Methods and devices for controlling an automatic switch to a substitute channel for p2p stations

Abstract

Two stations STAs willing to perform P2P communications set up a P2P session through a TDLS setup procedure or Wi-Fi direct setup procedure. The STAs negotiate, via their AP(s), a substitute channel s

Description

FIELD OF THE INVENTION The present invention generally relates to wireless communications and more specifically to the management of P2P communications in case of concurrent transmission on a base channel. BACKGROUND OF THE INVENTION 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. Stations involved in IEEE (RTM) 802.11 Basic Service Sets (BSSs) may further establish a direct link with another station to perform peer-to-peer (P2P) communications, while still being associated with the access point (AP) of the BSS. Exemplary mechanisms to establish a direct link include the TDLS (Tunneled Direct Link Setup) mechanism as endorsed by the IEEE 802.11z standard of 2008, and the WiFi Direct (RTM) mechanism. Competition exists between the communications to / from the AP within the BSS and the P2P communications. To reduce competition with the traffic involving the AP, the AP can indicate or recommend to the P2P stations substitute channel(s) to be used for the P2P communications, so as to minimize the impact of the P2P communication on the BSS operations. A known substitute channel is the “off-channel”, defined as a channel used by a station (STA) that does not overlap with the channel(s) used by the BSS of which the STA is a member, in IEEE P802.11-REVme / D6.0. To make use of the off-channel - or more generally a substitute channel - the P2P stations implement a switching mechanism to switch their operation channel from a “base” channel where the AP / BSS operates to the off-channel. As defined in IEEE P802.11-REVme / D6.0, the switching mechanism such as the “TDLS channel switching” requires the exchange of TDLS Channel Switch Request frames and TDLS Channel Switch Response frames, hence requires an access to the base channel It means the P2P stations cannot switch as long as the base channel is busy, e.g., due to OBSS or even due to intra-BSS communications (involving the AP). There is thus a need to improve the substitute channel usage for P2P communications. More generally, there is a need to improve roaming procedure to move from infrastructure AP to soft AP dedicated to P2P communication. SUMMARY OF INVENTION It is a broad objective of the present invention to overcome some of the foregoing concerns. The inventors have considered taking the substitute channel usage out of the known channel switch procedure, to create additional opportunities to use the substitute channel for P2P communications when the base channel is busy. In this respect, a communication method in a wireless network is proposed that comprises at a first station belonging to a first Basic Set Service (BSS): establishing a peer-to-peer (P2P) session between the first station and a second station, upon detecting busyness of a base channel, switching to a substitute channel to perform P2P communications with the second station. Optional features are defined below with reference to methods, while they can be transposed into device features. In some embodiments, the substitute channel is a subpart of a BSS operating channel defined by the first BSS, which substitute channel does not overlap with the base channel. This may advantageously be used in dense environment where no free channels are available or in the scope of APs coordination to have one substitute channel common between several APs. In some embodiments, the substitute channel does not overlap with a BSS operating channel defined by the first BSS. It is therefore defined outside the BSS operating channel to avoid any interference with the activities within the BSS. It is for example an off-channel in the meaning of the IEEE P802.11-REVme / D6.0. In some embodiments, the substitute channel is provided by a first AP of the first BSS. In particular embodiments, the substitute channel (received from the AP) is shared by the first station to the second station. In particular, the second station may submit the shared substitute channel to a second AP of a second BSS to which the second station belongs. This allows the second station to be confirmed that the substitute channel is compliant with the activities of the second BSS. In some embodiments, the substitute channel is provided as a Channel Usage information according to IEEE P802.11-REVme / D6.0 in a Channel Usage element of a Probe Response frame or a Channel Usage Response frame or a Beacon frame or a (Re)Association Response frame. The Response frames are sent by the first AP in response to corresponding Request frames. In some embodiments, the substitute channel is provided by the first AP as a channel selected from a list of channels supported by the first and second stations. A negotiation of supported channels may thus be performed between the stations before they submit the candidate channels to the AP for selection of the substitute channel for P2P communications. In some embodiments, detecting busyness of the base channel includes detecting Overlapping BSS (OBSS) traffic (i.e., OBSS interference with the base channel) and / or intra-BSS traffic not involving the first station nor the second station, on the base channel. The second station can supposedly be concerned by intra-BSS traffic (e.g., in a resource unit triggered by the AP that is included in the primary channel or in a secondary channel extending the primary channel to define the base channel for the intra-BSS traffic operation) only in case it also belongs to the first BSS. In some embodiments, the first and second stations exchange a list of Overlapping BSSs (OBSSs) detected by each of them, wherein the switching is triggered upon detecting OBSS traffic on the base channel from one OBSS of the list. This ensures the two stations triggers the automatic channel switch in the same circumstances. In some embodiments, the switching is further based on a prior authorization / enablement from a first AP of the first BSS to the first station to perform channel switching in case of base channel busyness. A better control of the medium and BSS by the AP is obtained. In some embodiments, the authorization / enablement to the first station to perform channel switching in case of base channel busyness and an enablement of non-primary channel access in the first BSS in case of Overlapping BSS (OBSS) traffic are mutually exclusive at the first station, wherein the non-primary channel access in the first BSS includes a channel switching of a primary channel of the first BSS to an anchor channel. The AP may thus control the enabling of either mechanism (automatic channel switch to the substitute channel or NPCA) at station level. The mutual exclusion - the two mechanisms cannot be enabled at the same time - is particularly important when the substitute channel for automatic channel switch and the anchor channel for NPCA are different. Indeed, it ensures the stations switch to the same channel in case of channel busyness, rather than possibly switching different channels in case both mechanisms are available to the stations at the same time. The mutual exclusion at station level does not forbid that two stations of the first BSS have different enabled mechanisms at the same time (the automatic channel switch for one and NPCA for the other). The AP may enable the automatic channel switch for a first group of stations in the BSS - e.g., those having a large amount of P2P data to exchange - and enable NPCA for a second group of stations in the BSS - e.g., those having no P2P data or few P2P data to exchange. Having a substitute channel for automatic channel switch that is different from the anchor channel for NPCA therefore allows the two groups of stations to continue communications over the substitute / anchor channel in case of busy primary channel, without interference with the other group. In some embodiments, the switching is further based on the presence of buffered P2P data to be transmitted and / or received by the first station. This contributes to a better use of the medium. In particular embodiments, the first and second stations exchange buffer status reports to report buffered P2P data. In some embodiments, the first station switches back to the base channel no later than an end of a duration specified in a frame based on which the busyness of the base channel is detected. For example, it may be the duration of the OBSS TXOP (TXOP Length of the OBSS frame) or the duration of an intra-BSS Trigger frame (Duration subfield in Common Info field) not involving the first station. Hence, the switch to the substitute channel lasts only the duration of the “interfering” TXOP occurring on the base channel. In some embodiments, a Target Wake Time (TWT) schedule is established to which the first and second stations belong, and a period where the first station (thus also the second station) switches to the substitute channel to perform P2P communications is included in a service period (SP) of the TWT schedule. The TWT schedule may be established by a single AP with which both stations are associated or be established through Multi-AP (MAP) coordination by two APs with which the two stations are respectively associated. For example, the TWT schedule may be established based on a periodic wakeup schedule (for the TDLS mechanism) or a Notice of Absence (for the WiFi Direct mechanism) previously negotiated between the two peer stations. In embodiments, the method further comprises operating the P2P communications with the second station over the substitute channel. 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 3 illustrates, using frame exchanges in a timeline, a TDLS direct link mechanism through a possible scenario for an initiator peer non-AP STA to handle P2P traffic; Figure 4 illustrates, using frame exchanges in a timeline, a WiFi Direct mechanism through a possible scenario for a P2P group formation by two peer stations; Figure 5 illustrates, using a flowchart, general steps of a communication method for an automatic channel switch for P2P communications in a wireless communication system such as system of Figure 1, according to embodiments of the present disclosure; Figure 6 illustrates, using an exemplary timeline, an automatic channel switch mechanism, applied by P2P stations detecting concurrent transmissions on their base channel, according to embodiments of the present disclosure; Figure 7 illustrates, using a flowchart, detailed steps of a communication method for an automatic channel switch for P2P communication in a wireless communication system such as system of Figure 1, according to embodiments of the present disclosure; Figures 8a, 8b and 8c respectively depict formats for a Channel Usage element, a Channel Usage Request frame and a Channel Usage Response frame, according to embodiments; Figure 9a shows a schematic representation a communication device in accordance with embodiments of the present invention; and Figure 9b shows a schematic representation of a wireless communication device in accordance with embodiments of the present invention. DETAILLED DESCRIPTION OF EMBODIMENTS Two stations willing to perform P2P communications set up a P2P session, negotiate, via their AP(s), a substitute channel such as an off-channel or a subpart of an operating channel of their BSS(s), exchange their buffer status reports. They sense the base channel of their BSS(s) to detect any OBSS or intra-BSS communications that are concurrent to the P2P communications. Upon detection, the stations switch to the substitute channel as negotiated with the AP(s), perform their P2P exchanges and switch back to the base channel no later than an end of the TXOP of the concurrent communication. 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 station or 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 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 BSS usually defines a BSS operating channel that includes additional 20 MHz channels - known as secondary channels - to the primary channel. The stations simultaneously contend on the primary channel for access to a communication channel which may be the BSS operating channel or a subpart thereof that includes the primary channel. The communication or “base” 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. As mentioned above, it is used for contention. 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 or base 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 BSS operating channel having an operation bandwidth (up to 320MHz in the latest P802.11 be / D7.0 standard dated August 2024; 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-2021 standard approved on February 9, 2021 and further evolved in P802.11be / D7.0. 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 (TF) 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 / duration 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). P802.11be / D7.0 introduces 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 multi-AP (MAP) system 100 formed by 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 each BSS operating channel (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 with it). A second wireless network BSS2 comprises an AP 120 and three associated non-AP STAs 121, 122 and 123. A third wireless network BSS3 comprises an AP 130 and three associated non-AP STAs 131,132 and 133. 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 and 130 are also referred to, respectively, as AP1, AP2 and AP3; non-AP STAs 111, 112 and 113 to STA11, STA12, STA13; non-AP STAs 121,122 and 123 to STA21, STA22, STA23; and non-AP STAs 131, 132 and 133 to STA31, STA32, STA33. 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 wireless network exchange data frames over the communication channel 100, under the management of the AP. A primary channel, usually 20 MHz channel, is defined per wireless network on which the management frames are exchanged. The other 20 MHz channels of the communication channel, if any, are known as secondary channels. 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 the joined BSSx. For example, the AID is a 16-bit value uniquely identifying the station. The stations (including the AP) compete one against another over the communication channel (including the primary channel and optionally secondary channels to increase bandwidth) using EDCA (Enhanced Distributed Channel Access) contention to access the communication channel in order to be granted a transmission opportunity (TXOP). The TXOP may then be used to transmit (single-user, SU) data frames or to implement multi-user (MU) transmissions. In the MU scheme, a single station, usually the AP of the wireless network BSSx, is allowed to schedule a MU transmission, i.e., multiple simultaneous transmissions to or from other stations of the wireless network BSSx. One implementation of such a MU scheme has been for example adopted in the IEEE 802.11 ax amendment standard, known as the Multi-User Uplink and Downlink OFDMA (MU UL and DL OFDMA) procedures. In the MU scheme, resources are defined over the 20 MHz channel or channels used, known as resource units. A resource unit may be a 20 MHz channel or a subpart thereof within a frequency breakdown of the channels. More generally, the resources may include space, frequency and time resources and may be obtained according to different multiplexing schemes. Examples of those schemes 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. In the IEEE 802.11 wireless local area networking standards, the multi-AP system 100 may correspond to an extended service set (ESS) and each of the wireless networks to a basic service set (BSS). Although the description of embodiments of the invention is given in the context of IEEE 802.11, the embodiments are not limited thereto and they may apply to other types of wireless networks and protocols. Interferences between the BSSs - known as Overlapping BSS (OBSS) interference - exist that are handled through various mechanisms added to the 802.11 standard. The 802.11 bn Working Group has recently introduced the Non-Primary Channel Access (NPCA) or Secondary Channel Access (SCA) as a new OBSS behaviour for the stations to improve OBSS interference management. The NPCA mechanism allows the stations (AP and non-AP) of BSSx to move from their common primary channel to a predefined secondary or “substitute” channel for channel access, when they detect OBSS interference on the primary channel. Once on the secondary channel used for NPCA, the stations (AP and non-AP STAs) can communicate one with the other during the duration of the TXOP of the OBSS interference (“OBSS TXOP”). The stations of the BSS go back to the primary channel for channel access, no later than the end of the OBSS TXOP. Figure 2 illustrates, using an exemplary timeline, the non-primary channel access mechanism, applied by BSS1 (AP1 and STA11) detecting OBSS interference from BSS2. Today's Wi-Fi, including versions up to 11be (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 for channel access. Regardless of whether secondary channels are idle or busy, these secondary channels remain inaccessible if the primary channel is occupied. In the example, the BSS operating band of BSS1, which may be announced by AP1 110 includes two subchannels, which are 80 MHz channel S1 and 40 MHz channel S2 respectively, and where each subchannel includes multiple 20 MHz channels and has one primary 20 MHz channel, i.e., one channel to perform medium / channel access using for example EDCA backoffs. 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. AP and STA’s operation channels include primary channel P1 and optionally one or more secondary channels. By using the NPCA mechanism, a STA can switch to the anchor channel P2 and enable one or more backoff procedures in the anchor channel P2 to operate on channel S2. In that respect, channel S2 and / or anchor channel P2 may be considered as “substitute” channels to the corresponding “base” channel, i.e., channel S2 and / or primary channel P1. On the 80MHz channel 1, while STA11 and AP1 perform backoff procedures, AP2 (which is an OBSS from BSS1 perspective) starts an OBSS TXOP 290. As the primary 20 MHz channel becomes busy due to the OBSS transmission, AP1 and STA11 switch their channel access operations from the primary channel P1 to the anchor (substitute) channel P2. Channel switch operation 221 a / b may take different time depending on the STAs’ ability (including hardware configuration). NPCA operations 222a / 222b start after both AP1 and STA11 have completely switched to the anchor channel P2. On the anchor channel, the STAs (STA11 and / or AP1) perform NPCA operations (222a / 222b) as follows. The STAs perform CCA for PPDU detection and decrement their backoff counter(s). A STA may transmit an initial control frame (ICF) after one of its backoff counters becomes 0 to confirm that the STA has successfully switched to the 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 receives 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 within OBSS TXOP 290 that uses the primary channel. No later than the end of OBSS TXOP 290, the STAs switch back to their primary (base) channel P1 and operating channel S1. The switching back is referenced 223a / 223b in the Figure. The STAs can initiate new transmissions through the complete operating channel S1 in a conventional manner. The NPCA mechanism is not fully efficient in hidden nodes situations. Indeed, one of the challenges for NPCA is the detection of an OBSS frame or activity on the primary channel (“OBSS interference”). As all the stations in a BSS are not located at the same position, the OBSS detection can differ from station to station. As a result, some stations may switch to the secondary channel based on their local OBSS interference detection while other stations of the same BSS may stay on the primary channel as they are unable to detect the OBSS interference. A refinement of the NPCA mechanism allows the AP to share a list of its OBSS APs to its associated stations. The list references all neighbouring APs within the detection range of the AP. The list may be used to trigger the channel switching: any station of the BSS that detects an OBSS frame on its primary channel may be authorized to switch to the anchor channel only if the OBSS of the detected OBSS frame matches an OBSS of the OBSS AP list provided by the AP. As a result, the stations detecting OBSS interference activate the NPCA mechanism only if the AP also switches to the anchor channel upon detecting the same trigger (OBSS frame). Hence, they can communicate with each other in an efficient way on the substitute channel S2. However, the NPCA mechanism or more broadly the OBSS interference management is not currently considering the P2P communications. P2P sessions can be established using so-called TDLS (“Tunneled Direct Link Setup”) and WiFi Direct mechanisms. Formerly endorsed by IEEE 802.11z standard in 2008, the TDLS mechanism enables devices (called TDLS peer STAs) to link directly to one another when both are already connected to the same AP (hence the same infrastructure BSS). To set up and maintain a direct link, the TDLS mechanism provides encapsulation of the setup frames, exchanged between the two TDLS peer STAs, in Data frames. This allows the setup frames to be transmitted transparently (or “tunneled”) through the AP. Figure 3 illustrates, using frame exchanges in a timeline, the TDLS direct link mechanism through a possible scenario for an initiator peer non-AP STA to handle P2P traffic. This example involves STA13 113 as the initiator for the P2P communication and STA12 112 as the partner or responder for the P2P communication. They both belong to the same BSS, and are associated with AP1 110. In the sequence, once STA13 and STA12 are associated with AP1 110 (association not shown), they can exchange data over the base channel through the AP. To reduce the amount of traffic that is transferred via AP 110 and to prevent congestion at AP 110, STA13 and STA12 may set up a TDLS session, i.e., a direct link between them to directly exchange data (P2P communication), while also remaining associated with the AP. In the sequence shown, a TDLS session or “TDLS direct link” is established between STA13 and STA12 (either of both can be the initiator of the TDLS direct link establishment). The establishment may include a TDLS discovery procedure (optional) and a TDLS setup procedure. TDLS discovery and setup procedures between STA13 and STA12 involve frames, known as TDLS Action frames, that are usually sent and received via intermediate AP1. The TDLS procedure is characterized by encapsulating signalling frames (TDLS Action frames) in 802.11 Data frames, which allows them to be transmitted through AP1 transparently. When attempting to discover TDLS stations in the same BSS, a series of frame exchanges is used. STA13, which is the initiator in the proposed scenario, sends a TDLS Discovery Request frame 321, tunneled through AP1 (relay illustrated by the black dot), to an individual destination station, here STA12. Destination station STA12 responds to the TDLS Discovery Request frame 321 with a TDLS Discovery Response frame 322 sent directly to STA13 (without relay by AP1). From that point, STA13 and STA12 know each other, meaning they know the other operates on the base channel setup with AP1. They can then establish a TDLS direct link. When attempting to establish a TDLS direct link over a single link with the discovered TDLS peer STA, a series of TDLS Action frame exchanges is used to set up the single link TDLS direct link. TDLS initiator STA13 first sends a TDLS Setup Request frame 323, tunneled through AP1 (relay illustrated by the black dot), to target TDLS responder STA12. This request frame conveys a “Link Identifier” element (and a “TDLS Multi-Link” in Multi Link case) element amongst the available lEs as defined in Table 9-130 of IEEE 802.11-REVme / D6.0 (June 2024), which include information about the capabilities (such as Power saving) of TDLS initiator STA13 and the AID thereof. TDLS responder STA12 responds with a TDLS Setup Response frame 324, also tunneled through AP1. This response frame conveys a “Link Identifier” element (and a “TDLS Multi-Link” in Multi-Link case) element along with information about the capabilities (such as Power saving) of TDLS responder STA12, its AID plus a status code that either accepts or rejects the setup request. If the Setup Request is accepted, TDLS initiator STA13 then sends a confirmation, TDLS Setup Confirm frame 325, still tunneled through AP1. This concludes the TDLS setup handshake. At this point, the two non-AP stations know the identity of each other with the AID assigned by the AP (and with their MLD MAC address in multi-link cases). As the setup frames are transmitted transparently through the AP, the AP does not need to be TDLS-aware or to have the same capabilities as the TDLS peer STAs involved in the TDLS-based peer-to-peer communication. When the TDLS direct link is established, the TDLS peer STAs can then start to communicate directly over the direct link, i.e., without relay by AP1: P2P traffic 326 can then be directly exchanged between STA13 and STA12 using the established TDLS session. TDLS peers STA13 and STA12 are then configured to accept Data frames received directly from the other TDLS peer STA. The P2P frames 326 are exchanged over the base channel (same frequency channel) of the BSS; therefore, the P2P traffic becomes concurrent to other traffic in the BSS from / to AP1 110. To avoid competition with the AP‘s traffic, the TDLS peer STAs that support TDLS channel switching can decide to perform a TDLS Channel Switch 330 to a Supported Channel, which therefore acts as a substitute channel to the base channel. The TDLS peer STAs inform each other about their supported channels during the TDLS setup procedure, i.e., the TDLS peer STAs include Supported Channels element and Supported Operating Classes element in all TDLS Setup Request and TDLS Setup Response frames that have a TDLS Channel Switching subfield equal to 1. More advantageously, the TDLS peer STAs may move from the base channel of the BSS to an off-channel, that is to say a channel that does not overlap the base channel(s) used by the access point (AP) / the BSS with which the TDLS peer STAs are associated. In other words, an off-channel is a channel that does not belong to the BSS operating channel and that can be used for P2P communication. The off-channel available for TDLS is supplied by the AP through a so-called Channel Usage element transmitted in Probe Response or Channel Usage Response frames. In some embodiments, the substitute channel is a subpart of the BSS operating channel. This may be used in dense environment where no free channels are available or in the scope of APs coordination to have one substitute channel common between several APs. Before switching from the base channel to the substitute channel, the TDLS peer STA is in PS (Power Save) mode with the AP and is not involved in an active Service Period with the AP. The TDLS STA initiator STA13 sends a TDLS Channel Switch Request frame 331 over the TDLS direct link. This frame includes the substitute or target channel, i.e., the destination channel (off-channel) of the intended channel switch. The substitute channel is selected by the TDLS STA initiator that initiates the channel switch, from the set of operating classes supported by both TDLS peer STAs (as exchanged during TDLS setup 320). Upon receiving the TDLS Channel Switch Request frame 331, the target partner STA12 responds with a TDLS Channel Switch Response frame 332 to accept or reject the Channel Switch. If the status code indicated in the response frame is set to REQUEST_DECLINED, both TDLS peer STAs continue to operate on the base channel. Otherwise, if the status code is set to SUCCESS in the response frame, both TDLS peer STAs move to the substitute channel (off-channel) before a switch time also indicated in the TDLS Channel Switch frames. The first transmission over the substitute channel does not start before the end of the switch time. Finally, after the switch time has elapsed, the initiator STA13 can start transmitting P2P data frames on the substitute channel. When operating via the substitute channel (off-channel), the TDLS peer STAs are in power save mode with the AP and can no longer communicate with him. Thus, they regularly switch back to the base channel in order to receive Beacon frames, look at the TIM (Traffic Indication Map) for any buffered packets, and communicate with other stations in the infrastructure network (BSS) managed by the AP. Details on the TDLS procedure are provided in IEEE 802.11z, and have been upgraded to be established over one link among possibly multiple links as introduced with the MLO of P802.11be / D7.0. To end the TDLS session, one of the TDLS peer STAs sends a TDLS Teardown frame 329 to the other. The TDLS Teardown Action field is encapsulated in a Data frame and transmitted to the TDLS peer STA directly or through the AP to tear down the TDLS direct link. In addition, the TDLS peer STAs may organise their TDLS session as they desire. For example, they may negotiate together periods of P2P activity and periods of P2P inactivity. They may negotiate a power saving mode (PSM) 340 and agree on a periodic wakeup schedule that defines such periods of P2P activity and periods of P2P inactivity. In order to enter the TDLS peer PSM, one of the TDLS peer STA (TDLS peer PSM initiator) sends a TDLS Peer PSM Request frame 341 to the TDLS peer STA (TDLS peer PSM responder), including a proposed periodic wakeup schedule. A Wakeup Schedule element is used to that end. It includes several fields: - Element ID field set to a value (equal to 102) to indicate that the information element is a Wakeup Schedule element. - Length field set to a value depending on the length of the Wakeup Schedule element. - Offset and Interval fields set to define, in microseconds, when the awake windows begin. The Interval field is nonzero and the Offset field is less than the Interval field. - Awake Window Slots field set to the duration of the awake window in units of backoff slots (such as defined by EDCA). - Maximum Awake Window Duration field set to the maximum duration of the awake window, in units of microseconds. - Idle Count field set to the number of consecutive awake windows during which no individually addressed frame is received from the TDLS peer STA before a TDLS peer STA deletes the wakeup schedule. When the TDLS peer PSM responder accepts the proposed wakeup schedule, it responds with a TDLS Peer PSM Response frame 342 indicating status code SUCCESS. Otherwise, the TDLS peer PSM responder responds with a TDLS Peer PSM Response frame indicating the appropriate status code for rejecting the schedule. An alternative schedule may be included in the TDLS Peer PSM Response frame when the status code is equal to TDLS_REJECTED_ALTERNATIVE_PROVIDED. The alternative schedule may be used by the TDLS peer PSM initiator to generate a new TDLS Peer PSM Request frame 341. This is a way for the TDLS peer STAs to negotiate a wakeup schedule. After successfully transmitting or receiving a TDLS Peer PSM Response frame indicating status code SUCCESS, the TDLS peer PSM initiator and TDLS peer PSM responder have established a periodic wakeup schedule between them. They wake up and perform P2P communications during the periods of P2P activity of the schedule, while they enter a power save mode during the periods of P2P inactivity of the schedule. An alternative to the TDLS mechanism is the Wi-Fi Direct, which advantageously applies when only one of the two peer stations is associated with AP1. "Software Access Point" (Soft AP) is a way to support Wi-Fi Direct. In Wi-Fi Direct, similarly to the soft AP, one of the P2P stations takes the lead on a P2P group, by providing some AP functionalities to the other P2P stations (such as discovery and registration services), to perform direct communications. A soft AP represents a software enabled AP, meaning that a device which has not been specifically made to be a router is modified, through a software, into a wireless AP, to operate as a soft AP. The use of the "Software Access Point" (Soft AP) is a new trend that allows devices to communicate directly with each other using methods similar to traditional WLAN, except without requiring the use of a central access point provided as an infrastructure of the WLAN. Figure 4 illustrates, using frame exchanges in a timeline, the WiFi Direct mechanism through a possible scenario for a P2P group formation by two peer stations. In the scenario, only STA13 113 is associated with AP1 110 while STA32 132 is not associated with AP1. In the example of the Figure, STA13 acts as a soft-AP or NSTR Mobile AP (such as defined in P802.11 be / D7.0) or a P2P Group Owner. The process 450 of forming or setting up a P2P group (or the like) is now explained. A Wi-Fi Direct connection is mainly performed through three processes including a device discovery 451, a service discovery 452 and group establishment 461-463. First process is the device discovery process 451 which is required when Wi-Fi P2P devices or stations, for example, a first and a second P2P stations (113, 132), recognize each other to configure a connection to establish the Wi-Fi P2P group. In this phase, a station alternates between a listen state and a search state. A first P2P station searches for neighbouring Wi-Fi P2P stations by repeatedly performing channel scan of IEEE 802.11 channels through listening to the so-called “social channels”, defined as channel 1, 6 and 11 in the 2.4GHz band, and searching these channels for a predetermined time period. A basic operation of the device discovery process performed during the Wi-Fi P2P group establishment is implemented by exchanging a Probe Request frame and a Probe Response frame of an IEEE 802.11 MAC protocol. These exchanges enable the P2P stations to discover each other on a nearby environment. Second process is the service discovery 452 which is performed after the device discovery process, to provide a function of exchanging information on services that each P2P station can support. That is, each P2P station may identify a supportable service protocol, a service and the like through exchange of a Request frame and a Response frame. P2P stations therefore exchange queries to discover the set of available services of each other and, based on this information, decide whether to continue the group formation or not. Third process is the group generation or establishment. A group owner (GO) negotiation process is performed by a three-way exchange including a GO Negotiation Request frame 461, a GO Negotiation Response frame 462 and a GO Negotiation Confirm frame 463. These frames allow the two stations to agree on which station will act as P2P GO, while the other one will act as a P2P client of the GO, and to agree on which channel the group will operate, which can be, for example, in the 2.4 GHz or 5 GHz bands and to share their P2P attributes. These information items (P2P attributes) may be carried in a P2P Information Element. For example, the P2P Capability attribute contains a set of parameters that can be used to establish a P2P connection. Security provisioning (not shown) starts after discovery has taken place and, if required, the respective roles have been negotiated upon forming the group. Once the P2P Group is established, new P2P stations can discover and join the P2P Group using active or passive scanning mechanisms like the ones used in traditional Wi-Fi networks. Like a traditional AP, a P2P GO announces itself through Beacon frames, and has to support power saving services for its associated clients. The P2P GO is also required to run a Dynamic Host Configuration Protocol (DHCP) server to provide P2P Clients with IP addresses (not represented in the figure). Upon successful Wi-Fi Direct Connection Setup between stations, the stations can then start to communicate directly over direct link (P2P data traffic 426). The P2P frames are exchanged over the base channel of the BSS; therefore, the P2P traffic becomes concurrent to other traffic in the BSS from / to AP1 110. In another variant, STA13 may join an already established P2P group of a Group Owner such as described above. As for the TDLS mechanism, the P2P stations belonging to the P2P group may negotiate a power saving mode (PSM) and agree on a periodic wakeup schedule in order to be awake only on certain periods of time. Wi-Fi Direct provides that the Group Owner may inform about its period or periods of absence (when it is in power saving mode) by including a Notice of Absence attribute or element in its Beacon frame 470 or in Probe Response frame (not shown in the figure), or using a Notice of Absence Action frame (not shown in the figure). Main information of this element is described below: - Count field to indicate the number of absence intervals. The field may be set to a value from 1 to 255. 255 means a continuous schedule; 0 is reserved and not used. - Duration field to indicate the maximum duration in units of microseconds that the P2P Group Owner can remain absent following the start of a Notice of Absence interval. - Interval field to indicate the length of the Notice of Absence interval in units of microseconds. - Start Time field to indicate the start time for the schedule expressed in terms of the lower 4 bytes of the TSF timer. The P2P group owner may also send the Notice Of Absence (NoA) element according to a presence request / response mechanism (not shown in the figure) initiated by the P2P client. To disconnect from a P2P Group, a P2P client may send a Disassociation frame 464 to its group owner. Similarly, a group owner may disconnect a P2P client or end a group session. In addition to the legacy off-channel management (as described above for the TDLS mechanism), P802.11be / D7.0 has recently adopted an improvement of the channel usage procedure by adding a new usage mode (value of the Usage Mode field set to 2 in a Channel Usage element) that allows a non-AP STA to request the assistance of its associated AP to setup a Channel-usage-aidable BSS on an off-channel that does not overlap the operating channels of any APs belonging to the ESS of its associated AP. A Channel-usage-aidable BSS is a BSS that is not a Channel-usage-aiding BSS, which is an infrastructure BSS whose AP performs channel coordination with at least one other non-co-hosted AP that has an overlapping BSS service area (BSA). Moreover, the recent modification of the standard allows a non-AP STA to negotiate with its associated AP the establishment of a peer-to-peer (P2P) TWT agreement through the Channel Usage procedure (Request / Response), the frames of which include, in that case, a TWT element. The P2P TWT agreement similarly to an individual TWT is negotiated between a non-AP station and its associated AP. The fixed scheduling resulting from the P2P TWT agreement corresponds to a period of unavailability of the stations in regards of its AP where the stations will move to the off-channel or a substitute channel. The P2P TWT agreement is negotiated for a given period of time. The peer-to-peer TWT negotiated is used for off-channel TDLS when Usage Mode field is set to 1, or for Channel-usage-aidable BSS, typically soft-AP when Usage Mode is set to 2. Besides, if a non-AP STA has already selected a channel for P2P communication, it can transmit a Channel Usage element with Usage Mode field set to 3, without any Channel Entry, to inform the AP about its unavailability during the peer-to-peer TWT agreement. The Target Wake Time (TWT) mechanism, originally defined in the IEEE 802.11 ah and 802.11 ax standards, has been adapted to be included in P802.11be / D7.0. An adaptation is known as the Restricted Target Wake Time (rTWT) which schedules dedicated (and protected) service periods (SPs) for stations to convey their latency sensitive traffic(s) over their BSS. An rTWT agreement is nothing more than a Broadcast TWT agreement negotiated between an AP and an associated non-AP station of the BSS of a given link. The non-AP station establishes with the AP membership in a Broadcast TWT (or rTWT) schedule. The rTWT Service Periods (SPs) of the rTWT schedule are advertised in broadcast management frames (e.g. Beacon frames, FILS Discovery frames and broadcast Probe Response frames), using an rTWT information about the negotiated rTWT SPs, typically a Broadcast TWT ID (bTWT ID). As defined in P802.11-REVme / D6.0, the usage of the off-channel follows a legacy behaviour that is based on repeated TDLS channel switches, which switches imply that the base channel is available to perform TDLS Channel Switch frame exchanges. The Wi-Fi Direct mechanism is even more limitative as there is no option to switch to a substitute channel to avoid competition over the base channel. This situation is of course not optimal because, due to the fact the base channel needs to be available for off-channel switch exchange, the P2P stations cannot switch when the base channel is busy due to OBSS or even due to some intra-BSS communications. Furthermore, the fixed P2P TWT scheduling cannot fit all the P2P communication needs, for instance in case of a P2P application with non-periodic or unexpected traffic or when the negotiated scheduling is not perfectly aligned with the arrival time of traffic from the P2P application. Therefore, a need exists to improve the substitute channel (e.g., off-channel) usage for P2P communications. More generally, there is a need to improve roaming procedure to move from infrastructure AP to soft AP dedicated to P2P communication. The disclosure proposes a method to extend the OBSS interference management concept to the P2P communication. One may note that with respect to P2P perspective, channel interference (blocking medium access for the P2P station to perform P2P communications) may come from OBSS interference indeed, but also from intra-BSS communications (from or to the AP of the BSS to which the P2P peer belongs) where the P2P station is not intended to participate in this communication. These blocking communications are also named “concurrent” transmissions in the description below. Concurrent OBSS transmissions for a station are those performed by an OBSS, while concurrent intra-BSS transmissions for a station are those performed within the BSS of that station but that do not involve the station itself. The methods of the present disclosure allow P2P stations to move to a substitute channel (e.g. off-channel) when they detect a concurrent transmission (or traffic or activity) on the base channel. In this respect a station belonging to a BSS, first establishes a peer-to-peer (P2P) session between itself and a second station (e.g., TDLS or Wi-Fi Direct session), and then, upon detecting busyness of a base channel, switching to a substitute channel to perform P2P communications with the second station. The base channel is part or all of the BSS operating channel defined for the BSS. It includes at least the primary channel of the BSS. The substitute channel may be anyone as described above: off-channel not overlapping with the channel(s) used by the BSS, a substitute channel not overlapping with the BSS operating channel, a substitute channel forming subpart of the BSS operating channel and not overlapping with the base channel. Contrary to the legacy behaviour, the station (in fact both peer stations) may automatically switch to the substitute channel without requiring frame exchanges, hence without requiring the base channel to be idle. This creates additional opportunities to use the substitute channel for P2P communications when the base channel is busy. Substitute channel usage for P2P communications is therefore improved. Figure 5 illustrates, using a flowchart, general steps of a communication method for an automatic channel switch for P2P communications in a wireless communication system such as system 100 of Figure 1, according to embodiments of the present disclosure. The method 500 is implemented at any station of a BSS, which station is involved in a P2P communication, preferably - but not necessarily - at a non-AP station. The method 500 starts at step 501 when a pair of P2P stations sets up a P2P session. The P2P session can be setup through a TDLS setup procedure such as described above with reference to Figure 3 or according to a Wi-Fi Direct setup procedure as described above with reference to Figure 4. During the setup procedure, the P2P stations exchange their capabilities carried in the TDLS Setup frames or GO Negotiation frames (respectively for TDLS and Wi-Fi Direct). The exchanged capabilities may include the support of the automatic channel switch according to the present disclosure - i.e., which defines whether a P2P station is able to perform an automatic channel switch upon detection of a concurrent transmission over their base channel. In embodiments, the setup procedure frames may include a list of OBSSs detected by each P2P station. By sharing their list of OBSSs, the P2P stations can find the OBSSs commonly detected and negotiate on which they can move to the recommended channel. In other words, the P2P stations exchange a list of Overlapping BSSs (OBSSs) detected by each of them, allowing the channel switching to be triggered upon detecting OBSS traffic on the base channel from one OBSS of the list. The substitute channel is preferably provided by an AP of the BSS. AP1 may provide the same substitute channel (off-channel) to P2P stations of its BSS (such as STA13 and STA12 in the scenario of Figure 3), for them to perform P2P communications. AP1 may provide the substitute channel to a P2P station of its BSS (such as STA13 in the scenario of Figure 4), which P2P station forwards the substitute channel to another P2P station (such as STA32) which is no associated with any AP / BSS: the substitute channel is shared by one P2P station to the other P2P station. In case the other station (e.g., STA32) is also associated with AP3 I BSS3 of the same ESS as AP1 I BSS1, a multi-AP (MAP) cooperation between AP1 and AP3 may be organized to provide the two P2P stations (STA13 and STA32) with the same substitute channel. Alternatively, the first P2P station (e.g., STA13) may still forward to the other P2P station (e.g., STA32) the substitute channel provided by its AP1, and the other P2P station may then submit the shared substitute channel to its AP. As an option, the AP or APs may provide multiple substitute channels that are therefore recommended candidates for the P2P stations for P2P communications. The P2P stations then agree on which substitute channel to use. In embodiments, to obtain a substitute channel from its associated AP, one P2P station may request assistance to the AP using the Channel Usage procedure, e.g., as defined in section 11.21.15 of IEEE P802.11-REVme / D6.0. Channel Usage information is provided by the AP, which Channel Usage information includes a set of channels provided by the AP to non-AP STAs for operation of a non-infrastructure network (such as Wi-Fi Direct) or an off-channel TDLS direct link. A non-AP STA (P2P station in the scenario of the disclosure) that supports Channel Usage and wish to use a non-infrastructure network or an off channel TDLS direct link may include both Supported Operating Classes (as defined in section 9.4.2.53 of IEEE 802.11-REVme / D6.0) and Channel Usage (as defined in section 9.4.2.84 of IEEE 802.11-REVme / D6.0) elements in a Probe Request frame, i.e., during an association procedure. This is to request Channel Usage information from the AP for supported operating classes. The AP supporting Channel Usage responds with a Probe Response frame including one or more Channel Usage elements. A Channel Usage element is illustrated in Figure 8a. Alternative to the association procedure, the non-AP STA supporting Channel Usage may send a Channel Usage Request frame at any time after association with the AP that supports the use of Channel Usage, to request the Channel Usage information for supported operating classes. The Channel Usage Request frame therefore includes both Supported Operating Classes and Channel Usage. And the AP supporting Channel Usage responds with a Channel Usage Response frame including one or more Channel Usage elements. In these embodiments, as the non-AP STAs may provide their supported channels (operating classes), the substitute channel provided by the AP may be a channel selected from a list of channels supported by the P2P stations. In embodiments, Channel Usage elements may also be included in a Beacon frame or a (Re)association Response frame from the AP (for the Beacon frame only) or from an unassociated AP (for the Beacon and (Re)association frames). When included in a Beacon or (Re)association frame, the Channel Usage element is called Gratuitous Channel Usage element, because it is only announced by the AP. To sum up these various embodiments, the substitute channel may be provided as a Channel Usage information according to IEEE P802.11-REVme / D6.0 in a Channel Usage element of a Probe Response frame or a Channel Usage Response frame or a Beacon frame or a (Re)Association Response frame Once a substitute channel is obtained from an AP, the P2P station can decide to use this channel for its forthcoming P2P communications. If several substitute channels are available (are provided by the AP), the P2P stations can negotiate the channel to use. This can be part of the P2P setup procedure described above when the substitute channels are obtained before the P2P setup for instance, through the Supported Channels element or through a new element dedicated to the substitute channels. In a case where both P2P stations are not associated to the same AP, they can individually request a substitute channel to their associated AP among Supported Channel supported by both P2P stations. For instance, they can request assistance to setup a Channel-usage-aidable BSS on an off-channel that does not have any infrastructure BSSs operated by any AP that belongs to the ESS of its associated AP by. This may be done by setting the Usage Mode field (Figure 8a) to the value 2. In embodiments, the Channel Usage element includes the address of the AP of the respective P2P station. With that, the APs could coordinate together to provide the same substitute channel to their respective P2P station as already mentioned above. Adding the address of the other AP in the Channel Usage element when the Usage Mode field is set to 2 aims to extend purpose of the request assistance to setup a Channel-usage-aidable BSS on an off-channel to Multi-AP coordination and not only limited to the APs of an ESS as currently done. In a variant, the definition of a common substitute channel through Multi-AP coordination could use a new value for the Usage Mode field among the available reserved value (for instance from 6-254). The MAP coordination for the substitute channel for P2P communications can rely on the usage of the Channel Usage element that carries Usage Mode field with a value equal to 4 (Channel-usage-aidable BSS channel switch request). In embodiments, the P2P stations add information in the Channel Usage element to signal their AP that the substitute channel will be used via the automatic channel switch procedure i.e., that the P2P stations will move upon detection of the busyness of their base channel. The P2P stations therefore declare to the AP their local enabling of the automatic channel switch procedure according to the present disclosure. In embodiments, the AP may authorize or not the usage of the automatic channel switch procedure in the Channel Usage response it sends to any non-AP station. Alternatively, a new Action frame may be used by the AP to provide the authorization or not. In a variant, the authorization (or not) could be included in NPCA element. In those various cases, a switching to the substitute channel for P2P communication is based on a prior authorization / enablement from the AP to the P2P station to perform channel switching in case of base channel busyness. In some embodiments, the NPCA and the automatic channel switch procedure are defined to be mutually exclusive, i.e., one of them only can be enabled at any time: the automatic channel switch procedure can be enabled only when NPCA is disabled, and vice versa. They can both be disabled at the same time. This is to simplify the OBSS AP management. In variants, a differentiated control (enablement / disablement) may be implemented depending on whether the base channel busyness is due to OBSS interference or due to intra-BSS traffic not involving the P2P stations; for example, the OBSS interference detection could be linked to the NPCA feature whereas the intra-BSS interference detection could be control independently through the automatic channel switch procedure. To allow simultaneous use (coexistence) of NPCA and the automatic channel switch procedure by separate groups of stations in the BSS, the substitute channel(s) used for the automatic channel switch is preferably selected or defined different from the anchor channel(s) used for NPCA. In embodiments where a P2P station gets the substitute channel from its AP and forwards it to the other P2P station, the following operations may be implemented. A first of the P2P stations can send a Channel Usage Request frame including a Channel Usage element that carries a Usage Mode field with a value equal to 4 to indicate that it prefers to switch the operating channel of the Channel-usage-aidable BSS to a substitute channel (to be defined) and to indicate supported or preferred channel. To that end, the first P2P station indicates the preferred Operating Channels by including one or more Operating class and Channel fields in the Channel Entry field of the Channel Usage element carried in the corresponding Channel Usage Request frame. The other P2P station receiving such frame then considers switching the operating channel of the Channel-usage-aidable BSS to a substitute channel that is one of the preferred channels of the other P2P station, i.e., one of those indicated in the received Channel Entry field of the Channel Usage element. In this respect, this other P2P station uses the Channel Usage procedure with its own AP to get one substitute channel among the ones proposed by the first P2P station. After receiving the substitute channel from its AP, the other P2P station transmits a Channel Usage Response frame to the first P2P station, in response to the Channel Usage Request frame. The Channel Usage Response frame includes a Channel Usage element with the Usage Mode field set to 4 and the substitute channel (operating class and channel) in the Channel Entry field. In a variant to request the AP to choose the substitute channel, the other P2P station, upon receiving the Channel Usage Request frame, selects the substitute channel from the received Channel Entry fields (channels proposed by the first P2P station) of the channel Usage element and informs its own AP about the substitute channel it has elected for P2P communications. In that case the other P2P station can include an indication in the Channel Usage Request frame to inform its AP that the channel defined in the Channel Entry field of the frame corresponds to the substitute channel negotiated with the first P2P station. In embodiments, the Channel Usage element may also include the address of the first P2P station and / or the address of the AP to whom the first P2P station is associated. This address of the AP could be used by the AP of the other P2P station to perform coordination of the substitute channel(s) for P2P communication. Any information mentioned above to drive the automatic channel switch can be added in the Channel Usage element or as a new element dedicated to the automatic channel switch in the frames exchanged that carry the Channel Usage element as for example a TWT element (see TWT element 886 of Figure 8b). Next to step 501, the two P2P stations may optionally (step 502) exchange buffer status reports BSRs to report buffered P2P data. This is for the P2P stations to decide to switch based on the presence of buffered P2P data to be transmitted and / or received by themselves. It also allows them to trigger medium access contention for P2P. Next, once the P2P stations have setup a P2P session, obtained / negotiated a substitute channel for P2P communication together and / or with their AP(s) and exchanged their buffer statuses, and in some cases have received from their AP(s) the authorization to perform the automatic channel switch procedure, they can use the automatic channel switch procedure when they detect busyness of their base channel (concurrent OBSS or intra-BSS communications). At step 503, the P2P station performs base channel busyness detection. Detecting busyness of the base channel may include detecting Overlapping BSS (OBSS) traffic (i.e., OBSS interference with the base channel) and / or intra-BSS traffic not involving the P2P stations, on the base channel. These traffics are concurrent to the P2P traffic to be performed between the P2P stations. Channel busyness detection usually allows the P2P station to obtain the duration of the busyness, from the Duration field specified in the detected frames. This may be a TXOP (Transmission Opportunity) duration in case of OBSS interference or intra-BSS interference. This may be a Duration set in a Trigger frame in case of an intra-BSS interference not involving the P2P STAs (no resource units are allocated to the P2P stations by the Trigger frame). In case of busyness detection, the P2P station switches at step 504 to the substitute channel as defined / obtained at step 501. The triggering of the switch may be further based on the BSRs exchanged at optional step 502: a switch is performed only if there is buffered P2P traffic at any of the two P2P stations, or only if the reported P2P traffic is above a predefined amount of data. The triggering of the switch may also be based on the remaining time in the base channel (e.g., remaining time of the OBSS TXOP or duration of the pending concurrent communication on the base channel). Next at step 505, the P2P station operates the P2P communications with the other P2P station over the substitute channel. No later than an end of the busyness duration (e.g., TXOP Duration), the P2P station switches back to the base channel. Preferably, this is done at the end of the busyness duration, such as the end of the OBSS TXOP or intra-BSS TXOP. In a variant wherein the AP wants to control the infrastructure and P2P communication occurring in its BSS, the AP could use the Dynamic Sub-band Operation (DSO) proposed by the IEEE 802.11 bn Task Group, to park the P2P communication (the P2P stations) in a sub-band of its operating band. This may be an alternative of the concurrent intra-BSS automatic channel switch but in that case fully controlled by the AP. This alternative is suitable in dense environment where no available off-channel can be allocated to the P2P communication. Figure 6 illustrates, using an exemplary timeline, the automatic channel switch mechanism, applied by P2P stations (STA13 and STA32 in the scenario) detecting concurrent transmissions on their base channel, here OBSS interference from BSS1 for STA32 viewpoint and intra-BSS without involving it for STA13 viewpoint. At time tO, the P2P stations detect a concurrent communication on their base channel (OBSS interference or intra-BSS communication without involving them or a combination thereof). This corresponds to step 503. For instance, if the P2P stations are not associated with the same AP, one P2P station can detect an intra-BSS communication that does not allocate it a timeslot (e.g., STA13 receives a Trigger frame from AP1 without any RU allocated to STA13), which intra-BSS communication is considered as an OBSS interference by the other P2P station which does not belong to the same BSS (e.g., STA32 considers the Trigger frame as an OBSS frame within an OBSS). When the two P2P stations are not associated to the same AP, we assume that the P2P stations share the same base channel (i.e., the two APs operate with the same primary channel) or if the P2P stations do not share the same base channel, the P2P stations are able to monitor several channels at the same time (e.g., Multi-radio device, EMLSR, concurrent device supporting to connect to both infrastructure and P2P at the same time...) and monitor the base channel of each other in addition to their own base channel. In embodiments, the P2P stations get the TXOP duration of the detected communication (e.g., either from the PHY RX vector or from the MAC header of the detected frame). In embodiments, if the detected communication belongs to the list of the common OBSS of the P2P stations, the P2P stations switch to the substitute channel previously shared or agreed on. For example, STA13 and STA32 detect a communication between AP1 and STA11 (belonging to BSS1 as STA13 does). This communication is considered as OBSS interference by STA32 and as a concurrent intra-BSS communication for STA13 since STA13 is not involved therein. When STA32 detects the OBSS communication from BSS1 to which STA13 belongs, either STA32 moves to the substitute channel to see whether STA13 has also moved or STA32 decodes the frame in BSS1 to determine whether the current TXOP is going to involve STA13 for the intra-BSS communication. Once all conditions to a channel switch are fulfilled, STA13 and STA32 actually switch their operation channel to the substitute channel. This corresponds to step 504 and is illustrated by switching operations 621a and 621b in Figure 6. The channel switch operation may take different time depending on the STAs’ ability (including hardware configuration). The P2P communications / operations 622a / 622b corresponding to step 505 start after both P2P stations (STA13 and STA32) have completely switched to the substitute channel. On the substitute channel, STA13 and STA32 perform P2P operations as follows. One or both P2P stations perform CCA for PPDU detection and decrement their backoff counter(s). A P2P station may transmit an initial control frame (ICF) after one of its backoff counters becomes 0 to confirm that the other P2P station has successfully switched to the substitute channel. The initial control frame may be an RTS frame or MU-RTS frame or any other control frame. The addressee P2P station may respond with an initial control response (ICR) frame after it receives the ICF. This is to confirm the addressee P2P station has also successfully switched to the substitute channel and that the P2P communication can occur. The ICR frame may be a CTS frame or any other control frame. The P2P station transmits a data frame after receiving the ICR frame. The other P2P station may respond with an acknowledgement (ACK) frame after receiving the data frame. The P2P frame exchanges in the substitute channel are done within the OBSS TXOP (or the like) that uses the base channel. Once the P2P transmissions have finished, and no later than the end of the OBSS TXOP (or more generally the end of the base channel occupancy by the concurrent OBSS or intra-BSS transmission), the P2P stations switch back to their base channel P1 and operating band S1 to communicate with the stations of their BSS. This corresponds to step 506. The switching back is referenced 623a / 623b in Figure 6. The P2P stations can initiate new transmissions through the complete operating band S1 in a conventional manner. Figure 7 illustrates, using a flowchart, detailed steps of a communication method for an automatic channel switch for P2P communication in a wireless communication system such as system 100 of Figure 1, according to embodiments of the present disclosure. The method 700 is implemented at any station of a BSS, which station is involved in a P2P communication, preferably - but not necessarily - at a non-AP station. Since the Figure details some steps of Figure 5, the same references between the two figures correspond to the same features (actions, steps...); their detailed description will be omitted to avoid useless repetitions. The method 700 starts at step 701 (setup of the P2P session) and 702 (negotiation of the substitute channel) which are similar to step 501 but split into two steps. Steps 701 and 702 may be swapped, i.e., the negotiation of the substitute channel with the AP may take place before the P2P session setup procedure. Next, once the P2P stations have setup a P2P session, obtained / negotiated a substitute channel for P2P communication together and / or with their AP(s), optionally exchanged their buffer statuses (not shown), and in some case received from their AP(s) the authorization to perform the automatic channel switch procedure, they are able the automatic channel switch procedure when they detect busyness of their base channel. For the time being, the P2P stations compete to access the medium over the base channel, in step 710. Competition is made overthe primary channel as a part ofthe base channel. If one ofthe P2P stations succeeds in accessing the medium (yes case in test 720), the P2P stations can communicate with each other over the base channel during step 721. Otherwise (No case in test 720 - the P2P stations fail to gain the medium on the base channel), it means they detect concurrent OBSS and / or intra-BSS communications (step 503). In response, they automatically switch to the substitute channel (step 504) to perform their P2P communication (step 505) for the TXOP duration occurring on the base channel. Next, the P2P stations return to their base channel (step 506) at the end ofthe P2P communication and / or no later than the end ofthe TXOP, in order to keep synchronization with their infrastructure BSS. In some embodiments that may supplement the various embodiments above, a Target Wake Time (TWT) schedule may be established to which the two P2P stations belong. The TWT schedule (or the like) may be used to authorize / enable the channel switch operations. In particular, a period where the P2P stations have switched to the substitute channel to perform P2P communications may be included in a service period (SP) ofthe TWT schedule. This ensures the use of the substitute channel for P2P operations is entirely kept with specific time (service) periods, for a better control ofthe P2P operations. For instance, the P2P stations can exchange information about their P2P scheduling after the P2P session has been setup. For example, the P2P stations can exchange their wakeup timing though a Wakeup Schedule element (section 9.4.2.61 in IEEE 802.11-REVme / D6.0) carried in the TDLS Peer PSM Request / Response frames or their Notification of Absence (WiFi Direct) carried in the Beacon frame from the Group Owner or in the P2P Presence Request / Response frames. Next, the automatic channel switch may be enabled or disabled according to the schedule of an individual TWT between both P2P stations or based on the scheduling of a broadcast TWT (bTWT or rTWT) in which they are both enrolled. In other words, the automatic channel switch to the substitute channel could be enabled for the duration that corresponds to the Service Period of the TWT agreement in which they are enrolled and be disabled out of this Service Period. For completeness, the Channel Usage element, Channel Usage Request frame and Channel Usage Response frames are detailed with reference to Figures 8a, 8b and 8c respectively. The Channel Usage information is a set of channels provided by an AP to non-AP STAs for operation of a Channel-usage-aidable BSS or an off-channel TDLS direct link. The channel usage information provided by the AP to the non-AP STA is to advise the STA on how to coexist with the infrastructure network. Besides, the non-AP STA may negotiate a P2P TWT agreement by including a TWT element in the Channel Usage request frame (Figure 8b) and the AP may accept the establishment of this P2P TWT agreement by including in its turn a TWT element in the Channel Usage response frame (Figure 8c). Moreover, a non-AP STA that has already selected a Channel for P2P communication may transmit a Channel Usage Request frame with the Usage Mode field of the Channel Usage element set to 3 and without a Channel Entry field to inform the AP about its unavailability during the P2P TWT agreement. With reference to Figure 8a, the data payload of a Channel Usage element is shown under reference 800. The Channel Usage element is made up of four fields: an Element ID field 810, a Length field 820, a Usage Mode field 830 and a Channel Entry field 840. Six different values are defined for the Usage Mode field 830 in IEEE P802.11-REVme / D6.0 as shown in the Figure: value 0 for Channel-usage-aidable BSS, value 1 for Off-channel TDLS direct link, value 2 for Channel-usage-aidable BSS in which none of the Channel-usage-aiding BSSs that belong to the same ESS operate on the channels identified by the Channel Entry field, value 3 for Unavailability indication, value 4 for Channel-usage-aidable BSS channel switch request, value 5 for Capability notification and finally value 255 for the Unknown request. The values 6 to 254 are reserved. The Channel Entry field 840 includes zero or more Operating Class 841 and Channel 842 fields. The Operating Class field 841 indicates an operating class value. The operating class is interpreted in the context of the country specified in the Beacon frame of the BSS. The Channel field 842 indicates a channel number, which is interpreted in the context of the indicated operating class. Operating Class and Channel numbers are defined in Annex E of IEEE P802.11-REVme / D6.0. Operating Class and Channel fields can be grouped together to identify a noncontiguous channel as described in 9.4.2.69.3 (Location Indication Channels subelement). In the present disclosure, embodiments provide using Operating Class and Channel fields to signal one or more substitute channels for P2P operations. With reference to Figure 8b, the Channel Usage Request frame 880 includes Category field 881, WNM field 882, Dialog token field 883, Channel Usage Element field 884, Supported Operating Classes Element field 885, TWT elements field 886 and Timeout Interval Element 887. These fields are further described hereafter: - The Category field 881 is set to a value indicating that the corresponding frame belongs to a Wireless Network Management category (value 10 according to Table 9-81 of IEEE P802.11-REVme / D6.0). - The WNM field 882 defined the type of the frame, i .e., a Channel Usage Request Frame (WNM Action field value equals 21, according to Table 9-536 of IEEE P802.11-REVme / D6.0). - The Dialog Token field 883 is the nonzero value chosen by the non-AP STA sending the Channel Usage Request frame to identify the request / response transaction. - The Channel Usage Element field 884 includes one or more Channel Usage elements to identify the request Usage Mode. - The Supported Operating Classes Element field 885 contains a Supported Operating Classes element to indicate the supported operating classes for the requested network type, consistent with the Country element advertised by the AP. - The TWT Elements field 886 includes zero or more TWT elements each containing only one individual TWT parameter set. When included in a Channel Usage Request frame, the TWT Elements field contains only one TWT element, except if used for the establishment of a P2P TWT agreement with a range of TWT parameter values. In this case, an additional TWT element is present. - The Timeout Interval Element field 887 is present when the TWT Elements field contains at least one TWT element; if present it contains a Timeout Interval Element (TIE) field. Otherwise, the Timeout Interval Element field is not present in this frame. With reference to Figure 8c, the Channel Usage Response frame 890 includes Category field 891, WNM field 892, Channel Usage Element field 893, Country String field 894, Power Constraint Element field 895, EDCA Parameter Set Element field 896, Transmit Power Envelope Element field 897, TWT elements field 898 and Timeout Interval Element 899. Only fields that differ from the Channel Usage Request frame 880 are further described hereafter: - The Country String field 894 is the value contained in the dot11 Countrystring attribute. - The Power Constraint Element field 895 includes zero or one Power Constraint elements. - The EDCA Parameter Set Element field 896 includes zero or one EDCA Parameter Set elements. - The Transmit Power Envelope element field 897 is defined in section 9.4.2.160 (Transmit Power Envelope element) of IEEE P802.11-REVme / D6.0. Figure 9a schematically illustrates a communication device 900 configured to implement at least one embodiment of the present invention, for instance any (AP or non-AP) station shown in Figure 1. The communication device 900 may preferably be a device such as a microcomputer, a workstation or a light portable device. The communication device 900 comprises a communication bus 913 to which there are preferably connected: a central processing unit 901, such as a processor, denoted CPU; a memory 903 for storing an executable code of methods or steps of the methods according to embodiments of the disclosure, as well as the registers adapted to record variables and parameters necessary for implementing the methods; and at least one communication interface 902 connected to a wireless communication network, for example a communication network according to one of the IEEE 802.11 family of standards or Wi-Fi alliance protocols, via transmitting and receiving antennas 904. Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 900 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 900 directly or by means of another element of the communication device 900. 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 902, in order to be stored in the memory of the communication device 900 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 9b is a block diagram schematically illustrating the architecture of the communication device 900, adapted to carry out, at least partially, the embodiments of the disclosure. As illustrated, device 900 comprises a physical (PHY) layer block 923, a MAC layer block 922, and an application layer block 921. The PHY layer block 923 (here an 802.11 standardized PHY layer) has the task of formatting, modulating on or demodulating from any 20MHz (or more) channel (primary, secondary, base, operating, substitute channel), and thus sending or receiving frames over the wireless radio medium used, such as 802.11 frames, for instance MAC data and management frames based on a 20MHz width to interact with legacy 802.11 stations, as well as of MAC data frames of OFDMA type having smaller width than 20MHz legacy (typically 2 or 5 MHz) to / from that radio medium. The MAC layer block or controller 922 preferably comprises a MAC 802.11 layer 924 implementing conventional 802.11 MAC operations, and additional block 925 for carrying out, at least partially, the embodiments of the disclosure. The MAC layer block 922 may optionally be implemented in software, which software is loaded into RAM 903 and executed by CPU 901. The MAC 802.11 layer 924 may implement an Upper-MAC stack along with a series of Lower-MAC modules. Preferably, the additional block 925, referred to as P2P / OBSS interference managing module which has different operations to implement parts of the invention, depending on the role played by the communication device 900. As the same device can play different roles over time, the additional block 925 is preferably designed to selectively perform the different operations relative to P2P and OBSS features. MAC 802.11 layer 924 and P2P / OBSS managing module 925 interact one with the other in order to process accurately communications over the medium, e.g. over single-user or OFDMA RUs addressed to multiple stations according to embodiments of the invention. On top of the Figure, application layer block 921 runs an application that generates and receives data packets, for example data packets such as a video stream. Application layer block 921 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 modificationswill 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 in a wireless network, comprising at a first station belonging to a first Basic Set Service (BSS):establishing a peer-to-peer (P2P) session between the first station and a second station,upon detecting busyness of a base channel, switching to a substitute channel to perform P2P communications with the second station.

2. The method of Claim 1, wherein the substitute channel is a subpart of a BSS operating channel defined by the first BSS, which substitute channel does not overlap with the base channel.

3. The method of Claim 1, wherein the substitute channel does not overlap with a BSS operating channel defined by the first BSS.

4. The method of Claim 1, wherein the substitute channel is provided by a first AP of the first BSS.

5. The method of Claim 4, wherein the substitute channel is shared by the first station to the second station.

6. The method of Claim 5, wherein the second station submits the shared substitute channel to a second AP of a second BSS to which the second station belongs.

7. The method of Claim 4, wherein the substitute channel is provided as a Channel Usage information according to IEEE P802.11-REVme / D6.0 in a Channel Usage element of a Probe Response frame or a Channel Usage Response frame or a Beacon frame or a (Re)Association Response frame.

8. The method of Claim 4, wherein the substitute channel is provided by the first AP as a channel selected from a list of channels supported by the first and second stations.

9. The method of Claim 1, wherein detecting busyness of the base channel includes detecting Overlapping BSS (OBSS) traffic and / or intra-BSS traffic not involving the first station nor the second station, on the base channel.

10. The method of Claim 1, wherein the first and second stations exchange a list of Overlapping BSSs (OBSSs) detected by each of them, wherein the switching is triggered upon detecting OBSS traffic on the base channel from one OBSS of the list.

11. The method of Claim 1, wherein the switching is further based on a prior authorization / enablement from a first AP of the first BSS to the first station to perform channel switching in case of base channel busyness.

12. The method of Claim 11, wherein the authorization / enablement to the first stationto perform channel switching in case of base channel busyness and an enablement of nonprimary channel access in the first BSS in case of Overlapping BSS (OBSS) traffic are mutually exclusive, wherein the non-primary channel access in the first BSS includes a channel switching of a primary channel of the first BSS to an anchor channel.

13. The method of Claim 1, wherein the switching is further based on the presence of buffered P2P data to be transmitted and / or received by the first station.

14. The method of Claim 13, wherein the first and second stations exchange buffer status reports to report buffered P2P data.

15. The method of Claim 1, wherein the first station switches back to the base channel no later than an end of a duration specified in a frame based on which the busyness of the base channel is detected.

16. The method of Claim 1, wherein a Target Wake Time (TWT) schedule is established to which the first and second stations belong, and a period where the first station switches to the substitute channel to perform P2P communications is included in a service period (SP) of the TWT schedule.

17. The method of Claim 1, further comprising operating the P2P communications with the second station over the substitute channel.

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

19. 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.

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