Method for performing spectrum management in a subscriber
premises network
Field of Invention
The present invention pertains to the field of spectrum
management, more particularly to the field of applying
spectrum management in a local area network, such as a
subscriber premises network.
Background
It is known to apply spectrum management to wireless
transmission systems and to digital subscriber line (DSL)
systems. Subscriber lines are physically collocated in
binders, in which a frequency and coupling length dependent
amount of crosstalk will originate between the signals
travelling over the respective lines. Just like multiple
access or co-channel interference in wireless transmitters,
DSL transmitters must therefore take into account certain
spectral restrictions in order to coexist with other,
similar or dissimilar systems. In an advanced form of
spectrum management, the power spectral densities (PSDs) of
multiple DSL transmitters are coordinated to e.g. achieve an
increase in the aggregate bit rate available to these
transmitters or even to decrease the total power to meet
certain target rates.
Summary
The present invention is based on the insight that the
presence of a local area network (LAN) at the premises of
the subscriber influences and is influenced by the
operational characteristics of this subscriber's DSL link.
It is therefore an object of the present invention to
jointly optimize the capacity and/or the power consumption
of the access link and the local link(s) .
In a first aspect of the present invention, there is
provided a method for performing spectrum management in view
of a predetermined constraint in a network comprising an
access link and a local area link, the access link and the
local area link being interf eringly coupled, the method
comprising: quantifying interference between the access link
and the local area link; determining a first spectral
configuration for a first transmitter operating over the
access link; and determining a second spectral configuration
for a second transmitter operating over the local area link;
wherein the determining of the first spectral configuration
and the determining of the second spectral configuration are
performed such that the respective achievable channel
capacities of the access link and the local area link meet
the predetermined constraint.
In an embodiment of the method according to the present
invention, the predetermined constraint comprises maximizing
the weighted sum of the respective channel capacities of the
access link and the local area link.
In an embodiment of the method according to the present
invention, the predetermined constraint comprises maximising
the lesser one of the respective channel capacities of the
access link and the local area link.
In an embodiment, the method according to the present
invention further comprises analyzing a topology of the
network to determine the predetermined constraint.
In an embodiment of the method according to the present
invention, the quantifying of the interference comprises:
cycling the first transmitter through an active state and a
passive state to determine a difference in received
interference from the first transmitter; cycling the second
transmitter through an active state and a passive state to
determine a difference in received interference from the
second transmitter; obtaining first information from a first
receiver operating over the access link to determine a
difference in received interference during the cycling of
the second transmitter; and obtaining second information
from a second receiver operating over the local area link to
determine a received interference during the cycling of the
first transmitter.
Here, a substantially passive state refers to a state in
which the PSD is reduced or set to zero on at least a
relevant fraction of the transmission bandwidth.
In a particular embodiment, the first transmitter and the
second transmitter are comprised in a customer premises
equipment, the quantifying of the interference being
controlled by a processor comprised in the customer premises
equipment, the processor being operatively coupled to the
first transmitter and the second transmitter, and the
processor being further configured to receive the first
information from the first receiver and the second
information from the second receiver.
In another particular embodiment, the quantifying of the
interference is controlled by a network management
apparatus, the network management apparatus being configured
to control the first transmitter, the second transmitter,
the first receiver, and the second receiver.
In a more particular embodiment, the network management
apparatus controls at least one of the first transmitter,
the second transmitter, the first receiver, and the second
receiver through a TR-069 protocol exchange.
While the processor may reside in a the customer premises
equipment that also comprises the access network termination
and an in-home network termination, the processor may also
quantify interference from and to access and in-home
transceivers outside of the customer premises equipment.
Likewise, the processor may control the configuration of
access and in-home transceivers outside of the customer
premises equipment.
According to another aspect of the present invention, there
is provided a computer program configured for carrying out
the method as described above.
According to another aspect of the present invention, there
is provided a customer premises equipment for use in the
method as described above.
According to another aspect of the present invention, there
is provided a network management apparatus for use in the
method as described above.
Brief Description of the Figures
Some embodiments of apparatus and/or methods in accordance
with embodiments of the present invention are now described,
by way of example only, and with reference to the
accompanying drawings, in which:
Figure 1 illustrates a first exemplary topology of a network
in which the invention may be used advantageously;
Figure 2 illustrates a second exemplary topology of a
network in which the invention may be used advantageously;
Figure 3 illustrates an exemplary network with a spectrum
manager according to the present invention; and
Figure 4 provides a flow chart of an embodiment of the
method according to the present invention.
Description of Embodiments
The skilled person will understand that any references to a
home network in the present description are strictly
exemplary and not intended to limit the scope of application
of the present invention to residential settings. The
invention is in fact also applicable to other settings in
which an access link and a local area network link are
present, including office, industry, hospitality, and
educational settings.
The number of transceivers shown in the figures is chosen
for illustrative purposes only, and does not limit the
generality of the invention in any way. Operations described
in relation to a given transceiver may apply, mutatis
mutandis, to other transceivers in the network.
It is known to apply spectrum management to digital
subscriber line (DSL) access systems. In an advanced form of
spectrum management, the power spectral densities of
multiple DSL transmitters are coordinated to achieve an
increase in the aggregate bit rate available to these
transmitters. Coordination can easily be achieved between
DSL lines that originate from a common access node (digital
subscriber line access multiplexer, DSLAM) , because all the
necessary information is centralized at that point. DSL
systems based on discrete multi-tone (DMT) transmission,
such as ADSL, VDSL, and their successors, are particularly
suited for advanced spectrum management, because these
systems allow per-tone power configuration (leading to a
frequency decoupling of the optimization problem) and
because they use a fixed symbol duration of 250 , which
may be synchronized between lines (leading to a further
decoupling of the optimization problem) .
Certain LAN communication technologies for use in the home
network (HN), such as HomePlug AV, G.hn and IEEE P1901, are
known to mutually interfere with the twisted pairs used by
DSL operators as they share some parts of the spectrum.
For example, G.hn technology can use the frequency band from
close to DC up to 100 MHz while VDSL2 is only restricted to
3 0 MHz. As a result of the mutual interference, the
attainable data rate of the copper access link is reduced by
20% to 50%. The problem is particularly notable in the
downstream direction due to the near-far effect between the
downstream transmitter and the home network transmitter: the
DSL DS signal received at the customer premises is already
attenuated by a certain amount that depends on the distance
between the customer premises equipment (CPE) and the access
node .
Not only the rate of the DSL line is impacted, but also the
stability of the lines, because of the transient noise
induced by the home network devices, which typically
transmit intermittently.
On the other hand, for some legacy home network technology
operating over a reduced frequency band, e.g. [0,30] MHz,
crosstalk induced by DSL into the home network link may
limit the capacity of the home network.
The present invention is inter alia based on the insight
that it is advantageous to have the spectra of both the
access and in-home link jointly optimized. However, the
present invention is also based on the realization that the
spectrum management advantages of DMT-based DSL systems
(frequency decoupling, time decoupling, and centralized
management) are not applicable to a mixed DSL/home network
environment. The present invention therefore introduces a
novel common spectrum manager for both the access and the
in-home link.
For example, the frequency decoupling that is present among
DSL systems is not present among a mix of DSL and in-home
systems. DSL uses DMT with filtering in the time domain,
which corresponds to a "sine" function in the frequency
domain. The carrier spacing and filtering are such that the
carrier frequency positions correspond to the zero crossings
of the "sine" functions of all other carriers. Therefore,
the different sub-channels or tones are orthogonal and the
transmit PSD at one tone does not cause significant intercarrier
interference into adjacent tones. In this way, the
spectral optimization problem in DSL is decoupled over
tones. Access and in-home systems use different carrier
frequencies, and as such the optimization problem does no
longer decouple over tones. One way to circumvent the issue
is by adapting the optimization framework such that the
inter-carrier interference can be modeled or estimated and
added to the interference observed on a particular carrier.
This means that the problem statement can no longer be
decoupled over tones, leading to higher processing
complexity. However, the higher processing complexity is
tempered by the low number of disturbing lines. While in an
access environment, typically tens of lines mutually
interfere, the number of mutually interfering lines in the
problem at hand is limited to one access link and one or a
few in-home links. The increased complexity due to coupling
over tones is therefore partly compensated by a reduced
complexity in the number of lines. Alternative ways to
circumvent the coupling over tones is to derive a PSD level
on a larger bandwidth scale, e.g. optimize over a limited
number of guide tones and interpolate to determine the PSD
of the remaining tones, instead of per tone.
The common spectrum manager may reside within a CPE that
integrates both the DSL and the home network chips, or could
be part of a separate management platform in the access
operator's network that talks to the in-home devices, e.g.
through the TR-069 protocol. This protocol could allow the
configuration of the overall transmit power, and certain
aspects of the shape of the PSD, such as the application of
spectral notches, amongst other things.
Two exemplary scenarios may be considered for approaching
the interactions between a DSL access network and an in-home
distribution network.
In the first exemplary scenario, illustrated in Figure 1 ,
the DSL access network, extending between an access node or
central office 140 and a line termination 110 at the
customer premises, collaborates with the in-home
distribution network 120—123 to provide the user with a
service, exemplified by server 160, offered from within the
wide area network, a.k.a. the "cloud" 150. In this scenario,
both networks share a common goal and spectral optimization
can be used to achieve that common objective.
In the first scenario, the aggregated downstream and
upstream net DSL data rate (on the path 140—110) should
match the net data rate on the home network (in the
illustrated example, the path 120—121—122), because the home
network is an extension of the access network. Functionally,
the goal is to avoid that either one of the DSL link or the
home network presents a bottleneck for the data flow.
For completeness, server 160 and wide area network 150 are
illustrated as being operatively connected to the access
node 140. Clearly, the path 160-150-140 contributes to the
quality of the end-to-end service delivery.
The net attainable DSL data rate depends on loop length,
noise conditions and the configured parameter set. The net
data rate in the home network depends on the corresponding
in-home parameters. Both also depend on the mutual
interference .
The method according to the present invention includes a
step in which this mutual interference is quantified. This
can be done by adapting the configuration on the devices and
observing the effects. For instance, the crosstalk from the
home network into the DSL link can be quantified by
comparing the quiet line noise (QLN) or signal-to-noise
ratio (SNR) when the home network device is turned off (or
notched on the relevant frequencies) to when it is on. The
difference between these measurements provides the crosstalk
noise power from home network. The interference from the DSL
link to the home network can be acquired in a similar way.
The required accuracy may allow further optimizations of the
method of the invention. In an advantageous embodiment, it
is sufficient to determine upper bounds on this
interference .
Depending on the home networking technology, a direct SNR or
QLN measurement may not be available. Nevertheless, an
indirect measure is provided by reading out and comparing
the throughput, i.e. the net data rate, when the DSL line is
on and off (or notched), respectively.
Having the crosstalk channel state information, known
spectrum balancing techniques can be applied for the joint
optimization step. The target may be to maximize the minimum
data rate of the DSL and home network link and/or to
minimize the power. This target acts as a predetermined
constraint for the optimization process. Depending on the
chosen optimization algorithm, such spectrum balancing may
lead to a frequency-dependent spectral shape in a format
consistent with conf igurationally options of the in-home or
access transmitter, or to simplified heuristic power back
off schemes .
As home network technologies may transmit intermittently, it
is advantageous to store different operational profiles for
the DSL link depending on whether the relevant home network
transmitter is active or not. This requires obtaining
information about the activity of the transmitter (by
detection, or by receiving anticipatory information directly
from the home network transmitter itself), and switching DSL
profiles with a very low reaction time.
In the second exemplary scenario, illustrated in Figure 2 ,
the DSL access network, extending between an access node or
central office 140 and a line termination 110 at the
customer premises, provides a first service, while the inhome
distribution network 123—122 provides a second (inhome)
service, such as media distribution from an in-home
media service, exemplified by the server shown along with
transceiver 123. Other elements of Figure 2 correspond to
the elements with the same numbers in Figure 1 .
Accordingly, the home network also carries data that does
not need to go out into (and does not come from) the access
network. In that scenario, spectral optimization should
balance the competing objectives of both networks.
The net data rate of the home network, when needed, can be
allowed to be higher than the net DSL data rate. This
modified constraint can be introduced in the general
spectrum optimization framework described above through e.g.
weight factors to trade off the competing targets. The
weighting would relate to the importance of the end-to-end
link from cloud to end-device (s) vis-a-vis the links between
the different in-home end devices.
Figure 3 conceptually illustrates how the method of the
present invention may be carried out in part or completely
from outside the home network. A network analyzer 170 is
operatively connected to one or more of the access node 140
and the customer premises equipment 100 via a network 150,
preferably by means of a remote configuration protocol. In
applicable cases, TR-069 may be used as the remote
configuration protocol.
Without loss of generality, the customer premises equipment
100 comprises a first transceiver 110 for interacting with
the DSL line and a second transceiver 120 for interacting
with the LAN. In order to carry out the method of the
present invention, the customer premises equipment 100 may
be instructed by the network analyzer 170 to selectively
activate the transceivers operating on the various links,
and to assess a measure of the mutual interference as
described above.
The customer premises equipment 100 may also act as a proxy
for other LAN transceivers 121—123 in the LAN, which may be
included in the method of the present invention. For this
purpose, the customer premises equipment 100 may be required
to relay management messages from and to the network
analyzer 170, optionally translating between the protocol
used by the network analyzer 170 (e.g., TR-069) and a
different management protocol used inside the LAN.
The method of the present invention is further conceptually
illustrated by the flow chart of Figure 4 . Although the
different process steps illustrated in Figure 4 are shown in
a certain order, this should not be taken to imply that the
chosen order is necessary to carry out the invention. As
will be clear from the description below, certain steps may
be reordered or even omitted without leaving the scope of
the invention.
In a preliminary step (not shown) the method of the present
invention may include determining the type of configuration
that needs to take place and the resulting performance
constraints, i.e. an configuration of the type described
above in connection with the first scenario, or a
configuration of the type described above in connection with
the second scenario. The step of quantifying the mutual
interference between access link and LAN link 410 may
accordingly include a sub-step of checking whether the endto-
end link, or each of the individual links, meets the
predetermined performance requirements, as the case may be.
In the next step or steps, the desired spectral
configuration for the access link transmitter is determined
420 and/or the desired spectral configuration for the LAN
link transmitter is determined 430, according to a known
spectrum allocation algorithm and in view of the constraints
determined before. The spectrum allocation algorithm may be
chosen so as to simply meet the predetermined constraints,
if possible, or to also optimize a certain utility function
(e.g., end-to-end throughput or throughput of a given link) .
In a subsequent step 440, the updated configuration
parameters are imposed on the affected transmitter (s).
As indicated by the arrow returning from step 440 to step
410, the process can be repeated periodically, to take a
dynamically varying interference environment into account.
Alternatively or additionally, the process may be repeated
asynchronously upon the occurrence of specific events, such
as the addition or removal of a transceiver in the relevant
part of the network.
A person of skill in the art would readily recognize that
steps of various above-described methods can be performed by
programmed computers. Herein, some embodiments are also
intended to cover program storage devices, e.g., digital
data storage media, which are machine or computer readable
and encode machine-executable or computer-executable
programs of instructions, wherein said instructions perform
some or all of the steps of said above-described methods.
The program storage devices may be, e.g., digital memories,
magnetic storage media such as a magnetic disks and magnetic
tapes, hard drives, or optically readable digital data
storage media. The embodiments are also intended to cover
computers programmed to perform said steps of the abovedescribed
methods.
The functions of the various elements shown in the Figures,
including any functional blocks labeled as "processors", may
be provided through the use of dedicated hardware as well as
hardware capable of executing software in association with
appropriate software. When provided by a processor, the
functions may be provided by a single dedicated processor,
by a single shared processor, or by a plurality of
individual processors, some of which may be shared.
Moreover, explicit use of the term "processor" or
"controller" should not be construed to refer exclusively to
hardware capable of executing software, and may implicitly
include, without limitation, digital signal processor (DSP)
hardware, network processor, application specific integrated
circuit (ASIC) , field programmable gate array (FPGA) , read
only memory (ROM) for storing software, random access memory
(RAM), and non volatile storage. Other hardware,
conventional and/or custom, may also be included. Similarly,
any switches shown in the FIGS, are conceptual only. Their
function may be carried out through the operation of program
logic, through dedicated logic, through the interaction of
program control and dedicated logic, or even manually, the
particular technique being selectable by the implementer as
more specifically understood from the context.
Claims
1 . A method for performing spectrum management in view of a
predetermined constraint in a network comprising an access
link and a local area link, said access link and said local
area link being interf eringly coupled, said method
comprising :
- quantifying interference between said access link and said
local area link;
- determining a first spectral configuration for a first
transmitter operating over said access link; and
- determining a second spectral configuration for a second
transmitter operating over said local area link;
wherein said determining of said first spectral
configuration and said determining of said second spectral
configuration are performed such that the respective
achievable channel capacities of said access link and said
local area link meet said predetermined constraint.
2 . The method of claim 1 , wherein said predetermined
constraint comprises maximizing the weighted sum of said
respective channel capacities of said access link and said
local area link.
3 . The method of claim 1 , wherein said predetermined
constraint comprises maximizing the lesser one of said
respective channel capacities of said access link and said
local area link.
4 . The method of claim 1 , further comprising analyzing a
topology of said network to determine said predetermined
constraint .
5 . The method of any of the preceding claims, wherein said
quantifying of said interference comprises:
- cycling said first transmitter through an active state and
a substantially passive state to determine a difference in
received interference from said first transmitter;
- cycling said second transmitter through an active state
and a substantially passive state to determine a difference
in received interference from said second transmitter;
- obtaining first information from a first receiver
operating over said access link to determine a difference in
received interference during said cycling of said second
transmitter; and
- obtaining second information from a second receiver
operating over said local area link to determine a received
interference during said cycling of said first transmitter.
6 . The method of claim 5 , wherein said first transmitter and
said second transmitter are comprised in a customer premises
equipment, said quantifying of said interference being
controlled by a processor comprised in said customer
premises equipment, said processor being operatively coupled
to said first transmitter and said second transmitter, and
said processor being further configured to receive said
first information from said first receiver and said second
information from said second receiver.
7 . The method of claim 5 , wherein said quantifying of said
interference is controlled by a network management
apparatus, said network management apparatus being
configured to control said first transmitter, said second
transmitter, said first receiver, and said second receiver.
8 . The method of claim 7 , wherein said network management
apparatus controls at least one of said first transmitter,
said second transmitter, said first receiver, and said
second receiver through a TR-069 protocol exchange.
9 . A computer program configured for carrying out the method
of any of the preceding claims.
10. A customer premises equipment for use in the method of
claim .
11. A network management apparatus for use in the method of
claim 7.