| GPS provides accurate location, speed and time information to global users, so it is applied widely to aviation, marine, land and some other fields, especially in military field. GPS's high precision, reliability and integrality depend on the number of visible satellites and their geometrical distribution. Furthermore, GPS has still not been used in some areas currently, such as mines, tunnels, indoor or underground. Pseudolites positioning technique is an effective tool to solve these problems. Making use of Pseudolites, the number of GPS satellites can be increased and at the same time their geometrical location can be improved.Pseudolites augment GPS positioning technique is emphasized on. Development, actuality and potential problems of the satellite navigation systems are discussed firstly, the history of GPS Pseudolite is introduced. In order to design and realize GPS pseudolite transmitter, pseudo-code spread spectrum communication is analyzed detailedly. The characteristics of M sequence, format of pseudolite C/A code , navigation messages are analyzed . Finally several positioning patterns of GPS Pseudolites are presented.GPS pseudolite transmitter is designed based on systemic research and analysis. Navigation messages (D codes) is generated by single chip and C language, C/A codes is accomplished byVHDL language and CPLD chip, at the same time, the D codes is modulo-2 added to the C/A codes in CPLD, then, the resultant bit-trains are modulated on the L1 carriers by BPSK mode, the whole function of pseudoltie is realized. Finally, In order to validate pseudolite transmitter , spectrum analyzer, oscillograph and GPS receiver are used to test its signal. The results show that the pseudolite's hardware and software are correct and effective.
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