Airborne communication networks
Being always connected via wireless services has become a part of most people’s lives. Ubiquitous broadband connectivity as well as the proliferation of internet services and apps have not only had a profound impact on how everyday communication in business and private life is approached, but many leisure activities, such as audio and video consumption and games, have also been taken over by digital solutions.
These developments do not halt before the aircraft cabin. The airline industry has provided in-flight entertainment systems since decades, but today many passengers also expect in-flight Wi-Fi connectivity to the internet. However, as aircraft fly high and fast and also in different regions of the world, the environment is a challenging one for traditional telecommunication solutions, which are of limited range and bandwidth and require dedicated radio spectrum. Therefore, the main means for in-flight connectivity today is satellite access using microwave transmission systems. The drawbacks of today’s satellite-based solutions are high infrastructure costs, the need for radio spectrum allocation, and long transmission path delays. Another option are cellular air-to-ground solutions, however, these are chiefly limited to overland flights.
A different concept for commercial air transport, which involves aircraft forming ad-hoc communication networks, has been proposed in the past and investigated especially by the Institute of Communications and Navigation of the German Aerospace Center (DLR). In this concept, aircraft within wireless network clusters can use multi-hop transmission to ground stations (or satellites) serving as internet gateways, which are several times the radio communication range away. Instead of using radio links, however, Bauhaus Luftfahrt proposed early on the use of free-space optical links to build a high-speed communication network based on laser transmission. The advantages lie in the high available modulation bandwidths and point-to-point capacities in the range of many gigabits per second. Additional possibilities may also arise from the mesh networking itself, even without a gateway to the internet. For example, the aircraft network may offer a larger set of up-to-date information and content to the passengers by “crowd sourcing” of data. Also, for example, weather data may be shared between aircraft for better flight management and safety, according to up-to-date meteorological information.
As laser links are susceptible to turbulence and clouds, link failures or outages may occur. Ideally, the system would be complemented with a radio-frequency backup solution in a hybrid approach, but in principle the network already offers intrinsic resilience to link outage due to path diversity in the network. In order to investigate the potentials and limitations of the concept, a simulation environment has been set up, which is capable of modelling worldwide air traffic based on a flight schedule database. Cloud data can be considered in order to assess the impact of weather on link availability. From the aircraft movements, statistics concerning aircraft-to-aircraft distances can be evaluated to find the number of expected neighbours, with which network clusters can be formed, in order to derive requirements on the communication system. The network itself can be simulated for a given communication range in order to assess metrics including the ratio of participating aircraft in different scenarios. The impact of adding satellite laser links on the network can also be assessed. Satellite links can be used either to maximise connectivity for a given number of connections or to optimise network performance by better distribution of data traffic loads.
The laser-based network will not replace traditional aeronautical radio systems in the future, but instead it holds the potential to add tremendous communication capacity to the air transport system. While the ad-hoc network is most efficient in regions with high air traffic density, aircraft on more remote routes still benefit from freed-up satellite communication capacity. Much like mobile phones, which switch between different access technologies including cellular and Wi-Fi, an aircraft may in the future switch between satellite, ground, or ad-hoc network connectivity based on the best connection currently available.
- Airborne communication networks
- In the airborne networks concept, aircraft within communication range connect with each other using laser links. When the aircraft density is sufficiently high, mesh networks form between aircraft and internet gateways, which may include ground stations, high-altitude platform stations (HAPS), and communication satellites. Thereby, access to online content is made available to all aircraft within the mesh cluster via multi-hop transmission. Moreover, data may be shared between aircraft, even without internet access.
- Air traffic has been increasing worldwide and is expected to do so in the future. As an increase in air traffic density on the one hand increases the amount of data transmissions in aviation and on the other hand improves the availability of network connections, the benefit of the scalability of the concept becomes obvious.