Research On Interference Characteristics And Detection Methods Of Low-frequency Time-code Signal

The ground-based radio time service system is one of the important information sources of PNT,and it can provide low to high precision time frequency signals and technical services for relevant scientific research and engineering applications.The low-frequency time-code time service system is a kind of successful application in the ground-based radio time service system,and it is also an indispensable and important component of Chinese time frequency service system.The low-frequency time-code signal which is in the LF band can propagate stability and widely,and it can meet the time service needs from hundreds of microseconds to milliseconds,and realize the time services in areas where satellite signal reception is difficult,such as underwater,indoors,urban canyons and so on,and have important application values.Aiming at the problem of the interference in the LF band where the low-frequency time-code signal is located,this paper analyzes the different interference types and interference characteristics in the LF band according to the characteristics of the lowfrequency time-code signal,and proposes the weighted detection algorithm which is more suitable for the low-frequency time-code signal based on the existing interference detection algorithm,and develops the low-frequency time-code interference analysis platform to collect the actual time service signal for interference detection and analysis.It provides a certain technical guarantee for the improvement of the time service signal quality,the design of the new signal system,the research of the anti-jamming technology and the improvement of the receiver performance,and plays a good role in promoting the wide industrial application of the low-frequency time-code time service technology.The specific work of this paper is as follows:(1)The representation form and the time and frequency domain characteristics of the low-frequency time-code signal are given through the in-deep research on the theoretical knowledge of the frequency band,modulation mode and coding form of the low-frequency time-code signal.Also the main concerned signal indexes in the signal reception and decoding are summarized.And on the basis of fully understanding the generation,transmission,propagation and reception of time-code signals,the common interference in the LF band is classified and simulated,and the time and frequency domain characteristics of different interference types are analyzed,according to the existing interference research foundation.(2)Based on the theory of the interference detection algorithm,the influence factors of detection probability and false alarm probability and the principle of the reference threshold,energy detection algorithm,consecutive mean excision algorithm(CME),forward consecutive mean excision algorithm(FCME)and the double threshold detection algorithm are analyzed.And the weighted detection algorithm which can detect the interference more efficiently and be more suitable for lowfrequency time-code signals is proposed,according to the characteristics of the lowfrequency time-code signal.(3)Five detection algorithms are implemented,and the detection performance of the detection algorithms under different interferences are compared by designing simulation experiments,including the detection performance of the algorithms with different false alarm probabilities and sampling points,the detection performance of the algorithms in the silent period and the non-silent period,and the differences in the determination of the interference detection bandwidth between the double-threshold detection algorithm and the weighted detection algorithm.(4)Through the design of the overall framework of the platform,the selection and configuration of hardware equipment,and the programming of interference analysis software,the interference analysis platform of the low-frequency time-code is designed and completed to acquire time-code signals and detect the interference.A signal vector generator is used to test the sensitivity of the platform,and the results show that the platform can collect the signal of-95 d Bm at a minimum,and the platform sensitivity is high enough.(5)On the basis of the previous research,the interference analysis platform is used to collect the actual time service signal in the different scenarios,and the interference of the received signal is detected by the detection algorithms,which are installed in the platform software.