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Simultaneous Sending of RTCM and Binary GPS Corrections
Thales-Ashtech GPS reference stations, which are used in GPS survey systems, are developed to generate differential corrections for remote GPS receivers at two formats. First of them is RTCM format, which is generally accepted by most of GPS survey receivers. Second is Ashtech binary format (RZ binary), which is used only by Thales-Ashtech GPS receivers. It's more noise resistant during transmission, and works faster.
Thales-Ashtech GPS reference stations are equipped in four RS232 serial ports. Simultaneous sending both of them is possible only thru two different ports. Moreover, both data frames start at this same moment. With this solution there is no possibility to send both corrections with one radio-modem (on this same frequency).
Solution for this problem is development special additional equipment, which receive both frames (from two ports) and send them thru one port multiplexed in time. This solution allows sending duly composed frames with one radio-modem at one frequency.
GPS receivers locate in radio range of reference station, connected with radio-modem tune up to base frequency, receive both corrections and automatically choice the correction accurate to working mode.
Another inconvenience connected with radio-modems is limited radio range caused by distance, terrain obstacle ect. That's why presented system was equipped with digital repeater device.
There was no possibility to simultaneous receiving and sending data at this same frequency. Digital repeater is responsible for receiving data, buffering and sending after define period.
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