Assisted medium synchronization recovery between access points

Abstract

Methods, devices, and systems for addressing interference issues in a wireless network using a multi-link device are provided. In one method, receiving, by a first access point (AP), a first frame sent by a station (STA) to a second AP, the first frame including a request for the second AP; and transmitting, by the first AP, a second frame to the second AP based on the first AP not receiving an acknowledgement frame destined for the STA from the second AP in response to the first frame. The request may be an AP assist request (AAR), and the request may be used for a second link. Further, the second frame may be arranged to notify the second AP of the request included in the first frame.

Description

TECHNICAL FIELD

[0001] The present invention relates to wireless networks, in particular local networks such as using the IEEE 802.11 standard. BACKGROUND

[0002] Wireless networks are often subject to interference from other networks. Transmissions of those other networks can prevent successful reception of messages sent between devices of the network in question, which hinders coordination of further transmissions in the network. As the complexity and density of networks increases, the impact of hindering coordination is felt more. SUMMARY

[0003] The inventors have recognised that the problem is serious in networks using so-called multi-link devices (MLD for short), because the level of complexity is greater - the need for coordination between devices increases. In the case where both the AP and the STA are MLDs, interference from another network (OBSS in the case of 802.11) on one link can have an impact on the other link, i.e. the problem of throughput loss becomes complex.

[0004] Aspects, embodiments and variants of the invention are therefore defined in the appended claims.

[0005] Thus, according to one aspect, there is provided a method comprising: receiving, by a first access point (AP), a first frame transmitted by a station (STA) to a second AP, the first frame comprising a request for the second AP; and transmitting, by the first AP to the second AP, a second frame based on the first AP not receiving an acknowledgement frame from the second AP to the STA in response to the first frame.

[0006] The second AP is able to detect that the first AP has not heard the first frame.

[0007] According to an embodiment, the request is an AP assisted request (AAR).

[0008] According to an embodiment, the request is for a second link.

[0009] According to an embodiment, the second frame is arranged to inform the second AP of the request comprised in the first frame.

[0010] According to an embodiment, receiving the first frame comprises receiving the first frame via a first link or a second link.

[0011] According to an embodiment, transmitting the second frame comprises transmitting the second frame via the first link or the second link.

[0012] According to an embodiment, the AAR requests the second AP to transmit a third frame to the STA via the second link.

[0013] According to an embodiment, the second frame assists the STA in resuming medium synchronization on the second link.

[0014] According to an embodiment, the second frame includes an indication of the second link.

[0015] According to an embodiment, the second frame includes an indication of the STA.

[0016] According to an embodiment, the second AP sends a third frame to the STA via the second link in response to the second frame.

[0017] According to an embodiment, the second frame includes a management frame.

[0018] According to an embodiment, the second frame includes a control frame.

[0019] According to an embodiment, the second frame includes a data frame.

[0020] According to an aspect, there is also provided a method comprising: receiving, by a first access point (AP), a first frame from a second AP, the first frame informing the first AP of a request sent by a station (STA) for the first AP; and based on receiving the first frame, sending, by the first AP, a second frame to the STA.

[0021] According to an embodiment, the first frame informs the first AP of an AAR operating on a second link.

[0022] According to an embodiment, the AAR requests the first AP to send a second frame to the STA via the second link.

[0023] According to an embodiment, the first frame assists the STA in resuming medium synchronization on the second link.

[0024] According to an embodiment, the first AP sends a second frame to the STA via the second link in response to the first frame.

[0025] According to an aspect, there is provided a method comprising: sending, by a station (STA), a first frame including a request for a first AP to a first AP; and receiving, by the STA, a second frame from a second AP in response to the first frame.

[0026] According to an embodiment, sending the first frame includes sending the first frame via a first link.

[0027] According to an embodiment, receiving the second frame includes receiving the second frame via a second link.

[0028] According to an embodiment, the second frame informs the STA to send a fourth frame to the first AP via the second link.

[0029] According to an aspect, there is provided a method comprising: receiving, by a first access point (AP), a first frame sent by a station (STA) to a second AP based on the first AP receiving, from the second AP, a second frame to the STA in response to the first frame; and sending, by the first AP to the second AP, a second frame informing the second AP of the first frame.

[0030] According to an embodiment, the first frame comprises at least one of a request frame, the request frame comprising an association request frame, a re-association request frame, a TWT setup request frame, a probe request frame, an RTS frame, a block ack request frame, a data frame, etc.

[0031] According to an embodiment, the second frame comprises a response frame, the response frame comprising at least one of an association response frame, a re-association response frame, a TWT response frame, a probe response frame, a CTS frame, or a BA frame.

[0032] According to an embodiment, the first AP and the second AP form a multi-AP group.

[0033] According to an embodiment, the first AP, the second AP, or the STA comprises a multi-link device (MLD).

[0034] According to an embodiment, the first link and the second link form a non-simultaneous transmit and receive (NSTR) link pair at the STA.

[0035] According to an embodiment, the management frame n comprises an active frame, the active frame comprising an active field indicating the second link and the STA.

[0036] According to an embodiment, the control frame comprises a trigger frame, the trigger frame comprising a user info list field indicating the second link and the STA.

[0037] According to an embodiment, the data frame comprises a QoS null frame, the QoS null frame comprising a high throughput (HT) control field indicating the second link and the STA.

[0038] According to an embodiment, the method comprises: sending, by the first AP to the second AP, a first indication of support by the first AP for inter-AP assisted medium synchronization recovery; and receiving, by the first AP from the second AP, a second indication of support by the second AP for inter-AP assisted medium synchronization recovery.

[0039] According to an aspect, there is provided a device arranged to perform, when acting as a first AP, operations comprising: receiving a first frame sent by a station (STA) to a second AP, the first frame comprising a request to the second AP; and based on the first AP receiving, from the second AP, an acknowledgement frame to the STA in response to the first frame, sending, to the second AP, a second frame informing the second AP of the request comprised in the first frame.

[0040] According to one aspect, there is provided a device arranged to perform, when acting as a first STA, operations comprising: receiving, by a first access point (AP) from a second AP, a first frame informing the first AP of a request by a station (STA) to the first AP; and transmitting, based on receiving the first frame, a second frame to the STA.

[0041] According to one aspect, there is provided a device arranged to perform, when acting as a STA, operations comprising: transmitting, by a station (STA) to a first AP, a first frame comprising a request to the first AP; and receiving, by the STA from a second AP, a second frame in response to the first frame. BRIEF DESCRIPTION OF DRAWINGS

[0042] Examples of several embodiments of the present disclosure are described herein with reference to the accompanying drawings.

[0043] Figure 1 An example wireless communication network in which embodiments of the present disclosure can be implemented is shown.

[0044] Figure 2 is a block diagram illustrating an example implementation of a station (STA) and an access point (AP).

[0045] Figure 3 An example medium access control (MAC) frame format is shown.

[0046] Figure 4 An example management frame that can be used as an active frame is shown.

[0047] Figure 5 An example control frame that can be used as a trigger frame is shown.

[0048] Figure 6 An example data frame that can be used as a quality of service (QoS) null frame is shown.

[0049] Figure 7 An example format of a physical layer (PHY) protocol data unit (PPDU) is shown.

[0050] Figure 8 An example reference model of a multi-link device (MLD) is shown.

[0051] Figure 9 An example of an AP MLD and an associated non-AP MLD is shown.

[0052] Figure 10 An example of multi-link setup between an AP MLD and a non-AP MLD is shown.

[0053] Figure 11An example of traffic identifier (TID) to link mapping in a multi-link communication environment is shown.

[0054] Figure 12 An example multi-AP network is shown.

[0055] Figure 13 An example network including a coordinated set of APs is shown.

[0056] Figure 14 An example multi-AP operation procedure is shown.

[0057] Figure 15 An example multi-AP sounding phase is shown.

[0058] Figure 16 An example multi-AP downlink data transmission phase is shown.

[0059] Figure 17 An example multi-AP uplink data transmission phase is shown.

[0060] Figure 18 An example format of an AP assisted request (AAR) control subfield that can be used in a data frame is shown.

[0061] Figure 19 An example of an existing AP assisted medium synchronization recovery procedure is shown.

[0062] Figure 20 Another example of an existing AP assisted medium synchronization recovery procedure is shown.

[0063] Figure 21 An example of an AP assisted medium synchronization recovery procedure according to an embodiment is shown.

[0064] Figure 22 Another example of an AP assisted medium synchronization recovery procedure according to an embodiment is shown.

[0065] Figure 23 Another example of an AP assisted medium synchronization recovery procedure according to an embodiment is shown.

[0066] Figure 24 An example active frame that can be used according to an embodiment is shown.

[0067] Figure 25 An example QoS null frame that can be used according to an embodiment is shown.

[0068] Figure 26 An example trigger frame that can be used according to an embodiment is shown.

[0069] Figure 27 Another example trigger frame that can be used according to an embodiment is shown.

[0070] Figure 28 An example process according to embodiments of the disclosure is shown.

[0071] Figure 29 An example process according to embodiments of the disclosure is shown.

[0072] Figure 30 An example process according to embodiments of the disclosure is shown.

[0073] Figure 31 An example process according to embodiments of the disclosure is shown.

[0074] Figure 32 An example process according to embodiments of the disclosure is shown. DETAILED DESCRIPTION

[0075] In the drawings, like reference numerals refer to like elements.

[0076] In this disclosure, various embodiments are presented as examples of how the disclosed technology can be implemented and / or how the disclosed technology can be practiced in environments and scenarios. It will be apparent to those of ordinary skill in the relevant art that various changes can be made in form and detail without departing from the scope. How to implement alternative embodiments will be apparent to those of ordinary skill in the art after reading the description. The present embodiments can not be limited by any described exemplary embodiments. Embodiments of the disclosure will be described with reference to the drawings. Limitations, features and / or elements from the disclosed example embodiments can be combined to create additional embodiments within the scope of the disclosure. Any drawing that highlights the functionality and advantages of the present disclosure is presented merely for purposes of example and illustration. The disclosed architectures are sufficiently flexible and configurable to allow it to be utilized in ways other than shown. For example, the actions listed in any flowchart can be reordered or optionally used in some embodiments.

[0077] Embodiments can be configured to operate as desired. The disclosed mechanisms can be performed when certain criteria are met, e.g., in a station, access point, radio environment, network, combinations of the above, etc. Example criteria can be based at least in part on, e.g., wireless device or network node configuration, traffic load, initial system setup, packet size, traffic characteristics, combinations of the above, etc. Various example embodiments can be applied when one or more criteria are met. Thus, example embodiments that selectively implement the disclosed protocols can be implemented.

[0078] In this disclosure, “a” and “an” and similar phrases are to be interpreted as “at least one” and “one or more.” Similarly, any term ending in “(s)” is to be interpreted as “at least one” and “one or more.” In this disclosure, the term “may” is to be interpreted as “may, for example.” In other words, the term “may” indicates that the phrase after the term “may” is an example of one of a number of suitable possibilities that can or can not be employed by one or more of the various embodiments. As used herein, the terms “comprises” and “consists of’ recite one or more components of the described element. The term “comprises” is interchangeable with “includes” and does not exclude unenumerated components from being included in the described element. In contrast, “consists of’ provides a complete enumeration of one or more components of the described element. The term “based on” as used herein can be interpreted as “based, at least in part, on” rather than, for example, “based solely on.” The term “and / or” as used herein represents any possible combination of the enumerated elements. For example, “A, B, and / or C” can represent A; B; C; A and B; A and C; B and C; or A, B, and C.

[0079] A is called a subset of B if every element of A is an element of B. In this specification, only non-empty sets and subsets are considered. For example, the possible subsets of B = {STAl, STA2} are: {STAl}, {STA2}, and {STAl, STA2}. The phrase “based on” (or, equivalently, “based at least on”) indicates that the phrase after “based on” is an example of one of a number of suitable possibilities that can or can not be employed by one or more of the various embodiments. The phrase “in response to” (or, equivalently, “at least in response to”) indicates that the phrase after “in response to” is an example of one of a number of suitable possibilities that can or can not be employed by one or more of the various embodiments. The phrase “in dependence of” (or, equivalently, “at least in dependence of”) indicates that the phrase after “in dependence of” is an example of one of a number of suitable possibilities that can or can not be employed by one or more of the various embodiments. The phrase “employ / using” (or, equivalently, “at least employ / using”) indicates that the phrase after “employ / using” is an example of one of a number of suitable possibilities that can or can not be employed by one or more of the various embodiments.

[0080] The term configured can relate to the ability of a device to be in an operational state or a non-operational state. Configured can refer to specific settings in a device that affect the operational characteristics of the device, whether the device is in an operational state or a non-operational state. In other words, hardware, software, firmware, registers, memory values, etc. can be "configured" within a device, whether the device is in an operational state or a non-operational state, to provide specific characteristics to the device. The term such as "a control message to cause in a device" can mean that the control message has parameters that can be used to configure specific characteristics or can be used to cause certain actions in a device, whether the device is in an operational state or a non-operational state.

[0081] In this disclosure, a parameter (or equivalently referred to as a field or an information element: IE) can include one or more information objects, and an information object can include one or more other objects. For example, if a parameter (IE) N includes a parameter (IE) M, and the parameter (IE) M includes a parameter (IE) K, and the parameter (IE) K includes a parameter (information element) J. Then, for example, N includes K, and N includes J. In example embodiments, when one or more messages / frames include multiple parameters, this means that the parameter in the multiple parameters is in at least one of the one or more messages / frames, but not necessarily in each of the one or more messages / frames.

[0082] Many of the presented features are described as optional using "may" or using parentheses. For brevity and readability, this disclosure does not explicitly recite every permutation that can be obtained by selecting from the set of optional features. This disclosure should be interpreted to expressly disclose all such permutations. For example, a system described as having three optional features can be embodied in seven ways, i.e., with only one of the three possible features, with any two of the three possible features, or with the three possible features.

[0083] Many of the elements described in the disclosed embodiments can be implemented as modules. A module is defined here as an element that performs a defined function and has a defined interface to other elements. The modules described in this disclosure can be implemented in hardware, software in combination with hardware, firmware, wetware (e.g., hardware with a biological element) or combinations thereof, which can be behaviorally equivalent. For example, a module can be implemented as a software routine in a computer language (e.g., C, C++, Fortran, Pascal, Java, Basic, Matlab, etc.) that is configured to execute on a hardware machine (e.g., a computer, a microprocessor, an ASIC, etc.). A module can also be implemented in hardware that

[0084] Figure 1 An example wireless communication network in which embodiments of the present disclosure can be implemented is shown.

[0085] As Figure 1 shown, the example wireless communication network can include an Institute of Electrical and Electronics Engineers (IEEE) 802.11 (WLAN) infrastructure network 102. The WLAN infrastructure network 102 can include one or more basic service sets (BSSs) 110 and 120 and a distribution system (DS) 130.

[0086] The BSSs 110-1 and 110-2 each include a set of access points (APs or AP STAs) and at least one station (STA or non-AP STA). For example, the BSS 110-1 includes an AP 104-1 and a STA 106-1, and the BSS 110-2 includes an AP 104-2 and STAs 106-2 and 106-3. The AP and at least one STA in a BSS perform an association procedure to communicate with each other. The DS 130 can be configured to connect the BSS 110-1 and the BSS 110-2. Thus, the DS 130 can enable an extended service set (ESS) 150. Within the ESS 150, the APs 104-1 and 104-2 are connected via the DS 130 and can have the same service set identification (SSID).

[0087] The WLAN infrastructure network 102 can be coupled to one or more external networks. For example, as shown in Figure 1 FIG. 1, the WLAN infrastructure network 102 can be connected to another network 108 (e.g., 802.X) via a portal 140. The portal 140 can be used as a bridge to connect the DS 130 of the WLAN infrastructure network 102 with the other network 108.

[0088] Figure 1 The example wireless communication network shown in FIG. 1 can further include one or more ad hoc networks or independent BSSs (IBSSs). An ad hoc network or IBSS is a network that includes a plurality of STAs that are within communication range of each other. The plurality of STAs are configured such that they can communicate with each other using direct peer-to-peer communications (i.e., not via an AP).

[0089] For example, in Figure 1 FIG. 1, the STAs 106-4, 106-5, and 106-6 can be configured to form a first IBSS 112-1. Similarly, the STAs 106-7 and 106-8 can be configured to form a second IBSS 112-2. Since an IBSS does not include an AP, it does not include a centralized management entity. Rather, the STAs within an IBSS are managed in a distributed manner. The STAs forming an IBSS can be fixed or mobile.

[0090] A STA that is a predetermined functional medium can include a medium access control (MAC) layer that complies with the IEEE 802.11 standard. A physical layer interface for the radio medium can be used between an AP and a non-AP station (STA). A STA can also be referred to using various other terms, including a mobile terminal, wireless device, wireless transmit / receive unit (WTRU), user device (UE), mobile station (MS), mobile subscriber unit, or subscriber. For example, the term “user” can be used to refer to a STA that participates in uplink multi-user multiple-input multiple-output (MU MIMO) and / or uplink orthogonal frequency-division multiple access (OFDMA) transmissions.

[0091] A physical layer (PHY) protocol data unit (PPDU) can be a composite structure including a PHY preamble and a payload in the form of a PHY service data unit (PSDU). For example, a PSDU can include a PHY preamble and a header and / or one or more MAC protocol data units (MPDUs). Information provided in the PHY preamble can be used by a receiving device to decode the subsequent data in the PSDU. In the case of a PPDU being sent over a bonded channel (a channel formed by channel bonding), the preamble field can be duplicated and sent in each of the multiple component channels. The PHY preamble can include both a legacy portion (or "legacy preamble") and a non-legacy portion (or "non-legacy preamble"). The legacy preamble can be used for packet detection, automatic gain control, and channel estimation, among other uses. The legacy preamble can also generally be used to maintain compatibility with legacy devices. The format, coding, and information provided in the non-legacy portion of the preamble are based on the particular IEEE 802.11 protocol to be used to send the payload.

[0092] A frequency band can include one or more sub-bands or frequency channels. For example, a PPDU conforming to the IEEE 802.11n, 802.11ac, 802.11ax, and / or 802.11be standard amendments can be sent on a 2.4 GHz, 5 GHz, and / or 6 GHz frequency band, each of which can be divided into multiple 20 MHz channels. A PPDU can be sent on a physical channel having a minimum bandwidth of 20 MHz. Larger channels can be formed through channel bonding. For example, a PPDU can be sent on a physical channel having a bandwidth of 40 MHz, 80 MHz, 160 MHz, or 520 MHz by bonding together multiple 20 MHz channels.

[0093] Figure 2 is a block diagram 200 illustrating example implementations of a STA 210 and an AP 260. As shown, the STA 210 can include at least one processor 220, a memory 230, and at least one transceiver 240. The AP 260 can include at least one processor 270, a memory 280, and at least one transceiver 290. The processors 220 / 270 can be operatively connected to the transceivers 240 / 290. Figure 2

[0094] The transceivers 240 / 290 can be configured to transmit / receive radio signals. In an embodiment, the transceivers 240 / 290 can implement the PHY layer of the corresponding device (STA 210 or AP 260).

[0095] ​In one embodiment, STA 210 and / or AP 260 may be a multi-link device (MLD), i.e., a device capable of operating on multiple links as defined by the IEEE 802.11be standard revision. Thus, STA 210 and / or AP 260 may each have multiple PHY layers. Multiple PHY layers can be implemented using one or more transceivers from transceivers 240 / 290.

[0096] Processors 220 / 270 can implement the PHY layer, MAC layer and / or logical link control (LLC) layer functions of the corresponding device (STA 210 or AP 260).

[0097] Processors 220 / 270 and / or transceivers 240 / 290 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processors. Memory 230 / 280 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage units.

[0098] When the embodiments are executed by software, the techniques (or methods) described herein can be performed using modules (e.g., procedures, functions, etc.) that perform the functions described herein. Modules can be stored in memory 230 / 280 and executed by processor 220 / 270. Memory 230 / 280 can be implemented (or located) within or outside of processor 220 / 270. Memory 230 / 280 can be operatively connected to processor 220 / 270 via various means known in the art.

[0099] Figure 3 An example format for MAC frame 300 is shown. In operation, the STA can construct a subset of MAC frames for transmission and can decode the received subset of MAC frames during verification. The specific subset of frames that the STA can construct and / or decode can be determined by the functions supported by the STA. The STA can use the Frame Check Sequence (FCS) contained in the frame to verify the received MAC frames and can interpret certain fields from the MAC header of all frames.

[0100] like Figure 3 As shown, MAC frame 300 includes a MAC header, a variable-length frame body, and a frame check sequence (FCS).

[0101] The MAC header includes a frame control field, an optional duration / ID field (not in PS-polling frames), an address field, an optional sequence control field, an optional QoS control field (only in QoS data frames), and an optional high throughput (HT) control field (only in +HTC frames).

[0102] The frame control field includes the following subfields: protocol version, type, subtype, to DS, from DS, more fragments, retry, power management, more data, protected frame, and high throughput control (+HTC).

[0103] The protocol version subfield is invariant in size and placement across all amendments of the IEEE 802.11 standard. For MAC frames, the value of the protocol version subfield is 0.

[0104] The type and subtype subfields together identify the function of the MAC frame. There are three frame types: control, data, and management. Each frame type has several defined subtypes. Bits within the subtype subfield are used to indicate specific modifications of the basic data frame (subtype 0). For example, in a data frame, the most significant bit (MSB) of the subtype subfield (bit 7 (B7) of the frame control field) is defined as the QoS subfield. When the QoS subfield is set to 1, it indicates a QoS subtype data frame, which is a data frame that contains a QoS control field in its MAC header. The second MSB of the subtype field (bit 6 (B6) of the frame control field when set to 1 in the data subtype) indicates a data frame that does not contain a frame body field.

[0105] The to DS subfield indicates whether the data frame is destined for a DS. The from DS subfield indicates whether the data frame originated from a DS.

[0106] The more fragments subfield is set to 1 in all data or management frames that carry a MAC service data unit (MSDU) or MAC management protocol data unit (MMPDU) following the MAC frame. It is set to 0 in all other frames in which the more fragments subfield is present.

[0107] The retry subfield is set to 1 in any data or management frame that is a retransmission of an earlier frame. It is set to 0 in all other frames in which the retry subfield is present. The receiving STA uses this indication to assist it in the process of eliminating duplicate frames. These rules do not apply to frames sent by a STA under the block acknowledgement agreement.

[0108] The power management subfield is used to indicate the power management mode of the STA.

[0109] The more data subfield indicates to a STA in power save (PS) mode the bufferable units (BUs) buffered for the STA at the AP. The more data subfield is valid in individually addressed data or management frames sent by the AP to the STA in PS mode. The more data subfield is set to 1 to indicate that there is at least one additional buffer BU for the STA.

[0110] The protected frame subfield is set to 1 if the frame body field contains information that has been processed by a ciphering algorithm.

[0111] The +HTC subfield indicates that the MAC frame 300 contains an HT Control field. Frames containing an HT Control field are referred to as +HTC frames. Control wrapper frames are +HTC frames.

[0112] The Duration / ID field of the MAC header indicates various content depending on the frame type and subtype and the QoS capabilities of the transmitting STA. For example, in a power save poll (PS-Poll) subtype control frame, the Duration / ID field carries the association identifier (AID) of the STA transmitting the frame in the 14 least significant bits (LSBs), and both of the 2 most significant bits (MSBs) are set to 1. In other frames transmitted by a STA, the Duration / ID field contains a duration value (in microseconds) used by the recipient to update the network allocation vector (NAV). The NAV is a counter that indicates to a STA the amount of time it must defer access to the shared medium.

[0113] The format of the MAC frame 300 can have up to four address fields. These fields are used to indicate the basic service set identifier (BSSID), source address (SA), destination address (DA), transmit address (TA), and receive address (RA). Some frames can not contain some of the address fields. Some address fields are designated using the relative location of the address field (1-4) within the MAC header, regardless of the type of address present in that field. Specifically, the address 1 field always identifies the intended recipient of the frame, and the address 2 field, when present, always identifies the transmitter of the frame.

[0114] The Sequence Control field includes two subfields, a Sequence Number subfield and a Fragment Number subfield. The Sequence Number subfield in a data frame indicates the sequence number of the MSDU (if not in an aggregated MSDU (A-MSDU)) or the sequence number of the A-MSDU. The Sequence Number subfield in a management frame indicates the sequence number of the frame. The Fragment Number subfield indicates the number of fragments of the MSDU or MMPDU. The fragment number is set to 0 in the first or only fragment of the MSDU or MMPDU, and is incremented by 1 for each consecutive fragment of that MSDU or MMPDU. In a MAC protocol data unit (MPDU) containing an A-MSDU, or in an MPDU containing an MSDU or MMPDU that is not fragmented, the fragment number is set to 0. The fragment number remains constant in all retransmissions of a fragment.

[0115] The QoS Control field identifies the traffic class (TC) or traffic stream (TS) to which the MAC frame 300 belongs. The QoS Control field can also indicate various other QoS-related, A-MSDU-related, and mesh-related information about the frame. This information can vary depending on the frame type, frame subtype, and type of sending STA. The QoS Control field is present in all data frames whose QoS Subfield of the Subtype subfield is equal to 1.

[0116] The HT Control field is present in QoS Data, QoS Null, and management frames as determined by the +HTC subfield of the Frame Control field. The control frame subtypes for which the HT Control field is present are control wrapper frames. A control frame described as +HTC (e.g., a request for a Request to Send (RTS) +HTC, a Clear to Send (CTS) +HTC, a Block Ack +HTC, or a Block Ack Request +HTC frame) means that the control frame is carried using a control wrapper frame.

[0117] The Frame Body field is a variable length field containing information specific to the individual frame type and subtype. It can include one or more MSDUs or MMPDUs. The minimum length of the frame body is 0 octets.

[0118] The FCS field contains a 32-bit Cyclic Redundancy Check (CRC) code. The FCS field value is computed over all fields of the MAC header and the Frame Body field.

[0119] Figure 4 An example management frame 400 that can be used as an active frame is shown. In the example, the management frame 400 includes a MAC header, a variable length frame body, and a frame check sequence (FCS). The MAC header includes a frame control field, a duration field, an address 1 field, an address 2 field, an address 3 field, a sequence control field, and an optional HT control field. The presence of the HT control field is determined by the +HTC subfield setting of the frame control field.

[0120] As Figure 4 shown, when used as an active frame, the frame body of the management frame includes an active field, a vendor specific element, a management message integrity code element (MME), a message integrity code (MIC), and an authentication mesh peer exchange element.

[0121] The active field includes a category field and an active details field. The active field provides a mechanism for specifying an extended management action. The category field indicates the category of the active frame. The active details field contains the details of the action requested by the active frame. For example, the active frame can be a public active frame. As Figure 4 shown, in the public active frame format, the active details field includes a public active field in the octet immediately following the category field, followed by a variable length public active details field.

[0122] One or more vendor-specific elements are optionally present. These elements are not present when the category subfield of the action field is vendor-specific.

[0123] The MME is present when the frame is a group-addressed robust action frame and the category of the (only MBSS) action frame does not support privacy for group addressing as indicated by the category value; otherwise the MME is not present.

[0124] The MIC element is present in a self-protected action frame if a pairwise master key (PMK) is shared between the sender and receiver of the frame; otherwise it is not present.

[0125] The authentication mesh peer exchange element is present in a self-protected action frame if a PMK is shared between the sender and receiver of the frame; otherwise it is not present.

[0126] Figure 5 An example format of a trigger frame 500 is shown. The trigger frame 500 can be used by an AP to allocate resources for and request one or more TB PPDU transmissions from one or more STAs. The trigger frame 500 can also carry other information needed by the responding STAs to send TB PPDUs to the AP.

[0127] As shown in FIG. 5, the trigger frame 500 includes a frame control field, a duration field, a receiver address (RA) field, a transmitter address (TA) field, a common information field, a user information list field, a padding field, and a FCS field. Figure 5

[0128] The frame control field includes the following subfields: protocol version, type, subtype, to DS, from DS, more fragments, retry, power management, more data, protected frame, and +HTC.

[0129] The duration field indicates various contents depending on the frame type and subtype and the QoS capabilities of the sending STA. For example, in a power save poll (PS-Poll) subtype control frame, the duration field carries the association identifier (AID) of the STA sending the frame in the 14 least significant bits (LSBs), and both of the 2 most significant bits (MSBs) are set to 1. In other frames sent by a STA, the duration field contains a duration value (in microseconds) used by the receiver to update the network allocation vector (NAV).

[0130] ​The RA field is the address of the STA intended to receive the incoming transmission from the sending station. If the trigger frame 500 is addressed to STAs belonging to a single BSS, the TA field is the address of the STA sending the trigger frame 500. If the trigger frame 500 is addressed to STAs from at least two different BSSs in a multi-BSSID set, the TA field is the transmitted BSSID.

[0131] The common info field specifies the trigger frame type of the trigger frame 500, the transmit power of the trigger frame 500 in dBm, and several key parameters of the TB PPDU sent by the STAs in response to the trigger frame 500. The trigger frame type of the trigger frame used by the AP to receive QoS data using UL MU operation is referred to as a basic trigger frame. Non-EHT non-AP HE STAs interpret the common info field as a HE variant. If B54 and B55 in the common info field are equal to 1, the non-AP EHT STAs interpret the common info field as a HE variant; otherwise the common info field is interpreted as an EHT variant. The HE variant common info field and the EHT variant common info field use the same encoding method for the trigger type, UL length, more TF, need CS, LDPC extra symbol segment, AP TX power, pre-FEC padding factor, PE disambiguation, and trigger related common info subfields.

[0132] The user info list field contains zero or more user info fields. There are three variants of the user info field, which are the special user info field, the EHT variant user info field, and the HE variant user info field.

[0133] The special user info field is a user info field that does not carry user specific information but carries extended common information not provided in the common info field. If the special user info field is included in the trigger frame, the special user info field flag subfield of the EHT variant common info field is set to 0, otherwise it is set to 1. The special user info field is identified by an AID 12 value of 2007 and is optionally present in the trigger frame generated by the EHT AP. The special user info field, if present, is located after the common info field of the trigger frame and carries information for the U-SIG field of the requested EHT TB PPDU. The PHY version identifier subfield indicates the PHY version of the requested TB PPDU that is not a HE TB PPDU. For EHT, the PHY version identifier subfield is set to 0. The other values from 1 to 7 are reserved. The UL bandwidth (BW) extension subfield, together with the UL BW subfield in the common info field, indicates the bandwidth of the requested TB PPDU from the addressed EHT STAs (i.e., the bandwidth in the U-SIG field of the EHT TB PPDU). The EHT spatial reuse n subfield carries the values in the corresponding spatial reuse n subfield to be included in the U-SIG field of the EHT TB PPDU. The U-SIG ignore and validation subfield carries the values in the ignore subfield and validation subfield of the U-SIG field of the requested EHT TB PPDU. The presence and length of the trigger related user info subfield in the special user info field depends on the variant of the trigger frame.

[0134] The EHT variant user info field contains per-STA user info fields addressed in the trigger frame 500. The per-STA user info field includes an AID 12 subfield, an RU allocation subfield, an UL FEC encoding type subfield, an UL EHT-MCS subfield, a reserved subfield, a spatial stream (SS) allocation / RA-RU info subfield, an UL target receive power subfield, and a power save (PS) 160 subfield to be used by the STA in the TB PPDU transmitted in response to the trigger frame 500, and a trigger-related user info subfield. The RU allocation subfield in the EHT variant user info field in the trigger frame that is not a MU-RTS trigger frame, along with the UL BW subfield in the common info field, the UL BW extension subfield in the special user info field, and the PS 160 subfield in the EHT variant user info field, identify the size and location of the RU or MRU. The value of the PS 160 subfield of the RU allocation subfield and B0 indicates 80 MHz frequency sub-blocks where the RU or MRU is located in 26-tone RU, 52-tone RU, 106-tone RU, 242-tone RU, 484-tone RU, 996-tone RU, 52+26-tone RU, and 106+26-tone RU. The value of the PS 160 subfield indicates 160 MHz segments where the RU or MRU is located in 2 996-tone RU, 996+484-tone MRU, and 996+484+242-tone MRU. The UL FEC encoding type subfield of the user info field indicates the code type of the requested EHT TB PPDU. The UL FEC encoding type subfield is set to 0 to indicate BCC and 1 to indicate LDPC. The UL EHT MCS subfield of the user info field indicates the EHT MCS of the requested EHT TB PPDU. The SS allocation subfield of the EHT variant user info field indicates the spatial stream of the requested EHT TB PPDU. The UL target receive power subfield indicates the expected received signal power, measured at the AP’s antenna connector and averaged over the antennas, for the EHT portion of the EHT TB PPDU sent on the allocated RU. The trigger-related user info subfield can be used by the AP to specify the preferred access category (AC) for each STA. The preferred AC setting can be the minimum priority AC traffic sent by the participating STA. The AP determines the list of participating STAs and the BW, MCS, RU allocation, SS allocation, Tx power, preferred AC, and maximum duration of the TB PPDU for each participating STA. The RA-RU info subfield is reserved in the EHT variant user info field.

[0135] Optionally, a padding field is present in the trigger frame 400 to extend the frame length, giving the receiving STA enough time to prepare a response transmitted a SIFS after the frame is received. The padding field, if present, is at least two octets long and set to all ones.

[0136] The FCS field is used by the STA to verify the received frame and to interpret certain fields from the MAC header of the frame.

[0137] Figure 6 An example data frame 600 that can be used as a QoS null frame is shown. A QoS null frame refers to a QoS data frame with a null frame body. The QoS null frame includes a QoS control field and an optional HT control field, which can contain a buffer status report (BSR) control subfield. The QoS null frame indicating buffer status information can be sent by a STA to an AP.

[0138] The QoS control field can include a traffic identifier (TID) subfield, an acknowledgment (Ack) policy indicator subfield, and a queue size subfield (or a transmit opportunity (TXOP) duration request subfield).

[0139] The TID subfield identifies the TC or TS for which a TXOP is being requested by setting the requested TXOP duration or queue size subfield. The encoding of the TID subfield depends on the access policy (e.g., allowed values 0 to 7 for an enhanced distributed channel access (EDCA) access policy to identify user priority of a TC or TS).

[0140] The ack policy indicator subfield, along with other information, identifies the Ack policy following the delivery of MPDUs (e.g., normal ack, implicit block ack request, no ack, block ack, etc.) The queue size subfield is an 8-bit field that indicates the amount of buffered traffic at the STA for a given TC or TS for transmission to the AP identified by the receiver address of the frame containing the subfield. The queue size subfield is present in a QoS null frame sent by a STA when bit 4 of the QoS control field is set to 1. The AP can use the information contained in the queue size subfield to determine the TXOP duration allocated to the STA or to determine the uplink (UL) resources allocated to the STA.

[0141] In frames sent by or to non-high efficiency (non-HE) STAs, the following rules can apply to the queue size value: The queue size value is an approximate total size of all MSDUs and A-MSDUs buffered at the STA in the delivery queue for MSDUs and A-MSDUs (excluding MSDUs or A-MSDUs contained in the current QoS data frame), rounded to the nearest multiple of 256 octets and expressed in units of 256 octets. The TID value is equal to the value indicated in the TID subfield of the QoS control field.

[0142] A queue size value of 0 is only used to indicate that there are no buffered transactions in the queue used for the specified TID.

[0143] The queue size value of 254 is used for all sizes greater than 64,768 octets.

[0144] The queue size value of 255 is used to indicate an unspecified or unknown size.

[0145] In frames sent from HE STA to HE AP, the following rules can be applied to queue size values.

[0146] The queue size value QS is the approximate total size in octet of all MSDUs and A-MSDUs buffered at the STA in the delivery queue for MSDUs and A-MSDUs (including MSDUs or A-MSDUs contained in the same PSDU as the frame containing the queue size subfield), where the TID value is equal to the value indicated in the TID subfield of the QoS control field.

[0147] The queue size subfield includes the scaling factor subfield in bits B14-B15 of the QoS control field and the unscaled value UV in bits B8-B13 of the QoS control field. The scaling factor subfield provides the scaling factor SF.

[0148] The STA obtains the queue size QS from the received QoS control field, which contains the scaling factor SF and the unscaled value UV, as shown below: QS= 16×UV, if SF equals 0; 1024 + 256 × UV, if SF equals 1; 17 408 + 2048 × UV, if SF equals 2; 148 480+32 768×UV, if SF equals 3 and UV is less than 62; >2 147 328, if SF equals 3 and UV equals 62; Unspecified or unknown if SF equals 3 and UV equals 63.

[0149] A TXOP duration request subfield, which can be included instead of the queue size subfield, indicates to the sending STA the duration (in 32-microsecond (us) units) of the next TXOP it needs for the specified TID. The TXOP duration request subfield is set to 0 to indicate that no TXOP is requested for the specified TID in the current service period (SP). The TXOP duration request subfield is set to a non-zero value to indicate a requested TXOP duration in the range of 32 us to 8160 us in increments of 32 us.

[0150] The HT control field can include an aggregation control (A-control) subfield. The A-control subfield can include a control list subfield, which includes one or more control subfields.

[0151] The control subfield can be a BSR control subfield, which can contain buffer status information for UL MU operation. The BSR control subfield can be formed by an access category index (ACI) bitmap subfield, an increment TID subfield, an ACI high subfield, a scaling factor subfield, a queue size high subfield, and a queue size full subfield of the HT control field.

[0152] The ACI bitmap subfield indicates the access categories for which buffer status is reported (e.g., B0: best effort (AC_BE), B1: background (AC_BK), B2: video (AC_VI), B3: voice (AC_VO), etc.). Each bit of the ACI bitmap subfield is set to 1 to indicate that the buffer status for the corresponding AC is included in the queue size of all subfields, and is set to 0 otherwise, unless the ACI bitmap subfield is 0, the increment TID subfield is 3, in which case the buffer status for all 8 TIDs is included.

[0153] The increment TID subfield indicates the number of TIDs for which the STA is reporting buffer status, in conjunction with the value of the ACI bitmap subfield.

[0154] The ACI high subfield indicates the ACI of the AC for which the BSR is indicated in the queue size high subfield. The ACI to AC mapping is defined as ACI value 0 mapping to AC_BE, ACI value 1 mapping to AC_BK, ACI value 2 mapping to AC_VI, and ACI value 3 mapping to AC_VO.

[0155] The scaling factor subfield represents the unit SF, in octets, of the queue size high subfield and the queue size full subfield.

[0156] The queue size high subfield indicates the amount of buffered traffic in SF octets for the AC identified by the ACI high subfield, which is intended for the STA identified by the receiver address of the frame containing the BSR control subfield.

[0157] The Queue Size All subfield indicates the amount of buffered traffic in SF-octets for all ACs identified by the ACI bitmap subfield intended for STAs identified by the receiver address of the frame containing the BSR control subfield.

[0158] The Queue Size High and Queue Size All values in the Queue Size High and Queue Size All subfields are the total size of all MSDUs and A-MSDUs buffered at the STA in the delivery queue for MSDUs and A-MSDUs associated with the ACs specified in the ACI High and ACI bitmap subfields, respectively, including MSDUs or A-MSDUs contained in the same PSDU as the frame containing the BSR control subfield, rounded to the nearest multiple of SF-octets.

[0159] A Queue Size value of 254 in the Queue Size High and Queue Size All subfields indicates that the amount of buffered traffic is greater than 254 x SF-octets. A Queue Size value of 255 in the Queue Size High and Queue Size All subfields indicates that the size of the amount of buffered traffic is unspecified or unknown. The Queue Size value of a QoS data frame containing fragments can remain unchanged even if the amount of queued traffic changes with the transmission of consecutive fragments.

[0160] A MAC service provides the ability to exchange MSDUs to a peer entity. To support this service, the local MAC uses underlying PHY-level services to transmit MSDUs to a peer MAC entity. This asynchronous MSDU transmission is performed on a connectionless basis.

[0161] Figure 7 An exemplary format of a PPDU is shown. As shown, the PPDU can include a PHY preamble, a PHY header, a PSDU, and a tail and padding bits.

[0162] The PSDU can include one or more MPDUs, such as a QoS data frame, M MPDUs, a MAC control frame, or a QoS null frame. In the case where the MPDUs carry a QoS data frame, the frame body of the MPDU can include an MSDU or an A-MSDU.

[0163] By default, MSDU transmission is best effort. That is, there is no guarantee that a transmitted MSDU will be successfully delivered. However, QoS facilities use a traffic identifier (TID) to specify differentiated services on a per-MSDU basis.

[0164] A STA can distinguish MSDU delivery according to the specified traffic class (TC) or traffic stream (TS) of the individual MSDU. The MAC sublayer entity determines the user priority (UP) of an MSDU based on the TID value provided with the MSDU. The QoS facility supports eight UP values. The UP values range from 0 to 7 and form an ordered sequence of priorities, where 1 is the lowest value, 7 is the highest value, and 0 falls between 2 and 3.

[0165] An MSDU with a particular UP is said to belong to the traffic class with that UP. Each MSDU can be provided to a UP directly in the UP parameter at the medium access control service access point (MAC SAP). An A-MPDU can include MPDUs with different TID values.

[0166] A STA can deliver a buffer status report (BSR) to assist the AP in allocating UL MU resources. A STA can implicitly deliver a BSR in the QoS control field or BSR control subfield (unsolicited BSR) of any frame sent to the AP, or explicitly deliver a BSR in a frame sent to the AP in response to a BSRP trigger frame (solicited BSR).

[0167] The buffer status reported in the QoS control field includes a queue size value for a given TID. The buffer status reported in the BSR control field includes an ACI bitmap, an increment TID, a high priority AC, and two queue size values.

[0168] A STA can report the buffer status of transmitted QoS null frames and QoS data frames to the AP in the QoS control field and report the buffer status of transmitted QoS null frames, QoS data frames, and management frames in the BSR control subfield (if present) in the QoS control field as described below.

[0169] A STA can report the queue size for a given TID in the queue size subfield of the QoS control field of a transmitted QoS data frame or QoS null frame; a STA can set the queue size subfield to 255 to indicate an unknown / unspecified queue size for that TID. A STA can aggregate multiple QoS data frames or QoS null frames in an A-MPDU to report the queue size for different TIDs.

[0170] A STA can report buffer status in the BSR control subfield of a transmitted frame if the AP has indicated its support for receiving the BSR control subfield.

[0171] A high-efficiency (HE) STA can report the queue size for the preferred AC indicated by the ACI high subfield in the queue size high subfield of the BSR control subfield. A STA can set the queue size high subfield to 255 to indicate an unknown / unspecified queue size for that AC.

[0172] An HE STA can report the queue size of ACs indicated by the ACI bitmap subfield in the Queue Size All subfield of the BSR control subfield. The STA can set the Queue Size All subfield to 255 to indicate unknown / unspecified BSR for those ACs.

[0173] Figure 8 An example reference model of a multi-link device (MLD) is shown. An MLD is an entity capable of managing communications over multiple links. An MLD can be a logical entity and can have more than one affiliated station (STA). An MLD can be an access point MLD (AP MLD) where the STAs affiliated to the MLD are AP STAs (or APs). An MLD can be a non-access point MLD (non-AP MLD) where the STAs affiliated to the MLD are non-AP STAs (or STAs).

[0174] Depending on the capabilities of both the transmitting AP MLD and non-AP MLD, communications across different frequency bands / channels can or can not occur simultaneously.

[0175] As shown in Figure 8 An MLD can have a single MAC service access point (MAC-SAP) to the LLC layer, which includes the MAC data service. An MLD can support multiple MAC sublayers coordinated by a sublayer management entity (SME). Each AP STA (or non-AP MLD) affiliated to an AP MLD (or non-AP MLD) has a different MAC address within the MLD.

[0176] The SME is responsible for coordinating the MAC sublayer management entities (MLMEs) of the MLD's affiliated STAs to maintain a single robust security network association (RSNA) key management entity and a single IEEE 802.1X authenticator or supplicant for multi-link operation (MLO).

[0177] The multi-link operation (MLO) procedure allows a pair of MLDs to discover, synchronize, (de-)authenticate, (re-)associate, disassociate, and manage resources on any common frequency band or channel supported by both MLDs. The authenticator and MAC-SAP of an AP MLD can be identified by the same AP MLD MAC address. The supplicant and MAC-SAP of a non-AP MLD can be identified by the same non-AP MLD-MAC address.

[0178] Figure 9 An example of an AP MLD and associated non-AP MLDs is shown.

[0179] As shown, the AP MLD has two affiliated APs (AP1 and AP2), and the non-AP MLD has two affiliated STAs (STA 1 and STA 2). The AP MLD and the non-AP MLD can be communicatively coupled through two links (Link 1 and Link 2), Link 1 is established between AP1 and STA1, and Link 2 is established between AP2 and STA2.

[0180] Generally, the MAC addresses of an MLD and its affiliated STAs are different from each other. For example, as shown, the AP MLD can have a MAC address M, AP 1 can have a MAC address w, and AP2 can have a MAC address x. Similarly, the non-AP MLD can have a MAC address P, STA 1 can have a MAC address y, and STA2 can have a MAC address z. Figure 9

[0181] As shown, for each MLD, the MAC sublayer can be further divided into an MLD upper MAC sublayer and an MLD lower MAC sublayer. The MLD upper MAC sublayer (MLD) performs functions that are common across all links. The MLD lower MAC sublayer performs functions that are local to each link. Some functions require joint processing of both the MLD upper MAC sublayer and the MLD lower MAC sublayer. Figure 9

[0182] MLD upper MAC sublayer functions can include: authentication, association, and re-association (between the AP MLD and the non-AP MLD); security association (e.g., pairwise master key security association (PMKSA), pairwise transient key security association (PTKSA)) and distribution of group temporal keys (GTK) / integrity GTK (IGTK) / beacon IGTK (BIGTK); sequence number (SN) / packet number (PN) assignment for frames to be encrypted by a pairwise transient key (PTK) for unicast frames; encryption / decryption of unicast frames using the PTK; selection of MLD lower MAC sublayer for transmission (TID-to-link mapping); reordering of packets to ensure in-order delivery for each BlockAck session; BlockAck scoreboard for individually addressed frames (in cooperation with the MLD lower MAC sublayer); optionally, the MLD upper MAC sublayer delivers BlockAck records on one link to the MLD lower MAC sublayer of the other link; and MLD-level management information exchange / indication via the MLD lower MAC sublayer MLD lower MAC sublayer functions can include:​​ Maintenance of link-specific GTK / IGTK / BIGTK (between APs attached to an AP MLD and STAs attached to a non-AP MLD); Link-specific encryption / decryption / integrity protection and PN allocation using GTK / IGTK / BIGTK (between APs attached to an AP MLD and STAs attached to a non-AP MLD); Link-specific management information exchange / indication (e.g., beacons); Link-specific control information exchange / indication (e.g., RTS / CTS, acknowledgements, etc.); Power saving states and modes; MAC address filtering for frame reception; and Block Ack scoreboards for individually addressed frames (in cooperation with the MLD upper MAC sublayer); optionally, the MLD lower MAC sublayer receives the Block Ack record on other links from the MLD upper MAC sublayer.

[0183] The multi-link (re)establishment between the non-AP MLD and the AP MLD can include an exchange of (re)association request / response frames. The (re)association request / response frame exchange for multi-link establishment can include two frames carrying a basic multi-link element.

[0184] In the (re)association request frame, the non-AP MLD indicates the links requested for (re)establishment and the capabilities and operating parameters of the requested links. The non-AP MLD can request (re)establishment of links with a subset of APs attached to the AP MLD. The links requested for (re)establishment and the capabilities and operating parameters of the requested links are independent of the existing established links with the associated AP MLD and the capabilities and operating parameters of the established links.

[0185] In the (re)association response frame, the AP MLD can indicate the accepted requested links and the rejected requested links for (re)establishment and the capabilities and operating parameters of the requested links. The AP MLD can accept a subset of the links requested for (re)establishment. The (re)association response frame is sent to the non-AP STAs attached to the non-AP MLD that sent the (re)association request frame.

[0186] An MLD requesting or accepting multi-link (re)establishment of any two links ensures that each link is on a different non-overlapping channel. After successful multi-link (re)establishment between the non-AP MLD and the AP MLD, the non-AP MLD and the AP MLD establish links for multi-link operation, and the non-AP MLD and the AP MLD (re)associate. For each setup link, the corresponding non-AP STA affiliated to the non-AP MLD is in the same association state as the non-AP MLD and is associated with the corresponding AP affiliated to the AP MLD. For each setup link, unless the functionality has been extended to the MLD level or otherwise specified, the functionality between the non-AP STA and its associated AP is enabled.

[0187] Figure 10 An example of multi-link setup between an AP MLD and a non-AP MLD is shown. As shown, the AP MLD has three affiliated APs: AP 1 operates in the 2.4 GHz band, AP 2 operates in the 5 GHz band, and AP 3 operates in the 6 GHz band. The non-AP MLD has three affiliated STAs: non-AP STA 1 operates in the 2.4 GHz band, non-AP STA 2 operates in the 5 GHz band, and non-AP STA 3 operates in the 6 GHz band.

[0188] The non-AP MLD can initiate multi-link setup by sending an association request frame to AP 1 affiliated to the AP MLD through non-AP STA 1. In the association request frame, the transmitter address (TA) field is set to the MAC address of non-AP STA 1 and the receiver address (RA) field is set to the MAC address of AP 1. The association request frame includes a basic multi-link element indicating the MLD MAC address of the non-AP MLD and the complete information of non-AP STA 1, non-AP STA 2, and non-AP STA 3. The association request frame can request the establishment of three links between the non-AP MLD and the AP MLD (the link between AP 1 and non-AP STA 1, the link between AP 2 and non-AP STA 2, and the link between AP 3 and non-AP STA 3).

[0189] The AP MLD can respond to the requested multi-link setup by sending an association response frame to the non-AP STA 1 affiliated to the non-AP MLD by the AP. In the association response frame, the TA field is set to the MAC address of the AP 1 and the RA field is set to the MAC address of the non-AP STA 1. The association response frame includes a basic multi-link element indicating the MLD MAC address of the AP MLD and the full information of the AP 1, AP 2 and AP 3. The association response frame signals the successful multi-link setup by establishing three links between the non-AP MLD and the AP MLD (link 1 between AP 1 and non-AP STA 1, link 2 between AP 2 and non-AP STA 2 and link 3 between AP 3 and non-AP STA 3).

[0190] By default, all TIDs at the non-AP MLD are mapped to all setup links for both uplink and downlink. The TID-to-link mapping mechanism allows the AP MLD and the non-AP MLD performing or performing the multi-link setup to specify how UL and DL QoS traffic corresponding to different TIDs (e.g., between 0 and 7) can be allocated to the setup links. In the negotiated TID-to-link mapping, a TID can be mapped to a set of links, which is a subset of the setup links from a single setup link to all setup links.

[0191] A setup link is defined as enabled for the non-AP MLD if at least one TID is mapped to this link in either DL or UL, and this setup link is defined as disabled if no TID is mapped to this link in both DL and UL. At any point in time, a TID is always mapped to at least one setup link in both DL and UL, which means that TID-to-link mapping change is only valid and successful if it does not result in a link set with a mapping consisting of zero setup links.

[0192] By default, all setup links are enabled. If a link is enabled for the non-AP MLD, it can be used for the exchange of individually addressed frames subject to the power state of the non-AP STAs operating on this link. Only MSDUs or A-MSDUs with TIDs mapped to the link can be transmitted on this link in the direction (DL / UL) corresponding to the TID-to-link mapping. Individually addressed management and control frames can be transmitted on any enabled link between the affiliated STAs of the non-AP MLD and the corresponding APs of the AP MLD in both DL and UL.

[0193] If a link is disabled for the non-AP MLD, the link can not be used for the exchange of individually addressed frames between the affiliated STAs of the non-AP MLD and the corresponding APs of the AP MLD.

[0194] If a TID is mapped in UL to a set of enabled links for the non-AP MLD, the non-AP MLD can use any link within the set of enabled links to transmit individually addressed MSDUs or A-MSDUs corresponding to the TID.

[0195] If a TID is mapped in DL to a set of enabled links for the non-AP MLD, the non-AP MLD can retrieve individually addressed BUs buffered at the AP MLD as MSDUs or A-MSDUs corresponding to the TID on any link in the set of enabled links. Conversely, the AP MLD can use any link within the set of enabled links to transmit individually addressed MSDUs or A-MSDUs corresponding to the TID, depending on the power state of the non-AP STA on each used link.

[0196] If the default mode is used, although the AP MLD can recommend links on which the non-AP MLD can retrieve BUs buffered by the AP MLD,

[0197] The non-AP MLD can retrieve buffered BUs on any enabled link, which are MMPDUs buffered at the AP MLD. The AP MLD can use any enabled link to transmit individually addressed bufferable management frames that are not measurement MMPDUs, subject to the power state of the non-AP STA on the used link.

[0198] If a STA affiliated to the non-AP MLD is in active mode on a link with a set of TIDs mapped for DL transmission, its associated AP affiliated to the AP MLD can transmit to the STA: MSDUs / A-MSDUs for the mapped set of TIDs of the non-AP MLD; and MMPDUs that are not measurement MMPDUs for the non-AP MLD or its affiliated STAs, unless these frames are transmitted to another STA affiliated to the same non-AP MLD and in active mode.

[0199] As mentioned above, in the default mapping mode, all TIDs are mapped to all established links for DL and UL, and all established links are enabled. If no, unsuccessful or torn down mapping negotiation for different TID-to-link mapping occurs, the non-AP MLD and the AP MLD performing the multi-link setup will operate in this mode.

[0200] In a multi-link (re)setup procedure, if the AP MLD has indicated support for TID-to-link mapping negotiation, the non-AP MLD can initiate TID-to-link mapping negotiation by including a TID-to-link mapping element in the (re)association request frame.

[0201] Upon receiving the (re)association request frame containing the TID-to-link mapping element, the AP MLD can reply the (re)association request frame according to the following rules. The AP MLD can accept the requested TID-to-link mapping indicated in the TID-to-link mapping element in the received (re)association request frame only when the AP MLD accepts the multi-link (re)establishment requesting to map all links for at least one TID. In this case, the non-AP MLD includes the TID-to-link mapping element in the (re)association response frame. Otherwise, the non-AP MLD indicates the rejection of the proposed TID-to-link mapping by including the TID-to-link mapping element suggesting the preferred TID-to-link mapping in the (re)association response frame.

[0202] After a successful multi-link (re)establishment, in order to negotiate the new TID-to-link mapping, the initiating MLD can send the individually addressed TID-to-link mapping request frame to the responding MLD that has indicated the support of TID-to-link mapping negotiation.

[0203] Upon receiving the individually addressed TID-to-link mapping request frame, the responding MLD sends the individually addressed TID-to-link mapping response frame to the initiating MLD according to the following rules. The responding MLD can accept the requested TID-to-link mapping indicated in the TID-to-link mapping element in the received TID-to-link mapping request frame by sending the TID-to-link mapping response frame. Otherwise, the responding MLD can indicate the rejection of the proposed TID-to-link mapping in the TID-to-link mapping response frame. The responding MLD can suggest the preferred TID-to-link mapping in the TID-to-link mapping response frame by including the TID-to-link mapping element in the TID-to-link mapping response frame.

[0204] An MLD can suggest the preferred TID-to-link mapping to the peer MLD by sending the unsolicited TID-to-link mapping response frame including the TID-to-link mapping element.

[0205] When the peer MLD indicates the preferred TID-to-link mapping, the MLD can consider the preferred TID-to-link mapping when the MLD initiates the new TID-to-link mapping. In addition, the AP MLD can consider the traffic flows affiliated to the non-AP MLD as well as the capabilities and constraints of the non-AP MLD, if any.

[0206] When the two MLDS have negotiated the TID-to-link mapping, the MLDs can tear down the negotiated TID-to-link mapping by sending the individually addressed TID-to-link mapping teardown frame. After the teardown, the MLDs operate in the default mapping mode.

[0207] When the MLD successfully negotiates the TID-to-link mapping with the peer MLD, both the MLD and the peer MLD update the uplink and / or downlink TID-to-link mapping information according to the negotiated TID-to-link mapping.

[0208] When the MLD has successfully negotiated the uplink and / or downlink TID-to-link mapping with the peer MLD, where bit position i of the link mapping field n in the TID-to-link mapping element is set to 0, TID n shall not be mapped to a link associated with link ID i in the uplink and / or downlink. When the MLD has successfully negotiated the uplink and / or downlink TID-to-link mapping with the peer MLD, where bit position i of the link mapping field n in the TID-to-link mapping element is set to 1, TID n is mapped to a link associated with link ID i in the uplink and / or downlink.

[0209] Figure 11 An example of TID-to-link mapping in a multi-link communication environment is shown. As shown, the multi-link communication environment includes an AP MLD with three affiliated APs and a non-AP MLD with three affiliated STAs.

[0210] During or after multi-link setup, the non-AP MLD and the AP MLD can negotiate TID-to-link mapping. The TID-to-link mapping maps TIDs at the non-AP MLD to UL and DL to establish links between the AP MLD and the non-AP MLD. For example, as shown, the TID-to-link mapping can map TIDs 0-6 in both UL and DL to link 1, and map TID 7 in UL and DL to link 2. Thus, links 1 and 2 are enabled, and link 3 is disabled. The TID-to-link mapping negotiation can be performed by exchanging association request / response frames or TID-to-link mapping request / response frames between the non-AP MLD and the AP MLD. Figure 11

[0211] Figure 12 An example multi-AP network 1200 is shown. The example multi-AP network 1200 can be a multi-AP network according to the Wi-Fi Alliance standard specification for multi-AP networks. As shown, the multi-AP network 1200 can include a multi-AP controller 1202 and a plurality of multi-AP groups (or multi-AP sets or AP candidate sets), including multi-AP group 1204, multi-AP group 1206, and multi-AP group 1208. Figure 12

[0212] ​​The multi-AP controller 1202 can be a logical entity that implements logic for controlling the APs in the multi-AP network 1200. The multi-AP controller 1202 can receive capability information and measurements from the APs and can trigger AP control commands and operations on the APs. The multi-AP controller 1202 can also provide onboarding functionality to onboard the APs and provision the APs onto the multi-AP network 1200.

[0213] The multi-AP group 1204, the multi-AP group 1206, and the multi-AP group 1208 can each include multiple APs. The APs in a multi-AP group are within communication range of each other. However, the APs in a multi-AP group need not have the same primary channel. As used herein, the primary channel of an AP refers to the default channel on which the AP monitors for management frames and / or for transmitting beacon frames. For a STA associated with an AP, the primary channel refers to the primary channel of the AP as advertised by the beacon frames of the AP.

[0214] In one approach, one of the APs in a multi-AP group can be designated as a master AP. The designation of the master AP can be done by the multi-AP controller 1202 or the APs of the multi-AP group. The master AP of a multi-AP group can be fixed or can change over time among the APs of the multi-AP group. An AP that is not the master AP of a multi-AP group is referred to as a slave AP.

[0215] In one approach, a multi-AP group or a set of AP candidates is a set of APs that can initiate or participate in multi-AP coordination. The APs in a multi-AP group can participate as slave APs in multi-AP coordination initiated by a master AP in the same multi-AP group. At least one of the APs in a multi-AP group should be capable of being a master AP.

[0216] In one approach, the APs in a multi-AP group can coordinate with each other, including coordinating transmissions within the multi-AP group. One aspect of the coordination can include coordinating to perform multi-AP transmissions within the multi-AP group. As used herein, a multi-AP transmission is a transmission event in which multiple APs (of a multi-AP group or a multi-AP network) transmit simultaneously over a period of time. The period of time for the simultaneous AP transmission can be a contiguous period of time.

[0217] Multi-AP group coordination can be enabled by the multi-AP controller and / or the master AP of the multi-AP group. In one approach, the multi-AP controller and / or the master AP can control the time and / or frequency sharing in a TXOP. For example, when one of the APs in a multi-AP group (e.g., the master AP) obtains a TXOP, the multi-AP controller and / or the master AP can control how to share the time / frequency resources of the TXOP with the other APs of the multi-AP group. In one implementation, the AP of the multi-AP group that obtains the TXOP becomes the master AP of the multi-AP group. The master AP can then share with one or more other APs of the multi-AP group a portion of the TXOP that it obtains (which can be the entire TXOP with the one or more other APs of the multi-AP group).

[0218] Multi-AP operation can be implemented by at least two APs that support multi-AP coordination within one or more multi-AP groups. An AP can support a multi-AP transmission scheme in a multi-AP network. A master AP can coordinate with slave AP(s) to implement multi-AP coordination and support multi-AP transmission. A slave AP can participate in multi-AP transmission. A master AP can select slave APs suitable for multi-AP transmission. A slave AP can be a candidate for multi-AP transmission before being designated by a master AP.

[0219] A multi-AP transmission scheme can include a transmission scheme such as coordinated OFDMA, coordinated time division multiple access (TDMA), coordinated spatial reuse, coordinated beamforming, joint transmission or reception (JT / JR), or a combination of two or more of the foregoing schemes.

[0220] Coordinated OFDMA and coordinated TDMA can be classified as coordinated TXOP, where the frequency or time resources of the TXOP can be used for coordinated interference. Coordinated spatial reuse (CSR) can provide reuse of the spatial domain to neighboring BSSs by adjusting the transmit power of the coordinating APs. Coordinated beamforming (CBF) can provide dedicated spatial steering with spatial radiation based on channel state information (CSI) feedback from the coordinating APs with the help of multiple antennas to suppress interference. JT / JR can detect data streams between multiple APs using distributed MIMO precoding or via shared CSI.

[0221] Figure 13 An example network 1300 including a set of coordinating APs is shown. As Figure 13 shown in FIG. 13 A, the set of coordinating APs can include two APs - AP 1302-1 and AP 1302-2. The set of coordinating APs can be a subset of an established multi-AP group. At least one STA can be associated with each of AP 1302-1 and 1302-2. For example, STA 1304-1 can be associated with AP 1302-1 and STA 1304-2 can be associated with AP 1302-2.

[0222] AP 1302-1 and AP 1302-2 can belong to the same multi-AP group as described above in Figure 1The same ESS described in FIG. 13. In this case, AP 1302-1 and AP 1302-2 can be connected through a DS to support ESS features. In addition, as part of the coordinated AP set, AP 1302-1 and AP 1302-2 can be connected through a backhaul. The backhaul is used to quickly share information between APs to support coordinated transmissions. The shared information can be channel state information or data to be transmitted to associated STAs. The backhaul can be a wired backhaul or a wireless backhaul. A wired backhaul is preferable for high capacity information transfer without burdening the main radio of the AP. However, a wired backhaul can require higher deployment cost and can impose greater constraints on AP placement. A wireless backhaul is preferable for its lower deployment cost and flexibility with respect to AP placement. However, because a wireless backhaul relies on the main radio of the AP to transmit information, the AP cannot transmit or receive any data while using a wireless backhaul.

[0223] Generally, one of AP 1302-1 and AP 1302-2 can act as a master AP, while the other acts as a slave AP. The master AP is the AP that is the owner of the TXOP. The master AP shares the frequency resources with the slave AP during the TXOP. When there are more than two APs in the coordination set, the master AP can share its TXOP with only a subset of the coordinated AP set. The role of the master AP can change over time. For example, the master AP role can be assigned to a particular AP for a period of time. Similarly, the slave AP role can be dynamically selected by the master AP or can be pre-assigned for a period of time.

[0224] Depending on the capabilities of the APs in the coordinated AP set, the APs can only make certain types of coordinated transmissions. For example, in Figure 13 If AP 1302-1 supports JT and CSR, while AP 1302-2 supports CSR and CBF, the two APs can only perform CSR as the coordinated transmission scheme. The APs can also prefer to perform single-AP transmissions for a period of time if the benefits of coordinated transmissions do not outweigh some of the drawbacks of coordinated transmissions, such as reduced flexibility and increased required computational power.

[0225] CSR is one type of multi-AP coordination that can be supported by AP 1301-1 and AP 1302-2, as Figure 13Spatial reuse using CSR can be more stable than non-AP coordinated spatial reuse schemes, such as SR based on overlapping basic service set (OBSS) packet detection (PD) and PSR based SR. For example, in example 1300, APs 1302-1 and 1302-2 can perform joint sounding operations in order to measure path loss (PL) on paths of network 1300. For example, the joint sounding operations can result in a measurement of PL 1308 for the path between APs 1302-1 and 1302-2, path loss 1310 for the path between AP 1302-1 and STA 1304-2, and path loss 1312 for the path between AP 1302-2 and STA 1304-1. The measured path loss information can then be shared between AP 1302-1 and AP 1302-2 (e.g., using a backhaul) to allow AP 1302-1 and AP 1302-2 to transmit to their associated STAs 1304-1 and 1304-2, respectively, at the same time. Specifically, one of APs 1302-1 and 1302-2 obtains a TXOP to be the master AP. The master AP can then send a CSR announcement frame to the other APs. In an embodiment, the master AP can perform a polling operation to poll the slave APs for packet availability for transmission before sending the CSR announcement frame. If at least one slave AP responds indicating packet availability, the master AP can proceed to send the CSR announcement frame. In the CSR announcement, the master AP can limit the transmit power of the slave APs in order to protect its own transmission to its target STA. The slave APs can similarly protect their own transmission to their target STAs by selecting a modulation scheme that enables a high enough signal to interference ratio (SIR) margin to support the interference due to the master AP's transmission to its target STA.

[0226] Figure 14 An example 1400 of a multi-AP operation procedure is shown. In example 1400, the multi-AP operation procedure is shown with respect to a multi-AP network including AP 1402 and AP 1404, and STA 1406 and STA 1408. In the example, AP 1402 and AP 1404 can form a multi-AP group. AP 1402 can be the master AP and AP 1404 can be a slave AP of the multi-AP group. For example, AP 1402 can obtain a TXOP that makes it the master AP of the multi-AP group. Alternatively, AP 1402 can be designated as the master AP by a multi-AP controller.

[0227] As Figure 14As shown, the multi-AP operation process may include a series of time phases, each of which may contain multiple frame exchanges within the multi-AP network. Specifically, the multi-AP operation process may include a multi-AP selection phase 1410, a multi-AP data sharing phase 1412, a multi-AP detection phase 1414, and a multi-AP data transmission phase 1416.

[0228] Multi-AP networks can perform multi-AP operations based on specific multi-AP transmission schemes. The multi-AP transmission scheme can be selected by the master AP based on the capabilities of the slave APs in the multi-AP group. Before multi-AP operation, slave APs can notify the master AP of their associated capability information, including the ability to support one or more multi-AP transmission schemes. Slave APs can also notify the master AP of their BSS information and the link quality information of the STAs associated with them. The master AP can receive information related to all available slave APs. This information can include capability information, BSS information, and link quality information. Based on the information provided by the available slave APs, the master AP can determine the slave APs to be assigned for multi-AP transmission and the specific multi-AP transmission scheme to be used during the multi-AP transmission phase.

[0229] The multi-AP selection phase 1410 may include procedures for the master AP to request, select, or specify (multiple) slave APs for a multi-AP group. For example... Figure 14 As shown, the multi-AP selection phase may include the transmission of frame 618 from AP 1402 and frame 1420 from AP 1404. AP 1402 may send frame 1418 to request information about the buffer status of AP 1404. In response, AP 1404 may send frame 1420 to inform AP 1402 of the buffer status of its associated STA and / or whether it intends to join the multi-AP operation. The multi-AP selection phase 1410 may also be used to exchange information related to multi-AP operation, including, for example, the BSS information of the APs and the link quality information between each AP and its associated STAs. The BSS information of the APs may include the BSS ID of the AP's BSS, the identifiers and / or capabilities of the STAs belonging to the BSS, information about the STAs' detection capabilities, information about the AP's MIMO capabilities, etc. The link quality information may include Received Signal Strength Indicator (RSSI), Signal-to-Noise Ratio (SNR), Signal-to-Interference Plus Noise Ratio (SINR), Channel State Information (CSI), and Channel Quality Indicator (CQI).

[0230] The multi-AP data sharing phase 1412 can include procedures for sharing data frames to be transmitted by the master AP and the APs among the selected slave APs to the associated STAs via direct connections between the APs. For some multi-AP data transmission schemes, the phase 1412 can be optional. For example, JT / JR can require the phase 1412 because data frames can be exchanged between the APs before or after the multi-AP data transmission phase 1416.

[0231] The multi-AP data sharing phase 1412 can be performed using a wired backhaul, an in-channel wireless backhaul, or an out-of-channel wireless backhaul. In some cases, the multi-AP data sharing phase 1412 can be performed on an in-channel backhaul, e.g., using the same wireless channel used for transmitting / receiving data to / from the STAs. For example, as shown in FIG. 14B, in the phase 1412, the AP 1402 can transmit a frame 1422 that can be received by the AP 1404. The frame 1422 can include MPDUs that the AP 1402 wishes to transmit to the associated STAs using a multi-AP operation. Similarly, the AP 1404 can transmit a frame 1424 that can be received by the AP 1402. The frame 1424 can include MPDUs that the AP 1404 wishes to transmit to the associated STAs using a multi-AP operation. Figure 14

[0232] The multi-AP probing phase 1414 can include procedures for multi-AP channel probing, including channel estimation and feedback of the channel estimation between the master AP, candidate slave AP(s), and the associated STAs. For some multi-AP transmission schemes, such as COFDMA, CDTMA, and CSR, the phase 1414 can be optional. For example, the phase 1414 can be performed by the master AP to assist in resource unit allocation when coordinating COFDMA transmissions.

[0233] The multi-AP data transmission phase 1416 can include exchanging data frames between the master AP, slave AP(s), and their associated STAs based on the multi-AP transmission scheme(s) determined by the master AP. Depending on the multi-AP transmission scheme to be used, the phase 1416 can include optional synchronization between the APs of the multi-AP group, followed by exchanging data frames between the APs and STAs within the multi-AP group.

[0234] The order of the phases 1410, 1412, 1414, and 1416 can be different from what is shown in FIG. 14A. For example, in COFDMA, the phase 1416 can occur immediately after the phase 1410, while in JT / JR, the phase 1412 can occur after the phase 1410. In addition, as mentioned above, some phases can be optional and can or can not be present. For example, the phase 1414 can not be required for COFDMA, but can be required for JT / JR. Figure 14 ​​

[0235] Figure 15 An example 1500 of a multi-AP sounding phase is shown. The multi-AP sounding phase 1500 can be an example of the multi-AP sounding phase 1414. As shown, the example 1500 can include a master AP 1502 and a slave AP 1504 of a multi-AP group. The example 1500 can also include a STA 1506 associated with the AP 702 and a STA 1508 associated with the AP 1504. Figure 15

[0236] As shown, the multi-AP sounding phase 1500 can include a frame exchange to allow the AP 1502 (master AP) to obtain channel state information (CSI) for channels in the multi-AP group. In an embodiment, the phase 1500 can include a first sub-phase 1510 and a second sub-phase 1512. Figure 15

[0237] During the first sub-phase 1510, the APs can initiate channel sounding and the STAs can estimate CSI. For example, the AP 1502 can send a frame 1514 to the AP 1504 (slave AP) to trigger multi-AP sounding. The frame 1514 can include a multi-AP trigger frame. Subsequently, the AP 1502 and the AP 1504 can transmit announcement frames 1516-1 and 1516-2 to their respective associated STAs 1506 and 1508, respectively, to announce the transmission of sounding frames. The frame 1516-1 and the frame 1516-2 can include multi-AP null data packet announcement (NDPA) frames. The frame 1516-1 and the frame 1516-2 can be sent simultaneously. Next, the AP 1502 and the AP 1504 can send frames 1518-1 and 1518-2 to the STAs 1506 and 1508, respectively. The frame 1518-1 and the frame 1518-2 can include multi-AP null data packet (NDP) frames. The STAs 1506 and 1508 receive the frame 1518-1 and the frame 1518-2, respectively, and perform channel estimation for the channels from the AP 1502 to the STA 1506 and from the AP 1504 to the STA 1508, respectively.

[0238] ​​During the second sub-phase 1512, the AP can initiate a process for the STAs to feedback channel estimates to the AP. For example, the AP 1502 can transmit a frame 1520 to trigger the STAs 1506 and 1508 to transmit their channel estimates to the AP 1502 and the AP 1504, respectively. The frame 1520 can comprise a multi-AP trigger frame. In response, the STAs 1506 and 1508 can transmit frames 1522 and 1524, respectively, including feedback of channel estimates to the AP 1502 and the AP 1504. The frames 1522 and 1524 can comprise NDP feedback frames. The feedback of channel estimates can comprise NDP feedback, CSI-related information, a beamforming report (BFR), or a channel quality indication (CQI) report.

[0239] Figure 16 An example 1600 of a multi-AP downlink data transmission phase is shown. The multi-AP downlink data transmission phase 1600 can be an example of the multi-AP data transmission phase 1516. As Figure 16 shown, the example 1600 can include a master AP 1602 and a slave AP 1604 of a multi-AP group. The example 1600 can also include a STA 1606 associated with the AP 1602 and a STA 1608 associated with the AP 1604.

[0240] As Figure 16 shown, the multi-AP downlink data transmission phase 1600 can include a frame exchange to enable the master AP 1602 to coordinate with the slave AP 1604 to perform a particular multi-AP transmission scheme with the STAs 1606 and 1608 associated therewith, respectively. The multi-AP transmission scheme can include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the above schemes.

[0241] As Figure 16 shown, the master AP 1602 can begin the phase 1600 by transmitting a frame 1610 to the AP 1604. The frame 1610 can include information about the AP 1604 (e.g., an identifier of the AP 1604), synchronization information, information about a particular multi-AP transmission scheme to be used, and / or information about a resource unit (RU) for the AP 1604 to use to acknowledge the frame 1610. The frame 1610 can comprise a control frame. For example, the frame 1610 can comprise a multi-AP trigger frame.

[0242] Frames 1610 can be received from AP 1604 and can be used to synchronize with master AP 1602. Subsequently, AP 1602 and AP 1604 can perform data transmissions to their associated STAs 1606 and 1608, respectively. Specifically, AP 1602 can transmit data frames 1612 to its associated STA 1606, and AP 1604 can transmit data frames 1614 to its associated STA 1608. Depending on the multiple-AP transmission scheme used, AP 1602 and AP 1604 can transmit frames 1612 and 1614 to STAs in different BSSs, respectively. For example, when the multiple-AP transmission scheme is JT / JR, AP 1602 can also transmit frames 1612 to STA 1608 associated with slave AP 1604, and AP 1604 can also transmit frames 1614 to STA 1608 associated with AP 1604. The resources used to transmit and receive frames 1612 and 1614 can depend on the particular multiple-AP transmission scheme employed.

[0243] AP 1602 and AP 1604 can transmit frames 1616 and 1618 to APs in different BSSs, respectively, when needed by the multiple-AP transmission scheme used. For example, when the multiple-AP transmission scheme is JT / JR, STA 1606 can also transmit frames 1616 to AP 1604, and STA 1608 can also transmit frames 1618 to AP 1602. The resources used to transmit and receive frames 1616 and 1618 can depend on the particular multiple-AP transmission scheme employed.

[0244] Figure 17 An example 1700 of a multiple-AP uplink data transmission phase is shown. Multiple-AP uplink data transmission phase 1700 can be an example of multiple-AP data transmission phase 1516. As shown, example 1700 can include a master AP 1702 and a slave AP 1704 of a multiple-AP group. Example 1700 can also include STAs 1706 and 1708 associated with AP 1702 and STA 1710 associated with AP 1704. Figure 17 AP 1702 and AP 1704 can perform data transmissions to their associated STAs 1706 and 1708, respectively. Specifically, AP 1702 can transmit data frames 1712 to its associated STA 1706, and AP 1704 can transmit data frames 1714 to its associated STA 1708. Depending on the multiple-AP transmission scheme used, AP 1702 and AP 1704 can transmit frames 1712 and 1714 to STAs in different BSSs, respectively. For example, when the multiple-AP transmission scheme is JT / JR, AP 1702 can also transmit frames 1712 to STA 1708 associated with slave AP 1704, and AP 1704 can also transmit frames 1714 to STA 1708 associated with AP 1704. The resources used to transmit and receive frames 1712 and 1714 can depend on the particular multiple-AP transmission scheme employed.

[0245] As shown, example 1700 can include a master AP 1702 and a slave AP 1704 of a multiple-AP group. Example 1700 can also include STAs 1706 and 1708 associated with AP 1702 and STA 1710 associated with AP 1704. Figure 17As shown, the multi-AP uplink data transmission phase 1700 can include frame exchanges to enable the master AP 1702 to coordinate with the slave AP 1704 to perform a particular multi-AP transmission scheme with STAs 1706, 1708, and 1710. The multi-AP transmission scheme can include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the above schemes.

[0246] As shown, the master AP 1702 can begin the phase 1700 by sending a frame 1712 to the AP 1704. The frame 1712 can include information related to the AP 1704 (e.g., an identifier of the AP 1704), synchronization information, information related to a particular multi-AP transmission scheme to be used, and / or information related to RUs for the AP 1704 to use to acknowledge the frame 1712. The frame 1712 can include a control frame. For example, the frame 1712 can include a multi-AP trigger frame. Figure 17

[0247] The AP 1704 can receive the frame 1712 and can synchronize with the master AP 1702 using the synchronization information. Subsequently, the APs 1702 and 1704 can use trigger frames to request uplink data transmissions from their associated STAs 1706, 1708, and 1710. Specifically, the AP 1702 can send a trigger frame 1714 to its associated STAs 1706 and 1708, and the AP 1704 can send a trigger frame 1716 to its associated STA 1710. Depending on the multi-AP transmission scheme used, the APs 1702 and 1704 can also send the frames 1714 and 1716, respectively, to STAs in different BSSs. For example, when the multi-AP transmission scheme is JT / JR, the AP 1702 can also send the frame 1714 to the STA 1710 associated with the slave AP 1704, and the AP 1704 can also send the frame 1716 to the STAs 1706 and 1708 associated with the master AP 1702. The resources used to send and receive the frames 1714 and 1716 can depend on the particular multi-AP transmission scheme employed.

[0248] ​The STAs 1706 and 1708 can respond with frames 1714, and the STA 1710 can respond with frame 1716. For example, the STAs 1706 and 1708 can transmit frames 1718 and 1720, respectively, to the AP 1702, and the STA 1710 can transmit frame 1722 to the AP 1704. The frames 1718, 1720, and / or 1722 can be transmitted simultaneously. The frames 1718, 1720, and 1722 can comprise data frames or null data frames. The STAs 1706, 1708, and 1710 can also transmit the frames 1718, 1720, and 1722, respectively, to the APs in different BSSs as needed by the multi-AP transmission scheme used. For example, when the multi-AP transmission scheme is JT / JR, the STAs 1706 and 1708 can also transmit the respective frames 1718 and 1720 to the AP 1704, and the STA 1710 can also transmit frame 1722 to the AP 1702. The resources used to transmit and receive the frames 1718, 1720, and 1722 can depend on the particular multi-AP transmission scheme employed.

[0249] A non-simultaneous transmit and receive (NSTR) mobile AP MLD is a mobile AP MLD that has at least one NSTR link pair. An NSTR link pair is a pair of links that correspond to a STA affiliated with the MLD, where receiver requirements cannot be met on one of the links when the STA affiliated with the MLD is transmitting on the other link. Each link of such a pair is a member of an NSTR link pair. For example, if a MLD concurrently supports transmission on link 1 and reception on link 2, but cannot concurrently support transmission on link 2 and reception on link 1, then link 1 and link 2 are an NSTR link pair of the MLD.

[0250] A simultaneous transmit and receive (STR) link pair is a pair of links that is not an NSTR link pair. When a MLD operates on a pair of links, a STA affiliated with the MLD and operating on a first link of the STR link pair shall access the wireless medium on the first link by following the rules for EDCA, regardless of any activity occurring on the second link of the STR link pair, unless explicitly stated otherwise.

[0251] All link pairs of an AP MLD that is not a NSTR mobile AP MLD and that operates on more than one link shall be STR link pairs. If an AP MLD that is not a NSTR mobile AP MLD operates on only one link, then any STR requirements and capabilities corresponding to the link pair no longer apply.

[0252] An AP affiliated to an AP MLD that has obtained permission to initiate transmission of frames of an AC on a link through the rules for EDCA can choose not to transmit any frames corresponding to that AC due to expected interference caused by transmissions at STAs operating on the other link of the NSTR link pair within the non-AP MLD of the intended recipient and due to lack of availability of alternative frames in the queue that would not introduce such interference.

[0253] A non-AP STA affiliated to a non-AP MLD operating on a link of an NSTR link pair can choose not to send any frames corresponding to that AC that it has obtained permission to initiate transmission of frames of an AC on a link through the rules for EDCA backoff or enabled by the AP as TXOP holder to use a portion of the obtained TXOP through the rules for triggered TXOP sharing due to expected interference caused by transmissions at the non-AP STA operating on the other link of the NSTR link pair within the non-AP MLD and due to lack of availability of alternative frames in the queue that would not introduce such interference.

[0254] A non-AP STA affiliated to a non-AP MLD or NSTR mobile AP MLD operating on an NSTR link pair is considered to have lost medium synchronization when another STA affiliated to the same MLD and operating on the NSTR link pair transmits a PPDU unless both STAs end their transmissions at the same time.

[0255] Another STA (affiliated to the same MLD and operating on the NSTR link pair) that has lost medium synchronization due to a transmission by one STA as described above can start the MediumSyncDelay timer and, if the transmission is longer than the MediumSyncThreshold, count down from the end of the transmission unless its previous MediumSyncDelay timer has not yet expired. If the transmission event is shorter than or equal to the MediumSyncThreshold, the STA can choose not to (re)start the MediumSyncDelay timer. The MediumSyncThreshold is set to 72 μβ.

[0256] If a STA operating on an NSTR link pair has lost medium synchronization due to a transmission by another STA affiliated to the same MLD and operating on the NSTR link pair and its previous MediumSyncDelay timer has not yet expired at the end of the transmission, it will continue the previous MediumSyncDelay timer unless, if the transmission is longer than the MediumSyncThreshold, the STA should update the timer value as described above.

[0257] AP-assisted medium synchronization recovery is a service provided by an AP MLD to assist a non-AP STA that has lost medium synchronization, which is affiliated to a non-AP MLD, to transmit a frame without causing a collision with another transmission.

[0258] An AP, which is affiliated to an AP MLD with dot11AAROptionImplemented equal to true, shall set the AAR (AP-assisted request) support subfield in the MLD Capabilities and Operation subfield in the Basic Multilink Element it sends to 1; otherwise, the AP shall set the AAR support subfield to 0.

[0259] A non-AP STA, which is affiliated to a non-AP MLD with dot11AAROptionImplemented equal to true and belongs to an NSTR link pair, shall send the AAR control subfield in a frame if it has received a Basic Multilink Element from an AP with the AAR support subfield equal to 1 and the assisting STA belonging to the NSTR link pair needs assistance to transmit a frame to its associated AP on another link, it requests an immediate response to its associated AP affiliated to the AP MLD.

[0260] The AAR control subfield sent by a STA shall indicate by setting the corresponding bit to 1 that the link identifier of the other assisting AP affiliated to the same AP MLD operates on the enabled link.

[0261] Each of the other assisting AP(s) affiliated to the AP MLD shall schedule a trigger frame to the assisting non-AP STA associated with it and affiliated to the non-AP MLD to request an UL frame after it successfully receives the AAR control subfield in the frame without the AP affiliated to the same AP MLD having already scheduled a frame exchange with another non-AP STA.

[0262] A non-AP STA with dot11AAROptionImplemented equal to false shall not send a frame containing the AAR control subfield to its associated AP.

[0263] A non-AP STA shall not send a frame containing the AAR control subfield with a value of 1 in the bit identifying the link identifier of its associated AP.

[0264] An AP shall not transmit the AAR control subfield in a frame to its associated non-AP STA.

[0265] Figure 18The example format 1800 of the AAR control subfield of a data frame is shown. The AAR control subfield contains a control ID subfield and a control information subfield. The control ID subfield indicates the value 9 of the AAR. The control information subfield contains information about the link identifier of the auxiliary AP attached to the AP MLD, which is requested to assist a non-AP STA (belonging to a non-simultaneous transmit and receive (NSTR) link pair) attached to a non-AP MLD in restoring its media synchronization. The auxiliary AP link ID bitmap subfield in the AAR control subfield indicates the link associated with the link identifier of the auxiliary AP attached to the AP MLD.

[0266] Figure 19 Example 1900 of an existing AP-assisted media synchronization recovery process is shown. Figure 19 As shown, Example 1900 includes AP 1902 and STA 1904. AP 1902 may include an AP MLD, which includes attached AP STAs 1902-1, 1902-2, and 1902-3. STA 1904 may include a non-AP MLD, which includes attached non-AP STAs 1904-1, 1904-2, and 1904-3. In Example 1900, for STA 1904, Link 1 and Link 2 are NSTR link pairs, Link 1 and Link 3 are NSTR link pairs, and Link 2 and Link 3 are STR link pairs. In Example 1900, AP STA 1902-2 and AP STA 1902-3 are requested to assist the non-AP STAs 1904-2 and 1904-3, respectively, in transmitting frames after losing media synchronization.

[0267] like Figure 19 As shown, Example 1900 can begin with non-AP STA 1904-1 sending data frame 1910 to AP STA 1902-1. Since links 1 and 2, and links 1 and 3 are NSTR link pairs for STA 1904, non-AP STAs 1904-2 and 1904-3 lose media synchronization due to the transmission of data frame 1910. Non-AP STAs 1904-2 and 1904-3 each start a MediumSyncDelay timer when non-AP STA 1904-1 finishes transmitting data frame 1910. To enable transmission on link 2, non-AP STA 1904-2 needs to receive frames on link 2 while the MediumSyncDelay timer is running, allowing it to restore media synchronization on link 2. Similarly, to enable transmission on link 3, non-AP STA 1904-3 needs to receive frames on link 3 while the MediumSyncDelay timer is running, allowing it to restore media synchronization on link 3.

[0268] In one example, data frame 1910 can include an AP Assistance Request (AAR) requesting that AP STAs 1902-2 and 1902-3 provide medium synchronization recovery assistance to non-AP STAs 1904-2 and 1904-3, respectively. That is, data frame 1910 can request that AP STAs 1902-2 and 1902-3 assist non-AP STAs 1904-2 and 1904-3, respectively, in recovering medium synchronization that was lost due to the transmission of data frame 1910 (by transmitting respective frames to non-AP STAs 1904-2 and 1904-3 on links 2 and 3, respectively). In one implementation, the bits for link 2 and link 3 in the AAR control subfield corresponding to the AAR are set to 1.

[0269] After AP STA 1902-1 receives data frame 1910, AP STA 1902-2 and AP STA 1902-3 transmit trigger frame 1912-1 and trigger frame 1912-2 to non-AP STA 1904-2 and non-AP STA 1904-3, respectively, which request uplink frame transmissions from non-AP STA 1904-2 and non-AP STA 1904-3. Upon receiving trigger frame 1912-1 and trigger frame 1912-2, respectively, non-AP STA 1904-2 and non-AP STA 1904-3 recover medium synchronization and can subsequently transmit respective data frames 1914-1 and 1914-2 to AP STA 1902-2 and AP STA 1902-3, respectively. Because trigger frames 1912-1 and 1912-2 enable non-AP STA 1904-2 and non-AP STA 1904-3 to recover medium synchronization, non-AP STA 1904-2 and non-AP STA 1904-3 can transmit respective data frames 1914-1 and 1914-2 without having to wait for the MediumSyncDelay timer to expire.

[0270] Figure 20 Another example 2000 of the existing AP-assisted medium synchronization recovery procedure described in FIG. 16 is shown. As in FIG. 16, the example 2000 includes a data frame 2010, a trigger frame 2012-1, and a trigger frame 2012-2. Figure 19 Figure 20 ​As shown, example 2000 includes AP 2002 and STA 2004. AP 2002 can include an AP MLD that includes affiliated AP STAs 2002-1 and 1902-2. STA 2004 can include a non-AP MLD that includes affiliated non-AP STAs 2004-1 and 2004-2. In example 2000, for STA 2004, link 1 and link 2 are an NSTR link pair. In example 2000, AP STA 2002-2, which is requested to assist a non-AP STA 1904-2 that lost medium synchronization, transmits a frame.

[0271] As Figure 20 shown, example 2000 can begin with non-AP STA 2004-1 transmitting a data frame 2010 to AP STA 2002-1 via link 1. Since link 1 and link 2 are an NSTR link pair for STA 2004, non-AP STA 2004-2 loses medium synchronization due to the transmission of data frame 2010. Non-AP STA 2004-2 starts a MediumSyncDelay timer for link 2 at the end of the transmission of data frame 2010 by non-AP STA 2004-1 via link 1. In order to be able to transmit on link 2, non-AP STA 1204-2 needs to receive a frame on link 2 while the MediumSyncDelay timer is running, which allows it to recover medium synchronization on link 2.

[0272] In an example, data frame 2010 can include an AAR that requests AP STA 2002-2 to provide medium synchronization recovery assistance to non-AP STA 2004-2. That is, data frame 2010 can request AP STA 2002-2 to help non-AP STA 2004-2 recover medium synchronization that was lost due to the transmission of data frame 2010 (by transmitting a frame on link 2 to non-AP STA 2004-2). In an implementation, the bit corresponding to link 2 in the AAR control subfield of the AAR is set to 1.

[0273] In example 2000, AP 2002 suffers from OBSS interference on link 1 at the time of the transmission of data frame 2010. The OBSS interference can be hidden from STA 2004. Due to OBSS inference, AP 2002 can not be able to receive data frame 2010 via link 1.

[0274] In an example, the AP 2002 can not transmit a block acknowledgement (BA) in response to the data frame 2010. In an example, the AP 2002 can not transmit a frame (e.g., a trigger frame) to the STA 2004 via link 2 to assist the non-AP STA 2004-2 to recover medium synchronization on link 2. Thus, the non-AP STA 2004-2 can not be able to recover medium synchronization on link 2 while the MediumSyncDelay timer is running and can have to wait for the expiration of the MediumSyncDelay timer in order to transmit a frame to the AP STA 2002-2 via link 2. Thus, traffic for transmission at the non-AP STA 2004-2 can be delayed.

[0275] As described further below, embodiments of the present disclosure address the above-described problems with existing AP-assisted medium synchronization recovery procedures. In an embodiment, a first AP can receive a first frame sent by a STA to a second AP, the first frame including an AP assistance request (AAR) for the second AP. The first frame can be transmitted on a first link and the AAR can be for a second link. Based on the first AP not receiving an acknowledgement frame from the second AP to the STA in response to the first frame, the first AP can send a second frame to the second AP, the second frame informing the second AP of the AAR included in the first frame. Based on receiving the second frame from the first AP, the second AP can send a third frame to the STA, thereby allowing the STA to recover medium synchronization on the second link. In another embodiment, based on the first AP not receiving an acknowledgement frame from the second AP to the STA in response to the first frame, the first AP sends a second frame to the STA. The first frame allows the STA to recover medium synchronization on the second link.

[0276] Figure 21 An example 2100 of an AP-assisted medium synchronization recovery procedure is shown in accordance with an embodiment. The example 2100 is provided for purposes of illustration only and is not exhaustive. As Figure 21As shown, example 2100 includes AP 2102 and AP 2104 and STA 2106. AP 2102 and / or AP 2104 can comprise an AP MLD. STA 2106 can comprise a non-AP MLD. In an example, AP 2102 includes affiliated AP STA 2102-1 and affiliated AP STA 2102-2. In an example, AP 2104 includes affiliated AP STA 2104-1 and affiliated AP STA 2104-2. In an example, STA 2106 includes affiliated non-AP STA 2106-1 and affiliated non-AP STA 2106-2. In an example, AP STA 2102-1, AP STA 2104-1, and non-AP STA 2106-1 operate on a first link (link 1). In an example, non-AP STA 2106-1 is associated with AP STA 2102-1. In an example, AP STA 2102-2, AP STA 2104-2, and non-AP STA 2106-2 operate on a second link (link 2). In an example, non-AP STA 2106-2 is associated with AP STA 2102-2.

[0277] In an embodiment, link 1 and link 2 form an NSTR link pair at STA 2106.

[0278] In an embodiment, AP STA 2102-1 and AP STA 2104-1 belong to different basic service sets (BSSs). In another embodiment, AP STA 2102-2 and AP STA 2104-2 belong to different BSSs.

[0279] In an embodiment, AP 2104 sends, to AP 2102 via link 1 or link 2, a first indication of support by AP 2104 for inter-AP assisted medium synchronization recovery capability. In another embodiment, AP 2104 receives, from AP 2102 via link 1 or link 2, a second indication of support by AP 2102 for inter-AP assisted medium synchronization recovery capability.

[0280] In Example 2100, it is assumed that both AP 2102 and AP 2104 support inter-AP assisted media synchronization recovery capability. In one example, supporting inter-AP assisted media synchronization recovery capability allows AP 2104 to send or receive frames (such as frame 2114 described below). In another example, supporting inter-AP assisted media synchronization recovery capability allows AP 2104 to receive and process frames sent by STA 2106 associated with AP 2102 (such as frame 2112 described below). In yet another example, supporting inter-AP assisted media synchronization recovery capability allows AP 2104 to send frames (such as frame 2314 described below) to STA 2106 associated with AP 2102.

[0281] In one example, AP STA 2102-1 and AP STA 2104-1 form a multi-AP group. In another example, AP STA 2102-2 and AP STA 2104-2 form a multi-AP group.

[0282] like Figure 21 As shown, Example 2100 can begin with non-AP STA 2106-1 sending the first frame 2112 to AP STA 2102-1 via Link 1. Since Link 1 and Link 2 are an NSTR link pair for STA 2106, non-AP STA 2106-2 loses media synchronization due to the transmission of the first frame 2112. Non-AP STA 2106-2 starts the MediumSyncDelay timer when non-AP STA 2106-1 finishes transmitting the first frame 2112. In order to be able to transmit on Link 2, while the MediumSyncDelay timer is running, non-AP STA 2106-2 needs to receive frames on Link 2, which allows it to restore media synchronization on Link 2.

[0283] In one embodiment, the first frame 2112 includes an AAR for AP 2102 on link 2. That is, the first frame 2112 requests AP 2102 to provide STA 2106 with media synchronization recovery assistance for link 2. In an example, the first frame 2112 may include an AAR requesting AP STA 2102-2 to provide media synchronization recovery assistance to non-AP STA 2106-2. That is, the first frame 2112 may request AP STA 2102-2 to help non-AP STA 2106-2 recover media synchronization lost due to the transmission of the first frame 2112 (by sending frames to non-AP STA 2106-2 on link 2). In one implementation, the bit corresponding to link 2 in the AAR control subfield of the AAR is set to 1. In one embodiment, the first frame 2112 may include a data frame.

[0284] In example 2100, AP 2102 suffers from OBSS interference on link 1 while STA 2106 transmits first frame 2112. The OBSS interference can be hidden from STA 2106. Due to the OBSS interference, AP 2102 can not be able to receive first frame 2112 via link 1. In an embodiment, AP 2104 receives first frame 2112 via link 1.

[0285] In an example, AP 2102 can not transmit a BA in response to first frame 2112. In an example, AP 2102 can not transmit a frame (e.g., a trigger frame) to STA 2106 via link 2 to assist non-AP STA 2106-2 to recover medium synchronization on link 2.

[0286] In an embodiment, based on AP 2104 not receiving an acknowledgement frame (e.g., a BA frame) from AP 2102 to STA 2106 in response to frame 2112 (not hearing an acknowledgement frame (e.g., a BA frame) from AP 2102 to STA 2106 in response to frame 2112), AP 2104 transmits second frame 2114 to AP 2102, which informs AP 2102 of the AAR included in first frame 2112. In an embodiment, transmitting second frame 2114 includes transmitting frame 2114 via link 1 or link 2. In example 2100, frame 2114 is transmitted via link 2, as shown. Figure 21

[0287] In an embodiment, second frame 2114 includes an indication of link 2. In another embodiment, second frame 2114 includes an indication of STA 2106. Second frame 2114 can be a management frame. For example, frame 2114 can be an activity frame. Second frame 2114 can be a control frame. For example, frame 2114 can be a trigger frame. Second frame 2114 can be a data frame. For example, frame 2114 can be a QoS null frame.

[0288] In an embodiment, AP 2102 transmits third frame 2116 to STA 2106 via link 2 in response to receiving second frame 2114. Third frame 2116 allows STA 2106 to recover medium synchronization on link 2, and STA 2106 can not need to wait for expiration of MediumSyncDelay timer before it can transmit a frame via link 2. Third frame 2116 can be a control frame or a management frame. In an example, third frame 2116 can be a trigger frame that requests STA 2106 to transmit fourth frame 2118 via link 2.

[0289] Figure 22 ​Another example 2200 of an AP-assisted medium synchronization recovery procedure is shown in accordance with an embodiment. The example 2200 is provided for purposes of illustration only and is not limiting. Figure 22 As shown, the example 2200 includes an AP 2202 and an AP 2204 and a STA 2206. The AP 2202 and / or the AP 2204 can include an AP MLD. The STA 2206 can include a non-AP MLD. In an example, the AP 2202 includes an affiliated AP STA 2202-1 and an affiliated AP STA 2202-2. In an example, the AP 2204 includes an affiliated AP STA 2204-1 and an affiliated AP STA 2204-2. In an example, the STA 2206 includes an affiliated non-AP STA 2206-1 and an affiliated non-AP STA 2206-2. In an example, the AP STA 2202-1, the AP STA 2204-1, and the non-AP STA 2206-1 operate on a first link (Link 1). In an example, the non-AP STA 2206-1 is associated with the AP STA 2202-1. In an example, the AP STA 2202-2, the AP STA 2204-2, and the non-AP STA 2206-2 operate on a second link (Link 2). In an example, the non-AP STA 2206-2 is associated with the AP STA 2202-2.

[0290] In an embodiment, the Link 1 and the Link 2 form an NSTR link pair at the STA 2206.

[0291] In an embodiment, the AP STA 2202-1 and the AP STA 2204-1 belong to different basic service sets (BSSs). In another embodiment, the AP STA 2202-2 and the AP STA 2204-2 belong to different BSSs.

[0292] In an embodiment, the AP 2204 sends, to the AP 2202 via the Link 1 or the Link 2, a first indication of support of inter-AP assisted medium synchronization recovery capability by the AP 2204. In another embodiment, the AP 2204 receives, from the AP 2202 via the Link 1 or the Link 2, a second indication of support of inter-AP assisted medium synchronization recovery capability by the AP 2202. It is assumed in the example 2200 that both the AP 2202 and the AP 2204 support the inter-AP assisted medium synchronization recovery capability.

[0293] In Example 2200, it is assumed that both AP 2202 and AP 2204 support inter-AP assisted media synchronization recovery capability. In one example, supporting inter-AP assisted media synchronization recovery capability allows AP 2204 to send or receive frames (such as frame 2214 described below). In another example, supporting inter-AP assisted media synchronization recovery capability allows AP 2204 to receive and process frames sent by STA 2206 associated with AP 2202 (such as frame 2212 described below). In yet another example, supporting inter-AP assisted media synchronization recovery capability allows AP 2204 to send frames to STA 2206 associated with AP 2202 (such as frame 2314 described below).

[0294] In one example, AP STA 2202-1 and AP STA 2204-1 form a multi-AP group. In another example, AP STA 2202-2 and AP STA 2204-2 form a multi-AP group.

[0295] like Figure 22 As shown, Example 2200 can begin with non-AP STA 2206-1 sending the first frame 2212 to AP STA 2202-1 via Link 1. Since Links 1 and 2 are an NSTR link pair for STA 2206, non-AP STA 2206-2 loses media synchronization due to the transmission of the first frame 2212. Non-AP STA 2206-2 starts the MediumSyncDelay timer when non-AP STA 2206-1 finishes transmitting the first frame 2212. In order to be able to transmit on Link 2, while the MediumSyncDelay timer is running, non-AP STA 2206-2 needs to receive frames on Link 2, which allows it to restore media synchronization on Link 2.

[0296] In one embodiment, the first frame 2212 includes an AAR for AP 2202 on link 2. That is, the first frame 2212 requests AP 2202 to provide STA 2206 with media synchronization recovery assistance for link 2. In an example, the first frame 2212 may include an AAR requesting AP STA 2202-2 to provide media synchronization recovery assistance to non-AP STA 2206-2. In other words, the first frame 2212 may request AP STA 2202-2 to help non-AP STA 2206-2 recover media synchronization lost due to the transmission of the first frame 2212 (by sending frames to non-AP STA 2206-2 on link 2). In one implementation, the bit corresponding to link 2 in the AAR control subfield of the AAR is set to 1. In one embodiment, the first frame 2212 may include a data frame.

[0297] In example 2200, AP 2202 suffers from OBSS interference on link 1 while STA 2206 transmits first frame 2212. The OBSS interference can be hidden from STA 2206. Due to the OBSS interference, AP 2202 can not be able to receive first frame 2212 via link 1. In an embodiment, AP 2204 receives first frame 2212 via link 1.

[0298] In an embodiment, AP 2202 can not transmit a BA in response to first frame 2212. In an embodiment, AP 2202 can not transmit a frame (e.g., a trigger frame) to STA 2206 via link 2 to assist non-AP STA 2206-2 to recover medium synchronization on link 2.

[0299] In an embodiment, based on AP 2204 not receiving an acknowledgement frame (e.g., a BA frame) from AP 2202 to STA 2206 in response to frame 2212 (not hearing an acknowledgement frame (e.g., a BA frame) from AP 2202 to STA 2206 in response to frame 2212), AP 2204 transmits second frame 2214 to AP 2202, second frame 2214 informing AP 2202 of the AAR included in first frame 2212. In an embodiment, transmitting second frame 2214 includes transmitting frame 2214 via link 1 or link 2. In example 2200, frame 2214 is transmitted via link 1, as shown. Transmitting frame 2214 via link 1 can provide diversity between multiple links to improve reliability of the transmission. Figure 22

[0300] In an embodiment, second frame 2214 includes an indication of link 2. In another embodiment, second frame 2214 includes an indication of STA 2206. Second frame 2214 can be a management frame. For example, frame 2214 can be an activity frame. Second frame 2214 can be a control frame. For example, frame 2214 can be a trigger frame. Second frame 2214 can be a data frame. For example, frame 2214 can be a QoS null frame.

[0301] In an embodiment, AP 2202 transmits third frame 2216 to STA 2206 via link 2 in response to receiving second frame 2214. Third frame 2216 allows STA 2206 to recover medium synchronization on link 2 and STA 2206 can not need to wait for expiration of MediumSyncDelay timer before it can transmit a frame via link 2. Third frame 2216 can be a control frame or a management frame. In an example, third frame 2216 can be a trigger frame requesting STA 2206 to transmit fourth frame 2218 via link 2.

[0302] Figure 23 ​Another example 2300 of an AP-assisted medium synchronization recovery procedure is shown in accordance with an embodiment. The example 2300 is provided for purposes of illustration only and is not limiting. Figure 23 As shown, the example 2300 includes an AP 2302 and an AP 2304 and a STA 2306. The AP 2302 and / or the AP 2304 can include an AP MLD. The STA 2306 can include a non-AP MLD. In an example, the AP 2302 includes an affiliated AP STA 2302-1 and an affiliated AP STA 2302-2. In an example, the AP 2304 includes an affiliated AP STA 2304-1 and an affiliated AP STA 2304-2. In an example, the STA 2306 includes an affiliated non-AP STA 2306-1 and an affiliated non-AP STA 2306-2. In an example, the AP STA 2302-1, the AP STA 2304-1, and the non-AP STA 2306-1 operate on a first link (Link 1). In an example, the non-AP STA 2306-1 is associated with the AP STA 2302-1. In an example, the AP STA 2302-2, the AP STA 2304-2, and the non-AP STA 2306-2 operate on a second link (Link 2). In an example, the non-AP STA 2306-2 is associated with the AP STA 2302-2.

[0303] In an embodiment, the Link 1 and the Link 2 form an NSTR link pair at the STA 2306.

[0304] In an embodiment, the AP STAs 2302-1 and 2304-1 belong to different basic service sets (BSSs). In another embodiment, the AP STAs 2302-2 and 2304-2 belong to different BSSs.

[0305] In an embodiment, the AP 2304 sends, to the AP 2302 via the Link 1 or the Link 2, a first indication of support of inter-AP assisted medium synchronization recovery capability by the AP 2304. In another embodiment, the AP 2304 receives, from the AP 2302 via the Link 1 or the Link 2, a second indication of support of inter-AP assisted medium synchronization recovery capability by the AP 2302. It is assumed in the example 2300 that both the AP 2302 and the AP 2304 support the inter-AP assisted medium synchronization recovery capability.

[0306] In Example 2300, it is assumed that both AP 2302 and AP 2304 support inter-AP assisted media synchronization recovery capability. In one example, supporting inter-AP assisted media synchronization recovery capability allows AP 2304 to send or receive frames (such as frame 2314 described below). In another example, supporting inter-AP assisted media synchronization recovery capability allows AP 2304 to receive and process frames sent by STA 2306 associated with AP 2302 (such as frame 2312 described below). In yet another example, supporting inter-AP assisted media synchronization recovery capability allows AP 2304 to send frames (such as frame 2314 described below) to STA 2306 associated with AP 2302.

[0307] In one example, AP STA 2302-1 and AP STA 2304-1 form a multi-AP group. In another example, AP STA 2302-2 and AP STA 2304-2 form a multi-AP group.

[0308] like Figure 23 As shown, Example 2300 can begin with non-AP STA 2306-1 sending the first frame 2312 to AP STA 2302-1 via Link 1. Since Link 1 and Link 2 are an NSTR link pair for STA 2306, non-AP STA 2306-2 loses media synchronization due to the transmission of the first frame 2312. Non-AP STA 2306-2 starts the MediumSyncDelay timer when non-AP STA 2306-1 finishes transmitting the first frame 2312. In order to be able to transmit on Link 2, while the MediumSyncDelay timer is running, non-AP STA 2306-2 needs to receive frames on Link 2, which allows it to restore media synchronization on Link 2.

[0309] In one embodiment, the first frame 2312 includes an AAR for AP 2302 on link 2. That is, the first frame 2312 requests AP 2302 to provide STA 2306 with media synchronization recovery assistance for link 2. In an example, the first frame 2312 may include an AAR requesting AP STA 2302-2 to provide media synchronization recovery assistance to non-AP STA 2306-2. In other words, the first frame 2312 may request AP STA 2302-2 to help non-AP STA 2306-2 recover media synchronization lost due to the transmission of the first frame 2312 (by sending frames to non-AP STA 2306-2 on link 2). In one implementation, the bit corresponding to link 2 in the AAR control subfield of the AAR is set to 1. In one embodiment, the first frame 2312 may include a data frame.

[0310] In example 2300, AP 2302 suffers from OBSS interference on link 1 when STA 2306 transmits first frame 2312. The OBSS interference can be hidden from STA 2306. Due to the OBSS interference, AP 2302 can not be able to receive first frame 2312 via link 1. In an embodiment, AP 2304 receives first frame 2212 via link 1.

[0311] In an example, AP 2302 can not transmit a BA in response to first frame 2312. In an example, AP 2302 can not transmit a frame (e.g., a trigger frame) to STA 2306 via link 2 to assist non-AP STA 2306-2 to recover medium synchronization on link 2.

[0312] In an embodiment, based on AP 2304 not receiving an acknowledgement frame (e.g., a BA frame) from AP 2302 to STA 2306 in response to frame 2312 (not hearing an acknowledgement frame (e.g., a BA frame) from AP 2302 to STA 2306 in response to frame 2312), AP 2104 transmits second frame 2314 to STA 2306. In an embodiment, transmitting second frame 2314 includes transmitting frame 2314 via link 2.

[0313] In an embodiment, second frame 2314 allows STA 2306 to recover medium synchronization on link 2 and STA 2306 can not need to wait for expiration of a MediumSyncDelay timer before it can transmit a frame via link 2. In an embodiment, second frame 2314 includes an indication to STA 2306. Second frame 2314 can be a management frame. For example, frame 2314 can be an activity frame. Second frame 2314 can be a control frame. For example, frame 2314 can be a trigger frame. In an embodiment, second frame 2314 informs STA 2306 to transmit fourth frame 2316 to AP 2302 via link 2.

[0314] In an embodiment, Figure 21 frame 2114 described in example 2100, Figure 22 frame 2214 described in example 2200, and Figure 23 frame 2314 described in example 2300 can be a management frame, such as an activity frame.

[0315] Figure 24An example activity frame 2400 that can be used in accordance with embodiments is shown. For example, the activity frame 2400 can be an embodiment of the frames 2114, 2214, and / or 2314. In an example, the activity frame 2400 can be a public activity frame. In an embodiment, the activity frame 2400 can include information indicating inter-AP assistance for medium synchronization recovery. In an embodiment, the information indicating inter-AP assistance for medium synchronization recovery includes an indication of a link for which medium synchronization recovery is requested and an indication of a requesting STA.

[0316] As shown, Figure 24 The activity frame 2400 can include an activity field 2402. In an embodiment, the activity field 2402 can include a category subfield 2410 indicating inter-AP assistance. In an example, the activity field 2402 can include an activity details field 2412. In an embodiment, the activity details field 2412 can include information indicating inter-AP assistance for medium synchronization recovery. In an example, the activity details field 2412 can include an optional subfield 2414 for an indication of a link for which medium synchronization recovery is requested and an optional subfield 2416 for an indication of a requesting STA. For example, the indication of a link can be a link identifier (ID). For example, the indication of a requesting STA can be a non-AP MLD association identifier (AID). In an example, the subfields 2414 and 2416 are present when the activity frame 2400 is sent by one AP to another AP. In another example, the subfields 2414 and 2416 can include reserved bits when the activity frame 2400 is sent by an AP to a non-associated STA.

[0317] In an embodiment, Figure 21 The frame 2114 described in Figure 22 The frame 2214 described in can be a data frame, such as a QoS null frame.

[0318] Figure 25 An example QoS null frame 2500 that can be used in accordance with embodiments is shown. For example, the QoS null frame 2500 can be an embodiment of the frames 2114 and 2214. In an embodiment, the QoS null frame 2500 can include information indicating inter-AP assistance for medium synchronization recovery. In an embodiment, the information indicating inter-AP assistance for medium synchronization recovery includes an indication of a link for which medium synchronization recovery is requested and an indication of a requesting STA.

[0319] As shown, Figure 25As shown, the QoS null frame 2500 can include an HT Control field 2502. In an embodiment, the HT Control field 2502 can include information indicating inter-AP assistance for medium synchronization recovery. In an embodiment, the information indicating inter-AP assistance for medium synchronization recovery includes an indication of a link for which medium synchronization recovery is requested and an indication of a requesting STA. In an example, the HT Control field 2502 can include an A Control subfield. The A Control subfield can include a control list subfield 2510, which includes one or more control subfields. In an embodiment, a control subfield can include information indicating inter-AP assistance for medium synchronization recovery. For example, the control subfield can be an inter-AP assistance A control subfield. In an example, the control subfield includes a control ID subfield 2520 for inter-AP assistance and a control information subfield 2522. The control information subfield 2522 can include a subfield 2524 for indicating a link for which medium synchronization recovery is requested and a subfield 2526 for indicating a requesting STA.

[0320] In an embodiment, Figure 21 the frame 2114 described in Figure 22 the frame 2214 described in Figure 23 and the frame 2314 described in

[0321] Figure 26 An example trigger frame 2600 that can be used in accordance with embodiments is shown. For example, the trigger frame 2600 can be an embodiment of the frame 2114 or 2214. In an embodiment, the trigger frame 2600 can include information indicating inter-AP assistance for medium synchronization recovery. In an embodiment, the information indicating inter-AP assistance for medium synchronization recovery includes an indication of a receiving AP, an indication of a link for which medium synchronization recovery is requested, and an indication of a requesting STA.

[0322] As Figure 26 shown, the trigger frame 2600 can include a common info field 2602 and a user info list field 2604.

[0323] In an embodiment, the trigger frame 2600 can be used by a first AP to inform a second AP of an inter-AP assistance request. In an embodiment, the user info list field 2604 of the trigger frame 2600 can include information indicating inter-AP assistance for medium synchronization recovery. In an example, the user info list field 2604 can include a field 2610. For example, the field 2610 can be an inter-AP assistance information field.

[0324] In an embodiment, as Figure 26As shown, the public information field 2602 can include a field flag field 2606 that indicates the presence of a field 2610 used in the user info list field 2604. In an embodiment, the public information field 2602 can include information that indicates inter-AP assistance. The format of the subfield carrying the information in the public information field 2602 can be similar to the field 2610 in the user info list field 2604.

[0325] In an embodiment, the field 2610 can include a subfield 2612 for indicating a second AP, a subfield 2614 for an indication of a link for which medium synchronization recovery is requested, and a subfield 2616 for an indication of a requesting STA. For example, the indication of the second AP can be an association identifier (AID) of the second AP. For example, the indication of the link can be a link identifier (ID). For example, the indication of the requesting STA can be an AID of the requesting STA.

[0326] Figure 27 Another example trigger frame 2700 that can be used in accordance with an embodiment is shown. For example, the trigger frame 2700 can be an embodiment of the frame 2314. In an embodiment, the trigger frame 2700 can be used by a first AP to provide medium synchronization recovery to a STA. The STA can be a STA that is not associated with the first AP. In an embodiment, the trigger frame 2700 can include information that indicates inter-AP assistance for medium synchronization recovery. In an embodiment, the information that indicates inter-AP assistance for medium synchronization recovery includes an indication of a recipient of a fourth frame from the STA. The fourth frame can be an immediate uplink transmission in response to the trigger frame 2700. The recipient can be a second AP that is associated with the STA.

[0327] As Figure 27 shown, the trigger frame 2700 can include a public information field 2702 and a user info list field 2704. The user info list field 2704 can include one or more user information fields 2710.

[0328] In an embodiment, the trigger frame 2700 can be used to trigger the STA to send the fourth frame. In an embodiment, the user info list field 2704 of the trigger frame 2700 can include information that indicates inter-AP assistance for medium synchronization recovery. In an example, the user information field 2710 can include a subfield 2712 that indicates a recipient of the fourth frame from the STA. For example, the subfield 2712 can be a flag value. In an implementation, the subfield 2712 can be set to 0 to indicate the transmitter of the trigger frame 2700 as the recipient of the fourth frame and can be set to 1 to indicate a second AP as the recipient of the fourth frame.

[0329] In an embodiment, as Figure 27As shown, the public information field 2702 can include a field flag field 2706 that indicates the presence of a field 2710 used in the user information list field 2702. In an embodiment, the public information field 2702 can include information that indicates inter-AP assistance.

[0330] As will be appreciated by those skilled in the art based on the teachings herein, embodiments described by the above examples can be readily extended to include more than two APs.

[0331] Figure 28 An example process 2800 according to an embodiment is shown. The example process 2800 is provided for purposes of illustration only and is not limiting of the embodiments. Process 2800 can be performed by a first AP.

[0332] As Figure 28 As shown, process 2800 begins at step 2802, which includes receiving, by a first AP, a first frame sent by a STA to a second AP, the first frame including an AP Assistance Request (AAR) for the second AP. In an embodiment, the STA is associated with the second AP but is not associated with the first AP.

[0333] In an embodiment, receiving the first frame includes receiving the first frame via a first link. In an embodiment, the AAR requests the second AP to send a third frame to the STA via a second link. In an embodiment, the first link and the second link form an NSTR link pair at the STA. In an example, the first link can include one of a 2.4 GHz frequency band, a 5 GHz frequency band, a 6 GHz frequency band, or a future to be defined frequency band. Similarly, the second link can include one of a 2.4 GHz frequency band, a 5 GHz frequency band, a 6 GHz frequency band, or a future to be defined frequency band, where the second link is different than the first link.

[0334] At step 2804, process 2800 includes sending, by the first AP to the second AP, a second frame based on the first AP receiving an acknowledgement frame from the second AP to the STA without responding to the first frame, the second frame informing the second AP of the AAR included in the first frame.

[0335] In an embodiment, sending the second frame includes sending the second frame via the first link or the second link. In an embodiment, the second frame assists the STA to recover medium synchronization on the second link. In an embodiment, the second frame includes an indication of the second link. In an embodiment, the second frame includes an indication of the STA. In an embodiment, the second AP sends the third frame to the STA via the second link in response to the second frame.

[0336] In one embodiment, the second frame includes a management frame. In another embodiment, the management frame includes an activity frame that includes an activity field indicating the activity of the second link and the STA.

[0337] In one embodiment, the second frame includes a control frame. In another embodiment, the control frame includes a trigger frame that includes a user information list field indicating the second link and the STA.

[0338] In one embodiment, the second frame includes a data frame. In another embodiment, the data frame includes a QoS empty frame that includes a high throughput (HT) control field indicating the second link and the STA.

[0339] In one embodiment, the first AP sends a first indication to the second AP of its support for inter-AP assisted media synchronization recovery capabilities. In another embodiment, the first AP receives a second indication from the second AP of its support for inter-AP assisted media synchronization recovery capabilities.

[0340] In one embodiment, the first AP and the second AP form a multi-AP group.

[0341] In one embodiment, the first AP, the second AP, or the STA includes a multi-link device (MLD).

[0342] Figure 29 An example process 2900 according to an embodiment is shown. The example process 2900 is provided for illustrative purposes only and is not intended to limit the embodiments. Process 2900 can be performed by a first AP.

[0343] like Figure 29 As shown, process 2900 begins at step 2902, which includes the first AP receiving a first frame from the second AP, the first frame informing the first AP of an AP Assist Request (AAR) sent by the STA for the first AP. The STA may be associated with the first AP but not with the second AP.

[0344] In one embodiment, receiving the first frame includes receiving the first frame via a first link or a second link. In one embodiment, the first frame notifies the first AP of an AAR operating on the second link. In one embodiment, the first link and the second link form an NSTR link pair at the STA. In one example, the first link may include one of the 2.4 GHz band, 5 GHz band, 6 GHz band, or a band to be defined in the future. Similarly, the second link may include one of the 2.4 GHz band, 5 GHz band, 6 GHz band, or a band to be defined in the future, wherein the second link is different from the first link.

[0345] In one embodiment, the AAR requests the first AP to send a second frame to the STA via the second link. In one embodiment, the first frame assists the STA in restoring media synchronization on the second link. In one embodiment, the first frame includes an indication of the second link. In one embodiment, the first frame includes an indication of the STA.

[0346] In one embodiment, the first frame includes a management frame. In another embodiment, the management frame includes an activity frame that includes an activity field indicating the activity of the second link and the STA.

[0347] In one embodiment, the first frame includes a control frame. In another embodiment, the control frame includes a trigger frame that includes a user information list field indicating the second link and the STA.

[0348] In one embodiment, the first frame includes a data frame. In another embodiment, the data frame includes a QoS empty frame, which includes a high throughput (HT) control field indicating the second link and the STA.

[0349] In step 2904, process 2900 includes: based on the receipt of the first frame, the first AP sends a second frame to the STA.

[0350] In one embodiment, sending the second frame includes sending the second frame via a second link. In one embodiment, in response to the first frame, the first AP sends the second frame to the STA via the second link.

[0351] In one embodiment, the first AP sends a first indication to the second AP of its support for inter-AP assisted media synchronization recovery capabilities. In another embodiment, the first AP receives a second indication from the second AP of its support for inter-AP assisted media synchronization recovery capabilities.

[0352] In one embodiment, the first AP and the second AP form a multi-AP group.

[0353] In one embodiment, the first AP, the second AP, or the STA includes a multi-link device (MLD).

[0354] Figure 30 An example process 3000 according to an embodiment is illustrated. The example process 3000 is provided for illustrative purposes only and is not intended to limit the embodiments. Process 3000 may be executed by a first AP.

[0355] like Figure 30 As shown, process 3000 begins at step 3002, which includes the first AP receiving a first frame sent by the STA to the second AP, the first frame including an AP Assist Request (AAR) for the second AP. The STA may be associated with the second AP but not with the first AP.

[0356] In an embodiment, receiving the first frame comprises receiving the first frame via a first link. In an embodiment, the AAR requests the second AP to transmit a third frame to the STA via a second link. In an embodiment, the first link and the second link form a pair of NSTR links at the STA. In an example, the first link can comprise one of a 2.4 GHz band, a 5 GHz band, a 6 GHz band, or a future to be defined band. Similarly, the second link can comprise one of a 2.4 GHz band, a 5 GHz band, a 6 GHz band, or a future to be defined band, wherein the second link is different from the first link.

[0357] In step 3004, the process 3000 includes transmitting, by the first AP, a second frame to the second AP based on the first AP receiving an acknowledgement frame from the second AP to the STA not responding to the first frame.

[0358] In an embodiment, transmitting the second frame comprises transmitting the second frame via the second link. In an embodiment, the second frame assists the STA to recover medium synchronization on the second link. In an embodiment, the second frame comprises an indication to the STA. In an embodiment, the second frame informs the STA to transmit a fourth frame to the second AP via the second link.

[0359] In an embodiment, the second frame comprises a management frame. In an embodiment, the management frame comprises an active frame comprising an active field indicating the STA.

[0360] In an embodiment, the second frame comprises a control frame. In an embodiment, the control frame comprises a trigger frame comprising a user info list field indicating the STA.

[0361] In an embodiment, the first AP transmits a first indication to the second AP of support by the first AP for inter-AP assisted medium synchronization recovery. In another embodiment, the first AP receives a second indication from the second AP of support by the second AP for inter-AP assisted medium synchronization recovery.

[0362] In an embodiment, the first AP and the second AP form a multi-AP group.

[0363] In an embodiment, the first AP, the second AP, or the STA comprises a multi-link device (MLD).

[0364] Figure 31 An example process 3100 according to an embodiment is shown. The example process 3100 is provided for purposes of illustration only and is not limiting of embodiments. Process 3100 can be performed by a STA.

[0365] As Figure 31As shown, the process 3100 begins at step 3102, which includes sending, by a STA to a first AP, a first frame including an AP Assistance Request (AAR) for the first AP. The STA can be associated with the first AP.

[0366] In an embodiment, sending the first frame includes sending the first frame via a first link. In an embodiment, the AAR requests the first AP to send a third frame to the STA via a second link. In an embodiment, the first link and the second link form an NSTR link pair at the STA. In an example, the first link can include one of a 2.4 GHz band, a 5 GHz band, a 6 GHz band, or a future to be defined band. Similarly, the second link can include one of a 2.4 GHz band, a 5 GHz band, a 6 GHz band, or a future to be defined band, where the second link is different from the first link.

[0367] At step 3104, the process 3100 includes receiving, by the STA from a second AP, a second frame in response to the first frame. The second STA can not be associated with the second AP.

[0368] In an embodiment, receiving the second frame includes sending the second frame via the second link. In an embodiment, the second frame assists the STA to recover medium synchronization on the second link. In an embodiment, the second frame includes an indication to the STA. In an embodiment, the second frame informs the STA to send a fourth frame to the first AP via the second link.

[0369] In an embodiment, the second frame includes a management frame. In an embodiment, the management frame includes an active frame including an active field indicating the STA.

[0370] In an embodiment, the second frame includes a control frame. In an embodiment, the control frame includes a trigger frame including a user info list field indicating the STA.

[0371] In an embodiment, the first AP sends a first indication to the second AP of support by the first AP for inter-AP assisted medium synchronization recovery. In another embodiment, the first AP receives a second indication from the second AP of support by the second AP for inter-AP assisted medium synchronization recovery.

[0372] In an embodiment, the first AP and the second AP form a multi-AP group.

[0373] In an embodiment, the first AP, the second AP, or the STA includes a multi-link device (MLD).

[0374] As will be appreciated by those skilled in the art based on the teachings herein, embodiments of the present disclosure are not limited to the first AP informing the second AP of the second AP’s AAR sent by a STA associated with the second AP. Indeed, as described below in Figure 32

[0375] Figure 32 An example process 3200 according to an embodiment is shown. The example process 3200 is provided for purposes of illustration only and is not limiting of embodiments. Process 3200 can be performed by a first AP.

[0376] As shown in Figure 32 Process 3200 begins, at step 3202, which includes receiving, by a first AP, a first frame sent by a STA to a second AP. The STA can be associated with the second AP but not associated with the first AP.

[0377] In an embodiment, receiving the first frame includes receiving the first frame via a first link.

[0378] At step 3204, process 3200 includes sending, by the first AP to the second AP, a third frame based on the first AP not receiving a second frame from the second AP to the STA in response to the first frame, the third frame informing the second AP of the first frame.

[0379] In an embodiment, sending the third frame includes sending the third frame via the first link or a second link. In an embodiment, the first link and the second link form an NSTR link pair at the STA. In an example, the first link can include one of a 2.4 GHz frequency band, a 5 GHz frequency band, a 6 GHz frequency band, or a frequency band to be defined in the future. Similarly, the second link can include one of a 2.4 GHz frequency band, a 5 GHz frequency band, a 6 GHz frequency band, or a frequency band to be defined in the future, where the second link is different than the first link.

[0380] In an embodiment, the third frame includes an indication of the second link. In an embodiment, the third frame includes an indication of the STA. In an embodiment, the second AP sends a fourth frame to the STA via the second link in response to the third frame.

[0381] In an embodiment, the third frame includes a management frame. In an embodiment, the management frame includes an activity frame including an activity field indicating the second link and the STA.

[0382] In an embodiment, the third frame includes a control frame. In an embodiment, the control frame includes a trigger frame including a user info list field indicating the second link and the STA.​

[0383] In an embodiment, the third frame comprises a data frame. In an embodiment, the data frame comprises a QoS null frame comprising a high throughput (HT) control field indicating the second link and the STA.

[0384] In an embodiment, the first AP and the second AP form a multi-AP group.

[0385] In an embodiment, the first AP, the second AP, or the STA comprises a multi-link device (MLD).

[0386] In an embodiment, the first frame comprises a request frame, the request frame comprising an association request frame, a re-association request frame, a target wake time (TWT) setup request frame, a probe request frame, a request to send (RTS) frame, a block ack (BA) request frame, a data frame, or the like.

[0387] In an embodiment, the second frame comprises a response frame, the response frame comprising an association response frame, a re-association response frame, a TWT setup response frame, a probe response frame, a clear to send (CTS) frame, a BA frame, or the like.

[0388] Thus, there is a method comprising: receiving, by a first access point (AP), a first frame transmitted by a station (STA) to a second AP, the first frame comprising a request for the second AP; and transmitting, by the first AP, a second frame to the second AP based on the first AP not receiving an acknowledgement frame from the second AP to the STA in response to the first frame.

[0389] In the method, the request can be an AP assisted request (AAR).

[0390] In the method, the request can be for a second link.

[0391] In the method, the second frame can be arranged to inform the second AP of the request comprised in the first frame.

[0392] In the method, receiving the first frame can comprise receiving the first frame via a first link.

[0393] In the method, transmitting the second frame can comprise transmitting the second frame via the first link or a second link.

[0394] In the method, the AAR can request the second AP to transmit a third frame to the STA via the second link.

[0395] In the method, the second frame can assist the STA to recover medium synchronization on the second link.

[0396] In the method, the second frame can comprise an indication of the second link.

[0397] In the method, the second frame can include an indication to the STA.

[0398] In the method, the second AP can transmit, in response to the second frame, a third frame to the STA via the second link.

[0399] In the method, the second frame can include a management frame.

[0400] In the method, the second frame can include a control frame.

[0401] In the method, the second frame can include a data frame.

[0402] There is a method comprising: receiving, by a first access point (AP), a first frame from a second AP, the first frame informing the first AP of a request by a station (STA) to the first AP; and transmitting, by the first AP to the STA based on receiving the first frame, a second frame.

[0403] In the method, the first frame can inform the first AP of an AAR operating on a second link.

[0404] In the method, the first AP can transmit, in response to the first frame, the second frame to the STA via the second link.

[0405] There is a method comprising: transmitting, by a station (STA), a first frame including a request to a first AP to a first AP; and receiving, by the STA from a second AP, a second frame in response to the first frame.

[0406] In the method, transmitting the first frame can include transmitting the first frame via a first link.

[0407] In the method, receiving the second frame can include receiving the second frame via a second link.

[0408] In the method, the second frame can inform the STA to transmit a fourth frame to the first AP via the second link.

[0409] There is a method comprising: receiving, by a first access point (AP), a first frame transmitted by a station (STA) to a second AP based on the first AP not receiving a second frame from the second AP to the STA in response to the first frame; transmitting, by the first AP to the second AP, a second frame informing the second AP of the first frame.

[0410] In the method, the first frame can include at least one of a request frame including an association request frame, a re-association request frame, a TWT request frame, a probe request frame, an RTS frame, a block ack request frame, or a data frame.

[0411] In the method, the second frame can include a response frame, the response frame including at least one of an association response frame, a re-association response frame, a TWT response frame, a probe response frame, a CTS frame, or a BA frame.

[0412] In the method, the first AP and the second AP can form a multi-AP group.

[0413] In the method, the first AP, the second AP, or the STA can include a multi-link device (MLD).

[0414] In the method, the first link and the second link can form a non-simultaneous transmit and receive (NSTR) link pair at the STA.

[0415] In the method, the management frame can include an active frame, the active frame including an active field indicating the second link and the STA.

[0416] In the method, the control frame can include a trigger frame, the trigger frame including a user info list field indicating the second link and the STA.

[0417] In the method, the data frame can include a QoS null frame, the QoS null frame including a high throughput (HT) control field indicating the second link and the STA.

[0418] In the method, there can be a first indication sent by the first AP to the second AP of support by the first AP for inter-AP assisted medium synchronization recovery; and a second indication received by the first AP from the second AP of support by the second AP for inter-AP assisted medium synchronization recovery.

[0419] There is a device arranged to perform operations comprising, when acting as a first AP: receiving a first frame sent by a station (STA) to a second AP, the first frame including a request to the second AP; and based on the first AP receiving an acknowledgement frame from the second AP to the STA in response to the first frame, sending a second frame to the second AP, the second frame informing the second AP of the request included in the first frame.

[0420] There is a device arranged to perform operations comprising, when acting as a first STA: receiving, by a first access point (AP) from a second AP, a first frame, the first frame informing the first AP of a request to the first AP sent by a station (STA); and based on receiving the first frame, sending a second frame to the STA.

[0421] There is a device arranged to perform operations comprising, when acting as a STA: sending, by a station (STA) to a first AP, a first frame including a request to the first AP; and receiving, by the STA from a second AP, a second frame in response to the first frame.

[0422] There is a wireless communication network comprising at least two APs and at least one STA according to the foregoing description.

[0423] A computer program product stored on a computer readable medium is provided, the computer program product being arranged to cause a processor to perform the foregoing method when run on the processor.

Claims

1. A method comprising: receiving, by a first access point (AP), a first frame sent by a station (STA) to a second AP, the first frame including a request to the second AP; and based on the first AP not responding to the first frame, receiving, by the first AP from the second AP, an acknowledgement frame to the STA, and 2. The method of claim 1, wherein, sending, by the first AP to the second AP, a second frame.

3. The method of claim 1 or 2, wherein, The request is an AP assistance request (AAR).

4. The method of any one of claims 1-3, wherein, The request is to the second link.

5. The method of any preceding claim, wherein, The second frame is arranged to inform the second AP of the request included in the first frame.

6. The method of any preceding claim, wherein, Receiving the first frame includes receiving the first frame via a first link.

7. The method of any preceding claim, wherein, Sending the second frame includes sending the second frame via the first link or a second link.

8. The method of any preceding claim, wherein, The AAR requests the second AP to send a third frame to the STA via the second link.

9. The method of any preceding claim, wherein, The second frame assists the STA to recover medium synchronization on the second link.

10. The method of any preceding claim, wherein, The second frame includes an indication of the second link.

11. The method of any preceding claim, wherein, The second frame includes an indication of the STA.

12. The method of any preceding claim, wherein, The second AP sends a third frame to the STA via the second link in response to the second frame.

13. The method of any preceding claim, wherein, The second frame includes a management frame.

14. The method of any preceding claim, wherein, The second frame includes a control frame. The second frame includes a data frame.

15. A method comprising: receiving, by a first access point (AP) from a second AP, a first frame, the first frame informing the first AP of a request to the first AP sent by a station (STA); and 16. The method of claim 15, wherein, based on receiving the first frame, sending, by the first AP to the STA, a second frame.

17. The method of any one of claims 15-16, wherein, The request is an AP assistance request (AAR).

18. The method of any one of claims 15-17, wherein, Receiving the first frame includes receiving the first frame via a first link or a second link.

19. The method of any one of claims 16-18, wherein, The first frame informs the first AP of the AAR operating on the second link.

20. The method of any one of claims 15-19, wherein, The AAR requests the first AP to send the second frame to the STA via the second link.

21. The method of any one of claims 15-20, wherein, The first frame assists the STA to recover medium synchronization on the second link.

22. The method of any one of claims 15-21, wherein, The first frame includes an indication of the second link.

23. The method of any one of claims 15-22, wherein, The first frame includes an indication of the STA.

24. The method of any one of claims 15-23, wherein, The first AP sends a second frame to the STA via the second link in response to the first frame.

25. The method of any one of claims 15-24, wherein, The first frame includes a management frame.

26. The method of any one of claims 15-25, wherein, The first frame includes a control frame. The first frame includes a data frame.

27. A method comprising: sending, by a station (STA) to a first AP, a first frame including a request to the first AP; and 28. The method of claim 27, wherein, receiving, by the STA from a second AP, a second frame in response to the first frame.

29. The method of claim 27 or 28, wherein, The request is an AP assistance request (AAR).

30. The method of any one of claims 27-29, wherein, Sending the first frame includes sending the first frame via a first link.

31. The method of any one of claims 28-30, wherein, Receiving the second frame includes receiving the second frame via a second link.

32. The method of any one of claims 27-31, wherein, The AAR requests the first AP to send a third frame to the STA via the second link.

33. The method of any one of claims 27-32, wherein, The second frame assists the STA to recover medium synchronization on the second link.

34. The method of any one of claims 27-33, wherein, The second frame includes an indication of the STA.

35. The method of any one of claims 27-34, wherein, The second frame informs the STA to send a fourth frame to the first AP via the second link. The second frame includes a management frame.

36. The method of any one of claims 27-35, wherein, The second frame comprises a control frame.

37. A method comprising: receiving, by a first access point (AP), a first frame sent by a station (STA) to a second AP; based on the first AP not receiving a second frame from the second AP to the STA in response to the first frame, sending, by the first AP to the second AP, a second frame informing the second AP of the first frame.

38. The method of claim 37, wherein, receiving the first frame comprises receiving the first frame via a first link.

39. The method of any one of claims 37-38, wherein, sending the second frame comprises sending the second frame via the first link or a second link.

40. The method of any one of claims 37-39, wherein, the second frame comprises an indication of the second link.

41. The method of any one of claims 37-40, wherein, the second frame comprises an indication of the STA.

42. The method of any one of claims 37-41, wherein, the second AP, in response to the second frame, sends a third frame to the STA via the second link.

43. The method of any one of claims 37-42, wherein, the second frame comprises a management frame.

44. The method of any one of claims 37-43, wherein, the second frame comprises a control frame.

45. The method of any one of claims 37-44, wherein, the second frame comprises a data frame.

46. The method of any one of claims 37-45, wherein, the first frame comprises at least one of a request frame, the request frame comprising an association request frame, a re-association request frame, a TWT request frame, a probe request frame, an RTS frame, a block ack request frame, or a data frame.

47. The method of any one of claims 37-46, wherein, the second frame comprises a response frame, the response frame comprising at least one of an association response frame, a re-association response frame, a TWT response frame, a probe response frame, a CTS frame, or a BA frame.

48. The method of any preceding claim, wherein, the first AP and the second AP form a multi-AP group.

49. The method of any preceding claim, wherein, the first AP, the second AP, or the STA comprises a multi-link device (MLD).

50. The method of any preceding claim, wherein, the first link and the second link form a non-simultaneous transmit and receive (NSTR) link pair at the STA.

51. The method of any one of claims 12-14, 24, 35, and 43, wherein, the management frame comprises an active frame, the active frame comprising an active field indicating the second link and the STA.

52. The method of any one of claims 12-14, 25, 36, and 44, wherein, the control frame comprises a trigger frame, the trigger frame comprising a user info list field indicating the second link and the STA.

53. The method of any one of claims 12-14, 25, and 46, wherein, the data frame comprises a QoS null frame, the QoS null frame comprising a high throughput (HT) control field indicating the second link and the STA.

54. The method of any preceding claim, comprising: sending, by the first AP to the second AP, a first indication of support by the first AP for inter-AP assistance with medium synchronization recovery; and receiving, by the first AP from the second AP, a second indication of support by the second AP for the inter-AP assistance with medium synchronization recovery.

55. A device arranged to perform operations comprising, when acting as a first AP: receiving a first frame sent by a station (STA) to a second AP, the first frame comprising a request to the second AP; and based on the first AP not receiving an acknowledgement frame from the second AP to the STA in response to the first frame, sending a second frame to the second AP, the second frame informing the second AP of the request comprised in the first frame.

56. A device arranged to perform operations comprising, when acting as a first STA: receiving, by a first access point (AP) from a second AP, a first frame informing the first AP of a request by a station (STA) to the first AP; and based on receiving the first frame, sending a second frame to the STA.

57. An apparatus arranged to perform, when acting as a STA, operations comprising: sending, by a station (STA) to a first AP, a first frame comprising a request to the first AP; and receiving, by the STA from a second AP, a second frame in response to the first frame.

58. A wireless communication network comprising at least two APs and at least one STA according to the preceding claims.

59. A computer program product stored on a computer readable medium which, when run on a processor, is arranged to cause the processor to perform the method of any of claims 1-54.

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