Joint Precoding and Resource Allocation Strategies Applied to a Large Direct Radiating Array for GEO Telecom Satellite Applications

The ever-rising demand for very high throughput satellites drives the requirements toward larger antennas benefiting from increased directivities and narrower beams. Narrow beams allow frequency reuse across the coverage and capacities as high as Tbps can be achieved. To flexibly allocate this capacity, an active deployable direct radiating array is an attractive solution with power flexibility and in-orbit coverage reconfiguration. This solution, however, requires very high numbers of radiating elements compared to more conventional reflector based solutions. Moreover, digital-only beamforming is power hungry due to the processing of large frequency bandwidths for each radiating element. Novel beamforming approaches must be investigated to save on-board power. A hybrid beamforming architecture based on analog beamforming at sub-array level and digital beamforming reduces the power consumption of the digital core. A disadvantage of hybrid beamforming is the appearance of grating lobes in the satellite field of view. A system approach to mitigate grating lobes is proposed. This strategy is based on the joint use of precoding and smart resource allocation. The impact of the non-uniformity of users distributions on capacity is also assessed.