| WiFi-based passsive radar uses the WiFi signal which is easily available in urban space as opportunity illuminator.Because it can realize real-time monitoring and early warning all-day and all-weather,WiFi-based passsive radar has the potential to be used in the task of indoor and outdoor moving target monitoring.At the same time,the system does not need to design waveforms,to allocate frequency bands and will not cause extra Electromagnetic pollution.Moreover,WiFi-based passsive radar can protect privacy compared to existing video surveillance systems.The key to realize the detection and tracking of moving target by WiFi-based passsive radar is to solve the problems of unsatisfactory WiFi signal waveform,radiation source selection and direct wave/multipath interference suppression.The thesis conducts in-depth research on these issues,using theoretical analysis,simulation testing and experimental verification methods.The main research contents are as follows:1.Aiming at the problem that the WiFi signal is not ideal for radar target detection,the time-frequency characteristics and ambiguity theory of WiFi signal are studied.The distance resolution,Doppler frequency resolution and sidelobe peak of the signal are analyzed.laid the foundation for the subsequent secondary peak suppression.2.Aiming at the problem that the downlink data traffic(used to measure the signal transmission time during the accumulation time)of the access point affects the system detection performance,a dynamic illuminator selection method based on traffic statistics and its system are proposed.The method selects the AP with the largest downlink data traffic as the illuminator,so that the detection performance of the system is optimal.3.Aiming at the false alarm and false detection caused by the distance sidelobe,the sidelobe suppression technology in the WiFi-based passsive radar is studied,and the suppression of the fixed position secondary peak of the distance dimension under OFDM modulation and DSSS modulation is realized.The possibility of false alarms and false detections brought by the sidelobe are decreased.4.Aiming at the problem of direct wave/multipath interference on the target echo,the direct wave/multipath interference suppression technology is studied.The extended cancellation algorithm is used to suppress the multipath interference,improve the signal to interference ratio and increase the reliability of target detection.5.Designed a WiFi-based passsive bistatic radar experimental system,using the software radio platform build an experimental platform,receiving reference signals and surveillance signals,processing echo signals.The key signal processing method is verified,and the distance measurement and speed measurement of the target of the athlete are realized.The purpose of monitoring the indoor moving target is achieved.The above work realized the reliable detection of moving targets by using WiFi signal as illuminator,which provided theoretical and experimental basis for the practical application of WiFi-based passsive bistatic radar. |
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