, speed, attitude, and even shape parameters.

It consists of a laser transmitter, an optical receiver, a turntable and an information processing system. The laser converts electrical pulses into light pulses and emits them. The optical receiver then converts the light pulses reflected from the target into electrical pulses and sends them to the display.

Because various objects reflect at different angles, even lane lines and road surfaces can be distinguished. Only the light beams of objects that are blocked cannot be detected. Since the speed of light is the fastest speed we know of, lidar is also the fastest of all radars.

There are still some problems in the large-scale commercial use of LiDAR. Li Zhenyu, senior vice president of Baidu Group and general manager of the Intelligent Driving Business Group, recently publicly stated: "LiDAR currently faces challenges: first, the difficulty of automotive-grade products is high, second, the cost is high, and third, the life span is short."

Two years ago, Tesla CEO Musk publicly said at a forum that "Anyone who uses lidar is a fool", so Tesla models still do not use lidar, but more and more smart cars in China are equipped with lidar.

The NIO ET7, which debuted at the Shanghai Auto Show, integrates a laser radar into the middle of the roof, allowing for a comprehensive view of targets ahead. It uses Innovusion products, which are said to be able to achieve 500-meter long-distance detection.

The Xiaopeng P5 autonomous driving system uses two 144-line laser radars. The two laser radars are customized automotive-grade Horiz laser radars from Livox, a subsidiary of DJI. A single automotive-grade Horiz laser radar has a lateral viewing angle of 120 degrees, a detection distance of 150 meters, and an angular resolution of up to 0.16 degrees. Combined with the XPILOT3.5 automatic assisted driving system, it can achieve NGP (automatic navigation) autonomous driving on highways and urban roads.

The solid-state laser radar of Germany's Ibeo company appears on the front bumper of Great Wall WEY Mocha. It can emit up to 256,000 points per pulse (the higher the number of points, the clearer the modeling image). After being received by a high-sensitivity receiver, it can complete the drawing of accurate point cloud, fully ensuring blind-spot detection of surrounding obstacles when driving at high speeds.

Five years ago, the price of a 64-line lidar was as high as US$100,000 (approximately RMB 700,000). Now, as many domestic lidar technology companies are working hard on technology research and development and striving to significantly reduce the cost of lidar through technological progress, the price of a 64-line lidar is expected to drop to US$200 (approximately RMB 1,300) in the short term.

With the continuous updating and iteration of autonomous driving technology, the performance of lidar will be further improved and the price will be further reduced. I believe that in a few years, we will see lidar become standard equipment in vehicles sold on the market.