Bandpass correlation of a spread spectrum signal

• US 6,456,644 B1
• Filed: 06/23/1997
• Issued: 09/24/2002
• Est. Priority Date: 06/23/1997
• Status: Expired due to Term

• Current Assignee: Landis+Gyr Innovations Incorporated (Landis+Gyr Group AG)
• Original Assignee: CellNet Data Systems, Inc. (Landis+Gyr Group AG)
• Inventors: Fulton, Forrest F., Froelich, Robert K., Ramberg, Erik A.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): LIU, SHUWANG
• Application Number:
  US08/880,578
• Time in Patent Office: 1,919 Days
• Field of Search: 375/254, 375/329, 375/367, 375/344, 375/130, 375/140, 375/132, 375/142, 375/147, 375/150, 370/342, 370/479, 455/296
• US Class Current: 375/130
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/70757 with increased resolution, i.e. higher than half a chip H04B1/70758 takes precedence
• CPC Class Codes: H04B 1/708 Parallel implementation

Abstract

A spread spectrum signal is processed after it is sampled at a selected sampling rate and tuned to a center frequency lower than the sampling rate and greater than zero. The signal is multiplied against a reference signal to produce a corresponding product output, and an accumulation output is formed by combining the product output with a phase-shifted version of the accumulation output.

Claims

1. An apparatus for use in processing a spread spectrum signal digitally sampled at a preselected sampling rate, the apparatus comprising:

a tuning element configured to downconvert the digitally sampled spread spectrum signal to a preselected center frequency which is a whole number fraction of the preselected sampling rate, and which is always greater than zero;

a multiplication element configured to multiply the digitally sampled spread spectrum signal against a reference signal to produce a corresponding product output at the preselected center frequency; and

an accumulation element configured to produce an accumulation output by combining at the preselected center frequency the product output and a phase-shifted version of the product output.

2. The apparatus of claim 1, wherein the center frequency equals approximately one-quarter the sampling rate.

3. The apparatus of claim 1, wherein the accumulation element is configured to combine the product output and a 180°

phase-shifted version of the accumulation output.

4. The apparatus of claim 3, further including a delay element configured to shift the accumulation output by two samples to produce the 180°

phase-shifted version of the accumulation output.

5. The apparatus of claim 4, wherein the delay element includes two single-sample delay registers.

6. The apparatus of claim 1, wherein the accumulation element is configured to combine the product output and a 360°

phase-shifted version of the accumulation output.

7. The apparatus of claim 6, further including a delay element configured to shift the accumulation output by four samples to produce the 360°

phase-shifted version of the accumulation output.

8. The apparatus of claim 1, wherein the accumulation element is configured to combine the product output with a version of the accumulation output phase-shifted by N times 180°

, where N is an integer greater than zero.

9. The apparatus of claim 1, further including an element configured to provide as output a quadrature component of the accumulation output.

10. The apparatus of claim 1, further including an element configured to provide as output an in-phase component of the accumulation output.

11. The apparatus of claim 1, wherein the multiplication element includes a digital multiplier.

12. The apparatus of claim 1, wherein the multiplication element includes a sign inverter.

13. A method for use in processing a spread spectrum signal digitally sampled at a preselected sampling rate, the method comprising:

tuning the digitally sampled spread spectrum signal to a preselected center frequency which is a whole number fraction of the preselected sampling rate, and which is always greater than zero;

multiplying the digitally sampled spread spectrum signal against a reference signal to produce a corresponding product output at the preselected center frequency; and

producing an accumulation output by combining at the preselected center frequency the product output and a phase-shifted version of the product output.

14. The method of claim 13, wherein the center frequency equals approximately one quarter the sampling rate.

15. The method of claim 13, wherein producing the accumulation output includes combining a 180°

phase-shifted version of the accumulation output with the product output.

16. The method of claim 13, further including shifting the accumulation output by two samples to produce the 180°

phase-shifted version of the accumulation output.

17. The method of claim 13, wherein producing the accumulation output includes combining a 360°

phase-shifted version of the accumulation output with the product output.

18. The method of claim 17, further including shifting the accumulation output by four samples to produce the 360°

phase-shifted version of the accumulation output.

19. The method of claim 13, wherein producing the accumulation output includes combining the product output with a version of the accumulation output phase-shifted by N times 180°

, where N is an integer greater than zero.

20. The method of claim 13, further including providing as an output a quadrature component of the accumulation output.

21. The method of claim 13, further including providing as an output an in-phase component of the accumulation output.

22. An apparatus for use in processing a spread spectrum signal digitally sampled at a preselected sampling rate, the apparatus comprising:

a digital multiplier configured to multiply the digitally sampled spread spectrum signal with a reference signal to produce a product output that includes only a carrier wave at a preselected center frequency when the digitally sampled spread spectrum signal and the reference signal are aligned, the preselected center frequency being a whole number fraction of the preselected sampling rate that is always greater than zero; and

an accumulation loop including;

a primary summer configured to receive the product output; and

two single-sample delay registers positioned in series after the primary summer, a first one of which receives its input from the primary summer and a second one of which provides its output to the primary summer for subtraction form the product output.

23. The apparatus of claim 22, further including:

two squaring circuits configured to square the magnitudes of outputs from the two delay registers; and

an adding circuit configured to add the squared magnitudes to produce a squared correlation value.