Extended range sounding procedure

Abstract

There are provided methods, device and computer programs products. In a method, there is transmitting, by an access point (AP) to a station (STA), a first frame, where the first frame comprises a first indication of a transmission, by the AP, after the first frame, of a null data physical layer protocol data unit (NDP) and a second indication of a nulling of one or more first subcarriers of a bandwidth of the NDP. Then there is transmitting, by the AP to the STA, the NDP, wherein the transmitting of the NDP comprises nulling the one or more first subcarriers of the bandwidth of the NDP.

Description

[0001] EXTENDED RANGE SOUNDING PROCEDURE

[0002] FIELD

[0003] The present invention relates to wireless networks, in particular those according to the IEEE™ 802.11 standard.

[0004] BACKGROUND

[0005] The current trends are toward increasingly dense deployments of wireless networks whilst meeting high requirements on data rates. Such networks use beamforming to achieve the performances requires which entails the use of channel sounding wherein devices measure characteristics (such as signal to noise and phase delay) of the channel between themselves. In channel sounding, one device sends a sounding packet to one or more devices and, in response, receives a report which it then uses to adjust its transmission parameters, for example to perform beamforming. It is desirable for the channel sounding process to be as accurate as possible.

[0006] SUMMARY

[0007] Embodiments of the present invention are defined in the appended claims.

[0008] In an embodiment, there is a method which comprises transmitting, by an access point (AP) to a station (STA), a first frame. The first frame comprises a first indication of a transmission, by the AP, after the first frame, of a null data physical layer protocol data unit (NDP); and a second indication of a nulling of one or more first subcarriers of a bandwidth of the NDP. There is also transmitting, by the AP to the STA, the NDP, wherein the transmitting of the NDP comprises nulling the one or more first subcarriers of the bandwidth of the NDP.

[0009] In an embodiment, one or more first subcarriers are for use by the STA to generate a beamforming report (BFR) based on the NDP, the first frame comprises a third indication of a nulling by the AP of one or more second subcarriers of the bandwidth of the NDP, the transmitting of the NDP by the AP to the STA is based on the third indication, and there is receiving, by the AP from the STA, the BFR.

[0010] Correspondingly, in an embodiment, a station (STA) may receive from an access point (AP), a first frame comprising a first indication of a transmission, by the AP, after the first frame, of a null data packet (NDP); and a second indication of a nulling of one or more first subcarriers of a bandwidth of the NDP. The STA may, on the second indication, generating, by the STA, a beamforming report (BFR). In an embodiment, one or more first subcarriers may be for use by the STA to generate a beamforming report (BFR) based on the NDP. The STA may receive from the AP, the NDP, and transmit to the AP, the BFR.

[0011] The nulling of the one or more first subcarriers of the bandwidth of the NDP allows the AP to boost the power for one or more second subcarriers of the bandwidth of the NDP that are not nulled, without violating a PSD limit for the NDP transmission. The increased transmission power for the one or more second subcarriers may allow the STA to receive the NDP with low channel estimation noise and to generate a higher accuracy BFR based on the NDP. This may be particularly useful where low power devices are being used.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Examples of several of the various embodiments of the present disclosure are described herein with reference to the drawings.

[0014] FIG. 1 illustrates example wireless communication networks in which embodiments of the present disclosure may be implemented.

[0015] FIG. 2 is a block diagram illustrating example implementations of a station (STA) and an access point (AP).

[0016] FIG. 3 illustrates a non-High Throughput (non-HT) Physical Layer Protocol Data Unit (PPDU), a High Throughput (HT) mixed PPDU, and a Very High Throughput (VHT) PPDU.

[0017] FIG. 4 illustrates a High Efficiency (HE) Single User (SU) PPDU, an HE Multi-User (MU) PPDU, and an HE Extended Range (ER) SU PPDU.

[0018] FIG. 5 illustrates an Extremely High Throughput (EHT) Multi-user (MU) PPDU.

[0019] FIG. 6 illustrates an Extremely High Throughput (EHT) Multi-user (MU) PPDU.

[0020] FIG. 7 illustrates an example null data PPDU (NDP) announcement (NDPA) frame format.

[0021] FIG. 8 illustrates an example format of an NDPA frame STA Info field.

[0022] FIG. 9 illustrates an example management frame which may be used as an action frame.

[0023] FIG. 10 illustrates an example EHT compressed beamforming / CQI frame.

[0024] FIG. 11 illustrates an example table of subcarrier indices for a compression beamforming feedback matrix.

[0025] FIG. 12 illustrates an example EHT non trigger based (non-TB) sounding sequence.

[0026] FIG. 13 illustrates an example of an EHT trigger based (TB) sounding sequence.

[0027] FIG. 14 illustrates an example allocation of non-distributed resource units (RUs).

[0028] FIG. 15 illustrates an example allocation of distributed RUs.

[0029] FIG. 16 illustrates an example that highlights a problem that may arise in association with an operation using a sounding procedure. FIG. 17 illustrates an example operation using a sounding procedure, according to an embodiment.

[0030] FIG. 18 illustrates an example operation using a sounding procedure, according to an embodiment.

[0031] FIG. 19 illustrates an example process according to an embodiment.

[0032] FIG. 20 illustrates an example process according to an embodiment.

[0033] DETAILED DESCRIPTION

[0034] In the present disclosure, various embodiments are presented as examples of how the disclosed techniques may be implemented and / or how the disclosed techniques may be practiced in environments and scenarios. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the scope. After reading the description, it will be apparent to one skilled in the relevant art how to implement alternative embodiments. The present embodiments may not be limited by any of the described exemplary embodiments. The embodiments of the present disclosure will be described with reference to the accompanying drawings. Limitations, features, and / or elements from the disclosed example embodiments may be combined to create further embodiments within the scope of the disclosure. Any figures which highlight the functionality and advantages are presented for example purposes only. The disclosed architecture is sufficiently flexible and configurable, such that it may be utilized in ways other than that shown. For example, the actions listed in any flowchart may be re-ordered or only optionally used in some embodiments.

[0035] Embodiments may be configured to operate as needed. The disclosed mechanism may be performed when certain criteria are met, for example, in a station, an access point, a radio environment, a network, a combination of the above, and / or the like. Example criteria may be based, at least in part, on for example, wireless device or network node configurations, traffic load, initial system set up, packet sizes, traffic characteristics, a combination of the above, and / or the like. When the one or more criteria are met, various example embodiments may be applied. Therefore, it may be possible to implement example embodiments that selectively implement disclosed protocols.

[0036] In this disclosure, “a” and “an” and similar phrases are to be interpreted as “at least one” and “one or more.” Similarly, any term that ends with the suffix “(s)” is to be interpreted as “at least one” and “one or more.” In this disclosure, the term “may” is to be interpreted as “may, for example.” In other words, the term “may” is indicative that the phrase following the term “may” is an example of one of a multitude of suitable possibilities that may, or may not, be employed by one or more of the various embodiments. The terms “comprises” and “consists of’, as used herein, enumerate one or more components of the element being described. The term “comprises” is interchangeable with “includes” and does not exclude unenumerated components from being included in the element being described. By contrast, “consists of’ provides a complete enumeration of the one or more components of the element being described. The term “based on”, as used herein, may be interpreted as “based at least in part on” rather than, for example, “based solely on”. The term “and / or” as used herein represents any possible combination of enumerated elements. For example, “A, B, and / or C” may represent A; B; C; A and B; A and C; B and C; or A, B, and C.

[0037] If A and B are sets and every element of A is an element of B, A is called a subset of B. In this specification, only non-empty sets and subsets are considered. For example, possible subsets of B = {STA1, STA2} are: {STA1}, {STA2}, and {STA1, STA2}. The phrase “based on” (or equally “based at least on”) is indicative that the phrase following the term “based on” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments. The phrase “in response to” (or equally “in response at least to”) is indicative that the phrase following the phrase “in response to” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments. The phrase “depending on” (or equally “depending at least to”) is indicative that the phrase following the phrase “depending on” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments. The phrase “employing / using” (or equally “employing / using at least”) is indicative that the phrase following the phrase “employing / using” is an example of one of a multitude of suitable possibilities that may, or may not, be employed to one or more of the various embodiments.

[0038] The term configured may relate to the capacity of a device whether the device is in an operational or non-operational state. Configured may refer to specific settings in a device that effect the operational characteristics of the device whether the device is in an operational or non-operational state. In other words, the hardware, software, firmware, registers, memory values, and / or the like may be “configured” within a device, whether the device is in an operational or nonoperational state, to provide the device with specific characteristics. Terms such as “a control message to cause in a device” may mean that a control message has parameters that may be used to configure specific characteristics or may be used to implement certain actions in the device, whether the device is in an operational or non-operational state.

[0039] In this disclosure, parameters (or equally called, fields, or Information elements: IES) may comprise one or more information objects, and an information object may comprise one or more other objects. For example, if parameter (IE) N comprises parameter (IE) M, and parameter (IE) M comprises parameter (IE) K, and parameter (IE) K comprises parameter (information element) J. Then, for example, N comprises K, and N comprises J. In an example embodiment, when one or more messages / frames comprise a plurality of parameters, it implies that a parameter in the plurality of parameters is in at least one of the one or more messages / frames but does not have to be in each of the one or more messages / frames.

[0040] Many features presented are described as being optional through the use of “may” or the use of parentheses. For the sake of brevity and legibility, the present disclosure does not explicitly recite each and every permutation that may be obtained by choosing from the set of optional features. The present disclosure is to be interpreted as explicitly disclosing all such permutations. For example, a system described as having three optional features may be embodied in seven ways, namely with just one of the three possible features, with any two of the three possible features or with three of the three possible features.

[0041] Many of the elements described in the disclosed embodiments may be implemented as modules. A module is defined here as an element that performs a defined function and has a defined interface to other elements. The modules described in this disclosure may be implemented in hardware, software in combination with hardware, firmware, wetware (e.g., hardware with a biological element) or a combination thereof, which may be behaviorally equivalent. For example, modules may be implemented as a software routine written in a computer language configured to be executed by a hardware machine (such as C, C++, Fortran, Java, Basic, MatLab or the like) or a modeling / simulation program such as Simulink, Stateflow, GNU Octave, or Lab VIEW MathScript. It may be possible to implement modules using physical hardware that incorporates discrete or programmable analog, digital and / or quantum hardware. Examples of programmable hardware comprise computers, microcontrollers, microprocessors, application-specific integrated circuits (ASICs); field programmable gate arrays (FPGAs); and complex programmable logic devices (CPLDs). Computers, microcontrollers, and microprocessors are programmed using languages such as assembly, C, C++ or the like. FPGAs, ASICs and CPLDs are often programmed using hardware description languages (HDL) such as VHSIC hardware description language (VHDL) or Verilog that configure connections between internal hardware modules with lesser functionality on a programmable device. The mentioned technologies are often used in combination to achieve the result of a functional module.

[0042] FIG. 1 illustrates example wireless communication network 100 in which embodiments of the present disclosure may be implemented. As shown in FIG. 1, the example wireless communication networks may include an Institute of Electrical and Electronic Engineers (IEEE) 802.11 (WLAN) infrastructure network 102. WLAN infra-structure network 102 may include one or more basic service sets (BSSs) 110 and 120 and a distribution system (DS) 130.

[0043] BSS 110-1 and 110-2 each includes a set of an access point (AP or AP STA) and at least one station (STA or non-AP STA). For example, BSS 110-1 includes an AP 104-1 and a STA 106-1, and BSS 110-2 includes an AP 104-2 and STAs 106-2 and 106-3. The AP and the at least one STA in a BSS perform an association procedure to communicate with each other.

[0044] DS 130 may be configured to connect BSS 110-1 and BSS 110-2. As such, DS 130 may enable an extended service set (ESS) 150. Within ESS 150, APs 104-1 and 104-2 are connected via DS 130and may have the same service set identification (SSID).

[0045] WLAN infra-structure network 102 may be coupled to one or more external networks. For example, as shown in FIG. 1, WLAN infra-structure network 102 may be connected to another network 108 (e.g., 802.X) via a portal 140. Portal 140 may function as a bridge connecting DS 130 of WLAN infra-structure network 102 with the other network 108. The example wireless communication networks illustrated in FIG. 1 may further include one or more ad-hoc networks or independent BSSs (IBSSs). An ad-hoc network or IBSS is a network that includes a plurality of STAs that are within communication range of each other. The plurality of STAs are configured so that they may communicate with each other using direct peer-to-peer communication (e.g., not via an AP).

[0046] For example, in FIG. 1, STAs 106-4, 106-5, and 106-6 may be configured to form a first IBSS 112-1. Similarly, STAs 106-7 and 106-8 may be configured to form a second IBSS 112-2. Since an IBSS does not include an AP, it does not include a centralized management entity. Rather, STAs within an IBSS are managed in a distributed manner. STAs forming an IBSS may be fixed or mobile.

[0047] A STA as a predetermined functional medium may include a medium access control (MAC) layer that complies with an IEEE 802. 11 standard. A physical layer interface for a radio medium may be used among the APs and the non-AP stations (STAs). The STA may also be referred to using various other terms, including mobile terminal, wireless device, wireless transmit / receive unit (WTRU), user equipment (UE), mobile station (MS), mobile subscriber unit, or user. For example, the term “user” may be used to denote a STA participating in uplink Multi-user Multiple Input, Multiple Output (MU MIMO) and / or uplink Orthogonal Frequency Division Multiple Access (OFDMA) transmission.

[0048] A physical layer (PHY) protocol data unit (PPDU) may be a composite structure that includes a PHY preamble and a payload in the form of a PLCP service data unit (PSDU). For example, the PSDU may include a PHY Convergence Protocol (PLCP) preamble and header and / or one or more MAC protocol data units (MPDUs). The information provided in the PHY preamble may be used by a receiving device to decode the subsequent data in the PSDU. In instances in which PPDUs are transmitted over a bonded channel (channel formed through channel bonding), the preamble fields may be duplicated and transmitted in each of the multiple component channels. The PHY preamble may include both a legacy portion (or “legacy preamble”) and a non-legacy portion (or “non-legacy preamble”). The legacy preamble may be used for packet detection, automatic gain control and channel estimation, among other uses. The legacy preamble also may generally be used to maintain compatibility with legacy devices. The format of, coding of, and information provided in the non-legacy portion of the preamble is based on the particular IEEE 802. 11 protocol to be used to transmit the payload.

[0049] A frequency band may include one or more sub-bands or frequency channels. For example, PPDUs conforming to the IEEE 802.1 In, 802. 1 lac, 802. 1 lax and / or 802. 1 Ibe standard amendments may be transmitted over the 2.4 GHz, 5 GHz, and / or 6 GHz bands, each of which may be divided into multiple 20 MHz channels. The PPDUs may be transmitted over a physical channel having a minimum bandwidth of 20 MHz. Larger channels may be formed through channel bonding. For example, PPDUs may be transmitted over physical channels having bandwidths of 40 MHz, 80 MHz, 160 MHz, or 520 MHz by bonding together multiple 20 MHz channels.

[0050] FIG. 2 is a block diagram 200 illustrating example implementations of a STA 210 and an AP 260. As shown in FIG. 2, STA 210 may include at least one processor 220, a memory 230, and at least one transceiver 240. AP 260 may include at least one processor 270, a memory 280, and at least one transceiver 290. Processor 220 / 270 may be operatively connected to memory 230 / 280 and / or to transceiver 240 / 290.

[0051] Processor 220 / 270 may implement functions of the PHY layer, the MAC layer, and / or the logical link control (LLC) layer of the corresponding device (STA 210 or AP 260). Processor 220 / 270 may include one or more processors and / or one or more controllers. The one or more processors and / or one or more controllers may comprise, for example, a general-purpose processor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a logic circuit, or a chipset, for example.

[0052] Memory 230 / 280 may include a read-only memory (ROM), a random-access memory (RAM), a flash memory, a memory card, a storage medium, and / or other storage unit. Memory 230 / 280 may comprise one or more non-transitory computer readable mediums. Memory 230 / 280 may store computer program instructions or code that may be executed by processor 220 / 270 to carry out one or more of the operations / embodiments discussed in the present application. Memory 230 / 280 may be implemented (or positioned) within processor 220 / 270 or external to processor 220 / 270. Memory 230 / 280 may be operatively connected to processor 220 / 270 via various means known in the art.

[0053] Transceiver 240 / 290 may be configured to transmit / receive radio signals. In an example, transceiver 240 / 290 may implement a PHY layer of the corresponding device (STA 210 or AP 260). In an example, STA 210 and / or AP 260 may be a multi -link device (MLD), that is a device capable of operating over multiple links as defined by the IEEE 802. 11 standard. As such, STA 210 and / or AP 260 may each implement multiple PHY layers. The multiple PHY layers may be implemented using one or more of transceivers 240 / 290.

[0054] FIG. 3 illustrates a non-High Throughput (non-HT) PPDU 310, a High Throughput (HT) mixed mode PPDU 320, and a Very High Throughput (VHT) PPDU 330.

[0055] Non-HT PPDU 310 may be used by STAs conforming to the IEEE 802. 1 la standard amendment. As shown in FIG. 3, non-HT PPDU 310 includes a non-HT Short Training field (L-STF), a non-HT Long Training field (L-LTF), a non-HT Signal field (L-SIG), and a Data field. The L-STF, L- LTF, and L-SIG form a 20 ps preamble of non-HT PPDU 310.

[0056] The L-STF may be used by a receiver of non-HT PPDU 310 to synchronize with the carrier frequency and frame timing of a transmitter of non-HT PPDU 310 and to adjust the receiver signal gain. The L-LTF may be used by the receiver of non-HT PPDU 310 to estimate channel coefficients in order to equalize the channel response (e.g., amplitude and phase distortion) in both the L-SIG and the Data fields of non-HT PPDU 310.

[0057] The L-SIG contains parameters needed to demodulate the Data field, which contains a payload of non-HT PPDU 310. The L-SIG may be equalized using the channel coefficients estimated using the L-LTF and demodulated to obtain the demodulation parameters of the Data field. The Data Field includes one or more symbols each having a duration of 4 is, where 3.2 is carry symbol information and 0.8 pis carry a Guard Interval (GI).

[0058] For non-HT PPDUs, the only supported bandwidth is 20MHz, which is divided into 64 subcarriers. As such, non-HT PPDU 310 may be encoded using a subcarrier spacing of 20MHz / 64 or 312.5kHz.

[0059] HT mixed mode PPDU 320 may be used by STAs conforming to the IEEE 802. 1 In standard amendment. HT mixed mode PPDU 320 can support MIMO to up to 4 spatial streams, which enhances spectral efficiency four folds. HT mixed mode PPDU 320 has a minimum preamble duration of 35.6 ps, which may increase depending on the number of spatial streams carried by the PPDU.

[0060] As shown in FIG. 3, HT mixed mode PPDU 320 includes an L-STF, an L-LTF, an L- SIG, an HT Signal field (HT-SIG) field, an HT Short Training field (HT-STF) field, one or more HT Long Training field (HT-LTF), and a data field. The HT-LTF and data fields include of one or more symbols each having a duration of 3.6 ps or 4 ps. In both cases, 3.2 ps carry symbol information while the remaining 0.4 ps or 0.8 ps carry a GI. The 0.4 ps long GI is called short GI while the 0.8 ps long GI is called regular or normal GI.

[0061] For HT mixed mode PPDUs, two bandwidths, 20 MHz and 140 MHz, may be supported. When the PPDU bandwidth is 20MHz, the band is divided into 64 subcarriers. When the PPDU bandwidth is 140 MHz, the band is divided into 128 subcarriers. In both cases, subcarrier spacing of 312.5 kHz is maintained.

[0062] VHT PPDU 330 may be used by STAs conforming to the IEEE 802. 1 lac standard amendment. VHT PPDU 330 can support MIMO transmission to up to 8 spatial streams, which enhances spectral efficiency eight folds. VHT PPDU 330 has a minimum preamble duration of 39.6 ps, which may increase depending on the number of spatial streams carried by VHT PPDU 330.

[0063] As shown in FIG. 3, VHT PPDU 330 includes an L-STF, an L-LTF, an L-SIG, a VHT Signal A field (VHT-SIG-A), a VHT Short Training field (VHT-STF), one or more VHT Long Training field (VHT-LTF), a VHT Signal B field (VHT-SIG-B), and a Data field. The VHT-LTF and Data fields of VHT PPDU 330 include one or more symbols each having a duration of 3.6 ps or 4 ps. In both cases, 3.2 ps carry symbol information while the remaining 0.4 ps or 0.8 ps carry of the GI. The 0.4 ps long GI is called the Short GI while the 0.8ps long is called regular or normal GI.

[0064] For VHT PPDUs, four bandwidths, 20 MHz, 40 MHz, 80 MHz, and 160 MHz, may be supported. When the PPDU bandwidth is 20MHz, the band is divided into 64 subcarriers. When the PPDU bandwidth is 40 MHz, the band is divided into 128 subcarriers. When the PPDU bandwidth is 80MHz, the band is divided into 256 subcarriers. When the PPDU bandwidth is 160 MHz, the band is divided into two 256-subcarrier 80MHz bands. In all cases, a subcarrier spacing of 312.5 kHz is maintained.

[0065] FIG. 4 illustrates a High Efficiency (HE) Single User (SU) PPDU 410, and an HE MultiUser (MU) PPDU 420, and an HE Extended Range (ER) SU PPDU 430. HE SU PPDU 410, HE MU PPDU 420, and HE ER SU PPDU 430 may be used by STAs conforming to the IEEE 802.1 lax standard amendment.

[0066] HE SU PPDU 410 supports higher spectral efficiency compared to VHT PPDU 330 due to increased subcarrier spacing and higher order modulation support. HE SU PPDU 410 has a minimum preamble duration of 44 ps.

[0067] As shown in FIG. 4, HE SU PPDU 410 includes an L-STF, an L-LTF, an L-SIG, a Repeated L-SIG (RL-SIG), an HE Signal A field (HE-SIG-A), an HE Short Training field (HE-STF) field, one or more HE Long Training field (HE-LTF), a Data field, and a PE field.

[0068] Similar to HE SU PPDU 410, HE MU PPDU 420 supports higher spectral efficiency compared to VHT PPDU 330. HE MU PPDU 420 also supports OFDMA. Due to denser subcarrier spacing (as in HE SU PPDU 410), HE MU PPDU 420 allows for payloads of multiple users to be multiplexed in the frequency domain in the Data field. HE MU PPDU 420 supports multiplexing the payload of up to 9 users in a single 20 MHz band. HE MU PPDU 420 has a minimum preamble duration of 47.2 ps, which may increase depending on the number of spatial streams carried by HE MU PPDU 420.

[0069] As shown in FIG. 4, HE MU PPDU 420 includes an L-STF, an L-LTF, an L-SIG, an RL- SIG, an HE-SIG-A, an HE Signal B Field (HE-SIG-B), an HE-STF field, one or more HE-LTF field, a Data field, and a PE field. It is noted that compared to HE SU PPDU 410, HE MU PPDU 420 further includes HE-SIG-B. HE-SIG-B contains indications per STA of RU allocations. A STA may use the indications in HE-SIG-B to locate its payload in HE MU PPDU 420.

[0070] For HE SU PPDU 410 and HE MU PPDU 420, the GI portion of the HE-LTF and Data field may be one of one of 0.8 ps, 1.6 ps, and 3.2 ps. An AP or STA may use a suitable GI duration depending on the channel conditions or capability of the target STA or AP.

[0071] For both HE SU PPDU 410 and HE MU PPDU 420, the information portion of the HE- LTF may be one of 3.2 ps, 6.4 ps, or 12.8 ps. Depending on the information portion duration, a subcarrier spacing of the HE-LTF may be one of: 312.5kHz if the information potion is 3.2 ps, 156.25kHz if the information portion is 6.4 ps, and 78.125kHz if the information portion is 12.8 ps. Unlike the HE-LTF, the information portion of the Data field for both HE SU PPDU 410 and HE MU PPDU 420 is always 12.8 ps. Hence, a subcarrier spacing of the Data field is always 78.125kHz corresponding to the duration of the information portion being 12.8 ps. When a 3.2 ps or 6.4 ps long HE-LTF is used by a transmitting STA to transmit HE SU PPDU 410 or HE MU PPDU 420, a receiving STA is required to interpolate the channel estimates to a subcarrier spacing resolution of 78.125kHz to match the subcarrier spacing of the Data field.

[0072] As shown in FIG. 4, HE ER SU PPDU 430 includes an L-STF, an L-LTF, an L-SIG, an RL-SIG, an HE-SIG-A, an HE-STF, one or more HE-LTF, a Data field, and a PE field. It is noted that compared to HE SU PPDU 410, HE ER SU PPDU 430 has an HE-SIG-A that is duplicated in the time domain (16 ps long instead of 8 ps long in HE SU PPDU 410). As such, both L-SIG (duplicated using RL-SIG) and HE-SIG-A are sent in duplicates, which allows a receiving STA to combine the two copies to increase the energy of the received signal. This results in an extended range of reception and increases transmission reliability between the transmitting STA and the receiving STA.

[0073] FIG. 5 illustrates an Extremely High Throughput (EHT) MU PPDU. EHT MU PPDU 510 supports OFDMA up to a bandwidth of 320MHz. EHT MU PPDU 510 can improve spectral efficiency due to support of a higher order modulation compared to other PPDUs (e.g., HE SU PPDU 410 and HE MU PPDU 420) while supporting the same number of spatial streams. EHT MU PPDU 510 has a minimum preamble duration of 47.2 ps, which may increase depending on the number of spatial streams carried by EHT MU PPDU 410.

[0074] As shown in FIG. 5, EHT MU PPDU 510 includes an L-STF, an L-LTF, an L-SIG, an RL-SIG, a Universal Signal field (U-SIG), an EHT Signal field (EHT-SIG), an EHT Short Training Field (EHT-STF), one or more EHT Long Training fields (EHT-LTF), a Data field, and a PE field. It is noted that according to the IEEE 802.1 Ibe standard amendment, EHT MU PPDU 510 may be used by a transmitting STA for both SU and MU transmissions.

[0075] The U-SIG is intended to ensure forward compatibility of EHT MU PPDU 510. This means that any future PPDUs that are backward compatible to IEEE 802.1 Ibe will contain the same U- SIG field and interpretation. Because of this, IEEE 802. 1 Ibe STAs will be able to understand at least in part a PPDU developed in a future amendment.

[0076] The EHT-SIG contains indications per STA of resource unit (RU) allocations. A STA may use the indications in the EHT-SIG to locate its payload in EHT MU PPDU 510.

[0077] The GI portion of the EHT-LTF and Data fields of EHT MU PPDU 510 may be one of: 0.8 ps, 1.6 ps, or 3.2 ps. An AP or STA may use a suitable GI duration depending on the channel conditions or capability of the target STA or AP.

[0078] The information portion of the EHT-LTF may be one of 3.2 ps, 6.4 ps, or 12.8 ps.

[0079] Depending on the information portion duration, a subcarrier spacing of the EHT-LTF may be one of: 312.5kHz if the information potion is 3.2 ps, 156.25kHz if the information portion is 6.4 ps, or 78. 125kHz if the information portion is 12.8 ps. The information portion of the Data field of EHT MU PPDU 410 is always 12.8 ps. Hence, a subcarrier spacing of the Data field is always 78.125kHz corresponding to the duration of the information portion being 12.8 ps. When a 3.2 ps long or a 6.4 ps long EHT-LTF is used by a transmitting STA to transmit EHT MU PPDU 410, a receiving STA is required to interpolate the channel estimates to a subcarrier spacing resolution of 78.125kHz to match the Data field subcarrier spacing.

[0080] FIG. 6 illustrates an EHT sounding null data PPDU (NDP) 600. EHT sounding NDP 600 may be used for sounding to one or more users. EHT sounding NDP 600 may be a variant of EHT MU PPDU 510. An EHT sounding NDP may be indicated by setting a “PPDU Type and Compression Mode” field of a U-SIG field of an EHT PPDU to 1, an EHT-SIG MCS field of an EHT-SIG field of the EHT PPDU to 0, and a “Number of EHT-SIG Symbols” field to 0 in the U-SIG field of the EHT PPDU. As shown in FIG. 6, EHT sounding NDP 600 comprises a non-high throughput (non-HT) short training field (L-STF), a non-HT long training field (L-LTF), a non-HT signal field (L-SIG), a repeated non-HT signal field (RL-SIG), a universal signal field (U-SIG), an EHT signal field (EHT-SIG), an EHT short training field (EHT-STF), an EHT long training field (EHT-LTF), and a packet extension (PE) field.

[0081] The L-STF, L-LTF, L-SIG, RL-SIG, U-SIG, and EHT-SIG fields may be referred to as pre-EHT modulated fields, while the EHT-STF, EHT-LTF, and PE fields may be referred to as EHT modulated fields.

[0082] The EHT-LTF field may comprise one or more EHT-LTF symbols. The number of EHT- LTF symbols may be indicated in a “number of EHT-LTF symbols” field of the EHT-SIG field.

[0083] The EHT-LTF field provides a means for a receiver of EHT sounding NDP 600 to estimate the MIMO channel between the set of constellation mapper outputs and the receive chains. A spatial stream may refer to one or more symbols that may be transmitted over multiple spatial dimensions that are created by the use of multiple antennas at both ends of a communications link. In an EHT MU PPDU, the transmitter provides training for Ass,r, total spatial streams used for the transmission of PSDU(s) in an r-th resource unit (RU). In an EHT TB PPDU, the transmitter of user u in the r-th RU provides training for Ass.r.u spatial streams used for the transmission of the PSDU. For each subcarrier in the r-th RU, the MIMO channel that can be estimated is an A<xxAss,r, total matrix.

[0084] An EHT transmission has a preamble that contains EHT-LTF symbols, where the data tones of each EHT-LTF symbol are multiplied by entries belonging to a matrix EHT-LTF, to enable channel estimation at the receiver. When single stream pilots are used in 2 * or 4 x EHT-LTF, the pilot subcarriers of each EHT-LTF symbol are multiplied by the entries of a matrix / ?u IT-LTF to allow receivers to track phase and / or frequency offset during MIMO channel estimation using the EHT-LTF. Single stream pilots are used for all spatial multiplexing modes (both UL and DL) defined in EHT except when 1 x EHT-LTF is used. EI IT-LTF is defined such that each modulated spatial stream in an RU is active on all subcarriers in that RU for which the EHT-LTF sequence takes a nonzero value.

[0085] In an EHT MU PPDU, the number of EHT-LTF symbols AEHT-LTF is indicated in the EHT-SIG field. In a non-OFDMA EHT MU PPDU or an EHT sounding NDP, the initial number of EHT- LTF symbols, initial AEHT-LTF, is a function of the total number of spatial streams Ass.

[0086] In order to improve the MIMO channel estimation for the reception of a non-OFDMA EHT MU PPDU or an EHT sounding NDP, the number of EHT-LTFs may be larger than the initial number of EHT-LTFs determined by the total number of spatial streams. If additional EHT-LTFs are used, then the total number of EHT-LTFs (which is signaled separately from Ass) can be no more than twice the initial number of EHT-LTFs determined by the number of spatial streams and chosen from the set {2 4 8}. Supporting additional EHT-LTFs is optional for the receiver, which is indicated by the maximum number of supported EHT-LTFs subfield of the EHT PHY capabilities information field. FIG. 7 illustrates an example null data PPDU (NDP) announcement (NDPA) frame 700. As shown in FIG. 7, example NDPA frame 700 includes a Frame Control field, a Duration field, a receiver address (RA) field, a transmitter address (TA) field, a Sounding Dialog Token field, a STA Info List field, and a frame check sequence (FCS).

[0087] The Frame Control field indicates a type (NDPA) of NDPA frame 700. The Duration field indicates a duration of NDPA frame 700. The RA field indicates an address of one or more receiver of NDPA frame 700. The TA field indicates an address of a transmitter of NDPA frame 700. The TA field is set to the address of a STA transmitting NDPA frame 700 or a bandwidth signaling TA of the STA transmitting NDPA frame 700.

[0088] The Sounding Dialog Token field includes an NDP Announcement Variant subfield and a Sounding Dialog Token Number subfield. Based on its value, the NDP Announcement Variant subfield indicates a variant of NDPA frame 700 from among four variants: a VHT NDP Announcement frame, an HE NDP Announcement frame, a Ranging NDP Announcement frame, and an EHT NDP Announcement frame. The NDP Announcement Variant subfield is set to 7 to identify NDPA frame 700 as an HE NDP Announcement frame. The NDP Announcement Variant subfield is set to 3 to identify NDPA frame 700 as an EHT NDP Announcement frame. In the HE NDP Announcement and the EHT NDP Announcement frame, the Duration, RA, and TA fields are set as in the VHT NDP Announcement frame. The Sounding Dialog Token Number subfield contains a value selected by the transmitter of NDPA frame 700 to identify NDPA frame 700.

[0089] The STA Info List field contains one or more STA Info fields. The STA Info List field includes at most one STA Info field per STA to which NDPA frame 700 is addressed in the RA field. If the STA Info List field includes only one STA Info field with a value less than 2008 in an AID 11 subfield, then in the case that NDPA frame 700 is a VHT, HE, or EHT NDP Announcement frame the RA field is set to the address of the STA indicated in the only STA Info field of NDPA frame 700. If STA Info List field includes more than one STA Info field with a value less than 2008 in the AID11 subfield, then the RA field is set to a broadcast address.

[0090] As shown in FIG. 7, a STA Info field may include an AID 11 subfield, a Partial Bandwidth (BW) Info subfield, an Nc Index subfield, a Feedback Type and Ng subfield, a Disambiguation subfield, and a Codebook Size subfield.

[0091] The AID11 subfield contains an identifier of a STA expected to process an EHT sounding NDP that follows NDPA frame 700 and to prepare sounding feedback based on the EHT sounding NDP.

[0092] The Partial BW Info subfield includes a Resolution subfield and a Feedback Bitmap subfield. The Resolution subfield indicates a resolution bandwidth for each bit in the Feedback Bitmap subfield. The Feedback Bitmap subfield indicates whether feedback is requested for each resolution bandwidth and is ordered from a lowest frequency to a highest frequency, followed by zeros. A bit in the Feedback Bitmap subfield set to 1 indicates that feedback is requested for the corresponding frequency with the resolution bandwidth. For example, a first position bit (Bl) of the Feedback Bitmap subfield set to 1 indicates a request for feedback for the lowest frequency at the indicated resolution bandwidth.

[0093] When NPDA frame 700 is an EHT NDP Announcement frame and the bandwidth of a PPDU carrying NDPA frame 700 is less than 320 MHz, bit B0 of the Resolution subfield is set to 0 to indicate a resolution bandwidth of 20 MHz.

[0094] When NDPA frame 700 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 700 is equal to 20 MHz, the first position bit (Bl) of the Feedback Bitmap subfield is set to 1 to indicate a request for feedback on a 242-tone RU. Bits B2-B8 of the Feedback Bitmap subfield are set to 0.

[0095] When NDPA frame 700 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 700 is equal to 40 MHz, the first position bit (Bl) and the second position bit (B2) of the Feedback Bitmap subfield respectively indicate a request for feedback on a respective 242- tone RU (of two 242-tone RUs) from lower frequency to higher frequency. Bits B3-B8 of the Feedback Bitmap subfield are set to 0.

[0096] When NDPA frame 700 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 700 is equal to 80 MHz, bits B 1-B4 of the Feedback Bitmap subfield set to 1 indicate a request for feedback on a 996-tone RU; otherwise, bits B1-B4 respectively indicate a request for feedback on a respective 242-tone RU (of four 242-tone RUs) from lower frequency to higher frequency. Bits B5-B8 of the Feedback Bitmap subfield are set to 0.

[0097] When NDPA frame 700 is an EHT NDP Announcement frame and the bandwidth of the PPDU carrying NDPA frame 700 is equal to 160 MHz, bits B1-B4 of the Feedback Bitmap subfield set to 1 indicate a request for feedback on a lower 996-tone RU (among a lower 996-tone RU and an upper 996-tone RU); otherwise, bits B1-B4 respectively indicate a request for feedback on a respective 242- tone RU (of four 242-tone RUs) from lower frequency to higher frequency in the lower 80 MHz of the 160 MHz PPDU bandwidth. Similarly, bits B5-B8 set to 1 indicate a request for feedback on the upper 996-tone RU (among the lower 996-tone RU and the upper 996-tone RU); otherwise, bits B5-B8 respectively indicate a request for feedback on a respective 242-tone RU (of the four 242-tone RUs) from lower frequency to higher frequency in the upper 80 MHz of the 160 MHz.

[0098] When NDPA frame 700 is an EHT Announcement frame and the bandwidth of the PPDU carrying NDPA frame 700 is equal to 320 MHz, bit B0 of the Resolution subfield set to 1 indicates a resolution bandwidth of 40 MHz. When bits Bl and B2 of the Feedback Bitmap subfield are both set to 1, they indicate a request for feedback request on a lowest 996-tone RU (among a lowest 996-tone RU, a second lowest 996-tone RU, a third lowest 996-tone RU, and a highest 996-tone RU); otherwise, bits B 1 and B2 respectively indicate a request for feedback on a respective 484-tone (of two 484-tone RUs) from lower frequency to higher frequency in a lowest 80 MHz of the 320 MHz PPDU bandwidth. When bits B3 and B4 of the Feedback Bitmap subfield are both set to 1, they indicate a request for feedback on the second lowest 996-tone RU; otherwise, bits B3 and B4 indicate respectively a request for feedback on a respective 484-tone RU (of two 484-tone RUs) from lower frequency to higher frequency in a second lowest 80 MHz of the 320 MHz PPDU bandwidth. When bits B5 and B6 of the Feedback Bitmap subfield are both set to 1, they indicate a request for feedback on the third lowest 996-tone RU; otherwise, B5 and B6 respectively indicate a request for feedback on respective 484-tone RU (of two 484-tone RUs) from lower frequency to higher frequency in a third lowest 80 MHz of the 320 MHz PPDU bandwidth. When bits B7 and B8 of the Feedback Bitmap subfield are both set to 1, they indicate a request for feedback on the highest 996-tone RU; otherwise, bits B7 and B8 indicate respectively a request for feedback on respective 484-tone RU (of two 484-tone RUs) from lower frequency to higher frequency in a highest 80 MHz of the 320 MHz PPDU bandwidth. The feedback tone set for each 484-tone RU is composed of the feedback tone sets of the two 242-tone RUs overlapping with the 484-tone RU.

[0099] Returning to FIG. 7, the Nc Index subfield indicates the number of columns of a beamforming feedback matrix (reported in a compressed beamforming report in response to NDPA frame 700) minus 1, if the feedback is SU feedback or MU feedback; and indicates the number of spatial streams of a CQI report (reported in a CQI report in response to NDPA frame 700) minus 1, if the feedback is CQI feedback.

[0100] The “Feedback Type and Ng” subfield indicates a feedback type and a subcarrier grouping, Ng, to be used by the STA generating the sounding feedback based on the EHT sounding NDP that follows NDPA 700. The feedback type may be SU feedback, MU feedback, or CQI feedback. The subcarrier grouping, Ng, indicates the number (e.g., 4, 16) of adjacent subcarriers that are to be grouped in a beamforming report. When grouping is used, a single beamforming feedback matrix is reported for each group of Ng adjacent subcarriers. The “Feedback Type and Ng” subfield and the Codebook Size subfield for EHT trigger-based (TB) sounding are the same as for HE TB sounding. The “Feedback Type and Ng” and the Codebook Size subfields for EHT non-TB sounding are the same as for HE non-TB sounding.

[0101] If NDPA frame 700 is an EHT NDP Announcement frame with more than one STA Info field that contains a value less than 2008 in the AID11 subfield, the RA field indicates a broadcast address, and the Nc Index subfield may be set as follows:

[0102] If the “Feedback Type and Ng” subfield and the Codebook Size subfield indicate single user (SU) or multi-user (MU), the Nc Index subfield indicates the number of columns in the compressed beamforming feedback matrix minus 1, Nc-1. Nc Index subfield values above 7 are reserved.

[0103] If the “Feedback Type and Ng” subfield and the Codebook Size subfield indicate channel quality information (CQI), the Nc Index subfield indicates the number of spatial streams in the CQI report minus 1, Nc-1. Nc Index subfield values above 7 are reserved.

[0104] If NDPA frame 700 is an EHT NDP Announcement frame with a single STA Info field that contains a value less than 2008 in the AID11 subfield, the RA field indicates an individual address, and the Nc index subfield is reserved. FIG. 8 illustrates an example STA Info field 800. STA Info field 800 may replace the STA Info field of NDPA frame 700 described above. For example, when the AID11 subfield of the STA info field is set to a particular value (e.g., 2047), the STA info field may have the format of STA Info field 800 described herein. As shown in FIG. 8, STA Info field 800 includes an AID11 subfield, a Disallowed Subchannel Bitmap subfield, and a Disambiguation subfield.

[0105] The AID11 subfield may be set to a particular value (e.g., 2047). When the AID11 subfield corresponds to a particular value (e.g., 2047), the Disallowed Subchannel Bitmap indicates the 20 MHz subchannels and the 242-tone RUs that are present in an HE sounding NDP announced by the NDPA frame, and the 242-tone RUs that are to be included in requested sounding feedback.

[0106] Each bit of the Disallowed Subchannel Bitmap corresponds to a respective 20 MHz subchannel of the BSS bandwidth. For example, the lowest numbered bit of the Disallowed Subchannel Bitmap corresponds to the 20 MHz subchannel of the BSS bandwidth with the lowest frequency of the set of 20 MHz subchannels within the BSS bandwidth. Each successive bit in the Disallowed Subchannel Bitmap corresponds to the next higher frequency 20 MHz subchannel of the 20 MHz subchannels within the BSS bandwidth.

[0107] FIG. 9 illustrates an example management frame 900 which may be used as an action frame. In an example, management frame 900 includes a MAC header, a variable length frame body, and a frame check sequence (FCS). The MAC header includes a frame control field, a duration field, an address 1 field, an address 2 field, an address 3 field, a sequence control field, and an optional HT control field. The presence of the HT control field is determined by the setting of a +HTC subfield of the frame control field.

[0108] As shown in FIG. 9, when used as an action frame, the frame body of management frame includes an action field, vendor specific elements, management message integrity code element (MME), message integrity code (MIC), and an authenticated mesh peering exchange element.

[0109] The action field includes a category field and an action details field. The action field provides a mechanism for specifying extended management actions. The category field indicates a category of the action frame. The action details field contains the details of the action requested by the action frame.

[0110] The MME is present when management frame protection is negotiated, the frame is a group addressed robust Action frame, and (MBSS only) the category of the action frame does not support group addressed privacy as indicated by category values; otherwise not present.

[0111] The MIC element is present in a self-protected action frame if a shared pairwise master key (PMK) exists between the sender and recipient of this frame; otherwise not present.

[0112] The authenticated mesh peering exchange element is present in a self-protected action frame if a shared PMK exists between the sender and recipient of this frame; otherwise not present.

[0113] FIG. 10 illustrates an example EHT compressed beamforming / CQI frame 1000. EHT Compressed Beamforming / CQI frame 1000 may be an Action No Ack frame of category EHT. The Action field of an EHT Compressed Beamforming / CQI frame contains the information including a Category field, an EHT Action field, an EHT MIMO Control field, an EHT Compressed Beamforming Report field, an EHT MU Exclusive Beamforming Report field, an EHT CQI Report.

[0114] The Category field is set to a value of 36 for EHT category.

[0115] The EHT Action field, in the octet immediately after the Category field, differentiates the EHT Action frame formats. The EHT Action field values associated with each frame format within the EHT category. The EHT Action field is set to a value of 0 for EHT Compressed Beamforming / CQI.

[0116] The EHT MIMO Control field comprises a Nc Index subfield, a Nr Index subfield, a BW subfield, a Grouping subfield, a Codebook Information subfield, a Feedback Type subfield, a Remaining Feedback Segments subfield, a First Feedback Segment subfield, a Partial BW Info subfield, a Sounding Dialog Token Number subfield.

[0117] In an EHT Compressed Beamforming / CQI frame not carrying all or part of an EHT compressed beamforming / CQI report, the Nc Index, Nr Index, BW, Grouping, Codebook Information, Feedback Type, and Sounding Dialog Token Number subfields are reserved, the First Feedback Segment subfield is set to 0, and the Remaining Feedback Segments subfield is set to 7.

[0118] The EHT Compressed Beamforming Report field carries the average SNR of each spatial stream and compressed beamforming feedback matrices for use by a transmit beamformer to determine steering matrices for explicit feedback beamforming.

[0119] The EHT MU Exclusive Beamforming Report field carries explicit feedback in the form of delta SNRs. The information in the EHT Compressed Beamforming Report field and the EHT MU Exclusive Beamforming Report field can be used by the transmit MU beamformer to determine the steering matrices for DL MU-MIMO.

[0120] The EHT CQI Report field carries the per-RU average SNRs of each spatial stream, where each per-RU average SNR is the arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested.

[0121] The EHT CQI Report field contains EHT CQI report information. EHT CQI Report information is included in the EHT compressed beamforming / CQI report if the Feedback Type subfield in the EHT MIMO Control field indicates CQI feedback.

[0122] The presence and contents of the EHT Compressed Beamforming Report field, EHT MU Exclusive Beamforming Report field, and EHT CQI Report field are dependent on the values of the Feedback Type subfield of the EHT MIMO Control field.

[0123] A Vendor Specific element is not present in the EHT Compressed Beamforming / CQI frame.

[0124] An EHT non-TB sounding sequence may be initiated by an EHT beamformer with an individually addressed EHT NDP announcement frame comprising exactly one STA Info field, followed after a short interframe space (SIFS) by an EHT sounding NDP. The EHT beamformee may respond after SIFS with an EHT compressed beamforming / CQI frame. FIG. 11 illustrates an example table 1100 of subcarrier indices for a compression beamforming feedback matrix as a function of channel width and a grouping (Ng). Ng indicates the number of adjacent subcarriers for which a single compressed beamforming feedback matrix is reported. Example table 1100 may correspond to subcarrier indices for compressed beamforming feedback matrix in accordance with an HE sounding protocol for sounding channel widths of 20 MHz, 40 MHz, 80 MHz, 160 MHz, and 80+80 MHz (i.e. 2 non-contiguous 80 MHz channel widths). An EHT sounding protocol or UHR sounding protocol may utilize the same set of subcarrier indices for compressed beamforming feedback corresponding to the same channel widths. This may be beneficial for EHT and / or UHR devices in terms of hardware complexity as the same hardware elements to support the new sounding protocols can be reused. In order to support new channel configurations (e.g. 320 MHz, punctured channels) that are not present in example table 1100 for channel sounding, an EHT or UHR sounding procedure may add a new set of subcarrier indices for the additional channel configurations.

[0125] Within the superset of subcarrier indices, when a bandwidth of the NDP is comprised in two non-contiguous frequency segments that comprise a frequency segment lower in frequency and a frequency segment higher in frequency (e.g. 80+80 MHz channel width), x(L) denotes subcarrier index x in the frequency segment lower in frequency, and x(H) denotes subcarrier index x in the frequency segment higher in frequency. Further, within the superset of subcarrier indices, an ellipsis ("...") denotes an arithmetic progression in Ng increments. It should be noted that pilot subcarriers are not skipped.

[0126] FIG. 12 illustrates an example 1200 of a non-trigger based (non-TB) sounding sequence. As shown in FIG. 12, example 1200 includes an AP 1202 and a STA 1204. Example 1200 may begin with AP 1202 initiating the non-TB sounding sequence by transmitting a 00 to STA 1204. NPDA frame 1210 may be an example of NDPA frame 700 described above. In an example, AP 1202 may be an EHT beamformer. In an example, NDPA frame 1210 may include a single STA Info field. The AID11 subfield of the STA Info field and the RA field of NDPA frame 1210 may be set to the AID of STA 1204.

[0127] NDPA frame 1210 may solicit SU feedback or CQI feedback from STA 1204. In an example, SU feedback may comprise a compressed beamforming report. In an example, the compressed beamforming report may comprise an average SNR of each spatial stream of an NDP that follows NDPA frame 1210 and compressed beamforming feedback matrices for use by AP 1202 to determine steering matrices for explicit feedback beamforming to STA 1204. In an example, CQI feedback may comprise a CQI report. In an example, the CQI report may comprise per-RU average SNRs of each spatial stream of the NDP. In an implementation, a per-RU average SNR may comprise an arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested.

[0128] A SIFS after transmitting NDPA frame 1210, AP 1202 transmits an NDP 1212. NDP 1212 may be an EHT sounding NDP. A SIFS after receiving NDP 1212, STA 1204 transmits a feedback frame 1214. Feedback frame 1214 may comprise an EHT compressed beamforming frame. For example, feedback frame 1214 may comprise an EHT compressed beamforming / CQI report. A TXVECTOR parameter CH_B AND WIDTH for a PPDU containing feedback frame 1214 may be set to indicate a bandwidth not wider than that indicated by an RXVECTOR parameter CH_B AND WIDTH of the EHT sounding NDP.

[0129] In an implementation, example 1200 may represent an EHT non-TB sounding sequence. As such, AP 1202 may represent an EHT beamformer, STA 1204 may represent an EHT beamformee, and NDP A frame 1210 may be an EHT NDPA. In an implementation, where the STA Info field in NDPA frame 1210 solicits SU feedback, the subcarrier grouping, Ng, codebook size, and the number of columns, Nc, used by STA 1204 for the generation of the SU feedback are determined by STA 1204. In an implementation, where the STA Info field in NDPA frame 1210 solicits CQI feedback, the Nc used by STA 1204 for the generation of the CQI feedback is determined by STA 1204. In an implementation, when SU feedback is solicited, bit B26 of the “Feedback Type And Ng” subfield, the Codebook Size subfield, and the Nc Index subfield of the STA Info field of NDPA frame 1210 are reserved.

[0130] Continuing with the EHT non-TB sounding sequence implementation, on receiving NDPA frame 1210 soliciting SU feedback, STA 1204 generates an EHT compressed beamforming report for SU feedback with Nc in the range 1 to 8, Ng = 4 or Ng=16, and codebook size (<|>,\| / )={4,2} or (<|),\| / ) = {6,4}. On receiving NDPA frame 1210 soliciting CQI feedback, STA 1204 generates an EHT CQI report for CQI feedback with Nc determined by STA 1204.

[0131] FIG. 13 illustrates an example 1300 of a trigger based (TB) sounding sequence. As shown in FIG. 13, example 1300 includes an AP 1302 and STAs 1304 and 1306. Example 1300 may begin with AP 1302 initiating the TB sounding sequence by transmitting an NDPA frame 1310 to STAs 1304 and 1306. NDPA frame 1310 may be an example of NDPA frame 1210 described above. In an example, AP 1302 may be an EHT beamformer. NDPA frame 1310 may include two STA Info fields with AID11 subfields set respectively to the AIDs of STAs 1304 and 1306. An RA field of NDPA frame 1310 may be set to a broadcast address.

[0132] NDPA frame 1310 may solicit SU feedback, MU feedback, or CQI feedback from STAs 1304 and 1306. In an example, SU feedback may comprise a compressed beamforming report. In an example, the compressed beamforming report may comprise an average SNR of each spatial stream and compressed beamforming feedback matrices for use by AP 1302 to determine steering matrices for explicit feedback beamforming to STAs 1304 and 1306. In an example, MU feedback may comprise a compressed beamforming report and an MU exclusive beamforming report. In an example, the MU exclusive beamforming report may comprise explicit feedback in the form of delta SNRs. In an example, CQI feedback may comprise a CQI report. In an example, the CQI report may comprise per-RU average SNRs of each spatial stream. In an implementation, a per-RU average SNR may comprise an arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested. In an example, AP 402 may be an EHT beamformer. NDPA frame 1210 may include a single STA Info field. The AID11 subfield of the STA Info field may be set to the AID of STA 1204.

[0133] A SIFS after transmitting NDPA frame 1310, AP 1302 transmits an NDP 1312. NDP 1312 may be an EHT sounding NDP. A SIFS after transmitting NDP 1312, AP 1302 transmits a trigger frame 1314. Trigger frame 1314 may be a beamforming report poll frame (BFRP) frame. Trigger frame 1314 may address STAs 1304 and 1306 as beamformees. A SIFS after receiving trigger frame 1314, STAs 1304 and 1306 may transmit respective feedback frames 1316 and 1318. Feedback frames 1316 and 1318 may each comprise an EHT compressed beamforming / CQI frame and may be carried in a TB PPDU. The EHT compressed beamforming / CQI frame may comprise one or more beamforming reports. For example, the beamforming report may comprise the compressed beamforming report, the MU exclusive beamforming report, or the CQI report.

[0134] In an implementation, AP 1302 may transmit additional trigger frames in the same TXOP to solicit feedback frames from EHT beamformees not addressed in trigger frame 1314. In an implementation, AP 1302 may not transmit a trigger frame that solicits a STA identified in NDPA frame 1310 unless the trigger frame is in the same TXOP as NDPA frame 1310.

[0135] In an implementation, example 1300 may represent an EHT TB sounding sequence. As such, AP 1302 may represent an EHT beamformer, STAs 1304 and 1305 may represent EHT beamformees, and NDPA frame 1310 may be an EHT NDPA.

[0136] In an implementation, as an EHT beamformer, AP 1302 may not transmit a BFRP Trigger frame that solicits a STA (e.g., STA 1304 or STA 1306) identified in NDPA frame 1310 unless the BFRP Trigger frame is in the same TXOP as the EHT TB sounding sequence. In an implementation, the STAs identified in NDPA frame 1310 are the same as the STAs identified in trigger frame(s) in the same TXOP.

[0137] In an implementation, as an EHT beamformer, AP 1302 may set all the bits of a “Feedback Segment Retransmission Bitmap” field of (e.g., BFRP) trigger frame 1314 to Is. (BFRP) trigger frame 1314 contains one or more User Info fields, each of which identifies an EHT beamformee (e.g., STA 1304 or STA 1306).

[0138] In an implementation, when NDPA frame 1310 solicits SU or MU feedback, a STA Info field in NDPA frame 1310 indicates the subcarrier grouping, Ng, codebook size, and the number of columns, Nc, to be used by the EHT beamformee identified by the STA Info field for the generation of the SU or MU feedback. In an implementation, when NDPA 1310 solicits CQI feedback, a STA Info field in NDPA frame 1310 indicates the Nc to be used by the EHT beamformee identified by the STA Info field for the generation of the CQI feedback.

[0139] In an implementation, as an EHT beamformee, when STA 1304 (or STA 1306) receives NDPA frame 1310 soliciting CQI feedback, STA 1304 / 1306 generates an EHT CQI report for CQI feedback with Nc determined by AP 1302.

[0140] In an implementation, as an EHT beamformee, when STA 1304 (or STA 1306) receives NDPA frame 1310 with a STA Info field identifying STA 1304 (or STA 1306) soliciting SU or MU feedback, STA 1304 (or STA 1306) generates an EHT compressed beamforming / CQI report using the feedback type, Ng, codebook size, and Nc indicated in the STA Info field. In an implementation, as an EHT beamformee, when STA 1304 (or STA 1306) receives (BFRP) trigger frame 1314 with a matching User Info field, STA 1304 (or STA 1306) transmits an EHT TB PPDU containing the EHT compressed beamforming / CQI report. In an implementation, AP 1302 transmits NDPA frame 1310 with a TA field set to a transmitted BSSID, and STA 1304 (or STA 1306) is a non-AP STA associated with an AP corresponding to a non-transmitted BSSID that supports receiving control frames with TA fields set to the transmitted BSSID, then the EHT compressed beamforming / CQI report sent by STA 1304 (or STA 1306) in response may include an RA field set to a MAC address of AP 1302.

[0141] In an implementation, if an EHT compressed beamforming / CQI report solicited by AP 1302 would result in a feedback frame (e.g., 1316 or 1318) that exceeds 11454 octets in length, then the EHT compressed beamforming / CQI report is split into up to eight feedback segments. Each feedback segment is included in a separate feedback frame and contains successive portions of the EHT compressed beamforming / CQI report. Feedback segments may be of equal length except the last feedback segment, which may be shorter. Each feedback frame that includes a feedback segment that is not the last feedback segment has a length of 11454 octets. Each feedback segment is identified by the value of the “Remaining Feedback Segments” subfield and the “First Feedback Segment” subfield in an EHT MIMO Control field of the feedback frame that includes the feedback segment. The other nonreserved subfields of the EHT MIMO Control field may be the same for all feedback segments. Feedback frames may be sent in an A-MPDU contained in a single PPDU and may be included in the A-MPDU in descending order based on values of the “Remaining Feedback Segments” subfield.

[0142] In an implementation, as an EHT beamformer, when AP 1302 transmits (BFRP) trigger frame 1324 to retrieve an EHT compressed beamforming / CQI report from an EHT beamformee (e.g., STA 1304 or STA 1306), AP 1302 solicits all possible feedback segments by setting to 1 all of the bits of the “Feedback Segment Retransmission Bitmap” subfield of the User Info field (of trigger frame 1324) identifying the EHT beamformee.

[0143] In an implementation, when an EHT beamformer (e.g., AP 1302) fails to receive some or all of the feedback segments of the EHT compressed beamforming / CQI report from an EHT beamformee (e.g., STA 1304 or STA 1306), the EHT beamformer may be configured to not transmit a further BFRP Trigger frame to request retransmission of the feedback segments. Instead of transmitting the further BFRP Trigger frame to request retransmission of the feedback segments, the EHT beamformer may repeat the entire EHT sounding sequence.

[0144] FIG. 14 illustrates an example allocation 1400 of non-distributed RUs. Tables 27-7, 27-8, and 27-9 of the IEEE 802. 11 standard provide RU indices and subcarrier ranges for RUs, for different RU type and PPDU bandwidth combinations. For example, for a 52-tone RU and a 20 MHz PPDU bandwidth, the PPDU may have four RUs, indexed RU 1, RU 2, RU 3, and RU 4. RU 1 corresponds to the subcarrier range [-121 : -70], RU 2 corresponds to the subcarrier range [-68: -17], RU 3 corresponds to the subcarrier range [17:68], and RU 4 corresponds to the subcarrier range [70: 121], For example, an allocation comprising RU 1, RU 2, RU 3, and RU 4 may be as illustrated by example allocation 1400. As shown, RU 1, RU 2, RU 3, and RU 4 each include a contiguous set of tones over a respective part of the PPDU bandwidth. The respective parts of the PPDU bandwidth covered by different RUs are nonoverlapping and may be separated from one another by one or more null tones. In an example where a PPDU comprises a single RU, the set of tones of the RU may cover the entire PPDU bandwidth.

[0145] FIG. 15 illustrates an example allocation 1500 of distributed RUs. The existing IEEE 802. 11 standard defines only RUs including contiguous sets of tones (e.g., as illustrated in FIG. 14). Such RUs are hereinafter referred to as non-distributed RUs (non-DRUs). U.S. Patent 11,044,057 proposes an RU, called distributed RU (DRU), that includes a non-contiguous set of tones spread over the PPDU bandwidth. An example allocation 1500 of distributed RUs is shown in FIG. 15. As shown, rather than an RU being composed of a contiguous set of tones that cover a respective part only of the PPDU bandwidth, a DRU may include a non-contiguous set of tones that may be spread over the entire bandwidth of the PPDU.

[0146] Spreading the RU over the entire PPDU bandwidth may significantly decrease the power spectral density (PSD) of the PPDU. This may enable the device (e.g., an AP or STA) transmitting the PPDU to operate in spectrum parts having more stringent PSD requirements. For example, expanded unlicensed use of the 6 Gigahertz Band permits operation over an additional 1.2 GHz of bandwidth (operating bands U-NII-5 (5.925-6.425 GHz), U-NII-6 (6.425-6.525 GHz), U-NII-7 (6.525-6.875 GHz), and U-NII-8 (6.875-7.125 GHz)). However, government regulation may require that devices utilizing some of the 6 GHz frequency bands support an automated frequency coordination (AFC) system, in order to operate as a standard power (SP) device (e.g. without stringent PSD requirements). AFC systems support may allow a wireless device to avoid interference with incumbent systems in the 6 GHz band. Implementation of AFC systems support, however, may result in higher development costs for wireless devices and hence, many 6 GHz devices may operate without it. Without AFC support, a wireless device may operate under low power indoor (LPI) mode, an operation mode that is strictly for indoor use. Example PSD requirements for the LPI mode are 5 dBm / MHz for an AP and -IdBm / MHz for a STA. In addition, a wireless device may operate under very low power (VLP) operation mode, an operation mode that doesn’t require AFC support and allows both indoor and outdoor use but is even more restrictive in terms of transmit power compared to the LPI mode (14 dBm Equivalent isotropic radiated power and -8 dBm / Mhz PSD). A device that spreads an RU over the entire PPDU bandwidth may leverage the lower PSD resulting from the use of distributed RUs to increase the transmit power of the PPDU while adhering to the stringent PSD requirements of LPI and VLP. This may be particularly useful in UL MU OFDMA as it may allow the transmit power of a transmitting STA to be boosted, thereby resulting in higher received powers for all tones transmitted by the STA, and a significantly enhanced overall spectrum efficiency. FIG. 16 illustrates an example 1600 that highlights a problem that may arise in association with an operation using a sounding procedure. As shown in FIG. 16, example 1600 includes an AP 1602, and STAs 1604 and 1606. STAs 1604 and 1606 may be associated with AP 1602.

[0147] In example 1600, AP 1602 may operate in a mode with reduced maximum PSD (e.g., LPI mode). In an implementation, when an AP operates in such a mode, the maximum PSD of the transmission may be limited, e.g., to avoid interfering with signals of other devices in close proximity. For example, in LPI mode, an example PSD limit for an AP, such as AP 1602, is 5 dBm / MHz, which results in a maximum of 18 dBm for 20 MHz of transmission bandwidth. This 18 dBm limit is significantly less than the 21 dBm for 20 MHz limit which, for example, may apply to SP AP transmit power.

[0148] As shown in FIG. 16, example 1600 may begin with AP 1602 transmitting a frame 1610 to STAs 1604 and 1606. In an example, frame 1610 may include an NDPA frame transmitted to initiate a sounding sequence to solicit feedback from STAs 1604 and 1606. The feedback may include one or more of, SU feedback, MU feedback, or CQI feedback. In an example, generation of the feedback by STAs 1604 and 1606 may include estimating of downlink channel coefficients between the AP and the STAs 1604 and 1606. In an example, the STA may apply smoothing to adjacent channel coefficients to reduce the effect of noise before generating the solicited feedback. In an example, the STA may not apply smoothing of adjacent channel coefficients if the channel coefficients have a high intrinsic variability between subcarriers.

[0149] In an example, SU feedback may comprise a compressed beamforming report. In an example, the compressed beamforming report may comprise an average SNR of each spatial stream and compressed beamforming feedback matrices for use by a transmit beamformer to determine steering matrices for explicit feedback beamforming.

[0150] In an example, MU feedback may comprise the compressed beamforming report and an MU exclusive beamforming report. In an example, the MU exclusive beamforming report may comprise explicit feedback in the form of delta SNRs.

[0151] In an example, CQI feedback may comprise a CQI report. In an example, the CQI report may comprise per-RU average SNRs of each spatial stream. In an implementation, each per-RU average SNR may comprise an arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested.

[0152] Continuing example 1600, because feedback was solicited by AP 1602 from STA 1604 and STA 1606, a SIFS 1640A after frame 1610 is transmitted, NDP frame 1612 is transmitted by AP 1602 to STA 1604 and STA 1606. NDP frame 1612 may be utilized by STA 1604 and STA 1606 to generate the BFRs solicited by AP 1602. In this example, because NDP frame 1612 was transmitted by AP 1602 at a lower dBm (e.g., 18 dBm) compared to a SP AP (e.g., 21 dBm), STAs 1604 and 1606 may incur a higher channel estimation noise 1689 based on the transmission of NDP 1612 as compared to a similar transmission by a SP AP. Because of additional sources of interference at edge STAs, channel estimation noise 1689 may be even higher for edge STAs.

[0153] As depicted in FIG. 16, a SIFS 1640B after NDP frame 1612 is transmitted by AP 1602, a trigger frame 1614 is transmitted by AP 1602 to trigger transmission by STA 1604 and STA 1606 of respective BFRs based on NDP frame 1612. A SIFS 1640C after trigger frame 1614 is transmitted by AP 1602, STA 1604 and STA 1606 respectively transmit BFRs 1616A-B to AP 1602. In an example, as described with FIG. 13 above, BFRs 1616A-B may comprise average SNR and beamforming feedback matrices for use by AP 1602 to determine steering matrices for explicit feedback beamforming. The beamforming steering matrices determined by AP 1602 based on BFRs 1616A-B may be used for subsequent beamformed transmissions to STA 1604 and STA 1606.

[0154] After receiving BFRs 1616A-B AP 1602 may transmit a PPDU 1680 to STA 1604 and STA 1606. In this example, PPDU 1680 is transmitted with explicit feedback beamforming based on BFRs 1616A-B. Because BFRs 1616A-B were generated based on NDP frame 1612 transmitted by AP 1602 at a lower power level than a non-AP would use, BFRs 1616A-B may include less accurate information (e.g., less accurate beamforming feedback matrices) for beamforming from AP 1602 to STA 1604 and STA 1606, as compared to BFRs generated based on an NDP transmission by a standard / regular AP. As a result of this less accurate information provided to AP 1602, the beamformed transmission of PPDU 1680 by AP 1602 may result in a receive failure 1699 at STAs 1604 and 1606.

[0155] Receive failure 1699 for PPDU 1680 may cause an inefficient and wasteful use of network resources, including wireless channel resources required to retransmit PPDU 1680, processing and power resources of AP 1602 to process and retransmit PPDU 1680, and the processing and power resources of STA 1604 and STA 1606 to perform additional sounding procedures for the retransmission of PPDU 1680.

[0156] In an embodiment that addresses the above-described problem, an AP may transmit to a STA, a first frame comprising a first indication of a transmission, by the AP, after the first frame, of a null data packet (NDP), and a second indication of a nulling of one or more first subcarriers of a bandwidth of the NDP. In another aspect, the AP may transmit to the STA, the NDP, where the transmitting of the NDP comprises nulling of the one or more first subcarriers of the bandwidth of the NDP. In another aspect, the AP receives from the STA, a beamforming report frame (BFR). The nulling of the one or more first subcarriers of the bandwidth of the NDP allows the AP to boost the power for one or more second subcarriers of the bandwidth of the NDP that are not nulled, without violating a PSD limit for the NDP transmission. The increased transmission power for the one or more second subcarriers allows the STA to receive the NDP with low channel estimation noise and to generate a higher accuracy BFR based on the NDP.

[0157] FIG. 17 illustrates an example 1700 of an operation using a sounding procedure according to an embodiment. As shown in FIG. 17, example 1700 includes an AP 1702, and STAs 1704 and 1706. STAs 1704 and 1706 may be associated with AP 1702. In example 1700, AP 1702 may operate in a mode with reduced maximum PSD (e.g., LPI mode). In an implementation, when an AP operates in such a mode, the maximum PSD of the transmission may be limited, e.g., to avoid interfering with signals of other devices in close proximity. For example, in LPI mode, an example PSD limit for an AP, such as AP 1702, is 5 dBm / MHz, which results in a maximum of 18 dBm for 20 MHz of transmission bandwidth. This 18 dBm limit is significantly less than the 21 dBm for 20 MHz limit which, for example, may apply to SP AP transmit power.

[0158] As shown in FIG. 17, example 1700 may begin with AP 1702 transmitting a frame 1710 to STAs 1704 and 1706. In an example, frame 1710 may include an NDPA frame transmitted to initiate a sounding sequence to solicit feedback from STAs 1704 and 1706. The feedback may include one or more of, SU feedback, MU feedback, or CQI feedback. In an example, generation of the feedback by STAs 1704 and 1706 may include estimating downlink channel coefficients between the AP and the STAs 1704 and 1706. In an example, the STA may apply smoothing to adjacent channel coefficients to reduce the effect of noise before generating the solicited feedback. In an example, the STA may not apply smoothing of adjacent channel coefficients when the channel coefficients have a high intrinsic variability between subcarriers.

[0159] In an example, SU feedback may comprise a compressed beamforming report. In an example, the compressed beamforming report may comprise an average SNR of each spatial stream and compressed beamforming feedback matrices for use by a transmit beamformer to determine steering matrices for explicit feedback beamforming. In an example, CQI feedback may comprise a CQI report. In an example, the CQI report may comprise per-RU average SNRs of each spatial stream. In an implementation, each per-RU average SNR may comprise an arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested.

[0160] As depicted, in an embodiment, frame 1710 includes a first indication 1720, a second indication 1725, and a third indication 1730. Notwithstanding the depiction of first indication 1720, second indication 1725, and third indication 1730 included in frame 1710, additional or alternative embodiments may include combinations of one or more of, first indication 1720, second indication 1725, and third indication 1730, as well as other indications.

[0161] In an embodiment, frame 1710 may be an NDPA frame, and first indication 1720 may indicate to STA 1704 and STA 1706 that AP 1702 will transmit, after the transmission of frame 1710, an NDP frame 1712. By first indication 1720, frame 1710 initiates a sounding procedure to solicit feedback from STA 1704 and STA 1706. In different implementations, frame 1710 may solicit one or more of SU feedback, MU feedback, or CQI feedback, from STA 1704 and STA 1706. In an example, first indication 1720 may correspond to a frame subtype field in frame 1710 indicating that frame 1710 is an NPDA frame as described in FIG. 7.

[0162] As depicted, in an embodiment, frame 1710 further includes second indication 1725. In example 1700, second indication 1725 comprises an indication of one or more first subcarriers of a bandwidth of NDP frame 1712. In an implementation, the one or more first subcarriers of the bandwidth of NDP frame 1712 may include a non-contiguous set of tones spread over the bandwidth of NDP frame. Similar to example allocation 1500 of distributed RUs shown in FIG. 15, rather than the one or more first subcarriers being composed of a contiguous set of tones that cover a respective part only of the bandwidth of NDP frame 1712, the one or more first subcarriers may include a non-contiguous set of tones that may be spread over the bandwidth of NDP frame 1712.

[0163] In an implementation discussed below, in transmitting NDP frame 1712, AP 1702 may null the one or more first subcarriers of NDP frame 1712. The transmission of NDP frame 1712 may thus include a non-contiguous set of non-nulled tones that are spread over the bandwidth of NDP frame 1712 are received by STAs 1704 and 1706.

[0164] As depicted, in an embodiment, frame 1710 further includes third indication 1730. In example 1700, third indication 1730 comprises an indication of one or more second subcarriers of the bandwidth of NDP frame 1712. In an implementation, the one or more second subcarriers include selected ones of the non-nulled tones of NDP frame 1712, e.g., the non-nulled tones are identified by the nulled tones of the one or more first subcarriers. The one or more second subcarriers may correspond to some or all of the non-nulled tones of NDP frame 1712. In an implementation, the third indication may be provided in a number of grouping (Ng) field of the frame 1710.

[0165] Continuing example 1700, a SIFS 1740A after frame 1710 is transmitted, AP 1702 may transmit NDP frame 1712. In contrast to the transmission of NDP frame 1612 described with FIG. 16 above, in an embodiment, AP 1702 transmits NDP frame 1712, based on the second indication. That is, AP 1702 may null (or transmit with a reduced power via) the one or more first subcarriers indicated by the second indication in transmitting NDP frame 1712. Because some of the tones of NDP frame 1712 are not used to transmit NDP frame 1712, the power on certain tones of NDP frame 1712 may be increased, with the PSD limit remaining at the lower LPI level described with FIG. 16 above. For example, when third indication 1730 is set to select one of every four tones from the bandwidth of NDP frame 1712, transmit power can be 18 dBm + 10*logl0(4) or 24 dBm / 20 MHz. Thus, embodiments described herein may transmit NDP frame 1712 at a higher transmit power compared to 18 dBm / 20 MHz used to transmit frame 1612 above, and the maximum 21 dBm / 20 MHz applied to SP APs.

[0166] Continuing example 1700, because feedback was solicited by AP 1702 from STA 1704 and STA 1706, NDP frame 1712 is transmitted by AP 1702 to STA 1704 and STA 1706, and respectively utilized to generate the BFRs solicited by AP 1702. In this example, because NDP frame 1712 was transmitted by AP 1702 at a higher dBm (e.g., 24 dBm) compared to the transmission of NDP frame 1612 (e.g., 18 dBm), STAs 1704 and 1706 incur a low channel estimation noise based on NDP frame 1712 compared to the higher channel estimation noise 1689 described with FIG. 16.

[0167] As depicted in FIG. 17, a SIFS 1740B after NDP frame 1712 is transmitted by AP 1702, a trigger frame 1714 is transmitted by AP 1702 to trigger transmission by STA 1704 and STA 1706 of respective BFRs based on NDP frame 1712. A SIFS 1740C after trigger frame 1714 is transmitted by AP 1702, STA 1704 and STA 1706 respectively transmit BFRs 1716A-B to AP 1702. In an example, as described with FIG. 13 above, the BFRs may comprise average SNR and beamforming feedback matrices for use by AP 1702 to determine steering matrices for explicit feedback beamforming. The steering matrices determined by AP 1702 based on BFRs 1716A-B may be used for subsequent beamformed transmissions to STA 1704 and STA 1706.

[0168] In an embodiment, a first predetermined set of subcarrier indices are associated with the one or more second subcarriers. STAs 1704 and 1706 may generate BFRs 1716A-B based on the first predetermined set of subcarrier indices. In an implementation, BFRs 1716A-B comprise a UHR compressed BFR. In an embodiment, the first predetermined set of subcarrier indices is based on a second predetermined set of subcarrier indices for feedback of an extremely high throughput (EHT) compressed BFR as shown in FIG. 11 above. In an example, the first predetermined set of subcarrier indices may correspond to the subcarrier indices shown in FIG. 11 without changes. In an embodiment, the first predetermined set of subcarrier indices excludes at least one subcarrier index of the second predetermined set of subcarrier indices. In an example, the first predetermined set of subcarrier indices for a channel width of 20 MHz and Ng=4 may correspond to the subcarrier indices shown in FIG. 11, but with indices - 122, -2, 2, and 122 excluded to cause the one or more second subcarriers to have a uniform minimum tone spacing of 4.

[0169] After BFRs 1716A-B are received by AP 1702, PPDU 1780 is transmitted to STA 1704 and STA 1706. In this example, PPDU 1780 is transmitted with explicit feedback beamforming based on BFRs 1716A-B. Because BFRs 1716A-B were generated based on NDP frame 1712 transmitted by AP 1702 at a higher energy level than NDP frame 1612 described with FIG. 16 above, the sounding procedure that was used by STAs 1604 and 1606 may perform better when used for the transmission of PPDU 1780 by AP 1702, and not result in a receive failure, such as receive failure 1699 in FIG. 16. Thus, at least based on the foregoing, embodiments depicted with FIG. 17 may avoid the problem described above with FIG. 16.

[0170] FIG. 18 illustrates an example 1800 of an operation using a sounding procedure according to an embodiment. As shown in FIG. 18, example 1800 includes an AP 1802, and STAs 1804 and 1806. STAs 1804 and 1806 may be associated with AP 1802. In example 1800, AP 1802 may operate in a mode with reduced maximum PSD (e.g., UPI mode). In an implementation, when an AP operates in such a mode, the maximum PSD of the transmission may be limited, e.g., to avoid interfering with signals of other devices in close proximity. For example, in UPI mode, an example PSD limit for an AP, such as AP 1802, is 5 dBm / MHz, which results in a maximum of 18 dBm for 20 MHz of transmission bandwidth. This 18 dBm limit is significantly less than the 21 dBm for 20 MHz limit which, for example, may apply to SP AP transmit power.

[0171] As shown in FIG. 18, the operation using a sounding procedure of example 1800 may begin with AP 1802 transmitting a frame 1810 to STAs 1804 and 1806. In an example, frame 1810 may comprise an NDPA frame transmited to initiate a sounding procedure to solicit feedback from STA 1804 and STA 1806. The feedback may include one or more of, SU feedback, MU feedback, or CQI feedback. In an example, generation of the feedback by STAs 1804 and 1806 may include estimating downlink channel coefficients between the AP and the STAs 1804 and 1806. In an example, the STA may apply smoothing to adjacent channel coefficients to reduce the effect of noise before generating the solicited feedback. In an example, the STA may not apply smoothing of adjacent channel coefficients when the channel coefficients have a high intrinsic variability between subcarriers.

[0172] In an example, SU feedback may comprise a compressed beamforming report. In an example, the compressed beamforming report may comprise an average SNR of each spatial stream and compressed beamforming feedback matrices for use by a transmit beamformer to determine steering matrices for explicit feedback beamforming. In an example, CQI feedback may comprise a CQI report. In an example, the CQI report may comprise per-RU average SNRs of each spatial stream. In an implementation, each per-RU average SNR may comprise an arithmetic mean of the SNR in decibels over the subcarriers of a 26-tone RU for which feedback is being requested.

[0173] Continuing example 1800, a SIFS 1840A after frame 1810 is transmited, AP 1802 may transmit an NDP frame 1812. As depicted, in an embodiment, NDP frame 1812 includes a first indication 1820, a second indication 1825, and a third indication 1830. Notwithstanding the depiction of first indication 1820, second indication 1825, and third indication 1830 included in NDP frame 1812, additional or alternative embodiments may include combinations of one or more of a first indication 1820, a second indication 1825, and a third indication 1830, as well as other indications.

[0174] As depicted, in an embodiment, frame 1810 further includes second indication 1825. In example 1800, second indication 1825 comprises an indication of one or more first subcarriers of a bandwidth of NDP frame 1812. In an implementation, the one or more first subcarriers of the bandwidth of NDP frame 1812 may include a non-contiguous set of tones spread over the bandwidth of NDP frame. Similar to the example allocation of distributed RUs shown in FIG. 15, rather than the one or more subcarriers being composed of a contiguous set of tones that cover a respective part only of the bandwidth of NDP frame 1812, the one or more first subcarriers of a bandwidth may include a non-contiguous set of tones that may be spread over the bandwidth of the NDP frame.

[0175] In an implementation discussed below, in transmiting NDP frame 1812, AP 1802 may null the one or more first subcarriers of NDP frame 1812. The transmission of NDP frame 1812 may thus include such that a non-contiguous set of non-nulled tones that are spread over the bandwidth of the NDP frame 1812 are received by STAs 1804 and 1806.

[0176] As depicted, in an embodiment, frame 1810 further includes third indication 1830. In example 1800, third indication 1830 comprises an indication of one or more second subcarriers of the bandwidth of NDP frame 1812. In an implementation, the one or more second subcarriers include selected ones of the non-nulled tones of NDP frame 1812, e.g., the non-nulled tones are identified by the nulled tones of the one or more first subcarriers. The one or more second subcarriers may correspond to some or all of the non-nulled tones of NDP frame 1812. In an implementation, the third indication may be provided in a number of grouping (Ng) field of the frame 1810.

[0177] Continuing example 1800, a SIFS 1840A after frame 1810 is transmitted, AP 1802 may transmit NDP frame 1812. In contrast to the transmission of NDP frame 1612 described with FIG. 16 above, in an embodiment, AP 1802 transmits NDP frame 1812 based on the second indication. That is, AP 1802 may null (or transmit with a reduced power via) the one or more first subcarriers indicated by the second indication in transmitting NDP frame 1812. Because some of the tones of NDP frame 1812 are not used to transmit NDP frame 1812, the power on certain tones of NDP frame 1812 may be increased, with the PSD limit remaining at the lower LPI level described with FIG. 16 above. For example, when third indication 1830 is set to select one of every four tones from the bandwidth ofNDP frame 1812, transmit power can be 18 dBm + 10*logl0(4) or 24 dBm / 20 MHz. Thus, embodiments described herein may transmit NDP frame 1812 at a higher transmit power compared to 18 dBm / 20 MHz used to transmit frame 1612 above, and the maximum 21 dBm / 20 MHz applied to SP APs.

[0178] Continuing example 1800, because feedback was solicited by AP 1802 from STA 1804 and STA 1806, NDP frame 1812 is transmitted by AP 1802 to STA 1804 and STA 1806, and respectively utilized to generate the BFRs solicited by AP 1802. In this example, because NDP frame 1812 was transmitted by AP 1802 at a higher dBm (e.g., 24 dBm) compared to the transmission ofNDP frame 1612 (e.g., 18 dBm), STAs 1804 and 1806 incur a low channel estimation noise based on NDP frame 1812 compared to the higher channel estimation noise 1689 described with FIG. 16.

[0179] As depicted in FIG. 18, a SIFS 1840B after NDP frame 1812 is transmitted by AP 1802, a trigger frame 1814 is transmitted by AP 1802 to cause transmission by STA 1804 and STA 1806 of respective BFRs based on NDP frame 1812.

[0180] A SIFS 1840C after trigger frame 1814 is transmitted by AP 1802, STA 1804 and STA 1806 respectively transmit BFRs 1816A-B to AP 1802. In an example, as described with FIG. 13 above, the BFRs may comprise average SNR and beamforming feedback matrices for use by AP 1802 to determine steering matrices for explicit feedback beamforming. The steering matrices determined by AP 1802 based on BFRs 1816A-B may be used for subsequent beamformed transmissions to STA 1804 and STA 1806.

[0181] After BFRs 1816A-B are received by AP 1802, PPDU 1880 is respectively transmitted to STA 1804 and STA 1806. In this example, PPDU 1880 is transmitted with explicit feedback beamforming based on BFRs 1816A-B. As depicted, because BFRs 1816A-B were generated based on NDP frame 1812 transmitted by AP 1802 at a higher energy level than NDP frame 1612 described with FIG. 16 above, the sounding procedure that was used by STAs 1604 and 1606 may perform better when used for the transmission of PPDU 1880 by AP 1802, and not result in a receive failure, such as receive failure 1699 in FIG. 16. Thus, at least based on the foregoing, embodiments depicted with FIG. 18 may avoid the problem described above with FIG. 16. FIG. 19 illustrates an example process 1900 according to an embodiment. Example process 1900 is provided for the purpose of illustration only and is not limiting of embodiments. Example process 1900 may be performed by STAs such as STA 1704, STA 1706, STA 1804, and / or STA 1806, for example. As shown in FIG. 19, process 1900 may include steps 1902 and 1904.

[0182] Step 1902 includes receiving, by a station (STA) from an access point (AP), a first frame comprising, a first indication of a transmission, by the AP, after the first frame, of a null data packet (NDP), and a second indication of a nulling (e.g., by the AP) of one or more first subcarriers of a bandwidth of the NDP. The first frame may include a data frame, a management frame, or a control frame. In an example, the first frame comprises a UHRNDP announcement frame. In an embodiment, example process 1900 further includes receiving, by the STA from the AP, the NDP using the bandwidth of the NDP.

[0183] Step 1904 includes based on the second indication, generating, by the STA, a BFR. In an embodiment, example process 1900 further includes transmitting, by the STA to the AP, the BFR. In an implementation, the transmitting of the BFR comprises transmitting the BFR in response to the transmitting of the NDP.

[0184] In an example, the first frame further comprises a third indication, with the third indication being associated with one or more second subcarriers of the bandwidth of the NDP. In an implementation, the third indication may be provided in a number of grouping (Ng) field of the first frame. The generating of the BFR may be based on the one or more second subcarriers.

[0185] In an embodiment, a first predetermined set of subcarrier indices may be associated with the one or more second subcarriers, and the generating of the BFR may be based on the first predetermined set of subcarrier indices. In an example, the BFR comprises a UHR compressed BFR, and the first predetermined set of subcarrier indices may be based on a second predetermined set of subcarrier indices for feedback of an extremely high throughput (EHT) compressed BFR. The first predetermined set of subcarrier indices excludes at least one subcarrier index of the second predetermined set of subcarrier indices. In an embodiment, to generate the BFR, the STA may generate, one or more compressed beamforming feedback matrices respectively corresponding to the one or more second subcarriers.

[0186] In an embodiment, receiving the NDP comprises receiving the NDP with the one or more first subcarriers nulled. In an implementation, receiving of the NDP with the one or more first subcarriers nulled comprises receiving the one or more first subcarriers with a first transmit power and the one or more second subcarriers using a second transmit power. A power threshold applied to the transmit power may be based on a thermal noise power of a bandwidth of the one or more first subcarriers, and the first transmit power may comprise transmit power that is less than a power threshold. In an additional example, the bandwidth is equal to 78.125 kHz. Additionally or alternatively, the first transmit power comprises transmit power that is less than the second transmit power. In additional or alternative embodiments, receiving of the NDP comprises receiving the one or more first subcarriers nulled or with zero energy, based on the second indication. In an example, generating of the BFR may include estimating of a downlink channel coefficients between the AP and the STA. In an example, the STA may apply a smoothing of adjacent channel coefficients based on the second indication of the nulling of one or more first subcarriers of the bandwidth of the NDP. In an example, if the second indication of the nulling indicates that there is zero energy on the one or more first subcarriers of the bandwidth of the NDP, the STA does not apply the smoothing of the downlink channel estimates.

[0187] In an example, first indication comprises an indication that the first frame comprises an NDP announcement frame, and the NDP announcement frame comprises an ultra-high reliability (UHR) NDP announcement frame. In an example, the first indication is provided in a sounding dialog token field of the first frame. In an example, the first indication is provided in a STA info field of the first frame. In an example, an association identifier (AID) of the STA info field comprises 2047. In an example, the second indication is provided in a sounding dialog token field of the first frame. In an example, the second indication is provided in a STA info field of the first frame. In an example, an AID of the second STA info field comprises 2047. In an example, the NDP comprises a UHR physical layer protocol data unit (PPDU). In an example, receiving the NDP comprises receiving the NDP via a non-distributed resource unit or a distributed resource unit. In an embodiment, process 1900 further includes receiving, by the STA from the AP, the NDP using the bandwidth of the NDP.

[0188] In an embodiment, the generating of the BFR comprises estimating a downlink channel between the AP and the STA. In an implementation, estimating the downlink channel between the AP and the STA comprises applying a smoothing of adjacent channel coefficients based on the second indication. In an implementation, based on the second indication of the nulling indicating that there is zero energy on the one or more first subcarriers of the bandwidth of the NDP, the STA does not apply the smoothing to the adjacent channel coefficients.

[0189] FIG. 20 illustrates an example process 2000 according to an embodiment. Example process 2000 is provided for the purpose of illustration only and is not intended to be limiting of embodiments. Example process 2000 may be performed by AP STAs such as AP 1702, and / or AP 1802, for example. As shown in FIG. 20, process 2000 may include steps 2002 and 2004.

[0190] Step 2002 includes transmitting, by an access point (AP) to a station (STA), a first frame comprising a first indication of a transmission, by the AP, after the first frame, of a null data packet (NDP), and a second indication of a nulling of one or more first subcarriers of a bandwidth of the NDP. In an example, the first frame further comprises a third indication, with the third indication being associated with one or more second subcarriers of the bandwidth of the NDP. In an implementation, the third indication may be provided in a number of grouping (Ng) field of the first frame. The generating of the BFR may be based on the one or more second subcarriers.

[0191] Step 2004 includes transmitting, by the AP to the STA, the NDP, with the transmitting of the NDP comprises nulling of the one or more first subcarriers of the bandwidth of the NDP. In an embodiment, a class of operation of the AP restricts the AP to transmit at least the NDP with a power spectral density (PSD) greater than a PSD threshold. The class of operation may include a low power indoor (LPI) operation or a very low power (VLP) operation.

[0192] In an embodiment, example process 2000 further includes receiving, by the AP from the STA, a beamforming report frame (BFR). The receiving of the BFR frame comprises receiving the BFR frame in response to the receiving the NDP. In an embodiment, example process 2000 further includes transmitting, by the AP from the STA, a trigger frame soliciting the BFR frame. In an implementation, receiving the BFR frame comprises receiving the BFR frame in response to the trigger frame.

[0193] In an implementation, ones of a first predetermined set of subcarrier indices are associated with the one or more second subcarriers, and where the first predetermined set of subcarrier indices are for use by the STA to generate the BFR frame. In an example, the BFR comprises a UHR compressed BFR, and the first predetermined set of subcarrier indices may be based on a second predetermined set of subcarrier indices for feedback of an extremely high throughput (EHT) compressed BFR. The first predetermined set of subcarrier indices excludes at least one subcarrier index of the second predetermined set of subcarrier indices. In an embodiment, to generate the BFR, the STA may generate, one or more compressed beamforming feedback matrices respectively corresponding to the one or more second subcarriers.

[0194] In an implementation, transmitting the NDP with the one or more first subcarriers nulled comprises transmitting the one or more first subcarriers with a first transmit power and the one or more second subcarriers using a second transmit power. A power threshold applied to the transmit power may be based on a thermal noise power of a bandwidth of the one or more first subcarriers, and the first transmit power may comprise transmit power that is less than a power threshold. In an additional example, the bandwidth is equal to 78.125 kHz. Additionally or alternatively, the first transmit power comprises transmit power that is less than the second transmit power. In additional or alternative embodiments, transmitting the NDP with the one or more first subcarriers nulled comprises transmitting the NDP with zero energy on the one or more first subcarriers, and the one or more first subcarriers nulled or not, based on the second indication.

[0195] In an example, first indication comprises an indication that the first frame comprises an NDP announcement frame, and the NDP announcement frame comprises an ultra-high reliability (UHR) NDP announcement frame. In an example, the first indication is provided in a sounding dialog token field of the first frame. In an example, the first indication is provided in a STA info field of the first frame. In an example, an association identifier (AID) of the STA info field comprises 2047. In an example, the second indication is provided in a sounding dialog token field of the first frame. In an example, the second indication is provided in a STA info field of the first frame. In an example, an AID of the second STA info field comprises 2047. In an example, the NDP comprises a UHR physical layer protocol data unit (PPDU). In an example, a resource unit of the NDP comprises a distributed resource unit or a nondistributed resource unit.

Claims

CLAIMS:

1. A method comprising : transmitting, by an access point (AP) to a station (STA), a first frame comprising: a first indication of a transmission, by the AP, after the first frame, of a null data physical layer protocol data unit (NDP); and a second indication of a nulling of one or more first subcarriers of a bandwidth of theNDP; and transmitting, by the AP to the STA, the NDP, wherein the transmitting of the NDP comprises nulling the one or more first subcarriers of the bandwidth of the NDP.

2. The method of claim 1 wherein the one or more first subcarriers are for use by the STA to generate a beamforming report (BFR) based on the NDP, wherein the first frame comprises a third indication of a nulling by the AP of one or more second subcarriers of the bandwidth of the NDP, wherein the transmitting of the NDP by the AP to the STA is based on the third indication, the method comprising receiving, by the AP from the STA, the BFR.

3. The method of claim 2, further comprising, receiving, by the AP from the STA, a beamforming report (BFR).

4. The method of claim 3, wherein the receiving of the BFR comprises receiving the BFR in response to the transmitting of the NDP.

5. The method of any of claims 3, further comprising transmitting, by the AP to the STA, a trigger frame soliciting the BFR.

6. The method of claim 5, wherein the receiving of the BFR comprises receiving the BFR in response to the trigger frame.

7. The method of any of claims 3-6, wherein the first frame further comprises a third indication, wherein the third indication is associated with one or more second subcarriers of thebandwidth of the NDP, and wherein the one or more second subcarriers are for use by the STA to generate the BFR based on the NDP.

8. The method of claim 7, wherein the third indication is provided in a number of grouping (Ng) field of the first frame.

9. The method of any of claims 7-8, wherein the third indication indicates a first set of subcarrier indices, and wherein each subcarrier index of the set of subcarrier indices is associated with a respective subcarrier of the one or more second subcarriers.

10. The method of claim 9, wherein the BFR comprises a compressed BFR.

11. The method of claim 10, wherein the first set of subcarrier indices is based on a second set of subcarrier indices for feedback of an extremely high throughput (EHT) compressed beamforming report.

12. The method of claim 11, wherein the first set of subcarrier indices excludes at least one subcarrier index of the second set of subcarrier indices.

13. The method of any of claims 7-12, wherein the BFR is generated by the STA based on one or more compressed beamforming feedback matrices respectively corresponding to the one or more second subcarriers.

14. The method of claim 13, wherein the one or more compressed beamforming feedback matrices are respectively generated by the STA for the one or more second subcarriers.

15. The method of any of claims 7-14, wherein the transmitting of the NDP comprises transmitting the one or more first subcarriers using a first transmit power and the one or more second subcarriers using a second transmit power.

16. The method of claim 15, wherein the first transmit power comprises a transmit power that is less than a power threshold.

17. The method of claim 16, wherein the power threshold is based on a thermal noise power of a bandwidth of the one or more first subcarriers.

18. The method of claim 17, wherein the bandwidth is equal to 78.125 kHz19. The method of any of claims 15-18, wherein the first transmit power comprises a transmit power that is less than the second transmit power.

20. The method of any of claims 2-19, wherein the first indication comprises an indication that the first frame comprises an NDP announcement frame.

21. The method of claim 20, wherein the NDP announcement frame comprises an ultra-high reliability (UHR) NDP announcement frame.

22. The method of any of claims 2-21, wherein the first indication is provided in a sounding dialog token field of the first frame.

23. The method of any of claims 2-21, wherein the first indication is provided in a STA info field of the first frame.

24. The method of claim 23, further comprising setting, by the AP, an association identifier (AID) of the STA info field to 2047.

25. The method of any of claims 2-24, wherein the second indication is provided in a sounding dialog token field of the first frame.

26. The method of any of claims 2-25, wherein the second indication is provided in a STA info field of the first frame.

27. The method of claim 26, further comprising setting, by the AP, an association identifier (AID) of the STA info field to 2047.

28. The method of any of claims 2-16, wherein the nulling of the one or more first subcarriers comprises transmitting the one or more first subcarriers with zero energy.

29. The method of any of claims 2-16, wherein the transmitting of the NDP comprises nulling the one or more first subcarriers or transmitting the one or first subcarriers with non-zero energy, based on the second indication.

30. The method of any of claims 2-29, wherein the NDP comprises an ultra-high reliability (UHR) physical layer protocol data unit (PPDU).

31. The method of any of claims 2-30, wherein the transmitting of the NDP comprises transmitting the NDP via a distributed resource unit.

32. The method of any of claims 2-30, wherein the transmitting of the NDP comprises transmitting the NDP via a non-distributed resource unit.

33. The method of any of claims 2-32, further comprising, receiving, by the AP from the STA, a second frame indicating a capability of the STA to support a processing of the second indication.

34. The method of claim 33, wherein the transmitting of the first frame is based on the capability.

35. The method of any of claims 2-34, wherein a class of operation of the AP restricts the AP to transmit at least the NDP with a power spectral density (PSD) lower than a PSD threshold.

36. The method of claim 35, wherein the class of operation comprises a low power indoor (LPI) operation or a very low power (VLP) operation.

37. A method comprising: receiving, by a station (STA) from an access point (AP), a first frame comprising: a first indication of a transmission, by the AP, after the first frame, of a null data packet(NDP); and a second indication of a nulling of one or more first subcarriers of a bandwidth of theNDP; and based on the second indication, generating, by the STA, a beamforming report (BFR).

38. The method of claim 37 wherein the one or more first subcarriers are for use by the STA to generate a beamforming report (BFR) based on the NDP, the method comprising: receiving, by the STA from the AP, the NDP, and transmitting, by the STA to the AP, the BFR.

39. The method of either of claims 37 or 38, further comprising, transmitting, by the STA to the AP, the BFR.

40. The method of claim 39, wherein the transmitting of the BFR comprises transmitting the BFR in response to receiving the NDP.

41. The method of claim 39, wherein the first frame comprises a trigger frame soliciting theBFR.

42. The method of any of claims 37 - 41, wherein the first frame further comprises a third indication, wherein the third indication is associated with one or more second subcarriers of the bandwidth of the NDP, and wherein the generating of the BFR is further based on the one or more second subcarriers.

43. The method of claim 42, wherein the third indication is provided in a number of grouping (Ng) field of the first frame.

44. The method of any of claims 37 - 43, further comprising receiving the NDP, wherein the receiving of the NDP comprises receiving the NDP with the one or more first subcarriers nulled.

45. The method of claim 44, wherein the receiving of the NDP comprises receiving the NDP with the one or more first subcarriers transmitted using a first transmit power and the one or more second subcarriers using a second transmit power.

46. The method of any of claims 44 - 45, wherein the receiving of the NDP with the one or more first subcarriers nulled comprises the receiving of the NDP with zero energy on the one or more first subcarriers.

47. The method of any of claims 44 - 45, wherein the receiving of the NDP comprises receiving the one or more first subcarriers nulled or with nonzero energy, based on the second indication.

48. The method of any of claims 37 -47, wherein the second indication is provided in a STA info field of the first frame.

49. The method of claim 37 - 48, wherein an AID of the second STA info field comprises 2047.

50. The method of any of claims 37 - 49, wherein the NDP comprises a UHR physical layer protocol data unit (PPDU).

51. The method of any of claims 37 - 50, wherein a resource unit of the NDP comprises a distributed resource unit.

52. The method of any of claims 37 - 51, wherein receiving the NDP comprises receiving theNDP via a non-distributed resource unit.

53. The method of any of claims 37 - 52, further comprising, transmitting, by the STA to the AP, a second frame indicating a capability of the STA to support a processing of the second indication.

54. The method of any of claims 37 - 53, further comprising, receiving, by the STA from the AP, the NDP using the bandwidth of the NDP.

55. The method of any of claims 37 - 54, wherein the generating of the BFR comprises estimating a downlink channel between the AP and the STA.

56. The method of claim 55, wherein estimating the downlink channel between the AP and the STA comprises applying a smoothing of adjacent channel coefficients based on the second indication.

57. The method of claim 56, wherein based on the second indication of the nulling indicating that there is zero energy on the one or more first subcarriers of the bandwidth of the NDP, the STA does not apply the smoothing to the adjacent channel coefficients.

58. A device, arranged to operate as an Access Point (AP) comprising:- a transceiver;- a processor, arranged to cause the transceiver to: transmit, to a station (STA), a first frame comprising: a first indication of a transmission, after the first frame, of a null data physical layer protocol data unit (NDP); and a second indication of a nulling of one or more first subcarriers of a bandwidth of the NDP; and transmit, to the STA, the NDP, wherein the transmitting of the NDP comprises nulling the one or more first subcarriers of the bandwidth of the NDP.

59. A method comprising: receiving, by a station (STA) from an access point (AP), a first frame comprising: a first indication of a transmission, by the AP, after the first frame, of a null data packet (NDP); and a second indication of a nulling of one or more first subcarriers of a bandwidth of theNDP; and based on the second indication, generating, by the STA, a beamforming report (BFR).

60. A computer program product, storable on a computer-readable medium and arranged, when run on a computer to execute the method of any of claims 1 - 57.

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