GB2528275A - Method and apparatus for system network installation using hybrid wired wireless connections - Google Patents

Abstract

The present invention concerns the field of multi-projector display systems that includes a plurality of projector nodes 105-1 to 105-6 among which at least one source device 101 provides a video stream and a plurality of display devices collectively display video in a combined display area. The nodes including the source device and the display devices are interconnected through wireless communication links. A set-up method determines a distribution scheme comprising chosen paths between nodes for transmission of sub-parts of the video stream, fulfilling the application needs under the constraint of paths capacity. When a solution cannot be found, the communication system is modified by replacing at least one wireless link between two nodes by a wired link. A distribution scheme for the modified communication system is then determined.

Description

METHOD AND APPARATUS FOR SYSTEM NETWORK INSTALLATION

USING HYBRID WIRED WIRELESS CONNECTIONS

FIELD OF THE INVENTION

The present invention generally concerns the field of multi-display systems that includes a plurality of nodes among which at least one source device provides a video stream and a plurality of display devices collectively display video in a combined display area. Also the nodes including the source device and the display devices are interconnected through a communication network.

The present invention concerns more particularly a method for configuring the communication network for wirelessly distributing video data in such a multi-display system, wherein some wired interconnections may be used to replace some wireless links in case a full wireless configuration does not fulfill the video distribution.

A detailed embodiment regards a multi-projector display system made of a plurality of video projectors. For ease of explanation below, reference is mainly made to such a multi-projector display system, although the invention may apply in other contexts comprising multi-monitor display systems.

BACKGROUND OF THE INVENTION

Multi-projector display systems are increasingly deployed to offer high-end video display of very large size and of very high quality, for example in the open air in a stadium for a sports event or a concert, or in a conference hall, or for teaching purposes or simulating purposes.

These are audio-visual projection systems made of several video projectors that tile the combined (or shared) display area and may be blended over the combined display area, i.e. may overlap partly or entirely. A variable number of video projectors may be instantiated.

The video projectors are fed with video data, for example live ultra-high definition (UHD) video. LJHD video generally refers to a sequence of 24, 25, 30, or 60 Hz video frames having 3,840 vertical lines and 2,160 horizontal lines corresponding to 3,840 x 2,160 pixels of 24 bits. Such video stream thus requires a considerable channel bandwidth of about several Gb/s (Gigabits per second) for transmission or processing. A variable number of sources of video data may be instantiated. It can be noted that the advantage of transferring uncompressed video data is to benefit from the highest quality since there is no compression, and providing a very low latency system allowing interactivity with the user, for instance for simulation tools. Due to the combined display area, the display devices of the multi-display systems have to locally output the appropriate portion of the source video stream for display. This requires video cutting function at the display devices to extract the relevant portion from the source video stream. For example, a multi-projector composite image display system may use an initial source video stream distributed over the network using one from two solutions: either using a centralised image signal splitter that duplicates the initial full source video stream and distributes the duplicates to all the display devices, or using a cascaded connection link between each display device through which the initial source video stream is duplicated and transmitted. Then, each display device cuts the appropriate portion that has to be locally displayed from the received source video stream, using its video cutting capabilities. Such basic approach cannot be used when the communication network has limited bandwidth, like a wireless network. In that case advanced network topology and advanced video distributing scheme shall be implemented according to the capacity of the network.

In the scope of this invention, the communication network is a wireless network allowing easy set-up of the system by the user. Wired installation of multi-projectors system may be a burden: typically the video source is located at ground level while video projectors are hanging from a ceiling or other structure.

Also, cabling sometimes requires long and costly cables in order to interconnect communication nodes. For very long distances, some repeaters may be added to guarantee correct signal shapes at the destination node. Moreover, especially in the case of outdoor installation, it may be difficult to install several cables first connecting the video source to video projectors and then interconnecting video projectors. For these reasons, a user of a multi-projection system is prone to install a full wireless system or a system with a limited number of wires.

In this context, a network adapter is attached to each device, video source and video projector, as external or internal equipment, and radio communication modules are provided to each network adapter.

As the performance of wireless technology has been greatly improved in terms of throughput, it becomes feasible to wirelessly transmit uncompressed video data requiring a data rate of few Gb/s. This becomes attainable with most recent wireless technologies like 60GHz millimeter wave operating in the 57-66 GHz unlicensed spectrum. 60 GHz-based communication systems are now standardized (e.g. IEEE 802.1 lad! WiGig, IEEE 802.15.3c! Wireless HD) and the research community has proposed several solutions and processes for transporting audio and video applications with a desired quality of service. The drawback of using 60GHz millimeter wave connections is that 60GHz signals are subjected to high attenuation by the air limiting the range (few meters), and 60GHz signals are blocked by obstacles. As a consequence, the quality of communications between two nodes may be poor or even not feasible due to masking conditions. Also, it may be difficult to perform broadcast communications from one transmitter node to a large set of receiver nodes. This is particularly true when high data rate are required, typically for uncompressed video transmission. As a solution, some intermediate relay nodes may be used to reach a destination node. Low data rate communication using more robust modulation and coding rate will less suffer from signal attenuation. Therefore, some control data can be exchanged between two nodes even if the transmission of uncompressed video data is not feasible with acceptable quality between these two nodes.

A video distribution scheme enabling video sub-areas of the source stream to be distributed to the multi-display system despite limited data rate capacity or bandwidth of the communication network should be determined.

The present invention has been devised to address one or more of the foregoing concerns.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method of set-up for distributing a data stream in a communication system comprising communication nodes, one node identified as a source device is providing the data stream, a plurality of nodes identified as destination devices being provided with a sub-part of the data stream, the real time distribution of the data stream to the right destination device constituting the application needs, at least one of the communication links between nodes being wireless, the method comprising: a step of determining a distribution scheme for the communication system comprising: a step of determining available transmission paths in the communication system; a step of determining the capacity of each determined path; and a step of selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity as the determined distribution scheme; wherein the method further comprises in case of failure of the step of selecting the distribution scheme: modifying the communication system by replacing at least one wireless link between two nodes by a wired link; and applying the step of determining a distribution scheme for the modified communication system.

Accordingly, the communication system is provided with a distribution scheme that fulfills the application needs.

In an embodiment, the step of selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity optimizes an objective variable.

Accordingly, the set-up method allows favoring a distribution scheme according to some criteria.

In an embodiment, the objective variable is the bandwidth of wireless links.

Accordingly, the set-up method allows favoring a distribution scheme according to the bandwidth of wireless links.

In an embodiment, the objective variable is the robustness of wireless links.

Accordingly, the set-up method allows favoring a distribution scheme according to the robustness of wireless links.

In an embodiment, the objective variable is the latency of the distribution.

Accordingly, the set-up method allows favoring a distribution scheme according to the latency of the distribution.

In an embodiment, selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity that optimizes an objective variable consists in solving the Multi-Commodity Flow problem defined by the communication characteristics of the communication system using a Simplex algorithm.

In an embodiment, the method comprises iteratively: determining a growing number of wireless links to be replaced by a wired link, this growing number beginning with value 1 For each possible location of the wired links in the communication system, applying the step of determining a distribution scheme for the modified communication system; stop iterating when at least one communication system corresponding to a determined distribution scheme has been obtained.

Accordingly, the communication system is provided with a distribution scheme that fulfills the application needs while minimizing the number of wire to be introduced.

In an embodiment, if several communication systems have been obtained for a given number of wired links the method further comprises: selecting the communication system corresponding to the determined distribution scheme that optimizes most the objective variable.

Accordingly, the set-up method allows favoring a distribution scheme according to some criteria while minimizing the number of wire to be introduced.

In an embodiment, if several communication systems have been obtained for a given number of wired links the method further comprises: selecting the communication system corresponding to the determined distribution scheme that minimizes the length of wires.

Accordingly, the communication system is provided with a distribution scheme that fulfills the application needs while minimizing the number of wire to be introduced that minimizes the length of wires.

In an embodiment, the step of determining the distribution scheme further comprises determining of each wireless path a type of modulation and an error correction code.

Accordingly, the communication system is provided with a distribution scheme that fulfills the application needs while minimizing the number of wire to be introduced further selecting for each wireless path the type of modulation and an error correction code.

In an embodiment, the type of modulation is determined in a predefined set of types of modulation.

In an embodiment, the error correction code is determined in a predefined set of errors correction codes.

In an embodiment, the method further comprises: displaying the wireless links to be replaced by wired links.

Accordingly, the user is able to easily determines the wires to install in the system.

According to another aspect of the invention there is provided a device for setting-up a distribution of a data stream in a communication system comprising communication nodes, one node identified as a source device is providing the data stream, a plurality of nodes identified as destination devices being provided with a sub-part of the data stream, the real time distribution of the data stream to the right destination device constituting the application needs, at least one of the communication links between nodes being wireless, the device comprising: a determining module for determining a distribution scheme for the communication system comprising:

B

a path determining module for determining available transmission paths in the communication system; a capacity determining module for determining the capacity of each determined path; and a selection module for selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity as the determined distribution scheme; wherein the device further comprises to be used in case of failure of the step of selecting the distribution scheme: a modifying module for modifying the communication system by replacing at least one wireless link between two nodes by a wired link; and an applying module for applying the step of determining a distribution scheme for the modified communication system.

In an embodiment, the selection module selects the distribution scheme fulfilling the application needs under the constraint of paths capacity optimizes an objective variable.

In an embodiment, the objective variable is the bandwidth of wireless links.

In an embodiment, the objective variable is the robustness of wireless links.

In an embodiment, the objective variable is the latency of the distribution.

In an embodiment, the selection module consists in a solver for solving the Multi-Commodity Flow problem defined by the communication characteristics of the communication system using a Simplex algorithm.

In an embodiment, the device comprises an iteration module which iterates on: determining a growing number of wireless links to be replaced by a wired link, this growing number beginning with value 1; For each possible location of the wired links in the communication system, applying the step of determining a distribution scheme for the modified communication system; stop iterating when at least one communication system corresponding to a determined distribution scheme has been obtained.

In an embodiment, it further comprises, to be used if several communication systems have been obtained for a given number of wired links: a selection module for selecting the communication system corresponding to the determined distribution scheme that optimizes most the objective variable.

In an embodiment, it further comprises, to be used if several communication systems have been obtained for a given number of wired links: a selection module for selecting the communication system corresponding to the determined distribution scheme that minimizes the length of wires.

In an embodiment, the determination module for determining the distribution scheme further comprises: a determination module for determining of each wireless path a type of modulation and an error correction code.

In an embodiment, the type of modulation is determined in a predefined set of types of modulation.

In an embodiment, the error correction code is determined in a predefined set of errors correction codes.

In an embodiment, the device further comprises: a display for displaying the wireless links to be replaced by wired links.

According to another aspect of the invention there is provided a computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to the invention, when loaded into and executed by the programmable apparatus.

According to another aspect of the invention there is provided a computer-readable storage medium storing instructions of a computer program for implementing a method according to the invention.

At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium, for example a tangible carrier medium or a transient carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device or the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RE signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 schematically shows a multi-projection system implementing embodiments of the invention; Figure 2 illustrates functional blocks of a network adapter implementing embodiments of the invention; Figure 3 illustrates the size of composite image displayed by the video projectors in the multi-projection system of Figure 1; Figure 4 illustrates a distribution scheme for the multi-projection system of Figure 1 with full wireless configuration compatible with the application requirements; Figure 5 illustrates an example of the IDMA sequence applied in the multi-projection system according to the distribution scheme of Figure 4; Figure 6 illustrates a distribution scheme for the multi-display system of Figure I with full wireless configuration but not compatible with the application requirements; Figure 7 illustrates a distribution scheme for the multi-display system of Figure I with a first hybrid wired-wireless configuration but not compatible with the application requirements; Figure 8 illustrates a distribution scheme for the multi-display system of Figure I with a second hybrid wired-wireless configuration compatible with the application requirements; Figure 9 illustrates a distribution scheme for the multi-display system of Figure I with a third hybrid wired-wireless configuration compatible with the application requirements; Figure 10 is a block diagram illustrating steps to determine a video distribution scheme according to embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention regards a set-up process to determine a distribution scheme of the video sub-parts of the source stream to be distributed from the source device to the displays. Based on a node discovery and the calculation of the available bandwidth of all links between nodes, a suitable distribution scheme is selected. It is looking for a distribution scheme fitting the application needs under the constraint of links capacity. It is also looked for optimizing wireless resources or the robustness of the wireless links.

Advantageously, when no full wireless solution may be determined, the set-up process looks for a modified communication system comprising some wired links to replace some wireless ones and where a suitable distribution scheme may be determined. The searched communication system should limit to a minimum the number of wired link introduced in the system. It also should minimize the wireless resources required or optimize the robustness of the wireless links. Once the communication system and the corresponding distribution scheme is determined, the wired links to be introduced in the system are displayed to the user for an actual cabling of the system while the wireless paths are configured.

We call a distribution scheme in this document the set of information needed to determine the distribution of a video stream from a source device to a plurality of display devices using a plurality of transmission nodes. Each display devices needs a sub-part of the video stream. The distribution scheme comprises the chosen paths between nodes used for the distribution along with which sub-part of the video stream is transmitted over each path.

Advantageously, the distribution scheme also comprises for wireless paths the modulation parameters to be used on this path.

Typically, the following steps would be applied to set-up a wireless multi-projection system. First, the user installs the devices (video source, video projectors), each device being attached to one network adapter to form a communication node. Then the user adds radio communications modules to each communication interface of network adapter. For instance, a network adapter provides two communication interfaces enabling wired connection or enabling the connection of multiple radio communication modules. Benefits of multiple radio is the potential extension of available bandwidth through radio channels aggregation, and the potential extension of space coverage (especially for 60GHz millimeter wave technology where typical antenna generates a radiation pattern covering a cone with an aperture of 1600 in best cases).

Then the user starts network adapters and enters the necessary information to the system. Typically, a master node is defined to manage the network, for instance this is a network adapter connected to a video source device. The master node receives some system parameters like the number of video projectors, the multiple display geometry (2 rows of 3 video projectors, the distances between video projectors, the video resolution of source video, the video resolution of displayed image, the ratio of overlapping areas.

The system is now ready for self-configuration. In an embodiment of the invention, it starts by node discovery and association. Once all nodes have been associated to the master node, the system proceeds to the assessment of wireless links quality. For that, a test pattern is successively transmitted by each radio communication module of each network adapter. The received signal strength is measured in each receiver node and for each available radio communication module. The results are transmitted by each node to the master node for the computation of video distributing scheme. An algorithm is executed to determine how the video source data will be transmitted from the video source device to all video projectors, if necessary using some video projectors as relay node. The algorithm shall take into account the capacity of each radio link, some of the links being not usable at all (e.g. masking conditions between two radio communication modules). The resulting system configuration is transmitted to each node in the network and the user is notified about the completion of the configuration process.

A problem occurs when the algorithm is unable to find a solution for video distribution, meaning that the wireless network capacity does not fulfill the application requirement. This may occur as some elements are not controllable in a wireless system like shadowing or interference due to reflections in an indoor context. Consequently, some wireless links can be strongly degraded so that some video projectors cannot receive their data. Reducing the video source resolution by decreasing the frame rate or applying chroma-sub sampling may be judged inacceptable by the user as it will alter the video rendering quality.

Another solution is to replace one or few wireless links by wired connections to increase the network capacity. However, the solution consisting in simply replacing a wireless connection with poor quality by a wired connection may be not applicable. Indeed, the number of communications interfaces available in a network adapter should be limited to not increase the cost of this equipment. It means that adding a wire in the system leads to remove one radio communication module of a first network adapter and to remove one radio communication module of a second network adapter. Through their wired communication interface, first network adapter and second network adapter can only communicate together, not with another network adapter. It means that the broadcast property of wireless communications, namely that one transmitter can reach simultaneously several receivers, is no more available for the wired communication interfaces: some wireless links] not replaced by wired links, are no more available. As a consequence, a distribution scheme shall be determined with this new system configuration but the algorithm may also fail again. It would be advantageous to provide the user one solution of cabling that enable video distribution. It would be also advantageous to minimize the number of wires to add. And it would be also advantageous to maximize the network robustness by minimizing the amount of data transmitted wirelessly still using the minimum number of wires.

Figure 1 schematically shows a multi-projection system 100 implementing an embodiment of the invention.

The exemplary multi-projection system 100 of Figure 1 comprises six video projectors or display devices 105-1 to 105-6 for video rendering and at least one source device 101 that provides a source video stream to the display devices. The source device is for example a video server that supplies video data of a source video stream.

The present invention regards the distribution of the source video stream to the various display devices. In case a plurality of source devices is provided, the invention as described below is implemented for each source video stream output from each source device. Below, reference is mainly made to a single source video stream.

Embodiments of the invention may involve a different number of video projectors and may involve video projectors without any source unit or with several source devices connected thereto. Indeed, some video projector may simultaneously display two streams from two different sources, for example in the case of picture in picture. Some video projectors may also be off, meaning they produce no display, but their communications means can be used for video data distribution. Stream identifiers make it possible to discriminate between the various source video streams, even if received locally by the same video projector.

The video projectors 105-1 to 105-6 are arranged to collectively display video in a combined display area. Each video projector thus contributes to more or less one sixth of the combined display. The aggregated display resolution is therefore more or less six times the display resolution of each individual video projector (provided that they have the same individual display resolution). A user may interact with a multi-projection controller (not shown) or with any of the video projectors, using conventional input means such as a keyboard or a mouse or a remote control] to design the layout of the combined display.

In the example of Figure 1, the six display devices 105-1 to 105-6 are disposed as a matrix in order to enable display of a larger area than the one proposed by each video projector. For instance, each video projector is being designed to display an area of 1,920 * 1,200 pixels (WIJXGA format), with overlapping areas in the order of 15% (horizontal) and 20% (vertical).

Overlapping areas, together with edge-blending correction function, advantageously provide smooth video transition for viewer, creating illusion of projection of a seamless, unified image. Blending technique guarantees that difference of luminance between adjacent projectors is not visible for a viewer.

The source device 101 provides video data to the multi-projection system 100, with resolution greater than the 1,920 * 1,200 pixels resolution of each projector 105-1 to 105-6. For example, the source device 101 provides 4K * 2K (3,840 * 2,160 pixels) resolution image.

Figure 1 also provides the shape of image 102 displayed by the 6 video display devices 105-I to 105-6 respectively displaying the sub-images 1, 2, 3, 4, and 6. Taking the example of sub-image 3, because of overlapping areas, some pixels of sub-image 3 are common with sub-image 1 only, some pixels are common with sub-images 1, 2, and 4, some pixels are common with sub-image 4 only, some pixels are common with sub-images 4, 5, and 6, and some pixels are common with sub-image 5 only.

The source device 101 and the display devices 105-1 to 105-6 are interconnected through a communication network made of wired and/or wireless communication links. Each of the devices is equipped with a network adapter external or integrated into the device (referred 110, 120, 130, 140, 150, 160, 170), to connect to the network and to exchange data with the other devices, in particular sub-part(s) of the source video stream that each projector has to display to obtain the full image projection. Wired links may be cable connection with guaranteed bandwidth of 5 Gb/s (as example)] and wireless links may be 60GHz radio signals able to sustain a maximum data rate of 3.7 Gb/s (as example) depending on radio environment conditions.

For each connection between the devices, each network adapter provides several communication interfaces for wired connection of for a wireless interface if a radio communication module is plugged. A network adapter is able to identify the nature (wired/wireless) of the interface, and in case of a wireless communication link, to discover and characterize the wireless link (for instance in terms of maximum data rate available). In this example, each network adapter features two communication interfaces and a radio communication module is installed by default on each communication interface. This is considered as the preferred configuration for a user installing the system. Radio communication modules are referred 111, 112 on network adapter 110; 121, 122 on network adapter 120; 131, 132 on network adapter 130; 141, 142 on network adapter 140; 151, 152 on network adapter 150; 161, 162 on network adapter 160; 171, 172 on network adapter 170.

Although the communication network as shown in the Figure 1 is made of only the source device 101 and the display devices 105-1 to 105-6, embodiments may include one or more relay nodes participating in the distribution of the video data. For the description below, reference is mainly made to the source and display devices excluding relay nodes, but the invention may implement the same routing function as described below to any of such relay nodes.

The determination of video distributing scheme involves determining routing paths for distributing elementary sub-streams (corresponding to spatial sub-areas of the frames) to their respective destination display devices, and involves cutting the source video stream into sub-streams that group elementary sub-streams.

Cutting operation is performed in the network adapter 170 connected to the source device 101. Working on elementary sub-streams makes it possible to reduce the bandwidth required over the communication links, by selecting appropriate routing paths, thereby overcoming the network bandwidth limitation.

Although the determination of video distributing scheme is performed at the same node or device in the description below, namely the network adapter 170, the invention encompasses situations where the actual determinations are split over several nodes of the communication network, provided they exchange the result of their respective determination each other.

It is proposed here that radio modules are installed on two opposite sides of network adapter so that the respective antenna will radiate in opposite direction. The purpose is to cover the maximum space with two radio communications modules. Moreover, in one possible embodiment, the network adapters are external and located on the rear side of the video projectors. The possible wireless links between video projectors themselves and between source device and video projectors are represented by the dashed lines in the Figure 1.

Below is explained how the system can determine the network topology with the list of available links and associated link capacity. As example, it is chosen that the master of the network is the node connected to the source device: the network adapter 170. For instance, with a medium access based on TDMA (Time Division Multiple Access) scheme, the master node periodically transmits a beacon frame determining the beginning of a data transmission sequence where each transmission time slot is allocated to one unique node of the network. Based on the reception of this beacon frame, non-master nodes (called slave nodes) can be synchronized and be informed about the IDMA sequence. Then a slave node can join the network sending a join request message during a contention time slot identified in the beacon frame. The master node receiving the join request message can grant the access to the network with a specific message. Also, a time slot is allocated to the new slave node. The new slave node can use this time slot to exchange information with the master node, but it can also use it to repeat the beacon frame received from the master node, or to repeat a join request message received during the contention time slot. This repetition allows slave nodes to be synchronized and associated even if they are not directly visible by the master node.

Through a dedicated user interface (remote control, keyboard...), the master node can get the parameters of the multi-projection system, especially the number of video projectors. Once all nodes have been associated to form the network, the master node triggers wireless links assessment. Each network adapter is able to detect if a radio communication module is connected or not to their communication interfaces, and it is able to inform other nodes through its dedicated transmission time slot. As a result, the master node knows the number of radio communication modules available in the network. The objective of wireless link assessment is to determine the achievable data rate for video transmission on each point-to-point link between two radio communication modules attached to two different nodes. The master node successively requests each network adapter to transmit a test pattern through one radio communication module. The other not transmitting nodes perform an RSSI (Received Signal Strength Indication) measurement or an equivalent link assessment. Once the measurement is performed, each node returns the measurement for the current transmitting node to all other nodes of the system.

Based on these results, for each wireless link, the master node can then select the best transmission mode, meaning modulation scheme and useful code rate to apply to each wireless link, in order that transmission on the link is the least subject to transmission errors given the provided Bit Error Rate (BER).

For a fixed modem symbol rate (Sr, in number of symbols per second), the gross bit rate (Gbr) provided by the modem increases with a modulation that provides more bits per symbol. For example, m (number of bits coded by symbol) is 1 for BPSK, 2 for QPSK and 4 for 16QAM modulations. Then the capacity of the wireless link is obtained as a function of the code rate (Cr) corresponding to the error correction code applied. The capacity C of the wireless link is C = Sr * Symbol_Size (in bits) * m * Cr * fRssl, where fRssl is a correcting factor taking into account transmission overhead for network management data, inter-frame gaps, preambles for physical layer synchronisation, but also taking into account bandwidth required for retransmission (transmission errors recovery). For a low RSSI value, the modulation scheme and the code rate will be selected low in order to provide a robust modulation and error code correction (low code rate). On the contrary, when RSSI value is good, the modulation scheme and the code rate will be selected high enabling more data transmission capability. Then the factor fRssI is selected according to the RSSI value in order to reserve bandwidth for data retransmission (necessary to obtain a desired Bit Error Rate at MAC output).

The selected policy for retransmission can be an automatic repeat request technique (ARO) where the destination node regularly transmits an acknowledgment message to the transmitter node identifying data packets not correctly received and to be retransmitted.

For example, if a modem generates a symbol of 220 ns, Sr = (1/220x109) = 4.54 x 106 symbols/s. For a symbol size of 42 bytes (336 bits), the maximum capacity at modem level with a 16-QAM modulation and a 2/3 code rate is C = (336*4.54 xl 06)*4*213 = 4 Gb/s. Considering the overhead used for transmission and the retransmission policy adopted for error recovery, the capacity at MAC level is reduced by a factor fRssl that is function of RSSI value and may be comprised in [0.5. .0.85] value interval.

In this embodiment, the radio communication modules conform to 802.11 ad standard in the 60GHz band. As defined by the standard, there are 32 MCS (modulation and coding scheme) available corresponding to different data rates at MAC level. For instance, in the described embodiment it is plan to use a limited number of MGS using single carrier modulation: MCS index 5 (BPSK, 1.25 GbIs), MCS index 9 (QPSK, 2.5 Gb/s) and MCS index 12 (16QAM, 4.62 GbIs). Then, applying a correction factor of 0.8, the maximum achievable data rate for the 3 MCS are respectively: 1 GbIs, 2 Gb/s and 3.7 Gb/s. For instance, with RSSI value normalized between 0 and 100, one can consider that between 0 and 25 the wireless link cannot be used, MCS index S only can be selected for RSSI between 26 and 50, MCS index 5 or 9 can be selected for RSSI between 51 and 75, MCS index 5, 9 or 12 can be used for RSSI above 76.

It can be noted that 4 radio channels are defined in the 60GHz frequency band dedicated to millimeter wave radio technology. The association of nodes and the wireless links assessment are performed using a single radio channel selected by the master node. Also wireless link assessment can be performed using one MCS selected by the master node, preferably the more robust MCS providing the lowest receiver sensitivity.

In Figure 1, the dashed lines represent the wireless links that have been detected as usable for video data transmission. For instance, the network adapter 170 is able to communicate with network adapter 120 only through radio communication module 171, but it is able to communicate simultaneously with network adapters 140 and 160 through radio communication module 172.

Also, the radio communication modules 111, 121, 152 and 162 are useless in this example because their position and the radiation pattern of their antenna do not allow reaching another radio communication module within the network.

The capacity of each link may be different as it depends on several parameters like distance, shadowing, or interference. It is assumed that the link assessment operation has stated that maximum available data rate is 3.7Gb/s for each link. Note that in case of wired link, the available data rate would have been set to 5 Gb/s for this link. This value is given as example as it depends on the transmission technique implemented. The transmission capacity C1.

between two network adapters referred i and j, with i!=j and both in the range [1.6], is the sum of capacities of the links (wired or wireless) existing between these two network adapters.

Figure 2 shows functional blocks of a network adapter like 110 connected to a video-projector device 105-1 to 105-6 or source device 101 (or integrated in these devices).

The network adapter 110 comprises: * a Random Access Memory (denoted RAM) 233, * an Electronically-Erasable Programmable Read-Only Memory (denoted EEPROM) 232, used to store information set by the user, such as a position of the video projector in the display matrix area.

* a micro-controller or Central Processing Unit (denoted CPU) 231, * a user interface controller 234, * a medium access controller (denoted MAC) 238, * a video processing controller 235, * a video Random Access Memory (denoted video RAM) 237.

* a video output 239 acting as an interface with a display device such as video projector 105-1 to 105-6, * a video input 236 acting as an interface with a video source device, as for example with source device 101.

The MAC 238 features two communication interfaces 221 and 222.

Network adapters can be interconnected through a specific network wire linking one communication interface of the first network adapter and one communication interface of the second network adapter. In the example of figure 2, the network adapter is connected to the two radio communication modules 111 and 112 denoted PHY A and PHY B. CPU 231, MAC 238, video processing controller 235, user interface controller 234 exchange control information via a communication bus 244, on which RAM 233 and EEPROM 232 are also connected. CPU 231 controls the overall operation of the network adapter 110 as it is capable of executing, from RAM 233, instructions pertaining to a computer program, once these instructions have been loaded from the memory EEPROM 232.

Using the user interface controller 234, the user can configure usage of each system, such as video-projector position in display matrix area, or can control each device such as device 105-1 to 105-6 to control output display, such as luminance, blending area compensation and so on. This interface can be a wired interface (like Ethernet, Universal Serial Bus USB) or a wireless interface (infrared, WiFi).

Video RAM 237 temporary stores all video data received from Video interface 236 (i.e. for a source device 101) or from communication interfaces 221 or 222 (i.e. from other nodes of the communication network) before the video data are processed. Preferably the video data are stored as raw video data, i.e. without any compression that would make it more difficult to process each frame independently (because compression often involves temporal prediction between different frames).

The video-processing controller 235 performs all necessary transformations of the video data stored in video RAM 237, such as cut of a frame into a sub-frame (elementary sub-stream creation).. Video cutting function of the network adapter 110 is designed to extract rectangular sub-area or sub-areas from each frame of a received video stream or sub-stream, the extracted rectangular sub-areas being then stored in Video RAM memory before being transmitted to another network adapter (i.e. to another node in the communication network) or before being transmitted to the video output 239 for local display by the local video projector.

Note that to generate the video output signal on interface 239, the video-processing controller 235 reconstructs the local image to be displayed locally from the sub-areas received through communication interfaces 221/222 and/or video interface 236. Communication through communication interfaces 221/222 requires MAC module 238, which is in charge of controlling the emission and reception of MAC frames conveying control data and/or video data.

Control data are used for the management of the communication protocol. They are involved in the process to associate nodes, in the determination of the links capacity (i.e. available bandwidth or data rate) and of the distribution scheme, and they are involved in sharing the results of these determinations with the other nodes of the network (e.g. the other devices of the multi-display system).

Video data are then sent or received through the MAC module 238 once the distribution (or transmission) scheme have been determined. Indeed, these schemes define which video data have to be sent on which communication links between the devices of the multi-display system.

A radio communication module 111 or 112 embeds a modem, a radio module and antennas. The radio module is responsible for processing a signal output by the modem before it is sent out by means of the transmitting antenna.

For example, the processing can be done by frequency transposition and power amplification processes. Conversely, the radio module is also responsible for processing a signal received by the receiving antenna before it is provided to the modem. The modem is responsible for modulating and demodulating the digital data exchanged with the radio module. Antenna for transmission and antenna for reception may be antenna with fixed radiation pattern but smart antenna may be used in association to beam-forming and beam-steering techniques. For control data sharing, antenna settings for both transmission and reception can be set to generate the widest possible radiation pattern (to reach several receivers simultaneously). For video data transmission and for point-to-point communications, antenna settings can be set to generate a narrow radiation pattern providing a better bit error rate compare to a wide radiation pattern. With such controllable antenna, extended link assessment shall be performed as each available radiation pattern can be tested. Radio module also provides means to measure RSSI (Radio Signal Strength Indication).

MAC 238 is able to manage reception on several communication interfaces simultaneously. The MAC 238 is also able to manage simultaneously several communication interfaces (wired or wireless), some for transmission and the other for reception of data, enabling data forwarding function.

Figure 3 illustrates the size of composite image displayed by the video projectors in the example of the multi-projection system of Figure 1. As each projector is able to display up to 1920 * 1200 pixels (WUXGA), the resolution of full image displayed by the 6 video projectors (referred 300) represents 4980 * 2200 pixels for overlapping areas of around 15% (horizontal) and 20% (vertical).

In the example, the video resolution of the source video is 3840 * 2160 pixels meaning that each video projector displays some black pixels (not visible).

These black pixels are represented by the dashed area in Figure 3. The useful pixels corresponding to video source image forms the composite image referred 102 with a size of 3840 * 2160 pixels. There are 2 *57Q black pixels per line and 2 * 20 black pixels per column.

E1 with i in the range [1:15] represents the elementary sub-area composing the full source image. Sub-image 1 is the sum of elementary sub-areas E1, [2, [4, and [. Sub-image 3 is the sum of elementary sub-areas [4, E5, E7, E5, E10, and E11. Overlapping areas represent 390 pixels for vertical part and 200 pixels for horizontal part. The size of useful pixels displayed by video projectors 105-1, 105-2, 105-5, and 105-6 (sub-images 1, 2, 5 and 6) represent 1350 * 1180 pixels. The size of useful pixels displayed by video projectors 105- 3 and 105-4 (sub-images 3 and 4) represent 1920 * 1180 pixels. In term of data rate, video source represents 4.78 Gb/s (3840 * 2160 * 24 * 24) with 24 bits / pixels and a frame rate of 24Hz. Each sub-image 1, 2, 5, or 6 represents a data rate of 0.92 GbIs, and each sub-image 3, or 4 represents a data rate of 1.30 Gb/s.

The data rate associated to each elementary sub-areas is approximately: 0.54 Gb/s for F1, 0.11 Gb/s for E2, 0.54 Gb/s for F3, 0.22 Gb/s for E4, 0.04 Gb/s for E5, 0.22 Gb/s for E6, 0.64Gb/sforF7, 0.13 Gb/s for E5, 0.64 Gb/s for E9, 0.22 Gb/s for E10, 0.04 Gb/s for E11, 0.22 Gb/s for F12, 0.54 Gb/s for E13, 0.11 Gb/s for F14, 0.54 Gb/s for F15.

Figure 4 illustrates a distribution scheme for the multi-projection system of Figure 1 with full wireless configuration compatible with the application requirements. It is equivalent to Figure 1 showing the useful wireless links with dashed lines, and indicating (inside bracket) the sub-image transmitted over each link. This illustrates the result of the algorithm determining the video distribution scheme. It corresponds to the ideal case where a solution exists for video distribution with a full wireless configuration. (12) represents the sub-image including sub-areas E1, F2, F3, F4, F5, and E6. It means that overlapping area between sub images 1 and 2 are not transmitted twice. Video cut operation generating sub areas F1 is performed by the network adapter 170. The network adapter 120 is able to keep sub areas F2, [3, F5, and F for local display of sub-image 2, and to forward sub areas E1, E2, E4, and E5 to network adapter 130.

Network adapter 130 relays these data to network adapter 110 (destination node). In the same way, from reception of (3,4,5,6) data (sum of sub areas from E4 to E15), the network adapter 140 generates the sub-image 4 for its local display and forward sub-areas composing (3,5) to network adapter 150. The network adapter 160 generates the sub-image 6 from reception of (3, 4, 5, 6) data Network adapters 140 and 160 simultaneously receive (3, 4, 5, 6) data from a single transmission from network adapter (170).

In this embodiment, the computation of video distribution scheme is centralized in the master network adapter 110 using the capacity of each link (including the MCS used for each link) and the multi-projection system parameters entered by the user. The computation corresponds to a solution of a Multi-Commodity Flow (MCF) problem, express as follows: 1°) A graph G(V,E) is considered, representing the communication network where the vertexes (set V) of the graph represent the devices of the multi-display system (devices 101, 105-1 to 105-6 with their corresponding network adapters) and the edges (set E) represent the communication links, either wired or wireless. Each edge or communication link (u,v) has a capacity c(u,v) representing the corresponding available bandwidth.

2°) M commodities T1, T2 TM defined by T1=(s1,d1,k1), where s1 is the source (source device 101), d1 is the destination (destination display device) and k1 the demand: here the throughput requirement corresponding to the size S1 of an elementary area E1 of the commodity i. Note that the throughput constraints k1 are obtained from the size S1 of the corresponding elementary area E1 (in term of pixels number). The size S1 is multiplied by: -the size of the information used for coding each colour of the pixel, also known as colour depth. Generally. colour depth is a value of 8, 12 or 16 bits, depending of video standard; -the number of colours to code, generally three colours (R for Red, G for Green and B for Blue); -the chroma sub-sampling used for the image. Typical sub-sampling applied as [4:4:4, 4:2:2, 4:2:0] results to a sub-sampling ratio of [100%, 66.6%, 50%]; -the frequency of video refresh, also known as the frame rate. Its value equals 60, 50, 30, 25 or 24 frames per second, depending on video standard.

Therefore in this example, a k1 throughput constraint is equal to: Ic = 3 * * Colour_depth * Frame_rate * sub_samplingj0 Bps.

3°) A flow is a non-negative function f: V->R+. The flow of commodity i along edge (u,v) is t(u,v).

The problem, once defined, is to find an assignment of the flows which satisfies the constraints: -L1f(u,v) «= c(u,v) referred to as the capacity constraints (the sum of the flows on one link cannot exceed the link capacity: and -Vi, * s1,cli EUEVJI(u,v) Ewevft(t2,1V') referred to as the flow conservation constraints (the sum of flows entering a relay node must be equal to the sum of flows going out from this relay node); and -Iwevfi(si,w) = = k1 referred to as the demand satisfaction constraints (the sum of flows going out from a source node and for a destination node must be equal to the sum of flows from this source node that enters the destination node).

In this problem, the variables f1(u,v) relative to the function f are referred to as the decision variables.

Once a radio communications module is used in the distribution scheme for data transmission, then a radio channel is allocated to this radio module.

This action automatically allocates the selected radio channel to the radio communication modules receiving the data. For instance 4 radio channels are defined in the 60GHz frequency band dedicated to millimeter wave radio technology (like 802.llad or 802.15.3c standard). When a radio channel is assigned to one radio module, it is better to not change it during operation because the switching operation is time consuming.

Then additional constraints must be introduced taking into account the correlation between paths. Indeed, two communication paths cannot be active simultaneously on the same radio channel if: -both paths use the same receiver, or -both paths use the same emitter (excluding multicast or broadcast cases), or -the receiver of a communication path is equal to the emitter of the other communication path.

In such a case, these communication paths are considered correlated and new constraints are added. This constraint for two correlated paths l1=(ui,vi) and 12=(u2,v2) is expressed as follow: Efi(ul,vl) + Efj(u2,v2) c(ul,v1) c(u2,v2) -It means that the bandwidth occupation shall be shared among the two paths.

Finally, a last criterion to configure the MCF problem is the objective variable. This is because the MCF problem may have several solutions and one solution should be selected. This selection is based on the solution which optimizes (maximizes or minimizes) an objective variable. This objective variable depends directly on the scenario and may optimize different parameters: bandwidth, robustness, latency.

The objective variable considered in this example is the robustness of the network, as the objective is to minimize the amount of data transmitted with the less robust MCS. If the amount of data to be transmitted on a given link represents a data rate of 1.5Gb/s, and if the capacity of this link is 3.7 Gb/s (corresponding to MCS index 12, the less robust MCS available here), then the algorithm will select the intermediate MCS (index 9) offering a sufficient data rate of 2 Gb/s.

On each radio channel, there may be M communications planned according to the distribution scheme with a total data rate used by the M communications equals to EL1ti(u,v). The objective of robustness can be expressed by minimizing the following objective variable: f1fi(u,v) computed for each available radio channel. The MCS for each wireless link is selected according to the final value of this variable.

The MCF problem can be solved, for example, using a "Simplex" algorithm, which determines how the transmissions of the elementary areas E need to be performed to fulfil the transmission of each elementary area to its destination display device.

The result of the algorithm leads to the determination of TDMA sequence where each TDMA time slot is allocated to a unique node for video data transmission. This is illustrated in the Figure 5 with an example of the TDMA sequence applied in the multi-projection system according to the distribution scheme of Figure 4.

Figure 5 graphically represents a TDMA sequence illustrating a cycle N, with time slots allocated to network adapters over the 4 available radio channels. For instance, the duration of a TDMA sequence is 2ms. The result of distribution scheme appears in the second part of TDMA sequence dedicated to video data transmission. The network adapter 170 owns transmission slot 511 on radio channel 0 to transmit data corresponding to sub-image (1,2) using radio communication module 171. Several MAC frames may be transmitted during one time slot. This will avoid having too long MAC frame with the risk to loose synchronization in radio receiver. Time slot 512 belongs to network adapter 120 and time slot 513 belongs to network adapter 130. Total useful bandwidth in radio channel 0 is 1.68 ÷ 0.92 ÷ 0.92 = 3.52 Gb/s. The less robust MCS is therefore used for time slots 511 512, 513.

Radio channel 1 is only used by network adapter 170 through radio communication module 172 to transmit sub-image (3,4,5,6) to both network adapters 140 and 160. Required data rate is 3.58 Gb/s. Once again the less robust MCS shall be selected.

Finally radio channel 3 is shared between network adapters 140 and 150 to distribute sub-image 3 and sub-image 5. The data rate required is 1.96 + 1.3 = 3.26 Gb/s. as for other radio channels, the less robust MCS shall be selected.

The first part of TDMA sequence concerns the allocation of short time slots for transmission of control data between nodes. It is a short period that should not exceeded i50ps. These time slots include the beacon frame transmission and may include acknowledgment message transmission to request video packet data retransmission. The time slot allocation follows the allocation of radio channels performed for video transmission. The network adapter 170 transmits one MAC frame simultaneously during both time slots 501 and 502 using both radio communication modules but over two different radio channels. In the same manner, network adapter 130 simultaneously transmits during time slots 504 and 505, and network adapter 140 simultaneously transmits during time slots 507 and 508. Only one time slot needs to be allocated to network adapters 110, 120, 150, 160 with respective time slots 506, 503, 510, 509.

As mentioned previously, a further problem solved by some embodiment of the invention consists in finding advantageous cabling solution in case the full wireless configuration cannot fulfil the application requirement. Back to the wireless link assessment step, it is now supposed that there is no link available between network adapters 110 and 130 because of some obstacles. Then the algorithm previously applied failed to find a solution. Figure 6 illustrates this failure providing example of distribution scheme not applicable. Indeed, this distribution scheme requires that sub-image (1,4,5,6) is first transmitted by communication module 141, then sub-image 1 is transmitted by the same radio communication module 141. The required bandwidth for this radio channel is 3.59 + 0.92 = 4.51 Gb/s which is largely above the capacity of 3.7Gb/s.

Some solutions may be found adding only one wire in the system, however the location of this cable cannot be decided following basic analysis of shadowing conditions. One can consider as abnormal that network adapters 110 and 130 cannot communicate wirelessly regarding their position. At first sight, it seems interesting to connect them through wire but the result is not all satisfactory. If the user decides to connect together by wire network adapters and 130 by removing radio communication modules 112 and 131, it appears that these network adapters can no more receive data from network adapters 120 or 140 (without an additional cable) and no distribution scheme can be found to fulfil the application requirement.

It is the same situation if network adapters 110 and 130 are connected by wire by removing radio communication modules 112 and 132 as illustrated in the Figure 7 with the wire referred 701 Here the radio communication module 122 from network adapter 120 has to receive sub-image (1,2,3) and to transmit sub-image (1,3). These operations requires a bandwidth of 2.72+ 1.96 = 4.68 Gb/s which is largely above the capacity of 3.7Gb/s.

The solution proposed in this embodiment is to let the system found a distribution scheme involving the minimum cabling operations. It consists in successively consider the various virtual network topologies with one cable between two network adapters, and to select for each topology the distribution scheme that maximize the network robustness. As explained previously, it means minimizing the amount of data transmitted wirelessly to be able to select the most robust MGS.

Two solutions are proposed with the illustrations of Figure 8 and Figure 9.

In Figure 8, the wire 801 is placed between network adapter 110 and 120 using interfaces 111 and 121 (not previously used for wireless communication). The amount of data transmitted wirelessly represents: 1.68 Gb/s on radio channel 0 with sub-image (1,2), 3.58 Gb/s on radio channel 1 with sub-image (3,4,5,6), and 3.26 Gb/s on radio channel 2 with sub-images (3,5) and (3). Intermediate MCS can be used on radio channel 0 (1.68 Gb/s), less robust MCS is used on radio channels 1 and 2. Sub-image (1) is transmitted on added wired link (0.92 Gb/s).

In Figure 9, the wire 901 is placed between network adapter 110 and using interfaces 111 and 152. The amount of data transmitted wirelessly represents: 2.18 Gb/s on radio channel 0 with sub-images 3 and (2,3), 3.59 Gb/s on radio channel 1 with sub-image (1,4,5,6), and 1.84 Gb/s on radio channel 2 with sub-images (1) and (5). Intermediate MCS can be used on radio channel 2 (1.84 Gb/s), less robust MCS is used on radio channels 0 and 1. Sub-image (1) is transmitted on added wired link (0.92 Gb/s).

Comparing both solutions, the one corresponding to figure 9 is preferred as it minimizes the amount of data transmitted wirelessly (especially considering less robust MCS). The decision may take also into account additional parameters like minimizing the length of cables to add, or considering the location of the cables. To ease installation, the user may request that only adjacent network adapters can be linked by wire. In such a case, the algorithm will find the solution of Figure 8 as the one preferred to satisfy user requirement.

Figure 10 is a block diagram illustrating steps to determine a video distribution scheme according to embodiments of the invention. In this embodiment, it is executed by the CPU 231 of network adapter 170.

In step 1000, the CPU 231 receives the multi-projection parameters through the user interface 234. These parameters are stored in EEPROM 232.

Step 1001 corresponds to the node association operation previously described.

Step 1002 corresponds to wireless link assessment process also previously described. The step 1004 corresponds to the execution of video distribution scheme algorithm based on initial network topology (preferably full wireless). In step 1005, it is checked if a solution compatible with application requirement can be found. If yes, in step 1006, the CPU ends the algorithm by identifying a distribution scheme that maximize the robustness of the network. Then in step 1007, the selected distribution scheme is transmitted to all nodes within the network and the user is notified about the successful completion of system set-up.

In case of failure to find a video-distribution scheme, CPU 231 moves from step 1005 to step 1008 to try to find solution considering additional wiring.

In step 1008 the number of cables is initialized to 1. In step 1009, CPU 231 selects one network topology with one cable connected between two network adapters, and in step 1010, it checks if a solution exists for this network topology, applying the video distribution scheme algorithm considering the selected network topology. It means that CPU 231 considers the highest link capacity for the wired link virtually created, and may need to consider that some wireless links are no more available. So, CPU 231 updates the capacity of each link accordingly. In step 1011, it is checked if one solution now exists. If yes, in step 1011, CPU 231 looks for a video distribution scheme that maximize the network robustness. Otherwise, CPU 231 directly goes to step 1013 to check if another network topology involving the same number of additional cables has not been tested yet. If yes, CPU 231 goes back to step 1009. If not, it means that all topology with a given number of additional cables have been tested. If there is still no solution (check in step 1014), CPU 231 needs to consider one more cable within the system. If one cable can be added (check in step 1016), then in step 1015, CPU 231 increments by one the number of cables and starts again the determination algorithm by step 1009. If no more cable can be added, it means that even the full wired configuration is not working: the video source resolution may be too high for the network capacity, and the user is notified about the failure in step 1020.

Being back in step 1014, if at least one solution has been found with a given number of cables, then CPU 231 proceeds to the selection of the best solution in term of network robustness in step 1017. The user is informed (step 1018) about the number of cables to add and their location. Once the user has acknowledged the modification, the distribution scheme is transmitted to all nodes and the system is ready to operate (step 1019).

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims (10)

1. CLAIMS1. A method of set-up for distributing a data stream in a communication system comprising communication nodes, one node identified as a source device is providing the data stream, a plurality of nodes identified as destination devices being provided with a sub-part of the data stream, the distribution of the data stream to the right destination devices constituting the application needs, at least one of the communication links between nodes being wireless, the method comprising: -a step of determining a distribution scheme for the communication system comprising: o a step of determining available transmission paths in the communication system; o a step of determining the capacity of each determined path; and o a step of selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity as the determined distribution scheme; wherein the method further comprises in case of failure of the step of selecting the distribution scheme: -modifying the communication system by replacing at least one wireless link between two nodes by a wired link; and -applying the step of determining a distribution scheme for the modified communication system.
2. 2. The method according to claim 1, wherein the step of selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity optimizes an objective variable.
3. 3. The method according to claim 2, wherein the objective variable is the bandwidth of wireless links.
4. 4. The method according to claim 2, wherein the objective variable is the robustness of wireless links.
5. 5. The method according to claim 2, wherein the objective variable is the latency of the distribution.
6. 6. The method according to any one claim 2 to 5, wherein selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity that optimizes an objective variable consists in solving the Multi-Commodity Flow problem defined by the communication characteristics of the communication system using a Simplex algorithm.
7. 7. The method of any one claim 2 to 6, wherein the method comprises iteratively: -determining a growing number of wireless links to be replaced by a wired link, this growing number beginning with value 1; -For each possible location of the wired links in the communication system, applying the step of determining a distribution scheme for the modified communication system -stop iterating when at least one communication system corresponding to a determined distribution scheme has been obtained.
8. 8. The method of claim 7, wherein if several communication systems have been obtained for a given number of wired links the method further comprises: -selecting the communication system corresponding to the determined distribution scheme that optimizes most the objective variable.
9. 9. The method of claim 8, wherein if several communication systems have been obtained for a given number of wired links the method further comprises: -selecting the communication system corresponding to the determined distribution scheme that minimizes the length of wires.
10. 10.The method according to any one claim 1 to 9, wherein the step of determining the distribution scheme further comprises: -determining for each wireless path a type of modulation and an error correction code.liThe method of claim 10, wherein the type of modulation is determined in a predefined set of types of modulation.12.The method of claim 10, wherein the error correction code is determined in a predefined set of errors correction codes.13. The method according to any one claim ito 12, wherein the method further comprises: -displaying the wireless links to be replaced by wired links.i4.A device for setting-up a distribution of a data stream in a communication system comprising communication nodes, one node identified as a source device is providing the data stream, a plurality of nodes identified as destination devices being provided with a sub-part of the data stream, the real time distribution of the data stream to the right destination device constituting the application needs, at least one of the communication links between nodes being wireless, the device comprising: -a determining module for determining a distribution scheme for the communication system comprising: o a path determining module for determining available transmission paths in the communication system; o a capacity determining module for determining the capacity of each determined path; and o a selection module for selecting the distribution scheme fulfilling the application needs under the constraint of paths capacity as the determined distribution scheme; wherein the device further comprises to be used in case of failure of the step of selecting the distribution scheme: -a modifying module for modifying the communication system by replacing at least one wireless link between two nodes by a wired link; and -an applying module for applying the step of determining a distribution scheme for the modified communication system.15.The device according to claim 14, wherein the selection module selects the distribution scheme fulfilling the application needs under the constraint of paths capacity optimizes an objective variable.16. The device according to claim 15, wherein the objective variable is the bandwidth of wireless links.17. The device according to claim 15, wherein the objective variable is the robustness of wireless links.18. The device according to claim 15, wherein the objective variable is the latency of the distribution.19. The device according to any one claim 15 to 18, wherein the selection module consists in a solver for solving the Multi-Commodity Flow problem defined by the communication characteristics of the communication system using a Simplex algorithm.20. The device of any one claim 15 to 19, wherein the device comprises an iteration module which iterates on: -determining a growing number of wireless links to be replaced by a wired link, this growing number beginning with value 1; -For each possible location of the wired links in the communication system, applying the step of determining a distribution scheme for the modified communication system -stop iterating when at least one communication system corresponding to a determined distribution scheme has been obtained.21.The device of claim 20, wherein it further comprises, to be used if several communication systems have been obtained for a given number of wired links: a selection module for selecting the communication system corresponding to the determined distribution scheme that optimizes most the objective variable.22.The device of claim 20, wherein it further comprises, to be used if several communication systems have been obtained for a given number of wired links: -a selection module for selecting the communication system corresponding to the determined distribution scheme that minimizes the length of wires.23.The device according to any one claim 14 to 22, wherein the determination module for determining the distribution scheme further comprises: -a determination module for determining for each wireless path a type of modulation and an error correction code.24. The device of claim 23, wherein the type of modulation is determined in a predefined set of types of modulation.25.The device of claim 23, wherein the error correction code is determined in a predefined set of errors correction codes.26. The device according to any one claim 14 to 25, wherein the device further comprises: a display for displaying the wireless links to be replaced by wired links.27.A computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to any one of claims 1 to 13, when loaded into and executed by the programmable apparatus.28.A computer-readable storage medium storing instructions of a computer program for implementing a method according to any one of claims ito 13.29.A method of determining a distribution scheme substantially as hereinbefore described with reference to, and as shown in Figure 10.