Undifferenced GPS ambiguity resolution using the decoupled clock model and ambiguity datum fixing

This paper describes a method of processing Global Positioning System (GPS) observations to achieve undifferenced ambiguity resolution. Dual-frequency carrier phase and pseudorange measurements are processed by specifying separate oscillator parameters for the carrier phase and pseudorange measurements. Carrier phase estimates of the oscillator errors are arbitrarily biased with respect to the pseudorange estimates, and ambiguity parameters are constrained to be integer-valued. A network solution is necessary to compute the satellite code and phase clocks required as fixed parameters in single-user Precise Point Positioning (PPP) solutions. In the PPP results presented here, the LAMBDA method was used to optimally resolve ambiguities at each epoch. Only a small improvement in position error is gained with 5-minute static processing over 24 hours. However, there is a significant reduction in convergence time, and with 30-second static processing after 60 minutes, 90% of solutions approach 2 cm horizontal error, compared to 10 cm for standard PPP.