Methods and apparatus for encoding information in a signal by spectral notch modulation
First Claim
1. A method of modulating a signal to encode information, comprising:
- modulating the signal in the time domain using a first modulation scheme to encode first information in the signal;
transforming the time-domain modulated signal into the frequency domain via a fast Fourier transform (FFT) of length N, such that the frequency-domain signal is represented by N frequency bins;
mapping information bits to a corresponding code comprising a set of M frequency bins that represent the information bits, the code being defined by identities of a particular combination of frequency bins that constitute the set, such that different combinations of M frequency bins constitute different codes that represent different information bits;
modulating the frequency-domain signal in the frequency domain using a second modulation scheme to encode second information in the signal by selectively nulling the M frequency bins from the signal represented by the N frequency bins, where M is greater than one and less than N to encode the information bits in the signal via the code defined by the particular combination of M frequency bins, wherein the number of information bits encoded by nulling the M frequency bins is greater than M;
transforming the selectively nulled signal to the time domain via an inverse FFT; and
transmitting the selectively hulled signal containing the first information and the second information.
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Abstract
A spectral notch modulation technique for encoding information in a signal involves transforming the signal into the frequency domain via a fast Fourier transform (FFT) of length N, such that the signal is represented by N frequency bins, selectively nulling M of the N frequency bins, where nulled combinations of M frequency bins respectively correspond to encoded information bits, transforming the selectively nulled signal to the time domain via an inverse FFT, and transmitting the selectively nulled signal. At the receiving end, the signal is demodulated to recover the encoded information by transforming the signal into the frequency domain via a fast Fourier transform (FFT) of length N, identifying the set of M nulled frequency bins among the N frequency bins, and converting the set of M nulled frequency bins to corresponding information bits.
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Citations
28 Claims
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1. A method of modulating a signal to encode information, comprising:
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modulating the signal in the time domain using a first modulation scheme to encode first information in the signal; transforming the time-domain modulated signal into the frequency domain via a fast Fourier transform (FFT) of length N, such that the frequency-domain signal is represented by N frequency bins; mapping information bits to a corresponding code comprising a set of M frequency bins that represent the information bits, the code being defined by identities of a particular combination of frequency bins that constitute the set, such that different combinations of M frequency bins constitute different codes that represent different information bits; modulating the frequency-domain signal in the frequency domain using a second modulation scheme to encode second information in the signal by selectively nulling the M frequency bins from the signal represented by the N frequency bins, where M is greater than one and less than N to encode the information bits in the signal via the code defined by the particular combination of M frequency bins, wherein the number of information bits encoded by nulling the M frequency bins is greater than M; transforming the selectively nulled signal to the time domain via an inverse FFT; and transmitting the selectively hulled signal containing the first information and the second information. - View Dependent Claims (2, 3, 4, 5, 25)
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6. A method of demodulating a signal to recover information encoded in the signal via spectral notch modulation, comprising:
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transforming the signal into a frequency domain signal via a fast Fourier transform (FFT) of length N, such that the frequency domain signal is represented by N frequency bins; identifying from the frequency domain signal a set of M nulled frequency bins among the N frequency bins, where M is greater than one and less than N and wherein a determination of which of the N frequency bins are the M nulled frequency bins is made from analysis of the frequency domain signal, wherein identities of the M nulled frequency bins, in combination, define a code that represents a number of information bits greater than M, such that different combinations of M frequency bins constitute different codes that represent different information bits; converting the set of M nulled frequency bins to corresponding information bits; transforming the frequency domain signal to the time domain via an inverse FFT; and demodulating the time domain signal to recover additional information encoded in the signal via modulation applied to the signal in the time domain. - View Dependent Claims (7, 8)
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9. An apparatus for encoding information in a signal by spectral notch modulation, comprising:
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a processor configured to generate a digital time-domain signal having a bandwidth that is divisible into frequency bins;
a modulator configured to modulate the digital time-domain signal in the time domain using a first modulation scheme to encode first information in the signal;an encoding module configured to map information bits to a corresponding code comprising a set of frequency bins that represent the information bits, the code being defined by identities of a particular combination of frequency bins that constitute the set, such that different combinations of frequency bins constitute different codes that represent different information bits, wherein the number of information bits represented by the code is greater than the number of frequency bins that constitute the set; a spectral notch modulator that converts the modulated digital time-domain signal to a frequency-domain signal, modulates the frequency-domain signal domain using a second modulation scheme to encode second information in the signal by excising from the frequency-domain signal the set of frequency bins selected by the encoding module to encode the information bits via the code defined by the particular combination of frequency bins, and converts the excised frequency-domain signal to an excised time-domain signal; and a digital-to-analog converter that converts the excised time-domain signal to an analog signal for transmission. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 26)
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19. An apparatus for demodulating a signal to recover information encoded in the signal via spectral notch modulation, comprising:
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an analog-to-digital converter configured to convert a received signal to a received digital time-domain signal; and a processor configured to;
convert the received digital time-domain signal to a frequency-domain signal comprising a plurality of frequency-domain samples corresponding to respective frequency bins;
identify a subset of the frequency bins that were nulled to effect the spectral notch modulation, wherein identities of the nulled frequency bins forming the subset, in combination, define a code that represents encoded information bits, such that different combinations of frequency bins constitute different codes that represent different information bits, wherein the number of information bits represented by the code is greater than the number of frequency bins in the subset that defines the code, and wherein identification of which frequency bins were nulled is determined from analysis of the frequency-domain signal; and
convert the subset of the frequency bins to corresponding information bits based on the combination of frequency bins that form the subset,wherein the processor is further configured to convert the frequency-domain signal to a time-domain signal and demodulate the time-domain signal to recover additional information encoded in the received signal via modulation applied in the time domain. - View Dependent Claims (20, 21, 22)
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23. A system for conveying information encoded in a signal by spectral notch modulation, comprising:
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means for generating a digital time-domain signal having a bandwidth that is divisible into frequency bins; means for modulating the signal in the time domain using a first modulation scheme to encode first information in the signal; means for mapping information bits to a corresponding code comprising a set of frequency bins that represent the information bits, the code being defined by identities of a particular combination of frequency bins that constitute the set, such that different combinations of frequency bins constitute different codes that represent different information bits, wherein the number of information bits represented by the code is greater than the number of frequency bins in the set that defines the code; means for converting the modulated digital time-domain signal to a frequency-domain signal; means for modulating the frequency-domain signal domain using a second modulation scheme to encode second information in the signal by excising from the frequency-domain signal the set of frequency bins selected by the means for mapping to encode the information bits via the code defined by the particular combination of frequency bins; means for converting the excised frequency-domain signal to an excised time-domain signal; and means for converting the excised time-domain signal to an analog signal for transmission. - View Dependent Claims (24, 27)
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28. A method of modulating a signal to encode information, comprising:
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transforming the signal into the frequency domain via a fast Fourier transform (FFT) of length N, such that the frequency-domain signal is represented by a set of N frequency bins; mapping information bits to a corresponding code comprising a set of M frequency bins that represent the information bits, the code being defined by identities of a particular combination of frequency bins that constitute the set of M frequency bins, such that different combinations of M frequency bins constitute different codes that represent different information bits; selectively nulling the M frequency bins from the signal represented by the N frequency bins, where M is greater than one and less than N, to encode the information bits in the frequency-domain signal via the code defined by the particular combination of M frequency bins, wherein the number of bits encoded by nulling M frequency bins is greater than M and is a function of the number of different combinations of M frequency bins within the set of the N frequency bins; transforming the selectively nulled signal to the time domain via an inverse FFT; and transmitting the selectively nulled signal.
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Specification