HK1144345A - Stable low power mode for multicarrier transceivers - Google Patents

Abstract

A stable Low Power Mode (LPM) for multicarrier transceivers is described that at least provides transmit power savings while enabling receiver designs that can easily operate without the detrimental effects of fluctuating crosstalk. In one exemplary embodiment, the LPM achieves power savings by reducing the number of used subcarriers without actually performing a power cutback on those subcarriers, thereby allowing a receiver to measure the SNR or noise levels and determine the crosstalk noise on the line regardless of a crosstalking modem being in a LPM or not.

Description

Stable low power mode for multicarrier transceivers

Information on related applications

The present application claims the benefit of U.S. patent application No.60/989,542 entitled "Stable Low Power Mode For Multicarrier Transceivers" filed on day 21 of 2007 and U.S. patent application No.61/011,267 entitled "Stable Low Power Mode For Multicarrier Transceivers-Second Edition" filed on day 16 of 2008, and the priority specified in 35u.s.c. 119(e), both of which are hereby incorporated by reference in their entirety.

Technical Field

The present invention relates generally to communication systems. More particularly, an exemplary embodiment of the present invention relates to power saving in a communication environment, particularly in an xDSL environment.

Disclosure of Invention

Exemplary aspects of the invention relate to a stable Low Power Mode (LPM) for a multicarrier transceiver that at least achieves transmit power savings while enabling receiver designs to operate easily without the deleterious effects of fluctuating crosstalk. In an exemplary embodiment, the LPM achieves power savings by reducing the number of subcarriers used without actually reducing the power on those subcarriers, thus allowing the receiver to measure the SNR or noise level and determine the crosstalk noise on the line, regardless of whether the crosstalk-causing modem is in the LPM or not.

One problem with the low power mode is that variations in the transmit power level cause variations in crosstalk into adjacent lines. This results in unsteady or fluctuating crosstalk that can cause bit errors and even retraining in other DSL connections in the link bundle.

The most common examples of problems caused by fluctuating crosstalk caused by LPM are as follows:

1. initialization is performed while the crosstalking transceiver is in LPM. A transceiver that performs initialization when a crosstalking transceiver is in LPM may allocate bits to subchannels that have good SNR when the crosstalking transceiver is in LPM, but poor SNR when the crosstalking transceiver returns to normal (full power) operation. Thus, when a crosstalking transceiver exits from the LPM, the transceiver may have many bit errors and even need to perform retraining.

2. On-line reconfiguration (OLR) (e.g., bit swapping, SRA, etc.) is performed while the crosstalk-causing transceiver is in the LPM. A transceiver performing OLR when a crosstalking transceiver is in LPM may allocate bits to subchannels that have good SNR when the crosstalking transceiver is in LPM, but very poor SNR when the crosstalking transceiver returns to normal (full power) operation. Thus, when a crosstalking transceiver exits from the LPM, the transceiver may have many bit errors and even need to perform retraining.

According to an exemplary embodiment, LPM achieves transmit power savings while enabling receiver design to operate without the detrimental effects of fluctuating crosstalk. LPM achieves power savings by reducing the number of subcarriers used without actually reducing the power on those subcarriers, thus allowing the receiver to measure SNR or noise level and determine crosstalk noise on the line regardless of whether the crosstalk-causing modem is in LPM or not. The power on these subcarriers may also be reduced to further achieve power savings.

Accordingly, aspects of the present invention relate to energy conservation.

Other aspects of the invention relate to power saving in a modem.

Further aspects of the invention relate to power saving in xDSL modems.

Still further aspects of the invention relate to energy saving in a multicarrier transceiver.

Further aspects relate to a multicarrier transceiver capable of receiving a plurality of subcarriers and to a method of determining a signal-to-noise ratio (SNR) over the plurality of subcarriers comprising measuring the SNR over a first subset of the plurality of subcarriers and using at least the measured SNR to estimate the SNR over a second subset of the plurality of subcarriers.

Still further aspects relate to a multicarrier transceiver capable of receiving a plurality of subcarriers, and to a method of determining a noise level on a plurality of subcarriers comprising measuring a noise level on a first subset of the plurality of subcarriers and estimating a noise level on a second subset of the plurality of subcarriers using at least the measured noise.

Still further aspects relate to a multicarrier transceiver capable of receiving a plurality of subcarriers comprising a receiver portion capable of measuring a signal-to-noise ratio (SNR) over a first subset of the plurality of subcarriers and capable of estimating the SNR over a second subset of the plurality of subcarriers using at least the measured SNR.

Still further aspects relate to a multicarrier transceiver capable of receiving a plurality of subcarriers comprising a receiver portion capable of measuring a noise level on a first subset of the plurality of subcarriers and capable of estimating a noise level on a second subset of the plurality of subcarriers using at least the measured noise.

Further aspects of the invention relate to a multicarrier transceiver capable of receiving a plurality of subcarriers comprising means for measuring a signal-to-noise ratio (SNR) over a first subset of the plurality of subcarriers and means for estimating the SNR over a second subset of the plurality of subcarriers using at least the measured SNR.

Further aspects relate to a multicarrier transceiver capable of receiving a plurality of subcarriers comprising means for measuring a noise level on a first subset of the plurality of subcarriers, and means for estimating a noise level on a second subset of the plurality of subcarriers using at least the measured noise.

Further aspects of the invention relate to any of the above aspects, wherein the first subset is defined as every nth subcarrier of the plurality of subcarriers, where N is a positive integer.

A further aspect of the present invention relates to any of the above aspects, wherein the measuring is performed during initialization.

Additional aspects of the invention relate to any of the above aspects, wherein the measurement is performed during Showtime (in-work), e.g., user data transmission.

Still further aspects relate to a method of determining a first SNR on a first subcarrier in a multicarrier receiver comprising measuring or determining a second SNR on a second subcarrier and determining the first SNR using at least the second SNR.

Further aspects of the invention relate to a method of determining a first SNR on a first subcarrier in a multicarrier receiver comprising measuring or determining a noise level on a second subcarrier and using at least the noise level to determine the first SNR.

Still further aspects relate to means for determining a first SNR on a first subcarrier in a multicarrier receiver comprising measuring or determining a second SNR on a second subcarrier and means for determining the first SNR using at least the second SNR.

Further aspects of the invention relate to an apparatus for determining a first SNR on a first subcarrier in a multicarrier receiver comprising means for measuring or determining a noise level on a second subcarrier and using at least the noise level to determine the first SNR.

A multicarrier transceiver capable of determining a first SNR on a first subcarrier in a multicarrier receiver and capable of measuring or determining a second SNR on a second subcarrier and capable of determining the first SNR using at least the second SNR.

Still further aspects relate to a multicarrier transceiver capable of determining a first SNR on a first subcarrier in a multicarrier receiver and capable of measuring or determining a noise level on a second subcarrier and capable of determining the first SNR using at least the second noise level.

Still further aspects of the invention relate to a multicarrier transceiver capable of transmitting a plurality of subcarriers in a low power mode, the low power mode method comprising transmitting a subset of the subcarriers transmitted in a full power mode during the low power mode, wherein the subcarriers transmitted in the low power mode are transmitted at a same power level as the power level transmitted in the full power mode.

Still other aspects relate to a multicarrier transceiver capable of transmitting a plurality of subcarriers comprising a transmit portion capable of transmitting a subset of the subcarriers transmitted in a full power mode during a low power mode, wherein the subcarriers transmitted in the low power mode are transmitted at a same power level as the power level transmitted in the full power mode.

Still further aspects of the invention relate to a multicarrier transceiver capable of transmitting a plurality of subcarriers comprising means for transmitting a subset of the subcarriers transmitted in a full power mode during a low power mode, wherein the subcarriers transmitted in the low power mode are transmitted at a same power level as the power level transmitted in the full power mode.

A further aspect of the invention relates to any of the above aspects, wherein the subset is defined as every nth subcarrier used in full power mode, where N is a positive integer.

Still further aspects of the invention relate to a low power mode for use in multicarrier communications that achieves power savings by using a subset of subcarriers transmitted in a full power mode, wherein the subset of subcarriers transmitted in the low power mode are transmitted at the same power level as the power level in the full power mode.

Further aspects of the invention relate to a low power mode wherein the subset is defined as every nth subcarrier used in full power mode, where N is a positive integer.

Still further aspects of the invention relate to a method of setting a low power mode comprising defining a subset of subcarriers used during a full power mode for use in the low power mode, wherein the subset is defined as every nth subcarrier used in the full power mode, wherein N is a positive integer.

Additional aspects of the invention relate to a method of configuring a low power mode, further comprising inputting a value of N into a management system for configuring a DSL transceiver.

Still further aspects relate to a method of configuring a low power mode further comprising the input being performed by a service provider.

These and other features and advantages of the present invention are described in, or will be readily understood from, the following detailed description of exemplary embodiments.

Drawings

Exemplary embodiments of the invention will be described in detail with reference to the following drawings, in which:

FIG. 1 illustrates an example communication system in accordance with this invention;

FIG. 2 illustrates an exemplary transmitter portion and receiver portion of modems in accordance with the present invention;

FIG. 3 illustrates an example method for measuring SNR and communicating using a designated carrier in accordance with this invention;

FIG. 4 illustrates an example method for measuring noise and communicating using a designated carrier in accordance with this invention; and

fig. 5 shows an example trellis diagram depicting communication between modems in accordance with the present invention.

Detailed Description

Exemplary embodiments of the present invention are described with respect to a low power mode in an xDSL environment. It should be understood, however, that the system and method of the present invention is generally applicable to any type of communication system using any communication protocol in any environment.

The exemplary systems and methods of the present invention are also described in terms of multicarrier modems (e.g., xDSL modems and VDSL modems) and associated communication hardware, software, and communication channels. However, to avoid unnecessarily obscuring the present invention, the following description omits well-known structures and devices that may be shown in block diagram form or otherwise summarized.

For purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the present invention. It should be understood, however, that the present invention may be practiced in various ways apart from the specific details set forth herein.

Further, while the exemplary embodiments illustrated herein show the components of the system as being collocated, it should be understood that the components of the system can be located at distant portions of a distributed network (e.g., a communication network and/or the Internet), or in a dedicated secure, unsecured and/or encrypted system. Thus, it should be understood that the components of the system can be incorporated into one or more devices (e.g., a modem), or configured on a particular node of a distributed network (e.g., a telecommunications network). As can be appreciated from the following description, for reasons of computational efficiency, the components of the system can be arranged anywhere in a distributed network without affecting the operation of the system. For example, the components can be located in a central office modem (CO, ATU-C, VTU-C), a customer premises modem (CPE, ATU-R, VTU-R), an xDSL management device, or a combination thereof. Similarly, one or more functional portions of the system can be distributed between the modem and an associated computing device.

Further, it should be understood that the links (including communication channels) connecting the elements (some not shown) may be wired links or wireless links, or any combination thereof, or any other known or later developed element capable of providing and/or communicating data to and from the connected elements. The term "module" as used herein may refer to any known or later developed hardware, software, firmware, or combination thereof that is capable of performing the function associated with that element. As used herein, the terms "determine," "calculate," and variations thereof are used interchangeably and include any type of methodology, process, mathematical operation or technique. "transmitting modem" and "transmitting transceiver" and "receiving modem" and "receiving transceiver" can be used interchangeably herein. In addition, the terms "transceiver" and "modem" have the same meaning and are used interchangeably. Likewise, the terms "transmitter" and "transmitting modem" have the same meaning and are used interchangeably, and further "receiver" and "receiving modem" have the same meaning and are used interchangeably.

Furthermore, although some of the exemplary embodiments described herein are directed to a transmitter portion of a transceiver performing a particular function, it should be understood that a corresponding complementary function is performed by a receiver portion of the transceiver. Thus, although may not be specifically shown in each example, the present disclosure is intended to include such respective complementary functionality in the same transceiver and/or another transceiver.

The communication system 1 comprises a transceiver 100 and a transceiver 200 interconnected by one or more links and one or more networks 5. In addition to known component parts, each transceiver 100 and 200 includes a transmitter part and a receiver part shown in more detail in fig. 2. In particular, transmitter portion 110 includes subcarrier management module 120, controller/memory 130, subcarrier table 140, and bit loading module 150. Receiver portion 210 includes SNR measurement module 220, subcarrier management module 230, SNR estimation module 240, bit loading module 250, controller/memory 255, noise measurement module 260, noise estimation module 270, power level measurement module 280, and subcarrier table 290. One or more of the transmitter portion 110 and the receiver portion 210 may also be connected to the management interface 330. The transmitter portion 110 and the receiver portion 210 are connected by a link, having subcarriers 1-N on the link.

As noted above, the systems, methods, techniques and protocols discussed herein will be described with respect to xDSL systems (e.g., the xDSL systems specified in ADSL2ITU-T G.993.2, ADSL2+ ITUG.993.5 and VDSL2ITU G.993.2, which are fully incorporated herein by reference).

In operation, for one or more Upstream (US) and Downstream (DS) channels, subcarriers to be used during LPM are identified and messages indicating the subcarriers are exchanged between modems. Further, messages are exchanged having bit allocations for one or more of the US and DS channels. Then, during LPM, the transmitter reduces transmission power by transmitting using only every nth subcarrier. The power level of each subcarrier transmitted during LPM is the same as during full power mode (i.e., no power reduction), thereby achieving a transmit power savings (1-1/N) ratio. For example, if N is 10 and the transmitter transmits subcarriers 33-255 at-40 dBm/Hz during Full Power Mode (FPM), the transmitter may transmit subcarriers 33, 43, 53,.. multidot.233, 243, 253 at-40 dBm/Hz during LPM. This may result in a 1-1/10-90% reduction in transmit power.

Operation of the exemplary receiver 210

According to an exemplary embodiment, to operate without the deleterious effects of fluctuating crosstalk caused by the LPMs of other transceivers in a link bundle (binder), receiver 210 is capable of:

1. during initialization and/or Showtime, receiver 210, in cooperation with SNR measurement module 220, measures SNRs on those subcarriers designated for transmission during LPM (whether or not the crosstalk-causing transceiver is in LPM mode), as managed by subcarrier management module 230.

2. Based on at least these SNR measurements, the receiver 210, in cooperation with the SNR estimation module 240, estimates the SNR on the intermediate subcarriers that are not designated for transmission during the LPM. Because the distance between the measured subcarriers is relatively small, i.e., N × 4.315kHz, the receiver can accurately estimate the SNR on the middle subcarrier using, for example, simple linear interpolation. The SNR estimation module 240 for the intermediate carrier can also be based on other measurements (e.g., measurements made for the intermediate sub-carrier), for example, if there are other noise sources (i.e., not from the transceiver causing crosstalk), such as Radio Frequency Interference (RFI), or noise from other traffic in the link bundle. For example, when the crosstalking transceiver is in LPM, the SNR of the intermediate subcarriers can also be measured by the SNR measurement module 220, and this information can be incorporated into the resulting SNR estimate for the intermediate subcarriers by the SNR estimation module 240.

In addition, other noise sources (e.g., unremoved echoes, inter-symbol or inter-channel interference, etc.) may also be used in the estimation of the SNR of the intermediate subcarriers by the SNR estimation module 240.

3. Receiver 210 uses the measured SNR on the LPM subcarriers and/or the estimated SNR on the intermediate subcarriers for the bit loading algorithm run by bit loading module 250 during initialization and/or Showtime OLR.

Using the above example, if subcarriers 33, 43, 53, etc. are designated for transmission during LPM, receiver 210 is able to measure the SNR on these subcarriers by SNR measurement module 220 and use the measured SNR to estimate the SNR on the intermediate subcarriers (i.e., subcarriers 34-42, 44-52, etc.) by SNR estimation module 240. Since there is only a distance of 10 x 4.3125-43.125 kHz between the subcarriers being measured, a simple linear interpolation method (which may be performed by the controller/memory 255) can provide sufficient performance.

Generally any form of interpolation may be used to estimate the SNR on the intermediate subcarriers. For example, the transceiver may use linear interpolation such that the SNR of the intermediate subcarrier is estimated as a straight line connecting the SNR on the ith measured subcarrier and the SNR on the (i + N) th measured subcarrier. Alternatively, the SNR between the measured subcarriers may be estimated using, for example, a known FEXT (far end crosstalk) or NEXT (near end crosstalk) coupling function.

It is noted that if receiver 210 measures the SNR of those subcarriers designated for transmission during LPM during Showtime and initialization, and uses these measurements to estimate the SNR on the other subcarriers, it does not matter which crosstalking transceivers are under LPM and which are not. This is because the power levels on the subcarriers designated for transmission during LPM remain in low and full power modes, and therefore the measured SNRs on these subcarriers are not dependent on the power modes of the other transceivers in the link bundle. Thus, if the receiver measures the SNR in this manner, all transceivers can enter and exit the LPM as quickly as possible without causing a problem of fluctuating crosstalk to each other.

Thus, in an embodiment, the LPM uses a subset of the subcarriers so that crosstalk can still be estimated by another transceiver in the link bundle.

Numerical example #1

Assume that the multicarrier system operates with the following subcarrier designations: 20. 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. It is assumed that the LPM has N-10 and that the subcarriers transmitted under the LPM are subcarriers numbered 20 and 30. Assume that the SNR measurement on subcarrier 20 is 25dB and the SNR measurement on subcarrier 30 is 15 dB. If simple linear interpolation is used to estimate the SNR on the middle subcarriers, the estimated SNRs for subcarriers 21, 22, 23, 24, 25, 26, 27, 28, and 29 may be 24dB, 23dB, 22dB, 21dB, 20dB, 19dB, 18dB, 17dB, and 16dB, respectively.

Numerical example #2

Assume that the multicarrier system operates with the following subcarrier designations: 20. 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. It is assumed that the LPM has N-10 and that the subcarriers transmitted under the LPM are subcarriers numbered 20 and 30. Assume that the SNR measurement on subcarrier 20 is 25dB and the SNR measurement on subcarrier 30 is 15 dB. It is also assumed that there is narrowband RFI affecting sub-carrier No. 25 and that the SNR measured on this sub-carrier is 20 dB. For all other intermediate subcarriers not affected by RFI, the estimated SNRs for subcarriers 21, 22, 23, 24, 26, 27, 28, and 29 may be 24dB, 23dB, 22dB, 21dB, 19dB, 18dB, 17dB, and 16dB, respectively, if simple linear interpolation is used. The SNR on subcarrier number 25 can be estimated as a result of the combination of RFI noise and DSL crosstalk. For example, if the estimated SNR due to DSL crosstalk is 20dB (as calculated in numerical example 1 above) and the SNR due to RFI is 20dB, the linear combination of these two SNRs may result in a total estimated SNR of 17dB for the subchannel 20.

Measuring noise level rather than signal-to-noise ratio (SNR)

Alternatively, or in addition to measuring the SNR by SNR measurement module 220, receiver 210 may measure the noise level on subcarriers designated for transmission by subcarrier management module 230 during LPM in cooperation with noise measurement module 260.

For example, to operate without the deleterious effects of fluctuating crosstalk caused by the LPMs of other transceivers in the link bundle, the receiver 210 can:

1. during initialization and/or Showtime, receiver 210, in cooperation with noise measurement module 260, measures the noise level on those subcarriers designated for transmission during LPM (regardless of whether the crosstalk-causing transceiver is in LPM or not). In addition, receiver 210, in cooperation with SNR measurement module 220, measures SNR on those subcarriers designated for transmission during LPM (regardless of whether the crosstalk-causing transceiver is in LPM or not).

2. Based on at least these noise measurements, the receiver 210, in cooperation with the noise estimation module 280, estimates the noise level (Ni) on the intermediate subcarriers not designated for transmission during LPM. Because the distance between the measured subcarriers is relatively small, i.e., N × 4.315kHz, the receiver can accurately estimate the noise level on the middle subcarrier using, for example, a simple linear interpolation method. If there are other noise sources (i.e. not from the cross-talk causing transceiver) such as Radio Frequency Interference (RFI), or noise from other devices in the link bundle, the estimation of the noise on the intermediate carrier can also be based on other measurements, such as measurements on the intermediate sub-carrier, for example.

For example, when the crosstalking transceiver is in LPM, the noise of the intermediate subcarriers may also be measured and this information may be incorporated into an estimate of the resulting noise of the intermediate subcarriers. In addition, other noise sources (e.g., unremoved echoes, inter-symbol or inter-channel interference, etc.) may be used for estimating the noise of the intermediate subcarriers.

3. During initialization and/or Showtime, receiver 210, in cooperation with power level measurement module 280, measures the received signal power level (Pi) on the intermediate subcarrier (i.e., the intermediate subcarrier not designated for transmission during LPM).

4. The receiver 210 then estimates the SNR on the intermediate subcarriers using the measured received signal power level (from step 3) and the estimated noise level (from step 2) in cooperation with the SNR estimation module 240. For example, the receiver 210 may estimate the SNR using the ratio Pi/Ni of each subcarrier.

5. Receiver 210 then uses the SNR on the LPM subcarrier and/or the estimated SNR on the intermediate subcarrier for the bit loading algorithm during initialization and Showtime OLR.

Using the above example, if subcarriers 33, 43, 53, etc. are designated for transmission during LPM, receiver 210 may measure the noise level on these subcarriers and use the measured noise to estimate the noise on the intermediate subcarriers (i.e., subcarriers 34-42, 44-52, etc.). Since there is only a distance of 10 x 4.3125-43.125 kHz between the measured subcarriers, simple linear interpolation may provide adequate performance. In general, any form of interpolation may be used to estimate the noise level on the intermediate subcarriers. For example, the transceiver may use linear interpolation such that the noise level of the intermediate subcarrier is estimated as a straight line connecting the noise level on the ith measured subcarrier and the noise level on the (i + N) th measured subcarrier.

Alternatively, the noise level between the measured subcarriers may be estimated using, for example, a known FEXT or NEXT coupling function. Receiver 210 may then use the measured signal power levels for subcarriers 34-42, 44-52, etc. and the estimated noise levels to estimate the SNRs on those subcarriers.

It should be noted that if receiver 210 measures the noise levels of those subcarriers designated for transmission during LPM during Showtime and initialization, and uses these measurements (along with the measured received signal power level) to estimate the noise levels on the other subcarriers, it does not matter which crosstalking transceivers are under LPM and which are not. This is because the power levels on the subcarriers designated for transmission during LPM remain in the low power and full power modes, and therefore the noise levels measured on these subcarriers are not dependent on the power modes of the other transceivers in the link bundle. Thus, if the receiver measures the noise level in this manner, all transceivers can enter and exit the LPM as quickly as possible without causing a problem of fluctuating crosstalk to each other.

Thus, in an embodiment, the LPM uses a subset of the subcarriers so that crosstalk can still be estimated by another transmitter in the link bundle.

Numerical example #3

Assume that the multicarrier system operates with the following subcarrier designations: 20. 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. It is assumed that the LPM has N-10 and that the subcarriers transmitted under the LPM are subcarriers numbered 20 and 30. Assume that the noise level measurement on subcarrier 20 is-55 dBm/Hz and the noise level measurement on subcarrier 30 is-65 dBm/Hz. Assume that the received signal power level is constant at-80 dBm/Hz. For example, if simple linear interpolation is used to estimate the noise level on the intermediate subcarriers, the estimated noise levels for subcarriers 21, 22, 23, 24, 25, 26, 27, 28, and 29 may be-56 dBm/Hz, -57dBm/Hz, -58dBm/Hz, -59dBm/Hz, -60dBm/Hz, -61dBm/Hz, -62dBm/Hz, -63dBm/Hz, and-64 dBm/Hz, respectively. Based on the received signal power level of-80 dBm/Hz, the estimated SNRs for subcarriers 21, 22, 23, 24, 25, 26, 27, 28, and 29 may be 24dB, 23dB, 22dB, 21dB, 20dB, 19dB, 18dB, 17dB, and 16dB, respectively, using this noise estimate.

Numerical example #4

Assume that the multicarrier system operates with the following subcarrier designations: 20. 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. It is assumed that the LPM has N-10 and that the subcarriers transmitted under the LPM are subcarriers numbered 20 and 30. Assume that the noise level measurement on subcarrier 20 is-55 dBm/Hz and the noise level measurement on subcarrier 30 is-65 dBm/Hz. Assume that the received signal power level is constant at-80 dBm/Hz. It is also assumed that there is narrow-band RFI affecting sub-carrier No. 25 and that the measured noise on this sub-carrier is-60 dBm/Hz. For all other intermediate subcarriers that are not affected by RFI, if simple linear interpolation is used, e.g., if noise on the intermediate subcarriers is estimated using simple linear interpolation, the estimated noise for subcarriers 21, 22, 23, 24, 26, 27, 28, and 29 may be-56 dBm/Hz, -57dBm/Hz, -58dBm/Hz, -59dBm/Hz, -61dBm/Hz, -62dBm/Hz, -63dBm/Hz, and-64 dBm/Hz, respectively. Based on the received signal power level of-80 dBm/Hz, the estimated SNRs for subcarriers 21, 22, 23, 24, 26, 27, 28, and 29 may be 24dB, 23dB, 22dB, 21dB, 19dB, 18dB, 17dB, and 16dB, respectively, using this noise estimate. The noise on subcarrier number 25 can be estimated as a result of the combination of RFI noise and DSL crosstalk. For example, if the estimated noise due to DSL crosstalk is-60 dBm/Hz (as calculated in numerical example 3 above), and the noise due to RFI is-60 dBm/Hz, the linear combination of these two noises may result in a total estimated noise of-63 dBm/Hz for the subchannel 20. Based on a received signal power level of-80 dBm/Hz, the resulting SNR may be, for example, 17 dB.

Subsets of subcarriers used during LPM

In the above example, the subset of subcarriers used during LPM is defined as every nth subcarrier transmitted during full power mode. Generally any definition of a subset of subcarriers may be used.

For example, instead of transmitting only 1 subcarrier every N subcarriers, the number L (L > 1) subcarriers may be transmitted every N subcarriers. For example, if L is 3 and N is 30 and the total number M is 90 subcarriers, numbered from 10 to 89, then the following subcarriers may be transmitted: 10. 11, 12, 40, 41, 42, 70, 71, 72. This results in a reduction of the number of subcarriers from 90 to 9, i.e. a power reduction factor of 10. As in the above example, other transceivers in the link bundle may determine crosstalk by measuring the SNR on known subcarriers (e.g., 10, 11, 12, 40, 41, 42, etc.) and estimating the SNR of the intermediate subcarriers (e.g., 13-39, 43-69, etc.). For example, other transceivers may estimate the SNR on the intermediate subcarriers using linear interpolation. Generally any form of interpolation may be used to estimate the SNR on the intermediate subcarriers. For example, the SNR on the middle subcarrier can be estimated using a known FEXT or NEXT coupling function.

In general, any algorithm for defining a subset of values in an array of subcarrier indices may be used to define the subset of subcarriers used during LPM.

Alternatively, or in addition, a subset of the subcarriers used during LPM may be defined as a list of subcarrier indices. For example, if there are a total of 90 subcarriers, numbered 10 to 89, the list can take any value, e.g., [13, 21, 34, 54, 60, 78, 88 ].

In an alternative embodiment, the subcarriers used during LPM are not fixed, but rather vary over time. This exemplary embodiment is referred to as a subcarrier scanning lpm (subcarrier scanning lpm). In this embodiment, a first subset of subcarriers is used for a first time period during LPM, a second subset of subcarriers is used during a second time period, and so on. For example, if there are 100 subcarriers, numbered 1 through 100, during the FPM, subcarriers 1-10 may be used for a first time period (e.g., 1 second or 1000 DMT symbols), subcarriers 11-21 may be used for a second time period (e.g., 1 second or 1000 DMT symbols), and so on. After ten time periods, all 100 subcarriers are transmitted during LPM. One major benefit of this approach is that a receiver measuring the SNR or noise level over 10 slot times is able to determine the SNR for all subcarriers without the need for estimation or interpolation (as described above) for the intermediate subcarriers. Defining a subset of subcarriers for LPM

The subset of subcarriers used during LPM may be defined by any of the following entities:

service provider (this has the advantage that the service provider can define subsets based on band planning, link bundle management problems, regulatory problems, etc.)

End user/consumer

CO Modem for upstream and/or downstream transmission (e.g. VTU-O or ATU-C)

CPE modem for upstream and/or downstream transmission (e.g. VTU-R or ATU-R)

-CPE receiver for downstream transmission

-CO receiver for uplink transmission

The subset of subcarriers, if defined by the service provider or end user, can be entered into the system through, for example, management interface 330. For example, the service provider can input index values for a subset of subcarriers by defining the value of N described above. For example, the service provider can specify through the management interface that, starting with subcarrier No. 33, every nth-12 subcarriers will be used for transmission during LPM. Alternatively, for example, the service provider can specify through the management interface that, starting from subcarrier No. 33 to subcarrier 512, every nth-12 subcarriers will be used for transmission during LPM, and starting from subcarrier No. 600 to subcarrier 900, every nth-6 subcarriers will be used for transmission during LPM. Alternatively, for example, the service provider may specify through the management interface 300 that more than 1 subcarrier is transmitted out of every N subcarriers, as described in the above example. Alternatively, or in addition, the service provider may specify a list of subcarriers used during LPM, where, for example, the list can take any value, e.g., [45, 59, 88, 123, 129, etc.

For subcarrier scanning LPM, the service provider may define a scanning time, i.e., a period of time during LPM for which a subset of the subcarriers are transmitted. For example, a service provider may specify that S-10 subcarriers are to be transmitted under LPM and that the scanning time is 100 ms. In this exemplary setup, under LPM, a first set of 10 subcarriers from the FPM may be transmitted in 100ms, followed by a subsequent set of 10 subcarriers in the next 100ms, and so on.

The transceiver (e.g., VTU-O, VTU-R, ATU-C or ATU-R) may also define a subset of subcarriers in a similar manner as described above in the examples with respect to the service provider.

Transmitting and receiving messages regarding LPM parameters.

When the service provider or CO modem defines a subset of the subcarriers used during LPM, this information may be sent from the CO modem (e.g., ATU-C or VTU-O) to the CPE (e.g., RT modem or ATU-R or VTU-R), as described later with respect to fig. 5. The information contained in this message may be stored in subcarrier table 289 under the direction of subcarrier management module 230 and indicate which subcarriers are used during LPM. For example, the message may include a list of subcarrier numbers, e.g., [78, 129, 343, 355, etc. Alternatively, for example, the message may include at least one value of N (as described in the above example). For example, if N is 10 during the LPM, every 10 th subcarrier may be transmitted. Alternatively, the message may include at least one value of N (as described in the above example) and at least one starting subcarrier index for indexing, for example. For example, N-10, and the start frequency index may be set to 33, which means that subcarriers numbered 33, 43, 53. Alternatively, the message may include at least one value of N (as described in the above example), at least one starting subcarrier index, and at least one ending subcarrier index, for example. For example, N-10, and the start frequency index may be set to 33 and the end subcarrier index may be set to 100, which means that subcarriers numbered 33, 43, 53,.., 83, 93 should be used during LPM. In general, any algorithm for defining a subset of values in an array of subcarrier indices may be used to define the subset of subcarriers transmitted by a message.

When the CPE modem or end user defines a subset of the subcarriers used during LPM, information may be sent from the CPE modem to the CO. The information included in the message can indicate which subcarriers are used during LPM. For example, the message may include a list of subcarrier numbers, e.g., [78, 129, 343, 355, etc. Alternatively, for example, the message may include at least one value of N (as described in the above example). For example, if N is 10 during the LPM, every 10 th subcarrier may be transmitted. Alternatively, the message may include at least one value of N (as described in the above example) and at least one starting subcarrier index for indexing, for example. For example, N-10, and the start frequency index may be set to 33, which means that subcarriers numbered 33, 43, 53. Alternatively, the message may include at least one value of N (as described in the above example), at least one starting subcarrier index, and at least one ending subcarrier index, for example. For example, N-10, and the start frequency index may be set to 33 and the end subcarrier index may be set to 100, which means that subcarriers numbered 33, 43, 53,.., 83, 93 should be used during LPM. In general, any algorithm for defining a subset of values in an array of subcarrier indices may be used to define the subset of subcarriers transmitted by a message.

In addition, for subcarrier scanning LPM, the scanning time would need to be exchanged via messages. The scan time may be defined in seconds, DMT symbols, etc., for example.

These messages may be sent during initialization and/or during Showtime. If the transceiver needs this information for measuring the SNR or noise level during initialization, the message needs to be sent before the receiving modem measures the SNR or noise level during initialization. In this case, the message may be sent during the g.hs or initialized channel discovery phase.

In addition, the subcarriers used during LPM may be updated or modified in Showtime or initialization. For example, a first message may be sent defining a first subset of subcarriers used in LPM, and a second message may be sent defining a second subset of subcarriers used in LPM. For example, the first message may define the first subset by a start index of 33 and a value of N-10, which means that every 10 th carrier is transmitted at LPM starting with subcarrier No. 33. And the second message may define a second subset by the start index 34 and the value of N-11, which means that every 11 th carrier is sent at LPM starting with subcarrier number 34.

Bit allocation values defining a subset of subcarriers in LPM

The bit allocation value (i.e., the number of bits transmitted on a subcarrier) for each subcarrier during LPM may be defined by the receiving modem, the transmitting modem, the CO modem for both DS and DS, the CPE modem for both US and DS, the service provider, or the end user.

In one embodiment, the bit allocation value is determined by the receiving modem. The CPE modem can thus determine the bit allocation value for the DS direction and/or the CO modem can determine the bit allocation value for the US direction. In an embodiment, the receiver may use the same bit allocation values as used during the FPM operation. In this case, the receiving modem does not need to transmit bit allocation values to the transmitting modem, since these bit allocation values may be the same as those used for FPM operations. Alternatively, the receiving modem may define a new bit allocation value for the subcarriers used during LPM. In this case, the new bit allocation value may be delivered to the transmitting modem through a message. Alternatively, the bit allocation value may be defined as a predetermined or negotiated reduction in the number of bits used during the FPM. For example, there may be a bit reduction of B-2, such that a subcarrier having B-8 bits during FPM may use B-6 bits during LPM. In this case, the receiving modem does not have to transmit the bit allocation value to the transmitting modem, since the bit allocation value can be calculated from the bit allocation value for the FPM operation. However, if B is determined by the receiving modem, the value of B may be communicated through messaging.

In an alternative embodiment, the bit allocation value is determined by the transmitting modem. Thus, the CPE modem may determine the bit allocation value for the US direction and/or the CO modem may determine the bit allocation value for the DS direction. In this case, for example, the transmitter may use the same bit allocation value as that used during the FPM operation. In this case, the transmitting modem does not have to transmit bit allocation values to the receiving modem, as these bit allocation values may be the same as those used for FPM operations. Alternatively, the transmitting modem may define new bit allocation values for the subcarriers used during LPM. In this case, the new bit allocation value may be delivered to the receiving modem via a message. Alternatively, the bit allocation value may be defined as a predetermined or negotiated reduction in the number of bits used during the FPM. For example, there may be a bit reduction of B-2, such that a subcarrier having B-8 bits during FPM may use B-6 bits during LPM. In this case, the transmitting modem does not have to transmit the bit allocation value to the receiving modem, since the bit allocation value can be calculated from the bit allocation value for the FPM operation. However, if B is determined through the sending modem, the value of B may be communicated through messaging.

In an alternative embodiment, the bit allocation value is determined by the service provider. Although it is not of practical significance to define the bit allocation values directly by the service provider, the service provider may indirectly define the bit allocation values by setting the LPM bit allocation values through a configurable reduction of the bit allocation values from the FPM operation. For example, the service provider may configure the value of B as described above. In addition, the service provider may configure a minimum required data rate for the LPM through the management interface.

In some cases, the bit allocation value for a subcarrier during the low power mode may be zero, i.e., no bits are transmitted on that subcarrier. This may occur, for example, if the bit reduction value B is set to 2 and the subcarrier has a bit allocation value of 2 during Showtime. In this case, the bit allocation value of the specific subcarrier may be set to 0 during the LPM. Under these conditions, non-data carrying a PRBS value may be allocated to the subcarrier, thereby signaling on the subcarrier. Alternatively, the subcarrier may not be transmitted in the LPM. Alternatively, the subcarrier may not be reduced by the bit reduction value B, but still use the bit allocation value of 2 during the LPM.

Exemplary method of LPM

This is an exemplary method of LPM configuration and system operation. In this example, the service provider configures the subcarriers used during LPM and the receiving modem determines the bit allocation values during the low power mode.

In this exemplary method of LPM, a service provider configures ADSL2+ service to use the LPM described in this invention. The ADSL2+ service uses subcarriers 6-32 for Upstream (US) transmissions and subcarriers 35-511 for Downstream (DS) transmissions. Through a management interface (e.g., MIB), the service provider may be configured such that, for example, every nth-10 subcarriers should be used for LPM in both the US and DS directions (in this example, the US and DS use the same value of N, but they may be different). Under this configuration, the following subcarrier numbers may be used for US LPM: 6. 16, 26. In addition, the last subcarrier 32 may be allocated to the LPM, thereby obtaining measurements for all possible US subcarriers used. Likewise, the following subcarrier numbers may be used for DS LPM: 33. 43, 53, 493, 503. In addition, the last subcarrier 511 may be allocated to the LPM, thereby obtaining measurements for all possible used DS subcarriers. Alternatively, for example, through a management interface (e.g., MIB), the service provider can configure such that every nth-10 subcarriers should be used for LPM in both US and DS directions, for example, and the starting subcarrier for indexing with respect to both US and DS should be subcarrier #10, for example.

In this configuration, US subcarriers 10, 20, and 30 may be used for US LPM and DS subcarriers 40, 50, 60. Alternatively, the service provider may configure the LPM subcarriers using a programmable list of subcarriers, e.g., [6, 13, 18, 24, 32] for US and [33, 53, 74, 95, 120, 150, 220, 283, 332, 442, 510] for DS.

After configuring the subcarriers used during LPM, the CO transceiver may send a message to the CPE transceiver (during initialization and/or Showtime) indicating which DS subcarriers are used under LPM. The message may include information (as described in the above example) that indicates the LPM subcarriers in a list, and/or with a value N that includes the starting subcarrier and the ending subcarrier, for example.

The CPE receiver may receive the message sent by the CO transceiver and send a message back to the CO transceiver indicating the bit allocation value of the DS LPM subcarrier. Thus, when entering the LPM, the CO transmitter may transmit using the bit allocation value conveyed in the message from the CPE transceiver.

Likewise, for the US direction, the CO transceiver may send a message to the CPE transceiver (during initialization and/or Showtime) indicating the bit allocation value for the US LPM subcarrier. Thus, when entering the LPM, the CPE transmitter may transmit using the bit allocation value conveyed in the message from the CO transceiver.

When measuring SNR and/or noise levels during initialization and/or Showtime, the receiving modem may first measure the SNR and/or noise level on the LPM subcarriers and then use this information to determine/count the SNR or noise level on the middle subcarrier. Thus, for example, if the service provider configures US subcarriers 6, 16, 26, 32 for US LPM, the CO receiver may measure the SNR and/or noise level on subcarriers 6, 16, 26, 32 and use this information to determine the SNR and/or noise level on the intermediate subcarriers 7-15, 17-26, 27-31. Likewise, the CPE receiver would do the same for the DS LPM subcarriers defined by the service provider.

Determining presence of a crosstalk-causing modem under LPM

By measuring the SNR on all subcarriers used during the FPM and detecting whether there is an increase in noise level (and/or a decrease in SNR) on the subcarriers used for the LPM by the crosstalk-causing modem, the receiver can determine whether there are other crosstalk-causing modems in the LPM. For example, if subcarriers 10, 20, 30 are used during LPM, the receiver may measure the SNR on subcarriers 10-30, and if the SNR on subcarriers 10, 20, and 30 is significantly increased compared to subcarriers 11-19 and 21-29, the receiver can know that there are crosstalk-causing modems in LPM. In this case, the receiver may use the measurements on subcarriers 10, 20, and 30 to estimate the SNR and/or noise level on the intermediate subcarriers (i.e., 11-19 and 21-29). On the other hand, if the SNR on LPM subcarriers 10, 20, and 30 is not increased, the receiving modem may know that there are no other crosstalk-causing modems under the LPM and the SNR and/or noise level of all subcarriers, including the intermediate subcarriers (i.e., 11-19 and 21-29), may be measured directly. In this way, the receiving modem will know that it is not experiencing fluctuating crosstalk when the crosstalk-causing modem enters and/or exits the LPM.

Thus, the LPM is detectable by the receiving modem, thus enabling the receiving modem to measure SNR and/or noise levels to determine a bit allocation table that will be stable and operate without error in the presence of fluctuating crosstalk caused by crosstalk-causing modems entering and/or exiting the LPM.

LPM does not require time constraints for reducing undulating crosstalk

Conventional LPM causes fluctuating (unstable) crosstalk that interferes with the operation of other DSL connections in the link bundle. To this end, conventional LPMs require a time constraint that limits how fast a transceiver can enter the LPM from the FPM, thereby reducing the number of PLM-to-FPM transitions that occur during a day.

One exemplary benefit of the LPM according to the present invention is that no time constraints are required for entering and exiting the LPM, as the LPM provides a method of measuring SNR and/or noise levels that is not dependent on the power mode state of the transceiver causing crosstalk in the link bundle. In addition, the receiving modem can detect whether the other transceiver is in LPM as described above.

Thus, for example, the LPM allows modems to enter and exit the LPM without time constraints for reducing the amount of fluctuating crosstalk in the system.

Fig. 3 illustrates an exemplary method for measuring SNR and entering a low power mode. In particular, control begins with step S300 and continues to step S310. In step S310, the SNR on the carrier designated for transmission during the low power mode is measured. Next, in step S320, the SNR on the carrier not designated for transmission is estimated. Then, in step S330, the one or more measured SNRs and the estimated SNRs are used for bit loading during one or more of initialization and Showtime OLR. Then, control proceeds to step S340.

In step S340, communication is started using the carrier designated for transmission during the LPM. Control then proceeds to step S350, where the control sequence ends in step S350.

Fig. 4 illustrates an exemplary method of entering a low power mode based on a noise level. Specifically, control begins with step S400 and continues to step S410. In step S410, the noise level on the subcarriers designated for transmission during LPM is measured. Next, in step S420, the SNR on the carrier designated for transmission during LPM is measured. Then, in step S430, the noise level on the carrier not designated for transmission during LPM is estimated. Then, control proceeds to step S340.

In step S440, the received signal power level (Pi) is measured for subcarriers not designated for transmission during one or more of initialization and Showtime. Then, control proceeds to step S450.

In step S450, the SNR on the carrier not designated for transmission is estimated using Pi and the estimated noise level. Next, in step S460, the SNR on the LPM subcarrier and/or the estimated SNR on the carrier not designated for transmission is used for bit loading during one or more of initialization and Showtime. Control then proceeds to step S470, where the control sequence ends in step S470.

Fig. 5 is an exemplary grid diagram showing messages exchanged between the CO and the CPE, the CO and the CPE allowing entry and exit from the low power mode. Specifically for the CO, control begins with step S500, and for the CPE, control begins with step S510. From the CO perspective, in step S505, the carriers used during the low power mode are identified. As described herein, the identification of these carriers can be performed by a number of different entities and based on one or more different criteria. Next, a message is sent from the CO to the CPE specifying which downstream carriers to use in the low power mode. The CO then receives a message of the bit allocation value of the downlink low power mode carrier. The CO then enters a low power mode and transmits in step S515 using the bit allocation value conveyed by the message from the CPE.

If the upstream subcarrier is also expected to enter the low power mode, the CO sends a message to the CPE of the bit allocation value for the upstream low power mode subcarrier. The transmission in low power mode continues until an exit low power mode message is sent from the CO to the CPE. Here, the CO can transition to transmitting using a bit allocation value such as full power mode, can reinitialize and determine a new bit allocation value, or transmit using some other predetermined bit allocation value. Control then proceeds to step S535, where the control sequence ends in step S535.

From the CPE' S perspective, a message is received from the CO indicating which downstream subcarriers are used in the low power mode, and a bit allocation value is determined in step S520. A message with the bit allocation value for the downlink low power mode subcarrier is passed to the CO. If the low power mode is also used for the uplink sub-carriers, the message is received by the CPE and in step S530 the CPE enters the low power mode and starts transmitting using the bit allocation value conveyed by the message from the CO. To exit the low power mode, a message is sent from the CPE to the CO, and as with the CO, can transition to sending at the FPM by using, for example, a bit allocation value for full power mode prior to entering the LPM, reinitializing and determining a new bit allocation value, or sending using some other predetermined bit allocation value. Full power mode communication is started in step S540, and control proceeds to step S550, where the control sequence ends in step S550.

Although the above-described flow diagrams have been discussed in terms of a particular order of events, it should be appreciated that the order can be changed without materially affecting the operation of the invention. In addition, the exact sequence of events need not be as illustrated in the exemplary embodiments, but rather the steps can be performed by one or the other transceiver in the communication system, as long as both transceivers are aware of the technique used for initialization. In addition, the exemplary techniques illustrated herein are not limited to the specifically illustrated embodiments, but can also be used with other exemplary embodiments, and each described feature is individually and separately claimable.

The above system can be implemented on a wired and/or wireless communication device, such as a modem, a multi-carrier modem, a DSL modem, an ADSL modem, an xDSL modem, a VDSL modem, a line card board, a power line modem, a wired or wireless modem, test equipment, a multi-carrier transceiver, a wired and/or wireless wide area/local area network system, a satellite communication system, a network-based communication system such as an IP, ethernet or ATM system, a modem with diagnostic capabilities, etc., or on a separately programmed general purpose computer having a communication device or in combination with at least any one of the following communication protocols: CDSL, ADSL2, ADSL2+, VDSL1, VDSL2, HDSL, DSL Lite, IDSL, RADSL, SDSL, UDSL, etc.

Furthermore, the systems, methods and protocols of this invention can be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA, PAL, modem, transmitter/receiver, any similar device, or the like. In general, any device capable of executing a state machine, and thus capable of executing the methods described herein, can be used to implement the various communication methods, protocols, and techniques in accordance with this invention.

Furthermore, the disclosed methods may be readily implemented using object-using software or object-oriented software development environments that provide portable source code that can be used on a variety of computer or workstation platforms. Alternatively, the disclosed system may be implemented partially or fully in hardware using standard logic circuits or VLSI design. Whether software or hardware is used to implement a system according to the present invention depends on the speed and/or efficiency requirements of the system, the particular function, and the particular software or hardware system or microprocessor or microcomputer system being used. The communication systems, methods and protocols illustrated herein can be readily implemented in hardware and/or software using any systems or structures, devices and/or software known or later developed by those of ordinary skill in the art based on the functional descriptions provided herein and using the general basic knowledge in the computer and telecommunications arts.

Further, for example, the disclosed methods may be readily performed in software including instructions executable by a processor, which can be stored on a computer-readable information storage medium, executed on a programmed general purpose computer with the cooperation of a controller and memory, a special purpose computer, a microprocessor, or the like. In these examples, the system and method of the present invention can be implemented as a program embedded in a personal computer, such as an applet,Or CGI script, a resource that is solidified in a server or computer workstation, a routine that is embedded in a specified communication system or system component. The system may also be implemented by physically incorporating the system and/or method into software and/or hardware systems, such as hardware and software systems of a communications transceiver.

It is therefore apparent that there has been provided, in accordance with the present invention, a system and method for conserving power in a communication environment. While the invention has been described in conjunction with a number of embodiments, it is evident that many alternatives, modifications and variations will be or are apparent to those of ordinary skill in the relevant art. Accordingly, it is intended to embrace all such alternatives, modifications, equivalents and variations that are within the spirit and scope of this invention.

Claims (74)

1. A communication system, comprising:

a first transceiver; and

a second transceiver operatively coupled to the first transceiver, wherein during a low power mode, only a subset of subcarriers transmitted in a full power mode are transmitted, and the subset of carriers are transmitted at the same power level as in the full power mode.

2. A communication system having a low power mode, comprising:

a first transceiver; and

a second transceiver operatively coupled to the first transceiver and in communication with the first transceiver over a plurality of subcarriers at a first power level, wherein a subset of the plurality of subcarriers are transmitted at the first power level during a low power mode.

3. The system of claim 1, wherein the subset is defined as every nth subcarrier used in the full power mode, and N is a positive integer.

4. The system of claim 2, wherein the subset is defined as every nth subcarrier used at the first power level, and N is a positive integer.

5. A system in a multicarrier receiver for configuring a low power mode, the system comprising a subcarrier management module that defines a subset for use in the low power mode among subcarriers used during a full power mode, wherein the subset is defined as every nth subcarrier used in the full power mode, and N is a positive integer.

6. The system of claim 5, wherein a value of N is input to configure a management interface of one or more xDSL transceivers.

7. The system of claim 6, wherein the inputting is performed by a service provider.

8. In a multicarrier transceiver capable of receiving a plurality of subcarriers, a method of determining signal-to-noise ratios (SNRs) on the plurality of subcarriers comprising measuring SNRs on a first subset of the plurality of subcarriers and estimating SNRs on a second subset of the plurality of subcarriers using at least the measured SNRs.

9. In a multicarrier transceiver capable of receiving a plurality of subcarriers, a method of determining a noise level on the plurality of subcarriers, the method comprising measuring a noise level on a first subset of the plurality of subcarriers and estimating a noise level on a second subset of the plurality of subcarriers using at least the measured noise.

10. In a multicarrier transceiver capable of receiving a plurality of subcarriers, comprising a receiver portion capable of measuring a signal-to-noise ratio (SNR) on a first subset of the plurality of subcarriers and capable of estimating the SNR on a second subset of the plurality of subcarriers using at least the measured SNR.

11. A multicarrier transceiver capable of receiving a plurality of subcarriers comprising a receiver portion capable of measuring a noise level on a first subset of the plurality of subcarriers and capable of estimating a noise level on a second subset of the plurality of subcarriers using at least the measured noise.

12. A multicarrier transceiver capable of receiving a plurality of subcarriers comprising means for measuring signal-to-noise ratios (SNRs) on a first subset of the plurality of subcarriers and means for estimating SNRs on a second subset of the plurality of subcarriers using at least the measured SNRs.

13. A multicarrier transceiver capable of receiving a plurality of subcarriers comprising means for measuring a noise level on a first subset of the plurality of subcarriers and means for estimating a noise level on a second subset of the plurality of subcarriers using at least the measured noise.

14. Other aspects of the invention relate to any of the above aspects, wherein the first subset is defined as every nth subcarrier of the plurality of subcarriers, where N is a positive integer.

15. The method of any of claims 8 to 14, wherein the measuring is performed during initialization.

16. A device according to any one of claims 8 to 14, wherein the measurement is performed during Showtime, which is a period of user data transmission.

17. A method of determining a first SNR on a first subcarrier in a multicarrier receiver comprising measuring or determining a second SNR on a second subcarrier and determining the first SNR using at least the second SNR.

18. A method of determining a first SNR on a first subcarrier in a multicarrier receiver comprising measuring or determining a noise level on a second subcarrier and using at least the noise level to determine the first SNR.

19. A method of determining a first SNR on a first subcarrier of a plurality of subcarriers in a multicarrier receiver comprising measuring or determining a noise level on a second subcarrier of the plurality of subcarriers and using at least the noise level to determine the first SNR.

20. Means for determining a first SNR on a first subcarrier in a multicarrier receiver comprising means for measuring or determining a second SNR on a second subcarrier and means for determining the first SNR using at least the second SNR.

21. Means for determining a first SNR on a first subcarrier in a multicarrier receiver comprising means for measuring or determining a noise level on a second subcarrier and for determining the first SNR using at least the noise level.

22. A multicarrier transceiver capable of determining a first SNR on a first subcarrier in a multicarrier receiver and capable of measuring or determining a second SNR on a second subcarrier and capable of determining the first SNR using at least the second SNR.

23. A multicarrier transceiver capable of determining a first SNR on a first subcarrier in a multicarrier receiver and capable of measuring or determining a noise level on a second subcarrier and capable of determining the first SNR using at least the second noise level.

24. A multicarrier transceiver capable of transmitting a plurality of subcarriers in a low power mode, the low power mode method comprising: transmitting a subset of subcarriers transmitted in a full power mode during the low power mode, wherein the subcarriers transmitted in the low power mode are transmitted at a same power level as transmitted in the full power mode.

25. A multicarrier transceiver capable of transmitting a plurality of subcarriers comprising a transmitter portion capable of transmitting a subset of subcarriers transmitted in a full power mode during a low power mode, wherein the subcarriers transmitted in the low power mode are transmitted at a same power level as transmitted in the full power mode.

26. A multicarrier transceiver capable of transmitting a plurality of subcarriers comprising means for transmitting a subset of the subcarriers transmitted in a full power mode during a low power mode, wherein the subcarriers transmitted in the low power mode are transmitted at a same power level as the power level transmitted in the full power mode.

27. The method according to any of claims 17-26, wherein the subset is defined as every nth subcarrier used in the full power mode, where N is a positive integer.

28. A low power mode for use in multicarrier communications that achieves power savings by using a subset of subcarriers transmitted in a full power mode, wherein the subset of subcarriers transmitted in the low power mode are transmitted at the same power level as in the full power mode.

29. The low power mode of claim 28, wherein the subset is defined as every nth subcarrier used in the full power mode, where N is a positive integer.

30. The low power mode of claim 28, wherein the subset is defined as any two or more subcarriers transmitted in the full power mode.

31. In a multicarrier transceiver communicating over a plurality of subcarriers at a first power level, a method for entering a low power mode comprising:

identifying one or more carriers used during the low power mode;

measuring the SNR on the identified carrier;

estimating the SNR on the unidentified carrier;

using the one or more measured SNRs and the estimated SNRs for bit loading; and

communicating using the identified carrier.

32. The method of claim 31, wherein the first power level is a full power level.

33. The method of claim 31, wherein the identified carrier is a subset of the plurality of carriers.

34. The method of claim 33, wherein the subset of carriers is transmitted at the first power level.

35. The method of claim 33, wherein the subset is defined as every nth subcarrier of the plurality of subcarriers, and N is a positive integer.

36. The method of claim 33, wherein the subset is defined as any two or more subcarriers transmitted at the first power level.

37. The method of claim 33, wherein the first power level is a full power level.

38. The method of claim 31, wherein the identified carrier is used for communication during the low power mode.

39. The method of claim 31, wherein the bit loading is performed during initialization or Showtime.

40. In a multicarrier transceiver communicating over a plurality of subcarriers at a first power level, a method for entering a low power mode comprising:

identifying one or more carriers used during the low power mode;

measuring a noise level on the identified carrier;

measuring SNR on identified carriers

Estimating a noise level on the unidentified carrier;

using one or more of the measured SNR on the identified carrier and the estimated SNR on the unidentified carrier for bit loading; and

the identified carrier is used for communication.

41. A method as defined in claim 40, further comprising measuring a received signal power level on an unidentified carrier during one or more of initialization and Showtime.

42. The method of claim 41, further comprising estimating SNR on unidentified carriers using the measured received signal power level and the estimated noise level.

43. The method of claim 40, wherein the first power level is a full power level.

44. The method of claim 40, wherein the identified carrier is a subset of the plurality of carriers.

45. The method of claim 44, wherein the subset of carriers is transmitted at the first power level.

46. The method of claim 44, wherein the subset is defined as every Nth subcarrier of the plurality of subcarriers, and N is a positive integer.

47. The method of claim 44, wherein the subset is defined as any two or more subcarriers transmitted at the first power level.

48. The method of claim 44, wherein the first power level is a full power level.

49. One or more means for performing the steps recited in any one or more of claims 8, 9, 15, 16, 17, 18, 19, 31-48, and 72-74.

50. A computer-readable storage medium storing instructions for performing the method steps recited in any one or more of claims 8, 9, 15, 16, 17, 18, 19, 31-48, and 72-74.

51. A multicarrier transceiver capable of communicating at a first power level over a plurality of subcarriers and capable of operating in a low power mode, comprising:

a subcarrier management module to receive an indication of one or more carriers used during the low power mode;

an SNR measurement module to measure SNR on the identified carriers;

an SNR estimation module that estimates SNR on unidentified carriers; and

a bit loading module to use the one or more measured SNRs and the estimated SNRs for bit loading.

52. The transceiver of claim 51, wherein the first power level is a full power level.

53. The transceiver of claim 51, wherein the identified carrier is a subset of the plurality of carriers.

54. The transceiver of claim 53, wherein the subset of carriers is transmitted at the first power level.

55. The transceiver of claim 53, wherein the subset is defined as every Nth subcarrier of the plurality of subcarriers, and N is a positive integer.

56. The transceiver of claim 53, wherein the subset is defined as any two or more subcarriers transmitted at the first power level.

57. The transceiver of claim 53, wherein the first power level is a full power level.

58. The transceiver of claim 51, wherein the identified carrier is used for communication during the low power mode.

59. The transceiver of claim 51, wherein the bit loading is performed during initialization or ShowTime.

60. A multicarrier transceiver capable of communicating at a first power level over a plurality of subcarriers and capable of operating in a low power mode, comprising:

a subcarrier management module to receive an indication of one or more carriers used during the low power mode;

a noise measurement module to measure a noise level on the identified carrier;

an SNR measurement module to measure SNR on the identified carriers;

a noise estimation module that estimates a noise level on an unidentified carrier; and

a bit loading module to use one or more measured SNRs on the identified carrier and the estimated SNRs on the unidentified carrier for bit loading.

61. The transceiver of claim 60, further comprising a power level measurement module that measures a received signal power level on the unidentified carrier during one or more of initialization and Showtime.

62. The transceiver of claim 61, wherein the SNR estimation module further estimates the SNR on the unidentified carrier using the measured received signal power level and the estimated noise level.

63. The transceiver of claim 60, wherein the first power level is a full power level.

64. The transceiver of claim 60, wherein the identified carrier is a subset of the plurality of carriers.

65. The transceiver of claim 64, wherein the subset of carriers is transmitted at the first power level.

66. The transceiver of claim 64, wherein the subset is defined as every Nth subcarrier of the plurality of subcarriers, and N is a positive integer.

67. The transceiver of claim 64, wherein the subset is defined as any two or more subcarriers transmitted at the first power level.

68. The transceiver of claim 64, wherein the first power level is a full power level.

69. The transceiver of claim 60, wherein information corresponding to the identified carriers is stored in a subcarrier table.

70. A low power mode for use in multicarrier communications that achieves power savings by using a subset of subcarriers transmitted in a full power mode, wherein the subset of subcarriers transmitted in the low power mode are transmitted at a same power level as the power level in the full power mode.

71. The low power mode of claim 70, wherein the subset is defined as every Nth subcarrier used in the full power mode, wherein N is a positive integer.

72. A method of configuring a low power mode, comprising defining a subset of subcarriers for use during a full power mode for use in a low power mode, wherein the subset is defined as every nth subcarrier used in the full power mode, wherein N is a positive integer.

73. A method according to claim 72, further comprising inputting a value of N into a management system for configuring an xDSL transceiver.

74. The method of claim 73, further comprising performing the inputting by a service provider.