System and method for downlink channel sounding for multiple access points

Abstract

This disclosure describes systems and methods for downlink channel sounding with respect to multiple access points (multiple APs). The system may be configured to provide one or more probe options. In a joint sounding option, a station may measure a combined downlink channel from all APs and may provide feedback regarding a composite channel. In individual sounding options, the station may individually measure downlink channels from each AP and may provide feedback on individual channels. In an implicit sounding option, each AP may estimate an uplink channel transmitted by the station. The uplink channel information may then be used to derive a corresponding downlink channel.

Description

[0001] Cross-references to related patent applications

[0002] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 618,631, filed on January 8, 2024, and U.S. Provisional Application No. 63 / 594,538, filed on October 31, 2023, the contents of each of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure generally relates to systems and methods for wireless communications between access points and wireless communication devices, including but not limited to downlink channel sounding with respect to multiple access points. Background Art

[0004] The market for wireless communication devices has been growing due to the increased use of portable devices, increased connectivity, and data transfer between various devices. Digital switching technology has facilitated the large-scale deployment of affordable, easy-to-use wireless communication networks. Wireless communication can operate according to various standards, such as IEEE 802.11x (e.g., Wi-Fi technology), Bluetooth, Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA). Using such technology, wireless communication devices can be connected to local area networks and the Internet without physical cables, thereby communicating across various spaces and ranges through radio frequencies. Summary of the invention

[0005] The technical solution of the present disclosure is intended to facilitate downlink channel sounding with respect to multiple access points. Wireless communication technologies (e.g., coordinated beamforming (CBF) using nulling) may rely on downlink channel state information (CSI) to obtain better performance. However, obtaining downlink CSI across a basic service set (BSS) may bring technical challenges. In a configuration with multiple access points (APs) belonging to different BSSs, current networking standards may limit the ability of access points (APs) and stations (STAs) to collect CSI between them outside their own BSSs. For example, an AP (AP1) from BSS1 may wish to obtain the downlink channel status between another AP (AP2) from BSS2 and a STA associated with BSS2. This information can be used for technologies such as CBF, where nulling interference expects to understand the downlink channels between all relevant APs and STAs, even if they belong to different BSSs. As a result, the inability to collect downlink CSI across different BSSs may hinder the effectiveness of wireless communication technologies in environments with multiple APs. The technical solution described herein can overcome these challenges by introducing various sounding processes and frame sequences to obtain cross-BSS downlink CSI.

[0006] At least one aspect of the technical solution relates to a system. The system may include a first access point (AP) configured to transmit a null data packet advertisement (NDPA) frame to trigger a detection process for a first group of one or more stations of the first AP. The NDPA frame may include a station information field having an association identifier (AID) value. The system may include a second AP, which triggers a detection process for a second group of one or more stations of the second AP relative to the first AP in response to the AID value. Both the first AP and the second AP may be configured to send one of a joint null data packet (NDP) frame or a sequential NDP frame to the first group of one or more stations of the first AP and the second group of one or more stations of the second AP. The first group of one or more stations of the first AP and the second group of one or more stations of the second AP may be configured to measure a downlink (DL) channel from each of the first AP and the second AP to form a composite channel. The first AP may be configured to transmit a beamforming report (BFRP) frame for the composite channel. The first AP may be configured to receive a trigger-based physical layer protocol data unit (PPDU) from each station receiving the BFRP frame to provide channel state information (CSI) based on the composite channel.

[0007] The first AP and the second AP may exchange one or more parameters. The one or more parameters may include at least one of a carrier frequency offset (CFO) for frequency alignment or a sampling frequency offset (SFO) for timing alignment for wireless communication. The NDPA may include information indicating at least one of the following: the type of sounding process, the type of channel state information (CSI) requested, or information about beamforming configuration, timing, or duration. The BFRP frame may include data corresponding to one or more stations in the first group of one or more stations and the second group of one or more stations. The data may indicate at least one of the following: a modulation and coding scheme, a spatial stream allocation, or a resource unit of the one or more stations.

[0008] The triggered-based PPDU transmitted by each station may provide the CSI including at least one of: a beamforming report, a beamforming matrix index, a signal-to-noise ratio, or a measure of performance of a modulation scheme. The first AP may dynamically adjust beamforming parameters based on the received triggered-based PPDU feedback according to the performance of the downlink channel of each station in the first group of one or more stations. The first AP may coordinate with the second AP to synchronize the timing and parameters of the sounding process to ensure accurate measurement of the composite channel by the stations in both groups.

[0009] One aspect of the technical solution relates to a system. The system may include a second AP, which is configured to transmit a null data packet announcement (NDPA) frame to a second group of one or more stations within a basic service set (BSS) of the second AP. The NDPA may include a field for signaling the first AP to prepare for the transmission of a null data packet (NDP) frame. The first AP may be configured to transmit the NDP frame to trigger a detection process for a first group of one or more stations of the first AP and a second group of one or more stations of the second AP. The preamble of the NDP frame may identify the BSS of the second AP. The second group of one or more stations may receive the NDP frame to measure a downlink (DL) channel relative to the first AP. The second AP may be configured to transmit one or more beamforming report (BFRP) frames for measurement of a downlink channel from a second group of one or more stations relative to the first AP. The second AP may be configured to receive a trigger-based physical layer protocol data unit (PPDU) from each station of the second set of one or more stations receiving the one or more BFRP frames to provide channel state information (CSI) based on the downlink channel.

[0010] The field of the NDPA frame may include an association identifier (AID) having a predetermined value to trigger the first AP to prepare the NDP frame. The NDPA frame transmitted by the second AP may be configured to indicate the desired CSI to be provided to one or more stations of the BSS of the second AP and to signal the first AP to prepare the transmission of the NDP frame. The NDP frame transmitted by the first AP may signal a BSS color in a preamble corresponding to the BSS of the second AP.

[0011] The second group of one or more stations of the second AP may transmit the trigger-based PPDU in response to the one or more BFRP frames including one or more parameters. The trigger-based PPDU may include a compressed beamforming report (CBR) including one or more measurements of the downlink channel according to the one or more parameters. The NDPA frame and the one or more BFRP frames may each include one or more media access control (MAC) addresses and one or more association identifiers (AIDs) corresponding to one or more stations in the second group of one or more stations of the second AP. The first AP and the second AP may exchange communications to determine the type of CSI to be collected on the downlink channel and identify the type of the determined CSI in the one or more BFRP frames. The second AP may be configured to identify the stations in the first group that are to participate in coordinated beamforming (CBF) using nulling based at least on information about the stations in the first group of one or more stations of the first AP. The second AP may be configured to transmit the NDPA frame to the stations in the first group to request the CSI from the stations to configure the second AP for CBF.

[0012] One aspect of the technical solution relates to a system. The system may include a first access point (AP) configured to transmit an implicit null data packet announcement (NDPA) frame to solicit an uplink triggered NDP (T-NDP) frame from a first group of one or more stations of the first AP. The NDPA frame may include a field for signaling a second AP to prepare to receive a transmission of the T-NDP frame. The NDPA frame may identify one or more parameters for the transmission of the T-NDP frame. The first AP and the second AP may be configured to receive the T-NDP frame from the first group of one or more stations of the first AP. The first AP and the second AP may be configured to estimate a respective uplink channel based at least on the T-NDP frame.

[0013] The NDPA frame may further include parameters for the T-NDP. The parameters may include at least one of the following: bandwidth, number of long training fields (LTFs), length of LTFs, guard interval, spatial stream position, number of spatial streams, or allocation of resource units. The first group of one or more stations may estimate their respective carrier frequency offset (CFO) and sampling frequency offset (SFO) based at least on data about the first AP from the T-NDP frame. The first AP and the second AP may exchange their respective estimates of uplink channels and coefficients for mapping the respective estimates of uplink channels to one or more downlink channels. The first AP and the second AP may synchronize their reception of the T-NDP frame to concurrently estimate uplink channels.

[0014] At least one aspect of the technical solution relates to a method. The method may include a first access point (AP) transmitting a null data packet advertisement (NDPA) frame to trigger a detection process for a first group of one or more stations of the first AP. The NDPA frame may include a station information field having an association identifier (AID) value. The method may include a second AP triggering a detection process for a second group of one or more stations of the second AP relative to the first AP in response to the AID value. The method may include both the first AP and the second AP sending one of a joint null data packet (NDP) frame or a sequential NDP frame to the first group of one or more stations of the first AP and the second group of one or more stations of the second AP. The method may include the first group of one or more stations of the first AP and the second group of one or more stations of the second AP measuring a downlink (DL) channel from each of the first AP and the second AP to form a composite channel. The method may include the first AP transmitting a beamforming report (BFRP) frame for the composite channel. The method may include receiving, by the first AP, a trigger-based physical layer protocol data unit (PPDU) from each station that receives the BFRP frame to provide channel state information (CSI) based on the composite channel.

[0015] The method may include exchanging one or more parameters between the first AP and the second AP. The one or more parameters may include at least one of a carrier frequency offset (CFO) for frequency alignment or a sampling frequency offset (SFO) for timing alignment for wireless communication. The NDPA may include information indicating at least one of the type of the sounding process, the type of channel state information (CSI) requested, or information about beamforming configuration, timing, or duration. The BFRP frame may include data corresponding to one or more stations in the first group of one or more stations and the second group of one or more stations. The data may indicate at least one of the modulation and coding scheme, spatial stream allocation, or resource unit of the one or more stations.

[0016] The method may include the triggered-based PPDU transmitted by each station providing the CSI including at least one of: a beamforming report, a beamforming matrix index, a signal-to-noise ratio, or a measure of performance of a modulation scheme. The method may include the first AP dynamically adjusting beamforming parameters based on the received triggered-based PPDU feedback according to the performance of the downlink channel of each station in the first group of one or more stations. The method may include the first AP coordinating with the second AP to synchronize the timing and parameters of the sounding process to ensure accurate measurement of the composite channel by the stations in both groups.

[0017] One aspect of the technical solution relates to a method. The method may include a second AP transmitting a null data packet announcement (NDPA) frame to a second group of one or more stations within a basic service set (BSS) of the second AP. The NDPA may include a field for signaling the first AP to prepare for transmission of a null data packet (NDP) frame. The method may include the first AP transmitting the NDP frame to trigger a detection process for a first group of one or more stations of the first AP and a second group of one or more stations of the second AP. The preamble of the NDP frame may identify the BSS of the second AP. The method may include the second group of one or more stations receiving the NDP frame to measure a downlink (DL) channel relative to the first AP. The method may include the second AP transmitting one or more beamforming report (BFRP) frames for measurement of a downlink channel from a second group of one or more stations relative to the first AP. The method may include the second AP receiving a trigger-based physical layer protocol data unit (PPDU) from each of the second group of one or more stations receiving the one or more BFRP frames to provide channel state information (CSI) based on the downlink channel.

[0018] The field of the NDPA frame may include an association identifier (AID) having a predetermined value to trigger the first AP to prepare the NDP frame. The method may include the NDPA frame transmitted by the second AP indicating the desired CSI to be provided to one or more stations of the BSS of the second AP and signaling the first AP to prepare the transmission of the NDP frame. The method may include the NDP frame transmitted by the first AP signaling a BSS color in a preamble corresponding to the BSS of the second AP.

[0019] The method may include transmitting the trigger-based PPDU by the second group of one or more stations of the second AP in response to the one or more BFRP frames including one or more parameters. The trigger-based PPDU may include a compressed beamforming report (CBR) including one or more measurements of the downlink channel according to the one or more parameters. The NDPA frame and the one or more BFRP frames may each include one or more media access control (MAC) addresses and one or more association identifiers (AIDs) corresponding to one or more stations in the second group of one or more stations of the second AP. The method may include the first AP exchanging communications with the second AP to determine a type of CSI to be collected on the downlink channel, and identifying the type of the determined CSI in the one or more BFRP frames. The method may include the second AP identifying the stations in the first group that are to participate in coordinated beamforming (CBF) using nulling based at least on information about the stations in the first group of one or more stations of the first AP. The method may include the second AP transmitting the NDPA frame to the stations in the first group to request the CSI from the stations to configure the second AP for CBF.

[0020] An aspect of the technical solution relates to a method. The method may include a first access point (AP) transmitting an implicit null data packet announcement (NDPA) frame to solicit an uplink triggered NDP (T-NDP) frame from a first set of one or more stations of the first AP. The NDPA frame may include a field for signaling a second AP to prepare to receive a transmission of the T-NDP frame. The method may include the NDPA frame identifying one or more parameters for the transmission of the T-NDP frame. The method may include the first AP and the second AP receiving the T-NDP frame from the first set of one or more stations of the first AP. The method may include the first AP and the second AP estimating respective uplink channels based at least on the T-NDP frame.

[0021] The NDPA frame may further include parameters for the T-NDP. The parameters may include at least one of: bandwidth, number of long training fields (LTFs), length of LTFs, guard interval, spatial stream position, number of spatial streams, or allocation of resource units. The method may include the first group of one or more stations estimating their respective carrier frequency offset (CFO) and sampling frequency offset (SFO) based at least on data about the first AP from the T-NDP frame. The method may include the first AP exchanging with the second AP respective estimates of their uplink channels and coefficients for mapping the respective estimates of the uplink channels to one or more downlink channels. The method may include the first AP synchronizing with the second AP their reception of the T-NDP frame to concurrently estimate the uplink channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various objects, aspects, features and advantages of the present disclosure will become more apparent and better understood by referring to the detailed description taken in conjunction with the accompanying drawings, wherein similar reference characters identify corresponding elements throughout. In the accompanying drawings, similar reference numerals generally indicate identical, functionally similar and / or structurally similar elements.

[0023] Figure 1A is a block diagram depicting a network environment including one or more access points in communication with one or more devices or stations;

[0024] 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;

[0025] Figure 2 An example system is described for coordinated partial rank zeroing in a multi-AP and multi-STA environment;

[0026] Figure 3 is an example plot of the signal space of STA transmissions in the context of single AP partial rank zeroing;

[0027] Figure 4 is an example drawing of two signal spaces transmitted by two STAs in the context of 2AP coordinated partial rank zeroing;

[0028] Figure 5 An example system is described for downlink channel sounding with respect to multiple access points;

[0029] Figure 6 is an example process for implementing a method for joint downlink channel detection for multiple access points;

[0030] Figure 7 is another example process for implementing a method for joint downlink channel sounding for multiple access points;

[0031] Figure 8 is another example process for implementing a method for joint downlink channel sounding for multiple access points;

[0032] Fig. 9 is another example process for implementing a method for joint downlink channel sounding for multiple access points;

[0033] Fig.10 is another example process for implementing a method for joint downlink channel sounding for multiple access points;

[0034] Fig.11 is an example process for implementing a method for individual downlink channel sounding for multiple access points;

[0035] Fig.12 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0036] Fig.13 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0037] Fig.14 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0038] Fig.15 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0039] Fig.16 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0040] Fig.17 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0041] Fig.18 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0042] Fig.19 is another example process for implementing a method for individual downlink channel sounding for a plurality of access points;

[0043] Fig. 20 is an example process for implementing a method for implicitly probing downlink channels with respect to multiple access points;

[0044] Fig.21 is another example process for implementing a method for implicitly probing downlink channels for multiple access points; and

[0045] Fig. 22 is another example process for implementing a method for implicitly probing downlink channels with respect to multiple access points.

[0046] The details of various embodiments of the method and system are set forth in the accompanying drawings and the description below. DETAILED DESCRIPTION

[0047] The following IEEE standards (including any draft versions of such standards) are hereby incorporated by reference in their entirety and are 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 ;IEEEP802.11ac TM ; and IEEE P802.11be TM to IEEE P802.11bn TM Although the present disclosure may refer to aspects of these standards, the present disclosure is in no way limited to these standards.

[0048] For the purpose of reading the description of the various embodiments below, the following description of the sections of the specification and their corresponding contents may be helpful:

[0049] - Section A describes a network environment and a computing environment that can be used to practice the embodiments described herein;

[0050] - Section B describes coordinated partial rank zeroing in multi-AP transmission.

[0051] - Section C describes an embodiment of downlink channel sounding with respect to multiple access points.

[0052] A. Computing and network environment

[0053] Before discussing specific embodiments of the present solution, it may be helpful to describe aspects of the operating environment and associated system components (eg, hardware elements) in conjunction with the methods and systems described herein. Figure 1A , depicting an embodiment of a network environment. In brief overview, the network environment includes a wireless communication system that includes one or more access points (APs) or network devices 106, one or more stations or wireless communication devices 102, and network hardware components or network hardware 192. The wireless communication device 102 may, for example, include a laptop computer, a tablet computer, a personal computer, and / or a cellular telephone device. Reference Figure 1B and1C The details of the embodiments of each station or wireless communication device 102 and AP or network device 106 are described in more detail. In one embodiment, the network environment may be an ad hoc network environment, an infrastructure wireless network environment, a subnet environment, etc. The network device 106 or AP may be operably coupled to the network hardware 192 via a local area network connection. In some embodiments, the network device 106 is a 5G base station. The network hardware 192, which may include routers, gateways, switches, bridges, modems, system controllers, appliances, etc., may provide a local area network connection for the communication system. Each of the network devices 106 or APs may have an associated antenna or antenna array to communicate with wireless communication devices in its area. The wireless communication device 102 may register with a specific network device 106 or AP to receive services from the communication system (e.g., via SU-MIMO or MU-MIMO configuration). For direct connections (e.g., point-to-point communications), some wireless communication devices may communicate directly via allocated channels and communication protocols. Some of the wireless communication devices 102 may be mobile or relatively stationary relative to the network device 106 or AP.

[0054] 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 wireless fidelity (Wi-Fi) or other standards. The network device 106 or AP may sometimes be referred to as a wireless access point (WAP). The network device 106 or AP may be implemented (e.g., configured, designed and / or constructed) for operation in a wireless local area network (WLAN). In some embodiments, the network device 106 or AP may be connected to a router (e.g., via a wired network) as a standalone device. In other embodiments, the network device 106 or AP may be a component of a router. The network device 106 or AP may provide access to a network to multiple devices. The network device 106 or AP may, for example, be connected 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 may be implemented to support standards for sending and receiving data using one or more radio frequencies. Those standards and the frequencies they use may be defined by IEEE (e.g., IEEE 802.11 standards). The network device 106 or AP may be configured and / or used to support public Internet hotspots and / or to extend the Wi-Fi signal range of the network on the network.

[0055] In some embodiments, the access point or network device 106 may be used for a wireless network (e.g., IEEE 802.11, Bluetooth, ZigBee, any other type of radio frequency based network protocol and / or variants thereof) (e.g., in a home, in a car, or in a building). Each of the wireless communication devices 102 may include a built-in radio and / or be coupled to a radio. Such wireless communication devices 102 and / or access points or network devices 106 may 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 may 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.

[0056] The network connection may include any type and / or form of network, and may include any of the following: a point-to-point network, a broadcast network, a telecommunications network, a data communications network, a computer network. The network topology may be a bus, a star, or a ring network topology. The network may be any such network topology known to those of ordinary skill in the art that is capable of supporting the operations described herein. In some embodiments, different types of data may be transmitted via different protocols. In other embodiments, the same type of data may be transmitted via different protocols.

[0057] The communication device 102 and the access point or network device 106 may be deployed as and / or executed on any type and form of computing device, such as a computer, network device, or appliance capable of communicating over any type and form of network and performing the operations described herein. Figure 1B and 1C A block diagram of a computing device 100 is depicted that may be used to practice embodiments of a wireless communication device 102 or a network device 106. Figure 1B and 1C As shown in FIG. 1 , each computing device 100 includes a processor 121 (eg, a central processing unit) and a main memory unit 122. Figure 1B As shown in FIG. 1 , computing device 100 may include storage device 128, installation device 116, network interface 118, I / O controller 123, display devices 124a to 124n, keyboard 126, and pointing device 127 (e.g., mouse). Storage device 128 may include an operating system and / or software. Figure 1C As shown in , each computing device 100 may 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.

[0058] 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 those manufactured by Intel Corporation of Santa Clara, California; by International Business Machines of White Plains, New York; or by Advanced Micro Devices of Sunnyvale, California. The computing device 100 may be based on any of these processors, or any other processor capable of operating as described herein.

[0059] The main memory unit 122 may 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 static random access memory (SRAM), dynamic random access memory (DRAM), ferroelectric RAM (FRAM), NAND flash memory, NOR flash memory, and any type or variation of solid-state drive (SSD). The main memory unit 122 may be based on any of the above-mentioned memory chips, or any other available memory chip capable of operating as described herein. Figure 1B In the embodiment shown in , processor 121 communicates with main memory unit 122 via system bus 150 (described in more detail below). Figure 1C An embodiment of the computing device 100 is depicted in which the processor communicates directly with the main memory unit 122 via the memory port 103. For example, in Figure 1C In the embodiment, the main memory unit 122 may be a DRDRAM.

[0060] Figure 1C An embodiment is depicted in which the main processor 121 communicates directly with the cache memory 140 via a secondary bus (sometimes referred to as a backside bus). In other embodiments, the main processor 121 communicates with the cache memory 140 using the system bus 150. 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. Figure 1C, the processor 121 communicates with various I / O devices 130 via a local system bus 150. Various buses may be used to connect the central processing unit or processor 121 to any of the I / O devices 130, such as a VESA VL bus, an ISA bus, an EISA bus, a Micro Channel Architecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or a NuBus. For embodiments in which the I / O device is a video display 124, the processor 121 may communicate with the display 124 using an Advanced Graphics Port (AGP). Figure 1C An embodiment of a computer or computer system 100 is depicted in which the main processor 121 can communicate directly with the I / O device 130b, such as via HYPERTRANSPORT, RAPIDIO, or INFINIBAND communication technology. Figure 1C Also depicted is an embodiment in which local busses and direct communications are mixed: processor 121 communicates with I / O device 130a using a local interconnect bus while communicating directly with I / O device 130b.

[0061] There may be a variety of I / O devices 130a to 130n in the computing device 100. Input devices include keyboards, mice, trackpads, trackballs, microphones, dials, touchpads, touch screens, and drawing tablets. Output devices include video displays, speakers, inkjet printers, laser printers, projectors, and thermal sublimation printers. Figure 1B , the I / O devices may be controlled by an I / O controller 123. The I / O controller may control one or more I / O devices, such as a keyboard 126 and a pointing device 127, such as a mouse or an optical pen. In addition, the I / O devices may also provide storage and / or installation media for the computing device 100. In yet other embodiments, the computing device 100 may provide a USB connection (not shown) to accept a handheld USB storage device, such as the USB flash drive family of devices manufactured by Twintech Industry, Inc. of Los Alamitos, California.

[0062] Reference again Figure 1B, the computing device 100 may support any suitable installation device 116, such as a disk drive, a CD-ROM drive, a CD-R / RW drive, a DVD-ROM drive, a flash drive, a tape drive of various formats, a USB device, a hard drive, a network interface, or any other device suitable for installing software and programs. The computing device 100 may further include a storage device, such as one or more hard drives or redundant arrays of independent disks, for storing an operating system and other related software and for storing application software programs (e.g., any program or software 120 used to implement (e.g., configured and / or designed for) the systems and methods described herein). Optionally, any of the installation devices 116 may also be used as a storage device. In addition, the operating system and software may be run from a bootable media.

[0063] In addition, the computing device 100 may include a network interface 118 to interface to a network through various connections, including, but not limited to, a standard telephone line, a LAN or WAN link (e.g., 802.11, T1, T3, 56kb, X.25, SNA, DECNET), a broadband connection (e.g., ISDN, Frame Relay, ATM, Gigabit Ethernet, Ethernet-over-SONET), a wireless connection, or some combination of any or all of the above. The connection may be established using 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). In one embodiment, 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). Network interface 118 may include a built-in network adapter, a network interface card, a PCMCIA network card, a card bus network adapter, a wireless network adapter, a USB network adapter, a modem, or any other device suitable for interfacing computing device 100 to any type of network capable of communicating and performing the operations described herein.

[0064] In some embodiments, the computing device 100 may include or be connected to one or more display devices 124a to 124n. Thus, any of the I / O devices 130a to 130n and / or the I / O controller 123 may include any type and / or form of appropriate hardware, software, or combination of hardware and software to support, enable, or provide for connection and use of the display device(s) 124a to 124n by the computing device 100. For example, the computing device 100 may include any type and / or form of video adapter, video card, driver, and / or library to interface, communicate, connect, or otherwise use the display device(s) 124a to 124n. In one embodiment, the video adapter may include multiple connectors to interface to the display device(s) 124a to 124n. In other embodiments, the computing device 100 may include multiple video adapters, each of which is connected to the display device(s) 124a to 124n. In some embodiments, any portion of the operating system of the computing device 100 may be configured for use with the multiple display devices 124a to 124n. In further embodiments, the I / O device 130 may be a bridge between the 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 FireWire 800 bus, an Ethernet bus, an AppleTalk bus, a Gigabit Ethernet bus, an Asynchronous Transfer Mode bus, a FibreChannel bus, a fiber optic bus, a Serial Attached Small Computer System Interface bus, a USB connection, or an HDMI bus.

[0065] Figure 1B and 1CA computing device 100 of the type depicted in the 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 the Unix and Linux operating systems, any version of the 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 a computing device and performing the operations described herein. Typical operating systems include (but are not limited to): Android produced by Google Inc.; WINDOWS 7, 8 and 10 produced by Microsoft Corporation in Redmond, Washington; MAC OS produced by Apple Computer in Cupertino, California; WebOS produced by Research In Motion (RIM); OS / 2 produced by International Business Machines in Armonk, New York; and Linux, a free-to-use operating system released by Caldera, Inc. in Salt Lake City, Utah, or any type and / or form of Unix operating system and other operating systems.

[0066] The computer system or computing device 100 may be any workstation, phone, desktop computer, laptop or notebook computer, server, handheld computer, mobile phone or other portable telecommunication device, media playback device, gaming system, mobile computing device, or any other type and / or form of computing, telecommunication or media device capable of communication. In some embodiments, the computing device 100 may have a different processor, operating system, and input device consistent with the device. For example, in one embodiment, the computing device 100 is a smart phone, mobile device, tablet computer, or personal digital assistant. In addition, 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 telecommunication device capable of communication and having sufficient processor power and memory capacity to perform the operations described herein.

[0067] Aspects of the operating environment and components described above will become apparent in the context of the systems and methods disclosed herein.

[0068] B. Coordinated Partial Rank Zeroing in Multi-Ap Transmission

[0069] When an AP transmits data to a specific intended recipient STA within its own basic service set (BSS), other STAs within the same or neighboring BSS (e.g., other WLANs) may be within range of the transmitting AP and experience interference. Interference may include any undesired interruption or degradation of a signal, communication, or system due to the presence of external signals, noise, or other factors that interfere with the intended transmission or reception of information. For example, when transmissions to different STAs occur simultaneously on the same channel, the interference caused by the transmissions may be difficult to resolve because the information from one or more of the transmissions may be unknown, and the relationship between the transmissions may be unknown. Such interference may result in delays, latency, or network packet loss, making data transmission within such networks more difficult, adversely affecting the user experience.

[0070] The technical solution of the present disclosure overcomes these challenges by providing or facilitating multi-AP coordinated beamforming (CBF) using nulling, where APs from different BSSs (e.g., WLANs) can configure their transmissions to send along spatial directions or vectors at which interference from these APs is minimized at unintended recipient STAs or clients. The technical solution may include client devices (STAs) that receive spatial streams from APs of their respective networks. A network (e.g., a WLAN of a particular AP) may include one or more basic service sets (BSSs) having APs and one or more STAs configured for wireless communication via the same AP (e.g., by configuring a local WLAN to the AP). Since an AP can transmit any number of data streams to any number of STAs within its BSS, STAs with unintended data streams may be within the wireless communication range of the transmitting AP and experience interference. The technical solution of the present disclosure may utilize the spatial orientation of unintended STA recipients and the beamforming capabilities of the AP to transmit data streams to its intended STAs along the spatial orientation where these transmissions are partially nulled at the locations of the unintended recipients. Thus, the technical solution of the present solution allows multiple APs to communicate at the same time and frequency (eg, transmit simultaneously on the same channel) while avoiding interference, thereby improving transmission throughput, reducing latency and minimizing spectrum usage to avoid interference.

[0071] The technical solutions of the present disclosure may include systems and methods of multi-AP coordinated beamforming (CBF) using nulling to facilitate coordinated partial rank nulling in multi-AP transmissions. CBF using nulling may include one of the candidate features being considered for next generation Wi-Fi standards (UHR, 11bn). Nulling may include any reduction or elimination of unwanted signals or interference at a receiver, such as by adjusting the phase and amplitude of an incoming signal. Nulling may include a technique in which an AP minimizes interference experienced by a STA by selectively reducing the strength or power of unwanted signals from other sources. Nulling may include a technique in which a system may combine one signal with another to create a null (e.g., eliminating the original signal). Nulling may be utilized or included to minimize AP interference seen by a STA due to transmissions of the AP to other STAs (in the same or different BSS as the first STA).

[0072] Partial rank nulling (also sometimes referred to as partial nulling) may include the AP minimizing (e.g., reducing to below an acceptable threshold) interference in a fewer number of dimensions or directions than the STA can receive. For example, partial rank nulling may include a technique for minimizing or reducing undesired signals or interference (e.g., to below an acceptable threshold level) without removing interference. For example, if a STA has two receive antennas (i.e., can receive signals in two dimensions or directions), partial rank nulling may minimize interference along only one dimension or direction seen by the STA. The present solution may provide a mechanism for coordinated partial rank nulling that minimizes interference at the STA for its own BSS and other BSSs (OBSSs) in which the AP concurrently transmits communications. The technical solution may also include an AP coordination mechanism to achieve the above-described partial rank nulling.

[0073] Partial rank zeroing for one's 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 zeroing can be used to improve overall system performance by reducing interference between multiple communication devices. For example, multiple devices can transmit and receive data via their antennas at the same time. Due to the spatial proximity between the devices, interference may occur between different devices. Interference can degrade the performance of the system, resulting in reduced data rates and reduced overall capacity. Partial rank zeroing for one's own BSS and other BSS access points can solve this problem by selectively zeroing the interference at the unintended receiving STA.

[0074] Reference now Figure 2, illustrating an example of a system 200 for implementing coordinated partial rank zeroing for multi-AP transmissions. The system 200 may include one or more access points (APs) 106 (e.g., Wi-Fi routers) that provide transmissions to stations or STAs 102 within their BSSs 250. The APs 106 may also have a wireless transmission range 255 that may include STAs 102 outside their BSSs (e.g., STAs that are not configured to a WLAN of a corresponding AP but are still able to receive transmissions or interference from these APs).

[0075] Figure 2 A first AP 106 and a second AP 106 may be included, the first AP 106 having a first BSS 250 including the first station 102 and the third station 102, and the second AP 106 having a second BSS 250 including the second station 102 and the 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, antennas 220, and spatial streams 240. Each of the STAs 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 spatial streams 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 that may cover or include the STAs 102 of its own BSS 250, and the STAs 102 outside its BSS 250. For example, the first range 255 of the first AP 106 may include the second STA 102 (e.g., a BSS from the second AP 106) in addition to the first and third STAs 102. Similarly, the second AP 106 may have a second signal range 255 that may include the first STA 102 (e.g., a BSS from the first AP 106) in addition to the second and fourth STAs 102.

[0076] Figure 2 An environment may be described in which APs 106 may coordinate their transmissions according to their previously negotiated and configured partial rank nulling. For example, system 200 may be used to provide single-AP partial rank nulling (e.g., partially nulling interference to non-receiving STAs within a BSS of a transmitting AP) and multi-AP partial rank nulling (e.g., partially nulling interference to non-receiving STAs within the same or different BSS relative to the transmitting AP).

[0077] The AP 106 may include any combination of hardware and software that allows wireless communication devices (e.g., STA 102) to wirelessly connect to a wired network or the World Wide Web or the Internet. The AP 106 may include any combination of hardware and software for facilitating wireless communication within the AP's WLAN for any STA 102 included in its BSS 250. The AP 106 may include one or more communication devices (e.g., Wi-Fi routers, switches, Bluetooth hubs, cellular network base stations), and may utilize any wireless communication protocol or standard (e.g., 802.11bn) for wireless communication.

[0078] The APs 106 and STAs 102 may be configured for wireless communication in a wireless communication network, such as a LAN, WAN, or cellular network. For example, each AP 106 may 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 of its own basic service set (BSS).

[0079] BSS 250 may include any one or more APs and client devices (e.g., STA 102) coupled to the APs within a specific coverage area (e.g., range 255). BSS 250 may provide infrastructure for AP 106 to provide network communications to STA 102 within its frequency coverage area. Within BSS 250, AP 106 may manage data distribution to various connected devices (e.g., STA 102), facilitate implementation of security protocols or functions, and roam as STA 102 may move in and out of its coverage area (e.g., range 255). Range 255 may include an area where signals from AP 106 may reach a receiving STA 102. The range 255 may include STAs 102 within the BSS 250 of a given AP 106 or STAs 102 that are part of the BSS 250 of another AP 106, for example, such as a first STA 102 that is part of a first BSS 250 of a first AP 106, but is also within a second range 255 of a second AP 106 that serves second and fourth STAs 102 of a second BSS 250.

[0080] The coordinator 205 may include any combination of hardware and software for coordinating communications between the APs 106 and / or the STAs 102. The coordinator 205 may include functionality (e.g., an application, computer code, or program) that facilitates coordination of communications (e.g., transmissions) between the APs 106 and the STAs 102 or among the APs 106. The coordinator 205 may include functionality for implementing a coordination phase to identify STAs 102 to which interference may be fully or partially nulled and exchanging STA 102 information between the APs 106. The coordinator 205 may include functionality for coordinating timing and frequency (e.g., exchanging timing and frequency information (e.g., communication bands or channels) between the APs 106). The coordinator 205 may generate, facilitate, implement, and apply settings or configurations to the APs 106 and / or the STAs 102 to facilitate coordinated partial rank nulling.

[0081] The coordinator 205 may include precoder functionality, such as a precoder algorithm for calculating a beamforming vector for each STA 102 to achieve partial rank zeroing. The precoder may include functionality for calculating a direction or vector for beamforming transmissions to the STA 102. The precoder may include functionality for utilizing information or data about a direction or vector at which interference at the STA 102 is minimized or reduced to a threshold below an acceptable interference level (e.g., achieving partial rank zeroing) to determine a direction or vector for beamforming transmissions to perform partial rank zeroing at such STA 102.

[0082] The coordinator 205 may include functionality for performing channel sounding for the STA 102. For example, the coordinator 205 may facilitate, instruct, or request each STA to measure one or more MIMO channels of each probing AP and provide the measurements back 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 estimates of the MIMO channels of the probing APs with the STA 102 (e.g., via a compressed beamforming report format (CBR) as provided in 802.11, or in Cartesian form). The coordinator 205 may exchange information of interfering APs 106 (e.g., APs 106 from external BSSs 250), such as when the STA 102 provides a linear transformation of the MIMO channel from the particular 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, a linear transformation of the MIMO channel may represent a projection onto one or more eigenmodels of the MIMO channel measured between the STA and the STA's own BSS's AP 106. For example, if the STA is receiving a particular number of expected spatial streams from its own AP 106 (e.g., the AP 106 from the STA's own BSS 250), the coordinator 205 may exchange (e.g., receive) a set of directions in which the AP 106 will minimize interference.

[0083] The coordinator 205 may include functionality for facilitating or performing channel sounding for the STAs 102. Channel sounding may include transmitting sounding information (e.g., a signal) and in response, receiving characteristics (e.g., signal strength, delay, and phase), and then using such received characteristics to determine the quality of the communication channel. The coordinator 205 may transmit (e.g., individually or jointly with the APs 106 of other BSSs 250) one or more null data packets (NDPs). The NDPs may be synchronized in time and / or frequency (e.g., between 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. The jointly transmitted NDP may be preceded by one or more NDP announcement (NDPA) frames. For example, the AP 106 may transmit an NDPA to all detected STAs 102 on behalf of all APs 106 performing channel sounding. For example, each of the APs 106 sends an NDPA to its own STA 102 in sequence. For example, all APs 106 transmit their NDPAs simultaneously but separately in frequency (e.g., via OFDMA), with each AP 106 addressing the STAs 102 within its own BSS 250. For example, the coordinator 205 may provide or facilitate a trigger frame transmitted by the APs 106, based on which all APs 106 participating in channel sounding may synchronize their carrier frequency offsets (CFOs) and the start times of their coordinated transmissions.

[0084] The communication controller 210 may include any combination of hardware and software for implementing wireless communications between the AP 106 and the STAs 102. The communication controller 210 may include functionality for providing and transmitting data (e.g., spatial streams) to the intended STAs 102. The communication controller 210 may transmit messages to the STAs 102, such as asking for information, data, or descriptions of directions or vectors 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 transmissions of the spatial streams 240 according to partial rank zeroing. For example, the communication controller 210 may configure the antenna 220 and any other settings to facilitate or implement transmissions of the spatial streams 240 according to a particular direction or vector (e.g., as determined by the coordinator 205) to implement partial rank zeroing at a particular STA 102. The communication controller 210 may control, manage, and implement transmissions (e.g., communications) according to timing and frequency (e.g., a selected channel or frequency band) and in the direction or vector in which the partial rank zeroing is implemented.

[0085] The AP 106 and / or the STA 102 may include a communication controller 210 to facilitate wireless communications with each other. The communication controller 210 may include and / or utilize a wireless communication interface, such as hardware and software, including transceivers, antennas, RF interfaces, ports, and processing devices, to facilitate communications via standards such as 802.11a / b / g / n / ac / ax, Bluetooth, cellular (e.g., 3G, 4G, 5G), Zigbee, Z-Wave, NFC, and others. The communication controller 210 may control the reception and transmission of signals, data, or messages to facilitate or implement multi-AP transmissions using coordinated partial rank zeroing.

[0086] The AP 106 may include a nulling function 215 for implementing nulling or partial rank nulling according to coordinated (e.g., agreed upon) communications between the APs 106. Partial rank nulling may include any technique or action in array signal processing for suppressing interference from signals from a particular direction while retaining signals coming from other directions. For example, partial rank nulling may include manipulating the array response to create a null or zero 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 undesirable signals or interference at a receiver (e.g., STA 102), for example, by adjusting the phase and amplitude of the incoming signal. The nulling function 215 may include any combination of hardware and software for minimizing or reducing undesirable signals or interference (e.g., to below an acceptable threshold level), such as without requiring complete removal of the interference.

[0087] The nulling function 215 may include functionality 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 transmission signal moves, is oriented, or is directed (e.g., as a vector), and may be specified by its location 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., sounding signals) measured from multiple angles, directions, or vectors, and identify the angle, direction, or vector from, along, or at which 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 interference is lowest or reduced to below a threshold (e.g., partial rank nulling). The nulling function 215 may then select the direction, angle, or vector corresponding to the lowest interference as the direction in which to partially null the signal from the AP 106.

[0088] AP 106 and station 102 may include antenna 220. Antenna 220 may include any transmit or receive antenna. Antenna 220 may include or be coupled to a communication chain 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).

[0089] The AP 106 and the station 102 may communicate spatial streams 240 (e.g., a spatial stream M of the AP 106 intended for a particular STA 102, or a total number of spatial streams N transmitted by the AP 106). The spatial stream 240 may include any data stream transmitted or received through 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 transmitting on multiple antennas, each spatial stream may use a unique beamforming vector, which may be different from the vectors used for other spatial streams transmitted on the same set of antennas. The spatial stream 240 may provide or facilitate improved throughput and reliability by using multiple antennas to create distinct data paths. The spatial stream 240 may be suitable for directivity control and transmission with partial rank zeroing.

[0090] The system 200 may include or use any number of spatial streams 240, including any independent data streams transmitted simultaneously on multiple antennas in a MIMO (multiple input multiple output) system. The system 200 may include a STA 102, which may be configured to communicate with a wireless network (e.g., a WLAN of a BSS 250) to receive and transmit data. The system 200 may allow the 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 the AP 106, which may minimize interference in several dimensions / directions. The number of dimensions or directions in which partial rank zeroing may reduce interference may be less than the number of spatial streams 240 that the STA 102 may receive. For example, if the STA has two receive antennas 220 (e.g., may receive signals in two dimensions or directions), then partial rank zeroing may minimize interference along one dimension or direction seen by the STA 102.

[0091] The number of spatial streams 240 that the STA 102 can support can vary based on the capabilities of the network and the MIMO configuration. For example, if the STA 102 has multiple receive antennas 220 and the network is configured for 2x2 MIMO, the STA 102 can simultaneously receive two spatial streams 240. Each spatial stream 240 can carry independent data, effectively increasing data capacity and improving overall throughput, data rate, increased system capacity, and / or wireless network reliability.

[0092] Referring now to Figure 3 , an example of a plot 300 of a transmitted signal space 302 received by STA102 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 BSS250 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.

[0093] For example, AP1 can transmit N = 3 spatial streams 240 to multiple STAs 102 within its BSS250 via downlink (DL) MU-MIMO. 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 transmission on the signal space 302 of STA1 is 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.

[0094] 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.

[0095] AP1 106 may include an appropriately constructed long training field (LTF) in its transmission so that STA1 102 may estimate both: i) the direction of its M expected streams, and (ii) the M different directions in which interference is minimized. The technical solution may include or provide a framework for a scenario in which an arbitrary number of APs 106 perform partial rank nulling toward an arbitrary number of STAs 102. For example, when two APs 106 are utilized, prior to implementing coordinated transmissions, a first AP 106 (e.g., AP1) and a second AP 106 (e.g., AP2) may perform coordination (e.g., during a coordination phase), wherein messages may be exchanged between AP1 and AP2 to identify each receiving STA for which interference is to be fully or partially nulled. For example, an AP 106 may identify a STA 102 that has more receive antennas than its expected spatial streams (e.g., antennas K=2, and received streams N=10, of which only M=1 are intended for the STA).

[0096] Such identified STAs may include interference that is sufficiently significant as seen from the OBSS AP to include nulling (e.g., the STA may have an interference signal strength or power above a certain threshold). For example, the threshold may include a background signal noise level, or a multiple of 2, 3, 4, 5, 10, or more of the background noise level. For example, the threshold may be defined with reference to other signals, such as the received signal strength, amplitude, or power of an expected stream (e.g., 1 / 2, 1 / 3, 1 / 4, or 1 / 8 of the signal strength, amplitude, or power of an expected received spatial stream).

[0097] For each STA identified to have its interference stream partially nulled, AP1 and AP2 may identify a set of linearly independent receive directions where interference from both APs will be minimized. Linearly independent receive directions may include distinct and unrelated paths, directions, or channels through which signals may be received by multiple receive antennas 220. AP1 and AP2 may dynamically change such a set of directions from one coordinated transmission to the next depending on: i) other receive STAs, and ii) the number of spatial streams expected for each STA.

[0098] 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 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 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.

[0099] Now refer 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 with coordinated partial rank nulling implemented by AP1 and AP2 in a multi-AP transmission example. Figure 4 This can correspond to an example where the present technical solution utilizes two APs 106 (e.g., 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 receiving 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 AP1 is minimized.

[0100] AP1 and AP2 may each transmit a total number N=2 spatial streams 240, of which only M=1 spatial stream 240 is intended to be received by STAs 102 of the respective transmitting AP 106's own BSS 250, where each receiving STA 102 includes K=2 receive antennas 220. For example, for STA1, the remaining one spatial stream from AP1 and two spatial streams from AP2 may produce interference that will be partially nulled. As illustrated, a total of three spatial streams are partially nulled (e.g., with Figure 4 The X-axis or X-direction in FIG.

[0101] As shown in plot 402, the interference stream 412 from AP1 and the interference 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 of AP1 is directed along a different direction (e.g., closer to the Y direction or more closely aligned with the Y direction) and is therefore 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) may 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 streams to be received at STA1. For example, the threshold may be as high as 5% of the total received signal strength of the desired spatial stream. For example, depending on the design, the threshold may be as high as 5%, 10%, 15%, 20%, 30%, or greater than 30%.

[0102] Similarly, as shown in plot 404, interfering streams 410 and 412 from AP1 and interfering stream 416 from AP2 are directed along the X direction of STA2 received signal space 408, and their signals are also minimized or removed along the Y direction, while the intended 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 is therefore not removed or minimized along the Y direction and is received by STA2. In some implementations, AP1 and AP2 may transmit streams 410, 412, 414, and 416 simultaneously in the presence and range of STA1 and STA2, and interference and non-interference of the streams may occur simultaneously. Therefore, AP1 and AP2 may transmit spatial streams to their own respective STAs 102 simultaneously and in a coordinated manner (e.g., at the same time and frequency), using partial rank zeroing to prevent interference to unintended STAs 102.

[0103] In one example, as part of the coordination phase, the APs 106 (e.g., AP1 and AP2) can exchange information about precoder algorithms used to calculate beamforming vectors for each STA 102 (e.g., STA1 and STA2) to achieve partial rank zeroing. For example, as part of the coordination phase, the APs 106 can exchange information, data, or descriptions of directional vectors in which interference is to be minimized at the receive antenna 220 of each STA. For example, as part of the coordination phase, a single AP 106 can calculate beamforming vectors for all spatial streams and share these vectors with other participating APs.

[0104] Using the information exchanged during the coordination phase, the receive directions in which interference is minimized for each STA 102 may be determined or generated based on or using a policy, such as a policy specified in a standard. The selection of a policy may be fixed as a "default" implementation, or may be determined based on the capabilities of the AP 106 and / or the STA 102. For example, for a STA to receive M expected spatial streams from an AP 106 of its own BSS 250, the policy may include the interfering AP 106 minimizing interference at the STA's receiver along M directions corresponding 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 a STA to receive M expected spatial streams from an AP of the STA's own BSS, the policy may include the interfering AP 106 minimizing interference at the STA's receiver along M directions corresponding to the M strongest eigenmodes of the channel between the STA 102 and the interfering AP 106.

[0105] 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 including the measurement. When measuring channels from different APs, the relative phase offsets of the receive antennas across the STAs 102 may be maintained at a constant value.

[0106] During the coordination phase, different independent variants and combinations thereof may be implemented. For example, STA 102 may feedback an estimate of the MIMO channel from the probing AP via 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 probing AP in Cartesian form. For example, for an AP 106 (e.g., an interfering AP) from another BSS 250 different from the STA's BSS 250, STA 102 may feedback a linear transformation of the MIMO channel from the AP 106. The linear transformation may be determined by a 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 the STA 102 and its own BSS AP 106. For example, for the probing AP 106, if the STA 102 is receiving M expected spatial streams from its own BSS AP 106, then the STA 102 may feedback a preferred set of M directions, where the corresponding AP may minimize interference.

[0107] As part of the coordination phase, the APs 106 (e.g., AP1 and AP2) may jointly perform channel sounding for the STAs 102. The APs 106 may jointly transmit null data packets (NDPs) that may be synchronized in time / frequency. The total number of sounding dimensions in the NDP may be equal to the total number of antennas 220 across the APs 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 to the STAs to be sounded across the BSSs 250 on behalf of all APs. For example, all APs 106 may transmit their NDPAs in sequence, wherein the NDPA of each AP addresses the STAs 102 within their own BSSs 250. For example, all APs 106 may transmit their NDPAs simultaneously, but separated in frequency (e.g., via OFDMA), wherein each AP 106 addresses the STAs 102 within their own respective BSSs 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 (CFO) relative to the AP 106 that transmitted the trigger frame and synchronize the start times of their coordinated transmissions.

[0108] In one aspect, the system 200 may be a system for coordinated partial rank zeroing in multi-AP transmissions, or a system for synchronous multi-AP transmissions with coordinated partial rank zeroing. The system 200 may include any number of APs 106, and the APs 106 may have overlapping BSSs 250 and overlapping ranges 255 for wireless communication. For example, a first AP 106 may have a first group (e.g., one or more) of STAs 102 within a first BSS 250 (e.g., a WLAN) of the first AP 106, and a second AP 106 may have a second group of STAs 102 (e.g., one or more STAs) within a second BSS 250. Each of the first AP 106 and the second AP 106 may include one or more STAs 102 of another BSS 250 (e.g., a neighboring AP 106) within its own range 255 for wireless communication.

[0109] The first AP 106 may be configured to transmit a first message to the second AP 106. The first message may be transmitted by the coordinator 205 as part of a coordination phase, wherein the AP 106 collects information jointly from STAs 102 belonging to any of its BSSs or individually from STAs 102 in its own BSS 250 and exchanges the collected information between the APs 106. The first message may identify a first station 102 of the first AP 106 for which interference from the second AP 106 is to be partially nulled. The first station 102 may be a STA that is part of the first BSS 250 of the first AP 106 (e.g., configured for wireless communication with the first AP 106 via the WLAN of the first AP 106).

[0110] The message may include a first direction in which interference from the second AP 106 is to be partially zeroed at the first station 102. For example, the first message may include a number of a first set of directions in which interference from the second AP at the first station is to be partially or completely zeroed. For example, the first message may include a first set of directions in which interference is to be partially or completely zeroed. For example, the first message may cause the second AP to identify the first set of directions in which interference to the first station is to be partially or completely zeroed.

[0111] The first direction or first set of directions may be a set of one or more linearly independent vectors or directions along which transmissions from the second AP 106 may be reduced to below a predetermined threshold (e.g., corresponding to a power or gain level of a signal or a threshold defined according to a noise signal level). The first message may include location information (e.g., a location of the STA relative to the AP 106, 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).

[0112] 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 a 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 is to be partially or completely zeroed. The second message may include or identify a second direction in which interference from the first AP is partially or completely zeroed at the second station 102. The second direction or second set of directions may be a linearly independent vector or direction along which transmissions from the first AP 106 may be reduced to below a predetermined threshold (e.g., corresponding to a power or gain level of a signal or a threshold defined according to a noise signal level). The second message may include location information (e.g., a location of a STA relative to an AP 106, coordinates of a STA relative to an AP 106, information about a spatial orientation of a STA, or any other information corresponding to a spatial orientation of a STA).

[0113] 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 of transmissions 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 a transmission from the second AP 106 to the second station 102. The time may be synchronized to be 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 a second direction to partially or completely null interference at the second station 102.

[0114] The first message may identify at least a first station 102 of the first AP 106 for which interference from the second AP 106 is to be nulled. The first message may identify at least a number of directions in which interference is to be partially nulled at the first station. The first message may identify directions in which interference is to be partially nulled at the first station 102. In addition, receipt of the first message may cause the second AP to identify a set of directions along which interference to the first station is to be partially nulled.

[0115] For example, since the beamforming vectors may be calculated for all receiving stations 102 as a whole, not just individual stations in isolation, the direction used to null the interference portion at a particular station may depend on which other stations 102 are receiving signals at the same time. In such instances, while the message may identify the station 102 for which interference is to be nulled, it may or may not identify a fixed constant direction for interference nulling for that particular station 102. For example, in some embodiments, the direction used 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 exchanging other information, such as a set of stations 102 with which each AP 106 is expected to communicate, the number of directions in which interference is to be nulled at each station, the direction or location of the station or AP, and the like. Such information, along with information collected about the channel between the AP 106 and the STA 102 acquired through a previous channel sounding process, may be used to independently determine the nulling direction for each station 102.

[0116] The first AP 106 may be configured to transmit a first spatial stream 240 including data for transmissions to the first station 102 at a set time and frequency. The first spatial stream 240 may be oriented so as to partially null interference from the first AP at the second station along a second set of directions. For example, the first AP 106 may beamform the first spatial stream 240 (e.g., including transmissions) to transmit at the second station 102 along a spatial vector or direction orthogonal to the first direction. The first data stream may 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), wherein the second stream is oriented so as to partially or completely null interference from the second AP at the first station 102 along the first set of directions. For example, the first data stream may be coordinated with a second data stream transmitted by the second AP to the second station at the time and frequency, wherein the second data stream is oriented so as to partially or completely null interference from the second AP at the first station along the first direction.

[0117] The first station 102 may be configured to receive wireless transmissions from the first AP via a wireless local area network (WLAN) of the first AP. The second station 102 may be configured to receive wireless transmissions from the second AP via the WLAN of the second AP. The first station 102 and the second station 102 may each be located within a first range 255 of wireless transmissions from the first AP 106 and a second range 255 of wireless transmissions from the second AP 106.

[0118] The first AP 106 may be configured to determine a spatial orientation of the one or more antennas 220 of the first AP 106 based at least on the second set of one or more directions. The spatial orientation of the one or more antennas 220 of the first AP 106 may be determined based at least on a location (e.g., coordinates or GPS location) of the first station, the second station, and / or the first AP 106. The first AP 106 may be configured to beamform transmissions relative to the first station 102 based at least on the spatial orientation of the one or more antennas 220 of the first AP 106.

[0119] The first AP 106 may be configured to exchange time and frequency for coordinating the transmissions of the first AP with the transmissions of the second AP with the second AP. For example, the coordinator 205 may exchange the channels or frequency bands on which communications are transmitted to its STAs 102, as well as the timing and frequency of the transmissions and / or the phase of the transmissions relative to each other. The first AP 106 may be configured to coordinate the transmissions by the first AP 106 to the first station 102 with the transmissions by the second AP to the second station using time and frequency.

[0120] The first AP 106 may be configured to receive a packet including information about the first client. The packet may include a network packet, message, or transmission that may include information about characteristics of a channel of the first station and / or the second station. The first AP 106 may be configured to identify information indicating a spatial orientation of the first client relative to the second AP from the received packet. For example, the first AP 106 may determine a linearly independent vector at the STA 102 at which interference at the STA 102 is partially or completely zeroed. The first AP 106 may be configured to determine a first set of one or more directions of the first client using the spatial orientation.

[0121] The first AP 106 may be configured to receive a third message from the second AP 106. The third message may identify a third station 102 of the second AP 106 (e.g., a STA 102 within the BSS 250 of the second AP 106) for which interference from the first AP 106 is to be partially or fully nulled. The third message may include a third direction to partially null interference at the first station along the third direction. The first AP 106 may configure one or more settings of the first AP 106 to coordinate with the second AP 106 the time and frequency of transmissions to the first station to be sent according to the third set of one or more directions to partially null interference at the third station. The first AP 106 may form a beam for transmissions to the first station according to the second set of one or more directions to partially null interference at the second station, and form the beam according to the third set of one or more directions to partially null interference at the third station.

[0122] 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 in 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 the plurality of streams to a plurality of STAs including the first STA. For example, the receiving STA 102 may have a number of receive antennas 220 that is not less than the number of spatial streams 240 directed to the receiving STA 102, and 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 the number of spatial streams 240 than directed to the receiving STA 102.

[0123] C. Used for about System and method for downlink (DL) channel detection of multiple access points

[0124] The present disclosure relates to candidate multi-access point technologies for acquiring additional channel state information to facilitate improved coordinated beamforming between overlapping APs. In a multi-AP configuration, when the CBF function is established, APs belonging to different BSSs can benefit from obtaining cross-BSSDL channel state information (CSI). The technical solution of the present disclosure provides various detection processes and frame sequences to obtain or exchange such CSI, including through joint detection, individual detection and implicit detection techniques. The joint detection technology may include a STA providing, obtaining or receiving feedback about a composite channel from two APs at the same time. In individual detection, the STA may transmit, obtain or exchange separate feedback reports for individual channels measured from each AP. Implicit detection technology may include uplink channel measurements (STA to AP) using null data packet (NDP) frames to infer downlink channels (AP to STA) taking into account radio path differences. Each of these detection options may be based on individual configuration changes and may be implemented within one or more TXOPs (transmission opportunities) with SIFS (short interframe space) to facilitate more efficient transmission.

[0125] Technical Solutions One or more systems and methods may be used for different implementations, configurations or examples of DL channel sounding for multiple access points. Any of the systems described in Sections A and B may be configured, constructed or implemented to implement, operate and / or use any of the options and techniques described in this disclosure.

[0126] Figure 5An example system 500 for downlink channel sounding with respect to multiple access points is illustrated. The example system 500 may include one or more basic service sets (BSSs) 250. Each BSS 250 may include one or more access points (APs) 205 and one or more stations (STAs) 230. Each AP 205 may include one or more null data packet advertisement (NDPA) frame generators 502, one or more beamforming report poll (BFRP) frame generators 506 for generating beamforming report poll (BFRP) frames 508, one or more sounding functions 510, one or more parameters 514, one or more coordinated beamforming frame selectors 516, and one or more channel state information (CSI) processors 518. The NDPA frame generator 502 may generate or include one or more NDPA frames 504. The BFRP frame generator 506 may generate or include one or more beamforming report poll (BFRP) frames 508. Each STA 230 may include one or more physical layer protocol data units (PDUs) 520 and one or more downlink channel measurement functions 524. The PDU 520 may include one or more channel state information 522. Figure 5 The first access point 205 and the second access point 205 in the embodiment are similar in function to Figure 2 The first access point 205 and the second access point 205 in. Figure 5 The STA 230 in the Figure 2 STA 230 in.

[0127] The NDPA frame generator 502 may include any combination of hardware and software for generating a null data packet announcement (NDPA) frame 504. Depending on the implementation, the NDPA frame 504 may include, correspond to, or refer to different variants, such as NDPA, null data packet (NDP), or implicit NDPA. The NDPA frame 504 may include a signaling frame for initiating and coordinating downlink channel sounding. The NDPA frame generator 502 may include, use, or access sounding information, such as parameters and configuration settings that define the characteristics of the NDPA frame 504. The parameters or configuration settings may include the type of sounding process, sounding sequence information, a STA information field with an identifier of the target STA, specifications of the type of feedback requested from each STA (e.g., CSI report format), the type of CSI requested, or information about beamforming configuration, timing, duration, and other parameters for coordinated transmission across multiple APs. The NDPA frame generator 502 may interact with other components within the AP 205 to facilitate the transmission of the generated NDPA frame 504 at a specified point during the downlink channel sounding process.

[0128] The NDPA frame generator 502 may be configured to transmit an NDPA frame 504 to trigger a detection process for the group of STAs 230. The NDPA frame 504 may include a STA information field having an association identifier (AID) value to identify the target STA 230. The station information field may include a structured data element within a communication protocol. For example, the station information field may be used as a container for information related to a specific wireless station (STA) within a network. The content of the station information field may vary depending on the specific protocol and its implementation. The AID may include an identifier assigned to a wireless station (STA) during an association process of the wireless station in the network. The AID value may be used by the second AP 205 to identify the STA 230 that is desired to participate in the detection process.

[0129] The NDPA frame generator 502 may be configured to transmit an NDPA frame 504 to the group of STAs 230 within a specific BSS 250 of the second AP 205. The NDPA frame 504 may include any information or data for indicating or announcing a sounding sequence or providing data for a sounding sequence. The NDPA frame 504 may include a field for signaling the first AP 205 to prepare for transmission of the NDPA frame 504. For example, the signal for preparing for transmission may provide information about an upcoming transmission, which the receiver may use to configure one or more settings for performing functions associated with the upcoming transmission. The field may include an AID having a predetermined value to trigger the first AP 205 to prepare the NDPA frame 504. The NDPA frame 504 may be configured to indicate the desired CSI format to the STA 230 and signal the first AP 205 to prepare for NDP transmission. The preamble of the NDPA frame 504 transmitted by the first AP 205 in response to the NDPA frame 504 may signal the BSS color of the BSS 250 corresponding to the second AP 205. The NDPA frame 504 may include parameters including identifiers of the target STAs 230 and specifications of the type of CSI feedback solicited from each STA 230 (e.g., format, spatial resolution, etc.). The NDPA frame 504 and any BFRP frames used in the options may include a MAC address and AID corresponding to the target STA 230. The first and second APs 205 may exchange communications to determine the type or format of the CSI 522, which may then be used or collected, for example, on a DL channel via a feedback mechanism. The CSI 522 may be communicated by the STAs 230 when reported via a feedback message.

[0130] The NDPA frame generator 502 may be configured to transmit an implicit NDPA frame 504 to solicit an uplink trigger NDP (T-NDP) frame from the group of STAs 230. The NDPA frame 504 may include a field for signaling that the second AP 205 is ready to receive a T-NDP frame. The NDPA frame 504 may identify parameters for transmission of the T-NDP frame. The NDPA frame 504 may include parameters for the T-NDP frame, such as bandwidth, LTF configuration, guard interval, spatial stream, or RU allocation.

[0131] The BFRP frame generator 506 may include any combination of hardware and software for generating the BFRP frame 508. The BFRP frame 508 may include a frame that requests CSI feedback from the STA 230 during downlink channel sounding. The BFRP frame generator 506 may access information and parameters that define the content of the BFRP frame 508. For example, the parameters may include an identifier of the target STA 230 and configuration settings (e.g., modulation and coding scheme, resource unit allocation, etc.) for how the STA 230 should respond to the BFRP using its CSI feedback, and other one or more parameters related to triggering coordinated transmission of BFRP across multiple APs 205. The BFRP frame generator 506 may interact with other components within the AP 205 to facilitate the transmission of the generated BFRP frame 508, for example, by transmitting the BFRP frame 508 to the appropriate module for transmission. The BFRP frame generator 506 may be configured to generate the BFRP frame 508 to solicit CSI feedback from the STA 230. The composite channel may be or include a form of CSI feedback estimated by the STA 230, such as in a joint sounding sequence.

[0132] The BFRP frame generator 506 may be configured to generate one or more BFRP frames 508 for DL ​​channel measurement from the STA 230 to the first AP 205. The BFRP frame 508 may include parameters that specify the type of CSI feedback solicited from the STA 230. The STA 230 may transmit a trigger-based PDU with CSI 522 based on the parameters, including a compressed beamforming report (CBR). The first and second APs 205 may exchange communications to determine the type of CSI. The BFRP frame 508 generated for the individual sounding may include information related to the second AP 205, such as an identifier or reference, to facilitate the sounding process.

[0133] The sounding function 510 may include any combination of hardware and software components for managing the downlink channel sounding process. The sounding function 510 may initiate the sounding process at designated timing points, for example, based on a trigger received from the NDPA frame generator 502. The sounding function 510 may define the specific sounding techniques to be used. The sounding techniques may include selecting a sounding sequence, adjusting parameters of the signals used in the sounding, and coordinating the sounding techniques across multiple APs 205.

[0134] The sounding function 510 may be configured to coordinate with one or more APs 205 to synchronize the timing and parameters of the sounding process to provide correct measurements of the composite channel by the STAs 230 in both groups. The second AP 205 may identify the STAs 230 in the first group associated with the first AP 205 to participate in the CBF and request CSI for the CBF.

[0135] A channel may include or refer to a downlink communication channel between the AP 205 and the STA 230. A channel may represent a physical path for a sounding signal to travel from the AP to the STA. During the sounding process, the AP 205 may transmit a sounding signal (e.g., a signal, a reference signal, etc.) via the channel. Data from these signals may be stored on the STA 230 or the AP 205. The signal may be configured to probe channel characteristics and enable the STA 230 to collect information about the channel response. Based on the received sounding signal, the STA 203 may estimate CSI indicating the strength of the channel, including factors such as signal strength, attenuation, and phase shift across different subcarriers or spatial streams.

[0136] Parameters 514 may include configurations that define how STA 230 responds to BFRP frames 508 transmitted by AP 205. Parameters 514 may specify how STA 230 formats and transmits its CSI feedback. Parameters 514 may include modulation and coding scheme (MCS), spatial stream allocation, and resource unit (RU) allocation. MCS parameters may define the modulation technique and / or error correction coding scheme that may be used by STA 230 to transmit its CSI feedback. Spatial stream allocation parameters may indicate how many spatial streams (independent data streams) STA 230 may use when transmitting its CSI feedback. RU allocation parameters may specify specific RUs within the overall wireless channel that STA 230 may use to transmit its CSI feedback.

[0137] The coordinated BFRP frame selector 516 may include any combination of hardware and software components for selecting a BFRP frame 508 based on a sounding process. The coordinated BFRP frame selector 516 may access information about the sounding process, such as whether the sounding uses coordinated transmission across multiple APs 205 or the capabilities of the target STA 230, etc. Based on the aforementioned information, the coordinated BFRP frame selector 516 may select a BFRP frame 508 to be transmitted for the sounding process. The coordinated BFRP frame selector 516 may interact with other components within the AP 205 to receive BFRP frames 508 for selection. If the sounding process does not use coordinated transmission, the coordinated BFRP frame selector 516 may select a single BFRP frame 508. The coordinated BFRP frame selector 516 may modify multiple BFRP frames 508 for coordinated transmission across multiple APs 205.

[0138] The CSI processor 518 may include any combination of hardware and software components for processing CSI feedback received from the STA 230 during the downlink channel sounding process. The CSI processor 518 may receive a CSI feedback report transmitted by the STA 230 in response to the BFRP frame 508 sent by the AP 205. The CSI 522 may be encoded in the feedback report using a specific format (e.g., compressed beamforming report (CBR)). The CSI processor 518 may decode the CSI 522 to extract relevant channel state details. In the case of multiple APs 205, the CSI processor 518 may receive feedback reports from STAs 230 that have been probed by multiple APs 205. The CSI processor 518 may extract features related to different applications from the CSI data 522. Features may include signal strength across different subcarriers or spatial streams, path loss estimates, delay spread characteristics, and Doppler shift information, among others.

[0139] A PDU 520 may refer to a unit of data exchanged between network layers within a communication protocol stack. A PDU 520 may include a header and a payload. The header of the PDU 520 may include control information for physical layer processing, such as a synchronization code, an MCS indicator, and an identifier of the receiving STA 230. The payload of the PDU 520 may include CSI data 522. The PDU 520 including the CSI data 522 may be transmitted by the STA 230 back to the AP 205 over a wireless channel. The PDU 520 may be a trigger-based PPDU transmitted by each STA 230. The trigger-based PPDU may provide CSI 522, including several parameters, such as a beamforming report, a beamforming matrix index, a signal-to-noise ratio, or a measure of the performance of a modulation scheme.

[0140] The DL channel measurement function 524 may include any combination of hardware and software components for extracting information about DL channel characteristics based on the sounding signal transmitted by the AP 205. The DL channel measurement function 524 may receive the sounding signal transmitted by the AP 205 over the DL channel. The sounding signal may include a pilot signal, a reference signal, or a specific waveform configured for channel sounding. The DL channel measurement function 524 may perform signal processing tasks such as filtering, synchronization, and channel estimation. The DL channel measurement function 524 may generate CSI data 522 specifying the DL channel conditions between the AP 205 and the associated STA 230. In this regard, the CSI data 522 may refer to information about the downlink channel conditions between the AP 205 and the STA 230. The specific format and content of the CSI 522 may depend on the capabilities of the sounding process and the wireless protocol. The first and second APs 205 may exchange parameters for alignment (e.g., carrier frequency offset (CFO) and sampling frequency offset (SFO)).

[0141] The example system 500 for downlink channel sounding with respect to multiple APs 205 may implement joint, individual, or implicit sounding configurations or options. The example system 500 may include components (e.g., NDPA frame generator 502, sounding function 510, beamforming report frame generator 506, coordinated beamforming frame selector 516, and CSI processor 518) that may be configured to implement multiple phases of sounding options. The phases of some of the sounding options (e.g., joint and individual sounding options) may include an announcement phase, a channel sounding phase, and a feedback phase.

[0142] The announcement phase may include one or more APs 205 transmitting a trigger or NDPA frame to initiate the sounding process. These frames may include data or information to inform the STA 230 or other APs 205 about a specific type of sounding sequence and the type of CSI feedback to be solicited in preparation for subsequent phases. The channel sounding phase may include one or more APs 205 transmitting a null data packet (NDP), which may be used by the STA 230 to estimate the corresponding downlink channel from the AP 205 in order to determine and prepare CSI feedback. The feedback phase may include one or more APs 205 soliciting CSI feedback from the STA 230 via a BFRP frame, and the STA 230 responding by transmitting CSI feedback (e.g., via a trigger-based PPDU). Although the present disclosure provides multiple examples or configurations of various joint, individual, and implicit sounding options, it should be understood that any configuration that mixes and matches any of the versions of these phases can be used for any other configuration. For example, the announcement phase operation of one joint sounding option may be used as the announcement phase operation of another joint sounding option or the announcement phase operation of another individual sounding option, or vice versa. For example, the channel sounding phase operation of one joint sounding option may be used as the channel sounding phase operation of another joint sounding option or the channel sounding phase operation of another individual sounding option, or vice versa. For example, the feedback phase operation from one joint sounding option may be used as the feedback phase operation of another joint sounding option or the feedback phase operation of another individual sounding option, or vice versa.

[0143] Reference now Figure 6, illustrating an example method 600 for joint downlink channel sounding for multiple access points. The method 600 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 600 may include actions 605 to 620. At 605, the method may include transmitting a Null Data Packet Announcement (NDPA) frame from a first AP to a second AP and one or more STAs. At 610, the method may include transmitting sounding information by the first AP and the second AP. At 615, the method may include transmitting a Beamforming Report (e.g., BFRP-1) frame from the first AP to solicit CSI feedback based on a composite channel. At 620, the method may include transmitting, by the STA in response to the BFRP-1 frame, a Trigger Based (TB) PPDU to provide CSI feedback.

[0144] At 605, the method may include a first AP transmitting an NDPA frame (e.g., an NDPA-1 frame) to trigger a detection process for a first group of stations associated with the first AP. The NDPA frame may include a station information field having an association identifier (AID) value. The NDPA frame may include a STA information field having a predefined AID value. The AID value in the STA information field may be read and identified by a second AP. For example, in response to receiving the AID value, the second AP may be triggered to participate in a detection process for STAs of the second AP (second group) relative to the first AP. The first AP and / or the second AP may exchange one or more parameters, such as a carrier frequency offset (CFO) and a sampling frequency offset (SFO), before the detection process for alignment of wireless communication.

[0145] The NDPA-1 frame may include information addressed to one or more (e.g., each) of the STAs associated with the first AP. The NDPA-1 frame may include additional information addressed to the STA, for example, indicating the type of detection process, the type of channel state information (CSI) requested, information about beamforming configuration, timing, or duration. The NDPA-1 frame may indicate a specific multi-AP detection sequence being used to distinguish the sequence from single AP detection or other multi-AP configurations. The NDPA-1 frame may be transmitted in a non-high throughput (HT) PPDU format, which may represent a type of data transmission format configured to operate at a lower maximum speed and typically in a narrower frequency bandwidth.

[0146] At 610, the method may include transmitting, by the first AP and the second AP, sounding information. The sounding information may include any information or data that facilitates channel estimation of a STA relative to one or more APs. The first AP and the second AP may coordinate or determine how to transmit the sounding information (e.g., sounding NDP transmission) to the STA of the first AP. For example, in response to receiving an NDPA-1 frame, the first AP and the second AP may coordinate transmissions to the STA to measure its DL channel. For example, the first AP and the second AP may transmit sounding information to the STA via a single joint NDP frame, which may include all desired information for the STA to measure the DL channels from the two APs. For example, the first AP and the second AP may transmit sounding information to the STA via two sequential NDP frames, each of which includes information for measuring the DL channels from a specific AP. The selection between the joint NDP and the sequential NDP may be determined by the first AP and the second AP through a prior negotiation or signaling mechanism.

[0147] Each STA addressed by and receiving the NDPA frame at 605 may measure downlink (DL) channels from one or more APs based on the received sounding information at 610. For example, the specific channel measured by the STA may depend on the sounding sequence and its association. For example, in a sounding sequence initiated by a first AP, a STA associated with the first AP may measure a channel from the first AP (e.g., H1) and a channel from a second AP (e.g., H2) to form a composite channel (e.g., H). If the sounding sequence is initiated by the first AP, the STA associated with the second AP may not participate in the sounding sequence. Once the individual channel measurements (H1 and H2) are completed, each STA may form a composite channel (referred to as "H") by concatenating the individual channel measurements in a predetermined order. In order to ensure accurate measurement of the composite channel by the STA, the first AP may coordinate with the second AP to synchronize the timing and parameters of the sounding process. For example, the STA may estimate the channel using a long training field (e.g., NDP) in the NDPA frame 504, which may include the received signal amplitude, the frequency or phase of the signal, or other information corresponding to the antennas at the AP and the STA.

[0148] At 615, the method may include transmitting a beamforming report poll (e.g., BFRP-1) frame to solicit CSI feedback. For example, the method may include a first AP transmitting a BFRP-1 frame to solicit CSI feedback. The BFRP-1 frame may request or solicit CSI feedback from associated STAs of the first AP based on a composite channel. The BFRP-1 frame may be transmitted in a non-HT PPDU format. For example, the BFRP-1 frame may indicate transmission parameters for each group of STAs. The transmission parameters may include factors such as a modulation and coding scheme (MCS), spatial stream allocation, and resource unit (RU) allocation for one or more STAs. The transmission parameters may be configured so that responses transmitted by each STA based on these settings can be decoded by the first AP and the second AP.

[0149] At 620, the method may include transmitting a trigger-based (TB) PPDU by the STA. For example, the STAs addressed by the BFRP-1 frame and receiving the BFRP-1 frame may jointly transmit a TB PPDU in response. Within the TB PPDU, each STA may feedback associated CSI (e.g., compressed beamforming report (CBR)) based on a composite channel. Each STA may transmit CSI feedback based on parameters assigned to the STA in the BFRP-1 frame. In the NDPA-1 and BFRP-1 frames transmitted by the first AP, the MAC address and AID may be the same as the MAC address and AID used by the first AP for single AP detection. The TB PPDU transmitted by each station may provide various CSI elements. For example, the CSI element may include a beamforming report, a beamforming matrix index, a signal-to-noise ratio, or a measure of the performance of a modulation scheme. The first AP and the second AP may dynamically adjust the beamforming parameters based on the received TB PPDU feedback according to the performance of the downlink channel of each station in the first group of one or more stations of the first AP.

[0150] Reference now Figure 7, illustrating another example method 700 for joint downlink channel sounding of multiple access points. The method 700 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 700 may include actions 705 to 740. At 705, the method may include transmitting a trigger frame (e.g., a trigger-1 frame) from a first AP to a second AP. At 710, the method may include transmitting a response frame (e.g., a response-1 frame) from the second AP to the first AP. At 715, the method may include jointly transmitting a multi-AP NDPA frame from the first AP and the second AP. At 720, the method may include transmitting sounding information from the first AP and the second AP. At 725, the method may include transmitting a trigger frame (e.g., a trigger-2 frame) from the first AP to the second AP. At 730, the method may include transmitting a response frame (e.g., a response-2 frame) from the second AP to the first AP. At 735, the method may include jointly transmitting a multi-AP BFRP frame from the first AP and the second AP. At 740, the method may include responding, by the STAs addressed in the BFRP frame, with a joint TB PPDU.

[0151] At 705, the method may include transmitting a trigger frame (e.g., a trigger-1 frame). For example, the first AP may transmit a trigger-1 frame to the second AP. The trigger-1 frame may include information about the associated STAs of the first AP for a multi-AP NDPA frame. The information may include details such as an AID or other identifier to address a specific STA. The trigger-1 frame may be transmitted in a non-HT PPDU format. The trigger-1 frame may include information about the associated STAs of the first AP to be associated with the multi-AP BFRP frame.

[0152] At 710, the method may include transmitting a response frame (e.g., a response-1 frame) from the second AP to the first AP. For example, after receiving the trigger-1 frame, the second AP may transmit the response-1 frame back to the first AP. The response-1 frame may include information about the associated STAs of the second AP for the multi-AP NDPA frame. The response-1 frame may be transmitted in a non-HTPPDU format. The response-1 frame may include information about the associated STAs of the second AP related to the multi-AP BFRP frame (e.g., if the trigger-1 includes corresponding information of the STAs of the first AP).

[0153] At 715, the method may include jointly transmitting a multi-AP NDPA frame from the first AP and the second AP. For example, based on the exchanged information in the trigger-1 frame and the response-1 frame, the first AP and the second AP may jointly transmit a multi-AP NDPA frame, intended for reception by a STA associated with the first AP and a STA associated with the second AP. The second AP may use information derived from the trigger-1 frame to pre-correct the associated CFO and SFO relative to the first AP. The second AP may apply a cyclic shift to its transmitted signal compared to the transmitted signal of the first AP to avoid cancellation during reception by the STA. The AP may transmit a multi-AP NDPA frame with a preamble separated from the payload. For example, for a multi-AP NDPA frame, two APs may transmit the same preamble content and the same payload content to achieve consistency so that the STA can correctly decode the content of the frame. The multi-AP NDPA frame may use a multi-AP MAC address for the transmitter address (TA) and BSSID fields in the MAC header, which is different from the TA used by each AP for a single AP NDPA frame. NDPA frames may use a multi-AP broadcast reception address (RA), which is different from the broadcast RA used by each AP for single-AP NDPA frames.

[0154] The special MAC address may be recognized or identified by the STA expected by the NDPA, where the STA maintains an additional MAC address to decode the multi-AP NDPA frame. The multi-AP NDPA frame may include a STA information field of the expected STA associated with the participating AP, where each STA information field uses an AID to address a specific STA, and the specific AID may be different from the AID used to address the corresponding STA in the single AP NDPA frame. Each STA information field may include information about the type of CSI feedback solicited from the STA addressed to it. The multi-AP NDPA frame may indicate a specific multi-AP detection sequence being used (e.g., to distinguish it from a single AP and / or other multi-AP detection sequence). The multi-AP NDPA frame may be transmitted in a non-HT PPDU format.

[0155] At 720, the first AP and the second AP may transmit sounding information. For example, the first AP and the second AP may transmit sounding information to the STA via a single joint NDP frame, and the sounding information may include information for the associated STA to measure downlink channels from the two APs. The first AP and the second AP may transmit sounding information to the STA via two sequential NDP frames, where each frame includes information for measuring channels from a specific AP. Based on the sounding process, the STA addressed by the multi-AP NDPA may measure DL channels, for example, H1 from the first AP and H2 from the second AP. The STA addressed by the multi-AP NDPA may form a composite channel H from H1 and H2. In some implementations, the exact selection may be determined via prior negotiation / signaling.

[0156] At 725, the first AP may optionally transmit a trigger frame (eg, a trigger-2 frame) to the second AP. The trigger-2 frame may include information about the first AP's associated STAs for the BFRP frame. The trigger-2 frame may be transmitted in a non-HT PPDU format.

[0157] At 730, the second AP may transmit a corresponding response-2 frame to the first AP in response to receiving the trigger-2 frame. The response-2 frame may include information about the associated STAs of the second AP for the BFRP frame. The response-2 frame may be transmitted in a non-HT PPDU format.

[0158] At 735, the method may include jointly transmitting a multi-AP BFRP frame from the first AP and the second AP. For example, the APs may jointly transmit the multi-AP BFRP frame. The multi-AP BFRP frame may be expected to be received by a STA associated with the first AP and a STA associated with the second AP. Prior to transmission, the second AP may pre-correct its CFO and SFO relative to the first AP. The correction may be estimated from information received in a trigger-1 or trigger-2 frame. The second AP may apply a cyclic shift to its transmitted signal compared to the signal of the first AP to avoid cancellation during reception by the STA. The first AP and the second AP may transmit a multi-AP BFRP frame with a preamble separated from the payload. For example, for a multi-AP BFRP frame, two APs may transmit the same preamble content and the same payload content to achieve consistency so that the STA can correctly decode the content of the frame. The multi-AP BFRP frame may use a unique multi-AP MAC address for the TA and BSSID fields in the MAC header. These addresses may be different from the TA and BSSID addresses used by each AP for a single AP BFRP frame. BFRP may use a special multi-AP broadcast RA that is different from the broadcast RA used by each AP for single-AP BFRP frames. A special MAC address may be recognized or identified by the STAs intended for BFRP. A STA may maintain an additional MAC address specifically for decoding multi-AP BFRP frames.

[0159] The multi-AP BFRP frame may include a user information field for each STA (from both the first AP and the second AP). The field may include an AID assigned to each STA, which may be different from the AID assigned to the STA within its corresponding network (BSS). The multi-AP BFRP frame may solicit CSI feedback about the composite channel H from the addressed STA. The feedback may be based on the composite channel information (H) measured during the sounding process. The multi-AP BFRP frame may be transmitted in a non-HT PPDU format. The BFRP frame may specify transmission parameters for each STA. The transmission parameters may include factors such as modulation and coding scheme (MCS), spatial stream allocation, and resource unit (RU) allocation. The transmission parameters may be configured so that the CSI feedback transmitted by each STA based on these settings can be decoded by the first AP and the second AP.

[0160] At 740, the method may include responding, by the STAs addressed in the BFRP frame, with a joint TB PPDU. For example, upon receiving a multi-AP BFRP frame, the STAs addressed in the frame may respond with a joint TB PPDU. Within the TB PPDU, each STA may transmit its CSI feedback (e.g., compressed beamforming report (CBR)) based on the composite channel information (H) measured during the sounding process. Each STA may transmit its feedback according to specific transmission parameters specified for the STA in the BFRP frame.

[0161] Reference now Figure 8 , illustrating another example method 800 for joint downlink channel sounding for multiple access points. The method 800 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 800 may include actions 805 to 825. At 805, the method may include jointly transmitting, by a first AP and a second AP, a single multi-AP NDP frame. At 810, the method may include transmitting, by a first AP and a second AP, long training fields (LTFs) that overlap in time and frequency. At 815, the method may include transmitting, by a first AP and a second AP, LTFs that overlap in time but are staggered in frequency. At 820, the method may include transmitting, by a first AP and a second AP, the LTFs in a time multiplexed manner. At 825, the method may include transmitting, by a first AP and a second AP, overlapping LTFs with frequency hopping.

[0162] At 805, the method may include jointly transmitting a single multi-AP NDP frame. For example, the first AP and the second AP may jointly transmit a single multi-AP NDP frame. The single multi-AP NDP frame may be expected to be received by a STA associated with the first AP or AP2. Prior to transmission, the second AP may pre-correct its CFO and SFO relative to AP1. The second AP may apply a cyclic shift to its transmitted signal compared to the signal of the first AP to avoid cancellation during reception by the STA. The multi-AP NDP frame may include a BSS color in the SIG field. The multi-AP BSS color may be different from the BSS color used by each AP in the corresponding single-AP NDP frame. Within the multi-AP NDP frame used by the STA for channel estimation, there may be different options for constructing a long training field (LTF). The LTF may occupy different bandwidths based on the frequency modulation plan defined in the Wi-Fi standard (e.g., 802.11ax, 802.11be, or a subsequent revision of 802.11). Options may include 1x tone planning (4x decimation), 2x tone planning (2x decimation), and 4x tone planning (non-decimation).

[0163] At 810, the method may include transmitting a long training field (LTF) by a first AP and a second AP. For example, the first AP and the second AP may transmit respective LTFs simultaneously (overlapping in time and frequency). Each AP may modulate its transmitted LTFs using a sequence orthogonal to the sequence used by the other APs. Both APs may transmit the same number of LTFs. The number of LTFs may be determined based on the total number of transmit antennas across the two APs. Both APs may use the same frequency modulation plan (1x, 2x, or 4x) as defined in the Wi-Fi standard. The STA may process the received LTFs using the corresponding orthogonal sequence of each AP to estimate the individual channels H1 (from AP1) and H2 (from AP2).

[0164] At 815, the method may include transmitting LTFs that overlap in time but are staggered in frequency. For example, the first AP and the second AP may transmit LTFs that overlap in time but are staggered in frequency according to a selected tone plan. For example, the method may include a 2x tone plan, for example, including tone indices [-500, -498, -496, ..., -6, -4, 4, 6, ..., 496, 498, 500] over a bandwidth of 80 MHz, where the first AP and the second AP transmit on alternating tones in a non-overlapping manner. For example, the first AP may transmit on tones with indices [-500, -496, ..., -8, -4, 6, ..., 494, 498] over a bandwidth of 80 MHz, and the second AP may transmit on tones with indices [-498, -494, ..., -6, 4, 8, ..., 496, 500].

[0165] The method may include 4x tone planning. For example, the method may include using tone indices [-500, -499, -498, ..., -4, -3, 3, 4, ..., 498, 499, 500] over a bandwidth of 80 MHz, wherein a first AP and a second AP may transmit on alternating tones in a non-overlapping manner. For example, a first AP may transmit on tones with indices [-500, -498, ..., -6, -4, 3, 5, ..., 497, 499] over a bandwidth of 80 MHz, and a second AP may transmit on tones with indices [-499, -497, ..., -5, -3, 4, 6, ..., 498, 500], wherein each AP may transmit on a pilot tone located on one side of DC (0 frequency). For example, the method may include a 4x tone plan in which a first AP and a second AP transmit on alternating tones in a non-overlapping manner such that each AP may transmit on a pilot tone that is symmetric about DC (i.e., the 0 frequency). For example, for a 4x tone plan including tone indices [-500, -499, -498, ..., -4, -3, 3, 4, ..., 498, 499, 500] over a bandwidth of 80 MHz, the first AP may transmit on a pilot tone with indices [-500, -498, ..., -256, -254, -251, -249, ..., -5, -3, 3, 5, ..., 249, 251, 254] over a bandwidth of 80 MHz. , 256, ..., 498, 500] and the second AP may transmit on a frequency tone with index [-499, -497, ... -255, -253, -252, -250, -248, ... -6, -4, 4, 6, ..., 248, 250, 252, 253, 255, ... 497, 499], wherein each AP may transmit on a pilot frequency tone that is symmetric about DC (0 frequency).

[0166] LTF tone planning of 2x or 4x may be supported, where allocations are split across APs, as indicated in the examples provided above. APs may transmit an equal number of LTFs, which may be determined by the maximum number of transmit antennas present across APs. Each STA may initially estimate individual channels H1 and H2, where H1 is estimated for the tones occupied by the first AP and H2 is estimated for the tones occupied by the second AP. The STA may interpolate or extrapolate the estimated individual channels H1 and H2 to tones not occupied by each AP before forming a composite channel. Each STA may individually track the common phase error (CPE) observed from each AP and may compensate for it independently.

[0167] At 820, the method may include transmitting the LTFs in a time multiplexed manner. For example, the first AP and the second AP may transmit the corresponding LTFs in a time multiplexed manner, indicating that the APs do not overlap in time. Each AP may transmit its LTF while the other remains silent (transmits zero). Each AP may transmit a different number of LTFs depending on the total number of its transmit antennas. The order in which the LTFs are transmitted may vary. For example, all LTFs from the first AP are transmitted first, followed by all LTFs from AP2. The LTFs from the APs may be staggered in time. The sorting information may be signaled in the SIG field of the NDP frame, predetermined by negotiation, or defined in the Wi-Fi standard. LTF frequency tone plans configured with 1x (4x decimation), 2x (2x decimation), or 4x (undecimated) may be used. The AP may select the same or different frequency tone plans for its LTFs. The STA may first estimate the individual channels H1 (from AP1) and H2 (from AP2) of the frequency tones occupied by each AP, respectively. The STA may interpolate or extrapolate the estimated channel to tones not occupied by each AP before forming a composite channel for beamforming purposes.Each STA may individually track the common phase error (CPE) observed from each AP and compensate for it independently.

[0168] At 825, the method may include transmitting overlapping LTFs with frequency hopping. For example, the AP transmits overlapping LTFs with frequency hopping. The total bandwidth occupied by the LTFs may be equally divided into two halves: unit 1 (U1) and unit 2 (U2). For example, for an NDP frame with 80MHz bandwidth and 1024 subcarriers (indexed as [-512...-1, 0, 1...511]), U1 may span the lower half frequency tone [-512...-1], and U2 may span the upper half frequency tone [0...511]. U1 and U2 may be mapped to resource units (RUs) defined in the Wi-Fi standard, where U1 represents the lower half bandwidth RU and U2 represents the upper half bandwidth RU. For example, for the same 80MHz bandwidth instance, U1 may correspond to 484-frequency tone RU1, and U2 may correspond to 484-frequency tone RU2, as defined in the Wi-Fi standard.

[0169] A total of 2N LTF symbols may be transmitted, where N is determined by the maximum number of transmit antennas across the two APs. LTF frequency modulation based on 1x, 2x, or 4x configurations (as permitted by the selected Wi-Fi standard) may be used. During the first N LTF symbol transmissions, the first AP may transmit its LTF signal on U1 (lower half bandwidth), and the second AP may transmit its LTF signal on U2 (upper half bandwidth). Based on the received signals, each STA may estimate two channel (H11 and H22) responses: H11 may be the channel from the first AP on U1 (lower half bandwidth). H22 may be the channel from the second AP on U2 (upper half bandwidth). During the second N LTF symbol transmissions, the first AP may transmit its LTF signal on U2 (upper half bandwidth), and the second AP may transmit its LTF signal on U1 (lower half bandwidth). Based on the received signals, each STA may estimate two additional channel (H12 and H21) responses. H12 may be the channel from the first AP on U2 (upper half bandwidth). H21 may be the channel from the second AP on U1 (lower half bandwidth).

[0170] Each STA can construct a composite channel for the entire bandwidth by combining the individually estimated channel components (H11, H12, H21, and H22). The composite channel on U1 can be formed by combining H11 (the first AP on U1) and H21 (the second AP on U1). The composite channel on U2 can be formed by combining H12 (the first AP on U2) and H22 (the second AP on U2). Each STA can individually track the CPE observed from each AP on each RU and compensate for it independently.

[0171] In some configurations, the AP may transmit multiple NDPs sequentially instead of a single multi-AP NDP. The first AP may start by transmitting its NDP frame identified by its BSS color. The STA may receive a signal from the first AP and estimate the channel response H1. The STA stores the channel response H1. After a short interframe space (SIFS), the second AP may transmit its NDP frame identified by its BSS color. The STA may estimate the channel response (H2) from the second AP and may store the channel response H2. The STA may take into account the changes in core-to-core gain and core-to-core phase that may occur between receiving NDP-1 and NDP-2. The core-to-core changes may be caused by factors such as automatic gain control (AGC) or analog-to-digital converter (ADC) differences. The STA may construct a composite channel from the estimated H1 (from AP1) and H2 (from AP2) after compensating for the changes in core-to-core gain and core-to-core phase between receiving NDP-1 and receiving NDP-2.

[0172] Reference now Fig. 9, illustrating another example method 900 for joint downlink channel sounding of multiple access points. The method 900 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 900 may include actions 905 to 935. At 905, the method may include transmitting an NDPA frame (e.g., an NDPA-1 frame) from a first AP. At 910, the method may include transmitting an NDPA frame (e.g., an NDPA-2 frame) from a second AP. At 915, the method may include transmitting sounding information to the STA by the first AP and the second AP via a single joint NDP frame or sequential NDP frames. At 920, the method may include initiating a feedback request by the first AP transmitting a BFRP frame (e.g., a BFRP-1 frame). At 925, the method may include responding by the STA receiving the BFRP frame (e.g., a BFRP-1 frame) using a joint TB PPDU. At 930, the method may include transmitting a BFRP frame (e.g., a BFRP-2 frame) from the second AP to solicit CSI feedback for the composite channel from STAs associated with the second AP. At 935, the method may include responding, by the STA receiving the BFRP frame (e.g., the BFRP-2 frame), using a joint TBPPDU.

[0173] At 905, the method may include transmitting an NDPA frame. For example, a first AP may transmit an NDPA-1 frame. The NDPA-1 frame may trigger a second AP to initiate its corresponding function. The NDPA-1 frame may trigger the second AP via a STA information field having a predefined AID value. The second AP may use the information in the NDPA-1 frame to estimate its own CFO and SFO relative to the first AP. The NDPA-1 frame may include a STA information field addressed to a STA associated with the first AP. The STA information field may identify the type of feedback solicited from each STA. The NDPA-1 frame may specify or indicate a multi-AP detection sequence being used to distinguish the sequence from a single AP detection or other multi-AP detection methods. The NDPA-1 frame may be transmitted in a non-HT PPDU format.

[0174] At 910, the method may include transmitting an NDPA frame. For example, the second AP may transmit an NDPA-2 frame in response to an NDPA-1 frame transmitted by the first AP. The NDPA-2 frame may include a STA information field addressed to a STA associated with the second AP. The NDPA-2 frame may include information about a multi-AP detection sequence being used. The NDPA-2 frame may also be transmitted in a non-HT PPDU format.

[0175] At 915, the method may include transmitting sounding information to the STA through a single joint NDP frame or a sequential NDP frame. For example, the first AP and the second AP may transmit sounding information to the STA through a single joint NDP frame, and the sounding information may include information for the STA to measure DL channels from the two APs. The first AP and the second AP may transmit sounding information to the STA through two sequential NDP frames, each of which includes information for measuring channels from a specific AP. The selection between the joint NDP or the sequential NDP may be determined by prior negotiation or a signaling mechanism. Each STA may measure DL channels from one or more APs based on the received sounding information. For example, the STA may measure channel H1 from the first AP and channel H2 from the second AP. Once the individual channel measurements (H1 and H2) are completed, each STA may form a composite channel H.

[0176] At 920, the method may include initiating a feedback request by transmitting a BFRP frame. For example, the first AP may initiate a feedback request by transmitting a BFRP-1 frame. The BFRP-1 frame may solicit CSI feedback for composite channel H from STAs associated with the first AP. The BFRP-1 frame may be transmitted in a non-HT PPDU format. The BFRP-1 frame specifies transmission parameters (e.g., MCS, spatial stream allocation, RU allocation, etc.) for each addressed STA. The transmission parameters may be configured so that a response TBPPDU transmitted by the STA based on these settings can be decoded by the first AP and the second AP.

[0177] At 925, the method may include responding by the STA using a joint TB PPDU. For example, the STAs addressed by and receiving the BFRP-1 frame may jointly transmit a TB PPDU in response. Each participating STA may feedback its CSI (e.g., CBR) based on the composite channel H. The feedback may be transmitted according to the transmission parameters assigned to the STA in the BFRP-1 frame.

[0178] At 930, the method may include transmitting a BFRP frame. For example, the second AP may transmit a BFRP-2 frame, which may solicit CSI feedback for composite channel H from STAs associated with the second AP. The BFRP-2 frame may be transmitted in a non-HT PPDU format. The BFRP-2 frame may specify transmission parameters for each addressed STA. The transmission parameters may be configured so that a response TB PPDU transmitted by the STA can be decoded by the first AP and the second AP.

[0179] At 935, the method may include responding, by the STA, using a joint TB PPDU. For example, the STAs addressed by and receiving BFRP-2 may jointly transmit a TB PPDU in response. Each STA may send CSI feedback (e.g., CBR) based on composite channel H. The feedback may be transmitted according to parameters assigned to the STA in the received BFRP-2 frame. For NDPA-1, NDPA-2, BFRP-1, and BFRP-2 frames, the MAC address and AID used by the first AP and the second AP may be the same as the MAC address and AID used for single AP probe transmission.

[0180] Reference now Fig.10 , illustrating another example method 1000 for joint downlink channel sounding of multiple access points. The method 1000 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1000 may include actions 1005 to 1025. At 1005, the method may include transmitting a trigger frame (e.g., a trigger-1 frame) from a first AP to a second AP. At 1010, the method may include jointly transmitting, by the first AP and the second AP, a coordinated OFDMA PPDU including an NDPA for each AP. At 1015, the method may include transmitting, by the first AP and the second AP, sounding information to the STA via a single joint NDP frame or sequential NDP frames. At 1020, the method may include transmitting a trigger frame (e.g., a trigger-2 frame) from the first AP to the second AP. At 1025, the method may include jointly transmitting, by the first AP and the second AP, a coordinated OFDMA PPDU including a BFRP (e.g., BFRP-1 and BFRP-2 frames) for each AP. At 1030, the method may include responding, by the STA addressed by the BFRP frame (e.g., BFRP-1 frame or BFRP-2 frame) with a joint TB PPDU.

[0181] At 1005, the method may include transmitting a trigger frame. For example, the first AP may transmit a trigger-1 frame to the second AP. The trigger-1 frame may indicate parameters for constructing a coordinated OFDMA frame for NDPA transmission. The parameters may include RU allocation, symbol duration, guard interval, and total transmission duration for each AP. The second AP may use the information in the trigger-1 frame to estimate its CFO and SFO relative to the first AP. The trigger-1 frame may be transmitted in a non-HT PPDU format. In addition, the trigger-1 frame may include parameters for constructing a coordinated OFDMA frame to be used for BFRP transmission. The trigger-1 frame may specify, for each STA associated with the AP, the RUs that are allowed to be used when responding to the BFRP using a TB PPDU.

[0182] At 1010, the method may include jointly transmitting a coordinated OFDMA PPDU that includes the NDPA of each AP. For example, a first AP and a second AP may jointly transmit a coordinated OFDMA PPDU that carries the NDPA associated with each AP. Prior to transmission, the second AP may pre-correct its CFO and SFO relative to the first AP (e.g., based on an estimate obtained from a trigger-1 frame). In addition, the second AP may apply a cyclic shift to its transmitted signal relative to the signal of the first AP to avoid cancellation during the preamble. Based on the parameters specified in trigger-1, the first AP may transmit an NDPA-1 frame, and the second AP may transmit an NDPA-2 frame on its corresponding allocated RU within the coordinated OFDMA frame. The NDPA-1 and NDPA-2 frames may include a STA information field addressed to one or more STAs associated with the corresponding AP (e.g., identified by their AIDs). The STA information field may specify or identify the type of feedback solicited from each STA. The NDPA frame may include information about the specific multi-AP detection sequence being used to distinguish the multi-AP detection sequence from single-AP detection or other multi-AP methods.

[0183] At 1015, the method may include transmitting sounding information to the STA through a single joint NDP frame or a sequential NDP frame. For example, the first AP and the second AP may transmit sounding information to the STA through a single joint NDP frame, and the sounding information may include all desired information for the STA to measure DL channels from the two APs. For example, the first AP and the second AP may transmit sounding information to the STA through two sequential NDP frames, each of which includes information for measuring channels from a specific AP. The selection between the joint NDP or the sequential NDP may be determined by prior negotiation or a signaling mechanism. Each STA may measure DL channels from one or more APs based on the received sounding information. For example, each STA may measure channel H1 from the first AP and channel H2 from the second AP. Once the individual channel measurements (H1 and H2) are completed, each STA may form a composite channel H.

[0184] At 1020, the first AP may transmit an optional trigger-2 frame to the second AP. The trigger-2 frame may specify or indicate parameters for constructing a coordinated OFDMA frame for BFRP transmission. The trigger-2 frame may define the RUs that are allowed to be used when responding to BFRP using a TB PPDU for STAs associated with each AP. The trigger-2 frame may be transmitted in a non-HT PPDU format. Upon receiving trigger 2 (if sent), the second AP may further refine or re-estimate its CFO and SFO relative to the first AP.

[0185] At 1025, the method may include jointly transmitting a coordinated OFDMA PPDU including a BFRP for each AP. For example, a first AP and a second AP may jointly transmit a coordinated OFDMA PPDU carrying a BFRP for each AP. Prior to transmission, the second AP may pre-correct its CFO and SFO relative to the first AP based on information received in a trigger frame (e.g., trigger-2 if sent, otherwise trigger-1). In addition, the second AP may apply a cyclic shift to its transmitted signal relative to the first AP's signal to avoid cancellation during the preamble. Based on parameters specified in a previous trigger frame (trigger-2 if sent, otherwise trigger-1), the first AP may transmit BFRP-1 on its respective allocated RU within the coordinated OFDMA frame, and the second AP may transmit BFRP-2. The BFRP-1 and BFRP-2 frames may solicit CSI feedback for composite channel H from corresponding STAs associated with the respective APs. The BFRP frame may specify transmission parameters for each addressed STA, such as MCS, spatial stream allocation, RU allocation, etc. The transmission parameters may be configured so that a response TB PPDU transmitted by the STA based on these settings may be decodable by both the first AP and the second AP.

[0186] At 1030, the method may include responding, by the STA, with a joint TB PPDU. For example, the STAs addressed by and receiving a BFRP frame (e.g., a BFRP-1 frame or a BFRP-2 frame) may jointly transmit a TB PPDU in response. Each participating STA may feedback CSI (e.g., CBR) based on a composite channel H. Feedback may be transmitted according to transmission parameters specified for the STA in the BFRP frame it receives. In some configurations, for NDPA-1, NDPA-2, BFRP-1, and BFRP-2 frames, the first AP and the second AP may use the same MAC address as used for their respective single AP probe transmissions.

[0187] Reference now Fig.11, illustrating an example method 1100 for individual sounding of downlink channels for multiple access points. The method 1100 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with Figures 1 to 5. The method 1100 may include actions 1105 to 1120. At 1105, the method may include transmitting, by the second AP, an NDPA frame targeted to a STA within an associated BSS. At 1110, the method may include transmitting, by the first AP, an NDP frame in response to the NDPA from the second AP. At 1115, the method may include transmitting, by the second AP, a BFRP frame to the target STA. At 1120, the method may include responding, by the target STA receiving the BFRP frame, using a joint TB PPDU.

[0188] At 1105, the method may include transmitting an NDPA frame by the second AP targeting a STA within an associated BSS. For example, the second AP may transmit an NDPA frame addressed to a STA within the BSS of the second AP (e.g., a second group of one or more STAs). The NDPA frame may specify or identify the desired type of CSI feedback for each addressed STA. The NDPA frame may include a field for signaling the first AP to prepare for NDP transmission, for example, using a predetermined AID value in the STA information field within the NDPA frame. The NDPA frame may include one or more association identifiers (AIDs) corresponding to the addressed station of the second AP. The NDPA frame may be transmitted in a non-HTPPDU format. The second AP may send the NDPA directly without waiting for a trigger from the first AP. For example, the second AP may determine which of its associated STAs may participate in coordinated beamforming (CBF) based on DL buffered traffic.

[0189] At 1110, the method may include transmitting an NDP frame by the first AP. For example, the first AP may transmit the NDP frame in response to an NDPA frame received from a second AP. The NDP frame may trigger a detection process for a STA associated with the second AP. The preamble of the NDP frame may include a BSS color corresponding to a BSS of the second AP. The preamble of the NDP frame may identify the BSS of the second AP. The NDP frame may include the same number of long training fields (LTFs) as a conventional single AP NDP transmitted by the first AP within the BSS associated with the first AP. A STA associated with a second AP addressed by the NDPA may measure a DL channel (H1) from the first AP based on the NDP frame.

[0190] At 1115, the method may include transmitting a BFRP frame to the addressed STA. For example, the second AP may transmit a BFRP frame to the addressed STA. The BFRP frame may solicit CSI feedback for DL ​​channel H1 (relative to the first AP) from STAs associated with the second AP (e.g., a second group of STAs) addressed by the NDPA at 1105. The BFRP frame may be transmitted in a non-HT PPDU format. The BFRP frame may include transmission parameters, such as MCS, spatial streams, and resource unit allocations for each STA in the BFRP frame. Each BFRP frame may include one or more AIDs corresponding to an addressed station in the second group (e.g., a STA associated with the second AP). The parameters may be configured so that the first AP can decode the response transmitted by each STA. The type of CSI feedback solicited in the NDPA and the transmission parameters for the feedback response (signaled in the BFRP) may be pre-negotiated between the first AP and the second AP. The pre-negotiation process may be transparent to the STAs associated with the second AP. The first AP and the second AP may exchange communications to determine a type of CSI to be collected on a DL channel and identify the determined type of CSI in one or more NDPA frames.

[0191] At 1120, the method may include responding, by the STA receiving the BFRP frame, using a joint TB PPDU. For example, a STA addressed by a BFRP frame and receiving the BFRP frame may respond by jointly transmitting a TB PPDU. The TB PPDU may enable the STA to provide CSI based on a DL channel (H1) measured by the STA when the NDP frame is received from the first AP. For example, each STA may feedback CSI (e.g., CBR) based on the DL channel H1 measured by the target STA. The CSI feedback may be transmitted according to the transmission parameters specified for each STA in the BFRP frame. The CSI feedback may be received directly by the first AP (over the air). The CSI feedback may be first received by the second AP and then forwarded to the first AP.

[0192] In some configurations, the MAC address and AID used in both the NDPA and BFRP frames may be the same as the MAC address and AID used by the second AP for single AP detection. The STAs associated with the second AP may not be aware that the first AP sent the NDP. It should be noted that a similar process may be implemented by swapping the roles of the first AP and the second AP, for example, for communication between the second AP and the STAs associated with the first AP.

[0193] Reference now Fig.12, illustrating another example method 1200 for individual downlink channel sounding of multiple access points. Method 1200 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with Figures 1 to 5. Method 1200 may include actions 1205 to 1225. At 1205, the method may include transmitting a trigger frame by a first AP to a second AP. At 1210, the method may include transmitting an NDPA frame by the second AP in response to receiving a trigger frame from the first AP. At 1215, the method may include transmitting an NDP frame by the first AP in response to an NDPA from the second AP. At 1220, the method may include transmitting a BFRP frame by the second AP to a target STA identified in the trigger frame. At 1225, the method may include jointly transmitting a TB PPDU by the target STA in response to the BFRP frame from the second AP.

[0194] At 1205, the method may include transmitting a trigger frame. For example, the first AP may transmit a trigger frame to the second AP. The trigger frame from the first AP may include information for the second AP to construct subsequent NDPA and BFRP frames. The trigger frame may include a set of STAs to be probed within a BSS associated with the second AP (i.e., whose channel state information (CSI) from the first AP is to be measured), the type of CSI feedback expected from each STA, and additional information for constructing the BFRP frame, such as the RU allocation for each STA, the MCS assigned to each STA, and the number of spatial streams (Nss) assigned to each STA being probed.

[0195] At 1210, the method may include transmitting, by the second AP, an NDPA frame. For example, based on information received in a trigger frame from the first AP, the second AP may transmit the NDPA frame. The NDPA frame from the second AP may be addressed to a specific STA within a BSS associated with the second AP, as identified in the trigger frame. The NDPA frame may be transmitted in a non-HT PPDU format.

[0196] At 1215, the method may include transmitting, by the first AP, an NDP frame. For example, the first AP may transmit the NDP frame in response to an NDPA received from a second AP. The preamble of the NDP frame may include a BSS color corresponding to a BSS of the second AP. The number of LTFs in the NDP frame may be the same as a conventional single-AP NDP transmitted by the first AP within the BSS associated with the first AP. Based on the NDP frame, a target STA associated with the second AP (which is addressed by the NDPA) may measure a DL channel (H1) from the first AP.

[0197] At 1220, the method may include transmitting, by the second AP, a BFRP frame to the target STA. For example, the second AP may transmit the BFRP frame to the target STA identified in the trigger frame. The BFRP frame from the second AP may solicit CSI feedback for channel H1 from the STA associated with the second AP. The BFRP frame may be transmitted in a non-HT PPDU format. The BFRP frame may include per-STA transmission parameters, such as MCS, spatial stream allocation, and RU allocation. The transmission parameters may be configured so that a response transmitted by the target STA based on the transmission parameters may be decoded by the first AP.

[0198] At 1225, the method may include jointly transmitting, by the target STAs, the TB PPDUs. For example, the target STAs may jointly transmit the TB PPDUs in response to receiving a BFRP frame from the second AP. Each STA may feedback CSI (e.g., CBR) based on the DL channel H1 measured by each target STA. The CSI feedback transmission may follow per-STA parameters specified in the received BFRP frame. The CSI feedback may be received directly by the first AP (over the air), or may be first received by the second AP and then forwarded to the first AP.

[0199] In some configurations, the MAC address and AID used in both the NDPA and BFRP frames may be the same as the MAC address and AID used by the second AP for single AP detection. The detection process may be transparent to the target STAs of the second AP. The target STAs of the second AP may not be aware that the first AP is transmitting NDP frames. A similar process may be implemented by swapping the roles of the first AP and the second AP, for example, for communication between the second AP and the STAs associated with the first AP.

[0200] Reference now Fig.13 , illustrating another example method 1300 for individual sounding of downlink channels of multiple access points. The method 1300 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1300 may include actions 1305 to 1320. At 1305, the method may include transmitting, by the first AP, a multi-AP NDPA frame. At 1310, the method may include transmitting, by the first AP, a multi-AP NDP frame. At 1315, the method may include transmitting, by the first AP, a multi-AP BFRP frame. At 1320, the method may include jointly transmitting, by the STAs addressed by the multi-AP BFRP frame, a TB PPDU.

[0201] At 1305, the method may include transmitting a multi-AP NDPA frame. For example, the first AP may transmit a multi-AP NDPA frame. The multi-AP NDPA frame may use a multi-AP MAC address for the TA and BSSID fields in the MAC header, which may be different from the conventional TA and BSSID addresses used by each AP for a single AP NDPA frame. The NDPA frame may use a multi-AP broadcast reception address (RA), which is different from the broadcast RA used by each AP for a single AP NDPA frame. The STA that is expected to receive the NDPA frame can recognize the address, for example, the STA may maintain an additional MAC address for decoding the multi-AP NDPA. The NDPA frame may include a STA information field for the STA associated with the first AP. The NDPA frame may include a STA information field for the STA associated with the second AP. Each STA information field may be addressed to the STA via an AID, which may be different from the AID used to address the STA in a conventional single AP NDPA frame. Each STA information field may specify or identify the type of CSI feedback solicited from the STA addressed by the STA information field. The multi-AP NDPA frame may indicate a specific multi-AP detection sequence being used to distinguish it from a single AP and other multi-AP detection sequences. The multi-AP NDPA frame format may be a non-HT PPDU.

[0202] At 1310, the method may include transmitting a multi-AP NDP frame. For example, the first AP may transmit the multi-AP NDP frame. The SIG field in the multi-AP NDP frame may indicate a predefined multi-AP BSS color that is different from the BSS color signaled in a conventional single-AP NDP within each BSS. The number of LTFs in the multi-AP NDP frame may be the same as a conventional single-AP NDP transmitted by the first AP within the BSS associated with the first AP. Based on the information in the multi-AP NDP, a STA addressed by the multi-AP NDP frame and receiving the multi-AP NDP frame may estimate a DL channel H1 from the first AP.

[0203] At 1315, the method may include transmitting a multi-AP BFRP frame. For example, the first AP may transmit a multi-AP BFRP frame. The multi-AP BFRP frame from the first AP may use the multi-AP MAC address for the TA and BSSID fields in the MAC header. The multi-AP MAC address used for the TA and BSSID fields in the MAC header may be different from the TA, BSSID address used by each AP for a single AP BFRP frame. The multi-AP BFRP frame may use a multi-AP broadcast RA, which is different from the broadcast RA used by each AP for a single AP BFRP frame. The multi-AP address may be identified by the STA that is expected to receive the BFRP. The BFRP frame may include a UserInfo field for the STA associated with the first AP. The BFRP frame may include a UserInfo field for the STA associated with the second AP. Each UserInfo field may have an AID assigned to each STA, which may be different from the AID assigned to the UserInfo field within its corresponding BSS. The multi-AP BFRP frame may solicit CSI feedback on the DL channel H1 from the STA associated with the first AP. The multi-AP BFRP frame may solicit CSI feedback on DL channel H1 from STAs associated with the second AP.The multi-AP BFRP frame format may be a non-HT PPDU.

[0204] At 1320, the method may include jointly transmitting a TB PPDU by the STAs addressed by the multi-AP BFRP frame. For example, the STAs addressed by the multi-AP BFRP frame and receiving the multi-AP BFRP frame may jointly transmit a TB PPDU in response. Each STA may transmit on the RU and spatial stream assigned to the STA in the multi-AP BFRP frame. Each STA may feedback CSI (e.g., CBR) based on the DL channel H1 measured from the first AP.

[0205] The process of the second AP with respect to the STAs associated with the first AP and the STAs associated with the second AP may be the same as described above, with the roles of the first AP and the second AP swapped.

[0206] Reference now Fig.14, illustrating another example method 1400 for individual downlink channel probing of multiple access points. The method 1400 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1400 may include actions 1405 to 1435. At 1405, the method may include transmitting, by a first AP, an NDPA frame (e.g., an NDPA-1 frame) as a trigger for a second AP. At 1410, the method may include transmitting, by a second AP, an NDPA frame (e.g., an NDPA-2 frame) in response to an NDPA frame from a first AP. At 1415, the method may include transmitting, by a first AP, a multi-AP NDP frame. At 1420, the method may include transmitting, by a first AP, a BFRP frame (e.g., a BFRP-1 frame) soliciting CSI feedback for channel H1 from STAs associated with the first AP. At 1425, the method may include responding, by STAs associated with the first AP, using a joint TB PPDU. At 1430, the method may include transmitting, by the second AP, a BFRP frame (eg, a BFRP-2 frame) soliciting CSI feedback for channel H1 from STAs associated with the second AP. At 1435, the method may include responding, by the STAs associated with the second AP, with a joint TB PPDU.

[0207] At 1405, the method may include transmitting, by the first AP, an NDPA frame. For example, the first AP may transmit an NDPA-1 frame, which may be used as a trigger for the second AP, for example, using a predetermined AID value within the STA information field. The NDPA-1 frame may include a STA information field addressed to STAs associated with the first AP. The STA information field may specify or identify the type of CSI feedback expected from each STA. The NDPA-1 frame may indicate a multi-AP sounding sequence being used to distinguish the sequence from single AP and other multi-AP sounding sequences. The format of the NDPA-1 frame may be a non-HT PPDU.

[0208] At 1410, the method may include transmitting, by the second AP, an NDPA frame. For example, the second AP may transmit an NDPA-2 frame including a STA information field addressed to STAs associated with the second AP. The STA information field may identify the type of feedback solicited from each STA. The NDPA-2 frame may indicate a multi-AP sounding sequence being used. The format of the NDPA-2 frame may be a non-HT PPDU.

[0209] At 1415, the method may include transmitting a multi-AP NDP frame. For example, the first AP may transmit the multi-AP NDP frame. The signal field (SIG field) in the multi-AP NDP frame from the first AP may indicate a multi-AP BSS color, which is different from the BSS color signaled in a conventional single-AP NDP within each BSS. The number of LTFs in the NDP frame may be the same as a conventional single-AP NDP transmitted by the first AP within its own BSS. A STA addressed by and receiving the NDPA-1 or NDPA-2 frame may measure a DL channel H1 from the first AP based on the information in the multi-AP NDP.

[0210] At 1420, the method may include transmitting, by the first AP, a BFRP frame soliciting CSI feedback. For example, the first AP may transmit a BFRP-1 frame soliciting CSI feedback for channel H1 from STAs associated with the first AP. The format of the BFRP-1 frame may be non-HTPPDU.

[0211] At 1425, the method may include responding, by the STAs associated with the first AP, with a joint TB PPDU. For example, the STAs associated with the first AP may respond with CSI feedback. The STAs associated with the first AP that are addressed by and receive the BFRP-1 frame may jointly transmit a TB PPDU in response. Each STA may feedback CSI (e.g., CBR) based on DL channel H1 from the first AP. The CSI feedback may be transmitted according to transmission parameters assigned to each STA in the BFRP-1 frame (e.g., MCS, spatial streams, and RU allocations).

[0212] At 1430, the method may include transmitting, by the second AP, a BFRP frame soliciting CSI feedback. For example, the second AP may transmit a BFRP-2 frame soliciting CSI feedback for channel H1 from STAs associated with the second AP. The format of the BFRP-2 may be a non-HTPPDU. Transmission parameters (e.g., MCS, spatial stream allocation, and resource unit (RU) allocation) specified for each STA in the BFRP-2 frame may be configured so that the first AP can correctly decode a response transmitted by the STA based on the transmission parameters.

[0213] At 1435, the method may include responding, by the STAs associated with the second AP, using a joint TB PPDU. For example, the STAs associated with the second AP that are addressed by and receive the BFRP-2 frame may jointly transmit a TB PPDU in response. Each STA may feedback CSI (e.g., CBR) based on the downlink channel H1 from the first AP. The CSI feedback may be transmitted according to the transmission parameters (e.g., MCS, spatial streams, and RU allocation) assigned to each STA in the BFRP-2 frame. In some configurations, the MAC address and AID used in NDPA-1 and BFRP-1 may be the same as the corresponding MAC address and AID used by the first AP for single AP detection. In some configurations, the MAC address and AID used in NDPA-2 and BFRP-2 may be the same as the corresponding MAC address and AID used by the second AP for single AP detection.

[0214] Reference now Fig.15 , illustrating another example method 1500 for individual sounding of downlink channels for multiple access points. The method 1500 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1500 may include actions 1505 to 1525. At 1505, the method may include transmitting, by a first AP, a trigger frame (e.g., a trigger-1 frame) to a second AP. At 1510, the method may include jointly transmitting, by the first AP and the second AP, a coordinated OFDMA PPDU including an NDPA for each AP in response to the trigger frame. At 1515, the method may include transmitting a multi-AP NDP frame from the first AP. At 1520, the method may include transmitting, by the first AP to the second AP, a trigger frame (e.g., a trigger-2 frame). At 1525, the method may include jointly transmitting, by the first AP and the second AP, a coordinated OFDMA PPDU including a BFRP for each AP. At 1530, the method may include jointly transmitting, by the STAs addressed by the BFRP of each AP, a TB PPDU.

[0215] At 1505, the method may include transmitting a trigger frame by the first AP to the second AP. For example, the first AP may transmit a trigger-1 frame indicating parameters for constructing a coordinated orthogonal frequency division multiple access (OFDMA) frame for transmitting NDPA information. The parameters in the trigger-1 frame may include aspects such as RU allocation, symbol duration, guard interval, and total duration for each AP. The parameters may be similar to the parameters used in the trigger frame to solicit TB PPDUs. The second AP may use the information in the trigger-1 frame to estimate CFO and SFO relative to the first AP. The format of the trigger-1 frame may be a non-HT PPDU. The trigger-1 frame may include parameters for constructing a coordinated OFDMA frame for BFRP, which may include information about allowed RUs for STAs for each AP to transmit TB PPDUs in response to the BFRP frame.

[0216] At 1510, the method may include jointly transmitting a coordinated OFDMA PPDU including an NDPA for each AP. For example, a first AP and a second AP may jointly transmit a coordinated OFDMA PPDU including an NDPA frame associated with each AP. Prior to transmission, the second AP may pre-correct the CFO and SFO relative to the first AP to ensure signal alignment. The second AP may apply a cyclic shift (e.g., for a preamble) to the signal it transmits relative to the first AP to avoid signal cancellation. Based on the parameters specified in trigger-1, the first AP and the second AP may transmit NDPA-1 and NDPA-2 on their allocated RUs, respectively. Each NDPA frame (NDPA-1 and NDPA-2) may include a STA information field for STAs addressed to the corresponding AP using their AIDs. The STA information field may specify or identify the type of feedback solicited from each STA. NDPA-1 and NDPA-2 may indicate a multi-AP detection sequence being used to distinguish the sequence from single AP and other multi-AP detection sequences.

[0217] At 1515, the method may include transmitting a multi-AP NDP frame. For example, the first AP may transmit the multi-AP NDP frame. The SIG field in the multi-AP NDP frame may indicate a multi-AP BSS color, which is different from the BSS color signaled in a conventional single-AP NDP within each BSS. The multi-AP NDP frame may include the same number of LTFs as a conventional single-AP NDP transmitted by the first AP within its own BSS. A STA addressed by and receiving the NDPA-1 or NDPA-2 may measure the DL channel H1 from the first AP using the NDP.

[0218] At 1520, the first AP may optionally transmit a trigger-2 frame to the second AP. Similar to trigger-1, the trigger-2 frame may specify parameters for constructing a coordinated OFDMA frame for BFRP and the allowed RUs for each AP's STA to transmit a TB PPDU in response to BFRP. The format of the trigger-2 frame may be a non-HT PPDU. If transmitted, the second AP may refine or re-estimate the CFO and SFO relative to the first AP.

[0219] At 1525, the method may include jointly transmitting a coordinated OFDMA PPDU including a BFRP for each AP. For example, a first AP and a second AP may jointly transmit a coordinated OFDMA PPDU including a BFRP frame for each AP. The second AP may pre-correct the CFO and SFO relative to the first AP before transmission. The second AP may apply a cyclic shift to its transmitted signal relative to the first AP to avoid signal cancellation (for the preamble). Based on the parameters specified in the previous trigger frame (trigger-2 if present, otherwise trigger-1), the first AP and the second AP may transmit BFRP-1 and BFRP-2 on their allocated RUs, respectively. BFRP-1 and BFRP-2 may solicit CSI feedback for DL ​​channel H1 from the STAs of the first AP and the STAs of the second AP, respectively. The transmission parameters specified for each STA in the BFRP frame (e.g., MCS, spatial stream allocation, and RU allocation) may be configured so that the first AP can correctly decode the response transmitted by the corresponding STA based on the transmission parameters.

[0220] At 1530, the method may include jointly transmitting a TB PPDU by the STAs. For example, the STAs addressed by BFRP-1 or BFRP-2 and receiving BFRP-1 or BFRP-2 may jointly transmit a TB PPDU in response. Each STA may feedback CSI (e.g., CBR) based on DL channel H1. The CSI feedback may be transmitted according to the transmission parameters specified for the STA in its corresponding BFRP frame.

[0221] In some configurations, the MAC addresses used in NDPA-1, NDPA-2, BFRP-1, and BFRP-2 may be the same as the corresponding MAC addresses used by the first AP and the second AP for single AP detection. The configuration for the second AP to detect STAs of the first AP and the second AP may be the same as the first AP, where the roles of the first AP and the second AP are swapped.

[0222] Reference now Fig.16, illustrating another example method 1600 for individual downlink channel sounding of multiple access points. The method 1600 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1600 may include actions 1605 to 1640. At 1605, the method may include transmitting, by a first AP, an NDPA frame (e.g., an NDPA-1 frame). At 1610, the method may include transmitting, by a second AP, an NDPA frame (e.g., an NDPA-2 frame) in response to an NDPA frame from the first AP. At 1615, the method may include transmitting, by the first AP, an NDP frame (e.g., an NDP-1 frame). At 1620, the method may include transmitting, by the second AP, an NDP frame (e.g., an NDP-2 frame). At 1625, the method may include transmitting, by the first AP, a BFRP frame (e.g., a BFRP-1 frame). At 1630, the method may include jointly transmitting, by STAs of the first AP in response to the BFRP-1, a TB PPDU. At 1635, the method may include transmitting, by the second AP, a BFRP frame (eg, a BFRP-2 frame). At 1640, the method may include jointly transmitting, by the STAs of the second AP, a TB PPDU in response to the BFRP frame (eg, the BFRP-2 frame).

[0223] At 1605, the method may include transmitting, by the first AP, an NDPA frame. For example, the first AP may transmit an NDPA-1 frame, which may be used as a trigger for the second AP, e.g., using a predetermined AID value within the STA Information field. The NDPA-1 frame may include a STA Information field addressed to one or more of the STAs associated with the first AP. The STA Information field may identify the type of feedback solicited from each STA, e.g., indicating that CSI feedback from two APs (H1 and H2) is solicited. The frame may also indicate a specific multi-AP sounding sequence being used. The format of the NDPA-1 frame may be a non-HT PPDU.

[0224] At 1610, the method may include transmitting an NDPA frame in response. For example, the second AP may transmit an NDPA-2 frame in response to the NDPA-1. The NDPA-2 frame may include a STA information field addressed to each of the STAs associated with the second AP. The STA information field may identify the type of feedback solicited from each STA, for example, indicating that CSI from two APs is solicited. The NDPA-2 frame may indicate a specific multi-AP sounding sequence being used to distinguish the sequence from a single AP and / or other multi-AP sounding sequences. The format of the NDPA-2 frame may be a non-HT PPDU.

[0225] At 1615, the method may include transmitting, by the first AP, an NDP frame. For example, the first AP may transmit an NDP-1 frame that includes the same number of LTFs as a regular single-AP NDP transmitted by the first AP within its associated BSS. A STA addressed by and receiving the NDPA-1 or NDPA-2 may measure the DL channel H1 from the first AP using information in the NDP-1 frame.

[0226] At 1620, the method may include transmitting, by the second AP, an NDP frame. For example, the second AP may transmit an NDP-2 frame that includes the same number of LTFs as a regular single-AP NDP transmitted by the second AP within its associated BSS. A STA addressed by and receiving the NDPA-1 or NDPA-2 may measure the DL channel H2 from the second AP using the information in the NDP-2.

[0227] At 1625, the method may include transmitting, by the first AP, a BFRP frame. For example, the first AP may transmit a BFRP-1 frame that solicits individual CSI reports corresponding to DL channels H1 and H2 from STAs associated with the first AP. The format of the BFRP-1 may be a non-HT PPDU. Transmission parameters (e.g., MCS, spatial stream allocation, and RU allocation) specified for each STA in the BFRP frame may be configured so that the first AP and the second AP may correctly decode responses transmitted by the STAs based on the transmission parameters.

[0228] At 1630, the method may include jointly transmitting a TB PPDU by the STAs of the first AP. For example, the associated STAs of the first AP that are addressed by BFRP-1 and receive BFRP-1 may jointly transmit a TB PPDU in response. Each STA may feedback two CSI reports, such as CBRs: one report based on channel H1 of the first AP and another report based on channel H2 of the second AP. The CSI reports may be transmitted according to transmission parameters specified for the STAs in the BFRP frame.

[0229] At 1635, the method may include transmitting, by the second AP, a BFRP frame. For example, the second AP may transmit a BFRP-2 frame that solicits individual CSI reports corresponding to DL channels H1 and H2 from STAs associated with the second AP. The format of the BFRP-2 may be a non-HT PPDU. The transmission parameters (e.g., MCS, spatial stream allocation, and RU allocation) specified for each STA in the BFRP frame may be configured so that both the first AP and the second AP may correctly decode a response transmitted by the STA based on the transmission parameters.

[0230] At 1640, the method may include jointly transmitting, by the STAs of the second AP, a TB PPDU. For example, the STAs of the second AP that are addressed by a BFRP frame (e.g., a BFRP-2 frame) and receive the BFRP frame may jointly transmit a TB PPDU in response. Each STA may feed back two CSI reports, e.g., CBR: one report based on channel H1 of the first AP and another report based on channel H2 of the second AP. The CSI reports may be transmitted according to transmission parameters specified for the STAs in the BFRP frame.

[0231] In some configurations, the MAC address and AID used in NDPA-1 and BFRP-1 may be the same as the corresponding MAC address and AID used by the first AP for single AP detection. In some configurations, the MAC address and AID used in NDPA-2 and BFRP-2 may be the same as the corresponding MAC address and AID used by the second AP for single AP detection.

[0232] Reference now Fig.17 , illustrating another example method 1700 for individual sounding of downlink channels for multiple access points. The method 1700 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1700 may include actions 1705 to 1730. At 1705, the method may include transmitting, by a first AP, a trigger frame (e.g., a trigger-1 frame). At 1710, the method may include jointly transmitting, by a first AP and a second AP, a coordinated OFDMA PPDU including an NDPA for each AP. At 1715, the method may include transmitting, by a first AP, an NDP frame (e.g., an NDP-1 frame). At 1720, the method may include transmitting, by a second AP, an NDP frame (e.g., an NDP-2 frame). At 1725, the method may include transmitting, from a first AP to a second AP, a trigger frame (e.g., a trigger-2 frame). At 1730, the method may include jointly transmitting, by the first AP and the second AP, a coordinated OFDMA PPDU including a BFRP for each AP. At 1735, the method may include jointly transmitting, by the STAs addressed by a BFRP frame (e.g., a BFRP-1 frame or a BFRP-2 frame), a TB PPDU.

[0233] At 1705, the method may include transmitting a trigger frame by the first AP. For example, the first AP may transmit a trigger-1 frame indicating parameters for constructing a coordinated OFDMA frame for transmitting NDPA information. The parameters may include aspects such as RU allocation, symbol duration, guard interval, and total duration for each AP. The parameters may be similar to the parameters used in the trigger frame for requesting a TBPPDU. The second AP may use the information in the trigger-1 frame to estimate the CFO and SFO relative to the first AP. The format of the trigger-1 frame may be a non-HT PPDU. The trigger-1 frame may include parameters for constructing a coordinated OFDMA frame for a BFRP frame, which may include information about the allowed RUs for each STA associated with the corresponding AP to transmit a TBPPDU in response to the BFRP frame.

[0234] At 1710, the method may include jointly transmitting a coordinated OFDMA PPDU including an NDPA for each AP. For example, a first AP and a second AP may jointly transmit a coordinated OFDMA PPDU including an NDPA frame associated with each AP. Prior to transmission, the second AP may pre-correct the CFO and SFO relative to the first AP to avoid signal cancellation. The second AP may apply a cyclic shift to the signal it transmits relative to the first AP, particularly for the preamble. Based on the parameters specified in the trigger-1 frame, the first AP and the second AP may transmit NDPA-1 and NDPA-2 on their allocated RUs, respectively. Each NDPA frame may be broadcast to the STAs of the corresponding AP and may include a STA information field that uses its AID to specify or identify the type of feedback expected from each STA. NDPA-1 and NDPA-2 may indicate a specific multi-AP detection sequence being used to distinguish the sequence from single AP and other multi-AP detection sequences.

[0235] At 1715, the method may include transmitting, by the first AP, an NDP frame. For example, the first AP may transmit an NDP-1 frame, which may include the same number of LTFs as a regular single-AP NDP transmitted by the first AP within its associated BSS. A STA addressed by and receiving the NDPA-1 or NDPA-2 may measure the DL channel H1 from the first AP using information in the NDP-1 frame.

[0236] At 1720, the method may include transmitting, by the second AP, an NDP frame. For example, the second AP may transmit an NDP-2 frame that may include the same number of LTFs as a regular single-AP NDP transmitted by the second AP within its associated BSS. A STA addressed by and receiving the NDPA-1 or NDPA-2 may measure the DL channel H2 from the second AP using the NDP-2 frame.

[0237] At 1725, the first AP may optionally transmit a trigger-2 frame to the second AP. Similar to the trigger-1 frame, the trigger-2 frame may indicate the parameters of the coordinated OFDMA frame for constructing the BFRP and the allowed RUs for the STAs of each AP to transmit TB PPDUs in response to the BFRP. The format of the trigger-2 frame may be a non-HT PPDU. If transmitted, the second AP may refine or re-estimate the CFO and SFO relative to the first AP.

[0238] At 1730, the method may include jointly transmitting a coordinated OFDMA PPDU including a BFRP for each AP. For example, a first AP and a second AP may jointly transmit a coordinated OFDMA PPDU including a BFRP-1 frame from the first AP and a BFRP-2 frame from the second AP. The second AP may pre-correct the corresponding CFO and SFO relative to the first AP before transmission. The second AP may apply a cyclic shift to its transmitted signal relative to the first AP to avoid signal cancellation (for the preamble). Based on the parameters specified in the previous trigger frame (trigger-2 if present, trigger-1 otherwise), the first AP and the second AP may transmit BFRP-1 and BFRP-2 addressed to their corresponding STAs on their allocated RUs, respectively. BFRP-1 and BFRP-2 may solicit two individual CSI reports corresponding to DL channels H1 and H2 from the STAs of the first AP and the STAs of the second AP, respectively. The transmission parameters (eg, MCS, spatial stream allocation, RU allocation, etc.) specified for each STA in the BFRP frame may be configured so that a response transmitted by each STA based on the transmission parameters may be correctly decoded by the first AP and the second AP.

[0239] At 1735, the method may include jointly transmitting, by the STAs, a TB PPDU. For example, STAs addressed by a BFRP frame (e.g., a BFRP-1 frame or a BFRP-2 frame) and receiving the BFRP frame may jointly transmit a TB PPDU in response. Each STA may feed back two CSI reports, e.g., CBR: one based on a channel of a first AP and another report based on a channel of a second AP. The CSI reports may be transmitted according to transmission parameters specified for the STA in the BFRP frame.

[0240] In some configurations, the MAC address and AID used in NDPA-1 and BFRP-1 may be the same as the corresponding MAC address and AID used by the first AP for single AP detection. In some configurations, the MAC address and AID used in NDPA-2 and BFRP-2 may be the same as the corresponding MAC address and AID used by the second AP for single AP detection.

[0241] Reference now Fig.18 , illustrating another example method 1800 for individual sounding of downlink channels of multiple access points. The method 1800 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1800 may include actions 1805 to 1825. At 1805, the method may include transmitting, by a first AP, an NDPA frame to STAs within its associated BSS. At 1810, the method may include transmitting, by a first AP, an NDP frame (e.g., an NDP-1 frame). At 1815, the method may include transmitting, by a second AP, an NDP frame (e.g., an NDP-2 frame). At 1820, the method may include transmitting, by a first AP, a BFRP frame to its associated STAs. At 1825, the method may include jointly transmitting, by STAs of the first AP that receive the BFRP frame, a TB PPDU.

[0242] At 1805, the method may include transmitting, by the first AP, an NDPA frame to the STAs. For example, the first AP may transmit the NDPA frame to the STAs within its BSS. The NDPA frame may be used as a trigger for the second AP, for example, using a predetermined AID value within the STA information field. The NDPA frame may include a STA information field addressed to one or more of the STAs associated with the first AP. The STA information field may identify the type of feedback solicited from each STA, for example, indicating that CSI from two APs is solicited. The format of the NDPA frame may be a non-HT PPDU. The NDPA frame may indicate a multi-AP detection sequence being used to distinguish the sequence from a single AP and other multi-AP detection sequences.

[0243] At 1810, the method may include transmitting, by the first AP, an NDP frame. For example, the first AP may transmit an NDP-1 frame, which may include the same number of LTFs as a regular single-AP NDP transmitted by the first AP within its associated BSS. The preamble of the NDP-1 frame may signal a BSS color corresponding to the BSS associated with the first AP. A STA associated with the first AP addressed by the NDPA frame may use the NDP-1 frame to measure a DL channel H1 from the first AP.

[0244] At 1815, the method may include transmitting, by the second AP, an NDP frame. For example, the second AP may transmit an NDP-2 frame that may include the same number of LTFs as a regular single-AP NDP transmitted by the second AP within its associated BSS. The preamble of the NDP-2 frame may signal a BSS color corresponding to the BSS associated with the second AP. A STA associated with the first AP addressed by the NDPA frame may use the NDP-2 frame to measure a DL channel H2 from the second AP.

[0245] At 1820, the method may include transmitting, by the first AP, a BFRP frame to the associated STAs. For example, the first AP may transmit a BFRP frame to the STAs within its BSS (which may be addressed in the NDPA frame) to solicit two individual CSI reports corresponding to DL channels H1 and H2 from the target STAs. The format of the BFRP frame may be a non-HT PPDU. The transmission parameters (e.g., MCS, spatial stream allocation, and RU allocation) specified for each STA in the BFRP frame may be configured so that a response transmitted by the STA based on the transmission parameters can be correctly decoded by the first AP and the second AP.

[0246] At 1825, the method may include jointly transmitting a TB PPDU by the STAs of the first AP. For example, the STAs of the first AP that are addressed by the BFRP frame and receive the BFRP frame may jointly transmit a TB PPDU in response. Each STA may feedback two CSI reports, such as CBRs: one based on channel H1 of the first AP and the other based on channel H2 of the second AP. The CSI report may be transmitted according to the transmission parameters specified for the STA in the BFRP frame. The CSI feedback may be received directly at the first AP (over the air). The CSI feedback may be received directly by the second AP (over the air). The CSI feedback may be first received by the first AP and then forwarded to the second AP. In some configurations, the MAC address and AID used in the NDPA and BFRP may be the same as the corresponding MAC address and AID used by the first AP for single AP detection.

[0247] Reference now Fig.19, illustrating another example method 1900 for individual downlink channel sounding of multiple access points. The method 1900 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 1900 may include actions 1905 to 1930. At 1905, the method may include transmitting an NDPA frame from a first AP to its STAs within a BSS. At 1910, the method may include transmitting an NDP frame (e.g., an NDP-1 frame) from the first AP. At 1915, the method may include transmitting an NDP frame (e.g., an NDP-2 frame) from a second AP. At 1920, the method may include transmitting a BFRP frame from the first AP to associated STAs. At 1925, the method may include jointly transmitting a TB PPDU (e.g., a TB PPDU-1) by the STAs associated with the first AP that are addressed by the BFRP frame. At 1930, the method may include jointly transmitting, by STAs associated with the first AP addressed by the BFRP frame, a TB PPDU (eg, TB PPDU-2).

[0248] At 1905, the method may include transmitting an NDPA frame by a first AP. For example, the first AP may transmit an NDPA frame to an associated STA within its BSS. The NDPA frame may be used as a trigger for a second AP, for example, using a predetermined AID value within a STA information field. The NDPA frame may include a STA information field addressed to a STA associated with the first AP. The STA information field may identify the type of feedback solicited from each STA. For example, the STA information field addressed to the first STA may indicate that CSI from two APs is solicited from the first STA. For example, the STA information field addressed to the second STA may indicate that CSI only from the first AP is solicited from the second STA. For example, the STA information field addressed to the third STA may indicate that CSI only from the second AP is solicited from the third STA. The format of the NDPA frame may be a non-HT PPDU. The NDPA frame may indicate a multi-AP detection sequence being used to distinguish the sequence from a single AP and other multi-AP detection sequences.

[0249] At 1910, the method may include transmitting, by the first AP, an NDP frame. For example, the first AP may transmit an NDP-1 frame, which may include the same number of LTFs as a regular single-AP NDP transmitted by the first AP within its associated BSS. The preamble of the NDP-1 frame may signal a BSS color corresponding to the BSS associated with the first AP. A STA associated with the first AP addressed by the NDPA frame may measure a DL channel H1 from the first AP using the NDP-1.

[0250] At 1915, the method may include transmitting, by the second AP, an NDP frame. For example, the second AP may transmit an NDP-2 frame, which may include the same number of LTFs as a regular single AP NDP transmitted by the second AP within its associated BSS. The preamble of the NDP-2 may signal a BSS color corresponding to the BSS associated with the second AP. A STA associated with the first AP addressed by the NDPA frame may use the NDP-2 frame to measure a DL channel H2 from the second AP.

[0251] At 1920, the method may include transmitting, by the first AP, a BFRP frame to associated STAs. For example, the first AP may transmit a BFRP frame to STAs within its BSS (which may be addressed in the NDPA) to solicit individual CSI reports corresponding to DL channels H1 and H2 from the target STAs. The format of the BFRP frame may be a non-HT PPDU. The BFRP frame may solicit feedback via two TB PPDU transmissions. The BFRP frame may specify or identify two separate sets of transmission parameters (e.g., MCS, spatial stream allocation, RU allocation for each STA), one set for each TB PPDU. The set-1 parameters may be configured so that a TB PPDU-1 transmitted by a STA and included in set-1 may be correctly decoded by the first AP. The set-2 parameters may be configured so that a TB PPDU-2 transmitted by a STA and included in set-2 may be correctly decoded by a second AP. Any STA included in both set-1 and set-2 may transmit both TB PPDU-1 and TB PPDU-2.

[0252] At 1925, the method may include jointly transmitting, by the STAs associated with the first AP, a TB PPDU. For example, the STAs associated with the first AP addressed by the BFRP frame via set-1 may jointly transmit a TB PPDU-1 in response. Each STA may feed back a CSI report (e.g., a compressed beamforming report (CBR)) based on channel H1 of the first AP. The CSI report may be transmitted according to a transmission parameter set-1 specified for the STA in the BFRP frame.

[0253] At 1930, the method may include jointly transmitting, by the STAs associated with the first AP, a TB PPDU. For example, the STAs associated with the first AP addressed by the BFRP frame via set-2 may jointly transmit a TB PPDU-2 in response. Each STA may feedback a CSI report (e.g., CBR) based on channel H2 of the second AP. The CSI report may be transmitted according to transmission parameter set-2 specified for the STA in the BFRP.

[0254] Explicit sounding options (e.g., sounding in which CSI feedback is explicitly solicited and obtained from STAs) may be categorized as joint sounding and individual sounding options. Examples of explicit sounding options may include methods 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, whose individual operations may be mixed and matched between these examples depending on the design. In some implementations, the explicit sounding option may include one or more stages. During the announcement stage, one or more APs may transmit a trigger and / or NDPA frame that initiates the sounding process. The NDPA frame may inform the STA and other APs about the specific type of sounding sequence and the type of CSI feedback solicited in preparation for subsequent stages. During the channel sounding stage, one or more APs may transmit a null data packet (NDP), which may be used by the STA to estimate the corresponding downlink channel from the AP to prepare for CSI feedback. During the feedback phase, one or more APs may solicit CSI feedback from STAs via BFRP frames, to which STAs respond by transmitting CSI feedback in TBPPDUs. It may be noted that as described by example methods 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, and 1900, the explicit sounding option outlines multiple variants of the three phases (announcement, channel sounding, and feedback) and describes specific combinations of these variants. It should be noted that more combinations of these variants of the announcement, channel sounding, and feedback phases are possible, which may result in more explicit sounding options.

[0255] Reference now Fig. 20 , illustrating an example method 2000 for implicit downlink channel sounding with respect to multiple access points. The method 2000 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 2000 may include actions 2005 to 2015. At 2005, the method may include transmitting, by a first AP, an implicit NDPA frame. At 2010, the method may include jointly transmitting, by all STAs associated with the first AP, addressed by the implicit NDPA frame, a T-NDP. At 2015, the method may include estimating, by the first AP and the second AP, uplink channels from participating STAs based on the received T-NDP.

[0256] At 2005, the method may include transmitting an implicit NDPA frame by the first AP. For example, the first AP may transmit an implicit NDPA frame to solicit an uplink T-NDP frame from a first group of STAs associated with the first AP. The implicit NDPA frame may be used as a trigger for the second AP, for example, using a predetermined AID value within the STA information field. The implicit NDPA frame may include a field for signaling the second AP to prepare to receive the transmission of the T-NDP frame. The implicit NDPA frame may identify the transmission parameters of the T-NDP, such as bandwidth, total number of LTFs, LTF duration, guard interval, spatial stream position of each STA, number of spatial streams of each STA, RU allocation of each STA, etc. Each STA information may be provided in the STA information field. Each STA information field may be addressed by the AID of each STA. The STA associated with the first AP may estimate the CFO and SFO relative to the first AP based on the received implicit NDPA frame. The format of the implicit NDPA frame may be a non-HT PPDU.

[0257] At 2010, the method may include jointly transmitting a T-NDP by all STAs associated with the first AP addressed by an implicit NDPA frame. For example, all STAs associated with the first AP addressed by an implicit NDPA frame may jointly transmit the T-NDP according to specified transmission parameters. The first AP and the second AP may receive the T-NDP frame transmitted by the STAs (e.g., the first group) associated with the first AP. Each STA may pre-compensate its estimated CFO and SFO based on the implicit NDPA frame.

[0258] At 2015, the method may include estimating uplink channels from participating STAs based on the received T-NDP. For example, the first AP and the second AP may estimate respective uplink channels from participating STAs based on the received T-NDP. The first AP may share its estimated uplink channel and any reciprocity coefficients desired for estimating the uplink channel or translating the uplink channel into one or more downlink channels with the second AP, and vice versa. The first AP and the second AP may synchronize their reception of T-NDP frames to concurrently estimate the uplink channel. In some configurations, the MAC address and AID used in the implicit NDPA frame may be the same as the MAC address and AID used by the first AP for single AP detection.

[0259] Reference now Fig.21, illustrating another example method 2100 for implicitly probing downlink channels for multiple access points. The method 2100 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 2100 may include actions 2105 to 2120. At 2105, the method may include transmitting, by a first AP, an implicit NDPA frame (e.g., an implicit NDPA-1 frame). At 2110, the method may include transmitting, by a second AP, an implicit NDPA frame (e.g., an implicit NDPA-2 frame). At 2115, the method may include jointly transmitting, by STAs associated with the first AP or the second AP, a T-NDP. At 2120, the method may include estimating, by the first AP and the second AP, an uplink channel from the T-NDP received from the participating STAs.

[0260] At 2105, the method may include transmitting an implicit NDPA frame by the first AP. For example, the first AP may transmit an implicit NDPA-1 frame, which may be used as a trigger for the second AP, for example, via a STA information field with a predetermined AID value, to transmit an implicit NDPA-2 and prepare a T-NDP. The implicit NDPA-1 frame may include information for the second AP about the allowed transmission parameters of the STAs of the second AP when transmitting the T-NDP, so that the second AP may include this information in the implicit NDPA-2 frame. The second AP may use the information in the implicit NDPA-1 frame to estimate its CFO and SFO relative to the first AP. The implicit NDPA-1 frame may solicit an uplink T-NDP from the STAs associated with the first AP, and may identify the transmission parameters of the T-NDP, such as bandwidth, total number of LTFs, LTF duration, guard interval, spatial stream position of each STA, number of spatial streams of each STA, RU allocation of each STA, etc. Each STA information may be provided in the STA information field. Each STA information field may be addressed by the AID of each STA. The STA associated with the first AP may estimate its CFO / SFO relative to the first AP based on the received implicit NDPA-1 frame. The implicit NDPA-1 frame may indicate the multi-AP detection sequence being used to distinguish the sequence from single AP and other multi-AP detection sequences. The format of the implicit NDPA-1 frame may be non-HT PPDU.

[0261] At 2110, the method may include transmitting an implicit NDPA frame by the second AP. For example, the second AP may transmit an implicit NDPA-2 frame after pre-compensating its estimated CFO / SFO relative to the first AP. The implicit NDPA-2 frame may solicit uplink T-NDP from the STA associated with the second AP, and may identify the transmission parameters of the T-NDP, such as bandwidth, total number of LTFs, LTF duration, guard interval, spatial stream position of each STA, number of spatial streams of each STA, RU allocation of each STA, etc. Each STA information may be provided in the STA information field. Each STA information field may be addressed by the AID of each STA. The STA associated with the second AP may estimate its CFO / SFO relative to the second AP (which itself has been pre-compensated relative to the first AP). The implicit NDPA-2 frame may indicate a specific multi-AP detection sequence being used to distinguish the sequence from a single AP and / or other multi-AP detection sequences. The format of the implicit NDPA-2 frame may be a non-HT PPDU.

[0262] At 2115, the method may include jointly transmitting, by the STAs associated with the first AP or the second AP, a T-NDP. For example, the STAs associated with the first AP or the second AP addressed by an implicit NDPA frame (from the first AP or the second AP) may jointly transmit the T-NDP frame according to the transmission parameters specified in the corresponding implicit NDPA frame. Each STA may pre-compensate its estimated CFO / SFO based on the corresponding implicit NDPA frame received by the STA.

[0263] At 2120, the method may include estimating, by the first AP and the second AP, uplink channels from the T-NDP. For example, based on the received T-NDP, the first AP and the second AP may estimate respective uplink channels from participating STAs. The first AP may share its estimated uplink channels (and any reciprocity coefficients desired to translate those uplink channels into downlink channels) with the second AP, and vice versa. In some configurations, the MAC address and AID used in the implicit NDPA-1 frame may be the same as the MAC address and AID used by the first AP for single AP detection. In some configurations, the MAC address and AID used in the implicit NDPA-2 frame may be the same as the MAC address and AID used by the second AP for single AP detection.

[0264] Reference now Fig. 22, illustrating another example method 2200 for implicit sounding of downlink channels for multiple access points. The method 2200 may be implemented using, for example, systems 200 and 500 or any of the features discussed in conjunction with FIGS. 1 to 5 . The method 2200 may include actions 2205 to 2220. At 2205, the method may include transmitting, by a first AP, a trigger frame (e.g., a trigger-1 frame) to a second AP. At 2210, the method may include jointly transmitting, by the first AP and the second AP, a coordinated OFDMA PPDU including an implicit NDPA for each AP. At 2215, the method may include jointly transmitting, by all STAs associated with the first AP and the second AP, a T-NDP. At 2220, the method may include estimating, by the first AP and the second AP, an uplink channel from the T-NDP received from the participating STAs.

[0265] At 2205, the method may include transmitting a trigger frame. For example, the first AP may transmit a trigger-1 frame to the second AP. The trigger-1 frame may indicate parameters for constructing a coordinated OFDMA frame for implicit sounding (implicit NDPA). The trigger-1 frame may specify parameters, including but not limited to RUs allocated to each AP, symbol duration, guard interval, total duration, etc., similar to a trigger frame for requesting TB-PPDU transmission. The trigger-1 frame may be used by the second AP to estimate its CFO and SFO relative to the first AP. The format of the trigger-1 frame may be a non-HT PPDU. The trigger-1 frame may include information about allowed transmission parameters for STAs of the second AP when responding to implicit NDPA using T-NDP.

[0266] At 2210, the method may include jointly transmitting a coordinated OFDM AP PPDU containing an implicit NDPA for each AP. For example, the first AP and the second AP may jointly transmit a coordinated OFDMA PPDU containing an implicit NDPA frame for each AP. Prior to transmission, the second AP may pre-correct its CFO and SFO relative to the first AP. In some configurations, the second AP may optionally apply a cyclic shift to its transmitted signal relative to the first AP to avoid signal elimination of the preamble. Within the coordinated OFDM AP PPDU, the first AP and the second AP may transmit their corresponding implicit NDPA frames (implicit NDPA-1 and implicit NDPA-2) on the allocated RU according to the parameters specified in the trigger-1 frame. Each implicit NDPA may solicit an uplink T-NDP from a corresponding STA associated with the AP. Each implicit NDPA may identify transmission parameters of the T-NDP, such as bandwidth, total number of LTFs, LTF duration, guard interval, spatial stream position of each STA, number of spatial streams of each STA, RU allocation of each STA, etc. Each STA information may be provided in the STA information field. Each STA information field may be addressed by the AID of each STA. The implicit NDPA frame may indicate a specific multi-AP detection sequence being used to distinguish the sequence from a single AP and / or other multi-AP detection sequences. Based on the received coordinated OFDMA PPDU, the STAs associated with the first AP and the second AP may estimate the corresponding CFO / SFO. In some configurations, the MAC address and AID used in the implicit NDPA frame of each AP may be the same as the MAC address and AID used by the corresponding AP for single AP detection.

[0267] At 2215, the method may include transmitting a T-NDP jointly by all STAs. For example, all STAs associated with the first AP and the second AP addressed by an implicit NDPA frame (from the first AP or the second AP) may jointly transmit a T-NDP frame according to the transmission parameters specified in the corresponding implicit NDPA frame. Each STA may pre-compensate its estimated CFO / SFO based on the received coordinated OFDMA PPDU.

[0268] At 2220, the method may include estimating, by the first AP and the second AP, uplink channels from the T-NDP. For example, based on the received T-NDP, the first AP and the second AP may estimate respective uplink channels from participating STAs. The first AP may share its estimated uplink channels with the second AP, as well as any reciprocity coefficients used to translate these uplink channels into downlink channels, and vice versa.

[0269] It should be noted that certain paragraphs of the present disclosure may refer to terms such as "first" and "second" in connection with devices, operating modes, transmission chains, etc., for the purpose of identifying or distinguishing each other or others. These terms are not intended to relate entities (e.g., first device and second device) only in time or according to a sequence, although in some cases, these entities may include such a relationship. These terms also do not limit the number of possible entities (e.g., devices) that can operate in a system or environment. The terms coupled or connected include indirect and direct couplings and connections.

[0270] Although the present disclosure has been described with respect to specific embodiments, those skilled in the art will recognize that many modifications are possible. For example, although specific examples of rules (including trigger conditions and / or resulting actions) and processes for generating recommended rules are described, other rules and processes may be implemented. Embodiments of the present disclosure may be implemented using a variety of computer systems and communication technologies, including but not limited to the specific examples described herein.

[0271] Embodiments of the present disclosure may be implemented using any combination of components and / or programmable processors and / or other programmable devices. The various processes described herein may be implemented in any combination on the same processor or on different processors. Where a component is described as being configured to perform certain operations, such configuration may be achieved, for example, by designing an electronic circuit to perform the operation, by programming a programmable electronic circuit (e.g., a microprocessor) to perform the operation, or any combination thereof. In addition, although the embodiments described above may refer to specific hardware and software components, those skilled in the art will appreciate that different combinations of hardware and / or software components may also be used, and that specific operations described as being implemented in hardware may also be implemented in software, or vice versa.

[0272] Computer programs incorporating various features of the present disclosure may be encoded and stored on a variety of computer-readable storage media; suitable media include disks or tapes, optical storage media such as compact disks (CDs) or DVDs (digital versatile disks), flash memory, and other non-transitory media. Computer-readable media encoded with program code may be packaged with a compatible electronic device, or the program code may be provided separately from the electronic device (e.g., via Internet download or as a separately packaged computer-readable storage medium).

[0273] Therefore, although the disclosure has been described with respect to particular embodiments, it should be understood that the disclosure is intended to cover all modifications and equivalents within the scope of the appended claims.

[0274] It should be understood that the disclosed embodiments do not represent all claimed innovations. Thus, certain aspects of the disclosure have not been discussed herein. Alternative embodiments may not yet be proposed for specific portions of the innovation, or alternative embodiments not further described may be available for a portion that should not be considered a waiver of those alternative embodiments. Therefore, it should be understood that other embodiments may be utilized, and functional, logical, operational, organizational, structural, and / or topological modifications may be made without departing from the scope of the disclosure. Thus, throughout the disclosure, all examples and / or embodiments are considered non-limiting.

[0275] Some embodiments described herein relate to methods. It should be understood that such methods may be computer-implemented methods (e.g., instructions stored in a memory and executed on a processor). Where the methods described above indicate that certain events occur in a certain order, the order of certain events may be modified. In addition, certain events may be performed repeatedly, concurrently with parallel processes where possible, and sequentially as described above. In addition, some embodiments may omit one or more of the described events.

[0276] Some embodiments described herein relate to computer storage products with non-transitory computer-readable media (also referred to as non-transitory processor-readable media) having thereon instructions or computer code for performing various computer-implemented operations. Computer-readable media (or processor-readable media) are non-transitory in the sense that they do not themselves include transitory propagating signals (e.g., propagating electromagnetic waves that carry information over a transmission medium such as space or cables). The media and computer code (also referred to as code) may be those designed and constructed for a specific purpose or purposes. Examples of non-transitory computer-readable media include, but are not limited to, magnetic storage media such as hard disks, floppy disks, and magnetic tapes; optical storage media such as compact disks / digital video disks (CD / DVDs), compact disk read-only memories (CD-ROMs), and holographic devices; magneto-optical storage media such as optical disks; carrier signal processing modules; and hardware devices specifically configured to store and execute program code, such as application specific integrated circuits (ASICs), programmable logic devices (PLDs), read-only memories (ROMs), and random access memory (RAM) devices. Other embodiments described herein relate to computer program products, which may include instructions and / or computer codes, such as those discussed herein.

[0277] Some embodiments and / or methods described herein may be implemented by software (executed on hardware), hardware, or a combination thereof. Hardware modules may include, for example, general purpose processors, field programmable gate arrays (FPGAs), and / or application specific integrated circuits (ASICs). Software modules (executed on hardware) may be expressed in various software languages ​​(e.g., computer code), including C, C++, Java, and the like.TM , Ruby, Visual Basic TM And / or other object-oriented, procedural or other programming languages ​​and development tools. Examples of computer code include, but are not limited to, microcode or microinstructions, machine instructions (e.g., instructions generated by a compiler), code for generating web services, and files containing higher-level instructions executed by a computer using an interpreter. For example, embodiments may be implemented using Python, Java, JavaScript, C++, and / or other programming languages ​​and software development tools. For example, embodiments may be implemented using imperative programming languages ​​(e.g., C, Fortran, etc.), functional programming languages ​​(Haskell, Erlang, etc.), logical programming languages ​​(e.g., Prolog), object-oriented programming languages ​​(e.g., Java, C++, etc.), or other suitable programming languages ​​and / or development tools. Additional examples of computer code include, but are not limited to, control signals, encryption codes, and compression codes.

[0278] The drawings are primarily for illustrative purposes and are not intended to limit the scope of the subject matter described herein. The drawings are not necessarily drawn to scale; in some instances, various aspects of the subject matter disclosed herein may be exaggerated or enlarged in the drawings to facilitate understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and / or structurally similar elements).

[0279] The actions performed as part of the disclosed method can be ordered in any suitable manner. Therefore, embodiments can be constructed in which processes or steps are performed in a different order than described, which may include performing some steps or processes simultaneously, even if shown as sequential actions in illustrative embodiments. In other words, it should be understood that such features may not necessarily be limited to a specific execution order, but may be any number of threads, processes, services, servers, and / or the like that can be performed serially, asynchronously, concurrently, in parallel, simultaneously, synchronously, and / or in a manner consistent with the present disclosure. Thus, some of these features may contradict each other because they cannot exist simultaneously in a single embodiment. Similarly, some features are applicable to one aspect of the innovation and not to other aspects.

[0280] Where a range of values ​​is provided, it is understood that each intervening value (to the tenth of the unit of the lower limit) between the upper and lower limits of the range and any other stated or intervening value in the stated range is encompassed within the disclosure unless the context clearly indicates otherwise. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any expressly excluded limits in the stated ranges. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also encompassed within the disclosure.

[0281] The phrase "and / or" as used in this specification and in the examples should be understood as "either or both" of the elements so combined, i.e., elements that exist in combination in some cases and in separation in other cases. Multiple elements listed with "and / or" should be interpreted in the same manner, i.e., "one or more" of the elements so combined. In addition to the elements explicitly identified in the "and / or" clause, other elements may optionally be present, whether or not they are related to the explicitly identified elements. Thus, as a non-limiting example, when used in conjunction with open-ended language such as "including", a reference to "A and / or B" may refer to only A (optionally including elements other than B) in one embodiment; to only B (optionally including elements other than A) in another embodiment; to both A and B (optionally including other elements) in yet another embodiment; etc.

[0282] As used herein in the specification and the embodiments, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating the items in the list, "or" or "and / or" should be interpreted as inclusive, that is, including at least one of multiple elements or element lists, but also including more than one, and optionally including additional unlisted items. Clearly indicate the opposite uniqueness terms, such as "only one of" or "exactly one of", or when used in the embodiments, "consisting of", will refer to including exactly one element in multiple elements or element lists. In general, the term "or" as used herein should be interpreted as indicating exclusive alternatives (that is, "one or the other, but not both") only when it is preceded by an exclusive term (such as "any one", "one of", "only one of" or "exactly one of"). When used in the embodiments, "essentially consisting of" should have its ordinary meaning used in the field of patent law.

[0283] As used herein in the specification and examples, the phrase "at least one" referring to a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each element explicitly listed in the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows that in addition to the elements explicitly identified in the list of elements referred to by the phrase "at least one", elements may optionally be present, whether related or unrelated to those elements explicitly identified. Thus, as a non-limiting example, "at least one of A and B" (or equivalently, "at least one of A or B", or equivalently "at least one of A and / or B") may refer to at least one (optionally including more than one) A, without B (and optionally including elements other than B) in one embodiment; to at least one (optionally including more than one) B, without A (and optionally including elements other than A) in another embodiment; to at least one (optionally including more than one) A and to at least one (optionally including more than one) B (and optionally including other elements) in yet another embodiment.

[0284] In the embodiments, as well as in the above description, all transitional phrases (e.g., "includes," "comprising," "carrying," "having," "containing," "involving," "holding," "consisting of," etc.) should be understood as open-ended, i.e., meaning including (but not limited to). As set forth in Section 2111.03 of the U.S. Patent Office Manual of Patent Examining Procedures, only the transitional phrases "consisting of" and "consisting essentially of" should be closed or semi-closed transitional phrases, respectively.

Claims

1. A system comprising: a first access point AP configured to transmit a Null Data Packet Advertisement NDPA frame to trigger a probing process for a first set of one or more stations of the first AP, wherein the NDPA is configured to trigger a second AP to transmit probing information; wherein both the first AP and the second AP are configured to transmit sounding information to the first set of one or more stations of the first AP, and each station of the first set of one or more stations of the first AP measures a downlink DL channel from each of the first AP and the second AP based on the sounding information to form a composite channel; wherein the sounding information comprises one of a joint null data packet (NDP) frame or a sequential NDP frame; wherein the first AP is configured to transmit a beamforming report poll (BFRP) frame for the composite channel; and Wherein the first AP is configured to receive a trigger-based physical layer protocol data unit (PPDU) from each of the first group of one or more stations receiving the BFRP frame to provide channel state information (CSI) based on the corresponding composite channel of each of the first group of one or more stations.

2. A system according to claim 1, wherein the first AP is configured to transmit a second NDPA frame to trigger a second detection process for the first group of one or more stations of the first AP, and transmit a second BFRP frame in response to the second detection process, wherein the second NDPA frame does not trigger the second AP to transmit detection information, wherein the NDPA frame and the second NDPA frame are configured to include the same values ​​of one or more media access control MAC addresses and one or more association identifiers AID for one or more stations in the first group of one or more stations corresponding to the first AP, and wherein the BFRP frame and the second BFRP frame are configured to include the same values ​​of one or more MAC addresses and one or more AIDs for one or more stations in the first group of one or more stations corresponding to the first AP.

3. The system of claim 1, wherein the NDPA comprises information indicating at least one of: a type of the sounding process, a type of requested channel state information (CSI), or information about beamforming configuration, timing, or duration.

4. The system of claim 1 , wherein the BFRP frame includes transmission parameters corresponding to one or more stations in the first group of one or more stations, wherein the transmission parameters are configured to allow the second AP to decode channel state information (CSI) from the triggered-based PPDU, data indicating at least one of the following: a modulation and coding scheme, a spatial stream allocation, or a resource unit of the one or more stations, and wherein each station in the first group of one or more stations transmits a triggered-based PPDU with the CSI according to the transmission parameters, and the second AP is configured to receive the triggered-based PPDU from the first group of one or more stations to decode the CSI.

5. A system according to claim 1, wherein the triggered PPDU transmitted by each station provides the CSI including at least one of the following: a beamforming report addressed to the first AP using the media access control MAC address of the first AP, a beamforming matrix index, a signal-to-noise ratio, or a measure of performance of a modulation scheme.

6. The system of claim 1, wherein the NDPA frame includes a station information field having an association identifier (AID) value, and wherein the second AP is configured to transmit probe information in response to the AID value.

7. The system according to claim 1, wherein the second AP is synchronized with the first AP based on the NDPA and at least one of the following: the timing and parameters of the detection process, the carrier frequency offset CFO or the sampling frequency offset SFO of the second AP relative to the first AP.

8. A system comprising: a second AP configured to transmit a Null Data Packet Announcement (NDPA) frame to a second group of one or more stations within a basic service set (BSS) of the second AP, the NDPA including a field for triggering the first AP to transmit a Null Data Packet (NDP) frame; wherein the first AP is configured to transmit the NDP frame to the second group of one or more stations of the second AP to trigger a sounding process, and the second group of one or more stations receive the NDP frame to measure a downlink DL channel relative to the first AP; and Wherein the second AP is configured to transmit one or more beamforming report poll (BFRP) frames to trigger feedback including channel state information (CSI) from the second set of one or more stations based on measuring the DL channel relative to the first AP.

9. The system of claim 8, wherein the field of the NDPA frame includes an association identifier AID having a predetermined value to trigger the first AP to prepare for transmission of the NDP frame.

10. The system of claim 8, wherein the NDPA frame transmitted by the second AP is configured to indicate the type of CSI to be fed back to the second group of one or more stations, wherein the one or more BFRP frames are configured to specify transmission parameters for each station in the second group of one or more stations to transmit a trigger-based physical layer protocol data unit (TB-PPDU) including the CSI.

11. The system of claim 8, wherein the NDP frame transmitted by the first AP indicates a BSS color in a preamble corresponding to the BSS of the second AP.

12. A system according to claim 10, wherein the second AP is configured to receive a trigger-based physical layer protocol data unit PPDU from each station of the second group of one or more stations that receive the one or more BFRP frames to provide channel state information CSI based on the downlink channel, and wherein the second group of one or more stations of the second AP transmits the trigger-based PPDU including one or more measured compressed beamforming reports CBR of the downlink channel in response to the one or more BFRP frames including one or more parameters, wherein the trigger-based PPDU is transmitted according to the transmission parameters specified in the BFRP.

13. The system of claim 8, wherein the NDPA frame and the one or more BFRP frames each include a first media access control MAC address and a first association identifier, AID, to address one or more stations in the second set of one or more stations, and wherein the second AP is configured to include the first MAC address and the first AID in each of a second NDPA frame and a second BFRP frame to address the one or more stations in the second set of one or more stations; The second NDPA frame does not trigger the first AP to transmit a second NDP frame.

14. A system according to claim 10, wherein the transmission parameters specified in the BFRP for the TB PPDU are configured for the first AP to decode the transmission from the second group of one or more stations; and wherein the first AP is configured to receive a trigger-based physical layer protocol data unit PPDU from each station in the second group of one or more stations according to the transmission parameters specified in the BFRP.

15. The system of claim 12, wherein the second AP is configured to: The second AP forwards the CSI from at least one station in the second group of one or more stations to the first AP.

16. A system comprising: a first access point AP configured to transmit an implicit null data packet advertisement (implicit NDPA) frame to solicit uplink trigger NDP (T-NDP) frames from a first set of one or more stations of the first AP, the implicit NDPA frame including a field for indicating that a second AP is ready to receive transmission of the T-NDP frame, the implicit NDPA frame identifying one or more parameters for the transmission of the T-NDP frame; wherein the first AP and the second AP are configured to receive the T-NDP frame from the first set of one or more stations of the first AP; and The first AP and the second AP are configured to estimate corresponding uplink channels based at least on the T-NDP frame.

17. The system of claim 16, wherein the implicit NDPA frame further comprises parameters for the T-NDP, the parameters comprising at least one of: bandwidth, number of long training fields (LTFs), length of LTFs, guard interval, spatial stream position, number of spatial streams, or allocation of resource units.

18. The system of claim 16, wherein the first set of one or more stations estimates their respective carrier frequency offset (CFO) and sampling frequency offset (SFO) relative to the first AP based at least on data about the first AP from the implicit NDPA frame.

19. The system of claim 16, wherein the first AP exchanges with the second AP respective estimates of their uplink channels and coefficients for mapping the respective estimates of the uplink channels to one or more downlink channels.

20. A system according to claim 16, wherein one or more media access control MAC addresses and one or more association identifiers AIDs used by the first AP in the implicit NDPA frame to address the first group of one or more stations are the same as one or more MAC addresses and one or more AIDs used by the first AP in a second NDPA frame to address the first group of one or more stations, wherein the second NDPA frame does not address the second AP.

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