IE42504B1

IE42504B1 - Improvements in or relating to the regeneration of carrier transmitted digitals signals

Info

Publication number: IE42504B1
Application number: IE475/76A
Authority: IE
Original assignee: Siemens Ag
Priority date: 1975-03-20
Filing date: 1976-03-08
Publication date: 1980-08-27
Also published as: LU74290A1; IT1058478B; DE2512350B2; SE405535B; NL7602951A; NO143555B; GB1543209A; FR2305074A1; NO143555C; IE42504L; DE2512350A1; FR2305074B1; CH613825A5; IL49179A0; SE7601582L; IL49179A; AU502624B2; JPS51118945A; NO760878L; DK122776A

Abstract

The additional transmission of digital signals via transmission paths set up for the transmission of low-frequency and carrier-frequency analog signals is possible provided that the digital signals are shifted to a higher frequency range by modulation with a carrier which has a suitable frequency and phase. One of the sidebands produced during the modulation is adequate for transmission, although this cannot be directly regenerated. The transmitted sideband is therefore first equalised, amplified and then fed to a modulation device (M) and also to an arrangement (TA) for clock and carrier derivation in which both the carrier (C) required for modulation and the clock (L) required for time regeneration are generated. The modulation produces a digital signal which is regenerated in a conventional regenerator (R) for digital signals which contains an amplitude regenerator (AR1) and a time regenerator (ZR). The described method and the arrangement are particularly suitable for use in PCM systems which also use an existing cable installed for carrier-frequency telephony.

Description

PATENT APPLICATION BY (71) SIEMENS AKTIENGESELLSCHAFT, A COMPANY ORGANISED AND EXISTING UNDER THE LAWS OF THE FEDERAL REPUBLIC OF GERMANY, OF BERLIN AND MUNICH, FEDERAL REPUBLIC OF GERMANY.

Putt 12|p 42S04 This invention relates to the regeneration of a carrier transmitted digital signal.

Investigations of transmission links for low frequency and carrier frequency signals have proved that it is also possible to transmit digital signals via these transmission links. In order to avoid disturbances in the low frequency transmission and carrier frequency transmission, the digital signals are used to amplitude-modulate a transmission carrier cf suitable frequency and are thus converted into a higher frequency range. For full exploitation of the transmission capacity of the transmission link, only a single sideband of the digital modulated (d.m.) carrier signal formed by the modulation is transmitted; generally this is the upper sideband. In the course of transmission via the transmission link, the attenuation of the transmission link produces a drop in the level of the d.m. carrier signal, and at the same time the noise level rises due to picked-up interferences. Therefore it is necessary to regenerate the carrier transmitted digital signals at periodic intervals in order to increase the signal-to-noise ratio.

It is in fact conceivable to reconvert the d.m. carrier signal from the transmission state back to the base-band state (demodulation to obtain the digital signal), and to regenerate the digital signal in terms of time and amplitude by means of a regenerator of known type. The conversion into the base-band state requires a carrier which is not transmitted and which therefore must be produced at the - 3 regenerator. To safeguard the pulse transmission, not only the local carrier frequency but alsb the phase of the local carrier produced at the regenerator must agree with that of the transmitted carrier. The digital signal occurring in the regenerator can be employed to obtain the local carrier. However, in the case of the transmission of specific pulse sequences, a plurality of stable phase states and thus ambiguities can occur which can lead to mis-synchronisation of the carrier. The ambiguity occurs in that the signal shape of the converted signal is dependent upon the phase state of the local carrier employed for conversion. If this local carrier is derived from the converted signal, however, different pulse sequences lead to different local carrier phases and thus to erroneous regenerated bits. Although it is possible to prevent the mis-synchronisation of the local carrier in the case of specific pulse sequences by the use of special intercept circuits, these are extremely expensive.

It is also possible to regenerate the carrier transmitted digital signal in the transmission state if the digital signal is in the form of a pseudo-ternary code and if a carrier is employed which has a frequency which is a whole-numbered multiple of half the bit repetition frequency of the digital signal and phase displaced by 90° in relation to the phase of the bit repetition frequency of the digital signal. However, difficulties again occur in such regeneration in respect of the phase synchronisation.

According to this invention there is provided a method of regenerating a carrier transmitted digital signal from a received single sideband of a digital modulated carrier signal, the modulating digital signal being in the form of a pseudo-ternary code and the transmission carrier frequency - 4 being a first whole-numbered multiple of half the bit repetition frequency of the digital signal and being synchronised 90° out of phase with the bit repetition frequency of the digital signal, comprising the steps of distortion-correcting the received sideband, deriving in dependence upon the distortion-corrected received sideband a local carrier having a frequency which is a second whole-numbered multiple of half the bit repetition frequency and a pulse train oscillation having a frequency which is double the frequency of the local carrier, converting the distortion-corrected received sideband into a regenerable digital signal in a converter to which the distortion-corrected received, sideband and the local carrier are supplied, and regenerating the regenerable ditital signal in respect of its amplitude in an amplitude regenerator and subsequently in respect of time in a time regenerator to which the pulse train oscillation is supplied.

It is preferable to use the upper sideband of the carrier frequency digital signal for transmission, as this results in a lower interference level in parallel lines for low-frequency and carrier frequency transmission.

In one embodiment of the method the received sideband is the upper sideband of the d.m. carrier signal and the conversion of the distortion-corrected upper sideband into the regenerable digital signal comprises the step of conver25 ting the distortion-corrected upper sideband into the baseband state of the digital signal. This provides the advantage that when the digital signal has been converted into the baseband state it can be regenerated in terms of amplitude and time with know baseband regenerators.

In an alternative embodiment of the method the received sideband is the upper sideband of the d.m. carrier signal - 5 and the conversion of the distortion-corrected upper sideband into the regenerable digital signal comprises the step of converting the distortion-corrected upper sideband into an intermediate state which is displaced by a whole-numbered multiple of half the bit repetition frequency in relation to the baseband state of the digital signal. This provides the advantage that, by appropriate selection of the intermediate stage, the frequency level of the digital signal is selectable within certain limits and can thus be better matched to other transmission devices, for example radio devices.

In a further alternative embodiment of the method the received sideband is the upper sideband of the d.m. carrier signal and the regenerable digital signal is produced in the converter by forming a lower side-band from the distortioncorrected upper sideband and combining this with the upper sideband. This provides the advantage that the signal remains in the transmission state, as a result of which no reconversion into the transmission state is needed following regeneration.

The production of the lower sideband in the converter again requires a local carrier so that here again the local carrier must be derived from the distortion-corrected received sideband.

For deriving the pulse train oscillation and the local carrier it is in many cases of use expedient to produce an oscillation in synchronism with the received sideband.

In a particularly simple embodiment of the method of the invention, the pulse train oscillation and the local carrier are obtained by filtering an oscillation possessing double the bit repetition frequency of the digital signal out from the distortion-corrected received sideband after rectifification thereof. This enables a separate oscillator - 6 to be dispensed with.

The invention also extends to a regeneration arrangement, for use in carrying out the method recited above, comprising a band-pass filter having an input to which the received sideband is applied and a pass-band corresponding to the frequency range of the received sideband; a first distortion corrector having an input connected to an output of the bandpass filter and a control input; a converter having an input connnected to an output of the first distor10 tion corrector, an input for the local carrier, and an output which is arranged to supply the regenerable digital signal; a pulse regenerator having an input connected to the output of the converter, an input for the pulse train oscillation, and at least one output which is arranged to produce the digital signal regenerated in respect of amplitude and time? a circuit arrangement for producing the pulse train oscillation and the local carrier and comprising a second distortion corrector having an input connected to the output of the first distortion corrector, a delay element having an input connected to an output of the second distortion corrector, a rectifier having an input connected to an output of the delay element, an amplitude regenerator having an input connected to an output of the rectifier, an oscillator a frequency divider having a division ratio of 2:1 and having an output connected to the input of the converter for receiving the local carrier, a pulse shaper having an input connected to an output of the oscillator and an output connected to an input of the frequency divider and to the input of the pulse regenerator for the pulse train oscillation, and a phase discriminator having a first input connected to an output of the amplitude regenerator, a second input connected to an output of the pulse shaper, and an output connected to an input of the oscillator for controlling the frequency thereof; and an 2 5 0 4 - 7 amplifier having an output connected to the control input of the first distortion corrector and an input connected to the output of either the first or the second distortion corrector or the converter.

Preferably the pulse regenerator comprises an amplitude regenerator, having an input which constitutes the input of the pulse regenerator which is connected to the converter and two putputs at which it is arranged to produce amplituderegenerated unipolar pulse sequences of opposite polarity, and a time regenerator having two inputs each of which is connected to a respective one of the outputs of the amplitude regenerator, a further input which constitutes the input of the pulse regenerator for the pulse train oscillation, and two outputs which constitute outputs of the pulse regenerator and at which it is arranged to produce the amplituderegenerated unipolar pulse sequences regenerated in time.

Advantageously, the second distortion corrector comprises a high-pass filter.

Such a regeneration arrangement provides a particular advantage in that determinate commencing conditions are achieved which ensure a high-speed start of operation following switch-on.

In an embodiment of the regeneration arrangement the converter comprises a modulator having an input which constitutes the input of the converter which is connected to the output of the first distortion corrector and having a local carrier input, a low-pass filter having an input connected to an output of the modulator, an amplifier having an input connected to an output of the low-pass filter and an output which constitutes the output of the converter, a band-pass filter having an input which constitutes the input - 8 of the converter for the local carrier, a further amplifier having an input connected to an output of the bandpass filter, and a delay element having an input connected to an output of the further amplifier and an output connected to the local carrier input of the modulator.

In this arrangement a conversion into the baseband state is effected by modulation with only a low outlay, but the low-pass filter is subject to particularly high requiredmen ts, including for example the requirement for tuning.

The conversion of the carrier frequency digital signal into the baseband state can alternatively be effected by means of a double conversion with two modulators and two different carrier frequencies. This Involves a somewhat more expensive but less critical converter. Accordingly in an alternative embodiment of the regeneration arrangement the converter comprises a first modulator having an input which constitutes the input of the converter which is connected to the output of the first distortion corrector and having a local carrier input, a bandpass filter having an input connected to an output of the first modulator, a second modulator having an input connected to an output of the band-pass filter and having a local carrier input, a low-pass filter having an input connected to an output of the second modulator, an amplifier having an input connected to an output of the low-pass filter and an output which constitutes the output of the converter, a pulse shaper having an input which constitutes the input of the converter for the local carrier, two further bandpass filters each having an input connected to a respective one of two outputs of the pulse shaper, two further amplifiers each having an input connected to an output of a respective one of the two further bandpass - 9 filters, and two further delay elements each having an input connected to an output of a respective one of the two further amplifiers, and an output connected to the local carrier input of a respective one of the first and second modulators.

It is alternatively possible to regenerate the carrier frequency digital signal in the transmission state. To enable this, in a further alternative embodiment of the regeneration arrangement the converter comprises a combining circuit having two inputs and an output, a first delay element having an input which constitutes the input of the converter which is connected to the output of the first distortion corrector and having an output conected to one of the inputs of the combining circuit, a modulator having an input which is connected to the output of the second distortion corrector, a local carrier input, and an output connected to the other input of the combining circuit, a second delay element having an input which constitutes the input of the converter for the local carrier and an output connected to the local carrier input of the modulator, a lowpass filter having an input connected to the output of the combining circuit, and an amplifier having an input connected to an output of the low-pass filter and an output which constitutes the output of the converter.

The invention will be further understood from the following description by way of example of embodiments thereof with reference to the accompanying drawings, in which:Figure 1 schematically illustrates a regeneration for regenerating carrier transitted digital signals; and Figs. 2, 3 and 4 schematically illustrate different - 10 forms of converting device for use in the arrangement illustrated in Fig. 1.

The regeneration arrangement illustrated in Fig. 1 serves to regenerate a carrier transmitted digital signal from the upper sideband, which is used for transmission purposes, of a d.m. carrier signal.

The modulating digital signal is in the form of a pseudo-ternary code and the transmission carrier frequency is a whole-numbered multiple of half the bit repetition frequency of the digital signal and is synchronised 90° out of phase with the bit repetition frequency of the digital signal. This latter step avoids having a d.c. component in the d.m. carrier signal.

The upper sideband covers the frequency range 0.5 ft 1.5, where fl is the normalised frequency (obtained as the frequency ratio f:f^) relative to the bit repetition frequency f^ of the digital signal. Wherever fl is used herein it is to be understood as representing a frequency so normalised. The arrangement comprises a signal input 1, a bandpass filter BP1, a distortion corrector El, an amplifier Vl, a converting device M, a pulse generator R, an arrangement TA for pulse train and local carrier derivation, and outputs 2, 3, 4 and 5.

The band pass filter BP1 has a pass band equal to the frequency range 0.5 4. fl 1.5 and serves to apply the transmitted upper sideband which is received at the signal input 1, and in particular to prevent low-frequency interferences from being applied, to the input of the distortion corrector El. On account of the fact that the attenuation of the transmission cable, which is for example a form of cable suited to the transmission of d.m. carrier signals, - 11 increases with frequency, the attenuation of the distortion corrector El is arranged to decrease with increasing frequency, resulting in an overall linear transmission of the signal amplitudes in the frequency range of interest. Prom the output of the distortion corrector El, the corrected and additionally amplified signal is conducted both to a signal input A of the device M and to a signal input E of the arrangement TA for pulse train and local carrier derivation. In the device M the received, corrected and amplified upper sideband is converted into a regenerable digital signal; three possible ways in which this conversion may be effected are described below with reference to Pigs. 2 to 4.

Prom an output D of the device M, the regenerable digital signal is conducted to a signal input K of the actual pulse regenerator R, which has a known form and comprises an amplitude regenerator AR1 and a time regenerator ZR. In the amplitude regenerator AR1 the supplied pseudo-ternary-coded signal, whose amplitude values can thus be +1, 0 and -1, is split into two unipolar pulee sequences corresponding to the amplitude values +1 and -1 and the amplitudes of three pulses sequences are regenerated. One of the unipolar pulse sequences is composed of the input pulses with positive amplitude and the other pulse sequence is composed of the input pulses with negative amplitude. Each of the two amplitude-regenerated pulse sequences is conducted separately from a respective output of the amplitude regenerator ARl to a respective input of the time regenerator ZR. The time regenerator ZR, which for example comprises two D-type bistable trigger stages the D inputs of which constitute the two inputs of the time regenerator ZR, is supplied with a pulse train oscillation from a pulse train input L of the regenerator R, and in 42S04 - 12 accordance with this pulse train oscillation emits the timeregenerated unipolar pulse sequences separately from two outputs from which the unipolar pulse sequences are conducted to the outputs 2 and 3 of the arrangement. Thus from the out5 put 2 a unipolar pulse sequence can be obtained which is corrected in respect of amplitude and time and which corresponds to the sequence of input pulses with positive amplitude, whereas an- analogous pulse sequence corresponding to negative amplitude input pulses can be obtained from the output 3. in dependence upon whether the regeneration arrangement is being used as an intermediate regenerator or an end regenerator, the outputs 2 and 3 can be connected to the two inputs of an output modulator with an adjoining bandpass filter, or to a hybrid circuit with an adjoining band pass filter, or to other parts of a line terminal device.

The distortion corrector El is an automatic distortion corrector whose attenuation level is controlled in dependence upon the level of the received signal. For this purpose a control input of the distortion corrector El is connected to the output of the amplifier VI. As shown by dashed-lines, the input of the amplifier VI can be connected to the output of the distortion corrector El, so that the distortion corrector El and the amplifier VI can be combined to form a single unit, or it can be connected to other terminal points, for example the output D of the device M or an output N of the arrangement TA for pulse train and local carrier derivation, at which the received signal possesses a higher level whereby amplifier stages may be dispensed with.

The arrangement TA for pulse train and local carrier derivation comprises a series connection of a distortion corrector E2, a transit time or delay element 1, a rectifier 2 5 0 4 - 13 GR, an amplitude regenerator AR2, a phase discriminator PD, a controlled generator G, a pulse shaper RF, and a frequencydivider FT. An output P of the pulse shaper RF is connected to a second input of the phase discriminator PD whereby a phase-locked-loop is formed.

The input of the distortion corrector E2, which for example comprises a high-pass filter and a subsequent , J' , amplifier, is directly connected to the input E of the arrange-» ment TA, and its output is connected to the input of the transit time element tl, and to the output N of the arrangement TA. This output may, in addition to being connected to the input of the amplifier VI, be connected to a second input B of the device M as shown by dashed lines.

The transit time element tl comprises a shift chain which serves to match the transit time of the signal in the arrangement TA to the transit time of the signal to be regenerated in the device M and the regenerator R, and thus accurately to match the phases of the produced pulse train and local carrier and the signal which is to be regenerated. The rectifier GR is connected to the output of the transit time element tl and serves to fold the received, corrected and amplified upper sideband over on itself, i.e. to rectify this upper sideband, so that the following amplitude regenerator AR2 receives a unipolar pulse sequence instead of pseudoternary pulses. This unipolar pulse sequence is amplituderegenerated in the amplitude regenerator AR2, and is applied to one input of the phase discriminator PD which compares the phase of this pulse sequence with that of the produced, pulse train and local carrier to produce a pulsed d.c. voltage which is conducted as a control voltage to a control input of the generator G. The generator G contains capacitance diodes whose capacitance changes in accordance with the - 14 42504 supplied control voltage thereby leading to a change in the frequency of the produced oscillations. The generator G is a sinusoidal generator, the sinusoidal oscillations from which are converted into rectangular pulses in the pulse shaper RF in known manner. The rectangular pulses emitted from the pulse shaper RF forms the timing signal or bit pulse train w^iich ^^cqa^ucted via an output H of the arrangement TA to the puls'e train input L of the regenerator R and to the output 5. When the regeneration arrangement is used as an end regenerator, other parts of the line terminal device can be fed with the bit pulse train from this output 5.

From the output of the pulse shaper RF, the produced timing signal is also conducted to the frequency divider FT which has a frequency division ratio of 2:1 and derives from the timing signal, the local carrier which is conducted to an output F of the arrangement TA and thence to a carrier input C of the device M and to the output 4. When the regeneration arrangement is employed as an intermediate regenerator, in the case of regeneration of the pulses in the baseband state or in an intermediate state, this local carrier output 4 is connected to the output modulator, whereas in the case of regeneration of the pulses in the transmission state (comprising upper and lower sidebands) the terminal 4 remains unconnected.

When the regeneration arrangement is used as an end regenera25 tor, in the case of regeneration of the pulses in the intermediate stage or in the transmission state, the local carrier output 4 is connected to an input of a further modulator, whereas in the case of regeneration of the pulses in the baseband stage such further modulator can be dispensed with and the output 4 can remain unconnected.

When the received upper sideband which is transmitted 43504 - 15 in the frequency range 0.5^. fi Z.1.5 is to be converted into the baseband state, the device M feeds the regenerator R with a regenerable digital signal in the frequency range Oifi^l. In this case for regeneration a bit pulse train with the frequency fi - 1 is required and is produced by the generator G, which oscillates at this frequency, in association with the pulse shaper RF. The frequency divider FT produces the local carrier required for the conversion and having the frequency fi = 1/2, which it emits to the device M. The output signal emitted at the output P of the pulse shaper RF is conducted to the second input of the phase discriminator PD in which the phase comparison can be effected at the frequency level fl = 1 or fl = 2 or between the two.

In the case of regeneration of the carrier transmittal digital signal in the transmission state or in an intermediate state, the generator G produces an oscillation with the frequency fl = 2. The generator G can oscillate either directly at this frequency or with the frequency fl = 1; in the latter case the oscillation is deliberately distorted and the first hamonic (fl = 2) is filtered out from the distorted signal. In each case the pulse shaper RF produces pulses, with the frequency fl = 2, which are conducted to the regenerator R and to the frequency divider FT. In this case the regenerator R obtains a signal which is to be regenerated which occurs in the frequency range 04 fl 1.5. A local carrier with the frequency fl = 1 is conducted from the frequency divider FT to the device M. The frequency of the required local carrier is thus again half the frequency of the timing pulse required for time regeneration.

Figs. 2, 3 and 4 which are described below represent different converting devices M which enable the regeneration 4350^ - 16 arrangement represented in Fig. 1 to be employed universally.

The converting device shown in Fig. 2 comprises a modulator Ml, a low-pass filter TPl, bandpass filter BP2, amplifiers V2 and V3, and a transit time element t2 and serves to convert the received, corrected, and amplified upper sideband into the baseband state thereby to produce a regenerable digital signal. For this purpose the input A of the converting device is connected to the input of the modulator Ml which modulates the upper sideband received in the frequency range 0.5 4, Ω 1-5 with a local carrier which is conducted to its local carrier input and possesses the frequency Ω = 1/2, and this produces a digital signal in the frequency range 04 Ω «4,1· The output of the modulator Ml is connected to the input of the low-pass filter TPl, whose blocking band commences at Ω = 1, which withholds residues of the received signal from the output. The output of the low-pass filter TPl is connected to the input of the amplifier V2 which serves for level adjustment and emits the digital signal to the signal output D of the converting device. The local carrier input of the modulator Ml is supplied with the local carrier required for modulation from the local carrier input C of the converting device via the bandpass filter BP2 which has a passband at the frequency Ω = 1/2, the amplifier V3, and the transit time element t2 which serves to set finely the phase of the local carrier. This element again consists of a transit time chain and supplements the transit time element tl of the arrangement TA.

The converting device shown in Fig. 3 comprises modulators M2 and M3, a loWpass filter TP3, bandpass filters BP3, BP4 and BP5, amplifiers V4, V5 and V6, transit time - 17 elements t3 and t4, and a pulse shaper PP and serves for double conversion of the received, corrected, and amplified upper sideband into the baseband state. Although the outlay for the device for double conversion shown in Fig. 3 is somewhat greater than that for single conversion as shown in Fig. 2, higher requirements can be made on the accuracy of the transmission, and/or the demands on the individual components can be reduced. Thus for example, when high requirements are made on the transmission quality, the lowpaBS filter TP1 contained in the device shown in Fig. 2 must be designed to be tunable, whereas in the case of the comparable low-pass filter TP3 in the device shown in Pig. this is not necessary.

Referring to Pig. 3, the received, corrected, and amplified upper sideband is conducted from the signal input A to the modulator M2 which, by modulation with a first local carrier of the frequency S2= 3.5, effects a first conversion of the received upper sideband. The output of the modulator M2 is connected to the input of the bandpass filter BP3, which blocks the residues of the modulating input signal, the first local carrier and the upper sideband produced during the modulation, so that only the lower sideband with a frequency range of 2 riP 4.3 is emitted to the subsequently connected modulator M3. This lower sideband is modulated in the modulator M3 with a second local carrier with the frequency Ω= 3. The output of the modulator M3 is connected to the input of the low-pass filter TP3 which possesses a pass band of 0/.841 and which blocks all the modulation products except for the lower sideband. This lower sideband is the regenerable digital signal which in the amplifier V4 is brought to the desired level and is conducted to the signal output D of the converting device. - 18 The carrier for the modulator M2 with the frequency fl= 3.5 and that for the modulator M3 with the frequency β = 3 are produced from a basic local carrier with the frequency ft = 1/2 which is emitted from the arrangement TA (Fig. 1) to the local carrier input C. This basic local carrier is applied to the pulse shaper PF which, from the rectangular oscillations with the frequency Ω = 1/2, produces very narrow triangular oscillations which are therefore rich in harmonics, from which the bandpass filter BP4 filters out the sixth harmonic with the frequency ft = 3.5 and the bandpass filter BP5 filters out the fifth harmonic with a frequency ft = 3- These filtered out harmonics are conducted via the amplifiers V5 and V6 respectively and the transit time elements t 3 and t4 respectively to the modulators M2 and M3 respectively.

The converting device shovm in Fig. 4 comprises a modulator M4, a low-pass filter TP4, an amplifier V7, transit time elements t5 and t6, and a combining circuit Z, and serves to produce at the output of the Filter TP4 the lower sideband of the carrier frequency digital signal in the transmission state. This converting device includes two signal paths to the combining circuit Z, namely a signal path from the signal input A, which is connected to the output of the distortion corrector El (Fig. 1), via the transit time element t5, and a signal path from the additional signal input B which is connected to the output of the distortion corrector E2 (Fig. 1), via the modulator M4. Via the first signal path, the received, corrected, and amplified upper sideband is conducted to one input of the combining circuit Z, whereas the modulator M4 contained in the second signal path modulates the additionally corrected - 19 upper sideband with a local carrier of the frequency Ω = 1, whereby the lower sideband is produced. The combining circuit Z is constructed in the form of a known hybrid circuit. If there can be no reactions between the transit time element t5 and the output of the modulator M4 then the two signal paths can instead be ohmically connected.

At the output of the combining circuit Z the carrier transmitted digital signal in its transmission state, which consists of the two sidebands, is produced and this is conducted via the low-pass filter TP4 and the amplifier V7 to the signal output D. The local carrier with the frequency 2 = 1 is conducted to the local carrier input of the modulator M4 from the local carrier input C of the converting device via the transit time element t6 which serves to set precisely the phase of the local carrier. This transit time element is again in the form of a shift chain.

Using the embodiments described above, ambiguities in the carrier synchronisation can be avoided of the pulse brain and carrier oscillations are derived from the distortioncorrected received side band, thus in the signal path prior to a signal conversion by means of a local carrier. The advantages are thus provided that the individual steps of the method involve comparatively little outlay and, on account of the reliable prevention of mi-synchronisation, no additional measures need be taken to exclude specific undesired pulse sequences, such as for example a 1-0-1-0 ... sequence.

Claims

1. CLAIMS:1. A method of regenerating a carrier transmitted digital signal from a received single sideband of a digital modulated carrier signal, the modulating digital signal being 5 in the form of a pseudo-ternary code and the transmission carrier frequency being a first whole-numbered multiple of half the bit repetition frequency of the digital signal and being synchronised -90° out of phase with the bit repetition frequency of the digital signal, comprising the steps of 10 distortion-correcting the received sideband, deriving in dependence upon the distortion-corrected received sideband a local carrier having a frequency which is a second wholenumbered multiple of half the bit repetition frequency and a pulse train oscillation having a frequency which is double 15 the frequency of the local carrier, converting the distortion-corrected received sideband into a regenerable digital signal in a converter to which the distortion-corrected received sideband and the local carrier are supplied, and regenerating the regenerable digital signal in respect of 20 its amplitude in an amplitude regenerator and subsequently in respect of time in a time regenerator to which the pulse train oscillation is supplied.

2. A method as claimed in Claim 1 wherein the received , sideband is the upper sideband of the digital modulated car25 rier signal and wherein the conversion of the distortioncorrected upper sideband into the regenerable digital signal comprises the step of converting the distortion-corrected upper sideband into the baseband state of the digital signal,

3. A method as claimed in Claim 1 vzherein the received 30 sideband is the upper sideband of the digital modulated carrier signal and wherein the conversion of the distortion42504 - 21 corrected upper sideband into the regenerable digital signal comprises the step of converting the distortioncorrected upper sideband into an intermediate state which is displaced by a whole-numbered multiple of half the bit repetition frequency in relation to the baseband state of the digital signal.

4. A method as claimed in Claim 1 wherein the received sideband is the upper sideband of the digital modulated carrier signal and wherein the regenerable digital signal is produced in the converter by forming a lower sideband from the distortion-corrected upper sideband and combining the lower sideband with the upper sideband.

5. A method as claimed in any of Claims 1 to 4 wherein for deriving the pulse train oscillation and the local carrier an oscillation is produced in synchronism with the received sideband.

6. A method as claimed in any of Claims 1 to 4 wherein the pulse train oscillation and the local carrier are obtained by filtering an oscillation possessing double the bit repetition frequency of the digital signal out from the distortion-corrected received sideband after rectification thereof.

7. A regeneration arrangement for use in carrying out the method of any of Claims 1 to 4 comprising a bandpass filter having an input to which the received sideband is applied and a pass-band corresponding to the frequency range of the received sideband; a first distortion corrector having an input connected to an output of the bandpass filter and a control input; a converter having an input connected to an output of the first distortion corrector, an input for the local carrier, and an output which is - 22 arranged to supply the regenerable digital signal; a pulse regenerator having an input connected to the output of the converter, an input for the pulse train oscillation, and at least one output which is arranged to produce the digital 5 signal regenerated in respect c£ amplitude and time; a circuit arrangement for producing the pulse train oscillation and the local carrier and comprising a second distortion corrector having an input connected to the output of the first distortion corrector, a delay element having an 10 input connected to an output of the second distortion corrector, a rectifier having an input connected to an output of the delay element, an amplitude regenerator having an input connected to an output of the rectifier, an oscillator, a frequency divider having a division ratio of 2:1 and having i5 an output connected to the input of the converter for receiving the local carrier, a pulse shaper having an input connected to an output of the oscillator and an output connected to an input of the frequency divider and to the input of the pulse regenerator for the pulse train oscillation, 20 and a phase discriminator having a first input connected to an output of the amplitude regenerator, a second input connected to an output of the pulse shaper, and an output connected to an input of the oscillator for controlling the frequency thereof; and an amplifier having an output 25 connected to the control input of the first distortion corrector and an input connected to the output of either the first or the second distortion corrector or the converter.

8. A regeneration arrangement as claimed in Claim 7 30 wherein the pulse regenerator comprises an amplitude regenera tor, having an input which constitutes the input of the puls 42S04 - 23 regenerator which is connected to the converter and two outputs at which it is arranged tD produce amplituderegenerated unipolar pulse sequences of opposite polarity, and a time regenerator having two inputs each of which is connected to a respective one of the outputs of the amplitude regenerator, a further input which constitutes the input of the pulse regenerator for the pulse train oscillation, and two outputs which constitute outputs of the pulse regenerator and at which it is arranged to produce the amplitude-regenerated unipolar pulse sequences regenerated in time.

9. A regeneration arrangement as claimed in Claim 7 or Claim 8 wherein the second distortion corrector comprises a high-pass filter.

10. A regeneration arrangement as claimed in any of Claims 7 to 9 wherein the converter comprises a modulator having an input which constitutes the input of the converter which is connected to the output of the first distortion corrector and having a local carrier input, a low-pass filter having an input connected to an output of the modulator, an amplifier having an input connected to an output of the low-pass filter and an output which constitutes the output of the converter, a bandpass filter having an input which constitutes the input of the converter, for the local carrier, a further amplifier having an input connected to an output of the bandpass filter, and a delay element having an input connected to an output of the further amplifier and an output connected to the local carrier input of the modulator.

11. A regeneration arrangement as claimed in any of Claims 7 to 9 wherein the converter comprises a first - 24 modulator having an input which constitutes the input of the converter which is connected to the output of the first distortion corrector and having a local carrier input, a bandpass filter having an input connected to an output of the first modulator, a second modulator having an input connected to an output of the bandpass filter and having a local carrier input, a low-pass filter having an input connected to an output of the second modulator, an amplifier having an input connected to an output of the low-pass filter and an output which constitutes the output of the converter, a pulse shaper having an input which constitutes the input of the converter for the local carrier, two further bandpass filters each having an input connected to a respective one of two outputs of the pulse shaper, two further amplifiers each having an input connected to an output of a respective one of the two further bandpass filters, and two further delay elements each having an input connected to an output of a respective one of the two further amplifiers and an output connected to the local carrier input of a respective one of the first and second modulators.

12. A regeneration arrangement as claimed in any of Claims 7 to 9 wherein the converter comprises a combining circuit having two inputs and an output, a first delay element having an input which constitutes the input of the converter which is connected to the output of the first distortion corrector and having an output connected to one of the inputs of the combining circuit, a modulator having an input which is connected to the output of the second distortion corrector, a local carrier input, and an output connected to the other input of the combining circuit, a second delay element having an input which constitutes the - 25 input of the converter for the local carrier and an output connected to the local carrier input of the modulator, a low-pass filter having an input connected to the output of the combining circuit, and an amplifier having an input 5 connected to an output of the low-pass filter and an output which constitutes the output of the converter.

13. A regeneration arrangement substantially as herein described with reference to Figs. 1 and 2, Figs. 1 and 3, or Figs. 1 and 4 of the accompanying drawings.