Sidelink relay connection with an intermediate relay device

Abstract

Various example embodiments relate to a sidelink based relay in a cellular communication network. An apparatus may comprise: means for receiving, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; means for appending the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; and means for transmitting the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

Description

SIDELINK RELAY CONNECTION WITH AN INTERMEDIATE RELAY DEVICETECHNICAL FIELD

[0001] Various example embodiments generally relate to the field of wireless communication. Some example embodiments relate to sidelink operation in a multi-hop scenario with at least one intermediate relay device.BACKGROUND

[0002] In wireless communications, access nodes of a cellular radio network may be configured to provide communication services to user equipment (UE), for example using a sidelink connection via another UE, also referred to as a sidelink based relay or a sidelink relay connection. Sidelink relay adaptation (SRAP) protocol is an example of a communication protocol for configuring and operating a sidelink connection. Different types of UEs may be configured support functionality corresponding to different versions or generations of such protocols.SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] Example embodiments of the present disclosure enable to improve cell barring in a cellular communication network. This and other benefits may be achieved by the features of the independent claims. Further example embodiments are provided in the dependent claims, the description, and the drawings.

[0005] According to a first aspect, an intermediate relay device is disclosed. The intermediate relay device may comprise: means for receiving, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; means for appending the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; and means for transmitting the appended uplink protocol data unit to a relay device or a thirdintermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

[0006] According to an example embodiment of the first aspect, the intermediate relay device comprises: means for receiving the uplink protocol data unit from a signalling channel configured for establishing a connection between the remote user equipment and the access node; and means for appending, prior to appending the uplink protocol data unit with the uplink protocol header, the uplink protocol data unit with a second uplink protocol header comprising a user equipment identifier of the remote user equipment and a preconfigured radio bearer identifier associated with the signalling channel.

[0007] According to an example embodiment of the first aspect, the signalling channel comprises a signalling channel of a sidelink radio link control, SL-RLC, protocol.

[0008] According to an example embodiment of the first aspect, the intermediate relay device comprises: means for receiving, from the relay device or the third intermediate relay device, a downlink protocol data unit comprising a plurality of downlink protocol headers, wherein an outermost downlink protocol header of the downlink protocol data unit comprises the user equipment identifier of the intermediate relay device and the radio bearer identifier of the intermediate relay device, and wherein a second outermost downlink protocol header of the downlink protocol data unit comprises the user equipment identifier of the remote user equipment or the second intermediate relay device and the radio bearer identifier of the remote user equipment or the second intermediate relay device; means for removing the outermost header of the downlink protocol data unit; and means for transmitting, based on the user equipment identifier of the remote user equipment or the second intermediate relay device and the radio bearer identifier of the remote user equipment or the second intermediate relay device, the downlink protocol data unit to the remote user equipment or the second intermediate relay device without the outermost downlink protocol header.

[0009] According to an example embodiment of the first aspect, the uplink protocol data unit further comprises a second uplink protocol header comprising: a user equipment identifier of the remote user equipment or the second intermediate relay device, and a radio bearer identifier of the remote user equipment or the second intermediate device.

[0010] According to an example embodiment of the first aspect, the intermediate relay device comprises: means for determining the radio bearer identifier of the intermediate relaydevice based on an identifier of an egress channel configured for transmission of the appended uplink protocol data unit.

[0011] According to an example embodiment of the first aspect, the intermediate relay device comprises: means for determining the user equipment identifier of the intermediate relay device based on a remote user equipment context of the intermediate relay device.

[0012] According to an example embodiment of the first aspect, the uplink protocol data unit comprises a layer two, L2, protocol data unit.

[0013] According to an example embodiment of the first aspect, the uplink protocol data unit comprises a sidelink relay adaptation protocol, SRAP, protocol data unit.

[0014] According to an example embodiment of the first aspect, the intermediate relay device comprises: means for receiving the uplink protocol data unit on a common control channel, CCCH, wherein the data field comprises at least one radio resource control, RRC, protocol message.

[0015] According to an example embodiment of the first aspect, the intermediate relay device comprises: means for transmitting, to the relay device or the third intermediate relay device, an indication of the data field comprising data received by the intermediate device from the remote user equipment or the second intermediate relay device.

[0016] According to an example embodiment of the first aspect, the indication comprises a preconfigured value of a reserved bit of the uplink protocol header.

[0017] According to an example embodiment of the first aspect, the intermediate relay device is configured to operate as another remote user equipment towards the relay device or the third intermediate relay device.

[0018] According to an example embodiment of the first aspect, the relay device is connected to the access node via a direct radio link, and / or the intermediate relay device is configured to operate as another relay device towards the remote user equipment or the second intermediate relay device.

[0019] According to an example embodiment of the first aspect, the sidelink based relay comprises the remote user equipment, the relay device, and one or more intermediate relay devices for data communication between the remote user device and the relay device.

[0020] According to a second aspect, an access node is disclosed. The access node may comprise: means for means for receiving, from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocolheaders associated with a remote user equipment and at least one intermediate relay device of a sidelink based relay of the cellular communication network between the access node and the remote user equipment; means for determining, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment; means for determining, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment; means for determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and means for providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0021] According to an example embodiment of the second aspect, the uplink protocol data unit comprises a layer two, L2, protocol data unit.

[0022] According to an example embodiment of the second aspect, the uplink protocol data unit comprises a sidelink relay adaptation protocol, SRAP, data unit.

[0023] According to an example embodiment of the second aspect, the upper protocol layer entity comprises a packet data convergence protocol, PDCP, entity.

[0024] According to a third aspect, a method is disclosed. The method may comprise: receiving, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; appending the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; and transmitting the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

[0025] According to an example embodiment of the third aspect, the method comprises: receiving the uplink protocol data unit from a signalling channel configured for establishing a connection between the remote user equipment and the access node; and appending, prior to appending the uplink protocol data unit with the uplink protocol header, the uplink protocol data unit with a second uplink protocol header comprising a user equipment identifier of the remote user equipment and a preconfigured radio bearer identifier associated with the signalling channel.

[0026] According to an example embodiment of the third aspect, the signalling channel comprises a signalling channel of a sidelink radio link control, SL-RLC, protocol.

[0027] According to an example embodiment of the third aspect, the method comprises: receiving, from the relay device or the third intermediate relay device, a downlink protocol data unit comprising a plurality of downlink protocol headers, wherein an outermost downlink protocol header of the downlink protocol data unit comprises the user equipment identifier of the intermediate relay device and the radio bearer identifier of the intermediate relay device, and wherein a second outermost downlink protocol header of the downlink protocol data unit comprises the user equipment identifier of the remote user equipment or the second intermediate relay device and the radio bearer identifier of the remote user equipment or the second intermediate relay device; removing the outermost header of the downlink protocol data unit; and transmitting, based on the user equipment identifier of the remote user equipment or the second intermediate relay device and the radio bearer identifier of the remote user equipment or the second intermediate relay device, the downlink protocol data unit to the remote user equipment or the second intermediate relay device without the outermost downlink protocol header.

[0028] According to an example embodiment of the third aspect, the uplink protocol data unit further comprises a second uplink protocol header comprising: a user equipment identifier of the remote user equipment or the second intermediate relay device, and a radio bearer identifier of the remote user equipment or the second intermediate device.

[0029] According to an example embodiment of the third aspect, the method comprises: determining the radio bearer identifier of the intermediate relay device based on an identifier of an egress channel configured for transmission of the appended uplink protocol data unit.

[0030] According to an example embodiment of the third aspect, the method comprises: determining the user equipment identifier of the intermediate relay device based on a remote user equipment context of the intermediate relay device.

[0031] According to an example embodiment of the second aspect, the uplink protocol data unit comprises a layer two, L2, protocol data unit.

[0032] According to an example embodiment of the third aspect, the uplink protocol data unit comprises a sidelink relay adaptation protocol, SRAP, protocol data unit.

[0033] According to an example embodiment of the third aspect, the method comprises: receiving the uplink protocol data unit on a common control channel, CCCH, wherein the data field comprises at least one radio resource control, RRC, protocol message.

[0034] According to an example embodiment of the third aspect, the method comprises: transmitting, to the relay device or the third intermediate relay device, an indication of the data field comprising data received by the intermediate device from the remote user equipment or the second intermediate relay device.

[0035] According to an example embodiment of the third aspect, the indication comprises a preconfigured value of a reserved bit of the uplink protocol header.

[0036] According to an example embodiment of the third aspect, the method comprises: operating as another remote user equipment towards the relay device or the third intermediate relay device.

[0037] According to an example embodiment of the third aspect, the relay device is connected to the access node via a direct radio link, and / or the intermediate relay device is configured to operate as another relay device towards the remote user equipment or the second intermediate relay device.

[0038] According to an example embodiment of the third aspect, the sidelink based relay comprises the remote user equipment, the relay device, and one or more intermediate relay devices for data communication between the remote user device and the relay device.

[0039] According to a fourth aspect, a method is disclosed. The method may comprise: receiving, from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocol headers associated with a remote user equipment and at least one intermediate relay device of a sidelink based relay of the cellular communication network between the access node and the remote user equipment; determining, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment; determining, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment; determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0040] According to an example embodiment of the fourth aspect, the uplink protocol data unit comprises a layer two, L2, protocol data unit.

[0041] According to an example embodiment of the fourth aspect, the uplink protocol data unit comprises a sidelink relay adaptation protocol, SRAP, data unit.

[0042] According to an example embodiment of the fourth aspect, the upper protocol layer entity comprises a packet data convergence protocol, PDCP, entity

[0043] According to a fifth aspect, an intermediate relay device is disclosed. The intermediate relay device may comprise: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the intermediate relay device at least to: receive, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; append the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; and transmit the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network. The instructions may be further configured to, when executed by the at least one processor, cause the intermediate relay device to perform the method of the third aspect, or any example embodiment(s) thereof.

[0044] According to a sixth aspect, an access node is disclosed. The access node may comprise: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the access node at least to: receive, from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocol headers associated with a remote user equipment and at least one intermediate relay device of a sidelink based relay of the cellular communication network between the access node and the remote user equipment; determine, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment; determine, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment; determine an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and provide the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment. The instructions may be further configured to, when executed by the at least one processor, cause the access node to perform the method of the fourth aspect, or any example embodiment(s) thereof.

[0045] According to a seventh aspect, an intermediate relay device is disclosed. The intermediate relay device may comprise: means for receiving, from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; means for receiving, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment; means for determining, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit; and means for transmitting the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel.

[0046] According to an example embodiment of the seventh aspect, the intermediate relay device may further comprise: means for receiving, from the relay device or the third intermediate relay device, a downlink protocol data unit comprising a downlink protocol header comprising the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user; and means for transmitting, based on the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment, the downlink protocol data unit to the remote user equipment or a second intermediate relay device with the downlink protocol header.

[0047] According to an example embodiment of the seventh aspect, the intermediate relay device may further comprise: means for receiving, from the access node a new user equipment identifier for the remote user equipment; means for replacing, in the uplink protocol header, the user equipment identifier of the remote user equipment with the new user equipment identifier of the remote user equipment; and means for transmitting, to the relay device or the third intermediate relay device via the egress channel, the uplink protocol data unit with the uplink protocol header comprising the new user equipment identifier of the remote user equipment.

[0048] According to an eighth aspect, an access node is disclosed. The access node may comprise: means for transmitting, to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relay device and between ingress and egress channels of the at leastone intermediate relay device for forwarding protocol data units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; means for receiving, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the access node and the relay device; means for determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and means for providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0049] According to an example embodiment of the eighth aspect, the access node comprises: means for transmitting, to the remote user equipment via the relay device and the at least one intermediate relay device, a downlink protocol data unit comprising a single downlink protocol header, wherein the single downlink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment.

[0050] According to an example embodiment of the eighth aspect, the access node comprises: means for determining a conflict between the user equipment identifier of the remote user equipment and a user equipment identifier of another remote user equipment associated with at least one of the relay device and the at least one intermediate relay device; means for assigning a new user equipment identifier for the remote user equipment; and means for transmitting the new user equipment identifier to the at least one of the relay device and the at least one intermediate device.

[0051] According to a ninth aspect, a method is disclosed. The method may comprise: receiving, from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receiving, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radiobearer identifier of the remote user equipment; determining, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit; and transmitting the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel.

[0052] According to an example embodiment of the ninth aspect, the method may further comprise: receiving, from the relay device or the third intermediate relay device, a downlink protocol data unit comprising a downlink protocol header comprising the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user; and transmitting, based on the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment, the downlink protocol data unit to the remote user equipment or a second intermediate relay device with the downlink protocol header.

[0053] According to an example embodiment of the ninth aspect, the method may further comprise: receiving, from the access node a new user equipment identifier for the remote user equipment; replacing, in the uplink protocol header, the user equipment identifier of the remote user equipment with the new user equipment identifier of the remote user equipment; and transmitting, to the relay device or the third intermediate relay device via the egress channel, the uplink protocol data unit with the uplink protocol header comprising the new user equipment identifier of the remote user equipment.

[0054] According to a tenth aspect, a method is disclosed. The method may comprise: transmitting, to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relay device and between ingress and egress channels of the at least one intermediate relay device for forwarding protocol data units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receiving, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the access node and the relay device; determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0055] According to an example embodiment of the tenth aspect, the method comprises: transmitting, to the remote user equipment via the relay device and the at least one intermediate relay device, a downlink protocol data unit comprising a single downlink protocol header, wherein the single downlink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment.

[0056] According to an example embodiment of the tenth aspect, the method comprises: determining a conflict between the user equipment identifier of the remote user equipment and a user equipment identifier of another remote user equipment associated with at least one of the relay device and the at least one intermediate relay device; assigning a new user equipment identifier for the remote user equipment; and transmitting the new user equipment identifier to the at least one of the relay device and the at least one intermediate device.

[0057] According to an eleventh aspect, an intermediate relay device is disclosed. The device may comprise: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the intermediate relay device at least to: receive, from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receive, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment; determine, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit; and transmit the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel. The instructions may be further configured to, when executed by the at least one processor, cause the intermediate relay device to perform the method of the ninth aspect, or any example embodiment(s) thereof.

[0058] According to a twelfth aspect, an access node is disclosed. The access node may comprise: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the access node at least to: transmit, to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relaydevice and between ingress and egress channels of the at least one intermediate relay device for forwarding protocol data units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receive, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the access node and the relay device; determine an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and provide the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment. The instructions may be further configured to, when executed by the at least one processor, cause the access node to perform the method of the ninth aspect, or any example embodiment(s) thereof.

[0059] According to a thirteenth aspect, a computer program, a computer program product, or a (non-transitory) computer-readable medium is disclosed. The computer program, computer program product, or (non-transitory) computer-readable medium may comprise instructions, which when executed by an apparatus, cause the apparatus at least to perform the method according to the third, fourth, ninth, or tenth aspect, or any example embodiment(s) thereof.

[0060] Example embodiments of the present disclosure can thus provide apparatuses, methods, computer programs, computer program products, or computer readable media for improving various aspects of wireless tethering. Any example embodiment may be combined with one or more other example embodiments. These and other aspects of the present disclosure will be apparent from the example embodiment(s) described below. According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims.DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings, which are included to provide a further understanding of the example embodiments and constitute a part of this specification, illustrate example embodiments and, together with the description, help to explain the example embodiments. In the drawings:

[0062] FIG. 1 illustrates an example of a cellular communication network with a sidelink based relay;

[0063] FIG. 2 illustrates an example of an apparatus configured to practice one or more example embodiments;

[0064] FIG. 3 illustrates an example of an architecture for a multi-hop sidelink based relay with an intermediate relay device;

[0065] FIG. 4 illustrates an example of an architecture for a multi-hop sidelink based relay with two intermediate relay devices;

[0066] FIG. 5 illustrates an example of a protocol stack of a cellular communication network;

[0067] FIG. 6 illustrates an example of a control plane protocol stack architecture for a multi-hop sidelink based relay;

[0068] FIG. 7 illustrates an example of a user plane protocol stack architecture for a multihop sidelink based relay;

[0069] FIG. 8 illustrates an example of a protocol data unit with a protocol header;

[0070] FIG. 9 illustrates an example of a protocol data unit without a protocol header;

[0071] FIG. 10 illustrates an example of appending protocol headers to an uplink protocol data unit received via a signaling channel configured for connection establishment;

[0072] FIG. 11 illustrates an example of appending a protocol header to an uplink protocol data unit received via another signalling channel;

[0073] FIG. 12 illustrates an example of a method for operating an intermediate relay node of a sidelink based relay of a cellular communication network;

[0074] FIG. 13 illustrates an example of a method for operating an access node of a cellular communication network;

[0075] FIG. 14 illustrates an example of another method for operating an intermediate relay node of a sidelink based relay of a cellular communication network; and

[0076] FIG. 15 illustrates an example of another method for operating an access node of a cellular communication network.

[0077] Like references are used to designate like parts in the accompanying drawings.DETAILED DESCRIPTION

[0078] Reference will now be made in detail to example embodiments, examples of which are illustrated in the accompanying drawings. The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0079] One objective for development of cellular communication systems may be to maintain interoperability between devices supporting different generations or releases (Rel) of standards, such as Rel-17, Rel-18, or Rel-19 of 3GPP standards. It may be for example desired to specify new solutions in order to support multi-hop sidelink operation, e.g., for a single indirect path via sidelink (SL) relay UEs operating based on SL relay functionality defined in earlier standard releases. For example, it may be desired to develop mechanisms to support at least up to two additional hop relays on top of a legacy single hop relay. It may be desired to provide support for one additional hop relay (e.g.., remote UE -> first relay UE -> last relay UE -> access node) and optionally extended this to two or more additional hops relays (e.g., remote UE -> first relay UE -> second relay UE -> last relay UE -> access node). An additional preference for the specified mechanisms may be extensibility to support two additional hop relays and to provide solutions that are forward compatible for future extensions for additional relays.

[0080] Example embodiments of the present disclosure provide solutions for implementing a multi-hop sidelink connection in view of the following: relay discovery and (re)selection, signalling support for relay UEs and remote UE authorization, impact on SRAP and QoS handling for multi-hop, and control plane procedures. Furthermore, the example embodiments support the following intra-gNB service continuity scenarios for multi-hop sidelink: intra-gNB multi-hop indirect to direct path switching using framework of earlier releases, intra-gNB multi-hop indirect to single-hop indirect path switching using framework of earlier releases, intra-gNB direct to multi-hop indirect path switching, intra-gNB single -hop indirect to multihop indirect path switching. The two latter scenarios may be related to path switching to a target indirect path comprising the last relay UE in “direct” RRC Connected mode and other intermediate relay(s) in “indirect” RRC Connected mode to the same cell.

[0081] FIG. 1 illustrates an example of a communication network with a sidelink based relay. Communication network 100 may comprise one or more access nodes 120, 122, 124. Access node(s) 120, 122, 124 may be part of a radio access network (RAN) configured to enable devices, such as remote UE 110, to access communication services provided by core network 140. In connection with communication network 100, access node(s) 120, 122, 124 and core network 140 may be collectively referred to as ‘network’. A UE may be referred to as a user device, a mobile device, or the like.

[0082] A UE, such as remote UE 110, may be configured to communicate with access node(s) 120, 122, 124 over a sidelink connection, for example via an intermediate relay (IR) device (e.g., IR UE 112), a relay device (e.g., relay UE 114). A remote UE may be a UE at which the sidelink connection is terminated. A remote UE may be therefore a terminal device to which the sidelink connection from the network is terminated. A relay UE may be a UE that is connected to an access node via a direct radio link, e.g., a radio link between an antenna of the relay UE and an antenna of an access node without any relay device in between. A relay UE may be also referred to as a relay device. An IR UE may be a UE that is communicatively located between a remote UE and a relay UE. An IR UE may be connected to a relay UE, a remote UE, or another IR UE via a direct radio link or, that is, a sidelink. An IR UE may be configured to operate as another relay device towards remote UE 110 or another IR UE. An IR UE may be also referred to as an IR device. Access nodes 120, 122, 124 may be also referred to as network devices.

[0083] The sidelink connection may be configured for example based on the 5G NR (New Radio) standard defined by the 3rdGeneration Partnership Project (3GPP), or any future standard or technology (e.g., 6G). Access nodes 120, 122, 124 may for example comprise 5thgeneration access nodes (gNB). Transmission by an access node to remote UE 110, e.g., via a sidelink connection, may be called downlink (DL) transmission. Transmission by remote UE 110 to an access node, e.g., via a sidelink connection, may be called uplink (UL) transmission. A UE may be therefore configured to operate as a transmitter for uplink transmissions and as a receiver for downlink transmissions. Access node(s) 120, 122, 124 may be configured to operate as a receiver for uplink transmissions and as a transmitter for downlink transmissions. The sidelink in sidelink based relay may be operated according to a sidelink protocol, such as for example the SRAP over a PC5 interface, among other sidelink protocols, as specified by 3GPP and as will be further described with reference to FIG. 5 and FIG. 6. SRAP is an exampleof a layer two (L2) protocol. RRC may be considered as layer 3 (L3). SDAP and PDCP may be considered as sub-layers of L2. Example embodiments of the present disclosure therefore provide a L2 multi-hop UE-to-network (U2N) relay scheme. Some example embodiments provide this functionality preserving backwards compatibility with devices limited to supporting earlier standard releases. Communication between relay UE 114 and access node 120 may be configured according to a Uu interface, as defined by 3GPP.

[0084] Communication network 100 may comprise a wireless communication network or a mobile communication network, such as for example a cellular communication network. UEs may be configured to communicate with access node(s) 120, 122, 124 using one or more logical channels and / or physical channels, for example a control channel such as the physical downlink control channel (PDCCH) or data channels such as the physical downlink shared channel (PDSCH) or the physical uplink shared channel (PUSCH). Shared data channels, e.g., PDSCH and PUSCH, may be shared by multiple UEs. An access node may be also referred to as an access point or a base station.

[0085] Core network 140 may be implemented with various network functions (NF), including, for example, one or more user plane functions (UPF) and one or more access and mobility management functions (AMF). A UPF may be configured to handle user data part of a communication session. A UPF may thus provide an interconnect point between the radio access network and a data network 150 configured to provide application services to remote UE 110 via core network 140 and the radio access network. For example, a UPF may be configured to handle encapsulation and decapsulation of user plane protocol(s), such as the GPRS (general packet radio service) tunnelling protocol for the user plane (GTP-U). An AMF may be configured to receive connection and session request related data from UE(s)(via an access node). An AMF may be configured to control connection and mobility management in communication network 100.

[0086] An access node 120, 122, 124 may be configured to communicate with UEs via one or more cells. For example, access node 120 may be configured to serve one or more UEs at cell 130. Access node 122 may be configured to serve UEs at cell 132. Access node 124 may be configured to serve UEs at cell 134. A cell may be configured to serve UEs at a certain geographical area at a certain radio frequency, or a range of radio frequencies around a centre frequency of the cell.

[0087] Considering the target of supporting at least two additional hop relays on top of relay UE 114, one challenge is to provide an effective solution that does not include major changes in standard. One approach for this is to allow use of legacy remote and relay UEs (e.g., Rel- 17 / 18 L2 U2N Remote and Relay UEs) as such for the new multi -hop relay scheme. This provides the benefit of enabling legacy devices to benefit from the new multi-hop solution. In addition, standardization of multi-hop solution is facilitated by enabling reuse of legacy functionalities and, on top of that, adding new enhancements to meet the objectives of future standard releases.

[0088] Communication network 100 may comprise other network function(s), network device(s), or protocol(s), in addition, or alternative to, those illustrated in FIG. 1. A network device may be configured to implement functionality of one or more network functions. Even though some embodiments have been described in the context of 5G, it is appreciated that embodiments of the present disclosure are not limited to this example network. Example embodiments may be therefore applied in any present or future communication networks.

[0089] FIG. 2 illustrates an example of an apparatus configured to practice one or more example embodiments. Apparatus 200 may be a device such as remote UE 110, IR UE 112, 112-1, 112-2, relay UE 114, or an access node 120, 122, 124 (e.g., as shown in FIG.l, FIG.3, or FIG.4), an access point, a base station, a radio network node, or a split portion thereof (e.g., a central or distributed unit of an access node), a network device, a terminal device, or in general any apparatus configured to implement functionality described herein. Apparatus 200 may comprise at least one processor 202. The at least one processor 202 may comprise, for example, one or more of various processing devices, such as for example a co-processor, a microprocessor, a controller, a digital signal processor (DSP), a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a microcontroller unit (MCU), a hardware accelerator, a special-purpose computer chip, or the like.

[0090] Apparatus 200 may further comprise at least one memory 204. The memory 204 may be configured to store, for example, computer program code 206 or the like, for example operating system software and application software. Memory 204 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination thereof. For example, the memory may be embodied as magnetic storage devices (such as harddisk drives, magnetic tapes, etc.), optical magnetic storage devices, or semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.). Memory 204 is provided as an example of a (non- transitory) computer readable medium. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0091] Apparatus 200 may further comprise a communication interface 208 configured to enable apparatus 200 to transmit and / or receive information. Communication interface 208 may comprise an external communication interface, such as for example a radio interface between remote UE 110 and access node(s) 120, 122, 124, a sidelink radio interface (e.g., PC5 interface) between remote UE 110 and IR UE 112 or between IR UE 112 and relay UE 114 or between IR UE 112-1 and IR UE 112-2, or a communication interface between a central unit and distributed unit(s) of an access node (e.g., an Fl-U and / or Fl-C interface). Communication interface 208 may comprise one or more radio transmitters or receivers, which may be coupled to one or more antennas or apparatus 200, or be configured to be coupled to one or more antennas external to apparatus 200.

[0092] Apparatus 200 may further comprise other components and / or functions such as user interface 210 comprising at least one input device and / or at least one output device. The input device may take various forms such a keyboard, a touch screen, or one or more embedded control buttons. The output device may for example comprise a display, a speaker, or the like.

[0093] When apparatus 200 is configured to implement some functionality, some component and / or components of apparatus 200, such as for example the at least one processor 202 and / or the at least one memory 204, may be configured to implement this functionality. Furthermore, when the at least one processor 202 is configured to implement some functionality, this functionality may be implemented using program code 206 comprised, for example, in the at least one memory 204.

[0094] The functionality described herein may be performed, at least in part, by one or more computer program product components such as software components. According to an example embodiment, apparatus 200 comprises a processor or processor circuitry, such as for example a microcontroller, configured by the program code 206, when executed, to execute the embodiments of the operations and functionality described herein. Program code 206 isprovided as an example of instructions which, when executed by the at least one processor 202, cause performance of apparatus 200.

[0095] Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), system-on-a-chip systems (SOCs), complex programmable logic devices (CPLDs), graphics processing units (GPUs), or the like.

[0096] Apparatus 200 may be configured to perform, or cause performance of, method(s) described herein or comprise means for performing method(s) described herein. In one example, the means comprises the at least one processor 202, the at least one memory 204 including instructions (e.g., program code 206) configured to, when executed by the at least one processor 202, cause apparatus 200 to perform the method(s). In general, computer program instructions may be executed on means providing generic processing functions. Such means may be embedded for example in a personal computer, a smart phone, a network device, or the like. The method(s) may be thus computer-implemented, for example based algorithm(s) executable by the generic processing functions, an example of which is the at least one processor 202. The means may comprise transmission or reception means, for example one or more radio transmitters or receivers, which may be coupled or be configured to be coupled to one or more antennas. Apparatus 200 may comprise, for example, a network device, for example, an access node, an access point, a base station, or a central / distributed unit thereof. Although apparatus 200 is illustrated as a single device, it is appreciated that, wherever applicable, functions of apparatus 200 may be distributed to a plurality of devices.

[0097] FIG. 3 and FIG. 4 illustrates example architectures for a multi-hop sidelink based relays with one and two IR devices, respectively. The sidelink based relay of FIG. 3 is similar to FIG. 1 in the sense that in comprises remote UE 110, IR UE 112, and relay UE 114. The sidelink based relay of FIG. 4 further comprises another IR UE 112-2, in addition to IR UE 112-1. An IR UE may be therefore connected with a direct radio link to remote UE 110 or another IR UE, which may be located either in the direction of remote UE 110 or in the direction of relay UE 114. An IR UE located between remote UE 110 and the IR UE in question may be referred to as a second IR UE, or more generally a second IR device. For example, IR UE 112- 1 may be considered to be a second IR UE for IR UE 112-2. IR UE 112-2 may be configuredto operate as another relay device towards IR UE 112-1. An IR UE located between relay UE 114 and the IR UE in question may be referred to as a third IR UE, or more generally a third IR device. For example, IR UE 112-2 may be considered to be a third IR UE for IR UE 112-1.

[0098] Example embodiments of the present disclosure provide enhancements suitable for sidelink protocols, such as SRAP, in order to implement a multi-hop relay scheme. For example, enhancements are provided across IR UE(s), relay UE (e.g., L2 U2N relay UE), and the access node to enable and facilitate enhanced multi-hop U2N relay functionality for serving a remote UE, wherein:- Remote UE 110 and / or relay UE 114 may be for example Rel-17 / 18 UEs, which do not support new multi-hop U2N relay mechanisms.- IR UE 112 may operate in a role of a relay UE (e.g., L2 U2N Relay UE) towards remote UE 110. IR UE 112 may operate in a role of a remote UE towards relay UE 114 (e.g., L2 U2N Relay UE2).- When an additional hop is added (cf. FIG. 4), another IR UE 112-2 may operate in a role of a relay UE (e.g., L2 U2N Relay UE) for IR UE 112-1.

[0099] The disclosed protocol enhancements may include different alternatives, considering for example that relay UE 114 may operate as a legacy UE that is not configured for the new multi-hop functionality. A first alternative may be used for example when relay UE 114 (e.g., the serving L2 U2N Relay UE) is a Rel- 17 / 18 UE or when relay UE 114 is configured by access node 120 (e.g., the serving gNB) to operate as a Rel-17 / 18 UE. A second alternative is provided for example for a case where relay UE 114 is Rel- 19 UE configured by access node 120 to operate as a Rel-19 UE, along with serving IR UE(s) 112, 112-1, 112-2, for remote UE 110.

[0100] According to the first alternative, a UE acting as a serving L2 U2N Relay UE (e.g., IR UE 112 or IR UE 112-1 towards remote UE 110, or relay UE 114 to IR UE 112 or IR UE 112-2, or IR UE 112-2 to IR UE 112-1, or relay UE 114 towards IR UE 112-2) may be configured with remote UE contexts of remote UE 110 or the IR UE connected to it with a direct radio link. Thus, the remote UE context of remote UE 110 may be hidden from UE(s) other than IR UE 112 (FIG. 3) or IR UE 112-1 (FIG. 7). The Remote UE context may comprise a local UE identifier (UE ID) of the corresponding remote UE and a radio bearer identifier (RB ID) of at least one, or each, radio bearer of the corresponding remote UE, which may be configured to be included in a protocol header of the sidelink relay, e.g., the SRAP header asillustrated in FIG. 9. This alternative provides for example the benefit of enabling to support multi-hop functionality with the serving L2 U2N Relay UE operating as a Rel-17 / 18 UE.

[0101] According to the second alternative, remote UE contexts of remote UE 110 may be configured across the serving IR UE(s) of the sidelink relay (e.g., IR UE 112, IR UE 112-1, IR UE 112-2) and relay UE 114 may be configured to operate as Rel-19 UEs.

[0102] According to a third alternative, a hybrid of the first and second alternatives may be applied, for example such that relay UE 114 is a Rel-17 / 18 UE. In this case, remote UE contexts of remote UE 110 may be configured across the serving IR UE 112-1 and IR UE 112-2 as in the second alternative. The last hop between IR UE 112-2 and relay UE 114 may be based on the first alternative.

[0103] FIG. 5 illustrates an example of a protocol stack of a cellular communication network. Communication network 100 may be operated based on a protocol stack comprising a plurality of protocol layers. The protocol stack may be arranged based on the open systems interconnection (OSI) model or a layer model of a particular standard. In one example, the protocol stack may comprise a service data adaptation protocol (SDAP) layer, which may receive data from an application layer for transmission. The SDAP layer may be configured to exchange data with the packet data convergence (PDCP) layer. The PDCP layer may be responsible of generation of data bursts comprising one or more data packets, for example based on data obtained from the SDAP layer.

[0104] The PDCP layer may provide data to one or more instances of the radio link control (RLC) layer, the different RLC instances may be configured for transmission / reception of data via different RLC channels. An RLC instance may be associated with corresponding MAC (medium access control) instance(s) of the MAC layer. The MAC layer may provide a mapping between logical channels of upper layer(s) and transport channels of the physical layer, handle multiplexing and demultiplexing of MAC service data units (SDU). Furthermore, the MAC layer may provide error correction functionality based on packet retransmissions, for example according to the hybrid automatic repeat request (HARQ) process. Physically separate transmission legs may be provided by the physical (PHY) layer, also known as Layer 1 (LI). Corresponding protocol stacks may be applied both at access nodes 120, 122, 124 and remote UE 110. IR UE(s) 112, 112-1, 112-2 and relay UE 114 may be also configured with corresponding protocol stacks. However, protocol stacks of these devices might not include some layers (e.g., PDCP, RRC, or SDAP layers). An apparatus, such as for example remoteUE 110, IR UE 112, 112-1, 112-2, relay UE 114, or access node 120, may comprise, or be configured to implement, e.g., by means of software, one or more of the protocol layers described herein.

[0105] Radio resource control (RRC) of remote UE 110 may be implemented based on different RRC states, alternatively referred to as RRC modes. When remote UE 110 is powered up, it may be in a disconnected state or an idle state (e.g., RRC_IDLE). Remote UE 110 may move to a connected state (e.g. RRC_CONNECTED), for example, through connection establishment to the network, for example via an L2 signalling channel (e.g., SL-RLC0) configured for this purpose. When remote UE 110 is in the connected state, e.g., connected to an access node, signaling radio bearer(s) may be configured to enable exchange of RRC data between UE 110 and the network. If remote UE 110 is not active for a certain time, remote UE 110 may move from the connected state to an inactive state (e.g. RRC_IN ACTIVE).

[0106] In the connected state, UE 110 may be associated with an RRC context. In the connected state, UE 110 may communicate with core network 140 via the radio access network, for example IR UE(s) 112, 112-1, 112-2, relay UE 114, and access node 120. The RRC context may comprise parameters configured to enable remote UE 110 and the network, e.g., access node 120, to communicate RRC data. In the connected state, the UE 110 may perform radio resource management (RRM) measurements, for example in relation to a mobility (handover) procedure. Remote UE 110 may report its measurement results to the network (e.g. via access node 120), for example periodically and / or in response to detecting a reporting triggering criterion to be fulfilled.

[0107] FIG. 6 and FIG. 7 illustrate examples of control and user plane protocol stack architectures for a multi-hop sidelink based relay. On the control plane the RRC and PDCP layers may be transparent to IR UE(s) 112, 112-1, 112-2, and relay UE 114. Therefore, the PC5 interface may be transparent to these protocol layers and an end-to-end control plane RRC connection may be established similar to a direct Uu interface connection between remote UE 110 and access node 120. Similarly, on the user plane an end-to-end PDCP connection may be established similar to a direct Uu interface connection between remote UE 110 and access node 120.

[0108] FIG. 8 illustrates an example of a protocol data unit (PDU) with a protocol header. PDU 800 may be for example an SRAP PDU and it may be applied for uplink and / or downlink transmission. The protocol header may comprise a radio bearer identifier (RB ID), which maybe generally indicative of (Uu) radio bearer identity of remote UE 110. The protocol header may comprise a UE ID, which may be generally indicative of a local identity of remote UE 110. However, according to example embodiments of this disclosure, these fields may alternatively comprise respective fields of an IR UE, when the IR UE operates in the role of a remote UE towards relay UE 114 or another IR UE. The protocol header may comprise other fields such as a D / C field indicative of whether the PDU is a control PDU or a data PDU, e.g., an SRAP data PDU or an SRAP control PDU, or fields reserved (R) for future use. In the example of FIG. 8, the protocol header comprises one D / C bit, two reserved bits, and an RB ID of five bits (Octet 1), a UE ID of eight bits (Octet 2), and a data field of eight bits (Octet 3). However, it is possible to configure such information with different number of bits. PDU 800 may further comprise a data field comprising, for example, an Uu PDCP PDU of a corresponding RB (e.g., either a signalling radio bearer, SRB, or a data radio bearer, DRB) indicated by the RB ID. PDUs transmitted on uplink and downlink may be called uplink and downlink PDUs, respectively. Protocol headers included in uplink and downlink PDUs may be called uplink and downlink protocol headers, respectively. Uplink and downlink headers may be similar or they may have different formats.

[0109] FIG. 9 illustrates an example of a protocol data unit without a protocol header. PDU 900 comprises the data field without any header. Such a PDU may be for example used on a signalling channel (e.g., signalling radio bearer zero, SRB0) configured for establishing a connection between the remote UE 110 and access node 120 (e.g., initial connection establishment). Upon establishment of the connection, access node 120 may configure remote UE 110 with a UE context (e.g., UE ID and RB ID), which enables remote UE 110 to subsequently use the PDU format of FIG. 8 with the protocol header.

[0110] FIG. 10 illustrates an example of appending uplink protocol headers to a protocol data unit received via a signalling channel configured for connection establishment. The functionality of an IR UE is described herein using IR UEs 112, 112-1 as examples.

[0111] IR UE 112, 112-1 may receive, from remote UE 110, an uplink PDU. The uplink PDU may comprise a data field without a protocol header. The uplink PDU may be a L2 PDU. The data field may therefore comprise L2 data, such as PDCP data that may carry either control-plane or user-plane data from a higher protocol layer above PDCP such as RRC or SDAP. In one example, the uplink PDU comprises an SRAP PDU. The uplink PDU may be received via a signalling channel of a sidelink radio link control (SL-RLC) protocol, such asfor example a sidelink RLC channel (SL-RLC CH) zero (SL-RLCO). The signalling channel (e.g., signalling radio bearer) may be configured for establishing a connection (e.g., an RRC connection) between remote UE 110 and access node 120. The signalling channel may be configured to be transmitted / received on a common control channel (CCCH), which may be a logical channel carried over one or more physical channels. The common control channel may be shared by multiple UEs. The uplink PDU may for example comprise SRBO data. IR UE 112, 112-1 may receive the uplink PDU from an ingress channel (e.g., ingress SL-RLC CH) having a particular ingress channel identifier. The data field of the uplink PDU may comprise data configured for establishment of a connection (e.g., RRC connection) between remote UE 110 and access node 120, for example RRC protocol message(s).

[0112] IR UE 112, 112-1 may be configured to operate in a role of a relay UE towards remote UE 110. IR UE 112, 112-1 may be however configured to operate in the role of a remote UE towards relay UE 114 or IR UE 112-2. IR UE 112, 112-1 may append the uplink PDU with uplink protocol headers comprising UE ID and RB ID of IR UE 112, 112-2 (e.g., own UE ID and RB ID) as well as UE ID and RB ID of remote UE 110. For example, IR UE 112, 112-1 may first append the received uplink PDU with a protocol header comprising UE ID and RB ID of remote UE 110 (cf. “Appended second header”). Subsequently, UE ID 112, 112-1 may append the uplink PDU with a protocol header comprising UE ID and RB ID of itself. IR UE 112, 112-1 may therefore append, prior to appending the uplink PDU the protocol header comprising its own UE ID and RB ID, the uplink PDU with a second uplink protocol header comprising UE ID and RB ID of remote UE 110. This provides the benefit of hiding the role of IR UE 112, 112-1 as an intermediate relay device and enabling IR UE 112, 112-1 to operate in the role of a remote UE to relay UE 114 or IR UE 112-2.

[0113] IR UE 112, 112-1 may determine its UE ID and RB ID based on its UE context, which IR UE 112, 112-1 may have received from access node 120 (e.g. via relay UE 114 or IR UE 112-2). IR UE 112, 112-1 may set the RB ID of remote UE 110 to a preconfigured value (e.g., “0”), in response to determining that the data field of the received uplink PDU comprises data of a particular signalling channel (e.g., SRB) configured for establishing a connection between remote UE 110 (e.g., in response to determining that the data field comprises SRBO data). IR UE 112, 112-1 may determine that the data field comprises such data based on the ingress channel of the uplink PDU being associated with the particular signalling channel.

[0114] IR UE 112, 112-1 may therefore obtain an appended uplink PDU, which may comprise its own UE ID and RB ID. IR UE 112, 112-1 may determine its RB ID based on an identifier of an egress channel configured for transmission of the appended uplink PDU, or uplink PDUs in general. For example, IR UE 112, 112-1 may use a subset, for example a number of least significant bits (LSB) of the egress channel identifier (e.g., five LSB bits) as the RB ID of IR UE 112, 112-1. The appended uplink PDU may further comprise the UE ID of remote UE 110 and / or the RB ID of remote UE 110. The uplink PDU may comprise the data field, e.g., SRBO data, as illustrated in FIG. 10.

[0115] IR UE 112, 112-1 may transmit the appended PDU to relay UE 114 or IR UE 112-2 for forwarding the uplink PDU towards access node 120. IR UE 112, 112-1 may determine the egress channel based on a configuration received from access node 120.

[0116] IR UE 112, 112-1 may transmit, to relay UE 114 or IR UE 112-2, an indication of the data field of the uplink PDU comprising data received by IR UE 112, 112-1 from remote UE 110 or another IR UE. In other words, this indication may indicate that the data field comprises data not received from remote UE 110, or in general a device to which the sidelink base relay is terminated. The indication may comprise a one-bit flag, for example in the protocol header that includes the UE ID and RB ID of IR UE 112, 112-1. The indication may comprise a preconfigured value of a reserved bit (R) of the uplink protocol header. This provides the benefit of enabling devices compliant with the new multi-hop relay functionality to be informed about the IR UE 112, 112-1 acting as an intermediate relay device. Backwards compatibility with legacy devices may be however preserved.

[0117] FIG. 11 illustrates an example of appending an uplink protocol header to a protocol data unit received via another signalling channel or data channel. In this example, the uplink PDU received by IR UE 112, 112-1 may comprise non-SRBO data, or in general data of a signalling channel that is not configured for connection establishment, e.g., initial connection establishment, or data of a data channel. The received uplink PDU may already include a protocol header comprising the UE ID and RB ID of remote UE 110 (cf. “Second header” in FIG. 11). If IR UE 112, 112-1 is connected to remote UE 110 via other IR UE(s), the received uplink PDU may further comprise protocol header(s) of the other IR UE(s). IR UE 112, 112-1 may be configured to append the protocol header (cf., “Appended header”) comprising its own UE ID and RB ID to the received uplink PDU, e.g., on top of the protocol header(s) included in the received uplink PDU, to obtain the appended uplink PDU. IR UE 112, 112-1 maytransmit the appended uplink PDU, now comprising the received and appended protocol headers to relay UE 114 or IR UE 112-2. This provides similar benefits as the examples of FIG. 10 in case of a non-SRBO data. IR UE 112, 112-1 may be therefore configured to forward a protocol header of remote UE 110 towards the access node. IR UE 112, 112-1 may be however configured to append the uplink PDU with its own protocol header.

[0118] As noted above, the procedure described with reference to FIG. 10 or FIG. 11 may be performed by one or more IR UEs belonging to the sidelink based relay. Access node 120 may receive the appended uplink PDU, possibly with headers appended by different IR UEs. When received by access node 120, the uplink PDU may therefore comprise the data field and a plurality of uplink protocol headers, for example uplink protocol headers associated with remote UE 110 and one or more IR UEs 112, 112-1, 112-2 of the sidelink based relay.

[0119] Upon reception of the uplink PDU, access node 120 may determine, from the different uplink protocol headers, the protocol header that is associated with remote UE 110. For example, access node 120 may remove headers of relay UE 114 and IR UE(s) 112, 112-1, 112-2 and extract data from the header located after the removed protocol headers. Access node 120 may be aware of the number of IR UE(s), and therefore the number of protocol headers, because access node 120 may be responsible for configuring the sidelink based relay.

[0120] Access node 120 may determine the RB ID of remote UE 110 from the protocol header of remote UE 110. Access node 120 may determine an upper protocol layer entity (e.g., PDCP entity) that corresponds to the RB ID of remote UE 110. In this context, upper protocol layer may refer to a protocol layer that is located in the protocol stack above the layer configured to provide the multi-hop sidelink based relay functionality. An upper protocol layer may be for example a layer 2 (L2) protocol such as PDCP. Access node 120 may then provide the data field to the determined upper protocol layer entity. This enables the content of the data field to be provided to a correct upper protocol layer entity regardless of hiding IR UE(s) 112, 112-1, 112-2 from other devices (e.g., remote UE 110 and relay UE 114) of the sidelink based relay. Backwards compatibility with devices not configured with the multi-hop sidelink based relay functionality may be therefore provided.

[0121] In downlink direction, corresponding operations may be performed by access node 120 and IR UE(s) 112, 112-1, 112-2. For example, access node 120 may generate downlink protocol headers IR UE(s) 112, 112-1, 112-2 and remote UE 110. In some example embodiments, access node 120 may also generate a downlink protocol header targeted to relayUE 114. The downlink protocol headers may have same or different structure as the uplink protocol headers (cf. FIG. 8). Access node 120 may append a downlink PDU (e.g., comprising a data field) with the downlink protocol headers of relay UE 114, IR UE(s) 112, 112-1, 112-2, and remote UE 110. Access node 120 may transmit the appended downlink PDU to relay UE 114 for forwarding the downlink PDU towards remote UE 110 (e.g., to IR UE 112, 112-2).

[0122] IR UE 112, 112-2 may receive the downlink PDU from relay UE 114, optionally via another IR UE. As noted above, the downlink PDU may comprise a plurality of uplink protocol headers. The outermost uplink protocol header of the downlink PDU may comprise the UE ID and RB ID of IR UE 112, 112-2. In case of IR UE 112, the second outermost uplink protocol header of the downlink PDU may comprise the UE ID and RB ID of remote UE 110. In case of IR UE 112-2, the second outermost uplink protocol header of the downlink PDU may comprise UE ID and RB ID of IR UE 112-1. IR UE 112, 112-2 may remove the outermost header of the downlink PDU. In general, IR UE 112, 112-2 may remove the downlink protocol header targeted to itself. IR UE 112, 112-2 may then transmit the downlink PDU to remote UE 110 or IR UE 112-1. IR UE 112, 112-2 may therefore forward the downlink PDU to remote UE 110 or IR UE 112-1 without its own protocol header, e.g., the outermost downlink protocol header of the received downlink PDU. The presence of IR UE(s) in the sidelink based relay may be therefore hidden from remote UE 110 and relay UE 114, thereby enabling backwards compatibility with legacy devices also at the downlink.

[0123] Example(s) of the functionality described herein will be now described in the scenario of Rel-17 / 18 UEs and PC5-SRAP protocol as an example. In uplink direction, remote UE 110 may transmit a PC5-SRAP PDU to IR UE 112, 112-1, which may be configured to act as a U2N Relay UE for remote UE 110, e.g., according to Rel-17 / 18. A PC5-SRAP PDU that carries SRB0 message might not include the SRAP header and be transmitted on SL-RLC0. A PC5-SRAP PDU that carries other than SBR0 message may include the SRAP header of two octets, as illustrated in FIG. 8.

[0124] PC5-SRAP operations at IR UE 112,112-1

[0125] Upon receiving a PC5-SRAP PDU from remote UE 110 on SL-RLC0, IR UE 112, 112-1 may add the SRAP header comprising the UE ID of remote UE 110 to the PC5-SRAP PDU (cf. “Appended second header” in FIG. 10. IR UE 112, 112-1 may set the RB ID in the SRAP header for the received PC5-SRAP PDU to zero. This may be similar to Uu-SRAP PDU generation for a SRB0 message received from a remote UE at the serving L2 U2N Relay UEin Rel-17 / 18. IR UE 112, 112-1 may then add another SRAP header (cf., “Appended header”) on top of the SRAP header. The appended SRAP header may comprise UE ID of the IR UE 112, 112-1 (e.g., configured in the remote UE contexts of IR UE 112, 112-1) and RB ID configured to IR UE 112, 112-1 for mapping PC5-SRAP PDU received on SL-RLCO from remote UE 110 and determining the egress SL-RLC CH configured for forwarding the received PC5-SRAP PDU. It is noted that the IR UE 112, 112-1 might not be configured with any data radio bearer (DRB), but instead with SL relay RLC CH(s). Thus, the RB ID in the second SRAP header may be configured to use a subset (e.g., 5 LSB bits) of the corresponding egress SL-RLC CH ID. In other option, the RB ID is the second SRAP header and mapping between the RB ID and the egress SL-RLC CH may be configured to the IR UE 112, 112-1 by access node 120 explicitly.

[0126] Upon receiving a PC5-SRAP PDU from remote UE 110 on other than SL-RLCO, IR UE 112, 112-1 may check the UE ID and RB ID in the header of the received PC5-SRAP PDU (cf. “Second header” in FIG. 11), and determine another SRAP header (cf., “Appended header”) to be added on top of the received SRAP header. The appended SRAP header may comprise the UE ID of the IR UE 112, 112-1 (e.g., configured in the L2 U2N remote UE contexts of IR UE 112, 112-1) and RB ID configured to IR UE 112, 112-1 for mapping the received PC5-SRAP PDU and determining the egress SL-RLC CH for forwarding the received PC5-SRAP PDU. The RB ID in the second SRAP header may be configured to use a subset of the corresponding egress SL-RLC CH ID, as already noted above for example.

[0127] SRAP handling at Rell7 / 18 L2 U2N relay UE

[0128] When configured as an L2 U2N Relay UE, relay UE 114 might be only aware of the outermost (e.g., topmost) SRAP header (“Appended header” in FIG. 10 and FIG. 11) and configured to perform packet forward according to this header, e.g., according to Rel-17. The embedded SRAP header may be therefore considered as upper layer data by relay UE 114.

[0129] Uu-SRAP at access node

[0130] Upon receiving a PC5-SRAP PDU from the IR UE 112, 112-2, relay UE 114 may check the UE ID and RB ID of IR UE 112, 112-2 in the second SRAP header and forward the received SRAP PDU to the serving access node on the corresponding egress Uu-RLC CH that is configured to map the RB ID of the UE ID, e.g., according to Rel-17 and / or Rel-18 specifications. IR UE 112, 112-2 may appear as a remote UE to relay UE 114. Upon receiving the PC5-SRAP PDU from relay UE 114, the Uu-SRAP layer at access node 120 may checkand determine, based on detecting the UE ID and RB ID of IR UE 112, 112-2 in the appended SRAP header, that the SRAP PDU is from IR UE 112, 112-2. Then, as access node 120 is aware of IR UE 112, 112-2 being configured to relay data to / from remote UE 110, access node 120 may further check the next SRAP header (“Appended second header” or “Second header” in FIG. 10 or FIG. 11) to determine that the data is from remote UE 110 and forward the data to the PDCP entity corresponding to the RB ID of remote UE 110 indicated in this SRAP header.

[0131] Note that similar functionality may be provided when multiple IR UEs are included in the sidelink based relay. For example, in case of FIG. 4, a PC5-SRAP PDU carrying data of remote UE 110 may arrive at access node 120 with a further SRAP header added by the IR UE 112-2 on top of the SRAP headers of remote UE 110 and IR UE 112-1. Thus, the number of SRAP headers may be equal to the number of hops in the L2 multi-hop U2N relay connection of remote UE 110.

[0132] In the downlink direction, reverse operations may be performed. Access node 120 may be configured to generate all the SRAP headers for the L2 multi-hop U2N relay of data to remote UE 110 and include them in an Uu-SRAP PDU carrying data of remote UE 110 before sending the Uu-SRAP PDU to relay UE 114.

[0133] In addition, or as an alternative, to appending the uplink PDU with additional protocol headers, e.g., as described with reference to FIG. 10 and FIG. 11, access node 120 may configure relay UE 114 and / or IR UE(s) 112, 112-1, 112-2 to receive and forward PDUs based on the UE ID and RB ID of remote UE 110 as follows. This provides the benefit of avoiding additional headers, which reduces signalling overhead.

[0134] For example, access node 120 may determine a mapping rule between ingress and egress channels of IR UE 112, 112-1, 112-2. The mapping rule may be configured for forwarding uplink PDUs on the sidelink based relay. The mapping rule may be associated the UE ID of remote UE 110 and the RB ID of remote UE 110. For example, the mapping rule may be configured to be applicable for a particular UE ID. The mapping rule may indicate an egress channel for a particular RB ID of a particular UE ID. Access node 120 may transmit (configure) the mapping rule to IR UE 112, 112-1, 112-2. IR UE 112, 112-1, 112-2 may receive the mapping rule from access node 120, for example via relay UE 114, optionally via one or more other IR UEs.

[0135] Forwarding of uplink PDUs may be configured for example as follows, now using IR UE 112-2 as an example. IR UE 112-2 may receive, from IR UE 112-1 via an ingress channel (e.g., ingress SL-RLC CH) an uplink PDU comprising an uplink protocol header. The uplink protocol header may comprise UE ID and RB ID of remote UE 110. Note that the uplink PDU may comprise a single uplink protocol header. For example, the uplink PDU may not include any protocol header appended by IR UE 112-1.

[0136] IR UE 112-2 may determine, based on the mapping rule, an egress channel for forwarding the uplink PDU. For example, IR UE 112-2 may determine an egress channel that corresponds to the ingress channel of the uplink PDU and that is configured for the UE ID of remote UE 112-1. IR UE 112-2 may transmit the uplink PDU via the determined egress channel to relay UE 114 or another IR UE.

[0137] This alternative enables functionality where an SRAP PDU with a single SRAP header including UE ID and RB ID of remote UE 110 is used across the serving IR UE(s) and relay UE 114. This is enabled by access node 120 configuring IR UE(s) 112, 112-1, 112-2 and / or relay UE 114 to receive and forward SRAP PDU of remote UE 110 based on UE ID and RB ID of remote UE 110 and the mapping rule between ingress and egress SL relay RLC CHs.

[0138] In downlink direction, IR UE 112, 112-2 may receive, from relay UE 114 or another IR UE, a downlink PDU comprising a (single) downlink protocol header. The downlink protocol header may comprise the UE ID of remote UE 110. The downlink protocol header may comprise the RB ID of remote UE 11. IR UE 112, 112-2 may forward the downlink PDU to remote UE 110 or another IR UE as such, e.g., without modifying the downlink protocol header. IR UE 112, 112-2 may determine the egress channel based on the UE ID and RB ID of remote UE 110, e.g., by applying the mapping rule in reverse direction. IR UE 112, 112-2 may transmit, based on the UE ID and the RB ID of remote UE 110, the downlink PDU to remote UE HO or lR UE 112-1. The transmitted downlink PDU may comprise the downlink protocol header.

[0139] When configuring IR UE(s) 112, 112-1, 112-2 to operate based on the protocol header of remote UE 110, a possible conflict may arise between UE ID assignments to different remote UEs. A conflict may arise when two or more remote UEs are configured with same UE ID. For example, IR UE 112 may perform an intra-cell relay reselection when the SL connection between the IR UE 112 and relay UE 114 is degrading and switch to a new relayUE capable of receiving and forwarding PDUs based on protocol header of remote UE 110 (cf., second alternative). However, the new relay UE may be serving another remote UE which is assigned with the same UE ID as remote UE 110. Thus, a conflict in UE ID assignment for different remote UEs may happen and be resolved as follows. In one option, the access node may reassign a new UE ID for at least one of the remote UEs impacted by the conflict and configure the at least one of the remote UEs and associated IR UE(s) and relay UE with the new UE ID. In another option, as the conflict may have a local impact to individual IR UE or relay UE associated with the remote UEs in the conflict, the access node may configure only the impacted individual IR UE or relay UE to switch the UE ID of at least one of the remote UEs for relaying PDU of the at least one of the remote UEs (e.g.., SRAP PDU) between the ingress and egress channels. In the example described above, the conflict may be local to the new relay UE and therefore the access node may configure the new relay UE to switch the UE ID of remote UE 110 for forwarding PDU(s) of remote UE 110 between IR UE 112 and the access node. The UE ID of remote UE 110 may remain unchanged to remote UE 110 and IR UE 112.

[0140] Access node 120 may determine a conflict between the UE ID of remote UE 110 and UE ID of another remote UE. Access node 120 may assign a new UE ID for remote UE 110. The new UE ID may be a UE ID that has not been assigned by access node 120 to other remote UEs. Access node 120 may transmit the new UE ID to relay UE 114 and / or IR UE(s) 112, 112- 1, 112-2, for example with a request, in a first option, to replace the UE ID of remote UE 110 with the new UE ID and release the UE ID or, in a second option, to switch between the UE ID of remote UE 110 and the new UE ID for forwarding PDU(s) between the ingress and egress channels. Access node 120 may transmit the new UE ID to IR UE(s) 112, 112-1, 112-2 via relay UE 114.

[0141] Relay UE 114 or IR UE 112, 112-1, 112-2 may receive the new UE ID of remote UE 110, for example within the request to replace or to switch the UE ID of remote UE 110. In the second option, upon reception of a PDU comprising the UE ID of remote UE 110 on an ingress channel, relay UE 114 or IR UE 112, 112-1, 112-2 may replace the UE ID with the new UE ID in the protocol header of the received PDU. IR UE 112, 112-1, 112-2 may transmit the PDU with the protocol header now comprising the new UE ID on a corresponding egress channel.

[0142] This functionality enables to resolve conflicts between UE IDs of remote UEs flexibly, considering for example that Rel-17 / 18 UE ID of 8-bit length may be kept while it is desired to for the access node ensure that the UE ID of remote UE 110 is unique for IR UE(s) 112, 112-1, 112-2 and relay UE 114. Conflicts may be beneficially resolved without reconfiguration of remote UE 110 or the other conflicting remote UE.

[0143] FIG. 12 illustrates an example of a method for operating an intermediate relay node of a sidelink based relay of a cellular communication network. The method may be performed by an apparatus, e.g., IR UE 112, 112-1, 112-2, or by a control apparatus configured to control the functioning thereof, when installed therein.

[0144] At operation 1201, the method may comprise receiving, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field.

[0145] At operation 1202, the method may comprise appending the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit.

[0146] At operation 1203, the method may comprise transmitting the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

[0147] FIG. 13 illustrates an example of a method for operating an access node of a cellular communication network. The method may be performed by an apparatus, e.g., access node 120, or by a control apparatus configured to control the functioning thereof, when installed therein.

[0148] At operation 1301, the method may comprise receiving, from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocol headers associated with a remote user equipment and at least one intermediate relay device of a sidelink based relay of the cellular communication network between the access node and the remote user equipment.

[0149] At operation 1302, the method may comprise determining, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment.

[0150] At operation 1303, the method may comprise determining, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment.

[0151] At operation 1304, the method may comprise determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0152] At operation 1305, the method may comprise providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0153] FIG. 14 illustrates an example of another method for operating an intermediate relay node of a sidelink based relay of a cellular communication network. The method may be performed by an apparatus, e.g., IR UE 112, 112-1, 112-2, or by a control apparatus configured to control the functioning thereof, when installed therein.

[0154] At operation 1401, the method may comprise receiving, from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment.

[0155] At operation 1402, the method may comprise receiving, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment.

[0156] At operation 1403, the method may comprise determining, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit.

[0157] At operation 1404, the method may comprise transmitting the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel.

[0158] FIG. 15 illustrates an example of another method for operating an access node of a cellular communication network. The method may be performed by an apparatus, e.g., access node 120, or by a control apparatus configured to control the functioning thereof, when installed therein.

[0159] At operation 1501, the method may comprise transmitting, to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relay device and between ingress and egress channels of the at least one intermediate relay device for forwarding protocoldata units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment.

[0160] At operation 1502, the method may comprise receiving, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the access node and the relay device.

[0161] At operation 1503, the method may comprise determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0162] At operation 1504, the method may comprise providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

[0163] Further features of the methods directly result for example from functionality of IR UE 112, 112-1, 112-2, relay UE 114, or access node 120, as described throughout the description, claims, and drawings, and are therefore not repeated here. An apparatus, for example a device such as IR UE 112, 112-1, 112-2, relay UE 114, or an access node, may be configured to perform or cause performance of any aspect of the method(s) described herein. Further, a computer program or a computer program product may comprise instructions for causing, when executed by an apparatus, the apparatus to perform any aspect of the method(s) described herein. Further, an apparatus may comprise means for performing any aspect of the method(s) described herein. According to an example embodiment, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform any aspect of the method(s).

[0164] Any range or device value given herein may be extended or altered without losing the effect sought. Also, any embodiment may be combined with another embodiment unless explicitly disallowed.

[0165] Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

[0166] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items.

[0167] The steps or operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the example embodiments described above may be combined with aspects of any of the other example embodiments described to form further example embodiments without losing the effect sought.

[0168] The term 'comprising' is used herein to mean including the method, blocks, or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0169] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. Expression “or” may be understood as a non-exclusive “or” and therefore a list or two or more elements indicated to be mutually optional by the expression ”or” means at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0170] Although subjects may be referred to as ‘first’ or ‘second’ subjects, this does not necessarily indicate any order or importance of the subjects. Instead, such attributes may be used solely for the purpose of making a difference between subjects.

[0171] As used in this application, the term ‘circuitry’ may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable) :(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s),that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims.

[0172] As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0173] It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from scope of this specification.

Claims

CLAIMS1. An intermediate relay device for a sidelink based relay of a cellular communication network, the intermediate relay device comprising: means for receiving, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; means for appending the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; and means for transmitting the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

2. The intermediate relay device according to claim 1, further comprising: means for receiving the uplink protocol data unit from a signalling channel configured for establishing a connection between the remote user equipment and the access node; and means for appending, prior to appending the uplink protocol data unit with the uplink protocol header, the uplink protocol data unit with a second uplink protocol header comprising a user equipment identifier of the remote user equipment and a preconfigured radio bearer identifier associated with the signalling channel.

3. The intermediate relay device according to claim 2, wherein the signalling channel comprises a signalling channel of a sidelink radio link control, SL-RLC, protocol.

4. The intermediate relay device according to any of claims 1 to 3, further comprising: means for receiving, from the relay device or the third intermediate relay device, a downlink protocol data unit comprising a plurality of downlink protocol headers, wherein an outermost downlink protocol header of the downlink protocol data unit comprises the user equipment identifier of the intermediate relay device and the radio bearer identifier of the intermediate relay device, and wherein a second outermost downlink protocol header of the downlink protocol data unit comprises the user equipment identifier of the remote userequipment or the second intermediate relay device and the radio bearer identifier of the remote user equipment or the second intermediate relay device; means for removing the outermost header of the downlink protocol data unit; and means for transmitting, based on the user equipment identifier of the remote user equipment or the second intermediate relay device and the radio bearer identifier of the remote user equipment or the second intermediate relay device, the downlink protocol data unit to the remote user equipment or the second intermediate relay device without the outermost downlink protocol header.

5. The intermediate relay device according claim 1, wherein the uplink protocol data unit further comprises a second uplink protocol header comprising: a user equipment identifier of the remote user equipment or the second intermediate relay device, and a radio bearer identifier of the remote user equipment or the second intermediate device.

6. The intermediate relay device according to any of claims 1 to 5, further comprising: means for determining the radio bearer identifier of the intermediate relay device based on an identifier of an egress channel configured for transmission of the appended uplink protocol data unit.

7. The intermediate relay device according to any of claims 1 to 6, further comprising: means for determining the user equipment identifier of the intermediate relay device based on a remote user equipment context of the intermediate relay device.

8. The intermediate relay device according to any of claims 1 to 7, wherein the uplink protocol data unit comprises a layer two, L2, protocol data unit.

9. The intermediate relay device according to any of claims 1 to 8, wherein the uplink protocol data unit comprises a sidelink relay adaptation protocol, SRAP, protocol data unit.

10. The intermediate relay device according to any of claims 1 to 9, further comprising:means for receiving the uplink protocol data unit on a common control channel, CCCH, wherein the data field comprises at least one radio resource control, RRC, protocol message.

11. The intermediate relay device according to any of claims 1 to 10, further comprising: means for transmitting, to the relay device or the third intermediate relay device, an indication of the data field comprising data received by the intermediate device from the remote user equipment or the second intermediate relay device.

12. The intermediate relay device according to claim 11, wherein the indication comprises a preconfigured value of a reserved bit of the uplink protocol header.

13. The intermediate relay device according to any of claims 1 to 12, wherein the intermediate relay device is configured to operate as another remote user equipment towards the relay device or the third intermediate relay device.

14. The intermediate relay device according to any of claims 1 to 13, wherein the relay device is connected to the access node via a direct radio link, and / or wherein the intermediate relay device is configured to operate as another relay device towards the remote user equipment or the second intermediate relay device.

15. The intermediate relay device according to any of claims 1 to 14, wherein the sidelink based relay comprises the remote user equipment, the relay device, and one or more intermediate relay devices for data communication between the remote user device and the relay device.

16. An access node of a cellular communication network, comprising: means for receiving, from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocol headers associated with a remote user equipment and at least one intermediate relay device of a sidelink basedrelay of the cellular communication network between the access node and the remote user equipment; means for determining, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment; means for determining, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment; means for determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and means for providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

17. The access node according to claim 16, wherein the uplink protocol data unit comprises a layer two, L2, protocol data unit.

18. The access node according to claim 16 or 17, wherein the uplink protocol data unit comprises a sidelink relay adaptation protocol, SRAP, data unit.

19. The access node according to any of claims 16 to 18, wherein the upper protocol layer entity comprises a packet data convergence protocol, PDCP, entity.

20. A method, comprising: receiving, by an intermediate relay device and from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; appending the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; and transmitting the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

21. A method, comprising: receiving, by an access node and from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocol headers associated with a remote user equipment and at least one intermediate relay device of a sidelink based relay of the cellular communication network between the access node and the remote user equipment; determining, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment; determining, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment; determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

22. An intermediate relay device for a sidelink based relay of a cellular communication network, the intermediate relay device comprising: means for receiving, from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; means for receiving, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment; means for determining, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit; and means for transmitting the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel.

23. The intermediate relay device according to claim 22, further comprising:means for receiving, from the relay device or the third intermediate relay device, a downlink protocol data unit comprising a downlink protocol header comprising the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user; and means for transmitting, based on the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment, the downlink protocol data unit to the remote user equipment or a second intermediate relay device with the downlink protocol header.

24. The intermediate relay device according to claim 22 or 23, further comprising: means for receiving, from the access node, a new user equipment identifier for the remote user equipment; means for replacing, in the uplink protocol header, the user equipment identifier of the remote user equipment with the new user equipment identifier of the remote user equipment; and means for transmitting, to the relay device or the third intermediate relay device via the egress channel, the uplink protocol data unit with the uplink protocol header comprising the new user equipment identifier of the remote user equipment.

25. An access node of a cellular communication network, comprising: means for transmitting, to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relay device and between ingress and egress channels of the at least one intermediate relay device for forwarding protocol data units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; means for receiving, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the access node and the relay device;means for determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and means for providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

26. The access node according to claim 25, further comprising: means for transmitting, to the remote user equipment via the relay device and the at least one intermediate relay device, a downlink protocol data unit comprising a single downlink protocol header, wherein the single downlink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment.

27. The access node according to claim 25 or 26, further comprising: means for determining a conflict between the user equipment identifier of the remote user equipment and a user equipment identifier of another remote user equipment associated with at least one of the relay device and the at least one intermediate relay device; means for assigning a new user equipment identifier for the remote user equipment; and means for transmitting the new user equipment identifier to the at least one of the relay device and the at least one intermediate device.

28. A method, comprising: receiving, by an intermediate relay device and from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receiving, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment; determining, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit; andtransmitting the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel.

29. A method, comprising: transmitting, by an access node and to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relay device and between ingress and egress channels of the at least one intermediate relay device for forwarding protocol data units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receiving, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the access node and the relay device; determining an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and providing the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

30. A computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to performing the method according to any of claims 20, 21, 28, or 29.

31. An intermediate relay device comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the intermediate relay device at least to: receive, from a remote user equipment or a second intermediate relay device, an uplink protocol data unit comprising at least a data field; append the uplink protocol data unit with an uplink protocol header comprising a user equipment identifier of the intermediate relay device and a radio bearer identifier of the intermediate relay device to obtain an appended uplink protocol data unit; andtransmit the appended uplink protocol data unit to a relay device or a third intermediate relay device for forwarding at least the data field of the appended uplink protocol data unit via the sidelink based relay towards an access node of the cellular communication network.

32. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to: receive, from a relay device, an uplink protocol data unit comprising a data field and a plurality of uplink protocol headers comprising uplink protocol headers associated with a remote user equipment and at least one intermediate relay device of a sidelink based relay of the cellular communication network between the apparatus and the remote user equipment; determine, from the plurality of uplink protocol headers, an uplink protocol header associated with the remote user equipment; determine, from the uplink protocol header associated with the remote user equipment, a radio bearer identifier of the remote user equipment; determine an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and provide the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

33. An intermediate relay device comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the intermediate relay device at least to: receive, from an access node via a relay device or a third intermediate relay device, a mapping rule between ingress and egress channels of the intermediate relay device for forwarding uplink protocol data units on the sidelink based relay, wherein the mapping rule is associated with a user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receive, from a second intermediate relay device via the ingress channel, an uplink protocol data unit comprising an uplink protocol header, wherein the uplink protocol header comprises the user equipment identifier of the remote user equipment and the radio bearer identifier of the remote user equipment;determine, based on the mapping rule, an egress channel for forwarding the uplink protocol data unit; and transmit the uplink protocol data unit to the relay device or the third intermediate relay device via the egress channel.

34. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to: transmit, to a relay device and at least one intermediate relay device of a sidelink based relay of the cellular communication network, mapping rules between ingress and egress channels of the relay device and between ingress and egress channels of the at least one intermediate relay device for forwarding protocol data units on the sidelink based relay, wherein the mapping rules are associated with at least one user equipment identifier of a remote user equipment and a radio bearer identifier of the remote user equipment; receive, from the relay device of the sidelink based relay, an uplink protocol data unit comprising a data field and a single uplink protocol header, wherein the single uplink protocol header comprises a user equipment identifier of the remote user equipment and a radio bearer identifier of the remote user equipment configured to be used on a direct radio link between the apparatus and the relay device; determine an upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment; and provide the data field to the upper protocol layer entity corresponding to the radio bearer identifier of the remote user equipment.

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