Methods and apparatus for encoding information in a signal by spectral notch modulation

• US 20070025456A1
• Filed: 07/29/2005
• Published: 02/01/2007
• Est. Priority Date: 07/29/2005
• Status: Active Grant

• Current Assignee: Harris Global Communications, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: McCrady, Dennis
• Granted Patent: US 7,746,939 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 5/02 Channels characterised by the type of signal

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.

Claims

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.

2. The method of claim 1, wherein the signal is a spread spectrum signal.

3. The method of claim 1, further comprising:

(e) additionally modulating the signal via at least one of;

phase shift keying, frequency shift keying, quadrature amplitude modulation, amplitude modulation, frequency modulation.

4. The method of claim 3, wherein the signal is encoded with a first type of information via the spectral notch modulation, and the signal is encoded with a second type of information via the modulation performed in (e).

5. The method of claim 4, wherein the first and second types of information are selected from the group consisting of:

time-of-arrival ranging signals, navigation signals, communications data, video signals, audio signals, overhead signals, control signals, handshaking signals, media access control signals, and alphanumeric data.

6. A method of demodulating a signal to recover information encoded in the signal via spectral notch modulation, 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) 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.

7. The method of claim 6, wherein the signal is a spread spectrum signal.

8. The method of claim 6, further comprising:

(d) demodulating the signal to recover information modulated via at least one of;

phase shift keying, frequency shift keying, quadrature amplitude modulation, amplitude modulation, frequency modulation.

9. An apparatus for encoding information in a signal by spectral notch modulation, comprising:

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.

10. The apparatus of claim 9, wherein the frequency domain signal includes N frequency bins and the spectral notch modulator excises M of the N frequency bins, wherein nulled combinations of M frequency bins respectively correspond to encoded information bits.

11. The apparatus of claim 9, wherein the spectral notch modulator comprises:

a discrete Fourier transform module that converts the digital time-domain signal to the frequency-domain signal, wherein the frequency-domain signal comprises a plurality of frequency-domain samples corresponding to respective frequency bins;

an excision module that selectively removes the frequency bins selected by the encoding module to cause spectral nulling of the frequency bins selected by the encoding module; and

an inverse discrete Fourier transform module that converts the excised frequency-domain signal to the excised time-domain signal.

12. The apparatus of claim 11, wherein the discrete Fourier transform module comprises a fast Fourier transform (FFT) and the inverse discrete Fourier transform module comprises an inverse FFT.

13. The apparatus of claim 9, wherein digital time-domain signal is a baseband signal, the system further comprising:

a digital mixer that up-converts the excised time-domain signal to an intermediate frequency signal and supplies the intermediate frequency signal to the digital-to-analog converter.

14. The apparatus of claim 13, further comprising a reconstruction filter that receives the analog signal from the digital-to-analog converter and supplies a filtered intermediate signal to an RF transmission module.

15. The apparatus of claim 9, wherein the digital time-domain signal is a spread spectrum signal comprising a sequence of samples of chips.

16. The apparatus of claim 9, wherein the signal comprises a ranging waveform for determining a range between two communication devices.

17. The apparatus of claim 9, wherein the apparatus is a mobile communication device.

18. The apparatus of claim 9, wherein the apparatus communicates with a plurality of communication devices in a network.

19. An apparatus for demodulating a signal to recover information encoded in the signal via spectral notch modulation, comprising:

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.

20. The apparatus of claim 19, wherein the frequency domain signal includes N frequency bins, and M of the N frequency bins are nulled, wherein nulled combinations of M frequency bins respectively correspond to encoded information bits.

21. The apparatus of claim 19, further comprising a time of arrival processor that determines a time of arrival of the received signal from the received time-domain signal.

22. The system of claim 19, further comprising a communications acquisition processor that acquires the received signal from the received time-domain signal.

23. A system for conveying information encoded in a signal by spectral notch modulation, comprising:

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.

24. The system of claim 23, further comprising:

means for converting the analog signal to a received digital time-domain signal;

means for converting the received digital time-domain signal to a received frequency-domain signal comprising a plurality of frequency-domain samples corresponding to respective frequency bins;

means for identifying the set of frequency bins that were excised; and

means for converting the set of the frequency bins to corresponding information bits.