Time and Phase Alignment of Distributed Gateways: Theoretical analysis and Experimental Demonstration

Very high throughput satellite systems have recently been developed to offer high-speed connectivity, especially in remote areas, planes and ships. The high data rates can be achieved by using a multibeam approach with an aggressive reuse of the available frequency resources. Due to the high number of user beams, the system must support a large aggregated bandwidth. Multiple-gateway architectures are a necessary solution to sustain the immense bandwidth requirements. Multiple-input multiple-output (MIMO) feeder links have been proposed to address the ground segment design challenges of multiple-gateway architectures. The deployment costs and the link availability performance can in particular benefit from this approach. However, to coordinate the operation of multiple gateways, high precision time and phase synchronization is necessary. In this paper, the effect of time and phase misalignment in MIMO feeder links is studied. Mathematical models that describe the performance limitation due to imperfect time and phase distribution for a 2x2 MIMO feeder link are introduced. Time and phase dissemination via optical fiber is considered for the synchronization of the ground stations. The ability of such systems for time distribution was tested through experiments. The bandwidth that can be supported is evaluated based on the measured residual timing error. Results showed that the achieved synchronization supports channel bandwidths of several GHz. On the other hand, a recently proposed phase synchronization approach is considered as a promising candidate for MIMO feeder links. Its phase stability performance is assessed and it is emphasized that requirements in terms of link outage are fulfilled.