Triggered sounding NDP

Abstract

The present disclosure relates to a method of uplink sounding signal triggered by an access point, AP, comprising the steps of: transmitting, by the AP, a trigger signal to one or more stations, STAs, to trigger transmission of a respective sounding signal from at least one of the one or more STAs in response to the trigger signal; receiving, by the AP, the respective sounding signal from the at least one STA; determining, by the AP, a precoder to be used by the at least one STA based on the respective sounding signal and transmitting corresponding precoder information to the at least one STA for data transmission; wherein the trigger signal comprises a null data packet announcement, NDPA, signal or a null data packet request, NDPR, signal and the sounding signal comprises a triggered sounding null data packet, NDP, signal; wherein the triggered sounding NDP signal is based on a trigger-based TB physical protocol data unit, PPDU, frame without payload or a very high throughput, EHT, multi-user, MU, PPDU frame without payload; and wherein a U-SIG portion of the TB PPDU frame or the EHT MU PPDU frame of the triggered sounding NDP signal comprises parameters indicating the triggered NDP transmission.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for uplink sounding signal triggering. BACKGROUND

[0002] Beamforming (BF) is widely used in Wi-Fi communications as a successful technique to improve performance in MIMO scenarios. Beamforming is a process by which a transmitting sender of a transmission can send a signal in a preferred direction to a receiver to improve the signal-to-noise ratio and transmission speed. In general, beamforming can be divided into two main types. Explicit beamforming is based on exchanging information about the characteristics of the radio channel between the sender and the receiver to extract improved performance from the radio channel based on channel quality measurements, while in implicit beamforming, a measurement frame is sent by a beam receiver, not a beamformer. The beamformer detects this frame and uses it for channel estimation, assuming reciprocity between the downlink channel and the uplink channel. The baseband digital signal varies according to the channel. Since 802.11n, beamforming has been supported.

[0003] In 802.11n, multiple sounding mechanisms are defined to support BF operation (e.g., implicit sounding using uplink signals, assuming reciprocity to determine beamforming weights or precoders; and explicit sounding transmitting dedicated signals so that the intended receiver (i.e., the beam receiver) calculates the precoding weights).

[0004] Beamforming in 802.11n requires both devices to implement the mutually recognized beamforming function. 802.11ac specifies that the access point (AP) has up to eight spatial streams, compared to four spatial streams specified in 802.11n. Multiple spatial streams can be used to send to multiple clients simultaneously.

[0005] In 802.11ac and 802.11ax, explicit sounding is the only mechanism defined to support BF operation.

[0006] Both downlink (DL) and uplink (UL) support beamforming.

[0007] DL beamforming is completely managed by the access point (AP), while the precoder can be adjusted according to the currently scheduled transmission. Different transmission schemes can require different precoders to achieve better performance. The AP will collect feedback information from different stations and can calculate the relevant precoder optimized for a specific packet.

[0008] In UL, the same procedure is applied, while the station (STA) acts as the beamformer and thus triggers the procedure and collects precoder feedback from the beam receiver (here the AP). This means that the STA holds the precoder information and decides when to apply which precoder.

[0009] According to existing protocols in 802.11ax, UL BF is supported by the STA sending a Null Data Packet, NDP, announcement (NDP-A) frame before the NDP, followed by an AP response with a beamforming report (BFR).

[0010] A new feature in 802.11ax (compared to earlier 802.11 standards) is the introduction of a Trigger Frame (TF) that instructs the intended receiver (typically a STA) to transmit in response to receiving the TF.

[0011] However, there is a lack of suitable formats for UL BF using triggered transmissions. SUMMARY

[0012] In view of the above, it is an object of the present disclosure to at least partly overcome the above-mentioned drawbacks and to enable setting of Tx parameters for a TB PPDU for a triggered sounding NDP in UL by the AP.

[0013] The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are evident from the dependent claims, the description and the attached drawings.

[0014] According to a first aspect, a method of uplink sounding signal triggered by an access point (AP) is provided, the method comprising the steps of: transmitting, by the AP, a trigger signal to one or more stations (STAs), thereby triggering transmission of a respective sounding signal from at least one of the one or more STAs in response to the trigger signal; receiving, by the AP, the respective sounding signal from the at least one STA; and determining, by the AP, a precoder to be used by the at least one STA based on the respective sounding signal and transmitting corresponding precoder information to the at least one STA for data transmission; wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the sounding signal comprises a triggered sounding Null Data Packet (NDP) signal; wherein the triggered sounding NDP signal is based on a payload-less Trigger Based (TB) Physical Protocol Data Unit (PPDU) frame or a payload-less Extremely High Throughput (EHT) Multi User (MU) PPDU frame; and wherein a U-SIG portion of the TB PPDU frame or the EHT MU PPDU frame of the triggered sounding NDP signal comprises a parameter indicating a triggered NDP transmission. Here, an optional EHT-SIG portion of the EHT MU PPDU frame of the triggered sounding NDP signal can be omitted.

[0015] The present disclosure provides a U-SIG portion of a TB PPDU or a U-SIG portion of an EHT MU PPDU frame of a triggered sounding NDP signal, the U-SIG portion comprising a parameter indicating a triggered NDP transmission. Thus, the AP can learn that the transmission is a triggered NDP transmission. The "triggered sounding NDP" signal is a new format of signal, which is different from the conventional sounding NDP signal. When using the new format of triggered sounding NDP (a variant of the existing PPDU type), no payload is involved, and STA identification can be done by using the physical properties of the transmitted signal (e.g. the power of the estimated channel per trigger source).

[0016] According to implementations, the PPDU type of the triggered sounding NDP signal - TB PPDU or EHT MU PPDU, and / or the PPDU type and compression mode field in the U-SIG part of the PPDU can be indicated. Here, Option 1 is a new variant of TB PPDU type with different U-SIG design, and Option 2 is a new variant of EHT MU PPDU with different U-SIG design and optional EHT-SIG field (redundant for triggered transmission). Both options enable the following properties: ensure all STAs transmit the same preamble content, identify that this is a requested NDP transmission (avoid hidden nodes or interferers), and allow the AP to reuse the detector of TB PPDU.

[0017] According to implementations, the PPDU type and compression mode field can be set to 2 or 3.

[0018] According to implementations, the PPDU type and compression mode field can be set to 0, and B2 of U-SIG-2 is set to 1 to indicate triggered sounding NDP.

[0019] According to implementations, the PPDU type and compression mode field can be set to 0, and the combination of 11 ignored bits of U-SIG can be used to indicate triggered sounding NDP.

[0020] According to implementations, the U-SIG part of the triggered sounding NDP signal can include an UL / DL field that can be set to 1.

[0021] According to implementations, the U-SIG part of the triggered sounding NDP signal can include a spatial reuse field that is reserved or set to not allowed, such that spatial reuse is not allowed when the triggered NDP transmission is indicated.

[0022] According to implementations, the bandwidth (BW) indicated in the U-SIG part of the triggered sounding NDP can be the same as the BW indicated by the NDPA or NDPR trigger signal.

[0023] According to implementations, the punctured channel information field of the U-SIG part can be reserved.

[0024] According to implementations, the EHT-SIG symbol number indication field of the U-SIG part can be reserved.

[0025] According to the U-SIG design of Option 1 of the Trigger Based NDP as an EHT TB PPDU variant, one or more changes to the U-SIG design can be introduced as defined in the above implementation manners: UL / DL shall be set to “1”, and / or BW shall be the same as indicated by NDPR, and / or if a Triggered NDP is indicated, spatial reuse is not allowed, thus the spatial reuse field can be set to “not allowed” or can be reserved.

[0026] According to the U-SIG design of Option 2 of the Trigger Based NDP as an EHT MU PPDU variant, one or more changes to the U-SIG design can be introduced as defined in the above implementation manners: a Triggered NDP does not need to punch a channel information - i.e. the field is reserved, and / or the EHT-SIG number of symbols is always 1 - i.e. the field is reserved, and / or UL / DL is set to “1”, and / or BW is the same as indicated by NDPR.

[0027] According to a second aspect, there is provided a method of uplink sounding signal triggering performed by a station (STA), the method comprising the steps of: receiving, by the STA, a trigger signal from an access point (AP); in response to the trigger signal, transmitting, from the STA, a sounding signal to the AP; receiving, by the STA, from the AP, precoder information corresponding to a precoder to be used by the STA for data transmission determined by the AP based on the sounding signal; wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the sounding signal comprises a Trigger Based (TB) Null Data Packet (NDP) signal; wherein the Trigger Based NDP signal is based on a TB Physical Protocol Data Unit (PPDU) frame without payload or an Extremely High Throughput (EHT) Multi User (MU) PPDU frame without payload; and wherein a U-SIG part of the TB PPDU or EHT MU PPDU frame of the Trigger Based NDP signal comprises a parameter indicating a Triggered NDP transmission.

[0028] The explanations and advantages provided above apply here. To avoid repetition, these will be omitted here and in the following.

[0029] According to an implementation, the PPDU type of the trigger-based sounding NDP signal, TB PPDU or EHT MU PPDU, and / or PPDU variant can be indicated in the PPDU type and compression mode field in the U-SIG portion.

[0030] According to an implementation, the PPDU type and compression mode field can be set to 2 or 3.

[0031] According to an implementation, the PPDU type and compression mode field is set to 0, and B2 of U-SIG-2 can be set to 1 to indicate a trigger-based sounding NDP.

[0032] According to an implementation, the PPDU type and compression mode field can be set to 0, and a combination of 11 ignored bits of U-SIG can be used to indicate a trigger-based sounding NDP.

[0033] According to an implementation, the U-SIG portion of the trigger-based sounding NDP signal can include a UL / DL field set to 1.

[0034] According to an implementation, the U-SIG portion of the trigger-based sounding NDP signal can include a spatial reuse field that is reserved or set to not allowed, such that spatial reuse is not allowed when the trigger-based NDP transmission is indicated.

[0035] According to an implementation, a bandwidth (BW) indicated in the U-SIG portion of the trigger-based sounding NDP can be the same as a BW indicated by an NDPA or NDPR trigger signal.

[0036] According to an implementation, a punctured channel information field of the U-SIG portion can be reserved.

[0037] According to an implementation, an EHT-SIG number of symbols indication field of the U-SIG portion can be reserved.

[0038] According to a third aspect, a method of uplink sounding signal triggering performed by an access point (AP) is provided, the method comprising the steps of: transmitting, by the AP, a trigger signal to one or more stations (STAs), thereby triggering transmission of a respective sounding signal from at least one of the one or more STAs in response to the trigger signal; receiving, by the AP, the respective sounding signal from the at least one STA; and determining, by the AP, a precoder to be used by the at least one STA based on the respective sounding signal, and transmitting corresponding precoder information to the at least one STA for data transmission; wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the sounding signal comprises a trigger-based sounding Null Data Packet (NDP) signal; wherein the trigger-based sounding NDP signal is based on an Extremely High Throughput (EHT) Trigger Based (TB) Physical Protocol Data Unit (PPDU) frame comprising a data portion; and wherein the EHT TB PPDU frame transmits K spatial streams (SSs) in an EHT Long Training Field (LTF) portion and N SSs in the data portion, the EHT TB PPDU frame being configured to allow K to be independent of N.

[0039] Thus, the present disclosure allows the EHT TB PPDU frame to be configured to allow the number K of spatial streams (SSs) in the EHT Long Training Field (LTF) portion to be independent of the number N of SSs in the data portion. In other words, the number N does not define the number K by a fixed relationship.

[0040] Such a modification of the TB PPDU transmission rule supports a case where the number of transmit (Tx) antennas is larger than the number of supported SSs.

[0041] According to an implementation, the number K of spatial streams (SSs) in the EHT Long Training Field (LTF) portion can depend on the number M of transmit antennas.

[0042] According to an implementation, the EHT LTF portion can include EHT LTF OFDM symbols, a number K of EHT LTF OFDM symbols is according to a number K of transmit antennas indicated by the at least one STA in the capability report.

[0043] According to an implementation, the AP can indicate through the NDPA signal which subset of transmit antennas the at least one STA is to use for transmission.

[0044] According to an implementation, the triggered sounding NDP can be received by the AP from a subset of transmit antennas of the at least one STA.

[0045] According to an implementation, a PPDU type of the triggered sounding NDP signal - EHT MU PPDU, and / or a PPDU variant can be indicated in a PPDU type and compression mode field in the U-SIG portion.

[0046] According to an implementation, the PPDU type and compression mode field can be set to 2 or 3.

[0047] According to an implementation, the PPDU type and compression mode field can be set to 0 and B2 of U-SIG-2 can be set to 1 to indicate a triggered sounding NDP.

[0048] According to an implementation, the PPDU type and compression mode field can be set to 0 and a combination of 11 ignored bits of U-SIG can be used to indicate a triggered sounding NDP.

[0049] Accordingly, in this aspect, and according to Option 1, a new variant of TB PPDU type is provided, where the number of SS in the EHT LTF (K) is independent of the number of SS in the data portion (N) from each other. In an exemplary case, the data portion will be transmitted with a single SS (N = 1) that is duplicated for all antennas, while K will depend on the number of Tx antennas indicated by the STA in the capability report.

[0050] According to Option 2, a new variant of TB PPDU type is provided, where the selected Tx antennas are indicated by the NDPR. The AP can indicate which subset of Tx antennas should be used for transmission, and the STA will transmit using the indicated subset (in this case, K can be smaller than or equal to the number of supported SS for data transmission).

[0051] According to a fourth aspect, there is provided a method of uplink sounding signal triggering performed by a station (STA), the method comprising the steps of: receiving, by the station (STA), a trigger signal from an access point (AP); in response to the trigger signal, transmitting, from the STA to the AP, a sounding signal; and receiving, by the STA from the AP, precoder information corresponding to a precoder to be used by the STA for data transmission determined by the AP based on the sounding signal; wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the sounding signal comprises a Trigger Based (TB) Null Data Packet (NDP) signal; wherein the trigger based sounding NDP signal is based on an Extremely High Throughput (EHT) TB Physical Protocol Data Unit (PPDU) frame comprising a data portion; and wherein the EHT TB PPDU frame transmits K spatial streams (SSs) in an EHT Long Training Field (LTF) portion and N SSs in the data portion, the EHT TB PPDU frame being configured to allow K to be independent of N.

[0052] The above-described explanations and advantages are applicable here. To avoid repetition, these will be omitted here and below.

[0053] According to an implementation, the number K of spatial streams (SSs) in the EHT Long Training Field (LTF) portion depends on the number M of transmit antennas.

[0054] According to an implementation, the EHT LTF portion comprises EHT LTF OFDM symbols, the number K of EHT LTF OFDM symbols being dependent on the number K of transmit antennas indicated by the at least one STA in the capability report.

[0055] According to an implementation, the AP can indicate by the NDPA signal which subset of transmit antennas the at least one STA is to use for transmission.

[0056] According to an implementation, the triggered sounding NDP can be received by the AP from a subset of transmit antennas of the at least one STA.

[0057] According to an implementation, the PPDU type of the triggered sounding NDP signal, EHT MU PPDU, and / or PPDU variant can be indicated in the PPDU type and compression mode field in the U-SIG part.

[0058] According to an implementation, the PPDU type and compression mode field can be set to 2 or 3.

[0059] According to an implementation, the PPDU type and compression mode field can be set to 0 and B2 of U-SIG-2 can be set to 1 to indicate triggered sounding NDP.

[0060] According to an implementation, the PPDU type and compression mode field can be set to 0 and the combination of 11 ignored bits of U-SIG can be used to indicate triggered sounding NDP.

[0061] According to a fifth aspect, there is provided an access point, AP, comprising processing circuitry configured to perform the method of uplink sounding signal triggering by the above-mentioned access point, AP, or any implementation thereof.

[0062] According to a sixth aspect, there is provided a station, STA, comprising processing circuitry configured to perform the method of uplink sounding signal triggering by the above-mentioned station, STA, or any implementation thereof.

[0063] According to a seventh aspect, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the above-mentioned methods of uplink sounding signal triggering.

[0064] According to a sixth aspect, there is provided a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out any of the above-mentioned methods of uplink sounding signal triggering. BRIEF DESCRIPTION OF DRAWINGS

[0065] In the following, embodiments of the present disclosure are described in more detail with reference to the accompanying drawings, in which:

[0066] Figure 1 An uplink, UL, beamforming scheme is illustrated.

[0067] Figure 2 An EHT NDP format is shown.

[0068] Figure 3A And Figure 3B A PPDU type and variant indication is shown.

[0069] Figure 4 A TB ranging NDP in 802.11az is shown.

[0070] Figure 5 An EHT TB PPDU variant for triggered sounding NDP is shown.

[0071] Figure 6 An EHT MU PPDU variant for triggered sounding NDP is shown.

[0072] Figure 7 A method according to the first aspect performed by an AP is shown.

[0073] Figure 8 A U-SIG design for new TB PPDU variant is shown.

[0074] Figure 9 A U-SIG design for new EHT MU PPDU variant is shown.

[0075] Figure 10 A method according to the second aspect performed by a STA is shown.

[0076] Figure 11 A method according to the third aspect performed by an AP is shown.

[0077] Figure 12 A U-SIG design for new EHT TB PPDU variant is shown.

[0078] Figure 13 A method according to the fourth aspect performed by a STA is shown.

[0079] Figure 14 A Tx antenna PHY element is shown.

[0080] Figure 15 An AP according to the fifth aspect is shown.

[0081] Figure 16 A STA according to the sixth aspect is shown.

[0082] Figure 17 Simulation results are shown. DETAILED DESCRIPTION

[0083] In the following description, reference is made to the accompanying drawings which form a part hereof, and which are shown by way of illustration of the specific aspects or embodiments of the present disclosure. It is understood that the aspects of the present disclosure can be used in other aspects, and that structural or logical changes can be made without departing from the scope of the present disclosure. 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.

[0084] For example, it is understood that the disclosure in relation to a described method also applies to a corresponding device or system configured to perform the method, and vice versa. For example, if one or more specific method steps are described, a corresponding device can include one or more units, e.g. functional units, for performing the described one or more method 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 more units, e.g. functional units, a corresponding method can include one step performed by the one or more units (e.g. one step performs the functionality of the one or more units, or a plurality of steps each performs the functionality of one or more of the units), even if such one or more 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 can be combined with each other, unless explicitly stated otherwise.

[0085] Further implementation details and advantages over the prior art will be described below.

[0086] Figure 1A general concept 100 of initializing data upload from one or more stations (STAs) 111, 112, 113 to an Access Point (AP) 121 is shown, which starts with a Null Data Packet Request Trigger Frame (NDPR TF) 131 sent by the AP 121 to the STAs 111, 112, 113 and the corresponding Null Data Packets (NDPs) 141, 142, 143 sent by one or more STAs 111, 112, 113 to the AP 121 in response. The NDPs 141, 142, 143 are packets containing a preamble including a Long Training Field (LTF) and can be used to estimate the physical channel between the AP 121 and the STAs 111, 112, 113. The NDPs 141, 142, 143 can be sent simultaneously by several STAs 111, 112, 113. To perform beamforming, the AP 121 uses these NDP signals 141, 142, 143 to determine precoding information. Thereafter, a basic TF 132 including a Beamforming Report (BFR) is sent to the STAs 111, 112, 113. The basic TF 132 is a frame carrying beamforming / precoding information such as precoding vectors or matrices, SNR corresponding to each precoder, etc. Upon receiving the basic TF 132, the STAs 111, 112, 113 start sending beamformed data 151, 152, 153 in the UL to the AP 121. The AP 121 acknowledges the reception of data blocks using Block Data Acknowledgement (BA) frames 133.

[0087] According to the prior art, a Null Data Packet (NDP) can be used as a frame for sounding procedures, which is transmitted by the same source that transmitted the NPD announcement (NDPA) frame immediately after the NPD announcement (NDPA) frame. The structure of an EHT NDP belongs to the EHT MU PPDU type, which is mainly used for transmissions that are not requested by the receiver (i.e. non-triggered transmissions). A PHY Protocol Data Unit (PPDU) that is transmitted in response to receiving a trigger frame (TF) is called a Trigger-Based (TB) PPDU. A STA 111, 112, 113 that is triggered to transmit in the UL is called a triggered STA. In a TB PPDU transmission, all transmit (Tx) parameters of the TB PPDU are set by the AP 121 and the AP 121 identifies each transmitter 111, 112, 113 via the decoded payload (e.g. MAC header).

[0088] As shown in Figure 2 The EHT NDP preamble 200 comprises a Universal Signal (U-SIG) 210 and an Extremely High Throughput Signal (EHT-SIG) 220, wherein the EHT-SIG 220 has only U-SIG overflow bits 211 (bits that belong to the U-SIG 210 but are located at the EHT-SIG 220 due to the limited U-SIG size).

[0089] Furthermore, in 802.11be (EHT), there are two main PPDU types: the EHT MU PPDU type and the TB PPDU type. All PPDUs are transmitted using one of these types. In addition, EHT defines several variants of these types. Variants reuse the same structure of the PPDU type, but can differ in the meaning of specific fields or the number of specific parameters.

[0090] Figure 3A and Figure 3BThe EHT PPDU type and variant is shown to be indicated in the U-SIG of the SIG field information 310 by a field named PPDU type and compression mode 311 (two bits) and a field named DL / UL (one bit) 312. Download is indicated by “0” represented by 312a and upload by “1” represented by 312b. For upload, the PPDU type and compression mode field values “0” represented by 311a and “1” represented by 311b indicate the PPDU types EHT TB and EHT MU, respectively, while the values “2” and “3” represented by 311c are not used at present.

[0091] As outlined above with reference to Figure 1 In the UL BF, the NDPs 141, 142, 143 are transmitted by the STAs 111, 112, 113 triggered by the AP 121. However, there is a difference between the current TB PPDU properties and the NDP format as outlined below.

[0092] At present, the TB PPDU has two main properties, namely (i) all Tx parameters are set by the AP 121 - this ensures alignment between all STAs 111, 112, 113 and thus the preamble of the TB PPDU can be detected by a third receiver and since the AP defines these parameters, the detection of the preamble can be skipped; and (ii) the AP 121 identifies each transmitter 111, 112, 113 via the decoded payload (e.g. MAC header), i.e. the successful reception of the data payload transmitted by the STAs 111, 112, 113 enables the AP 121 to identify the transmitter with a very low probability of error.

[0093] However, the current format of the NDP does not enable the same properties in the case of the UL BF with the AP 121 triggering a multi-user NDP transmission.

[0094] Therefore, it is desirable to have a new NDP design or alternative solution which enables the same properties in the UL BF triggered sounding NDP.

[0095] In the 802.11az standard, a TB PPDU is used and the AP 121 triggers multiple STAs 111, 112, 113 to transmit an NDP frame, while the STAs 111, 112, 113 transmit a TB PPDU without payload. Figure 4 An NDP frame 400 in the form of a TB PPDU 400 without data field is shown.

[0096] While the TB PPDUs without payload enable alignment between STAs 111, 112, 113, the TB PPDUs 400 without payload have the drawback that there is no robust STA 111, 112, 113 identification (which is less important for the purpose of 802.11az) making the TB PPDUs of 802.11az less robust in terms of beamforming.

[0097] Therefore, it can be seen that the format adopted by 802.11az does not provide the required properties.

[0098] A simple approach that can be considered in this regard is to use a regular TB PPDUs with some short payload instead of NDP. This can solve the identification problem and the alignment problem between STAs 111, 112, 113.

[0099] However, this approach has drawbacks and related problems. Some STAs 111, 112, 113 can have more transmit antennas than the number of spatial streams (SS) supported in UL TB transmission. The TB PPDUs format forces the number of SS in the EHT LTF part to be equal to the number of SS in the data part. Therefore, such STAs 111, 112, 113 cannot transmit from all Tx antennas. This results in partial channel matrix estimation at the AP and thus inaccurate beamforming precoders.

[0100] It can be seen that there are several formats that provide partial solutions to the problem, however, in order to fully achieve the targeted properties of alignment and identification, the present disclosure proposes to modify / change the design of the NDP and TB PPDUs.

[0101] Figure 5 A regular preamble 500 of a TB PPDUs with a U-SIG field 510 is shown. Furthermore, Figure 6 A regular preamble 600 of a TB PPDUs with a U-SIG field 610 and an optional EHT-SIG field 620 (redundant for triggered transmissions) is shown.

[0102] According to the present disclosure, the regular preamble of the TB PPDUs is reused since the partial fields are not relevant and can be redesigned for UL BF.

[0103] The main idea of the present disclosure is a new format of triggered NDP and TB PPDUs that can support the requirements of the UL BF protocol.

[0104] Two general possibilities are disclosed. The methods according to the first and second aspects provide a new format (a variant of the existing PPDU type) for triggered sounding NDP (in which there is no payload and STA identification can be done by the power of the estimated channel per triggered source (Spatial Stream, SS), see also Figure 17 and the description related below). The methods according to the third and fourth aspects provide a modification of the TB PPDU transmission rules to support the case where the number of Tx antennas is greater than the number of supported SSs.

[0105] Both methods provide a solution to the above-mentioned problem.

[0106] Figure 7 (see also Figure 1 , Figure 8 and Figure 9 ) shows a general formulation of a method according to the first aspect of the disclosure, performed by an access point (AP) 121, of uplink sounding signal triggered according to the first aspect, comprising the following steps:

[0107] 701 : transmitting, by the AP 121, a trigger signal to one or more stations (STAs) 111, 112, 113, thereby triggering transmission of a respective sounding signal from at least one of the one or more STAs 111, 112, 113 in response to the trigger signal;

[0108] 702: receiving, by the AP 121, the respective sounding signal from the at least one STA 111, 112, 113; and

[0109] 703: determining, by the AP 121, a precoder to be used by the at least one STA 111, 112, 113 based on the respective sounding signal, and transmitting corresponding precoder information to the at least one STA 111, 112, 113 for data transmission;

[0110] 704: wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the probe signal comprises a Trigger Based (TB) Null Data Packet (NDP) signal; wherein the TB NDP signal is based on a TB Physical Protocol Data Unit (PPDU) frame 800 or an Extremely High Throughput (EHT) Multi User (MU) PPDU frame 900 without payload; and wherein a U-SIG portion 810, 910 of the TB PPDU or EHT MU PPDU frame of the trigger based probe NDP signal comprises parameters indicating the trigger based NDP transmission.

[0111] The U-SIG portion 310, 311a, 510, 810 of the TB PPDU frame 500 of the trigger based probe NDP signal or the U-SIG portion 310, 311b, 610, 620, 910 of the EHT MU PPDU frame 600 comprises parameters indicating the trigger based NDP transmission (see Fig. 3, Figure 5 , Figure 6 , Figure 8 and Figure 9 ). Thus, the AP 121 can learn that this transmission is a trigger based NDP transmission. The “trigger based probe NDP” signal is a new format of signal, different from the conventional probe NDP signal. Using the new format of trigger based probe NDP (a variant of the existing PPDU type), no payload is involved and STA identification can be done by using the physical properties of the transmitted signal (e.g. the power of the estimated channel per trigger based source) (see Figure 17 ).

[0112] The advantage is to ensure that all STAs 111, 112, 113 transmit the same preamble content, identify that this is a requested NDP transmission (avoiding hidden nodes or interference), and enable the AP 121 to reuse the detector of the TB PPDU.

[0113] The general approach comprises two options, one option providing a new variant 500 of the TB PPDU type with a different U-SIG design 510 (e.g. based on Figure 5 ), the other option providing a new variant 600 of the EHT MU PPDU with a different U-SIG design 610 and an optional EHT-SIG field 620 (e.g. based onFigure 6 ).

[0114] Figure 8 A first embodiment is shown, related to a triggered sounding NDP 800 as an EHT TB PPDU variant. Several changes can be made to the U-SIG design 810, e.g. UL / DL 812 is set to “1” and BW 813 is the same as indicated by the NDPR. If a triggered NDP is indicated, no spatial reuse is allowed, so the spatial reuse field 814 can be set to “not allowed” or can be reserved. Field 811 indicates the PPDU mode and compression type.

[0115] Figure 9 A second embodiment is shown, related to a triggered sounding NDP 900 as an EHT MU PPDU variant. Field 911 indicates the PPDU mode and compression type. Several changes can be made to the U-SIG design 910, e.g. a triggered NDP does not need Puncturing Channel Information 915 so the corresponding field is reserved, the EHT-SIG number of symbols is always 1 and the corresponding field 916 is reserved, UL / DL 912 shall be set to “1” and BW 913 shall be the same as indicated by the NDPR.

[0116] Figure 10 (see also Figure 1 A general method of uplink sounding signal triggering by a STA 111, 112, 113 according to the second aspect is shown, comprising the following steps:

[0117] 1001 : receiving, by the STA 111, 112, 113, a trigger signal from an access point (AP) 121;

[0118] 1002: sending, from the STA 111, 112, 113, a sounding signal to the AP 121 in response to the trigger signal; and

[0119] 1003: receiving, by the STA 111, 112, 113, from the AP 121, precoder information corresponding to a precoder to be used by the STA 111, 112, 113 for data transmission, determined by the AP based on the sounding signal;

[0120] 1004: wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the probe signal comprises a Trigger Based (TB) Null Data Packet (NDP) signal; wherein the Trigger Based NDP signal is based on a payload-less TB Physical Protocol Data Unit (PPDU) frame 800 or a payload-less Extremely High Throughput (EHT) Multi User (MU) PPDU frame 900; and wherein a U-SIG portion 810, 910 of the TB PPDU or EHT MU PPDU frame of the Trigger Based NDP signal comprises parameters indicating the Trigger Based NDP transmission.

[0121] This corresponds to the general method according to the first aspect with the corresponding implementation Figure 8 and Figure 9 ) as described above.

[0122] Figure 11 A general method of uplink probe signal triggering by an AP 121 according to the third aspect is shown (see also Figure 1 and Figure 12 ) and comprises the following steps:

[0123] 1101 : transmitting, by the AP 121, a trigger signal to one or more stations (STAs) 111, 112, 113, thereby triggering transmission of a respective probe signal from at least one of the one or more STAs 111, 112, 113 in response to the trigger signal;

[0124] 1102: receiving, by the AP 121, the respective probe signal from the at least one STA 111, 112, 113; and

[0125] 1103: determining, by the AP 121, a precoder to be used by the at least one STA 111, 112, 113 based on the respective probe signal, and transmitting corresponding precoder information to the at least one STA 111, 112, 113 for data transmission;

[0126] 1104: wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the probe signal comprises a Trigger Based (TB) probe Null Data Packet (NDP) signal; wherein the TB probe NDP signal is based on an Extremely High Throughput (EHT) TB Physical Protocol Data Unit (PPDU) frame comprising a data portion; and wherein the EHT TB PPDU frame is configured to allow K spatial streams (SSs) 1250 in an EHT Long Training Field (LTF) portion and N SSs 1260 in the data portion, independently of each other.

[0127] This provides a new variant of a TB PPDU with payload.

[0128] As mentioned above, the problem with a TB PPDU (which comprises a payload) is that it is currently not possible to transmit different numbers of SSs in the EHT LTF portion and the data portion. Here, it is proposed to reuse the main format of the TB PPDU.

[0129] As Figure 12 illustrated, a first option involves a new variant 1200 of the TB PPDU type, where the number of spatial streams (SSs) of the EHT LTF portion and the data portion is different (K SSs for the EHT LTF portion, reference 1250; N SSs for the data portion, reference 1260). The number K and the number N can be chosen independently. In an example, the data portion can be transmitted with a single SS (N = 1) which is copied for all antennas, while K will depend on the number of Tx antennas indicated by the STA in the capability report. A second option involves a new variant of the TB PPDU type, where the selected Tx antennas are indicated by the NDPR. The AP can indicate which subset of Tx antennas should be used for the transmission, and the STA will transmit using the indicated subset (in this case, K can be smaller than or equal to the number of supported SSs for data transmission).

[0130] Figure 13 It is shown (see also Figure 1 and Figure 12) The general method of uplink sounding signal triggering performed by a STA according to the fourth aspect comprises the following steps:

[0131] 1301 : receiving, by a station (STA) 111, 112, 113, a trigger signal from an access point (AP) 121;

[0132] 1302: in response to the trigger signal, transmitting, from the STA 111, 112, 113, a sounding signal to the AP 121; and

[0133] 1303: receiving, by the STA 111, 112, 113, from the AP 121, precoder information corresponding to a precoder to be used by the STA 111, 112, 113 for data transmission determined by the AP 121 based on the sounding signal;

[0134] 1304: wherein the trigger signal comprises a Null Data Packet Announcement (NDPA) signal or a Null Data Packet Request (NDPR) signal, and the sounding signal comprises a Trigger Based (TB) Physical Protocol Data Unit (PPDU) frame comprising a data portion; and wherein the TB PPDU frame is an Extremely High Throughput (EHT) TB PPDU frame configured to allow K spatial streams (SSs) 1250 to be transmitted in an EHT Long Training Field (LTF) portion and N SSs 1260 to be transmitted in a data portion, K and N being independent.

[0135] However, this corresponds to the method performed by a STA 111, 112, 113 according to the third aspect.

[0136] As Figure 3A and Figure 3BAs shown and described above, the PPDU type and variant are indicated by the PPDU type and compression mode field 311 in the U-SIG 310. In this disclosure, several options are proposed for indicating the new variants. The DL / UL 312b is set to 1, and the same indication can be used for the relevant PPDU type for all aspects. These options include (i) a new value for the PPDU type and compression mode field - e.g., setting the PPDU type and compression mode field to "2" (or "3"); (ii) the U-SIG validation bit - setting the PPDU type and compression mode field to "0" and setting B2 of U-SIG-2 to "1" - can also be set to "1" in the NDPR; and (iii) a special ignore bit combination - setting the PPDU type and compression mode field to "0" and using a special combination of the 11 ignore bits of U-SIG for trigger-based NDP - can be set by the NDPR or TF and copied to the TB U-SIG.

[0137] To support accurate UL BF, the AP 121 needs to know the number of Tx antennas equipped by the STAs 111, 112, 113. Therefore, referring to Figure 14 , it is proposed to add a new PHY element 1400 to the capability report.

[0138] If the antenna selection option is used, the AP 121 needs to indicate the subset of Tx antennas used for the current sounding transmission. This can be achieved by the following two options. The first option is to indicate the first antenna index and 4 bits for indicating the number of antennas (8 bits in total). According to the second option, all Tx antennas can be divided into groups of 2, 4, or 8 antennas, and the AP 121 indicates the current group index. 2 bits are needed to indicate the group size, and 4 bits are needed to indicate the group index. For example, if divided into groups of 2 antennas, and when the AP 121 wants the STAs 111, 112, 113 to use antennas 5, 6 (3rdgroup), "00" can indicate the size of 2, and "0011" can indicate the 3rdgroup.

[0139] Figure 15 An access point (AP) 1500 according to a fifth aspect is shown. The AP 1500 comprises processing circuitry 1501 configured to perform the method of uplink sounding signal triggering according to the first aspect or the third aspect.

[0140] Figure 16 A station (STA) 1600 according to a sixth aspect is shown. The STA 1600 comprises processing circuitry 1601 configured to perform the method of uplink sounding signal triggering according to the second aspect or the fourth aspect.

[0141] The power of the estimated channel has been simulated to identify the capabilities of the STAs 111, 112, 113, 1600. The main idea is that if a STA 111, 112, 113, 1600 transmits a signal, the power of the estimated channel will be high. Otherwise, the power will be low. Thus, by setting an adjusted threshold, it is possible to identify which STAs 111, 112, 113, 1600 transmitted a signal and which did not.

[0142] The idea is to compare the power of the estimated channel, averaged over all subcarriers, with the average RSSI of the received signal (the triggered signal should exceed the threshold).

[0143] Two different scenarios at 20MHz have been simulated:

[0144] • Case 1: 2 STAs differ by 6dB

[0145] • Case 2: 2 STAs and an interfering signal have the same RSSI, and 1 STA has a low 6dB RSSI

[0146] • Both cases are simulated with CFO uniformly distributed in + / - 350Hz range, TGn-D channel and actual CHEST Figure 17 As can be seen in Table 1, in both cases, the weaker STA has a very good detection rate (100% at -1dB SNR), and there is no false positive with interference.

[0147] In summary, several benefits / motivations of the present disclosure are as follows:

[0148] • Solving the sounding NDP problem with several methods with minimal changes to the existing PPDU type

[0149] • The proposed solution efficiently solves the problem related to the UL BF procedure and enables to cover all possible scenarios

[0150] In several embodiments provided in the present application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other manners. For example, the described embodiments of the apparatus are merely exemplary. For example, the division of the units is merely logical function division, and can be other division in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections can be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units can be implemented in electronic, mechanical, or other forms.

[0151] Units described as separate units can be physically separate or can not be physically separate, and parts shown as units can be physical units or can not be physical units, can be located in one location, or can be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiments.

[0152] In addition, the functional units in the embodiments disclosed herein can be integrated into one processing unit, or each of the units can exist physically separately, or two or more units are integrated into one unit.

[0153] Abbreviations

[0154] • DL: Downlink

[0155] • UL: Uplink

[0156] • BF: Beamforming

[0157] • AP: Access Point

[0158] • PHY: Physical Layer

[0159] • MAC: Medium Access Control

[0160] • PPDU: PHY Protocol Data Unit

[0161] • STA: Station (which can be an AP STA or a non-AP STA)

[0162] • NDP: Null Data Packet, i.e., a packet containing a preamble (including a Long Training Field (LTF)) and used to estimate the physical channel between the beamformer and the beam receiver, so that the precoder can be calculated.

[0163] • NDPA: NDP Announcement, i.e., a frame sent before the NDP, indicating the format of the NDP (e.g., how many LTFs, which STAs need to respond, what parameters these STAs should use, etc.).

[0164] • BFR: Beamforming Report, i.e., a frame carrying beamforming / precoding information such as a precoding vector or matrix, an SNR corresponding to each precoder, etc.

[0165] • BA: Block-ACK: In 802.11, the receiver should usually respond to a data transmission by responding with an ACK; if multiple frames are sent within a single PPDU, each frame must be acknowledged

[0166] • TF: Trigger Frame: Introduced in 802.1 lax as a means to trigger one or more STAs to transmit simultaneously and synchronously with the triggering AP

[0167] The above-described embodiments are merely exemplary and complete disclosure is defined by the claims.

Claims

1. A method of uplink sounding signal triggering performed by an access point, AP, comprising: transmitting, by the AP, a trigger signal to one or more stations, STAs, triggering transmission of a respective sounding signal from at least one of the one or more STAs in response to the trigger signal; receiving, by the AP, the respective sounding signal from the at least one STA; and determining, by the AP, a precoder to be used by the at least one STA based on the respective sounding signal and transmitting corresponding precoder information to the at least one STA for data transmission; wherein the trigger signal comprises a null data packet announcement, NDPA, signal or a null data packet request, NDPR, signal and the sounding signal comprises a triggered sounding null data packet, NDP, signal; wherein the triggered sounding NDP signal is based on a trigger-based TB physical protocol data unit, PPDU, frame without payload or an extremely high throughput, EHT, multi-user, MU, PPDU frame without payload; and wherein a U-SIG portion of the TB PPDU frame or the EHT MU PPDU frame of the triggered sounding NDP signal comprises a parameter indicating a triggered NDP transmission. a PPDU type of the triggered sounding NDP signal is a TB PPDU or an EHT MU PPDU, and / or a PPDU type and compression mode field in the U-SIG portion indicates.

2. The method of claim 1, wherein, the PPDU type and compression mode field is set to 2 or 3.

3. The method of claim 2, wherein, the PPDU type and compression mode field is set to 0 and a B2 of U-SIG-2 is set to 1 to indicate a triggered sounding NDP.

4. The method of claim 2, wherein, the PPDU type and compression mode field is set to 0 and a combination of 11 ignored bits of U-SIG is used to indicate a triggered sounding NDP.

5. The method of claim 2, wherein, the U-SIG portion of the triggered sounding NDP signal comprises a UL / DL field set to 1.

6. The method according to one of claims 1 to 5, wherein, the U-SIG portion of the triggered sounding NDP signal comprises a spatial reuse field that is reserved or set to not allowed such that spatial reuse is not allowed when the triggered NDP transmission is indicated.

7. The method according to one of claims 1 to 6, wherein, a bandwidth, BW, indicated in the U-SIG portion of the triggered sounding NDP is the same as a BW indicated by a NDPA or NDPR trigger signal.

8. The method of any one of claims 1 to 7, wherein, a punctured channel information field of the U-SIG portion is reserved.

9. The method of any one of claims 1 to 8, wherein, an EHT-SIG number of symbols indication field of the U-SIG portion is reserved.

10. The method of any one of claims 1 to 9, wherein, 11. A method of uplink sounding signal triggering performed by a station, STA, comprising: receiving, by the STA, a trigger signal from an access point, AP; in response to the trigger signal, transmitting, by the STA, a sounding signal to the AP; receiving, by the STA, from the AP, precoder information corresponding to a precoder determined by the AP to be used by the STA based on the sounding signal for data transmission; ​ The trigger signal comprises a null data packet announcement (NDPA) signal or a null data packet request (NDPR) signal, and the probe signal comprises a trigger-based probe null data packet (NDP) signal. The trigger-based probe NDP signal is based on a trigger-based TB physical protocol data unit (PPDU) frame without payload or an extremely high throughput (EHT) multi-user (MU) PPDU frame without payload. The U-SIG portion of the trigger-based probe NDP signal comprises a parameter indicating a trigger-based NDP transmission.

12. The method of claim 11, wherein, The PPDU type and compression mode field in the U-SIG portion of the trigger-based probe NDP signal indicates a PPDU type and a compression mode.

13. The method of claim 12, wherein, The PPDU type and compression mode field is set to 2 or 3.

14. The method of claim 12, wherein, The PPDU type and compression mode field is set to 0, and a B2 of U-SIG-2 is set to 1 to indicate a trigger-based probe NDP.

15. The method of claim 12, wherein, The PPDU type and compression mode field is set to 0, and a combination of 11 ignored bits of U-SIG is used to indicate a trigger-based probe NDP.

16. The method according to one of claims 11 to 15, wherein, The U-SIG portion of the trigger-based probe NDP signal comprises a UL / DL field set to 1.

17. The method according to one of claims 11 to 16, wherein, The U-SIG portion of the trigger-based probe NDP signal comprises a spatial reuse field reserved or set to not allowed, such that spatial reuse is not allowed when indicating the trigger-based NDP transmission.

18. The method of any one of claims 11 to 17, wherein, A bandwidth (BW) indicated in the U-SIG portion of the trigger-based probe NDP is the same as a BW indicated by an NDPA or NDPR trigger signal.

19. The method of any one of claims 11 to 18, wherein, A punctured channel information field of the U-SIG portion is reserved.

20. The method of any one of claims 11 to 19, wherein, An EHT-SIG symbol number indication field of the U-SIG portion is reserved.

21. A method of uplink probe signal triggering performed by an access point (AP), comprising: sending, by the AP, a trigger signal to one or more stations (STAs), thereby triggering transmission of a respective probe signal from at least one of the one or more STAs in response to the trigger signal; receiving, by the AP, the respective probe signal from the at least one STA; and determining, by the AP, a precoder to be used by the at least one STA based on the respective probe signal, and sending corresponding precoder information to the at least one STA for data transmission; The trigger signal comprises a null data packet announcement (NDPA) signal or a null data packet request (NDPR) signal, and the probe signal comprises a trigger-based probe null data packet (NDP) signal. The trigger-based probe NDP signal is based on an extremely high throughput (EHT) trigger-based TB physical protocol data unit (PPDU) frame comprising a data portion. ​ wherein the EHT TB PPDU frame transmits K spatial streams (SSs) in an EHT long training field (LTF) portion and N SSs in the data portion, the EHT TB PPDU frame is configured to allow K to be independent of N.

22. The method of claim 21, wherein, The number K of spatial streams (SSs) in the EHT long training field (LTF) portion depends on the number M of transmit antennas.

23. The method of claim 21 or 22, wherein, The EHT LTF portion includes EHT LTF OFDM symbols, the number K of EHT LTF OFDM symbols is according to the number K of transmit antennas indicated by the at least one STA in a capability report.

24. The method of any one of claims 21-23, wherein, The AP indicates, through the NDPA signal, which subset of transmit antennas the at least one STA is to use for transmission.

25. The method of claim 24, wherein, The trigger-based sounding NDP is received by the AP from the subset of transmit antennas of the at least one STA.

26. The method of any one of claims 21 to 25, wherein, The PPDU type of the trigger-based sounding NDP signal, EHT MU PPDU, and / or the PPDU type and compression mode field in the U-SIG portion is indicated.

27. The method of any one of claims 21 to 26, wherein, The PPDU type and compression mode field is set to 2 or 3.

28. The method of any one of claims 21 to 27, wherein, The PPDU type and compression mode field is set to 0 and B2 of U-SIG-2 is set to 1 to indicate trigger-based sounding NDP.

29. The method of any one of claims 21 to 28, wherein, The PPDU type and compression mode field is set to 0 and the combination of 11 ignored bits of U-SIG is used to indicate trigger-based sounding NDP.

30. A method of uplink sounding signal triggering performed by a station (STA), comprising: receiving, by the station (STA), a trigger signal from an access point (AP); in response to the trigger signal, transmitting, from the STA, a sounding signal to the AP; and receiving, by the STA, precoder information from the AP corresponding to a precoder to be used by the STA for data transmission determined by the AP based on the sounding signal; wherein the trigger signal comprises a null data packet announcement (NDPA) signal or a null data packet request (NDPR) signal, and the sounding signal comprises a trigger-based sounding null data packet (NDP) signal; wherein the trigger-based sounding NDP signal is an extremely high throughput (EHT) trigger-based TB physical protocol data unit (PPDU) frame comprising a data portion; and wherein the EHT TB PPDU frame transmits K spatial streams (SSs) in an EHT long training field (LTF) portion and N SSs in the data portion, the EHT TB PPDU frame is configured to allow K to be independent of N.

31. The method of claim 30, wherein, The number K of spatial streams (SSs) in the EHT long training field (LTF) portion depends on the number M of transmit antennas.

32. The method of claim 30 or 31, wherein, The EHT LTF portion includes EHT LTF OFDM symbols, the number K of EHT LTF OFDM symbols is according to the number K of transmit antennas indicated by the STA in a capability report.

33. The method of any one of claims 30-32, wherein, The AP indicates, through the NDPA signal, which subset of transmit antennas the STA is to use for transmission.

34. The method of claim 33, wherein, The trigger-based sounding NDP is received by the AP from the subset of transmit antennas of the STA.

35. The method of any one of claims 30 to 34, wherein, The PPDU type of the trigger-based sounding NDP signal is an EHT MU PPDU, and / or the PPDU variant is indicated in the PPDU type and compression mode field in the U-SIG part.

36. The method of any one of claims 30 to 35, wherein, The PPDU type and compression mode field is set to 2 or 3.

37. The method of any one of claims 30 to 36, wherein, The PPDU type and compression mode field is set to 0, and B2 of U-SIG-2 is set to 1 to indicate a trigger-based sounding NDP.

38. The method of any one of claims 30 to 37, wherein, The PPDU type and compression mode field is set to 0, and a combination of 11 ignored bits of U-SIG is used to indicate a trigger-based sounding NDP.

39. An access point, AP, comprising processing circuitry configured to perform the method of any of claims 1-10 or any of claims 21-29.

40. A station, STA, comprising processing circuitry configured to perform the method of any of claims 11-20 or any of claims 30-38.

41. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1-38.

42. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1-38.

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