Multi-frequency GNSS Differential Code Bias Estimation Method And Application

The differential code bias(DCB)is the delay deviation of the GNSS code signal in the hardware channel of the satellite and the receiver.This hardware parameter must be deducted for the accurate ionosphere TEC extraction and modeling by GNSS,and the related TGD and BGD are also basic broadcast parameters in the GNSS broadcast ephemeris.At the same time,the accurate estimation of DCB can provide an important reference for the hardware and firmware performance of satellites and receivers.With the development of GNSS and its application requirements,it is increasingly essential to accurately determine the current multi-GNSS DCB parameters.In this thesis,the theoretical and experimental researches on the DCB solution of GNSS satellites and receivers are made,which are mainly divided into the following contents:(1)The calculation principle of GNSS differential code biases is introduced in detail.The DCB calculation model of DLR and IGG two mechanisms is compared and analyzed.The advantages and disadvantages of DCB solution using the approach of “pseudorange-leveled carrier-phase” are discussed.The influence of the factors such as the higher order ionospheric effects on the code observations required for DCB solution is analyzed.(2)This thesis proposes a multi-frequency GNSS DCBs estimation method based on the zero-mean benchmark constraint method,whitch takes into account satellite elevation angle,ionosphere accuracy and station latitude.The method is divided into two: a comprehensive correction model that takes into account factors such as phase center variation of the satellite and receiver antennas,also includes satellite-induced code pseudorange variation corrections for BeiDou;a comprehensive weighting model that takes into account factors such as satellite elevation angle and receiver latitude distribution,which is beneficial for improving the accuracy DCBs using stations worldwide.(3)The DCB of multi-frequency GPS,BDS,Galileo and QZSS satellites and receivers are resolved by the proposed DCB calculation model,and their long-term time series of GNSS DCB is obtained.For DCBs of GNSS satellites,we convert them to the same benchmark and compare them with the existing products,and analyze the influencing factors of their changes.For the DCB of GNSS receivers,we compare the DCBs of different brands of receivers,the differences and variations between receivers of different brands and different GNSSs are obtained.(4)Single-frequency,dual-frequency and tri-frequency uncombined PPP experiments of GPS,BDS,Galileo,and multi-GNSS were performed using CUM,DLR,IGG satellite and receiver DCB products,respectively,the influence of DCB parameters on positioning accuracy were analyzed.The results show that the DCB positioning accuracy solved in this thesis is better than the existing DLR,IGG and other institutions' products.(5)This thesis developed a DCB solving software based on the proposed DCB calculation model,named CUM-DCB(CUMt DCB)Software,which can perform multi-station and multi-day DCB solution and generate DCB product files of BSX(Bias-SINEX)format in batches.By comparing the existing DCB products,the DCB products obtained by the software meet the required accuracy of PPP and can be practically applied.