Research On Time - Varying Channel Modulation Technology Of XCTD Profile Based On ASK And DPSK

XCTD is referred to as the Expendable Conductivity Temperature Depth profile measurement equipment, and it is advanced profile detection equipment which has been developed successfully and developed rapidly in recent years. The XCTD can be used in a large amount because of the low cost, which provides an advanced detection method for the study of marine investigation, scientific research, military application and so on. At present, the research of XCTD profiler is more mature in United States and Japan, and the development XCTD in China is mainly in the initial stage of development.As the XCTD probe is influenced by the factors such as cost, weight, working environment and so on, the transmission line of channel uses a double-stranded metal enameled wire. The channel parameters will dynamic changes with the process of transmission line unfolded, and this feature will cause amplitude attenuation and phase delay very unstable which will result in serious distortion of the demodulation signal and reduce the accuracy of the demodulation signal in receiving terminal. So the problem of signal transmission has been the key problem to be solved in the research and development of the equipment, and how to improve the stability and accuracy of XCTD transmission system is the main purpose of this research.This paper firstly analyzes the characteristic of the XCTD transmission channel and channel parameters, and optimize the XCTD channel transmission circuit model by the characteristics of the transmission channel and the variation of the parameters to further improve the stability and accuracy of the XCTD transmission channel. Secondly, this paper introduces the characteristics of ASK frequency band transmission, and uses Simulink tool kit of Matlab to build the XCTD channel simulation circuit model based on ASK frequency band transmission, and confirms the transmission frequency, the detection depth and the ocean noise are the main factors which affect the transmission of the ASK frequency band transmission by analyzing the transmission channel and the actual detection environment specifically.This paper analyzs the influence of transmission channel on ASK modulation signal and determines that the influence of noise level on the accuracy of ASK frequency band transmission is the most by analyzing the variation of the error rate of the demodulation signal, so how to suppress the level of noise effectively is the key to solve the accuracy of ASK frequency band transmission and make sure the highest accuracy of transmission conditions.This paper analyzes the characteristics of DPSK band transmission and builds XCTD channel simulation circuit model based on DPSK band transmission, and analyzes the influence of the transmission channel on the DPSK modulation signal, then transmission rate,probing depth, and noise are the same as the factors affecting the accuracy of DPSK band transmission, but the main factor affecting the accuracy of the DPSK demodulation error rate is the same frequency of the carrier frequency, so we can determine the maximum range of the frequency offset of the demodulation carrier to meet the actual measurement requirements by analyzing the size of the error rate of the demodulation signal. The increasing of capacitive parameters in XCTD channel has great influence on the error rate of demodulation signal, which has important significance to improve the accuracy of measurement data and the stability of signal transmission.