Ultra-Wideband Automotive Radar

A lot of progress has been made for automotive radar during the last years. There are two types of automotive radar; “long-range radar at 77GHz with a range capability up to 200m“ for automatic cruise control (ACC) and “short-range radar at 24/26 and 79GHz up to 30m“ for anti-collision. Long radar with narrow radiation beam enables a automobile to maintain a cruising distance, while short-range radar has recently attracted attention because of many applications such as pre-crush warning, stop-and-go operation and lane change assist. The short-range radar with a very broad lateral coverage has a few significant problems to be overcome such as target detection and clutter suppression. This is because the widely radiated radar echo contains not only automobile echo, but also unwanted echoes called clutter. It is actually not easy to detect a target echo in increased clutter. Ultra-wideband impulse-radio (UWB-IR) radar with high range-resolution has recently attracted much attention for automotive use, because it offers many applications such as pre-crush warning and lane change assist. The followings provide an overview of this chapter; 1. Section 2 introduces various radar systems for automotive use. It begins with a discussion of radar technologies such as Pulse Doppler, FM-CW and UWB-IR. 2. UWB-IR radar requires high speed A/D devices which can directly process the received nanosecond pulse. For example, A/D devices of several GS/s or more should be required for the UWB-IR radar with a bandwidth of 1GHz, which have not been available yet. The use of wideband may also cause unacceptable interference on existing narrowband systems. Therefore, some interference mitigation scheme may be required for the radar emission in the future. To solve these problems, a stepped-FM radar scheme is introduced in Section 3, which does not require high speed A/D device and provides the co-existence with exisiting narrowband systems. 3. Short range radar is expected to provide a wide coverage in azimuth angle. Therefore, increased clutter makes it difficult to detect automobile target accurately. The clutter can be classified from automobile by the Doppler, but it will not be applicable to the UWB-IR. In Section 4, a scheme is introduced which estimates the Doppler by using the time-trajectory of radar echo and the measurement results are presented. 4. Automotive radar is required to detect automobile accurately, but not to detect clutters falsely, even in complicated traffic conditions. In order to satisfy the requirement, a target discrimination scheme with range profile matching is introduced in Section 5 and the measurement results are presented. The results show that the automobile type can be discriminated.