Holographic communications device and method

• US 4,972,480 A
• Filed: 01/10/1990
• Issued: 11/20/1990
• Est. Priority Date: 01/10/1990
• Status: Expired due to Term

• Current Assignee: Holowave Incorporated
• Original Assignee: General Dynamics Corporation
• Inventors: Rosen, Lowell
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Cain, David
• Application Number:
  US07/463,100
• Time in Patent Office: 314 Days
• Field of Search: 380/28, 380/46, 380/13, 380/38, 455/26, 455/28
• US Class Current: 380/46
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04K 2203/14 for the transfer of light or images, e.g. for video-surveillance, for television or from a computer screen
• CPC Class Codes: H04K 3/25 based on characteristics of target signal or of transmission as countermeasure against surveillance H04K3/827, e.g. using direct sequence spread spectrum or fast frequency hopping spread spectrum techniques H04B1/69
• CPC Class Codes: H04K 3/827 using characteristics of target signal or of transmission as countermeasure against jamming H04K3/25, e.g. using direct sequence spread spectrum or fast frequency hopping spread spectrum techniques H04B1/69

Abstract

A holographic device and method encrypts a time dependent data signal, s(t), by a complex time dependent phase shifting signal. This produces a new signal whose modulus is equal the absolute value of the data signal, s(t), but has widely spread the frequency of the data signal. This new complex signal is mathematically transformed, producing an amplitude and phase spectrum (or a real and imaginary transform spectrum) of signal components. The amplitude and phase signals are modulated into a radio frequency carrier (or some other radiating source) as quadrature components and transmitted. At the receiver, the quadrature signals are separated into an amplitude and phase components which are then mathematically inverse transformed. The result is a complex signal with a real and imaginary components. The resulting signal is an accurate representation of the original data signal if a complete signal is recovered. If only a portion of the frequencies transmitted are recovered, the modulus is still represents the data signal, but may have artifacts frequencies in the signal. The modulus may then be filtered to remove these artifact frequencies, recovering the reconstructed data signal.

Claims

1. In information communication systems wherein at a transmitting station, an information signal s(t) is encrypted by an encrypting unit, the resulting encrypted signal is applied to a carrier frequency in a modulator unit before the modulated frequency signal is transmitted to a receiving station where the modulated frequency signal is received, the received encrypted signal is extracted though a carrier frequency demodulation unit, then deciphered through a deciphering unit, the improvement of an holographic encrypting and deciphering system which comprises:

in said encrypting unit, means for modulating information signal s(t) by a complex time dependent code signal p(t) to create a complex pseudo-noise signal and means for transforming this pseudo-noise signal into another complex pseudo noise signal having a real spectral signal y_r (t) and an imaginary spectral signal y_i (t); and

in said modulator unit, means for modulating the carrier frequency with said complex pseudo-noise signal having real and imaginary components.

2. The improvement claimed in claim 1, wherein said information signal is a phase-shift-keyed signal and said improvement further comprises means for multiplying said phase-shift-keyed signal X (t) with a pseudo random complex noise signal p(t) to create a another complex pseudo random frequency modulated signal M(t) for feeding said means for transforming.

3. The improvement claimed in claim 2, wherein said means for transforming comprises means for producing an orthogonal transform of said frequency modulated signal.

4. The improvement claimed in claim 3, wherein said orthogonal transform is a Fourier Transform.

5. The improvement claimed in claim 4, wherein said Fourier transform is a Fast Fourier Transform.

6. The improvement claimed in claim 5, wherein said means for multiplying comprises an encoder combining X(t) with pseudo random signal having an exponential form e^iq(t).

7. The improvement claimed in claim 6, wherein said exponential form includes a periodic function of time.

8. The improvement claimed in claim 7, wherein the frequency bandwidth of M(t) signal is at least 1000 larger than the frequency bandwidth of X(t) signal.

9. The improvement claimed in claim 8, wherein said transform is a chirp transform.

10. The improvement claimed in claim 9, wherein said encrypting unit comprises means for modulating two data signals and to apply the resulting encrypted signals to two carrier frequencies.

11. The improvement claimed in claim 10, wherein said encrypting unit comprises means for quadrature modulating four data signals and to apply said resulting encrypted signals to two carrier frequencies

12. The improvement claimed in claim 11 which also comprises means to convert complex analog transformed signals to digital transformed signals prior to transmission.

13. In data communication systems wherein at a transmitting station, a time dependent signal, s(t), is encrypted by an encrypting unit, the resulting encrypted signal is applied to a carrier frequency in a modulator unit before the modulated frequency signal is transmitted to a receiving station where the receiver demodulates the carrier frequency through a demodulating unit and a received encrypted signal is extracted though a deciphering unit, the improvement of an holographic encrypting and deciphering system which comprises:

in said deciphering unit, means for inverse transforming said received demodulated signal by a complex phase signal p (t), to create a complex inverse transformed received signal y(t) having a real spectral signal component and an imaginary spectral signal component; and

in said deciphering unit, means for frequency demodulating said complex inverse transformed received signal, demodulating said complex signal c'"'"'(t) with a time dependent phase demodulating signal producing a reconstructed data signal, r'"'"'(t).

14. The improvement claimed in claim 13, wherein said improvement also comprises a low pass filter connected to the output of said frequency demodulating means and filtering specific low frequencies from r'"'"'(t).

15. The improvement claimed in claim 14, wherein said means for inverse transforming comprises an fast Fourier transformer microprocessor.

16. The improvement claimed in claim 14, wherein said means for inverse transforming comprises a chirp transformer.

17. The improvement claimed in claim 14 which also comprises means for providing a frame lockup signal supplied to said inverse transforming means.

18. The improvement claimed in claim 17, wherein said means for frame lockup signal comprises a power spectrum analyzer outputting a start signal to said inverse transforming means.

19. The improvement claimed in claim 18 which also comprises means for converting received complex digital signals to complex analog signals prior to inverse transforming.

20. A communications method for the secure and covert transmission of coded electromagnetic signals containing information comprising the steps of:

(1) generating said electromagnetic information signal;

(2) modulating said information signal with a time dependent phase signal to create a frequency modulated signal;

(3) transforming said frequency modulated signal into a complex modulated signal having a real spectral signal component and an imaginary spectral component;

(4) further modulating said complex modulated signal with a carrier frequency signal to create a coded noise-like signal; and

5) transmitting said noise-like signal.

21. A communications method for the secure reception of transmitted noise-like coded complex electromagnetic signal containing information comprising the steps of:

(1) receiving spectral portions of said noise-like coded complex electromagnetic signal;

(2) demodulating said noise-like coded complex signal with a carrier frequency signal to create a coded complex signal;

(3) inverse transforming said coded complex signal into a complex modulated signal having a real spectral signal component and an imaginary spectral component; and

(4) further demodulating said complex modulated signal with a time dependent phase signal to create a reconstructed information signal.