Method and apparatus for providing bidirectional
communication between segments of a home network
Field of the Invention
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.
Summary
It is an object of the present invention to improve
scalability and bidirectional interaction across domains in
home networks .
According to an aspect of the present invention, there is
provided a method for providing bidirectional communication
between segments of a home network, the method comprising:
receiving a first communication signal at a first interface
of an inter-domain bridge during a first time interval;
receiving a second communication signal at a second
interface of the inter-domain bridge during the first time
interval; generating a superimposed signal of the first
communication signal and the second communication signal;
transmitting the superimposed signal through the first
interface and the second interface during a second time
interval, the second time interval occurring after the first
time interval .
It is an advantage of the invention that network resources
can be used more efficiently, by carrying out data relaying
at the inter-domain bridges bidirectionally . The present
invention is based inter alia on the insight that
simultaneous transmission of different signals does not
necessarily obscure the content of the message, because a
transmitter can use its own copy of the transmitted message
as a filter to extract the peer's message from the combined
transmission .
The invention thus provides a form of network coding for use
in a home network, which is preferably conducted at the
physical, data link and/or network layer.
In an embodiment of the method of the present invention, the
generating of the superimposed signal comprises combining
binary data contents of the first communication signal with
binary data contents of the second communication signal by
applying an XOR-operation .
It is an advantage of this embodiment that the superposition
happens in a mathematically straightforward and easy-toimplement
manner. In this embodiment, the superposition can
advantageously be applied at the media access control (MAC) ,
layer, in which case the contents of the respective MAC
frames are taken as the binary data contents of the first
and second communication signal. Accordingly, the
superimposed MAC frames are handed down to the physical
layer and transmitted onto the media.
In an embodiment of the method of the present invention, the
generating of the superimposed signal comprises adding a
first physical parameter representing the first
communication signal to a second physical parameter
representing the second communication signal in the time
domain .
It is an advantage of this embodiment that the superposition
happens in a manner that requires minimal modifications to
the existing physical layer equipment. In this embodiment,
the superposition can advantageously be applied at the
physical layer, in which case the physical representations
of the respective communication signals, preferably of the
respective MAC frames, are combined before transmission onto
the media.
According to another aspect of the present invention, there
is provided a method for communicating with a terminal in a
different segment of a home network, the method comprising:
transmitting a first communication signal to an inter-domain
bridge during a first time interval; receiving a second
communication signal from the inter-domain bridge during a
second time interval; combining the transmitted first
communication signal and the received second communication
signal to extract a third communication signal,
corresponding to a transmission from the remote terminal
received at the inter-domain bridge.
This aspect of the invention translates the above described
method to the end points of the bidirectional communication.
In an embodiment of the method of the present invention, the
combining of the first communication and the second
communication signal comprises combining binary data
contents of the first communication signal with binary data
contents of the second communication signal by applying an
XOR-operation .
In an embodiment of the method of the present invention, the
combining of the first communication and the second
communication signal comprises subtracting a first physical
parameter representing the first communication signal from a
second physical parameter representing the second
communication signal in the time domain.
According to another aspect of the present invention, there
is provided a computer program configured to cause a
processor to carry out the method according to any of the
preceding claims.
According to another aspect of the present invention, there
is provided an inter-domain bridge comprising: a first
interface adapted to exchange signals with a first home
networking segment, a second interface adapted to exchange
signals with a second home networking segment,
a superposition agent, operatively coupled to the first
interface and the second interface, the superposition agent
being configured to generate a superimposed signal of a
first communication signal received from the first interface
and a second communication signal received from the second
interface, and to substantially simultaneously transmit the
superimposed signal through the first interface and the
second interface .
In an embodiment of the inter-domain bridge of the present
invention, the superimposed signal comprises a combination
of binary data contents of the first communication signal
with binary data contents of the second communication signal
obtained by applying an XOR-operation .
In an embodiment of the inter-domain bridge of the present
invention, the superimposed signal comprises an addition of
a first physical parameter representing the first
communication signal to a second physical parameter
representing the second communication signal in the time
domain .
According to another aspect of the present invention, there
is provided a communication terminal comprising: a
communication interface for exchanging signals with an
inter-domain bridge via a home network domain; a transmitter
for transmitting an outgoing communication signal through
the communication interface; a receiver for receiving an
incoming communication signal through the communication
interface; and means for removing a component corresponding
to the outgoing communication signal from the incoming
communication signal in order to arrive at a difference
signal .
In an embodiment of the communication terminal of the
present invention, the difference signal is a combination of
binary data contents of the incoming communication signal
with binary data contents of the outgoing communication
signal obtained by applying an XOR-operation.
In an embodiment of the communication terminal of the
present invention, the difference signal is a difference of
a first physical parameter representing the incoming
communication signal to a second physical parameter
representing the outgoing communication signal in the time
domain .
According to another aspect of the present invention, there
is provided a system comprising an inter-domain bridge and
two communication terminals as described above, the two
communication terminals being connected to the first
interface and the second interface .
The advantages of the apparatus, computer program, and
system according to the present invention are identical or
analogous to those of the above mentioned methods according
to the present invention.
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 an exemplary G.hn network architecture;
Figure 2 illustrates a portion of the network of Figure 1 in
more detail;
Figure 3 provides a flow chart of an embodiment of the
methods according to the present invention;
Figure 4 provides a block diagram of an embodiment of the
inter-domain bridge according to the present invention; and
Figure 5 provides a block diagram of an embodiment of the
communication terminal according to the present invention.
Detailed 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 several network segments are present in an
architecture similar to the one implied by G.hn, including
office, industry, hospitality, and educational settings.
Likewise, references to a "G.hn" network should not be
construed as limiting the invention to implementations
complying to that particular family of ITU-T
Recommendations .
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.
Reference is made to Figure 1 , which illustrates an
exemplary network 100 according to the G.hn network
architecture. A G.hn network is designed to operate over a
variety of in-house physical media, including twisted pairs,
power lines, and coaxial cabling, in a frequency band from
close to DC up to 100 MHz. G.hn networks are standardized to
use Orthogonal Frequency Division Modulation (OFDM) , a
modulation scheme which is also common in wireless systems
such as IEEE 802.11 wireless local area networks. While our
analysis has shown that the scheme of the invention works
well in networks with OFDM-based data transmission, the
skilled person will appreciate that the choice of modulation
scheme does not affect the applicability of the inventive
concept. Hence, the present invention may equally be applied
to networks using other modulation schemes, including
single-carrier schemes (e.g., quadrature amplitude
modulation - QAM) , code division multiple access (CDMA) ,
discrete multi-tone (DMT) , etc.
Each of the different types of physical media defines a
"domain" within the G.hn network. A G.hn network may
additionally interact with a wireless domain. Without loss
of generality, three domains 101, 102, 103 are shown in
Figure 1 . A number of inter-domain bridges (IDB) are shown,
of which we will henceforth focus, without loss of
generality, on the inter-domain bridge 400 present between a
first domain 101 and a second domain 102 .
Within each such domain, there may be a large number of
devices or terminals communicating with each other. Within a
particular domain, bidirectional communication is enabled by
means of a collision avoidance scheme. In the remainder of
the description, we will focus on a first terminal 501 in
the first domain 101, and a second terminal 502 in the
second domain 102 .
Communication between domains relies on the presence of
domain masters. In the network 100 of Figure 1 , a first
domain master 111 manages the first domain 101, while a
second domain master 112 manages the second domain 102 .
The present invention is based inter alia on the insight
that the involvement of the domain master in inter-domain
communication between any pair of terminals residing in
different domains causes serious scalability issues.
G.hn supports multi-port device functionality that can be
exploited to enable efficient inter-domain bi-directional
transmission. Considering the two terminals 501, 502, with
identical parameters but different service flow priority,
the higher priority flow will be given lower delay.
Often the available bandwidth may not be sufficient for all
the service flows and consequently, service flows with
higher priority will be assigned bandwidth resources at the
cost of service flows with lower priority. However, for a
large number of devices this approach may have long latency
since the queuing between the domains can reduce the
spectrum efficiency with increased costs and complexity. For
example, if the available bandwidth is adequate to provide a
single 100 Mbps transmission at a time, while two devices
are in a waiting list with the same priority level one of
the devices will have to wait to utilize the spectrum over
the inter-domain bridge 400.
According to embodiments of the invention, a joint use of
prioritizing and inter-domain bi-directional mechanism can
be used to improve the spectrum efficiency, where the bi
directional scheme is initiated through the logical link
control (LLC) function.
To initiate the inter-domain bi-directional mechanism a flow
priority and queuing list are used in a sense of control
parameters. Thus, based on these control parameters a list
of partner devices (each from a different domain) is formed,
which is called "partner list" . By choosing a pairs of
devices from the partner list, the LLC function triggers a
new logical interface (henceforth X-I controller) to
initiate the inter-domain mechanism. In addition, the
network device parameters such as latency or/and jitter can
be used as additional parameters to initiate the
communication .
This principle is illustrated in more detail in Figure 2 . In
this figure, communications flowing simultaneously from the
end points 501, 502 to the inter-domain bridge 400 in a
first stage are symbolized by a solid arrow, while the
(mixed) communications flowing back from the inter-domain
bridge 400 to the end points 501, 502 in a second,
subsequent stage are symbolized by a dotted arrow.
For the purpose of the present description, we assume that
the two terminals 501, 502 ask for the network resources to
achieve data communication of 100 Mbps . Next, acting as a
reservation protocol, the X-I interface coordinates the
transmission at the same time between a pair of devices from
the partner list by allocating the network resources (i.e.,
time signaling intervals) for data transmission of 100 Mbps.
Then, two devices are ready to start communication over the
designated inter-domain bridge 400 by using the allocated
time signaling intervals. In the first time slot (solid
arrows) , both devices A l and Bl send their full (100 Mbps)
data signals to the corresponding multi-port domain managers
111, 112, which are interconnected over the LLC function
with designated inter-domain bridge node 400. During the
second time slot (dotted arrows) the received signals on
different ports of inter-domain bridge node 400 are
superimposed and then, via the logical X-I interface, the
inter-domain bridge 400 sends commands to the first domain
manager 111 and the second domain manager 112 to broadcast
the superimposed signal within their corresponding network
domains 101, 102. Since both the first terminal 501 and the
second terminal 502 know their own signals, they are able to
subtract their information content and obtain the
information from the partner device.
Thus, using the control parameters (i.e., flow priority and
queuing list) the inter-domain bridge 400, through the X-I
interface, is able to initiate and coordinate bi-directional
communication between two devices 501, 502 from different
domains 101, 102.
The methods and apparatus according to the invention
therefore provide more efficient use of network resources,
by carrying out the data relaying at the inter-domain
bridges simultaneously in both direction.
The present invention is thus based inter alia on the
insight that simultaneous transmission of different signals
does not necessarily obscure the content of the message,
because a transmitter can use its own copy of the
transmitted message as a filter to extract the peer's
message from the combined transmission.
The terminals 501, 502 apply a form of crosstalk
cancellation or echo cancellation, in which the terminal's
own previously transmitted signal is assumed to be the
disturber. With adequate scheduling, the inter-domain bridge
400 can ensure that pairs of signals originating from a
given pair of terminals 501, 502 are always sent
simultaneously, which ensures that the intended recipient
will always be able to disentangle communications addressed
to it. Other terminals that receive the mixed communication
via the broadcast channel will normally not be able to
disentangle the communication, as they normally don't
dispose of a copy of the outgoing communication signal.
The invention is further based on the insight that the
mixing of communication signals, and thus also their
disentanglement, may happen at physical layer, or at the
packet level. In the latter case, the
combining/disentangling may consist of applying a logical
XOR operation to the two available signals in a bit-by-bit
basis .
Figure 3 provides a flow chart of an embodiment of the
methods according to the present invention. For clarity
reasons, steps carried out by an exemplary terminal 500
according to the present invention are illustrated in the
left-hand column, while steps carried out by an exemplary
inter-domain bridge 400 according to the present invention
are illustrated in the right-hand column. The steps of the
terminal's peer in the conversation are not explicitly
shown .
In a first step 310, the terminal 500 transmits a first
communication signal to inter-domain bridge 400. This step
corresponds to the first step 320 occurring at the interdomain
bridge 400, which consists of receiving this first
communication signal. In a second step 330, the inter-domain
bridge 400 receives a second communication signal, as a
result of a transmission by a second terminal (not shown) .
The aforementioned steps 310-330 may occur substantially
simultaneously .
In a next step 340, the inter-domain bridge 400 generates a
superimposed signal based on the first and second signals.
The superposition may take place at the packet level, e.g.
by the application of a bitwise XOR as mentioned above, or
at the physical level, by adding voltage levels or light
intensities representing the respective signals.
In a next step 350, the superimposed signals are
retransmitted by the inter-domain bridge 400 to the end
points 501, 502 (typically via the respective domain
managers 511, 512) .
Figure 4 provides a block diagram of an embodiment of the
inter-domain bridge 400 according to the present invention.
It comprises a first interface 410 adapted to exchange
signals with a first home networking segment (not shown, see
101 in Figures 1 and 2 ) , a second interface 420 adapted to
exchange signals with a second home networking segment (not
shown, see 101 in Figures 1 and 2 ) , and a superposition
agent 430, configured to generate a superimposed signal of
the first communication signal and the second communication
signal, and to substantially simultaneously transmit said
superimposed signal through the first interface 410 and the
second interface 420.
The skilled person will appreciate that the interfaces 410,
420 comprise a combination of the necessary hardware and
software to allow communication of the inter-domain bridge
400 with the network segment under consideration using the
applicable protocols. As schematically shown, the
superposition agent 430 is operatively coupled to the
interfaces 410, 420, i.e. it is enabled to transmit and
receive communication packets through these interfaces,
hence the required minimal receiving and transmitting
functions are implicitly present in the superposition agent
The first interface 410 is preferably configured to operate
over one of a twisted-pair segment, a coax segment (for
instance according to the MOCA standard) , and a power line
segment. The second interface 420 is preferably configured
to operate over another one of a twisted-pair segment, a
coax segment (for instance according to the MOCA standard) ,
and a power line segment.
Figure 5 provides a block diagram of an embodiment of the
communication terminal 500 according to the present
invention. It comprises a communication interface 510 for
exchanging signals with an inter-domain bridge 400 via a
home network domain 101; a transmitter 520 for transmitting
an outgoing communication signal through the communication
interface 510; a receiver 530 for receiving an incoming
communication signal through the communication interface
510; and means 540 for removing a component corresponding to
the outgoing communication signal from the incoming
communication signal in order to arrive at a difference
signal 599.
In the context of the present invention, the resulting
difference signal 599 represents the message of the
conversation peer, which is obtained after cancelling the
"self -crosstalk" out of the communication signal received
from the inter-domain bridge 400.
The skilled person will again appreciate that the interface
510 comprises a combination of the necessary hardware and
software to allow communication of the terminal 500 with the
network segment under consideration using the applicable
protocols. As schematically shown, the extraction means 540
is operatively coupled to the interface 510, i.e. it is
enabled to transmit and receive communication packets
through this interface, via transmitter 520 and receiver
530, respectively. The interface 510 is preferably
configured to operate over one of a twisted-pair segment, a
coax segment (for instance according to the MOCA standard) ,
and a power line segment.
Although the superposition agent 430 is represented in
Figure 4 by means of certain logical processing symbols,
this is done for illustrative purposes only, and not to
limit the invention to this particular form of signal
mixing. The same applies to the corresponding logical
symbols used to represent the means for removing a signal
component 540 in Figure 5 .
The functions of the various elements shown in the FIGs .,
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.
The various features, options, and configurations described
in connection with one or more apparatus according to the
present invention may be applied to the methods according to
the present invention and vice versa, without leaving the
scope of the present invention.
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 providing bidirectional communication
between segments of a home network, the method comprising:
receiving a first communication signal at a first interface
of an inter-domain bridge during a first time interval;
receiving a second communication signal at a second
interface of said inter-domain bridge during said first time
interval ;
generating a superimposed signal of said first communication
signal and said second communication signal;
transmitting said superimposed signal through said first
interface and said second interface during a second time
interval, said second time interval occurring after said
first time interval .
2 . The method of claim 1 , wherein said generating of said
superimposed signal comprises combining binary data contents
of said first communication signal with binary data contents
of said second communication signal by applying an XORoperation
.
3 . The method of claim 1 , wherein said generating of said
superimposed signal comprises adding a first physical
parameter representing said first communication signal to a
second physical parameter representing said second
communication signal in the time domain.
. A method for communicating with a terminal in a different
segment of a home network, the method comprising:
transmitting a first communication signal to an inter-domain
bridge during a first time interval;
receiving a second communication signal from said interdomain
bridge during a second time interval;
combining said transmitted first communication signal and
said received second communication signal to extract a third
communication signal, corresponding to a transmission from
said remote terminal received at said inter-domain bridge.
5 . The method of claim 4 , wherein said combining of said
first communication and said second communication signal
comprises combining binary data contents of said first
communication signal with binary data contents of said
second communication signal by applying an XOR-operation .
6 . The method of claim 4 , wherein said combining of said
first communication and said second communication signal
comprises subtracting a first physical parameter
representing said first communication signal from a second
physical parameter representing said second communication
signal in the time domain.
7 . A computer program configured to cause a processor to
carry out the method according to any of the preceding
claims .
8 . An inter-domain bridge comprising:
a first interface adapted to exchange signals with a first
home networking segment,
a second interface adapted to exchange signals with a second
home networking segment,
a superposition agent, operatively coupled to said first
interface and said second interface, said superposition
agent being configured to generate a superimposed signal of
a first communication signal received from said first
interface and a second communication signal received from
said second interface, and to substantially simultaneously
transmit said superimposed signal through said first
interface and said second interface .
9 . The inter-domain bridge of claim 8 , wherein said
superimposed signal comprises a combination of binary data
contents of said first communication signal with binary data
contents of said second communication signal obtained by
applying an XOR-operation .
10. The inter-domain bridge of claim 8 , wherein said
superimposed signal comprises an addition of a first
physical parameter representing said first communication
signal to a second physical parameter representing said
second communication signal in the time domain.
11. A communication terminal comprising:
a communication interface for exchanging signals with an
inter-domain bridge via a home network domain;
a transmitter for transmitting an outgoing communication
signal through said communication interface;
a receiver for receiving an incoming communication signal
through said communication interface; and
means for removing a component corresponding to said
outgoing communication signal from said incoming
communication signal in order to arrive at a difference
signal .
12. The communication terminal of claim 11, wherein said
difference signal is a combination of binary data contents
of said incoming communication signal with binary data
contents of said outgoing communication signal obtained by
applying an XOR-operation .
13. The communication terminal of claim 11, wherein said
difference signal is a difference of a first physical
parameter representing said incoming communication signal to
a second physical parameter representing said outgoing
communication signal in the time domain.
1 . A system comprising an inter-domain bridge according to
claim 8 and two communication terminals according to claim
11, said two communication terminals being connected to said
first interface and said second interface.