AALECS – The CS Demonstrator

The European Commission launched the AALECS (Authentic and Accurate Location Experimentation with the Commercial Service) project in January 2014 aiming for the demonstration of the real performance of future high accuracy and authentication services of Galileo.

EPOC

The outcomes of the project are two different platforms. The first one was a test-bed ready by mid-2014 which was used to demonstrate the CS capabilities in an early stage of the project, the EPOC (Early Proof-Of-Concept). The EPOC platform allowed carrying out a first demonstration of the main functionalities (transmission, encryption, tracking, authentication and positioning) of the Commercial Service in an early stage of the project.

In order to perform this demonstration the EPOC shall be able to close the loop of E6 data from its generation to its reception. Next figure depicts the communication links established between the EPOC and third parties and keeps the EPOC system as a blackbox.

epoc dataflow

During the summer of 2014 the EPOC tested the E6 external data transmission. Given the unique opportunity to use the real CS signals and the flexibility provided by the platform, the European Commission and the AALECS team agreed to make the tests as realistic as possible within the limits of the architecture. This included the generation of high-accuracy satellite orbit and clock predictions and data authentication, both with and without the spreading code signals encrypted. The EPOC experimentation activities with real signals in space started in July and finished in late September.

 

CSDEMO

The second outcome has been the official Commercial Service demonstrator platform. It is composed by several specialized modules designed to generate CS data, containing Authentication and High Accuracy data supporting a wide range of configurations, and to connect to the European GNSS Service Centre (GSC) for the transmission of real time CS data through the Galileo satellites.

The complete CS Demonstrator platform is a composed by four main elements: CS Receiver (RXP), CS Provider Test-bed (PTB), CS Emulator (EMU) and Signal Generator (SG).

CSDemoArch

 

The RXP is a Galileo Commercial Service receiver capable of processing Galileo CS signals, E1B, E6B and E6C. The RXP is able to log data and to communicate in real time with the PTB. An Authentication Client and a PVT client are included in the RXP. The Authentication Client is able to receive the E6/E1 navigation data, verify its authenticity, detect spoofing attacks and also communicate with an authentication server to test assisted authentication solutions. The PVT client is in charge of providing a High Accuracy PVT based on magicPPP .

The PTB is a platform that can communicate with external CS Providers and to test CS data provision either offline or with the real SIS. The PTB is the core of the CS Demonstrator and is able to receive and process recorded RXP data, containing the data and measurements from receivers used as monitor stations, based on either real or simulated SIS. In addition, the PTB can receive and process real-time station data, that is, the navigation data and measurements received by other external receiving stations).

Within the PTB platform, the algorithm units that are in charge of producing the different Commercial Service data solutions, either Authentication or High Accuracy data, are called CS Data Generators (DATAGENs), based on the abovementioned processed data.

The PTB implements the interface with the GNSS Service Centre (GSC) V1, which will be the route to send CS data to the Galileo satellites, via the Galileo GMS. It can also store CS data in files to feed a Signal Simulator.

The CS Signal Generator and Threat Simulator is a platform able to generate Galileo signals including E6 CS signals, and allowing the test of a receiver under different user conditions and threats. The project makes use of a CS Signal Generator and Threat Simulator offered by the European Commission. This equipment is located in EC Joint Research Centre (JRC) facilities at Ispra (Italy). It is based on a Spirent GSS9000 simulator. The RXP is able to receive the real SIS from either Galileo satellites or other GNSS signals, including simulated signals.

The PTB is capable of processing the contact plan with a list of uplink station (ULS) connection time periods over the duration of each test scenario. This contact plan is generated by the EMU (Commercial System Emulator), manually by the operator or taken from the GSC. The EMU is a platform able to emulate the Galileo system uplink and downlink capabilities, bandwidth and latency. It can carry out service volume simulations both of the bandwidth and satellite availability.

The CS Demonstrator Platform supports four different modes:

  • Replay Mode: It allows testing the CS data algorithms under deterministic conditions by means of a file-based communications between elements
  • Real Time Offline Mode: In this mode the PTB runs as in Replay Mode, but the input monitor station data are received in real time instead of using the recorded files, allowing testing the real-time functionalities of the CS Demonstrator platform, except the interface with the GSC.
  • Advanced Replay Mode (ARM): It allows testing performances real SIS-like without broadcasting CS data through the SIS. This mode is the focus of this paper.
  • Real Time Offline with GSC: It allows the integration and testing of the CS Demonstrator with the Galileo GMS through the CSP-GSC (CS Provider – GNSS Service Centre) interface.
  • Real Time SIS Mode: It allows testing the performance and data broadcast capability in with real SIS.

The CS Demonstrator platform has been successfully tested with all the aforementioned modes during the experimentation phase since the beginning of 2016, except for the Real Time SIS mode.

During 2016, several tests designed to assess and analyze the Galileo Open Service Navigation Message Authentication (OS NMA) performances have been undertaken by taking advantage of the CS Demonstrator element, together with the Signal Generator and Threat Platform available at the JRC.

Data transmission and bandwidth availabilities analysis has been performed as well to characterize the service volume achievable by simulation of the Full Operational Capability (FOC) Galileo. Standalone tests using the CS Demonstrator have been carried out in order to understand the future conditions to be faced during the experimentation with real SIS.

The CS Demonstrator platform was accepted by the end of 2015, being ready for performing tests through the SIS in Real-Time SIS Mode through the GNSS Service Centre.However, the GSC deployment is foreseen by the beginning of 2017, which implied that no tests with real SIS could be performed until then.

Due to this limitation, and in order to be able of running tests with real SIS throughout 2016 with which to derive meaningful and realistic conclusions for helping the European Commission with the final definition of the Galileo Commercial Service, the ARM module has been designed and introduced in the experimentation schedule of the AALECS project and preliminary tests have been conducted through 2016.