The wireless signal propagation characteristics from a satellite-based transmitter to an airborne receiver are of special interest for supplying the aircraft itself or the passengers with communication abilities. Applications in this scope are for example accessing the internet and multimedia content while on flight but also applications related to safety-of-life features like air traffic management. Especially applications incorporating safety-of-life features require not only an average reliability of the transmission link but rather a high availability and have stringent requirements on the continuity-of-service.
The main objectives of this project were to validate and extend existing satellite-to-aircraft channel propagation models and to investigate the characteristics of the satellite-to-helicopter channel. Several effects were considered such as ground reflections from various environmental patterns, multipath contributions originated by the aircraft itself, spatial and polarization diversity and the impact of the aircraft structure in dependence on the antenna locations on the antenna pattern.
This project aimed to elaborate a software tool modeling the satellite-to-aircraft propagation channel in order to understand and improve the satellite radio reception by the aircraft. The software development process is supported by experimental measurements with a view to different antenna, satellite and flight configurations. The experimental plan comprised four different aircraft types and diverse ground-based as well as airborne scenarios.
The project also provided a first characterization of interference in the bands reserved for aeronautical satellite communications at L- and Ka-bands.
The key challenge of the project was to plan, set-up and conduct complex experimental campaigns involving several aircrafts on ground and in flight. This is key to the provision of accurate experimental data to feed the channel model.
This project did not only characterize the propagation channel but it also took the full scenario determining the satellite-to-aircraft radio link into account (aircraft dynamics and maneuvering). This included impairing effects but also alternative system configurations like antenna/ polarization diversity.
The difference in both propagation links was analyzed and modelled accurately.
The activity improved the state-of-the-art channel model simulators that relied on a two-tap model with a Line Of Sight path and a ground-reflection path and implied several limitations. For example, they did not consider banking scenarios or satellites with changing positions. However, such scenarios may have significant impact on the channel behavior.
Therefore, an improved channel model simulator was implemented to allow propagation simulation for signals transmitted by a satellite and received by an aircraft for L- band transmissions. The channel model is substantially allowing more scenarios to be simulated (e.g. banking scenarios) and offered opportunities for extension of the model towards other frequency bands, types of aircraft or directed antennas. The surface reflection is modeled considering different surface such as water (representative of lakes and sea), grass or vegetated areas. As a basis for the channel model various measurements were performed and evaluated.
The project was divided into two phases. During the first phase, the main tasks were:
- Review of existing channel models and careful identification of gaps in the existing knowledge and experimental data and derivation of experimental requirements (requirements consolidation),
- Planning and design of the experiments with particular respect to the channel model’s demands,
- Selection/Design of measurement equipment.
- Demonstration of the experimental data analysis concept.
During Phase 2, once a sound experiment and data analysis had been proposed, the tasks were:
- Integration of measurement equipment,
- Execution of experiments,
- Data evaluation,
- Model development and testing,
- Development of simulation software tool,
- Additional measurements to countermeasure and verify the channel model and software tool.