Autopilot has become one of the most desirable Automotive Technology in the future, and laser radar, as the core equipment, has also received unprecedented attention because it has the advantages of high resolution, large amount of information and no visible light interference. But we can notice that the current mainstream automatic driving plan has not completely abandoned millimeter wave radar. What is the reason? Today we are going to talk about millimeter wave radar. What advantages does it have to compete with lidar?
The principle of distance measurement is like the general radar, which sends out the radio waves, then receives the echo, uses the time difference of the reflected wave of the obstacle to determine the distance of the obstacle, and uses the frequency offset of the reflected wave to determine the relative velocity. At present, there are three types of millimeter wave radar bands in the vehicle field.
24GHz this band is widely used in blind spot monitoring and lane changing assistance. Radar is installed in the rear bumper of the vehicle to monitor whether there is a vehicle on the two sides of the vehicle and whether it can change lanes. This band also has its disadvantages. First, the frequency is low, and the bandwidth is relatively narrow, only 250MHz.
The frequency of 77GHz is relatively high, and the bandwidth allowed by the international community is as high as 800MHz. The radar performance of this band is better than the 24GHz radar, so it is mainly used to assemble the front bumper of the vehicle, detect the distance from the front car and the speed of the front car, and realize the main function of the active safety field, such as emergency brake, automatic car heel and so on. Compared with 24G radar, 77G radar has a long distance, small size, easier installation, low power consumption, and better performance for pedestrians and bicycles and objects than 24G radar, which means that it can provide more security and better performance in more applications.
Finally, 79GHz, the largest feature of this band is that its bandwidth is very wide, more than 3 times higher than the 77GHz, which makes it very high resolution and can reach 5cm. This resolution is of great value in the field of autopilot, because autopilot needs to distinguish a lot of fine objects such as pedestrians, which requires high bandwidth. This band will be widely used in the field of automatic driving in the future.
In terms of wavelength, the wavelength of the 24GHz millimeter wave is 1.25cm, and the wavelength of the 77GHz millimeter wave is about 4mm, and the wavelength of the millimeter wave is more than 1000 times longer than the wavelength of the light wave, so it is more capable of penetrating the object. This reliability is difficult to be achieved by any other sensor, so the millimeter wave radar has a very difficult position in a field with high security and reliability requirements, such as ADAS.
Compared with lidar, the detection range of millimeter wave radar can easily exceed 200 meters, while lidar is generally less than 150 meters. Millimeter wave radar is more suitable for high-speed scenes.
Secondly, because of the high requirement of transceiver and assembly technology, the cost of lidar is difficult to reduce. Millimeter wave radar, because it is a silicon based chip, has no special expensive and complex technology, so the cost of millimeter wave radar has more advantages. The current price of millimeter wave radar is around 1 thousand and 500, and the price of lidar is still calculated in ten thousand units. And because the amount of data obtained by the lidar is far beyond the millimeter wave radar, a higher performance processor is needed to process the data, and the higher performance processor also means a higher price. Therefore, for engineers, millimeter wave radar is still the best choice in simple scenarios.
However, the shortcomings of the millimeter wave radar are also very intuitive, the detection distance is directly restricted by the frequency band loss, unable to perceive pedestrians, and can not accurately model all the surrounding obstacles. For the market prospect of millimeter wave radar, there will be 3-8 millimeter wave radars on one vehicle. At present, 7 of Mercedes Benz's high-end cars have been installed. The market size of vehicle millimeter wave radar will not be underestimated in the next few years.
There is a very important technology for the laser radar at present is the solid state laser radar, which is actually in line with the traditional radar and millimeter wave radar. The solid state laser radar is essentially the phase of adjusting each transmitting and receiving unit. The millimeter wave radar is the same principle, but the millimeter wave radar is the electromagnetic wave. The difficulty of implementation is much lower than that of the phase change in the optical band. In the future, the combination of solid-state lidar and millimeter wave radar may be a good choice.
Conclusion: millimeter wave radar is difficult to replace. Although there are shortcomings, the all-weather working condition is the biggest advantage. The accuracy of velocity and ranging is much higher than that of visual sensor. Compared with lidar, the penetration is better. But on the whole, this is not a conflict, because the future will go to the trend of fusion, especially for autopilot, and there is no doubt that the three sensors will merge with each other.