Characterizing ingress noise

1. A device to identify noise in a cable network, the device comprising:

a spectrum analyzer to:

obtain a frequency spectrum of a cable signal at a first cable network location, wherein the cable signal includes a digital signal from a digital source and noise from a noise source;

generate a time trace of a first parameter of the cable signal at a first frequency of the obtained frequency spectrum;

compute an autocorrelation function of the time trace;

identify a plurality of peaks in the autocorrelation function;

determine a time delay between the plurality of peaks based on a summation analysis of the computed autocorrelation function and the identified plurality of peaks; and

identify a first repetition frequency of a component of the noise from the time delay, wherein the first repetition frequency is indicative of a type of the noise source.

2. The device of claim 1 , comprising a display device to display at least one of the frequency spectrum and the first repetition frequency.

3. The device of claim 1 , comprising an output device to transmit the time delay to a remote device.

4. The device of claim 1 , comprising a hardware processor to implement the spectrum analyzer, the hardware processor comprising at least one of a Field-Programmable Gate Array (FPGA), a digital signal processor, and a microprocessor.

5. The device of claim 4 , comprising an input terminal to couple to the first cable network location, wherein the hardware processor comprises a radio frequency (RF) front end coupled to the input terminal of the device, and an ADC coupled to the RF front end, to digitize an output signal of the RF front end.

6. The device of claim 4 , comprising an input terminal to couple to the first cable network location, wherein to generate the time trace of the first parameter of the cable signal at the first frequency, the hardware processor is to at least one of:

dwell the spectrum analyzer at a first frequency band for a dwelling time and capture an output signal of the spectrum analyzer; and

perform a real-time fast Fourier transform (FFT) of the obtained frequency spectrum.

7. The device of claim 4 , wherein the time delay is a first time delay and the autocorrelation function includes peaks separated by a second time delay different from the first time delay, wherein the hardware processor is to:

remove, from the time trace, peaks corresponding to the first time;

compute the autocorrelation function to find the second time delay; and

determine a second repetition frequency based on the computed autocorrelation function.

8. The device of claim 7 , wherein to remove the peaks from the time trace, the hardware processor is to remove data points corresponding to the first time delay from the time trace, and fill in the removed data points.

9. The device of claim 4 , wherein the hardware processor is to:

generate a plurality of the time traces;

compute autocorrelation functions for the plurality of time traces;

average the computed autocorrelation functions; and

determine the time delay from the averaged autocorrelation functions.

10. The device of claim 4 , wherein the hardware processor is to:

(a) sum a plurality of values of the autocorrelation function at multiples of the time delay to calculate a summed value for the autocorrelation function;

(b) repeat (a) at a plurality of time delays different than the time delay to calculate a plurality of summed values; and

(c) select a time delay corresponding to a maximum value of the summed values.

11. A method to identify noise in a cable network, the method comprising:

obtaining, by a hardware processor, a frequency spectrum of a cable signal at a first cable network location wherein the cable signal includes a digital signal from a digital source and noise from a noise source;

generating a time trace of a parameter of the cable signal at a first frequency of the obtained frequency spectrum;

computing an autocorrelation function of the time trace;

identifying a plurality of peaks in the autocorrelation function;

determining a time delay between the plurality of peaks based on a summation analysis of the computed autocorrelation function and the identified plurality of peaks; and

identifying a first repetition frequency of a component of the noise from the time delay, wherein the first repetition frequency is indicative of a type of the noise source.

12. The method of claim 11 , comprising displaying at least one of the frequency spectrum and the first repetition frequency.

13. The method of claim 11 , comprising transmitting the time delay to a remote device.

14. The method of claim 11 , wherein generating the time trace comprises at least one of:

dwelling a spectrum analyzer at a first frequency band for a dwelling time and capturing an output signal of the spectrum analyzer; and

performing a real-time fast Fourier transform (FFT) of the obtained frequency spectrum.

15. The method of claim 11 , wherein the time delay is a first time delay and the autocorrelation function includes a second autocorrelation peak separated from the first peak by a second time delay different from the first time delay, the method comprising:

removing, by the hardware processor, peaks from the time trace corresponding to the first autocorrelation peak;

computing, by the hardware processor, the autocorrelation function to find the second autocorrelation peak; and

determining, by the hardware processor, a second repetition frequency based on the computed autocorrelation function.

16. The method of claim 15 , wherein removing the peaks from the time trace comprises removing data points corresponding to the first autocorrelation peak from the time trace, and filling in the removed data points.

17. The method of claim 15 , comprising:

obtaining a plurality of the time traces;

computing autocorrelation functions for the plurality of time trace;

averaging the computed autocorrelation functions; and

determining the first autocorrelation peak and the first time delay from the averaged autocorrelation functions.

18. The method of claim 11 , comprising:

(a) summing a plurality of values of the autocorrelation function at multiples of the time delay to obtain a summed value for the autocorrelation function;

(b) repeating (a) at a plurality of time delays different than the time delay to obtain a plurality of summed values; and

(c) selecting a time delay corresponding to a maximum value of the summed values.

19. A cable network testing device operable to test for ingress noise in a cable network, the cable network testing device comprising:

an input terminal to couple the cable network testing device to the cable network;

a spectrum analyzer to:

receive a cable signal from the cable network via the input terminal, wherein the cable signal includes a digital signal from a digital source and noise from a noise source;

generate a time trace of a first parameter of the cable signal at a first frequency of a frequency spectrum of the cable signal;

compute an autocorrelation function of the time trace;

identify a plurality of peaks in the autocorrelation function;

determine a time delay between the plurality of peaks based on a summation analysis of the computed autocorrelation function and the identified plurality of peaks; and

identify a first repetition frequency of a component of the noise from the time delay, wherein the first repetition frequency is indicative of a type of the noise source; and

a display to display at least one of the frequency spectrum and the first repetition frequency.