Research On Loran-C Signal Acquisition System And Signal Processing Method Of High Signal-to-Noise Ratio Station Chain

As a typical land-based radio navigation system,Loran-C system can provide PNT(Positioning Navigation and Timing,PNT)services in a large area of thousands of kilometers.The performance of Loran-C receiver,especially the correction accuracy of Loran signal propagation delay,determines the service capability of Loran navigation and positioning system.In order to improve the Loran receiving terminal’s space-varying and time-varying correction accuracy of Loran signal,it is necessary to monitor the Loran station signal for a long time and multi-point,so as to strengthen the understanding of Loran signal propagation law.The highperformance Loran-C signal acquisition and monitoring system is an important technical support for studying the variation law of Loran-C sky and ground wave signal,and provides basic research data for the radio wave propagation law and propagation delay correction of Loran-C sky and ground wave signal.By studying the acquisition technology of high-sensitivity and highdynamic Loran-C signals,this paper designs and implements a set of acquisition and monitoring system with high signal-to-noise ratio,which can simultaneously receive Loran-C sky and ground wave signals from different station chains is designed and implemented.This system has important practical significance for us to study the changing law of Loran-C signal and the development of Loran-C navigation receiver.This paper focuses on the research of high-performance Loran-C signal acquisition system,proposes a Loran-C signal synchronous sampling system and high signal-to-noise ratio stage chain signal processing method,and completes the design and implementation of the hardware and software of the Loran C acquisition system,as well as the testing and analysis of the collected data.The specific work content is as follows:(1)Design and implemented Loran-C signal acquisition system.The acquisition system uses FPGA(Field Programmable Gate Array,FPGA)as the main controller,clock taming technology and high precision Analog-to-Digital Converter(Analog-to-digital converter,ADC)as the core,uses GNSS(Global Navigation Satellite System,GNSS)timing second pulse to tame the local constant temperature crystal oscillator,achieves synchronization between the sampling clock and Universal Time Coordinated(Universal Time Coordinated,UTC).The frequency accuracy is 1.14×10-10,it ensures the accuracy and consistency of the sampling period and the signal transmission clock of the Loran station,so as to complete the extraction of useful signals by means of data processing.Among them,the Loran analog signal conditioning module will filter,couple and amplify the input antenna signal.The bandwidth of the bandpass filter is 85kHz115kHz,and the in-band signal gain is not less than 30dB,so that the input signal can reach the optimal signal input range of the analog-to-digital converter and improve the effective digits.(2)The research work of highly sensitive and dynamic signal acquisition module is completed,the synchronous acquisition system combined with adaptive control technology can receive station signals with large signal strength span and large signal strength difference.Based on the digital potentiometer of the signal conditioning module the ⅡC communication module and the dynamic range adjustment algorithm of the analog-to-digital converter are designed,and the amplification gain is adjusted dynamically by judging the amplitude of the input signal of each chain.Secondly,after the acquisition of the signal by the analog-to-digital converter controlled by FPGA,it is necessary to design a filter to filter out the out-of-band interference signal and noise in the collected data and simulate the filtered signal.Then,in the process of signal acquisition,according to the pulse Group Repetition Interval(Group Repetition Interval,GRI)of each chain signal of Loran-C system,FPGA is used to accumulate and process multiple chain signals to obtain the signals of each station with strong signal amplitude,so as to realize the effective acquisition of signals under the conditions of different distance stations with large signal strength difference and sky and ground wave intensity difference.(3)Design reliable data transmission protocol and high speed data transmission storage upper computer software,and use the stored data to complete analysis and processing.After filtering and caching,the collected data is sent to the upper computer for processing and storage using the reliable User Datagram Protocol(User Datagram Protocol,UDP)or USB 3.0(Universal Serial Bus,USB)high-speed data transmission protocol.The data transmission protocol designed in this paper solves the problems of data transmission rate and data packet loss,and has high effective bits and fast transmission rate.It can correctly and effectively receive the collected data and achieve long-time and real-time storage of data.Finally,The data stored by the upper computer is used to complete the system test and data analysis.The correctness and feasibility of the design method are verified by time domain and frequency domain analysis of the signal using the Pucheng transmitter in Shaanxi Province as an example.The experimental results show that the acquisition system can completely collect the Loran-C sky and ground wave mixed signals from different station chains,and the actual received signal has no obvious distortion,and the spectrum of the Loran-C sky and ground wave mixed signals basically coincides with that of the standard Loran-C signal.The research results of this paper not only provide basic research data for Loran-C sky and ground wave signal propagation law and signal propagation delay correction analysis,but also have important reference value for the study of Loran-C signal variation law and the development of Loran-C navigation receiver.