Setting sequences for multiple access point coordinated

Abstract

Technical solutions provide a setup sequence for coordinated beamforming (CBF) of multiple access points (APs) at a transmission opportunity (TXOP) stage. A first AP may transmit a notification indicating a CBF TXOP to a second AP capable of participating in the CBF and a first station of the first AP. The first AP may receive a first response from at least the first station identifying a first capability of the first station in response to the notification. The first AP may receive, in response to the notification, a second response from a second AP associated with a second one or more stations identifying a second capability of at least one of the second AP or a second one of the second one or more stations. The first AP may communicate data to the first station according to at least one of the first capability or the second capability during the CBF TXOP.

Description

[0001] Cross - reference to related patent applications

[0002] This application claims the benefit and priority of Indian Provisional Application No. 202421002187, filed on January 11, 2024, the entire content of which is incorporated herein by reference. Technical Field

[0003] The present disclosure generally relates to systems and methods for wireless communication between an access point and a wireless communication device, including (but not limited to) communication that reduces interference to an unintended communication device. Background Art

[0004] An access point (AP) (e.g., a Wi-Fi router) can facilitate wireless communication with any number of client wireless communication devices (also referred to as clients, stations, or STAs, e.g., smartphones, tablet computers, computers that can be within the wireless communication range of the AP). Sometimes, a client can experience interference caused by the AP transmitting data to other clients or STAs (e.g., within the same or a different wireless communication network). Such interference can be exacerbated when network density increases and transmission opportunities decrease. Summary of the Invention

[0005] The technical solution provides systems and methods that facilitate coordination of beamforming using mutual interference nulling for wireless communication between multiple access points and their respective STAs. When transmitting wireless communication to an intended STA, coordinated beamforming with nulling (CBF) can be used to minimize interference caused by the AP to an unintended receiving STA. When one AP transmits data to an STA within its own wireless local area network (WLAN), this data transmission can interfere with the communication of another STA in a different WLAN of another AP. Coordinated beamforming can be used to arrange or coordinate the beamforming of such transmissions by the AP to modify the transmission pattern and reduce or eliminate unwanted interference to an unintended STA receiver. However, it can be challenging for APs and STAs to arrange, set up, or coordinate these CBF operations between different APs and STAs because the CBF operations can depend on the capabilities of individual APs and STAs, which can vary widely depending on their type and design. The technical solution overcomes such challenges by providing devices, techniques, systems, and methods for multi-access point coordination of beamforming that allow an AP to configure its CBF operations to null unwanted interference based on data collected from the respective STAs of the APs involved.

[0006] Aspects of the technical solution relate to a system. The system may include a first access point (AP), which may be configured, for example, via instructions or data stored in a memory and accessed and executed by one or more processors of the first AP. The first AP may be configured to transmit a notification indicating a coordinated beamforming (CBF) transmission opportunity (CBF TXOP) to a second AP capable of participating in CBF and to one or more first stations associated with the first AP.

[0007] The first AP may be configured to receive, in response to the notification, a first response from at least a first station among the one or more first stations, identifying a first capability of the first station. The first AP may be configured to receive, in response to the notification, a second response from the second AP associated with one or more second stations, identifying a second capability of at least one of the second AP or a second station among the one or more second stations. The first AP may be configured to convey data to the first station during the CBF TXOP based on at least one of the first capability or the second capability.

[0008] The first AP may be configured to receive the second capability of the second station from the second AP in response to a second notification transmitted by the second AP to the one or more second stations including the second station. The second notification may request the capabilities of the one or more second stations. The one or more first stations may be selected from a group of stations associated with the first AP based on at least one of the downlink channel state information of the group of stations or the data traffic of the first AP to be transmitted to one or more stations in the group.

[0009] The first AP may be configured to reduce interference of the data conveyed to the first station relative to at least the second station. At least one of the notification, the first response, or the second response may include a triggered physical protocol data unit (TB PPDU). The first AP may be configured to select, for the CBF TXOP, one or more candidate stations of the first AP including the first station from the one or more first stations. The first AP may be configured to insert an indication of the one or more candidate stations into the notification for the second AP to use for data transmission to the second station with reduced interference at the first station according to the CBF.

[0010] The indication may include at least one of the following: an identifier of the first station, a value identifying the number of spatial streams (Nss) of the first station, or a resource unit (RU) of a frequency range allocated to the first station within a channel used by the first AP. The first AP may be configured to identify, from the second response, a parameter of the second capability of the second station. The parameter of the second capability may correspond to at least one of the following: the number of antennas of the second station, the amount of bandwidth of the second station, the sounding capability of the second station for channel sounding, the nulling capability of the second station for interference reduction, the downlink channel state information (CSI) of the second station relative to the first AP, the downlink CSI of the second station relative to the second AP, or a value identifying the number of spatial streams expected for the second station. The first AP may be configured to communicate data to the first station according to the parameter of the second capability to reduce interference from the communicated data at the second station. The first AP may be configured to transmit a trigger frame to the second AP to initiate communication of second data to at least the second station before communicating the data to the first station during the CBF TXOP.

[0011] Aspects of the technical solution relate to a method. The method may include transmitting, by a first access point (AP), a notification indicating a coordinated beamforming (CBF) transmission opportunity (CBF TXOP) to a second AP capable of participating in the CBF and one or more first stations associated with the first AP. The method may include receiving, by the first AP in response to the notification, a first response identifying a first capability of the first station from at least the first station among the one or more first stations. The method may include receiving, by the AP in response to the notification, a second response identifying a second capability of at least one of the second AP or a second station among the second one or more stations from the second AP associated with the second one or more stations. The method may include communicating, by the first AP during the CBF TXOP, data to the first station according to at least one of the first capability or the second capability.

[0012] The method may include receiving, by the first AP, the second capability of the second station from the second AP in response to a second notification transmitted by the second AP to the second one or more stations including the second station. The second notification may request capabilities of the second one or more stations. The one or more first stations may be selected from the group of stations associated with the first AP based on at least one of downlink channel state information of the group of stations associated with the first AP or data traffic of the first AP to be transmitted to one or more stations in the group.

[0013] The method may include reducing, by the first AP, interference of the data communicated to the first station relative to at least the second station. At least one of the notification, the first response, or the second response includes a Trigger-based Physical Protocol Data Unit (TB PPDU). The method may include the first AP selecting, from the first one or more stations, one or more candidate stations of the first AP including the first station for the CBF TXOP.

[0014] The method may include the first AP inserting an indication of the one or more candidate stations into the notification for use by the second AP to transmit data to the second station with reduced interference at the first station according to the CBF. The indication may include at least one of: an identifier of the first station, a value identifying the number of spatial streams (Nss) of the first station, or a resource unit (RU) of a frequency range allocated to the first station within a channel used by the first AP.

[0015] The method may include the first AP identifying, from the second response, a parameter of the second capability of the second station, the parameter of the second capability corresponding to at least one of: the number of antennas of the second station, the amount of bandwidth of the second station, the sounding capability of the second station for channel sounding, the nulling capability of the second station for interference reduction, the downlink channel state information (CSI) of the second station relative to the first AP, the downlink CSI of the second station relative to the second AP, or a value identifying the number of spatial streams expected for the second station. The method may include the first AP communicating data to the first station according to the parameter of the second capability to reduce interference from the communicated data at the second station.

[0016] Aspects of the technical solution relate to a system. The system may include an access point (AP) that may be configured to receive a first notification for a CBF TXOP from a different AP. The first notification may indicate a first capability. The AP may be configured to transmit, in response to the first notification, a second notification indicating a second capability to the different AP. The AP may be configured to transmit data to at least one of one or more stations associated with the AP during the CBF TXOP in response to the first notification according to at least one of the first capability or the second capability.

[0017] The AP may be configured to select the one or more stations from the group of stations based on at least one of the downlink channel state information of a group of stations associated with the AP or the data traffic of the AP to be transmitted to one or more stations in the group of stations. The AP may be configured to transmit a third notification indicating the CBF TXOP to the one or more stations. The AP may be configured to receive a third response indicating a third capability of at least one of the one or more stations in response to the third notification. The AP may be configured to transmit the second notification and the third notification concurrently. Description of the Drawings

[0018] Various objects, aspects, features, and advantages of the present disclosure will become more apparent and better understood by reference to the detailed description taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements.

[0019] Figure 1A is a block diagram depicting a network environment including one or more access points communicating with one or more devices or stations according to some embodiments.

[0020] Figure 1B and 1C is a block diagram depicting a computing device that may be used in conjunction with the methods and systems described herein according to some embodiments.

[0021] Figure 2 Illustrates an example system of coordinated partial rank nulling in a multi-AP and multi-STA environment according to some embodiments.

[0022] Figure 3 is an example plot of the signal space of STA transmissions in the context of single-AP partial rank nulling.

[0023] Figure 4 is an example plot of two signal spaces of two STA transmissions in the context of 2-AP coordinated partial rank nulling.

[0024] Figure 5 is an example block diagram of a system for multi-access point coordination using CBF with mutual interference nulling.

[0025] Figure 6 is an example flowchart of a method for multi-AP coordination to provide CBF.

[0026] Figure 7 is an example flowchart of a method for identifying and exchanging station information between APs.

[0027] Figures 8 to 12It is an example flowchart of a method for providing an instance CBF setup sequence for multiple APs and their associated stations.

[0028] Details of various embodiments of the method and system are set forth in the accompanying drawings and the description below. Detailed Description

[0029] The following IEEE standards (including any draft versions of these standards) are hereby incorporated by reference in their entirety and made a part of this disclosure for all purposes: Wi-Fi Alliance standards and IEEE 802.11 standards, including (but not limited to) IEEE 802.11a TM , IEEE 802.11b TM , IEEE 802.11g TM , IEEE P802.11n TM ; IEEE P802.11ac TM ; and IEEE P802.11be TM draft version D3.0 standard. Although aspects of these standards may be referenced in this disclosure, the disclosure is in no way limited by these standards.

[0030] For the purpose of reading the description of the various embodiments below, the following description of the sections of the specification and their corresponding content may be helpful:

[0031] - Section A describes the network environment and computing environment that can be used to practice the embodiments described herein;

[0032] - Section B describes coordinated partial rank nulling in multi-AP transmissions; and

[0033] - Section C describes multi-access point coordination for nulling mutual interference

[0034] A. Computing and network environment

[0035] Before discussing the specific embodiments of the solution, it may be helpful to describe aspects of the operating environment and associated system components (e.g., hardware elements) in connection with the methods and systems described herein.

[0036] Refer to Figure 1A , which depicts an embodiment of the network environment. Briefly summarized, the network environment includes a wireless communication system that includes one or more access points (APs) or network devices 106, one or more stations (also referred to as STAs) or wireless communication devices 102, and network hardware components or network hardware 192. The wireless communication device or STA 102 can include, for example, a laptop computer, a tablet computer, a personal computer, and / or a cellular phone device. Reference can be made to Figure 1B and 1CThe details of each station or the embodiments of the wireless communication device 102 and the AP or network device 106 are described in more detail (e.g., its internal hardware and software configuration). In one embodiment, the network environment can be an ad hoc network environment, an infrastructure wireless network environment, a subnet environment, etc. The network device 106 or AP can be operatively coupled to the network hardware 192 via a local area network connection. The network device 106 or AP can include, for example, a Wi-Fi device that provides a WLAN, or a 5G base station for providing a cellular network. The network hardware 192, which can include routers, gateways, switches, bridges, modems, system controllers, appliances, etc., can provide a local area network connection for the communication system. Each of the network devices 106 or APs can have an associated antenna or antenna array to communicate with wireless communication devices in its area. The wireless communication device 102 can register with a specific network device 106 or AP to receive services from the communication system (e.g., via SU-MIMO or MU-MIMO configurations). For direct connections (e.g., peer-to-peer communication), some wireless communication devices can communicate directly via an assigned channel and communication protocol. Some of the wireless communication devices 102 can be mobile or relatively stationary with respect to the network device 106 or AP.

[0037] In some embodiments, the network device 106 or AP includes a device or module (including a combination of hardware and software) that allows the wireless communication device 102 to connect to a wired network using Wi-Fi or other standards. The network device 106 or AP is sometimes referred to as a wireless access point (WAP). The network device 106 or AP can be implemented (e.g., configured, designed, and / or built) to operate in a wireless local area network (WLAN). In some embodiments, the network device 106 or AP can be connected to a router as a stand-alone device (e.g., via a wired network). In other embodiments, the network device 106 or AP can be a component of the router. The network device 106 or AP can provide access to the network for multiple devices. The network device 106 or AP can, for example, connect to a wired Ethernet connection and use a radio frequency link to provide a wireless connection for other devices 102 to utilize the wired connection. The network device 106 or AP can be implemented to support standards for sending and receiving data using one or more radio frequencies. Those standards and the frequencies they use can be defined by the IEEE (e.g., the IEEE 802.11 standards). The network device 106 or AP can be configured and / or used to support a public Internet hotspot and / or to extend the range of a Wi-Fi signal on the network.

[0038] In some embodiments, the access point or network device 106 can be used for a wireless network (e.g., IEEE 802.11, Bluetooth, ZigBee, any other type of radio - based network protocol, and / or variants thereof) within (e.g., within a home, vehicle, or building). Each of the wireless communication devices 102 can include a built - in radio and / or be coupled to a radio. Such wireless communication devices 102 and / or the access point or network device 106 can operate in accordance with various aspects of the present disclosure presented herein to enhance performance, reduce cost and / or size, and / or enhance broadband applications. Each wireless communication device 102 can have the ability to act as a client node seeking access to resources (e.g., data and connections to networked nodes such as servers) via one or more access points or network devices 106.

[0039] The network connection can include any type and / or form of network and can include any of the following: peer - to - peer network, broadcast network, telecommunications network, data communication network, computer network. The network topology can be a bus, star, or ring network topology. The network can be any such network topology known to those of ordinary skill in the art that can support the operations described herein. In some embodiments, different types of data can be transmitted via different protocols. In other embodiments, the same type of data can be transmitted via different protocols.

[0040] The communication device 102 and the access point or network device 106 can be deployed as any type and form of computing device and / or executed on any type and form of computing device, such as a computer, network device, or appliance capable of communicating on any type and form of network and performing the operations described herein. Figure 1B and 1C A block diagram depicting a computing device 100 that can be used to practice embodiments of the wireless communication device 102 or network device 106. As Figure 1B and 1C shown, each computing device 100 includes a processor 121 (e.g., a central processing unit) and a main memory unit 122. As Figure 1B shown, the computing device 100 can include a storage device 128, an installation device 116, a network interface 118, an I / O controller 123, display devices 124a to 124n, a keyboard 126, and a pointing device 127 (e.g., a mouse). The storage device 128 can include an operating system and / or software. As Figure 1C shown, each computing device 100 can also include additional optional elements that communicate with the central processing unit or processor 121, such as a memory port 103, a bridge 170, one or more input / output devices 130a to 130n, and a cache memory 140.

[0041] The central processing unit or processor 121 is any logic circuitry that responds to and processes instructions fetched from the main memory unit 122. In many embodiments, the central processing unit or processor 121 is provided by a microprocessor unit, such as: a microprocessor unit manufactured by Intel Corporation of Santa Clara, California; a microprocessor unit manufactured by International Business Machines of White Plains, New York; or a microprocessor unit manufactured by Advanced Micro Devices of Sunnyvale, California. The computing device 100 can be based on any one of these processors, or any other processor capable of operating as described herein.

[0042] The main memory unit 122 can be one or more memory chips capable of storing data and allowing any storage location to be directly accessed by the microprocessor or processor 121, such as any type or variant of static random access memory (SRAM), dynamic random access memory (DRAM), ferroelectric RAM (FRAM), NAND flash memory, NOR flash memory, and solid state drive (SSD). The main memory unit 122 can be based on any one of the above memory chips, or any other available memory chip capable of operating as described herein. In Figure 1B the embodiment shown, the processor 121 communicates with the main memory unit 122 via the system bus 150 (described in more detail below). Figure 1C An embodiment of the computing device 100 is depicted, where the processor communicates directly with the main memory unit 122 via the memory port 103. For example, in Figure 1C , the main memory unit 122 can be DRDRAM.

[0043] Figure 1C An embodiment is depicted in which the main processor 121 communicates directly with the cache memory 140 via a secondary bus (sometimes called a backside bus). In other embodiments, the main processor 121 uses the system bus 150 to communicate with the cache memory 140. The cache memory 140 typically has a faster response time than the main memory unit 122 and is provided by, for example, SRAM, BSRAM, or EDRAM. In Figure 1CIn the illustrated embodiment, the processor 121 communicates with various I / O devices 130 via the local system bus 150. Various buses can be used to connect the central processing unit or processor 121 to any of the I / O devices 130, such as, for example, the VESA VL bus, ISA bus, EISA bus, Micro Channel Architecture (MCA) bus, PCI bus, PCI-X bus, PCI-Express bus, or NuBus. For embodiments in which the I / O device is the video display 124, the processor 121 can use the Advanced Graphics Port (AGP) to communicate with the display 124. Figure 1C Depicts an embodiment of a computer or computer system 100 in which the main processor 121 can communicate directly with the I / O device 130b, for example, via HyperTransport, RapidIO, or InfiniBand communication technologies. Figure 1C Also depicts an embodiment in which a hybrid of local bus and direct communication is used: the processor 121 uses a local interconnect bus to communicate with the I / O device 130a while communicating directly with the I / O device 130b.

[0044] A variety of I / O devices 130a through 130n can be present in the computing device 100. Input devices include keyboards, mice, trackpads, trackballs, microphones, dials, touchpads, touchscreens, and digitizing tablets. Output devices include video displays, speakers, inkjet printers, laser printers, projectors, and dye-sublimation printers. As Figure 1B illustrated, the I / O devices can be controlled by an I / O controller 123. The I / O controller can control one or more I / O devices, such as the keyboard 126 and the pointing device 127, such as a mouse or an optical pen. Additionally, the I / O devices can also provide storage and / or installation media for the computing device 100. In still other embodiments, the computing device 100 can provide a USB connection (not shown) to accommodate a handheld USB storage device, such as a USB flash drive series device of the type manufactured by Twintech Industry, Inc. of Los Alamitos, California.

[0045] Referring again to Figure 1B, the computing device 100 can support any suitable installation device 116, such as a disk drive, CD-ROM drive, CD-R / RW drive, DVD-ROM drive, flash drive, tape drives of various formats, USB device, hard disk drive, network interface, or any other device suitable for installing software and programs. The computing device 100 can further include a storage device for storing an operating system and other related software and for storing application software programs (e.g., any program or software 120 for implementing (e.g., configured and / or designed for) the systems and methods described herein), such as one or more hard disk drives or redundant arrays of independent disks. Optionally, any of the installation devices 116 can also be used as a storage device. In addition, the operating system and software can run from a bootable medium.

[0046] In addition, the computing device 100 can include a network interface 118 to interface to a network through various connections, including (but not limited to) standard telephone lines, LAN or WAN links (such as 802.11, T1, T3, 56kb, X.25, SNA, DECNET), broadband connections (such as ISDN, frame relay, ATM, gigabit Ethernet, Ethernet-over-SONET), wireless connections, or some combination of any or all of the above connections. Various communication protocols (e.g., TCP / IP, IPX, SPX, NetBIOS, Ethernet, ARCNET, SONET, SDH, Fiber Distributed Data Interface (FDDI), RS232, IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11n, IEEE802.11ac, IEEE 802.11ad, CDMA, GSM, WiMax, and direct asynchronous connection) can be used to establish the connection. In one embodiment, the computing device 100 communicates with other computing devices 100' via any type and / or form of gateway or tunneling protocol (such as Secure Sockets Layer (SSL) or Transport Layer Security (TLS)). The network interface 118 can include a built-in network adapter, network interface card, PCMCIA network card, card bus network adapter, wireless network adapter, USB network adapter, modem, or any other device suitable for interfacing the computing device 100 to any type of network capable of communicating and performing the operations described herein.

[0047] In some embodiments, computing device 100 may include or be connected to one or more display devices 124a through 124n. Accordingly, any of I / O devices 130a through 130n and / or I / O controller 123 may include any type and / or form of suitable hardware, software, or a combination of hardware and software to support, enable, or provide the connection and use of (a) display device(s) 124a through 124n by computing device 100. For example, computing device 100 may include any type and / or form of video adapter, video card, driver, and / or library to interface, communicate, connect to, or otherwise use (a) display device(s) 124a through 124n. In one embodiment, the video adapter may include multiple connectors to interface to (a) display device(s) 124a through 124n. In other embodiments, computing device 100 may include multiple video adapters, where each video adapter is connected to (a) display device(s) 124a through 124n. In some embodiments, any portion of the operating system of computing device 100 may be configured to use multiple display devices 124a through 124n. In additional embodiments, I / O device 130 may be a bridge between system bus 150 and an external communication bus such as a USB bus, an Apple Desktop bus, an RS-232 serial connection, a SCSI bus, a FireWire bus, a FireWire800 bus, an Ethernet bus, an AppleTalk bus, a Gigabit Ethernet bus, an Asynchronous Transfer Mode bus, a FibreChannel bus, a fibre bus, a Serial Attached SCSI bus, a USB connection, or an HDMI bus.

[0048] Figure 1B and 1CThe computing device 100 of the type depicted may operate under the control of an operating system that controls the scheduling of tasks and access to system resources. The computing device 100 may run any operating system, such as any version of the MICROSOFT WINDOWS operating system, different versions of Unix and Linux operating systems, any version of MAC OS for Macintosh computers, any embedded operating system, any real-time operating system, any open-source operating system, any proprietary operating system, any operating system for mobile computing devices, or any other operating system capable of running on the computing device and performing the operations described herein. Exemplary operating systems include, but are not limited to: Android, produced by Google Inc.; WINDOWS 7, 8, and 10, produced by Microsoft Corporation of Redmond, Washington; MAC OS, produced by Apple Computer of Cupertino, California; WebOS, produced by Research In Motion (RIM); OS / 2, produced by International Business Machines of Armonk, New York; and Linux, a freely available operating system released by Caldera of Salt Lake City, Utah, or any type and / or form of Unix operating system and other operating systems.

[0049] The computer system or computing device 100 may be any workstation, telephone, desktop computer, laptop or notebook computer, server, handheld computer, mobile phone or other portable telecommunications device, media playback device, gaming system, mobile computing device, or any other type and / or form of computing, telecommunications, or media device capable of communicating. In some embodiments, the computing device 100 may have different processors, operating systems, and input devices consistent with the device. For example, in one embodiment, the computing device 100 is a smartphone, mobile device, tablet computer, or personal digital assistant. Additionally, the computing device 100 may be any workstation, desktop computer, laptop or notebook computer, server, handheld computer, mobile phone, any other computer, or other form of computing or telecommunications device capable of communicating and having sufficient processor power and memory capacity to perform the operations described herein.

[0050] In the context of the systems and methods disclosed herein, aspects of the operating environments and components described above will become apparent.

[0051] B. Coordinated partial rank zeroing in multi - AP transmission

[0052] When an AP transmits data to a specific intended recipient STA within its own basic service set (BSS), other STAs within the same or an adjacent BSS (e.g., other WLANs) can be within the range of the transmitting AP and experience interference. Interference can include any undesired interruption or degradation of a signal, communication, or system caused by the presence of an external signal, noise, or other factors that interfere with the intended transmission or reception of information. Interference can include unwanted signal interruptions caused by transmissions from one access point (AP), affecting the communication between another AP and its associated station (STA). CBF can mitigate such interference by adjusting the transmission mode to minimize signal overlap with unintended STA recipients. For example, when transmissions to different STAs occur simultaneously on the same channel, interference caused by the transmissions can be difficult to resolve because the information from one or more of the transmissions can be unknown and the relationship between the transmissions can be unknown. Such interference can result in latency, delay, or network packet loss, making data transmission within such networks more difficult and having an adverse impact on the user experience.

[0053] The technical solution of the present disclosure overcomes these challenges by providing or facilitating the use of zeroed multi-AP coordinated beamforming (CBF). CBF can include any technique or method in which multiple APs cooperatively adjust their beamforming patterns to deliver their signals or transmissions to the intended stations while minimizing or eliminating interference from such signals or transmissions at unintended stations. For example, APs from different BSSs (e.g., WLANs) can use CBF to configure their transmissions to be sent along a spatial direction or vector where interference from these APs is minimized at an unintended receiving STA or client. The technical solution can include client devices (STAs) that receive spatial streams from APs of their respective networks. A network (e.g., the WLAN of a particular AP) can include one or more basic service sets (BSSs) that have an AP and one or more STAs configured for wireless communication via the same AP (e.g., via a local WLAN configured to the AP). Since an AP can transmit any number of data streams to any number of STAs within its BSS, STAs that do not expect a data stream can be within the wireless communication range of the transmitting AP and experience interference. The technical solution of the present disclosure can utilize the spatial orientation of unintended STA receivers and the beamforming capabilities of APs to transmit data streams to their intended STAs along the spatial orientation where such transmissions are partially zeroed at the unintended receiver locations. In this way, the technical solution of this solution allows multiple APs to communicate at the same time and frequency (e.g., transmit simultaneously on the same channel), while avoiding interference, thereby increasing the throughput of the transmission, reducing latency, and minimizing spectrum usage to avoid interference.

[0054] The technical solution of the present disclosure can include systems and methods using zeroed multi-AP coordinated beamforming (CBF) to facilitate coordinated partial rank zeroing in multi-AP transmissions. Using zeroed CBF can include one of the candidate features being considered for the next generation Wi-Fi standard (UHR, 11bn). Zeroing can include any reduction or elimination of unwanted signals or interference at the receiver, such as by adjusting the phase and amplitude of the incoming signal. Zeroing can include a technique where an AP minimizes the interference experienced by an STA by selectively reducing the strength or power of unwanted signals from other sources. Zeroing can include a technique where the system can combine one signal with another to create a null (e.g., cancel the original signal). Zeroing can be utilized or included to minimize the AP interference seen by an STA due to transmissions from the AP to other STAs (in the same or different BSSs as the first STA).

[0055] Partial rank nulling (sometimes also referred to as partial nulling) can involve an AP minimizing (e.g., reducing below an acceptable threshold) interference in a smaller number of dimensions or directions than the STA can receive. For example, partial rank nulling can involve a technique for minimizing or reducing unwanted signals or interference (e.g., to below an acceptable threshold level) without completely removing the interference. For example, if the STA has two receive antennas (i.e., can receive signals in two dimensions or directions), then partial rank nulling can minimize interference along only one dimension or direction as seen by the STA. This solution can provide a mechanism for coordinated partial rank nulling that minimizes interference at the STA for the AP's own BSS and other BSSs (OBSSs) in which the AP is concurrently transmitting communications. The technical solution can also include an AP coordination mechanism to achieve the above partial rank nulling.

[0056] Partial rank nulling for its own BSS and other BSS access points can be implemented in a wireless communication system. For example, in a multi-user multiple-input multiple-output (MU-MIMO) system, partial rank nulling can be used to improve overall system performance by mitigating interference between multiple communication devices. For example, multiple devices can transmit and receive data simultaneously via their antennas. Due to the spatial proximity between the devices, interference can occur between different devices. The interference can degrade the performance of the system, resulting in a reduced data rate and an overall decrease in capacity. Partial rank nulling for its own BSS and other BSS access points can address this problem by selectively nulling the interference at the unintended recipient STAs.

[0057] Now refer Figure 2 , to illustrate an example of a system 200 for implementing coordinated partial rank nulling for multi-AP transmissions. The system 200 can include one or more access points (APs) 106 (e.g., Wi-Fi routers) that provide transmissions to stations or STAs 102 within their BSS 250. The AP 106 can also have a wireless transmission range 255 that can include STAs 102 outside its BSS (e.g., STAs that are not configured to the corresponding AP's WLAN but are still capable of receiving transmissions or interference from these APs).

[0058] Figure 2It may include a first AP 106 and a second AP 106. The first AP 106 has a first BSS 250 including a first station 102 and a third station 102, and the second AP 106 has a second BSS 250 including a second station 102 and a fourth station 102. Each of the first and second APs 106 may include one or more coordinators 205, a communication controller 210, a nulling function 215, an antenna 220, and a spatial stream 240. Each STA 102 (e.g., the first, second, third, and fourth stations 102 in the system 200) may include one or more antennas 220, a communication controller 210, a spatial stream function 235, and a spatial stream 240. In addition to the STAs 102 within its own BSS 250, each of the APs 106 may also have a wireless signal range 255, which may cover or include the STAs 102 within its own BSS 250 and the STAs 102 outside its BSS 250. For example, in addition to the first and third STAs 102, the first range 255 of the first AP 106 may also include the second STA 102 (e.g., from the BSS of the second AP 106). Similarly, in addition to the second and fourth STAs 102, the second AP 106 may also have a second signal range 255, which may include the first STA 102 (e.g., from the BSS of the first AP 106).

[0059] Figure 2 An environment can be described in which the AP 106 can coordinate its transmissions according to its pre-negotiated and configured partial rank nulling. For example, the system 200 can be used to provide single-AP partial rank nulling (e.g., nulling a part of the interference to non-receiving STAs within the BSS of the transmitting AP) and multi-AP partial rank nulling (e.g., nulling a part of the interference to non-receiving STAs within the same or different BSSs relative to the transmitting AP).

[0060] The AP 106 can include any combination of hardware and software that allows a wireless communication device (e.g., STA 102) to wirelessly connect to a wired network or the World Wide Web or the Internet. The AP 106 can include any combination of hardware and software for facilitating wireless communication within the WLAN of the AP for any STA 102 included in its BSS 250. The AP 106 can include one or more communication devices (e.g., Wi-Fi router, switch, Bluetooth hub, cellular network base station), and can utilize any wireless communication protocol or standard (e.g., 802.11) for wireless communication.

[0061] AP 106 and STA102 can be configured for wireless communication in a wireless communication network (such as a LAN, WAN, or cellular network). For example, each AP 106 can include, be associated with, be coupled to, provide, or facilitate a communication network (such as a WLAN of Wi-Fi) for any client or station 102 in its own basic service set (BSS).

[0062] BSS250 is a term used to identify a set of stations (such as devices) associated with the same wireless access point within a WLAN. For example, a BSS can identify a set or collection of one or more stations and / or one or more APs that communicate together within a wireless network. BSS250 can include one or more APs within a specific coverage area (such as range 255) and client devices (such as STA 102) coupled to the APs. BSS250 can provide infrastructure for an AP 106 to provide network communication to STA102 within its frequency coverage area. Within BSS250, an AP 106 can manage data distribution to various connected devices (such as STA 102), facilitate the implementation of security protocols or functions, and roam as STA 102 may move into and out of its coverage area (such as range 255). Range 255 can include the area where a signal from AP 106 can reach a receiving STA102. Range 255 can include STA 102 within the BSS250 of a given AP 106 or STA102 that is part of the BSS250 of another AP 106. For example, a first STA102 that is part of the first BSS250 of a first AP 106 but is also within the second range 255 of a second AP 106 that serves the second and fourth STA102 of a second BSS250.

[0063] The coordinator 205 can include any combination of hardware and software for coordinating communication between AP 106 and / or STA 102. The coordinator 205 can include functions (such as applications, computer code, or programs) that facilitate the coordination of communication (such as transmission) between AP 106 and STA 102 or among AP 106. The coordinator 205 can include functions for implementing a coordination phase to identify STA102 for which interference needs to be completely or partially nulled and for exchanging STA 102 information between AP 106. The coordinator 205 can include functions for coordinating timing and frequency (such as exchanging timing and frequency information (such as communication bands or channels) between AP 106). The coordinator 205 can generate, facilitate, implement, and apply settings or configurations to AP 106 and / or STA 102 to facilitate coordinated partial rank nulling.

[0064] The coordinator 205 may include a precoder function, such as a precoder algorithm for calculating a beamforming vector for each STA 102 to achieve partial rank nulling. The precoder may include a function for calculating the direction or vector for beamforming transmission to the STA 102. The precoder may include a function for: using information or data related to the direction or vector where interference at the STA 102 is minimized or reduced below a threshold of an acceptable interference level (e.g., achieving partial rank nulling) to determine the direction or vector for beamforming transmission to perform partial rank nulling at such STA 102.

[0065] The coordinator 205 may include a function for performing channel sounding on the STA 102. For example, the coordinator 205 may facilitate, indicate, or request each STA to measure one or more MIMO channels of each sounding AP and provide the measurement return to the coordinator 205. When measuring the channels of different APs 106, the relative phase offset across the receive antennas 220 for the STA 102 may be maintained at a constant value. The coordinator 205 may exchange with the STA 102 an estimate of the MIMO channels of the sounding APs (e.g., via a compressed beamforming report format (CBR) as provided in 802.11, or in Cartesian form). The coordinator 205 may exchange information about interfering APs 106 (e.g., APs 106 from an external BSS 250), such as when the STA 102 provides a linear transformation of the MIMO channels from the specific interfering AP 106. The linear transformation may be determined using a previously measured MIMO channel between the STA and its own AP 106 (e.g., the AP 106 of the STA's BSS 250). For example, the linear transformation of the MIMO channel may represent a projection on one or more eigenmodels of the MIMO channel measured between the STA and the AP 106 of its own BSS. For example, if the STA is receiving a specific number of expected spatial streams from its own AP 106 (e.g., the AP 106 from its own BSS 250), then the coordinator 205 may exchange (e.g., receive) a set of directions where the AP 106 will minimize interference.

[0066] The coordinator 205 may include functionality for facilitating or performing channel sounding for the STA 102. Channel sounding may include transmitting a signal and, in response, receiving characteristics (such as signal strength, delay, and phase), and then using such received characteristics to determine the quality of the communication channel. The coordinator 205 may transmit one or more null data packets (NDPs) (e.g., individually or jointly with the APs 106 of other BSSs 250). The NDPs may be synchronized in time and / or frequency (e.g., among multiple APs 106 performing simultaneous channel sounding). The number of sounding dimensions in the NDP may include the total number of antennas across the APs. NDPs transmitted jointly may precede one or more NDP announcement (NDPA) frames. For example, the AP 106 may transmit an NDPA to all the probed STAs 102 on behalf of all the APs 106 performing channel sounding. For example, each of the APs 106 sequentially sends an NDPA to its own STAs 102. For example, all the APs 106 simultaneously but individually in frequency (e.g., via OFDMA) transmit their NDPAs, where each AP 106 addresses the STAs 102 within its own BSS 250. For example, the coordinator 205 may provide or facilitate a trigger frame transmitted by the AP 106, based on which all the APs 106 participating in channel sounding may synchronize their carrier frequency offsets (CFOs) and the start time of their coordinated transmissions.

[0067] The communication controller 210 may include any combination of hardware and software for implementing wireless communication between the AP 106 and the STA 102. The communication controller 210 may include functionality for providing and transmitting data (such as spatial streams) to the intended STA 102. The communication controller 210 may transmit a message to the STA 102, such as information, data, or a description asking for the direction or vector in which interference is to be minimized at each STA 102. The communication controller 210 may include functionality for configuring the transmission characteristics of the AP 106 to perform and implement the transmission of the spatial stream 240 according to partial rank nulling. For example, the communication controller 210 may configure the antennas 220 and any other settings to facilitate or implement the transmission of the spatial stream 240 according to a particular direction or vector (e.g., as determined by the coordinator 205) to perform partial rank nulling at a particular STA 102. The communication controller 210 may control, manage, and implement the transmission (e.g., communication) according to timing and frequency (e.g., the selected channel or band) and the direction or vector in which partial rank nulling is performed.

[0068] AP 106 and / or STA 102 may include a communication controller 210 to facilitate wireless communication with each other. The communication controller 210 may include and / or utilize wireless communication interfaces that facilitate communication via standards such as 802.11a / b / g / n / ac / ax, Bluetooth, cellular (e.g., 3G, 4G, 5G), Zigbee, Z-Wave, NFC, and others, such as hardware and software, including transceivers, antennas, RF interfaces, ports, and processing devices. The communication controller 210 may control the reception and transmission of signals, data, or messages to facilitate or implement multi-AP transmission using coordinated partial rank nulling.

[0069] AP 106 may include a nulling function 215 for implementing nulling or partial rank nulling according to coordinated (e.g., agreed-upon) communication between the APs 106. Partial rank nulling may include any technique or action in array signal processing for suppressing interference from signals in a particular direction while retaining signals coming from other directions. For example, partial rank nulling may include manipulating the array response to create nulls or zeros in the radiation pattern of interference from a particular direction. The nulling function 215 may include any combination of hardware and software for reducing or eliminating unwanted signals or interference at a receiver (e.g., STA 102), such as by adjusting the phase and amplitude of incoming signals. The nulling function 215 may include any combination of hardware and software for minimizing or reducing unwanted signals or interference (e.g., to below an acceptable threshold level) (e.g., without completely removing the interference).

[0070] The nulling function 215 may include a function for measuring interference from a particular AP 106 from various receive vectors or directions relative to the STA 102. A direction may include any path or route along which a transmitted signal moves, is directed, or points (e.g., as a vector), and may be specified by its position relative to a reference point or object (e.g., an AP and / or STA). The nulling function 215 may identify or use signals (e.g., probe signals) measured from multiple angles, directions, or vectors and identify the angle, direction, or vector from, along, or at which the interference is lowest or below an acceptable threshold. The nulling function 215 may include or utilize a precoder (e.g., residing within the coordinator 205) to determine the direction or angle along which the interference is lowest or reduced below the threshold (e.g., partial rank nulling). Then, the nulling function 215 may select the direction, angle, or vector corresponding to the lowest interference as the direction in which to partially null the signals from the AP 106.

[0071] AP 106 and station 102 may include an antenna 220. Antenna 220 may include any transmitting or receiving antenna. Antenna 220 may include or be coupled to a communication link and / or transceiver that implements communication, including a chain of circuitry (e.g., amplifiers, filters, analog / digital and / or digital / analog converters, processors, signal combiners, and other circuitry that facilitates signal transmission or reception).

[0072] AP 106 and station 102 may communicate spatial streams 240 (e.g., spatial stream M intended for a particular STA 102 by AP 106, or the total number of spatial streams N transmitted by AP 106). Spatial stream 240 may include any data stream transmitted or received via a separate antenna in a MIMO wireless communication system. For example, a spatial stream may be transmitted or received on more than one antenna, and multiple spatial streams may share the same set of antennas. For example, when transmitted on multiple antennas, each spatial stream may use a unique beamforming vector that may be different from the vectors of other spatial streams transmitted on the same set of antennas. Spatial stream 240 may provide or facilitate improved throughput and reliability by using multiple antennas to create diverse data paths. Spatial stream 240 may be suitable for directional control and transmission with partial rank nulling.

[0073] System 200 may include or use any number of spatial streams 240, including any independent data stream transmitted simultaneously on multiple antennas in a MIMO (multiple-input multiple-output) system. System 200 may include STA 102, which may be configured to communicate with a wireless network (e.g., a WLAN of BSS 250) to receive and transmit data. System 200 may allow STA 102 to simultaneously receive multiple spatial streams 240 via one or more receive antennas 220 (e.g., two receive antennas for each STA 102). Each spatial stream 240 may represent an independent data stream transmitted from AP 106, which may minimize interference in several dimensions / directions. The number of dimensions or directions in which partial rank nulling may reduce interference may be less than the number of spatial streams 240 that STA 102 may receive. For example, if STA has two receive antennas 220 (e.g., can receive signals in two dimensions or directions), then partial rank nulling may minimize interference along one dimension or direction as seen by STA 102.

[0074] The number of spatial streams 240 that STA 102 may support may vary based on the capabilities of the network and the MIMO configuration. For example, if STA 102 has multiple receive antennas 220 and the network is configured for 2x2 MIMO, then STA 102 may simultaneously receive two spatial streams 240. Each spatial stream 240 may carry independent data, effectively increasing data capacity and improving overall throughput, data rate, increased system capacity, and / or wireless network reliability.

[0075] Referring now to Figure 3 , an example of a plot 300 of the signal space 302 of a transmission received by STA 102 is one aspect of the technical solution. As shown in plot 300, a station 102 (e.g., STA1) having a total of K = 2 receive antennas 220 can receive a total number N = 3 spatial data streams 240 transmitted by an AP 106 (AP1). STA1 can be within the BSS 250 of transmitting AP1 106 and can receive all 3 spatial data streams 240 transmitted by AP1, even though only one of these spatial data streams 240 is intended for STA1.

[0076] For example, AP1 can transmit N = 3 spatial streams 240 via downlink (DL) MU-MIMO to multiple STAs 102 within its BSS 250. Of the total N = 3 spatial data streams 240 transmitted by AP1, M = 1 stream (e.g., a single spatial data stream 240, where M < N) can be intended for STA1. Although plot 300 shows the STA1 stream (e.g., the stream intended for STA1) being directed at an angle from the X-axis, the remaining two spatial data streams 240 (e.g., interfering streams from AP1) are directed along the X-axis. The Y-axis (which is orthogonal or perpendicular to the X-axis) can represent the direction or vector along which transmissions on the signal space 302 of STA1 are nulled or partially nulled. Thus, the STA1 stream (at least partially directed along the Y-axis) has interference below a threshold in at least one direction and can thus be received by STA1. For example, the STA1 stream can have no interference in at least one direction.

[0077] In Figure 3 the example, the receiving station 102 (e.g., STA1) can have any number K of receive antennas 220 such that M < K < N, where M corresponds to the total number of data streams intended for the receiving station 102 and N corresponds to the total number of data streams transmitted by AP 106 to any number of receivers. In the plot 300 example, N = 3, M = 1, and K = 2. In such a scenario, in order for STA1 102 to be able to decode its own M intended spatial streams 240, AP1 106 can beamform the transmitted spatial streams such that the signal strength from the interfering streams (e.g., the N - M = 2 streams aligned with the X-axis) causes its signal at STA1 to be minimized in a set of M linearly independent directions when received at STA1 102. As shown by the STA1 stream, the M intended streams 240 can be recovered by STA1 102 by projecting them away from the X-axis.

[0078] AP1 106 may include, in its transmission, a properly configured Long Training Field (LTF) such that STA1 102 can estimate both: i) the directions of its M intended streams, and (ii) M distinct directions in which interference is minimized. The technical solution may include or provide a framework for scenarios in which any number of APs 106 perform partial rank nulling towards any number of STAs 102. For example, when two APs 106 are utilized, before implementing coordinated transmission, the first AP 106 (e.g., AP1) and the second AP 106 (e.g., AP2) may perform coordination (e.g., during a coordination phase), where messages may be exchanged between AP1 and AP2 to identify each receiving STA for which interference is to be completely or partially nulled. For example, AP 106 may identify an STA 102 that has more receiving antennas than its intended spatial streams (e.g., antenna K = 2, while the received streams N = 10, where only M = 1 is intended for the STA).

[0079] Such identified STAs may include interference that is sufficiently prominent as seen by the OBSS AP to include nulling (e.g., the STA may have an interference signal strength or power above a specific threshold). For example, the threshold may include the background signal noise level, or 2, 3, 4, 5, 10, or greater multiples of the background noise level. For example, the threshold may be defined with reference to other signals, such as the signal strength, amplitude, or power of the received intended streams (e.g., 1 / 2, 1 / 3, 1 / 4, or 1 / 8 of the signal strength, amplitude, or power of the expected received spatial stream).

[0080] For each STA identified to have its interfering streams partially nulled, AP1 and AP2 may identify a set of linearly independent receiving directions in which interference from the two APs will be minimized. Linearly independent receiving directions may include distinct and uncorrelated paths, directions, or channels through which signals may be received by multiple receiving antennas 220. AP1 and AP2 may dynamically change such a set of directions from one coordinated transmission to the next depending on: i) other receiving STAs, and ii) the number of spatial streams intended for each STA.

[0081] Once the set of directions is identified, AP1 and AP2 can start coordinated transmissions that are synchronized in both time and frequency. For example, out of the total number N1 of spatial streams transmitted from AP1, a subset of M1 spatial streams can be expected to be used for STA1 having a number K1 of receive antennas. The configuration can include the M1 spatial streams expected for STA1, which is less than the number K1 of receive antennas and also less than the total number N1 of spatial streams from AP1 (e.g., M1 < K1 < N1). Similarly, out of the N2 streams transmitted from AP2, M2 streams can be expected to be used for STA2 having K2 receive antennas such that M2 < K2 < N2. In such a configuration, both STA1 and STA2 can be selected, determined, or configured such that partial rank nulling is performed on them by AP1 or AP2. AP1 or AP2 can use beamforming for the directions on which partial rank nulling is to be performed to coordinate the transmission of their data streams in time and frequency to reduce interference and allow simultaneous transmissions.

[0082] Now referring to Figure 4 , example plots 402 and 404 illustrate the received signal space 406 of STA1 and the received signal space 408 of STA2, which are the receivers of transmissions in which coordinated partial rank nulling is implemented by AP1 and AP2 in a multi-AP transmission example. Figure 4 This can correspond to an example in which the present technical solution utilizes two APs 106 (such as Figure 2 those illustrated in). The APs 106 can apply appropriate beamforming vectors to their respective spatial streams 240 to transmit the streams at least along the specified directions or vectors as received by the intended STAs such that the same streams will be partially or fully nulled along the specified directions at the non-intended receiving STAs. For example, the beamforming vectors applied to the spatial streams can minimize the interference from both AP1 and AP2 at a set of M1 independent receive directions at STA1, as pre-agreed during the coordination phase. By projecting the streams onto such determined M1 directions, the M1 expected streams for STA1 can be recovered. For example, this can be similarly applied to STA2, which has a corresponding set of M2 directions. AP1 and AP2 can include appropriately constructed long training fields (LTFs) in the coordinated transmissions such that STA1, STA2 can estimate both: i) the directions of their respective expected streams, and (ii) the directions in which the interference from AP1 and AP2 is minimized.

[0083] AP1 and AP2 can each transmit a total number N = 2 spatial streams 240, where only M = 1 spatial stream 240 is expected to be received by the STA 102 of its own BSS 250 of the corresponding transmitting AP 106, and each receiving STA 102 includes K = 2 receiving antennas 220. For example, for STA1, the remaining one spatial stream from AP1 and the two spatial streams from AP2 can generate interference that will be partially nulled. As illustrated, a total of 3 spatial streams are partially nulled (e.g., aligned with the X-axis or X-direction in Figure 4 ).

[0084] As shown in drawing 402, the interfering streams 412 from AP1 and the interfering streams 414 and 416 from AP2 are directed along the X-direction of the STA1 received signal space 406 and removed or minimized along the Y-direction, while the desired stream 410 from AP1 is directed along a different direction (e.g., closer to the Y-direction or more closely aligned with the Y-direction) and thus is not removed or minimized along the Y-axis or Y-direction and is received by STA1. For example, the Y-axis (also referred to as the Y-direction) can be orthogonal or perpendicular to the X-axis (also referred to as the X-direction). For example, when the desired spatial stream has a component greater than a threshold in the Y-direction, the STA1 received signal space allows such a stream to be received at STA1. For example, the threshold can be as high as 5% of the total received signal strength of the desired spatial stream. For example, depending on the design, the threshold can be as high as 5%, 10%, 15%, 20%, 30%, or greater than 30%.

[0085] Similarly, as shown in drawing 404, the interfering streams 410 and 412 from AP1 and the interfering stream 416 from AP2 are directed along the X-direction of the STA2 received signal space 408, and their signals are also minimized or removed along the Y-direction, while the desired stream 414 from AP2 is directed along a different direction (e.g., closer to the Y-axis or more closely aligned with the Y-axis) and thus is not removed or minimized along the Y-direction and is received by STA2. In some embodiments, AP1 and AP2 can simultaneously transmit the streams 410, 412, 414, and 416 in the presence and range of STA1 and STA2, and the interference and non-interference of the streams can occur simultaneously. Thus, AP1 and AP2 can simultaneously and in a coordinated manner (e.g., at the same time and frequency) transmit spatial streams to their own corresponding STAs 102, using partial rank nulling to prevent interference to non-desired STAs 102.

[0086] In one example, as part of the coordination phase, the APs 106 (e.g., AP1 and AP2) may exchange information regarding a precoder algorithm that is used to calculate beamforming vectors for each STA 102 (e.g., STA1 and STA2) to achieve partial rank nulling. For example, as part of the coordination phase, the APs 106 may exchange information, data, or descriptions of direction vectors where interference will be minimized at the receiving antennas 220 of each STA. For example, as part of the coordination phase, a single AP 106 may calculate beamforming vectors for all spatial streams and share these vectors with other participating APs.

[0087] Using the information exchanged during the coordination phase, a receive direction for minimizing interference for each STA 102 may be determined or generated based on or using a policy (e.g., a policy specified in a standard). The choice of policy may be fixed to a "default" implementation, or may be determined based on the capabilities of the APs 106 and / or the STAs 102. For example, for an STA receiving M expected spatial streams from its own AP 106 of a BSS 250, the policy may include interfering with the AP 106 to minimize interference at the receiver of the STA along M directions that correspond to the M strongest eigenmodes of the channel between the STA 102 and its AP 106 (e.g., the AP 106 of the STA's own BSS 250). For example, for an STA receiving M expected spatial streams from the AP of the STA's own BSS, the policy may include interfering with the AP 106 to minimize interference at the receiver of the STA along M directions that correspond to the M strongest eigenmodes of the channel between the STA 102 and the interfering AP 106.

[0088] For example, as part of the coordination phase, AP1 and AP2 may each perform channel sounding on STA1 and STA2. Each STA 102 may measure the MIMO channel from each sounding AP 106 and may provide a response that includes the measurements. When measuring channels from different APs, the relative phase offsets across the receiving antennas of the STAs 102 may be maintained at a constant value.

[0089] During the coordination phase, different independent variants and their combinations may be implemented. For example, STA 102 may feedback an estimate of the MIMO channel from the sounding AP in a compressed beamforming report format (CBR) (e.g., one defined in 802.11). For example, STA 102 may feedback an estimate of the MIMO channel from the sounding AP in Cartesian form. For example, for an AP 106 (e.g., an interfering AP) from another BSS 250 different from the BSS 250 of the STA, STA 102 may feedback a linear transformation of the MIMO channel from the AP 106. The linear transformation may be determined by the previously measured MIMO channel between the STA and its own BSS AP. For example, the linear transformation may represent a projection on one or more eigenmodels of the MIMO channel measured between STA 102 and its own BSS AP 106. For example, for the sounding AP 106, if STA 102 is receiving M expected spatial streams from its own BSS AP 106, then STA 102 may feedback M preferred sets of directions, where the corresponding AP may minimize interference.

[0090] As part of the coordination phase, AP 106 (e.g., AP1 and AP2) may jointly perform channel sounding of STA 102. AP 106 may jointly transmit null data packets (NDPs) that may be time / frequency synchronized. The total number of sounding dimensions in the NDP may be equal to the total number of antennas 220 across AP 106. The jointly transmitted NDP may be preceded by one or more NDP announcement (NDPA) frames. For example, a single AP 106 may transmit an NDPA on behalf of all APs to the STAs to be sounded across BSS 250. For example, all APs 106 may transmit their NDPAs sequentially, where the NDPA of each AP addresses the STA 102 within its own BSS 250. For example, all APs 106 may transmit their NDPAs simultaneously but frequency-separated (e.g., via OFDMA), where each AP 106 addresses the STA 102 within its own corresponding BSS 250. The coordinated transmission may be preceded by a trigger frame transmitted by one of the APs 106. Based on the trigger frame, all participating APs 106 may synchronize their carrier frequency offsets (CFOs) relative to the AP 106 that transmitted the trigger frame and synchronize the start time of their coordinated transmission.

[0091] On the one hand, the system 200 can be a system for coordinated partial rank nulling in multi-AP transmission, or a system for synchronous multi-AP transmission with coordinated partial rank nulling. The system 200 can include any number of APs 106, and the APs 106 can have overlapping BSSs 250 and overlapping ranges 255 for wireless communication. For example, the first AP 106 can have a first group (e.g., one or more) of STAs 102 within the first BSS 250 (e.g., WLAN) of the first AP 106, and the second AP 106 can have a second group of STAs 102 (e.g., one or more STAs) within the second BSS 250. Each of the first AP 106 and the second AP 106 can include one or more STAs 102 of another BSS 250 (e.g., an adjacent AP 106) within its own range 255 for wireless communication.

[0092] The first AP 106 can be configured to transmit a first message to the second AP 106. The first message can be transmitted by the coordinator 205 as part of a coordination phase, where the APs 106 jointly collect information from the STAs 102 that belong to any of their BSSs, or individually collect information from the STAs 102 in their own BSS 250, and exchange the collected information between the APs 106. The first message can identify the first station 102 of the first AP 106 for which interference from the second AP 106 will be partially nulled. The first station 102 can be an STA that is part of the first BSS 250 of the first AP 106 (e.g., configured to communicate wirelessly with the first AP 106 via the WLAN of the first AP 106).

[0093] The message can include a first direction in which interference from the second AP 106 is partially nulled at the first station 102. For example, the first message can include the number of the first set of directions in which interference from the second AP at the first station will be partially or completely nulled. For example, the first message can include the first set of directions in which interference will be partially or completely nulled. For example, the first message can cause the second AP to identify the first set of directions in which interference to the first station will be partially or completely nulled.

[0094] The first direction or the first set of directions can be a set of one or more linearly independent vectors or directions along which transmissions from the second AP 106 can be reduced below a predetermined threshold (e.g., corresponding to the power or gain level of the signal or a threshold defined according to the noise signal level). The first message can include location information (e.g., the position of the STA relative to the AP 106, the coordinates of the STA relative to the AP 106, information about the spatial orientation of the STA, or any other information corresponding to the spatial orientation of the STA).

[0095] The first AP 106 may receive a second message from the second AP 106. The second message may be transmitted by the coordinator 205 during the coordination phase of the first and second APs 106. The second message may identify a second station of the second AP, for which interference from the first AP will be partially or fully nulled. The second message may include or identify a second direction in which interference from the first AP is partially or fully nulled at the second station 102. The second direction or second set of directions may be linearly independent vectors or directions along which transmissions from the first AP 106 may be reduced below a predetermined threshold (e.g., corresponding to the power or gain level of the signal or a threshold defined based on the noise signal level). The second message may include location information (e.g., the location of the STA relative to the AP 106, the coordinates of the STA relative to the AP 106, information about the spatial orientation of the STA, or any other information corresponding to the spatial orientation of the STA).

[0096] The first AP 106 may establish, set, modify, or configure one or more settings of the first AP 106. The one or more settings may be settings for establishing or coordinating with the second AP 106 the time and frequency for transmitting to the first station 102. The transmission may be a message, a request, a response to a request, or a network data packet (e.g., a packet of the spatial data stream 240). The time may be the time at which the first AP 106 will transmit a transmission to the first station 102. The time may be synchronized to the same time as the transmission from the second AP 106 to the second station 102. The time may be synchronized to a time different from the time at which the second AP 106 transmits a second transmission to the second station 102. The one or more settings may be used to cause the first AP 106 to send or transmit a transmission to the second station 102 according to the second direction to partially or fully null the interference at the second station 102.

[0097] The first message may identify at least the first station 102 of the first AP 106, for which interference from the second AP 106 will be nulled. The first message may identify at least a certain number of directions in which the interference will be partially nulled at the first station. The first message may identify the direction in which the interference will be partially nulled at the first station 102. Additionally, the receipt of the first message may cause the second AP to identify a set of directions along which the interference to the first station will be partially nulled.

[0098] For example, since beamforming vectors can be calculated for all receiving stations 102 in general and not just for individual stations in isolation, the direction for nulling the interfering portion at a particular station can depend on which other stations 102 are receiving signals simultaneously. In such instances, although the message may identify the station 102 at which the interference is to be nulled, it may or may not identify the fixed and constant direction for nulling the interference at that particular station 102. For example, in some embodiments, the direction for nulling may not be indicated or signaled by any AP, but rather each AP may independently determine or infer the nulling direction for different stations 102 based on the exchange of other information, such as a set of stations 102 that each AP 106 expects to communicate with, the number of directions at each station at which interference is to be nulled, the direction or location of the stations or APs, and the like. Such information, together with the information collected about the channels between the APs 106 and the STAs 102 through a previous channel sounding process, can be used to independently determine the nulling direction for each station 102.

[0099] The first AP 106 can be configured to transmit a first spatial stream 240 including the transmitted data to the first station 102 at a set time and frequency. The first spatial stream 240 can be directed so as to partially null the interference from the first AP at the second station along a second set of directions. For example, the first AP 106 can beamform the first spatial stream 240 (e.g., containing the transmission) to transmit along a spatial vector or direction orthogonal to the first direction at the second station 102. The first data stream can be coordinated with a second data stream transmitted by the second AP 106 to the second client 102 at the time and frequency (e.g., coordinated time and frequency), where the second stream is directed so as to partially or fully null the interference from the second AP at the first station 102 along a first set of directions. For example, the first data stream can be coordinated with a second data stream transmitted by the second AP to the second station at the time and frequency, where the second data stream is directed so as to partially null the interference from the second AP at the first station along the first direction.

[0100] The first station 102 can be configured to receive a wireless transmission from the first AP via the wireless local area network (WLAN) of the first AP. The second station 102 can be configured to receive a wireless transmission from the second AP via the WLAN of the second AP. The first station 102 and the second station 102 can each be located within a first range 255 of the wireless transmission from the first AP 106 and a second range 255 of the wireless transmission from the second AP 106.

[0101] The first AP 106 can be configured to determine the spatial orientation of one or more antennas 220 of the first AP 106 based at least on a second set of one or more directions. The spatial orientation of one or more antennas 220 of the first AP 106 can be determined based at least on the position (e.g., coordinates or GPS location) of the first station, the second station, and / or the first AP 106. The first AP 106 can be configured to beamform transmissions to the first station 102 based at least on the spatial orientation of one or more antennas 220 of the first AP 106 relative to the first station.

[0102] The first AP 106 can be configured to exchange time and frequency with the second AP 106 for coordinating the transmissions of the first AP and the second AP. For example, the coordinator 205 can exchange the channels or frequency bands for transmitting communications to its STAs 102, and the timing and frequency of the transmissions and / or the phases of the transmissions relative to each other. The first AP 106 can be configured to use time and frequency coordination for the transmission from the first AP 106 to the first station 102 and the transmission from the second AP to the second station.

[0103] The first AP 106 can be configured to receive a packet including information about a first client. The packet can contain a network packet, message, or transmission, which can contain information about the characteristics of the channels of the first station and / or the second station. The first AP 106 can be configured to identify from the received packet information indicating the spatial orientation of the first client relative to the second AP. For example, the first AP 106 can determine linearly independent vectors at the STA 102 where the interference at the STA 102 is partially or completely nulled. The first AP 106 can be configured to use the spatial orientation to determine a first set of one or more directions of the first client.

[0104] The first AP 106 can be configured to receive a third message from the second AP 106. The third message can identify a third station 102 of the second AP 106 (e.g., an STA 102 within the BSS 250 of the second AP 106) for which interference from the first AP 106 will be partially or fully nulled. The third message can contain a third direction such that the interference is partially nulled along the third direction at the first station. The first AP 106 can configure one or more settings of the first AP 106 to coordinate with the second AP 106 the time and frequency of the transmission to the first station to be sent according to a third set of one or more directions to partially null the interference at the third station. The first AP 106 can form a beam for the transmission to the first station according to a second set of one or more directions to partially null the interference at the second station, and form the beam according to the third set of one or more directions to partially null the interference at the third station.

[0105] The first AP 106 may be configured to transmit a plurality of streams 240 including transmissions to the first station 102. The number of streams 240 among the plurality of streams to be transmitted to the first station 102 may not exceed the number of antennas of the first station 102. The first AP may transmit a second plurality of streams including a plurality of streams to a plurality of STAs including the first STA. For example, the number of receive antennas 220 that the receiving STA 102 may have may be not less than the number of spatial streams 240 directed to the receiving STA 102, while the receiving STA 102 may be exposed to a number of spatial streams 240 of all STAs within the range 255 directed to the AP 106 and thus have more interference from a number of spatial streams 240 than the number of spatial streams 240 directed to the receiving STA 102.

[0106] C. Multi-Access Point Coordination for Nulling of Mutual Interference

[0107] Coordinated beamforming (CBF) may comprise a wireless communication technique in which antennas of multiple devices coordinate and focus the transmission of radio frequency signals towards a specific direction or location, for example to form a beam by such coordination. The multiple devices may coordinate to adjust the intensity of the transmitted radio signals and the signal clarity or integrity to aim or point towards a specific or identified receiving device. CBF may implement signal nulling, in which the transmitted signals from the antennas are controlled to actively partially or fully suppress or reduce interference with respect to a specific direction or location corresponding to an unintended recipient while maintaining the desired signal strength at the intended recipient device. CBF may involve two or more APs (e.g., three, four, or more APs) that simultaneously transmit to their respective associated stations, where each AP beamforms its transmitted signals to minimize the interference caused to those stations when the stations of the other APs receive their respective intended signals.

[0108] In a wireless communication system, interference from adjacent devices and environmental factors may degrade the signal quality. In a dense urban environment or an area with a high level of wireless activity, it may be inappropriate to use beamforming to only enhance the desired signal without considering interference. This may result in reduced data rates, increased latency, and unreliable connections, and pose challenges to achieving the desired performance and reliability in a wireless network. Although CBF with nulling may be used to minimize the interference caused by an AP to an unintended recipient STA, coordinating CBF between APs may be difficult due to the differences between different STAs across different BSSs.

[0109] The technical solution overcomes these challenges by providing a system and method for effectively coordinating CBF among different APs. The technical solution may include an AP identifying other APs that can participate in CBF, selecting candidate stations from the BSSs of the participating APs, and exchanging data regarding the station capabilities. The candidate stations may include any stations within BSS250 that can be selected as candidate stations for use in CBF. The AP may determine which stations will participate in CBF based on the station capabilities and coordinate with the remaining APs the set of stations involved in CBF. The candidate station capabilities may be or include any technical features, capabilities, or configurations of the STA, such as those corresponding to channel sounding, beamforming, or nulling, which can be used to determine the suitability of the station for participating in CBF. The AP may implement CBF using nulling (e.g., all or part) using parameters such as the common BSS color and association identifiers corresponding to the respective stations across the BSSs of the participating APs.

[0110] Figure 5 An example of a system 500 for implementing multi-access point coordination to nullify mutual interference is described. The example system 500 may incorporate, utilize, or include any features or functions of system 200 or examples 300 and 400, and vice versa. The system 500 may include one or more APs 205 that wirelessly communicate with one or more stations 230 via one or more wireless links 550. For example, a first AP 205 may wirelessly communicate 550 with a first station 230 that may be located in the BSS250 of the first AP. Similarly, a second AP 205 may wirelessly communicate 550 with a second station 230 that may be located in the BSS250 of the second AP. The first AP 205 and the second AP 205, and any additional APs 205, may wirelessly communicate with each other via one or more links 550 to coordinate CBF among themselves and with respect to any station 230 with which they communicate (including the first and second stations 230, or any other station 230 served by either of the APs 205).

[0111] Each AP 205 (including the first AP 205 and the second AP 205) may include one or more coordinated beamforming managers 505 for establishing and managing CBF, one or more station selectors 510 for selecting stations 230 for CBF operations, and one or more communication controllers 210 for controlling communication with other APs 205 and stations 230. Each communication controller 210 may include, serve, generate, receive, use, process, or manage one or more sequences 515, frames 520, parameters 525, and station capability data 520, each of which may be used in the process of coordinating CBF operations among the APs 205.

[0112] For example, system 500 may utilize a first AP 205 to identify a second AP 205 as an AP that is capable or available to participate in coordinated beamforming (CBF). The first AP 205 may utilize a station selector 510 to select one or more potential stations 230 within its own BSS 250 that participate in CBF using the station capability data 530 of station 230 and its own AP capability data 535, such as selecting a STA 230 that participates in CBF operations using channel and traffic characteristics. The station capability data 530 may include or indicate the capabilities, settings, or parameters of an individual station 230 that are related to the station 230's capabilities and functions with respect to CBF. The AP capabilities 535 may include characteristics or attributes that define the performance or functionality of the AP 205 for implementing wireless communication. The AP capability data 535 may include, for example, information regarding the amount of padding included in frames exchanged between the AP and the STA or frames exchanged between APs. Padding may provide additional processing time for the receiving device before it responds. The AP capability data 535 may include, for example, signals or data indicating the amount of padding requested by the receiving device or provided by the transmitting device. The first AP 205 may utilize a communication controller 210 to exchange with the second AP 205 one or more station capability data 530 indicating the capabilities of candidate stations 230. The second AP 205 may similarly collect the AP capability data 535 of the second AP 205 and the station capability data 530 of stations 230 in the second BSS 250 of the second AP 205, and then share this data with the first AP 205. Based on the collected and exchanged capabilities of all candidate stations 230, the first AP 205, the second AP 205, or the first and second APs 205 together may determine which stations 230 will participate in the CBF process. The first AP 205 and the second AP 205 may implement a sequence (e.g., sequence 515) between each other to establish a set of stations 230 for CBF.

[0113] During a sequence 515 (e.g., a handshake) for CBF establishment, the first AP 205 and the second AP 205 may exchange their AP capability data 535, such as the number or dimension of antennas they support, the detection capability and nulling capability of the AP. The first and second APs 205 may utilize a parameter 525, such as an indication of a designated common basic service set (BSS) color or an association identifier (AID) of the participating station 230. The AID may include a unique identifier used in a wireless network to identify and manage devices accessing the network within the same network infrastructure. The first AP 205 may handshake with an auxiliary AP to exchange candidate station capability data 530 (e.g., number of antennas, bandwidth, detection and nulling capabilities) or AP capability data 535 (e.g., maximum client limit). This first AP 205 may enter a CBF coordination phase with the second AP 205, determine parameters 525 for CBF operation (e.g., nulling direction, type or duration), and utilize information from the preamble of a frame from the auxiliary AP to perform CBF based on the common BSS color or AID.

[0114] The coordinated beamforming manager (CBM) 505 may include any combination of hardware and software for initiating, managing, and optimizing coordinated beamforming (CBF) among APs 205 in a wireless network. The CBM 505 may include functions for managing or orchestrating CBF activities among APs 205 to coordinate and facilitate resource allocation and interference mitigation. For example, the CBM 505 may include functions for managing or overseeing processes for identifying candidate or participating stations 230, identifying and exchanging capabilities (e.g., station capability data 530 or AP capability data 535), and coordinating the CBF sequence 515 among APs 205 during CBF setup.

[0115] The station selector 510 may include any combination of hardware and software for identifying and selecting a suitable station 230 within the range 255 of the AP 205. The station selector 510 may include the function of selecting stations 230 within one or more BSSs 250 that participate in CBF. The station selector 510 may utilize any combination of station capability data 530 or AP capability data 535 to select a suitable candidate station 230 based on various capabilities (such as the number of antennas of the AP or candidate station, bandwidth support, and nulling capability, which can be used to determine the suitability of the station 230 to participate in CBF). For example, the station selector 510 may be able to support STAs for CBF based on their reported capability identifiers exchanged during the CBF setup process between APs 205. For example, the station selector 510 may utilize traffic characteristics, such as information about the downlink data traffic of each STA 230 within its BSS 250 at the AP 205, or the attributes of the downlink data traffic available for each STA 230 at the AP 205. The attributes of the downlink data traffic may include specific QoS requirements, such as maximum allowable latency or minimum required data rate or zero packet loss, and may be intermittent and continuous data traffic. For example, the station selector 510 may utilize channel characteristics, such as RSSI observed at each STA 230 due to transmissions from each AP 205, the proximity of the STA 230 and a specific AP 205 relative to other APs 205, or the downlink channel state information (DL CSI) at each STA 230 relative to each AP 205.

[0116] The communication controller 210 may include functions for managing and facilitating communication exchanges between the AP and the stations 230 for CBF establishment and operation. The communication controller 210 may include the use, communication, or implementation of the sequence 515, and the exchange of frames 520, parameters 525, AP capability data 535, and station capability data 530 between APs 205 to coordinate and establish CBF between APs 205. For example, the communication controller 210 facilitates and manages the exchange of frames 520 between the AP 205 and the stations 230 and between different APs 205 during the CBF setup and data transmission phases.

[0117] The sequence 515 may include any specific series of actions or messages exchanged between APs 205 during the establishment, negotiation, or setup of CBF. The sequence 515 may include any exchange of information where the first AP may send information about a group of stations that will participate in CBF to the second AP, and where the second AP may respond with an acknowledgment or additional station-specific information to complete the CBF configuration or setup. The sequence 515 may include any arrangement or order of the exchange of messages, frames, notifications, or responses, for example, in combination with Figures 7 to 12Those discussed. Sequence 515 may include a set of predefined actions or steps within a wireless communication protocol, which may include coordinated beamforming operations between multiple access points and stations. Sequence 515 may include various communication sequences between APs 205 and between AP 205 and station 230, including handshake operations, acknowledgement exchanges, and data transfer sequences for establishing and maintaining CBF between AP 205 and its associated station 230. For example, sequence 515 may include the exchange of multi-user request to send (MU-RTS) frames, buffer status report poll (BSRP) frames, coordinated beamforming physical layer protocol data unit (CBF PPDU) transmissions, and trigger-based block acknowledgement (block ACK) control frames between APs 205 and between AP 205 and station 230 during the CBF setup and data transfer phases. The RTS frame may include a message or transmission that signals the intention to send data to one or more other devices on the WLAN network.

[0118] Frame 520 may include any message, transmission, or data structure that includes information for CBF. Frame 520 may include any transmission or message exchanged between APs 205 or between AP 205 and STA 230 during CBF setup coordination, operation, or sequence 515. Frame 520 may include and carry data (e.g., station capability data 520 or parameters 525). Frame 520 may include data regarding station capabilities, synchronization information, and control signals for effective coordination and operation of CBF between APs. For example, frame 520 may include a common initial control frame, such as a MU-RTS / BSRP frame that may be addressed to station 230 participating in a CBF transmission opportunity (TXOP). Multi-user request to send (MU-RTS) may include a transmission for facilitating or triggering communication from multiple devices (e.g., multiple STAs) based on reservations or coordinated time slots within a transmission period. Buffer status report poll (BSRP) may include a transmission for requesting buffer status information (e.g., buffer size, queue status, or priority information) regarding the amount of data queued for transmission at a station.

[0119] Frame 520 may include a notification frame, which may transmit information or data regarding a set of candidate stations 230 for CBF at the start of sequence 515. Frame 520 may include a response frame, which may be jointly transmitted by station 230 of AP 205 addressed or triggered by or in response to a common initial control frame. Frame 520 may include, for example, a CBF PPDU frame, a trigger-based block ACK, an empty data packet announcement (NDPA) frame, an empty data packet (NDP) frame, a beamforming report poll (BFRP) frame, a beamforming report (BFR) frame, or a multi-user block acknowledgement request (MU-BAR) frame.

[0120] Parameter 525 may include any settings, characters, values, or attributes for establishing and performing CBF. Parameter 525 may include settings or attributes for quantifying various capabilities or parameters of station 230 or AP 205 during the establishment, negotiation, or coordination of CBF. Parameter 525 may include or correspond to any station capability data 530 or AP capability data 535, and vice versa. Parameter 525 may include settings or attributes utilized during the CBF process to control various aspects of CBF operation. Parameter 525 may include the nulling direction, nulling type, duration of the transmission opportunity (TXOP), and other parameters affecting CBF performance. Parameter 525 may include channel state information (CSI) or any data corresponding to CSI. Parameter 525 may include the configuration of CBF between APs 205, facilitating nulling direction and synchronization for efficient data transmission. Parameter 525 may include any value, setting, attribute, or parameter exchanged or included in any frame 520 or corresponding to any station capability data 530 or any AP capability data 535. For example, parameter 525 may include the common BSS color, shared AID space, or common MAC address of a group of devices (e.g., STA230). For example, parameter 525 may include different AIDs corresponding to the selected common BSS color. Parameter 525 may include information or data regarding the type of probing process (joint and sequential), and the type or mode of CBF nulling (full rank, partial rank, combination of spatial streams for each client supported by CBF operation).

[0121] Station capability data 530 may include any data or information regarding the capabilities, settings, and parameters of individual stations 230 within an AP related to participating in CBF with station 230. Station capability data 530 may include parameter 525 corresponding to any information, such as the number of antennas of station 230, bandwidth support corresponding to the station or channel, or the probing and nulling capabilities of station 230, including data regarding whether the station supports a particular probing frame or has the ability to provide or determine channel state information. Station capability data 530 may include or utilize parameter 525 corresponding to the maximum client limit of station 230, antenna configuration, nulling capabilities, type and capacity of traffic handled by the station, path loss observations, role in the network topology (e.g., whether the station is a relay or a primary endpoint), and any data regarding channel conditions, interference levels, data loss, or network congestion. For example, station capability data 530 may include the capabilities reported by station 230 to AP 205 during the association of STA230 with BSS250 of AP 205. Such data may be used to guide the selection of suitable stations 230 participating in CBF and to inform the configuration of CBF parameters. Station capability data 530 may include channel characteristics, such as channel state information obtained using channel probing from one or more APs 205.

[0122] The access point (AP) capabilities 535 may include any characteristics or attributes that define the performance or functionality of the AP 205. The AP capabilities 535 may include characteristics or attributes related to wireless network communication. For example, the AP capabilities 535 may include the number of antennas for transmitting or receiving wireless signals supported by the AP 205, the bandwidth supported by the AP 205, the sounding capabilities supported by the AP 205 (e.g., joint sounding or individual sounding), or the nulling capabilities supported by the AP 205 (e.g., full-rank nulling, partial-rank nulling, maximum number of nulling dimensions). For example, the AP capabilities 535 may include the maximum number of OBSS stations (e.g., stations that may be part of CBF operation) whose information (e.g., including channel sounding reports) can be stored. The AP capabilities 535 may include precoder types, such as minimum mean square error (MMSE) or zero-forcing (ZF) techniques. For example, with respect to the AP capabilities 535 for nulling, relative to full-rank nulling, a first AP may minimize the interference seen by the STAs 230 of a second AP 205 along all orthogonal directions, where the STAs 230 of the second AP 205 may receive transmissions from the first AP (e.g., 2 such directions for a 2x2 STA). For example, relative to partial-rank nulling, the AP 205 may minimize the interference seen by the STAs 230 of a second AP 205 along a subset of all orthogonal directions, where the STAs of the second AP may receive transmissions from the first AP (e.g., 1 such direction for a 2x2 STA).

[0123] The AP capabilities 535 and the station capabilities 530 may be indicated or expressed using any combination of the parameters 525. The parameters 525 on the AP 205 or the STA 230 may correspond to various traffic characteristics or channel characteristics. For example, traffic characteristics may include data about network traffic, such as information about the downlink data traffic of each STA 230 within its BSS 250 at the AP 205, or the attributes of the downlink data traffic available to each STA 230 at the AP 205. Downlink data traffic attributes may include specific QoS requirements, such as maximum allowed latency or minimum required data rate or zero packet loss, and data traffic that may be intermittent and continuous. Channel characteristics may include data about communication channels, including the RSSI observed at each STA 230 due to transmissions from each AP 205, the proximity of the STA 230 to a particular AP 205 relative to other APs 205, or the downlink channel state information (DL CSI) at each STA 230 with respect to each AP 205. The AP capabilities 535 or the station capabilities data 530 may include channel characteristics, such as channel state information obtained using channel sounding from one or more APs 205.

[0124] At a high level, system 500 can be used to implement multiple phases of CBF coordination between AP 205 and stations 230. These phases of coordination can include one or more of an AP handshake phase, a CBF operation configuration phase, a STA identification and information exchange phase, a sounding phase, and a per transmission opportunity (TXOP) coordination phase. The AP handshake phase can occur during initial discovery, such as when setting up BSS 250 or during subsequent discovery of a monitored channel, and can be completed during final teardown of CBF coordination. The CBF operation configuration phase can include setting parameters (e.g., 525) and protocols (e.g., BSS color selection, association identifier (AID) assignment, or AP identification) required for coordinated beamforming. The station identification and information exchange phase can occur on a time scale of hundreds of milliseconds to about a few seconds and includes the AP identifying candidate stations 230 from a potentially larger pool of associated stations and exchanging corresponding station capabilities and other relevant data for CBF.

[0125] The sounding phase (e.g., occurring on a time scale typically less than 100 milliseconds) can involve the implementation of joint sounding and sequential sounding. A joint sounding sequence can include any communication process or sequence in which multiple stations or APs simultaneously transmit signals to measure and collect channel state information (CSI) across the network, e.g., in preparation for CBF. Sequential sounding can include any communication process or sequence in which stations or APs take turns transmitting signals in sequence, allowing each to individually collect CSI, e.g., one after another. The CSI collected via joint sounding or sequential sounding can be used to adjust, set, or optimize CBF to minimize interference or signal strength at a particular STA (e.g., an STA that is an unintended recipient of transmissions intended for other STAs).

[0126] Each TXOP coordination phase can include a CBF setup phase, in which the AP identifies the participating STAs to determine the corresponding directions for nulling, the type of nulling (full rank and partial rank), and exchanges information required for CBF data transmission (e.g., TXOP duration). This phase can occur on the time scale of sounding, or more frequently than sounding. During the CBF setup portion of each TXOP coordination phase, the AP can select among different frame sequences to complete the setup. If two APs each identify at least one participating station, then the CBF data exchange phase can occur during the SIFS period following CBF setup (e.g., within the same TXOP) and can include an optional initial control frame exchange, such as MU-RTS / CTS or BSRP / BSR, to signal to the STAs an upcoming CBF PPDU, followed by CBF PPDU transmission and ACK reception.

[0127] During the AP handshake phase, the AP can identify another AP on the same channel as being able to participate in CBF. This can be done by polling other APs, or by detecting the capabilities advertised by other APs (e.g., in beacon frames) or via centralized distribution of AP information to other APs. The APs can perform a handshake to exchange various capabilities, such as the number or dimensions of antennas supported by each AP, the detection capabilities of each AP (e.g., joint detection or sequential detection), and the nulling capabilities of each AP (e.g., full-rank nulling, partial-rank nulling, maximum number of supported nulling dimensions). For example, for full-rank nulling, the first AP can minimize the interference seen by the stations of the second AP along all orthogonal directions, where the stations of the second AP can receive transmissions from the first AP (e.g., two such directions for a station with two antennas). For example, for partial-rank nulling, the first AP can minimize the interference seen by the STAs of the second AP along a subset of all orthogonal directions, where the stations of the second AP can receive transmissions from the first AP (e.g., one such direction for a station with two antennas). The APs can also exchange the maximum number of OBSS clients (e.g., clients that can be part of CBF operations) for which their information (e.g., containing channel detection reports) can be stored by the corresponding AP, and the precoder type (e.g., MMSE, ZF, any vendor-specific variant).

[0128] The CBF operation configuration phase may include the selection of a BSS color, the assignment of AIDs, and the identification of APs. An AP may establish a common BSS color for CBF PPDUs. The BSS color may be selected to be unique from the perspective of the BSS color of any AP. Candidate stations of an AP (e.g., stations that may participate in a CBF TXOP) may be assigned different AIDs (e.g., corresponding to the selected BSS color), and may use such AIDs or colors to process frames as part of a CBF-TXOP initiated by any of the participating APs. For example, an AP may select a BSS color from among the BSS colors of the AP. Candidate STAs of other APs (e.g., APs whose BSS color is not selected) may be assigned different AIDs corresponding to the selected color and use them to process frames as part of a CBF-TXOP initiated by any of the participating APs. For example, an AP may select BSS color 0 for a CBF PPDU, which may not be interpreted as an OBSS PPDU by stations associated with any AP. The AID assignment may include the AP selecting a common AID space to assign to a combined set of candidate stations of two APs and may correspond to the selected BSS color. For example, in this combined set, no two candidate stations may have the same AID from the common space. The AP identification may include communicating the MAC addresses of the two APs to the candidate stations of each AP so that these stations can identify transmissions made by other APs within the context of CBF operation. For example, the solution may establish a single common MAC address for certain simultaneous transmissions (e.g., control frames), such as the TA of MU-RTS / BSRP. This may be the MAC address of any AP or a new MAC address assigned for CBF-related control frame transmissions from the AP. By using a special security key specific to such CBF transmissions, frames may have a MAC header / control / management frame protection scheme. The BSS color selection, AID assignment, and AP identification may be distributed to all participating APs and candidate stations prior to CBF operation. Stations associated with any AP may be notified of the possibility of CBF operation via parameters. This may prevent the station devices of the BSS of any AP from interpreting frames exchanged during CBF operation as belonging to an OBSS (e.g., as inferred from the BSS color or MAC address) and initiating concurrent uplink transmissions to an AP that may conflict with such frames.

[0129] The station identification and information exchange phase may include APs exchanging information about each other's candidate stations. For example, the APs may exchange relevant parameters or data about each other's candidate stations that may participate in an upcoming Coordinated Beamforming Transmission Opportunity (CBF TXOP). The CBF TXOP may be any predetermined or specified interval during which the AP and its associated STAs may communicate according to their established or coordinated beamforming. The CBF TXOP may include any combination of transmissions that may include CBF transmissions (e.g., transmissions that are partially or fully nulled with respect to one or more specific stations) or non-CBF transmissions (e.g., transmissions that are not nulled). During this interval, the APs and STAs may adjust their transmission modes to achieve partial or full nulling of interference at unintended receivers, thereby allowing simultaneous transmissions to multiple intended receivers without disrupting each other's signals. For example, the CBF TXOP may allow a first AP to communicate data to a first station within its own BSS while nulling the interference of the same communication at a second station (e.g., an unintended receiver) at the BSS of another (e.g., a second AP). Such coordination may improve the spectral efficiency of the APs and stations, allowing simultaneous communication between the first AP and its first STA and the second AP and its second STA without interference, thereby improving overall network performance.

[0130] Information (e.g., parameters regarding their respective stations exchanged between APs) can include, for example, the AID of each candidate STA, the physical capabilities of the candidate stations (e.g., operating bandwidth, maximum Rx Nss, sounding feedback capabilities, etc.), the MAC capabilities of each candidate STA (e.g., padding requirements, etc.), or a set of station groups identified by a group index. The group index can indicate one or more of the following information: a list of stations of a particular AP, the per-STA Nss of the group, the RU allocation of the group. This information can serve as a shorthand for future messages exchanged between APs, for example, on a per-TXOP basis. The station groups can include stations of only the first AP or only the second AP, or a mixture of both. The selection of candidate CBF stations can depend on various factors, such as whether the stations associated with an AP currently have traffic (e.g., downlink traffic expected for the stations at their associated or serving AP), the type of traffic of the stations, or the difference in path loss observed at the stations from the serving AP and interfering APs. For example, if the path loss difference (e.g., from the serving AP and interfering APs) observed at some stations is large enough, then the two APs can participate in concurrent transmissions to such STAs without nulling (e.g., via coordinated spatial reuse). Such stations may not be candidates for CBF. Instead, the AP can also signal that there are no candidate CBF STAs. The benefit of such an approach is to avoid exchanging "quasi-static" information (e.g., information that is not expected to change across two or more consecutive CBF TXOPs) on a per-TXOP basis. Since CBF can provide the maximum gain when each AP has DL traffic to a small number of stations, the information exchange can be relatively light (e.g., up to 4 stations across 2 APs). If any AP has downlink (DL) traffic to 4 or more stations within its BSS, then "in-BSS" DL-MUMIMO can cancel out some of the gain of CBF. If the path loss conditions permit, then some of the stations associated with either AP can be candidates for coordinated spatial reuse, and the remainder (e.g., less than or equal to 4) can be candidates for CBF.

[0131] For example, aspects of station identification and information exchange may include a polling-based sequence where one AP transmits a polling frame (e.g., querying the receiving AP for stations with traffic) to a second AP using a non-HT PPDU that may have padding. The polling frame may be a trigger frame that specifies transmission parameters for the receiving AP to use to transmit a response frame. The receiving AP may respond to the polling frame with a response frame that may include information of the stations of the receiving AP, which may be done using a non-HT PPDU. Each AP may send unsolicited notifications and station information (e.g., parameters) to the other AP in advance, and the other AP transmits an acknowledgement (ACK) of the received notification. After successful STA information exchange, several subsequent TXOPs may utilize this information for CBF operations, and either AP may initiate a subsequent CBF-TXOP. In an example, system 500 may include two or more APs 205, each AP having one or more stations 230 within its own BSS 250 and having a range 255 that includes at least one station 230 of the BSS 250 of another AP 205 among the two or more APs 205. Since the stations 230 of neighboring APs 205 have overlapping ranges 255, the APs 205 or stations 230 may experience interference during wireless communication exchanges. To reduce such interference, system 500 may provide a multi-AP CBF coordination function to facilitate the establishment and coordination of CBF between APs 205 and stations 230.

[0132] System 500 may include a first AP 205 configured to identify a second AP 205 capable of participating in coordinated beamforming (CBF). The first AP 205 may be configured to select one or more candidate stations of the first AP for CBF. The first AP 205 may be configured to exchange with the second AP 205 the capabilities (e.g., station capability data 530) of one or more candidate stations 230 participating in CBF. The first AP 205 may be configured to determine, at least based on the capabilities of one or more candidate stations 230 (e.g., station capability data 530), one or more stations 230 of the one or more candidate stations 230 to be included in CBF. The first AP 205 may be configured to execute a sequence 515 with the second AP 205 to exchange a set of stations 230 for CBF of the first AP 205 and the second AP 205 (e.g., stations 230 from the BSS 250 of the first and second APs 205). The first AP 205 may identify the determined one or more stations 230 to the second AP 205 as participating in CBF.

[0133] The first AP 205 may be configured to identify parameter 525. The first AP 205 may identify the common basic service set (BSS) color and the common association identifier (AID) space for a group of stations 230 participating in CBF. The first AP 205 may be configured to perform partial nulling relative to a first station 230 among a group of stations 230 in response to values (e.g., parameter 525) in the BSS color and the common AID space corresponding to the stations 230. For example, partial rank or full rank nulling operations may be performed through CBF coordination implemented by leveraging or exchanging parameter 525 (e.g., common BSS color and AID). For example, parameter 525 (e.g., bandwidth and detection capabilities) may be identified and utilized for nulling configuration or setting.

[0134] The first AP 205 may be configured to perform a handshake (e.g., sequence 515) with the second AP 205 to exchange the capabilities (e.g., station capability data 530) of one or more candidate stations 230. The capabilities (e.g., station capability data 530) may include one or more of the following: the number of antennas, the amount of bandwidth, one or more detection capabilities, one or more nulling capabilities (e.g., station capability data 530), or the maximum number of clients that may be part of CBF. For example, the handshake sequence 515 may include the APs 205 exchanging information about candidate stations 230 for CBF. The capabilities (e.g., station capability data 530) may include the number of antennas, bandwidth, and detection capabilities. The capabilities may include nulling capabilities or the maximum client limit of the AP capability data 535. The handshake may include information about the modulation and coding scheme (MCS) and its associated error vector magnitude (EVM).

[0135] The MCS may include or identify one or more parameters indicating the data rate or error correction level in wireless communication, which may be used, for example, to balance the speed of communication and the reliability of transmission. The MCS may define or set a combination of modulation type and error correction coding rate. For example, a value parameter above the threshold of the MCS may use 64 quadrature amplitude modulation (64-QAM) with a lower coding rate for faster data transmission (e.g., a transmission greater than the transmission rate threshold), while a value parameter of the MCS below the threshold may use BPSK with a higher coding rate for more reliable communication under poor signal conditions but at a lower transmission rate (e.g., a transmission less than the transmission rate threshold).

[0136] The first AP 205 may be configured to perform coordination with the second AP 205 to enter the CBF enabling phase. The coordination may include determining at least one of the nulling direction, nulling type, or duration of the transmission opportunity (TXOP) for one or more candidate stations. For example, the first AP 205 may be configured to identify at least one of a common basic service set (BSS) color or an association identifier (AID) corresponding to a station in a set of stations 230 from the preamble of a frame 520 from the second AP 205. The first AP 205 may be configured to perform CBF with respect to the stations 230 based on at least one of the common BSS color or AID. For example, the determination of the parameter 525 may include the first AP 205 predicting and preparing for CBF transmission based on the traffic profile and other factors. For example, the common BSS color or AID may be used for CBF coordination. The parameter 525 (e.g., the size of the cyclic prefix long training field (CP-LTF) and packet extension (T_PE)) may be used for CBF coordination.

[0137] The first AP 205 may be configured to identify a common media access control (MAC) address for simultaneous transmission from both the first AP 205 and the second AP 205. The first AP 205 may be configured to perform CBF at least based on the common MAC address. The first AP 205 may be configured to convey the MAC address of at least one of the first AP 205 or the second AP 205 to a set of stations 230. The common MAC address may be used by the first AP or the second AP to address the stations 230 participating in CBF. The STAs 230 participating in CBF may recognize the common MAC address. The stations 230 may receive the MAC address of the AP 205 participating in CBF. The APs 205 may convey the transmission opportunity duration and bandwidth information to each other and to the stations 230 to facilitate CBF.

[0138] The first AP 205 may be configured to transmit a beamforming report poll (BFRP) frame 520 to a first station 230 in a set of stations 230 configured for wireless communication with the first AP 205. For example, the transmission of the BFRP frame 520 may facilitate the stations 230 reporting channel characteristics to the AP 205 for adaptive CBF adjustment. The first AP 205 may be configured to receive, in response to the BFRP frame 502, a beamforming report (BFR) (e.g., frame 520) identifying one or more characteristics of one or more signals received by the first station from the first station 230. This may allow the AP 205 to adjust CBF based on real-time channel conditions. The first AP 205 may be configured to adjust CBF in response to the one or more characteristics.

[0139] The first AP 205 can be configured to select one or more candidate stations 230 based on at least one of the following: data traffic expected for the stations in one or more candidate stations, the type of data traffic expected for the stations, or the received signal strength indication (RSSI) or path loss observed at the stations from the first AP 205 or the second AP 205. For example, the AP 205 can select candidate stations based on the traffic profile and path loss observations. The second AP 205 can be configured to select one or more of its stations 230 to participate in CBF.

[0140] In some aspects, the standard for WLAN communication can include setting up CBF for two or more APs 205 to transmit to their respective associated STAs 230 simultaneously. Each AP 205 can beamform its signal to minimize interference to other STAs 230 of other APs 205. The described technical solutions can include systems and methods for multi-AP coordination to configure CBF in the context of two APs 205 or any other number of APs 205, including three, four, or more APs 205.

[0141] There can be several phases for coordinating CBF with nulling. These phases can include an AP 205 handshake, which can occur at initial discovery, such as when setting up the BSS or during subsequent discovery while monitoring the channel, or during the final tear-down of CBF coordination. The phases can include the configuration of CBF operations. The phases can include the identification and information exchange of stations 230, such as those that can occur on a time scale of 100 milliseconds to several seconds, where the AP 205 can identify candidate STAs 230 and exchange relevant information about CBF. The phases can include probing, which is carried out on a medium time scale of up to 100 milliseconds and can include, for example, joint and sequential probing. The phases can include per transmission opportunity (TXOP) coordination, which can include CBF setup, where the AP identifies or determines the participating STAs 230 to determine the corresponding direction of nulling or the type of nulling (e.g., full-rank and partial-rank nulling). The CBF setup can include the APs 205 exchanging information for CBF data transmission (e.g., TXOP duration). The CBF setup can include the APs 205 selecting different frame sequences to accomplish these tasks. The CBF setup can include the identification of the participating STAs 230.

[0142] CBF data exchange may occur after the CBF setup when at least two APs 205 have each identified at least one participating STA 230 as part of the CBF setup. The CBF data may include the two APs 205 transmitting CBF PPDUs, where each AP addresses its transmission to the participating STAs within its BSS while nulling, at least in part, the interference to the participating STAs in the BSS of the other AP. When the two APs 205 have each identified at least one participating STA 230, the CBF data coordination may occur within a short inter-frame space (SIFS) after the CBF setup (e.g., within the same TXOP). An optional initial control frame exchange (e.g., MU-RTS / CTS, BSRP / BSR, or others) may be used to signal the upcoming CBF PPDUs to the STAs 230. The CBF data may include CBF-PPDU transmissions and ACK receptions.

[0143] An AP 205 may identify another AP 205 on the same channel as being capable of participating in CBF, which may occur by polling the other AP 205, or implicitly by detecting the capabilities advertised (using, e.g., beacon frame 520) by the other AP 205, or by distributing the AP 205 information centrally to the other APs 205.

[0144] AP 205 can perform a handshake to exchange various capabilities (e.g., station capability data 530 or AP capability data 535), such as the number / dimension of Tx antennas supported by each AP 205, the bandwidth supported by each AP 205, the sounding capability of each AP 205 (e.g., joint sounding and individual sounding), the nulling capability of each AP 205 (e.g., full-rank nulling, partial-rank nulling, maximum number of supported nulling dimensions). For full-rank nulling, the first AP 205 can minimize the interference seen by the STA 230 of the second AP along all orthogonal directions, where the STA 230 of the second AP can receive transmissions from the first AP 205 (e.g., two such directions for a 2x2 STA 230). For partial-rank nulling, the first AP 205 can minimize the interference seen by the STA 230 of the second AP along a subset of all orthogonal directions, where the STA 230 of the second AP can receive transmissions from the first AP 205 (e.g., one such direction for a 2x2 STA). AP 205 can exchange its respective capabilities (e.g., AP capability data 535), such as the maximum number of overlapping BSS (OBSS) stations 230 whose information (e.g., containing channel sounding reports) can be stored by the AP 205, and the precoder type (e.g., MMSE, ZF, any vendor-specific variant). An AP-to-AP security key can be negotiated between AP 205s. After the initial handshake, AP 205 can enter the CBF enabled phase, which allows for further coordinated phases to occur. AP 205 can also signal the termination of the CBF enabled phase and disengage from further coordination.

[0145] On the one hand, system 500 may include a second AP 205 that is configured or capable of receiving requests from the first AP 205, and the requests may initiate data exchange involving one or more stations from the two APs. For example, in a scenario where the first AP 205 expects to establish a coordinated beamforming (CBF) session with the second AP 205, the first AP 205 may send a request (e.g., frame 520) to the second AP 205 to start the exchange. Upon receiving the exchange request, the second AP 205 may obtain first data from the first AP 205 and may represent the ability of the stations 230 of the first AP to participate in coordinated beamforming (CBF). For example, if the stations of the first AP 205 include MU-MIMO capabilities and support beamforming, the first data transmitted by the first AP 205 may include information about these capabilities. Subsequently, based on the identified capabilities of the stations 230 of the first AP 205, the second AP 205 may generate second data that details the capabilities of its own stations 230 for CBF participation. If the stations 230 of the second AP 205 are equipped with advanced beamforming capabilities and support receiving multi-user transmissions, the second data generated by the second AP may include these parameters 525. Then, the system 500 may execute a sequence to exchange a portion of the second data with the first AP 205, focusing on a set of stations 230 selected from the two APs 205 that meet the CBF utilization. This exchange may include negotiating with the first AP 205 to determine which stations from the first AP 205 and the second AP 205 have the necessary capabilities and are suitable for participating in the CBF session. The selection of these stations 230 may be determined by considering the capabilities of the two sets of stations 230, facilitating optimized CBF operation.

[0146] Configuring CBF operations between APs 205 may involve several steps. The APs 205 may establish a common BSS color for the CBF PPDU, which may be different from the BSS color of the APs or selected from one of the BSS colors of the APs. The candidate STAs of the two APs 205 (e.g., those that may participate in the CBF TXOP) may each be assigned a different AID. The different AIDs assigned to the candidate STAs may correspond to the selected common BSS color, such that the candidate STAs may process frames with this color as part of a CBF-TXOP initiated by either of the participating APs.

[0147] The AP can select a common BSS color from among one of the BSS colors of the APs. The candidate STAs 230 of other APs (i.e., whose BSS colors are not selected) are assigned different AIDs corresponding to the above-selected color and can be configured to handle frames with this color as part of a CBF-TXOP initiated by any of the participating APs. The AP 205 can select a common BSS color 0 for the CBF PPDU, which may not be interpreted by the STAs 230 associated with any of the APs 205 as an overlapping BSS PPDU.

[0148] Regarding AID assignment, the AP 205 can select a common AID space for assignment to the combined set of candidate STAs 230 of two APs 205. For example, in this combined set, no two candidate STAs 230 can have the same AID from the common space. For example, the AIDs assigned to the STAs 230 from the common AID space can correspond to the common BSS color.

[0149] The AP identification can include communicating the MAC addresses of the two APs 205 to the candidate STAs 230 of each AP 205 such that the STAs 230 of each AP can identify transmissions made by the other AP 205 within the context of CBF operations. The AP identification can include establishing parameter 525 (e.g., a single common MAC address). For example, a single common MAC address can be used in frames transmitted simultaneously by two APs to the STAs 230 associated with either AP. For example, a single common MAC address can be used in a transmission from the first AP 205 to the STAs 230 associated with the second AP 205. For example, a single common MAC address can be used in frame 520, which is a common initial control frame (e.g., the TA of MU-RTS or BSRP) addressed to the STAs 230 of either AP or both APs. For example, the single common MAC address can be the MAC address of either AP 205 or a designated new MAC address for CBF-related control frame transmissions from the AP 205.

[0150] By using a security key specific to such CBF transmissions, frame 520 with a single common MAC address can have a MAC header / control / management frame protection scheme. The BSS color selection, AID assignment, and AP identification can be distributed to all participating APs 205 and candidate STAs 230 prior to CBF operations. The STAs 230 associated with any of the APs 205 are notified of the possibility of CBF operations with parameter 525. This can be done to prevent the STA 230 devices of the BSS of any of the APs 205 from interpreting the frames exchanged during CBF operations as belonging to an overlapping BSS (e.g., as inferred from the BSS color or MAC address) and initiating concurrent uplink transmissions that may conflict with such frames 520 to their respective APs 205.

[0151] Now refer to Figure 6 and describe an example method 600 for multi-AP coordination that provides CBF. For example, method 600 may be implemented to implement a configuration of CBF operations or CBF settings. Method 600 may be implemented using, for example, system 200, system 500, or any of the features discussed in conjunction with Figures 1A to 5 Method 600 may include actions 605 to 625. At 605, the method may include identifying APs capable of performing CBF. At 610, the method may include selecting candidate stations. At 615, the method may include performing channel sounding and obtaining channel state information. At 620, the method may exchange station capabilities between APs. At 625, the method may execute a sequence to exchange a set of stations for CBF.

[0152] At 605, the method may include identifying APs capable of performing CBF. The method may include the first access point (AP) identifying a second AP capable of participating in coordinated beamforming (CBF). For example, the first AP may be configured to implement a handshake sequence with one or more other APs within the wireless communication range of the first AP. The handshake sequence may include the exchange of one or more frames. The handshake may identify one or more of the capabilities of the first AP or at least one of the one or more candidate stations. For example, the handshake may be used to identify, exchange, or convey one or more AP capability data of the involved APs (e.g., the first or second AP) or one or more station capability data of the STAs of the first AP or the second AP. For example, the identification of APs capable of performing CBF may be facilitated by a network controller or management entity (e.g., a coordinated beamforming manager), which may provide or propagate information to each individual AP on candidate CBF APs within its range or neighbors.

[0153] The first AP may identify one or more parameters, such as parameters corresponding to other APs within the communication range of the first AP. For example, the first AP may identify the MAC addresses of neighboring or nearby APs. The first AP may identify a common media access control (MAC) address for transmission from either or both of the first AP and the second AP. For example, the first AP may identify the CBF capabilities of the APs within the communication range. For example, the first AP may send a message that may trigger the receiving AP to provide a response indicating whether the second AP is capable of or is configured for CBF operations.

[0154] The method may include exchanging one or more AP capabilities. For example, the first and second APs may exchange the maximum number of clients that each AP can support as part of the CBF operation. The exchanged AP capabilities may include, for example, the number of antennas, the amount of bandwidth, one or more sounding capabilities, one or more nulling capabilities, the precoder type, the maximum number of stations that can be part of the CBF or the maximum number of candidate stations, traffic characteristics, channel characteristics (e.g., channel state information (CSI) that can be obtained from one or more stations using channel sounding initiated by one or more APs 205). The exchanged AP capabilities may include any of the AP capabilities 535 discussed herein.

[0155] For example, the method may include identifying a common BSS color or AID or AID space for a set of stations participating in CBF. For example, the BSS color or AID or AID space may be identified before identifying candidate STAs. The method may identify the common BSS color or AID space via the network configuration of the AP or through an over-the-air handshake across APs (e.g., when APs discover each other and exchange communications). The actual AID assignment to the STA (from the common AID space) may occur when the STA first associates with the AP (as currently implemented in 802.11), or may occur subsequently after the STA is identified as a candidate STA for the CBF operation in step 610.

[0156] At 610, the method may include selecting candidate stations. The method may include a first AP selecting one or more candidate stations of the first AP (e.g., candidate stations of the first AP included or used for CBF). The first AP may select the one or more candidate stations based on at least one of one or more parameters that can be exchanged using any one or more messages, which messages may include any type or form of frame, such as beacon frames, MU-RTS frames, CTS frames, BSRP frames, BSR frames, NDP frames, or NDPA frames. These frames may include or indicate any parameters or information about stations in the overlapping BSS of two or more stations, including any information about the data traffic expected for stations in one or more of the candidate stations, the type of data traffic expected for the stations, or the received signal strength indication (RSSI) or path loss observed at the stations from the first AP or the second AP.

[0157] The first AP may be configured to select one or more candidate stations participating in CBF of the first AP based on any information about the CBF capabilities of the second AP or the capabilities of any of the candidate or participating stations of the second AP. For example, the first AP may be configured to select (e.g., of the first AP) one or more candidate stations based on at least one of the following: data traffic expected for the stations in the one or more candidate stations, the type of data traffic expected for the stations, or the received signal strength indication (RSSI) or path loss observed at the stations from the first AP or the second AP. Similarly, the second AP may be configured to select one or more stations participating in CBF operations of the second AP based on any information about the CBF capabilities of the first AP or the capabilities of any of the candidate or participating stations of the first AP. Likewise, the first AP may be configured to deselect or remove one or more previously selected candidate stations of the first AP based on one or more parameters so that they do not participate in future CBF operations. Similarly, the second AP may be configured to deselect or remove one or more previously selected candidate stations of the second AP based on one or more parameters so that they do not participate in future CBF operations.

[0158] Parameters may be used for the selection of candidate STAs. For example, the parameters may include traffic characteristics, e.g., information about the data traffic expected for the stations, the type of data traffic expected for the stations. For example, the parameters may include channel characteristics, e.g., the received signal strength indication (RSSI) or path loss observed at the stations from the first AP or the second AP, the downlink (DL) CSI measured at the stations from the first AP or the second AP. For example, the parameters may include key performance indicators (KPIs) of the stations from previous CBF operations, e.g., the achieved throughput, SNR, or latency.

[0159] Parameters for selecting or deselecting candidate stations for CBF may include various criteria. For example, if the data traffic available for a station at its associated AP within a predetermined time period is greater than a predetermined threshold, then the station may be selected as a candidate station for CBF. For example, if the path loss difference (i.e., the path loss from an interfering AP minus the path loss from its associated AP) is within a predetermined range, then the station may be selected as a candidate station for CBF. For example, if the data traffic available for a station at its associated AP within a specific time period is below a second predetermined threshold, then a previously selected candidate station may be deselected or removed as a candidate station for CBF. For example, if the path loss difference (i.e., the path loss from an interfering AP minus the path loss from its associated AP) falls outside a second predetermined range, then a previously selected candidate station may be deselected or removed as a candidate station for CBF. For example, if one or more key performance indicators (KPIs) of a station under a previous CBF operation fail to meet predetermined criteria, such as throughput failing to exceed a minimum limit, SNR failing to exceed a minimum limit, or latency failing to be below a maximum limit, then a previously selected candidate station may be deselected or removed as a candidate station for CBF. For example, if the CSI obtained from operation 615 indicates that the station is not suitable for CBF operation, then a previously selected candidate station may be deselected or removed as a candidate station for CBF.

[0160] The method may include a first AP performing coordination with a second AP via a CBF enabling phase. The coordination may include determining (e.g., measuring, detecting, or receiving) one or more parameters of a station of the first AP or a station of the second AP. The parameters may include any one or more of the zeroing direction, zeroing type, or duration of a transmission opportunity (TXOP) of one or more candidate stations. The parameters may be used for the selection of candidate STAs. For example, traffic characteristics may be utilized, such as information about the data traffic expected for the station, the type of data traffic expected for the station. For example, channel characteristics, such as the received signal strength indication (RSSI) or path loss observed at the station from the first AP or the second AP, the downlink (DL) CSI measured at the station from the first AP or the second AP. Key performance indicators (KPIs) of stations from previous CBF operations, such as the achieved throughput, SNR, or latency.

[0161] The first AP can identify the common basic service set (BSS) color and the common association identifier (AID) space for a group of stations participating in CBF. The first AP can receive from the second AP or identify, via one or more frames and communication with the second AP or the stations of the second AP, one or more values of the common BSS color and AID of one or more stations of the second AP, and vice versa. The first AP can identify, from the preamble of a frame from the second AP, at least one of the common basic service set (BSS) color or the association identifier (AID) corresponding to a station in a group of stations. For example, when each AP communicates its candidate STA list with another AP, the communicating AP can identify the candidate STAs by their AIDs. For example, an AP can provide a list of AIDs of its candidate STAs to another AP. The method can implement one or more operations 610 after operation 605. The method can implement operation 610 in response to the result of or information obtained from one or more previously implemented operations 615 or 625.

[0162] At 615, the method can identify the capabilities of at least one of the first AP or one or more candidate stations of the first AP. For example, the method can perform channel sounding and obtain channel state information (CSI). The method can include exchanging any information related to performing CBF operations for the selected candidate stations between the APs and between the APs and the STAs. For example, an AP can exchange any data or parameters (e.g., AP capability data or station capability data) with its associated STA to establish or perform CBF operations. For example, the AP or the AP and the STA can exchange data or parameters corresponding to the maximum number of clients that can be part of the CBF for one or more of the stations. The STA or the AP can perform or facilitate channel sounding. For example, the AP and the STA can determine or estimate the characteristics and parameters of one or more wireless communication channels by transmitting a known signal and analyzing the received signal quality and characteristics. For example, the first AP or the second AP can initiate a channel sounding sequence, such as a joint sounding sequence or a sequential sounding sequence. For example, the channel sounding sequence can facilitate the measurement of downlink (DL) CSI at the stations. For example, a station associated with the first AP or the second AP can feedback or report the downlink (DL) CSI measured from its associated AP. For example, a station associated with the first AP can feedback or report the downlink (DL) CSI measured from the second AP. For example, a station associated with the second AP can feedback or report the downlink (DL) CSI measured from the first AP. For example, an AP can receive CSI feedback or reports from a station associated with another AP, or directly from a station, or from other APs, or from a network controller or management entity. The method can implement one or more operations 615 after operation 610.

[0163] For example, a first AP may be configured to transmit a beamforming report poll (BFRP) frame to a first station in a group of stations of the first AP. The first station may be a station (e.g., a client or STA) configured for wireless communication with the first AP (e.g., part of the BSS of the first AP). The first AP may be configured to receive, in response to the BFRP frame, a beamforming report (BFR) from the first station that identifies one or more characteristics of one or more signals received by the first station. The one or more characteristics may include, for example, any one or more of the features corresponding to the strength of the signal, such as the power or amplitude of the signal, the phase or phase shift of the signal, the signal-to-noise ratio (SNR) of the signal, the channel impulse response, the channel state information (e.g., information about the channel conditions, such as path loss, fading, or spatial correlation information), the angle of arrival of the signal, or any other information that can be used for the adjustment of beamforming.

[0164] At 620, the method may include the first AP determining, at least based on capabilities, one or more stations among the one or more candidate stations that participate in CBF. For example, the first AP may select, at least based on the capabilities of the stations (e.g., specific station capability data that matches, is consistent with, or otherwise corresponds to the AP capability data of the first or second AP), one or more stations that participate in CBF. For example, the first AP may select one or more stations based on the matching capabilities of the one or more stations and the capabilities of the first AP or the second AP (e.g., corresponding, matching, or otherwise acceptable data regarding the number of antennas, amount of bandwidth, one or more sounding capabilities, one or more nulling capabilities, precoder type, maximum number of stations that may be part of CBF, maximum number of candidate stations that may be supported in CBF, any network traffic characteristics, any channel characteristics, or any CSI data). The first AP may be configured to communicate at least one of a common media access control (MAC) address or the MAC address of the first AP or the MAC address of the second AP to a group of stations.

[0165] The method may include exchanging between APs and between an AP and its corresponding associated STAs any information related to performing CBF operations for a selected candidate station. The method may include an exchange between a first AP and a second AP of the capabilities of one or more candidate stations participating in CBF. The capabilities may include station capability data and parameters indicating the available settings, configurations, or capabilities of each of the candidate stations of the station. For example, the first AP may perform a handshake with the second AP to exchange the capabilities of one or more candidate stations or one or more APs. The one or more capabilities may include any one or more of the following: the number of antennas of one or more of the stations, the amount of bandwidth of one or more of the stations, the channels or frequency bands used by one or more of the stations, one or more sounding capabilities or configurations of one or more of the stations, one or more nulling capabilities or partial nulling capabilities of one or more of the stations, or the maximum number of clients that may be part of the CBF for one or more of the stations, or the maximum total number of spatial streams that may be transmitted during a CBF operation (e.g., by two APs) that one or more stations may support.

[0166] For example, the first and second APs may exchange information about stations expected to participate in one or more subsequent CBF transmission opportunities (TXOPs). The first AP may send information to the second AP, such as the AID of each candidate STA, the physical layer capabilities of each candidate station (e.g., station capability data), such as the operating bandwidth, the maximum number of receive spatial streams (e.g., receive Nss), the sounding feedback capabilities, and the MAC capabilities and any padding preferences. A group index may be used to identify a group of station groups, where each station group may include a list of the stations of the first AP in the group, a list of the stations of the second AP in the group, each STA Nss of the group, and the RU allocation of the group. These group indexes may serve as a shorthand for future messages exchanged between APs based on each TXOP to identify individual groups of STAs. A station group may include only the STAs of the first AP, only the STAs of the second AP, or a mixture of both.

[0167] For example, the information exchange may include four stations across two APs, which may aim to maximize the CBF impact or performance. For example, the information exchange may seek to avoid exchanging quasi-static information per TXOP, i.e., information that is common or unchanged across the TXOP may not be repeated per TXOP, but may be pre-shared. Such information may include one or more of the parameters related to the CBF PPDU (e.g., MCS of the SIG field, CP-LTF size, LDPC additional symbols, pre-FEC padding factor, presence of additional LTF, number of LTFs, etc.). For example, after the STA information is successfully exchanged, subsequent TXOPs may utilize this information for CBF operations, where either AP can initiate a subsequent CBF-TXOP based on the exchanged information. The first AP may include communicating a media access control (MAC) address to one or more stations associated with the BSS of the first AP (e.g., including candidate stations for CBF identified by the first AP). Similarly, the second AP may include communicating a media access control (MAC) address to one or more stations associated with the BSS of the second AP (e.g., including candidate stations for CBF identified by the second AP). The MAC address communicated by either AP may be the MAC address of the first AP, the MAC address of the second AP, or a common MAC address of both the first AP and the second AP (and any other APs included in the CBF). The first AP may include transmitting a beamforming report poll (BFRP) frame to a first station in a group of stations configured to communicate wirelessly with the first AP. The first AP may transmit BFRP frames to all stations identified for CBF. The first AP may receive a beamforming report (BFR) frame from the first station in the group of stations (or any other station that receives the BFRP frame) in response to the BFRP frame. The BFR frame may indicate or identify one or more characteristics of one or more signals received by the first station, or one or more parameters of the first station, such as information indicating signal strength, signal quality, signal direction, or channel condition or performance. The method may implement one or more operations 620 after operation 610.

[0168] The method may include the first AP identifying at least one of a common basic service set (BSS) color or an association identifier (AID) corresponding to a station in a group of stations from a preamble of a frame from the second AP, and performing CBF with respect to the station based on the at least one of the common BSS color or AID. The method may include the first AP identifying a common media access control (MAC) address for simultaneous transmission from both the first AP and the second AP, and performing CBF based at least on the common MAC address.

[0169] At 625, the method may include a first AP and a second AP performing a sequence to exchange (e.g., between the first AP and the second AP) a set of stations participating in a CBF of the first AP and the second AP. The first AP may identify, based on matching, corresponding, or acceptable station capability data, one or more stations (e.g., one or more stations selected or identified by the first AP as participating in the CBF) to the second AP as participating in the CBF.

[0170] The first AP may be configured to enter a CBF enabling phase to perform coordination with the second AP. The coordination or coordination phase may include determining at least one of the number of spatial streams, the direction of nulling, the type of nulling, or the duration of a transmission opportunity (TXOP) of one or more stations participating in the CBF among a set of stations of the first AP and the second AP. The first AP may be configured to perform CBF with the second AP after coordination, where the CBF is performed with respect to one or more stations among a set of stations of the first AP and the second AP.

[0171] The method may perform a sequence to identify or exchange a set of stations for CBF. The method may include a first AP and a second AP performing a sequence to exchange, between the first AP and the second AP, a set of stations of the first AP and a set of stations of the second AP for CBF. The sequence may include TXOP communication, e.g., each TXOP coordination. For example, the identified STAs may be used for subsequent TXOPs, and this may be repeated for different TXOPs. For example, each AP may identify, exchange, or utilize parameters for CBF transmission.

[0172] The parameters may include any one or more of the direction of nulling, the type of nulling, or the duration of a transmission opportunity (TXOP) of one or more stations of a set of stations of the first AP or a set of stations of the second AP. For example, each AP may identify the number of spatial streams (Nss), which may be used to communicate with each of the stations it identifies. The set of stations may be determined from one or more candidate stations based at least on the capabilities or the scheduled data traffic at their associated APs. The first AP may perform full rank nulling or partial rank nulling with respect to a first station among the set of stations selected for CBF. Nulling may be performed for a given station using or in response to a value in the BSS color and common AID space corresponding to the station. Nulling may be performed in response to CSI feedback obtained from a set of stations of the first AP or a set of stations of the second AP.

[0173] The method may include a first AP performing CBF based on coordination or communication with respect to a specific station to prepare for CBF operation using at least one of a common BSS color or an AID corresponding to the station. The first AP may perform CBF based at least on or using the common MAC address of the first AP and the second AP. The method may include the first AP adjusting CBF in response to one or more characteristics (such as information indicating signal strength, signal quality, signal direction, or channel condition or performance). The method may include identifying the null direction at each AP based on the STAs identified by each AP and their corresponding Nss, and the CSI obtained from the probe for the identified STA (e.g., at 615). The method may include each of the first AP and the second AP performing CBF to communicate data to its corresponding identified station using the corresponding identified Nss, while nulling the interference to the identified stations of other APs. The method may include each of the identified stations signaling the result of the performed CBF operation, such as whether the station can correctly receive the expected data. The method may implement one or more operations 625 after operation 620. The method may implement one or more operations 625 after operation 615.

[0174] Upon completion of operations 605 to 625, the APs and the stations of the APs may utilize the configurations and settings implemented at 605 to 625 to implement data communication with partial rank or full CBF. For example, the first and second APs may simultaneously transmit to their respective associated stations, where each AP beamforms the signal it transmits to minimize the interference caused to the stations of other APs when the other stations receive their respective expected signals from their corresponding APs.

[0175] Now refer to Figure 7 , an example method 700 for identifying and exchanging station information between APs is described. Method 700 may be implemented using, for example, system 200, system 500, or any of the features combined with Figures 1A to 5 discussed. Method 700 may include actions 705 to 715. At 705, the method may include the first AP sending a poll frame to the second AP. At 710, the method may include a short inter-frame space (SIFS). At 715, the method may include the second AP sending a response frame to the first AP.

[0176] At operation 705, the method may include a first AP sending a polling frame to a second AP. The polling frame may query the second AP as to whether there are any candidate STAs for CBF among the STAs associated with the second AP. For example, the first and second APs may exchange information about the stations expected to participate in one or more subsequent CBF transmission opportunities (TXOPs). The first AP may send any of the parameters discussed herein to the second AP. For example, the first AP may send information such as the AID of each candidate STA associated with the first AP, the physical layer capabilities of each candidate station (e.g., station capability data), such as the operating bandwidth, the maximum number of receive spatial streams (e.g., receive Nss), the sounding feedback capability, and the MAC capabilities and any padding preferences. A group index or information may be used to identify a group of stations. Such an indication or information may include one or more lists of stations of the first AP, such as a list of STAs included in the basic service set (BSS) of the AP. The index or information may include the number of spatial streams (Nss) assigned to each individual station (STA) (e.g., an STA in a multi-user MIMO setup). The Nss may determine or indicate the maximum number of parallel data streams that a station may transmit or receive for a given STA or group of STAs (e.g., per STA Nss). The index or information may include the resource unit (RU) allocation for a given STA or for a group of STAs or the assignment of a specific frequency range within the channel of the Wi-Fi AP (e.g., RU allocation). These individual or group indexes may be used as shorthand for future messages exchanged between APs based on each TXOP to identify and specify the settings or configurations of individual STA groups. These groups may include STAs associated with the first AP, STAs associated with the second AP, or a mix of both (e.g., STAs associated with both the first and second APs).

[0177] For example, method 700 may begin with an initial frame exchange performed by the first AP and the second AP. For example, the initial frame exchange may include the first AP sending an RTS or an initial control frame to the second AP, and the second AP responding to the first AP with a CTS or an initial response frame upon receipt of the RTS or initial control frame. The initial frame exchange may allow the first AP to determine whether the second AP is available for further communication. The initial frame exchange may be used for the purpose of reserving the wireless medium for further communication.

[0178] At action 710, the method may include a Short Inter-Frame Space (SIFS). The SIFS may allow the second AP to receive and process the received information. The second AP may determine candidate stations for the second AP. For example, the selection of candidate CBF stations for the second AP may depend on several factors such as whether the stations associated with the AP currently have data traffic expected for them at the associated AP, the type of data traffic of the stations, and the difference in path loss observed at the stations from their serving or associated AP and interfering APs (with which the stations are not associated). For example, if the path loss difference observed at a particular station (which is defined as the path loss observed at the station from the interfering AP minus the path loss observed at the station from its serving or associated AP) is significant (e.g., above a predetermined threshold), then the two APs may participate in concurrent transmission to such stations, e.g., via coordinated spatial reuse, without explicit nulling. The AP may signal that there are no candidate CBF stations.

[0179] At action 715, the method may include the second AP sending a response frame to the first AP. The response frame may include any information about candidate stations for the second AP to perform CBF, e.g., in response to a query from the first AP in the poll frame at action 705. For example, the method may include an exchange with a poll-based sequence and an unsolicited notification sequence. In the poll-based sequence at 705, the first AP may poll the second AP using a query frame for candidate stations to perform CBF. In response to the poll frame, the second AP may provide a response frame with information about its stations. The information included may include any parameters, including parameters related to the station or AP capabilities that may be used for CBF setup or configuration. The response frame may use the poll frame as a trigger frame to specify the parameters that the second AP will include in the response frame. For example, each AP may send an unsolicited notification with STA information to the other AP, where the receiving AP transmits an ACK. After the successful exchange of STA information, subsequent TXOPs may utilize this information to perform CBF operations, where either AP is able to initiate subsequent CBF-TXOPs based on the exchanged information.

[0180] Upon completion of operations 705 to 715, the APs and the stations of the APs may utilize the configurations and settings implemented at 705 to 715 to perform data communication with partial rank or full CBF. For example, the first and second APs may simultaneously transmit to their respective associated stations, where each AP beamforms the signals it transmits to minimize interference to the stations of the other AP when the other stations receive their respective expected signals from their respective APs.

[0181] Now refer to Figure 8 , an example method 800 that illustrates an example of providing a CBF setup sequence for multiple APs. Method 800 may use, for example, system 200, system 500, or in combination with Figures 1A to 5Implement any one of the features discussed. Method 800 may include actions 805 to 820. At 805, the method may include a first AP sending a first notification frame to a second AP. At 810, the method may include the second AP sending a first response frame to the first AP. At 815, the method may include the first AP sending a second notification frame to the second AP. At 820, the method may include the second AP sending a second response frame to the first AP. The frames transmitted as part of method 800 may belong to the same TXOP (e.g., adjacent or neighboring transmission frames of method 800 may be separated by a gap of SIFS).

[0182] At action 805, the first AP may send a first notification frame to the second AP. For example, the first AP may send a notification frame including a first list of participating stations associated with the first AP for an upcoming CBF TXOP. For example, the first list of participating stations may be selected from candidate stations previously identified by the first AP. For example, the first list of participating stations may include stations associated with the first AP for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., through channel sounding, such as joint sounding or sequential sounding). The first list of participating stations may include stations for which the first AP has pending data traffic to transmit. The information conveyed may include any type and form of parameters discussed herein. For example, for each station in the first list, the information may include each station AID, the number of spatial streams (Nss), and resource unit (RU) allocation. These parameters may be used to coordinate CBF operations. The first notification frame may also include padding to provide the second AP with sufficient time to identify its participating stations.

[0183] For example, method 800 may start with an initial frame exchange performed by the first AP and the second AP. For example, the initial frame exchange may include the first AP sending an RTS or an initial control frame (e.g., an initial notification frame) to the second AP, and the second AP responding to the first AP with a CTS or an initial response frame (e.g., an initial response frame) in response to or upon receiving the RTS or the initial control frame. The initial frame exchange may allow the first AP to determine whether the second AP is available for further communication. The initial frame exchange may be used for the purpose of reserving the wireless medium for further communication.

[0184] At action 810, the second AP responds to the first notification frame by sending a first response frame to the first AP. The response may include any parameters, such as parameters indicating any AP or station capabilities available for CBF configuration. The first response frame may include a second list of participating stations associated with the second AP for the upcoming CBF TXOP. For example, the second list of participating stations may be selected from the candidate stations previously identified by the second AP. For example, the second list of participating stations may include stations associated with the second AP for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., via multi-AP sounding, such as joint sounding or sequential sounding). For example, the second list of participating stations may include stations for which the second AP has pending data traffic to be transmitted in the upcoming TXOP. Similar to the first notification frame, the first response frame may include the per-station AID, Nss, and RU data for the stations of the second BSS in the second list. If there are no stations available for CBF, the first response frame may include a "no STA" indication. For example, both the first notification frame and the first response frame may include padding to ensure sufficient time for processing and preparation. The MCS of the participating STAs may depend on the set of other participating STAs with which they can be grouped together and may be computed on the fly or looked up from an MCS table previously computed for different STA groups. Additionally, the first response frame may be transmitted within a short inter-frame space (SIFS) period starting from the end of the first notification frame to facilitate timely communication between the APs.

[0185] At action 815, the method may include the first AP sending a second notification frame to the second AP. For example, upon receiving a first response frame that does not have a "no STA" indication, the first AP may send a second notification frame that may include information for constructing the preamble of a CBF PPDU (physical layer protocol data unit). Such information may include the per-station MCS, CBF PPDU duration, GI-LTF selection or value, number of LTFs, or other data for each station in the first list of participating stations associated with the first AP. Additionally, the second notification frame may signal the TXOP duration for the remainder of the TXOP. The second notification frame may provide information for subsequent initial control frames, including the user information field of the station of the first AP.

[0186] A user - info field or user information field can include any field of a data structure or control frame that can contain values, parameters, or details about an individual STA (e.g., a user) associated with an AP. The user - info field can include, for example, an STA identifier (e.g., a unique parameter or value of a station device, such as an AID), spatial stream information (e.g., the number of spatial streams allocated to the station device), MCS data (e.g., a parameter for the data rate or communication robustness of the station device), resource allocation data (e.g., information about allocated resource units for OFDMA), power control settings (e.g., a parameter for the power level of the station), or antenna configuration (e.g., data on how to set or configure antennas for beamforming). Padding can be included to facilitate the second AP having sufficient time to process the frame. This frame can signal whether an initial control frame should be transmitted. This frame can signal the amount of padding for the initial control frame. Additionally, the second notification frame can be transmitted within a short inter - frame space (SIFS) period starting from the end of the first response frame to facilitate timely communication between APs.

[0187] At action 820, the method can include the second AP sending a second response frame to the first AP. For example, upon receiving the second notification frame, the second AP can send a second response frame to the first AP. The second AP can include any parameters in the second response frame, such as parameters of any AP or station capabilities. This frame can include, for example, details of the TXOP duration of the remaining part of the TXOP or additional information for constructing the preamble of a CBF PPDU (e.g., the MCS of each station of a second list of associated stations related to the second AP). Similar to the second notification frame, the second response frame can contain information about the subsequent initial control frame and padding to facilitate sufficient processing time. The existence of the second response frame can be pre - negotiated between APs or signaled in a previous frame within the TXOP. It can signal any increase in the amount of padding required for the initial control frame. Additionally, the second response frame can be transmitted within a short inter - frame space (SIFS) period starting from the end of the second notification frame to facilitate timely communication between APs.

[0188] Upon completion of operations 805 to 820, the AP and the stations of the AP can utilize the configurations and settings implemented at 805 to 820 to perform data communication with partial - rank or full CBF. For example, the first and second APs can simultaneously transmit to their respective associated stations, where each AP beamforms the signals it transmits to minimize interference to the stations of the other AP when the other stations receive their respective expected signals from their corresponding APs.

[0189] Now refer to Figure 9, an example method 900 that describes another example of providing a CBF setup sequence for multiple APs. Method 900 can be implemented using, for example, system 200, system 500, or any of the features discussed in conjunction with Figures 1A to 5 Method 900 can include actions 905 to 910. At 905, the method can include a first AP sending a notification frame to a second AP. At 910, the method can include the second AP sending a response frame to the first AP. The frames transmitted as part of method 900 can belong to the same TXOP (e.g., frames transmitted adjacently or proximally in method 900 can be separated by a gap of SIFS).

[0190] At action 905, the method can include a first AP initiating a sequence by sending a notification frame to a second AP. The notification frame can be a type 1 notification frame. The type 1 notification frame can include a list of possible station groups for an upcoming CBF TXOP. Each station group can include one or more stations associated with each AP. For example, the stations in the station group can be selected from the candidate stations previously identified by each AP. For example, the stations in the station group can be selected from the stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., through channel sounding, such as joint sounding or sequential sounding). For example, the stations in the station group associated with the first AP can be selected from the stations for which the first AP has pending data traffic to be transmitted in the upcoming TXOP. For each station in the station group, each group can contain one or more of each station's AID, each station's Nss, and each station's RU indication or data. The group data for each group of stations can contain any per-station MCS information (e.g., the MCS information of each individual station in the group). The group data for each group of stations can contain each station's CBF PPDU duration (e.g., the duration of the CBF PPDU or the length of the time interval).

[0191] For example, the type 1 notification frame can contain information for constructing the preamble of the corresponding CBF PPDU, such as MCS information, information about the CBF PPDU duration, and other parameters. For each station group in the list, the MCS information can contain each station's MCS in the group associated with the first AP. The type 1 notification frame can include information for subsequent initial control frames, including the user information field of the station of the first AP and MU-RTS / BSRP, facilitating full communication between APs. Padding can be included to provide the second AP with sufficient time to identify the preferred group and prepare a response for the first AP.

[0192] At operation 905, the method may alternatively include the first AP starting the sequence by transmitting a Type 2 notification frame to the second AP, where the first AP lists only its own stations. The Type 2 notification frame may include an inclusive list of the first AP stations participating in the upcoming TXOP, which may convey information (e.g., parameters) (e.g., each station AID, Nss, and RU indication). The list of the first AP stations may be selected from the candidate stations previously identified by the first AP. The list of the first AP stations may be selected from the stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., via channel sounding, e.g., joint sounding or sequential sounding). The list of the first AP stations may be selected from the stations for which the first AP has pending data traffic to transmit in the upcoming TXOP. Additionally, the Type 2 notification frame may include information for constructing the preamble of the CBF PPDU, such as each station MCS information, CBF PPDU duration, GI-LTF selection, and number of LTFs. Additionally, the Type 2 notification frame may include details of subsequent initial control frames, including the common information field and user information field of the first AP stations. Padding may be included in the Type 2 notification frame to ensure that the second AP has sufficient time to prepare a response for AP1.

[0193] For example, method 900 may begin with an initial frame exchange performed by the first AP and the second AP. For example, the initial frame exchange may include the first AP sending an RTS or an initial control frame to the second AP, and the second AP responding to the first AP with a CTS or an initial response frame upon receipt of the RTS or initial control frame. The initial frame exchange may allow the first AP to determine whether the second AP is available for further communication. The initial frame exchange may be used for the purpose of reserving the wireless medium for further communication.

[0194] At action 910, the second AP may respond to the notification frame by transmitting a response frame to the first AP. The response frame may be transmitted within a Short Inter-Frame Space (SIFS) period starting from the end of the notification frame. The response frame may be a type 1 response frame. The type 1 response frame may be transmitted in response to a type 1 notification frame. The type 1 response frame may indicate a preferred station group in the list of groups signaled in the notification frame. The second AP may identify the preferred station group based on stations for which the second AP has pending data traffic to transmit in the upcoming TXOP. In the case where no preferred group is identified, the type 1 response may signal "no group". The type 1 response frame may contain the TXOP duration for the remainder of the CBF TXOP. If a preferred group is identified, the type 1 response frame may contain additional information to construct the preamble of the CBF PPDU for the participating STAs of the second AP (e.g., per-station MCS). The type 1 response frame may contain information for subsequent initial control frames, including MU-RTS / BSRP. The type 1 response frame may contain padding to provide sufficient processing time. The padding may provide the AP with sufficient time to complete precoder calculations in time for CBF PPDU transmission, facilitating seamless communication between APs.

[0195] The second AP may respond to the notification frame from the first AP by transmitting a type 2 response frame. The type 2 response frame may be transmitted in response to a type 2 notification frame. The type 2 response frame may contain a list of the second AP stations. Upon receiving the type 2 notification frame, the second AP may transmit to the first AP a type 2 response frame indicating the list of the second AP's participating stations for the upcoming TXOP. This list may contain each station AID, Nss, and RU indication, providing comprehensive information for the first AP to proceed with the CBF TXOP. The list of the second AP's stations may be selected from the candidate stations previously identified by the second AP. The list of the second AP's stations may be selected from stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., through multi-AP sounding, such as joint sounding or sequential sounding). The list of the second AP's stations may be selected from stations for which the second AP has pending data traffic to transmit in the upcoming TXOP. If no participating STAs are available for the second AP, the response frame may contain a "no STA" indication. The type 2 response frame may signal the TXOP duration for the remainder of the CBF TXOP. If at least one participating station of the second AP is identified, the type 2 response frame may contain additional information required to construct the preamble of the CBF PPDU (e.g., per-station MCS for the participating stations of the second AP). The type 2 response frame may contain information for subsequent initial control frames, including MU-RTS / BSRP. The type 2 response frame may contain padding to allow sufficient processing time for the first AP or the second AP. This comprehensive response facilitates seamless communication between APs, ensuring efficient CBF operation.

[0196] When operations 905 to 910 are completed, the AP and the stations of the AP can utilize the configurations and settings implemented at 905 to 910 to perform data communication with partial rank or full CBF. For example, the first and second APs can simultaneously transmit to their respective associated stations, where each AP beamforms the signals it transmits to minimize the interference caused to the stations of other APs when other stations receive their respective expected signals from their respective APs.

[0197] Now referring to Figure 10 , an example method 1000 for providing a CBF setting sequence for setting CBF for multiple APs (e.g., in each TXOP coordination phase) is described. Method 1000 can be implemented using, for example, system 200, system 500, or any of the features discussed in conjunction with Figures 1A to 5 . Method 1000 can include actions 1005 to 1020. At 1005, the method can include the first AP sending a notification to the second AP and the stations of the first AP. At 1010, the method can include the stations of the first AP sending a response frame to the first AP. At 1015, the method can include the second AP sending a response to the first AP. At 1020, the method can include the stations of the second AP sending a response to the second AP. The frames transmitted as part of method 1000 can belong to the same TXOP (e.g., the frames of adjacent or neighboring transmissions of method 1000 can be separated by a gap of SIFS).

[0198] At action 1005, the method can include the first AP initiating a CBF setting sequence by transmitting a notification frame to the second AP and the stations of the first AP. This notification can include one or more frames that can notify the second AP of the opportunity for a CBF-TXOP and can notify the candidate stations of the first AP of the upcoming CBF-TXOP. The notification frame can include an AP notification component intended for the second AP. The notification frame can include a STA notification component intended for one or more stations of the first AP. The notification frame can include a list of the stations of the first AP selected for the upcoming CBF-TXOP and can provide details (e.g., each station AID, Nss, and RU indication) to facilitate subsequent data transmission to these stations. The notification frame can also include information about the amount of padding it can provide within the transmission to allow the receiving device (e.g., AP or STA) to have additional processing time before it provides a response.

[0199] The notification frame may include padding to allow sufficient time for the second AP to prepare a response for the first AP or for the stations of the first AP to respond. For example, the first AP may receive (e.g., via a previous transmission) the desired amount of padding from the second AP, which the first AP may utilize to form the notification frame to grant the second AP the desired or requested processing or response time. The AP notification component may notify the second AP of the opportunity for a CBF-TXOP. The type of AP notification may include or follow any of the types of notification frames of the CBF setup sequence discussed in operation 705 of method 700, operation 805 of method 800, or operation 905 of operation 900. The type of AP notification signaled may be indicated in the frame or may be negotiated in advance between the APs (e.g., during the configuration of CBF operation). The STA notification component may notify one or more candidate stations of the first AP of an upcoming CBF-TXOP. The STA notification may be used as an initial control frame (e.g., MU-RTS / BSRP) prior to the CBF-TXOP for the stations of the first AP. The stations of the first AP may be selected from the CBF candidate stations previously identified by the first AP. The stations of the first AP may be selected from the stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., via channel sounding, such as joint sounding or sequential sounding). The stations of the first AP may be selected from the stations for which the first AP has pending data traffic to transmit in the upcoming TXOP.

[0200] For example, method 1000 may begin with an initial frame exchange performed by the first AP and the second AP. For example, the initial frame exchange may include the first AP sending an RTS or an initial control frame to the second AP, and the second AP responding to the first AP with a CTS or an initial response frame upon receipt of the RTS or initial control frame. The initial frame exchange may allow the first AP to determine whether the second AP is available for further communication. The initial frame exchange may be used for the purpose of reserving the wireless medium for further communication.

[0201] At operation 1010, the method may involve transmitting a response frame to the first AP. The response frame may be transmitted after a SIFS period from the end of the notification frame received from operation 1005. The response frame may be a Response 1 frame, which may be transmitted in response to receiving the notification frame at operation 1005. The Response 1 frame may include any station capability data or any other parameters corresponding to or related to the CBF function of the station of the first AP. The response frame may include padding to allow the first AP sufficient time to process the data. The station of the first AP may transmit the Response 1 frame to the first AP. Upon receiving the notification frame, one or more stations of the first AP notified by the notification frame may transmit the Response 1 frame to the first AP. The station may transmit the Response 1 frame to indicate its availability for the CBF TXOP. The STA of the first AP that receives the notification frame and transmits the Response 1 frame may remain in the receive mode on the same link for a minimum timeout period. The minimum timeout period may be negotiated in advance with the first AP after the Response 1 frame. If such STA does not detect a CBF PPDU within the timeout period, then it may exit this state after the timeout period. In some configurations, the second AP may also transmit the Response 1 frame to the first AP to confirm receiving the notification frame from the first AP. The second AP may transmit the Response 1 frame concurrently with the Response 1 frame transmitted by one or more stations of the first AP. The Response 1 frame transmitted by the second AP may occupy a frequency subband, RU, or spatial stream that is otherwise not occupied by the Response 1 frame transmitted by the stations of the first AP, which may allow the first AP to distinguish the Response 1 frame of the second AP from the Response 1 frame transmitted by the stations of the first AP.

[0202] At action 1015, the second AP may transmit a notification frame. The notification frame may be transmitted after the SIFS period starting from the end of the response frame from action 1010. The notification frame may be transmitted by the second AP to the first AP. For example, the second AP may send any AP capability data or any other parameters corresponding to or related to the CBF function of the second AP to the first AP. The notification frame may be transmitted by the second AP to one or more stations of the second AP (e.g., if any STA of the second AP is identified for CBF operation in the same TXOP). The notification frame may include an AP response component intended for the first AP. The notification frame may include a STA notification component intended for one or more stations of the second AP. The second AP may respond to the notification frame from the first AP at action 1005 by including an AP response to the first AP in the notification frame transmitted by the second AP. The AP response may be used to address the notification frame of the first AP and may include a list of participating stations of the second AP for this TXOP, conveying each station AID, Nss, and RU indication. If no such stations are available at the second AP, the AP response may include a "no STA" indication. The notification frame may include padding to allow the first AP sufficient time to process the data. For example, the second AP may receive (e.g., via a previous transmission) the desired amount of padding from the first AP, which the second AP may utilize to form the notification frame to grant the first AP the desired or requested processing or response time.

[0203] The type of the AP response may include or follow the type of the response frame of the CBF setup sequence of method 700 (e.g., at 715), 800 (e.g., at 810), or 900 (e.g., at 910), where the type of the response is selected to match the type of the AP notification in operation 1005 (e.g., the AP response type corresponding to 715 may be selected to match the AP notification type corresponding to 705, or the AP response type corresponding to 810 may be selected to match the AP notification type corresponding to 805, or the AP response type corresponding to 910 may be selected to match the AP notification type corresponding to 905). The second AP may send a STA notification to the stations of the second AP (e.g., any candidate stations that may be identified for CBF operation in this TXOP). The STA notification frame may be used as an initial control frame (e.g., MU-RTS / BSRP) to notify any STA of the second AP that is identified for this CBF TXOP. The notification frame transmitted by the second AP may include padding to provide sufficient time for either AP to prepare for CBF PPDU transmission or for the stations of the second AP to respond. The stations of the second AP may be selected from the candidate stations of the CBF previously identified by the second AP. The stations of the second AP may be selected from the stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., through channel sounding, such as joint sounding or sequential sounding). The stations of the second AP may be selected from the stations for which the second AP has pending data traffic to be transmitted in the upcoming TXOP).

[0204] At action 1020, any station of the second AP addressed by the notification frame at action 1015 may transmit its own response frame when receiving the notification frame from the second AP at action 1015. If no station of the second AP is identified, then this frame may be non-existent. If this response frame is transmitted, then this response frame may follow the notification frame transmitted at action 1015 immediately after the SIFS period. For example, the station of the second AP may send any station capability data or any other parameters corresponding to or related to the CBF function of the station of the second AP. The station of the second AP addressed by the STA notification component of the notification frame at action 1015 may transmit a response frame (e.g., response 2 frame) in response to receiving the notification frame.

[0205] For example, when the types of the AP notification and the AP response in 1005 and 1015 respectively follow those of the first notification frame at step 805 and the first response frame at step 810 of the CBF setup sequence discussed in conjunction with method 800, then the subsequent frames can be exchanged during the SIFS period after the final frame in the above exchange. For example, the second notification frame at step 815 of the CBF setup sequence discussed in conjunction with method 800 can be transmitted from the first AP to the second AP. For example, the second response frame at step 820 of the CBF setup sequence of method 800 can be transmitted from the second AP to the first AP.

[0206] Upon completion of operations 1005 to 1020, the AP and the stations of the AP can utilize the configurations and settings implemented at 1005 to 1020 to perform data communication with partial rank or full CBF. For example, the first and second APs can simultaneously transmit to their respective associated stations, where each AP beamforms the signals it transmits to minimize the interference caused to the stations of the other AP when the other stations receive their respective expected signals from their respective APs.

[0207] Now refer to Figure 11 , and illustrate example method 1100, which is another example of providing a CBF setup sequence for multiple APs. Method 1100 can be implemented using, for example, system 200, system 500, or any of the features discussed in conjunction with Figures 1A to 5 . Method 1100 can include actions 1105 to 1120. At 1105, the method can include the first AP sending a first notification to the second AP and the stations of the first AP. At 1110, the method can include the second AP and the stations of the first AP sending a first response to the first AP. At 1115, the method can include the second AP sending a second notification to the stations of the second AP. At 1120, the method can include the stations of the second AP sending a second response to the second AP. The frames transmitted as part of method 1100 can belong to the same TXOP (e.g., the frames transmitted adjacently or proximally in method 1100 can be separated by the gap of the SIFS).

[0208] At operation 1105, the method may include a first AP starting a setup sequence by transmitting one or more first notification frames to a second AP and stations of the first AP. The one or more first notification frames may notify the second AP of the opportunity for a CBF-TXOP. The one or more first notification frames may notify one or more stations of the first AP of an upcoming CBF-TXOP. The first notification frame may include details related to the CBF TXOP, such as each station AID, Nss, and RU indication of the stations of the first AP. The first notification frame may specify that responses to the first notification should be in the format of a TB PPDU. The first notification frame may specify the parameters for each addressed device (e.g., TX parameters for the second AP, stations of the first AP) required to transmit a response in the format of a TB PPDU. Additionally, padding may be included in the first notification frame to provide sufficient time for the second AP or one or more stations of the first AP to respond. For example, the amount of padding may be determined based on previously communicated AP capability data, which may indicate the amount of padding preferred or requested by the second AP. The stations of the first AP may be selected from among the candidate stations for the CBF previously identified by the first AP. The stations of the first AP may be selected from among the stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., through channel sounding, such as joint sounding or sequential sounding). The stations of the first AP may be selected from among the stations for which the first AP has pending data traffic to transmit in the upcoming TXOP.

[0209] The first notification frame may be a notification 1 frame. For example, the first AP may use a notification 1 frame to notify the second AP of the opportunity for a CBF-TXOP. The notification 1 frame may include or follow the notification frame of the CBF setup sequence, such as one of those discussed in conjunction with operation 705 of method 700, operation 805 of method 800, or operation 905 of method 900. The type of notification signaled may be indicated in the frame or negotiated in advance between the APs (e.g., during the configuration of CBF operation). For example, notification frame 1 may notify the STAs of the first AP of an upcoming CBF-TXOP (e.g., those STAs participating in the upcoming CBF-TXOP) by serving as an initial control frame (e.g., MU-RTS or BSRP). The notification frame 1 may specify that responses should be in the format of a TB PPDU. The notification frame-1 may specify the parameters of the response for each addressed device (second AP, stations of the first AP). The notification frame-1 may include padding to provide sufficient time for the second AP or the stations of the first AP to respond.

[0210] For example, method 1100 may begin with an initial frame exchange from the first AP and the second AP. For example, the initial frame exchange may include the first AP sending an RTS or an initial control frame to the second AP, and the second AP responding to the first AP with a CTS or an initial response frame upon receipt of the RTS or the initial control frame. The initial frame exchange may allow the first AP to determine whether the second AP is available for further communication. The initial frame exchange may be used for the purpose of reserving the wireless medium for further communication.

[0211] At action 1110, a station of the second AP or the first AP may transmit one or more first response frames to the first AP in response to one or more first notification frames. The one or more first response frames may be in the format of a TB PPDU. The first response frame may be addressed to the first notification frame from the first AP and contain relevant information regarding the CBF operation. The first response frame transmitted by the second AP may follow the selected type of response to match the notification type in action 1105. The first response frame of the second AP may contain a padding amount, which may be identified from previously communicated AP capability data that identifies the desired or requested padding amount to allow the first AP sufficient processing time. After transmitting the first response frame, the station of the first AP that transmitted the first response frame may remain in the receive mode on the same link for a pre-negotiated timeout period. Padding may be included to allow the first AP sufficient time to process the response. The first response frame may be transmitted after a SIFS period from the end of the first notification frame transmitted at action 1105.

[0212] The first response frame may include a Response 1 frame. The Response 1 frame may be transmitted by the second AP or the station of the first AP addressed by the Notification 1 frame to the first AP in response to receipt of the Notification 1 frame. The Response 1 frame may be transmitted in the format of a TB PPDU. For example, the Response 1 frame may contain any AP capabilities, any station capabilities, or any parameters corresponding to or related to the CBF function of the second AP or the station of the first AP. The second AP may respond to the first AP. The type of the second AP's response may follow the type of the response frame of the CBF setup sequence discussed in operation 715 of method 700, operation 810 of method 800, or operation 910 of method 900. The type of the response may be selected to match the type of the notification at 1005 (e.g., the response type corresponding to 715 may be selected to match the notification type corresponding to 705, or the response type corresponding to 810 may be selected to match the notification type corresponding to 805, or the response type corresponding to 910 may be selected to match the notification type corresponding to 905). The STA of the first AP that receives the Notification 1 frame and transmits the Response 1 frame may need to remain in the receive mode on the same link for a minimum timeout period (pre-negotiated with the first AP) after the Response 1 frame. If such STA does not detect (e.g., in response to not detecting) a CBF PPDU within the timeout period, then such STA may be allowed to exit this state after the timeout period.

[0213] At action 1115, the second AP may transmit one or more second notification frames to any station of the second AP. These stations may include any stations identified in the first notification or the first response for CBF operation in this TXOP. The stations of the second AP may be selected from the candidate stations of the CBF previously identified by the second AP. The stations of the second AP may be selected from the stations for which the first AP and the second AP have previously obtained downlink channel state information (CSI) (e.g., through channel sounding, such as joint sounding or sequential sounding). The stations of the second AP may be selected from the stations for which the second AP has pending data traffic to transmit in the upcoming TXOP. The second notification may be sent according to the response of the second AP in the first response frame. The second notification frame may be used as an initial control frame to notify any identified stations of the second AP of the upcoming CBF-TXOP. Padding may be included to provide sufficient time for either AP to prepare for CBF PPDU transmission and for the stations of the second AP to respond. The second notification frame may include padding, allowing the stations of the second AP sufficient time to process the data and provide any response.

[0214] The second AP may send a Notification 2 frame. The Notification 2 frame may be transmitted by the second AP to any STA of the second AP identified for CBF operation in the same TXOP. The Notification 2 frame may be sent according to the response of the second AP, which may be in response to the Response 1 frame. If no STA is identified, then this frame may be omitted. The Notification 2 frame may notify any STA of the second AP identified for this CBF TXOP by serving as an initial control frame (e.g., MU-RTS / BSRP). The Notification 2 frame may include padding to provide sufficient time for either AP to prepare the CBF PPDU or for the STA of the second AP to respond. The second notification frame or the Notification 2 frame may be transmitted after the SIFS period from the end of the first response frame transmitted at action 1110.

[0215] At operation 1120, any station of the second AP addressed by the second notification frame may transmit a second response frame to the second AP upon receipt of the second notification frame. If this second response frame is transmitted, then this second response frame may address the second notification frame. The second response frame may contain information similar to the first response frame. For example, a station of the second AP may transmit any station capabilities, or any parameters corresponding to or related to the CBF function of the station of the second AP. Padding may also be included to provide sufficient time for either AP to prepare for CBF PPDU transmission. The second response frame may be transmitted after a SIFS period from the end of the second notification frame transmitted at operation 1115. A station of the second AP may send the second response frame, which may be a Response 2 frame. The Response 2 frame may be transmitted by any STA of the second AP addressed by the Notification 2 frame in response to receipt of the Notification 2 frame (e.g., from 1115). If the Notification 2 frame is not transmitted, then this frame may be omitted or not present. For a STA that has not received the Notification 2 frame, this frame may be omitted or not present.

[0216] If the types of the notifications and responses at 1105 and 1110 follow the types of the first notification and first response frames of the CBF setup sequence of method 800, then the next frames may be exchanged during a SIFS period after the final frame in the previous exchange (e.g., after the second response frame at operation 1120). For example, a third notification frame corresponding to the second notification frame of the CBF setup sequence at operation 815 of method 800 may be transmitted by the first AP to the second AP. For example, a third response frame corresponding to the second response frame of the CBF setup sequence at operation 820 of method 800 may be transmitted by the second AP to the first AP.

[0217] Upon completion of operations 1105 to 1120, the AP and the stations of the AP may utilize the configurations and settings implemented at 1105 to 1120 to perform data communication with partial rank or full CBF. For example, the first and second APs may simultaneously transmit to their respective associated stations, where each AP beamforms the signals it transmits to minimize interference to the stations of the other AP when the other stations receive their respective expected signals from their respective APs.

[0218] Now referring Figure 12 , an example method 1200 for providing a CBF data sequence for multiple APs will be described. Method 1200 may use, for example, system 200, system 500, or in combination Figures 1A to 5Implement any one of the features discussed. Method 1200 may include actions 1205 to 1220. At 1205, the method may include the first AP and the second AP sending a common initial control frame to a station. At 1210, the method may include the station transmitting a response. At 1215, the method may include the first AP and the second AP sending a CBF PPDU. At 1220, the method may include the station sending a trigger-based block acknowledgment. Frames transmitted as part of method 1200 may belong to the same TXOP (e.g., adjacent or neighboring transmission frames of method 1200 may be separated by a gap of SIFS).

[0219] At action 1205, the method may include both the first AP and the second AP sending one or more common initial control (CIC) frames to stations of the first AP and the second AP. In a configuration where more than two APs are utilized, it should be understood that an AP may transmit CIC frames to any station of the APs involved. The one or more CIC frames may be transmitted by the first AP, the second AP, or both APs simultaneously. The CIC frames may be addressed to stations participating in the CBF TXOP. The APs may coordinate as to which AP(s) will transmit this frame. This transmission may occur or be negotiated during CBF setup, configuration of CBF operation, or an initial handshake. The CIC frames may be transmitted in a non-high throughput (non-HT) PPDU format, the content of which is determined by a previous CBF setup frame exchange. If transmitted by two APs, the responding AP may align its transmission CFO and timing relative to the TXOP initiating AP.

[0220] For example, the first and second APs may transmit CIC frames (e.g., MU-RTS or BSRP). The CIC frames may be transmitted by the first AP, the second AP, or both the first and second APs. The APs may coordinate as to which AP will transmit this frame during CBF setup, or during configuration of CBF operation, or during initial AP identification or handshake. The CIC frames may be generated or provided in a non-HT PPDU format, the content of which is determined by a previous CBF setup frame exchange. If transmitted by both the first and second APs, the responding AP may align its transmission CFO and timing relative to the TXOP initiating AP, e.g., by using the frame received during CBF setup as a reference. The CIC frames may include a single common MAC address (e.g., as from a previous negotiation identification), which may be recognized or known by one or more stations associated with either AP (e.g., by one or more of the candidate CBF stations of each AP addressed by the CIC frame).

[0221] For example, method 1200 may begin with an initial frame exchange from a first AP and a second AP. For example, the initial frame exchange may include the first AP sending an RTS or an initial control frame to the second AP, and the second AP responding to the first AP with a CTS or an initial response frame upon receipt of the RTS or the initial control frame. The initial frame exchange may allow the first AP to determine whether the second AP is available for further communication. The initial frame exchange may be used for the purpose of reserving the wireless medium for further communication.

[0222] At action 1210, the station transmits one or more responses in response to the CIC frame of action 1205. For example, the station may transmit a joint response (e.g., CTS or BSR) in response to receiving a common initial control frame. The one or more responses may be transmitted by the station individually or jointly, and may correspond to or be sent on behalf of all stations of all the first AP and the second AP addressed by the CIC frame. The station sets the receiver address field of the response to be equal to the transmitter address field of the previous CIC frame.

[0223] The station may provide a response (e.g., CTS or BSR). The response may be transmitted jointly by the STAs of the first AP and the second AP addressed by the common initial control frame in response to receiving such frames. The STAs may set the RA field of the response to be equal to the TA field of the previous common initial control frame. The response to the MU-RTS may include a CTS, and the response to the BSRP may include a BSR. The response frame at 1210 may follow the CIC frame at 1205 after a SIFS period. The response frame may include a single common MAC address (e.g., as identified from a previous negotiation) that may be recognized or understood by either AP.

[0224] At operation 1215, the first AP and the second AP may transmit one or more beamforming data units (BDUs), such as CBF PPDUs. For example, the first and second APs may transmit a CBF PPDU after a pause (e.g., SIFS) after receiving a response in operation 1210 (e.g., when the frames in operations 1205 and 1210 are optionally transmitted), or after a pause (e.g., SIFS) after the final frame in the CBF setup sequence. In some examples, a CBF trigger frame may precede the CBF PPDU. The CBF trigger may immediately follow the CBF PPDU after a SIFS. The CBF trigger may be transmitted by the first AP or the second AP. The CBF trigger may be transmitted after a pause (e.g., SIFS) after the response in operation 1210 (e.g., when the frames in operations 1205 and 1210 are optionally transmitted), or after a pause (e.g., SIFS) after the final frame in the CBF setup sequence. The CBF trigger may be a short control frame (e.g., a CTS frame). The CBF trigger may include a single common MAC address (e.g., as identified from a previous negotiation), which may be recognized or known by either AP or one or more stations associated with either AP (e.g., one or more of the candidate CBF stations of each AP addressed by the CIC frame in operation 1205). The two APs may align their transmissions. For example, the responding AP may use the frames received during CBF setup as a reference to align its transmission CFO or timing relative to the TXOP initiating AP. When transmitting the CBF trigger, it may also be used to align the AP transmissions for subsequent CBF PPDUs (e.g., the AP receiving the CBF trigger may align its transmission CFO or timing relative to the AP transmitting the CBF trigger). The payload portion of the CBF PPDU transmitted by each AP may be beamformed to minimize interference to stations of other APs. The preamble of the CBF PPDU may additionally identify the participating APs. The preamble of the CBF PPDU may signal that spatial reuse is not allowed.

[0225] The first and second APs may transmit CBF PPDUs. The CBF PPDUs may be transmitted jointly by the two APs. The CBF PPDUs may be transmitted during the SIFS period after receiving the response in 1210 (e.g., when transmitting the frames in steps 1205 and 1210), or during the SIFS period after the final frame in the CBF setup sequence, or during the SIFS period after a CBF trigger frame (e.g., a CBF trigger transmitted by one of the APs). The responding AP may align its transmission CFO and timing relative to the TXOP initiating AP (e.g., by using the frames received during CBF setup as a reference). The payload portion of the CBF PPDU transmitted by each AP may be beamformed by full-rank or partial-rank nulling to minimize interference to STAs of other APs. A portion of the preamble of the CBF PPDU may be transmitted by the two APs without nulling. This portion of the preamble may be sent by the two APs with the same content to avoid incorrect decoding at each STA due to interference when the contents are different. The BSS color field in the preamble may be filled with a common BSS color selected when configuring CBF operation. The preamble of the CBF PPDU may additionally identify the participating APs. The preamble of the CBF PPDU may additionally signal that spatial reuse is not allowed. The CBFPPDU at 1215 may be transmitted after the SIFS period starting from the end of the response transmitted at 1210.

[0226] At action 1220, the stations of all APs to which the CBF frame is transmitted may send block acknowledgments. For example, the stations of the two APs may send trigger-based block ACKs in the format of TB PPDUs. Each station may provide feedback with a block ACK indicating whether the MPDUs addressed to it in the CBF PPDU are correctly received. The stations may avoid interfering with each other by transmitting on non-overlapping RUs or on separate spatial streams. The preamble of the TB PPDU may signal the same BSS color as signaled in the preamble of the CBF PPDU.

[0227] The STAs of the first and second APs may send trigger-based block ACKs that can be transmitted in the format of TB PPDUs. Each STA may feedback a block ACK indicating whether the MPDUs addressed to it in the CBF PPDU are correctly received. For example, the STAs may avoid interfering with each other by transmitting on non-overlapping RUs or on independent spatial streams. For example, the preamble of the TB PPDU may signal the same BSS color as signaled in the preamble of the CBF PPDU. The transmission at 1220 may immediately follow the CBF PPDU at 1215 after the SIFS period.

[0228] Upon completion of operations 1205 to 1220, the AP and the stations of the AP can utilize the configurations and settings implemented at 1205 to 1220 to perform data communication with partial rank or full CBF. For example, the first and second APs can simultaneously transmit to their respective associated stations, where each AP beamforms the signals it transmits to minimize the interference caused to the stations of other APs when other stations receive their respective expected signals from their corresponding APs.

[0229] The CBF data sequence (e.g., one of those discussed in connection with method 1200) can start after the CBF setup sequence within the same TXOP, such as any of methods 700 to 1100 (e.g., SIFS after the CF setup sequence, or may start with other frames in between, where adjacent frames may be separated by SIFS). For example, the CBF data sequence can start when each AP identifies at least one participating STA during the CBF setup sequence. For example, during the CBF setup sequence, if the responding AP provides an "no STA" or "no group" indication to the TXOP initiating AP, then no CBF operation will occur for this TXOP. In this case, the TXOP initiating AP can continue to serve its STAs in the same TXOP (SIFS after the CBF setup sequence), but without CBF.

[0230] The CBF TXOP can include a combination of CBF transmissions (e.g., where transmissions are performed according to CBF) and non-CBF transmissions (e.g., where transmissions do not involve CBF). Such a combination of non-CBF and CBF transmissions can be implemented in three phases. In the first phase, the AP can identify the time T at which CBF communication can start during the upcoming TXOP. In the second phase, one or more APs can start non-CBF communication until time T. At the third phase, once time T occurs, CBF communication can start and be used for the remainder of the TXOP, or the participating APs can select any part of the TXOP to be performed using CBF.

[0231] In a first phase, a first AP may query a second AP as to whether the second AP will participate in CBF in an upcoming TXOP. The first AP may also signal the TXOP duration to the second AP. The second AP may respond with an indication of a future time T within this TXOP when it will be able to participate in CBF. For example, the second AP may defer its participation in CBF based on the unavailability of its candidate CBF STAs currently or their inability to receive one or more CBF transmissions directed thereto and its information or knowledge that they may become available at a future time (e.g., time T). The first phase may be implemented using, for example, 1005 or 1010 of method 1000, e.g., the first AP transmits a request or query to the second AP in 1005 as to whether the second AP will participate in CBF, and the second AP notifies the first AP at 1010 of the future time T at which the second AP may start participating in CBF. In some examples, the first phase may include actions 1005, 1010, 1015 of method 1000, where the second AP does not notify AP2-STA, but includes an indication of the future time T in its response to the first AP in action 1015. In some examples, the first phase may include actions 1105, 1110 of method 1100, where the second AP includes an indication of the future time T in its response to the first AP at action 1110.

[0232] In a second phase, after the response of the second AP from the first phase, the first AP may start one or more non-CBF transmissions to its STAs, where the total duration lasts until time T (e.g., when the CBF transmission is set to start). The second phase may include an acknowledgement (ACK) transmitted by the stations of the first AP (AP1-STA) in response to the non-CBF transmission from the first AP.

[0233] In a third phase, after time T, the first AP and the second AP may perform CBF transmission. For example, the third phase may be completed by the first AP sending a notification to the second AP to signal the end of the second phase and initiate the CBF transmission. For example, the second AP may infer the end of the second phase from the exchange between the first AP and the stations of the first AP. For example, the first AP and the second AP may coordinate the exchange in which the stations of the first AP and the second AP may participate in CBF via, for example, actions 1005, 1010, and 1015 of method 1000, or via actions 1105 and 1110 of method 1100. For example, the second AP may perform a handshake with the stations of the second AP for the upcoming CBF transmission via, for example, actions 1015 and 1020 of method 1000 or via actions 1115 and 1120 of method 1100.

[0234] After the CBF data sequence ends (e.g., after the sequence ends by SIFS, or within the same TXOP, or continue the TXOP), one or more actions may be implemented or occur. For example, the TXOP initiating AP may start a new CBF setup sequence, such as the sequence described by methods 700, 800, 900, 1000, or 1100. For example, a second CBF data sequence may be initiated, such as the sequence described by method 1200. The second CBF data sequence may follow the new CBF setup sequence. The TXOP initiating AP may continue the TXOP with non-CBF exchanges. The TXOP initiating AP may end the TXOP by not transmitting, allowing devices to contend for the medium (including itself).

[0235] Within the context of CBF, several different types of probe sequences may be utilized. For example, joint probing may include a station providing a single joint probe report covering the channels of two APs. For example, when a first station is associated with a first AP and a second station is associated with a second AP, the first station or the second station may each transmit a single joint probe report covering the channels of the two APs. In contrast, sequential probing requires the station to deliver two individual probe reports, one for each AP. In this scenario, a station associated with either AP may transmit two separate probe reports, one report for the downlink channel from each AP. These probe sequences may facilitate the improvement or optimization of communication between the AP and the station, thereby improving the overall efficiency and reliability of data transmission.

[0236] Examples of probe sequences may include joint probe sequences or sequential probe sequences. For example, a first STA (e.g., STA1) may be associated with a first AP (e.g., AP1), and a second STA (e.g., STA2) may be associated with a second AP (e.g., AP2). In a joint probing configuration, the STA may feedback a single joint probe report covering the channels of the two APs. Example options for MAC protocol sequences may include STAs of each BSS probed individually. For example, a first MAC protocol sequence for probing STA1 may be initiated (e.g., by AP1) for probing, and a second MAC protocol sequence for probing STA2 may be initiated (e.g., by AP2).

[0237] For example, a joint sounding sequence may include configurations such as: AP1 NDPA(STA1), SIFS, joint NDP(AP1+AP2), SIFS, AP1 BFRP(STA1), SIFS, STA1 BFR. In this scenario, the joint sounding sequence may include an action sequence for coordinating beamforming between AP1 and AP2 and the station (STA1). The sequence may start with an AP1-initiated Null Data Packet Announcement (NDPA) for STA1, followed by a Short Inter-Frame Space (SIFS). Then, both AP1 and AP2 may jointly transmit a Null Data Packet (NDP), indicating their cooperation, followed by SIFS. Next, AP1 may send a Beamforming Report Poll (BFRP) to STA1, allowing STA1 to prepare for beamforming operations (e.g., convey channel information). Finally, STA1 may respond with a Beamforming Report (BFR), containing feedback on the Channel State Information (CSI) measured with respect to AP1 and AP2.

[0238] For example, a sequential sounding sequence may include a scenario where the STA feeds back two individual sounding reports (one for each AP). An example option for the MAC protocol sequence may include a single-AP sequence where the STAs of each BSS individually sound, one AP at a time. For example, a sequential sounding sequence configuration may include AP1 NDPA(STA1), SIFS, AP1 NDP or AP2 NDP, SIFS, AP1BFRP(STA1), SIFS, STA1 BFR(AP1 or AP2). In this scenario, the sequential sounding sequence configuration may include actions that facilitate beamforming between access point AP1 (and potentially AP2) and station STA1. The sequence may start with an AP1-initiated NDPA for STA1, followed by SIFS. Subsequently, either AP1 or AP2 may transmit an NDP, which may be used as part of the sounding process, followed by SIFS. Next, AP1 may send a BFRP to STA1, allowing it to prepare for upcoming beamforming operations. STA1 may respond with a BFR directed at AP1 or AP2, containing feedback on the Channel State Information (CSI) measured with respect to AP1 or AP2.

[0239] For example, the sequential probe sequence configuration may include a multi-AP configuration where the STA of each BSS is probed separately for two APs. For example, the configuration may include AP1 NDPA(STA1), SIFS, AP1 NDP, SIFS, AP2 NDP, SIFS, AP1 BFRP(STA1), SIFS, STA1 BFR(AP1, AP2). In this setup, the sequential probe sequence may facilitate coordinated beamforming between access points AP1 and AP2 and STA1. The sequence may start with an NDPA from AP1 to STA1, followed by an SIFS. Then, AP1 may transmit an NDP, which may be followed by a second NDP transmission from AP2, where both NDPs contribute to the probing process, followed by an SIFS. Then, AP1 may send a BFRP to STA1 to prepare STA1 for the beamforming operation. STA1 may respond with a BFR pointing to both AP1 and AP2, including feedback on the channel state information (CSI) measured relative to AP1 and AP2.

[0240] In a sequence where AP1 initiates a probe sequence to its STA, AP2 may be configured to receive a BFR transmission from STA1. For this to happen, AP2 may prepare to receive the BFR by first decoding a previous BFRP frame transmitted by AP1, since the BFRP may contain information on how STA1 should encode a subsequent TB PPDU containing the BFR (e.g., MCS, PPDU bandwidth, RU index, spatial stream indication). AP2 may utilize the information from the previous BFRP to decode the BFR frame transmitted by the STA of AP1. For example, AP2 may utilize the transmission parameters of the BFR as specified in the BFRP, such as the MCS, PPDU bandwidth, RU index, or spatial stream indication for each STA of AP1 (e.g., STA1) addressed by the BFRP. AP1 may include some padding at the end of the BFRP to provide AP2 with enough time to decode the BFRP and prepare for the transmission of STA1. The amount of padding may be pre-negotiated between the APs (e.g., during the initial handshake).

[0241] Several considerations and optimizations can be related to various aspects of CBF operation. For example, padding can be used to facilitate the efficient utilization of CBF-TXOP, especially in scenarios where the responding AP may not have enough data to transmit to all stations. In such cases, the responding AP can fill the remaining duration of the CBF PPDU with padding bytes to maintain synchronization (e.g., manage time) and optimize resource utilization. Additionally, negotiation regarding the MU-RTS / BSRP rate and the content of the trigger frame for TB-ACK is crucial for optimizing communication between the AP and the STA, ensuring reliable data transmission, and minimizing overhead. Furthermore, considerations related to each AP's transmission power adjustment and trigger frame specification help optimize CBF operation and enhance network performance and reliability.

[0242] Compared to different CBF setup frame sequences, the sequence discussed in conjunction with method 800 can have different (e.g., higher) overhead compared to the sequence discussed in conjunction with method 900. For example, the sequence of method 900 with type 2 notification and type 2 response frames can utilize AP1 to select an MCS for the participating STAs of AP1 without the need to know which STAs of AP2 will participate. To promote robustness, the selected MCS can be lower than the value selected with prior knowledge of the participating STAs of AP2 (e.g., in method 800, or in method 900 with type 1 notification and type 1 response frames). For example, the sequence of method 900 can have different (e.g., lower) overhead compared to the sequence of method 800.

[0243] Other CBF setup / data frame sequences can be derived from the CBF setups discussed in conjunction with methods 700, 800, or 900. For example, a common initial control frame can be split into individual initial control frames (MU-RTS / BSRP) for each AP and merged with the previous CBF setup frame exchange. The initial control frame transmitted by the first AP can be merged with a notification frame (for the CBF setup frame sequence of method 900) or a second notification frame (for the CBF setup frame sequence of method 800). The initial control frame transmitted by the second AP can be merged with a response frame (for the CBF setup frame sequence associated with method 900) or a second response frame (for the CBF setup frame sequence associated with method 800). The STA associated with the first AP and addressed by the initial control frame of the first AP can wait until the second AP has transmitted its initial control frame and then jointly transmit a response (CTS / BSRP) to the initial control frame with the STA associated with the second AP and addressed by the initial control frame of the second AP.

[0244] Relative to the CBF preamble, the AP may agree on the common content, data, or parameters that can be signaled, such as BSS color, TXOP duration, bandwidth, punctured channel information, SIG MCS, spatial reuse, GI+LTF size, pre-FEC padding factor, LDPC extra symbols, the number of LTF symbols (including whether additional LTFs are needed), packet extension value (T_PE), PE disambiguation, the value of reserved bits, etc. Some of the common content can be determined through prior negotiation (e.g., invariant across multiple TXOPs, or not negotiated per TXOP), such as one or more of the following: PHY version identifier, pre-FEC padding factor (e.g., a value (e.g., 0) indicates padding to the full OFDM symbol boundary), TXOP duration (e.g., a value (e.g., 127) indicates the absence of information), spatial reuse (e.g., a value (e.g., 0) indicates that spatial reuse is not allowed), LDPC extra symbols (e.g., a value (e.g., 1) indicates the presence of LDPC extra symbols), BSS color, T_PE, PE disambiguation (e.g., value 1). Some other common content (e.g., the L-SIG LENGTH field) can be negotiated between APs per TXOP. The per-user content of each AP can be signaled in the preamble at different frequencies / tone, e.g., by each AP occupying a different content channel (e.g., in the UHR-SIG).

[0245] Regarding the transmission power of each AP for the CBF PPDU, due to the MCS-related EVM, the technical solution can use each AP to select its transmission power based on the highest data rate MCS used in the PPDU across STAs or the clients of two APs. Regarding padding, for the responding AP initiating the CBF-TXOP, it may not have enough data for one or more of its STAs to occupy the entire duration of the available CBF PPDU for transmission. In this case, the responding AP can fill the remaining duration of the CBF PPDU of such STAs with padding bytes. The rate for transmitting the initial control frame (e.g., MU-RTS or BSRP) can be pre-negotiated between APs (e.g., a fixed basic rate, or a fixed mapping to the basic rate based on the highest user MCS), or communicated per TXOP in the AP-AP handshake. For BSRP, the content of the triggered BA trigger frame can include the transmission power and the target RSSI setting, which can be pre-negotiated between APs or communicated per TXOP. The trigger frame for TB-ACK can include the trigger for the AMPDU. The trigger frame content (RU allocation, MCS / Nss per user) can be pre-negotiated between APs or negotiated per TXOP. MU-BAR can be handled such that each AP sequentially sends MU-BAR after the CBF PPDU and collects the TB block ACK (e.g., the AP can indicate to the STA that immediate confirmation may not be needed after the CBF PPDU, or the delayed block ACK can be utilized).

[0246] For example, any AP can utilize any of the frames transmitted by another AP to estimate or determine one or more relative carrier frequency offsets (CFOs) of itself relative to other APs. During channel sounding or data transmission, any AP can use the one or more CFOs estimated or determined relative to another AP. For example, any AP can pre-compensate or pre-correct its transmission based on the one or more CFOs estimated or determined relative to another AP to reduce its effective relative CFO of the pre-compensated or pre-corrected transmission relative to another AP. For example, when communicating to perform channel sounding or data transmission, the CFO of the first AP can be used by the first AP (or its station) to distinguish its transmission.

[0247] In a mesh deployment scenario, the root AP and the repeater APs can participate in CBF operations. The root AP can store data about the stations associated with the root AP or the repeater APs, including their respective traffic profiles. This data can provide additional understanding to facilitate the root AP in making informed decisions regarding CBF utilization and transmission optimization. For example, the root AP can know in advance which stations are associated with the repeater APs and know their corresponding traffic profiles. Thus, the root AP can better predict the availability of the traffic of the repeater AP stations and prepare CBF transmissions accordingly, thereby improving the overall network efficiency and performance. In addition, in a mesh deployment, the transfer of station information between the repeater AP and the root AP can be optimized to minimize overhead and simplify communication. By leveraging its leading knowledge and prediction capabilities, the root AP can effectively optimize CBF operations.

[0248] For example, in a mesh deployment, the root AP can be aware a priori of the STAs associated with the repeater AP and their traffic profiles. The root AP can be aware of which STAs can subsequently serve the repeater AP, since any downlink traffic destined for such STAs can be delivered to the repeater from the same router that also hosts the root AP. In such cases, the solution can limit the transfer of STA information from the repeater AP to the root AP. For example, the transfer of STA information may be relatively infrequent compared to the transfer from the root AP to the repeater AP. Additionally, the root AP may be able to better predict the availability of the traffic of the repeater AP STAs and prepare CBF transmissions in advance.

[0249] This can be reflected in the root AP being better able to predict when a TXOP is most likely to utilize CBF (e.g., if initiated), e.g., based on considering the amount and timing of traffic delivery to the repeater AP (for its STAs). For example, when a CBF-TXOP is initiated by the root AP with a CBF setup sequence associated with the method 900 of type 1 notification, this can result in a better selection of the candidate STA group. For example, by not providing or using the response from the repeater AP, the CBF setup sequence associated with method 900 can be further simplified. For example, when a CBF-TXOP is initiated by the root AP with a CBF setup sequence associated with the method 900 of type 2 notification, a better prediction of the MCS of the STAs of the root AP can be provided. In this scenario, the CBF setup sequence associated with method 900 can be further simplified by not using the response from the repeater AP, e.g., if the root AP already knows in advance which STAs will be selected by the repeater AP, their MCS, etc. For example, when the CBF-TXOP is initiated by the root AP, a better selection of the TXOP duration can be provided, e.g., due to considering the amount of traffic at different STAs that is pending transmission at the repeater AP.

[0250] If the CBF-TXOP is initiated by the repeater, it can do one or more of the following to reduce overhead. For example, it can reduce the amount of padding in the notification frame sent to the root AP, as the root AP may require (e.g., compared to the repeater) less time to prepare a response or a CBF data transmission. For example, it can perform only the TXOP handover to the root AP without communicating any information about the STAs of the repeater to the traffic (since the root AP may already know this).

[0251] References to “or” can be interpreted inclusively, such that any term described using “or” can indicate any one of a single, more than one, and all of the described terms. References to at least one of a list of terms can be interpreted as an inclusive or to indicate any one of a single, more than one, and all of the described terms. For example, a reference to “at least one of ‘A’ and ‘B’” can include only ‘A’, only ‘B’, and both ‘A’ and ‘B’. Such references used in conjunction with “comprising” or other open terms can include additional items.

[0252] Note that, for purposes of identifying or distinguishing one from another or others, certain paragraphs of this disclosure may refer to terms such as "first" and "second" with respect to subsets of transmitted spatial streams, sounding frames, responses, and devices. These terms are not intended to relate entities (e.g., a first device and a second device) solely in terms of time or sequence, but in some cases, these entities may include such a relationship. These terms also do not limit the number of possible entities (e.g., STAs, APs, beamformers, and / or beamformeess) that may operate in a system or environment. It should be understood that the above system may provide multiple ones of any or each of those components, and these components may be provided on a single machine or, in some embodiments, on multiple machines in a distributed system. Additionally, bit field positions may vary, and multi-bit words may be used. Further, the above system and method may be provided as one or more computer-readable programs or executable instructions embodied on or in one or more articles of manufacture (e.g., floppy disks, hard disks, CD-ROMs, flash memory cards, PROMs, RAMs, ROMs, or magnetic tapes). The programs may be implemented in any programming language (e.g., LISP, PERL, C, C++, C#) or in any byte code language (e.g., JAVA). The software programs or executable instructions may be stored as object code on or in one or more articles of manufacture.

[0253] Although the written description of the methods and systems above enables one of ordinary skill in the art to make and use their embodiments, one of ordinary skill in the art will understand and appreciate that there are variations, combinations, and equivalents to the specific embodiments, methods, and examples herein. Accordingly, the methods and systems of this disclosure should not be limited by the above embodiments, methods, and examples, but rather should be limited by all embodiments and methods within the scope and spirit of this disclosure.

Claims

1. A system, comprising: A first access point AP, configured to: Transmit a notification indicating a Coordinated Beamforming CBF Transmission Opportunity CBF TXOP to a second AP capable of participating in Coordinated Beamforming CBF and one or more first stations associated with the first AP; Receive, in response to the notification, a first response from at least a first station among the one or more first stations, identifying a first capability of the first station; Receive, in response to the notification, a second response from the second AP associated with one or more second stations, identifying a second capability of at least one of the second AP or a second station among the one or more second stations; And Transmit data to the first station during the CBF TXOP according to at least one of the first capability or the second capability.

2. The system according to claim 1, wherein the first AP is further configured to receive the second capability of the second station from the second AP in response to a second notification transmitted by the second AP to the one or more second stations including the second station, the second notification requesting the capabilities of the one or more second stations.

3. The system according to claim 1, wherein the one or more first stations are selected from a group of stations associated with the first AP based on at least one of the downlink channel state information of the group of stations associated with the first AP or the data traffic of the first AP to be transmitted to one or more stations in the group of stations.

4. The system according to claim 1, wherein the first AP is further configured to: Reduce the interference of the data transmitted to the first station relative to at least the second station.

5. The system according to claim 1, wherein at least one of the notification, the first response or the second response includes a Triggered Physical Protocol Data Unit TB PPDU.

6. The system according to claim 1, wherein the first AP is configured to: Select, for the CBF TXOP, one or more candidate stations of the first AP including the first station from the one or more first stations; and Insert an indication of the one or more candidate stations into the notification for the second AP to use for data transmission to the second station according to the CBF while reducing interference at the first station.

7. The system according to claim 6, wherein the indication includes at least one of the following: an identifier of the first station, a value of the number of spatial streams Nss identifying the first station, or a Resource Unit RU of a frequency range allocated to the first station within a channel used by the first AP.

8. The system according to claim 1, wherein the first AP is configured to: Parameters identifying the second capabilities of the second station from the second response, the parameters of the second capabilities corresponding to at least one of the following: the number of antennas of the second station, the amount of bandwidth of the second station, the sounding capabilities of the second station for channel sounding, the nulling capabilities of the second station for interference reduction, the downlink channel state information CSI of the second station relative to the first AP, the downlink CSI of the second station relative to the second AP, or a value identifying the number of spatial streams expected for the second station; and Transmit data to the first station according to the parameters of the second capabilities to reduce interference from the transmitted data at the second station.

9. The system according to claim 1, wherein the first AP is configured to: During the CBF TXOP, before transmitting the data to the first station, transmit a trigger frame to the second AP to initiate transmission of second data by the second AP.

10. A method, comprising: Transmitting, by a first access point AP, a notification indicating a coordinated beamforming CBF transmission opportunity CBF TXOP to a second AP capable of participating in CBF and one or more first stations associated with the first AP; Receiving, by the first AP in response to the notification, a first response identifying the first capabilities of the first station from at least the first station among the one or more first stations; Receiving, by the AP in response to the notification, a second response identifying the second capabilities of at least one of the second AP or a second station among the second one or more stations from the second AP associated with the second one or more stations; And Transmitting, by the first AP during the CBF TXOP, data to the first station according to at least one of the first capabilities or the second capabilities.

11. The method according to claim 10, comprising: Receiving, by the first AP, the second capabilities of the second station from the second AP in response to a second notification transmitted by the second AP to the second one or more stations including the second station, the second notification requesting the capabilities of the second one or more stations.

12. The method according to claim 11, wherein the one or more first stations are selected from the group of stations based on at least one of the downlink channel state information of the group of stations associated with the first AP or the data traffic of the first AP to be transmitted to one or more stations in the group.

13. The method according to claim 10, comprising: Reducing, by the first AP, interference of the data transmitted to the first station relative to at least the second station.

14. The method according to claim 10, wherein at least one of the notification, the first response, or the second response includes a trigger-based physical protocol data unit TB PPDU.

15. The method according to claim 10, comprising: Selecting, by the first AP from the one or more first stations, one or more candidate stations of the first AP including the first station for the CBF TXOP; And The first AP inserts an indication of the one or more candidate stations into the notification for the second AP to use for data transmission to the second station according to the CBF while reducing interference at the first station.

16. The method according to claim 15, wherein the indication includes at least one of the following: an identifier of the first station, a value of Nss identifying the number of spatial streams of the first station, or a resource unit RU of a frequency range allocated to the first station within a channel used by the first AP.

17. The method according to claim 10, comprising: The first AP identifies, from the second response, parameters of the second capabilities of the second station, the parameters of the second capabilities corresponding to at least one of the following: the number of antennas of the second station, the amount of bandwidth of the second station, the sounding capabilities of the second station for channel sounding, the nulling capabilities of the second station for reducing interference, the downlink channel state information CSI of the second station relative to the first AP, the downlink CSI of the second station relative to the second AP, or a value identifying the number of spatial streams expected to be used for the second station; and The first AP transmits data to the first station according to the parameters of the second capabilities to reduce interference from the transmitted data at the second station.

18. A system, comprising: An access point AP configured to: Receive a first notification for a CBF TXOP from a different AP, the first notification indicating a first capability; Transmit a second notification indicating a second capability to the different AP in response to the first notification; and Transmit data to at least one of one or more stations associated with the AP during the CBF TXOP in response to the first notification according to at least one of the first capability or the second capability.

19. The system according to claim 18, wherein the AP is configured to: Select the one or more stations from a group of stations associated with the AP based on at least one of the downlink channel state information of the group of stations associated with the AP or the data traffic of the AP to be transmitted to one or more of the group of stations; Transmit a third notification indicating the CBF TXOP to the one or more stations; and Receive a third response indicating a third capability of at least one of the one or more stations in response to the third notification.

20. The system according to claim 19, wherein the AP is configured to transmit the second notification and the third notification concurrently.

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