High‐precision GPS navigation with emphasis on carrier‐phase ambiguity resolution

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Abstract
GPS observables available for navigation—namely, L1 C/A and L1/L2 P code—and carrier phase are reviewed. The use of single‐ and double‐differenced observables to eliminate or reduce various errors is discussed. Two types of carrier‐phase ambiguity‐resolution methods without static initialization are described: carrier‐phase smoothing of the code, which yields an accuracy of up to a few cycles; and integer ambiguity resolution, which yields the correct integer values of the ambiguities. The former is now capable of rms positioning accuracies at the 50‐cm level using emerging high‐performance C/A code receivers, while the latter is capable of centimeter‐level accuracies for short separations between the monitor and remote stations. The latter includes the ambiguity function method (AFM) and various least‐squares search techniques. The results of a controlled trial to assess the capability of a least‐squares search technique to determine the integer ambiguities without static initialization, which is the standard shipborne case, are presented using various CIA and P code solutions. These results show a convergence time of less than 60 s for some of the P code‐based solutions.

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