Inter-du path change management for multipath rlaying

Abstract

Methods of configuring path changes in communication networks comprising a base station and plurality of user equipments.

Description

[0001] INTER-DU PATH CHANGE MANAGEMENT FOR MULTIPATH RLAYING

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to inter-DU path change in a multipath (MP) transmission system supporting Sidelink (SL) relaying. In particular, the present invention relates to the call flow addressed between the gNB-CU and the gNB-DU for managing the inter-DU path change for multipath and the exchanged messages to configure the gNB-DU, the relay UE and the remote UE.

[0004] BACKGROUND

[0005] The 3rd Generation Partnership Project (3GPP) has initiated the development of new radio access technology known as fifth-generation New Radio (5G NR) to respond to requirements related to very high reliability and very low latency. The 5G NR is not referred only to the enhancement of radio access technology but also to address a wide range of new services to be enabled by future mobile communication. Three distinctive categories of use cases are defined in NR from enhanced mobile broadband (eMBB), massive machine typing communication (mMTC) to Ultra-Reliable and Low Latency communication (URLLC).

[0006] A first version of Sidelink for 5G, or New Radio (NR) Sidelink, has been developed in 3GPP Release 16 as part of the 5G V2X Work Item (Wl), to support advanced vehicle-to- anything (V2X) scenarios and commercial applications and services in addition to complement former basic safety services. NR V2X addresses advanced driving use cases where vehicles are exchanging large amount of data while respecting a low latency requirement. NR Sidelink is designed to provide three basic transmission scenarios: broadcast, groupcast and unicast communications, while considering both out-of-coverage and in-network coverage deployment scenarios.

[0007] Based on the NR sidelink technology, 3GPP introduced the sidelink-based relaying functionality as part of the 3GPP Release 17 framework, where a relay UE may provide User Plane (UP) and Control Plane (CP) data relaying between a set of served remote UEs and the network (UE-to-network, or U2N, relay) or between a source remote UE, or source UE, and a target remote UE, or target UE (UE-to-UE, or U2U relay).

[0008] The purpose of the Release 17 sidelink relaying functionality was to both extend sidelink / network coverage and improve power efficiency, while considering a wider range of applications and services, including V2X, Public Safety and commercial applications and services. Some of these new V2X scenarios require ultra-reliability and low latency (URLLC) performance, in order to meet high-speed and high-density constraints, while requiring some network coverage extension, which may be achieved through sidelink relaying. This first version of the sidelink relaying functionality, as defined in the Release 17 specification, mainly aimed at supporting the UE-to-network (U2N) relay with basic functionalities and limited features. For better support of the use cases requiring sidelink relay, further enhancements are necessary in order to introduce the potential solutions identified during the Rel-17 study item. The follow-up 3GPP Release 18 work item “NR Sidelink Relay (SLR) Enhancements” has addressed several solutions considered as enhancement areas needed in NR Sidelink Relay system for the V2X, public safety and commercial use cases.

[0009] The multipath relay has been specified as a solution in the Release 18 NR SLR Enhancements Wl, where a remote UE is connected to the network via a direct path (e.g. the path is the link between the UE and a base station (also referred to as a gNB) of the network which link is referred to as a Uu link) and an indirect path (e.g. a path which includes a relay UE between the remote UE and the base station (also referred to as a gNB) of the network, where the link between the remote UE and the relay UE is referred to as a PC5 link and thus the path includes a PC5 link and a Uu link), with a potential to improve the reliability, the robustness and the throughput of communication.

[0010] This multipath relay solution aims to provide applications requiring high Uplink (UL) data rates on 5G terminals, to achieve the required UL data rate, especially at the edge of a cell. Furthermore, the multipath relaying can improve the reliability and the stability of the provided services while reducing the latency if one of the paths is suffering from deteriorating channel conditions.

[0011] Remote UEs configured for multipath relaying can transmit the data via multiple paths. The transmitted data is associated to a radio bearer configured by the network. In order to improve the reliability and / or the throughput, the data can be transmitted via multiple paths and thus, one radio bearer can be mapped to multiple configured paths. This radio bearer has been considered in RAN2 meetings for Release 18 multipath relaying scenarios and has been named “MP split bearer” or “MP bearer”. A MP bearer can be a Signaling Radio Bearer (SRB) for control data or a Data Radio Bearer (DRB) for user data.

[0012] As specified in SLR Wl in Release 18, the remote UE is connected to the same gNB via a direct path and via an indirect path. Thus, the remote UE is configured by the same gNB (intra-gNB) for multipath. However, a gNB in a split architecture can have a single gNB-CU (Control Unit) and multiple gNB-DUs (Distributed Unit). Each gNB-DU can support one or more cells. The gNB-DU is connected to the gNB-CU via F1 interface.

[0013] A remote UE in an intra-DU multipath configuration can be connected to a single gNB- DU for all the paths. For the case where the remote UE is connected via the direct link to a first gNB-DU and via the indirect link to a second gNB-DU within the same gNB, the multipath is called an inter gNB-DU multipath. In order to manage the paths in a multipath transmission system, RAN2 has agreed on six use cases including path addition (Case A and B), path release (case C and D), and path change (case E and G). These use cases are supported for intra-DU MP and inter-DU MP configurations. In an example, a remote UE connected in multipath to the same gNB-Dll can perform an inter-DU path change and thus, the remote UE is then connected to two different gNB-DUs in an inter-DU MP configuration.

[0014] RAN3 has addressed the case of inter-DU path addition where the new added path connects the remote UE to a new gNB-DU. In this case, the remote UE is connected to two different gNB-DUs in an inter-DU MP system. A Text Proposal has been published in R3- 230947 defining the different exchanged message between the gNB-CU and the different gNB-DUs (existing gNB-DU and the new gNB-DU) involved in the path addition.

[0015] Details of the call flows for inter-DU path addition and the information elements included in the F1AP exchanged messages including UE context setup and UE context modification has not yet been considered in RAN3 working group (WG). The details of the call flows for path release and the path change have not yet been investigated in RAN3 WG.

[0016] Furthermore, the path change consists of releasing the existing path and adding a new path within the multipath system. RAN2 WG has agreed to configure the path change with a single release-and-add procedure. The gNB-CU has to configure the source gNB-DU for modification or release of the multipath configuration and configure the target gNB-DU with the remote UE multipath context. Furthermore, the gNB-CU should configure the remote UE with a single release-and-add procedure. Thus, RAN3 WG should align with the single procedure of release-and-add for the path change in multipath transmission system.

[0017] The existing F1AP exchanged messages between the gNB-CU and the gNB-DU offers a UE context setup, modification and release procedures. The releasing of part or the entire UE context at the source gNB-DU may involve two F1AP messages including a UE context modification and then a UE context release after the configuration is complete at the remote UE as in R3-233020 for inter-DU direct path change. Thus, the existing procedure is not aligned with the single procedure of path change at the remote UE and may increase the latency by exchanging additional F1AP messages between the gNB-CU and the gNB-DUs.

[0018] Furthermore, the path change can be an intra-DU path change or inter-DU path change. The inter-DU multipath case is to be considered wherein the selected path change from a source gNB-DU to a target gNB-DU. Thus, an inter-DU path change may involve additional F1AP exchanged messages between the source gNB-CU and the involved gNB-DUs. As multipath is managed by two or more gNB-DUs in an inter-DU case, the coordination between the multiple gNB-DUs is to be considered also by the gNB-CU in order to manage correctly the resources and the control plane between the DUs. Finally, the path change is not yet considered in RAN3 WG and its impact on the F1AP exchanged messages for different use cases. Therefore, enhancements in the procedure of inter-DU path change and the coordination between Dlls in an inter-DU multipath transmission system are required which take account of the aforementioned issues.

[0019] SUMMARY

[0020] In accordance with a first aspect of the invention there is provided a method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at the CU, comprising: determining that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs; and sending, to the source DU of the selected path, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path.

[0021] The request may further include information for releasing or modifying, at the source DU of the selected path, a context of the remote UE, immediately upon or following a triggering condition.

[0022] The method may further comprise sending, to the target DU of the selected path, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

[0023] The message may further include at least one of:

[0024] MP path management configuration;

[0025] MP resource transfer information;

[0026] F1-C transfer path MP;

[0027] Configuration message for a relay UE;

[0028] Configuration message for the remote UE;

[0029] Release / Modify Command;

[0030] MP Duplication Deactivation;

[0031] SRB / DRB list to be released;

[0032] Uu RLC channels to be released;

[0033] MP Split Deactivation;

[0034] SRB / DRB list to be modified;

[0035] PC5 RLC channels to be released.

[0036] The request may further include at least one of:

[0037] Multipath, MP, path management configuration; Configuration message for the remote UE;

[0038] MP resource transfer information;

[0039] F1 -C transfer path M P;

[0040] Release / Modify Command;

[0041] MP Duplication Deactivation;

[0042] MP Split Deactivation;

[0043] Signaling Radio Bearer, SRB I Data Radio Bearer, DRB, list to be released;

[0044] SRB / DRB list to be modified; llu RLC channels to be released;

[0045] PC5 RLC channels to be released;

[0046] Configuration message for a relay UE;

[0047] Add / Modify Command;

[0048] SRB / DRB list to be added;

[0049] Uu RLC channels to be added.

[0050] In a case that the message and / or request includes MP path management configuration, the MP path management configuration includes at least one of:

[0051] Path management type;

[0052] Path ID;

[0053] A radio bearer ID; and

[0054] A timer or timers, optionally associated to a path management type.

[0055] The target DU for the selected path may be a source DU of another path of the at least two paths.

[0056] The target DU for the selected path may not be a source DU of another path of the at least two paths.

[0057] The selected path may be a direct path.

[0058] The method may further comprise receiving a measurement report from the remote UE, wherein said measurement report comprises an indication of the link quality of the direct path.

[0059] The CU may determine that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

[0060] The selected path may be an indirect path.

[0061] The method may further comprise receiving a measurement report from a relay UE of the indirect path, wherein said measurement report comprises an indication of the link quality of the indirect path.

[0062] The CU may determine that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report. A relay UE of the indirect path may perform path change from the source DU towards the target DU.

[0063] The remote UE may switch a connection from a relay UE of the indirect path towards a new relay UE having a connection to the target DU.

[0064] In accordance with a second aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at a source DU of a selected path among the at least two paths, comprising: receiving, from the CU, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path; and depending on a triggering condition, performing the release of the selected path.

[0065] The triggering condition may comprise one or more of: receiving, from the CU, configuration information for configuring the remote UE to establish a path with a target DU; receiving, from the CU, configuration information to configure the source DU with a context of the remote UE; receiving, from the remote UE, a notification indicating that a path with a target DU has been established; expiration of a timer configured by the CU; and expiration of a timer set at the source DU.

[0066] In accordance with a third aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at the remote UE, comprising: receiving configuration information for configuring the remote UE to establish a path with a target DU; and performing the establishment of a path with the target DU sending a notification indicating that a path with the target DU has been established.

[0067] The step of sending a notification indicating that a path with the target DU has been established may comprise sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the source DU. The step of sending a notification indicating that a path with the target DU has been established may comprise sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the target DU.

[0068] The step of sending a notification indicating that a path with the target DU has been established may comprise sending, in a case that the configuration information is received from the target DU, a notification indicating that a path with the target DU has been established to the source DU.

[0069] In accordance with a fourth aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at the CU, comprising: determining that a DU change for a selected path among the at least two paths is to be performed towards the target DU of the plurality of DUs; and sending, to the source DU of the selected path, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path.

[0070] The request may further include information for releasing or modifying, at the source DU of the selected path, a context of the remote UE, immediately upon or following a triggering condition.

[0071] The method may further comprise sending, to the target DU of the selected path, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

[0072] The message may further include at least one of:

[0073] MP path management configuration;

[0074] MP resource transfer information;

[0075] F1-C transfer path MP;

[0076] Configuration message for a relay UE;

[0077] Configuration message for the remote UE;

[0078] Release / Modify Command;

[0079] MP Duplication Deactivation;

[0080] SRB / DRB list to be released;

[0081] Uu RLC channels to be released;

[0082] MP Split Deactivation;

[0083] SRB / DRB list to be modified; PC5 RLC channels to be released.

[0084] The request may further include at least one of:

[0085] Multipath, MP, path management configuration;

[0086] Configuration message for the remote UE;

[0087] MP resource transfer information;

[0088] F1 -C transfer path M P;

[0089] Release / Modify Command;

[0090] MP Duplication Deactivation;

[0091] MP Split Deactivation;

[0092] Signaling Radio Bearer, SRB I Data Radio Bearer, DRB, list to be released;

[0093] SRB / DRB list to be modified; llu RLC channels to be released;

[0094] PC5 RLC channels to be released;

[0095] Configuration message for a relay UE;

[0096] Add / Modify Command;

[0097] SRB / DRB list to be added;

[0098] Uu RLC channels to be added.

[0099] In a case that the message and / or request includes MP path management configuration, the MP path management configuration may include at least one of:

[0100] Path management type;

[0101] Path ID;

[0102] A radio bearer ID; and

[0103] A timer or timers, optionally associated to a path management type.

[0104] The target DU for the selected path may be a source DU of another path of the at least two paths.

[0105] The target DU for the selected path may not be source DU of another path of the at least two paths.

[0106] The selected path may be a direct path.

[0107] The method may further comprise receiving a measurement report from the remote UE, wherein said measurement report comprises an indication of the link quality of the direct path.

[0108] The CU may determine that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

[0109] The selected path may be an indirect path.

[0110] The method may further comprise receiving a measurement report from a relay UE of the indirect path, wherein said measurement report comprises an indication of the link quality of the indirect path. The CU may determine that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

[0111] A relay UE of the indirect path may perform path change from the source DU towards the target DU.

[0112] The remote UE may switch a connection from a relay UE of the indirect path towards a new relay UE having a connection to the target DU.

[0113] In accordance with a fifth aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of user equipments, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at the source DU of a selected path among the at least two paths, comprising: receiving, from the CU, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path; and depending on a triggering condition, performing the release of the selected path.

[0114] The triggering condition may be one of: receiving, from the CU, configuration information for configuring the remote UE to establish a path with a target DU; receiving, from the CU, configuration information to configure the source DU with a context of the remote; receiving, from the remote UE, a notification indicating that a path with a target DU has been established; and expiration of a timer configured by the CU; and expiration of a timer set at the source DU.

[0115] In accordance with a sixth aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of user equipments, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at the remote UE, comprising: receiving configuration information for configuring the remote UE to establish a path with a target DU; performing the establishment of a path with the target DU; and sending a notification indicating that a path with the target DU has been established. The step of sending a notification indicating that a path with the target DU has been established may comprise sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the source DU.

[0116] The step of sending a notification indicating that a path with the target DU has been established may comprise sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the target DU.

[0117] The step of sending a notification indicating that a path with the target DU has been established may comprise sending, in a case that the configuration information is received from the target DU, a notification indicating that a path with the target DU has been established to the source DU.

[0118] In accordance with a seventh aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at a target DU for a selected path of the at least two paths, comprising: receiving, from the CU, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

[0119] The method may further comprise: sending, to the CU, a message including a context setup response.

[0120] The message may include a list of radio bearers and / or RLC channels that have been set up at the remote UE.

[0121] In accordance with an eighth aspect of the invention there is provided method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at a target DU for a selected path of the at least two paths, comprising: receiving, from the CU, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

[0122] The method may further comprise: sending, to the CU, a message including a context setup response. The message includes a list of radio bearers and / or RLC channels that have been set up at the remote UE.

[0123] In accordance with a ninth aspect of the invention there is provided n apparatus for a radio access network, RAN, node Central Unit, CU, node of a wireless network, the apparatus comprising: one or more processing units configured to perform the method according to the first or fourth aspects.

[0124] In accordance with a tenth aspect of the invention there is provided an apparatus for a distributed unit, DU, of a radio access network, RAN, node of a wireless network, the apparatus comprising: one or more processing units configured to perform the method according to the second, fifth, seventh or eighth aspects.

[0125] In accordance with an eleventh aspect of the invention there is provided an apparatus for a user equipment, UE, of a wireless network, the apparatus comprising: one or more processing units configured to perform the method third or sixth aspects.

[0126] In accordance with a twelfth aspect of the invention there is provided computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any of the first to eighth aspects.

[0127] In accordance with a thirteenth aspect of the invention there is provided computer- readable medium carrying a computer program according to the twelfth aspect.

[0128] BRIEF DESCRIPTION OF THE DRAWINGS

[0129] Different aspects of the invention will now be described, by way of example only, and with reference to the following drawings in which:

[0130] Figure 1 is a schematic diagram illustrating an example wireless communication system in which the present invention may be implemented according to one or more embodiments;

[0131] Figure 2 is a schematic diagram illustrating user plane stacks of some protocol layers involved in Sidelink relay operations for UE-to-network (U2N) based relaying;

[0132] Figure 3 is a flow diagram of an example method, of performing an inter-DU direct path change to an inter-DU multipath transmission system in accordance with embodiments of the invention;

[0133] Figure 4 is a flow diagram of an example method, of performing an inter-DU indirect path change to an inter-DU multipath transmission system in accordance with embodiments of the invention;

[0134] Figure 5 is a flow diagram of an example method, of performing an inter-DU direct path change to an intra-DU multipath transmission system in accordance with embodiments of the invention; Figure 6 is a flow diagram of an example method, of performing an inter-DU indirect path change to an intra-DU multipath transmission system in accordance with embodiments of the invention;

[0135] Figure 7a is a flowchart of a method performed at gNB-Cll in accordance with one or more embodiments of the present invention;

[0136] Figure 7b is a flowchart of a method performed at gNB-Dll in accordance with one or more embodiments of the present invention;

[0137] Figure 8 is a flowchart of a method performed at the remote UE in accordance with one or more embodiments of the present invention; and

[0138] Figure 9 is a block schematic diagram of an example wireless communication device in accordance with one or more embodiments of the present invention.

[0139] DETAILED DESCRIPTION

[0140] Figure 1

[0141] Figure 1 is a schematic diagram illustrating an example wireless communication system 100 in which the present invention may be implemented according to one or more embodiments. The wireless communication system 100 is a communication system capable of supporting sidelink relaying or multipath relaying and shows a sidelink relay arrangement or system (or network) including a plurality of nodes including one or more relay User Equipment (UE) serving one or more remote User Equipment (UE).

[0142] For instance, in Figure 1 , UE node 110 is served by network node 111 and may operate as a relay UE node relaying data between the UE node 113 (referred to as a remote UE node) and the network node 111 , hence performing UE-to-network (U2N) relay. In an example where the network node 111 is part of a cellular network, the relay UE 110 is served by a cell controlled by the network node 111.

[0143] UE node 120 is served by network node 111 and may also operate as a UE-to-network (U2N) relay UE node relaying data between one of the UE nodes 113, 130 (referred to as remote UE nodes) and the network node 111.

[0144] The network node 111 may be a base station of a wireless network, such as a fifthgeneration (5G) New Radio (NR) network or a Long Term Evolution (LTE) network. Figure 1 only shows the base station of the wireless network for clarity. For a 5G NR network, the network node 111 is referred to as a gNodeB, or gNB. The gNB 111 is split to a Centralized Unit gNB-CU 104 and multiple Distributed Units gNB-DUs 101 , 102 and 103. The gNB-CU provides support for the higher layers such as SDAP, PDCP and RRC layers while the gNB- DU provides support to the lower layers such as MAC and PHY. The gNB-DU may serve different cells. The gNB-CU is connected to the gNB-DU via F1 interface 101a, 102a and 103a. The gNB-CU may exchange different F1AP messages with the gNB-DU via the F1 interface. For instance, the gNB-Cll may configure the UE context at a selected gNB-Dll using the UE context management procedures in TS 38.473 section 8.3. Furthermore, the gNB-Cll may send the RRC messages to the UE in a RRC MESSAGE TRANSFER container to the gNB- DU to be forwarded later to the UE as specified in the TS 38.473, section 8.4.

[0145] Even though sidelink relay is most likely to be considered in the context of V2X networks, it is not intended that the invention is limited to UE nodes that are in, or part of, a vehicle. Each of the UE nodes (relay or remote) may be a wireless communication device located in or part of a vehicle or a Road Side Unit (RSU) or a wireless communication device of a Vulnerable Road User (VRU) (e.g. a mobile or portable communication device (such as a smart phone, PDA, laptop, or similar devices) of a pedestrian or cyclist). In the following, a relay UE node will also be referred to as a relay UE, a remote UE node will also be referred to as a remote UE and a network node will be referred to as a gNB. Although in the following description, embodiments and examples of embodiments of the present invention will be described with respect to a 5G NR network, it will be appreciated that it is not intended that the present invention is limited to 5G NR systems and may be used in any wireless communication systems supporting sidelink (or peer to peer) relay communications.

[0146] In an example shown in Figure 1 , in a UE-to-Network (or U2N) scenario with the UE 110 operating as a UE-to-Network relay UE, the UE-to-Network relay UE 110 connects the UE 113, operating as a remote UE, to the gNB-DU1 101. The remote UE 113 is connected to the relay UE 110 via or through a sidelink 113a which may be referred to as a PC5 hop or link or connection or interface or leg 113a.

[0147] Similarly, remote UE 130 has a PC5 hop, or link or connection or interface or leg 130c with the relay UE 120. A Uu hop or link or connection or interface or leg 120a connects the relay UE 120 to the gNB-DU2 102. PC5 connections are used for the relayed traffic of the remote UEs (113, 130) and the non-relayed traffic specific to the relay UE 110, 120, i.e. for the direct communications between relay UE 110, 120 and the other remote UEs (113,130). Therefore, the remote UE 113 is connected to the gNB-DU1 101 through the relay UE 110 with a PC5 hop 113a and a Uu hop 110a. For uplink communication, the remote UE 113 is the source node (or transmitter node for transmitting data) and the gNB-DU1 101 is the destination or target node (or receiver node for receiving data) for a sidelink relay connection established between the remote UE 113 and the gNB-DU1 101 with a PC5 hop 113a and a second Uu hop 110a. For downlink communication, the remote UE 113 is the destination or target node (or receiver node) and the gNB-DU1 101 is the source node (or transmitter node). Similarly, the remote UE 130 is connected to the gNB-DU2 102 through the relay UE 120 with a PC5 hop 130ca and a Uu hop 120a.

[0148] The remote UE may be connected to the gNB 111 via multiple paths in a multipath configuration. For instance, the remote UE 113 may be connected to the relay UE 110 covered by the gNB-DU1 101 in indirect path and may be connected to the gNB-DU1 101 in direct path. In Sidelink Relay Wl of release 18, the multipath is considered for intra-gNB case. Thus, the remote UE is connected with a direct path and an indirect path to the same gNB. However, the gNB 111 may have multiple gNB-DUs and thus, different MP configurations may be considered. In a first example, the remote UE may be connected via multiple paths to the same gNB-DU in an intra-DU MP configuration. In a second example, the remote UE may be connected with a first path to a first gNB-DU and with a second path to a second gNB-DU. Therefore, the remote UE is in inter-DU multipath configuration.

[0149] According to RAN2 WG agreements, six use cases are specified as path management to be further studied in release 18. The uses cases are divided between path addition (Case A and B), path release (case C and D), and path change (case E and G). These use cases are supported for intra-DU MP and inter-DU MP configurations. In an example, a remote UE connected in multipath to the same gNB-DU can perform an inter-DU path change and thus, the remote UE is then connected to two different gNB-DUs in an inter-DU MP configuration.

[0150] In a first example, the remote UE 113 may be connected in intra-DU MP configuration with a direct Uu link 113b and an indirect link via the relay UE 110 to the same gNB-DU1 101.

[0151] In a second example, the remote UE 113 may be connected in inter-DU MP configuration with a direct Uu link 113b to the gNB-DU1 and an indirect link via the relay UE 120 to the gNB-DU2 102.

[0152] In a third example, the remote UE 130 may be connected in intra-DU MP configuration with a direct Uu link 130a and an indirect link via the relay UE 120 to the same gNB-DU2 102.

[0153] In a fourth example, the remote UE 130 may be connected in inter-DU MP configuration with a direct Uu link 130b to the gNB-DU3 103 and an indirect link via the relay UE 120 to the gNB-DU2 102.

[0154] The four use cases are discussed later in figures 3 to 6 respectively with inter-DU path change procedure.

[0155] Figure 2

[0156] Figure 2 is a schematic diagram illustrating user plane stacks of some protocol layers involved in Sidelink relay operations for UE-to-network (U2N) based relaying.

[0157] In order to set up a relayed traffic between a first node (remote UE) and a second node (gNB or remote UE), a Sidelink relay architecture may be used according to the 3GPP TR 38.836. The user plane architecture or protocol stack is shown in Figure 2 and represents the Sidelink Relay adaptation layer called SRAP that is introduced between the PDCP layer and the RLC layer at the extreme nodes and above the RLC layer in the relay UE. This architecture was first documented in the TR 38.836 and finally refined in 3GPP TS 38.300 while the SRAP layer is defined in 3GPP TS 38.351. This architecture shown in Figure 2 shows the Sidelink relay architecture 200 for the UE- to-Network relay scenario. As shown in Figure 2 illustrating a UE-to-Network relay scenario, the remote UE, such as remote UE 113, has a PC5 SRAP layer 201 between its llu PDCP layer and its PC5 RLC layer. Similarly, the gNB, such as gNB 111 , has a llu SRAP layer 204 between its llu PDCP layer and its llu RLC layer.

[0158] As shown in Figure 2 related to a UE-to-Network relay scenario, at the relay UE, such as relay UE 110, there are two SRAP layers to interface with the PC5 hop 113a and the Uu hop 110a: the PC5 SRAP layer 202 is connected to the PC5 SRAP 201 of the remote UE 113 through the PC5 hop 113a; and the Uu SRAP layer or entity 203 is connected to the Uu SRAP layer 204 at the gNB side 111 through the Uu link 110a. A remote UE 113 establishes End-to- End (E2E) radio bearers 205 with the gNB 111. These radio bearers could be a Signalling Radio Bearer SRB or Data Radio Bearer DRB. Figure 2 shows an E2E Uu DRB between the remote UE 113 and the gNB 111 by way of example.

[0159] The PC5 SRAP layer 202 of the UE-to-Network relay UE 110 receives data or packets (traffic data or signalling) over or via ingress PC5 Relay RLC (Radio Link Control) channels 206 through the PC5-RLC layer from remote UE 113 (at PC5 hop 113a) in an uplink direction and transmits the packets to the Uu SRAP entity 203 of the same relay UE 110.

[0160] The Uu SRAP 203 entity will map the corresponding ingress PC5 Relay RLC channels 206 to egress Uu Relay RLC channels 207a and / or 207b at Uu link 110a. Thus, a mapping table is required for uplink and it is configured by gNB 111 at the Uu SRAP entity 203 of the relay UE 110.

[0161] The mapping table takes at its input an identifier of the remote UE 113 (e.g. L2-ID), an identifier of the E2E radio bearer 205 (e.g. the E2E Uu DRB 205 ID) and an identifier of the ingress PC5 Relay RLC channel (or bearer) 206 and identifies the egress Uu Relay RLC bearer ID where the E2E radio bearers are mapped. For example, the UE E2E bearer ID and remote UE ID can be obtained from the header of a data packet received at the Uu SRAP entity 203 via the PC5-SRAP entity 202. An example of an entry for an uplink mapping table with one entry configured at the Uu SRAP entity 203 is shown in Table 1 below. It will be appreciated that the mapping table will be configured so that it has an entry for each remote UE connected to the relay UE.

[0162] Table 1 At the llu side or link 110a, different radio bearers of the same remote UE or different remote UEs can be subject to N:1 mapping and data multiplexing over llu RLC channels 207a and 207b.

[0163] In the downlink direction, data or packets transmitted from gNB 111 arrive at the relay UE 110 through the Uu link 110a. The Uu SRAP layer 203 of the UE-to-Network relay UE 110 receives data or packets (traffic data or signalling) over or via ingress Uu Relay RLC channels 207a and 207b through the Uu-RLC layer from gNB 111 and transmits the packet to the PC5 SRAP entity 202 of the same relay UE 110. Those ingress Uu Relay RLC channels 207a and 207b will be mapped at the PC5 SRAP entity 202 of the relay UE 110 to the egress PC5 Relay RLC channels 206 at PC5 hop 113a. Thus, a mapping table is required for downlink and it is configured by the gNB 111 at PC5 SRAP entity 202 of the relay UE 110. The mapping table requires at its input the remote UE 113 L2-ID, the End-to-End radio bearer 205 ID and the ingress Uu Relay RLC channel (or bearer) 207a and 207b ID and identifies the egress PC5 Relay RLC channels (or bearer) 206 ID of the PC5 hop 113a. The End-to-End Radio bearer 205 is then mapped at the PC5 hop 113a to the egress PC5 Relay RLC channels 206. For example, the UE E2E bearer ID and remote UE ID can be obtained from the header of a packet received at the PC5 SRAP entity 202 via the Uu SRAP entity 203. An example of a downlink mapping table with one entry configured at the PC5 SRAP entity 202 is shown in Table 2 below. It will be appreciated that the mapping table will be configured so that it has an entry for each remote UE connected to the relay UE.

[0164] Table 2

[0165] As mentioned in 3GPP TS 38.351 , each SRAP entity has a transmitting part and a receiving part. Across the PC5 interface 113a, the transmitting part of the PC5 SRAP entity 201 at the remote UE 113 has a corresponding receiving part at PC5 SRAP entity 202 at the UE-to-Network Relay UE 110, and vice-versa. Across the Uu interface 110a, the transmitting part of the Uu SRAP entity 203 at the UE-to-Network Relay UE 110 has a corresponding receiving part at Uu SRAP entity 204 at the gNB 111 , and vice-versa. To summarize, the transmitting part of each SRAP entity at the UE-to-Network Relay UE 110 receives the data packet with its SRAP header from its corresponding receiving part (receiving part of the SRAP entity 202 forwards the data to the transmitting part of the SRAP entity 203 and vice-versa). The transmitting part of each SRAP entity owns a mapping table configured by the gNB 111 which allows the identification of the egress RLC channel (at Uu or PC5 link) based on the ingress RLC channel where the data packet is received and the UE and Bearer IDs carried in the SRAP header. We can note that specific mapping rules may be applied for SRBO and SRB1 as specified in TS38.351 and TS38.331.

[0166] In the case of the multi-path with one indirect and one direct path, the remote UE 113 and the gNB 111 may communicate with each other through both paths. Thereby, either node has two protocol stacks: one for the indirect path such as described above and one for the direct path. The split between the direct and / or the indirect path is performed at the PDCP layer of each node. For the direct path, in the downlink direction, data or packets transmitted from gNB 111 through the direct path arrive at the remote UE 113 via ingress Uu Direct Path RLC channel 208 of the Uu link 113b. On the other hand, in the uplink direction, data or packets transmitted from the remote UE 113 through the direct path arrive at the gNB 111 via ingress Uu Direct Path RLC channel 208 of the Uu link 112b.

[0167] Figure 3

[0168] Figure 3 is a flow diagram of an example method, of performing an inter-DU direct path change to an inter-DU multipath transmission system in accordance with embodiments of the invention;

[0169] According to this figure, the remote UE 130 may be connected to the source gNB- DU2 102 through a direct Uu link 130a and through an indirect link via the relay UE 120. The relay UE 120 may serve as U2N relay UE for relaying data in 301 between the remote UE 130 and the source gNB-DU2 102. The call flow in 300 represents the different exchanged messages between the gNB-CU and the gNB-DUs (e.g., 102 and 103) via the F1 interface (e.g., 102a and 103a respectively). The call flow 300 includes also the exchanged messages between the gNB-DUs (e.g., 102 and 103), the relay UE 120 and the remote UE 130 via the Uu links (120a, 130a and 130b) and PC5 link 130c.

[0170] The remote UE 130 is connected directly via 130a and indirectly via the U2N relay UE 120 to the same gNB-DU2 102 in intra-DU configuration. The data 301 is transmitted via the direct path 130a, and the indirect path via the relay UE 120 (links 130c and 120a) to the gNB- DU2 102. The data 301 is then transmitted between the gNB-DU2 102 and the gNB-CU 104.

[0171] The remote UE 130 may send measurement reports in 302 to the gNB-CU 104. The measurement reports may reflect the link quality at the direct path between the remote UE and the gNB-DU2. For example, the measurement reports in 302 may indicate a potential risk of service disruption because of radio link degradation at 130a hop. Thus, the gNB-CU may take the decision in 303 to change the direct path.

[0172] The existing multipath configuration can be either intra-DU configuration such as in the figure 1 with both direct (130a) and indirect (130c + 120a) paths from the remote UE 130 connected to the same gNB-DU2 or inter-DU configuration wherein the remote UE is connected to multiple gNB-DUs, using for instance 130b as direct path instead of 130a. In such an example, the remote UE can be connected to a first gNB-Dll for the first path and a second gNB-Dll for the second path in an inter-DU multipath configuration.

[0173] According to the measurement reports, the gNB-Cll 104 may take the decision in 303 to change the direct path. The direct path may change within the same gNB-DU2 by reselecting another cell. In this first case, the gNB-Cll 104 will exchange messages with the same gNB-DU2 and reconfigure the remote UE 130 (not illustrated on Figure 3). This case is called an intra-DU path change.

[0174] In another case, the gNB-CU 104 may decide de change the direct path from a source gNB-DU2 102 to a target gNB-DU3 103 (as illustrated in figure 3). This case is called an inter- DU path change. Thus, the gNB-CU should configure the source gNB-DU2 and the target gNB-DU3 for multipath inter-DU path change and reconfigure the remote UE 130.

[0175] According to the Rel-18 discussion on multipath, RAN WG2 has agreed to perform a single release-and-add procedure to reconfigure a remote UE for path change in a multipath configuration. The single release-and-add procedure consists of performing the release of the existing selected path and adding a new path in a single configuration. This single procedure sent by the gNB 111 to the remote UE 130 should be completed by RAN WG3 efforts on the exchanged messages between the gNB-DU and the gNB-CU to align with the single release- and-add. In one aspect, the present invention aims to provide new F1 messages exchange between gNB-DU(s) and the gNB-CU to support the single release-and-add procedure for inter-DU path change in a multipath transmission system.

[0176] In 303, the gNB-CU 104 may select the target gNB-DU3 for the direct inter-DU path change according to the measurement reports received in 302. Thus, the gNB-CU 104 may send F1AP message 304a to the gNB-DU3 103 to setup the remote UE context at 103. The message in 304a can be a UE context setup request message. According to one example, the F1AP message in 304a may include all or part of the following information:

[0177] MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the gNB-DU3. Moreover, this IE may include the RLC channel configuration for the corresponding remote UE.

[0178] Path management type: The gNB-CU 104 may indicate to the new gNB-DU3 103 a path establishment in the context of a path addition, or a path change in multipath transmission system.

[0179] Path ID: The gNB-CU 104 may indicate the Pcell ID to indicate a direct path establishment or a relay UE ID for an indirect path establishment. However, a second information may be used as the remote UE ID. A C-RNTI may designate a direct path and a L2-ID may indicate an indirect path. The radio bearers ID to be added and the RLC channels to be assigned to the remote UE 130

[0180] Timers associated to the path management type. A direct path addition or change may add a T304-like timer to the MP path management configuration. An indirect path addition or change may add a T420-like timer to the configuration.

[0181] MP resource transfer information: The gNB-DUs may allocate resources of the remote UE for the PC5 link 130c in mode 1 resource allocation or may not be able to perform the resource allocation in mode 1. Thus, the gNB-CU 104 may take the decision to give the hand to one of the gNB-DUs to perform the resource allocation of the PC5 link. In an example, the gNB-CU may include in the MP resource transfer information an indication of resource allocation. The indication may specify mode 1 or mode 2 or pre-configuration. If mode 1 indication, the gNB-DU3 is responsible of allocating resources to the remote UE. The gNB- DU3 may transfer the resource allocation information to the other gNB-DU in an inter-DU MP configuration to be aware of the reserved resources in order to avoid interferences at the remote UE 130. In case of mode 2, the remote UE 130 may then allocate autonomously its resources. In case of pre-configuration, the remote UE is preconfigured at PC5 link with preconfigured resources.

[0182] F1-C transfer path MP: In an inter-DU MP configuration, the control plane may be configured on one gNB-DU to send the signaling information to the remote UE. The gNB-CU 104 may decide to assign the control plane to one gNB-DU or both of them. In case of inter- DU path change, the gNB-CU may assign the F1-C to the target gNB-DU3.

[0183] The target gNB-DU3 103 may respond with a setup response in 304b. This message can be the UE context setup response specified in the TS 38.473. This message may include the list of radio bearers and the list of RLC channels that has been setup or failed. Moreover, the message may include the new C-RNTI associated to the remote UE. The message 304b may include a UE context setup failure and thus, the remote UE can not be connected to the target gNB-DU3.

[0184] RAN WG2 has considered the case where the signaling radio bearer (e.g., SRB1 and SRB2) is assigned to the direct path. Thus, the signaling messages such as the RRCReconfiguration messages will be sent through the direct path to the remote UE. In the case of direct path change, the gNB-CU 104 may need to assign the SRBs to the indirect path via the U2N relay UE 120, prior to release of the direct path. Thus, the U2N relay UE may then need to be reconfigured in 305 for bearer mapping.

[0185] Next, the gNB-CU 104 may configure the source gNB-DU2 102 for inter-DU direct path change by sending the message of UE context request for release-and-add in 306a. The message 306a includes the configuration of the source gNB-DU2 to release the selected path to be changed. Moreover, the message 306a includes the reconfiguration of the remote UE 130 to perform the release-and-add procedure for inter-DU path change.

[0186] Upon receiving the message in 306a, the gNB-DU2 102 may send the message in 308 including the release-and-add configuration to the remote UE 130 and wait for the Configuration complete in 310 after successful Random Access Procedure establishment in

[0187] 309 with the target gNB-DU3 in 103. The configuration complete in 309 may trigger then the release at the gNB-DU2 of the remote UE context (if no connection remaining between this gNB-DU2 and the remote UE) and applying the configuration at gNB-DU2 associated with the MP direct path change. The messages in 308 and 310 may be sent as RRC messages, e.g., RRCReconfiguration and RRCReconfigurationComplete respectively.

[0188] In a different instance, the gNB-DU2 102 may release the direct path after sending the RRCReconfiguration message in 308 to the remote UE 130, or trigger the release after timer expiration. The timer can be configured by the gNB-CU 104 or set at the gNB-DU2 102. Such an arrangement can avoid the need to wait for message 310.

[0189] In both cases, the gNB-CU 104 has sent a single command to the source gNB-DU2 requiring a release or a modification of the remote UE context at the source gNB-DU2 and furthermore, providing a configuration to the remote UE to apply the inter-DU direct path change configuration consisting of releasing the selected path and adding another path. The release / modification of the remote UE context at the source gNB-DU2 may be applied immediately or can be delayed until complete notification from the remote UE to be executed without the need of the gNB-CU 104 to resend later a release command. Thus, the message 306a may then simplify the procedure and align with the single release-and-add procedure for the path change in multipath. The gNB-CU may then receive the configuration complete in

[0190] 310 included either in the UE context response for release-and-add message 306b or separately in the UL RRC message transfer 311. Thus, a single F1AP message may trigger the configuration complete at the source gNB-DU2 and at the remote UE 130.

[0191] The UE context request for release-and-add F1AP message 306a may be introduced as a new F1AP message. It may also amend existing F1AP messages in TS 38.473 such as UE context modification request or UE release context command. According to one example, the F1AP message in 306a may include all or part of the following information:

[0192] MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the source gNB-DU2 102. Moreover, this IE may include the RLC channel configuration for the corresponding remote UE.

[0193] Path management type: The gNB-CU 104 may indicate to the source gNB-DU2 102 a path release or path change in the context of a path release or a path change in a multipath transmission system. A path release is considered when the remote UE 130 is connected to the source gNB-DU2 via a single path. A path modification is considered when the remote UE 130 is connected to the gNB-DU2 via at least two paths.

[0194] Path ID: The gNB-Cll 104 may indicate the Pcell ID to indicate that the selected path is a direct path. Otherwise, a relay UE ID may indicate a path release or path change of the indirect path. However, a second information may be used as the remote UE ID. A C-RNTI may designate a direct path and a L2-ID may indicate an indirect path.

[0195] The radio bearers ID to be released or modified and the RLC channels to be released at the remote UE 130

[0196] Timers associated to the path management type. A direct path release or change may add a first T304-like timer to the MP path management configuration. An indirect path release or change may add a second T420-like timer to the configuration.

[0197] Configuration message for remote UE 130: The gNB-CU may include in the message 306a the configuration of the remote UE for the path release or the path change. This configuration may be a release-and-add procedure or two separate procedures of release and add. The source gNB-DU2 may then forward the message(s) to the remote UE as in 308. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0198] MP resource transfer information: The gNB-DUs may allocate resources of the remote UE for the PC5 link 130c in mode 1 resource allocation or may not be able to perform the resource allocation in mode 1. Thus, the gNB-CU 104 may take the decision to give the hand to one of the gNB-DUs to perform the resource allocation of the PC5 link. In an example, the gNB-CU may include in the MP resource transfer information an indication of resource allocation. The indication may specify mode 1 or mode 2 or pre-configuration. If mode 1 indication, the source gNB-DU2 is responsible of allocating resources to the remote UE. The gNB-DU2 may transfer the resource allocation information to the other gNB-DU in an inter-DU MP configuration to be aware of the reserved resources in order to avoid interferences at the remote UE 130. In case of mode 2, the remote UE 130 may then allocate autonomously its resources. In case of pre-configuration, the remote UE is preconfigured at PC5 link with preconfigured resources.

[0199] F1-C transfer path MP: In an inter-DU MP configuration, the control plane may be considered on one gNB-DU to send the signaling information to the remote UE. The gNB-CU 104 may decide to assign the control plane to one gNB-DU or both of them. In case of inter- DU path change, the gNB-CU may assign the F1-C to the target gNB-DU2.

[0200] Release / Modify Command: This IE may include the release command or the modification command of the selected path. The cause may be included in the MP path management configuration or in this command, e.g., path release or path change.

[0201] MP Duplication Deactivation: The MP split SRBs / DRBs may have to deactivate the duplication during the path release or change MP Split Deactivation: The MP split SRBs / DRBs may have to deactivate the data split during the path release or change

[0202] SRB / DRB list to be released: A list of direct bearers (SRB and DRB) to be released for the direct path at the source gNB-DU2.

[0203] SRB / DRB list to be modified: A list of MP bearers or indirect bearers (SRB and DRB) to be modified for the indirect path at the source gNB-DU2. llu RLC channels to be released: The RLC channels of the direct path to be released.

[0204] The configuration of the remote UE may be included in the message 306a sent to the source gNB-DU2 102. However, the configuration may be sent separately in message 307 via the DL RRC message transfer. The 307 message can be sent before the message 306a in order to prepare for configuration of the remote UE before the release of the gNB-DU2. The configuration complete 310 may be forwarded to gNB-CU in a separate UL RRC message transfer 311.

[0205] In both cases, the configuration of the remote UE 130 for inter-DU path change will be forwarded by the source gNB-DU2 to the remote UE in 308. The configuration of the source gNB-DU2 by the gNB-CU in 306a to release or modify the remote UE context may be applied following a triggering condition. The triggering condition can be receipt of the inter-DU path change configuration of the remote UE, or after a timer expiry, or upon receipt of the configuration complete of the remote UE in 310.

[0206] Figure 4

[0207] Figure 4 is a flow diagram of an example method, of performing an inter-DU indirect path change to an inter-DU multipath transmission system in accordance with embodiments of the invention;

[0208] According to this figure, the remote UE 113 may be connected to the source gNB- DU1 101 through a direct Uu link 113b and through an indirect link via the relay UE 110. The relay UE 110 may serve as U2N relay UE for relaying data in 301 between the remote UE 113 and the source gNB-DU1 101. The call flow in 400 represents the different exchanged messages between the gNB-CU 104 and the gNB-DUs (e.g., 101 and 102) via the F1 interface (e.g., 101a and 102a respectively). The call flow 400 includes also the exchanged messages between the gNB-DUs (e.g., 101 and 102), the source relay UE 110, the target relay UE 120 and the remote UE 130 via the Uu links (113b, 110a and 120a) and PC5 link (113a and 113c).

[0209] The remote UE 113 is connected directly via 113b and indirectly via the source U2N relay UE 110 to the same gNB-DU1 101 in intra-DU configuration. The data 301 is transmitted via the direct path 113b and the indirect path via the source relay UE 110 to the gNB-DU1 101. The data 301 is then transmitted between the gNB-DU1 101 and the gNB-CU 104. The remote UE 113 and the source relay UE 110 may send measurement reports in 402 to the gNB-Cll 104. The measurement reports may reflect the link quality at the direct path between the remote UE and the gNB-DU1. For example, the measurement reports in 402 may indicate a potential risk of service disruption because of radio link degradation at one of the multipath hops 113a and / or 110a. Thus, the gNB-CU 104 may take the decision in 403 to change the indirect path.

[0210] According to the measurements reports, the gNB-CU may take the decision in 403 to change the indirect path. The indirect path may change within the same gNB-DU1 by reselecting another cell. In this first case, the gNB-CU 104 will exchange messages with the same gNB-DU1 and reconfiguring the remote UE 113, the source and the target relay UEs. This case is called an intra-DU path change.

[0211] In another case, the gNB-CU 104 may decide to change the indirect path from a source gNB-DU1 101 to a target gNB-DU2 102. This case is called an inter-DU path change. Thus, the gNB-CU should configure the source gNB-DU1 and the target gNB-DU2 for multipath inter- DU path change and reconfigure the remote UE 113, the source relay UE 110 and the target relay UE 120.

[0212] Changing the indirect path may involve either changing the source relay UE 110 (relay UE change) or performing inter-DU handover of the same relay UE 110. In the first case, the remote UE 113 will release its PC5 connection to the source relay UE 110 and establish a PC5 connection with the target relay UE 120. In the second case, the relay UE 110 may perform inter-DU handover and establish a new Uu link with a different gNB-DU. Both cases can be considered for inter-DU indirect path change and may impact the reconfiguration of the source relay UE 110.

[0213] According to the Rel-18 discussion on multipath, a single release-and-add procedure can be used to reconfigure a remote UE for path change in a multipath configuration. The single release-and-add procedure consists of performing the release of the existing selected path and adding a new path in a single configuration. This single procedure sent by the gNB 111 to the remote UE 113 should be completed by RAN WG3 efforts on the exchanged messages between the gNB-DU and the gNB-CU to align with the single release-and-add. In one aspect, the present invention aims to provide new F1 messages exchange between gNB- DU(s) and the gNB-CU to support the single release-and-add procedure for inter-DU path change in a multipath transmission system.

[0214] The gNB-CU 104 may select the target gNB-DU2 for the inter-DU indirect path change according to the measurement reports received in 402. Thus, the gNB-CU 104 may send F1AP message 404a to the gNB-DU2 102 to setup the remote UE context at 102. The message in 404a can be a UE context setup request message. According to one example, the F1AP message in 404a may include all or part of the following information: MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the gNB-DU2. Moreover, this IE may include the RLC channel configuration. The MP path management configuration may consider the configuration of the RBs and RLC channels of both remote UE 113, the source relay UE 110 (in case of inter-DU handover) and the target relay UE 120. The gNB-CU 104 may configure the target gNB-DU2 by setting up the remote UE and the source relay UE contexts for inter-DU relay UE 110 handover. In case of relay UE change, the gNB-CU 104 may setup the remote UE context in the target gNB-DU2.

[0215] Path management type: The gNB-CU 104 may indicate to the new gNB-DU2 102 a path establishment in the context of a path addition, or a path change in multipath transmission system.

[0216] Path ID: The relay UE ID may serve as a path ID for indirect path change. In case of relay UE change, the target relay UE ID is specified. In case of inter-DU relay UE handover, the relay UE ID at the source gNB-DU or target gNB-DU can be communicated.

[0217] The radio bearers ID to be added and the RLC channels to be assigned to the remote UE 130

[0218] Timers associated to the path management type. An indirect path addition or change may add a T420-like timer to the MP path management configuration.

[0219] Source relay UE information: in case of inter-DU handover, the gNB-CU 104 may then send additional information related to the number of remote UEs connected to the source relay UE 110 attempting to handover. The gNB-CU 104 may send the contexts of all the remote UEs connected to the source relay UE 110. Moreover, the gNB-CU may indicate the remote UEs with MP configuration and additional information on remote UE’s connected gNB-DUs.

[0220] MP resource transfer information: The gNB-DUs may allocate resources of the remote UE for the PC5 link 113c in mode 1 resource allocation or may not be able to perform the resource allocation in mode 1. Thus, the gNB-CU 104 may take the decision to give the hand to one of the gNB-DUs to perform the resource allocation of the PC5 link. In an example, the gNB-CU may include in the MP resource transfer information an indication of resource allocation. The indication may specify mode 1 or mode 2 or pre-configuration. If mode 1 indication, the gNB-DU2 is responsible of allocating resources to the remote UE for the new PC5 link 113c. The gNB-DU2 may transfer the resource allocation information to the other gNB-DU in an inter-DU MP configuration to be aware of the reserved resources in order to avoid interferences at the remote UE 113. In case of mode 2, the remote UE 113 may then allocate autonomously its resources. In case of pre-configuration, the remote UE is preconfigured at PC5 link 113c with pre-configured resources.

[0221] F1-C transfer path MP: In an inter-DU MP configuration, the control plane may be considered on one gNB-DU to send the signaling information to the remote UE. The gNB-CU 104 may decide to assign the control plane to one gNB-Dll or both of them. In case of inter- Dll path change, the gNB-Cll may assign the F1-C to the target gNB-DU2.

[0222] Configuration message for target relay UE 120: The gNB-Cll may include in the message 404a the configuration of the target relay UE for the indirect path change. This configuration may include the bearer mapping, the relay UE ID, the RLC channels ID. The target gNB-DU2 may then forward the configuration message to the relay UE 120 in 405. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0223] The target gNB-DU2 102 may respond with a setup response in 404b. This message can be the UE context setup response specified in the TS 38.473. This message may include the list of radio bearers and the list of RLC channels that has been setup or failed at remote UE 113 and the relay UE (110 or 120). Moreover, the message may include the new C-RNTI associated to the source relay UE 110 in case of inter-DU handover. The message 404b may include a UE context setup failure and thus, the remote UE cannot be connected to the target gNB-DU2.

[0224] The reconfiguration of both source relay UE 110 and target relay UE 120 may come in 405. The reconfiguration of the relay UEs may use F1AP messages between gNB-CU and the gNB-DUs (101 and 102).

[0225] In case of inter-DU source relay UE handover (not illustrated in figure 1), the source relay UE 110 may change the gNB-DU within the same gNB 111 while remaining connected to the remote UE 113. This inter-DU handover of the indirect path allows the remote UE 113 to be connected via indirect path to a different gNB-DU (i.e., gNB-DU2) than the direct path (i.e. , gNB-DU1). Thus, the inter-DU handover modifies the configuration of the remote UE 113 from intra-DU MP configuration to inter-DU MP configuration. For this instance, the gNB-CU may configure the target gNB-DU2 with the remote UE 113 context and the source relay UE 110 context as in 404a. Upon receiving the message response in 404b, the gNB-CU 104 may then send a configuration to the source relay UE 110 via the gNB-DU1. The configuration of the source relay UE sent by the gNB-CU to the gNB-DU1 may be carried for example in a DL RRC MESSAGE TRANSFER 407 providing the source relay UE configuration and / or the remote UE configuration. This message can be sent earlier to 406a in the call flow. The configuration(s) provided to the source gNB-DU 1 may then be forwarded to their destination (110 and / or 113). The configuration of either remote UE 113 or source relay UE 110 may be sent in message 406a.

[0226] The gNB-DU1 may then send the configuration to the source relay UE 110. The relay UE 110 may notify the remote UE 113 of an inter-DU handover procedure and apply the configuration by releasing the Uu hop 110a and reconnect to the gNB-DU2 102 after a Random-Access procedure. In case of inter-DU handover of the source relay UE 110, the release-and-add procedure is performed at the source relay UE 110. The remote UE already configured in multipath may then modify the RBs without releasing any of its connection.

[0227] In case of relay UE change wherein the remote UE 113 releases the source relay UE 110 to connect to a target relay UE 120 covered by a different gNB-DU, the gNB-CU 104 may configure both source relay UE 110 and target relay UE 120. For the source relay UE 110, the previous configuration sent to the source gNB-DU1 either in a separate F1AP message (DL RRC MESSAGE TRANSFER) or in message 406a can be considered. For the target relay UE 120, the gNB-CU 104 may then send the configuration included in 404a while setting the remote UE 113 context or later in a separate F1AP message (DL RRC MESSAGE TRANSFER).

[0228] The configuration complete of relay UEs 110 or 120 may then be sent to the gNB-CU in 406b or 404b respectively. A separate UL RRC MESSAGE TRANSFER may be used to carry the configuration complete to the gNB-CU.

[0229] The configuration of the source relay UE and / or the target relay UE may include the bearer mapping, the list of SRBs / DRBs, the Uu RLC channels and the relay UE ID.

[0230] Next, the gNB-CU 104 may configure the source gNB-DU1 101 for inter-DU indirect path change by sending the message of UE context request for release-and-add in 406a. The message 406a may include the configuration of the source gNB-DU1 to release the selected path to be changed. Moreover, the message 406a may include the reconfiguration of the remote UE 113 to perform the release-and-add procedure for inter-DU path change and / or the reconfiguration of the source relay UE 110 for inter-DU handover (releasing existing Uu path 110a and adding an new Uu path).

[0231] Upon receiving the message in 406a, the gNB-DU1 101 may send the message in 408 including the release-and-add configuration to the remote UE 113 and wait for the Configuration complete in 410. In case of relay UE change, the remote UE 113 may release the PC5 link 113a with the source relay UE 110 in 409b and establish the PC5 link 113c with the target relay UE 120 in 409a before sending the configuration complete message in 410. In case of source relay UE inter-DU handover, there is no need for steps 409a and 409b. The configuration complete in 410 may trigger then the release at the gNB-DU1 of the remote UE context and applying the configuration at gNB-DU1 associated with the MP indirect path change. The messages in 408 and 410 may be sent as RRC messages, e.g., RRCReconfiguration and RRCReconfigurationComplete respectively. Moreover, the configuration complete at the gNB-DU1 may be triggered by the remote UE configuration complete and the source relay UE configuration complete. Thus, upon receiving of the configuration complete from the remote UE 113 and the source relay UE 110, the gNB-DU 1 may then apply its configuration (sent by the gNB-Cll in 406a) and release the context of the remote UE and / or the source relay UE if needed.

[0232] In a different instance, the gNB-DU1 101 may release the indirect path after sending the RRCReconfiguration message 408 to the remote UE 113 (and / or source relay UE 110) or trigger the release after timer expiration. The timer can be configured by the gNB-CU 104 or set at the gNB-DU1 101. In such an arrangement there is no need to wait for message 410.

[0233] In both cases, the gNB-CU 104 has sent a single command to the source gNB-DU1 requiring a release of a modification of the remote UE context at the source gNB-DU1 and furthermore, providing a configuration to the remote UE 113 and to the source relay UE 110 to apply the inter-DU indirect path change configuration consisting of releasing the selected path and adding another path. The release / modification of the remote UE context at the source gNB-DU1 may be applied immediately or be delayed until complete notification from the remote UE 113 and / or the source relay UE 110 to be executed without the need of the gNB- CU 104 to resend later a release command. Thus, the message 406a may then simplify the procedure and align with the single release-and-add procedure for the path change in multipath. The gNB-CU may then receive the configuration complete of the remote UE 113 and / or the configuration complete of the relay UE 110 included either in the UE context response for release-and-add message 406b or separately in the UL RRC message transfer 411. Thus, a single F1AP message may trigger the configuration complete at the source gNB- DU1 , the remote UE 113 and the source relay UE 110.

[0234] The UE context request for release-and-add F1AP message 406a may be introduced as a new F1AP message. It may also amend existing F1AP messages in TS 38.473 such as UE context modification request or UE release context command. According to one example, the F1AP message in 406a may include all or part of the following information:

[0235] MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the gNB-DU1. Moreover, this IE may include the RLC channel configuration. The MP path management configuration may consider the configuration of the RBs and RLC channels of both remote UE 113 and the source relay UE 110. The gNB-CU 104 may configure the source gNB-DU1 to release or modify the remote UE context, to release the source relay UE context (in case of inter-DU handover).

[0236] Path management type: The gNB-CU 104 may indicate to the source gNB-DU1 101 a path release or path change in the context of a path release or a path change in a multipath transmission system. A path release is considered when the remote UE 113 is connected to the source gNB-DU1 via a single path. A path modification is considered when the remote UE 113 is connected to the gNB-DU1 via at least two paths. Path ID:, a relay UE ID may indicate a path release or path change of the indirect path. However, a second information may be used as the remote UE ID. A C-RNTI may designate a direct path and a L2-ID may indicate an indirect path.

[0237] The radio bearers ID to be released or modified and the RLC channels to be released at the remote UE 113

[0238] Timers associated to the path management type. A direct path release or change may add a first T304-like timer to the MP path management configuration. An indirect path release or change may add a second T420-like timer to the configuration.

[0239] Configuration message for remote UE 113: The gNB-CU may include in the message 406a the configuration of the remote UE for the path release or the path change. This configuration may be a release-and-add procedure or two separate procedures of release and add. The source gNB-DU1 may then forward the configuration message(s) to the remote UE as in 408. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0240] Configuration message for source relay UE 110: The gNB-CU may include in the message 406a the configuration of the source relay UE for the indirect path change. This configuration may include the bearer mapping, the relay UE ID, the RLC channels ID. Moreover, the configuration may include an inter-DU handover of the relay UE 110. The source gNB-DU1 may then forward the configuration message to the relay UE 110 in 405. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0241] MP resource transfer information: The gNB-DUs may allocate resources of the remote UE for the PC5 link 113a in mode 1 resource allocation or may not be able to perform the resource allocation in mode 1. Thus, the gNB-CU 104 may take the decision to give the hand to one of the gNB-DUs to perform the resource allocation of the PC5 link. In an example, the gNB-CU may include in the MP resource transfer information an indication of resource allocation. The indication may specify mode 1 or mode 2 or pre-configuration. If mode 1 indication, the source gNB-DU1 is responsible of allocating resources to the remote UE. The gNB-DU1 may transfer the resource allocation information to the other gNB-DU in an inter-DU MP configuration to be aware of the reserved resources in order to avoid interferences at the remote UE 113. In case of mode 2, the remote UE 113 may then allocate autonomously its resources. In case of pre-configuration, the remote UE is preconfigured at PC5 link with preconfigured resources.

[0242] F1-C transfer path MP: In an inter-DU MP configuration, the control plane may be considered on one gNB-DU to send the signaling information to the remote UE. The gNB-CU 104 may decide to assign the control plane to one gNB-DU or both of them. In case of inter- DU path change, the gNB-CU may assign the F1-C to the target gNB-DU1. Release / Modify Command: This IE may include the release command or the modification command of the selected path. The cause may be included in the MP path management configuration or in this command, e.g., path release or path change.

[0243] MP Duplication Deactivation: The MP split SRBs / DRBs may have to deactivate the duplication during the path release or change

[0244] MP Split Deactivation: The MP split SRBs / DRBs may have to deactivate the data split during the path release or change

[0245] SRB / DRB list to be released: A list of direct bearers (SRB and DRB) to be released for the direct path at the source gNB-DU2.

[0246] SRB / DRB list to be modified: A list of MP bearers or indirect bearers (SRB and DRB) to be modified for the indirect path at the source gNB-DU2. llu RLC channels to be released: The RLC channels of the llu hop 110a of the indirect path to be released.

[0247] PC5 RLC channels to be released: The RLC channels of the PC5 hop 113a of the indirect path to be released.

[0248] The configuration of the remote UE and / or the source relay UE may be included in the message 406a sent to the source gNB-DU1 101. However, the configuration may be sent separately in message 407 via the DL RRC MESSAGE TRANSFER. This message can be sent before the message 406a in order to prepare for configuration of the remote UE before the release of the gNB-DU1. The configuration complete 410 may be sent in a separate UL RRC MESSAGE TRANSFER 411.

[0249] In both cases, the configuration of the remote UE 113 for inter-DU path change will be forwarded by the source gNB-DU1 to the remote UE in 408. The configuration of the source gNB-DU1 by the gNB-CU in 406a to release or modify the remote UE context (and / or the source relay UE context) may be applied a triggering condition. The triggering condition can be upon receipt of the inter-DU path change configuration of the remote UE, or after a timer expiry or upon receipt of the configuration complete of the remote UE (and / or the source relay UE) in 410.

[0250] Figure 5

[0251] Figure 5 is a flow diagram of an example method, of performing an inter-DU direct path change to an intra-DU multipath transmission system in accordance with embodiments of the invention;

[0252] According to this figure, the remote UE 130 is connected in multipath to two different gNB-DUs (102 and 103). The remote UE 130 may be connected to the gNB-DU3 103 through a direct Uu link 130b and to the gNB-DU2 102 through an indirect link via the relay UE 120. The relay UE 120 may serve as U2N relay UE for relaying data in 501 between the remote UE 130 and the source gNB-DU2 102. The call flow in 500 represents the different exchanged messages between the gNB-Cll and the gNB-DUs (e.g., 102 and 103) via the F1 interface (e.g., 102a and 103a respectively). The call flow 500 includes also the exchanged messages between the gNB-DUs (e.g., 102 and 103), the relay UE 120 and the remote UE 130 via the Uu links (120a, 130a and 130b) and PC5 link 130c.

[0253] The remote UE 130 is connected directly via 130b to the gNB-DU3 103 and indirectly via the U2N relay UE 120 to the gNB-DU2 102, in an inter-DU configuration. The data 501 is transmitted via the direct path 130b and the indirect path via the relay UE 120. The data 501 is then transmitted between the gNB-DUs (102 and 103) and the gNB-CU 104 via the F1 interfaces 102a and 103a.

[0254] The figure 5 considers an inter-DU direct path change where the remote UE 130 change the direct path connected to the source gNB-DU 3 103 to the target gNB-DU2 102. In 500, the remote UE 130 is already connected to the target gNB-DU2 via the indirect path and thus, the target gNB-DU2 has the remote UE context. Thus, the call flow in 500 represents an inter-DU path change from inter-DU MP configuration to intra-DU MP configuration.

[0255] The remote UE 130 may send measurement reports in 502 to the gNB-CU 104. The measurements reports may reflect the link quality at the direct path between the remote UE and the gNB-DU3. For example, the measurement reports in 502 may indicate a better Uu link quality with the gNB-DU2 already connected to the remote UE via the indirect path. Thus, the gNB-CU may take the decision in 503 to change the direct path from gNB-DU3 to gNB-DU2.

[0256] According to the measurements results, and the decision in 503, the gNB-CU should configure the source gNB-DU3 and the target gNB-DU2 for multipath inter-DU path change and reconfiguring the remote UE 130. The gNB-CU 104 may configure the remote UE with a single release-and-add procedure for path change according to the last agreements in RAN WG2. In alignment with the single procedure, the gNB-CU may configure the source gNB-DU3 with a single F1AP message including the configuration of the source gNB-DU3 103 and / or the configuration of the remote UE 130.

[0257] The target gNB-DU2 has already the remote UE context for the indirect path. Thus, for inter-DU path change to an intra-DU MP configuration, the source gNB-CU 104 may configure the remote UE via the source gNB-DU3 or the target gNB-DU2. Both cases are considered in the description below.

[0258] Considering first the configuration of the target gNB-DU2, the gNB-CU 104 may modify the remote UE context to include the direct path configuration. Thus, the gNB-CU 104 may send a single F1AP message 504a to the gNB-DU2 102 to modify the remote UE context. The UE context request for release-and-add F1AP message 504a may be introduced as a new F1AP message. It may also amend existing F1AP messages in TS 38.473 such as UE context modification request. According to one example, the F1AP message 504a may include all or part of the following information:

[0259] MP path management configuration: This information element IE may include information on path management type, the path ID and the radio bearers to be configured at the target gNB-DU2 102. Moreover, this IE may include the RLC channel configuration for the corresponding remote UE.

[0260] Path management type: The gNB-Cll 104 may indicate to the target gNB-DU2 102 a path change in the context of a multipath transmission system.

[0261] Path ID: The gNB-Cll 104 may indicate the Pcell ID to indicate that the selected path is a direct path.

[0262] The radio bearers ID to be added or modified and the RLC channels to be added at the remote UE 130

[0263] Timers associated to the path management type. A direct path add or change may add a first T304-like timer to the MP path management configuration.

[0264] Configuration message for remote UE 130: The gNB-CU may include in the message 504a the configuration of the remote UE for the path addition or the path change. This configuration may be a release-and-add procedure or two separate procedures of release and add. The target gNB-DU2 may then forward the message(s) to the remote UE (not shown in figure 5) via the indirect path. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0265] Configuration message for relay UE 120: The gNB-CU may include in the message 504a the configuration of the relay UE for the direct path change. The gNB-CU 104 may need to assign the SRBs to the indirect path via the U2N relay UE 120. The U2N relay UE may then need to be reconfigured in 505 for bearer mapping.

[0266] Add / Modify Command: This IE may include the addition command or the modification command of the selected path. The cause may be included in the MP path management configuration or in this command, e.g., path addition or path change.

[0267] MP Duplication Deactivation: The MP split SRBs / DRBs may have to deactivate the duplication during the path release or change

[0268] MP Split Deactivation: The MP split SRBs / DRBs may have to deactivate the data split during the path release or change

[0269] SRB / DRB list to be added: A list of direct bearers (SRB and DRB) to be added for the direct path at the target gNB-DU2.

[0270] SRB / DRB list to be modified: A list of MP bearers or indirect bearers (SRB and DRB) to be modified for the indirect path at the target gNB-DU2.

[0271] Uu RLC channels to be added: The RLC channels of the direct path to be added. For the instance where the remote UE configuration is sent via the message 504a to the target gNB-DU2, the configuration complete of the remote UE is to be sent either to both gNB- DUs 102 and 103, or at least to the source gNB-DU3 in order to trigger the release of the remote UE context at 103 as in 502b.

[0272] The target gNB-DU2 102 may respond with a UE context response for release-and-add in 504b. This message can be the UE context modification response specified in the TS 38.473 or a new F1AP message. This message may include the list of radio bearers and the list of RLC channels that has been setup or failed. Moreover, the message may include the new C- RNTI associated to the remote UE. The message 504b may include a UE context setup failure and thus, the remote UE cannot be connected to the target gNB-DU2.

[0273] In an example, the gNB-DU2 may apply the configuration of direct path add and send the configuration for the remote UE and / or the relay UE respectively. Thus, the message 504b may come after 504a. In another example, the gNB-DU2 may send the configuration to the remote UE and / or the relay UE and then wait for configuration complete. After the configuration complete, the gNB-DU2 may then apply its configuration and modify the remote UE context. In this case, the configuration complete of the remote UE 130, the relay UE 120 (if needed) and the gNB-DU2 are sent in the message 504b.

[0274] Next, the gNB-CU 104 may configure the source gNB-DU3 103 for inter-DU direct path change by sending the message of UE context request for release-and-add in 502a. The message 502a includes the configuration of the source gNB-DU3 to release the selected path to be changed. Moreover, and in case of remote UE configuration sent to the source gNB- DU3, the message 502a may include the reconfiguration of the remote UE 130 to perform the release-and-add procedure for inter-DU path change.

[0275] Upon receiving the message in 502a, the gNB-DU3 103 may send the message in 508 including the release-and-add configuration to the remote UE 130 and wait for the Configuration complete in 510 after successful Random Access Procedure establishment in 509 with the target gNB-DU2 in 102. The configuration complete 510 may trigger then the release at the gNB-DU3 of the remote UE context (if no connection remaining with this gNB- DU2) and applying the configuration at gNB-DU3 associated with the MP direct path change. The messages in 508 and 510 may be sent as RRC messages, e.g., RRCReconfiguration and RRCReconfigurationComplete respectively.

[0276] As the remote UE 130 has an indirect path connection with the target gNB-DU2, the gNB-CU may decide to send the configuration of the remote UE in 504a. In this case, the configuration complete of the remote UE should be sent to the source gNB-DU3 in order to trigger the release of the remote UE context for its side. The gNB-CU 104 may send an indication in the configuration message 508 to send the complete message to the source gNB- DU2 or can be implicitly pre-configured at the remote UE. In a different instance, the gNB-DU3 103 may release the direct path after sending the RRCReconfiguration message in 508 to the remote UE 130 or trigger the release after timer expiration. The timer can be configured by the gNB-Cll 104 or set at the gNB-DU3 103. In such an arrangement, there is no need to wait for message 510.

[0277] In both cases, the gNB-Cll 104 has sent a single command to the source gNB-DU3 requiring a release of a modification of the remote UE context at the source gNB-DU3 and furthermore, providing a configuration to the remote UE to apply the inter-DU direct path change configuration consisting of releasing the selected path and adding another path. The release / modification of the remote UE context at the source gNB-DU3 may be applied immediately or wait for complete notification from the remote UE to be executed without the need of the gNB-CU 104 to resend later a release command. Thus, the message 502a may then simplify the procedure and align with the single release-and-add procedure for the path change in multipath. The gNB-CU may then receive the configuration complete in 510 included either in the UE context response for release-and-add message 502b or separately in the UL RRC message transfer 511. Thus, a single F1AP message may trigger the configuration complete at the source gNB-DU3 and at the remote UE 130.

[0278] The UE context request for release-and-add F1AP message 502a may be introduced as a new F1AP message. It may also amend existing F1AP messages in TS 38.473 such as UE context modification request or UE release context command. According to one example, the F1AP message in 504a may include all or part of the following information:

[0279] MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the source gNB-DU3 103. Moreover, this IE may include the RLC channel configuration for the corresponding remote UE.

[0280] Path management type: The gNB-CU 104 may indicate to the source gNB-DU3 103 a path release or a path change in the context of a path release or a path change in a multipath transmission system. A path release is considered when the remote UE 130 is connected to the source gNB-DU3 via a single path. A path modification is considered when the remote UE 130 is connected to the gNB-DU3 via at least two paths.

[0281] Path ID: The gNB-CU 104 may indicate the Pcell ID to indicate that the selected path is a direct path.

[0282] The radio bearers ID to be released or modified and the RLC channels to be released at the remote UE 130

[0283] Timers associated to the path management type. A direct path release or change may add a first T304-like timer to the MP path management configuration. An indirect path release or change may add a second T420-like timer to the configuration. Configuration message for remote UE 130: The gNB-Cll may include in the message 502a the configuration of the remote UE for the path release or the path change. This configuration may be a release-and-add procedure or two separate procedures of release and add. The source gNB-DU3 may then forward the message(s) to the remote UE as in 508. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0284] Release / Modify Command: This IE may include the release command or the modification command of the selected path. The cause may be included in the MP path management configuration or in this command, e.g., path release or path change.

[0285] MP Duplication Deactivation: The MP split SRBs / DRBs may have to deactivate the duplication during the path release or change

[0286] MP Split Deactivation: The MP split SRBs / DRBs may have to deactivate the data split during the path release or change

[0287] SRB / DRB list to be released: A list of direct bearers (SRB and DRB) to be released for the direct path at the source gNB-DU3.

[0288] SRB / DRB list to be modified: A list of MP bearers or indirect bearers (SRB and DRB) to be modified for the indirect path at the source gNB-DU3.

[0289] Uu RLC channels to be released: The RLC channels of the direct path to be released.

[0290] The configuration of the remote UE may be included in the message 502a sent to the source gNB-DU3 103. However, the configuration may be sent separately in message 506 via the DL RRC message transfer. The message 506 can be sent before the message 502a in order to prepare for configuration of the remote UE before the release of the gNB-DU3. The configuration complete 510 may be sent in a separate UL RRC message transfer 511.

[0291] In both cases, the configuration of the remote UE 130 for inter-DU path change will be forwarded by the source gNB-DU3 to the remote UE in 508. The configuration of the source gNB-DU3 by the gNB-CU in 502a to release or modify the remote UE context may be applied a triggering condition. The triggering condition can be upon receipt of the inter-DU path change configuration of the remote UE, or after a timer expiry or upon receipt of the configuration complete of the remote UE in 510.

[0292] For the case of figure 5 for inter-DU MP to intra-DU MP, the gNB-CU may send the remote UE 130 configuration to the source gNB-DU3 via the direct path or to the target gNB- DU2 via the indirect path. The gNB-DUs may then send the configuration to the remote UE 130. However, the complete notification may depend from the gNB-DU sending of the configuration.

[0293] In a first example, wherein the remote UE configuration is sent to the source gNB-DU3, the configuration complete may be sent to either the source gNB-DU3 or the target gNB-DU2. In a second example, wherein the remote UE configuration is sent to the target gNB- DU2, the configuration complete should be sent to the source gNB-DU3 in order to close the loop at the gNB-CU.

[0294] Figure 6

[0295] Figure 6 is a flow diagram of an example method, of performing an inter-DU indirect path change to an intra-DU multipath transmission system in accordance with embodiments of the invention;

[0296] According to this figure, the remote UE 113 is connected in multipath to two different gNB-DUs (101 and 102). The remote UE 113 may be connected to the gNB-DU1 101 through a direct Uu link 113b and to the gNB-DU2 102 through an indirect link via the relay UE 120. The relay UE 120 may serve as U2N relay UE for relaying data in 601 between the remote UE 113 and the source gNB-DU2 102. The call flow in 600 represents the different exchanged messages between the gNB-CU and the gNB-DUs (e.g., 101 and 102) via the F1 interface (e.g., 101a and 102a respectively). The call flow 600 includes also the exchanged messages between the gNB-DUs (e.g., 101 and 102), the relay UE 120 and the remote UE 113 via the Uu links (113b, 110a and 120a) and PC5 links (113a, 113c).

[0297] The remote UE 113 is connected directly via 113b to the gNB-DU1 101 and indirectly via the U2N relay UE 120 gNB-DU2 102, in an inter-DU configuration. The data 601 is transmitted via the direct path 113b and the indirect path via the relay UE 120. The data 601 is then transmitted between the gNB-Dus (101 and 102) and the gNB-CU 104 via the F1 interfaces 101a and 102a.

[0298] The figure 6 considers an inter-DU indirect path change where the remote UE 113 changes the indirect path connected to the source gNB-DU2 102 to the target gNB-DU1 101. In 600, the remote UE 113 is already connected to the target gNB-DU1 via the direct path 113b and thus, the target gNB-DU1 has the remote UE context. Thus, the call flow in 600 represents an inter-DU path change from an inter-DU MP configuration to an intra-DU MP configuration.

[0299] The remote UE 113 and the source relay UE 120 may send measurement reports in 602 to the gNB-CU 104. The measurement reports may reflect the link quality at the indirect path between the remote UE and the gNB-DU2 including the two links 113c and 120a. For example, the measurement reports in 602 may indicate a potential risk of service disruption because of radio link degradation at one of the multipath hops 113c and / or 120a. Thus, the gNB-CU 104 may take the decision in 603 to change the indirect path.

[0300] According to the measurements results, the gNB-CU 104 may decide to change the indirect path from a source gNB-DU2 102 to a target gNB-DU1 101. This case is called an inter-DU path change. Thus, the gNB-CU should configure the source gNB-DU2 and the target gNB-DU1 for multipath inter-DU path change and reconfigure the remote UE 113, the source relay UE 120 and the target relay UE 110.

[0301] Changing the indirect path may involve either changing the source relay UE 120 (relay UE change) or performing inter-DU handover of the same relay UE 120. In the first case, the remote UE 113 will release its PC5 connection 113c to the source relay UE 120 and establish a PC5 connection 113a with the target relay UE 110. In the second case, the relay UE 120 may perform inter-DU handover and establish a new Uu link with the gNB-DU1. Both cases can be considered for inter-DU indirect path change and may impact the reconfiguration of the source relay UE 120.

[0302] The gNB-CU 104 may configure the remote UE with a single release-and-add procedure for path change according to the last agreements in RAN WG2. In alignment with the single procedure, the gNB-CU may configure the source gNB-DU2 with a single F1AP message including the configuration of the source gNB-DU2 102 and / or the configuration of the remote UE 113.

[0303] The gNB-CU 104 may select the target gNB-DU1 for the inter-DU indirect path change according to the measurement reports received in 602. Thus, the remote UE 113 change from inter-DU MP configuration to intra-DU MP configuration.

[0304] The target gNB-DU1 has already the remote UE context for the direct path 113b. Thus, for inter-DU path change to an intra-DU MP configuration, the source gNB-CU 104 may configure the remote UE 113 via the source gNB-DU2 or the target gNB-DU1. Both cases are considered in the description below.

[0305] Considering first the configuration of the target gNB-DU1 , the gNB-CU 104 may modify the remote UE context to include the indirect path configuration. Thus, the gNB-CU 104 may send a single F1AP message 604a to the gNB-DU1 101 to modify the remote UE context. The UE context request for release-and-add F1AP message 604a may be introduced as a new F1AP message. It may also amend existing F1AP messages in TS 38.473 such as UE context modification request. According to one example, the F1AP message 604a may include all or part of the following information:

[0306] MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the gNB-DU1. Moreover, this IE may include the RLC channel configuration. The MP path management configuration may consider the configuration of the RBs and RLC channels of both remote UE 113, the source relay UE 120 (in case of inter-DU handover) and the target relay UE 110. The gNB-CU 104 may configure the target gNB-DU1 by setting up the remote UE and the source relay UE contexts for inter-DU relay UE 120 handover. In case of relay UE change, the gNB-CU 104 may setup the remote UE context in the target gNB-DU1. Path management type: The gNB-Cll 104 may indicate to the target gNB-DU1 102 a path establishment in the context of a path addition, or a path change in multipath transmission system.

[0307] Path ID: The relay UE ID may serve as a path ID for indirect path change. In case of relay UE change, the target relay UE ID is specified. In case of inter-DU relay UE handover, the relay UE ID at the source gNB-DU or target gNB-DU can be communicated.

[0308] The radio bearers ID to be added and the RLC channels to be assigned to the remote UE 113

[0309] Timers associated to the path management type. An indirect path addition or change may add a T420-like timer to the MP path management configuration.

[0310] Source relay UE information: in case of inter-DU handover, the gNB-CU 104 may then send additional information related to the number of remote UEs connected to the source relay UE 120 attempting to handover. The gNB-CU 104 may send the contexts of all the remote UEs connected to the source relay UE 120. Moreover, the gNB-CU may indicate the remote UEs with MP configuration and additional information on remote UE’s connected gNB-DUs.

[0311] Configuration message for remote UE 113: The gNB-CU may include in the message 604a the configuration of the remote UE for the path addition or the path change. This configuration may be a release-and-add procedure or two separate procedures of release and add. The target gNB-DU1 may then forward the message(s) to the remote UE 113 (not shown in figure 5) via the indirect path. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0312] Configuration message for target relay UE 110: The gNB-CU may include in the message 604a the configuration of the target relay UE for the indirect path change. This configuration may include the bearer mapping, the relay UE ID, the RLC channels ID. The target gNB-DU1 may then forward the configuration message to the relay UE 110 in 606. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0313] Add / Modify Command: This IE may include the addition command or the modification command of the selected path. The cause may be included in the MP path management configuration or in this command, e.g., path addition or path change.

[0314] MP Duplication Deactivation: The MP split SRBs / DRBs may have to deactivate the duplication during the path release or change

[0315] MP Split Deactivation: The MP split SRBs / DRBs may have to deactivate the data split during the path release or change

[0316] SRB / DRB list to be added: A list of direct bearers (SRB and DRB) to be added for the direct path at the target gNB-DU2.

[0317] SRB / DRB list to be modified: A list of MP bearers or indirect bearers (SRB and DRB) to be modified for the indirect path at the target gNB-DU2. llu RLC channels to be added: The RLC channels of the direct path to be added.

[0318] For the instance where the remote UE configuration is sent via the message 604a to the target gNB-DU1 , the configuration complete of the remote UE 113 is to be sent either to both gNB-DUs 101 and 102, or at least to the source gNB-DU2 in order to trigger the release of the remote UE context at 101 as in 605b.

[0319] The target gNB-DU1 101 may respond with a UE context response for release-and-add in 604b. This message can be the UE context modification response specified in the TS 38.473 or a new F1AP message. This message may include the list of radio bearers and the list of RLC channels that has been setup or failed. Moreover, the message may include the new C- RNTI associated to the remote UE. The message 604b may further include the C-RNTI to the source relay UE in case of inter-DU handover at 120. The message 604b may include a UE context setup failure and thus, the remote UE cannot be connected to the target gNB-DU1 .

[0320] The reconfiguration of both source relay UE 120 and target relay UE 110 may come in 606. The configuration of the relay UEs may use F1AP messages between gNB-CU and the gNB-DUs (101 and 102). The configuration information may be included in messages 604a and 605a.

[0321] In case of inter-DU source relay UE handover (not illustrated in figure 1), the source relay UE 120 may change the gNB-DU within the same gNB 111 while remaining connected to the remote UE 113. This inter-DU handover of the indirect path allows the remote UE 113 to be connected via indirect path to the same gNB-DU (i.e., gNB-DU1) as the direct path. Thus, the inter-DU handover modify the configuration of the remote UE 113 from inter-DU MP configuration to intra-DU MP configuration. For this instance, the gNB-CU may configure the target gNB-DU1 with the remote UE 113 context and / or the source relay UE 120 context (in case of inter-DU handover of the source relay UE 120) as in 604a. Upon receiving the message response in 604b, the gNB-CU 104 may then send a configuration to the source relay UE 120 via the gNB-DU2. The configuration of the source relay UE 120 sent by the gNB- CU to the gNB-DU2 may be carried for example in a DL RRC MESSAGE TRANSFER 607 providing the source relay UE configuration and / or the remote UE configuration. This message can be sent earlier to 605a in the call flow. The config uration(s) provided to the source gNB- DU2 may then be forwarded to their destination (120 and / or 113). The configuration of either remote UE 113 or source relay UE 120 may be sent in message 605a.

[0322] The gNB-DU2 may then send the configuration to the source relay UE 120. The relay UE 120 may notify the remote UE 113 of an inter-DU handover procedure and apply the configuration by releasing the Uu hop 120a and reconnect to the gNB-DU2 102 after a Random-Access procedure. In case of inter-DU handover of the source relay UE 120, the release-and-add procedure is performed at the 120. The remote UE 113 already configured in multipath may then modify the RBs without releasing any of its connection.

[0323] In case of relay UE change wherein the remote UE 113 release the source relay UE 120 to connect to a target relay UE 110 covered by the same gNB-DU1 , the gNB-CU 104 may configure both source relay UE 120 and target relay UE 110. For the source relay UE 120, the previous configuration sent to the source gNB-DU2 either in a separate F1AP message (DL RRC MESSAGE TRANSFER) or in message 605a can be considered. For the target relay UE 110, the gNB-CU 104 may then send the configuration included in 604a while modifying the remote UE 113 context or later in a separate F1AP message (DL RRC MESSAGE TRANSFER).

[0324] The configuration complete of relay UEs 110 or 120 may then be sent to the gNB-CU in 604b or 605b respectively. A separate UL RRC MESSAGE TRANSFER may be used to carry the configuration complete to the gNB-CU.

[0325] The configuration of the source relay UE and / or the target relay UE may include the bearer mapping, the list of SRBs / DRBs, the Uu RLC channels and the relay UE ID.

[0326] Next, the gNB-CU 104 may configure the source gNB-DU2 102 for inter-DU indirect path change by sending the message of UE context request for release-and-add in 605a. The message 605a may include the configuration of the source gNB-DU2 to release the selected path to be changed. Moreover, the message 605a may include the reconfiguration of the remote UE 113 to perform the release-and-add procedure for inter-DU path change and / or the reconfiguration of the source relay UE 120 for inter-DU handover (releasing existing Uu path 120a and adding a new Uu path).

[0327] Upon receiving the message in 605a, the gNB-DU2 102 may send the message in 608 including the release-and-add configuration to the remote UE 113 and wait for the Configuration complete in 610. In case of relay UE change, the remote UE 113 may release the PC5 link 113c with the source relay UE 120 in 609b and establish the PC5 link 113a with the target relay UE 110 in 609a before sending the configuration complete message in 610. In case of source relay UE inter-DU handover, there is no need for steps 609a and 609b. The configuration complete in 610 may trigger then the release at the gNB-DU2 of the remote UE context and applying the configuration at gNB-DU2 associated with the MP indirect path change. The messages in 608 and 610 may be sent as RRC messages, e.g., RRCReconfiguration and RRCReconfigurationComplete respectively. Moreover, the configuration complete at the gNB-DU2 may be triggered by the remote UE configuration complete and the source relay UE configuration complete. Thus, upon receiving of the configuration complete from the remote UE 113 and the source relay UE 120, the gNB-DU2 may then apply its configuration (sent by the gNB-Cll in 604a) and release the context of the remote UE and / or the source relay UE if needed.

[0328] In a different instance, the gNB-DU2 102 may release the indirect path after sending the RRCReconfiguration message 608 to the remote UE 113 (and / or source relay UE 120) or trigger the release after timer expiration. The timer can be configured by the gNB-CU 104 or set at the gNB-DU2 102. In such an arrangement, there is no need to wait for message 610.

[0329] In both cases, the gNB-CU 104 has sent a single command to the source gNB-DU2 requiring a release of a modification of the remote UE context at the source gNB-DU2 and furthermore, providing a configuration to the remote UE 113 and to the source relay UE 120 to apply the inter-DU indirect path change configuration consisting of releasing the selected path and adding another path. The release / modification of the remote UE context at the source gNB-DU2 may be applied immediately or wait for complete notification from the remote UE 113 and / or the source relay UE 120 to be executed without the need of the gNB-CU 104 to resend later a release command. Thus, the message 605a may then simplify the procedure and align with the single release-and-add procedure for the path change in multipath. The gNB-CU may then receive the configuration complete of the remote UE 113 and / or the configuration complete of the relay UE 120 included either in the UE context response for release-and-add message 605b or separately in the UL RRC message transfer 611. Thus, a single F1AP message may trigger the configuration complete at the source gNB-DU2, the remote UE 113 and the source relay UE 120.

[0330] The UE context request for release-and-add F1AP message 605a may be introduced as a new F1AP message. It may also amend existing F1AP messages in TS 38.473 such as UE context modification request or UE release context command. According to one example, the F1AP message 605a may include all or part of the following information:

[0331] MP path management configuration: This information element (IE) may include information on path management type, the path ID and the radio bearers to be configured at the gNB-DU2. Moreover, this IE may include the RLC channel configuration. The MP path management configuration may consider the configuration of the RBs and RLC channels of both remote UE 113 and the source relay UE 120. The gNB-CU 104 may configure the source gNB-DU2 to release or modify the remote UE context, to release the source relay UE context (in case of inter-DU handover).

[0332] Path management type: The gNB-CU 104 may indicate to the source gNB-DU2 102 a path release or path change in the context of a path release or a path change in a multipath transmission system.

[0333] Path ID:, a relay UE ID may indicate a path release or path change of the indirect path. However, a second information may be used as the remote UE ID. A C-RNTI may designate a direct path and a L2-ID may indicate an indirect path. The radio bearers ID to be released or modified and the RLC channels to be released at the remote UE 113

[0334] Timers associated to the path management type. A direct path release or change may add a first T304-like timer to the MP path management configuration. An indirect path release or change may add a second T420-like timer to the configuration.

[0335] Configuration message for remote UE 113: The gNB-CU may include in the message 605a the configuration of the remote UE for the path release or the path change. This configuration may be a release-and-add procedure or two separate procedures of release and add. The source gNB-DU2 may then forward the configuration message(s) to the remote UE as in 608. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0336] Configuration message for source relay UE 120: The gNB-CU may include in the message 605a the configuration of the source relay UE for the indirect path change. This configuration may include the bearer mapping, the relay UE ID, the radio bearers and the RLC channels ID to be released in case of source relay UE change. Moreover, the configuration may include an inter-DU handover of the relay UE 120. The source gNB-DU2 may then forward the configuration message to the relay UE 120 in 606. The message(s) can be included in the RRC container as a RRCReconfiguration message.

[0337] Release / Modify Command: This IE may include the release command or the modification command of the selected path. The cause may be included in the MP path management configuration or in this command, e.g., path release or path change.

[0338] MP Duplication Deactivation: The MP split SRBs / DRBs may have to deactivate the duplication during the path release or change

[0339] MP Split Deactivation: The MP split SRBs / DRBs may have to deactivate the data split during the path release or change

[0340] SRB / DRB list to be released: A list of direct bearers (SRB and DRB) to be released for the direct path at the source gNB-DU2.

[0341] SRB / DRB list to be modified: A list of MP bearers or indirect bearers (SRB and DRB) to be modified for the indirect path at the source gNB-DU2.

[0342] Uu RLC channels to be released: The RLC channels of the Uu hop 120a of the indirect path to be released.

[0343] PC5 RLC channels to be released: The RLC channels of the PC5 hop 113c of the indirect path to be released.

[0344] The configuration of the remote UE and / or the source relay UE may be included in the message 605a sent to the source gNB-DU2 102. However, the configuration may be sent separately in message 607 via the DL RRC MESSAGE TRANSFER. This message can be sent before the message 605a in order to prepare for configuration of the remote UE before the release of the gNB-DU2. The configuration complete 610 may be sent in a separate UL RRC MESSAGE TRANSFER 611.

[0345] In both cases, the configuration of the remote UE 113 for inter-DU path change will be forwarded by the source gNB-DU2 to the remote UE in 608. The configuration of the source gNB-DU2 by the gNB-CU in 605a to release or modify the remote UE context (and / or the source relay UE context) may be applied a triggering condition. The triggering condition can be upon receiving of the inter-DU path change configuration of the remote UE, or after a timer expiry or upon receiving the configuration complete of the remote UE (and / or the source relay UE) in 610.

[0346] For the case of figure 6 for inter-DU MP to intra-DU MP, the gNB-CU may send the remote UE 113 configuration to the source gNB-DU2 for the indirect path or to the target gNB- DU1 for the direct path. The gNB-DUs may then send the configuration to the remote UE 113. However, the complete notification may depend from the gNB-DU sending of the configuration.

[0347] In a first example, wherein the remote UE configuration is sent to the source gNB-DU2, the configuration complete may be sent to either the source gNB-DU2 or the target gNB-DU1 .

[0348] In a second example, wherein the remote UE configuration is sent to the target gNB- DU1 , the configuration complete should be sent to the source gNB-DU2 in order to close the loop at the gNB-CU.

[0349] Figure 7a

[0350] Figure 7a is a flowchart of a method performed at gNB-CU in accordance with one or more embodiments of the present invention;

[0351] The figure 7a represents the method 700 used at the gNB-CU 104 for inter-DU path change. The gNB-CU 104 may have different gNB-DUs (i.e., 101 , 102 and 103 in the figure 1). The figure 1 shows two remote UEs (113 and 130) in a multipath configuration. The UEs 110 and 120 may serve as U2N relay UEs in order to connect the remote UEs to the different gNB-DUs. The U2N relay UE 110 is connected to the gNB-DU1 101 and the U2N relay UE 120 is connected to the gNB-DU2 102. Different multipath configurations are considered in the figures 3, 4, 5 and 6 for inter-DU path change.

[0352] The inter-DU direct path change is discussed in the figures 3 and 5. The inter-DU direct path change may change the multipath configuration from intra-DU MP to inter-DU MP (figure 3) or vice versa (figure 5).

[0353] In figure 3, the remote UE 130 may have an intra-DU MP configuration while being connected via a direct path 130a and via an indirect path (130c+120a) using U2N relay UE 120 to the same gNB-DU2. The inter-DU direct path change may change the direct path 130a to 130b. Thus, the remote UE 130 may change from intra-DU multipath configuration to inter- DU multipath configuration with two paths to the gNB-DUs 101 and 102. In figure 5, the remote UE 130 may have an inter-DU MP configuration while being connected via a direct path 130b to the gNB-DU3 and via indirect path (130c+120a) with U2N relay UE 120 to the gNB-DU2. The inter-DU direct path change may change the direct path 130b to 130a. Thus, the remote UE 130 may change from inter-DU multipath configuration to intra-DU multipath configuration while being covered by a single gNB-DU2 102.

[0354] The inter-DU indirect path change is considered in the figures 4 and 6. The inter-DU direct path change may change the multipath configuration from intra-DU MP to inter-DU MP (figure 4) or vice versa (figure 6).

[0355] In figure 4, the remote UE 113 may have an intra-DU MP configuration while being connected via a direct path 113b and via indirect path (113a+110a) with U2N relay UE 110 to the same gNB-DU1. The inter-DU indirect path change may change the indirect path 113a+110a to 113c+120a. Thus, the remote UE 113 may change from intra-DU multipath configuration to inter-DU multipath configuration with connection to the gNB-DUs 102 and 103.

[0356] In figure 6, the remote UE 113 may have an inter-DU MP configuration while being connected via a direct path 113b to the gNB-DU1 and via indirect path (113c+120a) with U2N relay UE 120 to the gNB-DU2. The inter-DU indirect path change may change the indirect path 113c+120a to 113a+110a. Thus, the remote UE 113 may change from inter-DU multipath configuration to intra-DU multipath configuration while being covered by a single gNB-DU1 101.

[0357] According to the step 701 , the gNB-CU may receive measurement reports from the remote UE (113 or 130) and / or from the relay UEs (110 or 120) depending from the multipath configuration. This step 701 is optional but it may help the gNB-CU 104 to trigger a gNB-DU path change in 702.

[0358] The gNB-CU 104 may decide to perform an gNB-DU path change (303, 403, 503, 603). In this case, the remote UE (113, 130) configured in multipath may change either the gNB-DU of the direct path or the gNB-DU of the indirect path. This inter-DU path change may lead to different use cases as represented in the figures 3 to 6.

[0359] The gNB-CU 104 may decide to change either the gNB-DU of the direct path (figure 3) or the indirect path (figure 4) in an intra-DU MP configuration to an inter-DU MP configuration use cases. The gNB-CU 104 may also change the multipath from an inter-DU MP configuration to an intra-DU MP configuration by changing either the gNB-DU of the direct path (figure 5) or the indirect path (figure 6).

[0360] After the decision in 702, the gNB-CU 104 may then configure the different UEs (remote UE and relay UE) and the different gNB-DUs involved in the inter-DU path change. The figures 3 to 6 provide the call flows to illustrate in detail the different exchanged messages for the four different use cases. In the four use cases, the gNB-Cll 104 may configure the target gNB-Dll by setting up or modifying the remote UE context at the target gNB-Dll as in 304a, 404a, 504a and 604a. The modification of the remote UE context is provided when the remote UE is already connected to the target gNB-DU via another path as in figures 5 and 6. The modification of the remote UE context at the target gNB-DU may include the configuration of the remote UE and / or the target relay UE (for indirect path change). The gNB-CU may send the configurations to the target gNB-DU in a F1AP message via the F1 interface by amending existing F1AP messages such as UE context setup request or UE modification context request. New F1AP messages can be used such as UE context request for release-and-add aligned with the single release-and-add procedure associated to the path change in a multipath configuration.

[0361] In case of inter-DU MP configuration to intra-DU MP configuration, the target gNB-DU may have at least an existing path with the remote UE. Thus, the gNB-CU may include the configuration of the remote UE at this stage as in figures 5 and 6. In case of inter-DU indirect path change, the gNB-CU may send also the configuration of the target relay UE (figure 6).

[0362] The gNB-CU may receive the UE context response from the target gNB-DU with notification of completeness as in 304b, 404b, 504b and 604b. The notification may indicate the part of the configuration that has been setup or modified. In case of setup failure, the target gNB-DU may send a failure notification to the gNB-CU.

[0363] The gNB-CU may configure the source gNB-DU by configuring to release or modify the remote UE context. In case of intra-DU MP to inter-DU MP path change, the source gNB-DU may conserve at least one path and thus, a modification of the remote UE context is required. The gNB-CU may send F1AP message via the F1 interface as in 306a, 406a, 502a and 605a. The gNB-CU may amend existing F1AP messages such as UE context release command or UE modification context request. New F1AP messages can be used such as UE context request for release-and-add aligned with the single release-and-add procedure associated to the path change in a multipath configuration.

[0364] The gNB-CU may include the configuration of the source gNB-DU to release or modify a part of the MP configuration in the F1AP message. Moreover, the F1AP message may include the configurations of the remote UE and the source relay UE. This message (306a, 406a, 502a and 605a) is aligned with the single release-and-add procedure developed by RAN2 WG for the MP path change at remote UE. A single F1AP message may release or modify the remote UE context at the source gNB-DU and may include the configurations of the different UEs (i.e. remote UE and source relay UE) connected to the source gNB-DU in the multipath configuration.

[0365] The gNB-CU may close the path change loop when receiving a complete notification from the target gNB-DU, the source gNB-DU, the remote UE and the relay UEs (source and / or target). In an example, the gNB-Cll may choose to send the configurations of the UEs in a separate F1AP message as DL RRC MESSAGE TRANSFER (307, 407, 506 and 607). This alternative may provide more flexibility by providing the configuration of the UEs related to the multipath configuration before the change / release of the remote UE context at the source gNB- DU sent later by the gNB-CU in a different F1AP message. However, this method uses two F1AP messages and may address the use case of separate release and add procedures in MP path change.

[0366] Figure 7b

[0367] Figure 7b is a flowchart of a method performed at gNB-DU in accordance with one or more embodiments of the present invention.

[0368] The gNB 111 represented in figure 1 is split between the gNB-CU 104 and multiple gNB- DUs (101 , 102 and 103). The gNB-DU may receive the UE context F1AP messages from the gNB-CU via the F1 interface in order to manage the connection with the UE. Different F1AP messages exists between the gNB-CU and the gNB-DU described in the TS 38.473 including the UE context setup, modification or release.

[0369] In the inter-DU path change, the remote UE (113, 130) may change one of the paths from one gNB-DU to another gNB-DU. The flowchart 700b may represent the different steps followed either by the source gNB-DU or the target gNB-DU upon receiving a UE context request for an inter-DU path change for MP configuration.

[0370] In step 704, the involved gNB-DUs may be configured by the gNB-CU (i.e., source DU and target DU) with actions related to the remote UE context. Upon receiving the UE context request, the gNB-DU may identify a path management cause (addition, release or change) and the identity of the selected path (direct or indirect). The gNB-DU may receive the remote UE configuration and other relay UE configurations. The gNB-DU may then send the UE configurations in 705 to the remote UE and / or the relay UEs.

[0371] The gNB-DU may apply the UE context request in 706 after step 705 or after timer expiration. The gNB-DU may also wait for the UE configuration complete (remote UE and / or relay UE) before executing the gNB-DU configuration in 706.

[0372] The gNB-DU can be a source gNB-DU or a target gNB-DU. A source gNB-DU may release or modify the UE context for inter-DU path change in 706. A target gNB-DU may setup or modify the UE context for inter-DU path change in 706.

[0373] Upon receiving the UE context request, the source gNB-DU may identify a multipath inter-DU path change for the selected path. The source gNB-DU may modify or release the remote UE context in 706. The release of the remote UE context may occur in the case of inter-DU MP to intra-DU MP path change (e.g., figures 5 and 6) wherein the remote UE has no path connected to the source gNB-DU after inter-DU path change. The modification of the remote UE context may be used in the case of intra-DU MP to inter-DU MP path change (figures 3 and 4) wherein the remote UE remains connected to the source gNB-DU after inter- DU path change.

[0374] The target gNB-DU may setup or modify the remote UE context in 706. The gNB-DU may setup the remote UE context for a first path. This is the case of figures 3 and 4 representing an intra-DU MP to inter-DU MP path change, and wherein the target gNB-DU is not yet connected to the remote UE. The target gNB-DU may modify the remote UE context for an existing context. This is the case of figures 5 and 6 wherein the remote UE change from inter-DU MP to intra-DU MP configuration.

[0375] For the different alternatives listed above, the gNB-DU may receive a F1AP message from the gNB-CU including a configuration of the remote UE context at the gNB-DU in step 704. The F1AP message may include additional information related to the remote UE configuration and / or relay UE configuration (source relay UE or target relay UE).

[0376] In the figures 3 to 6, the source gNB-DU may receive F1AP message in 704 corresponding to the messages 304a, 404a, 502a and 605a. The F1AP message sent via the F1 interface may amend existing F1AP messages such as UE context release command or UE modification context request. New F1AP message can be used such as UE context request for release-and-add aligned with the single release-and-add procedure associated to the path change in a multipath configuration.

[0377] The F1AP message may include a release of a part or the entire remote UE context. The source gNB-DU may receive in 704 the configuration of the remote UE and the configuration of the source relay UE in the same F1AP message (304a, 404a, 502a and 605a) or in a separate message as the DL RRC MESSAGE TRANSFER (307, 407, 506 and 607). The source gNB-DU may then forward the configurations to either the remote UE or the source relay UE in 705.

[0378] The source gNB-DU may receive the configuration complete from the remote UE and / or the relay UEs in 707. In a first example, the source gNB-DU may wait for the receipt of the configuration complete in step 707 before applying the UE context configuration sent in 704. In a second example, the source gNB-DU may use a timer or apply directly the requested UE context after sending the remote UE configuration and / or the source relay UE configuration.

[0379] In an example of figure 3, the source gNB-DU may receive the UE context request for release-and-add in 704 or 304a, may send the remote UE configuration in 705 or 308 and the relay UE configuration 305 (if needed) and then release a part or the entire remote UE context independently from the remote UE configuration complete in 310. The source gNB-DU may then send a UE context response for release-and-add 304b with the configuration complete notification to the gNB-CU in 708. In another example of figure 5, the source gNB-Dll 103 may need to receive the configuration complete of the remote UE in 707 or 510 before releasing or modifying the remote UE context. In this use case, the target gNB-DU may receive the remote UE configuration in 704 and thus, the remote UE path change configuration may be forwarded by the target gNB-DU via the indirect path in 705. The source gNB-DU may receive the F1AP message 605a not including the remote UE configuration in 704. The source gNB-DU may identify the UE context configuration for the purpose of path change but may need to receive the configuration complete from the remote UE before releasing a part or the entire remote UE context.

[0380] The target gNB-DU may apply the remote UE context configuration in 706 (modify or setup) and may send a configuration complete in the F1AP messages in 708 (or 304b, 404b, 504b and 604b in the figures 3 to 6). In some cases, the F1AP message in 708 may include the remote UE or the target relay UE configuration complete. The gNB-DU may send the configuration complete of the UEs in a separate message as the UL RRC MESSAGE TRANSFER.

[0381] The source gNB-DU may apply the remote UE context configuration in 706 (modify or release) and may send a configuration complete in the F1AP message in 708 (or 306b, 406b, 502b and 605b in the figures 3 to 6). In some cases, the F1AP message in 708 may include the remote UE or the target relay UE configuration complete. The gNB-DU may send the configuration complete of the UEs in a separate message as the UL RRC MESSAGE TRANSFER 311 , 411 , 511 , 611.

[0382] The inter-DU indirect path change may manifest in an inter-DU handover of the source relay UE. Thus, this use case is considered as an inter-DU path change of the multipath configuration. In this case, the gNB-DU may receive a source relay UE configuration in 704 in addition to the remote UE configuration. Both configurations may use the single release-and- add procedure. The source relay UE may release the source gNB-DU and may establish the Uu path with the target gNB-DU. The source relay UE remains connected to the remote UE. The configuration complete at the remote UE and / or the source relay UE in 707 can be received by the source gNB-DU on the remaining path (if intra-DU MP) or by the target gNB- DU.

[0383] Figure 8

[0384] Figure 8 is a flowchart of a method performed at the remote UE in accordance with one or more embodiments of the present invention;

[0385] The remote UE 130 or 113 may be connected in multipath either to one gNB-DU in intra- DU MP configuration or multiple gNB-DUs in inter-DU MP configuration. The flowchart in 800 represents the remote UE performing inter-DU path change in a multipath transmission system.

[0386] The remote UE 113 or 130 may receive the path change configuration from the gNB-DU in 801 . In the different use cases, the remote UE may receive the configuration from the source gNB-DU. In figures 5 and 6, the remote UE is already connected to the target gNB-DU in inter- DU MP, and thus, the remote UE may receive the path change configuration from the target gNB-DU.

[0387] The remote UE may then apply the path change configuration in 802. The configuration may consider a single release-and-add procedure dedicated for MP path change. The remote UE may receive two separate configurations for releasing of the source gNB-DU and an addition of the target gNB-DU.

[0388] Upon the completion of the configuration, the remote UE may send a complete notification to the gNB-DU in 803. In case the remote UE has received the configuration information in 801 from the source gNB-DU, the remote UE may send the configuration complete in 803 through the source gNB-DU or target gNB-DU. The remote UE may send the configuration complete on both paths. The remote UE may implicitly select the path for the configuration complete or may be configured by either the gNB-DU or the gNB-CU with the preferred path.

[0389] In case the remote UE has received the configuration information in 801 from the target gNB-DU, the remote UE may send the configuration complete in 803 to the source gNB-DU in order to trigger the release or the modification of the remote UE context and the completeness of the inter-DU path change procedure.

[0390] Figure 9

[0391] Figure 9 shows a schematic representation of an example wireless communication device (apparatus) in accordance with one or more example embodiments of the present disclosure.

[0392] The wireless communication device 900 may preferably be a communication device capable of wireless communication such as a micro-computer or a workstation or a mobile device or a light portable device or a fixed device. The communication device 900 comprises a communication bus 913 to which there are preferably connected: a processing unit 911 , such as a microprocessor, and denoted CPU in Figure 9. The processing unit 911 may be a single processing unit or processor or may comprise two or more processing units or processors carrying out the processing required for the operation of the communication device 900. The number of processors and the allocation of processing functions to the central processing unit 911 is a matter of design choice for a skilled person; memory for storing data and computer programs containing instructions for the operation of the communication device 900. The computer programs may contain a number of different program elements (modules) or sub-routines containing instructions for a variety of operations and for implementing the methods in accordance with one or more embodiments of the invention; and at least one communication interface 902 for communicating with other devices or nodes in a wireless communication system, such as a wireless communication system of Figure 1. The at least one communication interface 902 may be connected to a communication network 903, such as a radio access network of the wireless communication system, over which digital data packets or frames or control frames are transmitted.

[0393] Each of the relay node and the plurality of nodes (e.g. the remote UEs and the network node) of the communication system 100 may comprise such a communication device 900.

[0394] The memory may include: a read only memory 907, denoted ROM, for storing computer programs for implementing the methods in accordance with one or more embodiments of the invention; a random-access memory 912, denoted RAM, for storing the executable code of methods according to one or more embodiments of the invention as well as the registers adapted to record variables and parameters necessary for implementing methods according to one or more embodiments of the invention.

[0395] Optionally, the communication device 900 may also include one or more of the following components: a data storage means 904 such as a hard disk, for storing computer programs for implementing methods according to one or more embodiments of the invention; a disk drive 905 for a disk 906, the disk drive being adapted to read data from the disk 906 or to write data onto said disk; a screen 909 for displaying decoded data and / or serving as a graphical interface with the user, by means of a keyboard 910 or any other user input means.

[0396] Preferably the communication bus provides communication and interoperability between the various elements included in the communication device 900 or connected to it. The representation of the bus is not limiting and in particular, the processing unit is operable to communicate instructions to any element of the communication device 900 directly or by means of another element of the communication device 900.

[0397] The disk 906 may optionally be replaced by any information medium such as for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, a USB key or a memory card and, in general terms, by an information storage means that can be read by a microcomputer or by a microprocessor, integrated or not into the communication device, possibly removable and adapted to store one or more programs whose execution enables methods according to embodiments of the invention to be implemented.

[0398] The executable code may optionally be stored either in read only memory 907, on the hard disk 904 or on a removable digital medium such as for example a disk 906 as described previously. According to an optional variant, the executable code of the programs can be received by means of the communication network 903, via the interface 902, in order to be stored in one of the storage means of the communication device 900, such as the hard disk 904, before being executed.

[0399] The processing unit 911 is preferably adapted to control and direct the execution of the instructions or portions of software code of the program or programs according to the invention, which instructions are stored in one of the aforementioned storage means. Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term "processor," as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0400] While the present invention has been described with reference to embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. It will be appreciated by those skilled in the art that various changes and modification might be made without departing from the scope of the invention, as defined in the appended claims. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0401] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

[0402] In the preceding embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit.

[0403] Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and / or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer- readable medium.

[0404] By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer- readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Claims

CLAIMS1 . A method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, Dlls, controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at the CU, comprising: determining that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs; and sending, to the source DU of the selected path, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path.

2. The method of claim 1 , wherein the request further includes information for releasing or modifying, at the source DU of the selected path, a context of the remote UE, immediately upon or following a triggering condition.

3. The method of claim 1 , wherein the method further comprises sending, to the target DU of the selected path, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

4. The method of claim 3, wherein the message further includes at least one of:MP path management configuration;MP resource transfer information;F1-C transfer path MP;Configuration message for a relay UE;Configuration message for the remote UE;Release / Modify Command;MP Duplication Deactivation;SRB / DRB list to be released;Uu RLC channels to be released;MP Split Deactivation;SRB / DRB list to be modified;PC5 RLC channels to be released.

5. The method of any one of the preceding claims, wherein the request further includes at least one of:Multipath, MP, path management configuration;Configuration message for the remote UE;MP resource transfer information;F1-C transfer path MP;Release / Modify Command;MP Duplication Deactivation;MP Split Deactivation;Signaling Radio Bearer, SRB I Data Radio Bearer, DRB, list to be released;SRB / DRB list to be modified; llu RLC channels to be released;PC5 RLC channels to be released;Configuration message for a relay UE;Add / Modify Command;SRB / DRB list to be added;Uu RLC channels to be added.

6. The method of claim 4 or 5, wherein, in a case that the message and / or request includes MP path management configuration, the MP path management configuration includes at least one of:Path management type;Path ID;A radio bearer ID; andA timer or timers, optionally associated to a path management type.

7. The method of any one of the preceding claims, wherein the target DU for the selected path is a source DU of another path of the at least two paths.

8. The method of anyone of the claims 1 to 6, wherein the target DU for the selected path is not a source DU of another path of the at least two paths.

9. The method of any preceding claim, wherein the selected path is a direct path.

10. The method of claim 9, further comprising receiving a measurement report from the remote UE, wherein said measurement report comprises an indication of the link quality of the direct path.

11. The method of claim 10 wherein the CU determines that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

12. The method of any of claims 1 to 8, wherein the selected path is an indirect path.

13. The method of claim 12, further comprising receiving a measurement report from a relay UE of the indirect path, wherein said measurement report comprises an indication of the link quality of the indirect path.

14. The method of claim 13, wherein the CU determines that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

15. The method of any of claims 12 to 14, wherein a relay UE of the indirect path performs path change from the source DU towards the target DU.

16. The method of any of claims 12 to 14, wherein the remote UE switches a connection from a relay UE of the indirect path towards a new relay UE having a connection to the target DU.

17. A method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at a source DU of a selected path among the at least two paths, comprising: receiving, from the CU, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path; and depending on a triggering condition, performing the release of the selected path.

18. The method of claim 15, wherein the triggering condition is one of: receiving, from the CU, configuration information for configuring the remote UE to establish a path with a target DU; receiving, from the CU, configuration information to configure the source DU with a context of the remote UE;receiving, from the remote UE, a notification indicating that a path with a target DU has been established; expiration of a timer configured by the CU; and expiration of a timer set at the source DU.

19. A method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at the remote UE, comprising: receiving configuration information for configuring the remote UE to establish a path with a target DU; and performing the establishment of a path with the target DU sending a notification indicating that a path with the target DU has been established.

20. The method of claim 19, wherein the step of sending a notification indicating that a path with the target DU has been established comprises sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the source DU.21 . The method of claim 19, wherein the step of sending a notification indicating that a path with the target DU has been established comprises sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the target DU.

22. The method of claim 19, wherein the step of sending a notification indicating that a path with the target DU has been established comprises sending, in a case that the configuration information is received from the target DU, a notification indicating that a path with the target DU has been established to the source DU.

23. A method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at the CU, comprising:determining that a DU change for a selected path among the at least two paths is to be performed towards the target DU of the plurality of DUs; and sending, to the source DU of the selected path, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path.

24. The method of claim 23, wherein the request further includes information for releasing or modifying, at the source DU of the selected path, a context of the remote UE, immediately upon or following a triggering condition.

25. The method of claim 23, wherein the method further comprises sending, to the target DU of the selected path, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

26. The method of claim 25, wherein the message further includes at least one of:MP path management configuration;MP resource transfer information;F1-C transfer path MP;Configuration message for a relay UE;Configuration message for the remote UE;Release / Modify Command;MP Duplication Deactivation;SRB / DRB list to be released;Uu RLC channels to be released;MP Split Deactivation;SRB / DRB list to be modified;PC5 RLC channels to be released.

27. The method of any one of claims 23 to 26, wherein the request further includes at least one of:Multipath, MP, path management configuration;Configuration message for the remote UE;MP resource transfer information;F1-C transfer path MP;Release / Modify Command;MP Duplication Deactivation;MP Split Deactivation;Signaling Radio Bearer, SRB / Data Radio Bearer, DRB, list to be released;SRB / DRB list to be modified; llu RLC channels to be released;PC5 RLC channels to be released;Configuration message for a relay UE;Add / Modify Command;SRB / DRB list to be added; llu RLC channels to be added.

28. The method of claim 26 or 27, wherein, in a case that the message and / or request includes MP path management configuration, the MP path management configuration includes at least one of :Path management type;Path ID;A radio bearer ID; andA timer or timers, optionally associated to a path management type.

29. The method of any one of claims 23 to 28, wherein the target DU for the selected path is a source DU of another path of the at least two paths.

30. The method of anyone of the claims 23 to 28, wherein the target DU for the selected path is not a source DU of another path of the at least two paths.

31. The method of any of claims 23 to 30, wherein the selected path is a direct path.

32. The method of claim 31 , further comprising receiving a measurement report from the remote UE, wherein said measurement report comprises an indication of the link quality of the direct path.

33. The method of claim 32, wherein the CU determines that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

34. The method of any of claims 23 to 30, wherein the selected path is an indirect path.

35. The method of claim 34, further comprising receiving a measurement report from a relay UE of the indirect path, wherein said measurement report comprises an indication of the link quality of the indirect path.

36. The method of claim 35, wherein the CU determines that a DU change for a selected path among the at least two paths is to be performed towards a target DU of the plurality of DUs based on the measurement report.

37. The method of any of claims 34 to 36, wherein a relay UE of the indirect path performs path change from the source DU towards the target DU.

38. The method of any of claims 34 to 36, wherein the remote UE switches a connection from a relay UE of the indirect path towards a new relay UE having a connection to the target DU.

39. A method for configuring a path change in a communication network comprising a base station and a plurality of user equipments, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at the source DU of a selected path among the at least two paths, comprising: receiving, from the CU, a request comprising an information element, IE, for configuring the source DU to support the DU change of the selected path; and depending on a triggering condition, performing the release of the selected path.

40. The method of claim 39, wherein the triggering condition is one of: receiving, from the CU, configuration information for configuring the remote UE to establish a path with a target DU; receiving, from the CU, configuration information to configure the source DU with a context of the remote; receiving, from the remote UE, a notification indicating that a path with a target DU has been established; and expiration of a timer configured by the CU; and expiration of a timer set at the source DU.41 . A method for configuring a path change in a communication network comprising a base station and a plurality of user equipments, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs, controlled by the CU, the base station serving a remoteUE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at the remote UE, comprising: receiving configuration information for configuring the remote UE to establish a path with a target DU; performing the establishment of a path with the target DU; and sending a notification indicating that a path with the target DU has been established.

42. The method of claim 41 , wherein the step of sending a notification indicating that a path with the target DU has been established comprises sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the source DU.

43. The method of claim 41 , wherein the step of sending a notification indicating that a path with the target DU has been established comprises sending, in a case that the configuration information is received from the source DU, a notification indicating that a path with the target DU has been established to the target DU.

44. The method of claim 41 , wherein the step of sending a notification indicating that a path with the target DU has been established comprises sending, in a case that the configuration information is received from the target DU, a notification indicating that a path with the target DU has been established to the source DU.

45. A method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, DUs controlled by the CU, the base station serving a remote UE via at least two paths, each of the at least two paths being managed by a source DU of the plurality of DUs, the method, at a target DU for a selected path of the at least two paths, comprising: receiving, from the CU, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

46. The method of claim 45, further comprising: sending, to the CU, a message including a context setup response.

47. The method of claim 46, wherein the message includes a list of radio bearers and / or RLC channels that have been set up at the remote UE.

48. A method for configuring a path change in a communication network comprising a base station and a plurality of users equipment, UEs, the base station comprising a central unit, CU, and a plurality of distributed units, Dlls controlled by the CU, the base station serving a remote UE via at least two paths, wherein the at least two paths comprises a first path managed by a source DU of the plurality of DUs and a second path managed by a target DU of the plurality of DUs, the method, at a target DU for a selected path of the at least two paths, comprising: receiving, from the CU, a message including information for setting up or modifying, at the target DU of the selected path, a context of the remote UE.

49. The method of claim 48, further comprising: sending, to the CU, a message including a context setup response.

50. The method of claim 49, wherein the message includes a list of radio bearers and / or RLC channels that have been set up at the remote UE.

51. An apparatus for a radio access network, RAN, node Central Unit, CU, node of a wireless network, the apparatus comprising: one or more processing units configured to perform the method as recited in any one of claims 1 to 16 or 23 to 38.

52. An apparatus for a distributed unit, DU, of a radio access network, RAN, node of a wireless network, the apparatus comprising: one or more processing units configured to perform the method as recited in any one of claims 17, 18, 39, 40 and 45 to 50.

53. An apparatus for a user equipment, UE, of a wireless network, the apparatus comprising: one or more processing units configured to perform the method as recited in claim 19 to22 or 41 to 44.

54. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 50.

55. A computer-readable medium carrying a computer program according to claim 54.

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