US9270831B2 - Systems and methods for G.vector initialization - Google Patents

Systems and methods for G.vector initialization Download PDF

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US9270831B2
US9270831B2 US13/458,865 US201213458865A US9270831B2 US 9270831 B2 US9270831 B2 US 9270831B2 US 201213458865 A US201213458865 A US 201213458865A US 9270831 B2 US9270831 B2 US 9270831B2
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lines
dsl
joining
vector
showtime
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US20120275591A1 (en
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Amitkumar Mahadevan
Kevin D. Fisher
Nicholas P. Sands
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Ikanos Communications Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
    • H04M11/062—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors using different frequency bands for speech and other data
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/32—Reducing cross-talk, e.g. by compensating
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L69/00—Network arrangements, protocols or services independent of the application payload and not provided for in the other groups of this subclass
    • H04L69/14—Multichannel or multilink protocols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter

Definitions

  • Apparatus, systems, methods, techniques, etc. are disclosed for initializing DSL lines in a vectored DSL system and, in some embodiments, providing shorter time duration for initialization of one or more joining DSL lines as compared to earlier apparatus, systems, methods, etc.
  • DSM3 Dynamic spectrum management level-3
  • vectoring is a technique in DSL communication systems for mitigating the crosstalk inherent in twisted-pair networks by cancelling or precoding the signals from a multiplicity of collocated transceivers.
  • Certain aspects of vectoring that can be considered background art are described in U.S. Patent Publ. No. 2009/0245340, U.S. Patent Publ. 2008/0049855, U.S. Patent Publ. No. 2010/0195478, U.S. Patent Publ. No. 2009/0271550, U.S. Patent Publ. No. 2009/0310502, U.S. Patent Publ. No. 2010/0046684 and U.S. Pat. No. 7,843,949.
  • the G.vector (G.993.5) standard provides a framework for actively cancelling far-end crosstalk (FEXT) among lines in the vectored DSL system.
  • This framework provides for lines to non-disruptively join the vectored system by enabling estimation of coefficients for mitigating FEXT (a precoder for downstream transmissions and a post-canceller for upstream transmissions) from and into the initializing (i.e., joining) lines.
  • This framework is created by introducing new phases (signaling as well as messaging) and modifying some of the existing phases of initialization provided by the G.993.2 (VDSL 2 ) standard.
  • the new signaling phases introduced by G. vector may be broadly partitioned into two groups. The first group is vector- 1 signals.
  • vector- 1 signals consist of sync symbols only with intervening silence (i.e., the transmitter goes quiet between sync symbols). Additionally, a predefined binary pilot sequence modulates tones of the sync-symbols.
  • the primary purpose of vector- 1 signals is to enable mitigation coefficient estimation for FEXT from the joining line(s) into the lines that are already in Showtime.
  • the second group is vector- 2 signals. These consist of sync symbols modulated by a pilot sequence as well as regular symbols carrying the special-operations channel (SOC) messages.
  • SOC special-operations channel
  • a typical G.vector initialization involves six distinct and non-overlapping G.vector signaling phases: Four non-overlapping phases comprising 0 -P-VECTOR 1 , R-P-VECTOR 1 , 0 -P-VECTOR 1 - 1 and R-P-VECTOR 1 - 1 ; One phase of overlapped 0 -P-VECTOR 2 and R-P-VECTOR 1 - 2 ; and One phase of overlapped 0 -P-VECTOR 2 - 1 and R-P-VECTOR 2 .
  • Pilot sequences are provisioned in G.vector to enable the accurate estimation of FEXT mitigation coefficients between any pair of lines in the vectored system.
  • the G.vector standard allows the vector control entity (VCE) to assign the pilot sequence to each line; however, it does not specify any details on the sequences that must be used (i.e. their choice, composition, etc. can be vendor-discretionary).
  • a common process uses a set of orthogonal sequences, wherein every user is assigned a unique sequence of length (or period) L.
  • L length
  • FEXT mitigation coefficients on a given tone (or sub-carrier) between any pair of users can be unambiguously resolved at the end of a pilot sequence period if L ⁇ N. This suggests that the duration of the vector- 1 or vector- 2 phases must be at least L sync-symbols (with L ⁇ N) to guarantee successful estimation of FEXT mitigation coefficients between any pair of users on a specific tone.
  • each new G.vector signaling phase must last at least 512 sync symbols (approximately 32 seconds for a 4 kHz symbol-rate system).
  • a typical G.vector initialization would require more than three minutes (6 phases ⁇ 32 seconds) of additional time over and above the time required for G.993.2 initialization (about 40 seconds).
  • Three or four minutes for initializing a G.vector line before entering Showtime is highly undesirable from a customer perspective, and most of this type of delay would be due to additional time spent in the G.vector signaling phases.
  • the problem can be further exacerbated when one pilot sequence period is insufficient to achieve vectored signal-to-noise ratio (SNR) performance that is reasonably close to ideal FEXT-free SNR due to the impact of noise in estimates of the FEXT mitigation coefficients, meaning multiple pilot-sequence periods may have to be accommodated in the G.vector signaling phases.
  • SNR signal-to-noise ratio
  • Methods, apparatuses e.g., DSL system hardware, DSL systems, vectoring control entities
  • techniques, systems computer program products comprising a non-transitory computer-usable medium having control logic stored therein for causing a computer to manufacture a DSL system and/or one or more DSL components or devices for performing vectored digital subscriber line system (DSL) processing for transmissions on a DSL line
  • computer program products comprising a non-transitory computer-usable medium having control logic stored therein for causing a computer to manufacture a DSL system and/or one or more DSL components or devices for performing vectored digital subscriber line system (DSL) processing for transmissions on a DSL line, etc.
  • DSL digital subscriber line system
  • a super-periodic orthogonal pilot sequence from a set of super-periodic orthogonal pilot sequences is assigned to each joining DSL line, wherein each such super-periodic orthogonal pilot sequence in the set has length Land is orthogonal to other sequences in the set over length T ⁇ L.
  • These super-periodic orthogonal pilot sequences are used on the joining DSL lines to generate at least T sync-symbols worth of initialization data, which is processed to generate initialization data and FEXT mitigation coefficients for use when the joining DSL lines become part of the vectored DSL line group.
  • Other variations, embodiments, etc. discussed herein are included.
  • a method for initializing a first joining DSL line and a second joining DSL line that are joining a first vectored DSL line group operating in Showtime includes: assigning a first super-periodic orthogonal pilot sequence to the first joining DSL line; assigning a second super-periodic orthogonal pilot sequence to the second joining DSL line, wherein the first and second super-periodic orthogonal pilot sequences have length Land are orthogonal over length T, wherein T ⁇ L; using the first and second super-periodic pilot sequences on the first and second joining DSL lines, respectively, to generate M sync-symbols worth of initialization data, wherein M ⁇ T; and processing the generated initialization data to generate joining DSL line FEXT mitigation coefficients.
  • FIG. 1 is a flow diagram illustrating an example general initialization method according to embodiments of the invention.
  • FIGS. 2-5 are flow diagrams illustrating one or more line joining methods, processes, techniques, etc. according to one or more DSL line initialization embodiments and/or implementations of the invention.
  • FIG. 6 is a schematic diagram illustrating one or more line joining methods, processes, techniques, etc. according to one or more DSL line initialization embodiments and/or implementations of the invention.
  • FIG. 7 is a DSL system implementing one or more line joining methods, processes, techniques, etc. according to one or more DSL line initialization embodiments and/or implementations of the invention.
  • Embodiments described as being implemented in software should not be limited thereto, but can include embodiments implemented in hardware, or combinations of software and hardware, and vice-versa, as will be apparent to those skilled in the art, unless otherwise specified herein.
  • an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein.
  • the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.
  • embodiments of the invention provide apparatuses and/or methodologies to reduce the duration of initialization phase of G.vector modems as compared to earlier systems and the like. These apparatuses and/or methodologies are applicable to both upstream and downstream vectoring and leverage the messaging mechanisms provided by G.vector to permit implementation in any G.vector capable CPE without modifications to the April 2010 G.vector scheme.
  • the conventional G.vector (G.993.5) standard provides a framework for the initialization of lines in a vectored DSL system in order to minimize disruption to lines that are already in Showtime and enjoying the benefits of far-end crosstalk (FEXT) cancellation.
  • this framework which consists of new phases and modifications to some existing phases of initialization provided by the G.993.2 (VDSL 2 ) standard, potentially increases initialization duration from ⁇ 40 seconds for G.993.2 to ⁇ 4 minutes for G.vector. Reducing such duration times of certain G.vector-specific initialization phases, while ensuring that FEXT from and into the initializing lines is adequately cancelled, represents a significant advancement in this field.
  • This detailed description taken in conjunction with the accompanying drawings, appendices and other disclosure information, describes apparatuses, systems, methods, techniques, etc. for initializing DSL lines, including initializing DSL lines joining a vectored system according to G.vector.
  • the VCE may specify the length of the downstream pilot sequence and upstream pilot sequence (they need not be the same) to a joining line only once.
  • G.vector does not permit flexibility in changing the length of either pilot sequence once it has been specified.
  • G.vector does provide the capability to change the bits of the pilot sequence for any line in Showtime—downstream as required (this is vendor specific) and upstream via the “pilot sequence update” command (G.vector Section 8.2).
  • embodiments of G.vector initialization according to the invention described herein exploit this G.vector capability to reduce the time required for G.vector initialization.
  • G.vector initialization will refer to a group of DSL lines already in vectored operation in Showtime as a “Showtime line group (SLG),” the “Showtime lines,” or the like. In such conditions, embodiments of G.vector initialization described herein can be implemented to reduce the initializing duration of joining lines, for example using the following processes or the like.
  • FIG. 1 illustrates an example process 100 utilizing one or more embodiments of G.vector initialization according to the invention.
  • a pilot sequence has length L
  • some embodiments assign a set of orthogonal sequences for the vectored system such that a subset of sequences are orthogonal to each other over lengths that are smaller than L; that is, within the selected subset, a given pilot sequence segment is orthogonal to another pilot sequence segment, where both segments have length less than L.
  • These subsets are referred to herein as “super-periodic” with period T ⁇ L.
  • step S 120 typically there will be an existing group of showtime lines, i.e. the SLG, whose crosstalk mitigation coefficients are fully populated and updated. As typically occurs, one or more new lines request to join the SLG. Accordingly, G.vector initialization needs to be performed.
  • a novel approach to G.vector initialization is performed whenever new lines join.
  • a unique subset of pilot sequences is assigned to joining lines from the set of orthogonal sequences prepared in step S 110 , which pilot sequences can be determined based on the number of lines requesting to join the group.
  • a distinct subset of pilot sequences can also be applied to the showtime lines, where a specific pilot sequence in this distinct subset may be assigned to more than one showtime line.
  • step S 140 vector- 1 initialization is performed for the joining lines only.
  • FIG. 6 shows an example of how vector- 1 initialization is performed when a distinct subset of pilot sequences have been assigned to two existing showtime lines, whose data signals are shown in plots 602 and 604 .
  • three lines (whose signals are shown in plots 606 , 608 and 610 ) are requesting to join the showtime lines.
  • the joining lines have been assigned pilot sequences S 1 , S 2 and S 3 as shown in plots 606 , 608 and 610 , respectively. As further shown in FIG.
  • step S 150 vector- 1 phases can be terminated much earlier than is possible in prior art approaches.
  • the pilots are optionally reassigned in the SLG lines if they were previously assigned in step S 130 .
  • step S 160 vector- 2 initialization is performed on the joining lines, using the same pilot sequences that were assigned in step S 140 .
  • no reduction in time is possible as compared to prior art approaches, however.
  • step S 170 after the vector- 1 and vector- 2 phases are complete, the crosstalk mitigation coefficients for all of the showtime lines (which now include the joining lines) are estimated. Thereafter, the new SLG can keep operating with adaptation of coefficients enabled. As further shown in FIG. 1 , whenever additional lines want to join, the process returns to step S 130 .
  • FIG. 2 illustrates a first example initialization process when one or more lines request to join a SLG.
  • step S 202 when one or more DSL lines (e.g., K lines) request to join the vectored system, the VCE chooses a subset of super-periodic pilot sequences (e.g., K+1 sequences) from the entire prepared set such as that described above in connection with FIG. 1 .
  • a subset of super-periodic pilot sequences e.g., K+1 sequences
  • step S 204 K of the K+1 sequences S 1 , S 2 and S 3 are assigned to the three joining lines, respectively.
  • step S 206 adaptation of FEXT mitigation coefficients among DSL lines already in Showtime is frozen or turned off, which is acceptable since these lines' coefficients are expected to have converged.
  • one or more remaining sequences in the selected chosen super-periodic subset may be assigned to each of the Showtime lines. For upstream this can be carried out using the above-noted “pilot sequence update” mechanism provided by G.vector, while for downstream, this may be done as required without any explicit communication to the CPEs.
  • the same sequence can be assigned to multiple Showtime lines. This guarantees orthogonality between the pilot sequence on each Showtime line and each of the joining lines and further assists in unambiguously resolving coefficients for mitigating FEXT from the joining lines into the Showtime lines.
  • skipping this step may be justified if FEXT from Showtime lines into other Showtime lines is expected to be almost perfectly mitigated (i.e., sync symbol errors on Showtime lines are not expected to contain any contribution due to FEXT from other Showtime lines).
  • the pilot sequences transmitted by Showtime lines are inconsequential.
  • one or more Showtime lines could, in some embodiments, transmit the exact same pilot sequence as a joining line without significantly jeopardizing the estimation of coefficients for mitigation of FEXT from the joining lines into Showtime lines.
  • a Showtime line and a joining line can transmit the exact same pilot sequence during the vector- 1 phases; in this case, any FEXT contribution arising from that pilot sequence can be completely attributed to the joining line, since FEXT from the Showtime line is assumed to be almost completely cancelled.
  • coefficients estimated based on information from the smaller number of T sync-symbols may have a larger estimation error and/or cause larger SNR degradation of active lines as compared to coefficient estimates based on information from L sync-symbols (L>T).
  • L sync-symbols L>T
  • pilot sequences for the Showtime lines in both downstream and upstream directions are reassigned at the end of the joining lines' vector- 1 phases, so that each Showtime line gets a unique and distinct sequence from the set of orthogonal sequences before the overlapped O-P-VECTOR 2 - 1 and R-P-VECTOR 2 phase begins.
  • the downstream pilot sequences may be updated any time after O-P-VECTOR 1 - 1 , preferably before O-P-VECTOR 2 , but at the latest before O-P-VECTOR 2 - 1 .
  • the upstream pilot sequences are updated immediately after R-P-VECTOR 1 - 2 and before information from R-P-VECTOR 2 is used for estimating coefficients for FEXT into the joining lines.
  • initialization continues until the vector- 2 phase is complete.
  • the overlapped O-P-VECTOR 2 - 1 and R-P-VECTOR 2 phase can be terminated after processing the information from a maximum of L sync-symbols with no reduction expected in the duration of this overlapped phase.
  • step S 216 adaptation of FEXT coefficients for lines in SLG can be resumed.
  • FIG. 3 illustrates another example initialization process when one or more lines request to join a SLG.
  • a subset of super-periodic pilot sequences e.g., K+1 sequences
  • step S 304 K of the K+1 sequences S 1 , S 2 and S 3 are assigned to the three joining lines, respectively.
  • step S 306 adaptation of FEXT mitigation coefficients among DSL lines already in Showtime is frozen or turned off, which is acceptable since these lines' coefficients are expected to have converged.
  • one or more remaining sequences in the selected chosen super-periodic subset may be assigned to each of the Showtime lines. For upstream this can be carried out using the above-noted “pilot sequence update” mechanism provided by G.vector, while for downstream, this may be done as required without any explicit communication to the CPEs.
  • the same sequence can be assigned to multiple Showtime lines. This guarantees orthogonality between the pilot sequence on each Showtime line and each of the joining lines and further assists in unambiguously resolving coefficients for mitigating FEXT from the joining lines into the Showtime lines.
  • step S 310 it is determined whether any vector- 1 phases of initialization remain to be performed.
  • the five vector- 1 phases e.g. non-overlapped phases 0 -P-VECTOR 1 , R-P-VECTOR 1 , 0 -P-VECTOR 1 - 1 and R-P-VECTOR 1 - 1 , and one phase of overlapped 0 -P-VECTOR 2 and R-P-VECTOR 1 - 2
  • the five vector- 1 phases e.g. non-overlapped phases 0 -P-VECTOR 1 , R-P-VECTOR 1 , 0 -P-VECTOR 1 - 1 and R-P-VECTOR 1 - 1 , and one phase of overlapped 0 -P-VECTOR 2 and R-P-VECTOR 1 - 2
  • the five vector- 1 phases e.g. non-overlapped phases 0 -P-VECTOR 1 , R-P-VECTOR 1 ,
  • step S 312 if all vector- 1 phases have not yet been performed, the next one is started (or the first one if this is the first time vector- 1 has been performed).
  • step S 314 online reconfiguration (OLR) mechanisms on the Showtime line group lines are disabled to ensure that there is no change in transmit power in the middle of a pilot sequence. This is preferably done because a mid-sequence change to the transmit power can potentially destroy orthogonality between different sequences.
  • OLR online reconfiguration
  • step S 316 FEXT coefficients from joining lines into Showtime lines are estimated after processing at least T sync-symbols in the current vector- 1 phase.
  • step S 318 FEXT coefficients from joining lines into Showtime lines are engaged. OLR is then re-enabled for lines in Showtime.
  • coefficients estimated based on information from T sync-symbols may have a larger estimation error and/or cause larger SNR degradation of active lines as compared to coefficient estimates based on information from L sync-symbols (L>T).
  • L sync-symbols L>T
  • a compromise might be required between significant vector- 1 phase duration reductions and associated SNR performance degradation of active lines. This compromise can be achieved in various ways—for example, by processing M ⁇ T, by performing more than one training pass, etc., as will be described in more detail below.
  • Processing then returns to step S 310 until all vector- 1 phases of initialization have been performed.
  • pilot sequences for the Showtime lines in both directions are reassigned at the end of the joining lines' vector- 1 phases, so that each Showtime line gets a unique and distinct sequence from the set of orthogonal sequences before the overlapped O-P-VECTOR 2 - 1 and R-P-VECTOR 2 phase begins.
  • the downstream pilot sequences may be updated any time after O-P-VECTOR 1 - 1 , preferably before O-P-VECTOR 2 , but at the latest before O-P-VECTOR 2 - 1 .
  • the upstream pilot sequences are updated immediately after R-P-VECTOR 1 - 2 and before information from R-P-VECTOR 2 is used for estimating coefficients for FEXT into the joining lines.
  • vector- 2 initialization continues. For example, overlapped O-P-VECTOR- 2 1 R-P-VECTOR 2 phase initialization is performed, and OLR is disabled for lines in Showtime. FEXT coefficients from all lines into joining lines are estimated after processing at least N sync-symbols, where N is the sum of the number of Showtime lines and joining lines.
  • step S 326 FEXT coefficients from all lines into joining lines are engaged and OLR is re-enabled for lines in Showtime.
  • the overlapped O-P-VECTOR 2 - 1 and R-P-VECTOR 2 phase can then be terminated.
  • step S 328 once all joining lines enter Showtime, adaptation of FEXT mitigation coefficients among all Showtime lines can then be performed as usual.
  • FIG. 4 illustrates another example initialization process when one or more lines request to join a SLG.
  • step S 404 the sequences S 1 , S 2 and S 3 are assigned to the three joining lines, respectively.
  • step S 406 adaptation of FEXT mitigation coefficients among DSL lines already in Showtime is frozen or turned off, which is acceptable since these lines' coefficients are expected to have converged.
  • coefficients estimated based on information from T sync-symbols may have a larger estimation error and/or cause larger SNR degradation of active lines as compared to coefficient estimates based on information from L sync-symbols (L>T).
  • L sync-symbols L>T
  • a compromise might be required between significant vector- 1 phase duration reductions and associated SNR performance degradation of active lines. This compromise can be achieved in various ways—for example, by processing M ⁇ T, by performing more than one training pass, etc., as will be described in more detail below.
  • step S 410 initialization continues with vector- 2 phases until they are completed.
  • the overlapped O-P-VECTOR 2 - 1 and R-P-VECTOR 2 phase can be terminated after processing the information from N sync-symbols, where N is the sum of the number of Showtime lines and joining lines.
  • step S 412 in the embodiment of FIG. 4 , it is useful to ensure that, as far as possible, Showtime lines are assigned pilot sequences that are not super-periodic. For example, if four lines are in Showtime, sequences S 4 , S 5 , S 6 , and S 7 , respectively, from step 110 can be assigned to these four lines, thus minimizing the need to reassign pilot sequences to Showtime lines when new lines join the system, and ensuring that the super-periodic pilot-sequences are available for the lines that might join in the future.
  • step S 414 adaptation of FEXT mitigation coefficients among all Showtime users can be resumed.
  • FIG. 5 illustrates another example initialization process when one or more lines request to join a SLG.
  • step S 504 the sequences S 1 , S 2 and S 3 are assigned to the three joining lines, respectively.
  • step S 506 adaptation of FEXT mitigation coefficients among DSL lines already in Showtime is frozen or turned off, which is acceptable since these lines' coefficients are expected to have converged.
  • step S 508 it is determined whether any vector- 1 phases of initialization remain to be performed.
  • the five vector- 1 phases e.g. non-overlapped phases 0 -P-VECTOR 1 , R-P-VECTOR 1 , 0 -P-VECTOR 1 - 1 and R-P-VECTOR 1 - 1 , and one phase of overlapped 0 -P-VECTOR 2 and R-P-VECTOR 1 - 2
  • the five vector- 1 phases e.g. non-overlapped phases 0 -P-VECTOR 1 , R-P-VECTOR 1 , 0 -P-VECTOR 1 - 1 and R-P-VECTOR 1 - 1 , and one phase of overlapped 0 -P-VECTOR 2 and R-P-VECTOR 1 - 2
  • the five vector- 1 phases e.g. non-overlapped phases 0 -P-VECTOR 1 , R-P-VECTOR 1 ,
  • step S 510 if all vector- 1 phases have not yet been performed, the next one is started (or the first one if this is the first time vector- 1 has been performed).
  • step S 512 online reconfiguration (OLR) mechanisms on the Showtime line group lines are disabled to ensure that there is no change in transmit power in the middle of a pilot sequence. This is preferably done because a mid-sequence change to the transmit power can potentially destroy orthogonality between different sequences.
  • OLR online reconfiguration
  • step S 514 FEXT coefficients from joining lines into Showtime lines are estimated after processing at least T sync-symbols in the current vector- 1 phase.
  • step S 516 FEXT coefficients from joining lines into Showtime lines are engaged and OLR is re-enabled for lines in Showtime.
  • coefficients estimated based on information from T sync-symbols may have a larger estimation error and/or cause larger SNR degradation of active lines as compared to coefficient estimates based on information from L sync-symbols (L>T).
  • L sync-symbols L>T
  • a compromise might be required between significant vector- 1 phase duration reductions and associated SNR performance degradation of active lines. This compromise can be achieved in various ways—for example, by processing M ⁇ T, by performing more than one training pass, etc., as will be described in more detail below.
  • initialization continues with vector- 2 .
  • the overlapped O-P-VECTOR- 2 1 R-P-VECTOR 2 phase is now performed after OLR for lines in Showtime is disabled.
  • FEXT coefficients from all lines into joining lines are estimated after processing at least N sync-symbols, where N is the sum of number of Showtime lines and joining lines.
  • step S 522 the FEXT coefficients from all lines into joining lines are engaged and OLR is re-enabled for lines in Showtime.
  • the overlapped O-P-VECTOR 2 - 1 and R-P-VECTOR 2 phase can be terminated.
  • step S 524 once joining lines enter Showtime, the usual adaptation of FEXT mitigation coefficients among all Showtime lines can be resumed.
  • a cold-start scenario occurs when no lines are in Showtime and the first group of lines is in the process of initialization. Such a scenario may occur after a power outage or scheduled maintenance at the CO side. In such a case, no coefficient estimation is necessary in the vector- 1 signaling phases and these phases may be restricted to their minimum duration as specified by G.vector, thereby reducing the initialization duration for the first group of joining lines.
  • duration of the vector- 1 phases might need to be extended to non-trivial multiples of T (i.e., nT symbols where n belongs to ⁇ 2, 3, . . . ⁇ ) in order to limit SNR degradation due to coefficient estimation error.
  • an initial estimate of coefficient based on information from T sync-symbols can be generated and then updated using the remaining (n-1) periods of T symbols.
  • a sync-symbol by sync-symbol least mean squares (LMS) update may be used, which requires the updated coefficient to be engaged in the signal path before the next update is performed.
  • LMS least mean squares
  • the process of repeatedly engaging updated coefficients into the signal path after every sync-symbol poses challenges from the standpoint of implementation speed, which may conspire to further extend the duration of the updating process.
  • An alternative method is the so-called “batch update” which also can be implemented in embodiments of the invention.
  • the same computations that were used to compute initial estimates over T sync symbols are used again after the initial estimates are engaged. However, with the initial estimates already engaged, repeating the computations over T sync symbols yields estimates of the residual FEXT coefficients. These residual FEXT coefficients are then added to the initial estimates to generate updated estimates.
  • An advantage of this batch update approach over the sync-symbol by sync-symbol LMS is that updated coefficients need to be engaged only after every T sync symbols, which relaxes the requirement on the speed of engaging the coefficients into the signal path.
  • Such batch-update approaches for FEXT mitigation coefficients allow these coefficients to be tracked over time while reducing the frequency of engaging the updated coefficients, i.e., writing the updated coefficients from software to hardware.
  • Such batch update approaches provide a realistic way to use information on consecutive sync-symbols to update FEXT mitigation coefficients during G. vector initialization of lines, thereby reducing the duration of the initialization.
  • the duration of the initialization phase of G.vector DSL modems can be reduced when compared to earlier systems.
  • FIG. 7 illustrates an example DSL system 700 that can implement G.vector initialization according to the embodiments of the invention described herein.
  • DSL lines 706 can be part of a Showtime line group or some or all can be joining lines.
  • the management unit 712 can be a VCE that assigns pilot sequences as needed during reduced-time initialization according to one or more embodiments.

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US10033431B2 (en) * 2013-05-05 2018-07-24 Lantiq Deutschland Gmbh Training optimization of multiple lines in a vectored system using a prepared-to-join group
KR101911809B1 (ko) * 2013-05-13 2018-10-25 란티크 베테일리궁스-게엠베하 운트 코 카게 벡터화된 시스템 내의 특수 동작 채널
WO2015127624A1 (zh) * 2014-02-27 2015-09-03 华为技术有限公司 串扰信道估计方法、矢量化控制实体及osd系统
US9509518B2 (en) * 2014-05-20 2016-11-29 Ikanos Communications, Inc. Method and apparatus for managing joining events for G.fast vectoring with discontinuous operation
WO2017079946A1 (zh) * 2015-11-12 2017-05-18 华为技术有限公司 用于数字用户线初始化的方法和装置

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CN103503398B (zh) 2017-02-08
JP5989093B2 (ja) 2016-09-07
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