The EPOC: AALECS’s First Step
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, although an extension of the testing is under discussion.
The EPOC platform has one main objective, which is to demonstrate the CS capabilities in an early stage of the AALECS 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 communications links established between the EPOC and third parties and keeps the EPOC system as a black box.
First of all, the EPOC receives satellites orbit and clocks predictions for the desired testing period. Only for tests with SCE enabled, the operator receives the NavSec from GMS, stores it in the EPOC archive and installs it in the receiver. With this information the operator can generate the CsData files and send them to GMS. A GMS operator ingests the files in the system and the CsData uploading starts to the satellites connected to an Uplink Station. Automatically, the Galileo satellites broadcast the received data through the E6 signal and the receiver records it. Finally the EPOC operator launches the analysis tool to obtain the transmission metrics, authentication solution and PVT solution.
The system designed to accomplish this objective is composed of three independent hardware and software items: the CS Receiver, the RXP-Host and EPOC-Host.
The system objectives directly imply that the EPOC shall have a GNSS Receiver able to receive the Galileo E6 signal, perform E6 ranging (with and without spreading code encryption), and decode data from the E6-B channel. Tracking of E1, E5, L1, L2 and L5 signals is also required to retrieve navigation and observation data, authenticate the received information through the E6 and calculate a PVT solution. For this purpose, the selected receiver is based on the RXP developed in the frame of the AALECS project, concretely on an early version of this element developed by IFEN and GMV. This “EPOC-RXP” includes two independent hardware items, the NAVXNTR receiver and the RXP-Host connected through a LAN connection to ease the exchange of information. Both the hardware and software of the NAVX-NTR are designed and developed by IFEN.
The RXP-Host hosts the NtrTerm software in charge of commanding the NavxNtr receiver, and the RXP-Host SW, which includes an authentication client and a PVT client to process the received CsData together with the observations gathered for Galileo and GPS.
In order to ease the operation activities, the platform for the RXP-Host included in the EPOC is a laptop with a Linux operating system installed. The data exchange between the NAVX-NTR and the RXP-Host is performed via TCP/IP, having both elements connected to the same network (or via direct link).
The EPOC-Host hosts the Data Generator in charge of processing the High Accuracy data and generate the authentication information, the historical archive, where all the generated and received data is stored and the analysis tool. This tool is in charge of analyzing the data generated against the transmitted one and also generating a PDF report with the most relevant information.
With these elements the physical layout remains as follows:
The EPOC has introduced two novel capabilities in a civil GNSS system. The first one is the dissemination of high accuracy data able to be used by a Precise Point Positioning algorithm, and the second one is the generation and dissemination of authentication information able to check the authenticity at data-level of the received information.