Patent ID: 6392590
Filing Date: 2002-05-21
Classification: G01S

Abstract:
A positioning device receiving positioning signals from a plurality of satellites to derive positional information, comprising:a downconversion unit receiving positioning signals from said plurality of satellites and converting the positioning signals to a predetermined intermediate-frequency signal; a plurality of carrier search units receiving an output from said downconversion unit to search for a frequency of a carrier wave of the positioning signals from the plurality of satellites, each of said carrier search units including a carrier generator generating an in-phase local carrier signal and a quadrate local carrier signal, a signal extraction unit using the predetermined intermediate-frequency signal from said downconversion unit and signals output from said carrier generator to separate an in-phase channel signal corresponding to said in-phase local carrier signal and a quadrate channel signal corresponding to said quadrate local carrier signal, and performing spectrum despread, first and second integrators each receiving a corresponding one of outputs from said signal extraction unit and integrating the corresponding output for a designated integration time, a storage circuit holding a plurality of integrals from said first and second integrators, each of said plurality of integrals being calculated for each said integration time, a frequency difference calculation unit deriving a frequency difference between a carrier frequency in the signal from said downconversion unit and a local carrier frequency, said frequency difference calculation unit deriving said frequency difference by i) providing Fast Fourier Transform for the integration stored in said storage circuit and corresponding to said in-phase channel signal, ii) correcting a direct-current component of frequency components obtained by the Fast Fourier Transform using the integration stored in said storage circuit and corresponding to said quadrate channel signal, and iii) selecting a frequency component with a maximum power among the frequency components, and a carrier search control unit using said frequency difference to update the frequency of said local carrier signals generated by said carrier generator, to search for the frequency of said carrier wave; and a positional information deriving unit using an output from said carrier search unit to extract navigation messages from the positioning signals from said plurality of satellites to derive positional information.