Research On Channel Modeling And Fault Diagnosis Of Leaky Coaxial Cable Network In Underground Coal Mine

Coal is the main source of energy in our country,and it plays an extremely important role in national economy and social development.Coal mine as a traditional high-risk industry,safety production has been restricting the development of the coal industry.The prevention and control of serious accidents and the promotion of stable and safe production of coal mines have become one of the key issues to be solved at the national level.In addition,informatization and intelligence are important directions for future mine construction.Coal mine mobile communication will become the core link of information and intelligent mine.Leaky communication,as an ideal mode of mine mobile communication,is widely used in underground coal mines.Leaky coaxial cable network is the most important part of leaky communication system.Its normal operation will affect the stability of the mine mobile communication and coal mine safety production.Therefore,fault diagnosis for leaky coaxial cable network is very necessary.The advanced fault diagnosis method is applied to the fault diagnosis of underground leaky coaxial cable network,which is of great significance for guaranteeing the stable operation of mine mobile communication and improving the grim situation of the current safe production.The establishment of leaky coaxial cable network channel model in underground coal mine is the basisi of fault diagnosis.As an important part of leaky communication system,leaky coaxial cable network is widely distributed in underground roadway.Due to the poor environment in underground coal mine,there are many problems such as large signal attenuation,wide interference sources and large time variation in leaky coaxial cable network channel.Therefore,the research of the leaky coaxial cable network channel model and the establishment of an accurate mathematical model can fully understand the transmission characteristics of the leaky coaxial cable network channel,which is of great significance to the fault diagnosis of the leaky coaxial cable network and to ensure the safety production of coal mines.At present,the most widely used and most effective fault diagnosis method for transmission lines is the reflection method.This method can be used not only for fault diagnosis of single transmission lines,but also for fault diagnosis of transmission line networks.The transmission distance of the transmitted signal in the transmission line is determined by its energy.Under the condition that the emission peak is limited,the transmission distance can only be guaranteed by increasing the width of the transmitted pulse,which will result in the decrease of the range resolution of the echoe.Moreover,compared with the ordinary cable,the coupling loss of the leaky coaxial cable will increase the attenuation of the signal,making the transmission distance limited.The linear frequency modulated pulse compression technology can solve the above problems.The chirp signal has large time-bandwidth product,which can reduce the peak power limit,effectively increase the energy of the signal,and can detect longer distance targets than other system signals.At the receiving end,matched filter technology is used to obtain narrow pulse,which improves the distance resolution of the echo and solves the contradiction between transmission distance and resolution.This paper focuses on the channel modeling and fault diagnosis of the leaky coaxial cable network.Based on the on-the-spot measurements of the components of the leaky coaxial cable network,the transmission characteristics,fault diagnosis and location of the leaky coaxial cable network are studied through theoretical derivation,simulation analysis and experimental verification.The channel model of the leaky coaxial cable network is established,and a fault diagnosis and location method applied to the leaky coaxial cable network is proposed.The main research work is as follows:The characteristics of the components of the leaky coaxial cable network are researched.Firstly,the principle,characteristics,function and composition of the leaky communication system are expounded,and the research object of this paper is determined.Then the components of the leaky coaxial cable network are analyzed,including the structural characteristics,classification and electrical characteristics of the leaky coaxial cable,and the working principle and characteristic parameters of the power splitter and bidirectional repeater.Finally,a vector network analyzer is used to measure the transmission characteristics of the leaky coaxial cable,and the S scattering parameters of the power splitter and bidirectional repeater.In order to obtain the transmission characteristic parameters of the leaky coaxial cable,the measured leaky coaxial cable characteristic curve is fitted by the least squares method,so that the fitting data and the measured data are very close.The average relative error of amplitude frequency curve and phase frequency curve is less than 5%.The measured S scattering parameters can more accurately characterize the transmission characteristics between all ports of the power splitter and bidirectional repeater,and lay a foundation for channel modeling and fault diagnosis.The channel modeling method of the leaky coaxial cable network in underground coal mine is researched.In order to analyze the complicated engineering problem of the the leaky coaxial cable network channel,the multipath channel model is analyzed based on the multipath propagation.Based on the analysis,the state transfer method is adopted to deduce the transfer function between the leaky coaxial cable network terminals,and the channel model of the leaky coaxial cable network is established.The complex engineering problem is transformed into discrete mathematical optimization problem.The particle swarm optimization algorithm is proposed to optimize the number of paths for signal transmission between terminals,so as to obtain a more accurate channel model.With the continuously advancing mining face,underground leaky coaxial cable network is developing in a more complex direction.So it will be very difficult to actually measure the channel transmission characteristics in the actual optimization.Therefore,for the leaky coaxial cable network that can obtain actual measured value,the measured value is used as the optimization objective to establish the objective function.For the leaky coaxial cable network that cannot obtain actual measured value,the maximum likelihood method is adopted to estimate the transmission characteristics of the leaky coaxial cable network.And this value is used as the optimization objective to establish the objective function.The detailed steps of the optimization algorithm to solve the practical problem are described.The proposed method is verified by simulation.Results show that the method of state transfer and particle swarm optimization algorithm is correct and feasible for the channel modeling of the leaky coaxial cable network.And the maximum likelihood method is used to analyze the channel characteristics of the leaky coaxial cable network when the measured value cannot be obtained.The estimated value is used as the optimization objective can also achieve the goal of optimizing the leaky coaxial cable network channel model.The fault diagnosis method of leaky coaxial cable based on pulse compression technology is researched.Firstly,the common faults and causes of the leaky coaxial cable and the diagnosis of common fault types are analyzed.The system composition and principle of fault diagnosis for leaky coaxial cable based on based on linear frequency modulated pulse compression technology are discussed.Then the real part and spectrum characteristics of chirp signal are analyzed.The key techniques of echo analysis are deeply studied.Pulse compression is a large time-bandwidth product signal implemented by matched filters.The working principle and design method of the matched filter are analyzed.Based on the analysis of the sidelobe suppression method of pulse compression output,a nonlinear combining sidelobe suppression method using matched filtering and hamming window is proposed,and the flow chart of signal processing is given.For the fault diagnosis of the leaky coaxial cable,conventional single pulse method and linear frequency modulation pulse compression method are used to verify the feasibility and effectiveness of the proposed method.The experimental system is built to further verify the good performance of the pulse compression technology.Results show that the linear frequency modulation pulse compression technology has a longer fault diagnosis distance and enough distance resolution,and this technique has better performance than the conventional method.For sidelobe suppression of echo signals,the performance of the proposed method is analyzed from both the sidelobe suppression level and mainlobe broadening coefficient,and the feasibility and correctness are simulated.Results show that the proposed method can suppress sidelobe signals and avoid widening the mainlobe width in the cable fault diagnosis,which greatly improves the accuracy of fault diagnosis.The fault diagnosis method of leaky coaxial cable network in underground coal mine is researched.Firstly,the common faults and causes of the leaky coaxial cable network are analyzed.According to the impedance value at the fault point,the leaky coaxial cable network faults are divided into hard faults and soft faults.Then,the fault location principle of leaky coaxial cable network is elaborated.The support vector machine is applied to analyze the echo curve after pulse compression,so as to complete the fault location of leaky coaxial cable network.The principle of support vector machine is described.The theoretical basis of support vector machine is the structural risk minimization criterion,which is applicable to the curve regression of high dimensional data.The model of support vector machine is established.The Gaussian function is selected as the kernel function of support vector machine.The cross validation method is used to select the parameters of the support vector machine model,including the penalty factor and the width of the kernel function.The specific steps of leaky coaxial cable network fault diagnosis and location are given.The proposed method is verified by simulation.Results show that the proposed method can accurately analyze the location and type of fault points in the leaky coaxial cable network.Moreover,this method has good robustness.