The biggest problem encountered in the application of RTK technology is the effective range of reference station calibration data. The spatial correlation of GPS errors gradually loses linearity as the distance between the reference station and the mobile station increases. Therefore, at longer distances (single frequency>10km, dual frequency>30km), the user data after differential processing still contains significant observation errors, leading to a decrease in positioning accuracy and the inability to solve the integer ambiguity of carrier phase. So, in order to ensure satisfactory positioning accuracy, the operating distance of traditional single machine RTK is very limited.

　　In order to overcome the shortcomings of traditional RTK technology, network RTK technology was proposed in the mid-1990s. In network RTK technology, the linear attenuation single point GPS error model is replaced by the regional GPS network error model, which estimates the GPS error model of a region using a GPS network composed of multiple reference stations and provides correction data for users in the network coverage area. What users receive is not the observation data of an actual reference station, but the data of a Virtual Reference Station, and the correction data of a reference grid that is close to their own location. Therefore, network RTK technology is also called Virtual Reference Station technology.

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