FFT inter frequency loss mitigation and GPS receiver including it

• US 20060251157A1
• Filed: 01/31/2006
• Published: 11/09/2006
• Est. Priority Date: 02/04/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Nemerix, SA
• Inventors: Brenner, Joel
• Granted Patent: US 7,643,542 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence

Abstract

Acquisition method for a localization receiver, in particular for a GPS receiver. It involves the calculation of an interpolated FFT spectrum (S′) of correlated signals in which the frequency lines corresponding to half-integer values of the frequency resolution defined by the FFT are obtained by a combination of both amplitude and phase values of the FFT spectrum (S).

Claims

1. A method for acquiring positioning signals of a geographic localization system, comprising the steps of:

obtaining a signal containing localization information;

combining the signal with a local pseudorandom code sequence obtaining a correlation signal;

obtaining a first spectrum of frequency of the correlation signal;

characterized by the steps of;

obtaining a second spectrum comprising intermediate-frequency data by complex combinations of amplitude and phase values of adjacent bins of the first spectrum;

searching for peaks in the second spectrum.

2. The method of claim 1, wherein said step of obtaining a second spectrum comprises calculating intermediate-frequency data obtained by complex combinations of amplitude and phase values of pairs of adjacent frequency bins of the first spectrum.

3. The method of claim 1, wherein said step of obtaining a second spectrum comprises calculating intermediate-frequency data obtained by complex combinations of amplitude and phase values of groups of more than two adjacent bins of the first spectrum.

4. The method of claim 1, wherein said step of obtaining a first spectrum of frequency involves a Fast Fourier Transform (FFT).

5. The method of claim 4, wherein said step of obtaining a second spectrum comprises rotations, sums and normalizations of complex numbers.

6. The method of claim 4, wherein said step of obtaining a second spectrum comprises only complex sums and complex multiplication by constants.

7. The method of claim 2, wherein said step of calculating intermediate-frequency data comprises:

a first complex rotation of a first value of the pair according to an angle;

a second complex rotation of the other value of the pair according to said angle in an opposite direction as the first complex rotation;

a sum of the complex numbers resulting from the first and second complex rotation.

8. The method of claim 2, wherein said step of calculating intermediate-frequency data comprises the evaluation of

9. Receiver for a geographic localization system, specially adapted for carrying out the method of claim 2.

12. Computer data carrier, capable of being read loaded in a memory of a digital processor system, containing program instructions to execute the method of claim 1 when loaded in the memory of the digital processor.

10. Receiver for a geographic localization system comprising:

a receiving section for obtaining a signal containing localization information;

demodulation and correlation means for multiplying the signal with a local pseudorandom code sequence obtaining a correlation signal;

Spectral extraction means for obtaining a first spectrum of frequency of the correlation signal;

characterized by;

interpolating means, for obtaining a second spectrum comprising intermediate-frequency data by complex combinations of amplitude and phase values of adjacent bins of the first spectrum;

a peak detection system, for searching peaks in the second spectrum.

11. The receiver of claim 10, wherein said interpolating means are adapted for the evaluation of