WO2001057983A1 - Procede et systeme de reduction du desequilibre capacitif dans les systemes d'emission de telecommunications - Google Patents

Procede et systeme de reduction du desequilibre capacitif dans les systemes d'emission de telecommunications Download PDF

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Publication number
WO2001057983A1
WO2001057983A1 PCT/US2001/003399 US0103399W WO0157983A1 WO 2001057983 A1 WO2001057983 A1 WO 2001057983A1 US 0103399 W US0103399 W US 0103399W WO 0157983 A1 WO0157983 A1 WO 0157983A1
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WO
WIPO (PCT)
Prior art keywords
wire
tip
transmission system
capacitive imbalance
ring
Prior art date
Application number
PCT/US2001/003399
Other languages
English (en)
Inventor
Steven Sheppard
Original Assignee
Next Level Communications, L.P.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Next Level Communications, L.P. filed Critical Next Level Communications, L.P.
Priority to AU2001233245A priority Critical patent/AU2001233245A1/en
Publication of WO2001057983A1 publication Critical patent/WO2001057983A1/fr

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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
    • H04L25/0264—Arrangements for coupling to transmission lines
    • H04L25/0272—Arrangements for coupling to multiple lines, e.g. for differential transmission
    • H04L25/0274—Arrangements for ensuring balanced coupling
    • 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
    • H04L25/10—Compensating for variations in line balance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M3/00—Automatic or semi-automatic exchanges
    • H04M3/18—Automatic or semi-automatic exchanges with means for reducing interference or noise; with means for reducing effects due to line faults with means for protecting lines
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M3/00—Automatic or semi-automatic exchanges
    • H04M3/22—Arrangements for supervision, monitoring or testing
    • H04M3/2209—Arrangements for supervision, monitoring or testing for lines also used for data transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q1/00—Details of selecting apparatus or arrangements
    • H04Q1/02—Constructional details
    • H04Q1/028—Subscriber network interface devices
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q1/00—Details of selecting apparatus or arrangements
    • H04Q1/02—Constructional details
    • H04Q1/14—Distribution frames

Definitions

  • the telephone system infrastructure that has been in place for many years. and specifically the local loop portion of the telephone plant that is used to connect subscribers * telephones to the telephone central office, can be used to provide high speed data services in addition to traditional analog voice services.
  • the telephone local loop typically comprises a portion of twisted wire pair cable that extends from a central office, a remote terminal, a remote access interface, a curbside terminal, or some other cable interface point, to a residence, an office building, an office complex, or some other subscriber location. When such a configuration is used for data transmission, data signals travel to subscriber locations over a twisted wire pair transmission path.
  • a twisted wire pair typically consists of two twisted wires, referred to in the industry as the tip wire and the ring wire. Twisted wire pair is used as a transmission medium because it supports differential transmission, a mode of communication in which information is transmitted as the difference between the currents in the tip and ring wires.
  • differential transmission is that noise or interference that couples to both wires of the twisted wire pair is not received as noise at the receiving end of the system, so long as the noise is of equal magnitude on both wires. This phenomenon is known as common mode rejection.
  • a system with a high common mode rejection ratio is able to reject noise signals that appear on both wires
  • radio frequency or other interfe ⁇ ng signals will not have a significant detrimental effect on communication if the interfe ⁇ ng signals couple equally to both wires, and if the receiving system has a high common mode rejection ratio.
  • Certain conditions can frequently lower a system's common mode rejection ratio by allowing noise and interference to be converted from a common mode signal to a differential mode signal.
  • a differential mode signal is one that has different magnitudes on the tip and ⁇ ng wires.
  • Common mode to differential mode conversion can a ⁇ se from physical imbalances between the wires in the twisted wire pair, imbalances in components attached to the wires, or other imbalances that give the tip and ⁇ ng wires different impedances with respect to a common reference such as ground.
  • One such imbalance is longitudinal capacitive imbalance, which is the difference in the capacitance between the tip wire and ground, on the one hand, and the capacitance between the ring wire and ground, on the other hand.
  • DSL Digital Subsc ⁇ ber Line
  • common mode to differential mode conversion can severely limit the achievable data rates, which may limit the types of services that can be provided over twisted wire pairs. As an example, it may not be possible to provide video services over a particular twisted wire pair transmission path because the noise that appears on the line. due to common mode to differential mode conversion, limits the data rate to one that is too low to support the transport of video signals.
  • An object of the invention is to provide methods and systems for avoiding or reducing the effects of excessive longitudinal capacitive imbalance between the tip and ring wires of a twisted wire pair transmission path, and for minimizing the conversion of common mode noise signals to differential mode noise signals in transmission systems comprised of a twisted wire pair transmission path.
  • the present invention teaches that common mode to differential mode conversion can be avoided, and transmission errors can be minimized. if a signal is transmitted using a lower po ⁇ ion of the frequency spectrum - less than abou t
  • the present invention encompasses transmitting signals carrying data at rates approaching and exceeding 25 Mb/s using high density transmission modulation formats such as 16-QAM (Quadrature Amplitude Modulation), constrained to a spectrum not exceeding about 5 MHz. as opposed to using lower density transmission modulation formats such as QPSK. (Quadrature Phase Shift Keying) in a spectral range exceeding 5 MHz.
  • high density transmission modulation formats such as 16-QAM (Quadrature Amplitude Modulation)
  • QPSK Quadrature Phase Shift Keying
  • the present invention comprises a method for avoiding the effects of excessive longitudinal capacitive imbalance between the tip and ring wires of a twisted wire pair transmission path, including the step of selecting a portion of frequency spectrum with an upper limit of about 5 MHz, or alternatively about 7 MHz, for the transmission of signals over the twisted wire pair transmission path.
  • a further aspect of the invention includes a method for achieving a target bit rate while avoiding the effects of excessive longitudinal capacitive imbalance between the tip and ring wires of a twisted wire pair transmission path, comprising the step of selecting an increased modulation density format or baud rate for transmitting signals, in preference to selecting a higher portion of frequency spectrum for transmitting the signals.
  • the present invention comprises a method for avoiding or reducing the effects of excessive longitudinal capacitive imbalance between the tip and ring wires of a twisted wire pair transmission path that employs lightning protectors, including the step of using either bias-independent lightning protectors, or lightning protectors with minimal bias-dependent capacitance.
  • the invention also encompasses twisted wire pair transmission systems that are comp ⁇ sed of bias-independent lightnine protectors or lightning protectors with mimmal bias-dependent capacitance, including systems in which such lightning protectors are comp ⁇ sed of gas tube protectors or networks of solid state and gas tube protectors
  • the present invention further comp ⁇ ses a method for avoiding or reducing the effects of excessive longitudinal capacitive imbalance between the tip and ⁇ ng wires of a twisted wire pair transmission path that also employs a cable connecting a demarcation point and a telecommunications device inside a subsc ⁇ ber location, including the step of avoiding shielding the cable (1 e . using an unshielded cable), or, if the cable is shielded.
  • the invention also encompasses transmission s stems that are comp ⁇ sed of a cable connecting a demarcation point and a telecommumcations device inside a subsc ⁇ ber location, wherein the cable is comp ⁇ sed of tip and ⁇ ng wires, and wherein the cable is either unshielded, or the cable shield is not grounded
  • the present invention comp ⁇ ses a method for avoiding or reducing the effects of excessive longitudinal capacitive imbalance between the tip and ⁇ ng wires of a twisted wire pair transmission path that includes a cross-connection device comp ⁇ sing the steps of cutting the tip and ⁇ ng wires inside the cross-connection dev ice to approximately equal lengths, twisting the tip and ⁇ ng wires into a twisted wire pair inside the cross-connection device, or both twisting the tip and ⁇ ng wires and cutting them to approximately equal lengths within the cross-connection device
  • the invention also encompasses transmission systems that are comp ⁇ sed of a cross-connection device, wherein the cross-connection device is comp ⁇ sed
  • FIG. 1 depicts a telecommunications transmission system comprising a central office, a transmission path, and a subscriber location, in which the methods of the present invention may be used, and into which the systems of the present invention may be incorporated.
  • FIG. 2 is a flow chart depicting a preferred embodiment of a method of the present invention for maintaining a target bit rate while avoiding the effects of excessive longitudinal capacitive imbalance.
  • FIG. 3 depicts an embodiment of a telecommunications transmission system of the present invention, comprising at least one lightning protector.
  • FIG. 4 depicts an embodiment of a telecommunications transmission sv stem of the present invention, comprising a demarcation point, a cable, and a telecommunications device.
  • FIG. 5 depicts an embodiment of a telecommunications transmission system of the present invention, comprising a cross-connection device.
  • FIG. 1 illustrates a telecommunications transmission system in which the methods of the present invention may be used, and into which the systems of the present invention may be incorporated.
  • the system supports the transmission and reception of signals.
  • the transmitted signals may comprise a telephone signal, a data signal, an Internet signal, a video signal, an audio signal, a facsimile signal, or any other type of signal, or combinations thereof.
  • the transmission system includes a central office 1 0. a transmission path 130, and a subscriber location 140.
  • the transmission system depicted in FIG. 1 is connected by a network transmission path 1 15 to a communications network 1 10.
  • the network transmission path 115 may be comprised of fiber optic or coaxial cable.
  • the communications network 110 may be comprised of a public switched telephone network, a packet-switched network, a public network, a private network, a data network, or any other type of network (or combination thereof) used in whole or in part to provide telecommunications services, as known to persons of skill in the art.
  • the transmission system is not connected by a network transmission path to a communications network.
  • the central office 120 depicted in FIG. 1 may be comprised of a switch or other components for routing signals, as known to persons of skill in the art.
  • the central office 120 is connected to a transmission path 130 by means known to persons of skill in the art.
  • the transmission path 130 which may be used to transport one or more signals, is comprised of a twisted wire pair or other differential transmission medium.
  • the transmission path 130 is comprised of a tip wire 131 and a ring wire 132.
  • the tip wire 131 and the ring wire 132 are used to carry or transport signals between the central office 120 and a subscriber location 140.
  • the tip wire 131 and the ring wire 132 may be comprised of copper wire or other mediums used for carrying or transporting signals, as known to persons of skill in the art.
  • the transmission system depicted in FIG. 1 can support differential transmission using tip wire 131 and ⁇ ng wire 132 through the use of currents, which, when generated at one end of the twisted wire pair, result in the transmission of signals across transmission path 130.
  • a differential signal transmitted from central office 120 results in currents on tip wire 131 and ⁇ ng wire 132, which cause a wave to propagate on transmission path 130. and which can be received at subscriber location 140.
  • a wave containing different information can be simultaneously transmitted from subsc ⁇ ber location 140 and received at central office 120.
  • the system depicted in FIG. 1 may comp ⁇ se means for transmitting signals in digital formats, as known to persons of skill in the art.
  • the system may, for example, encompass means for transmitting signals in QAM format, including 4-QAM. 8-QAM. 16- QAM. 64-QAM, 128-QAM. or 256-QAM, with an associated bit rate, as known to persons of skill in the art.
  • the QAM system may transmit a plurality of signal streams, wherein two or more of the streams have different modulation densities and bit rates.
  • the QAM system can transmit one or more signal streams, using only one modulation density and bit rate.
  • the bit rate of the QAM transmission may remain constant, or it may vary.
  • the system depicted in FIG 1 may also comp ⁇ se means for transmitting signals in DSL format, as known to persons of skill in the art.
  • Signals may be transmitted in Asymmet ⁇ c Digital Subsc ⁇ ber Line (ADSL) format, Very High Speed Digital Subsc ⁇ ber Line (VDSL) format, or in some other DSL format, as known to persons of skill in the art
  • a DSL system may transmit a plurality of signal streams, wherein at least two streams have different DSL formats and associated bit rates
  • a DSL system may transmit one or more signal streams using only one DSL format with its associated bit rate The bit rate of the DSL transmission may remain constant, or it may vary
  • the system depicted in FIG. 1 may comp ⁇ se a
  • QPSK or a Vestigial Sideband (VSB) system comp ⁇ sing means for transmitting signals in QPSK or VSB format, as known to persons of skill in the art.
  • VSB Vestigial Sideband
  • the system depicted in FIG 1 may use other systems, facilities, and techniques, as known to persons of skill in the art, for transmitting signals between a central office 120 and a subsc ⁇ ber location 140
  • the present invention comp ⁇ ses systems and methods for avoiding the effects of excessive longitudinal capacitive imbalance between the tip and ⁇ ng wires of transmission systems that transmit signals using differential transmission
  • a preferred embodiment of the present invention is a method of avoiding the effects of excessive longitudinal capacitive imbalance between the tip wire 131 and the ⁇ ng wire 132. comp ⁇ sing the step of selecting an upper limit, for the portion of the frequency spectrum used to transmit signals over the transmission path 130. of about 5 MHz. In an alternative preferred embodiment, the upper limit is selected to be about 7 MHz. Signals may be transmitted over transmission path 130 in the system depicted m FIG. 1 at a target bit rate, using a selected modulation density format and a target portion of the frequency spectrum
  • a preferred embodiment of the present invention is a method for achieving or maintaining the target bit rate, while avoiding the effects ot excessive longitudinal capacitive imbalance between the tip wire 131 and the ⁇ ng wire
  • Signals may also be transmitted over transmission path 130 in the system depicted in FIG 1 at a target bit rate, using a selected baud rate and a target portion of the frequency spectrum
  • a preferred embodiment of the invention is a method for achieving or maintaining the target bit rate, while avoiding the effects of excessive longitudinal capacitive imbalance between the tip wire 131 and the ⁇ ng wire 132. by increasing the baud rate of the transmitted signals in preference to selecting a higher portion of the frequency spectrum to transmit the signals
  • step 201 comprises the identification of potential combinations of modulation density and baud rate that can achieve the target bit rate. For example, if the target bit rate is 25 92 Mb/s, potential combinations of modulation density and bau ⁇ rate that are capable of achieving that target bit rate might be identified as either the combination of 32 QAM and 5 184 Mbaud. or 16 QAM and 6 48 Mbaud.
  • one or more of the candidate combinations of modulation density and baud rate are selected, based on the ability of the combinations to operate at frequencies below about 5 MHz.
  • candidate combinations are selected based on the ability to operate at frequencies below about 7 MHz. The selection of candidate combinations that can operate at frequencies below ei t her
  • 5 or 7 MHz is based on the discovery that longitudinal capacitive imbalance increases materially above those frequencies, and that, as a consequence, signal transmission typically degrades significantly above those frequencies.
  • the target bit rate is 25.92 MB/s.
  • the candidate combinations of modulation density and baud rate are either 32 QAM and 5.184 Mbaud. or 16 QAM and 6.48 Mbaud.
  • the former combination - 32 QAM and 5.184 Mbaud - is selected in step 202. because of its ability to operate at a frequency of below about 5 MHz.
  • a final combination of modulation density and baud rate is selected from the combinations that were identified in step 202.
  • This selection may ⁇ be made based on a number of factors, such as the desire to minimize overlap with other transmission frequencies being utilized either on the same or on adjacent transmission paths.
  • the selection in step 203 is made by choosing the combination with the lowest upper frequency limit, in preference to combinations with lower modulation densities but higher upper frequency limits.
  • step 202 may be omitted, so that no combination of modulation density and baud rate is eliminated from consideration based on a predetermined upper frequency limit.
  • FIG. 3 depicts an embodiment of a telecommunications transmission system of the present invention, comprising a Network Interface Device (NID) 135 at subscriber location 140.
  • NID 135 provides for high-voltage protection and serves as the interface between the transmission path 130 and the telecommunications system wiring or cabling inside subscriber location 140.
  • Demarcation point 138 is typically located at a point in or near subsc ⁇ ber location 140. as known to persons of skill in the art.
  • NID 135 comp ⁇ ses at least one lightning protector 139.
  • An embodiment of the method of a oiding the effects of excessive longitudinal capacitive imbalance between the tip wire 1 1 and the ⁇ ng wire 132 comprises the step of using one or more bias-independent lightning protectors 139
  • one or more lightning protectors 139 with minimal bias-dependent capacitance are used.
  • the bias- dependent capacitance of at least one lightning protector 139 is less than or equal to +1/2 picofarad.
  • At least one lightning protector 139 is comprised of a gas tube protector, a solid state protector, or a network of gas tube and solid state protectors. In yet other prefened embodiments, at least one lightning protector 139 is comp ⁇ sed of other mate ⁇ als capable of absorbing the effects of lightning, as known to persons of skill in the art.
  • FIG. 4 depicts an embodiment of a telecommunications transmission s stem of the present invention, comprising a telecommunications device 146 inside subscriber location 140, and a cable 144 connecting NID 135 and the telecommunications device 146
  • the transmission path 130 is connected to cable 144 in the subscriber location 140 at the demarcation point 138.
  • the transmission path 130 may be connected to cable 144 at a place other than the demarcation point 138.
  • the telecommunications device 146 shown in FIG. 4 may comprise a telephone, a computer, a video device, an audio device, a facsimile machine, a VCR, a set-top box. or another device for receiving signals, as known to persons of skill in the art.
  • Cable 144 is comprised of materials known to persons of skill in the art.
  • cable 144 comprises tip and ring wires.
  • cable 144 may comprise a coaxial cable, or another form of cable that uses differential transmission. Cable 144 may also comprise a shield, and may or may not be grounded.
  • the present invention teaches the use of an unshielded cable 144 in the subscriber location 140 in order to avoid the effects of excessive longitudinal capacitive imbalance between the tip and ring wires in cable 144.
  • the present invention also teaches a method comprised of the step of avoiding shielding the cable 144.
  • the present invention teaches that when cable 144 is shielded, the cable shielding is not to be grounded, in order to avoid excessive longitudinal capacitive imbalance between the tip and ⁇ ng wires in cable 144
  • the present invention also teaches a method compnsed of the step of avoiding grounding the cable shield of cable 144 The effects of excessive capacitive imbalance may also be reduced or avoided by ensunng that the tip and ⁇ ng wires are cut to the same length and/or twisted around each other FIG.
  • FIG. 5 depicts an embodiment of a telecommunications transmission system of the present invention, comprising a cross-connection device 160.
  • the cross-connection device 160 provides a means for configuring a telecommumcations network and dist ⁇ buting signals from a central office 120, which serves multiple subscnbers, to a single subsc ⁇ ber location 140.
  • the cross- connection device 160 also provides an efficient means for changing facility configurations and subsc ⁇ ber services.
  • a cross-connection device 160 may be external to subscriber location 140 Alternatively, a cross-connection device may be located inside a subscnber location (not depicted)
  • the cross-connection device 160 compnses a tip wire 131 and a ⁇ ng wire 132.
  • the tip wire 131 and the ring wire 132 within the cross-connection device 160 are cut so that they are approximately of equal length.
  • the difference in length between tip wire 131 and nng wire 132 is less than Vi inch.
  • tip wire 131 and nng wire 132 are twisted around each other so as to create a twisted wire pair within cross-connection device 160.
  • the present invention also teaches the methods comp ⁇ sing the steps of cutting tip wire 131 and nng wire 132 within cross- connection device 160 to approximately the same length, twisting tip wire 131 and ring wire 132 into a twisted wire pair, or both.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

La présente invention concerne des procédés et systèmes conçus pour atténuer ou éviter les effets du déséquilibre capacitif longitudinal affectant les systèmes d'émission émettant des signaux par émission différentielle telle que les systèmes d'émission comportant un chemin d'émission (130) à paire torsadée. Les procédés et systèmes de la présente invention optimisent la largeur de bande d'émission utilisée, y-compris notamment en choisissant un format de densité de modulation accrue ou un débit en bauds accru (201) de préférence à la sélection de la partie supérieure d'un spectre de fréquences (202).
PCT/US2001/003399 2000-02-03 2001-02-02 Procede et systeme de reduction du desequilibre capacitif dans les systemes d'emission de telecommunications WO2001057983A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001233245A AU2001233245A1 (en) 2000-02-03 2001-02-02 Method and system for reducing capacitive imbalance in telecommunications transmission systems

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US49666600A 2000-02-03 2000-02-03
US09/496,666 2000-02-03

Publications (1)

Publication Number Publication Date
WO2001057983A1 true WO2001057983A1 (fr) 2001-08-09

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Application Number Title Priority Date Filing Date
PCT/US2001/003399 WO2001057983A1 (fr) 2000-02-03 2001-02-02 Procede et systeme de reduction du desequilibre capacitif dans les systemes d'emission de telecommunications

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AU (1) AU2001233245A1 (fr)
WO (1) WO2001057983A1 (fr)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5539321A (en) * 1992-09-11 1996-07-23 Microtest, Inc. Apparatus for measuring the crosstalk in a cable
US6144399A (en) * 1999-03-25 2000-11-07 Mediaone Group, Inc. Passive system used to merge telephone and broadband signals onto one coaxial cable

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5539321A (en) * 1992-09-11 1996-07-23 Microtest, Inc. Apparatus for measuring the crosstalk in a cable
US6144399A (en) * 1999-03-25 2000-11-07 Mediaone Group, Inc. Passive system used to merge telephone and broadband signals onto one coaxial cable

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