1. An improved fully-coupled vehicle positioning system, comprising: a global positioning system (GPS) processor for providing GPS measurements including pseudorange, carrier phase, and Doppler shift, for a slave system; a data link for receiving GPS-like signal from a master system, where said GPS-like signal is a frequency shift GPS signal and generated by said master system; an inertial measurement unit (IMU) for providing inertial measurements including body angular rates and specific forces; a central navigation processor, which are connected with said GPS processor, said IMU and said data link, comprising an inertial navigation system (INS) processor, a Kalman filter, a new satellites/cycle slips detection module, and an on-the-fly ambiguity resolution module; and an input/output (I/O) interface connected to said central navigation processor; a GPS antenna of said master system for receiving GPS signal; a frequency mixer of said master system for shifting carrier frequency of said GPS signal received from said GPS antenna to generate said GPS-like signal; a data link of said master system for transmitting said GPS-like signal; wherein said GPS measurements from said GPS processor and GPS-like signal from said data link are passed to said central navigation processor and said inertial measurements are injected into said inertial navigation system (INS) processor; wherein said GPS-like signal is processed by said central navigation processor to derive GPS measurements; wherein an output of said INS processor and said GPS measurements are blended in said Kalman filter; an output of said Kalman filter is fed back to said INS processor to correct an INS navigation solution, which is then output from said central navigation processor to said I/O interface; wherein said INS processor provides velocity and acceleration data injected into said GPS processor to aid code and carrier phase tracking of GPS satellite signals; wherein an output of said GPS processor, an output of said data link, and an output of said INS processor are injected into a new satellites/cycle slips detection module to test the occurrence of new satellites and cycle slips, wherein as said new satellites/cycle slips detection module is on, said on-the-fly ambiguity resolution module is activated to resolve global positioning system satellite signal carrier phase integer ambiguities; wherein said on-the-fly ambiguity resolution module outputs the integer ambiguities into said Kalman filter to further improve positioning accuracy, and said INS processor outputs navigation data to said I/O interface.