Devices and methods for improved channel sounding in a WLAN

Abstract

An access point, AP, (110a) is disclosed for communication with one or more non-AP stations (120a,b) associated with the AP (110a) in a wireless local area network, WLAN, (100). The AP (110a) is configured to send a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame to the one or more non-AP stations (120a,b) and to send a Sounding NDP to the one or more non-AP stations (120a,b) using a plurality of transmission antennas (114a) of the AP (110a). The Sounding NDP comprises a plurality of subsets, including at least a first subset and a second subset, and the NDPA frame is indicative of the plurality of subsets used in the Sounding NDP.

Description

[0001] Devices and methods for improved channel sounding in a WLAN

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to wireless communications. More specifically, the present disclosure relates to devices and methods for improved channel sounding in a wireless local area network, WLAN, in particular a WLAN (also referred to as Wi-Fi network) according to the IEEE 802.11 framework of standards.

[0004] BACKGROUND

[0005] 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 Multi-AP, 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.

[0006] SUMMARY

[0007] It is an objective of the present disclosure to provide devices and methods for improved channel sounding in a wireless local area network, WLAN, in particular a WLAN (also referred to as Wi-Fi network) according to the IEEE 802.11 framework of standards.

[0008] 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.

[0009] According to a first aspect an access point, AP, for communication with one or more non-AP stations associated with the AP in a wireless local area network, WLAN, is provided. The AP according to the first aspect is configured to send a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame to the one or more non-AP stations associated with the AP. Moreover, the AP according to the first aspect is configured to send a Sounding NDP to the one or more non-AP stations associated with the AP using a plurality of transmission antennas of the AP, wherein the Sounding NDP comprises a plurality of subsets, including at least a first subset and a second subset, and wherein the NDPA frame is indicative of the plurality of subsets used in the Sounding NDP. The AP according to the first aspect is further configured to receive one or more beamforming feedback report, BFR, frames from the one or more non-AP stations associated with the AP, wherein each BFR frame comprises a first feedback information of a first MAP feedback information type based on the first subset used in the Sounding NDP and a second feedback information of a second MAP feedback information type (different to the first MAP feedback information type) based on the second subset used in the Sounding NDP. In other words, due to the NDPA frame’s indication regarding the first and second subset of the Sounding NDP each non-AP station includes the first feedback information (based on the first subset) of the first feedback type and the second feedback information (based on the second subset) of the second feedback type.

[0010] In a further possible implementation form, the first subset used in the Sounding NDP corresponds to one or more of the plurality of transmission antennas of the AP and the second subset of the Sounding NDP correspond to one or more of a plurality of transmission antennas of at least one further OBSS AP.

[0011] In a further possible implementation form, the AP is configured to send the Sounding NDP concurrently with the further OBSS AP as a joint Sounding NDP to the one or more non-AP stations associated with the AP. Based on the different MAP feedback information types the AP according to the first aspect and one or more neighboring OBSS APs may better adjust their coordinated beamforming for reducing mutual interference.

[0012] In a further possible implementation form, each BFR frame comprises for each of the plurality of subsets used in the Sounding NDP a Multiple In Multiple Out, MIMO, Control field, wherein each MIMO Control field comprises an indication, in particular an index, of the respective subset used in the Sounding NDP.

[0013] In a further possible implementation form, each MIMO Control field comprises an indication of the MAP feedback information type of the first feedback information or the second feedback information.

[0014] In a further possible implementation form, the NPDA frame is a control frame of Control Extension subtype.

[0015] In a further possible implementation form, the NDPA frame comprises a plurality of transmission antenna indices corresponding to the plurality of transmission antennas of the AP and to the first subset used in the following Sounding NDP and / or corresponding to a plurality of transmission antennas of a further OBSS AP and to the second subset used in the following Sounding NDP.

[0016] In a further possible implementation form, the NDPA frame provides a mapping between the plurality of transmission antenna indices and the plurality of subsets used in the Sounding NDP.

[0017] In a further possible implementation form, the NDPA frame provides the mapping between the plurality of transmission antenna indices and the plurality of subsets used in the Sounding NDP by indicating the total number of spatial streams and a first spatial stream index of the each further subset, in particular the index of the second subset.

[0018] In a further possible implementation form, the NDPA frame provides the mapping between the plurality of transmission antenna indices and the plurality of subsets used in the Sounding NDP by indicating the total number of spatial streams and the total number of subsets of the plurality of subsets used in the Sounding NDP.

[0019] In a further possible implementation form, the NDPA frame comprises an indication of the total number of spatial streams and the number of the plurality of subsets used in the Sounding NDP.

[0020] In a further possible implementation form, the NDPA frame comprises for each subset of the plurality of subsets used in the Sounding NDP an indication of one or more feedback parameters, in particular an Nc index indicative of the number of columns of a precoder, i.e. feedback matrix for providing the feedback information, and / or an indication of the MAP feedback type.

[0021] In a further possible implementation form, the indication of the MAP feedback type comprises a bitmap and wherein each bit of the bitmap corresponds to one of the plurality of subsets used in the Sounding NDP.

[0022] In a further possible implementation form, the NDPA frame comprises a plurality of STA Info fields corresponding to the same non-AP station, wherein each STA Info field corresponds to one of the plurality of subsets and comprises the indication of the one or more feedback parameters, in particular the Nc index, and / or the indication of the MAP feedback type.

[0023] According to a second aspect a method is provided for operating an access point, AP, for communication with one or more non-AP stations associated with the AP in a wireless local area network, WLAN. The method according to the second aspect comprises the steps of: sending a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame to the one or more non-AP stations; sending a Sounding NDP to the one or more non-AP stations using a plurality of transmission antennas of the AP, wherein the Sounding NDP comprises a plurality of subsets, including at least a first subset and a second subset, and wherein the NDPA frame is indicative of the plurality of subsets used in the Sounding NDP; and receiving one or more beamforming feedback report, BFR, frames from the one or more non-AP stations, wherein each BFR frame comprises a first feedback information based on the first subset used in the Sounding NDP and a second feedback information based on the second subset used in the Sounding NDP.

[0024] The method according to the second aspect can be performed by the AP according to the first aspect. Thus, further features of the method according to the second aspect result directly from the functionality of the AP according to the first aspect as well as its different implementation forms and embodiments described above and below.

[0025] According to a third aspect 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, is provided. The non-AP station according to the third aspect is configured to receive a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame from the AP. Moreover, the non-AP station according to the third aspect is configured to receive a Sounding NDP, wherein the Sounding NDP comprises a plurality of subsets, including at least a first subset and one or more further subsets, and wherein the NDPA frame is indicative of the plurality of subsets used in the Sounding NDP. The non-AP station according to the third aspect is configured to send a beamforming feedback report, BFR, frame to the AP associated with the non-AP station, wherein the BFR frame comprises a first feedback information of a first MAP feedback information type based on the first subset used in the Sounding NDP and a further feedback information of the one or more further MAP feedback information type based on the one or more further subsets used in the Sounding NDP.

[0026] In a further possible implementation form, the first subset used in the Sounding NDP corresponds to one or more of a plurality of transmission antennas of the associated AP and the second subset used in the Sounding NDP corresponds to one or more of a plurality of transmission antennas of at least one further OBSS AP.

[0027] In a further possible implementation form, the BFR frame comprises for each of the plurality of subsets used in the preceding Sounding NDP a Multiple In Multiple Out, MIMO, Control field, wherein each MIMO Control field comprises an indication, in particular an index, of the respective subset used in the Sounding NDP.

[0028] In a further possible implementation form, each MIMO Control field comprises an indication of the MAP feedback information type of the first feedback information or the second feedback information.

[0029] In a further possible implementation form, the NPDA frame is a control frame of Control Extension subtype.

[0030] In a further possible implementation form, the NDPA frame comprises a plurality of transmission antenna indices corresponding to the transmission antennas of the AP and to the first subset used in the following Sounding NDP and / or of a plurality of further transmission antennas corresponding to a further OBSS AP and to the one of the one or more further subsets used in the following Sounding NDP.

[0031] In a further possible implementation form, the NDPA frame provides a mapping between the plurality of transmission antenna indices and the plurality of subsets used in the following Sounding NDP. In a further possible implementation form, the NDPA frame provides the mapping between the plurality of transmission antenna indices and the plurality of subsets used in the following Sounding NDP by indicating the total number of spatial streams and a first spatial stream index of each of the one or more further subsets.

[0032] In a further possible implementation form, the NDPA frame provides the mapping between the plurality of transmission antenna indices and the plurality of subsets used in the following Sounding NDP by indicating the total number of spatial streams and the total number of subsets of the plurality of subsets used in the Sounding NDP.

[0033] In a further possible implementation form, the NDPA frame comprises an indication of the number of the plurality of subsets used in the Sounding NDP.

[0034] In a further possible implementation form, the NDPA frame comprises for each subset of the plurality of subsets used in the Sounding NDP an indication of one or more feedback parameters, in particular a Nc index indicative of the number of columns of a feedback matrix with the feedback information, and / or an indication of the MAP feedback type.

[0035] In a further possible implementation form, the indication of the MAP feedback type comprises a bitmap and wherein each bit of the bitmap corresponds to one of the plurality of subsets used in the Sounding NDP.

[0036] In a further possible implementation form, the NDPA frame comprises a plurality of STA Info fields corresponding to the same non-AP station, wherein each STA Info field comprises the indication of the one or more feedback parameters, in particular the Nc index, and / or the indication of the MAP feedback type.

[0037] According to a fourth aspect a method is provided 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 method according to the fourth aspect comprises the following steps: receiving a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame from the AP associated with the non- AP station; receiving a Sounding NDP, wherein the Sounding NDP comprises a plurality of subsets, including at least a first subset and one or more further subsets, and wherein the NDPA frame is indicative of the plurality of subsets used in the Sounding NDP; and sending a beamforming feedback report, BFR, frame to the AP associated with the non-AP station, wherein the BFR frame comprises a first feedback information of a first MAP feedback information type based on the first subset used in the Sounding NDP and a further feedback information of a further MAP feedback information type based on the one or more further subsets used in the Sounding NDP.

[0038] The method according to the fourth aspect can be performed by the non-AP station according to the third aspect. Thus, further features of the method according to the fourth aspect result directly from the functionality of the non-AP station according to the third aspect as well as its different implementation forms and embodiments described above and below.

[0039] According to a fifth aspect a computer program product is provided, comprising program code which causes a computer or a processor to perform the method according to the second aspect or the method according to the fourth aspect, when the program code is executed by the computer or the processor.

[0040] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

[0042] 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;

[0043] Fig. 2 illustrates a sounding procedure with a joint Sounding NDP implemented by an AP, an OBSS AP and a plurality of non-AP stations according to an embodiment;

[0044] Fig. 3 illustrates a sounding procedure with several sounding sequences implemented by an AP, an OBSS AP and a plurality of non-AP stations according to an embodiment;

[0045] Fig. 4 shows the format of a NDPA frame generated by an AP according to an embodiment;

[0046] Figs. 5a, b show the format of a field of a NDPA frame generated by an AP according to an embodiment for indicating different subsets of an ensuing Sounding NDP for two different embodiments;

[0047] Fig. 5c shows the format of a field of a NDPA frame generated by an AP according to an embodiment for indicating different MAP feedback information types;

[0048] Fig. 6 shows the format of a STA Info field of a NDPA frame generated by an AP according to an embodiment for indicating the number of columns of a precoder matrix for different subsets of an ensuing Sounding NDP and / or MAP Feedback Information type;

[0049] Fig. 7 shows the format of a MIMO Control field generated by a non-AP station according to an embodiment;

[0050] Fig. 8 shows a flow diagram illustrating steps of a method of operating an AP according to an embodiment; and

[0051] Fig. 9 shows a flow diagram illustrating a method of operating a non-AP station according to an embodiment.

[0052] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0053] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] 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.

[0055] 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.

[0056] Figure 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 110a, b according to an embodiment. The WLAN 100 may further comprise at least one further AP 11 Ob 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 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.

[0057] As further illustrated in figure 1 , the AP 110a (as well as the further AP 110b) may comprise a processing circuitry Il la 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 Il la 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 I l la, causes the AP 110a to perform the functions and methods described herein.

[0058] 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.

[0059] 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:

[0060] A-MPDUAggregate MPDU

[0061] A-MSDUAggregate MSDU

[0062] AP Access Point

[0063] BFR Beamforming Feedback Report

[0064] BSS Basic Service Set

[0065] BW Bandwidth

[0066] CoBF Coordinated Beamforming

[0067] CSI Channel State Information

[0068] DL Downlink

[0069] EHT Extremely High Throughput

[0070] E VM Error Vector Magnitude

[0071] FCS Forward Correction Sequence

[0072] LAN Local Area Network

[0073] LLC Logical Link Control MAC Medium Access Control

[0074] MAP Multiple Access Points

[0075] MIMO Multiple In Multiple Out

[0076] ML Multi-link

[0077] MPDU MAC Protocol Data Unit

[0078] NDP Null Data PPDU

[0079] NDPA NDP Announcement

[0080] OBSS Overlapping BSS

[0081] PHY Physical (layer)

[0082] PPDU Physical Layer Protocol Data Unit

[0083] RSSI Received Signal Strength Indicator

[0084] RU Resource Unit

[0085] SNR Signal to Noise Ratio

[0086] STA Station

[0087] TB Trigger Based

[0088] TF Trigger Frame

[0089] TXOP Transmit Opportunity

[0090] UL Uplink

[0091] WLAN Wireless Local Area Network

[0092] UHR Ultra-High Reliability

[0093] As used herein, an access point (AP), such as the APs 110a, b illustrated in figure 1, is a wireless station (STA) that provides access to other networks. An AP can support many connected, i.e. 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.

[0094] As used herein, 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 stations (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 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.

[0095] As alreadv described above, 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 BSS non-AP stations (in figure 1 referred to as STAs) only. 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 (illustrated by the straight dashed arrows in figure 1 ) at the receiver side is small enough to allow successful detection of the desired signal (illustrated by the curved solid arrows in figure 1 ).

[0096] In order to allow the APs 110a,b to construct precoders that maximize the performance of BSS STAs and minimize the interference to OBSS STAs a sounding procedure is performed that allows the estimation of the channels between all APs 110a, b and all STAs 120a-d. This means that each AP 110a, b has to transmit a training signal that will be received by its BSS STAs and the relevant OBSS STAs to allow estimating each of the relevant channels. Several different sounding procedures are known, which may be implemented by the APs 110a, b of figure 1 according to an embodiment.

[0097] A sounding procedure for multiple STAs defined by the current IEEE 802.11 framework of standards comprises the transmission of the following PPDUs: a PPDU carrying the NDPA frame which indicates the parameters of the upcoming training signal and the required feedback parameters; a Sounding NDP as the “training” signal to be measured by each solicited non-AP STA (either BSS STA or OBSS STA); a PPDU carrying the BFRP frame defining a request poll to initiate the transmission of the feedback report; and a PPDU carrying the BFR frame, i.e. a feedback transmission, including a MIMO Control Field which describes the provided feedback and the precoder matrices information.

[0098] A Multi- AP, MAP, sounding procedure implemented by the APs 110a,b may include a joint transmission of the PPDU carrying the Sounding NDP, where the APs 110a,b transmit concurrently. Another option, which may be implemented by the APs 110a,b, is a sequential sounding procedure, where each AP 110a, b performs its sounding procedure independently.

[0099] For the sounding procedure, where each AP 110a,b transmits the PPDU carrying the NDPA frame independently and the Sounding NDP is transmitted concurrently by one or more of the APs 110a, b, the non-AP stations 120a-d have to measure the Sounding NDP and send their feedback for the measured Sounding NDPs only to the associated AP 110a,b. The non-AP stations 120a-d are not aware of which AP 110a, b actually transmits each Sounding NDP and just estimate the channels from all the transmitting sources (antennas).

[0100] As will be described in the following under further reference to figure 2, which illustrates a sounding procedure with a joint NDP, the API 110a is configured to send a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame 201a to its associated non-AP station 120a.

[0101] In an embodiment, the AP 110a is configured to send the j oint Sounding NDP 203 concurrently with the AP 110b to the non- AP station 120a. The joint Sounding NDP 203 is a single PPDU comprising two subsets which correspond to the plurality of the transmit antennas 114a, b of the AP 110a and OBSS AP 110b. In other words, in an embodiment, the first subset 203a used in the joint Sounding NDP 203 corresponds to one or more of the plurality of transmission antennas 114a of the AP 110a and the second subset 203b of the joint Sounding NDP203 corresponds to one or more of the plurality of transmission antennas 114b of the OBSS AP 110b. For instance, in the example shown in figure 1, the first subset 203a of the joint Sounding NDP 203 corresponds to transmission antennas with the indices 1 to 4 of the AP 110a, while the second subset 203b of the joint Sounding NDP 203 corresponds to transmission antennas with the indices 5 to 8 of the OBSS AP 110b.

[0102] In response to sending a BFRP frame 205a to its associated non-AP station 120a for initiating the transmission of the feedback, the AP 110a is further configured to receive one or more beamforming feedback report, BFR, frames 207 from its associated non-AP station 120a. As illustrated in figure 2 and as will be described in more detail below, each BFR frame 207 comprises a first feedback information 207a of a first MAP feedback information type based on the first subset 203a used in the joint Sounding NDP 203 transmitted by API 110a and the OBSS AP 110b and a second feedback information 207b of a second MAP feedback information type (different from the first MAP feedback information type) based on the second subset 203b used in the joint Sounding NDP203. More specifically, in the example shown in figure 2, the first feedback information 207a is based on the first subset 203a of the joint Sounding NDP 203 corresponding to the transmission antennas with the indices 1 to 4, while the second feedback information 207b is based on the second subset 203b of the joint Sounding NDP 203 corresponding to the transmission antennas with the indices 5 to 8.

[0103] Thus, due to the NDPA frame’s 201a indication of the first and second subset 203a, b of the joint Sounding NDP 203 and the MAP feedback information type requested for each subset, each non-AP station 120a,b may include the first feedback information 207a (based on the first subset) of the first feedback type and the second feedback information 207b (based on the second subset) of the second feedback type in the BFR frame 207. As will be appreciated, based on the different MAP feedback information types the AP 110a and the OBSS AP 110b may better adjust their coordinated beamforming for reducing mutual interference to the non-AP STA1 120a.

[0104] As further illustrated in figure 2, the same sounding procedure as described above may be performed by the AP 110b and its associated non-AP station 120c. More specifically, the AP 110b may send an NDPA frame 211b and a joint Sounding NDP 213 concurrently with the AP 110a to its associated non-AP station 120c, wherein the joint Sounding NDP 213 comprises a single subset 213b, including at least a first subset 213b, and wherein the preceding NDPA frame 211b is indicative, i.e. comprises an indication of the plurality of subsets 213a, b used in the following joint Sounding NDP 213. In an embodiment, the first subset 213b used in the joint Sounding NDP 213 corresponds to one or more of the plurality of transmission antennas 114b of the OBSS AP 110b and the second subset 213a of the joint Sounding NDP 213, transmitted by API 110a, corresponds to one or more of the plurality of transmission antennas 114a of the API 110a. For instance, in the example shown in figure 1 , the first subset 213b of the joint Sounding NDP 213 corresponds to transmission antennas with the indices 1 to 4, while the second subset 213a of the joint Sounding NDP 213 corresponds to transmission antennas with the indices 5 to 8. In response to sending a BFRP frame 215b to its associated non-AP station 120c for initiating the transmission of the feedback, the AP 110b is further configured to receive one or more beamforming feedback report, BFR, frames 217 from its associated non-AP station 120c, wherein each BFR frame 217 comprises a first feedback information 217a of a first MAP feedback information type based on the first subset 213b used in the joint Sounding NDP 213 and a second feedback information 217b of a second MAP feedback information type (different to the first MAP feedback information type) based on the second subset 213a used in the joint Sounding NDP 213.

[0105] Thus, according to embodiments disclosed herein the non-AP stations 120a-d are informed by the APs 110a, b by means of the NDPAs 201a, 211b that the respective joint Sounding NDP 203, 213 is composed of several subsets (without indicating which subset corresponds to transmit antennas of which AP) that may require different feedback reports for each subset and in order to compute the precoder for each subset independently. In addition, the required feedback for each subset may require different format.

[0106] The sounding procedure illustrated in figure 2, which includes the transmission of a joint Sounding NDP 203, 213, may be used, for instance, in the case, when the total number of transmission antennas of all the APs, i.e. the AP 110a and the AP 110b, does not exceed the maximum number of allowed spatial streams, e.g. 8 spatial streams. Another case is when the total number of transmission antennas exceeds the number of allowed spatial streams. In this case, the sounding sequence initiated by each AP 110a,b may be repeated several times and at least one Sounding NDP may be transmitted by each AP, as illustrated in figure 3.

[0107] More specifically, in the embodiment shown in figure 3, the AP 110a transmits a NDPA frame 301 which indicates for a first subset 203a and the corresponding MAP feedback information type and a following Sounding NDP 303 to its associated non- AP station(s) 120a, b and receives, in response to transmitting a BFRP trigger frame 305, a BFR frame 307. In a further stage illustrated in figure 3, the AP 110a transmits a further NDPA frame 311 which indicates for a second subset 203b and the corresponding MAP feedback information type, but the following Sounding NDP 313 is transmitted by the OBSS AP 110b. In response to transmitting a BFRP frame 315, the AP 110a receives a BFR frame 317 from its associated non-AP station 120a. In a further stage illustrated in figure 3, the AP 110b transmits a NDPA frame 321 which indicates for a first subset 203a and the corresponding MAP feedback information type and a following Sounding NDP 323 to its associated non-AP station 120c and receives, in response to transmitting a BFRP frame 325, a BFR frame 327. In a further stage illustrated in figure 3, the AP 110b transmits a further NDPA frame 331 which indicates for a second subset 203b and the corresponding MAP feedback information type, but the Sounding NDP 333 is transmitted by the AP 110a. In response to transmitting a BFRP frame 335, the AP 110b receives a BFR frame 337 from its associated non-AP station 120c. As will be appreciated, similar to different MAP feedback information types corresponding to different subsets (as in the embodiment shown in figure 2), for the embodiment shown in figure 3 each feedback may include a different MAP feedback information type. More specifically, a MAP feedback information type of BFR frame 307 and BFR frame 317 may differ, as well as of BFR frame 327 and BFR frame 337.

[0108] As already mentioned above, 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. It has been proposed that in order to ensure a minimized mutual interference between the APs 110a, b and the OBSS STAs 120a-d in CoBF, the precoder should be computed differently for BSS and OBSS APs 110a, b. In an embodiment, each non-AP station 120a-d may compute a regular, SVD based feedback for the channel estimation of AP 110a, b, while for the channel estimation of the OBSS AP 110a, b, each non-AP station 120a-d may apply the U matrix of the BSS AP channel and then compute the orthonormal basis of U*HOBSS for each OBSS AP channel. In other words, when a joint Sounding NDP is transmitted, a different MAP feedback type is obtained for each subset 203a, b of the joint Sounding NDP (in the scenario illustrated in figure 3 each NDP 303, 313, 323, 333 consists of a single subset and the MAP feedback type differs between NDPs). As will be appreciated, each non-AP station 120a-d does not know which subset corresponds to transmit antennas of the AP or transmit antennas of the OBSS AP, but according to embodiments disclosed herein each non-AP station 120a-d knows which type of MAP feedback is to be provided for each subset, such as the subsets 203a, b.

[0109] As already described above, according to embodiments disclosed herein, an NDPA frame, such as the NDPA frames 201a, 211b of figure 2, comprises an indication of several subsets of the ensuing joint Sounding NDP(s). In an embodiment, the indication of the NDPA frame 201 a, 211 b may further indicate the requested feedback type per subset. In an embodiment, these or similar indications may be included in a MIMO Control Field to support transmitting feedback per each subset in the Sounding NDP and also validating the type of feedback per transmitted feedback. In the following further embodiments for a NDPA frame and a MIMO Control Field are described that support the transmission of a Joint Sounding NDP, where the joint Sounding NDP consists of several subsets 203a, b and different types of feedback may be requested per subset.

[0110] In an embodiment, the NDPA frame 201a includes the indication indicative of the presence of several subsets 203a, b in the following joint Sounding NDP. In an embodiment, each subset 203a, b may correspond to specific transmission antenna indices and a MAP feedback type may be indicated per subset. In an embodiment, the MIMO Control Field may include an indication of subset index that current feedback corresponds to and also the requested MAP feedback type.

[0111] Figure 4 shows the format of the NDPA frame 201a generated by the AP 110a according to an embodiment that is indicative, i.e. comprises an indication of the plurality of subsets 203a, b used in the Sounding NDP. In an embodiment, the NPDA frame 201a shown in figure 4 is a control frame of Control Extension subtype. As will be appreciated, in addition to the conventional fields 401, 402, 403, 404, 405, 408 and 409 the NPDA frame 201a shown in figure 4 comprises a field 406 for indicating the allocation of Nss (i.e. the number of spatial streams) per subset 203a, b within the Sounding NDP and a field 407 indicative of the requested MAP feedback type per subset, which both will be described in more detail in the following. In the embodiment shown in figure 4, the field 406 may have a size of 2 octets, while the field 407 may have a size of 1 octet. In the embodiment shown in figure 4, the fields 406, 407 are placed, by way of example, before the STA Info List 408 (since these fields 406, 407 are common for all the non-AP STAs 120a-d).

[0112] Figures 5a, b show two possible formats of the field 406 of the NDPA frame 201a of figures 2 and 4, as generated by the AP 110a, b according to an embodiment for indicating different subsets 203a, b of the ensuing Sounding NDP. More specifically, the formats of the field 406 indicate which transmission antennas used for the succeeding Sounding NDP are allocated to each subset 203a, b. The bit sizes indicated in figures 5a and 5b are based on the current IEEE 802.11 framework of standards that supports up to 8 total spatial streams per frame and thus up to 4 subsets may exist in the Sounding NDP.

[0113] In the embodiment shown in figure 5a, the field 406 indicates constantly 4 subsets by indicating the total number of spatial streams in a field 501, the index of the first spatial stream corresponding to a second subset of the plurality of subsets of the Sounding NDP in a field 502, the index of the first spatial stream corresponding to a third subset of the plurality of subsets of the Sounding NDP in a field 503, and the index of the first spatial stream corresponding to a fourth subset of the plurality of subsets of the Sounding NDP in a field 504. Unused subsets may be indicated by all zeros to prevent parsing errors. In a variant of the embodiment shown in figure 5a, instead of indicating the index of the first spatial stream of the different subsets, the fields 502, 503, 504 may indicate the index of the last spatial stream of the different subsets. In this case the Total Nss subfield 501 may be replaced by last #SS index of 1stsubset.

[0114] In the embodiment shown in figure 5b, the field 406 provides variable length per number of subsets in current transmission by using a field 511 indicating the number of subsets of the Sounding NDP, a field 512 indicating the total number of spatial streams, a field 513 indicating the index corresponding to the first spatial stream of a second subset of the plurality of subsets of the Sounding NDP, and an optional field 514 indicating the index of the first spatial stream corresponding to a third subset of the plurality of subsets of the Sounding NDP. In a variant of the embodiment shown in figure 5b, instead of indicating the index of the first spatial stream corresponding to the different subsets, the fields 513, 514 may indicate the index of the last spatial stream corresponding to the different subsets. In this case the Total Nss subfield 512 may be replaced by last #SS index of 1 st subset.

[0115] In an embodiment, where the non-AP stations 120a-d may be requested to provide to different types of MAP feedback information, a rule may be implemented by the APs 110a, b and the non-AP stations 120a-d according to which the precoder (i.e. the first feedback information 207a) for the first subset 203 is always obtained based on a regular SVD and for the remaining subsets an orthonormal basis of UA*H is to be used by each non-AP station 120a-d. According to a further embodiment a bitmap, as illustrated in figure 5c, may be included in the field 407 of the NDPA frame 201a shown in figure 4. In an embodiment, 4 bits of the bitmap 407 may be used, wherein each bit corresponds to a single subset 203a, b of the Sounding NDP. As will be appreciated, a MAP feedback type indication field 407 of size of 1 octet allows to extend an indication to more feedback types in the future.

[0116] As the different APs 110a, b may transmit different number of spatial streams and / or MAP Feedback Information type for each BSS STAs 120a-d, according to embodiments disclosed herein a precoder matrix (i.e. the feedback information) of different size may be computed by each non-AP station 120a-d per subset. In particular, the number of columns in the precoder matrix (Nc) may differ. Thus, according to an embodiment illustrated in figure 6 further fields 609, 610 and 611 may be added to the conventional fields 601-608 of a STA Info Subfield 600, wherein each of the fields 609, 610 and 611 indicates Nc, i.e. the number of columns of the precoder matrix per subset. The conventional field 604 corresponds the number of columns in the precoder matrix (Nc) that is required for the feedback corresponding the first subset. The new additional field 612 may provide a MAP Feedback Information Type for the plurality of subsets. In an embodiment, the order of indications, i.e. fields 609, 610, 611 may be aligned with the order of the subsets indicated in the NDPA frame 201a. In a further embodiment, all the feedback parameters may be different and multiple STA Info Subfields 600 per non-AP station 120a-d may be transmitted, wherein each subfield corresponds to a different subset.

[0117] Figure 7 shows the format of a MIMO Control field 700 generated by a non-AP station 120a-d according to an embodiment, wherein the MIMO Control field 700 provides the parameters of compressed feedback and in case of TB sounding may reflect the parameters indicated by the NDPA frame 201a. Thus, in order to allow each AP 110a, b to determine the correct precoder calculation and make sure that feedback is provided for all the subsets, the MIMO Control field 700 may include in addition to the conventional fields 701-705 and 707-712 a subset index indication 706a and a MAP Feedback Information type indication 706b, which may be provided by the reserved bits 706 of the MIMO Control field 700. The subset index indication 706a indicates which subset the current feedback corresponds to (assuming up to 4 subsets 2 bits will be sufficient), while the MAP Feedback Information type indication 706b is similar to the MAP Feedback Information type indicated in the NDPA frame 201a and, thus, allows to verify that the MAP Feedback Information type is correct per subset (1 bit is sufficient).

[0118] Figure 8 shows a flow diagram illustrating steps of a method 800 for operating the AP 110a of figure 1 for communication with the non-AP stations 120a,b associated with the AP 110a in the WLAN 100. The method 800 comprises a first step 801 of sending the NDPA frame 201a to the associated non-AP stations 120a, b. Moreover, the method 800 comprises a step 803 of sending a Sounding NDP to the non-AP stations 120a,b using the plurality of transmission antennas 114a of the AP 110a, wherein the Sounding NDP comprises a plurality of subsets 203a, b, including at least a first subset 203a and a second subset 203b, and wherein the NDPA frame 201 a is indicative of the plurality of subsets 203a, b used in the Sounding NDP. The method 800 comprises a further step 805 of receiving one or more BFR frames 207 from the non-AP stations 120a, b, wherein each BFR frame 207 comprises a first feedback information 207a (of a first MAP feedback type) based on the first subset 203a used in the Sounding NDP and a second feedback information 207b (of a second MAP feedback type different to the first feedback type) based on the second subset 203b used in the Sounding NDP.

[0119] As the method 800 can be implemented by the AP 110a (as well as the further OBSS AP 110b), further features of the method 800 result directly from the functionality of the AP 110a as well as its different embodiments described above and below.

[0120] Figure 9 shows a flow diagram illustrating a method 900 for operating the non-AP station 120a of figure 1 for communication with the AP 110a associated with the non-AP station 120a in the WLAN 100. The method 900 comprises a first step 901 of receiving the NDPA frame 201a from the associated AP 110a. Moreover, the method 900 comprises a second step 903 of receiving a Sounding NDP, wherein the Sounding NDP comprises a plurality of subsets, including at least a first subset 203a and a second subset 203b, and wherein the NDPA frame 201a is indicative of the plurality of subsets 203a, b used in the Sounding NDP. The method 900 comprises a third step 905 of sending a BFR frame 207 to the AP 110a, wherein the BFR frame 207 comprises a first feedback information 207a (of a first MAP feedback type) based on the first subset 203a used in the Sounding NDP and a second feedback information 207b (of a second MAP feedback type different to the first MAP feedback type) based on the second subset 203b used in the Sounding NDP.

[0121] As the method 900 can be implemented by the non-AP station 120a (as well as the other non-AP stations 120b-d), further features of the method 900 result directly from the functionality of the non-AP station 120a as well as its different embodiments described above and below.

[0122] 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 or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0123] 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.

[0124] 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.

[0125] 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.

Claims

CLAIMS1. An access point, AP, (110a) for communication with one or more non-AP stations (120a, b) associated with the AP (110a) in a wireless local area network, WLAN, (100), wherein the AP (110a) is configured to: send a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame (201a) to the one or more non-AP stations (120a, b); send a Sounding NDP (203) to the one or more non-AP stations (120a, b) using a plurality of transmission antennas (114a) of the AP (110a), wherein the Sounding NDP (203) comprises a plurality of subsets (203a, b), including at least a first subset (203a) and a second subset (203b), and wherein the NDPA frame (201a) is indicative of the plurality of subsets (203a, b) used in the Sounding NDP (203); and receive one or more beamforming feedback report, BFR, frames (207) from the one or more non-AP stations (120a,b), wherein each BFR frame (207) comprises a first feedback information (207a) based on the first subset (203a) used in the Sounding NDP (203) and a second feedback information (207b) based on the second subset (203b) used in the Sounding NDP (203).

2. The AP (110a) of claim 1, wherein the first subset (203a) used in the Sounding NDP (203) corresponds to one or more of the plurality of transmission antennas (114a) of the AP (110a) and wherein the second subset (203b) of the Sounding NDP (203) corresponds to one or more of a plurality of transmission antennas (114b) of a further AP (110b).

3. The AP (110a) of claim 2, wherein the AP (110a) is configured to send the Sounding NDP (203) concurrently with the further AP (110b) as a joint Sounding NDP (203) to the one or more non-AP stations (120a, b).

4. The AP (110a) of any one of the preceding claims, wherein each BFR frame (207) comprises for each of the plurality of subsets (203a, b) used in the Sounding NDP (203) a Multiple In Multiple Out, MIMO, Control field (700) and wherein each MIMO Control field (700) comprises an indication (706a) of the respective subset used in the Sounding NDP (203).

5. The AP (110a) of claim 4, wherein each MIMO Control field (700) comprises an indication (706b) of the MAP feedback information type of the first feedback information (207a) or the second feedback information (207b).

6. The AP (110a) of any one of the preceding claims, wherein the NPDA frame (201a) is a control frame of Control Extension subtype.

7. The AP (110a) of any one of the preceding claims, wherein the NDPA frame (201a) comprises a plurality of transmission antenna indices corresponding to the plurality of transmission antennas (114a) of the AP (110a) and to the first subset (203a) used in the Sounding NDP (203) and / or of a plurality of further transmission antenna indices corresponding to a plurality of transmission antennas (114b) of a further AP (110b) and to the second subset (203b) used in the Sounding NDP (203).

8. The AP (110a) of claim 7, wherein the NDPA frame (201a) provides a mapping (406) between the plurality of transmission antenna indices and the plurality of subsets (203a, b) used in the Sounding NDP (203).

9. The AP (110a) of claim 8, wherein the NDPA frame (201a) provides the mapping (406) between the plurality of transmission antenna indices and the plurality of subsets (203a, b) used in the Sounding NDP (203) by indicating the total number of spatial streams (501) and a first spatial stream index (502) of the second subset (203b).

10. The AP (110a) of claim 8, wherein the NDPA frame (201a) provides the mapping (406) between the plurality of transmission antenna indices and the plurality of subsets (203a, b) used in the Sounding NDP (203) by indicating the totalnumber of spatial streams (512) and the total number of subsets (511 ) of the plurality of subsets (203a, b) used in the Sounding NDP (203).

11. The AP ( 110a) of any one of the preceding claims, wherein the NDPA frame (201a) comprises for each subset of the plurality of subsets (203a, b) used in the Sounding NDP (203) an indication (406) of one or more feedback parameters and / or an indication (407) of the MAP feedback type.

12. The AP (110a) of claim 11 , wherein the indication (407) of the MAP feedback type comprises a bitmap (407) and wherein each bit of the bitmap (407) corresponds to one of the plurality of subsets (203a, b) used in the Sounding NDP (203).

13. The AP (110a) of claim 11 or 12, wherein the NDPA frame (201a) comprises a plurality of STA Info fields (600) and wherein each STA Info field (600) corresponds to one of the plurality of subsets and comprises the indication of the one or more feedback parameters (604, 609, 610, 611) and / or the indication of the MAP feedback type (605).

14. A method (800) for operating an access point, AP, (110a) for communication with one or more non-AP stations (120a, b) associated with the AP (110a) in a wireless local area network, WLAN, (100), wherein the method (800) comprises: sending (801 ) a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame (201 a) to the one or more non-AP stations ( 120a, b); sending (803) a Sounding NDP (203) to the one or more non-AP stations (120a, b) using a plurality of transmission antennas (114a) of the AP (110a), wherein the Sounding NDP (203) comprises a plurality of subsets (203a, b), including at least a first subset (203a) and a second subset (203b), and wherein the NDPA frame (201a) is indicative of the plurality of subsets (203a, b) used in the Sounding NDP (203); and receiving (805) one or more beamforming feedback report, BFR, frames (207) from the one or more non-AP stations (120a, b), wherein each BFR frame (207) comprises a first feedback information (207a) based on the first subset (203a) used in the Sounding NDP (203) and a second feedback information (207b) based on the second subset (203b) used in the Sounding NDP (203).

15. A non-access point, non-AP, station ( 120a) for communication with an AP (110a) associated with the non-AP station (120a) in a wireless local area network, WLAN, (100), wherein the non-AP station (120a) is configured to: receive aNull Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame (201a) from the AP (110a); receive a Sounding NDP (203) , wherein the Sounding NDP (203) comprises a plurality of subsets (203a, b), including at least a first subset (203a) and a second subset (203b), and wherein the NDPA frame (201a) is indicative of the plurality of subsets (203a, b) used in the Sounding NDP (203); and send a beamforming feedback report, BFR, frame (207) to the associated AP (110a), wherein the BFR frame (207) comprises a first feedback information (207a) based on the first subset (203a) used in the Sounding NDP (203) and a second feedback information (207b) based on the second subset (203b) used in the Sounding NDP (203).

16. The non-AP (120a) station of claim 15, wherein the first subset (203a) used in the Sounding NDP (203) corresponds to one or more of the plurality of transmission antennas (114a) of the associated AP (110a) and wherein the second subset (203b) used in the Sounding NDP (203) corresponds to one or more of a plurality of transmission antennas (114b) of a further OBSS AP (110b).

17. The non-AP station (120a) of claim 15 or 16, wherein the BFR frame (207) comprises for each of the plurality of subsets (230a, b) used in the preceding Sounding NDP (203) a Multiple In Multiple Out, MIMO, Control field (700) and wherein each MIMO Control field (700) comprises an indication (706a) of the respective subset used in the Sounding NDP (203).

18. The non-AP station (120a) of claim 17, wherein each MIMO Control field (700) comprises an indication (7062) of the MAP feedback information type of the first feedback information (207a) or the second feedback information (207b).

19. The non-AP station (120a) of any one of claims 15 to 18, wherein the NPDA frame (210a) is a control frame of Control Extension subtype.

20. The non-AP station (120a) of any one of claims 15 to 19, wherein the NDPA frame (201a) comprises a plurality of transmission antenna indices corresponding to the plurality of transmission antennas (114a) of the AP (110a) and to the first subset (203a) used in the Sounding NDP (203) and / or of a plurality of further transmission antenna indices corresponding to a plurality of transmission antennas (114b) of a further OBSS AP (110b) and to the second subset (203b) used in the Sounding NDP (203).

21. The non-AP station (120a) of claim 20, wherein the NDPA frame (201a) provides a mapping (406) between the plurality of transmission antenna indices and the plurality of subsets (203a, b) used in the following Sounding NDP.

22. The non-AP station (120a) of claim 21, wherein the NDPA frame (201a) provides the mapping (406) between the plurality of transmission antenna indices and the plurality of subsets (203a, b) used in the following Sounding NDP by indicating the total number of spatial streams (501) and a first spatial stream index (502) of the at least second subset (203b).

23. The non-AP station (120a) of claim 21, wherein the NDPA frame (201a) provides the mapping (406) between the plurality of transmission antenna indices and the plurality of subsets (203a, b) used in the following Sounding NDP by indicating the total number of spatial streams (512) and the total number of subsets (511 ) of the plurality of subsets (203a, b) used in the Sounding NDP.

24. The non-AP station (120a) of any one of claims 15 to 23, wherein the NDPA frame (201a) comprises for each subset of the plurality of subsets (230a, b) used in the Sounding NDP (203) an indication (406) of one or more feedback parameters and / or an indication (407) of the MAP feedback type.

25. The non-AP station (120a) of claim 24, wherein the indication (407) of the feedback type comprises a bitmap (407) and wherein each bit of the bitmap (407) corresponds to one of the plurality of subsets (203a, b) used in the Sounding NDP (203).

26. The non-AP station (120a) of claim 24 or 25, wherein the NDPA frame (201a) comprises a plurality of STA Info fields (600) and wherein each STA Info field (600) comprises the indication of the one or more feedback parameters (604, 609, 610, 611) and / or the indication of the MAP feedback type (612).

27. A method (900) for operating a non-access point, non-AP, station (120a) for communication with an AP (110a) associated with the non-AP station (120a) in a wireless local area network, WLAN, (100), wherein the method (900) comprises: receiving (901) a Null Data Physical Protocol Data Unit, NDP, announcement, NDPA, frame (201a) from the AP (110a) associated with the non-AP station (120a); receiving (903) a Sounding NDP (203) , wherein the Sounding NDP (203) comprises a plurality of subsets, including at least a first subset (203a) and a second subset (203b), and wherein the NDPA frame (201a) is indicative of the plurality of subsets (203a, b) used in the Sounding NDP (203); andsending (905) a beamforming feedback report, BFR, frame (207) to the AP (110a), wherein the BFR frame (207) comprises a first feedback information (207a) based on the first subset (203a) used in the Sounding NDP (203) and a second feedback information (207a) based on the second subset (203b) used in the Sounding NDP (203).

28. 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 (800) of claim 14 or the method (900) of claim 27 when the program code is executed by the computer or the processor.

Images