(TWT, R-TWT) procedure support and state switching for each link for the co-affiliated station of EMLSR or EMLMR

Abstract

The non-AP MLD operates in an EML mode that is applied to a set of EML links. The non-AP MLD receives a first beacon frame via a first link of the EML links from a first affiliated station, and the first beacon frame includes a TBTT related to a second beacon frame. Further, the non-AP MLD configures the first affiliated station to be in a receiving state at the TBTT in order to receive the second beacon frame.

Description

Technical Field

[0001] The present invention generally relates to wireless communication, and more specifically to multi-link (ML) communication.

Background Art

[0002] Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, and broadcast. These wireless networks can be multiple access networks that support 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 standard family adopted by the Institute of Electrical and Electronics Engineers (IEEE (registered trademark)) provides a number of mechanisms for wireless communication between STAs.

[0004] With the development of latency sensitive applications such as online games, real-time video streaming, virtual reality, and remote operation of drones and robots, it is necessary to consider requirements and problems of better throughput, low latency, and robustness. Such problems are currently being considered as the main purpose of issuing the next 802.11 major release known as 802.11be or EHT (Extremely High Throughput) by the IEEE 802.11 working group.

[0005] The IEEE P802.11be / D2.0 version (May 2022, hereinafter referred to as the "D2.0 standard") introduces Multi-Link (ML) Operation (MLO). MLO improves data throughput by enabling communication between STAs via multiple parallel and discontinuous communication links.

[0006] MLO enables a non-AP (Access Point) MLD (ML Device) to register with an AP MLD, that is, to discover, authenticate, associate, and set up multiple links with the AP MLD. Each link enables 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 Media Access Control (MAC) Service Access Point (SAP) for the Logical Link Control (LLC), and includes one MAC data service. Thus, an AP MLD is composed of multiple affiliated APs, and a non-AP MLD is composed of multiple affiliated non-AP STAs. The affiliated STAs of both the AP MLD and the non-AP MLD can use the 802.11 mechanism to communicate with the affiliated STAs of another MLD via each of the set up multiple communication links.

[0008] With the introduction of the spatial multiplexing capabilities of MLO and MLD, the D2.0 standard introduced new Operating Modes (OMs) called Enhanced Multi-Link Operating Mode (EML OM), namely the EMLSR (Enhanced Multi-Link Single Radio) mode and the EMLMR (Enhanced Multi-Link Multi-Radio) mode.

[0009] During the association phase, the non-AP MLD declares support for the EML operation mode (known as EML Capabilities) to the AP MLD. In the operation mode, the activation and deactivation of the EML operation mode are initiated by the non-AP MLD that sends a specific EHT action frame called "EML OM Notification". In the D2.0 standard, the two modes of EMLSR and EMLMR are considered mutually exclusive.

[0010] When the EMLMR mode is enabled, the non-AP MLD simultaneously listens for a set of active links (so-called EMLMR links, usually composed of two active links) to receive the Initial frame sent by the AP MLD and start frame exchange. Next, it aggregates some physical resources of different radios used in different links (so-called EMLMR links) to send and receive data of the supported transmit and receive spatial streams up to a predefined number, one EMLMR link (usually the link where the Initial frame was received) at a time. This number can be more than the number of transmit and receive spatial streams supported by each radio.

[0011] When the EMLSR mode is enabled, the non-AP MLD simultaneously listens for a set of active links (so-called EMLSR links, usually composed of two active links) to receive the Initial Control frame (e.g., MU-RTS trigger frame, BSRP trigger frame) from the AP MLD and start frame exchange. Next, it can perform data frame exchange with the AP MLD through only one EMLSR link (usually the link where the Initial Control frame was received) at a time.

[0012] This indicates that one of the EMLMR (or EMLSR) links is not completely independent of the other.

[0013] Furthermore, non-AP MLDs also have the ability to initiate frame exchanges with AP MLDs via one EMLSR or EMLMR link to transmit uplink data on their own. In such cases, STAs affiliated with non-AP MLDs operating in EMLSR or EMLMR mode do not need to send Initial Control frames or Initial frames to initiate frame exchanges with AP MLDs (non-triggered UL transmission), and access the wireless medium according to the rules defined in Section 10.3.2.4 (NAV setting and resetting) and Section 10.23.2 (HCF contention-based channel access (EDCA)) as specified in the IEEE802.11-2020 standard.

[0014] The EML mode mechanism coexists with other 802.11 mechanisms. Some of them (also called "link-specific procedures") are defined on a given wireless medium and operate on a given link of the EMLSR (or EMLMR) link independently of other links. For example, the so-called Target Wake Time (TWT) procedure and its most recent adaptation, the Restricted Target Wake Time procedure (known as rTWT or R-TWT).

[0015] The implementation of the EML mode may prevent link-specific procedures from functioning efficiently. As an example, the network activity of non-AP MLDs on the first EMLSR (or EMLMR) link may prevent non-AP MLDs from recognizing link-specific procedures (such as rTWT service periods) on other EMLSR (or EMLMR) links because non-AP MLDs cannot listen on other links while operating on the first link.

[0016] It is necessary to improve the coexistence between the EML mode and link-specific procedures. Summary of the Invention

[0017] The inventors have noticed that the reason non-AP MLDs cannot participate in link-specific procedures is that due to the network operation of non-AP MLDs on the first link, the MLD fails to receive the beacon frame that notifies the procedure on the other link.

[0018] Therefore, it is a broad object of the present invention to advantageously facilitate the reception of beacon frames. As a result, enhanced link-specific procedures compliant with the EML mode, taking into account the use of the EML mode, should be provided.

[0019] In this context, a communication method in a wireless network is provided for a non-access point (non-AP) multi-link device (MLD) operating in an Enhanced Multi-Link (EML) mode applied to a set of EML links, including the following: - Receiving, by a first affiliated station, a first beacon frame via a first link of the EML link, the first beacon frame including a Target Beacon Transmission Time (TBTT) related to a second beacon frame, and - Setting the first affiliated station to a receiving state at the TBTT to receive the second beacon frame.

[0020] It is understood that the first affiliated station operates on the first link and one or more other affiliated stations operate on other EML links.

[0021] Therefore, the non-AP MLD considers the predicted time (TBTT) of the next beacon frame received on the first link to set its own device to an appropriate reception mode (at the corresponding first affiliated station), regardless of network activities on other links of the EML link.

[0022] As a result, since the reception of the next beacon frame is guaranteed, the non-AP MLD will come to recognize the first link-specific procedure notified by the next beacon frame.

[0023] Any feature of the present invention is defined below with reference to a method, but these can be replaced with features of an apparatus.

[0024] In some embodiments, setting the first affiliated station includes ending an ongoing frame exchange via a second link of the EML link and switching the first affiliated station to an operating state suitable for receiving a second beacon frame.

[0025] It is understood that, initially, the first affiliated station is in an invalid frame exchange state due to the frame exchange via the second link.

[0026] Accordingly, the non-AP MLD decides to stop the current frame exchange in order to change the first affiliated station from the invalid frame exchange state to a reception state suitable for receiving the next beacon frame at the time when the next beacon frame is expected. Thus, due to the interruption of the frame exchange, the beacon frame can be correctly received on the first link.

[0027] In a particular embodiment, switching to an operating state suitable for receiving a second beacon frame includes switching the first affiliated station to a listening operating state. Advantageously, this allows the second affiliated stations to listen on their respective second EML links and, for example, receive another beacon frame simultaneously.

[0028] In certain embodiments, the second affiliated station must trigger a frame exchange sequence on the second link and ignore Initial frames that temporally overlap with the first beacon frame on the first link.

[0029] It is understood that the second affiliated station operates on a second link that is different from the first link.

[0030] This configuration ensures that the non-AP MLD receives the entire set of expected beacon frames regardless of the network activity on the second link.

[0031] More generally, this configuration relates to a communication method for a wireless network in a multi-link device (MLD) of a non-access point (non-AP) operating in an enhanced multi-link (EML) mode applied to a set of EML links, including: Configuring the second affiliated station of the non-AP MLD to trigger a frame exchange sequence on the second link of the EML link and ignore received Initial frames that temporally overlap with the beacon frame received by the first affiliated station of the non-AP MLD on the first link of the EML link.

[0032] In certain embodiments, switching to an operating state suitable for receiving the second beacon frame includes switching the first affiliated station to an active frame exchange state. This configuration prevents the non-AP MLD that has received the beacon frame from switching on the second link, for example, when the AP MLD transmits an Initial (Control) frame on the second link simultaneously with the second beacon frame.

[0033] In some embodiments, setting the first affiliated station includes switching the first affiliated station from the listening operation state to the active frame exchange state. Also in this case, for example, when the AP MLD transmits an Initial (Control) frame on the second link simultaneously with the second beacon frame, the non-AP MLD that has received the beacon frame is prevented from switching on the second link.

[0034] In some embodiments, setting the first affiliated station includes ending an ongoing frame exchange via the first link and maintaining the first affiliated station in the active frame exchange state.

[0035] This means that the first affiliated station does not immediately switch back to the listening operation state after the frame exchange ends. The end of the frame exchange may correspond to the end of the acquired transmission opportunity, or may be spontaneously triggered by the non-AP MLD due to the temporal proximity of the TBTT in order to configure the own device to receive the second beacon frame.

[0036] These embodiments avoid unnecessary state switching of the affiliated station while ensuring correct reception of the beacon frame.

[0037] In a particular embodiment, the first affiliated station is maintained in the active frame exchange state if the time distance from the end of the frame exchange to the TBTT is less than a predetermined threshold. For example, the predetermined threshold is at least the sum of the following: - The transition period required by the non-AP MLD to switch the state of the affiliated station from the listening operation state to the active or inactive frame exchange state, and - The transition period required by the non-AP MLD to switch the state of the affiliated station from the active or inactive frame exchange state to the listening operation state.

[0038] This enables fine control over which non-AP MLDs can benefit from maintaining the active frame exchange state and which non-AP MLDs that have ended frame exchange can attempt network activity on the second link. As a result, the utilization of the wireless network is improved.

[0039] In some embodiments, setting the first affiliated station is triggered at least by a first determined delay before the TBTT. For example, the first determined delay belongs to a group including the EMLSR active switching delay, the EMLMR active switching delay, and the maximum value of the EMLSR and EMLMR active switching delays. This configuration ensures that the first affiliated station is in the receiving state at the TBTT, meaning that the expected second beacon frame can be correctly received.

[0040] In some embodiments, the second beacon frame schedules the service period on the first link and, when the frame exchange within the service period ends, maintains the first affiliated station in the active frame exchange state until the end of the service period. In this configuration, the first affiliated station does not automatically switch back to the listening operating state immediately after the frame exchange ends, and the active frame exchange state continues until the entire service period (e.g., rTWT SP) ends. This increases the opportunity for non-AP MLDs to exchange frames during the service period and improves network efficiency.

[0041] In some embodiments, the second beacon frame schedules a service period on the first link, switches the first affiliated station to an active frame exchange state before the start of the service period, and maintains the active frame exchange state until the end of the service period. In this configuration, the first affiliated station is in an active frame exchange state throughout the service period (e.g., rTWT SP). This increases the opportunity for the non-AP MLD to perform frame exchanges during the service period and improves network efficiency.

[0042] In certain embodiments, the method includes switching the first affiliated station from an active frame exchange state to a listening operating state at the end of the service period.

[0043] In some embodiments, the second beacon frame includes another TBTT related to a third beacon frame that schedules a TWT service period on the first link, when the scheduled TWT service period is signaled with TWT persistence, the frame exchange performed by the second affiliated station on the second link of the EML link continues without the first affiliated station being set to a receiving state at another TBTT to receive the third beacon frame on the first link.

[0044] It is understood that the TWT persistence (the Broadcast TWT Persistence field of the TWT element) indicates the number of TBTTs for which there is a broadcast TWT service period corresponding to this broadcast TWT Parameter set. Since the TWT service period is repeated, the non-AP MLD does not need to obtain the next beacon frame that notifies the same information. Thus, these embodiments avoid interruption of network activity on the second link. This improves the efficiency of the network.

[0045] In some embodiments, the second beacon frame schedules a quiet period on the first link, and during the quiet period, until the end of the quiet period, switches the first affiliated station to an inactive frame exchange state. This means that during the quiet period, a second affiliated station operating on the second link of the EML link is switched to an active frame exchange state until the end of the quiet period. Thus, the non-AP MLD can quickly start frame exchange on the second link, and thus network efficiency is improved.

[0046] In some embodiments, the method further includes the non-AP MLD sending an instruction to the AP MLD to schedule, for the non-AP MLD, a service period that does not temporally overlap with any beacon frame transmitted by the AP MLD on the second link of the EML link in a future beacon frame. Such an instruction ensures that the non-AP MLD can receive the beacon frame on the second link regardless of the service period scheduled on the first link.

[0047] The present invention also relates to a communication method of a wireless network, including the following in an access point multi-link device (AP MLD) configured to perform a frame exchange operation with at least a given non-AP MLD operating in an enhanced multi-link (EML) mode applied to a set of EML links: Scheduling a service period of a predetermined non-AP MLD that does not temporally overlap with a beacon frame transmitted by the AP MLD on the second link of the EML link in a beacon frame transmitted by the AP MLD on the first link of the EML link.

[0048] As a result, the scheduled service period (such as rTWT SP) is no longer an obstacle for the non-AP MLD to correctly receive the beacon frame.

[0049] The present invention also relates to a communication method for a wireless network, including the following in an access point multi-link device (AP MLD) configured to execute a frame exchange operation with at least a given non-AP MLD operating in an enhanced multi-link (EML) mode applicable to a set of EML links: Transmitting an Initial frame that triggers a frame exchange sequence with at least one non-AP MLD operating in the EMLSR mode and at least one non-AP MLD operating in the EMLMR mode, The AP MLD ensures that the padding period of the Padding field of the Initial frame is greater than or equal to the maximum value of the values indicated by the EMLSR Padding Delay sub-field and the EMLMR Delay sub-field received from the non-AP MLD from which the frame exchange sequence was started.

[0050] Accordingly, the AP MLD can trigger both one or more non-AP MLDs operating in the EMLSR mode and one or more non-AP MLDs operating in the EMLMR mode, and the padding period indicated in the Initial frame (IC frame in the EMLSR mode and Initial frame in the EMLMR mode) ensures that all these non-AP MLDs (both MLDs operating in the EMLSR mode and MLDs operating in the EMLMR mode) have sufficient time to switch the state of the affiliated station from the listening operation state to the active / inactive frame exchange state.

[0051] In this regard, the present invention also provides a wireless communication device including at least one microprocessor configured to execute any of the methods as described above.

[0052] Another aspect of the present invention relates to a non-transitory computer-readable medium storing a program that, when executed by a microprocessor or a computer system in a wireless device, causes the wireless device to execute any of the methods as described above.

[0053] At least a part of the method according to the present invention can be implemented by a computer. Therefore, the present invention can take the form of an all-hardware embodiment, an all-software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects that can all generally be referred to herein as "circuits", "modules", or "systems". Furthermore, the present invention can take the form of a computer program product embodied in any tangible medium having computer-usable program code embodied therein.

[0054] Since the present invention can be implemented in software, the present invention can be embodied as computer-readable code for providing 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 electrical signals, electronic signals, optical signals, acoustic signals, magnetic signals, or electromagnetic signals, such as microwave signals or RF signals.

Brief Description of the Drawings

[0055] Hereinafter, embodiments of the present invention will be described only as an exemplary method with reference to the following drawings:

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Best Mode for Carrying Out the Invention

[0056] The techniques described in this specification can be used in various broadband wireless communication systems including communication systems based on orthogonal multiplexing schemes. 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 can utilize sufficiently different directions to simultaneously transmit data belonging to multiple user terminals such as wireless devices or STAs. A TDMA system can enable multiple user terminals to share the same frequency channel by dividing the transmitted signal into different time slots or resource units and allocating 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 can be referred to as tones, bins, etc. In OFDM, each subcarrier can be independently modulated with data. An SC-FDMA system can utilize interleaved FDMA (IFDMA) that transmits with subcarriers dispersed over the system bandwidth, localized FDMA (LFDMA) that transmits with a block of adjacent subcarriers, or extended FDMA (EFDMA) that transmits with multiple blocks of adjacent subcarriers.

[0057] The teachings of this specification can be incorporated (e.g., implemented or executed by an STA) into various devices (e.g., an STA). In some aspects, a wireless device or STA implemented in accordance with the teachings of this specification may or may not include an access point (referred to as an AP) (referred to as a non-AP STA or an STA).

[0058] The examples are described in the context of a WiFi (registered trademark) network, but the present invention can be used in any type of wireless network such as a mobile phone cellular network that implements, for example, a very similar mechanism.

[0059] AP includes, implements as, or may be known as NodeB, Radio Network Controller ("RNC"), evolved Node B (eNB), 5G Next Generation Base Station ("gNB"), Base Station Controller ("BSC"), Base Transceiver Station ("BTS"), Transceiver Function ("TF"), wireless router, wireless transceiver, Basic Service Set ("BSS"), Extended Service Set ("ESS"), Radio Base Station ("RBS"), or other terms.

[0060] Non-AP STA includes, implements as, or may be known as subscriber STA, subscriber unit, Mobile Station (MS), Remote Station, Remote Terminal, User Terminal (UT), User Agent, User Device, User Equipment (UE), User STA, or other terms. In some implementations, the STA may include a cellular phone, cordless phone, Session Initiation Protocol ("SIP") phone, Wireless Local Loop ("WLL") STA, Personal Digital Assistant ("PDA"), handheld device with wireless connectivity, or other suitable processing device connected to a wireless modem. Thus, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or 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, the non-AP STA may be a wireless node. Such a wireless node may provide connectivity to a network (e.g., a wide area network such as the Internet or a cellular network) via, for example, a wired or wireless communication link.

[0061] An AP manages a set of STAs (associated with or registered to the AP) that together constitute access to the wireless medium for communication purposes. The STAs (including the APs to which they are registered) form a service set, hereinafter called a basic service set (BSS) (other terms may be used). The same physical STA operating as an access point may manage two or more BSSs (and thus the corresponding WLANs), and thus each BSS is uniquely identified by a specific basic service set identifier (BSSID) and is managed by a different virtual AP implemented on the physical AP. Each STA is identified within the BSS by an identifier AID assigned by the AP at registration.

[0062] The 802.11 standard family defines various medium access control (MAC) mechanisms for driving access to the wireless medium.

[0063] As shown in the May 2022 draft IEEE P802.11be / D2.0, the current discussion in the 802.11be task group is to introduce multi-link operation (MLO) with respect to the operation of the MAC layer. MLO enables a multi-link device to establish or configure multiple links and operate them simultaneously.

[0064] A Multi-Link Device (MLD) is a logical entity that has multiple affiliated STAs (STAs), has a single Medium Access Control (MAC) service access point (SAP) for Logical Link Control (LLC), and includes one MAC data service. An Access Point Multi-Link Device (or AP MLD) corresponds to an MLD where each STA affiliated with the MLD is an AP (thus called an "affiliated AP"). A Non-Access Point Multi-Link Device (or non-AP MLD) corresponds to an MLD where each STA affiliated with the MLD is a non-AP STA (called an "affiliated non-AP STA"). In some literature, "Multi-Link Device", "ML Device" (MLD), "Multi-Link Logical Entity", "ML Logical Entity" (MLE), "Multi-Link Set" and "ML Set" are synonyms that refer to the same type of ML device. An exemplary architecture of a multi-link device will be described below with reference to FIGS. 1ab.

[0065] The multiple affiliated non-AP STAs of a non-AP MLD can set up communication links with the multiple affiliated APs of an AP MLD to form a multi-link channel.

[0066] The links established for an MLD (or "activated links") are theoretically independent, meaning that the channel access procedure and communication (to the communication medium) are executed independently for each link. Thus, different links can have different data rates (e.g., due to different bandwidths, number of antennas, etc.) and can be used for the communication of different types of information (each via a specific link).

[0067] Thus, 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 with an AP MLD and a non-AP STA affiliated with a non-AP MLD.

[0068] Affiliated APs and non-AP STAs operate on their respective channels in accordance with 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.

[0069] With multi-link aggregation, traffic associated with one MLD can theoretically be transmitted over multiple parallel communication links, increasing network capacity and maximizing the utilization of available resources.

[0070] From an architectural perspective, an MLD typically includes several radios for implementing an affiliated STA, but does not necessarily have the same number as the number of affiliated STAs. In particular, a non-AP MLD may operate with a larger number of affiliated STAs than the number of radios (it can also be reduced to one).

[0071] The D2.0 standard defines several enhanced multi-link operating modes (abbreviated as EML OMs) from this physical architecture, which are enhanced multi-link single radio (EMLSR) and enhanced multi-link multi-radio (EMLMR). The D2.0 standard states that the two modes of EMLSR and EMLMR are mutually exclusive.

[0072] In the association phase, the non-AP MLD declares support for the EMLSR and / or EMLMR modes to the AP MLD (in the so-called EML Capabilities). In the operating mode, the activation and deactivation of the EMLSR or EMLMR mode are initiated by the non-AP MLD, and the non-AP MLD sends a specific EHT action frame called "EML OM Notification" indicating the set of valid links (so-called EMLSR or EMLMR links) to which the activation of the EMLSR or EMLMR mode applies. Usually, the "EMLSR / EMLMR link" consists of two valid links. However, more valid links can be used.

[0073] When the EMLSR mode is enabled, the non-AP MLD simultaneously listens on the set of valid links of the "EMLSR link" to receive the Initial Control frames (e.g., MU-RTS trigger frames and BSRP trigger frames) sent by the AP MLD, and then can perform the data frame exchange with the AP MLD on only one link (usually the link on which the Initial Control frame was received) at a time. Each non-AP MLD may or may not support the EMLSR operating mode.

[0074] In the EMLMR mode, a non-AP MLD can aggregate a part of the physical resources of multiple radios for multiple valid links (so-called EMLMR links) to transmit and receive data up to a predetermined number of the supported transmit and receive spatial streams. Since this predetermined number is larger than the number of transmit and receive spatial streams supported for each radio, it provides throughput improvement and latency reduction. As an example, a multi-radio (MR) non-AP MLD that supports the EMLMR mode for two links (with associated radios) communicates via two links using two respective radios when the EMLMR mode is deactivated, such as in a 2x2 MIMO antenna configuration for each radio. On the other hand, in a 4x4 MIMO antenna configuration, for example, when the EMLMR mode is activated, the MR non-AP MLD aggregates the physical resources (usually antennas) of two radios and communicates via one of the two links using one of the radios. At the same time, the other link (the link whose physical antenna has been taken away) cannot be used.

[0075] When the EMLMR mode is enabled, the non-AP MLD simultaneously listens to a set of valid links of the "EMLMR links" to receive the Initial frame transmitted by the AP MLD and start frame exchange, and then can perform the data frame exchange with the AP MLD via only one EMLMR link (usually the link that received the Initial frame) at a time (aggregating radio resources).

[0076] In the following description, for simplicity of explanation, mainly the EMLSR mode will be described. However, similar considerations are also possible for the EMLMR mode.

[0077] FIG. 1 shows a typical 802.11 network environment including ML transmission between EML-compatible MLDs (compatible with EMLSR and EMLMR) in which the present invention can be implemented.

[0078] Wireless communication network 100 includes AP MLD 110 and two non-AP MLDs 120 and 130. In this example, it is assumed that the two non-AP MLDs are capable of executing EML, and within the EMLSR-related field and EMLMR-related field of EML Capabilities, they declare the capabilities corresponding to AP MLD 110 (these fields are hereinafter referred to as EMLSR Capabilities and EMLMR Capabilities, for example, sub-parts of EML Capabilities). Of course, other numbers of non-AP MLDs registered with AP MLD 110 and exchanging frames with AP MLD 110, or other (more) numbers of EML-capable non-AP MLDs, can also be assumed.

[0079] AP MLD 110 has a plurality of affiliated APs, two affiliated APs 111 and 112 (also referred to as AP1 and AP2 respectively) in the exemplary FIG. 1, and each operates as an 802.11 AP on an operating channel within one frequency band. Known 802.11 frequency bands include the 2.4 GHz band, 5 GHz band, and 6 GHz band. Of course, instead of or in addition to these three frequency bands, other frequency bands can be used.

[0080] Non-AP MLDs 120, 130 have a plurality of affiliated non-AP STAs, and each non-AP STA operates as an 802.11 non-AP STA in the BSS (managed by affiliated AP 111 or 112) to which it is registered. In the exemplary FIG. 1, two non-AP STAs 121 and 122 (also referred to as A1 and A2 respectively) are affiliated with non-AP MLD 120, and two non-AP STAs 131 and 132 (also referred to as B1 and B2 respectively) are affiliated with non-AP MLD 130.

[0081] For illustrative purposes, non-AP MLDs 120 and 130 are single-radio non-AP MLDs. For example, AP 111 is set to operate on channel 38 corresponding to an operating 40 MHz channel in the 5 GHz frequency band, and AP 112 is set to operate on channel 151 corresponding to another operating 40 MHz channel in the 5 GHz frequency band. In another example, affiliated STAs may operate in different frequency bands.

[0082] Each affiliated AP provides a link to the affiliated non-AP STA of the non-AP MLD (120 or 130) towards AP MLD 110. Thus, the link of each non-AP MLD can be identified simply by the identifier of its respective affiliated AP. In this context, each affiliated AP 111 and 112 can 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 can assign a link ID to the affiliated AP by incrementing the ID from 0 (for the first affiliated AP). Of course, other expressions such as "AP ID" can be used as variants.

[0083] To perform multi-link communication, each non-AP MLD 120, 130 needs to discover, authenticate, associate, and set up multiple links with AP MLD 110, and each link is established between the affiliated AP of AP MLD 110 and the affiliated non-AP STA of the non-AP MLD. Each such link, called an "active link, enabled link", enables individual channel access and frame exchange between the non-AP MLD and the AP MLD based on the supported capabilities exchanged during the association.

[0084] The discovery phase is called the ML discovery procedure, and the multi-link setup phase (or association phase) is called the ML setup procedure.

[0085] The ML discovery procedure enables a non-AP MLD to discover various links to an AP MLD provided by a wireless communication network 100, e.g., multiple affiliated APs. Accordingly, the ML discovery procedure attempts to advertise the various affiliated APs of the AP MLD along with their respective network information (e.g., including all or part of the capabilities and operating parameters). After the non-AP MLD discovers the wireless communication network 100 through the ML discovery procedure and after the MLD authentication procedure, the ML setup procedure can select a set of setup link candidates between the affiliated non-AP STAs of the non-AP MLD and some of the discovered affiliated APs and request the setup of these links to the AP MLD110, which can be accepted or rejected by the AP MLD. If accepted by the AP MLD, the non-AP MLD is provided with an Association Identifier (AID) by the AP MLD, and this AID is used for the affiliated non-AP of the non-AP MLD to wirelessly communicate with the corresponding affiliated AP via multiple links (communication channels). During the ML setup procedure, the non-AP MLD declares some or all of its capabilities. For example, it declares the capabilities of the EMLSR. For this purpose, appropriate fields are provided in the management frame. In particular, the management frames exchanged between the ML discovery and ML setup procedures include new information elements called Basic Multi-Link elements, which are specialized for multi-link operation (MLO). In fact, in all management frames containing Basic Multi-Link elements except the authentication frame, non-APs or AP MLDs that support EMLSR (dot11EHTEMLSROptionImplemented is true) or EMLMR (dot11EHTEMLMROptionImplemented is true) set the EMLSR or EMLMR Support bits in the EML Capabilities subfield of the Common Info field to 1.

[0086] 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).

[0087] The AP MLD 110, non-AP MLD 120, and non-AP MLD 130 are EMLSR compliant (dot11EHTEMLSROptionImplemented is true) or EMLMR compliant (dot11EHTEMLMROptionImplemented is true). The EMLSR or EMLMR capabilities (a subpart of the EML Capabilities) are exchanged during the ML discovery procedure and the multi-link setup phase.

[0088] The EMLSR and EMLMR capabilities currently defined in the D2.0 standard include the following subfields: - The "EMLSR Support" subfield indicates that the MLD supports EMLSR operation. The EMLSR Support subfield is set to 1 if the MLD supports EMLSR operation and 0 otherwise; - The 3-bit subfield of "EMLSR Padding Delay" indicates the minimum MAC padding period of the Padding field of the Initial Control frame required by the non-AP MLD, as defined in Enhanced multi-link single radio operation (Section 35.3.17). The table converts the 3-bit value to the padding delay in μs. This delay is used to define the transition period required for the MLD to switch the state of the affiliated station from the listening operation state to the active / inactive frame exchange state. This transition period is the sum of this delay and the duration of the Initial Control frame response, which will be described later. Therefore, this transition period is called the "EMLSR active switching delay"; - The 3-bit subfield of "EMLSR Transition Delay" indicates the transition delay time required for the 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 link. The table converts the 3-bit value to the delay in μs. For example, it is 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, and the values from 6 to 7 are reserved; - The "EMLMR Support" subfield indicates that the MLD supports the EMLMR operation. When the MLD supports the EMLMR operation, the EMLMR Support subfield is set to 1, and otherwise it is set to 0; - The 3-bit sub-field of "EMLMR Delay" indicates the minimum padding period required for switching the EMLMR link when the non-AP MLD operates in the EMLMR mode. This delay is used to define the transition period required for the MLD to switch the state of the affiliated station when starting or ending frame exchange. The transition period for frame exchange is the sum of this delay (EMLMR delay) and the duration of the Initial frame response described later. Therefore, this start transition period is called the "EMLMR active switch delay". - The "Transition Timeout" sub-field indicates the timeout value for the EML Operating Mode Notification frame exchange in EMLSR (or EMLMR).

[0089] When a non-AP MLD compatible with EMLSR (or EMLMR) attempts to operate in the corresponding mode on a set of active links called the EMLSR (or EMLMR) link, the STA affiliated with that non-AP MLD sends an EML Operating Mode (OM) Notification frame (specified in the D2.0 standard) with the EMLSR (or EMLMR) Mode sub-field of the EML Control field set to 1 to the AP affiliated with the AP MLD compatible with EMLSR (or EMLMR) (here, AP MLD110). The EMLSR (or EMLMR) link is indicated by setting the bit position of the EMLSR (or EMLMR) Link Bitmap sub-field 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 the link with link ID equal to i and is set to 1 to indicate that the link is a member of the EMLSR (or EMLMR) link.

[0090] An AP affiliated with an AP MLD that has received an EML Operating Mode Notification frame from a STA affiliated with a non-AP MLD shall then, for one of the STAs affiliated with the non-AP MLD, within the timeout interval starting at the end of the PPDU transmitted by the AP affiliated with the AP MLD, which is indicated in the Transition Timeout subfield of the EML Capabilities subfield of the Basic Multi-Link element, transmit an EML Operating Mode Notification frame as a confirmation response to the EML Operating Mode Notification transmitted by the STA affiliated with the non-AP MLD.

[0091] After successful transmission of an EML Operating Mode Notification frame via one of the EMLSR (or EMLMR) links by a STA affiliated with a non-AP MLD, the non-AP MLD operates in the EMLSR (or EMLMR) mode and the EMLSR is considered active (or the EMLMR is considered active).

[0092] When a non-AP MLD compliant with EMLSR attempts to disable the EMLSR (or EMLMR) mode, a STA affiliated with the non-AP MLD shall send an EML Operating Mode (OM) Notification frame (specified in the D2.0 standard) with the EMLSR (or EMLMR) Mode subfield in the EML Control field set to 0 to the AP affiliated with the AP MLD. Again, the AP affiliated with the AP MLD that receives the EML Operating Mode (OM) Notification frame from the STA affiliated with the non-AP MLD shall send the EML Operating Mode Notification frame as described above as a confirmation response to the EML Operating Mode (OM) Notification frame. After the successful transmission of the EML Operating Mode Notification frame by the STA affiliated with the non-AP MLD via one of the EMLSR (or EMLMR) links, the non-AP MLD shall disable the EMLSR (or EMLMR) mode.

[0093] The set of STAs affiliated with a non-AP MLD compliant with EMLSR (or EMLMR) operating on an EMLSR (or EMLMR) link may be all or some of the STAs affiliated with the non-AP MLD. This set of STAs is hereinafter referred to as the "EMLSR co-affiliated STAs" (or EMLMR co-affiliated STAs) of the non-AP MLD.

[0094] In the example of Figure 1, the EMLSR co-affiliated STAs of non-AP MLD 120 and non-AP MLD 130 operate on the same link (e.g., the same affiliated APs, AP1 and AP2), meaning they share the same EMLSR link.

[0095] FIG. 1a shows an exemplary 802.11be multi-link reference model for either AP MLD or non-AP MLD.

[0096] MLD includes a PHY layer 200, a MAC layer 220, a logical link control (LLC) sublayer, and upper layers.

[0097] The upper layers may include applications that generate traffic data or use the received traffic data.

[0098] The transmission and reception of traffic data are processed by the MAC 220 and PHY 200 layers. Such transmission and reception of traffic data may be performed via multiple links 20-x, 20-y, 20-z as introduced with reference to FIG. 1, such as 151, 152, 161, 162. Three links, and thus three affiliated stations, are shown. Of course, other configurations including two affiliated stations or more than three affiliated stations are also conceivable.

[0099] Traffic data is provided from the upper layers as a series of data frames, or "traffic streams". Each traffic stream and thus each data frame is associated with an access category (AC) as defined by the EDCA mechanism (FIG. 1b). This mapping between the stream or data frame and the AC is performed by the classifier 213.

[0100] Remember that 802.11 stations (AP and non-AP stations) hold four access categories (ACs), each having one or more corresponding transmission buffers or queues. The four ACs are conventionally defined as follows: - AC1 and AC0 are reserved for best effort and background traffic. These traffics have the second lowest priority and the 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 priorities respectively.

[0101] Data frames, also known as MSDUs (MAC service data units) input from the upper layers of the protocol stack, are mapped by classifier 213 to one of the four ACs and thus input into the queue of the mapped AC.

[0102] Figure 1b shows an implementation model with four transmission queues, one for each access category.

[0103] The 802.11be multi-link reference model reflects the fact that MLD can transmit and receive using multiple links, especially at the levels of MAC layer 220 and PHY layer 200.

[0104] MAC layer 220 includes one unified upper-MAC (UMAC) layer 230 and multiple lower-MAC (LMAC) layers 220-x, 220-y, 220-z combined with respective PHY layers 200-x, 200-y, 200-z, and each combination corresponds to link 20-x, 20-y, 20-z.

[0105] 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 provides a UMAC service access point (SAP) to the LLC and upper layers.

[0106] The UMAC230 is responsible for link-independent MAC procedures such as authentication, association, security association, sequence number assignment, encryption / decryption of MAC protocol data units (MPDUs), aggregation / de-aggregation, and acknowledgment scoreboarding procedures.

[0107] Each data unit (MSDU) with a priority of the type of traffic (User Priority (UP) and thus Traffic IDentifer (TID)) arriving at the MAC layer 220 from the upper layer (e.g., the link layer) is mapped to one of the ACs according to the mapping rules in the UMAC layer 230. And still 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) within the mapped AC.

[0108] Each LMAC220-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 procedures, e.g., EDCA221-x, 221-y, 221-z. Some functions require joint processing of both the UMAC230 and the LMAC220-x, 220-y, 220-z.

[0109] As shown in Figure 1ab, each EDCA221-x, 221-y, 221-z for each link performs contention for each queue on a per-link basis. In that regard, each AC has a set of unique queue contention parameters for each link, associated with priority values, thus defining higher or lower priority traffic for MSDUs. Therefore, there are multiple traffic queues for providing data traffic with different priorities for a given link. The contention window (CW) and the backoff value are known as EDCA variables and are specific to each link 20-x, 20-y, 20-z.

[0110] That is, each AC operates as a competing entity of an independent DCF on a given link, including the back-off engine 211 of each queue. Therefore, the back-off engine 211 of each queue is associated with each traffic queue 210 to use the queue competition parameters and subtract the back-off value (from CW) to initialize the back-off counter of each queue specialized for each AC and each link. The back-off counter is used to compete for access to links 20-x, 20-y, 20-z to transmit the data stored in the AC's queue. In fact, the back-off counter is decremented from the initial value when the medium is idle, and when the back-off counter reaches 0, transmission is permitted (access is permitted) to the corresponding affiliated STAs 201-x, 201-z.

[0111] When access to the wireless medium is permitted for the AC on the link, the MSDU stored for that AC is transmitted to the physical (PHY) layers 200-x, 200-y, 200-z for transmission via the link.

[0112] FIG. 2 shows, using a frame sequence, the EMLSR Operating Mode in the non-AP MLD 120 when the AP MLD 110 determines to use the EMLSR mode. Of course, here the EMLSR mode is emphasized as an example, but similar considerations are also possible for the EMLMR mode.

[0113] In this sequence, the non-AP MLD operates in the EMLSR mode, meaning that an EML Operating Mode Notification frame that activates the EMLSR mode has been successfully transmitted by the affiliated STA of the non-AP MLD 120. In other words, it means entering the active Enhanced Multi-Link Single Radio (EMLSR) mode applied to a specific set of two or more valid links.

[0114] Affiliated STAs 121 and 122 are co - affiliated STAs of the EMLSRs within the non - AP MLD120. Each affiliated STA can be in one of three defined states: a listening operation state, an active frame exchange state, and an inactive frame exchange state.

[0115] The non - AP MLD120 can listen simultaneously on its EMLSR links by putting the co - affiliated STAs of the corresponding EMLSRs for those links into the "awake" or "listening operation" state. For example, affiliated STAs A1, A2 are in the listening operation state (references 241, 242). The listening operation includes CCA (Clear Channel Assessment) and the reception of the Initial Control frame of the frame exchange initiated by the AP MLD. Thus, in the non - AP MLD 120, the co - affiliated STAs of two EMLSRs listen simultaneously for the reception of the Initial Control frame from the AP MLD.

[0116] When the AP MLD110 attempts to start frame exchange with one or more non-AP MLDs over one of the EMLSR links, it starts the frame exchange by sending an Initial Control frame 245 that explicitly triggers the non-AP MLDs. To some extent, the Initial Control frame schedules the non-AP MLDs. The Initial Control frame for frame exchange is sent 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 within the frame is set to a maximum value of 2). As defined in the D2.0 specification, the Initial Control frame must be a MU-RTS Trigger frame or a BSRP Trigger frame as defined in IEEE Standard 802.11ax (R)-2021. In the case of such a trigger frame format that includes one or more User Info fields, this condition means that frame 245 includes a User Info field addressed to the non-AP MLD, i.e., the AID12 field is set to the AID of the non-AP MLD (obtained at registration).

[0117] In this embodiment, and as indicated by reference "IC(A)", the Initial Control frame 245 explicitly triggers the non-AP MLD A120. The Initial Control frame can explicitly trigger multiple non-AP MLDs using multiple User Info fields therein.

[0118] The co - affiliated STAs of the non - AP MLD's EMLSR explicitly triggered by the Initial Control Frame 245 that received the frame (e.g., co - affiliated STA A1 in the embodiment) start the state change of the co - affiliated STAs of the non - AP MLD's EMLSR to be considered (e.g., the state change of co - affiliated STAs A1 and A2 in the embodiment), and send an Initial Control Frame Response (IC resp.) 246 to the AP AP1 affiliated with the AP MLD110.

[0119] After receiving the Initial Control Frame 245 of the frame exchange and sending the immediate response frame 246 as a response to the Initial Control Frame, the STA affiliated with the non - AP MLD that was listening on the corresponding link (e.g., co - affiliated STA A1 of the receiving - side EMLSR in the example) is configured to be able to transmit or receive frames on the active link where the Initial Control Frame 245 was received (e.g., link 151 in the example). For this purpose, a state - switching procedure is activated to switch the receiving - side co - affiliated STA of the EMLSR from the listening operation state 241 to the "active frame exchange" or "valid frame exchange" state referred to by 251 in the figure after the EMLSR active - switching delay. The receiving - side co - affiliated STA in this new state can receive a PPDU transmitted using multiple spatial streams on the link where the Initial Control Frame 245 was received. The EMLSR active - switching delay corresponds to the delay time required for the non - AP MLD to switch from the EMLSR listening operation mode to the EMLSR frame - exchange mode. As described above, this is specified by the EML Capabilities exchanged with the AP MLD (via the EMLSR Padding Delay).

[0120] At the same time, other co - affiliated STAs (e.g., STA A2 in the example) of the same non - AP MLD's other EMLSRs are set not to transmit or receive on other EMLSR links until the frame exchange is completed. For this purpose, a state - switching procedure is also activated for the co - affiliated STAs of other EMLSRs, and that STA is in turn switched from the listening operation state 242 to the "blindness frame" or "invalid frame exchange" state referred to as 252 in the figure. In particular, data is not transmitted by the AP MLD to the co - affiliated STAs of these other EMLSRs.

[0121] The state - switching of all co - affiliated STAs of all EMLSRs within the same non - AP MLD is indivisible and occurs simultaneously. This is because if a complete wireless resource chain (see Figure 9 below) is allocated to one STA and taken away from others, there will be problems. Regarding the EMLMR mode, the physical resources (e.g., antennas) of one wireless resource chain are allocated (aggregated) to other wireless resource chains, and as a result, the former is deprived of its transmission and reception capabilities (see Figure 9a below).

[0122] The above shows that when the non - AP MLD operates in the EMLSR mode (more generally, either the EMLSR mode or the EMLMR mode), it is either in the listening operation mode (where its co - affiliated STA is in the listening operation state) or in the frame - exchange mode (where one of its co - affiliated STAs is in the valid frame - exchange state and the other co - affiliated STAs are in the invalid frame - exchange state).

[0123] In the EMLSR mode, as will be described below with reference to Figure 9, only a single complete wireless resource allocated to the co - affiliated STA of the receiving - side EMLSR is available, while in the EMLMR mode, as will be described below with reference to Figure 9a, one antenna resource of the wireless stack is allocated to the other wireless stack, so simultaneous state changes are required.

[0124] It can be seen that only one of the jointly affiliated STAs of the EMLSR of the explicitly triggered non-AP MLD can perform a data frame exchange with the AP MLD at a time.

[0125] An exemplary frame exchange sequence is shown in FIG. 2, which includes the transmission (and thus downlink transmission) of the A-MPDU frame 255 by the affiliated AP AP1 to the jointly affiliated STA A1 of the EMLSR of the explicitly triggered non-AP MLD A 120, followed by the corresponding block acknowledgment response 256 from the latter.

[0126] In addition to the end of the frame exchange operated by the jointly affiliated STA of the receiving EMLSR, after the EMLSR Transition Delay defined in the EML Capabilities, the non-AP MLD 120 switches to the listening operation state of the EMLSR, and the jointly affiliated STA A1 of the receiving EMLSR switches to the listening operation state 241 similar to the other jointly affiliated STA A2 (listening operation state 242) of the EMLSR. Therefore, for each of the jointly affiliated STAs of the EMLSR, the state switching procedure is activated.

[0127] When one of the following conditions is met, the end of the frame exchange can be sensed by the non-AP MLD (here, the non-AP MLD 120): (1) During the timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, which starts at the end of a PPDU (e.g., acknowledgment 256) transmitted by the STA affiliated with the non-AP MLD as a response to the frame (e.g., A-MPDU frame 255) most recently received from the AP affiliated with the AP MLD, or at the end of the reception of a PPDU containing a frame from the AP to the STA affiliated with the AP MLD that does not require an immediate acknowledgment, the MAC of the STA affiliated with the non-AP MLD that received the Initial Control frame 245 did not receive a PHY-RXSTART.indication primitive. This indicates that the actual exchange with the AP MLD has ended without receiving subsequent frames from the AP MLD. (2) During the timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, which starts at the end of a PPDU (e.g., acknowledgment 256) transmitted by the STA affiliated with the non-AP MLD as a response to the frame (e.g., AP-MPDU frame 255) most recently received from the AP affiliated with the AP MLD, or at the end of the reception of a PPDU containing a frame from the AP to the STA affiliated with the AP MLD that does not require an immediate acknowledgment, the MAC of the STA affiliated with the non-AP MLD that received the Initial Control frame 245 received a PHY-RXSTART.indication primitive, and the STA affiliated with the non-AP MLD did not detect any of the following frames within the PPDU corresponding to the PHY-RXSTART.indication: - An individually addressed frame having an RA equal to the MAC address of the STA affiliated with the non-AP MLD, - A trigger frame having one of the User Info fields addressed to the STA affiliated with the non-AP MLD, - A CTS-to-self frame having an RA equal to the MAC address of the AP affiliated with the AP MLD. - A Multi-STA BlockAck frame having one of the Per AID TID Info fields addressed to a STA affiliated with a non-AP MLD, - An NDP Announcement frame having one of the STA Info fields addressed to a STA affiliated with a non-AP MLD, This is to handle the case where, after an actual exchange with the AP MLD, the non-AP MLD receives another frame not addressed to itself from the AP MLD (e.g., no data addressed to itself or no resources allocated to itself). (3) A STA affiliated with a non-AP MLD that has received the Initial Control frame 245 does not respond to the most recently received frame (e.g., the A-MPDU frame 255) from an AP affiliated with an AP MLD that requires an immediate response after the SIFS.

[0128] Since the non-AP MLD 120 has entered the EMLSR listening operation mode, the AP MLD can start a new frame exchange sequence (with either the non-AP MLD 120 or 130) by transmitting a new Initial Control frame.

[0129] In the example of the figure, the AP MLD110 decides to start such a new sequence again with the non-AP MLD 120 using its co-affiliated STA A2 122 of the EMLSR. Specifically, the AP MLD110 sends a new Initial Control frame 265 IC(A) that explicitly triggers the non-AP MLD A120 using another affiliated AP112, and this frame is received by the co-affiliated STA A2 122 of the EMLSR. The receiving co-affiliated STA A2 122 of the EMLSR 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 the EMLSR frame exchange mode, the receiving co-affiliated STA A2 122 of the EMLSR switches from the listening operation state 242 to the active frame exchange state 272, and the other co-affiliated STA A1 121 of the EMLSR simultaneously switches from the listening operation state 241 to the inactive frame exchange state 271. Thereafter, frames 275, 276 are exchanged during the frame exchange sequence until the end of the sequence where the non-AP MLD120 returns to the listening operation mode of the EMLSR.

[0130] The A-MPDU255 / 275 is provided only by way of example. For example, other types of frames such as a basic trigger frame for triggering UL transmission can be sent by the AP MLD. FIG. 2 shows a frame exchange where the acknowledgment 256 / 276 is composed of a single frame 255 / 275, but a simpler frame exchange may include only a single frame sent by the AP MLD without an acknowledgment, and a more complex frame exchange may include multiple exchange sequences, for example, cascaded TXOPs (Transmit Opportunities) of UL transmission (triggered by a basic trigger frame) and / or DL transmission (via a HE MU PPDU).

[0131] In this example, the advantages of the EMLSR mode in terms of throughput and latency are shown. Since the AP MLD can quickly switch from one link to another, it can improve communication performance while suppressing increases in complexity and cost.

[0132] In this example, the AP MLD 110 starts a frame exchange sequence with one or more specified non-AP MLDs. The D2.0 standard also permits a non-AP MLD to start a frame exchange sequence with an AP MLD. In other words, a STA affiliated with a non-AP MLD operating in the EMLSR mode does not need to transmit an Initial Control frame to start a frame exchange with the AP MLD. Such an affiliated STA accesses the wireless medium according to the rules defined in Section 10.3.2.4 (Setting and Resetting of NAV) and Section 10.23.2 (HCF Contention-Based Channel Access (EDCA)).

[0133] However, conventional medium access mechanisms (e.g., TWT or rTWT described later) are not defined with respect to the particularities of an EMLSR-active MLD (especially the state of co-affiliated STAs). It should be recalled that an EMLSR-compliant non-AP MLD becomes EMLSR-active after successfully exchanging an EML OM Notification frame with an EMLSR-compliant AP MLD. In this frame, the EMLSR Mode subfield in the EML Control field is set to 1, the EMLSR link is specified, and the corresponding co-affiliated STAs of the EMLSR are specified.

[0134] As described above, the foregoing description also applies to the EMLMR mode with the following matching in implementation, in particular: the EMLMR Delay is applied to both the EMLSR Padding Delay and the EMLSR Transition Delay; the Initial frame of the EMLMR mode matches the Initial Control frame of the EMLSR mode, and similarly the Initial frame response of the EMLMR mode matches the Initial Control frame response of the EMLSR mode; although not defined in the D2.0 standard, the EMLMR listening operation state / mode can be defined to match the EMLSR listening operation state / mode in which the co-affiliated EMLSR listens to their links before the aggregation of physical radio resources.

[0135] More generally, according to the implementation of the present invention, the following delays are defined to specify the timing of the EML switching operation. This standard is insufficient to provide guidance on these timings. Some of the EML Capabilities subfields in the Common Info field of the Basic Multi-Link element defined in the standard are reused for the newly defined delays.

[0136] "EML active switch delay"

[0137] The "EML active switch delay" is defined as the transition period required for the non-AP MLD to switch the state of the affiliated station from the awake or listening operation state to the active or inactive frame exchange state. The EML active switch delay ensures that the non-AP MLD has completed the switching operation before the frame exchange triggered by the AP MLD.

[0138] This delay is called the "EMLSR active switch delay" in the case of EMLSR operation and the "EMLMR active switch delay" in the case of EMLMR operation.

[0139] In the implementation of the active switching delay of EMLSR, EMLSR active switching delay = EMLSR Padding Delay + aSIFSTime + Transmission time of the Initial Control response frame: "EMLSR Padding Delay" is a 3-bit subfield of the EML Capabilities subfield in the Common Info field of the Basic Multi-Link element; "aSIFSTime" is the nominal time (in microseconds) required from when the MAC and PHY receive the end of a PPDU until the MAC and PHY process the frame within it and respond at the start of a PPDU containing a response frame as soon as possible, "Transmission time of the Initial Control response frame" is the time of the shortest Initial Control response frame used in the EMLSR link determined by the EMLSR Padding Delay by the non-AP MLD.

[0140] In the implementation of the active switching delay of EMLMR, EMLMR active switching delay = EMLMR Delay + aSIFSTime + Transmission time of the Initial response frame: "EMLMR Delay" is a 3-bit subfield of the EML Capabilities subfield in the Common Info field of the Basic Multi-Link element, "Transmission time of the Initial response frame" is the time of the shortest Initial response frame used in the EMLMR link determined by the EMLMR Delay by the non-AP MLD.

[0141] "EML transition delay (or EML de-active switch delay)"

[0142] "EML transition delay" is defined as the transition period required for a non-AP MLD to switch the state of an affiliated station from the active or inactive frame exchange state to the awake or listening operation state. The EML transition delay is useful for an AP MLD to determine when a non-AP MLD is ready to receive a subsequent Initial(Control) frame on any one of the EML links.

[0143] This delay is called "EMLSR transition delay" in the case of EMLSR operation and "EMLMR transition delay" in the case of EMLMR operation.

[0144] In an implementation, the EMLSR transition delay is a 3-bit sub-field of the "EMLSR transition delay" in the EML Capabilities sub-field.

[0145] In an implementation, the EMLMR transition delay is a 3-bit sub-field of the "EMLMR Delay" in the EML Capabilities sub-field.

[0146] In another embodiment, the EMLMR transition delay is determined as follows: EMLMR transition delay = EMLMR Delay + aSIFSTime + transmission time of the Initial response frame: "EMLMR Delay" is a 3-bit sub-field of the EML Capabilities sub-field "Transmission time of the Initial response frame" is the time of the shortest Initial response frame used on the EMLMR link estimated by the AP MLD.

[0147] The time of the Initial response frame may vary depending on the Initial frame. The AP MLD may estimate the time of the shortest Initial response frame (e.g., the CTS frame of the non-HT PPDU with the highest rate in the BSSBasicRateSet parameter) used on the EMLMR link.

[0148] In the case of non - AP MLD in EMLSR mode, the time to switch from the awake / listen operation to the frame exchange operation (EMLSR active switch delay) and the time to switch back from the frame exchange operation to the awake / listen operation (EMLSR transition or inactive switch delay) may be different or equal.

[0149] In the case of non - AP MLD in EMLMR mode, the time to switch from the awake / listen operation to the frame exchange operation (EMLMR active switch delay) and the time to switch back from the frame exchange operation to the awake / listen operation (EMLMR transition or inactive switch delay) may be different or equal.

[0150] Non - AP MLD can determine the value of the EMLMR Delay sub - field so as to satisfy the constraints related to both the EMLMR active switch delay and the EMLMR transition delay (for example, EMLMR Delay can correspond to the maximum value among the minimum allowable values of the EMLMR active switch delay and the EMLMR transition delay).

[0151] To explain the EMLMR operation according to an embodiment of the present invention, refer to the exemplary frame exchange sequence shown in FIG. 2.

[0152] Within a TXOP started by an AP affiliated with an AP MLD to which an EMLMR STA affiliated with a non - AP MLD acts as a TXOP responder, if any of the following conditions is satisfied and this is defined as the end of the frame exchange sequence, after the EMLMR transition delay (for example, "EMLMR Delay" or "EMLMR Delay + aSIFSTime + transmission time of the Initial response frame" as described above), the non - AP MLD switches to the per - link spatial stream capability defined by the EHT Capabilities element or the latest OM (if present): - The MAC of a STA affiliated with a non-AP MLD that has received an Initial frame 245 starts at the end of a PPDU (e.g., an acknowledgment 256) transmitted by the STA affiliated with the non-AP MLD as a response to the most recently received frame (e.g., an A-MPDU frame 255) from the AP affiliated with the AP MLD, or starts at the end of the reception of a PPDU containing a frame from the AP to the STA affiliated with an AP MLD that does not require an immediate acknowledgment, and does not receive a PHY-RXSTART.indication primitive during a timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay. - The MAC of a STA affiliated with a non-AP MLD that has received an Initial frame 245 starts at the end of a PPDU (e.g., an acknowledgment 256) transmitted by the STA affiliated with the non-AP MLD as a response to the most recently received frame (e.g., an A-MPDU frame 255) from the AP affiliated with the AP MLD, or starts at the end of the reception of a PPDU containing a frame from the AP to the STA affiliated with an AP MLD that does not require an immediate acknowledgment, receives a PHY-RXSTART.indication primitive during a timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, and the STA affiliated with the non-AP MLD does not detect any of the following frames within the PPDU corresponding to the PHY-RXSTART.indication: ○ A unicast frame having an RA equal to the MAC address of the STA affiliated with the non-AP MLD ○ A trigger frame having one of the User Info fields addressed to the STA affiliated with the non-AP MLD ○ A CTS-to-self frame having an RA equal to the MAC address of the AP affiliated with the AP MLD ○ A Multi-STA BlockAck frame having one of the Per AID TID Info fields addressed to the STA affiliated with the non-AP MLD ○ One of the STA Info fields addressed to the STA affiliated with the non-AP MLD and the NDP Announcement frame with the sounding NDP - The STA affiliated with the non-AP MLD that has received the Initial frame 245 does not respond to the most recently received frame (e.g., the A-MPDU frame 255) from the AP affiliated with the AP MLD that requires an immediate acknowledgment response after the SIFS.

[0153] In the above paragraph, the EMLMR STA refers to the non-AP STA affiliated with the non-AP MLD on the EMLMR link, and the OM refers to the Operation Mode notification.

[0154] To meet the low-latency requirements of EHT and improve the operation efficiency of UL MU, existing mechanisms are reused and improved within the D2.0 standard, and other new mechanisms are added.

[0155] The Stream Classification Service (SCS) mechanism originally defined in the IEEE802.11aa standard was adapted to be included in the D2.0 standard. The SCS mechanism for multi-link enables the non-AP MLD to define (delay-sensitive) traffic streams identified by the SCS identifier (SCSID) and advertise them to the AP MLD. By adapting the SCS mechanism, it becomes possible to define the QoS requirements of the SCS stream through the so-called QoS Characteristics element. In particular, the SCS stream can be classified as belonging to the TID class in the corresponding uplink (UL) or downlink (DL) direction.

[0156] The Target Wake Time (TWT) mechanism originally defined in the IEEE802.11ah and 802.11ax standards has been adapted to be included in the D2.0 standard. This adaptation, known as restricted Target Wake Time (rTWT), schedules individual (and protected) service periods (SPs) for stations (affiliated to a non-AP MLD) to transmit latency sensitive traffic (e.g., SCS streams) on its BSS. The rTWT agreement is nothing but the Broadcast TWT agreement negotiated between the AP of the BSS of a given link and the non-AP stations associated with it. The non-AP stations establish membership in the AP's Broadcast TWT (or rTWT) schedule. The schedule can be defined for several TIDs (e.g., QoS characteristics identified through the SCS mechanism). The rTWT Service Periods (SPs) of the rTWT schedule during which protected exchanges of SCS traffic streams can occur are advertised in broadcast management frames (e.g., beacons) using the rTWT information (usually the Broadcast TWT ID (bTWT ID)) regarding the negotiated rTWT SP.

[0157] The SCS mechanism is negotiated between the initiator's non-AP MLD and the AP MLD, but for each link, there still exist mechanisms such as TWT and rTWT that are negotiated between the affiliated STA of the non-AP MLD's initiator and the corresponding affiliated AP of the AP MLD.

[0158] For a given link, the non-AP station establishes membership in the AP's broadcast TWT schedule, and the AP distributes the broadcast TWT parameter set to the non-AP station. The non-AP station is called the TWT scheduled station, and the AP is called the TWT scheduling station.

[0159] Negotiation to become a member of, or to end membership in, an rTWT schedule (more generally, a Broadcast TWT) is carried out by an exchange of frames that transmit a TWT element as shown below, with the Negotiation Type subfield set to 3 (Broadcast TWT). In particular, a non-AP STA MLD may request to become a member of a TWT schedule by sending a TWT Request frame containing the TWT element for a given rTWT schedule to the associated AP MLD.

[0160] The AP then advertises the scheduled Broadcast TWT (or rTWT) using the Broadcast TWT element in management frames such as beacon frames, FILS Discovery frames, and broadcast Probe Response frames.

[0161] Figure 3 shows the format of a TWT element 300 adapted to be used for r-TWT according to the D2.0 standard.

[0162] The TWT element 300 is identified by an Element ID 301 and includes a "Control" field 310 and a field 320 for transmitting TWT parameter information.

[0163] The "Control" field 310 allows, through the "Negotiation Type" field 311, notification of whether the TWT is a Broadcast TWT or an individual TWT agreement. Thus, the MSB of the Negotiation Type subfield 311 is the Broadcast field, and when the MSB of subfield 311 is 1, the TWT element 300 is called a Broadcast TWT element. The other fields are of less importance in this description.

[0164] The "TWT Parameter Information" field 320 includes a single "Individual TWT Parameter Set" field (not shown) in the case of an individual TWT, and one or more "Broadcast TWT Parameter Set" fields having the format 320a shown in the figure in the case of a Broadcast TWT (when the Broadcast field of the "Negotiation Type" subfield is 1).

[0165] The first field of the "Broadcast TWT Parameter Set" field 320a is a Request Type field 330 that includes the following: - When issued by a TWT scheduled STA, the TWT Request Type subfield 331 is set to 1. Otherwise, it is set to 0 by the TWT scheduling STA (AP); - A TWT Setup Command subfield 332 indicating the type of TWT command: Request, Suggest, Demand, Reject when issued by a non-AP STA, and Accept, Alternate, Dictate, Reject when issued by the TWT scheduling AP; - A Trigger field 333 for indicating whether the TWT SP indicated by the TWT element 300 includes a trigger frame (the Trigger subfield is 1 for trigger activation in the case of r-TWT). Such a TWT SP is called a trigger-enabled TWT SP, and a non-AP station cannot start data transmission therein without a prior trigger from the AP; - When the Broadcast TWT Recommendation field 336 is set to 4, it indicates that the TWT defined in the Broadcast TWT element 300 is a Restricted TWT (r-TWT). In that case, the Broadcast TWT element 300 is also called a restricted TWT element (r-TWT IE), and the Broadcast TWT Parameter Set 320a is also called a Restricted TWT Parameter Set - The other sub-fields are not that important: ○ The "Last Broadcast Parameter Set" sub-field 334 is set to 0 to indicate another Broadcast TWT Parameter set following this set. The "Last Broadcast Parameter Set" sub-field is set to 1 to indicate that this is the last Broadcast TWT Parameter Set of the Broadcast TWT element ○ The "Flow Type" sub-field 335 indicates whether the TWT is announced (the TWT scheduling AP waits to receive a frame from the TWT scheduled STA to signal its awake state) or not (in the "announce" mode, the Flow Type sub-field is 0 for r-TWT as the r-TWT is a trigger-enabled TWT).

[0166] The other fields of the Restricted TWT Parameter Set field 320a are used to define the time parameters of the rTWT schedule as follows: - The Target Wake Time (TWT) field 340 indicates the next time (in microseconds) at which a station participating in the rTWT schedule should wake up for the next rTWT SP; - The Nominal Minimum TWT Wake Duration field 350 indicates the minimum time that a TWT scheduled STA is expected to be awake after the start time of the TWT SP in order to complete the frame exchange during the TWT Wake Interval. The TWT Wake Interval of the rTWT SP is a value calculated from the TWT Wake Interval Mantissa 360 and the TWT Wake Interval Exponent 337. This is represented in the number of units defined by the Wake Duration Unit subfield 312 of the Control field 310, which is usually 256 μs, for example.

[0167] The other fields of the Restricted TWT Parameter Set field 320a are used to define parameters specific to the Broadcast and Restricted nature of the rTWT SP: - Broadcast TWT Info field 370 ○ This transmits the identifier of the rTWT schedule (i.e., the Broadcast TWT ID 373 (bTWT ID) used to identify rTWT SPs belonging to the same rTWT schedule). Since this identifier is non-zero, the AP can schedule multiple sets of Broadcast TWT SPs with different sets of TWT parameters; ○ This identifies, through the Broadcast TWT Persistence subfield 374, the number of Target Beacon Transmission Times (TBTTs) at which Broadcast TWT SPs corresponding to this Restricted (more generally Broadcast) TWT Parameter Set exist; ○ Also, when set to 1, it signals that the r-TWT scheduling AP is unlikely to accept requests from STAs within the BSS to establish new memberships of the corresponding schedule (identified by bTWT ID 373) through the Restricted TWT Schedule Full subfield 372; ○ Finally, it also signals whether the Restricted TWT Traffic Info field 380 exists (by setting the field 371 to 1) through the Restricted TWT Traffic Info Present field 371 - The Restricted TWT Traffic Info field 380 is specific to the restriction of Broadcast TWT for specific traffic. This field is mandatory (therefore, the field 371 is forced to be set to 1) when the Broadcast TWT is related to the SCS LL stream (otherwise, the Traffic Info is related to the TID). ○ This includes the Traffic Info Control field 381, which indicates whether the following fields 382 and 383 are provided (e.g., "valid"). The DL TID Bitmap Valid subfield 3811 (respectively, the UL TID Bitmap Valid subfield 3812) indicates whether the Restricted TWT DL TID Bitmap field 382 (respectively, the Restricted TWT UL TID Bitmap field 383) has valid information. ○ The Restricted TWT DL TID Bitmap field 382 (respectively, the Restricted TWT UL TID Bitmap field 383) identifies TIDs (e.g., the TIDs permitted by rTWT as defined by the Restricted TWT element 300) as latency-sensitive traffic in the DL (respectively, UL) direction. The TID may define an SCS stream. A value of 1 at bit position k of the bitmap indicates that TID k is classified as a latency-sensitive traffic stream for the given transmission direction.

[0168] The TWT SP of the rTWT schedule is uniquely identified by the tuple <bTWT ID, MAC address of the TWT scheduling AP>, where the TWT scheduling AP is the affiliated AP of the link of the AP MLD.

[0169] With this element included in the TWT Request frame, the initiator STA can request to become an r-TWT scheduled STA with respect to the AP by negotiating an r-TWT SP for low-latency traffic. For example, the initiator STA (affiliated with a non-AP MLD) can negotiate a wake TWT, a wake interval, and the SCS streams permitted by the rTWT. The AP (the affiliated AP of the AP MLD on its link) provides a TWT Response frame accepting or rejecting the request. In other words, the STA requests membership in the rTWT schedule.

[0170] The TWT Request frame transmits a TWT element in which the Negotiation Type subfield 311 is set to 3 and the TWT Setup Command field 332 is set to Request TWT, Suggest TWT, or Demand TWT. The Restricted TWT Parameter Set 320a indicates the Broadcast TWT ID 373 of the rTWT schedule for which the STA is requesting to participate. The AP may respond (TWT Response frame) by maintaining the existing rTWT schedule for its bTWT ID (no new one), or providing an alternative set of parameters indicated in the TWT Request frame, or creating a new rTWT schedule with a new bTWT ID.

[0171] When negotiation and membership are complete, a legacy TWT / rTWT scheduled STA in the awake state may enter the Doze state and wake back up at the rTWT start time upon receiving a Beacon frame with a Restricted TWT element indicating the presence of an rTWT schedule, as advertised by the rTWT SP (e.g., via a Beacon frame). The Beacon frame indicates that the TWT scheduling AP will transmit a Trigger frame or an rTWT SP will transmit a DL BU to the TWT scheduled STA on that link.

[0172] At the start of each TWT / rTWT service period, expecting the TWT scheduled station to be in the awake state, the TWT scheduling AP typically uses OFDMA multi-user techniques (e.g., MU UL trigger-based transmission, MU DL transmission) to manage the rTWT SP and may allocate resource units to all or some of the TWT scheduled stations in the awake state.

[0173] Figure 4 shows a specific embodiment of the EMLSR operation mode in a non - AP MLD120 that negotiates an rTWT service with one of the AP MLD110 and EMLSR links (e.g., link 151) using a frame sequence. Of course, here the EMLSR mode is emphasized as an example, but similar considerations can be made for the EMLMR mode.

[0174] At the beginning of the sequence, the non - AP MLD enters the EMLSR listening operation mode, the co - affiliated STAs of the EMLSR are set to the listening operation mode, and they simultaneously listen to their respective EMLSR links. In response to receiving an EML OM Notification frame with the EMLSR Mode sub - field (in the EML Control field) set to 1, the non - AP MLD can enter the EMLSR listening operation mode. As a variant, the non - AP MLD can enter the EMLSR listening operation mode by switching back from the EMRSR frame exchange mode.

[0175] As shown by the EMLSR - active non - AP MLD120 in the EMLSR listening operation mode of Figure 4, both the EMLSR co - affiliated STAs A1 121 and A2 122 are in the listening operation states 410 and 411.

[0176] In the example of Figure 4, the EMLSR co - affiliated STA A1 is selected as the station that negotiated the rTWT schedule on link 151. It can be a station with a full radio or a station with a light (function - reduced) radio.

[0177] The non-AP MLD120 can simultaneously listen on its EMLSR link by putting the co-affiliated STAs of the corresponding EMLSRs to which those links belong into the "awake" or "listening operation" state. For example, the affiliated STAs A1 and A2 are in the listening operation state (see 410, 411). The listening operation includes CCA (Clear Channel Assessment) and receiving the Initial Control frame of the frame exchange initiated by the AP MLD. In the non-AP MLD120, the co-affiliated STAs of two EMLSRs thus simultaneously listen not only for the Initial Control frame from the AP MLD but also for the beacon frame (because such beacon frames are also radiated in a low MCS and non-non-HT format).

[0178] Therefore, by receiving the beacon frame 430, the affiliated STA A1 can determine the individual transmission window (rTWT) to be reserved for its own device on the link 151.

[0179] And at the start of this reserved rTWT service period, the AP MLD110 attempts to start a frame exchange with one or more non-AP MLDs on one of the EMLSR links and starts the frame exchange by transmitting an Initial Control frame 445 that explicitly triggers the non-AP MLD.

[0180] The co-affiliated STA of the EMLSR of the non-AP MLD that receives the frame explicitly triggered by the Initial Control frame 445 (for example, the affiliated STA A1 in the embodiment) starts the state change of the co-affiliated STA of the EMLSR of the non-AP MLD to be considered (for example, the state change of the affiliated STAs A1 and A2 in the embodiment) and transmits an Initial Control frame response (IC resp.) 446 to the AP AP1 affiliated with the AP MLD110.

[0181] When response 446 is sent, after the EMLSR active switching delay 499a, the non-AP MLD 120 switches to the EMLSR frame exchange mode, the co-affiliated STA A1 121 of the EMLSR switches from the listening operation state 410 to the active frame exchange state 420, and the co-affiliated STA A2 122 of the EMLSR simultaneously switches from the listening operation state 411 to the inactive frame exchange state 421.

[0182] Then, frames 455 and 456 are exchanged during the frame exchange sequence until the end of the sequence in which the non-AP MLD 120 switches back to the EMLSR listening operation mode.

[0183] Normally, the affiliated AP1 111 can send the basic trigger frame 455 to the co-affiliated STA A1 121 of the EMLSR to allocate an uplink resource unit for the non-AP MLD 120. In such a case, via the co-affiliated STA A1 121 of the EMLSR, the non-AP MLD 120 sends an EHT TB (Extremely High Throughput Trigger-Based) PPDU 456 in its allocated resource unit.

[0184] When the frame exchange on link 151 ends, the non-AP MLD 120 restarts the state switching procedure to return the co-affiliated STAs A1 121 and A2 122 of the EMLSR to the listening operation states 410 and 411. Therefore, the non-AP MLD120 switches back to the EMLSR listening operation mode. The switch-back 499b operates for only the EMLSR transition delay (specified in the EML Capabilities) after the end of the frame exchange during the service period.

[0185] When the AP1 111 affiliated with the AP MLD 110 transmits an Initial(Control) frame to initiate frame exchange with at least one non-AP MLD operating in the EMLSR mode and at least one non-AP MLD operating in the EMLMR mode, the AP shall ensure that the padding period of the Padding field of the Initial Control frame is greater than or equal to the maximum value of the values indicated in the EMLSR Padding Delay subfield and the EMLMR Delay subfield of the Basic Multi-Link element received from the non-AP MLD where the frame exchange was initiated. The transition period 499a falls within the delay generally referred to as the "EML active switch delay" from the perspective of the AP and is composed of the maximum values of the "EMLSR active switch" delay and the "EMLMR active switch" delay of the triggered station from the perspective of an individual STA MLD120.

[0186] In other words, the AP1 111 affiliated with the AP MLD 110 transmits an Initial frame to trigger frame exchange with at least one non-AP MLD operating in the EML Single-Radio (EMLSR) mode and at least one non-AP MLD operating in the EML Multi-Radio (EMLMR) mode. The AP MLD shall ensure that the padding period of the Padding field of the Initial frame is greater than or equal to the maximum value of the values indicated in the EMLSR Padding Delay subfield received from at least one non-AP MLD operating in the EMLSR mode and the EMLMR Delay subfield received from at least one non-AP MLD operating in the EMLMR mode.

[0187] The exemplary scenario of FIG. 4 shows that the EML operating mode and the TWT (e.g., rTWT) mechanism theoretically function in combination. As a result, the EML station can transmit latency-sensitive streams in individual transmission windows (rTWT) reserved for the EML station. However, there are still defects in the overall resulting mechanism: - The Initial Control frame 445 that explicitly triggers the non-AP MLD and the corresponding response 446 provide significant overhead within the critical resources for latency-sensitive streams. - To utilize the scheduled rTWT SP, the EML STA must know when the SP will occur: Therefore, the EML STA must also receive beacons, which are not yet envisioned in the 802.11be standard.

[0188] Generally, mechanisms and procedures that operate on a link-by-link basis, such as the exemplary Target Wake Time (TWT) and its most recent adaptation known as Restricted Target Wake Time (rTWT), may not fully adapt to EML modes where the EML SR and EML MR links are not completely independent.

[0189] After the first affiliated STA of the EML non-AP MLD negotiates the media access service or mechanism on the first link of its EML link, it has been required to efficiently manage the EML mode of the EML non-AP MLD. If such a mechanism (link-specific procedure) is determined based on the reception of beacon frames on the first link by the first affiliated STA, the latter should not be in blind mode during the reception of beacon frames. Therefore, the second affiliated STA of the same EML non-AP MLD should not be communicating via the second other link of the EML link during that period.

[0190] Typically, in a TWT schedule where an initiator non-AP station (e.g., STA A1) has established membership with the AP of a BSS (AP111), the affiliated STA (A1) must be awake (on link 151) for receiving beacon frames indicating the TWT service period, and thus must be available at the early start of the service period arriving in this rTWT schedule.

[0191] Further embodiments are described with respect to TWT (rTWT), but the present invention can be extended to other link-specific procedures and should not be limited to the TWT mechanism. As an example, a Quiet element corresponding to a scheduled quiet interval to protect r-TWT SP is also a mechanism specialized for each link (i.e., link-specific procedure).

[0192] Exemplary embodiments of the present invention are shown in FIGS. 5, 6a, 6b, and 6c.

[0193] FIG. 5 shows, using a flowchart, the steps (service period schedule acquisition and channel access procedures) performed by an EMLSR-active non-AP MLD to operate a TWT service according to an embodiment of the present invention. FIGS. 6a and 6b schematically show exemplary timelines of TWT operations as described in FIG. 5.

[0194] For simplicity of explanation, mainly only the EMLSR mode is referred to, but the same applies to the EMLMR mode.

[0195] This process starts at step 500, where the non-AP MLD enters the (EMLSR or EMLMR) listening operation mode, which means that its associated STA is set to the listening operation state, and thus, it is simultaneously listening on each of the (EMLSR or EMLMR) links. The non-AP MLD can enter the listening operation mode 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.

[0196] At step 510, the non-AP MLD waits (uplink) until it buffers latency-sensitive data to be sent to the AP MLD110. It can also consider latency-sensitive data (triggered direct link data) to be sent to other non-AP MLDs through the direct link under the control of the AP MLD110. As described above, such data is provided by the upper layer and can be stored in the buffer 210 of the non-AP MLD. The non-AP MLD determines the TWT negotiation to be activated on one of the EMLSR or EMLMR links (link 151 is one of the links selected in FIGS. 6a and 6b).

[0197] In some embodiments, when the TID-To-Link mapping is negotiated between the AP MLD and the non-AP MLD, mapping some TIDs to one set of links and some other TIDs to another set of links, the buffered latency-sensitive data corresponds to the TIDs permitted to be transferred on the selected link and is indicated in the bitmaps 3811 and / or 3912 of the TWT element 320a in the rTWT format.

[0198] In response to successfully establishing the TWT mechanism via the first link, a scheduling operation (identical to step 550, further described) regarding the reception date of the next beacon frame (i.e., the occurrence of the next TBTT) can be executed.

[0199] Next, in test step 520, due to various events, the non-AP MLD can perform the EML setting by itself according to the embodiment. This can be the detection of a beacon frame on the relevant link (the selected link, e.g., 151), or an EML event scheduled according to the present invention (e.g., an EML event scheduled before the start of the TWT service period).

[0200] EML events related to the reception of the Beacon frame (actual reception and / or scheduled events before the TBTT of the link) are processed through steps 530 to 550.

[0201] In fact, in that case, the non-AP MLD shall not perform frame exchange on the EMLSR or EMLMR link.

[0202] Various configurations are possible in step 530: - If there is no activity on any link, the non-AP MLD initiates a state transition procedure and continues in a listening operation mode where the co-affiliated STAs are obliged to maintain this listening mode until the reception of the beacon frame ends (steps 531 and 532). Further, these EML co-affiliated STAs must ignore the Initial Control frames addressed to their own device that temporally overlap with the beacon frame transmitted on the selected link (TBTT on the intended link). As an alternative embodiment, a selected co - affiliated STA (e.g., Link 1 151 corresponding to the selected link where a beacon frame is to be transmitted) is switched from a listening operation state to an active frame exchange state (step 531) so that it can perform frame exchange (even if it intends to receive a beacon frame). On the other hand, in parallel (synchronously or simultaneously), another co - affiliated STA of the link set of the EMLSR or EMLMR (e.g., one of Link 2) is switched from a listening operation state to an inactive frame exchange state (step 532). Thereby, reception of IC frames on other links is easily avoided. This case is shown in the sub - sequence "Case C" of FIG. 6c. - When there is a frame exchange on other EML links, co - affiliated STAs of other links are required to end their participation in the TXOP (Transmit Opportunity) and enter an EML mode suitable for receiving beacon frames. This case is shown in the sub - sequence "Case A" of FIG. 6a. The non - AP MLD initiates a state - switching procedure for each co - affiliated STA of the EMLSR or EMLMR and switches them back to the EML listening operation state. Thereby, the co - affiliated STA1 121 can be in a state where it can normally receive the beacon frame 430. - When there is a frame exchange on the selected EML link, the co - affiliated STA of the transmitting - side EMLSR (selected link) remains in the active frame exchange state and waits for the medium to return to the idle state (it can end the existing TXOP as the legacy station does when the TBTT time issuance is approaching). Co - affiliated STAs of other EMLSRs also maintain their current state (inactive, step 532). This sustains the reception of beacon frames. This case is shown in the sub - sequence "Case B" of FIG. 6b.

[0203] In other words, in step 530, the configuration of the selected co - affiliated STA or the first affiliated station (corresponding to the selected link or the first link, e.g., link 1 151, for which the beacon frame is to be transmitted) by the non - AP MLD120 includes the following: - Case A: End the ongoing frame exchange via the second link of the EML link and switch the first affiliated station to an operating state suitable for receiving the second beacon frame (e.g., in the first variant, by switching the first affiliated station to a listening operating state, in which case the second affiliated station triggers a frame exchange sequence via the second link and ignores any Initial frames that temporally overlap with the first beacon frame on the first link; in the second variant, by switching the first affiliated station to an active frame exchange state); or - Case B: End the ongoing frame exchange via the first link and maintain the first affiliated station in an active frame exchange state (e.g., maintain when the time distance to TBTT is less than a predetermined threshold, which in a particular embodiment is at least the sum of the (first) transition period required for the non - AP MLD to switch the state of its affiliated station from the listening operating state to an active or inactive frame exchange state and the (second) war - record period required for the non - AP MLD to switch the state of its affiliated station from an active or inactive frame exchange state to the listening operating state), or - Case C: Switch the first affiliated station from the listening operating state to an active frame exchange state.

[0204] As a result, in step 540, the co - affiliated STA of the selected EMLSR can receive the Beacon frame and analyze its content.

[0205] As an example of the content related to this embodiment, the TWT Information element 300 can be analyzed to verify the scheduling of the TWT service period (e.g., wake TWT and wake intervals via fields 340, 360, 337).

[0206] To quiet the STA during the r-TWT service period, the r-TWT scheduling AP can schedule a quiet interval that overlaps with the r-TWT SP of a given link. The overlapping quiet intervals can be scheduled by including one or more Quiet elements in the Beacon frame. Thus, the Quiet element is another example of the content related to this embodiment: namely, the non-AP MLD shall not transmit during any quiet interval. Further, the non-AP MLD thus determines that it must quiet one of its co-affiliated STAs during the quiet intervals corresponding to r-TWT service periods to which the non-AP MLD is not a member.

[0207] Next (step 550), the non-AP MLD can schedule an EML event in response to the mechanism determined through the Beacon frame.

[0208] First, the non-AP MLD schedules to wake up for the next TBTT on the selected link.

[0209] In other words, when the next TBTT occurs (considering that the occurrence of the current TBTT is related to the first Beacon frame), test step 520 is performed again, and steps 530 to 550 are performed again to indicate the detection of the EML event related to the next (second) Beacon frame. Thus, the non-AP MLD implements a communication method including the following: - Receiving, by a first affiliated station (e.g., STA A1), a first beacon frame via a first link (e.g., 151) of an EML link, wherein the first beacon frame includes a target beacon transmission time (TBTT) associated with a second beacon frame - Configuring, for receiving the second beacon frame, the first affiliated station (e.g., STA A1) to be in a receiving state at the TBTT

[0210] Optionally, after association with an AP MLD, it is considered that a non-AP MLD schedules events for TBTT timing on all EML links: this is to enable determination of link-specific procedures (e.g., Quiet elements for non-member TWT) for all EML links. If the link-specific procedure is negotiated in step 510, the non-AP MLD may schedule itself for beacon frames on the selected link for the first discovery of a TWT / rTWT element indicating the service period of the TWT service it negotiated.

[0211] Regarding further beacon TBTT scheduling related to TWT operation, a non-AP MLD may relax the constraints of each TBTT of the selected link: The notification of the Broadcast TWT Persistence subfield 374 can enable determination of the number of target beacon transmission times (TBTTs) for which there is a Broadcast TWT SP corresponding to this Restricted (more generally, Broadcast) TWT Parameter set, and thus intermediate TBTTs may be ignored (only the beacon frame of the last TBTT of the persistence information may contain new information).

[0212] In other words, in the context where the non-AP MLD sets the first affiliated station (e.g., STA A1) to be in the receiving state at the TBTT for receiving the second beacon frame, the second beacon frame includes another TBTT related to the third beacon frame that schedules the TWT service period on the first link. When the scheduled TWT service period is signaled with TWT persistence, the frame exchange performed by the second affiliated station continues on the second link of the EML link without setting the first affiliated station to be in the receiving state at another TBTT for receiving the third beacon frame on the first link.

[0213] As is apparent from FIGS. 6a to 6c, the scheduled event is preferably before the issue date and time (of the beacon frame or TWT period) so that "EML active switching delay" 499 / 499a etc. do not occur.

[0214] This is because the simultaneous switching defined previously and indicated by reference numeral 499 / 499a in the figure lasts for at most the EMLSR or EMLMR active switching delay time. In an embodiment, the EMLSR co-affiliated STA A1 is selected. It may be a station with a complete radio or a station with a light (function-reduced) radio. In practice, the switching of the EMLSR co-affiliated STA with a complete radio (requiring only antenna connection) is shorter than the switching of other EMLSR co-affiliated STAs with a light radio (because it requires physical and reconfiguration of the complete radio chain), so the non-AP MLD can adapt the scheduling to consider the appropriate timing 499 / 499a regarding its hardware configuration (e.g., reducing the scheduling margin of the link composed of a complete radio).

[0215] In addition, non-AP MLD can also adapt the scheduling to take into account the current activity before the relevant event: it can be assumed that the timing margin stops the existing TXOP (Figures 6a and 6b) before the handover delay 499 / 499a.

[0216] In fact, the scheduling operation is executed by the non-AP MLD at its upper MAC230. This is because this entity can collect management frame information from all links and accordingly configure the lower MAC entities 220-x / 220-y / 220-z. Since the upper MAC is responsible for frame decoding, it can obtain the TBTT of all links, and thus it is preferable for the U-MAC230 to control the activity of the L-MAC (for example, temporarily stop the activity on the medium or force the "listening" mode).

[0217] Also, as described in Figure 5, it is also conceivable to first stop the TXOP activity of the LL-MAC and then perform the EML setting switch.

[0218] When the reception of the beacon frame on Link 1 is completed, the non-AP MLD restarts the state switching procedure (step 590) to return its co-affiliated STA to the listening operation state. Therefore, the non-AP MLD switches back to the listening operation mode. The switchback operates only for the EMLSR transition delay (specified in the EML Capabilities) or the EMLMR transition delay (according to the implementation of the present invention described above) after the end of the frame exchange.

[0219] Returning to Test 520, the EML events scheduled in step 550 regarding the link-specific mechanism are processed through steps 560 to 580.

[0220] The purpose of step 560 is to set the non-AP MLD to an appropriate state on the associated link. Therefore, the state transition procedure is invoked for each co-affiliated STA of the EML, and thus: - If the scheduled EML event is associated with the (r-)TWT service period, the non-AP MLD aims to become active for that link when the (r-)TWT period starts. Therefore, the "first" link in step 561 is the link corresponding to the selected co-affiliated STA The STA affiliated with the non-AP MLD on the corresponding link (e.g., the co-affiliated STA A1 of the receiving EMLSR in the examples of FIGS. 6a and 6b) is set to be able to transmit or receive frames on the active link during the TWT service period (step 561). As will be further clarified, the co-affiliated STA A1 of the EMLSR does not need to receive the Initial Control frame for frame exchange, so it can save the resources of the TWT SP At the same time, the co-affiliated STAs of other EMLSRs of the same non-AP MLD (e.g., STA A2 in the examples of FIGS. 6a and 6b) are set not to transmit or receive on other EMLSR links until the TWT period ends. For this purpose, the state transition procedure is also activated for other co-affiliated STAs of the EMLSR, and by this state transition procedure, other co-affiliated STAs of the EMLSR are switched from the listening operation (step 562) to the "blind frame" or "invalid frame exchange" state - If the scheduled EML event is associated with the Quiet element of the (r-)TWT service period, the non-AP MLD aims to become inactive for that link when the quiet period starts Therefore, the jointly affiliated STAs (e.g., STA A1 in the example belonging to the link where the beacon frame was issued) of the selected EMLSRs of the same non-AP MLD are set not to transmit or receive until the frame exchange is completed (step 562). The jointly affiliated STAs of other EMLSRs of the same non-AP MLD may be switched to the listening operation state (if possible by hardware to complement the invalidation of one link), or, better yet, at most one of the jointly affiliated STAs of other EMLSRs of the same non-AP MLD (e.g., STA A2 in the example) switches from the listening operation state to the "active frame exchange" or "valid frame exchange" state (step 561). In other words, in the above context where the non-AP MLD sets the first affiliated station (e.g., STA A1) to the receiving state at the TBTT to receive the second beacon frame, the second beacon frame schedules a quiet period on the first link, and at the time of the quiet period, switches the first affiliated station to the invalid frame exchange state until the quiet period ends. Further, when the quiet period arrives, the non-AP MLD switches the second affiliated station to the valid frame exchange state on the second link of the EML link until the quiet period ends.

[0221] As already described, the "EML active switch delay" is preferably considered to enable the setting at an appropriate time.

[0222] The state switching of all co-affiliated STAs of the same non-AP MLD is indivisible and occurs simultaneously. This is because a complete wireless resource chain (see Figure 9a below) is allocated to one of the STAs, and the other STAs are deprived of the wireless resource chain. Regarding the EMLMR mode, the physical resources (such as antennas) of one wireless resource chain are allocated (aggregated) to other wireless resource chains, so the former is deprived of its transmit / receive capabilities (see Figure 9b below).

[0223] The above indicates that when the non-AP MLD operates in the EMLSR mode (more generally, either the EMLSR mode or the EMLMR mode), it is either in the listening operation mode (where its co-affiliated STA is in the listening operation state) or the frame exchange mode (where one of its co-affiliated STAs is in the active frame exchange state and the other co-affiliated STAs are in the inactive frame exchange state).

[0224] After the setting of step 560, step 570 (in the examples of Figures 6a and 6b, the co-affiliated STA A1 of the receiving EMLSR operates frame exchange on the active link (the first link) during the TWT service period) continues until step 580 (the end of the service period). This period is obtained from the TWT IE or the Quiet element.

[0225] In the case of TWT, the Nominal Minimum TWT Wake Duration field 350 indicates the minimum time that the TWT scheduled STA is expected to wake up from the start time of the TWT SP in order to complete frame exchange during the period of the TWT Wake Interval. Therefore, the fallback operates according to the EMLSR transition delay (specified in the EML Capabilities) after the end of the service period. This provides more space within the TWT SP for latency-sensitive data transmission.

[0226] An example of the frame exchange sequence is shown in the following figure.

[0227] Figures 6a and 6b show an extended frame exchange sequence for the TWT mechanism supported by the EMLSR station according to the present invention. For ease of explanation of the figures, only the EMLSR mode is mainly referred to, but the same applies to the EMLMR mode.

[0228] In an embodiment, the co - affiliated STA1 121 of the EMLSR is selected as the relevant station in the per - link procedure. It may be a station with a complete radio or a station with a lite (function - reduced) radio.

[0229] The simultaneous switching continues with the maximum active switching delay of the EMLSR, as defined previously and indicated by reference numerals 499a / 499b in the figure. In practice, the switching of the co - affiliated STA of the EMLSR with a complete radio (requiring only antenna connection) is shorter than that of the co - affiliated STA of other EMLSRs with a lite radio (because it requires physical and re - configuration of the complete radio chain). Therefore, the value considered for 499a / 499b may correspond to the radio configuration of STA A1 (or their respective maximum values).

[0230] As shown by the EMLSR active non - AP MLD120 in Figure 6a, both the co - affiliated STAs A1 121 and A2 122 of the EMLSR have switched from a listening operation (not shown in the past) to a "blind frame" or "invalid frame exchange" state 610 for STA1 121 and an "active frame exchange" or "valid frame exchange" state 611 for STA2 122, respectively.

[0231] As described above with respect to step 530, both the end of TXOP participation by STA A2 and the handover following period 499b are considered here, in particular, to end phases 610 and 611. The end of the TXOP can be carried out in several ways, such as by shortening the data communication, or by not responding to the peer device (AP of link 2), or, if STA A2 is the TXOP holder, by issuing a CF-End frame.

[0232] As a result, when a non-AP STA affiliated with a non-AP MLD and operating on one of the paired EMLSR or EMLMR links aims to receive a broadcast management frame (beacon frame 430) on the first link (151), and when a second non-AP STA (STA A2) affiliated with the same MLD participates in frame exchange on a second link (152) that overlaps with the TBTT of the first link, the second non-AP STA (STA A2) and its associated AP (referred to as the second AP) should follow the following rules: - The second AP, as the TXOP holder of the second link (152), should ensure that its TXOP ends more than T time before the TBTT of the first link. - The second non-AP STA (STA A2), as the TXOP holder of the second link (152), should ensure that its TXOP ends more than T time before the TBTT of the first link.

[0233] In an embodiment, T is equal to any of the following values: - When two non-AP STAs belong to a pair of EMLSR links, the EMLSR transition delay (499b) indicated in the EMLSR Transition Delay subfield. - When two non-AP STAs belong to a pair of EMLMR links, the EMLMR delay specified for the pair of EMLMR links indicated in the EMLMR Transition Delay subfield (e.g., according to the implementation, the previously defined EMLMR inactive handover delay).

[0234] When multiple non-AP STAs are operating within the TXOP of the second link (152), the second AP, acting as the TXOP holder of the second link (152), should ensure that T is greater than or equal to the maximum individual T value (previously determined here) for those non-AP STAs.

[0235] In other embodiments, T is equal to either of the following values: - When two non-AP STAs belong to a pair of EMLSR links, the EMLSR transition delay (499b) indicated in the EMLSR Transition Delay subfield; - When two non-AP STAs belong to a pair of EMLMR links, the EMLMR delay + aSIFSTime + the transmission time of the Initial response frame (e.g., depending on the implementation, the previously defined EMLMR inactive switching delay).

[0236] The period of the Initial response frame can vary depending on the Initial frame. The non-AP MLD and the AP MLD can determine the period during which the shortest Initial response frame is used in the EMLMR link (e.g., the CTS frame of the highest rate non-HT PPDU in the BSSBasicRateSet parameter).

[0237] When multiple non-AP STAs are operating within the TXOP of the second link (152), the second AP, acting as the TXOP holder of the second link (152), should ensure that T is greater than or equal to the maximum individual T value (previously determined here) for those non-AP STAs.

[0238] Simultaneous switching (e.g., putting all co-affiliated STAs into the "listening" mode) lasts for at most the EMLSR active switching delay or the previously defined EMLMR active switching delay.

[0239] In other words, the setting of the selected co - affiliated STA or the first affiliated station (STA A1) (corresponding to the selected link or the first link, e.g., link 1 151, for which the beacon frame is to be transmitted) by the non - AP MLD120 is triggered by at least a first determined delay before the TBTT (e.g., the EMLSR active switching delay, the EMLMR active switching delay, or the maximum value of the EMLSR and EMLMR active switching delays).

[0240] This enables the reception of the beacon frame of link 1 (by STA A1). Additionally, other co - affiliated STAs of the EML (here STA A2) must ignore any Initial Control frames addressed to the device that temporally overlap with the beacon frame of the selected link (the TBTT of the intended link).

[0241] This mode can also be advantageous for receiving beacon frames via two EML links (when they are temporally synchronized).

[0242] When the beacon frame is received, all co - affiliated STAs of the EML can perform normal operations.

[0243] Next, the reservation period arrives (630).

[0244] Compared with Figure 4, it is assumed that the EML scheduler schedules the switching of STA1 to the "active frame exchange" or "valid frame exchange" state before the start of the intended TWT SP630. Usually, the switching delay 499 / 499a (belonging to the group including the EMLSR active switching delay, the EMLMR active switching delay, and the maximum value of the EMLSR and EMLMR active switching delays) occurs before TWT SP630.

[0245] Similar to Case A, when this TWT SP630 is applied, the activity of the medium on the EML link must be stopped (not shown).

[0246] As a result, when a non-AP STA affiliated with a non-AP MLD and operating on one of the pairs of EMLSR links or EMLMR links is a member of the R-TWT SP on the first link (151); if a second non-AP STA (STA A2) affiliated with the same MLD is not a member of another R-TWT SP on the second link (152) that overlaps with the first SP, the second non-AP STA (STA A2) and its associated AP (referred to as the second AP) should follow the following rules: - The second AP as the TXOP holder of the second link (152) should ensure that its TXOP ends before T time before the start time of the R-TWT SP of the first link; - The second non-AP STA (STA A2) as the TXOP holder on the second link (152) should ensure that its TXOP ends before T time before the start time of the R-TWT SP (630) on the first link.

[0247] In an embodiment, T is equal to any of the following values: - When two non-AP STAs belong to a pair of EMLSR links, the EMLSR transition delay (499b) shown in the EMLSR Transition Delay subfield, - When two non-AP STAs belong to a pair of EMLMR links, the EMLMR delay specified for the pair of EMLMR links shown in the EMLMR Transition Delay subfield (for example, according to the implementation, the EMLMR inactive switching delay defined above).

[0248] When multiple non-AP STAs are members of the R-TWT SP of a first link (151) and operate within the TXOP of a second link (152), the second AP, as the TXOP holder of the second link (152), should ensure that T is greater than or equal to the maximum individual T value of the non-AP STAs of which they are members (determined here previously).

[0249] In other embodiments, T is equal to any of the following values: - When two non-AP STAs belong to a pair of EMLSR links, the EMLSR transition delay (499b) indicated in the EMLSR Transition Delay subfield, - When two non-AP STAs belong to a pair of EMLMR links, the EMLMR delay + aSIFSTime + the transmission time of the Initial response frame (e.g., the previously defined EMLMR inactive switching delay according to the implementation).

[0250] The period of the Initial response frame can vary depending on the Initial frame. The non-AP MLD and the AP MLD can determine the period during which the shortest Initial response frame is used in the EMLMR link (e.g., the CTS frame of the highest rate non-HT PPDU in the BSSBasicRateSet parameter).

[0251] When multiple non-AP STAs are members of the R-TWT SP of a first link (151) and operate within the TXOP of a second link (152), the second AP, as the TXOP holder of the second link (152), should ensure that T is greater than or equal to the maximum individual T value of the non-AP STAs of which they are members (determined here previously).

[0252] The Initial(Control) frame 445 and the corresponding response 446 used to explicitly trigger non-AP MLD provide significant overhead within the critical TWT SP resources for latency-sensitive streams. Since the TWT SP has already been determined, the non-AP MLD can set its affiliated EML STA so that it is ready to operate between TWT SPs 630.

[0253] When non-AP MLD 120 desires to start a frame exchange sequence with AP MLD 110 within TWT SP 630 (where co-affiliated STA A1 121 of EML SR is selected as the co-affiliated STA of the transmitting EML SR in the negotiated TWT), non-AP MLD 120 switches co-affiliated STA A1 121 of EML SR from the listening operation state 410 to the active frame exchange state 620, and concurrently (synchronously or simultaneously) switches co-affiliated STA A2 122 of EML SR from the listening operation state 411 to the inactive frame exchange state 621.

[0254] The listening operation state is restored and becomes operable after the end of TWT SP 630 corresponding to the rollback (within the period 499b defined by the EML SR Transition Delay set in the EML Capabilities).

[0255] In other words, in the context above where the non-AP MLD configures the first affiliated station (e.g., STA A1) to be in a receiving state at the TBTT to receive the second beacon frame, the second beacon frame schedules the service period on the first link. When the frame exchange within the service period is completed, the non-AP MLD maintains the first affiliated station in an active frame exchange state until the end of the service period. In certain embodiments, the non-AP MLD switches the first affiliated station to active frame exchange before the start of the service period and maintains it in the active frame exchange state until the end of the service period. Further, at the end of the service period, the non-AP MLD switches the first affiliated station from the active frame exchange state to a listening operation state.

[0256] The co-affiliated STAs of the EMLSR switch back to the listening operation mode for the entire service period 630, regardless of the duration field of the frame (basic trigger 455) that triggered it (or more generally, after the end of the frame exchange with its AP). This can support multiple frame exchanges with the AP during the service period 630 (if any) without the overhead of further Initial (Control) frame / response EML enabling sequences.

[0257] Figure 6b shows a variation of the frame exchange sequence compared to Figure 6a, where the co-affiliated STAs A1 121 and A2 122 of the EMLSR start in the "active frame exchange" or "valid frame exchange" state 611 for STA1 121 and in the "blind frame" or "invalid frame exchange" state 610 for STA2 122, respectively.

[0258] Only the underlined sequence of "Case B" is different.

[0259] STA1 121 is already operating on the EMLSR link 151 for frame exchange with the AP MLD.

[0260] Normally, according to 802.11be D0.5, when a non-AP MLD STA starts a TXOP, after the end of the TXOP, the non-AP MLD returns to the listening operation of the EMLSR link after the period indicated in the EMLSR Transition Delay subfield (499b).

[0261] This rule is applicable to the current situation where the TBTT is next to the TXOP. As already discussed, the TXOP of link 151 can be shortened to respect the TBTT time of that link.

[0262] The embodiment provides that the non-AP MLD maintains the current EML setting until the beacon frame is received: to enable the reception of the beacon frame, the co-affiliated STAA1 remains in the valid frame exchange state 620a, and the co-affiliated STA A2 remains in the invalid frame exchange state 621a (this avoids the change of the EML mode due to the reception of the Initial frame during that period).

[0263] In a different operation, the non-AP MLD first determines the remaining time at TBTT, and based on that time, determines whether to return to the listening operation mode or remain in the current EMLSR frame exchange mode. For example, if the time is long (e.g., if its value is higher than the threshold), the co-affiliated STA of the EMLSR returns to the listening operation mode (thus, the situation of case C shown in FIG. 6c occurs). And if the time is short (e.g., if its value is lower than the threshold), the co-affiliated STA of the EMLSR maintains the current state.

[0264] FIG. 6c first shows an extended frame exchange sequence ( "Case C") regarding the support of beacon frames by the EML station according to the embodiment.

[0265] Embodiments provide that a non-AP MLD switches only the co-affiliated STA of one EMLSR to an active state (e.g., switches the co-affiliated STA of the selected EMLSR to an effective frame exchange state, and switches the co-affiliated STA of the transmitting EMLSR that is ineffective for the co-affiliated STAs of other EMLSRs).

[0266] In the figure, the co-affiliated STA (corresponding to the selected link for which the beacon frame is intended, e.g., link 1 151) is switched from the listening operation state to the effective frame exchange state 660 so that frame exchange (even just attempting to receive a beacon frame) can be performed. In parallel (synchronously or simultaneously), other co-affiliated STAs of the set of EMLSR or EMLMR links (e.g., one of link 2) are switched from the listening operation state 411 to the ineffective frame exchange state 661.

[0267] Figure 6c also shows an extended frame exchange sequence ("Case D") regarding the support of the quiet period for the rTWT mechanism by the EML station according to the present invention.

[0268] This corresponds to the application of step 561 to the event of the scheduled quiet period. In an embodiment, this may correspond to a quiet period that encloses a (r-)TWT service period that the EML station is not a member of.

[0269] In this context, activity at the first link (where the beacon was received and the quiet period for TWT was indicated) is prohibited. Thus, another EML link can be used to become active during that time.

[0270] Thereafter, following the EMLSR mechanism, after the EMLSR active switching delay 499, from the perspective of placing one of the EMLSR co - affiliated STAs operable for frame exchange on a link different from the prohibited first link, the non - AP STA schedules a switch from the EMLSR listening operation mode to the EMLSR frame exchange mode. The EMLSR co - affiliated STA including the first link 151 where STA A1 received the beacon frame is invalidated.

[0271] In this example, the EMLSR co - affiliated STA A2 is switched from the listening operation state 411 to the active frame exchange state 651, and in parallel (synchronously or simultaneously), the transmitting - side EMLSR co - affiliated STA A1 is switched from the listening operation state 410 to the invalid frame exchange state 650.

[0272] Figures 7 and 8 show, using flowcharts, the steps that an EMLSR - active non - AP MLD executes to set up the TWT service. Basically, step 510 for determining an EML co - affiliated STA permitted to negotiate link services is detailed.

[0273] Figure 7 provides guidance when the TWT service has already been set up before the EML operation is about to be activated.

[0274] As an example, the non - AP MLD has one TWT service established on link 151 for co - affiliated STA A1 (step 710).

[0275] Step 720 corresponds to step 500 and means that the non - AP MLD attempts to operate in the EMLSR / EMLMR mode, activates the EMLSR / EMLMR mode, and an EML Operating Mode Notification frame indicating co - affiliated STAs A1 and A2 is successfully transmitted to the non - AP MLD 120.

[0276] Step 730 is for the purpose of indicating to the AP that, according to an embodiment, one of the EML links must be monitored for both the EML operation and per-link mechanisms (such as TWT). The purpose of such notification is for the AP to avoid link contention for the events to be monitored. In an embodiment, since the AP MLD controls the TWT and beacon schedules of all active links, the MLD AP is warned to avoid scheduling the TWT SP of the EML SR STA that overlaps with the beacons of other EML SR links. In other words, the non-AP MLD sends a notification to the AP MLD to schedule (on the first link) a service period of the non-AP MLD that does not temporally overlap with the beacon frame transmitted by the AP MLD on the second link of the EML link in future beacon frames. Such a notification guarantees that the non-AP MLD can receive the beacon frame via the second link 152 regardless of the service period scheduled on the first link 151.

[0277] As an exemplary support for such notification, there is bit B15 (338) of the TWT Request subfield 331 of the TWT element 300. Thus, the "EML" field 338 can indicate whether the TWT SP indicated by the TWT element 300 operates on a link where the EML operation is enabled and the non-AP MLD originator of the TWT element requests assistance from the AP to avoid EML link contention. (The AP is required to avoid scheduling the r-TWT SP for the EML STA that overlaps with the beacons on other EML links.)

[0278] FIG. 8 briefly illustrates the steps performed by a non-AP MLD attempting to limit the use of TWT services via a given number of links. Even if more links can be managed, it may seem complex and inefficient (because there are too many EML active / interrupted period switches).

[0279] In step 810, the EML non-AP MLD is already operating in the EML (EMLSR or EMLMR) mode. The non-AP MLD receives an internal request (e.g., from a local application on top of the MAC) to open a new TWT service. By increasing the number of links for which the EML event (step 550) is scheduled, the EML operating mode according to the previous embodiments (cases A to C in the previous figures) can be periodically forced. Thus, the non-AP MLD may be required to interrupt the existing TXOP more frequently. This can also occur frequently when the TBTT interval of the link is short.

[0280] If the number of links is more than the desired number, the non-AP MLD may reject the new (r)TWT of other links. The algorithm stops. Otherwise, the non-AP MLD may close the existing rTWT service on the first link (step 820) and reinstall it by adding it to the new upcoming TWT service on the second link (step 830). As an example from FIGS. 6a to 6c, this means that all TWT services are placed on a single link (here link 151).

[0281] In summary, the above-described embodiment provides that when a STA affiliated with the non-AP MLD attempts to receive a beacon frame scheduled at the TBTT on one (the first) link of its EML (EMLSR or EMLMR) links, the non-AP MLD must make it possible to listen on the EML (EMLSR or EMLMR) link. Thus, the following rules must be satisfied: - If another STA affiliated with the same non-AP MLD successfully obtains a TXOP on another link of the EML (EMLSR or EMLMR) link, the TXOP should be terminated before the TBTT of that (the first) link (see FIG. 6a, case A) - If the same STA affiliated with the same non-AP MLD is part of a TXOP on the intended (first) link of an EML (EMLSR or EMLMR) link, that STA may remain awake on that link until the TBTT (see Figure 6b, Case B). - A STA affiliated with the same non-AP MLD that is in a listening state on an EML (EMLSR or EMLMR) link must ignore Initial Control frames addressed to itself that overlap with the TBTT on the intended (first) link (e.g., temporally overlap with a beacon frame transmitted at the TBTT on the first link).

[0282] The reception of a beacon frame on one EML (EMLSR or EMLMR) link is satisfied if any of the following conditions are met: - A TWT or rTWT agreement is established on that EMLSR link - A Quiet element corresponding to a quiet interval is scheduled to protect the r-TWT SP.

[0283] Figure 9 schematically shows a possible architecture of an MLD for EMLSR. In this figure, as an example, the case where two non-AP STAs share the hardware resources of a non-AP MLD when the EMLSR mode is enabled is considered. The possible architecture of the MLD for EMLSR shown in this figure is for illustrative purposes, and other alternative architectures are also conceivable.

[0284] This architecture includes two radio stacks, a lightweight radio stack and a full radio stack.

[0285] A complete wireless stack includes a complete 802.11be MAC module 900a (which exchanges data with the upper layer), a complete 802.11be PHY module 905a connected to the complete MAC module, a complete radio frequency chain 915a connected to the complete PHY module, and an antenna 920a connected to the complete RF chain via an EMLSR switch 910.

[0286] A light wireless stack includes a light 802.11be MAC module 900b (which exchanges data with the upper layer), a light 802.11be PHY module 905b connected to the light MAC module, a light radio frequency chain 915b connected to the light PHY module, and an antenna 920b connected to the light RF chain via an EMLSR switch 910.

[0287] The EMLSR switch 910 is shared by two wireless stacks and is configured to switch the co - affiliated STAs of the EMLSR from / to the listening operating state to / from the active frame exchange state or the inactive frame exchange state when the EMLSR mode is enabled.

[0288] The wireless chain 900a / 905a / 915a is a complete wireless resource that enables the reception and transmission of any IEEE802.11 frame. In particular, it includes encoding and decoding modules for encoding and decoding any IEEE802.11 frame. On the other hand, the wireless chain 900b / 905b / 915b is a reduced - functionality (or "light") wireless resource that enables only the reception and transmission of specific IEEE802.11 frames. In particular, it includes only encoding and decoding modules for encoding and decoding specific frames using rates of 6Mbps, 12Mbps, or 24Mbps.

[0289] The figure on the lower left shows the function of the MLD when the non-AP MLD is in the EMLMR listening operation mode: The common EMLMR switch 910 connects each radio chain 900a / 905a / 915a and 900b / 905b / 915b to the antennas 920a and 920b respectively. Thus, each radio stack can be used to simultaneously listen to its respective link. As shown in the figure, two links are available. The complete radio chain 900a / 905a / 915a and the antenna 920a are configured to operate on Link 1, and the lightweight radio chain 900b / 905b / 915b and the antenna 920b are configured to operate on Link 2.

[0290] The figure in the lower center shows the function of the MLD when the 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 common EMLSR switch 910 connects the complete radio chain 900a / 905a / 915a to both antennas 920a and 920b, and the complete radio chain 900a / 905a / 915a and the antennas 920a / 920b are configured to operate on Link 1. Here, since the complete radio chain remains configured to operate on Link 1, the switching period from the EMLSR listening operation state to the active frame exchange state can be considered short. In fact, in this case, the switching only involves antenna switching. On the other hand, the common EMLSR switch 910 disconnects the lightweight radio chain 900b / 905b / 915b from the antenna 920b. In this configuration, the lightweight radio chain 900b / 905b / 915b cannot receive or transmit frames on Link 2. And only Link 1 is available.

[0291] The figure on the lower right shows the MLD function when the non-AP MLD switches to 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 common EMLSR switch 910 connects the complete wireless chain 900a / 905a / 915a to both antennas 920a, 920b, and the complete wireless chain 900a / 905a / 915a and the antennas 920a / 920b are configured to operate on Link 2. Here, since the complete wireless chain switches to operate on Link 2, the switching time from the listening operation state of the EMLSR to the active frame exchange state may be considered long. In fact, in this case, the switching includes both antenna switching and complete wireless chain setting switching. On the other hand, the common EMLSR switch 910 disconnects the light wireless chain 900b / 905b / 915b from the antenna 920b. In this configuration, the light wireless chain 900b / 905b / 915b cannot receive or transmit frames on Link 1. And only Link 2 is available.

[0292] The function of the common EMLSR switch 910 clearly shows that the state changes of the co-affiliated STAs of the two EMLSRs within the same MLD are necessarily simultaneous because the wireless chain is connected to either one STA or the other STA, and it is not possible for both STAs to be available simultaneously.

[0293] Figure 9a schematically shows the EMLMR-capable architecture of the MLD. In this figure, an example is given where two affiliated non-AP STAs share antenna resources when the EMLMR mode is activated.

[0294] This architecture includes two wireless stacks, one for each non-AP STA.

[0295] The wireless stack includes a complete 802.11be MAC module 900a' or 900b' (which exchanges data with the upper layer), a complete 802.11be PHY module 905a' or 905b' connected to the MAC module, a radio frequency chain 915a' or 915b' connected to the PHY module, an EMLMR switch 910' shared by two wireless stacks and configured to perform antenna resource aggregation when the EMLMR mode becomes active, and an antenna array 920a' or 920b'.

[0296] The figure at the lower left shows the function when the non - AP MLD is listening to the Initial frame: The common EMLMR switch 910' connects each antenna array to the RF chain. Thus, each wireless stack is complete and can serve each link, for example, using a 2x2 MIMO antenna configuration. As shown in the figure, two links are available.

[0297] The figure in the center - lower shows the function of the MLD when the non - AP MLD switches in the first EMLMR frame - exchange mode. The co - affiliated STAs of the EMLMR corresponding to Link 2 are in the active frame - exchange state, and the co - affiliated STAs of the other EMLMR corresponding to Link 1 are in the inactive frame - exchange state. The common EMLMR switch 910 aggregates the antenna resources to Link 2. To do this, the antenna array 920a' of the second wireless stack is connected to the RF chain 915b' of the first wireless stack. Thus, the first wireless stack operates in a 4x4 MIMO antenna configuration and can improve the throughput for Link 2. On the other hand, Link 1 becomes unavailable because its antenna array 920a' can no longer be used by the second wireless stack.

[0298] The figure on the lower right shows the function of the MLD when the non-AP MLD switches to the second EMLMR frame exchange mode. The co-affiliated STAs of the EMLMR corresponding to Link 1 are in the active frame exchange state, and the co-affiliated STAs of the other EMLMR corresponding to Link 2 are in the inactive frame exchange state. The common EMLMR switch 910' aggregates the antenna resources to Link 1. To do so, the antenna array 920b' of the first radio stack is connected to the RF chain 915a' of the second radio stack. Thus, the second radio stack operates in a 4x4 MIMO antenna configuration and can improve the throughput for Link 1. On the other hand, Link 2 becomes unavailable because its antenna array 920b' becomes unavailable for use in the first radio stack.

[0299] The function of the common EMLMR switch 910' clearly shows that the state changes of the co-affiliated STAs of two EMLMRs within the same MLD are necessarily simultaneous because the antenna resources are either connected to one STA or the other STA, but not available to both STAs simultaneously.

[0300] FIG. 10 schematically shows a communication device 1000 of a wireless network, typically one of the MLDs described above, configured to implement at least one embodiment of the present invention. The communication device 1000 can preferably be a device such as a microcomputer, a workstation, or a lightweight portable device. The communication device 1000 preferably includes a communication bus 1013 to which the following are connected: A central processing unit 1001, such as a processor denoted as CPU; A memory 1003 for storing registers adapted to record executable code of a method or method steps according to an embodiment of the present invention, and variables and parameters necessary for the implementation of the method; and At least two communication interfaces 1002 and 1002' connected to a wireless communication network (for example, a communication network conforming to one of the standards of the IEEE802.11 family) via transmission and reception antennas 1004 and 1004' respectively.

[0301] Preferably, the communication bus 1013 provides communication and interoperability between various elements included in or connected to the communication device 1000. The expression of the bus is not limiting. In particular, the central processing unit is operable to communicate instructions directly to any element of the communication device 1000 or through another element of the communication device 1000.

[0302] The executable code can be stored in the memory of a read-only, hard disk, or removable digital medium such as a disk. According to an optional variant, the executable code of the program can be received by the communication network via interface 1002 or 1002' so as to be stored in the memory of the communication device 1000 before being executed.

[0303] In one embodiment, the device is a programmable device that uses software to implement the embodiments of the present invention. However, alternatively, the embodiments of the present invention can be implemented wholly or partly in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC).

[0304] As described above, the present invention has been described with reference to specific embodiments, but the present invention is not limited to specific embodiments, and modifications within the scope of the present invention will be apparent to those skilled in the art.

[0305] Referring to the foregoing exemplary embodiments, many further changes and modifications will be suggested to those skilled in the art, but these embodiments are given by way of example only and are not intended to limit the scope of the invention, which is determined only by the appended claims. In particular, different features from different embodiments may be interchanged where appropriate.

[0306] In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims

1. A method for communication in a wireless network in a non-access point (non-AP) multi-link device (MLD) operating in an EML mode applied to a set of enhanced multi-link (EML) links, comprising: receiving, by a first affiliated station, a first beacon frame via a first link of the EML link, wherein the first beacon frame includes a target beacon transmission time (TBTT) related to a second beacon frame; configuring the first affiliated station to be in a receiving state at the TBTT for receiving the second beacon frame. A method.

2. Configuring the first affiliated station includes ending an ongoing frame exchange via a second link of the EML link and switching the first affiliated station to an operating state suitable for receiving the second beacon frame. The method according to claim 1.

3. Switching to an operating state suitable for receiving the second beacon frame includes switching the first affiliated station to a listening operating state. The method according to claim 2.

4. A second affiliated station triggers a frame exchange sequence on the second link and ignores an Initial frame that temporally overlaps with the first beacon frame on the first link. The method according to claim 3.

5. Switching to an operating state suitable for receiving the second beacon frame includes switching the first affiliated station to an active frame exchange state. The method according to claim 2.

6. Configuring the first affiliated station includes switching the first affiliated station from a listening operating state to an active frame exchange state. The method according to claim 1.

7. Configuring the first affiliated station includes ending an ongoing frame exchange via the first link and maintaining the first affiliated station in an active frame exchange state. The method according to claim 1.

8. Maintaining when the time distance to the TBTT is less than a predetermined threshold. The method according to claim 7.

9. The predetermined threshold is at least the transition period required by the non-AP MLD to switch the state of the affiliated station of the non-AP MLD from the listening operation state to the active frame exchange state or the inactive frame exchange state, and the transition period required by the non-AP MLD to switch the state of the affiliated station of the non-AP MLD from the active frame exchange state or the inactive frame exchange state to the listening operation state, and is the sum of these The method according to claim 8.

10. Setting the first affiliated station is triggered at least a first determined delay before the TBTT The method according to claim 1.

11. The first determined delay belongs to a group including the maximum value of the EMSR active switching delay, the EMLMR active switching delay, and the EMSR and EMLMR active switching delays The method according to claim 10.

12. The second beacon frame schedules a service period on the first link, and when frame exchange is completed within the service period, the first affiliated station is maintained in the active frame exchange state until the end of the service period The method according to claim 1.

13. The second beacon frame schedules a service period on the first link, switches the first affiliated station to the active frame exchange state before the start of the service period, and maintains it in the active frame exchange state until the end of the service period The method according to claim 1.

14. At the end of the service period, switch the first affiliated station from the active frame exchange state to the listening operation state The method according to claim 12 or 13.

15. The second beacon frame includes other TBTTs related to a third beacon frame that schedules a TWT service period on the first link. When the scheduled TWT service period is signaled with TWT persistence, without setting the first affiliated station to a receiving state with the other TBTTs for receiving the third beacon frame on the first link, continue frame exchange executed by a second affiliated station on a second link of the EML link. The method according to claim 1.

16. The second beacon frame schedules a quiet period on the first link, and during the quiet period, switch the first affiliated station to an inactive frame exchange state until the quiet period ends. The method according to claim 1.

17. During the quiet period, until the end of the quiet period, switch a second affiliated station to an active frame exchange state via a second link of the EML link. The method according to claim 16.

18. Further including transmitting, by the non-AP MLD, a notification for scheduling, in a future beacon frame, a service period of the non-AP MLD that does not temporally overlap with a beacon frame transmitted by an AP MLD via a second link of the EML link, to the AP MLD. The method according to claim 1.

19. A communication method of a wireless network in a non-access point (non-AP) multi-link device (MLD) operating in an EML mode applied to a set of enhanced multi-link (EML) links, including setting a second affiliated station to ignore an Initial frame that temporally overlaps with a beacon frame received by a first affiliated station on a first link of the EML link, and triggering a frame exchange sequence on a second link of the EML link. Method.

20. A communication method for a wireless network in an access point (AP) multi-link device (MLD) configured to perform a frame exchange operation with at least a predetermined non-access point (non-AP) multi-link device (MLD) operating in an EML mode applied in a set of enhanced multi-link (EML) links, In a beacon frame transmitted by the AP MLD on a first link of the EML link, scheduling a service period of the predetermined non-AP MLD that does not temporally overlap with a beacon frame transmitted by the AP MLD on a second link of the EML link Method.

21. A communication method for a wireless network in a non-access point (non-AP) multi-link device (MLD) operating in an EML mode applied in a set of enhanced multi-link (EML) links and an access point (AP) MLD configured to perform a frame exchange operation, Transmitting an Initial frame that triggers frame exchange between at least one non-AP MLD operating in EML Single-Radio (EMLSR) mode and at least one non-AP MLD operating in EML Multi-Radio (EMLMR) mode; The AP MLD ensures that the padding period of the Padding field of the Initial frame is greater than the maximum of the values indicated by the EMLSR Padding Delay subfield received from at least one non-AP MLD operating in the EMLSR mode and the EMLMR Delay subfield received from the at least one non-AP MLD operating in the EMLMR mode Method.

22. A wireless communication device, comprising at least one microprocessor configured to execute the method according to any one of claims 1, 19, 20 or 21 Wireless communication device.

23. 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 execute the method according to any one of claims 1, 19, 20 or 21 Non-transitory computer-readable medium.

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