AG Kommunikationstheorie


On the analysis and simulation of cable characteristics in aeronautical environment


Wired communication is still prominent in harsh environments like aeronautic applications due to, e.g., their high robustness against interference, their reliable data rates, and their high security. The amount of cables deployed in, e.g., an Airbus 380-800, sum up to a total length of about 480-530 km. Besides the ubiquitous influences due to interference and external noise, cable faults are a big issue in wired networks. It is obviously impossible to monitor such a gigantic infrastructure by measurements or visual inspection. Nevertheless, it is important to have an insight into the whole infrastructure to guarantee signal integrity and safety. Here, simulations can help building the tools for monitoring the network and to analyse signal integrity. Cable faults can be separated into two categories, hard faults (open and short circuits) and soft faults (e.g., insulation damage, sharp bending, untwisted twisted pair cables, and more). Cable faults will generally influence the impedance characteristic of a cable. Soft faults are of special interest as they are much harder to recognize due to the small impedance variations and they can eventually develop into hard faults. Experimental measurements are taken and analysed to see the influence of some typical damages on typical cables , which are used in aeronautical environment. It is known that Fast Ethernet, is mostly used in aircraft, e.g., the variant 100BASE-TX, also called pairs of a category 5 (CAT5) twisted pair cable in the A350/A380. It offers a 100 Mbit/s, full-duplex connection over two wire. A simulation approach is developed based on cascaded two-port networks with uniform and exponential taper lines. A frequency range up to 1 GHz is used to meet the specifications of 1000BASE-T1 (600 MHz) and a single pair of twisted pair cable is considered to simplify the analysis. The experimental results show that the influence of the evaluated damages on the selected shielded and unshielded twisted pair cables can be measured. The results differ not only for the different damages but also for equal damages on the different cable types, i.e., shielded or unshielded cables. An implementation of the simulation approach is done in MATLAB/Simulink. The simulation approach delivers good results for the measured cable faults and it can be shown that based on input parameters for a known fault a fault simulation at a different fault location is possible. The modified Simulink model of a cable model without damages shows the signal changes due to the cable faults. As expected, the experimental results indicated that UTP cables need special care due to their sensitivity to cable faults compared to STP cables. The simplicity and the possibility to extend the model due to its cascaded structure is the main advantage of the approach. It has also been shown that other damage models can easily be included and might deliver even better results for special fault simulations.

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