Digital Mobile Passive Leak Detection for Broadband Communication System

• US 20130322569A1
• Filed: 03/08/2013
• Published: 12/05/2013
• Est. Priority Date: 06/01/2012
• Status: Active Grant

• Current Assignee: ComSonics, Inc.
• Original Assignee: ComSonics, Inc.
• Inventors: Murphy, John J.
• Granted Patent: US 9,112,762 B2
• Time in Patent Office: Days
• US Class Current: 375/320
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits
• CPC Class Codes: H04L 27/3818 using coherent demodulation, i.e. using one or more nominally phase synchronous carriers H04L27/227 and H04L27/389 take precedence

Abstract

Passive detection of a quadrature amplitude modulated (QAM) signal amid noise is achieved by detection of a spectral component of a detected signal that corresponds to a known QAM symbol rate in, for example, a QAM modulated broadband communication system (BCS). Improved authentication can be provided by simultaneously detecting symbol rate components in two or more QAM bands. No modification of a broadband communication system such as by including a marker signal is required and thus there is no requirement for dedication of a portion of the broadband communication system spectrum or problem of marker signal interference with BCS signals.

Claims

1. A detector for detecting a quadrature amplitude modulated (QAM) signal, said detector comprising

a mixer to mix a detected signal with an oscillator output wherein said oscillator is tuned to operate at a carrier frequency of a QAM band, to develop a quadrature baseband signal,

a further mixer for mixing a signal corresponding to said quadrature baseband signal with an output of a further oscillator wherein said further oscillator is tuned to operate at a QAM symbol rate of said QAM band, and

a processor to analyze a spectrum of an output of said further mixer to detect presence of a signal at a frequency corresponding to said QAM symbol rate.

2. The detector as recited in claim 1, further comprising

a multiplier to multiply said quadrature baseband signal by itself to provide a squared instantaneous envelope signal as said signal corresponding to said detected signal.

3. The detector as recited in claim 1, wherein said processor is a fast Fourier transform processor.

4. The detector as recited in claim 1, further including a filter for pulse shaping of respective components of said baseband quadrature signal.

5. The detector as recited in claim 4, wherein said filter is matched to a pulse shaping filter in a QAM modulator.

6. The detector as recited in claim 4, wherein said filter is a raised root cosine low pass filter.

7. The detector as recited in claim 1, further including

an analog to digital converter for converting said baseline quadrature signal to digital form.

8. The detector as recited in claim 7, wherein said analog-to-digital converter samples said baseline quadrature signal at a rate of 15 MHZ or higher.

9. The detector as recited in claim 1, further including

a low pass filter to limit a spectrum of an output of said further mixer.

10. The detector as recited in claim 1, further including

a cascaded integration-comb decimator.

11. A method for detecting a quadrature amplitude modulated (QAM) signal, said method comprising steps of

mixing a detected signal with an oscillator output wherein said oscillator is tuned to operate at a carrier frequency of a QAM band, to develop a quadrature baseband signal,

further mixing a signal corresponding to said quadrature baseband signal with an output of a further oscillator wherein said further oscillator is tuned to operate at a QAM symbol rate of said QAM band, and

analyzing a spectrum of an output of said further mixer to detect presence of a signal at a frequency corresponding to said QAM symbol rate.

12. The method as recited in claim 11, further comprising

multiplying said quadrature baseband signal by itself to provide a squared instantaneous envelope signal as said signal corresponding to said detected signal.

13. The method as recited in claim 11, wherein said step of analyzing a spectrum comprises a fast Fourier transform process.

14. The method as recited in claim 11, further including pulse shaping of respective components of said baseband quadrature signal.

15. The method as recited in claim 14, wherein said pulse shaping is matched to pulse shaping in a QAM modulator.

16. The method as recited in claim 14, wherein said pulse shaping is performed by a raised root cosine low pass filter.

17. The method as recited in claim 11, further including

converting said baseline quadrature signal to digital form.

18. The method as recited in claim 17, wherein said analog-to-digital conversion samples said baseline quadrature signal at a rate of 15 MHZ or higher.

19. The method as recited in claim 11, further including

limiting a spectrum of a result of said further mixing step.

20. The method as recited in claim 11, further including

cascaded integration-comb decimation of a result of said analog-to-digital conversion.