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Upgrades to monitoring stations support EGNOS

May 29, 2017  - By

Upgrades to the monitoring stations underpinning Europe’s EGNOS satnav augmentation system will support its evolution, said the European Space Agency.

The current 40 Ranging and Integrity Monitoring Stations (RIMS) sites across Europe and beyond are the bedrock of the European Geostationary Navigation Overlay Service (EGNOS), supplying highly accurate and robust satnav information that can be relied on for safety-critical purposes.

Thales EGNOS V3 RIMS rack.

Once a second, these stations gather raw satnav data to transmit information on signal quality and range measurements to the GPS satellites, allowing EGNOS to identify and remove any error in the signals.

The resulting corrections are then passed to users via a trio of geostationary satellites, delivering a several-fold increase in precision plus “integrity” — a guarantee of navigation service — for safety-of-life applications.

The result is that the EGNOS-augmented signals are guaranteed to meet the extremely high performance standards set out by the International Civil Aviation Organisation standard, adapted for Europe by Eurocontrol, the European Organisation for the Safety of Air Navigation.

The signals from space can therefore be relied on routinely for safety-critical tasks, such as vertically guiding aircraft during landing approaches.

“These current RIMS V2 stations have some inherent limitations, which we’ve sought to tackle in this upgraded V3 design,” said Didier Flament, ESA’s EGNOS programme manager.

Airbus EGNOS V3 RIMS rack.

“For instance, our current stations work only with GPS frequencies L1/L2 P(Y), while the future post-2020 EGNOS system will be operating on a multi-constellation basis, additionally employing modernized GPS signals, notably on both the L2 (L2C) and L5 frequency bands, as well as other signals from Galileo, on the similar E1 and E5 frequency bands.

“Our experience working with RIMS has emphasized the significance on performance of factors such as signal scintillation — caused by the ever-changing ionosphere, the electrically active layer of the upper atmosphere — as well as other environmental threats such as interference and multipath signal reflection.

“So this upgraded design increased robustness to these factors, based on more stringent development and operating standards, along with innovative radio-frequency environment monitoring.

“It also includes upgraded receiver technology to accurately monitor potential GPS and Galileo signal distortion — ‘evil waveform’ signal anomalies — in full compliance with international standards.”

The RIMS V3 stations will be based in the same or similar secure location as today’s stations — typically airports or space-based telecommunication sites.

Dual tracking antenna concept incorporated in EGNOS V3 RIMS design.

The individual RIMS antennas themselves can be relatively compact, about 50 cm high, with links to receiver and computing equipment.

Most of the RIMS V2 station antennas are currently surrounded by dedicated protection structures that limit the impact of interference and multipath local effects.