Research On Loran-C Anti-Jamming Technology Based On Improved LMS Algorithm

Nowadays,although satellite-based navigation systems are widely used in various fields of society if satellite-based navigation systems are used as the only means of navigation,the security and stability of navigation timing services will face great threats.Because of its wide coverage and strong anti-jamming capability,the Loran-C navigation system is an ideal choice for a satellite-based navigation backup system and has become an important part of the national positioning and timing system.The research of interference suppression technology for Loran-C signals is the key to improving the receiver performance and is of great significance for the wide application of Loran-C systems.Therefore,this paper focuses on the anti-jamming technology of Loran-C signals in complex electromagnetic environments.The details are as follows:(1)Based on the analysis of the navigation principle of the Loran-C system and the common types of interference in the Loran-C signal,the main link of the anti-interference research is the Loran-C receiver,focusing on the impact of the common interference signals in its received signal on the Loran-C signal,to lay the foundation for the anti-interference method research.(2)Given the contradiction between the convergence speed and steady-state performance of the traditional LMS algorithm,we analyze the problems of the traditional adaptive filtering algorithm and the existing variable-step LMS algorithm and propose a variable-step LMS algorithm based on the symmetric Sigmoid function,which can take into account the convergence performance and steady-state performance.Through algorithm comparison and Loran-C signal filtering simulation experiment,it is shown that the improved algorithm has superior performance.(3)The limitations of the conventional bandpass filter in processing out-of-band interference are analyzed,and an interpolated FIR filter is designed for out-of-band anti-interference processing to achieve a 79.5%reduction in computational effort.Then,the in-band interference frequency detection method is investigated,and the signal spectrum is proposed to be divided with the spectral envelope and a threshold is set to obtain the interference frequency value.Finally,the improved algorithm is used in conjunction with a cascaded trap to form an adaptive trap.Simulation experiments show that the scheme further improves the anti-jamming performance of the Loran-C signal.(4)Analyzing the time-frequency characteristics of the actual received signal and using the designed anti-interference scheme to suppress the interference of the acquired signal,the experiments show that the proposed method can achieve better interference suppression of the acquired signal,thus providing a good signal basis for later data processing.In addition,the simulation test is carried out through the Modelsim simulation platform,and the output results are consistent with the MATLAB results,which verifies the feasibility of this method on the hardware platform.