Research On Several Crucial Problems In High Sensitivity GPS Receiving Techniques

Now, GPS is applied broadly in the world, but in the situation, the users are usually in the environments where there are good GPS signals. When the users are in the environments where there are not good signals, such as, indoor, in forests and in cities, GPS will not be able to be used well because of shading, multipath, and interference and so on. Indoor, forests and cities and so on are able to be called indoor environments. Compared with the common circumstance, signal power, TOA and reception S/N of GPS signals will be worsened much severely, and positioning precision of GPS receivers, availability of GPS signals and general performances of GPS will be declined in the indoor circumstance, so usual GPS receivers will be hard to acquire and track the signals from navigation satellites. However, the indoor environment is one of the main environments where humans live. In indoor environments, there are a lot of application needs of GPS, and high sensitivity GPS receiving technique is a kind of technique meeting the needs of positioning in indoor environments, so researches on high sensitivity GPS receiving technique are necessary in the extreme and the researches on high sensitivity GPS receivers become hot points currently.In the dissertation, at first, traits of GPS signals were introduced, and the characteristics of indoor GPS signals were analyzed. In terms of several crucial problems in high sensitivity GPS receiving techniques, the research plat of high sensitivity GPS receiving techniques was designed and implemented. On the basis of them, the system architecture for high sensitivity GPS receivers was designed, high sensitivity GPS acquisition and tracking techniques were analyzed and researched deeply, high sensitivity GPS carrier tracking architecture and the method of compensating for code Doppler were constructed, and two new methods of cross correlation mitigation : the parallel cross correlation subtraction method and the parallel cross correlation subtraction method based on frequency difference coefficient, and two new methods of code phase measurement fining : the LS(Least Square) fitting fining method and the generalized extended approximation fining method were created.By simulation tests, the effects of the two cross correlation mitigation methods were good and the practicality of them was high compared with the foregoing methods. The parallel cross correlation subtraction method based on frequency difference coefficient had much advantage on computation quantity, and was able to accelerate the acquiring speed of high sensitivity receivers and save the time of baseband signals processing.Simulation tests proved that the two new methods of code phase measurement fining had great advantages in accuracy, stability, and tracking performance separately over the other methods. The accuracy and tracking performance of the fining method by generalized extended approximation were the best, and the stability of the fining method by LS (Least Square) fitting was highest. Their computation quantity was little, and they were able to be implemented very easily. In the situations of low signal noise ratio and great Doppler frequency, they can induct tracking and acquire code phase measurement fining effects.In conclusion, the new methods have good application values to high sensitivity GPS receivers in indoor environments.