Research On Wireless Signal Intrtference Detection Technology In Rail Transit

The ground vehicle wireless communication system of urban rail transit is used to carry the dispatching,control and communication services of rail transit operation.When there is signal interference in the signal received by the communication system,it will affect the normal operation of the train.Therefore,it is an urgent problem to study the related technologies that can effectively detect whether there is interference signal in the wireless communication system.In this paper,detection methods based on fourth order cyclic cumulant are proposed for same frequency and adjacent frequency interference signals that may exist in rail transit environment,and the proposed methods are compared with traditional interference detection methods,and the following three aspects are carried out in detail:Firstly,the types of interference signals in rail transit wireless communication system are analyzed,and the traditional interference detection methods,including energy detection algorithm based on time domain and continuous mean removal(CME)algorithm based on frequency domain,are described and simulated.Theoretical analysis and simulation experiments show that both detection algorithms based on time domain and frequency domain are suitable for interference detection in silent period.In the quiet period,both algorithms have high recognition accuracy at low signal-to-noise ratio(SNR),but their detection performance is poor for the same frequency and adjacent frequency interference detection in the non-quiet period of rail transit environment.Secondly,aiming at the scene where traditional methods are not applicable,this paper proposes a narrowband adjacent frequency interference detection algorithm based on fourth order cyclic cumulant.The algorithm calculates the fourth order cyclic cumulant of the received narrowband signal,and detects the number of discrete spectral lines in the amplitude spectrogram of the fourth order cyclic cumulant.By comparing whether the number of discrete spectral lines is equal to the number of expected signals,it can be judged whether there is adjacent frequency interference signal in the received signal.The simulation results show that the recognition accuracy of the proposed algorithm can reach more than 80%when the SNR is greater than 2dB.For the detection of same frequency interference signals,this paper proposes a same frequency interference detection algorithm combining signal power with fourth order cyclic cumulant.Through theoretical analysis and simulation,the correctness of the proposed algorithm is verified.When the SNR is greater than 0dB,the recognition accuracy of the algorithm can reach more than 80%.At the same time,because the fourth order cyclic cumulant is insensitive to small frequency offset,the interference identification accuracy of the proposed algorithm can reach 80%for the received signal with Doppler effect in rail transit environment when the SNR is greater than 3dB.Thirdly,this paper introduces a technique to filter out the broadband signal in rail transit wireless communication systems.The approach involves converting the multi-carrier modulation signal into a single-carrier signal prior to detecting same frequency or adjacent frequency interference signals using a method similar to that of narrow band signal interference detection.According to the simulation results,the interference detection recognition rate of this method can exceed 95%when the SNR is above 0 dB.