The intelligent transportation microwave radar sensor technology detects information in real time. In recent years, with the development of the economy, the traffic demand is increasing day by day. Urban traffic congestion, frequent traffic accidents, and deterioration of the traffic environment have become common problems faced by all countries in the world. In addition, the traffic system is a complex integrated system, and traffic problems will be difficult to solve from the point of view of the road or the vehicle.
In the late 1980s and early 1990s, the Intelligent Transportation System (ITS=IntelligentTransportationSystem) was born at an important moment. Many developed and developing countries proposed their own development strategies, and tried to put forward their own development strategies through the development of ITS to drive their own vehicle-based vehicles. , communication, electronics, computer, network and other high-tech economic development. It is expected that the application of the intelligent transportation system can effectively improve traffic efficiency, reduce traffic congestion by 20%, reduce delay losses by 10-25%, reduce traffic accidents by 50-80%, reduce fuel consumption by 30%, and reduce exhaust emissions.
ITS is the development direction of the future transportation system. It is a management system of advanced information technology, data communication transmission technology, electronic sensing technology, control technology and computer technology in the entire ground traffic management system. A real-time, accurate and efficient integrated traffic management system.
Real-time traffic information is one of the most basic information sources of ITS. Only by accurately grasping the real-time traffic information of various roads can ITS effectively implement and play the role of traffic guidance and other traffic guidance. Therefore, the real-time detection technology of traffic information is the core of ITS technology. It is also one of the basic techniques.
1. Real-time detection technology of traffic information
With the continuous development of new technologies such as road traffic information monitoring, cloud computing, big data, Internet of Things, and the Internet of Vehicles, the technical means of traffic information detection are more diversified, and the collected information is also more abundant. At present, various traffic information collection technologies have been applied in practice, such as road contact traffic information collection technology - coil detection technology, newly developed road non-contact traffic information collection technology - video detection technology and radar detection technology. The traffic information collected through these technologies mainly includes the speed of each lane, traffic flow, lane occupancy, vehicle type, and headway.
Based on the principle of electromagnetic induction, the coil detection technology is a sensor buried under the road surface and a toroidal coil that passes a certain working current. When the car passes through the acquisition device, corresponding pressure will be generated, and with the change of the electric or magnetic field, the final acquisition device will convert these force and field changes into the required traffic information. After years of development, the pavement contact traffic information collection technology has been very mature, with high measurement accuracy and easy to master, and has always been in the leading position in the field of traffic information collection.
However, this kind of road contact type traffic collection device has inevitable shortcomings: installation or maintenance needs to temporarily hinder traffic, and the installation and construction volume is large; cutting and softening the road surface is easy to damage the road surface, especially bridges, interchanges, and it is strictly prohibited to cut construction sites on the road such as elevated roads. Use the toroidal coil, otherwise it will cause serious safety hazards; the use effect and service life are greatly affected by the quality of the road surface and the natural environment, and the service life of the toroidal induction coil is generally only 2 years; due to the limitation of its own measurement principle, the distance between vehicles is less than 3m detection accuracy is greatly reduced, and even cannot be detected normally.
The video detection technology uses the principle that the vehicle enters the detection area (virtual coil) to cause the background grayscale change to detect the vehicle, which is intuitive and reliable, and does not need to damage the road surface during installation. But the disadvantage is that it is difficult to identify moving vehicles. When shooting high-speed moving vehicles, you need a fast enough shutter (at least 1/3000px), enough pixels and a reliable image algorithm. In addition, it is greatly affected by luminosity and climatic conditions, requiring daily maintenance such as lens cleaning.
Microwave radar sensor radar detection technology is to use the change of radar electromagnetic wave return time or frequency for vehicle detection, easy installation and maintenance, long service life, almost no light, dust, wind, rain, fog, snow and other weather and climate effects. Therefore, compared with video detection technology, radar detection technology has greater application and development prospects as a new generation of road non-contact traffic information collection technology. The key to the application of microwave radar sensor radar technology to traffic information collection is to solve the problem of microwave (referring to electromagnetic waves with a wavelength of 1mm to 1m and a frequency of 300mhz to 300ghz, which are decimeter waves, centimeter waves, millimeter waves and submillimeter waves in radio waves. The general term for wave.) Radar echo signal extraction vehicle information problem. To put it simply, it is to use the speed and ranging functions of radar technology to realize real-time detection of traffic information.
2. Speed detection
The microwave radar sensor radar detection technology is based on the microwave Doppler (Doppler) effect. When microwaves encounter objects during propagation, they will be reflected, and the frequency of the reflected waves will change due to changes in the object's motion state. When the object is fixed, the frequency of the reflected wave remains the same; when the object moves closer to the wave source, the microwave reflected wave is compressed, causing the frequency to increase; when the object moves away from the wave source, the microwave reflected wave is stretched, causing the frequency reduce. This is the Doppler effect. Based on the principle of the Doppler effect, the speed of the vehicle can be accurately measured, the technology is mature, the price is relatively low, the installation and maintenance are simple (no damage to the road surface and traffic interruption, it can be installed in bridges, tunnels and other road sections where coils are difficult to install), easy to promote, etc. Features.
3. Traffic flow detection
The radar using the principle of frequency modulated continuous wave (FMCW, microwave with a certain frequency periodic linear continuous wave modulation) can well realize the distance detection function. Based on this ranging function, by measuring the distance and angle between the radar and the vehicle, it can be determined which lane the vehicle is in; in order to determine whether there is a vehicle in the lane, a series of continuous frequency modulation waves can be transmitted to each lane through the radar, and received from each lane. Electromagnetic wave signals reflected by vehicles in the lane. Since there is no Doppler frequency shift, the distance between the vehicle and the radar in the lane is different, and the reflected electromagnetic wave has a different frequency than the electromagnetic wave emitted by the current radar. The radar can analyze the frequency spectrum of the intermediate frequency signal, judge the intensity of the corresponding frequency component of each lane, and know whether there is a vehicle in each lane, so as to detect the traffic flow in the area and whether the lane is congested.
4. Detection of other traffic information parameters
Besides traffic flow and speed, other main traffic information parameters are vehicle type, lane occupancy and the distance ahead. Since the duration of the Doppler frequency can be measured, on the basis of obtaining the vehicle speed, the product of the speed and time is used to calculate the length of the vehicle, so as to obtain vehicle type information, such as long vehicles, medium and long vehicles, and short vehicles. By detecting the time when vehicles enter and exit the detection area, lane occupancy and head distance can be calculated.
However, the installation position of the microwave radar sensor equipment is different, and the accuracy of entering and leaving the detection area is also different. For example, since different detection sensitivities correspond to different moments, the side-mounted (top-mounted) microwave radar based on the FMCW principle can only complete the measurement of vehicles entering and leaving the detection area through modeling, giving the average speed and providing model reference, which is accurate performance depends on the model; front mounted microwave radar sensors can measure directly and accurately. Therefore, for application scenarios that only need to detect vehicle flow and roughly understand the average speed of vehicles, side-mounted (side) microwave radar is more suitable; for applications that require traffic information such as traffic flow, real-time speed, vehicle type, and head-to-head distance, it is very accurate. In this case, the microwave radar that is being installed (top-mounted) needs to be used.
