Periodic Reporting for period 1 - VERTIGO (VERy high Throughput Satellite-Ground Optical Link)
Período documentado: 2019-06-01 hasta 2020-05-31
The competitive telecommunication industry is more and more orientated towards mobile devices and broadband connectivity with its associated challenges the cost reduction per bit supplied to customers (€/Gbps) and the higher capacity of broadband. To stay competitive and face the concurrence of the ground fibered networks but also deliver similar telecommunication services to people in unserved or underserved regions by ground network (bridging the digital divide), satellite operators have to propose services of comparable performance and quality to ground operators offer, requesting cost efficient solutions from satellite systems vendors.
One of the first technological response coming from the Space industry challenged in turn is to develop more competitive solutions like Very High Throughput Satellite (VHTS). These growing needs in transmission capacity of telecom systems as well as the saturation of conventional RF bands have naturally encouraged the use of new frequency bands like Q/V bands whose technologies and equipment are now reaching maturity. However, in order to prevent the foreseeable congestion of these newly used frequency bands and to prepare for the future in the longer term, others are already envisaged such as the W band and a leap to optical technologies is considered as a serious alternative.
Optical feeder links are thus considered as a promising technology. Nevertheless, optical feeder links are still facing some implementation uncertainties, beyond the obvious issue of nebulosity which can be alleviated through site diversity approach. In this context, atmospheric propagation impairments and their mitigation techniques together with high power generation and management as well as efficient modulations are of primary importance in the design and sizing of the optical feeder link. In the past several experimentations on ground or in-flight have demonstrated part of these concepts and subsystems necessary to implement such high capacity systems. Simultaneous combination of all these concepts in comprehensive demonstrations has however not been implemented yet.
VERTIGO ambition is to establish the required breakthrough by developing the on-board and ground concepts and technologies enabling for a drastic increase of the link throughput towards and beyond 1 Tbps. VERTIGO major objectives are: 1) Throughput increase: while current space optical comms use 1bit/symb modulation formats, VERTIGO will prove advanced schemes with higher spectral and power efficiency, including RF-over-Fiber approach. 2) High optical power generation: to close the demanding link budgets, VERTIGO will develop on-board and ground means to raise the transmitted optical power, not only based on amplifier power increase, but also on incoherent/coherent power combining. 3) Mitigation of atmospheric propagation impairments, to make full use of throughput and power increases. Optomechanical techniques using adaptive optics and aperture diversity, and digital processing (error correction coding/interleaving) will be developed to enhance the robustness of future optical feeder links.
One of the first technological response coming from the Space industry challenged in turn is to develop more competitive solutions like Very High Throughput Satellite (VHTS). These growing needs in transmission capacity of telecom systems as well as the saturation of conventional RF bands have naturally encouraged the use of new frequency bands like Q/V bands whose technologies and equipment are now reaching maturity. However, in order to prevent the foreseeable congestion of these newly used frequency bands and to prepare for the future in the longer term, others are already envisaged such as the W band and a leap to optical technologies is considered as a serious alternative.
Optical feeder links are thus considered as a promising technology. Nevertheless, optical feeder links are still facing some implementation uncertainties, beyond the obvious issue of nebulosity which can be alleviated through site diversity approach. In this context, atmospheric propagation impairments and their mitigation techniques together with high power generation and management as well as efficient modulations are of primary importance in the design and sizing of the optical feeder link. In the past several experimentations on ground or in-flight have demonstrated part of these concepts and subsystems necessary to implement such high capacity systems. Simultaneous combination of all these concepts in comprehensive demonstrations has however not been implemented yet.
VERTIGO ambition is to establish the required breakthrough by developing the on-board and ground concepts and technologies enabling for a drastic increase of the link throughput towards and beyond 1 Tbps. VERTIGO major objectives are: 1) Throughput increase: while current space optical comms use 1bit/symb modulation formats, VERTIGO will prove advanced schemes with higher spectral and power efficiency, including RF-over-Fiber approach. 2) High optical power generation: to close the demanding link budgets, VERTIGO will develop on-board and ground means to raise the transmitted optical power, not only based on amplifier power increase, but also on incoherent/coherent power combining. 3) Mitigation of atmospheric propagation impairments, to make full use of throughput and power increases. Optomechanical techniques using adaptive optics and aperture diversity, and digital processing (error correction coding/interleaving) will be developed to enhance the robustness of future optical feeder links.
Based on a reference very high capacity mission scenario, the main requirements for an operational feeder link were derived to feed the design phase of the different subsystems. The feeder link capacity was assessed for both digital and analog modulation formats and under different propagation conditions and taking into account design assumptions for both ground and space terminals. The functional block architecture of the feeder link was established as well as mathematical models for these link budgets evaluation. From these assessments, baseline configurations were defined for the feeder link and preliminary SWaP features were evaluated. A preliminary eye safety analysis was also carried.
On the optical communication chain, progress was achieved on the definition, design and test plan of the different breadboards which will implement several modulation formats including both digital and analog. The considered modulation formats were beforehand discussed in order to discard options not relevant regarding in particular specificities of the transmission channel. The preliminary specifications for each block/component of the transmitter and receiver sections were provided and the way to emulated the propagation channel in an indoor environment was investigated and selected. The necessary digital signal processing was also described and hardware requirements defined.
On high optical power generation, the main design issues were described including pumping options of the fiber but also nonlinear effects mitigation. Numerical modeling of the optical performance of two amplifiers (multi-Watts and multi-tens of Watts classes) was carried out and performance simulated. As a mean to raise the achievable optical power beyond individual amplifiers capabilities, coherent combination techniques were reviewed detailing respective assets and limitations.
Finally, High power wavelength division multiplexer was designed after a technology review and a trade-off between the different multiplexing techniques based in particular on power handling capabilities but also channel count, channel spacing features.
The atmospheric propagation techniques were addressed first through the generation of propagation time series feeding the feeder link dimensioning. Two kind of optical ground stations were also designed for VERTIGO outdoor demonstration: one based on single aperture and adaptive optics and the other one based on a telescope array implementing aperture diversity. An evaluation of the expected perturbations and corrections performance experienced on outdoor demo Line of Sight was realized. In parallel, work was started on coding topic taking into account optical free-space propagation channel to find a relevant error correction algorithm.
Finally, exchanges were engaged with outdoor demonstration sites responsibles to initiate necessary interactions to deploy for the test campaign of the project the different parts of the demo (ground stations, space terminal emulator,…).
On the optical communication chain, progress was achieved on the definition, design and test plan of the different breadboards which will implement several modulation formats including both digital and analog. The considered modulation formats were beforehand discussed in order to discard options not relevant regarding in particular specificities of the transmission channel. The preliminary specifications for each block/component of the transmitter and receiver sections were provided and the way to emulated the propagation channel in an indoor environment was investigated and selected. The necessary digital signal processing was also described and hardware requirements defined.
On high optical power generation, the main design issues were described including pumping options of the fiber but also nonlinear effects mitigation. Numerical modeling of the optical performance of two amplifiers (multi-Watts and multi-tens of Watts classes) was carried out and performance simulated. As a mean to raise the achievable optical power beyond individual amplifiers capabilities, coherent combination techniques were reviewed detailing respective assets and limitations.
Finally, High power wavelength division multiplexer was designed after a technology review and a trade-off between the different multiplexing techniques based in particular on power handling capabilities but also channel count, channel spacing features.
The atmospheric propagation techniques were addressed first through the generation of propagation time series feeding the feeder link dimensioning. Two kind of optical ground stations were also designed for VERTIGO outdoor demonstration: one based on single aperture and adaptive optics and the other one based on a telescope array implementing aperture diversity. An evaluation of the expected perturbations and corrections performance experienced on outdoor demo Line of Sight was realized. In parallel, work was started on coding topic taking into account optical free-space propagation channel to find a relevant error correction algorithm.
Finally, exchanges were engaged with outdoor demonstration sites responsibles to initiate necessary interactions to deploy for the test campaign of the project the different parts of the demo (ground stations, space terminal emulator,…).
During this past period, progress beyond the current state of the art of space-ground optical links was initiated on the different topics addressed within VERTIGO: the preliminary design of all key building blocks was achieved aiming at the implementation of more advanced waveforms than implemented in recent demonstrations, the development of incomparable high optical power generation means compatible of telecom signal transmission and the development of ground stations together with opto-mechanical and digital atmospheric impairments mitigation techniques. Discussions on implementation of the demonstrations and related issues were also engaged with the different stakeholders to progress on the demonstrations definition. Through the two foreseen demonstrations, the different key building blocks required to implement an operational feeder link will be tested in different combination configurations in order to evaluate the achievable performance in a full-scale operational system.
This unprecedented combination of concepts will result in leading-edge system solutions. VERTIGO ambitions to pave the way towards very high throughput satellite systems (and thus to contribute to bridge the digital divide) and contribute to maintain EU technological leading edge and industry competitiveness.
This unprecedented combination of concepts will result in leading-edge system solutions. VERTIGO ambitions to pave the way towards very high throughput satellite systems (and thus to contribute to bridge the digital divide) and contribute to maintain EU technological leading edge and industry competitiveness.