EDCA Backoff Restart Procedures and State Switching in EMLSR or EMLMR Co-Affiliated Stations

Abstract

The non-AP MLD of the active EMLSR wants to initiate a frame exchange with the AP MLD over one of the EMLSR links. A first link is selected and the corresponding "first" Affiliated STA initiates an EDCA backoff procedure that decrements one or more backoff counters to access the first link. Alternatively, each EMLSR's co-affiliated STA may initiate an EDCA backoff procedure to access its respective link. In an embodiment, the first Affiliated STA is switched from a listening operation state to a valid frame exchange state before initiating the EDCA backoff procedure. In another embodiment, the first Affiliated STA initiates the EDCA backoff procedure first and is switched to a valid frame exchange state upon expiration of the backoff counter. The corresponding state switching procedure may be initiated to terminate with or in response to expiration of the backoff counter.

Description

[Technical field]

[0001] The present invention relates generally to wireless communications, and more particularly to Multi-Link (ML) communications. [Background technology]

[0002] Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single Carrier FDMA (SC-FDMA) networks.

[0003] The 802.11 family of standards, adopted by the Institute of Electrical and Electronics Engineers (IEEE®), provides a number of mechanisms for wireless communication between STAs.

[0004] With the development of latency sensitive applications such as online gaming, real-time video streaming, virtual reality, remote control of drones and robots, etc., the requirements and issues of better throughput, lower latency and robustness must be taken into consideration. Such issues are currently being considered by the IEEE 802.11 Working Group as the primary objectives for issuing the next major 802.11 release, known as 802.11be or Extremely High Throughput (EHT).

[0005] The IEEE P802.11be / D1.5 version (March 2022, hereinafter referred to as the "D1.5 standard") introduces Multi-Link (ML) Operation (MLO), which improves data throughput by enabling communication between STAs over multiple parallel and discontinuous communication links.

[0006] MLO allows a non-AP (Access Point) MLD (ML Device) to register with an AP MLD, i.e. discover, authenticate, associate and set up multiple links with the AP MLD. Each link allows channel access and frame exchange between the non-AP MLD and the AP MLD based on the supported capabilities exchanged during the association procedure.

[0007] An MLD is a logical entity that has multiple stations (STAs) and a single Medium Access Control (MAC) Service Access Point (SAP) to a Logical Link Control (LLC), containing one MAC data service. Thus, an AP MLD consists of multiple affiliated APs, and a non-AP MLD consists of multiple affiliated non-AP STAs. Affiliated STAs in both AP MLD and non-AP MLD can use 802.11 mechanisms to communicate with affiliated STAs in another MLD via each of the multiple communication links that are set up.

[0008] With the introduction of MLO and MLD spatial multiplexing capabilities, the D1.5 standard introduced new Operating Modes (OM) called Enhanced Multi-Link Operating Mode (EML OM), namely EMLSR (Enhanced Multi-Link Single Radio) mode and EMLMR (Enhanced Multi-Link Multi-Radio) mode.

[0009] A non-AP MLD declares its support for the EML mode of operation (known as EML Capabilities) to the AP MLD during the association phase. In this mode of operation, activation and deactivation of the EML mode of operation is initiated by the non-AP MLD sending a specific EHT action frame called "EML OM Notification". In the D1.5 standard, the two modes EMLSR and EMLMR are said to be mutually exclusive.

[0010] When the EMLMR mode is enabled, the non-AP MLD listens simultaneously to a set of active links (so-called EMLMR links, usually consisting of two active links) to receive the Initial frame sent by the AP MLD and start the frame exchange, and then can aggregate some physical resources of different radios used on different links (so-called EMLMR links) to transmit and receive data of up to a predefined number of supported receive and transmit spatial streams only via one EMLMR link at a time (usually the link on which the Initial frame was received), which may be more than the number of receive and transmit spatial streams supported by each radio.

[0011] When the EMLSR mode is activated, the non-AP MLD listens simultaneously on a set of valid links (the so-called EMLSR links, typically consisting of two valid links) to receive Initial Control frames (e.g., MU-RTS trigger frame, BSRP trigger frame) from the AP MLD to initiate frame exchange, and then can exchange data frames with the AP MLD only via one EMLSR link at a time (typically the link on which the Initial Control frame was received).

[0012] In addition, the non-AP MLD also has the ability to initiate frame exchange with the AP MLD over one EMLSR or EMLMR link by itself to transmit uplink data. In such a case, the STAs affiliated to the non-AP MLD operating in EMLSR or EMLMR mode do not need to transmit Initial Control or Initial frames to initiate frame exchange with the AP MLD (non-triggered UL transmissions) and access the wireless medium according to the rules defined in Section 10.3.2.4 (NAV Configuration and Reconfiguration) and Section 10.23.2 (HCF Contention-Based Channel Access (EDCA)) as specified in the IEEE 802.11-2020 standard.

[0013] However, conventional contention-based channel access procedures such as EDCA are not fully adapted to the EML mode, where the EMLSR or EMLMR links are not completely independent of each other. Therefore, it is necessary to improve the EDCA procedure for the EML mode. Summary of the Invention

[0014] It is a broad object of the present invention to provide an enhanced contention-based channel access procedure adapted to an EML mode, taking into account the EML Capabilities associated with the active EML mode (EMLSR or EMLMR).

[0015] The method for communicating in a wireless network according to the present invention comprises, in a non-access point (non-AP) multi-link device (MLD) operating in an active enhanced multi-link (EML) mode, the steps of: Initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure by a first station (STA) corresponding to a first link of a set of valid links to which an EML mode is applied that are affiliated with a non-AP MLD, to access the first link by decrementing a backoff counter; The method may include switching the first Affiliated STA from a listening operation state to an active frame exchange state to initiate a frame exchange with the AP MLD over the first link.

[0016] In an embodiment, switching the first Affiliated STA to the valid frame exchange state is performed before initiating an EDCA backoff procedure to decrement a backoff counter by the first Affiliated STA in the valid frame exchange state.

[0017] For example, a method of communication in a wireless network may be implemented in a non-access point (non-AP) Multilink Device (MLD) operating in an active Enhanced Multilink (EML) mode: Initiating a frame exchange with the AP MLD via a first link by a first STA corresponding to a first link of a set of valid links to which an EML mode affiliated with a non-AP MLD is applied; Initiating a frame exchange is The method includes switching the first affiliated STA from a listening operation state to a valid frame exchange state before initiating an enhanced distributed channel access (EDCA) backoff procedure that decrements a backoff counter to access the first link by the first affiliated STA in the valid frame exchange state.

[0018] In these embodiments, the EDCA backoff procedure is not affected by the STA's state switching, and therefore this first Affiliated STA is ready to perform a frame exchange as soon as its backoff counter expires.

[0019] In another embodiment, switching the first Affiliated STA to the valid frame exchange state is performed when the backoff counter reaches a value of zero.

[0020] For example, a method of communication in a wireless network may be implemented in a non-access point (non-AP) Multilink Device (MLD) operating in an active Enhanced Multilink (EML) mode: Initiating a frame exchange with the AP MLD via a first link by a first STA corresponding to a first link of a set of valid links to which an EML mode is applied, the first STA being affiliated with the non-AP MLD; Initiating a frame exchange is initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure by a first affiliated STA in a listening operational state to access the first link, the EDCA backoff procedure decrementing a backoff counter; Switching the first Affiliated STA from a listening operation state to a valid frame exchange enabled state when the backoff counter reaches a value of zero.

[0021] In these embodiments, while the backoff counter is being decremented, other co-affiliated STAs of the non-AP MLD are still in a listening state, which means that the AP MLD can still initiate frame exchanges with the other co-affiliated STAs despite the counter decrement by the first affiliated STA, thereby improving network communication.

[0022] In another embodiment for efficiently driving EDCA on EMLSR or EMLMR links to mirror their dependencies, in response to initiating a frame exchange with the AP MLD on a second link of a set of valid links where the EML mode applies, a backoff counter for driving EDCA on a first link of that set is paused.

[0023] For example, a method of communication in a wireless network may be implemented in a non-access point (non-AP) Multilink Device (MLD) operating in an active Enhanced Multilink (EML) mode: In response to initiating a frame exchange with the AP MLD over a second link of a set of valid links to which the EML mode applies, pausing a back-off counter that drives enhanced distributed channel access (EDCA) on a first link of the set.

[0024] Thus, a certain event occurring on the second link has a direct impact on the first link and on other links of the same EMLSR or EMLMR. Unlike known techniques, the suspension of the back-off counter for accessing a medium (link) no longer depends only on the idle / busy state of the target medium, but on the activity (frame exchange) on the link of the other EMLSR / EMLMR. This avoids obtaining EDCA access to the first link while the corresponding co-affiliated STA is unavailable (because the radio resources have been allocated to the co-affiliated STA by the frame exchange). It can be seen that this improves the efficiency of the EDCA procedure.

[0025] Although only one first link of the set is mentioned here, the invention can be applied to other links (different from the second link) of the EMLSR / EMLMR link set.

[0026] Optional features of the invention are defined below with reference to the method, but these can be replaced by apparatus features.

[0027] In some embodiments in which the decrement is performed while the first affiliated STA is in a valid frame exchange state, the method further includes aborting the decrement and applying one of a plurality of policies upon detecting that the first link becomes busy during the decrement of the backoff counter.

[0028] As an example, policy a) includes maintaining the first affiliated STA in a valid frame exchange state and resuming decrementation when the first link becomes idle again.

[0029] As another example, policy b) includes returning the first affiliated STA to a listening operating state regardless of the time determined based on the frame in which the detection occurred.

[0030] As yet another example, policy c) includes switching the first affiliated STA to a listening operation state for a predetermined period of time based on a period determined based on the frame in which the detection occurred before switching back to a valid frame exchange state to resume decrementation if the first link becomes idle again.

[0031] As yet another example, policy d) includes determining an identified period based on the frame in which the detection occurred, and deciding to apply one or the other of policies a), b), or c) depending on the determined period.

[0032] In some embodiments where the decrement is performed while the first Affiliated STA is in a listening state, the method further includes suspending the EDCA backoff procedure (i.e., the decrement of the backoff counter is stopped) upon receiving an Initial frame from the AP MLD over the second link of the set. The Initial frame is understood to be a frame that initiates a frame exchange initiated by the AP MLD. The Initial frame is known by this name in EMLMR mode and by the name "Initial Control frame" in EMLSR mode. Thus, the non-AP MLD may be involved in a new frame exchange initiated by the AP on the second link. This is possible because other co-affiliated STAs corresponding to the second link are still in a listening state while the backoff counter is being decremented.

[0033] More generally, the method may further include, upon receiving an Initial frame from the AP MLD via a second link of the set, determining whether to suspend the EDCA backoff procedure based on one of a number of criteria.

[0034] As a first example, the criteria may include determining whether the first Affiliated STA has been assigned full radio resources.

[0035] As another example, the criteria may determine whether the Initial frame is a MU-RTS trigger frame.

[0036] As yet another example, the criteria may include determining whether uplink data has already been preloaded in a transmission associated with only the first link compared to the second link.

[0037] As yet another example, the criteria may include determining whether the amount of buffered data is greater than a threshold.

[0038] These embodiments can be envisaged independently of the core definition of the invention above. As an independent concept, these embodiments relate to a method of communication in a wireless network, in a non-access point (non-AP) Multilink Device (MLD) operating in an active Enhanced Multilink (EML) mode: Initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure by a first STA that is in a listening operation state and that corresponds to a first link of a set of valid links to which an EML mode is applied and that is affiliated with a non-AP MLD, to access the first link by decrementing a backoff counter; The decrementing of the backoff counter is suspended upon receipt of an Initial frame from the AP MLD via the second link in the set, or more generally, upon receipt of an Initial frame from the AP MLD via the second link in the set, a decision is made as to whether to pause the decrementing of the backoff counter.

[0039] In some embodiments of the present invention, the switching of the first Affiliated STA includes initiating a state switching procedure of the first Affiliated STA while the first Affiliated STA is decrementing a back-off counter, such that the state switching procedure is terminated as soon as the back-off counter reaches a value of 0, thereby improving communication performance.

[0040] In another embodiment, switching the first co-affiliated STA includes initiating a state switching procedure of the first co-affiliated STA in response to the back-off counter reaching a value of 0. In this case, the first co-affiliated STA has not changed state when activity is sensed when the back-off counter is about to expire. This approach conserves opportunities for other co-affiliated STAs to access the medium. Thus, communication performance is improved.

[0041] In a particular embodiment, the method further includes transmitting a control frame over the first link in response to the backoff counter reaching a value of zero. The control frame may be a CTS-to-self frame or an RTS frame. This is to protect the resulting medium in case another MLD desires to access the same medium while the non-AP MLD is switching the state of its co-affiliated STA. This also contributes to improving the communication performance of the network.

[0042] According to a particular feature, the control frame includes padding to end the control frame after a short interframe space (SIFS) preceding the end of the state switching procedure, thereby ensuring protection of the medium during all transitional periods during which co-affiliated STAs are switched.

[0043] According to another particular feature, the first affiliated STA is assigned light radio resources in the listening operation state, while a separate second STA corresponding to a second link of the set, affiliated to a non-AP MLD, is assigned full radio resources in the listening operation state. In fact, the above protection is worth implementing when, in the EMLSR mode, the co-affiliated STA of the "active" EMLSR (here the first STA) is initialized with a light radio stack and requires a longer time (during a switch) to be configured with a full radio stack.

[0044] In some embodiments, the method includes setting a network allocation vector (NAV) of a first affiliated STA in a listening state upon sensing any control frame over the first link having an MCS value up to 2. This extends processing of frames by the affiliated STA in a listening state beyond just Initial Control frames (MU-RTS and BSRP trigger frames).

[0045] In some embodiments, the method includes simultaneously initiating an EDCA backoff procedure on two or more links of the set, where a first link is a link corresponding to a backoff counter of the EDCA backoff procedure that first reaches a value of 0. In other words, a separate second affiliated STA in a listening operation state corresponding to a second link of the set initiates an EDCA backoff procedure simultaneously with the initiation of the EDCA backoff procedure by the first affiliated STA. This increases the opportunities for non-AP MLDs to access the wireless network, improving communication performance.

[0046] In some embodiments, the method further includes switching a separate second STA corresponding to a second link of the set, affiliated to the non-AP MLD, from a listening operation state to an invalid frame exchange state simultaneously with the switching of the first affiliated STA.

[0047] In some embodiments, the method further includes returning the first and second affiliated STAs to a listening operational state upon completion of the frame exchange over the first link.

[0048] In some embodiments, initiating the frame exchange excludes transmitting an AP MLD Initial frame on the first link, which indicates that the present invention is directed to non-triggered uplink transmission of non-AP MLD in EML mode.

[0049] In some embodiments, the method further includes performing a frame exchange with the AP MLD over the first link (typically an uplink transmission at the initiative of the non-AP MLD) after the backoff counter reaches a value of zero.

[0050] In particular, with regard to fairness issues in accessing the wireless network, a particular problem with EDCA arises after an uplink (UL) transmission of a link of a second EMLSR or EMLMR, since the systematic use of the legacy EDCA backoff resume or restart procedures for the link of a first EMLSR or EMLMR of a link set of EMLSRs or EMLMRs is not adapted.

[0051] Therefore, it is also an objective of embodiments of the present invention to provide an EDCA backoff resume or restart procedure adapted for EML mode that takes into account EML Capabilities. In particular, some embodiments of the present invention specify a new EDCA backoff resume or restart procedure for STAs affiliated to a non-AP MLD operating on a first EMLSR or EMLMR link after a UL transmission is made on a second EMLSR or EMLMR link of the same EMLSR or EMLMR linkset.

[0052] In this context, the method may further include, again in non-AP MLD, restarting the back-off counter in response to completion of the frame exchange over the second link, applying a back-off restart strategy selected based on characteristics of the frame exchange.

[0053] "Restarting" the backoff counter should be understood as any technique for reinitiating the decrementation of the backoff counter, whether the decrement resumes from the last known / current value of the counter or restarts from a new counter value that reinitializes the backoff counter. These various options are described in more detail below.

[0054] Therefore, the strategy or policy for restarting the backoff counter of a link depends on what happens (frame exchange) on another link, contrary to the traditional approach for EDCA procedures. This shows that the problem of network access fairness can be mitigated by applying or tuning appropriate EDCA backoff restart procedures. In particular, the backoff counter associated with an AC of a link may be penalized if data from the same AC is transmitted over another link of the same EMLSR or EMLMR link set.

[0055] In some embodiments, the characteristics of the frame exchange include whether the frame exchange includes single-user uplink transmissions to the AP MLD, multi-user triggered-based uplink transmissions to the AP MLD, or only downlink transmissions from the AP MLD, allowing the network to adjust the penalty depending on whether non-AP MLDs get additional transmission opportunities (e.g., via triggered-based UL) compared to traditional EDCA (single-user UL) or downlink transmissions.

[0056] In some embodiments, the characteristics of the frame exchange include whether the frame exchange is a successful or unsuccessful uplink transmission to the AP MLD, allowing the network to adjust the penalty depending on whether the non-AP MLD is successful in utilizing its transmission opportunity.

[0057] Of course, the above embodiments (SU or MU transmission as a characteristic and success or failure of the transmission as another characteristic) can be advantageously combined, meaning that the SU UL or MU UL or DL ​​nature of the transmission and the success or failure status of the transmission are also taken into account. Of course, other characteristics of the frame exchange can also be used in the selection of the restart strategy or procedure.

[0058] In some embodiments, the restart strategy applied comprises one of the following: reinitializing the backoff counter using the current contention window before starting to decrement the backoff counter; reinitializing the backoff counter with a new contention window associated with the new EDCA mode before starting to decrement the backoff counter. It should be understood that the new EDCA mode is considered "new" compared to the current EDCA mode of its affiliated STA. For example, a STA operating on the second link may switch from a legacy EDCA mode to a multi-user EDCA (MU EDCA) mode with its own MU EDCA parameters including its own contention window value. Alternatively, a new EML EDCA mode (e.g., EMLSR EDCA mode and / or EMLMR EDCA mode) may be defined with its own EML EDCA parameters including its own contention window value that penalizes the AC more or less, in which case a STA operating on the second link may switch from a legacy EDCA mode to an EML EDCA mode. The backoff counter may be restarted from its current value and switched to another EDCA mode to penalize the backoff counter for the next reinitialization.

[0059] The use of the new EML EDCA mode differs substantially from known 802.11 technologies where only EDCA and MU EDCA modes are known. The EML EDCA mode corresponds to a specific set of EML EDCA parameters that are different from the EDCA and MU EDCA parameters and are transmitted (via beacon or probe response frames) from the affiliated AP to the co-affiliated STAs separately from the EDCA and MU EDCA parameters. The EML EDCA parameters are specific to each link and therefore may be different from one link to another or may be set to the same value across the entire link set of an EMLSR or EMLMR. Similar but distinct fields may be provided in the beacon / probe response frames to convey these parameters over each link.

[0060] Correspondingly, a method for communication in a wireless network includes, in a non-access point (non-AP) multi-link device (MLD) operating in an active enhanced multi-link (EML) mode: In response to a termination of a frame exchange with the AP MLD over a first link of the set of valid links to which the EML mode applies, the method may include switching an Enhanced Distributed Channel Access (EDCA) parameter of a back-off counter driving EDCA to a second link of the set from the current EDCA parameter to a different EML EDCA parameter, thereby defining an EML EDCA mode for the co-affiliated STA operating on the second link. An EML EDCA mode may be engaged on each link different from the first link of the set if there are multiple of them. The per-link EML EDCA modes may use link-specific EML EDCA parameters or may instead share the same EML EDCA parameters.

[0061] In this way, the penalty of EDCA in non-AP MLD can be adjusted for active EML mode.

[0062] In an embodiment, the frame exchange includes a (preferably successful) trigger-based uplink transmission to the AP MLD.

[0063] In some embodiments, the method further includes switching EDCA parameters of a backoff counter driving EDCA for the first link from the current EDCA parameters to different EML EDCA parameters in response to a completion of the frame exchange with the AP MLD over the first link. In other words, the first link over which the frame exchange takes place is penalized in the same way as the other EMLSR / EMLMR links of the set. The relevant backoff counters are those corresponding to the ACs transmitted during the frame exchange.

[0064] In another embodiment, the non-AP MLD stores a set of EML single-radio (EMLSR) EDCA parameters and a set of EML multi-radio (EMLMR) EDCA parameters, and different EML EDCA parameters are selected from the set of EMLSR EDCA parameters and the set of EMLMR EDCA parameters depending on whether the non-AP MLD is in EMLSR mode or EMLMR mode, respectively.

[0065] In another embodiment, the method further includes receiving a management frame (beacon or probe response frame) from the AP MLD, possibly including different EML EDCA parameters in addition to the EDCA parameters and the MU EDCA parameters. Correspondingly, a method of communication in a wireless network includes, in an access point (AP) multilink device (MLD) operable in an active enhanced multilink (EML) mode: transmitting a management frame to the non-AP MLD, the management frame including a set of EML EDCA parameters; The EML EDCA parameter is used to configure the Enhanced Distributed Channel Access (EDCA) of a non-AP MLD operating in EML mode to drive access to a first link of a set of links to which the EML mode applies upon completion of frame exchange with the AP MLD via a second link of the set.

[0066] Therefore, a new set of EDCA parameters is defined to penalize co-affiliated STAs when they obtain additional transmission opportunities (usually via trigger-based UL transmissions) while operating in EML mode.

[0067] The set of EML (or EMLSR and / or EMLMR) EDCA parameters may be added to the set of EDCA parameters in the management frame and / or may be added to the set of MU EDCA parameters in the management frame.

[0068] In certain embodiments, the restart strategy applied comprises one of the following: restarting the back-off counter from its current value in the case of a downlink transmission or a failed uplink transmission in a frame exchange; reinitializing the back-off counter using the current contention window before starting to decrement the back-off counter or restarting the back-off counter from its current value if a single user's uplink transmission in a frame exchange is successful; In the event of a successful multi-user trigger-based uplink transmission in a frame exchange, reinitializing the backoff counter using the current contention window or a new contention window associated with the new EDCA mode before starting to decrement the backoff counter or restarting the backoff counter from its current value (possibly switching the STA to another EDCA mode - e.g., MU EDCA mode or EML EDCA mode as defined above - to penalize the backoff counter for the next reinitialization).

[0069] In some embodiments, in response to initiating a frame exchange, a plurality of back-off counters driving EDCA to the first link for each of a plurality of access categories are paused; The restart strategy is applied to backoff counters of a plurality of suspended backoff counters corresponding to access categories exchanged during a frame exchange.

[0070] Therefore, all ACs benefiting from the frame exchange may be penalized by the applied restart strategy.

[0071] In some embodiments, the restart strategy includes a synchronization delay from the end of the frame exchange before restarting the backoff counter, which allows co-affiliated STAs of inactive links during the frame exchange to resynchronize with the medium.

[0072] In a particular embodiment, the inclusion of a synchronization delay in the restart strategy is contingent on the duration of the frame exchange being greater than a predetermined threshold. Such delay and threshold may be MediumSyncDelay and aMediumSyncThreshold, respectively, as defined in the D1.5 standard. This configuration prevents co-affiliated STAs from wasting time before contending for access to the medium again if the STAs have not lost synchronization from the medium.

[0073] According to a particular feature, the timer that counts down the synchronization delay is initialized with the MediumSyncDelay value provided by the AP MLD on the first link (e.g. in the Basic Multi-Link element of the last received frame from the associated AP). In particular, the timer can be set to 0 if a control frame with MCS value up to 2 is successfully received over the first link. Again, this is to avoid wasting time until the STAs contend again for access to the medium as soon as they have resynchronized with the medium (thanks to a successfully received frame).

[0074] In some embodiments, initiating the frame exchange includes detecting the expiration of another back-off counter driving EDCA to the second link. Preferably, the back-off counter and the another back-off counter are associated with the same access category. In this configuration, the co-affiliated STAs of the second link gain access to the link for SU transmissions of a particular AC. Thus, the restart strategy is applied to the back-off counter of the other link corresponding to the same particular AC. This ensures proper fairness treatment between the ACs.

[0075] In another embodiment, initiating the frame exchange includes receiving an Initial frame (including a known Initial Control frame in EMLSR mode) from the AP MLD over the second link, in particular, the Initial frame may be received while another backoff counter driving EDCA for the second link is being decremented.

[0076] In some embodiments, the method further includes, in response to a termination of the frame exchange over the second link, applying a different restart strategy based on characteristics of the frame exchange and restarting a different back-off counter driving EDCA to the second link.

[0077] In an embodiment, other restart strategies include one from the following: if the other backoff counter expires, reinitializing the other backoff counter using the updated contention window before starting to decrement the other backoff counter; restarting the other backoff counter from its current value and otherwise possibly switching the backoff engine to the other EDCA mode (e.g., MU EDCA mode or any EML EDCA mode defined above) in order to penalize the backoff counter for the next reinitialization if the trigger-based UL transmission is successful. In some embodiments, the other EDCA mode is the same as the new EDCA mode entered by the co-affiliated STA operating on the first link, meaning that both (or more) co-affiliated STAs switch to the same other EDCA mode (MU EDCA mode or EML EDCA mode) even though the set of MU or EML EDCA parameters they respectively use may be different since they are specific to each link. Alternatively, the co-affiliated STAs operating on the second link either remain in conventional EDCA mode or simply switch to MU EDCA mode (having benefited from trigger-based UL transmission), while the co-affiliated STAs operating on the first link switch to EML MU mode.

[0078] In some embodiments, the method further includes, in response to initiating the frame exchange, switching a second STA corresponding to the second link affiliated with the non-AP MLD from a listening operation state to a valid frame exchange state and switching a first STA corresponding to the first link affiliated with the non-AP MLD from a listening operation state to a invalid frame exchange state.

[0079] Relatedly, the present invention also provides a wireless communication device including at least one microprocessor configured to perform the steps of any of the above methods. The wireless communication device is a non-AP MLD.

[0080] In particular, a non-access point (non-AP) Multilink Device (MLD) capable of operating in active Enhanced Multilink (EML) mode must: means for initiating, by a first station (STA) corresponding to a first link of a set of valid links affiliated with a non-AP MLD and for which an EML mode is applicable, an Enhanced Distributed Channel Access (EDCA) backoff procedure for decrementing a backoff counter to access the first link; and means for switching the first affiliated STA from a listening operation state to an active frame exchange state to initiate a frame exchange with the AP MLD over the first link.

[0081] 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 wireless device, causes the wireless device to perform any method as defined above.

[0082] At least some of the methods according to the invention may be computer implemented. Accordingly, the invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be referred to generally herein as a "circuit," "module," or "system." Furthermore, the invention may take the form of a computer program product embodied in any tangible medium embodiment having computer usable program code embodied in the medium.

[0083] Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable device on any suitable carrier medium. Tangible non-transitory carrier media can include storage media such as floppy disks, CD-ROMs, hard disk drives, magnetic tape devices, or solid-state memory devices. Transitory carrier media can include signals such as electrical, electronic, optical, acoustic, magnetic, or electromagnetic signals, e.g., microwave or RF signals. [Brief description of the drawings]

[0084] Embodiments of the invention will now be described, by way of example only, with reference to the following drawings in which: [Figure 1] 1 illustrates a typical 802.11 network environment including ML transmissions between EML-enabled MLDs in which the present invention may be implemented; [Figure 1ab] 1 shows an exemplary 802.11be multilink reference model for MLD, AP MLD or non-AP MLD; [Diagram 2] Schematically shows the frame sequence of the EMLSR operation mode defined in the D1.5 standard; [Diagram 3] 1 illustrates, with a flowchart, the steps performed to operate a first contention-based channel access procedure with EMLSR active non-AP MLD according to a first embodiment; [Figure 4] 4 illustrates a schematic diagram of an exemplary timeline of a first contention-based channel access procedure as described in FIG. 3; [Figure 5a] 1 illustrates, with a flowchart, the steps performed for an EMLSR active non-AP MLD to operate a second contention-based channel access procedure according to a second embodiment; [Figure 5b] 1 illustrates, with a flowchart, the steps performed for an EMLSR active non-AP MLD to operate a second contention-based channel access procedure according to a second embodiment; [Figure 6a]5a and 5b show schematic timelines of alternative contention-based channel access procedures; [Figure 6b] We show a schematic representation of a more detailed scenario in Fig. 6a, taking into account the transition period during which the state of the EMLSR co-affiliated STAs switches; [Figure 7] 1 illustrates, with a flowchart, the steps performed for an EMLSR active non-AP MLD to operate a third contention-based channel access procedure according to a third embodiment; [Figure 8] 8 illustrates a schematic diagram of an exemplary timeline of the third contention-based channel access procedure described in FIG. 7; [Figure 9] 1 illustrates, with a flowchart, steps for handling restart of a backoff counter in EML mode according to an embodiment; [Figure 10a] 1 illustrates a schematic diagram of an exemplary timeline of a first EMLSR or EMLMR operation case with a back-off counter restart procedure according to an embodiment; [Figure 10b] 1 illustrates a schematic diagram of an exemplary timeline of a first EMLSR or EMLMR operation case with a back-off counter restart procedure according to an embodiment; [Figure 11] 10 shows a schematic diagram of an exemplary timeline of a second EMLSR or EMLMR operation case including a back-off counter restart procedure according to another embodiment, where the triggering event for frame exchange is the reception of an Initial frame; [Figure 12] 10 illustrates a schematic example timeline of a third EMLSR or EMLMR operation case including a back-off counter restart procedure according to yet another embodiment, where the triggering event for frame exchange is the reception of an Initial frame; [Figure 13] 1 shows a table collecting proposed EDCA backoff counter restart procedures or policies according to an embodiment; [Figure 14] Schematically illustrates an EMLSR-enabled architecture of an MLD for implementing an embodiment of the present invention; [Figure 15] Schematically illustrating an EMLMR-enabled architecture of an MLD for implementing an embodiment of the present invention; and [Figure 16] 1 shows a schematic diagram of a wireless communication device according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0085] The techniques described herein may be used for various broadband wireless communication systems, including communication systems based on orthogonal multiplexing. Examples of such communication systems include space division multiple access (SDMA) systems, time division multiple access (TDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and single carrier frequency division multiple access (SC-FDMA) systems. An SDMA system may utilize sufficiently different directions to simultaneously transmit data belonging to multiple user terminals, such as wireless devices or STAs. A TDMA system may allow multiple user terminals to share the same frequency channel by dividing a transmission signal into different time slots or resource units and assigning each time slot to a different user terminal. An OFDMA system utilizes orthogonal frequency division multiplexing (OFDM), which is a modulation technique that divides the overall system bandwidth into multiple orthogonal subcarriers or resource units. These subcarriers may be referred to as tones, bins, etc. In OFDM, each subcarrier may be independently modulated with data. An SC-FDMA system may utilize Interleaved FDMA (IFDMA), which transmits on subcarriers distributed across the system bandwidth, Localized FDMA (LFDMA), which transmits on blocks of contiguous subcarriers, or Enhanced FDMA (EFDMA), which transmits on multiple blocks of contiguous subcarriers.

[0086] The teachings herein may be incorporated into (e.g., implemented in or performed by) a variety of apparatuses (e.g., STAs). In some aspects, a wireless device or STA implemented in accordance with the teachings herein may or may not include an access point (referred to as an AP) (referred to as a non-AP STA or STA).

[0087] Although the embodiment is described in the context of a WiFi network, the invention may be used in any type of wireless network, such as, for example, a mobile telephone cellular network, which implements very similar mechanisms.

[0088] An AP may include, be implemented as, or be known as a NodeB, Radio Network Controller ("RNC"), evolved Node B (eNB), 5G Next Generation Base STA ("gNB"), Base STA Controller ("BSC"), Base Transceiver STA ("BTS"), Transceiver Function ("TF"), wireless router, wireless transceiver, Basic Service Set ("BSS"), Enhanced Service Set ("ESS"), Radio Base STA ("RBS"), or other terminology.

[0089] A non-AP STA may include, be implemented as, or be known as a subscriber STA, subscriber unit, mobile STA (MS), remote STA, remote terminal, user terminal (UT), user agent, user device, user equipment (UE), user STA, or other terminology. In some implementations, a STA may include a cellular telephone, a cordless telephone, a session initiation protocol ("SIP") telephone, a wireless local loop ("WLL") STA, a personal digital assistant ("PDA"), a handheld device with wireless connectivity capabilities, or other suitable processing device connected to a wireless modem. Thus, one or more aspects taught herein may be incorporated into a telephone (e.g., a cellular phone or a smartphone), 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 configured to communicate via a wireless or wired medium. In some aspects, a non-AP STA may be a wireless node. Such a wireless node may, for example, provide connectivity to a network (eg, a wide area network such as the Internet or a cellular network) via a wired or wireless communication link.

[0090] An AP manages a set of STAs (registered or associated with the AP) that together configure access to the wireless medium for communication purposes. The STAs (including the APs they register with) form a service set, hereafter called Basic Service Set (BSS) (other terms may be used). The same physical STA acting as an access point may manage two or more BSSs (and thus corresponding WLANs), each BSS being therefore uniquely identified by a specific Basic Service Set Identifier (BSSID) and managed by a separate virtual AP implemented in the physical AP. Each STA is identified within a BSS by an identifier AID that is assigned by the AP upon registration.

[0091] The 802.11 family of standards defines a variety of medium access control (MAC) mechanisms for driving access to the wireless medium.

[0092] Current discussions in the 802.11be task group, as outlined in the March 2022 draft IEEE P802.11be / D1.5, will introduce multi-link operation (MLO) for MAC layer operation. MLO allows a multi-link device to establish or configure multiple links and operate them simultaneously.

[0093] A multilink device (MLD) is a logical entity that has multiple Affiliated STAs (STAs), has a single Medium Access Control (MAC) Service Access Point (SAP) to a Logical Link Control (LLC), and contains one MAC Data Service ( ). An access point multilink device (or AP MLD) corresponds to an MLD where each STA affiliated to the MLD is an AP (hence referred to as an "affiliated AP"). A non-access point multilink device (or non-AP MLD) corresponds to an MLD where each STA affiliated to the MLD is a non-AP STA (hence referred to as an "affiliated non-AP STA"). In some literature, "multilink device", "ML device" (MLD), "multilink logical entity", "ML logical entity" (MLE), "multilink set" and "ML set" are synonymous terms referring to the same type of ML device. An exemplary architecture of a multilink device is described below with reference to FIG. 1ab.

[0094] Multiple affiliated non-AP STAs in a non-AP MLD can set up communication links with multiple affiliated APs in an AP MLD, forming a multi-link channel.

[0095] Links established for MLD (or "enabled links") are theoretically independent, meaning that channel access procedures (to the communication medium) and communications are performed independently on each link. Different links may therefore have different data rates (e.g., due to different bandwidths, number of antennas, etc.) and may be used (over each particular link) to communicate different types of information.

[0096] In this manner, a communication link or "link" corresponds to a given channel (e.g., 20 MHz, 40 MHz, etc.) in a given frequency band (e.g., 2.4 GHz, 5 GHz, 6 GHz) between an AP affiliated to an AP MLD and a non-AP STA affiliated to a non-AP MLD.

[0097] Affiliated APs and non-AP STAs operate on their respective channels according to one or more of the IEEE 802.11 standards (a / b / g / n / ac / ad / af / ah / aj / ay / ax / be) or other wireless communication standards.

[0098] Multi-link aggregation theoretically allows traffic associated with a single MLD to be transmitted over multiple parallel communication links, thereby increasing network capacity and maximizing the utilization of available resources.

[0099] From an architectural point of view, an MLD typically includes several radios to implement the Affiliated STAs, but it does not have to be the same number as the number of Affiliated STAs. In particular, a non-AP MLD may operate with a number of Affiliated STAs greater than the number of radios (or even as few as one).

[0100] The D1.5 standard defines several Enhanced Multilink Operating Modes (abbreviated EML OM) from this physical architecture: Enhanced Multilink Single Radio (EMLSR) and Enhanced Multilink Multi Radio (EMLMR). The D1.5 standard states that the two modes EMLSR and EMLMR are mutually exclusive.

[0101] A non-AP MLD declares support for EMLSR and / or EMLMR mode to an AP MLD during the association phase (in the so-called EML Capabilities). In the operational mode, activation and deactivation of EMLSR or EMLMR mode is initiated by the non-AP MLD, which sends a specific EHT action frame called "EML OM Notification" indicating among other things the set of valid links (so-called EMLSR or EMLMR links) to which the activation of EMLSR or EMLMR mode applies. Usually, an "EMLSR / EMLMR link" consists of two valid links. However, more valid links may be used.

[0102] When EMLSR mode is enabled, the non-AP MLD simultaneously listens to a set of enabled links of "EMLSR links" to receive Initial Control frames (e.g., MU-RTS trigger frames and BSRP trigger frames) sent by the AP MLD, and then can exchange data frames with the AP MLD on only one link at a time (usually the link on which the Initial Control frame was received). Each non-AP MLD may or may not support the EMLSR mode of operation.

[0103] In EMLMR mode, non-AP MLD can aggregate some of the physical resources of multiple radios for multiple active links (so-called EMLMR links) to transmit and receive data up to a predetermined number of supported receive and transmit spatial streams. This predetermined number is more than the number of supported receive and transmit spatial streams per radio, providing increased throughput and reduced latency. As an example, a multi-radio (MR) non-AP MLD supporting EMLMR mode on two links (with associated radios), such as in a 2x2 MIMO antenna configuration for each radio, communicates over two links using two respective radios when EMLMR mode is deactivated. On the other hand, MR non-AP MLD, such as in a 4x4 MIMO antenna configuration, aggregates the physical resources (usually antennas) of two radios when EMLMR mode is activated and communicates over one of the two links using one of the radios. At the same time, the other link (the link deprived of a physical antenna) cannot be used.

[0104] When EMLMR mode is enabled, the non-AP MLD simultaneously listens to a set of enabled links of "EMLMR links" to receive the Initial frame sent by the AP MLD and initiate frame exchange, and can then perform data frame exchange with the AP MLD (by aggregating radio resources) over only one EMLMR link at a time (usually the link that received the Initial frame).

[0105] In the following description, for simplicity, the EMLSR mode will be mainly described, but similar considerations can be made for the EMLMR mode.

[0106] FIG. 1 illustrates a typical 802.11 network environment including ML transmissions between EML-enabled MLDs (EMLSR and EMLMR capable) in which the present invention may be implemented.

[0107] Wireless communication network 100 includes AP MLD 110 and two non-AP MLDs 120 and 130. In this example, the two non-AP MLDs are assumed to be EML capable and declare their corresponding capabilities to AP MLD 110 in EMLSR-related and EMLMR-related fields of EML Capabilities (these fields are referred to below as EMLSR Capabilities and EMLMR Capabilities, e.g., subparts of EML Capabilities). Of course, a different number of non-AP MLDs registering with AP MLD 110 and exchanging frames with AP MLD 110, and a different (or greater) number of EML-capable non-AP MLDs may be envisioned.

[0108] The AP MLD 110 has multiple affiliated APs, two affiliated APs 111 and 112 (also called AP1 and AP2, respectively) in the exemplary FIG. 1, each operating as an 802.11 AP on an operating channel in one frequency band. Known 802.11 frequency bands include the 2.4 GHz band, the 5 GHz band, and the 6 GHz band. Of course, other frequency bands can be used instead of or in addition to these three frequency bands.

[0109] The non-AP MLD 120, 130 has multiple affiliated non-AP STAs, each of which operates as an 802.11 non-AP STA in the BSS (managed by the affiliated AP 111 or 112) to which it registers. In the exemplary FIG. 1, two non-AP STAs 121 and 122 (also referred to as A1 and A2, respectively) are affiliated to the non-AP MLD 120, and two non-AP STAs 131 and 132 (also referred to as B1 and B2, respectively) are affiliated to the non-AP MLD 130.

[0110] For illustrative purposes, non-AP MLDs 120 and 130 are single-radio non-AP MLDs. For example, AP 111 is configured to operate on channel 38, which corresponds to an operating 40 MHz channel in the 5 GHz frequency band, and AP 112 is configured to operate on channel 151, which corresponds to another operating 40 MHz channel, also in the 5 GHz frequency band. In another example, the affiliated STAs may operate in different frequency bands.

[0111] Each Affiliated AP provides a link towards the AP MLD 110 to the affiliated non-AP STAs in the non-AP MLD (120 or 130). Thus, each non-AP MLD link may be identified simply by the identifier of the respective Affiliated AP. In this context, each Affiliated AP 111 and 112 may be identified by an identifier called a "Link ID." The Link ID of each Affiliated AP is unique and does not change during the lifetime of the AP MLD. The AP MLD may assign a Link ID to an Affiliated AP by incrementing the ID from 0 (for the first Affiliated AP). Of course, other expressions such as "AP ID" may be used as variations.

[0112] To perform multi-link communication, each non-AP MLD 120, 130 needs to discover, authenticate, associate, and set up multiple links with the AP MLD 110, where each link is established between an affiliated AP of the AP MLD 110 and an affiliated non-AP STA of the non-AP MLD. Each such link, called an "enabled link," allows separate channel access and frame exchange between the non-AP MLD and the AP MLD based on the supported capabilities exchanged during association.

[0113] The discovery phase is called the ML discovery procedure, and the multilink setup phase (or association phase) is called the ML setup procedure.

[0114] The ML discovery procedure allows the non-AP MLD to discover the wireless communication network 100, for example, various links to the AP MLD provided by multiple affiliated APs. Thus, the ML discovery procedure tries to advertise various affiliated APs in the AP MLD with their respective network information (e.g., including all or part of their capabilities and operating parameters). After the non-AP MLD discovers the wireless communication network 100 through the ML discovery procedure and the MLD authentication procedure, the ML setup procedure can select a set of setup link candidates between the affiliated non-AP STAs in the non-AP MLD and some of the discovered affiliated APs, and request the AP MLD 110 to set up these links, which can be accepted or rejected by the AP MLD. If the AP MLD accepts, the non-AP MLD is provided with an Association Identifier (AID) by the AP MLD, which is used by the affiliated non-APs in the non-AP MLD to wirelessly communicate with the corresponding affiliated APs via multiple links (communication channels). During the ML setup procedure, a non-AP MLD declares some or all of its capabilities, e.g., EMLSR capabilities. To this end, appropriate fields are provided in management frames. In particular, management frames exchanged during ML discovery and ML setup procedures contain new information elements specific to Multi-Link Operation (MLO), called Basic Multi-Link elements. In virtually all management frames containing the Basic Multi-Link element, except authentication frames, a non-AP or AP MLD that is EMLSR-capable (dot11EHTEMLSROptionImplemented is true) or EMLMR-capable (dot11EHTEMLMROptionImplemented is true) sets the EMLSR or EMLMR Support bit in the EML Capabilities subfield of the Common Info field to 1.

[0115] For illustrative purposes, in the wireless communication network 100, during the ML setup procedure, two setup candidate links are requested by the non-AP MLD 120 and accepted by the AP MLD 110: a first link 151 between the affiliated AP 111 (AP1) and the affiliated non-AP STA 121 (A1), and a second link 152 between the affiliated AP 112 (AP2) and the affiliated non-AP STA 122 (A2). Similarly, two setup link candidates are requested by the multi-radio non-AP MLD 130 and accepted by the AP MLD 110: a first link 161 between the affiliated AP 111 (AP1) and the affiliated non-AP STA 131 (B1), and a second link 162 between the affiliated AP 112 (AP2) and the affiliated non-AP STA 132 (B2).

[0116] AP MLD 110, non-AP MLD 120, and non-AP MLD 130 are EMLSR capable (dot11EHTEMLSROptionImplemented is true) or EMLMR capable (dot11EHTEMLMROptionImplemented is true). EMLSR or EMLMR capabilities (subpart of EML Capabilities) are exchanged during the ML discovery procedure and the multilink setup phase.

[0117] The EMLSR and EMLMR capabilities currently defined in the D1.5 standard include the following subfields: - the "EMLSR Support" subfield indicates that the MLD supports EMLSR operations. The EMLSR Support subfield is set to 1 if the MLD supports EMLSR operations, otherwise it is set to 0; - The 3-bit subfield "EMLSR Padding Delay" indicates the minimum MAC padding duration of the Padding field of the Initial Control frame requested by non-AP MLD as defined in Enhanced multi-link single radio operation (clause 35.3.17). The table converts the 3-bit value into a padding delay in μs. This delay is used to define the transition period required for MLD to switch the state of an affiliated station from listening operation state to active / inactive frame exchange state. This transition period is the time length of the Initial Control frame response or Initial frame response, described below, plus this delay. This transition period is therefore called "EMLSR active switch delay" or "EMLMR active switch delay" depending on the active EML mode, or more generally, "EML active switch delay" in the following; - the 3-bit subfield "EMLSR Transition Delay" indicates the transition delay time required for a non-AP MLD to switch from the so-called frame exchange mode (on one of the active links) to the so-called listening operation mode on the active links. The table translates the 3-bit value into a delay in μs, e.g. set to 0 for 0 μs, 1 for 16 μs, 2 for 32 μs, 3 for 64 μs, 4 for 128 μs, 5 for 256 μs, values ​​from 6 to 7 are reserved; - the "EMLMR Support" subfield indicates that the MLD supports EMLMR operation. If the MLD supports EMLMR operation, the EMLMR Support subfield is set to 1, otherwise it is set to 0; - the 3-bit subfield "EMLMR Delay" indicates the minimum padding period required for switching an EMLMR link when a non-AP MLD operates in EMLMR mode. This delay is used to define the transition period required for the MLD to switch the state of an affiliated station when starting or ending a frame exchange; - The "Transition Timeout" subfield indicates the timeout value for EML Operating Mode Notification frame exchange in the EMLSR (or EMLMR).

[0118] When an EMLSR (or EMLMR)-capable non-AP MLD wishes to operate in the corresponding mode on a set of valid links, called EMLSR (or EMLMR) links, STAs affiliated to the non-AP MLD send EML Operating Mode (OM) Notification frames (as specified in the D1.5 standard) with the EMLSR (or EMLMR) Mode subfield of the EML Control field set to 1 to the APs affiliated to the EMLSR (or EMLMR)-capable AP MLD (here, AP MLD 110). EMLSR (or EMLMR) links are indicated by setting the bit position of the EMLSR (or EMLMR) Link Bitmap subfield of the EML Control field of the EML OM Notification frame to 1 for each of the EMLSR (or EMLMR) links. For example, in the EMLSR (or EMLMR) Link Bitmap, bit position i corresponds to a link whose link ID is equal to i, and is set to 1 to indicate that the link is a member of the EMLSR (or EMLMR) link.

[0119] An AP affiliated to the AP MLD that receives an EML Operating Mode Notification frame from a STA affiliated to a non-AP MLD then sends an EML Operating Mode Notification frame to one of the STAs affiliated to the non-AP MLD as an acknowledgment to the EML Operating Mode Notification sent by the STA affiliated to the non-AP MLD within the timeout interval indicated in the Transition Timeout subfield of the EML Capabilities subfield of the Basic Multi-Link element and starting at the end of the PPDU sent by the AP affiliated to the AP MLD.

[0120] After successful transmission of an EML Operating Mode Notification frame by a STA affiliated to the non-AP MLD over one of the EMLSR (or EMLMR) links, the non-AP MLD operates in EMLSR (or EMLMR) mode and EMLSR is considered to be active (or EMLMR is active).

[0121] When an EMLSR-enabled non-AP MLD wants to disable EMLSR (or EMLMR) mode, the STA affiliated to the non-AP MLD sends an EML Operating Mode (OM) Notification frame (specified in the D1.5 standard) with the EMLSR (or EMLMR) Mode subfield of the EML Control field set to 0 to the AP affiliated to the AP MLD. Again, the AP affiliated to the AP MLD that received the EML Operating Mode (OM) Notification frame from the STA affiliated to the non-AP MLD sends an EML Operating Mode Notification frame as above as an acknowledgment to the EML Operating Mode (OM) Notification frame. After the successful transmission of the EML Operating Mode Notification frame by the STA affiliated to the non-AP MLD via one of the EMLSR (or EMLMR) links, the non-AP MLD disables EMLSR (or EMLMR) mode.

[0122] The set of STAs affiliated to an EMLSR (or EMLMR)-enabled non-AP MLD operating on an EMLSR (or EMLMR) link may be all or a portion of the STAs affiliated to the non-AP MLD, and this set of STAs is hereinafter referred to as the "EMLSR co-affiliated STAs" (or EMLMR co-affiliated STAs) of the non-AP MLD.

[0123] In the example of FIG. 1, the co-affiliated STAs of the EMLSRs of non-AP MLD 120 and non-AP MLD 130 operate on the same link (eg, the same affiliated APs, AP1 and AP2), meaning they share the same EMLSR link.

[0124] FIG. 1a illustrates an exemplary 802.11be multilink reference model for MLD, either AP MLD or non-AP MLD.

[0125] MLD includes a PHY layer 200, a MAC layer 220, a Logical Link Control (LLC) sublayer and higher layers.

[0126] The upper layers may include applications that generate traffic data or use received traffic data.

[0127] The transmission and reception of traffic data is handled by the MAC 220 and PHY 200 layers. Such transmission and reception of traffic data may occur over multiple links 20-x, 20-y, 20-z, such as 151, 152, 161, 162 introduced with reference to Figure 1. Three links, and therefore three affiliated stations, are shown. Of course, other configurations including two affiliated stations or more than three affiliated stations are also contemplated.

[0128] Traffic data is provided from higher layers as a series of data frames, or "traffic streams". Each traffic stream, and therefore each data frame, is associated with an Access Category (AC), as defined in the EDCA mechanism (Fig. 1b). This mapping between streams or data frames and ACs is performed by classifier 213.

[0129] Recall that 802.11 stations (AP and non-AP stations) maintain four Access Categories (ACs), each with one or more corresponding transmit buffers or queues. The four ACs are conventionally defined as follows: - AC1 and AC0 are reserved for best effort and background traffic, which have the second lowest and lowest priority, respectively. - AC3 and AC2 are typically reserved for real-time applications (such as voice and video transmission). They have the highest and second highest priority, respectively.

[0130] Data frames, also known as MSDUs (MAC Service Data Units), coming from higher layers of the protocol stack are mapped by the classifier 213 to one of the four ACs and therefore entered into the queue of the AC to which they are mapped.

[0131] Figure 1b shows an implementation model with four transmit queues, one for each access category.

[0132] The 802.11be multi-link reference model reflects the fact that an MLD may transmit and receive using multiple links, particularly at the MAC layer 220 and PHY layer 200 levels.

[0133] The MAC layer 220 includes one Unified Upper-MAC (UMAC) layer 230 and multiple Lower-MAC (LMAC) layers 220-x, 220-y, 220-z associated with respective PHY layers 200-x, 200-y, 200-z, each combination corresponding to a link 20-x, 20-y, 20-z.

[0134] The UMAC 230 performs functions common to all links, and each LMAC 220-x, 220-y, 220-z performs functions local to each link 20-x, 20-y, 20-z. The UMAC layer provides a UMAC interface to the link-specific blocks 220-x, 220-y, 220-z and a UMAC Service Access Point (SAP) to the LLC and higher layers.

[0135] The UMAC 230 is responsible for link-independent MAC procedures such as authentication, association, security association, sequence number assignment, MAC Protocol Data Unit (MPDU) encryption / decryption, aggregation / deaggregation, and acknowledgment scoreboarding procedures.

[0136] Each type of traffic (each data unit (MSDU) with User Priority (UP) priority, and therefore Traffic IDentifer (TID)) arriving at the MAC layer 220 from a higher layer (e.g., the link layer) is mapped to one of the ACs according to a mapping rule in the UMAC layer 230. Then, also in the UMAC layer 230, the data unit (MSDU) is provided with the next available sequence number and stored in the queue corresponding to its TID (or UP) in the AC to which it is mapped. Recall that 802.11 stations map TIDs to ACs as follows (TIDx means TID=x): - TID1 and TID2 are mapped to AC0, which is typically used for background traffic, - TID0 and TID3 are mapped to AC1, which is typically used for best effort traffic, - TID4 and TID5 are mapped to AC2, which is typically used for video traffic, - TID6 and TID7 are mapped to AC3, which is typically used for voice traffic.

[0137] Each LMAC 220-x, 220-y, 220-z is responsible for link-specific functions such as channel access. In particular, each MLD Lower MAC includes its own contention-based channel access procedure, e.g., EDCA 221-x, 221-y, 221-z. Some functions require joint processing of both the UMAC 230 and the LMAC 220-x, 220-y, 220-z.

[0138] As shown in FIG. 1ab, each EDCA 221-x, 221-y, 221-z per link performs contention per link for each AC queue. In that respect, each AC has its own set of queue contention parameters (i.e., EDCA access parameters) per link, associated with a priority value, thus defining higher or lower priority traffic for an MSDU. Thus, there are multiple traffic queues for providing data traffic with different priorities for a given link. The arbitration inter-frame space (AIFSn), contention window (CW), and backoff values, known as EDCA access parameters, are specific to each AC of each link 20-x, 20-y, 20-z.

[0139] The default EDCA access parameters for 802.11 stations are shown in the table below: TIFF2025517276000002.tif44112

[0140] Also recall that for an 802.11 station, the backoff value is chosen randomly from the range [0,CW], with CW typically initialized with the value of CWmin. This backoff value is used to initialize the backoff counter (BC). During the backoff procedure, if the medium is sensed idle for a given slot time (typically 9 μs), the backoff counter is decremented by 1, and if the medium is sensed busy for a given slot time, the backoff counter is paused.

[0141] It should also be recalled that IEEE Standard 802.11ax-2021 introduced the multi-user (MU) EDCA parameter set in addition to the EDCA parameter set. 802.11ax stations have more medium access opportunities than legacy 802.11 stations, since they can transmit UL data using both EDCA contention-based and trigger-based transmissions. Therefore, to ensure fairness, IEEE Standard 802.11ax-2021 introduced the MU EDCA mechanism to deprioritize 802.11ax stations after trigger-based UL transmissions using the (less favorable) MU EDCA parameter set instead of the legacy EDC parameter set for a period specified in the so-called MU EDCA timer (one per AC). The use of the MU EDCA parameter set typically results in longer periods of contention and backoff. The AP signals the legacy EDCA parameter sets and the MU EDCA parameter sets in broadcast beacon frames and / or association response frames that it exchanges with non-AP STAs.

[0142] In the case of MLD, each AC or traffic queue 210 is mapped to one EDCA engine 221 per link. Thus, each backoff entity 211 of the EDCA engine 221 specific to a link uses queue contention parameters to initialize the backoff counters (BC) of each queue specific to AC and link, and is associated with each AC queue 210 for subtracting backoff values. In FIG. 1b, backoff counters BC[x0], BC[x1], BC[x2], BC[x3] are associated with traffic queues 210 of AC0, AC1, AC2, AC3, respectively, and are used simultaneously to compete for access to link 20-x. Similarly, backoff counters BC[y0], BC[y1], BC[y2], BC[y3] are associated with traffic queues 210 of AC0, AC1, AC2, AC3, respectively, and are used simultaneously to compete for access to link 20-y. Similarly, back-off counters BC[z0], BC[z1], BC[z2], and BC[z3] are associated with traffic queues 210 of AC0, AC1, AC2, and AC3, respectively, and are used simultaneously to compete for access to link 20-z. Here, the numbering proposed to easily identify the back-off counters is BC[Link, AC]. As an example, BC[z2] identifies the back-off counter corresponding to link 20-z and AC2. Then, it can be noticed that in MLD, the number of back-off counters is usually equal to the number of ACs times the number of links. In the example of FIG. 1b, the number of back-off counters is 4×3=12.

[0143] However, it must be pointed out that this number is the maximum possible number of backoff counters. This is obtained when the default TID-To-Link mapping is used for MLD. Along with multilink operation, the D1.5 standard defines a TID-To-Link mapping mechanism that allows AP MLD and non-AP MLD that have performed or are performing multilink setup to determine how to allocate UL and DL QoS traffic corresponding to TID values ​​from 0 to 7 to the setup links of the non-AP MLD. By default, all TIDs are mapped to all setup links, both DL and UL, and all setup links are enabled. As a result, when the default TID-To-Link mapping is used, the maximum number of backoff counters is actually implemented. However, when the TID-To-Link mapping is negotiated between the AP MLD and the non-AP MLD, mapping some TIDs to a set of links and other TIDs to a different set of links, the number of backoff counters is mechanically less. As an example, consider a TID-To-Link mapping negotiated such that TIDs 4 and 5 belonging to AC2 are mapped only to link 20-x. Only BC[x2] is used; BC[y2] and BC[z2] are unused in this case.

[0144] In the remainder of this description, unless explicitly stated, the use of the default TID-To-Link mapping is assumed.

[0145] The back-off counters are used to compete for access to the links 20-x, 20-y, or 20-z to transmit data queued in the AC. In effect, the back-off counters are decremented from an initialized value when the medium is idle, and the corresponding affiliated STA 201-x, 201-z is allowed to transmit (is granted access) when the back-off counter reaches zero. It is understood that the TID-To-Link mapping (negotiated or default) affects the number of BCs that are simultaneously decremented in the non-AP MLD to drive EDCA access to each link.

[0146] Once an AC on a given link is granted access to the wireless medium, the MSDUs stored in the traffic queue 210 corresponding to that AC are sent to the physical (PHY) layers 200-x, 200-y, 200-z for transmission over the given link.

[0147] When MLD is Multi-Radio and Simultaneous Transmission and Reception (STR) is enabled, each Affiliated STA operates on a link independently of other Affiliated STAs operating on other links.

[0148] 2 illustrates, with a frame sequence, the EMLSR mode of operation in the non-AP MLD 120 when the AP MLD 110 decides to use the EMLSR mode. Of course, the EMLSR mode is emphasized here as an example, but similar considerations can be made for the EMLMR mode.

[0149] In this sequence, the non-AP MLD operates in EMLSR mode, meaning that an EML Operating Mode Notification frame activating the EMLSR mode has been successfully sent by the affiliated STA of the non-AP MLD 120. In other words, it has entered an active Enhanced Multi-Link Single Radio (EMLSR) mode that applies to a specific set of two or more active links.

[0150] Affiliated STAs 121 and 122 are co-affiliated STAs of an EMLSR in a non-AP MLD 120. Each affiliated STA can be in one of three defined states: a listening operation state, a valid frame exchange state, and an invalid frame exchange state.

[0151] The non-AP MLD 120 can simultaneously listen on the EMLSR links by placing the co-affiliated STAs of the EMLSRs corresponding to those links in an "awake" or "listening" state. For example, affiliated STAs A1, A2 are in a listening state (references 241, 242). The listening includes a Clear Channel Assessment (CCA) and reception of an Initial Control frame of a frame exchange initiated by the AP MLD. Thus, in the non-AP MLD 120, the co-affiliated STAs of the two EMLSRs simultaneously listen to reception of an Initial Control frame from the AP MLD.

[0152] When the AP MLD 110 wishes to initiate a frame exchange with one or more non-AP MLDs on one of the EMLSR links, it initiates the frame exchange by transmitting an Initial Control frame 245 that explicitly triggers the non-AP MLD. To some extent, the Initial Control frame schedules the non-AP MLD. The Initial Control frame for the frame exchange is transmitted in an OFDM PPDU or non-HT duplicate PPDU format using a rate of 6 Mbps, 12 Mbps, or 24 Mbps (i.e., the MCS subfield in the frame is set to a value up to 2). As defined in the D1.5 standard, the Initial Control frame must be an MU-RTS trigger frame or a BSRP trigger frame, as defined in the IEEE standard 802.11ax-2021. Considering the trigger frame format according to a frame that includes one or more User Info fields, this condition means that the frame 245 includes a User Info field addressed to the non-AP MLD, e.g., the AID12 field is set to the AID of the non-AP MLD (obtained during registration).

[0153] In this example, and as indicated by the reference "IC(A)," the Initial Control frame 245 explicitly triggers non-AP MLD A 120. The Initial Control frame may explicitly trigger multiple non-AP MLDs using multiple User Info fields therein.

[0154] Upon receiving the Initial Control frame 245, a co-affiliated STA of the EMLSR of the non-AP MLD that is explicitly triggered (e.g., affiliated STA A1 in the embodiment) initiates a state change of the co-affiliated STA of the EMLSR of the non-AP MLD under consideration (e.g., a state change of affiliated STAs A1 and A2 in the embodiment) and sends an Initial Control frame response (IC resp.) 246 to AP AP1 affiliated to the AP MLD 110.

[0155] After receiving the Initial Control frame of the frame exchange 245 and sending an immediate response frame 246 in response to the Initial Control frame, the non-AP MLD affiliated STAs (e.g., the co-affiliated STAs A1 of the receiving EMLSR in this embodiment) that were listening on the corresponding link are configured to be able to transmit or receive frames on the active link on which the Initial Control frame 245 was received (e.g., link 151 in this embodiment). To this end, a state switching procedure is initiated upon reception of the frame 245, so that the co-affiliated STAs of the receiving EMLSR are switched from the listening operation state 241 to the "active frame exchange" or "valid frame exchange" state, referenced 251 in the figure, after the EMLSR active switch delay. In this new state, the co-affiliated STAs of the receiving EMLSR are able to receive PPDUs transmitted using multiple spatial streams on the link on which the Initial Control frame 245 was received. The EMLSR Active Switch Delay corresponds to the delay required for a non-AP MLD to switch from an EMLSR listening mode of operation to an EMLSR frame exchange mode. As mentioned above, this is derived from the notification specified in the EML Capabilities (via the EMLSR Padding Delay) exchanged with the AP MLD: Initial Control frame response 246 duration plus the EMLSR Padding Delay.

[0156] At the same time, other co-affiliated STAs of the same non-AP MLD (e.g., STA A2 in this example) are configured not to transmit or receive on other EMLSR links until the frame exchange is completed. To this end, a state switching procedure is also initiated for the co-affiliated STAs of the other EMLSRs, which in turn switch from the listening operation state 242 to a "blindness frame" or "invalid frame exchange" state, referenced 252 in the figure. In particular, the AP MLD prevents data from being transmitted to these co-affiliated STAs of the other EMLSRs.

[0157] The state switching of all EMLSR co-affiliated STAs in the same non-AP MLD is atomic and occurs simultaneously, since it is a matter of allocating a complete radio resource chain (see Figure 14 below) to one of the STAs and depriving the others of that chain. For EMLMR mode, the physical resources (e.g. antennas) of one radio resource chain are allocated (aggregated) to the other radio resource chain, resulting in the former being deprived of transmit and receive capabilities (see Figure 15 below).

[0158] The above indicates that when a non-AP MLD operates in EMLSR mode (or more generally, either EMLSR mode or EMLMR mode), it is either in listening operation mode (its co-affiliated STAs are in listening operation state) or in frame exchange mode (one of its co-affiliated STAs is in valid frame exchange state and the other co-affiliated STA is in invalid frame exchange state).

[0159] In EMLSR mode, a single complete radio resource is available allocated only to the co-affiliated STAs of the receiving EMLSR, as described below with reference to FIG. 14, whereas in EMLMR mode, simultaneous state changes are required since the antenna resources of one of the radio stacks are allocated to the other radio stack, as described below with reference to FIG. 15.

[0160] It can be seen that only one of the co-affiliated STAs of an explicitly triggered non-AP MLD EMLSR can exchange data frames with the AP MLD at a time.

[0161] An exemplary frame exchange sequence is shown in the figure, which includes an explicitly triggered transmission (hence downlink transmission) of an A-MPDU frame 255 by affiliated AP AP1 to co-affiliated STA A1 of the EMLSR of non-AP MLD A 120, followed by a corresponding block acknowledgement 256 from the latter.

[0162] This means that after the EMLSR Transition Delay specified in the EML Capabilities, as well as the completion of the frame exchange performed by the co-affiliated STAs of the receiving EMLSR, the non-AP MLD 120 switches to the listening operating state of the EMLSR, and the co-affiliated STA A1 of the receiving EMLSR switches to the listening operating state 241 as does the co-affiliated STA A2 of the other EMLSR (listening operating state 242). Thus, for each of the co-affiliated STAs of the EMLSR, a state switching procedure is initiated.

[0163] The end of a frame exchange may be sensed by a non-AP MLD (here non-AP MLD 120) if one of the following conditions is met: (1) The MAC of a non-AP MLD affiliated STA that received Initial Control frame 245 did not receive a PHY-RXSTART.indication primitive within a timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, starting at the end of a PPDU (e.g., Acknowledgement 256) sent by the non-AP MLD STA in response to a frame (e.g., A-MPDU frame 255) most recently received from an AP affiliated to the AP MLD, or starting at the end of reception of a PPDU containing a frame from an AP affiliated to the STA that does not require immediate acknowledgment. This indicates that the actual exchange with the AP MLD has ended without receiving a subsequent frame from the AP MLD. (2) The MAC of a STA affiliated to a non-AP MLD that received Initial Control frame 245 receives a PHY-RXSTART.indication primitive during a timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, starting at the end of a PPDU (e.g., Acknowledgement 256) sent by the STA in response to a frame most recently received from an AP affiliated to the AP MLD (e.g., AP-MPDU frame 255), or starting at the end of reception of a PPDU containing a frame from an AP affiliated to the STA that does not require immediate acknowledgment, and the STA affiliated to the non-AP MLD does not detect any of the following frames in the PPDU corresponding to the PHY-RXSTART.indication: - individually addressed frames with RA equal to the MAC address of a non-AP MLD affiliated STA; - a trigger frame with one of the User Info fields addressed to a non-AP MLD affiliated STA; - a CTS-to-self frame with RA equal to the MAC address of an AP that is affiliated to the AP MLD, - a Multi-STA BlockAck frame with one of the Per AID TID Info fields addressed to a non-AP MLD affiliated STA; - an NDP Announcement frame with one of the STA Info fields addressed to a non-AP MLD affiliated STA; This corresponds to the case where, after an actual exchange with the AP MLD, the non-AP MLD receives another frame from the AP MLD that is not addressed to the non-AP MLD (e.g., there is no data addressed to the non-AP MLD or there are no resources assigned to the non-AP MLD). (3) A STA affiliated to a non-AP MLD that received the Initial Control frame 245 does not respond to a frame (e.g., A-MPDU frame 255) most recently received from an AP affiliated to an AP MLD that requires an immediate response after a SIFS.

[0164] Now that the non-AP MLD 120 is in the EMLSR listening mode of operation, the AP MLD may initiate a new frame exchange sequence (with either the non-AP MLD 120 or 130) by sending a new Initial Control frame.

[0165] In the illustrated example, the AP MLD 110 decides to start such a new sequence again with the non-AP MLD 120 using its EMLSR co-affiliated STA A2 122. In particular, the AP MLD 110 uses the other affiliated AP 112 to send a new Initial Control frame 265 IC(A) that explicitly triggers the non-AP MLD A 120, which is received by the EMLSR co-affiliated STA A2 122. The receiving EMLSR co-affiliated STA A2 122 sends a response frame 266 to the Initial Control frame 265. After the EMLSR active switch delay, the explicitly triggered non-AP MLD 120 switches to EMLSR frame exchange mode, the receiving EMLSR co-affiliated STA A2 122 switches from listening operation state 242 to valid frame exchange state 272, and the other EMLSR co-affiliated STA A1 121 simultaneously switches from listening operation state 241 to invalid frame exchange state 271. Frames 275, 276 are then exchanged during the frame exchange sequence until the end of the sequence at which point the non-AP MLD 120 returns to the EMLSR listening operation mode.

[0166] The A-MPDU 255 / 275 is provided as an example only. Other types of frames may be transmitted by the AP MLD, such as, for example, a basic trigger frame to trigger a UL transmission. Although FIG. 2 shows a frame exchange in which the acknowledgement 256 / 276 consists of a single frame 255 / 275, a simpler frame exchange may include only a single frame transmitted by the AP MLD without an acknowledgement, and a more complex frame exchange may include multiple exchange sequences, such as cascaded TXOPs of UL transmissions (triggered by a basic trigger frame) and / or DL ​​transmissions (via the HE MU PPDU).

[0167] This example shows the advantages of EMLSR mode in terms of throughput and latency. AP MLD can quickly switch from one link to another, improving communication performance with less added complexity and cost.

[0168] In this example, the AP MLD 110 initiates a frame exchange sequence with one or more designated non-AP MLDs. The D1.5 standard also allows non-AP MLDs to initiate a frame exchange sequence with an AP MLD. In other words, STAs affiliated to a non-AP MLD operating in EMLSR mode do not need to transmit an Initial Control frame to initiate a frame exchange with the AP MLD. Such affiliated STAs access the wireless medium according to the rules defined in Sections 10.3.2.4 (NAV Configuration and Reset) and 10.23.2 (HCF Contention-Based Channel Access (EDCA)).

[0169] However, conventional contention-based channel access is not defined with respect to the particularities of an EMLSR-active MLD, particularly the state of co-affiliated STAs. Recall that an EMLSR-enabled non-AP MLD becomes EMLSR-active after successfully exchanging an EML OM Notification frame with an EMLSR-enabled AP MLD, in which the EMLSR Mode subfield of the EML Control field is set to 1, the EMLSR link is identified, and the corresponding EMLSR co-affiliated STAs are identified.

[0170] As mentioned above, the preceding description also applies to the EMLMR mode with, among others, the following matching: the EMLMR Delay applies to both the EMLSR Padding Delay and the EMLSR Transition Delay; the Initial frame in EMLMR mode aligns with the Initial Control frame in EMLSR mode, and similarly the Initial frame response in EMLMR mode aligns with the Initial Control frame response in EMLSR mode; although not specified in the D1.5 standard, the EMLMR listening operational state / mode may be defined to match the EMLSR listening operational state / mode in which co-affiliated EMLSRs are listening to their links prior to aggregation of physical radio resources.

[0171] The embodiments of the present invention seek to arrange the EDCA procedures to suit the particularities of the EMLSR or EMLMR of a co-affiliated STA in either EML mode.

[0172] In a first embodiment, initiation of a frame exchange by a co-affiliated STA of a "first" EMLSR or EMLMR includes: a first switching of a first co-affiliated STA from a listening operation state to an active frame exchange state; and before initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure that decrements a backoff counter to access the first link by the same first co-affiliated STA in a valid frame exchange state.

[0173] In these embodiments, the EML active non-AP MLD changes its operation mode to EML frame exchange mode by decrementing its back-off counter before starting contention on the wireless medium. As a result, state switching delays (EMLSR active switch delay or EMLMR active switch delay) are unlikely to affect the contention procedure with co-affiliated STAs, especially creating a risk that after contention is over, access to the medium has been gained by the other MLD, but the STA has not yet finished switching to transmit its first frame.

[0174] These first embodiments are illustrated by Figures 3 and 4, which highlight the EMLMR mode as an example. The same mechanism applies to the EMLMR mode with the matching terms mentioned above.

[0175] Fig. 3 illustrates by means of a flow chart the steps performed by the EMLSR active non-AP MLD to operate a first contention-based channel access procedure according to a first embodiment. Fig. 4 illustrates an example timeline of the first contention-based channel access procedure described in Fig. 3.

[0176] The process begins at step 310, where the non-AP MLD enters EMLSR listening mode of operation. That is, the co-affiliated STAs of that EMLSR are set to a listening operational state and simultaneously listen to their respective EMLSR links. The non-AP MLD may enter EMLSR listening mode of operation in response to receiving an EML OM Notification frame with the EMLSR Mode subfield (of the EML Control field) set to 1. As a variant, the non-AP MLD may enter EMLSR listening operation by switching back from EMLSR frame exchange mode.

[0177] As shown in FIG. 4 with the EMLSR active non-AP MLD 120 in the EMLSR listening mode of operation, EMLSR co-affiliated STAs A1 121 and A2 122 are both in listening operational states 410 and 411 .

[0178] At step 320, the non-AP MLD waits to buffer uplink data to transmit to the AP MLD 110. As mentioned above, such data may be provided from higher layers and stored in the buffer 210 of the non-AP MLD.

[0179] When such data is identified, the non-AP MLD attempts to initiate a contention-based channel access procedure to access one of the EMLSR links and transmit the buffered data.

[0180] To that end, select one of the EMLSR's co-affiliated STAs to perform the contention-based channel access procedure in step 330. The selected STA is called the sending EMLSR's co-affiliated STA, and the corresponding link is called the sending EMLSR link.

[0181] Any selection method may be used, for example relying on a round robin strategy, a random strategy, or a load balancing distribution strategy based on link occupancy (in such a case, EMLSR links with low occupancy are selected preferentially), or a radio-based strategy (in such a case, co-affiliated STAs of EMLSRs with current full radios are selected preferentially).

[0182] In the example of Figure 4, EMLSR's co-affiliated STA1 is selected, which may be a station with a full radio or a station with a light (reduced functionality) radio.

[0183] Next, in step 340, a state switching procedure is initiated by the non-AP MLD to switch mode from EMLSR listening operation mode to EMLSR frame exchange mode, and the co-affiliated STAs of the sending EMLSR are in frame exchange enabled state.

[0184] To this end, the co-affiliated STAs of the sending EMLSR are switched from a listening operation state to a valid frame exchange state (step 341), and in parallel (synchronously or simultaneously), the co-affiliated STAs of the other EMLSRs are switched from a listening operation state to a valid frame exchange state (step 342).

[0185] In some embodiments, step 340 is conditioned on detecting that the corresponding link is idle by CCA verification. This means that the co-affiliated STAs of the sending EMLSR perform CCA during or just before triggering the switchover to ensure that the link is idle, and thus, is ready for the EDCA backoff procedure. In these embodiments, the co-affiliated STAs of the sending EMLSR initiate or perform the switchover only if the corresponding link is detected as idle.

[0186] In FIG. 4 , when the non-AP MLD 120 initiates a frame exchange sequence with the AP MLD 110, desires to transmit buffered data, and selects the EMLSR co-affiliated STA A1 121 as the transmitting EMLSR co-affiliated STA, it switches (possibly after CCA verification) the latter (A1 121) from listening operation state 410 to valid frame exchange state 420, and in parallel (synchronously or simultaneously) switches the EMLSR co-affiliated STA A2 122 from listening operation state 411 to invalid frame exchange state 421.

[0187] The simultaneous switching continues up to the EMLSR active switch delay, defined above and shown in the figure by reference number 499. In practice, the switching of co-affiliated STAs of an EMLSR with a full radio (only antenna connection is required) is shorter than the switching of co-affiliated STAs of other EMLSRs with light radios (due to the need for physical and reconfiguration of the full radio chain).

[0188] Once the switch occurs, the co-affiliated STAs of the sending EMLSR operate a backoff procedure in the sending EMLSR link in step 350. As shown in Figure 4, the co-affiliated STA A1 121 of the sending EMLSR operates a backoff procedure 422 by decrementing the counters 211 (only one shown in the figure) of the ACs 210 that have data to transmit as long as the medium (sending EMLSR link 151) is sensed to be idle.

[0189] The backoff counter is decremented in a conventional manner.

[0190] If the medium becomes busy during the decrement, the non-AP MLD may adopt various alternative actions.

[0191] In the first operation, the co-affiliated STAs of the sending EMLSR remain in an active frame exchange state and wait for the medium to return to an idle state, while the co-affiliated STAs of the other EMLSRs maintain their current states.

[0192] In the second operation, the co-affiliated STAs of the EMLSR return to listening mode of operation regardless of whether the Duration field in the frame indicates the medium is busy. The non-AP MLD waits for a new opportunity to select one link for a new EDCA backoff procedure, such as initiating a new frame exchange with the AP MLD. Thus, the switchback is an uncontrolled period, as opposed to the third operation below.

[0193] In a third operation, the EMLSR's co-affiliated STAs still switch to a listening mode of operation, but only for a predefined period of time corresponding to the Duration field of the frame that made the medium busy. Once that period has expired, the EMLSR's co-affiliated STAs switch to their previous state (i.e., the sending EMLSR's co-affiliated STAs to a valid frame exchange state, and the other EMLSR's co-affiliated STAs to an invalid sending EMLSR's co-affiliated STAs). This switch to the previous state may be conditioned on detecting that the corresponding link is idle via CCA verification (as described above).

[0194] In the fourth operation, the non-AP MLD first determines the Duration field of the frame that made the medium busy, and based on the Duration value, decides whether to return to the listening operation mode or to stay in the current EMLSR frame exchange mode. For example, if the Duration is long, i.e., its value is higher than the high threshold, the EMLSR co-affiliated STAs are switched to the listening operation mode, similar to the second operation (i.e., no time limit). If the Duration is average, i.e., its value is between the low and high thresholds, the EMLSR co-affiliated STAs are switched to the listening operation mode for a predefined time, similar to the third operation. Also, if the Duration is short, i.e., its value is lower than the low threshold, the EMLSR co-affiliated STAs remain in the current state, similar to the first operation. In a variant, only one threshold is used to distinguish between the first operation (when the Duration is short) and the second or third operation (when the Duration is long).

[0195] When the backoff counter reaches zero (step 360), the co-affiliated STAs of the sending EMLSR perform a frame exchange with the AP MLD, in particular transmitting buffered uplink data of the non-AP MLD in step 370. In the example of Figure 4, the co-affiliated STA A1 121 of the sending EMLSR transmits an A-MPDU frame 424 corresponding to its buffered uplink data to the AP MLD 110 via its corresponding EMLSR link, i.e., link 151, when one backoff counter reaches zero.

[0196] Optionally, before transmitting the A-MPDU frame 424, the co-affiliated STA A1 121 of the transmitting EMLSR may transmit an RTS frame or a CTS-to-self frame to better protect the granted channel.

[0197] Upon completion of the frame exchange on link 151, the non-AP MLD 120 again initiates the state switching procedure to switch the EMLSR co-affiliated STAs A1 121 and A2 122 back to the listening operational states 410, 411. Thus, the non-AP MLD 120 returns to the EMLSR listening mode of operation. The switch back operates for the EMLSR Transition Delay (specified in EML Capabilities) after the completion of the frame exchange.

[0198] The first embodiment illustrated throughout Figures 3 and 4 may not be fully implemented because during the EDCA procedure (backoff decrement), the EMLSR co-affiliated STA A2 122 is unable to receive the Initial Control frame 265.

[0199] The second embodiment provides that initiation of a frame exchange by a co-affiliated STA of a “first” EMLSR or EMLMR includes: initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure by the first co-affiliated STA still in a listening state to access the first link, decrementing a backoff counter; before switching the first Affiliated STA from the listening operation state to the active frame exchange state when the backoff counter reaches a value of zero.

[0200] In these embodiments, the EML active non-AP MLD performs medium contention (by decrementing its backoff counter or counters) before changing its operation mode to the EML frame exchange mode. It is noted that the Initial Control frame received on the other link during the EDCA procedure may be taken into account by the EML active non-AP MLD.

[0201] These second embodiments are illustrated by figures 5a, 5b, 6a, 6b, 7 and 8, which highlight the EMLSR mode as an example. The same mechanism applies to the EMLMR mode with the matching terms mentioned above.

[0202] Figures 5a and 5b illustrate by means of a flow chart the steps performed by an EMLSR active non-AP MLD to operate a second contention-based channel access procedure according to a second embodiment. Figure 6a illustrates generally an exemplary timeline of the second contention-based channel access procedure as described in Figures 5a and 5b. Figure 6b illustrates generally an alternative timeline of the second contention-based channel access procedure as described in Figures 5a and 5b.

[0203] Similar to Figure 3, the process begins at step 310, where the non-AP MLD enters the EMLSR's listening mode of operation. This means that the EMLSR's co-affiliated STAs are set to listening operational states and are listening simultaneously to their respective links. As shown in Figure 6a, where the EMLSR active non-AP MLD 120 is in the EMLSR's listening mode of operation, the EMLSR's co-affiliated STAs A1 121 and A2 122 are both in listening operational states 610 and 611.

[0204] At step 320 , the non-AP MLD waits to buffer uplink data to send to the AP MLD 110 .

[0205] Once such data is identified, the non-AP STA selects, in step 330, one of the EMLSR's co-affiliated STAs to perform a contention-based channel access procedure. The selected STA is referred to as the sending EMLSR's co-affiliated STA, and the corresponding link is referred to as the sending EMLSR link. An exemplary selection procedure is provided above. In FIG. 6a, EMLSR's co-affiliated STA A1 121 is selected as the sending EMLSR's co-affiliated STA.

[0206] Next, the non-AP MLD initiates a contention-based channel access procedure to access the sending EMLSR link in step 535. The sending EMLSR's co-affiliated STAs operate a backoff procedure. As shown in FIG. 6a, the sending EMLSR's co-affiliated STA A1 121 decrements its backoff counter while in the listening operation state 610.

[0207] The backoff counter is decremented in a conventional manner.

[0208] Contrary to the D1.5 standard, which states that a co-affiliated STA of an EMLSR in a listening operation state should only react when it receives an Initial Control frame 245 or 265 (i.e., an MU-RTS trigger frame or a BSRP trigger frame), the embodiment provides that it should react and set its NAV when it receives any type of 802.11 control frame with MCS up to 2 (i.e., up to 24 Mbps). Such frames correspond to OFDM PPDU or non-HT duplicate PPDU formats using rates of 6 Mbps, 12 Mbps, or 24 Mbps. In fact, a co-affiliated STA of an EMLSR (even if equipped with a light radio) can decode the field Duration of such frames.

[0209] Upon receiving such a frame (with an MCS value up to 2), the transmitting EMLSR co-affiliated STA A1 121 performing EDCA procedures 612 in listening mode of operation 610 sets or updates its Network Allocation Vector (NAV) based on the Duration field of the frame, as indicated by reference numeral 613. The EDCA procedures can be resumed (614) when the NAV reaches zero.

[0210] In operation, this means that the co-affiliated STAs of the transmitting EMLSR receive, in step 540, OFDM PPDUs or non-HT duplicate PPDU formats using rates of 6, 12 or 24 Mbps.

[0211] Upon such receipt, the co-affiliated STAs of the sending EMLSR stop or abort the EDCA procedure in step 542, which means that the back-off counter is stopped from decrementing. The NAV of the co-affiliated STAs of the sending EMLSR is then set or updated based on the Duration field of the received frame in step 544. The co-affiliated STAs of the sending EMLSR then wait for the expiration of their NAV before resuming the EDCA procedure in step 546.

[0212] When the backoff counter finally reaches zero (step 550 - signifying the end of the EDCA procedure), the non-AP STA switches from the EMLSR listening operation mode to the EMLSR frame exchange mode in step 560, and the co-affiliated STAs of the transmitting EMLSR enter the active frame exchange state.

[0213] To this end, the co-affiliated STAs of the sending EMLSR are switched from a listening operation state to a valid frame exchange state (step 561), and in parallel (synchronously or simultaneously), the co-affiliated STAs of the other EMLSR are switched from a listening operation state to a valid frame exchange state (step 562).

[0214] In FIG. 6a, the non-AP MLD 120 initiates a frame exchange sequence with the AP MLD 110, desires to transmit buffered data, selects EMLSR co-affiliated STA A1 121 as the transmitting EMLSR co-affiliated STA, and when the backoff counter reaches zero, switches the latter (A1 121) from a listening operation state 610 to a valid frame exchange state 620, and in parallel (synchronously or simultaneously) switches EMLSR co-affiliated STA A2 122 from a listening operation state 611 to an invalid frame exchange state 621.

[0215] The simultaneous switching continues up to the EMLSR active switch delay specified above.

[0216] Once the switch is made, the co-affiliated STAs of the transmitting EMLSR transmit their buffered uplink data in step 370. In the example of Fig. 6a, the co-affiliated STA A1 121 of the transmitting EMLSR transmits an A-MPDU frame 624 corresponding to its buffered uplink data to the AP MLD 110 via the corresponding EMLSR link, i.e., link 151, when one backoff counter reaches 0.

[0217] Optionally, before transmitting the A-MPDU frame 624, the co-affiliated STA A1 121 of the transmitting EMLSR may transmit an RTS frame or a CTS-to-self frame to better protect the granted channel.

[0218] Upon completion of the frame exchange on link 151, non-AP MLD 120 again initiates the state switching procedure to transition EMLSR co-affiliated STAs A1 121 and A2 122 back to listening operational states 610, 611. Thus, non-AP MLD 120 switches back to EMLSR listening operational mode. The switch back operates for EMLSR Transition Delay (specified in EML Capabilities) after completion of frame exchange.

[0219] 6a, while in the listening operational state, the sending EMLSR co-affiliated STA A1 121 may again initiate the EDCA procedure with backoff counter decrement 632. Because the other EMLSR co-affiliated STA A2 122 is also listening to its EMLSR link 152, it may receive an Initial Control frame 634 from the co-affiliated AP AP2 112 over that EMLSR link while the sending EMLSR co-affiliated STA A1 121 is decrementing the backoff counter of the other EMLSR link 151.

[0220] In response to such reception, the non-AP MLD 120 may stop or suspend the EDCA procedure (and thus the decrement of the back-off counter) in STA A1 121, while the other EMLSR co-affiliated STA A2 122 may transmit an Initial Control frame response (IC resp.) 635 to trigger or initiate a state change in the EMLSR co-affiliated STA and thus execute a frame exchange with AP2 112 via the second link 152. Of course, other strategies may be implemented whereby the non-AP MLD 120 receiving the Initial Control frame 634 decides whether it is worthwhile to stop decrementing the back-off counter and execute an AP-initiated frame exchange, or to continue decrementing the back-off counter without responding to the Initial Control frame 634 in order to gain medium access for its own device to initiate a frame exchange for its own device. The decision in these strategies (stop or continue) may be based on various parameters and / or policies.

[0221] As an example, the amount of buffered data can be considered. If that amount is equal to or greater than a threshold, a strategy of continuing decrementing is preferred in order to ensure medium access for non-AP MLD transmissions. The Initial Control frame 634 is discarded and no response is sent. On the other hand, if the amount is low, an AP-initiated frame exchange is preferred (decrementing is stopped and a response 635 is sent).

[0222] As another example, if the co-affiliated STA A1 121 of the sending EMLSR is assigned a full wireless stack, it may be worth prioritizing access by this STA to mitigate the time required to switch the full wireless stack to the co-affiliated STA of the other EMLSR. Thus, the co-affiliated STA A1 121 of the sending EMLSR continues to decrement the backoff counter. The Initial Control frame 634 is discarded and no response is sent. On the other hand, if the co-affiliated STA A2 122 of the EMLSR is assigned a full wireless stack, it may be worth prioritizing this STA. Thus, the decrement is stopped and a response 635 is sent to perform an AP-initiated frame exchange.

[0223] As yet another example, if the Initial Control frame 634 is an MU-RTS trigger frame, indicating that the AP-initiated frame exchange is likely to be a downlink transmission, then the sending EMLSR's co-affiliated STA's own medium access is prioritized. Thus, the sending EMLSR's co-affiliated STA A1 121 continues to decrement the back-off counter. On the other hand, if the Initial Control frame 634 is a BSRP trigger frame, indicating that the AP-initiated frame exchange is likely to be an uplink transmission, then such AP-initiated frame exchange, which may have resource units for non-AP MLD to transmit, is prioritized. Thus, the decrement is stopped and a response 635 is sent to perform the AP-initiated frame exchange.

[0224] As yet another example, the decision may be based on the loading (or buffering) of previous uplink data in a buffer or queue for a particular one of the EMLSR links. Indeed, some implementations of AC in EDCA mechanisms require preloading of uplink data in a particular queue so that it can be transmitted when the associated back-off counter expires. Of course, this preloading may only be triggered in the vicinity of such counter expiry. The decision may be based on whether there has been such preloading: if uplink data has already been preloaded in the buffer for the first link on which the EDCA procedure is currently being performed, the co-affiliated STA A1 121 of the transmitting EMLSR continues to decrement the back-off counter in order to gain medium access for itself. On the other hand, if uplink data has not yet been preloaded in the buffer for the first link, the AP-initiated frame exchange takes priority. Thus, the decrementation is stopped and a response 635 is sent to perform the AP-initiated frame exchange.

[0225] If response 635 is sent, then after the EMLSR active switch delay, the non-AP MLD 120 switches to the EMLSR frame exchange mode, the EMLSR co-affiliated STA A2 122 switches from the listening operation state 611 to the valid frame exchange state 641, and the EMLSR co-affiliated STA A1 121 simultaneously switches from the listening operation state 610 to the invalid frame exchange state 640. Frames 644, 645 are then exchanged during the frame exchange sequence until the end of the sequence at which the non-AP MLD 120 switches to the EMLSR listening operation mode (not shown).

[0226] Typically, the affiliated AP2 112 may transmit a basic trigger frame 644 to the co-affiliated STA A2 122 of the EMLSR to allocate uplink resource units for the non-AP MLD 120 as specified in IEEE Standard 802.11ax-2021. In such a case, the non-AP MLD 120 transmits a High-Efficiency Trigger-Based (HE TB) PPDU 645 in the allocated resource units via the co-affiliated STA A2 122 of the EMLSR.

[0227] The final flowcharts of Figures 5a and 5b show a process for causing the non-AP MLD to pause or stop or abort the EDCA backoff procedure performed on the first link of the EMLSR link upon receiving an Initial Control frame from the AP MLD via the second link of the EMLSR link (e.g., the backoff counter or counter decrement is stopped).

[0228] The co-affiliated STA of the other EMLSR (the other of the co-affiliated STAs of the sending EMLSR that decrements the backoff counter) receives an Initial Control frame from the AP MLD in step 570. This means that the AP MLD requests a new EMLSR sequence exchange to be initiated on the EMLSR link corresponding to the co-affiliated STA of the other EMLSR.

[0229] In step 575, the co-affiliated STA of the sending EMLSR pauses the backoff procedure, which means that it stops decrementing the backoff counter.

[0230] Next, in step 580, the co-affiliated STA of the other EMLSR transmits a response to the Initial Control frame over its EMLSR link.

[0231] Then, according to the mechanism of the EMLSR, after the EMLSR active switch delay, in step 590, the non-AP STA switches from the EMLSR listening operation mode to the EMLSR frame exchange mode to act on the co-affiliated STAs of the other EMLSR for frame exchange.

[0232] For this purpose, the co-affiliated STAs of the other / requested EMLSR are switched from a listening operation state to a valid frame exchange state (step 591), and in parallel (synchronously or simultaneously), the co-affiliated STAs of the sending EMLSR are switched from a listening operation state to a valid frame exchange state (step 592).

[0233] This new mechanism can also be considered separately from the core aspect of the second embodiment, in this context, regarding a communication method in a wireless network in a non-AP MLD operating in an active EMLSR mode, comprising: Initiating an EDCA backoff procedure by a first STA that is in a listening operation state, is affiliated with the non-AP MLD, and corresponds to a first link of a set of valid links of the links to which the EMLSR mode is applied, to access the first link, the EDCA backoff procedure decrementing a backoff counter; Here, the decrement of the backoff counter is paused upon receiving an Initial Control frame from the AP MLD over the second link in the set.

[0234] In an embodiment, the decrement is resumed after the frame exchange initiated by the Initial Control frame is completed.

[0235] The scenario of Figure 6a may be particularly applicable when the co-affiliated STA of the sending EMLSR that decrements the backoff counter is a co-affiliated STA with a full radio. Indeed, in this case, the switch to the valid frame exchange state 620 is substantially instantaneous.

[0236] The situation is slightly different when the co-affiliated STA of the sending EMLSR is a co-affiliated STA with a light radio, as there is a longer transition between the listening operation state 611 and the active frame exchange state 641. During this transition period, non-AP MLD functionality may be different and care must be taken to ensure access to the wireless medium.

[0237] Figure 6b shows a more detailed scenario, taking into account the transition period of Figure 6a, in schematic form. The length of the transition period corresponds to the active switch delay of the EMLSR mentioned above. The flow charts of Figures 5a and 5b still apply.

[0238] Similar to FIG. 6a, EMLSR co-affiliated STAs A1 121 and A2 122 are both in listening operational states 610 and 611. EMLSR co-affiliated STA A1 121 is selected as the co-affiliated STA of the sending EMLSR. While in listening operational state 610, sending EMLSR co-affiliated STA A1 121 decrements its back-off counter (612). Upon receiving a control frame (with an MCS value up to 2), sending EMLSR co-affiliated STA A1 121 sets or updates its network allocation vector (NAV) based on the frame's Duration field (613). When the NAV reaches zero, the EDCA procedure may be restarted (614).

[0239] When the backoff counter of the sending EMLSR co-affiliated STA A1 121 reaches zero, the non-AP MLD 120 switches STA A1 121 from the listening operation state 610 to the valid frame exchange state 620, while in parallel (synchronously or simultaneously) switching the EMLSR co-affiliated STA A2 122 from the listening operation state 611 to the invalid frame exchange state 621.

[0240] In the first implementation, the non-AP MLD runs CCA during the transition period, e.g., during switching. In other words, to switch the co-affiliated STAs of the sending EMLSR, the non-AP MLD initiates a state switching procedure for this STA while the STA is decrementing its back-off counter, so that the state switching procedure ends as soon as the back-off counter reaches 0 (e.g., back-off counter expiry). Of course, the switching of the co-affiliated STAs of the other EMLSR is done synchronously / simultaneously.

[0241] The switching of the co-affiliated STAs of the sending EMLSR is indicated in the figure by reference numeral 622a, and the switching of the co-affiliated STAs of the other EMLSR is indicated in the figure by reference numeral 623a.

[0242] In such a case, the EDCA procedure (decrementing the backoff counter) is not affected by the switching mechanism, and the two operations (decrement and switch) can be performed simultaneously. The switching mechanism 622a (resp. 623a) is pre-activated corresponding to the EMLSR active switch delay, such that when the backoff counter reaches zero, the transmitting co-affiliated EMLSR STA A1 121 is in a valid frame exchange state (and the other co-affiliated EMLSR STA is in an invalid frame exchange state).

[0243] Similarly, the listening operational state is restored and becomes operational at the end of the transition period 625 corresponding to the switchback (the period defined by the EMLSR Transition Delay set in the EML Capabilities).

[0244] In the second embodiment, the non-AP MLD cannot operate CCA during the transition period, i.e., during switching. In such a case, the switching mechanism 622b (resp 623b in the figure) is activated after the back-off counter reaches zero. In other words, to switch the co-affiliated STAs of the sending EMLSR, the non-AP MLD initiates a state switching procedure for this STA in response to the back-off counter reaching the value 0. Of course, the switching of the co-affiliated STAs of the other EMLSR is performed in a synchronous / simultaneous manner.

[0245] Reference numbers 622b and 623b indicate this implementation.

[0246] Since there is a risk that the medium will be claimed by another MLD, it is advantageous to protect the medium during the transition period starting upon expiry of the back-off counter. In that regard, a protection frame 629 as a RTS (Request To Send) or CTS-to-self (Clear To Send) frame is transmitted by the co-affiliated STA A1 121 of the transmitting EMLSR during the switching procedure 622b before the transmission of the buffered uplink data 624 is actually performed. In other words, it is provided that in response to the back-off counter reaching the value 0, the non-AP MLD transmits a control frame on the link corresponding to the back-off counter.

[0247] To make the protected frame 629 readable by any legacy station on the medium, the frame preferably follows the format of an OFDM PPDU or non-HT duplicate PPDU using a rate of 6 Mbps, 12 Mbps, or 24 Mbps.

[0248] Since the length of the transition period is MLD dependent, the protection frame 629 is preferably sized to protect the medium until transmission 624. This may require that the protection frame 629 include padding to terminate the control frame after a point preceding the end of the state switching procedure by a short interframe space (SIFS). Since the non-AP MLD knows the active switch delay of the EMLSR and also knows the conventional length of the control frame used, it has no problem determining the amount of padding required. Thus, the co-affiliated STA A1 121 of the transmitting EMLSR can begin transmission 624 immediately after the frame 629, given a legal SIFS period.

[0249] The above embodiment provides that a co-affiliated STA (e.g., a sender) of a single EMLSR executes an EDCA procedure and thus decrements its back-off counter. However, in order to increase the chance of gaining access to the wireless medium, the embodiment may trigger an EDCA procedure in two or more or all co-affiliated STAs of the EMLSR of the same non-AP MLD. This is illustrated through FIG. 7 and FIG. 8. The EDCA back-off procedure is simultaneously initiated on two or more links of the EMLSR link. Of course, the link on which the co-affiliated station of the corresponding EMLSR is switched to the valid frame exchange state is the link corresponding to the link on which the back-off counter of the EDCA back-off procedure first becomes 0. As shown in the above figure, the EMLMR mode is highlighted as an example. The same mechanism is also applied to the EMLMR mode with the above-mentioned matching terminology.

[0250] 7 is a diagram illustrating, by means of a flow chart, steps performed by an EMLSR active non-AP MLD to operate a third contention-based channel access procedure according to a third embodiment. FIG. 8 is a diagram illustrating an example timeline of the third contention-based channel access procedure described in FIG. 7.

[0251] Similar to the above embodiment, the process begins at step 310, where the non-AP MLD enters the EMLSR listening mode of operation. That is, the EMLSR's co-affiliated STAs are set to a listening operational state and are therefore simultaneously listening to their respective links. As shown in FIG. 8 with the EMLSR's active non-AP MLD 120 in the EMLSR listening mode of operation, the EMLSR's co-affiliated STAs A1 121 and A2 122 are both in listening operational states 810 and 811.

[0252] At step 320 , the non-AP MLD waits to buffer uplink data to send to the AP MLD 110 .

[0253] If such data is identified, the non-AP STA no longer selects a co-affiliated STA of a single EMLSR, but instead operates the random backoff procedure simultaneously and independently for each EMLSR's co-affiliated STA A1 121 (step 813) and A2 122 (step 814) in step 720.

[0254] Again, as described above, the decrementing of the backoff counter may be paused upon receipt of the control frame (and thus the NAV being set).

[0255] When the backoff counter of either EDCA procedure 813, 814 reaches zero (step 730), the non-AP STA switches from the EMLSR listening operation mode to the EMLSR frame exchange mode in step 740, where the EMLSR co-affiliated STA corresponding to the expired backoff counter enters the valid frame exchange state. This EMLSR co-affiliated STA is called a "ready EMLSR co-affiliated STA."

[0256] To this end, the co-affiliated STAs of the ready EMLSR are switched from a listening operation state to a valid frame exchange state (step 741), and in parallel (synchronously or simultaneously), the co-affiliated STAs of the other EMLSR are switched from a listening operation state to a valid frame exchange state (step 742).

[0257] In Figure 8, both EMLSR co-affiliated STAs A1 121 and A2 121 are decrementing their backoff counters. STA A1 121 is the first whose backoff counter reaches zero and is therefore the ready STA. In response to the counter expiring, the ready STA A1 121 is switched from a listening operation state 810 to a valid frame exchange state 820, while in parallel (synchronously or simultaneously), the EMLSR co-affiliated STA A2 122 is switched from a listening operation state 811 to an invalid frame exchange state 821.

[0258] The simultaneous switching continues up to the active switch delay of the EMLSR mentioned above.

[0259] Once the switch occurs, the co-affiliated STAs of the ready EMLSR transmit their buffered uplink data in step 370. In the example of Figure 8, the co-affiliated STA A1 121 of the ready EMLSR transmits its buffered uplink data corresponding A-MPDU frame 825 to the AP MLD 110 via the corresponding EMLSR link, i.e., link 151 to the co-affiliated AP AP1 111 of the AP MLD 110.

[0260] Optionally, before transmitting the A-MPDU frame 825, the co-affiliated STA A1 121 of the ready EMLSR may transmit an RTS frame or a CTS-to-self frame to better protect the granted channel.

[0261] Upon completion of the frame exchange initiated by the ready EMLSR co-affiliated STA A1 121, as well as the EMLSR Transition Delay specified in the EML Capabilities, the non-AP MLD 120 switches back to the EMLSR listening operation mode, i.e., the ready EMLSR co-affiliated STA A1 121 switches back to the listening operation state 810 (listening operation state 811), as does the other EMLSR co-affiliated STA A2 122.

[0262] As previously described with reference to FIG. 1ab, in MLD, each AC is mapped to one EDCA engine per link.

[0263] In the case of Multi-Radio MLD with Simultaneous Transmission and Reception (STR), each affiliated STA operates on a link independently from other affiliated STAs operating on other links. In other words, the EDCA engine for one link can operate in a legacy manner because it is independent from other EDCA engines for other links. In the example of FIG. 1b, this means that EDCA engines 221-x, 221-y, 221-z and their respective backoff entities 211 can operate independently from the others in a legacy manner.

[0264] However, in the case of an MLD operating in EMLSR mode or EMLMR mode, an affiliated STA operating on an EMLSR or EMLMR link depends on another affiliated STA operating on another EMLSR or EMLMR link.

[0265] For example, when a co-affiliated STA of one EMLSR switches to an active frame exchange state on its EMLSR link, the co-affiliated STA of the other EMLSR automatically switches to an inactive frame exchange state on the other EMLSR link. This means that an EDCA engine that processes an EML link has some dependency on another EDCA engine that processes another EML link of the same EMLSR link set or EMLMR link set. This is because in an MLD operating in EML mode, data frame exchange is effectively only on one EML link of the set at a time. In the example of FIG. 1b, the EDCA engines 221-x, 221-y, 221-z and their respective back-off entities 211 cannot operate independently of each other in a legacy manner.

[0266] Therefore, the embodiment of the present invention seeks to arrange the EDCA procedure to suit the particularities of the EMLSR or EMLMR of its co-operating STAs.

[0267] In a non-AP MLD operating in an initially active EML mode, a back-off counter driving or managing EDCA access to a second link of a set of EMLSRs or EMLMRs may be paused in response to initiating a frame exchange with the AP MLD over a first link of the set, thereby avoiding obtaining EDCA access to the second link while the corresponding co-affiliated STA is unavailable (because the frame exchange has allocated radio resources to the co-affiliated STA). It can be seen that the efficiency of the EDCA procedure is improved.

[0268] As an example of a specific EDCA-related issue, if an MLD is operating in EMLSR or EMLMR mode on links 20-x and 20-z, and BC[x3] becomes 0, which allows the MLD access to link 20-x to transmit the MSDU stored in AC3, the following dependency emerges: - the other three backoff counters BC[x0], BC[x1], and BC[x2] belonging to the same EDCA engine 221-x are suspended for legacy 802.11 operation; - Since link 20-z is no longer operational due to MLD, the four back-off counters BC[z0], BC[z1], BC[z2], and BC[z3] belonging to EDCA engine 221-z are also suspended. This dependency is specific to MLD operating in EML mode on links 20-x and 20-z. In fact, when affiliated STA 201-x switches to a valid frame exchange state on EMLSR / EMLMR link 20-x for transmission, the other co-affiliated STA 201-z automatically switches to an invalid frame exchange state on the other EMLSR / EMLMR link 20-z. In the invalid frame exchange state, the co-affiliated STA cannot process the EDCA back-off procedure since medium sensing is not possible. - When the transmission of the MSDU stored in AC3 is completed on link 20-x, the MLD operating in EML mode switches back to a listening operational state on both links 20-x and 20-z. At this stage, another dependency appears between EDCA engine 221-x and EDCA engine 221-z, in particular between their respective back-off counters BC[x3] and BC[z3]: In the EDCA engine 221-x, the restart or reactivation of the backoff counters BC[x0], BC[x1], BC[x2], and BC[x3] can be handled in a legacy manner: BC[x0], BC[x1], and BC[x2] are restarted, and BC[x3] is reinitialized. - In the EDCA engine 221-z, the resumption or restart of the back-off counters BC[z0], BC[z1], BC[z2], BC[z3] is problematic. While BC[z0], BC[z1], BC[z2] may simply be restarted since no data from the corresponding ACs has been transmitted, this is not so trivial for BC[z3], which corresponds to the AC where the transmission occurred. In fact, the mere restart of BC[z3] may cause fairness problems among the ACs of the MLD, since in the next round BC[z3] may gain access to link 20-z to transmit again the MSDUs stored in AC3.

[0269] Therefore, a new strategy is proposed to manage EDCA backoff restart for STAs affiliated with a non-AP MLD operating in EML mode. In particular, embodiments of the present invention define a new EDCA backoff restart procedure for STAs affiliated with a non-AP MLD operating on a second EMLSR or EMLMR link after a UL transmission is made on a first EMLSR or EMLMR link of the same set.

[0270] In this regard, in response to the completion of the frame exchange on the first link, a restart strategy selected based on the characteristics of the frame exchange is applied to restart the paused backoff counter (driving access to the second link).

[0271] Therefore, the strategy or policy for restarting the backoff counter of one link depends on what happened (frame exchange) on another link. This differs from the traditional EDCA approach. It can be seen that by applying or tuning the appropriate EDCA backoff restart procedures, the problem of network access fairness can be mitigated. In particular, the backoff counter associated with an AC of a link can be penalized when data from the same AC is transmitted over other links of the same set of EMLSR or EMLMR links.

[0272] More specifically, after an uplink (UL) transmission of an ACm MSDU is made on a first EMLSR or EMLMR link of the same EMLSR or EMLMR link set, a restart procedure is proposed for the back-off counter 211BC[n,m] running in the EDCA engine 221-n of link n of the second EMLSR or EMLMR.

[0273] In practice, in response to the initiation of a frame exchange, a number of back-off counters driving EDCA on the second link for a respective number of access categories (e.g., one for each of the four ACs) are paused. In that case, the restart strategy may be applied to the paused back-off counters corresponding to the access categories exchanged during the frame exchange. In other words, if data from AC2 and AC3 are transmitted uplink over link 1 during the frame exchange, the paused back-off counters corresponding to AC2 and AC3 on link 2 may be restarted using the adapted restart strategy, and the paused back-off counters corresponding to the other ACs (AC0 and AC1) may be restarted in a conventional EDCA manner.

[0274] 9 illustrates, by way of a flow chart, the steps of handling the restart of the backoff counter in EML mode according to an embodiment of the present invention. For ease of explanation, we will mainly refer to EMLSR mode, but the same applies to EMLMR mode.

[0275] The process begins in step 900, where the non-AP MLD enters a listening mode of operation (EMLSR or EMLMR), which means that its co-affiliated STAs are set to a listening operational state, and therefore are simultaneously listening to their respective links. The non-AP MLD may enter the listening mode of operation in response to receiving an EML OM Notification frame with the corresponding Mode subfield (EMLSR or EMLMR Mode subfield of the EML Control field) set to 1.

[0276] A non-AP MLD may have all or some of its ACs in EDCA mode (e.g., using EDCA parameters for medium contention) and may already be in MU EDCA mode (i.e., using MU EDCA parameters for medium contention) if it has recently benefited from a trigger-based MU UL transmission for the corresponding AC. As is known, an MLD may switch an AC from MU EDCA mode back to EDCA mode upon expiration of the respective MU EDCA Timer.

[0277] In step 905, the non-AP MLD waits to buffer uplink data to transmit to the AP MLD 110. As described above, such data may be provided by higher layers and stored in the non-AP MLD's buffer 210. The non-AP MLD identifies all ACs that have buffered data to be transmitted to the AP MLD.

[0278] Next, for step 910, the non-AP MLD determines a back-off counter to be activated for contending for access to the EMLSR or EMLMR link (link 1 and link 2 in the figure).

[0279] In some embodiments, such as those based on the default TID-To-Link mapping, all backoff counters corresponding to the ACs identified for that link must be used for medium contention.

[0280] In some embodiments where TID-to-Link is negotiated, some TIDs (and therefore corresponding ACs) may be barred on one of the links, in which case non-AP MLD considers the negotiated TID-to-Link mapping and lists all backoff counters corresponding to the identified ACs for the links of the EMLMR or EMLSR's link set that are not barred.

[0281] In other embodiments, the non-AP MLD may decide to contend for access to only one of the set of links, rather than contending for both links simultaneously. To do so, the non-AP MLD selects one of its co-affiliated STAs to operate a contention-based channel access procedure. The selected STA is referred to as the transmitting co-affiliated STA, and the corresponding link is referred to as the transmitting link. In the embodiment shown in FIG. 12, described below, the non-AP MLD decides to contend for access to only link 152. The non-AP MLD may also decide to contend for access to different links for different ACs.

[0282] Any selection procedure may be used, for example a round robin strategy, a random strategy, or a load balancing strategy based on link occupancy (in which case the least occupied links in the set are selected in preference).

[0283] In yet another embodiment, the non-AP MLD considers the AIFSN value applicable to each backoff counter to determine when it can begin decrementing each backoff counter.

[0284] Once the backoff counters to be activated are known, they are started in step 915: they are decremented at each time slot as long as the corresponding link is sensed as idle. This continues until a frame exchange is initiated over one of the links in the set (test 920).

[0285] Various events allow non-AP MLD to detect the start of a frame exchange.

[0286] In some embodiments, e.g., corresponding to Figures 10a and 10b described below, the event is the expiration of one of the decremented backoff counters, in which case the non-AP MLD indeed gains access to the link corresponding to the expiring backoff counter in order to transmit data belonging to the AC corresponding to the expiring backoff counter.

[0287] In another embodiment specific to EML mode, e.g. corresponding to Figures 11 and 12 below, the event is the receipt of an Initial frame (known as an Initial Control frame 245 in EMLSR mode) from the AP MLD over one of the links, in which case the non-AP MLD is in fact involved in the frame exchange over that link.

[0288] Upon detecting the start of a frame exchange over one of the EMLSR or EMLMR links (say link 1), the non-AP MLD suspends all other active backoff counters competing for access to the same link in step 925. This is the legacy behavior of 802.11 stations.

[0289] Due to the dependencies between the links in the set, the non-AP MLD must also suspend all active backoff counters competing for access to the other link in step 930 (because due to the switchover described below, the non-AP MLD is no longer operating on this other link).

[0290] Next, in step 935, the non-AP MLD initiates a state switching procedure to switch its mode from listening operation mode to frame exchange mode, and the co-affiliated STA corresponding to link 1 (where the frame exchange is initiated) is placed in an active frame exchange state.

[0291] For this purpose, the co-affiliated STA is switched from a listening operation state to an active frame exchange state to perform frame exchange, and in parallel (synchronously or simultaneously), other co-affiliated STAs of the link set of the EMLSR or EMLMR under consideration (on link 2) are switched from a listening operation state to an inactive frame exchange state.

[0292] The non-AP MLD is now ready to exchange frames with the AP MLD over link 1 (step 940).

[0293] When the frame exchange over link 1 is completed (test 945), the non-AP MLD again initiates the state switching procedure (step 950) to return its co-affiliated STAs to a listening operation state. Thus, the non-AP MLD switches back to a listening mode of operation. The switch back occurs the EMLSR Transition Delay or EMLMR Delay (as specified in EML Capabilities) after the frame exchange is completed.

[0294] Next, the backoff counters for links 1 and 2 (which were paused in steps 925 and 930) are prepared for a subsequent contention (eg, for their respective next decrements) in step 955.

[0295] The backoff counter for link 1 (ie, the link over which the frame exchange occurred) may be restarted in a conventional manner.

[0296] When one backoff counter expires (i.e. when a non-AP MLD gains access to the medium for the corresponding AC, meaning a SU transmission), the backoff counter is reinitialized using the updated contention window (CW=CWmin for successful uplink transmission, CW=min(2.CW, CWmax) for unsuccessful uplink transmission). Other backoff counters not related to transmissions are simply restarted from their last values.

[0297] On the other hand, if the backoff counters have not expired (eg, the frame exchange was initiated by AP MLD), the backoff counters of the ACs involved in the frame exchange are simply restarted.

[0298] These ACs may remain in their current EDCA mode for link 1 (legacy EDCA mode using the set of EDCA parameters of the corresponding BC of link 1, or MU EDCA mode using the set of MU EDCA parameters of the corresponding BC of link 1), in which case the contention window of the next reinitialization of the BC is updated to CWmin. An AC being in a given EDCA mode for a link means that the use of the backoff counter corresponding to this AC to access the link is driven by the parameter set applicable to the given EDCA mode.

[0299] The non-AP MLD may also switch those ACs on link 1 from legacy EDCA mode to MU EDCA mode (e.g., using a set of MU EDCA parameters for medium contention) if they are currently in legacy EDCA mode and MU EDCA mode is activated on link 1. It may then reinitialize the MU EDCA Timer if a frame exchange includes a successful trigger-based MU UL transmission. The contention window for the next reinitialization of that BC may be the CWmin defined in the applied parameter set. Other backoff counters not related to the frame exchange are simply restarted from their last value.

[0300] Alternatively, the non-AP MLD may switch these ACs of link 1 from their current EDCA mode (legacy EDCA mode or MU EDCA mode) to a so-called EML EDCA mode. In fact, a new EML EDCA mode (e.g., EMLSR EDCA mode and EMLMR EDCA mode, if a distinction is provided between the management of the two EML modes) may be defined to provide a different set of EML EDCA parameters (e.g., in a beacon frame) for setting the back-off counter of this AC for accessing link 1 and a separate EMLEDCATimer for driving the switch back to the traditional EDCA mode of this AC.

[0301] As will be described below, switching of the AC of link 1 to another EDCA mode may be independent of switching of the AC of link 2 to another EDCA mode.

[0302] However, preferably, the switching of the ACs of link 1 and link 2 is dependent on each other. For example, the ACs of link 1 and link 2 may be switched to the same other EDCA mode (MU EDCA mode, EML EDCA mode, EMLSR EDCA mode, EMLMR EDCA mode) although the set of applied parameters may or may not have different values. In another example, when an AC of one of the links of the EMLSR / EMLMR set is switched to another EDCA mode, the same AC of the other links is also switched to another EDCA mode, although it may be different. For example, the AC of link 1, where the frame exchange took place, is switched to MU EDCA mode, and the same AC of the other link of the set (link 2 in the example) is switched to any EML EDCA mode, or vice versa.

[0303] This is summarized in column 1330 of FIG.

[0304] The backoff counters of link 2 (the other link in the EMLSR or EMLMR set of links) are also prepared for the next medium contention. Recall that these suspended backoff counters do not expire; the backoff counters of ACs not involved in the frame exchange over link 1 are simply restarted from their last values.

[0305] The restart strategy used for the backoff counters of the ACs involved in the frame exchange over link 1 is based on the characteristics of the frame exchange.

[0306] In an embodiment, the frame exchange is based on the success or failure of the uplink transmission to the AP MLD (e.g., based on the status of the frame exchange). For example, the backoff counter is simply restarted from its last value if the uplink transmission in the frame exchange fails. The same simple restart applies in the case of downlink transmission. In fact, in all cases, the non-AP MLD does not utilize the transmission opportunity on link 1. On the other hand, the backoff counter may be reinitialized if the uplink transmission in the frame exchange is successful, even if it has not expired. This is to guarantee the transmission opportunity on link 1 with respect to fairness between the MLDs of the network.

[0307] In some embodiments, which may be combined with the previous ones, the strategy is based on the nature of the frame exchange, for example, whether it includes a single-user uplink transmission to the AP MLD, a multi-user trigger-based uplink transmission to the AP MLD, or only downlink transmissions from the AP MLD.

[0308] For example, the backoff counters of the ACs involved in a frame exchange could be: - in the case of a frame exchange, a downlink transmission or, if an uplink transmission fails, is resumed; - On the other hand, if the SU UL transmission in a frame exchange is successful, the backoff counter is reinitialized using the current contention window or restarted from its current value before starting to decrement it. - Alternatively, in case of a successful multi-user trigger based uplink transmission in a frame exchange, before starting to decrement the back-off counter, it may be reinitialized using the current contention window or a new contention window associated with the new EDCA mode, or may be restarted from the current value. Similar to link 1 above, the AC may remain in the current EDCA mode (legacy EDCA mode or MU EDCA mode) for link 2, or may be switched from legacy EDCA mode to MU EDCA mode or EML EDCA mode, after which the MU EDCA Timer or the applicable EM EDCA Timer may be reinitialized.

[0309] The switching of the AC of link 2 to a new EDCA mode may be independent of the switching of the AC of link 1 to another EDCA mode, as described above, but preferably the switching of the AC of link 1 and the AC of link 2 are interdependent, as described above.

[0310] The above-mentioned "new EDCA mode" is one of the MU EDCA mode, the EML EDCA mode, the EMLSR EDCA mode and the EMLMR EDCA mode.

[0311] This is summarized in column 1340 of FIG.

[0312] If a frame exchange involves cascaded successive transmissions (which is the case, for example, when a frame exchange is initiated by AP MLD and cascades multiple TXOPs), successful transmissions are prioritized over failed uplink transmissions (for a given AC) in the selection of the restart strategy. In other words, as soon as one uplink transmission is successful for a given AC, the above strategy used in case of successful transmissions is applied to the backoff counter of the AC, without considering the strategy related to the failed transmissions.

[0313] Next at step 955, the backoff counter is prepared for the next medium contention if there is still buffered data to be transmitted (looping back to step 905).

[0314] 10a and 10b show schematic diagrams of an exemplary timeline for a first EMLSR or EMLMR operation case including a back-off counter restart procedure according to an embodiment of the present invention, where the triggering event for the frame exchange is the expiration of the back-off counter driving the EDCA of link 1 (link 151). This means that the frame exchange that takes place is a single-user (SU) uplink transmission.

[0315] In FIG. 10a, both co-affiliated STAs A1 121 and A2 122 decrement their back-off counters (step 915 above), but for purposes of illustration, few back-off counters are shown. Only one back-off counter decrement 1013 is shown for co-affiliated STA A1 121 on link 151, and one back-off counter decrement 1014 is shown for co-affiliated STA A2 122 on link 152. As an example, back-off counter decrements 1013 and 1014 correspond to the back-off counters of the same AC (here AC3) where UL transmission occurs during the frame exchange. These counters are BC[151,3] and BC[152,3], respectively.

[0316] For both links 151 and 152, the backoff counters of other ACs BC[151,0], BC[151,1], BC[151,2] and BC[152,0], BC[152,1], BC[152,2] are also decremented simultaneously with BC[151,3] and BC[152,3].

[0317] STA A1 121 is the first one whose backoff counter expires (step 920), where BC[151,3] reaches 0. Thus, STA A1 121 is the STA ready for transmission. In response to the expiration of counter BC[151,3], the ready STA A1 121 is switched from a listening operation state 1010 to a valid frame exchange state 1020 (step 935), and in parallel (synchronously or simultaneously), the co-affiliated STA A2 122 is switched from a listening operation state 1011 to an invalid frame exchange state 1021. Also, in response to the expiration of counter BC[151,3], the backoff counter decrement 1014 of backoff counter BC[152,3] is paused (step 930). The other backoff counters of links 151, 152 are also paused (steps 925, 930).

[0318] The simultaneous switching continues as described above up to the EMLSR active switch delay or the EMLMR active switch delay.

[0319] Once the switch occurs, the ready STA A1 121 transmits its buffered uplink data (step 940) in step 1025. In the example of Figure 10a, the ready co-affiliated STA A1 121 transmits an A-MPDU frame 1025 to the AP MLD 110 corresponding to its buffered uplink data of AC3 via an EMLSR or EMLMR link (e.g., link 151) to the AP MLD 110 corresponding to the co-affiliated AP1 111.

[0320] Optionally, before transmitting the A-MPDU frame 1025, the ready co-affiliated STA A1 121 may transmit an RTS frame or a CTS-to-self frame for better protection on the granted channel.

[0321] In addition to completing the frame exchange performed by the ready co-affiliated STA A1 121, after the EMLSR Transition Delay or EMLMR Delay specified in the EML Capabilities, the non-AP MLD 120 switches back to the listening operation mode (step 950), which means that the ready co-affiliated STA A1 121, as well as the other co-affiliated STA A2 122, switches back to the listening operation state 1010 (listening operation state 1011).

[0322] At this stage, both co-affiliated STAs A1 121 and A2 122 may process restarts of their back-off counters. On Figure 10a, back-off counter restart 1032 is represented for co-affiliated STA A1 121 of link 151, and back-off counter restart 1033 is represented for co-affiliated STA A2 122 of link 152. Back-off counter restart 1032 and 1033 correspond to back-off counters BC[151,3] and BC[152,3], respectively.

[0323] Referring to the table shown in Figure 13, the backoff counter restart 1032 and 1033 depends on the status of the previous UL transmission of the A-MPDU frame 1025 (e.g., whether the SU UL transmission was successful or unsuccessful). The case of Figure 10a is shown in the first row 1301.

[0324] The backoff counter restart 1032 strategy for BC[151,3] is shown in column 1330 .

[0325] If the previous SU UL transmission 1025 was successful, the backoff counter BC[151,3] is processed in the legacy manner: it is simply reinitialized using the EDCA parameters from the range [0,CW=CWmin] and processed using the conventional EDCA backoff procedure.

[0326] If the previous SU UL transmission 1025 was unsuccessful, the backoff counter BC[151,3] is processed in the legacy manner: it is simply reinitialized using the EDCA parameters from the range [0,CW=min(2xCW,CWmax)] and processed using the conventional EDCA backoff procedure.

[0327] The backoff counter restart 1033 strategy for BC[152,3] is shown in column 1340.

[0328] If the previous SU UL transmission 1025 was successful, the backoff counter BC[152,3] may be reinitialized from the range [0,CW=CW] using EDCA parameters and processed using conventional EDCA backoff procedures. In this case, BC[152,3] is reinitialized to account for the dependency with BC[151,3] and the fact that the non-AP MLD benefited from the transmission opportunity on link 151. This restores some fairness to compensate for the additional transmission opportunity for the MLD. However, since no UL transmissions from STA A2 122 have occurred on link 152, the contention window may maintain the same (current) value to reflect the current state of this link.

[0329] Alternatively, it may be restarted from the current value and processed through conventional EDCA backoff procedures, and then reinitialized from the range [0, CW=CW] and processed through conventional EDCA backoff procedures.

[0330] If the previous SU UL transmission 1025 was unsuccessful, the backoff counter BC[152,3] may be restarted from its current value and processed using conventional EDCA backoff procedures. In this case, because the SU UL transmission 1025 of AC3 on link 151 was unsuccessful, the priority of AC3 on link 152 is maintained intact by simply restarting the corresponding backoff counter BC[152,3] from its current value.

[0331] FIG. 10 b is similar to FIG. 10 a , except that an optional synchronization delay 1040 is added before the backoff counter restart 1033 for link 152 .

[0332] This optional synchronization delay reflects the fact that during the frame exchange, co-affiliated STA A2 122 may be in the invalid frame exchange state 1021 and lose synchronization with the medium. In fact, STA A2 122 could not sense link 152 during STA A1 121's UL transmission 1025 on link 151. This optional synchronization delay therefore allows co-affiliated STA A2 122, which has switched from the invalid frame exchange state 1021 back to the listening operation state 1011, to resynchronize on the medium before restarting any new EDCA procedures to contend for access to link 152. In other words, in these embodiments, the restart strategy includes a synchronization delay from the end of the frame exchange before restarting the backoff counter.

[0333] Synchronization is lost if the invalid frame exchange state 1021 lasts for more than a threshold, called aMediumSyncThreshold in the IEEE P802.11be / D1.5 draft. Thus, the application of the synchronization delay in the restart strategy is contingent on a period of frame exchange greater than such a predefined threshold.

[0334] The length of the synchronization delay is defined by the value contained in the Medium Synchronization Information field (if present) of the Basic Multi-Link element of the most recent frame received from the corresponding Affiliated AP (AP2 112 in the figure).

[0335] In practice, if loss of synchronization occurs, the restart of the backoff counter of Link 152 is frozen: a timer called MediumSyncDelay in the IEEE P802.11be / D1.5 draft and initialized with the value of the Medium Synchronization Information field is started by STA A2 122 immediately after switching back to the listening operating state 1011 (step 950). The timer counts down and, upon expiration, the backoff counter of Link 152 is started (decremented).

[0336] During the timer countdown, co-affiliated STA A2 122 may recover from the out-of-sync state, for example, by receiving any 802.11 control frame. In effect, the radio stack of co-affiliated STA A2 122 may then readjust with the timing of link 152, since it is able to decode the Duration field of such a frame. In effect, the MediumSyncDelay timer may be reset to zero upon successful reception of any type of 802.11 control frame with MCS set to up to 2 (i.e., up to 24 Mbps). Such reception reduces the synchronization delay 1040 and updates the NAV of STA A2 122.

[0337] In the scenario of Figure 10b, co-affiliated STA A2 122 is considered to be resynchronized to the medium either upon successful reception of an 802.11 control frame or upon expiration of the MediumSyncDelay timer. The next decrement of the backoff counter may then be initiated.

[0338] 11 illustrates a schematic diagram of an exemplary timeline for a second EMLSR or EMLMR operation case including a back-off counter restart procedure according to an embodiment of the present invention, where the triggering event for frame exchange is the reception of an Initial frame (in EMLMR mode) or an Initial Control frame (in EMLSR mode) from the AP MLD over link 151. In this scenario, the Initial frame is received while the back-off counters driving the EDCA of the same AC for links 151 and 152, respectively, are being decremented.

[0339] In Figure 11, both co-affiliated STAs A1 121 and A2 122 decrement their back-off counters (step 915 above). As in Figure 10a, few back-off counters are shown for illustrative purposes. In this example, only BC[151,3] and BC[152,3] are shown since it is assumed that traffic from AC3 is exchanged during the frame exchange. The same teaching below applies for any AC, known as the "transmitted AC," for which data is exchanged during the frame exchange (whose back-off counters are decremented simultaneously).

[0340] While in the listening operational state 1010 and while the transmitted backoff counter of its transmitted AC is decremented 1013, co-affiliated STA A1 121 receives an Initial Control frame (IC) or an Initial frame 1134 from co-affiliated AP AP1 111 via link 151. Co-affiliated STA A2 122 also decrements its backoff counter 1014.

[0341] In response to such reception, the non-AP MLD 120 pauses the decrement 1013 and 1014 of the transmitted backoff counters as well as the other backoff counters of the two links (steps 925, 930), initiates the state change of the co-affiliated STAs (step 935), and then transmits an Initial Control frame response (IC resp.) or Initial frame response 1135 to the co-affiliated AP AP1 111.

[0342] After an EMLSR active switch delay or an EMLMR active switch delay, co-affiliated STA A1 121 switches from a listening operation state 1010 to a valid frame exchange state 1020, and co-affiliated STA A2 122 switches from a listening operation state 1011 to an invalid frame exchange state 1021 simultaneously.

[0343] Once the switch occurs, co-affiliated STA A1 121 exchanges transmitted AC frames with co-affiliated AP AP1 111 via link 151 .

[0344] Typically, the affiliated AP1 111 may transmit a basic trigger frame 1144 to the affiliated STA A1 121 to allocate uplink (UL) resource units for the non-AP MLD 120 as specified in IEEE Standard 802.11ax-2021. The basic trigger frame 1144 may identify the transmission ACs on which data is permitted to be transmitted by the non-AP MLD triggered during the frame exchange. Alternatively, the triggered non-AP MLD may locally determine the ACs to be transmitted. In either case, the non-AP MLD 120 transmits a High-Efficiency Trigger-Based (HE TB) PPDU 1124 in its allocated resource units.

[0345] Alternatively, affiliated AP1 111 may perform direct DL transmission (without trigger frames) in which AP MLD 110 transmits a High-Efficiency Multi-User (HE MU) PPDU 1124' on link 151 via AP1 111. The HE MU PPDU 1124' may allocate resource units of link 151 to various affiliated STAs and provide a PPDU on each allocated resource unit.

[0346] In addition to completing this frame exchange, after the EMLSR Transition Delay or EMLMR Delay specified in the EML Capabilities, the non-AP MLD 120 switches back to listening operation mode (step 950), which means that the co-affiliated STA A1 121 switches back to listening operation state 1010, as does the other co-affiliated STA A2 122 (listening operation state 1011).

[0347] At this stage, both co-affiliated STAs A1 121 and A2 122 may process the restart of their back-off counters. In FIG. 11, a back-off counter restart 1132 for the back-off counter corresponding to the transmitted AC is shown for co-affiliated STA A1 121 on link 151, and a back-off counter restart 1133 for the same AC is shown for co-affiliated STA A2 122 on link 152. Back-off counter restarts 1132 and 1133 correspond to back-off counters BC[151,3] and BC[152,3], respectively, in this example. Other "non-transmitted" back-off counters (i.e., not involved in the frame exchange) are restarted from their current values ​​in the conventional manner.

[0348] Referring to the table shown in Figure 13, the backoff counter restart 1132 and 1133 for transmitted AC3 depends on the type of previous transmission (UL or DL) and, in case of UL transmission, on the status of the upcoming UL transmission of the HE TB PPDU frame 1124. In the case of Figure 11, this is shown in the second and third rows 1302 (for UL transmission) and 1303 (for DL ​​transmission only).

[0349] The backoff counter restart 1132 strategy for BC[151,3] is shown in column 1330.

[0350] If an UL transmission of AC3 data occurs during a frame exchange, and the previous MU UL transmission 1124 was successful, the backoff counter BC[151,3] is handled in a legacy manner: it is simply restarted from its current value, handled using the traditional EDCA backoff procedures, and may then be reinitialized (upon the first subsequent expiration) from the range [0,CW=CWmin] using the MU EDCA parameters. This is to penalize non-AP MLDs 120 that benefited from the TB uplink transmission opportunity.

[0351] If the previous MU UL transmission 1124 was unsuccessful, the backoff counter BC[151,3] is processed in the legacy manner: it is simply restarted from its current value and processed using conventional EDCA backoff procedures.

[0352] If only MU DL transmissions of AC3 data occur during a frame exchange, then whatever the status of the prior MU DL transmission 1124', the backoff counter BC[151,3] is processed in the conventional manner: it is simply restarted from its current value and processed using conventional EDCA backoff procedures.

[0353] The strategy for restarting the backoff counter 1133 for BC[152,3] is shown in column 1340.

[0354] When an UL transmission of AC3 data occurs during a frame exchange, if the previous MU UL transmission 1124 was successful, several options are available to restart the backoff counter BC[152,3], which may be used without discrimination.

[0355] The first option consists of reinitializing BC[152,3] from the range [0,CW=CW] using the current EDCA parameters and proceeding using the traditional EDCA backoff procedure. In this case, BC[152,3] is reinitialized (not simply restarted) to take into account the dependency from BC[151,3] and to restore some fairness. However, since no UL transmissions from STA A2 122 have occurred on link 152, the contention window CW maintains the same value to reflect the current state of this link.

[0356] The second option consists in reinitializing BC[152,3] from the range [0,CW=CWmin] using the MU EDCA or EML EDCA parameters (defined above) if not already in the corresponding MU EDCA or EML EDCA mode (and therefore switching to this mode occurs) and proceeding using the conventional EDCA backoff procedure. The MUEDCATimer or EMLEDCATimer may be set accordingly. In this case, BC[152,3] is reinitialized taking into account the dependency on BC[151,3] and using the MU or EML EDCA parameters to take into account the trigger-based UL transmission 1124 of AC3.

[0357] The third option consists of restarting BC[152,3] from its current value, proceeding using conventional EDCA backoff procedures, and (upon the first subsequent expiration) reinitializing if not already in MU or EML EDCA mode, using either the first option (from the range [0,CW]) or the second option (from the range [0,CWmin] using MU or EML EDCA parameters).

[0358] If the previous MU UL transmission 1124 was unsuccessful, the backoff counter BC[152,3] is restarted from its current value and processed using conventional EDCA backoff procedures. In this case, since the MU UL transmission 1124 of AC3 on link 151 failed, the priority of AC3 on link 152 is maintained intact by simply restarting the corresponding backoff counter BC[152,3] from its current value.

[0359] If the only MU DL transmission of AC3 data occurs during a frame exchange, regardless of the status of the previous MU DL transmission 1124', the backoff counter BC[152,3] is restarted from its current value and processed using conventional EDCA backoff procedures. In this case, because the previous MU DL transmission 1124' was a downlink transmission, the backoff counter BC[152,3] is mapped to AC3, which is associated with uplink traffic, and is restarted from its current value.

[0360] The optional synchronization delay 1040 of FIG. 10b may also be implemented in the scenario of FIG. 11 to compensate for possible loss of synchronization of co-affiliated STA A2 122 in invalid frame exchange state 1021.

[0361] 12 illustrates a schematic diagram of an exemplary timeline for a third EMLSR or EMLMR operation case including a backoff restart procedure according to an embodiment of the present invention, where the triggering event for frame exchange is the reception of an Initial frame (for EMLMR mode) or an Initial Control frame (for EMLSR mode) from the AP MLD on link 151. In this scenario, a frame exchange related to a transmitting AC takes place over link 151 after an Initial frame is received, but the backoff counter of that transmitting AC is not decremented on that link, whereas the backoff counter driving the EDCA of the same transmitting AC on the other link 152 is decremented.

[0362] As discussed above (step 910), the determination of which backoff counters should be decremented may be based on a variety of criteria.

[0363] The scenario of FIG. 12 applies specifically when the TID-to-Link mapping prohibits an AC (AC3 in the example) on link 151, but a trigger frame sent by the AP MLD 110 in a frame exchange allows this AC in TB MU UL transmissions.

[0364] The scenario in Fig. 12 also applies when the back-off counter decrement cannot start before the Initial frame 1134 is received. This can happen if the AIFSN value governing the operation of that back-off counter has a high value. By the way, this also applies in the case of AIFSN=0, which defines a specific MU EDCA mode in which EDCA of the AC (AC3 in the example) on the link 151 is disabled. Indeed, according to 802.11ax-2021, the MU AC Parameter Record field of the MU EDCA Parameter Set element may contain a value of 0 in the ACI / AIFSN field, thus indicating that EDCA is disabled for the period specified in the MU EDCA Timer of the corresponding AC.

[0365] Therefore, the backoff counter of one AC in link 2 may be decremented while the corresponding backoff counter of the same AC in link 1 is not decremented.

[0366] 12, only one backoff counter (corresponding to the transmitted AC over which data is to be transmitted during a frame exchange) is shown to be decremented by co-affiliated STA A2 122 operating on link 152 (step 915 above). However, multiple transmitted backoff counters may be simultaneously decremented by co-affiliated STA A2 122 while corresponding backoff counters of the same transmitted AC by co-affiliated STA A1 121 operating on link 151 are not decremented. In this example, BC[152,3] is decremented. Similar to FIG. 10a, other backoff counters BC[152,0], BC[152,1], BC[152,2] of other ACs are also decremented simultaneously with BC[152,3], and possibly other backoff counters BC[151,0], BC[151,1], BC[151,2] of co-affiliated STA A1 121 (not corresponding to AC3) are also decremented.

[0367] While in the listening operating state 1010, the co-affiliated STA A1 121 receives an Initial Control frame (IC) or an Initial frame 1134 from the co-affiliated AP AP1 111 via link 151. In parallel, the co-affiliated STA A2 122 decrements its backoff counter 1014.

[0368] In response to such reception, the non-AP MLD 120 pauses the backoff counter decrement 1014 (steps 925, 930), initiates a state change of the co-affiliated STA (step 935), and then sends an Initial Control frame response (IC resp.) or Initial frame response 1135 to the co-affiliated AP AP1 111.

[0369] After an EMLSR active switch delay or an EMLMR active switch delay, co-affiliated STA A1 121 switches from a listening operation state 1010 to a valid frame exchange state 1020, and co-affiliated STA A2 122 switches from a listening operation state 1011 to an invalid frame exchange state 1021 simultaneously.

[0370] When the switch occurs, the co-affiliated STA A1 121 exchanges frames with the co-affiliated AP AP1 111 via Link 151 .

[0371] Typically, the affiliated AP1 111 may transmit a basic trigger frame 1144 to the affiliated STA A1 121 to allocate uplink (UL) resource units for the non-AP MLD 120 as specified in IEEE Standard 802.11ax-2021. The basic trigger frame 1144 may specify the AC to be transmitted (here AC3). Alternatively, the triggered non-AP MLD may locally determine the AC to be transmitted. In either case, the non-AP MLD 120 transmits a High-Efficiency Trigger-Based (HE TB) PPDU 1124 in the allocated resource units.

[0372] Alternatively, affiliated AP1 111 may perform direct DL transmission (without trigger frames) in which AP MLD 110 transmits a High-Efficiency Multi-User (HE MU) PPDU 1124' on link 151 via AP1 111. The HE MU PPDU 1124' may allocate resource units of link 151 to various affiliated STAs and provide a PPDU on each allocated resource unit.

[0373] In addition to completing this frame exchange, after the EMLSR Transition Delay or EMLMR Delay specified in the EML Capabilities, the non-AP MLD 120 switches back to listening operation mode (step 950), which means that the co-affiliated STA A1 121 switches back to listening operation state 1010, as does the other co-affiliated STA A2 122 (listening operation state 1011).

[0374] At this stage, co-affiliated STA A2 122 may process its transmitted backoff counter restart. On Figure 12, backoff counter restart 1233 corresponding to backoff counter BC[152,3] is shown for co-affiliated STA A2 122 of link 152.

[0375] Similar to Figure 11, the backoff counter restart 1233 for AC3 depends on the type of previous transmission (UL or DL) and, in the case of a UL transmission, on the status of the upcoming UL transmission of the HE TB PPDU frame 1124. Again, the restart strategies available in this case are shown in Figure 13 in a box whose last column 1340 spans the second and third rows 1302 (for UL transmissions) and 1303 (for DL ​​transmissions only). The restart strategies are not repeated here for reasons of brevity.

[0376] FIG. 13 illustrates a table 1300 that collects proposed EDCA backoff counter restart procedures or policies according to an embodiment of the present invention.

[0377] Column 1310 collects exemplary trigger events that may suspend the decrementing of the back-off counter. Column 1320 indicates possible uplink transmission statuses for each event. Column 1330 collects, for each event and each transmission status, one or more back-off counter restart strategies to apply to the AC being transmitted (e.g., BC[151,3] in the above example). Column 1340 collects, for each event and each transmission status, one or more back-off counter restart strategies to apply to the AC being transmitted (e.g., BC[152,3] in the above example).

[0378] Row 1301 collects the backoff counter restart strategy to apply to the transmitted AC in case of SU UL transmission (e.g., when the trigger event for pausing the backoff counter decrement is the expiration of one backoff counter contention access to link 151).

[0379] Row 1302 collects the backoff counter restart strategy to apply to the transmitted AC in case of TB MU UL transmission (e.g., when the trigger event for pausing the backoff counter decrement is the receipt of an Initial frame or Initial Control frame on link 151 followed by trigger-based uplink traffic).

[0380] Row 1303 collects the backoff counter restart strategy to apply to the transmitted AC in the case of MU DL transmission (e.g., when the trigger event for pausing the backoff counter decrement is the receipt of an Initial frame or Initial Control frame on link 151 followed by downlink traffic).

[0381] Figure 14 shows a schematic diagram of an EMLSR-enabled architecture for MLD. In this diagram, two affiliated non-AP STAs share the hardware resources of a non-AP MLD when EMLSR mode is enabled. The EMLSR-enabled architecture for MLD shown in this diagram is for illustrative purposes only, and other alternative architectures are also possible.

[0382] The architecture includes two wireless stacks: a light wireless stack and a full wireless stack.

[0383] The complete wireless stack includes a complete 802.11be MAC module 1400a (exchanging data with upper layers), a complete 802.11be PHY module 1405a connected to the complete MAC module, a complete radio frequency chain 1415a connected to the complete PHY module, and an antenna 1420a connected to the complete RF chain via the EMLSR switch 1410.

[0384] The lite wireless stack includes a lite 802.11be MAC module 1400b (exchanges data with upper layers), a lite 802.11be PHY module 1405b connected to the lite MAC module, a lite radio frequency chain 1415b connected to the lite PHY module, and an antenna 1420b connected to the lite RF chain via the EMLSR switch 1410.

[0385] The EMLSR switch 1410 is shared by the two wireless stacks and is configured to switch the EMLSR co-affiliated STAs to / from a listening operation state to / from a frame exchange enabled or disabled state when the EMLSR mode is activated.

[0386] Radio chain 1400a / 1405a / 1415a is a complete radio resource that allows reception and transmission of any IEEE 802.11 frame. In particular, it includes encoding and decoding modules for encoding and decoding any IEEE 802.11 frame. Radio chain 1400b / 1405b / 1415b, on the other hand, is a reduced-function (or "lite") radio resource that allows reception and transmission of only specific IEEE 802.11 frames. In particular, it includes only encoding and decoding modules for encoding and decoding specific frames using rates of 6 Mbps, 12 Mbps, or 24 Mbps.

[0387] The bottom left diagram shows the functionality of MLD when non-AP MLD is in EMLMR listening operation mode: A common EMLMR switch 1410 connects each radio chain 1400a / 1405a / 1415a and 1400b / 1405b / 1415b to antennas 1420a and 1420b, respectively. Thus, each radio stack can be used to listen to each link simultaneously. As shown in the diagram, two links are available. The complete radio chain 1400a / 1405a / 1415a and antenna 1420a are configured to operate on link 1, and the light radio chain 1400b / 1405b / 1415b and antenna 1420b are configured to operate on link 2.

[0388] The diagram at the bottom center shows the function of MLD when non-AP MLD switches in the first EMLSR frame exchange mode. The co-affiliated STAs of the EMLSR corresponding to link 1 are in the active frame exchange state, and the co-affiliated STAs of the other EMLSR corresponding to link 2 are in the inactive frame exchange state. In that case, the EMLSR shared switch 1410 connects the complete radio chain 1400a / 1405a / 1415a to both antennas 1420a / 1420b, and the complete radio chain 1400a / 1405a / 1415a and antennas 1420a / 1420b are configured to operate on Link1. Here, since the complete radio chain remains configured to operate on Link1, the switching time from the EMLSR listening operation state to the active frame exchange state can be considered to be short. In fact, in this case, the switching is only an antenna switching. Meanwhile, the common EMLSR switch 1410 disconnects the light radio chain 1400b / 1405b / 1415b from the antenna 1420b. In this configuration, the light radio chain 1400b / 1405b / 1415b cannot receive or transmit frames on Link 2. And only Link 1 is available.

[0389] The bottom right diagram shows the function of MLD when non-AP MLD switches in the second EMLSR frame exchange mode. The co-affiliated STAs of the EMLSR corresponding to link 2 are in the active frame exchange state, and the co-affiliated STAs of the other EMLSR corresponding to link 1 are in the inactive frame exchange state. In that case, the shared switch 1410 of the EMLSR connects the complete radio chain 1400a / 1405a / 1415a to both antennas 1420a / 1420b, and the complete radio chain 1400a / 1405a / 1415a and antennas 1420a / 1420b are configured to work on Link2. Here, the switching time from the listening operation state of the EMLSR to the active frame exchange state is considered to be long because the complete radio chain switches to work on Link2. In fact, in this case, the switching includes both antenna switching and complete radio chain configuration switching. Meanwhile, the common EMLSR switch 1410 disconnects the light wireless chain 1400b / 1405b / 1415b from the antenna 1420b. In this configuration, the light wireless chain 1400b / 1405b / 1415b cannot receive or transmit frames on Link 1. And only Link 2 is available.

[0390] The functionality of the common EMLSR switch 1410 clearly indicates that state changes of co-affiliated STAs of two EMLSRs in the same MLD are necessarily simultaneous, since antenna resources are either connected to one STA or the other, but are never available to both STAs at the same time.

[0391] Figure 15 shows a schematic diagram of the EMLMR-enabled architecture of MLD, taking the case where two affiliated non-AP STAs share antenna resources as an example when EMLMR mode is enabled.

[0392] This architecture includes two wireless stacks, one for each non-AP STA.

[0393] The radio stack includes a complete 802.11be MAC module 1500a or 1500b (exchanging data with upper layers), a complete 802.11be PHY module 1505a or 1505b connected to the MAC module, a radio frequency chain 1515a or 1515b connected to the PHY module, an EMLMR switch 1510 shared by the two radio stacks and configured to perform antenna resource aggregation when the EMLMR mode is activated, and an antenna array 1520a or 1520b.

[0394] The diagram on the bottom left shows the functionality of non-AP MLD when listening for Initial frames: A common EMLMR switch 1510 connects each antenna array to an RF chain. Each radio stack is therefore complete and may serve each link using, for example, a 2x2 MIMO antenna configuration. As shown in the diagram, two links are available.

[0395] The bottom center diagram shows the function of MLD when non-AP MLD switches in the first EMLMR frame exchange mode. The co-affiliated STAs of the EMLMR corresponding to link 2 are in an active frame exchange state, and the co-affiliated STAs of the other EMLMRs corresponding to link 1 are in an inactive frame exchange state. The common EMLMR switch 1510 aggregates antenna resources to link 2 by connecting the antenna array 1520a of the second wireless stack to the RF chain 1515b of the first wireless stack. Thus, the first wireless stack can operate in a 4x4 MIMO antenna configuration and improve the throughput for link 2. Meanwhile, link 1 cannot be used because its antenna array 1520a is no longer available to the second wireless stack.

[0396] The bottom right diagram shows the function of MLD when non-AP MLD switches in the second EMLMR frame exchange mode. The EMLMR co-affiliated STAs corresponding to link 1 are in an active frame exchange state, and the other EMLMR co-affiliated STAs corresponding to link 2 are in an inactive frame exchange state. The common EMLMR switch 1510 aggregates antenna resources to link 1 by connecting the antenna array 1520b of the first wireless stack to the RF chain 1515a of the second wireless stack. Thus, the second wireless stack can operate in a 4x4 MIMO antenna configuration and improve the throughput for link 1. Meanwhile, link 2 cannot be used because its antenna array 1520b is no longer available to the first wireless stack.

[0397] The functionality of the common EMLMR switch 1510 clearly indicates that state changes of two EMLMR co-affiliated STAs in the same MLD are necessarily simultaneous since antenna resources are either connected to one STA or the other, but not available to both STAs at the same time.

[0398] 16 shows a schematic diagram of a communication device 1600, typically one of the MLDs described above, of a wireless network, configured to implement at least one embodiment of the present invention. The communication device 1600 may preferably be a device such as a microcomputer, a workstation or a lightweight handheld device. The communication device 1600 includes a communication bus 1613, preferably connected to: A central processing unit 1601, such as a processor, denoted as CPU; A memory 1603 for storing executable code of a method or method steps according to an embodiment of the invention and registers adapted to record variables and parameters necessary for the implementation of the method; and At least two communication interfaces 1602 and 1602' connected via transmit and receive antennas 1604 and 1604', respectively, to a wireless communication network (eg, a communication network according to one of the IEEE 802.11 family of standards).

[0399] Preferably, a communications bus 1613 provides communication and interoperability between various elements included in or connected to the communications device 1600. The representation of a bus is not limiting, in particular a central processing unit is operable to communicate instructions to any element of the communications device 1600 directly or by way of another element of the communications device 1600.

[0400] The executable code may be stored in a memory, either read-only, on a hard disk or on a removable digital medium, such as a disk. According to an optional variant, the executable code of the program may be received by the communication network, via the interface 1602 or 1602', to be stored in the memory of the communication device 1600 before being executed.

[0401] In one embodiment, the device is a programmable apparatus that uses software to implement embodiments of the invention, however, alternatively, embodiments of the invention may be implemented in whole or in part in hardware (e.g., in the form of an Application Specific Integrated Circuit or ASIC).

[0402] Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications that are within the scope of the present invention will be apparent to those skilled in the art.

[0403] Many further modifications and variations will be suggested to those skilled in the art upon reference to the exemplary embodiments described above, however, these embodiments are given by way of example only and are not intended to limit the scope of the invention, which is determined solely by the appended claims. In particular, different features from different embodiments may be interchanged where appropriate.

[0404] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do 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 used to advantage.

Claims

1. A method of communication in a wireless network, comprising: in a non-access point (non-AP) Multilink Device (MLD) operating in an active Enhanced Multilink (EML) mode, Initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure by a first station (STA) that is affiliated to the non-AP MLD and corresponds to a first link of a set of valid links to which the EML mode is applied, to access the first link by decrementing a backoff counter; switching the first affiliated STA from a listening operation state to an active frame exchange state to initiate a frame exchange with an AP MLD over the first link. method.

2. switching the first affiliated STA to the valid frame exchange state is performed before initiating the EDCA backoff procedure by the first affiliated STA in the valid frame exchange state to decrement the backoff counter. The method of claim 1.

3. pausing the decrementation upon detecting that the first link becomes busy during the decrementation of the backoff counter; a) maintaining the first affiliated STA in the active frame exchange state and resuming the decrement when the first link becomes idle again; b) switching the first affiliated STA back to a listening state regardless of the period identified in the frame in which the detection occurred; and c) switching the first affiliated STA back to the listening state for a predetermined period based on the period identified in the frame in which the detection occurred, and then switching back to a valid frame exchange state to resume the decrement when the first link becomes idle again; d) determining a period identified in the frame in which said detection occurred and deciding to apply one of policies a), b) or c) depending on said period determined; applying a policy from among The method of claim 2.

4. When the backoff counter reaches a value of 0, the first affiliated STA is switched to the active frame exchange state. The method of claim 1.

5. and suspending the EDCA backoff procedure upon receiving an Initial frame from the AP MLD via a second link of the set. The method of claim 1.

6. upon receiving an Initial frame from the AP MLD via a second link of the set, determining whether to suspend the EDCA backoff procedure; determining whether the first affiliated STA is assigned complete radio resources; determining whether the Initial frame is an MU-RTS Trigger frame; determining whether uplink data is already preloaded in a transmission related to only the first link; determining whether an amount of buffered data is greater than a threshold; [0036] The method of claim 1.

7. switching the first affiliated STA includes initiating a state switching procedure of the first affiliated STA while the first affiliated STA is decrementing the back-off counter, and terminating the state switching procedure when the back-off counter reaches a value of 0. The method of claim 1.

8. Switching the first affiliated STA includes initiating a state switching procedure for the first affiliated STA in response to the back-off counter reaching a value of zero. The method of claim 1.

9. and transmitting a control frame over the first link in response to the backoff counter reaching a value of zero. The method according to claim 8.

10. The control frame is a CTS-to-self frame or an RTS frame.

10. The method of claim 9.

11. The control frame includes padding to end the control frame after a time preceding the end of the state switch procedure by a short interframe space (SIFS).

10. The method of claim 9.

12. The first affiliated STA is assigned full radio resources in the listening operating state. The method according to claim 4.

13. and setting a network allocation vector (NAV) of the first affiliated STA in the listening state upon sensing a control frame having an MCS value up to 2 on the first link. The method of claim 1.

14. and initiating an EDCA backoff procedure simultaneously on two or more links of the set, the first link being the link corresponding to the link on which a backoff counter of the EDCA backoff procedure first reaches a value of zero. The method of claim 1.

15. and switching a separate second STA, which is affiliated to the non-AP MLD and corresponds to a second link of the set, from a listening operation state to an invalid frame exchange state concurrently with the switching of the first affiliated STA. The method of claim 1.

16. and switching the first affiliated STA and the second affiliated STA to the listening operation state upon completion of the frame exchange over the first link. The method of claim 15.

17. Initiating the frame exchange excludes sending an Initial frame to the AP MLD via the first link. The method according to claim 1 or 3.

18. and exchanging frames with the AP MLD via the first link after the backoff counter reaches a value of zero. The method of claim 1.

19. and suspending the back-off counter driving the EDCA of the first link of the set in response to initiating a frame exchange with the AP MLD via a second link of the set of valid links to which the EML mode is applied. The method of claim 1.

20. and in response to a completion of the frame exchange over the second link, restarting the back-off counter applying a restart strategy selected based on characteristics of the frame exchange.

20. The method of claim 19.

21. The characteristics of the frame exchange include whether the frame exchange includes a single-user uplink transmission to the AP MLD, a multi-user trigger-based uplink transmission to the AP MLD, or only a downlink transmission from the AP MLD.

21. The method of claim 20.

22. The characteristics of the frame exchange include whether the frame exchange is a success or failure of an uplink transmission to the AP MLD.

21. The method of claim 20.

23. The restart strategy applied is reinitializing the backoff counter using a current contention window before beginning to decrement the backoff counter; reinitializing the backoff counter using a new contention window associated with a new EDCA mode before starting to decrement the backoff counter; restarting said backoff counter from its current value; Includes one from 21. The method of claim 20.

24. The restart strategy applied is restarting the back-off counter from its current value in the case of a downlink transmission or a failed uplink transmission in the frame exchange; reinitializing a back-off counter using a current contention window before restarting the back-off counter from its current value if a single-user uplink transmission is successful in the frame exchange before starting to decrement the back-off counter or before restarting the back-off counter from its current value; if a multi-user trigger-based uplink transmission in the frame exchange is successful, reinitializing the back-off counter using a current contention window or a new contention window associated with a new EDCA mode before starting to decrement the back-off counter or restarting the back-off counter from its current value; Includes one from 21. The method of claim 20.

25. Responsive to initiating the frame exchange, a plurality of back-off counters driving EDCA of the first link for each of a plurality of access categories are paused; The restart strategy is applied to the back-off counters of the plurality of suspended back-off counters corresponding to the access categories exchanged during the frame exchange.

21. The method of claim 20.

26. The restart strategy includes a synchronous delay from the end of the frame exchange before restarting the backoff counter.

21. The method of claim 20.

27. Including the synchronization delay in the restart strategy is conditional on the duration of the frame exchange being greater than a predetermined threshold.

27. The method of claim 26.

28. A timer that counts down the synchronization delay is initialized with a Medium Synchronization value provided by the AP MLD over the first link.

27. The method of claim 26.

29. The timer is set to 0 upon successful reception over the first link of a control frame having an MCS value set to up to 2.

30. The method of claim 28.

30. Initiating the frame exchange includes detecting expiration of another backoff counter driving EDCA of the second link.

20. The method of claim 19.

31. The back-off counter and the other back-off counter are associated with the same access category.

31. The method of claim 30.

32. Initiating a frame exchange includes receiving an Initial frame from the AP MLD via the second link.

20. The method of claim 19.

33. The Initial frame is received while another backoff counter driving EDCA of the second link is being decremented.

33. The method of claim 32.

34. and, in response to a termination of the frame exchange over the second link, applying another restart strategy based on characteristics of the frame exchange and restarting another back-off counter driving the EDCA of the second link.

20. The method of claim 19.

35. The other restart strategy is: reinitializing the other backoff counter using the updated contention window before beginning to decrement the other backoff counter if the other backoff counter expires; otherwise restarting said other backoff counter from its current value; Includes one from 35. The method of claim 34.

36. and switching a second STA, which is affiliated with the non-AP MLD and corresponds to the second link, from a listening operation state to a valid frame exchange state in response to initiating the frame exchange, and switching a first STA, which is affiliated with the non-AP MLD and corresponds to the first link, from a listening operation state to a valid frame exchange state.

20. The method of claim 19.

37. A method of communication in a wireless network, comprising: in a non-access point (non-AP) Multilink Device (MLD) operating in an active Enhanced Multilink (EML) mode, and switching an Enhanced Distributed Channel Access (EDCA) parameter of a back-off counter driving EDCA of a second link of the set from a current EDCA parameter to a different EML EDCA parameter in response to completion of a frame exchange with the AP MLD via a first link of the set of valid links to which the EML mode is applied. method.

38. The frame exchange includes a trigger-based uplink transmission to the AP MLD.

38. The method of claim 37.

39. and switching an EDCA parameter of a back-off counter driving EDCA of the first link from a current EDCA parameter to a different EML EDCA parameter in response to terminating the frame exchange with the AP MLD over the first link.

38. The method of claim 37.

40. The non-AP MLD stores a set of EML single-radio (EMLSR) EDCA parameters and a set of EML multi-radio (EMLMR) EDCA parameters, and different EML EDCA parameters are selected from the set of EMLSR EDCA parameters and the set of EMLMR EDCA parameters depending on whether the non-AP MLD is in an EMLSR mode or an EMLMR mode, respectively.

38. The method of claim 37.

41. and receiving, from the AP MLD, a management frame including the different EML EDCA parameters in addition to EDCA parameters and multi-user (MU) EDCA parameters.

38. The method of claim 37.

42. A method of communication in a wireless network, comprising: an access point (AP) multilink device (MLD) operable in an active enhanced multilink (EML) mode, the method comprising: Send a management frame to the non-AP MLD, the management frame including a set of EML EDCA parameters; The EML EDCA parameters are used to configure Enhanced Distributed Channel Access (EDCA) of a non-AP MLD operating in the EML mode when frame exchange with the AP MLD is completed via a second link of the set, and drive access to a first link of a set of valid links to which the EML mode applies. method.

43. A non-access point (non-AP) multi-link device (MLD) capable of operating in an active enhanced multi-link (EML) mode, comprising: and an initiation means for initiating an Enhanced Distributed Channel Access (EDCA) backoff procedure by a first station (STA) that is affiliated with the non-AP MLD and corresponds to a first link of a set of valid links for which the EML mode is applicable, to access the first link, the initiation means decrementing a backoff counter. and switching means for switching the first affiliated STA from a listening operation state to an active frame exchange state to initiate a frame exchange with the AP MLD via the first link. Non-AP MLD.

44. A program stored therein that, when executed by a microprocessor or computer system within the wireless device, causes the wireless device to carry out the method of any one of claims 1, 37 or 42. A non-transitory computer readable medium.

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