EP4702688A1 - Enhanced reliability using duplicate transmission through multi-link operation - Google Patents

Abstract

A method for redundant transmission over a first and a second link comprising receiving a first MAC service data unit, MSDU, via a service access point, SAP, on an upper MAC sublayer of a first multi-link device, forwarding a first duplicate of the first MSDU to a first station, STA, on a lower MAC sublayer of the first multi-link device, and forwarding a second duplicate of the first MSDU to a second station on the lower MAC sublayer of the first multi-link device, creating, by the first station, a first header for a first MAC protocol data unit, MPDU, with the MAC address of the first station, the first MPDU comprising the first duplicate, and creating, by the second station, a second header for a second MPDU with the MAC address of the second station, the second MPDU comprising the second duplicate.

Description

Description

TITLE

Enhanced Reliability Using Duplicate Transmission Through

Multi-Link Operation

TECHNICAL FIELD

Wi-Fi is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and internet access, allowing nearby digital devices to exchange data by radio waves.

BACKGROUND

In industrial plants, like production facilities, deterministic wireless communication guaranteeing worst case latency and jitter and providing high reliability is required. Wi-Fi provides the technological basis for deterministic transmissions, but suffers from major problems such as non-determini- stic channel access of devices and interference during ongoing transmissions. A solution for the channel access problem is proposed in European patent application EP23160772.2 with the extension of MU EDCA, i.e. Multi-User (MU) Enhanced Distributed Channel Access (EDCA) , that allows the access point, AP, to access a channel with an upper bounded delay, e.g., of 55ps . Furthermore, wireless communication is prone to interference from outside the Basic Service Set (BSS) . This is either caused by other Wireless Local Area Networks, WLANs, in range or from alternative wireless access technologies, such as 5G, Bluetooth, or the like, operating in the same frequency band.

SUMMARY

The present disclosure intends to mitigate the effect of interference, in particular for 802.11be Wi-Fi networks, i.e. using Multi-Link Operation, MLO.

According to a first aspect a method for redundant transmission over a first and a second link is proposed. The method comprising receiving a first MAC service data unit , MSDU, via a service access point on an upper MAC sublayer of a first multi-link device . The method further comprising forwarding a first duplicate of the first MSDU to a first station on a lower MAC sublayer of the first multi-link device , and forwarding a second duplicate of the first MSDU to a second station on the lower MAC sublayer of the first multi-link device . The method further comprising creating, by the first station on the lower MAC sublayer, a first header for a first MAC protocol data unit , MPDU, with the MAC address of the first station, the first MPDU comprising the first duplicate , and creating, by the second station, a second header for a second MPDU with the MAC address of the second station, the second MPDU comprising the second duplicate .

According to a second aspect a method of redundant reception over a first and a second wireless link is proposed . The method comprising receiving a first MPDU with a MAC address of the first MLD and comprising a first duplicate of a first MSDU by a third station on a lower MAC sublayer of a second multi-link device , preferably via the first link, and receiving a second MPDU with a MAC address of the second MLD and comprising a second duplicate of the first MSDU by a fourth station on the lower MAC sublayer of the second multilink device , preferably via the second link .

According to a third aspect a first multi-link device , preferably comprising a processor and a memory, operative to perform the methods steps of the first aspect is proposed .

According to a fourth aspect a second multi-link device , preferably comprising a processor and a memory, operative to perform the method steps of the second aspect is proposed .

According to fi fth aspect a system for redundant transmission over a first and a second link between a first multi-link device according to the third aspect and a second multi-link device according to the fourth aspect is proposed . According to a sixth aspect a computer program comprising program code that when executed performs the steps according to the first aspect and/second aspect is proposed.

Thus, a duplication mechanism is proposed which sends multiple copies of the same data unit, i.e., duplicates, over different links by a transmitting multi-link device, MLD, and/or eliminates duplicates at the receiving MLD. For example, in case one of two or more independent links experience interference during a transmission and one or more data units, i.e. frames, are lost on that link, the second link might still transmit the duplicated data unit(s) successfully. The proposed multi-link operation duplication and/or elimination mechanism increases the probability of a successful transmission, for example, assuming non-overlapping spectrum resources, and thus increases the reliability of critical transmissions, e.g. in in Wi-Fi 7 networks.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an illustration of a first and a second multilink device in multi-link operation.

Figure 2 shows an illustration of a MAC architecture of a multi-link device.

Figure 3 shows an illustration of a physical layer packet data unit, PPDU, a MAC layer packet data unit, MPDU, and a MAC layer service data unit, MSDU.

Figure 4 shows an illustration of exemplary multi-link devices and the affiliated stations.

Figure 5 shows an illustration of a multi-link device redundantly transmitting duplicate MAC packet data units.

Figure 6 shows an illustration of a multi-link device receiving duplicate MAC packet data units.

Figure 7 shows two multi-link devices applying MAC packet data unit duplication and elimination on two links and non-redundant on a single link.

Figure 8 shows an illustration of a management frame. Figures 9 to 26 show exemplary method steps according to various embodiments.

DETAILED DESCRIPTION OF THE DRAWINGS

For the continuing evolution of Wi-Fi networks, the next generation of IEEE 802.11 wireless local area network (WLAN) technology, named Extremely High Throughput (EHT) , is under development by the 802.11be task group of IEEE (TGbe) , and is expected to be adopted by the Wi-Fi Alliance as Wi-Fi 7. EHT focuses on achieving an extreme increase in the peak throughput up to 30 Gbps, which is three times higher than that of Wi-Fi 6, while simultaneously reducing latency.

Multi-Link Operation, MLO, is a mandatory feature for IEEE 802.11be devices, cf. IEEE 802.11be D3.1 Annex B.4.3. MLO is planned for Release 1 of IEEE 802.11be. The first devices supporting IEEE 802.11be will also be available at that time.

MLO allows a multi-link device, MLD, to create up to 16 links which can be coordinated independently as shown in Figure 1. An MLD is a device with multiple PHY interfaces sharing the same interface to the Logical Link Control, LLC. Therein, a station, STA, is a logical entity that is a singly addressable instance of a medium access control, MAC, and physical layer PHY interface to the wireless medium.

IEEE 802.11be D3.1 defines standardized modifications to both the IEEE Std 802.11 physical layers (PHY) and the Medium Access Control Layer (MAC) that enable at least one mode of operation capable of supporting a maximum throughput of at least 30 Gbit/s, as measured at the MAC data service access point (SAP) , with carrier frequency operation between 1 and 7.250 GHz while ensuring backward compatibility and coexistence with legacy IEEE Std 802.11 compliant devices operating in the 2.4 GHz, 5 GHz, and 6 GHz bands. This amendment defines at least one mode of operation capable of improved worst case latency and jitter. In general, frame duplication and elimination increases the reliability of packet transmissions by sending copies of packets via disjoint links and eliminating duplications of the packets at receiver side. Notable examples of such duplication are IEEE 802.1CB Frame Replication and Elimination (ERE) , (industrial) Parallel Redundancy Protocol, (i)PRP, Broadcasting frames in IEEE 802.11 mesh networks, and 3GPP PDCP, TS 138 323 - V16.2.0 - 5G. The current version of the standard IEEE 802.11be Draft 3.1, available since March 2023, and the examples of the state of the art do not provide a specification for packet duplication using multi-link operation in 802.1 Ibe-compliant networks. More specifically, a frame duplication mechanism at the transmitting MLD, frame identification for duplicated frames and a duplication elimination mechanism at the receiving MLD are missing. Thus, an extension of the IEEE 802.11be based Multi-Link Operation mechanism is proposed herein that enables frame duplication. In the OSI model of computer networking, a frame is the protocol data unit at the data link layer. The data link layer is divided into two sublayers: logical link control LLC and media access control, MAC.

Multi-link operation, MLO, is the concurrent utilization of multiple radio links of different frequency channels/bands by a multi-link device, such as an access point, AP, a client, or both. It is a MAC-layer solution for concurrently using multiple links and thus exposes a single MAC service access point, SAP, to the upper sublayer of the data link layer, i.e., the logical link control, LLC, layer. Thus, the MAC SAP (function) provides one or more services to the LLC sublayer.

Each link of an MLD is regarded as a conventional single-link station, STA, and an MLD is considered to be a device affiliated with more than one STA. A station, STA, can be an access point, AP, or non-access point, non-AP, STA that provides link-specific, lower medium access control, MAC, and physical layer, PHY, services within an MLD. MLDs can thus be further classified into two types based on the type of the affiliated STAs . Firstly, an AP multi-link device , AP MLD : each of the af filiated STAs is an AP . Secondly, Non-AP multi-link device non-AP MLD : each of the af filiated STAs is a non-AP client STA.

To support Multi-Link Operation, MLO, for example in IEEE 802 . 11be devices , the architecture has been changed to logically separate the MAC layer into two sublayers called Upper MAC and Lower MAC as shown in Figure 2 . The Upper MAC sublayer provides functionalities which are common across all links whereas the Lower MAC sublayer is responsible for functionalities which are bound to a speci fic link .

In order to allow Multi-Link Devices , MLDs , to use multiple radios simultaneously the IEEE 802 . 11be standard requires MLDs to support MAC-layer functionalities both individually per interface ("Lower MAC" ) and commonly for all its interfaces ("Upper MAC" ) . The Upper MAC functionalities include for example :

Authentication and association

Selection of the MLD lower MAC sublayer for transmission Merging reception of packets from two or more links Coordination of distribution and management of EDCA parameters across the MLD lower MAC sublayers of the links .

Lower MAC functionalities include for example :

Link speci fic control information exchange like RTS / CTS or ACKs

Power save state and mode

Some of the functionalities described above require j oint processing among Upper and Lower MAC . For the success ful transmission and/or reception of duplicated frames , mainly the Upper MAC layer has to incorporate additional features .

Each af filiated STA of an MLD comprises a PHY and lower MAC components . On top of the set of af filiated STAs , an MLD has one upper MAC component to aggregate its set of affiliated STAs and provide LLC with a single MAC SAP.

Turning to Figure 3, encapsulation of an MAC service data unit, MSDU, into a MAC packet data unit, MPDU, and of an MPDU into a physical packet data unit, PPDU, is shown. A MAC service data unit, MSDU, is the service data unit that is received from the logical link control, LLC, sub-layer which lies above MAC layer in a protocol stack. The LLC and MAC sub-layers are collectively referred to as the data link layer, DLL.

Now, when the LLC sublayer sends the MSDU to the MAC sublayer, the MAC header information is added to the MSDU to identify it. The MSDU is then encapsulated in a MAC Protocol Data Unit, MPDU. A MSDU may be regarded as a payload of a MPDU. The MSDU may contain an IP packet, and additionally some LLC data. Thus, the payload of a MPDU may comprise the layer 3-7 information known as the MSDU. In general, an MPDU is also referred to as frame, or 802.11 frame. An MPDU is a frame that is passed from the MAC to the PHY layer. In any case the terms frame and MPDU are used interchangeably herein.

The MPDU may comprise the following three basic components: a MAC header, a frame body (comprising the payload, i.e. an MSDU, and a frame check sequence or frame correction sequence, FCS.

On the physical layer, PHY, the MPDU becomes physical layer service data unit, PSDU. The physical layer protocol data unit, PPDU, contains a preamble and one or more data fields. The preamble field contains the transmission vector format information. The data field contains the PPDUs payload, e.g., inter alia higher layer headers, such as medium access control (MAC) fields and cyclic redundancy check (CRC) . The transmission vector format and the PPDU structure vary between 802.11 versions. Figure 4 shows an example of an AP MLD with two affiliated APs communicating over Link 1 and Link 2.

MLO defines a set of procedures allowing communication over multiple links between MLDs. An MLD manages such communication over multiple links. Communication across links using different frequency bands or channels can occur simultaneously or not depending on the capabilities of both the AP MLD and the non-AP MLD.

The MLO procedures allow a pair of MLDs to discover, synchronize, (de) authenticate, (re) associate, disassociate, and manage links and other resources with each other on any common bands or channels that are supported by both MLDs.

Each MLD has a single MAC-SAP. Each AP affiliated with an AP MLD has a MAC address different from any other AP affiliated with the AP MLD, and each non-AP STA affiliated with a non-AP MLD has a MAC address different from any other non-AP STA affiliated with the non-AP MLD. The MLD MAC address of an MLD might be the same as the MAC address of one (affiliated) STA or might be different from the MAC address of any (affiliated) STA.

Figure 4 shows an AP MLD with MLD MAC address M and the MLD lower MAC sublayers of two affiliated APs (API with MAC address w and AP2 with MAC address x) . The AP MLD is associated with a non-AP MLD with MLD MAC address P and the MLD lower MAC sublayers of two affiliated STAs (STA1 with MAC address y and STA2 with MAC address z) are shown. Link 1 is established between API and STA1 and link 2 is established between AP2 and STA2. In general, the MAC address of an MLD and the MAC addresses of the STAs affiliated with the MLD are all different (e.g., M, P, w, x, y, and z have different values) . However, the architecture supports an implementation where M could equal either w or x, and where P could equal y or z . For simplicity, Figure 4 depicts a situation when there are two links , while in general , an MLD can support more than two links . The MAC-SAP of the AP MLD may be identi fied by the same AP MLD MAC address .

The MAC Sublayer is further divided into an MLD upper MAC sublayer and an MLD lower MAC sublayer . The MLD upper MAC sublayer performs functionalities that are common across all links , and the MLD lower MAC sublayer ( shared with an AP or non-AP STA af filiated with the MLD) performs functionalities that are local to each link . Some of the functionalities require j oint processing of both the MLD upper MAC sublayer and the MLD lower MAC sublayer . An AP MLD always operates in cooperation with one or more af filiated APs , one for each link . The MLD lower MAC sublayer components implement link speci fic functions that operate independently of the lower MAC in other af filiated APs . Use of these MLD lower MAC functions is shared by the AP MLD' s upper MAC sublayer, and the af filiated AP' s upper MAC sublayer . For example , the MLD 1 in Figure 4 may be the transmitting MLD and the MLD in Figure 4 may be the receiving MLD or second MLD, for the purpose of redundant transmission and/or reception over a first and a second link .

An illustration of a frame duplication in a first MLD is shown in Figure 5 . The MLD comprises a frame duplication mechanism on the transmitting MLD, MLD1 , and, as the case may be , a duplicate elimination mechanism on the receiving MLD, MLD2 , which is shown in Figure 6 .

It is thus proposed to duplicate frames on two or more individual links of a single MLD . Furthermore , it is proposed to tag the duplicated frames based on a sequence number, FS ID, added to the frame headers , i . e . , the same sequence number is used for duplicated frames on di f ferent lower MACs , and/or to filter the received frames and remove all duplicates except the first received frame . On the Upper MAC the MLD, MLD1, may comprise the following functionalities, e.g., implemented by a path management entity. An instance on the Upper MAC is needed which triggers link setup and/or teardown for links that use frame duplication. The MAC SAP provides interfaces for the Upper MAC to configure and/or manage the affiliated STA' s Lower MACs of an MLD. A mapping mechanism is proposed which maps traffic, i.e. one or more MSDUs, to individual links. For example, a priority based / traffic class mapping may be used. The priority based / traffic class mapping may comprise mapping a Traffic Identifier, TID, to multiple links, e.g., according to IEEE 802.11be D3.1. Alternatively, a flow-based mapping may be used. The flow-based mapping may comprise one or more management frame extensions for MLO-based frame duplication. Such a management frame extension may comprise a new multi-link element type like a "duplication multi-link element" for flowbased or TID-based duplication link setup.

A Traffic Identifier (TID) is an identifier used to classify a frame. When a MLD receives an 802.11 frame with a TID set for example for audio, the priority is given higher than a data frame for best effort purpose. Hence, based on the priority the proposed duplication mechanism for redundant transmission may be used. A traffic identifier, TID, may be any of the identifiers usable by higher layer entities to distinguish MAC service data units, MSDUs, to MAC entities that support quality of service, QoS, within the MAC data service. There are 16 possible TID values; eight identify traffic categories, TCs, and the other eight identify parameterized traffic streams, TSs. The TID is assigned to an MSDU in the layers above the MAC. By default, MSDU transport is on a best-effort basis. However, the QoS facility uses a traffic identifier, TID, to specify differentiated services on a per- MSDU basis.

A flow may be understood as a stream of one or more data packets such as MPDUs and may be identified by a flow ID, i.e., a flow identification number. Hence, based on a certain flow ID the proposed duplication mechanism for redundant transmission may be used.

On the Upper MAC the MLD may comprise the following functionalities, e.g., implemented by a labeling entity, for labeling of frames based on a Frame Sequence ID, FSID. The FSID may be stored in a duplicates list DLO on the Upper MAC of MLD1. Since current solutions for example as defined for mesh networks, cf. Section "9.2.4.4.1 Sequence Control field structure" in IEEE 802.11-2020, where a sequence number for mesh data frames as part of the QoS Control subfield is defined, cannot be applied for MLO frame duplication, as the MAC addresses for duplicated frames (i.e., the affiliated STAs/APs of an MLD device) differ and therefore the sequence numbers of duplicated frames would differ per link. Hence, an extension of existing header field format (s) Hl, H2 is proposed that supports identifying duplicated packets. This newly proposed one or more header fields can for example be (part of) an additional field in the QoS Control Subfield of a header (format) Hl, H2, e.g., of a data frames. For example, the following header field information for frame identification may be used Link ID, i.e., identifier of a link in an MLO setup; Flow ID, i.e., identifier of a flow which is transmitted on two or more links (in case flow-based link mapping is used, and/or an frame Sequence ID, i.e., an identifier of a duplicated frame, which for example that belongs to a flow or a TID.

The MAC sublayer entities may determine the user priority for MSDUs based on the TID values provided with those MSDUs .

Hence, the (Upper) MAC attempts to deliver MSDUs belonging to that TID in accordance with its configuration for that TID. When a QoS capable STA/AP transmit a data frame they will include QoS control field in WiFi header that include TID (Traffic Identifier) field. 3 bits of that field known as User Priority (or UP) value and determine the priority a WiFi frame get over the air. Since WiFi got 4 different traffic classes, two UP values map into each Access Category. Note that UP value 0 map to Best Effort (BE) in order to treat packet with no QoS marking with Best Effort Priority.

Primarily you classify traffic into 4 different Access Categories (Voice, Video, Best Effort & Background) .

On the Upper MAC the MLD may comprise a frame-based duplication mechanism. To that end, the Upper MAC may forward duplications of the MSDU to the Lower MACs (i.e., corresponding to the links over which the duplicates shall be transmitted) which are setup for frame duplication. Then the Frame Sequence ID may be incremented by the Upper MAC for a subsequent frame that is about to be duplicated. The duplicates of the MSDU may then be encapsulated by the stations STA1, STA2 on the Lower MAC. To that end, the MAC address of the first station STA1 may be inserted in the header (field) Hl of the first MPDU MPDU1, comprising the first duplicate. Furthermore, the MAC address of the second station STA2 may be inserted into the header (field) H2 of the second MPDU MPDU2, comprising the second duplicate.

The duplicate frames MPDU1, MPDU2 are then forwarded from the stations STA, STA2 on the lower MAC to the respective physical layer, PHY, for transmission of the respective link. To that end, the MPDU1 is encapsulated PPDU1 and MPDU2 is encapsulated in PPDU2.

On the Upper MAC the MLD may comprise a synchronous channel access among the plurality of links. To that end, different strategies for channel access for the different links of an MLD may be used. Distributed channel access makes synchronous transmissions on different links unlikely, i.e., each link manages its own EDCA queue, since both links need to win contention on their respective channel to start a synchronous transmission. Thus, channel access may be coordinated using for example one of the following approaches for a frame duplication scenario. For example, the duplicates may be transmitted synchronously by waiting for all links (over which the duplicates shall be transmitted) to individually access the channel. Additionally and/alternatively, the solution proposed in European patent application EP23160772.2 for MU EDCA may be used to guarantee channel access on individual links for the MLD, e.g., such that only OFDMA transmissions are used on the links (over which the duplicates shall be transmitted) . Thus, synchronizing channel access among different links may be required, i.e., Lower MACs may be synchronized via the Upper MAC. In any case, the duplicates may be transmitted asynchronously using independent EDCA queues on each link.

The synchronized transmission schedule of one or more lower MACs may be managed or controlled by upper MAC. Such management or control may comprise setting of a guard time for forwarding, or waiting for common/ successful channel access of all STAs, upper Mac provides schedule, lower MACs have guaranteed access time.

Figure 6 shows an illustration of a second multi-link device, MLD2, receiving duplicate MAC packet data units, i.e., receiving MLD. A duplicate elimination may be required at the receiving MLD. The receiving MLD may comprise an Upper MAC and/or Lower MAC for performing the following functions. The Upper MAC and/or Lower MAC of the receiving MLD may serve for identifying a frame, e.g., via a Frame ID, and/or in order to eliminate duplicates. For example, the frame received first by the Lower MAC, which may be identified by a Frame Sequence ID, FSID, will be forwarded to the Upper MAC sublayer. This may happen, when there is no corresponding FSID in a duplicate list, DL1, of the receiving MLD, MLD2.

The Upper MAC may manage a duplicates list, DL3, that contains all FSIDs that have already been received and/or processed by the receiving MLD. The duplicates list(s) , DL1, DL2, DL3, can be for example an efficient, shared memory among Upper MAC and Lower MACs of the receiving MLD. Information of received frames may for example be available in the duplicates lists DL1 , DL2 , DL3 for as long as the delay requirement of the respective MPDU or associated flow is not exceeded . Thus , sending time stamp of the frame and/or the delay requirement of the frame may be stored in the duplicates list DL1 , DL2 , DL3 ( together with the FS ID of that frame ) .

The following options are proposed for detecting duplicates at the receiving MLD, MLD2 . In a first option, the Lower MAC may perform the lookup in the duplicates list DL1 and drop or discard frames in case the lookup was success ful , i . e . , the FS ID of the frame received is found in the duplicates list DL1 . Duplicates received at the same time at di f ferent Lower MACs may however be forwarded to the Upper MAC, and eventually to higher layers .

In a second option, duplicates may be detected at the Upper MAC . In that case , one or more frames received ( including one or more duplicates ) may be forwarded from the one or more Lower MACs to the Upper MAC of the receiving MLD . The Upper MAC may then perform a lookup in the duplicates list DL3 and/or eliminate one or more frames which are already in the duplicates list DL3 . To that end, a comparison of the FS ID of the frame received and the one or more FS IDs in the duplicates list DL3 may be performed .

Since , a potential bottleneck at the Upper MAC may occur, for example when all duplicates have to be processed at Upper MAC a third option may be used . In the third option, Upper and Lower MAC may interact when detecting and/or discard one or more duplicates . To that end, a first lookup in the duplicates list DL1 , DL2 may be performed first at the Lower MAC, e . g . , in order to drop one or more of the duplicates . A second lookup in the duplicates list DL3 may be performed at the Upper MAC where duplicates that could not be detected at the Lower MACs are detected and/or discarded . Turning to Figure 7 an exemplary embodiment for a duplicate transmission and/or reception between a first MLD, MLDA, and a second MLD, MLDB, is illustrated.

It is assumed that the first and the second MLD MLDA, MLDB are set up for frame duplication, and thus MLO with redundant transmission and/or reception is successfully established. One or more frames with a first TID, i.e. TID 7, will be duplicated on Link 1 and Link 2, whereas frames with another TID, i.e. TID 5, are transmitted on a single link, i.e. Link n. Furthermore, it is assumed that a TID-to-Link mapping is already established. Then, the frames will be mapped or forwarded to the respective STA, STA1, STA2, STAn in order to be transmitted over the corresponding link. For example, a TID- to-Link mapping may be established by mapping a (single) TID to multiple links, for example by negotiation according to IEEE 802.11be D3.1.

The transmission of duplicated frames is further described in connection with Figure 7. A frame (with TID 7) for duplication is received by the MAC-SAP at the Upper MAC sublayer of the transmitting MLD, MLDA. The frame (with TID 7) for duplication is labeled with a unique Frame ID 01, also referred to as FSID. The frame for duplication, i.e. the frame with TID 7 and Frame ID 01) is forwarded to multiple lower MACs and is thus duplicated. The channel access may be synchronized among Link 1 and Link 2 in order to start a synchronous transmission of the duplicates (of the frame with TID 7 and Frame ID 01) and the duplicated frames are transmitted on both links. The reception of duplicated frames by the receiving MLD, MLDB, is described in the following. In this embodiment only the Lower MAC performs the duplicate check and/or duplicate discarding, however another option as described herein may be used. The frame with Frame ID 01 is received by STA1 of the second MLD, MLDB. After the station STA3 of the second MLD, MLDB, performs a lookup for Frame ID 01 in the duplicates list (e.g., located at the Lower MAC) and does not find a FSID Frame ID 01 in the list, the frame with FSID Frame ID 01 is added to the duplicates list and the frame is forwarded to the Upper MAC sublayer, and eventually to the MAC-SAP Endpoint of the second MLD, MLDB .

In case of a duplicate elimination mechanism by the Upper MAC layer of the second MLD, MLDB, the Upper MAC of the second MLD adds the FS ID 01 to the duplicates list ( located at the Lower MAC of the fourth station STA 4 ) of the fourth station .

The fourth station STA4 of the second MLD receives a frame with Frame ID 01 , and performs a lookup at its duplicates list ( located at the lower MAC of STA4 ) , finds Frame ID 01 in its ( local ) duplicates list and thus drops , eliminates or discards the identi fied duplicated frame at the Lower MAC of STA4 , i . e . , does not forward the identi fied duplicate to the Upper MAC of the second MLD, MLDB .

The Upper MAC of the second MLD, MLDB, may coordinate the removal of FS IDs from the Lower MACs local duplicates list , for example when the time the information is stored in the duplicates list exceeds the delay requirement of the frame . The delay requirement is assumed to be known for critical realtime flows .

It should be understood, that instead of a TID-to-Link mapping a Flow ID to link mapping may be used . In that case , the FlowID-to-Link mapping may be set up by a (multi- ) link control element of a management frame (MMPDU) . Hence , an MSDU may then be mapped according to its FlowID to respective one or more links .

The embodiments proposed allow for deterministic communication in IEEE 802 . 11be Wi-Fi networks , and beyond . A reduced average latency and j itter is achieved by the duplication of frames on disj oint paths and allows for a higher probability of success ful packet transmission . Furthermore , frame duplication on multiple links allows for an increased reliability by reducing the probability of retransmissions due to link failure or interference. Compared to the existing solutions the embodiments proposed requires less hardware for transmission of duplicates. In general, the use of MLO for redundant transmission reduces hardware costs and simplifies the network setup.

Turning to Figure 8, a management frame comprising a header, information elements and a frame check sequence, FCS, for setting up the MLO of an MLD with redundant transmission is shown. The IEEE 802.11 MAC distinguishes five different MAC addresses, the Basic Service Set Identification (BSSID) , Destination Address (DA) , Source Address (SA) , Receiver Address (RA) , and Transmitter Address (TA) . The management frame may serve for setting up the MLO of an MLD with redundant transmission is shown. 802.11 management frames share the structure shown in Figure 8. Management frames use information elements to communicate information to other systems. Management frames use fixed-length fields called fixed fields and variable-length fields called information elements. Information elements may be of varying size. Information elements are variable-length components of management frames. A generic information element has an ID number, a length, and a variable-length component.

The information elements, IES, included in the management frames allow MLDs to exchange their capabilities and/or operational parameters. With such purpose, the 802.11be defines the multi-link element, MLE . The MLE may be used for discovery and/or setup of one or more MLDs.

Hence, an information element, such as said multi-Link element in Figure 8, may be used to set up and/or to indicate changes with regard to the mapping of frames, e.g., between TID values and links. For example, all TIDs may be assigned, by said multi-link element, to all links, allowing a full adaptive load balancing strategy, as traffic may be moved partially or fully between multiple links. Furthermore, an information element, such as said multi-link element, may be used to assign a TID to two or more links for redundant transmission and/or reception . Thus , once an MLD is set up or configured a frame may be transmitted according to its TID over two or more links . Similarly, an MLD may be configured by said MLE in a management frame in order to receive a frame over said two or more links . That is , two or more links of an MLD may be enabled for redundant transmission and/or reception .

As mentioned herein, instead of a TID-to-Link mapping a flowID to link mapping may be performed . A data flow may be set up between stations of the receiving and/or transmitting MLD . A data flow may be identi fied by a flow ID . A data flow may be understood as a set of medium access control , MAC, service data units , MSDUs , to be delivered ( subj ect to the quality-of-service , QoS , parameter values provided) . A MAC entity may determine the applicable links for delivery of MSDUs belonging to a particular data flow based on a flow ID using provided with those MSDUs at the MAC service access point , MAC SAP .

Figures 9 to 26 show exemplary method steps according to various embodiments .

As shown in Figure 9 , in a step S I a first MSDU is received, by a first MLD, via a SAP on an upper MAC sublayer of the first MLD . In a step S2 a first duplicate of the first MSDU is forwarded to a first STA on a lower MAC sublayer of the first MLD . In a step S3 a second duplicate of the first MSDU is forwarded to a second STA on the lower MAC sublayer of the first MLD .

As shown in Figure 10 , in a step S4 , a first header for a first MPDU with the MAC address of the first STA is created by the first STA, the first MPDU comprising the first duplicate . In a step S5 , a second header for the second MPDU with the MAC address of the second STA is created by the second STA, the second MPDU comprising the second duplicate . In a step S6, as shown in Figure 11, a first STA on a lower MAC sublayer of a first multi-link device is determined. In a step S7, a second station on the lower MAC sublayer of the first multi-link device is determined. Steps S7 and/or S7 may be performed during set up, i.e., configuration of the MLD or during handling of one or more MSDUs by the MLD.

In a step S8, the first MPDU is transmitted by the first station in at least one first physical layer protocol data unit, PPDU, via the first link and in a step S8 the second MPDU comprising the second duplicate is transmitted in at least one second PPDU by the second station via the second link.

In a step S10, as shown in Figure 12, link-specific lower medium access control (MAC) and one or more physical layer (PHY) services are provided by the first and the second station of the first multi-link device. In a step Sil, a single MAC service access point (SAP) to a logical link control (LLC) sublayer, e.g., of a host device, is provided by the upper MAC sublayer of the first multi-link device.

As shown in Figure 13, in a step S12, a QoS value, e.g., a traffic identifier value, or a flow ID is determined relating to the first MSDU. In a step S13, the first station and the second station is determined based on the QoS value or the flow Id, e.g., by mapping the first duplicate to the first station and the second duplicate to the second station.

As shown in step S12 of Figure 14, a (multi-) link control element of a management frame, e.g., a MMPDU, may be determined. In a step S15, a first and a second station may be determined based on the (multi-) link control element. Said mul- ti-Link control element may serve for enabling a TID-to-link mapping or flow Id to link mapping as described herein. Hence, in a step S16, the upper MAC sublayer may be configured to forward MPDUs to the first and second station, e.g., in accordance with the configuration information provided in the multi-link control element.

As shown in step S17 of Figure 15, a sequence number, FSID, may be assigned to the first MPDU, preferably to a header field element of the first MPDU, most preferably to a QoS field element. In step S18, he same sequence number is assigned to the second MPDU, preferably to a header field element of the second MPDU, most preferably to a QoS field element. In a step S19, the sequence number (FSID) is incremented after forwarding the first and the second duplicate.

According to step S20 of Figure 16, a first transmission channel associated with the first link is accessed by the first station. In a step S21, a second transmission channel associated with the second link is accessed by the second station. Thus, in a step S22, the first and the second PPDU are synchronously transmitted over the first and the second link. Therein the first PPDU comprises the first MPDU and the second PPDU comprises the second MPDU.

As shown in Figure 17, in a step S23, a first channel access mechanisms is employed by the first station for accessing the first transmission channel. A second channel access mechanism is employed by the second station for accessing the second transmission channel as shown in step S24. Therein, as shown in step S25, the first channel access mechanism may be the same as or different to the second channel access mechanism.

It should be understood that, the steps described in connection with Figures 9 to 17 are preferably performed by the first MLD, i.e., the transmitting a MLD but that the transmitting MLD may become a receiving MLD, i.e., when receiving one or more PPDU from a transmitting MLD.

As shown in Figure 18, in a step S26, a first MPDU comprising a first duplicate of a first MSDU is received by a third station on a lower MAC sublayer of a second multi-link device. In a step S27 , a second MPDU comprising a second duplicate of the first MSDU is received by a fourth station on the lower MAC sublayer of the second multi-link device , preferably via the second link . It should be understood that the first MPDU and the first MSDU may correspond to the one that have been transmitted by the first MLD as described herein in order to establish a redundant transmission of an MSDU . Thus , one of the redundantly received PPDUs or MPDUs needs to be eliminated or discarded, e . g . , in order to avoid congestion or redundant information .

As shown in Figure 19 in step S28 , the first MPDU is forwarded by the third station on the lower MAC sublayer of the second multi-link device to a service access point on an upper MAC sublayer of the second multi-link device . In a step S29 , the second MPDU is forwarded by the fourth station on the lower MAC sublayer of the second multi-link device to the service access point on the upper MAC sublayer of the second multi-link device .

As shown in a step S30 of Figure 30 , the first MPDU is received by the third station in at least one first PPDU packet via a first link . In a step S31 , the second MPDU is received in at least one second PPDU by the fourth station via the second link . In a step S32 , the first and the second duplicate may thus be received synchronously or asynchronously .

As shown in Figure 21 , link-speci fic, lower medium access control (MAC ) and one or more physical layer ( PHY) services are provided by the third and the fourth station of the second multi-link device in a step S33 . In a step S34 , a single MAC service access point ( SAP ) to a logical link control (LLC ) sublayer, e . g . , of a host device , is provided by ( an entity of ) the upper MAC sublayer of the second multi-link device .

As shown in Figure 21 a third station on the lower MAC sublayer of the second multi-link device and the fourth station on the lower MAC sublayer of the second multi-link device are determined . This may take place either during configuration of the second multi-link device or during forwarding of the MPDUs . In a step S36 , the third and fourth station on the lower MAC sublayer of the second multi-link device are then to forward MPDUs to the upper MAC sublayer of the second multi-link device .

In a step S37 of Figure 23 , a sequence number, FS ID, of the first duplicate , preferably in a header field element of the first MPDU, most preferably in a QoS field element , is determined . In a step S38 , a sequence number, FS ID, of the second duplicate , preferably in a header field element of the second MPDU, most preferably in a QoS field element .

In a step S39 of Figure 24 , at least one sequence number ( FS ID) of the first and/or second duplicate or MPDU received by the second multi-link device is stored in at least one of the upper MAC sublayer, the third station on the lower MAC sublayer and the fourth station on the lower MAC sublayer . In a step S40 the sequence number ( FS ID) of the first and/or second duplicate or MPDU received is compared by the second multi-link device with the stored sequence number . In a step S41 , the first and/or second duplicate or MSDU is eliminated or discarded in case the sequence number is equal to the stored sequence number .

As shown in Step S42 of Figure 25 , at least one sequence number ( FS ID) of the first and/or second duplicate or MPDU received is stored by the second multi-link device in at least one of the upper MAC sublayer, the third station on the lower MAC sublayer and the fourth station on the lower MAC sublayer . In a step S43 , the sequence number of the first and/or second duplicate or MPDU received is compared with the stored sequence number . In a step S44 , the first and/or second duplicate is forwarded in case the sequence number is not equal to the stored sequence number . As shown in a step S45 of Figure 26 , at least one sequence number, FS ID, of the first and/or second duplicate received by the second multi-link device is stored in at least one of the upper MAC sublayer, the third station on the lower MAC sublayer and the fourth station on the lower MAC sublayer . In a step S46 , the sequence number of the first and/or second duplicate or MPDU received is stored for a predetermined time interval , wherein the time duration preferably corresponds to a delay requirement of the first MSDU or MPDU .

The steps described herein may be performed by a first and second MLD respectively and by a system comprising said first and second MLD . Furthermore , the steps described herein may be implemented by a computer program comprising program code that when executed, e . g . , by a first and/or second MLD as described herein, performs the steps as described herein .

Claims

1. A method for redundant transmission over a first and a second link comprising: receiving a first MAC service data unit, MSDU, via a service access point, SAP, on an upper MAC sublayer of a first multilink device (MLD1) , forwarding a first duplicate (MPDU1) of the first MSDU to a first station (STA1) , STA, on a lower MAC sublayer of the first multi-link device (MLD1) , and forwarding a second duplicate (MPDU2) of the first MSDU to a second station (STA) on the lower MAC sublayer of the first multi-link device (MLD1) , creating, by the first station (STA1) , a first header (Hl) for a first MAC protocol data unit (MPDU1) , MPDU, with the MAC address of the first station (STA1) , the first MPDU (MPDU1) comprising the first duplicate, and creating, by the second station (STA2) , a second header (H2) for a second MPDU (MPDU2) with the MAC address of the second station (STA2) , the second MPDU (MPDU2) comprising the second duplicate .

2. The method according to the preceding claim, determining the first station (STA1) on the lower MAC sublayer of the first multi-link device (MLD1) and determining the second station (STA2) on the lower MAC sublayer of the first multi-link device (MLD1) .

3. The method according to any one of the preceding claims, transmitting the first MPDU (MPDU1) by the first station (STA1) in at least one first physical layer protocol data unit (PPDU1) , PPDU, via the first link and the second MPDU in at least one second PPDU (PPDU2) by the second station via the second link.

4. The method according to any one of the preceding claims, providing link-specific lower medium access control (MAC) and one or more physical layer (PHY) services by the first and the second station (STA2) of the first multi-link device (MLD1) , providing a single MAC service access point (SAP) to a logical link control (LLC) sublayer by the upper MAC sublayer of first the multi-link device (MLD1) .

5. The method according to any one of the preceding claims, wherein the step of determining the first station (STA1) on the lower MAC sublayer of the first multi-link device (MLD1) and the second station (STA2) on the lower MAC sublayer comprises : determining a QoS value, e.g., a traffic identifier value, or flow Identifier relating to the first MSDU (MSDU1) , determining the first station (STA1) and the second station (STA2) based on the QoS value or flow ID, e.g., by mapping the first duplicate and/or the first MPDU (MPDU1) to the first station (STA1) and the second duplicate and/ or second MPDU (MPDU2) to the second station (STA) .

6. The method according to any one of the preceding claims, wherein the step of determining the first station (STA1) on a lower MAC sublayer of the first multi-link device (MLD1) and the second station (STA2) on the lower MAC sublayer comprises : determining a (multi-) link control element (MLE) of a management frame (MMPDU) , determining a first and a second station (STA1, STA2) based on the (multi-) link control element (MLE) and configuring the upper MAC sublayer to forward MPDUs to the first and second station (STA1, STA2) .

7. The method according to any one of the preceding claims, wherein forwarding the first duplicate of the first MSDU to the first station (STA1) and a second duplicate of the first MSDU to the second station (STA2) comprises: assigning a sequence number (FSID) to the first MPDU, preferably to a header field element of the first MPDU, most preferably to a QoS field element, and assigning the same sequence number to the second MPDU, preferably to a header field element of the second MPDU, most preferably to a QoS field element.

8. The method according to any one of the preceding claims, incrementing by the upper MAC sublayer the sequence number (FSID) after forwarding the first and/or the second duplicate and/or first and/or second MPDU.

9. The method according to any one of the preceding claims, accessing a first transmission channel associated with the first link by the first station (STA1) and accessing a second transmission channel associated with the second link by the second station (STA2) , and

(a) synchronously transmitting the first and the second PPDU (PPDU1, PPDU2) .

10. The method according to any one of the preceding claims, employing a first channel access mechanisms by the first station (STA1) for accessing the first transmission channel and employing a second channel access mechanism by the second station (STA2) for accessing the second transmission channel, wherein the first channel access mechanism is the same as the second channel access mechanism.

11. The method according to any one of the preceding claims, employing a first channel access mechanisms by the first station (STA1) for accessing the first transmission channel and employing a second channel access mechanism by the second station (STA2) for accessing the second transmission channel, wherein the first channel access mechanism is different to the second channel access mechanism.

12. A method of redundant reception over a first and a second wireless link comprising: receiving, by a third station (STA3) on a lower MAC sublayer of a second multi-link device (MLD2) , preferably via a first link, a first MPDU (MPDU1) comprising a first duplicate of a first MSDU, and receiving, by a fourth station (STA4) on the lower MAC sublayer of the second multi-link device (MLD2) , preferably via the second link, a second MPDU comprising a second duplicate of the first MSDU.

13. The method according to the preceding claim, forwarding the first MPDU (MPDU1) by the third station (STA1) on the lower MAC sublayer of the second multi-link device (MLD2 ) to a service access point on an upper MAC sublayer of the second multi-link device (MLD2) , and/or forwarding the second MPDU (MPDU2) by the fourth station (STA4) on the lower MAC sublayer of the second multi-link device (MLD2) to the service access point on the upper MAC sublayer of the second multi-link device (MLD2) .

14. The method according to any one of the preceding claims 12-13, receiving the first MPDU (MPDU1) by the third station (STA3) in at least one first PPDU (PPDU1) via a first link and the second MPDU (MPDU2) in at least one second PPDU (PPDU2) by the fourth station (STA4) via the second link.

15. The method according to any one of the preceding claims 12-14, providing link-specific, lower medium access control (MAC) and one or more physical layer (PHY) services by the third and the fourth station of the second multi-link device (MLD2) , providing a single MAC service access point (SAP) to a logical link control (LLC) sublayer, e.g., of a host device, by (an entity of) the upper MAC sublayer of the second multilink device (MLD2) .

16. The method according to any one of the preceding claims 12-15, determining the third station (STA3) on the lower MAC sublayer of the second multi-link device (MLD2) and the fourth station (STA4) on the lower MAC sublayer of the second multilink device (MLD2) , preferably by determining a (multi-) link control element of a management frame (MMPDU) , and most preferably determining the third and the fourth station based on the (multi-) link control element, configuring the third and fourth station on the lower MAC sublayer of the second multi-link device (MLD2) to forward MPDUs to the upper MAC sublayer of the second multi-link device (MLD2 ) .

17. The method according to any one of the preceding claims 12-16, wherein forwarding the first MPDU (MPDU1) by the third station (STA3) and the second MPDU (MPDU2) by the fourth station (STA4) comprises: determining a sequence number (FSID) of the first duplicate and/or the first MPDU (MPDU1) , preferably in a header field element of the first MPDU (MPDU1) , most preferably in a QoS field element, and determining a sequence number (FSID) of the second duplicate or the second MPDU (MPDU2) , preferably in a header field element of the second MPDU (MPDU2) , most preferably in a QoS field element.

18. The method according to any one of the preceding claims 12-17,

(a) synchronously receiving the first and the second duplicate and/or the first and/or second MPDU (MPDU1, MPDu2 ) .

19. The method according to any one of the preceding claims 12-18, storing at least one sequence number (FSID) of the first and/or second duplicate and/or the first and/or second MPDU (MPDul, MPDU2) received by the second multi-link device (MLD2 ) in at least one of the upper MAC sublayer, the third station (STAS) on the lower MAC sublayer and the fourth sta- tion (STA4) on the lower MAC sublayer, e.g., in a duplicates list (DL1, DL2, DL3) .

20. The method according to any one of the preceding claims 12-19, comparing the sequence number (FSID) of the first and/or second duplicate and/or first and/or second MPDU (MPDU 1, MPDU2) received by the second multi-link device (MLD2) with the stored sequence number, discarding the first and/or second duplicate and/or first and/or second MPDU (MPDU1, MPDU2) in case the sequence number is equal to the stored sequence number.

21. The method according to any one of the preceding claims 12-20, comparing the sequence number of the first and/or second duplicate and/or first and/or second MPDU (MPDU1, MPDU2) received with the stored sequence number, forwarding the first and/or second duplicate and/or first and/or second MPDU (MPDU1, MPDU2) in case the sequence number is not equal to the stored sequence number.

22. The method according to any one of the preceding claims 12-21, storing the sequence number of the first and/or second duplicate and/or first and/or second MPDU (MPDU1, MPDU2) received for a predetermined time interval, wherein the time duration preferably corresponds to a delay requirement of the first MPDU.

23. A first multi-link device, preferably comprising a processor and a memory, operative to perform the method steps of any one of the claims 1-11.

24. A second multi-link device, preferably comprising a processor and a memory, operative to perform the method steps of any one of the claims 12-22.

25 . A system for redundant transmission and/or reception over a first and a second link between a first multi-link device (MLD1 ) according to claim 23 and a second multi-link device (MLD2 ) according to claim 24 .

26 . A computer program comprising program code that when executed performs the steps of any one of the claims 1- 11 and/or 12-22 .