| Compared to traditional illuminations such as FM,5G has the advantages of wider bandwidth and higher carrier frequency,so it is more suitable for detecting small targets in low altitude areas.At the same time,the dense distribution of 5G base stations makes the coverage of the signal wider,and the target can be detected from multiple angles and in a full range.Although 5G has many advantages,5G is not a signal specially designed for radar,it has periodic components such as synchronization signals.Therefore,the 5G-based ambiguity function is not an ideal pushpin-shaped ambiguity function.Instead,there are many sidelobes,which will not only cause false warnings,but also mask the main lobes of weak target echoes,resulting in missed warnings.In order to solve this problem,based on the basic principle of passive bistatic radar and the analysis of 5G characteristics,this paper studies the ambiguity function characteristics and sidelobe suppression technology of5 G.The main contents are as follows:(1)Firstly,the process of signal processing by the passive bistatic radar is introduced.Secondly,based on the detection and positioning principle of passive bistatic radar and the characteristics of 5G,the detection performance of the 5G-based passive bistatic radar system is analyzed in detail.The analysis shows that the characteristics of 5G’s large bandwidth,high carrier frequency and denser base station distribution make it have a natural advantage in detecting small targets in low-altitude areas.In order to solve the problem that it is difficult to distinguish multiple targets appearing in the same range-Doppler domain in the received signal of passive bistatic radar,this paper proposes a method for multi-target DOA estimation of passive bistatic radar based on sparse reconstruction.This method can estimate the DOA of multiple targets appearing in the same range-Doppler domain.(2)The ambiguity function characteristics of the 5G-based passive bistatic radar signal are analyzed.Based on the modulation characteristics of 5G and ambiguity function theory to simulate the ambiguity function of 5G,and then the cause of various sidelobes in the ambiguity function and the influence of the sidelobes on the radar detection performance are deeply studied.From the above research,it can be found that the ambiguity function of 5G inherits some of the characteristics of the 4G ambiguity function,but also produces some changes,in which the cyclic prefix data in 5G also causes sidelobes in the time domain of its ambiguity function,and in the frequency domain,different types of sidelobes are generated due to differences in the structure of 4G.These sidelobes cause false warnings and missed warnings when the radar detects the target,so it is necessary to seek the corresponding sidelobes suppression technology.(3)In order to solve the problems that the traditional sidelobes suppression method is easy to cause new sidelobes,the amount of computation is large,and the frequency domain sidelobes cannot be suppressed,the method of mismatch filtering is introduced into the sidelobes suppression of 5G-based passive bistatic radar in this paper.Firstly,the cost function of integrated suppression of sidelobes in distance and frequency domain is constructed;then,in order to detect weak target echo signal,the length of the signal processed by 5G-based passive bistatic radar is relatively long,which leads to the problem that the calculation of the factor of the mismatch filter is relatively large.A segmented method is proposed to solve the mismatch filter factor,so as to realize the suppression of the short-distance sidelobes in the time domain and the periodic sidelobes in the frequency domain of the 5G ambiguity function;finally,the performance of the mismatch filtering algorithm is analyzed,and the influence of different signal parameters on the performance of the algorithm to suppress the sidelobes is discussed. |
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