FIELD OF THE INVENTION

The present invention relates to a method for the transmission of a frame by an access point of a wireless local area network, the frame enabling data to be sent in unicast mode and in multicast mode.

BACKGROUND

The establishment of wireless local area networks WLAN offers great flexibility to the users of roaming communication devices, such as computers, tablets, smartphones, etc. Such WLAN networks are established by access points AP. Such wireless local area networks WLAN thus facilitate the interconnection of devices within a dwelling or an office, by providing wireless local connectivity in order to avoid having recourse to interconnection cabling.

Wireless local area networks WLAN of the Wi-Fi type are for example known, as defined in IEEE 802.11 and the amendments thereof, such as for example the amendment IEEE 802.11ax.

So as to improve the use of the channel resources, the access point of a network compatible with the IEEE 802.11ax amendment (in the “Draft 2.0” version thereof) can make transmissions of the MU-MIMO type (“Multi-User-Multiple Inputs Multiple Outputs”). This makes it possible, by means of beamforming, to transmit data to a plurality of wireless terminals on the same channel resource. However, when the same data must be transmitted to a plurality of wireless terminals, the use of transmissions of the MU-MIMO type requires duplication of said data, so that each of the spatial streams contains said same set of data. Apart from this duplication of data, the use of transmissions of the MU-MIMO type requires the wireless terminals concerned to be sufficiently distant spatially so as to limit interferences, which is not always possible in the context of a wireless local area network WLAN.

Being able to send data to a plurality of destinations using dedicated link-layer addresses, e.g. Ethernet MAC (medium access control) or network layer (e.g. IP (Internet Protocol), is also known. However, this approach requires performing a link-layer decoding, or respectively network-layer decoding, in order to determine the actual destination of said data.

It is desirable to overcome these drawbacks of the prior art. It is thus desirable to provide a solution that makes it possible to make data transmissions to a plurality of destinations in a wireless local area network WLAN without having to duplicate said data and while limiting the decoding requirements at the link and network layers (and higher layers).

SUMMARY

To this end, the invention relates to a method for the transmission of a frame by an access point of a wireless local area network, the access point having implemented a phase of association with a plurality of wireless terminals. The method is such that the access point receives, during the association phase, from each wireless terminal compatible with transmissions in multicast mode, information indicating that said wireless terminal is compatible with transmissions in multicast mode. And, in order to transmit the frame, the access point performs the following steps: obtaining data to be transmitted in multicast mode to a plurality of destinations from among the compatible wireless terminals; obtaining data to be transmitted in unicast mode to at least one respective destination from among the wireless terminals; constructing a physical-layer header including: in a common signalling field, an identification of each channel resource intended to be used for making the frame transmission whether this be for the data to be transmitted in unicast mode or in multicast mode; in each field of a series of specific signalling fields, information representing an association between a channel resource identifier used and a unique identifier of a destination concerned or of a group of destinations concerned, so that each destination can determine each channel resource to listen to in order to receive the data that are addressed to it, whether it be in unicast mode or in multicast mode. Thus it is possible to transmit data from the access point to a plurality of wireless terminals without having to duplicate data and while remaining at the physical layer in order to identify said data.

According to a particular embodiment, in order to make a transmission in multicast mode to a plurality of destinations, the access point previously performs the following steps: receiving an instruction to create a group from a list of destinations; transmitting a group identifier to each destination of said group. And the series of specific signalling fields is such that, in order to indicate a transmission in multicast mode on a channel resource, a single specific field is defined for said channel resource in which the group identifier is indicated.

According to a particular embodiment, the series of specific signalling fields is such that, in order to indicate a transmission in multicast mode on a channel resource, as many specific signalling fields for said channel resource are included in the physical-layer header as there are destinations of said transmission in multicast mode.

According to a particular embodiment, the physical-layer header indicates that the frame contains data transmitted in multicast mode.

According to a particular embodiment, each specific signalling field indicates that there exists at least one other specific signalling field, subsequent in the physical-layer header, that is associated with the same destination or with at least one destination in the same group of destinations.

According to a particular embodiment, the access point cooperates with a device supplying virtual-reality data having an immersive image in which a plurality of users can immerse themselves by means of wireless terminals displaying respective regions of interest of said immersive image, and the device supplying virtual-reality data requests the access point to transmit in the frame data corresponding to an overlap zone of said regions of interest in multicast mode and the rest of the data of said regions of interest in unicast mode.

According to a particular embodiment, the device supplying virtual-reality data performs the following steps: calculating a cost function relating to the overlap zone; comparing the cost function calculated with a predefined threshold; requesting the access point to transmit the data relating to the overlap zone in multicast mode when the cost function calculated is below the predefined threshold; and requesting the access point to transmit the data relating to the overlap zone in unicast mode when the cost function calculated is below the predefined threshold.

According to a particular embodiment, the cost function is expressed as follows:

F=S0∑n=1N⁢Sn

where N represents the quantity of regions of interest in question, S0represents the size of the overlap zone, and Sn, ∀1≤n≤N, represents the size of the regions of interest indexed by n.

According to a particular embodiment, the device supplying virtual-reality data makes an alignment of the overlap zone on macroblock boundaries.

According to a particular embodiment, when a first set of wireless terminals has regions of interest that overlap and define a first overlap zone and a second set of wireless terminals has regions of interest that overlap with each other but which do not overlap with the regions of interest in the first set, the device supplying virtual-reality data determines the overlap zone and calculates the cost function independently for each set of wireless terminals.

According to a particular embodiment, when a first set of wireless terminals has regions of interest that overlap and define an overlap zone and a second set of wireless terminals has regions of interest that do not overlap with each other and which also do not overlap with the regions of interest of the first set, the device supplying virtual-reality data determines the overlap zone and calculates the cost function only for the first set of wireless terminals, and requests the access point to transmit, in unicast mode, the data of the region of interest of each wireless terminal in the second set.

According to a particular embodiment, the device supplying virtual-reality data performs the following steps: taking the regions of interest two by two and determining any overlap zone thereof; determining a sorted list of the regions of interest according to the overlap zones determined, so that the first two elements of the list have the largest overlap zone, and the regions of interest are next sorted by successively adding to the list the region of interest that has the largest overlap zone with the last element in the list; performing at least one iteration of the following steps: determining any overlap zone common to all the regions of interest present in the list; calculating a cost function for the common overlap zone determined and, if no common overlap zone has been able to be determined, considering the cost function as being above a predefined threshold; deciding that a transmission in multicast mode is possible for the data of the common overlap zone when the cost function is below the predefined threshold; excluding from the list the region of interest iterated in the last position when the cost function is above or equal to the predefined threshold and performing a new iteration.

According to a particular embodiment, the device supplying virtual-reality data is a residential gateway.

According to a particular embodiment, the frame is transmitted by the access point in accordance with an OFDMA technique.

According to a particular embodiment, the wireless local area network is of the Wi-Fi type.

The invention also relates to an access point of a wireless local area network, the access point being adapted to perform a frame transmission in said wireless local area network, the access point having implemented a phase of association with a plurality of wireless terminals. The access point comprises means for receiving, during the association phase, from each wireless terminal compatible with transmissions in multicast mode, information indicating that said wireless terminal is compatible with transmissions in multicast mode; and, to transmit the frame, the access point comprises: means for obtaining data to be transmitted in multicast mode to a plurality of destinations from among the compatible wireless terminals; means for obtaining data to be transmitted in unicast mode to at least one respective destination from among the wireless terminals; means for constructing a physical-layer header including: in a common signalling field, an identification of each channel resource intended to be used for making the frame transmission, whether this be for the data to be transmitted in unicast mode or in multicast mode; in each field in a series of specific signalling fields, information representing an association between a channel resource identifier used and a unique identifier of the destination concerned or group of destinations concerned, so that each destination can determine each channel resource to listen to in order to receive the data that are addressed to it, whether this be in unicast mode or in multicast mode.

The invention also relates to a computer program product comprising instructions for implementing, by a processor, the above method, when said program is executed by said processor. The invention also relates to an information storage medium storing a computer program comprising instructions for implementing, by a processor, the above method, when said program is executed by said processor.

The features of the invention mentioned above, as well others, will emerge more clearly from a reading of the following description of at least one example embodiment, said description being made in relation to the accompanying drawings, among which:

