GB2592689A - Method and apparatus for using multiple resource units per stations in a multiple user uplink OFDMA scheme - Google Patents

Abstract

A wireless network has an access point, AP, and a plurality of stations, STA. Communication in the wireless network is performed over a communication channel, which is split into a plurality of resource units (RUs), between the access point and the plurality of stations. A trigger frame is sent by the access point to the stations, the trigger frame allocating resource units to the stations for allowing the stations to send data through the allocated resource units. The trigger frame allocates at least two resource units to an identified station. Each RU may be defined by a size, in number of tones, and a location of the RU in the communication channel. The trigger frame may have at least one resource unit identifier for identifying one or more resource units. The trigger frame may have a plurality of fields per station, each field having the station identifier (e.g. AID) and an identifier of one or more of the RUs associated with the station identifier.

Description

METHOD AND APPARATUS FOR USING MULTIPLE RESOURCE UNITS PER STATIONS IN A MULTIPLE USER UPLINK OFDMA SCHEME

FIELD OF THE INVENTION

The present invention relates generally to communication networks and more specifically to wireless communication methods in wireless network comprising a plurality of stations, one of these stations playing the role of an access point, the other stations being connected to the access point, and corresponding devices.

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

BACKGROUND OF THE INVENTION

The IEEE 802.11 (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.

The 802.11ax standard (also called High-Efficiency Wireless (HEW)) and marketed as Wi-Fi 6 by Wi-Fi Alliance, has two modes of operation: - Single User: this is the conventional Enhanced Distributed Channel Access (EDCA). In this sequential mode, the wireless stations send and receive data one at a time once they secure (via EDCA contention) access to the medium (through EDCA contention); - Multi-User: this mode allows for simultaneous operation of multiple non-AP stations. The standard divides this mode further into Downlink and Uplink Multi-user. The AP acts as the central controller of all aspects of multi-user operation.

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 control frames, known as Trigger Frames (TF), which define 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.

In the 802.11ax amendment, one RU may be allocated by a basic trigger frame to a specific non-AP station using 16-bit Association IDentifiers (AlDs) assigned to them upon registration to the AP (so-called scheduled RUs).

Recently, trends in the 802.11 latest amendment (802.11be) is to increase the maximum throughput of a transmission. This will be mainly achieved by increasing the maximum bandwidth of the operating band up to 320 MHz. Another trend is to avoid collisions between non-AP stations or 25 between a non-AP station and the AP by making a more intensive usage of the Multi-user uplink mechanism Unfortunately, the usage of such large bandwidths creates additional problems, especially by increasing the probability of interference with other wireless systems. The main reason is that even if the usage of very wide operating bands is allowed, this will be limited in a first step to the high-end devices that will support those large bandwidths. Nevertheless, those high-end stations will have to coexist with stations operating on narrower operating bands.

As a result, the probability of partial interference on the wide operating band increases.

A better usage of such wide operating bands then requires a more flexible approach of the RU allocations in particular to accommodate narrow parts of the limitation.

More generally, information delivered by an 802.11ax Trigger Frame is seen as not being adapted to a flexible usage of the spectrum.

SUMMARY OF INVENTION

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

According to a first aspect of the invention, there is provided a method of communication over a communication channel of a wireless network, the wireless network comprising an access point and a plurality of stations, the communication channel being split into a plurality of resource units. The method comprises: -sending by the access point a trigger frame, the trigger frame allocating resource units to stations for allowing the stations to send data through the allocated resource units, wherein the trigger frame comprises an identifier of one station associated with at least two resource units allocated to the station.

The advantage of the method is to propose a solution to the poor spectrum usage during a multi-user uplink transmission using a wide transmission channel partially interfering with another communication system. The AP may allocate several RUs to a single non-AP station and several RUs may be used by a non-AP station during a multiuser uplink transmission. This allocation may be useful with a fragmented operating channel, for instance due to interferences.

The method may comprise other features, alone or in combination, such as -each resource unit is defined by a size, in number of tones, and a location of the resource unit in the communication channel; - the trigger frame comprises at least one resource unit identifier for identifying one or more resource units; - the trigger frame comprises at least two resource unit identifiers, each resource unit identifier identifying a single resource unit; -the resource unit identifier identifies a plurality of resource units; - the resource units are not contiguous in the communication channel or the resource units are contiguous in the communication channel; - the trigger frame comprises a plurality of fields per station, each field comprising the station identifier and an identifier of one or more of the resource units associated with the station identifier; - the trigger frame comprises a flag allowing the station to identity the last field in the trigger frame containing a resource unit identifier associated with the station; - the trigger frame comprises one field per station, the field comprising the station identifier and the one or more identifiers of the resource units associated with the station identifier; and/or - the trigger frame comprises an indicator indicating that at least two resource units are allocated to the station. Advantageously, these features facilitate the decoding by the non-AP station and/or avoid the overhead induced by the repetition of some transmission parameters identical for all or a part of the allocated resource units.

According to a second aspect of the invention, there is provided a method of communication over a communication channel of a wireless network, the wireless network comprising an access point and a plurality of stations, the communication channel being split into a plurality of resource units. The method comprises, by the station: - receiving the trigger frame; - decoding the trigger frame in order to determine the at least two resource units associated to the station.

In a particular embodiment, in a preliminary step, the station sends to the access point an information element indicating the capability of the station to receive the trigger frame.

According to a third aspect of the invention, there is provided a communication device for communicating over a communication channel of a wireless network comprising an access point and a plurality of stations, the communication channel being split into a plurality of resource units, the communication device, acting as the access point, comprising at least one microprocessor configured for carrying out the steps of the methods here above. At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entire hardware embodiment, an entire software embodiment (including 10 firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer-readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, 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 RE signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 illustrates a typical wireless communication system in which embodiments of the invention may be implemented; Figures 2A and 26 illustrate a conventional trigger-based (TB) MU 30 UL OFDMA transmission according to 802.11ax, Figures 3A to 3C present various formats of 802.11 frames according to the 802.11ax standard; Figures 4A and 4B illustrate a general embodiment of disclosed communication methods; Figure 5 illustrates, using a flowchart, an embodiment of the invention implemented at an AP station; Figure 6 illustrates, using a flowchart, an embodiment of the invention implemented at a non-AP station; Figure 7A to 7D illustrates various structures of a Trigger Frame; Figure 8 illustrates an example of MU UL transmission according to the disclosed embodiments; Figure 9A shows a schematic representation a communication device; and Figure 9B shows a schematic representation of a wireless communication device.

DETAILED DESCRIPTION

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

Aspects of the present disclosure generally relate to enhanced multi-user (MU) uplink (UL) protocols in wireless networks that allow the allocation by an AP of several RUs to a given station, and the usage of several RUs by a station for a MU UL transmission. As will be described in more detail herein, a station may send a trigger frame triggering MU transmissions with an appropriate signalling allocating several RUs per station. The present disclosure regards how the format of the trigger frame can be modified to efficiently handle the usage of several RUs per stations in a MU UL transmission.

The techniques described herein may be used for various broadband wireless communication systems, including communication systems that are based on an orthogonal multiplexing scheme. Examples of such communication systems include Spatial Division Multiple Access (SDMA) system, Time Division Multiple Access (TDMA) system, Orthogonal Frequency Division Multiple Access (OFDMA) system, and Single-Carrier Frequency Division Multiple Access (SCFDMA) system. An SDMA system may utilise different directions to simultaneously transmit data belonging to multiple user terminals. A TDMA system may allow multiple user terminals to share the same frequency channel by dividing the transmission signal into different time slots or resource units, each time slot being assigned to different user terminal. An OFDMA system utilises orthogonal frequency division multiplexing (OFDM), which is a modulation technique that partitions the overall system bandwidth into multiple orthogonal sub-carriers or resource units. These sub-carriers may also be called tones, bins, etc. With OFDM, each sub-carrier may be independently modulated with data. An SC-FDMA system may utilise interleaved FDMA (IFDMA) to transmit on sub-carriers that are distributed across the system bandwidth, localised FDMA (LFDMA) to transmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks of adjacent sub-carriers.

The teachings herein may be incorporated into (e.g., implemented within or performed by) a variety of apparatuses (e.g., stations). In some aspects, a wireless station implemented in accordance with the teachings herein may comprise an access point (so-called AP) or not (so-called non-AP station). An AP may comprise, be implemented as, or known as a Node B, Radio Network Controller ("RNC"), evolved Node B (eNB), Base Station Controller ("BSC"), Base Transceiver Station ("BTS"), Base Station ("BS"), Transceiver Function ("TF"), Radio Router, Radio Transceiver, Basic Service Set ("BSS"), Extended Service Set ("ESS"), Radio Base Station ("RBS"), or some other terminology.

A non-AP station may comprise, be implemented as, or known as a subscriber station, a subscriber unit, a mobile station (MS), a remote station, a remote terminal, a user terminal (UT), a user agent, a user device, user equipment (UE), a user station, or some other terminology. In some implementations, a non-AP station may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol ("SIP") phone, a wireless local loop ("WLL") station, a personal digital assistant ("PDA"), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a tablet, a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a global positioning system (GPS) device, or any other suitable device that is configured to communicate via a wireless medium. In some aspects, the non-AP station may be a wireless node. Such wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link.

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 (WLAN), 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 802.1 lax non-AP STA and an 802.1 lax 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.

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 stations. Each BSS is uniquely identified by a specific basic service set identifier, BSSID, and managed by a virtual AP implemented in the physical AR To access the medium, any station, including the AP, starts counting down a backoff counter designed to expire after a number of time slots 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, 01 320 MHz. The channels may include one 25 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 30 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 20 MHz 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 20 MHz 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 that 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.

With reference to Figure 2a, to actually perform such MU UL transmission, the 802.11ax standard splits a granted communication channel into resource units 201-204 (RUs) that are shared in the frequency domain by the multiple stations, based on Orthogonal Frequency Division Multiple Access (OFDMA) technique.

To finely control the MU UL transmissions by the non-AP stations 101107, the AP 110 sends a trigger frame 210 which defines how the channel is split into RUs and which non-AP station is allowed to transmit over each RU. In this example, trigger frame 210 assigns RU 201 to STA1, RU 202 to STA2, RU 203 to STA3 and RU 204 to STA4. The assignment is made using the AIDs of the non-AP stations.

Upon reception of trigger frame 210, each non-AP station determines its assigned RU thanks to its own AID and can start transmitting MU frames 220 (known as HE TB PPDU) over its assigned RU to the AP after a SIFS period after trigger frame 210.

Due to the triggering mechanism, the terms "trigger-based MU UL transmission" are used.

The AP closes the transmission opportunity by emitting an acknowledgment (Block Ack, BA, frame 240) towards the triggered stations. Figure 2b illustrates the same MU UL transmission from station 10 perspective.

Figures 3a and 3b illustrate various formats of 802.11 frames according to the 802.11 ax standards, draft version 6.0.

In these various PPDU (PLCP Protocol Data Unit) formats, the Data field refers to the payload data, which contains a PSDU (PLCP Service Data Unit) from/to MAC layer. PLCP stands for Physical Layer Convergence Procedure, which is a sublayer of the PHY layer interacting with the MAC layer. Note that PSDU and MPDU terms refer to the same but from different sublayer perspectives (PSDU from PHY sublayer and MPDU from MAC sublayer). The PLCP prepares the frame for transmission by taking the frame from the MAC sublayer and creating a PPDU (by adding a preamble and PHY header to the PSDU), then modulates and transmits the data as bits.

Figure 3a shows a non-HT (High Throughput) PPDU (Physical layer (PHY) Protocol Data Unit) format.

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

The L-STF and the L-LTF may be used for synchronisation and channel estimation. The L-SIG may include signalling information such as length information representing a length of the entire frame and rate information.

A trigger frame, such as IF 210 is a control frame following the 802.11 legacy non-HT PPDU format. This allows all the 802.11 stations to be aware when the AP accesses the medium, to avoid collisions.

While the MAC payload 340 is basically empty for classical control 5 frames (such as RTS or CTS frame), it is enhanced with an information structure for trigger frames.

Figure 3b illustrates the format of the trigger frame (the Data field 340 of the non-HT PPDU of Figure 3a) as described in section 9.3.1.23 of the 802.11ax standards, draft version 6.0, to perform MU UL OFDMA transmissions.

The trigger frame 210 contains several fields as defined in the IEEE standard 802.11ax and in particular it includes a single Common Info field 300 and a plurality of User Info fields 310.

Each User Info field 310 defines the assignment of the RUs to respective non-AP stations 101-107, as well as communication parameters to respect for UL communication with the AP. To do so, RU Allocation subfield 312 identifies the RU concerned (central frequency and frequency bandwidth), while AID12 subfield 311 carries the 12 LSBs of the AID of the non-AP station for which the RU is assigned.

Bit B39 313 of User Info field 310 is currently not used.

Trigger Dependent User info subfield 314 is mainly used to provide details on communication parameters defined by the other subfields of the User Info field 310. The content of Trigger Dependent User info subfield 314 depends on the type of trigger frame.

The User Info field as defined in 802.11ax thus clearly authorises only UL transmissions as only the source non-AP station is identified in Al D12 subfield Figure 3c illustrates the format of the trigger frame (the trigger dependent user info field 314 of a basic trigger frame. as described in section 9.3.1.23 of the 802.11 ax standards, draft version 6.0, to perform MU UL OFDMA 30 transmissions.

Bit 5 is currently not used and reserved for future use.

In the current version of the standard, the following applies regarding the allocation of resources: "An AP shall not transmit a Trigger frame that contains more than one User Info field with the same value in the AID12 subfield unless the value in the AID12 subfield is 0 or greater than 2007. The AP shall place User Info fields with the same value in the AID12 subfield together as a contiguous block in the Trigger frame. The AP shall place User Info fields with the AID12 subfield set to 0 or a value greater than 2007 after User Info fields with the AID12 subfield set to a value in the range 1 to 2007 (if any present)." (Draft 802.11ax D6.0 -6.5.2.2.4 Allowed settings of the Trigger frame fields and TRS Control subfield, page 350, lines 32-37) The AID12=0 code is associated to a random access protocol for stations associated to the AP. The AID12=2045 code is associated to a random access protocol for stations not associated to the AP. Typically, the last code is used to provide resource units to be used by a not associated station for requesting an association.

The codes above 2007 may be defined for groups of stations. Consequently, at reception of the trigger frame, the station has the following behaviour according to the current version of the standard: "A non-AP STA addressed by a User Info field in a Trigger frame (i.e., the AID12 subfield is equal to the 12 LSBs of the AID of the non-AP STA) may ignore the remainder of User Info fields in the Trigger frame." (Draft 802.11ax D6.0 -26.5.2.3 Non-AP STA behaviour for UL MU operation, page 353, lines 28-29) Figures 4A and 4B are flowcharts of a general embodiment of

methods to improve the prior art.

The method of communication concerns a wireless network comprising an access point AP and a plurality of stations, or non-AP stations, communicating over a communication channel. The non-AP station is known by the AP and has a station identifier AID. The communication channel is split into a plurality of resource units RUs.

The access of the non-AP station to the resource units for sending data is given by the access point to the stations by sending a trigger frame.

The method comprises the step 400, of Figure 4A, of sending by the access point the trigger frame. The trigger frame associates the station identifier AID of one station to at least two resource units.

From the stations perspective, Figure 4B, the method comprises: Receiving, step 450, the trigger frame; Decoding, step 460, the trigger frame in order to determine the at least two resource units associated to the station.

Detailed embodiments of the method are disclosed here under.

Figure 5 illustrates, using a flowchart, a detailed embodiment implemented at an AP station.

At step 500, the AP generates a trigger frame 710 according to format/structure described here under in relation with Figures 7a to 7d. According to the internal scheduling of the AP, a trigger frame identifying one or more non-AP stations is created. The transmission parameter's values for each user info field being determined for the intended transmitting non-AP station.

At step 501 the generated trigger frame is transmitted at least to the non-AP stations identified in the trigger frame (non-AP stations with AID12 unique identifier indicated in at least one of the user info field 710 of the trigger frame 510. In case of AID12 field indicating a random-access procedure (for instance AID12=0 or 2045), then the trigger frame is intended to be received by all the non-AP stations associated to the AP (AID12=0) or non-associated to the AP (AI D12=2045).

At step 502 the Phy layer of the AP is configured to be able to receive and decode the data that will be sent by the triggered non-AP stations. In particular, this step allows an AP to set up its internal decoding means (reception chains) to the different MCS or transmission parameters and to be potentially prepared to receive several PPDUs from different stations.

At step 503 the Phy layer of the AP listens and decodes the multi-user Uplink transmission transmitted by at least one of the triggered non-AP stations and sends the decoded data to the upper layers of the protocol stack (typically to the MAC layer).

Figure 6 illustrates, using a flowchart, a detailed embodiment of the method implemented at a non-AP station.

Upon reception by a non-AP station of a trigger frame 510 at step 601, step 602 is executed.

At step 602, the non-AP station optionally determines if the received trigger frame identifies one or more resource units (Ru allocations) dedicated to the receiving non-AP station by reading an indicator optionally present in the trigger frame.

The receiving non-AP station then decodes the received trigger frame according to one of the formats described here under.

Depending on the formats, the receiving stations may need to decode all the user info fields or can stop decoding upon determination of the latest Ru allocation allocated to the decoding non-AP station. According to another format, the receiving station may need to determine if a user info field dedicated to it contains several RU allocations by parsing the user info field, or by reading an indicator.

At step 603, the station receiving the trigger frame prepares one or more data packet to be sent on the one or more determined Ru allocation.

Figures 7a to 7d illustrate different trigger frame structure corresponding to different embodiments.

In a first trigger frame structure, the trigger frame 510 may contain several UIF 710 per non-AP station. In this case, each of the UIF 710 dedicated to a same non-AP station shares the same value of the AID12 field, the unique identifier of the non-AP stations. In this format, each RU, that is allocated by the AP to a given non-AP station, corresponds to a different UIF 710 with different values in the RU allocation field 711, but with the same AID12 value. This first format has several advantages. The first one is that the frame format is fully based on the 11ax frame format, and compatible with legacy stations. This means that it requires only reduced software modification of the non-AP stations eager to support the multiple RU per station feature. Another interesting advantage of this embodiment is that there is no obligation to have the same value for the transmission parameters. Typically, in this format, two U ID 710 dedicated to the same non-AP station may not only have different RU allocation (allowing the non-PA station to use several RUs), but also may have a different MCS value for different RU allocation. This means that a given non-AP station that supports this feature may use different modulation to transmit data simultaneously on two different RU allocation (central frequency and width). This can be very advantageous if the RU allocations allocated to a non-AP station are noncontiguous in the operating band and have different noise level, for instance requiring a lower MCS for the RU having the higher noise level in order to achieve a good transmission.

Even if this first format has several advantages, it also suffers of several drawbacks. The first one is the important overhead induced by the transmission of the transmission parameter's values for each RU allocation for a give non-AP station, even if most of them have the same values. Another drawback is that the non-AP station decoding a received trigger frame will have to decode all the U IF710 fields in order to be sure to determine all the RUs dedicated to it.

To overcome such drawbacks, alternative formats are described below.

In a first alternative format, to improve the decoding of a trigger frame by a receiving non-AP Station, an indicator indicating that several User Info fields per station are allowed can be added to the trigger frame (for instance in the common info field 300, by creating a new trigger frame type code value, or by adding information in the trigger dependent common info subfield of the common info field, or by using one reserved bit of the common field for this usage). In this case, stations will not stop immediately after finding a UIF dedicated to it, but continue to decode until the end of the user info fields of the current trigger frame.

If this indicator is not present, each station will save time by stopping upon finding a UIF dedicated to the station, as it will know that only one UIF will concern it.

In a second alternative format, the User Info Field 710 contains an indicator indicating if the current UIF is the last one intended to the same non-AP station in the trigger frame, or at least one of the following User Info field contains the same AID12 value. The decoding of a received frame is usually performed by starting from the bit of lower index to the bit of higher index (for instance from BO to B39 in the case of the User Info Field 310). In such a case, one possible encoding of this indicator is to use the reserved bit 312. This new bit called More RU Allocation 712 here under can be set to 0 in the last UIF trigger frame corresponding to a given AID, and 1 otherwise. This allows a receiving station to stop the decoding of the UlFs of a received trigger frame as soon as it decodes a UIF with an AID12 field containing its own AID and with a more Ru allocation field set to 0. In the case of a 320 MHz bandwidth allowing up to 144 RU allocations (16 channels of 20 MHz x 9 RUs of 26 tones per 20 MHz channel), the decoding gain can be very important. The Figure 7b illustrates the frame format according to a this disclosed format.

It is worth noting that first and second alternative formats can be used independently or in combination to be even more efficient.

The first and second alternative formats are associated with the first format.

In a second format different from the first format, more than one RU allocation can be signalled in a single User Info field. In this second format, the transmission parameter values are the same for all the RU allocations for a given station. This second embodiment is very efficient in terms of trigger frame length, but allows no flexibility with regard to the transmission parameter's values. In this embodiment, the RU allocation field 711 contains a new RU allocation value indicating the unique combination of RU allocations assigned to the stations. For instance, a new RU allocation value could indicate the usage of 30 the RU3 and RU4 as described in the example of Figure 8. This variant is requiring a lot of different values to indicate all the possible combination of RU allocations, but is simple to implement and compatible with legacy stations since they will ignore those new RU allocations.

In a first alternative format of this second format, the RU allocations are the same as in the existing 802.11ax amendment (defining the usage of only one RU), and in addition to the RU allocation field 711, additional RU allocations can be provided to the non-AP station. For example, Figure 7c provides a signalling, where the additional RU allocations are listed in the Trigger dependent user info field of the UIF 710. As a consequence, if the AP allocated n+1 RUs to a non-AP station (n0), one Ru allocation is indicated in the RU allocation field 711, and n other RU allocations are listed in the trigger dependent user info field.

In the example of Figure 7c, the additional RU allocations are concatenated at the end of the Trigger dependent User Info field as described in Figure 3c. This signalling avoids increasing the number of possible RU Allocation values and then avoid increasing the size of the RU Allocation field 711. On additional advantage of this signalling is that the format is fully compatible with the legacy stations (non-AP station that doesn't implement the invention), since the format is unchanged until the end of the preferred AC subfield of the Trigger dependent user info field.

To avoid decoding issue, an indicator may be present to indicate that the trigger dependent user info field is modified to contain multiple RUs. For instance, the reserved bit 721 may be used as an indicator, or the reserved bit B5 of the trigger dependent user info field. This indicator may also be implicitly included by creating a new type of trigger frame (a new value indicating for instance a basic trigger frame allowing multiple RUs per station). This indicator can be the same as in the first alternative format of the first format in case of combination of the first and second formats, or a new one if only the second format is implemented (only one user info field per station). This indicator allows the decoding station to know the type of format of the trigger dependent user info field.

A second alternative format to this second format consists in the creation of a new RU allocation 711 value dedicated to the multiple RU allocation signalling. This special value that is not currently used by the 802.11ax specification (for instance 255) indicates that several RUs are allocated to the station. In that case, the RU allocations can be found in the trigger dependent user info field as described in previous format. The main advantage is that this new value indicates a change in the format of the trigger dependent user info field so that the decoding station knows in advance the format to use. Preferably, this new value also encodes the number of RU allocations present in the trigger dependent user info field by reserving some bits, for instance the last bits, to encode the number of RU allocations. This additional encoding making even easier the work of the decoding station that can know the exact size of the trigger dependent user info field (n+1 Octets, with n= the number Ru allocations).

As already mentioned first and second formats can be used separately or in combination. In the case of the combination, the trigger frame 510 contains one or more User info fields 710 per station (with the same AID12 value as described in one of the alternatives of the first format) and each of the user info field 710 containing at one or more RU allocations (as described in one of the alternatives of the second format). This combination is the more efficient and flexible approach since it allows both to have a very compact trigger frame avoiding the repetition of transmission parameters values that are identical for several RU allocations by indicating all those RU allocations in a single user info field, and a flexible approach by allowing different transmission parameters per RU allocation by allowing the addition of several user info fields per station. The Figure 8 illustrates an allocation made by the access point AP that can be beneficial for the use of the combination. In this case, the non-AP station number 2 (STA2) have two very close and similar RU allocations 821 that will probably share the same transmission parameters. The non-AP station number 3 uses two RU allocations 822 and 823 of different widths and located in two different 20 MHz channels. In this latest case, the probability to have the same transmission parameters values is low and the AP may need to use two different user info fields to indicate those two sets of different transmission parameters values to the station 3.

In another aspect of the disclosed method, a station (AP or non-AP) may signal the support of this new feature (support of the multiple RUs per station). To do so, the station can send its capabilities into a dedicated information element during the association process (in one or several of the probe request, probe response, association request, association response, re-association request or re-association response frames). This information element contains an indicator (typically one bit) that indicates the capability of supporting the multiple RUs per station feature. In a variant or in addition to the previous capability bit, due to the fact that the support of multiple RU per station requires additional internal resources, the station can also indicate that it supports only a reduced version of the capability. Typically, one or two bits can encode the maximum number of RUs a station can use simultaneously. An alternative is the number of non-contiguous RUs that a station can handle simultaneously (RUs separated by one or more data tones). For instance, the combination of the two capabilities can be done thanks to the encoding of two bits (00 means no support, 01 support of up to 2 RUs, 10 supports of up to 3 RUs, and 11 support of 4 RUs).

Figure 9a schematically illustrates a communication device 900, either a non-AP station 101-107 or the access point 110, of the radio network 100, configured to implement at least one embodiment of the disclosed methods. The communication device 900 may preferably be a device such as a microcomputer, a workstation or a light portable device. The communication device 900 comprises a communication bus 913 to which there are preferably connected: - a central processing unit 901, such as a processor, denoted CPU; - a memory 903 for storing an executable code of methods or steps of the methods according to embodiments of the invention as well as the registers 25 adapted to record variables and parameters necessary for implementing the methods; and - at least one communication interface 902 connected to a wireless communication network, for example a communication network according to one of the IEEE 802.11 family of standards, via transmitting and receiving antennas 30 904.

Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 900 or connected to it. The representation of the bus is not limiting and in particular the central processing unit is operable to communicate instructions to any element of the communication device 900 directly or by means of another element of the communication device 900.

The executable code may be stored in a memory that may either be read only, a hard disk or on a removable digital medium such as for example a disk. According to an optional variant, the executable code of the programs can be received by means of the communication network, via the interface 902, in order to be stored in the memory of the communication device 900 before being executed.

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

Figure 9b is a block diagram schematically illustrating the architecture of the communication device 900, either the AP 110 or one of the stations 101107, adapted to carry out, at least partially, the disclosed methods. As illustrated, device 900 comprises a physical (PHY) layer block 923, a MAC layer block 922, and an application layer block 921.

The PHY layer block 923 (here an 802.11 standardised 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 100, such as 802.11 frames, for instance medium access trigger frames IF 510 (Figure 7) to reserve a transmission slot, MAC data and management frames based on a 20 MHz width to interact with legacy 802.11 stations, as well as of MAC data frames of OFDMA type having smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/from that radio medium.

The MAC layer block or controller 922 preferably comprises a MAC 802.11 layer 924 implementing conventional 802.11ax MAC operations, and additional block 925 for carrying out, at least partially, the invention. The MAC layer block 922 may optionally be implemented in software, which software is loaded into RAM 903 and executed by CPU 901.

Preferably, the additional block 925, referred to as Triggered Tx Parameters management module for selecting transmission parameters applied to transmissions following a medium access trigger frame through OFDMA resource units (sub-channels), implements the part of embodiments of the invention (either from station perspective or from AP perspective).

For instance, and not exhaustively, the operations for the station (AP or non-AP) may include, at the AP, generating and sending a trigger frame allocating a RU for DiL or UL transmission, wherein the IF indicates whether a transmission parameter for transmitting data over the RU is set by the AP or by the source station. The operations at the non-AP station may include configuring the PHY for emission/reception over DiL/UL RUs according to the provided indication, that is to say the transmitted PPDU frame has a HE SU PPDU when the indication is provided (otherwise follows the HE TB PPDU format commonly used for triggered operations).

MAC 802.11 layer 924, Triggered Tx Parameters management module 925 interact one with the other in order to process communications accurately over OFDMA RU addressed to multiple stations according to 20 embodiments of the disclosed methods.

On top of the Figure, application layer block 921 runs an application that generates and receives data packets, for example data packets such as a video stream. Application layer block 921 represents all the stack layers above MAC layer according to ISO standardisation.

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 making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular, the different features from different embodiments may be interchanged, where appropriate In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims (16)

1. CLAIMS1. A method of communication over a communication channel of a wireless network, the wireless network comprising an access point and a plurality of stations, the communication channel being split into a plurality of resource units, said method comprising: -sending by the access point a trigger frame, the trigger frame allocating resource units to stations for allowing the stations to send data through the allocated resource units, wherein the trigger frame comprises an identifier of one station associated with at least two resource units allocated to the station.
2. 2. The method of claim 1, wherein each resource unit is defined by a size, in number of tones, and a location of the resource unit in the communication channel.
3. 3. The method of claim1 or 2, wherein the trigger frame comprises at least one resource unit identifier for identifying one or more resource units.
4. 4. The method of claim 3, wherein the trigger frame comprises at least two resource unit identifiers, each resource unit identifier identifying a single resource unit.
5. 5. The method of claim 3, wherein the resource unit identifier identifies a plurality of resource units.
6. 6. The method of claim 5, wherein the resource units are not contiguous in the communication channel.
7. 7. The method of claim 5, wherein the resource units are contiguous in the communication channel.
8. 8. The method of claim 3, wherein the trigger frame comprises a plurality of fields per station, each field comprising the station identifier and an identifier of one or more of the resource units associated with the station identifier.
9. 9. The method of claim 8, wherein the trigger frame comprises a flag allowing the station to identity the last field in the trigger frame containing a resource unit identifier associated with the station.
10. 10. The method of claim 3, wherein the trigger frame comprises one field per station, the field comprising the station identifier and the one or more identifiers of the resource units associated with the station identifier.
11. 11. The method according to any one of claims 1 to 10, wherein the trigger frame comprises an indicator indicating that at least two resource units are allocated to the station.
12. 12. A method of communication over a communication channel of a wireless network, the wireless network comprising an access point and a plurality of stations, the communication channel being split into a plurality of resource units, said method comprising, by the station: - receiving the trigger frame; - decoding the trigger frame in order to determine the at least two resource units associated to the station.
13. 13. The method of claim 12, wherein, in a preliminary step, the station sends to the access point an information element indicating the capability of the station to receive the trigger frame.
14. 14. A communication device for communicating over a communication channel of a wireless network comprising an access point and a plurality of stations, the communication channel being split into a plurality of resource units, the communication device, acting as the access point, comprising at least one microprocessor configured for carrying out the steps of the method according to any one of the claims 1 to 11.
15. 15. A computer program product for a programmable apparatus, the 5 computer program product comprising a sequence of instructions for implementing a method according to any one of the claims Ito 13, when loaded into and executed by the programmable apparatus.
16. 16. A computer-readable storage medium storing instructions of a 10 computer program for implementing a method according to any one of the claims 1 to 13.