Time and phase alignment of distributed gateways: Theoretical analysis and experimental demonstration

Abstract

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 $N\times N$ MIMO feeder links is studied. The performance limitation due to imperfect time and phase distribution is analyzed. Synchronization via optical fiber is considered in this study. The accuracy of time distribution was verified through laboratory measurements. The impact of the residual timing error on the achievable system bandwidth was assessed. Results showed that several GHz of bandwidth can be supported. 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.