Ultra high-throughput satellite systems are expected to play an essential role in future beyond 5G and 6G networks. These systems must remain as flexible as possible to adapt to heterogeneous traffic demands, while also delivering the highest possible rate for dedicated services. Satellites flexible payloads are increasingly employing wideband output multiplexers. In this context, it is now more important than ever to evaluate frequency-dependent degradations on multicarrier signals. In particular, it is critical to characterize the distortions entailed by the output multiplexers filters. In this paper, models are presented and novel formulas are derived to determine the carrier-to-interference ratio resulting from these distortions. Derivations are oriented towards the applicability of either high-accuracy (e.g., for link budget) or low-complexity calculations (e.g., for real-time carrier allocation). The influence of key parameters such as the optimal decision instant, symbol rate and roll-off factor is thoroughly analyzed. Furthermore, formulas are evaluated in a practical scenario: the dynamic carrier allocation optimization. They are combined with efficient optimization algorithms to obtain the best performance based on user fairness. Relevant metrics such as accuracy, complexity and allocation gain are also investigated. In the end, the application of the proposed formulas and algorithms leads to a significant allocation gain that is increasing with the number of carriers. The feasibility of real-time dynamic carrier allocation to further increase the capacity of the next generation of satellite systems is emphasized.

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 NxN 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.