Sampling threshold and gain for satellite navigation receiver

• US 7,912,158 B2
• Filed: 11/08/2005
• Issued: 03/22/2011
• Est. Priority Date: 11/08/2005
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Navcom Technology, Inc. (Deere & Company)
• Inventors: Knight, Jerry Eugene, Cahn, Charles R.
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Yu; Lihong
• Application Number:
  US11/270,253
• Publication Number:
  US 20070104299A1
• Time in Patent Office: 1,960 Days
• Field of Search: 375/345
• US Class Current: 375/345
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: H03G 3/3052 in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 3/3089 Control of digital or coded signals
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A satellite navigation device including a flexible radio frequency (RF) receiver is described. The receiver receives a signal that includes at least a first spread-spectrum signal from a first satellite. The receiver has a first channel that includes an analog-to-digital (A/D) converter to sample and quantize the signal and an automatic gain control (AGC) to adjust an amplification of the signal. The A/D converter has a first non-zero quantization threshold magnitude and a second non-zero quantization threshold magnitude. The AGC may adjust a gain in accordance with the first non-zero quantization threshold magnitude. The gain may correspond to a first pre-determined probability of a non-zero sample and the second non-zero quantization threshold magnitude may correspond to a second pre-determined probability of a non-zero sample.

Claims

1. A satellite navigation device, comprising:

a receiver that receives a signal that includes at least a first spread-spectrum signal from a first satellite, the receiver having a first channel, the first channel including;

an analog-to-digital converter to sample the signal and determine quantized signal values having two, three, four, five, or more bits, to perform a first mapping of the quantized signal values to first sample values using a first non-zero quantization threshold magnitude, and to perform a second mapping of the first sample values to second sample values using a three-level quantization with a second non-zero quantization threshold magnitude;

an automatic gain control to adjust a gain of the signal; and

control logic to determine the gain such that the first mapping produces a first pre-determined probability of a respective non-zero first sample value of the first sample values.

2. The satellite navigation device of claim 1, wherein adjusting the gain and performing the first and second mappings reduce an effect of an interference signal on the receiver at an arbitrary ratio of interference signal power to receiver noise power.

3. The satellite navigation device of claim 1, wherein the quantized signal values have a number of bits selected from the group consisting of 2, 3, 4 and 5.

4. The satellite navigation device of claim 1, further comprising a dc-offset correction circuit to substantially reduce a dc-offset in the signal.

5. The satellite navigation device of claim 1, further comprising a look-up table to provide the first mapping and the second mapping to the analog-to-digital converter, and wherein non-zero first sample values in the first mapping are defined based on the first non-zero quantization threshold magnitude and non-zero second sample values in the second mapping are defined based on the second non-zero quantization threshold magnitude.

6. The satellite navigation device of claim 1, further comprising a down-conversion circuit, wherein the down-conversion circuit converts the signal from a first carrier frequency signal to a near baseband signal, the near baseband signal having a second carrier frequency signal substantially less than one-quarter of a sampling rate.

7. The satellite navigation device of claim 6, wherein the second carrier frequency signal is less than approximately 100 kHz.

8. The satellite navigation device of claim 6, further comprising a phase rotation circuit to perform a complex phase rotation on quantized quadrature samples of the near baseband signal such that a residual bias is substantially distributed uniformly over phase angles of 0 to 360°

and thereby averages to substantially zero over an integration period corresponding to the first spread-spectrum signal.

9. The satellite navigation device of claim 8, wherein the phase rotation circuit is configured to use a look-up table to perform the complex phase rotation.

10. The satellite navigation device of claim 1, further comprising a blanking circuit, wherein the blanking circuit, when enabled, sums a number of events where a respective sample of the signal exceeds a threshold during a time interval and disables the receiver if the number of events exceeds a value.

11. The satellite navigation device of claim 10, wherein the threshold is eight times the first non-zero quantization threshold magnitude.

12. A satellite navigation device, comprising:

a receiver mechanism that receives a signal that includes at least a first spread-spectrum signal from a first satellite, the receiver mechanism having a first channel, the first channel including;

means for sampling the signal and determining quantized signal values having two, three, four, five, or more bits, performing a first mapping of the quantized signal values to first sample values using a first non-zero quantization threshold magnitude, and performing a second mapping of the first sample values to second sample values using a three-level quantization with a second non-zero quantization threshold magnitude; and

means for adjusting a gain of the signal, the gain being determined such that the first mapping produces a first pre-determined probability of a respective non-zero first sample value of the first sample values.

13. A method of operating a satellite navigation device, comprising:

receiving a signal using a receiver, the signal including at least a first spread-spectrum signal from a first satellite;

adjusting a gain of the signal;

sampling the signal to determine quantized signal values having two, three, four, five, or more bits;

performing a first mapping of the quantized signals values to first sample values using the first non-zero quantization threshold magnitude; and

performing a second mapping of the first sample values to second sample values using a three-level quantization with a second non-zero quantization threshold magnitude;

wherein the gain is determined such that the first mapping produces a first pre-determined probability of a respective non-zero first sample value of the first sample values.

14. The method of claim 13, wherein adjusting the gain and performing the first and second mappings reduce an effect of an interference signal on the receiver at an arbitrary ratio of interference signal power to receiver noise power.

15. The method of claim 13, wherein the quantized signal values have a number of bits selected from the group consisting of 2, 3, 4 and 5.

16. The method of claim 13, further comprising substantially reducing a dc-offset in the signal.

17. The method of claim 13, wherein non-zero samples in the first mapping are determined based on the first non-zero quantization threshold magnitude and non-zero samples in the second mapping are determined based on the second non-zero quantization threshold magnitude.

18. The method of claim 17, wherein the first mapping and the second mapping use a look-up table.

19. The method of claim 13, further comprising converting the signal from a first carrier frequency signal to a near baseband signal, wherein the near baseband signal has a second carrier frequency signal substantially less than one-quarter of a sampling rate.

20. The method of claim 19, wherein the second carrier frequency signal is less than approximately 100 kHz.

21. The method of claim 19, further comprising performing a complex phase rotation on quantized quadrature samples of the near baseband signal such that a residual bias is substantially distributed uniformly over phase angles of 0 to 360°

and thereby averages to substantially zero over an integration period corresponding to the first spread-spectrum signal.

22. The method of claim 21, wherein performing the complex phase rotation includes determining the complex phase rotation using a look-up table.

23. The method of claim 13, further comprising summing a number of events where a respective sample of the signal exceeds a threshold during a time interval and temporarily disabling the receiving if the number of events exceeds a value.

24. The method of claim 23, wherein the threshold is eight times the first non-zero quantization threshold magnitude.