Analog scrambling with continuous synchronization

• US 5,278,907 A
• Filed: 03/01/1993
• Issued: 01/11/1994
• Est. Priority Date: 03/01/1993
• Status: Expired due to Term

• Current Assignee: Transcrypt International, Inc. (JVC Kenwood Corporation)
• Original Assignee: Transcrypt International, Inc. (JVC Kenwood Corporation)
• Inventors: Kabler, Ronald B., Snyder, Kenneth L.
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/024,408
• Time in Patent Office: 316 Days
• Field of Search: 380/9, 380/19, 380/48, 375/94, 375/97
• US Class Current: 380/274
• CPC Class Codes: H04K 1/04 by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band

Abstract

A device and method for scrambling and de-scrambling audio and voice communications including radio, cellular telephone, and conventional telephone communication. The audio communication can be scrambled using, for example, time varying pseudo-random spectral modification. Continuous data containing synchronization information is transmitted with the scrambled signal to eliminate time lags that occur with synchronization bursts and without detrimentally affecting audio quality.

Claims

1. A method of transmitting communications which are scrambled comprising:

scrambling an audio signal that is used to modulate a transmission RF carrier;

generating a continuous synchronization signal correlated to the scrambling of the audio signal;

combining the synchronization signal with the audio signal; and

so that the synchronization signal can be continuously transmitted with the audio signal to allow immediate initialization synchronization and continuous synchronization as long as the audio signal is transmitted.

2. The method of claim 1 wherein the transmission RF carrier is used in conventional telephone communications.

3. The method of claim 1 wherein the transmission RF carrier is used in radio communications.

4. The method of claim 1 wherein the transmission RF carrier is used in cellular telephone communications.

5. The method of claim 1 wherein the scrambling comprises spectral modification of the audio signal.

6. The method of claim 1 wherein the audio signal is band-passed prior to scrambling.

7. The method of claim 6 wherein the band passing removes control information utilized by some audio transmission systems.

8. The method of claim 5 wherein the scrambling comprises frequency inversion which utilizes a switching means which is switched according to a pseudo-random sequence.

9. The method of claim 1 wherein generation of the synchronization signal comprises generating data correlated to scrambling of the audio signal.

10. The method of claim 9 wherein the data is modulated to a data RF carrier frequency.

11. The method of claim 10 wherein the data RF carrier frequency is sub-audible in comparison to the audio signal.

12. The method of claim 9 wherein the data is put into a continuous data stream and made up of segments.

13. The method of claim 12 wherein the segments include a preamble, a synchronization code, and an error correction code.

14. The method of claim 10 further comprising combining the scrambled audio signal and the PSK modulated data RF carrier into a combined radio frequency band for transmission.

15. The method of claim 14 wherein the combined radio frequency band is modulated on the transmission RF carrier.

16. The method of claim 14 wherein the modulated synchronization signal comprises a sub-band of the scrambled audio signal.

17. The method of claim 14 further comprising filtering the combined scrambled audio and modulated signal prior to transmission.

18. The method of claim 1 further comprising decoding a transmitted signal by separating the sub-band from the radio frequency band containing the scrambled audio signal and the modulated synchronization signal, recovering the audio signal from the scrambled audio signal, and recovering data from the sub-band.

19. The method of claim 18 wherein the recovered data from the sub-band is utilized to synchronize the recovery of the audio from the scrambled audio.

20. The method of claim 19 wherein the recovered audio is output to a receiver.

21. An audio communication system comprising:

at least one transmitter including an encoder;

at least one receiver including a decoder;

the encoder comprising an audio band scrambler;

a sub-band generator which produces a frequency band which carries synchronization information on a continuous basis, and a combiner to combine the audible and sub-bands for transmission output;

the decoder comprising a separator to separate the audio and sub-bands, a synchronization information recovery device to recover the synchronization information, and an audio recovery device which utilizes the synchronization information to recover the audio communication.

22. The system of claim 21 wherein the transmitter and receiver are combined in a transceiver.

23. The system of claim 21 wherein the audio band scrambler includes a device to scramble an analog audio signal using time-varying, pseudo-random spectral modification.

24. The system of claim 23 wherein the audio band scrambler includes a frequency inverter device and a control device which generates a switching signal to operate the inverter in a pseudo-random fashion.

25. The system of claim 24 further comprising a microprocessor which includes an encryption algorithm to instruct the control device regarding generation of the switching signal.

26. The system of claim 21 wherein the sub-band is narrower than the audio band.

27. The system of claim 26 wherein the sub-band is in-band with the audio band.

28. The system of claim 26 wherein the sub-band is effectively sub-audible.

29. The system of claim 26 wherein the sub-band is effectively super-audible.

30. The system of claim 26 wherein the sub-band carries synchronization information by modulating data on a data carrier in a relatively narrow frequency band.

31. The system of claim 21 wherein the combiner comprises a summer device.

32. The system of claim 21 wherein the separator comprises frequency filters which pass selected frequency bands.

33. The system of claim 21 wherein the synchronization information recovery device includes a limiter and a data recovery decoder.

34. The system of claim 21 wherein the audio recovery device includes an inverter, a frequency generator which issues a switching signal to the inverter, and a microprocessor including a decryption algorithm.

35. A method of audio communication comprising:

scrambling an audio signal that is used to modulate a radio frequency signal;

combining with the audio signal data modulated to a frequency sub-band within the audio signal.

36. The method of claim 35 wherein the scrambling comprises analog scrambling using time varying pseudo-random spectral modification.

37. The method of claim 36 wherein the audio signal is generally of a band that includes a portion of the audible spectrum.

38. The method of claim 35 wherein the data includes synchronization information.

39. The method of claim 38 wherein the data includes error correction information.

40. The method of claim 38 wherein the data includes identification information.

41. The method of claim 35 wherein the frequency sub-band containing the data is a relatively low frequency within the audio band.

42. The method of claim 35 wherein the frequency sub-band containing the data is a relatively low frequency immediately below the audio band and is effectively a sub-audible band.

43. The method of claim 35 wherein the frequency sub-band containing the data is a relatively high frequency band within the audio band.

44. The method of claim 35 wherein the frequency sub-band containing the data is a relatively high frequency immediately above the audio band and is effectively super audible.

45. The method of claim 35 wherein the frequency band containing the data is a relatively narrow band within the audio signal.

46. The method of claim 35 wherein the data is modulated in the sub-band by PSK signalling.