Research On BDS/GPS Combined RTK Algorithm Based On Low-Cost Single Frequency Receiver

With the development of global satellite navigation system(GNSS),especially the continuous improvement of China's Beidou positioning system,GNSS navigation and positioning has been applied in various fields,such as pedestrian navigation,car navigation,surveying and mapping,precision agriculture and other fields.Although different areas require different precision of navigation and positioning,the demand for high-precision location service is increasing day by day.At present,the high-precision positioning technology generally adopts the more expensive dual-frequency or triple-frequency receiver and the high-end measurement type antenna.Howev-er,in order to make navigation and positioning technology better popularized and applied,it is very important to study the low cost receiver localization algorithm.In view of the compatibility and interoperability between BDS and GPS,relying on Hunan military integration project(Beidou navigation simulation and test da-ta center construction),this thesis studies a low cost single frequency BDS/GPS combined RTK algorithm by using low cost u-blox receiver data.The following two aspects were mainly studied:1)Based on the traditional cycle slips detection algorithm,a cycle slips de-tecting algorithm for GPS single frequency RTK is proposed,which is assisted by Doppler observations.Firstly,based on pseudorange and carrier phase noise estima-tion models,a random model of Doppler noise estimation is fitted by a large number of measured data.Then this algorithm combines two consecutive epochal Doppler observations with carrier phase difference observations to construct a Doppler-carrier phase difference sequence for real-time cycle slips detection.Lastly,the hypothesis-test method is applied to detect whether there is a cycle slips in the single frequency carrier phase observations.2)Based on the LAMBDA algorithm,an ambiguity algorithm for single fre-quency and single epoch combination of GPS/BDS is proposed.Aiming at the problem of rank-defect and ill-conditioned ambiguity resolution in the process of single frequency single epoch combined RTK positioning,pseudorange observations is introduced as auxiliary solution in this method.Firstly,we adopt the empiri-cal decentralization method to assign weights to the pseudorange and carrier phase observations,and obtain the floating resolution of ambiguities by weighted least squares.Then,by the descending order of variance-covariance matrix of the floating resolution of ambiguities and Cholesky triangular decomposition,the ill-conditioned ambiguity resolution can be eliminated.Finally,the modified floating solution is used to search the integer solution of ambiguity.In this thesis,the above two improved algorithms and two-system combined algorithm are verified by the measured data.The results show that the improved cycle slip detection algorithm can accurately detect the small cycle slips in the single frequency carrier phase observation data,and the detection sensitivity of the method is higher than that of the traditional code-phase difference sequence method.The improved LAMBDA algorithm not only can improve the positioning accuracy,but also reduce the correlativity of the ambiguity,which is suitable for RTK positioning.The combination of dual systems can improve the positioning accuracy;using low-cost receiver BDS/GPS combination RTK positioning horizontal accuracy can reach centimeter level,zenith direction for the sub-meter level.