Core technology for this is a real time capable network which was developed in cooperation with Jena-Optronik GmbH. This EVnet named network is in an operational status since October 2005. The acronym EVnet is derived from the tasks of the network as an experimental, development, and demonstration platform as well as for the verification of system properties of different GNSS via Internet. EVnet supports the transport and distribution of any type of data in real time from GNSS receiver and other sensors attached to GNSS sensor stations to the Central Processing and Control Facility (CPCF) as well as to the user over the Internet with broadcasting technologies. Furthermore data can be processed to multi level data and archived for later statistical analysis within the CPCF.
The EVnet structure is shown in Fig. 1. Core component is the CPCF. The operator can monitor the data flow and the generation of high grade data products as well as administrate the EVnet using command and control channels (C&C) between CPCF and sensor stations as well as the graphical operator interface (Fig. 2). This design allows a completely remote controlled operation of the EVnet and associated sensor stations. The data are transported between the different facilities using TCP/IP based streaming technology which support data transport in real time between sensor station and CPCF as well as between users (clients) and CPCF. Therefore the nearly world wide available Internet is the transport medium. With the scope of high flexibility EVnet is designed platform independent (Linux/Windows) in a modular way which supports an easy enhancement by additional data sources, devices, and navigation applications. The security of data transfer is ensured by standardized encryption technology and authentication mechanism with SSH (Secure SHell).
The Institute of Communication and Navigation started in 2002 building up a GNSS research network using EVnet technology. Over the years the network was expanded with the help domestic and foreign co-operation partners (Stanford University (USA), JAXA (Japan), SUPAERO (France), IRF (Sweden), ULL (Teneriffa/Spain), GSOC (Germany)). Today the research network has sensor stations on four continents (Fig. 3). The DLR in Neustrelitz where the central servers and the CPCF are placed is responsible for the maintenance of operation of the network.
All sensor stations are equipped with GNSS high rate data receivers (Topcon EGGD+, TOPCON Net-G3, Javad LGGD, Javad Delta G3T) which are capable to handle data rates up to 50 Hz. Some of the stations are additional equipped with meteorological sensors. Depending on the requirements for each sensor station it can be realised as master station with full remote capability and unbreakable power supply or in a simpler way as a “light” station with only one PC.
On the central processing facility real-time processors are developed and tested which can be used for the determination of signal quality (SISA) or for the retrieval of higher level data products (e.g. signal and position relevant information). As an example Fig. 4 shows the phase noise of one GPS satellite for L1 carrier frequency over time. In a second area of application these processors are arranged in project specific processor chains (e.g. complete local GBAS).
The DLR research network is the base for different projects in the areas of GBAS (ALEGRO, ASMS, FAGI), ionosphere monitoring (SWACI, PRIS) as well as derivation of specific measurement models within the scope of the development of new navigation algorithms (GalileoADAP).