On-line phase noise measurement for layered modulation

• US 7,463,676 B2
• Filed: 10/24/2003
• Issued: 12/09/2008
• Est. Priority Date: 10/25/2002
• Status: Expired due to Fees

• Current Assignee: The DIRECTV Group, Inc. (AT&T, Inc.)
• Original Assignee: The DIRECTV Group, Inc. (AT&T, Inc.)
• Inventors: Chen, Ernest C.
• Primary Examiner(s): Ghayour; Mohammed
• Assistant Examiner(s): WILLIAMS, LAWRENCE B
• Application Number:
  US10/692,539
• Publication Number:
  US 20040091033A1
• Time in Patent Office: 1,873 Days
• Field of Search: 375/226, 375/227, 375/224, 375/371, 375/222, 342/13, 455/318, 455/333, 702/111, 752/72, 324/613
• US Class Current: 375/222
• CPC Class Codes: H01Q 3/22 varying the orientation in accordance with variation of frequency of radiated wave
• CPC Class Codes: H04B 17/345 Interference values signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR] H04B17/336
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details

Abstract

A method and apparatus for measuring the phase noise of an low noise block (LNB) and other devices while the device under test is on line is disclosed. Using a signal processing procedure over a short duration of a received signal, the technique demodulates the signal to expose the phase history of the underlying carrier for measurement. In an exemplary apparatus timing and carrier recovery on A/D samples are performed conventionally, a linear phase is estimated from minimum mean square fitting to the recovered carrier phase history, the single tone carrier is removed from the recovered phase to yield a residual phase. A fast Fourier transform (FFT) can be performed on the residual phase to produce a phase noise spectral measurement at an input of the demodulator.

Claims

1. A system for measuring phase noise, comprising:

a tuner for tuning a signal from a low-noise block converter (LNB) and converting the tuned signal to a baseband signal;

at least one analog-to-digital converter (ADC) for capturing data from the baseband signal;

a timing processor for acquiring and tracking symbol timing of the captured data of the baseband signal;

a carrier processor for determining unwrapped phase history data from the tracked symbol timing;

a line fitting processor for determining a linear phase by fitting a straight line to the unwrapped phase history data; and

a subtractor for subtracting the linear phase from the phase history data to produce a residual phase of the carrier, wherein the residual phase of the carrier is substantially a performance measurement of the LNB.

2. The system of claim 1, further comprising a fast Fourier transform (FFT) processor for determining a phase noise spectrum from the residual phase from the subtractor.

3. The system of claim 2, wherein the phase noise spectrum is scaled to dBc/KHz.

4. The system of claim 1, wherein the line fitting processor performs a minimum mean square (MMS) operation on the phase history data to determine the linear phase.

5. The system of claim 1, wherein the signal comprises a satellite television signal.

6. The system of claim 1, wherein the captured data comprises a length based upon a lowest frequency of interest.

7. The system of claim 1, comprising more than one ADC and wherein the captured data comprises in-phase (I) and quadrature (Q) components.

8. A method for measuring phase noise, comprising the steps of:

tuning a signal from a low noise block converter (LNB) and converting the signal to a baseband signal;

capturing data from the baseband signal;

acquiring and tracking the captured data of the baseband signal to determine symbol timing tracked data;

determining unwrapped phase history from the symbol timing tracked data;

fitting a straight line to the unwrapped phase history data to determine a linear phase; and

subtracting the linear phase from the phase history data to produce a residual phase of the signal, wherein the residual phase is substantially a performance measurement of the LNB.

9. The method of claim 8, further comprising determining a phase noise spectrum from the residual phase with a fast Fourier transform (FFT) processor.

10. The method of claim 9, further comprising scaling the phase noise spectrum to dBc/KHz.

11. The method of claim 8, wherein fitting the straight line comprises performing a minimum mean square (MMS) operation on the phase history data to determine the linear phase.

12. The method of claim 8, wherein the signal comprises a satellite television signal.

13. The method of claim 8, wherein the captured data comprises a length based upon a lowest frequency of interest.

14. The method of claim 8, comprising more than one ADC and wherein the captured data comprises in-phase (I) and quadrature (Q) components.

15. A system for measuring phase noise, comprising:

means for tuning a signal from a low noise block converter (LNB) and converting the signal to a baseband signal;

means for capturing data from the baseband signal;

means for acquiring and tracking symbol dining of the captured data of the baseband signal;

means for determining unwrapped phase history data from the tracked symbol timing;

means for determining a linear phase by fitting a straight line to the unwrapped phase history data; and

means for subtracting the linear phase from the phase history data to produce a residual phase of the signal, wherein the residual phase is substantially a performance measurement of the LNB.

16. The system of claim 15, further comprising means for determining a phase noise spectrum from the residual phase with a fast Fourier transform (FFT) processor.

17. The system of claim 16, further comprising means for scaling the phase noise spectrum to dBc/KHz.

18. The system of claim 15, wherein the means for fitting the straight line comprises means for performing a minimum mean square (MMS) operation on the phase history data to determine the linear phase.

19. The system of claim 15, wherein the signal comprises a satellite television signal.

20. The system of claim 15, wherein the captured data comprises a length based upon a lowest frequency of interest.

21. The system of claim 15, comprising more than one ADC and wherein the captured data comprises in-phase (I) and quadrature (Q) components.