Method and Apparatus for Characterizing Modulation Schemes in an HFC Network

• US 20080101210A1
• Filed: 12/20/2006
• Published: 05/01/2008
• Est. Priority Date: 10/26/2006
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Moran III, John L., Thompson, Robert J., Moore, Charles S., Cooper, Michael J.
• Granted Patent: US 7,876,697 B2
• Time in Patent Office: Days
• US Class Current: 370/204
• CPC Class Codes: H04B 10/0775 Performance monitoring and measurement of transmission parameters
• CPC Class Codes: H04B 10/079 using measurements of the data signal
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/002 Algorithms with memory of the previous states, e.g. Markovian models

Abstract

The available modulation schemes of a network are analyzed to determine which ones contain excessive phase noise or narrowband interference. A network element is selected and assigned to a test channel at a first modulation scheme at a predetermined power level to achieve a predetermined PER. The network element transmits a test signal and the network controller measures the signal to noise ratio (SNR) in the received test signal. If the SNR is not within a predetermined tolerance range of an estimated SNR for the modulation scheme at the predetermined PER, the modulation scheme is determined to have excessive phase noise or narrowband interference. Each available modulation scheme is tested by instructing the network element to transmit the test signal using each modulation scheme and assigning the power level of each modulation scheme. The suitable modulation schemes may be determined.

Claims

1. An apparatus for characterizing modulation schemes for a network comprising:

a controller configured to instruct a network element to transmit a test signal at a test frequency at a first modulation scheme and a first power;

a receiver configured to receive the test signal from the network element; and

an equalizer which measures a signal to noise ratio of the test signal,

wherein the controller determines if the signal to noise ratio is within a predetermined range of an estimated signal to noise ratio, and the controller determines that the modulation scheme has excessive inband interference or phase noise when the signal to noise ratio is not within a predetermined range of an estimated signal to noise ratio.

2. The apparatus of claim 1, wherein the controller is further configured to instruct the network element to repeatedly transmit the test signal at other modulation schemes available, and to determine which modulation schemes provide a signal to noise ratio is within a predetermined range of an estimated signal to noise ratio.

3. The apparatus of claim 2, wherein the controller is further configured to instruct the network element to adjust the transmission power of the test signal to correspond with a predetermined packet error rate for each of the other modulation schemes.

4. The apparatus of claim 3, wherein the controller creates a list of optimum modulation schemes for the network to use.

5. The apparatus of claim 1, wherein the receiver is a receiver which is not assigned to handle communications between network elements, whereby a plurality of modulation schemes are characterized without interrupting communications between network elements and a cable modem termination system.

6. A method for characterizing modulation schemes for a network comprising the steps of:

selecting a network element to transmit a test signal at a test frequency at a first modulation scheme and a first power;

receiving the test signal from the network element;

measuring a signal to noise ratio of the test signal;

determining if the signal to noise ratio is within a predetermined range of an estimated signal to noise ratio, and

determining that the modulation scheme has excessive inband interference or phase noise when the signal to noise ratio is not within a predetermined range of an estimated signal to noise ratio.

7. The method of claim 6, further comprising the steps of:

instructing the network element to change the modulation scheme and transmit the test signal at other modulation schemes available; and

determining which modulation schemes provide a signal to noise ratio is within a predetermined range of an estimated signal to noise ratio.

8. The method of claim 7, further comprising the step of instructing the network element to adjust the transmission power of the test signal to correspond with a predetermined packet error rate for each of the modulation schemes.

9. The method of claim 8, further comprising the step of creating a list of optimum modulation schemes for the network to use.

10. The method of claim 6, wherein the step of receiving the test signal includes receiving the test signal at a receiver which is not assigned to handle communications between network elements, whereby a plurality of modulation schemes are characterized without interrupting communications between network elements and a cable modem termination system.

11. A computer readable medium carrying instructions for a computer to perform a method for characterizing modulation schemes for a network comprising the steps of:

selecting a network element to transmit a test signal at a test frequency at a first modulation scheme and a first power;

receiving the test signal from the network element;

measuring a signal to noise ratio of the test signal;

determining if the signal to noise ratio is within a predetermined range of an estimated signal to noise ratio, and

determining that the modulation scheme has excessive inband interference or phase noise when the signal to noise ratio is not within a predetermined range of an estimated signal to noise ratio.

12. The computer readable medium of claim 11, wherein the method further comprise performing the steps of:

instructing the network element to change the modulation scheme and transmit the test signal at other modulation schemes available; and

determining which modulation schemes provide a signal to noise ratio is within a predetermined range of an estimated signal to noise ratio.

13. The computer readable medium of claim 12, wherein the method further comprise performing the steps of instructing the network element to adjust the transmission power of the test signal to correspond with a predetermined packet error rate for each of the modulation schemes.

14. The computer readable medium of claim 13, wherein the method further comprises the step of creating a list of optimum modulation schemes for the network to use.

15. The computer readable medium of claim 11, wherein the step of receiving the test signal includes receiving the test signal at a receiver which is not assigned to handle communications between network elements, whereby a plurality of modulation schemes are characterized without interrupting communications between network elements and a cable modem termination system.

16. A network comprising:

a controller configured to instruct a network element to transmit a test signal at a test frequency at a first modulation scheme and a first power;

a receiver configured to receive the test signal from the network element; and

an equalizer which measures a signal to noise ratio of the test signal,

wherein the controller determines if the signal to noise ratio is within a predetermined range of an estimated signal to noise ratio, and the controller determines that the modulation scheme has excessive inband interference or phase noise when the signal to noise ratio is not within a predetermined range of an estimated signal to noise ratio.

17. The network of claim 16, wherein the controller is further configured to instruct the network element to repeatedly transmit the test signal at other modulation schemes available, and to determine which modulation schemes provide a signal to noise ratio is within a predetermined range of an estimated signal to noise ratio.

18. The network of claim 17, wherein the controller is further configured to instruct the network element to adjust the transmission power of the test signal to correspond with a predetermined packet error rate for each of the other modulation schemes.

19. The network of claim 18, wherein the controller creates a list of optimum modulation schemes for the network to use.

20. The network of claim 16, wherein the receiver is a receiver which is not assigned to handle communications between network elements, whereby a plurality of modulation schemes are characterized without interrupting communications between network elements and a cable modem termination system.