The main features of the “On-Ground Beamforming Techniques” project are:
- To review the OGB/OBB techniques in order to identify suitable techniques and solutions.
- To review the current and foreseen OGB/OBB systems and technologies. It would provide examples of systems implementing OGB highlighting potential issues and/or potential relevant solutions and technologies.
- To interview some mobile satellite operators to define mission scenarios where OGB systems would be appropriate.
- To derive the system scenarios from the mission scenarios. It would provide a framework for the assessment of the different solutions, i.e. OGB and OBB solutions.
- To analyse and trade-off the functionality distribution between the ground segment and the space segment. From this analysis, an architecture and preliminary design of the system for the different solutions (study cases) would be performed.
- To assess the performances of the selected scenarios through software simulations.
- To identify for each considered system scenarios the best suited solution(s).
- To define a roadmap for the ground segment and space segment technologies which shall be developed to implement the selected system solutions for the considered mission scenarios.
Following the interview with operators, two scenarios have been retained :
- one mission scenario at L-band with global coverage and similar target performances than Inmarsat-XL satellites and addressing mainly bidirectional mobile applications
- one mission scenario at S-band based on a regional coverage (EU27) with 11 linguistic beams on the FWD and 44 spot beams on the return direction and addressing both mobile broadcasting towards mobile terminals (through the FWD linguistic beam coverage) and bidirectional mobile application
Then a functional architecture and high level design of the system have been defined based on the two reference mission scenarios and two system design approaches (OGB and OBB). Five architectures have been identified, including a partial mission limited to 7MHz (using extended L-band allocation).
Analysis of calibration techniques, beam forming impairments and advanced signal processing allowed the trade-off of on-board and on-ground functionalities.
Various beamforming techniques have been investigated and simulated: fixed, adaptative LCMV and beamspace methods. The benchmarking of ground calibration was performed using spread spectrum techniques through simulations taking into account modelling of ground equipments impairments, propagation channel impairments and payload impairments.