Research On Carrier Phase Difference Method To Support On-the-fly Positioning

The Foundation of Global Navigation Satellite System(GNSS) brought about profoundchanges and development in the satellite radio navigation technology. At present, there arefour main Global Navigation Satellite System: Global Position System(GPS), GLONASS,Galileo and Beidou Satellite Navigation System(COMPASS). As the application fields ofglobal satellite navigation technology is expanding, using combination of observations indifferent frequency channel to enhance the accuracy of real-time positioning becomes a hotspot of research. Although the GPS modernization program has been put into effect, onlyminority satellites can broadcast the third civilian frequency, the users in our country cannotreceive the observation on this frequency. The signal scheme of COMPASS which developedindependently by our nation is provided with three center frequencies, therefore, this paperpresents the idea of using the linear combination of carrier phase observations in threefrequencies to increase the real-time positioning accuracy, mainly studies the on-the-flycarrier phase difference positioning based on GPS or COMPASS.Firstly, the model of carrier phase precise positioning based on GNSS and the errorsources which affect the positioning accuracy are analyzed, due to precise point positioningfailing to meet the requirement of on-the-fly positioning on positioning accuracy andreal-time performance, precise relative positioning is adopted as the better way. Usingdifferential method to eliminate the satellite clock bias and receiver clock bias difference,double difference carrier phase observation equation is established; Meanwhile, in order toweaken the influence of ionosphere and troposphere delay on positioning accuracy andreal-time performance, multi-frequency carrier phase observations linear combination isadopted.Based on the widely used dual-frequency observation combination theory, the mathmodels of carrier phase smoothing pseudo-range and dual-frequency carrier phasecombination are set up respectively, the method of using phase to improve pseudo-rangeaccuracy and principle of structure low-ionosphere model are analyzed. On that basis,tri-frequency carrier phase linear combination method is proposed: Under the premise in theinteger feature and validity of integer ambiguity, using the phase observation on each threebands, geometry-free and ionosphere-free linear combination models are structured. Based onnumerical simulation different coefficient schemes are acquired, optimal performance in all terms of combined wavelength, measurement noise, ionosphere delay and geometric errorachieved via proper coefficient distribution. Disposing observation data using tri-frequencycarrier phase linear combination method, ionosphere delay and geometry error can beweakened effectively. In preconditions of long wavelength and low noise, this method canenhance the ambiguity calculation success rate, reduce searching space and increasecomputing efficiency, thus realize on-the-fly fast integer ambiguity resolution.The fast ambiguity resolutions applied to on-the-fly carrier phase differential positioningare analyzed, the fundamental and calculating steps of LAMBDA and Cascading AmbiguityResolution are studied, meanwhile, the error factors affected ambiguity success rate areanalyzed. Taking geometry error, ionosphere delay, measurement noise and wavelength allinto account, the combination coefficient with high success rate are chosen. With the properfast integer ambiguity resolution, high-precision real-time positioning results can be obtained.Field data collection was carried out in outdoor environment in order to validate thefeasibility and availability of the proposed method. Based on the incapability of receiving realtri-frequency observation data, the scheme accorded with principle of geometry-free andionosphere-free model are obtained through numerical simulation, the comprehensiveperformance in weakening geometry error and ionosphere delay, low noise and wavelength ofthese schemes are analyzed. Compared the accuracy and performance between singlefrequency and duel-frequency carrier phase differential positioning, the results shows that theduel-frequency method can increase the CEP95accuracy by47.6%, the whole resolvingprocess takes only1.52s. Higher accuracy observation can be obtained by tri-frequencycombination method, therefore, tri-frequency differential positioning can achieve betterresults than single frequency in the same conditions. Meanwhile, as a further combinationmode, tri-frequency theory with higher precision and real-time performance is the properdispose method that supporting on-the-fly carrier phase differential positioning. Through thetri-frequency combination method, not only the system error of original observation can bedecreased, but also the accuracy and reliability of precise relative positioning based onCOMPASS carrier phase observations can be enhanced to meet required performance ofhigh-precision navigation and positioning system.