Devices and methods for providing multiple access point coordination schemes

Abstract

An access point, AP, for transmitting a coordinated beamforming downlink PPDU, to a corresponding non-AP station in a wireless local area network, WLAN, concurrently with PPDU transmissions between one or more other APs and one or more other corresponding non-AP stations in the WLAN in a coordinated beamforming transmission, the AP being configured to transmit a trigger frame, TF, to the corresponding non-AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, the uplink response to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission. A corresponding non-AP station and methods are also provided.

Description

[0001] DEVICES AND METHODS FOR PROVIDING MULTIPLE ACCESS POINT COORDINATION SCHEMES

[0002] TECHNICAL FIELD

[0003] This disclosure relates to wireless communications. More specifically, the present disclosure relates to devices and methods for providing multiple access point coordination schemes such as Coordinated Beamforming. In particular, those using a trigger based physical layer protocol data unit format.

[0004] BACKGROUND IEEE 802.11-based wireless local area networks, WLANs, (also referred to as Wi-Fi networks) have become popular at an unprecedented rate. Coordinated Beamforming, CoBF, is a Multiple Access Point, MAP, coordination scheme where two or more APs transmit concurrently using the same channel bandwidth by utilizing beamforming techniques to minimize mutual interference. Beamforming depends on channel sounding to determine how to radiate energy in a preferred direction. Many factors may influence how to steer a beam in a particular direction.

[0005] CoBF scheme is focused on downlink, DL, transmission, where the formats of the transmitted signals are designed to support concurrent communication within at least two Basic Service Set, BSS, networks. In particular, the preamble portion of the transmitted signals are partially aligned to ensure successful reception by any receiver. The alignment is achieved by using the same transmit parameters and incorporating the same information in the relevant fields of the preamble.

[0006] The current trigger based, TB, physical layer protocol data unit, PPDU, format assumes that non-AP stations, STAs, indicate the parameters in a universal signal field, U-SIG, that are defined by the AP in the trigger frame, TF. Moreover, some bits are provided within the TF and copied to the relevant bits of the TB, PPDU, U-SIG.

[0007] However, for implementing an aligned U-SIG across multiple APs not all necessary parameters are currently communicated. Moreover, there is no indication in the current TF which solicits CoBF TB PPDU. There is thus a need to provide an approach where the MAC level of the non-AP STA is instructed by the MAC (i.e. TF payload) to transmit the necessary format of the U-SIG.

[0008] SUMMARY

[0009] The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

[0010] According to one aspect there is provided an access point, AP, for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station in a wireless local area network, WLAN, concurrently with PPDU transmissions between one or more other APs and one or more other corresponding non-AP stations in the WLAN in a coordinated beamforming transmission, the AP being configured to transmit a trigger frame, TF, to the corresponding non-AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, the uplink response to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.This may allow for efficient control of uplink response parameters of coordinated beamforming transmissions and may allow for faster response with reduced overhead, thus improving the throughput and latency.

[0011] In an embodiment, the AP may be configured to: form a special user information field for the TF, the special user information field comprising the indication; and transmit to the corresponding non-AP station a TF comprising the formed special user information field. This may be an efficient way of providing the indication to the non-AP station in the TF.

[0012] In an embodiment, the indication may be at least partially given by one or more bits of the special user information field. This may be an efficient way of providing the indication to the non-AP station in the TF.

[0013] In an embodiment, the one or more bits of the special user information field may be one or more disregard bits of the special user information field. This may be an efficient way of providing the indication to the non-AP station in the TF.

[0014] In an embodiment, the indication may be given in a single bit of the special user information field. This may be a bit-efficient way of providing the indication in the TF.

[0015] In an embodiment, the single bit may be bit B25 of the special user information field. This may be a convenient bit for including the indication that was assigned for UHR and beyond features.

[0016] In an embodiment, the indication may be at least partially given by one or more of bits B26 to B31 and B32 to B37 of the special user information field. These may be convenient bit ranges for including the indication that were assigned for UHR and beyond features.

[0017] In an embodiment, the indication may be an indication that the uplink response is to have a U-SIG that is at least partially aligned with the U-SIG(s) of the one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission. This may allow the AP station to indicate to the non-AP station that the U-SIGs of the uplink responses should be at least partially aligned. This may reduce interference. In an embodiment, the indication may comprise an indication of at least one identifier to be included in the U-SIG of the uplink response. This may allow for control of the U-SIG format of coordinated beamforming trigger-based PPDU in the TF. In an embodiment, the at least one identifier may comprise a BSS color identifying the BSS of the AP. This may allow the BSS of the transmitting AP to be identified.

[0018] In an embodiment, the indication may comprise an additional BSS color to the BSS color identifying the BSS of the AP, wherein the additional BSS color identifies the BSS of another AP participating in the coordinated beamforming transmission. This may allow another transmitting AP participating in the coordinated beamforming transmission to be identified.

[0019] In an embodiment, the at least one identifier may comprise a BSS color defined for multiple APs participating in the coordinated beamforming transmission. This BSS color may be a single BSS color (i.e. only one color, which may be a special or dedicated BSS color) for the APs participating in the coordinated beamforming transmission.

[0020] In an embodiment, the indication may comprise a location in the U-SIG of the uplink response in which the identifier is to be included. This may allow the AP to indicate to the non-AP station where the identifier should be indicated in the uplink response.

[0021] In an embodiment, the location may be specified in a single bit of the special user information field. This may allow the AP to provide the location to the non-AP station in the TF.In an embodiment, the single bit may be bit B32 of the special user information field. This may be a convenient bit for including the location.

[0022] In an embodiment, the AP may be configured to: form a trigger dependent information field for the trigger frame, the trigger dependent information field comprising the indication; and transmit to the non-AP station a trigger frame comprising the formed trigger dependent information field. This provides an alternative way to provide one or more aspects of the indication to the non-AP station in the TF.

[0023] In an embodiment, the location may be specified in a single bit of the trigger dependent information field. This may allow the AP to indicate to the non-AP station where the identifier should be included in the uplink response.

[0024] In an embodiment, the single bit may be bit B5 of the trigger dependent information field. This may be a convenient bit for including the location that was assigned for UHR and beyond features.

[0025] In an embodiment, the uplink response may be to be transmitted using extremely high-throughput, EHT, or ultra-high reliability, UHR, trigger based, TB, PPDU format. This may allow for high throughput or high reliability.

[0026] According to another aspect there is provided a method for operating an access point, AP, for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station in a wireless local area network, WLAN, concurrently with PPDU transmissions between one or more other APs and one or more other corresponding non-AP stations in the WLAN in a coordinated beamforming transmission, the method comprising transmitting a trigger frame, TF, to the corresponding non-AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, the uplink response to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

[0027] This method may allow for efficient control of uplink response parameters of coordinated beamforming transmissions and may allow for faster response with reduced overhead, thus improving the throughput and latency.

[0028] According to another aspect there is provided a non-access point, non-AP, station for receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, in a wireless local area network, WLAN, concurrently with PPDU receptions by one or more other non-AP stations from one or more other corresponding APs in the WLAN in a coordinated beamforming transmission, the non-AP station being configured to receive a trigger frame, TF, from the corresponding AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, wherein the non-AP station is configured to transmit the uplink response using a trigger-based PPDU format, the uplink response having a preamble with content at least partially aligned with uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

[0029] This may allow for efficient control of uplink response parameters of coordinated beamforming transmissions and may allow for faster response with reduced overhead, thus improving the throughput and latency.

[0030] In an embodiment, the identifier may be a BSS color defined for multiple APs participating in the coordinated beamforming transmission. This BSS color may be a single BSS color (i.e. only one color, which may be a special or dedicated BSS color) for the APs participating in the coordinated beamforming transmission.In an embodiment, the non-AP station may be configured to copy the BSS color indicated in the special information user field to the current location of the BSS color in the U-SIG. This may allow the BSS color to be included in the uplink response. In an embodiment, the current location of the BSS color may be in one or more of bits B7 to B12 of the special user information field. This may be a convenient bit range for including the indication that was assigned for UHR and beyond features.

[0031] In an embodiment, the indication may comprise a first BSS color and a second BSS color at first and second locations of the special user information field respectively, wherein the non-AP station is configured to copy the first BSS color and the second BSS color to the first and the second locations of the U-SIG in the uplink response. This may allow the first and second BSS colors to be included in the TF in a relevant order and for the BSS colors that are indicated at the first and second locations of the special user information field of the TF to be copied to the first and second locations of the U-SIG in the solicited triggerbased PPDU respectively.

[0032] In an embodiment, the location may be specified in a single bit of a trigger dependent information field of the TF. This may be a bit-efficient way of including the location in the TF.

[0033] In an embodiment, the non-AP station may be configured to set a spatial reuse indication in the uplink response to ‘DISALLOW’ . This will protect the transmission from undesired interference signals and produce one or more additional bits to be used for other features.

[0034] According to another aspect there is provided a method for operating a non-access point, non-AP, station for communication with an AP associated with the non-AP station in a wireless local area network, WLAN, the AP and non-AP station being capable of receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, in a wireless local area network, WLAN, concurrently with PPDU receptions by one or more other non-AP stations from one or more other corresponding APs in the WLAN in a coordinated beamforming transmission, the method comprising receiving a trigger frame, TF, from the corresponding AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, wherein the non-AP station is configured to transmit the uplink response using a trigger-based PPDU format, the uplink response having a preamble with content at least partially aligned with uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

[0035] This method may allow for efficient control of uplink response parameters of coordinated beamforming transmissions and may allow for faster response with reduced overhead, thus improving the throughput and latency.

[0036] According to another aspect there is provided a computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the methods above when the program code is executed by the computer or the processor.

[0037] BRIEF DESCRIPTION OF THE FIGURES

[0038] The present disclosure will now be described by way of example with reference to the accompanying drawings. In the drawings: Fig. 1 shows a schematic diagram illustrating a WLAN including an AP according to an embodiment and a further OBSS AP in communication with a plurality of non-AP stations according to an embodiment.

[0039] Fig. 2 shows an example of a Coordinated Beamforming operation diagram.Fig. 3 shows an example modified U-SIG in CoBF DL PPDU.

[0040] Fig. 4 shows an example modified U-SIG in UL TB PPDU.

[0041] Fig. 5 shows an example of the proposed trigger frame, TF, design.

[0042] Fig. 6 shows another example of the proposed TF design.

[0043] Fig. 7 shows another example of the proposed TF design.

[0044] Fig. 8 shows another example of the proposed TF design.

[0045] Fig. 9 shows another example of the proposed TF design.

[0046] Fig. 10 shows a flow diagram illustrating steps of a method for implementation at an access point, AP, for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station in a wireless local area network, WLAN.

[0047] Fig. 11 shows a flow diagram illustrating steps of a method for implementation at a non-access point, non-AP, station for receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, in a wireless local area network, WLAN.

[0048] DETAILED DESCRIPTION

[0049] In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.

[0050] In order to provide a full CoBF operation, there is a need to design an uplink, UL, response to CoBF DL physical layer protocol data units, PPDUs. The current UL response from multiple non-AP STAs is obtained using trigger based, TB, PPDU where the transmission is solicited by the trigger frame, which is sent by the AP. TB PPDU is also a potential implementation for UL response to CoBF DL PPDU. In this implementation non-AP STAs from different BSS transmit in parallel a TB PPDUs using the same BW. Similar to CoBF DL, need to at least partially align the preamble portion of the transmitted signals.Fig. 1 shows a wireless communication system 100, in particular a wireless local area network, WLAN, in accordance with the IEEE 802.11 framework of standards (also referred to as a Wi-Fi network 100). The WLAN 100 comprises a first access point, AP, 110a according to an embodiment in communication with a plurality of associated non-AP stations 120a,b according to an embodiment. The WLAN 100 may further comprise at least one further AP 110b in communication with a further plurality of non-AP stations 120c, d associated with the further AP 110b. By way of example, the non-AP stations 120a, b and the further non-AP stations 120c, d may comprise smartphones, laptop computers, tablet computers, desktop computers or other types of wireless devices. As indicated, the stations, i.e. APs 110a,b and non-AP stations 120a-d, shown in figure 1 may be multiantenna stations and configured for beamforming, in particular coordinated beamforming, CoBF. To this end, by way of example, the AP 110a comprises a plurality of antennas 114a, the further overlapping basic service set, OBSS, AP 110b comprises a plurality of antennas 114b, and, as a representative exemplary, the non-AP station 120a comprises a plurality of antennas 124a.

[0051] As further illustrated in figure 1 , the AP 110a (as well as the further AP 110b) may comprise a processing circuitry Illa and a communication interface 113a, in particular a wireless communication interface 113a enabling communication in accordance with the IEEE 802.11 framework of standards. The processing circuitry Illa may be implemented in hardware and / or software and may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The AP 110a may further comprise a memory 115a configured to store executable program code which, when executed by the processing circuitry Illa, causes the AP 110a to perform the functions and methods described herein.

[0052] Likewise, the non-AP station 120a (as well as the other non-AP stations 120b-d shown in figure 1) may comprise a processing circuitry 121a and a communication interface 123a, in particular a wireless communication interface 123a enabling communication in accordance with the IEEE 802.11 framework of standards. The processing circuitry 121a may be implemented in hardware and / or software and may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The non-AP 120a may further comprise a memory 125a configured to store executable program code which, when executed by the processing circuitry 121a, causes the non-AP station 120a to perform the functions and methods described herein.

[0053] Before describing detailed embodiments of the AP 110a according to an embodiment and the non-AP station 120a according to an embodiment, in the following some technical background as well as terminology will be introduced making use of one or more of the following abbreviations and / or acronyms:

[0054] A-MPDU Aggregated MAC Protocol Data Unit

[0055] AP Access Point

[0056] BF Beamforming

[0057] BSS Basic Service Set

[0058] BW Bandwidth

[0059] CoBF Coordinated Beamforming

[0060] DL Downlink

[0061] EHT Extremely High Throughput

[0062] LAN Local Area Network

[0063] MAC Medium Access Control

[0064] MAP Multiple Access Points

[0065] MIMO Multiple In Multiple OutML Multi-link

[0066] MPDU MAC Protocol Data Unit

[0067] NDP Non-Data Packet

[0068] NDPA NDP Announcement

[0069] OBSS Overlapping BSS

[0070] PER Packet Error Ratio

[0071] PHY Physical (layer)

[0072] PPDU Physical Layer Protocol Data Unit

[0073] RSSI Received Signal Strength Indicator

[0074] RU Resource Unit

[0075] SNR Signal to Noise Ratio

[0076] STA Station

[0077] SVD Single Value Decomposition

[0078] TB Trigger Based

[0079] TF Trigger Frame

[0080] TXOP Transmit Opportunity

[0081] UL Uplink

[0082] WLAN Wireless Local Area Network

[0083] UHR Ultra-High Reliability

[0084] As used herein, an access point (AP), such as the APs 110a, b illustrated in figure 1 , is a wireless station that provides access to other networks. An AP can support many connected or associated non-AP STAs, such as the non-AP stations 120a-d illustrated in figure 1. APs use control information to control traffic flow over the wireless medium among all associated non-AP STAs within a BSS.

[0085] There are three main types of frames communicated between WLAN STAs, namely data, management, and control frames. Data traffic is exchanged between two or more STAs in a WLAN to facilitate communication, one of which is typically an AP. The data frames are either generated by the two or more STAs and / or by an external network. This traffic is delivered in a secured manner over the WLAN when the AP and the corresponding non-AP STAs negotiate a cryptographic encapsulation method and keys to encrypt the data traffic. Management frames are exchanged between the AP and one or more non-AP STAs in a BSS to establish and maintain the state of data communications. Security can be negotiated to encrypt or authorize data and / or management frames. Control frames are exchanged between the AP and the non-AP STAs in a BSS to control the flow of the data frame exchange.

[0086] As already mentioned above, and according to embodiments disclosed herein, the stations, i.e. APs 110a, b and non-AP stations 120a-d, shown in figure 1 may be multi-antenna stations and configured for beamforming, in particular coordinated beamforming, CoBF. CoBF is a Multi-AP, MAP, coordination scheme where the two (or more) APs 110a,b transmit concurrently using the same channel bandwidth by utilizing beamforming techniques to minimize mutual interference. In this coordination scheme each AP 110a,b exchanges data frames with its own associated BSS non-AP stations only (in figure 1 referred to as STAs). For example, in the scenario illustrated in figure 1 , STA1 120a and STA2 120b are associated with API 110a, while STA3 120c and STA4 120d are associated with AP2 110b. Each AP 110a, b exchanges the data frames only with its associated STAs, but each AP 110a, b applies a precoder (usually represented by a precoder matrix) such that the interference to the OBSS STAs is minimized when both APs transmit concurrently. In other words, the actual power of the signals, as illustrated by the straight dashed arrows in figure 1 , at the receiver side is small enough to allow successful detection of the desired signal, as illustrated by the curved solid arrows in figure 1.In the CoBF scheme, APs transmit concurrent DL PPDUs to their associated non-AP STAs while mutual interference for the OBSS non-AP STAs is minimized using beamforming techniques. Once the other OBSS APs have been discovered, an initiating AP starts a negotiation for an agreement with other OBSS AP that support the same CoBF scheme. After an agreement is set between the involved OBSS APs, each of the OBSS APs perform a sounding procedure to obtain the channel information feedback between itself, its associated non-AP STAs, and OBSS non-APs involved in the imminent CoBF transmission. As mentioned above, each AP computes a precoder based on the received channel information feedback from the non-AP STAs that ensures minimal interference with the OBSS STAs. After receiving CoBF DL PPDUs, STA are assumed to respond with at least an acknowledgement PPDU. Single TXOP may include several DL CoBF PPDUs and several UL responses (see example in figure 2). Note that CoBF Sounding procedure may not be performed in the same TXOP.

[0087] Fig. 2 shows an example of an CoBF message flow and operation diagram. First, in an announcement stage, the APs discover and respond to each other. In the following Pre-Tx stage the initiating AP provides a MAP trigger frame 202, and the CoBF sounding procedure 204 between all the relevant non-AP stations and APs takes place. After that, the CoBF transmission stage is executed. Whereby a MAP trigger frame 206 is transmitted. The involved APs then provide CoBF data DL PPDUs 208 and the involved non-AP stations provide UL responses 210.

[0088] The details of CoBF Downlink PPDU transmissions are well known and widely discussed in the IEEE standard 802.1 Ibn, and the DL PPDU preamble content is fully aligned between the APs. However, this is not the case for the Uplink Response and there are several methods proposed for the UL response transmission.

[0089] One proposed method assumes parallel trigger-based (TB) transmission of the UL PPDUs by all the STAs using the same BW. This transmission should be triggered by the APs using a trigger frame (TF). Transmitting parallel TB PPDUs might therefore also require preamble content alignment similar to CoBF DL PPDU. There is therefore proposed herein, parameters that may be required to be aligned within the UL preamble and a format of the TF that includes those parameters.

[0090] There is an existing U-SIG design for the CoBF DL PPDU. The U-SIG is a signal field transmitted as part of the PPDU, for example in EHT versions and above, which provides general description of the transmitted PPDU and common transmit parameters that allow all the receivers to determine PPDU format and decode the relevant data. U-SIG carries a BSS color which identifies the BSS of the transmitter and enables a receiver to determine if this transmission is relevant and has to be decoded. That is, transmitting APs can color code their transmissions so that associated non-AP stations, which know their own BSS color, can ignore a transmission which does not comprise a matching BSS color and only spend energy decoding those with a matching BSS color.

[0091] In CoBF, two APs from different BSSs may transmit simultaneously, thus BSS color indication of both APs should be relevant for the receivers of both APs. Two possible options to resolve this issue are proposed. Either indicate two BSS colors in the U-SIG of CoBF DL PPDU, or indicate a special BSS color known to STAs of both APs. Fig. 3 shows an example of an DL U-SIG design with two BSS colors. U-SIG1 not only comprises a first BSS color at bits B7 to B12, but a further BSS color may be entered in bits B20 to B25. These bits are otherwise disregarded or used as a validation bit, and if CoBF is not enabled the bits a left unchanged. In addition, in U-SIG2 a single bit B2 is proposed to indicate that this is a CoBF PPDU to instruct STAs to parse the rest of the fields correctly. That is, bit B2 of U-SIG2 may be used to indicate CoBF is enabled or disabled when the PPDU type indicates a UHR non-OFDMA DL MU MIMO transmission. Otherwise, B2 is a validation bit and is set to e.g.

[0092] 1.

[0093] An additional indication may be proposed to resolve the collision of STA IDs that might be equal for the STAs in different BSSs. A single bit may be used in the User Field of the UHR-SIG to indicate weather this STA ID belongs to first BSS color or second BSS color.In the case where a TB PPDU is used for UL response transmission for CoBF PPDU, the data portion would be transmitted by each STA using different resources allocated to it by the AP. It can be assumed that the APs agree on that before starting CoBF DL PPDU and thus there is no mutual interference issues for the data portion. However, the preamble portion is transmitted from all the STAs using the same BW. Thus, in order to allow third party receivers, or also participating APs, to decode the preamble the content of the U-SIG of TB PPDU must be aligned. This may be achieved by following the same design proposed for U-SIG of CoBF DL PPDU. I.e. if two BSS colors or a single special BSS color is accepted for DL, the U-SIG of TB PPDU for the CoBF UL Response can indicate two BSS colors or the special BSS color as well. In addition, and similarly to DL, a single bit may be used to indicate that this a CoBF TB PPDU. An example of such a U-SIG of TB PPDU with two BSS colors and CoBF indication is shown in Fig. 4.

[0094] Fig. 4 shows an example of a U-SIG of TB PPDU with two BSS Colors for CoBF UL Response. Similarly to that described in reference to figure 3, bits B20 to B25 may be used to indicate the second BSS color. Additionally, a further single bit B2 in U-SIG2 may be used to indicate that this TB PPDU is part of CoBF operation and therefore can be used to indicate that a second BSS color may be found at bits B20 to B25.

[0095] It should be noted that throughout this document CoBF DL PPDU stands for the DL PPDU that is transmitted using the CoBF MAP Coordination scheme and CoBF TB PPDU stands for the TB PPDU that is transmitted as UL Response to the CoBF DL PPDU.

[0096] Accordingly, in order to implement the above-described approach for the UL Response, there is a need to specify the trigger frame design. That is, the design of the TF that provides all the required parameters to construct the U-SIG of TB PPDU for the UL response transmission to M-AP coordinated transmissions. There is no indication of the BSS color in the current TF design. Moreover, there is no indication that current TF solicits CoBF TB PPDU. There is therefore a need to transmit a specific format of the U-SIG and also BSS color that should be copied to the U-SIG of the TB PPDU.

[0097] The proposed approach is to add the following indications to the TF. Firstly, an indication that the current TF solicits a TB PPDU with modified U-SIG format. For example, two BSS colors or a special BSS color, which is aligned between all the STAs. Secondly, an indication of the BSS color (either a single BSS color or two) that needs to be copied to the U-SIG of the TB PPDU. Thirdly, in the case of two BSS colors, an indication which color has to be in which bits of the UL Response in order to prevent interference caused by different values.

[0098] There is provided herein an access point, AP, for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station in a wireless local area network, WLAN, concurrently with PPDU transmissions between one or more other APs and one or more other corresponding non-AP stations in the WLAN in a coordinated beamforming transmission. The AP is configured to transmit a trigger frame, TF, to the corresponding non-AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited. The uplink response is to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission. There is further provided a non-access point, non-AP, station for receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, in a wireless local area network, WLAN, concurrently with PPDU receptions by one or more other non-AP stations from one or more other corresponding APs in the WLAN in a coordinated beamforming transmission. The non-AP station is configured to receive a trigger frame, TF, from the corresponding AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited. The non-AP station is configured to transmitthe uplink response using a trigger-based PPDU format, the uplink response having a preamble with content at least partially aligned with uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

[0099] The indication may be an indication that the uplink response is to have a U-SIG that is at least partially aligned with the U-SIG(s) of the one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission. The indication may comprise an indication of at least one identifier to be included in the U-SIG of the uplink response.

[0100] In addition, the same TF frame may be used to trigger the UL response of additional MAP coordination schemes, where parallel UL is required. For example, in a Coordinated Spatial Reuse scheme.

[0101] It should be understood that all the field sizes provided in the following example implementations are examples and actual implemented size may differ.

[0102] Fig. 5 shows an example of the proposed TF design. In this proposed approach, there is an indication in the TF that indicates this TF solicits an UL Response for the CoBF DL PPDU that will be transmitted using TB PPDU format. The UL Response has a modified U-SIG with aligned content for all BSSs participating in the transmission.

[0103] It may be assumed that the trigger frame that solicits a UL response for CoBF DL PPDU is transmitted in EHT variant with PHY Version indicated as UHR. Thus, it is proposed that a single disregard bit of the Special User Info Field can be used to indicate that TB PPDU with U-SIG of a new format is solicited. The indication may be a single bit field 502. For example, the single bit B25 of the Special User Info Field of the Basic Trigger Frame. Fig. 5 shows the Special User Info Field 500 of the proposed TF, indicating at bit B25 that CoBF is enabled.

[0104] A STA that receives a TF where CoBF is indicated as described above can be configured to act accordingly. The STA may be configured to copy all the relevant information to the U-SIG of the TB PPDU that is solicited by this TF. The STA may at least be configured to copy the BSS color that is indicated during CoBF DL PPDU. Additionally, the Spatial Reuse indication in TB PPDU may be set to ‘DISALLOW’ .

[0105] Accordingly, the AP may be configured to form a special user information field for the TF, the special user information field comprising the indication. The AP may then be configured to transmit to the corresponding non-AP station a TF comprising the formed special user information field. The non-AP station may in turn be configured to set the spatial reuse indication in the uplink response to ‘DISALLOW’.

[0106] The indication may be at least partially given by one or more bits of the special user information field. The one or more bits of the special user information field may be one or more disregard bits of the special user information field. The indication may be given in a single bit of the special user information field. The single bit may be bit B25 of the special user information field. In turn, the non-AP station may be configured to transmit the uplink response accordingly. The non-AP station may be configured to copy the BSS color to the current location of the BSS color in the U-SIG (that is, the typical location currently used in the U-SIG), when instructed to by a particular single bit value. For example, a single bit value may be used to instruct the copying of BSS color, e.g. depending on whether the bit value is 0 or 1.

[0107] Fig. 6 shows a further example of the proposed TF design. In this case, where a single bit indication 502 according to figure 5 is implemented, BSS color may be indicated as well. There is therefore defined an explicit indication of the BSS color that should be copied to the U-SIG of solicited TB PPDU. The indicated BSS color may be an additional second BSS color to theBSS color of the AP that transmits the TF, or a single special BSS color defined for the CoBF transmission. The at least one identifier may thus comprise a BSS color identifying the BSS of the AP.

[0108] The explicit indication 602 of the BSS color requires six bits within the Special User Info Field 600. For example, it may be possible to use bits B26 to B31 in the Special User Info Field oftheTF. BitsB26 to B31 are usually utilised forU-SIG disregard and validate, as are remaining bits B32 to B36. Bit B37 is also typically a reserved bit. Therefore, the indication may be at least partially given by one or more of bits B26 to B31 and B32 to B37 of the special user information field.

[0109] The non-AP station may be configured to copy the BSS color indicated in the special information user field to the current location of the BSS color in the U-SIG. The current location of the BSS color may be in one or more of bits B7 to B12 of the special user information field. Where the indication comprises a first BSS color and a second BSS color at first and second locations of the special user information field respectively, the non-AP station may be configured to copy the first BSS color and the second BSS color to the first and the second locations of the U-SIG in the uplink response.

[0110] As mentioned above, one possible approach discussed for CoBF DL PPDU is indication of two BSS colors of each of the participating APs. In this case, U-SIG of TB PPDU may also include two BSS colors, as depicted in Fig. 4. Therefore, the indication may comprise an additional BSS color to the BSS color identifying the BSS of the AP, wherein the additional BSS color identifies the BSS of another AP participating in the coordinated beamforming transmission.

[0111] Accordingly, the TF would need to indicate which BSS Color should be copied to the first location and which BSS color should be copied to the second location. This is needed so that each AP provides a UL response message with the same information in the same format so as to avoid interference.

[0112] In the case where a single special or dedicated BSS color is used, as mentioned above, the at least one identifier may comprise a BSS color defined for multiple APs participating in the coordinated beamforming transmission.

[0113] It is possible to use a single bit to indicate to which location the indicated BSS color (as shown in Fig. 6) should be copied. For example, if the single bit equals zero the BSS Color indicated in the Special User Info Field 600 may be copied to the current location of BSS Color in the U-SIG of TB PPDU, typically bits B7 to B12 as shown in Fig. 4. Otherwise, it may be copied to the location of the second BSS Color that will be defined for the U-SIG of CoBF TB PPDU. For example, bits B26 to B31 as shown in Figs. 3 and 4. Accordingly, the indication may comprise a location in the U-SIG of the uplink response in which the identifier is to be included.

[0114] There is more than one possible placement for the single bit indication of BSS color location.

[0115] Fig. 7 shows an example of where a single bit indication of BSS color location may be specified in the Special User Info Field 700. In this example, the indication 702 may be provided using bit B32 of the Special User Info Field of the TF. This is provided utilizing a further one of the otherwise U-SIG disregard and validate bits.

[0116] Fig. 8 shows another example of where a single bit indication of BSS color location may be placed in the trigger frame. In this example, the indication 802 may be provided using bit B5 of the Trigger Dependent Info Field 704 of Basic TF. This is typically a single reserved bit and thus is available for use. The location may thus be specified in a single bit of the trigger dependent information field.

[0117] Accordingly, the AP may be configured to form a trigger dependent information field for the trigger frame, the trigger dependent information field comprising the indication. The AP may be further configured to transmit to the non-AP station a trigger frame comprising the formed trigger dependent information field.As mentioned above, another option is to indicate both BSS Colors explicitly in the relevant order. Fig. 9 shows an example Special User Info Field 900 which indicates the BSS Colors at first and second 902 locations of the Special User Info Field 900 of the TF which should be copied to the first and the second locations of the U-SIG in solicited TB PPDU respectively. That is, the location of the BSS color in the Special User Info Field 900 may correspond to the location the information is copied to in the U-SIG. For example, the BSS color specified in bits B26-B31 602 of the Special User Info Field 900 may be copied to bits B7-B12 of U-SIG1, and the BSS color specified in bits B32-B37 902 of the Special User Info Field 900 may be copied to the location of the second BSS color, which may be indicated in bits B20-B25 of U-SIG1.

[0118] The proposed approach may be applied to a wireless local area network system supporting an IEEE 802.1 Ibn and / or 802.1 Ibq next-generation Wi-Fi protocols (such as Wi-Fi 8, or UHR, or applied to a wireless local area network system that supports millimeter wave (mmWave). The uplink response may be transmitted using extremely high-throughput, EHT, or unspecified high rate, UHR, trigger based, TB, PPDU format.

[0119] Fig. 10 shows a flow diagram illustrating the step of a method 1000 for implementation at an access point, AP, for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station in a wireless local area network, WLAN, concurrently with PPDU transmissions between one or more other APs and one or more other corresponding non-AP stations in the WLAN in a coordinated beamforming transmission. The method comprising the step 1002 of transmitting a trigger frame, TF,to the corresponding non-AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, the uplink response to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

[0120] As the method 1000 can be implemented by the AP 110a as well as the further OBSS AP 110b, further features of the method 1000 result directly from the functionality of the AP 110a as well as its different embodiments described above and below. Fig. 11 shows a flow diagram illustrating steps of a method 1100 for implementation at a non-access point, non-AP, station for receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, in a wireless local area network, WLAN, concurrently with PPDU receptions by one or more other non-AP stations from one or more other corresponding APs in the WLAN in a coordinated beamforming transmission. The method comprising the step 1102 of receiving a trigger frame, TF, from the corresponding AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, wherein the non-AP station is configured to transmit the uplink response using a trigger-based PPDU format, the uplink response having a preamble with content at least partially aligned with uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

[0121] As the method 1100 can be implemented by the non-AP station 120a as well as the other non-AP stations 120b-d, further features of the method 1100 result directly from the functionality of the non-AP station 120a as well as its different embodiments described above and below.

[0122] There is also provided herein according to the embodiments of the methods and apparatus described above, a computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method described in reference to figure 10 or the method described in reference to figure 11 when the program code is executed by the computer or the processor.

[0123] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware orsoftware) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0124] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

[0125] The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

[0126] In addition, functional units in the embodiments of the disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

[0127] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present disclosure may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the disclosure.

Claims

CLAIMS1. An access point, AP, (110a, 110b) for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station (120a, 120b, 120c, 120d) in a wireless local area network, WLAN, (100) concurrently with PPDU transmissions between one or more other APs (110b, 110a) and one or more other corresponding non-AP stations (120c, 120d, 120a, 120b) in the WLAN in a coordinated beamforming transmission, the AP being configured to transmit (1020) a trigger frame, TF, to the corresponding non-AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, the uplink response to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

2. The AP (110a, 110b) as claimed in claim 1 , wherein the AP is configured to :form a special user information field (500, 600, 700, 900) for the TF, the special user information field comprising the indication; andtransmit to the corresponding non-AP station a TF comprising the formed special user information field.

3. The AP (110a, 110b) as claimed in claim 2, wherein the indication is at least partially given by one or more bits (502, 602, 702, 902) of the special user information field.

4. The AP (110a, 110b) as claimed in claim 3, wherein the one or more bits of the special user information field are one or more disregard bits of the special user information field.

5. The AP (110a, 110b) as claimed in claim 3 or claim 4, wherein the indication is given in a single bit of the special user information field.

6. The AP (110a, 110b) as claimed in claim 5, wherein the single bit is bit B25 (502) of the special user information field.

7. The AP (110a, 110b) as claimed in claim 3 or claim 4, wherein the indication is at least partially given by one or more of bits B26 to B31 (502, 602) and B32 to B37 (702, 902) of the special user information field.

8. The AP (110a, 110b) as claimed in any preceding claim, wherein the indication is an indication that the uplink response is to have a U-SIG that is at least partially aligned with the U-SIG(s) of the one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

9. The AP (110a, 110b) as claimed in claim 8, wherein the indication comprises an indication of at least one identifier to be included in the U-SIG of the uplink response.

10. The AP (110a, 110b) as claimed in claim 9, wherein the at least one identifier comprises a BSS color identifying the BSS oftheAP.

11. The AP (110a, 110b) as claimed in claim 10, wherein the indication comprises an additional BSS color to the BSS color identifying the BSS of the AP, wherein the additional BSS color identifies the BSS of another AP participating in the coordinated beamforming transmission.

12. The AP (110a, 110b) as claimed in any of claims 8 to 11, wherein the at least one identifier comprises a BSS color defined for multiple APs participating in the coordinated beamforming transmission.

13. The AP (110a, 110b) as claimed in any of claims 8 to 12, wherein the indication comprises a location in the U-SIG of the uplink response in which the identifier is to be included.

14. The AP (110a, 110b) as claimed in claim 13 as dependent on any of claims 2 to 7, or as dependent on any of claims 8 to 13 as dependent on any of claims 2 to 7, wherein the location is specified in a single bit of the special user information field.

15. The AP (110a, 110b) as claimed in claim 14, wherein the single bit is bit B32 (702) of the special user information field.

16. The AP (110a, 110b) as claimed in any preceding claim, wherein the AP is configured to:form a trigger dependent information field (704) for the trigger frame, the trigger dependent information field comprising the indication; andtransmit to the non-AP station a trigger frame comprising the formed trigger dependent information field.

17. The AP (110a, 110b) as claimed in claim 16 as dependent on claim 13, wherein the location is specified in a single bit of the trigger dependent information field (704).

18. The AP (110a, 110b) as claimed in claim 17, wherein the single bit is bitB5 (802) of the trigger dependent information field.

19. The AP (110a, 110b) as claimed in any preceding claim, wherein the uplink response is to be transmitted using extremely high-throughput, EHT, or ultra-high reliability, UHR, trigger based, TB, PPDU format.

20. A method (1000) for implementation at an access point, AP, (110a, 110b) for transmitting a coordinated beamforming downlink physical layer protocol data unit, PPDU, to a corresponding non-AP station (120a, 120b, 120c, 120d) in a wireless local area network, WLAN, (100) concurrently with PPDU transmissions between one or more other APs (110b, 110a) and one or more other corresponding non-AP stations (120c, 120d, 120a, 120b) in the WLAN in a coordinated beamforming transmission, the method comprising transmitting (1002) a trigger frame, TF, to the corresponding non-AP station for triggerbased transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, the uplink response to be transmitted using a trigger-based PPDU format and having a preamble with content at least partially aligned with one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

21. A non-access point, non-AP, station (120a, 120b, 120c, 120d) for receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, (110a, 110b) in a wireless local area network, WLAN, (100) concurrently with PPDU receptions by one or more other non-AP stations (120c, 120d, 120a, 120b) from one or more other corresponding APs (110b, 110a) in the WLAN in a coordinated beamforming transmission, the non-AP station being configured to receive (1102) a trigger frame, TF, from the corresponding AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, wherein the non-AP station is configured to transmit the uplink response using a trigger-based PPDU format, the uplink response having a preamble with content at least partially aligned with uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

22. The non-AP station as claimed in claim 21, wherein the indication is at least partially given by one or more bits (502, 602, 702, 902) of a special user information field (500, 600, 700, 900) of the TF.

23. The non-AP station as claimed in claim 22, wherein the one or more bits of the special user information field are one or more disregard bits of the special user information field.

24. The non-AP station as claimed in claim 22 or claim 23, wherein the indication is given in a single bit of the special user information field.

25. The non-AP station as claimed in claim 24, wherein the single bit is bit B25 (502) of the special user information field.

26. The non-AP station as claimed in claim 22 or claim 23, wherein the indication is at least partially given by one or more of bits B26 to B31 (502, 602) and B32 to B37 (702, 902) of the special user information field.

27. The non-AP station as claimed in any of claims 21 to 26, wherein the indication is an indication that the uplink response is to have a U-SIG that is at least partially aligned with the U-SIG(s) of the one or more uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

28. The non-AP station as claimed in claim 27, wherein the indication comprises an indication of at least one identifier to be included in the U-SIG of the uplink response.

29. The non-AP station as claimed in claim 26, wherein the at least one identifier comprises a BSS color identifying the BSS oftheAP.

30. The non-AP station as claimed in claim 29, wherein the indication comprises an additional BSS color to the BSS color identifying the BSS of the AP, wherein the additional BSS color identifies the BSS of another AP participating in the coordinated beamforming transmission.

31. The non-AP station as claimed in claim 28, wherein the identifier is a BSS color defined for multiple APs participating in the coordinated beamforming transmission.

32. The non-AP station as claimed in any of claims 28 to 31 , wherein the indication comprises a location in the U-SIG of the uplink response in which the identifier is to be included.

33. The non-AP station as claimed in claim 32 as dependent on any of claims 21 to 24 or as dependent on any of claims 25 to 30 as dependent on any of claims 21 to 24, wherein the location is specified in a single bit of the special user information field.

34. The non-AP station as claimed in claim 33, wherein the single bit is bit B32 of the special user information field.

35. The non-AP station as claimed in claim 33 or claim 34, wherein the non-AP station is configured to copy the BSS color indicated in the special information user field to the current location of the BSS color in the U-SIG.

36. The non-AP station as claimed in claim 35, wherein the current location of the BSS color is in one or more of bits B7 to B12 of the special user information field.

37. The non-AP station as claimed in any of claims 29 to 36, wherein the indication comprises a first BSS color and a second BSS color at first and second locations of the special user information field respectively, wherein the non-AP station is16configured to copy the first BSS color and the second BSS color to the first and the second locations of the U-SIG in the uplink response.

38. The non-AP station as claimed in any of claims 32 to 33, wherein the location is specified in a single bit of a trigger dependent information field (704) of the TF.

39. The non-AP station as claimed in claim 38, wherein single bit is bit B5 (802) of the trigger dependent information field.

40. The non-AP station as claimed in any of claims 21 to 39, wherein the non-AP station is configured to set a spatial reuse indication in the uplink response to ‘DISALLOW’.

41. The non-AP as claimed in any of claims 21 to 40, wherein the uplink response is transmitted using extremely high-throughput, EHT, or ultra-high reliability, UHR, trigger based, TB, PPDU format.

42. A method (1100) for implementation at a non-access point, non-AP, station (120a, 120b, 120c, 120d) for receiving a coordinated beamforming downlink physical layer protocol data unit, PPDU, from a corresponding access point, AP, (110a, 110b) in a wireless local area network, WLAN, (100) concurrently with PPDU receptions by one or more other non-AP stations (120c, 120d, 120a, 120b) from one or more other corresponding APs (110b, 110a) in the WLAN in a coordinated beamforming transmission, the method comprising receiving (1102) a trigger frame, TF, from the corresponding AP station for trigger-based transmission of an uplink PPDU, wherein the TF comprises an indication that an uplink response for the coordinated beamforming downlink PPDU is solicited, wherein the non-AP station is configured to transmit the uplink response using a trigger-based PPDU format, the uplink response having a preamble with content at least partially aligned with uplink responses sent between the one or more other corresponding non-AP stations and the one or more other APs in the coordinated beamforming transmission.

43. A computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method of claim 20 or the method of claim 42 when the program code is executed by the computer or the processor.17

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