As telecommunication satellites attempt to keep pace with the increasing data rates and falling costs per Mbps delivered by terrestrial networks, the total throughput capability of VHTS systems has risen rapidly. The latest round of commercial spacecraft now offer total throughput in excess of the 1 TBps considered a distant target only a few years ago. To maintain the competitive position ofsatellite in the future even greater performance and cost improvements are needed in next generation systems.
There has been much focus on the development of the User link in such systems, with the limited RF bandwidth available pushing consideration of ever smaller spot beam sizes to yield higher frequency reuse factors, and giving rise to the adoption of techniques such as beam-hopping. For future systems however, the Feeder link will likely become the major bottleneck to further throughput growth. Various solutions have been proposed, including migrating to ever higher frequency bands (where greater spectrum bandwidth is available) such as Q/V (50/40 GHz), and sometimes to W-band (70/80 GHz), or moving to optical transmission schemes. These approaches also have inherent benefit of freeing up Feeder Link spectrum which might be re-applied to the User link, if licensing considerations permit. Their key challenges lie with the current maturity of the technologies required to realise these systems as well as the complexity created in theground segment.
A different architectural solution has also been identified based on in-orbit spatial diversity, or the fractionated spacecraft which is shortly to be the subject of a separate ESA study .Early investigations have suggested that the cost of connecting high capacity, remotely located, gateway stations to the terrestrial backbone network will become a major cost driver for the viability of future VHTS, prompting consideration of alternative approaches. One promising idea is to share or integrate the available user and feeder link spectrum and realise the feeder link function with a relatively large number of spatially diverse, small gateway systems, effectively increasing the frequency reuse factor of the Feeder Link spectrum.A key advantage of such an approachis that each distributed gateway can be relatively simple and small, and hence located close to terrestrial infrastructure (i.e. Internet Exchange Points) significantly reducing gateway connectivity and operational costs. An additional merit of this approach is that a number of network functions could be virtualized into central processing locations allowing a high degree of automation and upgradeability.
The space segment architecture may also be impacted with the differentiation between Forward and User links effectively being removed, offering opportunities for a more efficient payload design.In the frame of Very High Throughput Satellite (VHTS) systems, the activity is therefore to perform a system study to determine the technical feasibility of employing a large population of highly distributed small sized gateways to support future VHTS systems, considering the impact on both the space and ground segments. Specifically identifying:
- The flexibility and connectivity requirements that need to be embedded into the satellite payload in order to re-use the same spectrum for Gateways and User Terminals (e.g. beam hopping).
- The Gateway size/population trade-off interms of CAPEX and OPEX and the main limiting cost factors influencing this trade-off (e.g. antenna size, fibre interconnections).
- The limits of the large population of small sized Gateway architecture (e.g. up to which system capacity, up to how many Gateways).
- The impact of such a feeder network architecture with respect to Gateway reliability approach, coverage re-configuration, progressive Gateway rollout, and network automation.
The activity will also generate a comprehensive cost analysis of the economic feasibility of employing such an approach, considering the total cost of ownerrship and operation. The major outcomes of the study are expected to be:
- a demonstration of the viability of the outlined approach to prospective system architects and operators,
- identification of any critical technology gaps to realising such a system and proposed roadmaps for future development in both ground and space segments,
- identification of any relevant spin-in technologies from terrestrial communications systems, e.g. 5G, Dense Wavelength Division Multiplexing, DWDM, cloud computing, etc.