Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD OF LOOP AND RATE DEPENDENT
POWER CUTBACK
CROSS-REFERENCES TO RELATED APPLICATIONS
[0l] NOT APPLICABLE
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[02] NOT APPLICABLE
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER
PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK.
[03] NOT APPLICABLE
BACKGROUND OF THE 1NVENTTON
[04] The present invention relates generally to transfer of data using Digital
Subscriber Loop (DSL) technology, and specifically to a method for reducing
transmitter
power used for the transfer.
[05] Remote access and retrieval of data is becoming increasingly popular
in data communication. The proliferation of the Internet has provided a vast
network of
information that is available to the general public. As the Internet grows and
technology
advances, this information is becoming increasingly voluminous and the details
are become
increasingly intricate. What used to comprise mainly text information has
grown to include
still and moving images as well as sound. The increase in the volume of
information to be
transferred has presented a need for a high-speed Internet connection, since
traditional
telephone modems communicate at speeds too slow for efficient communication.
[06] One proposal for high-speed communication is the introduction of
Digital Subscriber Line (DSL) technology. The various DSL technologies include
asymmetric DSL (ADSL), high-speed DSL (HDSL), symmetric DSL (SDSL), Symmetric
High-Bit-Rate DSL (SHDSL) and Integrated Services Digital Network (ISDN) Basic
Rate
Interface (BRI) DSL systems. One of the most attractive features of DSL is
that it is
implemented using an infrastructure that already exists. DSL shares copper
twisted pair lines
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typically used for telephone communication. However, only a small portion of
the available
bandwidth of the twisted pair line (0 to 4kHz) is used for Plain Old Telephone
Service
(POTS). DSL takes advantage of the available frequency spectrum from 4kHz to
approximately 1.1 MHz for transmitting data.
[07] ADSL is currently the most practical form of DSL technology, and
therefore the most widely implemented. ADSL is asymmetric in that its
downstream (DS or
D/S -- to a subscriber) capacity is larger than its upstream (US or U/S --
from the subscriber)
capacity. An ADSL transceiver unit at a central office a central office or
remote loop carrier
(ATU-C) is used for sending downstream information and receiving upstream
information.
An ADSL transceiver unit at a remote location or user end (ATU-R) is used for
receiving
downstream information and sending upstream information. Typically, a Discrete
Multi-tone
(DMT) scheme is used. The spectrum from 4kHz to l.lMHz is divided into 256 sub-
channels, or tones, each having a bandwidth of 4.3125kHz. Each sub-channel
uses
Quadrature Amplitude Modulation (QAM) to carry 2 to 15 bitslQAM symbol.
[08] A predefined power level is used by the ATU-C for transmitting the
downstream signal. At the ATU-R, the achievable downstream rate is a function
of the
received signal level and of the receiver input-referenced noise levels. Where
the loop
attenuation is modest and the target downstream rate is lower than the
achievable rate, the
predefined ATU-C transmission level can be much higher than necessary.
Therefore, an
unnecessary amount of power is consumed by the ATU-C and additional crosstalk
noise is
induced in adjacent DSL lines. Reducing the ATU-C transmit level would both
save power
at the ATU-C and reduce crosstalk noise, improving the quality of signal on
adjacent lines.
From a crosstalk perspective, it is beneficial if the ATU-C transmit power can
be reduced
during both initialization and steady state (also referred to as "Showtime")
operation. If the
transmit power and resulting crosstalk is only reduced on entry to Showtime,
the higher
crosstalk levels during initialization may cause excessive errors and even
force
re-initialization on adjacent DSL lines.
[09] The benefit of such a power cutback can be significant in Digital Loop
Carner (DLC) applications, for example, where subscriber loops are typically
shorter than
seen at central office (CO)-resident line interfaces and where power and
thermal budgets are
tight. Assuming a DMT transmit signal with peak-to-average-ratio (PAR) of
l4.SdB,
downstream power cutback can yield significant savings on line driver power
alone.
[10] American National Standards Institute (ANSI) and International
Telecommunications Union (ITU) compliant ATU Cs reduce their transmitter power
on very
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short loops to avoid overloading the ATU-R. This reduction in downstream
transmission
power is often referred to as a "politeness cutback". The politeness cutback
is determined in
accordance with a loop loss estimate from an upstream signal path and applies
on loops
shorter than approximately 2-3kft 26AWG-equivalent. Other downstream
transmitter power
S cutbacks are also specified in the ITU splitterless ADSL standard (G.992.2,
which is also
known as G.lite) for reducing the downstream signal level to the ATU-R. This
cutback is
designed to address ADSL signal levels that could cause distortion in the
presence of an off
hook telephone set.
[1l] However, even with the implementation of the politeness cutback and
off hook cutback, the ATU-C often transmits at a greater power than necessary
and there is
no agreed-upon mechanism to implement a general downstream power cutback. It
is an
object of the present invention to obviate or mitigate at least some of the
above-mentioned
disadvantages.
BRIEF SUMMARY OF THE INVENTION
[12] In accordance with an aspect of the present invention, there is provided
a method for reducing power required for transmitting a signal from a first
transceiver to a
second transceiver. The method comprises the steps of estimating an excess
amount of
power used by the first transceiver for transmitting the signal, reducing the
first transceiver's
power use by the excess amount of power to a reduced power level, and
transmitting the
signal from the first transceiver using the reduced power level. The reduced
power level
achieves a transmission rate of the signal within a predefined tolerance of
its preferable rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[13] Embodiments of the invention will now be described by way of
example only with reference to the following drawings in which:
[14J FIG. 1 a is a graph illustrating a relationship between transmission rate
and loop length for signals transmitted at a plurality of power levels, in the
presence of forty-
nine G.Lite disturbers;
[15] FIG. 1b is a graph illustrating a relationship between transmission rate
and loop length for signals transmitted at a plurality of power levels, in the
presence of ten
HDSL disturbers;
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[16] FIG. lc is a graph illustrating a relationship between transmission rate
and loop length for signals transmitted at a plurality of power levels, in the
presence of five
adjacent binder T1 disturbers;
[17] FIGS. 2a and 2b are flowcharts of the process steps according to
embodiments of the present invention; and
[18] FIG. 3 is a block diagram of an ATU-C and an ATU-R that implement
embodiments of the present invention.
DETAILED DESCRIPTION OF THE 1NVENTION
[19] ATU-C power requirements can be reduced when there is an excess
signal-to-noise ratio (SNR) margin at the ATU-R receiver. It is possible to
determine an
amount of cutback possible given a target or maximum downstream data rate and
a target or
maximum downstream SNR margin. The target data rate is the rate at which the
ATU-C is to
transmit the downstream signal, and the SNR margin is a margin against SNR
degradation for
a specified bit-error-rate.
[20] Refernng to FIGS. 1 a through 1 c, the graphs illustrate attainable
downstream rates over loop lengths of 0-12k$ (26AWG). Each graph has a plot
illustrating
the estimated transmission rates with respect to the loop length with a DS
power cutback of
OdB, 6dB, l2dB, and lSdB in the presence of crosstalk from other DSLs on
adjacent pairs.
Full-rate ADSL (G.dmt and T1.413) are also illustrated for comparison. The
attainable rates
have been estimated assuming a 4dB SNR margin, a 3dB coding gain, use of
downstream
carriers 36-127, and a downstream receiver noise floor of -136.8dBm/Hz. The
politeness
cutback (of 0 to l2dB) is not shown in the graphs. However, the politeness
cutback is only
applied for loop lengths up to approximately 2kft (26AWG).
[21] Refernng to FIG. la, the crosstalk scenario is caused by forty-nine (49)
other G.lite disturbers. This case is typical of a residential neighborhood,
where Tl or HDSL
services in the same or adjacent binders is less common. It should be noted
that if all local
subscribers are being served off power cutback-capable digital loop carriers
(DLCs), the
G.lite crosstalk levels would actually be lower and the rates would be
improved over those
shown.
[22] Refernng to FIG. 1b, the crosstalk scenario is caused by ten (10)
HDSL disturbers. For this case, full capacity (l.SMbps) is possible with lSdB
of cutback for
loop lengths of up to 9kft (26AWG), within Carrier Serving Area (CSA) loop
engineering
rules.
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[23] Refernng to FIG. lc, the crosstalk scenario is caused by five (5)
adjacent binder T1 disturbers. With Tl disturbers in adjacent binders, full
capacity is
possible on a loop of length of up to 9kft with approximately 6dB of cutback.
[24] In order to implement an appropriate power cutback, it is necessary to
either obtain an estimate of the SNR at the receiver or develop a method for
determining the
amount of signal cutback possible while achieving the target downstream rate
and SNR
margin. A signal-to-additive-noise estimate (as opposed to signal-dependent-
noise estimate,
such as mis-equalization error) permits a more accurate estimate of the SNR
degradation
resulting from a signal level reduction. Once the cutback is determined, it is
communicated
between the ATU-C and the ATU-R and implemented by the ATU-C.
[25] Estimating the SNR and determining an optimal amount of
downstream transmit signal power cutback is most easily accomplished by the
ATU-R
receiver. Thus far, some proposals have been made in the ITU standards body to
permit this
and/or require the ATU-R to minimize downstream transmit power via the per-DMT-
carrier
gains when the maximum downstream SNR margin is exceeded. These methods are
not
required or supported in the current ADSL standards nor do they address ATU-C
transmit
(and generated crosstalk) levels during initialization. As a result, it is
preferable to have
methods for estimating downstream SNR and/or potential cutback in the ATU-C.
[26] The techniques described herein describe a downstream power cutback
mechanism that reduces downstream transmit power based on a metric of excess
SNR or
capacity at the downstream receiver (ATU-R). The following techniques can be
implemented with an ATU-R compliant with the current ADSL standards (ITU-T
6.992.1,
6.992.2 and ANSI T1.413 issue 2).
[27] The amount of downstream transmit power reduction that can be
tolerated for a given capacity target is a function of the loop and the
crosstalk environment,
which together determine the SNR per receiver sub-earner. Unfortunately, this
information
is not available to the ATU-C. This information may be inferred from the bits
per earner i
(B;s) and gains per earner i (6;s -- also called power per carrier) sent
during initialization.
Specifically, bits and gains information from the remote-end is transmitted
during R-B&G,
toward the end of the initialization. However, at this point it is too late to
implement a
downstream power cutback without impacting the ATU-R, which will at least need
to adapt
its receiver automatic gain control (AGC).
[28] Therefore, in the absence of explicit information from the ATU-R,
several approaches to initialization are disclosed that the potential for
power savings without
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significant capacity losses. For all cases, the amount of cutback versus the
measured
upstream power can be an operator-specified parameter, as will be appreciated
by a person
skilled in the art.
S [29] Approach A: Reduce downstream power based on measured upstream
power alone
[30] Downstream power cutback based on received upstream power at the
ATU-C is already part of the current standards for the politeness cutback. The
politeness
cutback is used on very short loops, approximately 0 to 2kft 26AWG equivalent,
so there is
no impact on downstream capacity regardless of the crosstalk noise environment
at the
ATU-R. The politeness cutback is performed to minimize the peak signal
handling
requirements of the ATU-R receiver on short loops. Since it is invoked on only
very short
loops, it has no impact on power consumption for a typical loop of length 6-
8kft.
[31] Refernng to FIGS. la-lc, it is possible to cutback the downstream
1 S power for loops longer than 2kft 26AWG-equivalent and maintain an
acceptable transmission
rate. However, the degree to which the power is cutback depends on one's
willingness to risk
a failure during full initialization. For example, a cutback of l2dB is
employed where the
Ioop length is estimated to be less than 9kft 26AWG-equivalent. Assuming that
the loop
length and equivalent downstream loop losses are adequately estimated from the
upstream
power measured at the ATU-C and there are no adjacent binder T1 disturbers,
the l2dB
cutback will not significantly reduce the DS capacity below approximately l
.SMbps.
[32] Unexpected capacity losses may still occur if the ATU-R is not capable
of meeting standard test cases because of a noisy front end or amplitude
modulation (AM)
ingress noise. In those cases, the cutback should be reduced or eliminated and
a second full
initialization triggered.
[33] Referring to TABLE 1 below, a downstream power cutback is
determined as a function of an estimated average of upstream loop attenuation.
The
estimated average loop attenuation provides an estimate of the loop length.
The upstream
loop attenuation is defined as the difference between the upstream reference
power measured
in dBm and the total upstream power measured by the ATU-C on subcarners 7-18
during
stage R-REVERB 1 of the initialization. The upstream reference power is
defined as the total
power used by the ATU-R for transmitting subcarriers 7-18 using the R-REVERB1
transmit
power spectral density (PSD) level.
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[34]
Average >15 >14>13 >12>1l>10 >9 >8 >7 >6 >5 >4 >3 >2 >I >0
U/S
loop attenuation
(dB)
D/S Power0 1 2 3 4 5 6 6 7 8 8 9 10 I 12 12
cut 1
back (dB)
[35] TABLE 1
[36] TABLE 1 has been constructed to minimize achievable downstream
rate loss with a 6dB SNR margin in the presence of 24 HDSL or 24 DSL near-end
crosstalk
(NEXT) sources. A person skilled in the art will appreciate that it is also
possible to provide
different cutback tables based on operator-provisioned parameters. These
parameters include
a maximum downstream rate and SNR margin. Generally, the cutback is more
aggressive
when the downstream rate andlor SNR margin are reduced, and less aggressive
when they are
increased.
[37] The operator can also be given the capability of overnding this
mechanism via an additional Operations, Administration and Maintenance (OAM)
parameter.
It is preferable that the maximum amount of cutback is kept to 12 dB as some
implementations may have problems in applying higher cutbacks in the analog
domain. A
cutback applied in the digital domain results in higher requirements for the
dynamic range of
a digital-to-analog converter (DAC) in the transmitter.
[38] In order to implement the above in accordance with the current ADSL
standards, the ATU-C adjusts its transmit power once the downstream power
cutback has
been determined. This is achieved early enough (before transmission of C-
REVERB) such
that the ATU-R can adjust its AGC without triggering a new initialization.
Note that this
mechanism is similar to the existing politeness cutback but is more aggressive
in reducing
downstream transmit levels. This cutback is motivated by power savings, unlike
the
politeness cutback (which attempts to avoid overloading an ATU-R receiver on
very short
loops).
[39] Approach B: Two basses through full-initialization during initial install
or when on-hook loop conditions chan;ie sit?nificantlx
[40] In an alternate embodiment, the ATU-C forces a second full
initialization once it has received the B;s, G;s, performance (SNR) margin,
and attainable rate
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from the ATU-R near the end of the first initialization procedure. A per-
Garner SNR (linear
scale) at the ATU-R is estimated as 1 O~3"B' + Gi + ",~r~n~20~ ~,~,here t is
the carrier number, B; is
the number of bits on carrier i, G; is the gain of carrier i in dB, and margin
is the SNR margin
reported by the ATU-R (in dB). The ATU-C uses the downstream SNR to perform a
S downstream rate (capacity) estimate and determines how much of a cutback can
be tolerated
for the target downstream rate and margin.
[41] The line rate capacity estimate, less forward error correction (FEC)
overhead, in bits per symbol period with no cutback is given by
SNR.
[42] C = ~ b; ; b; = rourad (logy (1 + r ' )) and 2 <_ b; <_ bm~ (1)
[43] where b",~ is the maximum number of bitslcarrier supported in the
ATU-R receiver, and
[44] r = 109'$+10-3)/10
[45] is the SNR. gap for a bit-error-rate of 10-7 with l OdB margin and 3dB
coding gain, for 6.992.2.
[46J The maximum cutback is determined such that the capacity with that
cutback, C', is greater than or equal to 0.98 x C, where
[47] C'= ~b;'; b'; = round (logz (1 + SNR; l cutback)) and 2 < b; < bmaX
r
[48] (2)
[49] The cutback is determined in linear form, corresponding to a multiple
of 2dB.
[50] The initialization procedure is then repeated with the ATU-C
transmitting at a power level including the cutback throughout the
initialization procedure.
[51] It should be noted that the ATU-R B;s, G;s, and performance margin
are based on measurements in C-MEDLEY that include both additive noise (e.g.,
crosstalk)
and signal-level-dependent noise, particularly mis-equalization error. The ATU-
C has no
direct information on the relative contribution of these two noise or error
types. If
mis-equalization error is the dominant limitation of SNR, then downstream
transmit levels
could be reduced more aggressively than the case where additive (signal-level-
independent)
noise is dominant.
[52] This process also requires approximately twice as long (up to about 20
seconds) to initialize the link, but only needs to be invoked whenever a
change has occurred
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in the noise environment at the ATU-R, for example, when a HDSL service is
newly
deployed. Such a change in environment may be detected as a degradation in
performance
during Showtime, including a reduction in the noise margin, an increase in
detected CRC
errors, and the like. Alternately, an environment change may be detected on a
failed power
cutback initialization following a period when the communication link is
powered down.
[53] Approach C: Reduce DS power by excess mar ig'n reported by ATU-R
[54] In another embodiment, negotiation of transmission rates for the
communication link occurs over a series of handshakes between the ATU-C and
the ATU-R.
The ATU-C begins by providing the ATU-R with a list of four (4) rate options
to be met. In
another alternate embodiment, the ATU-C further transmits the required SNR
margin to be
met. The ATU-R responds to those options indicating the highest rate, if any,
that can be
supported. It also provides the ATU-C with the average downstream loop
attenuation and the
SNR margin at that rate. The values should be approximately the same for all
carriers if the
G;s have been calculated to equalize the SNR margin across all Garners. If the
ATU-R is able
to support the highest transmission rate, with a SNR margin in excess of the
desired margin,
then a power reduction in the amount of the difference between the desired SNR
margin and
actual SNR margin can be realized. The difficulty with this approach is that
the ATU-R is
not necessarily designed to adapt to a signal level change at this point in
the initialization,
forcing a new full initialization.
[55] Approach D: Over-speci margin in first round of rate negotiations
[56] In yet another alternate embodiment, during the first round of rate
negotiations, the ATU-C specifies a SNR margin comprising a minimum SNR margin
and an
additional 'N' dB of SNR margin. If the ATU-R responds (in R-MSG-RA) that it
can
support a high link rate at the inflated SNR margin, the ATU-C drops its
transmitter power by
'N' dB and sets the required margin lower by an equivalent amount for the
second round of
rate negotiations. If, however, the ATU-R cannot support the target
transmission rate with
the inflated margin, the ATU-C does not cutback its transmit power, but still
reduces the
minimum required SNR margin (by 'N') for the second round of negotiations. As
with the
previous embodiment, the difficulty with this approach is that the ATU-R is
not necessarily
designed to adapt to a signal level change at this point in the
initialization, forcing a new full
initialization
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[57] More optimal techniques than those described above in Approaches
A-D require changes to the existing standards. The changes allow for a faster
initialization
and maximize the achievable cutback. These techniques are set forth in
Approaches E-F
below.
[58] Approach E: ATU-R signals attainable cutback implicitlyin
downstream G;s based on SNR measured in C-MEDLEY
[59] In yet another alternate embodiment the ATU-R can indicate a power
cutback implicitly by reducing the G;s to be used on each of the downstream
carriers where
there is excess SNR margin, based on SNR measurements made during C-MEDLEY. If
so,
this sets the downstream power cutback desired. With the current ADSL
standards, one
cannot assume that a vendor's ATU-R will specify the G;s in this manner. That
is, the
ATU-R may use the G;s only to equalize the margin on each Garner, while
keeping an overall
unnecessarily large SNR margin. The G;s are communicated to the ATU-C late in
the
initialization process. As a result, any change in transmit gain must be exact
as there is no
time for the ATU-R to adapt its receiver to an imprecise gain change before
the start of
Showtime. Practically, this causes the signal to be reduced in the digital
domain, before the
digital-to-analog converter (DAC), and can place excess demands on the DAC's
dynamic
range. This method has the disadvantage of not applying the cutback until the
G;'s are
implemented on entry to Showtime. As a result, the transmit level, and
resulting crosstalk
into adjacent lines, remains high through initialization.
[60] As described in Approach B above, the SNR measured by the ATU-R
in C-MEDLEY includes both signal-level-dependent and signal-level-independent
noise at
the ATU-R.
[61] Approach F: ATU-R signals attainable cutback implicitly
downstream G;s based on a signal-level-independent SNR or noiselerror signal
estimate
[62] In yet another alternate embodiment, the ATU-R determines the
amount of downstream power cutback that can be tolerated while meeting the
target
downstream rate and SNR margin. In order to determine the SNR impact of a
reduced
downstream transmit signal where mis-equalization error may be dominant, the
ATU-R
requires several parameters. These parameters include an estimate of the
receiver noise floor
over the downstream frequency band in the absence of the downstream signal, an
estimate of
the channel attenuation in the downstream band, and knowledge of the
provisioned
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downstream rates and margins (i.e., maximums and targets). The ATU-R
calculates the
achievable downstream cutback from the this information and communicates the
cutback
back to the ATU-C, which implements the cutback in time for the ATU-R to re-
adjust its
receiver AGC prior to the SNR estimation during C-MEDLEY. A sample method for
estimating the above-described parameters is described as follows.
[63] The ATU-R measures the received downstream power (during
C-REVERB1) and estimates the average loop attenuation, as per the current
standards, across
carriers 7-1 ~ based on a measured per-carrier received signal level and known
per-carrier
transmit signal levels in C-REVERB 1. C-REVERB 1 may be sent with a politeness
cutback.
The ATU-R is informed of the extent of the cutback via a message from the ATU-
C.
C-REVERB 1 may also be replaced by another standard-specific line probing
signal that
permits extrapolation of the channel attenuation over the downstream frequency
band but has
different spectral characteristics than those for C-REVERB 1.
[64] The ATU-R measures the received downstream noise level during
C-QUIET. A minimum noise floor measurement resolution capability may be
specified to
ensure that the ATU-R is capable of supporting a specific downstream power
cutback for a
given downstream loop loss and crosstalk noise environment. Any receiver AGC
should be
set to a value sufficient to resolve the noise level at the loop interface.
However, it should not
be set so high as to ignore noise contributions from its own front end. The
receiver may need
to budget for those noise sources if they become dominant at low AGC gain
settings.
[65] The ATU-C communicates the maximum, target and minimum
downstream transmission rates and SNR margins to the ATU-R. This can be
achieved, for
example, during C-MSGl in the current standard.
[66] The ATU-R calculates the amount of downstream cutback possible
without reducing estimated downstream capacity below the provisioned maximum
downstream rate at the provisioned maximum margin. The capacity calculations
are based on
a received signal (transmit signal less channel attenuation) and receiver
input referenced
noise levels as measured at each upstream carrier frequency and mapped to an
equivalent per-
carrier SNR, SNRi. Note that this capacity formulation is based on the
measured signal and
noise levels, independent of near end echo, timing fitter or mis-equalization
effects. An
additional 6dB of margin is included in the SNR gap figure used in the
capacity calculation to
cover these impairments, measurement tolerances, and for providing a hedge
against
introduction of more NEXT sources into the same binder group. The line rate
capacity
estimates are calculated using equations 1 and 2 as previously described.
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[67] The ATU-R communicates the required cutback to the ATU-C, for
example in a field of R-MSGS1. Allowing for a power cutback range of 0-lSdB in
1dB
steps, a 4-bit message field is required.
[68] After receiving and decoding the message from the ATU-R, the
ATU-C applies the power cutback approximately 500-3500 symbols into C-MEDLEY.
The
ATU-R is able to adapt its receiver gain to the new ATU-C transmit level over
this interval
prior to its final SNR estimation during C-MEDLEY.
[69] FIGS. 2a and 2b are flowcharts generally illustrating the process steps
detailed above in Approaches A-F. In FIG. 2a, in step 102 the ATU-C estimates
an excess
amount of power used for transmitting the downstream signal. The ATU-C may use
Approaches A-D to estimate the excess amount of power, as appropriate for each
particular
implementation. In step 104, the ATU-C reduces the power level of its
transmitted
(downstream) signal. In step 106, the ATU-C transmits the downstream signal at
the reduced
power level. The reduced power level achieves a transmission rate of the
downstream signal
within a predefined tolerance of its target rate.
[70] In FIG. 2b, in step 110 the ATU-R determines an amount of excess
power in the downstream signal transmitted from the ATU-C. In step 112, the
ATU-R
calculates an attainable reduced power level for the downstream signal. In
step 114, the
ATU-R communicates the reduced power level information to the ATU-C. The ATU-C
has
enough time to adjust its power level without requiring a second
initialization. The ATU-R
may use any one or more of Approaches E-F to determine the amount of excess
power,
calculate the attainable reduced power level, or communicating the reduced
power level
information, as appropriate.
[71] FIG. 3 is a block diagram of an ATU-C 120 and ATU-R 130 that
implement the processes of FIGS. 2a and 2b (as well as Approaches A-F), as
appropriate.
The ATU-C 120 includes a processor 122 that controls the ATU-C to implement
the above-
identified processes. The ATU-R 130 includes a processor 132 that controls the
ATU-R to
implement the above-identified processes. The processors 122 and 132 may be
implemented
as specific hardware (such as an application-specific integrated circuit or
field-programmable
gate array) or as general hardware (such as that would implement a computer
program or
microcode). The ATU-C 120 includes a downstream transmitter 124 and an
upstream
receiver I26. The ATU-R 130 includes an upstream transmitter 134 and a
downstream
receiver 136.
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CA 02436025 2003-07-23
WO 02/11369 PCT/USO1/23893
[72] Although the invention has been described with reference to certain
specific embodiments, various modifications thereof will be apparent to those
skilled in the
art without departing from the spirit and scope of the invention as outlined
in the claims
appended hereto.
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