Signal folding coherent acquisition for weak global positioning system (GPS) C/A coded signal

• US 6,975,690 B1
• Filed: 08/15/2001
• Issued: 12/13/2005
• Est. Priority Date: 08/15/2001
• Status: Expired due to Fees

• Current Assignee: Air Force Government of The United States of America As Represented By The Secretary
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Lin, David M., Tsui, James B. Y.
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): PUENTE, EVA YI ZHENG
• Application Number:
  US09/929,720
• Time in Patent Office: 1,581 Days
• Field of Search: 375/326, 375/147, 375/130, 701/213, 370/335, 370/252
• US Class Current: 375/326
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A simplified, weak GPS C/A code coherent acquisition method. When performing GPS signal acquisition, the strength of a signal received at a GPS receiver having an outside antenna is generally sufficiently strong such that only 1 ms of data needs to be used in acquisition to find the signal. However, for weak signals received at a GPS receiver, when the antenna is inside a building or vehicle, for example, a long record of data is needed for acquisition. The present invention reduces the calculation burden for GPS signal acquisition for a weak signal.

Claims

1. A simplified, weak GPS C/A code coherent acquisition method comprising the steps of:

receiving a weak global positioning system C/A code digitized data signal of a length of N ms, where N is an integer greater than 1

generating a complex radio frequency digitized signal with a length of N ms as a local reference signal;

first multiplying said digitized data signal from said receiving step with said digitized complex radio frequency signal;

dividing a product from said multiplying of digitized data signal with digitized complex radio frequency signal into N equal sections of data signals;

adding said data signals in N equal sections together from said dividing step;

first applying a fast Fourier transform to a sum of data signals from an output of said adding step

acquiring 1 ms of length of digitized C/A code of a preselected GPS satellite;

second applying a fast Fourier transform to said 1 ms of digitized C/A code of a preselected GPS satellite from of said acquiring step;

taking a complex conjugate of said fast Fourier transformation from said second applying step;

second multiplying said complex conjugate from said taking step with said fast Fourier transformation from said first applying step; and

taking an inverse fast Fourier transform of a product from said second multiplying steps, an index of the maximum of said inverse fast Fourier transform being an initial phase of the C/A code.

2. The simplified, weak GPS C/A code coherent acquisition method of claim 1 wherein said dividing step further includes the step of dividing an output of said first multiplying step into 10 equal sections.

3. The simplified, weak GPS C/A code coherent acquisition method of claim 2 wherein said dividing step further includes the step of dividing an output of said first multiplying step into 10 equal sections each containing 5000 data points.

4. The simplified, weak GPS C/A code coherent acquisition method of claim 1 wherein said receiving step further includes the step of receiving a weak global positioning system C/A code digitized data signal of a 10 ms length.

5. The simplified, weak GPS C/A code coherent acquisition method of claim 1 wherein said generating step further includes the step of generating a complex radio frequency digitized signal 10 ms long with a frequency of 100 Hz.

6. The simplified, weak GPS C/A code coherent acquisition method of claim 1 wherein said second applying step further comprises the step of second applying a 5,000 point fast Fourier transform 1 ms of digitized C/A code of a preselected GPS satellite from said acquiring step 3.

7. The simplified, weak GPS C/A code coherent acquisition method of claim 1 wherein said taking step further comprises the step of taking a 5,000 point inverse fast Fourier transform of a product the output of said second multiplying step.