Multi-access point coordinated beamforming

Abstract

A first access point (AP) receives a frame from a second AP. The frame represents a beamforming transmission by the first AP and the second AP, and an allowable reception interference level (ARIL) at a first station (STA) associated with the second AP, of a physical layer protocol data unit (PPDU) transmitted by the first AP to a second STA associated with the first AP for the beamforming transmission. Based on the ARIL, the first AP determines a beamforming weight set for beamforming transmission. The first AP transmits a beamformed PPDU based on the beamforming weight set for beamforming transmission to the second STA.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 601,791 filed November 22, 2023, the entirety of which is incorporated herein by reference. Brief explanation of the drawing

[0003] Some examples of various embodiments of the present disclosure are described herein with reference to the drawings. FIG. 1 illustrates an exemplary wireless communication network in which an embodiment of the present disclosure can be implemented. FIG. 2 is a block diagram illustrating an exemplary implementation of a station (STA) and an access point (AP). Figure 3 illustrates an exemplary multi-AP network. Figure 4 illustrates enhanced distributed channel access (EDCA) and coordinated orthogonal frequency division multiple access (CTDMA). Figure 5 illustrates an exemplary network including a coordinated set of APs. Figure 6 illustrates an exemplary multiple AP operation procedure. Figure 7 illustrates an exemplary multiple AP sounding step. FIG. 8 illustrates an exemplary multi-AP downlink data transmission step. FIG. 9 illustrates an exemplary multiple AP uplink data transmission step. Figure 10 illustrates an example of a controlled beamforming procedure. Figure 11 illustrates an example of another adjusted beamforming procedure. FIG. 12 illustrates an example of a beamforming procedure adjusted according to one embodiment. FIG. 13 illustrates an example of a different adjusted beamforming procedure according to one embodiment. FIG. 14 illustrates an example of a different adjusted beamforming procedure according to one embodiment. FIG. 15 illustrates an example of a trigger frame that can be used in an embodiment. FIG. 16 illustrates an exemplary process according to one embodiment. FIG. 17 illustrates another exemplary process according to one embodiment. Specific details for implementing the invention

[0004] In this disclosure, various embodiments are presented as examples of how the disclosed technology can be implemented and / or how the disclosed technology can be implemented in environments and scenarios. It will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the scope. After reading the description, methods for implementing alternative embodiments will be apparent to those skilled in the art. The present embodiments may not be limited by any of the exemplary embodiments described. Embodiments of the present disclosure will be described with reference to the accompanying drawings. Limitations, features, and / or elements from the exemplary embodiments disclosed may be combined to create additional embodiments within the scope of the present disclosure. Any drawings highlighting functions and benefits are presented for illustrative purposes only. The disclosed architecture is sufficiently flexible and configurable to be utilized in ways different from those depicted. For example, actions listed in any flowchart may be rearranged or used selectively in only some embodiments.

[0005] The embodiments may be configured to operate as needed. The disclosed mechanism may be performed when certain criteria are met, for example, in a station, access point, wireless environment, network, or combination thereof. Exemplary criteria may be based at least partially, for example, wireless device or network node configuration, traffic load, initial system setup, packet size, traffic characteristics, combinations thereof, etc. When one or more criteria are met, various exemplary embodiments may be applied. Thus, it may be possible to implement exemplary embodiments that optionally implement the disclosed protocol.

[0006] In this disclosure, singular expressions and similar phrases should be interpreted as “at least one” and “one or more.” Similarly, any term ending in the suffix “(s)” should be interpreted as “at least one” and “one or more.” In this disclosure, the term “may” should be interpreted as “e.g., may.” In other words, the term “may” indicates that the phrase following this term is an example of one of a number of suitable possibilities that may or may not be used in one or more of various embodiments. As used herein, the terms “comprise” and “comprise” enumerate one or more components of the element being described. The term “comprise” is interchangeable with “include” and does not exclude components not enumerated from being included in the element being described. In contrast, “comprise” provides a complete enumeration of one or more components of the element being described. As used herein, the term "based on" may be interpreted as "based at least in part on" rather than, for example, "based solely on." The term "and / or" as used herein indicates any possible combination of the 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.

[0007] 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 likewise “at least based on”) indicates that the phrase following the term “based on” is an example of one of a number of appropriate possibilities that may or may not be used in one or more different embodiments. The phrase “in response to” (or likewise “in response to”) indicates that the phrase following the phrase “in response to” is an example of one of a number of appropriate possibilities that may or may not be used in one or more different embodiments. The phrase "depending on" (or equally "at least depending on") indicates that the phrase following the phrase "depending on" is an example of one of a number of appropriate possibilities that may or may not be used in one or more various embodiments. The phrase "using / utilizing" (or equally "at least using / using") indicates that the phrase following the phrase "using / using" is an example of one of a number of appropriate possibilities that may or may not be used in one or more various embodiments.

[0008] The term "configured" may relate to the capacity of a device regardless of whether the device is in an operating or non-operating state. "Configured" may refer to a specific configuration of a device that affects the operating characteristics of the device, regardless of whether the device is in an operating or non-operating state. In other words, hardware, software, firmware, registers, memory values, etc., may be "configured" within the device to provide specific characteristics to the device, regardless of whether the device is in an operating or non-operating state. Terms such as "control messages generated by the device" may mean that, regardless of whether the device is in an operating or non-operating state, the control messages have parameters that can be used to configure specific characteristics or to implement specific behaviors of the device.

[0009] In the present disclosure, a parameter (or equivalently referred to as a field or an Information element (IE)) may include one or more information objects, and an information object may include one or more other objects. For example, if parameter (IE) N includes parameter (IE) M, parameter (IE) M includes parameter (IE) K, and parameter (IE) K includes parameter (IE) J, then, for example, N includes K and N includes J. In an exemplary example, when one or more messages / frames include multiple parameters, it means that one parameter within the multiple parameters is present in at least one of the one or more messages / frames, but does not need to be present in each of the one or more messages / frames.

[0010] Many of the presented features are described as optional using "~ may" or parentheses. For the sake of brevity and readability, this disclosure does not explicitly cite every permutation that can be obtained by selecting from the set of optional features. This disclosure should be interpreted as explicitly disclosing all such permutations. For example, a system described as having three optional features can be implemented in seven ways, namely, by only one of the three possible features, by any two of the three possible features, or by three of the three possible features.

[0011] Many of the elements described in the disclosed embodiments may be implemented as modules. A module is defined herein as an element that performs a defined function and has a defined interface to another element. The modules described in this disclosure may be implemented as hardware, software combined with hardware, firmware, wetware (e.g., hardware having biological elements), or a combination thereof, all of which are behaviorally equivalent. For example, a module may be implemented as a software routine written in a computer language configured to be executed by a hardware machine (e.g., C, C++, Fortran, Java, Basic, Matlab, etc.), or as a modeling / simulation program such as Simulink, Stateflow, GNU Octave, or LabVIEW MathScript. A module may be implemented using physical hardware that integrates individual or programmable analog, digital, and / or quantum hardware. Examples of programmable hardware include 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, and C++. FPGAs, ASICs, and CPLDs are often programmed using hardware description languages ​​(HDLs), such as VHSIC hardware description language (VHDL) or Verilog, to configure connections between internal hardware modules with less functionality in programmable devices. The aforementioned technologies are often used in combination to achieve the results of functional modules.

[0012] FIG. 1 illustrates an exemplary wireless communication network in which an embodiment of the present disclosure can be implemented.

[0013] As illustrated in FIG. 1, an exemplary wireless communication network may include an Institute of Electrical and Electronics Engineers (IEEE) 802.11 (WLAN) infrastructure network (102). The WLAN infrastructure network (102) may include one or more basic service sets (BSS) (110 and 120) and a distribution system (DS) (130).

[0014] BSS (110-1 and 110-2) each include a set of access points (AP or AP STA) and at least one set of stations (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 at least one STA within the BSS perform an association procedure to communicate with each other.

[0015] The DS (130) can be configured to connect the BSS (110-1) and the BSS (110-2). In this way, the DS (130) can enable an extended service set (ESS) (150). Within the ESS (150), the APs (104-1 and 104-2) are connected through the DS (130) and can have the same service set identification (SSID).

[0016] A WLAN infrastructure network (102) may be combined with one or more external networks. For example, as illustrated in FIG. 1, a WLAN infrastructure network (102) may be connected to another network (108) (e.g., 802.X) through a portal (140). The portal (140) may function as a bridge connecting the DS (130) of the WLAN infrastructure network (102) to the other network (108).

[0017] The exemplary wireless communication network illustrated in FIG. 1 may additionally include one or more ad-hoc networks or independent BSSs (IBSS). An ad-hoc network or IBSS is a network comprising multiple STAs within each other's communication ranges. The multiple STAs are configured to communicate with each other using direct P2P communication (i.e., without going through an AP).

[0018] 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 the IBSS does not include an AP, it does not include a centralized management entity. Rather, the STAs within the IBSS are managed in a distributed manner. The STAs forming the IBSS may be fixed or movable.

[0019] A STA as a defined functional medium may include a Media Access Control (MAC) layer compliant with the IEEE 802.11 standard. A physical layer interface to the radio medium may be used between an AP and a non-AP station (STA). A STA may also be referred to using various other terms including mobile terminal, radio device, radio transceiver unit (WTRU), user equipment (UE), mobile station (MS), mobile subscriber unit, or user. For example, the term "user" may be used to refer to a STA participating in uplink multiple user multiple input, multiple output (MU MIMO) and / or uplink orthogonal frequency division multiple access (OFDMA) transmission.

[0020] A Physical Layer (PHY) Protocol Data Unit (PPDU) may be a composite structure comprising a PHY preamble and a payload in the form of a PLCP Service Data Unit (PSDU). For example, a PSDU may include a PHY Convergence Protocol (PLCP) preamble and header and / or one or more MAC Protocol Data Units (MPDU). Information provided in the PHY preamble may be used by a receiving device to decode subsequent data in the PSDU. When a PPDU is transmitted over a joined channel (a channel formed through channel joining), the preamble field may be duplicated and transmitted over 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 may also generally be used to maintain compatibility with legacy devices. The format, coding, and information provided in the non-legacy part of the preamble are based on a specific IEEE 802.11 protocol to be used to transmit the payload.

[0021] A frequency band may include one or more subbands or frequency channels. For example, a PPU compliant with IEEE 802.11n, 802.11ac, 802.11ax, and / or 802.11be standard revisions may be transmitted over 2.4 GHz, 5 GHz, and / or 6 GHz bands, each of which may be divided into multiple 20 MHz channels. A PPPU may be transmitted over a physical channel having a minimum bandwidth of 20 MHz. Larger channels may be formed through channel splicing. For example, a PPDU may be transmitted over a physical channel having a bandwidth of 40 MHz, 80 MHz, 160 MHz, or 520 MHz by splicing multiple 20 MHz channels together.

[0022] FIG. 2 is a block diagram illustrating an exemplary implementation of an STA (210) and an AP (260). As shown in FIG. 2, the STA (210) may include at least one processor (220), a memory (230), and at least one transceiver (240). The AP (260) may include at least one processor (270), a memory (280), and at least one transceiver (290). The processor (220 / 270) may be operably connected to the memory (230 / 280) and / or the transceiver (240 / 290).

[0023] The processor (220 / 270) can implement the functions of the PHY layer, MAC layer, and / or Logical Link Control (LLC) layer of the corresponding device (STA (210) or AP (260)). The processor (220 / 270) may include one or more processors and / or one or more controllers. One or more processors and / or one or more controllers may include, 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.

[0024] The memory (230 / 280) may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage unit. The memory (230 / 280) may include one or more non-transient computer-readable media. The memory (230 / 280) may store computer program instructions or code that can be executed by the processor (220 / 270) to perform one or more of the operations / implements discussed in this application. The memory (230 / 280) may be implemented (or placed) within the processor (220 / 270) or outside the processor (220 / 270). The memory (230 / 280) may be operablely connected to the processor (220 / 270) through various means known in the art.

[0025] The transceiver (240 / 290) may be configured to transmit and receive wireless signals. In one embodiment, the transceiver (240 / 290) may implement the PHY layer of the corresponding device (STA (210) or AP (260)). In one embodiment, the STA (210) and / or AP (260) may be a multi-link device (MLD), which is a device capable of operating over multiple links as defined by the IEEE 802.11 standard. As such, the STA (210) and / or AP (260) may each implement multiple PHY layers. Multiple PHY layers may be implemented using one or more of the transceivers (240 / 290).

[0026] FIG. 3 illustrates an exemplary multi-AP network (300). The exemplary multi-AP network (300) may be a multi-AP network according to the Wi-Fi Federation standard specification for multi-AP networks. As illustrated in FIG. 3, the multi-AP network (300) may include multiple AP controllers (302) and a plurality of multiple AP groups (or multiple AP sets) (304, 306, and 308).

[0027] A multi-AP controller (302) may be a logical entity that implements logic for controlling APs in a multi-AP network (300). The multi-AP controller (302) may receive capability information and measurements from APs and may trigger AP control commands and operations for APs. The multi-AP controller (302) may also provide onboarding functions for onboarding and provisioning APs on the multi-AP network (300).

[0028] A multi-AP group (304, 306, and 308) may each include multiple APs. The APs in a multi-AP group are within each other's communication range and may coordinate their own transmissions and / or transmissions from associated STAs. A coordinated transmission may include all or some of the APs in the multi-AP group. A multi-AP group may also be referred to as a set of AP candidates, since the APs in the multi-AP group are considered candidates for a coordinated transmission initiated by one AP. The APs in a multi-AP group do not need to have the same primary channel. As used herein, a primary channel for an AP refers to the default channel that the AP uses to monitor management frames and / or transmit beacon frames. For a STA associated with an AP, a primary channel refers to the AP's primary channel advertised through the AP's beacon frames.

[0029] In one approach, a multi-AP group can be established by a coordinator AP during the multi-AP setup phase prior to any multi-AP coordination. APs in the multi-AP group other than the coordinator AP may be referred to as coordinated APs. The coordinator AP can establish one or more multi-AP groups. A coordinated AP can likewise be a member of multiple multi-AP groups. The coordinator AP of a multi-AP group can be a coordinated AP of another multi-AP group, and vice versa. In another approach, a multi-AP group can be manually established by a network administrator by configuring APs as part of the multi-AP group. In yet another approach, a multi-AP group can be established in a distributed manner by APs without a central controller. In this case, the AP can advertise its multi-AP capability in a beacon or other management frame (e.g., a public action frame). Other APs receiving a frame containing multi-AP capability information can perform multi-AP setup with the AP that advertised the multi-AP capability.

[0030] In one approach, one of the APs in a multi-AP group may be designated as the master AP. The designation of the master AP may be performed by the AP controller (302) or by the APs in the multi-AP group. The master AP of the multi-AP group may be fixed or may vary over time between the APs in the multi-AP group. The APs that are not the master AP of the multi-AP group are known as slave APs.

[0031] In one approach, APs in a multi-AP group may perform coordinated transmission together. One aspect of the coordination may include coordination for performing coordinated transmission within a multi-AP group. As used herein, coordinated transmission, also referred to as multi-AP transmission, is a transmission event in which multiple APs (of a multi-AP group or multi-AP network) transmit in a coordinated manner over a certain time interval. Coordinated transmission may include simultaneous transmission by multiple APs in a multi-AP group. The time interval of simultaneous AP transmission may be a continuous period. Multi-AP transmission may use different transmission techniques such as coordinated OFDMA (COFDMA), coordinated spatial reuse (CSR), joint transmit / receive (JT / JR), coordinated beamforming (CBF), and CTDMA, or a combination of two or more of the aforementioned techniques.

[0032] Multi-AP transmission can be enabled by an AP controller and / or by a master AP of a multi-AP group. In one approach, the AP controller and / or the master AP can control time and / or frequency sharing in a transmit opportunity (TXOP). For example, when one of the APs in a multi-AP group (e.g., the master AP) acquires a TXOP, the AP controller and / or the master AP can control how the time / frequency resources of the TXOP are shared with other APs in the multi-AP group. In one embodiment, the AP in the multi-AP group that acquires the TXOP becomes the master AP of the multi-AP group. The master AP can then share a portion of the acquired TXOP (which may be the entire TXOP) with one or more other APs in the multi-AP group.

[0033] Different multi-AP transmission methods may be suitable for different use cases from the perspective of privacy protection, including whether transmitted data can be shared with other BSSs in a multi-AP group. For example, some multi-AP transmission methods, such as CSR, CDTMA, Coordinated Frequency Division Multiple Access (CFDMA), COFDMA, and CBF, allow a master AP to coordinate slave APs by sharing control information among APs without the need to share user data between APs. The control information may include the AP's BSS information, link quality information of the channel between each AP and its associated STA, and information regarding the resources to be used to achieve multiplexing in the power, time, frequency, or spatial domains for multi-AP transmission. The control information exchanged between the master AP and the slave APs may be used for interference avoidance or interference nulling to avoid or null co-channel interference introduced to adjacent BSSs in a multi-AP network. Interference avoidance or interference nulling requires that data transmission between APs and STAs occur only within the same BSS. That is, 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 associated APs.

[0034] In contrast, other multi-AP transmission methods may allow a master AP to coordinate slave APs by sharing both control information and user data among the APs in a multi-AP group. The control information may include BSS information regarding the APs and link quality information of the channels between each AP and its associated STAs. By exchanging user data through backhaul, the master AP and slave APs may perform joint data transmission to achieve spatial diversity; for example, they may perform joint transmission (JT) for downlink transmission and joint reception (JR) for uplink transmission using distributed MIMO. Data transmission between an AP and a STA may include transmission within the same BSS and / or transmission across different BSSs. That is, an AP may transmit or receive data frames to or from its associated STAs as well as to STAs associated with other APs participating in the multi-AP transmission. Similarly, a STA may transmit or receive data frames to or from multiple APs.

[0035] Different multi-AP transmission methods 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 multi-AP transmission be located within the common signal coverage area of ​​the APs involved in multi-AP transmission. Generally, CBF may be suitable when a receiving STA experiences potential interference from other APs in the multi-AP group. By using channel-related information exchanged between APs, such as Channel State Information (CSI), Channel Quality Indication (CQI), or Compressed Beamforming (BF) feedback, APs can pre-code the signal to be transmitted to form a beam that increases power toward a target STA while reducing power that causes interference to STAs associated with adjacent APs. Use cases for JT / JR may require sufficient received signal power at the receiving STA for the JT and sufficient received signal power at the receiving AP for the JR. In contrast, CSR can perform multi-AP transmission using interference modulation. The signal power received at the STA associated with the AP transmitting data may be required to be much higher than the received interference power.

[0036] Different multi-AP transmission methods may require different levels of synchronization and may operate with or without backhaul between the master AP and slave AP of a multi-AP group. For example, CSR may require PPDU-level synchronization, whereas CBF may require symbol-level synchronization. Meanwhile, JT / JR may require backhaul as well as tight time / frequency / phase-level synchronization for data sharing between APs in a multi-AP group.

[0037] Different multi-AP transmission methods may have different levels of complexity regarding coordination between master and slave APs in a multi-AP group. For example, JT / JR may require very high complexity because both CSI and user data are shared among 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 time / frequency resources shared between CSI and APs. CSR may require low complexity because the amount of space reuse and traffic-related information that needs to be exchanged between APs may be small.

[0038] A multi-AP group may adopt static multi-AP operation, including a static multi-AP transmission method. A multi-AP network can also be dynamic for various reasons. For example, an STA may join or leave a multi-AP network, an STA may switch to sleep mode, or an AP or STA may change its location. These changes can lead to changes in the conditions underlying the selection of the multi-AP transmission method and may result in the loss of specific requirements for the multi-AP transmission method (e.g., synchronization, backhaul, coordination, etc.). This degrades the transmission quality in a multi-AP network.

[0039] In COFDMA, a master AP can share a portion of its TXOPs with multiple APs by allocating each of the available frequency resources (e.g., channels / subchannels) to each of the multiple APs. COFDMA is illustrated in FIG. 4 as a multi-AP channel access method compared to Enhanced Distributed Channel Access (EDCA). As illustrated in FIG. 4, in EDCA, channel access by multiple APs (e.g., AP1, AP2) can occur over consecutive time intervals (e.g., TXOPs). During a given channel access, the entire channel (e.g., 80 MHz) can be used by a single AP. In contrast, in COFDMA, access by multiple APs (multi-AP channel access) can occur over the same time interval (e.g., the same TXOP or the same portion of a TXOP) across orthogonal frequency resources. For example, as illustrated in FIG. 4, an 80 MHz channel can be divided into four non-overlapping 20 MHz channels, each allocated to a specific AP among the multiple APs. Multiple APs can transmit simultaneously in a coordinated manner during the same period to achieve multiple AP transmission. In multiple AP transmission, each of the multiple APs can transmit PPDU to one or more STAs.

[0040] FIG. 5 illustrates an exemplary network (500) including a coordinated set of APs. As illustrated in FIG. 5, the coordinated set of APs may include two APs (AP (502-1) and AP (502-2)). The coordinated set of APs may be a subset of an established multi-AP group. At least one STA may be associated with each of the APs (502-1 and 502-2). For example, STA (504-1) may be associated with AP (502-1), and STA (504-2) may be associated with AP (502-2).

[0041] APs (502-1 and 502-2) may belong to the same ESS described in FIG. 1. In this case, APs (502-1 and 502-2) may be connected by DS to support ESS features. Additionally, as part of a coordinated set of APs, APs (502-1 and 502-2) may be connected by a backhaul. Information is rapidly shared between APs using the backhaul to support coordinated transmission. The shared information may be channel state information or data to be transmitted to the associated STA. The backhaul may be a wired backhaul or a wireless backhaul. A wired backhaul is preferable for high-capacity information transmission that does not burden the AP's main wireless device. However, a wired backhaul may require higher deployment costs and impose greater constraints on AP deployment. A wireless backhaul is preferable for lower deployment costs and flexibility regarding AP deployment. However, because the wireless backhaul relies on the AP's main wireless device to transmit information, the AP cannot transmit or receive arbitrary data while the wireless backhaul is in use.

[0042] Typically, one of the APs (502-1 and 502-2) can act as the master AP, and the other as the slave AP. The master AP is the AP that owns the TXOP. The master AP shares frequency resources with the slave AP during the TXOP. If there are more than two APs in the coordinated set, the master AP can share the 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 certain period. Similarly, the slave AP role may be dynamically selected by the master AP or pre-assigned for a certain period.

[0043] Depending on the capabilities of the APs in a coordinated AP set, the APs may perform only specific types 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 perform only CSR as a coordinated transmission scheme. If the benefits of coordinated transmission do not outweigh the disadvantages of coordinated transmission (such as reduced flexibility and increased computing power required), the APs may prefer to perform a single AP transmission for a certain period.

[0044] CSR is a type of multi-AP coordination that can be supported by AP (502-1) and AP (502-2) as illustrated in FIG. 5. Spatial reuse using CSR can be more stable than non-AP coordination spatial reuse schemes such as OBSS PD-based SR and PSR-based SR. For example, in an exemplary network (500), APs (502-1 and 502-2) can perform a co-sounding operation to measure path loss (PL) in the paths of the exemplary network (500). For example, due to the co-sounding operation, a PL (508) for the path between APs (502-1 and 502-2), a path loss (510) for the path between AP (502-1) and STA (504-2), and a path loss (512) for the path between AP (502-2) and STA (504-1) can be measured. Then, the measured path loss information may be shared between the APs (502-1 and 502-2) (e.g., using backhaul) to allow simultaneous transmission by the APs (502-1 and 502-2) to their respective associated STAs (504-1 and 504-2). Specifically, one of the APs (502-1 and 502-2) acquires a TXOP to become the master AP. Then, the master AP may transmit a CSR notification frame to the other AP(s). In one embodiment, the master AP may perform a polling operation to poll the slave APs regarding packet transmission availability before transmitting the CSR notification frame. When at least one slave AP responds indicating packet availability, the master AP may transmit the CSR notification frame. In the CSR notification, the master AP may limit the transmission power of the slave APs to protect its own transmission to its target STA.Similarly, the slave AP can protect its own transmission to its target STA by selecting a modulation scheme that provides a signal-to-interference ratio (SIR) margin high enough to support interference caused by the master AP transmitting to its target STA.

[0045] FIG. 6 illustrates an example (600) of a multi-AP operation procedure. In the example (600), the multi-AP operation procedure is illustrated for a multi-AP network comprising APs (602 and 604) and STAs (606 and 608). In one example, the APs (602 and 604) may form a multi-AP group. AP (602) may be a master AP, and AP (604) may be a slave AP of the multi-AP group. For example, AP (602) may acquire a TXOP and make it the master AP of the multi-AP group. Alternatively, AP (602) may be designated as the master AP by a multi-AP controller.

[0046] As illustrated in FIG. 6, the multiple AP operation procedure may include a series of steps in time, each of which may include a plurality of frame exchanges within the multiple AP network. Specifically, the multiple AP operation procedure may include a multiple AP selection step (610), a multiple AP data sharing step (612), a multiple AP sounding step (614), and a multiple AP data transmission step (616).

[0047] A multi-AP network can perform multi-AP operations based on a specific multi-AP transmission scheme. The multi-AP transmission scheme can be selected by the master AP based on the capabilities of the slave APs in the multi-AP group. Before multi-AP operation, the slave AP may notify the master AP of capability information related to the slave AP, including the capability to support one or more multi-AP transmission schemes. The slave AP may also notify the master AP of BSS information of the slave AP's BSS and link quality information regarding the STA associated with the slave AP. The master AP may receive information regarding all available slave APs. The information regarding the slave APs may include capability information, BSS information, and link quality information. Based on the information provided by the available slave APs, the master AP may determine the slave AP to be designated for multi-AP transmission and the specific multi-AP transmission scheme to be used during multi-AP transmission during the multi-AP selection phase.

[0048] The multiple AP selection step (610) may include a procedure for requesting, selecting, or assigning slave AP(s) for a multiple AP group by a master AP. As illustrated in FIG. 6, the multiple AP selection step may include the transmission of a frame (618) from AP (602) and a frame (620) from AP (604). AP (602) may transmit the frame (618) to request information regarding the buffer status of AP (604). In response, AP (604) may transmit the frame (620) to notify AP (602) of its and associated STA buffer status and / or whether it intends to engage in multiple AP operation. The multiple AP selection step (610) may also be used to exchange information regarding multiple AP operation, for example, including BSS information of the AP and link quality information between each AP and its associated STA. The AP's BSS information may include the BSS ID of the AP's BSS, the identifier and / or capability of the STA belonging to the BSS, information regarding the sounding capability of the STA, information regarding the AP's MIMO capability, etc. The link quality information may include the Received Signal Strength Indicator (RSSI), Signal-to-Noise Ratio (SNR), Signal-to-Interference + Noise Ratio (SINR), Channel State Information (CSI), and Channel Quality Indicator (CQI).

[0049] The multiple AP data sharing step (612) may include a procedure for sharing data frames to be transmitted by the AP to the associated STA among the master AP and selected slave AP(s) through a direct connection between the APs. Step 612 may be optional for some multiple AP data transmission schemes. For example, Step 612 may be required for JT / JR because data frames may be exchanged between APs before or after the multiple AP data transmission step (616).

[0050] The multiple AP data sharing step (612) may be performed using wired backhaul, in-channel wireless backhaul, or off-channel wireless backhaul. In some cases, the multiple AP data sharing step (612) may be performed via in-channel backhaul, for example, using the same wireless channel used to transmit / receive data to / from the STA. For example, as illustrated in FIG. 6, in step 612, the AP (602) may transmit a frame (622) that can be received by the AP (604). The frame (622) may contain an MPDU that the AP (602) intends to transmit to the associated STA using multiple AP operations. Similarly, the AP (604) may transmit a frame (624) that can be received by the AP (602). The frame (624) may contain an MPDU that the AP (604) intends to transmit to the associated STA using multiple AP operations.

[0051] The multi-AP sounding step (614) may include a procedure for multi-AP channel sounding, which includes channel estimation and feedback of channel estimation among the master AP, candidate slave AP(s), and associated STA. Step 614 may be optional for some multi-AP transmission schemes such as COFDMA, CDTMA, and CSR. For example, step 614 may be performed by the master AP to assist in resource unit allocation when coordinating COFDMA transmission.

[0052] The multiple AP data transmission step (616) may include the exchange of data frames between the master AP, slave AP(s), and their associated STAs based on the multiple AP transmission scheme(s) determined by the master AP. Depending on the multiple AP transmission scheme(s) to be used, step 616 may include optional synchronization between the APs of the multiple AP group before the exchange of data frames between the APs and STAs within the multiple AP group.

[0053] The order of steps 610, 612, 614, and 616 may differ from that shown in FIG. 6. For example, in COFDMA, step 616 may occur immediately after step 610, whereas in JT / JR, step 612 may occur after step 610. Additionally, as previously mentioned, some steps may be optional and may or may not be present. For example, step 614 may not be required for COFDMA but may be required for JT / JR.

[0054] FIG. 7 illustrates an embodiment (700) of a multi-AP sounding step. The multi-AP sounding step (700) may be an example of a multi-AP sounding step (614). As illustrated in FIG. 7, the embodiment (700) may include a master AP (702) and a slave AP (704) of a multi-AP group. The embodiment (700) may further include an STA (706) associated with the AP (702) and an STA (708) associated with the AP (704).

[0055] As illustrated in FIG. 7, the multi-AP sounding step (700) may include frame exchange that enables the AP (702) (master AP) to obtain channel state information (CSI) of a channel in a multi-AP group. In one embodiment, step 700 may include a first sub-step (710) and a second sub-step (712).

[0056] During the first sub-step (710), the AP may initiate channel sounding, and the STA may estimate channel state information (CSI). For example, the AP (702) may trigger multiple AP sounds by transmitting frame (714) to the AP (704) (slave AP). Frame (714) may contain multiple AP trigger frames. Subsequently, the APs (702 and 704) may notify the transmission of sound frames by transmitting announcement frames (716-1 and 716-2) to their respective associated STAs (706 and 708). Frames (716-1 and 716-2) may contain multiple AP null data packet announcement (NDPA) frames. Frames (716-1 and 716-2) may be transmitted simultaneously. Next, APs (702 and 704) may each transmit frames (718-1 and 718-2) to STAs (706 and 708), respectively. Frames (718-1 and 718-2) may contain multiple 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.

[0057] During the second sub-step (712), the AP may initiate a procedure for the STA to feed back channel estimates to the AP. For example, the AP (702) may transmit a frame (720) to trigger the STA (706 and 708) to transmit channel estimates to the AP (702 and 704), respectively. The frame (720) may include multiple AP trigger frames. In response, the STA (706 and 708) may transmit frames (722 and 724), respectively, containing feedback of channel estimates to the AP (702 and 704). Frames (722 and 724) may include NDP feedback frames. The feedback of channel estimates may include NDP feedback, CSI-related information, beamforming reports (BFR), or channel quality indicator (CQI) reports.

[0058] FIG. 8 illustrates an embodiment (800) of a multi-AP downlink data transmission step. The multi-AP downlink data transmission step (800) may be an example of a multi-AP data transmission step (616). As illustrated in FIG. 8, the embodiment (800) may include a master AP (802) and a slave AP (804) of a multi-AP group. The embodiment (800) may further include an STA (806) associated with the AP (802) and an STA (808) associated with the AP (804).

[0059] As illustrated in FIG. 8, the multiple AP downlink data transmission step (800) may include frame switching that enables the master AP (802) to coordinate with the slave AP (804) to perform a specific multiple AP transmission scheme to each associated STA (806 and 808). The multiple AP transmission scheme may include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the aforementioned schemes.

[0060] As illustrated in FIG. 8, the master AP (802) may initiate step 800 by transmitting a frame (810) to the AP (804). The frame (810) may include information regarding the AP (804) (e.g., an identifier of the AP (804)), synchronization information, information regarding a specific multi-AP transmission scheme to be used, and / or information regarding a resource unit (RU) to be used by the AP (804) to acknowledge the frame (810). The frame (810) may include a control frame. For example, the frame (810) may include a multi-AP trigger frame.

[0061] The slave AP (804) can receive a frame (810) and synchronize with the master AP (802) using synchronization information. Subsequently, the APs (802 and 804) can each perform data transmission to their respective associated STAs (806 and 808). Specifically, the AP (802) can transmit a data frame (812) to the associated STA (806), and the AP (804) can transmit a data frame (814) to the associated STA (808). Depending on the multiple AP transmission scheme used, the APs (802 and 804) can each transmit frames (812 and 814) to STAs of different BSSs. For example, if the multi-AP transmission scheme is JT / JR, the AP (802) can also transmit frame (812) to the STA (808) associated with the slave AP (804), and the AP (804) can also transmit frame (814) to the STA (808) associated with the AP (804). The resources for transmitting and receiving frames (812 and 814) may vary depending on the specific multi-AP transmission scheme adopted.

[0062] STA (806 and 808) can each acknowledge frames (812 and 814). For example, STA (806) can transmit frame (816) to AP (802), and STA (808) can transmit frame (818) to AP (804). Frames (816 and 818) may include block acknowledgment (BA) frames. STA (806 and 808) can also transmit frames (816 and 818) to APs of different BSSs if required by the multiple AP transmission scheme used. For example, if the multiple AP transmission scheme is JT / JR, STA (806) can also transmit frame (816) to AP (804), and STA (808) can also transmit frame (818) to AP (802). The resources for transmitting and receiving frames (816 and 818) may vary depending on the specific multiple AP transmission scheme adopted.

[0063] FIG. 9 illustrates an embodiment (900) of a multiple AP uplink data transmission step. The multiple AP uplink data transmission step (900) may be an example of a multiple AP data transmission step (616). As illustrated in FIG. 9, the embodiment (900) may include a master AP (902) and a slave AP (904) of a multiple AP group. The embodiment (900) may further include STAs (906 and 908) associated with the AP (902), and STA (910) associated with the AP (904).

[0064] As illustrated in FIG. 9, the multi-AP uplink data transmission step (900) may include frame switching that enables the master AP (902) to coordinate with the slave AP (904) to perform a specific multi-AP transmission scheme with the STA (906, 908, and 910). The multi-AP transmission scheme may include COFDMA, CTDMA, CSR, CBF, JT / JR, or a combination of two or more of the aforementioned schemes.

[0065] As illustrated in FIG. 9, the master AP (902) may initiate step 900 by transmitting a frame (912) to the AP (904). The frame (912) may include information regarding the AP (904) (e.g., an identifier of the AP (904)), synchronization information, information regarding a specific multi-AP transmission scheme to be used, and / or information regarding a RU to be used by the AP (904) to acknowledge the frame (912). The frame (912) may include a control frame. For example, the frame (912) may include a multi-AP trigger frame.

[0066] The slave AP (904) can receive the frame (912) and synchronize with the master AP (902) using synchronization information. Subsequently, the APs (902 and 904) can request uplink data transmission from the associated STAs (906, 908 and 910) using the trigger frame. Specifically, the AP (902) can transmit the trigger frame (914) to the associated STAs (906 and 908), and the AP (904) can transmit the trigger frame (916) to the associated STA (910). Depending on the multi-AP transmission scheme used, the APs (902 and 904) may transmit the frames (914 and 916) to the STAs of different BSSs, respectively. For example, if the multi-AP transmission scheme is JT / JR, the AP (902) may also transmit frame (914) to the STA (910) associated with the slave AP (904), and the AP (904) may also transmit frame (916) to the STAs (906 and 908) associated with the AP (902). The resources for transmitting and receiving frames (914 and 916) may vary depending on the specific multi-AP transmission scheme adopted.

[0067] STAs (906 and 908) can respond to frame (914), and STA (910) can respond to frame (916). For example, STAs (906 and 908) can each transmit frames (918 and 920) to AP (902), while STA (910) can transmit frame (922) to AP (904). Frames (918, 920, and / or 922) can be transmitted simultaneously. Frames (918, 920, and 922) may include data frames or null data frames. STAs (906, 908, and 910) can also transmit frames (918, 920, and 922) to APs of different BSSs, respectively, if required by the multiple AP transmission scheme used. For example, if the multi-AP transmission scheme is JT / JR, the STA (906 and 908) may also transmit each frame (918 and 920) to the AP (904), and the STA (910) may also transmit frame (922) to the AP (902). The resources for transmitting and receiving frames (918, 920, and 922) may vary depending on the specific multi-AP transmission scheme adopted. The AP (902) may acknowledge frames (918 and 920) by transmitting a multi-STA BA frame (924) to the STA (906 and 908). The AP (904) may acknowledge frame (922) by transmitting a BA frame (926) to the STA (910).

[0068] FIG. 10 illustrates an embodiment (1000) of a coordinated beamforming procedure. The coordinated beamforming procedure enables two or more APs to transmit to multiple STAs using the same time and frequency resources without interference. As illustrated in FIG. 10, the embodiment (1000) includes APs (1002 and 1004) and STAs (1006 and 1008). STAs (1006 and 1008) may each be associated with an AP (1002 and 1004). APs (1002 and 1004) may form a coordinated AP set. In the embodiment (1000), it is assumed that AP (1002) is the master AP of the coordinated AP set and AP (1004) is the slave AP of the coordinated AP set.

[0069] In one embodiment, the coordinated beamforming procedure may include a sounding step / procedure, which APs (1002 and 1004) may each use to obtain channel state information from STAs (1006 and 1008). The sounding step / procedure may begin with AP (1002) transmitting a trigger frame (1010) to AP (1004). The trigger frame (1010) may be a multiple AP (MAP) trigger frame. The trigger frame (1010) triggers AP (1004) to perform the sounding procedure simultaneously with AP (1002). Subsequently, APs (1002 and 1004) may initiate the sounding procedure by simultaneously transmitting NDPA frames (1012-1 and 1012-2) to STAs (1006 and 1008), respectively. NDPA frames (1012-1 and 1012-2) may be MAP NDPA frames. NDPA frame (1012-1) notifies STA (1006) of the transmission of one or more sounding frames by AP (1002). NDPA frame (1012-2) notifies STA (1008) of the transmission of one or more sounding frames by AP (1004). NDPA frames (1012-1 and 1012-2) may be duplicate frames.

[0070] Next, APs (1002 and 1004) may simultaneously transmit NDP frames (1014-1 and 1014-2) to STAs (1006 and 1008), respectively. The NDP frames (1014-1 and 1014-2) may be MAP NDP frames. The NDP frames (1014-1 and 1014-2) may each contain a long training field (LTF) corresponding to a distinct spatial stream associated with the APs (1002 and 1004). The STAs (1006 and 1008) each receive the NDP frames (1014-1 and 1014-2) and use the NDP frames (1014-1 and 1014-2) to estimate the downlink channel from the AP (1002) and the downlink channel from the AP (1004). In another embodiment, APs (1002 and 1004) may transmit NDP frames (1014-1 and 1014-2) sequentially. STAs (1006 and 1008) each receive NDP frame (1014-1) and use NDP frame (1014-1) to estimate the downlink channel from AP (1002). Similarly, STAs (1006 and 1008) each receive NDP frame (1014-2) and use NDP frame (1014-2) to estimate the downlink channel from AP (1004).

[0071] Subsequently, AP (1002) may transmit a trigger frame (1016) to AP (1004). The trigger frame (1016) may be a MAP trigger frame. The trigger frame (1016) triggers AP (1004) to perform a channel estimation polling procedure simultaneously with AP (1002). AP (1002 and 1004) may initiate the channel estimation polling procedure by simultaneously transmitting BFRP frames (1018-1 and 1018-2) to obtain downlink channel estimates from STA (1006 and 1008). STA (1006 and 1008) may respond to the BFRP frames (1018-1 and 1018-2) respectively by transmitting BFR frames (1020-1 and 1020-2). A BFR frame (1020-1) transmitted to the AP (1002) may include an estimate of the downlink channel from the AP (1002) to the STA (1006) and an estimate of the downlink channel from the AP (1004) to the STA (1006). A BFR frame (1020-2) transmitted to the AP (1004) may include an estimate of the downlink channel from the AP (1004) to the STA (1008) and an estimate of the downlink channel from the AP (1002) to the STA (1008).

[0072] In an embodiment (not shown in FIG. 10), APs (1002 and 1004) may exchange downlink channel estimates received from STAs (1006 and 1008), respectively. Thus, AP (1002) may obtain an estimate of the downlink channel from AP (1002) to STA (1008) from AP (1004), and AP (1004) may obtain an estimate of the downlink channel from AP (1002) to STA (1006). In one embodiment, the exchange of downlink channel estimates may include AP (1002) sending a trigger frame to AP (1004) to request AP (1004) to send the downlink channel estimate received from STA (1008) to AP (1002). AP (1002) may include the downlink channel estimate received from STA (1006) in a trigger frame or a separate frame transmitted to AP (1004). In another embodiment, the exchange of downlink channel estimates may be performed via a backhaul link.

[0073] Using the obtained downlink channel estimate, APs (1002 and 1004) can each calculate a set of beamforming weights for a coordinated beamforming transmission including APs (1002 and 1004). APs (1002 and 1004) can further determine a modulation and coding scheme (MCS) for a coordinated beamforming transmission. As illustrated in FIG. 10, the coordinated beamforming transmission may include a first beamforming transmission (1024) by AP (1002) and a second beamforming transmission (1026) by AP (1004). The first beamforming transmission (1024) and the second beamforming transmission (1026) may overlap in time and frequency. In one embodiment, the AP (1002) can trigger a first beamforming transmission (1024) and a second beamforming transmission (1026) by transmitting a trigger frame (1022). The trigger frame (1022) may be a MAP trigger frame. The AP (1002 and 1004) may start the first beamforming transmission (1024) and the second beamforming transmission (1026) after a short inter-frame space (SIFS) following the transmission of the trigger frame (1022) by the AP (1002).

[0074] In one embodiment, the AP (1002) may calculate a first beamforming weight set for a first beamforming transmission (1024) based on an estimate of the downlink channel from the AP (1002) to the STA (1006) and / or an estimate of the downlink channel from the AP (1002) to the STA (1008). Similarly, the AP (1004) may calculate a second beamforming weight set for a second beamforming transmission (1026) based on an estimate of the downlink channel from the AP (1004) to the STA (1006) and / or an estimate of the downlink channel from the AP (1004) to the STA (1008). In one approach, the first beamforming weight set may be configured such that the first beamforming transmit (1024) includes a first beam carrying a first data stream in the direction of the STA (1006) and a null beam in the direction of the STA (1008). Thus, the beamforming transmit (1024) does not affect the ability of the STA (1008) to receive frames from another STA (e.g., AP (1004)). Similarly, the second beamforming weight set may be configured such that the second beamforming transmit (1026) includes a second beam carrying a second data stream in the direction of the STA (1008) and a null beam in the direction of the STA (1006). Thus, the beamforming transmit (1026) does not affect the ability of the STA (1006) to receive frames from another STA (e.g., AP (1002)).

[0075] However, in practice, beamforming weight calculation is a vendor-specific implementation. Different vendors / implementers may use different beamforming weight calculation algorithms, which may result in suboptimal nulling performance. For example, referring to FIG. 10, the APs (1002 and 1004) may be devices created by different vendors / implementers and thus may use different beamforming weight calculation algorithms to generate a first set of beamforming weights and a second set of beamforming weights, respectively. Thus, the first beamforming transmit (1024) may contain a null beam in the direction of the STA (1008) and may interfere with the reception of the second data stream carried by the second beamforming transmit (1026) by the STA (1008). Similarly, the second beamforming transmission (1026) may include a vinyl beam in the direction of the STA (1006) and may interfere with the reception of the first data stream carried by the first beamforming transmission (1024) by the STA (1006).

[0076] One solution to this problem may include the AP (1002) transmitting a beamforming weight set and optionally an indication of the MCS to the AP (1004) for use in coordinated beamforming transmission, as illustrated in FIG. 11. The beamforming weight set may be determined by the AP (1002) for the AP (1004) using the same beamforming calculation algorithm that the AP (1002) uses to determine its own beamforming weight set. However, this solution would result in significant overhead, particularly as the number of streams increases.

[0077] An embodiment of the present disclosure solves the aforementioned problems of conventional coordinated beamforming procedures as described above. In one embodiment, a first AP receives from a second AP a frame indicating the allowable received interference level (ARIL) at a first STA associated with the second AP, and a PPDU transmitted by the first AP to a second STA associated with the first AP for beamforming transmission by the first AP and the second AP. The first AP transmits a beamforming PPDU to the second STA and for beamforming transmission based on the ARIL. In one embodiment, the first AP determines a beamforming weight set for beamforming transmission based on the ARIL. The first AP transmits a beamforming PPDU based on the beamforming weight set. In one embodiment, the beamforming weight set is determined such that the interference level at the first STA caused by the first PPDU is lower than the ARIL. Thus, the nulling performance of the beamforming transmission is improved.

[0078] FIG. 12 illustrates an example (1200) of a beamforming procedure adjusted according to one embodiment. As illustrated in FIG. 12, the example (1200) includes APs (1202 and 1204) and STAs (1206 and 1208). STAs (1206 and 1208) may each be associated with an AP (1202 and 1204). APs (1202 and 1204) may form an adjusted AP set. In the example (1200), it is assumed that AP (1202) is the master AP of the adjusted AP set and AP (1204) is the slave AP of the adjusted AP set.

[0079] In one embodiment, the adjusted beamforming procedure may include a sounding step / procedure, which APs (1202 and 1204) may each use to obtain channel state information from STAs (1206 and 1208). The sounding step / procedure may be similar to the sounding procedure described above with reference to FIG. 10. At the end of the sounding step / procedure, APs (1002 and 1004) each receive a BFR frame from STAs (1206 and 1208). The BFR frame transmitted by STA (1206) to AP (1202) may include an estimate of the downlink channel from AP (1202) to STA (1206) and an estimate of the downlink channel from AP (1204) to STA (1206). A BFR frame transmitted by STA (1208) to AP (1204) may include an estimate of the downlink channel from AP (1204) to STA (1208) and an estimate of the downlink channel from AP (1202) to STA (1208). In one embodiment, AP (1202) and AP (1204) may exchange downlink channel estimates received from STA (1206) and STA (1208), respectively. Thus, AP (1202) may obtain an estimate of the downlink channel from AP (1202) to STA (1208) from AP (1204), and AP (1204) may obtain an estimate of the downlink channel from AP (1204) to STA (1206) from AP (1202). In one embodiment, the exchange of downlink channel estimates may include AP (1202) sending a trigger frame to AP (1204) to request AP (1204) to send downlink channel estimates received from STA (1208) to AP (1202). AP (1202) may include downlink channel estimates received from STA (1206) in the trigger frame or in a separate frame sent to AP (1204). In another embodiment, the exchange of downlink channel estimates may be performed over a backhaul link.

[0080] In one embodiment, after a sounding step / procedure, the AP (1202) may transmit a frame (1210) to the AP (1204). The frame (1210) may represent a beamforming transmission by the AP (1202) and the AP (1204). The beamforming transmission may be a coordinated beamforming transmission. For example, the frame (1210) may represent the start time of the beamforming transmission and / or the end time of the beamforming transmission. In one example, the start time of the beamforming transmission may be after SIFS following the end of the frame (1210).

[0081] The frame (1210) may further indicate a first acceptable received interference level (ARIL) at the STA (1206) (or resulting from) the first PPDU (1214) to be transmitted by the AP (1204) to the STA (1208) for / during beamforming transmission. In one embodiment, the first ARIL is determined by the AP (1202) based on a beamforming report element from the STA (1208). The AP (1202) may obtain a beamforming report element from the AP (1204) through which the STA (1208) transmits the beamforming report element. In one example, the beamforming report element may include an estimate of the downlink channel from the AP (1204) to the STA (1208). In another embodiment, the beamforming report element may additionally or alternatively include an estimate of the downlink channel from the AP (1202) to the STA (1208). In one embodiment, the first ARIL may be determined by the AP (1202) based on one or more of the estimates of the downlink channel from the AP (1204) to the STA (1208) and the estimates of the downlink channel from the AP (1202) to the STA (1208). In one embodiment, the frame (1210) may additionally include an indication of an MCS for use by the AP (1204) for beamforming transmission. In one embodiment, the indication of an MCS for use by the AP (1204) may include an indication of an interference level at the STA (1208). In one embodiment, the interference level at the STA (1208) may include an estimated interference level at the STA (1208) due to the PPDU (1212) transmitted by the AP (1202). AP (1204) can determine the maximum (highest order) MCS that can be successfully decoded by STA (1208) by using the estimate of the downlink channel from AP (1204) to STA (1208) and taking into account the estimated interference level indicated in STA (1208).

[0082] In one embodiment, the frame (1210) may be a trigger frame. The trigger frame may have a format as exemplified by the exemplary trigger frame (1500) shown in FIG. 15. The exemplary trigger frame (1500) may be a multi-AP trigger frame indicated by a trigger type field. In one embodiment, the trigger frame includes a user information field associated with the AP (1204) that indicates a first ARIL and / or MCS for use by the AP (1204). The user information field associated with the AP (1204) may include an identifier of the AP (1204). In one embodiment, the first ARIL may be indicated in bits B32 through B38 of the user information field as shown in FIG. 15. In one embodiment, the MCS may be indicated in bits B20 through B25 of the user information field as shown in FIG. 15. In another embodiment, the estimated interference level in the STA (1208) may be indicated in the user information field as bits B20 to B25 as an alternative to the MCS. In one embodiment, the trigger frame may include a common information field indicating beamforming transmission.

[0083] In one embodiment, using the obtained downlink channel estimate, the APs (1202 and 1204) can each calculate a first and second beamforming weight set for beamforming transmission. In one embodiment, the APs (1202 and 1204) can further determine each MCS for beamforming transmission. As illustrated in FIG. 12, the APs (1202 and 1204) may use proprietary or vendor-specific algorithms to determine each first and second beamforming weight set for beamforming transmission. That is, the APs (1202 and 1204) can determine the first and second beamforming weight sets independently.

[0084] In one embodiment, the AP (1204) may use the first ARIL indicated in the frame (1210) to determine a second beamforming weight set for beamforming transmission. In one embodiment, the AP (1204) uses the first ARIL to determine the second beamforming weight set, such that the interference level in the STA (1206) due to the first PPDU (1214) is lower than that of the first ARIL. This ensures that the nulling performance of the beamforming transmission meets the minimum acceptable performance. In another embodiment, after determining the second beamforming weight set, the AP (1204) may reduce the transmission power for transmitting the first PPDU (1214) based on the first ARIL.

[0085] Subsequently, as illustrated in FIG. 12, APs (1202 and 1204) can perform beamforming transmission, and the beamforming transmission includes transmission of the PPDU (1212) to the STA (1206) by the AP (1202) and transmission of the PPDU (1214) to the STA (1208) by the AP (1204). As previously described, the PPDUs (1212 and 1214) can be beamformed based on first and second beamforming weight sets determined by each AP (1202 and 1204). Additionally, as previously described, the PPDU (1214) can be beamformed based on the first ARIL indicated in the frame (1210).

[0086] In one embodiment, frame (1210) may be a trigger frame that triggers beamforming transmission by AP (1202 and 1204). AP (1202 and 1204) may start transmitting PPDU (1212 and 1214) after SIFS following the end of frame (1210).

[0087] In one approach, the first beamforming weight set may be configured such that the PPDU (1212) includes a first beam carrying a first data stream in the direction of the STA (1206) and a null beam in the direction of the STA (1208). Thus, the PPDU (1212) does not affect the ability of the STA (1208) to receive the PPDU (1214) from the AP (1204). Similarly, the second beamforming weight set may be configured such that the PPDU (1214) includes a second beam carrying a second data stream in the direction of the STA (1208) and a null beam in the direction of the STA (1206). More specifically, the level of interference caused by the PPDU (1214) at the STA (1206) is lower than the first ARIL indicated in the frame (1210). Therefore, PPDU (1214) does not affect the ability of STA (1206) to receive PPDU (1212) from AP (1202).

[0088] FIG. 13 illustrates an example (1300) of a different coordinated beamforming procedure according to one embodiment. As illustrated in FIG. 13, the example (1300) includes APs (1302 and 1304) and STAs (1306 and 1308). The STAs (1306 and 1308) may each be associated with an AP (1302 and 1304). The APs (1302 and 1304) may form a coordinated AP set. In the example (1300), it is assumed that AP (1302) is the master AP of the coordinated AP set and AP (1304) is the slave AP of the coordinated AP set.

[0089] In one embodiment, the adjusted beamforming procedure may include a sounding step / procedure, which APs (1302 and 1304) may each use to obtain channel state information from STAs (1306 and 1308). The sounding step / procedure may be similar to the sounding procedure described above with reference to FIG. 10. At the end of the sounding step / procedure, APs (1002 and 1004) each receive a BFR frame from STAs (1306 and 1308). The BFR frame transmitted by STA (1306) to AP (1302) may include an estimate of the downlink channel from AP (1302) to STA (1306) and an estimate of the downlink channel from AP (1304) to STA (1306). A BFR frame transmitted by STA (1308) to AP (1304) may include an estimate of the downlink channel from AP (1304) to STA (1308) and an estimate of the downlink channel from AP (1302) to STA (1308). In one embodiment, AP (1302 and 1304) may exchange downlink channel estimates received from STA (1306 and 1308), respectively. Thus, AP (1302) may obtain an estimate of the downlink channel from AP (1302) to STA (1308) from AP (1304), and AP (1304) may obtain an estimate of the downlink channel from AP (1304) to STA (1306) from AP (1302). In one embodiment, the exchange of downlink channel estimates may include AP (1302) sending a trigger frame to AP (1304) requesting that AP (1304) send downlink channel estimates received from STA (1308) to AP (1302). AP (1302) may include downlink channel estimates received from STA (1306) in the trigger frame or in a separate frame sent to AP (1304). In another embodiment, the exchange of downlink channel estimates may be performed over a backhaul link.

[0090] In one embodiment, after a sounding step / procedure, the AP (1302) may transmit a frame (1310) to the AP (1304). The frame (1310) may represent a beamforming transmission by the AP (1302) and the AP (1304). The beamforming transmission may be a coordinated beamforming transmission. For example, the frame (1310) may represent the start time of the beamforming transmission and / or the end time of the beamforming transmission. In one example, the start time of the beamforming transmission may be after SIFS following the end of the frame (1310).

[0091] In one embodiment, rather than explicitly indicating the first ARIL as in the embodiment of FIG. 12, the frame (1310) may indicate a method for determining a beamforming weight set for the PPDU (1314). The method for determining a beamforming weight set for the PPDU (1314) may be configured such that when the AP (1304) is used to transmit the PPDU (1314), the interference level caused by the PPDU (1314) at the STA (1306) is equal to or lower than the first ARIL. In one embodiment, the method for determining a beamforming weight set for the PPDU (1314) may be based on linear least mean squared error (MMSE) beamforming. In another embodiment, the method for determining a beamforming weight set for the PPDU (1314) may be based on zero-forcing beamforming.

[0092] In one embodiment, the frame (1310) may additionally include an indication of an MCS for use by the AP (1304) for beamforming transmission. In one embodiment, the indicated MCS may also be for use by the AP (1302) for beamforming transmission. In one embodiment, the indication of an MCS in the frame (1310) may include an indication of an interference level in the STA (1308). In one embodiment, the interference level in the STA (1308) may include an estimated interference level in the STA (1308) due to the PPDU (1312) transmitted by the AP (1302). The AP (1304) may determine the maximum MCS (highest order) that can be successfully decoded by the STA (1308) when considering the estimated interference level indicated in the STA (1308) by using an estimate of the downlink channel from the AP (1304) to the STA (1308).

[0093] In one embodiment, the frame (1310) may be a trigger frame. The trigger frame may have a format as exemplified by the exemplary trigger frame (1500) shown in FIG. 15. The exemplary trigger frame (1500) may be a multi-AP trigger frame indicated by a trigger type field. In one embodiment, the trigger frame includes a user information field associated with the AP (1304). In one embodiment, the MCS may be indicated in bits B20 through B25 of the user information field as shown in FIG. 15. In another embodiment, the estimated interference level at the STA (1308) may be indicated in bits B20 through B25 of the user information field as an alternative to the MCS. The user information field associated with the AP (1304) may include an identifier of the AP (1304). In one embodiment, the trigger frame may include a common information field indicating beamforming transmission. In one embodiment, the common information field may also include a method for determining beamforming weights for the PPDU (1314). For example, the method may be indicated in the trigger-dependent common information field of the common information field.

[0094] In one embodiment, using the obtained downlink channel estimate, the AP (1302 and 1304) can calculate a first and second beamforming weight set for beamforming transmission, respectively. In one embodiment, the AP (1302 and 1304) can further determine a respective MCS for beamforming transmission. In one embodiment, as illustrated in FIG. 13, the AP (1302) may use a proprietary or vendor-specific algorithm to determine the first beamforming weight set for beamforming transmission. In contrast, the AP (1304) may determine the second beamforming weight set for beamforming transmission using the beamforming weight calculation method shown in frame (1310). The beamforming weight calculation method shown in frame (1310) may be the same method used by the AP (1302).

[0095] Subsequently, as illustrated in FIG. 13, APs (1302 and 1304) can perform beamforming transmission, and the beamforming transmission includes transmission by AP (1302) of the PPDU (1312) to the STA (1306) and transmission by AP (1304) of the PPDU (1314) to the STA (1308). As previously mentioned, the PPDUs (1312 and 1314) can be beamformed based on first and second beamforming weight sets determined by each AP (1302 and 1304).

[0096] In one embodiment, frame (1310) may be a trigger frame that triggers beamforming transmission by AP (1302 and 1304). AP (1302 and 1304) may start transmitting PPDU (1312 and 1314) after SIFS following the end of frame (1310).

[0097] In one approach, the first beamforming weight set can be configured such that the PPDU (1312) includes a first beam carrying a first data stream in the direction of the STA (1306) and a null beam in the direction of the STA (1308). Thus, the PPDU (1312) does not affect the ability of the STA (1308) to receive the PPDU (1314) from the AP (1304). Similarly, the second beamforming weight set can be configured such that the PPDU (1314) includes a second beam carrying a second data stream in the direction of the STA (1308) and a null beam in the direction of the STA (1306). Thus, the PPDU (1314) does not affect the ability of the STA (1306) to receive the PPDU (1312) from the AP (1302).

[0098] FIG. 14 illustrates an example (1400) of a different coordinated beamforming procedure according to one embodiment. As illustrated in FIG. 14, the example (1400) includes APs (1402 and 1404) and STAs (1406 and 1408). The STAs (1406 and 1408) may each be associated with an AP (1402 and 1404). The APs (1402 and 1404) may form a coordinated AP set. In the example (1400), it is assumed that AP (1402) is the master AP of the coordinated AP set and AP (1404) is the slave AP of the coordinated AP set.

[0099] In one embodiment, the adjusted beamforming procedure may include a sounding step / procedure, and the AP (1402 and 1404) may each use it to obtain channel state information from the STA (1406 and 1408). The sounding step / procedure may be similar to the sounding procedure described above with reference to FIG. 10. At the end of the sounding step / procedure, the AP (1002 and 1004) each receive a BFR frame from the STA (1406 and 1408). The BFR frame transmitted by the STA (1406) to the AP (1402) may include an estimate of the downlink channel from the AP (1402) to the STA (1406) and an estimate of the downlink channel from the AP (1404) to the STA (1406). A BFR frame transmitted by STA (1408) to AP (1404) may include an estimate of the downlink channel from AP (1404) to STA (1408) and an estimate of the downlink channel from AP (1402) to STA (1408). In one embodiment, AP (1402 and 1404) may exchange downlink channel estimates received from STA (1406 and 1408), respectively. Thus, AP (1402) may obtain an estimate of the downlink channel from AP (1402) to STA (1408) from AP (1404), and AP (1404) may obtain an estimate of the downlink channel from AP (1404) to STA (1406) from AP (1402). In one embodiment, the exchange of downlink channel estimates may include an AP (1402) transmitting a trigger frame to the AP (1404) while requesting the transmission of downlink channel estimates received from the STA (1408) to the AP (1402) by the AP (1404). The AP (1402) may include downlink channel estimates received from the STA (1406) in the trigger frame or in a separate frame transmitted to the AP (1404). In another embodiment, the exchange of downlink channel estimates may be performed via a backhaul link.

[0100] In one embodiment, after the sounding step / procedure, AP (1402) may transmit a frame (1410) to AP (1404). The frame (1410) may represent a beamforming transmission by AP (1402) and AP (1404). The beamforming transmission may be a coordinated beamforming transmission. For example, the frame (1410) may represent the start time of the beamforming transmission and / or the end time of the beamforming transmission. In one example, the start time of the beamforming transmission may be after SIFS following the end of the frame (1410).

[0101] Frame (1410) may further describe a method for determining a set of beamforming weights for a PPDU to be transmitted by the AP (1404) for / during beamforming transmission. In one embodiment, the method for determining the set of beamforming weights may be based on linear MMSE beamforming. In another embodiment, the method for determining the set of beamforming weights may be based on zero-focusing beamforming.

[0102] In one embodiment, the frame (1410) may additionally include an indication of an MCS for use by the AP (1404) for beamforming transmission. In one embodiment, the indication of an MCS in the frame (1410) may include an indication of a first ARIL in the STA (1408). In one embodiment, the first ARIL may include an interference level in the STA (1408) caused by a PPDU (1412) transmitted by the AP (1402). The AP (1404) may determine a maximum (highest order) MCS that can be successfully decoded by the STA (1408) by taking into account the indicated first ARIL, using an estimate of the downlink channel from the AP (1404) to the STA (1408).

[0103] In one embodiment, the frame (1410) may be a trigger frame. The trigger frame may have a format as exemplified by the exemplary trigger frame (1500) shown in FIG. 15. The exemplary trigger frame (1500) may be a multi-AP trigger frame indicated by a trigger type field. In one embodiment, the trigger frame includes a user information field associated with the AP (1404), which indicates a method for determining beamforming weights for a PPDU to be transmitted by the AP (1404) and / or an MCS for use by the AP (1404). In one embodiment, the MCS may be indicated in bits B20 through B25 of the user information field as shown in FIG. 15. In another embodiment, a first ARIL may be indicated in bits B20 through B25 of the user information field as an alternative to the MCS. The user information field associated with the AP (1404) may include an identifier of the AP (1404). In another embodiment, the trigger frame may include a common information field containing a method for determining a beamforming weight for a PPDU to be transmitted by the AP (1404). For example, the method may be indicated in the trigger-dependent common information field of the common information field. In one embodiment, the common information field indicates a beamforming transmission.

[0104] In one embodiment, using the obtained downlink channel estimate, the AP (1402 and 1404) may calculate a first and second beamforming weight set for beamforming transmission, respectively. In one embodiment, the AP (1402 and 1404) may further determine a respective MCS for beamforming transmission, respectively. In one embodiment, as illustrated in FIG. 14, the AP (1402) may use a proprietary or vendor-specific algorithm to determine the first beamforming weight set for beamforming transmission. In one embodiment, the AP (1404) may calculate the ARIL in the STA (1406) for the PPDU to be transmitted by the AP (1404) using the beamforming weight calculation method indicated in the frame (1410). In one example, the beamforming weight matrix determined using the beamforming weight calculation method may be expressed as W for the subcarrier j of the PPDU. Correspondingly, the downlink channel matrix from AP (1404) to STA (1406) can be represented as H. In one embodiment, H can be obtained by AP (1404) using a joint sounding procedure described in detail with reference to the previously described embodiment (1000). Then, AP (1404) [represents] ARIL as |W HIt can be calculated as yx|^2, where y is the estimated received signal for subcarrier j and x is the transmitted symbol. In one example, the estimated received signal y for subcarrier j given the estimated noise level n and the transmitted symbol x can be expressed as y=Hx+n. After calculating the ARIL, the AP (1404) may use a proprietary or vendor-specific algorithm to determine a second beamforming weight set for beamforming transmission under conditions where the ARIL calculated using the determined second beamforming weight set is lower than or equal to the calculated ARIL. Otherwise, if the resulting ARIL using the determined second beamforming weight set is higher than the calculated ARIL, the AP (1404) may determine a second beamforming weight set for beamforming transmission using the beamforming weight calculation method indicated in the frame (1410).

[0105] Subsequently, as illustrated in FIG. 14, APs (1402 and 1404) can perform beamforming transmission, and the beamforming transmission includes transmission by AP (1402) of the PPDU (1412) to the STA (1406) and transmission by AP (1404) of the PPDU (1414) to the STA (1408). As previously described, the PPDUs (1412 and 1414) can be beamformed based on first and second beamforming weight sets determined by each AP (1402 and 1404).

[0106] In one embodiment, frame (1410) may be a trigger frame that triggers beamforming transmission by AP (1402 and 1404). AP (1402 and 1404) may start transmitting PPDU (1412 and 1414) after SIFS following the end of frame (1410).

[0107] In one approach, the first beamforming weight set may be configured to include a first beam carrying a first data stream in the direction of the STA (1406) and a null beam in the direction of the STA (1408) for the PPDU (1412). Thus, the PPDU (1412) does not affect the ability of the STA (1408) to receive the PPDU (1414) from the AP (1404). Similarly, the second beamforming weight set may be configured to include a second beam carrying a second data stream in the direction of the STA (1408) and a null beam in the direction of the STA (1406) for the PPDU (1414). More specifically, the level of interference caused by the PPDU (1414) at the STA (1406) is lower than the first ARIL indicated in the frame (1410). Therefore, PPDU (1414) does not affect the ability of STA (1406) to receive PPDU (1412) from AP (1402).

[0108] FIG. 16 illustrates an exemplary process (1600) according to one embodiment. The exemplary process (1600) is provided merely for illustrative purposes and does not limit the embodiment. The exemplary process (1600) may be performed by a first AP such as AP (1204, 1304, or 1404). As illustrated in FIG. 16, the process (1600) may include step 1602 and step 1604.

[0109] Step 1602 comprises the step of the first AP receiving from the second AP a beamforming transmission by the first AP and the second AP; and receiving a first frame representing a first ARIL in the first STA associated with the second AP of a first PPDU transmitted by the first AP to the second STA associated with the first AP for the beamforming transmission. In one embodiment, the first AP and the second AP are members of a coordinated AP set. In one embodiment, the first AP may be a slave AP of the coordinated AP set, and the second AP may be a master AP of the coordinated AP set. In one embodiment, the beamforming transmission includes a coordinated beamforming transmission.

[0110] Step 1604 includes the step of the first AP transmitting a first PPDU beamformed based on the first ARIL for beamforming transmission to the second STA.

[0111] In one embodiment, the process (1600) may further include the step of determining a first beamforming weight set such that the interference level caused by the first PPDU in the first STA is lower than the first ARIL. In one embodiment, the step of transmitting the first PPDU in step 1604 may further include the step of transmitting the first PPDU using the first beamforming weight set.

[0112] In another embodiment, the first frame represents a method for determining a beamforming weight set for the first PPDU. In one embodiment, the step of transmitting the first PPDU in step 1604 may further include the step of transmitting the first PPDU using a beamforming weight set determined using the indicated method. In one embodiment, the method for determining a beamforming weight set for the first PPDU may be based on linear least mean squared error (MMSE) beamforming or zero-forcing beamforming.

[0113] In another embodiment, rather than explicitly indicating the first ARIL within the first frame, the first frame represents a method for determining a beamforming weight set for the first PPDU. The process (1600) may further include the step of the first AP determining an interference level using the method for determining a beamforming weight set for the first PPDU. In one embodiment, the determined interference level corresponds to the first ARIL.

[0114] In one embodiment, the first frame includes a trigger frame. In one embodiment, the trigger frame includes a user information field associated with the first AP, and the user information field represents the first ARIL. In one embodiment, the trigger frame includes a common information field, and the common information field represents beamforming transmission.

[0115] In one embodiment, the step of transmitting the first PPDU in step 1604 includes the step of transmitting a first beam carrying a second frame in the direction of the second STA and a null beam in the direction of the first STA.

[0116] In one embodiment, the process (1600) may further include the step of the first AP receiving a third frame from the second AP that triggers the first AP to perform a sounding procedure. In one embodiment, the sounding procedure includes the step of the first AP transmitting a null data packet (NDP); and the step of the first AP receiving a third frame from the second STA that includes a beamforming report element associated with a channel between the first AP and the second STA. In one embodiment, the first ARIL is based on the beamforming report element.

[0117] In one embodiment, the process (1600) may further include the step of reducing the transmission power for transmitting the first PPDU based on the first ARIL.

[0118] In one embodiment, the first frame further includes an indication of an MCS. The process (1600) may further include the step of transmitting a first PPDU using the MCS. In one embodiment, the indication of the MCS includes an indication of an interference level at the second STA. In one embodiment, the interference level at the second STA may include an estimated interference level at the second STA due to the second PPDU transmitted by the second AP. The first AP may determine the MCS to be used by the first AP for beamforming transmission based on the estimated interference level at the second STA using an estimate of the downlink channel from the first AP to the second STA.

[0119] FIG. 17 illustrates another exemplary process (1700) according to one embodiment. The exemplary process (1700) is provided for illustrative purposes only and does not limit the embodiment. The exemplary process (1700) may be performed by a first AP such as AP (1202, 1302, or 1402).

[0120] As illustrated in FIG. 17, the process (1700) comprises step 1702, which includes the step of: a first AP to a second AP: beamforming transmission by the first AP and the second AP; and transmitting a first frame representing a first ARIL in the first STA associated with the first AP of a first PPDU transmitted by the second AP to a second STA associated with the second AP for the beamforming transmission. In one embodiment, the first AP and the second AP are members of a coordinated AP set. In one embodiment, the first AP may be a master AP and the second AP may be a slave AP of the coordinated AP set. In one embodiment, the beamforming transmission includes a coordinated beamforming transmission.

[0121] In another embodiment, the first frame represents a method for determining a beamforming weight set for the first PPDU. In one embodiment, the method for determining a beamforming weight set for the first PPDU may be based on linear least mean squared error (MMSE) beamforming or zero-forcing beamforming.

[0122] In another embodiment, rather than explicitly indicating the first ARIL within the first frame, the first frame indicates a method for determining a beamforming weight set for the first PPDU. The interference level of the first PPDU determined using the beamforming weight set for the first PPDU corresponds to the first ARIL.

[0123] In one embodiment, the first frame includes a trigger frame. In one embodiment, the trigger frame includes a user information field associated with the second AP, and the user information field represents the first ARIL. In one embodiment, the trigger frame includes a common information field, and the common information field represents beamforming transmission.

[0124] In one embodiment, the process (1700) may further include the step of the first AP transmitting a second PPDU comprising a first beam carrying a second frame in the direction of the first STA and a null beam in the direction of the second STA.

[0125] In one embodiment, the process (1700) may further include the step of the first AP transmitting a third frame to the second AP to trigger the second AP to perform a sounding procedure. In one embodiment, the sounding procedure includes the step of the first AP transmitting a null data packet (NDP); and the step of the first AP receiving from the first STA a third frame containing a beamforming report element associated with a channel between the second AP and the first STA. In one embodiment, the first ARIL is based on the beamforming report element.

[0126] In one embodiment, the first frame further includes an indication of an MCS, and the first PPDU is transmitted using the MCS. In one embodiment, the indication of the MCS includes an indication of an interference level at the second STA. In one embodiment, the interference level at the second STA may include an estimated interference level at the second STA due to the second PPDU transmitted by the first AP. The second AP may determine the MCS to be used by the second AP for beamforming transmission based on the estimated interference level at the second STA using an estimate of the downlink channel from the second AP to the second STA.

Claims

Claim 1 As a method, the first access point (AP) from the second AP, Beamforming transmission by the first AP and the second AP; and A method comprising: receiving a frame indicating an acceptable reception interference level (ARIL) at a first STA associated with the second AP of a physical layer protocol data unit (PPDU) transmitted by the first AP to a second station (STA) associated with the first AP for the beamforming transmission; the first AP determining a beamforming weight set for the beamforming transmission based on the ARIL; and the first AP transmitting the beamformed PPDU based on the beamforming weight set to the second STA for the beamforming transmission. Claim 2 As a method, the first access point (AP) from the second AP, Beamforming transmission by the first AP and the second AP; and A method comprising: receiving a first frame indicating a first acceptable reception interference level (ARIL) at a first STA associated with the second AP of a first physical layer protocol data unit (PPDU) transmitted by the first AP to a second station (STA) associated with the first AP for the beamforming transmission; and transmitting the first PPDU, which is beamformed based on the first ARIL, to the second STA by the first AP for the beamforming transmission. Claim 3 A method according to claim 2, further comprising the step of determining a first beamforming weight set such that the interference level in the first STA caused by the first PPDU is lower than the first ARIL, wherein the step of transmitting the first PPDU includes the step of transmitting the first PPDU using the first beamforming weight set. Claim 4 In paragraph 2, the first frame represents a method for determining a beamforming weight set for the first PPDU, and the step of transmitting the first PPDU further comprises the step of transmitting the first PPDU using the beamforming weight set determined using the indicated method. Claim 5 In paragraph 2, the first frame represents a method for determining a beamforming weight set for the first PPDU, and the interference level of the first PPDU in the first STA determined using the determined beamforming weight set corresponds to the first ARIL. Claim 6 A method according to any one of paragraphs 2 to 5, wherein the first frame includes a trigger frame. Claim 7 In paragraph 6, the trigger frame includes a user information field associated with the first AP, and the user information field represents the first ARIL, a method. Claim 8 A method according to claim 6 or 7, wherein the trigger frame includes a common information field, and the common information field indicates the beamforming transmission. Claim 9 In claim 4, the method for determining the beamforming weight set for the first PPDU comprises a linear minimum mean square error or zero forcing. Claim 10 A method according to any one of claims 2 to 9, wherein the step of transmitting the first PPDU comprises transmitting a first beam carrying a second frame in a first direction of the second STA and transmitting a null beam in a second direction of the first STA. Claim 11 A method according to any one of claims 2 to 10, wherein the first AP and the second AP are members of a coordinated AP set, the first AP is the master AP of the coordinated AP set, and the second AP is the slave AP of the coordinated AP set. Claim 12 A method according to any one of claims 2 to 11, further comprising the step of the first AP receiving a third frame from the second AP that triggers the first AP to perform a sounding procedure. Claim 13 In claim 12, the sounding procedure comprises: the step of the first AP transmitting a null data packet (NDP); and the step of the first AP receiving from the second STA a third frame comprising a beamforming report element associated with a channel between the first AP and the second STA. Claim 14 In paragraph 13, the above-mentioned first ARIL is a method based on the beamforming reporting element. Claim 15 A method according to any one of claims 2 to 14, further comprising the step of reducing the transmission power for transmitting the first PPDU based on the first ARIL. Claim 16 A method according to any one of claims 2 to 15, wherein the first PPDU comprises an ultra-high reliability PPDU. Claim 17 A method according to any one of claims 2 through 16, wherein the first frame further includes an indication of a modulation and coding set (MCS), and the method further includes the step of transmitting the first PPDU using the MCS. Claim 18 In paragraph 17, the method wherein the indication of the MCS includes an indication of the interference level in the second STA. Claim 19 In paragraph 18, the method comprises the interference level in the second STA including the estimated interference level in the second STA of the second PPDU transmitted by the second AP to the first STA for the beamforming transmission. Claim 20 As a method, the first access point (AP) becomes the second AP, Beamforming transmission by the first AP and the second AP; and A method comprising the step of transmitting a first frame indicating a first acceptable reception interference level (ARIL) at a first STA associated with the first AP of a first physical layer protocol data unit (PPDU) transmitted by the second AP to a second station (STA) associated with the second AP for the beamforming transmission. Claim 21 In paragraph 20, the above first frame represents a method for determining a beamforming weight set for the above first PPDU. Claim 22 In paragraph 20, the first frame represents a method for determining a beamforming weight set for the first PPDU, and the interference level of the first PPDU in the first STA determined using the beamforming weight set corresponds to the first ARIL. Claim 23 A method according to any one of claims 20 to 22, wherein the first frame includes a trigger frame. Claim 24 In paragraph 23, the trigger frame includes a user information field associated with the first AP, and the user information field represents the first ARIL, a method. Claim 25 A method according to claim 23 or 24, wherein the trigger frame includes a common information field, and the common information field indicates the beamforming transmission. Claim 26 In paragraph 22, the method for determining the beamforming weight set for the first PPDU comprises a linear minimum mean squared error or zero-forcing. Claim 27 A method according to any one of claims 20 to 26, wherein the first AP further comprises the step of transmitting a second PPDU comprising a first beam carrying a second frame in a first direction of the first STA and a null beam in a second direction of the second STA. Claim 28 A method according to any one of claims 20 to 27, wherein the first AP and the second AP are members of a coordinated AP set, the first AP is the master AP of the coordinated AP set, and the second AP is the slave AP of the coordinated AP set. Claim 29 A method according to any one of claims 20 to 28, further comprising the step of transmitting a third frame to the second AP, which triggers the second AP to perform a sounding procedure. Claim 30 In claim 29, the sounding procedure comprises: the step of the first AP transmitting a null data packet (NDP); and the step of the first AP receiving from the first STA a third frame comprising a beamforming report element associated with a channel between the second AP and the first STA. Claim 31 In paragraph 30, the above-mentioned first ARIL is a method based on the beamforming reporting element. Claim 32 A method according to any one of claims 20 to 31, wherein the first PPDU comprises an ultra-high reliability PPDU. Claim 33 A method according to any one of claims 20 to 32, wherein the first frame further includes an indication of a modulation and coding set (MCS), and the first PPDU is transmitted using the MCS. Claim 34 In paragraph 33, the method wherein the indication of the MCS includes an indication of the interference level in the second STA. Claim 35 In paragraph 34, the interference level in the second STA comprises the estimated interference level in the second STA of the second PPDU transmitted by the first AP to the first STA for the beamforming transmission. Claim 36 A device comprising: one or more processors; and a memory for storing instructions, wherein the instructions, when executed by the one or more processors, cause the device to perform a method according to any one of claims 1 to 35. Claim 37 A non-transient computer-readable medium comprising instructions that, when executed by one or more processors, cause said one or more processors to perform a method according to any one of claims 1 to 35.

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