#8Recognition sensors required for automated driving②
On one hand, as was described in the previous chapter, the initial detection system with laser radar may not be able to detect vehicles in front in bad weather and such. Millimeter-wave radar based on radio waves, on the other hand, isn't affected as much as laser radar which depends on laser light. It emits radio waves toward a vehicle in front, and measures the distance to the vehicle and the relative speed based on the time it takes for the radio waves to bounce back and the shift of frequency. It can also discriminate multiple vehicles with phase difference calculation.
Generally speaking, millimeter-wave radar doesn't have good angular resolution If you add reception antennas, the resolution improves. But that doesn't match the cost and/or size required in the automotive usage. So, to improve the angular resolution, some of them perform signal processing on the information obtained from the reception antenna.
Under such circumstances, recent attention is paid to laser radar again. As the laser radar has higher angular resolution in principle than that of the millimeter-wave radar, it can discriminate objects more accurately. As a result, the recognition of free-space, which is travelable by the vehicle, can be achieved. When the vehicle steers or changes lanes in the automated driving mode, the free-space recognition is essential.
The reduced recognition capability in bad weather, which had been a concern for more than 20 years, has now improved thanks to device and laser ability enhancement, enabling operation even in the light rain. Need for automated driving revived the laser radar.