## 4 Results  
According to the principle described in Section 4, the regional ionospheric delay model is established by using the real-time observations of four CORS in Nanjing area, and the update interval of the model is 5 s. Smartphone obtains the model data in real-time for positioning experiments. The real-time ionospheric modeling process is as shown in Figure 5 and the descriptions of steps are as follows:  
1. Receive real-time dual-frequency observations and navigation messages from CORS, and perform data preprocessing;
2. Smooth the ionospheric observations and calculate the latitude and longitude of the pierce point;
3. The observation vector of all CORS in a single-epoch is used to form an observation vector to construct an observation equation; the Kalman filter is used to filter the parameters in real-time to obtain a regional ionospheric model. GIM products have good applicability, and the post-processing GIM data can eliminate 80% of the ionospheric delay error. Therefore, this article regards the post-processing GIM file published by CODE as a standard. The Klobuchar model and the regional ionospheric model are used to calculate the ionospheric delay and electron content at the pierce point, and compare them with the standard to calculate the residuals of each satellite, as shown in Figures 6 and 7. Figure 5: The flow chart of real-time regional ionospheric model. As shown in Figure 7, the results of the Klobuchar remain basically unchanged during the experiment, and the results of the regional ionospheric model are changed with time slowly. In addition, the accuracy of the regional ionospheric model is less than 5 TECU for each system, and the error of the electron content calculated by the Klobuchar model is 5-10 TECU. It can be concluded that the regional ionospheric model can accurately reflect the ionospheric TEC distribution and its changes by comparing the results of the two models. Since the dual-frequency GNSS observations received by the smartphone are fewer and the quality is poor, the single-frequency data is selected for the ionospheric delay analysis. It can be seen from Figure 7 that the ionospheric correction error calculated by the Klobuchar model is about 5 m, and some satellites reach 10 m, while the error calculated by the regional ionospheric correction model is maintained at about 1 m. It can be found the regional ionospheric model can calculate the ionospheric delay correction more accurately. Figure 6: Electron content error at the pierce point. (**a**) Regional ionospheric model; (**b**) Klobuchar model. Figure 7: The RMS of ionospheric delay correction of the Klobuchar and the regional ionospheric model. Based on the above analysis, it can be considered that the regional ionospheric model has higher accuracy than the Klobuchar model. To verify the influence of the regional ionospheric model on the positioning results of smartphones, this article uses Xiaomi 8 B smartphone for positioning experiments, and selects carrier-smoothing pseudorange and PPP positioning model. The experimental plan is as follows:  
1. Ignore the ionospheric error and make no corrections;
2. Download the broadcast ephemeris and use Klobuchar to calculate the ionospheric delay;
3. Use observations of CORS to invert the regional ionospheric correction model to calculate the ionospheric delay in real-time. It can be seen from Figures 7 and 8 and Table 3 that the ionospheric delay error is one of the errors that cannot be ignored in the process of high-precision positioning of smartphones. Ignoring the influence of the ionosphere, the accuracy of pseudorange positioning results is low, the horizontal can reach 4 m, and the elevation can reach 10 m. It needs be weakened by appropriate models. Analyzing the influence of Klobuchar and regional ionospheric models on the results of the two positioning models, this article finds that using either pseudorange positioning or carrier positioning, the regional ionospheric model can effectively improve the positioning accuracy of smartphones.