ALLSAT GeoBase
The GSM-Controller, a product of ALLSAT GmbH in Hanover, can be regarded as a new and efficient solution to send DGPS differential corrections via mobile phones (GSM). The integrated GSM module enables you to send DGPS differential corrections via the RS232 port within the GSM net. The GSM-Controller works without an external PC; the unit configures itself! Consequently, the GSM-Controller is suitable for the stand-alone use to send RTCM differential corrections. The automatic switching from radio to GSM resulting in minimum telephone charges is unique. The choice of the correction carrier is done in the field with the GPS rover.
It consists of the following components:
Operation mode
The GSM-Controller works without an external PC. The input port is connected via the serial port to a data output device, e.g. a GPS receiver. Without an incoming call the DGPS data are directly passed on to the RS-232 data port, which can be connected to a radio modem. Once a GSM connection is set up the GSM-Controller automatically sends the differential corrections to the rover receiver and stops the data output to the radio modem at the same time. After the 'CONNECT' a permanent green light of the LED shows that an active data connection to the GSM handy of the rover is set up. If the data connection is stopped by the rover the DGPS data are again passed on to the radio modem. The GSM-Controller is now in a stand-by position. After an automatic re-initialisation (30 sec) a new GSM connection can be set up.
Status of the Controller
At the front side of the GSM-Controller there are two diodes showing the current working state of the micro controller and the GSM module. During the initialisation the green LED flashes at 1-second interval for one minute. After the initialisation is completed the red LED flashes at 10-second interval, which shows that the GSM-Controller works correctly. An occurring error during the initialisation (e.g. a wrong PIN) is shown by a permanent light of the red LED and the whole process is automatically repeated after 5 seconds. If the installation and the initialisation are done correctly the GSM-Controller automatically controls the data connection to the user. After the 'CONNECT' a permanent light of the green LED shows that an active data connection to the GSM handy of the rover is set up.
Configuration of the GPS receiver
The GPS receivers have to be initialised for the transmission of DGPS correction data. You can read up the respective orders in the reference manual. To configure the serial port enter the following parameters:
- Baud rate: 9600
- Data bits: 8
- Parity: no
- Stop bits: 1
- Protocol: no
Most of the GPS receivers are set by default to a baud rate of 4800 bps or 9600 bps. In the GSM net there is only a baud rate of 9600 bps possible. For this reason, you have to use a GPS receiver which can be set to a baud rate of 9600 bps.
Configuration of the GSM-Modems at the Rover
To dial you can either use a GSM handy and dial manually or preferably use a Siemens M20 GSM-modem with our controller software GART-2000. The setup of the GSM handy is described in the reference manual.
