A bifilar approach to power and data transmission over common wires in aircraft

Since digital control, monitoring and diagnostics of various mechanical, hydraulic, or electric functions have found their ways into aeronautical applications, there is an increasing demand for data communications. Local area networks and field bus solutions meeting aeronautics requirements have become standard. However these systems add considerably to an aircraft´s wiring harness complexity and weight. Transmitting data over power lines (Powerline Communications PLC) is proposed as a remedy against the progressive increase in wiring harness complexity. In a PLC approach dedicated wiring for data transmission may be completely removed and modem, coupling and filtering components can be integrated into the aircraft application equipment resulting in a solution providing a single connector for power and data. The power distribution for a significant amount of the systems in an aircraft is based on a single wire method in which the metal chassis is used for the current return path. Such a wiring solution is disadvantageous for PLC in achieving EMC standards compliancy and in regards to ingress of noise due to crosstalk. An alternative approach is therefore proposed to aeronautical onboard PLC that replaces the single wire by a double wire (bifilar approach), providing a homogenous and well defined symmetric transmission line (differential mode) for data, but maintaining the asymmetric mode with a common ground return path for the distribution of power (common mode). This solution improves the performance of a PLC based data network dramatically and is also the key to achieving compliance with existing EMC norms. It will be shown in this article that these benefits may outweigh the drawbacks of the required double wire cabling.