The surround sensing problem
Almost continuously, someone in the world dies from a traffic accident; countless more suffer injuries. Moreover, the economic losses caused by traffic accidents are reaching astronomical proportions. Vehicle manufacturers and their suppliers have made it their goal to avoid such accidents, or at least to mitigate their effects. Much automotive safety improvement can be made thanks to automotive electronics developments.
Analyses of the correlations between collisions and driver reactions have shown that a considerable number of accidents can be avoided by recognizing a hazard in sufficient time and making appropriate driving maneuvers. Such actions can be achieved by warning signals to the driver or by automatic longitudinal and lateral control of the vehicle (Driver Assist Systems). Suitable sensors are a requirement if the hazardous situation is to be identified. A resulting sensor network covers the area around the vehicle in conjunction with a suitable human-machine interface.
Electronic surround sensing systems form the basis of numerous Driver Assistance Systemssystems for warning or active intervention. One area of these Driver Assistance Systems is aimed at avoiding frontal collisions, which can be significantly reduced by accident warning systems and active braking intervention. Adaptive Cruise Control (ACC) is the first step in this direction.
Today's ACC systems are mainly based on radar systems in the millimeter wave range. Millimeter wave radar systems are divided into pulsed and continuous wave systems, which are in turn subdivided into frequency modulated continuous wave (FMCW) and spread spectrum systems. 77 GHz FMCW radar systems allow objects to be detected within a range of 1 to 150m. At the same time, their distance and speed relative to the host vehicleand with the right number of antennas, also their angle to the longitudinal axis of the vehicleare determined.
Surround sensing systemsAdaptive Cruise ControlUltrasonic-, radar-, video- and navigation-based systems
Passive and active systems
Safety and convenience systems
Driver support, passive safety, collision mitigation, and vehicle control systems, according to their function within the system
Surround sensing systems (see figure below) forming the basis of numerous Driver Assistance Systems are differentiated into:
Adaptive Cruise Control systems fall within the functional area of vehicle control and actively intervene in the longitudinal control of the vehicle. They decelerate the vehicle if it gets closer than a set minimum distance from the preceding vehicle and accelerate it to the set speed if there is a sufficiently large gap. ACC systems are currently installed as convenience systems. Their braking intervention is limited to a maximum of 30% of braking force capability; the driver is in ultimate control of the vehicle. Current ACC systems are therefore particularly suitable for roads with less traffic density, such as Interstates or highways.
With additional sensors, future ACC systems will be suitable for driving in heavy traffic in urban areas. Further developments of ACC Stop-and-Roll (S&R) and ACC Stop-and-Go (S&G) are intended to allow automatic stopping and starting in order to make lanes safer and improve traffic flow. The ultimate aim of these Driver Assistance Systems is 360-degree coverage of the area around the vehicle; in the area of vehicle control, the goal is to expand the ACC function to achieve complete longitudinal control.
Sensors for surround sensing
Covering the entire area around the vehicle requires a series of different sensors (see above). Two types of sensor, infrared (IR) sensors and long-range radar (LRR) sensors, are particularly well suited to ACC. IR sensors are used in LIDAR (light detection and ranging) systems and cover a range of up to 120m; in the case of 77 GHz LRR sensors, range can be extended up to 150m. IR sensors offer a price advantage compared with LRR sensors, but have the marked disadvantage that poor weather (heavy rain, snow, fog, dust, etc.) considerably reduces their working range.
Radar sensors, on the other hand, are almost entirely unaffected by weather conditions. Another important argument in favor of radar sensors is that they can be mounted concealed in the front of the vehicle; 77 GHz radar systems allow very small antenna sizes, permitting them to be installed almost anywhere. Consequently, present ACC systems primarily use 77 GHz LRR systems.