A look at the comparative performance of wired and wireless sensors, type of wireless sensors & interfaces, frequency performance, protocols, network topologies, and qualification standards.

The performance of avionics systems is dictated by the timely availability and usage of critical health parameters. Various sensors acquire and communicate the desired parameters. In current scenarios, sensors are hardwired and the number of sensors are growing due to automation, which increases the accuracy of intended aircraft functions.

Pictorial representation of the distribution of various wired sensors all over an aircraft. Although it does not include nearly all sensors, it does give some indication of the amount of wiring required throughout an aircraft, which is substantially high. This wiring contributes to weight of the aircraft and operational inefficiency due to fuel usage.
Sensors are distributed all over the aircraft and they are connected through wired networks for signal processing and communication. Line-replaceable units (LRUs) that integrate various sensors also use a wired approach for communication.

The use of a wired network approach poses challenges in terms of cable routing, stray capacitances, noise, mechanical structure, and added weight to the structure. The weight of hundreds of miles of wires and cables contributes significantly to the overall weight of the aircraft, and, of course, as the weight of aircraft increases, the required fuel quantity also increases. The key driver for airline operational cost is fuel.

Use of wireless sensors in aircraft brings in tremendous advantages in terms of design optimization, flexibility in sensor configuration, and weight optimization. However, even though the avionics industry is trying to adopt wireless sensors, there are some points of concern in deploying wireless sensors and networks across the aircraft. Some of the key factors to be considered for determining the feasibility of wireless technology and sensors are protocol, standards, compliance, and certification. Additional factors are internal and external infrastructure, various topologies for sensor networks, and expandability for the same. Signal integrity and fault detection methods are also key features of signal processing in aerospace applications.

Sensor Network Topologies

Typical wired sensor interface techniques.
Various wireless technologies can be considered for communication inside aircraft, and to take advantage of them it is necessary to address and understand the sensor network topologies that provide the architectural framework.

A peer-to-peer network allows each node to communicate directly with another node without needing to go through a centralized communications hub. Each peer device is able to function as both a “client” and a “server” to the other nodes on the network. This type of network can be used while communicating data from/to proximity sensor units.

Tree networks use a central hub called a root node as the main communications router. One level down from the root node in the hierarchy is a central hub. This lower level then forms a star network. The tree network can be considered a hybrid of both the star and peer-to-peer networking topologies. This type of network can be used while communicating data from/to fuel sensor units. Based on the location of the fuel tank, each of the nodes can transmit the related information to the main node.

Various wireless technologies available and their frequency of operation and modulation scheme.
Mesh networks allow data to “hop” from node to node, allowing the network to be self-healing. Each node is then able to communicate with each other as data is routed from node to node until it reaches the desired location. This type of network is one of the most complex and costs a significant amount of money to deploy properly. It can be used while communicating data from/to various data concentrator units.

Star networks are connected to a centralized communications hub. Nodes cannot communicate directly with one another; all communications must be routed through the centralized hub. Each node is then a “client” while the central hub is the “server”. This type of network can be used while communicating data from/to the central data concentrator unit, which gets connected to the flight-management computer.