| Triple-frequency or multi-frequency is the trend for almost all global navigation satellite systems,fast fixed ambiguity is a prerequisite for realize high-precision navigation and positioning.Significant researches have been carried out in the past 20 years,which mainly focus on the utilization of additional signal to speed up the integer ambiguity resolution.Although many researchers have done deep research on this filed and got rich results,nevertheless,it is still an issue that how to get the narrow-lane(NL)ambiguity of medium and long baselines quickly and reliably.Hence,this paper mainly focus on the research of fast triple-frequency ambiguity resolution for BDS,GPS.The main work and contributions of this thesis are as follows:1.The theory of the triple-frequency combination observables is analyzed,and its main problems are discussed.The combination model and error model of BDS and GPS observation are derived.The optimized selction of the optimal combination of three frequencies is made by the three indexes of wavelength,the ionospheric scale factor and the noise amplification coefficient,which gives the specific linear combination under different constraints.2.The performance of the TCAR algorithm is analyzed,and the error of the doubledifferenced ionospheric delay and the measure noise are calculated.It is pointed out that if the measurement noise of the carrier phase and the pseudo-range measurement noise are doubled at the same time,the error caused by the measurement noise in each step of the method will be doubled accordingly.Experimental results show that the effect of ionospheric delay on the ambiguity fixation of the NL is much greater than that of the wide-lane(WL)ambiguities,it is proved that this method eliminates the influence of the double-differenced ionospheric delay on the NL ambiguity under the short baseline,but the noise is seriously amplified,and the TCAR method is better than this algorithm.3.The performance of the TCAR,LAMBDA and GB-TCAR methods in the short baseline are analyzed.The experimental results show that the LAMBDA method is optimal and the GBTCAR is superior to TCAR method in the fixed success rate and reliability,The TCAR method is optimal in the complexity of the algorithm and the speed of the solution,and the triple-frequency fixed ambiguity is faster than the dual-frequency,as well as the reliability.4.An improved ambiguity resolution algorithm is proposed for TCAR method and GIFTCAR method to solve the problem that the AR success rate of medium and long baselines are not high.The algorithm estimates the ionospheric delay in real time,and it selects the optimal weight coefficient of the WL combination to solve the WL ambiguity,which is composed of geometryfree and ionosphere-free or weak ionosphere combination.Finally,the geometry-free and ionosphere-free model is used to fix the NL ambiguity.Experiments show that the modified algorithm can effectively resolve the WL and NL ambiguity,error of which is less than 0.2 cycles and 5 cycles respectively.Through smoothing of multi-epoch data,the ambiguity can be fixed reliably.5.This paper derives the double-differenced pseudo-range and inter-frequency multipath error extraction algorithms,and the effect of the double-differenced carrier multipath error on the BDS ambiguity resolution is discussed.The experimental results show that the double-differenced carrier multipath error is two orders of magnitude smaller than the double-differenced pseudorange multipath error,but it has benn seriously amplified to 1-5 times the wavelength of the combined observation by linear combination,and its impact on high-precision positioning of the WL and NL ambiguity fixed. |
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