Research On Key Technologies Of Post-Disaster Search And Rescue Equipment Based On Mobile Communication

Natural disasters are a huge threat that human beings have to face,and a safe,reliable and efficient search and rescue technology is always in urgent need.With the development of mobile communication technology and the popularization of smartphones,location-based services have become inseparable from people’s daily lives,providing new ideas for search and rescue.As the signal strength of mobile phones is much greater than the vital signs of the human body,search and rescue technology based on mobile communication can achieve high-precision positioning in a large range,providing the possibility for large-scale and rapid life detection.However,in practical applications,due to the limitations of some non-ideal conditions,traditional mobile communication positioning methods are difficult to apply directly to search and rescue.In this thesis,considering the actual needs of post-disaster search and rescue and considering the power consumption,volume,and weight limitations of mobile detection equipment,based on the mobile phone uplink passive positioning based on random access channel preamble detection,several key technologies such as high-resolution time delay estimation method,time-frequency synchronization error compensation method and high-precision position estimation method are deeply studied,and a prototype system of post-disaster search and rescue equipment based on mobile communication is built.The main work and innovations of this thesis include:1.Aiming at the problem that the traditional time delay estimation method cannot distinguish multi-user conflicts in random access channels,and the time delay estimation method with high resolution is computationally complex,this thesis proposes a time delay estimation method based on frequency extraction and spatial smoothing of multiple signal classification,and designs an adaptive frequency extraction covariance matrix construction and spectral peak search strategy based on a two-step detection process,which greatly improves the detection efficiency of random access channel preamble sequences.Simulation experiments show that compared with the preamble detection process using the traditional cross-correlation method and the multiple signal classification delay estimation method,the detection process designed in this thesis can reduce the overall computational complexity by 57.62%while maintaining similar delay estimation accuracy and resolution.2.Aiming at the problems that mobile search and rescue equipment uses traditional timing methods with large synchronization errors,unstable crystal oscillators and poor timing accuracy,and time-frequency asynchrony leads to deviations in time-of-arrival estimation errors,this thesis analyzes the effect mechanism of frequency offset on preamble sequence delay estimation errors,proposes an orthogonal frequency division differential time-frequency synchronization error compensation method based on the mutual power delay profile.In this method,the reference signal is simultaneously sent out in the subframe of the preamble sequence signal sent by the mobile phone,and the differential arrival time difference estimation is performed on the two signals,which is equivalent to adding a time stamp to the radio frequency signal,which It can completely eliminate the transmission delay error from the antenna,the radio frequency to the baseband processor,and realize the time-frequency synchronization error compensation.Experiments show that the method proposed in this thesis relaxes the time synchronization requirements between detection devices and can still achieve unbiased estimation when the clock stability is better than one ppm.Compared with the measurement process of traditional differential arrival time difference estimation method,the calculation amount can be reduced by up to 50%.3.Aiming at the problem that the traditional position estimation method has low accuracy due to the non-line-of-sight deviation of the delay estimation in the complex post-disaster environment,this thesis takes the minimum error entropy criterion as the basis and optimizes it,and proposes a multi-space-time joint differential time-of-arrival estimation method based on the minimum error entropy,obtains redundant observation information at different time and space positions through limited detection equipment,randomizes the fixed deviation,and realizes the suppression of interference such as non-line-of-sight deviation,presents a joint optimization method based on two-step weighted least squares and minimum error entropy grid search to achieve high-precision and fast position solution.Simulation experiments show that,compared with the nonlinear least squares estimation method,the positioning error of the method proposed in this thesis can be reduced by 19.5%.4.The post-disaster search and rescue equipment based on mobile communication is built as a test platform,miniaturized detection equipment is designed from the perspective of low power consumption,and the system design and theoretical algorithm proposed in this thesis are integrated and tested and verified by experiments.Experimental and thirdparty test results show that the detection equipment designed in this thesis can achieve a positioning accuracy of 5 meters under the condition of single-layer ruins.With the same number of nodes,the positioning accuracy is improved by 28.57%compared with the existing post-disaster rescue equipment based on the software radio platform.