WO2000054423A1 - Procede d'etablissement et d'adaptation de parametres de liaison de communication dans une transmission xdsl - Google Patents

Procede d'etablissement et d'adaptation de parametres de liaison de communication dans une transmission xdsl Download PDF

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Publication number
WO2000054423A1
WO2000054423A1 PCT/US2000/006020 US0006020W WO0054423A1 WO 2000054423 A1 WO2000054423 A1 WO 2000054423A1 US 0006020 W US0006020 W US 0006020W WO 0054423 A1 WO0054423 A1 WO 0054423A1
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WO
WIPO (PCT)
Prior art keywords
xtu
rate
symbol rate
symbol
modulation density
Prior art date
Application number
PCT/US2000/006020
Other languages
English (en)
Inventor
Jamie Esliger
Sabit Say
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 AU35173/00A priority Critical patent/AU3517300A/en
Publication of WO2000054423A1 publication Critical patent/WO2000054423A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
    • 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
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0044—Arrangements for allocating sub-channels of the transmission path allocation of payload
    • 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
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • 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
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier
    • 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
    • H04L2025/03592—Adaptation methods
    • H04L2025/03598—Algorithms
    • H04L2025/03611—Iterative algorithms
    • H04L2025/03656—Initialisation
    • H04L2025/03668—Initialisation to the value at the end of a previous adaptation period

Definitions

  • the present invention relates to methods for establishing and adapting communication link parameters, including symbol rate and transmission modulation density, in xDSL transmission systems.
  • Basic telecommunications services such as analog telephony, or Plain Old Telephony Service (POTS)
  • POTS Plain Old Telephony Service
  • high speed data services such as digital video and high speed Internet access.
  • local exchange carriers and other telecommunications service providers are working to find cost-effective ways of meeting the growing demand for those services .
  • Local loops are still largely comprised of twisted wire pair links.
  • Such links which were originally installed to provide narrowband POTS, usually employ copper wire as the electrical transmission medium.
  • Some twisted wire pair links have either been upgraded or replaced by the installation of fiber optic links, but the majority of local loop twisted wire pair links have been in place for many years.
  • Telecommunications service providers are currently exploring a number of technologies for providing high speed data services, including wireless technology, Hybrid Fiber Coax (HFC), Fiber-To-The-Curb (FTTC), Fiber-To-The- Home (FTTH) , Asymmetric Digital Subscriber Line (ADSL) , Symmetric Digital Subscriber Line (SDSL), High-speed Digital Subscriber Line (HDSL) , and Very-high-speed Digital Subscriber Line (VDSL) technology.
  • HFC Hybrid Fiber Coax
  • FTTC Fiber-To-The-Curb
  • FTTH Fiber-To-The- Home
  • ADSL Symmetric Digital Subscriber Line
  • SDSL Symmetric Digital Subscriber Line
  • HDSL High-speed Digital Subscriber Line
  • VDSL Very-high-speed Digital Subscriber Line
  • optical fiber connects the central office to a cross-connection device, and the last portion of the local loop - from the cross-connection device to the subscriber premise - is comprised of a twisted wire pair link.
  • the last portion of the local loop can also be comprised of other types of transmission facilities, as known to those of skill in the art.
  • xDSL refers to ADSL, SDSL, HDSL, VDSL, and other digital subscriber line technologies known to those of skill in the art.
  • xDSL technology enables telephone companies to provide high speed data services over local loops comprised in whole or in part of twisted wire pair links (or other transmission facilities), as in FTTN networks.
  • the transmission facility that connects a subscriber residence to the rest of the telecommunications network is terminated by a subscriber-side xDSL termination unit (SS-XTU) on the subscriber side, and a line-side xDSL termination unit (LS- XTU) on the line or central office side.
  • the LS-XTU receives signals from the upstream portion of the telecommunications network, and converts the signals from the format employed by the telecommunications network into xDSL format.
  • the SS-XTU receives the xDSL-modulated signals, demodulates them, and passes them on to various telecommunications devices at the subscriber residence.
  • the SS-XTU also transmits information in the upstream direction, where it is received by the LS-XTU, reformatted, and passed on to the telecommunications network.
  • the signal being transmitted is generally distorted by channel impairments, which results in intersymbol interference (ISI).
  • ISI intersymbol interference
  • a general means to reduce the error rates resulting from ISI is to use an equalizer.
  • the SS-XTU and the LS-XTU contain an equalizer designed to compensate for or reduce ISI.
  • One method of equalization is based on the use of previously detected symbols to suppress ISI in the present symbol being detected.
  • An equalizer that implements such a method is called a decision feedback equalizer (DFE) .
  • DFE decision feedback equalizer
  • DFEs contain both feedback and feed-forward filters.
  • the filter coefficients are commonly adjusted according to the mean-square error (MSE) criterion, which seeks to minimize the mean-square value of the error between the information symbol being transmitted and the estimate of that symbol at the output of the equalizer.
  • MSE mean-square error
  • the basic idea is to move the set of equalizer coefficients closer to the optimum set corresponding to the minimum MSE.
  • Other criteria such as peak distortion can be used to optimize filter coefficients.
  • Such criteria, as well as other types of equalizers and equalization methods, are known to those of skill in the art.
  • a typical approach in establishing communication between a LS-XTU and a SS-XTU is to transmit a signal from the LS-XTU to the SS-XTU at a predetermined symbol rate, and to attempt to determine a solution - i.e., to converge the equalizer coefficients on an optimum solution - for the transmitted signal.
  • a solution - i.e., to converge the equalizer coefficients on an optimum solution - for the transmitted signal.
  • the symbol rate is high - as it needs to be for xDSL transmission - such "blind" acquisition may cause the equalizer solution in the SS-XTU to diverge, especially if the transmission facility between the LS-XTU and SS-XTU contains bridged taps.
  • a telecommunications company Before a telecommunications company can provide xDSL- based high speed data services to a subscriber, it needs to select a symbol rate and modulation density to use for communication between xDSL termination units .
  • Telecommunications companies are likely to provide various high speed data services, such as digital video, Internet access, ethernet service, and telephone service, which differ in terms of bandwidth requirements.
  • the territories of telecommunication companies may also differ in terms of the length and quality of the transmission facilities between the line-side and subscriber-side termination units.
  • telecommunications companies need to maintain their ability to provide basic telecommunications services, such as POTS, Integrated Services Digital Network (ISDN), and Universal Digital Channel (UDC) service, which constitute primary sources of revenue, over the same facilities used to provide newer xDSL-based services . Consequently, a method for determining how to provide xDSL service should also specify parameters, such as an upstream and a downstream frequency range, that avoid or at least reduce the risk of interference with basic telecommunications services that are being provided either on the same link or on adjacent links.
  • basic telecommunications services such as POTS, Integrated Services Digital Network (ISDN), and Universal Digital Channel (UDC) service
  • the present invention provides a method for establishing and adapting communication link parameters in xDSL transmission systems.
  • the overall method includes the steps of establishing communication between xDSL termination units, and determining a maximum transmission modulation density that can be used for each of a plurality of predetermined symbol rates.
  • the invention provides additional, specific methods for performing those two steps: a symbol rate stepping method for establishing communication between xDSL termination units, and a rate training method for determining a maximum transmission modulation density that can be used for each of a plurality of predetermined symbol rates.
  • the symbol rate stepping method and the rate training method are used in the context of the overall method for establishing and adapting communication link parameters in xDSL transmission systems.
  • the symbol rate stepping method and the rate training method can be used independently.
  • the symbol rate stepping method is directed to an improved method of establishing communication between xDSL termination units at a given symbol rate. Rather than transmitting a signal at the final, desired symbol rate, and attempting to determine an equalizer solution "blindly" on that signal at the receiving termination unit, the present invention transmits a signal at a lower initial symbol rate, and iteratively steps up that rate by a symbol rate increment until the final, desired symbol rate is reached.
  • the equalizer solution that is determined for the signal at that symbol rate is held and used as the starting point for determining an equalizer solution for the signal at the next, increased symbol rate.
  • the symbol rate stepping method of the present invention which is directed to establishing communication between the LS-XTU and the SS-XTU at a desired symbol rate, comprises the steps of (a) setting an initial symbol rate equal to a first fraction of the desired symbol rate; (b) setting a symbol rate increment equal to a second fraction of the desired symbol rate; (c) initially setting a variable communication symbol rate equal to the initial symbol rate; (d) transmitting a signal from the LS-XTU to the SS-XTU at the variable communication symbol rate; (e) acquiring the signal transmitted at the variable communication symbol rate at the SS-XTU by determining a tentative equalizer solution for the signal transmitted at the variable communication symbol rate; (f) increasing the variable communication symbol rate by the symbol rate increment; (g) transmitting a signal from the LS-XTU to
  • the invention contemplates that the symbol rate stepping method can be used to establish communication between the LS-XTU and the SS-XTU in either the upstream direction, the downstream direction, or both.
  • the rate training method of the present invention is directed to determining, at each of a number of predetermined symbol rates, a maximum modulation density that can be used for communication between xDSL termination units. The maximum modulation density that is determined for each symbol rate can then be used to compute a maximum bit rate achievable at each symbol rate.
  • That information - the maximum modulation density and the maximum bit rate achievable at each symbol rate - can then be used to select an optimal combination of symbol rate and transmission modulation density capable of delivering a set of desired high speed data services over a particular local loop, as described below in the method for establishing and adapting link parameters.
  • the first step in the rate training method is to establish communication at a predetermined symbol rate between the xDSL transmission and reception units. This step can be accomplished using the symbol rate stepping method described previously. In a preferred embodiment, the signal-to-noise ratio at that predetermined symbol rate is then measured and used to determine the maximum transmission modulation density that can be used at the predetermined symbol rate. The maximum transmission modulation density and the predetermined symbol rate can then be used to compute the maximum bit rate achievable for the predetermined symbol rate. It is also possible to determine the maximum transmission modulation density and the maximum achievable bit rate for a number of predetermined symbol rates .
  • the rate training method can be executed upon the occurrence of a number of events, such as when the telecommunications system comprising the xDSL transmission and reception units is initialized, when the telecommunications system software is upgraded, or when xDSL transmission and reception units are power cycled.
  • a number of events such as when the telecommunications system comprising the xDSL transmission and reception units is initialized, when the telecommunications system software is upgraded, or when xDSL transmission and reception units are power cycled.
  • the maximum transmission modulation density and bit rate achievable for each predetermined symbol rate - and ultimately the optimal combination of symbol rate and transmission modulation density capable of delivering a desired set of high speed data services over a given local loop - can be determined every time a specified event occurs .
  • the execution of the rate training method upon the occurrence of a particular event potentially results in the selection of a different optimal symbol rate and transmission modulation density every time such an event occurs .
  • the rate training method of the present invention which is directed to determining a maximum transmission modulation density achievable for communicating between the LS-XTU and the SS-XTU at a selected symbol rate, comprises the steps of establishing communication between the LS-XTU and the SS-XTU using the selected symbol rate and an initial transmission modulation density; measuring a signal-to-noise ratio from the LS-XTU to the SS-XTU; and, responsive to the signal-to-noise ratio measurement, determining a maximum transmission modulation density for use between the LS-XTU and the SS-XTU at the selected symbol rate.
  • a maximum bit rate achievable between the LS-XTU and the SS-XTU can be computed for the selected symbol rate, responsive to the maximum transmission modulation density.
  • the invention contemplates that the rate training method can be used to determine a maximum transmission modulation density and a maximum bit rate achievable for communicating between the LS-XTU and the SS-XTU for a plurality of selected symbol rates, and in either the upstream direction, the downstream direction, or both.
  • the method for establishing and adapting link parameters of the present invention enables xDSL transmission and reception units to establish and adapt link parameters in a way that makes the delivery of both traditional telecommunications services and high speed data services possible.
  • the first step in the method for establishing and adapting link parameters is to select a downstream (LS-XTU to SS-XTU) spectral allocation scheme and an upstream (SS- XTU to LS-XTU) spectral allocation scheme. This may be accomplished by placing the upstream xDSL frequency range above the frequencies used by other telecommunications services on the link, and the downstream xDSL frequency range above the upstream xDSL frequency range. In addition, the upstream and downstream xDSL frequency ranges may be placed so as to minimize overlap with the frequency ranges of other telecommunication services being utilized on adjacent links.
  • the next step in the method for establishing and adapting link parameters is to determine the maximum transmission modulation density and corresponding maximum bit rate achievable for each of a plurality of preselected symbol rates. This step may be performed by using the rate training method described previously.
  • an optimal symbol rate and transmission modulation density are selected, based on the maximum transmission modulation density and maximum achievable bit rate for each preselected symbol rate.
  • the selection of an optimal symbol rate and transmission modulation density may be based on a number of factors, including the bit rate necessary to deliver a desired set of high speed data services, and various characteristics of the deployment environment of the local loop, such as the frequencies at which impulse noise and RF ingress are likely to occur.
  • the deployment characteristics of local loops are likely to vary by location and can be determined empirically. Because of the variance in service bit-rate requirements and deployment parameters, the optimal transmission modulation density chosen for the optimal symbol rate may be less than the maximum transmission modulation density capable of being used at the optimal symbol rate.
  • the method for establishing and adapting communication parameters between the LS-XTU and the SS-XTU comprises the steps of (a) determining a spectral allocation scheme by selecting an upstream frequency range for communication from the SS-XTU to the LS-XTU having a lower limit greater than the upper limit of frequency ranges utilized by pre-designated telecommunications services on the transmission facility, and selecting a downstream frequency range for communication from the LS-XTU to the SS-XTU having a lower limit greater than the upper limit of the upstream frequency range; (b) for a each of a plurality of preselected downstream symbol rates within the downstream frequency range, determining a maximum transmission modulation density and a corresponding maximum bit rate achievable; (c) responsive to the maximum transmission modulation density and the corresponding maximum bit rate achievable for each of the plurality of preselected downstream symbol rates, selecting a downstream symbol rate from the pres
  • the method for establishing and adapting link parameters may be further comprised of the steps of retrieving a set of deployment parameters for the transmission facility, as well as a service bit rate requirement for the transmission facility; and selecting a symbol rate and transmission modulation density in response to the set of deployment parameters and the service bit rate requirement.
  • the method for establishing and adapting link parameters also contemplates determining an optimum symbol rate and transmission modulation density capable of achieving the bit rate requirement while satisfying the set of deployment parameters, and selecting the optimum symbol rate and transmission modulation density as the symbol rate and transmission modulation density to use between a LS-XTU and a SS-XTU.
  • the invention contemplates that the method for establishing and adapting link parameters can be used to set and adapt communication parameters between a LS-XTU and a SS-XTU in either the upstream direction, the downstream direction, or both.
  • test set apparatus is used to simulate an xDSL termination unit at a subscriber premise and to verify the line performance of a given twisted wire pair link or other transmission facility without the need to enter a subscriber' s premises or to modify an actual xDSL termination unit.
  • FIG. 1 illustrates a Fiber-To-The-Neighborhood network in which the last portion of the local loop is comprised of a twisted wire pair link;
  • FIG. 2 provides a flow chart depicting a preferred embodiment of the symbol rate stepping method of the present invention
  • FIG. 3 provides a flow chart depicting a preferred embodiment of the rate training method of the present invention
  • FIG. 4A provides a table illustrating an example of minimum signal-to-noise ratios required to use specific transmission modulation densities
  • FIG. 4B provides a table illustrating an example of the data stored as a result of the execution of the rate training method of the present invention
  • FIG. 5 provides a flow chart depicting a preferred embodiment of the method for establishing and adapting link parameters of the present invention.
  • FIG. 6 illustrates a Fiber-To-The-Neighborhood network with a test set apparatus connected to the subscriber residence .
  • FIG. 1 illustrates a telecommunications local loop configuration in which the methods of the present invention may be utilized.
  • the local loop depicted in FIG. 1 connects various devices in the residence 190, such as computer 193, telephone 194, and television (TV) 199, to the Public Switched Telecommunications Network (PSTN) 100.
  • PSTN Public Switched Telecommunications Network
  • the local loop may also connect the devices in the residence 190 to an Asynchronous Transfer Mode (ATM) network 110, or to other private or non-switched public networks.
  • ATM Asynchronous Transfer Mode
  • the connection of the local loop to PSTN 100, ATM network 110, or other private or non-switched public networks occurs at a Broadband Digital Terminal (BDT) 130 at the central office.
  • BDT Broadband Digital Terminal
  • LS-XTU 340 is connected to BDT 130 via optical fiber 160.
  • LS-XTU 340 is located within the local loop.
  • LS-XTU 340 is located within the telephone company central office.
  • digital signals in a format that is similar to the Synchronous Digital Hierarchy (SDH) format may be transmitted to and from each LS-XTU 340 over optical fiber 160 at a rate of 155 Mb/s.
  • Optical fiber 160 may be a single-mode fiber and a dual wavelength transmission scheme may be used to communicate between LS-XTU 340 and BDT 130.
  • a single wavelength scheme may alternatively be used, in which low reflectivity components are used to permit transmission and reception on one fiber.
  • LS-XTU 340 is comprised of an xDSL modem 350, which provides for the transmission of high speed data over twisted wire pair drop cable 180 to and from residence 190.
  • the drop cable can comprise another type of transmission facility, as known to those of skill in the art.
  • xDSL refers to twisted wire pair digital subscriber loop transmission techniques, such as Asymmetric Digital Subscriber Line (ADSL) ,
  • SDSL Symmetric Digital Subscriber Line
  • HDSL High-speed Digital Subscriber Line
  • VDSL Very-high-speed Digital Subscriber Line
  • LS-XTU 340 receives signals from the upstream portion of the telecommunications network over optical fiber 160, converts those signals into xDSL format, and uses xDSL modem 350 to transmit the converted signals to the residence 190 via twisted wire pair drop cable i ⁇ O.
  • NID 360 is located on the side of the residence 190, at what is known in the industry as the network demarcation point. At a minimum, NID 360 provides lightning protection, as well as the ability to troubleshoot the network by allowing connection of a telephone or other test apparatus to the twisted wire pair drop cable 180 to determine if wiring problems exist on inside twisted wire pairs 181 or on inside coaxial cable 205. In an alternative configuration in which narrowband telephony signals are combined with the signals transmitted by xDSL modem 350 over twisted wire pair drop cable 180, NID 360 is also used to separate the narrowband telephony signals from the xDSL signals. In such a configuration, a telephone 194 is connected directly to NID 360 by inside twisted wire pair 181. In the system shown in FIG. 1, the signals received at
  • NID 360 are sent to SS-XTU 200 over inside twisted wire pair 181.
  • the signals received at NID 360 are sent to SS-XTU 200 over inside coaxial cable.
  • SS- XTU 200 forms part of a gateway 210, which serves as an interface to various devices in the residence 190, such as computer 193, telephone 194, and TV 199.
  • Devices in residence 190 may be connected to gateway 210 by inside twisted wire pairs 181, inside coaxial cable 205, or other connections known to those of skill in the art.
  • TV 199 may be connected to gateway 210 by an RCA or S-video connection.
  • FIG. 1 illustrates SS-XTU 200 located inside the living area of residence 190
  • SS-XTU 200 can be located in the basement, in the garage, in a wiring closet, in the attic, or in other spaces within residence 190.
  • SS-XTU 200 can also be located outside residence 190, in which case it may require a hardened enclosure and components that work over a larger range of temperatures and other environmental conditions than those used in termination units located inside subscriber residences. Techniques for developing hardened enclosures and selecting environment-tolerant components are known to those of skill in the art.
  • LS-XTU 340 and SS-XTU 200 include modems, and work in conjunction with each other to provide a path for the transmission of xDSL signals.
  • the xDSL signals may contain, among other things, Asynchronous Transfer Mode (ATM) cells, and may be combined with narrowband telephony signals.
  • ATM Asynchronous Transfer Mode
  • SS-XTU 200 receives xDSL-modulated signals from LS-XTU 340, demodulates them, deframes them, performs error-checking and correction on them, and produces ATM cells as its output.
  • SS-XTU 200 and LS-XTU 340 also communicate in the upstream direction, in which case SS-XTU 200 transmits xDSL-modulated signals to LS-XTU 340 over twisted wire pair drop cable 180 (or other transmission facility); LS-XTU 340 receives such signals, reformats them, and passes them on to the telecommunications network via optical fiber 160.
  • FIG. 2 provides a flow chart depicting a preferred embodiment of the symbol rate stepping method of the present invention.
  • the goal is to establish downstream communication between LS-XTU 340 and SS-XTU 200 at a desired symbol rate - in this example, approximately 4.86 Mbaud.
  • desired symbol rates may be selected, as would be apparent to those of skill in the art.
  • LS-XTU 340 rather than initially transmitting a signal at the desired symbol rate of approximately 4.86 Mbaud, LS-XTU 340 begins with an initial symbol rate of 1/4 of the desired symbol rate, or approximately 1.215 Mbaud.
  • Step 201 the initialization step, where the initial symbol rate is set to 1/4 of the desired symbol rate, or approximately 1.215 Mbaud.
  • the symbol rate increment is set to 1/8 of the desired symbol rate, or approximately 0.608 Mbaud;
  • the variable communication symbol rate is set to the initial symbol rate;
  • the transmission modulation density is set to QPSK.
  • Other initial symbol rates, symbol rate increments, and transmission modulation densities may be utilized, as apparent to those of skill in the art.
  • Step 202 of the preferred embodiment depicted in FIG. 2 a signal is transmitted from LS-XTU 340 to SS-XTU 200 at the variable communication symbol rate.
  • the transmitted signal is acquired at the equalizer at SS-XTU 200 by determining a tentative equalizer solution (i.e., a set of filter coefficients) for the variable communication symbol rate.
  • a tentative equalizer solution i.e., a set of filter coefficients
  • Step 203 a check is performed to see if downstream communication has been established at the desired symbol rate (in this embodiment, approximately 4.86 Mbaud). If it has, the symbol rate stepping method terminates. If downstream communication has not yet been established at the desired symbol rate, the method proceeds to Step 204, where the variable communication symbol rate is increased by the symbol rate increment (in this embodiment, approximately 0.608 Mbaud), yielding a new variable communication symbol rate.
  • the desired symbol rate in this embodiment, approximately 4.86 Mbaud
  • a signal is then transmitted from LS-XTU 340 to SS-XTU 200 at the new variable communication symbol rate, as shown in Step 205.
  • the previously determined tentative equalizer solution is used as the initial solution for acquiring the signal transmitted at the new variable communication symbol rate.
  • the tentative equalizer solution is held for use in acquiring the next transmitted signal.
  • Steps 203 through 205 are repeated iteratively until LS-XTU 340 and SS-XTU 200 communicate at the desired symbol rate.
  • upstream communication is established between SS-XTU 200 and LS-XTU 340 to acknowledge the acquisition of the transmitted signal and to synchronize each iteration.
  • the symbol rate stepping method of the present invention would proceed as follows. First, the variable communication symbol rate is set to the initial symbol rate, or approximately 1.215
  • a signal is then transmitted from LS-XTU 340 to SS- XTU 200 at approximately 1.215 Mbaud.
  • a tentative equalizer solution is determined for the approximately 1.215 Mbaud signal.
  • the variable communication symbol rate is then increased by the symbol rate increment, or approximately 0.608 Mbaud.
  • the new variable communication symbol rate is thus 1.215 + 0.608, or approximately 1.823 Mbaud.
  • a signal is then transmitted from LS-XTU 340 to SS-XTU 200 at the new variable communication symbol rate.
  • the previously determined tentative equalizer solution is used to initiate the determination of a solution for the new signal at approximately 1.823 Mbaud.
  • variable communication symbol rate is then increased by the symbol rate increment, or approximately 0.608 Mbaud.
  • the new variable communication symbol rate is thus 1.823 + 0.608, or approximately 2.431 Mbaud.
  • a signal is then transmitted from LS-XTU 340 to SS-XTU 200 at the new variable communication symbol rate.
  • the previously determined tentative equalizer solution is used to initiate the determination of a solution for the new signal at approximately 2.431 Mbaud.
  • the method of the present invention would thus proceed for 6 iterations to reach the desired symbol rate.
  • LS-XTU 340 and SS-XTU 200 would have established communication at the desired symbol rate of approximately 4.86 Mbaud.
  • the symbol rate stepping method is used to establish communication in the downstream direction.
  • the symbol rate stepping method of the present invention is also used to establish communication between SS-XTU 200 and LS-XTU 340 in the upstream direction.
  • FIG. 3 provides a flow chart depicting a preferred embodiment of the rate training method of the present invention.
  • a list of preselected symbol rates is maintained for use in the downstream direction. In a preferred embodiment, this list consists of four symbol rates: approximately 3.30 Mbaud, approximately 4.86 Mbaud, approximately 5.184 Mbaud, and approximately 6.48 Mbaud. Other symbol rates may be selected, as apparent to those of skill in the art.
  • Step 301 one of the preselected symbol rates is chosen.
  • Step 302 communication is established between LS- XTU 340 and SS-XTU 200 using the chosen symbol rate and a predetermined transmission modulation density.
  • the predetermined transmission modulation density is Quadrature Phase-Shift Keying (QPSK)
  • Step 302 is carried out by the symbol rate stepping method of the present invention, as discussed above.
  • QPSK Quadrature Phase-Shift Keying
  • Other methods of establishing communication and other transmission modulation densities may be used, as apparent to those of skill in the art.
  • Step 303 the signal-to-noise ratio is measured for the established connection.
  • FIG. 4B illustrates an example in which the signal-to-noise ratio for the selected symbol rate of approximately 4.86 Mbaud is 23 dB .
  • Step 304 in FIG. 3 the signal-to-noise ratio measurement is used to determine a maximum modulation density that can be used at the selected symbol rate. The determination of the maximum modulation density that can be used is based on a predetermined performance threshold. In other words, achieving a maximum acceptable bit error ratio (BER) at a given modulation density requires a minimum signal-to-noise ratio.
  • FIG. 4A illustrates an example of minimum signal-to-noise ratios for specific modulation densities. For example, in the embodiment shown in FIG. 4A, a modulation density of 16-QAM (Quadrature Amplitude
  • Modulation with a 16-point signal constellation requires a signal-to-noise ratio of at least 19 dB for a BER no higher than approximately 10 ⁇ 7 (before error correction) , or approximately 10 ⁇ 10 (after error correction) .
  • a 16-QAM modulation density could be used at a lower signal-to-noise ratio. The determination of acceptable performance thresholds is known to those of skill in the art.
  • the signal-to- noise ratio measured at the symbol rate of approximately 4.86 Mbaud is approximately 23 dB .
  • 32-QAM is thus recorded in the first row in the table in FIG. 4B as the maximum modulation density that can be used, in the example, with a symbol rate of 4.86 Mbaud.
  • the maximum achievable bit rate is computed, based on the selected symbol rate and the maximum modulation density, as depicted in Step 305 of FIG 3.
  • a 32-QAM maximum modulation density means that 5 bits can be transmitted per symbol, as known to those of skill in the art. Multiplying 5 bits/symbol times 4.86 million symbols/second (the selected symbol rate) results in a maximum achievable bit rate of approximately 24.3 Mb/s.
  • Step 307 another preselected symbol rate is chosen, and Steps 302 through 306 are repeated for the new symbol rate.
  • the table in FIG. 4B shows an example of the information that is determined and stored in a system with three preselected symbol rates: 4.86 Mbaud, 5.184 Mbaud, and 6.48 Mbaud.
  • the maximum bit rate achievable for each of those symbol rates is approximately 24.3 Mb/s, 25.92 Mb/s, and 25.92 Mb/s, respectively.
  • Other preselected symbol rates can be designated by those of skill in the art.
  • the rate training method is used to determine the maximum bit rate achievable for a number of preselected symbol rates in the downstream direction.
  • the maximum transmission modulation density is chosen from the group consisting of QPSK, 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, and 256-QAM. Other transmission modulation densities known to those of skill in the art may be permitted.
  • the rate training method can also be used to determine the maximum transmission modulation densities and maximum achievable bit rates that can be used in the upstream direction.
  • the preselected symbol rates in the upstream direction are 350 kbaud and 540 kbaud.
  • the maximum upstream transmission density may be chosen from the group consisting of QPSK, 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, and 256-QAM.
  • Other symbol rates and transmission modulation densities can be selected by those of skill in the art.
  • FIG. 5 provides a flow chart depicting a preferred embodiment of the method for establishing and adapting link parameters of the present invention.
  • Step 501 upstream and downstream frequency ranges are selected.
  • the lower limit of the upstream frequency range is set to 324 kHz
  • the lower limit of the downstream frequency range is set to 1.5 MHz.
  • the lower limit of the upstream frequency range is set to 570 kHz.
  • the method of the present invention avoids selecting frequencies for xDSL transmission that overlap with other telecommunications services possibly being used on the link, such as POTS, which typically has an upper frequency limit of 4 kHz, Integrated Services Digital Network Basic Rate Interface (ISDN BRI) , which typically has an upper frequency limit of 250 kHz, and Universal Digital Channel (UDC) , which has an upper frequency limit of 250 kHz.
  • POTS typically has an upper frequency limit of 4 kHz
  • ISDN BRI Integrated Services Digital Network Basic Rate Interface
  • UDC Universal Digital Channel
  • Preferred embodiments also minimize overlap with telecommunications services such as ADSL, SDSL, and HDSL, which typically have upper frequency limits from 500 kHz to 1.1 MHz, that are potentially being used on adjacent links.
  • Step 502 the stored data that was determined as part of the rate training method is retrieved.
  • An example of such data is the table shown in FIG. 4B.
  • a predetermined downstream service bit-rate requirement and a set of predetermined deployment parameters are also retrieved, as shown in Step 503.
  • the downstream service bit-rate requirement is 25.92 Mb/s.
  • a bit-rate requirement can be determined by one of skill in the art based on the high speed data services to be delivered to customers on a particular link.
  • the set of predetermined deployment parameters that is retrieved includes a signal- to-noise ratio (SNR) margin that is used to modify the minimum SNR required for each modulation density.
  • SNR signal- to-noise ratio
  • the SNR margin of 3 dB would be added to the minimum SNR required for each modulation density.
  • the minimum SNR required for QPSK modulation density would be 16 + 3, or 19 dB; the minimum SNR required for 16-QAM modulation density would be 19 + 3, or 22 dB; etc.
  • Those of skill in the art can determine an appropriate SNR margin for each deployment environment.
  • bit-rate requirement is 25.92 Mb/s
  • only two of the three preselected symbol rates shown in FIG. 4B would be capable of achieving that bit-rate requirement: 5.184 Mbaud (using 32-QAM) and 6.48 Mbaud (using 16-QAM).
  • bit-rate requirement 5.184 Mbaud (using 32-QAM)
  • 6.48 Mbaud using 16-QAM.
  • a lower symbol rate and a higher transmission modulation density typically provide more reliable service over longer distances than a higher symbol rate and a lower transmission modulation density.
  • Step 504 the selection of an optimal symbol rate and transmission modulation density, shown in Step 504, would result in the selection of 5.184 Mbaud as the optimal symbol rate and 32-QAM as the optimal transmission modulation density (rather than 6.48 Mbaud and 16-QAM. )
  • the deployment parameters might include the frequencies at which RF ingress is likely to occur, in which case the selection of an optimal symbol rate and modulation density combination would entail choosing a symbol rate and modulation density that avoid such frequencies.
  • the symbol rate and transmission modulation density capable of achieving the highest bit rate could be selected.
  • a symbol rate and transmission modulation density could be selected without reference to deployment parameters or to bit rate requirements.
  • the symbol rate and transmission modulation density combination that yields the highest signal-to-noise ratio margin could be selected.
  • a similar procedure could be used to select an upstream symbol rate and transmission modulation density.
  • FIG. 6 depicts a test set apparatus 400 that implements the methods described in this invention and simulates SS-XTU 200.
  • test set apparatus 400 is connected to NID 360 by twisted wire pair link 179 outside subscriber residence 190, and can be used to verify the performance of the twisted wire pair link 180 by working in conjunction with LS-XTU 340 to execute the methods of the present invention, as described in this specification.
  • test set apparatus 400 can be connected to NID 360 by another type of transmission facility, as known to those of skill in the art .

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Abstract

Ce procédé d'établissement et d'adaptation de paramètres de liaison de communication dans des systèmes de transmission à lignes d'abonnés numériques comprend les étapes consistant à déterminer une densité de modulation de transmission maximale, qui peut être utilisée pour plusieurs débits de symboles déterminés (201), à commencer la communication au niveau d'une fraction d'un débit de symboles final, jusqu'à ce que ce débit soit atteint. Dans chaque itération, une solution d'égalisation (202), déterminée pour le signal au niveau du débit de symboles actuel, est maintenue et utilisée en tant que point de départ de détermination d'une solution destinée au signal, au niveau du débit de symboles suivant, accru (204) ; le procédé consiste ensuite à mesurer un rapport signal/bruit au niveau d'un nombre de débits de symboles déterminés et à utiliser ces mesures pour déterminer la densité de modulation maximale et le débit binaire pouvant être atteint pour chaque débit de symboles déterminé.
PCT/US2000/006020 1999-03-10 2000-03-09 Procede d'etablissement et d'adaptation de parametres de liaison de communication dans une transmission xdsl WO2000054423A1 (fr)

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Cited By (3)

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WO2002039613A2 (fr) * 2000-11-10 2002-05-16 Siemens Aktiengesellschaft Procede pour determiner des parametres de reglage d'une unite de reception, unites associees et programme associe
EP1328081A1 (fr) * 2002-01-15 2003-07-16 Actelis Networks Inc. Gestion de largeur de bande basé sur SNR pour un ensemble de modems
WO2005027395A2 (fr) * 2003-09-11 2005-03-24 General Instrument Corporation Systemes de gestion de spectre et procedes de reseau par cable

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US5469495A (en) * 1993-05-28 1995-11-21 U S West Advanced Technologies, Inc. Method and apparatus for delivering secured telephone service in hybrid coaxial cable network
US5809033A (en) * 1995-08-18 1998-09-15 Adtran, Inc. Use of modified line encoding and low signal-to-noise ratio based signal processing to extend range of digital data transmission over repeaterless two-wire telephone link
US5999563A (en) * 1996-05-09 1999-12-07 Texas Instruments Incorporated Rate negotiation for variable-rate digital subscriber line signaling

Patent Citations (3)

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US5469495A (en) * 1993-05-28 1995-11-21 U S West Advanced Technologies, Inc. Method and apparatus for delivering secured telephone service in hybrid coaxial cable network
US5809033A (en) * 1995-08-18 1998-09-15 Adtran, Inc. Use of modified line encoding and low signal-to-noise ratio based signal processing to extend range of digital data transmission over repeaterless two-wire telephone link
US5999563A (en) * 1996-05-09 1999-12-07 Texas Instruments Incorporated Rate negotiation for variable-rate digital subscriber line signaling

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002039613A2 (fr) * 2000-11-10 2002-05-16 Siemens Aktiengesellschaft Procede pour determiner des parametres de reglage d'une unite de reception, unites associees et programme associe
WO2002039613A3 (fr) * 2000-11-10 2003-04-24 Siemens Ag Procede pour determiner des parametres de reglage d'une unite de reception, unites associees et programme associe
EP1328081A1 (fr) * 2002-01-15 2003-07-16 Actelis Networks Inc. Gestion de largeur de bande basé sur SNR pour un ensemble de modems
WO2005027395A2 (fr) * 2003-09-11 2005-03-24 General Instrument Corporation Systemes de gestion de spectre et procedes de reseau par cable
WO2005027395A3 (fr) * 2003-09-11 2005-06-23 Gen Instrument Corp Systemes de gestion de spectre et procedes de reseau par cable
US7616654B2 (en) 2003-09-11 2009-11-10 General Instrument Corporation Spectrum management systems and methods for cable networks

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