DE1916711B2 - METHOD AND CIRCUIT ARRANGEMENT FOR THE ASYNCHRONOUS TRANSMISSION OF BINARY DATA OVER A CHANNEL OF TIGHTLY LIMITED BANDWIDTH - Google Patents

Description

lation signal is obtained. The signal is processed again in a low-pass filter and an equalization or equalizer stage and is finally decoded in a full-wave rectifier. Before decoding, the pilot signal is recovered and fed to the signal detector in which the decoded signal is recovered in order to synchronize the signal decoding or detection with the signal generation at the transmitter. The synchronized signal is then processed in a signal regeneration stage, _Ί0 so that the original digital signal is finally obtained again.

Despite the simplified demodulation technique for the reduced carrier wave, this known System used a complicated logic for digital coding and filtering so that the system becomes very complex and expensive. (Article by Peter Leu t hold and Felix Ti si, »A single sideband system for data transfer «in the journal» Archive for Electronics and Transmission Technology «, Bd; 21, 1967, No. 7, pp. 354 to 362.)

All known systems using partial response transmission are generally on one Time control technology built up. On the other hand, systems that aim ■ to change the data sequence without Use of partial response techniques to increase, limit to relatively small data sequences. In the Both of the aforementioned systems are, in addition to timing or clocking, also relative Complex and expensive facilities are required, and there is also a phenomenon that known as quantized noise.

In a known facsimile transmission system in which clock-controlled binary signals are used be, with a biternary coding and decoding respectively at the input and output ends of the transmission channel is provided, the available bandwidth for transmission of image information is used to the maximum, and this system is also relatively insensitive to noise, which can be traced back to the synchronized nature of the 'decoding process. This optimal Embodiment can only be with the help of an expensive and relatively complex synchronization device, both for the transmission and the Receiving station.

With the latter system, a disadvantage can become noticeable when the system is used for transmission of image information is used, and this disadvantage is quantized noise. There clocking the original data signal reorientates the black-and-white transitions made in a Line scanning occur so that they coincide with the clock-controlled signal, the correspond to actually transmitted information does not exactly match the black and white transitions that are in the photocell occur when it sweeps the scan line. Since the clock-controlled system is only able to To reproduce black-and-white transitions in synchronization with the cycle time, the introduced Errors are approaching a bit interval and the resulting print can have significant degradation show what is based on the quantized noise.

The object on which the invention is based is now to provide a method and a device for an asynchronous binary data transfer in limited * »,. tr QnaihHndern to create with the one possible large information content per unit of time can be transmitted with little technical effort.

This object is achieved in that, according to the invention, the converted data are present in a maximum bit sequence of Kf ₁ , where Z _{1 is} the upper frequency of the zero response value of the transmission channel and K has a value which is less than 2, but which is equal to the value 2 approaches for a noise-free channel, are transmitted via a filter which has a linear phase-frequency characteristic, with an amplitude attenuation that increases uniformly with increasing frequency, which at a

Kf
Frequency - ~ - Less than 40% of the Mb

transfer value and its transfer function, with negligible overshoot, in

a time no more than at every transition

^Λ ./ι

is completed to produce at the receiving station a partial response waveform that is the NRZ waveform to obtain the received partial response waveform then at the receiving station a midpoint threshold for retrieving the binary ones and zeros, which the portions of the received waveform above and below the midpoint threshold correspond.

In contrast to the known methods and devices, the present invention relates to a non-synchronized transmission method and device, whereby the shaping or shaping of the Signal wave here without a complicated and expensive coding logic and decoding logic for NRZ pulses and is done without timing. This technology now enables information transfer speeds, which is only slightly smaller than that of a known biternary transmission system achieved transmission speed (binary partial response wave), these devices for such transmission technology are much more complex and also require clock control.

According to an advantageous embodiment, the filter with the linear phase-frequency characteristic can be used in place of the filter connect a transmission channel with the same properties as the filter.

In particular, the invention can experience an advantageous development that the filtering the binary NRZ waveform with a linear phase-frequency characteristic and an amplitude transfer function from

Λ if) =

Vi

2 /,

Λ if) = 0

is performed.

This method can be used very advantageously for facsimile transmission on voice telephone lines will.

A device which is suitable for carrying out the method according to the invention is identified through a scanner-writer unit operable in synchronism with a remote similar unit and scans; this unit also has an optical device for analyzing a document can be operated at a specified speed and resolution in order to produce a line scan signal

to generate speaking a maximum transmission sequence of about 4000 transitions per second; also a limiter responsive to the line scan signal to produce a binary NRZ waveform, which has transitions at the black and white transitions of the scan lines on the document; Further the device includes filter means responsive to the binary NRZ waveform and an amplitude transfer factor

A (f) =

2 /,

2 /,

A if) = 0

shows, where / Ί is about 2.17 kHz and the Filter means a linear phase-frequency characteristic for generating a partial response waveform owns; a stable oscillator is also provided, to which a frequency divider is connected in order to switch off deriving from the oscillator frequency a carrier wave with a frequency of about 2.4 kHz; a modulation device modulates the carrier wave with the partial response waveform, and a coupling device couples the modulated carrier wave to a telephone line, at the other end of which a similar one Unit is connected; Finally, the device has amplifier and transversal filter devices, responsive to the overcoupled signal from the telephone line to eliminate system and telephone line distortion in the signal received from the remote unit, as well as a vestigial sideband modulator which is based on the Signal from the amplifier and transversal filter means responds to the partial response waveform capture. Using a midpoint threshold that is responsive to the partial response waveform, a threshold detection centered in the middle of the partial response waveform is provided by a Original copy of the binary NRZ waveform. Finally, through a facility for Feeding the original copy of the binary NRZ waveform on the scanner-writer unit a facsimile copy of that on the remote similar unit scanned document written or printed.

Each such device may also have a gray signal generator which is based on the beginning of the transmission of a document image responds to send a signal for a limited interval, which is modulated at a level which represents the mean amplitude of the output of the limiter; also an electronic device that responds to the start of reception of a modulated carrier, in order to set the midpoint threshold during this interval so that it corresponds to the modulation value is equivalent to.

The electronic device for setting the midpoint threshold includes the following stages: one Gain control circuit for the amplifier and a transversal filter device and an electronic Circuit responsive to the output of the midpoint threshold to provide gain control and which maintains the set gain after this interval.

In such a circuit arrangement, the modulation characteristic is the amplitude of the modulation signal, and the carrier wave is amplitude-modulated. Furthermore, the intermediate modulation value of the modulation signal is a modulation amplitude which is almost half the peak values of the modulation amplitude which originates from the binary signal.

In the following the invention on the basis of an exemplary embodiment and with reference to the Drawings explained in more detail. It shows

Figs. 1 (a) and 1 (b) are amplitude timing diagrams useful for biternary signal theory,

F i g. 2 (a) and 2 (b) partial response signals in one

maximum bit sequence, both for known systems and door the system according to the present invention,

F i g. 3 is a block diagram of an NRZ binary wave transmission system according to the present invention,

F i g. 4 is a block diagram similar to that of FIG. 3, but for binary pulse signals,

F i g. 5 is a block diagram of a facsimile system in an embodiment according to the invention;

F i g. Figure 6 is a waveform diagram comparing known systems with the system of the present invention Invention and

F i g. 7 shows a filter amplitude curve diagram of a midpoint threshold.

Using the drawings, let me first give an overview of the digital partial response theory given in order to establish the necessary and appropriate criteria for the present invention to be able to.

Biternary signal theory can be described simply by the expressions "partial response" transmission, as described by IR Kretzmer in his brief "Binary dale message transmission with the help of partial response transmission" (brief G-IE. 5 on pp 451-456 of the First IEEE Annual Communications Convention Conference Record. June 7-9, 1965). There it is stated in summary: A partial response system sends a two-level signal over a channel, a memory ii storing binary input symbols and the binary sequence being recovered on the basis of detected levels characteristic of L , where L> / 1. In the case of biternary, η = 2 and L - 3. The key to recovering the original bitstream is to select the channel's response to a binary signal element in order to allow for controlled memory storage. It has been shown that a channel with the transfer amplitude function

Y (ω) = cos

0 < ω <

Υ (ω) 0 ω <

where ω - 2π /

and a linear phase-frequency characteristic U has an impulse response measured at a time = 0 at the top of the response which, with two exceptions, go through 0 _{at an odd multiple of a positive or negative V 4 /.} Di ₁ exceptions occur at T = ± '/ 4/1, like ii F i g. 1 (a).

If this response or response is used as a signaling element for binary signals in a synchronous random bit stream with a sequence of 2 f _x Bi per second and that results

If the signal is only ever measured at odd multiples of V4 / 1, the measured amplitudes only take three possible values; 0, A and 2A, which depends on whether the two answers near the measuring point correspond to two binary zeros, a 1 and a 0 (or vice versa) or two ones as in FIG. 1 (b). An examination of the superimpositions of various combinations of ones and zeros leads to the principle that in order to recover the original binary bit stream, one has to decode a bit as a "1" if the answer to the sampling two-point is 2 A , as a "zero «If the answer is 0 and a complement of the previously decoded bit if the answer is A. By providing a controlled memory in this way, ie a controlled intersymbol relationship, data can be transmitted in a higher order in a specially shaped channel than can usually be achieved using conventional memoryless binary transmission.

The previous theory was described in the form of a clock-controlled pulse signal input, at a

Y (/) = cos - ^ f- channel filtering

and recovering the original binary bit stream by utilizing the received ternary Signal and determination of which of the three states of the ternary signal is present at the time of blanking is. This is usually achieved with the help of two thresholds which are fixed and where the ternary signal than above the upper threshold, below the lower threshold or between the two thresholds is interpreted lying down.

If desired, two pulses of width '/, /' are used to signal what a so-called NRZ signal, the previously specified channel shape would not be optimal. According to the present In accordance with the invention, signaling without logical decoding and for NRZ pulses is achieved, namely without clocking while channel shaping is selected, allowing signaling sequences that are only slightly inferior to those obtained with the help of the more complex clock-controlled biternary systems can be achieved according to the state of the art.

First, consider the spectrum of a pulse and the transformation of a pulse bit stream into an NRZ signal from pulses with a width of V2 / 1. Since the spectrum of a pulse is linear, it is only necessary to multiply the NRZ signal by a spectral shape which is the reciprocal of the spectral shape of a pulse of width V2 / 1 - ^ ^{as the} spectrum of a pulse of width V2 / 1

Tlf. Jt /

With a cotangent channel shape, as expressed by A (f) , a clock-controlled binary NRZ signal with a bit sequence 2 Z _{1 can be} recovered, through the usual contact thresholds and a logical interpretation of the result according to the controlled inter-symbol relationship.

The original binary data stream can be recovered from the ternary signal, without Time control and a single threshold by controlling the system in such a way that it is in one slightly lower transmission bit rate or frequency works. This can be demonstrated by testing of the "eye oscillogram" (the oscilloscopic deflection of the received ternary wave), which results from an arbitrarily synchronized NRZ bitstream which

2 /,

2 room

follows. For a bit sequence of If ₁ , the eye oscillogram is that shown in Fig. 2 (a). The uniform horizontal line in the middle of the oscillogram corresponds to the response of a binary sequence of 101010. The basic frequency for this sequence is / 1 Hz and the function A (f) = 0 at / = Z ₁ . However, if the bit sequence is reduced so that the fundamental frequency of the 101010 sequence is less than Zi, the little "eyes" begin to open on the eye oscillogram, as shown in FIG. 2 (b). The step function rise time remains the same, but the dwell time between the transitions is increased. The amount of eye opening required for threshold detection in the middle of the threshold depends on the signal-to-noise ratio and the permissible error sequence. A value of a bit sequence of less than 2 Z ₁ is common in a channel with a given signal-to-noise ratio, this ratio can be defined as a bit sequence KZi, where K <2 and K is the value 2 for a noise-free one Approaching canal. For such a system, when a threshold is established, as in FIG. 2 (b) is indicated, the original binary sequence can be retrieved through the center of the small eyes.

The reduced bit sequence required to achieve this result can be provided so that it is compatible with the noise level by having an operable percentage narrow eye opening chooses and finds out at which Frequem

this occurs with regard to Zi, and they danr doubled to find the bit sequence. For average local calls, simpl Eye opening found to be satisfactory at 20% of peak response. this leads to

So, when an NRZ signal is used as an input, the channel shape must be as follows:

U _x ) =

cot

-φ

= 0.2 (rounded up).

The solution for J _x is found

= 0.91

AU) =

AU)

sin

π /

cot

2 /, 2Z ₁

A (fx) = 1.43 cot 1.43

= 1.43 (0.142) = 0.203.

Therefore, at / - / » - 0.91 / _{t there is} a 20% Auger opening, and a bit sequence vo

2372

1.82 /, bit / second and the original bit stream can be retrieved with a single midpoint threshold.

The channel shape for the NRZ signal with a reduced bit sequence, ie 1.82 J ₁ bit / second, remains the same as for the closed eye bit sequence, ie

^AU) -

2 /,

cot

^cot

T /

A system of this type is shown in FIG. 3, the message link between the filter and the Midpoint threshold is displayed. What has been achieved as an effect is the signaling with wider ones

Pulses, with the width Seconds is, seconds. If you wish

instead of

2 /,

If, to signal with pulses, the channel shape would have to be modified in order to convert the pulses into pulses with a width of 1 / 1,82Z ₁ . This can be achieved simply by dividing the spectrum of a pulse (linear) by the factor

sin

■ I

1.82 /, '1.82 / ,;

is multiplied to convert it according to a pulse of width 1 / 1.82 / as in Fig. 4 is displayed.

Of the systems shown in FIGS. 3 and 4 is only the system of FIG. 3 (NRZ signals) can be operated with non-synchronous data. This is the case because in the non-synchronous NRZ case the transitions can occur anywhere while if pulses are used that

to select signals that can be viewed as derived from respectively white and black areas, namely from zones of the document that is scanned by the photocell.

The information sequence of the system is dictated by the bandwidth of the telephone line used for this System is to be used, and the scanning speed of the scan writer 11 becomes accordingly chosen. As an example, the optical system in the scanner should have a zone of 0.0254 cm in Resolve diameter and scan lines are 0.0254 cm apart. The upper limit the bit sequence or frequency is 4000 bits / sec., and the corresponding linear scanning speed is 101.60 cm / sec. The desired resolution is achieved with a scanning system of this type, and with a bit sequence that does not exceed the capacity of the system, and in this way it is optimal Resolution achieves a transmission speed at which the bandwidth of the telephone line is used to the maximum.

The NRZ signal on line 14 passes through a pre-modulation filter 15, which the filter curve characteristic

A (f) = 0.725 / cot 0.725 /

Has. This filter also has a linear phase-to-frequency characteristic over the range of zero

to 2170 Hz. The magnitude 0.725 is the value of

sin

Kf ₁ 'Kf ₁

shape

would always pre-determine where the transitions are to be found in the data.

With reference to the F i g. 5 is now the invention in the case of application to a telephone facsimile system to be discribed.

A scan writer 11 operates in the transmitter section and samples the information that is being transmitted should, on a document and converts it into an analog signal on the line 12, this Signal represents black-or-white information. The signal on line 12 is preferably a photocell and a light source which scans the copy to be transmitted line by line to the analog facsimile signal to create. The scan recorder 11 also operates in response to signals on the line 10 to write or print black-on-white signals when the unit is a receiver is operated, the scanning process operating in synchronism with the remote transmitter scanner to obtain a Reconstruct facsimile copy of the original document.

The photocell signal on line 12 is two-value limited in limiter 13 to provide a binary non-zero return (NRZ) signal on line 14, as illustrated by waveform (a) in FIG. This limitation is achieved by providing a threshold for the analog signal on line 12, where / 1 equals 2.17 kHz. With a Z ₁ with a value of 2.17 kHz, the bit sequence of 1.82Zi is almost 4000 bits per second.

The output of the filter 15 is fed to an AM modulator 16, which has a 2.4 kHz carrier on the Line 17 is received from a frequency divider 18, the latter being the frequency of a precision crystal oscillator 19 divided by 1024, this oscillator oscillating at 2.4576 MHz.

The 2.4 kHz on the frequency divider 18 are also passed through a frequency divider 21 to to be provided on the 22.400 Hz line for synchronous operation of the motor drive23. The motor drives for the line and sheet scanning in the scanning recorder II are in view of the precision crystal oscillator 19 located in each unit is kept in sync. As in the aforementioned patent applications a start character assures the system that the read and write scans work from an initial position on the left edge of the sheet.

The output of the modulator 16 is fed to a residual sideband filter 24, which has a skew-symmetric

Irish attenuation relative to the carrier frequency of 2.4 kHz, with a relative amplitude transfer factor of 0.5 at the carrier frequency and a transfer factor of 0 to 3.0 kHz.
The signal from the filter 24 passes through a

Power amplifier 25 to excite a coupling coil 26 which is magnetically coupled to the handset 21 of a telephone set.

The reception of the facsimile signals is carried out with the same equipment as in Fig. 5 is shown,

digit, which is located in the receiving station. Telephone signals received over the telephone lines are magnetically attached to the telephone set 27 in the receiving station by means of a

2372

Koppelspiilc 28 coupled, to which a Entbrummspulo29 assigned. The 2.4 kHz ir-modulated signal picked up by telephone 27 is fed to an NF-Vcrslürker 31, which is a Signal for a transversal filter 32 provides.

The equalizer 32 provides equalization over the frequency range of almost 230 to 3000 Hz, and in addition, the equalizer also makes corrections to the amplitude and phase, namely with regard to incomplete filtering in other parts of the system.

The output of the filter 32 is fed to a full wave rectifier 33. The rectifier or detector 33 contains a downstream low-pass filter, and thus a midpoint threshold 35 is the recovered partial response modulation waveform (d) in Fig. 6 is supplied. The midpoint threshold 35 operates relative to the center of the waveform (d) and produces an output waveform (e) that is binary is how this depends on whether the waveform (d) is above or below the midpoint threshold lieg · .. The waveform (e) in Fig. 6 becomes a power amplifier 36 supplied, which in this way provides the black and white signals on line 10, to operate the recorder in the scan recorder 11.

After receiving a carrier from the filter 32, the detector 33 generates a signal on the line 37 Signal that represents the receipt of a message. This signal on line 37 passes to a “Start-stop” control 38, which keeps the recorder in the scan recorder 11 synchronized with the scan in the transmitting station starts.

The start-stop control 38 also provides a signal that controls the gain of the LF amplifier 31, to switch the midpoint threshold in a manner as will now be described. The receipt of a signal on the line 37, which indicates a detection in the detector 33, leads to Formation of an output pulse on the line 41, which excites a monostable circuit 42, the one has a relatively long pulse duration, such as B. 2 seconds. For the duration of the 2-second pulse output of the monostable multivibrator 42, an AND gate 43 is set to standby and allows 150 Hz signals the line 44 to the input of an up-down counter 45 through. The 150 Hz signal on the line 44 can be derived from any conventional source such as e.g. B. from the divider 55, from the oscillator 19 is driven.

The count in the counter 45 is converted into an analog voltage by a digital-to-analog matrix 46 converted, and this voltage is on the line 47 as the AGC potential for the amplifier 31 delivered. The direction of counting in counter 45 is determined by the relative polarity of the signal on the Line 48, which is obtained from the output of the midpoint threshold 35, is controlled.

If the transceiver of FIG. 5 sends a message, a document detector sees the Scan recorder 11 presents a transmission signal on line 51, which is fed to monostable multivibrator 42 to slightly lengthen the duration of the output pulse generated. This slightly lengthened Pulse period of the output of the monostable multivibrator 42 reaches the line 52 and thus to a Gray signal generator 53. The gray signal generator 53 provides a signal on line 54 which is sent to the filter 15 arrives and its amplitude is the midpoint between the amplitudes of the normal black and white NRZ signalc corresponds to that on the line 14 can be received. This so-called gray level signal on line 54 for a brief interval after a document has entered the Scanning recorder 11 was inserted, but before any black signal was scanned that a Signal on line 14 is generated.

ίο With a modulation value of a size that corresponds to the Corresponds to the gray level signal received by the detector 33 and fed to the threshold 35 the relative polarity of the output of the threshold 35 depends on the gain of the amplifier 31 since, when the modulation value is amplified above the midpoint threshold, an output polarity is obtained from the threshold 35, which is opposite to that which would occur if the Amplification of the amplifier 31 the gray signal

modulation value amplified to less than the midpoint threshold.

The high or low output of the midpoint threshold 35 comes on line 48 as negative feedback to the count of the Counter 45 to step forward or backward, as to change the gain of the Amplifier 31 is required to a value that is used to design the gray value modulation, which is the threshold 35 is supplied, corresponding to the midpoint threshold is required. The gain value of the Amplifier 31 is maintained throughout the transmission, since it is at the end of the two-second pulse from the monostable flip-flop 32, the AND gate 43 is brought out of readiness and the Count in counter 45 is held until the next message sequence occurs.

With a fixed gain of the amplifier 31, the signals corresponding to black and white are received and relative to a voltage level midway between the black and white signals split by the midpoint threshold 35, so that split in this way at a correct point to recover the original NRZ data signal.

Filter shapes, other than the cotangent shape previously described, can be used to achieve similar results. The general characteristics of these filters can be derived or obtained from considerations regarding the transition function of the filter for a particular case. If one considers the facsimile system that has just been described and has a resolution of 39.4 lines per centimeter and a scanning speed that has a maximum transmission rate of 4000 bits / sec. the NRZ pulse is no shorter than 250 microseconds. This means that the highest change from "1" to "0" equals 4000 transitions / sec. which corresponds to 39.4 lines / cm. The requirements for the jump functions are such that the filter transfer value on the 101010 mode should be 20% so that the highest data reversal sequence can be recovered by midpoint threshold detection. Thus, a point on the generalized filter amplitude versus the frequency response is equal to A (/) = 0.2, at / = 2 KC.

Let us now consider the analysis of the filter for the 1010 wave type by summing the Step functions of the filter on each of the transition

IS

flanken, the individual jump functions on three successive transitions in a maximum sequence, as in FIG. 7 (a) are shown in FIG. 7 (b), (c) and (d) given, The sumwe of this transition is shown in Figure 7 (e), and the recovered signal obtained by center threshold detection is shown in Fig. 7 (1). The necessary step function for such an execution is:

a) The step function must be damped negligibly run or negligible overshoot, so that z. B. the step function accordingly flank 1 has no disruptive effect on the correct timing of the exceedance the threshold of the step function of flank 3 has. If a damped oscillation is transmitted to the flat sections of the transition function or the frequency response corresponding to edge 1 occurs it could interfere with the location of the recovered edge 3 '.

b) The step function must be performed in less than or within two bit periods or 500 microseconds, be completed in the example given. When the step function rise time is longer Threshold errors can occur again corresponding to intersymbol interference appear. When the step function rise time is less than 500 microseconds the response or frequency response is acceptable, but the filter should have a larger one Have bandwidth. The best compromise in terms of bandwidth is therefore to the jump function application time is 500 microseconds or to choose two bit periods,

Now consider flank 3, which is shifted to the right in time by any amount <i. then

ίο would change the step function of edge 3 as well be moved the same amount. The threshold transition occurs a little later aiii and creates a complete recovery time for the dwell time between edge 2 and edge 3, regardless of their size,

15 · as long as it exceeds 250 microseconds. In this way, edge 3 can occur anywhere, and the filter is satisfactorily designed for non-synchronous data.
Further investigation shows that as long as the

minimum dwell time is 250 microseconds using a filter with those mentioned above Requirements with regard to the transition function a full recovery is achieved, If the dwell time falls below 250 microseconds or if the step function is longer than 500 microseconds or if a damped oscillation and an overshoot are permitted, there is intersymbol interference and the recovery is not good as far as the

The degree of deficiency is dependent.

1 sheet of drawings

Claims (7)

Threshold reveal the following: an amplification device (38, 42, 43, 55, 45, 46) Mr the amplifier (31) and a transverse device (32) and an electronic circuit (48, 45, 46), which on the output ( ! or midpoint threshold (35) responds in order to set the gain control, and which maintains the set reversal after this interval, circuit arrangement according to one of Claims 5 to 7, characterized in that the modulation characteristic is the amplitude of the modulation signal and the carrier wave is amplitude-modulated 9. Circuit arrangement according to claim 8, characterized in that the intermediate modulation value of the modulation signal is a modulation amplitude which is almost half the peak values of the modulation amplitude which originates from the binary signal. The invention relates to a method and a circuit arrangement for the asynchronous transmission of binary Data over a narrow bandwidth channel e, wherein the data is converted to a binary non-zero return waveform (NRZ waveform), that NRZ waveform is then transmitted over the channel, and the original binary data is generated from the NRZ waveform. There has been known a polybinary transmission method and apparatus for converting a conventional binary waveform to a waveform having at least four signal levels, the method also comprising recovering this polybinary waveform to the conventional binary waveform. The main features of this known method can be summarized as follows: A common binary digital waveform is converted into a polybinary digital waveform with b-levels, where b is an integer and greater than 3, in which the existing binary pulse with the output pulse which was generated in the previous (b-2) combinations of this step and in which a binary output pulse of 1 or the opposite polarity is generated in accordance with even or odd numbers of binary ones in this combination. This combination is then followed by a further step in which the successive (b-1) binary output pulses are added, a multi-level polybinary output signal then being obtained. This waveform is then filtered to remove the sharp edges of the multi-level polybinary output signal. This is done for the purpose of reducing the harmonics of the multi-level signal so that a limited bandwidth is sufficient for the transmission of this waveform. Such a "rounded" waveform can be transferred much better to conventional transmission systems. This waveform is then sent to a receiver or receiving station over a conventional transmission medium, such as a carrier system. At the receiving station, the level of the transmitted and received polybinary signal is sampled, specifically every pulse interval, in order to determine whether this detected level is an odd or an odd number. A binary pulse of one polarity is generated when an odd level is detected and a binary pulse of the opposite polarity is generated when an even level is detected. This system requires signal timing and ίο logical decoding of the transmitted signal at the receiving station which, however, means very complicated and expensive equipment (USA, Patent No. 3,337,863). In a further known system for digital data transmission over a transmission channel of limited bandwidth, a digital filter for what is known as pseudo-ternary coding and decoding of the transmitted data is used, this coding method making it possible to use a relatively simple single-sided band modulator which, according to the so-called phase method works. This known system works as follows: Before being encoded and digitally filtered, the digital data to be transmitted is transformed with the help of two change-of-state modulator stages, each composed of a flip-flop and an AND gate. The gates are controlled on the one hand by the information and on the other hand by a clock pulse. The data signal transformed in this way is fed to a shift register, which can consist of a chain of delay elements, and a pilot signal for synchronizing the signal detector on the receiving side is introduced via the AND gates. The digital filter consists of a shift register with 19 elements or cells, each of which has a flip-flop and a corresponding control logic. The digital filter carries out digital signal coding and filtering in the following way: A signal is derived from the transformed input signal with a time delay corresponding to the length of two input variables and then subtracted. As a result, the transfer function is given as a quotient of the Fourier spectrum of the minuend and subtrahend signals. As a result, the components of the Fourier spectrum of the signal obtained are suppressed for all odd multiples of half the pulse or bit frequency. This fact makes it possible to transmit a reduced carrier wave to which the aforementioned pilot signal is added. After filtering the signal in a low-pass filter, the single-sideband modulated signal is generated using a well-known phase method: The low-frequency input signal is fed directly to an amplitude modulator and at the same time fed to a second amplitude modulator via a 90 ° phase shifter with a large bandwidth. As a result, the two modulator output signals or carrier signals are phase-shifted by 90 °. The single-sided modulator output signal is formed by taking the sum or the difference between the modulator output signals. On the receiving side, after filtering through a bandpass filter and after passing through a frequency equalizer, the reduced carrier wave is modulated, and the transmitted low-frequency modulus 1. A method for the asynchronous transmission of binary data over a channel of narrowly limited bandwidth, wherein the data is converted into a binary waveform that does not return to zero (NRZ waveform), this NRZ waveform is then sent over the channel and from the NRZ Waveform the original binary data are generated, characterized in that the converted data, which are present in a maximum bit sequence of Kf ₁ , where /, is the upper frequency of the zero response value of the transmission channel and K has a value which is smaller than 2, which, however, approaches the value 2 for a noise-free channel, can be transmitted via a filter which has a linear phase-frequency characteristic, with an amplitude attenuation which increases uniformly with increasing frequency, which in the case of a Fre- Kf frequency - γ- ^ is less than 40% of the mid-band transfer value and its transfer function, with negligible excess swing at a time no more than is completed at each transition to obtain at the receiving station a partial response waveform corresponding to the NRZ waveform, that the received partial response waveform is then applied at the receiving station to a midpoint threshold for recovering the binary ones and zeros, these being above and below the Corresponding to the center threshold located sections of the received waveform. 2. The method according to claim 1, characterized in that instead of the filter with the linear Phase-frequency characteristic of a transmission channel with the same properties as the filter is used. 3. The method according to claim 1, characterized in that the filtering of the binary NRZ waveform with a linear phase-frequency characteristic and an amplitude transfer function from 50 A (f) = 0 is performed. 4. The method according to claims 1, 2 or 3, characterized by its use for facsimile transmission in voice phone lines. 5. Circuit arrangement for performing the method according to claims 1 to 4, characterized by 60 a scanner-writer unit operable in synchronism with a remote similar unit is and scans; an optical device in this unit, which is used to analyze a document with predetermined speed and resolution is operable to correspond to a line scan signal a maximum transition sequence of about 4000 transitions per second produce; a delimiter that applies to the line load signal! responds to a binary NRZ-Wcllcnform to generate the transitions at the black-and-white transitions of the scan lines on the Document has; a filter device. (15) responsive to the binary NRZ waveform and an amplitude transfer factor AU) = »/ Cot-SLOS / SΛ 2 /, 2 / i shows where /, is about 2.17 kHz and the filter means has a linear phase-frequency characteristic for generating a partial response waveform;
a stable oscillator;
a frequency divider for deriving a carrier wave having a frequency of about 2.4 kHz from the oscillator;
modulation means for amplitude modulating the carrier wave with the partial response waveform; a coupling device for coupling the modulated carrier wave to one another End of telephone line connected to the same unit; Amplifier and transversal filtering devices that act on the overcoupled from the telephone line Signal address to eliminate system and telephone line distortion in the signal received from the remote unit to compensate; a vestigial sideband demodulator responsive to the signal from the amplifier and transversal filter means for detecting the partial response waveform;
a midpoint threshold (35) responsive to the partial response waveform and providing threshold detection centered on the center of the partial response waveform to obtain an original copy of the binary NRZ waveform; and
means for supplying the original copy of the binary NRZ waveform to the scanner-writer unit to write or print a facsimile copy of the document scanned at the remote similar unit. 6. Circuit arrangement according to claim 5, characterized by a gray signal generator (53), which is responsive to the start of transmission of a document image, in order for a limited Interval to send a signal that is modulated at such a level that the amplitude center the output of the limiter, and electronic devices (38, 42, 43, 55. 45, 46), which respond to the start of reception of a modulated carrier, to during this Interval to set the midpoint threshold so that it corresponds to the modulation value. 7. Circuit arrangement according to claim 6, characterized in that the electronic devices for setting the center point