DE1762644A1 - Method for converting data signals - Google Patents

Description

Patent attorneys Dipl.-Ing. F. Weickmann,

Dipl.-Ing. H. Weickmann, D1PL.-PHYS. Dr. K. FiNCKE 1. _t Dipl.-Ing. FAWeickmann, Dipl.-Chem. B. Huber '}

SBiPO

XEROX CORPORATION, ^{8 MONKS 27} > ^DEN

Rochester. Η.γ. 14603 / üSA möhlstrasse 22, phone number

Method for converting data signals

The invention "relates to data transmission, in particular a method for converting non-synchronous data signals with two level values into non-synchronous data signals several level values.

Transmission channels are characterized by two properties that determine the transmission speed for data, namely the "width" of the frequency range in Hertz, ie the bandwidth, and the "height" of the power, which is normally specified by the "signal-to-noise ratio" . It is known that the data transmission speed of a channel can be increased beyond the value possible for binary data if the data is encoded with more than two signal levels, thereby increasing the "height" of the signal and the "height" of the channel without further increasing the bandwidth

001827/0685

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of the signal is used. This method has recently been widely used because of the data transfer speed requirements went beyond that of the binary values.

One known technique, known as Nyquist coding, is that ή bits are converted into 2 ⁿ signal levels. Each level thus represents a binary digit, and the transmitted level can therefore be uniformly decoded in the receiver. By converting the binary data signals into non-binary data characters, it is also possible to code at L signal levels, where L is not equal to 2 ⁿ . These methods usually have an efficiency of less than 100 %, as in general. There are integers m and η for which 2 ^{n is} equal to R ^m and R is a base other than 2. A third method consists in bringing about a correlation between the transmitted symbols in that the transmitted signal level is made dependent not only on the bit or bits to be transmitted during a given period of time, but also on the bit or bits transmitted during a preceding period or several periods of time In this case, the transmitted signal levels must generally be uniformly decoded in the receiver, but they must be stored and compared with subsequent symbols . In some cases calibrated precoding from binary to binary can be decodable

009827/0666

'# ■

17626Λ4

Symbols with multiple signal levels result. A well-known embodiment of this latter method is the recently developed "duobinary data transmission system ¹¹ " which is described by Adam Lender in Communications and Electronics, May 1963 »pages 214-218.

All of the above procedures require a clocked Division of the binary data into discrete time elements, i.e. in bits so that the information can be processed and encoded according to the states of the individual bits, for which the usual logic circuits are used. So far no method for coding non-clocked, i.e. non-synchronous two-level signals such as occur, for example, in black-and-white I facsimile systems, developed.

The object of the invention is therefore to improve data transmission in such a way that coding of unclocked two-level signals into signals with several levels is possible and can be used. Feraer should die'ErfiMiffig a concentration de? spectral! © iste ^ gsiliGhte siiefet syncSiEOrtSff elektriscliea 'Sigaale feei a.iGfeig © i? ea! Precpasaseii ers> c.gliefeQ £ i _s .. iam eis © iaaiälieaTsig mi clio ^ sieaow

The invention solves the problem with two level values in non-synchronous data signals with several level values during data transmission this task in that complementary signals of the two-level data signals are generated and that these and the two-level data signals optionally on the basis of a predetermined Probability factor are transmitted.

The invention also provides for performing this method a data transmission system, which is characterized by a non-synchronous two-level data signals emitting Signal transmitter, by a device for generating the data signals complementary to these data signals and by a device for the selective transmission of both data signals on the basis of a predetermined probability factor as three-level data signals with a predetermined power density spectrum »which is directly related with the power density spectrum of the two-level data signals stands.

For a better understanding, the invention is described below with reference to the figures. Show it:

Fig. 1 shows the block diagram of an arrangement for Duxohführung

of the method according to the invention, Fig. 2 edji functional diagram for understanding the arrangement shown in Fig. 1,

009827/0565

Fig. 5 shows the curves for the relative performance of different data transmission systems,

Pis. 4 the curves for the expected relative power of two-level and three-level data signals *

Fig. ₁ signal curves for various non-synchronous data signals with several signal levels,

6 shows a "special embodiment of an arrangement for carrying out the method according to the invention,

7 shows the block diagram for decoding the signals generated with the arrangement according to FIG. 6,

8 and 9 further exemplary embodiments of devices for carrying out the method according to the invention.

1 shows the circuit for generating a non-synchronous "dibinary" three-level signal from a non-synchronous two-level signal. The two-level input signal and the negative image, which is not just the logical inversion, but is generated by the inverter and voltage shifter 12, are fed to the transmission gates 34 and 16, which are controlled by the decision logic 10 positive direction is determined by the logic circuitry 10 with an arbitrary probability of, for example, 50 generally the transmission gate to be controlled. The parts with the signal

009827/066 5

' BATH

level zero remain unchanged. The output signal exists therefore from three signal levels whose non-zero parts can be positive or negative in the same way.

In FIG. 2, the signal profiles occurring at various points in the circuit according to FIG. 1 are shown. Figure 2A shows the waveform at the input of the circuit. FIG. 2B shows the output signal of the inverter and voltage shifter 12, which is the complementary signal with respect to FIG. 2A, but not just the logical inversion. Fig 2D and 2E show the output signals of the decision logic 10 corresponding to the arbitrary probability described above. These signals are selectively fed to the transmission gates 14 and 16 and generate the in 3-level non-synchronous data signal shown in FIG. 2C.

In Fig. 3 are the spectra of arbitrary waveforms of Signals are represented with leveled values. If the signal transitions of the input signal have a Poisson distribution, so is the power density spectrum of the input signal

where a is the durohsohnittliohe number of transitions per unit time and the angular velocity CJ 2 is 7TF · Under the same conditions can be shown that there · Leistunga-

009827/0668

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density spectrum of the output signal is:

⁴ (^ a ² + U ² J (2)

Equation 1 corresponds to a two-level signal that runs symmetrically to the zero line v. Pure a two-level signal, that is not symmetrical to the zero line, would there is also a direct current component in the equation. For the sake of simplicity, this portion is not taken into account in the following, since it is not important to the results.

According to the premise, the three-level signal has no direct current component. Equations 1 and 2 are in Pig. 3 shown in normalized form to show the relative power density spectra of two-level input signals and three-level output signals. Although none of these spectra ever theoretically When power reaches zero, it can be seen that the three-level "dibinary" signal is half that for any given power value Bandwidth of the two-level signal claimed. This reduction The bandwidth theoretically improves the performance of a transmission channel at a given data speed or enables the data speed to be increased for a given performance. However, as the number increases The signal level, the power reserve against noise and distortion, is reduced for signals with a peak at the peak of the same amplitude it is also to be expected that under be ~

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If the conditions regarding the transmission channel are correct, the performance, i.e. the possible data speed, gets worse. This one! »All is in Pig. 4 shown.

In FIG. 4, area A applies to a channel in which no spectrum is distorted. The power for two-level signals is better because of the larger signal-to-noise ratio. Area B applies to a channel with noticeable band edge distortion,

^ which refer to the two-level signal, but not to the Three-level signal affects it as this has a narrower spectrum Has. The three-level signal thus gives better performance. Area C applies to a channel in which the band edge distortion is so strong that it affects both types of signal. The power of the two-level signal is because of the larger Signal-to-noise ratio, in turn, is better, which is why a larger one Distance versus distortion results. In many transmission channels, however, the power value falls within range B, the shows that three-level signals with increasing tape edge displacement

™ distortion enable better performance.

The connection between baseband encoding and Low-pass parameters and low-pass channels described. These relationships are transferred to bandpass spectra and bandpass channels, when the baseband waveforms modulate a more sluggish be used. In general, they result in the same advantage, i.e. the information performance is more dependent on the Carrier frequency, which is analogous to the 81 ei ohe tr om references frequency

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17626U

the baseband signal acts, thus reducing the harmful effects certain tape edge distortions can be reduced.

A three-level signal can also be generated by the The polarity of a binary signal course is optionally reversed at each transition in the positive direction. This kind For example, the waveform can be referred to as a "forced change". Do the transitions of the input signal a Polsson distribution, the power density spectrum of the three-level signal results from:

S (CJ)

a (2a ² + ο ² )>

[a ² + (a ~ o) ² ] [a ² + (a + ω) ² ]

where the parameters correspond to those already described. This spectrum, which is also shown in FIG. 4, has an energy shift in relation to the frequency KUI1, but a maximum at the above. 0.145 of the mean transition rate, rather than near zero frequencies. The advantage of avoiding band edge distortions is therefore probably not that great, but the realization of the signal curves is easier.

A signal flow with more than three level values can be generated if every positive transition causes a change in level and every negative transition causes a change

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to the next level in a stepped manner until a limit value. . is reached in which the direction of change is reversed. This process continues until the opposite limit is reached and then reversed again, and so on. Two examples are given in Pig. 5B and 5C for one in Pig. The non-synchronous bilevel signal shown in Figure 5A is illustrated. In Pig. 5B is a non-synchronous Fünfpegel- ^ö ignal and shown in Fig. 5C is a non-synchronous seven level signal. It can be seen that the odd Fegel values correspond to the positive parts of the original binary signal, while the even level values correspond to the zero values of the original signal »

The hold shown in FIG. 6 is used to generate the spectrum given by Equation 2 given above. If the input signal has the value zero, the inverted signal is positive and the multivibrator 63 oscillates at its natural frequency of 50 kHz, for example. If the input signal is positive, the signal Buil is inverted ₉ and the multivibrator 63 is The flip-flop 64 is controlled by the multivibrator 63 and is switched on for odd counting steps and released for even counting steps. At the end of a part of the input signal with the value zero, the ilip-flop 64 remains on or off, which depends on whether the counting step was odd or even

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The upper gate 65 generates a positive output signal if both inputs are driven with the value zero, i.e. when the input signal is positive and the flip-flop 64 is on. The lower gate 66 produces a positive Output signal when the input signal is positive and the flip-flop 64 is off.

The output of the lower gate 66 is then in the inverter 67 inverted. Both output signals are in a summing circuit, not shown, to generate a Three-level signal composed, for example, a mean value of +9.5 volts, a positive value of +14 volts and a negative value of +5 volts. The result is an output of +14 volts for a positive Input signal and an odd counting step, starting from the off state, an output signal of +9.5 volts for a Input signal zero and an output signal of +5 volts for a positive input signal and an even counting step, starting from the off state. These voltages are only examples and other values can be used without departing from the basic principle of the invention.

This logic can be represented by the following table:

009827/0665

LOGICAL CONDITIONS

Input signal

Inverted input signal multivibrator 63

Flip-flop 64. An upper gate 65 output + lower gate 66 output 0

Inverter 67 +

Composite

Output signal +14

0
the end

the end

+5

On / Off 0 0

+9.5

It should be noted that the required probability for the decision of the polarity is achieved by using a long counting step at a high clock speed , i.e. if counting is long enough, the probability for an even counting step is equal to the probability for an uneven counting step. It is not necessary to reset the flip-flop for every counting operation, since the initial state is unimportant if counting is long enough

Fig. 7 shows the decoding of the non- synchronous. Three-level signals require circuitry when these signals are used as input signals. The Schmitt triggers 71 and 73 with the level values corresponding to the voltage used in the data transmission, which in the present case are 9.5 volts, are used to implement the three-level

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Information signals into a bi-level information signal. The Schmitt trigger 71 generates a signal for every signal value that is less than 9.5 volts during the Schmitt trigger 73 generates a signal for each input signal value that is greater than 9.5 volts. The output of the OR gate 75 is therefore the original two-level binary signal

It should be noted, however, that "if the input data are not randomly distributed, ie if the transitions are frequency with a certain relationship to the clock frequency, the decision for polarity will not be arbitrary and the expected spectrum will not result. This can occur with facsimile transmission, when a series of evenly spaced vertical lines is scanned horizontally. This phenomenon is observed when clocked data is used as input data. Ea is uncertain whether the output of a scanner scanning graphic lines is sufficient to produce this phenomenon is regular It can, however, probably be reduced or avoided by increasing the clock speed beyond the accuracy of the scanner or by adding an arbitrarily distributed bulk to the clock

In Pig. is θ 1st represented a "further Ausführungeform an arrangement sur performing de · erfindungagemäßen method · dl · for bee-fcimte Signalmuiter nioht" mpfindlioh. A noise generator 80, the output signal with the same truth

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-U-

Probability is positive or negative, is used to set or reset a flip-flop 85 when a transition of the input signal occurs in positive direction. This means that the output signal of the noise generator 80 via the limiter 81 to the AND gate 83 and via the inverter 82 is fed to AND gate 84. A non-synchronous two-level input signal is optionally fed to the inputs of the AND gates 83 and 84f, these AND gates being switched on according to the noise signals. The flip-flop 85 is set and reset accordingly. The non-synchronous two-level input signal is fed to the AND gate 87 and via the inverter and the voltage shifter 86 to the gate 88, these gates being optionally switched through and thus the non-synchronous three-level output signals as they have already been described with reference to FIG. 6 .

In Fig. 9 is shown for generating the dee spectrum according to the equation 3 erforderliohe circuit for forced Weoheel. It corresponds to the geseigten in flg. 6 circuit, with the difference that the astable multivibrator is absent and the reversal of the Bingangedaten is fed directly to the flip-flop 93rd The two-level input signal is fed to the inverter 91 and via the emitter follower 92 to the input of the NOR gate 94 " the input of the flip-flop" 93 and an input of the NOR gate "95. The operation corresponds to that of Sohaltung of Figure "6 with the sub-

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decided that the flip-flop 93 changes its state at the beginning of each signal part of the input signal with the value Hull. Those corresponding to the positive parts of the input signal Parts of the output signal change polarity during the Zero level remains unchanged. The output signal of the NOR gate 95 is via the inverter 96 together with the output signal of NOR gate 94 is fed to a summing network. The result is the non-synchronous three-level signal with a power density spectrum corresponding to that given above Equation 3

Methods and arrangements for shifting the power density spectrum to lower frequencies were described above, whereby a channel with a limited bandwidth can be used with greater efficiency. The described Circuits are made up of certain logical combination units, but only as Example were given. Other circuits and arrangements can also be used to perform the functions described be used. The exemplary embodiments described above are therefore only intended to explain the invention serve, but are not to be understood as limiting.

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Claims (14)

- 16 patent claims: 1. Method for converting non-synchronous data signals with two level values into non-synchronous data signals with several Level values during data transmission, characterized in that complementary signals are generated for the two-level data signals and that these and the bi-level data signals are optional are transmitted on the basis of a predetermined probability factor. 2. The method according to claim 1, characterized in that a Probability factor of 0.5 is used, 3. The method according to claim 1, characterized in that a probability factor corresponding to statistical probability is used. 4. The method according to claim 2, characterized in that the two-level data signals and the complementary signals alternately can be transferred with a probability factor of 0.5. 5 · Data transmission system for carrying out the method according to one of Claims 1 to 4 » characterized by a signal transmitter which does not emit synchronous two-level data signals, by a device (12) for generating the data signals complementary to these data signals, and by a device (14, 16) for optional transmission of both data signals 0 0 9 8 2 7/0565 • on the basis of a predetermined probability factor as three-level data signals with a predetermined one Power density spectrum, which is directly related to the power density spectrum of the two-level data signals stands. 6. Data transmission system according to claim 5, characterized daduroh, that the probability factor is 0.5. 7. Data transmission system according to claim 5, characterized in that that further a device (10) for the control corresponding to the predetermined probability factor the transmission equipment (14 »16) is provided. 8. Data transmission system according to claim 7 »characterized in that the control device has a noise generator (80) for generating noise signals with positive or negative components occurring with the same probability, controlled by the noise properties and the two-level input signals (Zatter-Sohaltungen (83, 84) for generating control signals for each positive transition of the two-level input signals and a flip-yiop circuit (85) connected to the gate circuit (83, 84) , which is adjusted and surUokgeetellt depending on the control elements and which Aneteu «events for the transmission» facilities (87, 88) 009827/0665 9 »Data transmission system for carrying out the procedure according to One of claims 1 to 4, characterized by a signal transmitter emitting non-synchronous two-level data signals, by a device (93) for generating first and second control signals, depending on the two-level data signals, and by means (94, 95, 96) for selectively transmitting the bilevel data signals depending on the first and second drive signals as three-level data signals with a predetermined power density spectrum which is directly related to the power density spectrum the two-level data signals. 10. Data transmission system according to claim 9, characterized in that the means for generating the first and second Ans expensive signals comprises a switching device (93) which is responsive to the zero level of the non-synchronous two-level data signals, and that the transmission devices from with the non-synchronous two-level data signals driven and consist to the switching device (93) gate circuits (94, 95, 96) connected to the dee, the positive parts of two-level data signal with polarity weohselnder transmitted. 11. Data transmissionBeyetem naoh Anapruoh 10, characterized in that the three-level data signal has the following power consumption spectrum 009827/0668 _{BAD 0RIG1NAL} S (C,)) = I. [a ² + (AO) ^2] [a ² + (a + 6J) ² J where a is the mean number of transitions per unit of time and CJJ is the angular velocity when the transitions of the bi-level data signals have a Poisson distribution. 12. Data transmission system according to claim 9 »characterized in that that the device for generating the first and second control signals one controlled with the two-level data signals, set with the zero level and with a positive one Level-locked multivibrator (63) and a switching device (64) connected to this for generating a signal a first polarity at an odd counting step of the multivibrator (63) and a signal of a second polarity comprises at an even counting step of the multivibrator (63), and that the transmission means (65, 66, 67) with the Signal transmitter and the switching device (64) are connected and transmit the positive parts of the bilevel data signals with alternating polarity. 13. Data transmission system according to claim 12, characterized in that the three-level data signals have a power density spectrum of the following equation: 009827/0565 where a is the mean number of transitions per unit of time and GJ is the angular velocity if the transitions are the Bi-level data signals have a Poisson distribution. 14. Method for converting non-synchronous data signals with two level values into non-synchronous data signals with several Level values during data transmission, characterized in that the level of the multilevel data signals for each positive and negative transition of the two-level data signals in steps up to a level limit value is changed, and then successively the level of the multilevel data signals for each positive and negative transition of the two-level data signals in a stepped manner up to a second level limit value of the multi-level data signals will be changed. 009827/0565