Fast ambiguity resolution for long-range reference station networks with ionospheric model constraint method

Ambiguity resolution (AR) speed is one of the most important performance indicators of a network RTK (real-time kinematics) system. Given the low correlation between the error sources of two stations, the effect of the atmospheric delay of double-difference observations cannot be ignored, thus making it difficult to fix the ambiguities. Ionospheric delay is one of the largest error sources affecting AR. This error source is reduced by the ionospheric-free combination with traditional methods. The AR speed of these methods is slow; generally, tens of minutes and even more are required for initialization. This study proposes an ionospheric model constraint (IMC) method to improve the AR speed. External information is not required apart from observations. The double-difference ionospheric delay is described with a regional double-difference ionospheric model, the coefficients of which are estimated as parameters together with ambiguities and tropospheric delays. Experimental results show that the initialization speed significantly improves by 72.5 % and that the AR speed for the newly risen satellites increases by 84.3 % with the proposed IMC method. Furthermore, the percentage of correctly fixed integer ambiguities after initialization increases to some extent.