Research On The Processing Models For GLONASS Inter Frequency Bias And Its Verification

With the development of multi-GNSS,the differential code bias(DCB)has been an increasing interest in the multi-frequency multi-GNSS community.Unlike code division multiple access(CDMA)mode used by GPS,BDS and Galileo etc.,the GLONASS signals are modulated with frequency division multiple access(FDMA)mode,and there was no combined GLONASS IFB product up to now.In this paper,IFB products of different frequencies of multiple receivers were calculated based on the undifferenced and uncombined PPP,and verifies their effectiveness and reliability by single frequency point positioning.1.The GLONASS IFB solution based on the geometry-free(GF)as well as the undifferenced and uncombined PPP were carried out and evaluated.Observations from CMONOC and IGS were collected for high(2014)and low(2017)ionospheric activity. Concerning the geometry-free solution,the STD was 0.85 ns and 0.51 ns for 2014 and 2017,respectively.Concerning the undifferenced and uncombined PPP solution,the IFB was further dependent on the signal frequencies,and the STD was 1.43 ns and 1.94 ns for and in 2014,and the STD was 0.97 ns and 1.17 ns for and in 2017.While the solution based on the geometry-free has higher precision, the undifferenced and uncombined PPP solution has its advantages for IFB estimation on each individual frequency,and more efficient in data processing.Thus,it is suggested that the geometry-free solution should be preferred for non-time-critical GF IFB concerned-only applications.Otherwise,the undifferenced and uncombined PPP solution is preferred.These IFB on each frequency was further converted to the ionosphere-free IFB and compared with the products of CODE analysis center to verify the validity.2.The effect of direct correction of GLONASS IFB was evaluated by GLONASS single-frequency pseudo-range point position,and the results showed that compared with the traditional positioning model,the accuracy could be effectively improved.In the regional stations,the average precision increase can be 11.6% in high ionospheric years,and 13.4% in low ionospheric years.At the global stations,the average increase can be 13.2% in high ionospheric years and 8.8% in low ionospheric years.