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To improve the service accuracy of the GNSS system and monitor the integrity of regional ionospheric activities, The BDSBAS system broadcasts the grid ionospheric correction parameters and GIVE to meet the precision approach needs. We use a planar fit algorithm to create an ionosphere map of the BDSBAS, in order to get a more accurate confidence bounds, we put forward a factor which is related to the Skewness and kurtosis of the residual distribution to control the decorrelation parameters to calculate the integrity parameter GIVE. The statistical results show that the ionospheric correction RMS of the BDSBAS grid-based single shell model is about 2~3 TECU, the correction percentage reaches 75%~79%; the GIVE envelope rate is better than 99.9%. Compared with the GPS basic navigation system, only adding the BDSBAS grid ionospheric correction can improve positioning accuracy by 20%~40%.

Almanac parameters can be used to assist signal acquisition for both conventional navigation and autonomous navigation. The extended validity of the almanac parameters not only enables the terrestrial receiver to make full use of almanac data when starting up,but also determines the frequency of the almanac uploaded and the satellite storage resources on-board for autonomous navigation with inter-satellite link observation. Based on analysis of the major perturbations of three types of BeiDou satellites and their effects on the long-term and long-period terms of the orbital elements,an almanac model with six orbital elements and five perturbation parameters is designed. The almanac fitting test is carried out based on the 90-day long arc orbit of BeiDou satellites in orbit throughout 2013. The results show that the new almanac model improves accuracy of almanac fitting. For Geostationary Earth Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO) satellites,position fitting error is reduced from 200 km to more than 10 km even to several km and velocity error is reduced from 15 m/s to 0.6 m/s. The accuracy of the new model is about 20 to 30 times higher than that of the conventional model. For Medium Earth Orbit (MEO) satellite,position fitting error is about 5 km and velocity error is about 0.6 m/s regardless of which model,and the accuracy of the new method is improved about 15%. For 10 km position error upper limit of inter-satellite link,the maximum fitting arc length of the conventional model is about 14 days,and the maximum fitting arc length of the new almanac model can be extended to 45 days. The new almanac model extends the validity of almanac parameters,and optimizes almanac model for BeiDou Navigation Satellite System (BDS).

Phase smoothing Pseudorange can effectively suppress the multipath effect on pseudorange, and there is no ambiguity problem, which has been widely studied and applied in the field of GNSS data processing. This paper made a systematic analysis and comparison of mathematical models for Hatch filter and CNMC phase smoothing pseudorange method. The ionsphere free combination of single frequency pseudorange through CNMC algorithm is proved equivalence with dual frequency hatch filter. On the assumption that there exists only random errors and the various measurements are independent, the accuracy expression of the CNMC method for smoothing pseudorange is deduced. Dual band hatch filter in the initialization period observation noise is bigger than CNMC smoothed pseudorange, but after a bit more than ten minutes, observation noise gradually gets better than CNMC smoothed pseudorange. BDS navigation system is qualified with serious and low-frequency characteristic for multipath errors through the comparison of OMC of double difference observation for real BDS short baseline, the conclusion that the phase smoothing pseudorange algorithm can greatly weaken the random error of original pseudorange, however, cant improve the system error is drawn. The system error of pseudorange smoothed by CNMC is at the save level with the original pseudorange, but the system error of pseudorange smoothed by double frequency hatch filter is increased. At last, relative positioning is carried through using the different kinds of phase smoothed pseudorange of that short baseline. The positioning results show that the positioning precision is improved from 0.797 m to 0.541 m using pseudorange smoothed by CNMC and the positioning precision is decreased to 1.160 m using pseudorange smoothed by hatch filter.