Free-space optical communication technologies will enable next generation of ultra high throughput satellite

Abstract

Ultra or Very High Throughput Satellites (U/VHTS), operating in the Ka-band (20/30GHz), are very large satellites with multi-beam coverage able to provide several hundreds of Gigabits up to few Terabits per second of aggregated throughput. The supply of these huge amounts of data to such a satellite is done by hundreds of wideband RF links, called feeder links, which operate in Ka-band (30GHz) and in Q/V-band (40/50GHz) between the satellite and a network of hundreds of ground (feeder/gateway) stations. Moreover, the poor availability of Q/V-band links in wet regions (such as Europe) requires additional back-up gateways (site diversity technique), further increasing the size of the ground network. In short, the cost of developing and operating such large station network becomes the major part of the cost of a VHTS and could become an obstacle to the development of the future generation of VHTS whose ambition is to exceed the Terabit of capacity. Today, none of the known techniques to reduce the number of gateway/feeder stations gives full satisfaction and have enough room for improvement. Thanks to an ESA supported study, nicknamed MATRIX for “Innovative fractionated satellite system enabling higher reuse of frequency”, Thales Alenia Space studied a very promising solution. The technical and economic feasibility of this new solution based on the concept of fractionation applied here to VHTS and on free space optical communication technologies, was demonstrated. The key feature of fractionated VHTS is Optical Inter-Satellite Links (OISL) that backhaul data intended to users from the Feeder Satellites to the User Satellite. Advantageously, these OISL makes use of analogue RF modulation of optical carriers. So, it allows deporting most of signal processing in the Feeder Satellites and therefore simplifying and alleviating the User Satellite. Finally, fractionated VHTS will allow a smooth and risk-free transition from RF feeder links to digital FSO feeder links. This paper presents the concept of fractionated VHTS as developed in the MATRIX study and highlights the role and benefits of FSO communication technologies in the development and operation of future Ultra High Throughput Satellite systems. It will focus on the Optical Inter-satellite Links, cornerstone of the system.