Coherent averaging for measuring traveling wave tube amplifier nonlinearity

• US 20050078778A1
• Filed: 10/08/2004
• Published: 04/14/2005
• Est. Priority Date: 04/27/2001
• Status: Active Grant

• Current Assignee: DIRECTV, LLC (AT&T, Inc.)
• Original Assignee: The DIRECTV Group, Inc. (AT&T, Inc.)
• Inventors: Chen, Ernest C.
• Granted Patent: US 7,502,430 B2
• Time in Patent Office: Days
• US Class Current: 375/346
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 2200/393 A measuring circuit being coupled to the output of an amplifier
• CPC Class Codes: H03F 3/58 using travelling-wave tubes
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 2027/0061 remodulation
• CPC Class Codes: H04L 27/183 Multiresolution systems
• CPC Class Codes: H04L 27/227 using coherent demodulation
• CPC Class Codes: H04L 27/366 Arrangements for compensating undesirable properties of the transmission path between the modulator and the demodulator

Abstract

A method and system provide the ability to measure a transmission performance characteristic. A signal is received and demodulated. An ideal signal is generated from the demodulated signal. The received signal is coherently averaged to reduce noise. The performance characteristic is the estimated TWTA nonlinearity from a difference between the coherently averaged ideal signal and received signal.

Claims

1. A method of measuring a transmission performance characteristic, comprising:

receiving a signal;

demodulating the signal;

generating an ideal signal from the demodulated signal;

coherently averaging the received signal to reduce noise; and

estimating the performance characteristic from a difference between the ideal signal and the coherently averaged received signal.

2. The method of claim 1, wherein the coherent averaging is performed after demodulation.

3. The method of claim 1, further comprising coherently averaging the ideal signal and wherein the performance characteristic is based on the difference between the coherently averaged ideal signal and coherently averaged received signal.

4. The method of claim 1, wherein the coherently averaging and estimating steps comprise:

aligning the received signal and the ideal signal sample-for-sample;

forming data pairs for corresponding samples;

sorting the data pairs to powers of the ideal signal samples; and

coherently averaging the received signals to reduce noise.

5. The method of claim 4, further comprising coherently averaging the ideal signals to reduce noise.

6. The method of claim 1, wherein the coherently averaging comprises coherently adding a given number of adjacent received signals;

the number representing the averaging ratio.

7. The method of claim 1, wherein the step of estimating the performance characteristic includes fitting a curve of the received signal versus the ideal signal.

8. The method of claim 7, wherein the curve is an AM-AM plot.

9. The method of claim 7, wherein the curve is an AM-PM plot.

10. The method of claim 1, further comprising inverse filtering the received signal to restore nonlinearity.

11. The method of claim 1, further comprising using a linear equalizer on the received signal to restore nonlinearity.

12. A system for measuring a transmission performance characteristic, comprising:

(a) a demodulator for demodulating a received signal;

(b) a signal generator for producing an ideal signal from the demodulated signal; and

(c) a processor for;

(i) coherently averaging the received signal to reduce noise; and

(ii) estimating the performance characteristic from a difference between the ideal signal and the coherently averaged received signal.

13. The system of claim 12, wherein the coherent averaging is performed after demodulation.

14. The system of claim 12, wherein the processor is further configured to coherently average the ideal signal and wherein the performance characteristic is based on the difference between the coherently averaged ideal signal and coherently averaged received signal.

15. The system of claim 12, wherein the processor is configured to coherently average and estimate by:

aligning the received signal and the ideal signal sample-for-sample;

forming data pairs for corresponding samples;

sorting the data pairs to powers of the ideal signal samples; and

coherently averaging the received signals to reduce noise.

16. The system of claim 15, wherein the processor is further configured to coherently average the ideal signals to reduce noise.

17. The system of claim 12, wherein the processor is configured to coherently average by coherently adding a given number of adjacent received signals;

the number representing the averaging ratio.

18. The system of claim 12, wherein the processor is configured to estimate the performance characteristic by fitting a curve of the received signal versus the ideal signal.

19. The system of claim 18, wherein the curve is an AM-AM plot.

20. The system of claim 18, wherein the curve is an AM-PM plot.

21. The system of claim 12, further comprising an inverse filter that is used on the received signal to restore nonlinearity.

22. The system of claim 12, further comprising a linear equalizer that is used on the received signal to restore nonlinearity.