EGNOS Future and Evolutions

EGNOS
Title	EGNOS Future and Evolutions
Author(s)	GMV.
Level	Basic
Year of Publication	2011

The European Space Agency (ESA) is currently completing the final qualification stages of the European Geostationary Navigation Overlay Service (EGNOS) and is in the process of developing the GALILEO system, a self-standing 30 satellite constellation for global satellite navigation. The European GNSS Evolution Program was defined in 2006 by ESA to address the second generation of these systems.

As part of the evolutions considered, three more RIMS are scheduled to be deployed in Agadir (Morrocco), Athens (Greece) and Alexandria (Egypt) providing the extension of EGNOS signal coverage to northern Africa.

Besides, processing improvements are scheduled for the EGNOS signal, including iono algorithm pre-processing fine tuning.

Finally, the deployment of EGNOS v3 is scheduled to cover the Multi-Constellation Regional System (MRS) concept and implement a GPS L5 augmentation service.

GNSS Evolution program FrameWork

As part of the GNSS Evolution program, ESA called for two parallel studies in the scope of a Multi-constellation Regional System (MRS), that is, the evolution of the EGNOS concept to cope within a multi-constellation environment (Galileo, GPS, others GNSS constellations), and a multi-frequency scenario (GPS L1, L5; Galileo L1, E5a, E5b, E6, etc..).

With this multi-constellation scenario, and with multiple frequencies available for navigation, the wide area regional augmentation systems must evolve and need to be adapted to this new behaviour. The next generation of the regional augmentation systems will not only be an adaptation of the architecture to the current state-of-art but also an important change of the concept. Considering only the new approach to the ground segment, this paper presents the alternative implementations of the integrity concepts, the different broadcast means and possible architectures analysed.

MRS mission is a natural evolution of a regional system, such as EGNOS, considering the advent of new constellations and new frequencies in the GNSS panorama. As GNSS modernisation plans are today under definition and other studies are assessing possible evolutions of GNSS systems beyond 2015, the MRS Study is focused on the 2012-2015 timeframe.

EGNOS Evolution Features

As a multi-constellation, multi-frequency and multi-broadcast system, the MRS system shall not only continue providing an SBAS service to L1 users but shall also cover GPS L5 and Galileo L1 and L5/E5 users. The system evolution considers different dissemination channels, including the SBAS GEO (Geostationary Earth Orbit) L1 and L5 channels, Galileo MEO (Medium Earth Orbit) ERIS (External Regional Integrity System) channels and other satellite or terrestrial means to be defined according to regional or user defined interests (e.g. SISNET, LORAN-C, etc).

The high level objectives defined by the Evolution program are the following:

• To maximize European ‘User’ Performance when combining EGNOS and Galileo infrastructures, allowing SoL service provision.
• To optimize cost of operation and infrastructure of both systems when combined in MRS, keeping independence of both systems and ensuring robustness against GNSS failures.
• To provide mainly an integrity service for safety of life aviation or liability critical applications.
• To provide regional GPS and Galileo integrity and continuity by using MRS and Galileo.
• Understood as a multi-constellation (GPS/GAL) multi-frequency (L1/E5) and multibroadcast (GEO, MEO and others) system, to provide a service assuming all combination of mono/multi constellation and mono/multi frequency users.
• To provide better availability of SBAS integrity for regions of poor GEO reception through additional Galileo ERIS MEO broadcast of integrity information or other means.
• To enhance ionosphere monitoring accuracy by adding Galileo observations or decrease number of RIMS.
• To broadcast new messages: Message Type 28 is one of the most solid candidates to be included a new message broadcast by EGNOS in future evolutions. This message contains matrices for two satellites per message, and each message is broadcast at the same rate as the long-term corrections (Message Type 25).

Benefits and New Services

Forthcoming constellation deployments (GALILEO, GLONASS M, COMPASS), combined with GPS, will enhance EGNOS performances as well as its robustness. Besides, they will allow the development of new services. These services have been studied in the frame of the MRS (Multi-constellation Regional Augmentation System) concept and include: Safety Of Life service (SOL), Open Services (OS), Liability Critical Services (LCS), Commercial Data Dissemination Services (CCDS), detailed below:

• Enhance User performances (SOL, aeronautical users): On the one hand, the existence of more signals belonging to new constellations will provide more information about the ionosphere and consequently better performances, specially under ionsopherically degraded conditions (forecast for the coming years http://science.nasa.gov/science-news/science-at-nasa/2006/10mar_stormwarning/). On the other hand, the provision of ionosphere measurements would reduce the number of RIMS required, lowering the cost of RIMS maintenance and reducing the EGNOS infrastructure cost.

Moreover, given the current SBAS standards that permit the augmentation of up to 51 satellites, the system could take advantage of the increasing number of constellations and satellites to provide increased continuity and availability with enhanced accuracy and higher navigation robustness to face signal blockages.

• New services (OS, LCS, CDDS): EGNOS Evolutions consider the provision of new services that may reach communities that can not benefit from current EGNOS signal due to environmental constraints. For this purpose the EGNOS system has studied to take the following steps:
  • Broadcast of EGNOS data through alternative channels.
  • Broadcast of new parameters.
  • Provision of authentication capabilities for Liability Critical Services (LCS).

System Architecture

Future EGNOS architecture shall be able to provide the new EGNOS features and services considered.

One important consideration when designing the EGNOS architecture is to define whether if EGNOS and Galileo should be independent. In this case, any event leading to a performance degradation in one of both systems shall not impact the other system performance and, in the event of such an ocurrence, switching from one system to the other would be feasible.

This consideration results in high level architecture designs that suggest:

• Dense collecting stations network.
• Hardware, Software and conception diversification (including monitoring stations, processing facilities and station networks).
• Mixed EGNOS communication channel (including GEO and MEO satellites).