Secondary channel access switching using spatial reuse operations

Abstract

A method for stations (STA) of a Basic Service Set (BSS) to switch from a primary channel access (CA) scheme to a secondary CA scheme. STA11 detects on primary channel, P1, interference from an overla

Description

FIELD OF THE DISCLOSURE The present disclosure generally relates to wireless communications and more specifically to wireless communications involving non-primary channel access. BACKGROUND OF THE DISCLOSURE The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. Furthermore, all embodiments are not necessarily intended to solve all or even any of the problems brought forward in this section. Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks. The WLAN (Wireless Local Area Network) technology based on the IEEE (Institute of Electrical and Electronics Engineers - RTM) 802.11 family standards provides a very simple distributed channel access mechanism. Distributed channel access means that a device, in IEEE 802.11 terminology known as a station (STA), either access point (AP) or a non-access point (non-AP), tries to access the channel when it has data to send, usually using contention schemes on a so-called primary channel. An operating band of 40, 80, 160 or 320MHz (or even more in the future) is usually made of a primary channel and one or more secondary channels (each channel being 20MHz or a multiple thereof). The primary channel is used for signalling (including channel access procedure such as the contention-based channel access method called Enhanced Distributed Channel Access - EDCA) and backwards compatibility, while the secondary channels are used to extend the bandwidth, hence to obtain higher throughput. The majority of the 802.11 features assume that the primary channel is idle to allow channel access. If the primary channel is busy for instance due to interference, stations should not send any frame even if the secondary channels are idle. This leads to a main drawback: if only the primary channel is busy, the secondary channels in the rest of the operating band remain unused during the occupancy time of the primary channel. So the bandwidth usage efficiency decreases a lot due to this rule. To overcome this drawback, the new task group 802.11 bn (Ultra High Reliability (UHR)) introduced a new 802.11 feature known as “secondary” or “non-primary” channel access procedure also referred to as SCA or NPCA mechanism. The principle of this procedure is detailed in Figure 2. Usually, AP and STAs perform backoff procedure in the primary backoff 20 MHz channel only, also called the primary channel. By using the NPCA mechanism, a STA / AP can enable one or more backoff procedures in the secondary channels. If the primary 20 MHz channel becomes busy because of an “inter-BSS” or “OBSS” TXOP obtained by a STA belonging to a neighbour or overlapping BSS (for “Basic Set Service”), also called OBSS, the sensing STA can switch to one of the secondary channels of its operating band to run another backoff procedure (other than the conventional one on the primary channel). The selected new 20MHz channel can be referred to as “anchor channel” or “NPCA Primary Channel” (NPCA PCH). Frame exchanges can then take place over the NCPA PCH, as long as the TXOP of the OBSS STA continues. No later than the end of the TXOP, the STA can switch back to its primary channel. Contribution IEEE802.11 -24 / 495 enhances this mechanism by proposing that a STA switching to the NPCA PCH send an ICF (initial control frame) on the NPCA PCH to validate its channel switching to the other STAs. This initial control frame may be a RTS frame or a MU-RTS frame. An acknowledgment frame (“immediate response”) sent in response allows validating the switching of the other STAs. However, the NPCA mechanism, even with the ICF, still does not optimize the use of the spectrum available, in particular in the case of hidden nodes that are unable to detect the inter-BSS or OBSS TXOP. Indeed, while some STAs automatically switch to the NPCA PCH upon detecting the inter-BSS or OBSS TXOP, those “hidden” STAs are unable to switch and receive the ICF and thus remain on the primary channel for channel access. It results in misalignment between the channels to be used by the stations of the BSS to perform channel access (i.e., to initiate a backoff procedure). Transmissions between STAs having switched to the NPCA PCH and STAs of the same BSS remaining on the primary channel are no longer possible. Accordingly, there is a need to improve the NPCA mechanism, so that bandwidth usage efficiency is optimized. SUMMARY OF THE DISCLOSURE It is a broad objective of the present disclosure to overcome some of the foregoing concerns. An aim of the disclosure is to improve the use of the medium within the operating band. It is achieved by enabling non-primary channel access operation, i.e., operations on secondary channels different from the primary channel, by AP or non-AP STA upon the detection of the OBSS packet on the primary channel. Co-pending UK application No 2409658.8, entitled “ANCHOR CHANNEL SWITCHING MECHANISM FOR MULTI-RADIO DEVICE” and filed on July 3rd, 2024, provides a way to manage hidden-node situations in case where a STA has two radios, such as multi-link devices. The co-pending application proposes that one radio remains the primary channel while the additional second radio, even low resources, operates on the anchor channel to detect a frame (such as the ICF) in order to initiate anchor channel access switch of the STA. Not all the stations have multiple radios. Therefore, there is a need to improve the NPCA mechanism in another way that would be applicable to a wider range of stations. The present disclosure intends to use the Spatial Reuse feature of IEEE 802.11 to provide the frame for switching channel access on the primary channel itself in case of reasonable OBSS interference, rather than on the target anchor channel as done with the ICF. This will allow any hidden STA - single-radio or multi-radio ones - to become aware of the OBSS, hence to switch to the anchor channel for channel access. Indeed, the Spatial Reuse (SR) feature can be used when two BSSs operate on the same channel and can hear each other with a received signal strength level higher than a Clear Channel Assessment (CCA) Energy Detect (ED) threshold. Conventionally, the CCA-ED threshold is used to decide whether the channel is idle or not. A neighbour BSS that can be heard at a signal strength level greater than the CCA-ED threshold is called an overlapping BSS (OBSS). Transmissions that overlap two BSS can be named inter-BSS transmissions (e.g., inter-BSS traffic, inter-BSS PPDU, and so on.). Below, the words “OBSS” and “inter-BSS” can be used interchangeably. With the SR feature, a STA can transmit in parallel with an ongoing OBSS transmission, provided the SR transmission is at an acceptably low transmit power. This is to avoid interfering back with the OBSS (or interfering at a tolerable level). The SR transmissions (at low power) are therefore additional to the conventional CSMA / CA transmissions (by the OBSS), hence creating more opportunities for parallel cochannel transmissions. In this context, the present disclosure proposes a communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels: detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, and transmitting, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme. The frame for switching a channel access is therefore transmitted in parallel with the OBSS transmission on the same primary channel. As known, the secondary channel access scheme operates medium access on a so-called “anchor” channel or NPCA PCH (NPCA primary channel) which is a secondary channel as opposed to the primary channel of the BSS. In embodiments, the method may further comprise, responsive to transmitting the frame, switching at the STA to the secondary channel access scheme. A complementary perspective of the disclosure regards a communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels: receiving, from another STA of the BSS and on the primary channel, a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme, and responsive to receiving the frame, configuring a radio of the STA to the secondary channel access scheme, for example by switching a radio from the primary channel access scheme to the secondary channel access scheme. Optional features are defined below with reference to methods, while they can be transposed into device features. In some embodiments, responsive to receiving the frame for switching, the STA transmits a response frame to the other STA. Correspondingly, the STA (transmitting the frame for switching) waits for a response frame to the frame for switching, from one or more other STAs, before performing operations on a secondary channel using the secondary channel access scheme. The response allows the transmitting STA (typically the AP) to know whether there are indeed other STAs that can use the frame for switching. As a consequence, the transmitting STA may continue transmitting such a frame for switching in the next opportunities to do so. In particular, the response frame may be transmitted over the primary channel before switching to the secondary channel access scheme. In that case, the STA (transmitting the frame for switching) may switch to the secondary channel access scheme after having received the response frame over the primary channel. Alternatively, the response frame may be transmitted over a secondary channel used for the secondary channel access scheme, after the STA (receiving the frame for switching) switched to the secondary channel access scheme. In that case, the response frame (transmitting the frame for switching) is received over a secondary channel used for the secondary channel access scheme, after the STA switched to the secondary channel access. This ensures that the concerned STAs have already switched to the NPCA PCH and are therefore ready for NPCA operations. In particular embodiments, the STA sends (or receives) an initial control frame over the secondary channel after having switched thereto, and the response frame is received (or transmitted) responsive to the initial control frame. The initial control frame (over the secondary channel or NPCA PCH) which is additional to the frame for switching helps the STAs to synchronize over the secondary channel. In particular embodiments, the response frame is received (or transmitted) over a bandwidth that encompasses the first channel and a secondary channel used for the secondary channel access scheme. In some embodiments, the response frame includes a Null Data Packet (NDP) feedback report response. This may be implemented together with a frame for switching that is of the NFRP type. This advantageously takes advantage of a yet-existing mechanism to provide efficient report about the states of the stations receiving the frame for switching. In particular, the NDP feedback report response may include a FEEDBACK_STATUS bit set to a first value (0) to indicate that the other STA transmitting the response frame received the frame for switching and did not detect the OBSS transmission or a second value (1) to indicate that the other STA received the frame for switching and did detect the OBSS transmission. This may help the AP to adjust the NPCA operations with those STAs suffering from OBSS interference and with those STAs not experiencing such OBSS interference. In some embodiments, the OBSS transmission meets spatial reuse operation criteria in case the received signal strength level of the OBSS transmission is lower than an OBSS packet detection (PD) level or in case the OBSS transmission includes a Parameterized Spatial Reuse Reception (PSRR) Physical Layer Protocol Data Unit (PPDU) having an Uplink (UL) Spatial Reuse subfield set to a Parameterized Spatial Reuse opportunity. It is known that the OBSS PD level for SR operation is higher than the conventional CCA-ED threshold. In other embodiments, transmitting the frame using the spatial reuse operation includes transmitting the frame over the same primary channel as the OBSS transmission, using a reduced transmit power that is function of the OBSS PD level or that is lower than a threshold defined based on a power level indicated in the UL Spatial Reuse subfield. Hence, threshold value (OBSS PD level) and transmit power are linked, so that one can be derived from the other. Similarly, a PSRT PPDU can be transmit only in case the intended transmit power is lower than the threshold based on a PSR value indicated in the OBSS transmission (PSRR PPDU). In some embodiments, the frame is transmitted without contention, a PIFS or a SIFS after having detected the OBSS transmission. This preferably applies to an AP that may have prioritized access over other STAs detecting the OBSS transmission. In other embodiments, the method may further comprise contending for SR medium access to the primary channel before transmitting the frame. This may apply to non-AP STAs only or, in a variant, to each and every STA (thus including the AP). “SR medium access” means an access to the medium in order to perform SR operation (i.e., to transmit using a reduced transmit power). In some embodiments, the AP may be the sole STA allowed to transmit the frame for switching, in which case there is neither contention nor prioritized access. Note that the contention implies dedicated behaviours at the STAs. In this respect, a dedicated communication method may be defined that comprises, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels: detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, contending for SR medium access to the primary channel, and while contending, receiving, from another STA of the BSS, on the primary channel, a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme, and responsive to receiving the frame while contending, stopping the contention operation - This may merely consist in stopping the decrement of a backoff counter (or multiple ones) - and switching to the secondary channel access scheme. In particular, if the STA wins the contention, it may send the channel access switching frame. In some embodiments, contending for SR medium access to the primary channel uses SR-EDCA parameters different from EDCA parameters used for non-SR medium access to the primary channel. In other embodiments where contention is conducted, in particular contention with multiple concurrent transmitting queues (such as EDCA), the frame is placed in the front of a transmitting queue having the highest priority for medium access on the primary channel, in order to be sent. As an example, the AC_VO can be targeted. Back to the STA sending the frame for switching, in some embodiments, the frame is transmitted over a composite channel that includes the primary channel on which the primary channel access scheme is performed and a secondary channel on which the secondary channel access scheme is performed. Thanks to this configuration, the frame also reserves the channel or channels for the NPCA. This eases the NPCA operations afterwards. In some embodiments, the frame is transmitted using a low Modulation and Coding Scheme (MCS) MCSO or the lowest data rate for non-HT PPDU. This increases the robustness of the frame, in particular to ensure that all the STAs of the BSS be aware of the channel access scheme switching. In some embodiments, the frame is transmitted during a Target Wake Time (TWT) service period (SP). This ensures that the STAs of the BSS are in an awake state to receive the frame for switching. In particular, the STA may wait for the next TWT SP after detection of the OBSS transmission to transmit the frame. In some embodiments, the frame includes a padding field to have a frame length higher than a switching time required by a STA of the BSS to switch from the primary channel access scheme to the secondary channel access scheme. The switching time depends on hardware considerations of the STA, for the latter to be able to configure its radio (or one of its radios) to operate medium / channel access on the secondary channel (or anchor channel). In some embodiments, the method may further comprise, at the STA, determining whether to transmit data on the primary channel using the spatial reuse operation or to transmit data on a secondary channel using a secondary channel access scheme, wherein transmitting the frame is responsive to determining to transmit data on the secondary channel using the secondary channel access scheme. In some embodiments, the frame for switching assigns distinct secondary channels to respective other STAs for them to switch to a secondary channel access scheme on the assigned secondary channel, for a duration of the OBSS transmission. Secondary channel access is therefore offered to the STAs over distinct channels, thereby improving the use of the wireless medium. Of course, multiple other STAs may be assigned the same secondary channel, provided that at least one other STA is assigned a distinct secondary channel. In embodiments, the frame for switching assigns, for a duration of the OBSS transmission, a secondary channel to another STA that has already switched to the secondary channel. This is to avoid multiple (and unnecessary) switching at this other STA. In other embodiments, the frame for switching also assigns the primary channel to one STA for Dynamic Subchannel Operation, for the duration of the OBSS transmission. This is to optimize use of the wireless medium. The allocated STA may be one of those not directly experiencing the OBSS interference, in order to allow them to use normal transmit power (and not reduced one for SR transmission). In alternative embodiments, the frame for switching does not assign the primary channel to any STA for Dynamic Subchannel Operation during the OBSS transmission. This reduces risks of interfered transmissions. Back to the STAs receiving the frame, the AP may play a central role for those STAs of the BSS that are too far from the STA transmitting frame. In this respect, the above defined communication method may further comprise, at the STA operating as an access point (AP) of the BSS, further responsive to receiving the frame, transmitting, to other STAs of the BSS and on the primary channel, a second frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme. This configuration particularly applies to the AP that has not detected the OBSS transmission (otherwise it would have switched to the secondary channel for secondary channel access). Hence, the second frame can be transmitted without Spatial Reuse restriction, e.g., without a reduced transmit power. Obviously, the AP may send this second frame before configuring its radio for secondary channel access scheme, in particular when the AP has a single radio which is switched from PCA to SCA (NPCA). The above approach allows the AP to propagate the OBSS detection to additional hidden nodes, for them to join the BSS operations on the (anchor) secondary channel. As above, the second frame may include a padding field to have a frame length higher than a switching time required by a STA of the BSS to switch from the primary channel access scheme to the secondary channel access scheme. In some embodiments, the second frame is transmitted over the primary channel on which the primary channel access scheme is performed and over a secondary channel on which the secondary channel access scheme is performed, and the second frame is configured to allocate: one or more first resource units to a first set of STAs of the BSS, the first resource units being included in a first subset of the operating channel that includes the primary channel, and one or more second resource units to a second set of STAs of the BSS, the second resource units being included in a second subset of the operating channel that includes the secondary channel. The first and second sets are preferably separate and not overlapping sets, as well as the first and second subsets of the operating channel. The second frame may be sent over the first and second subsets, even over the entire operating channel if not the same. The AP may keep its radio operating on the primary channel, while configuring another radio to operate on the secondary (anchor) channel for secondary channel access. In that way, the AP may still organize conventional transmissions (without Spatial Reuse restrictions) on the primary channel with the STAs that are not impacted by the OBSS transmission, while organizing NPCA (or SCA) transmissions on the secondary channel for those STAs impacted by the OBSS transmission. In other embodiments where the STA does not send the second frame for switching, the STA operates as an access point (AP) of the BSS, and configuring a radio of the AP responsive to receiving the frame includes: maintaining a first radio operating on the primary channel to perform the primary channel access scheme, and configuring a second and separate radio to operate on a secondary channel on which the secondary channel access scheme is performed. This configuration allows the AP to independently conduct PCA operations on the primary channel with the STAs that are not aware of the OBSS interference and NPCA operations on the secondary channel with any STA that is aware of the OBSS interference and has switched to the secondary channel (due to direct OBSS interference detection or due to the first frame reception). In some embodiments, any of the preceding methods may further comprise transmitting an initial control frame (ICF) on a secondary channel different from the primary channel after having switched to a secondary channel access scheme on the secondary channel in response to transmitting the frame for switching a channel access. This is for the transmitting STA to confirm that it has successfully switched to the anchor channel. In some embodiments, the frame for switching includes a Null Data Packet Feedback Report Poll (NFRP) Trigger frame. In particular, the NFRP Trigger frame may include a maximum duration available for use of the secondary channel access scheme. This notifies in advance the STAs about the length (duration) of the NPCA operations, for them to prepare their transmissions. In embodiments, the NFRP Trigger frame includes a field signalling whether a response frame to the frame for switching is requested or not from STAs scheduled by the NFRP Trigger frame and receiving it. In particular, the NFRP Trigger frame may include a field signalling a channel to transmit the response frame, from among the first channel and a secondary channel used for the secondary channel access scheme. Control of the responses by the stations receiving the frame for switching is therefore obtained. In embodiments, the NFRP Trigger frame includes a field signalling an identifier of an OBSS from where the OBSS transmission originates. This allows the stations receiving the frame for switching to be able to report whether or not they also suffer from the same OBSS interference. Such information helps the AP to properly schedule the STAs. In alternative embodiments to the NFRP Trigger frame, the frame for switching includes a Buffer Status Report Poll (BSRP) Trigger frame. Another aspect of the disclosure deals with OBSS-based criteria to not transmit the frame for switching. In this perspective, it includes a communication method that comprises, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels: detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, and deciding, in case the OBSS transmission encompasses a target secondary channel different from the primary channel or in case the OBSS transmission is shorter than a predefined duration threshold, not to transmit, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to an access scheme over the target secondary channel. This approach avoids having STAs switching to the NPCA PCH (target secondary channel) when it is useless, typically when the NPCA PCH also suffers from the OBSS interference or when the latter are quite short in a view it is more profitable to remain on the first channel for a (short) while. As a consequence, the method further comprises deciding, in case the OBSS transmission does not encompass a target secondary channel different from the primary channel or in case the OBSS transmission is longer than a predefined duration threshold, to transmit, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to an access scheme over the target secondary channel. As apparent from the above, new frames can be defined to implement embodiments of the disclosure. In this respect, the disclosure also provides a frame comprising a PHY Preamble, a Frame Control field, a Frame Check Sequence field and a padding field, wherein the Frame Control field signals the frame is a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme. The frame is based on the 802.11 frame format to be defined as short as possible given the OBSS constraints. A combination of all or part of the Control type and Subtype and Control Frame Extension subfields within the Frame Control field can be used to signal the CS-ICF frame type. In some embodiments, the frame includes a first field signalling a TXOP duration of a detected overlapping-BSS (OBSS) transmission and one or more optional fields from amongst: a second field signalling an identifier of the Basic Service Set (BSS) to which a station transmitting the frame belongs, a third field signalling a secondary channel for the secondary channel access scheme, a fourth field signalling an identifier of the OBSS and a fifth field signalling a bandwidth of the detected OBSS transmission. These various fields make it possible to precisely signal the OBSS interference as well as the target NPCA. In embodiments, the first field and the optional fields are additional to the PHY Preamble, Frame Control field, Frame Check Sequence field and padding field. No other fields may be needed in the frame. In variants that reduces the size of the frame, the first field and the optional field or fields are subfields within the PHY Preamble. Preferably the conventional Bandwidth, BSS Color and TXOP subfields of the Frame Control field can be reused to convey the above-mentioned information items. No other fields may be needed in the frame. In embodiments, the Frame Control field include a subfield whose value takes a different value depending on whether the frame is transmitted responsive to a detection of the OBSS transmission by the station transmitting the frame or responsive to another frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme received by the station transmitting the frame. Hence, various types of CS-ICF can be explicitly signalled within the frames themselves. In some embodiments, the padding field is configured for the frame to have a frame length higher than a switching time required by a station to switch from the primary channel access scheme to the secondary channel access scheme. Another aspect of the disclosure regards the declaration made by the stations to allow the above SR-based mechanisms to be applied. In this perspective, a frame to be transmitted by a station is defined that comprises a Capabilities element including one or more of: a first support field to signal whether or not the transmitting station supports untriggered uplink transmission during non-primary channel access operations, and a second support field to signal whether or not the transmitting station supports spatial reuse operation to transmit, on a primary channel experiencing inter-BSS interference, a frame to trigger at other stations a switching of channel access from a primary channel access scheme to a secondary channel access scheme. In particular, the first support field and second support field may be included in a MAC Capabilities Information field within the Capabilities element. Also, a frame to be transmitted by a station is defined that comprises an Operation element including one or more of a first mode field to signal an activation or deactivation of an operating mode where the transmitting station is not allowed to perform untriggered uplink transmission during non-primary channel access operations and a second mode field to signal an activation or deactivation of an operating mode where the transmitting station uses spatial reuse operation to transmit, on a primary channel experiencing inter-BSS interference, a frame to trigger at other stations a switching of channel access from a primary channel access scheme to a secondary channel access scheme. In particular, the first mode field and second mode field may be included in an Operation Information field within the Operation element. Correlatively, the disclosure also provides a wireless communication device comprising at least one microprocessor configured for carrying out any method as described above. Another aspect of the disclosure relates to a non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a wireless device, causes the wireless device to perform any method as described above. At least parts of the methods according to the disclosure may be computer implemented. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present disclosure may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium. Since the present disclosure can be implemented in software, the present disclosure can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a hard disk drive, a magnetic tape device or a solid-state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g., a microwave or RF signal. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the disclosure will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 illustrates an exemplary network environment in which embodiments of the present disclosure can be implemented; Figure 2 illustrates, using an exemplary timeline, a non-primary channel access mechanism; Figures 3a, 3b and 3c illustrate hidden-node situations for OBSS packet detection, in which embodiments of the present disclosure can be implemented; Figure 4 illustrates the relationship between OBSS PD level and the constraint on the Transmit Power employed by the OBSS PD Spatial Reuse feature; Figures 5, 6, 7, 8 and 9 illustrate, using exemplary timelines, communication methods involving one or more frames for switching a channel access from PCA to NPCA, according to some embodiments; Figure 10 illustrates, using a flowchart, general steps at a STA directly detecting OBSS interference, which is capable of sending a Channel Switch Initial Control Frame or CS-ICF, according to embodiments; Figure 11 illustrates, using a flowchart, general steps at another STA directly detecting OBSS interference, which is capable of sending a CS-ICF but does not gain access to do so; Figure 12 illustrates, using a flowchart, general steps at any STA unable to directly detect OBSS interference; Figures 13a and 13b illustrate exemplary frame formats of CS-ICF according to embodiments; Figure 14a shows a schematic representation of a wireless communication device in accordance with embodiments; Figure 14b illustrates schematically the architecture of the communication device of Figure 14a; Figure 15 illustrates exemplary frame formats of Capability and Mode indications according to embodiments; Figures 16 and 16a illustrate scenarios where multiple STAs detect an OBSS interference and conduct their switch to the NPCA PCH immediately or after a waiting time respectively, according to embodiments; Figures 17, 18a and 18b illustrate communication methods involving one or more frames for switching a channel access from PCA to NPCA having CS-ICR (Channel Switch -Initial Control Response) feedback according to embodiments; Figure 19 illustrates an exemplary frame format of CS-ICF based on the known NFRP (Null Data Packet Feedback Report Poll) Trigger frame, according to embodiments; Figures 20a, 20b and 20c illustrate communication methods involving one or more frames for switching a channel access from PCA to NPCA using Dynamic Subchannel Operation (DSO) according to embodiments; and Figure 21 illustrates, using a flowchart, general steps at STA which is capable of sending a CS-ICR in response to a received CS-ICF, according to embodiments. DETAILLED DESCRIPTION OF EMBODIMENTS The present specification regards communication methods where a first STA (including both non-AP STA and AP) of a BSS detects an OBSS (or inter-BSS) TXOP on its primary channel. The OBSS transmission meets the criteria for Spatial Reuse operations. The first STA transmits a NPCA switching frame (i.e., Channel Switch-ICF; CS-ICF) to other STAs of the BSS, on its primary channel (PCH) using the spatial reuse operation and a reduced transmit power. The frame indicates OBSS interference to those other STAs that are too far to detect it. The NPCA switching frame (i.e., CS-ICF) triggers a switching of channel access from PCA (taking place on the PCH) to NPCA (taking place on an anchor channel also called NPCA Primary Channel or “NPCA PCH”) at these other STAs. Next, the STAs perform NPCA operations on the NPCA PCH, even if some of them have not directly detected the OBSS interference. An AP receiving the NPCA switching frame may, in response, transmit a similar switching frame to propagate the OBSS interference information and the switching trigger to yet other STAs too far from the first STA to receive the NPCA switching frame. In summary, this disclosure proposes a new mechanism to mitigate the OBSS hidden node problem for NPCA by sending CS-ICF under the spatial reuse operation. The techniques described herein may be used for various broadband wireless communication systems, including communication systems that are based on an orthogonal multiplexing scheme. Examples of such communication systems include Spatial Division Multiple Access (SDMA) system, Time Division Multiple Access (TDMA) system, Orthogonal Frequency Division Multiple Access (OFDMA) system, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) system. An SDMA system may utilize sufficiently different directions to simultaneously transmit data belonging to multiple user terminals, i.e., wireless devices or stations. A TDMA system may allow multiple user terminals to share the same frequency channel by dividing the transmission signal into different time slots or resource units, each time slot being assigned to different user terminal. An OFDMA system utilizes orthogonal frequency division multiplexing (OFDM), which is a modulation technique that partitions the overall system bandwidth into multiple orthogonal sub-carriers or resource units. These sub-carriers may also be called tones, bins, etc. With OFDM, each sub-carrier may be independently modulated with data. An SC-FDMA system may utilize interleaved FDMA (IFDMA) to transmit on sub-carriers that are distributed across the system bandwidth, localized FDMA (LFDMA) to transmit on a block of adjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks of adjacent sub-carriers. The teachings herein may be incorporated into (e.g., implemented within or performed by) a variety of apparatuses (e.g., stations). In some aspects, a wireless device or station implemented in accordance with the teachings herein may comprise an access point (so-called AP) or not (so-called non-AP STA (station)). STA includes both AP and non-AP STA. An AP may comprise, be implemented as, or known as a Node B, Radio Network Controller (“RNC”), evolved Node B (eNB), 5G Next generation base station (gNB), Base Station Controller (“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, Basic Service Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station (“RBS”), or some other terminology. A non-AP station may comprise, be implemented as, or known as a subscriber station, a subscriber unit, a mobile station (MS), a remote station, a remote terminal, a user terminal (UT), a user agent, a user device, user equipment (UE), a user station, or some other terminology. In some implementations, a non-AP STA may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a tablet, a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a global positioning system (GPS) device, or any other suitable device that is configured to communicate via a wireless or wired medium. In some aspects, the non-AP station may be a wireless node. Such wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link. An AP manages a set of STAs (registered to it or associated with it) that together organize their accesses to the wireless medium for communication purposes. The STAs (including the AP to which they register) form a service set, here below referred to as basic service set, BSS (although other terminology can be used). A same physical STA acting as an access point may manage two or more BSSs (and thus corresponding WLANs): each BSS is thus uniquely identified by a specific basic service set identification, BSSID and managed by a separate virtual AP implemented in the physical AP. Each STA is identified within a BSS thanks to an identifier, AID, assigned to it by the AP upon registration. The 802.11 family of standards define various media access control (MAC) mechanisms to drive access to the wireless medium. For example, each BSS defines a main elementary channel of the wireless medium (known as a primary channel, usually a 20 MHz channel or a multiple of 20 MHz channel) on which the stations (including the AP) perform EDCA (or the like) contention using generally legacy EDCA parameters (defined in an EDCA Parameter Set provided by the AP). To increase bandwidth for the forthcoming transmission, the stations can simultaneously contend for additional 20 MHz channels, known as secondary channels. The communication or “operating” channel thus granted for transmission comprises the primary channel and optionally secondary channels. According to the 802.11 standard family, the primary channel is the common channel of operation for all stations that are members of the BSS. Usually, in a 20 MHz, 40 MHz, 80 MHz, 160 MHz, 80+80 MHz, 320 MHz BSS, the primary channel is a primary 20 MHz channel. Correspondingly, a non-primary channel is any 20 MHz channel other than the primary 20 MHz channel. A secondary channel is a channel associated with a primary channel used to create an operating channel wider than the primary channel alone. In a 40 MHz, 80 MHz, 160 MHz, 80+80 MHz or 320 MHz BSS, each secondary channel is a secondary 20 MHz channel. However, the notions of primary and secondary channels have been extended to channels having more than 20 MHz width. For example, the primary 40 MHz (resp. 80 MHz, 160 MHz) channel is the 40 MHz channel (resp. 80 MHz, 160 MHz) in an 80 MHz, 160 MHz, 80+80 MHz or 320 MHz BSS, formed by the primary channel (20 MHz) and one or more adjacent and aggregated secondary channels (20 MHz each), that is used to transmit 40 MHz (resp. 80 MHz, 160 MHz) physical layer (PHY) protocol data units (PPDUs). Similarly, a secondary X MHz channel (X = 20, 40, 80 or 160) is defined in a 2X (or more) MHz BSS as the X MHz channel adjacent to the primary X MHz channel that together form a primary 2X MHz channel (or the entire 2X MHz operating channel). The primary channel is used for signalling and backwards compatibility while the secondary channels are only used to extend throughput when sending data at full speed. This channel access based on the primary channel is known as the Primary Channel Access or “PCA”. Efficient medium usage within one operating channel having an operation bandwidth (up to 320MHz in the latest 802.11 be D6.0 standard; however may be wider in future amendments) has evolved along the evolution of the IEEE 802.11 standards. For example, dynamic bandwidth signalling feature was introduced in the IEEE 802.11ac amendment, preamble puncturing feature was introduced in the IEEE 802.11 ax standard and further evolved in the IEEE 802.11be amendments. For example, in order to address the issue of increasing bandwidth and decreasing latency requirements that are demanded for wireless communications systems in high-density environments, multi-user (MU) schemes have been developed to allow a single access point (AP) managing a Basic Service Set (BSS) to schedule MU transmissions, i.e., multiple simultaneous transmissions to non-AP stations (so-called MU Downlink or DL transmissions) or from non-AP stations (so-called MU Uplink or UL transmissions) triggered by the AP using a Trigger frame. The Trigger Frame allocates resource units to the non-AP stations of the same BSS, using Association IDentifiers (AlDs) assigned to them upon registration to the AP and / or using reserved AIDs designating a group of non-AP stations. The TF also defines the start of the MU UL transmission by the non-AP stations as well as the length thereof. After a non-AP station makes an MU UL transmission, it performs EDCA contention on the medium using temporarily a different (from the legacy ones) set of EDCA parameters, known as MU EDCA parameters (defined in a Multi-User (MU) EDCA Parameter Set provided by the AP). The current discussions in the task group 802.11 be, as illustrated by draft IEEE P802.11 be / D6.0, introduce the Multi-Link Operation (MLO) when it comes to MAC layer operation. The MLO allows multi-link devices to establish or setup multiple links and operate them simultaneously. A Multi-Link Device (MLD) is a logical entity and has more than one affiliated STA (STA) and has a single MAC service access point (SAP) to logical link control (LLC), which includes one MAC data service. Multiple affiliated non-AP STAs of a non-AP MLD can then setup communication links with multiple affiliated APs of an AP MLD, hence forming a multi-link channel. A communication link or “link” thus corresponds to a given channel (e.g., 20 MHz, 40 MHz, and so on) in a given frequency band (e.g., 2.4 GHz, 5 GHz, 6 GHz) between an AP affiliated with the AP MLD and a non-AP STA affiliated with the non-AP MLD. The description below mostly concentrates on a single link for ease of explanation. However, similar considerations can be made with respect to each link forming a multiple link set for MLD devices. Therefore, the term STA or “station” may refer to one affiliated STA of a non-AP MLD (non-AP STAs of a non-AP MLD), and AP may refer to one affiliated AP of an AP MLD. Figure 1 illustrates an exemplary network environment in which embodiments of the present disclosure can be implemented. The illustrated wireless network environment comprises a group of neighbouring wireless networks that operate over a common communication channel or wireless medium. The common communication channel may correspond to a part (e.g., 20 MHz) or all of their operating channels (e.g., 20 MHz, 40 MHz, 80 MHz, 160 MHz or 320 MHz). A first wireless network (or Basic Service Set) BSS1 comprises an access point (AP) 110 and three non-AP stations (STAs) 111, 112 and 113 associated with the AP 110 (i.e., registered to it). A second wireless network BSS2 comprises an AP 120 and three associated non-AP STAs 121, 122 and 123. In the following, BSSx represents any of the wireless networks, while 1x1, 1x2 and 1x3 any of the non-AP stations. Of course, another number of wireless networks and any number of non-AP stations per wireless network can be contemplated. In the present disclosure, APs 110, 120 are also referred to, respectively, as AP1, AP2. A device may act as an AP of one wireless network and at the same time may belong to another wireless network as an associated STA. All or part of the APs may be affiliated APs to the same AP MLD. They also can be separate devices. Any AP broadcasts management frames, such as beacon frames, to share parameters to be used for the functioning of its BSS. The stations (AP and non-AP) of each BSS exchange data frames over the communication channel 100, under the management of the AP, using the primary channel of the BSS and optional secondary channels aggregated to the primary channel. Note that for the present disclosure, the BSSs use the same primary channel. Each non-AP STA 1x1-1x3 registers to the AP 1x0 of one wireless network BSSx during an association procedure. During the association procedure over the primary channel, the AP assigns a specific Association Identifier (AID) to the requesting station. For example, the AID is a 16-bit value uniquely identifying the station. The stations (including the AP) compete one against another over the primary channel using EDCA (Enhanced Distributed Channel Access) contention to access the communication channel in order to be granted a transmission opportunity (TXOP) over an operating channel made of the primary channel and a secondary channel to increase bandwidth. It turns out that this conventional Primary Channel Access (PCA) scheme does not allow the stations to use any secondary channel while the primary channel is busy. This induces a waste of communication resources in case of primary channel use, even more massive as the operating channel has a large bandwidth (40 / 80 / 160 / 320 MHz). To meet low latency requirements as well as to increase efficiency of bandwidth usage, efforts have been made by the 802.11 bn group to reuse the lost secondary channels through a so-called non-primary channel access (NPCA) scheme, sometimes called Secondary Channel Access (SCA). Below, NPCA and SCA are used as synonyms. The basic idea is for stations of a BSS (including the AP) to opportunistically operate (in the meaning of performing contention, e.g., through backoff procedure) on a non-primary channel, i.e., a secondary channel, while the primary channel of that BSS is busy and thus blocked (e.g., due to an OBSS transmission). A typical usage of NPCA is when two stations (e.g., a non-AP station and its AP) have their network allocation vector (NAV) set from the OBSS transmission. They can both decide starting to operate on the non-primary channel, by switching their channel access mechanism (e.g., medium sensing and backoff procedure) on the non-primary channel they elect. It is expected that the stations have capability to monitor the non-primary channel at least to the extent of performing Clear Channel Assessment (CCA) to detect the presence of energy in the medium while it is not transmitting on the primary channel and vice-versa. The duration for which the two stations operate on the non-primary link is expected to be limited to the time for which the NAV in the primary channel was set by the OBSS transmission. Figure 2 illustrates, using an exemplary timeline, the non-primary channel access mechanism. Non-Primary Channel Access (NPCA) feature in UHR (Ultra High Reliability) enables an AP and a non-AP STA to communicate on a nonprimary channel when the primary channel is busy due to OBSS traffic. Today's Wi-Fi, including versions up to 11 be (Wi-Fi 7), generally does not allow for the use of the secondary channel while the primary channel is busy. In standard 802.11 practice, transmissions typically utilize 20 / 40 / 80 / 160 / 320 MHz channels, with one dedicated 20 MHz channel functioning as the primary channel. Regardless of whether secondary channels are idle or busy, these channels remain inaccessible if the primary channel is occupied. In the example, the BSS operating band, which may be announced by the AP1 110 includes two subchannels, which are 80 MHz channel 1 and 40 MHz channel 2, and where each subchannel includes multiple 20 MHz channels and has one backoff 20 MHz channel, i.e., one channel to perform medium / channel access. The first 80MHz channel 1 is composed of a set S1 of four 20MHz channels, including primary channel P1. Primary channel P1 is the primary channel on which the primary channel access or PCA scheme is performed. The second 40MHz channel 2 is composed of a set S2 of two 20MHz channels, including anchor channel P2. The anchor channel P2 is the secondary channel on which the secondary channel access SCA or NPCA scheme is performed. Set S2 is a subset of set S1. The anchor channel can be also referred as NPCA Primary Channel (NPCA PCH), Alternate Channel, Alternate Primary Channel, Temporary Subchannel, Temporary Primary Channel, Interim Subchannel, Interim Primary Channel, Transient Subchannel, Transient Primary Channel, Ephemeral Subchannel, Ephemeral Primary Channel, Fugacious Subchannel, Fugacious Primary Channel, Capricious Subchannel, Capricious Primary Channel, Secondary Subchannel, Secondary Primary Channel, Auxiliary Subchannel or Auxiliary Primary Channel. All these words can be used interchangeably. Below, reference is mainly made to NPCA PCH for the channel used for NPCA or SCA operations. Usually, AP and STAs perform backoff procedure in the primary backoff 20 MHz channel P1 only. By using the NPCA mechanism, a STA can enable one or more backoff procedures in the NPCA PCH P2. On the 80MHz channel 1, while STA11 and AP1 perform backoff procedures, AP2 (OBSS) starts an OBSS TXOP 220. As the primary 20 MHz channel becomes busy due to the OBSS transmission, AP1 and STA11 switch from the primary channel P1 to the NPCA PCH P2. Channel switch operation may take different time depending on the STAs’ ability (including hardware configuration). The duration of each STA’s channel switching operation, which may be called Channel switching delay or switching time or NPCA Switching Delay for switching from P1 to P2, and NPCA Switch Back Delay for switching back from P2 to P1, may be shared between the STAs before the NPCA operations for example during the association procedure. Switching operation is performed during the time shown as 221a / b / c / d. NPCA operations 222a / 222b start after both AP1 and STA11 have completely switched to the NPCA PCH. On the NPCA PCH, the STAs (STA11 and / or AP1) perform NPCA operations (222a / 222b) as follows. The STAs perform CCA for PPDU detection and decrement their backoff counter(s). A STA may transmit an initial control frame (ICF) after one of its backoff counters becomes 0 to confirm that the STA has successfully switched to the NPCA PCH. The initial control frame may be an RTS frame or MU-RTS frame or any other control frame. An addressee STA may respond with an initial control response (ICR) frame after it received the ICF. This is to confirm the addressee STA has also successfully switched to the NPCA PCH. The ICR frame may be a CTS frame or any other control frame. The STA transmits a data frame after receiving the ICR frame, e.g., a mere ACK frame. The other STA may respond with an acknowledgement (ACK) frame after receiving the data frame. The frame exchanges in the secondary 40MHz channel S2 are done no later than the end of the OBSS TXOP 220 that uses the primary channel. No later than the end of the OBSS TXOP 220, the STAs switch back to their primary channel P1 and operating band S1. The switching back is referenced 223a / 223b in the Figure. The STAs can initiate new transmissions through the complete operating band S1 in a conventional manner. OBSS hidden node is a critical problem for NPCA, which may degrade the overall performance. The NPCA mechanism is not efficient in hidden-node situations because those hidden nodes are unable to detect the OBSS TXOP 220, hence to spontaneously switch to the NPCA PCH P2. This disclosure proposes to use Spatial Reuse to mitigate the OBSS hidden node problem for NPCA. The mechanism proposed in this disclosure can be called “Spatial Reuse triggered NPCA”. As described in Figures 3a, 3b and 3c, several scenarios can lead to misunderstandings among the STAs using NPCA mechanism. BSS 300 is composed of AP1 310 and three STAs STA11 301 and STA12 302 and STA 13 303 (not shown in Figure 3a). It corresponds to BSS1 of Figure 1. BSS 320 (OBSS) is composed of AP2 321 and STA21 322. It corresponds to BSS2 of Figure 1. In the scenario of Figure 3a, AP observes OBSS but STA doesn’t. Only AP1 310 is in the range of the OBSS in such manner that each medium access of AP2 or STA21 is regarded as an OBSS interference for AP1. Therefore, AP1 sets its NAV (for “Network Allocation Vector”) to the length of the OBSS TXOP initiated by AP2 or STA21. On the other hand, STA11 and STA12 are not disturbed by the OBSS TXOP as they are too far; hence AP2 or STA21 is regarded as a “hidden node” from the knowledge of STA11 and STA12. In such a case, if the NPCA mechanism is automatically applied, AP1 switches to the NPCA PCH P2 while STA11 and STA12 stay on the primary channel P1 of their BSS 300. This behaviour entails a misalignment on the selection of the primary channel / NPCA PCH to be used to initiate a backoff procedure in the BSS 300. All transmissions between the AP and its associated STAs will thus fail. In the scenario of Figure 3b, STA observes OBSS but AP doesn’t. Only STA11 301 and STA13 303 are in the range of the OBSS in such manner that AP2 and STA21 are regarded as hidden nodes for the knowledge of AP1 and STA12. In the same way as for Figure 3a, if the NPCA mechanism is automatically applied, STA11 and STA13 switch to the NPCA PCH P2 while AP1 and STA12 stay on their primary channel P1. It entails similarly a misalignment on the selection of the primary channel / NPCA PCH to be used to initiate a backoff procedure in the BSS 300. Transmissions between the AP and its associated STAs will be likely to also fail. In the scenario of Figure 3c, AP1 and STA12 observe OBSS but STA11 and STA13 don’t. AP1 and STA12 are in the range of the OBSS in such manner that each medium access of AP2 or STA21 is regarded as an OBSS interference for AP1 and STA12. Therefore, AP1 and STA12 set their NAV (for “Network Allocation Vector”) to the length of the OBSS TXOP initiated by AP2 or STA21. On the other hand, STA11 and STA13 are not disturbed by the OBSS TXOP as they are too far; hence AP2 or STA21 is regarded as a “hidden node” from the knowledge of STA11 and STA13. In such a case, if the NPCA mechanism is automatically applied, AP1 and STA12 switch to the NPCA PCH P2 while STA11 and STA13 stay on the primary channel P1 of their BSS 300. It entails similarly a misalignment on the selection of the primary channel / NPCA PCH to be used to initiate a backoff procedure in the BSS 300. All transmissions between the AP1 and STA11 / STA13 will thus also fail. Accordingly, there is a need to improve the NPCA mechanism, so that bandwidth usage efficiency is optimized. To do so, the disclosure intends to use the Spatial Reuse (SR) feature of IEEE 802.11 to provide an indication to switch to NPCA to those hidden nodes that are unable to detect the OBSS TXOP. By sending such indicative frame on the primary channel P1 with a reduced transmit power (to comply with the SR feature requirements), instead of only transmitting an ICF on the NPCA PCH P2 after the switching, it is possible to reach all the stations that have not sensed the OBSS interference and thus have not yet switched to the NPCA PCH. In this perspective, a STA detects, on the primary channel P1, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation (in particular energy level requirements or PSR opportunity indication), and responsively transmits, to other STAs of its BSS and on the primary channel using the SR operation, a frame for switching a channel access from PCA to NPCA (or SCA). The STA can then switch to NPCA, meaning to a NPCA PCH. The STA may be the AP or a non-AP STA of the BSS. The frame can be broadcast to the other STAs of the same BSS. Correspondingly, another STA (of the same BSS) receives, from the STA and on the primary channel, the frame for switching a channel access from PCA to NPCA, and responsive to receiving the frame, configures one radio to NPCA, for example by switching the radio from PCA to NPCA. In other words, the radio is tuned to operate channel access on the NPCA PCH P2 rather than on the primary channel P1. Where the STA comprises a single radio, this radio is switched from PCA to NPCA, vice versa. Where the STA comprises two radios, the STA has two options: either switching the radio operating on the primary channel P1 (PCA scheme) to the NPCA PCH P2 (NPCA scheme) or configuring the second radio to operate on the NPCA PCH P2 while keeping its first radio on the primary channel P1. Thanks to the SR feature, the STA can transmit the frame in parallel with the ongoing OBSS transmission, provided the SR transmission is at an acceptably low transmit power. The disclosure uses the SR-based additional transmission opportunities to propagate the indication that the BSS is currently experiencing OBSS interference, hence that the STAs are invited to switch to NPCA. The Spatial Reuse operations are defined in section 26.10 of the IEEE Std 802.11 ax-2021 standard. Spatial reuse allows STAs to transmit frames under the OBSS traffic in the same channel with some conditions and transmission power constraints. Two SR operations exist: the OBSS Packet Detection(PD)-based spatial reuse (SR) operation and the Parametrized Spatial Reuse(PSR)-based spatial reuse operation. In OBSS PD-based SR operations, if the RSSI of the detected OBSS frame is lower than the specific threshold (OBSS_PDIevel), STA can continue the backoff procedure. A STA maintains the threshold (OBSS_PDIevel) in accordance with an equation (26-5) provided in subsection 26.10.2.4. In operation, if the RSSI (received signal strength level) of the detected OBSS frame is lower than the specific threshold, this OBSS frame does not update the basic NAV timer of the STA, meaning it continues the backoff procedure at the end of which it can transmit a PPDU under the specific constraint for the transmit power as defined in Equation (26-6) of subsection 26.10.2.5. The two equations are equivalent in such a way the STA can derive the OBSS PD level ‘OBSS_PDievei 402 from its maximum transmit power ‘Tx_PWRmax’ 404 or can derive the maximum transmit power ‘Tx_PWRmax’ from OBSS_PDievei. The relationship is illustrated in Figure 4. OBSS PD SR can be further split into two types, SRG (Spatial Reuse Group) OBSS PD and non-SRG OBSS PD. SRG is a group of BSSs identified by their BSS colors or partial BSSIDs and a dedicated SRG OBSS PD level can be maintained for the specific SRG. For non-SRG OBSS PD, one non-SRG OBSS PD level is maintained and used for all the STAs outside any SRG. Parameters to determine the SRG, non-SRG OBSS PD level, SRG OBSS PD level may be provided by the AP in a so-called Spatial Reuse Parameter Set element which may be present in the Beacon frames, Probe Response frames, and (Re)Association Response frames. A STA might adjust its OBSS PD level under the required constraints. In PSR-based SR operations, STA can continue the backoff procedure during the OBSS TXOP if it satisfies the condition indicated by the PSRR PPDU (i.e., OBSS Trigger frame) or the TB PPDU that follows the PSRR PPDU. A PSR-enabled AP sends a PSRR (Parameterized Spatial Reuse Reception) PPDU, that is a Trigger frame which contains a so-called UL Spatial Reuse subfield in the Common Info field that is neither PSR_DISALLOW nor PSR_AND_NON_SRG_OBSS_PD_PROHIBITED, but set to a PSR opportunity. If a PSR-enabled STA receives this PSRR PPDU, and if conditions for PSR operation (so called PSR opportunity) are satisfied, it may choose not to perform NAV update operations, and may continue the countdown of an existing backoff procedure. Then, if the STA gains the TXOP, the STA can send a PSRT (Parameterized Spatial Reuse Transmission) PPDU, which has the SR PPDU subfield of the CAS (Command and Status) Control field equal to 1, with the above transmit power constraints during the duration of TB PPDU, which is triggered by the Trigger frame of the PSRR PPDU. One of the parameters to determine the PSR opportunity is indicated in the PSRR PPDU, in particular in the UL Spatial Reuse subfield for HE STAs, and the EHT Spatial Reuse 1, EHT Spatial Reuse 2 fields in the Special User Info field are additionally used for EHT STAs. The detail of the PSR opportunity conditions is defined in subsection 26.10.3.2 of the IEEE 802.11 REVme D6.0 amendment and 35.10.3.1 of the IEEE 802.11 be D6.0 amendment. If both OBSS PD-based SR operation and PSR-based SR operation are enabled, there are some specific interaction operations as specified in subsection 26.10.4. First, if the PSRR PPDU is received during OBSS PD-based SR operations (i.e., OBSS_PDievei is used as a threshold for determination of an IDLE medium condition), the transmit power of the next PSRT PPDU is equal to or lower than the ‘TX_PWRmax’, calculated with this specific OBSS_PDievei using the equation (26-6). Second, if the STA receives a PPDU PSR opportunity that receives a PPDU that is identified as an inter-BSS PPDU (i.e., from the OBSS) with a value other than PSR_DISALLOW or PSR_AND_NON_SRG_OBSS_PD_PROHIBITED for the RXVECTOR parameter SPATIAL_REUSE and fails to identify an PSR opportunity based on the receipt of the PPDU, the STA disables OBSS PD SR operation on this PPDU. In addition, if the STA receives a PPDU that is identified as an inter-BSS PPDU with a value other than PSR_DISALLOW or PSR_AND_NON_SRG_OBSS_PD_PROHIBITED in the UL Spatial Reuse subfield of the Common Info field of a Trigger frame and fails to identify an PSR opportunity based on the receipt of the PPDU, the STA disables OBSS PD SR operation on the HE TB PPDU that is elicited by the Trigger frame. Figures 5, 6, 7, 8 and 9 illustrate, using exemplary timelines, communication methods involving one or more frames for switching a channel access from PCA to NPCA, according to some embodiments. The same initial scenario as the one of Figure 2 is used: one 80MHz channel 1 composed of the set S1 of four 20MHz channels including the primary channel P1 and a second 40MHz channel 2 composed of the set S2 of two 20MHz channels including the NPCA PCH P2. Set S2 is a subset of set S1. STAs of BSS1 300, i.e., AP1, STA11, STA12 and STA13 have enabled the new NPCA mechanism of the present disclosure, including the Spatial Reuse feature (either or both of OBSS PD-based SR and / or PSR-based SR). The proposed embodiments (and more generally the disclosure) can apply to both non-SRG OBSS PD-based SR and SRG OBSS PD-based SR in the same way. Therefore, those two schemes are not distinguished hereafter. In all proposed scenarios, one station detects OBSS interference (i.e., an OBSS TXOP or transmission). To use the Spatial Reuse feature, the station evaluates the received OBSS signal or the received OBSS packet with respect to SR criteria, such as the OBSS_PDievei threshold for OBSS PD-based SR or a PSR opportunity for PSR-based SR, before considering whether or not a frame for switching a channel access from PCA to NPCA is to be sent. Indeed, for OBSS PD-based SR, an OBSS transmission meets spatial reuse operation criteria when the received signal strength level of the OBSS transmission is lower than the OBSS packet detection (PD) level OBSS_PDievei. For PSR-based SR, an OBSS transmission meets spatial reuse operation criteria when the OBSS transmission includes a Parameterized Spatial Reuse Reception (PSRR) Physical Layer Protocol Data Unit (PPDU) having an Uplink (UL) Spatial Reuse subfield set to a Parameterized Spatial Reuse opportunity, whatever the signal level for the PSR (indicated in Table 27-23 of the 802.11 REVme D6.0). An additional criterion can be used with respect to the frame to be sent, namely the PSRT PPDU, in that the intended transmit power of the PSRT PPDU is lower than a threshold based on PSRmin. The relationship is defined in equation (35-6) of the 802.11 be D6.0 document for EHT PSR-based SR and in equation defined in the section 26.10.3.2 of 802.11 REVme D6.0 document for HE PSR-based SR. PSRmin is the smallest PSR value in case there exist multiple PSR values within the bandwidth of the PSRT PPDU, i.e., there are multiple resource units defined by the PSRR PPDU (Trigger frame), each having its own PSR value. PSR value is obtained using Table 27-23 from one of the following: For HE PSR-based SR: i) The value of the UL Spatial Reuse subfield in the Common Info field of the Trigger frame of the PSRR PPDU (based on Table 27-23). ii) The value of the RXVECTOR parameter Spatial Reuse of the HE TB PPDU that follows the PSRR PPDU. For EHT PSR-based SR: a) The value of the UL Spatial Reuse subfields in the Common Info field of the Trigger frame of the PSRR PPDU if the Special User Info field is not present in the Trigger frame, or b) The value of the EHT Spatial Reuse n subfield, 1 <=n<=2, in the Special User Info field of the Trigger frame of the PSRR PPDU if the Special User Info field is present in the Trigger frame, or c) The value of the RXVECTOR parameter Spatial Reuse of the TB PPDU that follows the PSRR PPDU. The usage of PSRmin is further defined in section 26.10.3.2 of the 802.11 REVme D6.0 and in section 35.10.3.1 of the 802.11 be D6.0 document. For ease of explanation, the frame for switching a channel access from PCA to NPCA is referred below to as frame CS-ICF, standing for “Channel Switch - Initial Control Frame”. The name of this frame “CS-ICF” can be different and it’s not limited to this. Furthermore, existing Control Frame could be extended to have the ability of triggering the channel switch as well. For conciseness below, it is mainly made reference to the OBSS PD-based SR, while the PSR-based SR applies in the same way with, however, different SR criteria as defined above. It is to be noted that an OBSS_PDievei threshold set relatively low allows the STA to use higher maximum transmit power to send the CS-ICF. This corresponds to situations where the OBSS is far from the STA. The counterpart of this setting is that only OBSS packets which have low received signal strength level allow transmitting the CS-ISF. On the contrary, an OBSS_PDievei threshold set relatively high allows the STA to use lower maximum transmit power to send the CS-ICF. This corresponds to situations where the OBSS can be quite closer to the STA. In these situations, more OBSS packets (which have higher received signal strength level) can be handled with the present disclosure. Also, as the OBSS signal is high, it is more likely that it is detected by all the STAs of the BSS, contrary to when the OBSS signal is low. That is why, it is preferred to set the OBSS_PDievei threshold to a relatively low value and use the CS-ICF to inform the other STAs (too far from the OBSS to detect OBSS interference) about the detected OBSS. Of course, the OBSS_PDievei threshold may be dynamically configured to find an appropriate value. As an example, a STA might monitor the beacons from the OBSS APs and measure their received signal strength level, subtract a value of 25dB (as an approximation to the required RSNI (Received Signal-to-Noise Indicator)) and use it as candidate OBSS_PDievei threshold. Figures 5 and 6 illustrate the same scenario with however different STAs detecting the OBSS interference, namely the AP of BSS1 in Figure 5 (corresponding to the situation of Figure 3a) and a non-AP STA in Figure 6 (corresponding to the situation of Figure 3b). In Figure 5, when the AP detects an OBSS TXOP which allows SR operation, the AP sends an CS-ICF to trigger NPCA. In details, AP1 detects the received signal strength level of the OBSS packet (OBSS TXOP 220) from AP2, while STA11 and STA12 do not. STA12 is not shown in the Figure for conciseness, but it is assumed to behave as STA11 behaves. AP1 implements at least one of the Spatial Reuse features: OBSS PD-based SR and / or PSR-based SR and it is enabled. In this case, upon detecting the OBSS packet, AP1 can start the Spatial Reuse operation (whatever the SR feature) if the OBSS packet meets the SR conditions I criteria, in particular with respect to the OBSS_PDievei threshold or the PSR opportunity. If it is determined that the SR feature can be used, AP1 sends the frame for switching a channel access from PCA to NPCA, i.e., frame CS-ICF 500, during the SR operation (OBSS PD-based SR or PSR-based SR). In some embodiments, AP1 has prioritized channel access over the non-AP STAs and can send the CS-ICF 500 without contention in a short interval after having detected the OBSS transmission, such as a SIFS (Short Interframe Space) or a PIFS (Priority Interframe Space). Prioritized access means that the non-AP STAs (also detecting the OBSS interference) may have to contend for SR medium access, i.e., by applying the EDCA mechanism to contend for medium access for Spatial Reuse before transmitting a CS-ICF (as discussed below with reference to Figure 6). Prioritizing the AP avoids potential collisions among CS-ICFs sent by multiple STAs. In particular embodiments that reduce complexity, only the AP is allowed to send the CS-ICF 500. In alternative embodiments, all STAs of BSS1 contend for SR medium access. Therefore, AP1 applies the EDCA mechanism to contend for medium access for SR before transmitting the CS-ICF 500. The conventional EDCA Parameters can still be used. However, in embodiments, special EDCA Parameters defined for this specific purpose of sending the CS-ICF can be used, meaning they are different from the conventional EDCA Parameters used for non-SR medium access. For example, a dedicated backoff counter (CS-ICF BC) can be used. In some embodiments using the four EDCA transmitting queue or the like, the CS-ICF 500 is preferably placed in the front of the transmitting queue having the highest priority for medium access on the primary channel, in order to be sent in urgence. In EDCA, it is the AC_VO queue. If the AP1 is able to detect the bandwidth of OBSS TXOP 220, and if the detected bandwidth covers the target NPCA PCH P2 (for NPCA use), AP1 may not send the CS-ICF 500 nor switch to the NPCA PCH P2 since the latter also suffers from interference by the OBSS traffic. The bandwidth of OBSS TXOP 220 may be identified by any means, for example, by the Bandwidth field in the PHY preamble of the OBSS PPDU and the channel allocations in the corresponding band, or by the bandwidth signalling TA indicated in the OBSS PPDU. If the duration of the detected OBSS TXOP 220 is shorter than the predefined or prenegotiated threshold to perform NPCA operations, AP1 may not send the CS-ICF 500 nor switch to the NPCA PCH P2. The threshold value may be set in the NPCA Minimum Duration Threshold value 1542 in the UHR Operation Information field 1540 of its own BSS (Figure 15 described below). In case of SR triggered NPCA mode, the threshold can be further shortened by considering the time that will be used to send the CS-ICF. This behaviour can be summarized as a communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels: detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, and deciding, in case the OBSS transmission encompasses a target secondary channel different from the primary channel or in case the OBSS transmission is shorter than a predefined duration threshold, not to transmit, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to a (secondary channel) access scheme over the target secondary channel. On the other hand, the STA may continue to utilize the legacy SR operation to benefit from the SR opportunity, i.e., to transmit over the primary channel using the SR restrictions. It means that the method may also comprise deciding, in case the OBSS transmission does not encompass a target secondary channel different from the primary channel or in case the OBSS transmission is longer than a predefined duration threshold, to transmit, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to a (secondary channel) access scheme over the target secondary channel. When the STAs contend for SR medium access, they have to stop their contention when one of them first gains access and transmit a CS-ICF. This is described below with reference to Figures 6 and 11. The CS-ICF 500 can be a newly defined Control frame or a Management frame. Figures 13a and 13b illustrate exemplary formats for a newly defined CS-ICF. The CS-ICF 500 can be an enhanced existing frame such as a Trigger frame. Figure 19 illustrates an exemplary enhanced NFRP Trigger frame format for a CS-ICF. The CS-ICF 500 is sent to the other STAs (STA11 and STA12) of BSS1 to indicate the detection of OBSS interference and to trigger a channel switching at the other STAs to the NPCA PCH P2 (i.e., to NPCA). The CS-ICF 500 can be a broadcast frame if there are multiple STAs associated with AP1, or a unicast frame if there is only one STA associated with AP1. Although AP1 sends the CS-ICF 500 with the reduced transmit power due to the constraint of SR features, robust MCS or data rate can be used for the CS-ICF 500 so that the receiver can properly decode the frame even with a low SNR. For example, the lowest MCS: MCSO or the lowest data rate with non-HT PPDU may be used for the CS-ICFs. The CS-ICF 500 may be transmitted on the primary 20MHz channel P1 only or may be extended to a wider bandwidth (e.g., 80MHz as shown in 501) if each 20MHz secondary channel is sensed as idle for a SIFS or a PIFS duration before sending the CS-ICF 500. It may be noted that the bandwidth-extended CS-ICF 501 may cover the NPCA PCH P2 for NPCA, in which case it advantageously obtains the TXOP on the NCPA PCH P2 and accelerates the channel access during NPCA operations 222a. In other words, CS-ICF may be sent in a non-HT duplicate PPDU which covers the NPCA Primary Channel to initiate TXOP of the NPCA Primary Channel. After having sent the CS-ICF 500 / 501, AP1 can switch to NPCA PCH P2 to start NPCA operations. When receiving the CS-ICF 500 / 501, STA11 and STA12 now understand that AP1 has detected OBSS interference. STA11 and STA12 can start NPCA operations on the NPCA PCH P2, meaning they switch from PCA (its CA channel on the primary channel) to NPCA (its CA channel on the NPCA PCH) during switching time 221 a / 221 b. As recalled above, the switching time 221 a and 221 b required by the STAs may differ depending on the STAs ability and hardware configuration. To allow the STAs to have entirely switched before the NPCA exchanges 222a / 222b start, the CS-ICF 500 / 501 includes a post-FCS padding field to have a frame length higher than the switching time required by the STAs to switch from PCA to NPCA. In this respect, the padding field follows (e.g., immediately) a previous “intermediate” FCS field. The latter is named “intermediate” because an additional FCS field may be provided after the padding field itself, at the end of the frame. AP1 may know the channel switch delays required by STA11 and STA12 beforehand, for example during the association procedure, and thus AP1 may adjust the length of the padding field (hence of the CS-ICF) accordingly. During NPCA operations 222a / 222b, AP1 and STA11 and STA12 may perform channel access on the NPCA PCH P2. They may use legacy EDCA mechanism to perform legacy EDCA contention. Alternatively, new EDCA Parameters dedicated to NPCA (“NP EDCA Parameters”) may be used, that are advertised by AP1 as the conventional EDCA Parameters are (e.g., in Beacon and Probe Response frames). Once the STA (AP1 or STA11 or STA12) gains access to the NPCA PCH P2 for NPCA transmissions 222a / 222b, it may send an ICF (e.g., RTS, MU-RTS Trigger frame for AP1) on the NPCA PCH P2 to confirm that it has successfully switched to the NPCA PCH. Although the Figure shows NPCA operations 222a / 222b on the NPCA PCH P2 only, other secondary channels such as upper 20MHz channel of S2 can also be used during the NPCA operations 222a / 222b, in particular if the PIFS CCA is clear on these secondary channels before PPDU transmission. No later than the end of OBSS TXOP220, AP1, STA11 and STA12 switch back (223a / 223b) to the primary channel P1 (i.e., to PCA). The switching back time 223a and 223b required by the STAs may differ depending on the STAs ability and hardware configuration. In Figure 6, when a STA detects an OBSS TXOP which allows SR operation, the STA sends a CS-ICF to trigger NPCA. In details, STA11 and STA13 can detect the received signal strength level of the OBSS packet (OBSS TXOP 220) from AP2, while AP1 and STA12 cannot. STA12 is not shown in the Figure for conciseness, but it is assumed to behave as AP1 behaves. STA11 and STA13 implement at least one of the Spatial Reuse features: OBSS PD-based SR and / or PSR-based SR and they are enabled. In this case, upon detecting the OBSS packet, STA11 and STA13 can start the Spatial Reuse operation (whatever the SR feature) if the OBSS packet meets the SR conditions I criteria, in particular with respect to the OBSS_PDievei threshold or the PSR opportunity. If it is determined that the SR feature can be used, STA11 or STA13 sends the frame for switching a channel access from PCA to NPCA, i.e., frame CS-ICF 600, during the SR operation (OBSS PD-based SR or PSR-based SR). To do so, STA11 and STA13 start contending for SR medium access in the primary channel, as already mentioned above with respect to Figure 5. For example, the legacy EDCA mechanism can be used for the contention and special EDCA Parameters can be defined for this specific purpose of sending the CS-ICF. In the scenario of the Figure, STA11 wins the contention and STA13 loses. Then, STA11 sends the CS-ICF 600 (similar to frame 500 defined above) during the SR operation. The CS-ICF 600 is sent to the other STAs (AP1 and STA12 and STA13) of BSS1 to indicate the detection of OBSS interference and to trigger the channel switching at those STAs to the NPCA PCH P2 (i.e., to NPCA). Similar to Figure 5, the CS-ICF 600 is sent with reduced transmit power due to SR constraints; the CS-ICF 600 can be a broadcast frame; low MCS can be used; and the CS-ICF 600 may be transmitted on the primary 20MHz channel P1 only or may be extended to a wider bandwidth (e.g., 80MHz as shown in 601); the CS-ICF 600 / 601 preferably include a post-FCS padding field to have a frame length higher than the switching time required by the STAs to switch from PCA to NPCA. If the STA11 / 13 is able to detect the bandwidth of OBSS TXOP 220, and if the detected bandwidth covers the target NPCA PCH P2 (for NPCA use), STA11 / 13 may not send the CS-ICF 600 nor switch to the NCPA PCH P2 since the latter also suffers from interference by the OBSS traffic. The bandwidth of OBSS TXOP 220 may be identified by any means, for example, by the Bandwidth field in the PHY preamble of the OBSS PPDU and the channel allocations in the corresponding band, or by the bandwidth signalling TA indicated in the OBSS PPDU. If the duration of the detected OBSS TXOP 220 is shorter than the predefined or prenegotiated threshold to perform NPCA operations, STA11 / 13 may not send the CS-ICF 600 nor switch to the NPCA PCH P2. The threshold value is set in the NPCA Minimum Duration Threshold value 1542 in the UHR Operation Information field 1540 of its own BSS. In case of SR triggered NPCA mode, the threshold can be further shortened by considering the time that will be used to send the CS-ICF. This behaviour at STA11 / 13 is similar to the behaviour described above with respect to AP1. After having sent the CS-ICF 600 / 601, STA11 can switch to NPCA to start NPCA operations. When receiving the CS-ICF 600 / 601, AP1 and STA12 can now understand that STA11 has detected OBSS interference. AP1 and STA12 can start NPCA operations 222a / 222b on the NPCA PCH P2, meaning they can switch from PCA (its CA channel on the primary channel P1) to NPCA (its CA channel on the NPCA PCH P2, during switching time 221a / 221b. On STA13 side, when receiving the CS-ICF 600 / 601 from STA11, it recognises that it failed to win the contention, hence it can stop its own contention and can then switch to NPCA to perform NPCA operations 222c on the NPCA PCH P2 with the other STAs. In other words, the operations at STA13 consist in detecting, on primary channel P1, an OBSS transmission that meets one or more criteria of a spatial reuse (SR) operation; contending for SR medium access to primary channel P1; and while contending, receiving, from another STA - here STA11 - of the BSS, on primary channel P1, a CS-ICF 600 and responsive to receiving the CS-ICF while contending, stopping the contention operation and switching to NPCA on the NCPA PCH. During the NPCA operations 222a / 222b / 222c, all the STAs may perform channel access on the NPCA PCH P2. As for Figure 5, they may use legacy EDCA mechanism or new EDCA Parameters dedicated to NPCA, before sending an ICF on the NPCA PCH P2 or an extended channel (including P2 and one or more other secondary channels such as upper 20MHz channel of S2). No later than the end of OBSS TXOP220, AP1, STA11, STA12 and STA13 switch back (223a / 223b / 223c) to the primary channel P1 (i.e., to PCA). In the scenario of Figure 6, by allowing the non-AP STA to send the CS-ICF 600 / 601, the chance of aligning the OBSS detection and the NPCA operations between the STAs of BSS1 is enhanced. Figures 7 and 8 illustrate enhanced scenarios compared to the scenario of Figure 6 in which the AP does not directly detect the OBSS interference and becomes aware about it thanks to the CS-ICF 600 by STA11 detecting the OBSS TXOP 220. In these enhanced scenarios, the AP further propagates the indication of OBSS interference to farther STAs of the BSS. Indeed, due to the reduced transmit power of the CS-ICF (due to the Spatial Reuse constraints), there are risks that some distant STAs of the BSS do not receive the CS-ICF 600. Therefore, responsive to receiving the CS-ICF, the AP - here AP1 - transmits, to other STAs of BSS1 and on the primary channel P1, another CS-ISF frame for switching a channel access from PCA to NPCA. This transmission comes together with the configuration of its (i.e., AP’s) radio to NPCA, for example by switching its radio to the NPCA PCH P2. The transmission preferably takes place before the switching. Similar to Figure 6, in Figure 7, STA11 and STA13 can detect the received signal strength level of the OBSS packet (OBSS TXOP 220) from AP2, while AP1 and STA12 cannot. STA11 wins the contention and sends the CS-ICF 600 (or 601), here denoted CS-ICF1, during the SR operation. That is why STA13 is not shown in the Figure for conciseness, but it is assumed to behave as STA13 of Figure 6. Still for conciseness, details on the CS-ICF and NPCA operations are not repeated here, but are similar to those of the scenario of Figure 6. In embodiments, the CS-ICF1 600 is addressed to AP1 only. In variants, it is a broadcast frame. In the scenario of Figure 7, AP1 and STA13 receive the CS-ICF1 600 while STA12 cannot due to its high distance from STA11 with respect to the low transmit power of the CS-ICF1 600. After having sent the CS-ICF1 600 / 601, STA11 can switch to NPCA to start NPCA operations. When receiving the CS-ICF1 600, AP1 and STA13 can now understand that STA11 has detected OBSS interference. AP1 and STA13 can start NPCA operations 222a by switching to NPCA. It is recalled that a STA, in particular the AP, may have two radios, in which case the “switching” may merely consist in configuring the second radio (the first one operating on the primary channel P1) to operate on the NPCA PCH P2. However, before switching to NPCA, AP1 sends another CS-ICF, namely CS-ICF2 700, to the other associated STAs (STA12 in this case) that are too far from transmitting STA11. CS-ICF2 700 may be the same type of frame as CS-ICF1 600, meaning it can be a broadcast frame if there are multiple targeted STAs, or a unicast frame if there is only one targeted STA; it may be sent a SIFS or a PIFS after CS-ICF1 600; it may be transmitted on the primary 20MHz channel P1 only or may be extended to a wider bandwidth (e.g., 80MHz as shown in 701); it may include some post-FCS padding, i.e., padding after an intermediate FCS. As AP1 has not directly detected OBSS interference, CS-ICF2 700 / 701 can be sent without reduced transmit power. In variants, AP1 knowing that there is some OBSS interference, may apply the reduced transmit power. Thanks to CS-ICF1 600 / 601 and CS-ICF2 700 / 701, all STAs (AP1 and STA11 / STA12 / STA13) now know about the OBSS interference and can switch their channel from the primary channel P1 to the NPCA PCH P2 (during switching operation 221a / 221b / 221d). In this embodiment, due to the two CS-ICFs, the first one (CS-ICF1) can be deprived of padding since time required for CS-ICF2 may be sufficient for STA11 to perform its channel switching. During the NPCA operations 222a / 222b / 222d, all the STAs may perform channel access on the NPCA PCH P2. As for Figure 6, they may use legacy EDCA mechanism or new EDCA Parameters dedicated to NPCA, before sending an ICF on the NPCA PCH P2 or an extended channel (including P2 and one or more other secondary channels such as upper 20MHz channel of S2). No later than the end of OBSS TXOP 220, AP1, STA11, STA12 and STA13 switch back (223a / 223b / 223d) to the primary channel P1 (i.e., to PCA). In the scenario of Figure 7, by allowing the non-AP STA to send the CS-ICF1 600 / 601 and AP1 to send the CS-ICF2 700 / 701, the chances of aligning the OBSS detection and the NPCA operations are enhanced. Turning now to Figure 8, the beginning of the scenario of this Figure is the same as in Figure 7 and thus does not need to be repeated in details. STA11 and STA13 can detect the received signal strength level of the OBSS packet (OBSS TXOP 220) from AP2, while AP1 and STA12 cannot. STA11 wins the contention and sends the CS-ICF 600 (or 601), here denoted CS-ICF1, during the SR operation. That is why STA13 is not shown in the Figure for conciseness. AP2, STA11, STA13 and AP1 behaves as in Figure 7, till the reception of CS-ICF1 600 / 601 by AP1 and the channel switch 221 b by transmitting STA11 and STA13. Before configuring itself for NPCA, AP1 sends an ICF, namely ICF3 frame 800 to its associated STAs (STA11 / STA12 / STA13 in this case) after a short interval such as a SIFS or a PIFS. The aim of that ICF3 800 is to manage PCA operations on the primary channel P1 (possibly extended with additional secondary 20MHz channels) while also managing NPCA operations on the NPCA PCH P2 (possibly extended). ICF3 frame 800 is a frame allocating resources to STAs for PCA operations and NPCA operations. This is achieved by transmitting the CS-ICF3 800 over the primary channel P1 (possibly extended) and the NPCA PCH P2 (possibly extended); wherein the CS-ICF3 800 allocates: PCA resource units (RUs) to a PCA set of STAs of BSS1 that do not suffer from OBSS interference, those PCA RUs being included in the PCA subset of channels (i.e., the primary channel P1 possibly extended), and NPCA RUs to a NPCA set of STAs of BSS1 that suffer from OBSS interference, those NPCA RUs being included in the NPCA subset S2 of channels (i.e., the NPCA PCH P2 possibly extended). Indeed, AP1 knows that STA12 cannot receive frames from the OBSS (AP2), meaning STA12 is not interfered by the OBSS and can still use the original primary channel P1 with AP1 during the OBSS TXOP 220 time period. Therefore, conventional RUs can be allocated to STA12 on the primary channel P1, while NPCA can be performed in parallel on the NPCA PCH P2with STA11 / STA13. Various embodiments can be contemplated for the AP to know which non-AP STAs belong to the PCA set of STAs (unable to detect the OBSS interference) and which ones belong to the NPCA set of STAs (able to detect the OBSS interference). This can be made by gathering station’s information. For example, the STAs may transmit to the AP (e.g., when associating), the list of neighbouring APs that they are able to detect (e.g., from which they can receive Beacon frames). Those non-AP STAs that have indicated AP2 in their neighbouring AP list can be considered by AP1 as the STAs forming the NPCA set with respect to AP2, while the other STAs form the PCA set with respect to AP2. In variants, AP1 may send a Beacon Request to its associated non-AP STAs to gather information about the surrounding APs of the stations. The associated STAs may reply with Beacon Reports which includes the information of surrounding APs. For example, the AP can send the Beacon Request without the optional SSID subelement. This requests a report for the default “wildcard SSID”, and the STA reports for all the Beacon frames it has received. The Beacon Report further includes an RCPI field and an RSNI field which respectively indicate the power level and the signal-to-noise indication of the received Beacon frame. Since the Beacon Report only includes the information about the surrounding APs, it can be extended to have additional information including the information of surrounding non-APs. Such information can be used to determine the existence of stations such as STA12 in the scenario of Figure 8. At the end, the AP is able to discriminate between its associated STAs that are in the vicinity of AP2 (the NPCA set of STAs) and those that are not (the PCA set of STAs). In other embodiments, the AP may gather the location of each of its associated non-AP STAs as well as the location of other APs, and then infer whether or not each associated STA may suffer from OBSS interference from AP2 (or BSS2). The position of each STA can be measured using the wireless positioning technology defined in 802.11 v, 802.11 me, 802.11 az, 802.11 bk amendment or any other wireless technology such as GNSS (Global navigation satellite system), Bluetooth (BLE or Bluetooth Low Energy) or UWB (802.15.4 or 802.15.4z), or the like. The AP may thus know the relative distance between each STAs. Hence, the AP can estimate the transmit power of the packet by analysing the received signal strength level and the relative distance from the transmitter to the AP. And then, the AP can estimate if that packet reaches another STA or not using the relative distance between the transmitter and the STA. As shown, the ICF3 800 is optionally transmitted over a composite channel (here the entire set S1) covering all 20MHz channels for PCA operations 224a / 224d and NPCA operations 222a / 222b. The ICF3 800 is transmitted over the primary channel P1 for the STAs operating according to the PCA scheme, to be able to identify their resources to be used. Similarly, the ICF3 800 is also transmitted over the NPCA PCH P2 for the STAs operating according to the NPCA scheme (hence already on the NPCA PCH), to be able to identify their resources to be used. ICF3 800 can be a Trigger frame which triggers MU UL PPDU. In the example of the Figure, ICF3 800 allocates the S2 channel resources 222a to STA11 / STA13 and primary 40MHz resources 224a to STA12. During the NPCA operations 222a / 222b and PCA operations 224a / 224d, UL / DL frame exchanges may be required to keep synchronization between the STAs during the OBSS TXOP 220, for proper reception by the single radio of AP1. In such a case, UL OFDMA triggered by ICF3 is the one to ensure the synchronization for the uplink traffic. For the downlink traffic, AP1 may utilize the DL OFDMA transmission. In both UL / DL OFDMA, RUs are properly allocated to the channel where the STAs are operating on. No later than the end of OBSS TXOP 220, STA11 and STA13 switch back (223b) to the primary channel P1 (i.e., to PCA). AP1 may also deactivate its second radio, hence only keeping its first radio activated (operating on the primary channel P1). In the scenario of Figure 8, by allowing some non-AP STAs, which are not interfered by the OBSS packet, to remain performing PCA triggered by ICF3 800 while some other non-AP STAs, which are interfered by the OBSS packet, start to perform NPCA, the chances of utilizing the entire operating bandwidth are enhanced. Figure 9 is a variant of Figure 8 where ICF3 800 is omitted. In this scenario, AP1 is initially operating on primary 20MHz or 40MHz channel when receiving the CS-ICF1 600 / 601. Responsive to that frame, AP1 enlarges its bandwidth to a wider bandwidth to additionally include the NPCA PCH P2 (possibly extended). In the Figure, AP1 extend to cover the entire set S1. The channel extension is made by activating an additional radio on the NPCA PCH P2 (possibly extended) - here on S2 - when receiving the CS-ICF1 600 / 601. The channel activation operation is depicted under reference 221a. Thanks to this additional radio on the NPCA PCH P2, AP1 may perform PCA 224a on the primary channel P1 and NPCA 222a on the NPCA PCH P2 independently. In this case, synchronization may not be required between PCA / NPCA so the transmission of ICF3 800 can be omitted. Furthermore, AP1 and STA11 (the STA that detected the OBSS interference) may agree on an NPCA PCH P2 that is a channel where interference between PCA 224a and NPCA 222a can be avoided, for example by putting the 20MHz NPCA PCH P2 apart from the PCA channels, as shown in the Figure. In this scenario of Figure 9, the AP maintains a first radio operating on the primary channel to perform PCA, and configures a second and separate radio to operate on a secondary channel (NPCA PCH) on which NPCA is performed. The NPCA and PCA operations 222a / 222b / 224a / 224d are then conducted during the OBSS TXOP 220. No later than the end of OBSS TXOP 220, STA11 and STA13 switch back (223b) to the primary channel P1 (i.e., to PCA). AP1 may also deactivate (223a) its second radio, hence only keeping its first radio activated (operating on the primary channel P1). In the above scenarios, the Spatial Reuse triggered NPCA feature may be activated all the time, meaning the STAs systematically seek to transmit a CS-ICF and then switch to the NPCA PCH P2 when the criteria are fulfilled. However, the BSS may mix STAs of different generations, meaning they do not necessarily support all the same features as the other STAs. In this context, support of features such as the Spatial Reuse triggered NPCA feature as well as operational activation / deactivation of those features can be declared. Figure 15 illustrates exemplary frame formats of Capability and Mode indications according to embodiments. The Spatial Reuse triggered NPCA feature is signalled. In addition, a No Untriggered UL Tx (NUUT) NPCA feature is also signalled. STA’s capabilities may be signalled in an UHR Capabilities element included for example in a Management frame such as a Beacon frame, Probe Request / Response frames, (Re)Association Request / Response frames, Action frames sent by the STA. STA’s operational modes (i.e., activation or deactivation of supported capabilities / features) may be signalled in an UHR Operation element included for example in a Management frame such as a Beacon frame, Probe Response frames, (Re)Association Response frames, Action frames sent by the STA, preferably by the AP managing a BSS which then presents the operation parameter for the entire BSS. All the frame formats shown in Figure 15 may have additional fields not indicated in the Figure and the order of each element except the Element ID, Length, Element ID Extension fields may be shuffled. Not all of the fields shown in the Figure are required to be present and some of them might be optional or removed. Not all of the fields are shown in the Figure and one or more fields not shown in the Figure may be added. The exact names of the fields can be different than the ones shown in the Figure. For example, the name “SR Triggered NPCA Supported” field is not limited to this and it can be for example “Spatial Reuse Triggered NPCA Support” field or “CS-ICF Triggered NPCA Supported” field, depending of the defined name of the mode. A frame to be transmitted by a station may comprise a (UHR or the like) Capabilities element including one or more of a first (NUUT NPCA) support field to signal whether or not the transmitting station supports untriggered uplink transmission during non-primary channel access operations and a second (SR triggered NPCA) support field to signal whether or not the transmitting station supports spatial reuse operation to transmit, on a primary channel experiencing inter-BSS interference, a frame to trigger at other stations a switching of channel access from a primary channel access scheme to a secondary channel access scheme. An element in the meaning of IEEE802.11 means a set of Element ID field, Length field, Element ID Extension field and Information field. The first (NUUT NPCA) support field and second (SR triggered NPCA) support field may be included in a (UHR or the like) MAC Capabilities Information field within the Capabilities element. A UHR Capabilities Information field may further include a NPCA Supported field to indicate whether NPCA operations are supported by the transmitting station (1 indicates that NPCA operations are supported, 0 indicates that NPCA operations are not supported). Field 1500 illustrates an exemplary format of such UHR Capabilities element, to indicate the Capabilities information related to the UHR features. It may include UHR MAC Capabilities Information field 1510 which gathers the Capabilities for UHR MAC features. 1510 may include NPCA Support field 1511, No Untriggered UL Tx NPCA Supported field 1512, SR triggered NPCA Supported field 1514. NPCA Supported field 1511 indicates whether the STA is capable of NPCA operations or not. No Untriggered UL Tx (so called NUUT hereafter) NPCA Supported field 1512 indicates whether the STA supports or not the mode of NPCA where the STA is not allowed to send untriggered UL (uplink) transmission. Untriggered UL (uplink) transmission means that the STA can transmit uplink frames to the AP without trigger from the latter, such as a trigger frame. SR Triggered NPCA Supported field 1514 indicates whether the STA is capable of the SR Triggered NPCA mode proposed in this disclosure. When this mode is activated, if an NPCA STA detects OBSS traffic which meets one of the conditions of Spatial Reuse operation (OBSS PD-based SR and / or PSR-based SR), the NPCA STA transmits an CS-ICF which triggers NPCA on the receiver NPCA STA. Turning to the activation / deactivation of such features, a frame to be transmitted by a station may comprise a (UHR or the like) Operation element including one or more of a first (NUUT NPCA) mode field to signal an activation or deactivation of an operating mode where the transmitting station is not allowed to perform untriggered uplink transmission during non-primary channel access operations and a second (SR triggered NPCA) mode field to signal an activation or deactivation of an operating mode where the transmitting station uses spatial reuse operation to transmit, on a primary channel experiencing inter-BSS interference, a frame to trigger at other stations a switching of channel access from a primary channel access scheme to a secondary channel access scheme. The first (NUUT NPCA) mode field and second (SR triggered NPCA) mode field may be included in a (UHR or the like) Operation Information field within the Operation element. Field 1520 illustrates an exemplary format of such UHR Operation element, to indicate the Operational information related to the UHR features. It may include UHR Operation Parameters field 1530, Basic UHR MCS And Nss Set field 1535, UHR Operation Information field 1540. UHR Operation Parameters field 1530 includes the operational parameters related to the UHR features. Basic UHR MCS And Nss Set field 1535 indicates the UHR-MCSs for each number of spatial streams in UHR PPDUs that are supported by all UHR STAs in the BSS (including IBSS and MBSS) for transmission and reception. UHR Operation Information field 1540 indicates the operational information related to the UHR features. Field 1530 corresponds to the UHR Operation Parameter field format which may include NPCA Operation Information Present field 1532. NPCA Operation Information Present field 1532 indicates whether NPCA operations are enabled at the station (e.g., AP) transmitting this field and whether the NPCA Operation Information field is present in the UHR Operation Information field 1540. Field 1540 corresponds to the UHR Operation Information field format which may include NPCA Operation Information if the NPCA Operation Information Present field 1532 indicates the existence. NPCA Operation Information may include NPCA Primary Channel field 1541, NPCA Minimum Duration Threshold field 1542, NPCA Switching Delay field 1543, NPCA Switch Back Delay field 1544 and NPCA Mode field 1550. The NPCA Primary Channel field 1541 indicates the channel number of a channel within the BSS bandwidth that corresponds to the channel that the NPCA AP and its associated NPCA non-AP STAs switch to perform NPCA operations. Hence, this is the NPCA PCH P2. The NPCA Minimum Duration Threshold field 1542 indicates the minimum duration of inter-BSS activity (inter-BSS PPDU or inter-BSS TXOP) that is required to have been indicated on the primary channel of the BSS as a necessary condition to permit an NPCA STA to switch to the NPCA primary channel to perform NPCA operations. The NPCA Switching Delay field 1543 indicates the time needed by an NPCA STA to switch from the BSS primary channel to the NPCA primary channel. The NPCA Switch Back Delay field 1544 indicates the time needed by an NPCA STA to switch from the NPCA primary channel to the BSS primary channel. The NPCA Mode field 1550 indicates the operating modes of NPCA. Field 1540 may also comprise optional Switch Waiting Duration field 1545 and optional Switch Back Waiting Duration 1546 when the embodiment of Figure 16a described below is implemented. Field 1550 corresponds to the NPCA Mode field format which indicates the operating modes of NPCA for the STA. NPCA Mode field includes No Untriggered UL Tx NPCA (NUUT) Mode Enabled field 1552 and SR Triggered NPCA Mode Enabled field 1554 that respectively indicates the activation / deactivation of the mode. NUUT Mode may be either activated / deactivated in a BSS level configuration or at per STA level. SR Triggered NPCA Mode may be either activated / deactivated in BSS level or at per STA level as well. If the AP of the BSS indicates deactivation of these modes, all the associated STA deactivate these modes. However, if the AP indicates activation, each associated STA may choose to activate or deactivate independently. In embodiments, either of the two modes can be enabled or disabled based on the other. For example, the SR triggered NPCA mode may be allowed (hence activated) only in case the NUUT mode is already activated. In embodiments, the SR triggered NPCA mode is activated only inside a TWT SP (described below) to ensure that the STAs of the BSS can receive the CS-ICF. By indicating and exchanging their capabilities and / or operation parameters, the STAs can know those of each other in the BSS. Any STA can then configure its NPCA operations based on this information. Figures 16 and 16a illustrate scenarios where multiple STAs detect the OBSS interference, namely AP1 and STA12 of BSS1 for the situation of Figure 3c). They assume the hidden-node situation as shown in Figure 3c. In these scenarios, the AP is configured to send the CS-ICF when the detected OBSS traffic satisfies the SR conditions and the non-AP STAs are configured not to send the CS-ICF even when the detected OBSS traffic satisfies the SR condition. In the scenario of Figure 16, the non-AP STAs can switch to the NPCA PCH P2 upon detecting the OBSS traffic (e.g., parsing the BSS Color inside the PHY header). This is the case for STA12. The other STAs of the BSS, such as STA11, can switch to the NPCA PCH P2 only upon detecting the CS-ICF sent by the AP. Any CS-ICF as above can be used. In the scenario of Figure 16a, switch waiting duration (shown as 1600) and switch back waiting duration (shown as 1602) are defined to control the switching of the non-AP STAs detecting the OBSS traffic as STA12. Those durations (from the detection of OBSS traffic) may be defined in Switch Waiting Duration field 1545 and Switch Back Waiting Duration 1546 (Figure 15) respectively. Other wording than ‘Waiting Duration” can be used, such as “Start time”. Switch waiting duration 1600 defines the time when the STA starts the channel switching after detecting the OBSS traffic. Knowing that the AP1 is operating in the SR Triggered NPCA mode, STA12 may decide to delay the switch start time for a while as shown as 1600. With this, STA12 may be able to receive CS-ICF that is sent from AP1 and to ensure that AP1 is going to switch to the NPCA PCH after the CS-ICF transmission. STA12 may suffer from the OBSS interference and may not be able to decode the CS-ICF correctly. In such a case, STA12 may decide not to delay the switch start time and switch to NPCA as soon as it detects the inter-BSS frame (Figure 16). For the switch back waiting duration 1602, if the NUUT NPCA Mode is enabled, STA12 may switch back to the primary channel when there is no frame received from AP1 over the NPCA PCH for a pre-determined switch back waiting duration 1602. The frame can be either a DL (Down Link) frame or a Trigger frame 1604. If the SR Triggered NPCA Mode is also enabled, knowing that AP1 may send a CS-ICF before switching to NPCA PCH, STA12 may configure a longer switch back waiting duration to accommodate the time for the CS-ICF transmission. This should be configured by taking the switch waiting duration 1600 into account since if the switch waiting duration 1600 is configured to wait for the CS-ICF transmission, the switch back waiting duration 1602 should not take CS-ICF transmission duration anymore. By properly setting the switch back waiting duration 1602, STA12 may be able to switch back to the primary channel and be ready for the potential frame exchange from the AP1 in case that AP1 did not hear the OBSS traffic and remained in the primary channel. The scenario of Figure 16a so described includes a communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels: detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, and waiting for a predefined duration before switching a channel access from a primary channel access scheme to a secondary channel access scheme. As mentioned above, the predefined duration includes the duration of the CS-ISF from the AP. It may include additional time such as a SIFS (or the like) and the duration of a CS-ISR (as described below) in case a response (CS-ISR) is provided to the CS-ISF. In addition, the method may further comprise sensing whether a frame is received from an access point of the BSS during a second predefined duration following the switching, and switching back to the primary channel access scheme in a case where no frame is received from the access point during the second predefined duration. STA may internally configure the SR Triggered NPCA Mode based on the NUUT NPCA mode configuration and vice versa. For example, when the NUUT NPCA mode is activated, the STA may also activate the SR Triggered NPCA. Since NUUT NPCA mode disallows a STA to send an UL frame without receiving Trigger frames, it is suitable for SR Triggered NPCA mode because the STA can wait for the AP switching to the NPCA PCH without sending UL frame. Furthermore, SR Triggered NPCA Mode may be activated inside a TWT (Target Wake Time) SP to ensure that the non-AP STAs of the BSS are awake and they can receive the CS-ISF from the AP. Or even if the SR Triggered NPCA Mode is activated, the AP may decide not to send the CS-ICF outside a TWT SP, meaning the AP waits for the next TWT SP after detection of the OBSS transmission to transmit the CS-ISF. In particular, it can wait for the next TWT SP that occurs during the OBSS TXOP and not too close to the end of the OBSS TXOP, and then transmits the CS-ISF during the TWT SP. This is because if the STAs are in the PS mode and in the doze state, the STAs cannot receive the CS-ICF. Inside a TWT SP, the STAs that are concerned in the TWT SP are in the awake state so they can receive the CS-ICF. The TWT SP can be either individual TWT or broadcast TWT. As mentioned above, a response (CS-ISR) can be provided to the CS-ISF, in order to confirm the other STAs indeed switch to the NPCA PCH P2. Figures 17, 18a and 18b illustrate communication methods involving one or more frames for switching a channel access from PCA to NPCA having CS-ICR (Channel Switch -Initial Control Response) feedback according to embodiments. Figure 17 assumes the hidden-node situation as shown in Figure 3a. The figure shows the case where the AP sends the CS-ICF and a non-AP STA sends back the CS-ICR; however, it is also applicable to the case where a non-AP STA sends the CS-ICF and the AP (or any other STA) sends back the CS-ICR. Figures 18a and 18b assume the hidden-node situation as shown in Figure 3c. In these scenarios of Figures 18a and 18b, the AP is configured to send the CS-ICF when the detected OBSS traffic satisfies the SR condition and the STAs are configured not to send CS-ICF even when the detected OBSS traffic satisfies the SR condition. The STAs may directly switch to the NPCA PCH upon detecting the OBSS traffic as in Figure 16 or apply the switch waiting duration 1600 as in Figure 16a. In the embodiments shown in Figure 5 to Figure 9, CS-ICF is sent from a STA without any response (CS-ICR) sent back from the STAs that receives the CS-ICF. One advantage of these embodiments (without CS-ICR) is to avoid the time of sending CS-ICR, and thus to operate the NPCA operations for a longer time. However, any CS-ICR feedback may have some advantages. For instance, if there is at least one STA that sends back the CS-ICR, the CS-ICF is worth to be sent as there are STAs that confirm they take it into account (and thus switch to the NPCA PCH). The AP may therefore continue to send CS-ICF at each next opportunity of OBSS traffic. Symmetrically, if no STA sends back the CS-ICR, the CS-ICF may be not worth to be sent as no STAs takes it into account: the AP may stop to send CS-ICF for a while, including e.g., the next opportunity in case of OBSS traffic. The AP can start again sending CS-ICF after a specific time interval or when it detects the configuration / environmental change (e.g., BSS Operation mode changes, AP moves, STA moves, new STA associates, new OBSS detected etc). Furthermore, the STA may temporally fail to receive the CS-ICF for example by being in the doze state. So, the AP may try several times to send the CS-ICF even though there is no CS-ICR feedback received. In this perspective, the AP (or any STA) waits for the response frame CS-ISR, from one or more other STAs, before performing NPCA operations on the NPCA PCH. Figure 17 illustrates an exemplary scenario where the CS-ICR is sent in the primary channel before the AP switches to the NPCA PCH. In this case, AP1 sends the CS-ICF 1700 in the primary channel P1. Preferably, the CS-ICF 1700 is sent in a wider bandwidth channel having multiple 20MHz channels, for instance that encompasses the NPCA PCH P2 as shown in 1701. The transmission power of CS-ICF 1700 / 1701 satisfies the restriction of SR operation in the primary channel P1 but preferably the restriction does not apply to the channels where OBSS traffic is not sent. When STA11 and / or STA12 receives CS-ICF 1700 (or 1701 having wider bandwidth), they send back CS-ICR 1702 in the primary channel P1 after a specific time interval such as the SIFS. CS-ICR 1702 is a frame that acknowledges reception of CS-ICF 1700 (from the AP in the present scenario) over the primary channel P1. The STAs may consider Carrier Sense to decide whether to send back the feedback or not. If the STA is capable of wider bandwidth than the primary 20MHz channel, the STA may send CS-ICR 1702 over a wider bandwidth as shown in 1704. It is advantageous for the CS-ICR 1704 to encompass the NPCA PCH P2 in order to set the NAV around the STAs that hears the CS-ICR 1702. In this scenario, CS-ICF 1700 does not need the intermediate FCS because the channel switch happens after the CS-ICR 1702 transmission at STA11 / STA12. Instead, CS-ICR 1702 may contain intermediate FCS to allow AP1 to switch before receiving the entire CS-ICR 1702. Channel switch at STA11 / STA12 happens when CS-ICR 1702 has been transmitted as shown in 1708. Channel switch at AP1 happens when CS-ICR 1702 is received (at least until the intermediate FCS if intermediate FCS is included in CS-ICR 1702) as shown in 1706. Figures 18a and 18b illustrate exemplary scenarios where the CS-ICR is sent over the NPCA PCH P2, after the STAs (including the AP) have switched to the NPCA PCH. In Figure 18a, AP1 sends the CS-ICF 1800a over the primary channel P1. Preferably, the CS-ICF 1800a is sent in a wider bandwidth channel having multiple 20MHz channels, for instance that encompasses the NPCA PCH P2 as shown in 1802a. The transmission power of the CS-ICF 1800a / 1802a satisfies the restriction of SR operation in the primary channel P1 but preferably the restriction does not apply to the channels where OBSS traffic is not sent. The STAs that receive the CS-ICF 1800a send back CS-ICR 1804a / 1806a in the NPCA PCH P2. CS-ICR 1804a / 1806a is a frame that acknowledges reception of CS-ICF 1800a / 1802a (from the AP in the present scenario) over the primary channel P1. In this scenario, it is advantageous that the CS-ICR 1804a / 1806a can be collected not only from STA11 / STA13 but also from STA12 that had already switched to the NPCA PCH P2 before receiving CS-ICF 1800a (as in Figure 16). By receiving CS-ICR 1804a / 1806a, AP1 can confirm that all the STA11 / STA12 / STA13 have switched to the NPCA PCH P2 and are ready for NPCA operations. In another embodiment, AP may indicate in the CS-ICF that the AP is not switching to the NPCA PCH by any reason. For example, the AP may decide to remain in the PCH and to perform Spatial Reuse operation. In this case, the AP may indicate the decision not to switch for example by setting the Target Channel field 1305 to the value of primary channel or by indicating in an additional field in the frame 1300 or 1944 (not specified in the figure). The CS-ICF may be sent as a broadcast frame to inform one or more STAs for the switching decision. The CS-ICF may be sent in a non-HT duplicated frame which covers both the NPCA PCH and PCH to inform the switching decision to the STAs both in the PCH and in the NPCA PCH. By receiving this CS-ICF, STAs can understand that the AP is not switching to the NPCA PCH so the STAs do not switch to the NPCA PCH and remain on the PCH. The CS-ICF can be sent by non-AP STA as well to indicate whether the non-AP STA is switching to the NPCA PCH or not. In Figure 18b, additional ICF 1808b is sent by AP1 after switching to the NPCA PCH P2. In this scenario, the first CS-ICF 1802b does not require immediate CS-ICR feedback; this is ICR 1808b sent over the NPCA PCH P1 that requires CS-ISR as a response. However, CS-ICR 1804b / 1806b is still a frame that acknowledges reception of CS-ICF 1800b / 1802b (from the AP in the present scenario) over the primary channel P1. This additional ICF 1808b helps the AP1 and the STAs (STA11 / STA12 / STA13) to synchronize their NPCA operations in the NPCA PCH P2. As another embodiment of CS-ICR, we assume the hidden-node situation as shown in Figure 3b. The Figure shows the case where the non-AP STA (STA11 or STA13) sends the CS-ICF and an AP sends back the CS-ICR; however, it is also applicable to the case where an AP sends the CS-ICF and the non-AP STA (or any other STA) sends back the CS-ICR. In this embodiment, when AP receives CS-ICF from one of its associated non-AP STAs (STA11 or STA13), the AP may decide not to switch to the NPCA PCH by any reasons. This decision is indicated in the CS-ICR and communicated to the associated non-AP STAs. By receiving the CS-ICR, the receiving STA can understand whether the AP is switching to the NPCA PCH or not. With this, the receiving STA may follow the AP’s operating channel. CS-ICR may be sent as a broadcast frame to let one or more STAs to receive the frame. CS-ICR may be sent in non-HT duplicate frame which covers both the NPCA PCH and PCH to inform the switching decision to the STAs both in the PCH and in the NPCA PCH. Receiving this frame in the NPCA PCH, STAs that have been already switched to the NPCA PCH may decide to remain in the NPCA PCH or to switch back to the PCH. It would be advantageous to let the AP decide the switching and other STAs to follow its decision. The CS-ICR can be sent by a non-AP STA as well to indicate whether the non-AP STA is switching to the NPCA PCH or not. In this case, CS-ICR may be sent as a unicast frame to the AP to let the AP receive the frame. Figures 20a, 20b and 20c illustrate communication methods involving one or more frames for switching a channel access from PCA to NPCA using Dynamic Subchannel Operation (DSO). The principle of the DSO procedure is the following one. A STA that can only operate on a subpart of the operating channel of its AP (e.g., only over the 160 MHz primary channel of the AP) can switch its own operating channel to a subchannel (or subband) of the operating channel of its AP (e.g., the 160 MHz secondary channel of the AP), which subchannel is out of the STA’s initial operating channel. Next, the STA can perform Downlink (DL) / Uplink (UL) OFDMA exchanges over the switched subchannel, after which it switches back to its initial operating channel. The scenarios of Figures 20a, 20b and 20c assume the hidden-node situation as shown in Figure 3c. The use of DSO in these scenarios allows different STAs to be directed to distinct channels for DSO, i.e., with dedicated access scheme over distinct channels. This aims at optimizing the use of the multiple channels. As shown in Figure 20c for example, multiple STAs may however be assigned the same secondary channel for DSO, provided that at least one other STA is assigned a distinct secondary channel for DSO. In these scenarios, the AP is configured to send a CS-ICF - referred here as DSO-ICF - when the detected OBSS traffic satisfies the SR condition and the STAs are configured not to send CS-ICF even when the detected OBSS traffic satisfies the SR condition. The DSO-ICF is sent by the AP1 under the SR operation as shown in 2000a, 2000b and 2000c. The difference of DSO-ICF compared to the CS-ICF of the previous scenarios is that DSO-ICF indicates different channels for the STAs that receive the ICF, whereas the CS-ICF of the above scenarios indicates only one NPCA PCH (which can be predetermined by the BSS or indicated in the CS-ICF, e.g., using Target Channel field 1305, Feedback Channel field 1940). DSO-ICF 2000a-c is preferably sent in non-HT duplicate PPDU which encompasses a by-default NPCA PCH P2. With this, the STA already switched to the by-default NPCA PCH can also receive the DSO-ICF in its NPCA PCH P2. The transmission power of DSO-ICF satisfies the restriction of SR operation in the primary channel P1 but preferably the restriction does not apply to the channels where OBSS traffic is not sent. By sending the DSO-ICF under SR operation, the BSS is able to use the medium more efficiently including not only the NPCA PCH P2 but also the other secondary channels. In Figures 20a and 20b, AP1 knowing or assuming that STA12 also detects the OBSS traffic and switches to the NPCA PCH P2 by itself, DSO-ICF 2000a / 2000b may assign NPCA PCH P2 to STA12 so that STA12 does not have to switch again from the NPCA PCH P2. In other words, the DSO-ICF frame for switching assigns, for a duration of the OBSS transmission, a secondary channel (NPCA PCH) to a STA that has already switched to the secondary channel. In the scenario of Figure 20a, the primary channel P1 is assigned to STA11 knowing or assuming that STA11 is not interfered by the OBSS TXOP. As a result, STA11 remains in the primary channel P2 and perform DSO operations on the primary channel P1 as shown in 2006a. In other words, the DSO-ICF frame for switching assigns the primary channel to one STA for Dynamic Subchannel Operation, for the duration of the OBSS transmission. STA13 is assigned the fourth 20MHz channel as shown in 2008a. Therefore, the DSO-ICF frame for switching assigns distinct secondary channels to respective STAs for them to switch to a secondary channel access scheme on the assigned secondary channel, for a duration of the OBSS transmission. They participate to DSO operation during this OBSS transmission duration. In the scenario of Figure 20b, the primary channel P1 is intentionally not assigned to any STA to avoid OBSS interference in the primary channel which may cause reception error in AP1 due to the low SINR in AP1, or reception error in STA11 due to the limited allowed transmission power of AP1 in the primary channel by the constraint of Spatial Reuse operation. In this scenario, AP1 conducts the DSO frame exchange sequence even if no response / activity is detected over the primary channel. STA11 is assigned to the second 20MHz channel as shown in 2006b and STA13 is assigned the fourth 20MHz channel as shown in 2008b. If the detected OBSS TXOP has a wider bandwidth (e.g., 40MHz), AP1 preferably avoid assigning any 20MHz channel of the OBSS TXOP bandwidth. Rather than assigning 20MHz channels, the AP may assign wider channels (multiples of 20MHz) or thinner channels. In the scenario of Figure 20c, AP1 may not know nor assume that STA12 has switched to the NPCA PCH P2 by itself when detecting the OBSS traffic. In this case, AP1 may assign another channel than the NPCA PCH P2 to STA12 which requires for the latter to switch again between channels. In this scenario, STA12 is assigned the fourth 20MHz channel as shown in 2004c, STA11 is assigned to the first 20MHz channel (primary channel) as shown in 2006c, STA13 is also assigned to the fourth 20MHz channel as shown in 2006c. Of course, as above, the primary channel may be excluded from assignment. In this scenario, two STAs are assigned the same (fourth) 20MHz channel to optimize the use of the channels. This may be beneficial should the two STAs wish to directly exchange frames (peer-to-peer). STA12 can receive DSO-ICF 2000c in the NPCA PCH P2 (third 20MHz channel in the Figure) and switch to the fourth 20MHz channel to perform the DSO operations. This scenario is less effective for the STA12 since it has to switch twice, first to the NPCA PCH P2 upon detecting OBSS traffic and then to the DSO subband responsive to DSO-ICF 2000c. However, it is advantageous for AP1 since it does not have to care about the situation of STA12 (whether it has switched on the NPCA PCH P2 or not). Although Figures 20a, 20b and 20c do not show CS-ISR feedback as in Figures 17 to 18b) and switch (back) waiting durations as in Figure 16a, variants thereof may involve such CS-ISR feedback and / or switch (back) waiting durations as discussed above. Figure 10 illustrates, using a flowchart, general steps at a STA directly detecting OBSS interference, which is capable of sending a CS-ICF. As mentioned previously, such station configured to send a CS-ICF can be only an AP or any STA (i.e., both APs and non-AP STAs). The process starts at step 1000 by detecting OBSS interference. An OBSS packet for any STA of BSS1 can be identified because it comes from a STA which is not associated with AP1 (BSS1). This OBSS packet could include a Control frame such as a RTS frame or a MU-RTS frame, or include a QoS data frame. In these frames (and more generally in any MAC frame), the STA of BSS1 decodes the MAC header of the received packet to read: the source address (address of the transmitting STA, corresponding to conventional Transmitter Address - TA) and / or the BSSID field, the Duration field. The source address (TA field) and / or the BSSID field makes it possible for the STA to determine whether the received packet is an OBSS packet (e.g., from a BSSID different from BSS1 or from a source that does not belong to BSS1) or not. The Duration field information makes it possible for the STA to estimate the duration of the OBSS packet (OBSS TXOP 220). The value of the Duration field is normally used by the STA to set its basic NAV when not applying the SR feature, meaning that the STA is no longer allowed to contend for medium access for the duration indicated in the Duration field. For the present disclosure and associated NPCA operations, the STA does not set the NAV and continues the backoff procedure if the received packet is a PSRR PPDU which provides the PSR opportunity or the received signal strength level of the OBSS packet is lower than the OBSS_PDievei threshold. For OBSS PD-based SR, the Duration field indicates the duration for NPCA operations, i.e., the latest when the STA operating under the NPCA scheme has to switch back to its primary channel (for PCA). For PSR-based SR, the Duration field (from the PSRR PPDU) indicates the duration of the PSR opportunity which allows the STA to send PSRT PPDU under the transmit power constraint. For the STA supporting both OBSS PD SR and PSR feature, the station may use both features in parallel depending on the received OBSS packet. Alternatively, the STA may decode the PHY preamble to identify the OBSS packet and its TXOP length. For example, BSS Color field of HE / EHT / UHR PPDU can be used to identify which BSS the PPDU is transmitted from. For VHT PPDU, GroupID field and Partial AID field can be used to identify the BSS. TXOP field of HE / EHT / UHR PPDU can be used to identify the TXOP length of the packet. Upon the detection of an OBSS packet, the STA checks (step 1001) the availability of the SR feature depending on its current configuration and the detected OBSS packet. For example, the STA checks whether the PPDU of the OBSS packet and the status of the STA satisfy the conditions to use the SR feature, in particular with respect to the OBSS_PDievei threshold or the PSR opportunity. If both OBSS PD SR and PSR are available, constraints defined in subsection 26.10.4 of the IEEE 802.11 standard can be considered. If no SR features are available, the STA proceeds to step 1005 to perform conventional NPCA. Otherwise, the STA proceeds to step 1002. At step 1002, if only one SR feature is available at test 1001, that SR feature is selected. In other words, step 1002 may be optional. If both SR features are available, the STA selects one of them. For example, if the STA is employing OBSS_PDievei as a threshold for determination of an IDLE medium condition prior to the reception of an PSRR PPDU, the intended transmit power of the next PSRT PPDU in the transmission queue as measured at the transmit antenna connector is made equal to or lower than the TX_PWRmax, calculated with this specific OBSS_PDievei threshold using Equation (26-6) mentioned above. At test 1003, the STA optionally checks whether the next data in the transmission queue should rather be sent with the selected SR feature which requires constraints on the transmit power or be sent using NPCA operations (or DSO operations), i.e., over the NPCA PCH P2 (or assigned channel) or set S2 of channels. In other words, the STA determines whether to transmit data on the primary channel P1 using the SR operation or to transmit data on the NPCA PCH P2 using NPCA. If the STA decides that it is better to send the data with the SR feature, it proceeds to step 1006 where it performs PCA (through EDCA contention) and sends and / or receives the data over the primary channel P1 under the transmit power constraint of the SR feature. Otherwise, if the STA decides that it is better to send the data using NPCA, it proceeds to step 1004 where it sends the CS-ICF 500 / 501 / 1701 / 1800a-b or CS-ICF1 600 / 601 or DSO-ICF 2000a-b over the primary channel P1 under the transmit power constraint of the SR feature to one or more STAs of BSS1. This is to trigger channel switch at those STAs that have not directly detected the OBSS interference. Step 1004 thus consists for the STA to transmit the CS-ICF or DSO-ICF responsive to determining to transmit data on the NPCA PCH P2 using NPCA. Various criteria may be used to perform test 1003. In some embodiments, a comparison between required data rate to send and / or receive the data and an estimated data rate achieved by the maximum transmit power can be made. The data rate may be estimated by the estimated SNR on the receiver side which depends on the distance from the STA. In other embodiments (as variants or in combination), the STA may determine whether the NPCA PCH P2 (targeted for NPCA) is busy or not (e.g., the OBSS packet may overlap the NCPA PCH, or any other interference on the NPCA PCH) to decide to stay on the primary channel and use the SR feature, or move to the NPCA PCH for NPCA operations. In other embodiments (as variants or in combination), the STA may consider the remaining duration of the OBSS TXOP 220: if too short, it appears better to stay on the primary channel. At step 1004, the STA sends the CS-ICF or DSO-ICF as already described above. For example, the STA - in particular the AP - may have priority access to the medium a SIFS or a PIFS after the OBSS interference detection. Non-AP STA may have less priority and may contend for SR medium access using the EDCA mechanism (with dedicated EDCA Parameters if needed). Once the CS-ICF or DSO-ICF has been sent, the STA, at step 1005, operates on the NPCA PCH P2 for NPCA. This may include switching its radio to NPCA or configuring a second and separate radio to NPCA. Next, the STA can exchange (send and / or receive) data on the NPCA PCH P2 (possibly extended into set S2). Step 1005 ends no later than the end of OBSS TXOP 220 by switching back to the primary channel P1. If the STA observes multiple OBSS packets, it can take all the OBSS packets into account and then respect the most severe transmit power constraint. The flowchart of Figure 10 is applicable to the OBSS-traffic-detecting STAs of Figures 5 to 9, Figures 16 to 18b, and also Figures 20a, 20b and 20c where a DSO-ICF is transmitted instead of a CS-ISF. Figure 11 illustrates, using a flowchart, general steps at another STA directly detecting OBSS interference, which is capable of sending a CS-ICF but does not gain access to do so. In particular, the STA performs contention to gain access to the primary channel in order to transmit a CS-ISF frame, but fails to win the contention. That means that another STA succeeded in transmit CS-ICF 500 / 501 or CS-ICF1 600 / 601. Therefore, at step 1100, the other STA receives CS-ICF 500 / 501 or CS-ICF1 600 / 601. This triggers test 1101 where the STA determines whether it was contending for SR medium access in order to transmit such CS-ICF or CS-ICF1. In the affirmative, the STA proceeds to step 1103 where it stops its contention. For instance, it stops decrementing its backoff counter(s). By stopping the contention, redundant transmission of CS-ICF or CS-ICF1 can be avoided. Next, the STA proceeds to step 1102 where it performs SCA as in step 1005 described above. In the negative of step 1101, the STA directly performs SCA at step 1102. Figure 12 illustrates, using a flowchart, general steps at any STA unable to directly detect OBSS interference. This STA is involved because it takes knowledge of the OBSS interference through the reception of a CS-ICF or DSO-ICF. Therefore, at step 1200, the STA receives an ICF (e.g., CS-ICF or DSO-ICF) as described above. This triggers test 1201 where the STA determines whether it has to send another CS-ICF or ICF in order to propagate the OBSS interference to other STAs of the BSS. In some embodiments, only the AP may transmit CS-ICF2 700 / 701 or ICF3 800, meaning that test 1201 may only consist for the STA to determine whether it is the AP or not. In other embodiments (e.g., distinguishing between the scenarios of Figure 8 and Figure 9), the AP may determine the opportunity to send an ICF3 800 or not. In other embodiments, no additional CS-ICF needs to be sent in case the received CS-ICF is ICF2 700 / 701 or ICF3 800 from the AP. In the negative of test 1201, the STA directly performs step 1203 described below. In the affirmative of test 1201, the STA sends (step 1202) an ICF (e.g., CS-ICF2 700 / 701 or ICF3 800) after a short interval such as a SIFS or a PIFS. Next, the STA proceeds to step 1203 where it performs SCA as in step 1005 described above. In some embodiments involving the reception of ICF3 800 at step 1200, the STA may perform SCA or PCA. Hence, step 1203 consists for the STA to perform channel access following the instruction of ICF3 800: e.g., some STAs are allocated resources in the PCA channels while others are allocated resources in the NPCA channels. Figure 21 illustrates, using a flowchart, general steps at STA which is capable of sending a CS-ICR in response to a received CS-ICF. This flow chart is applicable to the STAs (STA11 / STA12 / STA13) that implement the scenarios of Figure 17,18a and 18b. At step 2100, the STA receives a CS-ICF from the AP. In this CS-ICF, AP optionally indicates whether CS-ICR feedback is requested or not (e.g., indicated in the Feedback Required field 1952 or 1312 discussed below). If this indication is available, at optional test 2102, the STA checks whether the CS-ICR is requested or not. If the optional test 2102 is omitted, STA directly proceeds to 2104 or 2106 below depending on the default behaviour (i.e., to send the CS-ICR or not). If CS-ICR is not required, the STA proceeds to step 2104 and switches to NPCA PCH P2 where it proceeds to step 2116 to perform NPCA operations. If it is required, the STA proceeds to optional test 2106 to determine whether the CS-ICR feedback is requested in the primary channel or in the NPCA PCH. This may be indicated in the CS-ICF, e.g., in the Feedback Channel field 1952 or the Target Channel field 1305 (discussed below). If the STA applies the default behaviour specifying on which channel the CS-ICR has to be transmitted, test 2106 can be omitted and goes directly to step 2108 or 2112 depending on the default behaviour. If the CS-ICR is requested in the primary channel P1, the STA proceeds to step 2112 where it sends the CS-ICR on said primary channel P1. Next, it switches to NPCA PCH P2 at step 2114. If the CS-ICR is requested in the NPCA PCH P2, the STA proceeds to step 2108 where it switches to the NPCA PCH P2. Once on the NPCA PCH P2, the STA proceeds to step 2110 where it sends the CS-ICR on the NPCA PCH P2. After step 2110 or 2114, the STA proceeds to step 2116 where it performs NPCA operations on the NPCA PCH P2. Turning now to exemplary ICF / CS-ICFs, Figure 13a and 13b illustrate exemplary frame formats according to embodiments of the disclosure. They may apply to CS-ICF 500 / 501 or 600 / 601 of Figure 5 or Figure 6, CS-ICF1 of Figure 7 or Figure 8 or Figure 9, CS-ICF2 of Figure 7, ICF3 of Figure 8. Since some ICF / CS-ICFs are sent using the SR operation under the limited transmit power, the SNR at the receiver side may also be limited. Therefore, it is preferred to send the frame in a low data rate (i.e., low MCS) to be more likely to be successfully decoded at the receiver side. In other words, the frame (in particular CS-ICF) should be sent in a low data rate to be decodable by the receiver STA. Thus, the frame is preferably designed to be short in order to reduce the overhead even if it is sent with lower data rate. In this respect, the exemplary format of Figure 13b is an optimized version of the one of Figure 13a. The frame can be a newly defined Control frame or a Management frame or an update of an existing frame such as a Trigger frame. As shown in Figure 13a, 1300 shows a first example of a newly-defined Control frame. It contains PHY Preamble 1301 and Frame Control field 1302 as in the existing Control frames. Subfields included in the Frame Control field 1302 can be the same as the ones defined in IEEE 802.11 specification for a non-S1 G PPDU, as follows. Type and Subtype values are assigned to be identified as a new type. For example, Type value can be ‘01 ’ to indicate ‘Control type’ and Subtype value can be ‘1111 ’ to use the last reserved value to signal a CS-ICF or ICF. In variants, the Control Frame Extension subfield can be used to utilize more bits for the subtype definition. For example, Type value ‘01 ’, Subtype value ‘0110’ can be used to indicate a Control Frame Extension, and a reserved value for Control Frame Extension value such as ‘0101 ’ can be assigned to signal a CS-ICF or ICF. In some embodiments, the Control Frame Extension value can further be used to signal a type of CS-ICF or ICF, e.g., CS-ICF 500 / 501 / 600 / 601 with respect CS-ICF1 600 / 601 and / or CS-ICF2 700 / 701 and / or ICF3 800. Different values can be used to discriminate between all or part of these types. Alternatively, a separate ICF / CS-ICF type field 1311 can be defined in the Frame Control field 1302 to identify the type of ICF / CS-ICF. Duration field 1303 is used to inform about the TXOP duration of the detected OBSS packet / TXOP 220. The frame (e.g., CS-ICF) contains information that indicates the duration remained for the NPCA operations. To do so, the STA that sends the CS-ICF calculates the remaining time for the NPCA operations and set it to the Duration field 1303. Calculation can be done by using the duration of the detected OBSS TXOP (toBss_Txop), the duration used to detect OBSS TXOP and to send (may include contention or a fixed IFS) the CS-ICF (till the intermediate FCS if any) (tcs-icp) and the duration required for NPCA switching (switch and switch back) for each associated NPCA STA i (tswitchj, i = 1 to the number of NPCA STAs in the BSS), which is indicated by each STA. The duration remained for the NPCA operations can be calculated as toBss_Txop - (tcs-icF + tSwitch_max) where tswitch_max is the largest tswitchj among the NPCA STAs in the BSS or the largest tswitchj among the NPCA STAs that receives the CS-ICF. In embodiments requiring a CS-ICR, the duration of the response (tcs-icn) as well as the waiting time between the CS-ICF and the CS-ICR (typically a SIFS) can be taken into account. In that case, the duration remained for the NPCA operations can be calculated as toBss_Txop- (tcs-icF + SIFS + tcs-icn + tswitch_max). In a case where CS-ICF indicates that the STA (including both AP and non-AP) is not switching to the NPCA PCH, and if the STA is not requiring a CS-ICR, Duration field 1303 may be set to 0 to indicate that STA is not setting the NAV for the PCH. Otherwise, if CS-ICF indicates that the STA is not switching to the NPCA PCH, and if the STA is requiring a CS-ICR, Duration field 1303 may be set to SIFS + tcs-icnto indicate the NAV till the duration of CS-ICR. BSS identifier field 1304 is used to inform about the ID of BSS, experiencing the OBSS interference (hence BSS1 in the examples above). This can be the BSSID. Target Channel field 1305 informs about the NPCA PCH P2 to which switching for NPCA. This field can be omitted if the NPCA PCH P2 is pre-defined or pre-negotiated inside the BSS. OBSS identifier field 1306 informs about the ID of OBSS (BSS2 in the examples above) which can be set to the BSSID of the OBSS. This information can be used by any STA receiving the CS-ICF to identify whether the CS-ICF transmission results from OBSS interference from the same OBSS as detected by the STA itself. The OBSS identifier may further contain the ID of the OBSS packet (such as Sequence Number or Packet Number) to identify every single OBSS packet independently since the TXOP remaining time and bandwidth of the OBSS packet may be different for each OBSS packet. OBSS Bandwidth field 1307 informs about the bandwidth of the detected OBSS packet, i.e., 20MHz, 40MHz, and so on. Feedback Required field 1952 may be a one-bit field indicating whether a CS-ICR feedback is required or not (e.g., 0: Not required, 1: Required). HT Control field 1308 is included to include the PSRT PPDU field included in the CAS Control field, useful for PSR-based SR operations. It can be omitted, in particular when OBSS PD-based SR only is used as SR feature. CS-ICF may contain intermediate FCS field 1309. Intermediate FCS field 1309 contains an intermediate cyclic redundancy code is calculated as FCS field 1311 (below) except that the calculation fields only include all of the fields of the MAC header and the Frame Body field up to and excluding the Intermediate FCS field. Intermediate FCS 1309 is added to make a receiver STA able to verify the received frame using the Intermediate FCS field 1309 without waiting for the reception of FCS field 1311. Once the received frame is verified using the Intermediate FCS field 1309, the receiver STA can switch to the NPCA PCH P2. This allows the receiver STA to use the duration created by the Padding field 1310 for the switching procedure. Padding field 1310 is added after the Intermediate FCS field 1309 to add time for the channel switching operation for all of the STAs that are involved in the following NPCA. CS-ICF contains FCS field 1311. FCS field 1311 contains a 32-bit CRC (Cyclic Redundancy Code). The FCS field value is calculated over all of the fields of the MAC header and the Frame Body field except the Padding field 1310. As shown in Figure 13b, 1300 shows a second example of a newly defined Control frame. It contains PHY Preamble 1301 and Frame Control field 1302 as described above. Subfields 1303-1308 are omitted to be replaced by the existing fields or new fields in the PHY Preamble 1301. For example, 1320 shows the part of the U-SIG field defined in IEEE 802.11 be amendment for the PHY Preamble 1301. U-SIG field 1320 is included if the EHT MU PPDU format is used for the CS-ICF. Bandwidth field 1322 can be used to inform about the bandwidth of OBSS packet instead of OBSS Bandwidth field 1307. BSS Color field 1323 can be used to inform about the BSS instead of BSS identifier field 1304. TXOP field 1324 can be used to inform about the TXOP duration of the detected OBSS packet instead of Duration 1303 field. In embodiments, only these fields are changed (to be used in another way). Target Channel field 1305 is omitted, in particular when the NCPA PCH P2 is pre-defined or prenegotiated. OBSS identifier field 1306 is omitted, in particular when the STA receiving the CS-ICF treats all the OBSSs or OBSS traffics as one OBSS or OBSS traffic. Feedback Required 1312 is omitted by fixing the default requirement of sending CS-ICR without the Feedback Required field. HT Control 1308 is omitted by relaxing the requirement of PSRT PPDU and defining the CS-ICF as an exceptional frame which is allowed to be sent as PSRT PPDU without the HT Control field. Intermediate FCS field 1309, Padding field 1310 and FCS field 1311 function as explained above with reference to Figure 13a. In other embodiments, other fields are also added in the PHY Preamble 1301 for example in a new version of U-SIG field indicated by the PHY Version Identifier field 1321 for UHR PPDUs (for example use value ‘1’). It can be advantageous to put these information items into the PHY Preamble since the receiver STA can parse these information items earlier and can start switching to the NPCA PCH P2 earlier. Alternatively, both fields in the PHY preamble and in the MAC frame format can be maintained to be utilized by PHY and MAC layers respectively. For the specific case of ICF3 800 of Figure 8, conventional User Info fields can be additionally used to allocate the resources for PCA and for NPCA. That is why ICF3 800 may advantageously be a Trigger frame which, naturally, includes multiple User Info fields. Each User Info field includes an AID12 field that indicates which non-AP STA the User Info field is for. In addition, each User Info field includes an RU allocation field that indicates which resource unit or units the non-AP STA is allocated. For example, a Basic Trigger frame or an MU-RTS Trigger frame can be used as ICF3 800. Figure 19 illustrates another exemplary frame format of CS-ICF based on NFRP (Null Data Packet Feedback Report Poll) Trigger frame. Figures 13a and 13b introduced a new control frame for the CS-ICF for the sake of less overhead. However, it is also advantageous to reuse one existing Control frame and extend it. This can save the limited room for the Subtype value or the Control Frame Extension value. In addition, it eases implementation. Another advantage to use the NFRP Trigger frame is that NFRP Trigger frame allows to obtain feedback from a lot of STAs (i.e., 288 STAs maximum with 160MHz or 80+80MHz bandwidth in the IEEE802.11be amendment and can be potentially doubled using 320MHz bandwidth in a future IEEE 802.11 amendment) with a single trigger frame. 1900 illustrates the Trigger frame format. It is the same format of the 802.11 be Trigger frame format except the added Intermediate FCS field 1914. This field serves the same functionality as the Intermediate FCS field 1309 explained above with reference to Figure 13a. Embodiments may omit it in order to keep the 802.11 be format. Duration field 1904 can be set to a duration of required SR exchange over the primary channel P1. This includes the duration of the CS-ICF, and optionally a SIFS and the duration of the CS-ICR if the latter is required. In the Frame Control field (not shown in detail), Type and Subtype subfields are set to ‘01 ’ and ‘0010’ respectively, meaning it is a Trigger frame. In the Common Info field (not shown in detail), the Trigger Type field is set to 7, meaning NDP Feedback Report Poll (NFRP). 1930 illustrates the User Info field format in the NFRP Trigger frame. Feedback Type field 1936 indicates the type of the feedback the NFRP Trigger frame is requesting. In this disclosure, a new Feedback Type value 1: “CS-ICR” may be added as shown in 1960. By indicating this new Feedback Type value 1, the NFRP Trigger frame can be used as the CS-ICF proposed in this disclosure. When this Feedback Type value 1 is set, some additional fields can be valid such as Duration 1 field 1934 (which is a Reserved field in the 802.11 be format), Duration 2 field 1938 (which is a Reserved field in the 802.11 be format), Trigger Dependent User Info field 1944. Duration 1 field has nine bits and Duration 2 field has seven bits. These two fields are used together to indicate the duration remaining for the NPCA operations triggered by the CS-ICF. The value of the Duration field is calculated as explained above for the Duration field 1303. In other embodiments, Duration 1 field 1934 and Duration 2 field 1938 are omitted and the Duration field 1904 is used to indicate the duration remaining for the NPCA operations triggered by the CS-ICF. In this case, Trigger Dependent User Info can be also omitted and fields 1952 to 1956 can be mapped to the bits of fields 1934 and 1938. 1944 illustrates the Trigger Dependent User Info field format. This may be optionally added to User Info field 1930 to further enhance the CS-ICF information. Trigger Dependent User Info 1944 may contain Feedback Required field 1952, Feedback Channel field 1954, OBSS Identifier field 1956 and OBSS Bandwidth field 1956. Feedback Required field 1952 may be a one-bit field indicating whether CS-ICR feedback is required or not (e.g., 0: Not required, 1: Required). The number of STAs that can be scheduled to respond to the NFRP Trigger frame is calculated using equation: Nsta = 18 * 2BW * (MultiplexingFlag + 1), where “BW” is the value of the UL BW subfield (not shown in the figure) in the Common Info field of the NFRP Trigger frame, and “MultiplexingFlag” is the value indicated in the Number Of Spatially Multiplexed Users subfield 1942. Starting AID field 1932 defines the first AID of the range of AIDs that are scheduled to respond to the NFRP Trigger frame. Using the first AID and the number of STAs, STAs can identify whether they are scheduled to respond to the NFRP Trigger frame. If one STA receiving the NFRP Trigger frame is scheduled to respond, it sends back the CS-ICR if the Feedback Required field 1938 indicates “Required”. Otherwise, if the Feedback Required field 1952 indicates “Not Required”, the STA does not send back the CS-ICR. In this way, the AP that sends the CS-ICF can control the CS-ICR feedback transmission at the STAs receiving the CS-ICF. The AP may assign an AID, which is located in a specific range (to be targeted by the NFRP Trigger frame), to the STAs that support SR Triggered NPCA mode (or at least NPCA) to trigger CS-ICR from those STAs by a single CS-ICF. Feedback Channel field 1954 may be a one-bit field indicating whether the CS-ICR feedback is to be sent in the primary channel P1 or in the NPCA PCH P2 (e.g., 0: P1, 1: NPCA PCH P2) if the NPCA PCH is pre-negotiated between the STAs. In another embodiment, Feedback Channel field 1940 may be four-bits field that indicates which 20MHz subchannel the receiver STA has to use to send back the CS-ICR feedback. Values 0 to 15 can be mapped to each of the sixteen 20MHz subchannels allocated inside the maximum 320MHz BSS operating bandwidth. OBSS Identifier field 1956 is used to identify the detected OBSS. This may be a one-octet field which indicates the BSS Color of the detected OBSS. Alternatively, it can be a six-octet field which indicates the BSSID of the OBSS. OBSS Bandwidth field 1956 is used to indicate the bandwidth of the detected OBSS. This may be a three-bit field to indicate 20MHz, 40MHz, 80MHz, 80MHz+80MHz, 160MHz, 320MHz respectively using one three-bit pattern. Not all of the field in the Trigger Dependent User Info field 1944 are mandatory and some of them can be omitted. The order of each field can be different than the order shown in the Figure. In a different embodiment, Duration 1 field 1934 and Duration 2 field 1938 can be concatenated and be located in the Trigger Dependent User Info 1944 as one Duration field. Thanks to the NFRP Trigger frame, the non-AP STAs are asked to send a CS-ICR as an NDP (Null Data Packet) feedback report. Each non-AP STA is assigned a STARTING_STS_NUM and an RU_TONE_SET_INDEX to transmit a FEEDBACK STATUS bit (forming the NDP feedback report). The STARTING_STS_NUM parameter is set with the following equation, using the values of the Starting AID subfield in the User Info field of the eliciting Trigger frame: STARTING_STS_NUM = [(AID - Starting AID) / 18 / 2BW], The RU_TONE_SET_INDEX parameter is set using the following equation, with the value of the Starting AID subfield in the User Info field of the eliciting Trigger frame: RU_TONE_SET_INDEX = 1 + ((AID - Starting AID) mod (18 x 2BW)). The meaning of the FEEDBACK_STATUS bit is defined as follows for the new CS-ICR feedback type: 0 indicates that the STA received the CS-ICF and did not detect the OBSS traffic, 1 indicates that the STA received the CS-ICF and did detect the OBSS traffic. Based on the RXVECTOR parameter NDP_REPORT, which provides the detected status array for the resources of each spatial stream and tone set assigned by the Trigger frame, the AP can derive the list of AIDs from the resources to which an NDP feedback report response was sent and their responses. If an AID of a specific STA is not in the list, the AP assumes that the STA which has the AID has not sent a CS-ICR, and thus could not receive the CS-ICF. DSO-ICF used in Figures 20a, 20b and 20c can be an extension of BSRP (buffer status report poll) Trigger frame or MU-RTS Trigger frame, which follow the same overall frame format 1900. Duration field 1904 can be set to a duration of SR occupation on the primary channel P1. This may include the duration of the DSO-ICF, and optionally a SIFS and the duration of any response thereto, and the duration remaining for the DSO operations in case one STA is assigned the primary channel for DSO operations. In the Frame Control field, Type and Subtype subfields are set to ‘01’ and ‘0010’ respectively, meaning it is a Trigger frame. In the Common Info field, the Trigger Type field is set to 4, meaning Buffer Status Report Poll (BSRP). The User Info fields are however different from the NFRP Trigger frame. RU Allocation field in each User Info field of the BSRP Trigger frame is used to indicate which 20MHz subband the non-AP STA, that is specified by the AID12 field of the User Info field, is assigned to switch to. When the DSO-ICF is sent under the SR operation, the transmission power of DSO-ICF satisfies the restriction of SR operation in the PCH but preferably the restriction does not apply to the channels where OBSS traffic is not sent. DSO-ICF is sent in a non-HT duplicate PPDU which covers the NPCA Primary Channel to initiate TXOP of the NPCA Primary Channel and to be received by STAs that have already switched to the NPCA PCH detecting the OBSS traffic by themself. Figure 14a schematically illustrates a communication device 1400 configured to implement at least one embodiment of the present disclosure, for instance any of the (AP and non-AP) STAs shown in Figure 1. The communication device 1400 may preferably be a device such as a microcomputer, a workstation or a light portable device. The communication device 1400 comprises a communication bus 1413 to which there are preferably connected: a central processing unit 1401, such as a processor, denoted CPU; a memory 1403 for storing an executable code of methods or steps of the methods according to embodiments of the disclosure as well as the registers adapted to record variables and parameters necessary for implementing the methods; and at least one communication interface 1402 connected to a wireless communication network, for example a communication network according to one of the IEEE 802.11 family of standards, via transmitting and receiving antennas 1404. Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 1400 or connected to it. The representation of the bus is not limiting and in particular the central processing unit is operable to communicate instructions to any element of the communication device 1400 directly or by means of another element of the communication device 1400. The executable code may be stored in a memory that may either be read only, a hard disk or on a removable digital medium such as for example a disk. According to an optional variant, the executable code of the programs can be received by means of the communication network, via the interface 1402, in order to be stored in the memory of the communication device 1400 before being executed. In an embodiment, the device is a programmable apparatus which uses software to implement embodiments of the disclosure. However, alternatively, embodiments of the present disclosure may be implemented, totally or in partially, in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC). Figure 14b is a block diagram schematically illustrating the architecture of the communication device 1400, adapted to carry out, at least partially, the disclosure. As illustrated, device 1400 comprises a physical (PHY) layer block 1423, a MAC layer block 1422, and an application layer block 1421. The PHY layer block 1423 (here an 802.11 standardized PHY layer) has the task of formatting, modulating on or demodulating from any 20MHz channel or the common communication channel, and thus sending or receiving frames over the wireless radio medium used, such as 802.11 frames, for instance medium access trigger frames TF to reserve a transmission slot, MAC data and management frames based on a 20MHz width to interact with legacy 802.11 stations, as well as of MAC data frames of OFDMA type having smaller width than 20MHz legacy (typically 2 or 5 MHz) to / from that radio medium. The MAC layer block or controller 1422 preferably comprises a MAC 802.11 layer 1424 implementing conventional 802.11 be MAC operations, and additional block 1425 for carrying out, at least partially, the disclosure. The MAC layer block 1422 may optionally be implemented in software, which software is loaded into RAM 1403 and executed by CPU 1401. Preferably, the additional block 1425, referred to as NPCA managing module which has different operations to implement parts of the disclosure, depending on the role played by the communication device 1400. MAC 802.11 layer 1424 and NPCA Managing module 1425 interact one with the other in order to process accurately communications over the medium, e.g., to perform PCA or NPCA (with channel switching) when appropriate according to embodiments of the disclosure. On top of the Figure, application layer block 1421 runs an application that generates and receives data packets, for example data packets such as a video stream. Application layer block 1421 represents all the stack layers above MAC layer according to ISO standardization. Although the present disclosure has been described hereinabove with reference to specific embodiments, the present disclosure is not limited to the specific embodiments, and modificationswill be apparent to a skilled person in the art which lie within the scope of the present disclosure. Many further modifications and variations will suggest themselves to those versed in the art upon referring to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the disclosure, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate. In the claims, the word “comprising” does not exclude other elements or steps, and 5 the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims

1. A communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels:detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, andtransmitting, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme.

2. The method of Claim 1, further comprising, responsive to transmitting the frame, switching at the STA to the secondary channel access scheme.

3. The method of Claim 1, wherein the STA waits for a response frame to the frame for switching, from one or more other STAs, before performing operations on a secondary channel using the secondary channel access scheme.

4. The method of Claim 3, wherein the STA switches to the secondary channel access scheme after having received the response frame over the primary channel.

5. The method of Claim 3, wherein the response frame is received over a secondary channel used for the secondary channel access scheme, after the STA switched to the secondary channel access.

6. The method of Claim 3, wherein the STA sends an initial control frame over the secondary channel after having switched thereto, and the response frame is received responsive to the initial control frame.

7. The method of Claim 3, wherein the response frame is received over a bandwidth that encompasses the first channel and a secondary channel used for the secondary channel access scheme.

8. The method of Claim 3, wherein the response frame includes a Null Data Packet (NDP) feedback report response.

9. The method of Claim 8, wherein the NDP feedback report response includes a FEEDBACK_STATUS bit set to a first value (0) to indicate that the other STA transmitting the response frame received the frame for switching and did not detect the OBSS transmission or a second value (1) to indicate that the other STA received the frame for switching and did detect the OBSS transmission.

10. The method of Claim 1, wherein the OBSS transmission meets spatial reuse operation criteria in case the received signal strength level of the OBSS transmission is lowerthan an OBSS packet detection (PD) level or in case the OBSS transmission includes a Parameterized Spatial Reuse Reception (PSRR) Physical Layer Protocol Data Unit (PPDU) having an Uplink (UL) Spatial Reuse subfield set to a Parameterized Spatial Reuse opportunity.

11. The method of Claim 10, wherein transmitting the frame using the spatial reuse operation includes transmitting the frame over the same primary channel as the OBSS transmission, using a reduced transmit power that is function of the OBSS PD level or that is lower than a threshold defined based on a power level indicated in the UL Spatial Reuse subfield.

12. The method of Claim 1, wherein the frame is transmitted without contention, a PIFS or a SIFS after having detected the OBSS transmission.

13. The method of Claim 1, further comprising contending for SR medium access to the primary channel before transmitting the frame.

14. The method of Claim 13, wherein contending for SR medium access to the primary channel uses SR-EDCA parameters different from EDCA parameters used for non-SR medium access to the primary channel.

15. The method of Claim 13, wherein the frame is placed in the front of a transmitting queue having the highest priority for medium access on the primary channel, in order to be sent.

16. The method of Claim 1, wherein the frame is transmitted over a composite channel that includes the primary channel on which the primary channel access scheme is performed and a secondary channel on which the secondary channel access scheme is performed.

17. The method of Claim 1, wherein the frame is transmitted using a low Modulation and Coding Scheme (MCS) MCSO or the lowest data rate for non-HT PPDU.

18. The method of Claim 1, wherein the frame is transmitted during a Target Wake Time (TWT) service period (SP).

19. The method of Claim 18, wherein the STA waits for the next TWT SP after detection of the OBSS transmission to transmit the frame.

20. The method of Claim 1, wherein the frame includes a padding field to have a frame length higher than a switching time required by a STA of the BSS to switch from the primary channel access scheme to the secondary channel access scheme.

21. The method of Claim 1, wherein the padding field is provided after an intermediate Frame Check Sequence (FCS) field in the frame.

22. The method of Claim 1, further comprising, at the STA, determining whether to transmit data on the primary channel using the spatial reuse operation or to transmit data on a secondary channel using a secondary channel access scheme, wherein transmitting the frame is responsive to determining to transmit data on the secondary channel using the secondary channel access scheme.

23. The method of Claim 1, wherein the frame for switching assigns distinct secondary channels to respective other STAs for them to switch to a secondary channel access scheme on the assigned secondary channel, for a duration of the OBSS transmission.

24. The method of Claim 23, wherein the frame for switching assigns, for a duration of the OBSS transmission, a secondary channel to another STA that has already switched to the secondary channel.

25. The method of Claim 23, wherein the frame for switching also assigns the primary channel to one STA for Dynamic Subchannel Operation, for the duration of the OBSS transmission.

26. The method of Claim 23, wherein the frame for switching does not assign the primary channel to any STA for Dynamic Subchannel Operation during the OBSS transmission.

27. A communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels:receiving, from another STA of the BSS and on the primary channel, a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme, andresponsive to receiving the frame, configuring a radio of the STA to the secondary channel access scheme, for example by switching a radio from the primary channel access scheme to the secondary channel access scheme.

28. The method of Claim 27, further comprising, at the STA operating as an access point (AP) of the BSS, further responsive to receiving the frame, transmitting, to other STAs of the BSS and on the primary channel, a second frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme.

29. The method of Claim 28, wherein the second frame includes a padding field to have a frame length higher than a switching time required by a STA of the BSS to switch from the primary channel access scheme to the secondary channel access scheme.

30. The method of Claim 28, wherein the second frame is transmitted over the primary channel on which the primary channel access scheme is performed and over a secondary channel on which the secondary channel access scheme is performed, and the second frame is configured to allocate:one or more first resource units to a first set of STAs of the BSS, the first resource units being included in a first subset of the operating channel that includes the primary channel, andone or more second resource units to a second set of STAs of the BSS, the second resource units being included in a second subset of the operating channel that includes the secondary channel.

31. The method of Claim 27, wherein the STA operates as an access point (AP) of the BSS, and configuring a radio of the AP responsive to receiving the frame includes:maintaining a first radio operating on the primary channel to perform the primary channel access scheme, andconfiguring a second and separate radio to operate on a secondary channel on which the secondary channel access scheme is performed.

32. The method of Claim 27, wherein, responsive to receiving the frame for switching, the STA transmits a response frame to the other STA.

33. The method of Claim 32, wherein the response frame is transmitted over the primary channel before switching to the secondary channel access scheme.

34. The method of Claim 32, wherein the response frame is transmitted over a secondary channel used for the secondary channel access scheme, after the STA switched to the secondary channel access scheme.

35. The method of Claim 34, wherein the STA receives an initial control frame from the other STA over the secondary channel after having switched thereto, and the response frame is transmitted responsive to the initial control frame.

36. The method of Claim 34, wherein the response frame is transmitted over a bandwidth that encompasses the first channel and a secondary channel used for the secondary channel access scheme.

37. The method of Claim 32, wherein the response frame includes a Null Data Packet (NDP) feedback report response.

38. The method of Claim 37, wherein the NDP feedback report response includes a FEEDBACK_STATUS bit set to a first value (0) to indicate that the STA received the frame for switching and did not detect an overlapping-BSS (OBSS) transmission from an OBSS specified in the frame for switching or a second value (1) to indicate that the STA received the frame for switching and did detect an OBSS transmission from the OBSS specified in the frame for switching.

39. A communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels:detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation,contending for SR medium access to the primary channel, andwhile contending, receiving, from another STA of the BSS, on the primary channel, a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme, andresponsive to receiving the frame while contending, stopping the contention operation and switching to the secondary channel access scheme.

40. The method of Claim 2 or 27 or 39, further comprising transmitting an initial control frame on a secondary channel different from the primary channel after having switched to a secondary channel access scheme on the secondary channel, in response to transmitting the frame for switching a channel access.

41. The method of Claim 1 or 27 or 39, wherein the frame for switching includes a Null Data Packet Feedback Report Poll (NFRP) Trigger frame.

42. The method of Claim 41, wherein the NFRP Trigger frame includes a maximum duration available for use of the secondary channel access scheme.

43. The method of Claim 41, wherein the NFRP Trigger frame includes a field signalling whether a response frame to the frame for switching is requested or not from STAs scheduled by the NFRP Trigger frame and receiving it.

44. The method of Claim 41, wherein the NFRP Trigger frame includes a field signalling a channel to transmit the response frame, from among the first channel and a secondary channel used for the secondary channel access scheme.

45. The method of Claim 41, wherein the NFRP Trigger frame includes a field signalling an identifier of an OBSS from where the OBSS transmission originates.

46. The method of Claim 1 or 27 or 39, wherein the frame for switching includes a Buffer Status Report Poll (BSRP) Trigger frame.

47. A communication method comprising, at a station (STA) of a Basic Service Set (BSS) operating on an operating channel made of a primary channel and one or more secondary channels:detecting, on the primary channel, an overlapping-BSS (OBSS) transmission that meets one or more criteria of a spatial reuse (SR) operation, anddeciding, in case the OBSS transmission encompasses a target secondary channel different from the primary channel or in case the OBSS transmission is shorter than a predefined duration threshold, not to transmit, to other STAs of the BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to an access scheme over the target secondary channel.

48. The method of Claim 47, further comprising deciding, in case the OBSS transmission does not encompass a target secondary channel different from the primary channel or in case the OBSS transmission is longer than a predefined duration threshold, to transmit, to other STAs ofthe BSS and on the primary channel using the spatial reuse operation, a frame for switching a channel access from a primary channel access scheme to an access scheme over the target secondary channel.

49. A wireless communication device comprising at least one microprocessor configured for carrying out the method of Claim 1 or 27 or 39.

50. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a wireless device, causes the wireless device to perform the method of Claim 1 or 27 or 39.

51. A frame comprising a PHY Preamble, a Frame Control field, a Frame Check Sequence field and a padding field, wherein the Frame Control field signals the frame is a frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme.

52. The frame of Claim 51, including a first field signalling a TXOP duration of a detected overlapping-BSS (OBSS) transmission and one or more optional fields from amongst: a second field signalling an identifier of the Basic Service Set (BSS) to which a station transmitting the frame belongs, a third field signalling a secondary channel for the secondary channel access scheme, a fourth field signalling an identifier of the OBSS and a fifth field signalling a bandwidth of the detected OBSS transmission.

53. The frame of Claim 52, where the first field and the optional fields are additional to the PHY Preamble, Frame Control field, Frame Check Sequence field and padding field.

54. The frame of Claim 52, where the first field and the optional field or fields are subfields within the PHY preamble.

55. The frame of Claim 51, wherein the Frame Control field include a subfield whose value takes a different value depending on whether the frame is transmitted responsive to a detection of the OBSS transmission by the station transmitting the frame or responsive to another frame for switching a channel access from a primary channel access scheme to a secondary channel access scheme received by the station transmitting the frame.

56. The frame of Claim 51, wherein the padding field is configured for the frame to have a frame length higher than a switching time required by a station to switch from the primary channel access scheme to the secondary channel access scheme.

57. A frame to be transmitted by a station, comprising a Capabilities element including one or more of a first support field to signal whether or not the transmitting station supports untriggered uplink transmission during non-primary channel access operations, and a second support field to signal whether or not the transmitting station supports spatial reuse operation to transmit, on a primary channel experiencing inter-BSS interference, a frame to trigger at otherstations a switching of channel access from a primary channel access scheme to a secondary channel access scheme.

58. The frame of Claim 57, wherein the first support field and second support field are included in a MAC Capabilities Information field within the Capabilities element.5 59. A frame to be transmitted by a station, comprising an Operation element includingone or more of a first mode field to signal an activation or deactivation of an operating mode where the transmitting station is not allowed to perform untriggered uplink transmission during nonprimary channel access operations and a second mode field to signal an activation or deactivation of an operating mode where the transmitting station uses spatial reuse operation to transmit, on10 a primary channel experiencing inter-BSS interference, a frame to trigger at other stations a switching of channel access from a primary channel access scheme to a secondary channel access scheme.

60. The frame of Claim 59, wherein the first mode field and second mode field are included in an Operation Information field within the Operation element.

Images