Research On Some Key Problems Of Millimeterwave Detection System In Traffic Field

The field of communications and transport has become the artery, which bears the weight of society development. Safety, speed and comfort are the goals of the traffic development. But with the quick development of the traffic field, Safety becoms a serious problem, which restricts the further development of the traffic field. The vehicle which has advanced active safe guarding system and control system can detect obstacles and other vehicles by the forward-looking millimeter wave detection system and judge whether the danger is exit or not. And furthermore can control longitudinal range between vehicles according to anti-collision principle or practical demands. So the vehicle has excellent active anti-collision performance and these techniques not only enhance the driving safety but also improve the driving amenity and the highway capacity. All kinds of anti-collision detection system, longitudinal range control system and automotive braking system are the basement of the vehicle anti-collision system. The study on these has realistic social and economic meaning. The study of this dissertation covers the following aspects concerning the main work and creative research in the project. 1. The study background and present status are introduced. By comparing all kinds of anti-collision detection system, millimeter wave radar is proved to be more suit for practical traffic environment because it has immunity for the color and shape of target and its measurement accuracy is stable under the following conditions: rain, snow, fog and ambient air. 2. The measurement principle and performance index of millimeter wave radar have been discussed theoretically. On the view of the selection and design of waveform, new waveform named double-slope symmetrical saw-tooth wave is proposed to get better system response characteristic than conventional triangle waveform. Positive and negative frequency modulation signals of the new waveform are transmitted synchronously. So the whole measurement time is shortened and system response characteristic is enhanced. Another, the voltage control waveform was generated through the experiment. 3 In order to resolve the problem of multi-target detection, combining with the proposed waveform, the algorithm named variable combination multiple decision is proposed. The results of simulation test and theoretical analysis prove that the new waveform and algorithm can detect multi-target correctly. 4. The echo signal of detection system includes all kinds of noise and radio frequency interference usually. So, the sweep nonlinearity and power undulation in transmitting signal, the effect of noise and chirp interference signals are discussed in detail and simulation experiment is performed to test the above effects for beat signals. 5. For chirp interference signals, Wigner-Hough as one kind of time-frequency analysis methods is used to detect and separate beat frequency and Chirp interference signals. The validity of this method is tested by computer simulation. According to the moving characteristic of vehicle on the road, beat frequency is analyzed and the characteristic plane conception of beat frequency signal is proposed in WHT parameter space. 6. The calculation method of the safety distance is discussed and some examples are introduced. Based on these states, the methods of longitudinal range control in active anti-collision system are discussed. For sliding mode control, which has been applied to the longitudinal range control between the vehicles, tracking-differentiator is designed and applied in this dissertation to track the relative speed measured by millimeter wave detection system and get relative acceleration, which are the input control parameters of the longitudinal range control system. The performance of tracking-differential system is tested by actual rotational speed tracking-differential experiments and computer simulation.