We target VHTS/UHTS systems able to flexibly allocate the resource worldwide according to traffic demands. Digitally controlled phased arrays an obvious candidate for the user link of these systems. However, full digital control of large number of radiating elements across bandwidths of a few GHz gives rise to unaffordable power consumption. Hybrid analogue/digital beamforming can reduce the computational demands with some penalties on the coverage characteristics (due to e.g. grating lobes), which are ultimately reflected to compromised SNIR. In this project, we will investigate the co-design of active antenna architectures with the associated signal processing and resource allocation strategies that will optimise the end-to-end system performance.
Exploiting multi-user MIMO precoding, the project will seek to manage interference in the user link that arises from different antenna architectures under practical constraints on e.g. channel state information (CSI) and computational efficiencies. The performance will be benchmarked exploiting prior heritage on a payload evaluation framework under given resource constraints and traffic demands. The implementation of such signal processing will be investigated. Open loop techniques (no estimation of the CSI), and closed loop techniques (with relaxed techniques that averages the CSI over time slots with similar scenarii of active trafic) will be compared to brute force techniques (CSI assesment at each time slot). For the feeder link efficiency, spatial multiplexing is a promising MIMO scheme enabled by multiple antennas on the space and ground segments. To this end the project will focus on the MIMO feeder link schemes and their performance under practical constraints on e.g. synchronisation and CSI. Ultimately the project will deliver a simulation framework that will enable optimisation of resource allocation during planning and operation of future UHTS missions.
