DE1062286B - Transmission system for speech signals with bandwidth reduction and circuit arrangement for encryption - Google Patents

Description

GERMAN

PATENT OFFICE

kl. 21 a 2 36/22

INTERNATIONAL KL.

H04j; k

T15070VIIIa / 21a ²

REGISTRATION DAYi 26 AP R I L 19 5 8

NOTICE
THE REGISTRATION
AND ISSUE OF THE
EDITORIAL] JULY 30, 1959

The invention is based on the task that is necessary for the transmission of a continuous signal, in particular a voice signal to largely reduce the required bandwidth and the signal to encrypt as securely as possible in a simple way. To the well-known, very safe and at the same time right simple pulse encryption method; B. Addition of a key pulse sequence to the one to be encrypted Pulse train - To be able to apply to a continuous signal, this signal is initially to be used encode.

In the transmission system according to the invention for speech signals, in which to reduce the Bandwidth characteristics derived from the speech signal transmitted in two channels will be in the first. Channel per time-quantized sampled amplitude of the speech signal only transmit a code pulse or not, depending on whether the signal is sent to the Sampling time is greater or less than its mean value, and in the second channel is a slow one Transmit dynamic fluctuations proportional amplitude signal.

In the case of pulse code modulation, a. continuous signal of bandwidth b is queried with a pulse train of frequency 2b , and the signal amplitude present at the time of the respective sampling is converted into a binary number. If this binary number η has pulse positions, it can be used to express 2 "different amplitude values. With such a limited number qu targeted amplitude steps, a distortion of the transmitted signal occurs, which reduces the intelligibility of telephonic · Only one impulse is delivered or not delivered. The impulse then expresses through its presence or absence only whether the signal at the time of sampling is greater or less than its mean value, ie positive or negative, if you follow the mean value line as the ordinate.

With this simplified coding, all dynamic differences in the signal are lost because the positive half-wave: a signal with a small amplitude becomes exactly like the positive half-wave of the signal with maximum amplitude represented by only one pulse of the same amplitude. Obtain only the zero crossings of the signal remain. However, since the signal is sampled in a time-quantized manner, will not be the exact ones either. Zero crossing times are marked, but it is only recorded whether

the signal in a time interval - its polarity

has changed or not.

When examining the telephony audio transmission system for speech signals with bandwidth reduction and circuit arrangement

for encryption

Applicant:

Telefunken G.m.b.H., Berlin NW 87, Sickingenstrasse 71

Dipl.-Ing. Ernst Kettel, Ulm / Danube, has been named as the inventor

ability of such a circuit arrangement, the per time-quantized Scanning only delivers one code pulse - these code pulses are hereinafter referred to as Code signal - you can still find a surprisingly high level of intelligibility.

The quality of the transmission now suffers considerably if interference is still superimposed on the voice signal because the interference voltage is included in the pauses in speech between the individual words and syllables transmitted with the same amplitude as the speech itself, because of the complete amplitude limitation no dynamic differences are transmitted. Although the language so disturbed is still understandable, but eavesdropping is very exhausting and tiring, since the eavesdropper is also during the Speech pauses must concentrate on the equally strong background noise. The quality is through transmission one . the dynamic fluctuations, proportional amplitude signal in a second channel improved. A bandwidth of 30 Hz is sufficient for the transmission of the amplitude signal, one Increasing it to 200 Hz brings only a small gain in intelligibility.

If the amplitude signal is also to be encoded using one of the known pulse encoding methods, it must also be encoded. An investigation shows that an amplitude quantization of the amplitude signal accurate to 3% is sufficient, ie 2 ⁵ = 32 amplitude steps are required. The channel capacity of the amplitude signal is therefore only 5 * 2 * 30 = 300 bits. With a bandwidth of 3000 Hz to be transmitted, the code signal has a channel capacity of 1 * 2 * 3000 = 6000 bits, and a channel capacity of 6300 bits is therefore required for the entire signal.

909 579/293

: ': Comparative quality tests show that "with a pulse-code-modulated speech signal, two to three pulses per scan are transmitted must to achieve the same intelligibility .. Pie required channel capacity is then about 2.5 x 2 x 3000 = 15,000 bits; The gain in bandwidth in the coding according to the invention is therefore considerable.

It is, in fact .. known per se, a speech signal in split two channels, with the frequency information in one channel and the Dynamic fluctuations of the speech signal are transmitted, thereby making it even with a very unfavorable one Signal-to-interference level ratio in the transmission channel to enable transmission. (Philips Technische Rundschau, 1957/58, No. 3 of December 9, 57, pp. 69 to 80 and German patent specification 878 381). Since in these known systems but the frequency information by complete limitation of the continuous Speech signal is obtained, they are z. B. for the application of the pulse encryption, procedure, as they are possible with the invention, unsuitable.

The transmission system according to the invention is explained with reference to FIG. The speech signal is converted into the code signal c of the one channel α in the coder 1, which delivers or does not deliver only one code pulse per scan. In addition, the voice signal for the other channel b is rectified with diode 2. The low-pass filter 3 allows only the slow dynamic fluctuations, for example / <C30Hz, to pass, which are then possibly pulse-code-modulated in the encoder 4 to form the signal d of the second channel. On the receiving side, the code signal e of one channel and the pulse-code-modulated amplitude signal / of the other channel are used in the pulse-forming stages. 5 or 6 separated from the interference signals, and the amplitude signal f is converted into a continuous signal in the decoder 7 and in the low-pass filter 8, for example / <C30Hz. The code signal of the other channel modulated with the amplitude signal in the ring modulator 9 can, after passing through the low-pass filter 10, e.g. B. / = 3000Hz, can be monitored.

The coded speech signal supplied by the circuit arrangement according to the invention can be traced encrypt the well-known, relatively very secure impulse encryption method.

FIGS. 2 and 3 show two circuit arrangements as exemplary embodiments for the connection or Decryption of a speech signal encoded with the circuit arrangement according to the invention according to FIG. 1.

Corresponding to Fig. 2, the code signal c and the pulse-code-modulated amplitude signal d in the adding stages 11 and 12 each have a key pulse sequence or h, z. B. modulo · 2, added separately, whereby the encrypted signals c ' and d' arise. In addition, modulo η is defined as the sum of the remainder remaining after dividing the algebraic sum by η. With an addition modulo 2, only the numbers 0 or 1 can appear as a sum. On the receiver side, the encrypted code signal e ' and the encrypted amplitude

signal / 'is deciphered by adding, for example modulo 2, the key pulse sequence g or, respectively, h in the adding stages 13 and 14 and thereby the signals e and / are again obtained in plain text.

In Fig. 3, the code signal c and the pulse code modulated amplitude signal d are converted by an electronic switch 15 according to the time division multiplex method known per se into a single pulse sequence and in the adder 16 by addition, for. B. modulo 2, a key pulse train i to the signal / encrypted. At the receiver end, the encrypted pulse train k is added in the adder 17, e.g. B. modulo 2, the key pulse sequence i decrypted and by 'the electron switch 18 again in. The code signal e and the amplitude signal / split.

Claims (3)

Patent claims: 1. Transmission system for speech signals! In which to reduce the bandwidth of the speech ■ transmit signal-derived characteristic values in two channels are, characterized in that in the one channel per time-quantized sampled Amplitude of the speech signal only a code pulse is transmitted or not transmitted, depending on whether the signal at the sampling time is greater or less than its mean value, and that in the second channel into the slow one. Dynamic fluctuations proportional amplitude signal is transmitted. 2. A circuit arrangement for encrypting the signals supplied by the transmission system according to claim 1 in the two channels, characterized in that a key pulse sequence (g) is added to the code signal (c) of the one channel in an adder stage (11) and that in a second adding stage (12) to the pulse code modulated amplitude signal ( d) of the second channel, a second key sequence (h) is added (Fig. 2). 3. A circuit arrangement for encrypting the signals supplied by the transmission system according to claim 1 in the two channels, characterized in that a switch (15) the code signal (c) of one channel and the pulse-code-modulated amplitude signal (d) of the other channel according to the known per se Time division multiplexing is combined into a pulse train and that a key pulse train (i) is added to this pulse train in an adder (16) (Fig. 3). Considered publications:
German patent specification No. 878 381. 1 sheet of drawings