Lidar technology has new tricks
Automobile driving is divided into five stages, and the popularization of ADAS is a prerequisite for future autonomous driving. At the current stage of widespread application of ADAS, the fusion of multiple sensors is the future trend. This includes ultrasonic radar, cameras, infrared, laser radar, millimeter wave radar, etc. Millimeter wave radar will become the main sensor of ADAS systems first. Among them, radar is regarded as the key technology of autonomous vehicle, which is preparing for the golden age of the automotive sensor industry. How will radar sensor technology shape future cars?
Nowadays, radar technology is very popular, and there are numerous companies in this field. The most promising application of their products is in the direction of unmanned driving, as well as in fields such as intelligent docks and high-precision maps. Nowadays, radar products are also diverse, with both domestic and foreign designs becoming increasingly smaller in size and more beautiful in appearance. At present, TOF (Time of Flight) technology is widely used in radar technology. The principle is also very simple, by continuously sending light pulses to the target, and then using sensors to receive the light returned from the object, the distance to the target can be obtained by detecting the flight (round-trip) time of these emitted and received light pulses. At the 2018 Qingcheng Mountain China IC Ecological Summit Forum, Pan Weiqing from Hangzhou Aileda Technology Company introduced their achievements in laser radar.
Pan Weiqing also pointed out the problems with TOF technology. He mentioned that in the field of autonomous driving, the first issue with this technology is anti-interference. Currently, LiDAR uses direct detection and responds to all light entering the detector. However, if the radar faces sunlight during operation, it is easily affected by sunlight. Radar is like the human eye, and if the light intensity is too high, it cannot see the target, which poses a safety hazard; Another issue is in terms of quantity. Lidar is basically used for a single vehicle or a few vehicles. If it is truly used for commercial purposes in the future, most cars on the road will use this type of radar, making it difficult to identify whether the pulse is coming from nearby vehicles or the signal echo sent by oneself, resulting in interference problems; There are also hidden dangers in the detection range. Nowadays, radar considers that human eyes can safely display, and the emitted light rate is limited by human eyes and cannot be too high. In this way, it is difficult for the radar to achieve a detection range of 150 to 200 meters; In addition, the radar needs to be made into a solid state, so the most anticipated solution is OPA (phased array). This solution also has requirements for the radar and the host, and requires a small scanning aperture size. This means that it will introduce certain losses into this radar, further shortening the detection range of TOF radar.
Based on these factors, Eleda Technology has innovated and developed a new technology called FMCW radar. Its signal is continuous, the frequency is linear, and the frequency modulation is on the same frequency, which means there is a difference between the transmission frequency and the reception frequency. By detecting the difference between the two waves through optical mixing, the distance can be calculated through frequency conversion. By using this principle, the radar power is relatively far, and the detection distance can exceed 1 kilometer at a transmission power of 50 to 200 milliwatts. It can also work directly under sunlight without any interference from light. Another advantage is that it can accurately obtain speed at the same time, and its measurement accuracy for speed can reach 0.1 meters per second. Its key technologies are frequency modulation of light, coherent reception, signal analysis, and it is a relatively advanced coherent lidar.
Compared to TOF technology, FMCW has stronger anti-interference ability; Pan Weiqing introduced, "Its effective exploration sensitivity is very high, and direct effective detection can accurately test with only 10 photons. The requirement for working distance has far exceeded the requirements of car manufacturers. In addition, we adopt a 1550 band transmission power that is higher, detects speed information, and is fully compatible with solid-state scanning. This radar can also be integrated with millimeter wave at the chip level, and the working mechanism of the radar is very similar to that of millimeter wave. It can be shared in many modules, including signal modulation module and processing module; and this technology has very good optical performance
The automotive industry is experiencing a new wave of high-tech applications, and radar has an impressive technological roadmap that can achieve significant resolution improvements, as well as miniaturization and low cost of sensors. It has significant implications for the development of intelligent driving. In the near future, you may truly feel the outstanding performance of radar technology in ADAS, and maybe you will love it because of it
