Research On Improving The Transmission Performance Of XCTD Based On Multi-carrier Technology

XCTD is the abbreviation of the Expendable Conductivity-Temperature-Depth profiler.As one of typical products of the deep-sea abandoned profiler,it had been developed successfully and rapidly in recent years.At present,the United States and Japan are a leader in the XCTD technical aspects of the research in the world.but the development of XCTD technology in china is mainly in the initial stage.According to the design of the national marine technology center,the transmission line uses a double-stranded enameled wire to transmit data signal in XCTD measurement system.Because of the continuous change of the detection depth,the impedance parameters of the transmission channel are also changing,so that the measured hydrologic parameter data can not be transmitted to the receiver quickly and efficiently.Therefore,it is an important subject of XCTD research to study the transmission characteristics of the channel and design the appropriate communication sy stem to ensure the high speed and high speed transmission of the signal.In this paper,the XCTD channel circuit model is established and the transfer function of the channel is calculated,based on this,the transmission characteristics of the theoretical XCTD channel are analyzed.Aiming at the shortcomings of the theoretical circuit model,a laboratory XCTD channel test system is built,and the measured channel transmission characteristics are obtained by the combination of sweep frequency method and data fitting.Then the frequency domain characteristics of square wave is used to verify the measured results.And the influence of channel on different frequency composite waveforms is analyzed,which provides a theoretical basis for the design of communication system.Based on the characteristics of the XCTD channel,it is proposed that the multi carrier modulation technology is suitable for the XCTD channel transmission system because it has the characteristics of high frequency utilization.A simulation model and the measured system of the multi carrier communication system are set up,and the performance of multicarrier transmission system is compared with the performance of ASK band transmission system from two aspects of simulation and practical testing respectively.The results show that the multi carrier technology is suitable for the XCTD channel and can effectively improve the transmission performance of the XCTD system.