Method and apparatus for monitoring and controlling gain compression in a transmitted signal

• US 6,549,755 B2
• Filed: 04/01/2002
• Issued: 04/15/2003
• Est. Priority Date: 05/04/2001
• Status: Expired due to Term

• Current Assignee: Glowlink Communications Technology, Inc. (Singapore Technologies Engineering Limited)
• Original Assignee: Glowlink Communications Technology, Inc. (Singapore Technologies Engineering Limited)
• Inventors: Downey, Michael L., Chu, Jeffrey C., Estus, Robert W.
• Primary Examiner(s): Appiah, Charles N.
• Application Number:
  US10/114,373
• Publication Number:
  US 20020164950A1
• Time in Patent Office: 379 Days
• Field of Search: 455/91, 455/126-127, 455/69, 455/232.1, 455/236--23, 455/239--24, 455/245.1, 455/250.1, 455/13.4, 455/522, 455/430, 330/278, 375/345, 375/225, 375/227, 375/221, 370/249
• US Class Current: 455/13.4
• CPC Class Codes: H04B 7/1851 Systems using a satellite or space-based relay H04B7/18508, H04B7/18521 take precedence; providing specific services H04B7/18523 - H04B7/18576
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays
• CPC Class Codes: H04W 52/08 Closed loop power control
• CPC Class Codes: H04W 52/241 taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo

Abstract

A method and apparatus for monitoring and controlling the operating point of a satellite transponder amplifier. In one aspect of the invention, a time domain signal received at a ground station is digitally sampled. Then, a histogram of the received signal is computed. To form the histogram, the digital samples are categorized according to which of a plurality of amplitude ranges each sample falls within. When plotted as a graph, the number of occurrences within each amplitude range forms the histogram. Under low compression levels, the histogram generally appears as an approximately bell-shaped curve. However, under higher compression levels, the bell-shaped curve becomes distorted. By correlating the acquired histogram to a template histogram, an amount of compression can be determined. This amount of compression indicates the operating point of the transponder amplifiers. If desired, the transmission power levels used by the satellite can be adjusted to ensure that the amplifiers operate at desired levels of compression. The invention has an advantage over prior techniques in that the operating point of the transponder amplifiers can be more accurately determined. As such, the operating point can be more precisely adjusted.

Claims

1. A method for determining a level of gain compression in a wireless transmitted signal, the method implemented by communications equipment and comprising steps of:

receiving a wireless transmitted signal wherein the transmitted signal is amplified by an amplifier prior to transmission;

sampling the signal, thereby forming a series a digital samples representative of the signal in the time-domain;

forming an acquired histogram of the samples;

correlating the histogram to a template histogram pre-stored in machine readable memory; and

forming a correlation metric representative of similarity between the acquired histogram and the template histogram wherein the correlation metric is indicative of an amount of gain compression introduced into the wireless signal by the amplifier.

2. The method according to claim 1, further comprising inhibiting further gain compression based on the amount of gain compression thereby inhibiting signal quality deterioration caused by gain compression.

3. The method according to claim 2, further comprising controlling gain of the transmitted signal in a closed link power control loop based on received signal quality.

4. The method according to claim 1, wherein the signal is received by a ground station from a satellite transponder.

5. The method according to claim 1, wherein the signal is received by a satellite from a ground station.

6. The method according to claim 1, further comprising measuring effective isotropically radiated power when the gain compression is below a predetermined level and using the isotropically radiated power to determine an operating point of the amplifier.

7. The method according to claim 1, further comprising comparing the amount of gain compression to an amplifier gain curve to determine an operating point of the amplifier and, when the gain compression is lower than a predetermined level, using measured effective isotropically radiated power to determine the operating point.

8. The method according to claim 1, further comprising performing automatic gain control on the signal prior to said sampling.

9. The method according to claim 1, further comprising median filtering the samples of the wireless signal.

10. The method according to claim 1, further comprising forming the template histogram by obtaining samples of the signal.

11. The method according to claim 10, further comprising obtaining a plurality of template histograms.

12. The method according to claim 11, further comprising averaging the plurality of template histograms.

13. The method according to claim 10, wherein the samples for the template histogram are obtained while the amplifier operates in a linear region.

14. A system for determining a level of gain compression in a transmitted signal comprising communications equipment that controls gain of the transmitted signal in a closed link power control loop based on received signal quality and in which a histogram is computed from a received wireless transmitted signal and the computed histogram is correlated to a template histogram to determine the level of gain compression in the wireless transmitted signal, wherein the communications equipment inhibits further gain compression based on the amount of gain compression thereby inhibiting signal quality deterioration caused by gain compression.

15. The system according to claim 14, wherein the computed histogram is formed by the communications equipment sampling the transmitted signal in the time domain and determining a number of samples that fall into each of a plurality of amplitude ranges.

16. The system according to claim 14, wherein the communications equipment comprises a ground station that receives the signal from a satellite transponder.

17. The system according to claim 14, wherein the communications equipment comprises a satellite system that receives the signal from a ground station.

18. The system according to claim 14, wherein the communications equipment compares a level of gain compression to an amplifier gain curve to determine an amplifier operating point.

19. The method according to claim 18, wherein when the gain compression is lower than a predetermined level, effective isotropically radiated power is used to determine the operating point.

20. The system according to claim 14, wherein the communications equipment performs automatic gain control on the received signal prior to sampling the transmitted signal for computing the histogram.

21. The system according to claim 14, wherein the communications equipment median filters samples of the transmitted signal for computing the histogram.

22. The system according to claim 14, wherein the communications equipment forms the template histogram by obtaining samples of the transmitted signal.

23. The system according to claim 22, wherein the communications equipment obtains a plurality of template histograms.

24. The system according to claim 23, wherein the communications equipment averages the plurality of template histograms.

25. The system according to claim 22, wherein the communications equipment obtains the samples for the template histogram while the amplifier operates in a linear region.