Method and apparatus for detecting and processing global positioning system (GPS) signals

• US 7,545,894 B2
• Filed: 03/21/2005
• Issued: 06/09/2009
• Est. Priority Date: 03/19/2004
• Status: Expired due to Fees

• Current Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Original Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Inventors: Ziedan, Nesreen I., Garrison, James L.
• Primary Examiner(s): Torres; Juan A
• Application Number:
  US11/087,065
• Publication Number:
  US 20050232338A1
• Time in Patent Office: 1,541 Days
• Field of Search: 375/347, 340/426.19, 340/539.13, 342/357.05, 342/357.06, 342/357.12, 702/213, 701/213
• US Class Current: 375/347
• CPC Class Codes: G01S 19/243 Demodulation of navigation message
• CPC Class Codes: G01S 19/246 involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04L 2027/0065 Frequency error detectors H04L2027/0067 takes precedence

Abstract

A method acquires a location system signal that includes second data signals superimposed on the first data signals. The method includes iterating Doppler frequency offset values and time offsets to generate error signals, each representing a difference between summed consecutive correlation values and a corresponding estimated ideal value. Each error signal corresponds to a different time offset and an associated time period. The second data signal has a bit edge that occurs during the time period of each of the sums of consecutive correlation values. The presence of a bit edge during an associated time period increases the error signal. A measure of the minimum error is used to identify a time offset value that is used to develop a first determined Doppler frequency offset. A Kalman filter refines the first determined Doppler frequency offset.

Claims

1. A method for use in the acquisition of a location system signal, the location system signal including a first data signal and a second data signal superimposed on the first data signal, the method comprising:

a) generating an initial Doppler frequency offset value, the Doppler frequency offset representing a variance from a nominal frequency for the location system signal and a frequency of a received location system signal;

b) using the initial Doppler frequency offset value and at least one other Doppler frequency offset value to generate a plurality of error signals, each error signal representing a difference between a sum of consecutive correlation values and a corresponding estimated ideal value, each error signal corresponding to a different time offset and an associated time period in which the consecutive correlation values pertain, the second data signal having a bit edge during the time period of each of at least some of the sums of consecutive correlation values, and wherein a bit transition at the bit edge causes an increase in the error signal when the bit edge occurs during the associated time period;

c) identifying a time offset value wherein a measure of the error signal is minimal, the identified time offset value identifying the bit edge;

d) employing the identified time offset value to obtain a first determined Doppler frequency value; and

e) using a Kalman filter to generate a refined Doppler frequency offset value based at least in part on the first determined Doppler frequency value.

2. The method of claim 1, wherein each correlation value represents a correlation between a received signal and a code sequence, the code sequence comprising a replica of the first data signal.

3. The method of claim 2, wherein step a) further comprises adjusting the code sequence using the initial Doppler frequency offset.

4. The method of claim 2, wherein the code sequence is a C/A code sequence of a global positioning satellite (GPS) system.

5. The method of claim 4, wherein the second data signal includes a navigational data signal generated by a satellite in the GPS system.

6. The method of claim 3, wherein each time offset is approximately an integer multiple of the first data signal period.

7. The method of claim 1, wherein the time period associated with each sum of consecutive correlation values is approximately equal to the bit period of the second data signal.

8. The method of claim 1, wherein step a) further comprises analyzing a plurality of potential Doppler frequency offsets and selecting the initial Doppler frequency offset from the plurality of potential Doppler frequency offsets.

9. The method of claim 8, wherein step a) further comprises performing for each potential Doppler frequency offset a correlation between a received signal and a code sequence, the code sequence comprising a replica of the first data signal.

10. The method of claim 9, wherein step a) further comprises, for each potential Doppler frequency offset, adjusting the code sequence using the potential Doppler frequency offset.