Technique for determining carrier-to-noise ratio of selected channels in an access network

• US 6,757,522 B1
• Filed: 12/11/2000
• Issued: 06/29/2004
• Est. Priority Date: 12/11/2000
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Azarakhsh, Nozar, de Jesus Leano, Chrisanto, Tu, Nan, Mahesh, Harihara, Naegeli, Charles, Chen, Hungsan
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US09/735,200
• Time in Patent Office: 1,296 Days
• Field of Search: 455/423, 455/424, 455/67.11, 455/67.13, 725/107, 725/109-125
• US Class Current: 455/67.11
• CPC Class Codes: H04B 17/309 Measuring or estimating channel quality parameters
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]

Abstract

A technique is disclosed for determining a carrier-to-noise ratio (CNR) value for a selected channel of an access network. A background noise level on the selected channel is measured during a first time interval during which none of the network nodes are transmitting signals on the selected channel. A first signal strength on the selected channel is also measured during a second time interval during which a first network node is transmitting at least one signal on the selected channel. A CNR value for the selected channel may then be calculated using the measured background noise level information and the measured first signal strength information. According to a specific implementation, the calculation of the CNR value for the selected channel is not based upon an Error Vector Magnitude value associated with the signal transmitted from the first network node.

Claims

1. A method for determining a carrier-to-noise ratio (CNR) value for a selected channel of an access network, the access network including a plurality of network nodes which communicate with a Head End via at the selected channel, the method comprising:

measuring a background noise level on the selected channel during a first time interval when none of the network nodes are transmitting signals on the selected channel;

measuring a first carrier signal strength of a first network node on the selected channel during a second time interval when said first network node is transmitting at least one signal on the selected channel;

calculating a CNR value for the selected channel using the measured background noise level information and the measured first carrier signal strength information;

scheduling a first response request timeslot on the selected channel, said first response request timeslot specifying that no network device on the selected channel transmit signals during the first time interval; and

scheduling a second response request timeslot on the selected channel, said second response request timeslot specifying that the first network device transmit the at least one signal on the selected channel during the second time interval.

2. The method of claim 1 wherein the calculation of the CNR value for the selected channel is not based upon an error vector magnitude value associated with the at least one signal.

3. The method of claim 1 wherein the calculation of the CNR value is based on a carrier signal transmitted by the first network node on the selected channel, and is not based on signals transmitted by other network nodes using the selected channel.

4. The method of claim 1 wherein said first carrier signal strength measuring includes measuring the first carrier signal strength of the first network node on the selected channel during the second time interval when only said first network node is transmitting at least one signal on the selected channel.

5. The method of claim 1 wherein the first response request timeslot specifies a network device identifier corresponding to a NULL network device on the selected channel;

and

wherein the second response request timeslot specifies a network device identifier corresponding to the first network device.

6. The method of claim 1 wherein said first and second response request timeslots are each scheduled to immediately follow a respective initial ranging timeslot scheduled on the selected channel.

7. The method of claim 6 further comprising scheduling an initial ranging timeslot about every two seconds.

8. The method of claim 1 further comprising:

measuring a second signal strength of a second network node on the selected channel during a third time interval when only the second network node is transmitting at least one second signal on the selected channel; and

calculating a second CNR value for the selected channel using the measured background noise level information and the measured second signal strength information.

9. The method of claim 8 further comprising calculating an updated average CNR value for the selected channel using the measured background noise level information, the measured first carrier signal strength information, and the measured second signal strength information.

10. The method of claim 9 further comprising determining a respective CNR value for the selected channel using separate signals from each of the network nodes on the selected channel.

11. The method of claim 10 further comprising periodically re-computing the updated average CNR value for the selected channel using information relating to each of the respective CNR values.

12. The method of claim 1 wherein said access network is a cable network, said network nodes are cable modems, said selected channel corresponds to a selected upstream channel, and wherein the Head End comprises a Cable Modem Termination System (CMTS).

13. The method of claim 12 wherein the first and second response request timeslots correspond to station maintenance timeslots implemented according to a DOCSIS protocol.

14. The method of claim 12 wherein said first network node corresponds to a first cable modem, and wherein the calculation of the CNR value is based on signals transmitted by the first cable modem on the selected channel, and is not based on signals transmitted by other cable modems using the selected channel.

15. A method for determining a signal-to-noise ratio (SNR) value for a selected channel of an access network, the access network including a plurality of network nodes which communicate with a Head End via at the selected channel, the method comprising:

measuring a background noise level on the selected channel during a first time interval when none of the network nodes are transmitting signals on the selected channel;

measuring a first signal strength of a first network node on the selected channel during a second time interval when said first network node is transmitting at least one signal on the selected channel;

calculating a SNR value for the selected channel using the measured background noise level information and the measured first signal strength information;

scheduling a first response request timeslot on the selected channel, said first response request timeslot specifying that no network device on the selected channel transmit signals during the first time interval; and

scheduling a second response request timeslot on the selected channel, said second response request timeslot specifying that the first network device transmit the at least one signal on the selected channel during the second time interval.

16. The method of claim 15 wherein the calculation of the SNR value for the selected channel is not based upon an error vector magnitude value associated with the at least one signal.

17. The method of claim 15 wherein the calculation of the SNR value is based on signals transmitted by the first network node on the selected channel, and is not based on signals transmitted by other network nodes using the selected channel.

18. The method of claim 15 wherein said first signal strength measuring includes measuring the first signal strength of the first network node on the selected channel during the second time interval when only said first network node is transmitting at least one signal on the selected channel.

19. A computer program product for determining a carrier-to-noise ratio (CNR) value for a selected channel of an access network, the access network including a plurality of network nodes which communicate with a Head End via at the selected channel, the computer program product comprising:

a computer usable medium having computer code embodied therein, the computer readable code comprising;

computer code for measuring a background noise level on the selected channel during a first time interval when none of the network nodes are transmitting signals on the selected channel;

computer code for measuring a first signal strength of a first network node on the selected channel during a second time interval when said first network node is transmitting at least one signal on the selected channel;

computer code for calculating a CNR value for the selected channel using the measured background noise level information and the measured first signal strength information;

computer code for scheduling a first response request timeslot on the selected channel, said first response request timeslot specifying that no network device on the selected channel transmit signals during the first time interval; and

computer code for scheduling a second response request timeslot on the selected channel, said second response request timeslot specifying that the first network device transmit the at least one signal on the selected channel during the second time interval.

20. The computer program product of claim 19 wherein said first signal strength measuring code includes computer code for measuring the first signal strength of the first network node on the selected channel during the second time interval when only said first network node is transmitting at least one signal on the selected channel.

21. The computer program product of claim 19 further comprising computer code for scheduling said first and second response request timeslots to immediately follow a respective initial ranging timeslot scheduled on the selected channel.

22. The computer program product of claim 19 further comprising:

computer code for measuring a second signal strength of a second network node on the selected channel during a third time interval when only the second network node is transmitting at least one second signal on the selected channel; and

computer code for calculating a second CNR value for the selected channel using the measured background noise level information and the measured second signal strength information.

23. The computer program product of claim 22 further computer code for comprising calculating an updated average CNR value for the selected channel using the measured background noise level information, the measured first signal strength information, and the measured second signal strength information.

24. The computer program product of claim 23 further comprising computer code for determining a respective CNR value for the selected channel using separate signals from each of the network nodes on the selected channel.

25. The computer program product of claim 24 further comprising computer code for periodically re-computing the updated average CNR value for the selected channel using information relating to each of the respective CNR values.

26. The computer program product of claim 19 wherein said access network is a cable network, said network nodes are cable modems, said selected channel corresponds to a selected upstream channel, and wherein the Head End comprises a Cable Modem Termination System (CMTS).

27. A system for determining a carrier-to-noise ratio (CNR) value for a selected channel of an access network, the access network including a plurality of network nodes, the system comprising:

a Head End in communication with at least a portion of the network nodes, the Head End comprising;

at least one CPU;

memory;

at least one interface configured or designed to receive signals from at least one network node via the selected channel; and

at least one analog-to-digital (A/D) converter configured or designed to analyze signals on the selected channel;

the Head End being configured or designed to measure a background noise level on the selected channel during a first time interval when none of the network nodes are transmitting signals on the selected channel;

the Head End being further configured or designed to measure a first signal strength of a first network node on the selected channel during a second time interval when said first network node is transmitting at least one signal on the selected channel;

wherein the Head End is further configured or designed to calculate a CNR value for the selected channel using the measured background noise level information and the measured first signal strength information;

wherein the Head End is further configured or designed to schedule a first response request timeslot on the selected channel, said first response request timeslot specifying that no network device on the selected channel transmit signals during the first time interval; and

wherein the Head End is further configured or designed to schedule a second response request timeslot on the selected channel, said second response request timeslot specifying that the first network device transmit the at least one signal on the selected channel during the second time interval.

28. The system of claim 27 wherein said first signal corresponds to a first carrier signal on the selected channel.

29. The system of claim 27 wherein the calculation of the CNR value for the selected channel is not based upon an error vector magnitude value associated with the at least one signal.

30. The system of claim 27 wherein the Head End is further configured or designed to reserve use of the second response request timeslot exclusively for the first network node.

31. The system of claim 30 wherein the Head End is further configured or designed instruct each of the portion of network nodes to not transmit signals on the selected channel during the first time interval.

32. The system of claim 27 wherein said first and second response request timeslots are each scheduled to immediately follow a respective initial ranging timeslot scheduled on the selected channel.

33. The system of claim 27:

wherein the Head End is further configured or designed to measure a second signal strength of a second network node on the selected channel during a third time interval when only the second network node is transmitting at least one second signal on the selected channel; and

wherein the Head End is further configured or designed to calculate a second CNR value for the selected channel using the measured background noise level information and the measured second signal strength information.

34. The system of claim 33 wherein the Head End is further configured or designed to calculate an updated average CNR value for the selected channel using the measured background noise level information, the measured first signal strength information, and the measured second signal strength information.

35. The system of claim 27 wherein said access network is a cable network, said network nodes are cable modems, said selected channel corresponds to a selected upstream channel, and wherein the Head End comprises a Cable Modem Termination System (CMTS).

36. The system of claim 35 wherein the first and second response request timeslots correspond to station maintenance timeslots implemented according to a DOCSIS protocol.

37. A system for determining a carrier-to-noise ratio (CNR) value for a selected channel of an access network, the access network including a plurality of network nodes which communicate with a Head End via at the selected channel, the system comprising:

means for measuring a background noise level on the selected channel during a first time interval when none of the network nodes are transmitting signals on the selected channel;

means for measuring a first signal strength of a first network node on the selected channel during a second time interval when said first network node is transmitting at least one signal on the selected channel;

means for calculating a CNR value for the selected channel using the measured background noise level information and the measured first signal strength information;

means for scheduling a first response request timeslot on the selected channel, said first response request timeslot specifying that no network device on the selected channel transmit signals during the first time interval; and

means for scheduling a second response request timeslot on the selected channel, said second response request timeslot specifying that the first network device transmit the at least one signal on the selected channel during the second time interval.