Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
  • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
• • 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
  • H04J—MULTIPLEX COMMUNICATION
  • H04J1/00—Frequency-division multiplex systems
  • H04J1/02—Details
  • H04J1/12—Arrangements for reducing cross-talk between channels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/01—Equalisers
• • 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
  • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
  • H04L2025/03426—Arrangements for removing intersymbol interference characterised by the type of transmission transmission using multiple-input and multiple-output channels

Definitions

• N the number of vectored users A full, self-
• one embodiment is a method of performing per-tone FEXT (far-end crosstalk) mitigation
• the method comprises determining one or more instantaneous characteristics of an input signal, wherein the characteristics comprise at least one of an amplitude level of the input signal and energy level of the input signal
• the method further comprises determining whether to process the input signal for mitigation according to the one or more instantaneous characteristics of the input signal Based on the determination of whether to process the input signal for mitigation, the input signal is processed for mitigation
• Another embodiment comprises determining one or more instantaneous characteristics of an input signal, wherein the one or more instantaneous characteristics comprise one or more of amplitude of the input signal and an energy level of the input signal
• the method further comprises selecting one or more disturbers to cancel according to the one or more instantaneous characteristics, wherein selecting one or more disturbers is performed on a per-DMT (discrete multi-tone) symbol basis
• Another embodiment is a system that comprises an estimator configured to derive instantaneous characteristics for one or more disturbers
• the system further comprises a selector for selecting from among the one or more disturbers to cancel according to the instantaneous characteristics, wherein the selector is configured to compare the instantaneous characteristics to a threshold
• the system also comprises a far-end crosstalk (FEXT) mitigator for performing FEXT mitigation on only the selected disturbers
• FIG 1 illustrates the various types of crosstalk typically experienced in a
• FIG 2 illustrates a DSL system where the central office comprises a plurality of transceivers [001 1]
• FIG 3 illustrates an exemplary embodiment of vectorized downstream
• FIG 4 illustrates an exemplary embodiment of the vectored upstream
• FIG 5 illustrates the disturber input and its impact on a victim user, as experienced at the receiver of the victim
• FIG 6 illustrates an embodiment for selecting constellation points for partial self-FEXT cancellation
• FIG 7 illustrates other embodiments of decision boundaries that may be utilized for selecting disturber inputs for purposes of partial FEXT cancellation, as shown in FIG 6
• FIG 8 illustrates the projection of the self-FEXT of one disturber through two cross coupling different channels with the same amplitude, but of different phase
• FIG 9 illustrates the results of performing partial self-FEXT cancellation using the instantaneous level of the input signal to reduce the contribution of the self-FEXT to a level close to or less than that of the AWGN background noise
• FIG 10A illustrates one possible implementation of a precoder or canceller unit, in which the coefficients stored in a pseudo floating point format are expanded into the real and imaginary values
• FIG 10B depicts another implementation where the normalized coefficients
• FIG. 11A-C illustrate other possible implementations of a precoder or canceller unit based on the architecture depicted in FIG. 1 OB
• FIG. 12 shows one possible implementation of the complex multiplier shown in FIGS. 10A-B, 1 1A-C with added hardware circuitry that enables a zero output when both real and imaginary parts of the input data are zero.
• FIG. 13A illustrates one possible implementation of a multiplier circuit, which is being multiplexed between multiple disturbers' data input.
• FIG. 13B illustrates an embodiment for ordering of the coupling coefficients of each individual disturber into multiple victim users.
• FIG. 14A shows the general architecture of a precoder and the associated interface to the DSL PHY device of two DSL users N and M.
• FIG. 14B illustrates how a reduction in bandwidth can be realized on a self-FEXT precoder architecture, referred to as the off-diagonal precoder architecture.
• FIG. 14C shows the general architecture of an upstream canceller and the associated interface to the DSL PHY device of two DSL users N and M.
• FIG. 14D illustrates how a reduction in bandwidth can be realized on a self-FEXT canceller architecture, referred to as the off-diagonal canceller architecture.
• FIG. 15 illustrates an embodiment of an apparatus for executing the various components shown in FIG. 2.
• FIG. 16 depicts a top-level flow diagram for an embodiment of a process for performing partial self-FEXT cancellation in the system of FIG. 2.
• FIG 17 illustrates an exemplary embodiment of a 2x2 MIMO receiver in which the output of the dual FFT blocks are combined on a per-tone basis before demapping the two independent data streams
• FIG 18 illustrates an exemplary embodiment of a per-tone frequency domain echo canceller
• FIG 1 illustrates the various types of crosstalk typically experienced in a DSL system
• central office (CO) 110 comprises two transceivers 102 106 communicating over two subscriber lines to two sets of customer premises equipment (CPE) 104, 108 Transceiver 102 communicates with CPE 104, and transceiver 106 communicates with CPE 108
• CPE customer premises equipment
• transceiver 106 communicates with CPE 108
• interference may also be between the transmitter and receiver on the same subscriber line in both the upstream and downstream paths, which is the near-end echo of the transmit signal
• the term "far-end” refers to scenarios in which the source of interference is away from the receiving side, and the term “near-end” refers to scenarios in which the source of interference is close to the receiving side
• far-end refers to scenarios in which the source of interference is away from the receiving side
• near-end refers to scenarios in which the source of interference is close to the receiving side
• FIG 2 illustrates a DSL system 200 where the CO 230 comprises a plurality of transceivers represented by transceivers 240a, 240b, and 240c
• the transceivers are connected to CPEs 210a, 210b, 210c, respectively, through separate subscriber lines
• each subscriber line is broken down into its upstream and downstream paths
• the downstream paths for transceivers 240a-c are indicated by arrows 202a, 202b, 202c, respectively
• the upstream paths for transceivers 240a, 240b, 240c are indicated by arrows 204a, 204b, 204c, respectively
• only three of the M vectoring enabled CPEs are shown as CPEs 210a, 210b, 210c
• As signals are transmitted downstream from the CO 230 onto the DSL loops, a certain amount of energy leaks from one downstream CO transmitter into an adjacent CPE receiver, thereby creating undesired FEXT into adjacent
• FIG 3 illustrates an exemplary embodiment of the vectorized PMD DS layer 220 in FIG 2
• the PMD layer 220 resembles that shown in FIG 3 with a MIMO precoder 320 inserted between the mapper 304a, 304b, 304c and the IFFT 306a, 306b, 306c in each transceiver
• the detailed downstream PMD layers for transceivers 240a, 240b and 240c in FIG 2 are indicated as PMD layers 330a, 330b and 330c, respectively They include serial-to-parallel conversion blocks 302a, 302b, 302c to convert user data for the constellation mapper 304a, 304b, 304c, as well as parallel-to- se ⁇ al conversion blocks 308a, 308b, 308c to convert the IFFT output to the time domain processing blocks 310a, 310b, 310c
• the purpose of the MIMO precoder 320 is to compensate at the transmitter for the undesi
• the precoder operation can be seen as a matrix multiplication for each subcarrier across all the users in the vectored group
• the per-subcarrier precoder coefficient converges towards the inverse of the FEXT coupling channel matrix that exists among the vectored users
• the derivation of the precoder coefficients can be performed after a FEXT coupling channel analysis phase, during which known signal sequences are being transmitted by each transmitter with a well determined pattern Further details for deriving optimal precoding matrices can be found in U S Patent Application Ser No 1 1/845,040 filed on August 25, 2007, which is hereby incorporated by reference in its entirety
• FIG 4 illustrates an exemplary embodiment of the vectorized upstream
• the PMD layer 250 in FIG 4 comprises a MIMO canceller 420 inserted between the FFT 406a, 406b, 406c and the FEQ 405a, 405b, 405c
• the MIMO canceller 420 is inserted between the FEQ 405a, 405b, 405c and the demapper 404a, 404b, 404c
• the MIMO canceller 420 performs compensation at the receiver for undesired FEXT on the subscriber lines Cancellation is performed by means of a matrix operation (shown as canceller matrix 440) that receives data samples (/ e , FFT constellation outputs or FEQ constellation outputs) and outputs a compensated data sample for input to the FEQ or demapper
• PMD layers 430a, 430b and 430c are indicated as PMD layers 430a, 430b and 430c, respectively They include se ⁇ al-to-parallel conversion blocks 302a, 302b, 302c for converting time domain data processed in the time domain processing blocks 410a, 410b, 410c to the FFT block, as well as parallel-to-ser ⁇ al conversion blocks 402a, 402b, 402c for converting the demapper output to user data
• One aspect that enables vectoring is precisely the alignment and the synchronization of the transmitted and received DMT symbols
• the received DMT symbols are synchronized in vectoring enabled COs and CPEs
• This alignment is controlled by the CO 230 and is required for synchronous operation and ensures orthogonality among the M vectoring enabled users
• the orthogonality achieved by the synchronization and alignment of all users in a vectoring group allows for the simplification of the MIMO channel on a per- tone basis
• the equivalent MIMO system comprises N frequency channels, which can be viewed as independent tones
• partial self-FEXT cancellation comprises performing an ordering of users in the system based on coupling and input signal levels
• FEXT cancellation comprises a selection phase, whereby a determination regarding each disturber is made on whether or not to process the input of each respective disturber Each determination is made independently of the contribution by the other disturbers
• a threshold approach is implemented for the selection phase
• Various elements are used to determine the threshold that include but not limited to, the average input signal energy level, the amplitude of the coupling channel, and the targeted level of the residual FEXT after partial FEXT cancellation is performed It should be emphasized that various embodiments for partial self-FEXT cancellation result in a reduction of power consumption and allow multiplexing or sharing
• FEXT is a function of the coupling between the victim and the disturber in addition to the average transmit symbol power of the disturber
• a related partial cancellation problem involves intelligently choosing the tones for performing FEXT cancellation according to available computations resources in order to achieve, for example, an optimum performance objective given the available resources (referred to as "tone selection")
• tone selection can be jointly performed
• both line and tone selection algorithms that decide which disturbers to cancel for which tone, rely only on the energy couplings of the disturbers into the victim from the standpoint of statistical averages, while performing the actual crosstalk cancellation of the pre-selected inputs at every DMT symbol
• the same set of predetermined disturbers are cancelled for a given victim at each DMT symbol, regardless of the fact that the amount of instantaneous FEXT from a disturber to a victim is a function of both instantaneous constellation energy of the disturber and the magnitude of the coupling
• the average transmit power of the disturbers is constant and fixed a prion, it should be noted that the instantaneous symbol energy varies
• some embodiments are directed to considering each disturber's transmitted symbol independently This may be achieved based on the relative contribution to the self-FEXT of that individual user's transmitted symbol compared to either the self-FEXT contribution of other users' transmitted symbols at the same time or to the background noise level expected to be experienced by the victim It should also be emphasized that the embodiments described provide a higher gain in SNR when compared to conventional approaches involving line selection based on coupling only for a given tone
• the embodiments directed to partial FEXT cancellation with consideration of the level of the input data may be implemented in other systems where the input signal has a wide dynamic range (e.g., a QAM constellation) and where the corresponding coupling channel is represented by a single-tap complex or real coefficient
• a coupling channel is common in a system where OFDM is implemented in which the orthogonality between carriers results in a per-tone equivalent model, where each frequency bin can be evaluated independently of others.
• FIG 17 illustrates an exemplary embodiment of a 2x2 MIMO receiver 1700 in which the output of the dual FFT blocks 1704, 1712 are combined on a per-tone basis before demapping the two independent data streams
• the 2x2 MIMO receiver comprises a set of two direct path coefficients FEQm 1706a and FEQc 1706b along with a set of cross-coupling coefficients Cm c 1706d and Cc m 1706c, which subtract the interference of one channel into the other one
• the dual channel receiver also includes ser ⁇ al-to-parallel conversion blocks 1702a and 1702b for converting
• FIG 18 illustrates an exemplary embodiment of a per-tone frequency domain echo canceller, which is designed to cancel the impact of the transmitter constellation signal associated with each transmit tone into the corresponding received tone located at the same frequency in a full duplex frequency overlap system
• the per-tone frequency domain echo canceller 1820 receives an an input the output of the transmit mapper 1804 and generates a replica of the self-echo affecting the output of the FEQ 1838, to which it is subtracted
• the subtraction of the replica of the self-echo takes place for each tone at the output of the FFT block 1836 and before the FEQ 1838
• the transceiver 1800 includes a ser ⁇ al-to-parallel conversion block 1834 to convert time domain data processed in the time domain processing block 1832, as well as parallel- to-ser ⁇ al conversion block 1842 to convert the output of the demapper 1740 to user data
• the transceiver includes se ⁇ al-to-parallel conversion block 1802 to convert user data to the mapper 1804, as well as a parallel-to-se ⁇ al conversion block 1808 to convert the output of the I FFT block 1806 to the time domain block 1810
• the application of the partial cancellation scheme is incorporated for every tone in the selective processing of the transmit constellation signal according to its level relative to a threshold that is determined, on the one hand, by the echo coupling coefficient of the transmit tone and the corresponding received tone and, and on the other hand, by the target residual echo noise level after partial cancellation or target background noise to be achieved on the received tone
• FIG 5 illustrates the disturber input and its impact to the victim user, as seen at the receiver of the victim
• the disturber input is represented by a 128-po ⁇ nt QAM constellation 502, which cross-couples through the self-FEXT channel 504 and is superimposed on the victim signal 506, represented here as a 4 QAM signal
• the 4 QAM constellation (after direct channel equalization at the receiver) is shown with self-FEXT noise associated with the disturber
• the distribution of the received signal is compared to the same 4 QAM constellation points affected by an AWGN level of noise without self-FEXT
• an objective of the partial cancellation process is to reduce the level of self-FEXT to a level that is less than that of the background noise level
• the threshold to be applied for the determination of the input signal of the disturber considered in the cancellation process can be based on the energy of the constellation point of the input signal, and can therefore be applied, as a radius on the constellation input signal In particular, constellation points that fall below this
• FIG 8 illustrates the projection of the self-FEXT of one disturber through two different cross coupling channels of same amplitude, but of different phase
• One channel 802 does not induce a rotation of the disturber, while another channel 804 induces a clockwise rotation of ⁇ /4
• the distribution in the x and y directions of the error induced by the presence of the self-FEXT on the victim user are illustrated respectively for the two channels 802, 804, compared to the distribution of the same level of AWGN noise
• the variance of the error induced by the self-FEXT will differ based on the rotation introduced by the crosstalk channel
• the threshold to be determined can take into account not only the magnitude of the attenuation of the crosstalk channel, but also the phase of the cross-coupling
• an objective of performing partial self-FEXT cancellation using the instantaneous level of the input signal is to reduce the contribution of the self-FEXT to a level close to or less than that of the AWGN background noise experienced by the victim user in a self-FEXT free environment
• the distribution of the error signal after self-FEXT cancellation should be such that the variance ⁇ 2 > ⁇ 2 is close to the variance of a self-FEXT free environment ⁇ 2
• the determination of whether a particular constellation point input is utilized for the partial cancellation process comprises a comparison of the input constellation input signal along the x and y-axis against a set of predetermined thresholds, which are dependent on the relative amplitude of the real and imaginary dimensions of the self-FEXT crosstalk coupling coefficient
• the comparison is either preceded or followed by a comparison of the amplitude of the real and imaginary components of the input signals itself
• the relative amplitude of X with respect to Cr could be solely used to determine whether or not to consider the particular input signal
• the background noise affecting the victim user is assumed to be Gaussian noise
• the residual self-FEXT is a stochastic process that is determined by the known self-FEXT coupling channel coefficient and the known input signal
• the known input signal is limited to the constellation points falling within the boundaries defined by the threshold along the x-axis and y-axis
• the resultant signal is not per se Gaussian since the resultant signal is the sum of a Gaussian signal and a uniformly distributed signal with limited support, the resultant signal can be approximated by a Gaussian signal, the variance of which is equal to the variance of the two signals
• the derivation of the thresholds for the x and y inputs of the partial cancellation process should be determined such that the noise variance of the resulting signal falls below the variance needed along the x-axis and y-axis independently to satisfy a certain signal-to-noise ratio and bit error rate (BER) on the victim user constellation
• Another approach for determining the threshold considers the probability density function (pdf) of the FEXT in each bin (or signal energy) due to the contributions of every disturber The threshold is determined such that the combined self-FEXT falls below a certain level
• the complex precoder or canceller coefficient Cr + yC ⁇ will typically be coded with a pseudo-floating point format with 1 sign bit, E exponent bits and M mantissa bits The determination of the E exponent bits will be such that the mantissa bits represents a normalized value in the interval [-1 , 1]
• the complex precoder or canceller coefficient Cr + 7C1 may be expressed as a product C * (cr+jci) of a normalized complex value (cr+jci) and a real amplitude C In a fixed point two's-complement multiplication implementation, this product will typically be implemented as a shifter followed by a normalized complex multiplication Since the self-FEXT channel and precoder or canceller value attenuates
• a complex multiplier 602 which would output a constant zero value without toggling internal and external registers, when both X' and Y' input data are zero would conserve power in its operation and the combined downshift and complex multiplier would implement the input signal selection process that is exemplified in FIG 6 Only the constellation points that fall outside of the gray shaded box, the boundaries of which are determined by the threshold, will be considered in the partial cancellation process Reference is briefly made to FIG 12, which shows one possible implementation of the complex multiplier with added hardware circuitry that enables a zero output when both real and imaginary parts of the input data are zero
• the various embodiments described take advantage of the relative level of the self-FEXT disturbers affecting a victim user
• the coding of the self- FEXT coupling coefficient in a pseudo floating point format and the application of the corresponding exponent for a downshift of each input disturber data, which relates directly to the attenuation of the coupling between the given disturber and victim effectively allows a different threshold to be set for each disturber input data
• This per-disturber threshold will in effect equalize the amount of residual self-FEXT induced by each disturber into the victim user, thereby achieving the goal of partial cancellation
• the various embodiments described to this point primarily takes into account the relative amplitude of the couplings between all disturbers and the given victim, but does not consider explicitly the targeted residual FEXT noise level that is to be achieved on the victim user compared to the contribution level of the background noise
• the embodiments now described take that aspect into account For some embodiments of the partial FEXT cancellation scheme, the amount of residual self-FEXT signal on
• the use of a higher threshold in the architecture depicted in FIG. 1 OB corresponds to performing additional downshift to the input data using downshifters 701 and 703.
• the additional downshift of the input data should be compensated by an upshift of the coefficient or of the output data as illustrated in FIGS. 11 A, 11 B using the upshifters 711 , 716.
• the upshift compensation keeps the overall FEXT coupling coefficient magnitude identical regardless of the threshold selected for the selection of the input data based on the target SNR and desired residual self FEXT level on the victim user. Reference is made to FIG.
• 1 1 C which shows one implementation in which the original exponent bits used to represent the magnitude of the coupling coefficient are also being used for indicating the additional downshifting required as a function of the target residual FEXT level. Since the disturber input data is coded based on 16 bits, the maximum number of possible downshifts is limited to 16 (4 bits). However, the coefficient bus 726 is increased from 12 to 16 bits in order to allow for the storage of the complex precoder or canceller coefficient Cr + yCi in a format C" * (cr"+jci”), which consists of an exponent number including the additional downshift and a normalized complex value (cr"+jci") which can exceed the value of 1 in magnitude.
• the 16 bits coefficient bus 726 is aligned with the input of the multiplier in such a way that only the lower 12 bits are used whenever the number of additional downshifts sets by the target SNR/residual FEXT level is zero, thereby reverting to the embodiment shown earlier in FIG.
• FIG 13A illustrates one possible implementation of a multiplier circuit 902, which is multiplexed between multiple disturbers' data input If the data being fetched from the data bus 904 and downshifted appropriately according to the threshold defined for the particular disturber yields an all zero value the multiplexer 906 will discard the input and produce a zero output while fetching the next disturber/coefficient set to present at the multiplier input for computation
• the ability to benefit from time multiplexing the common resource presupposes that multiple input data can be presented to the multiplier 902 input in less than the time associated with one multiplication operation
• time multiplexing the common resource presupposes that multiple input data can be presented to the multiplier 902 input in less than the time associated with one multiplication operation.
• fifty percent of the disturbers' shifted input data is statistically zero across all disturbers for a given symbol, then a series of sets of input data and associated coefficients for multiple disturbers should be presented to the multiplier's unit, in case multiple consecutive shifted input data sets are all zeros
• FIG 13B illustrates an embodiment for ordering of the coupling coefficients of each individual disturber into multiple victim users that can be envisioned to facilitate the exploitation of another input multiplexing concept
• the precoder/canceller computation process is presented with disturber input data to be multiplied together with the selected disturber victim coefficients, which represents the coupling between the selected disturber and all victims users
• the process is performed in such a way that the input data corresponding to one disturber on a given tone is presented to the multiplication resource and processed with all coupling coefficients associated with the impact of this disturber into all victim users, which have been ordered a prion based on the magnitude of the coupling coefficients
• the coupling into victim user 5 has the smallest amplitude of all coupling of disturber 2 into any victims
• the downshifting associated with the coefficient of user 5 will be more than the one associated with user J, which is greater than the one associated with user 1 or even user 3
• the amount of downshifting associated with a particular victim user may produce a zero input to the multiplier's inputs, as illustrated on FIG 13B for user J Therefore, it should be emphasized that the processing of this given input signal for victim J can be avoided, together with the processing for all victim users that follow J in the ordering process associated with disturber 2
• the processing of the instantaneous signal of disturber 3 and the pre-fetching of the preordered coupling coefficients of this disturber into all victims may be performed It should be noted that such embodiments of the partial cancellation scheme provide both processing power conservation and resource sharing benefits Note also that the ordering can either follow the relative value of the downshifter or threshold associated with the coupling of the FEXT channel only, or in other embodiments, the ordering can follow the relative value of the downshifter or threshold associated with the coupling of the FEXT channel together with the targeted SNR or residual FEXT associated to each victim user
• the benefits of power conservation and resource sharing can be achieved by performing the ordering process according to the relative value of the threshold associated with the impact of the disturber under consideration into the various victim users
• multiplexing the input to the multiplier based on a threshold associated with the input data either reduces the amount of multiplication for a given set of disturbers, or results in a greater number of multiplications in a given time slot in order to achieve a greater number of disturber/victim precoding or cancellation processes
• a simple ordering of the coefficients of a given disturber into all victim users can be easily implemented in order to reduce the computation time associated with the multiplication of the impact of the given disturber into all victims
• ordering allows one to lump together the idle time of the multiplier spent on computing the negligible impact of one disturber into given victims, and bypass this computation
• the described embodiments also reduce the movement associated with coefficient fetches and other internal data transfers
• partial FEXT cancellation may be implemented such that a reduction of the data transfer between entities of the self-FEXT precoder and canceller architecture may be achieved
• an internal reduction in the data transfer in the self-FEXT precoder or canceller can also be realized, thereby reducing data bandwidth requirements
• the computed FEXT component of the disturber 2 for ordered victim users J and below does not need to be added to the partial FEXT cancellation accumulation associated with each victim user, thereby reducing internal data transfer
• the coefficient fetch operation following victim j for the disturber 2 in the preordered coefficient tables is not necessary, since the corresponding FEXT components of disturber 2 into the victims following victim j will not be processed, thereby also limiting some internal data transfer
• FIG 14A the general architecture of a precoder and the associated interface to the DSL PHY device of two DSL users N and M is shown
• the existence of a direct path for transmitting the data of DSL User N as well as the existence of a non-direct path, which primarily consists in the FEXT estimate from all other users (User M)
• the two elements are combined and transmitted on the line, but the actual partitioning of the processing is done as follows
• the DSL User N performs the constellation mapping and gain scaling of the User N data with full precision
• the data of User N is transferred across interface 1420 to the DSM3 processor 131 for precoding
• the precoding comprises two parts first it derives from the user N input data an estimate of the FEXT component from user N
• FIG 14D shows an embodiment of an off-diagonal differentiated architecture in which the direct path component of user N is recombined with the FEXT output estimate of user M on the DSL PHY layer and not on the DSM3 processor
• Such architecture allows for the reduction of bandwidth at the interface 1440 between the DSL PHY and DSM3 processor in case the input data of DSL user N at the output of FFT output buffer of user N falls below a certain threshold associated with the expected residual self-FEXT of user N into user M If the output of the FFT output buffer for a given tone falls below this predetermined threshold, the data is not transported to the DSM3 processor, thereby reducing the bandwidth at the interface
• the determination of the threshold associated to each disturber input is explained in this section
• two models may be implemented The first model considers the relative level of the overall residual self-FEXT induced after partial cancellation with respect to the amplitude of the background noise component affecting the victim user at that particular frequency
• the fact that the background noise affecting the victim user is Gaussian noise is considered, while the residual self FEXT is a stochastic process, which is completely determined by the known self-FEXT coupling channel coefficient and the known input signal, which is limited to the constellation points falling within the boundaries defined by the threshold along the x and y-axis
• the resultant signal is not per se Gaussian, since it is the sum of a Gaussian signal and a uniformly distributed signal with limited support However, it can be approximated by a Gaussian signal, of which the variance is equal to the sum of the variances of the two signals
• the derivation of the threshold for real and imaginary part are considered separately Further, it is assumed that the crosstalk energy from a given victim to a user is continuous and of a uniform pdf in any of the two directions considered separately However, the crosstalk energy might not be uniformly distributed in many QAM constellations The method presented below will still be applicable for nonuniform pdf of the crosstalk Moreover, a single common threshold for both the x and y directions can also be computed with the method presented The embodiment presented below serves only as an example of the method used to determine the threshold and in no way limits it
• E ⁇ residual FEXT disturber i ⁇ ⁇ lh ⁇ ⁇ ' ' ' - - - > 2(£, max - £-; ⁇ m )
• ⁇ lh is a threshold to be applied on the individual crosstalk energy of the various disturbers that impact the victim user. To report this threshold to each disturber's input signal, the coupling needs to be factored into the above equation.
• the concept of using a common threshold can be expanded to incorporate individualized thresholds for each disturber for a given victim.
• the thresholds are kept separate for each disturber
• the equation above can now be applied to obtain an individual threshold ( ⁇ 2 )' lh using the expectation method as outlined above
• the individual thresholds for each disturber relate to the common threshold derived at the output of the canceller by the coupling coefficient associated with each disturber
• Some embodiments employ the partial FEXT cancellation techniques described to achieve a reduction in power consumption of the self-FEXT precoder, canceller, multiplication operations
• Other embodiments focus on achieving a multiplexing of a set of given multiplier's resources among a greater number of disturbers
• Yet other embodiments are directed to applying the partial FEXT cancellation techniques described to reduce the data transfer between entities within the self-FEXT precoder and canceller architecture For example, this bandwidth reduction can be realized on a self-FEXT precoder and canceller architecture, of the type referred to as an off-diagonal architecture or "differentiated architecture," as described earlier in more detail
• the system 200 may comprise a DMT-based VDSL (Very High Bitrate DSL) system
• the system 200 includes N sets of CPE (customer premises equipment) or users ⁇ ⁇ ua, z I UD, 210c
• the system 200 further comprises a FEXT mitigator 137 for performing self-FEXT cancellation
• the FEXT mitigator 137 comprises a computation unit 131 for mitigating FEXT associated with the downstream direction, wherein for some embodiments, the computation unit 131 may be implemented as a MIMO (multiple-input/multiple-output) precoder, whereas for mitigating FEXT associated with the upstream direction, the computation unit 131 may comprise a MIMO canceller
• the computation unit 131 is tightly coupled with the upstream (US) and downstream
• the processor 1502 may include any custom made or commercially available processor, a central processing unit (CPU) or an auxiliary processor among several processors associated with the FEXT mitigator 137, a semiconductor based microprocessor (in the form of a microchip), one or more application specific integrated circuits (ASICs), a plurality of suitably configured digital logic gates, and other well known electrical configurations comprising discrete elements both individually and in various combinations to coordinate the overall operation of the computing system
• CPU central processing unit
• ASICs application specific integrated circuits
• the memory 1512 can include any one or a combination of volatile memory elements (e g , random-access memory (RAM, such as DRAM, and SRAM, etc )) and nonvolatile memory elements (e g , ROM, hard drive, CDROM, efc )
• the memory 1512 typically comprises a native operating system 1514, one or more native applications, emulation systems, or emulated applications for any of a variety of operating systems and/or emulated hardware platforms, emulated operating systems, etc
• the applications may include application specific software 1516 stored on a computer readable medium and executed by the processor 1502 and may include any of the modules 137, 131 , 132, 135, 139 described with respect to FIG 2
• the modules 137, 131 , 132, 135, 139 may also be embodied as hardware
• any of the components described above comprises software or code
• these components are embodied in a computer-readable medium for use by or in connection with an instruction execution system such as, for example, a processor in a computer system or other system
• an instruction execution system such as, for example, a processor in a computer system or other system
• a computer-readable medium refers to any tangible medium that can contain, store, or maintain the software or code for use by or in connection with an instruction execution system
• a computer- readable medium may store one or more programs for execution by the processing device 1502 described above
• the computer-readable medium may include a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory), and a portable compact disc read-only memory (CDROM)
• the FEXT mitigator 137 may further comprise mass storage 1526
• the mass storage 1526 may include a database 1528 for storing and managing data, such as bit-loading tables
• FIG 16 depicts a top-level flow diagram 1600 for an embodiment of a process for performing partial self-FEXT cancellation in the system of FIG 2
• the instantaneous characteristics of an input signal are determined
• the characteristics comprise at least one of an amplitude level of the input signal and energy level of the input signal
• the method further comprises dynamically allocating resources according to the determined instantaneous characteristics of the input signal
• Block 1630 proceeds by utilizing the allocated resources to perform FEXT cancellation of a disturber signal

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• 2010
  • 2010-02-26 JP JP2011552181A patent/JP5406315B2/ja active Active
  • 2010-02-26 CN CN201080018187.8A patent/CN102415040B/zh active Active
  • 2010-02-26 US US12/713,482 patent/US8644127B2/en active Active
  • 2010-02-26 WO PCT/US2010/025526 patent/WO2010099399A1/en active Application Filing
  • 2010-02-26 KR KR1020117020421A patent/KR101653433B1/ko active IP Right Grant
  • 2010-02-26 EP EP10746886.0A patent/EP2401834A4/en not_active Withdrawn

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