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:
- (a) 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;
(b) selectively nulling M of the N frequency bins, where M is less than N, wherein nulled combinations of M frequency bins respectively correspond to encoded information bits;
(c) transforming the selectively nulled signal to the time domain via an inverse FFT; and
(d) transmitting the selectively nulled signal.
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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.
81 Citations
24 Claims
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1. A method of modulating a signal to encode information, comprising:
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(a) 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;
(b) selectively nulling M of the N frequency bins, where M is less than N, wherein nulled combinations of M frequency bins respectively correspond to encoded information bits;
(c) transforming the selectively nulled signal to the time domain via an inverse FFT; and
(d) transmitting the selectively nulled signal. - View Dependent Claims (2, 3, 4, 5)
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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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(a) 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;
(b) identifying a set of M nulled frequency bins among the N frequency bins, where M is less than N, wherein nulled combinations of M frequency bins respectively correspond to encoded information bits; and
(c) converting the set of M nulled frequency bins to corresponding information bits. - 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;
an encoding module configured to select a set of frequency bins corresponding to information bits to be encoded;
a spectral notch modulator that converts the digital time-domain signal to a frequency-domain signal, excises from the frequency-domain signal the set of frequency bins selected by the encoding module, 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)
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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; and
converting the subset of the frequency bins to corresponding information bits. - 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 selecting a set of frequency bins corresponding to information bits to be encoded;
means for converting the digital time-domain signal to a frequency-domain signal;
means for excising from the frequency-domain signal the set of frequency bins selected by the encoding module;
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)
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Specification