DE1762441A1 - Procedure for transmitting speech in ciphered form and arrangement for carrying out the procedure - Google Patents

Description

M 966

PATENTANWÄLTE / Ό Z ^ HI

Dr.-Jng. HANS RUSCHKE Dipi.-Ir.g. HEJNZ AGULAR

BERLIN 33 Aiiguste-Vlktoria-Strasse IS

Telefonaktiebolaget LM Ericsson, Stockholm 32, Sweden

"Method for transmitting speech in encrypted form Form and arrangement for carrying out the procedure "

The invention relates to a method for transmitting speech in encrypted form from a Transmitter to a receiver and an arrangement for carrying out the procedure »

Known methods for transmitting encrypted speech are based on digitizing the Voice signal. The digital information is with usual Deals with encryption procedures, and the voice transmission takes place in digital form »The digital

U09818 / 10I7 setting

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sizing can either take place with the help of a vocoder, in which case the JSnd site facilities are quite expensive, or they come with pulse code modulation or delta modulation carried out.

The aim of the invention is a new method of transmitting ciphered speech with limited Requirements for the bandwidth and at the same time with negligible costs for the terminal equipment.

The method according to the invention is in essentially characterized in that the voice signal is converted into a pulse code, which is brought into encrypted form that the encrypted Pulse code is converted into a voice signal and the voice signal together with a synchronization signal transmitted to the receiver and converted there into a pulse code so that this code is deciphered and converting the recovered pulse code into a speech signal.

One arrangement for carrying out the method consists of an encoder in the transmitter, which converts the speech signal into a pulse code, a cipher arrangement which the received pulse code values, representing the samples in encrypted /

Pulse code values 009818/1017

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Converts pulse code values, a modulation device for adding a synchronization signal to the encrypted Signal, a decoder that converts the encrypted digital signals into a voice signal, and in the receiver from a coder that converts the encrypted speech signals received into a pulse code, from a deciphering device that recovers the pulse code from the digital values represented by the pulse code, which corresponds to the original language, and from a decoder, which from the pulse code the original Voice signal restored.

The invention is made with the help of a winter Embodiment described with reference to the accompanying drawing, in which

Fig. 1 shows a system which consists of a transmitter and a receiver for performing the Method according to the invention with the aid of the PGM principle consists, and

Fig. 2 shows a diagram showing the synchronization signal represents.

The talk signal is sent to a PGM encoder 3 via a filter 1 which suppresses a frequency band and whose suppressed frequency band is around the frequency 2 kHz and the purpose of which is described below, and via a low pass 2 with an upper limit

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frequency of 4 kHz given «The sampling of the speech signal is carried out at a frequency of 8 kHz, whereby the speech signals between 6-4 kHz can be converted into PCM signals in the PCM Godierer 3 in a known manner · The PCM signals then given to a cipher device 4 known per se, in which the are brought into ciphered form. These signals are then transmitted through a modulator 5 »the purpose of which will be described below a PCM decoder 6 in which they are converted into a voice frequency signal. In the end the signal runs through a low-pass filter 7 with the upper limit frequency of 4 kHz before it is transmitted. At the entrance of the PCM encoder, an incoming speech signal bl is shown schematically, and at the output of the PCM encoder becomes the ciphered form b2 of the speech signal displayed

On the receiver side, the incoming signal is passed through a low pass 8 with the upper limit frequency of 4 kHz and a filter with suppressed frequency band 9 on a PCM encoder. the PCM signals are converted back to their original form with the aid of a deciphering device 11, and the deciphered PCM signals are sent to a PCM decoder 12, which reproduces the original speech

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frequency signal restores «The restored Signals are sent to a consumer, e.g. a telephone receiver (not shown), via a low pass 13 given.

In order for the arrangement to work, it must The transmission medium will of course work linearly and without delay time ο Beyond that a synchronization between the scanning on the transmitter side and the die necessary on the receiver side According to the invention, synchronization is carried out in such a way that there is a frequency in the voice frequency band is introduced, which corresponds to an integer part (submultiple) of the sampling frequency, and the zero crossings this frequency are used for synchronization. This can be done by a a small part of the available voice frequency band is sacrificed. According to the example is the synchronization frequency chosen at 2 kHz at a sampling frequency of 8 kHz The purpose of the filter 1 is the removal of a narrow band around the frequency of 2 kHz from the frequency spectrum of the original voice signal, so that the synchronization frequency of 2 kHz in the encrypted PGM voice signal can be mixed with the help of the modulator 5. On the receiving end, this is increased by the frequency of 2

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The frequency band lying around kHz is filtered out of the received frequency band by the filter 9. on on the other hand, the synchronization signal of 2 kHz is obtained through a bandpass filter 14 and on the PCM encoder of the receiver given to this with the PCM decoder 6 of the transmitter with the help of the zero crossings to synchronize the synchronization signal Figo 2 shows the synchronization signal only with a and the encrypted speech signal b2 superimposed on £. It can be seen that with the adopted Values four samples are taken during each period of the synchronization frequency and that the zero crossings are used for synchronization can be. From Fig. 2 it can be seen that the amplitude of the synchronization signal can also be used can be used for automatic volume control. In the modulator 5, the amplitude value of the synchronization sfrequeniz added to or subtracted from each sample value. Every other sample has an unchanged ^ Value, while the intermediate values are added to the peak value of the synchronization frequency or from these are deducted. The output signal from the filter 14 is also sent to a device 15 for automatic volume control which is controlled by the maximum amplitude values of the synchronization signal will, so rush a volume adjustment can be carried out.

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The synchronization signal can also be added to the voice signal after the PCM decoder, how easy to see.

To avoid synchronization errors in transmission systems with single sideband and suppressed carrier wave due to a certain slight difference between the original carrier wave and the carrier wave generated in the receiver it may be suitable to use the difference between two signals instead of a synchronization signal. In this pail two signals are transmitted, ζ.Β »the frequencies 2.5 kHz and 500 Hz with one sampling frequency of 8 kHz according to the embodiment, so

that the difference between the two frequencies on the receiver side is always 2 kHz, regardless of a possible discrepancy between the carrier frequency oscillator of the transmitter and that of the receiver.

It is obvious that the expression “pulse code ¹ * means not only the PCM modulation as described in connection with the embodiment, but also the delta modulation.

Claims 009 * 18/10 * 7

Claims (1)

Patent claims: / IJ method for transmitting speech in encrypted form from a sender to a receiver, characterized in that the voice signal is converted into a pulse code, the pulse code is brought into encrypted form, the encrypted pulse code is converted into a speech signal and the voice signal is transmitted together with a synchronization signal to the receiver, where the voice signal is converted into a pulse code, the pulse code is deciphered and the recovered pulse code is converted into a voice signal. 2 _# Method according to claim 1, characterized in that the synchronization signal which 009818/1067 to the - 9 - T 966 it was added to the encrypted signal on the transmitter is an integer part of the sampling frequency used in the coding and is ar. whose Zero crossings aiii "of the. Receiver side for synchronization the scanning is used on the transmitter side and on the receiver side » 3. The method according to claim 2 or 3 »characterized in that the synchronization signal is dem encrypted signal is added after decoding. Ao method according to claim 2 or '5 », characterized in that the synchronization asignal is added to the encrypted sample value of the speech signal before decoding, be method according to claim 41, characterized in that that the synchronization signal is added to the speech signal so that3 the greatest amplitude of the synchronization signal alternately with a positive and negative sign every second AT sample value of the encrypted speech signal is added while the mean samples remain unchanged. 6. Procedure 009818/1087 «AD ORfGiNAu - 10 - T 966 6 · Method according to one of the preceding claims, characterized in that the peak values of the synchronization signal can be used as volume control signals. 7. Method according to one of the preceding claims, characterized in that the difference used for synchronization between two frequencies will. 8. An arrangement for performing the method according to claim 1, characterized in that it consists of a transmitter part with an encoder that converts the speech signal into a pulse code, an encryption device, which converts the received pulse code values, which represent the sample values, into encrypted pulse code values converts, a modulation device for adding a synchronization signal to the encrypted signal and consists of a deodorant, which the encrypted signals in e. α speech signal converts, and from one Bmpfängerteil with an encoder, which the received converts encrypted voice frequency signals into a pulse code, with a deciphering device, which restores the Pula code from the received pulse code, which corresponds to the original language, 009818/1087 BATH ORIGINAL and - 11 - T 966 and with a decoder that reads the original voice signal restores. 9. Arrangement according to claim 8, characterized in that the transmitter consists of a source which generates a synchronization frequency corresponding to an integer part of the sampling frequency in the pulse coding, and an arrangement "which mixes this synchronization frequency with the transmitted voice signal, the receiver Has filter to separate the integer part of the frequency from the received speech signal and to give it to the decoder of the receiver _β 10. Arrangement according to claim 8 or 9, characterized in that the transmitter is a filter device which contains a narrow band around the synchronization frequency from the original speech signal filters out. Lie arrangement according to one of claims 8 to 10, characterized in that the recipient contains a device for automatic volume control, to which the synchronization signal is fed and which forms a control signal * that proportionally is the peak value of the synchronization signal, to regulate the amplitude of the incoming voice frequency signal. 009818/1067 Heipa / Br. -42 .- Blank page