GB2560589B - Improved access management to multi-user uplink random resource units by a plurality of BSSs - Google Patents

Description

IMPROVED ACCESS MANAGEMENT TO MULTI-USER UPLINK RANDOM RESOURCE UNITS BY A PLURALITY OF BSSs

FIELD OF THE INVENTION

The present invention relates generally to communication networks and more specifically to the sending of data over a communication channel which is split into sub-channels (or Resource Units) that are available to groups of stations associated with a respective plurality of network cells.

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 forinstance an 802.11 ax composite channel for Uplink communication.

BACKGROUND OF THE INVENTION

The IEEE (RTM) 802.11 MAC family of standards (a/b/g/n/ac/etc.) defines a way wireless local area networks (WLANs) must work at the physical and medium access control (MAC) level. Typically, the 802.11 MAC (Medium Access Control) operating mode implements the well-known 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 - registered trademark) officially approved the 802.11 ax task group, as the successor of 802.11ac. The primary goal of the 802.11 ax task group consists in seeking for an improvement in data speed to wireless communicating devices used in dense deployment scenarios.

In this context, multi-user (MU) transmission has been considered to allow multiple simultaneous transmissions to/from different users in both downlink (DL) and uplink (UL) directions, e.g., from an Access Point (AP) to non-AP stations or from non-AP stations to an AP. These simultaneous transmissions are operated during a transmission opportunity (TXOP) 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 actually perform such multi-user transmission, it has been proposed to split a granted communication channel into sub-channels, also referred to as resource units (RUs), that are shared in the frequency domain by multiple non-AP stations, based for instance on the Orthogonal Frequency Division Multiple Access (OFDMA) technique.

The above is introduced with respect to a single group of non-AP stations that is managed by the access point with which each non-AP station has previously registered. In the 802.11 standard, such a group of non-AP stations together with the access point is known as a

Basic Service Set (BSS). The access point acts as a master to control the non-AP stations within the BSS. The simplest BSS consists of one access point and one non-AP station.

Each BSS is uniquely identified by a specific basic service set identification, BSSID. For a BSS operating in infrastructure mode, i.e. non-AP stations communicate through the AP, the specific BSSID is usually a 48-bit MAC address of the access point. The specific BSSID is the formal name of the BSS and is always associated with only one BSS.

Together with the specific BSSID, each BSS has its own service set identification, SSID, which is usually a human readable identifier of the BSS.

In a BSS, non-AP stations usually contend for access to a communication medium as described above.

Recent developments provide that a single physical AP can operate as the master of a plurality of BSSs, i.e. of a plurality of independent groups of non-AP stations. This avoids using one physical AP per BSS or WLAN. It also makes it possible to use the same primary channel for all BSSs (i.e., the same channel for contending access), thereby avoiding channel interference problems.

Such operating scheme where a plurality of BSSs is managed by the same physical AP is performed through virtual access points (virtual APs or VAPs). A virtual AP is a logical entity that resides within a physical Access Point (AP). To a non-AP client station, the VAP appears as an independent access point with its own unique BSSID. To implement virtual APs, multiple BSSIDs are used with associated SSIDs. The BSSIDs for the VAPs in the physical AP are usually generated from a base BSSID specific to the underlying physical AP, usually the base MAC address of the AP.

The terms Virtual AP, specific BSSID, BSS and SSID can be used synonymously throughout this document, to designate a group or cell of non-AP stations managed by a physical AP. Depending on the context, “specific BSSID” and “own SSID” may further refer to the identifier of a BSS/WLAN, either through a MAC address (specific BSSID) or a human readable identifier (own SSID).

Providing a plurality of SSIDs (or BSS) corresponds to providing various different networks in a particular area. It may give access to different resources and present services which may have differing management or security policies applied. This advantageously allows various categories of users, e.g. staff, students or visitors etc. to be provided with network services which are appropriate to them.

In conventional 802.11 approaches, only one SSID (or BSS) is advertised per signaling message such as a beacon frame. As a consequence, multiple beacons are used to advertise the SSIDs corresponding to the virtual APs configured at the physical AP. This solution is compatible with most 802.11 stations and also allows the SSIDs to support different capability sets.

However, the higher the number of BSSs, the higher the transmission of signaling messages, and as a consequence the higherthe channel use. This downside is further increased when all client stations receive the signaling messages (that may be transmitted at a low bit rate, usually at the lowest supported data rate)

To improve this situation of increased channel use in case of multiple BSSs, the 802.11v Wireless Network Management specification defines a mechanism to advertise multiple security profiles including BSSID/SSID advertisements, with a single beacon frame.

However, the resulting network management is not satisfactory. In particular, the medium access for uplink communication through trigger frames using contention access is performed independently for each BSS and the support for multi-BSS Trigger frames is not provided.

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 UL MU random access procedure in a wireless communication system comprising several BSS groups.

According to the present invention, there is provided a wireless communication method in a wireless network comprising a physical access point and stations organized into a plurality of groups, each group being managed by a virtual access point implemented in the physical access point, and the method comprises the following steps, at a station belonging to a first group: obtaining a joint set of at least one random access parameter value representative of parameters values to be used in common by stations of the plurality of groups to contend for access to a random resource unit of a transmission opportunity reserved for the plurality of groups; obtaining an individual set of random access parameters values to be used by the station to contend for access to a random resource unit of a transmission opportunity reserved for stations of the first group; determining an update parameter using at least one parameter value of the joint set and at least one parameter value of the individual set of random access parameters values; receiving a trigger frame from the physical access point, the trigger frame reserving a transmission opportunity on at least one communication channel of the wireless network, the transmission opportunity including random resource units that stations may access using a contention scheme; contending for access to a random resource unit of the transmission opportunity reserved by the received trigger frame, wherein contending uses the update parameter when the transmission opportunity is reserved by the received trigger frame for the plurality of groups.

According to the present invention, there is also provided a station device in a wireless network comprising a physical access point and a plurality of stations organized into groups, each group being managed by a virtual access point implemented in the physical access point, and the station, belonging to a first group, comprises at least one microprocessor configured for carrying out the following steps: obtaining a joint set of at least one random access parameters values to be used in common by stations of the plurality of groups to contend for access to a random resource unit of a transmission opportunity reserved for the plurality of groups; obtaining an individual set of random access parameter value representative of parameters values to be used by the station to contend for access to a random resource unit of a transmission opportunity reserved for stations of the first group; determining an update parameter using at least one parameter value of the joint set and at least one parameter value of the individual set of random access parameters values; receiving a trigger frame from the physical access point, the trigger frame reserving a transmission opportunity on at least one communication channel of the wireless network, the transmission opportunity including random resource units that stations may access using a contention scheme; contending for access to a random resource unit of the transmission opportunity reserved by the received trigger frame, wherein contending uses the update parameter when the transmission opportunity is reserved by the received trigger frame for the plurality of groups.

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.

Figure 2 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 3 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.

Figures 4a, 4b and 4c present the format of a beacon frame according to the 802.11 standard, including the Information Elements representative of the RAPS set and the Multi-BSS configuration.

Figure 5 illustrates some exemplary situations of the aforementioned issues of trigger frames belonging to distinct BSS contexts.

Figure 6 shows a schematic representation a communication device in accordance with embodiments of the present invention.

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

Figure 8 illustrates an exemplary transmission block of a non-AP station according to embodiments of the invention.

Figures 9a and 9b illustrate, using flowcharts, an embodiment of the invention implemented, respectively, at a physical access point and at a non-AP station belonging to a first group of stations.

Figures 10a and 10b illustrate, using flowcharts, general steps of an AP emitting a beacon frame for multiple BSS, according to embodiments of the invention.

Figures 11a and 11b illustrate, using flowcharts, general steps of a non-AP station contending for access to a random resource unit, according to embodiments of the invention.

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 non-AP 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.

Access to the shared radio medium to send data frames is based on the CSMA/CA technique, for sensing the carrier and avoiding collision by separating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtual mechanisms. Virtual carrier sensing is achieved by transmitting control frames to reserve the medium prior to transmission of data frames.

Next, a source station, including the AP, first attempts through the physical mechanism, to sense a medium that has been idle for at least one DIFS (standing for DCF InterFrame Spacing) time period, before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during the DIFS period, the source station continues to wait until the radio medium becomes idle.

To access the medium, the source station starts a countdown backoff counter designed to expire after a number of timeslots, chosen randomly in a contention window range [0, CW], CW (integer) being also referred to as the Contention Window size and defining the upper boundary of the backoff selection interval (contention window range). This backoff mechanism or procedure is the basis of the collision avoidance mechanism that defers the transmission time for a random interval, thus reducing probability of collisions on the shared channel. After the backoff time period, the source station may send data or control frames if the medium is idle.

One problem of wireless data communications is that it is not possible for the source station to listen while sending, thus preventing the source station from detecting data corruption due to channel fading or interference or collision phenomena. A source station remains unaware of the corruption of the sent data frames and continues to transmit the frames unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positive acknowledgements (ACK) of the sent data frames by a receiving station if the frames are received with success, to notify the source station that no corruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame, immediately after a period of time called Short InterFrame Space (SIFS).

If the source station does not receive the ACK within a specified ACK timeout or detects the transmission of a different frame on the channel, it may infer data frame loss. In that case, it generally reschedules the frame transmission according to the above-mentioned backoff procedure.

The wireless communication system of Figure 1 comprises a physical access point 110 configured to manage one or more WLANs (or BSSs), i.e. one or more groups of non-AP stations. Each BSS is managed by a virtual AP implemented in the physical AP.

In the example shown, the physical AP implements two virtual APs, virtual AP VAP-1 (110A) having MAC address MAC1 as specific BSSID to manage a first WLAN (BSS), and virtual AP VAP-2 (11 OB) having MAC address MAC2 as specific BSSID to manage a second WLAN (BSS). Of course more WLANs can be implemented, requiring a corresponding number of virtual APs to be implemented in the physical AP.

All MAC addresses for the virtual APs are generated based on (or “derive from”) a base MAC address specific to the physical access point, usually the base 48-bit MAC address of AP 110. For instance MAC, (T being a BSS index) used as specific BSSID(i) for virtual AP, is generated as follows, from the base MAC address BASE_BSSID: MAC, = BSSID(i) = (BASE_BSSID modified to set the n LSBs to zero) | ((n LSBs of BASE_BSSID) + i) modulo 2") where LSB refers to the least significant bits, “n” is an AP parameter (integer) such that 2 to the power n (2n) is the maximum number of BSSIDs supported by the access point, and T operator is an XOR operator. The specific BSSIDs thus differ one from the other by their n LSBs. The 48-n MSBs of the generated specific BSSIDs are all similar to the corresponding bits of BASE_BSSID.

As an example, virtual AP VAP-1 provides a WLAN with “guest” as SSID that one or more non-AP stations can join, while virtual AP VAP-2 provides a WLAN with “Employee” as SSID that other non-AP stations can join simultaneously. The security scheme for each WLAN may be different, e.g. WEP and WPA. A same device can usually join two WLANs simultaneously if it has two separate WLAN interfaces (e.g. wifi network cards). In that case, the device is considered as two non-AP stations in the network, each non-AP station being able to join only one WLAN at a time.

Some control frames sent by the AP are an important part of 802.11, for instance beacon frames and probe response frames. The non-AP stations are waiting for these frames to know about the available WLANs or BSSs.

These frames let the non-AP stations know that an AP and one or more WLANs are available, but also notify the non-AP stations about important information such as the corresponding SSID or SSIDs, the corresponding specific BSSID or BSSIDs, the communication mode (Infrastructure or Ad-Hoc), the security schemes used (e.g. Open, WEP, WPA-PSK or 802.1X), the transmission rates used, the channel in operation and optional Information Elements (IE).

When multiple BSSs are provided, multiple beacon frames are transmitted by the AP, one for each active BSS, usually each 100ms. It results in that the non-AP stations have to process beacon frames more frequently and that channel occupation due to control frames is increased (being noted that the control frames such as the beacon frames are transmitted at low rate, i.e. with higher channel occupation).

These drawbacks can be reduced for example by increasing the beacon interval (more than 100ms) so that the beacon frame of each BSS is sent less frequently. However, this may cause some stations not to detect the beacon frame of a given BSS when scanning, and thus to consider that a particular BSS (through its SSID) is not available.

To improve this situation, the 802.11v Wireless Network Management specification provides a mechanism to advertise multiple security profiles including BSSID advertisements. Thus, a single beacon frame is sent rather than multiple beacon frames in order to advertise a plurality of specific BSSIDs/SSIDs. In this mechanism, a new Information Element (IE) is defined (Multiple BSSID IE) in the beacon frames sent by one or the other of the multiple virtual APs (i.e. specific BSSIDs).

The transmitter address of such a beacon frame includes the specific BSSID of the transmitting virtual AP. Furthermore, the Multiple BSSID IE indicates that multiple BSSs is contemplated and provides an indication of the maximum number of BSSs, parameter “n”, to the non-AP stations, as well as the common, inherited information element values of all of the BSSs (e.g. so that all members of the set use a common operating class, channel, channel access functions, etc.) and the unique information elements of each of the other BSSs indexed by their BSSID indexes ‘i’ (i.e. different advertised capabilities of the various BSSs, including ones from the BSS of the transmitting VAP).

As mentioned above, a BSSID index Ϊ is a value between 1 and 2n-1, which identifies the BSSID. It may also be noted that the AP may include two or more Multiple BSSID elements containing elements for a given BSSID index in one Beacon frame.

Such a multi-BSS beacon frame may also transmit the base MAC address BASEJ3SSID to the stations.

To meet the ever-increasing demand for faster wireless networks to support bandwidth-intensive applications, 802.11ac is targeting larger bandwidth transmission through multi-channel operations. Figure 2 illustrates 802.11ac channel allocation that support composite channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz. 802.11ac introduces 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 station on the wireless network to transmit data.

The predefined subsets are shown in Figure 2 and correspond to 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHz and 40 MHz supported by 802.11 n. Indeed, the 20 MHz component channels 200-1 to 200-8 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” (200-3). For each composite channel, 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 basic set, i.e. managed by or registered to the same access point.

However, to make sure that no other station belonging to another 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.

As addressed earlier, the 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. 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. 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 (200-1 to 200-4) into at least one sub-channel, but preferably a plurality 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 3.

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

In this example, each 20 MHz channel (200-1,200-2, 200-3 or 200-4) is sub-divided in frequency into four OFDMA sub-channels or RUs 310 of size 5MHz. Of course the number of RUs splitting a 20 MHz channel may be different from four. 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 greaterthan 20 MHz, when included in a wider composite channel (e.g. 80 MHz).

Contrary to downlink OFDMA wherein the AP can directly send multiple data to multiple non-AP stations (supported by specific indications inside the PLCP header), a trigger mechanism has been adopted forthe AP to trigger MU uplink communications from various non-AP 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 Network Allocation Vector field (NAV) and for 802.11ax client 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 3, the AP sends a trigger frame (TF) 330 to the targeted 802.11 ax stations to reserve a transmission opportunity. The bandwidth or width of the targeted composite channel forthe transmission opportunity is indicated in the TF frame, meaning that the 20, 40, 80 or 160 MHz value is given. The TF frame is a control frame, according to the 802.11 legacy non-HT format, 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 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 resource units (RUs) 310. The multi-user feature of OFDMA allows the AP to assign different RUs to different client stations in order to increase competition. This may help to reduce contention and collisions on 802.11 networks.

The trigger frame 330 may designate “Scheduled” RUs, which may be reserved by the AP for certain non-AP stations, in which case no contention for accessing such RUs is needed for these stations. Such RUs and their corresponding scheduled non-AP stations are indicated in the trigger frame. For instance, a station identifier, such as the Association ID (AID) assigned to each non-AP station upon registration, is added in association with each Scheduled RU in order to explicitly indicate the non-AP station that is allowed to use each Scheduled RU. Such transmission mode is concurrent to the conventional EDCA mechanism.

The trigger frame TF may also designate “Random” RUs, in addition or in replacement of the “Scheduled” RUs. The Random RUs can be randomly accessed by the non-AP stations of the BSS. In other words, Random RUs designated or allocated by the AP in the TF may serve as basis for contention between non-AP stations willing to access the communication medium for sending data. A collision occurs when two or more non-AP stations attempt to transmit at the same time over the same RU. An AID equal to 0 may be used to identify random RUs. A random access procedure may be considered for 802.11 ax standard based on an additional backoff counter (OFDMA backoff counter, OBO counter or RU backoff counter, as further illustrated as 800 in Figure 8) for RU contention by the 802.11 ax non-AP stations, i.e. to allow them for performing contention between them to access and send data over a Random RU. The RU backoff counter is distinct from the EDCA backoff counters (as illustrated as 811 in Figure 8). However data transmitted in an accessed OFDMA RUs 310 is assumed to be served from same EDCA traffic queues (as illustrated as 810 in Figure 8).

The metrics or parameters of the OFDMA-based RU random access mechanism (such as the RU contention window range, used to draw the RU backoff) are signaled by an AP through beacon frames in a new Information Element, called the RAPS element (RAPS stands for OFDMA-based Random Access Parameter Set). The format of the RAPS element is further defined in Figure 4c. A non-AP station uses the RAPS element provided by the AP to which it is associated with. The RAPS is introduced with respect to a single BSS group of stations that is managed by one access point with which each non-AP station has previously registered.

As one can note, a non-AP station 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 differing 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 3, it results from the various possible accesses to the RUs that some of them are not used (31 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 RUs have collided (310c) 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 RUs, while other RUs may remain free.

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

The MU Uplink (UL) medium access scheme, including both scheduled RUs and random RUs, proves to be very efficient compared to conventional EDCA access scheme, especially in dense environments as envisaged by the 802.11 ax standard. This is because the number of collisions generated by simultaneous medium access attempts and the overhead due to the medium access are both reduced.

As a result, the usage of a Trigger Frame is naturally extended to cover multiple BSS. The Trigger frame is directed to non-AP stations belonging to at least two different BSSs that the AP intends to communicate.

In addition, non-associated stations (that is to say non-AP stations not yet associated to an AP) can use the RU random access procedure in order to be allowed to transmit data to the AP in any randomly allocated resource unit. Aim is to support easy association procedure in dense environments. An AID equal to 2045 may be used to identify random RUs to be used by non-associated stations to transmit data to an AP.

As currently designed, the RU random access mechanism (including the RAPS settings and the RU backoff management) is specific to a single BSS, meaning that only the non-AP stations belonging to a specific BSS are provided guidance to access the resource units included in the transmission opportunity reserved by the trigger frame emitted for such BSS. For instance, some exemplary issues will be further provided in regards to Figure 5.

Figure 4a represents an example format of a beacon frame usable in a 802.11 type WLAN. The represented format is given for illustrative purposes and other formats may be used. The beacon frame is a management frame used by access points in an infrastructure BSS to communicate throughout the serviced area the characteristics of the connection offered to the BSS members. Information provided in the beacon frame may be used by client stations for joining the network as well as client stations already associated with the BSS. The beacon frame can also be used by stations in an independent BSS (IBSS), i.e. an ad-hoc network that contains no access points. As an example, some stations may act as a soft-AP (software implemented), that is to say implementing all the functionalities of an 802.11 Access Point but in an ad-hoc or transient connection mode, typically for a specific purpose (e.g., for sharing documents during a meeting or playing multiple-player computer games).

Beacon frame 430 contains 24 octets of MAC header (fields 401 to 406), 0 to 2312 octets of Frame Body 407, and 4 octets of Frame Check Sequence (FCS) 408. The MAC header includes the following fields: a frame control field 401 (to indicate that the frame is a management frame of beacon subtype), a duration field 402 (set to zero), a RA (Receiver or Destination Address) field 403 (set to broadcast value FF:FF:FF:FF:FF:FF), a TA (Transmitter or Source Address) field 404, a BSSID field 405, and a sequence control 406. The BSSID field contains the identification (ID) of the BSS, which may be the MAC address of the access point servicing the BSS, i.e. identical to the content of the TA field. The Frame Body is a field of variable length and consists of two sets of fields: 1) fields that are mandatory 410, followed by 2) optional fields in the form of Information Elements (lEs) 411.

Mandatory information in field 410 may contain: a Timestamp representing the time at the access point, which is the number of microseconds the AP has been active, and allowing synchronization between non-AP stations in a BSS; Beacon Interval representing the number of time units (TUs) between successive target beacon transmission times (TBTTs); and capability Info to indicate requested or advertised optional capabilities and Supported Rates fields.

All Information Elements in field 411 share a common general format consisting of 1 octet Element ID field, a 1 octet Length field, an optional 1 octet Element ID Extension field, and a variable-length element-specific Information field. Each information element is identified by the contents of the Element ID and, when present, Element ID Extension fields as defined in the 802.11 standard. The Length field specifies the number of octets following the Length field.

It is possible to address non-AP stations of a plurality of BSSs with a single beacon frame transmitted by one of the virtual APs of the physical AP, rather than multiple beacon frames transmitted by multiple virtual APs. The virtual AP transmitting the beacon frame (thus having its MAC address in the TA 404 and BSSID 405 fields) is referred to as representative AP or transmitted BSSID. The other virtual APs of the physical AP are referred to as non-representative APs or non-transmitted BSSIDs, as their addresses do not appear in the TA 404 and BSSID 405 fields of the beacon frame. A Multiple BSSID information element is defined in the single beacon frame to carry the common, inherited information element values of all of the BSSIDs and information elements specific to the non-representative APs. The BSSIDs of the non-representative APs can thus be derived from the Multiple BSSID information element.

Figure 4b represents an example format of a Multiple BSSID information element.

The multiple BSSID information element, referenced 411a, comprises a 1-byte MAX BSSID indicator field 420 and a variable length Optional Sub-elements field 421.

More than one multiple BSSID information element may be included in a beacon frame. The MAX BSSID Indicator field is ‘ri, where 2n is the maximum number of BSSIDs supported by the access point, including the representative BSSID.

Optional Sub-elements field 421 contains zero or more sub-elements in its Data field, such as for example the “non-representative BSSID profile” sub-element.

The “non-representative BSSID profile” may be identified by a sub-element ID of value 0, and shall include the SSID and multiple BSSID-index sub-elements for each of the supported BSSIDs. It may include the Capabilities field followed by a variable number of information elements.

The AP may include two or more Multiple BSSID elements containing elements for a given BSSID index in one beacon frame.

When a non-AP station receives a beacon frame with a Multiple BSSID element that comprises a non-representative BSSID profile with only the mandatory elements (Capability element, SSID and multiple BSSID-index), it may inherit the complete profile from a previously received beacon frame.

Figure 4c represents an example format of a RAPS Information Element. A RAPS information element is used by non-AP stations to configure their UL MU random access mechanism. The ElementJD, and optionally the Element ID Extension, identify the RAPS format. A typical parameter that may be included in the RAPS information element is the range of the OFDMA contention window 441 (OCW Range) for 802.11 ax stations willing to initiate random access following reception of a trigger frame for random access. Such a random access trigger frame is a trigger frame having at least one Random access RU, that is to say at least one RU associated with no station (the AID subfield of the User Info field forthe RU set to 0). As a result, non-associated STAs can also transmit on such random RU because they have no AID.

The OCW Range field 441 may include subfields EOCWmin and EOCWmax holding parameters to calculate the minimum (OCWmin) and the maximum (OCWmax) values of the OCW (OFDMA contention window), e.g. as follows: • OCWmin = 2EOCWmin - 1; and • OCWmax = 2EOCWmax - 1. OCWmin represents the minimum value of OCWforthe initial UL transmission using UL OFDMA-based random access to be used by a station for initial or successful transmission. OCWmax represents the maximum value of OCW for UL OFDMA-based random access used by a station for its retransmission attempts of UL OFDMA-based random access.

An AP includes the RAPS element in Beacon and Probe Response frames it transmits.

Figure 5 illustrates an exemplary situation in which embodiments of the invention can be implemented.

For the sake of illustration, the Trigger Frames considered in the following are all Trigger Frames offering at least one random RU.

In the approach of Figure 5, the wireless network comprising a physical access point 110 and a plurality of stations organized into groups or sets, each group being managed by a virtual access point (e.g. VAP-1 110A and VAP-2 11 OB as illustrated in Figure 1) implemented in the physical access point. The AP has emitted a beacon 430 repetitively, containing parameters of each individual BSS group.

The stations contend for an access to the wireless network, and the contention process at each station starts or restarts once 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 PPDU transmission).

The physical access point thus performs the step of sending a plurality of trigger frames 330-1, 330-2, 330-3 on the wireless network to reserve successive transmission opportunities on at least one communication channel of the wireless network, each transmission opportunity being reserved for a specific group of stations (BSS) and including resource units that form the communication channel and that the stations of the specific group access to transmit data.

Consequently, the physical access point receives, in response to each trigger frame and during the corresponding reserved transmission opportunity, data 310 from one or more stations of the group specific to the trigger frame.

The AP thus performs several TXOP reservations according to the number of BSSs it wants to poll. Each reserved TXOP is independent from one another, in particular because the stations not addressed by the trigger frame set their NAV to the Duration Field specified in the Trigger Frame 330, and thus waits for this duration.

As an example, the AP acts as a VAP-1 to emit a first TF 330-1, aiming at triggering stations of group BSS-1. Secondly, it acts as VAP-2 to emit a TF 330-2, aiming at triggering stations of group BSS-2. At any moment, the AP may emit a Trigger Frame for multiple BSS groups (TF 330-3), aiming at triggering stations of whole BSS groups managed by the AP. As a result of detecting TF 330-3, a station will contend for access to the random RUs using parameters (RAPS) chosen according to embodiments of the invention.

Random access parameters defined according to embodiments of the invention may also be used by non-associated (i.e. non-registered) stations, i.e. not yet belonging to a specific BSS group, when trying to contend for access to a random RU advertised by the trigger frame. In fact, these non-associated stations may try to access because they are not addressed by the trigger frames and their NAV is not set.

The present invention seeks to provide a more efficient usage of the UL MU random access procedure in case of multiple BSS groups.

The inventors have contemplated considering the multi-BSSID group as a distinct BSS group, in particular regarding the parameters of the UL MU random access procedure. To do so, they propose allowing the AP to disclose a RAPS profile (also referred to as context) for the multiple-BSSID case, to be used by non-AP stations (including the non-associated stations) when triggered for uplink communication by a Trigger Frame addressed to a multi-BSS group.

More generally, the inventors have contemplated that non-AP stations adopt a distinct behavior for the random access procedure according to the type of the Trigger Frame (single or multiple BSS).

Practically, the inventors disclose the determination of a unique OFDMA backoff counter for RU contention by the 802.11ax non-AP stations, to be used both when receiving a trigger frame with random RU for a single BSS (TF 330-1 or TF 330-2) and when receiving a trigger frame with random RU for multiple BSS groups (TF 330-3).

Various embodiments are proposed below that all relate to a wireless communication methods and related devices.

Figure 6 schematically illustrates a communication device 600, 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 600 may preferably be a device such as a micro-computer, a workstation or a light portable device. The communication device 600 comprises a communication bus 613 to which there are preferably connected: • a central processing unit 611, such as a microprocessor, denoted CPU; • a read only memory 607, denoted ROM, for storing computer programs for implementing the invention; • a random access memory 612, 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 602 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 612 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 612 under the control of a software application running in the CPU 611.

Optionally, the communication device 600 may also include the following components: • a data storage means 604 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; • a disk drive 605 for a disk 606, the disk drive being adapted to read data from the disk 606 or to write data onto said disk; • a screen 609 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 610 or any other pointing means.

The communication device 600 may be optionally connected to various peripherals, such as for example a digital camera 608, each being connected to an input/output card (not shown) so as to supply data to the communication device 600.

Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 600 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 600 directly or by means of another element of the communication device 600.

The disk 606 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 607, on the hard disk 604 or on a removable digital medium such as for example a disk 606 as described previously. According to an optional variant, the executable code of the programs can be received by means of the communication network 603, via the interface 602, in order to be stored in one of the storage means of the communication device 600, such as the hard disk 604, before being executed.

The central processing unit 611 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 604 or in the read only memory 607, are transferred into the random access memory 612, 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 7 is a block diagram schematically illustrating the architecture of the communication device 600, either the AP 110 or one of stations 101-107, adapted to carry out, at least partially, the invention. As illustrated, device 600 comprises a physical (PHY) layer block 703, a MAC layer block 702, and an application layer block 701.

The PHY layer block 703 (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 330 (Figure 3) to reserve a transmission slot, MAC data and management frames based on a 20 MHz width to interact with legacy 802.11 stations, as well as of MAC data frames of OFDMA type having smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/from that radio medium.

The MAC layer block or controller 702 preferably comprises a MAC 802.11 layer 704 implementing conventional 802.11 ax MAC operations, and additional blocks 705 and 706 for carrying out, at least partially, the invention. The MAC layer block 702 may optionally be implemented in software, which software is loaded into RAM 612 and executed by CPU 611.

Preferably, the additional block 705, referred to as multiple BSS management module for controlling access to random OFDMA resource units (sub-channels) in case of multiple BSSs, implements the part of embodiments of the invention that regards non-AP station and/or AP operations of device 600.

For instance and not exhaustively, the operations forthe AP may include generating and sending beacon frames as defined below, i.e. beacon frames identifying a plurality of groups, instead of a single BSS, including a specific group referencing several BSSs (multiple-BSS group) forming the whole network cell, and then managing the RAPS profile for random access of resource units during the reserved TXOP to such multiple-BSS group; the operations for a station different from the AP may include analyzing received beacon frames to determine if the station is allowed to access some resource units in the context the trigger frames allow several BSSs to communicate during the reserved TXOP.

Preferably, the additional block 706, referred as to OFDMA Medium Access module for configuring and updating the OFDMA-based UL MU random access procedure, implements the part of embodiments of the invention that regards non-AP station operations of device 600. MAC 802.11 layer 704, multiple BSS management module 705 and OFDMA Medium Access module 706 interact one with the other in order to process accurately communications over multiple BSS groups according to embodiments of the invention.

On top of the Figure, application layer block 701 runs an application that generates and receives data packets, for example data packets of a video stream. Application layer block 701 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 802.11 ax by considering OFDMA sub-channels and multiple BSS groups. Although the proposed examples use the trigger frame 330 (see Figure 3) sent by an AP for a multi-user uplink transmissions, equivalent mechanisms can be used in a centralized or in an ad-hoc environment (i.e. without an AP).

Although the present invention is also described with reference to beacon frame embodiments, the present invention is not limited to beacon frame modification but also any 802.11 management frame such as the probe response frames.

Also the invention is not limited to the 802.11 ax context.

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

Figure 8 illustrates an exemplary transmission block of a communication non-AP station 600 according to embodiments of the invention.

As mentioned above, the station includes an EDCA channel access module and possibly an OFDMA access module 706, both implemented in the MAC layer block 702. The EDCA channel access module includes: a plurality of traffic queues 810 for serving data traffic at different priorities; Usually, four Access Categories (ACs) are the following in decreasing priority order: voice (or “AC_VO”), video (or “AC_VI”), best effort (or “AC_BE”) and background (or“AC_BG”). a plurality of queue backoff engines 811, each associated with a respective traffic queue for using a set of EDCA parameters, in particular to compute a respective queue backoff value, to be used by an associated backoff counter to contend for access to at least one communication channel in order to transmit data stored in the respective traffic queue.

Since the traffic queues or ACs operate concurrently in accessing the wireless medium, it may happen that two traffic queues of the same communication station have their backoff ending simultaneously. In such a situation, a virtual collision handler (812) of the MAC controller operates a selection of the AC having the highest priority between the conflicting ACs, and gives up transmission of data frames from the ACs having lower priorities.

Service differentiation between the ACs is achieved by setting different queue backoff parameters between the ACs, such as different CWmin, CWmax, AIFSN and/or different transmission opportunity duration limits (TXOPJJmit). This contributes to adjusting QoS. This is the EDCA access scheme.

The OFDMA access module includes an OBO backoff engine 800 separate from the queue backoff engines, for using RU contention parameters, in particular to compute an RU backoff value, to be used by an RU backoff counter to contend for access to the OFDMA random resource units defined in a received TF (sent by the AP for instance), in order to transmit data stored in either traffic queue in an OFDMA RU. The OBO backoff engine 800 is associated with a transmission module, referred to as OFDMA muxer 801. For example OFDMA muxer 801 is in charge, when the RU backoff value described below reaches zero, of selecting data to be sent from the AC queues 810.

The conventional AC queue back-off registers 811 drive the medium access request along EDCA protocol (channel contention access scheme), while in parallel, the OBO backoff engine 800 drives the medium access request onto OFDMA multi-user protocol (MU UL contention access scheme).

As these two contention access schemes coexist, the non-AP station implements a medium access mechanism with collision avoidance based on a computation of backoff values: - a queue backoff countervalue corresponding to a number oftime-slots the station waits (in addition to an AIFS period), after the communication medium has been detected to be idle, before accessing the medium. This is EDCA; - an RU backoff counter value corresponding to a number of idle random RUs the station detects, after a TXOP has been granted to the AP or any other station over a composite channel formed of RUs, before accessing the medium.

The multiple BSS management module 705 aims at storing RAPS profiles for at least two BSS groups, and supports the configuration of OBO backoff engine 800 for controlling access to random OFDMA resource units (sub-channels) for a given BSS group. This procedure will be further detailed according to description of Figure 10.

Figure 9a illustrates, using a flowchart, a first embodiment of the invention implemented at a physical access point.

At step 900, the AP sends a joint set of random access parameters values (RAPS, called MBSS-RAPS) to be used in common by non-AP stations of the plurality of groups identified in a multi-BSS trigger frame (sent at step 902) to contend for access to a random resource unit included in the transmission opportunity. The joint set of parameters values may be transmitted by the physical AP according to different variants, among which: transmission in a beacon frame either as a dedicated information element (Multiple BSSID element) or a RAPS element containing the parameters values forthe representative BSSID.

At step 901, the AP sends an individual set of random access parameters values (RAPS) to be used by non-AP stations belonging to the group identified in a single-BSS trigger frame (sent at step 902) to contend for access to a random resource unit included in the transmission opportunity. The individual set of parameters values may be transmitted by the physical AP in a beacon frame as a RAPS element contained in the non-representative BSSID profile subelement 421.

In a preferred embodiment, the parameters values of the MBSS-RAPS are proportional with those of RAPS of a given individual BSS group. As an example, if a given BSS group holds 10 stations whereas 100 are registered among the overall plurality of groups, then the physical AP may apply a scaling contention, e.g., OCWmin of MBSS-RAPS (OCWmin_MBSS_RAPS) is ten time greater than OCWmin of a RAPS (OCWmin_RAPS).

At step 902, a trigger frame is sent by the AP for reserving a transmission opportunity on at least one communication channel of the wireless network. The transmission opportunity includes random resource units that the non-AP stations may access using a contention scheme. In other words, the trigger frame comprises associations between resource units and stations that may be used by the stations to transmit data during a transmission opportunity.

On the one hand, the trigger frame may be a “multi-BSS trigger frame” (e.g. 330-3) that identifies a plurality of groups, stations of which are allowed to contend for access to the random resources units included in the transmission opportunity to transmit data. Such multi-BSS trigger frame may have a TA field equal to the representative BSSID address, that is to say the address used to emit the beacon frame.

On the other hand, the trigger frame may be a “single-BSS trigger frame” identifying a single group, stations of which are allowed to contend for access to the random resources units included in the transmission opportunity to transmit data. In a preferred embodiment, such single-BSS trigger frame may have a TA field equal to any non-representative BSSID address. An AID equal to 2045 may be used in a single or multi-BSS trigger frame. In the multi-BSS context, non-associated stations may use the RAPS of the representative BSSID.

At step 903, and in response to the reception ofthe trigger frame by a non-AP station, the AP receives, over the random resource unit, data from a non-AP station of a single group, or from one of the plurality of groups identified in the trigger frame.

Figure 9b illustrates, using a flowchart, an embodiment of the invention implemented at a non-AP station belonging to a first group. The communication network further comprises at least one second group.

At step 910, a beacon frame is received from the physical access point.

At step 911, a joint set of random access parameters is obtained to be used in common by stations of the first and second groups to contend for access to a random resource unit included in the transmission opportunity. For obtaining the joint set of random access parameters, the station has to detect and analyze the beacon frame received at step 910, separate from the trigger frame, received from the physical access point. According to the example of Figure 9a, the joint set is located in the representative BSSID group of elements of the beacon frame.

At step 912, an individual set of random access parameters is obtained to be used only by stations of the first group to contend for access to a random resource unit included in the transmission opportunity. The station obtains the individual set of random access parameters by decoding the beacon frame(s), separate from the trigger frame, received from the physical access point. According to the example of Figure 10a, each individual set is located in a nonrepresentative BSSID group of elements of the beacon frame; and the station locates its own inside the group of elements corresponding to the BSS with which the station is associated.

At step 913, the station determines a relationship between RAPS to be used in common by non-AP stations (also previously called MBSS-RAPS), and RAPS to be used by stations belonging to the group to which that station belongs to, that is to say the first group. The station may compute a scale factor based on at least one parameter of the RAPS from the joint set (multiple BSS), and based on at least one parameter of the RAPS of the single BSS the station is associated with.

This scale factor may be representative of the adaptation to apply to individual parameters to mimic the effects that may be obtained using the joint parameters, and may be used by the algorithms of Figures 11a or 11b when the station receives a Trigger Frame (initially sent by the AP at step 902) for multiple BSSs.

In an embodiment, the scale factor may be a ratio between a parameter value of the joint set and a parameter value of the individual set, e.g., the OCWmin parameter. In that case, Rraps may be equal to Rraps = OCWmin_MBSS_RAPS I OCWmin_RAPS with OCWmin_MBSS_RAPS, an initial value for the contention window OCW to be used by non-AP stations belonging to the multiple BSS, and OCWmin_RAPS an initial value for the contention window OCW to be used by non-AP stations belonging to the considered group. As a matter of fact, OCWmin is representative of the number of contending stations of a given BSS, and may be determined by the AP in order to optimize the efficiency of the random access mechanism.

Alternatively, the scale factor may be determined using the OCWmax parameter (e.g., Rraps = OCWmax_MBSS_RAPS / OCWmax_RAPS) or any combination of OCWmin and OCWmax, e.g., (OCWmax_MBSS_RAPS + OCWmin_MBSS_RAPS) I (OCWmax_RAPS + OCWmin_RAPS) or (OCWmax_MBSS_RAPS - OCWmin_MBSS_RAPS) I (OCWmax_RAPS -OCWmin_RAPS).

Alternatively, the scale factor may be determined using the EOCWmax parameter or any combination of EOCWmin and EOCWmax.

Alternatively, the scale factor may be determined as a difference between a parameter value of the joint set and a parameter value of the individual set, e.g., the EOCWmin parameter. In that case, Rraps may be equal to Rraps= EOCWmin_MBSS_RAPS — EOCWmin_RAPS.

This scale factor may be used to update an OBO counter as a function of 2Rraps (2 to the power Rraps) as illustrated by step 1102 of Figures 11a and 11b. This alternative offers the advantage of being easy to implement since the computation of 2Rraps corresponds to a shift of Rraps bits of the value, which is a very simple and fast operation to perform by a CPU.

Preferably, the scale factor RRAPS is only computed by stations belonging to a nonrepresentative BSS. As a result, the scale factor equals “1” for stations belonging to a representative BSS.

In another embodiment, the physical access point does not send the individual set of random access parameters values (e.g., step 901 of Figure 9a is not applied). In that case, the station cannot obtain the individual set by analyzing the beacon frame, and the station uses a previously stored value of the parameter used for determining the scale factor. In case no value was previously stored, the scale factor may be set to “1”. Other configurations may lead to a scale factor value of “1”. This may be the case for a station registered with the representative BSSID group, since in that case OCWmin_RAPS equals OCWmin_MBSS_RAPS.

In another embodiment, the physical access point does not send the joint set of random access parameters values (e.g., step 900 of Figure 9a is not applied). In that case, the station cannot obtain the joint set by analyzing the beacon frame, and the station determines the joint set of random access parameters values as a function of received individual sets, e.g., EOCWmin_MBSS_RAPS = MAX(EOCWmin_RAPS[k], k=1, m) with m the number of BSSID processed by the physical AP and MAX the maximum value .

In case the scale factor is still determined as a difference between two parameters values, Rraps may be equal to RRAPs[i]= MAX(EOCWmin_RAPS[k], k=1, m) - EOCWmin_RAPS[i] with m the number of BSSID processed by the physical AP, i the index of the BSS in which the given non-AP station belongs to, and MAX the maximum value.

Let us consider the example of a first, second and third BSS (e.g., m=3) having respectively an EOWmin value of 3, 4 and 5. The scale factor Rraps of the first BSS equals MAX(3;4;5) - 3=2, the scale factor Rraps ofthe second BSS equals MAX(3;4;5) - 4=1, and the scale factor Rraps ofthe third BSS equals MAX(3;4;5) - 5=0.

In a variant, a function different from MAX may be considered, such as MEAN corresponding to a mean of values, or MIN corresponding to the selection of a minimum value.

In a variant, the joint set function of individual sets may be used in case the scale factor corresponds to a ratio between parameters values.

Going back to Figure 9, step 913 may alternatively be applied after detecting that the received trigger frame is a multi-BSS trigger frame (step 1101).

At step 914, the station contends for access to the random resource unit using the obtained individual set of random access parameters and the determined relationship. This step is further detailed by description of Figures 11 a and 11 b.

Figures 10a and 10b illustrate, through flowcharts, two embodiments in which the AP generates and provides RAPS profiles for non-AP stations of various BSSs. Similar steps have the same references.

These methods are typically implemented in an access point ofthe invention.

Initially, a list of RAPS profiles (each for a given BSS) is generated in addition to classical (e.g. security) profiles and SSIDs to be advertised (step 1000).

The profiles ofthe representative BSSID group are provided in list of IE 411 ofthe beacon frame body 407. The profiles of at least one non-representative BSSID group are provided through Multiple BSSID elements 411a to be appended later in list 411 ofthe beacon frame body 407 (step 1001).

In case only one BSS is supported by the AP (“No” to test 1002), the algorithm continues to step 1005 comprising formatting the beacon frame and later periodically emitting that beacon frame (step 1006).

If multi-BSS support is available (“yes” to test 1002), a dedicated RAPS profile corresponding to the plurality of groups of stations is added to the Beacon Frame (steps 1003 and 1004).

This dedicated RAPS profile or element (further identified as MBSS-RAPS) aims to be used by any non-AP station ofthe network for contending access during a TXOP reserved for a plurality of groups of stations (e.g. by means of Trigger Frame 330-3 of Figure 5) to upload data to the AP.

The OCW Range (441) forthe MBSS-RAPS may be adapted to the whole cell; for example by averaging various EOCWmin and EOCWmax values used for the different BSS groups. The AP may use any proprietary or internal consideration for determining these values, as for example the density of non-AP stations, measured contention or network load encountered in each individual BSS it manages.

The algorithm then continues to step 1005 comprising formatting the beacon frame and later periodically emitting that beacon frame (step 1006). That beacon frame corresponds to the one received by a non-AP station at step 910 of Fig 9b.

Preferably, the MBSS-RAPS (which format is compliant with 411b) is directly provided as an Information Element in the list 411 : for that purpose, values of ElementJD and ElementJD Extension fields are used to guarantee that the MBSS-RAPS element is distinct from RAPS elements already defined for individual BSSs.

Alternatively, the MBSS-RAPS is defined through a distinct Multiple BSSID element 411a, identifying that the concerned BSS is a multiple BSS. This new multiple BSSID information element would comprise the same MAX BSSID indicator value, but the MBSS-RAPS is conveyed inside a newly defined Non-Representative BSSID Profile corresponding to all (or at least several) BSSs. This Non-Representative BSSID Profile for MBSS-RAPS transmission can be identified by a Sub-element ID of value distinct from 0.

As a result, the AP has managed transmission to the non-AP stations of an additional RAPS profile, called the MBSS-RAPS profile, and dedicated to the multi-BSS Trigger Frame case.

Figure 10b illustrates an alternative method to provide the MBSS-RAPS profile.

In order to limit the number of RAPS elements provided into the beacon frame, the basic profile of the representative BSSID, e.g., of the representative AP, is selected as MBSS-RAPS profile, i.e. joint profile for the BSSs (step 1014). That is to say the RAPS profile to be used by non-AP stations is the RAPS profile of the representative BSSID, (e.g., the BSS identified by BSSID field 405). As a result, the RAPS profile (embedding the MBSS-RAPS values) is located in the list 411, before any Multiple BSSID element 411a of non-representative BSSIDs. Access to this profile requires less processing and is quicker.

Optionally, the computation of values forming the OCW Range may be different from previous scheme as the parameters are identical for Trigger Frames received in a single representative BSS and multi-BSS contexts (step 1013).

The approach of Figure 10b saves bandwidth space in management frames such as the beacon frames.

The alternative method of Figure 10b provides further advantages of using the RAPS profile from the representative BSSID as a default profile: consequently, low-end AP devices may, by simplicity, only consider this profile for Trigger Frames issued both from their non-representative BSSID context (with condition that no specific RAPS is provided in their nonrepresentative BSSID) and for their multi-BSS context. Those AP devices are considered as low-end AP devices because they are limited in their RAPS capabilities to adapt per BSS to changing conditions (like number of registered stations, contention, etc.).

Finally, the Beacon Frame is modified by the AP to identify a plurality of RAPS profiles allowed to be used for performing uplink OFDMA transmission in random RUs.

Any non-AP station that wants to know which RAPS profile it can access, thus has to: 1) read, within the received beacon frame, a plurality of per-BSS RAPS parameter sections 411b additional to legacy information elements (inside 421); this includes representative and non-representative BSSID groups; 2) for at least one per-BSS parameter section 420 defining a BSSID: - determine, based on one BSSID field included in the per-BSS parameter section (405 or inside 411 a), whether it is willing to join this BSS group, - store, based on the BSSID, the RAPS profile inside its module 705.

Next, as further described by Figures 11a and 11b, in case the non-AP station is authorized to access the one or more determined random resource units for a received Trigger Frame, it accesses the RAPS profiles to initiate the random access procedure applicable to the reserved transmission opportunity.

Figures 11a and 11b illustrate, using flowcharts, two embodiments ofthe invention in which a non-AP station 600 contends for access to a random resource unit.

At step 1100, station 600 receives a trigger frame from an Access Point. This trigger frame corresponds to the one transmitted at step 902 of Figure 9.

At step 1101, station 600 may analyze the received trigger frame at the MAC layer.

In particular, TA and RA fields are analyzed. The station checks whether the received trigger frame identifies one (and then defines a single BSS scheme) or a plurality of groups (and then defines a multiple BSS scheme), with which it is registered (or willing to register with). It consists in checking whether one of TA or RA defines a plurality of BSSs, e.g. a set of BSSIDs, or not, i.e. if it includes BASE_BSSID or any other multi-BSS address like the representative BSSID.

The OBO counter may then be updated according to different methods (steps 1102 or 1106), depending if the trigger frame identifies one or a plurality of groups, stations of which are allowed to access the resource units to transmit data.

Going back to step 1101, if no multiple BSS scheme is used or if the multi-BSS address does not encompass the specific BSSID of station 600 (e.g. does not match BASE_BSSID to which station 600 is registered), the legacy OFDMA random access procedure may be applied with the conventional RAPS profile associated with the BSSID the station 600 is associated with.

The legacy OFDMA random access procedure comprises a first step of determining, from the received trigger frame, the sub-channels or RUs ofthe communication medium available for contention (the so-called “random RUs”). The random RUs can be determined using for instance a predetermined AID associated with each RU defined in the TF. In particular, a RU having an AID equal to 0 may be accessed by all non-AP stations belonging to the BSS managed by the Access Point having transmitted the trigger frame at step 902, a RU having an AID equal to 2044 may be accessed by all non-AP stations not belonging to the BSS managed by the Access Point having transmitted the given trigger frame, and a RU having an AID equal to 2045 may be accessed by all non-associated stations of the communication network. Preferably, the AID equal to 2044 may only be transmitted by the representative AP.

So the number of random Resource Units supporting the random OFDMA contention scheme (NbRu) is known at this stage. Determining the number of random RUs after reception of a trigger frame may be advantageous since the number of random RUs may vary from one trigger frame to another.

The legacy OFDMA random access procedure comprises a second step of decrementing the RU backoff counter (OBO) by the number of random RUs (NbRu), e.g., OBO= OBO - NbRu (step 1106) before contending access to a random resource unit of the transmission opportunity reserved by the received trigger frame (step 1109 including steps 1104 to 1108), depending on the updated OBO value. At step 1103, it is determined if the updated OBO value is negative. If the OBO is negative, then the station (third step) is allowed to select an RU for transmission (step 1104). Otherwise, the OBO is already prepared to wait a further trigger frame for random access and the algorithm stops.

Going back to step 1101, if the multiple BSS scheme is used (e.g. the multi-BSS address encompasses the BASE_BSSID to which station 600 is registered, that is to say the TA field of the Trigger Frame contains the representative BSSID value), then step 1102 may be performed that considers the multi-BSS profile (MBSS-RAPS) for the random access procedure.

The RU backoff counter is updated using a second method different from the first method of step 1106. Station 600 is configured to decrement the RU backoff value OBO based on the number of random resource units NbRu defined in the received trigger frame, and based on the scale factor Rraps previously computed at the reception of a beacon frame (step 913 of Fig 9b), e.g., OBO= OBO — NbRu I Rraps.

Optionally, the “NbRu I Rraps” value may be rounded down before decrementing it from the OBO.

This second method is adapted to the new context of contention (the entire plurality of groups managed by the physical AP). As the Rraps aims at reflecting the contention scaling between two BSSs (a single and the multi), then the OBO may handle that proportion.

Optionally, before the decrement operation, the OBO value can be checked against the OCWmax of the RAPS from the joint set (multiple BSS). In this optional case, if OBO* Rraps, is higherthan the OCWmax value of the RAPS from the joint set, the OBO can be limited to OBO= OCWmax / Rraps. This optional step prevents stations having a high OCWmax value in their own BSS, to be penalized in the context of the multiple BSS random access.

This scheme allows stations of various groups having accessing a random RU with the same fairness in between each other individual groups, and also in between stations pertaining to the representative BSS group.

Advantageously, the station may only manage one RU backoff counter (OBO), the value of which evolves depending on the type of trigger frame received (from its single BSS group or from the multiple-BSS joint set).

At the start-up of the system, the OBO value may be preferably initialized as equal to the value of OCWmin_RAPS (related to the single-BSS context). In that case, the OBO value to update is related to the single-BSS context, although the received trigger frame is a multi-BSS trigger frame.

At step 1103, it may be determined if the updated OBO value is negative. In case the OBO is still positive (and considered as not expired), the given station 600 is not eligible, and the process ends.

Otherwise, step 1104 may be executed to determine the RU the station can access through contention. The determined RU is randomly selected among the available random RUs of the trigger frame received at step 1100.

Next to step 1104, step 1105 may be performed during which station 600 accesses the RUs determined at step 1104 and transmits its trigger-based PPDU in uplink direction to the AP. Such data corresponds to the one received at step 903 of Fig 9a.

As commonly known, the AP sends an acknowledgment related to each received MPDU from multiple users inside the OFDMA TXOP, so that the non-AP station 600 may update its OCW contention value accordingly. It has to be noted that the OCW is always updated through the individual parameter set of the BSS group to which the non-AP station is associated (and not with the joint set of parameters).

Step 1106 may be executed when the UL OFDMA transmission finishes on an accessed random RU, upon having the status of transmission; either by receiving a positive or negative acknowledgment from the AP.

In case of successful OFDMA transmission on the selected random RU, OCW may be set to a (predetermined) low boundary value, for instance OCWmin of the RAPS of the station’s BSS, at step 1107.

In case of failing OFDMA transmission, OCW may be increased, for instance OCW = 2 * (OCW + 1) - 1, at step 1108. Preferably, OCW cannot be above OCWmax of the RAPS of the station’s BSS.

In a variant, the RU backoff counter may be updated at step 1102 so that OBO = OBO - Nbru * 2Rraps. This variant is particularly relevant when the scale factor corresponds to a difference of parameters, e.g., Rraps= EOCWmin_MBSS_RAPS - EOCWmin_RAPS. Optionally, according to that variant, the OBO value may then be checked against the OCWmax of the RAPS from the joint set (multiple BSS) before step 1102. In that case, if OBO * 2Rraps is higher than the OCWmax of the RAPS from the joint set, the OBO can be limited to OBO=OCWmax * 2_Rraps. This optional step prevents stations having a high OCWmax value in their own BSS, to be penalized in the context of the multiple BSS random access.

Figure 11b illustrates, using a flowchart, another embodiment ofthe invention in which a non-AP station 600 contends for access to a random resource unit. Similar steps have the same references.

At step 1100, station 600 receives a trigger frame from an Access Point. This trigger frame corresponds to the one transmitted at step 902 of Figure 9.

At step 1101, station 600 may analyze the received trigger frame at the MAC layer.

The OBO value may then be updated according to different methods, depending if the trigger frame identifies one or a plurality of groups, stations of which are allowed to access the resource units to transmit data.

If no multiple BSS scheme is used or if the multi-BSS address does not encompass the specific BSSID of station 600 (e.g. does not match BASE_BSSID to which station 600 is registered), step 1133 may be implemented which consists in determining if the OBO value local to the considered station is inferior or equal to a first threshold that may be equal to the number of detected-as-available random RUs. In case of successful verification, the OBO value is set to 0 (step 1122). Then, at step 1109, a RU is randomly selected among the detected-as-available RUs and data is transmitted inside the selected RU (steps 1104 to 1108).

If the OBO value is greater than the first threshold, the RU backoff counter (OBO) is updated according to a first method (step 1106). Preferably, the OBO value is decremented by the number of detected-as-available random RUs, e.g., OBO= OBO - NbRu, with NbRu the number of detected-as-available random RUs.

Going back to step 1101, if the multiple BSS scheme is used, then step 1123 is performed that determines if the OBO value is inferior or equal to a second threshold that may be equal to NbRu I Rraps. In case of successful verification, the RU backoff counter is set to 0 (step 1122). Then, at step 1109, a RU is randomly selected among the detected-as-available RUs and data is transmitted inside the selected RU (steps 1104 to 1108).

If the OBO value is greater than the threshold, the RU backoff counter (OBO) is updated according to a second method (1102). Station 600 may be configured to decrement the RU backoff value OBO based on the number NbRu of random resource units defined in the received trigger frame, and based on the scale factor Rraps previously computed at the reception of a beacon (step 913 of Fig 9b), e.g., OBO= OBO - NbRu I Rraps.

Optionally, the “NbRu I Rraps” value may be rounded down before decrementing it from the OBO.

In a variant, it may be determined if the OBO value is inferior or equal to a second threshold equal to Nbru * 2Rraps (step 1123). This variant is particularly relevant when the scale factor corresponds to a difference of parameters, e.g., Rraps= EOCWmin_MBSS_RAPS -EOCWmin_RAPS. If the OBO value is greater than that second threshold, the OBO value may be updated so that OBO = OBO - Nbru * 2Rraps. Optionally, according to that variant, the OBO value may be checked against the OCWmax of the RAPS from the joint set (multiple BSS) before step 1102. In that case, if OBO * 2Rraps is higher than the OCWmax of the RAPS from the joint set, the OBO can be limited to OBO=OCWmax * 2 - RraPs This optional step prevents stations having a high OCWmax value in their own BSS, to be penalized in the context of the multiple BSS random access.

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.

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 (19)

1. A wireless communication method in a wireless network comprising a physical access point and stations organized into a plurality of groups, each group being managed by a virtual access point implemented in the physical access point, the method comprising the following steps, at a station belonging to a first group: obtaining a joint set of at least one random access parameter value representative of parameters values to be used in common by stations of the plurality of groups to contend for access to a random resource unit of a transmission opportunity reserved for the plurality of groups; obtaining an individual set of random access parameters values to be used by the station to contend for access to a random resource unit of a transmission opportunity reserved for stations of the first group; determining an update parameter using at least one parameter value of the joint set and at least one parameter value of the individual set of random access parameters values; receiving a trigger frame from the physical access point, the trigger frame reserving a transmission opportunity on at least one communication channel of the wireless network, the transmission opportunity including random resource units that stations may access using a contention scheme; contending for access to a random resource unit of the transmission opportunity reserved by the received trigger frame, wherein contending uses the update parameter when the transmission opportunity is reserved by the received trigger frame for the plurality of groups.

2. The wireless communication method of Claim 1, wherein the update parameter comprises a scale factor defined as a ratio between a parameter value of the joint set and a parameter value of the individual set of random access parameters values.

3. The wireless communication method of Claim 1, wherein the update parameter comprises a scale factor defined as a difference between a parameter value of the joint set and a parameter value of the individual set of random access parameters values.

4. The wireless communication method of Claim 1, wherein at least one of the joint set and the individual set of random access parameters values are obtained by analyzing a received beacon frame sent by the physical access point.

5. The wireless communication method of Claim 1, wherein obtaining a joint set of at least one random access parameter value comprises determining a parameter value as a function of a plurality of individual sets of random access parameters values, each individual set of the plurality being associated to a group of stations.

6. The wireless communication method of Claim 1, further comprising handling one value of a backoff counter and one value of a contention window by the station to both manage contending for access to the random resource unit of stations belonging to the first group, and of stations belonging to the plurality of groups.

7. The wireless communication method of Claim 6, further comprising: determining if the received trigger frame specifically identifies the first group, or the plurality of groups; comparing the backoff counter value to a threshold, the threshold depending on the group or groups identified in the received trigger frame; and, determining if the station is allowed or not to access the random resource unit, depending on the result of the comparison.

8. The wireless communication method of Claim 7, wherein the comparing step comprises: updating the backoff counter value, depending on the group or groups identified in the trigger frame; and, determining if the updated backoff counter value is negative or null.

9. The wireless communication method of Claim 7, wherein if the backoff counter value is inferior or equal to the threshold, the method further comprises updating the backoff counter value, the update depending on the group or groups identified in the trigger frame.

10. The wireless communication method of Claim 8 or 9, wherein if the received trigger frame specifically identifies the first group, the updating step comprises subtracting a number of resource units available for contention from the backoff counter value.

11. The wireless communication method of Claim 8 or 9, wherein if the received trigger frame identifies the plurality of groups, the updating step comprises subtracting from the backoff counter value a number of resource units available for contention weighted by a function of the scale factor.

12. The wireless communication method of Claim 11, wherein the function of the scale factor is a two to the power of the scale factor function.

13. The wireless communication method of Claim 7, wherein if the received trigger frame specifically identifies the first group, the comparing step comprises determining if the backoff counter value is inferior or equal to a number of resource units available for contention.

14. The wireless communication method of Claim 7, wherein if the received trigger frame specifically identifies the plurality of groups, the comparing step comprises determining if the backoff counter value is inferior or equal to a number of resource units available for contention weighted by a function of the scale factor.

15. The wireless communication method of Claim 14, wherein the function of the scale factor is a two to the power of the scale factor function.

16. The wireless communication method of Claim 7, wherein if the station is allowed to access the random resource unit, the method further comprises: randomly selecting a resource unit among the available resource units, and transmitting data to the physical access point over the randomly selected resource unit.

17. The wireless communication method of Claim 16, further comprising: obtaining a transmission status in response to transmission of data; if transmission is successful, setting value of a contention window to a minimum value and if transmission is not successful, increasing value of the contention window.

18. A station device in a wireless network comprising a physical access point and a plurality of stations organized into groups, each group being managed by a virtual access point implemented in the physical access point, the station, belonging to a first group, comprising at least one microprocessor configured for carrying out the following steps: obtaining a joint set of at least one random access parameters values to be used in common by stations of the plurality of groups to contend for access to a random resource unit of a transmission opportunity reserved for the plurality of groups; obtaining an individual set of random access parameter value representative of parameters values to be used by the station to contend for access to a random resource unit of a transmission opportunity reserved for stations of the first group; determining an update parameter using at least one parameter value of the joint set and at least one parameter value of the individual set of random access parameters values; receiving a trigger frame from the physical access point, the trigger frame reserving a transmission opportunity on at least one communication channel of the wireless network, the transmission opportunity including random resource units that stations may access using a contention scheme; contending for access to a random resource unit of the transmission opportunity reserved by the received trigger frame, wherein contending uses the update parameter when the transmission opportunity is reserved by the received trigger frame for the plurality of groups.

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