| As a safety technology, collision avoidance system for road vehicle collects the information of the edge of roadway and measures range, velocity by detecting vehicles, passerby and roadblocks in the front of the car, then it can give an alarm, apply the brake or change the way to ensure road safety. Comparing with classical safety technology equipments (bumper, life belt, safety ballonet), wireless electronics are more initiative. Such a system in practical transportation applications can not only ensure traffic safety, but also reduce the loss. Therefore, study of collision avoidance system in vehicle is very significant.Radar at millimeter-wave band is the preferred sensor in collision avoidance system for vehicle; because it has good performance in bad weather condition and such complicated transportation circumstance. However, comparing with the other civilian radars, such as weather probe, ground penetrating radar etc, and false alarm has to be a critical issue. From international researches, there has long been an interest in signal waveform selection to enhance radar performance. This thesis does some research in transmit signal waveform design in radar to deal with the problem about false alarm.â… . Analysis of Traditional Signal WaveformFrequency modulation continuous wave (FMCW) has been well developed and are widely applied, which is the main type of radar signal now. However, the mono-oriented FMCW has range-velocity decoupling. If it is changed to be bi-oriented, there will be not exact result while the single target is detected, because only one part of frequency modulated segments is effective. Moreover this signal is inability to distinguish multiple targets. It is showed that FMCW is not fit to collision avoidance radar in vehicle.There has also been significant amount of attention focused on stepped frequency pulses (SFP) for lessening requests for signal processing equipment. Currently this signal is preferred in synthetic aperture radar (SAR). However, data utilized is low due to one result be given after a clutter of impulses processed. Another problem is that in the situation where the target and radar moves at a certain speed, the impact of this relative motion on system design should be considered. SFP is sensitive to moving target relative to radar, which results in target imaging not exactly. Although it can be solved by complex velocity compensating, in fact, it is not fit to collision avoidance radar in vehicle which needs lower cost and simpler structure.â…¡. Costas Coded SignalAmbiguity feature of frequency coded signal is related to the code, so costas sequence is selected, which has excellent ambiguity characteristic. Narrow mainlobe and lower sidelobes make signal have good range and velocity measurement resolution. Furthermore, ability of anti-jamming is improved. These features are favorable to collision avoidance radar in vehicle. Combining costas code and SFP not only deal with the problems of SFP, but also keep on the merits of this type of signal.Linear frequency modulated pulse deals with the problem of lower utilized data owning to rectangle subpulse. Costas code adopted among the pulses can decrease range-velocity decoupling. The rules about how to choose parameters ofsignal given in the thesis are summarized. Based on these rules, parameters of signal chosen in reason reduce the sidelobes of range, which make ambiguity function approximate to optimal signal.â…¢. Target DiscriminationAnti-collision radar in vehicle which can avoid vehicle collision relies heavily on target discrimination. Traditional radar signals have disadvantage in discrimina- ting targets, and signals improved on are not enough to achieve good impact. The signal used in this thesis belongs to high resolution radar, so its target imaging is based on one dimension range imaging. Rearranging the order of Costas sequence makes the signal have excellent feature in target discrimination. The thesis analyzes statistical and moving target resolution toward (or away) radar on theory, then the validity of the method is shown using simulation results.â…£. Anti-Cross InterferenceRadar used in vehicle is prone to be affected by cross interference owning to transportation circumstance. This thesis analyzes cross interference, and we know that classical radar signals can not restrain cross interference. Costas codes group adopted in signal makes costas waveform patterns with small cross- ambiguities, so cross interference is restrained depending on non-circle cross correlation among the codes. The simulation results show that the signal is superior to the traditional signals in radar in restraining cross interference capability, because target imaging is well and target can be discriminated.â…¤. ConclusionBased on the analysis of theory and simulation test about ambiguity, distinguishing target and cross interference of signal, the conclusion is given:â…°Costas waveform adopted in collision avoidance radar in vehicle gives a good approximation to the ideal thumbtack-like ambiguity function desired for high resolution delay-doppler imaging and measurement, although the ambiguity function of signal is not the optimal thumbtack pattern.â…±The effects of velocity on signal which adopted costas code are less thanSFP. The signal used in the thesis meets the need of collision avoidance radar in vehicle, while velocity compensating is not adopted. It is because that there is no fixed phase between pulses.â…²Utilizing costas code can satisfy the need to restrain cross interference. If costas code are selected at will, cross interference can be restrained at a certain extent. However, costas code group is nicer than costas code chosen at will on targets resolution when all frequencies of signal are destroyed.Signal waveform design is just one part of collision avoidance radar in vehicle. In the future, the whole system will be finished and run way will be given, and then there will be a test in practice. The great efforts will be made with this orientation.
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