Unmanned millimeter-wave radar sensor High-precision automotive sensor, in fact, millimeter-wave radar has been used in the automotive field for many years. The main purpose of adding automotive sensors is to achieve blind-spot monitoring and cruise control. With the development of technology, these two features gradually spread from high-end models to almost all models. With autonomous driving and ADAS, millimeter-wave radar plays an important role in the high-precision perception of the driving environment.
Millimeter Wave Radar What is Millimeter Wave:
Electromagnetic waves between 1-10mm have short wavelengths and wide frequency bands, making it easier to achieve narrow beams, with high radar resolution and less interference. Millimeter-wave radar is a high-precision sensor that measures the relative distance, speed and direction of the measured object, and was used in the military field in the early days. With the development and progress of radar technology, millimeter-wave radar sensors have begun to be used in automotive electronics, drones, intelligent transportation and other fields.
At present, the distribution frequency bands of vehicle-mounted millimeter-wave radars in different countries are different, but they are mainly concentrated in 24GHz and 77GHz, and a few countries (such as Japan) use the 60GHz frequency band. Since 77G is relative to the 24G future, the frequency band of the global automotive millimeter-wave radar will converge to the 77GHz frequency band (76-81GHz).
Vehicle millimeter wave radar principle:
The vehicle-mounted millimeter-wave radar sensor emits millimeter waves through the antenna, receives the reflected signal from the target, and obtains the physical environment information (such as relative distance, relative speed, angle, movement direction, etc.) around the vehicle quickly and accurately. ), and then perform target tracking, recognition and classification based on object information, data integration combined with vehicle body dynamic information, and intelligent processing through the central processing unit (ECU). After a reasonable decision, the driver will be notified or warned by means of sound, light, touch, etc., or actively intervene in the car in time to ensure the safety and comfort of the driving process and reduce the probability of accidents.
According to the different ways of radiating electromagnetic waves, millimeter-wave radar sensors mainly include pulsed systems and continuous wave systems. Continuous wave can be divided into continuous wave FSK (frequency shift keying), PSK (phase shift keying), CW (constant frequency continuous wave), FMCW (frequency modulated continuous wave) and other methods.
With high resolution, low signal processing complexity, low cost, and mature technology, FWCW radar has become a commonly used vehicle-mounted millimeter-wave radar. Tier1 suppliers such as Delphi, Denso, and Bosch all use FMCW modulation.
FMCW radar system mainly includes transceiver antenna, RF front-end, modulation signal, signal processing module, etc. The millimeter wave radar sensor detects the distance, direction and relative speed of the target through the correlation processing of the received signal and the transmitted signal.
Development status:
At present, millimeter-wave radars are mainly 24GHz and 77GHz. The 24GHz radar has a short measurement distance (5~30m) and is mainly used for the rear of the car; the 77GHz radar has a long measurement distance (30~70m) and is mainly used for the front and sides of the car. Millimeter wave radar mainly includes radar radio frequency front-end, signal processing system and back-end algorithm. In the existing products, the patent licensing cost of the radar back-end algorithm accounts for about 50% of the cost, the RF front-end accounts for about 40% of the cost, and the signal processing system accounts for about 10% of the cost.
RF front end:
The RF front end obtains the intermediate frequency signal by transmitting and receiving millimeter waves, and extracts information such as distance and speed from it. Therefore, the RF front end directly determines the performance of the radar system. At present, the RF front-end of millimeter-wave radar is mainly in the form of planar integrated circuit, hybrid microwave integrated circuit (HMIC) and monolithic microwave integrated circuit (MMIC). Among them, the MMIC RF front-end has low cost and high yield, and is suitable for mass production. In the production process, epitaxial MESFET, HEMT and HBT are generally used to wait for the equipment process. Among them, the GaAs-based HEMT process is the most mature and has excellent noise performance.
Signal processing system:
The signal processing system is also an important part of the radar. By embedding different signal processing algorithms, the IF signal is extracted from the RF front-end to obtain specific types of target information. The signal processing system is usually DSP to implement complex digital signal processing algorithms to meet the real-time requirements of radar.
Backend Algorithm:
Back-end algorithms account for a high proportion of the entire millimeter-wave radar cost. For millimeter-wave radar sensors, domestic researchers have proposed a large number of algorithms from the perspectives of frequency domain, time domain, and time-frequency analysis, and the accuracy of offline experiments is also high. However, domestic radar products mainly use the fast Fourier transform based on the frequency domain and its improved algorithm for analysis, and the measurement accuracy and scope of application are limited. Foreign algorithms are strictly protected by patents and are very expensive.
Advantage:
Millimeter-wave radar sensors have the characteristics of wavelength, frequency bandwidth (large frequency range), and strong penetration ability, forming the advantages of millimeter-wave radar:
1. Strong penetrating ability, not affected by weather. The atmosphere has an attenuating effect on the propagation of the radar band. Millimeter-wave radar has weaker attenuation than infrared, microwave, etc. in air, rain, fog, smoke, pollution, etc., and has strong penetrating ability.
2. The millimeter-wave radar has narrow beam, wide frequency band, high resolution, and is not affected by day and night.
3. Small size, compact and high recognition accuracy. Millimeter-wave wavelengths, small antenna diameters, and small component sizes make millimeter-wave radar systems small, lightweight, and easy to install in cars.
4. For the same object, the millimeter-wave radar has a large cross-sectional area and high sensitivity, and can detect and locate small targets.
5. It can realize remote sensing and detection. Millimeter-wave radar is divided into long-range radar (LRR) and short-range radar (SRR). Due to the weakening of millimeter-wave in the atmosphere, it can detect and perceive longer distances, of which long-range radar can reach more than 200 meters.
6. According to the many advantages of millimeter-wave radar, it currently occupies a large proportion in automotive anti-collision sensors. Millimeter wave/microwave radar data + cameras account for 70% of automotive collision avoidance sensors.
Relationship with driverless vehicles:
Usually, the driver of the vehicle is a licensed person who can judge the external environment through the eyes and ears, so as to drive the vehicle forward, turn and avoid obstacles. Drivers of driverless vehicles have changed from humans to machines, so the device for capturing external information has changed from eyes and ears to radar. Self-driving cars acquire external information through millimeter-wave radar sensors and, after analysis, respond to corresponding events.
How does the radar perform in real-world situations? How is the general performance? Cruise takes an unmanned vehicle as an example. Cruise's 5 lidars and 21 millimeter-wave radars are placed around the body. Among the 21 millimeter-wave radars, 12 are 79GHz radars provided by ALPS, 4 ARS-408 radars are installed on the front and rear of the body, and 5 high-resolution radars are installed on the front, rear, left and right sides, with a resolution of up to 4 cm.
The 12 79GHz millimeter-wave radar sensors work in a cascaded manner, that is, to determine whether the related objects operate synchronously, so that the unmanned vehicle can clearly perceive the surrounding 360° information and can track thousands of targets at the same time, which greatly improves the unmanned driving. The ability of the vehicle to deal with emergencies. The 12 79GHz millimeter-wave radars constitute a redundant system. While it would increase manufacturing costs and make the system look a bit bloated, it's trivial compared to its security performance benefits.
A system of many radars can always update the map around the driverless vehicle. So, to some extent, driverless vehicles are safer than human-driven vehicles. No matter how old a driver is, they can't always pay attention to the road conditions in the front and rear, but a machine driver can calmly judge the situation in all directions and make the best solution.
Market situation and future development prospects:
Millimeter-wave radar can realize a variety of autonomous driving functions. ADAS sensors mainly include cameras, millimeter-wave radar, laser, ultrasonic, and infrared. Millimeter-wave radar sensors have a long transmission distance, low atmospheric attenuation loss in the transmission window, and strong penetration, which can meet the requirements of vehicles for all-day climate adaptability. The characteristics of the millimeter-wave itself determine the small size and light weight of the millimeter-wave radar sensor equipment. . It makes up for the usage scenarios that cameras, lasers, ultrasonics, infrared and other sensors do not have in vehicle applications.
Installing a millimeter-wave radar on a car can measure the distance, angle and relative velocity from the radar to the object being measured. Millimeter-wave radar can realize adaptive cruise control (AdaptiveCruiseControl), forward collision warning (ForwardCollisionWarning), blind spot detection (BlindSpotDetection), assisted parking (Parkingaid), auxiliary lane change (Lanechangeassistant), independent cruise control (ACC) advanced driving assistance System (ADAS) functions. More common automotive millimeter-wave radars operate at frequencies around 24GHz and 77GH. The 24GHz radar system mainly realizes short-range detection (SRR), while the 77GHz system mainly realizes long-range detection (LRR).
The market space for millimeter wave radar is vast:
Due to the continuous improvement of automobile safety standards in various countries, the active safety technology Advanced Driver Assistance System (ADAS) has developed rapidly in recent years. Automotive millimeter-wave radar has become a recognized mainstream choice for automotive electronics manufacturers because it can work around the clock and has huge market demand. In 2014, the global automotive millimeter-wave radar market shipments were 19 million units. PlunkeetResearch predicts that by 2022, the global automotive millimeter-wave radars will be nearly 170 million units, with a compound annual growth rate of approximately 2015-2020. twenty four%.
At present, automotive millimeter-wave radars are developing rapidly. Generally, cars that support ADAS functions will use 2 or 3 millimeter-wave radar sensors. Audi A4 uses 5 millimeter-wave radars, and Mercedes-Benz S-Class uses 7 millimeter-wave radars. It is expected that millimeter-wave radars will be used in the future. The average number of radars will continue to grow, as will the demand for automotive radar PCBs.
