a spectrum

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Proceedings of 2007 IEEE International Conference on Grey Systems and Intelligent Services, November 18-20, 2007, Nanjing, China

A Spectrum Identification Method for UM71 Signal Based on Grey Relational Analysis
I. INTRODUCTION URRENTLY, as the increasing of the train speed, the cab signal equipments play an important role in guaranteeing the railway safety and improving the efficiency of railway transportation. The decoding accuracy and stability shows one of the important factors of the cab signal’s accuracy and stability. Therefore, optimizing the decoding method and continuously improving the antiinterference ability is a necessary and important work. At present UM71 signal is an important automation block signal in railway. However, in the usual method of UM71 frequency spectrum decoding, it is always using the difference of each border frequency spectrum line, so the threshold of interfering signal is always higher than the active threshold when there is a strong interfering signal. At this time, the accuracy of decoding is falling down and it made difficult to demodulating the UM71 signal. Grey system is a kind of system in which one part of the information is known and the other part is unknown [1]. For the frequency spectrum demodulation of UM71 signal, the frequency spectrum information of unmeasured signal is unknown, but the features of the frequency spectrum distributing is known. Because of this, it belongs to grey system, and we can use the grey system theory to analyse it.
Zhao Linhai,Zhang Hui,Xu Xun
Abstract—the thesis presents a spectrum identification method for UM71 signal based on grey relational analysis. The method connects the grey relational analysis and railway cab signal decoding, through calculating the grey relationship grade between the input signal spectrum vector and standard frequency spectrum feature vector of UM71 signal modulating frequency, getting the mapping relation of input signal and each UM71 modulating frequency, and it is the principle of decoding UM71 signal, and we can get the right Identification result. Comparing with other traditional signal frequency spectrum, this method sufficiently uses grey relational analysis which is easily carrying out and easy algorithm. The identification is based on the position and amplitude information of UM71 signal carrier frequency and primary side frequency. The experiment proved that the method has a strong anti-interference ability, and it can fulfill the need of railway.
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Fig.1. Sketch of UM71 signal
The analytic expression of UM71 signal in time domain is[2]: (1) f ( t ) = A cos( 2 π f 0 t + g ( t )) 1 1 − <t ≤ 2 π∆ ft 4 fs 4 fs (2) g( t ) = 1 2 π∆ f ( 2 f − t ) 1 < t ≤ 3 s 4 fs 4 fs Where, A is the signal amplitude envelope; f 0 is the carrier frequency; ∆f is the signal deviation and f s is the modulating frequency. The detailed features of UM71 signal are shown in Table I. UM71 signal frequency spectrum is a discrete line spectrum, which the carrier frequency is at the center and the modulating frequency is symmetry outspread with the modulating frequency as its space. Where, m is frequency modulation coefficient, m = ∆ f f s .
upper side frequency ( f h = f 0 + ∆f ) 2011 2611 1711 2311
n = 0 ~ 17
frequency deviation(Hz)
∆ f = ± 11
In the frequency spectrum, The relative amplitude of the carrier frequency component is:
Zhao Linhai is with the State Key Laboratory of Rail Traffic Control and Safety (Beijing Jiaotong University), Beijing, 100044. (e-mail: zhaolh@). Zhang Hui is with the School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing, 100044. (e-mail: 06120350@). Xu Xun is with the State Key Laboratory of Rail Traffic Control and Safety (Beijing Jiaotong University), Beijing, 100044. (e-mail: xuxun@).
Grey relational analysis is a kind of method which using the similarity or dissimilarity between the developing trend of factors to measure the correlation of each factors. This method has no critical requirement of the number of samples, and the compute time is low. The result is as same as qualitative analysis. It’s one of the ideal analysis method. II. UM71 SIGNAL AND ITS FREQUENCY SPECTRUM Currently, the UM71 automatic block system is widely used in China railway. The system use the modulating frequency as the features of information, different frequency represent different speed of the train. The purpose to receive and decode the UM71 signal which is transmit along the track circuit, is to receive the modulating frequency and demodulate it into the speed information and send it to the train control system. From the modulation method, the UM71 signal belongs to the continuous phase frequency shift keying (FSK) signal. As shown in Fig. 1.