Stephen Dominiak

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 aircrafts 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.

Model based design of an avionics Power Line Communications physical layer

Transmitting data over the aircraft power distribution network using Power Line Communications (PLC) technology provides an interesting solution for providing significant aircraft wiring weight, volume and complexity savings. A PLC protocol dedicated for real-time, safety-critical applications has been developed. The physical layer of the protocol is based on the international IEEE 1901 standard. An overview of the advanced digital signal processing techniques required to provide robust communications over the harsh power line communications channel is provided. In order to cope with the complexity in the realization of the physical layer, a process using model based design based on concepts from DO-254 and DO-331 is proposed. This process is used for the hardware-based design and verification of the PLC protocol.

A characterization of the broadband MIMO PLC channel in aircraft

The use of Multiple Input Multiple Output (MIMO) techniques for Power Line Communications (PLC) has been proven for the consumer market. As of 2011, MIMO is part of two PLC standards and products are already available for end users. PLC for avionics on the other hand is a niche technology. Fulfilling the high demands for safety-critical components makes the engineering of a PLC solution a challenging task. Many aircraft systems are powered by a three-phase alternating current system and already provide the necessary wiring for adopting MIMO techniques. Our goal is to develop next generation PLC systems for aircraft with MIMO technology.

Gains and limits of MIMO technology for safety-critical PLC applications

Many Power Line Communication (PLC) systems operate on top of multi-conductor infrastructures, which allows for the adoption of Multiple Input Multiple Output (MIMO) techniques. Current channel models for MIMO PLC do not consider terminal conditions and are focused on optimizing the average case. For safety-critical applications, however, the line terminations are important, as system performance has to be guaranteed for any conditions-including the worst case. In this paper, we present an analytical and a SPICE1-simulated channel model based on transmission line theory that is capable of incorporating terminal networks. Further, we evaluate the channel capacity and compare three different systems that could be deployed in a multi-conductor environment: A Single Input Single Output (SISO) system, multiple parallel SISO systems and a MIMO system. With our channel model we show that the terminal conditions have an impact on the overall signal attenuation, but also that they affect the relative cross-talk level compared to direct channels. Although we can confirm existing findings that MIMO techniques do provide performance gains, our results show that this is only true above a certain signal-to-noise ratio (SNR). For low SNRs, these gains decrease and in worst case, the gains over a SISO system are lost. Also, parallel SISO systems do not offer robust performance gains over single SISO systems, which discourages their use for safety-critical applications.