A reliable, versatile and intelligent datalink system (IDS)-the key for any real-time differential GPS application

Real-time positioning with differential GPS (DGPS) techniques results in an enormous spread of accuracies from 110 m (SPS) down to the cm-level. The realization of this ultimate accuracy has progressed very well in the past few years. Several solutions have been presented with test results and it seems that this outstanding measurement technique with GPS will be state-of-the-art very soon. The characteristic feature of all local real-time DGPS applications is a terrestrial datalink. For the design of universal and reliable telemetry, common usage is to define the desired accuracy and so the required speed of data transmission. Then a frequency must be found on which interference-free data transport is possible. Finally, a suitable modem for modulating the data is necessary. The drawback of this procedure for developing a datalink is that it is not flexible and baud rate or other specifications are not easy to change when further developments occur. A universal, intelligent datalink system (IDS) has therefore been developed. The IDS is not limited to GPS applications, but can also be used to up- and downlink several types of surveying measurement data. The paper discusses the system configuration, development strategies, and presents the results of different applications of IDS. One application shows the use of DGPS to navigate a vessel along predefined profiles on the River Danube. Another example is the DGPS reference station Vienna, which includes data transmission by cellular telephone. Additionally, the use of IDS for real-time surveying the accuracies to within a centimeter is discussed