Method for detecting radio frequency impairments in a data-over-cable system

• US 6,785,292 B1
• Filed: 05/28/1999
• Issued: 08/31/2004
• Est. Priority Date: 05/28/1999
• Status: Expired due to Term

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Vogel, Mark O.
• Primary Examiner(s): NGUYEN, HANH N
• Application Number:
  US09/322,513
• Time in Patent Office: 1,922 Days
• Field of Search: 370/493, 370/494, 370/495, 370/433, 370/431, 370/432, 370/458, 370/459, 370/247, 370/460, 370/461, 370/468, 370/347, 455/69, 455/552, 455/553, 725/5.1, 725/103, 725/125, 725/124, 725/111, 725/107, 375/222, 324/620, 709/226, 709/224, 709/225, 709/227, 709/228
• US Class Current: 370/433
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 69/16 Implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP]
• CPC Class Codes: H04L 69/164 Adaptation or special uses of UDP protocol
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details
• CPC Class Codes: H04N 21/2402 Monitoring of the downstream path of the transmission network, e.g. bandwidth available traffic monitoring in data switching networks H04L43/00; monitoring data switching networks utilization H04L43/0876
• CPC Class Codes: H04N 21/42676 for modulating an analogue carrier signal to encode digital information or demodulating it to decode digital information, e.g. ADSL or cable modem
• CPC Class Codes: H04N 21/42684 Client identification by a unique number or address, e.g. serial number, MAC address, socket ID network arrangements, protocols or services for addressing or naming H04L61/00
• CPC Class Codes: H04N 21/6118 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 21/64322 IP
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

A method and system for determining a source radio frequency impairment in a data-over-cable system. The method includes ascertaining reference signal-to-noise ratios and comparing them to signal-to-noise ratios that are measured when the system is in operation. The signal-to-noise ratios are measured under different selections of which cable modems transmit. The method determines whether there are degradations on one or more upstream channel and correlates the degradations to identify the source of the impairment. The identification of impairments helps ensure that the source of impairment may be removed from the data-over-cable system to provide better overall performance.

Claims

1. In a data-over-cable system, a method for determining a source of radio frequency impairment on an upstream path, the upstream path comprising an upstream channel, the upstream channel carrying data transmissions from a plurality of cable modems to a cable modem termination system, the method comprising the steps of:

ascertaining a reference signal-to-noise ratio;

measuring a plurality of signal-to-noise ratios during a plurality of active periods, wherein only one cable modem transmits during each active period;

comparing each measured signal-to-noise ratio to the reference signal-to-noise ratio to obtain a degradation value for the active period;

determining whether the degradation value is greater than a threshold, and if so,

logging parameters associated with the cable modem that is active during the active period;

correlating the logged parameters; and

identifying the source of radio frequency impairment;

wherein the step of identifying the source of radio frequency impairment comprises the steps of;

determining whether the reference signal-to-noise ratio is low, and if so,

determining whether parameters for the cable modems have been logged, and if not,

concluding that the source of radio frequency impairment is a radio frequency source that is external to the data-over-cable system, wherein the external radio frequency source interferes with the data transmission on the upstream channel.

2. In a data-over-cable system, a method for determining a source of radio frequency impairment on an upstream path, the upstream path comprising a plurality of upstream channels, each upstream channel carrying data transmissions from one of a plurality of cable modems to a cable modem termination system, the method comprising the steps of:

ascertaining a plurality of reference signal-to-noise ratios wherein each reference signal-to-noise ratio corresponds to an upstream channel;

scheduling a plurality of all-channels-active periods wherein all upstream channels are simultaneously active during each all-channels-active period and only one cable modem is transmitting on each of the active upstream channels;

logging degradation information for the all-channels-active periods;

scheduling a plurality of single-channel-active periods wherein only one upstream channel is active during each single-channel-active period and only one cable modem is transmitting on the active upstream channel;

logging degradation information for the single-channel-active periods;

correlating the logged degradation information for the single-channel-active periods; and

identifying the source of radio frequency impairment;

wherein the step of logging degradation information for the single-channel-active periods further comprises the step of;

alerting a user that the degradation information has been logged.

3. In a data-over-cable system, a method for determining a source of radio frequency impairment on an upstream path, the upstream path comprising a plurality of upstream channels, each upstream channel carrying data transmissions from one of a plurality of cable modems to a cable modem termination system, the method comprising the steps of:

ascertaining a plurality of reference signal-to-noise ratios wherein each reference signal-to-noise ratio corresponds to an upstream channel;

scheduling a plurality of all-channels-active periods wherein all upstream channels are simultaneously active during each all-channels-active period and only one cable modem is transmitting on each of the active upstream channels;

logging degradation information for-the all-channels-active periods;

scheduling a plurality of single-channel-active periods wherein only one upstream channel is active during each single-channel-active period and only one cable modem is transmitting on the active upstream channel;

logging degradation information for the single-channel-active periods;

correlating the logged degradation information for the single-channel-active periods; and

identifying the source of radio frequency impairment;

wherein the step of logging degradation information for the single-channel-active periods comprises, for each single-channel-active period;

measuring a signal-to-noise-ratio for the active upstream channel during the single-channel-active period;

measuring a plurality of noise floor values during the single-channel-active period, wherein each noise floor value corresponds to an inactive upstream channel in a plurality of inactive upstream channels, and wherein each inactive upstream channel is other than the active upstream channel;

comparing the measured signal-to-noise ratio to the reference signal-to-noise ratio that corresponds to the active upstream channel to obtain a degradation value for the active upstream channel;

determining whether the degradation value for the active upstream channel is greater than a threshold, and if so,

logging parameters associated with the cable modem that is transmitting on the active upstream channel;

comparing the measured noise floor value for the each inactive upstream channel to a corresponding reference noise floor value to obtain a degradation value for the each inactive upstream channel, wherein the reference noise floor value is associated with the reference signal-to-noise value for the inactive upstream channel; and

determining whether the degradation values for at least one inactive upstream channels are greater than the threshold, and if so,

logging the parameters associated with the cable modem that is transmitting on the active upstream channel, and

logging parameters associated with the inactive upstream channels.

4. The method of claim 3 wherein the threshold is defined by a user.

5. The method of claim 3 wherein each noise floor values is measured at the bandwidth of the corresponding upstream channel.

6. The method of claim 3 wherein the logged parameters that are associated with the cable modem are the measured signal-to-noise ratio and an identification value for the cable modem.

7. The method of claim 6 wherein the identification value for the cable modem is a Media Access Control address.

8. The method of claim 6 wherein the identification value for the cable modem is an Internet Protocol address.

9. The method of claim 6 wherein the identification value for the cable modem is a Service Identifier.

10. The method of claim 3 wherein the logged parameters that are associated with the inactive upstream channels are the measured noise floor values.

11. In a data-over-cable system, a method for determining a source of radio frequency impairment on an upstream path, the upstream path comprising a plurality of upstream channels, each upstream channel carrying data transmissions from one of a plurality of cable modems to a cable modem termination system, the method comprising, the steps of:

ascertaining a plurality of reference signal-to-noise ratios wherein each reference signal-to-noise ratio corresponds to an upstream channel;

scheduling a plurality of all-channels-active periods wherein all upstream channels are simultaneously active during each all-channels-active period and only one cable modem is transmitting on each of the active upstream channels;

logging degradation information for the all-channels-active periods;

scheduling a plurality of single-channel-active periods wherein only one upstream channel is active during each single-channel-active period and only one cable modem is transmitting on the active upstream channel;

logging degradation information for the single-channel-active periods,

correlating the logged degradation information for the single-channel-active periods; and

identifying the source of radio frequency impairment,

wherein the step of identifying the source of radio frequency impairment comprises the steps of;

determining whether a selection of the upstream channels have low reference signal-to-noise ratios, and if so,

determining whether the degradation information for the single-channel-active periods indicates no degradation for the selection, and if so,

determining whether the degradation information for the all-channels-active periods indicates no degradation on all upstream channels, and if so,

concluding that the source of radio frequency impairment is a radio frequency source that is external to the data-over-cable system, wherein the external radio frequency source interferes with the data transmission on the upstream channels.