Scheduled transmission opportunity (TXOP) allocation

Abstract

A first access point (AP) receives from a second AP a first frame comprising an indication of whether the second AP is able to receive a second frame before a scheduled transmission time of the second frame, where the second frame triggers the second AP to start communicating using a portion of a transmission opportunity (TXOP) of the first AP. The first AP transmits to the second AP a third frame indicating the scheduled transmission time of the second frame; and based on the indication indicating that the second AP is able to receive the second frame before the scheduled transmission time of the second frame, the first AP transmits to the second AP the second frame before the scheduled transmission time of the second frame.

Description

TITLEScheduled Transmission Opportunity (TXOP) AllocationCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 663,731 , filed June 25, 2024, which is hereby incorporated by reference in its entirety.BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Examples of several of the various embodiments of the present disclosure are described herein with reference to the drawings.

[0003] FIG. 1 illustrates example wireless communication networks in which embodiments of the present disclosure may be implemented.

[0004] FIG. 2 is a block diagram illustrating example implementations of a station (STA) and an access point (AP).

[0005] FIG. 3 illustrates an example multi-AP network.

[0006] FIG. 4 illustrates Enhanced Distributed Channel Access (EDCA) and Coordinated Orthogonal Frequency Division Multiple Access (COFDMA).

[0007] FIG. 5 illustrates an example network that includes a coordinated AP set.

[0008] FIG. 6 illustrates an example multi-AP operation procedure.

[0009] FIG. 7 illustrates an example multi-AP sounding phase.

[0010] FIG. 8 illustrates an example multi-AP downlink data transmission phase.

[0011] FIG. 9 illustrates an example multi-AP uplink data transmission phase.

[0012] FIG. 10 illustrates Enhanced Distributed Channel Access (EDCA) and Coordinated Time Division Multiple Access (CTDMA).

[0013] FIG. 11 illustrates an example of a Multi-User Request-to-Send (MU-RTS) trigger frame which may be used in a triggered Transmit Opportunity (TXOP) sharing (TXS) procedure.

[0014] FIG. 12 illustrates an example of a triggered TXS procedure (Mode =1).

[0015] FIG. 13 illustrates an example of a triggered TXS procedure (Mode =2).

[0016] FIG. 14 illustrates an example of an existing CTDMA procedure.

[0017] FIG. 15 illustrates an example that highlights a problem that may arise in association with an implementation of a CTDMA procedure.

[0018] FIG. 16 illustrates an example of a procedure according to an embodiment.

[0019] FIG. 17 illustrates another example of a procedure according to an embodiment.

[0020] FIG. 18 illustrates another example of a procedure according to an embodiment.

[0021] FIG. 19 illustrates another example of a procedure according to an embodiment.

[0022] FIG. 20 illustrates another example of a procedure according to an embodiment.

[0023] FIG. 21 illustrates an example process according to an embodiment.

[0024] FIG. 22 illustrates another example process according to an embodiment.DETAILED DESCRIPTION

[0025] In the present disclosure, various embodiments are presented as examples of how the disclosed techniques may be implemented and / or how the disclosed techniques may be practiced in environments and scenarios. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the scope. After reading the description, it will be apparent to one skilled in the relevant art how to implement alternative embodiments. The present embodiments may not be limited by any of the described exemplary embodiments. The embodiments of the present disclosure will be described with reference to the accompanying drawings. Limitations, features, and / or elements from the disclosed example embodiments may be combined to create further embodiments within the scope of the disclosure. Any figures which highlight the functionality and advantages, are presented for example purposes only. The disclosed architecture is sufficiently flexible and configurable, such that it may be utilized in ways other than that shown. For example, the actions listed in any flowchart may be re-ordered or only optionally used in some embodiments.

[0026] Embodiments may be configured to operate as needed. The disclosed mechanism may be performed when certain criteria are met, for example, in a station, an access point, a radio environment, a network, a combination of the above, and / or the like. Example criteria may be based, at least in part, on for example, wireless device or network node configurations, traffic load, initial system set up, packet sizes, traffic characteristics, a combination of the above, and / or the like. When the one or more criteria are met, various example embodiments may be applied. Therefore, it may be possible to implement example embodiments that selectively implement disclosed protocols.

[0027] In this disclosure, “a” and “an” and similar phrases are to be interpreted as “at least one” and “one or more.” Similarly, any term that ends with the suffix “(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” is indicative that the phrase following the term “may” is an example of one of a multitude of suitable possibilities that may, or may not, be employed by one or more of the various embodiments. The terms “comprises” and “consists of”, as used herein, enumerate one or more components of the element being described. The term “comprises” is interchangeable with “includes” and does not exclude unenumerated components from being included in the element being described. By contrast, “consists of’ provides a complete enumeration of the one or more components of the element being described. The term “based on”, as used herein, may 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 enumerated elements. For example, “A, B, and / or C” may represent A; B; C; A and B; A and C; B and C; or A, B, and C.

[0028] If A and B are sets and every element of A is an element of B, A is called a subset of B. In this specification, only non-empty sets and subsets are considered. For example, possible subsets of B = {STA1 , STA2} are: {STA1 }, {STA2}, and {STA1 , STA2}. The phrase “based on” (or equally “based at least on”) is indicative that the phrase following the term “based on” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments. The phrase “in response to” (or equally “in response at least to”) is indicative that the phrase following the phrase “in response to” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments. The phrase “depending on” (or equally “depending at least to”) is indicative that the phrase following the phrase “depending on” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments. The phrase “employing / using” (or equally “employing / using at least”) is indicative that the phrase following the phrase “employing / using” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments.

[0029] The term configured may relate to the capacity of a device whether the device is in an operational or non-operational state. Configured may refer to specific settings in a device that effect the operational characteristics of the device whether the device is in an operational or non-operational state. In other words, the hardware, software, firmware, registers, memory values, and / or the like may be “configured” within a device, whether the device is in an operational or nonoperational state, to provide the device with specific characteristics. Terms such as “a control message to cause in a device” may mean that a control message has parameters that may be used to configure specific characteristics or may be used to implement certain actions in the device, whether the device is in an operational or non-operational state.

[0030] In this disclosure, parameters (or equally called, fields, or Information elements: lEs) may comprise one or more information objects, and an information object may comprise one or more other objects. For example, if parameter (IE) N comprises parameter (IE) M, and parameter (IE) M comprises parameter (IE) K, and parameter (IE) K comprises parameter (information element) J. Then, for example, N comprises K, and N comprises J. In an example embodiment, when one or more messages / frames comprise a plurality of parameters, it implies that a parameter in the plurality of parameters is in at least one of the one or more messages / frames but does not have to be in each of the one or more messages / frames.

[0031] Many features presented are described as being optional through the use of “may” or the use of parentheses. For the sake of brevity and legibility, the present disclosure does not explicitly recite each and every permutation that may be obtained by choosing from the set of optional features. The present disclosure is to be interpreted as explicitly disclosing all such permutations. For example, a system described as having three optional features may be embodied in seven ways, namely with just one ofthe three possible features, with any two of the three possible features or with three of the three possible features.

[0032] Many of the elements described in the disclosed embodiments may 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 may be implemented in hardware, software in combination with hardware, firmware, wetware (e.g. hardware with a biological element) or a combination thereof, which may be behaviorally equivalent. For example, modules may be implemented as a software routine written in a computer language configured to be executed by a hardware machine (such as C, C++, Fortran, Java, Basic, Matlab or the like) or a modeling / simulation program such as Simulink, Stateflow, GNU Octave, or LabVIEWMathScript. It may be possible to implement modules using physical hardware that incorporates discrete or programmable analog, digital and / or quantum hardware. Examples of programmable hardware comprise: computers, microcontrollers, microprocessors, application-specific integrated circuits (ASICs); field programmable gate arrays (FPGAs); and complex programmable logic devices (CPLDs). Computers, microcontrollers and microprocessors are programmed using languages such as assembly, C, C++ or the like. FPGAs, ASICs and CPLDs are often programmed using hardware description languages (HDL) such as VHSIC hardware description language (VHDL) or Verilog that configure connections between internal hardware modules with lesser functionality on a programmable device. The mentioned technologies are often used in combination to achieve the result of a functional module.

[0033] FIG. 1 illustrates example wireless communication networks in which embodiments of the present disclosure may be implemented.

[0034] As shown in FIG. 1 , the example wireless communication networks may include an Institute of Electrical and Electronic Engineers (IEEE) 802.11 (WLAN) infra-structure network 102. WLAN infrastructure network 102 may include one or more basic service sets (BSSs) 110 and 120 and a distribution system (DS) 130.

[0035] BSS 110-1 and 110-2 each includes a set of an access point (AP or AP STA) and at least one station (STA or non-AP STA). For example, BSS 110-1 includes an AP 104-1 and a STA 106-1 , and BSS 110- 2 includes an AP 104-2 and STAs 106-2 and 106-3. The AP and the at least one STA in a BSS perform an association procedure to communicate with each other.

[0036] DS 130 may be configured to connect BSS 110-1 and BSS 110-2. As such, DS 130 may enable an extended service set (ESS) 150. Within ESS 150, APs 104-1 and 104-2 are connected via DS 130and may have the same service set identification (SSID).

[0037] WLAN infra-structure network 102 may be coupled to one or more external networks. For example, as shown in FIG. 1 , WLAN infra-structure network 102 may be connected to another network 108 (e.g.,802.X) via a portal 140. Portal 140 may function as a bridge connecting DS 130 of WLAN infra-structure network 102 with the other network 108.

[0038] The example wireless communication networks illustrated in FIG. 1 may 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 so that they may communicate with each other using direct peer-to-peer communication (i.e. , not via an AP).

[0039] For example, in FIG. 1, STAs 106-4, 106-5, and 106-6 may be configured to form a first IBSS 112- 1. Similarly, STAs 106-7 and 106-8 may 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, STAs within an IBSS are managed in a distributed manner. STAs forming an IBSS may be fixed or mobile.

[0040] A STA as a predetermined functional medium may include a medium access control (MAC) layer that complies with an IEEE 802.11 standard. A physical layer interface for a radio medium may be used among the APs and the non-AP stations (STAs). The STA may also be referred to using various other terms, including mobile terminal, wireless device, wireless transmit / receive unit (WTRU), user equipment (UE), mobile station (MS), mobile subscriber unit, or user. For example, the term “user” may be used to denote a STA participating in uplink Multi-user Multiple Input, Multiple Output (MU MIMO) and / or uplink Orthogonal Frequency Division Multiple Access (OFDMA) transmission.

[0041] A physical layer (PHY) protocol data unit (PPDU) may be a composite structure that includes a PHY preamble and a payload in the form of a PLOP service data unit (PSDU). For example, the PSDU may include a PHY Convergence Protocol (PLCP) preamble and header and / or one or more MAC protocol data units (MPDUs). The information provided in the PHY preamble may be used by a receiving device to decode the subsequent data in the PSDU. In instances in which PPDUs are transmitted over a bonded channel (channel formed through channel bonding), the preamble fields may be duplicated and transmitted in each of the multiple component channels. The PHY preamble may include both a legacy portion (or “legacy preamble”) and a non-legacy portion (or “non-legacy preamble”). The legacy preamble may be used for packet detection, automatic gain control and channel estimation, among other uses. The legacy preamble also may generally be used to maintain compatibility with legacy devices. The format of, coding of, and information provided in the non-legacy portion of the preamble is based on the particular IEEE 802.11 protocol to be used to transmit the payload.

[0042] A frequency band may include one or more sub-bands or frequency channels. For example, PPDUs conforming to the IEEE 802.11 n, 802.11 ac, 802.11 ax and / or 802.11 be standard amendments may be transmitted over the 2.4 GHz, 5 GHz, and / or 6 GHz bands, each of which may be divided into multiple 20 MHz channels. The PPDUs may be transmitted over a physical channel having a minimum bandwidth of 20 MHz. Larger channels may be formed through channel bonding. For example, PPDUs may betransmitted over physical channels having bandwidths of 40 MHz, 80 MHz, 160 MHz, or 520 MHz by bonding together multiple 20 MHz channels.

[0043] FIG. 2 is a block diagram illustrating example implementations of a STA 210 and an AP 260. As shown in FIG. 2, STA 210 may include at least one processor 220, a memory 230, and at least one transceiver 240. AP 260 may include at least one processor 270, a memory 280, and at least one transceiver 290. Processor 220 / 270 may be operatively connected to memory 230 / 280 and / or to transceiver 240 / 290.

[0044] Processor 220 / 270 may implement functions of the PHY layer, the MAC layer, and / or the logical link control (LLC) layer of the corresponding device (STA 210 or AP 260). Processor 220 / 270 may include one or more processors and / or one or more controllers. The one or more processors and / or one or more controllers may comprise, for example, a general-purpose processor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a logic circuit, or a chipset, for example.

[0045] Memory 230 / 280 may include a read-only memory (ROM), a random-access memory (RAM), a flash memory, a memory card, a storage medium, and / or other storage unit. Memory 230 / 280 may comprise one or more non-transitory computer readable mediums. Memory 230 / 280 may store computer program instructions or code that may be executed by processor 220 / 270 to carry out one or more of the operations / embodiments discussed in the present application. Memory 230 / 280 may be implemented (or positioned) within processor 220 / 270 or external to processor 220 / 270. Memory 230 / 280 may be operatively connected to processor 220 / 270 via various means known in the art.

[0046] Transceiver 240 / 290 may be configured to transmit / receive radio signals. In an embodiment, transceiver 240 / 290 may implement a PHY layer of the corresponding device (STA 210 or AP 260). In an embodiment, STA 210 and / or AP 260 may be a multi-link device (MLD), that is a device capable of operating over multiple links as defined by the IEEE 802.11 standard. As such, STA 210 and / or AP 260 may each implement multiple PHY layers. The multiple PHY layers may be implemented using one or more of transceivers 240 / 290.

[0047] FIG. 3 illustrates an example multi-AP network 300. Example multi-AP network 300 may be a multi- AP network in accordance with the Wi-Fi Alliance standard specification for multi-AP networks. As shown in FIG. 3, multi-AP network 300 may include a multi-AP controller 302 and a plurality of multi-AP groups (or multi-AP sets) 304, 306, and 308.

[0048] Multi-AP controller 302 may be a logical entity that implements logic for controlling the APs in multi- AP network 300. Multi-AP controller 302 may receive capability information and measurements from the APs and may trigger AP control commands and operations on the APs. Multi-AP controller 302 may also provide onboarding functionality to onboard and provision APs onto multi-AP network 300.

[0049] Multi-AP groups 304, 306, and 308 may each include a plurality of APs. APs in a multi-AP group are in communication range of each other and may coordinate their transmissions and / or transmissions from their associated STAs. Coordinated transmissions may involve all or a subset of the APs in a multi-AP group. A multi-AP group may also be referred to as an AP candidate set as APs in a multi-AP group are considered candidates for a coordinated transmission initiated by an AP. The APs in a multi-AP group are not required to have the same primary channel. As used herein, the primary channel for an AP refers to a default channel that the AP monitors for management frames and / or uses to transmit beacon frames. For a STA associated with an AP, the primary channel refers to the primary channel of the AP, which is advertised through the AP’s beacon frames.

[0050] In one approach, a multi-AP group may be established by a coordinator AP in a multi-AP setup phase prior to any multi-AP coordination. APs of the multi-AP group, other than the coordinator AP, may be referred to as the coordinated APs. A coordinator AP may establish one or more multi-AP groups. A coordinated AP may likewise be a member of multiple multi-AP groups. A coordinator AP of a multi-AP group may be a coordinated AP of another multi-AP group, and vice versa. In another approach, a multi- AP group may be established by a network administrator manually by configuring APs as part of the multi-AP group. In yet another approach, a multi-AP group may be established in a distributed manner by APs without a central controller. In this case, an AP may advertise its multi-AP capability in a beacon or other management frame (e.g., public action frame). Other APs that receive the frame with the multi- AP capability information may perform a multi-AP setup with the AP that advertised the multi-AP capability.

[0051] In one approach, one of the APs in a multi-AP group may be designated as a master AP. The designation of the master AP may be done by AP controller 302 or by the APs of the multi-AP group. The master AP of a multi-AP group may be fixed or may change over time between the APs of the multi- AP group. An AP that is not the master AP of the multi-AP group is known as a slave AP.

[0052] In one approach, APs in a multi-AP group may perform coordinated transmissions together. One aspect of coordination may include coordination to perform coordinated transmissions within the multi- AP group. As used herein, a coordinated transmission, also referred to as a multi-AP transmission, is a transmission event in which multiple APs (of a multi-AP group or a multi-AP network) transmit in a coordinated manner over a time period. Coordinated transmissions may involve simultaneous transmissions of a plurality of APs in a multi-AP group. The time period of simultaneous AP transmission may be a continuous period. The multi-AP transmission may use different transmission techniques, such as Coordinated OFDMA (COFDMA), Coordinated Spatial Reuse (CSR), Joint Transmission or Reception (JT / JR), Coordinated Beamforming (CBF), and CTDMA, or a combination of two or more of the aforementioned techniques.

[0053] Multi-AP transmissions may be enabled by the AP controller and / or by the master AP of the multi- AP group. In one approach, the AP controller and / or the master AP may control time and / or frequency sharing in a transmission opportunity (TXOP). For example, when one of the APs (e.g., the master AP) in the multi-AP group obtains a TXOP, the AP controller and / or the master AP may control how time / frequency resources of the TXOP are to be shared with other APs of the multi-AP group. In an implementation, the AP of the multi-AP group that obtains a TXOP becomes the master AP of the multi- AP group. The master AP may then share a portion of its obtained TXOP (which may be the entire TXOP) with one or more other APs of the multi-AP group.

[0054] Different multi-AP transmission schemes may be suitable for different use cases in terms of privacy protection, including whether transmitted data may be shared with other BSSs in the multi-AP group. For example, some multi-AP transmission schemes, such as CSR, CDTMA, coordinated frequency division multiple access (CFDMA), COFDMA, and CBF, enable a master AP to coordinate slave APs by sharing control information among APs, without requiring the sharing of user data among APs. The control information may include BSS information of APs, link quality information of channels between each AP and its associated STAs, and information related to resources to be used to achieve multiplexing in power, time, frequency, or special domains for multi-AP transmission. The control information exchanged among a master AP and slave APs may be used for interference avoidance or nulling to avoid or null cochannel interference introduced to neighboring BSSs in a multi-AP network. Interference avoidance or interference nulling requires that data transmissions between an AP and STAs are only within the same BSS. In other words, each AP transmits or receives data frames to or from its associated STAs, while each STA receives or transmits data frames to or from its associating AP.

[0055] By contrast, other multi-AP transmission schemes may enable a master AP to coordinate slave APs by sharing both control information and user data among APs in a multi-AP group. Control information may include BSS information related to APs and link quality information of channels between each AP and its associated STAs. By having user data exchanged over backhaul, the master AP and slave APs may perform data transmissions jointly to achieve spatial diversity, e.g., using distributed MIMO, for example, joint transmission (JT) for downlink transmissions and joint reception (JR) for uplink transmissions. The data transmissions between APs and STAs may include transmissions within the same BSS and / or across different BSSs. In other words, an AP may transmit or receive data frames to or from its associated STAs as well STAs associated with other APs participating in multi-AP transmission. Similarly, a STA may transmit or receive data frames to or from multiple APs.

[0056] Different multi-AP transmission schemes may be suitable for different use cases in terms of signal reception levels at STAs or APs within a multi-AP group. For example, CBF and JT / JR require that each STA involved in a multi-AP transmission be located within a common area of signal coverage of the APs involved in the multi-AP transmission. Generally, CBF may be suitable when a receiving STA suffersfrom potential interference from other APs in the multi-AP group. By using channel related information such as channel state information (CSI), channel quality indication (CQI), or compressed beamforming (BF) feedback exchanged among APs, an AP may pre-code a signal to be transmitted to form a beam that increases power toward a target STA while reducing the power that interferes with a STA associated with a neighboring AP. Use cases of JT / JR may require a sufficient received signal power at receiving STAs for JT and a sufficient received signal power at receiving APs for JR. By contrast, CSR may perform multi-AP transmission in an interference coordination manner. The received signal power at a STA associated with an AP transmitting data may be required to be much higher than the received interference power.

[0057] Different multi-AP transmission schemes may require different synchronization levels and may operate with or without a backhaul between a master AP and slave APs in a multi-AP group. For example, CSR may require PPDU-level synchronization, whereas CBF may require symbol-level synchronization. On the other hand, JT / JR may require tight time / frequency / phase-level synchronization as well as a backhaul for data sharing between APs in the multi-AP group.

[0058] Different multi-AP transmission schemes may have different complexity levels with regard to coordination between a master AP and slave APs in a multi-AP group. For example, JT / JR may require very high complexity due to both CSI and user data being shared between APs. CBF may require medium complexity due to the sharing of CSI. CFDMA, COFDMA and CTDMA may require medium or relatively low complexity due to the CSI and time / frequency resources to be shared between APs. CSR may require low complexity as the amount of information related to spatial reuse and traffic that needs to be exchanged between APs may be low.

[0059] A multi-AP group may adopt a static multi-AP operation including a static multi-AP transmission scheme. A multi-AP network may also be dynamic due to various reasons. For example, a STA may join or leave the multi-AP network, a STA may switch to a power save mode, or an AP or a STA may change its location. Such changes may lead to changes in the conditions underlying the selection of the multi- AP transmission scheme and may cause certain requirements (e.g., synchronization, backhaul, coordination, etc.) for the multi-AP transmission scheme to be lost. This results in an inferior quality of transmissions in the multi-AP network.

[0060] In COFDMA, the master AP may share a portion of its TXOP with multiple APs by assigning each of the multiple APs a respective frequency resource (e.g., channel / subchannel) of available frequency resources. COFDMA is illustrated in FIG. 4 as a multi-AP channel access, compared with Enhanced Distributed Channel Access (EDCA). As shown in FIG. 4, in EDCA, channel access by multiple APs (e.g., AP1 , AP2) may occur in consecutive time periods (e.g., TXOPs). During a given channel access, the channel (e.g., 80 MHz) in its entirety may be used by a single AP. In contrast, in COFDMA, access by multiple APs (multi-AP channel access) may take place in a same time period (e.g., same TXOP or sameportion of a TXOP) over orthogonal frequency resources. For example, as shown in FIG. 4, an 80 MHz channel may be divided into four non-overlapping 20 MHz channels, each assigned to a respective AP of the multiple APs. The multiple APs may transmit in a coordinated manner, simultaneously in the same time period, to achieve a multi-AP transmission. In the multi-AP transmission, each of the multiple APs may transmit a PPDU to one or more STAs.

[0061] FIG. 5 illustrates an example network 500 that includes a coordinated AP set. As shown in FIG. 5, the coordinated AP set may include two APs - AP 502-1 and AP 502-2. The coordinated AP set may be a subset of an established multi-AP group. At least one STA may be associated with each of APs 502-1 and 502-2. For example, a STA 504-1 may be associated with AP 502-1 , and a STA 504-2 may be associated with AP 502-2.

[0062] APs 502-1 and 502-2 may belong to the same ESS as described above in FIG. 1. In such a case, APs 502-1 and 502-2 may be connected by a DS to support ESS features. In addition, as part of a coordinated AP set, APs 502-1 and 502-2 may be connected by a backhaul. The backhaul is used to share information quickly between APs to support coordinated transmissions. The shared information may be channel state information or data to be sent to associated STAs. The backhaul may be a wired backhaul or a wireless backhaul. A wired backhaul is preferred for high-capacity information transfer without burdening the main radios of the APs. However, a wired backhaul may require a higher deployment cost and may place greater constraints on AP placement. A wireless backhaul is preferred for its lower deployment cost and flexibility regarding AP placement. However, because a wireless backhaul relies on the main radios of the APs to transfer information, the APs cannot transmit or receive any data while the wireless backhaul is being used.

[0063] Typically, one of APs 502-1 and 502-2 may act as a Master AP and the other as a Slave AP. The Master AP is the AP that is the owner of the TXOP. The Master AP shares frequency resources during the TXOP with the Slave AP. When there are more than two APs in the coordinated set, a Master AP may share its TXOP with only a subset of the coordinated AP set. The role of the Master AP may change over time. For example, the Master AP role may be assigned to a specific AP for a duration of time. Similarly, the Slave AP role may be chosen by the Master AP dynamically or can be pre-assigned for a duration of time.

[0064] Depending on the capability of APs in a coordinated AP set, the APs may only do certain type of coordinated transmissions. For example, in FIG. 5, if AP 502-1 supports JT and CSR while AP 502-2 supports CSR and CBF, both APs may only perform CSR as a coordinated transmission scheme. An AP may also prefer to perform single AP transmissions for a duration of time if the benefit of coordinated transmission does not outweigh some disadvantages with coordinated transmission such as reduced flexibility and increased computational power required.

[0065] CSR is one type of multi-AP coordination that may be supported by AP 501-1 and AP 502-2 as shown in FIG. 5. Spatial reuse using CSR can be more stable than non-AP coordinated spatial reuse schemes such as OBSS PD-based SR and PSR-based SR. For example, in example network 500, APs 502-1 and 502-2 may perform a joint sounding operation in order to measure path loss (PL) on paths of network 500. For example, the joint sounding operation may result in the measurement of PL 508 for the path between APs 502-1 and 502-2, path loss 510 for the path between AP 502-1 and STA 504-2, and path loss 512 for the path between AP 502-2 and STA 504-1. The measured path loss information may then be shared between APs 502-1 and 502-2 (e.g., using the backhaul) to allow for simultaneous transmissions by APs 502-1 and 502-2 to their associated STAs 504-1 and 504-2 respectively. Specifically, one of APs 502-1 and 502-2 obtains a TXOP to become the Master AP. The Master AP may then send a CSR announcement frame to the other AP(s). In an embodiment, the Master AP may perform a polling operation, before sending the CSR announcement frame, to poll Slave APs regarding packet availability for transmission. If at least one Slave AP responds indicating packet availability, the Master AP may proceed with sending the CSR announcement frame. In the CSR announcement, the Master AP may limit the transmit power of a Slave AP in order to protect its own transmission to its target STA. The Slave AP may similarly protect its own transmission to its target STA by choosing a modulation scheme that enables a high enough Signal to Interference Ratio (SIR) margin to support the interference due to the transmission of the Master AP to its target STA.

[0066] FIG. 6 illustrates an example 600 of a multi-AP operation procedure. In example 600, the multi-AP operation procedure is illustrated with respect to a multi-AP network that includes APs 602 and 604 and STAs 606 and 608. In an example, APs 602 and 604 may form a multi-AP group. AP 602 may be the master AP and AP 604 may be a slave AP of the multi-AP group. For example, AP 602 may obtain a TXOP making it the master AP of the multi-AP group. Alternatively, AP 602 may be designated as the master AP by a multi-AP controller.

[0067] As shown in FIG. 6, the multi-AP operation procedure may include a series of phases in time, each of which may contain a plurality of frame exchanges within the multi-AP network. Specifically, the multi- AP operation procedure may include a multi-AP selection phase 610, a multi-AP data sharing phase 612, a multi-AP sounding phase 614, and a multi-AP data transmission phase 616.

[0068] A multi-AP network may carry out a multi-AP operation based on a specific multi-AP transmission scheme. The multi-AP transmission scheme may be chosen by the master AP based on the capabilities of the slave APs in a multi-AP group. Prior to a multi-AP operation, a slave AP may inform the master AP of capability information related to the slave AP, including the capabilities of supporting one or more multi-AP transmission schemes. The slave AP may also inform the master AP of BSS information of the BSS of the slave AP and of link quality information for STAs associated with the slave AP. The master AP may receive information related to all available slave APs. The information related to slave APs mayinclude capability information, BSS information, and link quality information. Based on the information provided by available slave APs, the master AP may determine during a multi-AP selection phase the slave APs to be designated for a multi-AP transmission and a specific multi-AP transmission scheme to be used during the multi-AP transmission.

[0069] Multi-AP selection phase 610 may include procedures for soliciting, selecting, or designating slave AP(s) for a multi-AP group by a master AP. As seen in FIG. 6, the multi-AP selection phase may include transmissions of frame 618 from AP 602 and frame 620 from AP 604. AP 602 may transmit frame 618 to solicit information regarding the buffer status of AP 604. In response, AP 604 may transmit frame 620 to inform AP 602 of its and its associated STAs buffer status and / or whether it intends to join multi-AP operation. Multi-AP selection phase 610 may also be used to exchange information related to multi-AP operation, including BSS information of APs and link quality information between each AP and its associated STAs, for example. The BSS information of an AP may include a BSS ID of the BSS of the AP, identifiers and / or capabilities of STAs belonging to the BSS, information regarding sounding capabilities of the STAs, information regarding MIMO capabilities of the AP, etc. 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), channel quality indicator (CQI).

[0070] Multi-AP data sharing phase 612 may include procedures for sharing data frames to be transmitted by APs to associated STAs among the master AP and selected slave AP(s) via direct connections between APs. Phase 612 may be optional for some multi-AP data transmission schemes. For example, phase 612 may be required for JT / JR as data frames may be exchanged between APs before or after multi-AP data transmission phase 616.

[0071] Multi-AP data sharing phase 612 may be performed using a wired backhaul, an in-channel wireless backhaul, or an off-channel wireless backhaul. In some cases, multi-AP data sharing phase 612 may be performed over an in-channel backhaul, e.g., using the same wireless channel used to transmit / receive data to / from STAs. For example, as shown in FIG. 6, in phase 612, AP 602 may transmit a frame 622, which may be received by AP 604. Frame 622 may include MPDUs that AP 602 wishes to transmit to associated STAs using a multi-AP operation. Similarly, AP 604 may transmit a frame 624, which may be received by AP 602. Frame 624 may include MPDUs that AP 604 wishes to transmit to associated STAs using a multi-AP operation.

[0072] Multi-AP sounding phase 614 may include procedures for multi-AP channel sounding, including channel estimation and feedback of channel estimates among the master AP, candidate slave AP(s), and associated STAs. Phase 614 may be optional for some multi-AP transmission schemes, such as COFDMA, CDTMA, and CSR. For example, phase 614 may be performed by the master AP to aid in resource unit allocation when orchestrating a COFDMA transmission.

[0073] Multi-AP data transmission phase 616 may include exchange of data frames between the master AP, slave AP(s), and their associated STAs based on multi-AP transmission scheme(s) determined by the master AP. Depending on the multi-AP transmission scheme(s) to be used, phase 616 may include optional synchronization between APs of the multi-AP group, before exchange of data frames between APs and STAs within the multi-AP group.

[0074] The order of phases 610, 612, 614 and 616 may be different than shown in FIG. 6. For example, in COFDMA, phase 616 may occur immediately after phase 610, whereas, in JT / JR, phase 612 may occur after phase 610. Further, as mentioned above, some phases may be optional and may or may not be present. For example, phase 614 may not be required for COFDMA but may be required for JT / JR.

[0075] FIG. 7 illustrates an example multi-AP sounding phase 700. Example multi-AP sounding phase 700 may be an example of multi-AP sounding phase 614. As shown in FIG. 7, example multi-AP sounding phase 700 may include a master AP 702 and a slave AP 704 of a multi-AP group. Example multi-AP sounding phase 700 may further include a STA 706 associated with AP 702 and a STA 708 associated with AP 704.

[0076] As shown in FIG. 7, multi-AP sounding phase 700 may include frame exchanges to allow AP 702 (the master AP) to acquire channel state information (CSI) of channels in the multi-AP group. In an implementation, phase 700 may include a first subphase 710 and a second subphase 712.

[0077] During the first subphase 710, APs may initiate channel sounding and STAs may estimate channel state information (CSI). For example, AP 702 may transmit a frame 714 to AP 704 (the slave AP) to trigger multi-AP sounding. Frame 714 may comprise a multi-AP trigger frame. Subsequently, APs 702 and 704 may transmit respectively announcement frames 716-1 and 716-2 to their respective associated STAs 706 and 708 to announce the transmission of sounding frames. Frames 716-1 and 716-2 may comprise multi-AP null data packet announcement (NDPA) frames. Frames 716-1 and 716-2 may be transmitted simultaneously. Next, APs 702 and 704 may transmit respectively frames 718-1 and 718-2 to STAs 706 and 708 respectively. Frames 718-1 and 718-2 may comprise multi-AP null data packet (NDP) frames. STAs 706 and 708 receive frames 718-1 and 718-2 respectively and perform channel estimation of the channels from AP 702 to STA 706 and from AP 704 to STA 708, respectively.

[0078] During the second subphase 712, APs may initiate a procedure for STAs to feed back channel estimates to the APs. For example, AP 702 may transmit a frame 720 to trigger STAs 706 and 708 to transmit their channel estimates to APs 702 and 704 respectively. Frame 720 may comprise a multi-AP trigger frame. In response, STAs 706 and 708 may transmit respectively frames 722 and 724 including feedback of channel estimates to APs 702 and 704 respectively. Frames 722 and 724 may comprise NDP feedback frames. The feedback of channel estimates may include NDP feedback, CSI-related information, a beamforming report (BFR), or a channel quality indication (CQI) report.

[0079] FIG. 8 illustrates an example multi-AP downlink data transmission phase 800. Example multi-AP downlink data transmission phase 800 may be an example of multi-AP data transmission phase 616. As shown in FIG. 8, example multi-AP downlink data transmission phase 800 may include a master AP 802 and a slave AP 804 of a multi-AP group. Example multi-AP downlink data transmission phase 800 may further include a STA 806 associated with AP 802, and a STA 808 associated with AP 804.

[0080] As shown in FIG. 8, multi-AP downlink data transmission phase 800 may include frame exchanges to enable master AP 802 to coordinate with slave AP 804 to perform specific multi-AP transmission schemes with their associated STAs 806 and 808 respectively. The multi-AP transmission schemes may include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the aforementioned schemes.

[0081] As shown in FIG. 8, master AP 802 may begin phase 800 by transmitting a frame 810 to AP 804. Frame 810 may include information related to AP 804 (e.g., an identifier of AP 804), synchronization information, information related to a specific multi-AP transmission scheme to be used, and / or information related to a resource unit (RU) for use by AP 804 to acknowledge frame 810. Frame 810 may comprise a control frame. For example, frame 810 may comprise a multi-AP trigger frame.

[0082] Slave AP 804 may receive frame 810 and may use the synchronization information to synchronize with master AP 802. Subsequently, APs 802 and 804 may perform data transmission to their associated STAs 806 and 808 respectively. Specifically, AP 802 may transmit a data frame 812 to its associated STA 806, and AP 804 may transmit a data frame 814 to its associated STA 808. Depending on the multi- AP transmission scheme being used, APs 802 and 804 may transmit frames 812 and 814 respectively to STAs in different BSSs. For example, when the multi-AP transmission scheme is JT / JR, AP 802 may also transmit frame 812 to STA 808 associated with slave AP 804, and AP 804 may also transmit frame 814 to STA 808 associated with AP 804. The resources for transmitting and receiving frames 812 and 814 may depend on the specific multi-AP transmission scheme adopted.

[0083] STAs 806 and 808 may acknowledge frames 812 and 814 respectively. For example, STA 806 may transmit a frame 816 to AP 802, and STA 808 may transmit a frame 818 to AP 804. Frames 816 and 818 may comprise block ack (BA) frames. STAs 806 and 808 may also transmit frames 816 and 818 to APs in different BSSs, when required by the used multi-AP transmission scheme. For example, when the multi-AP transmission scheme is JT / JR, STA 806 may also transmit frame 816 to AP 804, and STA 808 may also transmit frame 818 to AP 802. The resources for transmitting and receiving frames 816 and 818 may depend on the specific multi-AP transmission scheme adopted.

[0084] FIG. 9 illustrates an example multi-AP uplink data transmission phase 900. Example multi-AP uplink data transmission phase 900 may be an example of multi-AP data transmission phase 616. As shown in FIG. 9, example multi-AP uplink data transmission phase 900 may include a master AP 902 and a slaveAP 904 of a multi-AP group. Example multi-AP uplink data transmission phase 900 may further include STAs 906 and 908 associated with AP 902, and a STA 910 associated with AP 904.

[0085] As shown in FIG. 9, example multi-AP uplink data transmission phase 900 may include frame exchanges to enable master AP 902 to coordinate with slave AP 904 to perform specific multi-AP transmission schemes with STAs 906, 908, and 910910. The multi-AP transmission schemes may include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the aforementioned schemes.

[0086] As shown in FIG. 9, master AP 902 may begin phase 900 by transmitting a frame 912 to AP 904. Frame 912 may include information related to AP 904 (e.g., an identifier of AP 904), synchronization information, information related to a specific multi-AP transmission scheme to be used, and / or information related to an RU for use by AP 904 to acknowledge frame 912. Frame 912 may comprise a control frame. For example, frame 912 may comprise a multi-AP trigger frame.

[0087] Slave AP 904 may receive frame 912 and may use the synchronization information to synchronize with master AP 902. Subsequently, APs 902 and 904 may solicit uplink data transmissions from their associated STAs 906, 908 and 910 using trigger frames. Specifically, AP 902 may transmit a trigger frame 914 to its associated STAs 906 and 908, and AP 904 may transmit a trigger frame 916 to its associated STA 910. Depending on the multi-AP transmission scheme being used, APs 902 and 904 may also transmit frames 914 and 916 respectively to STAs in different BSSs. For example, when the multi-AP transmission scheme is JT / JR, AP 902 may also transmit frame 914 to STA 910 associated with slave AP 904, and AP 904 may also transmit frame 916 to STAs 906 and 908 associated with AP 902. The resources for transmitting and receiving frames 914 and 916 may depend on the specific multi- AP transmission scheme adopted.

[0088] STAs 906 and 908 may respond to frame 914, STA 910 may respond to frame 916. For example, STAs 906 and 908 may transmit frames 918 and 920 respectively to AP 902, while STA 910 may transmit a frame 922 to AP 904. Frames 918, 920, and / or 922 may be transmitted simultaneously. Frames 918, 920, and 922 may comprise data frames or null data frames. STAs 906, 908, and 910 may also transmit frames 918, 920, and 922 respectively to APs in different BSSs, when required by the used multi-AP transmission scheme. For example, when the multi-AP transmission scheme is JT / JR, STAs 906 and 908 may also transmit respective frames 918 and 920 to AP 904, and STA 910 may also transmit frame 922 to AP 902. The resources for transmitting and receiving frames 918, 920, and 922 may depend on the specific multi-AP transmission scheme adopted. AP 902 may acknowledge frames 918 and 920 by transmitting a multi-STA BA frame 924 to STAs 906 and 908. AP 904 may acknowledge frame 922 by transmitting a BA frame 926 to STA 910.

[0089] FIG. 10 illustrates Enhanced Distributed Channel Access (EDCA) and Coordinated Time Division Multiple Access (CTDMA). In CTDMA, an AP (generally referred to as a master AP or a sharing AP) mayshare a portion of its TXOP with one or more APs (generally referred to as slave APs or shared APs). Specifically, the sharing AP may assign / allocate each of the one or more APs a respective time period within the TXOP of the sharing AP. A shared AP may use its allocated time period to communicate with one or more STA. CTDMA is illustrated in FIG. 10 as a multi-AP channel access scheme, compared with Enhanced Distributed Channel Access (EDCA). As shown in FIG. 10, in EDCA, channel access by multiple APs (e.g., AP1 , AP2) may occur in consecutive time periods (e.g., TXOPs), where each AP has its own TXOP. During a given channel access, the channel in its entirety may be used by a single AP for the duration of the TXOP. In contrast, in CTDMA, access by multiple APs may take place in a same TXOP over consecutive time periods. For example, as shown in FIG. 10, a TXOP may be divided into two non-overlapping time periods, each assigned to a respective AP of the multiple APs. The multiple APs may transmit in a coordinated manner in the same TXOP consecutively. In an example, as shown in FIG. 10, a master / sharing AP (e.g., AP1) may use itself a first portion of a first TXOP and may share a second portion of the first TXOP with a slave / shared AP (e.g., AP2). In another example, the master / shared AP (e.g., AP1) may share a first portion of a second TXOP with a slave / shared AP (e.g., AP2) and may use itself a second portion of the second TXOP.

[0090] Triggered TXOP sharing (TXS) is a technique introduced in the IEEE 802.11 be standard amendment. TXS allows an AP to allocate a time duration within an obtained TXOP to a STA for transmitting one or more non-trigger-based (non-TB) PPDUs. For the TXS procedure, the AP may transmit a multi-user request-to-send (MU-RTS) trigger frame with a triggered TXOP sharing mode subfield set to a non-zero value. The MU-RTS trigger frame is a trigger frame for triggering clear-to-send (CTS) frame(s) from multiple users. An MU-RTS trigger frame with the triggered TXOP sharing mode subfield set to a non-zero value is called an MU-RTS TXS trigger (MRTT) frame.

[0091] In an example, when the triggered TXOP sharing mode subfield is set to 1 , the STA may transmit the one or more non-TB PPDUs to the AP during the allocated time duration. In an example, when the triggered TXOP sharing mode subfield is set to 2, the STA may transmit the one or more non-TB PPDUs to the AP or a peer STA during the allocated time duration. The peer STA may be a STA with a connection for peer-to-peer (P2P) communication or direct communication with the STA. In an example, the direct wireless link is established according to the tunneled direct link setup (TDLS) protocol.

[0092] FIG. 11 illustrates an example of a Multi-User Request-to-Send (MU-RTS) trigger frame which may be used in a triggered Transmit Opportunity (TXOP) sharing (TXS) procedure. As shown in FIG. 11 , example MU-RTS trigger frame 1100 may comprise a frame control field, a duration field, a receiver address (RA) field, a transmitter address (TA) field, a common info field, a user info list field, a padding field, and / or frame check sequence (FCS) field.

[0093] In an example, the common info field may be a high-efficiency (HE) variant common info field or an extremely high throughput (EHT) variant common info field. An EHT variant common info field maycomprise, as shown in FIG. 11 , one or more of the following subfields: trigger type, UL length, more TF, CS required, UL BW, Gl and HE / EHT-LTF Type / Triggered TXOP sharing mode, number of HE / EHT-LTF symbols, LDPC extra symbol segment, AP Tx Power, Pre-FEC padding factor, PE disambiguity, UL spatial reuse, HE / EHT P160, special user info field flag, EHT reserved, reserved, or trigger dependent common info.

[0094] The trigger type subfield indicates that frame 1100 is an MU-RTS trigger frame.

[0095] The Gl and HE / EHT-LTF Type / Triggered TXOP sharing mode subfield may include a triggered TXOP sharing mode subfield. In an example, the triggered TXOP sharing mode subfield may be set to a non-zero value (e.g., 1 or 2). When the triggered TXOP sharing mode subfield is set to a non-zero value, an MU-RTS trigger frame is an MRTT frame. In an example, the triggered TXOP sharing mode subfield may be set to 1 . As such, the triggered TXOP sharing mode subfield may indicate that a STA indicated by an AID12 subfield of a user info field (of the user info list field) may transmit one or more non-TB PPDUs to the AP during a time indicated in the allocation duration subfield of the user info field. In another example, the triggered TXOP sharing mode subfield may be set to 2. As such, the triggered TXOP sharing mode subfield may indicate that a STA indicated by an AID12 subfield of a user info field (of the user info list field) may transmit one or more non-TB PPDUs to the AP or to a peer STA during the time indicated by the allocation duration subfield of the user info field. In an example, the peer STA may be a STA with a connection for P2P communication or direct communication with the STA.

[0096] The user info list field may include one or more user info fields. In an example, an EHT variant user info field may comprise, as shown in FIG. 11 , one or more of the following subfields: AID12, RU allocation, allocation duration, reserved, or PS160.

[0097] The AID12 subfield may indicate an association identifier (AID) of a STA that may use a time indicated by the allocation duration subfield.

[0098] The RU allocation subfield may indicate the location and size of the RU allocated for a STA indicated by the AID12 subfield.

[0099] The allocation duration subfield may indicate a time allocated by an AP transmitting MRTT frame 1100 (when triggered TXOP sharing mode subfield is a non-zero value). The allocated time may be a portion of a TXOP obtained by the AP. In an example embodiment, the allocation duration subfield may indicate a first time period.

[0100] FIG. 12 illustrates an example 1200 of a TXS procedure (Mode =1). As shown in FIG. 12, the TXS procedure may begin by an AP 1210 transmitting an MRTT frame 1220 to a STA 1211. MRTT frame 1220 may allocate a portion of a TXOP obtained by AP 1210 to STA 1211 and may indicate a TXS mode equal to 1. STA 1211 receiving MRTT frame 1220 may use the allocated time to transmit one or more non-TB PPDUs to AP 1210. The one or more non-TB PPDUs may comprise a data frame, a control frame, a management frame, or an action frame.

[0101] In an example, MRTT frame 1220 may comprise a triggered TXOP sharing mode subfield that indicates the TXS mode and / or subfield that indicates a first time period corresponding to the allocated time. In an example, the first time period may be set to a value of X microseconds (us).

[0102] STA 1211 may respond to MRTT frame 1220 by transmitting a CTS frame 1221 to AP 1210. Subsequently, STA 1211 may transmit non-TB PPDUs 1222, 1224 comprising one or more data frame to AP 1210 during the first time period indicated in MRTT frame 1220. In an example, AP 1210 may transmit one or more Block Ack (BA) frames 1223, 1225 in response to the one or more data frames contained in non-TB PPDUs 1222, 1224 received from STA 1211.

[0103] FIG. 13 illustrates an example 1300 of a TXS procedure (Mode =2). As shown in FIG. 13, the TXS procedure may begin by an AP 1310 transmitting an MRTT frame 1320 to a STA 1311. MRTT frame 1320 may allocate a portion of a TXOP obtained by AP 1310 to STA 1311 and may indicate a TXS mode equal to 2. STA 1311 receiving MRTT frame 1320 may use the allocated time to transmit one or more non-TB PPDUs to STA 1312. The one or more non-TB PPDUs may comprise a data frame, a control frame, a management frame, or an action frame.

[0104] In an example, MRTT frame 1320 may comprise a triggered TXOP sharing mode subfield that indicates the TXS mode and / or subfield that indicates a first time period corresponding to the allocated time. In an example, the first time period may be set to a value of Y microseconds (us).

[0105] STA 1311 may respond to MRTT frame 1320 by transmitting a CTS frame 1321 to AP 1310. Subsequently, STA 1311 may transmit non-TB PPDUs 1322, 1324 comprising one or more data frame to STA 1312 during the first time period indicated in MRTT frame 1320. In an example, STA 1312 may transmit one or more BA frames 1323, 1325 in response to the one or more data frames contained in non-TB PPDUs 1322, 1324 received from STA 1311.

[0106] In CTDMA, one approach for TXOP sharing may be achieved via the TXS procedure described above. The TXS procedure may be used to allow a sharing AP, which obtains a TXOP and is the TXOP owner, to allocate a time duration within its obtained TXOP to a shared AP for downlink and / or uplink transmission between the shared AP and its associated STAs.

[0107] FIG. 14 illustrates an example 1400 of an existing CTDMA procedure. As shown in FIG. 14, example 1400 may include AP 1402 and AP 1404. Each of APs 1402 and 1404 may serve one or more associated STAs. AP 1402 and AP 1404 may be members of a multi-AP group. AP 1402 may be a sharing / master AP of the multi-AP group. AP 1404 may be a shared / slave AP of the multi-AP group. In example 1400, it is assumed that AP 1402 and AP 1404 are within communication range of each other.

[0108] As shown in FIG. 14, the procedure may begin with AP 1402 transmitting a frame 1412 after obtaining a TXOP 1410. In an example, before transmitting frame 1412, AP 1402 may be configured to poll AP 1404 about buffered traffic of AP 1404 (including priorities of the buffered traffic of AP 1404) (not shown in FIG. 14). The buffered traffic of AP 1404 may include buffered traffic at AP 1404 for downlinktransmission to associated STA(s) of AP 1404 and / or buffered traffic at associated STA(s) of AP 1404 for uplink transmission to AP 1404. In another example, AP 1402 may have information in advance regarding the buffered traffic of AP 1404. AP 1402 may be configured to, when AP 1402 has advance information regarding the buffered traffic of AP 1404, not transmit a polling frame to receive updated information regarding the buffered traffic of AP 1404. Based on AP 1402 being configured not to transmit the polling frame, AP 1402 may not transmit a polling frame before transmitting frame 1412.

[0109] Based on the information about the buffered traffic of AP 1404, AP 1402 may transmit a frame 1412 comprising information regarding AP 1404 being scheduled to communicate within TXOP 1410. In an example, frame 1412 may indicate a scheduled transmission time (e.g., frame 1412 may indicate a duration, denoted T1 in FIG. 14, between frame 1412 and the scheduled transmission time) of a frame 1418 (e.g., a TXOP allocation frame), to be transmitted by AP 1402 to AP 1404, where frame 1418 allocates a portion of TXOP 141 O to AP 1404. In an example, frame 1412 may further indicate a duration of the portion (e.g., denoted T2 in FIG. 14) of TXOP 1410 to be allocated to AP 1404. In an example, AP 1402 may determine / configure the scheduled transmission time of frame 1418 based on an expected completion time of communication between AP 1402 and its associated STAs. In an example, the scheduled transmission time of frame 1418 may correspond to an exact time of transmission of frame 1418. In another example, the scheduled transmission time of frame 1418 may correspond to an estimate time or an approximate time of transmission of frame 1418.

[0110] In an example, frame 1412 may comprise a schedule announcement frame. In an example, the schedule announcement frame may comprise a trigger frame, such as an MU-RTS trigger frame. In an example, the scheduled transmission time of frame 1418 may be indicated in a duration field, a subfield of a common info field, or a subfield of a user info list field of the trigger frame. In an example, the duration of the portion of TXOP 1410 to be allocated to AP 1404 may be indicated in a subfield of a user info list field of the trigger frame.

[0111] On receiving frame 1412, AP 1404 may determine the scheduled transmission time (e.g., T1) of frame 1418 and the duration of the portion of TXOP 1410 to be allocated to AP 1404 in frame 1418. In response to frame 1412, AP 1404 may transmit a frame 1414 to AP 1402. In an example, frame 1414 may comprise a schedule announcement response frame. In another example, frame 1414 may comprise an acknowledgment frame. In another example, frame 1414 may comprise a clear-to-send (CTS) frame.

[0112] After receiving frame 1414, AP 1402 may communicate with one or more of its associated STAs during a time period 1416 of TXOP 1410, before the scheduled transmission time of frame 1418. In an example, during time period 1416, AP 1402 may transmit to one or more of its associated STAs downlink frames and / or may trigger one or more of its associated STAs to transmit uplink frames to AP 1402.

[0113] In example 1400, AP 1402 may finish communicating with its associated STAs by the scheduled transmission time of frame 1418. In an example, after finishing communicating with its associated STAs, AP 1402 may transmit frame 1418. In an example, AP 1402 may transmit frame 1418 at the scheduled transmission time of frame 1418. In another example, AP 1402 may transmit frame 1418 after the scheduled transmission time of frame 1418. In example 1400, AP 1402 may transmit frame 1418 a short inter-frame space (SIFS) after time period 1416, which may correspond to the scheduled transmission time of frame 1418.

[0114] In example 1400, frame 1418 may comprise an allocation for AP 1404. The allocation may indicate a first duration of a portion (denoted T2 in FIG. 14) of the TXOP allocated to AP 1404. In an example, frame 1418 may comprise an MRTT frame. In an example, the first duration may be indicated in an allocation duration subfield of a user info list field of the MRTT frame.

[0115] On receiving frame 1418, AP 1404 may transmit a frame 1420 to AP 1402. In an example, frame 1420 may comprise a response frame. In an example, where frame 1418 is an MRTT frame, frame 1420 may be a CTS frame. After transmitting frame 1420, AP 1404 may communicate with its associated STAs during a time period 1422 of the first duration of the portion of the TXOP allocated to AP 1404. In an example, during time period 1422, AP 1404 may transmit to one or more of its associated STAs downlink frames and / or may trigger one or more of its associated STAs to transmit uplink frames to AP 1404.

[0116] In example 1400, AP 1404 may finish communicating with its associated STAs by the end of the first duration (T2) of the portion of the TXOP allocated to AP 1404.

[0117] In an example, being the TXOP holder, AP 1402 may regain control of the TXOP a SIFS after the end of the first duration (T2). In another example, being the TXOP holder, AP 1402 may regain control of the TXOP a point coordination function (PCF) IFS (PIFS) after the end of the first duration (T2). As such, AP 1402 may transmit a frame 1424 a SIFS or a PIFS after the end of the first duration (T2). In an example, frame 1424 may comprise a control frame, a management frame, a data frame or an action frame. After regaining control of the TXOP, in an example, AP 1402 may communicate with one or more associated STAs and / or re-share the TXOP with other shared APs.

[0118] FIG. 15 illustrates an example 1500 that highlights a problem that may arise in association with an implementation of a CTDMA procedure. As shown in FIG. 15, example 1500 may include AP 1502 and AP 1504. Each of APs 1502 and 1504 may serve one or more associated STAs. AP 1502 and AP 1504 may be members of a multi-AP group. AP 1502 may be a sharing / master AP of the multi-AP group. AP 1504 may be a shared / slave AP of the multi-AP group. In example 1500, it is assumed that AP 1502 and AP 1504 are within communication range of each other.

[0119] As shown in FIG. 15, the procedure may begin with AP 1502 transmitting a frame 1512 after obtaining a TXOP 1510. In an example, before transmitting frame 1512, AP 1502 may be configured to poll AP 1504 about buffered traffic of AP 1504 (including priorities of the buffered traffic of AP 1504) (not shownin FIG. 15). The buffered traffic of AP 1504 may include buffered traffic at AP 1504 for downlink transmission to associated STA(s) of AP 1504 and / or buffered traffic at associated STA(s) of AP 1504 for uplink transmission to AP 1504. In another example, AP 1502 may have information in advance regarding the buffered traffic of AP 1504. AP 1502 may be configured to, when AP 1502 has advance information regarding the buffered traffic of AP 1504, not transmit a polling frame to receive updated information regarding the buffered traffic of AP 1504. Based on AP 1502 being configured not to transmit the polling frame, AP 1502 may not transmit a polling frame before transmitting frame 1512.

[0120] Based on the information about the buffered traffic of AP 1504, AP 1502 may transmit a frame 1512 comprising information regarding AP 1504 being scheduled to communicate within TXOP 1510. In an example, frame 1512 may indicate a scheduled transmission time (e.g., frame 1512 may indicate a duration, denoted T1 in FIG. 15, between frame 1512 and the scheduled transmission time) of a frame 1518 (e.g., a TXOP allocation frame), to be transmitted by AP 1502 to AP 1504, where frame 1518 allocates a portion of TXOP 1510 to AP 1504. In example 1500, frame 1518 may comprise an allocation for AP 1504. The allocation may comprise a first duration (denoted T2 in FIG. 15) of the TXOP allocated to AP 1504. In an example, frame 1518 may comprise an MRTT frame. In an example, the first duration may be indicated in an allocation duration subfield of a user info list field of the MRTT frame. In an example, frame 1512 may further indicate a duration of the portion (e.g., denoted T2 in FIG. 15) of TXOP 1510 to be allocated to AP 1504. In an example, AP 1502 may determine / configure the scheduled transmission time of frame 1518 based on an expected completion time of communication between AP 1502 and its associated STAs. In an example, the scheduled transmission time of frame 1518 may correspond to an exact time of transmission of frame 1518. In another example, the scheduled transmission time of frame 1518 may correspond to an estimate time or an approximate time of transmission of frame 1518.

[0121] In an example, frame 1512 may comprise a schedule announcement frame. In an example, the schedule announcement frame may comprise a trigger frame, such as an MU-RTS trigger frame. In an example, the scheduled transmission time of frame 1518 may be indicated in a duration field, a subfield of a common info field or a subfield of a user info list field of the trigger frame. In an example, the duration of the portion of TXOP 1510 to be allocated to AP 1504 may be indicated in a subfield of a user info list field of the trigger frame.

[0122] On receiving frame 1512, AP 1504 may determine the scheduled transmission time (e.g., T1) of frame 1518 and the duration of the portion of TXOP 1510 to be allocated to AP 1504 in frame 1518. In response to frame 1512, AP 1504 may transmit a frame 1514 to AP 1502. In an example, frame 1514 may comprise a schedule announcement response frame. In another example, frame 1514 may comprise an acknowledgment frame. In another example, frame 1514 may comprise a clear-to-send (CTS) frame.

[0123] In an example (not shown in FIG. 15), after transmitting frame 1514, AP 1504 may not be available to receive frame 1518 (and to respond to frame 1518) during T1 and before the scheduled transmission time of frame 1518. In an example, AP 1504 may not be available during T1 due to AP 1504 communicating with one or more of its associated STAs during T1. In another example, AP 1504 may not be available during T1 as AP 1504 may be in a power save mode until the scheduled transmission time of frame 1518. In another example, AP 1504 may not be available as AP 1504 may not have scheduled its upcoming communications with one or more of its associated STAs before the scheduled transmission time of frame 1518.

[0124] In another example as illustrated in example 1500, AP 1504 may be available to receive frame 1518 (and to respond to frame 1518) during T1 and before the scheduled transmission time of frame 1518. In an example, AP 1504 may be available as AP 1504 may be in a listening mode during T1. As such, AP 1504 may be available for a duration a SIFS after frame 1514 until the scheduled transmission time of frame 1518 (denoted T3 in FIG. 15). In another example, AP 1504 may be available for a portion of a duration less than the duration a SIFS after frame 1514 until the scheduled transmission time of frame 1518 (not shown in FIG. 15).

[0125] After receiving frame 1514, AP 1502 may communicate with one or more of its associated STAs during a time period 1516 of TXOP 1510, before the scheduled transmission time of frame 1518. In an example, during time period 1516, AP 1502 may transmit to one or more of its associated STAs downlink frames and / or may trigger one or more of its associated STAs to transmit uplink frames to AP 1502.

[0126] In example 1500, AP 1502 may finish communicating with its associated STAs before the scheduled transmission time of frame 1518. For example, AP 1502 may finish communicating with its associated STAs at least a duration T4 before the scheduled transmission time of frame 1518. In an example, the duration T4 may be longer than a threshold duration. For example, the threshold duration may be sufficiently long for an AP to communicate with one or more associated STAs.

[0127] In an example, after finishing communicating with its associated STAs during time period 1516, AP 1502 may be configured to wait until the scheduled transmission time of frame 1518 to transmit frame 1518 to AP 1504. As such, in example 1500, despite AP 1504 being available to receive a frame during T4, AP 1502 may not transmit frame 1508 until the end of T4, resulting in the channel being unused and channel resources wasted during T4. Accordingly, when the unused duration before the scheduled transmission time is long enough for an AP to communicate with one or more associated STAs but the unused duration cannot be used, the procedure may cause an inefficient utilization of time and resources.

[0128] After the end of the duration T4, AP 1502 transmits frame 1518 to AP 1504. AP 1504 may transmit a frame 1520 to AP 1502 in response to frame 1518. After transmitting frame 1520, AP 1504 may communicate with one or more of its associated STAs during a time period 1522 of the first duration of the TXOP allocated to AP 1504.

[0129] Embodiments of the present disclosure, as further described below, address the above-described problem. In an aspect, a first AP may receive from a second AP a first frame comprising an indication of whether the second AP is able to receive a second frame before a scheduled transmission time of the second frame, where the second frame triggers the second AP to start communicating using a portion of a TXOP of the first AP. In an embodiment, the first frame may indicate a capability of the second AP, where the capability corresponds to the second AP being capable of receiving the second frame before the scheduled transmission time of the second frame. In another embodiment, the first frame may indicate an operation mode of the second AP, where the operation mode indicates whether the second AP is enabled to receive the second frame before the scheduled transmission time of the second frame. The first AP may transmit to the second AP the second frame before the scheduled transmission time of the second frame, based on the indication indicating that the second AP is able to receive the second frame before the scheduled transmission time of the second frame. As such, time and resources may be utilized more efficiently when an AP shares its TXOP with another AP.

[0130] FIG. 16 illustrates an example 1600 of a procedure according to an embodiment. As shown in FIG. 16, example 1600 may include AP 1602 and AP 1604. Each of APs 1602 and 1604 may serve one or more associated STAs. AP 1602 and AP 1604 may be members of a multi-AP group. AP 1602 may be a sharing / master AP of the multi-AP group. AP 1604 may be a shared / slave AP of the multi-AP group. In example 1600, it is assumed that AP 1602 and AP 1604 are within communication range of each other.

[0131] As shown in FIG. 16, example 1600 may begin with AP 1604 transmitting a frame 1608 to AP 1602. In an embodiment, frame 1608 may comprise an indication of whether AP 1604 is able to receive a frame 1618 before a scheduled transmission time of frame 1618. In an embodiment, frame 1618 may be a frame that triggers AP 1604 to start communicating using a portion of a TXOP of AP 1602. In another embodiment, frame 1618 may indicate an allocation to AP 1604 of a portion of the TXOP of AP 1602. In an embodiment, frame 1608 may indicate a capability of AP 1604, where the capability corresponds to AP 1604 being capable of receiving frame 1618 before the scheduled transmission time of frame 1618 (in other words, AP 1604 supporting the capability of receiving frame 1618 before its scheduled transmission time). In an example, frame 1608 may comprise a medium access control (MAC) capabilities information field indicating the capability of AP 1604. In an example, frame 1608 may comprise a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame.

[0132] In an embodiment, AP 1602 and AP 1604 are members of a multi-AP group, and AP 1604 may transmit frame 1608 to AP 1602 during the coordination of the APs. In an example, AP 1604 may transmit frame 1608 to AP 1602 directly with no request / solicitation from AP 1602. In another example, AP 1604 may transmit frame 1608 to AP 1602 after receiving a request frame from AP 1602 (not shown in FIG. 16). In an example (as shown in FIG. 16), AP 1604 may transmit frame 1608 to AP 1602 before AP 1602obtains a TXOP 1610. In another example (not shown in FIG. 16), AP 1604 may transmit frame 1608 to AP 1602 after AP 1602 obtains TXOP 1610. In another example, AP 1604 may send the indication of capability in frame 1608 to AP 1602 via backhaul.

[0133] After receiving frame 1608, AP 1602 may determine whether AP 1604 is able to receive frame 1618 before the scheduled transmission time of frame 1618. In example 1600, the indication in frame 1608 may indicate that AP 1604 is able to receive frame 1618 before the scheduled transmission time of frame 1618.

[0134] AP 1602 may then transmit a frame 1612 to AP 1604 after obtaining TXOP 1610. In an example, before transmitting frame 1612, AP 1602 may be configured to poll AP 1604 about buffered traffic of AP 1604 (including priorities of the buffered traffic of AP 1604) (not shown in FIG. 16). The buffered traffic of AP 1604 may include buffered traffic at AP 1604 for downlink transmission to associated STA(s) of AP 1604 and / or buffered traffic at associated STA(s) of AP 1604 for uplink transmission to AP 1604. In another example, AP 1602 may have information in advance regarding the buffered traffic of AP 1604. AP 1602 may be configured to, when AP 1602 has advance information regarding the buffered traffic of AP 1604, not transmit a polling frame to receive updated information regarding the buffered traffic of AP 1604. Based on AP 1602 being configured not to transmit the polling frame, AP 1602 may not transmit a polling frame before transmitting frame 1612.

[0135] Based on the information about the buffered traffic of AP 1604, AP 1602 may transmit a frame 1612 comprising information regarding AP 1604 being scheduled to communicate within TXOP 1610. In an example, frame 1612 may indicate a scheduled transmission time (e.g., frame 1612 may indicate a duration, denoted T1 in FIG. 16, between frame 1612 and the scheduled transmission time) of a frame 1618 (e.g., a TXOP allocation frame), to be transmitted by AP 1602 to AP 1604, where frame 1618 allocates a portion of TXOP 1610 to AP 1604. In example 1600, frame 1618 may comprise an allocation for AP 1604. The allocation may comprise a first duration (denoted T2 in FIG. 16) of the TXOP allocated to AP 1604. In an example, frame 1618 may comprise an MRTT frame. In an example, the first duration may be indicated in an allocation duration subfield of a user info list field of the MRTT frame. In an example, frame 1612 may further indicate a duration of the portion (e.g., denoted T2 in FIG. 16) of TXOP 1610 to be allocated to AP 1604. In an example, AP 1602 may determine / configure the scheduled transmission time of frame 1618 based on an expected completion time of communication between AP 1602 and its associated STAs. In an example, the scheduled transmission time of frame 1618 may correspond to an exact time of transmission of frame 1618. In another example, the scheduled transmission time of frame 1618 may correspond to an estimate time or an approximate time of transmission of frame 1618.

[0136] In an example, frame 1612 may comprise a schedule announcement frame. In an example, the schedule announcement frame may comprise a trigger frame, such as an MU-RTS trigger frame. In anexample, the scheduled transmission time of frame 1618 may be indicated in a duration field, a subfield of a common info field, or a subfield of a user info list field of the trigger frame. In an example, the duration of the portion of TXOP 1610 to be allocated to AP 1604 may be indicated in a subfield of a user info list field of the trigger frame.

[0137] On receiving frame 1612, AP 1604 may determine the scheduled transmission time (e.g., T1) of frame 1618 and the duration of the portion of TXOP 1610 to be allocated to AP 1604 in frame 1618. In response to frame 1612, AP 1604 may transmit a frame 1614 to AP 1602. In an example, frame 1614 may comprise a schedule announcement response frame. In another example, frame 1614 may comprise an acknowledgment frame. In another example, frame 1614 may comprise a clear-to-send (CTS) frame.

[0138] In an example (not shown in FIG. 16), after transmitting frame 1614, AP 1604 may not be available to receive frame 1618 (and to respond to frame 1618) during T1 and before the scheduled transmission time of frame 1618. In an example, AP 1604 may not be available during T1 due to AP 1604 communicating with one or more of its associated STAs during T1. In another example, AP 1604 may not be available during T1 as AP 1604 may be in a power save mode until the scheduled transmission time of frame 1618. In another example, AP 1604 may not be available as AP 1604 may not have scheduled its upcoming communications with one or more of its associated STAs before the scheduled transmission time of frame 1618.

[0139] In another example as illustrated in example 1600, AP 1604 may be available to receive frame 1618 (and to respond to frame 1618) during T1 and before the scheduled transmission time of frame 1618, as indicated in frame 1608. In an example, AP 1604 may be available as AP 1604 may be in a listening mode during T1. In an example, AP 1604 may be available after a SIFS of receiving frame 1614 and until the scheduled transmission time of frame 1618 (denoted T3 in FIG. 16). In another example, AP 1604 may be available for a longer or shorter duration than T3. For example, AP 1604 may become available earlier than or later than a SIFS after receiving frame 1614 or may remain available until an earlier time than the scheduled transmission time of frame 1618.

[0140] After receiving frame 1614, AP 1602 may communicate with one or more of its associated STAs during a time period 1616 of TXOP 1610, before the scheduled transmission time of frame 1618. In an example, during time period 1616, AP 1602 may transmit to one or more of its associated STAs downlink frames and / or may trigger one or more of its associated STAs to transmit uplink frames to AP 1602.

[0141] In example 1600, AP 1602 may finish communicating with its associated STA(s) before the scheduled transmission time of frame 1618, with the remaining duration until the scheduled transmission time of frame 1618 being longer than the threshold duration. As mentioned above, the threshold duration may be sufficiently long for an AP to communicate with one or more associated STAs.

[0142] Based on the indication in frame 1608 indicating that AP 1604 is able to receive frame 1618 before the scheduled transmission time of frame 1618, AP 1602 may transmit frame 1618 to AP 1604 after the end of time period 1616 and before the scheduled transmission time of frame 1618. In an embodiment, AP 1602 may transmit frame 1618 a SIFS after the end of time period 1616.

[0143] In example 1600, frame 1618 may comprise an allocation for AP 1604. The allocation may indicate a first duration of a portion (denoted T4 in FIG. 16) of the TXOP allocated to AP 1604. In an example, frame 1618 may comprise an MRTT frame. In an example, the first duration may be indicated in an allocation duration subfield of a user info list field of the MRTT frame. In an embodiment, the first duration (e.g., T4) may be the same duration length as or a different duration length than the allocation duration (e.g., T2) indicated in frame 1612. In an embodiment, the start time of the first duration T4 is before the start time of the allocation duration T2 indicated in frame 1612. In an embodiment, the end time of the first duration T4 is before, the same as, or later than the end time of the allocation duration T2 indicated in frame 1612.

[0144] On receiving frame 1618 before the scheduled transmission time of frame 1618, AP 1604 may transmit a frame 1620 to AP 1602. In an example, frame 1620 may comprise a response frame. In an example, where frame 1618 is an MRTT frame, frame 1620 may be a CTS frame. After transmitting frame 1620, AP 1604 may communicate with its associated STAs during a time period 1622 of the first duration of the portion of the TXOP allocated to AP 1604. In an example, during time period 1622, AP 1604 may transmit to one or more of its associated STAs downlink frames and / or may trigger one or more of its associated STAs to transmit uplink frames to AP 1604.

[0145] In example 1600, AP 1604 may finish communicating with its associated STAs by the end of the first duration (T4) of the portion of the TXOP allocated to AP 1604.

[0146] In an example, being the TXOP holder, AP 1602 may regain control of the TXOP a SIFS after the end of the first duration (T4). In another example, being the TXOP holder, AP 1602 may regain control of the TXOP a point coordination function (PCF) IFS (PIFS) after the end of the first duration (T4). As such, AP 1602 may transmit a frame 1624 a SIFS or a PIFS after the end of the first duration (T4). In an example, frame 1624 may comprise a control frame, a management frame, a data frame or an action frame. After regaining control of the TXOP, in an example, AP 1602 may communicate with one or more associated STAs and / or re-share the TXOP with other shared APs.

[0147] As illustrated in example 1600, by AP 1604 signaling to AP 1602 that AP 1604 is able to receive frame 1618 before the scheduled transmission time of frame 1618, AP 1602 may transmit frame 1618 to AP 1604 as soon as AP 1602 finishes communicating with its associated STA(s) which enables AP 1604 to begin using the shared TXOP earlier improving the utilization of channel resources.

[0148] FIG. 17 illustrates another example 1700 of a procedure according to an embodiment. As shown in FIG. 17, example 1700 may include AP 1702 and AP 1704. Each of APs 1702 and 1704 may serve oneor more associated STAs. AP 1702 and AP 1704 may be members of a multi-AP group. AP 1702 may be a sharing / master AP of the multi-AP group. AP 1704 may be a shared / slave AP of the multi-AP group. In example 1700, it is assumed that AP 1702 and AP 1704 are within communication range of each other.

[0149] As shown in FIG. 17, example 1700 may begin with AP 1704 transmitting frame 1608. As in example 1600, frame 1608 may indicate a capability of AP 1704, where the capability corresponds to AP 1704 being capable of receiving frame 1618 before the scheduled transmission time of frame 1618 (in other words, AP 1704 supporting the capability of receiving frame 1618 before its scheduled transmission time). In an embodiment, frame 1618 may be a frame that triggers AP 1704 to start communicating using a portion of a TXOP of AP 1702. In another embodiment, frame 1618 may indicate an allocation to AP 1704 of a portion of the TXOP of AP 1702. In addition to signaling the capability of receiving frame 1618 before its scheduled transmission time as explained in example 1600, in example 1700, AP 1704 may additionally dynamically enable or disable its operation mode regarding whether AP 1704 is able to receive frame 1618 before the scheduled transmission time of frame 1618.

[0150] In an example, during a TXOP 1710 obtained by AP 1702, AP 1704 may transmit a frame 1711 to AP 1702. In an embodiment, frame 1711 may comprise an indication of whether AP 1704 is able to receive frame 1618 before a scheduled transmission time of frame 1618. In an embodiment, frame 1711 may indicate an operation mode of AP 1704, where the operation mode indicates whether the AP 1704 is enabled to receive frame 1618 before the scheduled transmission time of frame 1618. In an example, frame 1711 may comprise a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame. In another example (not shown in FIG. 17), AP 1702 may transmit frame 1711 to AP 1702 before AP 1702 obtaining TXOP 1710.

[0151] After receiving frame 1711 , AP 1702 may determine whether AP 1704 is able to receive frame 1618 before the scheduled transmission time of frame 1618. In example 1700, the indication in frame 1711 may indicate that AP 1704 is able to receive frame 1618 before the scheduled transmission time of frame 1618. Accordingly, AP 1702 may determine that AP 1702 may transmit frame 1618 to AP 1704 as soon as AP 1702 finishes communicating with its associated STA(s), before the scheduled transmission time of frame 1618.

[0152] After the transmission of frames 1608 and 1711 , the operation illustrated in example 1700 continues with AP 1702 transmitting frame 1612 to AP 1704, in an identical manner to the operation illustrated in example 1600, described above. For the purpose of simplification, the description of this operation as described above with respect to FIG. 16 is not repeated herein and is incorporated herein by reference with respect to FIG. 17. By AP 1704 signaling to AP 1702 that AP 1704 is able to receive frame 1618 before the scheduled transmission time of frame 1618 (e.g., the operation mode may correspond to enabling of receiving frame 1618 before the scheduled transmission time of frame 1618), AP 1702 may transmit frame 1618 to AP 1704 as soon as AP 1702 finishes communicating with its associated STA(s),which enables AP 1704 to begin using the shared TXOP earlier improving the utilization of channel resources.

[0153] FIG. 18 illustrates another example 1800 of a procedure according to an embodiment. In example 1800, after transmitting frame 1608 described above, AP 1704 may transmit a frame 1811 to AP 1702. In an embodiment, frame 1811 may comprise an indication of whether AP 1704 is able to receive a frame 1818 before a scheduled transmission time of frame 1818. In an embodiment, frame 1818 may be a frame that triggers AP 1704 to start communicating using a portion of a TXOP of AP 1702. In another embodiment, frame 1818 may indicate an allocation to AP 1704 of a portion of the TXOP of AP 1702. In an embodiment, frame 1811 may indicate an operation mode of AP 1704, where the operation mode indicates whether the AP 1704 is enabled to receive frame 1818 before the scheduled transmission time of frame 1818. In example 1800, the indication in frame 1811 may indicate that AP 1704 is not able to receive frame 1818 before the scheduled transmission time of frame 1818 (e.g., the operation mode may correspond to disabling of receiving frame 1818 before the scheduled transmission time of frame 1818). As such, on receiving frame 1811 , AP 1702 may determine that AP 1702 may transmit frame 1818 to AP 1704 at or after the scheduled transmission time of frame 1818, but not before the scheduled transmission time of frame 1818.

[0154] After the transmission of frames 1608 and 1811 , the operation illustrated in example 1800 continues with AP 1702 transmitting frame 1612 to AP 1704, in an identical manner to the operation illustrated in example 1600, described above. In response to frame 1612, AP 1704 may transmit frame 1614, described above, to AP 1702. After receiving frame 1614, AP 1702 may communicate with one or more of its associated STAs during a time period 1616. Although time period 1616 may end before the scheduled transmission time of frame 1818 as shown in FIG. 18, AP 1702 may transmit frame 1818 at or after the scheduled transmission time of frame 1818, based on the indication in frame 1811 indicating that AP 1704 is not able to receive frame 1818 before the scheduled transmission time of frame 1818. AP 1704 may respond to frame 1818 by transmitting a frame 1820 to AP 1702. Frame 1820 may be similar to frame 1620 described above. AP 1704 may then communicate with its associated STAs during a time period 1822 of the first duration of the portion of the TXOP allocated to AP 1704. In an example, during time period 1822, AP 1704 may transmit to one or more of its associated STAs downlink frames and / or may trigger one or more of its associated STAs to transmit uplink frames to AP 1704.

[0155] FIG. 19 illustrates another example 1900 of a procedure according to an embodiment. As shown in FIG. 19, example 1900 may include AP 1902 and AP 1904. Each of APs 1902 and 1904 may serve one or more associated STAs. AP 1902 and AP 1904 may be members of a multi-AP group. AP 1902 may be a sharing / master AP of the multi-AP group. AP 1904 may be a shared / slave AP of the multi-AP group. In example 1900, it is assumed that AP 1902 and AP 1904 are within communication range of each other.

[0156] As shown in FIG. 19, example 1900 may begin with AP 1904 transmitting frame 1608. As in example 1600, frame 1608 may indicate a capability of AP 1904, where the capability corresponds to AP 1904 being capable of receiving frame 1618 before the scheduled transmission time of frame 1618 (in other words, AP 1904 supporting the capability of receiving frame 1618 before its scheduled transmission time). In an embodiment, frame 1618 may be a frame that triggers AP 1904 to start communicating using a portion of a TXOP of AP 1902. In another embodiment, frame 1618 may indicate an allocation to AP 1904 of a portion of the TXOP of AP 1902. In addition to signaling the capability of receiving frame 1618 before its scheduled transmission time as explained in example 1600, in example 1900, AP 1704 may additionally dynamically enable or disable its operation mode regarding whether AP 1904 is able to receive frame 1618 before the scheduled transmission time of frame 1618.

[0157] In an example, during a TXOP 1910 obtained by AP 1902, AP 1902 may transmit a frame 1911 to AP 1904. In an embodiment, frame 1911 may solicit an operation mode of AP 1904. In another embodiment, frame 1911 may request that AP 1904 operate in an operation mode in which AP 1904 is enabled to receive frame 1618 before the scheduled transmission time of frame 1618. In response to frame 1911 , AP 1904 may transmit frame 1711 described above to AP 1702. In an embodiment, frame 1711 may comprise an indication of whether AP 1904 is able to receive frame 1618 before a scheduled transmission time of frame 1618. In an embodiment, frame 1711 may indicate the operation mode of AP 1904, where the operation mode indicates whether the AP 1904 is enabled to receive frame 1618 before the scheduled transmission time of frame 1618. In an example, frame 1711 may comprise a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame.

[0158] After receiving frame 1711 , AP 1902 may determine whether AP 1904 is able to receive frame 1618 before the scheduled transmission time of frame 1618. In example 1900, the indication in frame 1711 may indicate that AP 1904 is able to receive frame 1618 before the scheduled transmission time of frame 1618. Accordingly, AP 1902 may determine that AP 1902 may transmit frame 1618 to AP 1904 as soon as AP 1902 finishes communicating with its associated STA(s), before the scheduled transmission time of frame 1618.

[0159] After the transmission of frames 1608, 1911 and 1711, the operation illustrated in example 1900 continues with AP 1902 transmitting frame 1612 to AP 1904, in an identical manner to the operation illustrated in example 1600, described above. For the purpose of simplification, the description of this operation as described above with respect to FIG. 16 is not repeated herein and is incorporated herein by reference with respect to FIG. 19. By AP 1904 signaling to AP 1902 that AP 1904 is able to receive frame 1618 before the scheduled transmission time of frame 1618 (e.g., the operation mode may correspond to enabling of receiving frame 1618 before the scheduled transmission time of frame 1618), AP 1902 may transmit frame 1618 to AP 1904 as soon as AP 1902 finishes communicating with itsassociated STA(s), which enables AP 1904 to begin using the shared TXOP earlier improving the utilization of channel resources.

[0160] FIG. 20 illustrates another example 2000 of a procedure according to an embodiment. As shown in FIG. 20, example 2000 may include AP 2002 and AP 2004. Each of APs 2002 and 2004 may serve one or more associated STAs. AP 2002 and AP 2004 may be members of a multi-AP group. AP 2002 may be a sharing / master AP of the multi-AP group. AP 2004 may be a shared / slave AP of the multi-AP group. In example 2000, it is assumed that AP 2002 and AP 2004 are within communication range of each other.

[0161] As shown in FIG. 20, example 2000 may begin with AP 2004 transmitting frame 1608. As in example 1600, frame 1608 may indicate a capability of AP 2004, where the capability corresponds to AP 2004 being capable of receiving frame 1618 before the scheduled transmission time of frame 1618 (in other words, AP 2004 supporting the capability of receiving frame 1618 before its scheduled transmission time). In an embodiment, frame 1618 may be a frame that triggers AP 2004 to start communicating using a portion of a TXOP of AP 2002. In another embodiment, frame 1618 may indicate an allocation to AP 2004 of a portion of the TXOP of AP 2002. In addition to signaling the capability of receiving frame 1618 before its scheduled transmission time as explained in example 1600, in example 2000, AP 2004 may additionally dynamically enable or disable its operation mode regarding whether AP 2004 is able to receive frame 1618 before the scheduled transmission time of frame 1618.

[0162] After obtaining a TXOP 2010, AP 2002 may then transmit a frame 2012 to AP 2004. In an example, before transmitting frame 2012, AP 2002 may be configured to poll AP 2004 about buffered traffic of AP 2004 (including priorities of the buffered traffic of AP 2004) (not shown in FIG. 20). The buffered traffic of AP 2004 may include buffered traffic at AP 2004 for downlink transmission to associated STA(s) of AP 2004 and / or buffered traffic at associated STA(s) of AP 2004 for uplink transmission to AP 2004. In another example, AP 2002 may have information in advance regarding the buffered traffic of AP 2004. AP 2002 may be configured to, when AP 2002 has advance information regarding the buffered traffic of AP 2004, not transmit a polling frame to receive updated information regarding the buffered traffic of AP 2004. Based on AP 2002 being configured not to transmit the polling frame, AP 2002 may not transmit a polling frame before transmitting frame 2012. In an embodiment, AP 2002 may transmit frame 2012 based on the information about the buffered traffic of AP 2004.

[0163] In an embodiment, frame 2012 may comprise information regarding AP 2004 being scheduled to communicate within TXOP 2010. In an example, frame 2012 may indicate a scheduled transmission time (e.g., frame 2012 may indicate a duration, denoted T1 in FIG. 20, between frame 2012 and the scheduled transmission time) of a frame 1618 (e.g., a TXOP allocation frame), to be transmitted by AP 2002 to AP 2004, where frame 1618 allocates a portion of TXOP 2010 to AP 2004. In example 2000, frame 1618 may comprise an allocation for AP 2004. The allocation may comprise a first duration (denoted T2 in FIG. 20) of the TXOP allocated to AP 2004. In an example, frame 1618 may comprise an MRTT frame.In an example, the first duration may be indicated in an allocation duration subfield of a user info list field of the MRTT frame. In an example, frame 2012 may further indicate a duration of the portion (e.g., denoted T2 in FIG. 20) of TXOP 2010 to be allocated to AP 2004. In an example, AP 2002 may determine / configure the scheduled transmission time of frame 1618 based on an expected completion time of communication between AP 2002 and its associated STAs. In an example, the scheduled transmission time of frame 1618 may correspond to an exact time of transmission of frame 1618. In another example, the scheduled transmission time of frame 1618 may correspond to an estimate time or an approximate time of transmission of frame 1618.

[0164] In an example, frame 2012 may comprise a schedule announcement frame. In an example, the schedule announcement frame may comprise a trigger frame, such as an MU-RTS trigger frame. In an example, the scheduled transmission time of frame 1618 may be indicated in a duration field, a subfield of a common info field, or a subfield of a user info list field of the trigger frame. In an example, the duration of the portion of TXOP 2010 to be allocated to AP 2004 may be indicated in a subfield of a user info list field of the trigger frame.

[0165] In an embodiment, frame 2012 may further comprise a field soliciting an operation mode of AP 2004. In another embodiment, frame 2012 may further comprise a field requesting that AP 2004 operate in a first operation mode in which AP 2004 is enabled to receive frame 1618 before the scheduled transmission time of frame 1618. In an embodiment, where frame 2012 may comprise an MU-RTS trigger frame, the field may be provided in a common info field of the MU-RTS trigger frame.

[0166] On receiving frame 2012, AP 2004 may determine the scheduled transmission time (e.g., T1) of frame 1618 and the duration of the portion of TXOP 2010 to be allocated to AP 2004 in frame 1618. Furthermore, based on the field in frame 2012, AP 2004 may determine whether to enable receiving frame 1618 before the scheduled transmission time of frame 1618. In example 2000, AP 2004 may determine an operation mode to receive frame 1618 before the scheduled transmission time of frame 1618. In response to frame 2012, AP 2004 may transmit a frame 2014 to AP 2002, comprising the operation mode of AP 2004 (e.g., enabled to receive frame 1618 before the scheduled transmission time of frame 1618). In an example, frame 2014 may comprise a schedule announcement response frame. In another example, frame 2014 may comprise an acknowledgment frame. In another example, frame 2014 may comprise a clear-to-send (CTS) frame. In an example, where frame 2014 comprises the CTS frame, the operation mode may be provided in a frame control field of the CTS frame.

[0167] On receiving frame 2014, AP 2002 may determine that AP 2004 is able to receive frame 1618 before the scheduled transmission time of frame 1618.

[0168] After the transmission of frames 1608, 2012 and 2014, the operation illustrated in example 2000 continues with AP 2002 communicating in a time period 1616, in an identical manner to the operation illustrated in example 1600, described above. For the purpose of simplification, the description of thisoperation as described above with respect to FIG. 16 is not repeated herein and is incorporated herein by reference with respect to FIG. 20. By AP 2004 signaling to AP 2002 the indication in frame 2014 that AP 2004 is able to receive frame 1618 before the scheduled transmission time of frame 1618 (e.g., the operation mode may correspond to enabling of receiving frame 1618 before the scheduled transmission time of frame 1618), AP 2002 may transmit frame 1618 to AP 2004 as soon as AP 2002 finishes communicating with its associated STA(s), which enables AP 2004 to begin using the shared TXOP earlier improving the utilization of channel resources.

[0169] FIG. 21 illustrates an example process 2100 according to an embodiment. Example process 2100 is provided for the purpose of illustration only and is not limiting. Example process 2100 may be performed by a first AP, such as AP 1602, AP 1702, AP 1802, AP 1902, or AP 2002, for example.

[0170] As shown in FIG. 21 , process 2100 includes, in step 2110, receiving, by the first AP from a second AP, a first frame comprising an indication of whether the second AP is able to receive a second frame before a scheduled transmission time of the second frame. In an embodiment, the second frame triggers the second AP to start communicating using a portion of a TXOP of the first AP. In an embodiment, the first AP and the second AP are members of a multi-AP group. The first AP may be a sharing / master AP of the multi-AP group. The second AP may be a shared / slave AP of the multi-AP group.

[0171] In an embodiment, the first frame indicates a capability of the second AP, where the capability corresponds to the second AP being capable of receiving the second frame before the scheduled transmission time of the second frame. In an embodiment, the first frame comprises a medium access control (MAC) capabilities information field indicating the capability of the second AP.

[0172] In another embodiment, the first frame indicates an operation mode of the second AP, where the operation mode indicates whether the second AP (which supports the capability) is enabled to receive the second frame before the scheduled transmission time of the second frame. In an embodiment, process 2100 further comprises transmitting, by the first AP to the second AP, a third frame soliciting the operation mode of the second AP. In an embodiment, process 2100 further comprises receiving the first frame in response to the third frame. In another embodiment, process 2100 further comprises transmitting, by the first AP to the second AP, a third frame requesting that the second AP operate in a first operation mode in which the second AP is enabled to receive the second frame before the scheduled transmission time of the second frame. In an embodiment, process 2100 further comprises receiving the first frame in response to the third frame.

[0173] In an embodiment, the first frame comprises a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame.

[0174] In an embodiment, where the second AP is able to receive the second frame before the scheduled transmission time of the second frame, process 2100 further comprises receiving, by the first AP from the second AP, a fourth frame in response to the second frame. In an embodiment, the fourth framecomprises a clear-to-send (CTS) frame. In an embodiment, the second frame indicates an allocation to the second AP of a portion of the transmission opportunity (TXOP) of the first AP. In an embodiment, the second frame comprises a multi-user request-to-send triggered TXOP sharing (MU-RTS TXS) trigger (MRTT) frame.

[0175] In an embodiment, process 2100 further comprises transmitting, by the first AP to the second AP, a fifth frame comprising the scheduled transmission time of the second frame. In an embodiment, where the portion of the TXOP of the first AP is allocated to the second AP, the fifth frame further indicates a duration of the portion of the TXOP of the first AP. In an embodiment, the fifth frame further comprises a field soliciting an operation mode of the second AP. In another embodiment, the fifth frame further comprises a field requesting that the second AP operate in a first operation mode in which the second AP is enabled to receive the second frame before the scheduled transmission time of the second frame. In an embodiment, the fifth frame comprises a schedule announcement frame. In an embodiment, where the fifth frame comprises a multi-user request-to-send (MU-RTS) trigger frame, the field is provided in a common info field of the MU-RTS trigger frame.

[0176] In an embodiment, process 2100 further comprises receiving, by the first AP from the second AP, a sixth frame, in response to the fifth frame, comprising the operation mode of the second AP. In an embodiment, the sixth frame comprises a clear-to-send (CTS) frame. In an embodiment, the operation mode is provided in a frame control field of the CTS frame. In an embodiment, the sixth frame comprises the first frame.

[0177] In an embodiment, process 2100 further comprises transmitting by the first AP to the second AP, the second frame before the scheduled transmission, based on the indication indicating that the second AP is able to receive the second frame before the scheduled transmission time of the second frame.

[0178] FIG. 22 illustrates an example process 2200 according to an embodiment. Example process 2200 is provided for the purpose of illustration only and is not limiting. Example process 2200 may be performed by a first AP, such as AP 1604, AP 1704, AP 1804, AP 1904, or AP 2004, for example.

[0179] As shown in FIG. 22, process 2200 includes, in step 2210, transmitting, by the first AP to a second AP, a first frame comprising an indication of whether the first AP is able to receive a second frame before a scheduled transmission time of the second frame. In an embodiment, the second frame triggers the first AP to start communicating using a portion of a TXOP of the second AP.

[0180] In an embodiment, the first frame indicates a capability of the first AP, where the capability corresponds to the first AP being capable of receiving the second frame before the scheduled transmission time of the second frame. In an embodiment, the first frame comprises a medium access control (MAC) capabilities information field indicating the capability of the first AP. In an embodiment, the first AP and the second AP are members of a multi-AP group. The first AP may be a shared / slave AP of the multi-AP group. The second AP may be a sharing / master AP of the multi-AP group.

[0181] In an embodiment, the first frame indicates an operation mode of the first AP, where the operation mode indicates whether the first AP (which supports the capability) is enabled to receive the second frame before the scheduled transmission time of the second frame. In an embodiment, process 2200 further comprises receiving, by the first AP from the second AP, a third frame soliciting the operation mode of the first AP. In an embodiment, process 2200 further comprises transmitting the first frame in response to the third frame. In another embodiment, process 2200 further comprises receiving, by the first AP from the second AP, a third frame requesting that the first AP operate in a first operation mode in which the first AP is enabled to receive the second frame before the scheduled transmission time of the second frame. In an embodiment, process 2200 further comprises transmitting the first frame in response to the third frame.

[0182] In an embodiment, the first frame comprises a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame.

[0183] In an embodiment, where the first AP is able to receive the second frame before the scheduled transmission time of the second frame, process 2200 further comprises transmitting, by the first AP to the second AP, a fourth frame in response to the second frame. In an embodiment, the fourth frame comprises a clear-to-send (CTS) frame. In an embodiment, the second frame indicates an allocation to the first AP of a portion of the transmission opportunity (TXOP) of the second AP. In an embodiment, the second frame comprises a multi-user request-to-send triggered TXOP sharing (MU-RTS TXS) trigger (MRTT) frame.

[0184] In an embodiment, process 2200 further comprises receiving, by the first AP from the second AP, a fifth frame comprising the scheduled transmission time of the second frame. In an embodiment, where the portion of the TXOP of the second AP is allocated to the first AP, the fifth frame further indicates a duration of the portion of the TXOP of the second AP. In an embodiment, the fifth frame further comprises a field soliciting an operation mode of the first AP. In another embodiment, the fifth frame further comprises a field requesting that the first AP operate in a first operation mode in which the first AP is enabled to receive the second frame before the scheduled transmission time of the second frame. In an embodiment, the fifth frame comprises a schedule announcement frame. In an embodiment, where the fifth frame comprises a multi-user request-to-send (MU-RTS) trigger frame, the field is provided in a common info field of the MU-RTS trigger frame.

[0185] In an embodiment, process 2200 further comprises transmitting, by the first AP to the second AP, a sixth frame, in response to the fifth frame, comprising the operation mode of the first AP. In an embodiment, the sixth frame comprises a clear-to-send (CTS) frame. In an embodiment, the operation mode is provided in a frame control field of the CTS frame. In an embodiment, the sixth frame comprises the first frame.

[0186] In an embodiment, process 2200 further comprises receiving by the first AP from the second AP, the second frame before the scheduled transmission, based on the indication indicating that the first AP is able to receive the second frame before the scheduled transmission time of the second frame.

Claims

CLAIMSWhat is claimed is:

1. A method, comprising: receiving, by a first access point (AP) from a second AP, a first frame comprising an indication of whether the second AP is able to receive a second frame before a scheduled transmission time of the second frame, wherein the second frame triggers the second AP to start communicating using a portion of a transmission opportunity (TXOP) of the first AP; transmitting, by the first AP to the second AP, a third frame indicating the scheduled transmission time of the second frame; and based on the indication indicating that the second AP is able to receive the second frame before the scheduled transmission time of the second frame, transmitting by the first AP to the second AP, the second frame before the scheduled transmission time of the second frame.

2. A method, comprising: receiving, by a first access point (AP) from a second AP, a first frame comprising an indication of whether the second AP is able to receive a second frame before a scheduled transmission time of the second frame, wherein the second frame triggers the second AP to start communicating using a portion of a transmission opportunity (TXOP) of the first AP.

3. The method of claim 2, wherein the first frame indicates a capability of the second AP, and wherein the capability corresponds to the second AP being capable of receiving the second frame before the scheduled transmission time of the second frame.

4. The method of claim 3, wherein the first frame comprises a medium access control (MAC) capabilities information field indicating the capability of the second AP.

5. The method of claim 2, wherein the first frame indicates an operation mode of the second AP, and wherein the operation mode indicates whether the second AP is enabled to receive the second frame before the scheduled transmission time of the second frame.

6. The method of claim 5, further comprising: transmitting, by the first AP to the second AP, a third frame soliciting the operation mode of the second AP; and receiving the first frame in response to the third frame.

7. The method of claim 5, further comprising: transmitting, by the first AP to the second AP, a third frame requesting that the second AP operate in a first operation mode in which the second AP is enabled to receive the second frame before the scheduled transmission time of the second frame; andreceiving the first frame in response to the third frame.

8. The method of any of claims 2-7, wherein the first frame comprises a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame.

9. The method of any of claims 2-8, wherein the second AP is able to receive the second frame before the scheduled transmission time of the second frame, the method further comprising receiving, by the first AP from the second AP, a fourth frame in response to the second frame.

10. The method of any of claims 2-9, wherein the second frame indicates an allocation to the second AP of a portion of the transmission opportunity (TXOP) of the first AP.

11. The method of claim 10, wherein the second frame comprises a multi-user request-to-send triggered TXOP sharing (MU-RTS TXS) trigger (MRTT) frame.

12. The method of any of claims 2-11 , further comprising transmitting, by the first AP to the second AP, a fifth frame comprising the scheduled transmission time of the second frame.

13. The method of claim 12, wherein the portion of the TXOP of the first AP is allocated to the second AP, and wherein the fifth frame further indicates a duration of the portion of the TXOP of the first AP.

14. The method of any of claims 12-13, wherein the fifth frame further comprises a field soliciting an operation mode of the second AP.

15. The method of any of claims 12-13, wherein the fifth frame further comprises a field requesting that the second AP operate in a first operation mode in which the second AP is enabled to receive the second frame before the scheduled transmission time of the second frame.

16. The method of any of claims 12-15, wherein the fifth frame comprises a schedule announcement frame.

17. The method of any of claims 14-16, wherein the fifth frame comprises a multi-user request-to-send (MU- RTS) trigger frame, and wherein the field is provided in a common info field of the MU-RTS trigger frame.

18. The method of claim 14, further comprising receiving, by the first AP from the second AP, a sixth frame, in response to the fifth frame, comprising the operation mode of the second AP.

19. The method of claim 18, wherein the sixth frame comprises a clear-to-send (CTS) frame, and wherein the operation mode is provided in a frame control field of the CTS frame.

20. The method of any of claims 18-19, wherein the sixth frame comprises the first frame.21 . The method of any of claims 2-20, transmitting by the first AP to the second AP, the second frame before the scheduled transmission, based on the indication indicating that the second AP is able to receive the second frame before the scheduled transmission time of the second frame.

22. A method, comprising: transmitting, by a first access point (AP) to a second AP, a first frame comprising an indication of whether the first AP is able to receive a second frame before a scheduled transmission time of thesecond frame, wherein the second frame triggers the first AP to start communicating using a portion of a transmission opportunity (TXOP) of the second AP; receiving, by the first AP from the second AP, a third frame indicating the scheduled transmission time of the second frame; and based on the indication indicating that the first AP is able to receive the second frame before the scheduled transmission time of the second frame, receiving by the first AP from the second AP, the second frame before the scheduled transmission time of the second frame.

23. A method, comprising: transmitting, by a first access point (AP) to a second AP, a first frame comprising an indication of whether the first AP is able to receive a second frame before a scheduled transmission time of the second frame, wherein the second frame triggers the first AP to start communicating using a portion of a transmission opportunity (TXOP) of the second AP.

24. The method of claim 23, wherein the first frame indicates a capability of the first AP, and wherein the capability corresponds to the first AP being capable of receiving the second frame before the scheduled transmission time of the second frame.

25. The method of claim 24, wherein the first frame comprises a medium access control (MAC) capabilities information field indicating the capability of the first AP.

26. The method of claim 23, wherein the first frame indicates an operation mode of the first AP, and wherein the operation mode indicates whether the first AP is enabled to receive the second frame before the scheduled transmission time of the second frame.

27. The method of claim 26, further comprising: receiving, by the first AP from the second AP, a third frame soliciting the operation mode of the first AP; and transmitting the first frame in response to the third frame.

28. The method of claim 26, further comprising: receiving, by the first AP from the second AP, a third frame requesting that the first AP operate in a first operation mode in which the first AP is enabled to receive the second frame before the scheduled transmission time of the second frame; and transmitting the first frame in response to the third frame.

29. The method of any of claims 23-28, wherein the first frame comprises a quality of service (QoS) data frame, a QoS null frame, an action frame, a control frame, or a management frame.

30. The method of any of claims 23-29, wherein the first AP is able to receive the second frame before the scheduled transmission time of the second frame, the method further comprising transmitting, by the first AP to the second AP, a fourth frame in response to the second frame.31 . The method of any of claims 23-30, wherein the second frame indicates an allocation to the first AP of a portion of the transmission opportunity (TXOP) of the second AP.

32. The method of claim 31 , wherein the second frame comprises a multi-user request-to-send triggered TXOP sharing (MU-RTS TXS) trigger (MRTT) frame.

33. The method of any of claims 23-32, further comprising receiving, by the first AP from the second AP, a fifth frame comprising the scheduled transmission time of the second frame.

34. The method of claim 33, wherein the portion of the TXOP of the second AP is allocated to the first AP, and wherein the fifth frame further indicates a duration of the portion of the TXOP of the second AP.

35. The method of any of claims 33-34, wherein the fifth frame further comprises a field soliciting an operation mode of the first AP.

36. The method of any of claims 33-35, wherein the fifth frame further comprises a field requesting that the first AP operate in a first operation mode in which the first AP is enabled to receive the second frame before the scheduled transmission time of the second frame.

37. The method of any of claims 33-36, wherein the fifth frame comprises a schedule announcement frame.

38. The method of any of claims 35-37, wherein the fifth frame comprises a multi-user request-to-send (MU- RTS) trigger frame, and wherein the field is provided in a common info field of the MU-RTS trigger frame.

39. The method of claim 35, further comprising transmitting, by the first AP to the second AP, a sixth frame, in response to the fifth frame, comprising the operation mode of the first AP.

40. The method of claim 39, wherein the sixth frame comprises a clear-to-send (CTS) frame, and wherein the operation mode is provided in a frame control field of the CTS frame.41 . The method of any of claims 39-40, wherein the sixth frame comprises the first frame.

42. The method of any of claims 23-41 , receiving by the first AP from the second AP, the second frame before the scheduled transmission, based on the indication indicating that the first AP is able to receive the second frame before the scheduled transmission time of the second frame.

43. A device comprising: one or more processors; and memory storing instructions that, when executed by the one or more processors, cause the device to perform a method according to any of claims 1-42.

4. A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors, cause the one or more processors to perform a method according to any of claims 1-

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