Multi GNSS Reference Station

GSTP: Make Project: Multi GNSS Reference Station

 

Company	Country	Website
Capgemini Technology Services (Prime Contractor)	France	http://www.capgemini.com
OMP	Belgium	http://orbanmicrowave.com

The Multi GNSS Reference Station prototyped during GSTP project is a multi-constellation station, notably capable of receiving new GPS L5 and Galileo E1/E5a signals. 

The Multi GNSS Reference Station is a sustainable and performing solution permitting to cover future technological challenges in terms of Signal-In-Space tracking capacity and robustness to environmental perturbations, such as interferences and multipath.

The Station is based on Hardware COTS equipment, inherited from past GNSS and SBAS programs, so to take advantage of the most cost-effective and proven existing solutions.

Objectives

Based on Capgemini experience accumulated during past projects on GNSS Systems and SBAS Programs, the development of a Multi GNSS Reference Station (MGRS) Prototype is proposed in the frame of GSTP 6.2 Program. 

The MGRS station is a sustainable and performing solution permitting to cover future technological challenges in terms of Signal-In-Space acquisition and tracking capacity and robustness to environmental perturbations, such as interferences or multipath. The MGRS station is a multi-constellation station, notably capable of receiving new GPS L5 and Galileo E1 and E5a signals.

The objective of the GSTP 6.2 project is to propose a Prototype MGRS station based on selected COTS equipment and to demonstrate the compliance of these equipment with regards to stringent performance specifications associated to DFMC SBAS context. 

Features

The Multi GNSS Reference Station is made up of multiple COTS elements: 

• The Core Computer: it monitors and controls the subsystem equipment and brings support for software maintenance and test.
  The Core Computer also handles the data communication inside of the system as well as the reception of the GPS/Galileo/GEO measurements and navigation messages from the Receiver and elaboration of the Raw measurements for external computational entities. Moreover, it computes the GNSS robustness metrics and indicators, permitting to ensure the validity of the measurements obtained by the Receiver.
  The Core Computer proposed for the Station is the Safety Critical Computer Framework (S2CF), produced by Capgemini.

• The Receiver: it collects and acquires the satellite signals at RF level, and consequently provides Navigation Data and computes Raw measurements for each tracked satellite and each observed signal.
  The Receiver also provides System time synchronization (1PPS) based on frequency standard reference.
  The receiver selected for the Station is the COTS NovAtel GIII Receiver. 

• The Antenna Set: it is in charge of filtering and amplifying the SIS signal. The antenna converts the received signal in space to an RF signal acceptable for the Receiver. The key attributes of the Antenna Set are its gain across the coverage volume and frequency, a stable phase centre, a good rejection of out of band interferences and of multi path.
  The Antenna selected for the MGRS station has been designed and manufactured by Orban Microwave Products, based on their experience and knowledge in the GNSS domain. To meet the requirements, main efforts have been made on the design of the radiating element and of the low noise preamplifier. 

• The Cabinet and other COTS Elements: they are inherited from EGNOS RIMSD2 project. The solution is based on COTS products available on the market.

Project Plan

The first main part of GSTP Phase 1 project activities focused on the definition and the running of specific characterization tests so to determine the performances of the reception chain elements (including Receiver and Antenna) to the technical specification. This technical specification has been agreed at the beginning of GSTP Phase 1.

Tests have been conducted on GPS, Galileo and GEO constellations. Particular attention has been given to the performances of tracking GPS L5, Galileo E1 and Galileo E5a signals, since they have been tested and characterized for the first time, in opposition to GPS L1 C/A and GEO L1 signals that had been characterized during EGNOS RIMS-D2 project. The Prototype has been tested through laboratory GNSS simulation tests, emulating the specified environmental conditions, as interferences and multipath perturbations. Some tests have been performed with both Receiver and Antenna active part, for performances involving both Receiver and Antenna contributions. 

At the end of the characterization phase, a detailed analysis of the results has been performed, augmented by a specific work on the definition of improvements realizable at each element level so to reach the best performances for the global solution.

Another part of the GSTP Phase 1 activities was the follow-up of the design of the Antenna, namely of the radiating element and of the low noise preamplifier.

The GSTP Phase 1 ends by a Preliminary Design Review (PDR).

Key issues

Due to the novelty of this Multi Constellation Reference Station, a few challenges were to be faced.

The highly stringent performances and robustness expected for this MGRS station led to adaptations and specific modifications on different elements of the station, namely the Antenna and the Receiver software. As a result, the Station comported multiple new or prototyped elements, tested for the first time during this project.

Concerning the Antenna, the specifications of the radiating element and the pre-amplifier required a compromise between robustness to multipath and signal acquisition at low elevation angle. In fact, requirements ask for both a low directivity antenna with a good 5° elevation gain and a steep roll-off for low elevation gains.
As for the Receiver, the software used is a prototype especially developed to track Galileo signals. This software has been developed in advance for FAA needs, and not especially in the frame of GSTP project.

The lack of hindsight and testing on Galileo signals represents a significant issue for this project. Few observations and studies have been made on this constellation outside of the GSTP project, meaning that it is difficult to compare results with existing articles and researches.

Expected Main Benefits

The Multi GNSS Reference Station represents an innovative solution, covering the main technical and programmatic challenges of future GNSS, in particular for DFMC Systems involving new signals as GPS L5, Galileo E1 and Galileo E5a.

As a consequence, the possibility to acquired and track new GPS L5 and Galileo E1 and E5a signals is an advantageous capacity. As a result, a deepened knowledge of GPS L5 and Galileo E1/E5a signals has been acquired, as well as a better understanding of the behavior and performances of the COTS Receiver and Antenna when facing these new signals.

Moreover, the use of COTS elements brings a few benefits. First, it brings flexibility and agility, as the design, development and industrial phases can be done quickly and with limited effort. Also, Capgemini is able to add new constellations more easily thanks to expendability features of selected COTS products.

Second, Capgemini acts as a Reference Station integrator, providing the Core Computer (built with S2CF generic component), and procuring and integrating COTS Receiver and Antenna. Capgemini is thus able to provide a prototype, and step after, industrialized recurrent units at a competitive level of price.

Current Status (30/8/2018)

Phase 1 of GSTP project has ended, with all characterization tests conducted :

• TC-0001: SIS acquisition for rising satellite
• TC-0002: Satellite re-acquisition time
• TC-0003: GEO Satellite acquisition time
• TC-0004: Code and carrier error due to multipath
• TC-0005: Inter-system bias differences
• TC-0006: C/N  Accuracy
• TC-0007: Code and carrier error due to noise
• TC-0008: Maximum differential group delay
• TC-0009: Live data observation
• TC-0010: Receiver data latency

Note that some tests (TC-0005, TC-0008 and some of TC-0007 tests) have been conducted with the antenna active part in the testbed so to take into account its contribution.

The activities of performances characterization showed that the Reception Chain (involving Receiver and Antenna) proposed for the MGRS Station has globally good performances in terms of acquisition and tracking of GNSS signals.

Concerning receiver, the prototype software allowing to track Galileo signals showed good results as no bug has been encountered during the characterization tests phase.

Contacts

Project Manager:	Anne Lavielle	anne.lavielle@capgemini.com
	TECHNOCITE – Bât. Astria 5, rue Joseph Szydlowski 64185 Bayonne Cedex France	Capgemini Technology Services
	Phone: +33 5 33 78 33 31	Fax: +33 5 33 78 33 01
Additional Contact:	Olivier Sabaloue	olivier.sabaloue@capgemini.com
	TECHNOCITE – Bât. Astria 5, rue Joseph Szydlowski 64185 Bayonne Cedex France	Capgemini Technology Services
	Phone: +33 5 33 78 33 62	Fax: +33 5 33 78 33 01
ESA Technical Officers:	Rui Sarnadas Paolo Crosta