Transmitting radio waves to and from aircraft is one part of the airborne connectivity equation, but if the Wi-Fi network inside the cabin isn’t optimized for that particular aircraft, the quality of the service can suffer. Grenoble, France,-based Leti, a research arm of CEA Tech, has measured Wi-Fi signal propagation in a Falcon jet as part of a proof-of-concept test to see how cabin configurations affect wireless signal propagation in business aircraft.
The research is not just designed to improve the passenger experience, but also to lay the groundwork for networks of wireless sensors that are finding their way into modern aircraft. For a wireless sensor to provide reliable service, it must be able to connect to onboard networks without fail. Already wireless tire-pressure monitoring systems are installed as retrofit and forward-fit applications, and wireless sensors could replace wired systems for engine parameters, cabin pressurization systems, smoke detection, temperature monitoring, and more.
Leti researchers first evaluated conditions in a Falcon airframe, then used that information to build a cabin environment model and propagation channel emulator that allow lab testing of the Wi-Fi configuration before installation of the network in the aircraft.
“This is new, what we did with Dassault; how to test Wi-Fi for deployment in the aircraft, without immobilizing the aircraft,” said Lionel Rudant, Leti strategic marketing manager. “With this emulator you have the actual behaviors of wave propagation that you would have in the aircraft.”
The channel emulator is a device developed by the mobile phone industry, and it is also employed in automotive Wi-Fi installations, according to Rudant. “The environment around cars is complex and expensive to test on the road, with high-speed mobility. In the auto industry, such an emulator is used to test connectivity before integration.”
Modeling an aircraft cabin presented new challenges. Using sounding equipment to measure the impulse response of the radio frequency environment in the cabin, researchers investigated multiple points in the cabin, especially near seats and around wireless access points (Wi-Fi transceivers).
A variety of factors affected the Wi-Fi signals in the cabin, such as curtains, plastic coverings, bulkheads, passengers, etc. The geometry of the cabin also affects received signal strength. “The most important point,” he said, “is that there are multiple paths for propagation of radio waves in the metallic environment of the cabin, and with different path lengths, the pulse response can be spread out. This delays the spread of propagation, and causes fading of the signal due to the interference.”
The measurements allowed the Leti team to develop a model of the cabin environment, using a statistical approach or stochastic modeling. As Rudant explained, “You want to describe with your model an aircraft cabin environment, but you have lot of different situations in this cabin, so you need a statistics approach to cover all the configurations.”
Of course the aircraft manufacturer does provide guidelines for suitable Wi-Fi installations, but there are so many variations after the interior completion, he said, that questions remain about how to ensure a consistently high level of Wi-Fi performance. “With the model we can play the environments in the emulator and make sure that Wi-Fi performance is good enough.”
From the testing, Leti determined that Wi-Fi antenna location is a critical factor, in part because of the constraints on installing the several antennas needed inside the cabin. “One of the open questions was how to install different antennas,” Rudant said. “[Do we] separate them at different locations, or install all antennas in one array in the cabin? This is a very difficult question. The final performance of multi-antenna Wi-Fi strongly depends on the propagation environment. It’s about the ways how radio waves can reach each of the different antennas with independent properties but equal power. That is what is required for such Wi-Fi systems.”
Having completed the research project with Dassault, Leti hopes to apply the testing method to other airframe types, to optimize their Wi-Fi installations. “We want to work with different players to finalize the test method,” he said, “and have standardization, then deploy it in industry.” Rudant also sees an opportunity to work with manufacturers of onboard Wi-Fi systems to optimize Wi-Fi terminal installations.
“Aircraft manufacturers need a standard test method for the end user. These are critical questions, and it will probably pay for the testing services to insure there is very good Wi-Fi service in their aircraft,” he concluded.
