Method and apparatus for TWT coordination in multi-AP operation

Abstract

This is a method and device for TWT coordination in multi-AP operation. To reduce OBSS interference, neighboring APs in the AP's MAP coordination set receive a MAP coordination frame from the target AP managing the target BSS, which identifies the TWT schedule provided in the target BSS. The neighboring AP defines an OBSS TWT schedule with a TWT SP that at least partially overlaps with the TWT SP of the TWT schedule in the target BSS. The OBSS TWT schedule prohibits stations in the neighboring BSS from accessing the radio medium during the OBSS TWT SP. Alternatively, it defines reduced communication activity for those stations during the OBSS TWT SP by setting an OBSS EDCA parameter set to be used. In a further option, it indicates a temporary operating channel for stations in the neighboring BSS to switch to for their communication during the OBSS TWT SP.

Description

Technical Field

[0001] The present invention generally relates to wireless communication, and more particularly to cooperation in multi-AP operation.

Background Art

[0002] Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks can 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 IEEE (Institute of Electrical and Electronics Engineers, trademark) 802.11be draft standard task group aims to provide some cooperation between adjacent access points (APs) that manage separate BSSs in order to more efficiently utilize available time, frequency, and space resources, a so-called multi-access point (Multi-AP or MAP) technology. This is particularly important when adjacent APs operate on the same selected communication channel (or channels close enough to communicate with each other) where interference can occur. In that case, the BSS is called an overlapping BSS or OBSS.

[0004] The proposed MAP mechanism enables two or more adjacent APs to share resources with respect to frequency and / or time, and thus intends to prevent interference between them.

[0005] Currently, the MAP topic is a key feature of the 802.11bn task group, which succeeded the 802.11be task group. The scope of the MAP topic has been extended to optimized coordination not only regarding shared transmission but also regarding alternative mechanisms for OBSS interference reduction. In other words, MAP coordination has become one of the newly emerging features for interference management in WLAN networks, allowing multiple APs to cooperate to intelligently manage OBSS interference and improve network performance.

[0006] To propose TWT coordination for reducing OBSS interference, a contribution to the 802.11UHR study group, namely contribution 11-22-1530 (titled "Multi-AP Coordination for Next-Generation Wi-Fi"), was made. U.S. Patent Application Publication 2022 / 408355 discloses the same mechanism.

[0007] The Target Wake Time (TWT) mechanism, originally defined in IEEE 802.11ah, is one of the key features of the IEEE 802.11ax modification known as 802.11ax-2021. TWT allows for wake time negotiation between APs and associated stations (STAs) to improve power efficiency. In TWT operation, the STA simply needs to wake up at a pre-scheduled time negotiated with another STA or AP in the network.

[0008] TWT is adapted to be included in the IEEE 802.11be standard (final version D3.0). It is known as Restricted Target Wake Time (R-TWT), which schedules a dedicated (and protected) Service Period (SP) for stations (affiliated with non-AP multilink devices (MLDs), as introduced in IEEE 802.11be in some cases) to transmit their latency-sensitive traffic through their BSS. An R-TWT agreement is similar to a Broadcast TWT agreement negotiated between an AP-affiliated non-AP station and a BSS on a given link. The non-AP station establishes membership with the AP in a Broadcast TWT (or R-TWT) schedule. The R-TWT Service Period (SP) in the R-TWT schedule is advertised in a broadcasted management frame (e.g., a beacon) using R-TWT information about the negotiated R-TWT SP, typically a Broadcast TWT identifier (bTWTID).

[0009] The above contributions and publication US2022 / 408355 are intended to coordinate the R-TWT procedure with MAP. The R-TWT function is used to avoid OBSS interference between BSSs of MAP coordination groups, i.e., AP's MAP coordination sets.

[0010] In fact, in high-density deployment scenarios where adjacent BSSs corresponding to two or more APs overlap with each other, if one AP has an R-TWT schedule where the corresponding scheduled STA belongs to a geographic area that overlaps with an adjacent BSS, the R-TWT scheduled STA may face interference from the operation of the adjacent BSS.

[0011] To provide better protection for sensitive traffic during latency for its member STA, the proposed solution in contributions and publications addresses interference between neighboring BSS activity during a restricted TWT Service Period by managing the Quiet interval at the neighboring BSS.

[0012] To do this, when a target BSS has one or more R-TWT schedules, the target BSS sends a Quieting request to neighboring APs in its AP coordination set and shares its R-TWT schedules with them. If a neighboring AP accepts the Quieting request from the target AP, it sends a Quiet element to the station associated with it, where the Quiet element corresponds to the R-TWT schedule for which the target AP sent the Quieting request.

[0013] The Quiet element is a key component of the IEEE 802.11h standard, defining intervals in a channel during which no transmission occurs. It is primarily used to perform channel measurements, particularly to avoid interference with certain military radar technologies.

[0014] However, MAP R-TWT coordination based on the Quiet element is not satisfactory.

[0015] The first drawback of this cooperative scheme is that it is difficult for adjacent APs to locally schedule (within their own BSS) the quiet period (interval) corresponding to the R-TWT SP of the target BSS. In fact, the TBTT (Target Beacon Transmission Time) between two BSSs may not be (temporarily) aligned and may not have the same duration. Furthermore, Quiet elements and TWT elements do not use the same timing criterion: Quiet elements are based on TBTT (and therefore beacon frames), while TWT elements are based on a TSF (Time Synchronization Function) timer synchronized across all stations in the BSS.

[0016] The second drawback is closely related to the signaling of the Quiet element. Because it signals in beacon frames where the Quiet Count is strictly positive, the Quiet Period can only be effective after the next beacon frame. This shows that Quiet-based coordination cannot be applied immediately in adjacent BSSs.

[0017] The third drawback stems from the fact that the Quiet method is very aggressive in that all stations in adjacent BSSs are prohibited from transmitting. As a result, the medium is not used much by stations in adjacent BSSs.

[0018] A fourth drawback is the unmanaged situation of legacy devices (pre-802.11ax) when some Quiet elements are designated during TBTT. Generally, 802.11ah measurements were assumed to occur at most once per TBTT. Therefore, the proper use of Quiet elements should be limited to a single occurrence per TBTT, which may not meet the R-TWT schedule of the target BSS.

[0019] A fifth drawback is that the Quiet-based approach appears incompatible with multilink devices (MLDs). Indeed, IEEE 802.11be imposes several restrictions on how MLDs operate, particularly that an AP MLD and its affiliated EHT AP must not include any Quiet elements in its transmitted beacon or probe response frames that overlap with Quiet intervals scheduled and advertised by other APs associated with the same AP MLD. Thus, it appears extremely difficult to apply a Quiet interval that encompasses an R-TWT SP in at least one adjacent BSS (i.e., one link of the MLD) but at the same time does not encompass a Quiet period in another adjacent BSS of the same MLD (i.e., another link of the same MLD).

[0020] Therefore, it is necessary to provide more efficient TWT coordination in MAP operation, and more generally, to provide more efficient MAP operation and MAP coordination. [Overview of the project]

[0021] A broader objective of the present invention is to overcome some of the aforementioned problems. The inventors have found that by replicating the R-TWT or TWT SP of a target BSS in a corresponding TWT SP in an adjacent BSS, an adjacent AP can adjust the media access policy in that BSS to reduce or even avoid OBSS interference in the R-TWT SP of the target BSS.

[0022] In connection with this, a method of communication via a medium (or channel) in a wireless network, wherein in a second access point (AP) in a multi-AP (MAP) cooperative set of APs, The first AP, which manages the first Basic Service Set (BSS), receives a MAP coordinated frame that specifies the Target Wake Time (TWT) schedule provided in the said first BSS, A communication method is provided which, in response to such reception, transmits a frame to a second BSS station managed by the second AP, containing an overlapping BSS (OBSS) TWT element that defines a second TWT SP that is timely aligned with the first TWT Service Period (SP) of the first BSS TWT schedule.

[0023] "Timely aligned" or "time aligned" does not mean that the first TWT SP and the second TWT SP completely overlap. "Timely aligned" or "time aligned" is understood to mean that the first TWT SP and the second TWT SP overlap in such a way that there is no communication in the second BSS for the second TWT SP to benefit the first TWT SP. In this regard, it is preferable that the overlap is organized over at least the beginning of the first TWT SP. For example, the first TWT SP and the second TWT SP may start simultaneously, meaning that their start times are perfectly aligned in time. In this context, the second TWT SP may be shorter than the corresponding first TWT SP, while both SPs start simultaneously.

[0024] By using a second TWT SP, the second (adjacent) AP has the same timing criteria as the first (target) AP. Furthermore, TWT scheduling signaling can be performed by the second AP not only within beacon frames but also within other management frames, thus allowing the second TWT SP to be declared and started immediately. In addition, multiple second TWT SPs can be scheduled during each TBTT, while the quiet period-based restrictions for MLD no longer apply.

[0025] Furthermore, the second AP may, during the second TWT SP, adjust the media access policy for the stations associated with it, and thus provide a less aggressive method than known techniques for reducing OBSS interference.

[0026] Correspondingly, in a wireless network having a medium, a second access point (AP) device in a multi-AP (MAP) cooperation set of APs that manages a second basic service set (BSS), comprising: a receiver configured to receive a MAP cooperation frame specifying a Target Wake Time (TWT) schedule provided in the first BSS from a first AP that manages the first BSS; a transmitter configured to transmit, in response to receiving the MAP cooperation frame, a frame including an overlapping BSS (OBSS) TWT element that defines a second TWT service period (SP) that is time-aligned with a first TWT SP of the TWT schedule in the first BSS, to a station in the second BSS; and the second AP having the same is also provided.

[0027] This second (adjacent) AP has the same advantages as the method described above.

[0028] Optional features are defined below with reference to the method, but they can be transferred to the features of the device.

[0029] In some embodiments, the OBSS TWT element restricts communication activity of the stations in the second BSS during the first TWT SP of the first BSS. Exemplary restrictions on communication activity include driving restricted access to the medium, as described below. In this way, the second AP continues to control the risk of OBSS interference.

[0030] In some embodiments, the OBSS TWT element prohibits the stations in the second BSS from accessing the medium during the second TWT SP. As a result, the risk of OBSS interference is substantially reduced during the TWT SP of the first BSS.

[0031] In some embodiments, the OBSS TWT element indicates its temporary operating channel during the second TWT SP, so that the station of the second BSS can switch to that temporary operating channel for their communication.

[0032] In certain embodiments, the Minimum TWT Wake Duration field in the OBSS TWT element is set to 0.

[0033] In some embodiments, the OBSS TWT element defines a waiting time for a station in the second BSS to access the medium during a first TWT SP that is longer than the waiting time for a station in the first BSS to access the medium. This configuration provides a more permissive approach than media access prohibition. At the same time, priority is maintained for stations in the first BSS to gain access to the medium during the time-coordinated TWT schedule within the first BSS. Thus, communication within the second BSS is improved during the OBSS TWT schedule, while the risk of interference with the first BSS is substantially reduced thanks to the priority given to stations in the first BSS.

[0034] In some embodiments, the waiting time for the second BSS station is calculated based on the Minimum TWT Wake duration specified in the MAP Coordinate Frame. The first AP then maintains control over how neighboring BSSs can provide access to the medium during the TWT schedule. Thus, the first AP can dynamically adjust the waiting times of those neighboring BSSs over time.

[0035] In some embodiments, the OBSS TWT element includes a field that sets a minimum waiting time between the start of the second TWT SP and the station of the second BSS being able to access the medium.

[0036] In other embodiments, the OBSS TWT element includes a different OBSS EDCA parameter set from the legacy EDCA parameter set, which is applied by the second BSS station for competition for access to the medium during the second TWT SP. This approach advantageously extends known mechanisms to the OBSS parameters so that the second AP efficiently drives the standby time of its station when accessing the medium during the OBSS TWT SP.

[0037] In certain embodiments, the OBSS EDCA parameter set includes a degraded ECWmin value. Consequently, the second AP statistically waits for a longer period than in the conventional operating mode. This results in fewer media access attempts by that station and, therefore, less OBSS interference with the first BSS.

[0038] In other embodiments, the OBSS EDCA parameter set includes a degraded AIFSN value. Therefore, the second AP is driven to wait longer before beginning to decrement its backoff counter to gain access to the media. This results in prioritizing media access to stations with lower AIFSNs (essentially those of the first BSS), thus leading to less OBSS interference with the first BSS.

[0039] In some embodiments, the degraded AIFSN value is set by the second AP based on the minimum latency specified by the first AP in the MAP co-coordinate frame. In particular, the degraded AIFSN value may be set by the second AP to the Minimum TWT Wake Duration specified in the MAP co-coordinate frame, which is negotiated with the first AP by the second AP.

[0040] In another embodiment, the degraded AIFSN value is added to the legacy AIFSN value by the second BSS station to obtain the AIFSN value that should be applied when there is competition for access to the medium during the second TWT SP.

[0041] In some embodiments, the OBSS EDCA parameter set includes an OBSS EDCA timer that indicates the period for which a station in the second BSS uses the OBSS EDCA parameters before reverting to the legacy EDCA parameters, and the OBSS EDCA timer is based on the Minimum TWT Wake Duration field identified in the MAP Coordinate Frame. Thus, precise control of the station in the second BSS is provided to reduce the risk of OBSS interference (through the use of the OBSS EDCA parameters).

[0042] In some embodiments, the waiting time is specified in the MAP Cooperative Frame. In particular, the waiting time may be set to the duration of the first TWT SP.

[0043] In some embodiments, the second AP obtains information about its own second BSS interference stations that are interfering with the first BSS and its own second BSS free stations that are not interfering with the first BSS, and the OBSS TWT element restricts communication activity on the medium only for the interfering stations. This configuration optimizes the use of the second BSS because stations that do not interfere with the first BSS are not subject to the OBSS restriction according to the present invention. Therefore, they can continue normal use of the medium without the risk of OBSS interference with the first BSS.

[0044] In certain embodiments, frames containing OBSS TWT elements are transmitted only to interference stations.

[0045] In some embodiments, the second AP checks whether the TWT SP initially scheduled by the second AP within the second BSS overlaps with the first TWT SP.

[0046] In certain embodiments, the method further includes sending an affirmative response to the first AP if there is no overlap, and sending a negative response otherwise.

[0047] In some embodiments, the method further comprises converting timing information for a received TWT schedule in a first BSS based on a first clock applicable to the first BSS into timing information based on a second clock applicable to a second BSS, where the timing information in the OBSS TWT element is second clock-based timing information.

[0048] In some embodiments, the frame containing the OBSS TWT element is a beacon frame broadcast by the second AP in the second BSS. This allows all stations to be periodically notified by the second AP about the limitations on their communication activity during the OBSS TWT SP.

[0049] In some embodiments, the beacon frame includes an OBSS TWT Update counter, which is incremented each time an OBSS TWT parameter is updated in an OBSS TWT element.

[0050] In other embodiments, the frame containing the OBSS TWT element is a probe response frame transmitted by the second AP in the second BSS. This allows the second AP to identify the OBSS TWT schedule and OBSS TWT parameter set to the station early, specifically well before the next beacon frame.

[0051] In certain embodiments, the probe response frame is broadcast to a station on the second BSS.

[0052] In some embodiments, the OBSS TWT element is a restricted TWT element having a Restricted TWT Traffic Info section containing an enabled OBSS TWT field. The Restricted TWT Traffic Info section is defined in a series of IEEE 802.11be standards, e.g., D3.0. Therefore, the proposed signaling relies on existing sections without requiring new bits to be added to the existing format.

[0053] In some embodiments, the MAP cooperative frame is a beacon frame broadcast by a first AP within a first BSS.

[0054] In certain embodiments, the TWT schedule received by the second AP is defined by an addressed TWT element in the beacon frame that is dedicated to the station of the first BSS. In this case, a conventional TWT element, such as an R-TWT element, is reused without incurring additional signaling costs.

[0055] In some embodiments, the MAP coordinated frame is a dedicated unicast frame addressed by the first AP to the second AP via the medium or using an alternative communication medium. Using an alternative communication medium advantageously avoids any signaling costs in the BSS. In this case, links or networks affected by communication interference and where TWT coordination is expected may be identified in the MAP coordinated frame.

[0056] In other embodiments, a MAP cooperative frame is included in the negotiation process between the first AP and the second AP to establish a MAP TWT agreement. In this way, only the required TWT information is transmitted, and the entire conventional TWT element does not need to be transmitted.

[0057] In yet another embodiment, MAP co-coordinate frames are exchanged between a third AP co-affiliated with the first AP to the same first AP multilink device (MLD) and a fourth AP co-affiliated with the second AP to the same second AP MLD, with the third and fourth APs operating on links separate from the links on which the first and second APs operate. This utilizes MLD operation. Thus, the third AP transmits a MAP co-coordinate MAP on behalf of the first AP which is experiencing OBSS interference. The fourth AP, receiving the MAP co-coordinate frame, can then forward it to the second AP within the second AP MLD so that the second AP can perform TWT coordination according to the present invention.

[0058] Furthermore, the present invention relates to a communication method via a medium in a wireless network, wherein in a station of a Basic Service Set (BSS) managed by an AP in a multi-AP (MAP) cooperative set of access points (APs), The steps include receiving a frame from the AP that includes an overlapping BSS (OBSS) TWT element that defines the TWT Service Period (SP), The present invention provides a communication method that includes the step of switching from a legacy EDCA parameter set to an OBSS EDCA parameter set in order to compete for access to the medium between one of the TWT SPs.

[0059] Correspondingly, in a multi-AP (MAP) cooperative set of APs in a wireless network having a medium, the station device of the Basic Service Set (BSS) managed by the access point (AP), A receiver configured to receive frames from an AP that include an overlapping BSS (OBSS) TWT element that defines the TWT Service Period (SP), A station device is also provided having a communication module configured to switch from a legacy EDCA parameter set to an OBSS EDCA parameter set in order to compete for access to the medium during TWT SP.

[0060] The station and associated methods favorably reduce the risk of OBSS interference with other BSSs that have scheduled TWT SPs by using a dedicated OBSS EDCA parameter set. As mentioned above, the TWT SPs in the OBSS TWT schedule are actually defined in time-aligned with the TWT SPs scheduled (to be protected) in other BSSs.

[0061] The features of the options are defined below with reference to the method, but can be moved to the features of the device.

[0062] In some embodiments, the switching is performed so that the OBSS EDCA parameter set begins to be used when the TWT SP starts.

[0063] In some embodiments, the OBSS EDCA parameter set is included in the beacon frame broadcast by the AP.

[0064] In the modified version, the OBSS EDCA parameter set is included in the OBSS TWT element.

[0065] In some embodiments, the OBSS EDCA parameter set includes degraded AIFS values ​​and / or degraded ECWmin values.

[0066] In certain embodiments, the degraded AIFS value is added to the legacy AIFS value when there is competition for access to the medium during TWT SP.

[0067] In some embodiments, the method further includes returning to the legacy EDCA parameter set after the OBSS duration defined by the Minimum TWT Wake Duration field specified in the OBSS TWT element, or when the OBSS EDCA timer specified in the OBSS TWT element has elapsed.

[0068] In some embodiments, the method further includes, at the station, terminating any ongoing transmissions over the medium before the commencement of one(s) of the TWT SPs.

[0069] The present invention also relates to a communication method via a medium in a wireless network, wherein in a station of a Basic Service Set (BSS) managed by an AP in a multi-AP (MAP) cooperative set of access points (APs), Steps include receiving a frame from the AP that defines the TWT Service Period (SP), The present invention provides a communication method that includes the step of switching from an initial operating channel to a second operating channel in order to compete for access to a medium via a second operating channel during TWT SP.

[0070] Correspondingly, in a wireless network having a medium, a station device of a Basic Service Set (BSS) managed by an AP in a multi-AP (MAP) cooperative set of access points (APs): A receiver configured to receive frames defining the TWT Service Period (SP) from an AP, A station device is also provided having a communication module configured to switch from an initial operating channel to a second operating channel in order to compete for access to a medium via a second operating channel during TWT SP.

[0071] The station and associated methods favorably avoid OBSS interference with another BSS having a scheduled TWT SP by switching to a second (e.g., transient) operating channel, which is a dedicated OBSS EDCA parameter set. The TWT SP at least partially overlaps with a TWT SP (to be protected) in another BSS managed by another AP in the MAP coordination set.

[0072] In some embodiments, the received frame includes an overlapping BSS (OBSS) TWT element that defines the TWT SP.

[0073] The present invention also relates to a communication method via a medium in a wireless network, wherein in an access point (AP) managing a basic service set (BSS) in a multi-AP (MAP) cooperative set of access points (APs), The present invention provides a communication method comprising the steps of transmitting to a station of the BSS a legacy EDCA parameter set that defines EDCA parameters to be used by the station when there is a competition for access to the medium; a MU EDCA parameter set that defines MU EDCA parameters to be temporarily used by the station when there is a competition for access to the medium after an uplink multi-user (MU) transmission; and an OBSS EDCA parameter set defined by the AP for the BSS, which is time-matched with the adjacent TWT SP of the TWT schedule in the adjacent BSS, and defines OBSS EDCA parameters to be temporarily used by the station when there is a competition for access to the medium during an overlapping BSS (OBSS) Service Period.

[0074] In this regard, the AP broadcasts at least three distinct sets of EDCA parameters to be used by the station associated with it in each situation: for the MU EDCA parameter set, after the transmission of the UL MU HE TB PPDU and during the duration of the MU EDCA timer; for the OBSS EDCA parameter set, after the OBSS TWT SP is started and optionally during the duration of the OBSS EDCA timer; and for the legacy EDCA parameter set, in all other cases.

[0075] Correspondingly, the present invention also provides a wireless communication device having at least one microprocessor configured to perform any of the methods described above.

[0076] Another aspect of the present invention relates to a non-temporary computer-readable medium for storing a program that causes a wireless device to perform one of the methods described above, when executed by a microprocessor or computer system in the wireless device.

[0077] At least a portion of the methods according to the present invention can be implemented in a computer. Therefore, the present invention may take the form of a completely hardware embodiment, a completely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware embodiments, all of which may be commonly referred to here as “circuits,” “modules,” or “systems.” Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer-usable program code embodied in that medium.

[0078] Since the present invention can be implemented in software, it can be embodied as computer-readable code for providing a programmable device on any suitable transport medium. The tangible transport medium may include storage media such as hard disk drives, magnetic tape devices, or solid-state memory devices. The transient transport medium may include signals such as electrical signals, electronic signals, optical signals, acoustic signals, magnetic signals, or electromagnetic signals, such as microwave or RF signals. [Brief explanation of the drawing]

[0079] Next, embodiments of the present invention will be described, merely as examples, with reference to the following drawings: [Figure 1] Figure 1 shows an exemplary network environment in which an embodiment of the present disclosure can be implemented. [Figure 2] Figure 2 shows the format of the Quiet element according to the 802.11REVme D2.1 standard. [Figure 3a] Figures 3a and 3b show the format of a Target Wake Time (TWT) element adapted for use in r-TWT according to the 802.11be D3.0 standard. [Figure 3b] Figures 3a and 3b show the format of a Target Wake Time (TWT) element adapted for use in r-TWT according to the 802.11be D3.0 standard. [Figure 4a] Figure 4a is a flowchart illustrating the general steps in an AP of a communication method that provides TWT coordination in MAP operation according to an embodiment of the present invention. [Figure 4b] Figure 4b is a flowchart illustrating the general steps in a non-AP station of a communication method according to an embodiment of the present invention. [Figure 5]Figure 5 shows a transmission sequence that implements TWT coordination for reduced OBSS interference in MAP operation according to an embodiment of the present invention. [Figure 6] Figures 6 and 7 show the format of a Target Wake Time (TWT) element adapted for use for OBSS TWT according to an embodiment. [Figure 7] Figures 6 and 7 show the format of a Target Wake Time (TWT) element adapted for use for OBSS TWT according to an embodiment. [Figure 8a] Figure 8a is a schematic diagram of a communication device according to an embodiment of the present invention. [Figure 8b] Figure 8b is a schematic diagram of a wireless communication device according to an embodiment of the present invention. [Figure 9a] Figure 9a is a flowchart illustrating the general steps at an AP of a communication method that provides channel switching announcements corresponding to TWT coordination in MAP operation, according to an embodiment of the present invention. [Figure 9b] Figure 9b is a flowchart illustrating the general steps of a communication method according to an alternative embodiment of the present invention at a non-AP station. [Figure 10] Figure 10 shows a second transmission sequence that implements TWT coordination for reduced OBSS interference in MAP operation according to an alternative embodiment of the present invention. [Figure 11a] Figure 11a shows the format of a Channel Switch Announcement (CSA) frame adapted for use in OBSS TWT according to an embodiment of the present invention. [Figure 11b] Figure 11b shows the format of a Channel Switch Announcement (CSA) element adapted for use in an OBSS TWT according to an embodiment of the present invention. [Figure 12]Figure 12 shows the format of a Target Wake Time (TWT) element, which includes a Channel Switch Announcement (CSA) and is adapted for use for OBSS TWT, according to an embodiment of the present invention. [Modes for carrying out the invention]

[0080] The techniques described herein can be used for a variety of broadband wireless communication systems, including communication systems based on orthogonal multiplexing schemes. Examples of such communication systems include spatial division multiplexing (SDMA) systems, time division multiplexing (TDMA) systems, orthogonal frequency division multiplexing (OFDMA) systems, and single-carrier frequency division multiplexing (SC-FDMA) systems. SDMA systems can utilize sufficiently different directions to simultaneously transmit data belonging to multiple user terminals, i.e., radio equipment or stations. TDMA systems can enable multiple user terminals to share the same frequency channel by dividing the transmission signal into different time slots or resource units, each assigned to a different user terminal. OFDMA systems utilize orthogonal frequency division multiplexing (OFDM), a modulation technique that divides the entire system bandwidth into multiple orthogonal subcarriers or resource units. These subcarriers may also be called tones, bins, etc. In OFDM, each subcarrier can be independently modulated with data. The SC-FDMA system can utilize interleaved FDMA (IFDMA), which transmits over subcarriers distributed across the system bandwidth; localized FDMA (LFDMA), which transmits over blocks of adjacent subcarriers; or enhanced FDMA (EFDMA), which transmits over multiple blocks of adjacent subcarriers.

[0081] The teachings herein may be incorporated into various devices (e.g., stations) (e.g., implemented within the device or performed by the device). In some embodiments, the radio devices or stations implemented according to the teachings herein may include access points (so-called APs) or non-access points (so-called non-AP stations or STAs).

[0082] AP includes, and may be implemented as or known as, a Node B, a Radio Network Controller ("RNC"), an Evolved Node B (eNB), a 5G Next Generation Base Station (gNB), a Base Station Controller ("BSC"), a Base Transceiver Station ("BTS"), a Base Station ("BS"), a Transceiver Function ("TF"), a Radio Router, a Radio Transceiver, a Basic Service Set ("BSS"), an Extended Service Set ("ESS"), a Radio Base Station ("RBS"), or any other term.

[0083] Non-AP stations include, and may be implemented as, or known as, subscriber stations, subscriber units, mobile stations (MS), remote stations, remote terminals, user terminals (UT), user agents, user devices, user equipment (UE), user stations, or any other terms. In some implementations, an STA may include a mobile phone, cordless phone, Session Initiation Protocol ("SIP") phone, Wireless Local Loop ("WLL") station, Personal Digital Assistant ("PDA"), handheld device with wireless connectivity, or any other suitable processing device connected to a wireless modem. Thus, one or more embodiments taught herein may be incorporated into a telephone (e.g., a mobile 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 embodiments, a non-AP station may be a wireless node. Such wireless nodes may provide connectivity to, or to, a network (such as a wide area network like the Internet or a cellular network) via a wired or wireless communication link.

[0084] An AP manages a set of STAs (registered with or associated with itself), and these STAs aggregate access to the wireless medium for communication purposes. The STAs (including the APs to which they register) form a service set, which hereby (although other terms may be used) is referred to as a Basic Service Set (BSS). The same physical STA operating as an access point may manage two or more BSSs (and thus corresponding WLANs), and each BSS is thus uniquely identified by a specific Basic Service Set Identifier (BSSID) and managed by a separate virtual AP implemented on that physical AP. Each STA is identified within the BSS by an Identifier (AID) assigned by the AP at the time of registration.

[0085] The 802.11 family of standards defines various media access control (MAC) mechanisms for driving access to wireless media.

[0086] For example, to address the requirements for increased bandwidth and reduced latency in wireless communication systems in high-density environments, the MU (Multi-User) scheme has been developed, which allows a single access point (AP) managing a Basic Service Set (BSS) to schedule multiple simultaneous transmissions of the BSS to or from non-AP stations in a wireless network. The MU scheme is adopted in the 802.11ax-2021 standard, published in May 2019.

[0087] Thanks to the MU function, non-AP stations have the opportunity to gain access to the wireless medium via two access methods: the MU method and the conventional Enhanced Distributed Channel Access-EDCA (Single User) method.

[0088] Each BSS defines the primary channel (usually known as the 20MHz channel or a multiple of the 20MHz channel) of the radio medium on which stations (including APs) generally perform EDCA contention (conflict) using legacy EDCA parameters (defined in the EDCA parameter set provided by the AP). To increase the bandwidth for subsequent transmissions, stations may simultaneously compete for additional 20MHz channels known as secondary channels. Thus, the communication channels permitted for transmission include the primary channel and optionally the secondary channels.

[0089] The 802.11ax standard allows MU downlink (DL) transmissions to be performed by APs when they gain access to the radio medium for a Transmit Opportunity (TXOP). During an MU DL transmission on an authorized communication channel, the AP performs multiple simultaneous basic transmissions to various non-AP stations via so-called resource units (RUs). For example, resource units divide the communication channels of a radio network in the frequency domain, for instance, based on the Orthogonal Frequency Division Multiple Access (OFDMA) technique. The assignment of RUs to non-AP stations is signaled at the start of the MU downlink frame by providing an Association Identifier (AID) for each RU defined in the Transmit Opportunity (which is obtained individually by each station during the association procedure with the AP).

[0090] Furthermore, the 802.11ax standard allows MU uplink (UL) transmissions to be triggered by the AP when access to the wireless medium is obtained. During an MU UL transmission, various non-AP stations can simultaneously transmit data to the AP via resource units that form a communication channel. To control MU UL transmissions by non-AP stations, the AP preemptively transmits a control frame known as a trigger frame (TF). The trigger frame assigns resource units to non-AP stations on the same BSS using 16-bit Association IDentifiers (AIDs) assigned upon registration with the AP, and / or reserved AIDs that specify a group of non-AP stations. The TF also defines the start and length of the MU UL transmission by the non-AP station. After performing the MU UL transmission, the non-AP station performs EDCA contention on the medium using a different set of EDCA parameters (from the legacy ones) temporarily known as MU EDCA parameters (defined in the multi-user (MU) EDCA parameter set provided by the AP).

[0091] Current discussions in Task Group 802.11be are introducing Multilink Operation (MLO) in terms of MAC layer operation, as indicated by the March 2023 draft IEEE P802.11be / D3.0. MLO allows multilink devices to establish or set up multiple links and operate them simultaneously.

[0092] A multilink device (MLD) is a logical entity that has one or more affiliated STAs (STAs) and a single MAC service access point (SAP) to logical link control (LLC) containing one medium access control (MAC) data service. An access point multilink device (or AP MLD) corresponds to an MLD, where each STA affiliated with the MLD is an AP and is therefore called an "affiliated AP". A non-access point multilink device (or non-AP MLD) corresponds to an MLD, where each STA affiliated with the MLD is a non-AP STA and is therefore called an "affiliated non-AP STA". Depending on the literature, "multilink device", "ML device" (MLD), "multilink logical entity", "ML logical entity" (MLE), "multilink set", and "ML set" are synonyms for specifying the same type of ML device.

[0093] Furthermore, multiple associated non-AP STAs of a non-AP MLD can set up communication links with multiple associated APs of an AP MLD, and thus form a multilink channel.

[0094] Links established for MLD (or "enabled links") are theoretically independent, meaning that channel access procedures and communications (to the communication medium) are performed independently on each link. Therefore, different links may have different data rates (due to, for example, different bandwidths, number of antennas, etc.) and may be used to communicate different types of information (each via a specific link).

[0095] Therefore, a communication link or "link" corresponds to a given channel (e.g., 20MHz, 40MHz, etc.) in a given frequency band (e.g., 2.4GHz, 5GHz, 6GHz) between an AP associated with an AP MLD and a non-AP STA associated with a non-AP MLD.

[0096] Related APs and non-AP STAs operate on their respective channels in accordance with one or more of the IEEE 802.11 standard (a / b / g / n / ac / ad / af / ah / aj / ay / ax / be / bn) or other wireless communication standards.

[0097] Thanks to multilink aggregation, traffic associated with a single MLD can theoretically be transmitted across multiple parallel communication links, thereby increasing network capacity and maximizing the use of available resources.

[0098] The following explanation will focus primarily on a single link for the sake of clarity. However, similar considerations may be made for each link that forms a set of multiple links for an MLD device. Thus, the term STA or “station” may refer to one associated STA of a non-AP MLD (a non-AP STA of a non-AP MLD), and AP may refer to one associated AP of an AP MLD.

[0099] Figure 1 shows an exemplary network environment in which an embodiment of the present disclosure can be implemented.

[0100] The illustrated wireless network environment includes a multi-AP system 100 formed by a group of adjacent wireless networks operating over a common communication channel or wireless medium. The common communication channel may correspond to some (e.g., 20 MHz) or all of the operating channels (e.g., 20 MHz, 40 MHz, 80 MHz, 160 MHz, or 320 MHz).

[0101] A first wireless network (or basic service set) BSS1 includes an access point (AP) 110 and three non-AP stations (STAs) 111, 112, and 113 associated with (i.e., registered with) AP110. A second wireless network BSS2 includes AP120 and three associated non-AP STAs 121, 122, and 123. A third wireless network BSS2 includes AP130 and three associated non-AP STAs 131, 132, and 133. Hereinafter, BSSx represents one of the wireless networks, while 1x1, 1x2, and 1x3 represent one of the non-AP stations. Naturally, one can consider a different number of wireless networks and any number of non-AP stations for each wireless network. In this disclosure, AP110, 120, and 130 are also referred to as AP1, AP2, and AP3, respectively. The device may operate as an AP in one wireless network and simultaneously belong to another wireless network as an associated STA.

[0102] All or part of an AP may be associated APs for the same AP MLD. They may also be separate devices. Any AP broadcasts management frames, such as beacon frames, to share parameters that should be used for the functionality of its BSS.

[0103] Each wireless network station (AP and non-AP) exchanges data frames over communication channel 100 under the management of the AP. The primary channel, typically a 20MHz channel, is defined for each wireless network, where management frames are exchanged. Any other 20MHz channels in the communication channel, if any, are known as secondary channels.

[0104] In the context of the present invention, APs can communicate with each other either by using a BSS communication channel common to other BSSs, or by using a separate communication link (such as a separate wireless network or channel, an Ethernet® backhaul connecting all APs, or a direct link).

[0105] Each of the non-AP STA1x1~1x3 registers with AP1x0 of one wireless network BSSx during the association procedure. During the association procedure on the primary channel, the AP assigns a specific Association Identifier (AID) to the requesting station. For example, the AID is a 16-bit value that uniquely identifies the station.

[0106] Stations (including APs) compete with each other over communication channels (including a primary channel and optionally a secondary channel to increase bandwidth) using EDCA (Enhanced Distributed Channel Access) contention to access the communication channel so that they are given a Transmit Opportunity (TXOP). A TXOP can then be used to transmit (single-user (SU)) data frames or to perform multi-user (MU) transmissions. In the MU scheme, a single station, typically an AP in a wireless network BSSx, can schedule MU transmissions, i.e., multiple simultaneous transmissions with other stations in the wireless network. One implementation of such an MU scheme is adopted, for example, in the IEEE 802.11ax modification standard and is known as the Multi-User Uplink and Downlink OFDMA (MU UL and DL OFDMA) procedure. In the MU scheme, a resource is defined across one or more 20MHz channels used, and this is known as a resource unit.

[0107] More generally, resources may include spatial, frequency, and time resources and may be acquired according to different multiplexing schemes. Examples of these schemes 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.

[0108] The IEEE 802.11 Wireless Local Area Networking Standard allows a multi-AP system 100 to support an Extended Service Set (ESS), and each member of the wireless network to support a Basic Service Set (BSS).

[0109] The embodiments of the present invention are described in the context of IEEE 802.11, but the embodiments are not limited thereto and may be applied to other types of wireless networks and protocols.

[0110] To meet the low-latency requirements of 802.11be and to improve the efficiency of UL MU operation, existing mechanisms have been reused and improved, which are summarized here.

[0111] Quiet Element The Quiet element is a key component of the IEEE 802.11h standard. It defines an interval during which no transmission occurs on the current channel. This interval can be used to assist in performing channel measurements in BSS without interference from other STAs. Figure 2 shows the format of the Quiet element 200, taken from Figure 9-345 (titled "Quiet Element Format") of 802.11REVme D3.1.

[0112] The Quiet Count field 210 is set to the number of TBTTs (Beacon Time Tolls) until the next quiet interval begins (i.e., the preceding beacon interval). A value of 0 is reserved, and therefore the Quiet element can only be applied after the next beacon frame has been issued.

[0113] If the silent interval is repeated, the Quiet Period field 220 is set to the number of beacon intervals between the start of the regularly scheduled silent intervals defined by this Quiet element. Setting the Quiet Period field to 0 indicates that no periodic silent intervals are defined.

[0114] The Quiet Duration field 230 is set to the duration of the quiet interval, expressed in Time Units (1 TU = 1024 μs), thereby allowing stations to reserve their NAVs.

[0115] The Quiet Offset field 240 can be used to identify an additional offset after the start time, which must be less than one beacon interval. The Quiet Offset field is set to the offset of the start of the quiet interval from TBTT, identified by the Quiet Count field, represented by TU. The value of the Quiet Offset field is less than one beacon interval.

[0116] As described above, U.S. Patent Application Publication 2022 / 408355 proposes transmitting Quiet elements in adjacent BSSs that overlap with the R-TWT schedule in the target BSS. This is intended to protect the Service Period for STAs that are R-TWT members from other STAs that are not members of the R-TWT schedule in the BSS.

[0117] TWT The Target Wake Time (TWT) mechanism, originally defined in the IEEE 802.11ah and 802.11ax standards, has been adapted for inclusion in the 802.11be D3.0 standard. This adaptation is known as Restricted Target Wake Time (R-TWT), which schedules separate (protected) Service Periods (SPs) for stations (associated with non-AP MLDs) to carry latency-sensitive traffic through their BSSs. R-TWT agreement is simply a Broadcast TWT agreement negotiated between non-AP stations associated with APs on a given link's BSS. Non-AP stations establish membership with APs in the Broadcast TWT (or R-TWT) schedule. The schedule can be defined for several TIDs. The R-TWT Service Period (SP) of an R-TWT schedule is advertised in a broadcasted management frame (e.g., a beacon) using R-TWT information about the negotiated R-TWT SP, typically a broadcast TWT ID (bTWT ID).

[0118] Mechanisms such as TWT or R-TWT are negotiated on a per-link basis in the case of ML operation, i.e., between the associated STA of the non-AP MLD initiator and the corresponding associated AP of the AP MLD.

[0119] Given a link, a non-AP station establishes membership in the AP's broadcast TWT schedule, while the AP delivers a broadcast TWT parameter set to the non-AP station. The non-AP station is referred to as a TWT-scheduled station, while the AP is referred to as a TWT scheduling station.

[0120] Negotiations to become a member of or terminate membership in an R-TWT schedule (more generally a broadcast TWT) are performed using the exchange of frames carrying TWT elements, as described 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 Setup frame containing the TWT elements for a given R-TWT schedule to the AP MLD to which it is associated.

[0121] The AP then typically advertises the scheduled broadcast TWT (or R-TWT) in its management frame using the broadcast TWT element in beacon frames, FILS Discovery frames, and broadcast Probe Response frames.

[0122] Figures 3a and 3b show the format of the TWT element 300 adapted for use in TWT according to the D3.0 standard.

[0123] The TWT element 300 is identified by Element ID 301 and includes "Control" fields 310 and 320 for conveying TWT parameter information.

[0124] The "Control" field 310, through the Negotiation Type field 311, indicates whether the TWT is a broadcast TWT or an individual TWT agreement. The MSB of the Negotiation Type subfield 311 is the Broadcast field, and therefore the TWT element 300 is called a Broadcast TWT element when the MSB of the subfield 311 is 1 (otherwise it is a single individual TWT element). The other fields are not very important for this explanation.

[0125] The "TWT Parameter Information" field 320 includes a single "Individual TWT Parameter Set" field for individual TWTs (320b, Figure 3b), and one or more "Broadcast TWT Parameter Set" fields having the format 320a shown in Figure 3a for Broadcast TWTs (when the Broadcast field in the "Negotiation Type" subfield is 1).

[0126] The first field in the "Broadcast TWT Parameter Set" field 320a is the Request Type field 330, which includes: -When issued by a TWT Scheduled STA, the TWT Request subfield 331 is set to 1. Otherwise, when issued by a TWT Scheduled STA (AP), it is set to 0; -TWT Setup Command subfield 332 to indicate the type of TWT command, which is Request, Suggest, Demand, or Reject when issued by a non-AP STA, and Accept, Alternate, Dictate, or Reject when issued by a TWT scheduling AP; - The Trigger field 333 indicates whether the TWT SP indicated by the TWT element 300 contains a frame that triggers (the Trigger subfield is equal to 1 for a trigger-enabled R-TWT). Such a TWT SP is called a trigger-enabled TWT SP, and a non-AP station cannot start transmitting data internally without a previous trigger by the AP; - The Broadcast TWT Recommendation field 336 is set to 4 to indicate that the TWT described 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), while the Broadcast TWT Parameter Set 320a is called a Restricted TWT Parameter Set.

[0127] The other subfields of the Request Type field 330 are not very important: - The Last Broadcast Parameter Set subfield 334 is set to 0 to indicate that another Broadcast TWT parameter set follows this set. The Last Broadcast Parameter Set subfield is set to 1 to indicate that this is the last Broadcast TWT parameter set within the Broadcast TWT element; -The Flow Type subfield 335 indicates whether the TWT is announced (the TWT scheduling AP waits for a frame to be received from the TWT scheduled STA in order to signal its awakened state) (if r-TWT is in "announced" mode, the Flow Type subfield is equal to 0 for r-TWT, since r-TWT is a trigger-enabled TWT); -TWT Wake Interval Exponent subfield 337; and -reserved subfield 338.

[0128] The other fields within the Restricted TWT Parameter Set field 320a are used to define the time parameters for the R-TWT schedule, as follows: - The Target Wake Time (TWT) field 340 indicates the next time (in microseconds) that a station participating in the R-TWT schedule should wake up for the next R-TWT SP; The Nominal Minimum TWT Wake Duration field 350 indicates the minimum amount of time that a TWT-scheduled STA is expected to wake from the start time of a TWT SP in order to complete a frame exchange for the duration of the TWT wake interval. The TWT wake interval of the R-TWT SP is a value calculated from the TWT Wake Interval Mantissa 360 and TWT Wake Interval Exponent 337. It is expressed in a number of units, such as defined in the Wake Duration Unit subfield 312 of the Control field 310, for example, typically 256 μs.

[0129] The other fields in the Restricted TWT Parameter Set field 320a are used to define parameters specific to the broadcast and restricted nature of the R-TWT SP.

[0130] Regarding Broadcast TWT Info field 370, -This conveys the R-TWT schedule identifier, namely Broadcast TWT ID 373 (bTWT ID), which is used to identify R-TWT SPs belonging to the same R-TWT schedule. Therefore, this identifier, which is not 0, allows the AP to schedule multiple sets of Broadcast TWT SPs, each having a different set of TWT parameters; -This specifies the number of Target Beacon Transmission Time (TBTT) values ​​during which a Broadcast TWT SP exists that corresponds to this Restricted (more commonly, Broadcast) TWT parameter set, via the Broadcast TWT Persistence subfield 374; -This also signals that when set to 1 through the Restricted TWT Schedule Full subfield 372, the r-TWT scheduling AP is less likely to accept a request from the STA in the BSS to establish new membership in the corresponding schedule (identified by bTWT ID 373); -Finally, it also signals whether the Restricted TWT Traffic Info field 380 exists (1 in field 371) via the Restricted TWT Traffic Info Present field 371.

[0131] Regarding the Restricted TWT Traffic Info field 380, which is specific to restricting Broadcast TWTs for certain traffic, it is mandatory (and therefore field 371 is mandatory to be set to 1) when the broadcast TWT is associated with an LL (low latency) stream (i.e., the Traffic Info is associated with a TID). It includes the following fields: -Traffic Info Control field 381 indicates whether the following fields 382 and 383 are provided (i.e., "valid"). The DL TID Bitmap Valid subfield 3811 (and the UL TID Bitmap Valid subfield 3812, respectively) indicates whether the Restricted TWT DL TID Bitmap field 382 (and the Restricted TWT UL TID Bitmap field 383, respectively) has valid information. Subfield 3813 is reserved. -The Restricted TWT DL TID Bitmap field 382 (and the Restricted TWT UL TID Bitmap field 383, respectively) identifies the TID as delay-sensitive traffic for the DL (and UL, respectively) direction, i.e., the TID permitted in the R-TWT as defined by the Restricted TWT element 300. The TID can be a TID that defines an LL stream. A value of 1 at bit position k in the bitmap indicates that the TID k is classified as a delay-sensitive traffic stream for the transmission direction in question.

[0132] The TWT SP in the R-TWT schedule is<bTWT ID、TWTスケジューリングAPのMACアドレス> Uniquely identified by a tuple, where the TWT scheduling AP is the associated AP of the relevant link in the AP MLD.

[0133] Thanks to this TWT element included in the TWT Setup frame, an initiator's STA can request its AP to become an R-TWT scheduled STA by negotiating an R-TWT SP for its low-latency traffic. For example, the initiator's STA (e.g., the associated STA of a non-AP MLD) can negotiate the wake TWT, wake interval, and TID that should be allowed in the R-TWT. The AP (e.g., the associated AP of an AP MLD on its link) provides a TWT Response frame to accept or reject the request. In other words, the STA requests membership in the R-TWT schedule.

[0134] The TWT Setup 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 R-TWT schedule that the STA is requesting to join. The AP may respond (TWT Response frame) without a new R-TWT schedule for the bTWT ID (maintaining the existing one), provide an alternative set of parameters as shown in the TWT Setup frame, or create a new R-TWT schedule with the new bTWT ID.

[0135] Once negotiation and membership are complete, a conventional TWT / R-TWT scheduled STA in the awake state may enter the dose state after receiving a beacon frame with a Restricted TWT element indicating the presence of an R-TWT schedule, thanks to advertisements from an R-TWT SP (e.g., via a beacon frame), and may return to the awake state at the start time of the R-TWT. The beacon frame indicates an R-TWT SP that is attempting to send a trigger frame or a DL BU (Bufferable Unit) to the TWT scheduled STA on its link by a TWT scheduling AP.

[0136] At the start of each TWT / R-TWT Service Period, if the TWT scheduling AP expects the TWT scheduled stations to be in an awake state, it typically uses OFDMA multi-user technology (e.g., MU UL trigger-based transmission, MU DL transmission) to manage the R-TWT SP and, if necessary, provide resource units to all or some of the awake TWT scheduled stations.

[0137] Figure 3b shows the case of individual TWT elements for individual TWT sessions (i.e., initiated by a non-AP station). First, there is a negotiation phase in which the AP and target stations agree on a common set of parameters that are essentially the same as those for the Broadcast TWT (most relevant being Target Wake Time 340, TWT Wake Interval Exponent 337, and Minimum TWT Wake Duration 350).

[0138] The TWT parameter information field 320b for individual TWTs adds the following information: - The TWT Group Assignment field 351 provides the requesting STA with information about the TWT group to be assigned to the STA. This field includes the TWT Group ID subfield, the Zero Offset of Group subfield (optional), the TWT Unit subfield, and the TWT Offset subfield. The TWT Group ID subfield is an unsigned integer and indicates the identifier of the TWT group to be assigned to the requesting STA. A value of 0 in the TWT Group ID subfield is used to indicate a unique TWT group that includes all STAs in the BSS. -320b defines the TWT Channel field 354, which defines the channel that a station can temporarily use as the primary channel, in accordance with the individual agreement provided by -320b. - An optional field, NPD Paging field 355 (used for energy saving). -Link ID Bitmap field 356 (indicating the link to which the TWT element sent by the STA related to the Multilink Device (MLD) applies).

[0139] The Request Type field 3330 is different from the Request Type field 330 of the Broadcast TWT. In particular, -The Implicit subfield 3301 is set to 1 to indicate an implicit TWT and to 0 to indicate an explicit TWT; -The Flow type subfield 3302 specifies whether it is Announced (the scheduled STA signals its awake state at the start of the period) or Unannounced; - The TWT Flow Identifier subfield 3303 contains a 3-bit value that uniquely identifies specific information for this TWT request from other requests made between pairs of requesting and responding STAs of the same TWT. -TWT Protection subfield 3304 identified the mechanism used to protect TWT sessions from transmissions from external stations (to TWT schedules), such as RTS / CTS.

[0140] Returning to Figure 1, which shows multiple APs, Multi-AP (MAP) technology emerges, where APs 110, 120, and 130 cooperate to share a common communication channel once one of them is granted access to it. To do so, the APs exchange messages with each other to coordinate MAP communication and thus avoid interference.

[0141] MAP sharing on a common communication channel is resource-based. The amount of shared resources can be measured in units of time, frequency bandwidth, number of streams, amount of data or traffic (e.g., number of bytes), and / or any other appropriate unit, depending on the type of resource defined above. In this view, “shared resource,” “shared frequency bandwidth,” “shared channel,” and “shared resource unit” are synonymous and specify the resources that one AP provides to any other AP via MAP technology.

[0142] To coordinate MAP communication, an AP may be part of an AP-to-AP cooperation group or MAP cooperation set, the configuration of which is outside the scope of this invention. For example, an AP willing to cooperate may advertise its MAP cooperation capability to other APs by issuing a management frame, such as a beacon or a dedicated broadcast frame, in advance. A cooperation group is also called a set of candidate APs for MAP sharing. A cooperation set may include one or more APs.

[0143] The embodiments described below provide more efficient TWT coordination in MAP operation than Contribution 11-22-1530 and the corresponding publication US2022 / 408355 in order to mitigate interference between adjacent APs.

[0144] In these embodiments, the (restricted) TWT Service Period of the target BSS related to the MAP coordinating set is temporally replicated in the second (adjacent) BSS of the set through a new TWT period called the OBSS TWT, where the activity of the OBSS TWT is restricted to the STA of the second (adjacent) BSS.

[0145] To do so, the second AP managing the second (adjacent) BSS first receives a MAP coordination frame from the first AP managing the first target BSS, which identifies the TWT schedule provided in the first BSS. The second AP then, in response to this receipt, sends a frame to the station of the second BSS containing an overlapping BSS (OBSS) TWT element that defines a second TWT Service Period (SP) which is preferably temporally aligned with, or at least partially overlapping with, the first TWT SP of the TWT schedule in the first target BSS. Note that the overlap may be partial or complete across the first TWT SP. A complete overlap may correspond to a second TWT SP that is aligned with or encompasses the first TWT SP. Note that the use of an OBSS TWT element to define the second TWT SP is related to preferred implementations; naturally, other types of elements or other fields in the transmitted frame may be used to define the second TWT SP.

[0146] By processing the OBSS TWT schedule in a manner synchronized with the TWT schedule of the first target BSS, the second (adjacent) AP can adjust its own station's communication policy during the TWT schedule of the first target BSS, and thus adjust the risk of interference. Thus, TWT coordination is achieved.

[0147] A restrictive communication policy prefers a very low risk of interference that would impair communication efficiency in the second (adjacent) BSS. On the other hand, an overly permissive communication policy helps to enable more efficient communication within the BSS, but has the disadvantage of a higher risk of interference with overlapping BSSs.

[0148] As disclosed below, the OBSS TWT mechanism proposed by embodiments of the present invention is preferably based on Broadcast TWT, but differs from actual R-TWT.

[0149] Figure 4a shows, using a flowchart, the general steps of a communication method that provides TWT coordination in MAP operation according to an embodiment of the present invention. The communication method is performed at adjacent APs in a MAP coordination set.

[0150] The first AP in a MAP coordination, for example AP1 of BSS1 in Figure 1, plans a TWT or R-TWT schedule in its own “first” BSS, which is assumed to require TWT coordination with other BSSs in the MAP coordination set. Traditionally, Broadcast TWT operation allows the first AP to set up a shared TWT session for a group of stations in its BSS and periodically identify TWT parameters set within beacon frames to broadcast. Stations in a TWT broadcast agreement are required to wake up to receive only beacon frames containing instructions for the TWT broadcast session to which they belong. The AP may advertise existing TWT broadcast agreements so that stations can ask for membership in an existing TWT session or send a request to create a new TWT session, as described above.

[0151] The first AP (AP1) may decide to share this information about one or more schedules of its TWT with other (adjacent) APs in the MAP coordination set. In the following description, the first AP and its corresponding first BSS may also be referred to as the target AP and target BSS, respectively. Similarly, other APs and their corresponding BSSs may be referred to as the second or adjacency AP and second or adjacency BSS.

[0152] Therefore, in step 400, an adjacent AP in the MAP coordination set receives a MAP coordination frame from the target AP in the same MAP coordination set that identifies the TWT schedule. Thus, the adjacent AP that receives the TWT scheduling information processes the BSS that interferes with the target AP's target BSS. The adjacent AP could be, for example, AP2 of BSS2 in Figure 1.

[0153] Scheduling information can belong to a TWT element, whether it refers to a specific TWT in the target BSS or a Broadcast or Restricted TWT. Various methods can be assumed for receiving such TWT scheduling information (TWT elements) from the target BSS.

[0154] In the first embodiment, the TWT element shared by the target AP with neighboring APs is the TWT element 300 used by the target AP within its own target BSS to announce the TWT schedule. A description thereof is provided above (Figures 3a and 3b).

[0155] It is known that a target AP (AP1 in this example) periodically notifies a station of its target BSS (BSS1) about its TWT schedule by including such a TWT element (for example, having format 320a) in a beacon frame that it broadcasts in its BSS. In this context, the MAP coordination frame is a beacon frame broadcast by the first (target) AP in the first (target) BSS. In particular, the TWT schedule information received by the second (adjacent) AP is defined by the TWT element in the beacon frame addressed to the station in the first (target) BSS.

[0156] Naturally, any type of IEEE 802.11 frame may be used to transport the TWT element 300 from the target AP (AP1) to the adjacent AP (AP2). These may be action frames specific to the MAP scheme, exchanged in single-user mode between both APs, as illustrated for illustrative purposes by references 560 and 561 in Figure 5.

[0157] 802.11 frames may be exchanged over a radio medium shared between BSS1 and BSS2, or over another (radio or wired) medium. For example, an Ethernet backhaul may be established as an off-link or separate network between two APs (more generally between APs forming a MAP coordinating set) for forwarding such 802.11 frames carrying TWT elements. This off-link or separate network means that frames 560 and 561 (Figure 5) are exchanged over a link separate from the radio link in Figure 1 (forming various BSSs) and include link identification to identify the link or separate network where interference may affect communication. In these various options, the MAP coordinating frame is a dedicated unicast frame addressed by the first (target) AP to the second (adjacent) AP, either over a medium or using an alternative communication medium.

[0158] In a second embodiment, a MAP cooperative frame is included in the negotiation process between the first AP and the second AP to establish a MAP TWT agreement. This means that TWT elements are provided through a TWT agreement between the two APs, which can be used to initiate a (MAP) TWT session between the two APs.

[0159] A negotiation phase takes place between the target AP (AP1) and the neighboring AP (AP2) to agree on a minimum set of parameters related to the TWT schedule, including: -Target Wake Time (as field 340 of TWT) defines the next time in microseconds that a station participating in TWT-based communication should wake up for its TWT session within its BSS. In this embodiment, this information is used as an indication for the neighboring (receiving) AP about the start of the next TWT service period; - The TWT Wake Interval (defined by fields 337 and 360 with respect to field 312) defines the time interval between subsequent TWT sessions. Its value is greater than 0 when the TWT is periodic; and, - Minimum TWT Wake Duration (as field 350) defines the minimum duration a station must remain in an awake state from the start time of a TWT session so that the station can receive frames from other stations. In this embodiment, this information is used to drive a waiting period (idle) for a station on an adjacent BSS before attempting to issue a media access request. As will be discussed later in this description, this is intended to reduce the activity of adjacent stations on that adjacent BSS on the media and thus reduce the risk of OBSS interference.

[0160] Other conventional subfields of the TWT element are of less importance because the neighboring (receiving) AP does not need to know all the transmission rules for the TWT SP, which is dedicated only to the target BSS. For example, knowledge of trigger-enabled operation between TWT SPs is not useful for the neighboring AP to perform MAP coordination according to embodiments of the present invention. Therefore, it is not required in MAP coordination frames.

[0161] If several TWT SPs need to be protected and therefore must be advertised in the MAP coordination frame, the MAC addresses of the target AP and neighboring APs, along with the TWT Flow Identifier 3303 of the successful TWT MAP setup between those two APs, can be used to uniquely identify the TWT MAP agreement.

[0162] To create a new MAP TWT session, Request and Accept frames are the minimum set of messages exchanged between the two APs. However, multiple pairs of Suggest / Demand and Alternate / Dictate frames may be exchanged before a final MAP TWT agreement is reached. Negotiation allows for scheduling periods of simultaneous activity (TWT SP) in the two BSSs to their advantage, i.e., avoiding potentially overlapping TWT schedules.

[0163] In some embodiments, individual TWT elements, as shown in Figure 3b, may be used in frames 560 and 561. In this case, the TWT Group Assignment field 351 may be used to indicate that this is a MAP TWT exchange between two APs. As an example, the TWT Group ID subfield within the TWT Group Assignment field 351 indicates the index of the MAP cooperative session or group (if any).

[0164] Frames exchanged by two APs during negotiation can be identified by each of them as coming from a device outside of its own BSS simply by analyzing the MAC frame header. For example, AP2 may identify that the MAC address source of an received frame is the MAC address of AP1, which does not belong to BSS2. Optionally or alternatively, an SSID can be randomly generated for a MAP coordinating set when the set is formed, and such exchanged frames can be identified when the SSID used for address 3 in the MAC header is not set in either BSS2 or BSS1, but is set to the randomly generated SSID for the MAP coordinating set.

[0165] A third embodiment relates to a specific case of an MLD with multiple links. In these embodiments, a MAP coordination frame is exchanged between a third AP associated with a first AP MLD (same as the target AP) and a fourth AP associated with an adjacent AP MLD (same as the adjacent AP). Thus, the frame is carried on a link separate from the link on which the target AP and adjacent AP operate and generate OBSS interference; i.e., it is forwarded from another associated AP of AP1 MLD. The third AP transmits a MAP coordination MAP on behalf of the target AP experiencing OBSS interference, and the fourth AP, receiving the MAP coordination frame, may forward it to the adjacent AP in the adjacent AP MLD for the adjacent AP to perform TWT coordination.

[0166] This could be the case for 802.11be / bn devices (multilink enabled) depending on the radio bandwidth coverage. For example, 2.4GHz provides wider coverage than 6GHz. And there may be OBSS interference between a subset of stations on two BSSs in the 6GHz band while two corresponding APs of two AP MLDs are out of range of each other. In that case, AP1 operating on the 2.4GHz band for the first AP MLD can notify AP2 operating on the same band for the second AP MLD about such OBSS interference; that is, the MAP coordination frame notifying TWT coordination is carried on a link other than the 6GHz link experiencing the OBSS interference. In this context, frames 560 and 561 (Figure 5) are exchanged on separate links and include link identification where interference affects communication.

[0167] In step 400, when a MAP coordinating frame containing TWT information relating to the TWT schedule of BSS1 is received by a neighboring AP, in step 410, the neighboring AP (optionally) performs clock mapping of the timing information contained in the received TWT information. In practice, the TWT time field shared by the target AP in reality is specific to that target AP (AP1) and is represented using a time or clock reference known only to the target BSS. Therefore, the TWT time field is not linked at all to any time or clock reference used by a neighboring AP (AP2). For example, a target AP sending a beacon frame (e.g., propagating a TWT element) sets the timestamp value of the beacon frame to the value of its local Time Synchronization Function (TSF) timer, which corresponds to the time when the data symbol containing the first bit of the timestamp is sent to the PHY, plus the delay of the target AP required for the path from the MAC-PHY interface to its interface with the radio medium (WM) through its local PHY.

[0168] Therefore, in step 410, the neighboring AP converts the timing information of the received TWT schedule in the target BSS based on a first clock (or time reference) applicable to the target BSS into timing information based on a second clock (or time reference) applicable to the neighboring BSS. Then, as described below, the timing information in the OBSS TWT element transmitted within the neighboring BSS is second clock-based timing information.

[0169] The main fields involved in such time conversions include Target Wake Time (as TWT-field 340).

[0170] For an adjacent AP to have knowledge of the time shift (or TSF offset) between two clocks (and to determine the time shift for time correction / conversion), the target AP may advertise the TSF timestamp in the TWT element it sends to the adjacent AP within the MAP cooperative frame. Exemplary diagrams are provided below with reference to Figures 6 and 7 (elements 6813, 711, and 684).

[0171] Alternatively (not shown), the target AP may advertise a time standard by transmitting a Timing Advertisement element in a TWT carrier frame, such as a MAP Cooperative Frame, which includes frame exchanges during MAP TWT negotiation (the Time Advertisement element is described in section 9.4.2.60 of 802.11REVme D2.1). This element may describe the time source corresponding to the time standard and an estimate of the offset between that time standard and the indicated TSF timer (timestamp) provided in the MAP Cooperative Frame. This Time Advertisement element may be included in a TWT element used for TWT coordination (for example, in subfields 6813 or 684).

[0172] In other embodiments where the two APs are directly connected via a backhaul (e.g., an Ethernet backhaul), step 410 can be avoided because cross-AP synchronization may exist by synchronizing the APs over the LAN (Local Area Network) formed by the backhaul.

[0173] Once the time shift (TSF offset) between the two BSSs is determined, the time characteristics of the OBSS TWT schedule in the adjacent BSS (BSS2) to protect the TWT schedule of the target BSS (BSS1) are known, in particular, the TWT timing information expressed using the clock reference of the target BSS. As described above, the OBSS TWT schedule is intended to define an OBSS TWT SP that is preferably aligned with or overlaps (completely or partially) with the TWT SP of the target BSS.

[0174] Using this knowledge, the neighboring AP verifies in step 420 whether the OBSS information fits an existing reservation period in the neighboring BSS. In fact, the neighboring AP does not impose a limited communication policy within its BSS during a service period dedicated to centralized communication for its own BSS, particularly with respect to low-latency data traffic (for R-TWTs scheduled in its neighboring BSS). Therefore, the second AP checks whether the first TWT SP (for TWTs scheduled in the target BSS) overlaps with a TWT SP initially scheduled by the neighboring AP in the neighboring BSS. To do this, the neighboring AP determines whether the TWT parameters (start and end times) obtained from the MAP coordinated frame (after translation if necessary) from the target AP do not encompass any period scheduled by the neighboring AP in its own BSS. Such a period could typically be any TWT service period already scheduled in the neighboring BSS, or a similar period that is convenient for communication with the neighboring BSS. In another embodiment, an adjacent AP may use the timing of the TWT SP of a TWT scheduled in the target BSS to set up or modify its own TWT SP settings within that adjacent BSS.

[0175] MAP coordination can be accepted by neighboring APs if no interference is detected during the scheduled period. Therefore, a neighboring AP may send an acknowledgment (affirmative check) to the target AP if there is no overlap, and a negative acknowledgment otherwise. The response may be a TWT Response frame with an acceptance (or rejection) code. In case of rejection, the process terminates.

[0176] If accepted, the neighboring AP then calculates or constructs an OBSS TWT schedule for its own BSS adapted to the target BSS's TWT schedule in step 430. To do so, it constructs an OBSS TWT element.

[0177] This step will address two issues.

[0178] The first issue concerns the timing of OBSS TWT SPs in the OBSS TWT schedule. As mentioned above, they are preferably time-aligned with the TWT SPs scheduled in the target BSS.

[0179] In some embodiments, considering the determined time shift (TSF offset), they may have the same start time, meaning the TWT (field 340) is the same. In a modified example, it may be assumed that the OBSS TWT SP starts slightly before the TWT SP scheduled in the target BSS.

[0180] The OBSS TWT SP may have the same length as the TWT SP scheduled in the target BSS, meaning, for example, that the Minimum TWT Wake Duration fields are the same. In variations, a larger or shorter Minimum TWT Wake Duration may be defined for the OBSS TWT schedule compared to the TWT schedule of the target BSS. If it is inclusive, the Minimum TWT Wake Duration is larger. If there is overlap, the Minimum TWT Wake Duration may be larger or shorter.

[0181] The second issue concerns communication activity that can enable neighboring APs to ensure TWT coordination with stations on their BSS, i.e., reduced OBSS interference with the target BSS. In fact, it is required that communication activity of stations on neighboring BSSs be limited during scheduled TWT SPs on the target BSS. In addition, stations on neighboring BSSs are expected to terminate their transmissions before the start of scheduled TWT SPs on the target BSS.

[0182] In the first embodiment relating to the second problem, the OBSS TWT element prohibits stations of the second BSS from accessing the medium during the second TWT SP. Thus, it announces a TWT service period during which no station of the second BSS can access the medium. It aims to provide a TWT schedule in which stations of the BSS cannot attempt to join, or which the AP always rejects if they intend to. In other words, the TWT schedule can correspond to idle TWT schedules in which stations of the BSS cannot join.

[0183] An OBSS TWT element 600 that signals such a first embodiment is disclosed in Figure 6, which has fields similar to those in Figures 3a and 3b.

[0184] The OBSS TWT element 600 remains a Broadcast TWT. R-TWT operation is preferable because it aims to provide protected access to a set of stations, and therefore it is not an R-TWT element. Optionally, the OBSS TWT element is positioned at a specific declination of the R-TWT element (as described later with respect to fields 670 and 680).

[0185] The Control field 610 is the same as the Control field 310 above, and the Negotiation Type field 611 has its MSB set to 1 (Broadcast TWT).

[0186] The TWT Parameter Information field 620 has the same format as the TWT Parameter Information field 320. In particular, the Request Type field 630, like the Request Type field 330, includes a Trigger field 633 set to 0 to indicate that the OBSS SP of the OBSS schedule is not trigger-enabled. The other fields within field 630 (631, 632, 634, 635, 636, 637) are less important and are similar to their corresponding fields 331, 332, 334, 335, 336, and 337.

[0187] Several other fields within the TWT Parameter Set field 620 are used to define time parameters for the OBSS TWT schedule, as follows: - The Target Wake Time (TWT) field 640 indicates the next time (in microseconds) when the next OBSS TWT SP will start. As mentioned above, it may correspond to the TWT identified in the MAP Cooperative Frame, which is converted on the time basis of the adjacent BSS; - The Nominal Minimum TWT Wake Duration field 650 indicates the minimum amount of time from the start time of the OBSS TWT SP that a TWT scheduled station in an adjacent BSS is expected to be awake in order to complete a frame exchange for the duration of the TWT wake interval. In embodiments, since no transmission from the station is required, the duration may be set to 0: the Minimum TWT Wake Duration field in the OBSS TWT element 600 is set to 0.

[0188] Several other fields in the TWT Parameter Set field 620 are used to define parameters specific to the Broadcast and Restricted nature of the TWT SP, including a Broadcast TWT Info field 670 similar to the Broadcast TWT Info field 370 described above, and an optional Restricted TWT Traffic Info field 680 specific to the restrictions on the Broadcast TWT for particular traffic.

[0189] With respect to field 670, the Broadcast TWT ID 673 (bTWT ID), used as a non-zero identifier for the OBSS TWT schedule, allows the neighboring AP to schedule multiple sets of Broadcast TWT SPs, each having a different set of OBSS TWT parameters. The Broadcast TWT Persistence subfield 674 identifies the number of Target Beacon Transmission Time (TBTT) during which a Broadcast TWT SP exists that corresponds to this Restricted (more commonly Broadcast) TWT parameter set, which is based on a calculation performed by the neighboring AP in step 410. The Restricted TWT Schedule Info subfield 672 indicates whether the neighboring AP is likely to accept a request from its (neighboring) BSS station to establish new membership in the corresponding OBSS TWT schedule. Preferably, a value of 2 is selected to indicate that it is unlikely that such a request to establish new membership from the BSS station will be accepted.

[0190] With respect to the optional Restricted TWT Traffic Info field 680, its use in an OBSS TWT schedule may be as follows: the Restricted TWT DL TID Bitmap field 682 and the Restricted TWT UL TID Bitmap field 683 respectively identify the absence of traffic. An additional subfield in the Traffic Info Control field 681, namely the OBSS TWT subfield 6813, may explicitly indicate that the current TWT element is an OBSS TWT element for an OBSS TWT schedule. In this way, the OBSS TWT element 600 is a Restricted TWT element having a Restricted TWT Traffic Info section 680 containing the OBSS TWT field 6813 that is enabled.

[0191] In some embodiments where a target AP wishes to advertise a TSF timestamp in a TWT element that it transmits to neighboring APs in the MAP coordination set (as described above with respect to step 410), a separate Timestamp field 684 may be provided within the Restricted TWT Traffic Info field 680 of the OBSS TWT element 600. The OBSS TWT subfield 6813 may be used to signal the presence of a TSF timestamp in the Timestamp field 684, in addition to indicating the OBSS nature of the TWT element.

[0192] The Timestamp field 684 represents the Timing Synchronization Function (TSF) of the TWT frame's source. The Timestamp field is 8 octets long and represents the number of microseconds the AP was active. The timestamp value is reset to 0 when it reaches its maximum value (2^64 microseconds or ~580,000 years).

[0193] Next, referring to a second embodiment concerning the second issue (communication activity for stations between OBSS TWT SPs), the OBSS TWT element 600 announces a TWT service period during which stations of the adjacent BSS (BSS2) can access the medium using a less aggressive medium access method (i.e., a lower priority) than in the first embodiment. It is proposed that the OBSS TWT element 600 defines a waiting time for stations of the adjacent BSS to access the medium during the first TWT SP that is greater than the waiting time for stations of the target BSS to access the medium. Thus, stations of the adjacent BSS have more time to issue medium access, and they perform CCA (channel sensing) for a longer time (corresponding to a larger AIFS, as described below) which allows stations of the target BSS (BSS1) to have priority in accessing the medium.

[0194] In some embodiments, the waiting time for the second BSS station is calculated based on the Minimum TWT Wake Duration (as field 350) specified in the MAP Cooperative Frame (for example, in the TWT element broadcast by the target AP in its beacon frame, or in the duration agreed upon during the MAP TWT agreement established through frame exchange 560 / 561).

[0195] An OBSS TWT element 600 signaling such a second embodiment is disclosed in Figure 7, which is a modification of Figure 6. This modification includes an additional section to the TWT Parameter Information field 720 (620 in Figure 6 and 320a / b in Figures 3a and 3b), namely an OBSS TWT Info field 790. The purpose of this additional section is to provide OBSS TWT parameters related to the waiting time, and optionally the TSF timestamp described above.

[0196] As shown in the diagram, the Timestamp field 684 (as described above) may be provided in a new section, OBSS TWT Info 790. The presence of this field is signaled through a dedicated 1-bit field (Timestamp Valid field 711) in the Traffic Info Control field 791 that initiates OBSS TWT Info 790.

[0197] In some embodiments, the OBSS TWT Info 790 of the OBSS TWT element 600 may directly include a field (not shown) that sets the minimum waiting time after the OBSS TWT SP (described by the OBSS TWT element) has started before a station of an adjacent BSS can access the medium.

[0198] In a preferred embodiment, the wait time is indirectly encoded through a new set of EDCA parameters called the OBSS EDCA Parameter Set. In this context, the OBSS TWT Info 790 of the OBSS TWT element 600 includes an OBSS EDCA Parameter Set 793 that is different from the legacy EDCA Parameter Set and should be applied by stations of neighboring BSSs to have contention for access to the medium during OBSS TWT SPs. Neighboring APs can then drive the wait time of their own stations by adjusting the EDCA parameters of the OBSS EDCA Parameter Set. This also means that those stations must use this particular set of parameters when each new OBSS TWT SP starts and revert to the legacy EDCA Parameter Set when the OBSS TWT SP ends or after a dedicated timer has elapsed. The presence of the OBSS EDCA Parameter Set field is signaled through a dedicated 1-bit field (EDCA Param Valid 712) in the Traffic Info Control field.

[0199] Therefore, the OBSS EDCA Parameter Set 793 embeds this element 793, providing the information required by the station for proper operation of media access between OBSS TWT SPs. In other words, for infrastructure BSSs such as BSS2, the OBSS EDCA Parameter Set element is used by AP2 to establish policies (by changing default MIB attribute values) in order to modify the policies when member stations (STA21, STA22, STA23) perform media access.

[0200] Various embodiments of the OBSS EDCA Parameter Set 793 are shown in Figure 7.

[0201] A first embodiment corresponding to format 793a reuses the legacy format for the EDCA Parameter Set element, as follows:

[0202] The QoS Info field and Update EDCA Info field are reserved (not used). The format of the Parameter Record field 730 for AC_BE, AC_BK, AC_VI, and AC_VO is conventional.

[0203] The ACI / AIFSN subfield 731 typically contains the ACI subfield and the AIFSN subfield. The AC Index (ACI) value refers to the AC that all parameters in this record correspond to. The AIFSN subfield indicates the number of slots after SIFS that the STA will defer before calling backoff or starting transmission. AIFSN stands for "Arbitration InterFrame Space Number".

[0204] The ECWmin / ECWmax subfield 732 encodes the CWmin and CWmax values ​​in exponential form, respectively. ECW stands for "EDCA Contention Window".

[0205] The TXOP Limit field 733 is not specified when TWT SP is considered. Therefore, a TXOP Limit field set to 0 (which has special meaning) may be used.

[0206] In embodiments that seek to provide less aggressive media access than pure prohibition, it may be conceivable that a larger ECWmin than the default is used in the BSS. Therefore, the OBSS EDCA Parameter Set includes a degraded ECWmin value.

[0207] In other embodiments that aim to provide less aggressive media access, the AIFSN value may be adjusted (essentially increased) to delay backoff reduction by adjacent BSS stations, and therefore to delay any media access. In that case, the OBSS EDCA Parameter Set includes a degraded AIFSN value.

[0208] A second embodiment corresponding to format 793b reuses a known format for the MU EDCA Parameter Set element. While conventional MU EDCA Parameter Set elements are used by APs to control the use of EDCA by non-AP802.11be / HE stations following the transmission of a specific UL MU HE TB PPDU, here it is proposed that a neighboring AP in a MAP coordination set use it to control the use of EDCA by its non-AP station within a specific OBSS TWT SP. This element is used as follows:

[0209] The QoS Info field is reserved (not used). The format of the Parameter Record field 740 for MU AC_BE, MU AC_BK, MU AC_VI, and MU AC_VO is conventional.

[0210] Each field element 740 includes the same subfields ACI / AIFSN731 and ECWmin / ECWmax732, and the MU EDCA Timer subfield 743. The MU EDCA Timer field must be set to a value of 0 as reserved. The subfields ACI / AIFSN731 and ECWmin / ECWmax732 are as described above and may carry degraded ECWmin and / or degraded AIFSN values.

[0211] However, in some embodiments, the timer defined by this field 743 may be used to drive a station in an adjacent BSS to switch from the OBSS EDCA parameter set to the legacy EDCA parameter set. This is to restore the legacy parameters when the OBSS TWT SP protecting the scheduled TWT SP in the target BSS terminates. In these embodiments, the OBSS EDCA parameter set includes an OBSS EDCA timer that indicates the duration for which the station in the adjacent BSS uses the OBSS EDCA parameters before switching back to the legacy EDCA parameters.

[0212] For example, the MU EDCA Timer field 743 (carrying the OBSS EDCA timer value) may be based on the Minimum TWT Wake Duration field (as field 350) identified in the MAP Coordination Frame, and in particular set to the value of that field. The MU EDCA Timer field 743 indicates the duration of time the station uses the OBSS EDCA parameter for the corresponding AC in units of 8 TU. Each TU may be defined by the Wake Duration Unit field 312.

[0213] In these embodiments, an adjacent BSS station can perform an independent backoff procedure during the OBSS TWT SP to control media access based on parameters from the OBSS EDCA parameter set.

[0214] A third embodiment, corresponding to format 793c, reuses the ACI / AIFSN field 731 on its own to form the OBSS EDCA Parameter Set 793. In that field, only the AIFSN subfield may be significant (the ACI subfield is not used) to indicate the number of slots that the station will defer after SIFS before calling backoff or initiating transmission. The indicated AIFSN value applies to all ACs during the OBSS TWT SP.

[0215] In any of these embodiments (793a, 793b, or 793c), the AIFSN value may be used alone to defer the call to backoff decrement.

[0216] In a variation, the AIFSN value may define an additional slot that the station adds to the legacy EDCA AIFSN value for each AC category in order to postpone such calls. In other words, the degraded AIFSN value (identified in field 731) is added to the legacy AIFSN value (defined, for example, in the legacy EDCA parameter set) by the station of the adjacent BSS to obtain the AIFSN value that applies when there is a contention for access to the medium during the OBSS TWT SP.

[0217] The adjacent AP must determine the minimum value of the AIFSN subfield, whatever embodiment 793a, 793b, or 793c may be.

[0218] In some embodiments, the minimum value of the AIFSN subfield 731 may be set to 2, particularly when added to the legacy AIFSN value. This value provides a media access slot countdown shift that is favorable to the target BSS (BSS1), so that the queue for each AC of a station in the adjacent BSS (BSS2) is shifted two slots behind compared to the target BSS.

[0219] In other embodiments, the minimum value of the AIFSN subfield 731 may be set to the maximum AIFSN value used by the stations of the target BSS (BSS1). For example, the default value of AC_BK may be set to 7. This allows all queues from the target BSS (BSS1) to be given priority over the highest priority queue in the neighboring BSS (BSS2). Naturally, larger values ​​can also be assumed. These can ensure that media access is always permitted to the stations of the target BSS. For example, the Minimum TWT Wake Duration provided in the MAP Coordinate Frame (as in field 350) may be considered to align an AIFSN close to this delay. In that case, the wait time is specified in the MAP Coordinate Frame and is set to the duration of the TWT SP scheduled in the target BSS, or to the negotiated Minimum TWT Wake Duration.

[0220] While the above embodiment provides an OBSS EDCA Parameter Set (793) within an OBSS TWT element 600, variations may also envision providing such a parameter set in a beacon frame periodically broadcast by a neighboring AP. If different OBSS EDCA parameter sets are used for different OBSS TWT schedules of neighboring BSSs, the OBSS EDCA parameter sets may be provided in the beacon frame in relation to the bTWT ID of each OBSS TWT schedule. In these variations, it can be seen that the AP broadcasts various EDCA parameter sets.

[0221] Therefore, a method of communication via a medium is also provided in the wireless network, and this method includes the following steps in the AP managing the BSS within the AP's MAP coordination set: Send to a station in a BSS the following: a legacy EDCA parameter set defining EDCA parameters to be used by the station when there is a conflict for access to the media; a multi-user (MU) EDCA parameter set defining MU EDCA parameters to be temporarily used by the station when there is a conflict for access to the media after an UpLink MU transmission; and an OBSS EDCA parameter set defined by the AP for the BSS, which is consistent with or overlaps with the adjacent TWT SP of the TWT schedule in the adjacent BSS, and is temporarily used by the station when there is a conflict for access to the media during the overlapping BSS (OBSS) Service Period. Preferably, all three sets are included in the same beacon frame broadcast by the AP in that BSS.

[0222] Returning to Figure 4a, once the OBSS TWT element 600 is prepared in step 430, the neighboring AP (AP2) sends a frame to its associated station on its BSS containing the OBSS TWT element 600, which defines an OBSS TWT SP that is consistent with or overlaps with the TWT SP scheduled on the target BSS (BSS1). This is step 440, which corresponds to the announcement of the OBSS TWT schedule on the neighboring BSS.

[0223] In some embodiments, the frame containing the OBSS TWT element 600 is a beacon frame broadcast by an adjacent AP in an adjacent BSS. Thus, all stations in that BSS can receive the OBSS TWT schedule and restrict their communication activity during the OBSS TWT SP. These beacon-based embodiments allow adjacent APs to periodically identify the TWT parameter set.

[0224] In an alternative embodiment, the frame containing the OBSS TWT element 600 is a probe response frame transmitted by an adjacent AP in an adjacent BSS. The probe response frame may be broadcast to all stations in the BSS, but may be addressed to a specific subset thereof. This probe-based approach allows adjacent APs to identify the OBSS TWT schedule and OBSS TWT parameter set more quickly (prior to the next TBTT) compared to beacon frames.

[0225] Therefore, the determination of neighboring APs for using conventional beacon frames or probe response frames can be based on the start time of the next OBSS TWT SP. In particular, probe response frames containing OBSS TWT parameters are preferably issued when the start time of the next OBSS TWT SP is scheduled before the next TBTT (beacon frame).

[0226] An adjacent AP can transmit the OBSS TWT element 600 to all stations associated with its device, thereby restricting all communication activity of those stations during the OBSS TWT SP. However, there are situations where such restriction is excessive. This is the case, for example, for stations that are far enough away from the target BSS that they cannot generate OBSS interference with the target BSS. While it is valuable to allow these stations to maintain their entire communication activity during the OBSS TWT SP, other stations on the same adjacent BSS will have their communication activity restricted. The adjacent AP may then attempt to create those interfering stations to participate in the OBSS TWT schedule.

[0227] In this regard, the neighboring AP (AP2) may first obtain information about interfering stations of its own BSS (BSS2) that are interfering with the target BSS (BSS1), and then obtain information about free (or non-interfering) stations of its own BSS that are not interfering with the target BSS. Next, the neighboring AP may decide to transmit the OBSS TWT element 600 only to the interfering stations. This may be done using individually addressed probe response frames or individually addressed TWT setup frames that have a TWT Grouping (not shown in the figure) command value in the TWT Setup Command field 332 and a TWT Request field 331 equal to 0 (the transmitting AP is a TWT scheduling station).

[0228] As a result, the OBSS TWT element restricts communication activity on the medium to interference stations only.

[0229] Referring now to an adjacent BSS (BSS2) station, Figure 4b shows, using a flowchart, general steps of the communication method according to an embodiment of the present invention at such a station.

[0230] As explained above, the OBSS TWT element 600 does not define an explicit restriction on the class of traffic to be transmitted within the OBSS TWT SP (i.e., EDCA access category), but rather defines a restriction on media access itself (i.e., EDCA access).

[0231] In step 450, the BSS2 station receives an OBSS TWT element 600 (corresponding to either Figure 6 or 7) from its AP (AP2) in a beacon frame or probe response frame. The OBSS TWT element defines an OBSS TWT schedule with OBSS TWT SPs that are consistent with or overlap with the TWT SPs scheduled (to be protected) in the target BSS (BSS1).

[0232] Depending on the embodiment, the OBSS TWT element may include an OBSS EDCA parameter set that provides parameters for the station to limit its communication activity between OBSS TWT SPs.

[0233] Step 460 consists of the station waiting for the next OBSS TWT SP to start.

[0234] In the first embodiment corresponding to Figure 6 above, the OBSS TWT element 600 indicates that the OBSS TWT schedule is not available to accept new membership. In that case, the station does not request to establish membership in such an OBSS TWT schedule and remains in a dozed state (i.e., no communication activity) during the OBSS TWT SP.

[0235] In the second embodiment corresponding to Figure 7 above, the station is permitted to have some transmission activity in the BSS in accordance with the constraints or limitations defined in the OBSS TWT element 600 (typically according to the OBSS EDCA parameter set).

[0236] In both cases, it should be noted that the station is expected to cease any transmission activity before the OBSS TWT scheduled SP.

[0237] In the second embodiment, in step 470, the station applies the parameters of the OBSS EDCA Parameter Set 793 advertised by its AP (AP2). Then, as described above, the station may apply the degraded AIFSN value 731 and / or the degraded ECWmin value 732, and optionally the OBSS EDCA Timer 743, to control the use of EDCA during OBSS TWT SPs. Thus, referring here to the above description in relation to Figure 7, step 470 consists of the station switching from the legacy EDCA parameter set to the OBSS EDCA parameter set in order to compete for access to the medium during one of the OBSS TWT SPs. The switch is made so that the OBSS EDCA parameter set begins to be used when the OBSS TWT SP starts.

[0238] Step 480 consists of the station waiting for the OBSS TWT SP to finish.

[0239] At the end of the SP, the legacy EDCA parameters are restored (step 490). To do this, the station switches back to the legacy EDCA parameter set (from the OBSS EDCA parameter set). This can be after the end of the OBSS TWT SP, i.e., after the OBSS duration defined by the Minimum TWT Wake Duration field 650 identified in the OBSS TWT element 600. In variations where the OBSS EDCA Timer 743 is used, this is done when the OBSS EDCA Timer 743 identified in the OBSS TWT element has elapsed.

[0240] Next, the station invokes the new (traditional) EDCA backoff procedure.

[0241] Figure 5 shows a transmission sequence that implements TWT coordination for reduced OBSS interference in MAP operation according to an embodiment of the present invention. While the explanation uses 802.11 single-user frames, alternatively, equivalent frames may be used in multi-user operation.

[0242] The proposed example includes two BSSs within a MAP coordination set, e.g., BSS1 and BSS2 in Figure 1.

[0243] Firstly, the two APs directly exchange their TWT scheduling information through frames 560 and 561 (step 400 above). This can be a negotiation between the two APs.

[0244] According to some embodiments, AP1 provides MAP TWT scheduling that conforms to the format of individual TWT(320b) or Broadcast TWT(320a) in its BSS1. The MAP TWT scheduling is included, for example, in a MAP Cooperative Frame 560.

[0245] Once MAP scheduling negotiations are complete, AP1 and AP2 will continue their independent operations on their respective BSSs.

[0246] Typically, AP1 sends a regular beacon frame 500 for each duration interval of TBTT1. In this example, TBTT1 is shorter than TBTT2 (used by AP2 in its own BSS2). As an alternative or supplement to frame exchange 560-561, MAP TWT scheduling can also be obtained directly by AP2 from beacon frame 500. This is because a TWT element 320 exists within such a beacon frame for the station in BSS1. Note that this TWT element can also arise from negotiation 560-561 (if any). Such a TWT element 320 in a beacon frame is typically a Broadcast TWT element or a restricted-TWT element (which is a specific Broadcast TWT element).

[0247] In the example shown in the figure, beacon frame 500 is transmitted by AP1 in BSS1 at T0 and T4, and subsequent TWT SPs for BSS1, TWT SP540 and TWT SP541, corresponding to timings T1-T2 and T5-T6, respectively. TWT SP540 and 541 are periods that are subjected to OBSS interference with BSS2 and require protection using TWT coordination between AP1 and AP2.

[0248] In BSS2, beacon frame 550 is transmitted by AP2 at T3.

[0249] An embodiment of TWT coordination according to the present invention operates as follows: Once MAP TWT negotiation 560 / 561 is completed, AP2 can determine that the first TWT SP540 (T1-T2) in BSS1 will occur before the next TBTT T3 (i.e., before the beacon frame to be transmitted).

[0250] The MAP TWT protection scheme can be provided before T3 by sending a probe response frame 551 containing an OBSS TWT element 520 that notifies about the OBSS TWT schedule (and therefore SP) within BSS2. The probe response frame 551 may be broadcast to reach all stations in BSS2, or it may be sent to a specific subset of stations in BSS2, for example, stations that have been determined to interfere with BSS1.

[0251] In the example shown in the figure, the OBSS TWT element 520 announces OBSS TWT SP530 (start time aligned with TWT SP540), and the BSS2 station can access the medium using a degraded medium access scheme, for example, depending on the degraded AIFSN value and / or degraded ECWmin value described above (optionally included in the OBSS EDCA parameter set 793). The OBSS TWT element 520 may be as described above with respect to Figure 7. As a result, a subset of stations may communicate in BSS2 during OBSS TWT SP530, and the CCA sensing 599 of those stations (Minimum TWT Wake Duration 650, as defined in OBSS TWT element 600) will take longer than that of the BSS1 station during TWT SP540. This ensures that BSS1 takes precedence over BSS2 when accessing the medium during a scheduled TWT SP540.

[0252] In this example, STA22 does not detect any communication activity within its range. As a result, it performs a backoff countdown after the CCA sensing period of 599 and may begin transmitting if it gains access to the medium.

[0253] Naturally, the OBSS TWT element 520 can alternatively announce an OBSS TWT SP in which media access is prohibited for BSS2 stations.

[0254] This is the case, for example, with an OBSS TWT element 520 that announces the next OBSS TWT SP531, accompanied by a beacon frame 550 transmitted by AP2 that indicates that media access to the BSS2 station is prohibited. The OBSS TWT element 520 may be as described above with respect to Figure 6. In this case, there is no communication at all in BSS2 during OBSS TWT SP531, and therefore, no OBSS interference with BSS1 is avoided during TWT SP541.

[0255] The CCA sensing period 599 corresponds to T1-T2' and can be set so that T2' reaches T2. For example, Minimum TWT Wake Duration 650, as defined in OBSS TWT element 600, can be set to Minimum TWT Wake Duration 350 of the TWT SP in the target BSS1, i.e., as defined in TWT element 300 of the beacon frame 500 transmitted by AP1.

[0256] This scenario demonstrates that two different communication activity policies are used for OBSS TWT SPs 530 and 531. Naturally, one same policy (controlled access with access denied or latency) can be used across multiple OBSS TWT SPs in the same OBSS TWT schedule.

[0257] The situation may require AP1 and AP2 to update their negotiations 560 / 561 (not shown in the diagram). To handle such updates over time, beacon frame 550 may advise the OBSS TWT Update Counter field to follow updates associated with the OBSS TWT schedule (for example, using the identifier bTWT ID). The OBSS TWT Update counter field may be defined as an unsigned integer initialized to 0, which is incremented each time an update to the OBSS TWT parameters occurs. In this case, the BSS2 station can recognize any significant changes in the OBSS TWT schedule and retrieve the updated parameters from beacon frame 550.

[0258] Figure 8a schematically shows a communication device 800 configured to implement at least one embodiment of the present invention, for example, one of the (AP and non-AP) stations shown in Figure 1. The communication device 800 is either a coordinator device, a coordinated device, a mere station managed by a coordinator, or a coordinated device in a multi-AP set.

[0259] The communication device 800 may preferably be a device such as a microcomputer, a workstation, or a lightweight portable device.

[0260] The communication device 800 is, The central processing unit 801, which is referred to as the CPU, and other components such as the processor; The present invention has a memory 803 for storing executable code of a method or step of a method according to an embodiment of the present invention, and registers adapted to record variables and parameters necessary to perform the method; and a communication bus 813 to which at least one communication interface 802 connected via transmit and receive antennas 804 to a wireless communication network, for example, a communication network conforming to one of the IEEE 802.11 family standards.

[0261] Preferably, the communication bus provides communication and interoperability between various elements included in or connected to the communication device 800. The representation of the bus is not limited, and in particular, the central processing unit can operate to communicate instructions directly to any element of the communication device 800 or using another element of the communication device 800.

[0262] The executable code may be stored in memory, which may be read-only, a hard disk, or a removable digital medium such as a disk. According to an optional modification, the program's executable code may be received via the communication network through interface 802 in order to be stored in the memory of the communication device 800 before execution.

[0263] In some embodiments, the device is a programmable device that uses software to implement embodiments of the present invention. However, alternatively, embodiments of the present invention may be implemented in whole or in part in hardware (for example, in the form of an application-specific integrated circuit (ASIC)).

[0264] Figure 8b is a schematic block diagram showing the architecture of a communication device 800 adapted to at least partially carry out the present invention. As shown, the device 800 has a physical (PHY) layer block 823, a MAC layer block 822, and an application layer block 821.

[0265] PHY layer block 823 (here, the 802.11 standardized PHY layer) has the task of transmitting or receiving 802.11 frames, which are medium access trigger frames TF for reserving frames, e.g., transmit slots based on a 20 MHz width for interacting with legacy 802.11 stations, MAC data, and management frames, and OFDMA type MAC data frames having a width smaller than 20 MHz legacy (typically 2 or 5 MHz), to or from the radio medium, by formatting, modulating, or demodulating from any 20 MHz channel or common communication channel and thus over the radio medium used.

[0266] The MAC layer block or controller 822 preferably includes a MAC 802.11 layer 824 that implements the MAC operation of conventional 802.11be and an additional block 825 for at least partially carrying out the present invention. The MAC layer block 822 may optionally be implemented in software, the software being loaded into RAM 803 and executed by CPU 801.

[0267] Preferably, an additional block 825, called a multi-AP interference management module, has different operations for carrying out part of the present invention, depending on the role played by the communication device 800. Since the same device can play different roles over time, the additional block 825 is preferably designed to selectively perform different operations.

[0268] For example, though not exhaustive, the operations for communication device 800 operating as an AP include the following: -MAP TWT Negotiation Frame Replacement for 560 / 561, - Converting the timing of the received TWT schedule information into the timing information of its local clock (TSF), setting an OBSS TWT element that defines an OBSS TWT SP that is temporally aligned or overlaps with the TWT SP of the target BSS, declaring a communication activity policy for the OBSS TWT SP, determining stations of its own BSS that interfere with the target BSS, and providing an OBSS TWT element in a beacon frame or a probe response frame.

[0269] The operation of the communication device 800 operating as a non-AP station in a BSS that interferes with the target BSS includes receiving an OBSS TWT element from an AP for the device itself, determining media access rules / policies, extracting a degraded AIFSN / ECWmin or an OBSS EDCA parameter set, switching to a degraded value of the OBSS TWT SP, later switching back to legacy EDCA parameters, and performing EDCA contention using the degraded value during the OBSS TWT SP.

[0270] The MAC 802.11 layer 824 and the multi-AP interference management module 825 interact with each other to accurately process communications via the medium, for example, via an OFDMA RU addressed to a plurality of stations according to embodiments of the present invention.

[0271] In the figure above, the application layer block 821 executes an application that generates and receives data packets, such as data packets of a video stream. The application layer block 821 represents all stack layers above the MAC layer according to ISO standardization.

[0272] Figures 9a, 9b, and 10 illustrate a third embodiment (related to the second problem), where communication activity for stations between OBSS TWT SPs is offloaded to a separate channel. An OBSS TWT element may include channel indications (or a list thereof) along with an OBSS EDCA parameter set that provides parameters for that station to restrict the communication activity of the station between OBSS TWT SPs.

[0273] In other words, the OBSS TWT element 600 announces a TWT service period during which a station on an adjacent BSS (BSS2) can access the medium via a different channel than the operating channel initially used by the adjacent BSS station. Thus, instead of stopping or reducing access to the medium by the adjacent BSS station as in the first and second embodiments, communication can be maintained while preventing interference with the target BSS during the first TWT SP. Hereinafter, the channel initially used by the station will be referred to as the initial operating channel, and the other channel will be referred to as the second channel or temporary operating channel. The initial operating channel is usually the primary channel (the channel on which beacon frames are exchanged), but it may also be a secondary channel.

[0274] Therefore, the channel switch attempts to move BSS2 to the temporary operating channel.

[0275] In an infrastructure BSS, the decision to switch to a new operating channel is made solely by the AP of the BSS. The AP may utilize information in the Supported Channels element and the results of measurements taken by the AP and other STAs in the BSS to assist in selecting a new channel. The Supported Channels information element, according to the IEEE 802.11 series standards, describes the subbands supported by the station (it consists of a first channel number, which is the lowest channel in the supported subbands, followed by the number of channels in the subbands). Generally, channel switching is used very rarely by the AP. A third embodiment of the present invention considers using this mechanism advantageously when an OBSS TWT is about to occur.

[0276] In addition, an AP may utilize information in the Supported Channels element provided by other APs in the MAP coordination group. Negotiation of the channel to be selected among the supported channels may be provided by frame exchange 560 / 561, where each AP (here AP1 or AP2) exchanges information about at least one second channel to be used for channel switching during the OBSS TWT. According to some embodiments, where the AP provides MAP TWT scheduling (frames 560 / 1060 / 561 / 1061) in the format of the individual TWT (320b), the TWT Channel field 354 may be used to indicate the negotiated or proposed second channel. Naturally, an adjacent BSS (BSS2) may still determine the second channel as the temporary operating channel by itself without advertising or negotiating with other APs in the MAP group.

[0277] Figure 9a shows, using a flowchart, the general steps in an AP of a communication method that provides channel switching announcements corresponding to TWT coordination in MAP operation according to a third embodiment of the present invention.

[0278] In the example in Figure 10, the adjacent (second) AP remains AP2, and the method in Figure 9a is performed.

[0279] Similar to step 400 in Figure 4a, where an adjacent (second) AP in a MAP coordinating set receives a MAP coordinating frame from the target (first) AP in the same MAP coordinating set that identifies the TWT schedule, here the adjacent AP in the MAP coordinating set receives channel information from the target AP (step 900). Various types of channel information are possible. Channel information may relate to information in the Supported Channels element advertised for its BSS by the target AP (through its emitted management frame, such as a beacon frame). In variations, or in addition, channel information may relate to information about interfering channels as a result of measurements made by the AP and other STAs in the target AP's BSS. In variations, or in addition, channel information may relate to information about negotiated channels (or a list thereof) as a result of channel assignment for OBSS TWTs in the MAP set.

[0280] In step 910, the AP attempts to select a second channel that is supported by all relevant STAs and conforms to the channel information received from the target AP. In other words, the AP compares the channel to the received list of channels to determine if it can be accommodated locally. If the channel is accommodable, it is selected as the second (or temporary) channel and announced to the BSS.

[0281] In step 920, the neighboring AP in MAP coordination notifies its associated STA that it has switched from the initial operating channel to the second operating channel. Note that the association with the STA is maintained when advertising the switch.

[0282] Three exemplary mechanisms can be envisioned for announcing channel switch information (CSA, Channel Switch Announcement): - Use the Channel Switch Announcement (or Equivalent) until the desired channel switching time. The format of such a frame is shown in Figure 11a, 1100. As will be discussed later, this may require having two frames: a first frame sent before the OBSS TWT to indicate when to switch on the temporary operating channel, and a second frame (during the OBSS TWT) to warn when to switch back to the initial operating channel; - Use a Channel Switch Announcement element (or equivalent) in the beacon frame or probe response frame; the format of such an element is shown by 1150 in Figure 11b. As will be discussed later, this may require having two elements: a first element used to switch to the temporary operating channel and a second element used to switch back to the initial operating channel; -As further shown by element 1280 in Figure 12, a combination of channel switch information and OBSS TWT schedule is used. In this exemplary mechanism, steps 920 and 930 are combined into a single step because this element combines the two pieces of information to be advertised.

[0283] The advantage of the first CSA mechanism (frame 1100, Figure 11a) is that the advertisement frame conforms to legacy devices. By configuring existing elements of the IEEE 802.11 specification, with their parameter values ​​corresponding to the start and end of OBSS TWT timing, the legacy station will employ the appropriate channel switch.

[0284] The third advantage of the CSA mechanism is its optimization in framing, resulting in less messaging overhead (essentially timing information transmitted only in beacon frames) and reduced overhead in beacon or management frames (requiring only channel and TWT timing indication). On the other hand, this mechanism can only be used by newer generation stations (with updated software) because legacy stations will not decode the new format.

[0285] Any combination of the three CSA mechanisms can be envisioned, whether or not the AP is intended to enable legacy devices to understand and apply CSA information.

[0286] Next, step 930 corresponds to step 440, which is the announcement of the OBSS TWT schedule in the adjacent BSS.

[0287] Various frame and element formats for supporting CSA operation are disclosed here.

[0288] Figure 11a shows the format of a Channel Switch Announcement (CSA), frame 1100, adapted for use in OBSS TWT according to an embodiment.

[0289] The diagram provides a legacy format for the Extended Channel Switch Announcement frame (according to IEEE P802.11-REVme / D4.0 9.6.7.7 as of August 2023) so that legacy stations can follow the advertisements and operate the switching. Any other format is possible (e.g., the Channel Switch Announcement frame according to IEEE P802.11-REVme / D4.0 9.6.2.6, August 2023, or any proprietary frame).

[0290] The Channel Switch Mode field 1101 indicates any restrictions on transmissions until the channel switch. As a result, by using the Channel Switch Announcement frame, the AP can cause stations within the BSS to cease transmissions until the channel switch occurs by setting the Channel Switch Mode field within the Channel Switch Announcement element to 1. The Channel Switch frame should be scheduled so that some or all of the STAs within the BSS, including power-save mode STAs, have an opportunity to receive the Channel Switch Announcement element prior to the switch.

[0291] The New Channel Number field 1102 identifies the second (temporary) 20 MHz channel on which to operate after the switch.

[0292] The Channel Switch Count field 1103 indicates the number of Target Beacon Transmission Times (TBTTs) until the AP transmitting the frame switches to the new (temporary) channel. Preferably, a value of 0 is used to indicate that the switch may occur at any time after the frame containing that element has been transmitted. Thus, frame 1100 should be transmitted with respect to a guard interval that is considered the minimum duration to give stations the time to perform those switches prior to the switch (see more details regarding period 1099 shown in FIG. 10).

[0293] If present, the Wide Bandwidth Channel Switch field 1105 indicates the bandwidth of the BSS after the channel switch.

[0294] Other fields are of less importance and can be omitted or ignored.

[0295] Optionally, other frames may be considered for advertising CSA operations. For example, channel usage procedures may be used by APs to help stations operate channel switches during OBSS TWT by exchanging Channel Usage Request and Response frames, or by APs sending unsolicited channel usage response frames.

[0296] For example, the exchange of channel usage frames is performed only by an AP, with some of the stations it manages that interfere with the first AP.

[0297] A channel usage request / response frame may contain zero or more TWT elements along with one or more Channel Usage elements.

[0298] Therefore, an OBSS TWT agreement can be established between the STA and the AP associated with it by exchanging channel usage request and response frames that include the OBSS TWT element and the Timeout Interval Element field (600).

[0299] (According to IEEE P802.11-REVme / D4.0 9.4.2.84, August 2023) The Channel Usage element defines the channel usage information for the BSS. The format of the Channel Usage element consists of a Usage Mode field and a list of Channel Entry fields. The Usage Mode field number (the value listed in Table 9-268 in the above reference), which identifies the use of the recommended channels listed in the Operating Class / Channel Number pair field of the Channel Usage element, may be given a new value that defines the OBSS TWT usage mode. For example, the Usage Mode field may be set to a new value of 5.

[0300] Figure 11b shows the format of a Channel Switch Announcement (CSA) element 1150 adapted for use in an OBSS TWT according to an embodiment.

[0301] The Channel Switch Announcement element 1150 is used by the AP to advertise when it is switching to a new channel and the channel number of that new channel.

[0302] The Channel Switch Mode field 1101 indicates any restrictions on transmission until the channel switch occurs. The AP can stop transmitting to the STA in the BSS until the channel switch occurs by setting the Channel Switch Mode field in the Channel Switch Announcement element to 1. A value of 0 is preferred here because it is not intended to prevent transmission on the original channel before the switch, as is indicated in the beacon frame.

[0303] The New Channel Number field 1102 is set to the channel number to which the STA is moving.

[0304] The Switch Time field 1104 indicates the maximum time delta between the TBTT and the switching date and time of the last beacon frame transmitted by the AP on the current channel.

[0305] Optionally, other formats (or combinations thereof) may be considered: - Legacy Channel Switch Announcement elements, including fields 1101, 1102, and the Channel Switch Count field (described in Figure 9-219 of IEEE P802.11-REVme / D4.0, August 2023), are set to the TBTT number until the STA transmitting the Channel Switch Announcement element switches to the second channel (a value of 0 indicates that the switch will occur at any time after the frame containing that element has been transmitted). -A Wide Bandwidth Channel Switch sub-element (as defined in IEEE P802.11-REVme / D4.0, 9.4.2.159, August 2023) may exist when channel switching alters the BSS operating channel frequency and bandwidth compared to the original bandwidth in the initial channel. - (as defined in IEEE P802.11-REVme / D4.0, 9.4.2.18, August 2023) Secondary Channel Offset element.

[0306] Figure 12 shows the format of a Target Wake Time (TWT) element, which includes a Channel Switch Announcement (CSA) and is adapted for use for OBSS TWT, according to a third embodiment.

[0307] This enhanced TWT element 1280, as a variation of the element in Figures 6 and 7, includes additional fields 9814 and 985 related to information about the temporary channel.

[0308] As shown in Figure 12, the Target Channel field 985 may be provided in an additional section, either OBSS TWT Info 790 (Figure 7) or Restricted TWT Traffic Info field 680 (Figure 6). The presence of this field is signaled through a dedicated 1-bit field (Channel Switch Valid field 1214) in the Traffic Info Control field.

[0309] The Target Channel field indicates the channel number for the second channel operation between OBSS TWT SPs, interpreted in the context of the BSS operation class. The channel number is defined in 802.11REVme D4.0 Annex E. Optionally (not shown), the Operating Bandwidth field allows for an operating bandwidth greater than 20 MHz.

[0310] Now, moving towards an adjacent BSS (BSS2) station, Figure 9b shows a general step in one of those stations using a flowchart of the communication method according to the third embodiment of the present invention.

[0311] In step 950, the BSS2 station receives the OBSS TWT element 600 in the beacon frame or probe response frame and CSA information (1100, 1150, or 1280) from its AP (AP2).

[0312] Legacy stations may apply the algorithm when the received CSA information (1100, 1150) is advertised according to the first and / or second mechanism. Non-legacy stations may apply the algorithm when the received CSA information (1100, 1150, or 1280) is advertised according to the first, second, and / or third mechanism.

[0313] According to an optional embodiment in which the OBSS TWT is transmitted via a Channel Usage element, upon receiving a Channel Usage element in a probe response or in an unsolicited channel usage response frame, the receiving station uses the channel usage information as part of the channel selection process to initiate off-channel OBSS TWT communication.

[0314] The result of step 950 is an indication of the selected target's (second) channel for the switchover, and the appropriate timing for the switchover.

[0315] Step 960 consists of the station waiting for the next OBSS TWT SP to start.

[0316] In step 970, the station (including the AP) selects a second channel and operates the switching. In embodiments that apply constraints or limitations defined in the OBSS TWT element 600 (typically according to the OBSS EDCA parameter set), the station may perform a backoff procedure for access on the selected channel using the provided EDCA parameter (793), or it may wait to receive a frame (e.g., a trigger frame emitted by AP2) on this channel.

[0317] Step 980 consists of the station waiting for the OBSS TWT SP to finish.

[0318] At the end of the SP, the station switches back to the initial operating channel (step 990). In some embodiments, legacy EDCA parameters are restored.

[0319] Several variations can be considered for the switching steps corresponding to the start / end dates and times (steps 960 and 980). The waiting step 960 may preferably be a valid target date and time, meaning that the channel switching must be completed at this target date and time. The waiting step 980 may be a start date and time at which the switching operation can be initiated.

[0320] In step 990, the station ending its second channel operation returns to normal operation on the initial operating channel. The station may have further data, packets, or frames to transmit.

[0321] Figure 10 shows a second transmission sequence that implements TWT coordination for reduced OBSS interference in MAP operation according to a third embodiment of the present invention.

[0322] This sequence is similar to Figure 5, except that a channel switch is performed for the OBSS TWT SP.

[0323] Firstly, the two APs directly exchange their TWT scheduling information, along with CSA information, via frames 1060 and 1061 (step 900 above). This can be a negotiation between the two APs. Adjacent APs in a MAP coordination set receive channel information from each other.

[0324] Once MAP scheduling negotiations are complete, AP1 and AP2 will continue their independent operations in their respective BSSs.

[0325] Similar to the example in Figure 5, the beacon frame 1000 is transmitted by AP1 in BSS1 to indicate the subsequent TWT SP (TWT SP1040) for BSS1.

[0326] In BSS2, the beacon frame 1050 and the probe response frame 1051 are transmitted by AP2.

[0327] These management frames include an OBSS TWT element 520 supplemented by at least one CSA indication (1150). Preferably, the first CSA indication 1150 provides the date and time (T1) to start the TWT, while the second CSA indication indicates when to switch back to the original channel (T3).

[0328] When a CSA indication takes format 1280 (instead of 1150), only one element 1280 is provided within the management frame.

[0329] In this sequence, Channel Switch Announcement frames 1100a and 1100b are also indicated, which can be sent before and after each OBSS TWT SP, respectively. The first frame (1100a) is sent before the OBSS TWT to indicate when to switch to the temporary second channel, and the second frame (1100b, emitted on the second channel during the OBSS TWT) is sent to warn when to switch back to the original channel on which the BSS operates.

[0330] As has already been noted, if a non-AP STA in BSS receives a Channel Switch Mode field (1101) with a value of 1 in frame 1100, it is not permitted to transmit any further frames on that channel until the scheduled channel switch occurs. Therefore, frames 1100a and 1100b must be issued close to their own timing deadlines with respect to the delay 1099 detailed below.

[0331] This solution is more secure compared to any protection for OBSS TWTs, including the Quiet element considered in prior art.

[0332] Note that the timing delay 1099 in the diagram represents the time it takes for the station to switch its operating channel. Typically, an AP may receive a Channel Switch Timing element from its managed station containing information about the required channel switching time in microseconds (as defined in IEEE P802.11-REVme / D4.0 section 9.4.2.62, August 2023). In a variation where the OBSS EDCA Timer 743 is not used for EDCA parameters, the AP may decide to use the OBSS EDCA Timer field 743, identified in the OBSS TWT element, as an indication of the maximum switching time to consider when entering / exiting the OBSS TWT SP. This means that the receiving station is not expected to communicate or receive frames during its maximum switching period.

[0333] If it is permissible to perform switching after the start of the OBSS TWT (date and time T1), and both the second and third embodiments are considered (i.e., some stations operate according to the second embodiment while some other stations, such as legacy stations, operate according to the third embodiment), the duration of delay 1099 (Figure 10) may be set to correspond to the CCA sensing period 599 (Figure 5).

[0334] In one embodiment, a station receiving a switching announcement from its associated AP may refrain from sending frames to the AP on the second channel until it receives a frame from the AP on the second channel. Thus, the AP considers sending an initial frame first when the switch occurs (indicated by frame 1110). Preferably, a trigger frame can be considered to be issued for a trigger station that also switched its operating channel.

[0335] A third embodiment is illustrated by the use of a Channel Switch Announcement. In practice, several mechanisms can be envisioned to apply channel switching operation: -As shown in the diagram, BSS channel switch, Furthermore, recent technologies and protocols such as the following: - Secondary Channel Access (SCA) operation, which is not activated until the primary channel is detected as free; - Subchannel Selective Transmission (SST) operation (including SST elements within beacon frames); and / or -Dynamic sub-band operation (DSO).

[0336] A combination of the first, second, and third embodiments can be envisioned. Channel switching is an attempt to move the BSS to a new operating channel. The goal is to minimize disruption to the BSS in this process, but it should be recognized that channel switching may not be able to successfully move all STAs. Therefore, the AP may decide which of its management stations must perform the channel switching. In an implementation, the AP may request only legacy stations that cannot understand the OBSS TWT and / or cannot switch their operating channels by applying degraded EDCA parameters. In this implementation, the AP selects a second channel supported by those legacy stations.

[0337] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to these specific embodiments, and modifications within the scope of the present invention will be obvious to those skilled in the art.

[0338] Many further modifications and changes are suggested to those skilled in the art by reference to the exemplary embodiments given above, using only examples, and are not intended to limit the scope of the invention as determined solely by the appended claims. In particular, different features from various embodiments can be substituted as needed.

[0339] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude the plural. The mere fact that different features are described in different dependent claims does not imply that combinations of these features cannot be used to one's advantage.

Claims

1. A method of communication via a medium in a wireless network, wherein in a second access point (AP) in a multi-AP (MAP) cooperative set of APs, Receiving a MAP coordination frame from a first AP managing a first Basic Service Set (BSS) that specifies a first Target Wake Time (TWT) Service Period (SP) provided in the said first BSS, A communication method comprising: in response to such reception, transmitting a frame to a station of a second BSS managed by the second AP that defines a second TWT SP that at least partially overlaps with the first TWT SP of the first BSS.

2. The method according to claim 1, wherein the frame sent to the station includes an overlapping BSS (OBSS) TWT element for defining the second TWT SP.

3. The method according to claim 1, wherein the second TWT SP is time-matched with the first TWT SP.

4. The method according to claim 1, wherein the start time of the second TWT SP is aligned with the start time of the first TWT SP.

5. The method according to claim 2, wherein the OBSS TWT element restricts the communication activity of the second BSS station during the first TWT SP of the first BSS.

6. The method according to claim 2, wherein the OBSS TWT element prevents the second BSS station from accessing the medium during the second TWT SP.

7. The method according to claim 2, wherein the OBSS TWT element indicates a temporary operating channel for the second BSS station to switch to for their communications during the second TWT SP.

8. The method according to claim 6, wherein the Minimum TWT Wake Duration field in the OBSS TWT element is set to 0.

9. The method according to claim 5, wherein the OBSS TWT element defines a waiting time for the second BSS station to access the medium that is longer than the waiting time for the first BSS station to access the medium during the first TWT SP.

10. The method according to claim 9, wherein the standby time for the station of the second BSS is calculated based on the Minimum TWT Wake duration identified in the MAP Coordinate Frame.

11. The method according to claim 9, wherein the OBSS TWT element includes a field that sets a minimum waiting time between the start of the second TWT SP and the station of the second BSS being able to access the medium.

12. The method according to claim 9, wherein the OBSS TWT element includes an OBSS EDCA parameter set different from the legacy EDCA parameter set, which is applied by the station of the second BSS for the OBSS TWT element to compete for access to the medium between the second TWT SPs.

13. The method according to claim 12, wherein the OBSS EDCA parameter set includes a degraded ECWmin value and / or a degraded AIFSN value.

14. The method according to claim 13, wherein the degraded AIFSN value is set by the second AP based on the minimum latency identified by the first AP in the MAP cooperative frame.

15. The method according to claim 14, wherein the degraded AIFSN value is negotiated with the first AP by the second AP and set to a Minimum TWT Wake Duration specified in the MAP Coordinated Frame.

16. The method according to claim 13, wherein the degraded AIFSN value is added to the legacy AIFSN value by the station of the second BSS in order to obtain an AIFSN value to be applied when there is competition for access to the medium during the second TWT SP.

17. The method according to claim 12, wherein the OBSS EDCA parameter set includes an OBSS EDCA timer indicating the period for which the OBSS EDCA parameters are used before the station of the second BSS reverts to the legacy EDCA parameters, the OBSS EDCA timer is based on the Minimum TWT Wake Duration field identified in the MAP Coordinate Frame.

18. The method according to claim 9, wherein the waiting time is specified in the MAP cooperative frame.

19. The method according to claim 2, wherein the second AP obtains information regarding interference stations of its own second BSS that are interfering with the first BSS and free stations of its own second BSS that are not interfering with the first BSS, and the OBSS TWT element restricts communication activity in the medium to only the interference stations.

20. The method according to claim 19, wherein the frame including the OBSS TWT element is transmitted only to the interference station.

21. The method according to claim 1, wherein the second AP checks whether the TWT SP initially scheduled by the second AP within the second BSS overlaps with the first TWT SP.

22. The method according to claim 21, further comprising sending an affirmative response to the first AP if there are no duplicates, and sending a negative response otherwise.

23. The method according to claim 2, further comprising converting timing information for the first TWT SP received in the first BSS based on a first clock applicable to the first BSS into timing information based on a second clock applicable to the second BSS, wherein the timing information in the OBSS TWT element is second clock-based timing information.

24. The method according to claim 2, wherein the frame including the OBSS TWT element is a beacon frame broadcast by the second AP in the second BSS.

25. The method according to claim 24, wherein the beacon frame includes an OBSS TWT Update counter which is incremented each time the OBSS TWT parameter in the OBSS TWT element is updated.

26. The method according to claim 2, wherein the frame including the OBSS TWT element is a probe response frame transmitted by the second AP in the second BSS.

27. The method according to claim 2, wherein the OBSS TWT element is a restricted TWT element having a Restricted TWT Traffic Info section containing an enabled OBSS TWT field.

28. The method according to claim 1, wherein the MAP coordinated frame is a beacon frame broadcast by the first AP in the first BSS.

29. The method according to claim 28, wherein the first TWT SP received by the second AP is defined by a TWT element in the beacon frame addressed to the station of the first BSS.

30. The method according to claim 1, wherein the MAP coordinated frame is a dedicated unicast frame addressed by the first AP to the second AP via the medium or using an alternative communication medium.

31. The method according to claim 1, wherein the MAP coordination frame is included in a negotiation process between the first AP and the second AP to establish a MAP TWT agreement.

32. The method according to claim 1, wherein the MAP cooperative frame is exchanged between a third AP which is interconnected with the first AP for the same first AP multilink device (MLD) and a fourth AP which is interconnected with the second AP for the same second AP MLD, and the third AP and the fourth AP operate on links separate from the links on which the first AP and the second AP operate.

33. In a wireless network having a medium, a second AP device in a multi-AP (MAP) cooperative set of access points (APs) managing a second basic service set (BSS), wherein the second AP is: A receiver configured to receive a MAP coordination frame from a first AP managing a first BSS, which identifies a first Target Wake Time (TWT) Service Period (SP) provided in the first BSS, A second AP device having a transmitter configured to transmit to a station of the second BSS a frame that, in response to the reception of the MAP coordinate frame, defines a second TWT SP that at least partially overlaps with the first TWT SP of the first BSS.

34. A communication method via a medium in a wireless network, in a station of a Basic Service Set (BSS) managed by APs in a multi-AP (MAP) cooperative set of access points (APs), The steps include receiving a frame from the AP that includes an overlapping BSS (OBSS) TWT element that defines a TWT Service Period (SP), A communication method comprising the step of switching from a legacy EDCA parameter set to an OBSS EDCA parameter set in order to compete for access to the medium during a TWT SP.

35. The method according to claim 34, wherein the switching is performed such that the OBSS EDCA parameter set begins to be used when the TWT SP starts.

36. The method according to claim 34, wherein the OBSS EDCA parameter set is included in the beacon frame broadcast by the AP.

37. The method according to claim 34, wherein the OBSS EDCA parameter set is included in the OBSS TWT element.

38. The method according to claim 34, wherein the OBSS EDCA parameter set includes degraded AIFS values ​​and / or degraded ECWmin values.

39. The method according to claim 38, wherein the degraded AIFS value is added to the legacy AIFS value when there is competition for access to the medium during the TWT SP.

40. The method according to claim 34, further comprising returning to the legacy EDCA parameter set after an OBSS duration defined by the Minimum TWT Wake Duration field specified in the OBSS TWT element, or after an OBSS EDCA timer specified in the OBSS TWT element has elapsed.

41. The method according to claim 34, further comprising, at the station, terminating any ongoing transmissions over the medium before the commencement of the TWT SP.

42. A station device of a Basic Service Set (BSS) managed by an AP in a multi-AP (MAP) cooperative set of access points (APs) in a wireless network having a medium, A receiver configured to receive frames from the AP that include an overlapping BSS (OBSS) TWT element that defines a TWT Service Period (SP), A station device having a communication module configured to switch from a legacy EDCA parameter set to an OBSS EDCA parameter set in order to compete for access to the medium between the TWT SPs.

43. A method of communication via a medium in a wireless network, in a station of a Basic Service Set (BSS) managed by an AP in a multi-AP (MAP) cooperative set of access points (APs), The steps include receiving a frame from the AP that defines the TWT Service Period (SP), A communication method comprising the step of switching from an initial operating channel to a second operating channel in order to compete for access to the medium via a second operating channel during the TWT SP.

44. The method according to claim 43, wherein the TWT SP at least partially overlaps with a TWT SP in another BSS managed by another AP of the MAP Coordination Set.

45. The method according to claim 43, wherein the received frame includes an overlapping BSS (OBSS) TWT element that defines the TWT SP.

46. In a wireless network having a medium, a station device of a Basic Service Set (BSS) managed by an access point (AP) in a multi-AP (MAP) cooperative set of access points (APs): A receiver configured to receive frames defining the TWT Service Period (SP) from the AP, A station device having a communication module configured to switch from an initial operating channel to a second operating channel in order to compete for access to the medium via a second operating channel during the TWT SP.

47. A method of communication via a medium in a wireless network, wherein in an access point (AP) managing a basic service set (BSS) in a multi-AP (MAP) cooperative set of access points (APs), A communication method comprising the steps of transmitting to a station of the BSS a legacy EDCA parameter set defining EDCA parameters to be used by the station when there is a competition for access to the medium; a MU EDCA parameter set defining MU EDCA parameters to be temporarily used by the station when there is a competition for access to the medium after an uplink multi-user (MU) transmission; and an OBSS EDCA parameter set defining OBSS EDCA parameters to be temporarily used by the station when there is a competition for access to the medium during an overlapping BSS (OBSS) Service Period defined by the AP for the BSS, which at least overlaps with adjacent TWT SPs in the TWT schedule of adjacent BSSs.

48. A non-temporary computer-readable medium storing a program that, when executed by a microprocessor or computer system in a wireless device, causes the wireless device to perform the method according to any one of claims 1 to 32, 34 to 41, 43, and 47.

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