Telegraphy – Systems – Printing
Patent
1981-03-19
1983-07-12
Cangialosi, Sal
Telegraphy
Systems
Printing
179 15M, 178 2213, H04K 900
Patent
active
043932762
ABSTRACT:
The present invention relates to a secure communication system for analog signals which preserves the bandwidth of the original message signal by employing scrambling, or masking, techniques in the frequency domain instead of the time domain. At the transmitting end, the message signal x.sub.a (t) is sequentially passed through a Fourier transform processor (12) and a scrambling arrangement (14) before being masked to form a secure Fourier transform sequence X.sub.s (n). The secure message signal x.sub.s (t) is formed by passing the secure sequence X.sub.s (n) through an inverse Fourier transform processor (16) which produces a secure signal x.sub.s (t) comprising the same bandwidth as the original message signal x.sub.a (t). At the receiving end, the secure signal x.sub.s (t) is passed through a Fourier transform processor (22) and a descrambling arrangement (24) which performs the conjugate operation of the above-described scrambling arrangement, and "un-masks" the secure Fourier transform to reform the original Fourier transform X.sub.a (n). The original message signal x.sub.a (t) is recovered by passing the Fourier transform X.sub.a (n) through an inverse Fourier transform processor (26).
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Electronic Design, vol. 9, (4/26/79) pp. 78-85 Schrim.
IEEE Trans. on Info. Theory, vol. IT-25, No. 3 (5/79) pp. 261-274, Wyner Analog Scrambing that does not Expand Bandwidth.
Electronics, (6/21/79), pp. 107-120 Hindin, LSI-Based Data Enoryption Discourages Data Thief.
IEEE Trans. on Info. Theory, vol. IT-25, No. 4 (7/79) pp. 415-425 Wyner (II).
Bell Telephone Laboratories Incorporated
Cangialosi Sal
Pfeifle Erwin W.
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