Study of the immunity of the GSM-R against electromagnetic disturbances present on moving trains

Transcription

1 Study of the immunity of the against electromagnetic disturbances present on moving trains Virginie Deniau, INRETS, France R. Adriano, S. Dudoyer, N. Ben Slimen, J. Rioult, P. Massy, B. Meyniel, M. Berbineau, A. Raux and E. Smulders

2 Outline The system Characterisation and Analysis of the disturbances received by antennas Impact of the supply voltage on the disturbances Estimation of the impact of the transient disturbances on the BER of communications Immunity testing on communications in laboratory Detection of transients disturbances for diagnostic in-situ Conclusion, future works Railcom final conference, UIC, Paris, 21 april 2009

3 ERTMS and ERTMS: European Rail Traffic Management System Harmonised signaling standards throughout Europe : Global System for Mobiles-RAILWAYS radio system for providing voice and data communication between the track and the train Data and voice transmissions

4 PCRD 6 STREP The is based on the standard GSM Phase 2+ the modulation type is GMSK (Gaussian Minimum Shift Keying). Specific frequencies: MHz for the up-link (trains base stations) MHz for the down-link (base stations trains) 200 khz frequency spacing between each channel + Advanced functions specifically developed for rail. group calls, ads or calls broadcast, location-based connections, call pre-emption in case of emergency Base Transceiver Station (BTS) close to the tracks The distance between base stations 3-4 km antennas on the roof of the trains

5 PCRD 6 STREP The is a Time Division Multiple Access (TDMA) system For each carrier frequency (physical channel) - data are organized per periodic TDMA frame, with a period of ms. - each TDMA frame is divided into 8 time intervals of 577 μs long called "Time Slots" Each Time Slot (logical channel) - includes 156 bits which 148 bits of information. The one bit transmission duration is about 3.7 µs.

6 PCRD 6 STREP Carrier frequencies physical channels Frequency MHz MHz MHz MHz user 1 TDMA frame= 4.6 ms user 2 user 3 user 4 user 5 user 6 user 7 8 logical channels 200 khz user 8 user 1 burst user 2 Time slot 577 μs user µs bit time user 4 user 5 user 6 user 7 user 8 Time

7 Characterisation and Analysis of the disturbances received by antennas

8 The disturbances received by antennas Main potential EM disturbances for the : Public GSM, UMTS 900 on frequency channels adjacent to the frequency bands «permanent» disturbances Transients coming from the catenary - pantograph sliding contact On-board measurements: 1. To characterise the coverage levels of the permanent disturbances 2. To characterise the level of noise produced by the transients in the frequency bands 3. To characterise the time characteristics and the repetition rate of the transients

9 Analysis of transient disturbances received by antennas Characterisation of the noise levels produced by the transients in the frequency bands: F.F.T Power (dbm) Power (dbm) 300 MHz 1 GHz S11-antenna -35 dbm frequencies are systematically covered -35 dbm

10 Time caracteristics of the transient disturbances Characterisation of the time characteristics of the transients : A A 100% 90% 50% Duration time 10% Rise time time

11 Time caracteristics of the transient disturbances Statistical study with about collected transients on trains: Probability Density Function x 10 7 Duration experimental distribution empirical distribution Duration (s) x 10-8 Probability Density Function x ns ns 0 Rise Time experimental distribution empirical distribution Rise time (s) x Duration (s) Typical duration = 5 ns Rise time (s) Typical rise time = 0.4 ns

12 Analysis of transient disturbances received by antennas Characterisation of the repetition rate «Rr» of the transients : Measurements performed in 400 µs time windows Objective: to establish distributions of the time delays between the transients according to the operating conditions 0.6 Amplitude (V) Time delay Amplitude (V) µs Time (s) x transient/ 10 µs 400 µs transient/ 5µs 400 µs Very variable Rr according to the trains operating conditions

13 Number of transient disturbances Analysis of transient disturbances received by antennas Number of transients in each 400 µs time window : file 800 order Successive time windows 1568 recorded files Time duration of the measurements process 400 µs Time Window + Loading Time = ~ 1 s 4.5 µs medium time delay between two successive transients Over a 1500 s Measurements duration :1568 recorded files ==> 0,95 s Measurement equipment was continuously detecting transients

14 Impact of the supply voltages on the time characteristics of the transients About 300 transient disturbances collected under 1500 Vcc and Vac Comparison of the rise times Time (ns) 2 x Vcc x 10-9 Rise Time = 0.4 ns Typical rise time Vcc = 0.4 ns

15 Impact of the supply voltages on the noise levels over the channels About 300 transient disturbances collected under 1500 Vcc and Vac FFT of the 300 transients and post pocess to extract the maximal noise level over the frequency bands Vcc Maximal Amplitude 921 MHz MHz Vcc MHz-925 MHz : Down-link

16 Impact of the supply voltages on the peak values About 300 transient disturbances collected under 1500 Vcc and Vac Peak value F.F.T Power (dbm) 921 MHz-925 MHz Vcc Peak Amplitude -40 Maximal Amplitude 921 MHz MHz Vcc

17 Estimation of the impact of the transient disturbances on the BER of communications

18 Transient disturbances and BER on transmissions Hypothesis : GSM burst Transients duration << duration of one bit approximated by a punctual event, Transients produce high levels of interference in the band, Transients produce an arbitrary decision in a bit inside the burst (worst case?). BER = 2 1 R R r S Rs is the symbol rate of the communication system Rr represents the repetition rate of the transients Railcom final conference, UIC, Paris, 21 april 2009

19 Immunity testing on communications in laboratory

20 Immunity testing on communications Test set-up : CMU MHz BER = Erroneous bits * 100% total number of bits Over 1200 speech frames Mobile Loop back combiner -40dB Combiner 50 Ω load CMU 200 SMIQ Spectrum analyzer Calibration of the power levels SMIQ GSM Public MHz Signal generator Directional combiner Amplifier

21 combiners Mobile CMU 200 Spectrum analyzer Arbitrary signal generator SMIQ Oscilloscope Railcom final conference, UIC, Paris, 21 april 2009

22 Immunity testing on communications Power calibration based on the preliminary on-board measurements: Mobile CMU MHz? SMIQ GSM Public MHz? Combiner load? Signal generator : measurement campaign for coverage levels and specifications -90 dbm < < -25 dbm GSM public: measurement campaign for measurements of coverage levels Maximum level -25 dbm Transients: analysis by applying FFT Maximum level -35 dbm

23 Immunity testing on communications Wave form of the transients based on the statistical distributions: CMU MHz 1 Double exponential model duration = 5 ns rise time = 0.4 ns Mobile Combiner load 2 Application of Bandpass numerical filter or modulation with a sinus SMIQ GSM Public MHz Signal generator 3 - Normalization to 1V peak to peak 4 Variation of the repetition rate

24 Immunity testing on communications CMU MHz Mobile combiner Combiner 50 Ω -40 Power (dbm) without transients GSM Spectrum analyzer Maxhold GSM Public MHz Transient Frequency (MHz) Railcom final conference, UIC, Paris, 21 april 2009

25 Immunity testing on communications CMU MHz Mobile combiner Combiner 50 Ω µs time interval 10 µs time interval 20 µs time interval Spectrum analyzer Maxhold GSM Public MHz Transient Power (dbm) ms time interval without transients Time interval Frequency (MHz) Time interval 10 µs for the immunity tests Railcom final conference, UIC, Paris, 21 april 2009

26 BER and RXQUAL Rxqual: parameter employed to control the quality of the service in situ Quality level i Range of values Typical values of BER

27 Immunity tests - Results Railcom final conference, UIC, Paris, 21 april 2009

28 - 17/23 - Railcom final conference, UIC, Paris, 21 april 2009 Impact of public GSM signals MHz Mobile Combiner FREQUENCY POWER (dbm) GSM public FREQUENCY GSM public POWER (dbm) Measured BER (%) RXQUAL GSM Public MHz MHz MHz dbm

29 Impact of the transient disturbances in presence of public GSM Transients with TI = 90 µs Transients with TI = 150 µs Transients with TI = 550 µs BER without Transient BER (%) Rxqual = GSM public power (dbm) Rxqual = 1

30 BER induced by two different collected transients MHz BER (%) power = -70 dbm Railcom final conference, UIC, Paris, 21 april 2009 Mobile Recorded transient D=6.1 ns and RT= 0.35 ns Recorded transient D=6.75 ns and RT= 0.4 ns Transients time interval (µs) Combiner Signal generator Transients collected on board

31 Comparisons between measured and estimated BER power = -70 dbm Mobile MHz Combiner Transient collected on board RT= 0.35 ns, D= 6.1 ns (V) Temps (µs) V Signal generator Variable Time interval Time V Double exponential Model RT= 0.4 ns and D= 5 ns t FT () t = A exp exp γ () t BER 1 Rr = 2 R t RT Prediction of the BER S

32 Comparisons between measured and estimated BER BER (%) power = -70 dbm S/N=1 over the duration of the transient estimation du BER (%) transitoire réel modèle de transitoire 1 BER = 2 Rr Rs (V) Temps (µs) Intervalle de temps entre les transitoires (µs) Time interval between transients V t FT t RT () t = A exp exp γ () t Double exponential Model RT= 0.4 ns and D= 5 ns

33 Detection of transient disturbances for diagnostic in-situ

34 Characterisation of the noise level Over 300 transients Maximal Amplitude 921 MHz MHz Noise level varies between -40 dbm and -70 dbm Reception level can Vary between About -20 dbm and -92 dbm The definition of a maximum level of noise is not adapted to this application We propose to control the recurrence of the transient disturbances and to compare it with the Rxlevel of the GSM- R signal

35 Minimum power level to keep a BER inferior to 1.13 % Required Power (dbm) BER>1.13 % Variable power Mobile With Collected transient D=6.1 ns, RT = 0.35 ns With Collected transient D=6.75 ns, RT = 0.4 ns BER<1.13 % Transients time interval (µs) MHz Combiner Signal generator

36 Detection of the transient disturbances Method employed during the project is to «count» the transient is too «heavy» for a diagnostic methodology in situ Approach proposed Reflexion S-parameters of the antennas 0-10 Sii (db) S11 - straight antenna S11 - oblique antenna EMI Test Receiver In zero span Measures 1point/3.7 µs Frequency (MHz) 850 MHz Free channel Railcom final conference, UIC, Paris, 21 april 2009

37 Detection of the transient disturbances Approach proposed - Results Arbitrary waveform generator Test sequence EMI Test Receiver 70 µs 200 µs Model transient 70 µs 200 µs Real transient Power (dbm) Time (ms) Advantage: we collect 1 point by transient disturbance

38 Conclusion Complete characterisation of the time characteristics of the transient disturbances produced by the catenary-pantograph sliding contact! Characterisation with a antenna the bandwidth of the antenna can impact the rise time distribution obtained Proposition of a prediction method of the BER induced by the transients observed on board as a function of the repetition rate of the transients Proposition of a laboratory testing method to control the immunity of the communications against EM disturbances representative of the in situ conditions (+ permanent and transient disturbances simultaneously) Proposition of a methodology to preliminary verify the conditions required to guarantee the quality of the communications