| Bio-radar uses electromagnetic waves as detecting media and can penetrate through non-medal obstacles, such as clothes, walls, building ruins, etc., to non-contact sense human subjects. Compared with the non-contact technologies such as infrared, optical and so on, bio-radar is unaffected by light and detection angle and has the characteristic of all-day detection. So it has great prospects in the application of medicine, public security and military areas. The bio-radar technology has experienced two stages, narrowband and ultra-wide band(UWB) bio-radar, between which the UWB bio-radar has higher range resolution, improved penetration, better near-field and compatible properties, and is the research hotspot at present. Currently, UWB bio-radar technology has basically achieved the detection, identification and positioning of human subjects, but it has only one type of practical instrument, namely UWB search-and –rescue(SAR) bio-radar, which mainly aims at detecting survivors buried under building ruins after disasters such as earthquake or building collapse. So the study of UWB bio-radar mostly focuses on the key scientific problems, such as the positioning of a human subject, detection of multiple subjects and behavior movements, however, the problems in practical use are little considered. for example, the “SJ-3000” UWB SAR bio-radar which is developed by our research group, has well applied in many applications such as the earthquakes of Wenchuan, Yushu, Ludian, etc. Based on those practical uses, we find that the various interferences existed in the detection scene and affected the detection performance of the instrument. Therefore, surrounding interference is one key problem that should be considered in the application of UWB bio-radar.Studies at home and abroad shows that the interference in the practical use of UWB bio-radar mainly comes from two origins: one is the interference caused by moving objects in the surroundings, such as grasses in winds, movements of the bio-radar's operators, etc; the other is various narrowband radio frequency interference(RFI) such as GPS, mobile phones and wireless signals. On the basis of long term research and application of UWB bio-radar, our research group finds that the interference caused by moving objects is mainly caused by the grasses in winds since the movements of the bio-radar's operators can be limited. Moreover, UWB bio-radar is only used in practical SAR after disasters. It mainly has low center frequencies(<500MHz) to ensure good penetration through building ruins. The GPS and mobile phone signals do not overlap with UWB bio-radar in spectrum. So the main origin of narrowband RFI is the intercom signals extensively used by those SAR personnel.Based on the above analysis, mainly aiming at the narrowband RFI interference caused by intercom and the interference caused by grasses in winds, this thesis carries out systematic and experimental study on UWB bio-radar's environmental interference and its suppression technique.This thesis focuses on the following works:1. Quantitative study has been performed on the environmental interference of UWB bio-radar, and the impact of interference caused by narrowband RFI and grasses in winds on the respiration detection performance of UWB bio-radar has been determined: 1) the interference caused by narrowband RFI and grasses in winds relates with range of the interference resources, the influence on the detection declines as the range increases; 2) the impact range of the narrowband RFI is greater than that of grasses in winds and does not depend on the time window of the radar, and declines slower with the increasing of the range. The impact range of the grasses in winds is less than that of the narrowband RFI, and can be totally eliminated by setting the interference resource beyond the time window; 3) the narrowband RFI does not related with the resource angle but the interference caused by grasses in winds does, and the impact of the latter becomes less as the resource being set further from the antennas' main lobe.2. Echo processing experiment has been performed and new algorithms has been proposed to suppress the interference caused by narrowband RFI and grasses in winds. Utilizing the range interrelated characteristic of the human respiratory response detected by UWB bio-radar, the range moving average(RMA) based narrowband RFI suppression algorithm has been proposed by performing moving average on the range dimension of UWB bio-radar's echo data. To suppress the interference caused by grasses in winds, by using the periodic characteristic of respiration meanwhile, the UWB echo processing algorithm has been established on the basis of adaptive multichannel singular spectrum analysis(MSSA).3. Simulated detection experiment of UWB bio-radar has been performed, in which the results from the quantitative experiment and the algorithms from the processing experiment have been verified. The experiment results show that the RMA algorithm is simple in scheme and stable in performance, and can basically eliminate the narrowband RFI' impact on UWB bio-radar. The adaptive MSSA algorithm needs no empirical threshold during its signal reconstruction, and can suppress most interference caused by moving grasses in winds except the extreme case(the interference resource closely attached the antennas).4. Coping strategies have been established for the environmental interference suppression in practical use of UWB bio-radar: 1) the RMA algorithm can be used in UWB bio-radar to effectively suppress all the narrowband RFI. The extreme case in which the resource is 0m from the antennas(e.g. the operator uses intercoms) should be avoided when conditions permit in practice; 2) the adaptive MSSA algorithm can be used in UWB bio-radar to effectively suppress most interference caused by grasses in winds. The extreme case in which the resource is 0m from the antennas should be avoided and the interference can be totally eliminated by setting the interference resource beyond the radar's time window if conditions permit in practice.Innovations in this thesis are listed below:1. We determine the impact of the interference cause by narrowband RFI and moving grasses in winds on the performance of UWB bio-radar, and set up the coping strategies for the environmental interference suppression in practical use of UWB bio-radar. Those works have great significance on the application of UWB bio-radar.2. We utilize the range interrelated characteristics of the UWB respiratory response to propose new interference suppression algorithms to cope with the narrowband RFI and moving grasses in winds. The algorithms can improve UWB bio-radar's anti-interference capability and its practical performance. |
PDF Full Text Request