Monitoring the System State
The simultaneous adjustment and complete modeling of multi-station observations allows the determination of orbit errors, ionospheric and tropospheric delays as well as the reduction of multipath effects. Antenna phase center variations (PCV) are corrected by using calibrated antennas. This enables the use of different antenna types within a network. Beside the above mentioned state parameters GNSMART contains a complete model for satellite receiver clocks. This allows GNSMART to completely model the absolute state of the system with carrier phase accuracy. Through this, future requirements can be fulfilled in an optimal sense (expansion to regional and global networks, higher accuracy or new applications).
Due to the complete system model of GNSMART, there is no restriction in network size; i.e. in general, GNSMART can be used for global, regional and local applications. There is no limit for the number of stations within a network. For sufficient redundancy, the minimum number of stations within a network should be five. If a high number of stations (e.g. 50) are processed, the computation can easily be splitted to multiple computers.
The bigger the number of stations within a network is, the longer the distances between the stations can be. As an example, if for a 5 station network the distances are between 50 and 70 kilometers, it is possible for the same accuracy requirements to have more than 100 kilometer distances for a 15 station network. With reduced requirements, especially for the initialization time, even longer distances are possible (GNSMART sparse network). With reduced requirements, especially for the initialization time, even longer distances are possible (GNSMART sparse network).
Central or Decentral Concept
Networks may be organized in an central or decentral way. In the central configuration all observations are simultaneously processed in an computing center. The software module GNREF can be configured to run at the remote reference station or in the computing center. The decentral configuration allows the estimation of state information on every reference station utilizing the observation of neighboring stations. Any mixture of central an decentral concept is possible.
Data transmission within a GNSMART network is managed by GNCOM. Different media like computer networks (TCP/IP, NetBios), modem lines (ISDN, GSM) and broadcast radio can be used. The primary concept of GNSMART utilizes a broadcast signal, which allows GNSMART to work with simplex communication media. This is one main advantage over systems relying on duplex communication links.
Reference information can be made available to the user through the following accepted international standardized interfaces:
The additional information from the network processing may be supplied as FKP or VRS. Due to the complete state model, GNSMART is capable of supporting future standard definitions, since the data content of such techniques can be derived from the state vector. Communication to the user is performed through the same media as within the network. The advantage of broadcasting information through radio, DAB or Internet is available. The data signals may be encrypted for charging and access control. Additionally the communication with a rover is conducted with SMARTgate. SMARTgate integrates access control and charging functionality, besides automatic connection features and fallback options to different media.
Geo++ GNSMART rigorously supports the different currently used formats for Real-Time Network applications. These are the termed concepts
- FKP (“Flächenkorrekturparameter”, areal correction parameter)
- MAC (Master Auxiliary Concept)
- VRS (Virtual Reference Station)
In addition to these concepts Geo++ GNSMART provides flexible features, extensions and improvements to further enhance and adjust the functionality for any given application.
The GNSMART System
The components of GNSMART (with details of corresponding Geo++® products) are as follows: