Optimal downstream power back-off for digital subscriber lines

A method comprising determining a plurality of power spectrum density (PSD) profiles for a plurality of cabinet-deployed digital subscriber lines (DSLs) comprising jointly and iteratively determining a plurality of cutoff frequencies based on crosstalk coupling parameters among the DSLs, wherein the cutoff frequencies and PSD profiles are in one to one correspondence, and wherein each profile comprises a reduced PSD portion below the cutoff frequency of the profile and a maximum PSD portion above the cutoff frequency.

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Digital subscriber line (DSL) technologies can provide a large bandwidth for digital communications over existing subscriber lines. When transmitting data over the subscriber lines, crosstalk interference can occur between the transmitted signals over adjacent twisted-pair phone lines, for example in a same or nearby bundle of lines. Crosstalk may limit the performance of some DSL technologies, such as asymmetric DSL 2 (ADSL2) and very high bit rate DSL 2 (VDSL2). Crosstalk may occur in mixed deployment scenarios, where cabinet-deployed lines and exchange-deployed lines operate within relatively short proximity or in the same binder. For example, cabinet-deployed lines (with relatively shorter deployment distances) may introduce crosstalk interference into the exchange-deployed lines (with relatively longer deployment distances). At a point where the cabinet-deployed lines enter the shared binder, signals in the exchange-deployed lines may have already traveled some distance and somewhat attenuated. Thus, the far-end crosstalk (FEXT) introduced at this point may significantly affect the signals in the exchange-deployed lines—sometimes completely overpowering the desired transmission signals. This crosstalk problem may be referred to as the “near-far” problem.

SUMMARY

In one embodiment, the disclosure includes a method comprising determining a plurality of power spectrum density (PSD) profiles for a plurality of cabinet-deployed DSLs comprising jointly and iteratively determining a plurality of cutoff frequencies based on crosstalk coupling parameters among the DSLs, wherein the cutoff frequencies and PSD profiles are in one to one correspondence, and wherein each profile comprises a reduced PSD portion below the cutoff frequency of the profile and a maximum PSD portion above the cutoff frequency.

In another embodiment, the disclosure includes an apparatus comprising a processor configured to determine a plurality of power spectrum density (PSD) profiles for a plurality of cabinet-deployed DSLs comprising jointly and iteratively determining a plurality of cutoff frequencies based on crosstalk coupling parameters among the DSLs, wherein the cutoff frequencies and PSD profiles are in one to one correspondence, and wherein each profile comprises a reduced PSD portion below the cutoff frequency of the profile and a maximum PSD portion above the cutoff frequency.

In yet another embodiment, the disclosure includes an apparatus comprising a processor configured to determine crosstalk coupling parameters among a plurality of DSLs, jointly and iteratively determine a cutoff frequency for each of a plurality of power spectrum density (PSD) profiles corresponding to the plurality of DSLs, wherein each cutoff frequency is based on a target data rate for the corresponding DSL and a plurality of the crosstalk coupling parameters, and for each DSL, adjust a downstream signal power, wherein the downstream signal power on a DSL is based on the determined PSD profile corresponding to the DSL.

In yet another embodiment, the disclosure includes a method implemented in a Spectrum Management Center (SMC) comprising optimizing downstream power backoff (DPBO) parameters of a plurality of cabinet-deployed DSLs based on crosstalk coupling parameters among the cabinet-deployed DSLs, wherein the DPBO parameters include a plurality of cutoff frequencies, each of which corresponds to one of the plurality of DSLs.

DETAILED DESCRIPTION

In order to reduce crosstalk for downstream transmissions in DSL systems and address potential issues such as the “near-far” problem, a spectrum management technique referred to as downstream power back-off (DPBO) may be used. The DPBO technique may reduce the downstream transmit power spectrum density (PSD) (sometimes referred to as power spectral density) on shorter loops, and thereby reduce the downstream power injected at a flexibility point (e.g., a cabinet). As a result, the downstream FEXT, coupled from the disturbing DSL systems (e.g., cabinet-deployed lines) at the flexibility point into the victim DSL systems (e.g., exchange-deployed lines), may be weakened.

Conventional DPBO is a static spectrum management technique that may be used to reduce crosstalk. However, conventional DPBO may be typically configured to meet a single data-rate requirement. In use, since a plurality of signals may transmit at different rates in different lines, the DPBO may not ensure service requirements (e.g., data-rate or quality of service) for each line. For example, if the DPBO performance is limited to a data-rate that is lower than the rate requirement for a first cabinet-deployed line, adequate service may not be provided over the first line. In comparison, if the supported data-rate is higher than the rate requirement of a second cabinet-deployed line, the DPBO scheme may cause high power consumption and excess crosstalk in the second line. Alternatively, dynamic spectrum management (DSM) techniques may be used to reduce crosstalk and achieve service requirements in a plurality of lines. The DSM techniques may be based on algorithms that optimize the PSD of a transmitter (e.g., a modem), such as iterative waterfilling, iterative spectrum balancing, and optimal spectrum balancing. Disadvantages of such algorithms may include poor performance (e.g., using iterative waterfilling) or relatively high computational complexity (e.g., using iterative spectrum balancing or optimal spectrum balancing), which may lead to implementation difficulties.

An adaptive scheme of DPBO for a single line may overcome the drawbacks of conventional DPBO and/or DSM techniques. The adaptive DPBO scheme attempts to optimize PSD parameters on a line-by-line basis, so that its spectral friendliness may be maximized (minimized crosstalk) while meeting a target data rate. In use, the adaptive DPBO scheme may determine an optimal PSD mask (or profile) based on the current downstream transmit PSD and the required data rate of a line. After an initial optimization, PSD parameters, such as a maximum cutoff frequency of DPBO, may be periodically (but not too frequently) updated in a central office (CO) management information base (MIB). For example, when channel conditions improve (e.g., drop in noise level), the cutoff frequency of DPBO may increase, so that the frequency span of DPBO may be expanded to improve its spectral friendliness. In comparison, when the channel conditions worsen (e.g., rise in noise level), the cutoff frequency may decrease, so that the frequency span of DPBO may be narrowed to maintain the required data rate. The adaptive DPBO scheme for a single line may lead to higher performance than conventional DPBO and/or DSM, and may be implemented using algorithms with relatively lower computational complexity.

In practice, a DBPO scheme (e.g., conventional, DSM, or adaptive) may configure and optimize a PSD mask100, as illustrated inFIG. 1. The PSD mask100may correspond to a configured power vs. frequency profile for a transmitted signal in a subscriber line. The PSD mask100may comprise a reduced PSD portion110and a maximum PSD portion120. The reduced PSD portion110may correspond to frequencies less than or equal to DPBOFMAX which may be referred to as a maximum DPBO frequency or a cutoff frequency. The transmit PSD (TXPSD(f)) in the reduced PSD portion110may decrease as the frequency (f) increases. For example, the TXPSD(f) vs. frequency(f) curve of the reduced PSD portion110may comprise a predicted exchange PSD mask (PEPSD(f)), which may be constant over a short frequency range then decrease nonlinearly (or linearly). The function PEPSD(f) may be empirically determined. Generally, as the frequencies increase below the cutoff frequency, the crosstalk in the lines deployed by the exchange and the cabinet may increase. Thus, to reduce the crosstalk, the PSD of the signals transmitted from the cabinet at the higher end of this range (closer to DPBOFMAX) may be decreased and the PSDs of the signals transmitted from the exchange may be maintained.

In contrast, the maximum PSD portion120may correspond to frequencies greater than or equal to about DPBOFMAX, where TXPSD(f) may remain constant as the frequency(f) increases. For example, in the TXPSD(f) vs. frequency(f) curve, the maximum PSD portion120may be equal to about a DPBO exchange site maximum PSD (DPBOEPSD(f)). At such range above the cutoff, the frequencies may be substantially high and may not be suitable for transmissions over relatively long distances from the exchange to a plurality of customer premise equipments (CPEs) due to, for example, dispersion effects. Consequently, such frequency channels may be dedicated to the lines from the cabinet to the CPEs, which may allow for higher PSDs at a maximum limit, e.g. DPBOEPSD(f). As shown in the PSD mask200, TXPSD(f) may be expressed mathematically as follows:

TXPSD⁡(f)={PEPSD⁡(f),f<DPBOFMAXDPBOEPSD⁡(f),f≥DPBOFMAX.
Further, PEPSD(f) may be expressed as follows:
PEPSD(f)=DPBOEPSD(f)−(DPBOESCMA+DPBOESCMB·√{square root over (f)}+DPBOESCMC·f)·DPBOESEL,
where DPBOESEL may be an electrical loop length of a cable between the exchange and the cabinet, and DPBOESCMA, DPBOESCMB, and DPBOESCMC may be parameters of a frequency response model of the cable. The equation above and at least some of the parameters may be described in the International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) Recommendation G.997.1 entitled “Physical layer management for digital subscriber line (DSL) transceivers,” April 2009, which is incorporated herein by reference.

As mentioned previously, in a conventional DPBO scheme for reducing crosstalk, the cutoff frequency DPBOFMAX may be typically fixed, for example, to about 2.2 Megahertz (MHz). Such a value may be chosen to meet a required data-rate, e.g. equal to about four megabits per second (Mbps) or about five Mbps, in a single line deployed by the cabinet. The PSDs may be configured for a single line that corresponds to that data-rate but not for other lines from the cabinet. A conventional DPBO scheme may be relatively easy to implement and require substantially no or little knowledge about the binder topology of the lines (e.g., only the distance between the exchange and the cabinet). However, such scheme may not meet the multiple data-rate requirements at the cabinet. For example, if the data-rate supported using the optimized PSD is lower than the required data rate for a line, the line may not provide adequate service. Alternatively, if the supported data-rate is higher than the required data rate for a line, additional power may be unnecessarily consumed and crosstalk may be increased in the line.

To optimize the PSDs for a plurality of lines deployed from the cabinet, the total transmitted signal power in the lines may be configured using a DSM technique. Using DSM, the PSDs may be set based on the binder topology (e.g., the length of the different lines and cabinet location) and on the required rates of the lines. The DSM technique may be based on any of a number of DSM algorithms, such as iterative waterfilling, optical spectrum balancing, or iterative spectrum balancing. The iterative waterfilling algorithm may not require knowledge of the binder topology, but may yield poor performance in a mixed exchange/cabinet deployment scenario. The optical spectrum balancing and iterative spectrum balancing algorithms may yield optimal or near-optimal performance, but may require a centralized control. Additionally, such algorithms may be relatively more complex and difficult to implement, for example, when the quantity of lines in the network is relatively high. Further, the PSD masks resulted from DSM techniques may sometimes contain steep regions which may not be compliant with existing standards.

An adaptive scheme may be used instead of the conventional DPBO and DSM schemes to improve the PSD configuration and optimization and achieve reduced crosstalk. In the adaptive scheme, the cutoff frequency DPBOFMAX in the PSD mask may vary for each line depending on the required data-rates of the lines. For example, the PSDs of the lines that have different data-rates may be configured using PSD masks based on different DPBOFMAX values. The PSD values in the PSD masks may be configured to reduce the crosstalk between the lines, and the DPBOFMAX values in the PSD masks may be selected to optimize the PSDs to meet the required data-rates of the lines. As such, the adaptive scheme may be implemented to minimize or reduce the crosstalk and the power consumption in the lines, while meeting the service requirements of the lines. The adaptive scheme may be based on DPBO, and may be simpler to implement in comparison to a DSM technique. For example, the adaptive scheme may require the distance between the exchange and the cabinet, but not the knowledge of other binder topology. Additionally, the adaptive scheme may have less stringent memory requirements in comparison to the DSM technique.

FIG. 2illustrates a chart of an exchange/cabinet rate tradeoff200between a plurality of exchange and cabinet-deployed lines. The exchange/cabinet rate tradeoff200may be represented by a curve210that comprises a plurality of points. The curve210represents exchange rate and cabinet rate pairs configured using a conventional DPBO scheme. The points correspond to a compromise between exchange rate and cabinet rate pairs to limit crosstalk in the lines. Accordingly, when the frequency channels in the exchange-deployed lines and the exchange rates are increased, the frequency channels in the cabinet-deployed lines and the cabinet rates may be decreased to reduce the crosstalk. For example, when the exchange rate in an exchange-deployed line for a first CPE is relatively low (e.g., equal to about one Mbps), the cabinet rate in a cabinet-deployed line for the first CPE may be relatively high (e.g., equal to about eight Mbps). In comparison, when the exchange rate for a second CPE is higher (e.g., equal to about three Mbps), the cabinet rate for the second CPE may be lower (e.g., equal to about 5.5 Mbps).

Using a conventional DPBO, the configured PSDs may meet a data-rate requirement in a single line, which may correspond to a single point on the curve210. In contrast, the adaptive scheme may be used to optimize the PSDs to reduce crosstalk and meet a plurality of data-rates in a plurality of lines, which may correspond to a plurality of points on the curve210. The adaptive scheme may be used by varying the value of DPBOFMAX to match the data-rates in the lines. For example, the DPBOFMAX value may be reduced for higher cabinet rates (on the right side of the curve210) or may be increased for lower cabinet rates (on the left side of the curve210). Thus, the PSDs may be optimized according to the required data-rates in the cabinet-deployed lines and the data-rates in the exchange-deployed lines may be maintained.

FIG. 3illustrates a chart of an exchange/cabinet rate optimization300between a plurality of exchange and cabinet-deployed lines. The exchange/cabinet rate optimization300may be represented by a curve302that comprises a plurality of points. The points correspond to exchange rate and cabinet rate pairs in the lines, where the PSDs have been optimized. Suppose, for the purpose of illustration, that the points correspond to eight exchange-deployed lines that have a distance equal to about five kilometers (km) and eight cabinet-deployed lines that have a distance equal to about three km. The cabinet is located at about four km from the exchange. Accordingly, the PSDs may be optimized using the adaptive scheme described above by varying the cutoff frequency to match the data-rates in the lines. For example, to optimize the PSDs for the higher cabinet rates in the curve302, the adaptive scheme may be used to reduce the DPBOFMAX value. Alternatively, to optimize the PSDs of the lower cabinet rates, the DPBOFMAX value may be increased.

The curve302may be compared to a curve310that represents exchange rate and cabinet rate pairs configured using a conventional DPBO scheme, e.g. similar to the curve310. Unlike the curve302, the curve310may meet data-rate requirements for a single exchange rate and cabinet rate pair (denoted by “x”), which corresponds to the conventional DPBO scheme (e.g., at about 2.2 MHz). The supported exchange rate and cabinet rate pair on the curve310may match another point on the curve302, which corresponds to an optimized PSD using the adaptive scheme. However, the remaining points on the curve310may not meet the data-rate requirements for other exchange rate and cabinet rate pairs. Consequently, a cabinet target rate equal to about six Mbps (indicated by an arrow) may be supported using the adaptive scheme but not the conventional DPBO scheme.

Although the adaptive DPBO scheme described above may yield lower complexity and higher performance over the conventional and/or DSM schemes, it may still hold certain drawbacks. For example, when configuring the transmit PSDs of a plurality of DSL systems to their respective optimal conditions, the convergence of optimal PSDs may be slow, due to a lack of coordination among the plurality of DSL systems. Since the adaptive algorithm is per line based, each line may run the algorithm autonomously and optimize its own parameters (e.g., DPBOFMAX of the PSD mask100). Consequently, it is possible that, when one line has already converged to an optimal DPBOFMAX, other lines may still have yet to finish the optimization process. Thus, the total convergence time may be prolonged. Further, since the adaptive DPBO scheme for a first line may not take into account the influences of other lines (e.g., in the same binder), the optimized PSD for the first line may be subject to deterioration and/or instability. For example, the crosstalk coupling among the plurality of lines may change periodically, which may affect the first line that just finished optimizing its PSD. Due to the changing crosstalk interference from other lines into the first line, the once optimal PSD may become suboptimal. Consequently, the optimization process may have to be performed again, which may take many reinitiations and iterations. Sometimes dramatic changes in the PSDs of the other lines may even cause the condition of the optimized first line to become unstable because of retrains or reinitializations.

Disclosed herein is a system and method for joint optimization of a plurality of downstream transmit PSDs corresponding to a plurality of subscriber lines. The method may comprise an adaptive DPBO scheme to reduce the crosstalk among the lines and meet the service requirements of the lines, such as data-rates for providing adequate services. For each line, the PSD of the transmitted signals in the line may be configured and optimized using an algorithm based on a cutoff frequency of a PSD mask. The cutoff frequency may vary line-by-line according to the required data-rates. In the disclosed system and method, the joint optimization of the cutoff frequencies may take into account not only the required data rate of a line, but also the influence of the conditions of other lines in the bundle. Therefore, the coordinated algorithm may obtain fast convergence of optimal PSDs for the plurality of lines. The method may be relatively simple to implement and may lead to a higher performance of the overall DSL network than the conventional and/or DSM algorithms.

FIG. 4illustrates a schematic diagram of an embodiment of a DSL system400. The DSL system400may be a VDSL2 system, an ADSL2 system, an ADSL2 plus (ADSL2+) system, or any other DSL system. The DSL system400may comprise an exchange402, a cabinet404coupled to the exchange402by a cable405, and a plurality of CPEs406, which may be coupled to the exchange402and/or the cabinet404via a plurality of subscriber lines408. At least some of the subscriber lines408may be bundled in a binder409. Additionally, the DSL system400may optionally comprise a network management system (NMS)410and a public switched telephone network (PSTN)412, both of which may be coupled to the exchange402. In other embodiments, the DSL system400may be modified to include splitters, filters, management entities, and various other hardware, software, and functionality.

The NMS410may be a network management infrastructure that processes data exchanged with the exchange402and may be coupled to one or more broadband networks, such as the Internet. The PSTN412may be a network that generates, processes, and receives voice or other voice-band signals. In an embodiment, the exchange402may be a server located at a CO and may comprise switches and/or splitters, which may couple the NMS410, the PSTN412, and the subscriber lines408. For instance, the splitter may be a 2:1 coupler that forwards data signals received from the subscriber lines408to the NMS410and the PSTN412, and forwards data signals received from the NMS410and the PSTN412to the subscriber lines408. Further, the splitter may optionally comprise one or more filters to help direct data signals between the NMS410, the PSTN412, and the subscriber line408. Additionally, the exchange402may comprise at least one DSL transmitter/receiver (transceiver), which may exchange signals between the NMS410, the PSTN412, and the subscriber lines408. The signals may be received and transmitted using the DSL transceiver, such as a modem. In an embodiment, the DSL transceiver may comprise a forward error correction (FEC) codeword generator that generates FEC data, an interleaver that interleaves the transmitted data across a plurality of tones, or both. For instance, the DSL transceiver may use a discrete multi-tone (DMT) line code that allocates a plurality of bits for each sub-carrier or tone in each symbol. The DMT may be adjusted to various channel conditions that may occur at each end of a subscriber line. In an embodiment, the DSL transceiver of the exchange402may be configured to transmit data at similar or different rates for each subscriber line408.

In an embodiment, the cabinet404may be located at a distribution center between the CO and customer premises and may comprise switches and/or splitters, which may couple the exchange402to the CPEs406. For instance, the cabinet404may comprise a DSL access multiplexer (DSLAM) that couples the exchange402to the CPEs406. Additionally, the cabinet404may comprise a DSL transceiver, which may be used to exchange signals between the exchange402and the CPEs406. The DSL transceiver may process the received signals or may simply pass the received signals between the CPEs406and the exchange402. The splitter in the cabinet404may be a N:1 coupler (where N is an integer) that routes data signals received from the exchange402to N CPEs406, and routes data signals received from the N CPEs406to the exchange402. The data signals may be transmitted and received using the DSL transceiver. Further, the splitter of the cabinet404may optionally comprise one or more filters to help direct data signals between the exchange402and the CPEs406via the corresponding subscriber lines408. In an embodiment, the DSL transceiver may be configured to transmit data to the CPEs406at similar or different rates and/or power for each subscriber line408, as described in detail below. The cabinet404may also be referred to herein as remote terminal (RT) interchangeably.

In an embodiment, the CPEs406may be located at the customer premises, where at least some of the CPEs406may be coupled to a telephone414and/or a computer416. The telephone414may be hardware, software, firmware, or combinations thereof that generates, processes, and receives voice or other voice-band signals. The CPE406may comprise a switch and/or a splitter, which may couple the subscriber lines408and the telephone414and the computer416. The CPE406may also comprise a DSL transceiver to exchange data between the CPE406and the exchange402via the subscriber line408. For instance, the splitter may be a 2:1 coupler that forwards data signals received from the subscriber line408to the telephone414and the DSL transceiver, and forwards data signals received from the telephone414and the DSL transceiver to the subscriber line408. The splitter may optionally comprise one or more filters to help direct data signals to and from the telephone414and the DSL transceiver. The DSL transceiver (e.g., a modem), may transmit and receive signals through the subscriber lines408. For instance, the DSL transceiver may process the received signals to obtain the transmitted data from the exchange402, and pass the received data to the telephone414, the computer416, or both. The CPEs406may be coupled to the exchange402directly via the subscriber lines408and/or via the subscriber lines408and the cabinet404. For example any of the CPEs406may be coupled to a subscriber line408from the exchange402and/or a subscriber line408from the cabinet404. The CPEs406may access the NMS410, the PSTN412, and/or other coupled networks via the subscriber lines408deployed by the exchange402and/or the cabinet404.

In an embodiment, the subscriber lines408may be telecommunications paths between the exchange402and the CPE406and/or between the cabinet404and the CPEs406, and may comprise one or more twisted-pairs of copper cable. Crosstalk interference may occur between the tones or signals transported through the subscriber lines408that are deployed by the exchange402and the cabinet404, e.g. in the binder409. The crosstalk interference may be related to the power, frequency, and travel distance of the transmitted signals and may limit the communications performance in the network. For instance, when the PSD of the transmitted signals increase, e.g. over a range of frequencies, the crosstalk between the adjacent subscriber lines108may increase and hence the data-rates may decrease. To reduce or limit the crosstalk in the lines, the DSL transceiver of the cabinet404may be configured to control and adjust the PSD of the signals or tones transmitted downstream, e.g. to the CPEs406, in any of the subscriber lines408. The DSL transceiver may be used to reduce the PSD of a transmitted signal in a line to ensure a sufficient data-rate that meets service requirements. The PSD may be controlled, e.g. using software, hardware, firmware, or combinations thereof, according to a PSD profile or mask to reduce crosstalk. The PSD mask may be optimized to meet the service requirements for any of the lines, such as the data-rate in the subscriber line408.

In a joint adaptive DPBO scheme for a plurality of subscriber lines (e.g., deployed from a cabinet), the issues of slow convergence and potential instability may be eliminated or minimized via coordination of the plurality of lines. For example, DPBO parameters (e.g., DPBOFMAX of the PSD mask100) for a line may be optimized by not only considering the required data-rate of the line itself, but also considering the PSDs of other lines and the crosstalk coupling information among the plurality of lines. As a result, the convergence of optimal PSDs for the plurality of lines may be made faster, since fewer iterations or retrainings may be needed. Further, the overall conditions of the plurality of lines may be made more stable.

There may be a variety of algorithms to implement the joint optimization DBPO scheme. In an embodiment, a DPBOFMAX value for each line may be calculated based on an algorithm that may be implemented using hardware, software, firmware, or combinations thereof. For example, the algorithm may be implemented at a cabinet (e.g., a DSLAM) or in a network management system which comprises a local spectrum management center (SMC). The algorithm may configure a plurality of PSD masks (e.g., PSD mask200) corresponding to a plurality of subscriber lines. An embodiment of an algorithm is presented in pseudo code in Table 1, where:N may refer to the total number of subscriber lines to configure PSD masks;K may refer to the total number of subcarriers;∀n denotes “for all n” or for n=1, 2, . . . , N;∀k denotes “for all k” or for k=1, 2, . . . , K;DPBOFMAXminnmay refer to the minimum allowed value of the cutoff frequency DPBOFMAX for line n;DPBOFMAXmaxnmay refer to the maximum allowed value of DPBOFMAX for line n;DPBOFMAXtolnmay refer to the tolerance (i.e. smallest step or resolution) of iteration of DPBOFMAX for line n;fkmay refer to the center frequency of subcarrier k;fsmay refer to the DMT symbol rate;bmaxmay refer to the maximum allowed number of bits per subcarrier;sknmay refer to the transmit PSD of line n on subcarrier k;skmmay refer to the transmit PSD of line m on subcarrier k;hkn,mmay refer to the crosstalk coupling function from line m (disturbing line) into line n (victim line) on subcarrier k.hkn,nmay refer to the gain of line n on subcarrier k.σknmay refer to the power of background noise of line n on subcarrier k (e.g., due to thermal noise);Rtargetnmay refer to the required (or target) data rate for line n;Rnmay refer to the current or intermediate data rate for line n; andΓ may refer to the Signal to Noise Ratio (SNR) gap to capacity.

In the implementation of the above algorithm, as illustrated in Table 1, the final value of DPBOFMAXnmay be referred to as the cutoff frequency for line n. The transmit PSD for line n may be given by:

The search range of the parameter DPBOFMAX for each of the plurality of lines may be decreased iteratively. For example, in each iteration, the algorithm may first reduce the search range of DPBOFMAX for line one by a half while keeping DPBOFMAX for all other lines and their transmit PSDs fixed. Then, the algorithm may reduce the search range of DPBOFMAX for line two by a half while keeping DPBOFMAX for all other lines and their transmit PSDs fixed. The same process may be repeated until all lines are covered. After the search ranges of DPBOFMAX for all lines are reduced by half, the algorithm may enter a next iteration. Such an iterative process may be guaranteed to converge, because each iteration reduces the search range of the parameter DPBOFMAX by a half via a bisection search. The iterative process may stop, after the search range of DPBOFMAX for each of the plurality of lines has been reduced to a pre-set tolerance frequency range. The iterative process may produce cutoff frequencies for each of the N lines.

The complexity of the adaptive DPBO algorithm is O(K×log2(K)) per line, where K is the number of subcarriers in a MEDLEY set. The MEDLEY set may refer to a set of subcarriers used during the DSL initialization and may be defined in various ITU recommendations. Since the complexity may be linear with the number of subscriber lines, the disclosed algorithm may be relatively simple to implement in a network comprising a large number of lines (e.g., several thousand or more lines). For example, in some applications, the number of subcarriers may be approximately 4000, and the number of lines N may be in the thousands. Compared with some conventional DPBO and/or DSM algorithms whose complexity may be exponential with the number of lines and thus relatively difficult to implement in a network comprising a large number of lines, the low complexity of the disclosed algorithm may prove advantageous.

In the joint optimization of cutoff frequencies for the plurality of DSLs, various parameters, such as crosstalk coupling functions among all lines (e.g., hkn,mfor all k, n and m (m≠n) in the algorithm in Table 1), gains (e.g., hkn,nfor all k and n), and background noises (e.g., σknfor all kand n), may be determined before an execution of the algorithm. Also, initial values of sknfor all k and for n=2, 3, . . . N may be determined before the start of the algorithm. Then, in each iteration step, the search range of the cutoff frequency DPBOFMAX for each line may be reduced based on comparison of a derived current data rate (e.g., Rnfor all n) and a target data rate of the line (e.g., Rtargetnfor all n). If the derived current data rate is higher than the target data rate, the DPBOFMAX may only be searched in the upper half of its previous range. Otherwise, if the derived current data rate is lower than the target data rate, the DPBOFMAX may only be searched in the lower half of its previous range.

Further, the derivation of the current data rate for a given line may take into account, not only its own parameters, but also the parameters of other lines. These considered parameters may include transmit PSDs and crosstalk coupling functions among all lines. For example, the computation of Rnin the algorithm of Table 1 for a given line n incorporates the terms hkn,m, sknfor all k, n and m (m≠n), thus taking into account crosstalk coupling and PSDs for other lines. These parameters may be assumed to be constant throughout all iteration steps, or they may be updated during each iteration step. Consequently, the final DPBOFMAX for a line may be the result of a joint (and iterative) optimization based on the conditions of all lines. When the conditions of other lines change (e.g. increase in crosstalk coupling), jointly optimized DPBOFMAX may be adjusted accordingly to maintain optimal or near-optimal PSD. As a result, the plurality of lines may obtain maximum spectral friendliness, while meeting their target data rates. The coordination among the lines may lead to an overall higher performance as well as increased stability of the DSL network.

In an embodiment, a variety of events may trigger the execution of the algorithm shown in Table 1. Examples of the triggering events may include, but are not limited to, the addition of a new line to an existing bundle of lines, the reinitiation of an active line in the bundle, and changes in the background noise for some of the lines. In addition, the DPBOFMAX value for the plurality of lines may be varied, e.g. in a dynamic manner, to maintain the required data rates of the lines over a time period or a showtime. In some cases, regulatory constraints may limit the minimum and/or maximum value allowed for the cutoff frequency DPBOFMAX. Such constraint may be incorporated in the adaptive scheme for reducing crosstalk, for example, by manually setting DPBOFMAXminnin the algorithm above to a minimum value that is allowed for DPBOFMAX for line n.

FIG. 5aandFIG. 5billustrate two flowcharts of an embodiment of a joint and iterative PSD optimization method500, which may be used to configure a plurality of PSD masks corresponding to a plurality of cabinet-deployed lines in an architecture such as the DSL system400inFIG. 4. The method500may configure cutoff frequencies of the PSD masks in order to optimize the downstream transmit PSDs. The optimized PSDs may reduce crosstalk among the lines while meeting their required data rates in the lines. The reduction in crosstalk may also avoid or limit unnecessary power consumption in the lines.

The method500may start in step505, where a variety of parameters pertaining to a plurality of lines (e.g., N lines where N is an integer greater than one) may be determined. The variety of parameters may be determined via any suitable known technique or approach. For example, the parameters may be determined through measurement, estimation, derivation, or any combinations thereof. The parameters may include, but are not limited to, crosstalk coupling functions or parameters (e.g., hkn,mfor all k, n and m (m≠n) in the algorithm of Table 1) among all lines, gains (e.g., hkn,nfor all k and n), and background noises (e.g., σknfor all k and n) of all lines. The parameters may be assumed to remain constant during an implementation of the method500. Alternatively, if desired, the parameters may be updated during an implementation of the method500. Further, step505may also set various initial parameters for each line (e.g., line n), such as a maximum allowed cutoff frequency DPBOFMAXmaxn, a minimum allowed cutoff frequency DPBOFMAXminn, and an iteration tolerance DPBOFMAXtoln.

Next, in step510, a line (e.g., line n) may be selected from the N lines to configure its transmit PSD profile (or mask). The selected line n may be any line in a bundle, not necessarily starting from the first line. The PSD profiles of all N lines may be configured in the method500. Alternatively, depending on application, only a subset of lines may be configured while still using parameters pertaining to all N lines.

Next, the method500may enter an iterative process to optimize a cutoff frequency for the selected line n. An iterative process may comprise one or more iteration sequences, and an iteration sequence comprise a plurality of steps in the method500. An iteration sequence may start in step515, where a line (e.g., line m) may be selected from the N lines to reduce the search range of its corresponding cutoff frequency. It should be understood that, in each iteration sequence, the method500may actually reduce the search ranges of cutoff frequencies corresponding to all N lines by half. Therefore, the line m selected in step515may be independent from the line n selected in step510.

Next, the iteration sequence may continue in step520, where the method500may determine if the difference between an upper boundary and a lower boundary of the search range is greater than the iteration tolerance, which is set in step505. The upper and lower boundaries of the search range of the cutoff frequency may be initially set to be the maximum and minimum allowed cutoff frequencies for the line m (selected in step515), respectively. Then, in each iteration sequence, the search range may be reduced by a half. If the condition in step520is met, the method500may proceed to step525. Otherwise, the method500may proceed to step540. In step525, the cutoff frequency of the line m may be set to the intermediate (or average) of the upper and lower boundaries of the search range.

Next, in step530, a current data rate of the line m may be determined. It should be noted that the current data rate may be determined jointly based on not only parameters of the line m, but also parameters of all other N−1 lines in a binder. For example, parameters such as transmit PSDs, crosstalk coupling functions, gains, and background noises may be accounted in the determination of the current data rate. Among the accounted parameters, the transmit PSD for the line m may be derived from the cutoff frequency set in step525, and the transmit PSDs for all other N−1 lines may be assumed to be fixed for the current iteration sequence. The joint determination of the current data rate may take into account the varying conditions of other lines, thus leading to a more accurate and improved determination.

Next, in step535, the search range of the cutoff frequency DPBOFMAX for the line m may be reduced by half based on comparison of the current data rate and a target data rate. For example, if the derived current data rate is higher than the target data rate, the DPBOFMAX may only be searched in the upper half of its previous range. Otherwise, if the derived current data rate is lower than the target data rate, the DPBOFMAX may only be searched in the lower half of its previous range.

Next, in step540, the method500may determine if there are more lines to reduce the search range of its cutoff frequency. As mentioned above, in each iteration sequence, the method500may actually reduce the search ranges of all cutoff frequencies corresponding to all N lines by half. If the condition in the block540is met, the method500may return to step520to reduce the search ranges of cutoff frequencies for the remaining lines in the binder. Otherwise, the method500may conclude that all search ranges are reduced by half and the current iteration sequence is over. Thus, the method500may proceed to step545.

In step545, the method500may determine if additional iteration sequences are needed to optimize the cutoff frequency for the line n selected in step510. This may be achieve by calculating the difference between the (reduced) upper and lower boundaries of the search range and seeing if it is smaller than or equal to the iteration tolerance. If the condition in the block545is met, the method500may deem that the cutoff frequency for the line n is already sufficiently optimized, and thus proceed to step550. Otherwise, the method500may return to step515to enter a next iteration sequence, where the search ranges of cutoff frequencies for all N lines may be further reduced by half. Next, in step550, the PSD mask for line n may be configured based on the optimized cutoff frequency, and an optimal transmit PSD may be determined accordingly. Next, in step555, the method500may determine if there are more lines to configure PSD masks. If the condition in the block555is met, the method500may return to step510to configure PSD masks for the remaining lines in the binder. Otherwise, the method500may end.

The joint and iterative DPBO scheme disclosed herein may also be illustrated in a relatively simpler layout.FIG. 6shows a flow chart of an embodiment of a joint and iterative PSD optimization method600, which may be used to configure a plurality of PSD masks corresponding to a plurality of cabinet-deployed lines in an architecture such as the DSL system100inFIG. 4. The method600may configure cutoff frequencies of the PSD masks in order to optimize the downstream transmit PSDs. The optimized PSDs may reduce crosstalk among the lines while meeting their required data rates in the lines. The reduction in crosstalk may also avoid or limit unnecessary power consumption in the lines.

The method600may start in step610, where a variety of parameters pertaining to a plurality of lines (e.g., N lines where N is an integer greater than one) may be determined. The variety of parameters may be determined via any suitable known technique or approach. For example, the parameters may be determined through measurement, estimation, derivation, or any combinations thereof. The parameters may include, but are not limited to, crosstalk coupling functions or parameters (e.g., hkn,mfor all k, n and m (m≠n) in the algorithm of Table 1) among all lines, gains (e.g., hkn,nfor all k and n), and background noises (e.g., σknfor all k and n) of all lines. The parameters may be assumed to remain constant during an implementation of the method600. Alternatively, if desired, the parameters may be updated during an implementation of the method600. Further, step610may also set various initial parameters for each line (e.g., line n), such as DPBOFMAXminn, DPBOFMAXmaxn, and DPBOFMAXtoln.

Next, in step620, a line may be selected from the N lines to configure its transmit PSD profile (or mask). The selected line may be any line in a bundle, not necessarily starting from the first line. The PSD profiles of all N lines may be configured in the method600. Alternatively, depending on application, only a subset of lines may be configured while using parameters pertaining to all N lines.

Next, in step630, the cutoff frequency DPBOFMAX may be iteratively optimized for the selected line. Each iteration herein may actually reduce the search ranges of DPBOFMAX frequencies for all N lines by a half. The reduction of search range for each line may be based on comparison of a derived current data rate and a target data rate of the corresponding line. If the derived current data rate is higher than the target data rate, the DPBOFMAX may only be searched in the upper half of its previous range. Otherwise, if the derived current data rate is lower than the target data rate, the DPBOFMAX may only be searched in the lower half of its previous range.

In an embodiment, step630may use the algorithm illustrated in Table 1 to derive the current data rate. Herein, the derivation of the current data rate for a line may take into account the parameters of all N lines, such as their transmit PSDs, background noises and crosstalk coupling functions. Some of the accounted parameters (e.g., background noises and crosstalk coupling functions obtained in step610) may remain constant. Also, some of the accounted parameters (e.g., transmit PSDs) may be updated during each iteration via any suitable algorithm. For example, in one algorithm, the transmit PSD of a cable may be determined based on the frequency (f), a maximum limit of the PSD mask (e.g., DPBOEPSD), the electrical loop length of the cable between the exchange and the cabinet (e.g., DPBOESEL), and parameters of the frequency response of the cable, according to U.S. patent application Ser. No. 12/634,994 entitled “Optimizing the Transmit Power Spectrum Density (PSD) of a Remotely Deployed Line to Ensure Spectral Compatibility,” which is incorporated herein by reference. In step630, since the derivation of the current data rate, in each iteration, may account for conditions of other lines, the final cutoff frequency for the selected line, after the convergence of all iterations, may be the result of a joint (or coordinated) optimization. Such a joint and iterative optimization algorithm may lead to improvement of the overall performance and/or stability of the DSL network.

Next, in step640, the method600may determine if there are more lines to configure PSD profiles. If the condition in the block640is met, the method600may return to step620to configure PSDs for the remaining lines in the binder. Otherwise, the method600may proceed to step650. In step650, desired signals may be transmitted downstream on the plurality of lines for which PSD profiles have been configured. For example, the signals may be transmitted from a cabinet to a plurality of CPEs.

The method600may be implemented via a low complexity algorithm and may improve the overall performance of a DSL network. For example, regarding the “near-far” problem described previously, the disclosed algorithm may help minimize or reduce the impact of crosstalk introduced from the cabinet-deployed lines into the exchange-deployed lines, thus maximizing the spectral friendliness of the cabinet-deployed lines. In addition, the method500may be fully compliant with current DSL standards, such as the ITU-T Recommendation G.993.2 entitled “Very-high-speed digital subscriber line transceivers 2 (VDSL2),” February 2006, and ITU-T Recommendation G.992.3 entitled “Asymmetric digital subscriber line transceivers 2 (ADSL2),” April 2009, and ITU-T Recommendation G.997.1 entitled “Physical layer management for digital subscriber line (DSL) transceivers,” April 2009, all of which are incorporated herein by reference.

FIG. 7illustrates an embodiment of a network unit700, which may comprise a processor or a transceiver as described above, e.g., within a network or system. The network unit700may comprise a plurality of ingress ports710and/or receiver units712for receiving data, logic unit or processor720to process signals and determine where to send the data to, and a plurality of egress ports730and/or transmitter units732for transmitting data to other systems. The logic unit or processor720may be configured to implement any of the schemes described herein, such as the joint and iterative PSD optimization method500, and may be implemented using hardware, software, or both. For example, the logic unit or processor720may include or be coupled to a computer-readable medium, which may be programmed to compute a plurality of cutoff frequencies according to the algorithm in Table 1.

The schemes described above may be implemented on any general-purpose network component, such as a computer or network component with sufficient processing power, memory resources, and network throughput capability to handle the necessary workload placed upon it.FIG. 8illustrates a typical, general-purpose network component or computer system800suitable for implementing one or more embodiments of the methods disclosed herein, such as the joint and iterative PSD optimization method500. The general-purpose network component or computer system800includes a processor802(which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage804, read only memory (ROM)806, random access memory (RAM)808, input/output (I/O) devices810, and network connectivity devices812. The processor802may be implemented as one or more CPU chips, one or more cores (e.g., a multi-core processor), or may be part of one or more application specific integrated circuits (ASICs) and/or digital signal processors (DSPs). The processor802may be configured to implement any of the schemes described herein, including the joint and iterative PSD optimization method500, which may be implemented using hardware, software, or both. For example, the processor802may include or be coupled to a computer-readable medium, which may be programmed to compute a plurality of cutoff frequencies according to the algorithm in Table 1.

The secondary storage804is typically comprised of one or more disk drives or tape drives and is used for non-volatile storage of data and as an over-flow data storage device if RAM808is not large enough to hold all working data. Secondary storage804may be used to store programs that are loaded into RAM808when such programs are selected for execution. The ROM806is used to store instructions and perhaps data that are read during program execution. ROM806is a non-volatile memory device that typically has a small memory capacity relative to the larger memory capacity of secondary storage804. The RAM808is used to store volatile data and perhaps to store instructions. Access to both ROM806and RAM808is typically faster than to secondary storage804.