GPS Global Positioning System
United States already announced around 2006 GPS satellite system terminates execution of the SA policies and offer users continue to standard positioning service (SPS). This means when user real time GPS point positioning precision from? 00 m increase to about 30 m. Recent United States Army revealed that SA could be earlier, this means that the efficiency of GPS positioning in the next century will be greatly improved.
Current movements in the sky most of the GPS satellites are first generation II satellite, namely type II and IIA satellites. Starting from 1997, II-the second generation of satellites was launched first IIR-type satellites. IIR satellite in the future will gradually replace the existing type II and IIA satellites. Relative to type II and IIA satellites, IIR satellite equipped with one order of magnitude higher frequency stability of new rubidium atomic clock; users receive the L1 and L2 signal power greater than ever before; it can send and receive other GPS satellite navigation data, to form the GPS satellite positioning between capacity, which will reduce the delay of GPS satellite data transmission.