On-Line Diagnosis using Orthogonal Multi-Tone Time Domain Reflectometry in a Lossy Cable Wafa BEN HASSEN*, Fabrice AUZANNEAU*, Luca INCARBONE*, François PERES** and Ayeley P. TCHANGANI** (*) CEA, LIST, Laboratoire de Fiabilisation des Systèmes Embarqués, F-91191 Gif-sur-Yvette, France. (**) ENIT, LGP, Laboratoire Génie de Production 65000 Tarbes, France www.cea.fr
Context Motivation Context: Embedded electronic explosion. Embedded systems complexity increase. «X-by-wire» technology appearance. Motivations: Cable length increase. Connections number increase. Faults number caused by cables increase. Solution, interest advantages: Solution: wiring networks diagnosis system. Interest: detect, locate and characterize faults. Advantages: maintenance cost reduction (time, resources, etc.), system reliability increase, etc. CEA. All rights reserved DACLE Division March 2013 2
AUTOMOBILE CIVIL AIRCRAFT MARITIME Context Motivation 4 400 2500 40 200 1200 1 10 100 1000 10000 Km FIGHTER AIRCRAFT TRAIN FPSO Cumulative Cables Length in the Transport Field CEA. All rights reserved DACLE Division March 2013 3
Reflectometry: State of the Art Questions (1/2) A wideband test signal is injected down the wire. During its propagation, a part of its energy reflects back to the injection port when it crosses impedance discontinuities. The analysis of the received signals, called reflectogram, gives information about the wire faults (presence, position, type). Fault Analysis S Incident Wave Reflected Wave R Transmitted Wave CEA. All rights reserved DACLE Division March 2013 4
TDR: Time Domain Reflectometry FDR: Frequency Domain Reflectometry S/STDR: Sequence /Spread Spectrum TDR MCR: Multi-Carrier Reflectometry MCTDR: Multi-Carrier TDR OMTDR: Orthogonal Multi-tone TDR MCR State of the Art Questions (2/2) MCTDR OMTDR S/STDR FDR 2006 2009 2013 TDR 2003 2005 TDR injects a pulse (Gaussian, rectangular, etc.) down the cable under test. FDR uses a set of sinusoidal waves. 2001 On-Line diagnosis While STDR uses a Pseudo Noise (PN) code as test signal, SSTDR employs a sine wave modulated PN code. MCR and MCTDR inject a sum of sine waves using Inverse Digital Fourier Transform (IDFT). CEA. All rights reserved DACLE Division March 2013 5
Wave propagation Model in a cable RLCG Propagation Model: Telegrapher s equations: R: Resistance L: Inductance C: Capacity G: Condutance Propagation constant: Characteristic impedance: Angular Frequency: CEA. All rights reserved DACLE Division March 2013 6
OMTDR: Motivation OMTDR= Orthogonal Multi-Tone Time Domain Reflectometry Frequency Spectrum of N Tones B = N f Parallel data transmission Bandwidth Division Orthogonality among tones Total Bandwidth Control Data Rate Increase Spectral Efficiency Interference Avoidance Orthogonality condition f = 1/T s f 0 f f 2 f 1 f 1 f 2 T s =OFDM symbol duration CEA. All rights reserved DACLE Division March 2013 7
OMTDR: Signal Generation Random bit Generation x m (t) The n th tone is expressed as: Time domain: Frequency domain: x m,1 x m,0 2 2 OFDM frame x m,n 2 2 t Parameter Definition T s Useful OFDM symbol duration T G Guard interval duration T = T s + T G f Total OFDM symbol duration Frequency spacing among consecutive tones CEA. All rights reserved DACLE Division March 2013 8
OMTDR: Signal Generation The baseband OFDM signals is written as: Time domain: Frequency domain: unlimited spectrum (sinc) CEA. All rights reserved DACLE Division March 2013 9
In discrete domain, the sample of OFDM signal is: OMTDR: Signal Generation The OFDM signal autocorrelation is: Problem of side lobes: unsuitable for reflectometry diagnosis Solution: use butterworth filter with frequency-cut equal to 1/T CEA. All rights reserved DACLE Division March 2013 10
OMTDR: Diagnosis Signal Test Injection Reflected Signal processing The received signal : The measured reflected signal: Diagnosis Block Diagram reflection coefficient Injection port Load at the extremity Z l (ω) CEA. All rights reserved DACLE Division March 2013 11
Cliquez pour modifier OMTDR: le style Communication du titre Signal Test Injection Signal eception The transmitted signal: Transmission coefficient CEA. All rights reserved DACLE Division March 2013 12
Cliquez pour modifier Resource le Allocation style du Policy titre N: Number of tones H(KxN): Allocation Matrix K: Number of sensors N diag (k): Number of tones for sensor k The coefficient X m,n permits to control the signal Spectrum as: CEA. All rights reserved DACLE Division March 2013 13
Simulation Results: Lossy Cable Study Network: Transmission Line Soft Fault S1 S2 Sensor Parameter Notation Value Cable length L 100m Sensor Total Bandwidth B 0 MHz 256 MHz Prohibited Bandwith 64 MHz 192 MHz Characteristic Impedance Z c 50 Ω Number of Tones N 512 Tones spacing f 0.5 MHz Useful symbol duration T u 224 µs Guard Interval duration T G 28 µs CEA. All rights reserved DACLE Division March 2013 14
Tones Allocation for Sensors S1 and S2 Simulation Results: Lossy Cable Time Domain Frequency Domain CEA. All rights reserved DACLE Division March 2013 15
Simulation Results: Lossy Cable End of Line Detection 70m 30m Hard Fault Detection: Open Circuit S1 S2 CEA. All rights reserved DACLE Division March 2013 16
Soft Fault Detection 39.5m 60m Simulation Results: Lossy Cable Soft Fault variation S1 S2 Capacitance variation Inductance variation C = 50% L = 50% 0.5m CEA. All rights reserved DACLE Division March 2013 17
Simulation Results: Lossy Cable Communication among sensors Matching between sensor and cable to avoid signal reflection BER increases when the fault severity increases Communication gives an additional information for decision making about the cable state CEA. All rights reserved DACLE Division March 2013 18
Simulation Results: Y Shaped Network Communication among sensors Y Shaped Network l 1 =50 m l 2 =60 m l 3 =110 m Soft fault at 19.5m from junction Fault on line W 2 or W 3? CEA. All rights reserved DACLE Division March 2013 19
Simulation Results: Y Shaped Network Communication among sensors Y Shaped Network l 1 =50 m l 2 =60 m l 3 =110 m BER(S 1 to S 2 )> BER(S 1 to S 3 ) Fault on line W 2 CEA. All rights reserved DACLE Division March 2013 20
OMTDR: Orthogonal Multi-Tone Time Domain Reflectometry Conclusion Perspectives Ensures on-line diagnosis. Improves soft faults detection. Ensures communication among senors to avoid faults localisation ambiguities Future Works: OMTDR will be tested on more complex wiring networks. OMTDR will be implemented in an electronic card (embedded environment). CEA. All rights reserved DACLE Division March 2013 21
Thanks for your attention Centre de Grenoble 17 rue des Martyrs 38054 Grenoble Cedex Centre de Saclay Nano-Innov PC 172 91191 Gif sur Yvette Cedex