Method and apparatus for assessing the quality of a
communication channel in a multi -domain network
Technical Field
The present invention pertains to the field of home
networks, more in particular to the field of data
transmission over diverse physical home network segments.
Background
In home networks, in particular home networks according to
the G.hn family of Recommendations developed by the ITU-T
(see ITU-T Rec . G.9961) , communication between domains is
conducted via domain managers. This architecture has limited
scalability and does not allow for true bidirectional
interaction across domains. Additionally, known channel
probing schemes for such networks tend to be inefficient.
Summary
Accordingly, it is an object of embodiments of the present
invention to provide a more efficient channel probing scheme
for multi-domain networks.
According to an aspect of the present invention, there is
provided a method for assessing the quality of a
communication channel in a multi-domain network, the method
comprising at a device attached to said communication
channel: transmitting a probe signal onto said communication
channel, said transmitting being coordinated with the
transmission of at least one alien probe signal by another
network node; subsequently to said transmitting, receiving a
mixed feedback signal, said mixed feedback signal comprising
a first component corresponding to said probe signal and a
second component corresponding to said at least one alien
probe signal; extracting said first component from said
mixed feedback signal; and assessing the quality of said
communication channel on the basis of said extracted first
component; wherein said probe signal and said at least one
alien probe signal are designed to facilitate their
separation after having been superimposed.
In an embodiment of the method according to the present
invention, said probe signal and said at least one alien
probe signal have a substantially identical temporal and
spectral extent, except for a relative cyclic shift in the
time domain.
According to an aspect of the present invention, there is
provided a method to be applied in assessing the quality of
a plurality of communication channels in a multi -domain
network, the method comprising at a bridge attached to said
plurality of communication channels: receiving a plurality
of coordinated probe signals from said respective
communication channels; superimposing said plurality of
coordinated probe signals to form a mixed feedback signal;
and subsequently to said receiving, transmitting said mixed
feedback signal onto said plurality of communication
channels; wherein said coordinated probe signals are
designed to facilitate their separation after having been
superimposed .
In an embodiment of the method according to the present
invention, said probe signal and said at least one alien
probe signal have a substantially identical temporal and
spectral extent, except for a relative cyclic shift in the
time domain.
According to an aspect of the present invention, there is
provided a computer program configured to cause a processor
to carry out the method of any of the preceding claims .
According to an aspect of the present invention, there is
provided an apparatus for assessing the quality of a
communication channel in a multi-domain network, the
apparatus being adapted to produce a probe signal, the
apparatus comprising: a physical layer interface, adapted
to transmit said probe signal onto said channel, and to
subsequently receive a mixed feedback signal from said
channel; a filtering agent, operatively connected to said
physical layer interface, said filtering agent being
configured to extract a component corresponding to said
probe signal from said mixed feedback signal; and a probe
signal processor, operatively connected to said filtering
agent, said probe signal processor being configured to
assess the quality of said communication channel on the
basis of said extracted component; wherein said probe signal
is designed to facilitate its separation after having been
superimposed onto a probe signal from a peer apparatus.
In an embodiment, the apparatus according to the present
invention further comprises a cyclic shifter configured to
apply a cyclic shift to said probe signal prior to
transmission by said physical layer interface, said cyclic
shift being different from a cyclic shift applied by said
peer apparatus .
According to an aspect of the present invention, there is
provided an apparatus for bridging a plurality of
communication channels in a multi-domain network, the
apparatus comprising: a plurality of physical layer
interfaces, adapted to transmit and receive signals over
respective ones of said plurality of communication channels;
and a signal combination agent, operatively connected to
said plurality of physical layer interfaces, said signal
combination agent being configured to generate, upon
receiving probe signals from said physical layer interfaces,
a mixed feedback signal representing a superposition of said
probe signals; wherein said apparatus is configured to
transmit said mixed feedback signal onto said plurality of
communication channels.
In an embodiment of the apparatus according to the present
invention, said probe signals are designed to facilitate
their separation after having been superimposed
In an embodiment of the apparatus according to the present
invention, said probe signals have a substantially identical
temporal and spectral extent, except for a relative cyclic
shift in the time domain
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 channel usage during the channel
assessment stage according to a known method;
Figure 2 schematically illustrates an exemplary network
architecture in which embodiments of the present invention
may be deployed;
Figure 3 illustrates channel usage during the channel
assessment stage according to an embodiment of the present
invention;
Figure 4 schematically illustrates an apparatus according to
an embodiment of the present invention;
Figure 5 schematically illustrates an apparatus according to
another embodiment of the present invention; and
Figure 6 schematically illustrates the interaction between
elements of an embodiment of the present embodiment .
Detailed Description of Embodiments
International Telecommunication Union (ITU) G.hn standard
was defined to enable the broadband data communication
required by in-house high data rate (i.e., broadband)
applications. In G.hn, different domains are available for
the in-house network access over different mediums (e.g.,
the copper twisted-pairs, coax, power line cables) . However,
the available network resources (e.g., frequency spectrum)
are limited by the characteristics of the medium and
structure of the network. In general, the G.hn medium (s) can
be seen as a broadcast channel (s), where devices share the
same medium and available network resources.
To improve spectrum efficiency (i.e., throughput, latency,
etc.) a bi-directional mechanism, where both the transmitter
and the receiver communicate as a part of the same
transmission session, between two nodes may be used for
sessions that are bi-directional in nature. One example is
transmission control protocol (TCP) session. The bi
directional mechanism in G.hn is available only to nodes
communicating directly within the same domain with two
service flows:
(i) the forward flow from the originating node to the
endpoint node (assigned by the originating node) ;
and
(ii) the reverse flow from the endpoint node to the
originating node (assigned by the endpoint node) .
However, for inter-domain bi-directional communication in
G.hn the channel assessment is required for coherent
detection. This is a challenging task since multiple devices
access the same network resources at the same time based on
time division multiple access (TDMA) scheme.
The channel assessment probe frame is specified in current
version of ITU-T G.9960 Recommendation. The payload of the
probe frame shall contain a number of symbol frames with no
data. The number of the symbol frames (and OFDM symbols)
shall be indicated in the PHY- frame header via the PRBSYM
field and can be of size 4 , 8 , 12, 64 OFDM payload
symbols in the probe frame. The probe frames (i.e., signals)
are sent/received based on TDMA scheme either directly
between two devices (where one device acts as a domain
master) or via a relay.
Unlike direct (relay-less) and relay-assisted sessions in
G.hn home networks, where signals from different users are
separated in time to avoid interference, in bi-directional
inter-domain G.hn communication, the device's probe signals
interfere in the same time slot. Bi-directional inter-domain
G.hn communication is described in European patent
application no. 11305586.7 in the name of the Applicant,
filed on 16 May 2011, the content of which is incorporated
in its entirety by this reference.
Hence, in the case of probe transmission, a domain master
cannot estimate the CSIs of different home network devices.
Although the invention is described in the context of G.hn
networks, the skilled person will understand that this is
done for illustrative purposes only, and that the invention
is not limited to G.hn networks. Any reference to G.hn or
G.hn related terminology should be understood as applying
equally to similar multi-domain network architectures. This
includes home networks, i.e. networks for residential use.
Figure 1 diagrammatically illustrates a straightforward
method to avoid this problem In G.hn networks, which
consists of allocating different 5 time slots, essentially
performing probe signaling in a time-division multiple
access (TDMA) fashion.
A s shown in Figure 1 , the information about the channel must
be fed back to the device after each probe transmission.
This will reduce the network throughput since the G.hn home
network may have a large number of operating devices. Thus,
the channel assessment for inter-domain communication in
G.hn may be important and limiting factor for different home
network services where the content is kept within the
network and/or distributed over different domains.
It is an object of the present invention to provide a more
efficient channel assessment for inter-domain bi-directional
transmission in G.hn home networks. The invention is inter
alia based on the insight of the inventor that the
throughput, and thus the efficiency, can be improved by
reducing the required number of signaling intervals within
the probe frames and the domain master. The invention is
further based on the insight of the inventor that this
reduction can be achieved by judiciously combining the
transmission of several signals in a manner that allows
reconstruction of the original signals.
G.hn supports multi-port device functionality that can be
exploited to enable efficient inter-domain bi-directional
transmission. In this example we consider inter-domain bi
directional communication between two devices A i and B i from
different domains A and B , respectively.
Figure 2 provides a schematic representation of the proposed
architecture of a network, preferably a home network, more
preferably a G.hn network, comprising two domains 101, 102
(corresponding for instance to the aforementioned domains A
and B ) , where two partner devices 501, 502 (corresponding
for instance to the aforementioned devices A i and Bi) ask for
the network resources to send their corresponding probe
signals .
The LLC function of the Inter-domain bridge 400 triggers a
new logical interface (henceforth X-I interface) to initiate
the inter-domain mechanism between the targeted pair of
devices 501, 502. Acting as a reservation protocol, the X-I
interface coordinates the transmission at the same time
between them according to the partner list. Finally, the two
devices 501, 502 are ready to start with transmission over
the designated inter-domain bridge (IDB) 400 by using the
allocated time signaling intervals.
With reference to Figure 3 , the two stages of the channel
probing scheme according to the present invention will now
be described in more detail.
In the first time slot, identified as "Stage 1 " in Figure 3 ,
both devices A i and B i (501, 502) send their respective probe
signals PA and PB , to the corresponding multi-port DMs (see
Fig. 2), which are interconnected over the LLC function with
designated IDB node 400.
The probe signals PA and PB from both devices are designed in
such way so as to avoid interference during Stage 1 . In that
way, both devices A i and B i (501, 502) can access the network
resources at the same time. This constraint can be met by
cyclically shifting one of the probe signals (e.g., PB of Bi)
in the time domain. Consequently, the frequency spectrum of
the probe signal PB will be shifted in the frequency domain
with respect to the frequency spectrum of the probe signal PA
of device A i. Accordingly, the frequency domain envelopes of
the probe signals as received through the respective
channels will not overlap, which in turn allows the
receivers to extract the corresponding channel transfer
function in the frequency domain without interference from
the partner device's probe signal.
For illustrative purposes only, the above concept can be
further explained by the following mathematical derivation.
Without loss of generality, we consider a first probe signal
pA , associated with domain A , and a second probe signal p B ,
associated with domain B , where p B is in fact a cyclically
delayed version of the same probe signal, such that, in the
time domain, the following expression holds true:
P ( = ( od a
where "mod" denotes the modulo operator.
Turning to a frequency domain representation, and using HA
and HB to denote the channel matrices of domains A and B ,
respectively, the combined probe signal as received at the
inter-domain bridge 400 can be expressed as follows:
R = + HBpB = H p + H p e -ί f )
Mathematically, the situation is therefore equivalent to
receiving the single probe signal pA through a combined
channel with the following associated channel matrix:
H = HA + HB e-i(P
the value of which can be estimated by calculating
R
H = —
P
where R represents the received combined probe signal . With
a suitable choice of f (which is in turn achieved by a
suitable choice of ) , it can be ensured that HA and HB can
be separately determined in the expression for H , such that
the distortions introduced by the respective media of
domains A and B can be assessed individually.
In the second time slot, identified as "Stage 2 " in
Figure 3 , the probe signals as received on different ports
of IDB node 400 are superimposed. Next, the IDB 400 causes
the combined probe signals to be broadcast by A-DM and B-DM
in their respective domains.
If more than two devices are used in the scheme according to
the present invention, the cyclic shift parameters should be
designed to avoid spectrum overlapping in the frequency
domain for every pair of probe signals, while keeping in
mind that the shift should be larger than the guard
interval. Consequently, by using the cyclic shift parameters
and partner list, the IDB 400 is able to initiate and
coordinate channel assessment for inter-domain bi
directional communication between two devices from different
domains.
An exemplary IDB node 400 according to an embodiment of the
present invention is schematically illustrated in Figure .
The node 400 is capable of being operatively connected to at
least two domains 101, 102 (corresponding for instance to
the aforementioned domains A and B ) , via appropriate
physical interfaces 441, 442. Probe signals that are
substantially simultaneously received at these physical
interfaces 441, 442 are relayed to a signal combination
agent 420. The received probe signals are cyclically shifted
relative to each other as described above. Additionally, a
small amount of non-cyclic relative delay may be due to
different propagation delays in the respective domains 101,
102 .
The combined probe signal as generated by the signal
combination agent 420 is made available to the transmission
logic of the node 400, preferably to the X-I interface
controller 410, which causes the combined probe signal to be
broadcast on the target domains 101, 102, as feedback
information for the originating devices in these domains.
The channel assessment at the receiver ends 501, 502 is
rather simple. For the purpose of this description and
without loss of generality, the receiver ends 501, 502 are
assumed to correspond to the aforementioned devices A i and
B i. Since both A i and B i know their own respective probe
signals, they are each preferably configured to subtract any
interference caused by that their own respective signal,
which may be present as "echo" at the destination. The
corresponding channel information is subsequently estimated
in the frequency domain between A and the partner device
by first dividing the received signal with the transmitted
probe signal to obtain an estimate of the "combined" channel
transfer function, and then decomposing this "combined"
channel transfer function into the contributions of the
respective domains 101, 102. Assuming the probe signals were
designed to be decomposable by applying the cyclic shift as
described above, knowledge of the cyclic shift parameter
allows restoring the frequency spectrum of the channel back
to its original form. It will be understood that in the
scheme according to the present invention, only a relative
cyclic shift is required to render the combined signals
decomposable, so it is possible to have one probe signal
that is not shifted.
An exemplary embodiment of a device 500 according to an
embodiment of the present invention is schematically
illustrated in Figure 5 . The devices 501, 502 of the
description above may be implemented according to the
architecture of device 500. The device 500 is capable of
being operatively connected to at least one domain 100
(corresponding for instance to one of the aforementioned
domains A and B ) , via an appropriate physical interface 540.
The device 500 comprises a probe signal generator 560
configured to generate an appropriate probe signal for
transmission over the domain 100 via the physical layer
interface 540. Prior to transmission, the probe signal is
cyclically shifted by the cyclic shifter 550, if necessary.
The term "probe signal generator" must not be interpreted to
imply that the probe signal is generated on-the-fly in the
device 500; the generator may retrieve a standardized probe
signal from a memory, and present this to the cyclic shifter
550 for further processing. Alternatively, the generator may
retrieve a pre- shifted probe signal from a memory, and
present this for transmission to the physical layer
interface 540 .
The feedback signal corresponding to the probe signal,
consisting of a reflected superposition of the original
probe signal and that of one or more other devices, is
received at the physical interfaces 540 and relayed to the
signal filtering agent 530. The signal filtering agent 530
may be operatively connected to the probe signal generation
560 to receive information about the transmitted probe
signal from the latter for interference cancellation
purposes. Furthermore, the signal filtering agent 530 uses
the special mathematical properties of the combined feedback
signal to separate the relevant reflection of the device's
own probe signal. The signal filtering agent 530 is
operatively connected to the cyclic shifter 550 or otherwise
capable of obtaining information about the cyclic shift that
was applied to the transmitted probe signal, in order to
remove the shift from the received version of the signal.
The device 500 further comprises logic, designated as probe
signal processor 520, configured to analyze the received
feedback in order to assess the properties of the physical
medium. A physical layer configuration agent 510 preferably
uses the results of this assessment to determine the most
appropriate physical layer transmission parameters, and to
configure the physical layer interface accordingly.
The functions of the various elements shown in the figures,
including any functional blocks labeled as "processors" ,
"controllers", or "agents", 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 figures 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 .
The proposed method procedure flow is illustrated by the
flow diagram of Figure .
A first step 610 represents processing carried out by the
devices 501, 502 attached to the respective domains 101,
102. Device A i 501 prepares its probe signal PA in sub-step
611, and device B i 502 prepares its probe signal PB in substep
612. These sub-steps 611, 612 are appropriately
coordinated to ensure that the resulting probe signals PA and
PB are subjected to a relative cyclic shift (this implies
that only at least one of the signals PA and PB needs to
undergo an actual shift) . This coordination is schematically
represented by the dashed double arrow between the boxes
representing sub-steps 611 and 612.
A second step 620 represents the processing at the IDB 400,
which implies interaction between the domain managers DM-A
and DM-B associated with the respective domains A and B on
the one hand, and the LLC X-I interface controller, which is
responsible for coordinating the transmissions on said
domains, on the other hand. The LLC X-I interface controller
maintains a partner list for this purpose, which in the
example used above includes a partnership between A i and B i.
A third step 630 again represents processing carried out by
the devices 501, 502 attached to the respective domains 101,
102 . Device A i 501 receives the combined retransmitted probe
signal in sub-step 631, and device B i 502 receives the
combined retransmitted probe signal in sub-step 632. No
further coordination between the sub-steps 631, 632 is
necessary at this point, provided that both devices are
aware of the relative cyclic shift that was applied in the
first step 610. Further processing of the received combined
retransmitted probe signal is then applied as explained in
connection with Figure 5 .
The result of applying the method according to the described
embodiment of the invention is that each device 501, 502 has
access to the feedback signal corresponding to the probe
signal it transmitted. This access is represented by the
dashed arrows from the TX processing sub-steps 611 and 612
to the RX processing sub-steps 631 and 632, respectively.
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 .
Claims
1 . A method for assessing the quality of a communication
channel in a multi-domain network, the method comprising at
a device attached to said communication channel :
- transmitting a probe signal onto said communication
channel, said transmitting being coordinated with the
transmission of at least one alien probe signal by another
network node;
- subsequently to said transmitting, receiving a mixed
feedback signal, said mixed feedback signal comprising a
first component corresponding to said probe signal and a
second component corresponding to said at least one alien
probe signal;
- extracting said first component from said mixed feedback
signal ;
- assessing the quality of said communication channel on the
basis of said extracted first component;
wherein said probe signal and said at least one alien probe
signal are designed to facilitate their separation after
having been superimposed.
2 . The method according to claim 1 , wherein said probe
signal and said at least one alien probe signal have a
substantially identical temporal and spectral extent, except
for a relative cyclic shift in the time domain.
3 . A method to be applied in assessing the quality of a
plurality of communication channels in a multi -domain
network, the method comprising at a bridge attached to said
plurality of communication channels:
- receiving a plurality of coordinated probe signals from
said respective communication channels;
- superimposing said plurality of coordinated probe signals
to form a mixed feedback signal;
- subsequently to said receiving, transmitting said mixed
feedback signal onto said plurality of communication
channels ;
wherein said coordinated probe signals are designed to
facilitate their separation after having been superimposed.
4 . The method according to claim 3 , wherein said probe
signal and said at least one alien probe signal have a
substantially identical temporal and spectral extent, except
for a relative cyclic shift in the time domain.
5 . A computer program configured to cause a processor to
carry out the method of any of the preceding claims .
6 . An apparatus for assessing the quality of a communication
channel in a multi-domain network, the apparatus being
adapted to produce a probe signal, the apparatus comprising:
- a physical layer interface, adapted to transmit said
probe signal onto said channel, and to subsequently receive
a mixed feedback signal from said channel;
- a filtering agent, operatively connected to said physical
layer interface, said filtering agent being configured to
extract a component corresponding to said probe signal from
said mixed feedback signal; and
- a probe signal processor, operatively connected to said
filtering agent, said probe signal processor being
configured to assess the quality of said communication
channel on the basis of said extracted component;
wherein said probe signal is designed to facilitate its
separation after having been superimposed onto a probe
signal from a peer apparatus.
7 . The apparatus according to claim 6 , further comprising a
cyclic shifter configured to apply a cyclic shift to said
probe signal prior to transmission by said physical layer
interface, said cyclic shift being different from a cyclic
shift applied by said peer apparatus.
8 . An apparatus for bridging a plurality of communication
channels in a multi-domain network, the apparatus comprising
- a plurality of physical layer interfaces, adapted to
transmit and receive signals over respective ones of said
plurality of communication channels;
- a signal combination agent, operatively connected to said
plurality of physical layer interfaces, said signal
combination agent being configured to generate, upon
receiving probe signals from said physical layer interfaces,
a mixed feedback signal representing a superposition of said
probe signals;
wherein said apparatus is configured to transmit said mixed
feedback signal onto said plurality of communication
channels .
9 . The apparatus of claim 8 , wherein said probe signals are
designed to facilitate their separation after having been
superimposed .
10. The apparatus of claim 9 , wherein said probe signals
have a substantially identical temporal and spectral extent,
except for a relative cyclic shift in the time domain.