RRC resume utilizing UE-based timing advance

Abstract

A method of establishing connections to a User Equipment, UE, comprising: receiving S21, before or when entering a Radio Resource Control, RRC, inactive state, from a network node, configuration infor

Description

TECHNOLOGY

[0001] The present disclosure relates to RRC Resume from RRC INACTIVE, in particular to RRC Resume by RACH-less access to a cell utilizing UE-based timing advance. BACKGROUND

[0002] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0003] Random access procedure is used whenever the UE needs to (re)establish an RRC connection to a cell, e.g. at initial access from Radio Resource Control IDLE, RRC IDLE, to transition from RRCINACTIVE to RRCCONNECTED, at handover to a new cell, etc. The procedure includes some message exchange and takes some time (which can be between 10 to 100 ms depending on Random Access Channel, RACH, configuration and RACH load) before the UE can receive / transmit data. In case the UE has delay critical data for transmission, the delay caused by RACH procedure should be avoided and RACH-less access will be preferred.

[0004] Therefore, initial access of the UE causes some delay that can be problematic for usecases that can benefit from a faster access.

[0005] However, RACH-less access requires the UE to have Timing Advance, TA, of the cell as well as an UL grant for its transmission. The UE based TA - based on measurements -may be used in L1 / L2 triggered mobility, LTM, cell switch which is in RRC CONNECTED. A UE in RRC INACTIVE which is configured for Configured Grant based - Small Data Transmission, CG-SDT, has also TA and configured grant as long as it will resume in the same cell as it was released to and during a given validity time. However, the following issues still remain to be resolved.

[0006] There is no mechanism for the UE to apply UE-based TA in RRC INACTIVE beyond the validity time if the UE will resume in the same cell as it was released to; and there is no mechanism for the UE to resume in a different cell than it was released using RACH-less access.

[0007] Besides the mechanisms introduced in 3GPP for UE-based TA calculation and CG-based SDT, there is not relevant prior-art for solving the above issues relating to initial access delay.

[0008] One prior art that proposes a solution to the initial access delay problem investigated in this disclosure is slice specific RACH enhancement introduced in Rei. 17, wherein the RACH enhancements enabled that UE could do prioritized random access using a lower back-off timer or higher power ramping co-efficient such that the prioritized UE can be decoded faster in case of a contention.

[0009] Similarly, also the same RACH enhancements have introduced isolated random access resources that is dedicated to a specific slice. This enables that the random access load from some group of UEs will not cause delay to that prioritized UEs.

[0010] However, these solutions have only decreased the random access delay caused due to contention (i.e., two UEs transmitting the same preamble at the same time).

[0011] Hence, there is a need to provide a fast initial access for the UE, in particular a fast RACH-less access procedure for the UE, and in particular when considering UE mobility, and further in particular aiming at solving the above technical issues. SUMMARY

[0012] In accordance with a first aspect of the present disclosure, there is provided a User Equipment, UE, comprising: at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to: receive, before or when entering a Radio Resource Control, RRC, inactive state, from a network node, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state, wherein the plurality of candidate cells comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell, wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells, wherein the UE is further configured to, while in the RRC inactive state: determine to transition from the RRC inactive state to the RRC connected state in response to an indication relating to data associated with the target cell; determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell.

[0013] In some examples, the determination of the TA value comprises maintaining a last TA value for the last serving cell before entering the RRC inactive state and / or updating the last TA value, and / or the determination of the TA value comprises determining a new TA value for the target cell being one of the plurality of candidate cells.

[0014] In some examples, the TA-related configurations comprise a TA measurement period for UE measurement on reference signals from the plurality of candidate cells for determining the TA value for the target cell, and the UE is further configured to periodically update the TA value for the target cell based on the TA measurement period.

[0015] In some examples, the configuration information comprises Dynamic Grant related, DG-related configurations at least for the target cell.

[0016] In some examples, the DG-related configurations comprise a configuration to receive a downlink control information or a behavior to select a downlink control channel to monitor to receive the DG.

[0017] In some examples, the DG-related configurations comprise a DG timer at least for the target cell, wherein the UE is configured to monitor for a dynamic grant for transmission of the data associated with the target cell before the DG timer expires.

[0018] In some examples, the UE is configured to start the DG timer in response to receiving, from the target cell, a paging message associated with the dynamic grant for transmission of the data associated with the target cell.

[0019] In some examples, if, before the DG timer expires, the UE receives the dynamic grant from the target cell and the UE has a valid TA value for the target cell, the UE is configured to perform the RACH-less access to the target cell based on the received dynamic grant and the determined TA value for the target cell.

[0020] In some examples, the UE is configured to stop the DG timer in response to receiving the dynamic grant from the target cell. [0021 ] In some examples, the configuration information further comprises for each candidate cell a corresponding DG timer.

[0022] In some examples, the configuration information further comprises a RACH-less resume timer at least for the target cell, wherein the UE is configured to perform UE-based determination of the TA value for the target cell before the RACH-less resume timer expires.

[0023] In some examples, the UE is configured to start the RACH-less resume timer in response to receiving, from the plurality of candidate cells, an RRC-release command for entering into the inactive state.

[0024] In some examples, in response to receiving from the target cell a dynamic grant for the data associated with the target cell after expiry of the RACH-less resume timer or in response to receiving from the target cell a paging message associated with a dynamic grant for transmission of the data associated with the target cell after expiry of the RACH-less resume timer, the UE is configured to perform RACH access to the target cell.

[0025] In some examples, if, at the time of expiry of the RACH-less timer, the UE determines not having received an indication relating to data associated with the target cell, the UE is configured to stop determining the TA value.

[0026] In some examples, in response to determining not having a valid TA for the target cell, the UE is configured to perform RACH access to the target cell.

[0027] In some examples, the target cell is one of the neighboring cells and the UE is further configured to calculate the TA value for the one neighboring cell based on the following: a TA value associated with the last serving cell, reference signal measurements associated with the last serving cell, and reference signal measurements associated with the one neighboring cell.

[0028] In some examples, the configuration information further comprise a TA Timer at least for the target cell, and the TA Timer is restarted by the UE each time the timing advance value is updated.

[0029] In accordance with a second aspect of the present disclosure, there is provided a network node of a radio access network, configured to establish communication to a UE, the network node comprising: at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the network node at least to: transmit, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state, wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell, wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells, wherein the configuration information is configured to cause the UE to, while in the RRC inactive state: determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

[0030] In some examples, the configuration information comprises Dynamic Grant related, DG-related configurations at least for the target cell.

[0031] In some examples, the network node is configured to control the last serving cell, wherein the network node is configured to obtain, from the one or more neighboring cells, the DG-related configurations and / or the TA-related configurations for at least one of the one or more neighboring cells, or the network node is configured to configure the one or more neighboring cells for providing the UE with the DG-related configurations and / or the TA-related configurations.

[0032] In some examples, the network node is configured to transmit to the UE an indication associated with data to be transmitted to the UE from a cell controlled by the network node.

[0033] In some examples, the network node is configured to transmit to the UE a paging message associated with a dynamic grant for transmission of the data associated with the target cell and / or a dynamic grant for transmission of the data associated with the target cell.

[0034] In some examples, the network node is configured to receive from the UE a message requesting the RACH-less access to a cell controlled by the network node.

[0035] In accordance with a third aspect of the present disclosure, there is provided a method of a User Equipment, UE, the method comprising: receiving, before or when entering a Radio Resource Control, RRC, inactive state, from a network node, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state, wherein the plurality of candidate cells comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell, wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells, wherein the method further comprises, while the UE is in the RRC inactive state: determining to transition from the RRC inactive state to the RRC connected state in response to an indication relating to data associated with the target cell; determining, for the target cell, the TA value based on the TA-related configurations; and performing the RACH-less access to the target cell based on the determined TA value for the target cell.

[0036] In accordance with a fourth aspect of the present disclosure, there is provided a method of a network node of a radio access network, configured to establish communication to a UE, the method comprising: transmitting, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state, wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell, wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for the target cell, wherein the method further comprises causing the UE to, based on the configuration information, while the UE is in the RRC inactive state: determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

[0037] In accordance with a fifth aspect of the present disclosure, there is provided a computer program comprising instructions for causing an apparatus to perform the method according to the third aspect or or causing an apparatus to perform the method according to the fourth aspect.

[0038] In accordance with a sixth aspect of the present disclosure, there is provided a memory storing computer readable instructions for causing an apparatus to perform the method according to the third aspect or or causing an apparatus to perform the method according to the fourth aspect.

[0039] In accordance with a seventh aspect of the present disclosure, there is provided a first 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 instruction which, when executed by the at least one processor, cause the first network node at least to: establish a connection with a user equipment apparatus (UE) via a serving cell; transmit, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state, wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell, wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells, wherein the configuration information is configured to cause the UE to, while in the RRC inactive state: determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

[0040] In accordance with an eighth aspect of the present disclosure, there is provided a second network node that supports at least one of the distributed unit, DU, functionality or a layer 2 protocol of a radio access network, and which supports a first cell, further comprising: at least one processor; and at least one memory storing instruction which, when executed by the at least one processor, cause the second network node at least to: establish a connection with a user equipment apparatus (UE) via the first cell acting as a serving cell; transmit, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state, wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell, wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells, wherein the configuration information is configured to cause the UE to, while in the RRC inactive state: determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

[0041] In addition, according to some other example embodiments, there is provided, for example, a computer program product for a wireless communication device comprising at least one processor, including software code portions for performing the respective steps disclosed in the present disclosure, when said product is run on the device. The computer program product may include a computer-readable medium on which said software code portions are stored. Furthermore, the computer program product may be directly loadable into the internal memory of the computer and / or transmittable via a network by means of at least one of upload, download and push procedures.

[0042] While some example embodiments will be described herein with particular reference to the above application, it will be appreciated that the present disclosure is not limited to such a field of use, and is applicable in broader contexts.

[0043] Notably, it is understood that methods according to the present disclosure relate to methods of operating the apparatuses according to the above example embodiments and variations thereof, and that respective statements made with regard to the apparatuses likewise apply to the corresponding methods, and vice versa, such that similar description may be omitted for the sake of conciseness. In addition, the above aspects may be combined in many ways, even if not explicitly disclosed. The skilled person will understand that these combinations of aspects and features / steps are possible unless it creates a contradiction which is explicitly excluded.

[0044] Implementations of the disclosed apparatuses may include using, but not limited to, one or more processor, one or more application specific integrated circuit (ASIC) and / or one or more field programmable gate array (FPGA). Implementations of the apparatus may also include using other conventional and / or customized hardware such as software programmable processors, such as graphics processing unit (GPU) processors.

[0045] Other and further example embodiments of the present disclosure will become apparent during the course of the following discussion and by reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Example embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0047] Figure 1 schematically illustrates an example of a UE-based timing advance determination according to an example embodiment of the present disclosure;

[0048] Figure 2 schematically illustrates an example of a signaling diagram for RRC Resume using CG-based SDT according to an example embodiment of the present disclosure;

[0049] Figure 3 schematically illustrates an example of a signaling diagram for an RRC Resume procesure based on UE determination of TA, in particular for the obtaining of the configuration information relating to Configured Grant, according to an example embodiment of the present disclosure;

[0050] Figure 4 schematically illustrates an example of a signaling diagram for an RRC Resume procesure based on UE determination of TA, in particular for the UE performing the RRC Resume procedure based on the obtained configuration information relating to Configured Grant, according to an example embodiment of the present disclosure; and

[0051] Figure 5 schematically illustrates an example of a signaling diagram for an RRC Resume procesure based on UE determination of TA, in particular for the obtaining of the configuration information relating to Dynamic Grant, according to an example embodiment of the present disclosure;

[0052] Figure 6 schematically illustrates an example of a signaling diagram for an RRC Resume procesure based on UE determination of TA, in particular for the UE performing the RRC Resume procedure based on the obtained configuration information relating to Dynamic Grant, according to an example embodiment of the present disclosure. DESCRIPTION OF EXAMPLE EMBODIMENTS

[0053] In the following, different exemplifying embodiments will be described using, as an example of a communication network to which examples of embodiments may be applied, a communication network architecture based on 3GPP standards for a communication network, such as a 5G / NR, without restricting the embodiments to such an architecture, however. It is apparent for a person skilled in the art that the embodiments may also be applied to other kinds of communication networks where mobile communication principles are integrated with a D2D (device-to-device) or V2X (vehicle to everything) configuration, such as SL (side link), e.g. Wi-Fi, worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, mobile ad-hoc networks (MANETs), wired access, etc. Furthermore, without loss of generality, the description of some examples of embodiments is related to a mobile communication network, but principles of the disclosure can be extended and applied to any other type of communication network, such as a wired communication network.

[0054] The following examples and embodiments are to be understood only as illustrative examples. Although the specification may refer to “an”, “one”, or “some” example(s) or embodiment s) in several locations, this does not necessarily mean that each such reference is related to the same example(s) or embodiment(s), or that the feature only applies to a single example or embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, terms like “comprising” and “including” should be understood as not limiting the described embodiments to consist of only those features that have been mentioned; such examples and embodiments may also contain features, structures, units, modules, etc., that have not been specifically mentioned.

[0055] A basic system architecture of a (tele)communication network including a mobile communication system where some examples of embodiments are applicable may include an architecture of one or more communication networks including wireless access network subsystem(s) and core network(s). Such an architecture may include one or more communication network control elements or functions, access network elements, radio access network elements, access service network gateways or base transceiver stations, such as a base station (BS), an access point (AP), a NodeB (NB), an eNB or a gNB, a distributed unit (DU) or a centralized / central unit (CU), which controls a respective coverage area or cell(s) and with which one or more communication stations such as communication elements or functions, like user devices or terminal devices, like a user equipment (UE), or another device having a similar function, such as a modem chipset, a chip, a module etc., which can also be part of a station, an element, a function or an application capable of conducting a communication, such as a UE, an element or function usable in a machine-to-machine communication architecture, or attached as a separate element to such an element, function or applicati on capable of conducting a communication, or the like, are capable to communicate via one or more channels via one or more communication beams for transmitting several types of data in a plurality of access domains. Furthermore, core network elements or network functions, such as gateway network elements / functions, mobility management entities, a mobile switching center, servers, databases and the like may be included.

[0056] 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.

[0057] A gNB Central Unit (gNB-CU) 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 terminates the Fl interface connected with the gNB-DU.

[0058] A gNB Distributed Unit (gNB-DU) 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.

[0059] A gNB-CU-Control Plane (gNB-CU-CP) 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 terminates the El interface connected with the gNB-CU-UP and the Fl-C interface connected with the gNB-DU.

[0060] A gNB-CU-User Plane (gNB-CU-UP) 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 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 incorporated by reference.

[0061] Different functional splits between the central and distributed unit are possible, e.g., called options: Option 1 (1 A-like split): • 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 RF are in the distributed unit. Option 2 (3C-like split): • 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): • 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): • 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.

[0062] A gNB supports different protocol layers, e.g., Layer 1 (LI) - physical layer.

[0063] 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.: • The physical layer offers to the MAC sublayer transport channels; • The MAC sublayer offers to the RLC sublayer logical channels; • The RLC sublayer offers to the PDCP sublayer RLC channels; • The PDCP sublayer offers to the SDAP sublayer radio bearers; • The SDAP sublayer offers to 5GC QoS flows; • Comp, refers to header compression and Segm. To segmentation; • Control channels include (BCCH, PCCH).

[0064] 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.

[0065] A RAN (Radio Access Network) 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.

[0066] The gNB CU and gNB DU parts may e.g., be co-located 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, 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.

[0067] A gNB-DU supports one or multiple cells, and could thus serve as e.g., a serving cell for a user equipment (UE).

[0068] 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).

[0069] 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).

[0070] A UE is e.g., either in RRCCONXECTED state or in RRC JNACTIVE state when an RRC connection has been established. [0071 ] In RRC CONNECTED state a UE may: • store the AS context; • transfer unicast data to / from the UE; • monitor control channels associated with the shared data channel to determine if data is scheduled for the data channel; • provide channel quality and feedback information; • perform neighboring cell measurements and measurement reporting.

[0072] The RRC protocol includes e.g. the following main functions: • RRC connection control; • measurement configuration and reporting; • establishment / modification / release of measurement configuration (e.g. intrafrequency, inter-frequency and inter-RAT measurements); • setup and release of measurement gaps; • measurement reporting.

[0073] The general functions and interconnections of the described elements and functions, which also depend on the actual network type, are known to those skilled in the art and described in corresponding specifications, so that a detailed description thereof may omitted herein for the sake of conciseness. However, it is to be noted that several additional network elements and signaling links may be employed for a communication to or from an element, function or application, like a communication endpoint, a communication network control element, such as a server, a gateway, a radio network controller, and other elements of the same or other communication networks besides those described in detail herein below.

[0074] A communication network architecture as being considered in examples of embodiments may also be able to communicate with other networks, such as a public switched telephone network or the Internet. The communication network may also be able to support the usage of cloud services for virtual network elements or functions thereof, wherein it is to be noted that the virtual network part of the telecommunication network can also be provided by non-cloud resources, e.g. an internal network or the like. It should be appreciated that network elements of an access system, of a core network etc., and / or respective functionalities may be implemented by using any node, host, server, access node or entity etc. being suitable for such a usage. Generally, a network function can be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., a cloud infrastructure.

[0075] Furthermore, a network element, such as communication elements, like a UE, a terminal device, control elements or functions, such as access network elements, like a base station / BS, a gNB, a radio network controller, a core network control element or function, such as a gateway element, or other network elements or functions, as described herein, and any other elements, functions or applications may be implemented by software, e.g., by a computer program product for a computer, and / or by hardware. For executing their respective processing, correspondingly used devices, nodes, functions or network elements may include several means, modules, units, components, etc. (not shown) which are required for control, processing and / or communication / signaling functionality. Such means, modules, units and components may include, for example, one or more processors or processor units including one or more processing portions for executing instructions and / or programs and / or for processing data, storage or memory units or means for storing instructions, programs and / or data, for serving as a work area of the processor or processing portion and the like (e.g. ROM, RAM, EEPROM, and the like), input or interface means for inputting data and instructions by software (e.g. floppy disc, CD-ROM, EEPROM, and the like), a user interface for providing monitor and manipulation possibilities to a user (e.g. a screen, a keyboard and the like), other interface or means for establishing links and / or connections under the control of the processor unit or portion (e.g. wired and wireless interface means, radio interface means including e.g. an antenna unit or the like, means for forming a radio communication part etc.) and the like, wherein respective means forming an interface, such as a radio communication part, can be also located on a remote site (e.g. a radio head or a radio station etc.). It is to be noted that in the present specification processing portions should not be only considered to represent physical portions of one or more processors, but may also be considered as a logical division of the referred processing tasks performed by one or more processors. It should be appreciated that according to some examples, a so-called “liquid” or flexible network concept may be employed where the operations and functionalities of a network element, a network function, or of another entity of the network, may be performed in different entities or functions, such as in a node, host or server, in a flexible manner. In other words, a “division of labor” between involved network elements, functions or entities may vary case by case.

[0076] As illustrated above, the present disclosure generally seeks to provide fast RRC Resume from RRC IXACTIVE by RACH-less access to a cell, in particular utilizing UE-based timing advance (TA), and in particular when considering UE mobility.

[0077] In the present disclosure, candidate, candidate cell, candidate target cell, and target cell, are used interchangeably.

[0078] In the present disclosure, the current serving cell, when being considered at the point of time when the UE enters into the RRC_inactive state, becomes the last serving cell before the UE enters the RRCjnactive state. Therefore, the two terms “current serving cell” and “last serving cell” refer to the same cell that is currently serving the UE before the UE enters the RRC inactive state.

[0079] References are now made to the figures. In particular, it is to be noted that identical or like reference numbers used in the figures of the present disclosure may, unless indicated otherwise, indicate identical or like elements, such that repeated description thereof may be omitted for reasons of conciseness. UE-based timing advance (TA)

[0080] Figure 1 schematically illustrates an example of a UE-based timing advance determination according to an example embodiment of the present disclosure.

[0081] A UE in RRCCONNECTED has TA for its serving cell. A procedure is defined by 3GPP Rel-18 [Further NR mobility enhancements, RP-231475] which is also known as L1 / L2 triggered mobility (LTM), to determine the TA towards a neighboring cell based on knowledge about the TA of the serving cell and measurements on a neighboring cell. The configuration is provided by source gNB in LTM Configuration (LTM-Config) and LTM-Candidate IE. If Itm-UE-MeasuredTA-ID of a candidate cell (given in LTM-Candidate IE) and Itm-ServingCellUE- MeasuredTA-ID of the serving cell (given in LTM-Config IE) are provided to a UE and have same value, then the UE estimates based on the UE implementation a timing advance to apply from a first transmission on the candidate cell that is after the reception of a cell switch command for the candidate cell. The high-level procedure is as follows: 0. The Rx timing difference is calculated between the measured DL sync, signal from a neighboring cell with the measured DL sync, signal from a serving cell. This timing difference is multiplied by two to consider the propagation delay in the round trip and to calculate the offset that needs to be added to the current timing advance value. This assumes symmetrical DL and UL path. 1. TA corresponding to the UE’s serving cell (Celli) is known. 2. NW configures the UE to determine TA for another cell (Cell2). 3. The UE can determine the TA for a neighboring cell based on the received configuration and L3 measurements on the serving cell and the neighboring cell. 4. UE can utilize the determined TA for RACH-less LTM access using a configured grant where the configured grant is provided to the UE, e.g., for LTM, configured grant is provided in the target cell configuration which the UE applies upon reception of the cell switch command.

[0082] Timing Advance, TA2, for the second cell (cell2) can be determined as: TA2 = TA of the celll + 2 (Rx timing difference between cell 1 and cell2) - 2 (TAE) - OtherEstError

[0083] When cells are synchronized, timing advance error (TAE) which is relative difference in time of transmission of the simultaneous signals between any pair of cells can be assumed as zero.

[0084] OtherEstError refers to any error that can be caused by the UL / DL reciprocity or estimator implementation / method error which for this disclosure is assumed to be zero or known by the UE.

[0085] The corresponding change in the specification [TS38.331] is provided below: 5.3.5.18.6 LTM cell switch execution 1> if the LTM-Candidate IE in Itm-Config indicated by lower layers or for the selected cell in accordance with 5.3.7.3 contains the field Itm-UE-MeasuredTA-ID'. 2> if the value of Itm-UE-MeasuredlA-ID is not equal to the value of Itm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID’. 3> replace the value of Itm-ServingCellUE-MeasuredTA-lD in VarLTM-ServingCellUE-MeasuredTA-ID with the value received within Itm-UE-MeasuredTA-ID', 3> for each LTM-Candidate IE in Itm-Config: 4> if the value of Itm-UE-MeasuredTA-ID within LTM-Candidate IE is equal to the value of Itm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID: 5> inform lower layers that UE is configured with UE-based TA measurements for the LTM-Candidate', 4> else: 5> inform lower layers that UE is not configured with UE-based TA measurements for die LTM-Candidate.

[0086] It is also specified in TS 38.213 [section 21]: 21 Ll / L2-triggered mobility procedures Itm-UE-MeasuredTA-ID of a candidate cell and Itm-ServingCellUE-MeasuredTA-ID of the serving cell are provided to a UE and have same value, the UE estimates based on the UE implementation a timing advance to apply from a first transmission on the candidate cell that is after the reception of a cell switch command for the candidate cell [11. TS 38.321], CG-based small data transmission 5

[0087] Figure 2 schematically illustrates an example of a signaling diagram for RRC Resume using CG-based SDT according to an example embodiment of the present disclosure.

[0088] Mobile-originated small data transmission (MO-SDT) in RRC inactive was specified in 3GPP Rel-17. A UE in RRCINACTIVE who wants to transmit small amount of data and return to RRC INACTIVE can apply MO-SDT using a 2-step or 4-step RACH (RA-SDT) or 10 perform RACH-less access using a configured grant (CG-SDT).

[0089] In accordance with this disclosure and as shown in Figure 2, the approach is the CG-based SDT as follows: • At step S21: the UE is in RRC-CONNECTED state; • At step S22: the UE is configured for CG-SDT in RRCRelease with 15 suspendConfig when transitioning to RRC_INACTIVE mode. This configuration includes the following: o Type 1 CG configuration. Multiple CG configurations can be provided. It is also possible to provide CG resources for a subset of SSBs with a bitmap indicated to the UE. o cg-SDT-RSRP-ThresholdSSB threshold is used to determine valid beam(s) for CG selection. CG-SDT procedure can be initiated only if there is an CG provided on an SSB with RSRP above a threshold. o cg-SDT-TimeAlignmentTimer and cg-SDT-RSRP-ChangeThreshold are configured for CG-SDT TA (Timing Alignment) validation. CG-SDT resources are released when cg-SDT-TimeAlignmentTimer expires or if, upon SDT procedure initiation, the RSRP has changed more than the cg-SDT-RSRP-ChangeThreshold. • At step S23: the UE has entered into or is in the RRCJNACTIVE mode or state, and is further configured to, until the cg-SDT-TimeAlignmentTimer expires, maintain (e.g., store) the TA value that is obtained before the UE enters into the RRCJNACTIVE mode. Further, the UE is configured to, until the cg-SDT-TimeAlignmentTimer expires, maintain (e.g., store) the CG resources obtained in accordance with the CG-SDT configuration received in step S22; • In the next step, there may be two options or alternatives in which the UE proceeds with the RRC Resume. • In option 1, the cg-SDT-TimeAlignmentTimer expires without the UE having a need for e.g., MO access, or the UE has (re-)selected a different cell (i.e., different from the last serving cell before the UE enters RRC-inactive state) due to UE mobility, in which cases, as shown with step S24a, the UE is configured to release the CG-SDT configuration received in step S22; • In option 2, the UE determines to initiate access due to need of transmitting MO data and the UE has determined that the CG-SDT configuration received in step S22 is valid, in which case the UE is configured to perform or initiate RACH-less RRC Resume procedure.

[0090] In the scenario of Figure 2, CG-based SDT is initiated only if: • UE is in the cell that was its Primary Cell (PCell) when RRCRelease was received, • Data volume of the pending UL data across all Resource Blocks (RBs) configured for SDT is below configured threshold, • The DL RSRP (reference signal received power) is above a configured sdt-RSRP-Threshold, if configured, • CG-SDT resources are configured for the selected UL carrier (Normal UL, NUL, or Supplementary UL, SUL), • At least one SSB (Synchronization Signal Block) configured with CG-SDT resources with SS-RSRP above cg-SDT-RSRP-ThresholdSSB is available, • UL TA is valid (cg-SDT-TimeAlignmentTimer is running and RSRP has not changed more than cg-SDT-RSRPChangeThreshold), and • All the radio bearers with data available are allowed to use CG-SDT (based on LCH restrictions).

[0091] In view of the above, it is proposed in accordance with the present disclousure an apparatus and a method for fast initial access. The fast initial access is enabled via a RACHless RRCResume operation. The RACHless transmission is enabled through a new UE technique called UE based TA. The present disclosure proposes enhancements to enable UE based TA operation for an inactive mode UE. Seen from NW and UE point of view it is proposed in accordance with the present disclosure the following solution: NW view: • Obtaining configured grant(s) and corresponding validity timer(s) for a UE from one or more neighbouring cells, • Transmitting own allocated configured grant and the corresponding timer set to be used for UE based TA operation to the UE upon transitioning the UE to RRC_INACTIVE, • Transmitting obtained allocated configured grant(s) and the corresponding timer(s) from one or more neighbouring cells to the UE upon transitioning the UE to RRCJNACTIVE, • Transmitting configuration for measurements related to UE-based TA calculation / maintenance. UE view: • Receiving configured grant and corresponding validity time for the serving cell upon receiving RRCRelease with suspend (transition to RRCINACTIVE), • Receiving configured grant(s) and corresponding validity timer(s) for one or more nonserving cells upon receiving RRCRelease with suspend (transition to RRC INACTIVE), or dynamic grant related configurations, • Receiving configuration to calculate / maintain TA for its camped cell, • Utilizing the configuration to calculate the TA for the camped cell and / or the last camped cell, • Utilizing the TA for RACH-less access to the camped cell if valid configured grant from the cell is available.

[0092] It is therefore proposed in accordance with the present disclosure a RACH-less RRC resume procedure or configuration for the UE based on a determination of the TA value by the UE. Based on this proposed approach, the present disclosure further proposes a configured grant (or configured allocation) based alternative and a dynamic grant (or dynamic allocation) based alternative, with the difference being in the manner of the uplink resource allocation. Configured grant (CG) based alternative

[0093] For simplicity and ease of understanding, the procedure in accordance with this alternative is provided in two Figures.

[0094] Therein, Figure 3 illustrates steps on source (current serving) cell obtaining CG from one or more neighboring cells (candidates for UE’s cell reselection due to mobility) and providing these CGs along with its own CG, TA, and timer related to each CG to the UE and an indication for UE to use UE based TA.

[0095] Further, Figure 4 illustrates steps taken at UE to utilize the received and / or updated configuration information for a fast RACH-less access whenever it needs to resume its connection again.

[0096] The example shown in Figure 3 relates to an inter-gNB case, but the present disclosure is also applicable for intra-gNB.

[0097] Steps as illustrated in Error! Reference source not found, are described in detail below. • Step S31: UE (UE1 in the example) is in RRCCONNECTED in CellO controlled by gNBO (current source cell). o The UE has valid TA from source cell in this RRC state. UE may store the DL sync, signal timing at the time of last timing advance update reception from the source cell. • Step S32: Source gNB (gNBO) acquires configured grant resource for one or more candidate cells (candidate cells are referred to as cells that has provided a CG for the UE) controlled by other gNBs for the UE (gNBl and gNB2 in this example). The cells are set with respect to the RAN notification area of the UE. In a broader sense, the source gNB is also considered to be a candidate cell to which the UE may resume to after the UE has transitioned or resumed from the RRCinactive state back to the RRC active state. o The CG is requested before source gNB releases UE1 to RRC INACTIVE state. o The gNBs controlling the candidate cells can provide requested CG and a timer that indicates validity of CG or reject based on gNB implementation and resource availability. Along these the gNBs should also provide C-RNTI, CS-RNTI search space configuration to monitor downlink control channel (PDCCH) for the UE in case configured grant Type 2 will be used. • Step S33: Source gNB transitions UE1 to RRC INACTIVE by RRCReleases with suspendConfig. o gNBO may provide CG and Timing Alignment Timer for the UE to use if it needs to resume to the same cell (legacy acc. from SDT). o Additionally, gNBO provides measurement configuration for UE1 to update the TA of Cell 0 / gNB0 after it transitions to RRC INACTIVE. The measurement configuration may indicate using the serving cell measurements (S-measure) for cell-reselection measurements or provide different periodicity. ■ The measurement configuration may indicate UE the measurement configuration for all candidate cells to maintain TA for all candidate cells. o Additionally, gNBO provides the available acquired CG(s) and corresponding timer(s) from candidate target cell(s). o The configuration may indicate whether the CG Typel or Type2 will be used. • Step S34: While in RRCIN ACTIVE, UE keeps the last serving cell’s TA (gNBO) and the provided CG during the time it is valid and utilize the received configuration in step S33 to periodically measure SSBs from CellO gNBO to update the corresponding TA from the last serving cell. o In another embodiment, UE can also measure the SSBs from candidate / neighbouring cells to maintain TA of the candidate cells. • Step S34a: In an embodiment, the periodicity of SSB measurements for TA update may be adjusted based on UE’s mobility state and / or the radio link conditions, e.g., a UE in high mobility and / or bad radio link condition may measure more frequently to adjust the TA more often than a stationary or low mobility UE or a UE in cell center with good radio link condition. This may be based on NW configuration at step S33 or UE implementation. • Step S34b: Additionally or alternatively to step S34a, in another embodiment, the UE stores the frame timing (or any specific means to store the timing of the signal received) of the last measured downlink (DL) signal received from gNBO with the corresponding TA update. The frame timing may be used to update the TA based on the difference between the new frame timing and the last stored frame timing (i.e., to calculate the RX timing difference using the last and updated frame timings). • Step S34c: Additionally or alternatively to steps S34a and / or S34b, in another embodiment, upon each new measurement of frame timing, the TA measurement is updated and the stored frame timing measurement and corresponding TA is replaced.

[0098] Steps as illustrated in Error! Reference source not found, are described in detail below. • Step S41: UE is in RRCINACTIVE in the cell at which it was released to, i.e. UE’s last serving cell during RRC connection, CellO (gNBO). o The UE has received configurations for UE-based TA estimation along with the CG from gNBO and possibly one or more neighboring cells from which it has acquired CG. For details, refer to step S33 in Figure 3. In this example there is a CG available from a cell at gNBl but not from gNB2. o UE maintains the TA for the CellO. For details refer to step S34 in Figure 3. ■ In an alternative embodiment UE may maintain also TA for cell 1.

[0099] Depending on whether the UE has re-selected to a new / different cell compared to the last serving cell before entering into the RRCJnactive state, it is proposed in accordance with the present disclosure the following procedures for the UE to perform RRC Resume in the following cases, namely Case 1, Case 2 and Case 3.

[00100] While the UE is still camped on the same cell as its last serving cell before transitioning to RRC inactive (Casel), • Step S42a: if there is no need to resume RRC connection due to MO or MT call until CG validity timer expires, when the CG validity timer expires, it stops updating the UE-based TA (option 1.1), and flush the stored CG and TA information. o In one option, if there is no expiration of the given CG (no CG validity timer is given) provided to the UE, the UE may keep updating the UE-based TA. o The same timer can be used at the network side to release the CG and other related UE context. • Step S42b: if the UE needs to resume RRC connection due to MO or MT call and it has a valid CG and a valid TA, it initiates RACH-less access (i.e., sending RRC Resume message using the CG directly without transmitting any RA preamble and receiving a RAR) to its camped cell using the CG and the (latest) estimated UE-based TA (option 1.2).

[00101] If the UE reselects to a new cell for which it has received a CG in step S41 (Case 2), • Step S43: If the CG validity timer associated with the new cell is still running, the UE calculates the TA corresponding to the new (camped / serving) cell (controlled by gNBl in this example) based on the TA of the last (camped / serving) cell, the last measurements on the last cell, and measurements for timing of the DL-RS of the new cell, where the (DL) measurements for timing of the DL-RS on the last cell and the new cell is needed to determine the Rx timing difference. Similar to steps S34 in Figure 1, the UE keeps the TA of its camped cell updated. o In one option, if there is any timing alignment error (TAE) between the timing of the two cells (last cell and the new cell and not synchronized), that can also be provided to the UE (in step S33 in Figure 3). The source and candidate cells may communicate to derive the TAE between them. The UE may take into account TAE on top of the Rx timing difference to determine TA. o In another embodiment, UE may have already maintained TA for the candidate cell. o UE stops the CG validity timer if it initiates RRCResume transmission. o In one alternative the CG validity timer is candidate cell specific. ■ And UE starts all CG validity timers after transitioning to inactive state. o In one alternative - there can be a single CG validity timer configured This will oversee the validity of all CGs. • Step S44a: if there is no need to resume RRC connection due to MO or MT call until CG validity timer expires, when the CG validity timer expires, it stops updating the TA (option 2.1). • Step S44b: if the UE needs to resume RRC connection due to MO or MT call and it has valid CG and TA, it initiates RACH-less access to its camped cell using the CG and the UE-based TA (option 2.2). o In case of configured grant type 2 is used, UE starts monitoring PDCCH using configured scheduling RNTI (CS-RNTI) and search space on for reception for the activation of the configured grant. ■ The network will send periodic DCIs (over PDCCH) for the activation of the grant after paging the UE. ■ Similarly, the CS-RNTI may be used for mobile originating traffic, in case the network knows or estimates the arrival of the MO traffic. This can be estimated through message periodicity or other application layer awareness.

[00102] If the UE reselects to a new cell (controlled by gNB2 in this example) for which it has not received a CG in stepl (Case 3), • Step S45: If the UE still has a valid CGfrom the last camped cell (controlled by gNBl), it keeps measurements on the last camped cell and updates the corresponding TA. This may become useful in case the UE reselects again to a new cell with a valid CG (e.g., cells controlled by gNBO or gNBl). o In case another candidate cell becomes stronger than the last camped cell - UE may switch to measuring that camped cell instead. This may be indicated with an indication to the UE. o In another embodiment the UE may be configured to release the UE based TA configuration for inactive mode if it re-selects to a non-candidate cell. • Step S46: if the UE needs to resume RRC connection due to MO or MT call it initiates normal RACH-based access to its camped cell (gNB2 in this example). Dynamic grant (DG) based alternative

[00103] For simplicity and ease of understanding the procedure in accordance with this alternative is provided in two Figures.

[00104] Therein, Figure 5 illustrates steps on source (current serving) cell and one or more neighboring cells (candidates for UE’s cell reselection due to mobility) preparing for DG along with providing / configuring paging for RACH-less access for the UE; as well as the cells providing the UE with DG-related parameters / configurations, TA-related parameters / configurations, and timers related to DG and RACH-less Resume; and preferably an indication for UE to use UE based TA.

[00105] Further, Figure 6 illustrates steps taken at UE to utilize the received and / or updated configuration information as shown in Figure 5 for a fast RACH-less access whenever it needs to resume its connection again.

[00106] Steps as illustrated in Figure 5 are described in detail below. • Step S51: UE (UE1 in the example) is in RRC CONNECTED in CellO controlled by gNBO (current source cell). The UE has valid TA from source cell in this RRC state. • Step S52: Before releasing the UE to idle mode, the source gNB contacts candidate gNBs for RACH-less Resume procedure for the UE using dynamic grant. o This pre-configures the gNBs to transmit a periodic or other type of dynamic grants to the UE along the paging message. o This configuration will allocate a cell specific id to the UE. ■ For example, CS-RNTI, C-RNTI or others. o This configuration may allocate a search space configuration to the UE to monitor PDCCH with dynamic grant. o In one alternative no RNTI is provided to the UE. UE is configured to take part of the M-TMSI from the paging message to use for decoding the dynamic grant. ■ The paging message may be enhanced with a single bit to indicate to the UE that a dynamic grant will follow the paging message. o Similarly, UE can be configured to receive dynamic grant information from the system information of the cell it is camping such as search space (including coreset information) information and DCI to monitor. • Step S53: Source gNB releases UE to RRC Inactive mode providing the configurations necessary to calculate UE based TA for candidate cells, also a dynamic grant timer and a RACH-less resume timer. o RACH-less resume timer: ■ In some exemplary embodiments, the RACH-less resume timer is started by the UE once it receives the RRCRelease command. ■ In some exemplary embodiments, if the RACH-less resume timer expires, • If UE has received the dynamic grant or the paging message, it initiates RACH-based RRC Resume procedure, otherwise, • UE release all RACH-less resume related parameters and stops the procedures. ■ In some exemplary embodiments, UE stops the RACH-less resume timer if it initiates RRCResume transmission. ■ In one alternative RACH-less resume timer is a single timer for the UE to monitor how long UE should do UE based TA update in inactive mode. ■ In another alternative RACH-less resume timer is reset after each cell reselection procedure. • In other alternatives there can be other triggers such as from application layer to re-start the RACH-less resume timer. o The intent of reset is expecting that UE will resume connection with network quite soon, thus the necessity to maintain TA for a fast resume procedure. o Dynamic grant timer: ■ In some exemplary embodiments, Dynamic grant timer is started after UE receives a paging message. ■ In some exemplary embodiments, the UE does not start random access procedure while this timer is running and waits for a dynamic grant. ■ In some exemplary embodiments, if this timer expires UE initiates RACH-based RRC Resume procedure. ■ In some exemplary embodiments, UE stops the DG timer if it receives a DG successfully. ■ In one alternative the DG timer is candidate cell specific. • And UE starts all DG validity timers after transitioning to inactive state. ■ In one alternative - there can be a single DG validity timer configured • This will oversee the validity of all DGs.

[00107] According to the present disclosure, the maintenance / update of TA in step S54 of Figure 5 can refer to step S34 including step S34a to S34c of Figure 3.

[00108] Steps as illustrated in Figure 6 are described in detail below. • Step S61: UE is in RRCIN ACTIVE in the cell at which it was released to, i.e. UE’s last serving cell during RRC connection, CellO (gNBO.) o The UE has received configurations for UE-based TA estimation along with the list of cells that provides a DG from gNBO. For details, refer to description of Figure 4. In this example DG transmission is acknowledged by gNBl but not by gNB2. o UE maintains the TA for the CellO. For details refer to step S54 in Figure 5. ■ In an alternative embodiment UE may maintain also TA for cell 1.

[00109] Depending on whether the UE has re-selected to a new / different cell compared to the last serving cell before entering into the RRCinactive state, it is proposed in accordance with the present disclosure the following procedures for the UE to perform RRC Resume in the following cases, namely Case 1, Case 2 and Case 3.

[00110] While the UE is still camped on the same cell as its last serving cell before transitioning to RRC inactive (Casel), • (Option 1.1) step S62a: if there is no need to resume RRC connection due to MO or MT call until RACH-less Resume timer expires, when the RACH-less Resume timer expires, it stops updating the UE-based TA (option 1.1), and flush the TA information. o In one option, if there is no RACH-less resume timer provided to the UE, the UE may keep updating the UE-based TA. o The same timer can be used at the network side to determine not to send DG to the UE after paging. • (Option 1.2) Step S62b: if the UE needs to resume RRC connection due to MO call OR it does not have a valid TA, it initiates RACH based Resume. • (Option 1.3) Step S62c: if the UE needs to resume RRC connection due to MT call and it has a valid TA, it initiates RACH-less Resume with DG procedure. Network sends the paging message. Network may add a single bit to the paging message to indicate a dynamic grant will follow the paging message. o Step S62d: UE starts the DG timer, and starts monitoring the cell for a dynamic grant. ■ In case UE does not receive a DG and the DG timer expires the UE initiates RACH-based Resume procedure. ■ If the indication is used by the network the UE starts monitoring DG, only if the indication is received by the UE. This case makes the preconfiguration unnecessary. o Step S62e: UE receives a DG from the base station. The DG is allocated on the pre-configured RNTI and search space to the UE, or the RNTI UE calculated from the TMSI included in the paging message. o Step S62f: UE sends the Resume message on the DG using the TA it has been maintaining (i.e., sending RRC Resume message using the DG directly without transmitting any RA preamble and receiving a RAR) to its camped cell using the DG and the (latest) estimated UE-based TA. ■ After receiving the RRC Resume from the UE, the gNB may indicate to neighbour gNBs that it has received a message from the UE, such that if the other gNBs are blindly transmitting DGs they can stop this.

[00111] If the UE reselects to a new cell for which is configured for DG in stepl (Case 2), • Step S63: If the RACH-less resume timer is still running, the UE calculates the TA. o UE calculates the TA of the new (camped / serving) cell, based on the TA of the last cell, the last measurements on the last (camped / serving) cell, and measurements on the new cell, where the (DL) measurements on the last cell and the new cell is needed to determine the Rx timing difference. Similar to steps S54 in Figure 5, the UE keeps the TA of its camped cell updated. o After the TA update the procedure is the same as in Case 1.

[00112] If the UE reselects to a new cell (controlled by gNB2 in this example) for which it is not configured with DG in step S61 (Case 3), then the steps take place like in Case 3 of configured grant case.

[00113] In summary, it is proposed in accordance with the present disclosure a fast RRC Resume operation, based on UE determining / maintaining / updating timing advance (e.g., through measurements in idle mode).

[00114] As shown in Figure 2, when determining a transition from RRCjnactive to RRC connected e.g., due to need for MO access, the TA value is determined, for instance by checking if UL TA is valid (e.g., valid when cg-SDT-TimeAlignmentTimer is running and (measured) RSRP has not changed more than cg-SDT-RSRPChangeThreshold), with the threshold being determined by source gNB by configuration e.g. of cg-SDT-RSRPChangeThreshold (part of CG-SDT configuration). When it is determined that the UL TA is valid, the UE performs a RACHless access.

[00115] Therein, the TA determination may be perfomed in the following manners: TA determination done by the gNB o UE continuously sending UL messages, and the network can track the timing of the UL messages arriving from the UE and can send small corrections to the UL timing of the UE. o UE may send a RACH to the network, the network calculates the uplink timing of the preamble, and sends the timing advance to the UE such that the UL message for PUSCH channel (compared to PRACH channel that UE used) should be in which manner. - UE based TA calculation in connected mode o UE measures the candidate cell's reference signals and source cell's reference signal. UE calculates the timing between the reference signal of candidate gNB and the source cell. UE adds the timing offset on top of the serving cell timing advance and calculates the timing advance for the candidate cell.

[00116] The current TA validity is captured in MAC spec 38.321 as follows: 5.27.2 TA Validation for CG-SDT RRC configures the following parameters for TA validation for CG-SDT: cg-SDT-RSRP-ChangeThreshold'. RSRP threshold for the increase / decrease of RSRP for time alignment validation. The MAC entity shall, upon the reception of CG-SDT configuration: 1 >store the current RSRP of the downlink pathloss reference for TA validation as defined in TS 38.331 [5] clause 5.7.17. The MAC entity shall consider the TA of the initial CG-SDT transmission with CCCH message to be valid when the following conditions are fulfilled: 1> The RSRP values for the stored downlink pathloss reference and the current downlink pathloss reference are valid according to TS 38.133

[11] ; and 1> Compared to the stored downlink pathloss reference RSRP value, tire current RSRP value of the downlink pathloss reference calculated as specified in TS 38.133

[11] has not increased / decreased by more than cg-SDT-RSRP-ChangeThreshold, if configured; and 1> cg-SDT-TimeAlignmentTimer is running.

[00117] According to the present disclosure, UE stores the timing of the reference signal measurement from the last time (time 0) the timing advance is updated, and compares it to the timing (time 1) of the current reference signal measurement. UE calculates the difference and multiplies it with two to add for the time the signal takes to come to UE and the signal takes to go to the gNB and adds this to the current timing advance value stored. And the UE stores the timing of the last reference signal to be able to do a next timing advance update.

[00118] Accordingly, the new timing advance can be determined as: TA new = TA of the cell 1 + 2 (Rx timing difference between cell 1 reference signal at time 0 and cell 1 reference signal at time 1)-2 (TAE) - OtherEstError

[00119] Therefore, while in the procedure shown in Figure 2 it is only checked whether the old TA (e.g., the TA stored for the last serving cell before entering into the RRC-inactive state) is still valid, the present disclosure proposes measurement and calculation of a new TA e.g., for a new campled or serving cell if the UE has re-selected a new cell e.g., due to UE mobility, as well as proposes updating and maintaining of the old TA for the last serving cell if the UE still camps on the new cell with which the resume to RRCinactive is associated.

[00120] Further, the present disclosure resolves a specific problem: There is no mechanism for the UE to apply UE-based TA in RRCINACTIVE beyond the validity time if the UE will resume in the same cell as it was released to.

[00121] In view of that problem, it is shown in Figure 2 the situation where TAT is running, UE maintains a TA value, e.g., by means of a TAT timer, which however cannot solve the above problem. The timing advance may not be valid if UE moves and will have a different uplink timing alignment. This timer is not able to enable this behavior in a technical way if UE is moving.

[00122] According to the present disclosure, for solving the above problem, it can be introduced a TA timer, in addition to the CG timer, wherein the two timers (e.g., the length of the respective timers) may have the following relationship, as e.g.: If TA timer = CG timer: when the TA timer expires, there is no need to maintain TA, as no CG resource are available; If TA timer >CG timer: when the TA timer expires, there is no need to maintain TA, as no CG resource are available; If TA timer <CG timer: UE maintains TA beyond TA expiration based on e.g. configured measurements, etc. to maintain a valid TA for the whole period till CG timer expires such that RACHless access remains possible till CG timer expires.

[00123] Further, in accordance with the present disclosure, UE is enabled / allowed to update the TA and access to the target cell with a more accurate timing advance also before the timing advance timer expires.

[00124] Therefore, the present disclosure ensures that the UE accesses the cell with an update or fresh timing advance.

[00125] Accordingly, in Figure 2, there is only timer TAT for both TA and CG, which means in Fig. 2 that CG resources are assigned only till TA timer expires, while in Figure 3 according to the present disclosure a new CG timer (independent from the TA timer) is introduced with more flexibility to allocate resources and the TA is maintained or even enhanced by constant, periodic, more accurate measurements, so that an optimized RACHless access is enabled till CG timer expires.

[00126] It is noted that, although in the above-illustrated example embodiments (with reference to the figures), the messages communicated / exchanged between the network components / elements may appear to have specific / explicit names, depending on various implementations (e.g., the underlining technologies), these messages may have different names and / or be communicated / exchanged in different forms / formats, as can be understood and appreciated by the skilled person.

[00127] According to some example embodiments, there are also provided corresponding methods suitable to be carried out by the apparatuses (network elements / components) as described above, such as the UE, the CU, the DU, etc.

[00128] It should nevertheless be noted that the apparatus (device) features described above correspond to respective method features that may however not be explicitly described, for reasons of conciseness. The disclosure of the present document is considered to extend also to such method features. In particular, the present disclosure is understood to relate to methods of operating the devices described above, and / or to providing and / or arranging respective elements of these devices.

[00129] Further, according to some further example embodiments, there is also provided a respective apparatus (e.g., implementing the UE, the CU, the DU, etc., as described above) that comprises at least one processing circuitry, and at least one memory for storing instructions to be executed by the processing circuitry, wherein the at least one memory and the instructions are configured to, with the at least one processing circuitry, cause the respective apparatus to at least perform the respective steps as described above.

[00130] Yet in some other example embodiments, there is provided a respective apparatus (e.g., implementing the UE, the CU, the DU, etc., as described above) that comprises respective means configured to at least perform the respective steps as described above.

[00131] It is to be noted that examples of embodiments of the disclosure are applicable to various different network configurations. In other words, the examples shown in the above described figures, which are used as a basis for the above discussed examples, are only illustrative and do not limit the present disclosure in any way. That is, additional further existing and proposed new functionalities available in a corresponding operating environment may be used in connection with examples of embodiments of the disclosure based on the principles defined.

[00132] It should also to be noted that the disclosed example embodiments can be implemented in many ways using hardware and / or software configurations. For example, the disclosed embodiments may be implemented using dedicated hardware and / or hardware in association with software executable thereon. The components and / or elements in the figures are examples only and do not limit the scope of use or functionality of any hardware, software in combination with hardware, firmware, embedded logic component, or a combination of two or more such components implementing particular embodiments of the present disclosure.

[00133] It should further be noted that the description and drawings merely illustrate the principles of the present disclosure. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the present disclosure and are included within its spirit and scope. Furthermore, all examples and embodiment outlined in the present disclosure are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the proposed method. Furthermore, all statements herein providing principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof. List of abbreviations: CG Configured Grant CG-SDT Configured Grant based - Small Data Transmission DG Dynamic Grant MO Mobile Originated MT Mobile Terminated TA Timing Advance / Timing Alignment TAE Timing Alignment Error TAT Time Alignment Timer RNTI radio network temporary identifier CS-RNTI configured scheduling RNTI C-RNTI Cell RNTI TMSI Temporary Mobile Subscriber Identity DCI Downlink Control Information

Claims

1. A User Equipment, UE, comprising:at least one processor, andat least one memory storing instructions that, when executed by the at least one processor, cause the UE at least to:receive, before or when entering a Radio Resource Control, RRC, inactive state, from a network node, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state,wherein the plurality of candidate cells comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell,wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells,wherein the UE is further configured to, while in the RRC inactive state:determine to transition from the RRC inactive state to the RRC connected state in response to an indication relating to data associated with the target cell;determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell.

2. The UE according to claim 1, wherein the determination of the TA value comprises maintaining a last TA value for the last serving cell before entering the RRC inactive state and / or updating the last TA value, and / or the determination of the TA value comprises determining a new TA value for the target cell being one of the plurality of candidate cells.

3. The UE according to claim 1 or claim 2, wherein the TA-related configurations comprise a TA measurement period for UE measurement on reference signals from the plurality ofcandidate cells for determining the TA value for the target cell, and the UE is further configured to periodically update the TA value for the target cell based on the TA measurement period.

4. The UE according to any one of claims 1 to 3, wherein the configuration information comprises Dynamic Grant related, DG-related configurations at least for the target cell.

5. The UE according to claim 4, wherein the DG-related configurations comprise a configuration to receive a downlink control information or a behavior to select a downlink control channel to monitor to receive the DG.

6. The UE according to claim 4 or claim 5, wherein the DG-related configurations comprise a DG timer at least for the target cell, wherein the UE is configured to monitor for a dynamic grant for transmission of the data associated with the target cell before the DG timer expires.

7. The UE according to claim 6, wherein the UE is configured to start the DG timer in response to receiving, from the target cell, a paging message associated with the dynamic grant for transmission of the data associated with the target cell.

8. The UE according to claim 6 or claim 7, wherein if, before the DG timer expires, the UE receives the dynamic grant from the target cell and the UE has a valid TA value for the target cell, the UE is configured to perform the RACH-less access to the target cell based on the received dynamic grant and the determined TA value for the target cell.

9. The UE according to any one of claims 6 to 8, wherein the UE is configured to stop the DG timer in response to receiving the dynamic grant from the target cell.

10. The UE according to any one of claims 6 to 9, wherein the configuration information further comprises for each candidate cell a corresponding DG timer.

11. The UE according to any one of claims 1 to 10, wherein the configuration information further comprises a RACH-less resume timer at least for the target cell, wherein the UE is configured to perform UE-based determination of the TA value for the target cell before the RACH-less resume timer expires.

12. The UE according to claim 11, wherein the UE is configured to start the RACH-less resume timer in response to receiving, from the plurality of candidate cells, an RRC-release command for entering into the inactive state.

13. The UE according to claim 11 or claim 12, wherein in response to receiving from the target cell a dynamic grant for the data associated with the target cell after expiry of the RACH-less resume timer or in response to receiving from the target cell a paging message associated with a dynamic grant for transmission of the data associated with the target cell after expiry of the RACH-less resume timer, the UE is configured to perform RACH access to the target cell.

14. The UE according to any one of claims 11 to 13, wherein if, at the time of expiry of the RACH-less timer, the UE determines not having received an indication relating to data associated with the target cell, the UE is configured to stop determining the TA value.

15. The UE according to any one of claims 1 to 14, wherein in response to determining not having a valid TA for the target cell, the UE is configured to perform RACH access to the target cell.

16. The UE according to any one of claims 1 to 15, wherein the target cell is one of the neighboring cells and the UE is further configured to calculate the TA value for the one neighboring cell based on the following: a TA value associated with the last serving cell, reference signal measurements associated with the last serving cell, and reference signal measurements associated with the one neighboring cell.

17. The UE according to any one of claims 1 to 16, wherein the configuration information further comprise a TA Timer at least for the target cell, and the TA Timer is restarted by the UE each time the timing advance value is updated.

18. A network node of a radio access network, configured to establish communication to a UE, the network node comprising:at least one processor, andat least one memory storing instructions that, when executed by the at least one processor, cause the network node at least to:transmit, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state,wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell,wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells,wherein the configuration information is configured to cause the UE to, while in the RRC inactive state:determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

19. The network node according to claim 18, wherein the configuration information comprises Dynamic Grant related, DG-related configurations at least for the target cell.

20. The network node according to claim 18 or 19, wherein the network node is configured to control the last serving cell, wherein the network node is configured to obtain, from the one or more neighboring cells, the DG-related configurations and / or the TA-related configurations for at least one of the one or more neighboring cells, or the network node is configured to configure the one or more neighboring cells for providing the UE with the DG-related configurations and / or the TA-related configurations.

21. The network node according to any one of claims 18 to 20, wherein the network node is configured to transmit to the UE an indication associated with data to be transmitted to the UE from a cell controlled by the network node.

22. The network node according to any one of claims 18 to 21, wherein the network node is configured to transmit to the UE a paging message associated with a dynamic grant for transmission of the data associated with the target cell and / or a dynamic grant for transmission of the data associated with the target cell.

23. The network node according to any one of claims 18 to 22, wherein the network node is configured to receive from the UE a message requesting the RACH-less access to a cell controlled by the network node.

24. A method of a User Equipment, UE, the method comprising:receiving, before or when entering a Radio Resource Control, RRC, inactive state, from a network node, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state,wherein the plurality of candidate cells comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell,wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells,wherein the method further comprises, while the UE is in the RRC inactive state:determining to transition from the RRC inactive state to the RRC connected state in response to an indication relating to data associated with the target cell;determining, for the target cell, the TA value based on the TA-related configurations; andperforming the RACH-less access to the target cell based on the determined TA value for the target cell.

25. A method of a network node of a radio access network, configured to establish communication to a UE, the method comprising:transmitting, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state,wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell,wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for the target cell,wherein the method further comprises causing the UE to, based on the configuration information, while the UE is in the RRC inactive state:determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

26. A computer program comprising instructions for causing an apparatus to perform the method according to claim 24 or claim 25.

27. A memory storing computer readable instructions for causing an apparatus to perform the method according to claim 24 or claim 25.

28. A first 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; andat least one memory storing instruction which, when executed by the at least one processor, cause the first network node at least to:establish a connection with a user equipment apparatus (UE) via a serving cell;transmit, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configurationinformation being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state,wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell,wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least for a target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells,wherein the configuration information is configured to cause the UE to, while in the RRC inactive state:determine, for the target cell, the TA value based on the TA-related configurations; and perform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.

29. A second network node that supports at least one of the distributed unit, DU, functionality or a layer 2 protocol of a radio access network, and which supports a first cell, further comprising:at least one processor; andat least one memory storing instruction which, when executed by the at least one processor, cause the second network node at least to:establish a connection with a user equipment apparatus (UE) via the first cell acting as a serving cell;transmit, before or when the UE enters a Radio Resource Control, RRC, inactive state, to the UE, configuration information associated with a plurality of candidate cells for the UE to perform a Random Access Channel less, RACH-less access, the configuration information being further associated with a state transition of the UE from the RRC inactive state to an RRC connected state,wherein the plurality of candidate cells is associated with the network node and comprises a last serving cell of the UE before the state transition and / or one or more neighboring cells of the last serving cell,wherein the configuration information comprises Timing Advance related, TA-related configurations for determining a Timing Advance, TA, value at least fora target cell from the plurality of candidate cells, wherein the target cell is the last serving cell or one of the neighboring cells,wherein the configuration information is configured to cause the UE to, while in the RRC inactive state:5 determine, for the target cell, the TA value based on the TA-related configurations; andperform the RACH-less access to the target cell based on the determined TA value for the target cell, for transitioning to the RRC connected state.43

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