Methods, devices, and computer programs for improving determination of when to change values of privacy enhancement parameters of a multi-link wireless station in a BSS context

Abstract

At least an embodiment of a method for determining a time at which a value of a parameter of a non-access point, AP, station affiliated with a non-AP multi-link device, MLD, is to be modified, the method comprising, at the non-AP station configured to communicate over a link with an AP affiliated with an AP MLD: obtaining a time offset, relatively to a time reference at the AP, associated with the link; and determining a time at which a value of the parameter is modified, wherein the time is determined as a function of the time offset and of a time counter of the affiliated station, the time counter being associated with the link.

Description

[0001] METHODS, DEVICES, AND COMPUTER PROGRAMS FOR IMPROVING DETERMINATION OF WHEN TO CHANGE VALUES OF PRIVACY ENHANCEMENT PARAMETERS OF A MULTI-LINK WIRELESS STATION IN A BSS CONTEXT

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to wireless communications and more specifically to user privacy during wireless communications.

[0004] BACKGROUND OF DISCLOSURE

[0005] The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. Furthermore, all embodiments are not necessarily intended to solve all or even any of the problems brought forward in this section.

[0006] Today, the evolution of wireless systems has brought privacy concerns at the forefront, driven by user demand and requirements of the General Data Protection Regulation (GDPR). The global wireless industry is faced with the growing need to protect users’ personally identifiable information from increasingly sophisticated user tracking and user profiling activities, while continuing to improve wireless services and the user experience.

[0007] In particular, the Media Access Control (MAC) address of a user’s device constitutes a piece of data that can be used to track this user. Indeed, the access points (APs) of wireless networks can monitor the locations of mobile devices (tablets, laptops, mobile phones, etc.) of a user without his / her consent, by means of their MAC addresses. This is because mobile phones are configured to discover surrounding access points to wireless networks. As a user moves, his / her mobile phone sends requests to determine if there are any access points nearby, these requests identifying the mobile phone which sends these requests and including in particular the MAC address of the mobile phone. Access points that hear these requests can respond. In the context of Wi-Fi networks as defined by IEEE 802.11 standards (Wi-Fi is a trademark), this procedure is called Probe Request / Response exchange.

[0008] So even when a mobile phone is not connected to a Wi-Fi network, surrounding access points may receive its MAC address. It is then possible to track a user by reconstructing his / her trajectory from access points to which his / her mobile phone has sent its MAC address. In addition, if the mobile phone has been associated with one of the access points (i.e., the user has connected to an associated Wi-Fi network through that access point) and the user has provided personal identification information (name, place of residence, etc.) in the past, the access point may have recorded in a database the MAC address of the phone in association with the items of identification information. Therefore, even if the user is not connected to the Wi-Fi network, these items of identity information could be recovered by comparing the MAC address contained in a Probe Request to the MAC address used for the past association.

[0009] In the context of Wi-Fi networks, a solution has been proposed by the IEEE 802.11 working group to limit the risk of a user being tracked, and consists in dynamically modifying the MAC address of the user device. This mechanism is called Randomized and Changing MAC (RCM) procedure. It has been originally introduced as a privacy enhancing feature in the 802.11aq Pre-Association Service Discovery Task Group and finally included in the standard IEEE Std 802.11-2020. It comprises periodical change of the MAC address of a non-AP station or STA (i.e., a station which is not an access point) to a random value, while the non-AP station is not associated with a network (or, equivalently, with an access point). The non-AP station may construct the randomized MAC address from the locally administered address space as defined in IEEE Std 802®- 2014 and IEEE Std 802c™-2017.

[0010] More specifically, a new Management Information Base (MIB) variable controllable by an external management entity has been specified. This variable is called ‘dotH MACPrivacyActivated’. When dot1 IMACPrivacyActivated is set to “true”, the non- AP station can apply specific mechanisms for enhancing the privacy at MAC level, including RCM.

[0011] The MAC address, or Elll-48 address, of a device is an Extended Unique Identifier (EUI) composed of 48 bits. It can be administered universally or locally. A universally administered address is uniquely assigned to the device by the manufacturer. On the contrary, a locally administered address is assigned to the device by software or a network administrator, and replaces the physical burned-in address. The second-least significant bit of the first octet of the MAC address, i.e., the seventh bit of the first octet of the address, also referred to as “U / L bit” (for “Universal / Local bit”), indicates whether it is universally (when set to 0) or locally (when set to 1) administered. The least significant bit of the first octet of the MAC address, i.e., the eighth bit of the first octet of the address, also referred to as “l / G bit” (for“lndividual / Group bit”), indicates whether the frame is sent to only one receiving device (when set to 0, indicating unicast transmission) or to a plurality of devices (when set to 1 , indicating multicast transmission). When the RCM mechanism is operated in the non-AP station, the MAC address of the non-AP station is randomly changed (for instance periodically). More specifically, the ll / L bit is set to 1 , the l / G bit is set to 0, and the remaining 46 bits are randomly generated by using a pseudorandom function (PRF), or can be obtained by any other means (for instance received from AP, or taken in a predefined list of addresses).

[0012] Unfortunately, RCM is not sufficient to preserve privacy of a device in view of advanced technics of data traffic analysis that create a kind of digital fingerprint of the devices. To overcome this issue, a set of Enhanced Data Privacy (EDP) parameters that would allow an eavesdropper to fingerprint a device has been identified. Among these EDP parameters, identifiers like the MAC address or the Association Identifier (AID) are of course the most important ones, but other parameters like the Sequence Number (SN) or the Packet Number (PN) present in the non-encrypted part of the data frames are also listed. The value of the MAC address and AID transmitted in clear over the air in the MAC header of a transmitted frame are called respectively OTA_MAC and OTA_AID.

[0013] In the scope of IEEE 802.11 bi, a standard currently under drafting, solutions have been proposed to change the EDP parameters of a station associated with an AP, (including the MAC address) to avoid being tracked by a potential eavesdropper. It is observed that EDP parameters can be divided into two sub-categories that are the Client Privacy Enhancement parameters (CPE parameters), that are dedicated to the enhancement of data privacy of a client (non-AP station) parameters, and the Basic Service Set (BSS) Privacy Enhancement parameters (BPE parameters), that are dedicated to the enhancement of the BSS privacy. Accordingly, CPE parameters avoid a non-AP station to be tracked in a given BSS or Extended Service Set (ESS), while BPE parameters avoid an AP station, and especially a mobile AP station, to be tracked (for instance a mobile phone sharing its internet connection via Wi-Fi to other devices like a camera or a gaming device).

[0014] To avoid a non-AP station to be tracked, the set of EDP parameters should be valid only for a limited period of time called Epoch in the following. In particular, the existing solutions to the tracking issue are all relying on the fact that both AP and non- AP stations operate the change of MAC address on their respective side, at the same instant. To that end, the Epoch start time needs to be known by both the AP and the non- AP stations. Not only the Epoch start time needs to be known by both the AP and the no-AP stations, but it needs to be accurate enough to avoid discarding frames that are not addressed with the expected address from the receiver point of view. In addition, in the cases where several non-AP stations are associated with the same AP, it is beneficial to change a set of non-AP stations at the same time (in particular to create additional confusion in an eavesdropper’s mind). In the latter case, the Epoch time needs to be known by a set of non-AP stations and the AP station.

[0015] In order for an AP station and one or more non-AP stations to share the Epoch start time, it has been recently proposed to rely on an instant defined by a regular absolute time (Timing synchronization function or TSF time), or on a constant instant (offset) that is relative to the reception of a frame (typically a beacon frame).

[0016] Recent proposed solutions rely on the fact that the Epoch start time is synchronized among all the links of the different stations.

[0017] In the scope of the IEEE 802.11be amendment development, multi-link stations have been introduced, and the configurations of the established links can be modified using a procedure called multi-link reconfiguration. During a multi-link reconfiguration, a link can be added, or removed. Unfortunately, in case of Multi-Link reconfiguration existing solutions cannot guaranty to maintain the synchronization between links for the epoch start time determination.

[0018] There is then a need to provide a method to determine the Epoch start time that is resilient to the change of link configuration.

[0019] SUMMARY OF THE DISCLOSURE

[0020] The present disclosure has been devised to address one or more of the foregoing concerns.

[0021] In the scope of the ROM, determining the start time of a new Epoch is a key point of the MAC address change mechanism.

[0022] The current disclosure describes a method to determine the starting time of an Epoch that is compatible with the Multi-Link architecture of the latest amendment of the IEEE 802.11 standard, and especially that can avoid any loss of synchronization for the Epoch start time computation in case of link reconfiguration.

[0023] According to a first aspect of the disclosure, it is provided a method of determining a time at which a value of a parameter of a non-access point, AP, station affiliated with a non-AP multi-link device, MLD, is to be modified, the method comprising, at the non- AP station configured to communicate over a link with an AP affiliated with an AP MLD: obtaining an offset, relatively to a time reference at the AP, associated with the link; and determining a time at which a value of the parameter is modified, wherein the time is determined as a function of the offset and of a counter of the affiliated station, the counter being associated with the link.

[0024] Accordingly, the method of the disclosure makes it possible to improve determining when to change values of privacy enhancement parameters of a multi-link wireless station in a BSS context by making, for each non-AP station, the determination of the instant of change independent between the links.

[0025] According to some particular embodiments, the obtaining comprises receiving the offset from the AP, over the link.

[0026] Still according to some particular embodiments, the offset represents time units.

[0027] Still according to some particular embodiments, the offset represents an Epoch number offset indicating a number of Epoch intervals since Epoch start time on the link.

[0028] Still according to some particular embodiments, the Epoch number offset is received during setting Enhanced Data Privacy, EDP, parameters within the affiliated station.

[0029] Still according to some particular embodiments, the Epoch number offset is received within a set of Enhanced Data Privacy, EDP, parameters of a Group Epoch Sequence, in response to assigning the affiliated station to the Group Epoch Sequence or to a request from the affiliated station to create or to join the Group Epoch Sequence.

[0030] Still according to some particular embodiments, the obtaining comprises determining the offset as a function of another offset received by another non-AP station affiliated with the non-AP MLD from the AP over another link and a link offset between the link and the other link.

[0031] Still according to some particular embodiments, the offset represents time units.

[0032] Still according to some particular embodiments, the offset represents an Epoch number offset indicating a number of Epoch intervals since Epoch start time on the link.

[0033] Still according to some particular embodiments, the link offset is received from the AP during setup of the link.

[0034] Still according to some particular embodiments, the time is further determined as a function of a reference start time based on the time reference.

[0035] Still according to some particular embodiments, the method further comprises determining the reference start time.

[0036] Still according to some particular embodiments, the time is further determined as a function of a pseudo-random variation time.

[0037] Still according to some particular embodiments, the offset is a difference between the time reference and the counter, at a given time. Still according to some particular embodiments, the method further comprises, if the link is reconfigured, computing an updated value of the offset as a function of another offset obtained from another non-AP station affiliated with the non-AP MLD and a link offset between the link and another link linking the other non-AP station to the AP.

[0038] Still according to some particular embodiments, the counter is a Timing Synchronization Function, TSF, counter.

[0039] Still according to some particular embodiments, the counter is an Epoch Interval counter

[0040] Still according to some particular embodiments, the time reference is based on an internal reference clock of the AP.

[0041] According to a second aspect of the disclosure, it is provided a processing unit in a non-access point, AP, multi-link device, MLD, for determining a time at which a value of a parameter of a non-AP station affiliated with the non-AP MLD is to be modified, the processing unit being configured to carry out each of the steps of the method described above.

[0042] Accordingly, the device of the disclosure makes it possible to improve determining when to change values of privacy enhancement parameters of a multi-link wireless station in a BSS context by making, for each non-AP station, the determination of the instant of change independent between the links.

[0043] At least parts of the methods according to some embodiments of the disclosure may be computer implemented. Accordingly, some embodiments of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", a "module", or a "system". Furthermore, some embodiments of the present disclosure may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

[0044] Since some embodiments of the present disclosure can be implemented in software, some embodiments of the present disclosure can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, 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

[0045] Embodiments of the disclosure will now be described, by way of example only, and with reference to the following drawings in which:

[0046] Figure 1 illustrates an example of a network system in which some embodiments of the disclosure may be implemented;

[0047] Figure 2a illustrates an example of steps carried out in a non-AP station when it is added to a Group Epoch Sequence, according to some embodiments of the disclosure;

[0048] Figure 2b illustrates an example of steps carried out in a non-AP station when starting a new Individual Epoch Series, according to some embodiments of the disclosure;

[0049] Figure 3a illustrates an example of a sequence of group Epoch start times for a group of non-AP stations associated with the same AP station, according to some embodiments of the disclosure;

[0050] Figure 3b describes timing event computation formulas associated with Figure 3a and used in Figures 8a to 8c;

[0051] Figure 4a illustrates an example of a sequence of Individual Epoch start times for a single non-AP station associated with its AP station;

[0052] Figure 4b illustrates timing event computation formulas associated with Figure 4a, according to some embodiments of the disclosure and used in Figures 8a to 8c;

[0053] Figure 4c illustrates an example of a sequence of EDP Epochs for a single non- AP station associated with its AP station according to an implementation;

[0054] Figure 4d illustrates an example of a sequence of consecutive EDP Epochs with their associated EDP Epoch start times and transition period according to an implementation;

[0055] Figure 4e illustrates an example of a sequence of consecutive EDP Epochs with their associated EDP Epoch start times, margin period and transition period according to an implementation;

[0056] Figure 5 illustrates an example of coexistence of a sequence of group and individual Epochs for a non-AP station associated with an AP station;

[0057] Figure 6a schematically illustrates an example of associations of Multi-link devices configured to implement at least some embodiments of the present disclosure;

[0058] Figure 6b schematically represents an example of an embodiment of the present disclosure for computing an epoch start time using an AP internal reference clock; Figure 6c schematically represents an example of a sequence of epochs that start time is computed using an AP internal reference clock, according to an embodiment of the present disclosure;

[0059] Figure 7a illustrates a STA info subfield of a Basic Multi-link information element transmitted by an AP affiliated to an AP MLD as defined by the IEEE 802.11be amendment;

[0060] Figure 7b illustrates an Information Element containing the parameters of a Groups Epoch series according to some embodiment of the disclosure;

[0061] Figure 7c illustrates an example of a frame format for an Individual Epoch series request according to some embodiment of the disclosure;

[0062] Figure 7d illustrates an example of a frame format for an Individual Epoch series response according to some embodiment of the disclosure;

[0063] Figure 7e illustrates an example of a frame format for an (Enhanced Data Privacy) Epoch request frame, according to some embodiments of the disclosure;

[0064] Figure 7f illustrates an example of a frame format for an (Enhanced Data Privacy) Epoch Response frame, according to some embodiments of the disclosure;

[0065] Figure 7g illustrates an example of an Information Element (IE) containing parameters of an Epoch series (Individual or Group) according to some embodiments of the disclosure;

[0066] Figure 7h illustrates an example of an EDP Epoch Settings Field containing parameters of an Epoch series (Individual or Group), according to some embodiments of the disclosure;

[0067] Figure 7i illustrates an example of an EDP Epoch Settings Field containing parameters of an Epoch series (Individual or Group), according to some embodiments of the disclosure;

[0068] Figure 8a illustrates an example of steps carried out in a non-AP station when waking up after a sleep period, according to some embodiments of the disclosure;

[0069] Figure 8b illustrates an example of steps carried out in a station (AP station or non-AP station belonging to a Group), when the associated Group Epoch timer expires and a new Group Epoch is about to start, according to some embodiments of the disclosure;

[0070] Figure 8c illustrates an example of steps carried out in a station (AP station or non-AP station) when an Individual Epoch timer expires and a new Individual Epoch is about to start, according to some embodiments of the disclosure; Figure 9a illustrates an example of a frame exchange sequence carried out in an AP station to initiate a Group Epoch Series, according to some embodiments of the disclosure;

[0071] Figure 9b illustrates an example of a frame exchange sequence when a non-AP station wants to initiate an Individual Epoch Series, according to some embodiments of the disclosure;

[0072] Figure 9c illustrates an example of frame exchange between a requester station and a responder station to request creation of an EDP Epoch sequence according to some embodiment of the disclosure; and

[0073] Figure 10 schematically illustrates an example of a communication device configured to implement at least some embodiments of the present disclosure.

[0074] DETAILED DESCRIPTION OF THE DISCLOSURE

[0075] According to some embodiments of the disclosure, it is determined when to change values of privacy enhancement parameters of a multi-link wireless station in a BSS context, in particular of Client Privacy Enhancement (CPE) parameters.

[0076] Instants of change of CPE parameters define successive usage periods (indexed 0, 1 , ... , n, n+1 , etc.), referred to as ‘Epoch’, during each of which given values of the CPE parameters (e.g., a MAC address) are to be used. In some implementations, a usage period starts with a transition period during which both old values (pertaining to previous usage period ‘n’) and new values (pertaining to the current usage period ‘n+1’) of the CPE parameters may be considered. In some implementations, constraints may be applied to the use of old values during the transition period. For example, it may be allowed to use an old MAC address, @MAC(n), as transmitter address for the transmission of already generated and buffered frames, but the old MAC address @MAC(n) should no longer be used for the generation of a new frame since the current usage period (n+1) has started and thus, a new MAC address, @MAC(n+1) should be used. In other implementations, the change of CPE parameters between two usage periods is strictly applied, i.e., not any transition period is implemented and only the CPE parameters (e.g., CPE_parameters(n)) of a given usage period (e.g., usage period ‘n’) should be used.

[0077] In any case, an accurate determination of the Epoch starting time is essential to enable the parameter change mechanisms to function properly.

[0078] According to some embodiments of the disclosure, a set of instants (called Reference Times in the following) is determined based on a fixed frequency starting at an initial time To, and an effective Epoch start time is determined from each Reference Time using a pseudo-random variation time (called AT in the following). The effective Epoch start time may be determined for a particular non-AP station (Individual Epoch start time) or may be determined for all the non-AP stations of a group of stations (Group Epoch start time). Still according to some embodiments of the disclosure, the effective Epoch start time may be determined on a link basis, as a function of a reference clock (time) directly or indirectly controlled by an AP station and as a function of a time offset between the reference clock (time) and a counter associated with each of the links.

[0079] Still according to some embodiments of the disclosure, the time offset may be expressed in time units of seconds, milliseconds, etc. or in Epoch interval unit. In the latter case, the time offset may then be equal to the Epoch number offset times the Epoch interval, the Epoch number offset representing the number of Epochs since Epoch start time on a given link. The time offset, expressed either in time units or in Epoch interval units, may be referred to simply as the offset in the disclosure.

[0080] Still according to some embodiments of the disclosure, the offset represents a TSF time offset between links, e.g., from a Basic Multi-link information element transmitted by an AP affiliated to an AP MLD. According to other embodiments, the offset indicates the number of Epoch intervals since the epoch start time on a given link (Epoch number offset) and thus represents the time since the epoch start time by considering the epoch interval unit (duration).

[0081] Figure 1 illustrates an example of a network system in which some embodiments of the disclosure may be implemented.

[0082] For the sake of illustration, Figure 1 represents an 802.11 network (i.e. , a Wi-Fi network) system 100 comprising four wireless devices: an access point station (AP) 105 and three non-AP stations (STAs) 110a, 110b, and 110c. The AP station and / or the non- AP stations may be an AP multi-link device (MLD) and non-AP MLDs, respectively. In case of MLD, one or more non-AP stations may be affiliated to a non-AP MLD, and one or more AP stations may be affiliated to an AP MLD.

[0083] Of course, the number of non-AP stations 110a, 110b, and 110c may be different from three. AP station 105 provides wireless connections between non-AP stations 110a, 110b, 110c and a wider network, such as the Internet (not represented). The connection of one of non-AP station 110a, 110b, and 110c to AP 105 may be performed by a standardized process called association. Once a non-AP station is associated with the AP station, the non-AP station can send data to the network and receive data from the network through the AP station.

[0084] AP station 105 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. It can be a standalone product or it may be integrated in a device, for instance in a broadband remote access server (BRAS).

[0085] Non-AP stations 110a, 110b, and / or 110c may comprise, be implemented as, or known as a subscriber’s station, a subscriber unit, a mobile station (MS), a remote station, a remote terminal, a user terminal (UT), a user agent, a user’s device, a user equipment (UE), a user station (STA), or some other terminology. In some implementations, a non-AP station may be or 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 a smartphone), 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, some of non-AP stations 110a, 110b, and 110c may be wireless nodes. Such a 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.

[0086] AP station 105 manages a set of stations that together organize their accesses to the wireless medium for communication purposes. All the stations (AP station 105 and non-AP stations 110a, 110b, and 110c) form a service set, which may be referred to as basic service set, BSS (although other terminology can be used). It is noted that AP station 105 may manage more than one BSS: each BSS is thus uniquely identified by a specific basic service set identifier (BSSID) and managed by a separate virtual AP station implemented in physical AP station 105. Figures 2a and 2b illustrate examples of steps for setting non-AP stations in order to determine an effective Epoch start time.

[0087] Figure 2a illustrates an example of steps carried out in a non-AP station when it is added to a Group Epoch Sequence, according to some embodiments of the disclosure, a Group Epoch Sequence (or Group Epoch Series) being a sequence of Epochs used by a set of non-AP stations associated with the same AP, to change values of privacy enhancement parameters at the same time. A Group Epoch Sequence may be defined by a set of parameters (Group Epoch parameters or Group Epoch Series parameters) comprising a Group Epoch reference Time (To) and a Group Epoch Interval (GEI), making it possible to compute an effective Epoch start time. It may also comprise other parameters such as a range of values (Time Range) of a pseudo-random number to be used for computing the effective Epoch start time, a policy and / or a reference of a link (RefLink Id) that is to be used as a time reference.

[0088] The steps illustrated in Figure 2a are executed when a non-AP station determines it is added to a Group Epoch Series. This may be done upon an association of the non- AP station with the AP, for example by receiving an Information Element (e.g., Information Element (IE) 720 in Figure 7b) including the Group Epoch series parameters (e.g., in a beacon, in a probe response, or in association response frames). This can also be done upon reception of a Group Epoch indication (e.g., Group Epoch indications 910 to 912 in Figure 9a).

[0089] In some embodiment, a non-AP MLD receives the Group Epoch parameters from its AP MLD (Epoch initiator) including: GEI = Group Epoch Interval, T0= initial Group Epoch reference Time, a Time Range, and a RefLink Id.

[0090] Epoch parameters (GEI, TO, Time Range, and RefLink Id of the Reference Link used as a time reference), have same value for all links, and are used to determine Epoch start time and non-AP STA CPE parameters

[0091] Epoch parameters can be sent in an encrypted IE, or encrypted frame as described with reference to Figures 7b to 7g.

[0092] After association, each non-AP MLD computes the value n corresponding to the number of Group Epoch elapsed since last TSF reset on its Master Link. n = [(current TSF -To- RefLink Offset) I GEI]

[0093] In some embodiment, the value of n is transmitted by the AP in the Epoch Number

[0094] Offset 792b The Non-AP STA can then determine next Group Epoch reference Time

[0095] Tn+1 =T0+ (n+1) x GEI

[0096] Then before next Group Epoch reference Time, non-AP STA and AP station compute the CPE parameters for the non-AP STA:

[0097] CPE_PARAMn+1 = PRF-M\L(PTK*, “ERCM”, Tn+1)

[0098] ATn+1 = PRF-128\64(GTK*, “ERCM”, Tn+1) mod (Time range)

[0099] GETn+1 = Tn+1 + ATn+1 + RefLink Offset.

[0100] This embodiment highlights using a time reference as input for the generation of the CPE parameters of this Epoch

[0101] As illustrated in Figure 2a with step 200, the non-AP station recovers from its internal memory the Group Epoch series parameters that may be contained in the last received information element contained, for example, in a beacon (e.g., beacon 900 in Figure 9a) or in a Group Epoch Indication (e.g., Group Epoch Indication 910 in Figure 9a). These parameters may include the starting Time (To), and the fix Group Epoch Interval (GEI), but also a policy.

[0102] Figure 9a describes some example of frame exchanges that provides the Group Epoch series parameters to the non-AP station. Upon reception of those parameters’ values, the non-AP station stores the Group Epoch series parameters' values in its internal memory.

[0103] Next, at step 202, the non-AP station determines the current Group Epoch iteration value denoted n, based on the TSF time, the Group Epoch reference Time (To) and the Group Epoch Interval (GEI), for example using the formula 332 of Figure 3b: n = [(current TSF -To- RefLink Offset) I GEI] where:

[0104] To and GEI are part of the Group Epoch series parameters, and

[0105] RefLink Offset = offset of the TSF counter of the current link compared to the Reference Link (of id RefLink ID) with a 2 ps resolution.

[0106] To is the value of the first reference time for the Epoch on the Reference Link.

[0107] It is noted that, if no beacon is received on current link (Multi-link Power save mode for instance), no direct reading of RefLink Offset is available via the TSF Offset (e.g., TSF Offset 710 in Figure 7a). This is also the case, as illustrated in Figure 6, if the reference link selected by the AP MLD 600 is the Linkl .

[0108] In that case, RefLink Offset may be approximated using 2 TSF Offsets fields 710 of the Basic MultiLink info element received on a reporting link: TSF Offset field for RefLink in received beacon: TSF OffsetRefunk = FIOOr((TSFRefLink TSF eporting) / 2).

[0109] RefLink Offset = 2 x TSF OffsetRefunk

[0110] =2 X FlOOr ((TSF efLink " TSF current) / 2)

[0111] ~ FlOOr ((TSF efLink " TSF reporting) / 2) FIOOT ((TSFcurrent " TSF eporting ) / 2) « 2x (TSF OffSetRefLink - TSF Offsetcurrent)

[0112] At step 204, the station computes the next Group Epoch start Time of the Group Epoch series, denoted GETn. To do so, the station first recovers the latest Group Epoch series parameters stored in memory (step 200) and then computes the next Group Epoch start Time, for example using the formula 330 in Figure 3b that reads as follows: GETn=Tn+ ATn+ RefLink Offset where: n is the iteration number that is incremented by one (i.e. , n=n+1) compared to the recovered value. In some embodiments, the value of n is not determined based on a stored value, it is directly computed using the formula 332 in Figure 3b;

[0113] Tn is the reference time at iteration n, that may be determined using one of the formulas 331 in Figure 3b. In some embodiments, the value Tn is obtained thanks to the previous values stored in memory at step 208 during the CPE parameters computation according to the following formula: Tn=Tn-1 + GEL In some embodiments, Tn is computed using the initial reference time TO (e.g., reference time TO 300 in Figure 3a) and the iteration value n according to the following formula: Tn=T0 + (n x GEI);

[0114] - ATnis a pseudo-random variation time at iteration n. For the sake of illustration, it may be computed using a shared pseudo-random generation function taking input parameters in parameters shared among the stations belonging to the group associated with the Group Epoch series, and at least the Reference Time Tn. An example of determining ATnis provided with formula 333 in Figure 3b:

[0115] ATn=PRF-128\64(GTK*, “ERCM”, Tn) mod (Time range) where the PRF-128 function is as defined in the IEEE 802.11 series. In this example, the function generates 128 pseudo-random bits and only the first 64 ones are kept to generate ATn(as indicated with the 128\64 notation). In this example, the secret key GTK*, used as input of the function, is derived from the GTK that is a key provided by the AP to the non-AP station upon association, and then is known by all the stations associated with the AP. The last input parameter “ERCM” is a context indicating that the generation is dedicated to the Enhanced Randomized and Changing MAC address feature. Finally, in order to obtain a time duration ATnin a predefined duration range of Time Range value (e.g., Time Range value 729 in Figure 7b), the pseudo-random generation result is computed modulo “Time Range”. This formula is only provided as an example. Other pseudorandom generation functions shared by all the stations of the Group may be used. Other input parameters may also be used, a key point being to generate a ATnvalue that is predictable for all stations belonging to the group and from the AP; and

[0116] RefLink Offset is as defined in previous step 202.

[0117] After the determination of the next GET, the station initiates, at step 205, a timer that expires at the next Group Epoch Start Time.

[0118] Next, at step 206, the station computes the next values of the CPE parameters. In the case of an AP, the AP computes the next values of the CPE parameters for each non-AP station belonging to the group. In the case of a non-AP station, the non-AP station only computes its own CPE parameters’ values. The generation of the CPE parameters’ values is out of scope of the current disclosure, but an example of generic formula to generate the CPE parameters for a given non-AP station is provided in formula 334 in Figure 3b:

[0119] CPE-Param = PRF-M\L(PTK*, “ERCM”, Tn)

[0120] In this example, a pseudo-random generation function generating M pseudorandom bits is used and L bits are used (as indicated with the M\L notation) to create all the CPE parameters’ values for a given non-AP station. The private key PTK*, used to generate the CPE parameters for a given non-AP station, is derived from the PTK (KDK) that is a secret key created during association process and that is only known by the non-AP station and the AP. Other input parameters are identical to those used in formula 333.

[0121] At step 208, the station stores in memory all the computed CPE parameters’ values. In the case of an AP, it stores all the CPE parameters’ values of each of the non- AP station belonging to the group. In some embodiments, the station also stores the value of n and Tnas computed in step 204, but also the value of the GETn-i corresponding to the start time of the current Epoch (this value being used in particular circumstances, for example as described in optional step 832 in Figure 8c). Figure 2b illustrates an example of steps carried out in a non-AP station when starting a new Individual Epoch Series, according to some embodiments of the disclosure.

[0122] As illustrated, a first step (step 210) aims at determining the Individual Epoch parameters. According to some embodiments, the non-AP station recovers the Individual Epoch series parameters’ values stored in its internal memory (for example during the setup of the Individual Epoch series), being noted that these values cannot be modified during the non-AP station sleep.

[0123] Next, during step 214, the first Individual Epoch start Time, denoted lETo, is determined. According to some embodiments, lETo = ITo, wherein ITo is negotiated with the AP via a Start Time field (e.g., Start Time field 732 in Figure 7c) of an Individual Epoch request and response frames (e.g., Individual Epoch request and response frames 730 et 740 in Figures 7c and 7d, respectively), and stored in the internal memory after a successful negotiation with the AP (e.g., reception of an Individual Epoch response frame 740 with an error code 750 set to success).

[0124] Next, after having determined the first IET, the station initiates, at step 215, a timer that expires at the next Individual Epoch Start Time.

[0125] Next, at step 216, the station computes the next values of the CPE parameters. In the case of an AP, the AP station computes the next values of the CPE parameters for the non-AP station associated with this Individual Epoch start Time. In the case of a non-AP station, the non-AP station computes its own CPE parameters’ values. The generation of the CPE parameters’ values is out of scope of the current disclosure, but an example of generic formula to generate the CPE parameters for a given non-AP station is provided in formula 434 in Figure 4b:

[0126] CPE-Param = PRF-M\L(PTK*, “ERCM”, ITn)

[0127] In this example, a pseudo-random generation function generating M pseudorandom bits is used and L bits are used (as indicated with the M\L notation) to create all the CPE parameters’ values for a given non-AP station. The private key PTK* used to generate the CPE parameters for a given non-AP station is derived from the PTK that is a secret key created during association process and that is only known by the non-AP station and the AP. Other input parameters are identical to those used in formula 333 in Figure 3b.

[0128] Next, at step 218, the station stores in memory all the computed CPE parameters’ values. In the case of an AP, it stores all the CPE parameters’ values of the considered non-AP station. In some embodiments, if a non-AP STA (Epoch initiator), requests an individual Epoch management, the non-AP STA negotiates, via an Individual Epoch request (e.g., Individual Epoch request 730 in Figure 7c), following Epoch parameters with the AP: Individual Epoch Interval: IEI

[0129] First Individual Epoch start Time: IET0 (precise time indicated by the STA, AT0=0), and associated RefLink ID

[0130] Max duration of Epochs (for example expressed in iteration): N

[0131] N=0: Undetermined duration (association life time)

[0132] N=1 : one shot @MAC change

[0133] N>1 : determined duration.

[0134] Note 1 : Epoch parameters (IEI, IET0, N, and RefLink ID) are encrypted and not known by other STA

[0135] Note 2: For individual Epoch, IET0=IT0

[0136] AP and non-AP STA can then compute future individual epoch reference times. n = [(current TSF - IET0) / IEI]

[0137] ITn+1=IET0+ (n+1) x IEI

[0138] Before the next individual epoch reference time, the non-AP STA and AP compute at once both future Epoch start time, and associated CPE params for the non- AP STA.

[0139] (CPE_PARAMn+1 , AITn+1) = PRF-M\L(PTK*, “ERCM”, ITn+1)

[0140] IETn+1=ITn+1 + AITn+1 + RefLink Offset

[0141] In these embodiments, CPE Parameters are computed thanks to a unique PRF call using as input parameters: a key derived from the PTK, and the reference starting time of the Epoch.

[0142] Figure 3a illustrates an example of a sequence of Group Epoch start times for a group of non-AP stations associated with the same AP station, according to some embodiments of the disclosure. Figures 3a and 3b describe how can be performed Variable Group Epoch start boundary computation.

[0143] To avoid an easy determination of the epoch start time by an eavesdropper, the start time of each EDP epoch is determined by introducing a pseudo random variation around a reference start time occurring at a regular interval. In other words, to prevent an eavesdropper from easily predicting the EDP Epoch start time, a pseudo random variation is applied around a planned EDP Epoch start time to determine the start time of each EDP Epoch on each link.

[0144] In an embodiment, Group Epoch start Time (GET) is based on a fixed frequency with a limited pseudo-random variation.

[0145] In this embodiment, some reference times To (300), Ti (301) to Tn(303) are defined and used for the computation of the effective Group Epoch starting Times GETo (320), GETi (321) to GETn(323).

[0146] Reference times T occur at a regular interval of Group Epoch Interval (GEI) value in number of ps and started with the first occurrence To (300) defined by the AP. The reference time Tnis defined as the TSF counter value of the reference link corresponding to the group Epoch Reference Time number n.

[0147] In other words, Tn=TSF counter value of the group Epoch Reference Time number n.

[0148] In some embodiments, the non-AP station is a multi-link device (MLD) associated with an AP multi-link device (MLD) through at least one link. In the case of an AP MLD, the reference link is a link selected by the AP among its active links, that is used as a reference to determine the TSF differences between the different links.

[0149] TSF counter may be different between two links of a given MLD STA: a constant difference (TSF Offset) between the TSF values of the different links of the same MLD may exist, but the clock drift between two links of the same MLD should be limited to a maximum value (set to 30ps in the case of the IEEE 802.11 be amendment). These offsets may be communicated to the non-AP stations using a Basic multi-link information element, for example transmitted in the beacons, as described in more detail by reference to Figures 7a to 7d.

[0150] In these embodiments, Epoch’s start times of all non-AP STAs affiliated to a single non-AP MLD are aligned in time.

[0151] Non-simultaneous transmit and received (NSTR) mobile APs are a specific case of APs where the AP are not able to simultaneously receive and transmit on two different links. In this case, the IEEE 802.11be amendment precise that for NSTR mobile AP, TSF Offset Present field is always set to 0, but drift between APs is limited to 25 ps.

[0152] Example values may be respectively: GEI = 10 minutes and Time Range = 2 minutes.

[0153] In the case of a single link AP, the reference link is the only link provided by the AP and the TSF Offset is always 0. In the example of Figure 3a, the Group Epoch start Times GETo to GETnare determined based on the respective reference times To to Tn. According to formula 300 in Figure 3b: GETn=Tn+ ATn + RefLink Offset, as described in more detail by reference to Figure 8b. References ATo 310, ATi 311 and ATn313 are for example pseudo-random variations AT.

[0154] Figure 3b illustrates some examples of formulas for computing the Group Epoch start Time at iteration n (GETn), the reference time at iteration n (Tn), the iteration (n), the pseudo-random variation time at iteration n (ATn), and the values of the CPE parameters at iteration n (CPE-Param), as described with reference to Figure 2a.

[0155] Figure 4a illustrates an example of a sequence of Individual Epoch start times for a single non-AP station associated with its AP station. Figures 4a and 4b describe how can be performed Variable Individual Epoch boundary computation.

[0156] In one embodiment, Individual Epoch start Time (IET) is based on a fixed frequency with a limited pseudo-random variation.

[0157] In this embodiment, some reference times ITo (400), Ti (401) to ITn(403) are defined and used for the computation of the effective Individual Epoch starting Times lETo (420), lETi (421) to IETn(423).

[0158] Reference times IT occur at a regular interval of Individual Epoch Interval (I El) value in number of ps and started with the first occurrence ITo (400) defined during the negotiation between the requesting non-AP station and the AP (as described with reference to Figure 9b). The reference time ITnis defined as the TSF counter value of the reference link corresponding to the Individual Epoch Reference Time number n.

[0159] In other words, ITn=TSF counter value of the Individual Epoch Reference Time number n.

[0160] In some embodiments, the non-AP station is a multi-link device (MLD) associated with an AP multi-link device (MLD) through at least one link. In the case of an AP MLD, the reference link is a link selected by the AP among its active links, is used as a reference to determine the TSF differences between the different links.

[0161] As described with reference to Figure 3a, TSF counter may be different between two links of a given MLD STA: as illustrated in Figure 4a, the Individual Epoch start Times lETo to IETnare determined based on the respective reference times ITo to ITn, according to the formula 430 in Figure 4b: IETn=ITn+ AITn + RefLink Offset (as described with reference to Figure 8c). References AITo 410, AITi 411 and AITn413 are for example pseudo-random variations AIT.

[0162] It is observed here that a non-AP station may require a more frequent change of CPE parameters than proposed by the AP using a Group Epoch series.

[0163] Example values may be respectively: IEI = 3 minutes and Time Range = 30 seconds for non-AP stations.

[0164] Figure 4b illustrates some examples of formulas for computing the Individual Epoch start Time at iteration n (I ETn), the reference time at iteration n (ITn), the iteration (n), the pseudo-random variation time at iteration n (AITn), and the values of the CPE parameters at iteration n (CPE-Param), as described with reference to Figure 2b.

[0165] Figure 4c illustrates an example of a sequence of EDP Epochs for a single non- AP station associated with its AP station according to an implementation. The figure illustrates an example of EDP Epoch timeline and describes the Active and Retiring EDP Epochs determination procedure.

[0166] An AP MLD has one active EDP Epoch associated with a given non-AP MLD.

[0167] A non-AP MLD has one active EDP Epoch.

[0168] An EDP Epoch becomes active for a given non-AP MLD when the EDP Epoch start time occurs, and ends when another EDP Epoch becomes active for the same non- AP MLD.

[0169] Upon the starting time of a new Active EDP Epoch, the immediately preceding EDP Epoch becomes the retiring EDP Epoch for a given time window called EDP transition period (450, 451 , 452).

[0170] A retiring EDP Epoch is then the EDP Epoch which was active immediately prior to the current active EDP Epoch.

[0171] In the example of the figure 4c, EDP Epoch 1 (460) becomes active at t1 and retired at t2 when EDP Epoch 2 (461) become active at its turn.

[0172] During the EDP transition period, the FA parameters (i.e. , the EDP parameters) applied during the retiring EDP Epoch remain valid.

[0173] Figure 4d illustrates an example of a sequence of consecutive EDP Epochs with their associated EDP Epoch start times tnand transition period tpnaccording to an implementation. An EDP Epoch starts with a transition period during which the preceding EDP parameters assigned to a non-AP station remain valid. A transition period terminates at the end of a transition timeout interval or before the end of the transition timeout interval, after the completion of the successful transmissions or retransmissions initiated during the preceding EDP Epoch, whichever comes first.

[0174] In some embodiment, during the transition period of an EDP epoch, the EDP parameters assigned to a non-AP MLD during the preceding EDP epoch remains valid only for the following operations:

[0175] — Completion of a frame exchange;

[0176] — Completion of a TXOP.

[0177] In this embodiment, a transition period terminates at the end of a transition timeout interval or at the beginning of the next epoch margin, whichever comes first.

[0178] The coexistence of Group Epoch and more frequent Individual Epoch, for a given non-AP station, is described with reference to Figure 5.

[0179] Figure 4e illustrates an example of a sequence of consecutive EDP Epochs with their associated EDP Epoch start times (Boundaries), margin period and transition period according to an implementation.

[0180] The next epoch boundary is derived from the value of the first epoch TSF start time.

[0181] At the start of the new group EDP epoch, CPE AP MLDs and CPE non-AP MLD begin using the new FA parameters to anonymize selected OTA fields when transmitting new individual frames. CPE AP MLDs and CPE non-AP MLD continue using these anonymization parameters for the duration of the epoch.

[0182] In other words, from the start of one EDP epoch until the start of the next EDP epoch for that EDP group, the new frame anonymization parameters are used to anonymize the selected OTA fields of all new individual frames transmitted during the epoch.

[0183] To account for clock drifts, the CPE non-AP MLD and CPE AP MLD begin to accept individually addressed frames that use the new FA parameters during a margin period for a duration equal to dot11 EDPEpochStartTimeMargin before the start of the new epoch. The CPE non-AP MLD and CPE AP MLD accept individually addressed frames with the old FA parameters for a duration equal to dotH EDPEpochTransitionTime after the start of the new epoch.

[0184] Figure 5 illustrates an example of coexistence of a sequence of group and individual Epochs for a non-AP station associated with an AP station. In other words, this figure shows an example of coexistence of Group and Individual RCM. Indeed, it may happen that one or more non-AP stations belong to a Group Epochs while still needing to use an Individual Epoch, for example upon a request from an application started in the non-AP stations.

[0185] In some embodiment, by default, 802.11 bi non-AP STA follows Group Epoch.

[0186] If a non-AP STA negotiates an Individual Epoch to the AP, the non-AP STA may either:

[0187] Opt1 : Only follow Individual Epochs (ignore Group Epochs)

[0188] Opt2: Follow both Individual and Group Epochs.

[0189] In case of opt2, additional rules are required to avoid selecting an Individual Epoch start time too close from the Group Epoch start Time.

[0190] Priority should be given to Group Epoch: to ensure “mass” effect of group change; because it is easier to cancel Individual Epoch change (impact on 1 STA).

[0191] If time between next Individual and Group epoch start time is lower than a TBD time (e.g., 1s), then Individual Epoch is ignored.

[0192] |GETn - IETp| < 1s => lETp is ignored by both AP and non-AP STA and non-AP STA only change its CPE parameters at GETn.

[0193] Such additional rules are described with reference to optional step 832 in Figure 8c, and Figure 5 highlights the effects of this optional step.

[0194] In this example, a non-AP station, belonging to a group associated with a Group Epoch series defined by the initial reference Time To (300), initiates an Individual Epoch series with a first Individual Epoch start time at lETo (420).

[0195] According to this example, the Individual Epoch start Time at iteration p (IETP) (423) is too close to the next Group Epoch start Time corresponding to iteration n (GETn) (323), i.e. , the difference between the Individual Epoch start Time and the Group Epoch start Time, denoted ATn,P(500), is lower than a predefined threshold. As a consequence and according to the optional step 832 in Figure 8c, the Individual Epoch Start Time IETP(423) is skipped and the CPE parameters are only changed at the beginning of the next Group Epoch start Time GETn(323). Figure 6a schematically illustrates an example of associations of Multi-link devices configured to implement at least some embodiments of the present disclosure.

[0196] According to the illustrated example, the AP MLD 600 offers 2 links (linkl referenced 651 and Iink2 referenced 652) for association. Still according to this example, MLD STA1 611 is associated with the AP MLD 600 and establishes two active links on linkl and Iink2, while MLD STA2 612 also associated with AP MLD 600 only establishes one link (Iink2).

[0197] Figure 6b schematically represents an example of an embodiment of the present disclosure for computing an epoch start time using an AP internal reference clock.

[0198] In order to determine the same instant in time for an EDP epoch start time on every link of every non-AP station belonging to the same EDP group, there is a need for a common time reference.

[0199] To avoid issues during link reconfiguration, this common reference needs not be one of the TSF counters of the setup links.

[0200] According to some embodiments of the present disclosure, the AP uses an internal reference, and indicates the TSF offset value between this reference clock and the TSF counter of the link used for EDP setup procedure, during the EDP setup procedure.

[0201] In the example of Figure 6b, the AP uses an internal reference clock, it being noted that other reference clock or reference time, directly or indirectly under the control of the AP, that may transmit such a reference clock or reference time to the non-AP stations, could be used. Using such a reference clock or reference time has the advantage of being link agnostic. This means that even if any one of the links of a multilink station is reconfigured, or even suppressed, the station can still maintain the synchronization of the epoch start time.

[0202] Upon reception of an EDP Epoch Settings field, for example EDP Epoch Settings field 790 in Figure 7h, the non-AP station stores the transmitted parameters, and especially a TSF offset value (e.g., a TSF offset value contained in the “Link TSF offset” field 792 of EDP Epoch Settings field 790 in Figure 7h), in relation to the considered link. The TSF offset value represents a time offset between the reference clock or reference time directly or indirectly controlled by the AP and a time counter, for example a TSF counter, associated with the link, that is managed by the considered non-AP station and created or updated at the time at which the link is configured or reconfigured. The TSF offset value makes it possible to compute an epoch TSF start time of the considered link from a theoretical epoch reference TSF start time that may correspond to the epoch reference TSF start time of the AP.

[0203] Figure 7i illustrates another embodiment of the invention where the Link TSF Offset 792b represents the offset in terms of number of Epoch intervals elapsed since the start of the Epoch sequence, and the first epoch TSF start time 784b directly gives the reference TSF start time of the considered link.

[0204] Alternatively, the TSF offset value makes it possible to compute an epoch reference TSF start time of the considered link from a theoretical epoch reference TSF start time that may correspond to the epoch reference TSF start time of the AP (or from a first theoretical epoch reference TSF start time corresponding to the first epoch reference TSF start time of the AP). In turn, the epoch reference TSF start time of the considered link makes it possible to compute an epoch TSF start time of the considered link.

[0205] According to a particular embodiment, the TSF offset associated with each link of a non-AP MLD (i.e., the TSF offset of each non-AP station affiliated with a non-AP MLD) is sent by the AP to the corresponding non-AP station. However, since the time differences between the TSF offsets of the non-AP stations affiliated with a non-AP MLD (or the link TSF offsets or the link time offsets), that correspond to the time differences between internal reference time counters of these non-AP stations, are transmitted by the AP to these non-AP stations during setup, only the TSF offset of one non-AP station affiliated with a non-AP MLD needs to be sent, the other non-AP stations affiliated with the non-AP MLD being able to compute their TSF offset as a function of the received TSF offset and of the time differences between the TSF offsets.

[0206] Therefore, in some embodiments, the non-AP MLD only stores the received EDP parameters in relation to the current link, not at the link level. Accordingly, each of the other non-AP stations affiliated with the same non-AP MLD may compute their TSF offset from the received TSF offset and the time difference between the received TSF offset and the TSF offset of the current link. Likely, in case of multi-link reconfiguration changing the TSF offset of the receiving link, the non-AP station may update its TSF offset based on the TSF offset of another non-AP station affiliated with the same non-AP M LD, making it possible for the non-AP to compute the epoch TSF start time of the considered link.

[0207] In some other embodiments, the non-AP MLD stores these parameters at the link level, for all of its link or for one or more other links (i.e., other than the considered link). In such embodiments, the non-AP MLD then converts the received TSF Offset that is related to the current link (i.e., the link used to send the EDP Epoch setting field), to an offset related to each of the other links or to the one or more other links. Accordingly, for a given link, the TSF counter value for this link, corresponding to the EDP Epoch start time, can be determined by using the value of the TSF Offset value between the current link and the link used during the EDP epoch setup procedure, received in the latest Basic Multi-Link element exchange.

[0208] In these embodiments, in case of multi-link reconfiguration, the AP do not have to send an update of the EDP epoch sequence on any link, even if the link used during EDP epoch setup is removed or modified.

[0209] More precisely, for each link and at any point of time, for any EDP epoch number n (n > 0) in an EDP epoch sequence, the start time of the EDP epoch for the receiving link is computed according to the formula:

[0210] EpochLinkTSFStartTime(n) = ReferenceTSFStartTime(n) + TSFOffset + AIT with:

[0211] ReferenceTSFStartTime(n) = FirstReferenceTSFStartTime + n x Epochinterval AIT = int (KDF-Hash-Length(PGTK, "ERCM", ReferenceTSFStartTime(n))) mod RandTR and where: n is the current number of the EDP epoch in the EDP epoch sequence;

[0212] ReferenceTSFStartTime(n) is the TSF counter value for the AP reference corresponding to the start time of the EDP epoch number n in the EDP epoch sequence;

[0213] TSFOffset is the value indicated in the Link TSF Offset field of EDP Epoch Settings Field;

[0214] Epochinterval is the value in TU corresponding to the Epoch Interval Duration field of the EDP Epoch Settings field;

[0215] TSFLink is the current value of the internal TSF counter of the link used during the EDP Epoch Settings exchange;

[0216] KDF-Hash-Length is the key derivation function as defined in IEEE 802.11 series using the hash algorithm identified by the AKM suite selector;

[0217] Length is the number of bits to derive. 64-bits are derived for AIT ;

[0218] FirstReferenceTSFStartTime is the value indicated in the First Epoch TSF Start Time field of the EDP Epoch Settings Field; and RandTR is the value in Til corresponding to the Time Range field, of the EDP Epoch Settings field.

[0219] In some embodiments, the link TSF timer value corresponding to the start time of the EDP epoch number n is called EpochTSFStartTime(n) and is computed according to the formula:

[0220] EpochTSFStartTime(n) = PlannedEpochTSFStartTime(n) for the link + AIT(n)

[0221] PlannedEpochTSFStartTime(n) = FirstPlannedEpochTSFStartTime + (n - EpochNumberOffset) x Epochinterval mod 264

[0222] AIT(n) = int (KDF- / 7as / 7-Lengf / 7(PGTK, "ERCM", Seed + (n x Epoch Interval))) mod TimeRangeTU and where: n is the current number of the EDP epoch in the EDP epoch sequence.

[0223] PlannedEpochTSFStartTime(ri) is the TSF timer value of the link corresponding to the nominal start time of the EDP epoch number n in the EDP epoch sequence. This planned start time (also referred to as Reference start Time) occurs at a regular time interval equal to the epoch interval.

[0224] EpochNumberOffset is the value indicated in the Epoch Number Offset field of the EDP Epoch Settings field.

[0225] Epochinterval is the value in Til corresponding to the Epoch Interval field of the EDP Epoch Settings field.

[0226] KDF-Hash-Length is the key derivation function using the hash algorithm identified by the AKM suite selector.

[0227] Length is the number of bits to derive. 16 bits are derived for AIT.

[0228] FirstPlannedEpochTSFStartTime is the value of the first epoch TSF start time, initialized, upon reception of an EDP element by the STA with the First Epoch TSF Start Time value of the EDP element of the received EDP Epoch Settings field.

[0229] TimeRangeTU is the value in Til corresponding to the value of the Epoch Start Time Variation Range field multiplied by the number of Til in the Epoch Interval Unit field of the EDP Epoch Settings field.

[0230] PGTK is the cryptographic key assigned by an EDP AP MLD that is used to manage the group EDP epoch, distributed to the EDP non-AP MLDs associated with the EDP AP MLD.

[0231] Seed is the Group Epoch Seed field value of the received EDP Epoch Settings field. It is worth noting that in some embodiments, the number of the current Epoch of an EDP epoch sequence can be maintained as a counter starting at 0 for the first epoch of the sequence and incremented by one after the start of the next epoch in the sequence.

[0232] In the example illustrated in Figure 6b, the AP selects the TSF reference 660 as the reference clock for the EDP epoch synchronization. For the sake of illustration, two links are enabled by the AP: link 1 and Iink2, each having respectively a TSF counter 670, and 680.

[0233] In this example, the TSF counter of link 1 started 600 us after the AP reference TSF counter (reference clock), and TSF counter of link 2 started 300 us after the AP reference TSF Counter. Therefore, the TSF offset for link 1 is 600, as indicated with reference 672, and the TSF offset for link 2 is 300, as indicated with reference 682. For sake of clarity, small offset values are used here, but off course they could be much higher (e.g., milliseconds to hours order of magnitude).

[0234] In this example, the ReferenceTSFStartTime(n) is determined as being equal to 10,000us, as indicated with reference 661 , and ATn = 500us. Accordingly, and according to the previous formula, regarding link 1 , the TSF counter value reaches the value 9,400us at ReferenceTSFStartTime(n) time (ReferenceTSFStartTime(n) = 10,000 - 600), as indicated with reference 674, and the corresponding EpochLinkTSFStartTime(n) is equal to 9,900us (EpochLinkTSFStartTime(n) = 10,000 - 600 + 500), as indicated with reference 676. Likewise, regarding link 2, the TSF counter value reaches the value 9,700us at ReferenceTSFStartTime(n) time (ReferenceTSFStartTime(n) = 10,000 - 300), as indicated with reference 684, and the corresponding EpochLinkTSFStartTime(n) is equal to 10,200us (EpochLinkTSFStartTime(n) = 10,000 - 300 + 500), as indicated with reference 686.

[0235] Figure 6c schematically represents an example of a sequence of epochs that start time is computed using an AP internal reference clock, according to an embodiment of the present disclosure.

[0236] Figure 6c follows the same example as Figure 6b, and shows a sequence of epochs of a given epoch sequence according to some embodiments of the disclosure.

[0237] Figure 7a represents a frame format 700 illustrating a STA info field format of a Basic Multi-link information element transmitted by an AP affiliated to an AP MLD as defined by the IEEE 802.11be amendment. Field 710 contains the TSF Offset between links, indicating the TSF offset between the reported link and the link on which the frame is sent.

[0238] The IEEE 802.11 be amendment states that:

[0239] - TSF Offset between links (Toffset) may be sent in the TSF Offset subfield of STA info field of the Basic Multi-Link element, if the TSF Offset Present field of the STA control field is set to 1 ,

[0240] - Clock drift between two APs on a given AP-MLD is limited to ±30 ps

[0241] - Toffset between the TSF timer of the reported AP (TA) and the TSF timer of the reporting AP (TB) is encoded as a 2s complement signed integer with units of 2 ps, and

[0242] - Toffset is calculated as Toffset= Floor ((TA - TB) / 2).

[0243] Figure 7b illustrates an example of an Information Element (IE) 720 containing parameters of a Group Epoch Series according to some embodiments of the disclosure. Information Element (IE) 720 complies with section 9.4.2 of the IEEE 802.11-2020 standard and fields 721 and 722, representing the element identifier and the length of the IE, respectively, are those defined in this standard specification.

[0244] The Group ID field 728 may contain an identifier allowing future modification of the Group Epoch series by sending a broadcast frame containing an IE with the new parameter’s values, for example in a beacon frame (e.g., beacon frame 900 in Figure 9a), in a probe response frame, in an association response frame, or in a Group Epoch Indication frame (e.g., Group Epoch Indication frame 910 in Figure 9a).

[0245] The Policy field 723 may provide some items of information regarding the group Epoch series such as the following: the group Epoch series is Optional for the receiving non-AP station, meaning that the AP put in place this Group Epoch series but the non-AP station may decide to ignore it. In this case, the non-AP station should follow the group Epoch series until it successfully negotiates an individual group Epoch series with an exclusive policy; the group Epoch series is Mandatory for the receiving non-AP station, meaning that the non-AP station should follow the group Epoch series, but the non-AP station may also negotiate a non-exclusive Individual Epoch series with the AP; the group Epoch series is Exclusive for the receiving non-AP station, meaning that the non-AP station has to follow the group Epoch series and cannot request an individual Epoch series; the group Epoch series is Global, meaning that all the CPE parameters of the different links of a MLD non-AP station are changed at the same time; and the group Epoch series is Local, indicating that only the CPE parameters, associated with the link on which the frame is received, are changed.

[0246] For the sake of illustration, field Policy 723 may be encoded as a bitmap, each bit indicating one of the different parameters of the policy (Optional / Mandatory, Exclusive / Non-Exclusive, Global / Local).

[0247] Start Time field 724 indicates the reference time To (e.g., reference time 300 in Figure 3a) of the Group Epoch series.

[0248] Interval 725 indicates the Group Epoch Interval (GEI) of the Group Epoch series.

[0249] Duration field 726 indicates the duration of the Group Epoch series. For the sake of illustration, value 0 for this field may indicate that there is no time limit for the series. This duration may be indicated in a number of iterations, in a Time Unit (TU) value, or in any other time indication units.

[0250] Link Id 727 indicates, in case of a multi-link device, the Link Identifier of the link that is used as time reference for the expression of the reference time To.

[0251] Time Range 729 indicates the range of value the pseudo-random variation AT (e.g., pseudo-random variation ATo 310, ATi 311 , or ATn313 in Figure 3a), may be selected in.

[0252] Figure 7c illustrates an example of a frame format for an Individual Epoch request frame 730, according to some embodiments of the disclosure.

[0253] The Individual Epoch request frame 730 comprises a header as defined in IEEE 802.11 standard. In addition, it comprises a Policy field 731 , a Start time field 732, an Interval field 733, a duration field 734, and a Time Range field 735.

[0254] Policy field 731 indicates how the non-AP station intends to handle the requested Individual Epoch series with regard to potential existing Group Epoch series. The policy may provide one of the following items of information:

[0255] - Exclusive, meaning that the non-AP station will only follow the Individual Epoch series regardless of Group Epoch series or

[0256] - Non-Exclusive, meaning that the non-AP station will follow both the requested

[0257] Individual Epoch series and also any Group Epoch series it belongs to.

[0258] Start time 732 indicates the first Individual Epoch start time of the series that is also used as first reference time ITo (e.g., reference time 400 in Figure 4a). The time reference may be the TSF counter on the link the non-AP station sends the request frame 730.

[0259] Interval 733 indicates the Individual Epoch Interval (IEI) of the requested Individual Epoch series.

[0260] Duration 734 indicates the duration of the Group Epoch series. This duration may be indicated in a number of iterations, in Time Unit (TU) value, or in any other time indication units. According to particular embodiments, the two following values have specific meaning: value 0 indicates that there is no time limit for the series and value 1 indicates that the series contains only one iteration. This specific value allows a non-AP station to request a change of its CPE parameters at a specified instant defined by the value of the Start Time field 732. After this change of CPE parameters, the non-AP station follows the potential Group Epoch series of the groups it belongs to. The usage of this value 1 is especially useful if the non-AP station has to change its CPE parameters upon upper layer request (application request for instance).

[0261] Time Range 735 indicates the range of value the pseudo-random variation AT (e.g., pseudo-random variation AITo 410, AITi 411 , or AITn413 in Figure 4a) may be selected in.

[0262] Figure 7d illustrates an example of a frame format for an Individual Epoch Response frame 740, according to some embodiments of the disclosure.

[0263] The Individual Epoch Response frame 740 comprises a header as defined in IEEE 802.11 standard. In addition, it comprises an Error Code field 750 and, optionally, a Policy field 731 , a Start time field 732, an Interval field 733, a duration field 734, and / or a Time Range field 735.

[0264] Error Code field 750 contains the response of the AP to the Individual Epoch series creation request. If the AP rejects the request of the non-AP station, the fields 731 to 735 may contain an alternative proposal for the Individual Epoch Series creation.

[0265] On the contrary, if the AP agrees on the Individual Epoch series creation for the requesting non-AP station, the Error Code 750 should indicate Success, and the fields 731 to 735 are optionally not present.

[0266] Figure 7e illustrates an example of a frame format for an (Enhanced Data Privacy) Epoch request frame 760, according to some embodiments of the disclosure. Frame 760 has similar fields than frame 730 of Figure 7c. Same reference numbers are used for these fields. Relatively to frame 730, frame 760 has an additional new Group ID field 768 allowing a requester station to notify the responder station the Group I D to which the requester station would like to participate.

[0267] Figure 7f illustrates an example of a frame format for an (Enhanced Data Privacy) Epoch Response frame 770, according to some embodiments of the disclosure. Frame 770 has similar fields than frame 740 of Figure 7d. Same reference numbers are used for these fields. Relatively to frame 740, frame 770 has an additional new Group ID field 778 indicating to a responder station which Group I D is allocated to the requester station.

[0268] Figure 7g illustrates an example of an Information Element (IE) 780 containing parameters of an Epoch series (Individual or Group) according to some embodiments of the disclosure. In embodiments, the Epoch series can be renamed as EDP (Enhanced Data Privacy) Epoch Sequence. Information Element 780 has similar fields than Information Element 720 of Figure 7b. Same reference numbers are used for these fields.

[0269] The Information Element (IE) 780 complies with section 9.4.2 of the IEEE 802.11- 2020 standard and fields 721 , 722 and 781 , representing the element identifier, the length of the IE and the Element ID extension field, respectively, are those defined in this standard specification.

[0270] The Group ID field 788 may contain an identifier allowing future modification of the Epoch series. The Group ID field series is used also to differentiate Individual and Group Epoch sequence. For instance, when the Group ID field is set to 0, the corresponding EDP Epoch Sequence is an individual EDP Epoch Sequence. Otherwise, the Group ID field identifies a Group EDP Epoch sequence.

[0271] The Policy field 783 may provide some items of information regarding the group Epoch series such as the following: the Group EDP Epoch sequence is optional for the receiving non-AP station, meaning that the AP put in place this Group Epoch series but the non-AP station may decide to ignore it. In this case, the non-AP station should follow the Group EDP Epoch sequence until it successfully negotiates an individual EDP Epoch sequence with an exclusive policy; the Group EDP Epoch sequence is Mandatory for the receiving non-AP station, meaning that the non-AP station should follow the Group EDP Epoch sequence, but the non-AP station may also negotiate a non-exclusive Individual EDP Epoch sequence with the AP; the Group EDP Epoch sequence is Exclusive for the receiving non-AP station, meaning that the non-AP station has to follow the Group EDP Epoch sequence and cannot request an individual EDP Epoch sequence; the Group EDP Epoch sequence is Global, meaning that all the CPE parameters of the different links of a MLD non-AP station are changed at the same time; and the Group EDP Epoch sequence is Local, indicating that only the CPE parameters, associated with the link on which the frame is received, are changed.

[0272] For the sake of illustration, field Policy 783 may be encoded as a bitmap, each bit indicating one of the different parameters of the policy (Optional / Mandatory, Exclusive / Non-Exclusive, Global / Local).

[0273] Start Time field 784 indicates the reference time To (e.g., reference time 300 in Figure 3a) of the Group EDP Epoch sequence. The Start Time field may be set to 0 when the corresponding EDP Epoch sequence parameter element is included in an EDP Epoch Sequence request frame sent by a non-AP STA to indicate a request to become a member of the Group EDP Epoch Sequence identified by the Group Identifier field 788.

[0274] Interval 785 (also referred to as Epoch Interval Length) indicates the Epoch Interval (GEI) of the EDP Epoch sequence.

[0275] Duration field 786 indicates the duration of the EDP Epoch sequence. For the sake of illustration, value 0 for this field may indicate that there is no time limit for the series. This duration may be indicated in a number of iterations, in a Time Unit (TU) value, or in any other time indication units. In another embodiment, a special value (for instance the maximum value that the field may take) for this field 726 may indicate that there is no time limit for the sequence. This duration may be indicated in a number of iterations, in a multiple of Time Unit (TU) value, Beacon Interval, or in any other time indication unit. A special value (for instance 0) for this field 786 may indicate that the sender of the frame request to exit from the group. Alternatively or in addition, a special value (for instance 0) for this field may indicate that the recipient of the frame has to leave the group. This may be for example sent prior cancelation of the group. Another special value (for instance 1) may indicate a request for a one-shot change of parameters (not establishing a sequence). In another embodiment, this field only supports the special values, reducing the required size of the field to 2 bits for instance.

[0276] Link Id 787 indicates, in case of a multi-link device, the Link Identifier of the link that is used as time reference for the expression of the reference time To. Time Range 789 indicates the range of value the pseudo-random variation AT (e.g., pseudo-random variation ATo 310, ATi 311 , or ATn313 in Figure 3a), may be selected in.

[0277] Figure 7h illustrates an example of an EDP Epoch Settings Field 790 containing parameters of an Epoch series (Individual or Group) according to some embodiments of the disclosure. According to some embodiments, EDP Epoch Settings Field 790 is transmitted upon EDP epoch setup during association or at any time upon an AP or non- AP station request.

[0278] In this embodiment, the EDP Epoch Settings Field sent from the AP station requesting the inclusion in an existing EDP epoch sequence, or advertising non-AP stations of an existing EDP epoch, may include, in particular, one or several of the three following fields: a control field 791 containing a bitmap, wherein each bit indicates whether a corresponding field is present in the frame, a “Link TSF offset” field 792 containing a time offset, for example as described with reference to Figure 6b, and a transition duration field 793 (or Epoch Transition Period field) indicating the duration of the transition period. The Epoch Transition Period field contains the duration of the transition period expressed in epoch interval units.

[0279] In some embodiments, the transition duration field 793 can be expressed in the same unit as the field duration 786. This makes it possible to have a transition duration in the order of magnitude of the epoch durations. In the case of transmission of the EDP Epoch Settings Field by a non-AP station to request the creation of a group or to join an existing one, the value of the Link TSF Offset is not applicable. In this case, the field may for instance not be present (e.g., the corresponding bit in the control field is set to 0), or may be set to a reserved value (e.g., the maximum value that can be encoded for this field).

[0280] According to some embodiments, the First Epoch TSF Start Time field, referenced 784, may contain the value of the TSF counter of the receiving link at the start time of the first EDP epoch of the sequence (i.e., EDP epoch number 0).

[0281] Still according to some embodiments, the Link TSF offset field, referenced 792, value may be expressed in 2 time units (TUs) and may contain the offset between the AP internal reference clock (or any other time reference) and the TSF counter of the receiving link, at any given time (i.e., TSF Ref -TSF Link).

[0282] Still according to some embodiments, the Time Range field (also referred to as Epoch Start Time Variation Range field), referenced 789, may contain the range of values, expressed in Epoch Interval, used by the AP and each non-AP station member of the EDP group to determine a random delay added to the EDP epoch reference start time (EpochLinkTSFStartTime). In some embodiment, within the EDP element 790, if the Epoch Start Time Variation Range field is present, the Epoch Start Time Variation Range field value does not exceed 20% of the Epoch Interval Length 785 subfield value.

[0283] Figure 7i illustrates an example of an EDP Epoch Settings Field 790 containing parameters of an Epoch series (Individual or Group) according to some embodiments of the disclosure. According to some embodiments, EDP Epoch Settings Field 790 is transmitted upon EDP epoch setup during association or at any time upon an AP or non- AP station request.

[0284] In this embodiment, the EDP Epoch Settings Field sent from the AP station requesting the inclusion in an existing EDP epoch sequence, or advertising non-AP stations of an existing EDP epoch, may include, in particular, one or several of the three following fields: a Group Epoch Seed 782 field containing a seed selected by the AP for pseudo rando computation. In some embodiments, the Group Epoch Seed field is present only if the First Epoch TSF Start Time field 784b is present. If the Group Epoch Seed field is present, the Group Epoch Seed field value is the same for each transmission to any member of an EDP group for a given EDP Epoch sequence. In some embodiment, the Group Epoch Seed field 782 value is set to different values for two different EDP Epoch sequences. The Group Epoch Seed field value can be for instance set to a value representative of the creation time of the EDP epoch sequence. a First Epoch TSF Start Time field 784b containing the first planned epoch TSF start time presented as the TSF timer value of the link in which this field was sent. - An Epoch Number Offset field 792b that contains the epoch number n of the epoch with a planned epoch start time equal to the First Epoch TSF Start Time field 784b value on the receiving link. In some embodiments, the Epoch Number Offset field 792b is present only if the First Epoch TSF Start Time field 784b is present.

[0285] According to some embodiments, the First Epoch TSF Start Time field, referenced 784b, may contain the value of the TSF counter of the receiving link at the start time of the first EDP epoch of the sequence (i.e., EDP epoch number 0).

[0286] Still according to some embodiments, the Link TSF offset field, referenced 792b, value may be expressed in 2 Tils and may contain the offset between the AP internal reference clock (or any other time reference) and the TSF counter of the receiving link, at any given time (i.e., TSF Ref -TSF Link).

[0287] Figure 8a illustrates an example of steps carried out in a non-AP station implementing some embodiments of the disclosure, upon waking up after a sleep period. After waking up from a sleep period, a non-AP station should be sure to use the right CPE parameters’ values, otherwise it may discard frames dedicated to it or may face rejection of its transmitted frames to the AP. The reason is that during a long period of time, several Epochs may have elapsed, or the AP may have changed the Group Epoch parameters for instance.

[0288] During step 800, the non-AP station determines the latest group Epoch parameters. This can be done by checking its internal memory, or by waiting at least the reception of one beacon (e.g., beacon 900 in Figure 9a) to recover the latest Group Epoch parameters information.

[0289] Next, during step 812, the non-AP station determines the current iteration number n of the Group Epoch series. Step 812 is similar to step 202 and thus, the non-AP station may use, for instance, the formula 332 in Figure 3b: n = [(current TSF -To- RefLink Offset) I GEI] where:

[0290] To and GEI are part of the Group Epoch series parameters, and

[0291] RefLink Offset = offset of the TSF counter of the current link compared to the Reference Link (of id RefLink ID) with a 2 ps resolution.

[0292] To is the value of the first reference time for the Epoch on the Reference Link. Again, it is noted that if no beacon is received on current link (Multi-link Power save mode for instance), no direct reading of RefLink Offset is available via the TSF Offset (e.g., TSF Offset 710 in Figure 7a). This is also the case, as illustrated in Figure 6, if the reference link selected by the AP MLD 600 is the Link!

[0293] In that case, RefLink Offset may be approximated using 2 TSF Offsets fields (e.g., TSF Offset 710 in Figure 7a) of the Basic MultiLink info element received on a reporting link:

[0294] - TSF Offset field for RefLink in received beacon: TSF OffsetRefLink = FIOOr((TSFRefLink TSFReporting) / 2).

[0295] RefLink Offset = 2 x TSF OffsetRefLink

[0296] =2 X FlOOr ((TSFRefLink - TSF current) / 2)

[0297] ~ FlOOr ((TSFRefLink - TSF reporting) / 2) FIOOT ((TSFcurrent " TSFReporting ) / 2)

[0298] « 2x (TSF OffsetRefLink - TSF Offsetcurrent)

[0299] In addition, the current Group Epoch start Time (GETn, i.e., the time when the current Group Epoch of iteration number n started) is determined during step 812, for example according to the formula 330, in Figure 3b, as explained with reference to step 204 in Figure 2a, but using the iteration number n as determined in step 812 without incrementing it.

[0300] Next, at step 814, the non-AP station recovers the Individual Epoch series parameters stored in its internal memory (being noted that these values cannot be modified during the non-AP station sleep), like in step 210 in Figure 2b. If these values are not null (i.e., the Individual Epoch series has been set up), the non-AP station determines, during step 816, the current iteration number p of the Individual Epoch series, for example by applying formula 432 in Figure 4b that is very similar to the formula used at step 812 except that the Epoch series parameters corresponds to the individual Epoch series. Formula 432 is the following: p = [(current TSF -IT0- RefLink Offset) 1 1 El] where ITO correspond to the first Individual Epoch start time of the series and I El correspond to the Individual Epoch Interval, these two values being part of the Individual Epoch series parameters exchanged (for example exchanged in the frame 730 or 740 in Figure 7c or 7d) during the Individual Epoch series negotiation (as described with reference to Figure 9b). Reflink Offset and current TSF have the same signification as in previous step 812.

[0301] Next, during step 818, the non-AP station determines the current CPE parameters’ values it should use. To that end, it is first determined which of the Group Epoch start Time (GETn) and Individual Epoch Start Time (IETP) occurred the more recently. Then, the current CPE parameters’ values to apply are determined, for example by applying the step 206 for computing CPE parameters based on Group Epoch parameters values or 216 respectively for CPE parameters values computed based on Individual Epoch parameters values.

[0302] In some embodiments, an Epoch starts with a transition period during which both the new and old CPE parameters’ values may be used for a given non-AP station. In such embodiments, optional step 820 is carried out to determine previous CPE parameters’ values that correspond to the old CPE parameters’ values that may still be valid. This step may be performed by carrying out steps similar to steps 814 and 818 with a respective value of iteration of n-1 and p-1 .

[0303] Next, during step 820, it is determined which of the GETn, GETn-i, IETnand IETn. 1 occurred the latest before the time determined at step 818. Then, the associated CPE parameters’ values are computed, for example according to step 206 or 216, with the corresponding iteration number.

[0304] Finally, the determined Current CPE parameters’ values are applied as new CPE parameters’ values (step 850) and potentially the previous CPE parameters’ values as the old CPE parameters’ values.

[0305] Figure 8b illustrates an example of steps carried out in a station (AP station or a non-AP station belonging to the group) implementing some embodiments of the disclosure, when a Group Epoch timer expires.

[0306] When a Group Epoch Timer expires, this means that a new Group Epoch of a Group Epoch series is starting.

[0307] At step 822, similar to step 820, the station recovers some of the parameters’ values computed in steps 204 and 206 in Figure 2a or in Figure 8b (in a previous iteration), including the value of the current iteration n, the value of the reference time Tn(e.g., reference time 303 in Figure 3a), and the values of all the CPE parameters.

[0308] Next, the station applies the recovered CPE parameters’ values at step 851 , similar to step 850. This step is out of scope of the current disclosure but covers for instance the change of the current MAC address of a non-AP station, and the obfuscation of the PN or SN parameters. In some embodiments, the start of a new Epoch is made of a transition period during which the old and new set of CPE parameters’ values may be used. In such embodiments, the current CPE parameters’ values replace the old CPE parameters’ values, and are replaced by the new CPE parameters’ values previously computed. In the case of an AP station, the change of CPE parameters’ values is made for each non-AP station belonging to the group.

[0309] Next, during step 204, the station computes the next Group Epoch start Time of the Group Epoch series. To that end, the station first recover the latest Group Epoch series parameters’ values stored in memory (as described with reference to step 800 in Figure 8a) and then computes the next Group Epoch start Time, for example using the formula 330 in Figure 3b that reads as follows:

[0310] GETn=Tn+ ATn+ RefLink Offset as described by reference to step 204 in Figure 2a.

[0311] Next, during step 206, the station computes the next CPE parameters’ values. In the case of an AP, the AP computes the next CPE parameters’ values for each non-AP station belonging to the group. In the case of a non-AP station, the non-AP station only computes its own CPE parameters’ values. The generation of the CPE parameters’ values is out of scope of the current disclosure, but as described above, an example of generic formula to generate the CPE parameters’ values for a given non-AP station is given in formula 334 in Figure 3b that reads as follows:

[0312] CPE-Param = PRF-M\L(PTK*, “ERCM”, Tn) as described by reference to step 206 in Figure 2a.

[0313] Next, during step 208, the station stores in memory all the computed CPE parameters’ values. In the case of an AP station, it stores all the CPE parameters’ values of each of the non-AP stations belonging to the group. In some embodiments, the station also stores the value of n and Tnas computed in step 204, but also the value of the GETn. 1 corresponding to the start time of the current Epoch (this value being used in optional step 832 in Figure 8c).

[0314] Figure 8c illustrates an example of steps carried out in a station (AP station or a non-AP station) implementing some embodiments of the disclosure, when an Individual Epoch timer expires.

[0315] When an Individual Epoch Timer expires, this means that a new Individual Epoch of an Individual Epoch series is starting for the associated non-AP station.

[0316] During a first step (step 830), the station recovers some of the parameters’ values computed in step 214 in Figure 2b or in step 835 in Figure 8c (in a previous iteration) and in step 216 in Figure 2b or in Figure 8c (in a previous iteration), including the value of the current iteration n, the value of the reference time ITP(e.g., the value of the reference time 403 in Figure 4a), and the values of all the CPE parameters. During optional step 832, the station determines whether the current Individual Epoch start time is too close or not to the last or the next Group Epoch start time. This optional step ensures that a non-AP station will not change too rapidly of CPE parameters to avoid overlapping transition periods for the same non-AP station, that would create unstable behaviour where the station should support more than one old and one new CPE parameters set values. To that end, the station computes the minimum value of the time difference, denoted ATn,P(referenced 500 in Figure 5), between the current IETP(referenced 423 in Figures 4a and 5) and the next GETn(referenced 323 in Figures 323 and 5) stored in memory at step 208 in Figures 2a and 8b, and of the time difference between the current IETPand the previous GETn-i stored in memory at step 208 in Figures 2a and 8b (or computed using the formula 330 in Figure 3b). If this difference is over a predefined threshold, there is no Epoch collision and step 821 is executed, otherwise, the values of the CPE parameters are not changed (i.e. , step 821 is skipped) and step 835 is executed.

[0317] At step 821 , the station applies the recovered CPE parameters. This step is out of scope of the current disclosure but covers for instance the change of the current MAC address of a non-AP station, and the obfuscation of the PN or SN parameters. In some embodiments, the start of a new Epoch is made of a transition period during which the old and new set of CPE parameters’ values may be used. In such embodiments, the current CPE parameters’ values replace the old CPE parameters’ values, and are replaced by the new CPE parameters’ values previously computed.

[0318] At step 835, the station computes the next Individual Epoch start Time (IET) of the Individual Epoch series. To that end, the station first recovers the latest Individual Epoch series parameters’ values stored in memory (as described by reference to step 814 in Figures 2b and 8a) and then computes the next Individual Epoch start Time using, for example, the formula 430 in Figure 4b that reads as follows:

[0319] IETn=ITn+ AITn+ RefLink Offset where: n is the iteration number that is incremented by one (i.e., n=n+1) compared to the recovered value. In some embodiments, the value of n is not determined based on a stored value, it is directly computed using the formula 432 in Figure 4b;

[0320] ITnis the reference time at iteration n, that may be determined using, for example one of the formulas 431 in Figure 4b. In some embodiments, the value ITnis obtained thanks to the previous values stored in memory at step 218 in Figure 2b or 8c (in a previous iteration) during the computation of the CPE parameters’ values according to the following formula: ITn=ITn-i + I El

[0321] In some embodiments, ITnis computed using the initial reference time ITo (e.g., reference time 400 in Figure 4a) and the iteration value n according to the following formula: ITn=ITo + (n x IEI);

[0322] - AITnis a pseudo-random variation time at iteration n. For the sake of illustration, it may be computed using a shared pseudo-random generation function taking input parameters in parameters shared among the AP station and the non-AP station, and at least the Reference Time IT n. On example of generation of AITnis indicated in the formula 433 in Figure 4b:

[0323] AITn=PRF-128\64(PTK*, “ERCM”, ITn) mod (Time range) where the PRF-128 function is as defined in the IEEE 802.11 series. In this example, the function generates 128 pseudo-random bits and only the first 64 ones are kept to generate AITn(as indicated with the 128\64 notation). In this example, the secret key PTK* used as input of the function derivates from the PTK that is a key generated by the AP and the non-AP stations upon association, and then is known only by the non-AP station and the AP station. The last input parameter “ERCM” is a context indicating that the generation is dedicated to the Enhanced Randomized and Changing MAC address feature. Finally, in order to obtain a time duration AITnin a predefined duration range of a Time Range value (e.g., Time Range value 735 in Figures 7c and 7d), the pseudo-random generation result is computed modulo the Time Range value. This formula is only provided as an example, other pseudo-random generation functions shared by the AP station and the non-AP station may be used. Other input parameters can also be used, the key point being to generate a AITnvalue that is predictable for the AP station and the non-AP station.

[0324] RefLink Offset is as defined in step 812 in Figure 8a.

[0325] After the determination of the next IET, the station initiates, at step 215, a timer that expires at the next Individual Epoch Start Time.

[0326] Next, during step 216, the station computes the next CPE parameters’ values. In the case of an AP station, the AP station computes the next CPE parameters’ values for the non-AP station associated with this Individual Epoch start Time. In the case of a non- AP station, the non-AP station computes its own CPE parameters’ values. The generation of the CPE parameters’ values is out of scope of the current disclosure, but an example of generic formula to generate the CPE parameters’ values for a given non- AP station is provided with formula 434 in Figure 4b that reads as follows:

[0327] CPE-Param = PRF-M\L(PTK*, “ERCM”, ITn)

[0328] In this example, a pseudo-random generation function generating M pseudorandom bits is used and L bits are used (as indicated with the M\L notation) to create all the CPE parameters’ values for a given non-AP station. The private key PTK* used to generate the CPE parameters for a given non-AP station is derived from the PTK that is a secret key created during association process and that is only known by the non-AP station and the AP station. Other input parameters are identical to those used in formula 333 in Figure 3b.

[0329] At step 218, the station stores in memory all the computed CPE parameters’ values. In the case of an AP station, it stores all the CPE parameters’ values of the non- AP station. In some embodiments, the station also stores the value of n and Tn, as computed in step 835.

[0330] In another embodiment, since the same function is used with the same inputs to generate both the AITnand the CPE-Parameters, step 216 is executed at the same time as step 835 by calling the PRF function only once. A generic example of this function is described in formula 435 in Figure 4b that reads as follows:

[0331] (CPE-Paramn, AITn) = PRF-M\L(PTK*, “ERCM”, ITn)

[0332] After this call, AITnis computed modulo the Time Range value 735.

[0333] Figure 9a illustrates an example of a frame sent by an AP station to one or more non-AP stations to indicate the parameters of a Group Epoch series according to some embodiments of the disclosure. This procedure, called Group EDP Epoch advertisement, allows an AP MLD to provide same EDP Epoch parameter set to one or more of its associated non-AP STA.

[0334] In a first embodiment, the AP sends a beacon frame 900 that may be broadcasted in clear, or send to one or more non-AP stations associated with it and encrypted.

[0335] In a second embodiment, the AP may send a Group Epoch Indication frame 910, 911 , or 912 to a non-AP station or to a group of non-AP stations. In one embodiment, the Group Epoch Indication frames 910, 911 , or 912 are dedicated protected Action frames (910, 911 , 912) used during Group EDP Epoch advertisement process. For Group EDP Epoch advertisement, the usage of dedicated protected Action frames during Group EDP Epoch advertisement process for an AP MLD allows to provide same EDP Epoch parameter set to one or more of its associated non-AP STAs. Upon reception of one of these frames 900, or 910 to 912, the non-AP station stores the Groups Epoch series parameters in its internal memory for future use.

[0336] Figure 9b illustrates an example of frame exchange between a non-AP station and the AP station it is associated with to request creation of an Individual Epoch series according to some embodiment of the disclosure. This procedure called individual EDP Epoch negotiation process, allows to negotiate the EDP Epoch parameter set between a non-AP MLD and its associated AP MLD.

[0337] When a non-AP station determines that it needs an Individual Epoch series, for instance due to different privacy requirements compared to the level of privacy offered by the AP station (typically the frequency of CPE parameters changes), a non-AP station sends an Individual Epoch Request frame 930 (e.g., according to Individual Epoch request frame 730 of Figure 7c) to the AP station it is associated with. In the case of multi-link devices, this request is sent through one of the active links between the AP MLD and the non-AP MLD. The starting time (e.g., starting time 732 in Figures 7c and 7d) is evaluated compared to the TSF counter associated with this link. In response to the Individual Epoch Request frame 930, the AP station may receive from the AP station an Individual Epoch Response frame 940 (e.g., according to Individual Epoch response frame 740 of Figure 7d) that may comprise an agreement or an alternative proposal for the Individual Epoch Series creation, as described above.

[0338] In one embodiment, the frames 930 and 940 are dedicated protected Action frames during an individual EDP Epoch negotiation process. For individual EDP Epoch negotiation, the usage of dedicated protected Action frames during an individual EDP Epoch negotiation process allows to negotiate the EDP Epoch parameter set between a non-AP MLD and its associated AP MLD.

[0339] Figure 9c illustrates an example of frame exchange between a requester station and a responder station to request creation of an EDP Epoch sequence according to some embodiment of the disclosure. The EDP Epoch sequence is an Individual EDP Epoch sequence if, for example, the Group I D field 788 of Figure 7e is set to 0 or a Group EDP Epoch sequence otherwise. When the requester station is a non-AP MLD, in that case the responder is an AP MLD with which the non-AP MLD is associated. On the reverse, when the requester station is an AP MLD, the responder is a non-AP MLD. This procedure called EDP Epoch negotiation process, allows to negotiate the EDP Epoch parameter set between a non-AP MLD and its associated AP MLD. When a requester station determines that it needs an EDP Epoch sequence, for instance due to different privacy requirements compared to the level of privacy offered by the BSS (typically the frequency of CPE parameters changes), a requester station sends an EDP Epoch Request frame 950 (e.g., according to EDP Epoch request frame 760 of Figure 7e) to the responder station. In the case of multi-link devices, this request is sent through one of the active links between the requester MLD and the responder MLD. The starting time (e.g., starting time 732 in Figure 7c, or 732 in Figure 7e) is evaluated compared to the TSF counter associated with this link. If the requester station wants to join an already created Group EDP Sequence, the Starting Time is set to 0. In response to the EDP Epoch Request frame 950, the requester station may receive from the requester station an EDP Epoch Response frame 960 (e.g., according to EDP Epoch response frame 770 of Figure 7f) that may comprise an agreement or an alternative proposal for the EDP Epoch sequence creation, as described above.

[0340] In one embodiment, the frames 950 and 960 are dedicated protected Action frames during an EDP Epoch negotiation process. For EDP Epoch negotiation, the usage of dedicated protected Action frames during an EDP Epoch negotiation process allows to negotiate the EDP Epoch parameter set between a non-AP MLD and its associated AP MLD.

[0341] In another embodiment, the requester station is an EDP AP station and the responder is an EDP non-AP station. Upon the reception of an EDP Epoch Sequence Request frame containing an EDP Epoch Sequence parameters element 780 of Figure 7g with the Group ID field not set to 0, an EDP non-AP STA sends an EDP Epoch Sequence Response frame to acknowledge or not the membership to the Group EDP Epoch sequence defined in the just received EDP Epoch Sequence Request frame. The Group Identifier field of the EDP Epoch Sequence Response frame is set to the same value of the Group Identifier field of the just received EDP Epoch Sequence Request frame. The other fields of the EDP Epoch Sequence parameters element of the an EDP Epoch Sequence Response frame are reserved.

[0342] In another embodiment, the requester station is an EDP non-AP station and the responder is an EDP AP station. When an EDP non-AP STA sends an EDP Epoch Sequence Request frame containing an EDP Epoch Sequence parameters element 780 of Figure 7g with the Group ID field not set to 0, the EDP non-AP STA intends to withdraw its membership to the group identified by the Group Identifier field. Upon the reception of this EDP Epoch Sequence Request frame, an EDP AP STA sends an EDP Epoch Sequence Response frame to acknowledge or not the withdrawal of the EDP non-AP STA to the EDP Epoch sequence defined in the just received EDP Epoch Sequence Request frame.

[0343] Figure 10 schematically illustrates an example of a communication device that may correspond any of the stations described by reference to Figure 1 , of a wireless network, configured to implement at least some embodiments of the disclosure. The communication device, referenced 1000, may preferably be a device such as a microcomputer, a workstation, or a light portable device. Communication device 1000 may comprise a communication bus 1013 to which may be connected:

[0344] - a central processing unit 1001 , such as a processor, denoted CPU;

[0345] - a memory 1003, denoted MEM, 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

[0346] - at least two communication interfaces 1002 and 1002’ connected to the wireless communication network, for example a communication network according to one of the IEEE 802.11 family of standards, via transmitting and receiving antennas 1004 and 1004’, respectively.

[0347] Preferably, communication bus 1013 may provide communication and interoperability between the various elements included in the communication device 1000 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 1000 directly or by means of another element of the communication device 1000.

[0348] 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 1002 or 1002’, in order to be stored in the memory 1003 of communication device 1000 before being executed.

[0349] In some embodiments, communication device 1000 may be a programmable apparatus which uses software to implement embodiments of the disclosure. However, alternatively, some embodiments of the disclosure may be implemented, totally or in partially, in hardware (for example, in the form of an Application Specific Integrated Circuit or ASIC). Embodiment(s) of the disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a “non-transitory computer-readable storage medium”) to perform the functions of one or more of the above-described embodiment(s) and / or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and / or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard-disk, a random-access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), etc.), a flash memory device, a memory card, and the like.

[0350] Expressions such as “comprise”, “include”, “incorporate”, “contain”, “is” and “have” are to be construed in a non-exclusive manner when interpreting the description and its associated claims, namely construed to allow for other items or components which are not explicitly defined also to be present. Reference to the singular is also to be construed in be a reference to the plural and vice versa.

[0351] A person skilled in the art will readily appreciate that various parameters disclosed in the description may be modified and that various embodiments disclosed may be combined without departing from the scope of the disclosure.

Claims

46CLAIMS1. A method for determining a time at which a value of a parameter of a non-access point, AP, station affiliated with a non-AP multi-link device, MLD, is to be modified, the method comprising, at the non-AP station configured to communicate over a link with an AP affiliated with an AP MLD: obtaining an offset, relatively to a time reference at the AP, associated with the link; and determining a time at which a value of the parameter is modified, wherein the time is determined as a function of the offset and of a counter of the affiliated station, the counter being associated with the link.

2. The method of claim 1 , wherein the obtaining comprises receiving the offset from the AP, over the link.

3. The method of claim 1 or claim 2, wherein the offset represents time units.

4. The method of claim 1 or claim 2, wherein the offset represents an Epoch number offset indicating a number of Epoch intervals since Epoch start time on the link.

5. The method of claim 4, wherein the Epoch number offset is received during setting Enhanced Data Privacy, EDP, parameters within the affiliated station.

6. The method of claim 5, wherein the Epoch number offset is received within a set of Enhanced Data Privacy, EDP, parameters of a Group Epoch Sequence, in response to assigning the affiliated station to the Group Epoch Sequence or to a request from the affiliated station to create or to join the Group Epoch Sequence.

7. The method of claim 1 , wherein the obtaining comprises determining the offset as a function of another offset received by another non-AP station affiliated with the non-AP MLD from the AP over another link and a link offset between the link and the other link.

8. The method of claim 7, wherein the offset represents time units.

479. The method of claim 7, wherein the offset represents an Epoch number offset indicating a number of Epoch intervals since Epoch start time on the link.

10. The method of claim 9, wherein the link offset is received from the AP during setup of the link.

11. The method of any one of claims 1 to 10, wherein the time is further determined as a function of a reference start time based on the time reference.

12. The method of claim 11 , further comprising determining the reference start time.

13. The method of any one of claims 1 to 12, wherein the time is further determined as a function of a pseudo-random variation time.

14. The method of any one of claims 1 to 13 wherein the offset is a difference between the time reference and the counter, at a given time.

15. The method of any one of claims 1 to 14, further comprising, if the link is reconfigured, computing an updated value of the offset as a function of another offset obtained from another non-AP station affiliated with the non-AP MLD and a link offset between the link and another link linking the other non-AP station to the AP.

16. The method of any one of claims 1 to 15, wherein the counter is a Timing Synchronization Function, TSF, counter.

17. The method of any one of claims 1 to 15, wherein the counter is n Epoch Interval counter.

18. The method of any one of claims 1 to 17, wherein the time reference is based on an internal reference clock of the AP.

19. A computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing each of the steps of themethod according to any one of claims 1 to 18 when loaded into and executed by the programmable apparatus.

20. A non-transitory computer-readable storage medium storing instructions of a computer program for implementing each of the steps of the method according to any one of claims 1 to 18.

21. A processing unit in a non-access point, AP, multi-link device, MLD, for determining a time at which a value of a parameter of a non-AP station affiliated with the non-AP MLD is to be modified, the processing unit being configured to carry out each of the steps of the method according to any one of claims 1 to 18.

Images