GPS导航基础知识.ppt

GPS导航基础知识 A brief introduction to GPS Navigation What is GPS? Global Positioning system A network of satellites that continuously transmit coded information, which makes it possible to precisely identify locations on earth by measuring distance from the satellites. History of GPS The first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. Using a constellation of five satellites, it could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the Timation satellite which proved the ability to place accurate clocks in space, a technology that GPS relies upon. In the 1970s, the ground-based Omega Navigation System, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. How does GPS works？ The space segment The space segment is composed of the NAVSTAR GPS satellites. The constellation of the system consists of 24 satellites in six 55o orbit planes Four satellites in each plane The orbit period of each satellite is 11 hours and 58 minutes The information from satellite Two pseudorandom signals: Protected (P) code Coarse acquisition code Satellite frequencies L1 (1575.42 MHz): Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code, plus the new L1C on future Block III satellites. L2 (1227.60 MHz): P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites. L3 (1381.05 MHz): Used by the Nuclear Detonation (NUDET) Detection System Payload (NDS) to signal detection of nuclear detonations and other high-energy infrared events. Used to enforce nuclear test ban treaties. L4 (1379.913 MHz): Being studied for additional ionospheric correction. L5 (1176.45 MHz): Proposed for use as a civilian safety-of-life (SoL) signal (see GPS modernization). This frequency falls into an internationally protected range for aeronautical navigation, prom