GB2584886A - Adjustable range of aids allowed for random access in short feedback procedures in wireless networks - Google Patents

Abstract

A random access mechanism for short feedback procedure where an AP keeps control on the number of stations competing for random access. The AP provides a NFRP trigger frame (Null Data Packet Feedback Report Poll) wherein an access type indication defines whether tone sets are accessed on a random basis, and a range scaling field defining a scale factor to design the range of AIDs authorized to compete. A non-AP station uses the access type indication to detect random access scheme and then use the scale factor to obtain, from a conventional range of AIDs, an extended polling range of station AIDs authorized to access the tone sets on a random basis. If the station determines its AID belongs to the polling range, it randomly selects one tone set to send a NDP (Null Data Packet) feedback report response. The AP can adjust the scale factor depending on network statistics to mirror a level of contention. A Range Scaling of Zero may indicate scheduled access, while Range Scaling of Non-Zero may indicate random access. The second range may be the first range multiplied by the range scaling factor. The first range may be the number of available RU tone sets.

Description

ADJUSTABLE RANGE OF AIDS ALLOWED FOR RANDOM ACCESS IN SHORT FEEDBACK PROCEDURES IN WIRELESS NETWORKS

FIELD OF THE INVENTION

The present invention relates generally to communication networks and more specifically to wireless communication methods in a wireless network and corresponding communication devices, such as an access point (AP) and non-AP stations.

BACKGROUND OF THE INVENTION

The IEEE 802.11 (RTM) family of standards provides multi-user (MU) schemes to allow a single access point (AP) to schedule MU transmissions, i.e. multiple simultaneous transmissions to or from non-AP stations or "nodes", in the wireless network. This approach increases bandwidth and decreases latency requirements compared to original 802.11 networks.

MU downlink (DL) transmission is allowed where the AP performs multiple simultaneous elementary transmissions, over so-called resource units (RUs), to various non-AP stations. As an example, the resource units split a communication channel of the wireless network in the frequency domain, based for instance on Orthogonal Frequency Division Multiple Access (OFDMA) technique.

MU uplink (UL) transmissions are also allowed that are triggered by the AP. Various non-AP stations can simultaneously transmit to the AP over the resource units forming the MU UL transmission. To control the MU UL transmission by the non-AP stations, the AP sends a control frame, known as a Trigger Frame (TF), which defines a plurality of resource units for the non-AP stations.

Various variants of trigger frames exist depending on the nature of information the non-AP stations can provide in response. The main variant is the basic trigger frame for the non-AP stations to send any data they wish.

Some RUs may be allocated in a basic trigger frame to specific non-AP stations using 16-bit Association IDentifiers (AIDs) assigned to them upon registration to the AP (so-called scheduled RUs).

Others RUs (known as random RUs) are available to the non-AP stations using a contention-based access scheme. Only three types of trigger frames are known that provide such random access to RUs, namely the Basic Trigger frame, the BQRP Trigger frame and the BSRP Trigger frame. This scheme is known as UL OFDMA-based random access (UORA) scheme.

UORA is useful for wireless networks because it provides opportunities for the non-AP stations to transmit, without the AP having polled them to know their needs for transmission. However, it suffers from various drawbacks.

It suffers from a low maximum efficiency of 37% (successfully used random RUs) to be compared to 37% of unused random RUs and 26% of random RUs with collisions.

The lost random RUs (either unused or collided) occur on large transmission durations (because transmitting non-AP stations have usually substantial amounts of data to transmit during UORA). This substantially decreases network efficiency.

Also, the handling of the contention-based access scheme by the non-AP stations is complex because congestion parameters have to be properly managed by the non-AP stations.

For instance, in multi-BSS environments, the non-AP station should adapt its congestion parameters each time it communicates with a different BSS.

And, it is not possible to adapt the contention per non-AP station or group of non-AP stations, in particular to implement a priority mechanism between the non-AP stations, or to adapt (or tune) the contention over time, for instance when the congestion conditions change quickly.

Usually, congestion parameters for all the non-AP stations, that control the congestion and collision rate, are only pushed occasionally by a beacon frame or provided once at the early registration stage.

There is a need to improve this situation, in particular forthe AP to have better control on congestion when proposing random access to some channel resources.

A variant trigger frame to the basic trigger frame is the Null-Data-Packet (NDP) Feedback Report Poll (NFRP) trigger frame implementing the so-called Null-Data-Packet (NDP) Feedback Report procedure. This procedure allows the AP to collect feedback that is not channel sounding from multiple non-AP stations in a more efficient manner than with a basic trigger frame.

The AP sends a NFRP Trigger frame to solicit NDP feedback report responses from many non-AP stations that are identified by a range of scheduled AIDS in the NFRP Trigger frame. The NDP feedback report response from a non-AP station is a HE trigger-based (TB) feedback NDP. The procedure is shod compared to the duration of an UL transmission triggered by a basic Trigger frame, mainly because the NDP in response is short. It also has a low and stable latency compared to conventional "Carrier Sense Multiple Access with Collision Avoidance" CSMA-CA mechanisms when used in dense environments.

However, the NDP Feedback Report procedure also suffers from some limitations. For instance, it can address a limited set of (usually 18 or 36 for a 20Mhz wide operating band) continuous AIDS which may be punctured (some AIDs may not be assigned to non-AP stations or have been released when non-AP stations leave the AP during the lifetime of the network). The limited continuous set of AIDS is not adapted to the gathering of feedback responses from a high number of non-AP stations, i.e. per BSS basis. Furthermore, the AP has limited control on the range, only deciding a starting AID for the range.

SUMMARY OF INVENTION

The present invention seeks to overcome some of the foregoing concems.

In this context, the invention provides a communication method in a wireless network, comprising the following steps at a (non-AP) station: receiving, from an access point, AP, a null data packet, NDP, feedback report poll, NFRP, trigger frame, the NFRP trigger frame defining a first range of association identifiers, AIDS, of stations authorized to access a plurality of resource unit, RU, tone sets for NDP feedback report responses, determining, from the NFRP trigger frame, an access scheme to the RU tone sets, when it is determined a random access to the RU tone sets, obtaining a scale factor from a range scaling field in the NFRP trigger frame, obtaining a second range of station AIDS from the first range and the scale factor, when an AID of the station is included in the second range, randomly selecting a responding RU tone set from the plurality of RU tone sets, and sending a NDP feedback report response on the selected responding RU tone set. Correspondingly, the invention provides a communication method in a wireless network, comprising the following steps at an access point: sending, to (non-AP) stations, a null data packet, NDP, feedback report poll, NFRP, trigger frame, the NFRP trigger frame defining a first range of association identifiers, AIDS, of stations authorized to access a plurality of resource unit, RU, tone sets for NDP feedback report responses, wherein the NFRP trigger frame further includes an access type indication defining whether the RU tone sets are accessed on a random basis by the stations, and a range scaling field defining a scale factor to obtain, from the first range, a second range of AlDs of stations authorized to access the plurality of RU tone sets on the random basis, and receiving, from at least one responding station having an AID in the second range, a NDP feedback report response on a responding RU tone set.

Consequently, the invention provides a short random access procedure for the stations where the AP has control on the number of addressed stations. The AP can then optimize network efficiency for random access. This is achieved by adjusting the scale factor using the range scaling field, e.g. to current network conditions. For instance, the AP may appropriately adjust a ratio between the number of stations attending to access one of RU tone sets on a random basis and the number of RU tone sets reserved by the AP For illustrative purposes, the AP may have currently assigned only 20 AIDS to stations in the range of AIDS [45,80], where few stations have an AID in punctured subrange [45,62] and the majority of stations have an AID in subrange [63,80]. With the invention, for a NDP Feedback Report procedure, the AP may provide 18 RU tone sets (or any other number) for random access and allow a higher number of AIDS, for instance 36 in the range from 45 to 80, to access them. All the stations of the range (i.e. the 20 stations) will contend to access one of random access RU tone sets, which appear satisfactory usage of the RU tone sets. In sharp contrast, the known techniques can only address 18 stations of the range [45,62], thereby allowing few stations to use the RU tone sets. A number of such RU tone sets will remain unused, thereby drastically reducing network efficiency.

The present invention also allows the current 802.11ax formats to be kept.

Correlatively, the invention also provides a communication device, either the AP or a non-AP station, comprising at least one microprocessor configured for carrying out the steps of any of the above methods.

Optional features of embodiments of the invention are defined in the appended claims. Some of these features are explained here below with reference to a method, while they can be transposed into device features.

In some embodiments, determining an access scheme is based on a trigger type field in the NFRP trigger frame. This option advantageously keeps retro-compatibility with legacy stations that will ignore the new type of trigger frame, or a feedback type field in the NFRP trigger frame. This option advantageously makes it possible to keep the current version of the NFRP trigger frame, or a value of the range scaling field in the NFRP trigger frame. This option also makes it possible to keep the current version of the NFRP trigger frame and existing feedback types. Correspondingly, from AP perspective, the access type indication is provided with a specific value in a trigger type field or a feedback type field or the range scaling field in the NFRP trigger frame.

In some embodiments where the range scaling field is used to signal the access scheme, a zero value in the range scaling field defines a scheduled access to the RU tone sets and a non-zero value in the range scaling field defines a random access to the RU tone sets. It means that the range scaling field conveys the access type indication. Of course, another value of the field could be used as a variant, for instance the highest possible value (given the number

of bits forming the field).

In some embodiments, an access type indication defining an access scheme to the RU tone sets is separate from a Starting AID field defining the first AID of the first range.

In some embodiments, the scale factor equals 2RA-SF, where RA_SF is a value of the range scaling field. This simplifies the computation of the scale factor for the stations. In addition, the particular zero value provides a scale factor of 1 (2°) which can be easily exploited as an access type indication for scheduled access to the RU tone sets. Of course, other functions or correspondence schemes between RA_SF and the scale factor may be provided, for instance using correspondence tables.

In some embodiments, the second range corresponds to the first range rescaled by the scale factor. This means the range width (or size) is rescaled by the factor. For instance, the second range has the same starting AID as the first range with a range width multiplied by the scale factor. This makes it possible to keep the current meaning of fields in the NFRP trigger frames, while providing an easy-implemented computation process.

Preferably, the range scaling field is a two-bit or three-bit field. This allows 4 or 8 rescaling levels to be defined for AID range adjustment, or 3 or 7 rescaling levels if one value (e.g. zero value) is kept to signal the random access scheme. These options reduce the amount of bits to be processed. For illustrative purposes, a scale factor computed with a power of two makes it possible with 7 rescaling levels (i.e. only 3 bits) to provide a second range covering all the assignable AIDs for a mere 20MHz channel (18 x 27 = 2304 > 2007 assignable AIDs). A two-bit range scaling field may be enough when the first range (and thus the number of RU tone sets) comprises a higher number of AIDs (for wider channels with or without MIMO). For instance, an 80MHz channel with MIMO provides 144 RU tone sets. 4 rescaling levels may thus provide a second range covering all the assignable AIDs (144 x 24 = 2304 > 2007 assignable AIDS). It turns that a bit length of the range scaling field may depend on a width the first range (i.e. depend on a channel bandwidth field "UL mike' and a multiplexing flag field specified in the NFRP trigger frame).

Of course, other bit lengths may be used to provide a higher number of rescaling levels.

In some embodiments, the range scaling field is included in a Reserved field of a User Info field of the NFRP trigger frame according to Draft 4.1 of IEEE 802.11ax. This approach keeps retro-compatibility because it keeps unchanged the other fields currently used.

In a variant, the range scaling field is included in a Trigger Dependent Common Info field of a Common Info field of the NFRP trigger frame according to Draft 4.1 of IEEE 802.11ax.

In some embodiments, the responding station has an AID outside the first range. This shows benefits of the rescaling of the present invention, as the AP now receives NDP responses from stations that would not be scheduled using conventional NFRP techniques.

In some embodiments, the method further comprises determining the NDP feedback report response to be sent depending on a feedback type field in the NFRP trigger frame. This allows the responding station to appropriately use the tones in the randomly selected RU tone set.

In some embodiments, the first range includes the same number of AIDS as the number of RU tone sets in the plurality. This may advantageously correspond to the conventional signaling in a NFRP trigger frame itself. For instance, the first range is (determined from) defined by fields in the NFRP trigger frame, including a starting AID field, a channel bandwidth field and a multiplexing flag field. All these fields are those defined in Draft 4.1 of IEEE 802.11ax.

In some embodiments, the method further comprises, when it is determined a scheduled access to the RU tone sets, selecting a responding RU tone set from the plurality of RU tone sets based on the position of an AID of the station within the first range. The station is thus able to respond to the NFRP trigger frame for both access schemes, scheduled or random, to the RU tone sets.

In some embodiments, the method may further comprise, at the station: receiving, from the AP, a subsequent trigger frame reserving a plurality of resource units, wherein a resource unit is assigned to the station based on an index of the responding RU tone set, responsive to the subsequent trigger frame, sending a trigger-based PPDU response on the assigned resource unit.

Correspondingly, the method may further comprise sending by the AP a subsequent trigger frame reserving a plurality of resource units, wherein a resource unit is assigned to the responding station using an index of the responding RU tone set. Up to nine responding stations may be targeted in the subsequent trigger frame per 20MHz channel.

In this approach, the random access by the stations is moved from the conventional basic trigger frame to the NFRP trigger frame. It advantageously reduces the impact of unused random resource units on network efficiency because unused random resource units are lost for a shorter duration. The subsequent trigger frame assigns the RUs to specific stations that reported they have a need (i.e. not random RUs), thereby avoiding unused resource units for longer durations as in the known techniques.

In some embodiments, randomly selecting a responding RU tone set is based on a contention-based access method using a decrementing NFRP backoff, NBO, counter of the station. Use of NFRP backoff counters by the stations allows contention policy to be dynamically adjusted. The NFRP backoff counter may be a new backoff counter or an already existing 802.11ax backoff counter, for instance the OFDMA backoff counter or OBO counter.

In specific embodiments, if the NBO counter is not greater than a number of RU tone sets in the NFRP trigger frame, the station randomly selects one of the RU tone sets (and may set the NBO counter to zero), otherwise the station decrements the NBO counter by the number of RU tone sets in the Trigger frame. This may be repeated upon receiving each of successive NFRP trigger frames. Advantageously, this approach dynamically regulates the random access to the RU tone sets between the various stations.

In specific embodiments implementing NBO counter when a subsequent trigger frame is received, the method may further comprise, at the station, determining whether an acknowledgment of the trigger-based PPDU response is received from the AP, and in case of successful trigger-based PPDU response transmission, setting a NFRP contention window, NCW, to a predefined value, and initializing the NBO counter to an integer value randomly selected from a uniform distribution in the range 0 to NCW, and in case of unsuccessful trigger-based PPDU response transmission, updating the NCW to 2 x NCW + 1 when NCW is less than a predefined maximum value, and randomly selecting the NBO counter in the range of 0 and NCW.

Again, this approach dynamically regulates the random access to the RU tone sets between the various stations.

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 communication device, causes the communication 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 communication methods and devices.

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

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. 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 communication system in which embodiments of the invention may be implemented; Figure 2 illustrates two usages of trigger frames; Figures 2a and 2b illustrate, using flowcharts, corresponding general steps at the access point and at a non-AP station, respectively; Figure 3a illustrates the format of a trigger frame, in particular of NFRP type; Figure 3b illustrates the format of TB NDP PPDU; Figure 4 shows a schematic representation a communication device in accordance with embodiments of the present invention; Figure 5 schematically illustrates functional blocks of a communication device in accordance with embodiments of the present invention; Figure 6 illustrates, using the same scenario as Figure 2, some embodiments of the invention providing random access to the RU tone sets during the NDP short feedback report procedure; Figures 6a and 6b illustrate, using flowcharts, corresponding general steps at the access point and at a non-AP station, respectively; Figure 7 illustrates a range scaling field in a NFRP trigger frame according to embodiments of the invention; Figure 8 illustrates, using a flowchart, exemplary general steps for an access point to determine NFRP Random Access contention Parameters according to other embodiments of the invention; Figure 9 illustrates, using a flowchart, exemplary general steps for any non-AP station to determine the NFRP Random Parameters (NFRP-RAPS) from the management frame received from the AP and to use them, according to the other embodiments of the invention; and Figure 10 illustrates, using a flowchart, general steps at a non-AP station using contention parameters to access the NFRP RU tone sets according to the other 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.

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

Figure 1 illustrates a communication system in which several communication stations (or "nodes") 101-107 exchange data frames over a radio transmission channel 100 of a wireless local area network (VVLAN), under the management of a central station, or access point (AP) 110, also seen as a station of the network. 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.

In the following, the word "station" refers to any kind of station. The wording "access point station", or in short "access point" (AP), refers to the station playing the role of access point 110. The wording "non-access point station", or in short "non-AP station", or client station (STA) refers to the other stations 101-107. In the following, the terms HE STA and HE AP refer respectively to an 802.11ax non-AP STA and an 802.11ax AP.

Access to the shared radio medium to send data frames is primarily 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 or transmitting 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.

The wireless communication system of Figure 1 comprises physical access point 110 configured to manage the WLAN BSS (Basic Service Set), i.e. a group of non-AP stations which have previously registered to the AP. A physical access point 110 may be configured to manage two or more WLANs (or BSSs), i.e. two or more groups of station. Each BSS is uniquely identified by a specific basic service set identifier, BSSID, and managed by a virtual AP implemented in the physical AP.

To access the medium, any station, including the AP, starts counting down a backoff counter designed to expire after a number of timeslots when the medium is sensed as idle. The backoff counter is chosen randomly in a so-called contention window [0, CW], where CW is an integer. This backoff mechanism or procedure, also referred to as Distributed Coordination Function (DCF) contention-based channel access scheme, is the basis of the collision avoidance mechanism that defers the transmission time for a random interval, thus reducing the probability of collisions on the shared channel. After the backoff time expires (i.e. the backoff counter reaches zero), the source station may send data or control frames if the medium is still idle.

Conventional single-user transmission can occur on at least a primary 20MHz channel (used for contention) and some secondary 20Mhz channels: The resulting bandwidth of an operating channel may be e.g. 20 MHz, 40 MHz, 80 MHz, 80+80 MHz, or 160+160 MHz, or 320 MHz. The channels may include one or more subcarriers or tones, for instance a 20 MHz channel is made of 242 tones.

Management of quality of service (QoS) has been introduced at station level in the wireless networks, through well-known EDCA mechanism defined in the IEEE 802.11e standard. Developments in the 802.11ax standard seek to enhance efficiency and usage of the wireless channel for dense environments.

In this perspective, multi-user (MU) transmission features have been considered that allow multiple simultaneous transmissions to/from different non-AP stations in both downlink (DL) and uplink (UL) directions from/to the access point. 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 legacy 20MHz channel into at least one subchannel, but preferably a plurality of sub-channels (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. In some embodiments, the bandwidth of the RUs may be based on a number of active data subcarriers. In some embodiments, the bandwidth of the RUs is based on 26, 52, 106, 242 (a whole 20MHz channel), 484 (40MHz channel), 996 (80MHz channel), or 2x996 (80+80Mhz or 160Mhz channel) active data subcarriers or tones.

While the MU DL transmission is fully managed by the AP, the MU UL transmission requires the AP sends a control frame to the non-AP station to trigger the simultaneous MU UL transmissions from the non-AP stations. Such control frame is known as a Trigger Frame (TF), various variants of which exist depending on the usage of the MU UL sub-carriers desired by the AP.

Figure 2 illustrates two usages of trigger frames. In the exemplary embodiment shown a shod feedback report procedure according to 802.11ax (as described in section "26.5.7 NDP feedback report procedure" of Draft D4.1 of IEEE 802.11ax) is shown followed by an UL MU operation (as described in section "26.5.2 UL MU operation" of Draft D4.1 of IEEE802.11ax) based on the results of the short feedback report procedure.

The NDP feedback report procedure allows the AP 110 to collect feedback that is not channel sounding from multiple non-AP STAs 101-107. The AP sends an NFRP Trigger frame to solicit NDP feedback report response from many non-AP STAs that are identified by a range of scheduled AIDS ("802.11ax range" in the following description) in the NFRP Trigger frame. A non-AP STA uses the information carried in the NFRP Trigger frame to know if it is scheduled, and in this case, may send a NDP feedback report response, usually a HE TB feedback NDP. Next, based on the received NDP feedback report responses, the AP may, using UL MU operation, solicit simultaneous immediate response frames from one or more of the responding non-AP STAs.

The example shown considers a single 20 MHz channel. Of course, the bandwidth of the channel and the number of RUs splitting a 20 MHz channel may be different from what is depicted. Figures 2a and 2b illustrate, using flowcharts, corresponding to general steps at the AP and a non-AP STA, respectively.

The scenario begins at phase 199 wherein the AP 110 accesses the wireless medium. For example, the AP perform a contention-based method (which may include a clear channel assessment and an EDCA backoft) to acquire access to the wireless medium.

Upon accessing the medium, the AP 110 polls non-AP STAs to know their needs for transmission. To do so, it sends an NFRP trigger frame 200 which is a specific trigger frame. It identifies non-AP STAs by an 802.11ax range of scheduled AIDs. This is step S260 of Figure 2a.

With reference to Figure 3a, like each and every 802.11ax trigger frame, NFRP trigger frame 200 comprises: a frame header with a standardized "Frame Control" field, a standardized "Duration" field, an "RA" field set to a broadcast MAC address, and a "TA" field set to a MAC address of the AP transmitting the trigger frame,

a "Common Info" field 310,

one or more "User Info" fields 350, and

padding and FCS fields.

The "Common Info" field 310 comprises a "Trigger Type" subfield 320 which specifies the type of the trigger frame. For instance, NFRP trigger frame 200 is signaled by a value 7 in the "Trigger Type" subfield 320. It also comprises a 2-bit "UL BW field 330 specifying the bandwidth of the channel considered, e.g. BW=0 to define a 20MHz bandwidth, BW=1 for a 40MHz bandwidth, BW=2 for an 80MHz bandwidth, BW=3 for an 80+80MHz or 160MHz bandwidth (see Table 9-31c of the D4.1 version of 802.11ax). It ends by a Trigger Dependent Common Info subfield 340 of variable length whose content depends on the "Trigger Type" subfield 320. The other fields shown are of less importance for the present invention.

Specific to the trigger frame of NFRP type, a single "User Info" field 350 is provided that comprises a 12-bit Starting AID field 351, a first reserved 9-bit portion 352, a 4-bit feedback type field 353, a second reserved 7-bit portion 354, a 7-bit UL Target RSSI field 355 and a 1-bit

multiplexing flag field 356.

The Starting AID comprises the starting AID of the 802.11ax range of AIDs targeted by the NFRP trigger frame 200, i.e. scheduled to respond to the poll. The range size or width NSTA is defined by the "UL BW' field 330 together the 1-bit multiplexing flag field 356, using the following formula NSTA = 18 x 2Bw x (MultiplexingFlag + 1) For instance, when the MultiplexingFlag is set to 0 (no MIMO), 18 non-AP STAs are requested to answer with a feedback response, per 20MHz operating channel. When the MultiplexingFlag is set to 1, 36 non-AP STAs are scheduled per 20MHz operating channel. It may be noted that some AIDS in the 18 or 36-wide range may not be currently assigned to a non-AP STA.

The multiplexing flag field 356 defines whether spatiality (MIMO) is provided: the flag indicates the number (minus 1) of non-AP STAs that are multiplexed on the same set of tones in the same RU.

The "feedback type" field 353 indicates a type of feedback that is being polled by the AP. For the time being, 802.11ax D4.1 only defines a feedback type equal to 0 that is a resource request. The corresponding polling thus seeks to know whether the responding non-AP STAs 101-107 are requesting UL resources to transmit PPDUs to the AP 110.

In the example of Figure 2, the NFRP trigger frame 200 is sent (step S260) in a 20MHz primary channel. However, as already discussed, the NFRP trigger frame 200 may also be sent through an extended channel such as 40MHz, 80MHz or lamer bands to extend the number of polled stations. By sending trigger frame 200, the AP reserves a transmission opportunity 260 (TXOP) corresponding to the duration specified inside the NFRP trigger frame. If the NFRP trigger frame is sent over an overall width larger than the primary 20MHz channel, the 802.11ax standard envisages that the NFRP trigger frame is duplicated (replicated) on each other 20MHz channels forming the targeted composite channel. Thanks to the duplication of control-type frames in non-HT format, it is expected that every nearby legacy node (non-HT or 802.11ac nodes) receiving the NFRP trigger frame (or a duplicate thereof) on its primary channel, then sets its NAV to the value specified in the NFRP trigger frame. This prevents these legacy nodes from accessing the channels of the targeted composite channel during the TXOP.

Each non-AP STA receiving frame 200 is able to first analyze the received frame 200 to determine whether the non-AP STA is concerned with it, in particular to determine whether the non-AP STA is associated with the BSSID indicated in the TA field of the frame (or if the indicated BSSID pertains to a multiple BSSID set for which the non-AP STA is member of).

In case of positive determination, it then determines whether received frame 200 is a NFRP trigger frame, thanks to the type specified in Trigger Type field 320. These determinations form step S270 (Figure 2b).

Next, the non-AP STA determines whether it is scheduled by the received NFRP trigger frame (step S272). It is made by checking whether its AID value (assigned to the non-AP STA by the AP upon registration to the AP) falls within the 802.11ax range [ "Starting AID"; "Starting AID"+ NSTA j as obtained from the fields UL BW 330, Starting AID 351 and Multiplexing flag 356 of the received NFRP trigger frame 200.

When the non-AP STA is not scheduled, nothing more happens at the station.

If it is scheduled by the NFRP trigger frame, the scheduled non-AP STA determines a RU tone set index, i.e. a RU tone set 210 on which the non-AP STA will transmit energy in response to the NFRP trigger frame. This is step S274. The non-AP STA usually selects a responding RU tone set based on the position of its AID within the above 802.11ax range, meaning the first RU tone set for the non-AP station having the Starting AID as own AID, and so on.

Table 27-30 of 802.11ax D4.1 describes an example of how the tones forming 80MHz, 40MHz, 20MHz channels are grouped into sets of tones.

For instance, 216 tones (indexed from -113 to -6 and 6 to 113) forming a 20MHz channel are split into six bundles 250 of 36 continuous tones. Next each RU tone set is formed by two tones from each bundle (usually consecutive tones that are collocated from one bundle to the other), thereby resulting in 18 RU tone sets, each having a unique index RU_TONE_SET_INDEX. The two tones obtained from each bundle are assigned to two respective groups forming the RU tone set. It means that each RU tone set is formed of two groups of tones 210a and 210b.

For illustrative purposes, the tone set with RU_TONE_SET_INDEX=6 in a 20MHz channel without spatiality is made of the two following groups of tones (subcarrier indices): Group 210a: -103, -67, -31, 16, 52, 88 Group 210b: -102, -66, -30, 17, 53, 89 In this example, 6 tones are replicated in each group over the 20MHz channel, each tone from one of the six bundles of tones 250.

A RU tone set is thus made of two adjacent groups of tones (-103 is adjacent to - 102, -67 to -66 and so on.), each group being made of non-adjacent tones (-103 not adjacent to -67 and so on.).

Basically, the tone set index for the scheduled non-AP STA is computed from the difference between STA's AID value and "Starting AID" value. For instance, if this difference plus 1 equals 6, the above-detailed tone set is scheduled for the non-AP STA considered.

Next at step S276, the non-AP STA generates the NDP feedback report response to be sent to the AP.

In particular, the non-AP STA has to transmit energy on the first group 210a of subcarriers or tones to indicate a first response to the feedback type (field 353) polled by the NFRP trigger frame 200, and on the other hand, the non-AP STA must transmit energy on the second group 210b of subcarriers or tones to indicate a second response to the feedback type.

The response is named FEEDBACK_STATUS in the current D4.1 version of 802.11ax. For instance, for the Feedback Type field 353 set to 0 (Resource request), FEEDBACK_STATUS is set to 0 when the non-AP STA requests resource with buffered bytes for transmission between 1 and a resource request buffer threshold; FEEDBACK_STATUS is set to 1 when the non-AP STA requests resource with buffered bytes for transmission above the resource request buffer threshold.

The non-AP station thus determines the NDP feedback report response to be sent depending on the feedback type field in the NFRP trigger frame.

Table 27-30 of 802.11ax D4.1 specifies which group of tones within a tone set has to be used depending on the FEEDBACK_STATUS value.

At step S276, the non-AP STA thus determines the FEEDBACK_STATUS value and therefore the group of tones to be used, either 210a or 210b, depending on the feedback it wishes to report to the AP.

Next at step S278, the non-AP STA transmits energy of the group corresponding to the FEEDBACK_STATUS value in the RU tone set of the determined RU_TONE_SET_INDEX.

For illustration, Station 1 (corresponding to RU_TONE_SET_INDEX=1) transmits energy on its first group of tones 210a (as consequence, group 210b is represented with a dash line). On the contrary, Station 2 (corresponding to RU_TONE_SET_INDEX=1) transmits energy on its second group of tones 210b.

Technically, the HE TB NDP Feedback PPDU 211 used as a feedback response is a single packet with no real data payload as shown in Figure 3b. The PHY preamble 212 is emitted on 20 MHz width (thus several non-AP STAs may emit the same preamble) and the 'payload' is composed of a series of HE-LTF symbols 213, located on the tones forming the selected group 210a or 210b, to be used for the transmitted feedback (energy).

Then, the physical layer of the AP receives and decodes (S262) the RU tone sets where energy is present, to provide to its MAC layer a list of used RU_TONE_SET_INDEX and the corresponding Feedback responses (FEEDBACK_STATUS values).

Thanks to the fields UL BW 330, Starting AID 351 and Multiplexing flag 356 of the NFRP trigger frame 200 sent at step S260, the AP is able to retrieve that AID of each non-AP STA responding to the trigger frame 200. The MAC layer entity of the AP is thus able to determine those NDP-scheduled non-AP STAs who have responded.

At step S264, the AP can send a subsequent trigger frame 220 (Figure 2) to offer new opportunities (RUs) to the responding non-AP STAs, for example a 'Basic' type trigger frame or any convenient type. The 'Basic' type trigger frame is signaled by a "Trigger Type" subfield 320 having value 0.

Based on an AP's decision and the collected feedback responses 211, the trigger frame 220 may define a plurality of data resource units (RUs) 230 (here of 26 tones -of course other numbers of tones may be used). The multi-user feature of OFDMA allows the AP to assign different RUs to different non-AP STAs in order to increase competition. This helps to reduce contention and collisions inside 802.11 networks.

These RUs are scheduled RU assigned to the feedback-responding non-AP STAs, using the AIDS retrieved at step S264.

The trigger frame 220 may for instance include a plurality of User Info fields (Figure 3a) for a respective plurality of scheduled RUs, each User Info field setting an AID (so-called AID12 field) of the scheduled non-AP STA for a given RU in the channel.

The non-AP STAs thus receive the subsequent trigger frame 220 and determine whether they are scheduled (step S280).

In the affirmative, the non-AP STA can use the RU scheduled to it (i.e. the one with the AID corresponding to the non-AP STA) and transmit data (HE TB PPDU) to the AP.

According to the exemplary illustration, Station 1 and Station 2 can thus be granted a RU 230. As an example, Station 1 emits a HE TB PPDU 231 in a first RU 230-1, and Station 2 emits a QoS_Null with Buffer Status Report (the HE TB PPDU is a MAC-PDU with no data payload but with a MAC header containing a BSR) in a second RU 230-2. As the Qos_Null is smaller, the second RU 230-2 is filled in with padding to match the transmission length specified in the trigger frame 220.

Upon receiving the HE TB PPDU 231, the AP acknowledges (or not) the data on each RU by sending a multi-STA block acknowledgment (BA) response (240 -Figure 2), making it possible for each sending non-AP STA to know when its data transmission is successful (reception of the ACK) or not (no ACK after expiry of a time-out). This is step S266.

These explanations show the intent of the NFRP trigger frame mechanism according to the current version of the 802.11ax standard: to receive feedbacks in a short time from a great number of associated non-AP stations.

The overall MU Uplink (UL) medium access sequence, including both NDP Feedback RUs and UL MU scheduled RUs, seems more efficient than conventional EDCA access scheme, especially in dense environments as envisaged by the 802.11ax 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. The NFRP trigger frame 200 allows information to be requested from 18 non-AP stations per 20 MHz channel (more with spatial multiplexing), and the Basic trigger frame 220 allows RUs to be proposed to up to 9 stations which have shown their interest to be triggered (by responding to the NFRP trigger frame).

However, the Null-Data-Packet (NDP) Feedback Report procedure suffers from limitations, notably because of the number of triggered (scheduled) non-AP stations. As the mechanism is based on fixed 802.11ax range of AIDs (from Starting AID 351) where some AIDS in the 802.11ax range may not be used (e.g. released during the lifetime of the network cell), several successive NFRP polling phases are required to have better knowledge of the resource needs of more stations with a view of offering an efficient delivery of the data traffic compared to the required polling overhead.

The inventors have thus contemplated providing random access to the RU tone sets of a NFRP trigger frame.

However, conventional techniques for managing random access (i.e. contention-based access) suffer from some defects which prevent the AP from appropriate control on the non-AP stations. Indeed, the handling of congestion parameters to control non-AP stations is complex, without providing appropriate reactivity to network changes and without allowing the AP to give priority to some non-AP stations when appropriate.

The present invention seeks to overcome the foregoing limitations. In this perspective, the invention provides random access to RU tone sets in a NDP Feedback Report procedure where the AP has control on the number of non-AP stations that can concurrently access the limited number of RU tone sets.

To this end, embodiments of the present invention provide a random access mechanism for short feedback procedure wherein the AP specifies, in the NFRP trigger frame, an access type indication defining whether the RU tone sets are accessed on a random basis by the non-AP stations and a range scaling field defining a scale factor for the non-AP stations to obtain, from conventional 802.11ax range of scheduled AIDs, a second (polling) range of AIDs of stations authorized to access the plurality of RU tone sets on a random basis.

Any non-AP station receiving such "random-access" (RA) NFRP trigger frame thus determines therefrom the access scheme to the RU tone sets. And, when it is determined a random access, the non-AP station obtains the scale factor from the range scaling field, computes the second (polling) range of station AIDS from the conventional 802.11ax range and the scale factor. The second range is used to access the RU tone sets. In particular, if the AID of the non-AP station is included in the second (polling) range, the non-AP station randomly select a responding RU tone set from the plurality of RU tone sets. A NDP feedback report response can thus be sent on the selected responding RU tone set.

Compared to known techniques, the AP thus receives a NDP feedback report response from at least one responding non-AP station having an AID in the second (polling) range and outside the conventional 802.11ax range.

The non-AP station may contend for access to the corresponding subcarriers or tones or may compute a backoff value prior to selecting a RU tone set index, the backoff value being compared to an available range of RU tone sets provided by the RA-NFRP trigger frame for random access.

Consequently, the AP has control (through the range scaling field) on the design of the second (polling) range compared to the conventional 802.11ax range that is defined by the Starting AID 351, the channel bandwidth 330 and the multiplexing flag 356. It may adjust the number of non-AP stations allowed to compete for randomly accessing the RU tone sets of the NDP Feedback Report procedure. This adjustment may take into account network statistics as described below to dynamically provide optimum random access efficiency given the varying network congestion.

At its end, the AP can discriminate between unused RU tone sets and used RU tone sets, so that a subsequent trigger frame, for instance a basic one, is sent to provide new transmission opportunities (RUs) to responding non-AP stations. The overall scheme (random-based NDP feedback report procedure supplemented with a subsequent trigger frame) offers an efficient MU UL random scheme for the non-AP STAs because the random access is moved to the short NDP feedback report procedure compared to conventional UORA with large duration.

Indeed, one unused RU tone set has lower impact on network efficiency than one unused OFDMA RU (UORA).

Figure 4 schematically illustrates a communication device 400 of the radio network 100, either the AP 110 or any non-AP STA 101-107, configured to implement at least one embodiment of the present invention. The communication device 400 may preferably be a device such as a micro-computer, a workstation or a light portable device. The communication device 400 comprises a communication bus 413 to which there are preferably connected: a central processing unit 411, such as a microprocessor, denoted CPU; a read only memory 407, denoted ROM, for storing computer programs for implementing the invention; -a random-access memory 412, 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 402 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/be protocols. The frames are written from a FIFO sending memory in RAM 412 to the network interface for transmission or are read from the network interface for reception and writing into a FIFO receiving memory in RAM 412 under the control of a software application running in the CPU 411.

Optionally, the communication device 400 may also include the following components: a data storage means 404 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; -a disk drive 405 for a disk 406, the disk drive being adapted to read data from the disk 406 or to write data onto said disk; -a screen 409 for displaying decoded data and/or serving as a graphical interface with the user, by means of a keyboard 410 or any other pointing means.

The communication device 400 may be optionally connected to various peripherals, such as for example a digital camera 408, each being connected to an input/output card (not shown) so as to supply data to the communication device 400.

Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 400 or connected to it. The representation of the bus is not!imitative and in particular the central processing unit is operable to communicate instructions to any element of the communication device 400 directly or by means of another element of the communication device 400.

The disk 406 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 embodiments of the invention to be implemented.

The executable code may optionally be stored either in read only memory 407, on the hard disk 404 or on a removable digital medium such as for example a disk 406 as described previously. According to an optional variant, the executable code of the programs can be received by means of the communication network 403, via the interface 402, in order to be stored in one of the storage means of the communication device 400, such as the hard disk 404, before being executed.

The central processing unit 411 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 404 or in the read only memory 407, are transferred into the random access memory 412, 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 35 ASIC).

Figure 5 is a block diagram schematically illustrating the architecture of the communication device 400 adapted to carry out, at least partially, the invention. As illustrated, communication device 400 comprises a physical (PHY) layer block 503, a MAC layer block 502, and an application layer block 501.

The PHY layer block 503 (e.g. a 802.11 standardized PHY layer) has the task of formatting, modulating on or demodulating from any 20 MHz channel or the composite channel, and thus sending or receiving frames over the radio medium used 100, such as 802.11 frames, for instance single-user frames, such as control frames (e.g. ACK, Trigger Frame), MAC data and management frames, based on a 20 MHz width to interact with legacy 802.11 stations or with 802.11ax/be in legacy mode (such as for Trigger Frames), as well as MAC data frames of OFDMA type having preferably smaller width than 20 MHz legacy (typically 2 or 5 MHz), as well as NDP frames having preferably a PHY header transmitted on 20MHz width and a short payload consisting on energy located on non-contiguous subcarriers or tones, to/from that radio medium.

The MAC layer block or controller 502 preferably comprises a MAC 802.11 layer 504 implementing conventional 802.11ax/be MAC operations, and an additional block 505 for carrying out, at least partially, embodiments of the invention. The MAC layer block 502 may optionally be implemented in software, which software is loaded into RAM 412 and executed by CPU 411.

Preferably, the additional block 505 referred to as NDP Feedback Management module 505 is configured to implement steps according to embodiments that are performed by the communication device 400, notably transmitting operations for a transmitting/responding station and receiving operations for a receiving station.

Interfaces 506 and 507 are used by the MAC and PHY layer blocks to interact and to exchange information through TXVECTOR (from the MAC to the PHY layer -506) and the 20 RXVECTOR (from the PHY to the MAC block -507). The TXVECTOR and RXVECTOR are defined in the clause 27.2.2 of the draft 4.1 of the 802.11ax standard.

On top of the Figure, application layer block 501 runs an application that generates and receives data packets, for example data packets of a video stream. Application layer block 501 represents all the stack layers above MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using various exemplary embodiments.

Although some of the proposed examples use the trigger frames 200 and 220 (see Figure 2) sent by an AP for a multi-user (MU) uplink (UL) transmissions, equivalent mechanisms can be used in a centralized or in an ad hoc environment (i.e. without an AP). It means that the operations described below with reference to the AP may be performed by any station in an ad hoc environment. In particular, subsequent scheduling to provide scheduled transmission opportunities to the NFRP responding non-AP stations may be provided that is different from the 802.11ax UL MU operation.

Figure 6 uses the same timeline as Figure 2 to illustrate first embodiments of the invention providing random access to the RU tone sets during the NDP short feedback report procedure. Figures 6a and 6b illustrate, using flowcharts, corresponding general steps at the AP and a non-AP STA, respectively. The reference numbers are unchanged when referring to the same elements, frames and steps as in Figures 2.

At step S660, the AP 110 polls a large group of non-AP STAs to know their needs for transmission, by sending a NFRP trigger frame 600 wherein an access type indication is set to define whether the RU tone sets are accessed on a random basis by the stations, and in case of random access, a range scaling field defining a scale factor for the non-AP stations to determine the large group of authorized AIDs from the conventional 802.11ax range of AIDs.

Thanks to the indication, the non-AP STAs can know that a random scheme is requested for sending their feedback response to the AP.

Thanks to the scale factor, the AP can authorize a varying large number of non-AP stations to randomly access the RU tone sets.

Step S660 comprises multiple sub-steps.

At sub-step S6600, the AP determines whether the next NFRP trigger frame 600 should offer scheduled (SCH) or random access (RA) to the RU tone sets that it defines. A decision can be based on a systematic approach (e.g. alternation between a scheduled one and a random one) or on any other rule.

At sub-step S6605, the AP determines the number NRU of resources (here RU tone sets) to allocate to the non-AP stations. The number may depend on the outcome of sub-step S6600. Conventional determination may be used in the case of a scheduled access to the RU tone sets.

This sub-step, in particular for random access, can be performed using statics built upon receiving previous random access trigger based PPDUs (UORA and/or Random Access-based short Feedback procedures). Those PPDUs are received after transmission of a trigger frame for random access and contains the responses from the non-AP stations via a random access procedure to the AP.

This is not the result of the random access transmission (i.e. collided or not) that has interest, but rather the number of RUs or RU tone sets used.

The average usage ratio is preferably used, that is defined by the number of used RUs or RU tone sets divided by the total number of sur RUs/RU tone sets proposed for random access by a given trigger frame. The ratio is measured during successive random access sessions. It gives a good view of the need for random access resources. Indeed, the theoretically ideal ratio should be 36.8% (similar to the well-known performances of the slotted ALOHA protocol) corresponding to the case where the number of random access RUs/RU tone sets is equal to the number of contending non-AP stations. Therefore, applying this ratio to the total number of non-AP stations registered in the call gives a theoretically ideal number NRU of required RU tone sets.

The AP may use more precise statistics, for instance specific to a given group of non-AP stations. For instance, the AP may gather random-access-related statistics per AID range when it assigns AIDS from a given range to non-AP STAs according to some STA characteristics: RSSI, capabilities, etc. The AP may thus adjust the number NRU per AID range.

The AP can then infer UL BW value 330 and multiplexing flag 356 that match (or approximate) the number NRU such that NRU = Nreedback x 2BW x (MultiplexingFlag + 1). As currently defined in 802.11ax D4.1, Nfeedback=18.

If the number NRU of required RU tone sets is too high with respect to the available bandwidth (including MIMO if any), or if the AP decides to reserve a portion of the available bandwidth for scheduled MU UL operation (e.g. 20MHz out of 40MHz), the number NRU is automatically reduced to what the bandwidth available for random access permits (BW 330 and multiplexing flag 356 are obtained based on the reduced value of NRU). In that case, the AP will use the next sub-steps to adjust the number of contending non-AP stations given NRU.

Next to sub-step S6605, sub-step S6610 determines the Starting AID value 351 to be set in the NFRP trigger frame 600 for random access.

Typical Starting AID value can be the lowest AID assigned to a currently active and registered (to the AP) non-AP station. Such value potentially lets it possible to authorize all the registered non-AP stations to contend for (random) access to the RU tone sets (provided that the scale factor determined below is adapted).

Other determination rules may be used. For instance, the AP may decide to assign (to non-AP STAB) AIDs from different AID ranges depending on respective STA's characteristics. As an example, range 100-300 is used for one type of non-AP stations (e.g. that do not support MU UL) and range 400-500 for another type of non-AP stations (e.g. supporting random access), The AP may thus set the Starting AID value 315 to 100 or 400 (beginning of the range) to only poll non-AP stations of one type. Consequently, the AP can apply priority mechanisms on the non-AP stations.

Sub-steps S6605 and S6610 are independent one to each other and can be executed in a reverse order: the AP may first determine the Starting AID based on a type of non-AP stations it wants to poll and then determine the number NRU of resources required.

In case of scheduled scheme (determined at sub-step S6600), next sub-step is S6625 described below. Otherwise, next sub-step is S6615 where the AP determines a number NSTA of non-AP stations to poll. By this sub-step, the AP determines the contention level on the random access RU tone sets.

A maximum efficiency of the random access procedure is obtained for a number of contending non-AP stations equal to the number of available RU tone sets. It means that the number of non-AP stations trying to access the RU tone sets on a random basis should be equal (or as close as possible) to the number NRU of RU tone sets previously determined.

However, as all the non-AP stations of a given AID range are not trying or willing to access the RU tone sets on a random basis (some may have no data to transmit, some may be asleep or in power save mode), the AP may use additional statistics to set NSTA to a larger number than NRU.

For instance, the AP may build statistics such as the average random access rate, computed as the ratio between the number of polled non-AP stations and the number of used RU tone sets from previous NRFP-based random accesses. Consequently, NsTA may be the result of NRU multiplied by such ratio. The ratio and NSTA may be updated dynamically as new NRFP-based random accesses are performed.

Once NSTA is known, sub-step S6620 determines the value of the scale factor defining the ratio between the polling range of AIDs to poll in order to authorize NSTA non-AP stations to random access and the conventional (802.11 ax) range of AIDs corresponding to NRU.

As mentioned above, the range of assignable AIDs may be punctured. Therefore, it is often that the polling range width NAID of authorized AIDs must be larger than NsTA to actually authorize NSTA non-AP stations to contend for random access to the RU tone sets.

The AP thus determines a temporary polling range of AIDs, starting at the Starting AID and containing at the number NSTA of non-AP stations to poll. A temporary scale factor SFiemp is determined by computing the ratio between the width or size of the temporary polling range and the number NRU of RU tone sets offered to random access.

The temporary polling range and scale factor may be definitive ones in case the coding of this scale factor SFiemp is lossless.

In lossy embodiments, the temporary scale factor is encoded based on a power of 2, meaning that an integer RA_SF is searched so that 2RA-SF equals the temporary scale factor or approximates it. For instance, RA_SF = floor [ log2(SFtemp) ] [logarithm to base 2]. The ceiling function may be used instead of the floor function. In that case, the final scale factor SF is 2RA-SF and the final polling range is the range starting from Starting AID with a width NAID equal to NRU x SF.

Next at sub-step S6625, the NFRP trigger frame 600 (either for scheduled or random access) is built and sent. Usually, the NFRP trigger frame 600 is prepared and placed in a transmission buffer to be transmitted during the next transmission opportunity for the AP.

In particular, UL BW value and multiplexing flag determined at sub-step S6605 are provided in fields 330 and 356 respectively; Starting AID obtained at sub-step S6610 is added to field 351.

The AP adds an access type indication defining whether the RU tone sets are accessed on a random basis by the non-AP stations or whether a scheduled access is proposed. Various embodiments are contemplated.

In first embodiments, the access scheme is defined in the Trigger Type field 320. This means that conventional NFRP type (value 7) is used in case of scheduled access and a new dedicated RA-NFRP type (e.g. value 8) is used to signal random access to the RU tone sets.

These first embodiments allow a new frame format to be defined, in particular by adapting the Trigger Dependent Common Info field 340 so as to contain a range scaling field (discussed below, in particular with reference to Figure 7) to convey the above RA_SF value.

In second embodiments, the access scheme is defined in the Feedback Type field 353. For both scheduled and random access schemes, the trigger frame 600 is of the NFRP type (field 320 set to 7) wherein the Feedback Type field takes specific values for random access.

For instance, currently used value 0 indicate Resource Request (as feedback type) for the scheduled non-AP stations. Another value, e.g. 1, may merely indicate random access is provided to the RU tone sets, without any type of feedback required. In a variant, the other value may simultaneously indicate random access is offered for Resource Request only (i.e. the FEEDBACK_STATUS provided in response responds to the amount of resources compared to a threshold).

Of course, other Feedback Type values may be defined for other purposes (power sensing, data queue evaluation, sleep state) and provided for both scheduled and random access schemes.

The second embodiments advantageously prevent from creating a new type of trigger frame, meaning the decoding of the frames remain unchanged (this is only the interpretation of the Feedback Type value that modifies the non-AP station's behavior).

In third embodiments, the access scheme is defined through the value of a range scaling field conveying the above RA_SF value. For both scheduled and random access schemes, the trigger frame 600 is of the NFRP type (field 320 set to 7) and the Feedback Type field may be set as conventionally done.

The value 0 in the range scaling field should correspond to a scale factor of 2°=1 which is meaningless to modify the conventional 802.11ax range of AIDS. Therefore, this value (0) may be used to indicate scheduled (i.e. conventional) access to the RU tone sets, while a nonzero value may indicate random access. Of course, other specific values for scheduled access may be used.

The AP also adds to the NFRP trigger frame 600 a range scaling field (already introduced above) that includes the value of RA_SF (or 0 for instance in case of scheduled access for the third embodiments). This is this information item that makes it possible to define the scale factor SF (.2RA_sF) to obtain, from the 802.11ax range of AIDS, the polling range of AIDS of non-AP stations authorized to access the plurality of RU tone sets on the random basis.

The range scaling field may be a two-bit or three-bit field in the NFRP trigger frame 600. With three bits, the field can have a value between 0 and 7 giving a Scale Factor value between 1 and 128. For a typical NFRP trigger frame offering 18 RU tone sets, the AP can then poll up to 2304 non-AP stations on a random basis, which that is more than the number of available AIDS the AP can assigned to non-AP stations upon registration.

Various positions in the NFRP trigger frame 600 can be used for the range scaling

field.

For instance, the range scaling field is included in a Reserved field of a User Info field, either field 352 or field 354, of the NFRP trigger frame 600. Figure 7 illustrates the addition of a 3-bit range scaling field 3540 in the Reserved field 354.

In a variant, the range scaling field is included in the Trigger Dependent Common Info field 340 of the Common Info field 310 of the NFRP trigger frame 600. This variant may be used for the first embodiments above (where a new Trigger Frame type is defined).

At step S270, any non-AP station 101-107 receives the NFRP Trigger frame 600 and decodes it. If the receiving non-AP station belongs to a BSS (or virtual BSS) of the transmitting AP, the Trigger Frame is not filtered by the PHY layer as defined in the standard. The filtering is made on so-called "colors" defined in the 802.11ax standard, which mandates that the BSS colors of all the multiple BSSs managed by a single AP are the same.

At step 5671, the non-AP STA determines, from the NFRP trigger frame, an access scheme to the RU tone sets. It thus retrieves the access type indication provided by the AP in the NFRP trigger frame 600.

The non-AP STA may merely read the value of the Trigger Type field 320 for the first embodiments: either it is 7 meaning a scheduled access scheme is requested or it is 8 meaning that a random access scheme is implemented.

The non-AP STA may merely read the value of the Feedback Type field 353 for the second embodiments: e.g. either it is 0 meaning a scheduled access scheme (with Resource Request type) is requested or it is 1 meaning that a random access scheme (possibly with Resource Request type) is implemented.

For the third embodiments, the non-AP STA may merely read the value of range scaling field 3540: e.g. either it is 0 meaning a scheduled access scheme is requested or it is non-zero meaning that a random access scheme is implemented.

In case of scheduled access scheme, the process continues at step S272 of Figure 2.

Otherwise (random access scheme), next step is step S672 where the non-AP STA determines the number NRU of RU tone sets available for random access.

The non-AP station computes NRU = Nfeedback X 2BW X (MultiplexingFlag + 1), with BW retrieved from field 330 and MultiplexingFlag retrieved from field 356.

Step S672 substantially corresponds to the determination of the conventional 802.11ax range of AIDS (made of NRU together with the Starting AID 351).

Next step is step S673 where the non-AP station obtains the polling range of AIDs.

This is done by first retrieving RA_SF from the range scaling field 3540, then by obtaining a scale factor SF from RA_SF of the range scaling field: SF=2RA_SF, then by computing the width NAID of the polling range as following: NAID = NRU x SF and by retrieving the Starting AID from field 351. The polling range is thus [ "Starting AID"; "Starting AID"+ NAID].

The polling range thus corresponds to the 802.11ax range rescaled by the scale factor SF, meaning the range width (or size) is rescaled by SF. In particular, the polling range has the same starting AID as the 802.11ax range with a range width multiplied by the scale factor. Next, step S674 consists for the non-AP station to determine whether it is targeted by the received NFRP trigger frame or not. In particular, it includes checking whether the AID of the non-AP station is included in the polling range. If the STA's AID is lower than the sum of the Starting AID 351 and NAM value determined at step S673, then the non-AP station is addressed by the current NFRP trigger frame, and can therefore contend to access one of the available RU tone sets on a random basis.

In the negative, the process ends.

In the affirmative, the process continues at step S675.

At step S675, the non-AP STA determines a random RU tone set 210 to send its short NDP feedback report response 211. The selection of the RU tone set is made on a random basis by selecting an index from among the available indexes. All the RU tone sets are available for contention.

The number of RU tone set indexes (NRu) has been determined at step S672.

The non-AP STA may then randomly select a random RU tone set Index to send its short feedback: RA_NFRP_SET_INDEX = random [ 0, NRU -1]. Here, it is chosen to start the indexes at 0. In variant, the first index may have another value, e.g. 1 or above, and the provided formulae are modified accordingly.

In this random access procedure, the non-AP STA may still indicate different responses to the feedback type (field 353) polled by the RA-NFRP trigger frame 600, depending on the group of tones used within the selected random RU tone set: for example, transmitting on the first group of RU tones 210a may indicate a FEEDBACK_STATUS equal to 0, and transmitting on the second group of RU tones 210b may indicate a FEEDBACK_STATUS equal to 1. In that case, the NDP feedback report response is transmitted on one of the two groups of tones. Once the random RU tone set (RA_NFRP_SET_INDEX) has been randomly selected at step S675, the non-AP STA determines the FEEDBACK_STATUS value, if any at step S276 and then transmits the NDP Feedback Report response 211 using the appropriate group of tones in the selected random RU tone set (step S278): for instance, Station 1 transmits energy (NDP) on RU tone sets 210a as illustrated in Figure 6.

The non-AP STA transmits the header 212 of TB Feedback PPDU 211 on the 20MHz channel corresponding to the selected RA_NFRP_SET_INDEX, and transmits on each of the subcarrier indexes forming the group for the FEEDBACK_STATUS value, the value of the HE-LTF sequence 213.

As become apparent in the Figures, due to the random selection, some RU tone sets may be not randomly selected, so that the corresponding tone groups 210a and 210b are left unused. Such situation is shown by reference 610e in the Figure.

Also, the random selection of RA_NFRP_SET_INDEX may result in having two or more non-AP STAs selecting the same RU tone set. Such situation is shown by reference 610c in the Figures.

Anyway, the AP receives and decodes (S262) the RU tone sets where energy is present, to provide to its MAC layer a list of used RU_TONE_SET_INDEX and the corresponding Feedback responses (FEEDBACK_STATUS values) if any. At this stage, it is not possible for the AP to know which RU tone sets with energy are collided (610c) or not.

In particular, due to the invention, the AP receives responses from responding non-AP stations having AIDs in the polling range in case of random access, some of them possibly in the extended part of the range, i.e. outside the 802.11ax range defined by UL BW 330 and Multiplexing flag 356.

At step S664, the AP can send a subsequent trigger frame 620 to offer new opportunities (RUs) to the responding non-AP STAs, for example a 'Basic' type trigger frame or any convenient type. Preferably, the scheduled RUs are of narrow width (26 tones) to offer a maximum of nine RUs per 20MHz channel. The AP may choose a subset of the responding non-AP STAs.

In case where the NFRP trigger frame 600 was based on a scheduled access scheme, the subsequent trigger frame 620 is built conventionally as described in Figure 2a.

In case where the NFRP trigger frame 600 was based on a random access scheme, the AP does not know, at this stage, which non-AP STAs have emit energy on a given RU tone set 210. Consequently, it is impossible for the AP to schedule the responding non-AP STAs through their AIDS in the trigger frame 620.

The AP may thus assign a scheduled resource unit to a responding station using the index RU_TONE_SET_INDEX of the corresponding responding RU tone set to define the AID (so-called AID12 field) associated with the scheduled RU.

The AP may directly use the index RU_TONE_SET_INDEX as value for the AID12

field.

However, in order to avoid these scheduled index-based AIDs to fall on conventionally-used AIDs (for BSS or for individual non-AP STAs, typically values from 1 to 2007 and some values below 2048 such as 2045 and 2046, and value 4095 is reserved to indicate start of a Padding field), the AID associated with the scheduled resource unit in the subsequent trigger frame may be built from the index RU_TONE_SET_INDEX of the responding RU tone set and from an offset value Offset_AID.

For instance, the AID12 field of a User Info field defining the scheduled RU may be set to RA_NDP_AID: RA_NDP_ AID = Offset_AID + RA_NFRP_SET_INDEX + STARTING_STS_NUM x Nfeedback X 213w where RA_NFRP_SET_INDEX is a selected one from the indexes of the responding RU tone sets used by the responding non-AP STA, STARTING_STS_NUM is parameter handling the spatial multiplexing. It is a station parameter that corresponds to a starting spatial stream number minus 1. It is set to 0 if the MultiplexingFlag 356 of the NFRP trigger frame 600 is set to 0 (no spatial multiplexing), otherwise it is set as follows: STARTING_STS_NUM = entire_value ( RA_NFRP_SET_INDEX / Nfeedback / 26W) The Offset_AID parameter is a predetermined offset value known by the non-AP STAs and the AP. In some embodiments, the Offset_AID parameter is transmitted by the AP to the stations in a management frame, e.g. periodically in beacon frames (each 100 ms).

Preferably, the Offset_AID parameter is selected such that any subsequent RA_NDP_AID falls outside the legacy range of Association Identifiers (AIDs) provided by AP to associated non-AP STAs. For instance, the offset value is 2048 or above. It is then added to the index RA_NFRP_SET_INDEX of the responding RU tone set to form the AID (AID12 field) associated with the scheduled resource unit.

Using an offset value of 2048 to form the 12-bit AID field makes it possible to work on the MSB (set to 1) to easily distinguish between conventional AIDs and those used for the present invention. Furthermore, it allows scheduled RUs for non-AP STAs responding to the RANFRP trigger frame 600 to be mixed with scheduled RUs for other non-AP stations directly per their own AID value, with no risk of misunderstanding.

In case of mixing, the subsequent trigger frame 620 first declares all the resource units (it may be a single one) assigned to individual non-AP stations using their own assigned AID, and then declares all resource units (may be a single one) assigned to responding non-AP stations using indexes RA_NFRP_SET_INDEX of the responding RU tone sets (preferably using RA_NDP_ AID).

Of course, the subsequent trigger frame 620 may only comprise resource units for non-AP stations responding to the RA-NFRP trigger frame 600 (i.e. RUs with only AID12 set based on RA_NDP_ AID).

In all case, the subsequent trigger frame may only comprise scheduled resource units (assigned to respective individual non-AP stations) without random RUs.

At step S664, the AP 110 thus sends the subsequent basic trigger frame 620 so built.

Any non-AP STA receiving the subsequent trigger frame 620 thus determines (step S680) whether it is scheduled, i.e. whether a resource unit is assigned to the non-AP station based on the index RA_NFRP_SET_INDEX of the responding RU tone set determined and used by the non-AP station at steps S675 and S278.

The non-AP STA having responded to the NFRP trigger frame 600 uses the formula above to determine its own RA_NDP_ AID and compares it to the AID12 fields specified in the User Info fields of the subsequent trigger frame 620. The non-AP STA thus determines whether an AID associated with a scheduled resource unit in the subsequent trigger frame corresponds to the index RA_NFRP_SET_INDEX used given the predefined offset value Offset_AID.

In a preferred embodiment where Offset_AID is set to value 2048, all RUs with MSB set to 1 are analyzed in order than the remaining value (not considering the MSB bit) equals to the RU tone set index RA_NFRP_SET_INDEX the non-AP station has previously used.

Of course, in case of mixing RUs with conventional AIDS and index-based AIDs, the non-AP station may be scheduled twice, in which case it should give priority to a scheduled RU with its own AID in order to offer the RU with its index-based AID (if any) to any other colliding non-AP STA having responded on the same RU tone set. In other words, if the non-AP station also determines in the subsequent trigger frame a resource unit that has an associated AID corresponding to an AID assigned by the AP to the non-AP station, the non-AP station discards or disregards the resource unit with the AID corresponding to the index of the selected responding RU tone set to use the resource unit with the assigned AID to send the trigger-based PPDU response. This approach reduces risks of collision in the RUs and may be easily achieved through the order of RU declaration performed by the AP in the subsequent trigger frame 620. Indeed, the non-AP STA may disregard any further User Info fields as soon as it finds one with its own AID.

Therefore, placing the RUs with AIDs assigned upon registration before the RUs with index-based AIDs allows the above priority scheme to be naturally performed.

The non-AP station may thus first determine whether one Resource Unit is allocated to it by positively finding its station AID in the AID12 field of one RU. If not found, a further determination is performed in case that the non-AP station has previously sent a NDP feedback response 211 in response to the random-access NFRP trigger frame 600. The further determination relies on the formula for determining RA_NDP_AID value, considering the RU tone index RA_NFRP_SET_INDEX used for the NDP Feedback report response and the predetermined offset value (Offset_AID).

In case of positive determination at step 5680, the non-AP STA can use the RU scheduled to it and transmit data 231 (TB PPDU) to the AP. This is step S282. The TB PPDU 231 contains the MAC address of the sending non-AP station, making it possible for the AP to identify each sending non-AP station, in particular to retrieve the AID assigned to each sending non-AP station upon registration.

The AP 110 thus receives the TB Data PPDU 231 over the multiple scheduled RUs.

It can then acknowledge (or not) the data on each RU by sending a multi-STA block acknowledgment (BA) response 240, making it possible for each sending non-AP STA to know when its data transmission is successful (reception of the ACK) or not (no ACK after expiry of a time-out). This is step S266.

For instance, it may not acknowledge data over RU 230-3 (Figure 6) as it detects a collision.

As the acknowledgment (no collision) generally uses the AIDS of the sending non-AP stations, the AP 110 may obtain an AID of the responding non-AP stations using the MAC addresses specified in the TB Data PPDU 231 and thus retrieved therefrom. The stations are thus only discriminated at this final stage.

The example of Figure 6 shows a single TXOP 660 during which the NDP Feedback Report procedure and subsequent UL MU operation are both conducted. This ensures that the feedback responses 211 are still relevant when they are exploited by the AP to provide the subsequent UL MU operation based on these responses. In addition, it advantageously avoids a random tone set index to be kept by a non-AP station outside the TXOP; otherwise, this would require keeping in memory this random index for further usage by Data trigger frame TF 620 or until a next NFRP trigger frame 600.

However, TXOP 660 may be split into two separate TXOPs, and/or alternatively several subsequent trigger frames 620 (possibly cascaded) may be issued in order to address more non-AP stations responding to the NFRP trigger frame 600 (as only 9 maximum stations per 20Mhz can be triggered for data RU transmission per Basic trigger frame).

The proposed random access scheme provides good efficiency: the collision is largely performed on the NDP feedback responses 211 which are shorter in duration, and the RUs used for TB PPDU 231 are never empty.

The best theoretical probabilities for classical random access distributions (such as slotted ALOHA -type) are the following: probability of no collision (success) nearly 37%, compared to 37% for empty, and 26% collisions. This offers a theoretical efficiency ratio of 37% for UORA for instance.

The implementation of the present invention substantially improves this situation as the random access is moved to the short time NDP Feedback report procedure. It turns that no random RUs (and thus no empty RUs) are met in the subsequent UL MU operation (triggered by trigger frame 620).

Applying a random selection among 18 RU tone set index during the NDP Feedback report procedure provides approximately 6.66 (6) success indexes in addition to 4.68 (4) collisions (for a total of 10 full occupied indexes). As a result, it is expected that most of these occupied slots could be later scheduled in the TB PPDU (there is no scheduling for empty RU indexes). Finally, on average, the maximum efficiency for the transmission above 9 RUs would be: 37 / (37+26) = 58.7% as there are no longer empty RUs. This is a high improvement compared to the conventional 37% of UORA scheme.

Also by setting the range scaling field to appropriate scale factor values, the AP can dynamically control the number of non-AP stations concurrently contending to RU tone sets of a short feedback procedure. This allows the AP to achieve optimized network efficiency for random access.

Figures 8 to 10 illustrate another embodiment of the present invention. Preceding description provides at step S675 a random selection of the RU tone set: RA_NFRP_SET_INDEX = random [ 0, NRU -1].

In these other embodiments, randomly selecting a responding RU tone set is based on a contention-based access method using a decrementing NFRP backoff, NBO, counter local to the non-AP station. The NBO is handled using NFRP Random Access contention parameters including a NFRP contention window.

These other embodiments advantageously adapt in a suitable way the random access scheme for NFRP RU Tone set indexes to the contention currently perceived in the network.

Figure 8 illustrates, using a flowchart, exemplary general steps for the AP 110 to determine NFRP Random Access contention Parameters to be used by the non-AP stations when contending to the RA RU tone sets 210 and to build and send a management (e.g. beacon) frame including these Parameters.

A NFRP Random Access Parameter Set (NFRP-RAPS) is defined at the AP for management of the network. The NFRP-RAPS may include a Contention Window Range that indicates the minimum and maximum values of the contention window to be used by station for NFRP with random access; the range being composed of [NCW., NCWmax] (NCW standing for NFRP Contention Window). The NFRP-RAPS may also include the above-mentioned Offset_AID which indicates the offset for computation of the RA_NDP_AID value to be used in Basic Trigger Frame(s) following the NFRP with RA.

The NFRP-RAPS may be set and then be transmitted per BSSID (and thus determined per BSS).

These values are sent by the AP to the non-AP stations as a reference value for the latter.

At step 800, the AP gathers NFRP-RA and NFRP-RA-OFDMA statistics.

NFRP-RA statistics are gathered at the end of each NFRP-RA transmission (211) from non-AP stations responding to a RA-NFRP trigger frame 600: the AP collects and analyses the number of RU tone sets (210) that are unused for each previous RA-NFRP trigger frame 600.

The statistics may be saved for a sliding monitoring period. All the values are stored as NFRP-RA statistics.

NFRP-RA-OFDMA statistics are gathered at the end of each MU UL OFDMA transmission (231) from the non-AP stations triggered by a subsequent (to RA-NFRP) trigger frames 620: the AP collects and analyses the number of scheduled RUs that are collided and well used for each previous trigger frame. The statistics may be saved for a sliding monitoring period.

All the values are stored as NFRP-RA-OFDMA statistics.

At step 801, the AP computes or updates the NFRP-RAPS based on the gathered statistics.

NCWmin can be adjusted based on NFRP-RA statistics, that is to say upon each transmission, or only after a predefined set of transmissions, of TB NDP Feedback responses 211. This value may have a substantial big impact on the efficiency metric related to unused RU tone set indexes.

NCWmax can be adjusted based on NFRP-RA-OFDMA statistics, that is to say upon each MU UL OFDMA transmission or only after a predefined set of MU UL OFDMA transmissions triggered by a trigger frame 620. This value may have a substantial impact on the efficiency metric, as it drives the collision ratio.

In some embodiments, the AP may want to select a greater NCWmin contention window resulting in more NDP tone set indexes being unused. This is because the unused tone set indexes are early discriminated.

The AP may determine the NFRP-RAPS per each BSS it administrates, based on the statistics.

Alternatively, in case of multiple BSSID, NFRP-RAPS computed/updated for the transmitted BSSID may be used as a default profile for the non-transmitted BSSID. Consequently, low-end AP devices may, by simplicity, only consider this profile for trigger frames 600/620 issued both from their non-transmitted BSSID contexts (with condition that no specific NFRP-RAPS is provided in their non-transmitted BSSID) and for their multi-BSS context. Those APs are considered as low-end APs because they are limited in their NFRP-RAPS capabilities to adapt the NFRP-RAPS per each BSS to changing conditions (like number of registered stations, contention, etc.).

The AP may also use any proprietary or internal consideration for determining these NFRP-RAPS values, as for example the density of stations, measured contention or network load encountered in each individual BSS it manages.

Next to step 801, steps 802, 803, 804 and 805 are in charge of building and broadcasting the management frame (e.g. beacon frame) conveying the obtained NFRP-RAPS to all the stations of the network (or to stations of a given BSS). Step 802 considers the case of multiple BSSs to encode each NFRP-RAPS per BSS (step 803) before forming the beacon frame with all the NFRP-RAPS (step 804). The beacon frame is then sent periodically (e.g. each 100 ms) at step 805.

Consequently, the non-AP stations periodically receive a new reference NFRP-RAPS element values as default contention parameters for their local NFRP contention scheme according to embodiments of the invention.

In a possible embodiment, the NFRP-RAPS element set is identical as the UL OFDMA-based Random Access (UORA) Parameter Set element specified by the 802.11ax standard for the UORA procedure. A Contention Window range (called OCW Range in the standard) is used to indicate the minimum and maximum values of the OFDMA contention window: it has to be re-used for [NCWmin, NCWmax] range according to the invention. This approach reduces the amount of parameters to share.

Figure 9 illustrates, using a flowchart, exemplary general steps for any non-AP station to determine the NFRP Random Parameters (NFRP-RAPS) from the management frame received from the AP and to use them, according to embodiments of the invention.

To perform contention on the RU tone sets for NFRP, the non-AP station maintains an internal NCW contention window and an internal NBO counter. NCW is an integer in the range NCWmm to NCW... The non-AP station obtains NCWmin and NCWmax from the last received NFRP-RAPS Parameter Set element carried in a management frame from the AP. If the station is associated with a non-transmitted BSSID of a multiple BSSID set, and a NFRP-RAPS is present in the non-transmitted BSSID profile, the non-AP station determines NCW,,,in and NCW,,,a"through this non-transmitted BSSID profile (otherwise the non-AP station inherits the NFRP-RAPS form the transmitted BSSID profile).

As shown in the Figure, upon receiving a new beacon frame from the AP (step 900), the non-AP decode the frame to retrieve the NFRP-RAPS for the appropriate BSS if any (step 901).

Next, at step 902, the non-AP station sets its local lower boundary NCWmin of the selection range [NCWrin, NCWmax] to the NCWmin reference value as decoded from the received beacon frame, and do the same for the local upper boundary NCWmax based on the NCWmax reference value as decoded.

Next, the current NCW value of the non-AP station is reset to NCWmm (step 903). These updated values will be used for the next random generation of the NBO value (random selection from range [0,NCW]).

Figure 10 illustrates, using a flowchart, general steps at a non-AP station using contention parameters to access the NFRP RU tone sets. Figure 10 is based on Figures 2b and 6b, where similar reference numbers correspond to similar elements, frames and steps.

As for Figure 6b, the non-AP station receives a NFRP trigger frame 600 (S270), determines whether it provides random access (S671) and if so, the non-AP station determines NRU (S672) and the polling range of AIDs (S673) before determining whether it is polled or not (S674).

If it is polled, next at step S1073, the non-AP station retrieved its local contention parameters, that is to say NBO and NCW.

NCW is initially set to NCWmin and NBO is initially randomly drawn from [0, NCW]. In particular, each time the non-AP station associates with (or intends to transmit to) a different AP (or a different BSSID for non-AP STA with Multiple BSSID feature implemented), the non-AP station shall initially (i.e. prior to an initial transmission attempt triggered by the RA-NFRP trigger frame) set the value of NCW to NCWrin, and shall initialize its NBO counter to a random value drawn from a uniform distribution in the range 0 to NCW.

Step S675 of randomly selecting a RU tone set (or RA_NFRP_SET_INDEX) is updated to consider the new NFRP contention scheme.

It comprises a first sub-step S1074 of determining, from the received RA-NFRP trigger frame 600, the NFRP Tone Set Indexes available (or eligible) for contention, i.e. NRU as defined above, and then of decrementing the NBO counter, e.g., NBO= NBO -NRU.

For instance, if the NBO counter is not greater than the number NRU of eligible RU tone sets in the RA-NFRP trigger frame, the non-AP station sets the NBO counter to zero, otherwise the non-AP station decrements the NBO counter by the number NRU of eligible RU tone sets in the Trigger frame.

Next at sub-step S1075, the non-AP station determines whether the resulting NBO value is negative or null.

If NBO is positive, NBO is already prepared to wait a further RA-NFRP trigger frame 600 for random access. The non-AP station is considered as not eligible to contend for access for the present RA-NFRP trigger frame 600, and the process ends for this trigger frame 600.

If NBO is negative or null (i.e. the NBO counter was not greater than the number NRu), then the non-AP station randomly selects (S1076) one of the eligible RU tone sets, in particular randomly selects RA_NFRP_SET_INDEX.

RA_NFRP_SET_INDEX is for instance randomly drawn from the available random tone indexes [ 0, NRU -1], as already described above.

In a variant, the non-AP station may use the last non null (and non-negative) NBO counter (i.e. before step 51074) as RA_NFRP_SET_INDEX. This approach is still a random selection as the NBO counter has been randomly drawn. The RA_NFRP_SET_INDEX is selected in accordance to the value of NBO counter (which is also a random value, that fits into the range [0, NRU]).

Once the RA_NFRP_SET_INDEX is known, the process continues with already-described steps S276 (determination of the FEEDBACK_STATUS value), S278 (transmission of the TB NDP feedback PPDU 211 on the appropriate group of tones), S680 (reception of the subsequent trigger frame 620 scheduling a RU for RA_NDP_AID corresponding to the non-AP station) and S282 (sending of a TB PPDU 231 in UL direction in response to the subsequent trigger frame 620).

As shown in Figure 6a for instance, the AP then sends a Multi-STA Block Acknowledgment (BA) response 240 at step S266. Although this acknowledgment is directly relying on reliability concerns (e.g. increasing of the sequence number of correct MPDU frames and liberation of space in transmission buffers), this information is important for contention mechanism of the RA-NFRP scheme. Indeed, this is the first time for the non-AP station to be aware of the correct completeness of the random access. It may thus adapt its contention parameters accordingly, for instance its NCW contention value.

Step S1084 is executed when the UL OFDMA transmission finishes on an accessed scheduled RU, upon having the status of transmission; either by receiving a positive or negative acknowledgment from the AP (a negative acknowledgment may be determined by not receiving an acknowledgment after an UL OFDMA transmission). Step 51084 thus determines whether the UL OFDMA transmission was successful or not, for instance by determining whether an acknowledgment of the trigger-based PPDU response is received from the AP (if not, the transmission was unsuccessful).

In case of successful MU UL OFDMA transmission, the non-AP station sets the NFRP contention window, NCW, to a (predetermined) low boundary value, for instance NCWmin of the NFRP-RAPS of the station's BSS, and initializes the NBO counter to an integer value randomly selected from a uniform distribution in the range 0 to NCW. This is step S1086.

In case of unsuccessful MU UL OFDMA transmission, the non-AP station may double NCW and draw a new NBO value. For instance, it updates the NCW to 2 x NCW + 1 when NCW cannot be above NCW,,a" of the NFRP-RAPS of the station's BSS, and randomly selects the NBO counter in the range of 0 and NCW. This is step S1088.

In the case that the non-AP station has transmitted NDP energy 211 on a randomly-selected RU tone set due to the expiration of its NBO counter (step 51074) but the non-AP station has not been scheduled in the subsequent trigger frame 620 (no step S282), the NCW value local to the non-AP station is not updated through steps S1086 or S1088, but kept unchanged. This is because the missing scheduling (by trigger frame 620) may be due to a decision (or selection) by the AP (e.g. too many non-AP stations may have responded to the RA-NFRP trigger frame 600 compared to the 9 RUs available for subsequent UL MU OFDMA transmission). No information is provided on tone contention, so the value of NCW is kept unchanged.

The embodiment of Figure 10 thus relates to a contention method based on a computation of backoff values corresponding to a number of RU Tone Sets or corresponding Indexes a non-AP station waits before sending energy on a RU Tone Set.

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

Many further modifications and variations will suggest themselves to those versed in the art upon referring 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 (25)

1. CLAIMS1. A communication method in a wireless network, comprising the following steps at a station: receiving, from an access point, AP, a null data packet, NDP, feedback report poll, NFRP, trigger frame, the NFRP trigger frame defining a first range of association identifiers, AIDS, of stations authorized to access a plurality of resource unit, RU, tone sets for NDP feedback report responses, determining, from the NFRP trigger frame, an access scheme to the RU tone sets, when it is determined a random access to the RU tone sets, obtaining a scale factor from a range scaling field in the NFRP trigger frame, obtaining a second range of station AIDS from the first range and the scale factor, when an AID of the station is included in the second range, randomly selecting a responding RU tone set from the plurality of RU tone sets, and sending a NDP feedback report response on the selected responding RU tone set.
2. 2. The communication method of Claim 1, wherein determining an access scheme is based ona trigger type field in the NFRP trigger frame, ora feedback type field in the NFRP trigger frame, or a value of the range scaling field in the NFRP trigger frame.
3. 3. The communication method of Claim 1, further comprising determining the NDP feedback report response to be sent depending on a feedback type field in the NFRP trigger frame.
4. 4. The communication method of Claim 1, further comprising, when it is determined a scheduled access to the RU tone sets, selecting a responding RU tone set from the plurality of RU tone sets based on the position of an AID of the station within the first range.
5. 5. The communication method of Claim 1, further comprising, at the station: receiving, from the AP, a subsequent trigger frame reserving a plurality of resource units, wherein a resource unit is assigned to the station based on an index of the responding RU tone set, responsive to the subsequent trigger frame, sending a trigger-based PPDU response on the assigned resource unit.
6. 6. The communication method of Claim 1, randomly selecting a responding RU tone set is based on a contention-based access method using a decrementing NFRP backoff, NBO, counter of the station.
7. 7. The communication method of Claim 6, wherein if the NBO counter is not greater than a number of RU tone sets in the NFRP trigger frame, the station randomly selects one of the RU tone sets, otherwise the station decrements the NBO counter by the number of RU tone sets in the NFRP trigger frame.
8. 8. The communication method of Claim 5 and of Claim 6, further comprising, at the station, determining whether an acknowledgment of the trigger-based PPDU response is received from the AP, and in case of successful trigger-based PPDU response transmission, setting a NFRP contention window, NCW, to a predefined value, and initializing the NBO counter to an integer value randomly selected from a uniform distribution in the range 0 to NCW, and in case of unsuccessful trigger-based PPDU response transmission, updating the NCW to 2 x NCW + 1 when NCW is less than a predefined maximum value, and randomly selecting the NBO counter in the range of 0 and NCW.
9. 9. A communication method in a wireless network, comprising the following steps at an access point: sending, to stations, a null data packet, NDP, feedback report poll, NFRP, trigger frame, the NFRP trigger frame defining a first range of association identifiers, AIDs, of stations authorized to access a plurality of resource unit, RU, tone sets for NDP feedback report responses, wherein the NFRP trigger frame further includes an access type indication defining whether the RU tone sets are accessed on a random basis by the stations, and a range scaling field defining a scale factor to obtain, from the first range, a second range of AlDs of stations authorized to access the plurality of RU tone sets on the random basis, and receiving, from at least one responding station having an AID in the second range, a NDP feedback report response on a responding RU tone set.
10. 10. The communication method of Claim 9, wherein the access type indication is provided with a specific value in a trigger type field or a feedback type field or the range scaling field in the NFRP trigger frame.
11. 11. The communication method of Claim 9, wherein the responding station has an AID outside the first range.
12. 12. The communication method of Claim 9, further comprising sending by the AP a subsequent trigger frame reserving a plurality of resource units, wherein a resource unit is assigned to the responding station using an index of the responding RU tone set.
13. 13. The communication method of Claim 1 or 9, wherein a zero value in the range scaling field defines a scheduled access to the RU tone sets and a non-zero value in the range scaling field defines a random access to the RU tone sets.
14. 14. The communication method of Claim 1 or 9, wherein an access type indication defining an access scheme to the RU tone sets is separate from a Starting AID field defining the first AID of the first range.
15. 15. The communication method of Claim 1 or 9, wherein the scale factor equals 2RA-SE, where RA_SF is a value of the range scaling field.
16. 16. The communication method of Claim 1 or 9, wherein the second range corresponds to the first range rescaled by the scale factor.
17. 17. The communication method of Claim 16, wherein the second range has the same starting AID as the first range with a range width multiplied by the scale factor.
18. 18. The communication method of Claim 1 or 9, wherein the range scaling field isa two-bit or three-bit field.
19. 19. The communication method of Claim 1 or 9, wherein a bit length of the range scaling field depends on a width the first range.
20. 20. The communication method of Claim 1 or 9, wherein the range scaling field is included in a Reserved field of a User Info field of the NFRP trigger frame according to Draft 4.1 of IEEE 802.11ax.
21. 21. The communication method of Claim 1 or 9, wherein the range scaling field is included in a Trigger Dependent Common Info field of a Common Info field of the NFRP trigger frame according to Draft 4.1 of IEEE 802.11ax.
22. 22. The communication method of Claim 1 or 9, wherein the first range includes the same number of AIDS as the number of RU tone sets in the plurality.
23. 23. The communication method of Claim 1 or 9, wherein the first range is defined by fields in the NFRP trigger frame, including a starting AID field, a channel bandwidth field and a multiplexing flag field.
24. 24. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a communication device, causes the communication device to perform the communication method of Claim 1 or 11.
25. 25. A communication device comprising at least one microprocessor configured for carrying out the steps of the communication method of Claim 1 or 11.