How to manage timing advance for inactive UEs

Abstract

A method and wireless communication device (2400) operating as a network entity (e.g., a base station or a distributed unit of a distributed base station) in a satellite-based radio access network efficiently manages timing advance (TA) information for a user equipment (UE) while transitioning from an inactive state to a connected state or performing small data transmission. The method (2100) performed by the NE maintains (2125) pre-inactive state TA information related to the UE's communications over a non-terrestrial network before the UE switched to the inactive state. Receives (2130) an active state resume request from the user equipment (UE). If the user equipment (UE) does not provide a current full TA value in the resume request, transmits (2134) a calculated resume TA correction to the user equipment (UE) using the pre-inactive state TA information.

Description

[Technical Field]

[0001] This document generally describes wireless communication methods and devices that communicate using a non-terrestrial network (NTN). More specifically, described embodiments relate to timing advance (TA) information for user equipment (UE) transitioning from an inactive state to a connected state or performing small data transmission (SDT). [Background technology]

[0002] This background discussion is provided for the purpose of generally providing context for the disclosed technology. The work of the inventors described above is not admitted expressly or impliedly as prior art to the present disclosure to the extent described in this background section, including aspects of the description that may not qualify as prior art at the time of filing.

[0003] The objective behind the development of fifth-generation (5G) technology is to provide a unified framework for types of communication such as enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and massive machine-type communications (mMTC).

[0004] 5G technology primarily relies on legacy terrestrial networks. However, the 3rd Generation Partnership Project (3GPP®) organization is proposing to extend 5G communications to non-terrestrial networks (NTNs) using 5G “New Radio” (NR) technology or Long Term Evolution (LTE), tailored for narrowband Internet of Things (NB-IoT) or enhanced machine-type communications (eMTC) scenarios. In non-terrestrial networks (NTNs), RF transceivers are mounted on satellites, unmanned aircraft systems (UAS), also known as drones, balloons, airplanes, or other suitable devices. For simplicity, the following description refers to all such devices as satellites. In addition to satellites, non-terrestrial networks (NTNs) may include satellite gateways connecting the non-terrestrial networks (NTNs) to public data networks, feeder links between the satellite gateways and satellites, service links between satellites, and inter-satellite links (ISLs) when the satellites form a satellite constellation.

[0005] Satellites belong to one of several types based on their altitude, orbit, and beam footprint size. Types include low Earth orbit (LEO), medium Earth orbit (MEO), geostationary orbit (GEO), unmanned aircraft system (UAS) platforms (with high altitude platform stations (HAPS)), and highly elliptical orbit (HEO) satellites. Geostationary orbit (GEO) satellites are also known as geosynchronous orbit (GSO) satellites. Low Earth orbit (LEO) / medium Earth orbit (MEO) satellites are also known as non-geostationary orbit (NGSO) satellites.

[0006] A geostationary orbiting GSO satellite can communicate to one or several satellite gateways deployed in the satellite's target coverage area (e.g., a region or even a continent). A non-geostationary orbiting GSO satellite may communicate with one or several serving satellite gateways at different times. The non-terrestrial network NTN is designed to ensure continuity of service and feeder links between consecutively serving satellite gateways with sufficient duration to facilitate mobility anchoring and handover.

[0007] Satellites may support transparent or regenerative (with onboard processing) payloads and typically generate several beams for a given service area bounded by a field of view. The beam footprint typically has an elliptical shape and depends on the onboard antenna configuration and elevation angle. For transparent payload implementations, the satellite may provide RF filtering, and frequency conversion and amplification, but may not modify the waveform signal. For regenerative payload implementations, the satellite may apply RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and coding / modulation. This approach is substantially equivalent to satellites performing most of the functions of a base station, such as a gNB.

[0008] A user equipment (UE) communicating via a non-terrestrial network (NTN) experiences propagation delay when communicating via a satellite to a terrestrial network entity or a network entity (NE) of a radio access network (RAN). In this document, a network entity (NE) is a physical device that operates as a base station (BS), i.e., as a distributed unit (DU) of a base station (BS), or that hosts the functionality of a core network (CN). In such a scenario, the user equipment (UE) and the radio access network (RAN) can cooperate to compensate for the propagation delay based on the location information of the user equipment (UE) and the satellite. The radio access network (RAN) comprises a terrestrial network entity (NE) and a satellite, i.e., a non-terrestrial network (NTN). The radio access network (RAN) is aware of the serving satellite of the user equipment (UE), but may not be aware of the exact location of the user equipment (UE) within the area (cell) served by the satellite. The user equipment (UE) can estimate the delay from the satellite to the user equipment (UE) and report it to the radio access network (RAN), allowing the radio access network (RAN) to accurately estimate the round trip delay for scheduling uplink (UL) transmissions. The radio access network RAN ​​needs to schedule every uplink UL transmission assuming that the user equipment UE is at the edge of the cell (i.e., assuming the longest possible round-trip delay of the cell) without knowing the delay from the satellite to the user equipment UE. Such scheduling can significantly delay uplink UL transmissions, especially when the user equipment UE in the radio resource control (RRC_INACTIVE) state (RRC is an acronym for radio resource control) performs the radio resource control (RRC) connection resumption procedure or the small data transmission (SDT) procedure to communicate data. In these cases, such scheduling prolongs the entire radio resource control (RRC) connection resumption / small data transmission (SDT) procedure, resulting in increased latency. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2022 / 0070811 Summary of the Invention [Problem to be solved by the invention]

[0010] Conventionally, there is no suitable strategy for a user equipment (UE) to provide a timing advance TA report when resuming connection to a radio access network (RAN) after an inactive state or when performing a small data transmission (SDT) procedure (without leaving an inactive state). On the one hand, the path to / from the user equipment (UE) may have changed during the inactive state of the user equipment (UE). On the other hand, an automatic timing advance TA report wastes communication resources and time if the path to / from the user equipment (UE) has changed only a small amount. [Means for solving the problem]

[0011] Generally speaking, the techniques described herein enable a network entity NE (i.e., a base station BS or a unit of a distributed base station BS) to manage timing advance TA information of a user equipment UE, which selectively sends a timing advance TA report according to a predetermined rule when resuming connection with a radio access network RAN ​​or when performing small data transmission SDT. The network entity NE maintains the timing advance TA information of the user equipment UE when the user equipment UE enters an inactive state, and is configured to use the timing advance TA information of the user equipment UE in a manner depending on whether the user equipment UE provides a timing advance TA report when it starts to resume connection to the network or when performing small data transmission SDT. The absence of a timing advance TA report from the user equipment UE during the inactive state may indicate that (i) the difference between the user equipment UE's re-evaluated timing advance TA and the timing advance TA before the user equipment UE entered the inactive state is less than a predetermined threshold, (ii) the user equipment UE uses the same satellite / cell as before entering the inactive state, and / or (iii) the small data transmission SDT size enables the small data transmission SDT to be communicated using the uplink UL resources allocated in response to the small data transmission SDT preamble random access. The network entity NE may send an instruction to the user equipment UE to transmit a timing advance TA regardless of (i) to (iii). Selectively transmitting a timing advance TA report avoids timing advance TA-related signaling that wastes time and communication resources, while supporting both the user equipment UE and the network entity NE to use appropriate timing advance TA-related information to communicate via the satellite. [Brief explanation of the drawings]

[0012] [Figure 1A]1 is a block diagram of a wireless communication system in which user equipment and network entities implement timing advance TA reporting techniques in accordance with various embodiments. [Figure 1B] 1B is a block diagram of a distributed base station BS having a centralized unit CU and distributed units DU, the distributed base station BS being configured to operate in the system of FIG. 1A. [Figure 2A] FIG. 2 is a block diagram showing protocol stacks for user equipment UE communication with a terrestrial base station BS. [Figure 2B] 1B is a block diagram showing a protocol stack for the user equipment UE of FIG. 1A to communicate with the central unit CU and the distributed units DU. FIG. [Figure 3A] FIG. 1 is a block diagram of the transparent payload non-terrestrial network NTN architecture. [Figure 3B] FIG. 1 is a block diagram of a transparent payload non-terrestrial network NTN architecture in which a base station BS connects to multiple satellites through the same satellite gateway. [Figure 4A] 3B illustrates a user plane protocol stack for use in the non-terrestrial network NTN architecture shown in FIG. 3A. [Figure 4B] 3B illustrates a control plane protocol stack for use with the architecture of FIG. 3A. [Figure 5A] This shows the relationship between timing advance (TA) and propagation delay in the case of communication between user equipment (UE) and base station (BS) via satellite. [Figure 5B] 1 shows the relationship between timing advance TA and propagation delay for two different user equipments UE served by the same satellite. [Figure 6] 1 shows the components of a full timing advance TA applied by a user equipment UE using a satellite (i.e., communicating via a non-terrestrial network NTN). [Figure 7] 10 shows a sequence of messages that lead to the user equipment UE obtaining an NTA for uplink UL transmission. [Figure 8A] FIG. 10 is a messaging diagram illustrating a scenario in which a user equipment UE configured with a timing advance TA reporting configuration decides whether to send a timing advance TA report to a distributed unit DU of a base station BS during a radio resource control RRC connection resumption procedure. [Figure 8B] FIG. 10 is a messaging diagram illustrating a scenario in which a user equipment UE configured with a timing advance TA reporting configuration decides whether to send a timing advance TA report to a distributed unit DU of a base station BS during a radio resource control RRC connection resumption procedure. [Figure 8C] FIG. 10 is a messaging diagram illustrating a scenario in which a user equipment UE configured with a timing advance TA reporting configuration decides whether to send a timing advance TA report to a distributed unit DU of a base station BS during a radio resource control RRC connection resumption procedure. [Figure 8D] FIG. 10 is a messaging diagram illustrating a scenario in which a user equipment UE configured with a timing advance TA reporting configuration decides whether to send a timing advance TA report to a distributed unit DU of a base station BS during a radio resource control RRC connection resumption procedure. [Figure 9A] Figure 1 is a messaging diagram of a scenario in which, when performing a radio resource control (RRC) connection resumption procedure when the broadcasted (satellite-related) system information does not contain a positive indication for the user equipment UE to provide a timing advance TA report, the user equipment UE decides whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 9B]Figure 1 is a messaging diagram of a scenario in which, when performing a radio resource control (RRC) connection resumption procedure when the broadcasted (satellite-related) system information does not contain a positive indication for the user equipment UE to provide a timing advance TA report, the user equipment UE decides whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 9C] Figure 1 is a messaging diagram of a scenario in which, when performing a radio resource control (RRC) connection resumption procedure when the broadcasted (satellite-related) system information does not contain a positive indication for the user equipment UE to provide a timing advance TA report, the user equipment UE decides whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 9D] Figure 1 is a messaging diagram of a scenario in which, when performing a radio resource control (RRC) connection resumption procedure when the broadcasted (satellite-related) system information does not contain a positive indication for the user equipment UE to provide a timing advance TA report, the user equipment UE decides whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 10A] Figure 1 is a messaging diagram of a scenario in which, when the broadcasted system information comprises a positive indication for the user equipment UE to send a timing advance TA report, performing a radio resource control RRC connection resumption procedure causes the user equipment UE to decide whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 10B] Figure 1 is a messaging diagram of a scenario in which, when the broadcasted system information comprises a positive indication for the user equipment UE to send a timing advance TA report, performing a radio resource control RRC connection resumption procedure causes the user equipment UE to decide whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 10C] Figure 1 is a messaging diagram of a scenario in which, when the broadcasted system information comprises a positive indication for the user equipment UE to send a timing advance TA report, performing a radio resource control RRC connection resumption procedure causes the user equipment UE to decide whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 10D] Figure 1 is a messaging diagram of a scenario in which, when the broadcasted system information comprises a positive indication for the user equipment UE to send a timing advance TA report, performing a radio resource control RRC connection resumption procedure causes the user equipment UE to decide whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state. [Figure 11A] 1 is a messaging diagram of a scenario in which a user equipment UE, previously configured with a timing advance TA reporting configuration, decides whether to send a timing advance TA report during a small data transmission (SDT) procedure. [Figure 11B] 1 is a messaging diagram of a scenario in which a user equipment UE, previously configured with a timing advance TA reporting configuration, decides whether to send a timing advance TA report during a small data transmission (SDT) procedure. [Figure 11C] 1 is a messaging diagram of a scenario in which a user equipment UE, previously configured with a timing advance TA reporting configuration, decides whether to send a timing advance TA report during a small data transmission (SDT) procedure. [Figure 12A] This is a messaging diagram of a scenario in which, when initiating a small data transmission SDT procedure with the new cell, the user equipment UE decides whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state, if the broadcasted system information of the new cell carries a positive indication for the user equipment UE to provide a timing advance TA report upon establishing / re-establishing / resume procedure of a radio resource control (RRC) connection with the new cell. [Figure 12B] Figure 10 is a messaging diagram of a scenario in which, upon initiating a small data transmission SDT procedure with the new cell, the user equipment UE decides whether to send a timing advance TA report to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering the inactive state, if the broadcasted system information of the new cell provides a positive indication for the user equipment UE to provide a timing advance TA report upon establishing / re-establishing / resuming a radio resource control (RRC) connection with the new cell. [Figure 13]FIG. 10 is a messaging diagram of an example scenario in which the user equipment UE decides not to report a timing advance TA to a new cell (network entity NE / base station BS) other than the cell (network entity NE / base station BS) to which the user equipment UE was connected before entering an inactive state when initiating a small data transmission SDT procedure with the new cell, when the broadcasted system information of the new cell does not contain a positive indication for the user equipment UE to report a timing advance TA upon establishing / re-establishing / resuming a radio resource control (RRC) connection with the new cell. [Figure 14] 4 is a flow diagram of a method performed by the distributed unit DU to determine and process differential k_offset values ​​for a user equipment UE according to one embodiment; [Figure 15A] 4 is a flow diagram of a method performed by a distributed unit DU to provide a differential k_offset value to a user equipment UE during a radio resource control RRC connection resumption procedure according to one embodiment; [Figure 15B] Figure 10 is a flow diagram of a method performed by a distributed unit DU to provide a differential k_offset value to a user equipment UE during a radio resource control RRC connection resumption procedure without having the user equipment UE report a full timing advance TA value, according to one embodiment; [Figure 16A] 4 is a flow diagram of a method performed by a distributed unit DU to provide a user equipment UE with a sufficiently large resource to report a timing advance TA in a particular random access RA procedure according to one embodiment; [Figure 16B] 4 is a flow diagram of a method performed by a distributed unit DU to provide a user equipment UE with a sufficiently large resource to report a timing advance TA in a random access RA procedure according to one embodiment; [Figure 17] 4 is a flow diagram of a method performed by a distributed unit DU for controlling a user equipment UE via system information to report a timing advance TA in a radio resource control RRC connection resumption procedure according to one embodiment; [Figure 18A] 3 is a flow diagram of a method performed by a base station to determine a differential k_offset value for a user equipment UE during a radio resource control (RRC) connection resumption procedure according to one embodiment; [Figure 18B] 1 is a flow diagram of a method performed by a base station to determine a differential k_offset value for a user equipment (UE) during a radio resource control (RRC) connection resumption procedure without having the user equipment (UE) report a full timing advance (TA) value, according to one embodiment; [Figure 19A] 4 is a flow diagram of a method performed by a base station to determine a differential k_offset value for a user equipment UE during a small data transmission SDT procedure according to one embodiment; [Figure 19B] 1 is a flow diagram of a method performed by a base station to determine a differential k_offset value for a user equipment UE during a small data transmission SDT procedure without having the user equipment UE report a full timing advance TA value, according to one embodiment; [Figure 20] 1 is a flow diagram of a method executed by a base station BS to control a user equipment UE via system information to report a timing advance TA in a small data transmission SDT procedure according to one embodiment; [Figure 21] 1 is a flow diagram of a method executed by a network entity NE (for example a base station BS or a distributed unit DU of a distributed base station BS) connected to a user equipment UE according to one embodiment. [Figure 22] 22 is a flow diagram of a wireless communication method 2200 performed by a network entity NE (eg, a base station BS, or a distributed unit DU of a distributed base station BS) according to another embodiment. [Figure 23] 10 is a flow diagram of a communication method performed by a network entity NE (eg, a base station BS or a distributed unit DU of a distributed base station BS) according to yet another embodiment. [Figure 24]1 is a block diagram of a wireless communication device configured to perform the above-described method for managing a timing advance (TA) when an inactive user equipment (UE) resumes a radio access network (RAN) connection and / or initiates a small data transmission (SDT) procedure, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] As described in more detail below, a user equipment (UE) and / or a network entity (NE) of a radio access network RAN ​​use the techniques described in this section to manage timing advance TA reporting when the user equipment UE transitions from an inactive to an active state of a radio resource control protocol between the user equipment UE and the radio access network RAN ​​and / or when the user equipment UE performs small data transmission SDT.

[0014] 1A , a wireless communication system 100 includes a user equipment (UE) 102, a base station (BS) 104, a base station (BS) 106, and a core network (CN) 110. The base stations 104 and 106 operate within a radio access network (RAN) 105 connected to the core network (CN) 110. The core network (CN) 110 may be implemented, for example, as an evolved packet core (EPC) 111 or a fifth generation (5G) core (5GC) 160. The core network (CN) 110 may also be implemented as a sixth generation (6G) core, in other examples.

[0015] The base station 104 serves user equipment UEs in cell 124, and the base station 106 serves user equipment UEs in cell 126. If the base stations 104 and / or 106 are gNBs, the cells 124 and / or 126 are each New Radio NR cells. If the base stations 104 and / or 106 are ng-eNBs or eNBs, the cells 124 and / or 126 are Evolved Universal Terrestrial Radio Access (E-UTRA) cells. The cells 124 and 126 may be in the same radio access network notification area (RNA) or different radio access network notification areas (RNA). Generally, the radio access network RAN ​​105 comprises any number of base stations, each covering (i.e., serving user equipment UEs in) one, two, three, or any other suitable number of cells. For example, the base station 104 may also cover the cell 125. User equipment UE 102 supports at least one of a 5G_New Radio NR (or simply "New Radio NR") or Evolved Universal Terrestrial Radio Access (E-UTRA) air interface to communicate with one or both base stations 104 and 106. Each of the base stations 104, 106 connects to the core network CN 110 via an interface (e.g., an S1 interface or an NG interface). The base stations may also be interconnected via an interface (e.g., an X2 interface or an Xn interface for interconnecting New Radio NG_Radio Access Network RAN ​​nodes).

[0016] The core network CN 110 may be hosted by one or more physical devices, which may be co-located. In this document, the base stations and physical devices hosting the core network functions / modules may be referred to as network entities NEs. Among other components, the evolved packet core EPC 111 comprises a serving gateway (SGW) 112, a mobility management entity (MME) 114, and a packet data network gateway (PGW) 116. The serving gateway SGW 112 is generally configured to forward user plane packets related to voice calls, video calls, Internet traffic, etc. The mobility management entity MME 114 is configured to manage authentication, registration, paging, and other related functions. The packet data network gateway PGW 116 provides connectivity from user equipment UE to one or more external packet data networks (e.g., Internet networks and / or Internet Protocol (IP) Multimedia Subsystem (IMS) networks). Similarly, among other components, 5GC 160 comprises a User Plane Function (UPF) 162, an Access and Mobility Management Function (AMF) 164, and / or a Session Management Function (SMF) 166. Generally speaking, the User Plane Function UPF 162 is configured to forward user plane packets related to audio calling, video calling, Internet traffic, etc., the Access and Mobility Management Function AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the Session Management Function SMF 166 is configured to manage PDU sessions.

[0017] 1A , base station 104 supports (i.e., covers and serves user equipment UEs therein) cell 124, and base station 106 supports cell 126. Because cell 124 and cell 126 may overlap, user equipment UE 102 selects, reselects, or switches between one of cell 124 and cell 126. To directly exchange messages or information, base station 104 and base station 106 support an X2 interface or an Xn interface. In general, core network CN 110 connects to any suitable number of base stations that support New Radio NR cells and / or Evolved Universal Terrestrial Radio Access (EUTRA) cells.

[0018] As described in more detail below, the user equipment UE 102 and / or the network entity NE of the radio access network RAN ​​105 (e.g., the first base station BS 104 and / or 106) may utilize the techniques described in this section when the radio connection between the user equipment UE 102 and the radio access network RAN ​​105 is suspended, such as when the user equipment UE 102 operates in an "inactive state" comprising a radio resource control RRC_IDLE state and a radio resource control RRC_INACTIVE state of the radio resource control RRC protocol.

[0019] The base station 104 includes processing hardware 130, which includes one or more general-purpose processors (e.g., CPUs) 132 and non-transitory computer-readable memory 134 that stores instructions executed by the one or more general-purpose processors. Additionally or alternatively, the processing hardware 130 may include a special-purpose processing unit. The processor 132 is configured to process data that the base station 104 receives in an uplink direction or transmits in a downlink direction according to various techniques described in this section. The processing hardware 130 also includes a transceiver 136 (a term that also refers to antenna(s) and radio frequency front-end electronics, not separately shown in this figure) configured to transmit data in the downlink direction and receive data in the uplink direction. The base station 106 includes generally similar components. In particular, the components (140, 142, 144, and 146) of the base station 106 are similar to the components (130, 132, 134, and 136), respectively.

[0020] The user equipment UE 102 comprises processing hardware 150, which comprises one or more general-purpose processors 152, such as CPUs, and non-transitory computer-readable memory 154 that stores machine-readable instructions executable by the one or more general-purpose processors and / or special-purpose processing units. The processors 152 are configured to process data for the user equipment UE 102 to transmit in the uplink direction and / or receive in the downlink direction. The processing hardware 150 may also comprise a transceiver 156 (a term which also refers here to antenna(s) and radio frequency front-end electronics, not shown separately in this figure) configured to transmit and receive data.

[0021] FIG. 1B is a block diagram of a distributed base station 170. Any one or both of the base stations 104 and 106 of FIG. 1A may use a distributed base station (BS) architecture. The base station 170 includes a centralized unit (CU) 172 and one or more distributed units (DUs) 174 (only one shown). The centralized unit CU 172 includes processing hardware, such as one or more general-purpose processors (e.g., CPUs), and computer-readable memory storing machine-readable instructions executable by the general-purpose processor(s), and / or special-purpose processing units. For example, the centralized unit CU 172 may include a Packet Data Convergence Protocol (PDCP) controller, a Radio Resource Control (RRC) controller, and / or a Radio Resource Control (RRC) inactivity controller. In some embodiments, the centralized unit CU 172 may include a Radio Link Control (RLC) controller configured to manage or control one or more Radio Link Control (RLC) operations or procedures. In further embodiments, the centralized unit CU 172 does not include a Radio Link Control (RLC) controller.

[0022] In some embodiments (such as the embodiment shown in FIG. 1B ), the central unit CU 172 comprises a central unit control plane CU-CP 172A as a logical node hosting the control plane portion of the packet data convergence protocol PDCP protocol of the central unit CU 172. The central unit CU 172 may also comprise central unit user plane(s) CU-UP 172B as logical nodes hosting the user plane portion of the packet data convergence protocol PDCP protocol and / or the service data adaptation protocol (SDAP) protocol of the central unit CU 172. The central unit control plane CU-CP 172A may transmit control information (e.g., radio resource control (RRC) messages and F1 application protocol messages). The central unit user plane CU-UP 172B may transmit data packets (e.g., service data adaptation protocol (SDAP_PDUs) or Internet Protocol packets).

[0023] The central unit control plane CU-CP 172A can be connected to multiple central unit user planes CU-UP 172B via an E1 interface. The central unit control plane CU-CP 172A selects an appropriate central unit user plane CU-UP 172B for a service requested by the user equipment UE 102. In some embodiments, a single central unit user plane CU-UP 172B can be connected to multiple central unit control planes CU-CP 172A via an E1 interface. The central unit control plane CU-CP 172A can be connected to one or more distributed units DU 174 via an F1-C interface. The central unit user plane CU-UP 172B can be connected to one or more distributed units DU 174 via an F1-U interface under the control of the same central unit control plane CU-CP 172A. In some embodiments, one distributed unit DU 174 can be connected to multiple central unit user planes CU-UP 172B under the control of the same central unit control plane CU-CP 172A. In such an embodiment, connectivity between the central unit user plane CU-UP 172B and the distributed unit DU 174 is established by the central unit control plane CU-CP 172A using bearer context management functions.

[0024] The distributed unit DU 174 (which may be one of multiple distributed units DU of a distributed base station) comprises processing hardware, which may include one or more general-purpose processors (e.g., CPUs) and computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. For example, the processing hardware may include a Medium Access Control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., random access procedures) and / or a Radio Link Control (RLC) controller configured to manage or control one or more Radio Link Control (RLC) operations or procedures. The processing hardware may also include a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0025] In some embodiments, the radio access network RAN ​​105 supports integrated access backhaul (IAB) functionality. In some implementations, the distributed unit DU 174 operates as an IAB node and the central unit CU 172 operates as an IAB donor. For the embodiments described in this section, the radio access network RAN ​​105 supports non-terrestrial based network (non-terrestrial network NTN) functionality.

[0026] FIG. 2A is a block diagram illustrating a protocol stack 200 for user equipment UE communication with terrestrial base stations, such as eNB / ng-eNB 203 and gNB / en-gNB 205 (which may correspond, for example, to base stations 104 and / or 106 of FIG. 1A).

[0027] The Evolved Universal Terrestrial Radio Access EUTRA physical layer PHY 202A provides transport channels to the Evolved Universal Terrestrial Radio Access EUTRA_MAC sublayer 204A, which in turn provides logical channels to the Evolved Universal Terrestrial Radio Access EUTRA_RLC sublayer 206A. The Evolved Universal Terrestrial Radio Access EUTRA_RLC sublayer 206A then provides RLC channels to the Evolved Universal Terrestrial Radio Access EUTRA_Packet Data Convergence Protocol PDCP sublayer 208 and, in some cases, to the New Radio NR_Packet Data Convergence Protocol PDCP sublayer 210. Similarly, the New Radio NR_PHY 202B provides transport channels to the New Radio NR_MAC sublayer 204B, which in turn provides logical channels to the New Radio NR_RLC sublayer 206B. The new radio NR_RLC sublayer 206B then provides data transfer services to the new radio NR_Packet Data Convergence Protocol PDCP sublayer 210. The new radio NR_Packet Data Convergence Protocol PDCP sublayer 210 can then provide data transmission services to the service data adaptation protocol SDAP 212 or the radio resource control (RRC) sublayer (not shown in FIG. 2A ). In some embodiments, the user equipment UE 102 supports both the Evolved Universal Terrestrial Radio Access (EUTRA) and new radio NR stacks, as shown in FIG. 2A , and supports handover between an Evolved Universal Terrestrial Radio Access (EUTRA) base station and a new radio NR base station and / or supports DC over the Evolved Universal Terrestrial Radio Access (EUTRA) interface and the new radio NR interface. As further shown in FIG. 2A , the user equipment UE 102 can support layering of the new radio NR_Packet Data Convergence Protocol PDCP 210 over the Evolved Universal Terrestrial Radio Access (EUTRA) RLC 206A and the service data adaptation protocol SDAP sublayer 212 over the new radio NR_Packet Data Convergence Protocol PDCP sublayer 210.

[0028] The Evolved Universal Terrestrial Radio Access EUTRA_Packet Data Convergence Protocol PDCP sublayer 208 and the New Radio NR_Packet Data Convergence Protocol PDCP sublayer 210 receive packets, which may be referred to as service data units SDUs (e.g., from an Internet Protocol IP layer layered directly or indirectly on the Packet Data Convergence Protocol PDCP layer 208 or 210), and output packets, which may be referred to as protocol data units PDUs (e.g., to the Radio Link Control RLC layer 206A or 206B). For simplicity, this document will refer to both service data units SDUs and protocol data units PDUs as "packets" unless the distinction between service data units SDUs and protocol data units PDUs is relevant.

[0029] In the control plane, the Evolved Universal Terrestrial Radio Access EUTRA_Packet Data Convergence Protocol PDCP sublayer 208 and the New Radio NR_Packet Data Convergence Protocol PDCP sublayer 210 can provide a signaling radio bearer SRB or a radio resource control RRC sublayer (not shown in FIG. 2A ) to exchange, for example, radio resource control RRC messages or non-access stratum NAS messages. In the user plane, the Evolved Universal Terrestrial Radio Access EUTRA_Packet Data Convergence Protocol PDCP sublayer 208 and the New Radio NR_Packet Data Convergence Protocol PDCP sublayer 210 can provide a data radio bearer DRB to support data exchange. The data exchanged in the New Radio NR_Packet Data Convergence Protocol PDCP sublayer 210 can be Service Data Adaptation Protocol SDAP_PDUs, IP packets, or Ethernet packets.

[0030] 2B illustrates a simplified example protocol stack 250 by which the user equipment UE 102 can communicate with the distributed unit DU 174 and the central unit CU 172. The radio protocol stack 200 of FIG. 2A is functionally divided by the radio protocol stack 250 of FIG. 2B as shown. The central unit CU in either base station 104 or 106 can hold all control and higher layer functions (e.g., radio resource control RRC 214, service data adaptation protocol SDAP 212, new radio NR_packet data convergence protocol PDCP 210), while lower layer operations (e.g., new radio NR_RLC 206B, new radio NR_MAC 204B, and new radio NR_PHY 202B) are delegated to the distributed unit DU. To support connectivity to 5GC, the New Wireless NR_Packet Data Convergence Protocol PDCP210 provides signaling radio bearers SRB to the Radio Resource Control RRC214, and the New Wireless NR_Packet Data Convergence Protocol PDCP210 provides data radio bearers DRB to the Service Data Adaptation Protocol SDAP212, which provides signaling radio bearers SRB to the Radio Resource Control RRC214.

[0031] FIG. 3A illustrates a particular type of non-terrestrial network NTN deployment, called a transparent payload architecture, which includes a satellite gateway 302 and a "transparent" satellite 304 for extending the range of the Uu interface. The satellite 304 implements frequency conversion and radio frequency (RF) amplifiers in both the uplink and downlink directions. The satellite function is similar to that of an analog RF repeater. Consequently, the satellite 304 repeats the uU radio interface from the feeder link (between the non-terrestrial network NTN gateway and the satellite) to the service link (between the satellite and the user equipment UE) in the downlink direction, and vice versa in the uplink direction. The satellite radio interface (SRI) on the feeder link is Uu, and the non-terrestrial network NTN gateway 302 supports all necessary functions to forward signals on the Uu interface. The non-terrestrial network NTN gateway 302 may be co-located with a base station (e.g., eNB or gNB) 104 or may be connected to the base station 104 via a wired link. It is also possible to connect multiple non-terrestrial network NTN gateways to a base station. Different transparent satellites can be connected to the same terrestrial base station via the same non-terrestrial network NTN gateway or via different non-terrestrial network NTN gateways.

[0032] Figure 3B shows a different type of non-terrestrial network NTN deployment with two different satellites (304 and 306) connected to the same base station 104 through the same non-terrestrial network NTN gateway 302. The two satellites (304 and 306) cover (possibly overlapping) areas on the Earth's surface by using two different Physical Cell IDs (PCIs).

[0033] The non-terrestrial network NTN user plane protocol stack UPPS, which includes user equipment UE 102, satellite 304, non-terrestrial network NTN gateway 302, new wireless NR base station (i.e., gNB) 104, and user plane function UPF 162, is shown in Figure 4A. The diagram of the non-terrestrial network NTN UPPS is similar to that of the terrestrial network TN, with the addition of two new nodes, the satellite 304 and the non-terrestrial network NTN gateway 302, which are located in the middle of the new wireless NR-Uu interface. Communication from / to the user equipment UE utilizes a physical layer 402, a MAC layer 404, and a radio link control (RLC) layer 406. Furthermore, communication from / to the user equipment UE utilizes a packet data convergence protocol (PDCP) 408 and a service data adaptation protocol (SDAP) 410. Communication to / from the gNB user plane function UPF uses the L1 layer 401 (i.e., 5G physical layer), the L2 layer 402 (i.e., 5G data link layer), and the Internet Protocol IP 405. Communication to / from the gNB user plane function UPF also uses the User Datagram Protocol UDP 407 and the General Packet Radio System GPRS Tunneling Protocol to carry user data GTP-U 409 (where the acronym GPRS stands for General Packet Radio System).

[0034] The control plane protocol stack CPPS of the non-terrestrial network NTN shown in Figure 4B is also similar to that of the terrestrial network TN. The differences between the user plane protocol stack UPPS of Figure 4A and the control plane protocol stack CPPS of Figure 4B will now be explained. Instead of the service data adaptation protocol SDAP 410 in the user plane protocol stack UPPS, the control plane protocol stack CPPS includes a radio resource control RRC layer 411. Furthermore, the stream control transmission protocol SCTP 413 and the next generation application protocol NGAP 414 replace UDP 407 and NGAP 409. Descriptions of these protocols and communication phases are given in the corresponding 3GPP® technical specifications.

[0035] With respect to satellite movement patterns, there are three types of service links supported in the non-terrestrial network NTN. Earth-fixed for satellites providing beam(s) that continuously cover the same geographic area (e.g., geostationary GEO / GSO satellites); Quasi-Earth-fixed for satellites that provide beam(s) covering one geographic area during limited periods and a different geographic area during other periods (e.g., low Earth orbit (LEO) / medium Earth orbit (MEO) satellites with steerable beams available); Earth moving type for satellites that provide beam(s) whose coverage area slides over the Earth's surface (e.g., low Earth orbit (LEO) / medium Earth orbit (MEO) satellites using fixed or non-steerable beams).

[0036] Thus, an eNB connected via a non-terrestrial network NTN can provide either quasi-Earth fixed cell coverage or Earth mobile cell coverage using low Earth orbit (LEO) / medium Earth orbit (MEO) satellites. The eNB provides Earth fixed cell coverage using geostationary Earth orbit (GEO) satellites.

[0037] While the transparent payload architecture shown in Figures 3A / 3B is the current focus of 3GPP® development, a regenerative payload architecture that installs base station (BS) functionality on the satellite is also a possible non-terrestrial network (NTN) deployment. In such an architecture, only Uu exists between the satellite and the user equipment (UE). In general, the techniques herein can be applied to both transparent payload architectures and regenerative payload architectures.

[0038] When time domain resources are allocated in a terrestrial network (TN), the spacing between the downlink control information (DCI) scheduling the uplink UL data transmission and the physical uplink shared channel (PUSCH) carrying the uplink UL data is indicated via a k2 value, which is indicated in the downlink control information (DCI) in terms of slots. Similarly, the spacing between the physical downlink shared channel (PDSCH) carrying the downlink DL data and the physical uplink control channel (PUCCH) carrying the user equipment (UE)'s HARQ feedback related to the received downlink DL data is indicated via a k1 value, which is indicated (also in terms of slots) in the downlink control information (DCI) scheduling the downlink DL data. When time domain resources are allocated in a non-terrestrial network (NTN), in addition to the above k1 and k2 values, the user equipment (UE) needs to further delay the physical uplink control channel (PUCCH) transmission or the physical uplink shared channel (PUSCH) transmission to compensate for signal propagation time. This additional delay is known as the scheduling delay "k_offset," which accounts for the round-trip delay between the user equipment (UE) and the base station. FIG. 5A shows an example illustrating the relationship between k_offset and propagation time to / from the user equipment UE in a non-terrestrial network (NTN) scenario. In this example, the downlink DL signal propagation time corresponds to four slots, so the user equipment UE_DL timing lags the base station BS_DL timing by four slots. To align the base station BS_DL timing with the base station BS_UL timing, the user equipment UE needs to perform physical uplink shared channel (PUSCH) / physical uplink control channel (PUCCH) transmissions with a timing advance (TA) equal to eight slots (i.e., twice the round trip delay or propagation time, since the uplink UL propagation time is the same as the downlink DL propagation time). In this case, when the base station BS schedules an uplink UL transmission for the user equipment UE, the base station BS needs to ensure that the shortest interval between the uplink UL transmission and the physical downlink control channel (PDCCH) that schedules the uplink UL transmission is eight slots.Otherwise, there is not enough time for the user equipment UE to prepare / perform uplink UL transmission by applying a timing advance TA of 8 slots, i.e., k_offset in this case must be at least 8 slots long.

[0039] 5B shows another example with two different user equipments UE, i.e., a first user equipment UE1 and a second user equipment UE2, served by the same base station BS / satellite. In this example, the second user equipment UE2 is relatively closer to the base station BS than the first user equipment UE1, so the propagation delay from the base station BS to the second user equipment UE2 (3 slots) is also smaller than the propagation delay from the base station BS to the first user equipment UE1 (4 slots). As a result, the first user equipment UE1 and the second user equipment UE2 need to apply timing advances TA equal to 8 slots and 6 slots, respectively, to align the base station BS_UL timing with the base station BS_DL timing. Since the first user equipment UE1 and the second user equipment UE2 apply different timing advances TA, the first user equipment UE1 and the second user equipment UE2 also have different k_offset values. In this example, the k_offset value of the first user equipment UE1 is 8 slots, while the k_offset value of the second user equipment UE2 is 6 slots.

[0040] In a non-terrestrial network (NTN) environment, in addition to the k1 and k2 values ​​already signaled in the physical downlink control channel (PDCCH), the base station BS also needs to signal a k_offset value to the user equipment UE before PDCCH delivery so that the user equipment UE can perform uplink UL transmission at the correct timing (e.g., k1+k_offset or k2+k_offset) as instructed by the base station BS. The k_offset is delivered to the user equipment UE via two components: (1) a cell-specific scheduling offset "cell-specific k_offset" and (2) a user equipment UE-specific scheduling offset "delta k_offset". The "cell-specific k_offset" is the common part of the k_offset values ​​that are the same for all user equipments UE in the same cell. The "delta k_offset" is the difference between the user equipment UE's actual k_offset value and the cell-specific k_offset value and is signaled to each user equipment UE individually. In one embodiment, a cell-specific k_offset value is broadcast in the (satellite-related) system information, which reflects the actual k_offset value of the user equipment UE that is farthest from the satellite. A differential k_offset value is signaled separately to the user equipment UE via a specific MAC_CE named "Differential Koffset_MAC_CE", which is then subtracted from the cell-specific k_offset value to obtain the actual k_offset value (i.e., the farther the user equipment UE is from the satellite, the smaller the differential k_offset).

[0041] In order to provide the user equipment UE with an accurate differential k_offset value, the base station BS needs to accurately know the round trip delay between the user equipment UE and the base station BS. The round trip delay corresponds to the timing advance TA applied by the user equipment UE when performing uplink UL transmission, so the base station BS can determine the differential k_offset value of the user equipment UE by obtaining the timing advance TA applied by the user equipment UE. In communication via a non-terrestrial network NTN (i.e., satellite 304) as shown in Figure 6, the user equipment UE has three components: (1) a common timing advance TA, (2) a user equipment UE-specific timing advance TA, and (3) a timing advance TA correction (collection) N. TA The common timing advance TA (i.e., common for all user equipments UE communicating to the same base station BS via the same satellite) is equal to twice the propagation time to / from the base station BS when the uplink time synchronization reference point is located at the first base station BS104 (i.e., in the case of a co-located non-terrestrial network NTN gateway 302 and the first base station BS104, 2 * D1 / c, where c is the speed of light). The user equipment UE-specific TA is equal to twice the propagation time to / from the satellite 304 depending on the distance D3 between the satellite 304 and the user equipment UE 102. That is, the user equipment UE-specific timing advance TA=2 * D3 / c. The common timing advance TA is known to the base station BS and can be broadcast in the system information block. The user equipment UE-specific timing advance TA is known to the user equipment UE but not to the base station BS. The user equipment UE can report timing advance TA information to make the base station BS aware of the user equipment UE-specific timing advance TA.

[0042] The user equipment UE receives timing advance correction (TA correction) N from the base station BS. TA7 shows how the user equipment UE performs uplink UL transmission (e.g., random access preamble transmission, physical uplink shared channel PUSCH transmission, or physical uplink control channel PUCCH transmission) by applying both the common timing advance TA and the user equipment UE-specific timing advance TA before receiving N. TA An example is shown below that demonstrates how the base station BS_DL timing is acquired. In this example, the propagation delay is four slots long, so the base station BS_DL timing lags the base station BS_DL timing by four slots. The user equipment UE first determines the UE-specific timing advance TA by acquiring the distance between the user equipment UE and the connected satellite. This can be calculated based on the GNSS information available at the user equipment UE and the ephemeris information provided by the network. The user equipment UE then acquires the common timing advance TA by acquiring satellite-related system information, and applies both the common timing advance TA and the UE-specific timing advance TA during uplink UL transmission. In this example, even after the user equipment UE applies both the common timing advance TA and the UE-specific timing advance TA, the base station BS_UL timing still lags the base station BS_DL timing by a small amount. Therefore, the base station BS sends a Timing Advance Command (TAC) MAC_CE to inform the user equipment UE of the amount of timing advance that the user equipment UE needs to further apply to align the base station BS_DL timing with the base station BS_UL timing. The additional timing advance amount provided in the Timing Advance Command TAC_MAC_CE is used to adjust the N TA and has to be applied by the user equipment UE starting from the next uplink UL transmission. In this example, the base station BS_UL timing lags the base station BS_DL timing, so N TA is a positive value, but if the base station BS_UL timing is ahead of the base station BS_DL timing, N TAcan be negative. N TA After obtaining the timing advance TA, the user equipment UE performs uplink UL transmission while performing full timing advance TA (common timing advance TA + user equipment specific timing advance TA + N TA ) and be able to apply them.

[0043] Unlike the terrestrial base station BS, the user equipment UE specific timing advance TA (i.e., the part of the complete timing advance TA) compensated by the user equipment UE is not known to the base station BS. Therefore, the non-terrestrial network NTN_base station BS sends a timing advance command MAC_CE (i.e., N TA ) the user equipment UE does not know the full timing advance TA that the user equipment UE will apply after transmitting the timing advance TA information element (TA_OFFSET). As a result, the non-terrestrial network NTN base station BS cannot estimate the round trip delay and must schedule uplink UL transmissions with an additional delay (i.e., k_offset) corresponding to the worst-case (i.e., longest) round trip delay between the user equipment UE and the base station BS. To make the non-terrestrial network NTN base station BS aware of the full timing advance TA of the user equipment UE, the 3GPP® user equipment UE is currently configured to report the full timing advance TA by sending a timing advance TA report MAC_CE to the base station BS. The user equipment UE reports its full timing advance TA to the base station BS under several circumstances. For example, the user equipment UE may receive a radio resource control (RRC) message with a timing advance TA reporting configuration (i.e., with a tar-Config information element). The timing advance TA reporting configuration is used to determine whether the user equipment UE should send another timing advance TA report, i.e., whether the timing advance TA currently applied by the user equipment UE is greater than or equal to X from the previously reported timing advance TA. offset The offset value used when the difference is greater than X offsetIn another example, upon handover to another base station BS or when re-establishing a radio resource control (RRC) connection to another base station BS, the user equipment UE sends a timing advance TA report to the new base station BS if it is instructed (i.e. receives an indication) in the handover command or in a system information broadcast message.

[0044] However, the existing strategy is unclear as to whether and under what conditions a user equipment (UE) in the radio resource control (RRC_INACTIVE) state should report its full timing advance (TA) when attempting to resume a radio resource control (RRC) connection (i.e., when sending a radio resource control (RRC) connection resume request message to the base station (BS)). If the user equipment (UE) does not report its full timing advance (TA) during the radio resource control (RRC) connection resume procedure, the base station (BS) must assume the worst case (i.e., the longest round-trip delay) while scheduling an uplink UL grant during the radio resource control (RRC) connection resume procedure, since it does not know the round-trip delay. This will prolong the entire radio resource control (RRC) connection resume procedure, resulting in increased mobile-originated (MO) or mobile-terminated (MT) data latency. On the other hand, forcing every user equipment (UE) to report its full timing advance (TA) during the radio resource control (RRC) connection resume procedure is not resource-efficient. This is because it requires the network to allocate larger MSG3 grant or MSGA_Physical Uplink Shared Channel PUSCH resources globally, which may ultimately result in wasted resources since the timing advance TA of a particular user equipment UE (e.g., a stationary user equipment UE) may not have changed since the user equipment UE last reported its timing advance TA.

[0045] The conventional approach also makes it unclear whether a user equipment (UE) in the radio resource control (RRC_INACTIVE) state should report its full timing advance (TA) to the base station (BS) when initiating or during a small data transmission (SDT) procedure. If the user equipment (UE) transmits all small data transmission (SDT) data in one go, it would be inefficient for the user equipment (UE) to report its timing advance (TA) because the user equipment (UE) would immediately return to the radio resource control (RRC_INACTIVE) state and the base station (BS) would not be able to utilize / apply the determined user equipment (UE)-specific scheduling offset (i.e., differential k_offset). On the other hand, if the user equipment (UE) has subsequent data transmissions following the first small data transmission, preventing the user equipment (UE) from reporting its full timing advance (TA) would result in overly conservative scheduling of the subsequent data transmissions, thereby increasing overall data latency. This document proposes techniques to minimize uplink (UL) data latency and avoid unnecessary signaling overhead for determining whether and when to report the user equipment (UE) timing advance (TA).

[0046] 8A-13 illustrate several scenarios in which a user equipment (UE) and / or a network element (NE; network entity, e.g., a base station (BS), a distributed unit (DU), or a central unit (CU)) performs techniques related to timing advance TA reporting by an inactive user equipment (UE). In these figures, time flows from the top to the bottom of the page. That is, a first action (e.g., signaling) occurs before a second action depicted directly below the first action. Similar events in FIGS. 8A-13 are labeled with similar reference numbers, and differences are explained below as necessary. For example, event 802 is similar to events 902, 1002, 1102, 1202, and 1302. For simplicity in the following description, the term "inactive state" refers to the radio resource control (RRC_INACTIVE) state or the radio resource control (RRC_IDLE) state. The terms "connected state" or "active state" refer to the radio resource control (RRC_CONNECTED) state.

[0047] 8A is a messaging diagram of a scenario 800A in which user equipment UE 102 communicates with a first base station BS 104 (more precisely, with a distributed unit DU 174 of the first base station BS 104) via a satellite 304. The first base station BS 104 comprises a central unit CU 172 and a distributed unit DU 174. The user equipment UE 102 initially operates in a connected state (802) and connects to the first base station BS 104 via a service link provided by the satellite 304. The user equipment UE 102 then receives system information from the distributed unit DU 174 (804), the system information comprising non-terrestrial network NTN-specific information comprising an ephemeris, a common timing advance TA, and a cell-specific k_offset (i.e., cellSpecificKoffset). The user equipment UE 102 may receive the system information before transitioning to the connected state. After that, the user equipment UE 102 acquires its GNSS coordinates, calculates the distance between the user equipment UE 102 and the satellite 304 according to the acquired ephemeris information and the GNSS coordinates, and determines a user equipment UE-specific timing advance TA based on the calculated distance (806). Later, the user equipment UE 102 applies both the common timing advance TA and the user equipment UE-specific timing advance TA while transmitting a random access (RA) preamble or uplink UL data to the distributed unit DU 174 (808). Upon receiving the random access RA preamble or uplink UL data, the distributed unit DU 174 first forwards the uplink UL data (if not a random access RA preamble) to the central unit CU 172 (810), and determines the N timing advance TA for the user equipment UE 102. TA Next, the user equipment UE 102 determines the value of N TA The timing advance command (TAC_MAC_CE) is transmitted with a value of 812. Events 804, 806, 808, 812, and optionally 810 correspond to the common timing advance TA, the user equipment (UE) specific timing advance TA, and N in FIG. TA , are collectively referred to as (and collectively shown in subsequent figures) as procedures 811 for obtaining the

[0048] The central unit CU 172 then generates a radio resource control RRC reconfiguration message comprising a timing advance TA reporting configuration (e.g., tar-Config) for the user equipment UE 102 and sends 814 a "central unit CU to distributed unit DU" message (e.g., a downlink DL_Radio Resource Control RRC_Message_Transfer message) comprising the radio resource control RRC reconfiguration message (e.g., a radio resource control RRCReconfiguration message) to the distributed unit DU 174. The distributed unit DU 174 then sends 816 the radio resource control RRC reconfiguration message to the user equipment UE 102. In some embodiments, the central unit CU 172 receives 816 a "distributed unit DU to central unit CU" message (e.g., a user equipment UE_Context_Modification_Required message or a user equipment UE_Context_Modification_Response message) comprising the timing advance TA reporting configuration from the distributed unit DU 174. In response to the timing advance TA reporting configuration, the user equipment UE 102 sends 818 to the distributed unit DU 174 an uplink UL_MAC_PDU comprising a Timing_Advance_Report_MAC_CE, where the Timing_Advance_Report_MAC_CE is the first complete timing advance TA value (i.e., common timing advance TA+user equipment UE specific timing advance TA+N) applied by the user equipment UE for uplink UL transmission. TAAfter receiving (e.g., in response to) the Timing_Advance_Report_MAC_CE, the distribution unit DU 174 transmits 820 to the user equipment UE 102 a Differential_Koffset_MAC_CE comprising the first differential k_offset value. In some embodiments, the distribution unit DU 174 determines the first differential k_offset value based on the first full timing advance TA value reported by the user equipment UE 102 and the cell-specific k_offset value. Since events 814, 816, 818, and 820 are reporting timing advance TA, the differential k_offset (N TA ) are collectively referred to as procedure 821 for obtaining (and collectively shown in subsequent figures).

[0049] In response to the radio resource control RRC reconfiguration message, the user equipment UE 102 sends a radio resource control RRC reconfiguration complete message to the distributed unit DU 174, which in turn sends the radio resource control RRC reconfiguration complete message to the central unit CU 174. In some embodiments, the user equipment UE 102 includes the radio resource control RRC reconfiguration complete message in an uplink UL_MAC_PDU of event 818. In other embodiments, the user equipment UE 102 sends the radio resource control RRC reconfiguration complete message to the distributed unit DU 174 in an uplink UL_MAC_PDU that is different from the uplink UL_MAC_PDU of event 818.

[0050] After the distributed unit DU 174 sends the first differential k_offset value to the user equipment UE 102, the central unit CU 172 determines a data inactivity state for the user equipment UE 102 (i.e., the user equipment UE 102 is in a connected state and is not exchanging data with the first base station BS 104). In response to the determination, the central unit CU 172 transitions the user equipment UE 102 to an inactive state by sending a "central unit CU to distributed unit DU" message (e.g., a user equipment UE_Context_Release_Command message) comprising a radio resource control RRC release message (e.g., a radio resource control RRC Release message) (822). In some embodiments, the radio resource control RRC release message comprises a SuspendConfig information element (IE) that configures the user equipment UE 102 to transition to the inactive state. The distributed unit DU 174 then sends a radio resource control (RRC) release message to the user equipment UE 102 (824), and in some embodiments, the distributed unit DU 174 may send a "Distributed Unit DU to Central Unit CU" message to the central unit CU 172 (825) comprising the first full timing advance TA value and / or the first differential k_offset value of the user equipment UE 102. After sending the "Distributed Unit DU to Central Unit CU" message to the central unit CU 172 (825) comprising the first full timing advance TA value and / or the first differential k_offset value of the user equipment UE 102, the distributed unit DU 174 may release / discard the first full timing advance TA value and / or the first differential k_offset value of the user equipment UE 102. In response to the radio resource control (RRC) release message or the SuspendConfig_IE, the user equipment UE 102 may then update the timing advance TA reporting configuration (e.g., X provided in the TA_Release_Config_IE). offset value) and transitions to the inactive state (826).

[0051] Later, the user equipment UE 102 in the inactive state decides to resume the active state (805), i.e., the user equipment UE initiates a radio resource control (RRC) connection resumption procedure to transmit uplink UL data, responding to the paging message received from the distributed unit DU 174, or performing a radio access network RAN-based area notification update RNAU. Meanwhile, the user equipment UE 102 determines whether the difference between the complete timing advance TA value currently applied by the user equipment UE 102 (i.e., the second complete timing advance TA value) and the first complete timing advance TA value reported at event 818 is equal to or greater than the value X configured in the timing advance TA reporting configuration. offsetThe user equipment UE 102 determines (879A) that the timing advance value TA_Report_MAC is equal to or greater than the threshold value (i.e., meets the threshold criterion), and therefore determines to transmit a second complete timing advance (TA) value to the base station BS during a radio resource control (RRC) connection resumption procedure. In response to the determination, the user equipment UE 102 initiates a random access (RA) procedure using the distributed unit DU 174 (828A) and selects a group of random access RA preambles by taking into account the size of the timing advance TA_Report_MAC. In some embodiments, the random access RA procedure is a four-step random access RA procedure. In other embodiments, the random access RA procedure is a two-step random access RA procedure. In response to initiating the random access RA procedure, the user equipment UE 102 transmits a random access RA preamble of the selected random access RA preamble group to the distributed unit DU 174. In the case of a four-step random access RA procedure, the distributed unit DU 174 transmits a random access RA response to the user equipment UE 102 in response to the random access RA preamble. The random access RA response comprises an uplink UL grant used by the user equipment UE 102 to transmit 830A an uplink UL_MAC_PDU (MPDU: MAC Protocol Data Unit) comprising a radio resource control RRC resume request message (e.g., a radio resource control RRC ResumeRequest message) and a TA_Report_MAC_CE comprising the second complete timing advance TA value to the distributed unit DU 174. In the case of a two-step random access RA procedure, the user equipment UE 102 transmits 830A an MPDU comprising a radio resource control RRC resume request message and a TA_Report_MAC_CE comprising the second complete timing advance TA value to the distributed unit DU 174 using the uplink UL grant indicated in the system information broadcast by the distributed unit DU 174.

[0052] Upon receiving the uplink_MAC protocol data unit UL_MPDU comprising the radio resource control RRC resume request message and the timing advance TA_Report_MAC_CE, the distributed unit DU 174 transmits a "Distributed Unit DU to Central Unit CU" message (e.g., an Initial_Uplink UL_RRC_Message_Transfer message) comprising the radio resource control RRC resume request message to the central unit CU 172 (832A), while also transmitting a downlink_MAC protocol data unit DL_MPDU comprising the Contention_Resolution_ID_MAC_CE to the user equipment UE 102 for contention resolution (834A). In some embodiments, the distributed unit DU 174 may include a Differential_Koffset_MAC_CE comprising the second differential k_offset value in the downlink DL_MPDU at event 834A. Alternatively, the distributed unit DU 174 may transmit the Differential_Koffset_MAC_CE at event 838A. In some embodiments, the distribution unit DU 174 determines the second differential k_offset value based on the second full timing advance TA value reported by the user equipment UE 102 and the cell-specific k_offset value.

[0053] In response to the radio resource control RRC Resume Request message, the central unit CU 172 sends a “Central Unit CU to Distributed Units DU” message (836A) to the distributed unit DU 174, comprising a radio resource control RRC Resume message (e.g., a radio resource control RRCResume message), which sets up a new timing advance TA reporting configuration for the user equipment UE 102 (i.e., comprises a SetupRelease{TAR-Config} type with the option “setup”). The new timing advance TA reporting configuration at event 836A may be similar to or different from the timing advance TA reporting configuration at event 814. The distributed unit DU 174 then sends a radio resource control RRC Resume message (838A) to the user equipment UE 102. Upon receiving the new timing advance TA reporting configuration, the user equipment UE 102 replaces the timing advance TA reporting configuration received at event 814 with the timing advance TA reporting configuration received at event 838A. In some embodiments, the distributed unit DU 174 receives a "Distributed Unit DU from Central Unit CU 172" message before sending the Contention_Resolution_ID_MAC_CE to the user equipment UE 102. In such a case (i.e., event 836A occurs before event 834), the distributed unit DU 174 may send a downlink DL_MAC_PDU to the user equipment UE 102 comprising the Contention_Resolution_ID_MAC_CE and a radio resource control RRC resume message (i.e., 834A and 838A may be combined) and may also include the Differential_Koffset_MAC_CE in the downlink DL_MAC_PDU. In some embodiments, the radio resource control RRC resume message at 836A / 838A does not include the timing advance TA reporting configuration (i.e., except for the tar-Config_IE), thereby causing the user equipment UE 102 to apply the timing advance TA reporting configuration it maintained before transitioning to the inactive state at event 824.

[0054] Upon receiving the radio resource control RRC Resume message with the new timing advance TA reporting configuration or without the tar-Config_IE, the user equipment UE 102 transitions to a connected state (840) and sends an uplink UL_MPDU with a radio resource control RRC Resume Complete message (e.g., a radio resource control RRC ResumeComplete message) and a TA_Report_MAC_CE with the third complete timing advance TA value to the distributed unit DU 174 (842A). The distributed unit DU 174 then sends a "distributed unit DU to central unit CU" message (e.g., an uplink UL_RRC_Message_Transfer message) with the radio resource control RRC Resume Complete message to the central unit CU 174 (844). After receiving the TA_Report_MAC_CE, the distributed unit DU 174 determines a third differential k_offset value based on the third complete timing advance TA value reported by the user equipment UE 102 and the cell-specific k_offset value. In some embodiments, the distribution unit DU 174 may transmit (846) Differential_Koffset_MAC_CE to the user equipment UE 102. In some embodiments, if the determined third differential k_offset value is similar to the second differential offset value that the distribution unit DU 172 transmitted in event 834A, the distribution unit DU 172 may omit event 846 (i.e., do not transmit Differential_Koffset_MAC_CE). Note that steps 842A, 844, and 846 are possible but not required.

[0055] In some embodiments, the user equipment UE 102 has already reported a second complete timing advance TA value in the same radio resource control RRC restart procedure, and the difference between the third complete timing advance TA and the second complete timing advance TA is less than the configured value X offsetSince the third complete timing advance TA value is less than 842A, in response to event 838A, the user equipment UE 102 transmits to the distributed unit DU 174 an uplink UL_MPDU that does not include the third complete timing advance TA value (842A).

[0056] Figure 8B is a messaging diagram of a scenario 800B that is similar to the scenario 800A shown in Figure 8A. The differences between Figure 8A and Figure 8B are described below. In response to sending 832A a "distributed unit DU to central unit CU" message comprising a radio resource control RRC resume request message to the central unit CU 172, the distributed unit DU 174 receives 836B a "central unit CU to distributed unit DU" message comprising a radio resource control RRC resume message releasing the first timing advance TA reporting configuration (i.e., comprising a SetupRelease{TAR-Config} type having the option "RELEASE"). The distributed unit DU 174 then sends 838B a radio resource control RRC resume message comprising an instruction to cause the user equipment UE 102 to release the first timing advance TA reporting configuration.

[0057] Upon receiving the radio resource control RRC resume message with an instruction to release the first timing advance TA reporting configuration, the user equipment UE 102 transitions to a connected state (840) and sends a downlink DL_MPDU comprising only a radio resource control RRC resume complete message (e.g., a radio resource control RRCResumeComplete message) to the distributed unit DU 174 (842B). Unlike in event 842A, the user equipment UE 102 does not send a full timing advance TA value at event 842B because in this scenario the user equipment UE 102 has discarded the first timing advance TA reporting configuration. The distributed unit DU 174 then sends a "distributed unit DU to central unit CU" message (e.g., an uplink UL_RRC_Message_Transfer message) transferring the radio resource control RRC resume complete message to the central unit CU 174 (844).

[0058] Figure 8C is a messaging diagram of a scenario 800C, which is similar to the scenario 800A shown in Figure 8A. The differences between Figure 8A and Figure 8C are explained below. After the user equipment UE 102 in an inactive state decides 805 to resume an active state (i.e., has initiated a radio resource control (RRC) connection resumption procedure to transmit uplink UL data, and has responded to a paging message received from the distributed unit DU 174 or has performed a radio access network RAN-based area notification update RNAU), the user equipment UE 102 determines whether the difference between the full timing advance TA value currently applied by the user equipment UE (i.e., the second full timing advance TA value) and the first full timing advance TA value reported at event 818 (shown in Figure 8A) is equal to the value X configured in the timing advance TA reporting configuration. offset(i.e., does not meet the threshold criterion) (879C). Therefore, unlike scenario 800A, the user equipment UE decides not to transmit the second complete timing advance (TA) value to the base station BS during the radio resource control (RRC) connection resumption procedure. Considering this decision, the user equipment UE 102 initiates a random access (RA) procedure using the distributed unit DU 174 (828C) and selects a random access RA preamble group by excluding the size of the timing advance TA_Report_MAC_CE. To initiate the random access RA procedure, the user equipment UE 102 transmits a random access RA preamble belonging to the selected random access RA preamble group to the distributed unit DU 174. In the case of a four-step random access RA procedure, the distributed unit DU 174 transmits a random access RA response to the user equipment UE 102 in response to the random access RA preamble. The random access RA response comprises an uplink UL grant used by the user equipment UE 102 to transmit 830C an uplink UL_MAC_PDU (MPDU) comprising only a radio resource control RRC resume request message (e.g., a radio resource control RRC ResumeRequest message). In the case of a two-step random access RA procedure, the user equipment UE 102 transmits 830C a MAC protocol data unit MPDU comprising only a radio resource control RRC resume request message by using the uplink UL grant indicated in the system information broadcast by the distributed unit DU 174.

[0059] Upon receiving the uplink UL_MPDU comprising only the radio resource control RRC resume request message (830C), the distributed unit DU 174 sends a "distributed unit DU to central unit CU" message (e.g., Initial_Uplink UL_Radio Resource Control RRC_Message_Transfer message) for transferring the radio resource control RRC resume request message to the central unit CU 172 (832C). The "distributed unit DU to central unit CU" message further comprises an IE / field "Request_TA" for retrieving pre-inactive state timing advance TA information of the user equipment UE maintained in the central unit CU, i.e., for requesting a first full timing advance TA value and / or a first differential k_offset value of the user equipment UE 102 from the central unit CU 174. In response to the “distributed unit DU to central unit CU” message, the central unit CU 172 sends (836C) to the distributed unit DU 174 a “central unit CU to distributed unit DU” message comprising a radio resource control RRC message (e.g., a radio resource control RRCResume message), a first full timing advance TA value of the user equipment UE 102, and / or a first differential k_offset value of the user equipment UE 102. When the message comprises a timing advance TA reporting configuration, it may set up a new timing advance TA reporting configuration for the user equipment UE 102.

[0060] Upon receiving the "distributed unit DU from central unit CU 172" message at event 836C, the distributed unit DU 174 transmits a downlink DL_MPDU comprising a Contention_Resolution_ID_MAC_CE to the user equipment UE 102 for contention resolution (834C), and then transmits a radio resource control RRC resume message to the user equipment UE 102 (838C). The distributed unit DU 174 may include a Differential_Koffset_MAC_CE conveying a second differential k_offset value of the user equipment UE 102 in the downlink DL_MPDU transmitted at event 834C. Alternatively, the distributed unit DU 174 may transmit the Differential_Koffset_MAC_CE in the message transmitted at event 838C. The distributed unit DU 174 may send a downlink DL_MPDU comprising the Contention_Resolution_ID_MAC_CE, the Differential_Koffset_MAC_CE, and the radio resource control RRC resumption message to the user equipment UE 102 (834C). The distributed unit DU 174 may determine a second differential k_offset value for the user equipment UE 102 based on the first differential k_offset value received at event 836C. Alternatively, the distributed unit DU 174 may determine the second differential k_offset value for the user equipment UE 102 based on the first complete timing advance TA value and the cell-specific k_offset value received at event 836C.

[0061] Figure 8D is a messaging diagram of a scenario 800D that is similar to the scenario 800C shown in Figure 8C. The differences between Figure 8D and Figure 8C are explained below. In scenario 800D, after sending a "distributed unit DU to central unit CU" message comprising a radio resource control RRC resume request message to the central unit CU 172 (832C), the distributed unit DU 174 receives a "central unit CU to distributed unit DU" message comprising a radio resource control RRC resume message that releases the previous timing advance TA reporting configuration (i.e., comprises a SetupRelease{TAR-Config} type with the option "RELEASE") (836C). The distributed unit DU 174 then sends a radio resource control RRC resume message to the user equipment UE 102 (838D).

[0062] Upon receiving the radio resource control RRC resume message, the user equipment UE 102 transitions to the connected state 840 and sends a downlink DL_MPDU comprising only a radio resource control RRC resume complete message (e.g., a radio resource control RRCResumeComplete message) to the distributed unit DU 174 (842B). Compared to event 842A, the user equipment UE 102 has discarded the timing advance TA reporting configuration in this scenario, so the user equipment UE 102 does not send the full timing advance TA value at event 842B. The distributed unit DU 174 then sends a "distributed unit DU to central unit CU" message (e.g., an uplink UL_RRC_Message_Transfer message) transferring the radio resource control RRC resume complete message to the central unit CU 174 (844).

[0063] 9A is a messaging diagram of a scenario 900A in which a user equipment UE 102, configured to report a timing advance (TA) before entering an inactive state while in an initial cell (i.e., communicating with a base station 104 using a satellite 304), moves to a new cell (i.e., communicating with a base station 104 using a satellite 304). In this scenario 900A, the new cell does not broadcast a positive indication in the system information requesting the user equipment UE to report a timing advance (TA) upon establishing / re-establishing / resuming a radio resource control (RRC) connection with the new cell. The user equipment UE 102 initially operates in a connected state (902) and connects to a first base station BS 104 via a service link for the first cell provided by the satellite 304. The user equipment UE 102 and the base station 104 then report a common timing advance (TA), a user equipment UE-specific timing advance (TA), and N TA , and timing advance TA, and reports the differential k_offset (i.e., N TA8A , and the first base station BS104 is not necessarily a distributed base station. For example, in step 921, the user equipment UE 102 receives a first timing advance TA reporting configuration in a radio resource control RRC reconfiguration message from the first base station BS104, transmits a first full timing advance TA value to the first base station BS104, and receives a first differential k_offset value from the first base station BS104. After performing steps 911 and 921, the user equipment UE 102 receives a radio resource control RRC release message from the first base station BS104 (924) and transitions to an inactive state in response to the radio resource control RRC release message. The user equipment UE 102 subsequently selects or reselects and camps (927) on a second cell (e.g., cell 126 of FIG. 1A) supported by a second base station BS 106 via the satellite 306. When the second base station BS 106 establishes / re-establishes / resumes a radio resource control (RRC) connection while camped on the second cell (i.e., flag_TA_report is absent or indicates a "false" value), the second base station BS 106 broadcasts (950) system information that does not include a positive indication for the user equipment UE to report a timing advance (TA). The user equipment UE 102 camped on the second cell decides to initiate resumption of the active state via a radio resource control (RRC) resumption procedure with the second base station BS 106 to transmit uplink UL data, respond to paging information received from the second base station BS 106, or perform a radio access network (RAN) notification area update. To initiate a radio resource control RRC connection resumption procedure, the user equipment UE 102 initiates 928 a random access RA procedure (e.g., a two-step random access RA or a four-step random access RA procedure) with the second base station BS 106 and sends 930 a radio resource control RRC resumption request message to the second base station BS 106. In this scenario, the user equipment UE 102 decides not to report a second complete timing advance (TA) value to the second base station BS 106 during the radio resource control RRC connection resumption procedure.Because the system information of the new cell (satellite 306, second base station BS106) does not include a positive indication to report the timing advance TA upon performing a radio resource control RRC connection establishment / re-establishment / resumption procedure with the new cell, the user equipment UE 102 may release the first timing advance TA reporting configuration received from the first base station BS 104 in response to selecting, reselecting, or camping on the second cell, or in response to initiating a radio resource control RRC connection resumption procedure with the second cell. Thus, the user equipment UE 102 transmits 930 an uplink UL_MAC_PDU comprising a radio resource control RRC resumption request message to the second base station BS 106 without including the timing advance TA_Report_MAC_CE. In response to receiving the radio resource control RRC resumption request, the second base station BS106 (or the central unit CU of the second base station BS106) sends a Retrieve_UE_Context_Reeq user equipment UExp message to the first base station BS104 (or to the central unit CU of the first base station BS104) (932). The second base station BS106 then receives a Retrieve_UE_Context_Response message from the first base station BS104 (or from the central unit CU of the first base station BS104) (936). The second base station BS106 may include an IE / field “Request_TA” in the Retrieve_UE_Context_Request message to request a first full timing advance TA value, a first different k_offset value, and / or a first timing advance TA reporting configuration for the user equipment UE102. The first base station BS104 may include the first full timing advance TA value, the first differential k_offset value, and / or the first timing advance TA reporting configuration in a Retrieve_UE_Context_Response message in response to the IE / field "Request_TA" included in the Retrieve_UE_Context_Request message.The first base station BS104 may include the first full timing advance TA value, the first differential k_offset value, and / or the first timing advance TA reporting configuration in the Retrieve_UE_Context_Response message regardless of the content in the Retrieve_UE_Context_Request message. The second base station BS106 may release the first timing advance TA reporting configuration. The first base station BS104 may refrain from including the first timing advance TA reporting configuration in the Retrieve_UE_Context_Response message, and the first base station BS104 may release the first timing advance TA reporting configuration after sending the Retrieve_UE_Context_Response message.

[0064] After receiving the Retrieve_UE_Context_Response message, the second base station BS 106 sends a radio resource control RRC Resume message setting up a new (i.e., second) timing advance TA reporting configuration (e.g., tar-Config) for the user equipment UE 102 (938A). The second timing advance TA reporting configuration may be similar to or different from the first timing advance TA reporting configuration. The second base station BS 106 may generate the second timing advance TA reporting configuration based on the first timing advance TA reporting configuration or may generate the second timing advance TA reporting configuration independently of the first timing advance TA reporting configuration. In response to the radio resource control RRC Resume message, the user equipment UE 102 transitions to a connected (i.e., active) state (940) and sends a radio resource control RRC Resume Complete message to the second base station BS 106 (942A). The user equipment UE 102 may generate a TA_Report_MAC_CE comprising a second full timing advance TA value for the user equipment UE 102 in response to the second timing advance TA reporting configuration. The user equipment UE 102 may send an uplink UL_MPDU comprising a radio resource control RRC resume complete message and the timing advance TA_Report_MAC_CE to the second base station BS 106 (942A), or may send the uplink UL_MPDU comprising the timing advance TA_Report_MAC_CE to the second base station BS 106 after sending the radio resource control RRC resume complete message. After receiving the TA_Report_MAC_CE from the user equipment UE 102, the second base station BS 106 determines a second differential k_offset value for the user equipment UE 102 and then sends a downlink DL_MPDU comprising a Differential_Koffst_MAC_CE comprising the second differential k_offset value to the user equipment UE 102 (946).

[0065] Figure 9B is a messaging diagram of scenario 900B, which is similar to scenario 900A shown in Figure 9A. The differences between Figure 9A and Figure 9B are described below. After having received (936) the Retrieve_UE_Context_Response message, the second base station BS106 determines not to obtain timing advance TA information from the user equipment UE. In consideration of this decision, the second base station BS106 releases the first timing advance TA reporting configuration of the user equipment UE 102 in a radio resource control RRC Resume message (i.e., with a SetupRelease{TAR-Config} type having the option "Release"). The second base station BS106 then sends (938B) a radio resource control RRC Resume message to the user equipment UE 102. In response to receiving the radio resource control RRC Resume message releasing the timing advance TA reporting configuration, the user equipment UE 102 refrains from reporting timing advance TA information (e.g., a second complete timing advance TA value) to the second base station BS106. If the user equipment UE102 releases the first timing advance TA reporting configuration when selecting, reselecting or camping on the second cell, or when initiating a radio resource control RRC connection resumption procedure on the second cell, the second base station BS106 may omit the release indication in the radio resource control RRC resumption message.

[0066] Figure 9C is a messaging diagram for scenario 900C, which is similar to scenario 900A shown in Figure 9A. The differences between Figures 9A and 9C are described below. In scenario 900C, user equipment UE 102 retains a first timing advance TA reporting configuration in response to selecting, reselecting, or camping on a second cell, or in response to initiating a radio resource control RRC connection resumption procedure on the second cell. In this scenario, the first base station BS 104 includes the first timing advance TA reporting configuration in the Retrieve_UE_Context_Response message (936), and the second base station BS 106 determines to retain the first timing advance TA reporting configuration for the user equipment UE 102. Therefore, after receiving the Retrieve_UE_Context_Response message, the second base station BS 106 sends a radio resource control RRC resumption message to the user equipment UE 102 without including any timing advance TA reporting configuration (i.e., without including tar-Config) (938C). After receiving (e.g., in response to) a radio resource control RRC resumption message that excludes the timing advance TA reporting configuration, the user equipment UE 102 transitions to a connected state (940) and continues to use the first timing advance TA reporting configuration until the difference between the first full timing advance TA value reported in step 921 and the full timing advance TA value currently applied by the user equipment UE 102 (i.e., the second full timing advance TA value) exceeds a threshold X offset In this scenario, the timing advance TA difference is greater than or equal to the threshold X offsetSince the threshold criterion is met by being equal to or greater than (or alternatively, slightly greater than) the second complete timing advance TA value, the user equipment UE 102 determines to report the second complete timing advance TA value to the second base station BS 106. The user equipment UE 102 transmits (942A) a radio resource control RRC resume complete message and an uplink UL_MPDU comprising the timing advance TA_Report_MAC_CE (TA_Report_MAC_CE comprising the second complete timing advance TA value of the user equipment UE 102) to the second base station BS 106. After transmitting the radio resource control RRC resume complete message, the user equipment UE 102 may transmit the uplink UL_MPDU comprising the timing advance TA_Report_MAC_CE to the second base station BS 106. The second base station BS106 then (after receiving the TA_Report_MAC_CE from the user equipment UE102) determines a second differential k_offset value for the user equipment UE102 and transmits 946 a downlink DL_MPDU to the user equipment UE102 comprising a Differential_Koffset_MAC_CE comprising the second differential k_offset value.

[0067] Figure 9D is a messaging diagram of a scenario 900D that is similar to the scenario 900C shown in Figure 9C. The differences between Figure 9C and Figure 9D are explained below. In scenario 900D, the user equipment UE 102 receives a message when the timing advance TA difference is greater than a threshold X offsetThe user equipment UE 102 determines (979D) that the second differential k_offset value for the user equipment UE 102 is less than TA, and therefore, the user equipment UE decides not to report the second complete timing advance TA value to the second base station BS 106. In consideration of this decision, the user equipment UE 102 transmits (942B) an uplink UL_MPDU comprising only a radio resource control RRC resume complete message to the second base station BS 106. After receiving the radio resource control RRC resume complete message, the second base station BS 106 determines (946) a second differential k_offset value for the user equipment UE 102 based on the first differential k_offset value for the user equipment UE 102 previously received at event 936, and then transmits (946) a downlink DL_MPDU to the user equipment UE 102 comprising a Differential_Koffset_MAC_CE comprising the second differential k_offset value.

[0068] 10A is a messaging diagram for scenario 1000A. User equipment UE 102, previously configured with a timing advance TA reporting configuration, moves to a new cell, which broadcasts a positive indication in the system information for the user equipment UE to report timing advance TA information upon establishing / re-establishing / resuming a radio resource control (RRC) connection with the new cell. In scenario 1000A, user equipment UE 102 initially operates in a connected (active) state connected to a first base station BS 104 in a first cell via a service link provided by a satellite 304 (1002). The user equipment UE 102 and base station 104 then communicate a common timing advance TA, a user equipment UE-specific timing advance TA, and a N TA, and procedure 1021 (similar to procedure 821) for reporting the timing advance TA and obtaining the differential k_offset. In procedure 1021, the user equipment UE 102 receives a first timing advance TA reporting configuration in a radio resource control RRC reconfiguration message from the first base station BS 104, sends a first full timing advance TA value to the first base station BS 104, and receives a first differential k_offset value from the first base station BS 104. After performing procedures 1011 and 1021, the user equipment UE 102 receives a radio resource control RRC release message from the first base station BS 104 (1024) and transitions to an inactive state in response to the radio resource control RRC release message (1026). The user equipment UE 102 subsequently selects or reselects and camps 1027 on a second cell (e.g., cell 126 of FIG. 1A) supported by a second base station BS 106 via the satellite 306. The second base station BS 106 establishes / reestablishes / resumes a radio resource control (RRC) connection with the second cell (i.e., flag_TA_report is present and indicates a value of "true") and broadcasts 1050 system information with a positive indication for the user equipment UE to report a timing advance (TA). The user equipment UE 102 camping on the second cell transmits uplink UL data and determines 1005 to initiate a radio resource control (RRC) connection resumption procedure with the second base station BS 106 to respond to paging information received from the second base station BS 106 or to perform a radio access network (RAN) notification area update. After this determination, the user equipment UE102 checks the difference between the first full timing advance TA value reported in procedure 1021 and the full timing advance TA value currently applied by the user equipment UE102 (i.e., the second full timing advance TA value) and determines (1079A) that the difference is greater than or equal to the threshold Xoffset included in the first timing advance TA reporting configuration.Further to events 1005 and 1079A, the user equipment UE 102 then initiates a random access RA procedure (e.g., a two-step random access RA or a four-step random access RA procedure) (1028A) and selects a random access RA preamble group by considering the size of the timing advance TA_Report_MAC. The user equipment UE 102 then transmits to the second base station BS 106 (1030A) a radio resource control RRC resume request message using the uplink UL resources obtained by initiating the random access RA procedure, the uplink UL_MPDU including the TA_Repport_MAC_CE including the second full timing advance TA value. In response to receiving the radio resource control RRC Resume Request message and the timing advance TA_Report_MAC_CE, the second base station BS106 (or the central unit CU of the second base station BS106) sends a Retrieve_UE_Context_Request message to the first base station BS104 (or the central unit CU of the first base station BS104) (1032A) and also sends a downlink DL_MPDU comprising a Contention_Resolution_ID_MAC_CE to the user equipment UE 102 for contention resolution (1034A). The second base station BS106 (or the central unit CU of the second base station BS106) may include a Differential_Koffset_MAC_CE comprising the second differential k_offset value in the downlink DL_MPDU at event 1034A. Alternatively, the second base station BS106 (or the central unit CU of the second base station BS106) may send the differential Differential_Koffset_MAC_CE at event 1038A. The second base station BS106 (or the central unit CU of the second base station BS106) may determine a second differential k_offset value based on the second complete timing advance TA value reported by the user equipment UE102 and the cell-specific k_offset value of the cell currently selected by the user equipment UE102 (e.g., cell 126).

[0069] In response to the radio resource control RRC Resume Request message, the first base station BS104 (or a central unit CU of the first base station BS104) sends a Retrieve_UE_Context_Response message to the second base station BS106 (1036A). The first base station BS104 may include the first full timing advance TA value, the first differential k_offset value, and / or the first timing advance TA reporting configuration in the Retrieve_UE_Context_Response message. The second base station BS106 may release the first timing advance TA reporting configuration. The first base station BS104 may refrain from including the first timing advance TA reporting configuration in the Retrieve_UE_Context_Response message. The first base station BS104 may then release the first timing advance TA reporting configuration in response to sending the Retrieve_UE_Context_Response message.

[0070] After receiving the Retrieve_UE_Context_Response message, the second base station BS 106 sends a radio resource control RRC Resume message setting up a new (i.e., second) timing advance TA reporting configuration (e.g., tar-Config) for the user equipment UE 102 (1038A). The second timing advance TA reporting configuration may be similar to or different from the first timing advance TA reporting configuration. That is, the second base station BS 106 may generate the second timing advance TA reporting configuration based on the first timing advance TA reporting configuration, or may generate the second timing advance TA reporting configuration independently of the first timing advance TA reporting configuration. In some embodiments, the base station BS does not include the timing advance TA reporting configuration in the radio resource control RRC Resume message. In response to the radio resource control RRC Resume message, the user equipment UE 102 transitions to a connected (active) state (1040) and sends a radio resource control RRC Resume Complete message to the second base station BS 106 (1042A). In response to a radio resource control RRC resume message with the second timing advance TA reporting configuration or without the timing advance TA reporting configuration, the user equipment UE 102 may generate a TA_Report_MAC_CE with a third complete timing advance TA value for the user equipment UE 102. The user equipment UE 102 may send 1042A a radio resource control RRC resume complete message and an uplink UL_MPDU with the timing advance TA_Report_MAC_CE to the second base station BS 106, or may send the uplink UL_MPDU with the timing advance TA_Report_MAC_CE to the second base station BS 106 after sending the radio resource control RRC resume complete message.After receiving the TA_Report_MAC_CE from the user equipment UE 102, the second base station BS 106 determines a third differential k_offset value for the user equipment UE 102 and then transmits a downlink DL_MPDU to the user equipment UE 102 comprising a Differential_Koffset_MAC_CE comprising the third differential k_offset value (1046A).

[0071] If the user equipment UE 102 has already reported a second complete timing advance TA value in the same radio resource control RRC resume procedure, the difference between the third complete timing advance TA and the second complete timing advance TA is less than the configured value X in the timing advance TA reporting configuration. offset When it is less than 1042A, in response to event 1038A, the user equipment UE 102 may transmit a downlink DL_MPDU to the second base station BS 106 that does not include the third full timing advance TA value (1042A).

[0072] Figure 10B is a messaging diagram of scenario 1000B, which is similar to scenario 1000A shown in Figure 10A. The differences between Figure 10A and Figure 10B are explained below. In scenario 1000B, after having received the Retrieve_UE_Context_Response message 1036A, the second base station BS106 (or the central unit CU of the second base station BS106) sends a radio resource control RRC resumption message 1038B to the user equipment UE 102, releasing the first timing advance TA reporting configuration (i.e., having a Setup_Release(TAR-Config) type with option "RELEASE").

[0073] Upon receiving the radio resource control RRC Resume message, the user equipment UE 102 transitions to a connected (active) state 1040 and sends 1042B a downlink DL_MPDU comprising only a radio resource control RRC Resume Complete message (e.g., a radio resource control RRC ResumeComplete message) to the second base station BS 106. Unlike event 1042A, the user equipment UE 102 in this scenario has discarded the timing advance TA reporting configuration, so the user equipment UE 102 does not send a full timing advance TA value at event 1042B.

[0074] Figure 10C is a messaging diagram of a scenario 1000C, which is similar to the scenario 1000A shown in Figure 10A. The differences between Figure 10A and Figure 10C are explained below. After the user equipment UE 102 in an inactive state decides to resume an active state 1005 (to transmit uplink UL data and respond to a paging message received from the second base station BS 106 or to perform a radio access network RAN-based area notification update RNAU), the user equipment UE 102 determines whether the difference between the complete timing advance TA value currently applied by the user equipment UE (i.e., the second complete timing advance TA) and the first complete timing advance TA value reported in procedure 1021 is equal to the value X configured in the timing advance TA reporting configuration. offsetThe user equipment UE 102 then determines 1079C that the second complete timing advance TA value is smaller than the first complete timing advance TA value. The user equipment UE 102 then does not transmit the second complete timing advance TA value to the base station BS during the radio resource control RRC connection resumption procedure. The user equipment UE 102 initiates 1028C a random access (RA) procedure with the second base station BS 106 and selects a random access RA preamble group that excludes the size of the timing advance TA_Report_MAC_CE. The user equipment UE 102 initiates the random access RA procedure by transmitting a random access RA preamble from the selected random access RA preamble group to the second base station BS 106. In the case of a four-step random access RA procedure, the second base station BS 106 transmits a random access RA response to the random access RA preamble, the random access RA response comprising an uplink UL grant used by the user equipment UE 102 to transmit 1030C an uplink UL_MAC_PDU (MPDU) comprising only a radio resource control RRC resumption request message (e.g., a radio resource control RRC ResumeRequest message). In the case of a two-step random access RA procedure, the user equipment UE 102 transmits an MPDU comprising only a radio resource control RRC resume request message using the uplink UL grant indicated in the system information broadcast by the distributed unit DU 174 (1030C).

[0075] Upon receiving the uplink UL_MPDU comprising only the radio resource control RRC resume request message, the second base station BS106 sends a Retrieve_UE_Context_Request message to the first base station BS104 (1032C). The Retrieve_UE_Context_Request message further comprises an IE / field “Request_TA” used to request the first base station BS104 to provide the first (pre-inactive state) full timing advance TA value and / or the first differential k_offset value for the user equipment UE 102. In response to the Retrieve_UE_Context_Request message, the first base station BS104 sends a Retrieve_UE_Context_Response message to the second base station BS106 (1036C) comprising the first full timing advance TA value, the first differential k_offset value, and / or the first timing advance TA reporting configuration for the user equipment UE 102. After receiving the Retrieve_UE_Context_Response message, the second base station BS106 determines a second differential k_offset value for the user equipment UE 102 based on the first complete timing advance (TA) value of the user equipment UE 102 and the cell-specific k_offset value of the cell (e.g., cell 126) currently selected by the user equipment UE 102. Alternatively, the second base station BS106 determines the second differential k_offset value for the user equipment UE 102 based on the first (pre-inactive state) differential k_offset value of the user equipment UE 102. The second base station BS106 then transmits a downlink DL_MPDU comprising a Contention_Resolution_ID_MAC_CE for contention resolution (1034C). The second base station BS106 may include a Differential_Koffset_MAC_CE comprising the second differential k_offset value of the user equipment UE 102 in the downlink DL_MPDU at event 1034C.Alternatively, the second base station BS106 may transmit Differential_Koffset_MAC_CE at event 1038A, and a radio resource control RRC resumption message with or without a timing advance TA reporting configuration is transmitted to the user equipment UE102 in response to the radio resource control RRC resumption request message.

[0076] Figure 10D is a messaging diagram for scenario 1000D, which is similar to scenario 1000C shown in Figure 10C. The differences between Figure 10D and Figure 10C are explained below. After having received 1036C the Retrieve_UE_Context_Response message from the first base station BS104, the second base station BS106 sends 1038C to the user equipment UE102 a radio resource control RRC resumption message releasing the previous timing advance TA reporting configuration (i.e., with a SetupRelease{TAR-Config type} having option "RELEASE").

[0077] Upon receiving the radio resource control RRC Resume message, the user equipment UE 102 transitions to a connected (active) state 1040 and transmits 1042B an uplink UL_MPDU comprising only a radio resource control RRC Resume Complete message (e.g., a radio resource control RRC ResumeComplete message) to the second base station BS 106. Unlike event 1042A, in this scenario the user equipment UE 102 discards the first timing advance TA reporting configuration, so the user equipment UE 102 does not transmit a full timing advance TA value at event 1042B.

[0078] 11A is a messaging diagram of a scenario 1100A in which a user equipment UE configured with a timing advance TA reporting configuration performs a small data transmission SDT with the network using a single data transmission. In scenario 1100A, a user equipment UE 102 initially operates in a connected state communicating 1102 with a first base station BS 104 over a service link provided by a satellite 304 for a first cell. The user equipment UE 102 and the base station 104 then communicate a common timing advance TA, a user equipment UE-specific timing advance TA, and N TA, and a procedure 1121 (similar to 821) for reporting the timing advance TA and obtaining the differential k_offset value. In procedure 1121, the user equipment UE 102 has received a first timing advance TA reporting configuration in a radio resource control (RRC) reconfiguration message from the first base station BS 104 and transmits a first full timing advance TA value to the first base station BS 104. The user equipment UE 102 then receives the first differential k_offset value from the first base station BS 104. After performing procedures 1111 and 1121, the central unit CU172 determines a data inactivity state of the user equipment UE 102 (i.e., the user equipment UE 102 in a connected state has no data activity with the first base station BS 104). In response to the determination, the central unit CU 172 sends 1122 a "central unit CU to distributed unit DU" message (e.g., a user equipment UE_Context_Release_Command message) comprising a radio resource control RRC release message (e.g., a radio resource control RRCRelease message) to transition the user equipment UE 102 to an inactive state. The radio resource control RRC release message may include a SuspendConfig information element (IE) that configures the user equipment UE 102 to transition to an inactive state. In this case, the radio resource control RRC release message further comprises a small data transmission SDT configuration that enables the user equipment UE 102 to transmit user data of the inactive state. The distributed unit DU 174 then sends 1124 a radio resource control RRC release message to the user equipment UE 102. The distributed unit DU 174 may send to the central unit CU 172 a “Distributed Unit DU to Central Unit CU” message comprising the first complete timing advance TA value and / or the first differential k-offset value of the user equipment UE 102 (1125).

[0079] Later, in the inactive state, the user equipment UE 102 determines 1152 to perform a small data transmission SDT procedure due to arrival of uplink UL traffic belonging to a small data transmission SDT_Data Radio Bearer DRB / Signaling Radio Bearer SRB. In light of this decision, the user equipment UE 102 initiates 1128 a two-step or four-step random access (RA) procedure by transmitting a random access RA preamble allocated for small data transmission SDT purposes to the distributed unit DU 174 of the first base station BS 104. Upon receiving an uplink UL grant / resource in response to the random access RA preamble transmission, the user equipment UE 102 checks whether the uplink UL grant / resource is large enough to accommodate all pending small data transmission SDT data (i.e., pending uplink UL data belonging to small data transmission SDT_Data Radio Bearer DRB / Signaling Radio Bearer SRB) plus a radio resource control (RRC) resume request message. Since in this scenario the uplink UL grant / resources are large enough to accommodate all pending small data transmission SDT data and the radio resource control RRC resume request, the user equipment UE 102 decides to transmit all pending small data transmission SDT data in one go and therefore decides not to transmit a Buffer_Status_Report (BSR) MAC_CE on the uplink UL grant / resources 1154A. Following the decision, the user equipment UE 102 sends an MPDU comprising the radio resource control RRC resume request message and the pending small data transmission SDT data to the distributed unit DU 174 without including a buffer status report BSR_MAC_CE or a timing advance TA_Report_MAC_CE 1130A.

[0080] Upon receiving the uplink UL_MPDU comprising the radio resource control RRC resume request message and the uplink UL data, the distributed unit DU 174 sends 1132 to the central unit CU 172 a "Distributed Unit DU to Central Unit CU" message (e.g., Initial_Uplink UL_RRC_Message_Transfer message) comprising the radio resource control RRC resume request message, and then sends 1156 the uplink UL data to the central unit CU 172. The distributed unit DU 174 also sends 1134A to the user equipment UE 102 a downlink DL_MPDU comprising the Contention_Resolution_ID_MAC_CE for contention resolution. In response to the radio resource control RRC resume request message, the central unit CU 172 retrieves the context of the user equipment UE 102 and sends 1158 a “central unit CU to distributed unit DU” message comprising a radio resource control RRC release message (e.g., a radio resource control RRC release message) to the distributed unit DU 174, where the radio resource control RRC release message may further include a SuspendConfig_IE and a small data transmission SDT configuration. The distributed unit DU 174 then sends 1160 a radio resource control RRC release message to the user equipment UE 102. In this example, the distributed unit DU 174 receives the “central unit CU to distributed unit DU” message comprising the radio resource control RRC release message after sending the Contention_Resolution_ID_MAC_CE to the user equipment UE 102, but the distributed unit DU 174 is enabled to receive the “central unit CU to distributed unit DU” message before sending the Contention_Resolution_ID_MAC_CE to the user equipment UE 102. In such a case (ie, 1158 occurs earlier than 1134A), the distributed unit DU 174 may send the Contention_Resolution_ID_MAC_CE along with a radio resource control RRC release message to the user equipment UE 102 (ie, 1134A and 1160 may be combined).The user equipment UE 102 then transitions to the inactive state upon receiving a radio resource control RRC release message (1162).

[0081] Figure 11B is a messaging diagram of scenario 1100B, which is similar to scenario 1100A shown in Figure 11A. The differences between Figure 11A and Figure 11B are explained below. Similar to scenario 1100A, in scenario 1100B, upon receiving an uplink UL grant / resource in response to a random access RA preamble transmission at event 1128, the user equipment UE 102 checks whether the uplink UL grant / resource is large enough to accommodate all pending small data transmission SDT data (i.e., pending uplink UL data belonging to small data transmission SDT_Data Radio Bearers DRBs / Signaling Radio Bearers SRBs) plus radio resource control RRC recursion request messages. In scenario 1100B, since the uplink UL grant / resources are not large enough to accommodate all pending small data transmission SDT data and radio resource control RRC resume requests, the user equipment UE 102 segments the pending small data transmission SDT data and decides to transmit a buffer status report BSR_MAC_CE by using the available uplink UL grant / resources (1154B) to inform the network about the subsequent small data transmission SDT data transmission. The user equipment UE 102 then determines whether the difference between the complete timing advance TA value currently applied by the user equipment UE (i.e., the second complete timing advance TA value) and the first complete timing advance TA value reported in procedure 1121 is equal to or greater than the value X configured in the first timing advance TA reporting configuration. offset In scenario 1100B, the timing advance TA difference is checked to see if it is greater than or equal to the threshold (1179B). XoffsetSince the threshold criterion is met, the user equipment UE 102 sends an uplink UL_MPDU to the distributed unit DU 174 (1130B) comprising a radio resource control RRC resume request message, a buffer status report BSR_MAC_CE, and a TA_Report_MAC_CE comprising the second complete timing advance TA value. If the uplink UL grant / resources can accommodate the segment, the user equipment UE 102 may further include a segment of small data transmission SDT data in the transmitted MPDU at event 1130B.

[0082] Upon receiving the uplink UL_MPDU at event 1130B, the distributed unit DU 174 (A) sends 1132 to the central unit CU 172 a “Distributed Unit DU to Central Unit CU” message (e.g., Initial_Uplink_UL_RRC_Message_Transfer message) comprising a radio resource control RRC resume request message, (B) determines a second differential k_offset value for the user equipment UE 102 based on the user equipment UE 102's received second complete timing advance TA value, and (C) sends 1134B to the user equipment UE 102 a downlink DL_MPDU comprising a Contention_Resolution_ID_MAC_CE and a Differential_Koffset_MAC_CE comprising the second differential k_offset value. The distributed unit DU 174 may also send 1156 a segment of small data transmission SDT data to the central unit CU 172 if it received the segment of small data transmission SDT data at event 1130B.

[0083] In response to the radio resource control RRC Resume Request message, the central unit CU 172 retrieves the user equipment UE 102's context (e.g., timing advance TA information for the first / pre-inactive state) and sends 1158 a "central unit CU to distributed unit DU" message comprising a radio resource control RRCRelease message to the distributed unit DU 174. The radio resource control RRCRelease message may further include a SuspendConfig_IE and a small data transmission SDT configuration. Upon receiving 1164 the "central unit CU to distributed unit DU" message comprising the radio resource control RRC Release message, the distributed unit DU 174 sends 1164 a physical downlink control channel PDCCH comprising an uplink UL grant for the user equipment UE to the user equipment UE 102 to accommodate the subsequent data transmission indicated by receiving the buffer status report BSR_MAC_CE in step 1130B. In response to receiving the uplink UL grant, the user equipment UE 102 rechecks whether the uplink UL grant is large enough to accommodate all pending small data transmission SDT data. In this example, since the uplink UL grant provided in step 1164 is large enough to accommodate all pending small data transmission SDT data, the user equipment UE 102 determines to transmit all pending small data transmission SDT data in one go and therefore determines not to transmit a buffer status report BSR_MAC_CE in the uplink UL grant (1166). Following the determination, the user equipment UE 102 transmits an uplink UL_MPDU comprising only uplink UL data to the distribution unit DU 174 without including a buffer status report BSR_MAC_CE or a timing advance TA_Report_MAC_CE (1168). Upon receiving the uplink UL data, the distributed unit DU 174 transmits 1170 the uplink UL data to the central unit CU 172, and then transmits 1160 a radio resource control RRC release message to the user equipment UE 102. Upon receiving the radio resource control RRC release message, the user equipment UE 102 remains in an inactive state 1162.

[0084] Figure 11C is a messaging diagram of scenario 1100C, which is similar to scenario 1100B shown in Figure 11B. The differences between Figure 11C and Figure 11B are explained below. Similar to scenario 1100B, in scenario 1100C, the user equipment UE 102 has segmented the pending small data transmission SDT data and decides to send a buffer status report BSR_MAC_CE on the available uplink UL grant / resources (1154B) to inform the network about the subsequent small data transmission SDT data transmission. The user equipment UE 102 then determines whether the difference between the complete timing advance TA value currently applied by the user equipment UE (i.e., the second complete timing advance TA value) and the first complete timing advance TA value reported in procedure 1121 is equal to or greater than the value X configured in the first timing advance TA reporting configuration. offset Unlike in scenario 1100B, the timing advance TA difference is greater than or equal to the threshold X offset Since the timing advance TA difference is less than 1179C, the timing advance TA difference does not meet the threshold criterion and the user equipment UE sends an uplink UL_MPDU with a radio resource control RRC resume request message and a buffer status report BSR_MAC_CE (i.e., without the timing advance TA_Report_MAC_CE) to the distributed unit DU 174 1130C. If the uplink UL grant / resources can accommodate such a segment, the user equipment UE 102 may further include a segment of small data transmission SDT data in the MPDU sent at event 1130C.

[0085] Upon receiving the uplink UL_MPDU at event 1130C, the distributed unit DU 174 sends a "Distributed Unit DU to Central Unit CU" message (e.g., Initial_Uplink UL_RRC_Message_Transfer message) comprising a radio resource control RRC resume request message to the central unit CU 172 (1132C). The "Distributed Unit DU to Central Unit CU" message further comprises an IE / field "Request_TA" used to request a first full timing advance TA value and / or a first differential k_offset value for the user equipment UE 102 from the central unit CU 174.

[0086] In response to the "Distributed Unit DU to Central Unit CU" message, the central unit CU172 sends to the distributed unit DU174 a "Central Unit CU to Distributed Unit DU" message (1158C), the "Central Unit CU to Distributed Unit DU" message comprising a radio resource control RRC release message (e.g., a radio resource control RRCRelease message), a first complete timing advance TA value of the user equipment UE102, and / or a first differential k_offset value of the user equipment UE102, and the radio resource control RRC release message may also include a SuspendConfig_IE and a small data transmission SDT configuration.

[0087] Upon receiving the "Central unit CU to distributed unit DU" message at event 1158C, the distributed unit DU 174 transmits 1134C a downlink DL_MPDU to the user equipment UE 102 comprising a Contention_Resolution_ID_MAC_CE for contention resolution, and then transmits 1164 a physical downlink control channel PDCCH to the user equipment UE 102 providing an uplink UL grant for the user equipment UE. The distributed unit DU 174 may include 1164C a Differential_Koffset_MAC_CE in the downlink DL_MPDU conveying a second differential k_offset value for the user equipment UE 102, the second differential k_offset value being determined based on the first differential k_offset value or on the first complete timing advance TA value received at event 1158C.

[0088] 12A is a messaging diagram of a scenario 1200A in which a user equipment UE configured with a timing advance TA reporting configuration moves to a new cell and performs a small data transmission SDT procedure with the new cell. In this scenario, the new cell broadcasts system information including a positive indication for the user equipment UE to report timing advance TA information when establishing / re-establishing / resuming a radio resource control (RRC) connection with the new cell. The user equipment UE 102 initially operates in a connected state 1202 and connects to a first base station BS 104 via a service link provided by a satellite 304 for the first cell. The user equipment UE 102 and the base station 104 then communicate a common timing advance TA, a user equipment UE-specific timing advance TA, and N TA, and procedure 1221 (similar to procedure 821) for reporting the timing advance TA and obtaining the differential k_offset. In procedure 1221, the user equipment UE 102 receives a first timing advance TA reporting configuration in a radio resource control RRC reconfiguration message from the first base station BS 104, transmits a first full timing advance TA value to the first base station BS 104, and receives a first differential k_offset value from the first base station BS 104. After performing procedures 1211 and 1221, the user equipment UE 102 receives a radio resource control RRC release message from the first base station BS 104 (1224) and transitions to an inactive state in response to the radio resource control RRC release message (1226). The radio resource control RRC release message at event 1224 may further include a SuspendConfig_IE and a small data transmission SDT configuration. The user equipment UE102 subsequently establishes / re-establishes / resumes a radio resource control (RRC) connection with the second cell (i.e., flag_TA_report is present and indicates a value of "true") and selects or reselects and camps (1227) on a second cell (e.g., cell 126 of FIG. 1A) supported by the second base station BS106, which broadcasts (1250) system information with a positive indication for the user equipment UE to report a timing advance (TA).

[0089] After camping on the second cell, the user equipment UE 102 determines 1252 to perform a small data transmission SDT procedure due to arriving uplink UL traffic belonging to a small data transmission SDT_Data Radio Bearer DRB / Signaling Radio Bearer SRB. In light of this determination, the user equipment UE 102 initiates 1228 a two-step or four-step random access (RA) procedure by transmitting a random access RA preamble allocated for small data transmission SDT purposes to the second base station BS 106. Upon receiving an uplink UL grant in response to the random access RA preamble transmission, the user equipment UE 102 determines whether the uplink UL grant / resources are large enough to accommodate all pending small data transmission SDT data (i.e., pending uplink UL data belonging to small data transmission SDT_Data Radio Bearer DRB / Signaling Radio Bearer SRB) plus the radio resource control (RRC) resume request message. Since the uplink UL grant / resources in this example are not large enough to accommodate all pending small data transmission SDT data and radio resource control RRC resume requests, the user equipment UE 102 segments the pending small data transmission SDT data and decides to send 1254 a buffer status report BSR_MAC_CE on the uplink UL grant / resources to inform the network about the subsequent small data transmission SDT data transmission. The user equipment UE 102 then determines whether the difference between the full timing advance TA value currently applied by the user equipment UE (i.e., the second full timing advance TA value) and the first full timing advance TA value reported in step 1221 is equal to or greater than the value X configured in the first timing advance TA reporting configuration. offset In this scenario, the timing advance TA difference is greater than or equal to the threshold X offsetSince the threshold criterion is met (1279A), the user equipment UE transmits (1230A) to the second base station BS 106 an uplink UL_MPDU comprising a radio resource control RRC Resume Request message, a buffer status report BSR_MAC_CE, and a TA_Report_MAC_CE comprising the second complete timing advance TA value. If the uplink UL grant / resources can accommodate such a segment, the user equipment UE 102 may further include a segment of small data transmission SDT data in the transmitted MPDU at event 1230A.

[0090] Upon receiving the uplink UL_MPDU at event 1230A, the second base station BS106 (A) sends 1232A a Retrieve_UE_Context_Request message to the first base station BS104, (B) determines a second differential k_offset value for the user equipment UE 102 based on the received second full timing advance TA value for the user equipment UE 102, and (C) sends 1234A a downlink DL_MPDU to the user equipment UE 102 comprising a Contention_Resolution_ID_MAC_CE and a Differential_Koffset_MAC_CE comprising the second differential k_offset value. In response to the Retrieve_UE_Context_Request message, the first base station BS104 returns the context of the user equipment UE 102 by sending 1236A a Retrieve_UE_Context_Response message that does not include timing advance TA information for the user equipment UE's pre-inactivity state.

[0091] Upon receiving the buffer status report BSR_MAC_CE in step 1230A, the second base station BS106 understands that the user equipment UE 102 requires subsequent data transmission. Accordingly, upon receiving the Retrieve_UE_Context_Response message, the second base station BS106 transmits a physical downlink control channel PDCCH to the user equipment UE 102, providing an uplink UL grant for the user equipment UE (1264). In response to receiving the uplink UL grant, the user equipment UE 102 rechecks whether the uplink UL grant is large enough to accommodate all pending small data transmission SDT data. Because the uplink UL grant provided in step 1264 is large enough to accommodate all pending small data transmission SDT data, the user equipment UE 102 decides to transmit all pending small data transmission SDT data in one go (1266), and therefore decides not to transmit the buffer status report BSR_MAC_CE in the uplink UL grant (1266). Following the determination, the user equipment UE 102 transmits an uplink UL_MPDU comprising only the uplink UL data, without the buffer status report BSR_MAC_CE or the timing advance TA_Report_MAC_CE, to the second base station BS 106 (1268). Upon receiving the uplink UL data, the second base station BS 106 transmits a radio resource control RRC release message to the user equipment UE 102 (1260), which may further include a SuspendConfig_IE and a small data transmission SDT configuration. Upon receiving the radio resource control RRC release message, the user equipment UE 102 remains in an inactive state (1262).

[0092] Figure 12B is a messaging diagram of scenario 1200B, which is similar to scenario 1200A shown in Figure 12A. The differences between Figure 12A and Figure 12B are explained below. Similar to scenario 1200A, in scenario 1200B, the user equipment UE 102 has segmented pending small data transmission SDT data and decides 1254 to transmit a buffer status report BSR_MAC_CE on available uplink UL grants / resources to inform the network about the subsequent small data transmission SDT data transmission. Following the decision, the user equipment UE 102 determines whether the difference between the complete timing advance TA value currently applied by the user equipment UE (i.e., the second complete timing advance TA value) and the first complete timing advance TA value reported in procedure 1221 is equal to or greater than the value X configured in the first timing advance TA reporting configuration. offset In this scenario, the timing advance TA difference is greater than or equal to the threshold X offset (i.e., does not meet the threshold criterion) (1279B), the user equipment UE transmits an uplink UL_MPDU (1230B) comprising a radio resource control RRC Resume Request message and a buffer status report BSR_MAC_CE (i.e., does not include a timing advance TA_Report_MAC_CE) to the second base station BS 106. If the uplink UL grant / resources can accommodate the segment, the user equipment UE 102 may further include a segment of small data transmission SDT data in the transmitted MPDU at event 1230B.

[0093] Upon receiving the uplink UL_MPDU at event 1230B, the second base station BS106 sends (1232B) a Retrieve_UE_Context_Request message to the first base station BS104. The Retrieve_UE_Context_Request message further comprises an IE / field "Request_TA" that is used to request a first full timing advance TA value and / or a first differential k_offset value for the user equipment UE102 from the first base station BS104.

[0094] In response to the Retrieve_UE_Context_Request_message, the first base station BS 104 sends 1236B to the second base station BS 106 a Retrieve_UE_Context_Response message comprising the first complete timing advance TA value for the user equipment UE 102 and / or the first differential k_offset value for the user equipment UE 102. Upon receiving the Retrieve_UE_Context_Response message at event 1236B, the second base station BS 106 sends 1234B a downlink DL_MPDU comprising the Contention_Resolution_ID_MAC_CE to the user equipment UE 102 for contention resolution, and then sends 1264 a physical downlink control channel PDCCH to the user equipment UE 102 scheduling an uplink UL grant for the user equipment UE. In some embodiments, the second base station BS106 may include in the downlink DL_MPDU at event 1234B a Differential_Koffset_MAC_CE comprising a second differential k_offset value for the user equipment UE 102, the second differential k_offset value being determined based on the first (pre-inactivity state) complete timing advance TA value received at event 1236B and a cell-specific k_offset value for the cell (e.g., cell 126) selected by the user equipment UE 102. In some embodiments, the second differential k_offset value transmitted at event 1234B is determined by the second base station BS106 based on the first (pre-inactivity state) differential k_offset value for the user equipment UE 102 received at event 1236B.

[0095] Figure 13 is a messaging diagram of scenario 1300, which is similar to scenario 1200A shown in Figure 12A. The differences between Figure 13 and Figure 12A are described below. Similar to 1227, in scenario 1300, user equipment UE 102 has selected or reselected and is camped 1327 on a second cell (e.g., cell 126 of Figure 1A) supported by a second base station BS 106. Unlike in scenario 1200A, in scenario 1300, upon establishing / reestablishing / resuming a radio resource control (RRC) connection with the second cell, the second base station BS 106 broadcasts 1350 system information that does not include a positive indication for the user equipment UE to report a timing advance (TA) (i.e., flag_TA_report is not present or indicates a "false" value). Consequently, the user equipment UE 102 does not report its full timing advance TA to the second base station BS 106, and the user equipment UE 102 then does not receive the second differential k_offset value from the second base station BS 106 for the upcoming small data transmission SDT procedure. Thus, after a decision 1354 similar to 1254, the user equipment UE 102 determines whether the difference between the full timing advance TA value currently applied by the user equipment UE (i.e., the second full timing advance TA value) and the first full timing advance TA reported in procedure 1321 is equal to or greater than the value X configured in the first timing advance TA reporting configuration. offset Furthermore, the user equipment UE 102 does not include a TA_Report_MAC_CE in the radio resource control RRCResume message, and subsequently the user equipment UE 102 does not receive a Differential_Koffset_MAC_CE at event 1334.

[0096] 14 is a flow diagram of a method 1400 performed by a distributed unit DU (e.g., distributed unit DU 174) to determine and process a differential k_offset value for a user equipment UE, according to one embodiment. Initially, the distributed unit DU receives 1414 a "Central Unit CU to Distributed Unit DU" message from the central unit CU (corresponding to step 814 of FIG. 8A) comprising a radio resource control RRC message to be delivered to the user equipment UE, the radio resource control RRC message comprising a timing advance TA reporting configuration (e.g., tar-Config_IE). The distributed unit DU then transmits 1416 a radio resource control RRC message comprising the timing advance TA reporting configuration to the user equipment UE. In response, the distributed unit DU receives from the user equipment UE a first complete timing advance TA value (i.e., common timing advance TA + user equipment UE-specific timing advance TA + N TA ) (1418). The distribution unit DU determines a first differential k_offset value for the user equipment UE based on the cell-specific k_offset value and the received first full timing advance TA value. In one embodiment, the distribution unit DU determines the first differential k_offset value for the user equipment UE by subtracting the cell-specific k_offset value from the first full timing advance TA value (i.e., differential k_offset = first full timing advance TA - cell-specific k_offset).

[0097] The distributed unit DU sends 1420 a differential Koffset_MAC_CE comprising the determined first differential k_offset value for the user equipment UE to the user equipment UE and receives 1422 a "central unit CU to distributed unit DU" message comprising a radio resource control RRC release message for the user equipment UE from the central unit CU, where the radio resource control RRC release may include a SuspendConfig_IE. The distributed unit DU then sends 1424 a radio resource control RRC release message to the user equipment UE and forwards 1425 the first complete timing advance TA value and the first differential k_offset value for the user equipment UE to the central unit CU. Finally, 1490 the distributed unit DU releases / discards 1490 the first complete timing advance TA and the first differential k_offset value for the user equipment UE.

[0098] 15A is a flow diagram of a method 1500A performed by a distributed unit DU (e.g., distributed unit DU 174) to provide a differential k_offset value to a user equipment UE during a radio resource control RRC connection resumption procedure, according to one embodiment. The distributed unit DU first performs the method / procedure 1400 for determining and processing a first differential k_offset value for the user equipment UE. The distributed unit DU then receives 1530A from the user equipment UE an uplink UL_MPDU comprising a radio resource control RRC resumption request message and a second complete timing advance TA value in a MSG3 grant or in a MSGA_Physical Uplink Shared Channel PUSCH resource. In response to the radio resource control RRC resume request message, the distributed unit DU sends to the central unit CU a "distributed unit DU to central unit CU" message comprising the radio resource control RRC resume request message (1532A), and then determines a second differential k_offset value for the user equipment UE based on the cell-specific k_offset value and the received second complete timing advance TA value (1519A).

[0099] The distributed unit DU sends to the user equipment UE (block 1534) a Contention_Resolution_ID_MAC_CE that repeats (echoes) the first / most significant 40 bits of the radio resource control RRC resume request message received in block 1530A and a Differential_Koffset_MAC_CE that comprises the second differential k_offset value determined for the user equipment UE. The distributed unit DU then receives from the central unit CU a "Central Unit CU to Distributed Unit DU" message that comprises a radio resource control RRC resume message for the user equipment UE (block 1536A). In this figure, operation 1534 occurs earlier than operation 1536A, but operation 1534 could also occur after operation 1536A. Similarly, in this figure, Contention_Resolution_ID_MAC_CE 1534 is sent after operations 1532A and 1519A, but it can be sent any time after operation 1530A. Finally, the distributed unit DU sends a radio resource control RRC resume message to the user equipment UE (block 1538). If operation 1536A occurs earlier than operation (ie, transmit) 1534, transmit 1538 and 1534 may be merged (combined).

[0100] 15B is a flow diagram of a method 1500B performed by a distributed unit DU (e.g., distributed unit DU 174) to provide a differential k_offset value to a user equipment UE during a radio resource control RRC connection resumption procedure without having the user equipment UE report a full timing advance TA value, according to one embodiment. Initially, the distributed unit DU performs the method / procedure 1400 for determining and processing a first differential k_offset value for the user equipment UE. The distributed unit DU then receives a radio resource control RRC resume request message from the user equipment UE on an MSG3 grant or MSGA_Physical Uplink Shared Channel (PUSCH) resource (1530B). In response to the radio resource control RRC resume request message, the distributed unit DU sends to the central unit CU a radio resource control RRC resume request message and a “distributed unit DU to central unit CU” message comprising a field / IE for requesting the first differential k_offset and / or first full timing advance TA value for the user equipment UE (1532B). In response, the distributed unit DU receives from the central unit CU a "central unit CU to distributed unit DU" message comprising a radio resource control RRC resume message (1536B). The "central unit CU to distributed unit DU" message also comprises a first differential k_offset value for the user equipment UE and / or a first complete timing advance TA value for the user equipment UE. The distributed unit DU then determines 1519B a second differential k_offset value for the user equipment UE based on the first differential k_offset value or based on the first complete timing advance TA value received in 1536B.

[0101] The distributed unit DU sends 1534 to the user equipment UE the first / most significant 40 bits of the radio resource control RRC resume request message received in 1530B and the Contention_Resolution_ID_MAC_CE that repeats the second differential k_offset value determined for the user equipment UE in 1519B. In this figure, the Contention_Resolution_ID_MAC_CE is sent 1534 after 1532B, 1536B, and 1519B, but it can be sent any time after 1530B. Finally, the distributed unit DU sends 1538 a radio resource control RRC resume message to the user equipment UE.

[0102] 16A is a flow diagram of a method 1600A performed by a distributed unit DU (e.g., distributed unit DU 174) to provide a user equipment UE with a sufficiently large resource to report a timing advance (TA) in a specific random access RA procedure (e.g., a random access RA triggered by a radio resource control (RRC) connection resumption procedure), according to one embodiment. The distributed unit DU first broadcasts system information (e.g., a system information block) comprising a configuration of random access resources available for reporting the user equipment UE's timing advance (1601A). The distributed unit DU then receives from the user equipment UE a random access preamble (1628A) belonging to the random access resource used to report the user equipment UE's timing advance (1628A). The distributed unit DU then transmits to the user equipment UE a random access response (1629) comprising an uplink UL grant for the user equipment UE to transmit MSG3, which may contain a radio resource control (RRC) message and a timing advance (TA_Report_MAC_CE). If the preamble received in 1628A belongs to a preamble assigned to a two-step random access RA procedure, the distributed unit DU skips operation 1629. The distributed unit DU then receives from the user equipment UE a TA_Report_MAC_CE comprising the full timing advance TA value (1630). Finally, the distributed unit DU sends to the user equipment UE a Differential_Koffset_MAC_CE comprising the differential k_offset value determined based on the full timing advance TA value received in 1630 (1634).

[0103] 16B is a flow diagram of a method 1600B performed by a distributed unit DU (e.g., distributed unit DU 174) to provide a user equipment UE with a sufficiently large resource to report a timing advance (TA) in a random access (RA) procedure, according to one embodiment. First, the distributed unit DU broadcasts system information comprising a positive indication for the user equipment UE to report timing advance (TA) information during a radio resource control (RRC) connection establishment / re-establishment / resumption procedure (1601B). Next, the distributed unit DU receives from the user equipment UE a random access preamble belonging to a specific random access preamble group (e.g., random access RA preamble group B) (1628B). In response, the distributed unit DU transmits to the user equipment UE a random access response comprising an uplink UL grant for the user equipment UE to transmit MSG3 (1629), where the uplink UL grant can carry a radio resource control (RRC) message and a timing advance (TA_Report_MAC_CE). If the preamble received in 1628B belongs to a preamble assigned to a two-step random access RA procedure, the distributed unit DU skips 1629. The distributed unit DU then receives from the user equipment UE a TA_Report_MAC_CE comprising the full timing advance TA value (1630). Finally, the distributed unit DU sends to the user equipment UE a Differential_Koffset_MAC_CE comprising the differential k_offset value determined based on the full timing advance TA value received in 1630 (1634).

[0104] 17 is a flow diagram of a method 1700 performed by a distributed unit DU (e.g., distributed unit DU 174) to control a user equipment UE via system information to report a timing advance (TA) value in a radio resource control (RRC) connection resumption procedure, according to one embodiment. Initially, the distributed unit DU broadcasts 1750 system information (e.g., a system information block) comprising a positive indication for the user equipment UE to report a timing advance (TA) value during a radio resource control (RRC) connection establishment / reestablishment / resumption procedure. The method 1700 then comprises method 1500A or 1500B, depending on whether the distributed unit DU receives a full timing advance (TA) value with a radio resource control (RRC) resumption request message from the user equipment UE. If the distributed unit DU receives a full timing advance (TA) value with a radio resource control (RRC) resumption request message, the method 1700 proceeds to perform the operations of method 1500A; otherwise, the method 1700 proceeds to perform the operations of method 1500B.

[0105] 18A is a flow diagram of a method 1800A performed by a base station (e.g., a second base station BS 106) to determine a differential k_offset value for a user equipment UE during a radio resource control (RRC) connection resume procedure, according to one embodiment. Initially, in block 1850, the base station BS broadcasts system information comprising a positive indication for the user equipment UE to report a full timing advance (TA) value during a radio resource control (RRC) connection establishment / re-establishment / resumption procedure. The base station BS receives an uplink UL_MPDU from the user equipment UE in an MSG3 grant or in an MSGA_Physical Uplink Shared Channel (PUSCH) resource, comprising a radio resource control (RRC) resume request message and the full timing advance (TA) value (1830A). The base station BS then sends a Retrieve_UE_Context_Request message to the anchor base station BS (1832A). The base station BS determines (1819A) a differential k_offset value for the user equipment UE based on the cell-specific k_offset value and the received full timing advance TA value.

[0106] The base station BS then transmits to the user equipment UE (1834A) a Contention_Resolution_ID_MAC_CE that repeats the first / most significant 40 bits of the radio resource control RRC resume request message received in block 1830A and a Differential_Koffset_MAC_CE that comprises the determined differential k_offset value. In response to the request transmitted in 1832, the base station BS receives from the anchor base station BS a Retrieve_UE_Context_Response message that may comprise a timing advance TA reporting configuration for the user equipment UE (1836A). In this figure, operation 1834A occurs earlier than operation 1836A, but operation 1834A is allowed to occur later than operation 1836A. Similarly, in this figure, the Contention_Resolution_ID_MAC_CE is transmitted after operations 1832A and 1819A, but it can be transmitted any time after operation 1830A. Finally, the base station BS sends a radio resource control RRC resume message to the user equipment UE 1838. If operation 1836A occurs earlier than operation 1834A, operations 1838 and 1834A may be merged.

[0107] 18B is a flow diagram of a method 1800B performed by a base station (e.g., a second base station BS 106) to determine a differential k_offset value for a user equipment UE during a radio resource control RRC connection resumption procedure without having the user equipment UE report a full timing advance TA value, according to one embodiment. Initially, the base station BS broadcasts 1850 system information comprising a positive indication to report the full timing advance TA value for the user equipment UE during a radio resource control RRC connection establishment / reestablishment / resumption procedure. The base station BS then receives 1830B an uplink UL_MPDU comprising a radio resource control RRC resumption request message within an MSG3 grant or within an MSGA_Physical Uplink Shared Channel (PUSCH) resource from the user equipment UE. At 1832B, the base station BS sends a Retrieve_UE_Context_Request message to the anchor base station BS, the Retrieve_UE_Context_Request message comprising fields for requesting the first differential k_offset value and / or the full timing advance TA value for the user equipment UE. The base station BS then receives 1836B from the anchor base station BS a Retrieve_UE_Context_Response message comprising the first differential k_offset value and / or the full timing advance TA value for the user equipment UE. The Retrieve_UE_Context_Response may also comprise a timing advance TA reporting configuration for the user equipment UE. Method 1800 then proceeds with operation 1819B, whereby the base station BS determines a second differential k_offset value for the user equipment UE based on the full timing advance TA value and the cell-specific k_offset value of the cell currently selected by the user equipment UE. In some embodiments, the base station BS determines the second differential k_offset value for the user equipment UE based on the first differential k_offset value of the user equipment UE.

[0108] The base station BS transmits to the user equipment UE (1834B) a Contention_Resolution_ID_MAC_CE that repeats the first / most significant 40 bits of the radio resource control RRC resume request message received in 1830B and a Differential_Koffset_MAC_CE that comprises the second differential k_offset value. In this figure, the Contention_Resolution_ID_MAC_CE is transmitted after 1832B, 1836B, and 1819B, but it can be transmitted any time after block 1830B. Finally, the base station BS transmits to the user equipment UE a radio resource control RRC resume message (1838). Blocks 1838 and 1834B can be merged.

[0109] 19A is a flow diagram of a method 1800A performed by a base station (e.g., a second base station BS106) to determine a differential k_offset value for a user equipment UE during a small data transmission SDT procedure, according to one embodiment. Initially, the base station BS receives an uplink UL_MPDU from the user equipment UE in an MSG3 grant or in an MSGA_Physical Uplink Shared Channel (PUSCH) resource (1930), comprising a radio resource control (RRC) resume request message, a buffer status report (BSR_MAC_CE), and a complete timing advance (TA) value. The radio resource control (RRC) resume request message is transmitted for the purpose of small data transmission SDT. The base station BS then transmits a Retrieve_UE_Context_request message (1932A) to the anchor base station BS to which the user equipment UE was connected before entering the inactive state. At 1919A, the base station BS determines a differential k_offset value for the user equipment UE based on the cell-specific k_offset value and the received complete timing advance (TA) value. The base station BS sends to the user equipment UE (1934A) a Contention_Resolution_ID_MAC_CE that repeats the first / most significant 40 bits of the radio resource control (RRC) resume request message received in block 1930A and a Differential_Koffset_MAC_CE that comprises the determined differential k_offset value. In response to the request sent in 1932A, the base station BS receives from the anchor base station BS a Retrieve_UE_Context_Response message that may comprise a timing advance TA reporting configuration for the user equipment UE (1936A). In this figure, operation 1934A occurs earlier than operation 1936A, but operation 1934A could also occur after operation 1936A. Similarly, in this figure, the Contention_Resolution_ID_MAC_CE is sent (1934A) after operations 1932A and 1919A, but it can be sent any time after operation 1930A. Finally, the base station BS transmits to the user equipment UE a physical downlink control channel PDCCH indicating uplink UL grant for subsequent data transmission (1964A).The delay between the physical downlink control channel PDCCH and the uplink UL grant is determined based on the cell specific k_offset value of the user equipment UE and the differential k_offset value.

[0110] 19B is a flow diagram of a method 1900B performed by a base station (e.g., a second base station BS 106) to determine a differential k_offset value for a user equipment UE during a radio resource control RRC connection resumption procedure without having the user equipment UE report a full timing advance TA value, according to one embodiment. Initially, the base station BS receives an uplink UL_MPDU from the user equipment UE in a MSG3 grant or in a MSGA_Physical Uplink Shared Channel (PUSCH) resource, comprising a radio resource control RRC resume request message and a buffer status report BSR_MAC_CE (1930B), the radio resource control RRC resume request message being transmitted for the purpose of a small data transmission SDT. The base station BS then sends a Retrieve_UE_Context_Request message to the anchor base station BS (to which the user equipment UE was connected before entering the inactive state) (1932B), comprising fields for requesting a first differential k_offset value and / or a full timing advance TA value for the user equipment UE. The base station BS then receives 1936B a Retrieve_UE_Context_Response message from the anchor base station BS, the Retrieve_UE_Context_Response message comprising the first differential k_offset value and / or the full timing advance TA value for the user equipment UE. The Retrieve_UE_Context_Response may also comprise a timing advance TA reporting configuration for the user equipment UE.

[0111] The base station BS then determines (1919B) a second differential k_offset value for the user equipment UE based on the full timing advance TA value and a cell-specific k_offset value of the cell currently selected by the user equipment UE. In some embodiments, the base station BS determines a second differential k_offset value for the user equipment UE based on the first differential k_offset value of the user equipment UE. The base station BS then sends (1934B) to the user equipment UE a Contention_Resolution_ID_MAC_CE that repeats the first / most significant 40 bits of the radio resource control RRC Resume Request message received in block 1930B and a Differential_Koffset_MAC_CE comprising the second differential k_offset value. In this figure, the Contention_Resolution_ID_MAC_CE is sent in 1934B after operations 1932B, 1936B, and 1919B, although operation 1934B may occur any time after operation 1930B.

[0112] Finally, the base station BS transmits to the user equipment UE a physical downlink control channel PDCCH indicating an uplink UL grant for a subsequent data transmission (1964B), the delay between the physical downlink control channel PDCCH and the uplink UL grant being determined based on the cell-specific k_offset value of the user equipment UE and a second differential k_offset value.

[0113] 20 is a flow diagram of a method 2000 performed by a base station BS (e.g., a second base station BS 106) to control via system information whether a user equipment UE reports a timing advance (TA) in a small data transmission (SDT) procedure, according to one embodiment. Initially, the base station BS broadcasts 2050 system information comprising a positive indication for the user equipment UE to report a full timing advance (TA) value during a radio resource control (RRC) connection establishment / reestablishment / resumption procedure. Method 200 then proceeds with operation of either method 1900A or 1900B depending on whether the base station BS receives a full timing advance (TA) value with a radio resource control (RRC) resume request message from the user equipment UE. If the base station BS receives a full timing advance (TA) value with a radio resource control (RRC) resume request message, method 2000 continues with operation of method 1900A; otherwise, method 2000 continues with operation of method 1900B.

[0114] 21 is a flow diagram of a method 2100 performed by a network entity NE (e.g., a base station BS or a distributed unit DU of a distributed base station BS) connected to a user equipment UE according to one embodiment. The method 2100 comprises maintaining (2125) (similar to 825, 1425) pre-inactivity state timing advance TA information associated with the user equipment UE's communications via a non-terrestrial network before the user equipment UE switches to an inactive state (e.g., 826). The method 2100 further comprises receiving (2130) (similar to 830) a request to resume an active state from the user equipment UE, and, if the user equipment UE does not provide a current full timing advance TA value in the request, transmitting (2134) (similar to 834) a calculated resumed timing advance TA correction to the user equipment UE using the pre-inactivity state timing advance TA information.

[0115] 22 is a flow diagram of a wireless communication method 2200 performed by a network entity NE (e.g., a base station BS or a distributed unit DU of a distributed base station BS) according to one embodiment. The method 2200 comprises receiving 2230 a request to resume an active state via a first satellite from a user equipment UE that was connected to a second user equipment UE via a second satellite before entering the inactive state (similar to 1030). The method 2200 further comprises retrieving 2232 pre-inactivity state timing advance TA information from the first network entity NE (similar to 1032) related to the user equipment UE's communication with the first network entity NE via the first satellite, and transmitting 2234 a calculated resume timing advance TA correction using the pre-inactivity state timing advance TA information to the user equipment UE (similar to 1034).

[0116] 23 is a flow diagram of a communication method 2300 performed by a network entity NE (e.g., a base station BS or a distributed unit DU of a distributed base station BS) according to one embodiment. The method 2300 comprises receiving (2330) a small data transmission SDT indication from a user equipment UE in an inactive state after communicating to a radio access network RAN ​​via a non-terrestrial-based network (similar to 1130). The method 2300 further comprises transmitting (2334) a timing advance TA correction to the user equipment UE based on pre-inactive state timing advance TA information if the small data transmission SDT indication comprises a small data transmission SDT size and omits the full timing advance TA value. Optionally (as suggested by the dashed box), the method 2300 may comprise retrieving (2332) pre-inactive state information.

[0117] 24 is a block diagram of a wireless communication device 2400 (e.g., a second base station BS106 or a distributed unit DU174) configured to perform the method for managing a timing advance (TA) described above when an inactive user equipment (UE) resumes a radio access network (RAN) connection and / or initiates a small data transmission (SDT) procedure, according to one embodiment. The wireless communication device 2400 includes an antenna 2402 connected to a radio frequency (RF) front end 2404 and at least one RF transceiver 2406 (e.g., an LTE transceiver, a 5G_New Radio NR transceiver, or other transceiver) for communicating to the user equipment (UE) via the radio access network (RAN) (non-terrestrial network (NTN)). The antenna and RF front end may be tuned to one or more frequency bands (e.g., subcarriers) as specified by, for example, 3GPP LTE, 5G_New Radio NR, and 6G communication standards, as implemented by the respective transceivers. The wireless communication device 2400 also includes one or more processor(s) 2410 and a computer-readable storage medium CRM 2412. The processor(s) 2410 may be single-core or multi-core processors, and the computer-readable storage medium CRM 2412 includes any suitable memory / storage other than for propagating signals. For example, the memory / storage may include random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), and / or flash memory usable to store device data 2414, and a timing advance manager 2416 for implementing the various techniques described herein. The computer-readable storage medium CRM 2412 stores instructions executable by the processor(s) 2410 to facilitate user plane communications, control plane signaling, and user interaction.The timing advance TA reporting manager 2416, which may be implemented as hardware logic and / or circuitry as well as software, triggers various steps and actions associated with timing advance TA information.

[0118] In the above figures, a description of one of the above figures may apply to other of the above figures. Any events or actions described above may be optional. For example, dashed events or actions may be optional. In some embodiments, "message" is used and can be replaced with "information element (IE)" or vice versa. In some embodiments, "IE" is used and can be replaced with "field" or vice versa. In some embodiments, "configuration" can be replaced with "configurations" or "configuration parameters" or vice versa.

[0119] A user device (e.g., user equipment UE 102) capable of implementing the techniques of this disclosure may be any suitable device capable of wireless communication, such as a smartphone, tablet computer, laptop computer, mobile game console, point-of-sale (POS) terminal, health management device, drone, camera, media streaming dongle or other personal media device, wearable device such as a smartwatch, wireless hotspot, femtocell, or broadband router. Furthermore, a user device may in some cases be embedded in an electronic system such as a vehicle head unit or advanced driver assistance system (ADAS). Still further, a user device may operate as an Internet of Things (IoT) device or a mobile internet device (MID). Depending on the type, a user device may include one or more general-purpose processors, computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0120] Certain embodiments are described in this disclosure as comprising logic, or several components or modules. The modules may be software modules (e.g., code or machine-readable instructions stored on a non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. For example, a hardware module may comprise dedicated circuitry or logic that is permanently configured (e.g., as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), digital signal processor (DSP), or other application-specific processor) to perform certain operations. A hardware module may also include programmable logic or circuitry (e.g., contained within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated, permanently configured circuitry or in temporarily configured circuitry (e.g., configured by software) may involve cost and time considerations.

[0121] If implemented in software, the techniques may be provided as part of an operating system, a library used by multiple applications, a particular software application, etc. The software is executable by one or more general-purpose processors or one or more special-purpose processors.

Claims

1. A wireless communication method (2100) performed by a network entity NE connected to a user equipment UE, said wireless communication method comprising: maintaining (2125) pre-inactivity state Timing Advance (TA) information associated with the user equipment UE communicating via a non-terrestrial based network NTN that is a satellite-based cell before the user equipment UE switches to an inactive state; receiving (2130) a request to resume an active state from the user equipment (UE); if the user equipment UE does not provide a current full timing advance (TA) value in the resume request, transmitting to the user equipment UE (2134) a resume timing advance (TA) correction to be applied to communication after the user equipment UE resumes the active state, the resume timing advance (TA) correction having been calculated using the pre-inactive state timing advance (TA) information; A wireless communication method comprising:

2. The restart timing advance (TA) modification corresponds to a Differential_set as defined in the 3GPP (registered trademark) technical specifications. The wireless communication method of claim 1 .

3. The pre-inactive state timing advance TA information is a first complete timing advance (TA) value applied by the user equipment (UE) before switching to the inactive state; or a first differential k_offset value used by the user equipment UE before switching to the inactive state; At least one of The wireless communication method of claim 1 .

4. The wireless communication method further comprises, upon receiving a second full timing advance TA value as the current full timing advance TA value from the user equipment UE, transmitting a second differential k_offset value as the restarted timing advance TA correction calculated by using the second full timing advance TA value to the user equipment UE. The wireless communication method according to any one of claims 1 to 3.

5. The wireless communication method further comprises: sending a timing advance TA reporting configuration to the user equipment (UE); receiving, from the user equipment (UE), a timing advance TA report prepared in accordance with the timing advance TA reporting configuration, the timing advance TA report comprising the pre-inactive state timing advance TA information; The wireless communication method according to any one of claims 1 to 3, comprising:

6. The wireless communication method further comprises transmitting a time difference threshold to the user equipment UE in the timing advance TA reporting configuration to enable the user equipment UE to transmit updated timing advance TA information when a difference between a first complete timing advance TA value applied by the user equipment UE before switching to the inactive state and the current complete timing advance TA exceeds a time difference threshold. The wireless communication method of claim 5.

7. The wireless communication method further comprises transmitting a positive indication to the user equipment UE; the positive indication requests the user equipment UE to report timing advance (TA) information; The wireless communication method according to any one of claims 1 to 3.

8. said network entity NE is a distributed unit DU of a distributed base station which also comprises a central unit CU, The step of maintaining the pre-inactive state timing advance (TA) information comprises: transmitting from the distributed unit DU to the central unit CU the pre-inactivity state timing advance TA information comprising a first complete timing advance TA value applied by the user equipment UE before switching to the inactivity state; discarding the inactive pre-state timing advance (TA) information from the distributed unit (DU); the wireless communication method further comprising: retrieving the pre-inactive state timing advance (TA) information from the central unit (CU); The wireless communication method according to any one of claims 1 to 3.

9. The step of retrieving the pre-inactivity state timing advance (TA) information from the central unit (CU) further comprises the step of sending a radio resource control (RRC) resume request message to the central unit (CU); the radio resource control RRC resume request message comprises an indicator requesting the central unit CU to transmit the pre-inactivity state timing advance (TA) information to the distributed unit DU.

9. The wireless communication method of claim 8.

10. A wireless communication method (2200) performed by a first network entity (NE), said wireless communication method comprising: receiving (2230) a request to resume an active state via a first satellite from a user equipment UE that was connected to a second user equipment UE via a second satellite before entering the inactive state; retrieving (2232) from the second user equipment UE, pre-inactivity state timing advance (TA) information associated with the user equipment UE that communicates to the second user equipment UE via the second satellite; transmitting 2234 to the user equipment (UE) via the first satellite a resumed timing advance TA correction to be applied to communications after the user equipment (UE) resumes the active state, the resumed timing advance TA correction having been calculated using the pre-inactive state timing advance TA information; A wireless communication method comprising:

11. The wireless communication method further comprises broadcasting system information; the system information comprises a cell-specific timing advance (TA) and a positive indication for the user equipment (UE) to report timing advance (TA) information. The wireless communication method of claim 10.

12. A wireless communication method (2300) performed by a first network entity (NE) in a radio access network (RAN), said wireless communication method comprising: receiving (2330) a small data transmission SDT indication from an inactive user equipment UE after communicating to said radio access network RAN ​​via a non-terrestrial network NTN cell as a satellite-based non-terrestrial network NTN cell; if the small data transmission SDT indication comprises a small data transmission SDT size and omits a full timing advance TA value, sending a timing advance TA correction to the user equipment UE based on pre-inactivity state timing advance TA information of the user equipment UE communicating to the radio access network RAN ​​via the non-terrestrial network NTN cell before entering the inactive state (2334); A wireless communication method comprising:

13. The wireless communication method further comprises retrieving the pre-inactivity state timing advance (TA) information.

13. The wireless communication method of claim 12.

14. The step of retrieving pre-inactive state timing advance (TA) information comprises: sending a timing advance TA information request to a second network entity NE to which the user equipment UE was destined for the communication using a satellite before the user equipment UE entered the inactive state; receiving the pre-inactivity state timing advance TA information from the second network entity NE in response to the timing advance TA information request; Equipped with 14. The wireless communication method of claim 13.

15. said first network entity NE being a distributed unit DU of a distributed base station which also comprises a central unit CU, The step of retrieving pre-inactive state timing advance (TA) information comprises: sending a timing advance TA information request to said central unit CU; receiving the pre-inactive state timing advance (TA) information from the central unit (CU); Equipped with 14. The wireless communication method of claim 13.

16. The pre-inactive state timing advance TA information is a first complete timing advance (TA) value applied by the user equipment (UE) before switching to the inactive state; or a first differential k_offset value used by the user equipment UE before switching to the inactive state; At least one of A wireless communication method according to any one of claims 12 to 15.

17. a transceiver (2406); A processor (2410); a computer-readable storage medium (2412) storing executable instructions for the processor to perform the wireless communication method of any one of claims 1, 10, and 12 using the transceiver; A wireless communication device (2400) comprising:

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