Sampling threshold and gain for satellite navigation receiver

• US 20070104299A1
• Filed: 11/08/2005
• Published: 05/10/2007
• Est. Priority Date: 11/08/2005
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Navcom Technology, Inc. (Deere & Company)
• Inventors: Knight, Jerry, Cahn, Charles
• Granted Patent: US 7,912,158 B2
• Time in Patent Office: Days
• 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 and quantize the signal, the analog-to-digital converter having a first non-zero quantization threshold magnitude and a second non-zero quantization threshold magnitude; and

an automatic gain control to adjust a gain of the signal,

wherein the gain is determined at the first non-zero quantization threshold magnitude to produce a first pre-determined probability of a non-zero sample, and wherein the second non-zero quantization threshold magnitude corresponds to a second pre-determined probability of a non-zero sample.

2. The satellite navigation system of claim 1, wherein amplifying the signal using the gain and quantizing the signal using the second non-zero quantization threshold magnitude 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 system of claim 1, wherein the analog-to-digital converter outputs values having a number of bits selected from the group consisting of 2, 3, 4 and 5.

4. The satellite navigation system of claim 3, wherein the first non-zero quantization threshold magnitude corresponds to a first range of output values and the second non-zero quantization threshold magnitude corresponds to a second range of output values.

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

6. The satellite navigation system of claim 1, wherein the analog-to-digital converter uses a look-up table, the look-up table including a first mapping and a second mapping, and 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.

7. The satellite navigation system 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.

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

9. The satellite navigation system of claim 7, 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.

10. The satellite navigation system of claim 9, wherein the phase rotation circuit uses a look-up table to perform the complex phase rotation.

11. The satellite navigation system 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.

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

13. 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;

a first means to sample and quantize the signal, the first means having a first non-zero quantization threshold magnitude and a second non-zero quantization threshold magnitude;

a second means to amplify the signal, the second means having a gain determined at the first non-zero quantization threshold magnitude,

wherein the gain corresponds to a first pre-determined probability of a non-zero sample and the second non-zero quantization threshold magnitude corresponds to a second pre-determined probability of a non-zero sample.

14. A method, comprising:

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

determining a gain for amplifying the signal using a first non-zero quantization threshold magnitude; and

sampling and quantizing the signal using a second non-zero quantization threshold magnitude,

wherein the gain corresponds to a first pre-determined probability of a non-zero sample and the second non-zero quantization threshold magnitude corresponds to a second pre-determined probability of a non-zero sample.

15. The method of claim 14, wherein amplifying the signal using the gain and quantizing the signal using the second non-zero quantization threshold magnitude reduce an effect of an interference signal on the receiver at an arbitrary ratio of interference signal power to receiver noise power.

16. The method of claim 14, wherein the quantizing outputs values having a number of bits selected from the group consisting of 2, 3, 4 and 5.

17. The method of claim 16, wherein the first non-zero quantization threshold magnitude corresponds to a first range of output values and the second non-zero quantization threshold magnitude corresponds to a second range of output values.

18. The method of claim 14, further comprising substantially reducing a dc-offset in the signal.

19. The method of claim 14, wherein quantizing further includes a first mapping and a second mapping, 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.

20. The method of claim 19, wherein the first mapping and the second mapping use a look-up table.

21. The method of claim 14, 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.

22. The method of claim 21, wherein the second carrier frequency signal is less than approximately 100 kHz.

23. The method of claim 21, 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.

24. The method of claim 23, wherein the performing the complex phase rotation further includes determining the complex phase rotation using a look-up table.

25. The method of claim 14, 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.

26. The method of claim 25, wherein the threshold is eight times the first non-zero quantization threshold magnitude.