CA2010763A1 - Digital signal transmission system - Google Patents
Digital signal transmission systemInfo
- Publication number
- CA2010763A1 CA2010763A1 CA002010763A CA2010763A CA2010763A1 CA 2010763 A1 CA2010763 A1 CA 2010763A1 CA 002010763 A CA002010763 A CA 002010763A CA 2010763 A CA2010763 A CA 2010763A CA 2010763 A1 CA2010763 A1 CA 2010763A1
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- CA
- Canada
- Prior art keywords
- interference
- digital
- transmission system
- equalizer
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 230000008054 signal transmission Effects 0.000 title claims description 17
- 230000005540 biological transmission Effects 0.000 claims abstract description 30
- 238000001514 detection method Methods 0.000 claims description 13
- 230000003044 adaptive effect Effects 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 12
- 230000007704 transition Effects 0.000 claims description 3
- 238000012545 processing Methods 0.000 claims description 2
- 230000000694 effects Effects 0.000 claims 2
- 238000001914 filtration Methods 0.000 claims 2
- 230000006978 adaptation Effects 0.000 description 3
- 238000004891 communication Methods 0.000 description 3
- 238000005457 optimization Methods 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000012937 correction Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 230000002452 interceptive effect Effects 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 230000011664 signaling Effects 0.000 description 2
- 230000001154 acute effect Effects 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 238000000638 solvent extraction Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
- H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
- H04L25/03057—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception with a recursive structure
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Dc Digital Transmission (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The invention relates to a digital transmission system for the simultaneous transmission of several binary digital signals via separate wire pairs in a single cable. In addition to a threshold-value detector, an interference-value predictor is used. The scanning values of the latter are derived from a difference signal between a Nyquist-equalized signal and a detected signal. The interference protection against crosstalk is considerably increased in this way.
The invention relates to a digital transmission system for the simultaneous transmission of several binary digital signals via separate wire pairs in a single cable. In addition to a threshold-value detector, an interference-value predictor is used. The scanning values of the latter are derived from a difference signal between a Nyquist-equalized signal and a detected signal. The interference protection against crosstalk is considerably increased in this way.
Description
20~(~763 DIGITAL SIGNA~ TRANSNISSION SYSTEM
BACKGROUND OF THE INVENTION
Field of the Invention The invention relates to a digital signal transmission system for the simultaneous transmission of several signals via separate wire pairs in a multi-pair cable.
Description of the Prior Art Digital transmission systems with maximal bit rates of 2.048 Mbit/s for the multiple use of multi-pair symmetrical low-frequency cables are known. AMI-coded or HDB3-coded line ~ignal~ are predominantly transmltted via the Nyquist-equalized channel of the wire pair and are threshold detected. These conventionàl procedures are ~ery ~ensitive to cro~stalk interferences from similar transmission systems which operate on adjacent pairs in the same cabIe. This I, ¦ problem is partlcularly acute when bidirectional signals, independent of each other, are transmitted in the same cable. The proceduxes are also sensitive to impulsive interferences caused by the character transmission of electro-mechanical switched systems.
`~
20~0763 These interferences limit the maximum field length or regeneration space that may be bridged and also, in the case of a fixed field length, limit the number of transmission systems of the same kind that can be located in the same cable.
The main source of interference is crosstalk, which is caused by signals of systems of the same kind which operate on ad;oining pairs within the same cable. Therefore, a greater field length cannot be achieved by increasing the transmitter power, but only by an improved system design. Further interference is i caused by the crosstalk of rare pulses with high' energy, which originate from asymmetrical signaling r~ procedures on pairs that are still used for traditional analog voice transmis6ion. The spectral energy density of such pulses is concentrated at frequencies which are low compared to the data rate. The transmitted pulses are stretched over many symbol lntervals T by the di~perslve medium, resulting in a strong attenuation at hlgh frequencies.
An optimum solution to the detection of a digital signal with severe inter-symbol interference and ,~, , colored noise is achieved by using a Maximum-Likelihood-Sequence-Estimation using the Viterbi-algorithm, as explained by G. S. Forney, Jr., "Maximum-Likelihood-. ~
'., - : ' t ' , . :, Sequence-Estimation (MLSE) of Di~ital Sequences in the Presence of Inter-Symbol Interference", IEEE Trans.
Information Theory, Vol. IT-18, pp. 363-378, May 1972.
The complete MLSE procedure would require tracing numerous paths through a trellis and therefore cannot be realized at the desired data rate. A modified version using a threshold detector with decision feedback which corresponds to a state reduction of the MLSE procedure down to one state was implemented, as described by M. V. Eyuboglu, S. U. Quershi, "Reduced State Sequence Estimation With Set Partitioning and Decision Feedback", IEEE Trans. communications, Vol.
COM-35, pp. 13-20, January 1988. For this receiver type, as well as for the optimum detector, the highest reliability i5 achieved by using a four-level ~quaternary) ba~e band ~ignal without redundance (provided that no additional equipment for decoding of hannel codes i~ tolerated).
, ~ ~
~ -3-- 2o.~0763 SUMMARY OF THE INVENTION
The present invention contemplates a digital transmission system for the simultaneous transmission of several digital signals via separate wire pairs located in a multi-pair cable.
The dominating near-end crosstalk experienced when there are a large number of systems transmitting on pairs within the same cable, is avoided by using a cable which is divided into quads, with the wire pairs ; 10 within the same quad all handling signaling in the same direction. When this configuration is used, the resulting noise may be approximated by colored Gaussian noise. Thus, a bundle cable with spiral quads can be f fully wired when each spiral guad is used for the tran3mission of signals in one direction only.
i A binary signal would be affected by the channel ;~ attenuation which grows for an lncr~asing freguency in a much more rigorou~ manner. Therefore, a quaternary ~ignaling (1.024 M baud) is used in the present invention. The binary, scrambled digital source signals axe re-coded into redundance-free quaternary transmitted signals.
,~
~,:
~ -4-.~
2U~0763 The received signals, which are Nyquist-distorted and suffer from low frequency attenuation, are adaptively equalized in a symbol-interference-free manner, and the low-frequency signal portions that have been lost along the transmission path are recovered by means of a quantized feedback (decision-feedback equalization).
The signals which are equalized in an interference-free manner are detected by means of a simple threshold detector. From the difference between a received signal value present at the optimum detection time and the useful value of the received signal estimated on ~ the basis of the decision, an estimate of the !~J interference is obtained by subtraction. On the basis i~
of previous estimated interference values and the ¢urrent estimated interference value, a prediction of the interference at the next detection time is made by f~ means of a linear filter. This predicted value is subtra¢ted from tho slgnal value at the next detection time, in order to achieve a reduction in the effective ;~
Z~3~ interference power.
The prediction of the interference value is possible because, on the basis of the crosstalk frequency response and by means of the equalization, linear statistical links within the interference i,jlZZ ~
' ~Z
,~,Z ~ ~:
~: :
201~763 process, which is produced in its predominant part by cross-talk of signals of the same kind in the multi-pair cable, are formed. The interference predictor filter can also be used adaptively for minimization of the remaining residual interference power.
The predominant part of the receiver is realized digitally, in accordance with the methods known from digital signal processing. The receiver, in this way, achieves the maximum possible interference protection against crosstalk interferences in the case of the use of a threshold value detector. However, only small losses in the signal-to-noise ratio, as compared with optimal detection (correlation receiver for all possible symbol sequences), must be accepted.
The novel tran6mission proces6 is characterized by the fact that, instead of the QR structure (decision-feedback equalization) of the interference value prediction with a double realization o~ the predictor filter in the signal path and in the ~e~dback path, ZO which is designated as optimal in Adaptive ~ilters, by I
M. L. Honig and D. G. Mes6erschmitt, Kluwer Academic Publi6hers, Bo6ton, (1984), a simple structure of the s~ interference-value predictor with a single realization of the predictor ~ilter is used in the present case.
This is because, in the case of the present use, the ,., ~o76~
quaternary signal is the optimal of all redundance-free transmitted signals. The ætructure according to the drawing is found to be superior to the QR structure for this quaternary signal.
~ An additional characterizing feature is the separate possibility of adjustment of the filters for the (linear and decision-feedback) equalization and for the interference-value prediction made possible in this way. By this means, different setting algorithms for these filters and different adaptation speeds for equalization and interference-value prediction can be selected. A setting of the interference-value prediction that is slower as compared with the equalization produces a distinct broadening of the range for transmis~ion properties (cable length, wire diameter, type of interference) within which a 7' successful adaptation is possible for an identical I ` coefficient number of the digital filters. In ,1 addltion, by means of the ~tructure with separate ~i 20 setting algorithms for the equalizer (zero-forcing algorithm) and interference-value prediction (minimum-mean-square algorithm?, a more effective interference ~::
suppression 1s aahieved in the case of stationary operation than when a common setting procedure is selected for all filter~.
,~ ~
,~
...... , ,,- , . ,.. ;.. ~,, ,:.; ,.,.. , .. , .. , ,. , , , ,. , . , ~ , ~ . .
- , ,, ,- - ,;, , " , , - ;,:; -;~0~0763 - Another identifying characteristic of the novel transmission process is that analog compromise-type preliminary equalization is carried out to reduce the coefficient number of the linear and of the decision-feedback part of the adaptive, digitally realized equalizer. This is designed in such a way that a ; whitened match filter, as in "Detectors and Optimum Receiver Filters for Digital Signals with Intersymbol , Interference", Part I and Part II, by J. Huber, s 10 Frequency 41 (1987), pp. 161-167 and pp. 189-196, is contained as a factor and that, in this way, a transition from a continuous-~ime signal to discrete-time scanning values without loss of information is ensured. In this way, this compromise equalizer corresponds to the optimal Nyquist filter for the cable attenuation and cross-talk transmission function q, .
expected on average, This usually results in roll-off-~actor~ the pul~e ~haper part o~ the compromise equalizer that are between 0.3 and 0.6 and which lead to optimum increases in the signal-to-noise ratio.
As another characterizing feature of the transmission system is achievement of an optimization of the detection time on the basis of the coefficients set in the linear adaptive equalizer, which is also carried out in an adaptive manner. In this way, long-,,' ', ;, ',' ,.' '' ''' '. :' ' ' : `,, ' `.', ," ' ' ;, :' ' ', .. ;. ., ~ . : . :, . : . ,, , :, " .
X0~0763 term variations of cable properties or of the oscillator for the timing recovery in the receiver are equalized.
The invention can be used advantageously in local subscriber line networks for increasing the field length for 2.048 Mbit/s transmission. The predominant number of subscribers is reached in this way without a regenerative repeater. As a result of the improved interference protection against crosstalk and impulsive interferences, a very high degree of assignment of the local connecting cables with 2.048 Mbit/s systems of the same kind with a relatively large field length can be achieved. By means of a skillful selection of the different setting algorithms for the equalization and the interference-value prediction, the high-pass ~iltering system becomes completely effective against the unsteady impulsive interferences.
DESCRIPIION OF TNE DRA,WING
, An exemplifying embodiment of the invention is represented in the drawing which is a schematic diagram.
:.
'3:
g _ i: :
,?:
,~ .. : . , . ,`, , ., , , .,. . : . , . , . :
2010~6~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A redundance-free four-stage (quaternary) line signal is transmitted on a wire pair of a multi-pair cable. The multi-pair cable is a bundle cable with spiral quads with the pairs in each quad used for transmission in one direction only. The signal is etrongly dietorted and attenuated on the way to a receiver, in accordance with the transmission function of the wire pair, and is present at a receiver input as an intelligence signal e(t). The intelligence signal e(t) is superposed by crosstalk interferences from ., , ~; transnission systems of the same kind operated on adjacent wires in the same quad, and from unsteady impulsive interferences of electro-mechanical switched systQme.
Both the intelligence eignaI and all interferences at the receiver input are ~ilterèd w1th a high-pass ~ilter. This high-pae~ filter HP reduces the low-frequency impulsive interferences. A linear equalizer 2 and decision-feedback equalizer 3 eliminate the impulsive interferences of the intelligence signal e(t) according to the first Nyquist criterion. By dividing the linear equalizer 2 into an analog compromise equalizer KE having a fixed setting and an adjustable ~ 10-, ~ , : ~
:
. :v , . . -. . ~ . ~:
20~0763 digital equalizer DE, the number of required coefficients, cO through cL~ of the equalizer DE is reduced.
The output signal of the analog compromise equalizer KE is scanned by the symbol clock pulse T to produce a sequence of discrete scanning values (ei~.
The discrete values (ei) are analyzed with the transverse filter TF2 of the adjustable digital equalizer ~E in accordance with the setting of the coe~ficients aO through CL, to produce a sequence of the discrete-time openings (di). The detection time is established on the basis of the coefficients CO through CL to achieve optimization of the detection time to compensate for long-term variations of cable properties or of the oscillator for the timing recovery. The optimization of the detection time is related to the moment o~ scanning. The concept iB to use the Q~iciQnts to ad~u~t the tact. Such a moment for : scanning may, for example, be any one of the following:
L
; 20 ¦Cj¦ = Max o :, ~ or .
i ~ ~
,~
.... .
2o~0~63 L-l ¦ = Max = o or CL = Max A compensation signal dQRi is derived from a detected signal vi via a transverse filter TF3 of the decision-feedback equalizer 3 in accordance with the coefficients bo through bM. m is compensation signal dQRi is intended to cancel distortion caused by the high-pass filter HP. The distorted signal, with its scanning values ki, is formed by means of a difference function where ki = di ~ dQRi. The distorted signal ki contains an intelligence signal component and an interf~rence-~lgnal component.
:The adaptive setting of the coefficients cO
:
~ through cL and bo through bM is performed as described , by K. P. Graf and J. Huber, two of the inventors, in "Design and Performance of an All-Digital Adaptive z.048 Mbit/s Data Transmission System Us1ng Noise Prediction", Proceedings of International Symposium on ; ~
f~
: " .,, . , ", ,, , , , : -, : , , . , :- . . .
Circuits and Systems (ISCAS~, May 1989, which is incorporated herein by reference. The method uses the known zero-forcing algorithm as described in Principles of Data Communication, R. W. Lucky, J~ Salæ and E. J.
Weldon, Jr., McGraw-Hill, New York, 1968.
An adaptation of an interference-value predictor 1 with coefficients Pl through PN is carried out completely independently of the setting of the distortion. The known minimum-mean-square algorithm, also described in Principles of Data Communication, is used in this case. The scanning values ri f the predictor input signal are formed by subtraction of the detected signals vi from the compensated and equalized signal ki, which is delayed by the duration of one symbol interval T, such that ri = ki_l - vi. The signal ki i~ superposed by colored interference which ~' 7 is caused primarily by crosstalk, and there is an absence o~ ~ignl~icant whito interference in ki. These scanning values of the difference signals ri are analyzed with the transverse filter TFl of the lnterference-value predictor 1 in such a way that the predict~ble part of the interference mi is subtracted from the scanning values ki to form values xi which are provided to the detector SD. Thus, only the intelligence signal component and the interfering .
~1:: :~
~". ,,, . ,.. , ;., .... ,., . ", . , ~.. ,.... " ., -; . ..... ....
2Q~()763 component are present at the input of the threshold-value detector SD as a signal xi, without a correlation within the intelligence signal component and the interfering component. The decision process therefore provides greater interference protection, because of the de-correlation.
The complexity of an implementation of the present invention may be greatly reduced by application of the sign algorithm wherein only the signs of the signals that are used for the adaptive filter coefficient settings are used. It has been found that by merely using the signs of the signals for the coefficient correction settings rather than the values of the signals themselve~, the hardware may be greatly simplified while the correction produced is still sati~factory.
With the system of the invention it is possible to achieve a total attenuation of 44 dB. The roll-off-~actor o~ the receiving ~ilter may be 0.5. The system provides a possible transmission range of nearly 3 km on copper conductors of 0.4 mm diameter and nearly 5 km on copper conductors of 0.6 mm diameter.
An implementation of the present invention, including experimental results, is further described in the article, "Deslgn and Performance of an A11 Digital :, , Adaptive 2.048 Mbit/s Data Transmission System Using Noise Prediction", written by two of the inventors.
, ~
,~
~, :
L:~
~, , .;
.., ~
,~.~,. , , .
.',5. . ' . ~ . ,
BACKGROUND OF THE INVENTION
Field of the Invention The invention relates to a digital signal transmission system for the simultaneous transmission of several signals via separate wire pairs in a multi-pair cable.
Description of the Prior Art Digital transmission systems with maximal bit rates of 2.048 Mbit/s for the multiple use of multi-pair symmetrical low-frequency cables are known. AMI-coded or HDB3-coded line ~ignal~ are predominantly transmltted via the Nyquist-equalized channel of the wire pair and are threshold detected. These conventionàl procedures are ~ery ~ensitive to cro~stalk interferences from similar transmission systems which operate on adjacent pairs in the same cabIe. This I, ¦ problem is partlcularly acute when bidirectional signals, independent of each other, are transmitted in the same cable. The proceduxes are also sensitive to impulsive interferences caused by the character transmission of electro-mechanical switched systems.
`~
20~0763 These interferences limit the maximum field length or regeneration space that may be bridged and also, in the case of a fixed field length, limit the number of transmission systems of the same kind that can be located in the same cable.
The main source of interference is crosstalk, which is caused by signals of systems of the same kind which operate on ad;oining pairs within the same cable. Therefore, a greater field length cannot be achieved by increasing the transmitter power, but only by an improved system design. Further interference is i caused by the crosstalk of rare pulses with high' energy, which originate from asymmetrical signaling r~ procedures on pairs that are still used for traditional analog voice transmis6ion. The spectral energy density of such pulses is concentrated at frequencies which are low compared to the data rate. The transmitted pulses are stretched over many symbol lntervals T by the di~perslve medium, resulting in a strong attenuation at hlgh frequencies.
An optimum solution to the detection of a digital signal with severe inter-symbol interference and ,~, , colored noise is achieved by using a Maximum-Likelihood-Sequence-Estimation using the Viterbi-algorithm, as explained by G. S. Forney, Jr., "Maximum-Likelihood-. ~
'., - : ' t ' , . :, Sequence-Estimation (MLSE) of Di~ital Sequences in the Presence of Inter-Symbol Interference", IEEE Trans.
Information Theory, Vol. IT-18, pp. 363-378, May 1972.
The complete MLSE procedure would require tracing numerous paths through a trellis and therefore cannot be realized at the desired data rate. A modified version using a threshold detector with decision feedback which corresponds to a state reduction of the MLSE procedure down to one state was implemented, as described by M. V. Eyuboglu, S. U. Quershi, "Reduced State Sequence Estimation With Set Partitioning and Decision Feedback", IEEE Trans. communications, Vol.
COM-35, pp. 13-20, January 1988. For this receiver type, as well as for the optimum detector, the highest reliability i5 achieved by using a four-level ~quaternary) ba~e band ~ignal without redundance (provided that no additional equipment for decoding of hannel codes i~ tolerated).
, ~ ~
~ -3-- 2o.~0763 SUMMARY OF THE INVENTION
The present invention contemplates a digital transmission system for the simultaneous transmission of several digital signals via separate wire pairs located in a multi-pair cable.
The dominating near-end crosstalk experienced when there are a large number of systems transmitting on pairs within the same cable, is avoided by using a cable which is divided into quads, with the wire pairs ; 10 within the same quad all handling signaling in the same direction. When this configuration is used, the resulting noise may be approximated by colored Gaussian noise. Thus, a bundle cable with spiral quads can be f fully wired when each spiral guad is used for the tran3mission of signals in one direction only.
i A binary signal would be affected by the channel ;~ attenuation which grows for an lncr~asing freguency in a much more rigorou~ manner. Therefore, a quaternary ~ignaling (1.024 M baud) is used in the present invention. The binary, scrambled digital source signals axe re-coded into redundance-free quaternary transmitted signals.
,~
~,:
~ -4-.~
2U~0763 The received signals, which are Nyquist-distorted and suffer from low frequency attenuation, are adaptively equalized in a symbol-interference-free manner, and the low-frequency signal portions that have been lost along the transmission path are recovered by means of a quantized feedback (decision-feedback equalization).
The signals which are equalized in an interference-free manner are detected by means of a simple threshold detector. From the difference between a received signal value present at the optimum detection time and the useful value of the received signal estimated on ~ the basis of the decision, an estimate of the !~J interference is obtained by subtraction. On the basis i~
of previous estimated interference values and the ¢urrent estimated interference value, a prediction of the interference at the next detection time is made by f~ means of a linear filter. This predicted value is subtra¢ted from tho slgnal value at the next detection time, in order to achieve a reduction in the effective ;~
Z~3~ interference power.
The prediction of the interference value is possible because, on the basis of the crosstalk frequency response and by means of the equalization, linear statistical links within the interference i,jlZZ ~
' ~Z
,~,Z ~ ~:
~: :
201~763 process, which is produced in its predominant part by cross-talk of signals of the same kind in the multi-pair cable, are formed. The interference predictor filter can also be used adaptively for minimization of the remaining residual interference power.
The predominant part of the receiver is realized digitally, in accordance with the methods known from digital signal processing. The receiver, in this way, achieves the maximum possible interference protection against crosstalk interferences in the case of the use of a threshold value detector. However, only small losses in the signal-to-noise ratio, as compared with optimal detection (correlation receiver for all possible symbol sequences), must be accepted.
The novel tran6mission proces6 is characterized by the fact that, instead of the QR structure (decision-feedback equalization) of the interference value prediction with a double realization o~ the predictor filter in the signal path and in the ~e~dback path, ZO which is designated as optimal in Adaptive ~ilters, by I
M. L. Honig and D. G. Mes6erschmitt, Kluwer Academic Publi6hers, Bo6ton, (1984), a simple structure of the s~ interference-value predictor with a single realization of the predictor ~ilter is used in the present case.
This is because, in the case of the present use, the ,., ~o76~
quaternary signal is the optimal of all redundance-free transmitted signals. The ætructure according to the drawing is found to be superior to the QR structure for this quaternary signal.
~ An additional characterizing feature is the separate possibility of adjustment of the filters for the (linear and decision-feedback) equalization and for the interference-value prediction made possible in this way. By this means, different setting algorithms for these filters and different adaptation speeds for equalization and interference-value prediction can be selected. A setting of the interference-value prediction that is slower as compared with the equalization produces a distinct broadening of the range for transmis~ion properties (cable length, wire diameter, type of interference) within which a 7' successful adaptation is possible for an identical I ` coefficient number of the digital filters. In ,1 addltion, by means of the ~tructure with separate ~i 20 setting algorithms for the equalizer (zero-forcing algorithm) and interference-value prediction (minimum-mean-square algorithm?, a more effective interference ~::
suppression 1s aahieved in the case of stationary operation than when a common setting procedure is selected for all filter~.
,~ ~
,~
...... , ,,- , . ,.. ;.. ~,, ,:.; ,.,.. , .. , .. , ,. , , , ,. , . , ~ , ~ . .
- , ,, ,- - ,;, , " , , - ;,:; -;~0~0763 - Another identifying characteristic of the novel transmission process is that analog compromise-type preliminary equalization is carried out to reduce the coefficient number of the linear and of the decision-feedback part of the adaptive, digitally realized equalizer. This is designed in such a way that a ; whitened match filter, as in "Detectors and Optimum Receiver Filters for Digital Signals with Intersymbol , Interference", Part I and Part II, by J. Huber, s 10 Frequency 41 (1987), pp. 161-167 and pp. 189-196, is contained as a factor and that, in this way, a transition from a continuous-~ime signal to discrete-time scanning values without loss of information is ensured. In this way, this compromise equalizer corresponds to the optimal Nyquist filter for the cable attenuation and cross-talk transmission function q, .
expected on average, This usually results in roll-off-~actor~ the pul~e ~haper part o~ the compromise equalizer that are between 0.3 and 0.6 and which lead to optimum increases in the signal-to-noise ratio.
As another characterizing feature of the transmission system is achievement of an optimization of the detection time on the basis of the coefficients set in the linear adaptive equalizer, which is also carried out in an adaptive manner. In this way, long-,,' ', ;, ',' ,.' '' ''' '. :' ' ' : `,, ' `.', ," ' ' ;, :' ' ', .. ;. ., ~ . : . :, . : . ,, , :, " .
X0~0763 term variations of cable properties or of the oscillator for the timing recovery in the receiver are equalized.
The invention can be used advantageously in local subscriber line networks for increasing the field length for 2.048 Mbit/s transmission. The predominant number of subscribers is reached in this way without a regenerative repeater. As a result of the improved interference protection against crosstalk and impulsive interferences, a very high degree of assignment of the local connecting cables with 2.048 Mbit/s systems of the same kind with a relatively large field length can be achieved. By means of a skillful selection of the different setting algorithms for the equalization and the interference-value prediction, the high-pass ~iltering system becomes completely effective against the unsteady impulsive interferences.
DESCRIPIION OF TNE DRA,WING
, An exemplifying embodiment of the invention is represented in the drawing which is a schematic diagram.
:.
'3:
g _ i: :
,?:
,~ .. : . , . ,`, , ., , , .,. . : . , . , . :
2010~6~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A redundance-free four-stage (quaternary) line signal is transmitted on a wire pair of a multi-pair cable. The multi-pair cable is a bundle cable with spiral quads with the pairs in each quad used for transmission in one direction only. The signal is etrongly dietorted and attenuated on the way to a receiver, in accordance with the transmission function of the wire pair, and is present at a receiver input as an intelligence signal e(t). The intelligence signal e(t) is superposed by crosstalk interferences from ., , ~; transnission systems of the same kind operated on adjacent wires in the same quad, and from unsteady impulsive interferences of electro-mechanical switched systQme.
Both the intelligence eignaI and all interferences at the receiver input are ~ilterèd w1th a high-pass ~ilter. This high-pae~ filter HP reduces the low-frequency impulsive interferences. A linear equalizer 2 and decision-feedback equalizer 3 eliminate the impulsive interferences of the intelligence signal e(t) according to the first Nyquist criterion. By dividing the linear equalizer 2 into an analog compromise equalizer KE having a fixed setting and an adjustable ~ 10-, ~ , : ~
:
. :v , . . -. . ~ . ~:
20~0763 digital equalizer DE, the number of required coefficients, cO through cL~ of the equalizer DE is reduced.
The output signal of the analog compromise equalizer KE is scanned by the symbol clock pulse T to produce a sequence of discrete scanning values (ei~.
The discrete values (ei) are analyzed with the transverse filter TF2 of the adjustable digital equalizer ~E in accordance with the setting of the coe~ficients aO through CL, to produce a sequence of the discrete-time openings (di). The detection time is established on the basis of the coefficients CO through CL to achieve optimization of the detection time to compensate for long-term variations of cable properties or of the oscillator for the timing recovery. The optimization of the detection time is related to the moment o~ scanning. The concept iB to use the Q~iciQnts to ad~u~t the tact. Such a moment for : scanning may, for example, be any one of the following:
L
; 20 ¦Cj¦ = Max o :, ~ or .
i ~ ~
,~
.... .
2o~0~63 L-l ¦ = Max = o or CL = Max A compensation signal dQRi is derived from a detected signal vi via a transverse filter TF3 of the decision-feedback equalizer 3 in accordance with the coefficients bo through bM. m is compensation signal dQRi is intended to cancel distortion caused by the high-pass filter HP. The distorted signal, with its scanning values ki, is formed by means of a difference function where ki = di ~ dQRi. The distorted signal ki contains an intelligence signal component and an interf~rence-~lgnal component.
:The adaptive setting of the coefficients cO
:
~ through cL and bo through bM is performed as described , by K. P. Graf and J. Huber, two of the inventors, in "Design and Performance of an All-Digital Adaptive z.048 Mbit/s Data Transmission System Us1ng Noise Prediction", Proceedings of International Symposium on ; ~
f~
: " .,, . , ", ,, , , , : -, : , , . , :- . . .
Circuits and Systems (ISCAS~, May 1989, which is incorporated herein by reference. The method uses the known zero-forcing algorithm as described in Principles of Data Communication, R. W. Lucky, J~ Salæ and E. J.
Weldon, Jr., McGraw-Hill, New York, 1968.
An adaptation of an interference-value predictor 1 with coefficients Pl through PN is carried out completely independently of the setting of the distortion. The known minimum-mean-square algorithm, also described in Principles of Data Communication, is used in this case. The scanning values ri f the predictor input signal are formed by subtraction of the detected signals vi from the compensated and equalized signal ki, which is delayed by the duration of one symbol interval T, such that ri = ki_l - vi. The signal ki i~ superposed by colored interference which ~' 7 is caused primarily by crosstalk, and there is an absence o~ ~ignl~icant whito interference in ki. These scanning values of the difference signals ri are analyzed with the transverse filter TFl of the lnterference-value predictor 1 in such a way that the predict~ble part of the interference mi is subtracted from the scanning values ki to form values xi which are provided to the detector SD. Thus, only the intelligence signal component and the interfering .
~1:: :~
~". ,,, . ,.. , ;., .... ,., . ", . , ~.. ,.... " ., -; . ..... ....
2Q~()763 component are present at the input of the threshold-value detector SD as a signal xi, without a correlation within the intelligence signal component and the interfering component. The decision process therefore provides greater interference protection, because of the de-correlation.
The complexity of an implementation of the present invention may be greatly reduced by application of the sign algorithm wherein only the signs of the signals that are used for the adaptive filter coefficient settings are used. It has been found that by merely using the signs of the signals for the coefficient correction settings rather than the values of the signals themselve~, the hardware may be greatly simplified while the correction produced is still sati~factory.
With the system of the invention it is possible to achieve a total attenuation of 44 dB. The roll-off-~actor o~ the receiving ~ilter may be 0.5. The system provides a possible transmission range of nearly 3 km on copper conductors of 0.4 mm diameter and nearly 5 km on copper conductors of 0.6 mm diameter.
An implementation of the present invention, including experimental results, is further described in the article, "Deslgn and Performance of an A11 Digital :, , Adaptive 2.048 Mbit/s Data Transmission System Using Noise Prediction", written by two of the inventors.
, ~
,~
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.',5. . ' . ~ . ,
Claims (20)
1. A system for the simultaneous transmission of several binary digital signals via separate wire pairs, located in a multi-pair cable, in which the binary, scrambled digital signals are re-coded into quaternary signals and the bi-directional signal transmissions, independently of each other, are carried in the same low-frequency cable, the received signals are Nyquist-distorted, the low-frequency signal portions lost on the transmission path are recovered by means of a quantized feedback (QR) and the resulting signal is threshold-detected and the predominant part of the receiver is realized by means of methods known from digital signal processing in order to obtain the maximum possible interference protection according to theory against crosstalk interferences, characterized by the fact that, in addition to the conventional threshold-value detector (SD), known in itself, an interference-value predictor (1) with the coefficients P1 through PN is used, whose scanning values (ri) are derived from the difference signal (ri) between the Nyquist-distorted signal (ki-1) and the detected signal (vi), so that uncorrelated interference values, which are effectively reduced for the detection process,,are formed from the original colored interference value.
2. A digital transmission system according to claim 1, having a receiver structure comprising:
a high-pass filter (HP);
a linear equalizer (2) with the coefficients co through cL;
decision-feedback equalizer (3) with the coefficients bo through bM: and only one interference-value predictor (1) for digital signals with more than three amplitude stages.
a high-pass filter (HP);
a linear equalizer (2) with the coefficients co through cL;
decision-feedback equalizer (3) with the coefficients bo through bM: and only one interference-value predictor (1) for digital signals with more than three amplitude stages.
3. A digital transmission system according to claim 2, wherein the linear and decision-feedback equalizers and the interference-value predictor utilize different coefficient setting algorithms with different setting speeds.
4. A digital transmission system according to claim 3, wherein the zero-forcing algorithm is used for the equalizers and the minimum-mean-square algorithm is used for the interference-value predictor, so that low-frequency unsteady impulsive interferences are suppressed, without cancelling the effect of the high-pass filtering upon the unsteady impulsive interference.
5. A digital signal transmission system according to claim 2, wherein only the signs of the values that are used for adaptive filter coefficient settings are used by application of the sign algorithm.
6. A digital signal transmission system according to claim 2, wherein the linear equalizer comprises:
an analog compromise equalizer (KE), with a fixed setting; and an adjustable, digital equalizer (DE) connected to an output of the compromise equalizer, whereby the number of coefficients required (co - cL
and bo - bM) for the linear equalizer (2) and the decision-feedback equalizer (2) are reduced and an information-loss-free transition from a continuous-time digital siignal (e(t)) to a discrete-time signal (ei) is realized.
an analog compromise equalizer (KE), with a fixed setting; and an adjustable, digital equalizer (DE) connected to an output of the compromise equalizer, whereby the number of coefficients required (co - cL
and bo - bM) for the linear equalizer (2) and the decision-feedback equalizer (2) are reduced and an information-loss-free transition from a continuous-time digital siignal (e(t)) to a discrete-time signal (ei) is realized.
7. A digital signal transmission system according to claim 2, wherein the detection time is established on the basis of the coefficients (cO
through cL) of the linear equalizer.
through cL) of the linear equalizer.
8. A digital signal transmission system according to claim 1, wherein only the signs of the values that are used for adaptive filter coefficient settings are used by application of the sign algorithm.
9. A digital signal transmission system according to claim 1, wherein the system is used for the transmission of 2.048 Mbit/s to local subscriber lines, to increase the field length, with simultaneous occupancy of the cables with systems of the same kind.
10. A digital signal transmission system according to claim 9, wherein all wire pairs in a bundle cable with spiral quads can be used when each spiral quad is used for the transmission of signals in one direction only.
11. A system for the simultaneous bi-directional transmission of several binary digital signals via separate wire pairs, located in a multi-pair cable, in which the signals are re-coded into quaternary signals, said system including a receiver, comprising:
means for providing quantized feedback of a received signal;
a threshold-value detector for detecting, the received signal that is subject to quantized feedback;
and an interference-value predictor with the coefficients P1 through PN, whose scanning values are derived from a difference signal between a Nyquist-distorted signal and the detected signal, so that uncorrelated interference values, which are effectively reduced for the detection process, are formed from an original colored interference value.
means for providing quantized feedback of a received signal;
a threshold-value detector for detecting, the received signal that is subject to quantized feedback;
and an interference-value predictor with the coefficients P1 through PN, whose scanning values are derived from a difference signal between a Nyquist-distorted signal and the detected signal, so that uncorrelated interference values, which are effectively reduced for the detection process, are formed from an original colored interference value.
12. A digital transmission system according to claim 11, having a receiver structure comprising:
a high-pass filter (HP):
a linear equalizer (2) with the coefficients cO through cL;
decision-feedback equalizer (3) with the coefficients bo through bM; and only one interference-value predictor (1) for digital signals with more than three amplitude stages.
a high-pass filter (HP):
a linear equalizer (2) with the coefficients cO through cL;
decision-feedback equalizer (3) with the coefficients bo through bM; and only one interference-value predictor (1) for digital signals with more than three amplitude stages.
13. A digital transmission system according to claim 12, wherein the linear and decision-feedback equalizers and the interference-value predictor utilize different coefficient setting algorithms with different setting speeds.
14. A digital transmission system according to claim 13, wherein the zero-forcing algorithm is used for the equalizers and the minimum-mean-square algorithm is used for the interference-value predictor, so that low-frequency unsteady impulsive interferences are suppressed, without cancelling the effect of the high-pass filtering upon the unsteady impulsive interference.
15. A digital signal transmission system according to claim 12, wherein only the signs of the value that are used for adaptive filter coefficient settings are used by application of the sign algorithm.
16. A digital signal transmission system according to claim 12, wherein the linear equalizer comprises:
an analog compromise equalizer (KE), with a fixed setting; and an adjustable, digital equalizer (DE) connected to an output of the compromise equalizer, whereby the number of coefficients required (cO - cL
and bo - bM) for the linear equalizer (2) and the decision-feedback equalizer (2) are reduced and an information-loss-free transition from a continuous-time digital signal (e(t)) to a discrete-time signal (ei) is realized.
an analog compromise equalizer (KE), with a fixed setting; and an adjustable, digital equalizer (DE) connected to an output of the compromise equalizer, whereby the number of coefficients required (cO - cL
and bo - bM) for the linear equalizer (2) and the decision-feedback equalizer (2) are reduced and an information-loss-free transition from a continuous-time digital signal (e(t)) to a discrete-time signal (ei) is realized.
17. A digital signal transmission system according to claim 12, wherein the detection time is established on the basis of the coefficients (cO
through cL) of the linear equalizer.
through cL) of the linear equalizer.
18. A digital signal transmission system according to claim 11, wherein only the signs of the values that are used for adaptive filter coefficient settings are used by application of the sign algorithm.
19. A digital signal transmission system according to claim 11, wherein the system is used for the transmission of 2.048 Mbit/s to local subscriber lines, to increase the field length, with simultaneous occupancy of the cables with systems of the same kind.
20. A digital signal transmission system according to claim 19, wherein all wire pairs in a bundle cable with spiral quads can be used when each spiral quad is used for the transmission of signals in one direction only.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3905695A DE3905695A1 (en) | 1989-02-24 | 1989-02-24 | DIGITAL TRANSFER SYSTEM |
| DEP3905695.3 | 1989-02-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2010763A1 true CA2010763A1 (en) | 1990-08-24 |
Family
ID=6374811
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002010763A Abandoned CA2010763A1 (en) | 1989-02-24 | 1990-02-23 | Digital signal transmission system |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0387498B1 (en) |
| CN (1) | CN1020144C (en) |
| AT (1) | ATE129840T1 (en) |
| CA (1) | CA2010763A1 (en) |
| DE (2) | DE3905695A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2697648B2 (en) * | 1994-12-26 | 1998-01-14 | 日本電気株式会社 | Decision feedback equalizer |
| US7327222B2 (en) | 2001-11-29 | 2008-02-05 | Nokia Corporation | Transmission system for transmitting data via current conducting branches |
| CN101986629B (en) * | 2010-10-25 | 2013-06-05 | 华为技术有限公司 | Method and device for estimating narrowband interference as well as receiving equipment thereof |
| CN109613882A (en) * | 2018-12-07 | 2019-04-12 | 迈智视觉(厦门)科技有限公司 | A kind of anti-interference processing method of signal terminal transmission process |
-
1989
- 1989-02-24 DE DE3905695A patent/DE3905695A1/en not_active Ceased
-
1990
- 1990-01-20 AT AT90101148T patent/ATE129840T1/en not_active IP Right Cessation
- 1990-01-20 DE DE59009827T patent/DE59009827D1/en not_active Expired - Fee Related
- 1990-01-20 EP EP90101148A patent/EP0387498B1/en not_active Expired - Lifetime
- 1990-02-23 CA CA002010763A patent/CA2010763A1/en not_active Abandoned
- 1990-02-24 CN CN90101166A patent/CN1020144C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0387498A3 (en) | 1991-11-06 |
| DE59009827D1 (en) | 1995-12-07 |
| CN1045319A (en) | 1990-09-12 |
| EP0387498A2 (en) | 1990-09-19 |
| EP0387498B1 (en) | 1995-11-02 |
| DE3905695A1 (en) | 1990-08-30 |
| ATE129840T1 (en) | 1995-11-15 |
| CN1020144C (en) | 1993-03-17 |
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