Process and device for speech scrambling and unscrambling in speech transmission

PROCEDURE AND EQUIPMENT FOR CODING AND DECODING A TALK

audio transmission

Extract

The method of the present invention and the apparatus based on the method comprises converting a digitized speech signal into a complex signal with a filter having a bandwidth corresponding to the bandwidth of the transmission channel, the sampling frequency. In which the complex signal thus obtained is reduced, it is phase modulated by a code signal generated by a random number generator, and combined with an additional randomly distributed phase modulated pilot signal to be combined into an encoded payload to be transmitted. The payload is transmitted in sequence, along with a prefix for receiver-side synchronization and payload compensation.

On the receiving side, the phase modulated pilot signal coefficients produced there are calculated for a number from the digitized received signal, again after complex filtering and a corresponding reduction in the sampling rate, during a preamble recognition phase when initializing the payload decoding phase. The encoded transmitted signal is separated on the transmitting page

11550 99 · ···· “~ from the superimposed phase modulated pilot signal by means of a synchronized pilot signal generated on the receiver side, and the resulting phase modulated coded digital speech signal is decoded by the preamble controlled rate code signal generated on the receiver side.

In contrast to known speech coding methods, the present invention has the advantage of being very secure, of very good speech intelligibility, and of recognizing the speaker, despite being fully consistent with the transmission bandwidths available in analogue radio networks and telephony.

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Ρ9 £ 0 {33 3

PUBLICATION LITERATURE

PROCEDURE AND EQUIPMENT FOR VOICE CODING AND DECODING

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for encoding and decoding speech in voice transmissions and / or transmissions. audio transmission apparatus having an end unit for digitizing a speech signal and adapting a transmit signal to a particular transmission channel and / or digitizing a received signal and adapting the conditioned received signal to a sound reproducing apparatus.

Speech coding There are several known methods for decoding, which are briefly summarized as follows:

First Digitization of speech signals, coding of digital values ​​and their transmission as digital data with a MODEM.

Second Storing a series of speech signals, dividing the series into several smaller time intervals, and transmitting these subsets in a different order from the original order.

Third Divide the spectrum to be transmitted into smaller sub-ranges and transmit a signal produced by swapping the sub-ranges of the spectrum.

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4th Frequency band inversion, that is to say, the exchange of high and low frequencies of the transmitted audio frequency spectrum with a constant or variable dividing point (mirror frequency method).

5th 2-4. a combination of the procedures described in.

The known processes have the following basic drawbacks:

Method 1) generally uses the same channels for transmitting digital data as for unencrypted speech. As these channels provide only limited bandwidth, data reduction procedures are required. After reconstruction of this (reduced) data on the customer side, it is not possible to identify the speaker securely.

In procedure 2), for physiological reasons, the number of intervals and their length can only be varied within narrow limits c. This makes the transmitted signal easy to decode.

The transitions between the interchanged sub-intervals on the receiver side are generally not phase-reconstructed, so that the signal quality is audibly degraded relative to the uncoded signal.

In this method, there is a perceptible delay between speech and signal transmission, which in some types of transmission channels causes an echo to the speaker.

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In process 3), for physiological reasons, the number of spectral sub-intervals and the bandwidth are within narrow limits. As a result, the transmitted signal can be easily decoded. For filters required for the generation and reconstruction of sub-spectra, inevitable bandwidth overlaps degrade transmission quality.

In method 4), it is possible to decode the transmitted signal with relatively little technical effort. The encoded signal remains relatively intelligible; an experienced person can eavesdrop on conversations without a technical aid.

In method 5), combinations of different methods generally increase the security against decryption; however, the disadvantageous properties are added together, thus reducing the signal-to-noise ratio and these solutions are limited to some simple arrangement of the transmission channels.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for encoding and decoding speech in a voice transmission which can be produced as a module of compact design (which can be retrofitted) and which is known in the art. provides significantly better security than third party equipment against eavesdropping and evaluation by third parties.

For this task, we have the following additional requirements for speech coding:

- Good speech intelligibility;

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- Speaker recognition;

Slight difference in quality compared to uncoded operation;

- User-friendly functionality and operation;

Automatic detection of encoded signals on the receiver side;

- Use in analogue radio networks and telephone technology;

- Respect the available transmission bandwidths.

The object of the present invention is solved by a method suitable for encoding and decoding speech in voice transmission, wherein

converting a digitized speech signal with a first complex input filter having a bandwidth corresponding to the bandwidth of the transmission channel to a complex signal, which is phase modulated by a code signal controlled by pseudorandom numbers; with a prefix for receiver-side synchronization and payload balancing, as a complex signal, we pass it through a first complex output filter in which a real output filter is used. · · ····

Generating a -5 output signal which is conditioned to a transmit signal after digital-to-analog conversion, and on the receiver side

converting the digitized received signal to a complex signal using a second complex input filter having a bandwidth corresponding to the bandwidth of the transmission channel,

- with this complex signal, during the prefix recognition phase, on the one hand, the phase-modulated pilot signal initialized in a pseudorandom distribution on a customer side is initialized, and on the other hand, separated by the synchronized pilot signal generated on the receiver side, and decoding the resulting phase-modulated coded digital speech signal by inverse phase modulation on the receiving side, using a controlled-rate code signal, and transmitting it as a complex signal through a second complex output filter which generates a real output signal after digital-analog conversion. .

An important aspect of the process of the present invention is, after the input-side digitization, that complex filtering is carried out on both the transmitter and receiver sides, preferably by means of a Hilbert filter. THE • · · · ····

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filtering to produce a complex signal from a real signal at which the sampling frequency is reduced; the bandwidth of the complex filter corresponds to the reduced sampling frequency. The operations important for the further process are then performed with complex signals at a reduced clock frequency.

On the output side, for the complex signal, it is advantageous to increase the sampling frequency on both the transmitting side and the receiving side by inserting zeros in the data stream. A complex filter, preferably also a Hilber filter, serves as an interpolation filter that produces a real signal with a sampling frequency corresponding to the channel bandwidth.

The apparatus of the present invention serves to encode and decode speech in voice transmission devices having an end unit for digitizing a speech signal and adapting a transmit signal to a predetermined transmission channel and / or digitizing a received signal and adapting the conditioned received signal to a speech reproduction device. On the transmitter side, a code generator controlled by a (pseudo) random number generator controls a digital phase modulator which phase modulates the digitized speech signal,

- the phase-modulated speech signal is combined with a phase-modulated pilot signal provided by a pilot signal generator, also randomly distributed, into a useful edge j,

- a preamplifier generates a preamble for receiver-side synchronization and payload balancing, which is coupled to the terminal unit in sequence with the payload signal via a switchable switch at a specific rate, and on the receiver side

- a digital equalizer filter which compensates for distortions in the transmission channel of the digitized received signal, having equalization coefficients calculated and set during the reception of the prefix, is received within the received present by a prefix recognition unit that triggers the filtering of the prefixes depending on a given section of the prefix for him in a higher computing unit, and initializes the decoding of the payload by activating a clock synchronization unit which, on the one hand, by complex multiplication of the received demodulated pilot signal with a pilot tone generated on the receiver side, to correct the sampling rate &lt;

a control signal, and on the other hand, by controlling a random number generator also initiated by clock synchronization from the pilot tone generated by the client pilot tone generator, transmits a phase modulated pilot signal via a phase modulator, which is connected to the transmitted pilot signal by subtracting controlled ···· ····

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a phase demodulator converts an unmodulated digital speech signal which is coupled to a terminal to convert to a voice signal.

Further preferred embodiments and features of the method and apparatus for encoding and decoding speech of the present invention are set forth in the dependent claims.