Positioning device and method capable of reducing the amount of operation

• US 6,392,590 B1
• Filed: 01/06/2000
• Issued: 05/21/2002
• Est. Priority Date: 07/07/1999
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Kagemoto, Tetsuya
• Primary Examiner(s): ARTHUR JEANGLAUDE, GERTRUDE
• Application Number:
  US09/478,529
• Time in Patent Office: 866 Days
• Field of Search: 701/213, 701/214, 701/207, 701/215, 342/357.01, 342/357.02, 342/357.05, 342/353, 342/387, 342/465, 342/357.06, 342/357.03, 455/12.1, 455/13.2
• US Class Current: 342/357.68
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence

Abstract

A Positioning device includes a downconversion unit receiving positioning signals from satellites and converting the signals to an intermediate-frequency signal, and carrier search units using an output from the downconversion unit to search for a carrier wave of the received signals. The carrier search unit separates the received signal into in-phase and quadrate channel signals and spectrum-despreads them and then applies real Fast Fourier Transform to them. Of each frequency component, a signal corresponding to 0 Hz is corrected with a sum of all quadrate channel components to obtain a frequency difference between a local carrier and the carrier wave.

Claims

1. 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.

2. The positioning device according to claim 1, wherein said frequency difference calculation unit:

said frequency difference calculation unit corrects the direct-current component by adding an imaginary part to the direct-current component, a sum of the integrals stored in said storage circuit and corresponding to said quadrate channel signal being applied as the imaginary part, calculates a power of each of said frequency components, and provides said frequency difference based on the frequency with the maximum power.

3. The positioning device according to claim 2, wherein said signal extraction unit includes:

a carrier multiplier multiplying a signal from said downconversion unit by a respective one of said in-phase and quadrate local carriers generated by said carrier generator, to generate said in-phase and quadrate channel signals;

a code generator generating a code signal corresponding to a specific one of said plurality of satellites; and

a code multiplier multiplying an output from said code generator by respective one of said in-phase and quadrate channel signals.

4. The positioning device according to claim 2, wherein said frequency difference calculation unit multiplies the sum of the integrals stored in said storage circuit and corresponding to said quadrate cannel signal and the direct-current component of frequency components resulting from said Fast Fourier Transform by a predetermined coefficient to correct the direct-current component resulting from said Fast Fourier Transform.

5. The positioning device according to claim 2, wherein said carrier search control unit sets a frequency of said local carrier depending on integrals from said first and second integrators when a first estimated frequency equal to a carrier frequency being generated by said carrier generator plus said frequency difference and a second estimated frequency equal to the carrier frequency being generated by said carrier generator minus said frequency difference are each set as said carrier frequency.

6. The positioning device according to claim 2, wherein when a predetermined threshold is exceeded by a sum of a predetermined number of integrals stored in said storage circuit and corresponding to said in-phase channel signal each squared and then together summed up and a predetermined number of integrals stored in said storage circuit and corresponding to said quadrate channel signal each squared and then together summed up, said frequency difference calculation unit uses the integrals stored in said storage circuit and corresponding to said in-phase channel signal to provide Fast Fourier Transform and regards a sum of all the integrals stored in said storage circuit and corresponding to said quadrate channel signal as the imaginary part of the direct-current component of frequency components resulting from said Fast Fourier Transform, to calculate the power for each of said frequency components.

7. A positioning method receiving a signal from a plurality of satellites to derive positional information, comprising the steps of:

receiving a signal from said plurality of satellites and converting said signal to a signal of a predetermined intermediate-frequency;

multiplying said intermediate-frequency signal by an in-phase carrier signal and a quadrate carrier signal 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;

despreading a spectrum of each of said in-phase and quadrate channel signals;

integrating said signals each having the despread spectrum for a respective predetermined integration time;

providing Fast Fourier Transform for the integration corresponding to said in-phase channel signal;

correcting a direct-current component of frequency components obtained by the Fast Fourier Transform using the integration corresponding to said quadrate channel signal;

selecting a frequency component with a maximum power among the frequency components to provide said frequency difference;

using said frequency difference to update a frequency of said in-phase and quadrate carrier signals to search for a frequency of said carrier wave;

using said carrier wave searched, to extract navigation messages from the signals from said plurality of satellites to derive positional information.

8. The positioning method according to claim 7, the step of correcting includes the step of multiplying a sum of the integrals corresponding to said quadrate channel signal and a direct-current component of frequency components resulting from said Fast Fourier Transform by a predetermined coefficient to correct said direct-current component resulting from said Fast Fourier Transform.

9. The positioning method according to claim 7, wherein the step of integrating is followed by the step of determining whether the step of providing Fast Fourier Transform is to be followed depending on whether a predetermined threshold is exceeded by a sum of a predetermined number of integrals corresponding to said in-phase channel signal each squared and then together summed up and a predetermined number of integrals corresponding to said quadrate channel signal each squared and then together summed up.