Research On Compression And Encryption Technology Of Track Frequency Shift Signal Based On Compressed Sensing

Track frequency shift signal has become a main system to speed up railway, inter-city railway, the special line for passenger transport and high-speed automatic block. It is also the basic ground signal for the cab signal, LKJ and Dynamic Monitoring System (DMS). At the same time, the influences on on-board equipment storage load, security and bandwidth requirements of train-ground wireless transmission and the transmission delay are also growing. Therefore, it is significant to research a method that is fast and efficient, safe and reliable to compress and encrypt the track frequency shift signal.At present, the method of track frequency shift signal compression is mainly based on Wavelet or Wavelet packet transformation. It discusses the track frequency shift signal under the high SNR and in a way of reserving the Wavelet coefficient of corresponding frequency-band datas, which can easily delete the useful train exception information beside the sub-band. Therefore, this shortcoming may cause the method failed. The safety of the train-ground remote wireless transmission mainly based on encryption. But because of the large number of track frequency shift signal datas, the cipher text in the process of remote wireless transmission is greatly influenced by the bandwidth and transmission delay. In this regard, a new method is proposed to compress and encrypt track frequency shift signal according to the compression features of compressed sensing and the sparse characteristic in its frequency domain.The main research of this thesis includes the following several aspects:(1) The basic knowledge of Compressed Sensing theory and track frequency shift signal are introduced. First, the basic principle of compressed sensing, signal processing conditions and application, and the common reconstruction methods are introduced. Meanwhile, this part analyses the time-frequency domain characteristic of the track frequency shift signal and its sparse conditions when using this theory, explains the rationality of processing track frequency shift signal based on compressed sensing theory.(2) In order to overcome the disadvantages of large storage load of the vehicle equipment, the demanding bandwidth in the train-ground of the wireless transmission and low compression efficiency in existing technology, a method based on the compressed sensing theory is proposed in this thesis to compress the track frequency shifting signal. The method draws on the ideas of the compression of Compressed Sensing theory and combines with sparse characteristics of track frequency shift signal in frequency domain. It uses Gaussian random matrix with RIP features to compress and observe, optimize and reconstruct the sparse coefficients, which effectively improves the compression efficiency and the reconstruction precision of the track frequency shift signal. The compression and observation model not only alleviates the storage load of the vehicle equipment, reduces the wireless transmission bandwidth and transmission delay, but also improves the security of the signal datas wireless transmission. The experiment results show that the proposed method has the advantages of high compression efficiency, well real-time performance and small reconstruction error.(3) Combining the advantages of chaotic system and the compression scheme of processing track frequency shift signal based on compressed sensing theory, a method based on extension tent map is proposed to construct the key controlled observation matric, which can simultaneously compress and encrypt the track frequency shift signal. The method effectively avoid to storage and transmit the observation matric elements and signal datas, which greatly improves the security of the wireless network datas transmission. Meanwhile, the chaotic system can provide flexible dimension of observation matric according to the input parameter changes and has high flexibility. Theoretical analysis and experimental results show that this method is extremely sensitive to key initial value and has advantages of large key space, high security and well real-time compression effectiveness.Finally, the research work of this thesis is comprehensively summarized, and the future researches on compressed sensing theory used in the field of track frequency shift signal are discussed.