WO2024088492A1

WO2024088492A1 - Design of link adaptation training feedback report frame

Info

Publication number: WO2024088492A1
Application number: PCT/EP2022/079492
Authority: WO
Inventors: Arik Klein; Shimon SHILO; Ezer Melzer; Yaron Ben-Arie
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2022-10-23
Filing date: 2022-10-23
Publication date: 2024-05-02

Abstract

A method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs. For a multi user, MU, feedback, the LAT feedback report shall be triggered by the soliciting STA if the preceding LAT Announcement frame includes more than a single Per-STA Info. For a single user, SU, feedback, the LAT feedback frame can be implicitly solicited by a preceding LAT Announcement frame that includes only a single Per-STA Info followed by LAT PPDU, after a predefined IFS.

Description

Design of Link Adaptation Training Feedback Report frame

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of link adaptation in wireless network communication systems, aiming at improving the speed of the adaptation process.

BACKGROUND

Advanced Wi-Fi standards, such as 802.11ax and 802.11be, support a very high data rate, e.g. 4.8Gbps up to 23Gbps. Link Adaptation, LA, is a mechanism for tuning the transmitting, TX, scheme and parameters, such as the PHY rate, specified by the Modulation Coding Scheme, MCS, the number of streams, and frequency allocation, Resource Unit, RU choice, etc. The tuning process attempts to optimally adapt the parameters to the instantaneous conditions of a radio link, e.g. channel quality and interference, while accommodating other system constraints and requirements.

One of the most popular implementations is the Minstrel algorithm (https://wireless.wiki.kernel.org/en/developers/documentation/mac80211/ratecontrol/minstrel).

In the Minstrel algorithm, the rate-defining parameters are slowly varied via a ‘trial and error’ procedure, based on the received acknowledgements, ACKs, or block acknowledgements, BACKs, on transmitted data packets reported by the receiver, RX. 'Slowly' here pertains to the fact that it may take a very long time for the algorithm to converge to the optimal set of parameters, such that some pre-defined metric target is reached, e.g. a packet error rate PER = 10%. Here optimal should be understood in the sense of long-time averaging.

On top of the BACKs/ACKs, several feedback types aiding LA are supported today in the specifications of the WLAN IEEE 802.11 standards, for example: i) Signal to Noise Ratio, SNR, (channel quality indicator, CQI) per resource unit RU: a station, STA, may be instructed to compute and to feed back to the soliciting access point, AP, the SNR for specific RUs, based on the sounding null data packet, NDP. However, the problem arises whether the AP may trust the computations performed at the STA side. For example, the question might arise what is the relationship between the SNR and the link performance, given the specific STA’s receiver implementation, and how it might influence the computations. ii) MCS Feedback (MFB): the STA may indicate which MCS it prefers. This might be an acceptable metric since it takes into consideration the STA’s implementation. However, this approach is often not implemented, and furthermore, the accuracy of the MFB is not mandated/tested by the WLAN specification, WLAN IEEE 802.11. iii) A Control High Efficiency Link Adaptation, A-CTRL HLA: An LA control message is included in the frame header as part of any data or management frame sent by the non-AP STA. The specific LA control message may be added in the High-Throughput, HT, Control part, when indicated as High-Efficiency, HE, variant by any HE STA.

Within this context, for a single physical layer rate, PHY rate, there should be a predefined map, e.g. a table, of pairs of a Modulation and Coding Scheme and a value of a Number of Spatial Streams, MCS and N_ss. This pair may be denoted by <MCS, N_ss>. Here, <MCS, N_ss> may also be referred to as a tuple. Thus, for each PHY rate Index value there should be at least a single <MCS, N_ss> tuple. Then, the link adaptation training, LAT, feedback report should be triggered for a multi user, MU, feedback by an associated I originating I soliciting access point, AP.

In view of the above, the design of a Link Adaptation Training Announcement frame needs to take into account the following requirement: it should list the non-AP STAs that should measure the LAT PPDU, PHY Protocol Data Unit, and it should list the corresponding measurement parameters per non-AP STA. Accordingly, a Link Adaptation Training Feedback Report frame, sent back from an intended recipient non-AP STA in response to a LAT announcement frame followed by a LAT PPDU which were transmitted by an soliciting STA, needs to list the <MCS, N_ss> tuples and RUs to which the LAT feedback report refers, and include in the feedback report the link performance metrics corresponding to each entry in the list as measured by the non-AP STA sending the LAT feedback report.

Furthermore, the LAT Feedback Report Poll Trigger Frame, TF, needs to be adapted to enable the triggering of the Link Adaptation T raining feedback report from more than one non-AP STA.

SUMMARY

In view of the above, the present disclosure relates to methods and apparatuses for communication in the field of fast link adaptation in wireless network communication systems.

The disclosure is defined by the scope of the independent claims. The dependent claims provide advantageous embodiments of the present disclosure. According to a first aspect, provided is a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, the method comprising: transmission of a LAT feedback frame to the soliciting STA by the one or more responding STAs, wherein the transmissions start a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

According to a second aspect, provided is a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, the method comprising: transmission of a LAT feedback frame to the soliciting STA by the responding STA, wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype; wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Thus according to the first aspect, for a multi user, MU, feedback, the LAT feedback report shall be triggered by the soliciting STA if the preceding LAT Announcement frame includes more than a single Per-STA Info. According to the second aspect, for a single user, SU, feedback, the LAT feedback frame can be implicitly solicited by a preceding LAT Announcement frame that includes only a single Per-STA Info followed by LAT PPDU after a predefined IFS. For the SU feedback a trigger frame, TF, might be included but it is not mandatory to include it for the SU feedback case.

Thus, a LAT Feedback frame is created which carries several different measured link performance metrics. This will provide the soliciting side / transmitting side with a reliable estimate of the expected performance for several combination of MCS, N_ss, and RU within a relatively short time. The soliciting side will transmit a LAT PPDll containing a pre-defined, i.e. known, set of codewords to the recipient side, using different MCS and N_ss values in some, e.g. single or multiple Rll(s). The recipient will respond with the measured BER, or count of erroneous bits per codeword as feedback. Here, when accounting for larger error rates and rounding up, we can use up to 1 byte to indicate the number of erroneous bits in a codeword. The soliciting side can ‘convert’ the reported BER metric into PER metric, if desired. This enables the soliciting side to quickly gather some insight into the expected performance, so it can use the RU-MCS-/V_ss combination, which meets some pre-determined criterion when transmitting to each recipient. Therefore, this method can be used to significantly shorten the convergence time of (data only) ACK/BACK-based ‘outer-loop’ LA mechanisms, such as Minstrel; in other words, it does not necessarily replace link adaptation mechanisms such as Minstrel, but rather helps them converge faster.

In a possible first implementation form of the method according to the first aspect as such or in a possible first implementation form of the method according to the second aspect as such, the frame body of the LAT feedback frame further comprises: a LAT Feedback Control field comprising a collection of parameters relating to measurements upon which the LAT feedback from a responding STA is based; and a field containing a set of per resource unit, RU, Feedback results information, Per-RU Feedback Results Info set, containing link performance metrics which were measured by the responding STA, the Measured Metrics.

Within this description, Bit Error Rate, BER, is one example for a link performance metric. Other examples for a link performance metric may include the (absolute) number of bits in error, which might possibly be quantized according to some granularity, or a SNR value measured in dB.

In a possible second implementation form of the method according to any preceding implementation form of the method according to the first aspect or in a possible second implementation form of the method according to any preceding implementation form of the method according to the second aspect, the LAT Feedback Control field comprises at least the following sub-fields: a sub-field indicating an index of a codeword, Codeword Index, indicating the codeword used for the LAT; a sub-field indicating the size of a RU corresponding to the Measured Metrics included in each Per-RU Feedback Results Info field; a sub-field comprising a bitmap indicating which RUs have been measured by the responding STA; a sub-field comprising a bitmap indicating which metrics are measured and fed back by the responding STA. In a possible third implementation form of the method according to the first or second implementation form of the method according to the first aspect or in a possible third implementation form of the method according to the first or second implementation form of the method according to the second aspect, the Per-RLI Feedback Results Info set comprises at least the following fields: a sub-field indicating an Element ID; a sub-field indicating an Element ID Extension; a sub-field indicating a length, Length; and one or more Per-RLI Feedback Results Info fields.

In a possible fourth implementation form of the method according to the third implementation form of the method according to the first aspect or in a possible fourth implementation form of the method according to the third implementation form of the method according to the second aspect, wherein the amount of info fields comprised in the set of Per-RLI Feedback Results Info fields is dependent at least on: a bandwidth of a channel, Channel Bandwidth; the size of a Rll corresponding to the Measured Metrics; the bitmap indicating which Rlls were measured by the responding STA; wherein a valid Rll index is set to 1 , indicating the Rlls to which the measured metrics refer.

In a possible fifth implementation form of the method according to the third or fourth implementation form of the method according to the first aspect or in a possible fifth implementation form of the method according to the third or fourth implementation form of the method according to the second aspect, wherein each of the Per-RLI Feedback Results Info fields comprises at least the following sub-fields: a sub-field indicating an index of the Rll, Rll index; a sub-field indicating a set of PHY rates for which each reported metric was measured; a sub-field containing a number M indicating the number of PHY rates included in the PHY Rate Index set, where M is an integer in the range of 0 - 15; and a sub-field containing k sets of Measured Metrics, where k is an integer larger than 0.

In a possible sixth implementation form of the method according to the fifth implementation form of the method according to the first aspect or in a possible sixth implementation form of the method according to the fifth implementation form of the method according to the second aspect, wherein for a set of measured metrics x, where x = 1 ,2,... ,k, the measured values of metric x are provided per PHY Rate indicated in the PHY Rate Index set, wherein the size of a sub-field representing each metric value is dependent on the measured metric type and is indicated as a nonzero value in the LAT feedback Control field I Measured Metrics Info bitmap sub-field, wherein: a value of 01 indicates a size of the metric value being represented by one byte; a value of 10 indicates a size of the metric value being represented by two bytes. In a possible seventh implementation form of the method according to the fifth or sixth implementation form of the method according to the first aspect, or in a possible seventh implementation form of the method according to the fifth or sixth implementation form of the method according to the second aspect, wherein the number of erroneous bits per codeword serves as a measured metric, wherein valid values of the measured metric are integers in the range 0 - 254, wherein a value of 0 - 253 correspondingly indicates the number of erroneous bits, and wherein a value of 254 indicates at least 254 erroneous bits.

In a possible eighth implementation form of the method according to any one of the fifth to seventh implementation form of the method according to the first aspect, or in a possible eighth implementation form of the method according to any one of the fifth to seventh implementation form of the method according to the second aspect wherein invalid values corresponding to each measured metric are indicated by: a value of 255, if the metric value is represented by a one-byte sub-field; and a value of 65535, if the metric value is represented by a two-byte subfield.

The present disclosure also provides a third aspect of a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, the method comprising: transmitting a LAT Announcement frame from the soliciting STA, to the one or more responding STAs, followed by a link adaptation physical layer protocol data unit, LAT-PPDU; transmitting a dedicated trigger frame, TF, from the soliciting STA to the one or more responding STAs, the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs, provided that the one or more responding STAs have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; receiving, by the soliciting STA the LAT feedback frame from the one or more responding STAs; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a fourth aspect of a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, the method comprising: transmitting a LAT Announcement frame from the soliciting STA to the responding STA, followed by a link adaptation training physical layer protocol data unit, LAT-PPDU; receiving, by the soliciting STA, a LAT feedback frame, the LAT feedback frame transmitted from the responding STA upon determining that a preceding LAT Announcement frame received by the responding STA includes only a single per station information, Per-STA Info, intended for the responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a fifth aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, wherein the one or more responding STAs are configured to: transmit a LAT feedback frame to the soliciting STA, by the one or more responding STAs, wherein the transmissions start a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a sixth aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, wherein the responding STA is configured to: transmit a LAT feedback frame to the soliciting STA by the responding STA, wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category. In a possible first implementation form of the apparatus according to the fifth aspect as such or a possible first implementation form of the apparatus according to the sixth aspect as such, wherein the frame body of the LAT feedback frame further comprises: a LAT Feedback Control field comprising a collection of parameters relating to measurements upon which the LAT feedback from a responding STA is based; and a field containing a set of per resource unit, RU, Feedback results information, Per-RLI Feedback Results Info set containing link performance metrics which were measured by the responding STA, the Measured Metrics.

In a possible second implementation form of the apparatus according to any preceding implementation form of the apparatus according to the fifth aspect or in a possible second implementation form of the apparatus according to any preceding implementation form of the apparatus according to the sixth aspect, the LAT Feedback Control field comprises at least the following sub-fields: a sub-field indicating an index of a codeword, Codeword Index, indicating the codeword used for the LAT; a sub-field indicating the size of a RU corresponding to the Measured Metrics included in each Per-RU Feedback Results Info field; a sub-field comprising a bitmap indicating which RUs have been measured by the responding STA; a sub-field comprising a bitmap indicating which metrics are fed back by the responding STA.

In a possible third implementation form of the apparatus according to the first or second implementation form of the apparatus according to the fifth aspect or in a possible third implementation form of the apparatus according to the first or second implementation form of the apparatus according to the sixth aspect, the Per-RU Feedback Results Info set comprises at least the following fields: a sub-field indicating an Element ID; a sub-field indicating an Element ID Extension; a sub-field indicating a length, Length; and one or more Per-RU Feedback Results Info fields.

In a possible fourth implementation form of the apparatus according to the third implementation form of the apparatus according to the fifth aspect or in a possible fourth implementation form of the apparatus according to the third implementation form of the apparatus according to the sixth aspect, wherein the amount of info fields comprised in the set of Per-RU Feedback Results Info fields is dependent at least on: a bandwidth of a channel, Channel Bandwidth; the size of a RU corresponding to the Measured Metrics; the bitmap indicating which RUs were measured by the responding STA; wherein a valid RU index is set to 1 , indicating the RUs to which the measured metrics refer.

In a possible fifth implementation form of the apparatus according to the third or fourth implementation form of the apparatus according to the fifth aspect or in a possible fifth implementation form of the apparatus according to the third or fourth implementation form of the apparatus according to the sixth aspect, wherein each of the Per-RU Feedback Results Info fields comprises at least the following sub-fields: a sub-field indicating an index of the Rll, Rll index; a sub-field indicating a set of PHY rates for which each reported metric was measured; a sub-field containing a number M indicating the number of PHY rates included in the PHY Rate Index set, where M is an integer in the range of 0 - 15; and a sub-field containing k sets of Measured Metrics, where k is an integer larger than 0.

In a possible sixth implementation form of the apparatus according to the fifth implementation form of the apparatus according to the fifth aspect or in a possible sixth implementation form of the apparatus according to the fifth implementation form of the apparatus according to the sixth aspect, wherein for a set of measured metrics x, where x = 1 ,2, ... ,k, the measured values of metric x are provided per PHY Rate indicated in the PHY Rate Index set, wherein the size of a sub-field representing each metric value is dependent on the measured metric type and is indicated as a nonzero value in the LAT feedback Control field I Measured Metrics Info bitmap sub-field, wherein: a value of 01 indicates a size of the metric value being represented by one byte; a value of 10 indicates a size of the metric value being represented by two bytes.

In a possible seventh implementation form of the apparatus according to the fifth or sixth implementation form of the apparatus according to the fifth aspect or in a possible seventh implementation form of the apparatus according to the fifth or sixth implementation form of the apparatus according to the sixth aspect, wherein the number of erroneous bits per codeword serves as a measured metric, wherein valid values of the measured metric are integers in the range 0 - 254, wherein a value of 0 - 253 correspondingly indicates the number of erroneous bits, and wherein a value of 254 indicates at least 254 erroneous bits.

In a possible eighth implementation form of the apparatus according to any one of the fifth to seventh implementation form of the apparatus according to the fifth aspect or in a possible eighth implementation form of the apparatus according to any one of the fifth to seventh implementation form of the apparatus according to the sixth aspect, wherein invalid values corresponding to each measured metric are indicated by: a value of 255, if the metric value is represented by a one-byte sub-field; and a value of 65535, if the metric value is represented by a two-byte sub-field.

The present disclosure also provides a seventh aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, wherein the soliciting STA is configured to: transmit a LAT Announcement frame from the soliciting STA, to the one or more responding STAs, followed by a link adaptation physical layer protocol data unit, LAT-PPDU; transmit a dedicated trigger frame, TF, from the soliciting STA to the one or more responding STAs, the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs, provided that the one or more responding STAs have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; receive the LAT feedback frame from the one or more responding STAs; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides an eighth aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, wherein the soliciting STA is configured to: transmit a LAT Announcement frame from the soliciting STA to the responding STA, followed by a link adaptation training physical layer protocol data unit, LAT-PPDU receive, by the soliciting STA, a LAT feedback frame, the LAT feedback frame transmitted from the responding STA upon determining that a preceding LAT Announcement frame received by the responding STA includes only a single per station information, Per-STA Info, intended for the respective responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a ninth aspect of a computer program product comprising program code for performing the method according to any one of the implementation forms of the method according to the first aspect or the first aspect as such, or the method according to any one of the implementation forms of the method according to the second aspect or the second aspect as such, or the method according to the third aspect as such or the method according to the fourth aspect as such, when executed on a computer or a processor.

The present disclosure also provides a tenth aspect of a non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform performing the method according to any one of the implementation forms of the method according to the first aspect or the first aspect as such, or the method according to any one of the implementation forms of the method according to the second aspect or the second aspect as such, or the method according to the third aspect as such or the method according to the fourth aspect as such.

The present disclosure also provides an eleventh aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, comprising a transmitting unit, respectively, wherein the transmitting unit is configured to: transmit a LAT feedback frame to the soliciting STA, by the one or more responding STAs, wherein the transmissions starts a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a twelfth aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, comprising a transmitting unit, respectively, wherein the transmitting unit is configured to: transmit a LAT feedback frame to the soliciting STA by the responding STA, wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a thirteenth aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, wherein the soliciting STA comprises: a transmitting unit configured to transmit a LAT Announcement frame from the soliciting STA, to the one or more responding STAs, followed by a link adaptation physical layer protocol data unit, LAT-PPDU, and transmit a dedicated trigger frame, TF, from the soliciting STA to the one or more responding STAs, the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs, provided that the one or more responding STAs have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; a receiving unit configured to receive the LAT feedback frame from the one or more responding STAs; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

The present disclosure also provides a fourteenth aspect of an apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, wherein the soliciting STA comprises: a transmitting unit configured to transmit a LAT Announcement frame from the soliciting STA to the responding STA, followed by a link adaptation training physical layer protocol data unit, LAT-PPDU; a receiving unit configured to receive a LAT feedback frame, the LAT feedback frame transmitted from the responding STA upon determining that a preceding LAT Announcement frame received by the responding STA includes only a single per station information, Per-STA Info, intended for the respective responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Any of the above-mentioned devices may also be termed apparatuses. Any of the above- mentioned apparatuses may be embodied on an integrated chip.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 illustrates schematically an example of an Infrastructure BSS in a wireless communication system.

FIG. 2 illustrates a predefined table of possible combinations of MCS and N_ss values and their associated PHY rate indices according to a further embodiment of the present disclosure.

FIG. 3 shows Signal to Noise Ratio, SNR, in (dB) versus Packet Error Rate, PER. FIG. 4 illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, according to a first embodiment of the present disclosure, for multi user or single user mode of operation, namely for MU or SU mode, respectively, for short.

FIG. 5 illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, according to a first embodiment of the present disclosure, for SU mode.

FIG. 6 illustrates a LAT Feedback frame and structure of a LAT Feedback frame according to the first embodiment of the present disclosure.

FIG. 7 illustrates a structure of a LAT Feedback Control field according to a second embodiment of the present disclosure.

FIG. 8 illustrates a structure of a field indicating a set of Per-RU feedback results information according to a third embodiment of the present disclosure.

FIG. 9 illustrates a further embodiment of the present disclosure with respect to details of the RU bitmap indication sub-field of FIG. 6.

FIG. 10 illustrates the details according to FIG. 8.

FIG. 11 illustrates a further embodiment of the present disclosure with respect to details of RU bitmap indication sub-field of FIG. 6.

FIG. 12 illustrates the details according to FIG. 11.

FIG. 13 illustrates further details of the Per-RU Feedback Results Info field according to a fifth embodiment of the present disclosure.

FIG. 14 illustrates an example for an individual set of measured link performance metrics for the Per-RU Feedback Results Info field according to a sixth embodiment of the present disclosure.

FIG. 15 illustrates a further embodiment of the present disclosure further for providing a link adaptation training, LAT, feedback frame in a wireless local access network, for MU mode.

FIG. 16 illustrates the further embodiment of FIG. 15 the present disclosure for providing a link adaptation training, LAT, feedback frame in a wireless local access network, for SU mode.

FIG. 17 illustrates a further embodiment of the present disclosure providing an apparatus in a wireless local access network, WLAN, for MU mode.

FIG. 18 illustrates the further embodiment of FIG. 17 of the present disclosure providing an apparatus in a wireless communication network, WLAN, for SU mode.

FIG. 19 illustrates a further embodiment of the present disclosure providing an apparatus in a wireless local access network, WLAN, for MU mode. FIG. 20 illustrates the further embodiment of FIG. 19 of the present disclosure providing an apparatus in a wireless communication network, WLAN, for Sil mode.

DESCRIPTION

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 disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the 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 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.

FIG. 1 shows an example of a wireless communication system 100. The communication system 100 includes an access point, AP, 105 that is serving one or more of stations, STAs, 110, 112, 114, 116, and 118. The AP 105 typically controls aspects of communication with its associated stations such as radio frequency channel, transmission power limit, authentication and security. In some cases, in the communication system 100 the wireless resources for both uplink transmissions, i.e. links from STAs to AP, and downlink transmissions, i.e. links from AP to STAs, may be accessed by transmitters based on a distributed contention mechanism commonly referred to as carrier sensing multiple access with collision avoidance (CSMA/CA). In some examples, APs are referred to as Node Bs, evolved Node Bs (eNBs), next generation (NG) Node Bs (gNBs), master eNBs (MeNBs), secondary eNBs (SeNBs), master gNBs (MgNBs), secondary gNBs (SgNBs), network controllers, control nodes, base stations, access nodes, transmission points (TPs), transmission-reception points (TRPs), cells, carriers, macro cells, femtocells, pico cells, and so on, while STAs may also be commonly referred to as user equipment (UEs), mobile stations, mobiles, terminals, users, subscribers, stations, and the like. APs may provide wireless access in accordance with one or more wireless communication protocols, e.g., Wi-Fi 802.11a/b/g/n/ac/ad/ax/ay/be, the Third Generation Partnership Project (3GPP) long term evolution (LTE), LTE advanced (LTE-A), 5G, 5G LTE, 5G NR, High Speed Packet Access (HSPA), etc. While it is understood that communication systems may employ multiple APs capable of communicating with a number of stations, only one AP 105 and five stations 110-118 are illustrated in Figure 1 for simplicity.

In IEEE 802.11 , a data payload is encoded in the physical (PHY) layer to provide efficient transmission, error detection capability, error correction capability, or a combination thereof. In IEEE 802.11 compliant wireless networks, the data payload may be encoded using either binary convolutional coding (BCC) or low-density parity check (LDPC) encoding. In the case of BCC encoding, the whole stream of information bits is fed sequentially into a generator that generates coded bits. Each contiguous subset of coded bits is a function of the information bits currently residing in the buffer of the generator, which is typically approximately 6 bits in size. In the case of LDPC encoding, several codeword sizes are defined. The information bits are divided into separate, non-overlapping portions. The portions undergo separate encoding. In order to align with the predefined LDPC codeword sizes, the information bits may be padded with so-called shortening bits, and in order to match the required coding rate the output may be punctured or repeated.

As indicated above, for a single physical layer rate, PHY rate, there should be a predefined map, e.g. a table, of pairs of a Modulation and Coding Scheme and a value of a Number of Spatial Streams, MCS and N_ss. This pair may be denoted by <MCS, N_ss>. Here, <MCS, N_ss> may also be referred to as a tuple. Thus, each <MCS, N_ss> tuple is represented by a single value of PHY rate Index. Then, the link adaptation training, LAT, feedback report should be triggered for a multi user, MU, feedback transmission by an associated access point, AP. Here, MU feedback is defined if the preceding LAT Announcement frame includes more than a single per station, Per-STA, info. Single User, SU, feedback report might be triggered using a trigger frame, TF frame.

In more detail, when transmitting of training data to a responder, this should indicate to the responder which codewords, CWs, and their respective MCS and N_ss , i.e. the pair or tuple are transmitted within the training data packet, i.e. the PPDll. Thus, the training data packet should include an overhead. This way, also indicators of the respective position of the CWs and their respective MCS and N_ss may be transmitted. For the overhead, several options may be selected:

Option 1 : According to the first option, the overhead may comprise explicitly signaling each MCS value as well as N_ss value using a predetermined number of bits. This may be done via an extremely high throughput signal field, EHT-SIG/LA-SIG. In particular, 4 bits may be used to indicate each MCS value and 2 or 3 bits to indicate the number of spatial streams, N_ss. It should be understood, that also different numbers of bits might be used.

Option 2: According to the second option, the overhead may indicate each combination of MCS and N_ss to be used by indicating a corresponding entry from a predefined table. The predefined table may list some or all PHY rate indices, wherein each PHY rate index is associated in a predefined manner with a unique pair of MCS and N_ss values. In particular, the table may rank all combinations of MCS and N_ss in ascending order of PHY throughput, for example requiring 16*8=128 combinations, and may indicate each combination from this list, for example using 7 bits per index.

FIG. 2 illustrates the second option by showing ten out of 128 possible combinations of MCS and N_ss, as an example. In more detail, FIG. 2 illustrates a table showing ten columns indexed 0, 1 , ... 9 with possible combinations of MCS and N_ss and indicating the number of bits per tone for each of the ten combinations. The MCS values in the table in FIG. 2 follow the conventions of the IEEE 802.11 WLAN standard, each value indicating a specific modulation type and coding rate.

Option 3: According to the third option, the table as described for the second option may be further shortened to include only a subset of the combinations shown in FIG. 2, but omitting impractical combinations, for example MCS 0 with N_ss=2 from the table. Thereby, the table may be significantly shorter than the table for option 2; for example, the table may only include 32 combinations instead of 128 combinations.

Option 4: According to the fourth option, the overhead may include for a single value of N_ss, an indication of the used values of the MCS and the order of the used values of the MCS. In other words, according to this option, the overhead may include an index referring to one out of a predefined list of options, for a single value of N_ss, indicating the values of MCS and the order of the MCSs. Option 5: According to the fifth option, the overhead may include an index pointing to a specific entry in a predefined table indicating the order of modulated codewords with their respective MCS and N_ss combinations, using a field with a predefined number of bits. In other words, the overhead may include an indicator to an entry in a predefined table specifying the order of CWs with MCS and N_ss combinations.

Within the context of the present disclosure, for achieving a possibly reduced LA convergence time, the originator needs as quickly as possible a reliable estimate of the expected performance, at least per several combinations of MCS and RU. A focus should be put on coded Bit Error Rate, BER, as the reported link performance metric, as is indicated in FIG. 5.

FIG. 3 shows Signal to Noise Ratio, SNR, in (dB) versus Packet Error Rate, PER. FIG. 3 shows four tuples of MCS and N_ss, i.e <MCS, N_ss> being <0, 1 >, <7, 1 >, <4, 2>, and <2, 1 >. For each of these tuples, the PER is shown and the respective BER is also shown.

Considering a practical operating PER of below 20-30%, the respective BER is in the order of 2-3%. The largest number of info bits in a codeword is 1620, corresponding to coding rate of 5/6, and 2-3% of that results in -30-50 erroneous bits.

Thus, for the following, the focus should be on the BER as the reported link performance metric.

Embodiment 1

FIG. 4 illustrates a first embodiment of the present disclosure. FIG. 4 illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network. According to FIG. 4, the wireless local access network comprises a soliciting station, STA, and one or more responding STAs. The method comprises: a step 251 of transmission of a LAT feedback frame to the soliciting STA by the one or more responding STAs, wherein the transmission starts a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA. Here, the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Here, it should be noted that the dedicated trigger frame follows after the reception of a preceding LAT Announcement frame followed by link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS. Otherwise, the STA will not send any LAT feedback frame since it does not have any valid LAT measurements to send.

Similarly, FIG. 5 illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, the method comprising: a step 351 of transmission of a LAT feedback frame to the soliciting STA by the responding STA, wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA. Here, the LAT feedback frame is a management frame of an “Action No Ack” subtype; wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Here, a dedicated Trigger frame, TF, should be understood as a TF defined for LAT feedback report. The dedicated TF may include an indication to a subset of the intended recipient STAs I responding STAs, comprising only non-access point stations, non-AP STAs, included in the N per station information fields, Per-STA Info, of LAT announcement frame, where N is an integer larger than 0.

For example, the transmitted dedicated TF may be designated as a LAT feedback Report Poll. For the case of a LAT feedback Report Poll, the TF include a subset of only the non-AP STAs that were included in the Per-STA Info of the preceding LAT Announcement frame. In a method for polling a Link Adaption T raining, LAT, feedback report in a wireless communication network, WLAN, comprising a soliciting STA and one or more intended recipient STAs. This particularly relates to the case of Multi-link operation, MLO. For multi-link operation, MLO, the recipient STAs are affiliated with a multi-link device, MLD. Here, the LAT feedback report trigger frame, TF, polls for the following LAT feedback reports. Feedback reports are measured on the same link on which the LAT feedback report poll TF is transmitted; and/or feedback reports are measured on other links than the link on which the LAT feedback report poll TF is transmitted, wherein the feedback reports are measured by non-AP STAs affiliated with the same MLD. For example: the LAT Report Poll TF may be sent over a 6 GHz link. Then, it includes a request for recent measurements taken on 6 GHz link and 5 GHz link, i.e. from non-AP STAs affiliated with the same non-AP MLD. Furthermore, the LAT feedback report TF may comprise a trigger dependent part and an indication is added to the trigger dependent part. The trigger dependent part may include at least a part comprising link information; and/or a part containing a dialog token, the dialog token indicating a report of a specific measurement.

FIG. 6 illustrates a LAT Feedback frame 201 and a structure of a LAT Feedback frame according to the first embodiment of the present disclosure. In FIG. 6 the LAT Feedback frame 201 is a management frame, i.e. the LAT Feedback frame 201 is of the Frame type Management type. The structure of the LAT Feedback frame 201 comprises a Management Header field, MAC Header, 210, a field including the body of the frame, Frame Body, 212, and frame check sequence, FCS, 214.

As indicated in FIG. 6, the Frame Body, 212, comprises a collection of sub-fields 301. As indicated in FIG. 6, a sub-field 310 indicates a new action category, Action Category, and correspondingly a sub-field 312 indicates a value for the action category, Action Category value. Here, for example, the sub-fields 310 and 312 may be filled by Action category: LAT (Link Adaptation Training), Action category value: Link Adaptation Training feedback. Here, using Management Action No ACK frame may dynamically enable inclusion of various elements for future extensions while keeping the length, in bytes, of the entire frame as minimal as needed.

The collection of sub-fields 301 of FIG. 6 further includes a sub-field 314 indicating control of the LAT Feedback, LAT Feedback Control field. The LAT Feedback Control field may include the collection of parameters according to which the LAT report was measured. Further, the collection of sub-fields 301 of FIG. 6 includes a sub-field 316 indicating a set of feedback result information per RU, Set of Per-RU Feedback Results Info. The set of sub-field 316 includes a group of Per-RU Feedback Results Info, each related to a specific RU on which the non-AP STA measured the received codewords. Here, the Per-RU Feedback Results Info includes the measured metric values for each subset of <MCS, N_ss> tuples that the non-AP STA has been requested to measure, per specific RU. Embodiment 2

FIG. 7 further illustrates a structure of a LAT Feedback Control field according to a second embodiment of the present disclosure. FIG. 7 shows the collection of sub-fields 301 of FIG. 6. The elements of the collection of sub-fields 301 are the same as indicated for FIG. 6 and it is referred to FIG. 6 for explanation.

FIG. 7 further illustrates that the LAT Feedback Control field 314 may include a subset of subfields 401 . The subset of sub-fields 401 of FIG. 7 may include at least the following sub-fields:

A sub-field 412 indicating an index of a codeword, Codeword Index. This refers to the codeword to be used for training. That is, the codeword is to be used in a subsequent LAT Physical Layer Protocol Data Unit, PPDU, following the LAT Announcement frame after a predefined InterFrame Space, IFS.

Here, in the case where a single codeword is being used in the LAT PPDU by the soliciting side, i.e. the originator, e.g. with this codeword being predefined within some standard specification or being signaled earlier to all STAs involved in the process, the Codeword Index sub-field 412 might be omitted from the LAT Feedback Control field 314.

The subset of sub-fields 401 of the LAT Feedback Control field 314 as illustrated in FIG. 7 further includes a sub-field 416 indicating the granularity for encoding of the RU, RU granularity. The granularity may also be understood as the size of a resource unit, RU, corresponding to the metric for measurement. For example, the granularity, RU granularity, may be one of 20 MHz, 40 MHz, 80 MHz, 160 MHz, and 320 MHz.

The subset of sub-fields 401 of the LAT Feedback Control field 314 as illustrated in FIG. 7 further may further include a sub-field 418, RU Bitmap indication, comprising a bitmap indicating which RUs should be measured.

Furthermore, the subset of sub-fields 401 of the LAT Feedback Control field 314 as illustrated in FIG. 7 further includes a sub-field 420 indicating a bitmap for the measured metrics, Measured Metrics Info bitmap. The Measured Metrics Info bitmap 420 may be represented as a 16-bit bitmap. The Measured Metrics Info bitmap 420 indicates which link performance metrics are measured and fed back. It should be noted that in the case where a single performance metric is being used, e.g. with a predefined metric according to some standard specification or a metric which is signaled earlier to the STAs involved in the process, the Measured Metrics Info bitmap sub-field 420 may be omitted from the subset of sub-fields 401 of the LAT Feedback Control field 314 of this embodiment.

Furthermore, depending on specific application needs, further sub-fields may be added to the set of sub-fields 401 of FIG. 7 as a descriptive information to the LAT Feedback Control field 314. These further sub-fields may include a Dialog token field, Dialog token, 410, that indicates an identifier of the specific LAT sequence. These sub-fields may further include a field indicating a Channel Bandwidth field 414, Channel Bandwidth, which indicates the BW of the LAT PPDU. Here, the encoding may relate to the following values: 20 MHz / 40 MHz / 80 MHz/ 160 MHz / 320 MHz.

Finally, reserved sub-fields 422 may be included in the subset of sub-fields 401 , as well.

From the above, it should be understood that embodiment 2 may be combined with embodiment 1.

Embodiment 3

FIG. 8 illustrates a further embodiment of the present disclosure. Building on FIGs 6 and 7 and its corresponding explanations, FIG. 8 illustrates a collection of sub-fields 301 including a subfield 316 indicating a set of Per-RU feedback results information according to a third embodiment of the present disclosure. The sub-field 316 was already introduced in FIGs. 6 and 7, respectively. The collection of sub-fields 301 was also already introduced in FIGs. 6 and 7, respectively.

FIG. 8 illustrates the sub-field 316 may further include a subset of sub-fields 501 including: a sub-field 510 indicating an identification of an element, Element ID. For extension, the subset of sub-fields 501 further includes a sub-field 512 indicating an extension of the Element ID. This may be accompanied by a sub-field 514 indicating a length, Length, for the Element. Furthermore, the set of sub-fields includes one or more sub-field(s) 516 indicating information on feedback results for respective RU index, RU index Feedback Results Info field. Here, the amount of info fields comprised in the set of Per-RU Feedback Results Info fields 516 is dependent at least on: a bandwidth of a channel, Channel Bandwidth; the size of a RU corresponding to the Measured Metrics; the bitmap indicating which RUs were measured by the responding STA, 110, 112, 114, 116, 118; wherein a valid RU index is set to 1 , indicating the RUs to which the measured metrics refer. Embodiment 4

FIG. 9 illustrates a further embodiment of the present disclosure with respect to details of the RU bitmap indication sub-field of FIG. 7. FIG. 10 illustrates further details according to FIG. 9. According to a first option, as indicated above, the Rll Bitmap indication includes 16 bits. Here, a valid Rll Index is dependent on the Rll Granularity, as detailed in the table shown in FIG. 9: FIG. 9 illustrates the Rll Granularity, i.e. the Rll size corresponding to the measured metric; referring to the encoding using the following values: 20 MHz 1 40 MHz I 80 MHz/ 160 MHz 1 320 MHz. The second column of the table of FIG. 9 indicates respective ranges of valid Rll indexes. Here, for this table the bit value of each valid RU Index may be set to either 0 or 1 . In contrast, the bit value of an invalid RU Index wherein for each invalid index of an RU, the value of the bit of the invalid index of the RU determined by: i) setting the value of the bit to 0; or else ii) duplicating the values of the bits corresponding to all valid indexes for each invalid index.

The diagram shown in FIG. 10 illustrates the method for indicating the invalid RU Index in the RU bitmap, per selected RU Granularity, based on embodiment 2. In FIG. 10, white squares indicate valid RU indexes whereas grey squares indicate invalid RU indexes. Here, corresponding to FIG. 9, for 20 MHz granularity we have 16 valid RU indexes corresponding to 16 bits, i.e. bits 0 - 15, in FIG. 10. For 40 MHz granularity, we have 8 valid RU indexes corresponding to the first eight bits, 0 - 7. The remaining 8 bits, 8 - 15, indicate invalid RU indexes for 40 MHz in FIG. 10. Likewise, for 80 MHz granularity we have 4 valid RU indexes corresponding to the first four bits, 0 - 3, in FIG. 10. The remaining 12 bits, 4 - 15, indicate invalid RU indexes for 80 MHz in FIG. 10. Furthermore, for 160 MHz granularity, we have 2 valid RU indexes corresponding to the first two bits, 0 - 1. The remaining 14 bits, 3 - 15, indicate invalid RU indexes for 160 MHz in FIG. 10. Finally, for 320 MHz granularity, we have one valid RU index corresponding to the first bit, bit 0. The remaining 15 bits, 1 - 15, indicate invalid RU indexes for 320 MHz in FIG. 10. It should be noted that the invalid indexes would be ignored by the receiver.

According to a second option, the RU Bitmap indication includes 16 bits, similar as for the first option. Here, a valid RU Index is dependent on the RU Granularity, as detailed in the table shown in FIG. 11 : FIG. 11 illustrates the RU Granularity, i.e. the RU size corresponding to the measured metric; referring to the encoding using the following values: 20MHz I 40MHz I 80 MHz/ 160 MHz I 320 MHz. The second column of the table of FIG. 11 indicates respective values of valid RU indexes. Here, for this table the bit value of each valid RU Index may be set to either 0 or 1. In contrast, the bit value of an invalid RU Index is determined by : i) setting the value of the bit to 0; or else ii) setting the closest valid index being lower than the invalid index for the same RU granularity. The value of the bit is then set to the bit value determined by the closest valid index being lower than the invalid index for the same Rll granularity. For example, according to the table shown in FIG. 11 , for a granularity, Rll granularity, of 80MHz, the value for the invalid Rll Index 7 will be set to the value of the valid Rll Index 4, which is the closest lowest valid index.

The following diagram shown in FIG. 12 graphically illustrates, based on embodiment 2, for indicating the invalid Rll Index in the Rll bitmap, per selected Rll Granularity. In FIG. 12, white squares indicate valid Rll indexes whereas grey squares indicate invalid Rll indexes. Here, corresponding to FIG. 10, for 20 MHz granularity we have 16 valid Rll indexes corresponding to 16 bits, i.e. bits 0 - 15, in FIG. 10. For 40 MHz granularity, we have 8 valid Rll indexes. The 8 valid Rll indexes are indicated by bits 0, 2, 4, 6, 8, 10, 12, 14. The remaining 8 bits, i.e. bits 1 , 3, 5, 7, 9, 11 , 13, and 15, indicate invalid Rll indexes for 40 MHz in FIG. 12. Likewise, for 80 MHz granularity we have 4 valid Rll indexes corresponding to bits 0, 4, 8, and 12. The remaining 12 bits, i.e. bits 1 , 2, 3, 5, 6, 7, 9, 10, 11 , 13, 14 and 15, indicate invalid Rll indexes for 80 MHz in FIG. 12. Furthermore, for 160 MHz granularity, we have 2 valid Rll indexes corresponding to bits 0 and 8. The remaining 14 bits, i.e. bits 1 , 2, 3, 4, 5, 6, 7, 9, 10, 11 , 12, 13, 14, and 15 indicate invalid Rll indexes for 160 MHz in FIG. 12. Finally, for 320 MHz granularity, we have one valid Rll index corresponding to the first bit, bit 0. The remaining 15 bits, i.e. bits 1 - 15, indicate invalid Rll indexes for 320 MHz in FIG. 12.

In any case, it should be understood that the values in the invalid indexes would be ignored by the receiver.

Embodiment 5

In a further embodiment of the present disclosure, FIG. 13 illustrates further details of the Per- Rll Feedback Results Info field 516 according to a fifth embodiment of the present disclosure. The Per Rll Feedback Results Info field 516 was already introduced for embodiment 3. The subset of sub-fields 501 was also already introduced for embodiment 3, FIG. 8. From this, already it should be clear that embodiment 5 may be combined with embodiment 3.

As illustrated in FIG. 13, the Per-RLI Feedback Results Info field 516 comprises a subset of sub-fields 601. The subset of sub-fields 601 includes at least the following sub-fields: a subfield 610, RU Index, indicating the RU Index to which the field information refers. A sub-field 612, PHY Rate Info Length providing a value in the range 0-15, and indicating the number of PHY rate indices included in the PHY Rate Index set, sub-field 614, for that specific RU. A sub- field 614, PHY Rate Index set, referring to a set of M PHY rate indices, <MCS, N_ss> tuples, in which the codeword is transmitted per Rll for that user.

The set of sub-fields 601 further includes several fields 616-1 , ... , 616-k which refer to sets of measured metrics. Here, the number k is a positive integer. The exact amount of sets is dependent on the measured metrics indicated as a nonzero value in the Measured Metrics Info bitmap in the preceding LAT Announcement frame, cf. sub-field 420 in FIG. 7.

FIG. 13 indicates an example for a set of measured metrics, indicated as 701. Here, the first field 616-1 is illustrated, i.e. expanded. It should be understood that other fields may be selected. The set 616-1 includes fields 716-1 , ... , 716-M relating to M PHY rate indexes, where M is a positive integer. Each field includes a measured value for the first set of measured metrics.

Embodiment 6

In a further embodiment of the present disclosure, FIG. 14 illustrates an individual set of metrics for the Per-RU Feedback Results Info field according to a sixth embodiment of the present disclosure. FIG. 14 and its embodiment is closely related to FIG. 13 and its corresponding embodiment such that the embodiments of FIG. 13 and FIG. 14 may be combined. It should be noted that in general the sub-fields 510’, 512’, 514’ and 516’ correspond or are the same as in FIG. 13. Likewise the sub-fields 610’, 612’, 614’ and 616- T are the same as in FIG. 13. The subset of sub-fields 50T corresponds to the subset of sub-fields 501 of FIG. 13 but with a single RU Index Feedback Results Info field in the subset and thus a specific selection of a length in the Length field. Likewise the subset of sub-fields 60T corresponds to the sub-field 601 of FIG. 13 with a specific RU Index value, field 610’, and a specific PHY Rate Info Length 612’. Here, the first set, 616- T is further detailed. Here, a Metric x set indicates a set of the measured values of metric for a codeword per PHY Rate indicated in the PHY Rate Index set. The size of each Metric value is dependent on the measured metrics indicated as a nonzero value in the Measured Metrics Info bitmap. Here, 01 - indicates 1-byte size metric, 10 - indicates 2-byte size metric.

For the example shown in FIG. 14, for valid values per metric we may have, for instance: Metric 1 - count of Erroneous bits per codeword, EBPC, where 0-253 indicates number of erroneous bits, 254 indicates at least 254 erroneous bits.

Here, Invalid I N/A value will be indicated separately. For instance: a value of 255 will be used if the metric value includes 1 byte, where the measured metric is encoded as “01” in the LAT Announcement I Per-STA Info. A value of 65535 will be used if the metric value includes 2 bytes, where the measured metric is encoded as “10” in the LAT Announcement I Per-STA Info.

In the example in FIG. 14, the following are the parameters that specific non-AP STA has been measured for Metrid : Rll Index = 1 , PHY Rate Length = 4, PHY Rate Indexes: 10, 20,50, N/A, Metric 1 measured values: 10, 0, 255,255. The illustration in FIG. 14 shows the values as set in the corresponding Per-RLI Feedback Results Info field.

Embodiment 7

FIG. 15 illustrates a further embodiment of the present disclosure. FIG. 15 illustrates providing a link adaptation training, LAT, feedback frame in a wireless local access network for a multi user mode of operation, MU mode. The method illustrated in FIG 15. illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising: a step 450 of transmitting a LAT Announcement frame from the soliciting STA to the one or more responding STAs, followed by a link adaptation physical layer protocol data unit, LAT-PPDU; a step 451 of transmitting a dedicated trigger frame, TF, from the soliciting STA to the one or more responding STAs, the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs, provided that the one or more responding STAs have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; and ; a step 453 of receiving, by the soliciting STA the LAT feedback frame from the one or more responding STAs; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

FIG. 15 illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, in a multi-user case. The following FIG. 16 illustrates the corresponding method in case of a single user providing feedback to the soliciting STA.

FIG. 16 illustrates a method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, for a single user mode of operation, SU mode, the WLAN comprising a soliciting station, STA, and a responding STA, the method comprising: a step 550 of transmitting a LAT Announcement frame from the soliciting STA to the responding STA, followed by a link adaptation training physical layer protocol data unit, LAT-PPDU; a step 551 of receiving, by the soliciting STA a LAT feedback frame, the LAT feedback frame transmitted from the responding STA upon determining that a preceding LAT Announcement frame received by the responding STA includes only a single per station information, Per-STA Info, intended for the responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Embodiment 8

FIG. 17 illustrates a further embodiment of the present disclosure. FIG. 17 illustrates an apparatus 30 in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, the one or more responding STAs comprising a transmitting unit 3501 , respectively, wherein the transmitting unit 3501 is configured to transmit a LAT feedback frame to the soliciting STA (105), by the one or more responding STAs, wherein the transmissions starts a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Embodiment 9

FIG. 18 illustrates a further embodiment of the present disclosure. FIG. 18 illustrates an apparatus 30 in a wireless communication network, WLAN, comprising a soliciting station, STA, and one responding STA, wherein the soliciting STA comprises: a transmitting unit 3502 wherein the transmitting unit 3502 is configured to transmit a LAT feedback frame to the soliciting STA by the responding STA, wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Embodiment 10

FIG. 19 illustrates a further embodiment of the present disclosure. FIG. 19 illustrates an apparatus 20 in a wireless local access network, WLAN, comprising a soliciting station, STA, and one or more responding STAs, wherein the soliciting STA comprises: a transmitting unit 4501 configured to transmit a LAT Announcement frame from the soliciting STA, to the one or more responding STAs, followed by a link adaptation physical layer protocol data unit, LAT- PPDll, and transmit a dedicated trigger frame, TF, from the soliciting STA to the one or more responding STAs, the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs, provided that the one or more responding STAs have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; a receiving unit 4503 configured to receive the LAT feedback frame from the one or more responding STAs; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

Embodiment 11

FIG. 20 illustrates a further embodiment of the present disclosure. FIG. 20 illustrates an apparatus 20’ in a wireless local access network, WLAN, comprising a soliciting station, STA, and a responding STA, wherein the soliciting STA comprises: a transmitting unit 4502 configured to transmit a LAT Announcement frame from the soliciting STA to the responding STA, followed by a link adaptation training physical layer protocol data unit, LAT-PPDU; a receiving unit 4504 configured to receive a LAT feedback frame, the LAT feedback frame transmitted from the responding STA upon determining that a preceding LAT Announcement frame received by the responding STA includes only a single per station information, Per-STA Info, intended for the responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame comprises a frame body, wherein the frame body comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category. Abbreviations

• ACK: Acknowledge

• AP: Access Point

• BA[CK]: Block-ACK - in 802.11 , typically a receiver is expected to respond to a data transmission by responding with an ACK; if multiple frames are transmitted within a single PPDll, each has to be acknowledged

• BCC: Binary Convolutional Coding

• BER: Bit Error Rate

• BSS: Basic Serving Set

• CQI: Channel Quality Indicator

• EHT: Extremely HT

• HE: High Efficiency

• H LA: HE Link Adaptation

• HT: High Throughput

• LA: Link Adaptation

• LAT: LA Training

• LDPC: Low-Density Parity Check

• MAC: Medium Access Control

• MCS: Modulation & Coding Scheme

• MFB: MCS Feedback

• ML: Multi Link

• MLD: ML Device

• MLO: ML Operation

• MSDU: MAC Service Data Unit

• MU: Multi User

• N_SS: Number of Spatial Streams

• PER: Packet Error Rate

• PHY: Physical Layer

• PPDU: PHY Protocol Data Unit

• RU: Resource Unit

• SNR: Signal-to-Noise Ratio

• STA: Station (in general, can be either an AP STA or a non-AP STA)

• SU: Single User • TF: Trigger Frame - in 802.11ax, the Trigger Frame was introduced as a means to trigger a STA or multiple STAs to transmit simultaneously and in sync to the triggering AP

• WLAN: Wireless Local Access Network

Claims

1 . A method for providing a link adaptation training, LAT, feedback frame in a wireless local access network (100), WLAN, comprising a soliciting station, STA (105), and one or more responding STAs (110, 112, 114, 116, 118), the method comprising:

(251) transmission of a LAT feedback frame (201) to the soliciting STA (105) by the one or more responding STAs (110, 112, 114, 116, 118), wherein the transmissions starts a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

2. A method for providing a link adaptation training, LAT, feedback frame in a wireless local access network (100), WLAN, comprising a soliciting station, STA (105), and a responding STA (110, 112, 114, 116, 118), the method comprising:

(351) transmission of a LAT feedback frame (201) to the soliciting STA (105) by the responding STA (110, 112, 114, 116, 118), wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype; wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

3. The method according to claim 1 or 2, wherein the frame body (212) of the LAT feedback frame (201) further comprises: a LAT Feedback Control field (314) comprising a collection of parameters relating to measurements upon which the LAT feedback from a responding STA (110, 112, 114, 116, 118) is based; and a field (316) containing a set of per resource unit, RU, Feedback results information, Per-RU Feedback Results Info set, containing link performance metrics which were measured by the responding STA (110, 112, 114, 116, 118), the Measured Metrics.

4. The method according to claim 3, wherein the LAT Feedback Control field (314) comprises at least the following sub-fields: a sub-field (412) indicating an index of a codeword, Codeword Index, indicating the codeword used for the LAT ; a sub-field (416) indicating the size of a RU corresponding to the Measured Metrics included in each Per-RU Feedback Results Info field; a sub-field (418) comprising a bitmap indicating which RUs have been measured by the responding STA (110, 112, 114, 116, 118); a sub-field (420) comprising a bitmap indicating which metrics are measured and fed back by the responding STA (110, 112, 114, 116, 118).

5. The method according to claim 3 or 4, wherein the Per-RU Feedback Results Info set (316) comprises at least the following fields: a sub-field (510) indicating an Element ID; a sub-field (512) indicating an Element ID Extension; a sub-field (514) indicating a length, Length; and one or more Per-RU Feedback Results Info fields (516).

6. The method according to claim 5, wherein the amount of info fields comprised in the set of Per-RU Feedback Results Info fields (516) is dependent at least on: a bandwidth of a channel, Channel Bandwidth; the size of a RU corresponding to the Measured Metrics; the bitmap indicating which RUs were measured by the responding STA (110, 112, 114, 116, 118); wherein a valid RU index is set to 1 , indicating the RUs to which the measured metrics refer.

7. The method according to claim 5 or 6, wherein each of the Per-RU Feedback Results Info fields (516) comprises at least the following sub-fields: a sub-field (610) indicating an index of the Rll, Rll index; a sub-field (614) indicating a set of PHY rates for which each reported metric was measured; a sub-field (612) containing a number M indicating the number of PHY rates included in the PHY Rate Index set, where M is an integer in the range of 0 - 15; and a sub-field (616-1 , ... , 616-k) containing k sets of Measured Metrics, where k is an integer larger than 0.

8. The method according to claim 7, wherein for a set of measured metrics x, where x = 1 ,2,... ,k, the measured values of metric x are provided per PHY Rate indicated in the PHY Rate Index set (614), wherein the size of a sub-field representing each metric value is dependent on the measured metric type and is indicated as a nonzero value in the LAT feedback Control field (314) or in the Measured Metrics Info bitmap sub-field (420), wherein: a value of 01 indicates a size of the metric value being represented by one byte; a value of 10 indicates a size of the metric value being represented by two bytes.

9. The method according to claim 7 or 8, wherein the number of erroneous bits per codeword serves as a measured metric, wherein valid values of the measured metric are integers in the range 0 - 254, wherein a value of 0 - 253 correspondingly indicates the number of erroneous bits, and wherein a value of 254 indicates at least 254 erroneous bits.

10. The method according to any one of claims 7 to 9, wherein invalid values corresponding to each measured metric are indicated by: a value of 255, if the metric value is represented by a one-byte sub-field; and a value of 65535, if the metric value is represented by a two-byte sub-field.

11. A method for providing a link adaptation training, LAT, feedback frame in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and one or more responding STAs (110, 112, 114, 116, 118), the method comprising:

(450) transmitting a LAT Announcement frame from the soliciting STA (105), to the one or more responding STAs (110, 112, 114, 116, 118), followed by a link adaptation physical layer protocol data unit, LAT-PPDU;

(451) transmitting a dedicated trigger frame, TF, from the soliciting STA (105) to the one or more responding STAs (110, 112, 114, 116, 118), the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs (110, 112, 114, 116, 118), provided that the one or more responding STAs (110, 112, 114, 116, 118) have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame;

(453) receiving, by the soliciting STA (105) the LAT feedback frame (201) from the one or more responding STAs (110, 112, 114, 116, 118); wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

12. A method for providing a link adaptation training, LAT, feedback frame in a wireless local access network (100), WLAN, comprising a soliciting station, STA (105), and a responding STA (110, 112, 114, 116, 118), the method comprising:

(550) transmitting a LAT Announcement frame from the soliciting STA (105) to the responding STA (110, 112, 114, 116, 118), followed by a link adaptation training physical layer protocol data unit, LAT-PPDU;

(551) receiving, by the soliciting STA (105), a LAT feedback frame (201), the LAT feedback frame (201) transmitted from the responding STA (110, 112, 114, 116, 118) upon determining that a preceding LAT Announcement frame received by the responding STA (110, 112, 114, 116, 118) includes only a single per station information, Per-STA Info, intended for the respective responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

13. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and one or more responding STAs (110, 112, 114, 116, 118), wherein the one or more responding STAs (110, 112, 114, 116, 118) are configured to: transmit a LAT feedback frame (201) to the soliciting STA (105), by the one or more responding STAs (110, 112, 114, 116, 118), wherein the transmissions starts a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.

14. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and a responding STA (110, 112, 114, 116, 118), wherein the responding STA (110, 112, 114, 116, 118) is configured to: transmit a LAT feedback frame (201) to the soliciting STA (105) by the responding STA (110, 112, 114, 116, 118), wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.

15. The apparatus according to claim 13 or 14, wherein the frame body (212) of the LAT feedback frame (201) further comprises: a LAT Feedback Control field (314) comprising a collection of parameters relating to measurements upon which the LAT feedback from a responding STA (110, 112, 114, 116, 118) is based; and a field (316) containing a set of per resource unit, RU, Feedback results information, Per-RU Feedback Results Info set, containing link performance metrics which were measured by the responding STA (110, 112, 114, 116, 118), the Measured Metrics.

16. The apparatus according to claim 15, wherein the LAT Feedback Control field (314) comprises at least the following sub-fields: a sub-field (412) indicating an index of a codeword, Codeword Index, indicating the codeword used for the LAT ; a sub-field (416) indicating the size of a RU corresponding to the Measured Metrics included in each Per-RLI Feedback Results Info field; a sub-field (418) comprising a bitmap indicating which Rlls have been measured by the responding STA (110, 112, 114, 116, 118); a sub-field (420) comprising a bitmap indicating which metrics are measured and fed back by the responding STA (110, 112, 114, 116, 118).

17. The apparatus according to claim 15 or 16, wherein the Per-RLI Feedback Results Info set comprises at least the following fields: a sub-field (510) indicating an Element ID; a sub-field (512) indicating an Element ID Extension; a sub-field (514) indicating a length, Length; and one or more Per-RU Feedback Results Info fields (516).

18. The apparatus according to claim 17, wherein the amount of info fields comprised in the set of Per-RU Feedback Results Info fields (516) is dependent at least on: a bandwidth of a channel, Channel Bandwidth; the size of a RU corresponding to the Measured Metrics; the bitmap indicating which RUs were measured by the responding STA (110, 112, 114, 116, 118); wherein a valid RU index is set to 1 , indicating the RUs to which the measured metrics refer.

19. The apparatus according to claim 17 or 18, wherein each of the Per-RU Feedback Results Info fields (516) comprises at least the following sub-fields: a sub-field (610) indicating an index of the RU, RU index; a sub-field (614) indicating a set of PHY rates for which each reported metric was measured; a sub-field (612) containing a number M indicating the number of PHY rates included in the PHY Rate Index set, where M is an integer in the range of 0 - 15; and a sub-field (616-1 , ... , 616-k) containing k sets of Measured Metrics, where k is an integer larger than 0.

20. The apparatus according to claim 19, wherein for a set of measured metrics x, where x = 1 ,2,... ,k, the measured values of metric x are provided per PHY Rate indicated in the PHY Rate Index set (614), wherein the size of a sub-field representing each metric value is dependent on the measured metric type and is indicated as a nonzero value in the LAT feedback Control field (314) or in the Measured Metrics Info bitmap sub-field (420), wherein: a value of 01 indicates a size of the metric value being represented by one byte; a value of 10 indicates a size of the metric value being represented by two bytes.

21. The apparatus according to claim 19 or 20, wherein the number of erroneous bits per codeword serves as a measured metric, wherein valid values of the measured metric are integers in the range 0 - 254, wherein a value of 0 - 253 correspondingly indicates the number of erroneous bits, and wherein a value of 254 indicates at least 254 erroneous bits.

22. The apparatus according to any one of claims 19 to 21 , wherein invalid values corresponding to each measured metric are indicated by: a value of 255, if the metric value is represented by a one-byte sub-field; and a value of 65535, if the metric value is represented by a two-byte sub-field.

23. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and one or more responding STAs (110, 112, 114, 116, 118), wherein the soliciting STA (105) is configured to: transmit a LAT Announcement frame from the soliciting STA (105), to the one or more responding STAs (110, 112, 114, 116, 118), followed by a link adaptation physical layer protocol data unit, LAT-PPDU; transmit a dedicated trigger frame, TF, from the soliciting STA (105) to the one or more responding STAs (110, 112, 114, 116, 118), the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs (110, 112, 114, 116, 118), provided that the one or more responding STAs (110, 112, 114, 116, 118) have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; receive the LAT feedback frame (201) from the one or more responding STAs (110, 112, 114, 116, 118); wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.

24. An apparatus in a wireless local access network (100), WLAN, comprising a soliciting station, STA (105), and a responding STA (110, 112, 114, 116, 118), wherein the soliciting STA (105) is configured to: transmit a LAT Announcement frame from the soliciting STA (105) to the responding STA (110, 112, 114, 116, 118), followed by a link adaptation training physical layer protocol data unit, LAT-PPDU; receive, by the soliciting STA (105), a LAT feedback frame (201), the LAT feedback frame (201) transmitted from the responding STA (110, 112, 114, 116, 118) upon determining that a preceding LAT Announcement frame received by the responding STA (110, 112, 114, 116, 118) includes only a single per station information, Per-STA Info, intended for the respective responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field indicating an Action Category; and a field indicating an Action Category value corresponding to the Action Category.

25. A computer program product comprising program code for performing the method according to any one of the preceding claims 1 to 12 when executed on a computer or a processor.

26. A non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the method of any one of claims 1 to 12.

27. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and one or more responding STAs (110, 112, 114, 116, 118), comprising a transmitting unit (3501), respectively, wherein the transmitting unit (3501) is configured to: transmit a LAT feedback frame (201) to the soliciting STA (105), by the one or more responding STAs (110, 112, 114, 116, 118), wherein the transmissions starts a predefined inter frame space, IFS, after each of the responding STAs received a dedicated trigger frame, TF, intended for the respective responding STA from the soliciting STA, and wherein the TF followed a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was preceded by a LAT Announcement frame which was determined by the respective responding STA to include per station information, Per-STA Info, intended for the respective responding STA; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.

28. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and a STA (110, 112, 114, 116, 118), comprising a transmitting unit (3502), respectively, wherein the transmitting unit (3502) is configured to: transmit a LAT feedback frame (201) to the soliciting STA (105) by the responding STA (110, 112, 114, 116, 118), wherein the transmission starts a predefined inter frame space, IFS, after the responding STA completed the reception of a link adaptation training physical layer protocol data unit, LAT-PPDU, wherein the LAT-PPDU was received after the responding STA determined that a preceding LAT Announcement frame includes only a single per station information, Per-STA Info, intended for the responding STA; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.

29. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and one or more responding STAs (110, 112, 114, 116, 118), wherein the soliciting STA (105) comprises: a transmitting unit (4501) configured to: transmit a LAT Announcement frame from the soliciting STA (105), to the one or more responding STAs (110, 112, 114, 116, 118), followed by a link adaptation physical layer protocol data unit, LAT-PPDU, and transmit a dedicated trigger frame, TF, from the soliciting STA (105) to the one or more responding STAs (110, 112, 114, 116, 118), the dedicated TF triggering transmission of a LAT feedback frame after a predefined inter frame space, IFS, the LAT feedback frame being transmitted by the one or more responding STAs (110, 112, 114, 116, 118), provided that the one or more responding STAs (110, 112, 114, 116, 118) have been included in the per station information, Per-STA Info, intended for the respective responding STA, in the LAT Announcement frame; a receiving unit (4503) configured to receive the LAT feedback frame (201) from the one or more responding STAs (110, 112, 114, 116, 118); wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.

30. An apparatus in a wireless local access network, WLAN, comprising a soliciting station, STA (105), and a responding STA (110, 112, 114, 116, 118), wherein the soliciting STA (105) comprises: a transmitting unit (4502) configured to transmit a LAT Announcement frame from the soliciting STA to the responding STA, followed by a link adaptation training physical layer protocol data unit, LAT-PPDU; a receiving unit (4504) configured to receive a LAT feedback frame (201), the LAT feedback frame (201) transmitted from the responding STA (110, 112, 114, 116, 118) upon determining that a preceding LAT Announcement frame received by the responding STA (110, 112, 114, 116, 118) includes only a single per station information, Per-STA Info, intended for the responding STA and followed by a link adaptation training physical layer protocol data unit, LAT-PPDU, after a predefined inter frame space, IFS; wherein the LAT feedback frame (201) is a management frame of an “Action No Ack” subtype, wherein the LAT feedback frame (201) comprises a frame body (212), wherein the frame body (212) comprises: a field (310) indicating an Action Category; and a field (312) indicating an Action Category value corresponding to the Action Category.