Study of the immunity of the GSM-R against
electromagnetic disturbances present on moving
trains
Virginie Deniau, INRETS, France
virginie .deniau@inrets.fr
R. Adriano, S. Dudoyer, N. Ben Slimen, J. Rioult, P. Massy, B. Meyniel, M. Berbineau, A.
Raux and E. Smulders
Railcom final conference, UIC, Paris, 21 april 2009
Outline
• The GSM-R system
• Characterisation and Analysis of the disturbances
received by GSM-R antennas
• Impact of the supply voltage on the disturbances
• Estimation of the impact of the transient
disturbances on the BER of GSM-R communications
• Immunity testing on GSM-R communications in
laboratory
• Detection of transients disturbances for diagnostic
in-situ
• Conclusion, future works
Railcom final conference, UIC, Paris, 21 april 2009
ERTMS and GSM-R
ERTMS: European Rail Traffic Management System
Harmonised signaling standards throughout Europe
GSM-R : Global System for Mobiles-RAILWAYS
radio system for providing voice and data communication between
the track and the train
GSM-R
Data and voice
transmissions
Railcom final conference, UIC, Paris, 21 april 2009
GSM-R
GSM-R
PCRD 6
STREP
The GSM-R is based on the standard GSM Phase 2+
the modulation type is GMSK (Gaussian Minimum Shift Keying).
Specific frequencies:
876-880 MHz for the up-link (trains → base stations)
921-925 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
GSM-R antennas on the roof of the trains
Railcom final conference, UIC, Paris, 21 april 2009
GSM-R
PCRD 6
STREP
The GSM-R 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 4.615 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.
Railcom final conference, UIC, Paris, 21 april 2009
GSM-R
PCRD 6
STREP
924.8 MHz
user 8
user 6
user 7
user 5
user 4
user 2
user 3
user 1
user 8
user 6
user 7
user 5
user 4
user 2
user 3
924.6 MHz
TDMA frame= 4.6 ms
user 1
Frequency
Carrier frequencies
physical channels
8 logical channels
Time slot
577 μs
921.4 MHz
200 kHz
921.2 MHz
Railcom final conference, UIC, Paris, 21 april 2009
burst
3.7 µs
bit time
Time
Characterisation and Analysis of
the disturbances received by
GSM-R antennas
Railcom final conference, UIC, Paris, 21 april 2009
The disturbances received by GSM-R
antennas
Main potential EM disturbances for the GSM-R:
• Public GSM, UMTS 900 on frequency channels adjacent to the GSM-R
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
GSM-R frequency bands
3. To characterise the time characteristics and the repetition rate of the
transients
Railcom final conference, UIC, Paris, 21 april 2009
Analysis of transient disturbances received by
GSM-R antennas
Power (dBm)
• Characterisation of the noise levels produced by the transients
in the GSM-R frequency bands:
300 MHz
Power (dBm)
F.F.T
Railcom final conference, UIC, Paris, 21 april 2009
≈ -35 dBm
1 GHz
GSM-R frequencies
are systematically
covered
S11-antenna
≈ -35 dBm
Time caracteristics of the transient
disturbances
• Characterisation of the time characteristics of the transients :
A
A
100%
90%
50%
10%
time
Duration
Railcom final conference, UIC, Paris, 21 april 2009
time
Rise time
Time caracteristics of the transient
disturbances
• Statistical study with about 20000 collected transients on trains:
Duration
Probability Density Function
experimental distribution
empirical distribution
15
10
5
20 ns
0
0
0.5
Rise Time
9
3
Probability Density Function
7
x 10
1
Duration (s)
1.5
2
-8
x 10
Duration (s)
Typical duration = 5 ns
Railcom final conference, UIC, Paris, 21 april 2009
x 10
experimental distribution
empirical distribution
2.5
2
1.5
1
1 ns
0.5
0
2
4
6
Rise time (s)
8
Rise time (s)
Typical rise time = 0.4 ns
10
-10
x 10
Analysis of transient disturbances
received by GSM-R 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)
0.4
Time delay
0.2
0
-0.2
400 µs
-0.4
0
1
1
Amplitude (V)
2
3
4
-4
x 10
Time (s)
0.15
1 transient/ 10 µs
0.5
0.1
1 transient/ 5µs
0.05
0
0
-0.5
-1
0
-0.05
400 µs
1
2
3
4
-0 1
400 µs
Very variable Rr according to the trains operating conditions
Railcom final conference, UIC, Paris, 21 april 2009
Analysis of transient disturbances
received by GSM-R antennas
• Number of transients in each 400 µs time window :
9090
8080
7070
Number of 6060
5050
transient
disturbances 4040
3030
2020
1010
0 00
0
≈ 4.5 µs medium time delay
between
two successive transients
200
400
600
800
1000
file
order1000
800
1200
1400
1600
200 400 600
1200 1400 1600
Successive time windows 1568 recorded files
Time duration of the measurements process
400 µs Time Window
+
Loading Time
=~1s
Over a 1500 s Measurements duration :1568 recorded files ==> 0,95 s
Measurement equipment was continuously detecting transients
Railcom final conference, UIC, Paris, 21 april 2009
Impact of the supply voltages on the time
characteristics of the transients
About 300 transient disturbances collected under 1500 Vcc and 25000 Vac
Comparison of the rise times
-9
Time x(ns)
10
2
1500 Vcc
1.5
1
= 0.4 ns
0.5
0
0
50
100
-9
2
25000 Vcc
150
200
250
300
Rise Time
x 10
Typical
rise time
1.5
1
= 0.4 ns
0.5
0
0
50
100
150
Railcom final conference, UIC, Paris, 21 april 2009
200
250
300
Impact of the supply voltages on the noise
levels over the GSM-R channels
About 300 transient disturbances collected under 1500 Vcc and 25000 Vac
FFT of the 300 transients and post pocess to extract the maximal
noise level over the GSM-R frequency bands
-40
-50
1500 Vcc
-60
-70
-80
0
50
100
150
200
250
300
250
300
Maximal Amplitude 921 MHz - 925 MHz
-40
-50
25000 Vcc
-60
-70
-80
0
50
100
150
200
921 MHz-925 MHz : Down-link GSM-R
Railcom final conference, UIC, Paris, 21 april 2009
Impact of the supply voltages on the peak
values
About 300 transient disturbances collected under 1500 Vcc and 25000 Vac
F.F.T
1500 Vcc
921 MHz-925 MHz
Power (dBm)
Peak value
2
-40
1.5
-50
1
-60
0.5
-70
0
0
50
100
150
200
250
300
-80
0
50
Peak Amplitude
25000 Vcc
-40
1.5
-50
1
-60
0.5
-70
0
50
100
150
150
200
250
300
250
300
Maximal Amplitude 921 MHz - 925 MHz
2
0
100
200
250
Railcom final conference, UIC, Paris, 21 april 2009
300
-80
0
50
100
150
200
Estimation of the impact of the
transient disturbances on the
BER of GSM-R communications
Railcom final conference, UIC, Paris, 21 april 2009
Transient disturbances and BER on GSM-R
transmissions
Hypothesis :
GSM burst
• Transients duration << duration of one bit
→ approximated by a punctual event,
• Transients produce high levels of
interference in the GSM-R band,
• Transients produce an arbitrary decision in
a bit inside the burst (worst case?).
BER =
1 Rr
⋅
2 RS
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
Immunity testing on GSM-R
communications in laboratory
Railcom final conference, UIC, Paris, 21 april 2009
Immunity testing on GSM-R
communications
• Test set-up :
CMU 200
924.8 MHz
BER =
Erroneous bits * 100%
total number of bits
Over 1200 speech frames
GSM-R
Mobile
50 Ω load
Loop back
combiner
Combiner
Directional combiner
Spectrum analyzer
Calibration of the
power levels
SMIQ
CMU 200
-40dB
Amplifier
SMIQ
GSM Public
925.2 MHz
Railcom final conference, UIC, Paris, 21 april 2009
Signal generator
combiners
GSM-R
Mobile
CMU 200
Spectrum
analyzer
Arbitrary
signal
generator
SMIQ
Oscilloscope
Railcom final conference, UIC, Paris, 21 april 2009
Immunity testing on GSM-R
communications
• Power calibration based on the preliminary on-board measurements:
CMU 200
924.8 MHz
?
GSM-R
Mobile
load
GSM public:
measurement campaign for
measurements of coverage levels
→ Maximum level ≈ -25 dBm
Combiner
?
SMIQ
GSM Public
925.2 MHz
GSM-R :
measurement campaign for
coverage levels and specifications
→ -90 dBm < GSM-R < -25 dBm
?
Signal generator
Railcom final conference, UIC, Paris, 21 april 2009
Transients:
analysis by applying FFT
→ Maximum level ≈ -35 dBm
Immunity testing on GSM-R
communications
• Wave form of the transients based on the statistical distributions:
1 – “Double exponential model”
• duration = 5 ns
• rise time = 0.4 ns
CMU 200
924.8 MHz
load
GSM-R
Mobile
2 – Application of
“Bandpass
numerical filter” or
modulation with a
sinus
Combiner
SMIQ
GSM Public
925.2 MHz
Signal generator
3 - Normalization to 1V peak to peak
4 – Variation of the repetition rate
Railcom final conference, UIC, Paris, 21 april 2009
Immunity testing on GSM-R
communications
CMU 200
924.8 MHz
50 Ω
GSM-R
Mobile
combiner
Combiner
Power (dBm)
-50
-60
without transients
-70
GSM-R
GSM
-40
Spectrum analyzer
Maxhold
-80
-90
-100
920
922
924
926
Frequency (MHz)
928
Railcom final conference, UIC, Paris, 21 april 2009
930
GSM Public
925.2 MHz
Transient
Immunity testing on GSM-R
communications
CMU 200
924.8 MHz
GSM-R
Mobile
50 Ω
combiner
Combiner
-40
4 µs time interval
-50
Spectrum analyzer
Maxhold
10 µs time interval
Power (dBm)
20 µs time interval
-60
GSM Public
925.2 MHz
Transient
1.7 ms time interval
without transients
-70
-80
Time interval
-90
-100
920
Time interval ≥ 10 µs
for the immunity tests
922
924
926
Frequency (MHz)
928
Railcom final conference, UIC, Paris, 21 april 2009
930
BER and RXQUAL
Rxqual: parameter employed to control the quality of the service in situ
Quality level i
Range of values
Railcom final conference, UIC, Paris, 21 april 2009
Typical values
of BER
Immunity tests - Results
Railcom final conference, UIC, Paris, 21 april 2009
Impact of public GSM signals
GSM-R
924.8 MHz
GSM-R
Mobile
1
2
3
4
5
6
GSM-R
FREQUENCY
GSM-R
POWER
(dBm)
GSM public
FREQUENCY
GSM public
POWER
(dBm)
Measured
BER (%)
RXQUAL
924.8 MHz
-70
925.2 MHz
-70
0.004
0
-52
0.011
0
-30
0.01
0
-17
0.086
0
-15
0.137
1
-12
0.44
2
+ 55 dBm
- 17/23 Railcom final conference, UIC, Paris, 21 april 2009
Combiner
GSM Public
925.2 MHz
Impact of the transient disturbances in
presence of public GSM
2.0 BER (%)
Transients with TI = 90 µs
Transients with TI = 150 µs
Transients with TI = 550 µs
BER without Transient
1.6
1.2
Rxqual = 3
0.8
0.4
Rxqual = 1
0.0
-60
-50
-40
-30
-20
GSM public power (dBm)
Railcom final conference, UIC, Paris, 21 april 2009
-10
0
BER induced by two different collected
transients
GSM-R
924.8 MHz
GSM-R power = -70 dBm
GSM-R
Mobile
Combiner
2.0
1.8
Recorded transient D=6.1 ns and RT= 0.35 ns
1.6
Recorded transient D=6.75 ns and RT= 0.4 ns
BER (%)
1.4
Signal generator
1.2
1.0
Transients collected
on board
0.8
0.6
0.4
0.2
0.0
0
400
800
1200
Transients time interval (µs)
Railcom final conference, UIC, Paris, 21 april 2009
1600
Comparisons between measured and
estimated BER
Transient collected on board
GSM-R power = -70 dBm
RT= 0.35 ns, D= 6.1 ns
GSM-R
924.8 MHz
GSM-R
Mobile
0.3
0.2
0.1
(V) 0
‐0.1
‐0.2
‐0.3
Combiner
Signal generator
0 0.1 0.2 0.3 0.4
Temps (µs)
Double exponential Model
RT= 0.4 ns and D= 5 ns
⎛ ⎛ t ⎞
⎛ t ⎞⎞
V (t ) = A⎜⎜ exp⎜ −
⎟ − exp⎜ −
⎟ ⎟⎟γ (t )
FT
RT
⎝
⎠
⎝
⎠⎠
⎝
V Variable Time interval
Prediction of the BER
Time
BER =
Railcom final conference, UIC, Paris, 21 april 2009
1 Rr
⋅
2 RS
Comparisons between measured and
estimated BER
BER (%)
2.0
GSM-R power = -70 dBm
S/N=1 over the duration of the transient
BER =
estimation du BER (%)
0.3
0.2
transitoire réel
1.6
1 Rr
⋅
2 Rs
0.1
(V) 0
modèle de transitoire
‐0.1
‐0.2
1.2
‐0.3
0 0.1 0.2 0.3 0.4
Temps (µs)
0.8
⎛ ⎛ t ⎞
⎛ t ⎞⎞
V (t ) = A⎜⎜ exp⎜ −
⎟ − exp⎜ −
⎟ ⎟⎟γ (t )
⎝ RT ⎠ ⎠
⎝ ⎝ FT ⎠
0.4
0.0
0
200
400
600
800
1000 1200 1400
Intervalle de temps entre les transitoires (µs)
Time interval between transients
Railcom final conference, UIC, Paris, 21 april 2009
1600
Double exponential Model
RT= 0.4 ns and D= 5 ns
Detection of transient
disturbances for diagnostic
in-situ
Railcom final conference, UIC, Paris, 21 april 2009
Characterisation of the noise level
Over 300 transients
-40
Noise level varies between
-40 dBm and -70 dBm
-50
-60
-70
-80
0
50
100
150
200
250
300
Maximal Amplitude 921 MHz - 925 MHz
GSM-R 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 GSMR signal
Railcom final conference, UIC, Paris, 21 april 2009
Minimum GSM-R power level to keep a
BER inferior to 1.13 %
Variable GSM-R power
GSM-R
924.8 MHz
GSM-R
Mobile
Combiner
Required GSM-R Power (dBm)
-64
-66
With Collected transient D=6.1 ns, RT = 0.35 ns
-68
With Collected transient D=6.75 ns, RT = 0.4 ns
-70
-72
BER<1.13 %
-74
-76
-78
BER>1.13 %
-80
0
400
800
1200
Transients time interval (µs)
Railcom final conference, UIC, Paris, 21 april 2009
1600
Signal generator
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 GSM-R antennas
0
|Sii| (dB)
-10
-20
-30
-40
-50
300
EMI Test Receiver
In zero span
Measures 1point/3.7 µs
Railcom final conference, UIC, Paris, 21 april 2009
|S11|- straight antenna
|S11|- oblique antenna
400
500
600
700
800
Frequency (MHz)
900
1000
850 MHz
Free channel
Detection of the transient disturbances
Approach proposed - Results
EMI Test Receiver
Arbitrary waveform generator
-20
Test sequence
Model
transient
200 µs
Real
transient
Power (dBm)
70 µs
-30
200 µs
70 µs
-40
-50
-60
-70
-80
0.0
0.5
1.0
Time (ms)
Advantage: we collect 1 point by transient disturbance
Railcom final conference, UIC, Paris, 21 april 2009
1.5
2.0
Conclusion
• Complete characterisation of the time characteristics of the transient
disturbances produced by the catenary-pantograph sliding contact
!
Characterisation with a GSM-R 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
GSM-R 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
Railcom final conference, UIC, Paris, 21 april 2009