Methods and System for Determining a Dominant Impairment of an Impaired Communication Channel

• US 20100158093A1
• Filed: 12/23/2008
• Published: 06/24/2010
• Est. Priority Date: 12/23/2008
• Status: Active Grant

• Current Assignee: ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Moran, John L. III, Thompson, Robert J., Moore, Charles S., Cooper, Michael J.
• Granted Patent: US 8,081,674 B2
• Time in Patent Office: Days
• US Class Current: 375/227
• CPC Class Codes: H04B 17/0085 using test signal generators
• 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]
• CPC Class Codes: H04W 52/343 taking into account loading or congestion level

Abstract

Methods are described for identifying a dominant impairment on a communication channel impaired by an interference issue. The methods include systematic examination of total power loading, systematic examination of signal power reduction, statistical examination of communication channel noise power, and systematic examination of interleaver effectiveness. Each relates to automatically diagnosing and characterizing distortion-based interference issues by monitoring the performance of a communication channel during a testing procedure. These methods enable a technician or engineer to remotely diagnose distortion-based interference issues relatively quickly without having to use external test equipment and without having to deploy technicians to various locations within the cable plant. A system by which these methods can be implemented is also disclosed.

Claims

1. A method for determining whether distortion or noise is the dominant impairment on an impaired communication channel, comprising the steps of:

establishing a sample size (N), a test duration, and a query rate for developing a complementary cumulative density function (CCDF) statistical measure of test signal measurements on a test channel;

selecting and remotely instructing a network element to transmit test signals on the test channel;

monitoring test signals at a headend of the test channel and recording measurements of signal-to-noise ratio (SNR) and Receive Power Level (Pr) on the test channel for samples 1 to N at the established query rate for the established duration;

developing a CCDF for Receive Noise Power Level (Nr) from samples 1 to N, where Nr=Pr-SNR for each sample;

obtaining a theoretically expected CCDF of Receive Noise Power Level for an Additive White Gaussian Noise (AWGN) dominated impairment on the test channel; and

comparing the CCDF for Receive Noise Power Level developed from samples 1 to N relative to the theoretically expected CCDF of Receive Noise Power Level for an AWGN-dominated impairment and concluding therefrom whether the dominant impairment is distortion or noise.

2. A method according to claim 1, wherein, if the comparing step indicates that the CCDF for Receive Noise Power Level developed from samples 1 to N is degraded by an amount in excess of that of the theoretically expected CCDF of Receive Noise Power Level for an AWGN-dominated impairment, then the dominant impairment is concluded to be distortion.

3. A method according to claim 2, wherein, if the comparing step indicates that the CCDF for Receive Noise Power Level developed from the samples 1 to N is substantially the same as that of the theoretically expected CCDF of Receive Noise Power Level for an AWGN-dominated impairment, then the dominant impairment is concluded to be distortion.

4. A method according to claim 3, wherein all of said measuring, instructing, monitoring, developing, comparing, and concluding steps are accomplished automatically and remotely of the network element by a cable modem termination system (CMTS) unit at a headend of the test channel.

5. A method for determining a burst duration nature of a dominant impairment on an impaired communication channel, comprising the steps of:

obtaining a minimum acceptance performance value for at least one of modulation error ratio (MER_MIN), signal-to-noise ratio (SNR_MIN), packet error rate (PER_MIN), and bit error rate (BER_MIN) for a test signal on a test channel;

setting a current interleaver setting of the test channel to a lowest available setting and remotely instructing a network element to receive a test signal on the test channel;

monitoring the test signal at a headend of the test channel and measuring at least one of modulation error ratio (MER), signal-to-noise ratio (SNR), packet error rate (PER), and bit error rate (BER); and

comparing the measurement taken for the test signal to the corresponding minimum acceptance performance value and determining therefrom whether the current interleaver setting represents an upper bound of the dominant impairment of the test channel.

6. A method according to claim 5, further comprising the steps of setting the current interleaver setting to the next highest available setting and remotely instructing the network element to receive the test signal on the test channel when the current interleaver setting is determined not to represent an upper bound of the dominant impairment of the test channel.

7. A method according to claim 6, further comprising the step of recording the current interleaver setting as the optimum burst protection setting when the current interleaver setting is determined to represent an upper bound of the dominant impairment of the test channel.

8. A method according to claim 7, wherein during said measuring steps, measurements are taken and recorded for each of modulation error ratio (MER), signal-to-noise ratio (SNR), packet error rate (PER), and bit error rate (BER).

9. A method according to claim 8, wherein if during said comparing step it is determined that, for the measurements taken at the current interleaver setting, MER≧

MER_MIN, SNR≧

SNR_MIN, PER≦

PER_MIN and BER≦

BER_MIN, then the current interleaver setting is recorded as the optimum burst protection setting that represents an upper bound of the dominant impairment of the test channel.

10. A method according to claim 9, wherein if during said comparing step it is determined that, for the measurements taken at the current interleaver setting, MER<

MER_MIN, SNR<

SNR_MIN, PER>

PER_MIN and BER>

BER_MIN, then the current interleaver setting is reset to the next highest available setting and the network element is instructed to receive the test signal on the test channel and said monitoring, measuring, comparing and determining steps are repeated.

11. A method according to claim 7, wherein all of said measuring, instructing, monitoring, comparing, and determining steps are accomplished automatically and remotely of the network element by a cable modem termination system (CMTS) unit at the headend of the test channel.

12. A system for characterizing a dominant impairment on an impaired communication channel, comprising:

a cable modem termination system (CMTS) unit configured to remotely instruct a network element to receive test signals on a forward path of a test channel;

said CMTS unit having a transmitter configured to transmit the test signals from the network element and a processing unit configured to measure and record signal-to-noise ratio (SNR) measurements for said test signals and configured to make comparisons relating to said measurements; and

said processing unit of said CMTS configured to automatically determine from said comparisons whether distortion or noise is the dominant impairment or a burst protection setting that represents an upper bound of the dominant impairment on the test channel.

13. A system according to claim 12, wherein said CMTS is configured to sample and record SNR and Receive Power Level (Pr) measurements for the test signals on the test channel for samples 1 to N at a pre-determined query rate and for a pre-determined duration.

14. A system according to claim 13 wherein said processing unit is configured to compute a complementary cumulative density function (CCDF) statistical measure from said samples 1 to N for Receive Noise Power Level (Nr), where Nr=Pr-SNR for each sample.

15. A system according to claim 14, wherein said processing unit is configured to compare the CCDF of Receive Noise Power Level computed from samples 1 to N relative to a theoretically expected CCDF of Receive Noise Power Level for an Additive White Gaussian Noise (AWGN) dominated impairment on the test channel.

16. A system according to claim 15, wherein said processing unit is configured to provide an indication that distortion is the dominant impairment on the test channel when the CCDF of Receive Noise Power Level computed from samples 1 to N is degraded in an amount in excess of that of the theoretically expected CCDF of Receive Noise Power Level for an AWGN dominated impairment.

17. A system according to claim 16, wherein said processing unit is configured to provide an indication that noise is the dominant impairment on the test channel when the CCDF of Receive Noise Power Level computed from samples 1 to N is substantially the same as that of the theoretically expected CCDF of Receive Noise Power Level for an AWGN dominated impairment.

18. A system according to claim 12, wherein said processing unit is configured to set and reset the interleaver setting of the test channel and measure and record measurements of modulation error ratio (MER), signal-to-noise ratio (SNR), packet error rate (PER), and bit error rate (BER) of test signals transmitted at different interleaver settings.

19. A system according to claim 18, wherein said processing unit is configured to compare the measurements of MER, SNR, PER and BER at a current interleaver setting relative to corresponding values corresponding to a minimum acceptance performance value for modulation error ratio (MER_MIN), signal-to-noise ratio (SNR_MIN), packet error rate (PER_MIN), and bit error rate (BER_MIN) for the test signal on the test channel, and wherein said processing unit is configured to compare the measurements taken for the test signal at the current interleaver setting to the corresponding minimum acceptance performance values and determine therefrom whether the current interleaver setting represents an upper bound of the dominant impairment of the test channel.

20. A system according to claim 19, wherein said processing unit is configured to reset the current interleaver setting to the next highest available setting and record new measurements until the measurements at the current interleaver setting comply with:

MER≧

MER_MIN, SNR≧

SNR_MIN, PER≦

PER_MIN and BER≦

BER_MIN; and

wherein said processing unit is configured to provide an indication of the interleaver setting providing an optimum burst protection setting that represents an upper bound of the dominant impairment of the test channel.