Research And Realization Of Key Technology For GPS Receiver

In general, the GPS receiver’s main functions include down conversion and sampling of the received radio frequency signal, GPS visible satellite search and acquision,code and carrier tracking of the acquired signals, decoding of the navigation message,and calculation of the navigation solution. The acquired signal and its parameters are passed to a tracking module. The tracking module performs code, phase, and Doppler shift tracking to obtain an accurate estimate of the parameters. The phase and Doppler shift estimates are used to wipe off the carrier and, consequently, decode the navigation message. The code-delay estimate is used to wipe off the code, calculate the pseudo range and, consequently, the navigation solution.Tracking loop could not discriminate the error in replica parameters at low SNR due to noise. The accuracy of GPS receiver will be reduced due to erroneous parameters.Traditional tracking loops underutilized the variance of noise in integration result.Local replica parameters are continually corrected in tracking loop using correlation integration value. Similarly, the prediction stage and the correction stage are cyclically executed in the Kalman filter. The structure of GPS signal and tracking loops in conventional GPS receivers were analyzed. The combination of phase detector and loop filter in tracking model could be replaced by the Kalman filters proposed in this paper. Measurements are coherent integration and incoherent integration. States contains phase of C/A code, phase of carrier, Doppler shift, and Doppler rate. Two extended square-root Kalman filter algorithms were developed for code and carrier respectively. Carlson algorithm and Potter algorithm were used for numerical stability. The simulation results indicated that the Kalman model worked well for a /0of 13 d B/Hz while the reversal of navigation data bits and the accuracy results from acquision were available.