GB2561686A

GB2561686A - Resource units for non-associated stations in a multi-user downlink transmission of a 802.11AX network

Info

Publication number: GB2561686A
Application number: GB1802907.4A
Authority: GB
Inventors: Nezou Patrice; Viger Pascal; Baron Stéphane; Sevin Julien
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2017-04-21
Filing date: 2018-02-22
Publication date: 2018-10-24
Anticipated expiration: 2038-02-22
Also published as: GB201706409D0; GB201802907D0; GB2561686B; GB2561616A

Abstract

In a wireless network a station determines a downlink resource unit (RU) assigned to an association identifier (AID) reserved for stations not associated with an access point (AP), from a plurality of downlink RUs comprised in a multi-user (MU) downlink transmission. The station receives a frame from the AP on the determined downlink RU. The invention also provides sending a frame to the AP using an uplink RU of a plurality of uplink (UL) resources units provided in a multi-user UL transmission towards the AP within a transmission opportunity (TXOP) granted to the AP, wherein the plurality of UL RUs are distributed according to an allocation scheme. Based on at least one allocation scheme feature of the UL RU a downlink RU is determined. The STA receives a frame from the AP on the determined RU. The allocation scheme feature may be the frequency distribution of the RUs. The AID reserved for stations not associated with the AP may be an 11-bit ID equal to 2045. The wireless network may be based on 802.11ax and may use OFDMA RUs.

Description

(54) Title of the Invention: Resource units for non-associated stations in a multi-user downlink transmission of a 802.11AX network

Abstract Title: Determining resource units in a multi-user downlink transmission (57) In a wireless network a station determines a downlink resource unit (RU) assigned to an association identifier (AID) reserved for stations not associated with an access point (AP), from a plurality of downlink RUs comprised in a multi-user (MU) downlink transmission. The station receives a frame from the AP on the determined downlink RU. The invention also provides sending a frame to the AP using an uplink RU of a plurality of uplink (UL) resources units provided in a multi-user UL transmission towards the AP within a transmission opportunity (TXOP) granted to the AP, wherein the plurality of UL RUs are distributed according to an allocation scheme. Based on at least one allocation scheme feature of the UL RU a downlink RU is determined. The STA receives a frame from the AP on the determined RU.

The allocation scheme feature may be the frequency distribution of the RUs. The AID reserved for stations not associated with the AP may be an 11-bit ID equal to 2045. The wireless network may be based on 802.11 ax and may use OFDMA RUs.

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RESOURCE UNITS FOR NON-ASSOCIATED STATIONS IN A MULTI-USER DOWNLINK TRANSMISSION OF A 802.11 AX NETWORK

FIELD OF THE INVENTION

The present invention relates generally to wireless communication networks comprising an access point (AP) and stations and more specifically to the transmission of data frames within a transmission opportunity made of sub-channels or Resource Units, and corresponding devices.

The invention finds application in wireless communication networks, in particular to the access of an 802.11ax composite channel and of OFDMA Resource Units forming for instance an 802.11 ax composite channel for Downlink communication from the access point to the stations. One application of the method regards wireless data communication over a wireless communication network using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), the network being accessible by a plurality of station devices.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC family of standards (a/b/g/n/ac/etc.) defines a way wireless local area networks (WLANs) work at the physical and medium access control (MAC) level. Typically, the 802.11 MAC (Medium Access Control) operating mode implements the wellknown Distributed Coordination Function (DCF) which relies on a contention-based mechanism based on the so-called “Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) technique.

More recently, Institute of Electrical and Electronics Engineers (IEEE) officially approved the 802.11 ax task group, as the successor of 802.11ac. The primary goal of the 802.11ax task group consists in seeking for an improvement in data speed to wireless communicating devices (or stations) used in dense deployment scenarios.

In this context, multi-user (MU) transmission has been considered to allow multiple simultaneous transmissions to/from different stations (i.e. users) registered to the AP, in both downlink (DL) and uplink (UL) directions from/to the AP, during a transmission opportunity granted to the AP over a 20MHz (or more) communication channel.

In the uplink, multi-user transmissions are used to mitigate the collision probability. This is because multiple non-AP stations are allowed to transmit simultaneously.

To actually perform such multi-user transmission, it has been proposed to split a granted communication channel (or transmission opportunity granted to the AP) into subchannels, also referred to as resource units (RUs), that are usually shared in the frequency domain between multiple users (non-AP stations/nodes), based for instance on Orthogonal Frequency Division Multiple Access (OFDMA) technique.

Both multi-user Downlink OFDMA and Uplink OFDMA mechanisms offer overhead reduction as key benefit.

To perform multi-user (MU) Downlink OFDMA transmission, the AP sends an MU packet over the whole granted communication channel, meaning that, from an RU point-of-view, the same preamble is transmitted. Next, RU-dependent payload is sent by the AP, meaning the payload varies from one RU to the other, within the whole granted communication channel. The assignment of the RUs to the stations is signalled at the beginning of the MU Downlink frame, by providing an association identifier (AID) of a station for each RU defined in the transmission opportunity.

Such an AID is individually obtained by each station when registering or associating with the AP during an association procedure, that is to say when the station joins the group of stations managed by the AP. During the association procedure, the not-yetassociated station or “unassociated station” and the AP exchange a series of single user (SU) 802.11 management frames in order to enter into an authenticated and associated state for the station. A result of the association procedure is that an AID is assigned to the station, enabling it to use MU communications (resource units).

An AID is usually formed by the 11 least significant bits of a 12-bit identifier.

One station is thus registered or associated with the AP and has an AID, or is not yet registered or unassociated with the AP and has no AID until registration is completed.

A group of stations together with the access point is known as a Basic Service Set (BSS). To be noted that the range of available AIDs has to be shared between the several groups of stations (i.e. several BSSs) that could be handled by the same physical access point (though instantiating virtual access points).

To perform multi-user (MU) Uplink OFDMA transmission, the AP sends a control frame, known as Trigger Frame (TF), to the stations prior they can access one RU assigned to them. The assignment of the RUs to the stations is signalled in a similar way as above (for Downlink transmission using AIDs), but in the payload of the TF packet.

As a station is usually provided with a single transceiver, assignment of multiple RUs to one and the same station shall not be allowed in 802.11 ax, for both multi-user Downlink and Uplink transmissions.

Thus, at most one RU is assigned to a station, but all the stations will be offered the same RU length.

The association procedure introduced above appears to be bandwidth consuming. This is mainly because the SU management frame are transmitted at low bit rate (usually the lowest supported data rate) over the 20MHz channel, in order for legacy stations (i.e. not implementing 802.11 ax) to be able to understand the common 802.11 preamble. This is also because each SU management frame requires a specific access to the medium by the station, and thus requires for the station to wait until being granted a new medium access. As the number of BSSs increases in the same area and/or as the number of stations within a BSS substantially increases, more channel bandwidth is lost due to such SU signaling, and the cost to access the medium by the stations increases.

Recently, the 802.11 ax task group has proposed a mechanism for the AP to reserve one or more RUs of a multi-user Uplink OFDMA transmission for not-yet-associated or “unassociated” stations (which are 802.11 ax compliant). This is for these stations to speed up their registration to the AP, by transmitting request management frames over such reserved RUs (in MU Uplink OFDMA mode). The proposed mechanism relies on the use of a predefined AID value equal to 2045 to indicate the random RUs the not-yet-associated stations can access through contention.

Even with this new mechanism, the response management frames from the AP are performed using low bit rate SU signaling. This is because, by failing to have an own AID, these not-yet-associated stations cannot be assigned with RUs in a MU Downlink transmission. It remains that channel bandwidth is still wasted.

The current operating mode of the 802.11 ax multi-user feature is thus not fully satisfactory, for at least the above downsides regarding the SU signaling for registration.

SUMMARY OF INVENTION

It is a broad objective of the present invention to improve this situation, i.e. to overcome some or all of the foregoing limitations. In particular, the present invention seeks to provide a more efficient usage of the MU Downlink transmission from the AP.

In particular, the Multi-User Downlink communication protocol is enhanced to allow stations to efficiently identify their RUs in the MU Downlink transmission from the AP where no AID can be used. This is for instance the case for not-yet-associated or unassociated stations.

In this context, the present invention proposes enhanced wireless communication methods in a wireless network comprising an access point and stations.

In embodiments, any station registering or associating with the access point being associated with or assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the method comprises the following steps, at one of the stations:

determining a downlink resource unit assigned to an association identifier reserved for stations not associated with the access point (meaning the AID is at least not associated with a specific station), from a plurality of downlink resource units comprised in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point; and receiving a frame from the access point on the determined downlink resource unit.

In other embodiments, the method comprises the following steps, at one of the stations:

sending a frame to the access point using an uplink resource unit of a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the plurality of uplink resource units are distributed according to an allocation scheme;

determining, based on at least one allocation scheme feature of the uplink resource unit, a downlink resource unit from a plurality of downlink resource units comprised in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point; and receiving a frame from the access point on the determined downlink resource unit.

From the AP perspective, an enhanced wireless communication method in a wireless network comprising an access point and stations is also proposed.

In embodiments, any station registering or associating with the access point being associated with or is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the method comprises the following steps, at the access point:

building a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, the plurality of downlink resource units comprising a downlink resource unit assigned to an association identifier reserved for stations not associated with the access point (meaning the AID is at least not associated with a specific station); and sending a frame to a station on the downlink resource unit assigned to an association identifier reserved for stations not associated with the access point.

In other embodiments, the method comprises the following steps, at the access point:

receiving a frame from a station on an uplink resource unit of a plurality of uplink resource units comprised in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the plurality of uplink resource units are distributed according to an allocation scheme;

building a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, the plurality of downlink resource units comprising a downlink resource unit having at least one matching allocation scheme feature with the uplink resource unit; and sending a frame (usually a response to the frame received on the uplink RU) to the station on the downlink resource unit.

802.11ax already proposes a prefixed number of RU allocation schemes for a 20MHz channel, that each defines a specific distribution of RUs (e.g. in terms of RU size, frequency band, RU positions along the frequency direction in 802.11 ax) within the 20MHz channel. The RU allocation scheme is for instance declared in the HE-SIG-B field of the MU Downlink frame or in an equivalent field of a trigger frame.

Different RU allocation schemes may be used for each 20MHz channel forming a composite channel of 40MHz or 80MHz or 160MHz width.

By using a downlink RU that matches, according to some RU allocation scheme criteria/features, an uplink RU already used, AID is no longer needed for the station to identify, in a Downlink transmission, which downlink RU to listen to. This is particularly advantageous for communication with stations which have not yet been associated with the AP (i.e. which have no AID).

In the other embodiments, by using AID not associated with stations during MU Downlink transmissions, the invention offers the AP with the opportunity to address stations deprived of AID, such as stations not associated with the AP. The AID not associated with specific stations may then be reserved for stations not associated with the AP for particular embodiments. Again, such stations may easily identify, in a Downlink transmission, which downlink RU to listen to.

As extensively described below, these approaches may be implemented during the association procedure for such not-yet-associated stations. As a result, medium occupancy and global latency for the association procedure are substantially reduced in an 802.11 ax network.

MU Downlink transmission is thus significantly improved compared to known 802.11 ax current requirements.

Also, there is provided a wireless communication device forming station in a wireless network comprising an access point and stations.

In embodiments, any station registering or associating with the access point being associated with or is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the device forming station comprises at least one microprocessor configured for carrying out the steps of:

In other embodiments, the device forming station comprising at least one microprocessor configured for carrying out the steps of:

Also, there is provided a wireless communication device forming access point in a wireless network comprising an access point and stations.

In embodiments, any station associating with the access point is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the device forming access point comprises at least one microprocessor configured for carrying out the steps of:

building a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, the downlink plurality of resource units comprising a downlink resource unit assigned to an association identifier reserved for stations not associated with the access point (meaning the AID is at least not associated with a specific station); and sending a frame to a station on the downlink resource unit assigned to an association identifier reserved for stations not associated with the access point.

In other embodiments, the device forming access point comprising at least one microprocessor configured for carrying out the steps of:

Optional features of these embodiments are defined in the appended claims with reference to methods. Of course, same features can be transposed into system features dedicated to any device according to the embodiments of the invention.

In embodiments for the station, the method may further comprises, at the station, sending a frame to the access point using an uplink resource unit of a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the plurality of uplink resource units are distributed according to an allocation scheme. In that case, determining the downlink resource unit assigned to an association identifier not associated with a specific station, and in particular reserved for stations not associated with the access point, may also be based on at least one allocation scheme feature of the uplink resource unit.

Conversely for the AP, the method may further comprises, at the access point, receiving a frame from a station on an uplink resource unit of a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the resource units of the plurality of uplink resource units are distributed according to an allocation scheme. In that case, the downlink resource unit assigned to an association identifier not associated with a specific station, and in particular reserved for stations not associated with the access point, in the built plurality of downlink resource units may have at least one matching allocation scheme feature with the uplink resource unit.

In some embodiments, determining the downlink resource unit is based on a number of downlink resource units assigned to the association identifier reserved for stations not associated with the access point, in the multi-user downlink transmission.

In one implementation, if the number of downlink resource units is one, the single downlink resource unit assigned to the association identifier reserved for stations not associated with the access point is selected as being the determined downlink resource unit for receiving the frame.

In one implementation, if the number of downlink resource units is more than one, one downlink resource unit assigned to the association identifier reserved for stations not associated with the access point is selected as being the determined downlink resource unit for receiving the frame, wherein the selecting is based on at least one allocation scheme feature of an uplink resource unit used by the station to send a frame to the access point. The uplink resource unit may be one among a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, and wherein the plurality of uplink resource units are distributed according to an allocation scheme.

In some embodiments, and preferably (but not only) when it is determined the multi-user downlink transmission comprises a single determined downlink resource unit assigned to the association identifier reserved for stations not associated with the access point, the station may further comprise checking whether the frame received in the determined downlink resource unit is addressed to the station, prior to decoding the frame. It means the station further comprises checking whether the determined downlink resource unit contains a frame addressed to the station, so to trigger the receiving, and subsequent decoding, of the frame in case of a positive checking. This approach is to discard a frame if it is not addressed to the station.

In embodiments related to the association procedure of stations with the AP, the station is not associated with the access point, and the frame in the uplink resource unit is a request management frame in a process of associating the station with the access point, while the frame in the downlink resource unit is a response management frame in response to the request management frame. In this context, the invention substantially improves the global latency for the association procedure.

In some embodiments, the allocation scheme feature includes a position of the resource unit in the corresponding plurality of resource units, according to the allocation scheme. For instance, if the uplink resource unit corresponds to RU at position #3 in the RU allocation scheme (as indicated in a trigger frame triggering the MU Uplink transmission), the downlink resource unit for downlink transmission may be the one at position #3 in the plurality of downlink RUs. This may be regardless of whether the two RUs share the same frequency range (or range of tones) or not.

This feature or criterion is easily identified by the AP and the station, while requiring little information to temporarily store from the uplink RU in order to build the downlink RU.

In variants, the allocation scheme feature includes a frequency band of the resource unit in the corresponding plurality of resource units distributed in the frequency domain according to the allocation scheme. This may be regardless of whether the two RUs share the same position in their respective plurality of RUs. For instance the downlink RU has exactly the same tones as the uplink RU, within the considered 20MHz channels. Also, it may be contemplated having the downlink RU starting at or ending with exactly the same tone as the uplink RU (even if their RU sizes are different).

In other variants, the allocation scheme feature includes a size of the resource unit in the corresponding plurality of resource units, according to the allocation scheme. For instance, if the uplink RU is 52-tones width, the downlink RU can be identified as being one (or the one) being also 52-tones width. It may be noted that one or more other criteria may be used to identify the right downlink RU from amongst several candidates (for instance if several 52tones width RUs are defined in the plurality of downlink RUs). An exemplary other criterion is a predefined AID assigned to the downlink RU, as introduced below.

Of course, all or part of the position criterion, frequency band criterion and size criterion may be combined to determine or build the downlink RU relatively to the uplink RU.

In some embodiments, any station registering or associating with the access point is associated with or assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the uplink and/or downlink resource units are assigned to a predefined association identifier not associated with a specific station, and in particular reserved for stations not associated with the access point. Although the predefined association identifier is not dedicated to a specific station, it makes it possible for the stations (e.g. not-yet-associated stations) to quickly identify an uplink RU according to the invention and to verify the allocation scheme feature on few RUs to find the appropriate downlink RU. This reduces processing at the station.

In specific embodiments, the uplink and downlink resource units are assigned to the same predefined association identifier not associated with a specific station, in particular reserved for stations not associated with the access point. This is to simplify the processing at both the AP and the stations.

According to a specific feature, the association identifier not associated with a specific station is an 11-bit identifier equal to 2045. In a particular case, this association identifier is reserved for stations not associated with the access point.

In some embodiments, the pluralities of uplink and downlink resource units belong to the same transmission opportunity granted to the access point. This approach reduces latency in a frame exchange initiated between the AP and the station (e.g. related to an association procedure).

In specific embodiments, the plurality of downlink resource units in the multi-user downlink transmission directly follows the plurality of uplink resource units comprised in the multi-user uplink transmission within the same transmission opportunity granted to the access point. This means without intermediary (downlink or uplink) resource units between them. This however does not exclude the presence of acknowledgment. This approach optimizes the latency

In variants, the plurality of uplink resource units comprised in the multi-user uplink transmission and the plurality of downlink resource units in the multi-user downlink transmission are separated by at least one third plurality of resource units provided for a multi-user uplink or downlink transmission within the same transmission opportunity granted to the access point. It makes it possible for the AP to schedule intermediary MU Downlink or Uplink transmissions within the same TXOP, to improve exchanges with the stations.

In other variants, the pluralities of uplink and downlink resource units belong to different transmission opportunities granted to the access point. This may give to the AP enough time to prepare the responses to the not-yet-associated stations that have sent requests through a so-called “uplink RU” of an MU Uplink transmission.

In some embodiments, the resource units of each plurality are distributed in the frequency domain according to the respective allocation scheme. This applies to the RUs defined in 802.11 ax.

In some embodiments, the plurality of uplink resource units provided in the multiuser uplink transmission is triggered in the transmission opportunity by a trigger frame sent by the access point. This particularly applies to 802.11 ax networks.

Another aspect of the invention relates to a non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device, causes the device to perform any method as defined above.

The non-transitory computer-readable medium may have features and advantages that are analogous to those set out above and below in relation to the methods and devices.

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, microcode, 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. A tangible carrier medium may comprise a storage medium such as a hard disk drive, a magnetic tape device or a solid state memory device and 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 RF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent to those skilled in the art upon examination of the drawings and detailed description. Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings.

Figure 1 illustrates a typical wireless communication system in which embodiments of the invention may be implemented;

Figures 2a to 2g present various formats of 802.11 frames according to the

802.11 ax standard;

Figure 3 illustrates an exemplary sequence of management frames allowing a notyet-associated station to discover and register with a given Access Point;

Figure 4 illustrates 802.11ac channel allocation that support channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

Figure 5 illustrates an example of 802.11 ax uplink OFDMA transmission scheme, wherein the AP issues a Trigger Frame for reserving a transmission opportunity of OFDMA subchannels (resource units) on an 80 MHz channel as known in the art;

Figure 6 illustrates, through an exemplary situation of data transmission in a WLAN, drawbacks of the current version of 802.11 ax;

Figure 7 shows a schematic representation a communication device in accordance with embodiments of the present invention;

Figure 8 shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention;

Figure 9a illustrates the impact of embodiments of the present invention on the exemplary situation of Figure 6 described above for not-yet-associated stations in the process of associating with the AP;

Figure 9b illustrates an alternative to Figure 9a;

Figure 9c illustrates another alternative to Figures 9a and 9b;

Figure 9d illustrates a general embodiment in which a plurality of downlink resource units are allocated to multiple unassociated stations;

Figure 10a illustrates, using a flow chart, main steps at the access point in relation with an MU Uplink transmission it triggers, implementing teachings of the present invention;

Figures 10b and 10c illustrate, using flow charts, main steps at the access point in relation with an MU Downlink transmission it triggers when implementing embodiments of the present invention;

Figure 11a illustrates, using a flow chart, main steps at an unassociated station in relation with an MU Uplink transmission triggered by an access point;

Figures 11b and 11c illustrate, using flow charts, main steps at an unassociated station in relation with an MU Downlink transmission triggered by an access point according to embodiments of the invention; and

Figures 12a and 12b illustrate, through two exemplary situations of data transmission in a WLAN, embodiments of the invention in which one MU Downlink resource unit is used by the AP to send data to unassociated stations.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limiting exemplary embodiments and by reference to the figures.

Figure 1 illustrates a communication system in which several communication nodes (or stations) 101-107 exchange data frames over a radio transmission channel 100 of a wireless local area network (WLAN), under the management of a central station, or access point (AP) 110. The radio transmission channel 100 is defined by an operating frequency band constituted by a single channel or a plurality of channels forming a composite channel.

While the communication system of Figure 1 shows a single physical access point 110, the AP 110 may support multiple BSSs (also called set of “virtual APs”) and be configured to manage one or more WLANs (or BSSs), i.e. one or more groups of stations. Each BSS has to be uniquely identified by a specific basic service set identification, BSSID.

To achieve this configuration, the physical AP 110 may implement two (or more) virtual APs to manage two (or more) WLANs, for instance:

virtual AP 1 VAP-1 (not shown) having MAC address MAC1 as specific BSSID to manage a first WLAN (BSS) with “guest” as SSID, and virtual AP 2 VAP-2 (not shown) having MAC address MAC2 as specific BSSID to manage a second WLAN (BSS) with “Employee” as SSID.

Some stations can register or “associate” with VAP-1 and thus join the first WLAN “guest”, while other stations can simultaneously register with VAP-2 and thus join the second WLAN “Employee”.

For the stations to be aware of available WLANs (or BSSs) and of the information defining them (for instance corresponding SSID or SSIDs, corresponding specific BSSID or BSSIDs, communication mode including Infrastructure or Ad-Hoc, protection security schemes used including Open, WEP, WPA-PSK or 802.1X, support transmission rates used, channel in operation, and any optional Information Elements), the AP sends some control or management frames, including beacon frames and probe response frames which have substantially the same content.

A probe response frame is emitted by the AP to a specific station in response to a probe request frame broadcast by the station. This takes place in an active discovery procedure where the station successively scans the 20MHz channels and broadcast probe request frames therein. In the active discovery procedure, the station has to periodically remind its effective presence by sending new probe request frames.

On the other hand, a passive discovery procedure has been implemented where the AP voluntarily and periodically (e.g. each 100 ms) broadcasts a beacon frame to declare the WLAN to the stations.

Both beacon frames and probe response frames are used in any version of 802.11, meaning that they are sent at lowest bit rate using a non-HT (high throughput) PPDU (PLCP Protocol Data Unit) format as shown in Figure 2a.

This format is simple as it contains a preamble made of three fields that can be understood by any station according to any version of 802.11: L-STF (Legacy Short Training Field), L-LTF (Legacy Long Training Field) and L-SIG (Legacy Signal Field) fields; followed by a Data field containing the payload data, here the information defining the WLAN to declare.

The repetition of the probe request/response frames or of the beacon frames preempts a non-negligible part of network bandwidth. This part substantially increases with multiple WLANs that must share the same communication channels, and also with multiple physical APs (possibly some implementing multiple BSSs), since multiple beacons are thus broadcast (one for each active BSS).

The discovery procedure (using beacon frames or probe response frames) may be the initial part of a more general association procedure during which a station registers or associates with an AP to join a corresponding WLAN.

Figure 3 illustrates an exemplary sequence of management frames allowing a notyet-associated station to discover and register/associate with a given Access Point. It comprises three phases: WLAN discovery, authentication and association, at the end of which the station enters into an authenticated and associated state with the AP. Note that the station may be currently associated with a first AP (i.e. belonging to a first WLAN) and willing to join a second WLAN.

802.11 networks make use of a number of options for the first phase of 802.11 probing or discovering. For instance, for an enterprise deployment, the search for a specific network may involve sending a probe request frame out on multiple channels that specifies the network name (SSID) and bit rates.

More generally, prior to association with the AP, the stations gather information about the APs by scanning the channels one by one either through passive scanning (passive discovery procedure introduced above) or active scanning (active discovery procedure introduced above).

In the passive scanning mode, the station scans through successively each 20MHz channel and waits to listen for beacon frames (declaring SSID) on the scanned channel, regardless of whether the stations has already connected to a specific SSID before or not.

In the active scanning mode, the stations send out probe request frames 310 on each wireless 20MHz channel. The probe request frames may contain the SSID of a specific WLAN that the station is looking for or the probe request frames may not contain a specific SSID meaning the station is looking for “any” SSID in the vicinity of the station.

In response to receiving a probe request frame, the AP checks whether the station has at least one common supported data rate or not. If there is a compatible data rate, the AP responds with a probe response frame 320, the content of which is similar to a beacon frame: advertising of the SSID (wireless network name), of supported data rates, of encryption types if required, and of other 802.11 capabilities ofthe AP.

An acknowledgment frame 330 may be sent by the station, in response to receiving the probe response frame 320.

It is also common for a station that is already associated with an AP to send probe request frames regularly onto other wireless channels to maintain an updated list of available WLANs with best signal strengths. Thanks to this list, when the station can no longer maintain a strong connection with the AP, it can roam to another AP with a better signal strength using the second and third phases ofthe association procedure.

The second phase is the 802.11 authentication once a WLAN to join has been chosen by the station. In particular, the station chooses a compatible WLAN from the probe response frames it receives.

802.11 was originally developed with two authentication mechanisms: the first authentication mechanism, called “open authentication”, is fundamentally a NULL authentication where the station says “authenticate me” and the AP responds with “yes”. This is the mechanism used in almost all 802.11 deployments; the second authentication mechanism, namely the WEP/WPA/WPA2, is a shared key mechanism that is widely used in home networks or small Wi-Fi deployments and provides security.

During the 802.11 authentication phase, the station sends a low-level 802.11 authentication request frame 340 to the selected AP setting, for instance, the authentication to open and the sequence to 0x0001 .The AP receives the authentication request frame 340 and responds to the station with an authentication response frame 350 set to open indicating a sequence of 0x0002.

Note that some 802.11 capabilities allow a station to low-level authenticate to multiple APs without being associated with them (i.e. without belonging to corresponding WLANs). This speeds up the whole association procedure when the station moves between APs. Indeed, while a station can be 802.11 authenticated to multiple APs, it can only be actively associated and transferring data through a single AP at a time.

Next, the station has to perform actual association with the AP from the low level authentication step. This is the next phase of actual 802.11 association by which the station actually joins the WLAN cell. This stage finalizes the security and bit rate options and establishes the data link between the station and the AP. The purpose of this final exchange is for the station to obtain an Association Identifier (AID) to be used to access the medium and send data within the joined WLAN.

Note that the station may have joined a first network and may roam from one AP to another within the physical network. In that case, the association is called a re-association.

Once the station determines which AP (i.e. WLAN) it would like to be associated with, the station sends an association request frame 360 to the selected AP. The association request frame contains chosen encryption types if required and other compatible 802.11 capabilities.

If the elements in the association request frame match the capabilities of the AP, the AP creates an Association ID (AID) for the station and responds with an association response frame 370 with a success message granting network access to the station.

Now the station is successfully associated with the AP, data transfer can begin in the chosen WLAN using the physical medium.

Note that when an AP receives a data frame from a station that is authenticated but not yet associated, the AP responds with a disassociation frame placing the station into an authenticated but unassociated state. It results that the station must re-associate itself with the AP to join the corresponding WLAN.

The probe response frame 320, authentication request/response frames 340 and 350 and association request/response frames 360 and 370 are unicast management frames emitted in an 802.11 legacy format, known as a single user (SU) format. This is a format used for point-to-point communication (here between the AP and the station). Each of these unicast management frames is acknowledged by an ACK frame 330.

As indicated above, all the management frames (310, 320, 340, 350, 360, 370) and the ACK frames (330) use the lowest common rate supported by both the station and the AP (e.g. 24mbps or less).

To meet the ever-increasing demand for faster wireless networks to support bandwidth-intensive applications, 802.11ac and later versions (802.11 ax for instance) implement larger bandwidth transmission through multi-channel operations. Figure 4 illustrates an 802.11ac channel allocation that supports composite channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz.

IEEE 802.11ac introduced support of a restricted number of predefined subsets of 20MHz channels to form the sole predefined composite channel configurations that are available for reservation by any 802.11ac (or later) station on the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHz and 40 MHz supported by 802.11η. Indeed, the 20MHz component channels 400-1 to 400-8 are concatenated to form wider communication composite channels.

In the 802.11ac standard, the channels of each predefined 40MHz, 80MHz or 160MHz subset are contiguous within the operating frequency band, i.e. no hole (missing channel) in the composite channel as ordered in the operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels that may or may not be frequency contiguous. The 80 MHz and 40 MHz channels are respectively composed of two frequency adjacent or contiguous 40 MHz and 20 MHz channels, respectively. However the present invention may have embodiments with either composition of the channel bandwidth, i.e. including only contiguous channels or formed of non-contiguous channels within the operating band.

A station (including the AP) is granted a transmission opportunity (TxOP) through the enhanced distributed channel access (EDCA) mechanism on the “primary channel” (400-3). Indeed, for each composite channel having a bandwidth, 802.11ac designates one channel as “primary” meaning that it is used for contending for access to the composite channel. The primary 20MHz channel is common to all stations (STAs) belonging to the same BSS, i.e. managed by or registered with the same local Access Point (AP).

However, to make sure that no other legacy station (i.e. not belonging to the same set) uses the secondary channels, it is provided that the control frames (e.g. RTS frame/CTS frame or trigger frame described below) reserving the composite channel are duplicated over each 20MHz channel of such composite channel.

Transmissions in such composite channels is made from one station to the other (including the AP) using HE single user (SU) PPDU, the format of which is shown in Figure 2b. It comprises, in addition to the conventional preamble (L-STF, L-LTF, L-SIG) readable by any legacy station, RL-SIG, HE-SIG-A, HE-STF, HE-LTF, Data and PE fields.

The IEEE 802.11ac standard enables up to four, or even eight, 20 MHz channels to be bound. Because of the limited number of channels (19 in the 5 GHz band in Europe), channel saturation becomes problematic. Indeed, in densely populated areas, the 5 GHz band will surely tend to saturate even with a 20 or 40 MHz bandwidth usage per Wireless-LAN cell.

Developments in the 802.11 ax standard seek to enhance efficiency and usage of the wireless channel for dense environments.

In this perspective, one may consider multi-user (MU) transmission features, allowing multiple simultaneous transmissions to different users in both downlink (DL) and uplink (UL) directions, once a transmission opportunity has been reserved and granted to the AP. In the uplink, multi-user transmissions can be used to mitigate the collision probability by allowing multiple non-AP stations to simultaneously transmit to the AP.

To actually perform such multi-user transmission, it has been proposed to split a granted 20MHz channel (400-1 to 400-4) into at least one sub-channel, but preferably into a plurality of sub-channels 310 (elementary sub-channels), also referred to as sub-carriers or resource units (RUs) or “traffic channels”, that are shared in the frequency domain by multiple users, based for instance on Orthogonal Frequency Division Multiple Access (OFDMA) technique.

This is illustrated with reference to Figure 5.

The multi-user feature of OFDMA allows the AP to assign different RUs to different stations in order to increase competition within a reserved transmission opportunity TXOP. This may help to reduce contention and collisions inside 802.11 networks.

In this example, each 20 MHz channel (400-1, 400-2, 400-3 or 400-4) is subdivided in the frequency domain into four OFDMA sub-channels or RUs 510 of size 5MHz. Of course the number of RUs splitting a 20 MHz channel may be different from four, and the RUs may have different sizes. For instance, between two to nine RUs may be provided (thus each having a size between 10 MHz and about 2 MHz). It is also possible to have a RU width greater than 20 MHz, when included inside a wider composite channel (e.g. 80 MHz).

Regarding the MU downlink transmission (from the AP to the stations), the AP can directly send multiple data to multiple stations in the RUs, by simply providing specific indications within the preamble header of the PPDU sent during the TXOP, and then sending data in the data field. RUs used in the downlink direction are known as downlink RUs, while RUs used in the uplink direction are known as uplink RUs.

Figure 2c illustrates the HE MU (Multi-User) PPDU format (HE-MU) used in

802.11 ax for transmissions to one or more stations, in particular for MU downlink transmissions from AP to a plurality of stations.

The HE-MU PPDU includes the same preamble as the non-HT PPDU (Figure 2a) which is always transmitted at low bit rate. This is for all the devices, especially the legacy ones not implementing 802.11ac/ax, to be able to understand the preamble for any of the transmission modes.

Since multiple stations are intended recipients or addressees of the OFDMA downlink transmissions, the AP needs to tell the stations in which resource unit they will find their data. To achieve such signaling, 802.11 ax provides the HE-SIG-B field 200 as shown in the Figure in which stations are assigned to RUs.

The SIG-B field 200 is only found in the downlink HE-MU-PPDU and contains two types of fields as shown in Figure 2e: a single Common Block field 220 and one or more User Specific fields 230.

The single Common Block field 220 defines, through an RU allocation field, the RU distribution for the current transmission opportunity (the other fields are of less importance). The format substantially follows the same format as the downlink RU allocation provided in a Trigger Frame as introduced below.

802.11 ax defines a set of predefined RU allocation schemes for 20MHz channels as shown in Figure 2f. The RU allocation field of Common Block field 220 thus references N 8bit indexes pointing to entries of table of Figure 2f.

Each such entry defines an RU allocation scheme, i.e. how the 20MHz channel is split into consecutive downlink RUs. The entry gives precisely the position (according to frequency increasing order), the size in terms of tones and the frequency range of each RU inside an MU transmission.

For instance, the first entry (index=00000000) defines nine 26-tone-width downlink RUs at positions #1 to #9. The frequency band of downlink RU at position #i is thus from the [26*(i-1 )+1 ]^th tone to the (26*i)^th tone of the considered 20MHz channel. If the AP wants to define a plurality of downlink RUs having this specific distribution, the RU allocation field of Common Block field 220 is set to value 00000000.

The 12^th entry (index=00001011) of the table of predefined RU allocation schemes defines for instance a first 52-tone-width downlink RU (position #1), followed by second, third and fourth downlink RUs with a 26-tones width (positions #2, #3 and #4), followed by fifth and sixth downlink RUs with a 52-tones width (position #5 and #6).

The User Specific fields 230 define information related to each downlink RU defined in the Common Block field, and are provided in the same order as the downlink RUs are successively defined in the Common Block field. For instance, the n^th declared User Specific field 230 gives information about the n^th downlink RU as defined in the Common Block field, i.e. downlink RU at position #n.

Each User Specific field 230 includes the AID of the addressee station (‘STA-ID’ field; provided by the AP during the association procedure of Figure 3), and also other information such as modulation and coding schemes, spatial streams, etc., which are of less importance here.

As only a single downlink RU can be allocated to a given station, the signaling that enables a station to decode its data is carried in only one User Specific field (corresponding to the single RU).

Based on the resource distribution provided in the Common Block field and each corresponding User Specific field, a station can easily know which resource unit has been allocated to it and thus in which downlink RU it will receive its data from the AP.

The HE-SIG-B is encoded on a per-20 MHz basis using BCC and is sent on the station’s preferred band so that the station’s signaling information is sent on the same band as the payload.

Things are different for the MU uplink transmissions, because the AP must control when and how (in which RU) the stations must emit data.

Contrary to the MU downlink transmission, a trigger mechanism has been adopted for the AP to trigger MU uplink communications from various non-AP stations. This is for the AP to have such control on the stations.

To support a MU uplink transmission (during a TXOP pre-empted by the AP), the 802.11ax AP has to provide signalling information for both legacy stations (i.e. non-802.11ax stations) to set their NAV and for 802.11 ax stations to determine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11ax stations, meaning 802.11 stations of previous technologies that do not support OFDMA communications.

As shown in the example of Figure 5, the AP sends a trigger frame (TF) 530 to the targeted 802.11 ax stations to reserve a transmission opportunity. The bandwidth or width of the targeted composite channel for the transmission opportunity is signalled in the TF frame, meaning that the 20, 40, 80 or 160 MHz value is signalled.

The TF frame is a control frame, according to the 802.11 legacy non-HT format shown in Figure 2a, and is sent over the primary 20MHz channel and duplicated (replicated) on each other 20MHz channels forming the targeted composite channel. Due to the duplication of the control frames, it is expected that every nearby legacy station (non-HT or 802.11ac stations) receiving the TF on its primary channel, then sets its NAV to the value specified in the header of the TF frame. This prevents these legacy stations from accessing the channels of the targeted composite channel during the TXOP.

Based on an AP’s decision, the trigger frame TF may define a plurality of uplink resource units (RUs) 510. The multi-user feature of OFDMA allows the AP to assign different RUs to different stations in order to increase competition. This may help to reduce contention and collisions inside 802.11 networks.

The information about the RU distribution in the requested transmission opportunity and about the assignment of stations to the uplink RUs is indicated in the payload of the MAC frame carried in the Data field (shown in Figure 2a). Indeed, the MAC payload is basically empty for classical control frames (such as RTS or CTS frame), but is enhanced with an information structure for Trigger Frames: an RU allocation field defines the allocated uplink RUs (i.e. RU distribution in the TXOP) while one or more User Info fields indicates the information related to each respective uplink RU (in the same order as provided by the RU allocation info field). In particular, the Address field in each User Info field provides the AID of the station to which the corresponding uplink RU is assigned.

These various fields are similar to those (Common Block and User Specific) defined above with reference to Figures 2e and 2f.

The trigger frame 530 may define “Scheduled” uplink RUs, which may be reserved by the AP for certain stations in which case no contention for accessing such RUs is needed for these stations. Such scheduled RUs and their corresponding scheduled stations are indicated in the trigger frame (the Address field ofthe User Info field for the scheduled RU is set to the AID of the station). This explicitly indicates the station that is allowed to use each Scheduled RU. Such transmission mode competes with the conventional EDCA mechanism within the station to access the medium.

If a station finds that there is no User Info field for Scheduled RUs in the Trigger frame 530 carrying its AID in the Address field, then the station should not be allowed to transmit in a Scheduled RU ofthe TXOP triggered by the TF.

The trigger frame TF 530 may also designate “Random” uplink RUs (also referred to as “Random Access” (RA) RUs), in addition or in replacement ofthe “Scheduled” RUs. The Random RUs can be randomly accessed by stations. In other words, Random RUs designated or allocated by the AP in the TF may serve as basis for contention between stations willing to access the communication medium for sending data. A collision occurs when two or more stations attempt to transmit at the same time over the same random RU.

Such random RUs are signalled in the TF by using specific reserved AID in the Address field ofthe User Info field corresponding to the RU. For instance, an AID equal to 0 is used to identify random RUs available for contention by stations associated with the AP emitting the trigger frame (i.e. belonging to the same BSS). On the other hand, an AID equal to 2045 may be used to identify random uplink RUs available for contention by not-yet-associated or “associated” stations (i.e. not belonging to the same BSS as the AP sending the TF 530).

Note that several random RUs with AID=0 and/or with AID=2045 may be provided by the same TF.

A random allocation procedure may be considered for 802.11 ax standard based on an additional backoff counter (OFDMA backoff counter, or OBO counter or RU counter) for random RU contention by the 802.11 ax non-AP stations, i.e. to allow them performing contention between them to access and send data over a Random RU. The RU backoff counter is distinct from the classical EDCA backoff counters (as defined in 802.11e version). However data transmitted in an accessed OFDMA RUs 510 is assumed to be served from same EDCA traffic queues.

The RU random allocation procedure comprises, for a station of a plurality of 802.11ax stations having a positive RU backoff value (initially drawn inside an RU contention window range), a first step of determining, from a received trigger frame, the sub-channels or RUs ofthe communication medium available for contention (the so-called “random RUs”, either identified by a value 0 for already-associated stations or a value 2045 for unassociated stations), a second step of verifying if the value ofthe RU backoff value local to the considered station is not greater than the number of detected-as-available random RUs, and then, in case of successful verification, a third step of randomly selecting a RU among the detected-as20 available RUs to then send data. In case the second step is not verified, a fourth step (instead of the third) is performed in order to decrement the RU backoff counter by the number of detected-as-available random RUs.

As one can note, a station having no Scheduled RU is not guaranteed to perform OFDMA transmission over a random RU for each TF received. This is because at least the RU backoff counter is decremented upon each reception of a Trigger Frame by the number of proposed Random RUs, thereby deferring data transmission to a subsequent trigger frame (depending of the current value of the RU backoff number and of the number of random RUs offered by each of further received TFs).

Back to Figure 5, it results from the various possible accesses to the uplink RUs that some of them are not used (51 Ou) because no station with an RU backoff value less than the number of available random RUs has randomly selected one of these random RUs, whereas some other uplink RUs have collided (as example 510c) because at least two of these stations have randomly selected the same random RU. This shows that due to the random determination of random RUs to access, collision may occur over some uplink RUs, while other RUs may remain free.

The Uplink transmission of data by the stations in the RUs 510 is made using HE Trigger-Based PPDUs (HE_Trig) as shown in Figure 2d in each uplink RU accessed by the stations. Each HE-Trig PPDU carries a single transmission (i.e. from one station to the AP) in response to the trigger frame 530. This HE-Trig PPDU frame format has a format quite similar to the one of HE SU PPDU, except the duration of the HE-STF field is 8 ps.

Once the stations have used the Scheduled and/or Random RUs to transmit data to the AP, the AP responds with a Multi-User acknowledgment (not shown in Figure 5) to acknowledge the data received on each uplink RU.

Figure 2g illustrates a typical format of a MAC frame 230 that may be carried in the Data field of the different PPDUs as shown in Figures 2a-2d, i.e. either in downlink direction by the AP or in uplink direction by the stations.

The illustrated MAC frame contains 24 octets of MAC header, 0 to 2312 octets of Frame Body 207, and 4 octets of Frame Check Sequence (FCS) 208. The MAC header includes among other fields: a frame control field 201, a duration field 202, a RA (Receiver or Destination Address) field 203 and a TA (Transmitter or Source Address) field 204.

In downlink direction for instance, the RA field 203 is set to the MAC address of the station to be destined (unicast MAC address) or to the broadcast value FF:FF:FF:FF:FF:FF if the MAC frame is destined to all stations (broadcast MAC address). The Frame Body is a field of variable length and e.g. its information may be a frame exchanged during the association process (e.g. as described below with reference to Figure 6). For example, the MAC frame body 207 may encapsulate management frames sent by the AP during the association procedure (as explained above with reference to. Figure 3). The control field 201 in this case indicates that the MAC frame is a management frame.

Figure 6 illustrates, through an exemplary situation of data transmission in a WLAN, drawbacks of the current version of 802.11 ax.

In this exemplary situation, the wireless network comprising a physical access point 110 and a plurality of associated stations STA2, STA3, STA4, STA5, STA7 and STA8 and a plurality of unassociated 802.11 ax stations STA1 and STA6.

The AP 110 emits periodically a beacon frame 610, containing parameters of WLAN/BSS group(s).

All stations (including the AP) contend for an access to the wireless network using conventional EDCA scheme. The contention process (backoff counters) at each station starts or restarts each time the wireless network is detected as idle for a predefined time period (usually DIFS time period after the end of a previous TXOP, for instance after an acknowledgment from the AP or after end of a PPDU transmission).

When accessing to the medium, the AP 110 sends a trigger frame 530 to reserve a MU UL transmission opportunity (TXOP#1) on at least one communication channel of the wireless network. The trigger frame 530 defines resource units for the MU Uplink OFDMA transmission in TXOP#1, including one or more random RUs associated with AID=2045 (i.e. dedicated or reserved or assigned to unassociated stations like STA1 and STA6). This is for the not-yet-associated stations to speed up their association procedure, while reducing medium access and occupancy. In the example, two random RUs with AID=2045 are provided, the other RUs being Scheduled RUs and/or random RUs with AID=0 (i.e. dedicated or reserved or assigned to already-associated stations like STA2, STA3, STA4, STA5, STA7 and STA8).

In response to the TF 530, the AP receives data on the uplink RUs 510 from one or more stations during the MU Uplink OFDMA transmission time. This includes data transmitted over Scheduled RUs but also over Random RUs.

In particular, the AP may receive request management frames (e.g. 310, 340, 360) from not-yet-associated 802.11 ax stations such as STA1 and STA6, over the Random RUs with AID=2045.

Upon receiving the data and management frames over the uplink RUs 510 forming the MU Uplink OFDMA transmission, the AP 110 responds with a Multi-STA BlockAck Frame 640 using a HE SU PPDU (having a “receiving address” RA field of the encapsulated MAC frame set with a broadcast address). Note that the AP acknowledges receipt to each sending station by providing, in the Multi-STA BlockAck Frame, the AID of the sending station for which data have been correctly received. As no AID has been associated with each not-yet-associated station, the Multi-STA BlockAck Frame is modified to receive the MAC address of each not-yetassociated station for which the requested management frame has been correctly received.

Next to TXOP#1, the AP 110 may again gain access to the medium for a new TXOP, referred to as TXOP#2, to perform a MU Downlink OFDMA transmission.

As the AP may only assign an AID to a downlink RU of the MU Downlink OFDMA transmission, the AP cannot use the MU Downlink OFDMA transmission to provide response management frames (e.g. 320, 350, 370) to the unassociated stations, here STA1 and STA6. In the current version of 802.11 ax, the MU Downlink OFDMA transmission is restricted to alreadyassociated stations. It means that the response management frames (from the AP to the stations) are still to be conveyed using the legacy single user (SU) mode: for instance, the AP 110 waits until accessing again the medium for a new TXOP (here TXOP#3), during which the AP 110 sends for instance a probe response frame 320 to STA1 using an HE SU PPDU 630-1; and waits again until accessing again the medium for another TXOP (here TXOP#4), during which the AP 110 sends for instance an authentication response frame 350 to STA6 using an HE SU PPDU 630-2. In all cases, an acknowledgment ACK 330 may be received from the addressee station.

The need to use HE SU PPDUs for handling the response management frames is not satisfactory: on one hand, it introduces delays in the network management because the AP 110 has to contend for new accesses to the network; on the other hand, it inefficiently uses the medium for a long time, given the few data to be transmitted, because the HE SU PPDUs are send at low bit rate.

These various drawbacks of the current version of 802.11 ax (illustrated through an exemplary situation of exchange of management frames, but which may concern any other type of frames) show that a more efficient usage of the MU Downlink transmission is sought.

The inventors have contemplated allowing downlink RUs in the MU Downlink transmission to be addressed (assigned) to stations without using AIDs, for instance to stations deprived of AIDs such as unassociated stations.

A first novel idea relies on using a specific AID which has not been associated with a specific station when registering/associating, for instance an association identifier reserved for stations not associated with the access point such as AID=2045.

Thus, an AP willing to address stations having no AID may provide a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, wherein the plurality of downlink resource units comprises a downlink resource unit assigned to an association identifier not associated with a specific station (e.g. reserved for stations not associated with the access point). Next, the AP may send a frame to a station on such a downlink resource unit reserved for stations not associated with the access point.

It makes it possible for the addressee station or stations to simply determine a downlink resource unit assigned to an association identifier not associated with a specific station (e.g. reserved for stations not associated with the access point such as AID=2045), from a plurality of downlink resource units comprised in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point. Next, the station may receive a frame from the access point on the determined downlink resource unit.

A second novel idea relies on a matching in terms of RU profile between an uplink RU already used by a station in the MU Uplink transmission and a downlink RU the AP will use in the MU Downlink transmission to provide a frame to the same station.

Thus, when the station sends (or conversely the AP received) a frame (e.g. a request management frame of a not-yet-associated station) to the access point using an uplink resource unit of a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the plurality of uplink resource units are distributed according to an allocation scheme (e.g. frequency-distributed), the AP may build a plurality of downlink resource units comprised in a multi-user downlink transmission from the access point within the same or a next transmission opportunity granted to the access point, the plurality of downlink resource units comprising a downlink resource unit having at least one matching allocation scheme feature with the uplink resource unit, and then send a frame (e.g. a response management frame) to the station on the downlink resource unit.

In this context, the station only has to determine the downlink resource unit, based on the allocation scheme feature of the uplink resource unit it has used, and then receives the frame from the access point on the determined downlink resource unit.

In embodiments, such determination by the station may depend on the number of downlink resource units assigned to the association identifier not associated with a specific station (e.g. reserved for stations not associated with the access point), in the multi-user downlink transmission. This is to provide the ability for the stations to switch between two behaviors.

For example, if only one downlink RU with a predefined identifier reserved for unassociated stations (e.g. AID=2045) is contained in a MU downlink transmission, each unassociated station may be considered as recipient of the downlink RU, i.e. the downlink RU may potentially contain a frame addressed to that station. For instance, the downlink RU may contain a frame for one of the unassociated stations or contain a broadcast frame for all unassociated stations. In this behaviour, the allocation scheme of the MU uplink transmission is not taken into account.

Each recipient station may check the RA field (receiver or destination address) of the (MAC) frame(s) contained in that downlink RU in order to keep (“receive”) only that(those) for which the station is the addressee.

On the other hand, if more than one downlink RU with a predefined identifier reserved for unassociated stations (e.g. AID=2045) is contained in a MU downlink transmission, an unassociated station has to determine its assigned downlink resource unit, if any, based on the allocation scheme feature of the uplink resource unit it has used. If such downlink RU matching the allocation scheme feature is found, the unassociated station receives the frame from the access point on that determined downlink resource unit.

In that case, each downlink RU has only one recipient station. Thus, the unassociated station may optionally check the RA field of the (MAC) frame(s) contained in that downlink RU to confirm that the frames are indeed addressed to it.

Even when implementing the checking step, the unassociated station takes benefit from the uplink signalling to determine which downlink RU to decode. Advantageously, in either cases (one downlink RU or a plurality of downlink RUs not assigned to a specific station), each unassociated station does not have to decode more than one downlink RU.

Thus, an unassociated non-AP station that receives a MU DL frame (e.g. an HE MU PPDU) containing RUs with the STA-ID equal to 2045, shall be considered as the recipient of a RU with the STA-ID equal to 2045 if one of the following conditions occurs:

• There is only one RU with the STA-ID equal to 2045 in the MU DL frame; and • The STA has previously sent a management request frame in response to a Trigger frame containing Random Access-RU(s) with AID set to 2045, and the RU with STA-ID equal to 2045 has the same RU allocation as the RU allocation of the RA RU carrying the request in the previously sent MU UL frame (e.g. an HE TB PPDU according to 802.11 ax).

Note that a MU DL RU with AID=2045 may also be referred to as a “broadcast RU”. With this naming, a broadcast RU may contain a unicast MAC frame (RA field corresponding to a unicast MAC address) or a broadcast MAC frame (RA field corresponding to a broadcast MAC address).

Note also that providing multiple RUs with the STA-ID equal to 2045 in an HE MU PPDU may be viewed as an exception to a general requirement of not having more than one downlink RU addressed to an associated STA. In other words, if the list of STAs that are recipients of the transmitted HE MU PPDU are represented by an array STA_ID_LIST, a STA_ID_LIST element with a particular (AID) value shall not appear more than once in the array except if:

• the value identifies an unallocated RU (e.g. 2046); or • the value is 2045, which identifies a broadcast RU destined to an unassociated

STA.

According to embodiments, and from the AP perspective, the AP sends to an unassociated STA an association response frames in a broadcast RU (e.g. with AID=2045) considering the following constraints:

• multiple broadcast RUs (AID=2045) may be inserted in a HE MU PPDU;

• if only one broadcast RU (AID=2045) is inserted in a HE MU PPDU, the broadcast RU can be addressed to one or all unassociated STAs;

• if multiple broadcast RUs (AID=2045) are inserted in a HE MU PPDU, each broadcast RU is addressed to only one unassociated STA;

• to send an association response frame to an unassociated STA;

the AP may use the same RU allocation for the broadcast RU (AID=2045) as the RU allocation of the RA RU (AID=2045) used by the unassociated STA to send the corresponding association request frame (cf. Figure 9d);

the AP may use a single broadcast RU (AID=2045) embedding a broadcast MAC frame to broadcast an association response frame to all unassociated STAs (cf. Figure 12a); or the AP may use a single broadcast RU (AID=2045) embedding a unicast MAC frame addressed to the unassociated STA (cf. Figure 12b).

A broadcast RU containing a unicast MAC frame addressed to an unassociated station may include an information identifying an uplink resource unit to be used by the unassociated station in a multi-user uplink transmission opportunity following the multi-user downlink transmission opportunity to provide an acknowledgement to the access point. The UMRS control field as defined in draft 2.1 of standard IEEE 802.11 ax may be used to indicate which UL RU must be used by the unassociated STA to acknowledge the MPDU.

It results from these ideas that MU Downlink transmission can be efficiently extended to unassociated stations, and more generally to any stations without using an AID assigned to a specific station. Preferably an AID reserved for stations not associated with the access point is used.

MU Downlink transmission is thus significantly improved compared to known current 802.11 ax requirements.

Figure 7 schematically illustrates a communication device 700, either a non-AP station 101-107 or the access point 110, of the radio network 100, configured to implement at least one embodiment of the present invention. The communication device 700 may preferably be a device such as a micro-computer, a workstation or a light portable device. The communication device 700 comprises a communication bus 713 to which there are preferably connected:

• a central processing unit 711, such as a microprocessor, denoted CPU;

• a read only memory 707, denoted ROM, for storing computer programs for implementing the invention;

• a random access memory 712, denoted RAM, for storing the executable code of methods according to embodiments of the invention as well as the registers adapted to record variables and parameters necessary for implementing methods according to embodiments of the invention; and • at least one communication interface 702 connected to the radio communication network 100 over which digital data packets or frames or control frames are transmitted, for example a wireless communication network according to the 802.11ax protocol. The frames are written from a FIFO sending memory in RAM 712 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 712 under the control of a software application running in the CPU 711.

Optionally, communication device 700 may also include the following components:

• a data storage means 704 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention;

• a disk drive 705 for a disk 706, the disk drive being adapted to read data from the disk 706 or to write data onto said disk;

• a screen 709 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 710 or any other pointing means.

The communication device 700 may be optionally connected to various peripherals, such as for example a digital camera 708, each being connected to an input/output card (not shown) so as to supply data to the communication device 700.

Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 700 or connected to it. The representation of the bus is not limiting and in particular the central processing unit is operable to communicate instructions to any element of the communication device 700 directly or by means of another element of the communication device 700.

The disk 706 may optionally be replaced by any information medium such as for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, a USB key or a memory card and, in general terms, by an information storage means that can be read by a microcomputer or by a microprocessor, integrated or not into the apparatus, possibly removable and adapted to store one or more programs whose execution enables a method according to the invention to be implemented.

The executable code may optionally be stored either in read only memory 707, on the hard disk 704 or on a removable digital medium such as for example a disk 706 as described previously. According to an optional variant, the executable code of the programs can be received by means of the communication network 703, via the interface 702, in order to be stored in one of the storage means of the communication device 700, such as the hard disk 704, before being executed.

The central processing unit 711 is preferably adapted to control and direct the execution of the instructions or portions of software code of the program or programs according to the invention, which instructions are stored in one of the aforementioned storage means. On powering up, the program or programs that are stored in a non-volatile memory, for example on the hard disk 704 or in the read only memory 707, are transferred into the random access memory 712, which then contains the executable code of the program or programs, as well as registers for storing the variables and parameters necessary for implementing the invention.

In a preferred embodiment, the apparatus is a programmable apparatus which uses software to implement the invention. However, alternatively, the present invention may be implemented in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC).

Figure 8 is a block diagram schematically illustrating the architecture of the communication device 700, either the AP 110 or one of stations 101-107, adapted to carry out, at least partially, the invention. As illustrated, device 700 comprises a physical (PHY) layer block 803, a MAC layer block 802, and an application layer block 801.

The PHY layer block 803 (here an 802.11 standardized PHY layer) has the task of formatting, modulating on or demodulating from any 20MHz channel or the composite channel, and thus sending or receiving frames over the radio medium used 100, such as 802.11 frames, for instance medium access trigger frames TF 530 (Figure 5) to reserve a transmission slot, MAC data and management frames based on a 20MHz width to interact with legacy 802.11 stations, as well as of MAC data frames of OFDMA type having smaller width than 20MHz legacy (typically 2 or 5 MHz) to/from that radio medium.

The MAC layer block or controller 802 preferably comprises a MAC 802.11 layer 804 implementing conventional 802.11 ax MAC operations. The MAC layer block 802 may optionally be implemented in software, which software is loaded into RAM 712 and executed by CPU 711.

The device 700 further comprises an additional block 805, referred to as RU profile management module for controlling usage of Downlink OFDMA resource units (sub-channels), and implements the part of embodiments of the invention (either from station perspective or from AP perspective). The additional block 805 may be implemented at the MAC layer block

802 and/or the physical layer block 803, and thus may interact with both blocks. In one implementation, the additional block 805 receives formed MAC frames for encapsulation in MU DL frames.

For instance and not exhaustively, the operations for the AP may include determining an uplink RU used by a station in MU Uplink transmission for which no AID is available (e.g. an AID reserved for unassociated stations), storing RU allocation scheme features related to the used uplink RU, building an MU Downlink transmission with downlink RUs including a downlink RU that matches the stored RU allocation scheme features and sending a response to the station within such matching downlink RU. The operations for a station different from the AP may include keeping track of RU allocation scheme features of an uplink RU used to transmit data (e.g. request) to the AP in MU Uplink transmission, determining a downlink RU in MU Downlink transmission that matches the RU allocation scheme features of the RU used in order to read the response provided by the AP on this matching downlink RU.

MAC 802.11 layer 804, RU Profile management module 805 and PHY layer block

803 interact one with the other in order to process accurately communications over Downlink OFDMA RU addressed to a station without using an AID associated with said station, according to embodiments of the invention.

On top of the Figure, application layer block 801 runs an application that generates and receives data packets, for example data packets of a video stream. Application layer block 801 represents all the stack layers above MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using various exemplary embodiments in the context of IEEE 802.11 ax by considering OFDMA RUs.

Although the proposed examples are also mainly described with reference to the management frames of the 802.11 association process, the present invention is not limited to such management frame transmission but may apply to any 802.11 data or control frame.

Figure 9a illustrates the impact of embodiments of the present invention on the exemplary situation of Figure 6 described above for not-yet-associated stations STA1 and STA6 in the process of associating with the AP.

The AP 110 is granted TXOP#1 and sends the same trigger frame 530 as in Figure 6 to reserve a MU UL transmission opportunity. This trigger frame 530 defines at least one random RU with AID=2045 (here two such random RUs). Not-yet-associated stations STA1 and STA6 send request management frames to the AP in the random RUs 510 with AID=2045 (the other RUs are used by other stations).

The AP acknowledges the received frames using a Multi-STA BlockAck frame 640.

During this sequence, both AP and stations perform specific operations in order to save one or more allocation scheme features that define the uplink RUs used by STA1 and STA6.

This includes one or more of the following information: a position of the uplink resource unit in the allocation scheme used (i.e. in the corresponding entry of Figure 2f); a frequency band of the uplink resource unit in the allocation scheme used (i.e. which tones in the 20MHz channel according to the corresponding entry of Figure 2f); a size of the uplink resource unit in the allocation scheme used (i.e. in the number of tones as shown in the corresponding entry of Figure 2f).

For instance, Figure 10a illustrates, using a flow chart, main steps at the AP in relation with an MU Uplink transmission it triggers.

At step 1010, the MU Uplink transmission is initiated with trigger frame 530.

If the AP receives a frame from a not-yet-associated station on a random RU with AID=2045 (test 1020), the AP stores the RU profile, i.e. relevant allocation scheme features, of the uplink RUs used and associates each of them with the transmitted not-yet-associated station, at step 1030. The frame is for example a request management frame.

For instance, the AP may store the MAC address of the not-yet-associated station (which is obtained in the request management frame received) together with the 8-bit index corresponding to the allocation scheme used (Figure 2f) and the position of the uplink RU used from amongst the list defined by the allocation scheme used. These three items of information make it possible for the AP to retrieve any of the above-mentioned allocation scheme features.

In case of negative test 1020, the algorithm loops back to step 1010, waiting for the transmission of a new trigger frame.

Next to step 1030, the AP sends, at step 1040, acknowledgments to the transmitting stations, including the not-yet-associated stations having sent e.g. request management frames.

Correspondingly, Figure 11a illustrates, using a flow chart, main steps at a not-yetassociated station in relation with an MU Uplink transmission triggered by the AP.

The process starts at step 1110 where the not-yet-associated station detects a trigger frame 530 sent by the AP, that includes one or more random RUs with AID=2045.

In that case, the not-yet-associated station willing to register/associate with the AP contends for access to such a random RUs with AID=2045. When such a random RU is granted to the not-yet-associated station, the latter transmits a request frame such as a request management frame (310, 340, 360 depending on which phase ofthe association procedure the station is entering) in the accessed random RU 510 with AID=2045. This is step 1120.

If an acknowledgment is received from the AP (test 1130) meaning that the AP will respond to the request in the future, the not-yet-associated station stores the RU profile, i.e. relevant allocation scheme features, ofthe random RUs used. This is step 1140.

For instance, the not-yet-associated station may store the 8-bit index corresponding to the allocation scheme used (Figure 2f) and the position ofthe uplink RU used from amongst the list defined by the allocation scheme used.

Turning back to Figure 9a, the AP initiates a MU Downlink transmission in the same TXOP#1. This is possible thanks to the cascading option provided by 802.11ax (the AP may enable a cascading field in the header of trigger frame 530 in order to warn the stations that it will cascade several MU transmissions, either Downlink or Uplink, during the granted TXOP). Alternatively, after the Multi-STA BlockAck frame 640, the AP may preempt the medium by waiting less than the DIFS period (the other station will thus no have time to start decrementing their backoff counter to contend for access to the medium).

In this example, the AP will respond to the received frames, e.g. request management frames, during the MU Downlink transmission using the teachings of embodiments ofthe invention.

To do so, the AP builds the MU Downlink transmission with a particular RU allocation profile that takes into account the stored RU profiles of the uplink RUs (with AID=2045) used by STA1 and STA6. In particular, the AP provides, in the MU Downlink transmission, a first downlink RU with AID=2045 having the same allocation scheme feature (for instance same position) as the uplink RU used by STA1, and a second downlink RU with AID=2045 having the same allocation scheme feature as the uplink RU used by STA6.

It means that the various resource units for the not-yet-associated stations in both MU Downlink and Uplink transmissions, are signalled using the same predefined association identifier not associated with any particular station, in particular reserved for unassociated stations, here AID=2045.

In the example of the Figure, STA1 has transmitted its probe request frame 310 in the uplink RU at position #1 during the MU Uplink transmission 510. In that case, the AP builds the MU Downlink transmission with a downlink RU at position #1 which also has AID=2045.

Similarly, STA6 has transmitted its authentication request frame 340 in the uplink RU at position #6 during the MU Uplink transmission 510. In that case, the AP builds the MU Downlink transmission with a downlink RU at position #6 which also has AID=2045.

Of course, another allocation scheme feature than the uplink RU position can be used, as introduced above.

Thanks to this approach, not-yet-associated stations STA1 and STA6 knows that the first and sixth resource units in the MU Downlink transmission are destined to them, provided they are assigned to AID=2045. It means that, in this embodiment, two criteria are combined for the not-yet-associated station to identify a downlink RU addressed to it: first, the downlink RU may be assigned with AID=2045; second, the relevant allocation scheme features must match with the uplink RU used in the MU Uplink transmission when sending a previous frame, e.g. the request management frame.

The AP 110 thus sends the responses to the not-yet-stations using the downlink RUs 920 with AID=2045 so built (the other downlink RUs are used conventionally). In the present example, the AP sends the probe response frame 320 to STA1 using the first downlink RU (position #1) and sends the authentication response frame 350 to STA6 using the sixth downlink RU (position #6).

Finally, the not-yet-associated stations STA1 and STA6 receive and decode the response frames sent by the AP on these two downlink RUs in response to their previous request frames, and acknowledge good reception by an uplink transmission 940.

As it is readily apparent from this Figure compared to Figure 6, successive SU transmissions (630-1 and 630-2) for management frames are now avoided, resulting in a simplification of the association procedure for not-yet-associated STAs and a more efficient usage of the network. This is particularly advantageous to manage the association of new stations in dense networks as 802.11ax.

Figure 10b illustrates, using a flow chart, main steps at the AP in relation with an MU Downlink transmission it triggers when implementing embodiments of the present invention. These operations follow the reception of one or more request management frames from not-yetassociated stations, and describe how the AP transmits response frames thereto using a MU DL transmission.

At step 1050, the AP determines whether or not one or more response management frames are ready to be sent in response to request management frames received from not-yet-associated stations during a previous MU Uplink transmission.

In the affirmative, at step 1060, the AP builds a MU Downlink frame (i.e. a plurality of downlink resource units assigned to downlink transmission from the access point within a transmission opportunity granted to the access point) comprising, for each response frame to send, a downlink resource unit that matches the allocation scheme feature stored for the corresponding not-yet-associated station (i.e. that matches the allocation scheme feature of uplink resource unit used by said station to send its request frame in the MU Uplink transmission). For instance, the downlink and uplink RUs may have the same position in the allocation scheme used. Each such downlink resource unit is declared in HE-SIG-B in association with AID=2045.

Next, at step 1070, the AP 110 sends each response management frame on the corresponding downlink RU with AID=2045, to the appropriate not-yet-associated station.

Correspondingly, Figure 11b illustrates, using a flow chart, main steps at a not-yetassociated station in relation with an MU Downlink transmission triggered by the AP according to embodiments of the invention. These operations describe how such a station decodes a response management frame received from the AP in a MU Downlink transmission.

The not-yet-associated station has already sent a request management frame to the AP using an uplink RU with AID=2045 in a previous MU Uplink transmission.

The process starts when a MU Downlink frame is received to determine, at step 1150, whether or not the frame includes downlink resource units with AID=2045.

In the negative, the not-yet-associated station waits for a next MU Downlink frame.

In the affirmative, the station determines, at step 1160, whether or not one of the downlink RUs with AID=2045 has allocation scheme features matching those stored at step 1140. This may simply consist in verifying whether or not a downlink RU with AID=2045 has the same position as the one (uplink RU) used in the previous MU Uplink transmission.

In case a matching downlink RU with AID=2045 is found, the not-yet-associated station selects this downlink RU to read the frame sent by the AP (step 1170).

The response management frame is thus decoded from this downlink RU and forwarded for instance to the MAC 802.11 layer block 804 (step 1180).

While Figure 9a illustrates a situation where the downlink resource units of the MU Downlink transmission to provide the response directly follows the uplink resource units of the MU Uplink transmission by which the request has been sent, within the same transmission opportunity granted to the access point, other embodiments may provide that the uplink resource units assigned to uplink transmission by which the request has been sent and the downlink resource units assigned to downlink transmission to provide the response are separated by one or more other MU transmissions, either Downlink or Uplink, within the same transmission opportunity granted to the access point.

This is illustrated in Figure 9b which shows that one or more MU transmissions can be inserted between transmission 510 and transmission 920.

This embodiment gives time to the AP to prepare the response management frames.

Another situation is illustrated in Figure 9c where the downlink resource units of the MU Downlink transmission to provide the response and the uplink resource units of the MU

Uplink transmission by which the request has been sent belong to two separate transmission opportunities granted to the access point.

Between the two separate TXOPs, any station may contend and access to the medium to send data.

This embodiment also gives time to the AP to prepare the response management frames.

In the embodiments of Figures 9b and 9c, the AP may avoid inserting, between the two transmissions, “intermediary” MU Downlink frames containing a downlink resource unit with AID=2045 matching the relevant allocation scheme feature or features of an uplink RU previously used by an unassociated station to send a request frame to the AP and that is now waiting for a response (management) frame from the AP. This advantageously avoids the unassociated station to read a downlink RU which eventually does not contain a frame addressed to it.

It should be noted however that avoiding such “intermediary” MU Downlink frame(s) is(are) not mandatory. If “intermediary” MU Downlink frame(s) are inserted between the two transmissions, an unassociated station that reads a downlink RU with AID=2045 (matching its relevant allocation scheme feature or features) which contains a frame not addressed to it will simply ignore the frame (by determining for instance whether or not the RA field 203 is its own MAC address) and continue monitoring for another MU Downlink frame containing a downlink resource unit with AID=2045 matching its relevant allocation scheme feature or features.

Figure 9d illustrates the general embodiment in which a plurality of downlink resource units (950) are allocated to multiple unassociated stations within the MU DL frame. In the illustrated embodiment, several RUs with AIDs equal to 2045 are signalled in the HE-SIG-B at locations corresponding to UL requests. The AP may use these downlink RUs with AID=2045 to send response frames to unassociated stations, such as a probe response and an authentication response.

Another embodiment is illustrated in Figure 12a in which a unique downlink resource unit (1210) is allocated to unassociated stations (i.e. with AID=2045) within the MU DL frame. The AP may use this single downlink RU with AID=2045 to send a response frame to unassociated stations as a broadcast frame (i.e. with RA field 203 set to broadcast address).

As explained below, as a single downlink RU with AID=2045 is provided, the unassociated stations do not check the matching with their relevant allocation scheme feature or features. They all read the frame(s) of this single downlink RU with AID=2045. Due to the absence of allocation scheme feature check, the position of this downlink resource unit with AID=2045 within the MU DL frame can be anywhere. Figure 12a illustrates steps 1058 and 1054 at the AP side of the flowchart of Figure 10c described below.

A variation is illustrated in Figure 12b in which a unique downlink resource unit (1220) is allocated to unassociated stations within the MU DL frame. This may be because the

AP decides sending a unique response to a specific unassociated station. In that case, the RA field 203 ofthe frame sent through the unique downlink resource unit with AID=2045 (1220) is set to the MAC address ofthe destined unassociated station. Figure 12b illustrates steps 1053 and 1054 at the AP side ofthe flowchart of Figure 10c described below.

These illustrations show that, depending on the number of downlink RUs defined in the MU DL transmission, the unassociated stations may switch from a first behaviour where they check the matching of the downlink RUs with AID=2045 with their relevant allocation scheme feature or features (e.g. if there are more than a single downlink RU with AID=2045) before accessing/reading the matching downlink RU and a second behaviour where they do not perform the check (e.g. if there is a single downlink RU with AID=2045) and directly access/read the downlink RU.

In the second behaviour, it is unassociated stations’ responsibilities to check whether the frame(s) sent over the unique downlink RU is addressed to them or not, e.g. by checking the RA field 203 (broadcast address or the MAC address specific to the station). Such check of the RA field 203 may optionally be done by the unassociated stations with the first behaviour.

Thanks to embodiments ofthe present invention, several RUs with AID=2045 can be used in the same MU Downlink transmission to send response management frames to respective not-yet-associated stations. This is advantageous in dense and active networks (e.g. rail stations where a lot of stations connect and disconnect the network in a short time).

Advantageously, the AP may regularly provide a trigger frame with a lot of (possibly only) random RUs with AID=2045. Preferably the allocation scheme ofthe first entry of Figure 2f is used to offer a maximum number of opportunities for the not-yet-associated stations to perform their association procedure. The AP may thus provide, quickly after, a MU Downlink transmission matching the same allocation scheme, to provide the response management frames.

Figure 10c illustrates, using a flow chart, main steps at the AP in relation with one or more MU Downlink transmissions embedding frames destined to unassociated stations according to other embodiments ofthe invention. Note that the MU Downlink transmission may also embed frames intended to already-associated stations, but these transmissions may use conventional methods and are not further described here.

In the following description a predefined identifier value of 2045 is chosen to designate MU DL RUs reserved for unassociated stations. Of course this value is given for illustration only and any other predefined value or signalling means may be adopted.

At step 1051, the AP determines whether there is a list of pending frames (e.g. response management frames or any other type of frames) waiting for transmission to unassociated stations. Again, other frames intended for associated stations may also be handled in parallel or sequentially by the AP.

If the list of pending frames is not empty, it is determined at step 1052 whether the list contains a broadcast frame (i.e. a MPDU packet with a RA field 203 set to the broadcast value FF:FF:FF:FF:FF:FF). If a broadcast frame is found, it is selected at step 1053 for transmission. A single downlink RU with AID=2045 is included in a MU DL frame comprising the selected frame (step 1054). The downlink RU can be located anywhere within the MU DL frame (an example is illustrated in Figure 12a). The MU DL frame may be built at the time of inclusion of the downlink RU with AID=2045, or may be formed earlier by module 805 of the AP, for example at the time other downlink RUs destined for already-associated stations are defined.

If the list does not contain a broadcast frame (test 1052 negative), the number of frames pending for transmission is determined at step 1057. If only one frame is present in the list, that frame is selected (step 1058) and included in the MU DL frame (step 1054). Similarly as for step 1053, only one downlink RU with AID=2045 is included in the MU DL frame (as shown for instance in Figure 12b).

If multiple frames are present in the list (number of frames to send greater than one at test 1057), multiple frames are selected from the list at step 1059. Preferably, all response frames that follow the reception of request frames received on uplink RUs from unassociated stations (e.g. according to flowchart of Figure 10a) are selected in order to be transmitted to the corresponding unassociated stations. The design of the downlink RUs with AID=2045 for the response frames can be based on at least one allocation scheme feature of the uplink RUs used by the unassociated stations. Of course, the response frame for a specific unassociated station will be sent over the downlink RU matching the allocation scheme feature of the uplink RU used by the same station when requesting the AP.

The number of frames selected at step 1059 may be limited to a number of downlink RUs available, for instance of downlink RUs available to be assigned to AID=2045. This may be the case if some downlink RUs are already assigned to specific already-associated stations.

At step 1061, multiple downlink RUs with AID value 2045 are included in the MU DL frame. The MU DL frame is previously built or is built at the time of the inclusion. The included downlink resource units with AID=2045 match the allocation scheme features stored for the corresponding unassociated stations respectively (i.e. each downlink RU matches the allocation scheme feature of the uplink resource unit used by said station to send a frame in the MU Uplink transmission).

For instance, the AP, that received a RA RU carrying a management request frame from an unassociated STA, may transmit a management response frame in HE MU PPDU (i.e. MU DL frame) using a broadcast RU identified by a STAJD (AID) equal to 2045 and having the same RU allocation as the RU allocation of the received RA RU.

At step 1055, the MU DL frame is transmitted by the AP. Finally, at step 1056, the list of pending frames is updated by removing the selected frames that have been transmitted (and acknowledged), and the steps of the flowchart are repeated from step 1051.

The flowchart illustrated in Figure 10c describes one possible implementation for handling the transmission of frames for unassociated stations according to embodiments of the invention. However other implementation variants may be contemplated.

For example, the broadcast frame may be given a lower priority relatively to other frames in the list, meaning one or more frames may be selected first for transmission although a broadcast frame is present in the list. The broadcast frame is then only transmitted after all or a certain number of frames (based on age or other criteria) are transmitted from the list.

In another variant, instead of selecting multiple frames at step 1059, the AP may decide to select only one frame among the list of multiple frames to send. In this case, the MU DL frame will contain only one downlink RU with AID=2045 comprising the selected frame. Step 1061 is cancelled in this variant. The selected frame is included in a MU DL frame as described at step 1054.

Correspondingly, Figure 11c illustrates, using a flow chart, main steps at an unassociated station in relation with an MU Downlink transmission triggered by the AP. These operations describe how such an unassociated station decodes a frame received from the AP in a MU Downlink transmission.

The process starts by checking when a MU Downlink frame (HE MU PPDU) is received by the station (step 1151). This is similar to step 1150 at Figure 11b.

If a MU Downlink frame is received (test at step 1151 positive), the station determines at step 1152 whether multiple downlink RUs with AID equal to 2045 are included in the received MU DL frame.

If multiple downlink RUs with an AID value 2045 are found (test at step 1152 positive), the unassociated station enters a first behavior where it checks whether a previously stored RU profile matches with the RU allocation of one of the downlink resource units having AID=2045 contained in the just received MU DL frame (step 1153). A RU profile may be previously stored by the station following the execution of flowchart of Figure 11a for example (e.g. transmission of a request frame in a MU UL RU with AID=2045 and storing the profile of the uplink RU as described in step 1140). Thus, a RU profile is stored if the unassociated station has already sent a request frame to the AP using an uplink RU with AID=2045 in a previous MU Uplink transmission.

The matching test at step 1153 may simply consist in verifying whether or not a downlink RU with AID=2045 has the same position as the one used in the previous MU Uplink transmission.

The matching test at step 1153 may also be that the STA has previously sent a management request frame in response to a Trigger frame containing RA-RU(s) with AID set to 2045, and the broadcast RU with STA-ID (AID) equal to 2045 has the same RU allocation as the RU allocation of the RA-RU carrying the request in the previously sent HE TB PPDU.

If the test at step 1153 is positive, the unassociated station is considered as recipient of the matching downlink RU, which means that the matching downlink RU potentially contains a MAC frame destined to the unassociated station. The matching downlink RU is then selected at step 1154 for decoding. Optionally, the unassociated station checks whether the RA field 203 of the MAC frame conveyed in the selected matching downlink RU corresponds to the unassociated station MAC address prior to decoding.

If the test at step 1153 is negative, the unassociated station is the recipient of no downlink RU. The unassociated station waits for the reception of new MU DL frames with AID=2045 at step 1151.

At step 1155, the frame encapsulated in the selected downlink RU with AID=2045 is decoded, and forwarded for instance to the MAC 802.11 layer block 804. The encapsulated frame may be a response frame.

If a single downlink RU with an AID value 2045 is found at step 1152 (test negative), the unassociated station enters a second behavior where it does not check any matching between a stored RU profile and the single downlink RU. The unassociated station is (automatically) considered as recipient of that downlink RU. The unassociated station then checks at step 1156 whether the RA field 203 of the MAC frame corresponds to the unassociated station MAC address or to a broadcast address. In the affirmative, the downlink RU is selected at step 1157 and the frame contained therein decoded at step 1155. In the negative, the unassociated station waits for the reception of new MU DL frames with AID=2045 at step 1151.

Note that in any case, and in particular when multiple downlink RUs with AID=2045 are determined at step 1152, the unassociated station eventually decodes at most one downlink RU with AID=2045. This makes it easy for the unassociated station to determine whether it is recipient of a downlink RU or not and, in the affirmative, to locate the downlink RU for which the unassociated station is the recipient.

Note also that an unassociated station that receives a MU DL frame containing RUs with the STA-ID (AID) equal to 2045, is considered as the recipient of a RU with the STAID equal to 2045 if one of the following condition occurs:

• there is only one RU with the STA-ID equal to 2045 in the MU DL frame (test 1152 negative);

• the STA has previously sent a (e.g. management) request frame in response to a Trigger frame containing RA-RU(s) with AID set to 2045, and the broadcast RU with STA-ID equal to 2045 has the same RU allocation as the RU allocation of the RA-RU carrying the request in the previously sent MU UL frame (test 1153 positive).

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.

The description above focuses on RUs that are distributed in the frequency domain. Variants may contemplate having RUs distributed in the time domain, in replacement or in combination with a frequency-based distribution. In any case, the allocation scheme features describing a specific RU may be obtained from the allocation scheme used.

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

1. A wireless communication method in a wireless network comprising an access point and stations, any station associating with the access point being assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, the method comprising the following steps, at one of the stations:

determining a downlink resource unit assigned to an association identifier reserved for stations not associated with the access point, from a plurality of downlink resource units comprised in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point; and receiving a frame from the access point on the determined downlink resource unit.

2. The method of Claim 1, further comprising, at the station, sending a frame to the access point using an uplink resource unit of a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the plurality of uplink resource units are distributed according to an allocation scheme, wherein determining the downlink resource unit assigned to an association identifier reserved for stations not associated with the access point is also based on at least one allocation scheme feature of the uplink resource unit.

3. The method of Claim 1, wherein determining the downlink resource unit is based on a number of downlink resource units assigned to the association identifier reserved for stations not associated with the access point, in the multi-user downlink transmission.

4. The method of Claim 3, wherein if the number of downlink resource units is one, the single downlink resource unit assigned to the association identifier reserved for stations not associated with the access point is selected as being the determined downlink resource unit for receiving the frame.

5. The method of Claim 3, wherein if the number of downlink resource units is more than one, one downlink resource unit assigned to the association identifier reserved for stations not associated with the access point is selected as being the determined downlink resource unit for receiving the frame, wherein the selecting is based on at least one allocation scheme feature of an uplink resource unit used by the station to send a frame to the access point.

6. The method of Claim 5, wherein the uplink resource unit is one among a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, and wherein the plurality of uplink resource units are distributed according to an allocation scheme.

7. The method of any one of Claims 1 to 6, further comprising, at the station, checking whether the frame received in the determined downlink resource unit is addressed to the station, prior to decoding the frame.

8. A wireless communication method in a wireless network comprising an access point and stations, any station associating with the access point being assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, the method comprising the following steps, at the access point:

building a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, the plurality of downlink resource units comprising a downlink resource unit assigned to an association identifier reserved for stations not associated with the access point; and sending a frame to a station on the downlink resource unit assigned to an association identifier reserved for stations not associated with the access point.

9. The method of Claim 8, further comprising, at the access point, receiving a frame from a station on an uplink resource unit of a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the resource units of the plurality of uplink resource units are distributed according to an allocation scheme;

wherein the downlink resource unit assigned to an association identifier reserved for stations not associated with the access point in the built plurality of downlink resource units has at least one matching allocation scheme feature with the uplink resource unit.

10. The method of Claim 8, wherein if more than one downlink resource unit assigned to an association identifier reserved for stations not associated with the access point is comprised in the built plurality of downlink resource units, each downlink resource unit assigned to an association identifier reserved for stations not associated with the access point has at least one matching allocation scheme feature with an uplink resource unit;

wherein the uplink resource unit is among a plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, and wherein the uplink resource units of the plurality of uplink resource units are distributed according to an allocation scheme.

11. A wireless communication method in a wireless network comprising an access point and stations, the method comprising the following steps, at one of the stations:

12. A wireless communication method in a wireless network comprising an access point and stations, the method comprising the following steps, at the access point:

building a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, the plurality of downlink resource units comprising a downlink resource unit having at least one matching allocation scheme feature with the uplink resource unit; and sending a frame to the station on the downlink resource unit.

13. The method of Claim 2, 9, 11 or 12, wherein the station is not associated with the access point, and the frame in the uplink resource unit is a request management frame in a process of associating the station with the access point, while the frame in the downlink resource unit is a response management frame in response to the request management frame.

14. The method of Claim 2, 9, 11 or 12, wherein the allocation scheme feature includes a position of the resource unit in the corresponding plurality of resource units, according to the allocation scheme.

15. The method of Claim 2, 9, 11 or 12, wherein the allocation scheme feature includes a frequency band of the resource unit in the corresponding plurality of resource units distributed in the frequency domain according to the allocation scheme.

16. The method of Claim 2, 9, 11 or 12, wherein the allocation scheme feature includes a size of the resource unit in the corresponding plurality of resource units, according to the allocation scheme.

17. The method of Claim 11, wherein any station associating with the access point is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the uplink and/or downlink resource units are assigned to a predefined association identifier reserved for stations not associated with the access point.

18. The method of Claim 12, wherein any station associating with the access point is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, and the uplink and/or downlink resource units is assigned to a predefined association identifier reserved for stations not associated with the access point.

19. The method of Claim 2, 9, 17 or 18, wherein the uplink and downlink resource units are assigned to the same predefined association identifier reserved for stations not associated with the access point.

20. The method of Claim 1, 8, 17 or 18, wherein the association identifier reserved for stations not associated with the access point is an 11 -bit identifier equal to 2045.

21. The method of Claim 2, 9, 11 or 12, wherein the pluralities of uplink and downlink resource units belong to the same transmission opportunity granted to the access point.

22. The method of Claim 21, wherein the plurality of downlink resource units in the multi-user downlink transmission directly follows the plurality of uplink resource units comprised in the multi-user uplink transmission within the same transmission opportunity granted to the access point.

23. The method of Claim 21, wherein the plurality of uplink resource units comprised in the multi-user uplink transmission and the plurality of downlink resource units in the multi-user downlink transmission are separated by at least one third plurality of resource units provided for a multi-user uplink or downlink transmission within the same transmission opportunity granted to the access point.

24. The method of Claim 2, 9, 11 or 12, wherein the pluralities of uplink and downlink resource units belong to different transmission opportunities granted to the access point.

25. The method of Claim 1, 8, 11 or 12, wherein the resource units of each plurality are distributed in the frequency domain according to the respective allocation scheme.

26. The method of Claim 2, 9, 11 or 12, wherein the plurality of uplink resource units provided in the multi-user uplink transmission is triggered in the transmission opportunity by a trigger frame sent by the access point.

27. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device, causes the device to perform the method of Claim 1,8, 11 or 12.

28. A wireless communication device forming station in a wireless network comprising an access point and stations, any station associating with the access point is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, the device forming station comprising at least one microprocessor configured for carrying out the steps of:

29. A wireless communication device forming access point in a wireless network comprising an access point and stations, any station associating with the access point is assigned a unique association identifier used by the access point to assign, to the station, a resource unit in a transmission opportunity granted to the access point, the device forming access point comprising at least one microprocessor configured for carrying out the steps of:

building a plurality of downlink resource units in a multi-user downlink transmission from the access point within a transmission opportunity granted to the access point, the downlink plurality of resource units comprising a downlink resource unit assigned to an association identifier reserved for stations not associated with the access point; and sending a frame to a station on the downlink resource unit assigned to an association identifier reserved for stations not associated with the access point.

30. A wireless communication device forming station in a wireless network comprising an access point and stations, the device forming station comprising at least one microprocessor configured for carrying out the steps of:

sending a frame to the access point using an uplink resource unit of an plurality of uplink resource units provided in a multi-user uplink transmission towards the access point within a transmission opportunity granted to the access point, wherein the plurality of uplink resource units are distributed according to an allocation scheme;

31. A wireless communication device forming access point in a wireless network comprising an access point and stations, the device forming access point comprising at least one microprocessor configured for carrying out the steps of:

Intellectual

Property

Office

Application No: GB 1802907.4 Examiner: Mr Daniel Davies