Overlapping basic service set sounding termination

Abstract

A first access point (AP) transmits, to a second AP, a first frame soliciting whether the second AP wishes to participate in a joint null data packet (NDP) sounding sequence for a coordinated beamforming (Co-BF) transmission. The first AP receives, from the second AP, a second frame indicating whether the second AP wishes to participate in the joint NDP sounding sequence. After receiving the second frame, the first AP transmits, to the second AP, an NDP announcement (NDPA) frame initiating the joint NDP sounding sequence. The first AP transmits a first NDP after a short interframe space (SIFS) from the NDPA frame. The first AP transmits, to a first station (STA), a beamforming report poll (BFRP) trigger frame after transmitting the first NDP. The first AP receives, from the first STA, a beamforming report.

Description

Docket No.: 24-3066PCTTITLE OVERLAPPING BASIC SERVICE SET SOUNDING TERMINATION CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 739,849, filed December 30, 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 extremely high throughput (EHT) sounding null data PPDU (NDP).

[0011] FIG. 9 illustrates an example null data PPDU (NDP) announcement (NDPA) frame format.

[0012] FIG. 10 illustrates an example control frame which may be used as a trigger frame.

[0013] FIG. 11 illustrates an example EFIT compressed beamforming / channel quality indication (CQI) frame.

[0014] FIG. 12 illustrates an example of a trigger based (TB) sounding sequence.

[0015] FIG. 13 illustrates an example management frame which may be used as an action frame.

[0016] FIG. 14 illustrates an example of sequential NDP sounding.

[0017] FIG. 15 illustrates an example of joint NDP sounding.

[0018] FIG. 16 illustrates an example multi-AP downlink data transmission phase.

[0019] FIG. 17 illustrates an example multi-AP uplink data transmission phase.

[0020] FIG. 18 illustrates an example of NDP sounding procedures

[0021] FIG. 19 further illustrates a problem that may arise in NDP sounding procedures.

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

[0023] FIG. 21 illustrates an example of another procedure according to an embodiment.

[0024] FIG. 22 illustrates an example of a further procedure according to an embodiment.

[0025] FIG. 23 illustrates an example of a further procedure according to an embodiment.Docket No.: 24-3066PCT

[0026] FIG. 24 illustrates an example of a further procedure according to an embodiment.

[0027] FIG. 25 illustrates another example process according to an embodiment.

[0028] FIG. 26 illustrates another example process according to an embodiment.DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] 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.Docket No.: 24-3066PCT

[0032] 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.

[0033] 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.

[0034] In this disclosure, parameters (or equally called, fields, or Information elements: IBs) 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.

[0035] 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 of the three possible features, with any two of the three possible features or with three of the three possible features.Docket No.: 24-3066PCT

[0036] 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.

[0037] FIG. 1 illustrates example wireless communication networks in which embodiments of the present disclosure may be implemented.

[0038] 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 infra-structure network 102 may include one or more basic service sets (BSSs) 110 and 120 and a distribution system (DS) 130.

[0039] 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.

[0040] 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).

[0041] 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.

[0042] 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 aDocket No.: 24-3066PCTplurality 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).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] A frequency band may include one or more sub-bands or frequency channels. For example, PPDUs conforming to the IEEE 802.11n, 802.11ac, 802.11ax and / or 802.11be 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 be transmitted over physical channels having bandwidths of 40 MHz, 80 MHz, 160 MHz, or 520 MHz by bonding together multiple 20 MHz channels.

[0047] 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 transceiverDocket No.: 24-3066PCT240. 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.

[0048] 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.

[0049] 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.

[0050] 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

[0051] 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.

[0052] 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.

[0053] 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 channelDocket No.: 24-3066PCTthat 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.Docket No.: 24-3066PCT

[0058] 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 co-channel 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.

[0059] 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.

[0060] 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 suffers from 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.Docket No.: 24-3066PCT

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 same portion 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.

[0065] 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 andDocket No.: 24-3066PCT502-2. 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] CSR is one type of multi-AP coordination that may be supported by AP 502-1 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 overlapping basic service set (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 example 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 aDocket No.: 24-3066PCTpolling 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.

[0070] 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.

[0071] 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.

[0072] 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 may include 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.

[0073] 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, forDocket No.: 24-3066PCTexample. 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).

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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 ofthe multi-AP group, before exchange of data frames between APs and STAs within the multi-AP group.

[0078] 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.

[0079] FIG. 7 illustrates an example 700 of a multi-AP sounding phase. Example 700 may be an example of multi-AP sounding phase 614. As shown in FIG. 7, example 700 may include a master AP 702 and a slaveDocket No.: 24-3066PCTAP 704 of a multi-AP group. Example 700 may further include a STA 706 associated with AP 702 and a STA 708 associated with AP 704.

[0080] As shown in FIG. 7, example 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, example 700 may include a first subphase 710 and a second subphase 712.

[0081] 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.

[0082] 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.

[0083] FIG. 8 illustrates an EHT sounding NDP 800. EHT sounding NDP 800 may be used for sounding to one or more users. EHT sounding NDP 800 may be a variant of an EHT multi-user (MU) PPDU used by STAs conforming to the IEEE 802.11 be standard amendment. An EHT sounding NDP may be indicated by setting a "PPDU Type and Compression Mode” field of a U-SIG field of an EHT PPDU to 1, an EHT-SIG MCS field of an EHT-SIG field of the EHT PPDU to 0, and a "Number of EHT-SIG Symbols” field to 0 in the U-SIG field of the EHT PPDU. In an example, an ultra high reliability (UHR) NDP used by STAs conforming to the IEEE 802.11 bn standard amendment may use the same, or similar, structure as EHT sounding NDP 800 In an example, a UHR NDP may have the same fields as the EHT sounding NDP but with a PHY version ID in the U-SIG field indicating UHR instead of EHT. In addition, the EHT-SIG field as shown in FIG. 8 may be replaced by a UHR-SIG field which may have different carried information compared to the EHT-SIG field but with the same modulation and transmission procedure. Further, CBF may use an EHT sounding NDP 800, a UHR NDP format (to the extent a UHR NDP format differs from an EHT format), or a high efficiency (HE) NDP format used by STAs conforming to the IEEE 802.11ax.Docket No.: 24-3066PCT

[0084] As shown in FIG.8, EHT sounding NDP 800 comprises a non-high throughput (non-HT) short training field (L-STF), a non-HT long training field (L-LTF), a non-HT signal field (L-SIG), a repeated non-HT signal field (RL-SIG), a universal signal field (U-SIG), an EHT signal field (EHT-SIG), an EHT short training field (EHT-STF), an EHT long training field (EHT-LTF), and a packet extension (PE) field.

[0085] The L-STF, L-LTF, L-SIG, RL-SIG, U-SIG, and EHT-SIG fields may be referred to as pre-EHT modulated fields, while the EHT-STF, EHT-LTF, and PE fields may be referred to as EHT modulated fields.

[0086] The EHT-LTF field may comprise one or more EHT-LTF symbols. The number of EHT-LTF symbols may be indicated in a "number of EHT-LTF symbols” field of the EHT-SIG field.

[0087] The EHT-LTF field provides a means for a receiver of EHT sounding NDP 800 to estimate the MIMO channel between the set of constellation mapper outputs and the receive chains. A spatial stream may refer to one or more symbols that may be transmitted over multiple spatial dimensions that are created by the use of multiple antennas at both ends of a communications link In an EHT MU PPDU, the transmitter provides training for NSS,r, total spatial streams used for the transmission of PSDU(s) in an r-th resource unit (RU). In an EHT TB PPDU, the transmitter of user u in the r-th RU provides training for NSS,r,u spatial streams used for the transmission of the PSDU. For each subcarrier in the r-th RU, the MIMO channel that can be estimated is an NRX x NSS.r, total matrix.

[0088] An EHT transmission has a preamble that contains EHT-LTF symbols, where the data tones of each EHT-LTF symbol are multiplied by entries belonging to a matrix PEHT-LTF, to enable channel estimation at the receiver. When single stream pilots are used in 2 x or 4 x EHT-LTF, the pilot subcarriers of each EHT-LTF symbol are multiplied by the entries of a matrix REHT-LTF to allow receivers to track phase and / or frequency offset during MIMO channel estimation using the EHT-LTF. Single stream pilots are used for all spatial multiplexing modes (both UL and DL) defined in EHT except when 1 x EHT-LTF is used. PEHT-LTF is defined such that each modulated spatial stream in an RU is active on all subcarriers in that RU for which the EHT-LTF sequence takes a nonzero value.

[0089] In an EHT MU PPDU, the number of EHT-LTF symbols NEHT-LTF is indicated in the EHT-SIG field. In a non-OFDMA EHT MU PPDU or an EHT sounding NDP, the initial number of EHT-LTF symbols, initial NEHT-LTF, is a function of the total number of spatial streams NSS.

[0090] In order to improve the MIMO channel estimation for the reception of a non-OFDMA EHT MU PPDU or an EHT sounding NDP, the number of EHT-LTFs may be larger than the initial number of EHT-LTFs determined by the total number of spatial streams. If additional EHT-LTFs are used, then the total number of EHT-LTFs (which is signaled separately from NSS) can be no more than twice the initial number of EHT-LTFs determined by the number of spatial streams and chosen from the set {2 4 8}. Supporting additional EHT-LTFs is optional for the receiver, which is indicated by the maximum number of supported EHT-LTFs subfield of the EHT PHY capabilities information field.Docket No.: 24-3066PCT

[0091] FIG. 9 illustrates an example NDPA frame 900. As shown in FIG. 9, example NDPA frame 900 includes a Frame Control field, a Duration field, a receiver address (RA) field, a transmitter address (TA) field, a Sounding Dialog Token field, a STA Info List field, and a frame check sequence (FCS).

[0092] The Frame Control field indicates a type (NDPA) of NDPA frame 900. The Duration field indicates a duration of NDPA frame 900. The RA field indicates an address of one or more receiver of NDPA frame 900. The TA field indicates an address of a transmitter of NDPA frame 900. The TA field is set to the address of a STA transmitting NDPA frame 900 or a bandwidth signaling TA of the STA transmitting NDPA frame 900.

[0093] The Sounding Dialog Token field includes an NDP Announcement Variant subfield and a Sounding Dialog Token Number subfield. Based on its value, the NDP Announcement Variant subfield indicates a variant of NDPA frame 900 from among four variants: a VHT NDP Announcement frame, an HE NDP Announcement frame, a Ranging NDP Announcement frame, and an EHT NDP Announcement frame. The NDP Announcement Variant subfield is set to 2 to identify NDPA frame 900 as an HE NDP Announcement frame. The NDP Announcement Variant subfield is set to 3 to identify NDPA frame 900 as an EHT NDP Announcement frame. In the HE NDP Announcement and the EHT NDP Announcement frame, the Duration, RA, and TA fields are set as in the VHT NDP Announcement frame. The Sounding Dialog Token Number subfield contains a value selected by the transmitter of NDPA frame 900 to identify NDPA frame 900.

[0094] The STA Info List field contains one or more STA Info fields. The STA Info List field includes at most one STA Info field per STA to which NDPA frame 900 is addressed in the RA field. If the STA Info List field includes only one STA Info field with a value less than 2008 in an AID11 subfield, then in the case that NDPA frame 900 is a VHT, HE, or EHT NDP Announcement frame the RA field is set to the address of the STA indicated in the only STA Info field of NDPA frame 900. If STA Info List field includes more than one STA Info field with a value less than 2008 in the AID11 subfield, then the RA field is set to a broadcast address.

[0095] A STA Info field may include an AID 11 subfield, a Partial Bandwidth (BW) Info subfield, an Nc Index subfield, a Feedback Type and Ng subfield, a Disambiguation subfield, and a Codebook Size subfield.

[0096] The AID11 subfield contains an identifier of a STA expected to process an EHT sounding NDP that follows NDPA frame 900 and to prepare sounding feedback based on the EHT sounding NDP.

[0097] The Partial BW Info subfield includes a Resolution subfield and a Feedback Bitmap subfield. The Resolution subfield indicates a resolution bandwidth for each bit in the Feedback Bitmap subfield. The Feedback Bitmap subfield indicates whether feedback is requested for each resolution bandwidth and is ordered from a lowest frequency to a highest frequency, followed by zeros. A bit in the Feedback Bitmap subfield set to 1 indicates that feedback is requested for the corresponding frequency with the resolution bandwidth. For example, a first position bit (B1) of the Feedback Bitmap subfield set to 1 indicates a request for feedback for the lowest frequency at the indicated resolution bandwidth.Docket No.: 24-3066PCT

[0098] When NDPA frame 900 is an EHT NDP Announcement frame and the bandwidth of a PPDU carrying NDPA frame 900 is less than 320 MHz, bit BO of the Resolution subfield is set to 0 to indicate a resolution bandwidth of 20 MHz.

[0099] When NDPA frame 900 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 900 is equal to 20 MHz, the first position bit (B1) of the Feedback Bitmap subfield is set to 1 to indicate a request for feedback on a 242-tone RU. Bits B2-B8 of the Feedback Bitmap subfield are set to 0.

[0100] When NDPA frame 900 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 900 is equal to 40 MHz, the first position bit (B1) and the second position bit (B2) of the Feedback Bitmap subfield respectively indicate a request for feedback on a respective 242-tone RU (of two 242-tone RUs) from lower frequency to higher frequency. Bits B3-B8 of the Feedback Bitmap subfield are set to 0.

[0101] When NDPA frame 900 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 900 is equal to 80 MHz, bits B1-B4 of the Feedback Bitmap subfield set to 1 indicate a request for feedback on a 996-tone RU; otherwise, bits B1-B4 respectively indicate a request for feedback on a respective 242-tone RU (of four 242-tone RUs) from lower frequency to higher frequency. Bits B5-B8 of the Feedback Bitmap subfield are set to 0.

[0102] When NDPA frame 900 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 900 is equal to 160 MHz, bits B1-B4 of the Feedback Bitmap subfield set to 1 indicate a request for feedback on a lower 996-tone RU (among a lower 996-tone RU and an upper 996-tone RU); otherwise, bits B1-B4 respectively indicate a request for feedback on a respective 242-tone RU (of four 242-tone RUs) from lower frequency to higher frequency in the lower 80 MHz of the 160 MHz PPDU bandwidth. Similarly, bits B5-B8 set to 1 indicate a request for feedback on the upper 996-tone RU (among the lower 996-tone RU and the upper 996-tone RU); otherwise, bits B5-B8 respectively indicate a request for feedback on a respective 242-tone RU (of the four 242-tone RUs) from lower frequency to higher frequency in the upper 80 MHz of the 160 MHz.

[0103] When NDPA frame 900 is an EHT Announcement frame and the bandwidth of the PPDU carrying NDPA frame 900 is equal to 320 MHz, bit B0 of the Resolution subfield set to 1 indicates a resolution bandwidth of 40 MHz. When bits B1 and B2 of the Feedback Bitmap subfield are both set to 1, they indicate a request for feedback request on a lowest 996-tone RU (among a lowest 996-tone RU, a second lowest 996-tone RU, a third lowest 996-tone RU, and a highest 996-tone RU); otherwise, bits B1 and B2 respectively indicate a request for feedback on a respective 484-tone (of two 484-tone RUs) from lower frequency to higher frequency in a lowest 80 MHz of the 320 MHz PPDU bandwidth. When bits B3 and B4 of the Feedback Bitmap subfield are both set to 1 , they indicate a request for feedback on the second lowest 996-tone RU; otherwise, bits B3 and B4 indicate respectively a request for feedback on a respective 484-tone RU (of twoDocket No.: 24-3066PCT484-tone RUs) from lower frequency to higher frequency in a second lowest 80 MHz of the 320 MHz PPDU bandwidth. When bits B5 and B6 of the Feedback Bitmap subfield are both set to 1, they indicate a request for feedback on the third lowest 996-tone RU; otherwise, B5 and B6 respectively indicate a request for feedback on respective 484-tone RU (of two 484-tone RUs) from lower frequency to higher frequency in a third lowest 80 MHz of the 320 MHz PPDU bandwidth. When bits B7 and B8 of the Feedback Bitmap subfield are both set to 1 , they indicate a request for feedback on the highest 996-tone RU; otherwise, bits B7 and B8 indicate respectively a request for feedback on respective 484-tone RU (of two 484-tone RUs) from lower frequency to higher frequency in a highest 80 MHz of the 320 MHz PPDU bandwidth. The feedback tone set for each 484-tone RU is composed of the feedback tone sets of the two 242-tone RUs overlapping with the 484-tone RU.

[0104] Returning to FIG. 9, the Nc Index subfield indicates the number of columns of a beamforming feedback matrix (reported in a compressed beamforming report in response to NDPA frame 900) minus 1 , if the feedback is SU feedback or MU feedback; and indicates the number of spatial streams of a CQI report (reported in a CQI report in response to NDPA frame 900) minus 1, if the feedback is CQI feedback.

[0105] The “Feedback Type and Ng’’ subfield indicates a feedback type and a subcarrier grouping, Ng, to be used by the STA generating the sounding feedback based on the EHT sounding NDP that follows NDPA frame 900. The feedback type may be SU feedback, MU feedback, or CQI feedback. The subcarrier grouping, Ng, indicates the number (e.g., 4, 16) of adjacent subcarriers that are to be grouped in a beamforming report. When grouping is used, a single beamforming feedback matrix is reported for each group of Ng adjacent subcarriers. The “Feedback Type and Ng’’ subfield and the Codebook Size subfield for EHT trigger-based (TB) sounding are the same as for HE TB sounding. The “Feedback Type and Ng” and the Codebook Size subfields for EHT non-TB sounding are the same as for HE non-TB sounding.

[0106] If NDPA frame 900 is an EHT NDP Announcement frame with more than one STA Info field that contains a value less than 2008 in the AID11 subfield, the RA field indicates a broadcast address, and the Nc Index subfield may be set as follows:— If the “Feedback Type and Ng” subfield and the Codebook Size subfield indicate single user (SU) or multi-user (MU), the Nc Index subfield indicates the number of columns in the compressed beamforming feedback matrix minus 1, Nc-1 . Nc Index subfield values above 7 are reserved.— If the “Feedback Type and Ng” subfield and the Codebook Size subfield indicate channel quality information (CQI), the Nc Index subfield indicates the number of spatial streams in the CQI report minus 1, Nc-1. Nc Index subfield values above 7 are reserved.

[0107] If NDPA frame 900 is an EHT NDP Announcement frame with a single STA Info field that contains a value less than 2008 in the AID11 subfield, the RA field indicates an individual address, and the Nc index subfield is reserved.Docket No.: 24-3066PCT

[0108] In an example, a UHR NDP Announcement frame used by STAs conforming to the IEEE 802.11 bn standard amendment may use the same, or similar, structure as NDPA frame 900. In an example, a UHR NDP Announcement frame may have the same fields as the EHT NDP Announcement frame but with an NDPA version field indicating that the EHT NDP Announcement frame is followed by a UHR Sounding NDP instead of an EHT Sounding NDP, and that the UHR NDP Announcement frame is soliciting a UHR Compressed Beamforming / CQI frame instead of an EHT Compressed Beamforming / CQI frame as discussed below.

[0109] FIG. 10 illustrates an example format of a trigger frame 1000. Trigger frame 1000 may be used by an AP to allocate resources for and solicit one or more TB PPDU transmissions from one or more STAs. Trigger frame 1000 may also carry other information required by a responding STA to transmit a TB PPDU to the AP.

[0110] As shown in FIG. 10, trigger frame 1000 includes 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 an FCS field.

[0111] The Frame Control field includes the following subfields: protocol version, type, subtype, To DS, From DS, more fragments, retry, power management, more data, protected frame, and +HTC.

[0112] The Duration field indicates various contents depending on frame type and subtype and the QoS capabilities of the sending STA. For example, in control frames of the power save poll (PS-Poll) subtype, the Duration field carries an association identifier (AID) of the STA that transmitted the frame in the 14 least significant bits (LSB), and the 2 most significant bits (MSB) are both set to 1. In other frames sent by STAs, the Duration field contains a duration value (in microseconds) which is used by a recipient to update a network allocation vector (NAV).

[0113] The RA field is the address of the STA that is intended to receive the incoming transmission from the transmitting station . The TA field is the address of the STA transmitting trigger frame 1000 if trigger frame 1000 is addressed to STAs that belong to a single BSS. The TA field is the transmitted BSSID if trigger frame 1000 is addressed to STAs from at least two different BSSs of the multiple BSSID set.

[0114] The Common Info field specifies a trigger frame type of trigger frame 1000, a transmit power of trigger frame 1000 in dBm, and several key parameters of a TB PPDU that is transmitted by a STA in response to trigger frame 1000. The trigger frame type of a trigger frame used by an AP to receive QoS data using UL MU operation is referred to as a basic trigger frame. A non-EHT non-AP HE STA interprets the Common Info field as HE variant. A non-AP EHT STA interprets the Common Info field as HE variant if B54 and B55 in the Common Info field are equal to 1; and interprets the Common Info field as EHT variant otherwise. The HE variant Common Info field and the EHT variant Common Info field use the same encoding method for the Trigger Type, UL Length, More TF, CS Required, LDPC Extra Symbol Segment, AP TX Power, Pre-FEC Padding Factor, PE Disambiguity, and Trigger Dependent Common Info subfields.Docket No.: 24-3066PCT

[0115] The User Info List field contains zero or more User Info fields. There are three variants for the User Info field, which are the Special User Info field, the EHT variant User Info field, and the HE variant User Info field.

[0116] The Special User Info field is a User Info field that does not carry the user specific information but carries the extended common information not provided in the Common Info field. If the Special User Info field is included in the Trigger frame, then the Special User Info Field Flag subfield of the EHT variant Common Info field is set to 0, otherwise it is set to 1 . The Special User Info field is identified by an AID12 value of 2007 and is optionally present in a Trigger frame that is generated by an EHT AP. The Special User Info field, if present, is located immediately after the Common Info field of the Trigger frame and carries information for the U-SIG field of a solicited EHT TB PPDU. The PHY Version Identifier subfield indicates the PHY version of the solicited TB PPDU that is not an HE TB PPDU. The PHY Version Identifier subfield is set to 0 for EHT. Other values from 1 to 7 are reserved. The UL Bandwidth (BW) Extension subfield, together with the UL BW subfield in the Common Info field, indicates the bandwidth of the solicited TB PPDU from the addressed EHT STA (i.e., the bandwidth in the U-SIG field of the EHT TB PPDU). The EHT Spatial Reuse n subfield carries the values to be included in the corresponding Spatial Reuse n subfield in the U-SIG field of the EHT TB PPDU. The U-SIG Disregard And Validate subfield carries the values to be included in the Disregard and Validate subfields of the U-SIG field of the solicited EHT TB PPDUs. The presence and length of the Trigger Dependent User Info subfield in the Special User Info field depends on the variant of the Trigger frame.

[0117] The EHT variant User Info field contains a User Info field per STA addressed in trigger frame 1000. The per STA User Info field includes, among others, an AID12 subfield, an RU Allocation subfield, a UL FEC Coding Type subfield, a UL EHT-MCS subfield, a Reserved subfield, a Spatial Stream (SS) Allocation / RA-RU information subfield, a UL Target Receive Power subfield, and a Power Save (PS) 160 subfield to be used by a STA in a TB PPDU transmitted in response to trigger frame 1000, and a Trigger Dependent User Info subfield. The RU Allocation subfield in an EHT variant User Info field in a Trigger frame that is not an MU-RTS Trigger frame, along with the UL BW subfield in the Common Info field, the UL BW Extension subfield in the Special User Info field, and the PS160 subfield in the EHT variant User Info field, identifies the size and the location of the RU or MRU. The values of PS160 subfield and B0 of RU Allocation subfield indicate the 80 MHz frequency subblock in which the RU or MRU is located for 26-tone RU, 52-tone RU, 106-tone RU, 242-tone RU, 484-tone RU, 996-tone RU, 52+26-tone RU, and 106+26-tone RU. The values of PS160 subfield indicates the 160 MHz segment in which the RU or MRU is located for 20996-tone RU, 996+484-tone MRU, and 996+484+242-tone MRU. The UL FEC Coding Type subfield of the User Info field indicates the code type of the solicited EHT TB PPDU. The UL FEC Coding Type subfield is set to 0 to indicate BCC and set to 1 to indicate LDPC. The UL EHT-MCS subfield of the User Info field indicates the EHT-MCS of the solicited EHT TB PPDU. The SS Allocation subfield of the EHT variant User Info field indicates the spatial streams of the solicited EHT TB PPDU. The UL Target Receive Power subfield indicatesDocket No.: 24-3066PCTthe expected receive signal power, measured at the AP’s antenna connector and averaged over the antennas, for the EHT portion of the EHT TB PPDU transmitted on the assigned RU. The Trigger Dependent User Info subfield can be used by an AP to specify a preferred access category (AC) per STA. The preferred AC sets the minimum priority AC traffic that can be sent by a participating STA. The AP determines the list of participating STAs, along with the BW, MCS, RU allocation, SS allocation, Tx power, preferred AC, and maximum duration of the TB PPDU per participating STA. The RA-RU Information subfield is reserved in the EHT variant User Info field.

[0118] The Padding field is optionally present in management frame 400 to extend the frame length to give recipient STAs enough time to prepare a response for transmission one SIFS after the frame is received. The Padding field, if present, is at least two octets in length and is set to all 1s.

[0119] The FCS field is used by a STA to validate a received frame and to interpret certain fields from the MAC headers of a frame.

[0120] FIG. 11 illustrates an example EHT compressed beamforming / CQI frame 1100. EHT Compressed Beamforming / CQI frame 1100 may be an Action No Ack frame of category EHT. The Action field of an EHT Compressed Beamforming / CQI frame contains the information including a Category field, an EHT Action field, an EHT MIMO Control field, an EHT Compressed Beamforming Report field, an EHT MU Exclusive Beamforming Report field, an EHT CQI Report.

[0121] The Category field is set to a value of 36 for EHT category.

[0122] The EHT Action field, in the octet immediately after the Category field, differentiates the EHT Action frame formats. The EHT Action field values associated with each frame format within the EHT category. The EHT Action field is set to a value of 0 for EHT Compressed Beamforming / CQI.

[0123] The EHT MIMO Control field comprises a Nc Index subfield, a Nr Index subfield, a BW subfield, a Grouping subfield, a Codebook Information subfield, a Feedback Type subfield, a Remaining Feedback Segments subfield, a First Feedback Segment subfield, a Partial BW Info subfield, a Sounding Dialog Token Number subfield.

[0124] In an EHT Compressed Beamforming / CQI frame not carrying all or part of an EHT compressed beamforming / CQI report, the Nc Index, Nr Index, BW, Grouping, Codebook Information, Feedback Type, and Sounding Dialog Token Number subfields are reserved, the First Feedback Segment subfield is set to 0, and the Remaining Feedback Segments subfield is set to 7.

[0125] The EHT Compressed Beamforming Report field carries the average SNR of each spatial stream and compressed beamforming feedback matrices for use by a transmit beamformer to determine steering matrices for explicit feedback beamforming.

[0126] The EHT MU Exclusive Beamforming Report field carries explicit feedback in the form of delta SNRs. The information in the EHT Compressed Beamforming Report field and the EHT MU Exclusive BeamformingDocket No.: 24-3066PCTReport field can be used by the transmit MU beamformer to determine the steering matrices for DL MU-MIMO.

[0127] The EHT CQI Report field carries the per-RU average SN Rs of each spatial stream, where each per-RU average SNR is the arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested.

[0128] The EHT CQI Report field contains EHT CQI report information. EHT CQI Report information is included in the EHT compressed beamforming / CQI report if the Feedback Type subfield in the EHT MIMO Control field indicates CQI feedback.

[0129] The presence and contents of the EHT Compressed Beamforming Report field, EHT MU Exclusive Beamforming Report field, and EHT CQI Report field are dependent on the values of the Feedback Type subfield of the EHT MIMO Control field.

[0130] A Vendor Specific element is not present in the EHT Compressed Beamforming / CQI frame.

[0131] A beamforming report poll (BFRP) trigger frame may be a variation of the trigger frame 1000 illustrated in FIG. 10, above. In an example, the Trigger Dependent Common Info subfield is not present in the BFRP Trigger frame. The Trigger Dependent User Info subfield of the BFRP Trigger frame may include a Feedback Segment Retransmission Bitmap subfield. The Feedback Segment Retransmission Bitmap subfield may indicate the requested feedback segments of an HE or EHT compressed beamforming / CQI report. If the bit in position n (n=0 for LSB and n=7 for MSB) is 1, then the feedback segment with the Remaining Feedback Segments subfield in the HE MIMO Control field equal to n is requested. If the bit in position n is 0, then the feedback segment with the Remaining Feedback Segments subfield in the HE MIMO Control field equal to n is not requested.

[0132] If a BFRP Trigger frame solicits an EHT compressed beamforming / CQI report, all of the bits in the Feedback Segment Retransmission Bitmap subfield are set to 1.

[0133] In an example, a UHR compressed beamforming / CQI frame used by STAs conforming to the IEEE 802.11bn standard amendment may use the same, or similar, structure as the EHT compressed beamforming / CQI frame 1100. In an example, a UHR compressed beamforming / CQI frame may have the same fields as the EHT compressed beamforming / CQI frame 1100 but with a UHRAction field indicating that the EHT compressed beamforming / CQI frame 1100 is a feedback frame in accordance to a previously received UHR NDP Announcement frame and a UHR Sounding NDP.

[0134] FIG. 12 illustrates an example 1200 of a trigger based (TB) sounding sequence. As shown in FIG.12, example 1200 includes an AP 1202 and STAs 1204 and 1206. Example 1200 may begin with AP 1202 initiating the TB sounding sequence by transmitting an NDPA frame 1210 to STAs 1204 and 1206. NDPA frame 1210 may be an example of NDPA frame 900 described above. In an example, AP 1202 may be an EHT beamformer. NDPA frame 1210 may include two STA Info fields with AID11 subfields set respectively to the AIDs of STAs 1204 and 1206. An RA field of NDPA frame 1210 may be set to a broadcast address.Docket No.: 24-3066PCTWhile example 1200 is discussed as an EHT beamformer, this is merely an example. Example 1200, and other examples described throughout, may use UHR beamforming by replacing EHT frame(s) with corresponding UHR frame(s).

[0135] NDPA frame 1210 may solicit SU feedback, MU feedback, or CQI feedback from STAs 1204 and 1206. In an example, SU feedback may comprise a compressed beamforming report. In an example, the compressed beamforming report may comprise an average SNR of each spatial stream and compressed beamforming feedback matrices for use by AP 1202 to determine steering matrices for explicit feedback beamforming to STAs 1204 and 1206. In an example, MU feedback may comprise a compressed beamforming report and an MU exclusive beamforming report. In an example, the MU exclusive beamforming report may comprise explicit feedback in the form of delta SNRs. In an example, CQI feedback may comprise a CQI report. In an example, the CQI report may comprise per-RU average SNRs of each spatial stream. In an implementation, a per-RU average SNR may comprise an arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested. In an example, AP 1202 may be an EHT beamformer. NDPA frame 1210 may include a first STA Info field and a second STA Info field. The AID11 subfield of the first STA Info field may be set to the AID of STA 1204. The AID11 subfield of the second STA Info field may be set to the AID of STA 1206.

[0136] A SIPS after transmitting NDPA frame 1210, AP 1202 transmits an NDP 1212. NDP 1212 may be an EHT sounding NDP. A SIFS after transmitting NDP 1212, AP 1202 transmits a trigger frame 1214. Trigger frame 1214 may be a beamforming report poll frame (BFRP) frame. Trigger frame 1214 may address STAs 1204 and 1206 as beamformees. A SIFS after receiving trigger frame 1214, STAs 1204 and 1206 may transmit respective feedback frames 1216 and 1218. Feedback frames 1216 and 1218 may each comprise an EHT compressed beamforming / CQI frame and may be carried in a TB PPDU. The EHT compressed beamforming / CQI frame may comprise one or more beamforming reports. For example, the beamforming report may comprise the compressed beamforming report, the MU exclusive beamforming report, or the CQI report.

[0137] In an implementation, AP 1202 may transmit additional trigger frames in the same TXOP to solicit feedback frames from EHT beamformees not addressed in trigger frame 1214. In an implementation, AP 1202 may not transmit a trigger frame that solicits a STA identified in NDPA frame 1210 unless the trigger frame is in the same TXOP as NDPA frame 1210.

[0138] In an implementation, example 1200 may represent an EHT TB sounding sequence. As such, AP 1202 may represent an EHT beamformer, STAs 1204 and 1206 may represent EHT beamformees, and NDPA frame 1210 may be an EHT NDPA.

[0139] In an implementation, as an EHT beamformer, AP 1202 may nottransmit a BFRP Trigger frame that solicits a STA (e.g., STA 1204 or STA 1206) identified in NDPA frame 1210 unless the BFRP Trigger frameDocket No.: 24-3066PCTis in the same TXOP as the EHT TB sounding sequence. In an implementation, the STAs identified in NDPA frame 1210 are the same as the STAs identified in trigger frame(s) in the same TXOP.

[0140] In an implementation, as an EHT beamformer, AP 1202 may set all the bits of a “Feedback Segment Retransmission Bitmap” field of (e.g., BFRP) trigger frame 1214 to 1s. (BFRP) trigger frame 1214 contains one or more User Info fields, each of which identifies an EHT beamformee (e.g., STA 1204 or STA 1206).

[0141] In an implementation, when NDPA frame 1210 solicits SU or MU feedback, a STA Info field in NDPA frame 1210 indicates the subcarrier grouping, Ng, codebook size, and the number of columns, Nc, to be used by the EHT beamformee identified by the STA Info field for the generation of the SU or MU feedback. In an implementation, when NDPA frame 1210 solicits CQI feedback, a STA Info field in NDPA frame 900 indicates the Nc to be used by the EHT beamformee identified by the STA Info field for the generation of the CQI feedback.

[0142] In an implementation, as an EHT beamformee, when STA 1204 (or STA 1206) receives NDPA frame 1210 soliciting CQI feedback, STA 1204 / 1206 generates an EHT CQI report for CQI feedback with Nc determined by AP 1202.

[0143] In an implementation, as an EHT beamformee, when STA 1204 (or STA 1206) receives NDPA frame 1210 with a STA Info field identifying STA 1204 (or STA 1206) soliciting SU or MU feedback, STA 1204 (or STA 1206) generates an EHT compressed beamforming report using the feedback type, Ng, codebook size, and Nc indicated in the STA Info field.

[0144] In an implementation, as an EHT beamformee, when STA 1204 (or STA 1206) receives (BFRP) trigger frame 1214 with a matching User Info field, STA 1204 (or STA 1206) transmits an EHT TB PPDU containing the EHT compressed beamforming / CQI report. In an implementation, AP 1202 transmits NDPA frame 1210 with a TA field set to a transmitted BSSID, and STA 1204 (or STA 1206) is a non-AP STA associated with an AP corresponding to a non-transmitted BSSID that supports receiving control frames with TA fields set to the transmitted BSSID, then the EHT compressed beamforming / CQI report sent by STA 1204 (or STA 1206) in response may include an RA field set to a MAC address of AP 1202.

[0145] In an implementation, if an EHT compressed beamforming / CQI report solicited by AP 1202 would result in a feedback frame (e.g., 1216 or 1218) that exceeds 11454 octets in length, then the EHT compressed beamforming / CQI report is split into up to eight feedback segments. Each feedback segment is included in a separate feedback frame and contains successive portions of the EHT compressed beamforming / CQI report. Feedback segments may be of equal length except the last feedback segment, which may be shorter. Each feedback frame that includes a feedback segment that is not the last feedback segment has a length of 11454 octets. Each feedback segment is identified by the value of the “Remaining Feedback Segments” subfield and the “First Feedback Segment” subfield in an EHT MIMO Control field of the feedback frame that includes the feedback segment. The other non-reserved subfields of the EHT MIMO Control field may be the same for all feedback segments. Feedback frames may be sent in an A-MPDU contained in a single PPDU andDocket No.: 24-3066PCTmay be included in the A-MPDU in descending order based on values of the “Remaining Feedback Segments" subfield.

[0146] In an implementation, as an EHT beamformer, when AP 1202 transmits (BFRP) trigger frame 1214 to retrieve an EHT compressed beamforming / CQI report from an EHT beamformee (e.g., STA 1204 or STA 1206), AP 1202 solicits all possible feedback segments by setting to 1 all of the bits of the “Feedback Segment Retransmission Bitmap” subfield of the User Info field (of trigger frame 1214) identifying the EHT beamformee.

[0147] In implementation, as an EHT beamformer, if AP 1202 fails to receive some or all of the feedback segments of the EHT compressed beamforming / CQI report from an EHT beamformee (e.g., STA 1204 or STA 1206), AP 1202 may not transmit a further BFRP T rigger frame to request retransmission of the feedback segments. Instead, AP 1202 may repeat the entire EHT sounding sequence.

[0148] As feedback frames 1216 and 1218 (e g., TB PPDUs carrying feedback frames 1216 and 1218) are transmitted by STAs 1204 and 1206 simultaneously in response to trigger frame 1214, precorrection of time, frequency, sampling clock, and power (in the case of a High Efficiency (HE) TB PPDU or extremely high throughput (EHT) TB PPDU) by STAs 1204 and 1206 may be necessary to mitigate synchronization and interference issues at AP 1202. Specifically, frequency and sampling clock precorrections may be needed to prevent inter-carrier interference. Power precorrection may be necessary to control interference between the TB PPDUs carrying feedback frames 1216 and 1218.

[0149] In an implementation, trigger frame 1214 includes in a User Info field an uplink (UL) Target Receive Power subfield that indicates whether a STA among STAs 1204 and 1206 is to transmit TB PPDUs carrying feedback frames 1216 and / or 1218 at a maximum transmit power. The maximum transmit power may correspond to the STA's maximum transmit power for the assigned HE-MCS. The respective STA transmits the TB PPDU carrying feedback frames 1216 or 1218 at the maximum transmit power when the UL Target Receive Power subfield indicates that the maximum transmit power is to be used. Otherwise, the STA calculates the transmit power, Txp™, of the TB PPDU for the assigned HE-MCS using the equation:Txpwr =PLDL + TargetRxpwrwhere PLDLis the downlink pathloss and TargetRxpwris the expected receive signal power, in units of dBm, as indicated by the UL Target Receive Power subfield in the User Info field of trigger frame 1214. If STA 1204 and / or STA 1206 applies beamforming to the TB PPDU carrying feedback frame 1216 and / or 1218, the respective STA may take into account the beamforming gain when calculating the transmit power.

[0150] In an implementation, STA 1204 and / or STA 1206 computes PLDLusing the equation:where TxpP,ris the AP’s transmit power, in units of dBm / 20 MHz, as indicated by an AP Tx Power subfield of a Common Info field of trigger frame 1214 and Rxpwris the receive signal power, in units of dBm / 20MHz,Docket No.: 24-3066PCTof trigger frame 1214 at an antenna connector of the STA. Rxpwrmay be an average of the receive signal power over the antennas on which the average PLDLis being computed.

[0151] Due to the finite accuracy of clock generating circuits of an AP and a STA, an AP and an associated STA tuned to the same carrier frequency may have errors in their generated carrier frequencies in reference to the ideal carrier frequency. When an AP receives a TB PPDU as in example 1200, the AP may observe a baseband signal whose center frequency has an offset (i.e. carrier frequency offset or CFO) from the DC subcarrier. Similarly, an AP receiving the symbols of a TB PPDU sampled using its own clock may observe that the TB PPDU signal is generated at a clock offset (i.e. symbol clock offset or SCO) from its own sampling clock. Both SCO and CFO may result in receive errors when not properly mitigated. In order to limit the effects of CFO and SCO, a STA compensates for carrier frequency offset (CFO) error and symbol clock error with respect to trigger frame 1214 when the TB PPDU carrying feedback frame 1216 and / or 1218 is a TB PPDU or a non-HT or non-HT duplicate PPDU with the TXVECTOR parameter TRIGGER_RESPONDING set to true. After compensation, the absolute value of residual CFO error with respect to trigger frame 1214 shall not exceed the following levels when measured at the 10% point of a complementary cumulative distribution function (CCDF) of CFO errors in Additive White Gaussian Noise (AWGN) at a received power of -60 dBm in the primary 20 MHz channel: 350 Hz for the data subcarriers of a TB PPDU; 2 kHz for a non-HT PPDU or non-HT duplicate PPDU. The residual CFO error measurement on an HE TB PPDU shall be made after the HE-SIG-A field. The residual CFO error measurement on an EHT TB PPDU shall be made after the U-SIG field. The residual CFO error measurement on a non-HT or non-HT duplicate PPDU shall be made after the L-STF field. The symbol clock error shall be compensated by the same ppm amount as the CFO error.

[0152] FIG. 13 illustrates an example management frame 1300 which may be used as an action frame. In an example, management frame 1300 includes a MAC header, a variable length frame body, and a frame check sequence (FCS). The MAC header includes a frame control field, a duration field, an address 1 field, an address 2 field, an address 3 field, a sequence control field, and an optional HT control field. The presence of the HT control field is determined by the setting of a +HTC subfield of the frame control field.

[0153] As shown in FIG. 13, when used as an action frame, the frame body of management frame includes an action field, vendor specific elements, management message integrity code element (MME), message integrity code (MIC), and an authenticated mesh peering exchange element.

[0154] The action field includes a category field and an action details field. The action field provides a mechanism for specifying extended management actions. The category field indicates a category of the action frame. The action details field contains the details of the action requested by the action frame. For example, the action frame may be a public action frame. As shown in FIG. 13, in the public action frame format, the action details field includes a public action field, in the octet immediately after the category field, followed by a variable length public action details field.Docket No.: 24-3066PCT

[0155] One or more vendor specific elements are optionally present. These elements are absent when the category subfield of the Action field is vendor-specific.

[0156] The MME is present when management frame protection is negotiated, the frame is a group addressed robust Action frame, and (MBSS only) the category of the action frame does not support group addressed privacy as indicated by category values; otherwise not present.

[0157] The MIC element is present in a self-protected action frame if a shared pairwise master key (PMK) exists between the sender and recipient of this frame; otherwise not present.

[0158] The authenticated mesh peering exchange element is present in a self-protected action frame if a shared PMK exists between the sender and recipient of this frame; otherwise not present.

[0159] FIG. 14 illustrates an example 1400 of sequential NDP sounding. Example 1400 may include two APs 1402 and 1404. Example 1400 may further include a STA 1406 associated with AP 1402 and a STA 1408 associated with AP 1404. APs 1402 and 1404 may form a multi-AP group. In example 1400, AP 1402 may wish to perform a coordinated beamforming procedure or coordinated spatial reuse procedure with AP 1404. AP 1402 may be the AP coordinating / controlling the coordinated beamforming procedure. As such, AP 1402 may be referred to as a master / sharing AP, and AP 1404 may be referred to as a slave / shared AP. As illustrated, example 1400 may include a channel sounding phase 1410 and a channel sounding phase 1420. In an embodiment, example 1400 may be performed by AP 1402 and AP 1404 periodically or as necessary, to collect the necessary channel feedback for a coordinated beamforming or coordinated spatial reuse operation.

[0160] During channel sounding phase 1410, AP 1402 may use TB sounding (e.g. , as discussed above in relation to example 1200 illustrated in FIG. 12) to acquire CSI of a channel between AP 1402 and STA 1406. For example, AP 1402 may transmit an NDPA frame 1412. NDPA frame 1412 may be an example of NDPA frame 900 described above and may be used for TB sounding like NDPA frame 1210 illustrated in FIG. 12. In an example, NDPA frame 1412 is addressed to STAs associated with transmitting AP 1402 (e.g., NDPA frame 1412 is addressed to STA 1406 associated with AP 1402).

[0161] After transmitting NDPA frame 1412, AP 1402 may transmit an NDP 1414. NDP 1414 may be an EHT sounding NDP, like NDP 1212 described above in example 1200. STA 1406 determines an estimate of the channel (CSI) between AP 1402 and STA 1406 based on NDP 1414. After transmitting NDP 1414, AP 1402 may transmit a trigger frame 1416. Trigger frame 1416 may be a BFRP frame, corresponding to trigger frame 1214 in example 1200, and may address STA 1406 as a beamformee. Like example 1200, while example 1400 is discussed as an EHT beamformer, this is merely an example. Example 1400, and other EHT examples described throughout, may use UHR beamforming by replacing EHT frame(s) with corresponding UHR frame(s).

[0162] After receiving trigger frame 1416, STA 1406 may transmit a feedback frame 1418. Like feedback frames 1216 and 1218 in example 1200, feedback frame 1418 may be carried in a TB PPDU and may includeDocket No.: 24-3066PCTone or more beamforming reports with CSI information for the channel between STA 1406 and AP 1402 (e.g., a compressed beamforming report, an MU exclusive beamforming report, or a CQI report). AP 1402 may receive feedback frame 1418 and may use the CSI information for the channel between STA 1406 and AP 1402 for coordinated beamforming with AP 1404 to STAs 1406 and 1408, as discussed further below. In the coordinated beamforming, AP 1402 transmits a beamformed transmission to STA 1406 (with nulling towards STA 1408) and AP 1404 transmits a beamformed transmission to STA 1408 (with nulling towards STA 1406).

[0163] During channel sounding phase 1420, AP 1402 and AP 1404 may use TB sounding to acquire CSI of a channel between AP 1404 and STA 1406. For example, AP 1402 may transmit an NDPA frame 1422. NDPA frame 1422 may be an example of NDPA frame 900 described above, and may be used for TB sounding like NDPA frame 1210 illustrated in FIG. 12.

[0164] As in channel sounding phase 1410, in an example, NDPA frame 1422 is addressed to STAs associated with AP 1402 (e.g., STA 1406). AP 1404 may also receive NDPA frame 1422. After receiving NDPA frame 1422 from AP 1402, AP 1404 may transmit an NDP 1424 (e.g., to STA 1406 or as a broadcast). In an example, AP 1402 and AP 1404 may negotiate in advance that AP 1404 uses NDPA frames from AP 1402 to trigger transmission of an NDP from AP 1404 to STA 1406 (e.g., an overlapping basic service set (OBSS) STA for AP 1404). In an example, an OBSS STA for an AP is a STA that is a member of a BSS operating on the same channel as the AP's BSS and within (either partly or wholly) the AP's basic service area (BSA). As one example, AP 1402 may include an indication in NDPA frame 1422 that AP 1404 should trigger transmission of NDP 1424 from AP 1404 to STA 1406.

[0165] NDP 1424 may be an EHT sounding NDP, like NDP 1414 and NDP 1212 described above in example 1200. STA 1406 determines an estimate of the channel (CSI) between AP 1404 and STA 1406 based on NDP 1424. After AP 1404 transmits NDP 1424, AP 1402 may transmit a trigger frame 1426. Like trigger frame 1416, trigger frame 1426 may be a BFRP frame, corresponding to trigger frame 1214 in example 1200, and may address STA 1406 as a beamformee.

[0166] After receiving trigger frame 1426, STA 1406 may transmit a feedback frame 1428. Like feedback frame 1418 and feedback frames 1216 and 1218 in example 1200, feedback frame 1428 may be carried in a TB PPDU and may include one or more beamforming reports. Based on STA 1406 receiving NDP 1424 from AP 1404, these beamforming reports may include CSI information for the channel between STA 1406 and AP 1404 (e.g., a compressed beamforming report, an MU exclusive beamforming report, or a CQI report). In an example, AP 1404 receives feedback frame 1428 from STA 1406 and may use the CSI information for the channel between STA 1406 and AP 1404 for coordinated beamforming with AP 1402 to STAs 1406 and 1408.

[0167] After AP 1402 completes channel sounding phase 1410 and channel sounding phase 1420 for its associated STAs (e.g., STA 1406), AP 1404 may repeat the same procedure for its associated STAs (e.g., STA 1408). For example, AP 1404 may use a third and fourth channel sounding phase (not pictured),Docket No.: 24-3066PCTanalogous to the illustrated channel sounding phases 1410 and 1420, to acquire CSI for a channel between AP 1404 and STA 1408, and for a channel between AP 1402 and STA 1408. AP 1402 and AP 1404 may use this CSI information for the coordinated beamforming to STAs 1406 and 1408.

[0168] FIG. 15 illustrates an example 1500 of joint NDP sounding. Example 1500 may include two APs 1502 and 1504. Example 1500 may further include a STA 1506 associated with AP 1502, and a STA 1508 associated with AP 1504. APs 1502 and 1504 may form a multi-AP group. In example 1500, AP 1502 may wish to perform a coordinated beamforming procedure or coordinated spatial reuse procedure with AP 1504. AP 1502 may be the AP coordinating / controlling the coordinated beamforming procedure. As such, AP 1502 may be referred to as a master / sharing AP, and AP 1504 may be referred to as a slave / shared AP. In an embodiment, example 1500 may be performed by AP 1502 and AP 1504 periodically or as necessary, to collect the necessary channel feedback for a coordinated beamforming or coordinated spatial reuse operation.

[0169] As illustrated, example 1500 may include a channel sounding phase 1510 and a channel sounding phase 1520. In an example, during channel sounding phase 1510, AP 1502 and AP 1504 may perform both sounding phases discussed in example 1400, simultaneously, for STA 1506. During channel sounding phase 1520, AP 1502 and AP 1504 may perform both sounding phases discussed in example 1400, simultaneously, for STA 1508.

[0170] During channel sounding phase 1510, AP 1502 may transmit an NDPA frame 1512. NDPA frame 1512 may be an example of NDPA frame 900 described above and may be used for TB sounding like NDPA frame 1210 illustrated in FIG. 12. In an example, NDPA frame 1512 is addressed to STAs associated with transmitting AP 1502 (e.g., NDPA frame 1512 is addressed to STA 1506 associated with AP 1502).

[0171] AP 1504 may receive NDPA frame 1512. In an example, AP 1502 and AP 1504 may negotiate in advance that AP 1504 uses NDPA frames from AP 1502 to trigger transmission of an NDP from AP 1504 to STA 1506. As one example, AP 1502 may include an indication in NDPA frame 1512 that AP 1504 should trigger transmission of NDP 1515 from AP 1504 to STA 1506 (e.g., after a SIFS duration). In an example, AP 1502 may transmit NDP 1514 to STA 1506, simultaneous with AP 1504 transmitting NDP 1515 to STA 1506. For example, AP 1502 may transmit NDP 1514 after a SIFS duration following transmission of NDPA frame 1512.

[0172] In an example, NDP 1514 and NDP 1515 are transmitted orthogonally in the code domain to avoid collision. For example, NDP 1514 and NDP 1515 may use orthogonal rows of a P matrix used in MIMO LTFs. This allows STA 1506 to simultaneously estimate CSI for a channel between STA 1506 and AP 1502 (e.g., based on NDP 1514), and for a channel between STA 1506 and AP 1504 (e.g., based on NDP 1515).

[0173] After transmitting NDP 1514, AP 1502 may transmit a trigger frame 1516. Trigger frame 1516 may be a BFRP frame, corresponding to trigger frame 1214 in example 1200, and may address STA 1506 as a beamformee.Docket No.: 24-3066PCT

[0174] After receiving trigger frame 1516, STA 1506 may transmit a feedback frame 1518. Like feedback frames 1216 and 1218 in example 1200, feedback frame 1518 may be carried in aTB PPDU and may include one or more beamforming reports with CSI information (e g., a compressed beamforming report, an MU exclusive beamforming report, or a CQI report). In an example, feedback frame 1518 may include CSI information for both the channel between STA 1506 and AP 1502 (e.g., based on NDP 1514), and for the channel between STA 1506 and AP 1504 (e.g., based on NDP 1515). In an example, the feedback included in feedback frame 1518 may be based on large V-based feedback where the eigen-vectors span the antennas across both AP 1502 and AP 1504.

[0175] AP 1502 may receive feedback frame 1518 from STA 1506 and may use the CSI information for the channel between STA 1506 and AP 1502 for coordinated beamforming with AP 1504 to STAs 1506 and 1508. Similarly, AP 1504 may also receive feedback frame 1518 from STA 1506, and may use the CSI information for the channel between STA 1506 and AP 1504 for the coordinated beamforming with AP 1502 to STAs 1506 and 1508. In the coordinated beamforming, AP 1502 transmits a beamformed transmission to STA 1506 (with nulling towards STA 1508) and AP 1504 transmits a beamformed transmission to STA 1508 (with nulling towards STA 1506).

[0176] As discussed, channel sounding phase 1510 illustrates joint sounding for STA 1506 associated with AP 1502. In an example, channel sounding phase 1520 corresponds to channel sounding phase 1510, but for STA 1508 associated with AP 1504 instead of STA 1506 associated with AP 1502. AP 1504 may transmit an NDPA 1522, and AP 1502 and AP 1504 may simultaneously transmit an NDP 1524 and an NDP 1525 (e.g., using orthogonal transmission in the code domain to avoid collision, as discussed above for NDP 1514 and NDP 1515 in channel sounding phase 1510) AP 1504 may transmit a trigger frame 1526 (e g., a BFRP frame, like trigger frame 1516) to STA 1508.

[0177] After receiving trigger frame 1526, STA 1508 may transmit a feedback frame 1528 with CSI information for both the channel between STA 1508 and AP 1504 (e.g., based on NDP 1524), and for the channel between STA 1508 and AP 1502 (e.g., based on NDP 1525). AP 1504 may receive feedback frame 1528 and may use the CSI information for the channel between STA 1508 and AP 1504 for coordinated beamforming with AP 1502 to STAs 1506 and 1508. Similarly, AP 1502 may also receive feedback frame 1528 from STA 1508, and may use the CSI information for the channel between STA 1508 and AP 1502 for the coordinated beamforming to STAs 1506 and 1508.

[0178] FIG. 16 illustrates an example 1600 of a multi-AP downlink data transmission phase. Example 1600 may be an example of multi-AP data transmission phase 616. As shown in FIG. 16, example 1600 may include a master AP 1602 and a slave AP 1604 of a multi-AP group. Example 1600 may further include a STA 1606 associated with AP 1602, and a STA 1608 associated with AP 1604.

[0179] As shown in FIG. 16, example 1600 may include frame exchanges to enable master AP 1602 to coordinate with slave AP 1604 to perform specific multi-AP transmission schemes with their associated STAsDocket No.: 24-3066PCT1606 and 1608 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.

[0180] As shown in FIG. 16, master AP 1602 may begin example 1600 by transmitting a frame 1610 to AP 1604. Frame 1610 may include information related toAP 1604 (e.g., an identifier of AP 1604), 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 1604 to acknowledge frame 1610. Frame 1610 may comprise a control frame. For example, frame 1610 may comprise a multi-AP trigger frame.

[0181] Slave AP 1604 may receive frame 1610 and may use the synchronization information to synchronize with master AP 1602. Subsequently, APs 1602 and 1604 may perform data transmission to their associated STAs 1606 and 1608 respectively. Specifically, AP 1602 may transmit a data frame 1612 to its associated STA 1606, and AP 1604 may transmit a data frame 1614 to its associated STA 1608. Depending on the multi-AP transmission scheme being used, APs 1602 and 1604 may transmit frames 1612 and 1614 respectively to STAs in different BSSs. For example, when the multi-AP transmission scheme is JT / JR, AP 1602 may also transmit frame 1612 to STA 1608 associated with slave AP 1604, and AP 1604 may also transmit frame 1614 to STA 1608 associated with AP 1604. The resources for transmitting and receiving frames 1612 and 1614 may depend on the specific multi-AP transmission scheme adopted.

[0182] STAs 1606 and 1608 may acknowledge frames 1612 and 1614 respectively. For example, STA 1606 may transmit a frame 1616 to AP 1602, and STA 1608 may transmit a frame 1618 to AP 1604. Frames 1616 and 1618 may comprise block ack (BA) frames. STAs 1606 and 1608 may also transmit frames 1616 and 1618 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 1606 may also transmit frame 1616 to AP 1604, and STA 1608 may also transmit frame 1618 to AP 1602. The resources for transmitting and receiving frames 1616 and 1618 may depend on the specific multi-AP transmission scheme adopted.

[0183] FIG. 17 illustrates an example 1700 of a multi-AP uplink data transmission phase. Example 1700 may be an example of multi-AP data transmission phase 616. As shown in FIG. 17, example 1700 may include a master AP 1702 and a slave AP 1704 of a multi-AP group. Example 1700 may further include STAs 1706 and 1708 associated with AP 1702, and a STA 1710 associated with AP 1704.

[0184] As shown in FIG. 17, example 1700 may include frame exchanges to enable master AP 1702 to coordinate with slave AP 1704 to perform specific multi-AP transmission schemes with STAs 1706, 1708, and 1710. The multi-AP transmission schemes may include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the aforementioned schemes.

[0185] As shown in FIG. 17, master AP 1702 may begin example 1700 by transmitting a frame 1712 to AP 1704. Frame 1712 may include information related to AP 1704 (e.g., an identifier of AP 1704), synchronization information, information related to a specific multi-AP transmission scheme to be used, and / or informationDocket No.: 24-3066PCTrelated to an RU for use by AP 1704 to acknowledge frame 1712. Frame 1712 may comprise a control frame. For example, frame 1712 may comprise a multi-AP trigger frame.

[0186] Slave AP 1704 may receive frame 1712 and may use the synchronization information to synchronize with master AP 1702. Subsequently, APs 1702 and 1704 may solicit uplink data transmissions from their associated STAs 1706, 1708 and 1710 using trigger frames. Specifically, AP 1702 may transmit a trigger frame 1714 to its associated STAs 1706 and 1708, and AP 1704 may transmit a trigger frame 1716 to its associated STA 1710. Depending on the multi-AP transmission scheme being used, APs 1702 and 1704 may also transmit frames 1714 and 1716 respectively to STAs in different BSSs. For example, when the multi-AP transmission scheme is JT / JR, AP 1702 may also transmit frame 1714 to STA 1710 associated with slave AP 1704, and AP 1704 may also transmit frame 1716 to STAs 1706 and 1708 associated with AP 1702. The resources for transmitting and receiving frames 1714 and 1716 may depend on the specific multi-AP transmission scheme adopted

[0187] STAs 1706 and 1708 may respond to frame 1714, STA 1710 may respond to frame 1716. For example, STAs 1706 and 1708 may transmit frames 1718 and 1720 respectively to AP 1702, while STA 1710 may transmit a frame 1722 to AP 1704. Frames 1718, 1720, and / or 1722 may be transmitted simultaneously. Frames 1718, 1720, and 1722 may comprise data frames or null data frames. STAs 1706, 1708, and 1710 may also transmit frames 1718, 1720, and 1722 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 1706 and 1708 may also transmit respective frames 1718 and 1720 to AP 1704, and STA 1710 may also transmit frame 1722 to AP 1702. The resources for transmitting and receiving frames 1718, 1720, and 1722 may depend on the specific multi-AP transmission scheme adopted. AP 1702 may acknowledge frames 1718 and 1720 by transmitting a multi-STA BA frame 1724 to STAs 1706 and 1708. AP 1704 may acknowledge frame 1722 by transmitting a BA frame 1726 to STA 1710.

[0188] FIG. 18 shows an example 1800 that illustrates NDP sounding procedures, such as the sequential NDP sounding procedure illustrated in FIG. 14 and the joint NDP sounding procedure illustrated in FIG. 15. As shown in FIG. 18, example 1800 includes APs 1802 and 1804. APs 1802 and 1804 may form a multi-AP group. In example 1800, AP 1802 may wish to perform a coordinated beamforming (COBF) procedure with AP 1804 in a TXOP obtained by AP 1802. AP 1802 may be the AP coordinating / controlling the COBF procedure. As such, AP 1802 may be referred to as a master / sharing AP, and AP 1804 may be referred to as a slave / shared AP.

[0189] As shown in FIG. 18, example 1800 may begin with traffic for transmission by AP 1804. In an example, the traffic may be for transmission using COBF (e.g., using a COBF PPDU). A COBF PPDU may be any PPDU format that is used by a sharing AP (e.g., AP 1802) and a shared AP (e.g., AP 1804) to beamform their respective data streams during a COBF transmission. In an example, a COBF PPDU may include a UHR multi-user (MU) PPDU with an indication of COBF transmission in the U-SIG field. In exampleDocket No.: 24-3066PCT1800, AP 1804 may have one or more buffered bufferable unit(s) (BU) available for transmission using a COBF PPDU. A buffered BU available for transmission using a COBF PPDU may include any buffered BU for any STA that is capable of responding as a beamformee during an NDP sounding procedure for COBF transmission.

[0190] AP 1802 and AP 1804 may then perform a sounding sequence 1812 and a sounding sequence 1814 (e.g., as part of a sounding procedure for coordinated beamforming). For example, AP 1802 may be a member of a first BSS (e.g., along with a first one or more associated STAs), and AP 1804 may be a member of a second, different, BSS (e.g., along with a second one or more associated STAs). In an example, the first BSS of which AP 1802 is a member may be an overlapping basic service set (OBSS) with the second BSS ofwhich AP 1804 is a member. Sounding sequences 1812 and 1814 may be used by AP 1802 and AP 1804 to sound STAs in these separate BSSs, for COBF: sounding sequence 1812 may be used by AP 1802 and AP 1804 to sound the first BSS of which AP 1802 is a member (e.g., to sound channels between the first one or more STAs associated with the first BSS, and each of AP 1802 and AP 1804), while sounding sequence 1814 may be used by AP 1802 and AP 1804 to sound a second BSS of which AP 1804 is a member (e.g., to sound channels between the second one or more STAs associated with the second BSS, and each of AP 1802 and AP 1804).

[0191] Thus, as one example, sounding sequences 1812 and 1814 may correspond with sounding sequences in a sequential sounding procedure, as discussed in example 1400 illustrated in FIG. 14. In this example, AP 1802 may correspond with AP 1402 discussed in example 1400 and AP 1804 may correspond with AP 1404 discussed in example 1400. During sounding sequence 1812, AP 1802 and AP 1804 may perform both channel sounding phase 1410 and channel sounding phase 1420 in example 1400, to sound channels between each respective AP and the first one or more STAs in the first BSS associated with AP 1802 (e.g., STA 1406 in example 1400). During sounding sequence 1814, AP 1802 and AP 1804 may again perform both channel sounding phase 1410 and channel sounding phase 1420 in example 1400, this time to sound channels between each respective AP and the second one or more STAs in the second BSS associated with AP 1804 (e.g., STA 1408 in example 1400).

[0192] As another example, sounding sequences 1812 and 1814 may correspond with sounding sequences in a joint sounding procedure, as discussed in example 1500 illustrated in FIG. 15. In this example, AP 1802 may correspond with AP 1502 discussed in example 1500 and AP 1804 may correspond with AP 1504 discussed in example 1500. In an example, sounding sequence 1812 may correspond with channel sounding phase 1510 in example 1500, and both AP 1802 and AP 1804 may sound channels between the respective APs and the first one or more STAs in the first BSS associated with AP 1802 (e.g., STA 1506 in example 1500). Sounding sequence 1814 may correspond with channel sounding phase 1520 in example 1500, and both AP 1802 and AP 1804 may sound channels between the respective APs and one or more STAs in the second BSS associated with AP 1804 (e.g., STA 1508 in example 1500).Docket No.: 24-3066PCT

[0193] Thus, in an example, AP 1802 and AP 1804 may perform both sounding sequence 1812 and sounding sequence 1814 to sound channels for two BSSs, to facilitate COBF by AP 1802 and AP 1804.

[0194] As illustrated in example 1800, AP 1802 may transmit a poll 1816 to AP 1804, and AP 1804 may respond with a response 1818. AP 1804 may indicate in response 1818 that AP 1804 has data to send via COBF. AP 1802 may receive response 1818. In an example, AP 1802 and AP 1804 may then transmit a PPDU 1820 using COBF (e.g ., to a STA associated with AP 1804).

[0195] AP 1802 may then transmit another poll 1822 to AP 1804, and AP 1804 may respond with another response 1824. AP 1804 may indicate in response 1824 that AP 1804 has no data to send via COBF. For example, AP 1804 may have no buffered BU to transmit to STAs that support responding as a beamformee in a COBF transmission. As another example, AP 1804 may prioritize transmission of buffered BUs to STAs that do not support COBF (e.g., for a subsequent duration). AP 1802 may then transmit a PPDU 1826. In an example, AP 1802 may transmit PPDU 1826 without beamforming, or using beamforming from AP 1802 alone (e.g., without using COBF from both AP 1802 and AP 1804).

[0196] In an example, AP 1802 and AP 1804 perform additional sounding sequences 1828 and 1830. For example, AP 1802 and AP 1804 may repeat sounding periodically (e.g., at a defined interval) to facilitate transmission using COBF. In an example, sounding sequences 1828 and 1830 correspond with sounding sequences 1812 and 1814, discussed above, and AP 1802 and AP 1804 both sound STAs in their respective BSS.

[0197] FIG. 19 shows an example 1900 that further illustrates a problem that may arise in NDP sounding procedures, such as the sequential NDP sounding procedure illustrated in FIG. 14 and the joint NDP sounding procedure illustrated in FIG. 15. In an example, APs 1802 and 1804 in example 1900 correspond to APs 1802 and 1804 discussed in example 1800 in FIG. 18.

[0198] As shown in FIG. 18, example 1800 may begin with AP 1802 and AP 1804 performing a sounding sequence 1812 and a sounding sequence 1814 (e.g., as part of a sounding procedure or coordinated beamforming). In an example, sounding sequences 1812 and 1814 in example 1900 correspond to sounding sequences 1812 and 1814 discussed in example 1900 in FIG. 19. Thus, in an example, AP 1802 and AP 1804 may perform both sounding sequence 1812 and sounding sequence 1814 to sound channels for two BSSs, to facilitate COBF by AP 1802 and AP 1804.

[0199] In example 1900, however, unlike example 1800, AP 1804 may not have any data to send via COBF after sounding sequences 1812 and 1814 For example, AP 1804 may have no buffered BU to transmit to STAs that support responding as a beamformee in a COBF transmission. As another example, AP 1804 may prioritize transmission of buffered BUs to STAs that do not support COBF (e.g., for a subsequent duration).

[0200] As illustrated in example 1800, AP 1802 may transmit a poll 1916 to AP 1804, and AP 1804 may respond with a response 1818. AP 1804 may indicate in response 1918 that AP 1804 has no data to send via COBF. Thus, AP 1802 may transmit a PPDU 1920. In an example, AP 1802 may transmit PPDU 1920Docket No.: 24-3066PCTwithout beamforming, or using beamforming from AP 1802 alone (e.g., without using COBF from both AP 1802 and AP 1804). AP 1802 may then transmit another poll 1922 to AP 1804, and AP 1804 may respond with another response 1924. AP 1804 may indicate in response 1924 that AP 1804, again, has no data to send via COBF. Thus, AP 1802 may transmit another PPDU 1926. Similar to transmission of PPDU 1920, AP 1802 may transmit PPDU 1926 without beamforming, or using beamforming from AP 1802 alone (e.g., without using COBF from both AP 1802 and AP 1804).

[0201] As illustrated, AP 1804 identifies traffic for COBF after AP 1802 transmits PPDU 1926 (e.g., without using COBF). For example, AP 1804 may receive buffered BUs to transmit to STAs that support responding as a beamformee in a COBF transmission, or may prioritize transmission of buffered BUs to STAs that support responding as a beamformee in a COBF transmission. In an example, AP 1802 and AP 1804 perform additional sounding sequences 1828 and 1830. For example, AP 1802 and AP 1804 may repeat sounding periodically (e.g., at a defined interval) to facilitate transmission using COBF. In an example, sounding sequences 1828 and 1830 correspond with sounding sequences 1812 and 1814, discussed above, and AP 1802 and AP 1804 both sound STAs in their respective BSS.

[0202] A problem with this technique, however, is that the sounding sequence 1814 is not needed. AP 1802 and AP 1804 perform sounding sequence 1814, to facilitate COBF, but in example 1900 AP 1802 and AP 1804 do not actually transmit any data using COBF: instead, AP 1802 transmits PPDUs 1920 and 1926. For example, AP 1804 may be able to determine, prior to sounding sequence 1814, that AP 1804 has no data to send via COBF. Yet AP 1802 and AP 1804 still perform sounding sequence 1814. Further, where traffic for COBF transmission by AP 1804 becomes available, or is expected to become available, near the end of the sounding interval (e.g., shortly before sounding sequences 1828 and 1830, as illustrated in example 1800), the channel is likely to have changed sufficiently that sounding should be repeated and sounding sequence 1814 is unnecessary. Performing sounding sequence 1814, when it is not necessary, is wasteful and inefficient, because the resources used by AP 1802 and AP 1804 for sounding sequence 1814 are wasted. Communication performance (e.g., throughput, resource utilization efficiency, etc.) may be degraded by this unnecessary sounding.

[0203] Embodiments of the present disclosure, as further described below, address the above-described problem of existing technologies. In an aspect, a first access point (AP) receives, from a second AP, a first null data physical layer protocol data unit (NDP) announcement frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission. The first AP is configured to transmit a second NDP announcement frame during a first time period of the sounding procedure when the first AP has a downlink (DL) buffered bufferable unit (BU) for transmission via the COBF transmission. Based on absence at the first AP of DL buffered BUs for transmission via the COBF transmission, the first AP transmits, to the second AP and during the sounding procedure, a second frame truncating the sounding procedure. By truncating theDocket No.: 24-3066PCTsounding procedure, the APs may avoid expending resources that would have been wasted, had the sounding procedure been completed unnecessarily.

[0204] In another aspect, a first AP transmits, to a second AP, a first frame. The first frame may solicit whether the second AP wishes to participate in a sounding sequence. The sounding sequence may be a joint null data packet (NDP) sounding sequence. The joint NDP sounding sequence may be for a coordinated beamforming (Co-BF) transmission. The first AP may receive, from the second AP, a second frame. The second frame may indicate whether the second AP wishes to participate in the joint NDP sounding sequence. The first AP may transmit, to the second AP, an NDP announcement (NDPA) frame. The NDPA frame may initiate the joint NDP sounding sequence. The first AP may transmit the NDPA after receiving the second frame. The first AP may transmit a first NDP. The first AP may transmit the first NDP after a short interframe space (SIFS) from the NDPA frame. The first AP may transmit, to a first station (STA), a beamforming report poll (BFRP) trigger frame after transmitting the first NDP. The first AP may receive, from the first STA, a beamforming report. The first AP may comprise an initiating AP for the joint NDP sounding sequence. The second AP may comprise a responding AP for the joint NDP sounding sequence. The first AP and the second AP may each comprise an ultra high reliability (UHR) Co-BF beamformer. The first frame may comprise a Co-BF sounding invite frame. The second frame may comprise a Co-BF sounding response frame. The second frame may indicate that the second AP accepts to participate in the joint NDP sounding sequence. The NDPA frame may comprise a receiver address (RA) field set to a broadcast address. The NDPA frame may comprise a plurality of STA info fields. The plurality of STA info fields may indicate an association identifier (AID) for a second STA associated with the first AP. The first NDP may comprise an extremely high throughput (EHT) NDP. The first AP may transmit the first NDP simultaneously with the second AP transmitting a second NDP. The second AP may transmit the second NDP in response to the NDPA frame. The beamforming report may comprise a compressed beamforming / CQI report. The BFRP trigger frame may comprise a Feedback Segment Retransmission Bitmap field that comprises a plurality of bits. The first AP may set all of the plurality of bits of the Feedback Segment Retransmission Bitmap field to 1. The Feedback Segment Retransmission Bitmap field may indicate that the first AP solicits all possible feedback segments. The Feedback Segment Retransmission Bitmap field may be comprised in a user info field of the BFRP trigger frame.

[0205] In another aspect a first AP transmits, to a second AP, a first null data physical layer protocol data unit (NDP) announcement frame. The first NDP announcement frame may initiate a sounding procedure for a coordinated beamforming (COBF) transmission. The first AP may be configured to receive, from the second AP, a second NDP announcement frame during the sounding procedure. The first AP may receive, from the second AP and during the sounding procedure, a second frame truncating the sounding procedure.

[0206] FIG. 20 illustrates an example 2000 of a procedure according to an embodiment. As shown in FIG.20, example 2000 includes APs 2002 and 2004 and STAs 2006 and 2008. STA 2006 may be associatedDocket No.: 24-3066PCTwith AP 2002 and STA 2008 may be associated with AP 2004. APs 2002 and 2004 may form a multi-AP group (e.g., a coordinating AP set). In example 2000, AP 2002 may wish to perform a coordinated beamforming procedure with AP 2004 in a TXOP obtained by AP 2002 (and / or AP 2004). AP 2002 may be the AP coordinating / controlling the coordinated beamforming procedure. As such, AP 2002 may be referred to as a master / sharing AP, and AP 2004 may be referred to as a slave / shared AP. AP 2004 may be considered an OBSS AP relative to AP 2002 or STA 2006.

[0207] As shown in FIG.20, example 2000 may begin with a sounding sequence 2010, as part of a sounding procedure with an expected sounding procedure duration 2030. In an embodiment, sounding sequence 2010 may correspond to channel sounding phase 1510 of the joint NDP sounding procedure illustrated in FIG. 15. That is, sounding sequence 2010 may serve for STA 2006 to estimate both the first channel from AP 2004 to STA 2006 and a second channel from AP 2002 to STA 2006, and to transmit feedback with CSI for both the first and second channels The CSI may comprise at least one of: channel coefficients of the respective channels, uncompressed beamforming feedback matrices computed based on the channel coefficients, and compressed beamforming feedback matrices computed based on the channel coefficients.

[0208] As such, sounding sequence 2010 may begin with AP 2002 transmitting to AP 2004 an NDPA frame 2012. In response to NDPA frame 2012, AP 2002 and AP 2004 each transmit a respective NDP (or sounding frame PPDU) 2014 and 2015 (e.g., a SIFS after NDPA frame 2012). As discussed above for example 1500 in FIG. 15, NDPs (or sounding PPDUs) 2014 and 2015 may be transmitted over orthogonal resources such that they do not interfere with each other.

[0209] STA 2006 measures the first channel from AP 2002 to STA 2006 based on NDP (or sounding PPDU) 2014 and determines first feedback comprising CSI for the first channel based on the measurement. Similarly, STA 2006 measures the second channel from AP 2004 to STA 2006 based on NDP (or sounding PPDU) 2015 and determines second feedback comprising CSI for the second channel based on the measurement. Subsequently, e.g., a SIFS after transmission of NDPs (or sounding PPDUs) 2014 and 2015, AP 2002 transmits to STA 2006 BFRP frame 2016 soliciting the first feedback and the second feedback. In response to BFRP frame 2016, STA 2006 transmits frame 2018 comprising the first feedback and the second feedback. Frame 2018 may comprise a compressed beamforming / channel quality indication (CQI) frame.

[0210] In an example, AP 2004 does not have any frames to send via COBF. For example, AP 2004 may have no buffered BUs to transmit to STAs that support responding as a beamformee in a COBF transmission (e.g , STA 2008). As another example, AP 2004 may prioritize transmission of buffered BUs to STAs that do not support COBF (e.g., for a subsequent duration). Alternatively, AP 2004 may not wish to undertake a COBF transmission for another suitable reason. For example, AP 2004 may be unavailable during the COBF transmission, may identify the presence of a coexistence event during the COBF transmission, or may identify the presence of a restricted target wake time (r-TWT) service period during the COBF transmission. In an example, a coexistence event may occur such that the same wireless device containing an AP may need toDocket No.: 24-3066PCTuse its radio (e.g. antenna, transmit / receive amplifiers, baseband processors) to transmit or receive a non-Wi-Fi signal (e.g. Bluetooth) on an interval that may overlap with the COBF transmission. Similarly, an r-TWT service period, where other non-AP STAs or APs that are members of the r-TWT SP have increased priority, may prevent an AP from accessing the channel until the end of the r-TWT SP.

[0211] In an embodiment, AP 2004 truncates the sounding procedure (e.g., prior to the conclusion of the expected sounding procedure duration 2030). Truncating the sounding procedure may also be referred to as terminating the sounding procedure, cancelling the sounding procedure, or ending the sounding procedure. For example, during a time period 2020, AP 2004 may transmit a frame 2022 to AP 2002 truncating the sounding procedure. In an embodiment, AP 2004 transmits frame 2022 prior to AP 2004 and AP 2002 initiating an expected second sounding sequence for STA 2008 (e.g., prior to initiating channel phase 1520 illustrated in example 1500). In another embodiment, AP 2004 transmits frame 2022 during the second sounding sequence (e.g., for STA 2008), and prior to completion of the second sounding sequence. In an embodiment, the sounding sequence 2010 and the expected second sounding sequence for STA 2008 are expected to occur during a same TXOP (e.g., a same TXOP obtained by AP 2002). In another embodiment, the sounding sequence 2010 occurs during a first TXOP (e.g., a first TXOP obtained by AP 2002) and the expected sounding sequence for STA 2008 is expected to occur during a second TXOP (e.g., a second TXOP obtained by AP 2004).

[0212] In an embodiment, frame 2022 may be an NDPA variant frame. For example, frame 2022 may contain a field indicating truncation of the sounding procedure. Alternatively, frame 2022 may be a different frame format, such as an action frame, a contention free-end (CF-END) frame, or any other suitable frame.

[0213] In an embodiment, based on receiving frame 2022, AP 2002 truncates / cancels / terminates the sounding procedure. AP 2002 may also cancel the COBF transmission with AP 2004, intended for after the sounding procedure. Further, after receiving frame 2022, AP 2002 may confirm truncating the sounding procedure by transmitting a frame 2024 (e.g., a CF-END frame). For example, when the expected second sounding sequence is scheduled to be transmitted using the same TXOP as sounding sequence 2010, frame 2024 transmitted by AP 2002 may reset the network allocation vector (NAV) of STAs that may have been set until the end of the expected sounding procedure duration 2030, so channel access can occur without waiting for the NAV to expire. It is noted that in embodiments where frame 2022 is a CF-END frame, STAs hearing frame 2022 may reset their NAVs based on frame 2022, before receiving frame 2024.

[0214] Further, in an embodiment, AP 2002 may indicate to AP 2004 (e.g., prior to beginning sounding sequence 2010) whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2002 may transmit a frame to AP 2004 (e.g., prior to beginning sounding sequence 2010) indicating whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. As another example, NDPA frame 2012 may indicate whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. Alternatively, AP 2002 and AP 2004Docket No.: 24-3066PCTmay know before beginning sounding sequence 2010 whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2002 and 2004 may negotiate this information during formation of the multi-AP group.

[0215] In an embodiment, truncating the sounding procedure (e.g., when AP 2004 does not have data to transmit using COBF) may avoid expending resources that would have been wasted, had the sounding procedure been completed unnecessarily.

[0216] FIG. 21 illustrates an example 2100 of a procedure according to an embodiment. As shown in FIG.21, example 2100 includes APs 2102 and 2104 and STAs 2106 and 2108. STA 2106 may be associated with AP 2102 and STA 2108 may be associated with AP 2104. APs 2102 and 2104 may form a multi-AP group (e.g., a coordinating AP set). In example 2100, AP 2102 may wish to perform a coordinated beamforming procedure with AP 2104 in a TXOP obtained by AP 2102 (and / or AP 2104). AP 2102 may be the AP coordinating / controlling the coordinated beamforming procedure. As such, AP 2102 may be referred to as a master / sharing AP, and AP 2104 may be referred to as a slave / shared AP. AP 2104 may be considered an OBSS AP relative to AP 2102 or STA 2106.

[0217] As shown in FIG. 21, example 2100 may begin with channel sounding phase 2110. In an embodiment, channel sounding phase 2110 relates to in-BSS sounding for AP 2102 (e.g., for AP 2102 to sound STA 2106 associated with AP2102), and may correspond to channel sounding phase 1410 illustrated in example 1400 in FIG. 14.

[0218] As such, channel sounding phase 2110 may begin with AP 2102 transmitting an NDPA frame 2112. After transmitting NDPA frame 2112, AP 2102 may transmit an NDP 2114. After transmitting NDP 2114, AP 2102 may transmit a BFRP frame 2116. After receiving BFRP frame 2116, STA 2106 may transmit a feedback frame 2118. The feedback frame 2118 may include feedback with CSI for the channel between AP 2102 and associated STA 2106. The CSI may comprise at least one of: channel coefficients of the channel, uncompressed beamforming feedback matrices computed based on the channel coefficients, and compressed beamforming feedback matrices computed based on the channel coefficients.

[0219] As shown in FIG. 21, example 2100 may continue with channel sounding phase 2120. In an embodiment, channel sounding phase 2120 relates to cross-BSS sounding for AP 2104 (e.g., for AP 2104 to sound STA 2106 associated with AP2102), and may correspond to channel sounding phase 1420 illustrated in example 1400 in FIG. 14.

[0220] As such, channel sounding phase 2120 may begin with AP 2102 transmitting an NDPA frame 2122. After receiving NDPA frame 2122 from AP 2102, AP 2104 may transmit an NDP 2124. After AP 2104 transmits NDP 2124, AP 2102 may transmit a BFRP frame 2126. After receiving BFRP frame 2126, STA 2106 may transmit a feedback frame 2128. The feedback frame 2128 may include feedback with CSI for the channel from AP 2102 to cross-BSS STA 2106. The CSI may comprise at least one of: channel coefficientsDocket No.: 24-3066PCTof the channel, uncompressed beamforming feedback matrices computed based on the channel coefficients, and compressed beamforming feedback matrices computed based on the channel coefficients.

[0221] Example 2100 may then continue with channel sounding phase 2130. In an embodiment, channel sounding phase relates to in-BSS sounding for AP 2104 (e.g., for AP 2104 to sound STA 2108 associated with AP 2104), and may correspond to repeating channel sounding phase 1410 for the BSS of which AP 1404 is a member, as discussed above for example 1400 illustrated in FIG. 14.

[0222] In an embodiment, AP 2104 does not have any frames to send via COBF. For example, AP 2104 may have no buffered BUs to transmit to STAs that support responding as a beamformee in a COBF transmission (e.g., STA 2108). As another example, AP 2104 may prioritize transmission of buffered BUs to STAs that do not support COBF (e.g., for a subsequent duration). Alternatively, AP 2104 may not wish to undertake a COBF transmission for another suitable reason. For example, AP 2104 may be unavailable during the COBF transmission, may identify the presence of a coexistence event during the COBF transmission, or may identify the presence of a restricted target wake time (r-TWT) service period during the COBF transmission.

[0223] In an embodiment, AP 2104 truncates the sounding procedure (e.g., prior to the conclusion of the channel sounding phase 2130). Truncating the sounding procedure may also be referred to as terminating the sounding procedure, cancelling the sounding procedure, or ending the sounding procedure. For example, during a time period 2140, AP 2104 may transmit a frame 2132 to AP 2102 truncating the sounding procedure. In an embodiment, frame 2132 may correspond to frame 2022 discussed above for example 2000 and illustrated in FIG. 20.

[0224] In an embodiment, AP 2104 transmits frame 2132 prior to AP 2104 and AP 2102 initiating channel sounding phase 2130. In another embodiment, AP 2104 transmits frame 2122 during channel sounding phase 2130, and prior to completion of channel sounding phase 2130. In an embodiment, channel sounding phases 2110, 2120, and 2130 are expected to occur during a same TXOP (e.g., a same TXOP obtained by AP 2102). In another embodiment, channel sounding phases 2110 and 2120 occur during a first TXOP (e.g., a first TXOP obtained by AP 2102) and channel sounding phase 2130 is expected to occur during a second TXOP (e.g., a second TXOP obtained by AP 2104).

[0225] In an embodiment, frame 2132 may be an NDPA variant frame. For example, frame 2132 may contain a field indicating truncation of the sounding procedure. Alternatively, frame 2132 may be a different frame format, such as an action frame, a contention free-end (CF-END) frame, or any other suitable frame.

[0226] In an embodiment, based on receiving frame 2132, AP 2102 truncates / cancels / terminates the sounding procedure. AP 2102 may also cancel the COBF transmission with AP 2104, intended for after the sounding procedure. Further, after receiving frame 2132, AP 2102 may confirm truncating the sounding procedure by transmitting a frame 2134 (e.g., a CF-END frame). For example, when channel sounding phase 2130 is scheduled to be transmitted using the same TXOP as channel sounding phases 2110 and 2120,Docket No.: 24-3066PCTframe 2134 transmitted by AP 2102 may reset the NAV of STAs that may have been set until the end of the expected sounding procedure duration, so channel access can occur without waiting for the NAV to expire. It is noted that in embodiments where frame 2132 is a CF-END frame, STAs hearing frame 2132 may reset their NAVs based on frame 2132, before receiving frame 2134.

[0227] In another embodiment, AP 2104 may truncate channel sounding phase 2120 (e.g., prior to completion of channel sounding phase 2120). For example, AP 2104 may indicate truncation of the channel sounding in NDP 2124. AP 2102 may receive NDP 2124 and may truncate the sounding procedure and / or transmit a frame (e.g., a CF-END frame) confirming truncation of the sounding procedure.

[0228] Further, in an embodiment, AP 2102 may indicate to AP 2104 (e.g., prior to beginning channel sounding phase 2110) whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2102 may transmit a frame to AP 2104 (e.g., prior to beginning channel sounding phase 2110) indicating whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. As another example, NDPA frame 2112 (or NDPA frame 2122) may indicate whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. Alternatively, AP 2102 and AP 2104 may know before beginning channel sounding phase 2110 whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2102 and 2104 may negotiate this information during formation of the multi-AP group.

[0229] In an embodiment, truncating the sounding procedure (e.g., when AP 2104 does not have data to transmit using COBF) may avoid expending resources that would have been wasted, had the sounding procedure been completed unnecessarily.

[0230] FIG. 22 illustrates an example 2200 of a procedure according to an embodiment. As shown in FIG.22, example 2200 includes APs 2002 and 2004 and STAs 2006 and 2008. In an embodiment, APs 2002 and 2004, and STAs 2006 and 2008, described in example 2200 may correspond to APs 2002 and 2004, and STAs 2006 and 2008, described in example 2000.

[0231] As shown in FIG.22, example 2200 may begin with a sounding sequence 2010, as part of a sounding procedure with an expected sounding procedure duration 2030. In an embodiment, sounding sequence 2010 and expected sounding procedure duration 2030 described in example 2200 correspond with sounding sequence 2010 and expected sounding procedure duration 2030 described in example 2000. That is, sounding sequence 2010 may correspond with channel sounding phase 1510 of the joint NDP sounding procedure illustrated in FIG. 15.

[0232] In an embodiment, after sounding sequence 2010, AP 2004 does not have any frames to send via COBF, or AP 2004 otherwise does not wish to undertake sounding for a COBF transmission. For example, like in example 2000 described above, AP 2004 may have no buffered BUs to transmit to STAs that support responding as a beamformee in a COBF transmission (e.g., STA 2008). As another example, AP 2004 may prioritize transmission of buffered BUs to STAs that do not support COBF (e.g., for a subsequent duration),Docket No.: 24-3066PCTmay be unavailable during the COBF transmission, may identify the presence of a coexistence event during the COBF transmission, or may identify the presence of a restricted target wake time (r-TWT) service period during the COBF transmission. In an embodiment, AP 2004 truncates the sounding procedure (e.g., prior to the conclusion of the expected sounding procedure duration 2030).

[0233] For example, AP 2004 may be expected to transmit an NDPA frame 2222 during a time period 2220, as part of an expected second sounding sequence (e.g., for sounding STA 2008 associated with AP 2004). In an embodiment, AP 2004 may, instead, decline to transmit NDPA frame 2222 during time period 2220. AP 2002 may use the absence of NDPA frame 2222, from AP 2004, to truncate the sounding procedure (e.g., prior to the end of the expected sounding procedure duration 2030). In an embodiment, AP 2002 may wait a point coordination function interframe space (PIFS) duration for transmission of NDPA frame 2222 by AP 2004. If there is no transmission of NDPA frame 2222 during that time period, AP 2002 may truncate the sounding procedure. In an embodiment, the sounding sequence 2010 and the expected second sounding sequence for STA 2008 are expected to occur during a same TXOP (e.g., a same TXOP obtained by AP 2002). In another embodiment, the sounding sequence 2010 occurs during a first TXOP (e.g., a first TXOP obtained by AP 2002) and the expected sounding sequence for STA 2008 is expected to occur during a second TXOP (e.g., a second TXOP obtained by AP 2004).

[0234] In an embodiment, AP 2002 may also cancel the COBF transmission with AP 2004, intended for after the sounding procedure. Further, after identifying the lack of transmission of NDPA frame 2222 by AP 2004, AP 2002 may confirm truncating the sounding procedure by transmitting a frame 2224 (e.g., a CF-END frame). For example, frame 2224 transmitted by AP 2002 may reset the NAV of STAs that may have been set until the end of the expected sounding procedure duration 2030, so channel access can occur without waiting for the NAV to expire.

[0235] Further, in an embodiment, AP 2002 may indicate to AP 2004 (e.g., prior to beginning sounding sequence 2010) whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2002 may transmit a frame to AP 2004 (e.g., prior to beginning sounding sequence 2010) indicating whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. As another example, NDPA frame 2012 may indicate whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. Alternatively, AP 2002 and AP 2004 may know before beginning sounding sequence 2010 whether AP 2004 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2002 and 2004 may negotiate this information during formation of the multi-AP group.

[0236] In an embodiment, truncating the sounding procedure (e.g., when AP 2004 does not have data to transmit using COBF) may avoid expending resources that would have been wasted, had the sounding procedure been completed unnecessarily.Docket No.: 24-3066PCT

[0237] FIG. 23 illustrates an example 2300 of a procedure according to an embodiment. As shown in FIG.23, example 2300 includes APs 2102 and 2104 and STAs 2106 and 2108. In an embodiment, APs 2102 and 2104, and STAs 2106 and 2108, described in example 2300 may correspond to APs 2102 and 2104, and STAs 2106 and 2108, described in example 2100.

[0238] As shown in FIG. 23, example 2300 may begin with a channel sounding phase 2110 and a channel sounding phase 2120. In an embodiment, channel sounding phase 2110 and channel sounding phase 2120 described in example 2300 correspond with channel sounding phase 2110 and channel sounding phase 2120 described in example 2100. That is, channel sounding phase 2110 and channel sounding phase 2120 may correspond with channel sounding phases 1410 and 1420 of the sequential NDP sounding procedure illustrated in FIG. 14.

[0239] In an embodiment, after channel sounding phase 2120, AP 2104 does not have any frames to send via COBF, or AP 2104 otherwise does not wish to undertake sounding for a COBF transmission. For example, like in example 2100 described above, AP 2104 may have no buffered BUs to transmit to STAs that support responding as a beamformee in a COBF transmission (e.g., STA 2108). As another example, AP 2104 may prioritize transmission of buffered BUs to STAs that do not support COBF (e.g., for a subsequent duration), may be unavailable during the COBF transmission, may identify the presence of a coexistence event during the COBF transmission, or may identify the presence of a restricted target wake time (r-TWT) service period during the COBF transmission. In an embodiment, AP 2104 truncates the sounding procedure (e.g., prior to the conclusion of channel sounding phase 2130).

[0240] For example, AP 2104 may be expected to transmit an NDPA frame 2332 during a time period 2340, as part of channel sounding phase 2130 (e.g., for sounding STA 2108 associated with AP 2104). In an embodiment, AP2104 may, instead, decline to transmit NDPA frame 2332 during time period 2340. AP 2102 may use the absence of NDPA frame 2332, from AP 2104, to truncate the sounding procedure (e.g., prior to the end of channel sounding phase 2130). In an embodiment, AP 2102 may wait a PIFS duration for transmission of NDPA frame 2332 by AP 2104. If there is no transmission of NDPA frame 2332 during that time period, AP 2102 may truncate the sounding procedure.

[0241] In an embodiment, channel sounding phases 2110, 2120, and 2130 are expected to occur during a same TXOP (e.g., a same TXOP obtained by AP 2102). In another embodiment, channel sounding phases 2110 and 2120 occur during a first TXOP (e.g., a first TXOP obtained by AP 2102) and channel sounding phase 2130 is expected to occur during a second TXOP (e.g., a second TXOP obtained by AP 2104).

[0242] In an embodiment, AP 2102 may also cancel the COBF transmission with AP 2104, intended for after the sounding procedure. Further, after identifying the lack of transmission of NDPA frame 2332 by AP 2104, AP 2102 may confirm truncating the sounding procedure by transmitting a frame 2334 (e.g., a CF-END frame). For example, frame 2334 transmitted by AP 2102 may reset the NAV of STAs that may have beenDocket No.: 24-3066PCTset until the end of the expected sounding procedure duration, so channel access can occur without waiting for the NAV to expire.

[0243] Further, in an embodiment, AP 2102 may indicate to AP 2104 (e.g., prior to beginning channel sounding phase 2110) whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2102 may transmit a frame to AP 2104 (e.g., prior to beginning channel sounding phase 2110) indicating whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. As another example, NDPA frame 2112 (or NDPA frame 2122) may indicate whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. Alternatively, AP 2102 and AP 2104 may know before beginning channel sounding phase 2110 whether AP 2104 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2102 and 2104 may negotiate this information during formation of the multi-AP group.

[0244] In an embodiment, truncating the sounding procedure (e.g., when AP 2104 does not have data to transmit using COBF) may avoid expending resources that would have been wasted, had the sounding procedure been completed unnecessarily.

[0245] FIG. 24 illustrates an example 2400 of a procedure according to an embodiment. As shown in FIG.24, example 2400 includes APs 2402 and 2404 and STAs 2406 and 2408. STA 2406 may be associated with AP 2402 and STA 2408 may be associated with AP 2404. APs 2402 and 2404 may form a multi-AP group (e.g., a coordinating AP set). In example 2400, AP 2402 may wish to perform a coordinated beamforming (COBF) procedure with AP 2404 in a TXOP obtained by AP 2402 (and / or AP 2404). AP 2402 may be the AP coordinating / controlling the COBF procedure. As such, AP 2402 may be referred to as a master / sharing AP, and AP 2404 may be referred to as a slave / shared AP AP 2404 may be considered an OBSS AP relative to AP 2402 or STA 2406.

[0246] As shown in FIG. 24, example 2400 may begin with AP 2402 transmitting a frame 2412 to AP 2404. In an embodiment, frame 2412 may solicit from AP 2404 whether AP 2404 wishes to participate in sounding for COBF transmission. In an embodiment, AP 2404 transmits a response frame 2414, indicating whether AP 2404 wishes to participate in sounding for COBF transmission. AP 2402 may receive frame 2414 and may use the indication to determine whether to undertake sounding for only the BSS of which AP 2402 is a member, or sounding for both the BSS of which AP 2402 is a member and the BSS of which AP 2404 is a member.

[0247] In another embodiment, frame 2412 may solicit feedback from AP 2404 for a COBF transmission. For example, frame 2412 may solicit, from AP 2404, the presence at AP 2404 of one or more DL buffered BU for transmission via the COBF transmission. Alternatively, or in addition, frame 2412 may solicit, from AP 2404, availability or unavailability of AP 2404 during the COBF transmission. Alternatively, or in addition, frame 2412 may solicit, from AP 2404, a presence of a coexistence event during the COBF transmission.Docket No.: 24-3066PCTAlternatively, or in addition, frame 2412 may solicit, from AP 2404, a presence of a restricted target wake time (r-TWT) service period during the COBF transmission.

[0248] In this embodiment, AP 2404 may transmit frame 2414 in response to frame 2412, and may include the feedback solicited in frame 2412. For example, frame 2414 may indicate any combination of: the presence at AP 2404 of one or more DL buffered BU for transmission via the COBF transmission, availability or unavailability of AP 2404 during the COBF transmission, the presence of a coexistence event during the COBF transmission, and the presence of an r-TWT service period during the COBF transmission. In an embodiment, AP 2402 receives frame 2414 and uses the indicated feedback to determine whether to undertake sounding for only the BSS of which AP 2402 is a member, or sounding for both the BSS of which AP 2402 is a member and the BSS of which AP 2404 is a member.

[0249] In an embodiment, AP 2402 receives frame 2414 and determines to undertake sounding for both the BSS of which AP 2402 is a member and the BSS of which AP 2404 is a member (e.g., for COBF). AP 2402 may perform sounding sequence 2420 and sounding sequence 2430, to sound these separate BSSs. For example, AP 2402 and AP 2404 may perform sounding sequence 2420 to sound STA 2406, associated with AP 2402, and may perform sounding sequence 2430 to sound STA 2408, associated with AP 2404. In an embodiment, the sounding sequence 2420 and the sounding sequence 2430 may be expected to occur during a same TXOP (e.g., a same TXOP obtained by AP 2402). In another embodiment, sounding sequence 2430 occurs during a first TXOP (e.g., a first TXOP obtained by AP 2402) and sounding sequence 2430 is expected to occur during a second TXOP (e.g., a second TXOP obtained by AP 2404).

[0250] Thus, as one example, sounding sequences 2420 and 2430 may correspond with sounding sequences in a sequential sounding procedure, as discussed in example 1400 illustrated in FIG. 14 In this example, AP 2402 may correspond with AP 1402 discussed in example 1400 and AP 2404 may correspond with AP 1404 discussed in example 1400. During sounding sequence 2420, AP 2402 and AP 2404 may perform both channel sounding phase 1410 and channel sounding phase 1420 in example 1400, to sound channels between each respective AP and STA 2406. During sounding sequence 2430, AP 2402 and AP 2404 may again perform both channel sounding phase 1410 and channel sounding phase 1420 in example 1400, this time to sound channels between each respective AP and STA 2408.

[0251] As another example, sounding sequences 2420 and 2430 may correspond with sounding sequences in a joint sounding procedure, as discussed in example 1500 illustrated in FIG. 15. In this example, AP 2402 may correspond with AP 1502 discussed in example 1500 and AP 2404 may correspond with AP 1504 discussed in example 1500. In an example, sounding sequence 2420 may correspond with channel sounding phase 1510 in example 1500, and both AP 2402 and AP 2404 may sound channels between the respective APs and STA 2406. Sounding sequence 2430 may correspond with channel sounding phase 1520 in example 1500, and both AP 2402 and AP 2404 may sound channels between the respective APs and STA 2408.Docket No.: 24-3066PCT

[0252] Thus, in an embodiment, AP 2402 and AP 2404 may perform both sounding sequence 2420 and sounding sequence 2430 to sound channels for two BSSs, to facilitate COBF by AP 2402 and AP 2404. Alternatively, in an embodiment, AP 2402 and / or AP 2404 may truncate the sounding procedure. For example, AP 2402 may use frame 2414 to determine that COBF will not be performed and sounding should only be performed for the BSS of which AP 2402 is a member. This truncates the sounding procedure that would normally include both sounding sequence 2420 and sounding sequence 2430 to instead perform sounding for only the BSS of which AP 2402 is a member.

[0253] As another example, AP 2402 and AP 2404 may initiate a sounding procedure that includes both sounding sequence 2420 and sounding sequence 2430, to sound both the BSS of which AP 2402 is a member and the BSS of which AP 2404 is a member and eventually perform COBF, but AP 2402 and / or AP 2404 may truncate the sounding procedure before the completion of sounding sequence 2430. For example, as discussed above in relation to example 2000 illustrated in FIG. 20 and example 2100 illustrated in FIG.21, the responding AP (e.g., AP 2404) may truncate the sounding procedure by transmitting a frame to AP 2402 (e.g., frame 2022 in example 2000 or frame 2132 illustrated in FIG. 21). As another example, as discussed above in relation to example 2200 illustrated in FIG. 22 and example 2300 illustrated in FIG. 23, the responding AP (e.g., AP 2404) may truncate the sounding procedure by declining to transmit an expected NDPA (e.g., NDPA frame 2022 or NDPA frame 2332). In any of these examples, AP 2402 may transmit a frame (e.g., frame 2024, 2134, 2224, or 2334) confirming truncation / truncating the sounding procedure (e.g., AP 2402 may transmit a CF-END frame).

[0254] Further, in an embodiment, AP 2402 may indicate to AP 2404 (e.g., prior to beginning sounding sequence 2420 or sounding sequence 2430) whether AP 2404 is allowed, required, requested, or not allowed to truncate the sounding procedure. For example, AP 2402 may transmit a frame to AP 2404 (e.g., prior to beginning sounding sequence 2420 or sounding sequence 2430) indicating whether AP 2404 is allowed, required, requested, or not allowed to truncate the sounding procedure. As another example, frame 2412 may indicate whether AP 2404 is allowed, required, requested, or not allowed to truncate the sounding procedure. Alternatively, AP 2402 and AP 2404 may know, before beginning sounding sequence 2420 or sounding sequence 2430, whether AP 2404 is allowed, required, requested, or not allowed to truncate the sounding procedure.

[0255] In an embodiment, truncating the sounding procedure (e.g., when AP 2402 does not wish to perform COBF or does not have data to transmit using COBF) may avoid expending resources that would have been wasted, had the sounding procedure been completed unnecessarily.

[0256] FIG. 25 illustrates an example process 2500 according to an embodiment. Example process 2500 may be performed by a suitable AP, such as APs 2004, 2104, or 2404 illustrated in FIGS. 20-24, for example. As shown in FIG. 25, process 2500 may include step 2502.Docket No.: 24-3066PCT

[0257] Step 2502 includes receiving, by a first access point (AP) from a second AP, a first frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission. In an embodiment the second AP includes any suitable AP, including APs 2002, 2102, or 2402 illustrated in FIGS. 20-24, for example.

[0258] Step 2504 includes truncating the sounding procedure.

[0259] In an embodiment, the sounding procedure comprises a first sounding sequence and a second sounding sequence.

[0260] In an embodiment, the first sounding sequence comprises sounding a first channel between the first AP and a first STA associated with the second AP.

[0261] In an embodiment, the second sounding sequence comprises sounding a second channel between the first AP and a second STA associated with the first AP.

[0262] In an embodiment, the first sounding sequence further comprises sounding a third channel between the second AP and the first STA associated with the second AP

[0263] In an embodiment, the second sounding sequence further comprises sounding a fourth channel between the second AP and the second STA associated with the first AP.

[0264] In an embodiment, truncating the sounding procedure occurs prior to completion of the second sounding sequence.

[0265] In an embodiment, truncating the sounding procedure comprises the first AP not initiating the second sounding sequence.

[0266] In an embodiment, the first AP is configured to initiate the second sounding sequence based on receiving the first frame.

[0267] In an embodiment, the first AP is configured to truncate the sounding procedure, prior to completion of the second sounding sequence, based on at least one of: the first AP not having a downlink (DL) buffered bufferable unit (BU) for transmission via the COBF transmission, unavailability of the first AP during the COBF transmission, presence of a coexistence event during the COBF transmission, or presence of a restricted target wake time service period during the COBF transmission.

[0268] In an embodiment, the first AP being configured to initiate the second sounding sequence comprises the first AP being configured to transmit a first null data physical layer protocol data unit (NDP) announcement frame during a first time period of the sounding procedure.

[0269] In an embodiment, the first frame comprises a second NDP announcement frame.

[0270] In an embodiment, process 2500 further includes transmitting, by the first AP, an NDP in response to the first frame.

[0271] In an embodiment, truncating the sounding procedure, comprises: transmitting, by the first AP to the second AP, a second frame truncating the first sounding procedure.Docket No.: 24-3066PCT

[0272] In an embodiment, process 2500 further comprises receiving, by the first AP from the second AP, an indication requesting / allowing the first AP to transmit the second frame, wherein the transmitting of the second frame is further based on the indication.

[0273] In an embodiment, the indication is provided in the first frame or in a fourth frame received, by the first AP, from the second AP.

[0274] In an embodiment, the fourth frame comprises a trigger frame or an action frame.

[0275] In an embodiment, the second frame comprises a field indicating to the second AP that the first AP truncates the sounding procedure.

[0276] In an embodiment, a frame format of the second frame comprises at least one of: a null data packet announcement frame, or an action frame.

[0277] In an embodiment, the second frame comprises a contention free-end (CF-END) frame.

[0278] In an embodiment, truncating the sounding procedure comprises receiving, by the first AP from the second AP, a third frame.

[0279] In an embodiment, the third frame comprises at least one of: a CF-end frame, an action frame, or an NDP announcement frame.

[0280] In an embodiment, the receiving of the third frame is based on the first AP not transmitting a fourth frame during the sounding procedure.

[0281] In an embodiment, the process 2500 further includes receiving, by the first AP from the second AP and before receiving the first frame, a fifth frame soliciting feedback from the first AP for the COBF transmission.

[0282] In an embodiment, the feedback comprises one of: presence of a DL buffered BU for transmission via the COBF transmission, availability / unavailability of the first AP during the COBF transmission, presence of a coexistence event during the COBF transmission, or presence of a restricted target wake time service period during the COBF transmission.

[0283] In an embodiment, process 2500 further includes transmitting, by the first AP to the second AP, the feedback.

[0284] In an embodiment, the feedback is used by the second AP to determine whether to sound a single basic service set (BSS) or a plurality of BSSs.

[0285] In an embodiment, the first AP and second AP are members of a coordinating AP set.

[0286] In an embodiment, the sounding procedure comprises at least one of: a joint NDP sounding procedure, or a sequential NDP sounding procedure.

[0287] In an embodiment, the sounding procedure comprises an ultra high reliability (UHR) trigger based sounding procedure.

[0288] In an embodiment, the first sounding sequence and the second sounding sequence occur during a same transmit opportunity (TXOP).Docket No.: 24-3066PCT

[0289] In an embodiment, the first sounding sequence and the second sounding sequence occur during different TXOPs.

[0290] In an embodiment, the first sounding sequence occurs during a TXOP obtained by the second AP.

[0291] In an embodiment, the second sounding sequence occurs during a TXOP obtained by the first AP.

[0292] In an embodiment, based on the truncating the sounding procedure, the first AP does not perform the COBF transmission.

[0293] FIG. 26 illustrates another example process 2600 according to an embodiment. Example process 2600 may be performed by a suitable AP, including APs 2002, 2102, or 2402 illustrated in FIGS. 20-24, for example . As shown in FIG. 26, process 2600 may include step 2602.

[0294] Step 2602 includes transmitting, by a first access point (AP) to a second AP, a first frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission. In an embodiment, the second AP includes any suitable second AP, including APs 2004, 2104, or 2404 illustrated in FIGS. 20-24, for example

[0295] Step 2604 includes truncating the sounding procedure.

[0296] In an embodiment, sounding procedure comprises a first sounding sequence and a second sounding sequence.

[0297] In an embodiment, the first sounding sequence comprises sounding a first channel between the first AP and a first STA associated with the first AP.

[0298] In an embodiment, the second sounding sequence comprises sounding a second channel between the first AP and a second STA associated with the second AP.

[0299] In an embodiment, the first sounding sequence further comprises sounding a third channel between the second AP and the first STA associated with the first AP.

[0300] In an embodiment, the second sounding sequence further comprises sounding a fourth channel between the second AP and the second STA associated with the second AP.

[0301] In an embodiment, truncating the sounding procedure occurs prior to completion of the second sounding sequence.

[0302] In an embodiment, truncating the sounding procedure comprises the second AP not initiating the second sounding sequence.

[0303] In an embodiment, the second AP is configured to initiate the second sounding sequence based on receiving the first frame.

[0304] In an embodiment, the second AP is configured to truncate the sounding procedure, prior to completion of the second sounding sequence, based on at least one of: the second AP not having a downlink (DL) buffered bufferable unit (BU) for transmission via the COBF transmission, unavailability of the second AP during the COBF transmission, presence of a coexistence event during the COBF transmission, or presence of a restricted target wake time service period during the COBF transmission.Docket No.: 24-3066PCT

[0305] In an embodiment, the second AP being configured to initiate the second sounding sequence comprises the second AP being configured to transmit a first null data physical layer protocol data unit (NDP) announcement frame during a first time period of the sounding procedure.

[0306] In an embodiment, wherein the first frame comprises a second NDP announcement frame.

[0307] In an embodiment, process 2600 further comprises receiving, by the first AP from the second AP, an NDP in response to the first frame.

[0308] In an embodiment, truncating the sounding procedure, comprises: receiving, by the first AP from the second AP, a second frame truncating the first sounding procedure.

[0309] In an embodiment, process 2600 further comprises transmitting, by the first AP to the second AP, an indication requesting / allowing the second AP to transmit the second frame, wherein the transmitting of the second frame is further based on the indication.

[0310] In an embodiment, the indication is provided in the first frame or in a fourth frame transmitted, by the first AP, to the second AP.

[0311] In an embodiment, the fourth frame comprises a trigger frame or an action frame.

[0312] In an embodiment, the second frame comprises a field indicating to the first AP that the second AP truncates the sounding procedure.

[0313] In an embodiment, a frame format of the second frame comprises at least one of: a null data packet announcement frame, or an action frame.

[0314] In an embodiment, the second frame comprises a contention free - end (CF-END) frame.

[0315] In an embodiment, truncating the sounding procedure comprises transmitting, by the first AP to the second AP, a third frame.

[0316] In an embodiment, the third frame comprises at least one of: a CF-end frame, an action frame, or an NDP announcement frame.

[0317] In an embodiment, the transmitting of the third frame is based on the first AP not receiving a fourth frame, from the second AP, during the sounding procedure.

[0318] In an embodiment, process 2600 further includes transmitting, by the first AP to the second AP and before transmitting the first frame, a fifth frame soliciting feedback from the second AP for the COBF transmission.

[0319] In an embodiment, the feedback comprises one of: presence of a DL buffered BU for transmission via the COBF transmission, availability / unavailability of the second AP during the COBF transmission, presence of a coexistence event during the COBF transmission, or presence of a restricted target wake time service period during the COBF transmission.

[0320] In an embodiment, process 2600 further comprises receiving, by the first AP from the second AP, the feedback.Docket No.: 24-3066PCT

[0321] In an embodiment, the feedback is used by the first AP to determine whether to sound a single basic service set (BSS) or a plurality of BSSs.

[0322] In an embodiment, the first AP and second AP are members of a coordinating AP set.

[0323] In an embodiment, the sounding procedure comprises at least one of: a joint NDP sounding procedure, or a sequential NDP sounding procedure.

[0324] In an embodiment, the sounding procedure comprises an ultra high reliability (UHR) trigger based sounding procedure.

[0325] In an embodiment, the first sounding sequence and the second sounding sequence occur during a same transmit opportunity (TXOP).

[0326] In an embodiment, the first sounding sequence and the second sounding sequence occur during different TXOPs.

[0327] In an embodiment, the first sounding sequence occurs during a TXOP obtained by the first AP

[0328] In an embodiment, the second sounding sequence occurs during a TXOP obtained by the second AP.

[0329] In an embodiment, based on the truncating the sounding procedure, the second AP does not perform the COBF transmission.

[0330] In an embodiment, an AP or STA in accordance with the above-described embodiments (e.g., any AP or STA as described in FIGS. 6-7, 12, or 14-26) may perform operations according to a Co-BF sounding operation as described below. A person of skill in the art based on the teachings herein would appreciate that the below described features and operations may be readily combined with the above-described embodiments.

[0331] Transmit beamforming, DL MU-MIMO, and Co-BF involve knowledge of the channel state to compute a steering matrix that is applied to a transmit signal to optimize reception at one or more receivers. UHR STAs may use an EHT sounding protocol to determine channel state information for beamformed transmissions other than Co-BF.

[0332] UHR STAs may use a UHR sounding protocol to determine channel state information for Co-BF transmission. The UHR sounding protocol may be the same as an EHT TB sounding protocol, except as specified for Co-BF. For Co-BF, the UHR sounding protocol may provide an explicit feedback mechanism defined as UHR Co-BF sounding sequences. The UHR Co-BF sounding sequences may include a UHR Co-BF sequential NDP sounding sequence and a UHR Co-BF joint NDP sounding sequence. In the UHR Co-BF sounding sequences, a UHR Co-BF beamformee may measure a channel using a training signal transmitted by one or two UHR beamformers and may send back a transformed estimate of the channel state. A UHR beamformer may use the transformed estimate to derive a steering matrix.Docket No.: 24-3066PCT

[0333] A UHR Co-BF beamformee may return an estimate of the channel state via an EHT compressed beamforming / CQI report using MU feedback type. A UHR Co-BF beamformee may segment an EHT compressed beamforming / CQI report frame when segmentation is appropriate.

[0334] A UHR Co-BF beamformer may support a maximum MPDU length for an EHT Compressed Beamforming / CQI Report frame that is the minimum of 11 454 octets and the maximum length of the EHT Compressed Beamforming / CQI Report frame that the UHR Co-BF beamformer intends to solicit from one or more UHR Co-BF beamformees.

[0335] The term UHR Co-BF beamformer refers to a UHR AP that operates as an MU beamformer. The term UHR Co-BF beamformee refers to a UHR non-AP STA that operates as an MU beamformee. A UHR Co-BF beamformee is required to support only full bandwidth MU feedback.

[0336] A type of feedback solicited by a UHR Co-BF beamformer from a UHR Co-BF beamformee may be indicated in the Feedback Type And Ng field and the Codebook Size field in the STA Info field identifying the UHR Co-BF beamformee in a UHR NDP Announcement frame.

[0337] A bandwidth of feedback solicited by a UHR Co-BF beamformer from a UHR Co-BF beamformee may depend on a Partial BW Info field in the STA Info field identifying the UHR Co-BF beamformee in the UHR NDP Announcement frame, a bandwidth of a PPDU carrying the UHR NDP Announcement frame, and an operating bandwidth of the UHR Co-BF beamformee. The bandwidth of the PPDU carrying the UHR NDP Announcement frame and a subsequent EHT sounding NDP may be the same.

[0338] Full bandwidth MU feedback may refer to a feedback mode in which a feedback RU or MRU size indicated in the Partial BW Info field of the UHR NDP Announcement frame spans all available bandwidth within an operating bandwidth of the UHR Co-BF beamformee.

[0339] If the operating bandwidth of the UHR Co-BF beamformee is larger than or equal to the bandwidth of the EHT sounding NDP, the available bandwidth may be an entire PPDU bandwidth of the EHT sounding NDP when preamble puncturing is not applied on the PPDU, and may be an entire occupied PPDU bandwidth of the EHT sounding NDP when preamble puncturing is applied on the PPDU.

[0340] A UHR Co-BF beamformer may set the Partial BW Info field in a UHR NDP Announcement frame to a value that is listed for settings for bandwidth and the Partial BW Info field in an EHT NDP Announcement frame.

[0341] A UHR NDP Announcement frame may refrain from requesting feedback on any RU that is signaled as punctured in a U-SIG field of an EHT sounding NDP that follows the UHR NDP Announcement frame.

[0342] A UHR Co-BF beamformee may indicate a maximum supported data rate used in an EHT TB PPDU carrying an EHT compressed beamforming / CQI report in a TB Sounding Feedback Rate Limit field in a UHR PHY Capabilities Information field in a UHR Capabilities element transmitted by the UHR Co-BF beamformee.Docket No.: 24-3066PCT

[0343] A UHR Co-BF beamformer may refrain from soliciting an EHT TB PPDU with a BFRP Trigger frame that indicates a data rate greater than a data rate indicated by the UHR Co-BF beamformee in the TB Sounding Feedback Rate Limit field. A data rate indicated in the BFRP Trigger frame may be computed based on an RU Allocation field, a PS160 field, a UL EHT-MCS field, and an SS Allocation field in an EHT variant User Info field of the BFRP Trigger frame. The data rate may be computed based on a 1.6 ps Gl.

[0344] A UHR Co-BF beamformer that initiates a UHR Co-BF sounding sequence using a Co-BF Sounding Invite frame may be referred to as an initiating AP. A UHR Co-BF beamformer that responds to a Co-BF Sounding Invite frame from the initiating AP may be referred to as a responding AP.

[0345] To perform a UHR Co-BF sounding, an initiating AP may transmit a UHR NDP Announcement frame with three or more STA Info fields and an RA field set to a broadcast address. The STA Info fields may be identified only with an AP ID and AID values corresponding to the responding AP and to non-AP UHR STAs associated with the initiating AP.

[0346] The UHR NDP Announcement frame may be followed after a SIFS by an EHT sounding NDP transmitted from the responding AP in a UHR Co-BF sequential NDP sounding sequence, or by EHT sounding NDPs simultaneously transmitted from the initiating AP and the responding AP in a UHR Co-BF joint NDP sounding sequence. The one or more EHT sounding NDPs may be followed after a SIFS by a BFRP Trigger frame transmitted from the initiating AP. Subsequent BFRP Trigger frames, when present in the UHR Co-BF sounding sequence, may be transmitted after a SIFS following an EHT TB PPDU transmitted in response to a previous BFRP Trigger frame. Each UHR Co-BF beamformee that is addressed by a BFRP Trigger frame may respond after a SIFS with an EHT TB PPDU. All BFRP Trigger frames used within the UHR Co-BF sounding sequence may be EHT variant BFRP Trigger frames.

[0347] A UHR Co-BF sequential NDP sounding sequence may comprise an EHT TB sounding sequence and a cross-BSS UHR Co-BF sounding sequence. A UHR Co-BF beamformer may support a UHR Co-BF sequential NDP sounding sequence.

[0348] A UHR Co-BF sequential NDP sounding sequence initiated by one AP may comprise an EHT TB sounding sequence to collect channel state information from one or more associated non-AP STA(s), and a cross-BSS UHR Co-BF sounding sequence for a responding AP to collect channel state information from the same STA(s). The cross-BSS UHR Co-BF sounding sequence may use a sounding sequence corresponding to EHT TB sounding, except that the initiating AP may transmit the UHR NDP Announcement frame to solicit an EHT sounding NDP from the responding AP. The UHR NDP Announcement frame may be sent only to the responding AP and to non-AP UHR STA(s) associated with the initiating AP.

[0349] An EHT TB sounding sequence and a cross-BSS UHR Co-BF sounding sequence in a UHR Co-BF sequential NDP sounding sequence may be performed in different TXOPs or in the same TXOP.

[0350] When an EHT TB sounding sequence and a cross-BSS UHR Co-BF sounding sequence in a UHR Co-BF sequential NDP sounding sequence are performed in different TXOPs, an ordering of the EHT TBDocket No.: 24-3066PCTsounding sequence and the cross-BSS UHR Co-BF sounding sequence may be implementation dependent. A beamformer may skip the EHT TB sounding sequence when the beamformer already has in-BSS channel state information needed from all associated STA(s).

[0351] When an EHT TB sounding sequence and a cross-BSS UHR Co-BF sounding sequence in a UHR Co-BF sequential NDP sounding sequence are performed in the same TXOP, the cross-BSS UHR Co-BF sounding sequence may be performed first. A subsequent EHT NDP Announcement in the EHT TB sounding sequence may be transmitted after a SIFS following an EHT TB PPDU.

[0352] Before the cross-BSS UHR Co-BF sounding sequence, a Co-BF Sounding Invite frame and a Co-BF Sounding Response frame may be exchanged between an initiating AP and a responding AP. The responding AP may indicate acceptance or declination to participate in the cross-BSS UHR Co-BF sounding sequence in the Co-BF Sounding Response frame. Information indicating a minimum sounding NSS capability of participating non-AP STAs may be exchanged using the Co-BF Sounding Invite frame and the Co-BF Sounding Response frame.

[0353] In a UHR Co-BF sequential NDP sounding sequence, to collect channel state information (e.g., all the required channel state information) used to compute a steering matrix for Co-BF transmission, both UHR Co-BF beamformers may initiate a UHR Co-BF sequential NDP sounding sequence to solicit channel state information from their own associated non-AP STA(s).

[0354] An EHT TB sounding sequence and a cross-BSS UHR Co-BF sounding sequence in a UHR Co-BF sequential NDP sounding sequence may be performed in different TXOPs or in the same TXOP.

[0355] UHR Co-BF sequential NDP sounding sequences initiated by a pair of UHR Co-BF beamformers may be performed in the same TXOP or in different TXOPs.

[0356] When UHR Co-BF sequential NDP sounding sequences initiated by a pair of UHR Co-BF beamformers are both performed in the same TXOP, each UHR Co-BF beamformer may perform only one UHR Co-BF sequential NDP sounding sequence. In a same-TXOP case, the TXOP duration may be limited such that the TXOP duration does not exceed 8 ms.

[0357] A UHR Co-BF beamformer may support a UHR Co-BF joint NDP sounding sequence.

[0358] A UHR Co-BF joint NDP sounding sequence uses the same sounding sequence as EHT TB sounding, except that an initiating AP may transmit a UHR NDP Announcement frame followed after a SIFS by EHT sounding NDPs transmitted simultaneously by both the initiating AP and a responding AP. The UHR NDP Announcement frame may be sent only to the responding AP and to non-AP UHR STAs associated with the initiating AP.

[0359] Before the UHR Co-BF joint NDP sounding sequence, a Co-BF Sounding Invite frame and a Co-BF Sounding Response frame may be exchanged between the initiating AP and the responding AP. The responding AP may indicate acceptance or declination to participate in the UHR Co-BF joint NDP sounding sequence in the Co-BF Sounding Response frame. The information of the minimum sounding NSS capabilityDocket No.: 24-3066PCTof participating non-AP STAs may be exchanged by the Co-BF Sounding Invite frame and the Co-BF Sounding Response frame.

[0360] In a UHR Co-BF joint NDP sounding sequence, to collect all the required channel state to compute a steering matrix for Co-BF transmission, both UHR Co-BF beamformers may initiate the UHR TB joint NDP sounding to solicit channel state from their own associated non-AP STA(s).

[0361] UHR Co-BF joint NDP sounding sequences initiated by a pair of UHR Co-BF beamformers may be performed in the same TXOP or in different TXOPs.

[0362] In either a cross-BSS UHR Co-BF sounding sequence or a UHR Co-BF joint NDP sounding sequence, a responding AP uses information carried in a BFRP Trigger frame to receive a subsequent EHT TB PPDU transmitted by one or more non-AP STA(s) associated with an initiating AP.

[0363] When UHR Co-BF joint NDP sounding sequences initiated by a pair of UHR Co-BF beamformers are both performed in the same TXOP, each UHR Co-BF beamformer may perform only one UHR Co-BF joint NDP sounding sequence. In a same-TXOP case, the TXOP duration does not exceed 8 ms.

[0364] A UHR Co-BF beamformer that sends a BFRP Trigger frame may set the Feedback Segment Retransmission Bitmap fields of the BFRP Trigger frame to all 1s.

[0365] A UHR Co-BF beamformer may initiate a UHR Co-BF sounding sequence when the feedback is computed based on parameters supported by the UHR Co-BF beamformee(s) associated with the initiating AP. A UHR Co-BF beamformer may refrain from initiating a UHR Co-BF sounding sequence when the feedback would be computed based on parameters not supported by the UHR Co-BF beamformee(s) associated with the initiating AP.

[0366] A UHR Co-BF beamformer that transmits a UHR NDP Announcement frame may set the AID11 field of a first STA Info field to 2047 and the AID11 field of a second STA Info field to a responding AP identifier.

[0367] In a UHR Co-BF sounding sequence, the Starting Spatial Streams field in a UHR NDP Announcement is set to 0 in a UHR Co-BF sequential NDP sounding sequence and is set to 1 in a UHR Co-BF joint NDP sounding sequence.

[0368] A UHR Co-BF beamformer that transmits a UHR NDP Announcement frame to one or more UHR Co-BF beamformees may set the AID11 field to the 11 least significant bits of the AID of each UHR Co-BF beamformee starting from the third STA Info field. A UHR NDP Announcement frame does not include multiple STA Info fields that have the same value in the AID11 field.

[0369] In a UHR Co-BF sounding sequence, a STA Info field in the UHR NDP Announcement frame that solicits MU feedback indicates the subcarrier grouping, Ng, codebook size, and number of columns, Nc, to be used by the UHR Co-BF beamformee identified by the STA Info field for generation of MU feedback.

[0370] A UHR Co-BF beamformer that transmits a UHR NDP Announcement frame may set the Partial BW Info field in a STA Info field to indicate the feedback subcarrier indices of a solicited EHT compressed beamforming / CQI report. The UHR Co-BF beamformer may set the Partial BW Info field such that theDocket No.: 24-3066PCTsubcarrier indices scidx(i), for i = 0, 1, .... Ns-1 , fall within the operating channel width of the corresponding UHR Co-BF beamformee.

[0371] A UHR Co-BF beamformer sets the TXVECTOR parameter CH_BANDWIDTH or CH_BANDWIDTH_IN_NON_HT and the Partial BW Info field of the UHR NDP Announcement frame based on the operating channel width of the beamformee, the operating channel width of the beamformer, and the feedback RU or MRU size.

[0372] A UHR Co-BF beamformee that receives a UHR NDP Announcement frame as part of a UHR Co-BF sounding sequence with a STA Info field identifying the UHR Co-BF beamformee and soliciting MU feedback generates a UHR compressed beamforming / CQI report using the feedback type, Ng, codebook size, and Nc indicated in the STA Info field.

[0373] If the UHR Co-BF beamformee receives a BFRP Trigger frame with a matching User Info field, the UHR Co-BF beamformee transmits an EHT TB PPDU containing the EHT compressed beamforming / CQI report.

[0374] A UHR Co-BF beamformee that transmits an EHT compressed beamforming / CQI frame sets the Partial BW Info field of the EHT MIMO Control field to indicate the range of subcarriers for which compressed beamforming / CQI information is provided. The Partial BW Info field is set to the value of the Partial BW Info field of the NDP Announcement frame for the UHR Co-BF beamformee.

[0375] An AP that sends a BFRP Trigger frame may allocate sufficient resources for the EHT TB PPDU response for each UHR Co-BF beamformee to include all solicited feedback, including feedback that is segmented and including an HT Control field in each frame.

[0376] A UHR Co-BF beamformer that sends a BFRP Trigger frame to solicit an EHT TB PPDU from more than one UHR Co-BF beamformee in a cross-BSS UHR Co-BF sounding sequence or a UHR Co-BF joint NDP sounding sequence applies non-MU-MIMO OFDMA.

[0377] A UHR Co-BF beamformee receiving a BFRP Trigger frame with a matching STA Info field transmits an EHT TB PPDU containing the EHT compressed beamforming / CQI report.

[0378] A UHR Co-BF beamformer that sends a BFRP Trigger frame to retrieve an EHT compressed beamforming / CQI report from a UHR Co-BF beamformee may solicit all possible EHT Sounding Feedback Segment fields by setting all bits in the Feedback Segment Retransmission Bitmap field to 1 in the User Info field identifying the UHR Co-BF beamformee.

[0379] A UHR Co-BF beamformer that fails to receive some or all feedback segments of the EHT compressed beamforming / CQI report from the UHR Co-BF beamformee may refrain from using a BFRP Trigger frame to request retransmission of the feedback segments.

[0380] For UHR Co-BF sounding that uses an EHT sounding NDP, the TXVECTOR parameters for the EHT sounding NDP may be configured as follows:- FORMAT is set to EHT_MU.Docket No.: 24-3066PCT— APEP_LENGTH is set to 0.— EHT_LTF_TYPE is set to 2*EHT-LTF.— GI_TYPE is set to either 0.8 ps Gl or 1.6 ps Gl.— Number Of EHT-LTF Symbols is set to 4 or 8.— NSS is set to 4 or 8 spatial streams.— CH_BANDWIDTH is set to the value indicated in the special STA Info field.— SPATIAL_REUSE is set to PSR_AND_NON_SRG_OBSS_PD_PROHIBITED.— BSS_COLOR is set to the value indicated in the special STA Info field.— TXOP_DURATION is set to either 127 or a defined value.

[0381] The intended recipient or recipients of an EHT sounding NDP are the STA or STAs addressed by the STA Info field or fields in the immediately preceding UHR NDP Announcement frame.

[0382] In an embodiment, an AP or STA in accordance with the above-described embodiments (e g., any AP or STA as described in FIGS. 6-7, 12, or 14-26) may further perform operations according to an MAPC framework as described below. A person of skill in the art based on the teachings herein would appreciate that the below described features and operations may be readily combined with the above-described embodiments.

[0383] The MAPC framework includes a set of schemes, including Co-BF, Co-SR, Co-TDMA, Co-RTWT, and Co-CR, and associated procedures in which APs operating their basic service sets (BSSs) on the same primary 20 MHz channel coordinate to reduce interference levels and to improve network performance, including medium utilization efficiency, communication reliability, and latency.

[0384] An AP may use a MAPC scheme with another AP if the AP has established an agreement for that MAPC scheme by following common MAPC procedures or via other means outside the scope of this description.

[0385] The common procedures described herein are applicable to all MAPC coordination schemes. MAPC discovery procedures enable APs to advertise and discover MAPC capabilities and parameters. MAPC agreement negotiation procedures enable APs to establish, update, or tear down MAPC agreements. Procedures that are specific to individual coordination schemes may be performed separately.

[0386] In some examples, two APs that belong to the same extended service set (ESS) may enable the use of MAPC schemes via mechanisms other than MAPC discovery and MAPC agreement negotiation procedures.

[0387] MAPC discovery procedures enable APs to advertise and discover MAPC capabilities and MAPC parameters of other APs.

[0388] An AP may advertise its MAPC capabilities, common MAPC parameters, and parameters specific to MAPC schemes by transmitting a MAPC Discovery Request frame to a broadcast address or as an individually addressed frame to another AP.Docket No.: 24-3066PCT

[0389] If an AP receives a soliciting MAPC Discovery Request frame from a transmitting AP, the receiving AP may respond by sending a MAPC Discovery Response frame to a broadcast address or as an individually addressed Management frame to the transmitting AP. A value of a Dialog Token field of the MAPC Discovery Response frame may be set equal to a value of a Dialog T oken field of the soliciting MAPC Discovery Request frame.

[0390] An AP that transmits a MAPC Discovery Request frame or a MAPC Discovery Response frame may include a Per-Scheme Profile subelement in a reported MAPC element for each MAPC scheme for which the AP signals capability. The AP may omit a MAPC Scheme Request Set field in the reported Per-Scheme Profile subelements.

[0391] If an AP that transmits a MAPC Discovery Request frame or a MAPC Discovery Response frame to a peer AP sets a MAPC Security Supported field carried in the MAPC element to a value of one, the AP may include a Robust Security Network Element (RSNE) field and a Robust Security Network Extension Element (RSNXE) field in a Security Profile subelement of the MAPC element.

[0392] MAPC agreement negotiation procedures enable establishment, update, or teardown of MAPC agreements through negotiation. An AP may follow the procedures described herein, in addition to schemespecific procedures, to establish, update, or tear down MAPC agreements.

[0393] A MAPC requesting AP is an AP that initiates a MAPC negotiation for one or more MAPC schemes with another AP. A MAPC requesting AP may refrain from initiating a MAPC negotiation for a specific MAPC scheme with a peer AP if the peer AP indicates non-support for that MAPC scheme in a MAPC Common Info field reported in a most recently received MAPC Discovery Request frame, MAPC Discovery Response frame, or MAPC Negotiation Request frame.

[0394] A MAPC responding AP is an AP that responds to a MAPC requesting AP.

[0395] A MAPC requesting AP may initiate a MAPC negotiation for one or more MAPC schemes by sending an individually addressed MAPC Negotiation Request frame to another AP. The MAPC Negotiation Request frame may include a MAPC element including at least one Per-Scheme Profile subelement in a MAPC Schemes Info field. A Per-Scheme Profile subelement for a specific MAPC scheme may be omitted if the MAPC requesting AP has not indicated support for that MAPC scheme in a MAPC Capabilities field carried in the MAPC element. When a Per-Scheme Profile subelement is included, the Per-Scheme Profile subelement may carry a MAPC Scheme Request Set field including at least one MAPC Scheme Request field.

[0396] Each Per-Scheme Profile subelement of the MAPC Schemes Info field in a MAPC Negotiation Request frame may carry one or more requests for a specific MAPC scheme.

[0397] A MAPC responding AP that receives an individually addressed MAPC Negotiation Request frame from a MAPC requesting AP may respond by sending an individually addressed MAPC NegotiationDocket No.: 24-3066PCTResponse frame to the MARC requesting AP. A value of a Dialog Token field of the MAPC Negotiation Response frame may be set equal to a value of a Dialog Token field of the MAPC Negotiation Request frame.

[0398] A Status Code field of the MAPC Negotiation Response frame may be set to SUCCESS if the MAPC responding AP accepts at least one request carried in the received MAPC Negotiation Request frame. Otherwise, the MAPC responding AP may set a Status Code field to indicate a rejection status code.

[0399] The MAPC Negotiation Response frame may include a MAPC element including one Per-Scheme Profile subelement in a MAPC Schemes Info field for each Per-Scheme Profile subelement included by the MAPC requesting AP in the MAPC Negotiation Request frame.

[0400] In the MAPC Negotiation Response frame, each Per-Scheme Profile subelement may include a MAPC Scheme Request field with a MAPC Operation Type field set to a value of 3, 4, or 5. If the MAPC Operation Type field is set to 3 or 4, a MAPC Request Parameter Set field may be omitted. A MAPC Operation Type field set to 3 may indicate acceptance of a request. A MAPC Operation Type field set to 4 may indicate rejection of a request. A MAPC Operation Type field set to 5 may indicate rejection of a request with an indication that a subsequent request may be accepted with parameter values included by the MAPC responding AP in a MAPC Request Parameter Set field. A MAPC Operation Type field set to 5 may be omitted when a MAPC Request Parameter Set field is not present for a corresponding MAPC scheme.

[0401] After two APs establish a MAPC agreement, either AP may initiate a MAPC negotiation as a MAPC requesting AP to update or tear down the MAPC agreement.

[0402] To request establishment of a new MAPC agreement, a MAPC requesting AP may set a MAPC Operation Type field to a value of zero. When the MAPC Operation Type field is set to zero, a MAPC Request Parameter Set field may be included according to scheme-specific rules for each MAPC scheme.

[0403] A MAPC requesting AP may refrain from requesting establishment of a new MAPC agreement for a specific MAPC scheme if a MAPC responding AP indicates that MAPC agreement establishment is disabled for that MAPC scheme in a most recently received MAPC Discovery Request frame, MAPC Discovery Response frame, or MAPC Negotiation Request frame.

[0404] A MAPC responding AP may accept, reject, or reject with suggested alternative parameters for MAPC agreement establishment by following MAPC agreement negotiation procedures. If a MAPC responding AP accepts a request to establish a new MAPC agreement for a specific MAPC scheme, the MAPC requesting AP and the MAPC responding AP are considered to have established a MAPC agreement for that specific MAPC scheme.

[0405] A MAPC requesting AP and a MAPC responding AP may establish up to one MAPC agreement for each of Co-BF, Co-SR, and Co-TDMA, and up to one MAPC agreement per restricted target wake time (R-TWT) schedule for Co-RTWT.Docket No.: 24-3066PCT

[0406] A MAPC requesting AP may refrain from indicating agreement update or agreement teardown for a MAPC scheme in a MAPC Negotiation Request frame when no established MAPC agreement exists for that MAPC scheme between the MAPC requesting AP and the MAPC responding AP

[0407] When an AP participates in MAPC negotiation to establish one or more new MAPC agreements, the AP may additionally assign an AP identifier (AP ID) to a peer AP with which the AP establishes a MAPC agreement.

[0408] An AP ID corresponds to an association identifier value. The same AP ID value may not be assigned by an AP or by an affiliated multi-link device (MLD) to any other station (STA). The same AP ID value may not be assigned by any other AP within a same multiple BSSID set to any other STA. The same AP ID value may not be assigned by any other AP MLD having any affiliated AP within the same multiple BSSID set to any other non-AP MLD.

[0409] When an AP belongs to a multiple BSSID set, an assigned AP ID value may be greater than 2n, where n is a value carried in a MaxBSSID Indicator field.

[0410] To assign an AP ID to another AP, an AP may include an AP ID field in a MAPC element.

[0411] A MAPC requesting AP may omit an AP ID field in a MAPC element carried in a transmitted MAPC Negotiation Request frame unless no MAPC agreement exists between the MAPC requesting AP and the MAPC responding AP for any of Co-BF, Co-SR, or Co-TDMA and the MAPC requesting AP is requesting establishment of a new MAPC agreement for at least one of Co-BF, Co-SR, or Co-TDMA.

[0412] A MAPC responding AP may omit an AP ID field in a MAPC element carried in a transmitted MAPC Negotiation Response frame unless no MAPC agreement exists between the MAPC requesting AP and the MAPC responding AP for any of Co-BF, Co-SR, or Co-TDMA and the MAPC responding AP accepts a new MAPC agreement for at least one of Co-BF, Co-SR, or Co-TDMA.

[0413] If all MAPC agreements among Co-BF, Co-SR, and Co-TDMA between two APs cease to exist, AP IDs assigned by the MAPC requesting AP and the MAPC responding AP are no longer valid.

[0414] To request a parameter update for an established MAPC agreement, a MAPC requesting AP may set a MAPC Operation Type field to a value of one. When the MAPC Operation Type field is set to one, a MAPC Request Parameter Set field may be included according to scheme-specific rules.

[0415] A MAPC responding AP may accept, reject, or reject with suggested alternative parameters for an update of an existing MAPC agreement. If the MAPC responding AP rejects the update by setting the MAPC Operation Type field to a value of four or five, the agreement update procedure fails and parameters of the MAPC agreement remain unchanged.

[0416] To request teardown of an established MAPC agreement, a MAPC requesting AP may set a MAPC Operation Type field to a value of two in a MAPC Scheme Request field that carries the request. When the MAPC Operation Type field is set to two, a MAPC Request Parameter Set field may be omitted.Docket No.: 24-3066PCT

[0417] A MAPC responding AP may accept a request to tear down an existing MAPC agreement by following MAPC agreement negotiation procedures.

[0418] When a MAPC requesting AP tears down a last MAPC agreement among Co-BF, Co-SR, and Co-TDMA with a MAPC responding AP, mutually assigned AP IDs may be released and become available for reassignment.

Claims

Docket No.: 24-3066PCTCLAIMSWhat is claimed is:

1. A method comprising:transmitting, by a first access point (AP) to a second AP, a first frame soliciting whether the second AP wishes to participate in a joint null data packet (NDP) sounding sequence for a coordinated beamforming (Co-BF) transmission;receiving, by the first AP from the second AP, a second frame indicating whether the second AP wishes to participate in the joint NDP sounding sequence;after receiving the second frame, transmitting, by the first AP to the second AP, an NDP announcement (NDPA) frame initiating the joint NDP sounding sequence;transmitting, by the first AP, a first NDP, after a short interframe space (SIPS) from the NDPA frame;transmitting, by the first AP to a first station (STA), a beamforming report poll (BFRP) trigger frame after transmitting the first NDP; andreceiving, by the first AP from the first STA, a beamforming report.

2. The method of claim 1 , wherein first AP comprises an initiating AP for the joint NDP sounding sequence and the second AP comprises a responding AP for the joint NDP sounding sequence.

3. The method of any of claims 1-2, wherein the first AP and the second AP each comprise an ultra high reliability (UHR) Co-BF beamformer.

4. The method of any of claims 1-3, wherein the first frame comprises a Co-BF sounding invite frame.

5. The method of any of claims 1-4, wherein the second frame comprises a Co-BF sounding response frame.

6. The method of any of claims 1-5, wherein the second frame indicates that the second AP accepts to participate in the joint NDP sounding sequence.

7. The method of any of claims 1-6, wherein the NDPA frame comprises a receiver address (RA) field set to a broadcast address.

8. The method of any of claims 1-7, wherein the NDPA frame comprises a plurality of STA info fields.

9. The method of claim 8, wherein the plurality of STA info fields indicate an association identifier (AID) for a second STA associated with the first AP.

10. The method of any of claims 1-9, wherein the first NDP comprises an extremely high throughput (EHT) NDP.

11. The method of any of claims 1-10, wherein the first AP transmits the first NDP simultaneously with the second AP transmitting a second NDP.

12. The method of claim 11, wherein the second AP transmits the second NDP in response to the NDPA frame.Docket No.: 24-3066PCT13. The method of any of claims 1-12, wherein the beamforming report comprises a compressed beamforming / CQI report.

14. The method of any of claims 1-13, wherein the BFRP trigger frame comprises a Feedback Segment Retransmission Bitmap field that comprises a plurality of bits.

15. The method of claim 14, wherein the first AP sets all of the plurality of bits of the Feedback Segment Retransmission Bitmap field to 1.

16. The method of any of claims 14-15, wherein the Feedback Segment Retransmission Bitmap field indicates that the first AP solicits all possible feedback segments.

17. The method of any of claims 14-16, wherein the Feedback Segment Retransmission Bitmap field is comprised in a user info field of the BFRP trigger frame.

18. A method comprising:receiving, by a first access point (AP) from a second AP, a first null data physical layer protocol data unit (NDP) announcement frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission, wherein the first AP is configured to transmit a second NDP announcement frame during a first time period of the sounding procedure when the first AP has a downlink (DL) buffered bufferable unit (BU) for transmission via the COBF transmission; and based on absence at the first AP of DL buffered BUs for transmission via the COBF transmission, transmitting, by the first AP to the second AP and during the sounding procedure, a second frame truncating the sounding procedure.

19. A method comprising:receiving, by a first access point (AP) from a second AP, a first frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission; andtruncating the sounding procedure.

20. The method of claim 19, wherein the sounding procedure comprises a first sounding sequence and a second sounding sequence,wherein the first sounding sequence comprises sounding a first channel between the first AP and a first STA associated with the second AP, andwherein the second sounding sequence comprises sounding a second channel between the first AP and a second STA associated with the first AP.

21. The method of claim 20, wherein the first sounding sequence further comprises sounding a third channel between the second AP and the first STA associated with the second AP.

22. The method of any of claims 20-21 , wherein the second sounding sequence further comprises sounding a fourth channel between the second AP and the second STA associated with the first AP.

23. The method of any of claims 20-22, wherein truncating the sounding procedure occurs prior to completion of the second sounding sequence.Docket No.: 24-3066PCT24. The method of any of claims 20-23, wherein truncating the sounding procedure comprises the first AP not initiating the second sounding sequence.

25. The method of any of claims 20-24, wherein the first AP is configured to initiate the second sounding sequence based on receiving the first frame.

26. The method of any of claims 20-25, wherein the first AP is configured to truncate the sounding procedure, prior to completion of the second sounding sequence, based on at least one of:the first AP not having a downlink (DL) buffered bufferable unit (BU) for transmission via the COBF transmission;unavailability of the first AP during the COBF transmission,presence of a coexistence event during the COBF transmission, orpresence of a restricted target wake time service period during the COBF.

27. The method of any of claims 25-26, wherein the first AP being configured to initiate the second sounding sequence comprises the first AP being configured to transmit a first null data physical layer protocol data unit (NDP) announcement frame during a first time period of the sounding procedure.

28. The method of any of claims 19-27, wherein the first frame comprises a second NDP announcement frame.

29. The method of any of claims 19-28, further comprising transmitting, by the first AP, an NDP in response to the first frame.

30. The method of any of claims 19-29, wherein truncating the sounding procedure, comprises:transmitting, by the first AP to the second AP, a second frame truncating the first sounding procedure.

31. The method of claim 30, further comprising receiving, by the first AP from the second AP, an indication requesting / al lowing the first AP to transmit the second frame, wherein the transmitting of the second frame is further based on the indication.

32. The method of claim 31 , wherein the indication is provided in the first frame or in a fourth frame received, by the first AP, from the second AP.

33. The method of claim 32, wherein the fourth frame comprises a trigger frame or an action frame.

34. The method of any of claims 30-33, wherein the second frame comprises a field indicating to the second AP that the first AP truncates the sounding procedure.

35. The method of claim 34, wherein a frame format of the second frame comprises at least one of:a null data packet announcement frame; oran action frame.Docket No.: 24-3066PCT36. The method of any of claims 30-34, wherein the second frame comprises a contention free - end (CF- END) frame.

37. The method of any of claims 19-29, wherein truncating the sounding procedure comprises receiving, by the first AP from the second AP, a third frame.

38. The method of claim 37, wherein the third frame comprises at least one of:a CF-end frame;an action frame; oran NDP announcement frame.

39. The method of any of claims 37-38, wherein the receiving of the third frame is based on the first AP not transmitting a fourth frame during the sounding procedure.

40. The method of any of claims 19-39, further comprising receiving, by the first AP from the second AP and before receiving the first frame, a fifth frame soliciting feedback from the first AP for the COBF transmission.

41. The method of claim 40, wherein the feedback comprises one of:presence of a DL buffered BU for transmission via the COBF transmission; availability / unavailability of the first AP during the COBF transmission,presence of a coexistence event during the COBF transmission, orpresence of a restricted target wake time service period during the COBF transmission.

42. The method of any of claims 40-41, further comprising:transmitting, by the first AP to the second AP, the feedback.

43. The method of claim 42, wherein the feedback is used by the second AP to determine whether to sound a single basic service set (BSS) or a plurality of BSSs.

44. The method of any of claims 19-43, wherein the first AP and second AP are members of a coordinating AP set.

45. The method of any of claims 19-44, wherein the sounding procedure comprises at least one of:a joint NDP sounding procedure; ora sequential NDP sounding procedure.

46. The method of any of claims 19-45, wherein the sounding procedure comprises an ultra high reliability (U HR) trigger based sounding procedure.

47. The method of claim 20, wherein the first sounding sequence and the second sounding sequence occur during a same transmit opportunity (TXOP).

48. The method of claim 20, wherein the first sounding sequence and the second sounding sequence occur during different TXOPs.

49. The method of claim 48, wherein the first sounding sequence occurs during a TXOP obtained by the second AP.Docket No.: 24-3066PCT50. The method of any of claims 48-49, wherein the second sounding sequence occurs during a TXOP obtained by the first AP.

51. The method of any of claims 19-50, wherein, based on the truncating the sounding procedure, the first AP does not perform the COBF transmission.

52. A method comprising:transmitting, by a first access point (AP) to a second AP, a first null data physical layer protocol data unit (NDP) announcement frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission, wherein the first AP is configured to receive, from the second AP, a second NDP announcement frame during the sounding procedure; andreceiving, by the first AP from the second AP and during the sounding procedure, a second frame truncating the sounding procedure.

53. A method comprising:transmitting, by a first access point (AP) to a second AP, a first frame initiating a sounding procedure for a coordinated beamforming (COBF) transmission; andtruncating the sounding procedure.

54. The method of claim 53, wherein the sounding procedure comprises a first sounding sequence and a second sounding sequence,wherein the first sounding sequence comprises sounding a first channel between the first AP and a first STA associated with the first AP, andwherein the second sounding sequence comprises sounding a second channel between the first AP and a second STA associated with the second AP.

55. The method of claim 54, wherein the first sounding sequence further comprises sounding a third channel between the second AP and the first STA associated with the first AP.

56. The method of any of claims 54-55, wherein the second sounding sequence further comprises sounding a fourth channel between the second AP and the second STA associated with the second AP.

57. The method of any of claims 54-56, wherein truncating the sounding procedure occurs prior to completion of the second sounding sequence.

58. The method of any of claims 54-57, wherein truncating the sounding procedure comprises the second AP not initiating the second sounding sequence.

59. The method of any of claims 54-58, wherein the second AP is configured to initiate the second sounding sequence based on receiving the first frame.

60. The method of any of claims 54-59, wherein the second AP is configured to truncate the sounding procedure, prior to completion of the second sounding sequence, based on at least one of:Docket No.: 24-3066PCTthe second AP not having a downlink (DL) buffered bufferable unit (BU) for transmission via the COBF transmission;unavailability of the second AP during the COBF transmission,presence of a coexistence event during the COBF transmission, orpresence of a restricted target wake time service period during the COBF.

61. The method of any of claims 59-60, wherein the second AP being configured to initiate the second sounding sequence comprises the second AP being configured to transmit a first null data physical layer protocol data unit (NDP) announcement frame during a first time period of the sounding procedure.

62. The method of any of claims 53-61 , wherein the first frame comprises a second NDP announcement frame.

63. The method of any of claims 53-62, further comprising receiving, by the first AP from the second AP, an NDP in response to the first frame.

64. The method of any of claims 53-63, wherein truncating the sounding procedure, comprises:receiving, by the first AP from the second AP, a second frame truncating the first sounding procedure.

65. The method of claim 64, further comprising transmitting, by the first AP to the second AP, an indication requesting / al lowing the second AP to transmit the second frame, wherein the transmitting of the second frame is further based on the indication.

66. The method of claim 65, wherein the indication is provided in the first frame or in a fourth frame transmitted, by the first AP, to the second AP.

67. The method of claim 66, wherein the fourth frame comprises a trigger frame or an action frame.

68. The method of any of claims 64-67, wherein the second frame comprises a field indicating to the first AP that the second AP truncates the sounding procedure.

69. The method of claim 68, wherein a frame format of the second frame comprises at least one of:a null data packet announcement frame; oran action frame.

70. The method of any of claims 64-68, wherein the second frame comprises a contention free - end (CF- END) frame.

71. The method of any of claims 53-63, wherein truncating the sounding procedure comprises transmitting, by the first AP to the second AP, a third frame.

72. The method of claim 71, wherein the third frame comprises at least one of:a CF-end frame;an action frame; oran NDP announcement frame.Docket No.: 24-3066PCT73. The method of any of claims 71-72, wherein the transmitting of the third frame is based on the first AP not receiving a fourth frame, from the second AP, during the sounding procedure.

74. The method of any of claims 53-73, further comprising transmitting, by the first AP to the second AP and before transmitting the first frame, a fifth frame soliciting feedback from the second AP for the COBF transmission.

75. The method of claim 74, wherein the feedback comprises one of:presence of a DL buffered BU for transmission via the COBF transmission; availability / unavailability of the second AP during the COBF transmission,presence of a coexistence event during the COBF transmission, orpresence of a restricted target wake time service period during the COBF.

76. The method of any of claims 74-75, further comprising:receiving, by the first AP from the second AP, the feedback.

77. The method of claim 76, wherein the feedback is used by the first AP to determine whether to sound a single basic service set (BSS) or a plurality of BSSs.

78. The method of any of claims 53-77, wherein the first AP and second AP are members of a coordinating AP set.

79. The method of any of claims 53-78, wherein the sounding procedure comprises at least one of:a joint NDP sounding procedure; ora sequential NDP sounding procedure.

80. The method of any of claims 53-79, wherein the sounding procedure comprises an ultra high reliability (UHR) trigger based sounding procedure.

81. The method of claim 54, wherein the first sounding sequence and the second sounding sequence occur during a same transmit opportunity (TXOP).

82. The method of claim 54, wherein the first sounding sequence and the second sounding sequence occur during different TXOPs.

83. The method of claim 82, wherein the first sounding sequence occurs during a TXOP obtained by the first AP.

84. The method of any of claims 82-83, wherein the second sounding sequence occurs during a TXOP obtained by the second AP.

85. The method of any of claims 53-84, wherein, based on the truncating the sounding procedure, the second AP does not perform the COBF transmission.

86. A device comprising:one or more processors; andmemory storing instructions that, when executed by the one or more processors, cause the device to perform a method according to any of claims 1-85.Docket No.: 24-3066PCT87. 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

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