| 摘要 |
A receiver employs a pre-correlation filter to determine the precise timing of, for example, a PRN code on the quadrature channel of a received signal, using an image of the average chip shape that the filter forms for a PRN code on the in-phase channel. The image is expressed as a time series of complex power measurements along the length of a single chip. The averaging process retains the detail of the composite in-phase signal (direct plus multipath signals) while reducing the level of signal noise by an amount proportional to the length of the averaging process. An analysis of the image reveals that there is, in the in-phase channel signal that is averaged, information from the quadrature channel signal. The quadrature channel signal information produces, in the image of the average chip shape of the in-phase channel PRN code, a "wiggle" that corresponds to the timing of the chips of the quadrature channel PRN code. The receiver detects the chip edges of the quadrature PRN code directly from an analysis of the high frequency phase modulations of the complex vector of samples that represents the average chip shape. Using GPS signals, the receiver detects the P-code transitions by synchronizing to the 10.23 MHz phase modulations in the complex vector of samples that represent the averaged chip shape. The receiver uses the detected P-code transitions and, more particularly, the P-code transitions that are closest to the C/A code transitions, to produce P-code phase information that the receiver uses pseudorange calculations to remove biases associated with timing differences between the transmission of the in-phase and quadrature PRN codes.
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