DE1916711C3 - Method and circuit arrangement for the asynchronous transmission of binary data over a channel with a narrow bandwidth - Google Patents

Description

The invention relates to a method and a circuit arrangement for asynchronous transmission of binary data over a channel of narrowly limited hand width, the data being converted into a binary waveform (NRZ waveform) that does not return to zero, this NRZ waveform then being converted over the channel is sent 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 pc'ybinary waveform to the conventional binary waveform. The essential features of this known method can be summarized as follows: A usual binary digital waveform is converted into a polybinary digital waveform with /> - Pcgeln, where h is an integer and greater than 3. in which the existing binary pulse is combined with the output pulse generated in the previous (/> - 2) combinations of this step and in which a binary output pulse of I 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 multiply 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 transmitted 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 poly 'binary signal is sampled, each pulse m-interval, to determine whether this recorded level is even or odd A binary pulse:

one polarity is created when a ueven number liger level is detected, and a binary pulse dei

opposite polarity is generated when eirj

even level was detected.

In this system, signal timing is untj

ίο logical decoding of the signal sent to the

Receiving station required, but this means complicated and expensive equipment (USA.

Patent 3,337,863). In another known system for a digi

Tal data transmission over a transmission channel of limited bandwidth, a digital filter for so-called pseudaternary coding and decoding of the transmitted data is used] whereby this coding method enables the use of a relatively simple 'insideband modulator, which according to the; ^ mentioned phase method works. This well-known system works as follows: The digital data to be transmitted are transformed before their coding and digital expressions using two change-of-state modulator modules, each made up of a flip-flop and an AND gate put together. The spouses 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 consists of a chain \ on | The digital filter consists of a Sehielvregiste with 19 elements or cells, each of which has a flip-flop and a corresponding control logic. The digital Filter performs digital signal coding and filtering in the following way

4c From the transformed input signal, the signal will correspond with a time delay », derived from the length of two input variables and then subtracted.

As a result, the transfer function is given as a quotient of the Eourier spectrum of the minuend and subtrahend signals. As a result, the components of the Eourier spectrum of the received signal are suppressed for all odd multiples of half the pulse or hit frequency. This fact makes it possible to transmit a reduced carrier wave to which the previously mentioned pilot signal is added. After filtering the signal in a low-pass filter, d; Single sideband modulated signal generated according to 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 edge width. As a result, the two modulator output signals or carrier signals are phase shifted by 90 ". The viewing modulator output signal is formed by using the sum or the difference between the modulator output signals.

After filtering, dme is a bandpass filter on the receiving screen and after passing through cjne Frcqucnzcntzcrrcr the reduced carrier wave dcodulated, and the transmitted Nicderfreciucnz-Modu

lation signal is obtained. The signal is again processed in a low-pass filter and a compensation odcf equalizer stage and is finally processed in decoded by a full wave rectifier. Before decoding, the pilot signal is recovered and dem Signal detector, in which the decoded signal is recovered, fed to the signal decoding or detection with the signal calibration on Synchronize transmitter. The synchronized signal is then processed in a signal processing stage, so that you finally get the original digital signal again.

Despite the simplified Dcmodulalionstcchnik for the reduced carrier wave with this known System used a complicated logic for digital coding and filtering so that the system becomes very complex and expensive. (Article by Peter Lc ut ho Id and Felix Tisi, »Ein Einscitenbandsyslem for data transfer «in the magazine» Archive for Electronics and Transmission Technology «, Vol. 21, 1967. No. 7, pp. 354 to 362.)

All known systems using partial claim transmission are generally based on a timing technique. On the other hand, systems that aim to increase the data sequence without using partial response techniques must be limited to relatively small data sequences. In the two systems mentioned above, in addition to timing or clocking, relatively complex and expensive facilities are also required, ^ ₀ and a phenomenon also occurs which is known as quantized noise.

In a known facsimile transmission system, in which clock-controlled binary signals are used, with bit binary coding and decoding is provided at the input and output ends of the transmission channel, respectively the available bandwidth for the transmission of image information is used to the maximum, and this system is also relatively insensitive to noise, which can be attributed 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.

In the latter system, a disadvantage may be felt when the system is used to transmit image information, and this disadvantage is the quantized noise. Since the clocking of the original data signal reorientates the black-and-white transitions that occur in a line scan so that they coincide with the clock-controlled signal, the information actually transmitted does not exactly correspond to the black-and-white transitions that occur in the photocell, when it sweeps the scan line. Because the clock-controlled system is only able to. To reproduce black and white transitions in synchronization with the clock time, the introduced error may approach a bit interval and the resulting printout may show significant degradation due to the quantized noise.

The object on which the invention is based is to create a method and a device for asynchronous binary data transmission in limited channel bands, in which the largest possible information content can be transmitted per unit of time 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 _t , where /, is the upper frequency of the zero response value of the transmission channel and K has a value that is less than 2, but which is equal to 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 that increases uniformly with increasing frequency, which at a

Kf
Frequency - ^ - is less than 40% of the band center transfer ratio and its transfer function, with negligible overshoot, in

a time no more than - ^ y- at each transition has been completed to provide a partial claim at the receiving station, that of the NRZ-Wcllenform corresponds to obtaining the received Tcil response shape then at the receiving station of a center point to retrieve the binary ones and zeros, these being the above and below the midpoint threshold corresponding sections of the received waveform.

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 Signalwclle here without a complicated and laborious one Coding logic and decoding logic for NRZ-Impulsc and without time control is carried out. This technology now enables information transfer speeds, which is only slightly smaller than that of a known bitter transmission system Transmission speed achieved (binary partial threshold). taking 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 a transmission channel with the same properties as the F'iitcr enter.

In detail, the invention can be ci-e advantageous further development that the filtering of the binary NRZ waveform with a linear phase-frequency characteristic and an amplitude transfer function of

A If) = ^ f cot

A (f) = 0

f> fx

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 which can be operated to analyze a document at a predetermined speed and resolution in order to produce a line scan signal.

ZS ⁷ O

speaking of a maximum transfer sequence of generate about 4000 transitions per second; also a limiter that acts on the line bias signal responds to produce a binary NRZ waveform which transitions at the black and white transitions which has scan lines on the document; The device also has a filling device. those on the binary N'RZ-Wcllcnform responds and an Aniplitudenübei load factor

Aif) = ■■ ⁷ ^ cot jj 0 </ </,

A if) = ■ 0 />./,

shows, where /, is about 2.17 kHz and the filter device has a linear phase-frequency character for generating a partial principle has; a stable oscillator is also provided, which is followed by a frequency divider to convert the oscillator frequency into a carrier wave with a Derive frequency of about 2.4kHz; a modulation device modulates the carrier wave with the Tcilansprcchwcllcnform. 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 transvcrsal filter devices. which respond to the cross-coupling signal from the telephone line to the system and telephone line Compensate for distortions in the signal received from the remote unit as well a Rcsisciiciibandrnodulator on the Signal from the amplifier and transvcrsal filter means responds to the Tcil response waveform capture. With the help of a midpoint sore throat. which responds to the Tcilansprcchwcllcnform, will a socket in the middle is provided centered on the partial response waveform to obtain an original copy of the binary NRZ waveform. Finally, a device / um feeds the original copy of the binary NRZ waveform a facsimile copy of that on the remote similar unit to the scanner writer unit scanned document written or printed.

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

The electronic device for setting the midpoint threshold includes the following stages; one Gain control circuit for the amplifier and a Transver> alfilteinrichtung and a. electronic Circuit responsive to the output of the midpoint wave 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 is the intermediate modulation value of the modulation signal has a modulation amplitude that is almost half the peak values of the Modulalionsamplitudc resulting from the binary signal.

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

Fig. 1 (a) and I (b) amplitude-time diagrams, which are useful for bitter signal history,

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

maximum bit sequence, both for known systems and also for 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 door binary pulse signalc,

F i g. 5 is a block diagram of a facsimile system in one embodiment of the invention.

F i g. 6 shows a waveform diagram for comparison known systems with the system of the present invention and

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

On the basis of the drawings, let me first give an overview of the digital Tcil response transmission method given in order to establish the necessary and appropriate criteria for the present invention to be able to.

Bit-related signal theory can be described simply by the expressions "partial claim transmission, as described by!. R. K ret ζ m er is described in his pleading "Binary data message transfer with the help of partial contact transfer" (pleading G-IE. 5 on pp. 451 456 οΠΙκ First IEEE Annual Communications Convention Conference Record. June 7 9 . 1% 5). In summary, it is stated there: E: in Tcilansprcchsystem sends a two-peg signal over a channel, a memory / 1 storing binary input symbols and the binary sequence being retrieved on the basis of /. Characterizing detected levels, where L is η . In the case of bit binary, / 1 = 2 and L = 3. The key to recovering the original bit stream is the selection of the channel's claim to a binary signal element. to enable a controlled or controlled memory storage. It has been shown that a channel with the transfer amplitude function

Y (in) = COS ~ - 0 <cn <fi>,

2 (O |

Y {in) Om <«.,,

where «> = 2nf

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

If this response or response as a signaling element for binary signals in a synchronous Random bit stream with a sequence vr> n 2 /, BiI is used per second and that results "

209681/37:

2 8 30

Signal is only ever measured at odd multiples of V4./1, the measured amplitudes only take three possible values; 0. Λ and 2/1, which depends on whether the two answers near the measuring point correspond to two binary zeros, an I and a 0 (or vice versa) or two ones as in F ^:. G. 1 (b). An examination of the superimpositions of various combinations of the ones and zeros leads to the principle that one. in order to recover the original binary bit stream, a bit has to be decoded as an "I". if the answer is 2/1 to the scanning double. 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 alignment in this way, ie a controlled inter-symbol alignment. one can transmit data in a higher sequence in a specially shaped channel than can usually be achieved using conventional, memoryless binary transmission units.

The previous theory was described in the form of a clocked pulse signal input, at a

Y (f) = cos

JLL
2 /,

Channel filtering

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

If it is desired to signal f \ with two pulses of width ', which results in a so-called NRZ signal, the previously specified channel shape would not be optimal .icin. According to the present invention, signaling without logical detection and for NRZ pulses is achieved, and that without clocking. while channel shaping is selected to allow signaling sequences that are only slightly less than those achieved with the more complex clocked bilateral systems of the prior 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 ' ₂ /. 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 V ₂ /. The spectrum of a pulse with a width './2 / 1 ' ^st

sin

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

AIf) =

* f_

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

The original binary data stream can be extracted from the ternary Signal can be recovered, without timing and a single threshold by one

ίο the system controls in such a way that it is in a slightly lower transmission bit sequence or frequency is working. This can be demonstrated by examining the "eye oscillogram" (the oscilloscopic deflection of the received normal wave), which results from an arbitrarily synchronized NRZ bit stream, the

η f .τ / '

A (/) = - ■■ - cot -

² room ^{2 year}

follows. For a bit sequence of 2 / ", the eye oscillogram is that shown in Figure 2 (a). The uniform horizontal line in the center of the oscillogram corresponds to the response of a binary sequence of 101010. The fundamental frequency for this sequence is /, Hz and the function A [f) = 0 at / = / i- However, if the bit sequence c is reduced so that the basic frequency of the 101010 sequence is less than /, the little "eyes" begin to open in the eye oscillogram as shown in Fig. 2 (b). The step function increase rate remains the same, but the difference between transitions is lengthened. The amount of eye opening required to detect threshold in the middle of the threshold depends on The signal-to-noise ratio and the permissible error sequence depend on a value of a Bilsequencec of less than 2/1 is usual in a channel with a given signal-to-noise ratio, whereby this ratio can be defined as a bit sequence Kf ₁ , w if K <2 and K approaches the value 2 for a noise-free channel. 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 that is required. in order to achieve this result, it can be provided that that it is compatible with the noise level by having an operable percentage narrow eye opening chooses and finds out at which frequencies?

this occurs with regard to /, and then doubles it to find the bit sequence. For the average on-site call lines, an eye opening of 20% of the peak response would be found satisfactory. this leads to

A (f _x ) =

2 /,

L · - = 0.2 (rounded up).

The solution for f _x is found
-4 = 0.91

cot

A (f _x ) = 1.43 cot 1.43
= 1.43 (0.142) = 0.203.

Therefore, at f-f _x = 0.91 f _{x, there is} a 20% eye opening, and a bit sequence voi

2830

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

The channel shape for the NRZ signal at a reduced bit sequence, i.e. 1.82 / bit / second, remains the same as for the closed eye bit sequence, d. H.

AU) - 4icot " ^f

2 /,

2 /.

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

Pulses, where the width is - [^ fT seconds,

instead of

Seconds. If you wish

should, to signal with pulses, would have to be the channel shape can be dealt with to convert the pulses into pulses with a width of 1 / 1.82 /. This can can be achieved simply by dividing the spectrum of a pulse (linear) by the factor

sm

• τ /
Γ.82. / Ϊ

■ 71Λ
1.82 / y

sin

/ -? £ shape 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

ίο system in the scanner 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 have the capacity of the System, and in this way a transmission speed is achieved with optimal resolution 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

is multiplied to convert it according to a pulse with a width of 1,1.82 /, as shown in FIG. 4th is displayed.

Of the systems shown in FIGS. 3 and 4 is only the system of FIG. 3 (NRZ signaie) 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

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

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

A scanning writer 11 operates in the transmitter section and scans the information to be transmitted on a document and converts it into an analog signal on the line 12, this signal representing black-or-white information. The signal on line 12 is preferably derived from a photocell and a light source which is the copy to be transmitted. Is scanned line by line to generate the analog facsimile signal. The scan writer 11 also operates in response to signals on the line 10 to write or print black-on-white signals when the unit is operated as a receiver, the scan operating in synchronism with the remote transmitter scanner to provide a facsimile - Reconstruct a copy of the original document.

The photocell signal on line 12 is in the limiter 13 two-value limited in order to on the line 14 a binary signal of the type not to zero Returning (NRZ) as illustrated by waveform (a) in FIG. 6. This Limitation is achieved by providing a threshold for the analog signal on line 12.

A (f) = 0.725 / cot 0.725 /

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

up to 2170 Hz. The magnitude 0.725 is the value of Λ,

where /, equal to 2, i7kHz beirägi. 'viii a /, mii With a value of 2.17 kHz, the bit sequence is 1.82 /, almost 4000 bits per second.

The output of the filter 15 is fed to an AM modulator 16 which receives a 2.4 kHz carrier on line 17 from a frequency divider 18, the latter dividing the frequencies of a precision crystal oscillator 19 by 1024, this oscillator at 2.4576 MH / swings.

The 2.4 kHz on the frequency divider 18 are also passed through a frequency divider 21 in order to provide H / on the line 22,400 for synchronous operation of the motor drive 23. The motor drives for the line and sheet scanning in the scanning writer 11 are kept synchronous in view of the precision crystal oscillator 19 which is located in each unit. As described in the patent application cited above, a start signal in the system ensures that the read and write scans operate 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 skew-symmetrical 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 a coupling coil 26 excite, which is magnetically coupled to the handset 27 of a telephone set

The reception of the facsimile signals is carried out with the same equipment as in FIG. 5, located in the receiving station. Telephone signals received over the telephone lines are magnetically attached to the telephone set 27 in the receiving station with the help of a

2830

I 916711

Coupling coil 28 coupled to which a hum coil 29 is assigned The 2.4 kHz modulated signal, which was tapped from the telephone 27 is fed to an LF amplifier 31, which is a Provide a signal for a transversal filter equalizer 32

The equalizer 32 provides equalization over the frequency range from 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 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 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 located. The waveform (e) in FIG. 6 is fed to a power amplifier 36, in this way the Black and white signals on line 1 (1 provides to the recorder in the scan recorder 11 operate.

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. An AND gate 43 is used for the duration of the 2-second pulse output of the monostable multivibrator 42 put on standby and lets 150 Hz signals on 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 becomes analog Voltage through a digital-to-analog matrix 46 converted, and this voltage is on the line 47 as WR potential for amplifier 31 The Ki mg of the count in the 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 a message sends, a document detector in the scan recorder 11 sees a send signal on the line 51 before that the monostable multivibrator 42 is fed to slightly the duration of the output pulse generated to extend. 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 reaches filter 15 and whose amplitude is the center point between the amplitudes of the normal black and white NRZ signals corresponds to that on the line 14 can be received. This so-called gray

level signal on line 54 causes the door to open short interval after a document has been inserted into the scan writer 11, but bevoi any black signal has been sampled that a signal is generated on line 4.

With a modulation value of a magnitude corresponding to the gray level signal received by the detector 33 was received and the threshold 35 was fed, the relative polarity of the output depends on the dei Threshold 35 from the gain of amplifier 31

away. there. if 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 arrives on line 48 and two as negative feedback to the count of the * counter 45 go forward or backward zi let like this to change the gain dei Amplifier 31 to a value is required. the additional design of the gray value modulation that the swell 35 is supplied, corresponding to the center point threshold is required. The gain .wert de; Amplifier 31 is used throughout the transmission retained because at the end of the two-second pulse from the monostable trigger circuit 32 the AND gate 43 is brought out of readiness and the count in the counter 45 is held until the next message sequence occurs.

When the gain of the amplifier 31 is fixed, the signals corresponding to black and white become 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 you consider the facsimile system that has just been described and has a resolution of 39.4 lines per centimeter and a scanning speed. which corresponds to a maximum transmission sequence before 4000 bit / sec, the NRZ pulse is not! less than 250 microseconds. This means that the highest sequence of changes from "1" to "0" equals 4000 transitions / sec. which is 39.4 lines / cm. The requirements of the step function 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 j '= 2 KC.

The task now is to analyze the filter for the 1010-wave type are considered by summing the step functions of the filter on each of the transition

/ ο

flank. The individual jump functions on three successive transitions in a maximum sequence, as in FIG. 7 (a) are shown in FIGS. 7 (b), (c) and (d) given. The sum of these transitions is shown in Figure 7 (e), and the recovered Signal obtained by midpoint threshold detection is shown in Fig. 7 (f). the necessary step function for such an execution is:

a) The step function must be negligibly damped or negligibly overshoot, so that z. B. the step function corresponding to the flank 1 no disturbing effect on the correct timing of the crossing of the threshold of the step function of the flank 3 has. When a damped oscillation on the flat sections of the transition function or of the frequency response corresponding to edge 1 occurs, it could be related to the location of the recovered Interfere with flank 3 '.

b) The step function must be 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 If the response or the frequency response is acceptable the filter would need a larger one Have bandwidth. The best compromise in terms of bandwidth is therefore to choose the step function rise time equal to 500 microseconds or two bit periods.

Now let us consider the edge 3, which is shifted to the right in time by some amount f i. then

the step function of flank 3 would also be shifted by the same amount. The Schwelienübergang occurs a little later and creates a full recovery time for the dwell time between of flank 2 and flank 3, regardless of their size.

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

Further investigation shows that. as long as dk

minimum dwell time is 250 microseconds using a filter with the previously mentioned requirements regarding the transitional radio tion 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 an intersymbol interference. and the recovery is not flawless what dated

The degree of deficiency is dependent.

1 sheet of drawings

Claims (9)

Patent claims: 1. Method for the asynchronous transmission of binary data over a channel of narrowly limited bandwidth, whereby the data is converted into a binary waveform that does not return to zero (NRZ waveform), this NRZ waveform is then transmitted 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 / i is the upper frequency of the zero response value of the transmission channel and K has a value that is less than 2, which, however, approaches the value 2 for a noise-free channel, can be transmitted via a filter which has a linear phase-Fren'ienzcharacteristic, with an amplitude attenuation that 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 vibrate, not more than ~~ ^ τ ~ at a time each transition is completed to at the receiving station a partial response waveform that corresponds to the NRZ-We "'enform to obtain that the received partial response waveform is then sent the receiving station of a midpoint threshold for recovering the binary ones and Zeros are supplied, these being those above and below the midpoint threshold Corresponding to sections of the received waveform. 2. The method according to claim 1, characterized in that that instead of the filter with the linear phase-frequency characteristic, a transmission channel is used with the same properties as the filter. 3. The method according to claim 1, characterized in that that filtering the binary NRZ waveform with a linear phase-frequency characteristic and an amplitude transfer function of A (f) = ^ ^l A (f) = 0 ^z ./i is performed. 4. The method according to claims I, 2 or 3, characterized by its use for facsimile transmission in voice lines. 5. Circuit arrangement / ur implementation of the method according to claims 1 to 4, characterized through 60 a scanner-writer unit that synchronously is operable and scanning with a remote similar unit; an optical device in this unit, which is used to analyze a document with predetermined speed and resolution is operable to a Zcilcnabtastsignal accordingly a maximum transition sequence of about 4000 transitions per second produce; a limiter that acts on the line scan signal responds to a binary NRZ waveform to generate the transitions at the black-and-white transitions of the scan lines on the Document has; filter means (15) responsive to the binary NRZ waveform and an amplitude transfer factor A (f) = 0 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;
a modulation device 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 converter equipment gen. that respond to the coupled signal from the telephone line to 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). which is responsive to the partial response waveform and provides threshold detection centered on the center of the partial response waveform to obtain an original copy of the binary NR / 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 the 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 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 threshold contain: a gain control circuit (38, 42, 43, 55, 45, 46) for the Amplifier (31) and a transversal filter device (32) and an electronic circuit (48. 45, 46). which responds to the output of the midpoint threshold (35) to set the gain control and which maintains the set gain after this interval. 8. 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 claims, characterized in that the intermediate modulation value of the modulation signal is a modulation amplitude which is almost half of the peak values of the modulation amplitude which originates from the binary signal.