Objectives Due to the generally lower quality of observation data from low-cost receivers, primarily characterized by a high occurrence rate of gross errors and frequent cycle slips in the measurements, fixing ambiguities for precise point positioning (PPP) is difficult. Furthermore, the positioning process often experiences repeated reconvergence. To improve the positioning accuracy and convergence speed of low-cost global navigation satellite system (GNSS) receivers, an improved IGG (Institute of Geodesy and Geophysics) Ⅲ robust model is proposed.

Methods The observation data quality of two low-cost GNSS receivers is analyzed in detail, and the SinoGNSS receiver is selected as the research object accordingly. An improved IGG Ⅲ robust model suitable for low-cost receivers is developed based on the classical IGG Ⅲ robust model. The proposed model uses Kalman filtering post-fit residuals to further analyze the quality of observations involved in the solution, and combines cycle slip identification results for outlier identification. PPP with ambiguity resolution (PPP-AR) experiments are performed with static data collected by the SinoGNSS receiver in different observation environments, and the model's improved performance is analyzed in terms of positioning accuracy and convergence characteristics.

Results Experimental verification confirms that the improved IGG Ⅲ robust model significantly enhances horizontal positioning accuracy in open-sky environments. Compared with the classical model, it achieves notable accuracy gains for single-system PPP-AR: The positioning accuracy in the east and north directions is increased by 16.81% and 38.33% respectively for global positioning system (GPS) single-system PPP-AR, by 5.61% and 1.39% respectively for BeiDou satellite navigation system (BDS) single-system PPP-AR, and by 11.46% and 35.75% respectively for GPS+BDS dual-system PPP-AR. In occluded environments, the improved IGG Ⅲ robust model also achieves significant positioning accuracy gains over the classical model. For single-system and dual-system PPP-AR, the positioning accuracy in the east, north, and up directions is increased as follows: by 11.23%, 2.65%, and 23.14% for GPS single-system PPP-AR, by 14.96%, 12.35%, and 5.76% for BDS single-system PPP-AR, and by 12.52%, 21.15%, and 8.21% for GPS+BDS dual-system PPP-AR, respectively.

Conclusions The improved IGG Ⅲ robust model outperforms the classical model in positioning accuracy and ambiguity resolution performance. It delivers reliable performance in both open-sky and occluded environments, and significantly enhances the robustness of single-system and dual-system PPP-AR solutions. Its convergence performance is comparable to the classical model in open-sky environments, while exhibiting notable advantages in occluded environments.