A Multifunctional Automotive Short Range Radar System

The paper presents a 24GHz radar system which has been developed since 1997 by s.m.s smart microwave sensors GmbH in close co-operation with Volkswagen AG. A number of test cars have been equipped with this multi-functional system. It was designed to detect objects in the vicinity of a vehicle, either only at the front and/or at the back or even with full 360° coverage. It uses distributed small and intelligent radar units and performs detection, tracking, object classification and data fusion algorithms using latest DSP technology. Not only parking aid, but also blind spot surveillance, ACC support and pre-crash sensing applications can be realized. Introduction In the recent past 77GHz radar systems have been introduced in the passenger car market. The first application for those radars was the ACC (Adaptive Cruise Control) function. It was implemented as a new comfort feature in the cruise control systems which before did not control the distance to the vehicle ahead [2]. Technology in this frequency range is still quite expensive, and if it was possible to apply 24GHz radars for the application, the ACC systems would be much cheaper. But for those “long” range (1...200m) applications the 24GHz ISM-Band technology is not suitable, because of the large antenna apertures which would be required. The 77GHz systems, however, have one significant disadvantage, too: all systems on the market or under development usually cover only a small angular section (typically 10...15°) in front of the car. Hence, even simple stop&go scenarios can not be handled with those systems, because after a “stop” situation, the radar is not able to scan the full width of the lane for obstacles (in particular at short range) to enable the “go”. The reason for this is the layout of the antenna, which is designed to have a high gain and to provide a good signal-to-noise ratio even with reflections from distant targets. Even if the antenna was redesigned and made broader, there will never be a realistic chance to cover more than 60-120° with only one central sensor in front of the car. For the intended applications at “short” range (0...20-40m) ► Parking Aid ► Blind Spot surveillance ► ACC Support ► Pre-Crash Obstacle Detection a system design which used distributed sensors appears to be much better suited. A 360° coverage becomes possible. Moreover, with the inexpensive 24GHz RF frontends, combined with low-price automotive DSPs the cost is not very high. The Radar Network Thus a network comprising up to 20 distributed radars (“Sensor-Processors”, see Figure 1) and a central ECU was designed and built up. The number of radars can be determined by the car manufacturer and can be adapted to the mechanical conditions of the equipped vehicle type. The software in the central processor is prepared to handle any number of sensors between 1 and 20. Each individual radar measures range and speed of all detected objects. It does not determine the angular position of the object. The target data are transmitted via CAN. The calculation of the exact position is done by the central processor in a sophisticated triangulation and tracking algorithm. The central processor does also perform the communication with the vehicle, controls the HMI, in particular the “Parking Aid Bar Displays”, and synchronizes all sensors. The cycle time can be made as low as 10ms, or even faster, depending on the desired range interval. CAN Power SensProc 1 CAN Power SensProc N Central Processor Sychronization Tracking Human-Machine-Interface Diagnosis Display Control CAN Communication (ext.) CAN Power CAN Internal CAN