Study Of Satellite Positioning And Navigation Algorithms

Satellite positioning systems, which can be used worldwide 24 hours a day under any weather, are representations of most advanced positioning systems. t is required that GPS user has to track at least four satellites for positioning. Although it is designed that GPS has to reach that require, in fact GPS user doesn't track four satellites when it lies where was blocked. In order to reduce the number required for positioning as well as keep certain positioning precision, this thesis proposes a new positioning algorithm that uses only three satellites. When the user can track two satellites only, Pseudolite is used to resolve the problem.First, this thesis introduces the GPS simply. Then it is proved that Doppler and range measurements can be extracted from positioning signal. After taken into consideration that in practice measurements are always biased, PseudoDoppler and PseudoRange measurements are defined. Then based on the definitions, a model called Doppler-Range algorithm in this thesis which uses only three satellites for three dimensional positioning is set up and proved. Next, constellation model of a satellites are simulated. Based on these parameters and Doppler-Range algorithm model mentioned above, positioning calculation using Doppler-Range algorithm can be used in practice.After that, precision of positioning is discussed and dilution of positioning (DOP) of the Doppler-Range algorithm is defined. The parameters what affect the figure of DOP are then discussed. Simulation results show that Doppler-Range algorithm can be used under certain restrictions. What needs to be done in procedure of constellation and positioning signal design in order to obtain certain degree of precision can also be determined from simulation results.