Characterizing Broadband Communication Networks

• US 20070121712A1
• Filed: 11/08/2006
• Published: 05/31/2007
• Est. Priority Date: 11/10/2005
• Status: Active Grant

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Acterna LLC (Lumentum Holdings Inc.)
• Inventors: Okamoto, Koji
• Granted Patent: US 8,325,613 B2
• Time in Patent Office: Days
• US Class Current: 375/222
• CPC Class Codes: H04L 1/24 Testing correct operation
• CPC Class Codes: H04L 2025/03808 Transmission of equaliser coefficients
• CPC Class Codes: H04L 25/0216 with estimation of channel length
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

A remote testing device, including a cable modem circuit, requests an IP address from a remote cable modem termination system (CMTS) and receives back IP connection information including adaptive equalizer coefficients, which represent compensation and/or correction for transmission path noise. Using the equalizer coefficients, the remote testing device can determine a phase response, phase angles for each frequency increment over a channel bandwidth, and group delay.

Claims

1. A testing device for determining a phase response in a transmission path of a communication network comprising:

a coupler for sending and receiving broadband RF signals to and from the communication network;

a cable modem circuit for generating an RF transmission signal to request an IP address from a cable modem termination system (CMTS), and for receiving IP connection information, including pre-equalization coefficient information relating to the transmission path between the testing device and the CMTS, therefrom; and

a processing circuit connected to the cable modem circuit for receiving the pre-equalization coefficient information from the cable modem circuit, and for determining the phase response of the transmission path from the pre-equalization coefficient information.

2. The testing device according to claim 1, wherein the processing circuit generates a frequency response from the phase response.

3. The testing device according to claim 2, wherein the processing circuit performs a discrete Fourier transform on the phase response to generate the frequency response.

4. The testing device according to claim 2, wherein the processing circuit generates a list of phase angles for each frequency increment over a bandwidth of a channel.

5. The testing device according to claim 4, wherein each phase angle is determined by calculating the tan⁻

1 of an imaginary portion of a frequency response value divided by a real portion of the frequency response value.

6. The testing device according to claim 4, wherein the processing circuit determines group delay from the list of phase angles.

7. The testing device according to claim 6, wherein the processing circuit determines the group delay by calculating a difference in phase angle between two frequency points, and multiplying the difference by a scaling factor.

8. The testing device according to claim 6, wherein the processing circuit determines the group delay by calculating a first derivative of a function defining the phase angles.

9. The testing device according to claim 6, further comprising a display for displaying the phase response and/or the group delay.

10. A method for determining a phase response in a transmission path of a communication network comprising:

providing a testing device with a cable modem circuit, a processing circuit, and a coupler for sending and receiving broadband RF signals to and from the communication network;

generating an RF transmission signal in the cable modem circuit to request an IP address from a cable modem termination system (CMTS);

receiving IP connection information in the cable modem circuit, including pre-equalization coefficient information relating to the transmission path between the testing device and the CMTS;

receiving the pre-equalization coefficient information in the processing circuit from the cable modem circuit; and

determining the phase response of the transmission path from the pre-equalization coefficient information.

11. The method according to claim 10, further comprising generating a frequency response from the phase response.

12. The method according to claim 11, wherein the processing circuit performs a discrete Fourier transform on the phase response to generate the frequency response.

13. The method according to claim 11, further comprising generating a list of phase angles for each frequency increment over a bandwidth of a channel.

14. The method according to claim 13, wherein each phase angle is determined by calculating the tan⁻

1 of an imaginary portion of a frequency response value divided by a real portion of the frequency response value.

15. The method according to claim 13, further comprising determining group delay from the list of phase angles.

16. The method according to claim 15, wherein the processing circuit determines the group delay by calculating a difference in phase angle between two frequency points, and multiplying the difference by a scaling factor.

17. The method according to claim 15, wherein the processing circuit determines the group delay by calculating a first derivative of a function defining the phase angles.