Any position on the Earth’s surface can be determined by measuring the distance to a group of satellites.
Specialised navigation satellites continuously send their position to Earth to measure this distance. From the time the satellite signals need to cover the distance to Earth the distance to a measuring point can be derived. From the distance to at least three satellites the wanted position can be calculated. However, coordinates determined in this manner may be off the true position by two to twenty meters. The inaccuracy results from satellite signal errors as a result of technical imperfections and outer influences.
The ascos service can be used all across Germany with positioning receivers from all recognized manufacturers.
To determine positions by using ascos you will need a positioning receiver, the so-called rover, and a mobile radio communication device. In most cases the communication device will be a mobile phone, or a modem equipped with a mobile radio card. The rover receives the navigation satellite signals. Via mobile radio communication the rover will transmit its initially approximate position to the ascos computation centre. The rover-data will be compared to data of ascos reference stations surrounding the rover. The exact position of these base stations is known, and the deviation between the satellite signal and the true base station location can be computed.
The results of this calculation are the so-called area correction parameters (Flächenkorrekturparameter, FKP). With intervals of a second the computation centre transmits updated area correction parameters back to the rover. The rover uses this information for a corrected determination of its precise position.
The ascos service is based on reference stations owned by the provider of the service, AXIO-NET, as well as on SAPOS®-reference stations.
ascos reference stations are set up in secure locations and guarantee availability 24 hours a day, seven days a week. High-performance, professional dual-frequency GPS and GLONASS receivers and antennas are permanently installed at reference stations. Full-time reference station availability is backed through uninterrupted power supply (UPS) devices at each station. The entire installation is protected against lightning.
ascos uses signals provided by American GPS and Russian GLONASS navigation satellites.
The ascos network provides correction data for both satellite systems. By using both GPS and GLONASS, satellite signal availability is greatly enhanced even in difficult locations.
As soon as the first satellite signals of the proposed European system Galileo will be available, ascos will also provide Galileo correction data.
Data transmission between rover positioning systems and ascos is carried out in GSM standard which is also used in mobile telephone communication, or in GPRS.
Maximum availability of the service is secured by using mobile telephone networks. Upon calling ascos via GSM, users transmit their current position to the computation centre in standardised NMEA format, compatible to the older RTCM2.0 format.
The networking software uses ascos reference station data to form correction models.
From these models, Virtual Reference Stations (VRS) are calculated for the approximate position transmitted by the user. In addition, area correction parameters (Flächenkorrekturparameter, FKP) are determined. Systematic sources of error are almost completely removed by these correction models. The computation process of a VRS is run individually for every ascos user. The global FKP can be individualised for the position of every rover by the receiver device.