Time alignment synchronization with a candidate cell before an execution phase of a layer 1 / layer 2 triggered mobility procedure, and related devices, methods and computer programs

Abstract

Devices, methods and computer programs for time alignment synchronization with a candidate cell before an execution phase of a layer 1 / layer 2 triggered mobility procedure are disclosed. At least some example embodiments may allow moving the co-ordination of preamble collisions from a centralized unit to a source distributed unit.

Description

[0001] TIME ALIGNMENT SYNCHRONIZATION WITH A CANDIDATE CELL BEFORE AN EXECUTION PHASE OF A LAYER 1 / LAYER 2 TRIGGERED MOBILITY PROCEDURE , AND RELATED DEVICES , METHODS AND COMPUTER PROGRAMS

[0002] TECHNICAL FIELD

[0003] The disclosure relates generally to communications and, more particularly but not exclusively, to time alignment synchroni zation with a candidate cell be fore an execution phase of a layer 1 / layer 2 triggered mobility procedure , as well as related devices , methods and computer programs .

[0004] BACKGROUND

[0005] Handover is a process of transferring an ongoing communication session of a user device from one serving cell to another in a connected state .

[0006] Traditionally, a serving cell change has been triggered by layer 3 ( L3 ) measurements .

[0007] Lower layer ( that is , layer 1 ( LI ) / layer 2 ( L2 ) ) -triggered mobility ( LTM) allows a serving cell change via L1 / L2 -signalling, while keeping the configuration of upper layers and / or minimizing changes of the configuration of the lower layers .

[0008] BRIEF SUMMARY

[0009] The scope of protection sought for various example embodiments of the invention is set out by the independent claims . The example embodiments and features , i f any, described in this speci fication that do not fall under the scope o f the independent claims are to be interpreted as examples useful for understanding various example embodiments of the invention .

[0010] An example embodiment of a user device comprises at least one processor, and at least one memory storing instructions that , when executed by the at least one processor, cause the user device at least to establish a connection towards a source network node of a radio access network via a source cell supported by the source network node . The instructions , when executed by the at least one proces sor , further cause the user device at least to receive , from the radio access network, a configuration indicating at least one candidate cell for the user device to connect to . The instructions , when executed by the at least one processor, further cause the user device at least to receive , from the radio access network, a timing advance , TA, parameter, including a TA - radio network temporary identi fier, RNTI , associated with a configured candidate cell . The instructions , when executed by the at least one processor, further cause the user device at least to use the TA parameter in case of a related TA procedure being triggered .

[0011] In an example embodiment , alternatively or in addition to the above-described example embodiments , the source network node supports at least one of a distributed unit , DU, functionality or a layer 2 protocol of the radio access network .

[0012] In an example embodiment , alternatively or in addition to the above-described example embodiments , the configuration is related to layer 1 / layer 2 triggered mobility, LTM .

[0013] In an example embodiment , alternatively or in addition to the above-described example embodiments , the user device is further caused to : receive , from the radio access network, an RRCReconf iguration message including the TA-RNTI , and reconfigure the user device with the LTM .

[0014] In an example embodiment , alternatively or in addition to the above-described example embodiments , the user device is further caused to : receive , from the source network node , a message including a TA acquisition trigger to trigger the related TA procedure for the configured candidate cell with the associated TA-RNTI .

[0015] In an example embodiment , alternatively or in addition to the above-described example embodiments , the user device is further caused to : transmit a random access request message towards the triggered candidate cell , receive , from the candidate cell , a random access response message , and subsequently transmit a message including the TA-RNTI associated with the triggered candidate cell towards the triggered candidate cell .

[0016] In an example embodiment , alternatively or in addition to the above-described example embodiments , the user device is further caused to : after receiving, from the triggered candidate cell , the random access response message , subsequently transmit a message including the TA-RNTI associated with the triggered candidate cell towards the source cell .

[0017] In an example embodiment , alternatively or in addition to the above-described example embodiments , the user device is further caused to : after receiving, from the triggered candidate cell , the random access response message , subsequently refraining from at least one of : starting a related contention resolution procedure , starting a related contention resolution timer, or considering the TA acquisition invalid when a related contention resolution timer expires .

[0018] In an example embodiment , alternatively or in addition to the above-described example embodiments , the related TA procedure relates to at least one of : a TA acquisition procedure , an early TA acquisition procedure , a TA acquis ition with a random acces s procedure , or a TA re-acquisition procedure .

[0019] In an example embodiment , alternatively or in addition to the above-described example embodiments , the at least one candidate cell for the user device to connect to includes at least one of : a target cell for the user device to switch to , or a target cell for the user device to add as a second radio link connection .

[0020] In an example embodiment , alternatively or in addition to the above-described example embodiments , the TA parameter is a user device specific parameter assigned by the associated configured candidate cell .

[0021] In an example embodiment , alternatively or in addition to the above-described example embodiments , together with the TA parameter an associated timer is as signed indicating a time period for the TA parameter to be considered valid by the user device .

[0022] An example embodiment of a source network node comprises at least one proces sor, and at least one memory storing instructions that , when executed by the at least one processor, cause the source network node at least to establish a connection towards a user device via a source cell of a radio access network supported by the source network node . The instructions , when executed by the at least one processor, further cause the source network node at least to transmit , to the user device via the radio access network, a configuration indicating at least one candidate cell for the user device to connect to . The instructions , when executed by the at least one processor, further cause the source network node at least to transmit , to the user device via the radio access network, a timing advance , TA, parameter, including a TA - radio network temporary identi fier, RNTI , associated with a configured candidate cell .

[0023] In an example embodiment , alternatively or in addition to the above-described example embodiments , the source network node supports at least one of a distributed unit , DU, functionality or a layer 2 protocol of the radio access network .

[0024] In an example embodiment , alternatively or in addition to the above-described example embodiments , the configuration is related to layer 1 / layer 2 triggered mobility, LTM.

[0025] In an example embodiment, alternatively or in addition to the above-described example embodiments, the source network node is further caused to: transmit, to the user device via the radio access network, an RRCRe- conf iguration message including the TA-RNTI.

[0026] In an example embodiment, alternatively or in addition to the above-described example embodiments, the source network node is further caused to: transmit, to the user device, a message including a TA acquisition trigger to trigger the related TA procedure for the configured candidate cell with the associated TA-RNTI.

[0027] In an example embodiment, alternatively or in addition to the above-described example embodiments, the source network node is further caused to: receive, from the user device, a message including the TA-RNTI associated with the triggered candidate cell.

[0028] In an example embodiment, alternatively or in addition to the above-described example embodiments, the related TA procedure relates to at least one of: a TA acquisition procedure, an early TA acquisition procedure, a TA acquisition with a random access procedure, or a TA re-acquisition procedure.

[0029] In an example embodiment, alternatively or in addition to the above-described example embodiments, the TA parameter is a source network node specific parameter assigned by the associated configured candidate cell.

[0030] In an example embodiment, alternatively or in addition to the above-described example embodiments, together with the TA parameter an associated timer is assigned indicating a time period for the TA parameter to be considered valid by the user device.

[0031] An example embodiment of a target network node in a candidate handover target cell comprises at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the target network node at least to receive a random access request from a user device via a candidate cell associated with a timing advance , TA, - radio network temporary identi fier, RNTI , for a related TA procedure triggered by a TA acquisition trigger . The instructions , when executed by the at least one processor, further cause the target network node at least to transmit , to the user device via the candidate cell , a random access response message . The instructions , when executed by the at least one processor, further cause the target network node at least to receive a message including the TA-RNTI associated with the triggered candidate cell from the user device via the candidate cell .

[0032] In an example embodiment , alternatively or in addition to the above-described example embodiments , the at least one candidate cell includes at least one of : a target cell for the user device to switch to , or a target cell for the user device to add as a second radio l ink connection .

[0033] In an example embodiment , alternatively or in addition to the above-described example embodiments , the TA parameter is a user device specific parameter assigned by the associated configured candidate cell .

[0034] An example embodiment of a method comprises establishing, by a user device , a connection towards a source network node of a radio access network via a source cell supported by the source network node . The method further comprises receiving, at the user device from the radio access network, a configuration indicating at least one candidate cell for the user device to connect to . The method further comprises receiving, at the user device from the radio access network, a timing advance , TA, parameter, including a TA - radio network temporary identi fier, RNTI , associated with a configured candidate cell . The method further comprises using, by the user device , the TA parameter in case of a related TA procedure being triggered . An example embodiment of a method comprises establishing, by a source network node , a connection towards a user device via a source cell of a radio access network supported by the source network node . The method further comprises transmitting, from the source network node to the user device via the radio access network, a configuration indicating at least one candidate cell for the user device to connect to . The method further comprises transmitting, from the source network node to the user device via the radio access network, a timing advance , TA, parameter, including a TA - radio network temporary identi fier, RNTI , associated with a configured candidate cell .

[0035] An example embodiment of a method comprises receiving, a random access request at a target network node from a user device via a candidate cell associated with a timing advance , TA, - radio network temporary identi fier, RNTI , for a related TA procedure triggered by a TA acquisition trigger . The method further comprises transmitting, from the target network node to the user device via the candidate cell , a random access response message . The method further comprises receiving, a message including the TA-RNTI associated with the triggered candidate cell at the target network node from the user device via the candidate cell .

[0036] An example embodiment of an apparatus comprises means for carrying out a method according to any of the above-described example embodiments .

[0037] An example embodiment of a computer program product comprises program code configured to perform a method according to any of the above-described example embodiments when the computer program product is executed on a computer .

[0038] DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings , which are included to provide a further understanding of the embodiments and constitute a part of this specification, illustrate embodiments and together with the description help to explain the principles of the embodiments . In the drawings :

[0040] FIG . 1 shows an example embodiment of the subj ect matter described herein illustrating an example system, where various embodiments of the present disclosure may be implemented;

[0041] FIG . 2A shows an example embodiment of the subj ect matter described herein illustrating a user device ;

[0042] FIG . 2B shows an example embodiment of the subj ect matter described herein illustrating a source network node ;

[0043] FIG . 20 shows an example embodiment of the subj ect matter described herein illustrating a target network node ;

[0044] FIGS . 3A to 3B show an example embodiment of the subj ect matter described herein illustrating a method in a first preamble collision scenario ;

[0045] FIGS . 4A to 40 show an example embodiment of the subj ect matter described herein illustrating a method in a second preamble collision scenario ;

[0046] FIG . 5 shows an example embodiment of the subj ect matter described herein illustrating a method in a no preamble collision scenario ;

[0047] FIGS . 6A to 6B show an example embodiment of the subj ect matter described herein illustrating an LTM preparation procedure ;

[0048] FIG . 7 shows an example embodiment of the subj ect matter described herein illustrating a method for a user device ;

[0049] FIG . 8 shows an example embodiment of the subj ect matter described herein illustrating a method for a source network node ;

[0050] FIG . 9 shows an example embodiment of the subj ect matter described herein illustrating a method for a target network node ; and FIG . 10 shows an example embodiment of the subj ect matter described herein illustrating a method in an inter-CU scenario .

[0051] Like reference numerals are used to designate like parts in the accompanying drawings .

[0052] DETAILED DESCRIPTION

[0053] Reference will now be made in detail to embodiments , examples of which are illustrated in the accompanying drawings . The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utili zed . The description sets forth the functions of the example and the sequence of steps for constructing and operating the example . However, the same or equivalent functions and sequences may be accomplished by di f ferent examples .

[0054] Fig . 1 illustrates example system 100 , where various embodiments of the present disclosure may be implemented . System 100 may comprise a radio access network 110 of a fi fth generation ( 5G) new radio (NR) network or a network beyond 5G wireless networks . An example representation of system 100 is shown depicting user device 200 , source network node device 210 in first cel l

[0055] 111 , and target network node device 220 in second cel l

[0056] 112 . As will be discussed in more detail below, first cell 111 represents a source cel l for user device 200 in a handover, and second cell 112 represents a candidate target cell for user device 200 in the handover . Even though only one target network node device 220 and second cell 112 are shown in Fig . 1 for clarity, system 100 may compri se more than one target network node device 220 and second cell 112 , and thereby more than one candidate target cell .

[0057] At least in some embodiments , radio access network 110 may be comprised in one or more massive machine- to-machine (M2M) network (s) , massive machine type communications (mMTC) network(s) , internet of things (loT) network(s) , industrial internet-of-things (IIoT) network^) , enhanced mobile broadband (eMBB) network(s) , ultra-reliable low-latency communication (URLLC) network^) , and / or the like. In other words, radio access network 110 may be configured to serve diverse service types and / or use cases, and it may logically be seen as comprising one or more networks.

[0058] User device 200 may include, e.g., a mobile phone, a smartphone, a tablet computer, a smart watch, or any hand-held, portable and / or wearable device. User device 200 may also be referred to as a user equipment (UE) . Network nodes 210, 220 may comprise, e.g., a base station. The base station may include, e.g., any device suitable for providing an air interface for client devices to connect to a wireless network via wireless transmissions .

[0059] At least in some embodiments, network nodes 210, 220 may be logically split into nodes called centralized units (CUs) and distributed units (DUs) . For example, the CUs may host higher layer protocols, such as radio resource control (RRC) , service data adaptation protocol (SDAP) , and / or packet data convergence protocol (PDCP) . The DUs may host, e.g., radio link control (RLC) , medium access control (MAC) , and / or higher physical (PHY) layers.

[0060] The following description provides further details of examples of network nodes. In a 5G NR network, a gNodeB (also known as gNB) may include, e.g., a node that provides NR user plane and control plane protocol terminations towards the UE and that is connected via a NG interface to the 5G core (5GC) , e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 3.2, which is hereby incorporated by reference herein. A gNB supports various protocol layers, e.g., Layer 1 (LI) - physical layer, Layer 2 (L2) , and Layer 3 (L3) .

[0061] The layer 2 (L2) of NR is split into the following sublayers: Medium Access Control (MAC) , Radio Link Control (RLC) , Packet Data Convergence Protocol (PDCP) and Service Data Adaptation Protocol (SDAP) , where, e.g. :

[0062] The physical layer offers to the MAC sublayer transport channels;

[0063] The MAC sublayer offers to the RLC sublayer logical channels;

[0064] The RLC sublayer offers to the PDCP sublayer RLC channels;

[0065] The PDCP sublayer offers to the SDAP sublayer radio bearers;

[0066] The SDAP sublayer offers to 5GC quality of service (QoS) flows;

[0067] "Comp." refers to header compression and "Segm." refers to segmentation;

[0068] Control channels include broadcast control channel (BCCH) and physical control channel (PCCH) .

[0069] Layer 3 (L3) includes e.g., radio resource control (RRC) , e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 6, which is hereby incorporated by reference herein.

[0070] A gNB central unit (gNB-CU) includes, e.g., a logical node hosting, e.g., radio resource control (RRC) , service data adaptation protocol (SDAP) , and packet data convergence protocol (PDCP) protocols of the gNB or RRC and PDCP protocols of the en-gNB, that controls the operation of one or more gNB distributed units (gNB-DUs) . The gNB-CU terminates the Fl interface connected with the gNB-DU. A gNB-CU may also be referred to herein as a CU, a central unit, a centralized unit, or a control unit. A gNB Distributed Unit (gNB-DU) includes, e.g., a logical node hosting, e.g., radio link control (RLC) , media access control (MAC) , and physical (PHY) layers of the gNB or en-gNB, and its operation is partly controlled by the gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the Fl interface connected with the gNB-CU. A gNB-DU may also be referred to herein as DU or a distributed unit.

[0071] A gNB-CU-Control Plane (gNB-CU-CP) includes, e.g., a logical node hosting, e.g., the RRC and the control plane part of the PDCP protocol of the gNB-CU for an en-gNB or a gNB. The gNB-CU-CP terminates the El interface connected with the gNB-CU-User Plane (gNB-CU- UP) and the Fl-C interface connected with the gNB-DU.

[0072] A gNB-CU-User Plane (gNB-CU-UP) includes, e.g., a logical node hosting, e.g., the user plane part of the PDCP protocol of the gNB-CU for an en-gNB, and the user plane part of the PDCP protocol and the SDAP protocol of the gNB-CU for a gNB. The gNB-CU-UP terminates the El interface connected with the gNB-CU-CP and the Fl-U interface connected with the gNB-DU, e.g., according to 3GPP TS 38.401 V16.6.0 (2021-07) section 3.1, which is hereby incorporated by reference herein.

[0073] Different functional splits between the central and distributed unit are possible, e.g., called options :

[0074] Option 1 (lA-like split) :

[0075] The function split in this option is similar to the 1A architecture in dual connectivity (DC) . RRC is in the central unit. PDCP, RLC, MAC, physical layer, and RE are in the distributed unit.

[0076] Option 2 (3C-like split) :

[0077] The function split in this option is similar to the 3C architecture in DC. RRC and PDCP are in the central unit. RLC, MAC, physical layer, and RE are in the distributed unit. Option 3 (intra RLC split) :

[0078] Low RLC (partial function of RLC) , MAC, physical layer, and RF are in the distributed unit. PDCP and high RLC (the other partial function of RLC) are in the central unit.

[0079] Option 4 (RLC-MAC split) :

[0080] MAC, physical layer, and RF are in the distributed unit. PDCP and RLC are in the central unit.

[0081] Or else, e.g., according to 3GPP TR 38.801 V14.0.0 (2017-03) section 11, which is incorporated by reference herein.

[0082] As used herein, the term "network node" may refer to any of a gNB, a gNB-CU, a gNB-DU, a gNB-CU-CP, or a gNB-CU-UP, or any combination of them.

[0083] A RAN (radio access network) node or network node such as, e.g. a gNB, base station, gNB-CU, or gNB- DU, or parts thereof, may be implemented using, e.g., an apparatus with at least one processor and / or at least one memory with processor-readable instructions ("program") configured to support and / or provision and / or process CU and / or DU related functionality and / or features, and / or at least one protocol (sub-) layer of a RAN (radio access network) , e.g. layer 2 and / or layer 3.

[0084] The gNB-CU and gNB-DU parts may, e.g., be colocated or physically separated. The gNB-DU may even be split further, e.g., into two parts, e.g., one including processing equipment and one including an antenna. A central unit (CU) may also be called BBU / REC / RCC / C- RAN / V-RAN, O-RAN, or part thereof. A distributed unit (DU) may also be called RRH / RRU / RE / RU, or part thereof. Hereinafter, in various example embodiments of the present disclosure, a network node, which supports at least one of central unit control plane functionality or a layer 3 protocol of a radio access network, may be, e.g., a gNB-CU-CP. Similarly, a network node, which supports at least one of distributed unit functionality or a layer 2 protocol of the radio access network, may be, e . g . , a gNB-DU .

[0085] A gNB-CU may support one or multiple gNB-DUs . A gNB-DU may support one or multiple cells and, thus, could support a serving cell for a user equipment apparatus (UE) or support a candidate cell for handover, dual connectivity, and / or carrier aggregation, among other procedures.

[0086] The user equipment apparatus (UE) may be or include a wireless or mobile device, an apparatus with a radio interface to interact with a RAN (radio access network) , a smartphone, an in-vehicle apparatus, an loT device, or a M2M device, among other types of user equipment. Such a UE may include: at least one processor; and at least one memory including program code; where the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform certain operations, such as, e.g., RRC connection to the RAN. In embodiments, the UE may be configured to generate a message (e.g., including a cell ID) to be transmitted via radio towards a RAN (e.g., to reach and communicate with a serving cell) . In embodiments, the UE may generate and transmit and receive RRC messages containing one or more RRC PDUs (packet data units) . Persons skilled in the art will understand RRC protocol as well as other procedures a UE may perform.

[0087] The following description provides further details of examples of contention resolution, based on3GPP TS 38.321 V17.5.0 (2023-06) section 5.1.5 which is hereby incorporated by reference herein.

[0088] Regarding contention resolution and, in particular, related to the 'do not start contention resolution' step and the further processing, the following describes exemplary implementation details:

[0089] Once Msg3 is transmitted the MAC entity shall: 1> if the Msg3 transmission (i.e. initial transmission or HARQ retransmission) is related to an early TA acquisition procedure for a candidate cell during an LTM procedure:

[0090] 2> do not start or restart the ra-Con- tentionResolutionTimer after the end of the Msg3 transmission;

[0091] 2> start or restart the timeAlign- mentTimer after the end of the Msg3 transmission;

[0092] 2> monitor the PDCCH while the timeAlign- mentTimer is running regardless of the possible occurrence of a measurement gap;

[0093] 2> if notification of a reception of a PDCCH transmission of the serving source cell is received from lower layers:

[0094] 3> if the PDCCH transmission includes a trigger for early TA (re- ) acquisition for the candidate cell ;

[0095] 4> consider this Contention Resolution not successful;

[0096] 4> initiate the Random Access procedure towards the triggered candidate cell;

[0097] 3> if the PDCCH transmission includes a trigger for a cell switch or cell addition for the candidate cell;

[0098] 4> consider this Contention Resolution successful ;

[0099] 4> initiate the RACHless procedure towards the triggered candidate cell;

[0100] 2> if no notification of a reception of a PDCCH transmission of the serving source cell related to the candidate cell is received from lower layers:

[0101] 3> if the timeAli gnmentTimer expires,

[0102] 4> discard the TEMPORARY_C-RNTI ;

[0103] 4> consider the Contention Resolution not successful. 3> if the Contention Resolution is considered not successful:

[0104] 4> flush the HARQ buffer used for transmission of the MAC PDU in the Msg3 buffer;

[0105] 4> increment

[0106] PREAMBLE TRANSMISSION_COUNTER by 1;

[0107] 4> if PREAMBLE TRANSMISSION_COUNTER = preambleTransMax + 1:

[0108] 4> indicate a Random Access problem to upper layers.

[0109] 4> if this Random Access procedure was triggered for SI request:

[0110] 5> consider the Random Access procedure unsuccessfully completed.

[0111] In the following, various example embodiments will be discussed. At least some of these example embodiments described herein may allow time alignment synchronization with a candidate cell early, i.e., before an execution phase of a lower layer triggered mobility procedure .

[0112] Furthermore, at least some of the example embodiments described herein may allow moving the co-ordination of preamble collisions from a CU to a source DU.

[0113] Furthermore, at least some of the example embodiments described herein may result in no need to reserve preambles at handover target side (e.g., legacy dedicated ones or reserved sets like a contention based random access (CBRA) pool) .

[0114] Furthermore, at least some of the example embodiments described herein may allow transmitting a random access response (RAR) directly by a candidate target cell, and hence a timing advance command (TAG) may arrive at a user device side quickly (within a RAR window) .

[0115] Furthermore, at least some of the example embodiments described herein may result in a user device performing an early time alignment synchronization not needing to listen to a candidate target cell for signi ficantly longer than needed when a Msg2 is also delivered to the user device directly by the target cell .

[0116] Furthermore , at least some of the example embodiments described herein may result in no need for contention resolution, as there is no need to send uplink a downlink control information ( DCI ) to a user device to complete a random access (RA) procedure .

[0117] Furthermore , at least some of the example embodiments described herein may be used in inter-CU scenarios since the disclosure relates to sending a TA validity message once a timing advance radio network temporary identi fier ( TA-RNTI ) medium access control control element (MCE ) is decoded at the target cell side (using, e . g . , FlAP / XnAP / NGAP ) .

[0118] Furthermore , at least some of the example embodiments described herein may be simple to implement since the disclosed user device and base station behaviours are close to legacy procedures .

[0119] Furthermore , at least some of the example embodiments described herein may result in no need for coordinating preamble collisions at a CU level .

[0120] Furthermore , at least some of the example embodiments described herein may allow the disclosed TA- RNTI concept to be used in a basic scenario outside of mobility to re-acquire UL time alignment in a primary cell ( PCell ) .

[0121] At least in some embodiments , in an initial phase user device may be in an RRC_CONNECTED state in a source cell , and the source cel l MAC may be configured with a TA resolution timer as a part of LTM-speci fic MAC configuration .

[0122] At least in some embodiments , an LTM preparation phase may comprise at least some of the following :

[0123] - a source cell may send an LTM handover ( HO) request , and ask each candidate target cell for assignment of a TA-RNTI for a capable user device ( i . e . , for a user device capable of following the procedure disclosed below in more detail) ,

[0124] - candidate target cells may provide the set of TA-RNTIs for a capable user device as a part of the LTM configuration which may then be sent to the source cell (although may not be used by the source cell itself) ,

[0125] - the source cell may configure the user device with an LTM configuration comprising the TA-RNTI (s) (one per candidate target cell) . At this stage, the user device may know for which candidate target cells it will perform a TA-RNTI based CBRA once requested to synchronize with them by the source cell. The user device may also be provided by source cell's TA-RNTI for LTM purposes.

[0126] Fig. 2A is a block diagram of user device 200, in accordance with an example embodiment.

[0127] User device 200 comprises one or more processors 202 and one or more memories 204 that comprise computer program code. User device 200 may also include other elements, such as transceiver 206 configured to enable user device 200 to transmit and / or receive information to / from other devices, as well as other elements not shown in Fig. 2A. In one example, user device 200 may use transceiver 206 to transmit or receive signalling information and data in accordance with at least one cellular communication protocol. Transceiver 206 may be configured to provide at least one wireless radio connection, such as for example a 3GPP mobile broadband connection (e.g., 5G or 6G) . Transceiver 206 may comprise, or be configured to be coupled to, at least one antenna to transmit and / or receive radio frequency signals .

[0128] Although user device 200 is depicted to include only one processor 202, user device 200 may include more processors. In an embodiment, memory 204 is capable of storing instructions, such as an operating system and / or various applications. Furthermore, memory 204 may include a storage that may be used to store, e.g., at least some of the information and data used in the disclosed embodiments.

[0129] Furthermore, processor 202 is capable of executing the stored instructions. In an embodiment, processor 202 may be embodied as a multi-core processor, a single core processor, or a combination of one or more multi-core processors and one or more single core processors. For example, processor 202 may be embodied as one or more of various processing devices, such as a coprocessor, a microprocessor, a controller, a digital signal processor (DSP) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, a neural network (NN) chip, an artificial intelligence (Al) accelerator, a tensor processing unit (TPU) , a neural processing unit (NPU) , or the like. In an embodiment, processor 202 may be configured to execute hard-coded functionality. In an embodiment, processor 202 is embodied as an executor of software instructions, wherein the instructions may specifically configure processor 202 to perform the algorithms and / or operations described herein when the instructions are executed.

[0130] Memory 204 may be embodied as one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination of one or more volatile memory devices and non-volatile memory devices. For example, memory 204 may be embodied as semiconductor memories (such as mask ROM, PROM (programmable ROM) , EPROM (erasable PROM) , flash ROM, RAM (random access memory) , etc . ) . User device 200 may comprise any of various types of devices used directly by an end user entity and capable of communication in a wireless network, such as a user equipment (UE) . Such devices include but are not limited to smartphones, tablet computers, smart watches, lap top computers, internet-of-things (loT) devices, massive machine-to-machine (M2M) devices, massive machine type communications (mMTC) devices, industrial internet-of-things (IIoT) devices, enhanced mobile broadband (eMBB) devices, ultra-reliable low-latency communication (URLLC) devices, and / or devices mounted in vehicles, etc.

[0131] When executed by at least one processor 202, instructions stored in at least one memory 204 cause user device 200 at least to establish a connection towards source network node 210 of radio access network 110 via source cell 111 supported by source network node 210.

[0132] The instructions, when executed by at least one processor 202, further cause user device 200 at least to receive, from radio access network 110, a configuration indicating at least one candidate cell for user device 200 to connect to. For example, the configuration may be related to layer 1 / layer 2 triggered mobility, LTM.

[0133] The instructions, when executed by at least one processor 202, further cause user device 200 at least to receive, from radio access network 110, a timing advance (TA) parameter, including a TA - radio network temporary identifier (RNTI) associated with configured candidate cell 112. For example, the TA parameter may be user device 200 specific parameter assigned by associated configured candidate cell 112.

[0134] At least in some embodiments, together with the TA parameter an associated timer may be assigned indicating a time period for the TA parameter to be considered valid by user device 200. The instructions , when executed by at least one processor 202 , further cause user device 200 at least to use the TA parameter in case of a related TA procedure being triggered . For example , the related TA procedure may relate to a TA acquisition procedure , an early TA acquisition procedure , a TA acquisition with a random access procedure , and / or a TA re-acquisition procedure .

[0135] At least in some embodiments , source network node 210 may support a distributed unit DU functionality and / or a layer 2 protocol of radio access network 110 .

[0136] At least in some embodiments , user device 200 may be further caused to : receive , from radio access network 110 , an RRCReconf iguration message including the TA-RNTI , and reconfigure user device 200 with the LTM .

[0137] At least in some embodiments , user device 200 may be further caused to : receive , from source network node 210 , a message including a TA acquisition trigger to trigger the related TA procedure for configured candidate cell 112 with the associated TA-RNTI .

[0138] At least in some embodiments , user device 200 may be further caused to : transmit a random access request message towards triggered candidate cell 112 , receive , from candidate cell 112 , a random access response message , and subsequently transmit a message including the TA-RNTI associated with triggered candidate cell 112 towards triggered candidate cell 112 .

[0139] At least in some embodiments , user device 200 may be further caused to : after receiving, from triggered candidate cell 112 , the random access response message , subsequently transmit a message including the TA-RNTI associated with triggered candidate cell 112 towards source cell 111 .

[0140] At least in some embodiments , user device 200 may be further caused to : after receiving, from triggered candidate cell 112 , the random access response message , subsequently refraining from starting a related contention resolution procedure, starting a related contention resolution timer, and / or considering the TA acquisition invalid when a related contention resolution timer expires.

[0141] At least in some embodiments, at least one candidate cell 112 for user device 200 to connect to may include a target cell for user device 200 to switch to, and / or a target cell for user device 200 to add as a second radio link connection.

[0142] When executed by at least one processor 202, instructions stored in at least one memory 204 may further cause user device 200 at least to perform: in response to being triggered by source network node 210 located in handover source cell 111 to perform a time alignment synchronization with target network node 220 located in candidate handover target cell 112 in a lower layer (i.e., layer 1 (LI) / layer 2 (L2) ) triggered mobility (LTM) procedure before an execution phase of the LTM procedure: transmitting a timing advance radio network temporary identifier (TA-RNTI) medium access control control element (MCE) to target network node 220.

[0143] The TA-RNTI MCE comprises a TA-RNTI assigned to user device 200 by target network node 220 in a preparation phase of the LTM procedure.

[0144] For example, the TA-RNTI may be assigned from a common pool of RNTIs. At least in some embodiments, the TA-RNTI may not be used for any transmission in either direction (e.g., not used as a scrambling sequence by any physical channel) .

[0145] At least in some embodiments, the transmitting of the TA-RNTI MCE may be performed by using a random access response (RAR) uplink (UL) grant received from target network node 220. For example, the TA-RNTI MCE may be transmitted in an msg3 transmission scheduled by the received RAR UL grant. At least in some embodiments, the msg3 transmission may be scrambled with a temporary cell RNTI (Temp C-RNTI) .

[0146] For example, the TA- RNTI MCE may include a fixed size UL MCE with a dedicated logical channel identification (LCID) or a dedicated one-octet enhanced LCID (eLCID) . At least in some embodiments, the TA-RNTI MCE may be used as an Msg3 of an CBRA to carry the TA-RNTI (e.g., using a RAR grant and scrambled with a Temp C- RNTI) .

[0147] At least in some embodiments, a standard MAC subheader for a fixed size medium access control (MAC) packet data unit (PDU) may be used (R / R / LCID / (eLCID) ) . For example, either two reserved bits and a 6-bit LCID may be used when an LCID is decided to be used for the TA-RNTI MCE. Alternatively, two reserved bits and a 6- bit LCID (set to 34) may be used in a first octet and an 8-bit eLCID may be used in a second octet when a one- octet eLCID is decided to be used for the TA-RNTI MCE.

[0148] The instructions, when executed by at least one processor 202, may further cause user device 200 at least to perform refraining from starting a contention resolution procedure.

[0149] At least in some embodiments, the refraining from starting the contention resolution procedure may comprise refraining from starting a contention resolution, stopping listening to target network node 220, and / or restarting communication with source network node 210.

[0150] The instructions, when executed by at least one processor 202, may further cause user device 200 at least to perform transmitting a TA acquired MCE to source network node 210 to indicate to source network node 210 that a TA with target network node 220 has been acquired for the assigned TA-RNTI.

[0151] For example, the TA acquired MCE may include a fixed size UL MCE with a dedicated LCID or a dedicated one-octet eLCID. At least in some embodiments, the TA acquired MCE may be used to carry the TA-RNTI as a part of the early TA synchroni zation in the LTM procedure . At least in some embodiments , the TA acquired MCE may be sent by user device 200 in a physical UL shared channel ( RUSCH) transmission scrambled with its C-RNTI to source cell 210 to inform that a TAC has been received from target cell 220 and an Msg3 has been sent to it . At least in some embodiments , the TA acquired MCE may trigger a scheduling request indication ( SRI ) which may inform source cell 210 that user device 200 is back and allow to deliver the TA Acquired MCE to source cell 210 immediately .

[0152] At least in some embodiments , the TA acquired MCE may use a standard MAC subheader for a fixed si ze MAC PDU (R / R / LCID / ( eLCID) ) . For example , two reserved bits and a 6-bit LCID may be used when an LCID is decided to be used for the TA Acquired MCE . Alternatively, two reserved bits and a 6-bit LCID ( set to 34 ) may be used in a first octet and an 8-bit eLCID may be used in a second octet when a one-octet eLCID is decided to be used for the TA Acquired MCE .

[0153] Fig . 2B is a block diagram of source network node 210 , in accordance with an example embodiment . In the disclosed embodiments , source network node device 210 is located in first cell 111 which represents a source cell for user device 200 in a handover . At least in some embodiments , source network node 210 may support a distributed unit DU functionality and / or a layer 2 protocol of radio access network 110 .

[0154] Source network node 210 comprises one or more processors 212 and one or more memories 214 that comprise computer program code . Source network node 210 may also include other elements , such as transceiver 216 configured to enable source network node 210 to transmit and / or receive information to / from other devices , as well as other elements not shown in Fig . 2B . In one example , source network node 210 may use transceiver 216 to transmit or receive signalling information and data in accordance with at least one cellular communication protocol. Transceiver 216 may be configured to provide at least one wireless radio connection, such as for example a 3GPP mobile broadband connection (e.g., 5G or 6G) . Transceiver 216 may comprise, or be configured to be coupled to, at least one antenna to transmit and / or receive radio frequency signals.

[0155] Although source network node 210 is depicted to include only one processor 212, source network node 210 may include more processors. In an embodiment, memory 214 is capable of storing instructions, such as an operating system and / or various applications. Furthermore, memory 214 may include a storage that may be used to store, e.g., at least some of the information and data used in the disclosed embodiments.

[0156] Furthermore, processor 212 is capable of executing the stored instructions. In an embodiment, processor 212 may be embodied as a multi-core processor, a single core processor, or a combination of one or more multi-core processors and one or more single core processors. For example, processor 212 may be embodied as one or more of various processing devices, such as a coprocessor, a microprocessor, a controller, a digital signal processor (DSP) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, a neural network (NN) chip, an artificial intelligence (Al) accelerator, a tensor processing unit (TPU) , a neural processing unit (NPU) , or the like. In an embodiment, processor 212 may be configured to execute hard-coded functionality. In an embodiment, processor 212 is embodied as an executor of software instructions , wherein the instructions may speci fically configure processor 212 to perform the algorithms and / or operations described herein when the instructions are executed .

[0157] Memory 214 may be embodied as one or more volatile memory devices , one or more non-volatile memory devices , and / or a combination of one or more volatile memory devices and non-volatile memory devices . For example , memory 214 may be embodied as semiconductor memories ( such as mask ROM, PROM (programmable ROM) , EPROM ( erasable PROM) , flash ROM, RAM ( random access memory) , etc . ) .

[0158] Source network node 210 may comprise a base station . The base station may include , e . g . , a 5G or 6G base station ( gNB ) or any such device providing an air interface for user devices to connect to a wireless network via wireless transmissions . At least in some embodiments , source network node 210 may be logically split into a centrali zed unit ( CU) and a distributed unit ( DU) .

[0159] When executed by at least one processor 212 , instructions stored in at least one memory 214 cause source network node 210 at least to establish a connection towards user device 200 via source cell 111 of radio access network 110 supported by source network node 210 .

[0160] The instructions , when executed by at least one processor 212 , further cause source network node 210 at least to transmit , to user device 200 via radio access network 110 , the configuration indicating the at least one candidate cell for user device 200 to connect to .

[0161] The instructions , when executed by at least one processor 212 , further cause source network node 210 at least to transmit , to user device 200 via radio access network 110 , the TA parameter, including the TA-RNTI associated with the configured candidate cell 112 . At least in some embodiments , source network node 210 may be further caused to : transmit , to user device 200 via radio access network 110 , the RRCRecon- figuration message including the TA-RNTI .

[0162] At least in some embodiments , source network node 210 may be further caused to : transmit , to user device 200 , the message including the TA acquisition trigger to trigger the related TA procedure for configured candidate cell 112 with the associated TA-RNTI .

[0163] At least in some embodiments , source network node 210 may be further caused to : receive , from user device 200 , the message including the TA-RNTI associated with triggered candidate cell 112 .

[0164] When executed by at least one processor 212 , instructions stored in at least one memory 214 may further cause source network node 210 at least to perform receiving the TA acquired MCE from user device 200 indicating that the TA with target network node 220 located in candidate handover target cell 112 has been acquired for the TA-RNTI assigned to user device 200 by target network node 220 in the preparation phase of the LTM procedure .

[0165] The instructions , when executed by at least one processor 212 , may further cause source network node 210 at least to perform starting a TA resolution timer for the assigned TA-RNTI and target network node 220 .

[0166] For example , the TA resolution timer may be run at a source cell on a per candidate target cell / TA-RNTI -basis . At least in some embodiments , the TA resolution timer may be used as a time limitation to confirm the validity of an early TA acquisition in the LTM procedure . At least in some embodiments , the TA resolution timer may be used as a part of TA resolution instead of a contention resolution . At least in some embodiments , the TA resolution timer may be used as a part of BS ' MAC LTM configuration of a serving cel l and defined as an enumeration in which the values are comparable to the ones defined for a contention resolution timer (user device MAC side ) multiplied by a large enough factor ( inter-DU / inter-CU backhaul communication may be taken into account ) .

[0167] The instructions , when executed by at least one processor 212 , may further cause source network node 210 at least to perform : in response to target network node 220 indicating a success ful reception of the TA-RNTI MCE comprising a TA-RNTI before the started TA resolution timer expiring : stopping the started TA resolution timer, determining that the TA synchroni zation of user device 200 with target network node 220 before the LTM execution phase succeeded, and continuing with the LTM procedure .

[0168] At least in some embodiments , the instructions , when executed by at least one processor 212 , may further cause source network node 210 to perform : in response to the started TA resolution timer expiring : determining that the TA synchroni zation of user device 200 with target network node 220 before the LTM execution phase failed, and triggering user device 200 to re-perform the TA synchroni zation of user device 200 with target network node 220 before the LTM execution phase .

[0169] Further features of source network node 210 directly result from the functionalities and parameters of user device 200 and thus are not repeated here .

[0170] Fig . 2C is a block diagram of target network node 220 , in accordance with an example embodiment . In the disclosed embodiments , target network node device 220 is located in second cell 112 which represents a candidate target cell for user device 200 in a handover .

[0171] Target network node 220 comprises one or more processors 222 and one or more memories 224 that comprise computer program code . Target network node 220 may also include other elements , such as transceiver 226 configured to enable target network node 220 to transmit and / or receive information to / from other devices , as well as other elements not shown in Fig. 2C. In one example, target network node 220 may use transceiver 226 to transmit or receive signalling information and data in accordance with at least one cellular communication protocol. Transceiver 226 may be configured to provide at least one wireless radio connection, such as for example a 3GPP mobile broadband connection (e.g., 5G or 6G) . Transceiver 226 may comprise, or be configured to be coupled to, at least one antenna to transmit and / or receive radio frequency signals.

[0172] Although target network node 220 is depicted to include only one processor 222, target network node 220 may include more processors. In an embodiment, memory 224 is capable of storing instructions, such as an operating system and / or various applications. Furthermore, memory 224 may include a storage that may be used to store, e.g., at least some of the information and data used in the disclosed embodiments.

[0173] Furthermore, processor 222 is capable of executing the stored instructions. In an embodiment, processor 222 may be embodied as a multi-core processor, a single core processor, or a combination of one or more multi-core processors and one or more single core processors. For example, processor 222 may be embodied as one or more of various processing devices, such as a coprocessor, a microprocessor, a controller, a digital signal processor (DSP) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, a neural network (NN) chip, an artificial intelligence (Al) accelerator, a tensor processing unit (TPU) , a neural processing unit (NPU) , or the like. In an embodiment, processor 222 may be configured to execute hard-coded functionality. In an embodiment , processor 222 is embodied as an executor of software instructions , wherein the instructions may speci fically configure processor 222 to perform the algorithms and / or operations described herein when the instructions are executed .

[0174] Memory 224 may be embodied as one or more volatile memory devices , one or more non-volatile memory devices , and / or a combination of one or more volatile memory devices and non-volatile memory devices . For example , memory 224 may be embodied as semiconductor memories ( such as mask ROM, PROM (programmable ROM) , EPROM ( erasable PROM) , flash ROM, RAM ( random access memory) , etc . ) .

[0175] Target network node 220 may comprise a base station . The base station may include , e . g . , a 5G or 6G base station ( gNB ) or any such device providing an air interface for user devices to connect to a wireless network via wireless transmissions . At least in some embodiments , target network node 220 may be logically split into a centrali zed unit ( CU) and a distributed unit ( DU) .

[0176] When executed by at least one processor 222 , instructions stored in at least one memory 224 cause target network node 220 at least to receive the random acces s request from user device 200 via candidate cell 112 associated with the TA-RNTI for the related TA procedure triggered by the TA acquisition trigger .

[0177] The instructions , when executed by at least one processor 222 , further cause target network node 220 at least to transmit , to user device 200 via candidate cel l 112 , the random access response message .

[0178] The instructions , when executed by at least one processor 222 , further cause target network node 220 at least to receive the message including the TA-RNTI associated with triggered candidate cell 112 from user device 200 via candidate cell 112 . When executed by at least one processor 222 , instructions stored in at least one memory 224 may cause target network node 220 at least to perform receiving from user device 200 the TA-RNTI MCE comprising the TA- RNTI assigned to user device 200 by target network node 220 in the preparation phase of the LTM procedure .

[0179] The instructions , when executed by at least one processor 222 , may further cause target network node 220 at least to perform : in response to a success ful decoding of the received TA-RNTI MCE comprising the assigned TA-RNTI : refraining from proceeding with the contention resolution procedure and indicating a success ful reception o f the TA-RNTI MCE to source network node 210 located in handover source cell 111 . For example , the success ful reception of the TA-RNTI MCE may be indicated via an Fl application protocol ( F1AP ) procedure .

[0180] In other words , F1AP messages (here referred to as TA Valid ( TA-RNTI ) ) may be used to carry a TA-RNTI which has been success fully decoded by target cell 220 in an Msg3 ( a list of TA-RNTI s may be sent ) .

[0181] At least in some embodiments , the indication of the success ful reception of the TA-RNTI MCE may further be indicated via an XnAP : TA valid -message or an NGAP : TA valid -message .

[0182] Further features of target network node 220 directly result from the functionalities and parameters of user device 200 and source network node 210 , and thus are not repeated here .

[0183] Examples of diagrams 300 , 400 and 500 describe the behaviour of user devices and network nodes with regards to validity of a timing advance command ( TAC ) calculated and sent by a candidate target cell . A TAC may be cons idered as valid for a user device i f it has been calculated based on a Msgl transmission performed by this user device . It means that , in case of a preamble collision, the validity of a TAC may be questionable . Figs. 3A to 3B illustrate an example signalling diagram 300 of a method in a first preamble collision scenario in accordance with an example embodiment. Fig. 3B is a direct continuation of Fig. 3A. Specifically, diagram 300 relates to preamble collision between the user device 200 performing the disclosed early TA synchronization (denoted as TA-UE1) and a user device 240 performing a random access (RA) procedure for some other reason (denoted as L-UE) .

[0184] At operation 301, user device 200 may be configured with a single TA-RNTI on a per candidate target cell -basis as part of the LTM configuration. TA-RNTIs may be assigned by candidate target cells.

[0185] At operation 302, source cell 210 may trigger user device 200 to perform early TA synchronization to chosen candidate target cell 220 (e.g., according to physical DL control channel (PDCCH) order) . If a TA- RNTI for this target cell is configured, user device 200 may continue with the disclosed CBRA.

[0186] At operations 303 and 304, TA-UE1 200 and L-UE 240 may send a same RA preamble identification (RAPID= to a same cell of a same T-DU 220 using a same physical RA channel (PRACH) occasion in both time and frequency domains which may result with a same RA-RNTI (i.e., preamble collision may occur) .

[0187] At operation 305, both TA-UE1 200 and L-UE 240 may receive and accept the same RAR.

[0188] At operation 306, TA-UE1 200 may use a RAR grant and send a Msg3, i.e., a TA-RNTI MCE comprising the TA-RNTI assigned at operation 301 by this candidate target cell. The Msg3 may be scrambled with a Temp C- RNTI. At operation 307, TA-UE1 200 may refrain from starting a contention resolution procedure. For example, this may mean that TA-UE1 200 stops listening to candidate target cell 220 and restarts communication with source cell 210. At operation 308, TA-UE1 200 may inform source cell 210 that a TA with candidate target cell 220 has been acquired for a certain TA-RNTI (RAR received, Msg3 sent) . This may be done, e.g., by sending a TA acquired MCE to source cell 210. Here, source cell 210 knows what target cell 220 it is related to based on operation 302.

[0189] At operation 309, source cell 210 may start a TA resolution timer for the TA-RNTI and candidate target cell 220.

[0190] At operation 310, L-UE 240 may proceed with a legacy RA procedure by sending an Msg3 using the same resources that were used by TA-UE1 200 at operation 306. (the result of the preamble collision) . L-UE 240 may start a contention resolution timer.

[0191] At operation 311, at candidate target cell 220 side, multiple Msg3 transmissions using the same RUSCH resources may result in:

[0192] - a cyclic redundancy check (CRC) failure: there is no winner which means that both TA- UE1 200 and L-UE 240 are likely "time- aligned with each other",

[0193] - only the Msg3 sent by L-UE 240 is decoded successfully: among others, this means that L-UE 240 is time-aligned with target cell 220, but TA-UE1 200 is not, or

[0194] - only the Msg3 from TA-UE1 200 is decoded successfully: among others, this means that TA-UE1 200 is time-aligned with target cell 220, but L-UE 240 is not.

[0195] Here, target cell 220 may decide on how to proceed, e.g., based on the decoded Msg3.

[0196] A) in case of the CRC failure:

[0197] At operation 312, the contention resolution timer may expire at L-UE 240 side. L-UE 240 may restart the RA procedure.

[0198] At operation 313, the TA resolution timer may expire at source cell 210. Source cell 210 may assume that the early TA synchronization of TA-UE1 200 failed. TA-UE1 200 may be triggered to perform the early TA synchronization one more time.

[0199] At operation 314, source cell 210 trigger the early TA synchronization again.

[0200] B) in case of the L-UE 240 Msg3 decoded successfully:

[0201] At operation 315, target cell 220 may continue the RA procedure for L-UE 240 in a legacy way by performing contention resolution (e.g., CR MCE + Msg4 or DCI) at operation 316.

[0202] At operation 317, the TA resolution timer may expire at source cell 210. Source cell 210 may assume that the early TA synchronization of TA-UE1 200 failed. TA-UE1 200 may be triggered to perform the early TA synchronization one more time.

[0203] At operation 318, source cell 210 m ay trigger the early TA synchronization again.

[0204] C) in case of the TA-UE1 Msg3 decoded successfully:

[0205] At operation 319, the contention resolution timer may expire at L-UE 240 side. L-UE 240 may restart the RA procedure.

[0206] At operation 320, target cell 220 may refrain from proceeding with the contention resolution procedure (TA-RNTI MCE decoded) .

[0207] Instead, target cell 220 may inform source cell 210 about the successful decoding of the TA-RNTI MCE containing a certain TA-RNTI. F1AP:TA Valid (TA-RNTI) may be sent by target cell 220 to CU 230 (operation 321) which may send this message to source cell 210 (operation 322) . Based on the decoded TA-RNTI and information gathered during the LTM preparation phase, target cell 220 may determine source cell 210 for TA-UE1 200.

[0208] At operation 323, source cell 210 may stop the TA resolution timer. Source cell 210 may assume that the early TA synchronization of TA-UE1 200 was successful. The LTM procedure may continue at operation

[0209] 324.

[0210] Figs. 4A to 4C illustrate an example signalling diagram 400 of a method in a second preamble collision scenario in accordance with an example embodiment. Fig. 4B is a direct continuation of Fig. 4A, and Fig. 4C is a direct continuation of Fig. 4B. Specifically, diagram 400 relates to preamble collision between two user devices 200, 200B performing the disclosed early TA synchronization (denoted as TA-UE1 and TA-UE2) .

[0211] At operation 401, TA-UE1 200 and TA-UE1 200B may be assigned by candidate target cell 220 with TA- RNTI1 and TA-RNTI2, respectively.

[0212] At operations 407 and 411, TA-UE1 200 and TA- UE1 200B may send TA-RNTI MCEs containing TA-RNTI1 and TA-RNTI2, respectively.

[0213] At operations 408 and 412, TA-UE1 200 and TA- UE1 200B may refrain from starting the contention resolution procedure and stop listening to candidate target cell 220.

[0214] Instead, at operations 409 and 413, TA-UE1 200 and TA-UE1 200B may inform their source cells 210, 210B about the successful receipt of the TAG and about the sending of the TA-RNTI MCEs to candidate target cell 220.

[0215] At operations 410 and 414, source cells 210, 210B may start TA resolution timers for the TA-RNTI1 and TA-RNTI, respectively.

[0216] At operation 415, candidate target cell 220 may deal with one of three possibilities similar to the case of the preamble collision with L-UE 240 illustrated in diagram 300.

[0217] In case of a CRC failure, the TA resolution timer may expire at source cells 210, 210B of TA-UE1 200 and TA-UE1 200B (operations 416 and 418) which may imply that the early TA synchronization may have to be repeated by both of user devices 200, 200B. In the case when either the TA-RNTI MCE from TA-UE1 200 or the TA-RNTI MCE from TA-UE1 200B has been decoded success fully, candidate target cell 220 may inform the appropriate source cel l 210 or 210B about the success ful decoding . The winning user device may continue with the LTM procedure . For the other one , the TA resolution timer may expire at its source cell which implies a restart of the early TA synchroni zation procedure .

[0218] The rest of the operations in diagram 400 are similar to their counterparts in diagram 300 , and thus their descriptions are not repeated here .

[0219] Fig . 5 illustrates an example signalling diagram 500 of a method in a no preamble collision scenario in accordance with an example embodiment .

[0220] In case of no preamble collision, the TA-RNTI MCE may be decoded at candidate target cell 220 success fully . The procedure may be completed in the same way as described for the winning user device in diagrams 300 , 400 , and thus their description is not repeated here .

[0221] In the examples of diagram 600 of Figs . 6A- 6B, an example of the LTM preparation procedure is illustrated in more detail . Fig . 6B is a direct continuation of Fig . 6A.

[0222] The inter-DU scenario is illustrative, and aspects of the present disclosure may be applied to intra- DU scenarios , as well . Where the source DU and target DU are supported by di f ferent CUs , the source DU may be supported by a source CU and the target DU may be supported by a target CU, which can communicate via an Xn interface . As mentioned above , the terms "transmit towards" , "receive from" , and "cooperate with" ( and their variations ) , include communications that may or may not involve communications through one or more intermediate devices or nodes . It is intended that any description referring to a DU shall also be treated as though the description refers to a network node which supports at least one of DU functionality or a layer 2 protocol of a radio access network (RAN) . It is intended that any description referring to a CU shall also be treated as though the description refers to a network node which supports at least one of CU functionality or a layer 3 protocol of a radio access network (RAN) .

[0223] The paragraphs below describe various signals and operations. It will be understood that the described signals may have associated operations and the described operations may have associated signals. Accordingly, a described signal may also be an operation and a described operation may also be a signal.

[0224] The signals and operations are merely illustrative, and variations are contemplated to be within the scope of the present disclosure. In embodiments, variations may include other signals and operations not illustrated in any of FIGS. 6A-6B. In embodiments, variations may not include every signal and operation illustrated in any one figure. In embodiments, the signals and operations may be implemented in a different order than that illustrated in any of FIGS. 6A-6B. Such and other embodiments are contemplated to be within the scope of the present disclosure.

[0225] Referring now to Figs. 6A-6B, and as mentioned above, the illustrations show an approach in which a target DU / candidate target cell allocates the same user specific TA-RNTI for both TA acquisition and handover procedure, and the source DU is relied upon to inform the target DU (through one or more CU) when the UE uses the user specific TA-RNTI to perform TA acquisition.

[0226] Referring now to Fig. 6A / 6B, example signals and operations are shown in which the same user specific TA-RNTI is allocated for both TA acquisition and handover procedure, and the user specific TA-RNTI is specified to the UE in an RRC message. Prior to signal 601 , the UE has established a connection with a DU ( i . e . , source DU) that supports the serving cel l which serves the UE and has establi shed a ( logical ) connection with the CU that supports the DU .

[0227] For signal 601 , the UE transmits an L3 measurement report towards the source DU, and the source DU receives the L3 measurement report from the UE . Persons skilled in the art will understand an L3 measurement report , which may include averaged measurement samples of reference signals for a serving cell , for example . An L3 measurement report may indicate , for example , that a UE is nearing an edge of a cel l and, thus , handover procedures should be initiated . For signal 602 , the source DU forwards the L3 measurement report using uplink (UL ) RRC message trans fer by transmitting the L3 measurement report towards the CU, and the CU receives the L3 measurement report from the source DU . For operation 603 , the CU performs a handover (HO) decision, based on the L3 measurement report , about whether a handover should be prepared . For the illustrated embodiment , the CU decides that an LTM handover should be prepared and identi fies candidate target cells for the handover . In the illustration, the target DU is identified as supporting one or more o f the candidate target cells .

[0228] For s ignal 604 , the CU transmits a UE context setup request towards the target DU to prepare the target DU for handover by setting up the UE context in the target DU . The target DU receives the UE context setup request from the CU and sets up the UE context . For signal 605 , the target DU provides an acknowledgement by transmitting a UE context setup response towards the CU, and the CU receives the UE context setup response from the target DU . Although one target DU is illustrated, there may be more than one target DU i f there are multiple candidate target cells . The signals at 604 and 605 may be used for each target DU and for multiple candidate target cells. The description below will refer to candidate target cell (s) to indicate there may be one candidate target cell or multiple candidate target cells and, where appropriate, will refer to target DU(s) supporting the candidate target cell (s) . If a target DU and the source DU are supported by different CUs, the CUs may communicate using an Xn interface. For convenience, only one CU is illustrated (a CU supporting the source DU) , but it is intended for the disclosed technology to apply to multi-CU situations, as well.

[0229] For signal 605, and in accordance with aspects of the present disclosure, the target DU also transmits towards the CU information specifying a user specific TA-RNTI usable by the UE to communicate with the target DU for TA acquisition of a candidate target cell (e.g., a cell that is supported by the target DU) and for cell change to the candidate target cell. The user specific TA-RNTI may include, for example, a random access (RA) preamble and RA occasion that is allocated by the target DU and reserved for the UE to use for TA acquisition for the candidate target cell and for handover procedure for the candidate target cell (when non-RA-based handover is not possible) .

[0230] For signal 606, the CU transmits a UE context modification request towards the source DU for modification of the UE context in the source DU, if needed, and for the provision of target cell information (e.g., target cell RS configuration, TCI states, etc.) . The source DU receives the UE context modification request from the CU, modifies the UE context (if needed) , and receives the target cell information. For signal 607, the source DU provides an acknowledgment by transmitting a UE context modification response towards the CU, and the CU receives the UE context modification response from the source DU. For operation 608, the CU creates an RRC reconfiguration message, which includes a measurement configuration for an LI cell change, a configuration of prepared candidate target cell (s) (e.g., cell (s) supported by the target DU) , and a TA acquisition configuration and trigger for the candidate target cell (s) . The TA acquisition configuration may specify the method for a UE to acquire TA. In accordance with aspects of the present disclosure, the method for the UE to acquire TA is an RA-based method, and the user specific TA-RNTI provided by the target DU (for signal 605) can be specified in the RRC reconfiguration message, to be set up in the UE and used by the UE to acquire TA for the candidate target cell and to perform handover procedure to the candidate target cell (when non-RA-based cell switch is not possible) .

[0231] For signal 609, the CU transmits the RRC reconfiguration message towards the source DU using a downlink (DL) RRC message transfer, and the source DU receives the RRC reconfiguration message from the CU. As mentioned above, the RRC reconfiguration message specifies the user specific TA-RNTI usable by the UE for acquiring TA for a candidate target cell and for handover procedure for the candidate target cell. For signal 610, the source DU transmits the RRC reconfiguration message towards the UE to forward it to the UE, and the UE receives the RRC reconfiguration message from the source DU. The UE performs a reconfiguration based on the RRC reconfiguration message. For signal 611, the UE responds by transmitting a RRC reconfiguration complete message towards the source DU using an uplink (UL) RRC message transfer, and the source DU receives the RRC reconfiguration complete message from the UE . For signal 612, the source DU transmits the RRC reconfiguration complete message towards the CU to forward it to the CU, and the CU receives the RRC reconfiguration complete message from the source DU. In embodiments, the signals 609-612 may be described as part of a logical connection between the UE and the CU, such that the CU transmits the RRC message towards the UE, and the UE receives the RRC message from the CU.

[0232] In embodiments, the signals and operations 601- 612 described above may be referred to as a preparation phase. After the preparation phase is an early synchronization phase for early TA acquisition.

[0233] In the early synchronization phase, for operation 613, the UE may perform downlink (DL) synchronization with candidate target cells. Persons skilled in the art will understand downlink synchronization. For operation 614, the source DU decides to trigger TA acquisition. For signal 615, the source DU transmits a PDCCH order towards the UE to trigger TA acquisition, and the UE receives the PDCCH order from the source DU.

[0234] In accordance with aspects of the present disclosure, for signals 616 and 617, the source DU informs the target DU (via the CU) that it triggered TA acquisition for the UE (e.g., UE identified as UE X) . For signal 616, the source DU transmits a message towards the CU indicating that the source DU triggered TA acquisition for the UE, and the CU receives the message from the source DU. For signal 617, the CU relays the message to the target DU by transmitting the message towards the target DU, and the target DU receives the message .

[0235] For operation 618, the target DU, based on receiving the message from the source DU, anticipates that it will receive the user specific TA-RNTI (e.g., RA preamble and occasion) it allocated for signal 605, and the target DU deduces this user specific TA-RNTI for a candidate target cell (rather than for a handover procedure) .

[0236] For signal 619, the UE initiates RA procedure with the target DU using the user specific TA-RNTI specified in the RRC reconfiguration message (signal 610) to acquire TA for a candidate target cell. For operation 620, based on the target DU deducing that the RA procedure is for TA acquisition, the target DU respond with a random access response (RAR) which provides TA information but has no grant of uplink resources for a RRC connect request message.

[0237] In embodiments, and as shown in Fig. 6A, once the UE receives the PDCCH order, it may not immediately perform the RA procedure to the target DU for TA acquisition. Instead, the UE may start a timer to delay the RA procedure (signal 619) so that the source DU may have time inform the target DU (signals 616, 617) that TA acquisition has been triggered for the UE . In embodiments, the timer may be configured in the RRC reconfiguration message (signals and operations 608-610) or in the PDCCH order (signal 615) .

[0238] In embodiments, as a variation (not shown) , the source DU may transmit the PDCCH order (signal 615) after it transmits the message indicating TA acquisition has been triggered (signal 616) . In such embodiments, the source DU may transmit the message for signal 616 and then wait for a specific time window (timer) before it transmits the PDCCH order for signal 615.

[0239] After the early synchronization phase is the execution phase and then the completion phase. In the execution phase, the UE, based on its configuration, provides periodic LI measurement reports. Persons skilled in the art will understand LI measurements. For signal 621, the UE provides LI measurement reporting and periodically transmits LI measurement reports towards the source DU, and the source DU receives the periodic LI measurement reports from the UE . For operation 622, the source DU decides whether the UE should change serving cells. In embodiments, the source DU may decide that the UE should change serving cells if the LI measurements fall below a threshold, for example. Once the source DU decides that the UE should be handed over to a cell (e.g., target cell supported by target DU) , the source DU triggers the cell switch using a cell switch command (e.g., a MAC CE) .

[0240] For signal 623, the cell switch command (e.g., MAC CE) is transmitted by the source DU towards the UE, and the UE receives the cell switch command (e.g., MAC CE) from the source DU. In response to the cell switch command, the UE applies the RRC configuration for the target cell indicated by the cell switch command, to switch to the target DU / target cell as the serving cell. In embodiments, the UE may perform random access (RA) procedure to the target cell, as shown for signal 624, if needed, to acquire TA for the target cell. However, in embodiments, the UE may be configured to not perform RA procedure to the target DU if it has already acquired the TA value of the target cell.

[0241] In accordance with aspects of the present disclosure, for signal 624, if random access procedure is needed, the UE may use the same allocated user specific TA-RNTI (e.g., random access preamble and occasion) as the user specific TA-RNTI described in connection with signal 619. In contrast to the message for signals 616 and 617, the source DU does not transmit any message to the target DU indicating the triggering of a handover. Accordingly, in the RA procedure for signal 624, the target DU may provide a random access response (RAR) that includes TA information as well as a grant of uplink (UL) resources for the UE to transmit a RRC connection request message.

[0242] The UE switches to the configuration of the target cell supported by the target DU. For signal 625, the UE transmits an RRC reconfiguration complete message towards the target DU using already configured uplink (UL) resources, and the target DU receives the RRC reconfiguration complete message from the UE . For signal 626, The target DU forwards the RRC reconfiguration complete message using UL RRC message transfer to transmit the RRC reconfiguration complete message towards the CU, and the CU receives the RRC reconfiguration complete message from the target DU . For signal 627 , the CU transmits a UE context release command towards the source DU to release the UE context from the source DU, and the source DU receives the UE context release command from the CU . The source DU releases the UE context in response to the UE context release command . For signal 628 , the source DU transmits a UE context release complete message towards the CU, and the CU receives the UE context release complete message from the source DU . The CU performs path switch to the target DU as the new DU supporting the serving cell .

[0243] Accordingly, for the example of Fig . 6A and Fig . 6B, the source DU is relied upon to inform the target DU when the allocated user specific TA-RNTI will be used for TA acquisition, so that the target DU can deduce the purpose of a RA procedure by the UE . Thus , when the target DU receives the user speci fic TA-RNTI ( e . g . , RA preamble and occasion) but does not receive a corresponding message from the source DU, the target DU may deduce that the RA procedure is for a handover ( rather than for TA acquisition) .

[0244] Fig . 10 illustrates an example signalling diagram 1000 of a method in an inter-CU scenario in accordance with an example embodiment .

[0245] In the example embodiments of diagrams 300 , 400 and 500 , it has been assumed that both S-DU 210 and T- DU 220 are under control of a same CU 230 . However, the disclosure is applicable to an inter-CU scenario also . In such a case , the di f ference would be related to how T-DU 220 under control o f CU2 230B may inform S-DU 210 about the success ful decoding of the TA-RNTI MCE comprising a certain TA-RNTI . As a solution, at least in some embodiments , an additional XnAP / NGAP may be used, as illustrated in diagram 1000 in which operation numbering is aligned with the one in diagram 500 . Regardless of availability of an active Xn link between CUI 230A and CU2 230B, the same F1AP : TA valid ( TA-RNTI ) messages may be used to communicate between DU and CU as described above .

[0246] When an active Xn link is available between CUI 230A and CU2 230B, an XnAP : TA valid ( TA-RNTI ) message may be used to propagate information about the successful decoding of the TA-RNTI from CU2 230B to CUI 230A.

[0247] Otherwise , an NGAP : TA valid ( TA-RNTI ) message may be used to propagate the above-mentioned information from CU2 230B to 5GC 250 and from 5GC 250 to CUI 230A.

[0248] In case of communication over Xn, CU2 230B may identi fy the right DU ( the one which handles the source cell of TA-UE ) based on the decoded TA-RNTI and the information gathered during the LTM preparation phase in a similar way to how it is done for the intra-CU case . This is because the LTM preparation may be reali zed over Xn as well . The same may be done by CUI 230A. In case of communication over NG, addressing may be taken care by CUs to make it transparent for 5GC 250 ( all identi fiers are known to CUs based on the decoded TA-RNTI and the information gathered during the LTM preparation phase which, in this case , may be done over NG) .

[0249] Fig . 7 illustrates an example flow chart of method 700 for user device 200 , in accordance with an example embodiment .

[0250] At operation 701 , user device 200 establishes the connection towards source network node 210 of radio access network 110 via source cell 111 supported by source network node 210 .

[0251] At operation 702 , user device 200 receives from radio access network 110 the configuration indicating the at least one candidate cell for user device 200 to connect to .

[0252] At operation 703 , user device 200 receives from radio access network 110 , the TA parameter, including the TA-RNTI associated with configured candidate cell 112 .

[0253] At operation 704 , user device 200 uses the TA parameter in case of the related TA procedure being triggered .

[0254] Embodiments and examples with regard to Fig . 7 may be carried out by user device 200 of Fig . 2A. Operations 701-704 may, for example , be carried out by at least one processor 202 and at least one memory 204 . Further features of method 700 directly resulting from the functionalities and parameters of user device 200 are not repeated here . Method 700 can be carried out by computer program ( s ) or portions thereof .

[0255] Another example of an apparatus suitable for carrying out the embodiments and examples with regard to Fig . 7 comprises means for : establishing, at operation 701 , the connection towards source network node 210 of radio access network 110 via source cell 111 supported by source network node 210 ; receiving, at operation 702 , from radio access network 110 , the configuration indicating at least one candidate cell for user device 200 to connect to ; receiving, at operation 703 , from radio access network 110 , the TA-RNTI associated with configured candidate cell 112 ; and using, at operation 704 , the TA parameter .

[0256] Fig . 8 illustrates an example flow chart of method 800 for source network node 210 , in accordance with an example embodiment .

[0257] At operation 801 , source network node 210 establishes the connection towards user device 200 via source cell 111 of radio access network 110 supported by source network node 210 .

[0258] At operation 802 , source network node transmits 802 , to the user device 200 via the radio access network 110 , the configuration indicating the at least one candidate cell for user device 200 to connect to .

[0259] At operation 803 , source network node transmits , to the user device 200 via the radio access network 110 , the TA parameter including the TA-RNTI associated with configured candidate cell 112 .

[0260] Embodiments and examples with regard to Fig . 8 may be carried out by source network node 210 of Fig . 2B . Operations 801- 803 may, for example , be carried out by at least one processor 212 and at least one memory 214 . Further features of method 800 directly resulting from the functionalities and parameters of source network node 210 are not repeated here . Method 800 can be carried out by computer program ( s ) or portions thereof . Another example of an apparatus suitable for carrying out the embodiments and examples with regard to Fig . 8 comprises means for : establishing, at operation 801 , the connection towards user device 200 via source cell 111 of radio access network 110 supported by source network node 210 ; transmitting, at operation 802 , to user device 200 via radio access network 110 , the configuration indicating the at least one candidate cell for user device 200 to connect to ; and transmitting, at operation 803 , to user device 200 via radio acces s network 110 , the TA parameter including the TA-RNTI associated with configured candidate cell 112 .

[0261] Fig . 9 illustrates an example flow chart of method 900 for target network node 220 , in accordance with an example embodiment .

[0262] At operation 901 , target network node 220 receives the random access request from user device 200 via candidate cel l 112 associated with the TA-RNTI for the related TA procedure triggered by the TA acquisition trigger . At operation 902 , target network node 220 transmits to user device 200 via candidate cell 112 the random access response message .

[0263] At operation 903 , target network node 220 receives the message including the TA-RNTI associated with the triggered candidate cell 112 from user device 200 via candidate cell 112 .

[0264] Embodiments and examples with regard to Fig . 9 may be carried out by target network node 220 of Fig . 2C . Operations 901- 903 may, for example , be carried out by at least one processor 222 and at least one memory 224 . Further features of method 900 directly resulting from the functionalities and parameters of target network node 220 are not repeated here . Method 900 can be carried out by computer program ( s ) or portions thereof .

[0265] Another example of an apparatus suitable for carrying out the embodiments and examples with regard to Fig . 9 comprises means for : receiving, at operation 901 , the random access request from user device 200 via candidate cell 112 associated with the TA-RNTI for the related TA procedure triggered by the TA acquisition trigger ; transmitting, at operation 902 , to user device 200 via candidate cell 112 , the random acces s response message ; and receiving, at operation 903 , the message including the TA-RNTI associated with triggered candidate cell 112 from user device 200 via candidate cell 112 .

[0266] User device 200 may comprise means for performing at least one method described herein . In one example , the means may compri se at least one proces sor 202 , and at least one memory 204 storing instructions that , when executed by at least one processor 202 , cause user device 200 to perform the method .

[0267] Source network node 210 may comprise means for performing at least one method described herein . In one example , the means may compri se at least one proces sor 212, and at least one memory 214 storing instructions that, when executed by at least one processor 212, cause source network node 210 to perform the method.

[0268] Target network node 220 may comprise means for performing at least one method described herein. In one example, the means may comprise at least one processor 222, and at least one memory 224 storing instructions that, when executed by at least one processor 222, cause target network node 220 to perform the method.

[0269] The functionality described herein can be performed, at least in part, by one or more computer program product components such as software components. According to an embodiment, user device 200, source network node 210 and / or target network node 220 may comprise a processor or processor circuitry, such as for example a microcontroller, configured by the program code when executed to execute the embodiments of the operations and functionality described. Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs) , Application-specific Integrated Circuits (ASICs) , Application-specific Standard Products (ASSPs) , System- on-a-chip systems (SOCs) , Complex Programmable Logic Devices (CPLDs) , Tensor Processing Units (TPUs) , and Graphics Processing Units (GPUs) .

[0270] Any range or device value given herein may be extended or altered without losing the effect sought. Also, any embodiment may be combined with another embodiment unless explicitly disallowed.

[0271] Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the speci fic features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims .

[0272] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It wil l further be understood that reference to ' an ' item may refer to one or more of those items .

[0273] The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate . Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subj ect matter described herein . Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the ef fect sought .

[0274] The term ' comprising ' is used herein to mean including the method, blocks or elements identi fied, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements .

[0275] It will be understood that the above description is given by way of example only and that various modi f ications may be made by those s kil led in the art . The above speci fication, examples and data provide a complete description of the structure and use of exemplary embodiments . Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments , those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this speci fication .

Claims

CLAIMS :

1. A user device (200) , comprising: at least one processor (202) ; and at least one memory (204) storing instructions that, when executed by the at least one processor (202) , cause the user device (200) at least to: establish a connection towards a source network node (210) of a radio access network (110) via a source cell (111) supported by the source network node (210) ; receive, from the radio access network (110) , a configuration indicating at least one candidate cell for the user device (200) to connect to; receive, from the radio access network (110) , a timing advance, TA, parameter, including a TA - radio network temporary identifier, RNTI, associated with a configured candidate cell (112) ; and use the TA parameter in case of a related TA procedure being triggered.

2. The user device (200) according to claim 1, wherein the source network node (210) supports at least one of a distributed unit, DU, functionality or a layer 2 protocol of the radio access network (110) .

3. The user device (200) according to claim 2, wherein the configuration is related to layer 1 / layer 2 triggered mobility, LTM.

4. The user device (200) according to claim 3, wherein the user device (200) is further caused to: receive, from the radio access network (110) , an RRCRe- conf iguration message including the TA-RNTI, and reconfigure the user device (200) with the LTM.

5. The user device (200) according to claim 4, wherein the user device (200) is further caused to: receive, from the source network node (210) , a messageincluding a TA acquisition trigger to trigger the related TA procedure for the configured candidate cell (112) with the associated TA-RNTI.

6. The user device (200) according to claim 5, wherein the user device (200) is further caused to: transmit a random access request message towards the triggered candidate cell (112) , receive, from the candidate cell (112) , a random access response message, and subsequently transmit a message including the TA-RNTI associated with the triggered candidate cell (112) towards the triggered candidate cell (112) .

7. The user device (200) according to claim 6, wherein the user device (200) is further caused to: after receiving, from the triggered candidate cell (112) , the random access response message, subsequently transmit a message including the TA-RNTI associated with the triggered candidate cell (112) towards the source cell (111) .

8. The user device (200) according to claim 6, wherein the user device (200) is further caused to: after receiving, from the triggered candidate cell (112) , the random access response message, subsequently refraining from at least one of: starting a related contention resolution procedure, starting a related contention resolution timer, or considering the TA acquisition invalid when a related contention resolution timer expires.

9. The user device (200) according to claim 1, wherein the related TA procedure relates to at least one of: a TA acquisition procedure, an early TA acquisition procedure, a TA acquisition with a random access procedure, or a TA re-acquisition procedure.

10. The user device (200) according to claim 1, wherein the at least one candidate cell (112) for the user device (200) to connect to includes at least one of: a target cell for the user device (200) to switch to, or a target cell for the user device (200) to add as a second radio link connection.

11. The user device (200) according to claimI, wherein the TA parameter is a user device (200) specific parameter assigned by the associated configured candidate cell (112) .

12. The user device (200) according to claimII, wherein together with the TA parameter an associated timer is assigned indicating a time period for the TA parameter to be considered valid by the user device (200) .

13. A method (700) , comprising: establishing (701) , by a user device (200) , a connection towards a source network node (210) of a radio access network (110) via a source cell (111) supported by the source network node (210) ; receiving (702) , at the user device (200) from the radio access network (110) , a configuration indicating at least one candidate cell for the user device (200) to connect to; receiving (703) , at the user device (200) from the radio access network (110) , a timing advance, TA, parameter, including a TA - radio network temporary identifier, RNTI, associated with a configured candidate cell (112) ; and using (704) , by the user device (200) , the TA parameter in case of a related TA procedure being triggered .

14. An apparatus, comprising means for carrying out the method (700) according to claim 13.

15. A source network node (210) , comprising: at least one processor (212) ; and at least one memory (214) storing instructions that, when executed by the at least one processor (212) , cause the source network node (210) at least to perform: establish a connection towards a user device (200) via a source cell (111) of a radio access network (110) supported by the source network node (210) ; transmit, to the user device (200) via the radio access network (110) , a configuration indicating at least one candidate cell for the user device (200) to connect to; and transmit, to the user device (200) via the radio access network (110) , a timing advance, TA, parameter, including a TA - radio network temporary identifier, RNTI, associated with a configured candidate cell (112) .

16. The source network node (210) according to claim 15, wherein the source network node (210) supports at least one of a distributed unit, DU, functionality or a layer 2 protocol of the radio access network (110) .

17. The source network node (210) according to claim 16, wherein the configuration is related to layer 1 / layer 2 triggered mobility, LTM.

18. The source network node (210) according to claim 17, wherein the source network node (210) is further caused to: transmit, to the user device (200) via the radio access network (110) , an RRCReconf iguration message including the TA-RNTI.

19. The source network node (210) according to claim 18, wherein the source network node (210) is further caused to: transmit, to the user device (200) , a message including a TA acquisition trigger to trigger the related TA procedure for the configured candidate cell (112) with the associated TA-RNTI.

20. The source network node (210) according to claim 19, wherein the source network node (210) is further caused to: receive, from the user device (200) , a message including the TA-RNTI associated with the triggered candidate cell (112) .

21. The source network node (210) according to claim 15, wherein the related TA procedure relates to at least one of: a TA acquisition procedure, an early TA acquisition procedure, a TA acquisition with a random access procedure, or a TA re-acquisition procedure.

22. The source network node (210) according to claim 15, wherein the TA parameter is a source network node (210) specific parameter assigned by the associated configured candidate cell (112) .

23. The source network node (210) according to claim 22, wherein together with the TA parameter an associated timer is assigned indicating a time period for the TA parameter to be considered valid by the user device (200) .

24. A method (800) , comprising: establishing (801) , by a source network node (210) , a connection towards a user device (200) via a source cell (111) of a radio access network (110) supported by the source network node (210) ; transmitting (802) , from the source network node (210) to the user device (200) via the radio accessnetwork (110) , a configuration indicating at least one candidate cell for the user device (200) to connect to; and transmitting (803) , from the source network node (210) to the user device (200) via the radio access network (110) , a timing advance, TA, parameter, including a TA - radio network temporary identifier, RNTI, associated with a configured candidate cell (112) .

25. An apparatus, comprising means for carrying out the method (800) according to claim 24.

26. A target network node (220) , comprising: at least one processor (222) ; and at least one memory (224) storing instructions that, when executed by the at least one processor (222) , cause the target network node (220) at least to perform: receive a random access request from a user device (200) via a candidate cell (112) associated with a timing advance, TA, - radio network temporary identifier, RNTI, for a related TA procedure triggered by a TA acquisition trigger; transmit, to the user device (200) via the candidate cell (112) , a random access response message; and receive a message including the TA-RNTI associated with the triggered candidate cell (112) from the user device (200) via the candidate cell (112) .

27. The target network node (220) according to claim 26, wherein the at least one candidate cell (112) includes at least one of: a target cell for the user device (200) to switch to, or a target cell for the user device (200) to add as a second radio link connection.

28. The target network node (220) according to claim 26, wherein the TA parameter is a user device(200) specific parameter assigned by the associated configured candidate cell (112) .

29. A method (900) , comprising: receiving (901) , a random access request at a target network node (220) from a user device (200) via a candidate cell (112) associated with a timing advance, TA, - radio network temporary identifier, RNTI, for a related TA procedure triggered by a TA acquisition trigger; transmitting (902) , from the target network node (220) to the user device (200) via the candidate cell (112) , a random access response message; and receiving (903) , a message including the TA- RNTI associated with the triggered candidate cell (112) at the target network node (220) from the user device (200) via the candidate cell (112) .

30. An apparatus, comprising means for carrying out the method (900) according to claim 29.

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