U.S. patent application number 14/547823 was filed with the patent office on 2016-05-19 for determining downstream power back-off parameters.
The applicant listed for this patent is Adtran Inc.. Invention is credited to Arlynn W. Wilson.
Application Number | 20160142098 14/547823 |
Document ID | / |
Family ID | 55962651 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160142098 |
Kind Code |
A1 |
Wilson; Arlynn W. |
May 19, 2016 |
DETERMINING DOWNSTREAM POWER BACK-OFF PARAMETERS
Abstract
Methods, systems, and apparatus for determining values of
downstream power back-off parameters are disclosed. In one aspect,
a method includes receiving cable loss data of a cable configured
to deliver a digital subscriber line (DSL) signal; identifying a
cable model that characterizes a cable loss value at a frequency
over a length of the cable; and determining a set of downstream
power back-off (DPBO) parameter values of the cable model based on
a product of a pseudo-inverse of a frequency matrix including a
plurality of different frequencies and a vector of the cable loss
data that includes a plurality of cable loss values with respect to
the plurality of different frequencies of the pseudo-inverse of the
frequency matrix.
Inventors: |
Wilson; Arlynn W.;
(Huntsville, AL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Adtran Inc. |
Huntsville |
AL |
US |
|
|
Family ID: |
55962651 |
Appl. No.: |
14/547823 |
Filed: |
November 19, 2014 |
Current U.S.
Class: |
379/1.03 ;
379/22.04; 379/22.05 |
Current CPC
Class: |
H04B 3/487 20150115;
H04M 3/34 20130101; H04B 3/32 20130101 |
International
Class: |
H04B 3/32 20060101
H04B003/32; H04B 3/487 20060101 H04B003/487; H04M 3/34 20060101
H04M003/34 |
Claims
1. A method comprising: receiving cable loss data of a cable
configured to deliver a digital subscriber line (DSL) signal;
identifying a cable model that characterizes a cable loss value at
a frequency over a length of the cable; obtaining cable loss values
at a plurality of different frequencies; generating a frequency
matrix of the plurality of different frequencies, wherein the
frequency matrix comprises a plurality of columns, each column
comprising the plurality of different frequencies each raised to a
respective exponent and determining a set of downstream power
back-off (DPBO) parameter values of the cable model based on a
product of a pseudo-inverse of the frequency matrix and a vector of
the cable loss values.
2. The method of claim 1, further comprising determining a
downstream power spectrum density (PSD) mask based on the set of
DPBO parameter values.
3. The method of claim 1, wherein the cable model is represented
by: (DPEOESCMA+DPBOESCMB {square root over
(f)}+DPBOESCMCf)DPBOESEL; wherein f represents frequency and
DPBOESEL represents the length of the cable, and the set of DPBO
parameter values comprises values of DPBOESCMA, DPBOESCMB, and
DPBOESCMC.
4. The method of claim 3, further comprising determining a
downstream power spectrum density (PSD) mask based on the set of
DPBO parameters according to: (DPEOEPSD(f)-(DPBOESCMA+DPBOESCMB
{square root over (f)}+DPBOESCMCf)DPBOESEL, wherein DPBOEPSD(f)
represents a PSD mask without downstream power back-off.
5. The method of claim 1, wherein receiving cable loss data of a
cable comprises receiving cable loss data of a cable based on a
dual ended line test (DELT).
6. The method of claim 1, wherein receiving cable loss data of a
cable comprises receiving cable loss data of a cable based on
insertion loss measurements using a test device.
7. The method of claim 1, wherein receiving cable loss data of a
cable comprises receiving cable loss data of a cable based on
estimation of loss loop characteristics from loop records.
8. A device, comprising: a memory storing instructions executable
by one or more processors; one or more data processing devices
configured to interact with the memory and execute the instructions
that cause the device to be configured to: receive cable loss data
of a cable configured to deliver a digital subscriber line (DSL)
signal; identify a cable model that characterizes a cable loss
value at a frequency over a length of the cable; obtain cable loss
values at a plurality of different frequencies; generate a
frequency matrix of the plurality of different frequencies, wherein
the frequency matrix comprises a plurality of columns, each column
comprising the plurality of different frequencies each raised to a
respective exponent and determine a set of downstream power
back-off (DPBO) parameter values of the cable model based on a
product of a pseudo-inverse of the frequency matrix and a vector of
the cable loss values.
9. The device of claim 8, further configured to determine a
downstream power spectrum density (PSD) mask based on the set of
DPBO parameter values.
10. The device of claim 8, wherein the cable model is represented
by: (DPBOESCMA+DPBOESCMB {square root over
(f)}+DPBOESCMCf)DPBOESEL; wherein f represents frequency and
DPBOESEEL, represents the length of the cable, and the set of DPBO
parameter values comprises values of DPEOESCMA, DPBOESCMB, and
DPBOESCMC.
11. The device of claim 10, further configured to determine a
downstream power spectrum density (PSD) mask based on the set of
DPBO parameters according to: DPBOEPSD(f)-(DPBOESCMA+DPBOESCMB
f+DPBOESCMCf)DPBOESEL; wherein DPBOEPSD(f) represents a PSD mask
without downstream power back-off.
12. The device of claim 8, wherein the cable loss data of a cable
comprises cable loss data of a cable obtained based on a dual ended
line test (DELT).
13. The device of claim 8, wherein the cable loss data of a cable
comprises cable loss data of a cable obtained based on insertion
loss measurements using a test device.
14. The device of claim 8, wherein the cable loss data of a cable
comprises cable loss data of a cable obtained based on estimation
of loss loop characteristics from loop records.
15. A system, comprising: a network including a plurality of
devices; and one or more data processing devices configured to:
receive cable loss data of a cable configured to deliver a digital
subscriber line (DSL) signal; identify a cable model that
characterizes a cable loss value at a frequency over a length of
the cable; obtain cable loss values at a plurality of different
frequencies; generate a frequency matrix of the plurality of
different frequencies, wherein the frequency matrix comprises a
plurality of columns, each column comprising the plurality of
different frequencies each raised to a respective exponent and
determine a set of downstream power back-off (DPBO) parameter
values of the cable model based on a product of a pseudo-inverse of
the frequency matrix and a vector of the cable loss values.
16. The system of claim 15, wherein the one or more data processing
devices is further configured to determine a downstream power
spectrum density (PSD) mask based on the set of DPBO parameter
values.
17. The system of claim 15, wherein the cable model is represented
by: (DPBOESCMA+DPBOESCMB f+DPBOESCMCf)DPBOESEL; wherein represents
frequency and DPBOESEL represents the length of the cable, and the
set of DPBO parameter values comprises values of DPBOESCMA,
DPBOESCMB, and DPBOESCMC.
18. The system of claim 17, wherein the one or more data processing
devices is further configured to determine a downstream power
spectrum density (PSD) mask based on the set of DPBO parameters
according to: DFBOEPSD(f)-(DPBOESCMA+DPBOESCMB {square root over
(f)}+DPBOESCMCf)DPBOESEL, wherein DPBOEPSD(f) represents a PSD mask
without downstream power back-off.
19. The system of claim 15, wherein the cable loss data of a cable
comprises cable loss data of a cable obtained based on a dual ended
line test (DELT).
20. The system of claim 15, wherein the cable loss data of a cable
comprises cable loss data of a cable obtained based on insertion
loss measurements using a test device.
21. The system of claim 15, wherein the cable loss data of a cable
comprises cable loss data of a cable obtained based on estimation
of loss loop characteristics from loop records.
22. The method of claim 1, wherein the frequency matrix of the
plurality of different frequencies comprises: a first vector
comprising the plurality of different frequencies each raised to
the exponent 0; a second vector comprising the plurality of
different frequencies each raised to the exponent 1/2; and a third
vector comprising the plurality of different frequencies each
raised to the exponent.
Description
BACKGROUND
[0001] This specification relates to data transmissions in a
telecommunications environment.
[0002] As demand for network services increases, access network
providers are implementing new technologies to provide access
network services to more subscribers and/or to provide more
services to at least some of the subscribers. In some
implementations, the access network providers can utilize at least
a portion of their legacy access network infrastructure to deploy
additional (e.g., higher bandwidth) services, while keeping
existing access networks that they have been using to provide
services to subscribers.
SUMMARY
[0003] In general, one innovative aspect of the subject matter
described in this specification can be embodied in methods that
include receiving cable loss data of a cable configured to deliver
a digital subscriber line (DSL) signal; identifying a cable model
that characterizes a cable loss value at a frequency over a length
of the cable; and determining a set of downstream power back-off
(DPBO) parameter values of the cable model based on a product of a
pseudo-inverse of a frequency matrix including a plurality of
different frequencies and a vector of the cable loss data that can
include a plurality of cable loss values with respect to the
plurality of different frequencies of the pseudo-inverse of the
frequency matrix.
[0004] Another innovative aspect of the subject matter described in
this specification can be embodied in a device that includes a
memory storing instructions executable by one or more processors;
one or more data processing devices configured to interact with the
memory and execute the instructions that cause the device to be
configured to: receive cable loss data of a cable configured to
deliver a digital subscriber line (DSL) signal; identify a cable
model that characterizes a cable loss value at a frequency over a
length of the cable; and determine a set of downstream power
back-off (DPBO) parameter values of the cable model based on a
product of a pseudo-inverse of a frequency matrix including a
plurality of different frequencies and a vector of the cable loss
data that can include a plurality of cable loss values with respect
to the plurality of different frequencies of the pseudo-inverse of
the frequency matrix.
[0005] Another innovative aspect of the subject matter described in
this specification can be embodied in a system that includes a
network including a plurality of devices; and one or more data
processing devices configured to: receive cable loss data of a
cable configured to deliver a digital subscriber line (DSL) signal;
identify a cable model that characterizes a cable loss value at a
frequency over a length of the cable; and determine a set of
downstream power back-off (DPBO) parameter values of the cable
model based on a product of: a pseudo-inverse of a frequency matrix
including a plurality of different frequencies and a vector of the
cable loss data that can include a plurality of cable loss values
with respect to the plurality of different frequencies of the
pseudo-inverse of the frequency matrix.
[0006] These and other embodiments can each optionally include one
or more of the following features. Methods can include the action
of determining a downstream power spectrum density (PSD) mask based
on the set of DPBO parameter values.
[0007] The cable model can be represented by (DPBOESCMA+DPBOESCMB
{square root over (f)}+DPBOESCMCf)DPBOESEL; wherein f represents
frequency and DPBOESEL represents the length of the cable, and the
set of DPBO parameter values can include values of DPBOESCMA,
DPBOESCMB, and DPBOESCMC.
[0008] Methods can include the action of determining a downstream
power spectrum density (PSD) mask based on the set of DPBO
parameters according to:
DPBOEPSD(f)-(DPBOESCMA+DPBOESCMB {square root over
(f)}+DPBOESCMCf)DPBOESEL,
wherein DPBOEPSD (f) represents a PSD mask without downstream power
back-off.
[0009] Receiving cable loss data of a cable can include receiving
cable loss data of a cable based on a dual ended line test
(DELT).
[0010] Receiving cable loss data of a cable can include receiving
cable loss data of a cable based on insertion loss measurements
using a test device.
[0011] Receiving cable loss data of a cable can include receiving
cable loss data of a cable based on estimation of loss loop
characteristics from loop records.
[0012] Particular embodiments of the subject matter described in
this specification can be implemented so as to realize one or more
of the following advantages. The example techniques described
herein can allow co-existence of legacy access technologies (e.g.,
asymmetric digital subscriber line (ADSL)) and new access
technologies (e.g., very-high-bit-rate digital subscriber line
(VDSL)) that share common transmission media (e.g., twisted pair
links). The example techniques described herein can facilitate the
ability to provide satisfactory services using each of the
technologies over a same wire binder that includes multiple twisted
pair cables. In particular, the example techniques provide
computationally efficient implementations for determining cable
model parameters for downstream power back-off (DPBO), and can
provide more accurate estimation of the cable model parameters by
using a large number of cable loss data points. Accordingly, more
effective DPBO can be performed based on the determined cable model
parameters. These more accurate estimated cable model parameters
can reduce crosstalk between ADSL and VDSL signals that are
transmitted over a same wire binder. In some implementations, the
example techniques can be implemented as an automated process or
application compatible with various network protocols and can be
efficiently implemented and executed.
[0013] The details of one or more embodiments of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram of an example telecommunications
network.
[0015] FIG. 2 is a flow chart of an example process for determining
downstream power back-off (DPBO) parameters.
[0016] FIG. 3 is a plot showing example measured cable loss values
and estimated cable loss values based on the DPBO parameters
determined according to an implementation.
[0017] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0018] This document discusses techniques that can be used when
deploying higher bandwidth services such as very-high-bit-rate
digital subscriber line (VDSL), for example, in a localized
distribution area (DA) that includes subscribers who were
originally served from a Central Office (CO) (e.g., outside of the
distribution area) using legacy services such as asymmetric digital
subscriber line (ADSL). The VDSL can utilize at least a portion of
the existing infrastructure (e.g., copper wires) of the legacy ADSL
access network for delivering, to the subscribers, higher speed
internet access than that provided by the legacy ADSL access
network. For example, the VDSL signals can be generated at an
intermediate location between a CO and a subscriber premises. The
intermediate location is also referred to as an injection point or
flexibility point in ITU-T Recommendation G.997.1. For brevity,
this document will refer to the intermediate location as a
flexibility point. The VDSL signal can be injected into a
subscriber line (e.g., a twisted pair cable) that was previously
used to transmit an ADSL signal. As such, the VDSL signal and the
ADSL signal can share the same transmission media (e.g., using
twisted pair cables in the same wire binder) from the flexibility
point to the subscriber premises.
[0019] In order to deploy VDSL and ADSL over twisted pairs that are
in the same binder, it may be necessary to control the transmit
power of the VDSL signal so that the VDSL signal does not overwhelm
the ADSL signal. In some instances, the ADSL signal that originated
from the CO may have been impaired and/or attenuated during the
transmission from the CO to the flexibility point. Therefore, the
transmit power of the VDSL signal injected at the flexibility point
can be selected, based at least in part, on the amount of
impairment/attenuation that the ADSL signal experiences during the
transmission from the CO to the flexibility point to reduce, for
example, the crosstalk between the VDSL signal and ADSL signal.
[0020] Downstream power back-off (DPBO) can be used to
control/adjust the transmit power of the VDSL signal that is
injected at the flexibility point. In some implementations, DPBO
can be performed by the intermediate transceiver at the flexibility
point to reduce or otherwise control the transmit power of the VDSL
signal. Controlling the transmit power using DPBO can include
determining and applying a transmit power spectral density (PSD)
mask to suppress, attenuate, or otherwise modify the transmit PSD
of the VDSL signal, for example, to ensure the VDSL signal has the
same or a comparable power level relative to the ADSL signal (e.g.,
within a specified amount of the ADSL power level). The transmit
PSD mask can be determined, for example, based on the amount of
attenuation experienced by the ADSL signal from the CO to the
flexibility point.
[0021] In some instances, the attenuation experienced by the ADSL
signal can be referred to as cable loss, which is commonly referred
to as insertion loss, or any other reductions or impairments of the
signal that are caused as the signal travels over a cable or
conductor. The cable loss of a signal can depend on a transmission
frequency, transmission distance (or cable length), cable type,
cable mode, or other factors. For example, for an ADSL signal
transmitted over a particular bandwidth, the cable loss values of
the ADSL signal can be different at different frequencies across
the bandwidth.
[0022] In some instances, a cable model (or a simplified model) can
be used to characterize the cable loss of a signal transmitted at a
particular frequency over a given length of a cable. The
characterized cable loss can be expressed, for example, as one or
more cable loss values specifying an amount of cable loss
experienced by the signal. The cable model can include multiple
parameters that help quantify a specific cable loss value for a
given frequency and cable length. As the cable loss relies on
various implementation factors, a single set of fixed or default
cable loss parameters may provide less than a desired level (or
required level) of accuracy with respect to cable loss values for
all cables and/or wire binders in one or more distribution areas of
a telecommunications network. A higher level of cable loss value
accuracy may be achieved, for example, by determining or
calibrating cable model parameters of each particular distribution
area, for example, based on the cable loss data of each particular
distribution area of the telecommunications network. The higher
level of cable loss accuracy can be used to improve the reliability
of the telecommunications network, for example, by reducing the
crosstalk between the ADSL and VDSL signals.
[0023] Example techniques for determining values of a set of cable
model parameters for performing DPBO are described in more detail
below. For brevity, the cable model parameters for performing DPBO
are referred to as DPBO parameters in this document. In some
implementations, the values of the DPBO parameter can be determined
based on measured or estimated cable loss data that are obtained,
for example, based on a dual ended line test (DELT), insertion loss
measurements detected by test equipment, estimation of loss loop
characteristics from loop records, or other sources.
[0024] In some implementations, the example techniques provide a
computationally efficient solution for determining DPBO parameter
values based on a large number of data loss data values.
Specifically, the example techniques enable a direct computation of
the DPBO parameter values based on a product of a pseudo-inverse of
a frequency matrix and a vector of the cable loss data. Based on
the determined DPBO parameter values, the cable loss of
[0025] ADSL signals across its occupied bandwidth over a given
transmission distance can be estimated. Accordingly, the DPBO can
be applied to the VDSL signal based on the determined cable loss of
the ADSL signal.
[0026] The example techniques described herein can be implemented
as, or in, methods, computer program products, apparatus, devices,
etc., for example, to perform DPBO and manage crosstalk between
co-existing ADSL and VDSL signals transmitted over twisted pair
cables that are in a same wire binder.
[0027] Throughout this document, ADSL is used as an example legacy
technology while VDSL is used as an example forward-deployed
technology. ADSL can include ADSL, ADSL2, ADSL2+, ADSL2++, or other
versions. Similarly, VDSL can include VDSL defined in standard
International Telecommunication Union (ITU) G.993.1, VDSL2 defined
in standard ITU G.993.2, or other versions. These technologies are
used for purposes of illustration, and are not intended to limit
the scope of this document. The example techniques described herein
can be applied to additional or different access technologies and
telecommunications networks that share common transmission
media.
[0028] Throughout this document, the terms downlink, downstream
(DS), and downstream communications are used to refer to
communications transmitted toward the end user or subscriber, while
the terms uplink, upstream (US), and upstream communications are
used to refer to communications transmitted toward the service
provider (e.g., a telecommunications service provider's central
office).
[0029] The discussion that follows with reference to FIG. 1
introduces components of an example telecommunications network that
can be configured to determine DPBO parameters and perform DPBO.
The description referencing FIG. 2 provides details regarding an
example method for performing DPBO. Particularly, details of
example techniques for determining DPBO parameters are described.
FIG. 3 is a plot showing simulation results of an application of
the example method for determining DPBO parameters described in
FIG. 2.
[0030] FIG. 1 is a block diagram of an example telecommunications
network 100. In some implementations, the telecommunications
network 100 utilizes a combination of fiber optic cables (e.g.,
fiber link 112) and twisted pair cables (e.g., twisted pair cables
122a, 122b, 122c) to provide network services (e.g., xDSL services)
to subscribers. In the example shown in FIG. 1, the
telecommunications network 100 deploys both legacy services such as
ADSL and higher bandwidth services such as VDSL. The
telecommunications network 100 includes a central office 110 (also
referred to as an exchange), an intermediate transceiver 120, and
multiple customer-premises equipment (CPE) (e.g., VSDL2 modem 132a
and ADSL modem 132b) at end user locations 130a and 130b. The end
user locations 130a and 130b can also be referred to as
customer/subscriber premises. The telecommunications network 100
can include additional or different components and features and can
be configured in a different manner than the example
telecommunications network 100 in FIG. 1.
[0031] As shown in FIG. 1, the central office 110 is coupled to a
network 104 that can be the Internet, an internet service provider
(ISP) network, a public switched telephone network (PSTN), an
Internet Protocol television (IPTV) network, or another network
that provide various network services such as voice, video, data,
or a combination of them. The central office 110 can be connected
to a CPE directly or through the intermediate transceiver 120.
[0032] For example, the central office 110 is connected to the ADSL
modem 132b at customer premises 130b using twisted pair cables 122b
and 122c that originate at the central office 110. The twisted pair
cable 122b can be used to establish an ADSL connection between the
central office 110 and the ADSL modem 132b. Typically, there is a
crossbox 134 in the field where the VDSL signal at the intermediate
injection location 120 joins the ADSL signal originating from the
CO 110. The first section of twisted pair cable from the CO 110 to
the crossbox 134 is called the F1 cable (e.g., cable 122b) and the
twisted pairs where the two DSLs coexists after the crossbox 134 is
called the F2 cable (e.g., cable 122c). Thus, ADSL signals
generated at the central office 110 can be transmitted over the
twisted pair cables 122b and 122c to the ADSL modem 132b at the
customer premises 130b.
[0033] The central office 110 is also connected to the intermediate
transceiver 120 by the fiber link 112, and the intermediate
transceiver 120 is further connected to the VSDL2 modem 132a at
customer premises 130a using the twisted pair cables 122a. In this
case, a VSDL connection is established between the intermediate
transceiver 120 and the VSDL2 modem 132a using the twisted pair
cables 122a. In general, the intermediate transceiver 120 can be
installed at various locations, such as at a network facility
(e.g., at or near the central office CO 110), a remote node, a
cabinet, a hub near the customer premises, or any intermediate
point between the central office 110 and the customer premises
130a, 130b.
[0034] The intermediate transceiver 120 can be implemented, for
example, as one or more of a digital subscriber line access
multiplexer (DSLAM), a VTUC (downstream VDSL) transmitter, or
another device. In general, the DSLAM can connect a high-speed
network line (e.g., the fiber link 112) to multiple subscriber
lines (e.g., the twisted pair cables 122a) and establish a VDSL
connection between the DSLAM and a VDSL modem over each of the
subscriber line. The DSLAM can, in the downstream direction,
de-multiplex a high-speed data stream from the high-speed network
line into multiple subscriber data streams and route the data
streams over the twisted pair cables to multiple subscribers. For
example, the DSLAM 120 in FIG. 1 can generate a VDSL signal based
on the input signal from the fiber optic link 112 and transmit the
VDSL signal over the twisted pair cables 122a to the VDSL modem
132a at the customer premises 130a. In the upstream direction, the
DSLAM 120 can multiplex the data streams from the subscriber lines
for transmission across the fiber link 112 to the central office
110.
[0035] In some implementations, the twisted pair cables 122a can
share the same wire binder 124 with a portion of the twisted pair
cables (e.g., the twisted pair cable 122c) between the intermediate
transceiver 120 and the customer premises (e.g., the ADSL modem
132b). In some instances, the ADSL signal transmitted over the
twisted pair cable 122c can be degraded by signal attenuation, loop
insertion loss, or other cable loss over the electrical distance d
114 between the central office 110 and the intermediate transceiver
120. The electrical distance d 114 can represent the length of the
twisted pair cable 122b between the central office 110 and the
intermediate transceiver 120. To avoid the ADSL signal being
overwhelmed by the VSDL signal generated at the intermediate
transceiver 120 and to reduce crosstalk between the ADSL signal and
the VSDL signal within the wire binder 124, the intermediate
transceiver 120 can perform DPBO to control the power of the VSDL
signal injected at the intermediate transceiver 120. In some
implementations, the power of the VDSL signal can be set to a
specified power level. For example, the VDSL signal can be set to a
power level that is the same or within a specified amount relative
to the power level of the ADSL signal at the intermediate
transceiver 120 (e.g., at the distance d from the central office
110).
[0036] As discussed in more detail below, using DPBO to control the
power of the VDSL signal can require an estimation of DPBO
parameter values. In some implementations, these parameters need to
be accurate enough to provide an expected or required quality of
service (QoS). Example techniques for estimating DPBO parameters in
an accurate and computationally efficient manner are described
below.
[0037] FIG. 2 is a flow chart of an example method 200 for
performing downstream power back-off (DPBO). The method 200 can be
performed, for example, using various devices discussed above with
respect to FIG. 1, or any other appropriate devices. As an example,
the example method 200 can be performed by the intermediate
transceiver 120 (e.g., by an ADSL Transceiver Unit Remote "ATUR"
(downstream ADSL receiver)), or a controller (e.g., a computer)
coupled to the intermediate transceiver 120. In some
implementations, the example method 200 can be performed upon
network initialization, reconfiguration, reset, or other system
changes. The example method 200 can be performed periodically
(e.g., at specified intervals for system maintenance) or from time
to time (e.g., upon a request of a service provider or a network
administrator).
[0038] Cable loss data of a cable configured to deliver a digital
subscriber line (DSL) signal are obtained (210). The cable can be
the example twisted pair cables 122b of FIG. 1 or another cable.
The cable can be configured to deliver ADSL, VSDL, or other DSL
signals.
[0039] The cable loss data can include frequency-dependent loss
information (HLOG). For instance, the cable loss data can include
cable loss values at one or more frequencies over one or more cable
lengths. As an example, the cable loss data can include a vector of
cable loss values corresponding to multiple different frequencies
over the same electrical distance d 114 between the central office
110 and the intermediate transceiver 120. The cable loss data can
be represented in other format (e.g., a matrix, a table, etc.) and
can include additional or different attributes.
[0040] The cable loss data can be obtained based on tests,
measurements, estimation, or other techniques. In some instances,
the cable loss data can be obtained based on dual ended line test
(DELT). For example, in order to determine the cable loss data
(e.g., the cable loss data of the F1 cable section 122b) using the
components in FIG. 1, an ADSL CPE modem can be placed at the
location of the forward deployed DSLAM 120 and be connected with
the CO 110 to a DSLAM port that is currently providing ADSL service
to the neighborhood. The CO 110 can run DELT to provide the
frequency dependent loss parameters associated with DELT.
Alternatively, a test set measurement would be taken at the
intermediate location 120 facing back towards the CO 110. In
another implementation, test equipment can be placed at the CO 110
and at the injection point 120 to measure the loss in cable 122b.
The HLOG results of the DELT diagnostics can provide cable loss
values at different frequencies over the electrical distance d 114
between the CO 110 and the DSLAM 120.
[0041] In some instances, cable loss data can be obtained based on
insertion loss measurements. For example, a test device or
equipment can be used to collect a sweep of insertion loss
measurements with respect to multiple frequencies over a certain
cable length (e.g., the electrical distance between the CO 110 and
the DSLAM 120).
[0042] In some instances, cable loss data of a cable can be
obtained based on estimation of loop loss characteristics of the
cable from loop records. For instance, service providers can have
loop records that indicate topology, length, environment, cable
types, or other configurations of the cables deployed in a network.
For example, the loop records can include the lengths gauge of the
cable and the presence of bridged taps and their respective lengths
describing the actual loop topology of the F1 cable pair that
connects the ADSL circuits from the CO to the intermediate
location. The loop loss characteristics can be estimated by
creating a well known two port equivalent lumped parameter model
from the loop topology and calculating the insertion loss
characteristics of the equivalent circuit. Based on the loop loss
characteristics, cable loss values at different frequencies can be
calculated.
[0043] A cable model that represents a cable loss value over a
length of the cable is identified (220). In some instances, the
cable model can characterize and quantify frequency-dependent cable
losses of the cable using multiple DPBO parameters. An example
cable model is given in relationship (1):
H(f)=(DPBOESCMA+DPBOESCMB {square root over
(f)}+DPBOESCMCf)DPBOESEL (1).
[0044] In the above relationship, H (f) represents a cable loss
value (e.g., in dB) at a frequency fDPBOESEL represents a length of
the cable. The DPBOESEL can be, for example, the electrical
distance d 114 between the CO 110 and the DSLAM 120 where the VSDL
signal subject to DPBO is injected. DPBOESCMA, DPBOESCMB, and
DPBOESCMC are three scalar DPBO parameters.
[0045] Given the values of the DPBO parameters, DPBOESCMA,
DPBOESCMB, and DPBOESCMC, the cable loss value at an arbitrary
frequency can be obtained according to the cable model.
Accordingly, for DPBO, a power spectral density (PSD) mask that
shapes the power spectrum of the VSDL signal injected at the
intermediate transceiver 120 can be determined based on the cable
model with the DPBO parameters.
[0046] A set of DPBO parameter values of the cable model are
determined (230). For example, the DPBO parameters values can
include the values of DPBOESCMA, DPBOESCMB, and DPBOESCMC of the
example cable model in relationship (1). The DPBO parameter values
can be determined based on the cable loss data obtained at 210, for
example, by line/curve fitting or other mathematical
manipulations.
[0047] In some implementations, the DPBO parameter values can be
determined based on a product of a pseudo-inverse of a frequency
matrix F and a vector of the cable loss data L. The cable loss
vector L can include multiple cable loss values with respect to
multiple different frequencies that correspond to the multiple
different frequencies of the pseudo-inverse of the frequency matrix
F.
[0048] For example, the vector of the cable loss data L can include
N cable loss values, i.e., L=[L.sub.1, L.sub.2, . . . ,
L.sub.N].sup.T with respect to N different frequencies {f.sub.i,
i=1, 2, . . . , N}. The frequency matrix F can include a column of
1's, a column of square root of {f.sub.i} and a column of
{f.sub.i}, as shown in relationship (2):
F = [ 1 f 1 f 1 1 f N f N ] . ( 2 ) ##EQU00001##
[0049] In some implementations, normalization of the
frequency-dependent parameters can be performed based on the fixed
frequency for which DPBOESEL is chosen. As an example, if the
frequency corresponding to DPBOESEL is 1 MHz, the frequencies can
be normalized to the frequency used to define DPBOESEL (e.g.,
MHz).
[0050] In order to estimate values of DPBOESCMA, DPBOESCMB, and
DPBOESCMC (denoted as A, B and C in below equations) of this cable,
the cable model in relationship (1) can be rewritten as:
F [ A B C ] .apprxeq. 1 L 1 MHz [ L 1 L N ] ; ( 3 ) L 1 MHz =
DPBOESEL . ( 4 ) ##EQU00002##
[0051] The values of parameters DPBOESCMA, DPBOESCMB, and DPBOESCMC
can be calculated based on a product of the pseudo-inverse of F and
the vector of the cable loss data L, for example, as shown in
relationship (5). Note that the vector L can include more than
three frequency-dependent cable loss values (i.e., N>3).
[ A B C ] .apprxeq. 1 L 1 MHz ( F T F ) - 1 F T [ L 1 L N ] . ( 5 )
##EQU00003##
[0052] Different variations and modifications of the above example
techniques can be implemented. The example techniques enable a
computationally efficient and direct calculation of the DPBO
parameter values. By using the matrix-vector product, the example
techniques can compute the DPBO parameter values based on a large
number of cable loss values at once without iterations. For
instance, the cable loss data obtained by DELT HLOG data can
include tens or hundreds of cable loss values at different
frequencies that span a spectrum of interest. These cable loss
values can be arranged in a vector L, and a frequency matrix F can
be constructed based on the corresponding frequencies of the cable
loss values according to the relationship (2). DPBO parameter
values can then be efficiently computed according to relationship
(5) based on the tens or hundreds of cable loss values. In some
instances, the more cable loss values, the more accurate the DPBO
parameter values can be obtained, resulting in more effective
implementation of DPBO.
[0053] A downstream PSD mask is determined based on the set of DPBO
parameter values (240). In some instances, determining a downstream
PSD mask can include determining an estimated attenuated PSD mask.
The estimated attenuated PSD mask can be, for example, an
estimation of the PSD mask of the ADSL signal at the flexibility
point. In some implementations, the predicted attenuated PSD mask,
denoted as EPSD (f) can be given by:
EPSD(f)=DPBOEPSD(f)-(DPBOESCMA+DPBOESCMB {square root over
(f)}+DPBOESCMCf)DPBOESEL (6).
[0054] Here, DPBOEPSD(f) can represent a PSD mask without
downstream power back-off (e.g., a transmitted PSD at the CO). The
values of parameters DPBOESCMA, DPBOESCMB, and DPBOESCMC obtained
at 230 can be substituted into relationship (6) for calculating the
predicted attenuated PSD mask EPSD(f). In some instances, the
predicted attenuated PSD mask EPSD (f) can be regarded as the
transmitted PSD at the CO minus the attenuation of the signal
experienced during the transmission from the CO to the flexibility
point.
[0055] In some implementations, determining a downstream PSD mask
can include determining a downstream backed-off PSD mask, denoted
as DPBOPSD. The downstream backed-off PSD mask can be, for example,
a PSD mask of the VDSL signal to be transmitted by the intermediate
transceiver 120 at the flexibility point that is subject to DPBO.
In some implementations, the downstream backed-off PSD mask can be
determined based on the predicted attenuated PSD mask, EPSD(f). In
some implementations, the downstream backed-off PSD mask can be
further determined based on a frequency range (e.g., with a maximum
and/or minimum frequency), a maximum magnitude, a PSD mask
override, or other factors.
[0056] In some implementations, the intermediate transceiver 120
can perform DPBO by applying the downstream backed-off PSD mask to
the VDSL signal (e.g., as the transmit PSD mask). As such, the
power level of the VDSL signal is reduced or controlled based on
the cable loss of the coexisting ADSL signal. In some
implementations, additional or different techniques can be used to
perform DPBO of the VDSL signal based on the determined DPBO
parameter values.
[0057] FIG. 3 is a plot 300 showing example measured cable loss
values and estimated cable loss values based on the DPBO parameters
determined according to an implementation. FIG. 3 shows the example
cable loss values in dB over frequencies ranging from less than 0.2
MHz to about 1.20 MHz. Specifically, the curve 310 represents the
example cable loss values obtained based on HLOG results captured
by DELT. The curve 320 represents the estimated cable loss values
using the example signal model in relationship (1) based on the
DPBO parameter values that are determined according to the example
method 200 described in FIG. 2. As illustrated, the estimated cable
loss values 320 accurately represent the measured cable loss values
310 across the entire frequency band ranging from about 0.3 MHz to
1.20 MHz. The example results in FIG. 3 demonstrate the
effectiveness of the example method 200 for determining DPBO
parameter values that are based on a product of a pseudo-inverse of
a frequency matrix F and a vector of the cable loss data L.
[0058] While this specification contains many specific
implementation details, these should not be construed as
limitations on the scope of any inventions or of what may be
claimed, but rather as descriptions of features specific to
particular embodiments of particular inventions. Certain features
that are described in this specification in the context of separate
embodiments can also be implemented in combination in a single
embodiment. Conversely, various features that are described in the
context of a single embodiment can also be implemented in multiple
embodiments separately or in any suitable subcombination. Moreover,
although features may be described above as acting in certain
combinations and even initially claimed as such, one or more
features from a claimed combination can in some cases be excised
from the combination, and the claimed combination may be directed
to a subcombination or variation of a subcombination.
[0059] Thus, particular embodiments of the subject matter have been
described. Other embodiments are within the scope of the following
claims. In some cases, the actions recited in the claims can be
performed in a different order and still achieve desirable results.
In addition, the processes depicted in the accompanying figures do
not necessarily require the particular order shown, or sequential
order, to achieve desirable results.
* * * * *