PROCESSING MIXED PSEUDORANGE AND CARRIER PHASE GPS DATA

This paper describes an optimal combination procedure for processing t he pseudorange and the carrier phase data in GPS applications which yi elds results identical to the standard estimation method and reduces t he amount of filter computation by about one half. The regression equa tions for the pseudorange and carrier phase measurements taken at the same time are written. The measurements are then inversely scaled by t he standard deviation of the noise so that the noise covariance is pro portional to the unit matrix. Next, the equations are transformed orth ogonally to form two transformed measurements. One of the measurements is equivalent to a direct measurement on the carrier phase bias param eter. Within one continuous carrier phase tracking session, this type of derived measurements can be collapsed into one single measurement b y simple averaging. This way the number of data to be processed by the filter is essentially half the original one, and the total computatio n time is essentially half that of the conventional method. The above procedure assumes the ionosphere delay is eliminated by linear combina tion of the L1 and L2 signals. If the ionosphere delay is of interest, it may be modeled explicitly, in which case there are four, instead o f two, measurements for one time point in the regression equation. The procedure for solving the equation is modified. But a similar orthogo nal transformation can be applied and the amount of computation is red uced by a factor of four.