Support for link-by-link (TWT, R-TWT) procedures and state switching for EMLSR or EMLMR co-affiliated stations

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

[0002] Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing available network resources. Examples of such multiple-access networks include code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, and single-carrier FDMA (SC-FDMA) networks.

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

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

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

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

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

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

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

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

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

[0012] This shows that one side of the EMLMR (or EMLSR) link is not completely independent of the other.

[0013] Additionally, a non-AP MLD also has the ability to initiate frame exchange with an AP MLD via one EMLSR or EMLMR link to transmit uplink data. In such a case, STAs affiliated with a non-AP MLD operating in EMLSR or EMLMR mode do not need to transmit an Initial Control frame or an Initial frame to initiate frame exchange with the AP MLD (non-triggered UL transmission), and access the wireless medium according to the rules defined in Section 10.3.2.4 (NAV Configuration and Reconfiguration) and Section 10.23.2 (HCF Contention-Based Channel Access (EDCA)) as specified in the IEEE 802.11-2020 standard.

[0014] EML mode mechanisms coexist with other 802.11 mechanisms, some of which (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 the other links, such as the so-called Target Wake Time (TWT) procedure and its more recent adaptation known as the Restricted Target Wake Time procedure (called rTWT or R-TWT).

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

[0016] The coexistence of EML mode and link-specific procedures needs to be improved. Summary of the Invention

[0017] The inventors have realized that the inability of a non-AP MLD to participate in a link-specific procedure is due to network operation of the non-AP MLD on a first link causing that MLD to fail to receive beacon frames announcing the procedure on the other link.

[0018] It is therefore a broad object of the present invention to favour the reception of beacon frames, which should provide enhanced link-specific procedures that take into account the use of EML mode and are adapted to the EML mode.

[0019] In this context, a method of communication in a wireless network is provided in 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: - receiving, by a first affiliated station, a first beacon frame over a first link of the EML link, the first beacon frame including a Target Beacon Transmission Time (TBTT) associated with a second beacon frame; - Configuring the first affiliated station to be in a receive state at the TBTT to receive the second beacon frame.

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

[0021] Therefore, the non-AP MLD takes into account the expected time (TBTT) of the next beacon frame to be received on the first link to set itself (at the corresponding first affiliated station) into the appropriate receive mode, regardless of network activity on other links of the EML link.

[0022] As a result, reception of the next beacon frame is guaranteed, and the non-AP MLD becomes aware of the first link-specific procedure announced by the next beacon frame.

[0023] Any features of the invention are defined below with reference to a method, but these may be replaced by device features.

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

[0025] Upon frame exchange over the second link, the first affiliated station is initially found to be in an invalid frame exchange state.

[0026] Therefore, the non-AP MLD determines to stop the current frame exchange at the time when the next beacon frame is expected 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, thereby allowing the beacon frame to be correctly received on the first link due to the interruption of the frame exchange.

[0027] In certain embodiments, switching to an operational state suitable for receiving the second beacon frame includes switching the first affiliated station to a listening operational state, which advantageously enables the second affiliated station to listen on a respective second EML link to, for example, simultaneously receive another beacon frame.

[0028] In a particular embodiment, the second affiliated station must trigger a frame exchange sequence on the second link and ignore the Initial frame that overlaps in time 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 expected beacon frame regardless of network activity on the second link.

[0031] More generally, the present configuration relates to a wireless network communication method in 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: 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 to ignore a received Initial frame that overlaps in time with a 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 operational state suitable for receiving the second beacon frame includes switching the first affiliated station to an enabled frame exchange state. This configuration prevents a non-AP MLD that received the beacon frame from switching on the second link, for example, if the AP MLD transmits an Initial (Control) frame on the second link simultaneously with the second beacon frame.

[0033] In some embodiments, configuring the first affiliated station includes switching the first affiliated station from a listening operation state to an active frame exchange state, again preventing a non-AP MLD that received the beacon frame from switching on the second link, for example, if the AP MLD transmits an Initial (Control) frame on the second link concurrently with the second beacon frame.

[0034] In some embodiments, configuring the first affiliated station includes terminating an ongoing frame exchange over the first link and maintaining the first affiliated station in a valid frame exchange state.

[0035] This means that the first affiliated station does not immediately switch back to a listening state after the end of the frame exchange, which may correspond to the end of an acquired transmission opportunity, or may be spontaneously triggered by a non-AP MLD due to the proximity of the TBTT in time to set itself up to receive the second beacon frame.

[0036] These embodiments avoid unnecessary state switching of affiliated stations while ensuring correct reception of beacon frames.

[0037] In certain embodiments, the first affiliated station remains in a valid 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 transition period required for non-AP MLD to switch the state of its affiliated stations from a listening operation state to an enabled or disabled frame exchange state, and - The transition period required for a non-AP MLD to switch the state of its affiliated stations from an enabled or disabled frame exchange state to a listening operation state.

[0038] This allows for fine-grained control over which non-AP MLDs can benefit from maintaining valid frame exchange state and which non-AP MLDs that have terminated frame exchange can attempt network activity on the second link, thereby improving wireless network utilization.

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

[0040] In some embodiments, the second beacon frame schedules a service period on the first link, and upon completing a frame exchange within the service period, maintains the first affiliated station in an active frame exchange state until the end of the service period. In this configuration, the first affiliated station does not automatically switch back to a listening operation state as soon as the frame exchange ends, but remains in the active frame exchange state until the end of the entire service period (e.g., rTWT SP). This increases the opportunities for non-AP MLDs to exchange frames during the service period, improving 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 for the entire service period (e.g., rTWT SP). This increases the opportunities for non-AP MLDs to exchange frames during the service period, improving network efficiency.

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

[0043] In some embodiments, the second beacon frame includes another TBTT associated with a third beacon frame that schedules a TWT service period on the first link; If the scheduled TWT service period is signaled in 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 configured to receive at another TBTT to receive the third beacon frame on the first link.

[0044] It is understood that the TWT persistence (Broadcast TWT Persistence field of the TWT element) indicates the number of TBTTs for which the broadcast TWT service period corresponding to this broadcast TWT parameter set exists. Because the TWT service period is repeated, there is no need for the non-AP MLD to obtain the next beacon frame advertising the same information. Therefore, these embodiments avoid interrupting network activity on the second link, which improves network efficiency.

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

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

[0047] The present invention also relates to a communication method for a wireless network, in an Access Point Multilink Device (AP MLD) configured to perform frame exchange operations with at least a given non-AP MLD operating in an Enhanced Multilink (EML) mode applied to a set of EML links, including: In a beacon frame transmitted by the AP MLD on a first link of the EML link, scheduling a service period of a predetermined non-AP MLD that does not overlap in time with a beacon frame transmitted by the AP MLD on a second link of the EML link.

[0048] As a result, scheduled service periods (such as rTWT SPs) are no longer an obstacle for non-AP MLDs to correctly receive beacon frames.

[0049] The present invention also relates to a communication method for a wireless network, in an Access Point Multilink Device (AP MLD) configured to perform frame exchange operations with at least a given non-AP MLD operating in an Enhanced Multilink (EML) mode applied to a set of EML links, including: transmitting an Initial frame that triggers a frame exchange sequence with at least one non-AP MLD operating in EMLSR mode and at least one non-AP MLD operating in EMLMR mode; The AP MLD ensures that the padding duration in the Padding field of the Initial frame is equal to or greater than the maximum value of the values ​​indicated in the EMLSR Padding Delay subfield and the EMLMR Delay subfield received from the non-AP MLD where the frame exchange sequence was initiated.

[0050] Therefore, an AP MLD can trigger both one or more non-AP MLDs operating in EMLSR mode and one or more non-AP MLDs operating in EMLMR mode, and the padding period indicated in the Initial frame (the IC frame in EMLSR mode and the Initial frame in EMLMR mode) ensures that all these non-AP MLDs (both MLDs operating in EMLSR mode and MLDs operating in EMLMR mode) are sufficient to switch the state of their affiliated stations from the listening operation state to the enable / disable frame exchange state.

[0051] Relatedly, the present invention also provides a wireless communication device including at least one microprocessor configured to carry out any of the methods described above.

[0052] Another aspect of the present invention relates to a non-transitory computer-readable medium having stored thereon a program that, when executed by a microprocessor or computer system within a wireless device, causes the wireless device to perform any of the methods described above.

[0053] At least part of the methods according to the present invention may be computer-implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be referred to generally herein as a "circuit," "module," or "system." Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium having computer-usable program code embodied in the medium.

[0054] Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable device on any suitable carrier medium. Tangible, non-transitory carrier media can include storage media such as floppy disks, CD-ROMs, hard disk drives, magnetic tape devices, or solid-state memory devices. Transitory carrier media can include signals such as electrical, electronic, optical, acoustic, magnetic, or electromagnetic signals, e.g., microwave or RF signals. [Brief explanation of the drawings]

[0055] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings: [Figure 1] 1 illustrates a typical 802.11 network environment including ML transmission between EML-enabled MLDs in which the present invention may be implemented; [Figure 1ab] 1 shows an exemplary 802.11be multilink reference model for MLD, either AP MLD or non-AP MLD; [Figure 2] Schematic example of frame sequence for EMLSR operation mode specified in the D2.0 standard; [Figure 3] Shows the format of the Target Wake Time (TWT) element adapted to be used in r-TWT according to the D2.0 standard; [Figure 4] 1 illustrates, with frame sequences, an EMLSR operation mode of a non-AP MLD with rTWT service negotiated on one of the AP MLD and EMLSR links according to a specific embodiment of the present invention; [Figure 5] 1 illustrates, with a flowchart, the steps performed by an EMLSR active non-AP MLD according to an embodiment of the present invention; [Figure 6a] 1 illustrates an extended frame exchange sequence for the TWT mechanism supported by an EMLSR station according to a first embodiment of the present invention; [Figure 6b] 1 illustrates an extended frame exchange sequence for the TWT mechanism supported by an EMLSR station according to a second embodiment of the present invention; [Figure 6c] 10 illustrates an extended frame exchange sequence for the TWT mechanism supported by an EMLSR station according to a third embodiment of the present invention; [Figure 7] Illustrate with a flowchart the steps performed by an EMLSR active non-AP MLD when TWT service is already set up before EML operation is activated; [Figure 8] Illustrates, with the aid of a flowchart, the steps performed by an EMLSR active non-AP MLD that seeks to limit the use of TWT services on a given number of links; [Figure 9] 1 illustrates a schematic diagram of an EMLSR-enabled architecture of an MLD for implementing an embodiment of the present invention; [Figure 9a] 1 illustrates schematically an EMLMR-enabled architecture of an MLD for implementing an embodiment of the present invention; [Figure 10] 1 shows a schematic diagram of a wireless communication device according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0056] The techniques described herein may be used in various broadband wireless communication systems, including communication systems based on orthogonal multiplexing. Examples of such communication systems include spatial 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. SDMA systems may utilize sufficiently different directions to simultaneously transmit data belonging to multiple user terminals, such as wireless devices or STAs. TDMA systems may allow multiple user terminals to share the same frequency channel by dividing the transmission signal into different time slots or resource units and assigning each time slot to a different user terminal. OFDMA systems utilize orthogonal frequency division multiplexing (OFDM), which is a modulation technique that divides the overall system bandwidth into multiple orthogonal subcarriers or resource units. These subcarriers may be referred to as tones, bins, etc. In OFDM, each subcarrier may be independently modulated with data. An SC-FDMA system may utilize Interleaved FDMA (IFDMA), which transmits on subcarriers distributed across the system bandwidth, Localized FDMA (LFDMA), which transmits on blocks of adjacent subcarriers, or Enhanced FDMA (EFDMA), which transmits on multiple blocks of adjacent subcarriers.

[0057] The teachings herein may be incorporated into (e.g., implemented in or performed by) a variety of apparatuses (e.g., STAs). In some aspects, a wireless device or STA implemented in accordance with the teachings herein may or may not include an access point (referred to as an AP) (referred to as a non-AP STA or STA).

[0058] Although the embodiments are described in the context of a WiFi network, the invention can be used in any type of wireless network, such as, for example, a mobile telephone cellular network, which implements very similar mechanisms.

[0059] An AP may include, be implemented as, or be known as a NodeB, Radio Network Controller ("RNC"), Evolved Node B (eNB), 5G Next Generation Base STA ("gNB"), Base STA Controller ("BSC"), Base Transceiver STA ("BTS"), Transceiver Function ("TF"), Wireless Router, Wireless Transceiver, Basic Service Set ("BSS"), Enhanced Service Set ("ESS"), Radio Base STA ("RBS"), or other term.

[0060] A non-AP STA may include, be implemented as, or be known as a subscriber STA, subscriber unit, mobile STA (MS), remote STA, remote terminal, user terminal (UT), user agent, user device, user equipment (UE), user STA, or other terminology. In some implementations, a STA may include a cellular telephone, a cordless telephone, a session initiation protocol ("SIP") telephone, a wireless local loop ("WLL") STA, a personal digital assistant ("PDA"), a handheld device with wireless connectivity capabilities, or other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a telephone (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 satellite radio), a global positioning system (GPS) device, or any other suitable device configured to communicate via a wireless or wired medium. In some aspects, a non-AP STA may be a wireless node. Such a wireless node may, for example, provide connectivity to a network (eg, a wide area network such as the Internet or a cellular network) via a wired or wireless communication link.

[0061] An AP manages a set of STAs (registered or associated with the AP) that together constitute access to the wireless medium for communication purposes. The STAs (including the APs with which they register) form a service set, hereafter referred to as a Basic Service Set (BSS) (although other terms may be used). The same physical STA acting as an access point may manage two or more BSSs (and thus corresponding WLANs), each BSS being therefore uniquely identified by a specific Basic Service Set Identifier (BSSID) and managed by a separate virtual AP implemented in the physical AP. Each STA is identified within a BSS by an identifier AID assigned by the AP upon registration.

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

[0063] Current discussions in the 802.11be task group, as outlined in the May 2022 draft IEEE P802.11be / D2.0, will introduce multi-link operation (MLO) to the MAC layer operation, allowing a multi-link device to establish or configure multiple links and operate them simultaneously.

[0064] A multilink device (MLD) is a logical entity that has multiple affiliated STAs (STAs), has a single medium access control (MAC) service access point (SAP) for a logical link control (LLC), and contains one MAC data service. An access point multilink device (or AP MLD) corresponds to an MLD in which each STA affiliated to the MLD is an AP (hence referred to as an "affiliated AP"). A non-access point multilink device (or non-AP MLD) corresponds to an MLD in which each STA affiliated to the MLD is a non-AP STA (referred to as an "affiliated non-AP STA"). In some literature, the terms "multilink device," "ML device" (MLD), "multilink logical entity," "ML logical entity" (MLE), "multilink set," and "ML set" are synonyms referring to the same type of ML device. An exemplary architecture of a multilink device is described below with reference to FIG. 1b.

[0065] Multiple affiliated non-AP STAs in a non-AP MLD can set up communication links with multiple affiliated APs in an AP MLD, forming a multi-link channel.

[0066] Links established for MLD (or "enabled links") are theoretically independent, meaning that channel access procedures (to the communication medium) and communication are performed independently on each link. Thus, different links may have different data rates (e.g., due to different bandwidths, number of antennas, etc.) and may be used (over each particular link) to communicate different types of information.

[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 according to one or more of the IEEE 802.11 standards (a / b / g / n / ac / ad / af / ah / aj / ay / ax / be) or other wireless communication standards.

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

[0070] From an architectural perspective, an MLD typically includes several radios to implement affiliated STAs, but the number does not have to be equal to the number of affiliated STAs. In particular, a non-AP MLD may operate with a number of affiliated STAs greater than the number of radios (or even as few as one).

[0071] The D2.0 standard defines several enhanced multi-link operating modes (abbreviated EML OM) from this physical architecture: Enhanced Multi-Link Single Radio (EMLSR) and Enhanced Multi-Link Multi-Radio (EMLMR). The D2.0 standard states that the two modes, EMLSR and EMLMR, are mutually exclusive.

[0072] Non-AP MLD declares support for EMLSR and / or EMLMR mode to AP MLD during the association phase (in the so-called EML Capabilities). In operational mode, activation and deactivation of EMLSR or EMLMR mode is initiated by non-AP MLD, which sends a specific EHT action frame called "EML OM Notification" indicating, among other things, the set of valid links (so-called EMLSR or EMLMR links) to which the activation of EMLSR or EMLMR mode applies. Typically, an "EMLSR / EMLMR link" consists of two valid links. However, more valid links may be used.

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

[0074] In EMLMR mode, non-AP MLD can aggregate some of the physical resources of multiple radios for multiple active links (so-called EMLMR links) to transmit and receive data up to a predetermined number of supported receive and transmit spatial streams. This predetermined number is greater than the number of receive and transmit spatial streams supported per radio, providing improved throughput and reduced latency. As an example, a multi-radio (MR) non-AP MLD supporting EMLMR mode with two links (each with associated radios) communicates over two links using each of the two radios when EMLMR mode is deactivated, such as in a 2x2 MIMO antenna configuration for each radio. On the other hand, an MR non-AP MLD aggregates the physical resources (usually antennas) of the two radios when EMLMR mode is activated, such as in a 4x4 MIMO antenna configuration, and uses one of the radios to communicate over one of the two links. At the same time, the other link (the link with the deprived physical antenna) is unavailable.

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

[0076] In the following description, for simplicity, the EMLSR mode will be mainly described, but similar considerations can be made for the EMLMR mode.

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

[0078] Wireless communication network 100 includes AP MLD 110 and two non-AP MLDs 120 and 130. In this example, the two non-AP MLDs are assumed to be EML-capable and declare their corresponding capabilities to AP MLD 110 in EMLSR-related and EMLMR-related fields of their EML Capabilities (these fields are hereinafter referred to as EMLSR Capabilities and EMLMR Capabilities, e.g., subparts of EML Capabilities). Of course, a different number of non-AP MLDs registering with and exchanging frames with AP MLD 110, as well as a different (or greater) number of EML-capable non-AP MLDs, may be envisioned.

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

[0080] The non-AP MLDs 120, 130 have multiple affiliated non-AP STAs, each operating as an 802.11 non-AP STA in the BSS (managed by the affiliated AP 111 or 112) to which it registers. In the exemplary FIG. 1 , two non-AP STAs 121 and 122 (also referred to as A1 and A2, respectively) are affiliated with the non-AP MLD 120, and two non-AP STAs 131 and 132 (also referred to as B1 and B2, respectively) are affiliated with the 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 configured to operate on channel 38, which corresponds to an operating 40 MHz channel in the 5 GHz frequency band, and AP 112 is configured to operate on channel 151, which corresponds to another operating 40 MHz channel, also in the 5 GHz frequency band. In another example, affiliated STAs may operate on different frequency bands.

[0082] Each affiliated AP provides a link toward the AP MLD 110 to affiliated non-AP STAs in the non-AP MLD (120 or 130). Thus, each non-AP MLD link may be identified simply by the identifier of the respective affiliated AP. In this context, each affiliated AP 111 and 112 may be identified by an identifier called a "link ID." The link ID of each affiliated AP is unique and does not change during the lifetime of the AP MLD. The AP MLD may assign link IDs to affiliated APs by incrementing the ID from 0 (for the first affiliated AP). Of course, other terms, such as "AP ID," may be used as variations.

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

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

[0085] The ML discovery procedure enables a non-AP MLD to discover wireless communication network 100, e.g., various links to an AP MLD provided by multiple affiliated APs. Accordingly, the ML discovery procedure attempts to advertise various affiliated APs in the AP MLD along with their respective network information (e.g., including all or part of their capabilities and operating parameters). After the non-AP MLD discovers wireless communication network 100 through the ML discovery procedure and the MLD authentication procedure, the ML setup procedure can select a set of candidate link setups between affiliated non-AP STAs in the non-AP MLD and some of the discovered affiliated APs and request the AP MLD 110 to set up these links, which can be accepted or rejected by the AP MLD. If the AP MLD accepts, the non-AP MLD is provided with an Association Identifier (AID) by the AP MLD, which is used by the affiliated non-APs in the non-AP MLD to wirelessly communicate with their corresponding affiliated APs over multiple links (communication channels). During the ML setup procedure, a non-AP MLD declares some or all of its capabilities, e.g., EMLSR capabilities. To do this, appropriate fields are provided in management frames. In particular, management frames exchanged during the ML discovery and ML setup procedures contain a new information element specific to multi-link operation (MLO), called the Basic Multi-Link element. In fact, in all management frames containing the Basic Multi-Link element, except authentication frames, a non-AP or AP MLD that is EMLSR-capable (dot11EHTEMLSROptionImplemented is true) or EMLMR-capable (dot11EHTEMLMROptionImplemented is true) sets the EMLSR or EMLMR Support bit in the EML Capabilities subfield of the Common Info field to 1.

[0086] For illustrative purposes, in wireless communication network 100, during an ML setup procedure, two setup candidate links are requested by non-AP MLD 120 and accepted by AP MLD 110: a first link 151 between affiliated AP 111 (AP1) and affiliated non-AP STA 121 (A1), and a second link 152 between affiliated AP 112 (AP2) and affiliated non-AP STA 122 (A2). Similarly, two setup link candidates are requested by multi-radio non-AP MLD 130 and accepted by AP MLD 110: a first link 161 between affiliated AP 111 (AP1) and affiliated non-AP STA 131 (B1), and a second link 162 between affiliated AP 112 (AP2) and affiliated non-AP STA 132 (B2).

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

[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 operations. The EMLSR Support subfield is set to 1 if the MLD supports EMLSR operations, otherwise it is set to 0; - The 3-bit subfield "EMLSR Padding Delay" indicates the minimum MAC padding duration in the Padding field of the Initial Control frame requested by non-AP MLD, as defined in Enhanced multi-link single radio operation (clause 35.3.17). The table converts the 3-bit value into a padding delay in μs. This delay is used to define the transition period required for MLD to switch the state of an affiliated station from the listening operation state to the active / inactive frame exchange state. This transition period is the duration of the Initial Control frame response (described below) plus this delay. Therefore, this transition period is called the "EMLSR active switch delay"; - The 3-bit subfield "EMLSR Transition Delay" indicates the transition delay time required for a non-AP MLD to switch from the so-called frame exchange mode (on one of the active links) to the so-called listening operation mode on the active links. The table converts the 3-bit value into a delay in μs, e.g., 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 values ​​from 6 to 7 are reserved; - The "EMLMR Support" subfield indicates that the MLD supports EMLMR operation. If the MLD supports EMLMR operation, the EMLMR Support subfield is set to 1, otherwise it is set to 0; - The 3-bit subfield "EMLMR Delay" indicates the minimum padding period required for switching the EMLMR link when a non-AP MLD operates in EMLMR mode. This delay is used to define the transition period required for the MLD to switch the state of an affiliated station when initiating or terminating a frame exchange. The transition period for a frame exchange is the time length of the initial frame response (described later) plus this delay (EMLMR delay). Therefore, this initiation transition period is called the "EMLMR active switching delay"; - The "Transition Timeout" subfield indicates the timeout value for EML Operating Mode Notification frame exchange in the EMLSR (or EMLMR).

[0089] When an EMLSR (or EMLMR)-capable non-AP MLD wishes to operate in the corresponding mode on a set of valid links, called EMLSR (or EMLMR) links, a STA affiliated with the non-AP MLD sends an EML Operating Mode (OM) Notification frame (as specified in the D2.0 standard) with the EMLSR (or EMLMR) Mode subfield of the EML Control field set to 1 to the AP affiliated with the EMLSR (or EMLMR)-capable AP MLD (here, AP MLD 110). The EMLSR (or EMLMR) links are indicated by setting the bit position of the EMLSR (or EMLMR) Link Bitmap subfield of the EML Control field of the EML OM Notification frame to 1 for each EMLSR (or EMLMR) link. For example, in the EMLSR (or EMLMR) Link Bitmap, bit position i corresponds to the link whose link ID is equal to i and is set to 1 to indicate that the link is a member of the EMLSR (or EMLMR) link.

[0090] An AP affiliated to an AP MLD that receives an EML Operating Mode Notification frame from a STA affiliated to a non-AP MLD then transmits an EML Operating Mode Notification frame to one of the STAs affiliated to the non-AP MLD as an acknowledgment of the EML Operating Mode Notification sent by the STA affiliated to the non-AP MLD within the timeout interval indicated in the Transition Timeout subfield of the EML Capabilities subfield of the Basic Multi-Link element and beginning at the end of the PPDU sent by the AP affiliated to the AP MLD.

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

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

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

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

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

[0096] The 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 received traffic data.

[0098] Transmission and reception of traffic data is handled by the MAC 220 and PHY 200 layers. Such transmission and reception of traffic data may occur over multiple links 20-x, 20-y, and 20-z, such as links 151, 152, 161, and 162 introduced with reference to FIG. 1. Three links, and therefore three affiliated stations, are shown. Of course, other configurations including two affiliated stations or more than three affiliated stations are also contemplated.

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

[0100] Recall that 802.11 stations (AP and non-AP stations) maintain four access categories (ACs), each with one or more corresponding transmit buffers or queues. The four ACs are conventionally defined as follows: - AC1 and AC0 are reserved for best effort and background traffic, which have the second lowest and lowest priority, respectively. - AC3 and AC2 are typically reserved for real-time applications (such as voice and video transmissions). They have the highest and second highest priority, respectively.

[0101] Data frames, also known as MSDUs (MAC Service Data Units), coming from higher layers of the protocol stack are mapped by the classifier 213 to one of the four ACs and are therefore entered into the queue of the AC to which they are mapped.

[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 an MLD may transmit and receive using multiple links, particularly at the MAC layer 220 and PHY layer 200 levels.

[0104] The 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, each combination corresponding to a link 20-x, 20-y, 20-z.

[0105] The UMAC 230 performs functions common to all links, and each LMAC 220-x, 220-y, 220-z performs functions local to each link 20-x, 20-y, 20-z. The UMAC layer provides a UMAC interface to the link-specific blocks 220-x, 220-y, 220-z and a UMAC Service Access Point (SAP) to the LLC and upper layers.

[0106] The UMAC 230 is responsible for link-independent MAC procedures such as authentication, association, security association, sequence number allocation, MAC Protocol Data Unit (MPDU) encryption / decryption, aggregation / deaggregation, and acknowledgement scoreboarding procedures.

[0107] Each data unit (MSDU) with a priority of traffic type (User Priority (UP) and therefore Traffic IDentifer (TID)) arriving at the MAC layer 220 from a higher layer (e.g., link layer) is mapped to one of the ACs according to a mapping rule in the UMAC layer 230. Then, also in the UMAC layer 230, the data unit (MSDU) is provided with the next available sequence number and stored in the queue corresponding to its TID (or UP) within the mapped AC.

[0108] Each LMAC 220-x, 220-y, 220-z is responsible for link-specific functions such as channel access. In particular, each MLD Lower MAC includes its own contention-based channel access procedure, e.g., EDCA 221-x, 221-y, 221-z. Some functions require joint processing by both the UMAC 230 and the LMAC 220-x, 220-y, 220-z.

[0109] As shown in Figure 1a, each EDCA 221-x, 221-y, 221-z per link performs contention for each queue per link. In that regard, each AC has its own set of queue contention parameters per link, associated with a priority value, thus defining higher or lower priority traffic for an MSDU. Thus, multiple traffic queues exist for a given link to serve data traffic with different priorities. The contention window (CW) and backoff values, known as EDCA variables, are specific to each link 20-x, 20-y, 20-z.

[0110] That is, each AC operates as an independent DCF contention entity on a given link, including a respective queue backoff engine 211. Thus, each queue backoff engine 211 is associated with a respective traffic queue 210, using the queue's contention parameters and subtracting a backoff value (from the CW) to initialize a per-AC, per-link specific backoff counter for each queue. The backoff counter is used to contend for access to the links 20-x, 20-y, 20-z to transmit data stored in the AC's queue. In practice, the backoff counter is decremented from its initialized value when the medium is idle, and when the backoff counter reaches zero, the corresponding affiliated STA 201-x, 201-z is allowed to transmit (is granted access).

[0111] Once an AC on a link is granted access to the wireless medium, the MSDUs stored for that AC are sent to the physical (PHY) layers 200-x, 200-y, 200-z for transmission over the link.

[0112] 2 illustrates, using a frame sequence, the EMLSR operating mode in the non-AP MLD 120 when the AP MLD 110 decides to use the EMLSR mode. Of course, the EMLSR mode is emphasized here as an example, but similar considerations can be made for the EMLMR mode.

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

[0114] Affiliated STAs 121 and 122 are co-affiliated STAs of the EMLSR in the non-AP MLD 120. Each affiliated STA can be in one of three defined states: a listening operation state, a valid frame exchange state, and an invalid frame exchange state.

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

[0116] When the AP MLD 110 wishes to initiate a frame exchange with one or more non-AP MLDs on one of its EMLSR links, it initiates the frame exchange by transmitting 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 a frame exchange is transmitted in an OFDM PPDU or non-HT duplicate PPDU format using a rate of 6 Mbps, 12 Mbps, or 24 Mbps (i.e., the MCS subfield in the frame is set to its maximum value of 2). As defined in the D2.0 standard, the Initial Control frame must be an MU-RTS Trigger frame or a BSRP Trigger frame, as defined in IEEE Standard 802.11ax-2021. For such trigger frame formats that include one or more User Info fields, this condition means that the 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 during registration).

[0117] In this example, and as indicated by the reference "IC(A)," the Initial Control frame 245 explicitly triggers the non-AP MLD A 120. The Initial Control frame may explicitly trigger multiple non-AP MLDs using multiple User Info fields therein.

[0118] Explicitly triggered by the received Initial Control frame 245, the co-affiliated STA of the non-AP MLD EMLSR (e.g., co-affiliated STA A1 in the embodiment) initiates a state change of the co-affiliated STA of the non-AP MLD EMLSR under consideration (e.g., a state change of co-affiliated STAs A1 and A2 in the embodiment) and sends an Initial Control frame response (IC resp.) 246 to the AP AP1 affiliated to the AP MLD 110.

[0119] After receiving the frame exchange Initial Control frame 245 and transmitting an immediate response frame 246 in response to the Initial Control frame, the STAs affiliated with the non-AP MLD that were listening on the corresponding link (e.g., the co-affiliated STA A1 of the receiving EMLSR in the example) are configured to transmit or receive frames on the active link on which the Initial Control frame 245 was received (e.g., link 151 in the example). To this end, a state switching procedure is initiated to switch the co-affiliated STAs of the receiving EMLSR from the listening operation state 241 to the "active frame exchange" or "enabled frame exchange" state, referenced 251 in the figure, after an EMLSR active switching delay. In this new state, the co-affiliated STAs of the receiving EMLSR can receive PPDUs transmitted using multiple spatial streams on the link on which 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 mentioned above, this is specified by the EML Capabilities (via EMLSR Padding Delay) exchanged with the AP MLD.

[0120] At the same time, other co-affiliated STAs of the same non-AP MLD (e.g., STA A2 in the example) are configured not to transmit or receive on the other EMLSR link until the frame exchange is completed. To this end, a state switching procedure is also initiated for the co-affiliated STAs of the other EMLSRs, which in turn switch from the listening operation state 242 to the "blindness frame" or "invalid frame exchange" state referenced at 252 in the figure. In particular, the AP MLD prevents data from being transmitted to these co-affiliated STAs of the other EMLSRs.

[0121] The state switching of all EMLMR co-affiliated STAs in the same non-AP MLD is inseparable and occurs simultaneously, since it is a matter of allocating a complete radio resource chain (see Figure 9 below) to one of the STAs and depriving the others of that chain. For EMLMR mode, the physical resources (e.g., antennas) of one radio resource chain are allocated (aggregated) to another radio resource chain, resulting in the former being deprived of transmit and receive capabilities (see Figure 9a below).

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

[0123] In EMLSR mode, a single complete radio resource is available allocated only to the co-affiliated STAs of the receiving EMLSR, as described below with reference to FIG. 9, whereas in EMLMR mode, the antenna resources of one of the radio stacks are allocated to the other radio stack, requiring simultaneous state changes, as described below with reference to FIG. 9a.

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

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

[0126] This means that after the EMLSR Transition Delay specified in the EML Capabilities, in addition to the completion of the frame exchange operated by the co-affiliated STAs of the receiving EMLSR, the non-AP MLD 120 switches to the listening operational state of the EMLSR, and the co-affiliated STA A1 of the receiving EMLSR switches to the listening operational state 241, as does the co-affiliated STA A2 of the other EMLSR (listening operational state 242). Thus, a state switching procedure is initiated for each of the co-affiliated STAs of the EMLSR.

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

[0128] Now that the non-AP MLD 120 is in EMLSR listening mode of operation, the AP MLD may initiate a new frame exchange sequence (with either the non-AP MLD 120 or 130) by sending a new Initial Control frame.

[0129] In the illustrated example, the AP MLD 110 decides to start such a new sequence again with the non-AP MLD 120 using its EMLSR's co-affiliated STA A2 122. Specifically, the AP MLD 110 uses the other affiliated AP 112 to transmit a new Initial Control frame 265 IC(A) that explicitly triggers the non-AP MLD A120, and this frame is received by the EMLSR's co-affiliated STA A2 122. The receiving EMLSR's co-affiliated STA A2 122 transmits a response frame 266 to the Initial Control frame 265. After the EMLSR active switching delay, the explicitly triggered non-AP MLD 120 switches to EMLSR frame exchange mode, the receiving EMLSR's co-affiliated STA A2 122 switches from listening operation state 242 to valid frame exchange state 272, and the other EMLSR's co-affiliated STA A1 121 simultaneously switches from listening operation state 241 to invalid frame exchange state 271. Frames 275, 276 are then exchanged during the frame exchange sequence until the end of the sequence at which point the non-AP MLD 120 returns to the EMLSR's listening operation mode.

[0130] The A-MPDU 255 / 275 is provided for illustrative purposes only. Other types of frames may be transmitted by the AP MLD, such as, for example, a basic trigger frame to trigger an UL transmission. While FIG. 2 shows a frame exchange in which the acknowledgment 256 / 276 consists of a single frame 255 / 275, a simpler frame exchange may include only a single frame transmitted by the AP MLD without an acknowledgment, and a more complex frame exchange may include multiple exchange sequences, for example, cascaded Transmit Opportunities (TXOPs) of UL transmissions (triggered by the basic trigger frame) and / or DL ​​transmissions (via the HE MU PPDU).

[0131] This example shows the advantages of EMLSR mode in terms of throughput and latency. AP MLD can quickly switch from one link to another, improving communication performance with less added complexity and cost.

[0132] In this example, the AP MLD 110 initiates a frame exchange sequence with one or more designated non-AP MLDs. The D2.0 standard also allows non-AP MLDs to initiate a frame exchange sequence with an AP MLD. In other words, STAs affiliated with a non-AP MLD operating in EMLSR mode do not need to send an Initial Control frame to initiate a frame exchange with the AP MLD. Such affiliated STAs access the wireless medium according to the rules defined in Section 10.3.2.4 (NAV Configuration and Reset) and Section 10.23.2 (HCF Contention-Based Channel Access (EDCA)).

[0133] However, conventional medium access mechanisms (e.g., TWT or rTWT, described below) are not defined with respect to the particularities of an EMLSR-active MLD (in particular, the state of co-affiliated STAs). Recall that an EMLSR-capable non-AP MLD becomes EMLSR-active after successfully exchanging an EML OM Notification frame with an EMLSR-capable AP MLD, in which the EMLSR Mode subfield of the EML Control field is set to 1, the EMLSR link is identified, and the co-affiliated STAs of the corresponding EMLSR are identified.

[0134] As mentioned above, the preceding description also applies to EMLMR mode with the following matching in particular implementation: EMLMR Delay applies to both EMLSR Padding Delay and EMLSR Transition Delay; EMLMR mode Initial Frame aligns with EMLSR mode Initial Control Frame, and similarly EMLMR mode Initial Frame Response aligns with EMLSR mode Initial Control Frame Response; Although not specified in the D2.0 standard, the EMLMR listening operational state / mode may be defined to match the EMLSR listening operational state / mode in which co-affiliated EMLSRs are listening to their links prior to aggregation of physical radio resources.

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

[0136] "EML active switch delay"

[0137] The "EML Active Switching Delay" is defined as the transition period required for a non-AP MLD to switch the state of an affiliated station from an awake or listening operation state to an enabled or disabled frame exchange state. The EML Active Switching Delay ensures that the non-AP MLD has completed its switching operation before the frame exchange triggered by the AP MLD.

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

[0139] In the implementation of EMLSR active switching delay, EMLSR active switching delay = EMLSR Padding Delay + aSIFSTime + Initial Control response frame transmission time: "EMLSR Padding Delay" is a 3-bit subfield of the EML Capabilities subfield of the Common Info field of the Basic Multi-Link element; "aSIFSTime" is the nominal time (in microseconds) it takes for the MAC and PHY to receive the end of a PPDU and process the frames within it and respond with the start of a PPDU containing the earliest possible response frame, The "Initial Control Response Frame Transmission Time" is the time of the shortest Initial Control Response frame used on the EMLSR link for which the EMLSR Padding Delay is determined by non-AP MLD.

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

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

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

[0143] This delay is called the "EMLSR transition delay" for EMLSR operation and the "EMLMR transition delay" for EMLMR operation.

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

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

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

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

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

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

[0150] The non-AP MLD may determine the value of the EMLMR Delay subfield to satisfy constraints related to both the EMLMR active switching delay and the EMLMR transition delay (e.g., the EMLMR Delay may correspond to the maximum value of the minimum allowable values ​​of the EMLMR active switching delay and the EMLMR transition delay).

[0151] To illustrate EMLMR operation according to an embodiment of the present invention, reference is made to the exemplary frame exchange sequence shown in FIG.

[0152] In a TXOP initiated by an AP affiliated to an AP MLD with an EMLMR STA affiliated to a non-AP MLD as the TXOP responder, the non-AP MLD switches to the per-link spatial stream capabilities defined by the EHT Capabilities element or the latest OM (if present) after an EMLMR transition delay (e.g., "EMLMR Delay" or "EMLMR Delay + aSIFSTime + Initial Response Frame Transmission Time" as described above) if any of the following conditions are met, which is defined as the end of the frame exchange sequence: - the MAC of a STA affiliated to the non-AP MLD that received the Initial frame 245 does not receive a PHY-RXSTART.indication primitive within a timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, starting at the end of a PPDU (e.g., Acknowledgement 256) sent by the STA affiliated to the non-AP MLD in response to a frame (e.g., A-MPDU frame 255) most recently received from an AP affiliated to the AP MLD, or starting at the end of reception of a PPDU containing a frame to the STA from an AP affiliated to the AP MLD that does not require immediate acknowledgment; - The MAC of a STA affiliated to the non-AP MLD that received Initial frame 245 receives a PHY-RXSTART.indication primitive during a timeout interval of aSIFSTime + aSlotTime + aRxPHYStartDelay, starting at the end of a PPDU (e.g., Acknowledgment 256) sent by the STA affiliated to the non-AP MLD in response to a frame (e.g., A-MPDU frame 255) most recently received from an AP affiliated to the AP MLD, or starting at the end of reception of a PPDU containing a frame to the STA from an AP affiliated to the AP MLD that does not require immediate acknowledgment, and the STA affiliated to the non-AP MLD does not detect any of the following frames in the PPDU corresponding to the PHY-RXSTART.indication: o Individually addressed frames with RA equal to the MAC address of a non-AP MLD affiliated STA o Trigger frames with one of the User Info fields addressed to a non-AP MLD affiliated STA ○ CTS-to-self frame with RA equal to the MAC address of the AP affiliated to the AP MLD Multi-STA BlockAck frames with one of the Per AID TID Info fields addressed to non-AP MLD affiliated STAs o NDP Announcement frame with one STA Info field addressed to a non-AP MLD affiliated STA and a sounding NDP - A STA affiliated with a non-AP MLD that received Initial frame 245 does not respond to a most recently received frame (e.g., A-MPDU frame 255) from an AP affiliated with an AP MLD that requires immediate acknowledgment after a SIFS.

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

[0154] To meet the low latency requirements of EHT and increase the operational efficiency of UL MUs, existing mechanisms have been reused and improved within the D2.0 standard, and other new mechanisms have been added.

[0155] The Stream Classification Service (SCS) mechanism, originally defined in the IEEE 802.11aa standard, has been adapted for inclusion in the D2.0 standard. The SCS mechanism for multilink allows a non-AP MLD to define and advertise (delay-sensitive) traffic streams, identified by an SCS Identifier (SCSID), to the AP MLD. The adaptation of the SCS mechanism makes it possible to define the QoS requirements of SCS streams through the so-called QoS Characteristics element, and in particular to classify SCS streams as belonging to a TID class in the corresponding uplink (UL) or downlink (DL) direction.

[0156] The target wake time (TWT) mechanism originally defined in the IEEE 802.11ah and 802.11ax standards has been adapted for inclusion in the D2.0 standard. This adaptation, known as restricted target wake time (rTWT), schedules a separate (and protected) service period (SP) 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 more than a Broadcast TWT agreement negotiated between the AP and associated non-AP stations in a given link's BSS. Non-AP stations establish membership in a Broadcast TWT (or rTWT) schedule with the AP. Schedules can be defined for several TIDs (e.g., QoS characteristics identified through SCS mechanisms). The rTWT Service Periods SP of the rTWT schedule, during which the protected exchange of SCS traffic streams may occur, are advertised in broadcast management frames (e.g., beacons) using the rTWT information (typically the Broadcast TWT ID (bTWT ID)) related to the negotiated rTWT SP.

[0157] Although the SCS mechanism is negotiated between the initiator's non-AP MLD and AP MLD, there are still mechanisms such as TWT and rTWT that are negotiated on a per-link basis, i.e., between the initiator's affiliated STA in the non-AP MLD and the corresponding affiliated AP in the AP MLD.

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

[0159] Negotiation to become a member of an rTWT schedule (or more generally, broadcast TWT) or to terminate membership is performed by an exchange of frames carrying TWT elements 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 elements for a given rTWT schedule to its 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] FIG. 3 shows the format of a TWT element 300 adapted for use in an 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 carrying TWT parameter information.

[0163] The "Control" field 310 makes it possible to signal whether the TWT is a Broadcast TWT or an Individual TWT agreement through the "Negotiation Type" field 311. Therefore, the MSB of the Negotiation Type subfield 311 is a Broadcast field, and if the MSB of the subfield 311 is 1, the TWT element 300 is called a Broadcast TWT element. The other fields are of less importance for the present description.

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

[0165] The first field in the "Broadcast TWT Parameter Set" field 320a is the Request Type field 330, which contains the following: - If 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); - TWT Setup Command subfield 332 indicating the type of TWT command: Request, Suggest, Demand, Reject when issued by a non-AP STA, Accept, Alternate, Dictate, Reject when issued by a TWT scheduling AP; - a Trigger field 333 for indicating whether the TWT SP indicated by the TWT element 300 contains a trigger frame (the Trigger subfield is 1 for trigger enablement in the case of r-TWT). Such a TWT SP is called a trigger-enabled TWT SP, and a non-AP station cannot start transmitting data in it without a prior trigger by 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 this 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 subfields are less important: The "Last Broadcast Parameter Set" subfield 334 is set to 0 to indicate another Broadcast TWT Parameter Set following this set. The "Last Broadcast Parameter Set" subfield is set to 1 to indicate this is the last Broadcast TWT Parameter Set for the Broadcast TWT element. o The "Flow Type" subfield 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 (the Flow Type subfield is 0 for r-TWT in "Announce" mode, since r-TWT is a trigger-enabled TWT).

[0166] Other fields in the Restricted TWT Parameter Set field 320a are used to define the time parameters of the rTWT schedule, as follows: - Target Wake Time (TWT) field 340 indicates the next time (in microseconds) that stations 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 of the TWT SP to complete a frame exchange of the TWT Wake Interval duration. The TWT Wake Interval of an rTWT SP is calculated from the TWT Wake Interval Mantissa 360 and the TWT Wake Interval Exponent 337. It is expressed in units defined in the Wake Duration Unit subfield 312 of the Control field 310, e.g., typically 256 μs.

[0167] Other fields in 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 o It carries 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). This identifier is non-zero, allowing the AP to schedule multiple sets of Broadcast TWT SPs with different sets of TWT parameters; o It specifies, via the Broadcast TWT Persistence subfield 374, the number of Target Beacon Transmission Times (TBTTs) for which there are Broadcast TWT SPs corresponding to this Restricted (or more generally Broadcast) TWT Parameter Set; o It also signals, when set to 1, through the Restricted TWT Schedule Full subfield 372, that the r-TWT scheduling AP is unlikely to accept requests from STAs within the BSS to establish new membership in the corresponding schedule (identified by bTWT ID 373); Finally, it also signals through the Restricted TWT Traffic Info Present field 371 whether the Restricted TWT Traffic Info field 380 is present (field 371 set to 1). - The Restricted TWT Traffic Info field 380 is specific to the restriction of Broadcast TWT to a particular traffic. This field is mandatory (thus field 371 is forced to be set to 1) if the Broadcast TWT is related to an SCS LL stream (otherwise the Traffic Info is related to a TID). o It includes a Traffic Info Control field 381 that indicates whether the following fields 382 and 383 are provided (e.g., "Valid"): DL TID Bitmap Valid subfield 3811 (respectively, UL TID Bitmap Valid subfield 3812) indicates whether the Restricted TWT DL TID Bitmap field 382 (respectively, Restricted TWT UL TID Bitmap field 383) has valid information. o The Restricted TWT DL TID Bitmap field 382 (respectively, Restricted TWT UL TID Bitmap field 383) identifies TIDs (e.g., TIDs allowed in the rTWT defined by the Restricted TWT element 300) as latency-sensitive traffic in the DL (respectively, UL) direction. The TIDs may define SCS streams. A value of 1 in bit position k of the bitmap indicates that TID k is classified as a latency-sensitive traffic stream for that transmission direction.

[0168] The TWT SP for the rTWT schedule is:<bTWT ID、TWTスケジューリングAPのMACアドレス> The TWT scheduling AP is uniquely identified by the tuple of AP MLD for that link.

[0169] This element in the TWT Request frame allows an initiator STA to request the AP to become an r-TWT scheduled STA by negotiating an r-TWT SP for low-latency traffic. For example, the initiator STA (affiliated to a non-AP MLD) may negotiate the wake TWT, wake interval, and SCS streams allowed in the rTWT. The AP (affiliated to the AP MLD on that 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 carries a TWT element with the Negotiation Type subfield 311 set to 3 and the TWT Setup Command field 332 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 that the STA is requesting to join. The AP may respond (TWT Response frame) with either no new rTWT schedule for that bTWT ID (keep the existing one), or provide an alternative set of parameters indicated in the TWT Request frame, or create a new rTWT schedule with the new bTWT ID.

[0171] Once negotiation and membership are complete, a conventional TWT / rTWT scheduled STA in the awake state may enter the Doze state after receiving a Beacon frame with a Restricted TWT element indicating the existence of an rTWT schedule, advertising the rTWT SP (e.g., via a Beacon frame), and switch back to the awake state at the rTWT start time. The Beacon frame indicates the rTWT SP on which the TWT scheduling AP intends to send a Trigger frame or DL ​​BU to the TWT scheduled STA on that link.

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

[0173] 4 illustrates, using a frame sequence, a particular embodiment of the EMLSR mode of operation in a non-AP MLD 120 that has negotiated rTWT service with the AP MLD 110 over one of the EMLSR links, e.g., link 151. Of course, the EMLSR mode is emphasized here as an example, but similar considerations apply to the EMLMR mode.

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

[0175] As shown in FIG. 4 with EMLSR active non-AP MLD 120 in EMLSR listening mode of operation, EMLSR co-affiliated STAs A1 121 and A2 122 are both in listening operational states 410 and 411 .

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

[0177] The non-AP MLD 120 can simultaneously listen on the EMLSR links by placing the co-affiliated STAs of the EMLSRs corresponding to those links in an "awake" or "listening" state. For example, affiliated STAs A1 and A2 are in a listening state (references 410 and 411). The listening state includes clear channel assessment (CCA) and reception of Initial Control frames of a frame exchange initiated by the AP MLD. In the non-AP MLD 120, the co-affiliated STAs of the two EMLSRs therefore simultaneously listen to receive not only Initial Control frames from the AP MLD but also beacon frames (because such beacon frames are also emitted with a low MCS and a non-HT format).

[0178] Thus, by receiving the beacon frame 430, the affiliated STA A1 can determine the individual transmission window (rTWT) that should be reserved for it on the link 151.

[0179] Then, at the start of this reserved rTWT service period, the AP MLD 110 attempts to initiate a frame exchange with one or more non-AP MLDs on one of the EMLSR links, and initiates the frame exchange by sending an Initial Control frame 445 that explicitly triggers the non-AP MLDs.

[0180] A co-affiliated STA of the non-AP MLD EMLSR (e.g., affiliated STA A1 in the embodiment) that receives the frame explicitly triggered by the Initial Control frame 445 initiates a state change of the co-affiliated STA of the non-AP MLD EMLSR under consideration (e.g., a state change of affiliated STAs A1 and A2 in the embodiment) and sends an Initial Control frame response (IC resp.) 446 to the AP AP1 affiliated to the AP MLD 110.

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

[0182] Frames 455, 456 are then exchanged during the frame exchange sequence until the end of the sequence at which point the non-AP MLD 120 switches back to the EMLSR listening mode of operation.

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

[0184] When the frame exchange on link 151 is completed, non-AP MLD 120 again initiates the state switching procedure to return EMLSR co-affiliated STAs A1 121 and A2 122 to the listening operational states 410, 411. Thus, non-AP MLD 120 switches back to the EMLSR listening operational mode. Switchback 499b operates for the EMLSR transition delay (specified in EML Capabilities) after the frame exchange within the service period is completed.

[0185] When AP1 111 affiliated with the AP MLD 110 transmits an Initial (Control) frame initiating a frame exchange with at least one non-AP MLD operating in EMLSR mode and at least one non-AP MLD operating in EMLMR mode, the AP ensures that the padding period in the Padding field of the Initial Control frame is greater than or equal to the maximum 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 with which the frame exchange was initiated. The transition period 499a, from the perspective of an individual STA MLD 120, falls within a delay commonly referred to as the "EMLSR active switch delay" from the perspective of the AP, and is comprised of the maximum of the "EMLSR active switch" delay and the "EMLMR active switch" delay of the triggered station.

[0186] In other words, AP1 111 affiliated with AP MLD 110 transmits an Initial frame that triggers a frame exchange with 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 in the Padding field of the Initial frame is greater than or equal to the maximum of the values ​​indicated in the EMLSR Padding Delay subfield received from at least one non-AP MLD operating in EMLSR mode and the EMLMR Delay subfield received from at least one non-AP MLD operating in EMLMR mode.

[0187] The example scenario in Figure 4 shows that the EML operating mode and the TWT (e.g., rTWT) mechanism can theoretically work together. They allow an EML station to transmit a latency-sensitive stream in a separate transmission window (rTWT) reserved for the EML station. However, the resulting overall mechanism still has flaws: - The Initial Control frame 445 that explicitly triggers non-AP MLD and the corresponding response 446 provide significant overhead in critical resources for latency-sensitive streams. - To take advantage of scheduled rTWT SPs, EML STAs must know when the SPs will occur; therefore, EML STAs must also perform beacon reception, which is not yet assumed in the 802.11be standard.

[0188] In general, mechanisms and procedures that operate on per-link procedures, such as the exemplary Target Wake Time (TWT) and its recent adaptation known as Restricted Target Wake Time (rTWT), may not be fully applicable to the EML mode where the EMLSR and EMLMR links are not fully independent.

[0189] It has been desired to efficiently manage the EML mode of an EML non-AP MLD after a first Affiliated STA of an EML non-AP MLD has negotiated a medium access service or mechanism on the first link of the EML link. If such a mechanism (link-specific procedure) is determined based on reception of a beacon frame on the first link by the first Affiliated STA, the latter should not be in a blind mode during reception of the beacon frame, and therefore a second Affiliated STA of the same EML non-AP MLD should not be communicating over a second other link of the EML link during that period.

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

[0191] Although further embodiments are described with respect to TWT (rTWT), the present invention can be extended to other link-specific procedures and should not be limited to TWT mechanisms. As an example, the Quiet Element corresponding to the scheduled quiet intervals to protect r-TWT SPs is also a link-specific mechanism (i.e., a link-specific procedure).

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

[0193] Figure 5 illustrates, by means of a flow chart, the steps (service period schedule acquisition and channel access procedure) performed by an EMLSR active non-AP MLD to operate a TWT service according to an embodiment of the present invention. Figures 6a and 6b schematically illustrate an example timeline of TWT operation as described in Figure 5.

[0194] For simplicity of explanation, we will mainly refer to the EMLSR mode only, but the same applies to the EMLMR mode.

[0195] The process begins at step 500, where the non-AP MLD enters the (EMLSR or EMLMR) listening mode of operation, meaning that its co-affiliated STAs are set to a listening state of operation, and are therefore simultaneously listening to their respective (EMLSR or EMLMR) links. The non-AP MLD may enter the listening mode of operation in response to receiving an EML OM Notification frame with the corresponding Mode subfield (EMLSR or EMLMR Mode subfield of the EML Control field) set to 1.

[0196] In step 510, the non-AP MLD waits to buffer latency-sensitive data to be transmitted to the AP MLD 110 (uplink). It may also consider latency-sensitive data to be transmitted to other non-AP MLDs over the direct link under the control of the AP MLD 110 (triggered direct link data). As mentioned above, such data may be provided from a higher layer and stored in the non-AP MLD's buffer 210. The non-AP MLD determines the TWT negotiation to be activated on one of the EMLSR or EMLMR links (link 151 is the one selected in FIGS. 6a and 6b).

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

[0198] In response to the successful establishment of the TWT mechanism over the first link, a scheduling operation (identical to step 550, further described) may be performed regarding the date of reception of the next beacon frame (i.e., the next TBTT occurrence).

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

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

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

[0202] Various configurations are possible for step 530: - If there is no activity on any link, a state switching procedure is initiated by the non-AP MLD and the co-affiliated STAs remain in the listening mode of operation, where they are obligated to maintain this listening mode until the beacon frames are no longer received (steps 531 and 532). Furthermore, these EML co-affiliated STAs must ignore Initial Control frames addressed to them that overlap in time with beacon frames 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 over which the 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 a frame exchange (even though it is willing to receive the beacon frame), while in parallel (synchronously or simultaneously), other co-affiliated STAs of the EMLSR or EMLMR's link set (e.g., one of Link 2) are switched from a listening operation state to an inactive frame exchange state (step 532). This easily prevents the reception of IC frames on other links. This case is shown in the subsequence "Case C" of FIG. 6c. - If there is a frame exchange on the other EML link, the co-affiliated STAs on the other link are requested to terminate their participation in the Transmit Opportunity (TXOP) and enter the EML mode suitable for receiving beacon frames. This case is shown in the subsequence "Case A" in Figure 6a. The non-AP MLD initiates a state switching procedure for each co-affiliated STA in the EMLSR or EMLMR to switch back to the EML listening operational state, so that co-affiliated STA1 121 is ready to receive beacon frames 430 successfully. - If there is a frame exchange on the selected EML link, the co-affiliated STAs (selected link) of the sending EMLSR remain in an active frame exchange state and wait for the medium to return to an idle state (they may terminate existing TXOPs, as legacy stations do when the TBTT time is approaching). The co-affiliated STAs of the other EMLSRs also maintain their current state (invalid, step 532). This allows them to continue receiving beacon frames. This case is shown in the subsequence "Case B" of Figure 6b.

[0203] In other words, in step 530, the configuration of the selected co-affiliated STA or first affiliated station (corresponding to the selected link or first link, e.g., link 1 151, over which the beacon frame is to be transmitted) by the non-AP MLD 120 includes: - case A: terminate the ongoing frame exchange over the second link of the EML link and switch the first affiliated station to an operating state suitable for receiving a second beacon frame (for example, in a first variant, by switching the first affiliated station to a listening operating state, in which case the second affiliated station shall trigger a frame exchange sequence over the second link and shall ignore any Initial frame that overlaps in time with the first beacon frame on the first link, or in a second variant, by switching the first affiliated station to an active frame exchange state); or Case B: Terminate the ongoing frame exchange over the first link and maintain the first affiliated station in a valid frame exchange state (e.g., maintain if the time distance to TBTT is less than a predetermined threshold, which in certain embodiments is at least the sum of the (first) transition period required for the non-AP MLD to switch the state of the affiliated station from a listening operation state to a valid or invalid frame exchange state and the (second) transition period required for the non-AP MLD to switch the state of the affiliated station from a valid or invalid frame exchange state to a listening operation state), or - Case C: Switch the first affiliated station from a listening operation state to an active frame exchange state.

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

[0205] As an example of the relevant context for this embodiment, the TWT Information element 300 may be analyzed to ascertain the scheduling of the TWT service period (eg, wake TWT and wake interval via fields 340, 360, 337).

[0206] To quiet a STA during an r-TWT service period, the r-TWT scheduling AP may schedule a quiet interval that overlaps with the r-TWT SP of a given link. The overlapping quiet interval may be scheduled by including one or more Quiet elements in a Beacon frame. Thus, the Quiet element is another example of content relevant to this embodiment: a non-AP MLD must not transmit during any quiet interval. Furthermore, a non-AP MLD thus determines that one of its co-affiliated STAs must be quiet during a quiet interval corresponding to an r-TWT service period of 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, at the next TBTT occurrence (considering that the current TBTT occurrence 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 an EML event related to the next (second) beacon frame. Thus, non-AP MLD implements a communication method that includes: receiving, by a first affiliated station (e.g., STA A1), a first beacon frame via a first link (e.g., 151) of the EML link, the first beacon frame including a target beacon transmission time (TBTT) associated with a second beacon frame; - Setting the first affiliated station (e.g., STA A1) to receive at TBTT to receive the second beacon frame.

[0210] Optionally, after association with the AP MLD, the non-AP MLD may schedule events for TBTT timing on all EML links, so that it can determine link-specific procedures (e.g., Quiet Elements for non-member TWTs) for all EML links. If link-specific procedures are negotiated in step 510, the non-AP MLD may schedule its own device for beacon frames on the selected links for initial discovery of TWT / rTWT elements indicating the service period of the TWT service it negotiated.

[0211] With regard to further beacon TBTT scheduling related to TWT operation, non-AP MLD may relax the constraints of each TBTT of the selected link: notification of the Broadcast TWT Persistence subfield 374 may make it possible to determine the number of target beacon transmission times (TBTTs) in which there is a Broadcast TWT SP corresponding to this Restricted (or more generally Broadcast) TWT Parameter set; therefore, 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 above context in which non-AP MLD sets a first affiliated station (e.g., STA A1) to be in a receiving state at a TBTT to receive a second beacon frame, if the second beacon frame includes another TBTT associated with a third beacon frame that schedules a TWT service period on the first link, and the scheduled TWT service period is signaled in 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 a receiving state at another TBTT to receive the third beacon frame on the first link.

[0213] As is clear from Figures 6a to 6c, the scheduled event is preferably prior to the publication date and time (of the beacon frame or TWT period) so that there is no "EML active switch delay" 499 / 499a etc.

[0214] This is because the simultaneous switching, as defined above and indicated by reference numerals 499 / 499a in the figure, lasts at most the EMLSR or EMLMR active switching delay time. In the embodiment, the EMLSR co-affiliated STA A1 is selected. It may be a station with a full radio or a station with a light (reduced functionality) radio. In practice, since the switching of an EMLSR co-affiliated STA with a full radio (requiring only an antenna connection) is shorter than the switching of another EMLSR co-affiliated STA with a light radio (because it requires physical and reconfiguration of the full radio chain), the non-AP MLD can adapt its scheduling to take into account the appropriate timing 499 / 499a with respect to its hardware configuration (e.g., reduce the scheduling margin for links configured with full radios).

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

[0216] In practice, the scheduling operation is performed by the non-AP MLD in its upper MAC 230, since this entity can collect management frame information from all links and configure the lower MAC entities 220-x / 220-y / 220-z accordingly. Since the upper MAC is responsible for frame decoding, it can obtain the TBTT of all links, and therefore it seems preferable for the U-MAC 230 to control the activity of the L-MAC (e.g., temporarily stop activity on the medium or force a "listening" mode).

[0217] As explained in Figure 5, it is also possible to first stop the TXOP activity of LL-MAC and then switch the EML setting.

[0218] Upon completion of beacon frame reception on link 1, the non-AP MLD again initiates the state switching procedure to return its co-affiliated STAs to the listening operation state (step 590). Thus, the non-AP MLD switches back to the listening operation mode. The switchback operates for the EMLSR transition delay (specified in EML Capabilities) or the EMLMR transition delay (as described above, depending on the implementation of the present invention) after the frame exchange ends.

[0219] Returning to test 520, the EML event scheduled in step 550 for the link-specific mechanism is processed via steps 560 through 580.

[0220] The purpose of step 560 is to set the non-AP MLD to the appropriate state on the associated link. Therefore, a state switching procedure is invoked for each co-affiliated STA in the EML, thus: If the scheduled EML event is associated with a (r-)TWT service period, non-AP MLD aims to be active for that link when the (r-)TWT period begins. Thus, the "first" link in step 561 is the link corresponding to the selected co-affiliated STA. The non-AP MLD-affiliated STAs on the corresponding links (e.g., the co-affiliated STA A1 of the receiving EMLSR in the example of FIGS. 6a and 6b) are configured to be able to transmit or receive frames on the active links during the TWT service period (step 561). As will become clearer, the co-affiliated STA A1 of the EMLSR does not need to receive Initial Control frames for frame exchange, thereby saving resources in the TWT SP. At the same time, other EMLSR co-affiliated STAs in the same non-AP MLD (e.g., STA A2 in the example of FIGS. 6a and 6b) are configured not to transmit or receive on other EMLSR links until the TWT period expires. To this end, a state switching procedure is also initiated for the other EMLSR co-affiliated STAs, which switches the other EMLSR co-affiliated STAs from listening operation (step 562) to a "blind frame" or "invalid frame exchange" state. - If a scheduled EML event is associated with the Quiet element of the (r-)TWT service period, non-AP MLD aims to be disabled on that link when the Quiet Period begins. To that end, the co-affiliated STAs of the selected EMLSR of the same non-AP MLD (e.g., STA A1 in the example belonging to the link from which the beacon frame was issued) are set not to transmit or receive until the frame exchange is completed (step 562). The co-affiliated STAs of the other EMLSRs of the same non-AP MLD may be switched to a listening operation state (if possible by the hardware to compensate for the fact that one link has been disabled), or better, at most one of the co-affiliated STAs of the other EMLSRs of the same non-AP MLD (e.g., STA A2 in the example) switches from the listening operation state to an "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 a receive state at the TBTT to receive the second beacon frame, the second beacon frame schedules a quiet period on the first link, and during the quiet period, switches the first affiliated station to an inactive frame exchange state until the quiet period ends. Furthermore, the non-AP MLD switches the second affiliated station to an active frame exchange state on the second link of the EML link upon the quiet period until the quiet period ends.

[0221] As mentioned above, the "EML Active Switch Delay" is preferably taken into account to enable the settings at the appropriate date and time.

[0222] The state switching of all EMLMR co-affiliated STAs in the same non-AP MLD is inseparable and occurs simultaneously, since one of the STAs is assigned a complete radio resource chain (see Figure 9a below) while the other STAs are deprived of their radio resource chain. Regarding EMLMR mode, the physical resources (e.g., antennas) of one radio resource chain are allocated (aggregated) to the other radio resource chain, thus depriving the former of its transmit / receive capabilities (see Figure 9b below).

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

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

[0225] For TWT, the Nominal Minimum TWT Wake Duration field 350 indicates the minimum time a TWT-scheduled STA is expected to be awake from the start of the TWT SP to complete a frame exchange for the duration of the TWT Wake Interval. Therefore, reversion operates within the EMLSR transition delay (specified in 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 a frame exchange sequence is shown in the figure below.

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

[0228] In an embodiment, the EMLSR's co-affiliated STA1 121 is selected as the associated station in a link-by-link procedure, which may be a station with a full radio or a station with a light (reduced functionality) radio.

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

[0230] As shown in the EMLSR active non-AP MLD 120 of FIG. 6 a, both EMLSR co-affiliated STAs A1 121 and A2 122 have switched (previously, not shown) from listening operation 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 mentioned above with respect to step 530, both the termination of TXOP participation by STA A2 and the switch following period 499b are considered here specifically to terminate phases 610 and 611. The termination of the TXOP can be performed in several ways, such as by shortening the data communication, by not responding to the other device (AP of link 2), or by issuing a CF-End frame if STA A2 is the TXOP holder.

[0232] As a result, if a non-AP STA affiliated to a non-AP MLD and operating on one of the paired EMLSR or EMLMR links seeks to receive a broadcast management frame (beacon frame 430) on a first link (151), and a second non-AP STA (STA A2) affiliated to the same MLD participates in a frame exchange on a second link (152) that overlaps with the TBTT of the first link, then 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 is completed at least T times 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 is terminated at least T times before the TBTT of the first link.

[0233] In embodiments, T is equal to one of the following values: - EMLSR transition delay (499b) indicated in the EMLSR Transition Delay subfield if two non-AP STAs belong to a pair of EMLSR links; - If two non-AP STAs belong to an EMLMR link pair, the EMLMR delay specified for the EMLMR link pair (e.g., the EMLMR inactive switching delay specified above, depending on the implementation) is indicated in the EMLMR Transition Delay subfield.

[0234] If multiple non-AP STAs are operating on the TXOP of the 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 (determined here above) for those non-AP STAs.

[0235] In other embodiments, T is equal to one of the following values: - EMLSR transition delay indicated in the EMLSR Transition Delay subfield if two non-AP STAs belong to a pair of EMLSR links (499b); - If two non-AP STAs belong to a pair of EMLMR links, EMLMR Delay + aSIFSTime + Initial Response Frame Transmission Time (e.g., EMLMR Inactive Switching Delay specified above, depending on the implementation).

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

[0237] If multiple non-AP STAs are operating on the TXOP of the 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 (determined here above) for those non-AP STAs.

[0238] A simultaneous switch (eg, putting all co-affiliated STAs into "listening" mode) lasts at most the EMLSR active switch delay or the EMLMR active switch delay specified above.

[0239] In other words, the configuration of the selected co-affiliated STA or first affiliated station (STA A1) (corresponding to the selected link or first link, e.g., link 1 151, over which the beacon frame is to be transmitted) by the non-AP MLD 120 is triggered at least a first determined delay (e.g., the EMLSR active switching delay, the EMLMR active switching delay, or the maximum value of the EMLSR and EMLMR active switching delays) before the TBTT.

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

[0241] This mode may also be advantageous for receiving beacon frames over two EML links (if they are synchronized in time).

[0242] Once the beacon frame is received, all co-affiliated STAs of the EML may carry out normal operations.

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

[0244] Compared with Fig. 4, it is assumed that the EML scheduler schedules the switching of the "active frame exchange" or "valid frame exchange" state of STA1 before the start of the intended TWT SP 630. Typically, the switching delay 499 / 499a (belonging to the group including EMLSR active switching delay, EMLMR active switching delay, and the maximum value of EMLSR and EMLMR active switching delay) occurs before the TWT SP 630.

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

[0246] As a result, if a non-AP STA affiliated to a non-AP MLD and operating on one of a pair of EMLSR or EMLMR links is a member of an R-TWT SP on a first link (151); if a second non-AP STA (STA A2) affiliated to the same MLD is not a member of another R-TWT SP on a second link (152) that overlaps with the first SP, then 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 at least 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 T times before the start time of the R-TWT SP (630) on the first link.

[0247] In embodiments, T is equal to one of the following values: - EMLSR transition delay (499b) indicated in the EMLSR Transition Delay subfield if two non-AP STAs belong to a pair of EMLSR links; - If two non-AP STAs belong to an EMLMR link pair, the EMLMR delay specified for the EMLMR link pair (e.g., the EMLMR inactive switching delay specified above, depending on the implementation) is indicated in the EMLMR Transition Delay subfield.

[0248] If multiple non-AP STAs are members of the R-TWT SP of the first link (151) and operate with TXOPs of the 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 (determined here above) of those member non-AP STAs.

[0249] In other embodiments, T is equal to one of the following values: - EMLSR transition delay (499b) indicated in the EMLSR Transition Delay subfield if two non-AP STAs belong to a pair of EMLSR links; - If two non-AP STAs belong to a pair of EMLMR links, EMLMR Delay + aSIFSTime + Initial Response Frame Transmission Time (e.g., EMLMR Inactive Switching Delay specified above, depending on the implementation).

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

[0251] If multiple non-AP STAs are members of the R-TWT SP of the first link (151) and operate with TXOPs of the 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 (determined here above) of those member non-AP STAs.

[0252] The Initial (Control) frame 445 and corresponding response 446 used to explicitly trigger non-AP MLD provide significant overhead in critical TWT SP resources for latency-sensitive streams, and since the TWT SP has already been determined, the non-AP MLD may configure its affiliated EML STAs so that they are ready to operate during the TWT SP 630.

[0253] If the non-AP MLD 120 wishes to initiate a frame exchange sequence with the AP MLD 110 during TWT SP630 (in which the EMLSR's co-affiliated STA A1 121 was selected as the transmitting EMLSR's co-affiliated STA in the negotiated TWT), it switches the EMLSR's co-affiliated STA A1 121 from the listening operation state 410 to the valid frame exchange state 620, and in parallel (synchronized or simultaneously) switches the EMLSR's co-affiliated STA A2 122 from the listening operation state 411 to the invalid frame exchange state 621.

[0254] The listening operation state is restored and becomes operable after the TWT SP630 corresponding to the switchback is completed (period 499b defined by the EMLSR Transition Delay set in the EML Capabilities).

[0255] In other words, in the above context in which the non-AP MLD configures the first affiliated station (e.g., STA A1) to enter a receive state at the TBTT to receive the second beacon frame, the second beacon frame schedules a service period on the first link, and upon completing the frame exchange within the service period, the non-AP MLD maintains the first affiliated station in an active frame exchange state until the end of the service period. In a particular embodiment, the non-AP MLD 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. Furthermore, 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] An EMLSR co-affiliated STA switches back to a listening mode of operation for the entire service period 630, regardless of the duration field of the frame that triggered it (basic trigger 455) (or more generally, after the end of the frame exchange with that AP). This may support multiple frame exchanges with the AP (if any) during the service period 630 without requiring the overhead of additional Initial (Control) frame / response EML enable sequences.

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

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

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

[0260] Normally, according to 802.11be D0.5, if a non-AP MLD STA initiates a TXOP, the non-AP MLD switches back to listening operation on the EMLSR link after the TXOP ends and the period indicated in the EMLSR Transition Delay subfield (499b).

[0261] This rule is adapted 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 reception of a beacon frame: to be able to receive the beacon frame, the co-affiliated STA A1 remains in the valid frame exchange state 620a, and the co-affiliated STA A2 remains in the invalid frame exchange state 621a (this avoids a change of EML mode due to the reception of an Initial frame during that period).

[0263] In a different operation, the non-AP MLD first determines the remaining time in the TBTT, and then, based on that time, decides whether to return to listening mode of operation or stay in the current EMLSR frame exchange mode. For example, if the time is long (e.g., its value is higher than a threshold), the EMLSR co-affiliated STAs will switch back to listening mode of operation (thus resulting in the situation of Case C shown in Figure 6c). If the time is short (e.g., its value is lower than a threshold), the EMLSR co-affiliated STAs will maintain their current state.

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

[0265] Embodiments provide that the non-AP MLD switches only one EMLSR's co-affiliated STAs to an active state (e.g., switches the selected EMLSR's co-affiliated STAs to a valid frame exchange state, and switches the other EMLSR's co-affiliated STAs to an invalid sending EMLSR's co-affiliated STAs).

[0266] In the figure, a co-affiliated STA (corresponding to the selected link for which the beacon frame is intended, e.g., link 1 151) is switched from a listening operation state to an active frame exchange state 660 so that a frame exchange (even if only attempting to receive the beacon frame) can be performed, and in parallel (synchronized or simultaneously), another co-affiliated STA of the set of EMLSR or EMLMR links (e.g., one of link 2) is switched from a listening operation state 411 to an inactive frame exchange state 661.

[0267] FIG. 6c also shows an extended frame exchange sequence ("Case D") for supporting quiet periods for the rTWT mechanism by an EML station according to the present invention.

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

[0269] In this context, activity on the first link (beacon received, indicating a quiet period for TWT) is prohibited, so another EML link can be used to become active in the meantime.

[0270] Thereafter, in accordance with the EMLSR mechanism, after an EMLSR active switching delay 499, the non-AP STA is scheduled to switch from the EMLSR listening operation mode to the EMLSR frame exchange mode with a view to locating one of the EMLSR co-affiliated STAs operable for frame exchange on a link different from the prohibited first link. The EMLSR co-affiliated STAs including the first link 151 on which STA A1 received the beacon frame are disabled.

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

[0272] 7 and 8 show, using a flow chart, the steps performed by an EMLSR active non-AP MLD to set up TWT service, essentially detailing step 510 for determining EML co-affiliated STAs that are allowed to negotiate link service.

[0273] Figure 7 provides guidance for the case where the TWT service is already 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 EMLSR / EMLMR mode, activates EMLSR / EMLMR mode, and an EML Operating Mode Notification frame is successfully sent to the non-AP MLD 120 indicating affiliated STAs A1 and A2.

[0276] Step 730, according to an embodiment, is intended to indicate to the AP that one of the EML links should be monitored for both EML operations and per-link mechanisms (such as TWT). The purpose of such notification is to avoid link contention for AP-monitored events. In an embodiment, since the AP MLD controls the TWT and beacon scheduling for all active links, the MLD AP is alerted to avoid scheduling TWT SPs for EMLSR STAs that overlap with beacons for other EMLSR links. In other words, in a future beacon frame, the non-AP MLD sends a notification to the AP MLD to schedule a service period for the non-AP MLD (on the first link) that does not overlap in time with beacon frames transmitted by the AP MLD on the second link of the EML links. Such notification ensures that the non-AP MLD can receive beacon frames over the second link 152, regardless of the service period scheduled for the first link 151.

[0277] An exemplary support for such notification 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 EML operation is enabled and the non-AP MLD originator of the TWT element requests AP assistance to avoid EML link contention (the AP is requested to avoid scheduling r-TWT SPs for EML STAs that overlap with beacons on other EML links).

[0278] Figure 8 briefly describes the steps performed by a non-AP MLD that attempts to limit the use of TWT services over a given number of links. Even if it were possible to manage more links, it might appear complex and inefficient (due to too many EML active / suspended period switches).

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

[0280] If the number of links is greater than desired, the non-AP MLD may reject new (r)TWTs on 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 along with the new upcoming TWT service on the second link (step 830). In the example of Figures 6a-6c, this means that all TWT services are located on a single link (here, link 151).

[0281] In summary, the above-described embodiments provide that if a STA affiliated with a non-AP MLD intends to receive a beacon frame scheduled with a TBTT on one (first) of its EML (EMLSR or EMLMR) links, the non-AP MLD must be enabled to listen on the EML (EMLSR or EMLMR) link. Therefore, the following rules must be satisfied: - If another STA affiliated to the same non-AP MLD successfully acquires a TXOP on another link of the EML (EMLSR or EMLMR) link, it should terminate the TXOP before the TBTT of that (first) link (see Figure 6a, Case A). - If the same STA affiliated to 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 TBTT (see Figure 6b, Case B). - STAs affiliated with the same non-AP MLD that are listening on an EML (EMLSR or EMLMR) link MUST ignore Initial Control frames addressed to them that overlap with the TBTT on the intended (first) link (e.g., overlap in time with a beacon frame transmitted at the TBTT on the first link).

[0282] 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 over that EMLSR link - To protect the r-TWT SP, a Quiet element corresponding to the Quiet Interval is scheduled.

[0283] Figure 9 shows a schematic diagram of an EMLSR-enabled architecture for an MLD. This diagram illustrates an example in which two non-AP STAs share the hardware resources of a non-AP MLD when EMLSR mode is enabled. The EMLSR-enabled architecture for an MLD shown in this diagram is for illustrative purposes only, and other alternative architectures are also possible.

[0284] The architecture includes two wireless stacks: a light wireless stack and a full wireless stack.

[0285] The complete wireless stack includes a complete 802.11be MAC module 900a (which exchanges data with upper layers), 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 the EMLSR switch 910.

[0286] The light wireless stack includes a light 802.11be MAC module 900b (which exchanges data with upper layers), 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 the two wireless stacks and is configured to switch the EMLSR co-affiliated STAs from / to a listening operation state or to / from an enabled frame exchange state or an disabled frame exchange state when the EMLSR mode is enabled.

[0288] Radio chains 900a, 905a, and 915a are complete radio resources that allow the reception and transmission of any IEEE 802.11 frame. Specifically, they include encoding and decoding modules for encoding and decoding any IEEE 802.11 frame. Meanwhile, radio chains 900b, 905b, and 915b are reduced-function (or "lite") radio resources that allow the reception and transmission of only specific IEEE 802.11 frames. Specifically, they include only encoding and decoding modules for encoding and decoding specific frames using rates of 6 Mbps, 12 Mbps, or 24 Mbps.

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

[0290] The bottom-center diagram illustrates the functionality of the non-AP MLD when switching 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, while the co-affiliated STAs of the other EMLSR corresponding to link 2 are in the inactive frame exchange state. In this 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 antennas 920a / 920b are configured to operate on link 1. Here, because 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 switching the antenna. Meanwhile, the common EMLSR switch 910 disconnects the light radio chain 900b / 905b / 915b from antenna 920b. In this configuration, the light radio chain 900b / 905b / 915b cannot receive or transmit frames on link 2, and only link 1 is available.

[0291] The bottom right diagram illustrates the functionality of the non-AP MLD when switching to a second EMLSR frame exchange mode. The co-affiliated STAs of the EMLSR corresponding to link 2 are in an active frame exchange state, while the co-affiliated STAs of the other EMLSR corresponding to link 1 are in an inactive frame exchange state. In this 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 antennas 920a / 920b are configured to operate on Link 2. Here, the switching time from the EMLSR listening operation state to the active frame exchange state can be considered long because the complete radio chain is switched to operate on Link 2. In fact, in this case, the switching includes both an antenna switch and a complete radio chain configuration switch. Meanwhile, the common EMLSR switch 910 disconnects the light radio chain 900b / 905b / 915b from the antenna 920b. In this configuration, the light radio chain 900b / 905b / 915b cannot receive or transmit frames on link 1, and only link 2 is available.

[0292] The common EMLSR switching 910 functionality clearly indicates that state changes of co-affiliated STAs of two EMLSRs in the same MLD are necessarily simultaneous, since the radio chain is either connected to one STA or the other, but not both STAs are available at the same time.

[0293] Figure 9a shows a schematic diagram of an EMLMR-enabled architecture for MLD, where two affiliated non-AP STAs share antenna resources when EMLMR mode is activated.

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

[0295] The radio stack includes a complete 802.11be MAC module 900a' or 900b' (which exchanges data with upper layers), 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 the two radio stacks and configured to perform antenna resource aggregation when EMLMR mode is activated, and an antenna array 920a' or 920b'.

[0296] The diagram on the bottom left shows the functionality when non-AP MLD is listening to the Initial frame: A common EMLMR switch 910' connects each antenna array to an RF chain. Each radio stack is therefore complete and may serve each link using, for example, a 2x2 MIMO antenna configuration. As shown in the diagram, two links are available.

[0297] The bottom-center diagram illustrates the functionality of non-AP MLD when switching to a first EMLMR frame exchange mode. The EMLMR co-affiliated STAs corresponding to link 2 are in an enabled frame exchange state, while the other EMLMR co-affiliated STAs corresponding to link 1 are in a disabled frame exchange state. The common EMLMR switch 910 aggregates antenna resources to link 2 by connecting the antenna array 920a' of the second wireless stack to the RF chain 915b' of the first wireless stack. Therefore, the first wireless stack operates in a 4x4 MIMO antenna configuration, which may improve throughput for link 2. Meanwhile, link 1 becomes unavailable because its antenna array 920a' is no longer available to the second wireless stack.

[0298] The bottom right diagram illustrates the functionality of non-AP MLD when switching to a second EMLMR frame exchange mode. The EMLMR co-affiliated STAs corresponding to link 1 are in an enabled frame exchange state, while the other EMLMR co-affiliated STAs corresponding to link 2 are in an disabled frame exchange state. The common EMLMR switch 910′ aggregates antenna resources to link 1 by connecting the antenna array 920b′ of the first wireless stack to the RF chain 915a′ of the second wireless stack. Therefore, the second wireless stack operates in a 4x4 MIMO antenna configuration, which may improve throughput for link 1. Meanwhile, link 2 becomes unavailable because its antenna array 920b′ is no longer available to the first wireless stack.

[0299] The functionality of the common EMLMR switch 910' clearly shows that state changes of two EMLMR co-affiliated STAs in the same MLD are necessarily simultaneous, since antenna resources are either connected to one STA or the other, but not both STAs, at the same time.

[0300] 10 shows a schematic diagram of 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 may preferably be a device such as a microcomputer, a workstation or a lightweight handheld 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 executable code of a method or method steps according to an embodiment of the present invention, and registers adapted to record 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 according to one of the standards of the IEEE 802.11 family) via transmitting and receiving antennas 1004 and 1004' respectively.

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

[0302] The executable code may be stored in a memory, either read-only, on a hard disk, or on a removable digital medium, such as a disk. According to an optional variant, the executable code of the program may be received by the communication network, via the interface 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 apparatus that uses software to implement embodiments of the invention, however, embodiments of the invention may alternatively be implemented in whole or in part in hardware (e.g., in the form of an Application Specific Integrated Circuit or ASIC).

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

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

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

Claims

1. A wireless network communication method in a non-access point (non-AP) multi-link device (MLD) operating in an Enhanced multi-link (EML) link set in an EML mode, comprising: a first receiving step of 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) associated with a second beacon frame; a second receiving step of receiving, by the first affiliated station, the second beacon frame at the TBTT that schedules a quiet period on the first link; and a switching step of switching the first affiliated station to a state in which the first affiliated station does not transmit or receive frames during the quiet period until the quiet period ends. method.

2. The second receiving step includes terminating 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 of claim 1.

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

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

5. Switching the first affiliated station 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 of claim 2.

6. The second receiving step includes switching the first affiliated station from a listening operation state to an active frame exchange state. The method of claim 1.

7. The second receiving step includes terminating an ongoing frame exchange over the first link and maintaining the first affiliated station in a valid frame exchange state. The method of claim 1.

8. If the time distance to the TBTT is less than a predetermined threshold, the system maintains the time distance. The method of claim 7.

9. The predetermined threshold value is at least a transition period required for the non-AP MLD to switch the state of the non-AP MLD affiliated station from a listening operation state to an active frame exchange state or a state in which no frame is transmitted or received; and a transition period required for the non-AP MLD to switch the state of the non-AP MLD affiliated station from the active frame exchange state or the state in which the frame is not transmitted or received to the listening operation state. The method of claim 8.

10. The second receiving step is triggered at least a first determined delay before the TBTT. The method of claim 1.

11. The first determined delay belongs to a group including an EMLSR active switch delay, an EMLMR active switch delay, and a maximum of the EMLSR and EMLMR active switch delays. The method of claim 10.

12. The second beacon frame schedules a service period on the first link, and upon completing a frame exchange within the service period, maintains the first affiliated station in a valid frame exchange state until the end of the service period. The method of claim 1.

13. 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 first affiliated station in the active frame exchange state until the end of the service period. The method of claim 1.

14. At the end of the service period, the first affiliated station is switched from the active frame exchange state to a listening operation state.

14. The method of claim 12 or 13.

15. The second beacon frame includes another TBTT associated with a third beacon frame that schedules a TWT service period on the first link, and if the scheduled TWT service period is signaled in TWT persistence, continue the frame exchange performed by a second affiliated station on a second link of the EML link without configuring the first affiliated station to be in a receiving state in the other TBTT to receive the third beacon frame on the first link. The method of claim 1.

16. During the quiet period, switch a second affiliated station to an active frame exchange state via a second link of the EML link until the end of the quiet period. The method of claim 1.

17. and transmitting, by the non-AP MLD, a notification to the AP MLD via a second link of the EML link to schedule, in a future beacon frame, a service period for the non-AP MLD that does not overlap in time with a beacon frame transmitted by the AP MLD. The method of claim 1.

18. A wireless communication device operating as a non-access point (non-AP) multi-link device (MLD) operating in an Enhanced multi-link (EML) mode in a set of EML links, comprising: a first receiving means for receiving, by a first affiliated station, a first beacon frame including a target beacon transmission time (TBTT) associated with a second beacon frame via a first link of the EML link; second receiving means for receiving, by the first affiliated station, the second beacon frame at the TBTT that schedules a quiet period on the first link; and a switching means for switching the first affiliated station to a state in which it does not transmit or receive frames during the quiet period until the quiet period ends. Wireless communication devices.

19. A program that causes a computer possessed by a wireless communication device to execute the method described in claim 1.

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