Research On The Characteristics Of XCTD Communication Channel

As an ocean exploration devices,Expendable Conductivity Temperature Depth(XCTD)Vessel carried undersea expendable instruments is used for measuring seawater conductivity,temperature and other environmental parameters at different depths.This paper presented approaches to model the communication channel for vessel carried expendable measuring instruments and analyze channel intrinsic properties to ensure the signal transmission accuracy and stability.First of all,according to the working procedure,based on the classic transmission line model,the distributed parameters transmission line model of the channel was established.Using the established channel model as foundation stone,the methods to analyze the channel transient and frequency response based on finite difference time domain(FDTD)method and Baum-Liu-Tesche(BLT)equation were described.Finally,a brief introduction of the soft realization and simulation for analyzing the channel property is presented.The main research contents are as follows:1.The transmission channel model and its key parameters is the foundation for channel analysis.For the cable parameters calculating,the classical method was coupled with the differential and integral calculus.For the solenoid parameters calculating,a double layer model for capacitance calculation which is more concise was proposed according to the actual structure of the solenoid.Furthermore,the channel model as well as the value of each distributed parameters had been verified with experimental measurements.The test results are consistent with the theoretical results in the instruments working frequency range.It shows that the parameters theoretical analysis and the channel model is feasible and can provide guidance for design of the matching circuit and improving the accuracy of transmission scheme.2.In order to analyzing the intrinsic properties,a method to analyze the channel transient and frequency response based on finite difference time domain(FDTD)method and Baum-Liu-Tesche(BLT)equation was presented.For the transient response analysis,an improved FDTD method is presented to analyze transient response in any location of channel with arbitrary terminal loads.For the frequency response analysis,the BLT equation is coupled with the thoughts of electromagnetic topology to analyze the frequency response in the node of transmission channel.Furthermore,the channel transient and frequency response are compared with the experimental measurement,and the test results are consistent with the theoretical results in the frequency range.3.Based on the e channel transient and frequency response analyzing,a series simulation of transmission channel of XCTD were introduced,Such as channel characteristic impedance and wave propagation speed.The relation between the transient response and the relaxing length of channel when XCTD working was simulated.Similarly the relation between the transient response and the value in the channel load was also simulated.