Protocol and frame format for coordinated beamforming

Abstract

The present disclosure provides a method and apparatus for coordinated beamforming. An aspect of the present disclosure provides a method. The method comprises the step of transmitting a request for channel state information (CSI) associated with one or more STAs and the first AP to one or more stations (STAs) associated with the plurality of collaborative APs by a first access point (AP) of the plurality of collaborative APs. The method further comprises the step of receiving a response comprising the CSI associated with one or more STAs and the first AP. The method further comprises the step of transmitting a sounding request to a second AP of the plurality of collaborative APs, indicating to the second AP to request the CSI associated with one or more STAs and the second AP from one or more STAs. The method further comprises the step of sharing CSI information between the first AP and the second AP.

Description

Technology Field

[0001] Cross-reference

[0002] This application claims the benefit of priority to U.S. Regular Patent Application No. 17 / 484,709, filed on September 24, 2021, under the heading “Protocol and Frame Format for Coordinated Beamforming,” the contents of which are incorporated herein by reference in their entirety.

[0003] Technology field

[0004] The present invention relates to the field of communication networks, and in particular to a procedure and frame structure for coordinated beamforming (CoBF). Background Technology

[0005] CoBF is likely to be a key feature of the Multi-Access Point (M-AP) collaboration topic in 802.11be Release 2 (R2). There are still several unresolved issues regarding the introduction of CoBF into IEEE 802.11. The first issue is determining how selected user information can be shared between coordinated APs. Existing protocols do not provide appropriate procedures for sharing selected user information between coordinated APs. The second issue relates to the precoder calculation of participating APs in CoBF. Currently, precoder calculations vary by vendor. Vendor-specific precoder calculations are unsuitable for CoBF due to the potential for interference caused by such calculations.

[0006] Therefore, a procedure and frame structure for CoBF that removes or alleviates one or more limitations of the prior art is required.

[0007] This background information is provided to disclose information that the applicant determines to be relevant to the present invention. It is not necessarily acknowledged, nor should it be interpreted, that any of the foregoing information constitutes prior art to the present invention.

[0008] The present disclosure provides methods and apparatus related to coordinated beamforming. A first aspect of the present disclosure provides a method. The method comprises the step of transmitting a request for one or more STAs and channel state information (CSI) associated with the first AP to one or more stations (STAs) associated with the first AP by a first access point (AP) of a plurality of collaborative APs. The method further comprises the step of receiving a response by the first AP from one or more STAs, comprising the CSI associated with the one or more STAs and the first AP. The method further comprises the step of transmitting a sounding request by the first AP to a second AP of the plurality of collaborative APs, indicating to the second AP to request one or more STAs and the CSI associated with the second AP from one or more STAs. The method further comprises the step of receiving a first AP-AP shared message by the first AP from the second AP, comprising the CSI associated with one or more STAs and the second AP. The method further comprises the step of transmitting a second AP-AP shared message by the first AP to the second AP, comprising the CSI associated with one or more STAs and the first AP. The method can provide a Media Access Control (MAC) protocol that shares information between participating APs in CoBF.

[0009] In some embodiments of the first aspect, the second AP-AP shared message comprises a frame including: an identifier of the first AP; an indication that the frame is an AP-AP shared frame; one or more STAs associated with the first AP; one or more CSIs associated with the first AP and one or more streams per STA of the one or more STAs associated with the first AP; and one or more fields representing one or more of precoder information associated with the second AP. The method may further provide a frame format for sharing information between participating APs in CoBF.

[0010] In some embodiments of the first aspect, the method further comprises the step of calculating a plurality of precoders by a first AP, wherein each calculated precoder corresponds to each AP of the plurality of collaborative APs and is based on one or more STAs and CSI information associated with each AP. The method may further provide for calculating precoder information for participating APs in CoBF.

[0011] In some embodiments of the first aspect, the step of transmitting a request for a CSI associated with one or more STAs and a first AP further comprises the step of transmitting a Null Data Packet Notice (NDPA) to each of the one or more STAs. In some embodiments, the step of transmitting a request for a CSI associated with one or more STAs and a first AP further comprises the step of transmitting a Null Data Packet (NDP) to each of the one or more STAs in a shortest interframe interval (SIFS) time unit after transmitting the NDPA. In some embodiments, the request for a CSI associated with one or more STAs and a first AP further comprises the step of transmitting a beamforming report frame from each of the one or more STAs in a SIFS time unit after transmitting the NDP.

[0012] In some embodiments of the first aspect, precoder information represents a calculated precoder among a plurality of precoders. In some embodiments, precoder information represents a precoder index representing a method for calculating a precoder. In some embodiments, one or more STAs and CSIs associated with the first AP are displayed in the selected user field of the frame. In some embodiments, the identifier of the first AP is displayed in the transmitter address (TA) field of the Media Access Control (MAC) header of the frame. The method may further provide for sharing information between cooperating APs that may be required for CoBF.

[0013] A second aspect of the present disclosure provides a different method. The method comprises receiving a first shared message from a second AP by a first access point (AP), the first AP and the second AP collaborate. The method further comprises transmitting a second shared message by the first AP to the second AP, the second shared message comprising a frame including an identifier of the first AP; an indication that the frame is an AP-AP shared frame; one or more stations (STA) associated with the first AP; a CSI associated with the first AP; one or more streams per STA of one or more STAs associated with the first AP; and one or more fields representing one or more of precoder information associated with the second AP. The method may further provide a frame format for sharing information between participating APs in CoBF.

[0014] In some embodiments of the second aspect, the method further includes the step of calculating a precoder associated with the second AP based on a CSI associated with the second AP by the first AP. In some embodiments, the precoder information associated with the second AP represents the calculated precoder associated with the second AP. In some embodiments, the precoder information associated with the second AP represents a precoder index representing the precoder calculation method. In some embodiments, the CSI associated with the first AP is displayed in the selected user field of the frame. In some embodiments, the identifier of the first AP is displayed in the transmitter address (TA) field of the Media Access Control (MAC) header of the frame. The method may further provide for sharing information between cooperating APs that may be required for CoBF.

[0015] A third aspect of the present disclosure provides a different method. The method comprises the step of transmitting a request for channel state information (CSI) associated with one or more STAs and the first AP by a first access point (AP) of a plurality of collaborative APs to one or more stations (STAs) associated with the plurality of collaborative APs. The method further comprises the step of receiving a response by the first AP from one or more STAs, comprising the CSI associated with one or more STAs and the first AP. The method further comprises the step of transmitting a sounding request by the first AP to a second AP of a plurality of collaborative APs, indicating to the second AP to request the CSI associated with one or more STAs and the second AP from one or more STAs. The method further comprises the step of transmitting a first AP-AP shared message by the first AP to the second AP, comprising the CSI associated with one or more STAs and the first AP. The method further comprises the step of receiving a second AP-AP shared message by the first AP from the second AP, comprising the CSI associated with one or more STAs and the second AP. The method may provide an alternative MAC protocol for sharing information between participating APs in CoBF.

[0016] In some embodiments of the third aspect, the method further includes the step of calculating a termination time for a plurality of collaborative APs to collect corresponding CSIs by the first AP.

[0017] In some embodiments of the third aspect, the second AP-AP sharing message comprises a frame including: an identifier of the second AP; an indication that the frame is an AP-AP sharing frame; one or more STAs associated with the second AP; one or more CSIs associated with the second AP and the STA; and one or more fields representing one or more of precoder information associated with the first AP. The method may further provide a frame format for sharing information between participating APs in CoBF. The method may further provide sharing information between collaborating APs that may be required in CoBF.

[0018] A fourth aspect of the present disclosure provides another method. The method comprises receiving a sounding request from a second AP of a plurality of collaborative APs by a first access point (AP) of a plurality of collaborative APs, indicating that the first AP should request channel state information (CSI) from one or more stations (STAs) associated with the plurality of collaborative APs. The method further comprises transmitting a request for one or more STAs and CSIs associated with the first AP by the first AP to one or more STAs. The method further comprises receiving a response from one or more STAs by the first AP, comprising CSIs associated with the first AP and one or more STAs. The method further comprises receiving a first AP-AP shared message from the second AP by the first AP, comprising CSIs associated with one or more STAs and the second AP. The method further comprises transmitting a second AP-AP shared message by the first AP to the second AP, comprising CSIs associated with one or more STAs and the first AP. The method may provide a MAC protocol for sharing information between participating APs in CoBF.

[0019] In some embodiments of the fourth aspect, the second AP-AP shared message comprises a frame including: an identifier of the first AP; an indication that the frame is an AP-AP shared frame; one or more STAs associated with the first AP; one or more CSIs associated with the first AP and the STA; and one or more fields representing one or more of precoder information associated with the second AP. The method may further provide a frame format for sharing information between participating APs in CoBF.

[0020] In some embodiments of the fourth aspect, the method further comprises the step of calculating a plurality of precoders by a first AP, wherein each calculated precoder corresponds to each AP of the plurality of collaborative APs and is based on one or more STAs and CSI information associated with each AP. In some embodiments, the precoder information is the calculated precoder among the plurality of precoders. The method may further provide for sharing information between collaborative APs that may be required for CoBF.

[0021] A fifth aspect of the present disclosure provides another method. The method comprises receiving a sounding request from a second AP of a plurality of collaborative APs by a first access point (AP) of a plurality of collaborative APs, indicating that the first AP should request channel state information (CSI) from one or more stations (STAs) associated with the plurality of collaborative APs. The method further comprises transmitting a request for one or more STAs and CSIs associated with the first AP by the first AP to one or more STAs. The method further comprises receiving a response from one or more STAs by the first AP, comprising CSIs associated with the one or more STAs and the first AP. The method further comprises transmitting a first AP-AP shared message by the first AP to the second AP, comprising CSIs associated with the one or more STAs and the first AP. The method further comprises receiving a first AP-AP shared message by the first AP from the second AP, comprising CSIs associated with the one or more STAs and the second AP. In some embodiments of the fifth aspect, the second AP-AP shared message comprises an identifier of the second AP; an indication that the frame is an AP-AP shared frame; The method includes a frame comprising one or more STAs associated with a second AP; a CSI associated with one or more STAs and the second AP; and one or more fields representing one or more of precoder information associated with a first AP. The method may provide a MAC protocol for sharing information between participating APs in CoBF. The method may further provide a frame format for sharing information between participating APs in CoBF.

[0022] A sixth aspect of the present disclosure provides another method. The method comprises the step of transmitting, by a first access point (AP) of a plurality of collaborative APs, a request for one or more STAs and channel state information (CSI) associated with the first AP to one or more stations (STAs) associated with the plurality of collaborative APs. The method further comprises the step of receiving, by the first AP, a response from one or more STAs including the CSI associated with the first AP. The method further comprises the step of transmitting, by the first AP, a sounding request to a second AP of a plurality of collaborative APs, indicating to the second AP to transmit a request for one or more STAs and the CSI associated with the second AP to one or more STAs. The method further comprises the step of receiving, by the first AP, a first AP-AP shared message from the second AP including the CSI associated with one or more STAs and the second AP. The method further comprises the step of receiving a sounding request from the first AP by the second AP. The method further comprises the step of transmitting, by the second AP, a request for one or more STAs and the CSI associated with the second AP to one or more STAs. The method further includes the step of receiving a response from one or more STAs by the second AP, the response including a CSI associated with one or more STAs and the second AP. The method further includes the step of transmitting a first AP-AP shared message by the second AP to the first AP. The method may provide a MAC protocol for sharing information between participating APs in CoBF.

[0023] According to the seventh aspect, a device is provided, and the device includes a module configured to perform methods according to different aspects described herein.

[0024] According to the eighth aspect, a device is provided, the device comprises a memory configured to store a program; and a processor configured to execute a program stored in the memory, and when a program stored in the memory is executed, the processor is configured to perform methods of different aspects described herein.

[0025] According to the ninth aspect, a computer-readable medium is provided, the computer-readable medium stores program code executed by a device, and the program code is used to perform methods of different aspects described herein.

[0026] According to the tenth aspect, a chip is provided, the chip includes a processor and a data interface, and the processor uses the data interface to read instructions stored in memory to perform different aspects described herein.

[0027] Other aspects of the present disclosure provide devices and systems configured to implement methods according to different aspects disclosed herein. For example, a wireless station and an access point may be configured with a machine-readable memory comprising instructions that configure the device to perform the methods disclosed herein when executed by a processor of the devices.

[0028] Embodiments have been described above along with aspects of the invention that may be implemented. Those skilled in the art will understand that the embodiments may be implemented not only with the described aspects but also with other embodiments of those aspects. Where embodiments are mutually exclusive or incompatible, this will be apparent to those skilled in the art. Some embodiments may be described in relation to one aspect, but may also apply to other aspects as will be apparent to those skilled in the art. Brief explanation of the drawing

[0029] Further features and advantages of the present invention will become apparent from the following detailed description taken together with the accompanying drawings. FIG. 1 illustrates multiple AP collaboration according to an embodiment of the present disclosure. FIG. 2 illustrates a protocol for AP-AP sharing in CoBF according to an embodiment of the present disclosure. FIG. 3 illustrates an alternative protocol for AP-AP sharing in CoBF according to an embodiment of the present disclosure. FIG. 4 illustrates a frame format for an AP-AP shared frame according to an embodiment of the present disclosure. FIG. 5 illustrates a 2-AP CoBF having one selected station (STA) in each participating AP according to an embodiment of the present disclosure. FIG. 6 is a schematic diagram of an electronic device capable of performing some or all of the above methods and features explicitly or implicitly described herein, according to another embodiment of the present invention. It should be noted that throughout the attached drawings, identical features are identified by the same reference number. Specific details for implementing the invention

[0030] Channel State Information (CSI) functionality was first introduced in 802.11n in the context of Multiple Input Multiple Output (MIMO). As will be recognized by those skilled in the art, CSI training sequences can be designed to measure channel characteristics between a transmitter and a receiver. CSI can represent how an electromagnetic signal propagates from a transmitter to a receiver and the combined effects of scattering, fading, and power attenuation depending on the distance of the signal.

[0031] CSI can reflect the radio signal propagation characteristics for the link from transmitter to receiver at a specific carrier frequency. CSI measurements can include information as the radio signal is transmitted through surrounding objects and people in the time, frequency, and spatial domains. CSI measurements may include amplitude changes of the CSI in the time domain, phase shifts of the CSI in the spatial and frequency domains (e.g., transmitting / receiving antennas and carrier frequencies), and phase shifts of the CSI in the time domain.

[0032] As previously mentioned, Coordinated Beamforming (CoBF) is likely to be a key feature of the Multi-Access Point (M-AP) collaboration topic for 802.11be R2. There are several standard issues in introducing CoBF into IEEE 802.11. The first standard issue is that selected user information must be shared wirelessly between coordinated APs. The second standard issue is determining the coordinating AP (referred to as the master AP in some contexts) and the coordinated AP (referred to as the slave in some contexts). As will be recognized by those skilled in the art, the second issue can be resolved during the M-AP setup phase. The third standard issue is determining how to set up or define an interference alignment precoder between the coordinated APs. The embodiments described herein can resolve the first and third standard issues.

[0033] FIG. 1 illustrates multi-AP collaboration according to an embodiment of the present disclosure. In one embodiment, a multi-AP collaboration system (100) includes a first AP (AP1) (102) and a second AP (AP2) (112). AP1 (102) and AP2 (112) simultaneously transmit frames to one or more associated STAs, which indicates that AP1 (102) and AP2 (112) are collaborating (which may be referred to as M-AP collaboration). Although two APs are illustrated, those skilled in the art will understand that an M-AP collaboration system may include more than two APs.

[0034] Each AP may be associated with one or more STAs. For example, AP1 (102) is associated with STA1 (104) and STA1-U (106). Similarly, AP2 (112) is associated with STA2 (114) and STA2-U (116). Although multiple STAs may be associated with an AP, an AP may select one or more STAs for scheduling. For example, AP1 (102) selects STA1 (104) for scheduling, but STA1-U (106) is not selected. Similarly, AP2 selects STA2 (114) for scheduling, but STA2-U (116) is not selected. Therefore, the channel (120), (122), (124) and (126) is formed between the AP (AP1 (102) and AP2 (112)) collaborating with the STA (STA1 (104) and STA2 (114)) selected for frame transmission. As illustrated, (120) is the channel between STA1 (104) and AP1 (102). The superscript "11" indicates that the channel is between STA1 (104) and AP1 (102). The subscript "M1XN1" indicates the size of the H matrix (H represents the channel), where "M1" indicates the number of receiver (RX) antennas of STA1 (104) and "N1" indicates the number of transmitter (TX) antennas of AP1 (102). Likewise, (122) is a channel between STA2 (114) and AP1 (102), and (124) is a channel between STA1 (104) and AP2 (112), and (126) is the channel between STA2 (114) and AP2 (112).

[0035] In the context of beamforming, there may be two ways for M-AP collaboration. The first way is CoBF, which means that beamforming is coordinated between the collaborated APs (e.g., AP1 (102) and AP2 (112)). The second way is co-transmission, which means that the collaborative APs transmit frames together. Co-transmission may indicate that each collaborative AP shares data from a selected STA with another AP.

[0036] As mentioned in this specification, each collaborative AP may select one or more STAs from among the associated STAs. In the embodiment of FIG. 1, AP1 (102) selects STA1 (104), and AP2 (112) selects STA2 (114). After one or more STAs are selected, each collaborative AP shares the information of the selected one or more STAs with other collaborative APs. The embodiments described in this specification may provide a protocol for sharing the selected STAs among the collaborative APs.

[0037] The embodiments described herein may provide for calculating an interference-aligned precorder. Referring to FIG. 1, as will be recognized by those skilled in the art, (122) and (124) is interference, whereas, (120) and (126) is used for actual information data. Therefore, to reduce interference (122) and It is desirable to minimize (124) as much as possible. Therefore, interference must be managed appropriately. As part of interference management, one or more interference-aligned precoders can be calculated and shared between collaborative APs.

[0038] As will be known to those skilled in the art, during the sounding process (260) (see FIG. 2), collaborative APs, for example, AP1 (102) and AP2 (112), can collect CSI information from all participating STAs. STA1 (104) is a channel When feedback information associated with (120) is transmitted to AP1 (102), AP2 (112) can eavesdrop on the feedback information. Likewise, STA1 (104) is channel When the feedback information associated with (124) is transmitted to AP2 (112), AP1 (102) can overhear the feedback information.

[0039] Calculating precoders based on collected CSI information is not yet standardized, and each vendor calculates its own precoder (since when an AP transmits beamforming packets to a STA, the STA does not need to know which type of beamforming is being applied). However, in the case of collaborative APs, if each AP calculates its own precoder independently, interference may occur, causing packets transmitted by the AP to fail to reach their destination (e.g., one or more receiver STAs). Therefore, to minimize any potential interference, the precoder calculation of collaborative APs must be managed. Managing precoder calculation may involve wirelessly sharing precoder information between collaborative APs before transmitting one or more beamforming packets.

[0040] The embodiments described herein may provide protocols and frame formats associated with the CoBF scheme. As will be recognized by those skilled in the art, CoBF restricts information sharing between coordinated APs, but such information sharing cannot be completely avoided. Since the embodiments described herein may define what information to be shared between coordinated APs, they may provide the necessary protocols and frame formats based on the defined information.

[0041] FIG. 2 illustrates a protocol for AP-AP sharing in CoBF according to an embodiment of the present disclosure. The protocol (200) is based on serial sounding in which NDPA and NDP are transmitted serially by each of the collaborating APs. In the protocol (200), two APs (AP1 (102) and AP2 (112)) collaborate. The collaborating APs include a coordinating AP (e.g., AP1 (102)) and one or more coordinated APs (e.g., AP2 (112)).

[0042] As will be recognized by those skilled in the art, the sounding packet contains one or more of the NDPA, NDP, and Beamforming Reporting (BFRP) trigger frames. The BFRP trigger frame is used when there is more than one participating STA and is used to simultaneously receive CSI reports from each of the more than one participating STA.

[0043] In an embodiment, each cooperating AP continuously transmits sound packets. For example, a coordinating AP (AP1 (202)) transmits one or more participating STAs (e.g., STA 11 to STA 1N (206), STA 21 to STA 2M Simultaneously transmit NDPA1 (210) to (208). STA 11 to STA 1N (206) refers to one or more STAs associated with AP1 (202), and likewise STA 21 to STA 2M (208) refers to one or more STAS associated with AP2 (204).

[0044] After transmitting NDPA1 (210), in a shortest interframe interval (SIFS) time unit, the coordinating AP (AP1 (202)) is one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M(208) Send NDP1 (214) to each simultaneously (216).

[0045] Each of one or more participating STAs, for example, STA 11 to STA 1N (206) and STA 21 to STA 2M (208) can calculate the CSI between STA and AP1 (202). For example, STA 11 STA 11 CSI can be calculated between and AP1 (202), and STA 1N STA 1N CSI can be calculated between and AP1 (202). Similarly, STA 21 STA 21 CSI can be calculated between and AP1 (202), and STA 2N STA 2N CSI can be calculated between AP1 (202).

[0046] In an embodiment where one or more STAs participate in the protocol (200), after transmitting NDP1 (214) in SIFS time units, the coordinating AP (AP1 (202)) sends a BFRP trigger frame (218) to the participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M (208) transmits simultaneously (202).

[0047] After receiving the BFRP trigger frame (218), in SIFS time units, one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M (208) Each can then transmit the calculated CSI report to AP1 (202) (226). Participating STAs, e.g., STA 11 to STA 1N (206) and STA21 to STA 2M (208) simultaneously transmits CSI reports (222 and 224) to AP1 (202) (226).

[0048] After receiving one or more CSI reports (222 and 224) from participating STAs in SIFS time units, a coordinating AP, e.g., AP1 (202), may send a sounding request frame (228) to the next collaborating AP (e.g., AP2 (204)) according to the sequence of the sounding process (260).

[0049] After receiving a sounding request frame (228), in a SIFS time unit, the coordinated AP (AP2 (204)) may send an acknowledgment frame (230) to the coordinated AP (AP1 (202)). Then, in a SIFS time unit, the coordinated AP (AP2 (204)) may send one or more participating STAs, for example, STA 11 to STA 1N (206) and STA 21 to STA 2M (208) NDPA2 (232) is transmitted simultaneously to each (234). After transmitting NDPA2 (232), in SIFS time units, the coordinated AP (AP2 (204)) is one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M (208) Send NDP2 (236) to each simultaneously (238).

[0050] One or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M Each of (208) can calculate the CSI between STA and AP2 (204). For example, STA 11 STA 11 CSI can be calculated between AP2 (204), and STA1N STA 1N CSI can be calculated between and AP1 (202). Similarly, STA 21 STA 21 CSI can be calculated between AP2 (204), and STA 2N STA 2N CSI can be calculated between AP2 (204).

[0051] In an embodiment where more than one STA participates in the protocol (200), after transmitting NDP2 (236) in SIFS time units, the coordinated AP (AP2 (204)) is a participating STA, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M A BFRP trigger frame (240) is simultaneously transmitted to (208) (242). As will be understood by those skilled in the art, in an embodiment where only one STA participates, a BFRP trigger frame does not need to be transmitted.

[0052] After receiving the BFRP trigger frame (240), in SIFS time units, one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M (208) Each can then send their calculated CSI report to AP2 (204) (248). Participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M (208) simultaneously transmits their CSI reports (244 and 246) to AP2 (204) (248).

[0053] Each of the collaborative APs (including one or more coordinated APs, e.g., AP2 (204) and a coordinated AP, e.g., AP1 (202)) may take multiple BFRP trigger steps depending on the number of STAs participating in the sounding procedure. For example, if there are too many STAs involved for each participating AP to poll CSI reports in a one-time BFRP trigger frame transmission, each participating AP may need to poll CSI reports multiple times in multiple BFRP TF transmissions.

[0054] FIG. 2 illustrates two collaborative APs (coordinating AP (AP1 (202)) and coordinated AP (AP2 (204)), but those skilled in the art will understand that there may be more than two collaborative APs. In the case of multiple coordinated APs (e.g., AP2 (204) and AP3 (not shown)), in SIFS time units after AP2 (204) receives CSI reports (244 and 246) from a participating STA, AP2 (204) sends a sounding request frame to the next coordinated AP, e.g., AP3. AP3 may send an Ack to AP2 (204) (in SIFS time units after receiving the sounding request frame). Then in SIFS time units, AP3 sends one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M NDPA can be transmitted simultaneously to each of (208). Then, in SIFS time units, AP3 transmits one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M NDPs can be sent simultaneously to each of (208). One or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2MEach of (208) can calculate the CSI between the STA and AP3. After transmitting the NDP, in SIFS time units, AP3 can then simultaneously transmit a BFRP trigger frame to each of one or more participating STAs. After receiving the BFRP trigger frame, in SIFS time units, one or more participating STAs, e.g., STA 11 to STA 1N (206) and STA 21 to STA 2M Each of (208) can simultaneously transmit the calculated CSI report to AP3.

[0055] When the last adjusted AP (the sequence of serial sounding can be set during the setup phase) terminates the sounding process (260) (when the CSI report action frame is collected by the last AP), an AP-AP shared frame must be transmitted, that is, the AP-AP shared frame also includes the termination of the serial sounding process (260).

[0056] The sequence of AP-AP shared frame transmission may be in reverse order of the sounding sequence. In FIG. 2, the sounding sequence starts with the coordinating AP (AP1 (202)) and then with the coordinating AP (AP2 (204)). Thus, the AP-AP shared frame transmission process (262) starts with the coordinating AP2 (204) and then with the coordinating AP (AP1 (202)). In the illustrated embodiment of FIG. 2, after receiving CSI reports (244 and 246) in SIFS time units, the coordinating AP2 (204) transmits an AP-AP shared frame (250) to a collaborating AP, e.g., the coordinating AP1 (202) (252). After receiving the AP-AP shared frame (250) in SIFS time units, the coordinating AP1 (202) transmits an AP-AP shared frame (254) to a collaborating AP, e.g., the coordinating AP2 (204) (256).

[0057] For multiple coordinated APs (e.g., AP2 (204) and AP3 (not shown)), the sequence of AP-AP shared frame transmissions may be as follows: AP3, AP2 (204), and AP1 (202). Thus, after receiving CSI reports from one or more participating STAs, in an SIFS time unit, AP3 may transmit an AP-AP shared frame to the last collaborating AP (e.g., AP1 (202)) according to the sequence of the AP-AP shared frame transmission process. Then, in an SIFS time unit, AP2 (204) may transmit an AP-AP shared frame to the last collaborating AP (e.g., AP1 (202)) according to the sequence of the AP-AP shared frame transmission process. After collecting all AP-AP shared frames from the coordinated APs (AP2 (204) and AP3) in SIFS time units, the coordinated AP1 (202) can then transmit AP-AP shared frames to all coordinated APs (in this case, AP2 (204) and AP3).

[0058] According to the sequence of the AP-AP shared frame transmission process (262), when a frame (e.g., frame (254)) from the last collaborating AP (in this embodiment, the coordinating AP (AP1) (202)) is received by all participating APs, the AP-AP shared frame transmission process (262) is terminated. The AP-AP shared frame (254) may include user selection information from the coordinating AP as further described herein.

[0059] As mentioned in this specification, a collaborative AP and one or more coordinated APs (including a sequence of collaborative APs for continuously transmitting sounding packet frames) are determined in the setup phase.

[0060] FIG. 3 illustrates an alternative protocol for AP-AP sharing in CoBF according to an embodiment of the present disclosure. In FIG. 3, the sounding sequence process of FIG. 3 is similar to the sounding sequence process (260) of FIG. 2. However, the AP-AP shared frame transmission process (362) is performed in the reverse order of the AP-AP shared frame transmission process (262). Thus, the AP-AP shared frame transmission process (362) is performed in the same order as the sounding sequence process (260), for example, AP1 starts the process (362) and AP2 ends the process (362).

[0061] According to one embodiment, the coordinating AP (AP1 (202)) configures the end time of the sounding process (260) by the last coordinated AP (e.g., AP2 (204) in FIG. 3). The coordinating AP (AP1 (202)) may calculate the end time of the sounding process (260) based on one or more of the collaborating AP, SIFS time units, and participating STAs. After the last coordinated AP, in this embodiment AP2 (204), receives CSI reports (244 and 246) from the participating STA in SIFS time units, the coordinating AP (AP1) (202) transmits an AP-AP shared frame (254) to the last collaborating AP (in this embodiment AP2 (204)) according to the sequence of the AP-AP shared frame transmission process (362) (302). After receiving the AP-AP shared frame (254), the coordinated AP (AP2 (204)) transmits the AP-AP shared frame (250) to the cooperating AP (e.g., AP1 (202)) in SIFS time units (304).

[0062] For multiple coordinated APs (e.g., AP2 (204) and AP3 (not shown)), the sequence of AP-AP shared frame transmissions may be as follows: AP1 (202), AP2 (204), and AP3. According to one embodiment, the AP-AP shared frame transmission process may be as follows: AP1 (202) sets the end time of the sounding process (260) by the last coordinated AP (e.g., AP3). After the last coordinated AP, e.g., AP3, receives a CSI report from a participating STA, in SIFS time unit, the coordinated AP (AP1 (202)) transmits an AP-AP shared frame to the last collaborating AP (e.g., AP3) according to the sequence of the AP-AP shared frame transmission process. After receiving the AP-AP shared frame, in SIFS time unit, the coordinated AP (AP2 (204)) transmits an AP-AP shared frame to the last collaborating AP (e.g., AP3) according to the sequence of the AP-AP shared frame transmission process. After collecting all AP-AP shared frames from the participating APs (in this case, AP1 (202) and AP2 (204)) in SIFS time units, the last AP (AP3) can then transmit AP-AP shared frames to all participating APs (in this case, AP1 (202) and AP2 (204)) according to the sequence of the AP-AP shared frame transmission process.

[0063] According to the sequence of the AP-AP shared frame transmission process, when a frame from the last collaborating AP is received by all participating APs, the AP-AP shared frame transmission process terminates. The last AP-AP shared frame may include user selection information from the coordinating AP, as further described herein.

[0064] The embodiments described with reference to FIGS. 2 and FIGS. 3 may provide a Media Access Control (MAC) protocol for participating APs to share necessary information with each other in CoBF.

[0065] FIG. 4 illustrates a frame format for an AP-AP shared frame according to an embodiment of the present disclosure.

[0066] The frame format (400) may be a frame format for the AP-AP shared frames of FIGS. 2 and 3 (e.g., AP-AP shared frames (250 and 254)). The frame format may include one or more of a PHY header field (402), a MAC header field (404), an AP identifier (ID) field (406) indicating the identifier of the transmitting AP, a selected user field (408), a precoder index field (410), and a frame check sequence (FCS) field (412).

[0067] In one embodiment, the PHY header (402) and the MAC header (404) may share the same format as the NDPA frame. The MAC header (404) may indicate that the frame is an AP-AP shared frame. The MAC header (404) may include a subframe type indicating that the frame is an AP-AP shared frame. In another embodiment, the AP-AP shared frame may be represented through an NDPA variant frame that may be provided in future designs.

[0068] In another embodiment, the AP ID field may not exist, in which case the AP ID information may be displayed in the MAC header field (404) through the transmitter address (TA) field (within the MAC header field). In another embodiment, the AP ID information may be displayed through the AP ID field (406).

[0069] The selected user field (408) may represent a list of selected users (one or more selected STAs) of the participating APs indicated in the AP ID field (406). As discussed with reference to FIG. 1, each collaborating AP may select one or more STAs from its associated STAs. Then, the selected STAs are shared among the collaborating APs through an AP-AP shared frame transmission process according to the embodiments described with reference to FIG. 2 and FIG. 3.

[0070] The selected user field (408) may further indicate the number of streams per selected user. The selected user field (408) may further indicate a user ID (which may be a MAC address or an associated ID (AID)). The selected user field (408) may further indicate bandwidth (BW), modulation and coding system (MCS), and other related information.

[0071] The selected user field (408) may also include CSI information between the corresponding AP and each selected STA. If the precoder calculation is not standardized, i.e., depending on the implementation, the AP-AP shared frame may need to include an interference alignment (IA) CoBF precoder field (411). Therefore, if the precoder calculation is not standardized, the precoder index field (410) may need to be replaced with the IA CoBF precoder field (411).

[0072] In an embodiment where the AP-AP shared frame includes an IA CoBF precoder field (411), the IA CoBF precoder field may be indicated by the last collaborating AP (e.g., 262 and 362) in the AP-AP shared transmission process. For example, in an embodiment following FIG. 2, the IA CoBF precoder field (411) may be indicated by the coordinating AP (AP1 (202)) via, for example, the AP-AP shared frame (254); and in an embodiment following FIG. 3, the IA CoBF precoder field (411) may be indicated by the coordinating AP (AP2 (204)) via, for example, the AP-AP shared frame (250).

[0073] The selected user may be determined from among the STAs associated with the corresponding participating AP. For example, the selected user for a coordination AP, e.g., AP1 (202), is determined or selected by the coordination AP from among the STAs associated with the coordination AP, and similarly, the selected user for a coordinated AP, e.g., AP2 (204), is determined or selected by the coordination AP from among the STAs associated with the coordination AP. In an embodiment following FIG. 2, if the AP ID field (406) indicates a coordination AP (e.g., AP1 (202)), the AP-AP shared transmission procedure (262) may be terminated (e.g., if the AP-AP shared frame (252) indicates a coordination AP ID in the AP ID field). In an embodiment of FIG. 2, the coordination AP (AP1 (202)) may further indicate a precoder index in the precoder index field (410) if the precoder is standardized for CoBF.

[0074] As discussed in this specification, in the case of a collaborative AP, it is desirable to manage potential interference. Managing interference may include calculating a precoder index. The calculation of the precoder index may be standardized. The precoder index field (410) may indicate a method for calculating the precoder index.

[0075] As will be known to those skilled in the art, CSI information received during the sounding sequence process (260) (e.g., CSI report frames (222, 224, 244, 246)) may be required for precoder calculation. As such, during the AP-AP shared transmission process (262 and 363), CSI information is shared between collaborating APs. CSI information may be displayed in a selected user field (408).

[0076] In some embodiments, the precoder for all collaborating APs is calculated by the last AP of the AP-AP shared transmission process (262 and 363) and can be shared among the collaborating APs. For example, in the embodiment of FIG. 2, the last AP of the AP-AP shared transmission process (262) is a coordinating AP (AP1 (202)) that calculates the precoder for all collaborating APs and can share the calculated precoder with the corresponding collaborating APs. Similarly, in the embodiment of FIG. 3, the last AP of the AP-AP shared transmission process (362) is a coordinating AP (AP2 (204)) that calculates the precoder for all collaborating APs and can share the calculated precoder with the corresponding collaborating APs.

[0077] FIG. 5 illustrates a 2-AP CoBF having one selected STA for each participating AP, according to an embodiment of the present disclosure. FIG. 5 is similar to FIG. 1 and illustrates a collaborating AP and a selected STA. The collaborating APs perform co-coordinated beamforming (BF) transmission. As described herein, (122) and (124) It is desirable to minimize or cancel interference between the collaborating APs by removing channels. To do so, it is necessary to manage the interference.

[0078] In one embodiment, managing interference may include applying zero-focusing beamforming (ZF-BF). In ZF-BF, channels at each collaborating AP can be aggregated and reconfigured. For example, at AP1 (102), the channels are (120) and (122) is included. Therefore, the channels aggregated in AP1 are It is given as and can be denoted as C1. Likewise, in AP2(112), the channel is (124) and (126) is included. Therefore, the aggregated channels in AP2 (112) are It is given as and can be represented as C2.

[0079] The ZF-BF based IA precoder in AP1 (202) can be obtained by taking the pseudo-inverse of the C1 matrix and then taking the first K1 column. The ZF-BF based IA precoder in AP2 (112) can be obtained by taking the pseudo-inverse of the C2 matrix and then taking the last K2 column. K1 is the rank of the transmission by AP1, and K2 is the rank of the transmission by AP2.

[0080] Once the AP-AP sharing process (262 or 362) is completed, all participating APs assume that the selected STA (including the number of streams to be scheduled for each STA) will be scheduled for CoBF. As mentioned, each participating AP can calculate the aggregated channels based on the channels formed between the participating AP and the selected STA, and then take the pseudo-inverse of the aggregated channels. In the case of 2-AP coordination, the coordinating AP can take the first K1 column of the aggregated channels for the precoder, where K1 represents the size of the coordinating AP's transmission rank. The coordinating AP can take the last K2 column of the aggregated channels for the precoder, where K2 represents the size of the coordinating AP's transmission rank.

[0081] In some embodiments, the last participating AP in the AP-AP sharing process may calculate a precoder for all collaborating APs according to ZF-BF and share the calculated precoder with the corresponding APs through an AP-AP sharing frame. For example, in the embodiment of FIG. 2, Coordinating AP1 (202) may calculate its own ZF-BF IA precoder and the ZF-BF IA precoder of the coordinated AP, e.g., AP2 (204), and share the calculated precoder with the corresponding AP through an AP-AP sharing frame (254). Similar to the embodiment of FIG. 3, Coordinating AP2 (204) may calculate its own ZF-BF IA precoder and the ZF-BF IA precoder of the coordinated AP (in the case of multiple coordinated APs) and the coordinated AP, e.g., AP1 (202), and share the calculated precoder with the corresponding AP through an AP-AP sharing frame (250).

[0082] As described in this specification, all collaborating APs share their CSI information through a sounding sequence process (260). Accordingly, the AP responsible for calculating the precoder for all collaborating APs (e.g., AP1 (202) in FIG. 2 and AP2 in FIG. 3) can calculate the precoder because it knows the CSI information received from each collaborating AP. After calculating the precoder, the responsible AP can transmit an AP-AP shared frame containing the calculated precoder to the collaborating APs in an AP-AP shared frame indicated by the IA CoBF precoder field (411).

[0083] After receiving the calculated precoder, the receiving AP (e.g., AP2 (204) in FIG. 2 and AP1 (202) in FIG. 3) and the responsible AP can coordinate using the calculated precoder and transmit CoBF packets simultaneously through an AP-AP shared frame.

[0084] In some embodiments, the transmission or transmitter (TX) power may need to be kept constant below a certain level regardless of the number of TX chains, for example, in accordance with Federal Communications Commission (FCC) regulations. Accordingly, the precoder may need to be normalized, for example, according to the MIMO configuration.

[0085] In the embodiment, the precoder at AP1 can be denoted as P1 and the precoder at AP2 can be denoted as P2, and then, the new normalized precoder is for AP1 and AP2, respectively. and It can be written as.

[0086] " " can represent a Euclidean norm obtained by squaring the size of each P matrix element, summing the results for all elements, and then applying the square root operation. Thus, the Euclidean norm can be obtained as the square root of the sum of the sizes of all matrix elements. In some embodiments, TX power normalization for each precoder of the participating AP can be performed individually. Thus, each participating AP can perform its own TX power normalization.

[0087] Precoder information may differ for each subcarrier in one or more participating STAs. It is desirable for the phase precoder information to be continuous from one subcarrier to another. However, since not all subcarriers of one or more STAs may have a reference signal for channel estimation, one or more STAs may rely on interpolation or smoothing for channel estimation.

[0088] When beamforming (BF) is applied to a frame, the phase information (of the precorder between subcarriers) can be discontinuous between tones, which can cause difficulties in estimating the channel through interpolation. Therefore, in some embodiments, a phase continuity process may be applied during beamforming to avoid the problem of phase discontinuity. In some embodiments, during the sounding process, channel estimation for CSI information measurement may be performed using an 802.11 Long Training Field (LTF) based reference signal. In these embodiments, CSI information may be acquired from all tone group number (Ng) tones and finally from all tones.

[0089] In the embodiment, P0, P1, P2, ... may represent column vectors of a precoding matrix for each tone 0, 1, 2, etc., based on CSI information during sound processing. Accordingly, the continuous phase-based precoding column vectors of the precoding matrix are It could be, and here , And, is an updated one with phase continuity, i.e., It can represent the described procedure (here, , And, is an updated one with phase continuity, that is, (can represent) is repeated until the tone of each OFDM symbol ends. The phase continuity process for each precoder of the participating AP can be performed individually. Therefore, each participating AP can perform its own phase continuity process during beamforming.

[0090] The embodiments described herein may provide a procedure for AP-AP shared transmission including collaborating APs. The embodiments described herein may further provide a format for an AP-AP shared frame.

[0091] FIG. 6 is a schematic diagram of an electronic device (600) capable of performing some or all of the methods and features described explicitly or implicitly in this specification according to different embodiments of the present invention. For example, a computer with network functions may be configured as the electronic device (600). In some embodiments, the electronic device (600) may be a UE, AP, STA, etc., as recognized by those skilled in the art.

[0092] As illustrated, the electronic device (600) may include a processor (610), a specialized processor such as a central processing unit (CPU) or a graphics processing unit (GPU) or other such processor unit, memory (620), a non-transient mass storage unit (630), an input-output interface (640), a network interface (650), and a transceiver (660), all of which are coupled to communicate via a bidirectional bus (670). According to a given embodiment, some or all of the illustrated elements may be utilized, or only a subset of the elements may be utilized. Additionally, the electronic device (600) may include multiple instances of a given element, such as a plurality of processors, memory, or transceivers. Additionally, elements of the hardware device may be coupled directly to other elements without a bidirectional bus. Furthermore, or instead of a processor and memory, other electronic devices such as integrated circuits may be used to perform the necessary logical operations.

[0093] The memory (620) may include any type of non-transient memory, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), and any combination thereof. The mass storage element (630) may include any type of non-transient storage device, such as a solid-state drive, a hard disk drive, a magnetic disk drive, an optical disk drive, a USB drive, or any computer program product configured to store data and machine-executable program code. According to a given embodiment, the memory (620) or the mass storage element (630) may record instructions and commands executable by the processor (610) to perform any of the above-described method operations.

[0094] Embodiments of the present invention may be implemented using electronic hardware, software, or a combination thereof. In some embodiments, the present invention is implemented by one or more computer processors that execute program instructions stored in memory. In some embodiments, the present invention is partially or fully implemented in hardware, for example, by using one or more field programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs) to rapidly perform processing tasks.

[0095] While specific embodiments of the technology have been described herein for illustrative purposes, it will be understood that various modifications may be made without departing from the scope of the technology. Accordingly, this specification and the drawings should be regarded only as examples of the invention as defined by the appended claims and are deemed to include any and all modifications, variations, combinations, or equivalents that fall within the scope of the invention. In particular, the scope of the technology includes providing a computer program product or program element for storing a machine-readable signal and controlling the operation of a computer according to the method of the technology, or a program storage unit or memory device such as a magnetic or optical wire, tape, or disk, and / or structuring some or all of the components according to the system of the technology.

[0096] The operation related to the method described herein may be implemented as coded instructions within a computer program product. That is, the computer program product is a computer-readable medium on which software code for executing the method is recorded when the computer program product is loaded into memory and executed on a microprocessor of a wireless communication device.

[0097] Additionally, each operation of the present method may be executed on any computing device, such as a personal computer, server, PDA, etc., and according to one or more or parts thereof of one or more program elements, modules, or objects generated from any programming language, such as C++, Java, etc. Additionally, each operation, or a file or object, etc., implementing said operation may be executed by special-purpose hardware or a circuit module designed for said purpose.

[0098] Through the description of the embodiments described above, the present invention may be implemented using only hardware, or using software and a necessary general-purpose hardware platform. Based on this understanding, the technical solution of the present invention may be implemented in the form of a software product. The software product may be stored on a non-volatile or non-transient storage medium, which may be a compact disc read-only memory (CD-ROM), a USB flash disk, or a removable hard disk. The software product includes a number of instructions that enable a computer device (a personal computer, a server, or a network device) to execute the method provided in the embodiments of the present invention. For example, such execution may correspond to the simulation of a logical operation described herein. The software product may additionally or alternatively include a number of instructions that enable a computer device to execute an operation for configuring or programming a digital logic device according to the embodiments of the present invention.

[0099] Although the present invention has been described with reference to specific features and embodiments, it is evident that various modifications and combinations can be made without departing from the invention. Accordingly, the specification and drawings should be regarded only as examples of the invention as defined by the appended claims and should be deemed to include any and all modifications, variations, combinations, or equivalents that fall within the scope of the invention.

Claims

Claim 1 As a method, the first access point (AP) of a plurality of collaborative access points (APs) transmits a request for channel state information (CSI) associated with the one or more STAs and the first AP to one or more stations (STAs) associated with the plurality of collaborative APs by the first AP; the first AP receives a response from the one or more STAs including the CSI associated with the one or more STAs and the first AP by the first AP; the first AP transmits a sounding request to the second AP of the plurality of collaborative APs, indicating to the second AP to request the CSI associated with the one or more STAs and the second AP from the one or more STAs by the first AP; the first AP receives a first AP-AP shared message from the second AP including the CSI associated with the one or more STAs and the second AP by the first AP; the first AP transmits a second AP-AP shared message to the second AP including the CSI associated with the one or more STAs and the first AP by the first AP; and the first AP transmits a plurality of precoders A method comprising a step of calculating, wherein each calculated precoder corresponds to each AP of the plurality of collaborative APs and is based on CSI information associated with one or more STAs and each AP. Claim 2 A method according to claim 1, wherein the second AP-AP shared message comprises: an identifier of the first AP; an indication that the frame is an AP-AP shared frame; one or more STAs associated with the first AP; the CSI associated with the one or more STAs and the first AP; one or more streams per STA of the one or more STAs associated with the first AP; and one or more fields representing one or more of precoder information associated with the second AP. Claim 3 delete Claim 4 In paragraph 2, the method wherein the precoder information represents a calculated precoder among the plurality of precoders. Claim 5 In paragraph 2, the above-mentioned precoder information is a method representing a precoder index representing a precoder calculation method. Claim 6 In paragraph 2, the method wherein the CSI associated with the one or more STAs and the first AP is displayed in a selected user field of the frame. Claim 7 In paragraph 2, the identifier of the first AP is displayed in the transmitter address (TA) field of the media access control (MAC) header of the frame. Claim 8 A method comprising: receiving a first shared message from a second AP by a first access point (AP), the first AP and the second AP collaborate, the first AP and the second AP collaborate; transmitting a second shared message by the first AP to the second AP, the second shared message comprising the first AP's identifier; an indication that the frame is an AP-AP shared frame; one or more stations (STA) associated with the first AP; a CSI associated with the first AP; one or more streams per STA of the one or more STAs associated with the first AP; and one or more fields representing one or more of the precoder information associated with the second AP; and calculating a precoder associated with the second AP by the first AP based on the CSI associated with the second AP. Claim 9 delete Claim 10 In claim 8, the precoder information associated with the second AP represents the calculated precoder associated with the second AP. Claim 11 In claim 8 or 10, the precoder information associated with the second AP represents a precoder index representing a precoder calculation method. Claim 12 In paragraph 8 or 10, the method wherein the CSI associated with the first AP is displayed in the selected user field of the frame. Claim 13 A method according to claim 8 or 10, wherein the identifier of the first AP is displayed in the transmitter address (TA) field of the media access control (MAC) header of the frame. Claim 14 A device comprising at least one processor and at least one machine-readable medium storing executable instructions, wherein the executable instructions, when executed by the at least one processor, a first access point (AP) of a plurality of collaborative access points (APs) transmits a request for channel state information (CSI) associated with the one or more STAs and the first AP to one or more stations (STAs) associated with the plurality of collaborative APs, receives a response from the one or more STAs including the CSI associated with the one or more STAs and the first AP, transmits a sounding request to a second AP of the plurality of collaborative APs indicating to the second AP to request the CSI associated with the one or more STAs and the second AP from the one or more STAs, receives a first AP-AP shared message from the second AP including the CSI associated with the one or more STAs and the second AP, transmits a second AP-AP shared message to the second AP including the CSI associated with the one or more STAs and the first AP, and calculates a plurality of precoders. A device configured such that each calculated precoder corresponds to each AP of the plurality of collaborative APs and is based on CSI information associated with one or more STAs and each AP. Claim 15 In paragraph 14, the device comprises a second AP-AP shared message including: an identifier of the first AP; an indication that the frame is an AP-AP shared frame; one or more STAs associated with the first AP; the CSI associated with the one or more STAs and the first AP; one or more streams per STA of the one or more STAs associated with the first AP; and one or more fields representing one or more of precoder information associated with the second AP. Claim 16 delete Claim 17 In paragraph 15, the device, wherein the precorder information represents a calculated precorder among the plurality of precorders. Claim 18 In paragraph 15 or 17, the device, wherein the precoder information represents a precoder index representing a precoder calculation method. Claim 19 In paragraph 15 or 17, the device, wherein the CSI associated with one or more STAs and the first AP is displayed in the selected user field of the frame. Claim 20 In paragraph 15 or 17, the identifier of the first AP is displayed in the transmitter address (TA) field of the media access control (MAC) header of the frame, the device.

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