On the Influence of Different Network Correction Formats on Network RTK Performance

A large variety of countries all over the world have established GPS reference station networks in the last years and are using network software today to provide a correction stream to the user as a routine service. These data streams are corrected for regional atmospheric effects, orbit errors and other systematic effects derived from the network solution. Currently most of these installations are using the VRS (Virtual Reference Station) technique to transport the correction stream in form of RTCM 2.3, RTCM 3.0 or CMR from the server to the field user. The VRS technique requires bidirectional communication, which is available via GSM, GPRS and other cell phone based data transmission methods. While the VRS method is the most common technique used, the RTCM committee is currently discussing a network proposal for broadcast transmission of network corrections, which will be useful for radio systems and Internet based multicast solutions. The focus of the paper is on the characterization of the influence of different interpolation schemes and the ability to derive tropospheric and ionospheric models. In the VRS case these models and interpolation schemes are applied in the server while they are applied in the rover in the RTCM network format case. Advantages and disadvantages of both methods are presented. Other aspects discussed are the required bandwidth for the different formats, the influence of the network message update rates, the influence of the scheduling on the start- up of the RTK rover and the effect of different network shapes on the rover performance. The paper presents results of performance analyses performed to compare the VRS solution with the RTCM network solution in different networks. Accuracy, initialization performance and reliability of RTK systems working with the formats are compared to quantify the performance differences.