A Study Of The Atomic Clock Aiding GPS In CGTR-OTE Mobile Positioning

The Galileo system being built in Europe is the only one worldwide satellite navigation system established for civil purpose. This system will be built up in 2008. China is the first Non-EU country taking part in Galileo plan. In order to promote Galileo application in China, China is cooperating with Europe to establish the China Galileo Test Range (CGTR), which is served for development and demonstration of Galileo receiver and application systems. CGTR consists of three parts: inside test environment (ITE), outside test environment (OTE) and application demonstration center (ADC). Aiming at the mobile positioning required by OTE in CGTR, This thesis investigates the performance of a atomic clock aided GPS receiver and determines the benefits of a rubidium clock, while focusing on the improvement in navagation accuracy and availability. The motivation for employing an atomic clock in a GPS receiver is that the timing is precise and stable enough so that the receiver clock offset from GPS time can be assumed known, avoiding its estimation. Therefore, GPS navigation can proceed by estimating only the position coordinates(x,y,z),i.e,only three satellites are needed. If the receiver clock offset is precisely known,the immediate question is in what environment and to what extent the position accuracy will be improved. Chapter 2 will answer this question by analyzing the relationship between clock offset error and position error,and looking into the effect of satellite geometry on their relationship.While a quadratic function is an effective model to estimate the clock offset on the basis of GPS measurements, previous independent measurements are needed to estimate the parameters of the quadratic function. The available number of independent measurements depends upon the coorelation time of the measurements. In differential mode, the effects of both SA and ionosphere are substantially removed, and the correlation time is reduced to about 1 minute. The need for a more effective and practical and practical model and measurements will be briefly reviewed, then the characteristics of a rubidium clock are examined using precise post-mission precise satellite orbits and clock corrections. Based on these characteristics, a rubidium clock model for both stand-alone and differential GPS is developed. A practical navigation algorithm, in while the clock offset is estimated by a sequential process is developed.To further improve GPS navigation availability, the integration of rubidium clock aided GPS with a baremeter and a gyro is investigated. The combination of precise clock aided GPS with a barometer is an ideal integration. When the satellite geometry is good, the rubidium clock is used to improve vertical accuracy, and in turn, the calibration accuracy of the barometer. When the number of visible satellites falls to two,the stable rubidium clock and the more accurately calibrated barometer will provide the good measurements of clock offset and height information, and navigation quality can still be maintained. The gyro is also helpful over short periods of time, when there is only one visible satallite. Field tests in a controlled environment was conducted to evalute the navigation performance of the rubidium clock aided GPS and the integrated navigation system. Eventually, describes the tests and analyzes the results.