WO2025011820A1

WO2025011820A1 - Fast connected state resumption

Info

Publication number: WO2025011820A1
Application number: PCT/EP2024/065197
Authority: WO
Inventors: Ahmad AWADA; Sanjay Goyal; Panagiotis SPAPIS; Ugur Baran ELMALI; Bernhard Wegmann
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-07-10
Filing date: 2024-06-03
Publication date: 2025-01-16
Anticipated expiration: 2026-01-10

Abstract

According to an aspect, there is provided a solution in which a user equipment configured to support operating in an inactive state is able perform a RACH-less access via a selected cell in case a timing advance value and an uplink configuration of the selected cell are considered still valid.

Description

FAST CONNECTED STATE RESUMPTION

TECHNICAL FIELD

Various example embodiments generally relate to the field of telecommunication systems . In particular, some example embodiments relate to a solution for performing a fast connected state resumption from an inactive state .

BACKGROUND

A user equipment may have an RRC_INACTIVE (RRC, Radio Resource Control ) state , an RRC_CONNECTED state and an RRC_IDLE state in a wireless communication network, for example , a 5G network . The purpose of the RRC_INACTIVE state is to enable lean signaling and energy-ef ficient support of NR services through an optimi zed state transition . A user equipment (UE ) moves from the RRC_IDLE state to RRCjCONNECTED state after establishing an RRC connection to a cell . Later on, a serving cell associated with the UE may decide to move the UE to the RRC_INACTIVE or RRC_IDLE state due to , for example , inactivity ( i . e . no user plane data to be sent ) .

The RRC_INACTIVE state enables to resume a suspended RRC connection and start the transmission of small or sporadic data with a much lower initial access delay and associated signaling overhead as compared to the RRC_IDLE state . This is achieved by allowing a faster transition from the RRC_INACTIVE state to the RRC_CONNECTED state . At the same time , a UE in RRC_INACTIVE state is able to achieve similar power savings as in RRC_IDLE compared to RRC_CONNECTED . Furthermore , compared to keeping the UE in the RRCjCONNECTED state , the RRC_INACTIVE state minimi zes mobility signaling both to a radio access network (RAN) and to a core network) since the UE is still in CM- CONNECTED state .

When moving from the RRC_INACTIVE state to the RRC_CONNECTED state , the RRC resumption procedure towards the last serving gNB or new gNB, however, requires that the UE performs either a 4-step or a 2- step random access procedure which delays the resumption of RRC connection .

SUMMARY

This summary is provided to introduce a selection of concepts in a simpli fied form that are further described below in the detailed description . This summary is not intended to identi fy key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

Example embodiments of the present disclosure provides a solution in which a fast radio resource control (RRC ) is enabled without needing to perform a random access procedure . This and other benef its may be achieved by the features of the independent claims . Further example embodiments are provided in the dependent claims , the description, and the drawings .

According to a first aspect , a user equipment configured to support operating in an inactive state , may comprise at least one processor and at least one memory storing instructions which, when executed by the at least one processor, cause the user equipment at least to establish a connection towards a network node that supports at least one of central unit control plane , CU- CP, functionality or a layer 3 protocol of a radio access network, RAN, to operate in a connected state via a serving cell ; receive , from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH- less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cel l ; operate in the inactive state ; monitor a need to transition from the inactive state to the connected state ; select , in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell ; and perform a RACH-less access via the selected cell in case the timing advance value and the UL configuration of the selected cell are considered still valid .

In an example embodiment of the first aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the TA value associated with the at least one cell .

In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to receive , from a serving network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, a trigger to acquire the TA values of the at least one non-serving cell ; and acquire the TA values of the at least one non-serving cell in response to the received instruction .

In an example embodiment of the first aspect , the information relating to a TA value and a UL configuration of at least one cell comprises a TA value for each of the at least one non-serving cel l and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell .

In an example embodiment of the first aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the UL configuration of the at least one cell for a validity period .

In an example embodiment of the first aspect , the information relating to a TA value and a UL configuration of at least one cell comprises the UL configuration of each of the at least one cell .

In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to start a timer in response to transiting to operate in the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the timer has not expired .

In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; start a timer in response to transiting to operate in the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the timer and the TAT associated with the selected cell have not expired .

In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cel l to be valid, when the TAT associated with the selected cell has not expired .

In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to store , before operating in the inactive state , first measurements relating to the at least one non-serving cell ; store , after deciding to resume the connection from the inactive state to the connected state , second measurements relating to the at least one non-serving cell ; and consider the TA value and the UL configuration of the selected cel l to be valid, when the second measurement relating to the selected cell di f fers from the first measurement relating to the selected cell less than a predetermined threshold amount .

In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to store , before operating in the inactive state , beam identi f iers of the at least one cell ; upon deciding to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell , compare the beam identi fier of the selected cell to the stored beam identi fiers of the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the beam identi fier of the selected cell is among the stored beam identi fiers . According to a second aspect , a network node that supports at least one of central unit control plane , CU- CP, functionality or a layer 3 protocol of a radio access network, may comprise at least one processor ; and at least one memory storing instructions which, when executed by the at least one processor, cause the network node at least to establish a connection towards a user equipment to operate in a connected state via a serving cell ; and transmit , to the user equipment , a message including an instruction to operate in an inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH- less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell .

In an example embodiment of the second aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the TA value associated with the at least one cell .

In an example embodiment of the second aspect , the information relating to a TA value and a UL configuration of at least one cell comprises a TA value for each of the at least one non-serving cel l and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell .

In an example embodiment of the second aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the UL configuration of the at least one cell for a validity period .

In an example embodiment of the second aspect , the information relating to a TA value and a UL configuration of at least one cell comprises the UL configuration of each of the at least one cell .

In an example embodiment of the second aspect , the instructions , when executed by the at least one processor, cause the network node at least to receive , from at least one network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, acquisition information of a timing advance , TA, for at least one cell , wherein the at least one distributed unit comprises at least one of a serving DU controlling a serving cell and a target DU controlling a target cell .

According to a third aspect , a method performed by a user equipment configured to support operating in an inactive state may comprise establishing a connection towards a network node that supports at least one of central unit control plane , CU-CP , functionality or a layer 3 protocol of a radio access network, RAN, to operate in a connected state via a serving cell ; receiving, from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cel l to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell ; operating in the inactive state ; monitoring a need to transition from the inactive state to the connected state ; selecting, in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell ; and performing a RACH-less access via the selected cell in case the TA value and the UL configuration of the selected cell are considered still valid .

In an example embodiment of the third aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the TA value associated with the at least one cell .

In an example embodiment of the third aspect , the method may comprise receiving, from a serving network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, a trigger to acquire the TA values of the at least one non-serving cell ; and acquiring the TA values of the at least one non-serving cell in response to the received instruction .

In an example embodiment of the third aspect , the information relating to a TA value and a UL configuration of at least one cell comprises a TA value for each of the at least one non-serving cel l and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell .

In an example embodiment of the third aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the UL configuration of the at least one cell for a validity period .

In an example embodiment of the third aspect , the information relating to a TA value and a UL configuration of at least one cell comprises the UL configuration of each of the at least one cell .

In an example embodiment of the third aspect , the method may comprise starting a timer in response to transiting to operate in the inactive state ; deciding to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and considering the TA value and the UL configuration of the selected cell to be valid, when the timer has not expired .

In an example embodiment of the third aspect , the method may comprise resuming a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; starting a timer in response to transiting to operate in the inactive state ; deciding to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and considering the TA value and the UL configuration of the selected cell to be valid, when the timer and the TAT associated with the selected cell have not expired .

In an example embodiment of the third aspect , the method may comprise resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; deciding to resume the connection from the inactive state to the connected state in a cel l selected from the at least one cel l ; and considering the TA value and the UL configuration of the selected cell to be valid, when the TAT associated with the selected cell has not expired .

In an example embodiment of the third aspect , the method may comprise storing, before operating in the inactive state , first measurements relating to the at least one non-serving cell ; storing, after deciding to resume the connection from the inactive state to the connected state , second measurements relating to the at least one non-serving cell ; and considering the TA value and the UL configuration of the selected cell to be valid, when the second measurement relating to the selected cell di f fers from the first measurement relating to the selected cell less than a predetermined threshold amount .

In an example embodiment of the third aspect , the method may comprise storing, before operating in the inactive state , beam identifiers of the at least one cell ; upon deciding to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell , comparing the beam identifier of the selected cell to the stored beam identi fiers of the at least one cell ; and considering the TA value and the UL configuration of the selected cell to be valid, when the beam identi fier of the selected cell is among the stored beam identi fiers .

According to a fourth aspect , a method performed by a network node that supports at least one of central unit control plane , CU-CP, functionality or a layer 3 protocol of a radio access network, may comprise establishing a connection towards a user equipment to operate in a connected state via a serving cel l ; and transmitting, to the user equipment , a message including an instruction to operate in an inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cel l to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell .

In an example embodiment of the fourth aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the TA value associated with the at least one cell .

In an example embodiment of the fourth aspect , the information relating to a TA value and a UL configuration of at least one cell comprises a TA value for each of the at least one non-serving cel l and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell .

In an example embodiment of the fourth aspect , the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the UL configuration of the at least one cell for a validity period .

In an example embodiment of the fourth aspect , the information relating to a TA value and a UL configuration of at least one cell comprises the UL configuration of each of the at least one cell .

In an example embodiment of the fourth aspect , the method comprises receiving, from at least one network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, acquisition information of a timing advance , TA, for at least one cell , wherein the at least one distributed unit comprises at least one of a serving DU controlling a serving cell and a target DU control ling a target cell .

According to a fi fth aspect , a computer program is disclosed . The comprise program may comprise instructions that , when executed by an apparatus , cause the apparatus to perform a method according to the third or fourth aspect , or any example embodiment thereof .

According to a sixth aspect , a (non-transitory ) computer readable medium is disclosed . The (non- transitory) computer readable medium may comprise program instructions that , when executed by an apparatus , cause the apparatus to perform a method according to the third or fourth aspect , or any example embodiment thereof . According to a seventh aspect , a user equipment served configured to support operating in an inactive state may comprise means for establishing a connection towards a network node that supports at least one of central unit control plane , CU-CP , functionality or a layer 3 protocol of a radio access network, RAN, to operate in a connected state via a serving cell ; receiving, from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cel l to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell ; operating in the inactive state ; monitoring a need to transition from the inactive state to the connected state ; selecting, in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell ; and performing a RACH-less access via the selected cell in case the TA value and the UL configuration of the selected cell are considered still valid .

According to an eighth aspect , a network node that supports at least one of central unit control plane , CU- CP, functionality or a layer 3 protocol of a radio access network may comprise means for establi shing a connection towards a user equipment to operate in a connected state via a serving cell ; and transmitting, to the user equipment , a message including an instruction to operate in an inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell .

Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings .

DESCRIPTION OF THE DRAWINGS

The accompanying drawings , which are included to provide a further understanding of the example embodiments and constitute a part of this speci fication, illustrate example embodiments and together with the description help to understand the example embodiments . In the drawings :

FIG . 1 illustrates an example of a split access node architecture .

FIG . 2 illustrates an example of a new radio radio resource control state machine with RRC state transitions .

FIG . 3 illustrates an example of an apparatus configured to practice one or more example embodiments .

FIG . 4 illustrates a signaling diagram according to an example embodiment .

FIG . 5A illustrates a signaling diagram according to an example embodiment .

FIG . 5B illustrates a signaling diagram according to an example embodiment .

FIG . 6 illustrates example of a method according to an example embodiment .

FIG . 7 illustrates example of a method according to another example embodiment . Like references are used to designate like parts in the accompanying drawings .

DETAILED DESCRIPTION

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

FIG. 1 illustrates an example of a split access node architecture. An access node, represented by a gNB 100, may be split, functionally and/or physically, to a central unit (CU) 108 and one or more distributed units (DU) 102-1, 102-2, ..., 102-N. The CU 108 may be also referred to as a gNB-CU and the DU(s) be also referred to as gNB-DU(s) . The CU 108 may comprise a control plane (CP) and user plane (UP) entities, represented by a gNB- CU-CP 104 and a gNB-CU-UP 106, respectively. The gNB-CU- CP 104 may be configured to control communication of signaling data that enables transfer of user/application data at the user plane. User plane communications may be provided by one or more gNB-CU-UPs 106 associated with the gNB-CU-CP 104. CU 108 and DU(s) may be configured to provide radio access network (RAN) services to device (s) , represented by user equipment (UE) 110, at one or more cells.

Control and user plane entities of the CU 108 may communicate via a communication interface, such as for example an El interface. The CU 108 may communicate with a DU 102-n (n = 1...N) over a communication interface, such as for example an Fl interface. The Fl interface may comprise control and user plane interfaces (Fl-C, Fl-U) between the DU 102-n and the control and user plane entities of the CUs 108, respectively. The DU(s) 102-1 to 102-N may be collectively referred to as the DU(s) 102, where N is a positive integer ranging for example from 1 to 100. However, higher values, such as for example up to 2³⁶-l, are possible as well.

The CU/DU-split architecture enables disaggregation of the RAN, thus enabling operators to utilize different vendors for different network nodes, but also to enable network vendors to split their network implementations for scalability purposes. For example, control and user planes may be separated to their own entities, thereby enabling control and user plane functions to be dimensioned separately. The split may be however (almost) invisible to a user equipment (UE) and therefore, at the UE side, the protocol layers may be (mostly) unaware of the split, except for minor parts which the UE may implicitly determine from the associated RRC configuration.

The following description may provide further details of alternatives, modifications and variances: a gNB comprises e.g., a node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC, e.g., according to 3GPP TS 38.300 V16.6.0 (2021-06) section 3.2 incorporated by reference.

The gNB-CU 108 comprises e.g., a logical node hosting e.g., RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs . The gNB-CU 108 terminates the Fl interface connected with the gNB-DU.

The gNB-DU 102-1, 102-2, 102-N comprises e.g., a logical node hosting e.g., RLC, MAC and 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.

The gNB-CU-CP 104 comprises 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 104 terminates the El interface connected with the gNB-CU-UP 106 and the Fl-C interface connected with the gNB-DU.

The gNB-CU-UP 106 comprises 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 106 terminates the El interface connected with the gNB-CU-CP 104 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 incorporated by reference .

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

Option 1 (lA-like split) : o The function split in this option is similar to the 1A architecture in DC. RRC is in the central unit. PDCP, RLC, MAC, physical layer and RE are in the distributed unit.

Option 2 (3C-like split) : o 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 RF are in the distributed unit.

Option 3 (intra RLC split) : o 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.

Option 4 (RLC-MAC split) : o MAC, physical layer and RF are in the distributed unit. PDCP and RLC are in the central unit.

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

A gNB supports different protocol layers, e.g., Layer 1 (LI) - physical layer.

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. : o The physical layer offers to the MAC sublayer transport channels; o The MAC sublayer offers to the RLC sublayer logical channels; o The RLC sublayer offers to the PDCP sublayer RLC channels; o The PDCP sublayer offers to the SDAP sublayer radio bearers; o The SDAP sublayer offers to 5GC QoS flows; o Comp, refers to header compression and Segm. To segmentation; o Control channels include (BCCH, PCCH) .

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 incorporated by reference. A Radio Access Network (RAN) node or network node like 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 computer-readable instructions (computer 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.

The gNB CU and gNB DU parts may e.g., be co-located or physically separated. The gNB CU may include two parts a CU-CP and a CU-UP part. The CU-CP part may even be split, e.g. in a first CP part located at the CU, and a second CP part located at the DU. This first and second CP part may perform different RRC operations and processing, e.g. central and local operations, respectively, or overlapping operations which may need coordination. 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, the CU- CP (or more generically, the CU) may also be referred to as a (first) network node that supports at least one of central unit control plane functionality or a layer 3 protocol of a radio access network; and similarly, the DU may be referred to as a (second) network node that supports at least one of distributed unit functionality or the layer 2 protocol of the radio access network.

A gNB-DU supports one or multiple cells, and could thus serve as e.g., a serving cell for a user equipment (UE) . A user equipment (UE) may 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, a M2M device, or else. Such UE or apparatus may comprise: at least one processor; and at least one memory including computer program code; wherein 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, like e.g. RRC connection to the RAN. A UE is e.g., 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) . A UE may generate and transmit and receive RRC messages containing one or more RRC PDUs (Packet Data Units) .

The UE may have different states (e.g., according to 3GPP TS 38.331 V16.5.0 (2021-06) sections 42.1 and 4.4, incorporated by reference) .

A UE is e.g., either in RRC_CONNECTED state or in RRC_INACTIVE state when an RRC connection has been established .

In RRCJCONNECTED state a UE may: o store the AS context; o transfer unicast data to/from the UE; o monitor control channels associated with the shared data channel to determine if data is scheduled for the data channel; o provide channel quality and feedback information; o perform neighboring cell measurements and measurement reporting.

The RRC protocol includes e.g. the following main functions : o RRC connection control; o measurement configuration and reporting; o establishment/modif ication/release of measurement configuration (e.g. intrafrequency, inter-frequency and inter-RAT measurements) ; o setup and release of measurement gaps; o measurement reporting.

FIG. 2 illustrates an example of an new radio (NR) radio resource control (RRC) state machine with RRC state transitions .

The RRC INACTIVE state 202 enables to quickly resume a suspended RRC connection and start the transmission of small or sporadic data with a much lower initial access delay and associated signaling overhead as compared to the RRC IDLE state. This is achieved by allowing a faster transition from RRC INACTIVE state 202 to the RRC CONNECTED state 200 having about 10 ms Control Plane (CP) delay. At the same time, a UE in the RRC INACTIVE 202 is able to achieve similar power savings as in the RRC IDLE 204, benefiting from, for example, a much larger period of PDCCH monitoring (for example, paging) and relaxed measurements (for example, for cell (re)- selection) compared to the RRC CONNECTED state 200. Furthermore, compared to keeping the UE in the RRC CONNECTED state 200, the RRC INACTIVE state 202 minimizes mobility signaling both to a radio access network (RAN) (for example, RRC measurement reporting, handover messages) and to a core network (for example, to/from the AMF) since the UE is still in the CM-CONNECTED state. A UE in the RRC INACTIVE state 202 can move within an area configured by RAN without any notification (i.e. RAN Notification Area (RNA) ) and using a unique identifier ( Inactive-RNTI (I-RNTI) ) . This RNA can cover a single or multiple cell ( s ) and shall be contained within the UE registration area set by the AMF . A RAN- based Noti fication Area Update (RNAU) procedure is run by the UE periodically and when the UE re-selects to a cell that does not belong to the configured RNA.

When a UE is moved to the RRC INACT IVE state 202 via an RRC release message with suspend configuration, the UE Access Stratum (AS ) context , which is neces sary for the quick resume of the RRC connection, is maintained both at the UE side and RAN side . The context contains for instance bearer configuration parameters according to the latest RRC configuration and AS security context pointing to the integrity protection, ciphering algorithms and the AS keys .

FIG . 3 illustrates an example of an apparatus 300 configured to practice one or more example embodiments . The apparatus 300 may comprise a user node , a user equipment , an access node , an access point , base station, a radio network node , or a split portion thereof , or in general a device configured to implement functionality described herein . The apparatus 300 may comprise at least one processor 302 . The at least one processor 302 may comprise , for example , one or more of various processing devices , such as for example a co-processor, a microprocessor, a controller, a digital signal processor ( DSP ) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as , for example , an application speci fic integrated circuit (AS IC ) , a field programmable gate array ( FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, or the like .

The apparatus 300 may further comprise at least one memory 304 . The memory 304 may be configured to store , for example, computer program code or the like, for example operating system software and application software. The memory 304 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and/or a combination thereof. For example, the memory may be embodied as magnetic storage devices (such as hard disk drives, magnetic tapes, etc.) , optical magnetic storage devices, or semiconductor memories (such as mask ROM, PROM (programmable ROM) , EPROM (erasable PROM) , flash ROM, RAM (random access memory) , etc.) . The memory 304 is provided as an example of a (non-transitory ) computer readable medium. The term "non-transitory, " as used herein, is a limitation of the medium itself (i.e., tangible, not a signal ) as opposed to a limitation on data storage persistency (e.g., RAM vs . ROM) .

The apparatus 300 may further comprise a communication interface 308 configured to enable the apparatus 300 to transmit and/or receive information. The communication interface 308 may comprise an internal or external communication interface, such as for example an El, Fl, Fl-C, and/or F2-C interface. The apparatus 300 may further comprise other components and/or functions such as for example a user interface (not shown) comprising at least one input device and/or at least one output device. The input device may take various forms such a keyboard, a touch screen, or one or more embedded control buttons. The output device may for example comprise a display, a speaker, or the like.

When the apparatus 300 is configured to implement some functionality, some component and/or components of the apparatus 300, such as for example the at least one processor 302 and/or the at least one memory 304, may be configured to implement this functionality. Furthermore, when the at least one processor 302 is configured to implement some functionality, this functionality may be implemented using program code 306 comprised, for example, in the at least one memory 304.

The functionality described herein may be performed, at least in part, by one or more computer program product components such as software components. According to an example embodiment, the apparatus 300 comprises a processor or processor circuitry, such as for example a microcontroller, configured by the program code 306, when executed, to execute the embodiments of the operations and functionality described herein. Program code 306 is provided as an example of instructions which, when executed by the at least one processor 302, cause performance of the apparatus 300.

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

The apparatus 300 may be configured to perform method (s) described herein or comprise means for performing method (s) described herein. In one example, the means may comprise the at least one processor 302, the at least one memory 304 including program code 306 configured to, when executed by the at least one processor 302, cause the apparatus 300 to perform the method ( s ) . Although the apparatus 300 is illustrated as a single device , it is appreciated that , wherever applicable , functions of the apparatus 300 may be distributed to a plurality of devices .

In an example embodiment , the apparatus 300 may be a user equipment (UE ) configured to support operating in an inactive state .

The UE may be configured to establish a connection towards a network node that supports at least one of central unit control plane ( CU-CP ) functionality or a layer 3 protocol of a radio access network (RAN) to operate in a connected state via a serving cell ; receive , from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance ( TA) value and an uplink (UL) configuration of at least one cel l to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell ; operate in the inactive state ; monitor a need to transition from the inactive state to the connected state ; select , in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell ; and perform a RACH-less access via the selected cell in case the timing advance value and the UL configuration of the selected cell are considered still valid . As there is no need to perform a random access procedure , the state change from the inactive state to the connected state is fast .

The information relating to a TA value and a UL configuration of at least one cell may comprise an instruction to maintain the TA value associated with the at least one cell . This may enable the UE to perform a fast RRC Resumption of the connection from RRC inactive state to the last serving cell or any other neighboring cell by not performing the random access procedure .

The UE may be configured to receive , from a serving network node that supports at least one of distributed unit ( DU) functionality or a layer 2 protocol of a radio access network, a trigger to acquire the TA values of the at least one non-serving cel l ; and acquire the TA values of the at least one non-serving cell in response to the received instruction . This may enable a solution in which the TAs acquired for the non-serving cells can be used either to perform RACH-les s handover ( in the RRC connected state ) or to perform a RACH-less RRC resumption from the RRC inactive to the RRC connected state .

The information relating to a TA value and a UL configuration of at least one cel l may comprise a TA value for each of the at least one non-serving cell and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell . This may enable a solution in which the TAs acquired for the non-serving cells can be used either to perform RACH-less handover ( in the RRC connected state ) or to perform a RACH-less RRC resumption from the RRC inactive to the RRC connected state .

The information relating to a TA value and a UL configuration of at least one cell may comprise an instruction to maintain the UL configuration of the at least one cell for a validity period . This may enable a solution in which limiting the validity period of the UL configuration can help the network to reduce the possible cost of resource reservation associated with performing the RACH-less RRC resumption . In an example embodiment , the validity period can be set to + infinity by the network i f the radio resource reservation is not an issue .

The information relating to a TA value and a UL configuration of at least one cell may comprise the UL configuration of each of the at least one cell .

The UE may be configured to start a timer in response to transiting to operate in the inactive state ; decide to resume the connection from the inactive state to the connected state in a cel l selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the timer has not expired . This may enable a solution in which the timer may help the UE to determine i f the UL configuration is still valid to be used, i . e . , to determine i f the network still keeps the UL radio resources that are reserved for the UE or to a group of UEs in case the resources are common .

The UE may be configured to resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; start a timer in response to transiting to operate in the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the timer and the TAT associated with the selected cell have not expired . This may enable a solution in which resuming the TAT may help the UE to determine i f the acquired/obtained TA values for the serving and non-serving cells are sti ll valid to be used for the RACH-less RRC resumption .

The UE may be configured to resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cel l ; and consider the TA value and the UL configuration of the selected cell to be val id, when the TAT associated with the selected cell has not expired . This may enable a solution in which the UE can use the TAT to check the validity of the TA and UL configurations for performing the RACH-less RRC resumption .

The UE may be configured to store , before operating in the inactive state , first measurements relating to the at least one non-serving cell ; store , after deciding to resume the connection from the inactive state to the connected state , second measurements relating to the at least one non-serving cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the second measurement relating to the selected cell di f fers from the first measurement relating to the selected cell less than a predetermined threshold amount . This may enable a solution in which the deviation in the measurement results can be a metric that can be used by the UE to determine i f there are changes in radio propagation and as such determine i f the acquired TA is still valid or not .

The UE may be configured to store , before operating in the inactive state , beam identi fiers of the at least one cell ; upon deciding to resume the connection from the inactive state to the connected state in a cell selected from the at least one cel l , compare the beam identi fier of the selected cel l to the stored beam identi fiers of the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the beam identi fier of the selected cell is among the stored beam identi f iers . This may enable a solution in which, the deviation in, for example , the strongest detected set of beams can be a metric that can be used by the UE to determine i f there are changes in radio propagation and as such determine i f the acquired TA is still valid or not .

In an example embodiment , the apparatus 300 may be a network node that supports at least one of central unit control plane , CU-CP, functionality or a layer 3 protocol of a radio access network .

The CU may be configured to establi sh a connection towards a user equipment to operate in a connected state via a serving cell ; and transmit , to the user equipment , a message including an instruction to operate in an inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cel l to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one nonserving cell . This may enable a solution in which maintaining the UL TA and the configuration allows the UE to perform the RACH-less RRC resumption .

The information relating to a TA value and a UL configuration of at least one cell may comprise an instruction to maintain the TA value associated with the at least one cell . This may enable a solution in which maintaining the TAs and UL configuration for multiple cells increases the chances that the UE performs the RACH-less RRC resumption .

The information relating to a TA value and a UL configuration of at least one cel l may comprise a TA value for each of the at least one non-serving cell and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell . This may enable a solution in which the maintained TA and UL configuration allow the UE to perform the RACH- less RRC resumption in case it resumes the connection in a cell which is di f ferent from the one which has instructed the UE to transit to the RRC inactive state .

The information relating to a TA value and a UL configuration of at least one cell may comprise an instruction to maintain the UL configuration of the at least one cell for a validity period .

The CU may be conf igured to receive , from at least one network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, acquisition information of a timing advance , TA, for at least one cell , wherein the at least one distributed unit comprises at least one of a serving DU controlling a serving cel l and a target DU controlling a target cell .

FIG . 4 illustrates a signaling diagram according to an example embodiment .

At 408 , an UE 400 may be served by a distributed unit DU1 402 controlling a serving cell 1 .

At 410 , the UE 400 may be configured with Ll /2 Triggered Mobility ( LTM) to candidate target cells 2 and 3 ( i . e . non-serving cells 2 and 3 ) of the DU1 402 . In the LTM, the decision about a cell change is based on LI measurements and is made in the medium access control (MAC ) layer in a distributed unit .

At 412 , the UE 400 may report LI beam measurements for the serving cel l 1 and prepared target cells 2 and 3 .

At 414 , based on the received LI beam measurements , the serving cell 1 may trigger the UE using physical downlink control channel (PDCCH) orders to acquire the timing advances (TA) for candidate cells 2 and 3. One PDCCH order may be used for each TA acquisition.

At 416, the UE 400 may obtain the TAs of the candidates cells. This may be achieved, for example, by sending the physical random access channel (PRACH) preamble to the target cell and receiving the estimated TA from the serving cell. In another example embodiment, the TA may be estimated without the PRACH preamble transmission. The UE 400 may derive the TA based on Rx timing difference between one of the current serving cells and the candidate cell, the time of f set/dif f erence between the cells (if any) , as well as TA value for the current serving cell. In another example embodiment, the UE 400 may send a random access channel (RACH) preamble or perform a complete random access channel (RACH) procedure, and the TA value may be provided to UE 400 by the serving cell or the target cell. In an example embodiment, the TA value may be provided to the UE 400 immediately or later when required, for example, by the CU 406, when the inactive state is triggered. For the serving cell 1, the UE 400 may have already acquired the TA value and the TAT associated with the serving cell 1.

In another example embodiment, the TA of a target cell may be known by the network and does not need to be acquired by the UE . Instead, it may be signaled to the UE 400. For example, the TA of the target cell may be either 0 (in case of very small cells) or equal to that of one of the current serving cells in case the serving and target cells are co-located. This means that the network does not have to trigger the UE 400 to acquire the TA of the target cell. Instead, the known TAs may be signaled to the UE, for example, as part of the RRC reconfiguration message. At 418 and 420, a central unit (CU) 406 may be informed about the acquisition of the TA for cells 2 and 3 from the serving DU1 402 and a target DU2 404. In an example embodiment, the serving DU1 402 and the target DU2 404 may transmit the TA values for the cells 2 and 3 in case the TA values are not delivered immediately to the UE 400. In case the estimated TA value has been received by the serving DU1 402 from the target DU2 404 and is not delivered immediately to the UE 400, the serving DU1 402 or the target DU2 404 may provide the obtained TA value to the CU 406 in 418 and 420, and the obtained TA values may then be provided to the UE 400 when transiting the UE 400 to RRC inactive state later at 426.

At 422, the CU 406 makes the decision to transit the UE 400 to the RRC inactive state.

At 424, the CU 406 may inform the serving DU1 402 to keep reserved uplink (UL) radio resource information, i.e. UL grants of cells 1 and 2, for a certain time duration. The same may occur at 428 with respect to the DU2 404 controlling the cell 3. In an example embodiment, the time duration may have infinity as its value. In an example embodiment, the UL grant may be a dedicated UL grant to the UE 400. In another example embodiment, the UL grant may be a common grant to multiple UEs (i.e., a grant-free UL grant) . In another example embodiment, the UE may already have an UL grant of the cell 1, but the UE 400 may be configured to use a common grant.

At 426, the CU 406 may instruct the UE 400 to transit to the RRC inactive state and maintain the acquired TAs of the serving cell 1 and the target cells 2 and 3 along with their corresponding UL configuration for a certain time duration. The time duration may include infinity as a possible value. In an example embodiment, the CU 406 may provide also the TA values for the serving cell 1 and the target cells 2 and 3 if the TAs have earlier been received from the DU1 402 and the DU2 404. In an example embodiment, the CU 406 may set the time duration to the remaining validity time of the TA corresponding to a cell. In order to perform this, the CU 406 may fetch from the DUs 402, 404 the remaining TA validity time for the cells 1, 2 and 3, and configure different time durations for each of cells 1, 2 and 3.

At 430, the DU1 402 transmits a UE context release complete message to the CU 406.

At 432, the UE 400 is now in the RRC inactive UNCONNECTED state.

FIG. 5A illustrates a signaling diagram according to an example embodiment. In this example, the network may keep the configured UL grants for the remaining time alignment timer (TAT) duration after transiting the UE to the RRC inactive state. In an example embodiment, the steps illustrated in FIG. 4 may have been performed before the example illustrated in FIG. 5A.

At 500, the UE 400 may transit from the RRC connected state to the RRC inactive state.

At 502, in RRC inactive state the UE 400 may resume the TATs for the cells 1, 2 and 3 upon transiting to the RRC inactive state. The TATs may have been started in the RRC connected state, and the TATs may supervise the validity of the acquired TA.

At 504, the UE 400 may decide to resume the connection in the cell 3. The cell 3 may be the camped/selected cell that is determined using the cell reselection procedure. In an example embodiment, if there are multiple suitable cells for the cell reselection, the UE 400 may prioritize the cell for which it has a valid TA. At 506, if the TA of the cell 3 is still valid (i.e., the TAT has not expired yet) , the UE 400 may at 508 send an RRC resume request message using the acquired TA and UL grants. In other words, the UE 400 may perform a RACH-less access via the selected cell in case the TA value and the UL configuration of the selected cell are considered still valid.

At 510, the CU 406 may transmit an RRC resume message to the UE 400.

At 512, after receiving the RRC resume message, the UE 400 is now in the RRC connected CM-CONNECTED state, and at 514 the UE 400 may send an RRC resume complete message to the CU 406.

If the TAT has already expired at 506, the steps 508-514 are not performed and the UE 400 may perform a random access procedure.

FIG. 5B illustrates a signaling diagram according to an example embodiment. In this example, configured UL grants are valid for a duration time T that is configured by the network. In other words, the duration time T supervises the validity of the UL grants upon receiving the command from the CU to transit to the RRC inactive state. In an example embodiment, the steps illustrated in FIG. 4 may have been performed before the example illustrated in FIG. 5B .

At 516, the UE 400 may transit from the RRC connected state to the RRC inactive state.

At 518, the UE 400 may store, for example, upon moving to the RRC inactive state, measurements X of the cells to which it has acquired the TA values. In this example, these cells comprise a serving cell and candidate cells 2 and 3. In an example embodiment, the measurement may be a downlink pathloss reference, for example, the highest beam measurement, linear average of the N (>=1) highest beam measurements above a threshold, L3 or LI cell/beam measurement.

At 520, the UE 400 may start a timer T upon moving to the RRC inactive state.

At 522, the UE 400 may decide to resume the connection in the cell 3. The cell 3 may be the camped/selected cell that is determined using the cell reselection procedure. In an example embodiment, if there are multiple suitable cells for the cell reselection, the UE 400 may prioritize the cell for which it has a valid TA.

At 524, the UE 400 may store the actual measurements Y of the serving cell and the candidate cells 2 and 3 upon initiating the RRC resumption procedure.

At 526, the UE 400 may determine whether the TA is still valid. This may be performed, for example, by determining that the timer T has not expired yet and the measurements of the cell 3 did not change much, (i.e., the measurement Y differs from the measurement X less than a predetermined threshold amount) . In an example embodiment, the UE 400 may compare if the actual L3 or LI cell/beam measurements or downlink pathloss measurement of the selected cell (measurement Y) did not increase or decrease by more than set dB threshold amount than those of the measurement X. In an example embodiment, the measured quantity may be reference signal received power (RSRP) , reference signal received quality (RSRQ) or a signal-to-interf erence-plus-noise ratio (SINR) .

If the TA is still valid, at 528 the UE 400 may send an RRC resume message using the acquired TA and the UL grants. In other words, the UE 400 may perform a RACH- less access via the selected cell in case the TA value and the UL configuration of the selected cell are considered still valid.

At 530, the CU 406 may transmit an RRC resume message to the UE 400.

At 532, after receiving the RRC resume message, the UE 400 is now in the RRC connected CM-CONNECTED state, and at 534 the UE 400 may send an RRC resume complete message to the CU 406.

If the TA was not valid at 526, the steps 528-534 are not performed and the UE 400 may perform a random access procedure.

In an example embodiment, the duration time T for the configured UL grants may be configured separately than the TAT supervising the TA validity. At 526, after deciding to transit to the RRC connected state, the UE 400 may check if it has both a valid TA and a valid configured UL grant for the selected cell. In case of both a valid TA (i.e., the TAT has not expired yet) and a valid configured UL grant (i.e., the timer T has not expired yet) , the UE may apply the acquired TA and perform a RACH-less RRC resumption of the connection using the valid configured UL grant. If any of the timers, the TAT or the timer T, has expired, the UE may 400 perform a random access procedure for the RRC resumption .

In an example embodiment, steps 518 and 524 may be omitted and thus at 526 the measurements are not taken into account when determining whether the TA is still valid. Thus, the measurements can be used as an additional criterion to determine whether the TA that is acquired is still valid or not to perform a RACH-less RRC resumption.

In an example embodiment, the UE 400 may store, upon receiving a command to transit to the RRC inactive state, beam identifiers of neighboring target cells for which the TA and/or the uplink radio resource information has been obtained. The beam identifiers may be associated with a quasi-co-location reference signal such as a synchronization signal block (SSB) or channel State information reference signal (CSI-RS) identifier or a transmission configuration indication (TCI) state identifier. When then deciding to resume the connection towards a cell for which the TA has been obtained, the UE 400 may compare the beam identifier of the selected cell to the beam identifiers of neighboring target cells for which the TA and/or the uplink radio resource information has been obtained, and transmit the resume message using the TA associated with the selected cell and the uplink radio resource information associated with the selected cell when the beam identifier of the selected cell is among the stored beam identifiers. Thus, the beam selection may be used as an additional criterion to determine whether the TA that is acquired is still valid or not to perform a RACH-less RRC resumption.

FIGS. 5A and 5B illustrate various embodiments that use the TAT, timer and validity period. In some embodiments, the validity period of the uplink radio resource is the same as the remaining time duration of TAT when resumed in step 502 of FIG. 5A. In another embodiment, the validity period of the uplink radio resource may be set differently or independently from the remaining time duration of the TAT when resumed in step 502 of FIG. 5A. In another embodiment, the timer T started in FIG. 5B may be used to supervise 1) the validity of the acquired Tas, or 2) the validity of the uplink radio resources, or 3) the validity of the acquired TAs and the uplink radio resources. FIG . 6 illustrates example of a method according to an example embodiment . The method may be performed by a user equipment (UE ) configured to support operating in an inactive state .

At 600 , the method may comprise establishing a connection towards a network node that supports at least one of central unit control plane ( CU-CP ) functionality or a layer 3 protocol of a radio access network (RAN) to operate in a connected state via a serving cell .

At 602 , the method may comprise receiving, from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance ( TA) value and an uplink (UL ) configuration of at least one cel l to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cel l comprises at least one of a serving cell and at least one non-serving cell .

At 604 , the method may comprise operating in the inactive state .

At 606 , the method may comprise monitoring a need to transition from the inactive state to the connected state .

At 608 , the method may compri se selecting, in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell .

At 610 , the method may comprise perform a RACH-less access via the selected cell in case the TA value and the UL configuration of the selected cell are considered still valid .

FIG . 7 illustrates example of a method according to another example embodiment . The method may be performed by a network node that supports at least one of central unit control plane, CU-CP, functionality or a layer 3 protocol of a radio access network.

At 700, the method may comprise establishing a connection towards a user equipment to operate in a connected state via a serving cell.

At 702, the method may comprise transmitting, to the user equipment, a message including an instruction to operate in an inactive state, wherein the message further includes information relating to a timing advance (TA) value and an uplink (UL) configuration of at least one cell to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state, wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell.

Further features of the methods directly result from the functionality of DU(s) , CU(s) , or UE, as described throughout the description, claims, and drawings, and are therefore not repeated here. An apparatus may be configured to perform or cause performance of any aspect of the method (s) described herein. Further, a computer program or a computer program product may comprise instructions for causing, when executed by an apparatus, the apparatus to perform any aspect of the method (s) described herein. Further, an apparatus may comprise means for performing any aspect of the method (s) described herein. According to an example embodiment, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform any aspect of the method ( s ) . Any range or device value given herein may be extended or altered without losing the ef fect sought . Also , any embodiment may be combined with another embodiment unless explicitly disallowed .

Although the subj ect matter has been described in language speci fic to structural features and/or acts , it is to be understood that the subj ect matter defined in the appended claims is not necessarily limited to the speci fic 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 .

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 al l of the stated benefits and advantages . It will further be understood that reference to ' an ' item may refer to one or more of those items .

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

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

As used herein, "at least one of the following: <a list of two or more elements>" and "at least one of <a list of two or more elements>" and similar wording, where the list of two or more elements are joined by "and" or "or", mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements .

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

As used in this application, the term 'circuitry' may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable) : (i) a combination of analog and/or digital hardware circuit (s) with software/ firmware and (ii) any portions of hardware processor (s) with software (including digital signal processor ( s ) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit (s) and or processor ( s ) , such as a microprocessor ( s ) or a portion of a microprocessor ( s ) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example , as used in this appl ication, the term circuitry also covers an implementation of merely a hardware circuit or processor ( or multiple processors ) or portion of a hardware circuit or processor and its ( or their ) accompanying software and/or firmware . The term circuitry also covers , for example and i f applicable to the particular claim element , a baseband integrated circuit or processor integrated circuit for a mobi le device or a similar integrated circuit in server, a cellular network device , or other computing or network device .

It will be understood that the above description is given by way of example only and that various modi fications may be made by those skilled 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 scope of this speci fication .

Claims

1 . A user equipment configured to support operating in an inactive state , the user equipment comprising : at least one processor ; and at least one memory storing instructions which, when executed by the at least one processor, cause the user equipment at least to : establi sh a connection towards a network node that supports at least one of central unit control plane , CU- CP, functionality or a layer 3 protocol of a radio access network, RAN, to operate in a connected state via a serving cell ; receive , from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH-less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell ; operate in the inactive state ; monitor a need to transition from the inactive state to the connected state ; select , in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell ; and perform a RACH-less access via the selected cell in case the TA value and the UL configuration of the selected cell are considered still valid .

2 . The user equipment according to claim 1 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the TA value associated with the at least one cell .

3 . The user equipment according to claim 2 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : receive , from a serving network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, a trigger to acquire the TA values of the at least one non-serving cell ; and acquire the TA values of the at least one nonserving cell in response to the trigger .

4 . The user equipment according to claim 1 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises a TA value for each of the at least one non-serving cell and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell .

5 . The user equipment according to any one of claims 1 - 4 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises the UL configuration of each of the at least one cell .

6 . The user equipment according to any one of claims 1 - 5 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the UL configuration of the at least one cell for a validity period .

7 . The user equipment according to claim 6 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : start a timer in response to transiting to operate in the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid when the timer has not expired .

8 . The user equipment according to claim 6 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; start a timer in response to transiting to operate in the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the timer and the TAT associated with the selected cell have not expired .

9 . The user equipment according to claim 6 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : resume a time alignment timer, TAT , in response to transiting from the connected state to the inactive state ; decide to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the TAT associated with the selected cell has not expired .

10 . The user equipment according to claim 7 or 8 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : store , before operating in the inactive state , first measurements relating to the at least one nonserving cell ; store , after deciding to resume the connection from the inactive state to the connected state , second measurements relating to the at least one non-serving cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the second measurement relating to the selected cell di f fers from the first measurement relating to the selected cell less than a predetermined threshold amount .

11 . The user equipment according to any of claims 7 - 10 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : store , before operating in the inactive state , beam identi fiers of the at least one cell ; upon deciding to resume the connection from the inactive state to the connected state in a cell selected from the at least one cell , compare the beam identi fier of the selected cell to the stored beam identi fiers of the at least one cell ; and consider the TA value and the UL configuration of the selected cell to be valid, when the beam identi fier of the selected cell is among the stored beam identi fiers .

12 . A network node that supports at least one of central unit control plane , CU-CP , functionality or a layer 3 protocol of a radio access network, comprising : at least one processor ; and at least one memory storing instructions which, when executed by the at least one processor, cause the network node to at least to : establi sh a connection towards a user equipment to operate in a connected state via a serving cell ; and transmit , to the user equipment , a message including an instruction to operate in an inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH- less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell .

13 . The network node according to claim 12 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the TA value associated with the at least one cell .

14 . The network node according to claim 12 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises a TA value for each of the at least one non-serving cell and comprises an instruction to maintain the TA value associated with each of the at least one non-serving cell .

15 . The network node according to any one of claims 12 - 14 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises an instruction to maintain the UL configuration of the at least one cell for a validity period .

16 . The network node according to any one of claims 12 - 15 , wherein the information relating to a TA value and a UL configuration of at least one cell comprises the UL configuration of each of the at least one cell .

17 . The network node according to any of claims 12 - 16 , wherein the instructions , when executed by the at least one processor , cause the network node at least to receive , from at least one network node that supports at least one of distributed unit , DU, functionality or a layer 2 protocol of a radio access network, acquisition information of a timing advance , TA, for at least one cell , wherein the at least one distributed unit comprises at least one of a serving DU controlling a serving cell and a target DU controlling a target cell .

18 . A method performed by a user equipment configured to support operating in an inactive state , the method comprising : establishing a connection towards a network node that supports at least one of central unit control plane , CU-CP, functionality or a layer 3 protocol of a radio access network, RAN, to operate in a connected state via a serving cell ; receiving, from the network node , a message including an instruction to operate in the inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH- less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell ; operating in the inactive state ; monitoring a need to transition from the inactive state to the connected state ; selecting, in case the need to transition to the connected state is determined, to access the RAN via a selected cell of the at least one cell ; and performing a RACH-less access via the selected cell in case the timing advance value and the UL configuration of the selected cell are considered still valid .

19 . A method performed by a network node that supports at least one of central unit control plane , UUCP, functionality or a layer 3 protocol of a radio access network, the method comprising : establishing a connection towards a user equipment to operate in a connected state via a serving cell ; and transmitting, to the user equipment , a message including an instruction to operate in an inactive state , wherein the message further includes information relating to a timing advance , TA, value and an uplink, UL, configuration of at least one cell to enable a RACH- less access via a cell of the at least one cell in case of resuming from the inactive state to the connected state , wherein the at least one cell comprises at least one of a serving cell and at least one non-serving cell .

20. A computer program comprising instructions for causing an apparatus to carry out the method of any of claims 18 - 19.