TAILIEUCHUNG - GPS - đường dẫn quán tính và hội nhập P3

Signal Characteristics and Information Extraction Why is the GPS signal so complex? GPS was designed to be readily accessible to millions of military and civilian users. Therefore, it is a receive-only passive system for a user, and the number of users that can simultaneously use the system is unlimited. Because there are many functions that must be performed, the GPS signal has a rather complex structure. | Global Positioning Systems Inertial Navigation and Integration Mohinder S. Grewal Lawrence R. Weill Angus P. Andrews Copyright 2001 John Wiley Sons Inc. Print ISBN 0-471-35032-X Electronic ISBN 0-471-20071-9 3 Signal Characteristics and. Information Extraction Why is the GPS signal so complex GPS was designed to be readily accessible to millions of military and civilian users. Therefore it is a receive-only passive system for a user and the number of users that can simultaneously use the system is unlimited. Because there are many functions that must be performed the GPS signal has a rather complex structure. As a consequence there is a correspondingly complex sequence of operations that a GPS receiver must carry out in order to extract desired information from the signal. In this chapter we characterize the signal mathematically describe the purposes and properties of the important signal components and discuss generic methods for extracting information from these components. MATHEMATICAL SIGNAL WAVEFORM MODELS Each GPS satellite simultaneously transmits on two L-band frequencies denoted by i and which are and MHz respectively. The carrier of the Lx signal consists of an in-phase and a quadrature-phase component. The in-phase component is biphase modulated by a 50-bps data stream and a pseudorandom code called the C A-code consisting of a 1023-chip sequence that has a period of 1 ms and a chipping rate of MHz. The quadrature-phase component is also biphase modulated by the same 50-bps data stream but with a different pseudorandom code 30 MATHEMATICAL SIGNAL WAVEFORM MODELS 31 called the P-code which has a chipping rate and a one-week period. The mathematical model of the waveform is s t A 2P d t c t cos fflt ff ZPQd t p t sin fflt d where PI and Pq are the respective carrier powers for the in-phase and quadraturephase carrier components d t is the 50-bps data modulation c t and p t are the respective C A and P .

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