Investigating the Accuracy of Code Based DGNSS as a Function of Correction Data Age, Baseline Length, and Ionospheric Activity

Stand-alone Global Navigation Satellite System (GNSS) receivers often lack sufficient accuracy for high-precision applications, leading to the use of Differential GNSS (DGNSS) to improve accuracy. This is vital in aviation and maritime navigation. However, challenges arise in applications where continuous correction data transmission is impractical due to limited connectivity or power. In addition, the distance from reference stations and the age of correction data can lead to pseudorange error decorrelation, affecting positioning accuracy. Understanding these factors is crucial to optimizing DGNSS in situations with limited real-time data or distant reference stations. This study analyzed the effects of baseline length and correction data age on positioning accuracy using data from the Automatic GNSS network Switzerland (AGNES). It considered 28 Local Area DGNSS (LADGNSS) networks with baselines ranging from 20 km to 250 km, assessing absolute positioning errors at three levels of ionospheric activity and correction data ages up to 1 h. The software RTKLIB was used for DGNSS position calculations and to compare results with standard Pseudorange (PR) error estimation methods. The study found that with short baselines and current correction data, an accuracy (CEP50) of 15 cm is achievable regardless of ionospheric activity. Under low ionospheric conditions, baseline length has minimal impact, maintaining a CEP50 of 33 cm even with a baseline of 250 km. Corrections less than 14 min old consistently yielded sub-meter accuracy for baselines up to 100 km and nominal ionospheric activities. During high ionospheric activity, baseline length and corrections age significantly affect accuracy. The study concludes that sub-meter accuracy is attainable even under high ionospheric conditions without close proximity to the base station and with slightly outdated correction data, which outperforms all considered stand-alone positioning approaches.