US 4,068,094 A · Method and apparatus for the scrambled transmission of spoken information via a telephony channel

Abstract

A method of scrambling and unscrambling speech transmissions by first dividing the speech frequencies into two frequency bands and reversing their order by modulating the speech information, the width of the bands being varied by varying the carrier frequency used in the modulation process, adding to the reversed frequency bands at least one supplementary signal derived from the modulation process and transmitting the resultant signal. The transmitted signal is unscrambled by first subtracting from it a supplementary signal which is generated at the receiving station from the received scrambled signal, the last mentioned supplementary signal being identical to that added to the reversed frequency band signal prior to transmission and then subjecting the resultant signal to the same modulation processes as referred to above to reassemble the frequency bands into a frequency band containing substantially the same speech frequencies as those that are scrambled. Apparatus for carrying out the above method can comprise a separate transmitter and receiver or a single transmitter/receiver whose mode of operation is controlled by a speech key, the transmitter and receiver each including a frequency scrambling device employing modulators and a time scrambling device for generating the supplementary signal.

Claims32

Dependent claims

A method for scrambling, transmitting, receiving and unscrambling speech information, comprising scrambling the speech information with respect to frequency so as to produce an intermediate signal by selecting a given band of frequencies from the speech information, generating a first control signal, dividing said given band into two complementary subbands having a band width ratio which varies as a function of the first control signal and exchanging the subbands within said given frequency band;

scrambling the thus produced intermediate signal with respect to time so as to produce a further scrambled signal by deducing at least one echo signal from the intermediate signal and adding it to the intermediate signal with time lags;
transmitting the further scrambled signal via a telephony channel and receiving it;
unscrambling the received signal with respect to time so as to recover the intermediate signal by providing time lags so as to recover the echo signal from the received signal and subtracting the echo signal from the latter;
and
unscrambling the thus recovered intermediate signal with respect to frequency so as to recover the speech information by generating a second control signal identical to the first control signal and submitting the intermediate signal to the same steps as the speech information was submitted to when scrambled to produce the intermediate signal, thereby using said second control signal instead of said first control signal.

2 more elements

A method of scrambling speech information over a telephonic channel, wherein at the transmitting end there are carried out the following steps of:

a. selecting from the speech information a given band of frequencies,
b. generating a first control signal,
c. dividing said given band into two complementary subbands having a band width ratio which varies as a function of the first control signal,
d. exchanging the subbands within said given frequency band,
e. adding to the signal formed in accordance with step (d) at least one supplementary signal which is dependent thereon with time lags produced by means of a second control signal,
f. subsequently transmitting the scrambled signal formed in accordance with steps (a) to (e) via the telephonic channel, and
wherein at the receiving end there are carried out the steps of:
aa. generating a third control signal which is identical with the second control signal,
bb. producing time lags by means of the third control signal,
cc. recovering the supplementary signal by using the time lags produced in accordance with step (bb) from the scrambled signal arriving via the telephonic channel and subtracting the recovered supplementary signal from the scrambled signal,
dd. generating a fourth control signal which is identical with the first control signal,
ee. recovering a speech information which is at least similar to the original speech information from the remaining signal of step (cc) by performing the steps (a), (c) and (d), and using the fourth control signal instead of the first control signal.

9 more elements

Apparatus for transmitting and receiving speech, comprising a transmitting station having a modulating device generating from the speech band two interchanged complementary frequency subbands disposed within the band width of a telephony channel, a time scrambling device for adding with given time lags between each other at least one positive or negative echo to the modulation product which appears at the output of the modulating device to provide a scrambled signal for transmission on the telephony channel, and a first means for generating a first code signal for controlling the modulating device so as to vary the ratio of the band widths of said complementary frequency subbands and for controlling the time scrambling device so as to vary the time lags as a function of said first code signal;

said apparatus further including a receiver having a time unscrambling device for regenerating the echo from the received scrambled signal and subtracting it from the received scrambled signal, a demodulating device demodulating the signal from which the echo has been subtracted and converting the demodulated product into a signal at least similar to the speech signal, and a second means for generating a second code signal which is identical to the first code signal for controlling the time unscrambling device and the demodulating device.

Dependencies are inferred from the claim text.

Method and apparatus for the scrambled transmission of spoken information via a telephony channel

Life of this patent

Method and apparatus for the scrambled transmission of spoken information via a telephony channel

Life of this patent

Abstract

Claims32