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 INVENTION The present invention generally relates to wireless communications and more specifically to wireless communications involving non-primary channel access. BACKGROUND OF THE INVENTION 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 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 OBSS TXOP obtained by an OBSS STA belonging to a neighbour 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”. Frame exchanges can then take place over the anchor channel, 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 anchor channel send an IGF (initial control frame) on the anchor channel 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 available spectrum, in particular in the case of hidden nodes that are unable to detect the OBSS TXOP. Indeed, while some STAs automatically switch to the anchor channel upon detection the OBSS TXOP, those “hidden” STAs are unable to switch and detect the ICF and remain on the primary channel for channel access. It results in a misalignment on the selection of the channel to be used to perform channel access (i.e., to initiate a backoff procedure). Transmissions between STAs having switched to the anchor channel 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 INVENTION It is a broad objective of the present invention to overcome some of the foregoing concerns. An aim of the invention 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 nodes 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 invention 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 the ICF. This will allow any hidden STA - single-radio or multi-radio ones - to become aware of the OBSS, hence to switch on 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). 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 invention 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 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 invention 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, 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 PIPS 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 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. 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. The above approach allows the AP to propagate the OBSS detection to additional hidden nodes, forthem 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) with the STAs that are not impacted by the OBSS transmission, while organizing NPCA (or SCA) transmissions forthose 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 (IGF) 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. As apparent from the above, new frames can be defined to implement the inventions. In this respect, the invention 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 an anchor 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. Correlatively, the invention also provides a wireless communication device comprising at least one microprocessor configured for carrying out any method as described above. Another aspect of the invention 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 invention may be computer implemented. Accordingly, the present invention 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 invention 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 invention can be implemented in software, the present invention 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 invention 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; Figure 3a and 3b illustrate hidden nodes 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; Figure 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 of the invention; 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 of the invention; Figure 14a shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention; and Figure 14b illustrates schematically the architecture of the communication device of Figure 14a. DETAILLED DESCRIPTION OF EMBODIMENTS The present specification regards communication methods where a first STA of a BSS detects an OBSS TXOP on its primary channel. The OBSS transmission meets the criteria for Spatial Reuse operations. The first STA transmits a NPCA switching frame to other STAs of the BSS, on its primary channel 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 triggers a switching of channel access from PCA to NPCA at these other STAs. Next, the STAs perform NPCA operations on an anchor channel, 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. 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 a 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 802.11 be 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. 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 I 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. 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 anchor channel 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 anchor channel 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, may be shared between STAs before the NPCA operation 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 anchor channel. On the anchor channel, the STAs (STA11 and / or AP1) perform NPCA operation (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 anchor channel. 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 anchor channel. 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. The NPCA mechanism is not efficient in hidden nodes situations because those hidden nodes are unable to detect the OBSS TXOP 220, hence to spontaneously switch to the anchor channel P2. As described in Figures 3a and 3b, 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, 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 “hidden nodes” from the knowledge of STA11 and STA12. In such a case, if the NPCA mechanism is automatically applied, AP1 switches to the anchor channel 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 / anchor channel 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, 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 anchor channel P2 while AP1 and STA12stay on their primary channel P1. It entails similarly a misalignment on the selection of the primary / anchor channel 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. Accordingly, there is a need to improve the NPCA mechanism, so that bandwidth usage efficiency is optimized. To do so, the invention 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 anchor channel 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 anchor channel. 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. 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 anchor channel 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 anchor channel P2 (NPCA scheme), or configuring the second radio to operate on the anchor channel 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 invention 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 802.1 lax-2021 standard. Two SR operations exist: the OBSS Packet Detection-based SR operation and the Parametrized-SR-based SR operation. In OBSS PD-based SR operations, a STA maintains an OBSS PD level in accordance with an equation (26-5) provided in subsection 26.10.2.4. In operation, if the received signal strength level of the OBSS packet is lower than the maintained OBSS PD level, this OBSS frame does not update the basic NAV timer of the STA. The STA can continue its backoff procedure and 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’ from its transmit power ‘Tx_PWR’ 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, 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 802.11REVme 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_PROHI BITED 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. Figure 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 anchor channel 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 invention, 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 invention) 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 has to evaluate 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 802.1 IREVme 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 802.1 IREVme 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 802.1 IREVme D6.0 and in section 35.10.3.1 of the 802.11be 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_PDeve set relatively low allows the STA to use higher maximum transmit power to send the CS-ICF. This corresponds to situations where the OBSS must be far from the STA. The counterpart of this setting is that only OBSS packets which has low received signal strength level allow transmitting the CS-ISF. On the contrary, an OBSS_PDievei 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 invention. 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 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 may be dynamically configured to find an appropriate value. As an example, a STA might monitor the beacons from the OBSS APs and measure its 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. 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 4a) and a non-AP STA in Figure 6 (corresponding to the situation of Figure 4b). In Figure 5, 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 / 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. 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 respect to Figures 6 and 11. The CS-ICF 500 can be a newly defined Control frame or a Management frame or an update of an existing frame such as a Trigger frame. Figures 13a and 13b illustrate exemplary formats for a CS-ICF in the meaning of the invention. This 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 those STAs to the anchor channel 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 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: MCS0 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 anchor channel P2 for NPCA, in which case it advantageously obtains the TXOP on the anchor channel P1 and accelerates the channel access during NPCA operations 222a. After having sent the CS-ICF 500 / 501, AP1 can switch to NPCA to start NPCA operation. When receiving the CS-ICF 500 / 501, STA11 and STA12 now understand that AP1 has detected OBSS interference. STA11 and STA12 can start NPCA operation on the anchor channel P2, meaning they switch from PCA (its CA channel on the primary channel) to NPCA (its CA channel on the anchor channel, during switching time 221a / 221b. As recalled above, the switching time 221a and 221b 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. AP1 may know the channel switch delay 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). During NPCA operation 222a / 222b, AP1 and STA11 and STA12 may perform channel access on the anchor channel 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 anchor channel P2 for NPCA transmissions 222a / 222b, it may send an ICF (e.g. RTS, MU-RTS Trigger frame for AP1) on the anchor channel P2 to confirm that it has successfully switched to the anchor channel. Although the Figure shows NPCA operations 222a / 222b on the anchor channel 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). In Figure 6, 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 / 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 starts 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 anchor channel 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. After having sent the CS-ICF 600 / 601, STA11 can switch to NPCA to start NPCA operation. 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 operation 222a / 222b on the anchor channel P2, meaning they switch from PCA (its CA channel on the primary channel) to NPCA (its CA channel on the anchor channel, 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 anchor channel 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 anchor channel. During the NPCA operation 222a / 222b / 222c, all the STAs may perform channel access on the anchor channel P2. As for Figure 5, they may use legacy EDCA mechanism or new EDCA Parameters dedicated to NPCA, before sending an ICF on the anchor channel 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 STAto send the CS-ICF 600 / 601, the chance of aligning the OBSS detection and the NPCA operation 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 radio to NPCA, for example by switching its radio to the anchor channel 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-ICF 600 / 601, STA11 can switch to NPCA to start NPCA operation. When receiving the CS-ICF1 600, AP1 and STA13 can now understand that STA11 has detected OBSS interference. AP1 and STA13 can start NPCA operation 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 anchor channel 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. 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 anchor channel P2 (during switching operation 221a / 221b / 221d). In this embodiment, due to the two CS-ICF, the first one (CS-ICF1) can be deprived of post-FCS padding since time required for CS-ICF2 may be sufficient for STA11 to perform its channel switching. During the NPCA operation 222a / 222b / 222d, all the STAs may perform channel access on the anchor channel P2. As for Figure 6, they may use legacy EDCA mechanism or new EDCA Parameters dedicated to NPCA, before sending an ICF on the anchor channel 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 / 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 chance of aligning the OBSS detection and the NPCA operation is enhanced. The beginning of the scenario of Figure 8 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 221b by transmitting STA11 and STA13. Before configuring itself for NPCA, AP1 sends another CS-ICF, namely CS-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 CS-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 anchor channel P2 (possibly extended). This is achieved by transmitting the CS-ICF3 800 over the primary channel P1 (possibly extended) and the anchor channel 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 anchor channel 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 between 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 anchor channel P2 with 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 the stations 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 802.11v, 802.11 me, 802.11az, 802.11bk 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 CS-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 CS-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 CS-ICF3 800 is also transmitted over the anchor channel P2 for the STAs operating according to the NPCA scheme (hence already on the anchor channel), to be able to identify their resources to be used. The CS-ICF3 800 can be a Trigger frame which triggers MU UL PPDU by allocating the S2 channel resources 222a to STA11 / STA13 and primary 40MHz resources 224a to STA12. During the NPCA operation 222a / 222b and PCA operation 224a / 224d, UL / DL frame exchanges may be required to be synchronized during the OBSS TXOP 220, for the proper reception by the single radio of AP1. In such a case, UL OFDMA triggered by the CS-ICF3 is the one to ensure the synchronization for the uplink traffic. For the down link 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 TXOP220, 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 the CS-ICF3 800 while some other non-AP STAs, which are interfered by the OBSS packet, start to perform NPCA, the chance of utilizing the entire operating bandwidth is enhanced. Figure 9 is a variant of Figure 8 where the CS-ICF3 800 can be 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 anchor channel 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 anchor channel 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 anchor channel P2, AP1 may perform PCA 224a on the primary channel P1 and NPCA 222a on the anchor channel P2 independently. In this case, synchronization may not be required between PCA / NPCA so the transmission of the CS-ICF3 800 can be omitted. Furthermore, AP1 and STA11 (the STA that detected the OBSS interference) may agree on an anchor channel P1 that is a channel where interference between PCA 224a and NPCA 222a can be avoided, for example by putting the 20MHz anchor channel 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 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). 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 and / or the BSSID field, the Duration field. The source address 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 invention and associated NPCA operation, 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. 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_PDevei using Equation (26-6) mentioned above. At test 1003, the STA optionally checks whether the next data in the transmission queue should be better sent with the selected SR feature which requires constraints on the transmit power or be better sent using NPCA operations, i.e., over the anchor channel P2 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 anchor channel 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 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 orCS-ICF1 600 / 601 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 500 / 501 or CS-ICF1 600 / 601 responsive to determining to transmit data on the anchor channel 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 anchor channel P2 (targeted for NPCA) is busy or not (e.g. the OBSS packet may overlap the anchor channel, or any other interference on the anchor channel) to decide to stay on the primary channel and use the SR feature, or move to the anchor channel for NPCA. 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 500 / 501 or CS-ICF1 600 / 601 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 500 / 501 or CS-ICF1 600 / 601 has been sent, the STA, at step 1005, operates on the anchor channel 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 anchor channel 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. 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 orCS-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 (from any embodiment described above). Therefore, at step 1200, the STA receives an CS-ICF (whatever CS-ICF 500 / 501 or CS-ICF1 600 / 601 or CS-ICF2 700 / 701 or CS-ICF3 800). This triggers test 1201 where the STA determines whether it has to send another CS-ICF in order to propagate the OBSS interference to other STAs of the BSS. In embodiments, only the AP may transmit CS-ICF2 700 / 701 or CS- 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 CS-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 CS-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) CS-ICF2 700 / 701 (or CS-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 CS-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 CS-ICF3 800: e.g., some STAs are allocated resources in the PCA channels while others are allocated resources in the NPCA channels. Turning now to exemplary CS-ICFs, Figure 13a and 13b illustrate exemplary frame formats according to embodiments of the invention. 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, CS-ICF3of Figure 8. Since some 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 CS-ICF in a low data rate (i.e., low MCS) to be more likely to be successfully decoded at the receiver side. Thus, the CS-ICF 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 CS-ICF 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 fora non-S1G 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 the CS-ICF. In variants, the Control Frame Extension subfield can be used to utilize more bits for the subtype definition. For example, Type value ‘0T, 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 the CS-ICF. In some embodiments, the Control Frame Extension value can further be used to signal a type of CS-ICF, e.g. CS-ICF 500 / 501 / 600 / 601 with respect CS-ICF1 600 / 601 and / or CS-ICF2 700 / 701 and / or CS-ICF3 800. Different values can be used to discriminate between all or part of these types. Alternatively, a separate CS-ICF type field 1311 can be defined in the Frame Control field 1302 to identify the type of CS-ICF. Duration field 1303 is used to inform about the TXOP duration of the detected OBSS packet / TXOP 220. 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 anchor channel P2 to which switching for NPCA. This field can be omitted if the anchor channel 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 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. 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. HT Control field 1308 is included to include the PSRT PPDU field included in the CAS Control field, useful for PSR-based SR operations. Therefore, it can be omitted, in particular when OBSS PD-based SR only is used as SR feature. FCS field 1309 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. Padding field 1310 is added after the FCS field 1308 to gain time for the channel switching operation for all of the STAs that are involved in the following NPCA. 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 802.11be amendment forthe PHY Preamble 1301. U-SIG field 1320 is included if the EHTMU PPDU format is used forthe 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 anchor channel 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 in this case. 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. FCS field 1309 and Padding field 1310 function as explained above with reference to Figure 13a. In other embodiments, other fields are also added into 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 anchor channel 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 CS-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 CS-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 may be used as CS-ICF3 800. Figure 14a schematically illustrates a communication device 1400 configured to implement at least one embodiment of the present invention, 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 invention 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 invention. However, alternatively, embodiments of the present invention 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 invention. 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 OFDMAtype 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 802.11be MAC operations, and additional block 1425 for carrying out, at least partially, the invention. 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 invention, 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 invention. 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 invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention. 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 invention, 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 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)ofa 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 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.

4. The method of Claim 3, 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.

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

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

7. The method of Claim 6, 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.

8. The method of Claim 6, 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. The method of Claim 13, 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.

15. The method of Claim 13, 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.

16. The method of Claim 13, 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.

17. The method of Claim 13, 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.

18. A communication method comprising, at a station (STA)ofa 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.

19. The method of Claim 2 or 13 or 18, 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.

20. A wireless communication device comprising at least one microprocessor configured for carrying out the method of Claim 1 or 13 or 18.

21. 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 13 or 18.

22. 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.

23. The frame of Claim 22, 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 an anchor 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.

24. The frame of Claim 23, where the first field and the optional fields are additional to the PHY Preamble, Frame Control field, Frame Check Sequence field and padding field.

25. The frame of Claim 23, where the first field and the optional field or fields are subfields within the PHY preamble.

26. The frame of Claim 22, wherein the Frame Control field include a subfield whose value takes a different value depending on whether the frame is transmitted responsive to a 5 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.

27. The frame of Claim 22, 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 10 channel access scheme to the secondary channel access scheme.

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