Orthogonal Multi-tone Time Domain Reflectometry

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In OMTDR-based reflectometry, an OFDM signal is fed in, which is a signal that uses multiple mutually orthogonal carriers for digital data transmission in order to avoid interference between reflectometers connected to an identical network. Thus, the test signal itself is used to transmit information.

In this variant of TDR measurements, multiple sensors are used at different ends of the network to maximize diagnostic coverage, even for complex networks. After all, due to signal attenuation due to the distance traveled and the many nodes, this is a challenge. The idea of the OMTDR measurement method, much like MCTDR, is to divide the bandwidth into multiple sub-bands with orthogonal and then overlapping sub-carriers, which allows maximization of spectral efficiency and control of the full spectrum. It is then possible to avoid the unwanted frequency band by canceling the corresponding part of the OMTDR signal.

The aim of OMTDR is to control the total measurement bandwidth, increase data rate and spectral efficiency, and avoid interference. OMTDR provides communication between sensors to overcome ambiguity in fault localization, thus improving soft fault detection. For example, the reflected signal can be acquired for different load conditions to detect soft faults such as insulation defects. For this purpose, the reflected signal is correlated with the transmitted signal. The result is a reflectogram, which shows corresponding maxima (correlation peaks) at the points of the cable sections that are not matched in terms of impedance. The reflectogram helps to localize soft errors and to estimate the severity of these faults by displaying the time responses.