Study On Blind Method For Passive Bistatic Radar Target Detection

Passive bistatic radar, also known as passive coherent location (PCL) radar,belongs to a new radar system. Passive bistatic radar, different from the conventionalradar, doesn’t emit electromagnetic waves, but to use a variety of communications,broadcast signals (such as FM radio, television stations, GSM base stations and GPSsatellites, etc.) as illuminators, to passively receive the reflected echo signals fromtarget for target detection and imaging. In structure, passive bistatic radar belongs to thebistatic radar configurations, it can’t easily be found by the enemy, and thus it has betteranti-jamming and anti-radiation missiles capabilities; And by means of UHF and VHFsignal characteristics, passive bistatic radar also has good anti-stealth and low-altitudedetection capabilities; Except that, it also has the advantages of portable, low-cost, nospectrum allocation, no electromagnetic pollution and no blind spot detection etc.Therefore, in order to cope with the complexity of modern battlefield environment,passive bistatic radar has become an effective way of target detection and has importantresearch significance.This thesis focuses on several specific issues in the passive bistatic radar targetdetection system, such as the direct wave reconstruction, clutter cancellation, parameterestimation, data fusion and so on; the main research results obtained are as follows:1. For a complex battlefield environment, there may be multiple illuminationsources around the receiver, the basic information of illuminator is unknown (mainlythe direction of base station and the signal waveform), can not distinguish between theinterested signals and interference signals, and can not determine the mathing betweenthe illuminator and target parameter in the target detection. Considering that most of thecommunication signal is cyclostationary, we propose a blind method to suppressinterference. Cyclostationary information of signal is made to estimate the direct signaldirection while suppressing interference from other base stations, which finally obtainrelatively accurate direct signal. In the target detection stage, we derive equivalencebetween ambiguity function and second-order cyclostationarity, and propose secondorder conjugate cyclostationary instead of ambiguity functions to achieve matchingbetween interested base station and target parameter.2. Considering reference signal containing the multipath, and then both thereference channel and surveillance channel require clutter cancellation in the actualprojects, we propose the blind source separation to extract the direct signal and the target echo signal directly from the sole surveillance channel, which achieve the goal ofdecreasing the computational complexity and enhancing the weak echo signal. For theconventional blind source separation not suitable for the ill-posed problem in thepassive bistatic radar, we propose to enhance the weak target by using cyclostationarity,and apply to the underdetermined case in which the number of antennas is less than thenumber of signal sources. In the signal separation stage, a robust oblique projectionmethod is given to extract the target echo signal from the mixed signals containingnoise.3. Taking into account the advantages of OFDM signal in synchronization andanti-jamming, we propose passive radar target detection method based on OFDM signalcharacteristics. For the problem of reference signal information in passive radar may notbe directly acquired, we propose a blind method to estimate the OFDM parameters.Taking into account the side peaks in the ambiguity function of OFDM is caused by theperiodicity of pilot signals, but also because of the equivalence between ambiguityfunction and the second-order cyclostationarity, we propose to estimate the periodicityof pilot signals, which obtain the pilot position information, then to achieve the clutterchannel impulse response estimation and reconstruct the direct signal.4. For the most current communication and broadcasting systems using OFDMmodulated signal, and supporting single frequency network structure, we adviseOFDM-SFN passive bistatic radar to improve target detection reliability. But in the SFN,the multiple signals from different directions to detect target, it is most likely to causethe large delay spread. Furthermore, transmitting the orthogonal subcarriers, OFDM isvery sensitive to the carrier frequency offset. For these two problems, in the case ofhaving no illuminator information, we propose to covert the large time delay into asmall delay by using the array antenna, model a new tensor receivers, and simultaneousestimate delay and Doppler frequency offset by using joint diagonalization method,which solve the poor estimation accuracy of frequency-domain blind source separationalgorithm in the large delay spread.5. For the large delay in OFDM-SFN, suggests another way to send and receivebased on cyclic shift and space-time coding, the receiver will be able to use a singleantenna to combat the large delay spread, which achieve the goal of simplifying thesystem configuration at the receiver. And for two-step positioning error in theconventional location algorithm for the SFN multi-station positioning, we adopt to usethe direct target location based on OFDM signal characteristics. Compared with the conventional positioning method, the proposed can achieve higher estimation accuracy,especially in the low SNR.