ION GNSS 2012
Session B5: Next Generation GNSS Integrity

Title: The GATE Test Infrastructure and its Use for Galileo Integrity Tests to Support ESA`s European GNSS Evolution Programme
Author(s): E. Wittmann,T. Zink, G. Heinrichs, IFEN GmbH, Germany; D. Lekaim, H. Delfour, D. Joly, Thales Alenia Space, France; M. Jeannot, M. Tossaint, European Space Agency, The Netherlands
Date/Time: Friday, September 21, 2012, 11:03 a.m.
Room: 204 (NCC)

Over the past years GATE has become well known for being the only Galileo test and development range worldwide where already today - several years before the full operability of the Galileo system in space - navigation is possible with realistic Galileo signals on three frequencies simultaneously in an outdoor environment, located in Berchtesgaden in the southeast of the German Alps. Although relying on a ground based infrastructure, the certified GATE system is able to radiate the original navigation signals from eight "virtual" Galileo satellites, including simulation of natural influences like ionosphere or troposphere delays and adaptation of other signal characteristics as well as signal strength. Furthermore, GATE includes the capability to induce dedicated "Feared Events" and integrity alerts for one or several satellites of the current Galileo conªstellation simulated.

Thanks to these sophisticated features that are fully under GATE operator´s control, the test infrastructure allows for performing various individual integrity test scenarios including GPS and GATE/Galileo dual constellation RAIM as well as testing of receivers with (A)RAIM functionalities implemented. These test scenarios will support the European GNSS Evolution Programme (EGEP), which is an ESA programme to undertake research and development in and verification of technologies relating to regional space-based augmentation systems (SBAS) and global navigation satellite systems (GNSS). The implementation of EGEP is done, amongst others, by EGEP test beds providing operational support to experimentation and demonstration campaigns, like the "High Integrity Safety critical regional augmentation Test-Bed" (HISTB) and the Multi-Constellation Regional System Land Users Test-Bed (MLUTB). The main objective of these experimentations is to provide technical elements allowing to determine if the EGNOS V3 foreseen new features are feasible and of interest.

The aim of HISTB is to facilitate the running of experiments and use cases relating to high-integrity aeronautical performance using e.g. SBAS data. HISTB will utilize a modernized SPEED (Support Platform for EGNOS Evolutions and Demonstrations) platform enhanced in the frame of the EGEP activity. The GATE infrastructure will serve here as a test environment for HISTB for several use cases identified for integrity related aeronautical test scenarios.

In the HISTB context, one main test objective is to assess the augmentation performance improvements for GPS/Galileo bi-frequency/bi-constellation SBAS user processing. For this reason the SPEED platform will provide GPS/Galileo augmentation message types (MT) to GATE, including live GPS bi-frequency correction data. GATE will augment the Galileo part of the MT SBAS data with live calculated GATE clock corrections. The complete live SBAS data stream will then be transmitted as GNSS SIS signal to the GATE user via a GATE local GEO-like dissemination signal on L1, implemented on two GATE transmitting stations. Test campaigns undertaken for HISTB will be performed as static open sky tests at locations with good and un-shadowed visibility to all eight GATE transmitting stations and using real helicopter test flights in the GATE test bed of Berchtesgaden.

A further test scenario of HISTB will be to assess the detection capabilities of new integrity concepts like the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) user algorithm under satellite feared event (FE) conditions. For this purpose the GATE processing facility, which can be considered as the "heart" of the GATE system, will be modified to generate sophisticated clock feared events, allowing to manipulate pseudoranges of the GATE signals transmitted according to realistic error scenarios, like e.g. the GPS PRN 30 clock drift event in June 2006. Although GATE was not designed to simulate/validate a real integrity environment (system integrity risks, hazardous misleading information HMI etc.) of a satellite navigation system like Galileo, GATE can be used to calculate integrity performance parameters like horizontal/vertical protection and alert limits for the ARAIM scenarios identified. As GATE will be capable to initiate FEs for different fault scenarios like single fault on single frequency (E1 or E5a) or multiple faults on dual/multiple frequencies (e.g. E1 and E5a), the paper will present preliminary results of the fault detection and exclusion capabilities of the implemented ARAIM.

To execute the GATE HISTB tests as mentioned above, a special test receiver called GATE Test User Receiver will be used, which was developed by IFEN. It is a multi-frequency/multi-constellation GNSS receiver, capable of MOPS D EGNOS user processing and with bi-frequency SBAS (L1/L5 or L1/L2) and ARAIM functionality.

With respect to MLUTB, this EGEP test bed shall investigate, develop and demonstrate two possible future services, the Proof-Of-Position Service (POPS) and the Emergency Service (ES). POPS is for non-safety-of-life users, e.g. road users in urban or sub-urban environments, which still require some level of integrity, with relaxed integrity risk, relaxed time-to-alarm but possibly reduced horizontal alarm limits. GATE will serve for MLUTB as a POPS test environment for road test scenarios in sub-urban environments with increased levels of multipath and shadowing effects. MLUTB will provide to GATE GPS/Galileo integrity/augmentation data, incorporated into the I/NAV messages of E1 and E5b, which will be transmitted via the GATE GEO-like dissemination channel to the GATE user in the test bed.

Distinctive test campaigns for HISTB and MLUTB in GATE will be performed in summer and autumn 2012.

The paper will provide an overview of the GATE infrastructure and its segment design, its functionalities as well as to the design and implementation upgrades done in the framework of HISTB and MLUTB. A description of the test set-up and execution will be given also considering the dedicated test cases that have been identified for the EGEP test campaigns.

Furthermore, the paper will present results of RAIM user integrity tests undertaken in the upgraded GATE test range with eight transmit stations as well as including preliminary results on the experimentations performed for HISTB and MLUTB.

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