Abstract

An improved method and apparatus for effecting code synchronization in a global positioning system receiver is disclosed herein. Within the receiver, digital in-phase (I) and quadrature (Q) samples of a plurality of received pseudorandom noise (PRN) encoded signals are provided to a code synchronization circuit. The code synchronization circuit is designed for coherent-mode operation when the receiver has achieved phase-lock with one of the PRN encoded signals, and operates in a non-coherent mode otherwise.The code synchronization circuit includes an I-channel correlator for producing a coherent-mode discrimination signal by correlating in-phase (I) samples of a first of said PRN encoded signals with a discrimination pattern, wherein the first PRN encoded signal is encoded with a first PRN code. The discrimination pattern is comprised of two or more PRN code modulation components, the phases of which are adjusted based on the value of a code phase control signal obtained by averaging or otherwise processing the coherent-mode discrimination signal.During non-coherent mode operation, both the in-phase (I) and quadrature (Q) samples of one of the PRN-encoded signals are correlated with a discrimination pattern and with a locally-generated replica of the PRN code. The results of the two I-channel correlations are then multiplied, as are the results of the Q-channel correlations. The resultant product signals generated during the multiplications are then combined into a non-coherent mode discrimination signal.