Simultaneous call transmission detection
AssigneePark Air Systems Limited
InventorsDesmond Keith PHILLIPS, Paul Andrew Noble
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Abstract
A method of determining the presence of a secondary carrier signal in a time-domain sum-signal including a primary carrier signal is disclosed, the method comprising: transforming the sum-signal into the frequency domain; extracting at least one peak corresponding to a heterodyne tone from the transformed sum-signal; determining the presence of a secondary carrier signal in the sum-signal based on said at least one peak. A corresponding apparatus is also disclosed.
Claims73
A method of determining the presence of a secondary carrier signal in a time-domain sum-signal including a primary carrier signal, the method comprising:
- transforming the sum-signal into the frequency domain;
- extracting at least one peak corresponding to a heterodyne tone from the transformed sum-signal;
- determining the presence of a secondary carrier signal in the sum-signal based on said at least one peak.
A method according to any preceding claim wherein the step of transformation into the frequency domain is performed using a Fourier Transform (FT).
A method according to any preceding claim wherein the step of transformation into the frequency domain is performed using a discrete transform comprising input and output bins.
A method according to any preceding claim wherein determining the presence of a secondary transmission comprises performing a symmetry analysis on said peak.
A method of determining the presence of a second carrier signal in a time-domain sum-signal, the method comprising:
- identifying a primary carrier signal within the sum-signal;
- attenuating the primary carrier signal from within the sum signal;
- extracting at least one peak corresponding to a heterodyne tone;
- performing a symmetry analysis on said at least one peak to determine the presence of a secondary transmission.
A method according to any preceding claim wherein the presence of a secondary transmission is determined only if a peak corresponding to the carrier of a primary transmission is present.
A method according to any preceding claim wherein following peak extraction, if two peaks are within a minimum frequency separation of one another, the peaks are combined into a single peak prior to determination of the presence of a secondary carrier.
A method according to any preceding claim wherein the sum-signal is decimated so as to reduce the bandwidth.
A method according to any preceding claim wherein the sum-signal is sampled.
A method according to any preceding claim wherein the sum-signal is sampled in overlapping blocks.
A method according to any preceding claim further comprising:
- estimating a noise floor of the down-converted signal;
- subtracting a measure of said noise floor from the signal prior to peak extraction.
A method according to any preceding claim further comprising alerting an operator to the presence of a secondary transmission.
A method of reducing windowing artefacts in a time/frequency transform of a signal:
- applying a windowing function to a signal;
- mapping the signal onto the input of an oversampled transform;
- wherein a central part of the transform input has zero-valued input bins;
- performing a time/frequency transform;
- outputting a frequency spectrum of the signal.
A method according to any preceding claim wherein the signal comprises voice communication.
An apparatus adapted to carry out a method according to any preceding claim.
An apparatus for determining the presence of a secondary carrier signal in a time-domain sum-signal including a primary carrier signal, the apparatus comprising:
- means for transforming the sum-signal into the frequency domain;
- means for extracting at least one peak corresponding to a heterodyne tone from the transformed sum-signal;
- means for determining the presence of a secondary carrier signal in the sum-signal based on said at least one peak.
An apparatus for determining the presence of a second carrier signal in a time-domain sum-signal, the method comprising:
- means for identifying a primary carrier signal within the sum-signal;
- means for attenuating the primary carrier signal from within the sum signal;
- means for extracting at least one peak corresponding to a heterodyne tone;
- means for performing a symmetry analysis on said at least one peak to determine the presence of a secondary transmission.
An apparatus for reducing windowing artefacts in a time/frequency transform of a signal:
- means for applying a windowing function to a signal;
- means for mapping the signal onto the input of an oversampled transform;
- wherein a central part of the transform input has zero-valued input bins;
- means for performing a time/frequency transform;
- means for outputting a frequency spectrum of the signal.
A method substantially as described herein and/or illustrated with reference to the accompanying drawings.
An apparatus substantially as described herein and/or illustrated with reference to the accompanying drawings.
A radio substantially as described herein and/or illustrated with reference to the accompanying drawings.
Dependencies are inferred from the claim text.