Mobile devices, access network nodes, and methods

Abstract

At the time of configuration, candidate access network nodes are disclosed that perform the initial access procedure with the access network nodes without using random access channels.

Description

[Technical Field]

[0001] This disclosure relates to wireless communication systems and devices that operate in accordance with the 3rd Generation Partnership Project (3GPP®) standards or their equivalents or derivatives. [Background technology]

[0002] This disclosure relates particularly to improvements in mobility procedures that avoid using random access channels for initial access to new cells in so-called "5G" (or "Next Generation (NG)" or "New Radio (NR)") systems and subsequent systems, especially (but not limited to) in the context of non-terrestrial networks (NTN).

[0003] The initial development of 3GPP standards was called Evolved Packet Core (EPC) Network Long-Term Evolution (LTE) and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and was commonly referred to as "4G." More recently, the terms "5G" and "new radio" (NR) have begun to be used to refer to evolving communication technologies expected to support a variety of applications and services. Various details of 5G networks are described in the "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Network (NGMN) Alliance, which can be obtained, for example, from https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G through the so-called 3GPP Next Generation (NextGen) Radio Access Network (RAN) and 3GPP NextGen Core Network.

[0004] Under 3GPP standards, a NodeB (or eNB in ​​LTE, and gNB in ​​5G) is a radio access network (RAN) node (or simply an “access node,” “access network node,” or “base station”) through which communication devices (user equipment or “UE”) connect to the core network and communicate with other communication devices or remote servers. For simplicity, this application uses the terms access network node, RAN node, or base station to refer to any such access node.

[0005] For simplicity, this application uses the terms mobile device, user device, or UE to refer to any communication device that can connect to a core network via one or more base stations. While this application may refer to mobile devices in its description, it will be understood that the described technology can be implemented on any (mobile and / or generally stationary) communication device that can connect to a communication network to transmit / receive data, whether such communication device is controlled by human input or by software instructions stored in memory.

[0006] In current 5G architectures, the structure of a gNB can be divided into two or more parts. In some RAN implementations, there are two parts, sometimes called a “control unit” (Central Unit: CU or gNB-CU) and a “distributed unit” (DU or gNB-DU), connected by an F1 interface. This makes it possible to use a “split” architecture. Typically, a “split” architecture separates a “higher” CU layer (such as the Packet Data Convergence Protocol (PDCP) layer and the Radio Resource Control (RRC) layer, but not limited to these) and a “lower” DU layer (such as the Radio Link Control (RLC) layer, the Media Access Control (MAC) layer, and the Physical (PHY) layer, but not limited to these) from a specific CU and one or more DUs connected to and controlled by that CU via an F1 interface. Therefore, for example, the upper-layer CU functions of several gNBs can be centrally implemented (for example, by a single processing unit, or in a cloud-based or virtualized system) while each gNB maintains its own separate lower-layer DU functions locally.

[0007] 3GPP is also working with the satellite communications industry to define integrated satellite and terrestrial network infrastructure in the context of 5G. This is referred to as a non-terrestrial network (NTN), a term that refers to a network or segment of a network that uses aircraft or spacecraft for transmitting data and control signaling. Satellites refer to spacecraft in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geostationary Earth Orbit (GEO), or Highly Elliptical Orbit (HEO). Aircraft refer to High Altitude Platforms (HAPs) that encompass Unmanned Aircraft Systems (UAS), including tethered UAS, lighter-than-air UAS, and heavier-than-air UAS, all of which typically operate in a quasi-geostationary state at altitudes of 8-50 km.

[0008] 3GPP Technical Report (TR) 38.811 is a study on New Radio for supporting such terrestrial networks. This study includes, among other things, NTN deployment scenarios and related system parameters (architecture, altitude, orbit, etc.), as well as a description of the adaptation of the 3GPP channel model for non-terrestrial networks (propagation conditions, mobility, etc.). Non-terrestrial networks are, - To help accelerate the deployment of 5G services in areas that are not serviced or have inadequate service, in order to upgrade the performance of terrestrial networks. - To enhance service reliability by providing service continuity to user equipment or mobile platforms (e.g., passenger vehicles, aircraft, ships, high-speed trains, buses), - To improve service availability everywhere, especially for critical communications, and for future rail / maritime / air communications, and - It is expected that 5G network scalability will be enabled by providing efficient multicast / broadcast resources for data distribution to the network edge or directly to user devices.

[0009] Non-terrestrial network access typically involves the following elements, among others: -NTN terminal: This may refer to a 3GPP UE or a UE specific to the satellite system if the satellite does not directly serve a 3GPP UE. - A service link refers to a radio link between user equipment and a space / airborne platform (which may also be added to the radio link with the ground-based RAN). - Space or aerial platform - It features a gateway that connects a satellite or air access network to the core network. The gateway is almost always co-located with a base station (e.g., a gNB), i.e., - A feeder link should be understood as referring to a wireless link between a gateway and a space / airborne platform.

[0010] A satellite or airborne object typically generates several satellite beams over a given area. These beams typically have an elliptical footprint on the Earth's surface. The beam footprint can move across the Earth along with the movement of the satellite or airborne object in its orbit. Alternatively, the beam footprint may be (temporarily) fixed to the Earth, in which case several beampointing mechanisms (mechanical or electronic maneuvering mechanisms) can be used to compensate for the movement of the satellite or airborne object. There are various options for beam identification purposes. One option is that multiple (nearby / adjacent) satellite beams may have the same associated physical cell ID (PCI), and therefore the PCI may remain unchanged as the UE3 moves between beams in a set of beams sharing the PCI. Alternatively, there may be a one-to-one relationship between the PCI and the satellite beams (at least within the coverage area of ​​a particular satellite containing multiple beams).

[0011] 5G coverage is primarily beam-based, not cell-based. There is no cell-level reference channel from which cell coverage can be measured. Instead, each cell has one or more so-called synchronization signal block (SSB) beams (different from satellite beams or NTN beams). The SSB beams form a matrix of beams that cover the entire cell area. Each SSB beam carries the SSB, including the primary synchronization signal (PSS), secondary synchronization signal (SSS), and physical broadcast channel (PBCH).

[0012] The UE searches for SSB beams and performs measurements such as synchronization signal reference signal received power (SS-RSRP), synchronization signal reference signal received quality (SS-RSRQ), and / or synchronization signal to noise or interference ratio (SS-SINR). The UE maintains a set of candidate beams that may include beams from multiple cells. Thus, PCI and beam ID (or SSB index) distinguish SSB beams from one another. In essence, an SSB beam is like a minicell that can exist within a larger cell. Once the UE has discovered and selected a cell (and / or SSB beam in the case of 5G), it can attempt to access that cell and / or SSB beam using an initial radio resource control (RRC) connection setup procedure that includes a random access procedure.

[0013] For example, once a UE detects and selects a cell (and / or beam in the case of 5G), the UE may attempt to access that cell and / or beam using an initial radio resource control (RRC) connection setup procedure, which typically involves four distinct steps of a random access procedure. In the case of 5G, before attempting initial access, the UE may perform the transmission of a preamble to the network (e.g., a base station such as a gNB) via a physical random access channel (PRACH / RACH) to initiate a random access procedure (also referred to as a RACH procedure or simply RACH) to gain synchronization on the uplink (UL). This step is often referred to as a PRACH transmission or simply a message (message 1: Msg1) transmission. In response, the network responds with a random access response (RAR). A RAR includes a timing-alignment (TA) command to indicate the reception of a preamble and adjust the UE's transmission timing based on the timing of the received preamble, an uplink grant field indicating the resources to be used on the uplink for a physical uplink shared channel (PUSCH), a frequency hopping flag to indicate whether the UE transmits on PUSCH with or without frequency, an MCS field that allows the UE to determine the modulation and coding scheme (MCS) for the PUSCH transmission, and a transmit power control (TPC) command value to set the power for the PUSCH transmission. The RAR transmission step is often referred to as a message 2 (Msg2) transmission.Next, the UE sends message 3 (or "Msg3") to the network via the physical uplink shared channel (PUSCH) based on the information in the RAR. The specific message sent by the UE in this step, and the content of the message, depend on the context in which the random access procedure is being used. However, in the example of an initial radio RRC connection setup, Msg3 contains an RRC setup request or similar message carrying a temporary, randomly generated UE identifier. The network responds with message 4 (or "Msg4"), carrying the randomly generated UE identifier received in Msg3 for the purpose of resolving any conflicts between different UEs using the same preamble sequence. If successful, Msg4 also transitions the UE to a connected state.

[0014] Similar random access procedures may also be used in other contexts within NR, including, for example, handover, connection re-establishment, and request UL scheduling when dedicated resources for scheduling requests are not configured for the UE.

[0015] In addition to the four-step random access procedure described above, a so-called two-step random access procedure has also been developed. The two-step random access procedure is primarily intended to support (ultra) low-latency communication, 10ms control plane latency, fast handover, efficient channel access in unlicensed spectrum, and transmission of small data packets, among other things. However, this procedure can also be applied to larger cells, such as non-terrestrial cells. The main difference is that the four-step random access procedure requires two round-trip cycles between the UE and the base station, while the two-step random access procedure aims to reduce latency and control signaling overhead by using a single round-trip cycle between the UE and the base station. In effect, this is achieved by combining the UE's PRACH preamble (Msg1) transmission and the scheduled PUSCH transmission (Msg3) into a single message (referred to as "MsgA"). Similarly, the random-access response (RAR / Msg2) and the conflict resolution message (Msg4) from the base station to the UE are combined in a two-step random-access procedure (referred to as "MsgB").

[0016] A competition-based PRACH procedure is described as will be understood by those skilled in the art, but a non-competition-based (or "non-competition-free") procedure may also be used in which a dedicated preamble is assigned to the UE by the base station.

[0017] In addition to the RACH-based initial access procedure described above, a so-called RACH-less access procedure was introduced in the context of handover procedures under development for later releases of the LTE standard, also with the aim of providing latency reduction. RACH-less handovers reduce data connection interruption time during each handover and therefore reduce overall handover execution time because they eliminate the need to perform random access when initially accessing the target cell.

[0018] Figure 1 is a simplified sequence diagram showing the handover procedure with RACH-less initial access to the target cell.

[0019] As shown in Figure 1, before the handover begins, RAN node 5A-1 (e.g., a base station) is servicing and communicating with UE3 in S102. In the RACH-less handover procedure (as with other handover procedures), the handover preparation phase S110 begins when the serving RAN node 5A-1 (acting as source RAN node 5A-1) first decides to initiate the handover in S114 based on measurement reports from UE3, such as in S112 (e.g., measurement reports triggered by a specific measurement report event, or periodic measurement reports). Source RAN node 5A-1 begins preparing target RAN node 5A-2 (e.g., a base station) for the handover by sending a handover request message in S116.

[0020] Assume that the target RAN node 5A-2 decides to permit the handover request (e.g., based on appropriate admission control). At S118, the target RAN node 5A-2 prepares for the handover at layer 1 / layer 2 (L1 / L2) and sends a handover request confirmation message (such as a "handover request confirmation") to the source RAN node 5A-1. This handover request confirmation message includes an RRC message (such as an RRCConnectionReconfiguration message) generated by the target RAN node 5A-2 to instruct the change / reconfiguration of the UE's RRC connection for the purpose of handover. The RRC reconfiguration message is provided in a so-called "transparent" container that is sent to the UE to perform the handover (in an information element that is neither read nor changed by the receiving node, but instead transferred unchanged). The container includes a new cell radio network temporary identifier (C-RNTI), a target base station security algorithm identifier for the selected security algorithm, and in some cases several other parameters, namely, system information blocks (SIBs) of access parameters, etc.

[0021] This RRC reconfiguration message includes mobility control information parameters related to network-controlled mobility (handover). In the case of a RACH-less handover, this mobility control information includes an indication (such as a RACH skip information element (IE) indicating that the initial access to the target should be RACH-less, i.e., the RACH should be skipped).

[0022] The mobility control information also indicates a timing adjustment indication (e.g., in the case of handover, the primary TAG (primary TAG: PTAG), or in the case of secondary cell group (SCG) change, the primary secondary TAG (primary secondary TAG: PSTAG)) of the target timing advance, and includes (e.g., in the "targetTA" IE) the value of the timing offset (N TA ) between the uplink radio frame and the downlink radio frame for the UE3 to use the timing advance group (timing advance group: TAG) as a target.

[0023] The mobility control information may also optionally include a pre-allocated uplink grant (i.e., "configured grant" (configured grant: CG)) for use in RACH-less initial access in the target cell of the target RAN node 5A-2. This can be provided (e.g., in the "ul-ConfigInfo" IE, etc.) as uplink configuration information indicating, for example, the number of hybrid automatic repeat request (hybrid automatic repeat request: HARQ) processes configured for the pre-allocated uplink grant, the scheduling interval and startoffset within the subframe in which the UE3 can determine the periodic uplink transmission opportunity, and the frequency resources and time resources of the target cell used for uplink transmission.

[0024] Source RAN node 5A-1 initiates the handover execution phase in S120 by sending an RRC reconfiguration message (including mobility control information) to UE3 in S122. UE3 receives the RRC reconfiguration message with the necessary parameters (i.e., new C-RNTI, target base station security algorithm identifier, target base station SIB, etc.) and is consequently instructed by source RAN node 5A-1 to perform the handover. As described above, in the case of a RACH-less handover, the RRC reconfiguration message includes a timing adjustment indication and, optionally, a pre-allocated uplink grant for access to the target base station. In the case of a RACH-less handover, UE3 does not need to delay the execution of the handover to deliver the HARQ / ARQ response to source RAN node 5A-1.

[0025] Since a RACH-less handover is configured (for example, by an RRC reconfiguration message including a RACH skip), UE3 configures the lower layers to apply a RACH skip to the target master cell group (MCG). UE3 performs synchronization with the target RAN node 5A-2 in S126 based on the timing alignment indicator. To facilitate this, the MAC entity of the UE has a configurable timer (e.g., a timeAlignmentTimer) for each TAG. The timer is used to control how long the MAC entity considers the serving cells belonging to the relevant TAG to be uplink time-aligned. When UE3 (and therefore the MAC entity) is configured to skip RACH, the MAC entity applies the timing advance value indicated by the timing alignment indicator to the primary TAG and starts the timer associated with this TAG. UE3 derives a key specific to target RAN node 5A-2 and configures the security algorithm selected for use in the target cell.

[0026] After receiving the RRC reconfiguration message, UE3 attempts to access the primary cell (PCell) of target RAN node 5A-2 during the first available physical uplink shared channel (PUSCH) opportunity. If a pre-allocated uplink grant is provided in the uplink configuration information, this defines the first available PUSCH opportunity. If no pre-allocated uplink grant is included, UE3 monitors the physical downlink control channel (PDCCH) of the target base station to receive an uplink grant (i.e., a "dynamic" grant) in order to perform initial access without using the RACH procedure. Thus, UE3 receives the ("dynamic") uplink grant via the target cell's PDCCH (as seen in S128). UE3 uses the first available uplink grant after synchronization to the target cell.

[0027] Upon successful completion, to confirm the handover, if UE3 has an uplink grant (received via pre-allocated periodic or PDCCH), UE3 will, in S130, use the uplink grant (received via pre-allocated periodic or PDCCH) to send an RRC reconfiguration complete message (such as an RRCConnectionReconfiguration Complete message) to target RAN node 5A-2. The RRC reconfiguration complete message will include a C-RNTI (along with uplink buffer status reports and / or uplink data, whenever possible). Target RAN node 5A-2 verifies the C-RNTI sent in the RRC reconfiguration complete message. This allows target RAN node 5A-2 to begin sending data to UE3 after scheduling the appropriate downlink resources using PDCCH, as seen in S132.

[0028] The handover procedure is completed for UE3 when it receives the MAC control element (MAC CE) of the UE conflict resolution identification information from the target RAN node 5A-2 (in S134), or when UE3 receives the PDCCH addressed to its C-RNTI from the target RAN node 5A-2 after sending the initial uplink transmission.

[0029] Subsequently, UE3 can release pre-allocated uplink grant resources (if configured) in S136.

[0030] The RACH-less access procedure provides a relatively short time window between the completion of handover preparation and the completion of handover execution. If the uplink grant to be used for the first uplink message (i.e., the RRC message indicating handover completion) is a pre-allocated "configured" (periodic) grant by the target RAN node, this time window is essentially the period from when the uplink resources are reserved, during which the uplink resources are used, until these uplink resources are released. If the uplink grant to be used for the first uplink message is dynamically scheduled, this time window is essentially the period for scheduling blind decoding using PDDCH. [Prior art documents] [Patent Documents]

[0031] [Patent Document 1] European Patent Application Publication No. 4109965 [Patent Document 2] U.S. Patent Application Publication No. 2018 / 0049079 [Patent Document 3] U.S. Patent Application Publication No. 2018 / 0332507 [Patent Document 4] U.S. Patent Application Publication No. 2021 / 0120551 [Non-patent literature]

[0032] [Non-Patent Document 1] The "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Networks (NGMN) Alliance is available from https: / / www.ngmn.org / 5g-white-paper.html. [Overview of the project] [Problems that the invention aims to solve]

[0033] Recently, it has been agreed that RACH-less handover should be supported for NTN (e.g., NR and later). In this regard, the current consensus is that RACH-less handover for NTN will be a Layer 3 (L3) mobility procedure similar to the procedure in Figure 1 as a baseline. However, because obtaining the precise timing advance of the NTN target cell being moved without using a conventional random access procedure is complex, implementing RACH-less handover in the NTN context is more complex and difficult. In the case of NTN RACH-less handover, the timing advance of the target cell (N TAIt is assumed that the network will indicate (implicitly or explicitly) whether the initial timing advance is identical to the source cell's timing advance or is explicitly provided in some way by the network. However, how the initial timing advance is obtained for the target cell remains precisely defined. To reduce random access congestion in the target cell, dynamic grants from the target cell for RACH-less push transmissions will also be supported. In the context of NTN, the discussion of RACH-less handovers focuses on scenarios where the same feeder link / gateway is used before and after the handover. The question of whether RACH-less handovers should be limited to such handover scenarios involving the same feeder link / gateway is debatable.

[0034] However, while introducing a RACH-less L3 mobility procedure based on the procedure in Figure 1 as a baseline may offer some advantages in the context of some handovers in NTN scenarios, these advantages may be relatively limited, as such network-centric handover procedures may not be used as widely as anticipated.

[0035] Furthermore, in the case of a service link / satellite change (service link switchover / satellite switchover) resulting from a new satellite feeder link providing a new service link to the same base station, the physical RAN hardware (i.e., what implements the base station) and the radio resources used for the UE3 to connect to the wider network remain unchanged. However, when there is a change in the satellite relaying communications between the UE and the network, it is generally considered preferable to change the PCI of the cell serving the UE3. However, if the PCI changes, from the UE3's perspective, there are two different cells (one appearing and the other disappearing). As a result, the UE3 performs an L3 handover or RRC re-establishment to connect to the new cell. This results in inefficiencies in terms of the amount of signaling and the delay caused by the service interruption. A proposal has been made in which the PCI is not changed and therefore an L3 handover is not triggered, but this is also not ideal as the "soft" switchover required in this case is not efficient. [Means for solving the problem]

[0036] This disclosure aims to provide one or more devices and / or one or more related methods that at least partially address or contribute to addressing one or more of the above-mentioned problems.

[0037] In particular, the inventors noticed that while introducing a RACH-less L3 mobility procedure based on the procedure in Figure 1 as a baseline may offer some advantages in the context of some handovers in NTN scenarios, the advantages may be relatively limited, especially in the context of NTN (but not limited to), as UE-centric handover procedures are more common and prevalent.

[0038] Specifically, given the very frequent handovers (especially in the context of Earth-moving cell scenarios) and the increasing number of UEs handing over simultaneously (in quasi-Earth-fixed cell scenarios), the use of more UE-centric handover procedures, such as so-called conditional handovers (CHOs), is likely to become more desirable. A CHO is a handover that does not occur until the UE being handed over (not the network) determines that one or more handover execution conditions are met. If one or more handover execution conditions are met, the UE performs the handover. Upon receiving a CHO configuration from the network, the UE begins evaluating one or more execution conditions, and then stops evaluating one or more execution conditions once the handover has been performed.

[0039] The inventors understand that CHO is likely to be a far more important and fundamental feature in the context of 5G (and beyond) systems, particularly for NTN scenarios. This is because, in effect, if CHO is present, the measurement reporting and subsequent handover command signaling that would otherwise be required can be avoided in order to determine that the handover conditions are met and to trigger the handover execution. Instead, the execution conditions and RRC configuration (potentially for multiple different target cells) are pre-configured well in advance of the possible time when the handover needs to be performed. Such CHO can also reduce the delay associated with handover interruptions, which can be much longer in NTN scenarios than in conventional terrestrial network scenarios.

[0040] However, in the context of CHO, particularly in NTN scenarios, while it is desirable to introduce RACH-less access, it is generally considered not easy to implement, and there is a common perception against doing so. This is because, in the case of CHO, it is unknown whether, or when, a handover to any particular target cell for which a handover is pre-prepared will actually occur. Therefore, it is difficult for the target RAN node (base station) to decide whether and when to initiate the transmission of any dynamic grant to the UE for the target cell. Furthermore, if pre-allocated grants are used, the target RAN node does not know whether the pre-allocated grant will ever be used, and if so, whether it will be used in real time. Therefore, such pre-allocated grants may be wasted.

[0041] In one embodiment, a method is provided which is performed by a candidate access network node, the method comprising receiving at least one message from the serving access network node to at least one candidate cell of a candidate access network node from the serving cell of the serving access network node to request user equipment (UE) to prepare for a conditional handover, the at least one candidate cell being a candidate to be the target cell for the conditional handover, and the candidate access network node being a candidate to be the target access network node for the conditional handover, the method comprising sending at least one message to the serving access network node containing configuration information relating to a conditional handover to at least one candidate cell, the configuration information including information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel.

[0042] The method may further include scheduling at least one resource for uplink communication for use by the UE in an access procedure, and, if the UE performs an access procedure to access at least one candidate cell, receiving an uplink message from the UE sent using the at least one resource for uplink communication scheduled by the candidate access network node.

[0043] The uplink message can indicate that a conditional handover to at least one candidate cell has been completed in the UE.

[0044] The method may further include receiving a notification from a serving access network node that a conditional handover to at least one candidate cell has been initiated or will be initiated, and receiving an uplink message based on the notification.

[0045] This method may further include dynamically scheduling at least one resource for uplink communication based on a notification, and receiving uplink messages using at least one resource for uplink communication.

[0046] The method further includes pre-configuring at least one resource for uplink communication before receiving a notification, and receiving based on the notification may further include decoding the uplink message based on the notification.

[0047] Scheduling may involve the dynamic scheduling of at least one resource for uplink communication.

[0048] This method may further include receiving time information from a serving access network node indicating the predicted time when a UE will leave a serving cell and / or the predicted time when a UE will enter at least one candidate cell, and the timing of dynamic scheduling is based on this time information.

[0049] Scheduling may include pre-configuring at least one resource for uplink communication as a configured grant.

[0050] A configured grant may be specifically configured to be used by the UE for uplink communication in access procedures related to conditional handovers.

[0051] The configured grant can be configured for competition-based uplink communications.

[0052] Configuration information regarding conditional handovers may include scheduling information for configuring the configured grants.

[0053] Configuration information regarding conditional handovers may include time information that constitutes the period during which the configured grant is valid.

[0054] Time information can be configured to define the period during which a configured grant is valid for a further duration of time-based conditions for triggering a conditional handover.

[0055] The method may further include receiving additional time information from the serving access network node indicating the predicted time when the UE will leave the serving cell and / or the predicted time when the UE will enter at least one candidate cell, the time information being based on the additional time information.

[0056] In another embodiment, a method is provided which is performed by a serving access network node, the method comprising sending at least one message from the serving cell of the serving access network node to at least one candidate cell of a candidate access network node to at least one candidate cell in the candidate access network node in order to request user equipment (UE) to prepare for a conditional handover, the at least one candidate cell being a candidate to be a target cell for the conditional handover, and the at least one candidate access network node being a candidate to be a target access network node for the conditional handover, the method comprising receiving at least one message from the target access network node containing configuration information regarding a conditional handover to at least one candidate cell, and transmitting configuration information regarding a conditional handover to the UE, the configuration information including information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel.

[0057] The method may further include receiving a first notification from the UE that a conditional handover to at least one candidate cell has been initiated or will be initiated, and sending a second notification to the candidate access network node that a conditional handover to at least one candidate cell has been initiated or will be initiated.

[0058] The method may further include receiving time information from the UE indicating the predicted time for the UE to leave the serving cell and / or the predicted time for the UE to enter at least one candidate cell, and transmitting the time information to at least one candidate access network node.

[0059] In another embodiment, a method is provided which is performed by user equipment (UE), the method comprising receiving configuration information relating to a conditional handover from a serving cell of a serving access network node to at least one candidate cell of at least one candidate access network node, wherein at least one candidate cell is a candidate to be the target cell of the conditional handover, and at least one candidate access network node is a candidate to be the target access network node of the conditional handover, and the configuration information includes information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel.

[0060] The method may further include performing an access procedure to access a specific candidate cell of a specific candidate access network node, the access procedure may include sending an uplink message to the specific candidate access network node that has been sent using at least one resource for uplink communication scheduled by the specific candidate access network node.

[0061] This method may further include sending a notification to the serving access network node that a conditional handover to at least one candidate cell has been initiated or is about to be initiated.

[0062] This method may further include sending time information to the serving access network node indicating the predicted time at which the UE will leave the serving cell and / or the predicted time at which the UE will enter at least one candidate cell.

[0063] In another embodiment, a method is provided which is performed by user equipment (UE), which includes sending an initial uplink message to an access network node using at least one uplink resource as part of an initial access procedure that does not involve the use of a random access channel, wherein at least one uplink resource is a resource configured for conflict-based uplink communication, and the method includes, if no conflict resolution indication is received from the access network node within a first period, retransmitting the initial uplink message to the access network node using at least one uplink resource, if a conflict resolution indication is received from the access network node within the first period, treating the initial access procedure as having been successfully completed in further communication with the access network node, and if no conflict resolution indication is received from the access network node within a second period, treating the initial access procedure as not having been successfully completed.

[0064] The method may further include, if a conflict resolution indication is not received from the access network node within a first period and is still not received within a third period beginning from the end of the first period, repeatedly resending the initial uplink message to the access network node using at least one uplink resource.

[0065] This method may further include performing a fallback initial access procedure using a random access channel if a conflict resolution indication is not received from the access network node within a second period.

[0066] If a conflict resolution notification is received from an access network node, the notification may include at least some of the information contained in the uplink message.

[0067] If a conflict resolution notification is received from an access network node, the notification may be provided using a media access control (MAC) control element (CE).

[0068] If a conflict resolution notification is received from an access network node, the notification may be provided using downlink control information (DCI).

[0069] DCI can be encoded using the radio network temporary identifier (RNTI) associated with the UE.

[0070] In another embodiment, a method is provided which is performed by an access network node, comprising receiving an initial uplink message from user equipment (UE) using at least one uplink resource, which is configured for conflict-based uplink communication, as part of an initial access procedure that does not involve the use of a random access channel, and the method comprises sending a conflict resolution indication to the UE and treating the initial access procedure as successfully completed in further communication with the UE.

[0071] In another embodiment, a method is provided which is performed by user equipment (UE), which includes communicating with an access network node in a first cell provided by the access network node via a first non-terrestrial platform, based on a connectivity configuration, and receiving cell-related information from the access network node via the first non-terrestrial platform, which is applied to the first cell when the first cell is provided by the access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or to a second cell provided by the access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform, which includes preparing for communication via the second non-terrestrial platform based on the cell-related information following a change in the non-terrestrial platform, and continuing communication with the access network node based on a connectivity configuration in the first cell, or in the second cell if the second cell replaces the first cell.

[0072] Cell-related information may include a new physical cell identifier (PCI) that applies to the first cell when it is provided by an access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or to the second cell provided by an access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform.

[0073] This method may further include (re)detecting the first cell, or the second cell if the second cell replaces the first cell, based on a new PCI, before continuing communication.

[0074] Cell-related information may include information indicating the time when changes to the non-ground platform will be made and / or other conditions that will be met at that time.

[0075] Cell-related information may include supporting information regarding the second non-terrestrial platform.

[0076] This method may further include obtaining support information about the second non-terrestrial platform that has been broadcast via the second non-terrestrial platform before continuing communication.

[0077] This method may further include temporarily interrupting the uplink communication before continuing the communication.

[0078] This method may further include recalculating the timing alignment for communication via a second non-terrestrial platform before continuing communication.

[0079] In another embodiment, a method is provided which is performed by an access network node, which, based on a connectivity configuration, communicates with user equipment (UE) in a first cell provided by the access network node via a first non-terrestrial platform, and transmits cell-related information to the UE via the first non-terrestrial platform, which is applied to the first cell when the first cell is provided by the access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or to a second cell provided by the access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform, and the method is provided which, based on a connectivity configuration, communicates with the UE in the first cell, or in the second cell if the second cell replaces the first cell.

[0080] In another embodiment, a candidate access network node is provided, the candidate access network node includes means for receiving at least one message from the serving access network node to at least one candidate cell of the candidate access network node from the serving cell of the serving access network node to request user equipment (UE) to prepare for a conditional handover, the at least one candidate cell being a candidate to be the target cell for the conditional handover, the candidate access network node being a candidate to be the target access network node for the conditional handover, the candidate access network node includes means for sending at least one message to the serving access network node including configuration information relating to a conditional handover to at least one candidate cell, the configuration information including information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel.

[0081] In another embodiment, a serving access network node is provided, the serving access network node includes means for sending at least one message from the serving cell of the serving access network node to at least one candidate cell of a candidate access network node to at least one candidate access network node in order to request user equipment (UE) to prepare for a conditional handover, the at least one candidate cell being a candidate to be a target cell for the conditional handover, and the at least one candidate access network node being a candidate to be a target access network node for the conditional handover, the serving access network node includes means for receiving at least one message from a target access network node containing configuration information relating to a conditional handover to at least one candidate cell, and means for sending configuration information relating to a conditional handover to the UE, the configuration information including information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel.

[0082] In another embodiment, user equipment (UE) is provided, which includes means for receiving configuration information from a serving access network node relating to a conditional handover from a serving cell of a serving access network node to at least one candidate cell of at least one candidate access network node, wherein at least one candidate cell is a candidate to be the target cell of the conditional handover, and at least one candidate access network node is a candidate to be the target access network node of the conditional handover, and the configuration information includes information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel.

[0083] In another embodiment, user equipment (UE) is provided, which includes means for transmitting an initial uplink message to an access network node using at least one uplink resource as part of an initial access procedure that does not involve the use of a random access channel, wherein at least one uplink resource is a resource configured for conflict-based uplink communication; means for retransmitting the initial uplink message to the access network node using at least one uplink resource if no conflict resolution indication is received from the access network node within a first period; means for treating the initial access procedure as successfully completed in further communication with the access network node if a conflict resolution indication is received from the access network node within a first period; and means for treating the initial access procedure as not successfully completed if no conflict resolution indication is received from the access network node within a second period.

[0084] In another embodiment, an access network node is provided, which includes means for receiving an initial uplink message from user equipment (UE) using at least one uplink resource, as part of an initial access procedure that does not involve the use of a random access channel, wherein at least one uplink resource is a resource configured for conflict-based uplink communication; means for sending a conflict resolution indication to the UE; and means for treating the initial access procedure as successfully completed in further communication with the UE.

[0085] In another embodiment, user equipment (UE) is provided, the user equipment (UE) comprises means for communicating with an access network node in a first cell provided by the access network node via a first non-terrestrial platform, based on a connection configuration, and means for receiving cell-related information from the access network node via the first non-terrestrial platform, which applies to the first cell when the first cell is provided by the access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or to a second cell provided by the access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform, the user equipment comprises means for preparing for communication via the second non-terrestrial platform based on cell-related information following a change in the non-terrestrial platform, and means for continuing communication with the access network node in the first cell, or in the second cell if the second cell replaces the first cell, based on a connection configuration.

[0086] In another embodiment, an access network node is provided, which, based on a connection configuration, includes means for communicating with user equipment (UE) in a first cell provided by the access network node via a first non-terrestrial platform, and means for transmitting cell-related information to the UE via the first non-terrestrial platform, the cell-related information being applied to the first cell when the first cell is provided by the access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or to a second cell provided by the access network node via a second non-terrestrial platform replacing the first cell following a change in the non-terrestrial platform, and the access network node includes means for continuing communication with the UE in the first cell or in the second cell if the second cell replaces the first cell, based on a connection configuration.

[0087] To facilitate understanding for those skilled in the art, this disclosure is described in detail in the context of 3GPP systems (including NTN's 5G network), but the principles of this disclosure may also be applicable to other systems. While this disclosure is primarily motivated by NTN use cases, exemplary embodiments may also be applicable to other use cases, including handovers, particularly conditional handovers (CHOs).

[0088] The aspects of this disclosure are described in the attached independent claims, and optional but beneficial features are described in the attached dependent claims.

[0089] Aspects of the present disclosure extend to computer program products such as computer-readable storage media that internally store corresponding systems, devices, and instructions, the instructions being operable to program a programmable processor to perform the methods described above or as stated in the claims, and / or to program a computer appropriately adapted to provide the device stated in any of the claims.

[0090] Each feature disclosed herein (this term includes the claims) and / or shown in the drawings may be incorporated into this disclosure independently of (or in combination with) any other disclosed and / or illustrated features, where it is technically feasible to do so. In particular, but not limited to, any feature of a claim dependent on a particular independent claim may be introduced into that independent claim in any combination or individually, provided that doing so does not result in a technical incompatibility or result in something that does not make technical sense.

[0091] Exemplary embodiments of the present disclosure are described herein by reference to the accompanying drawings. [Brief explanation of the drawing]

[0092] [Figure 1] This is a simplified sequence diagram illustrating the handover procedure involving RACH-less initial access to the target cell. [Figure 2] This figure schematically illustrates a mobile (cellular or wireless) communication system to which exemplary embodiments of the present disclosure may be applied. [Figure 3] Figure 2 is a schematic diagram showing a non-terrestrial network (NTN) wireless access network that may be used in the communication system shown. [Figure 4] Figure 2 is a simplified diagram of a portion of the ASN.1 definition of the data structure of NTN configuration information elements that can be used in the communication system shown in Figure 2. [Figure 5A]This diagram shows the possible architectures for NTN RAN. [Figure 5B] This diagram shows the possible architectures for NTN RAN. [Figure 5C] This diagram shows the possible architectures for NTN RAN. [Figure 6] Figure 2 is a simplified sequence diagram showing a RACH-based conditional handover procedure that may be used in the communication system. [Figure 7] This diagram shows a typical service link / satellite transition scenario where there is a service link / satellite change serving the area where the UE is located. [Figure 8] This is a simplified sequence diagram showing a RACH-less conditional handover procedure that may be used in the communication system shown in Figure 2. [Figure 9] Figure 2 is a simplified time-frequency diagram showing how uplink grants can be configured for competition-based push in the communication system. [Figure 10] This is a simplified sequence diagram showing a RACH-less initial access procedure using competition-based PUSCH, which may be used in the communication system shown in Figure 2. [Figure 11] This is a simplified sequence diagram showing another RACH-less conditional handover procedure that may be used in the communication system shown in Figure 2. [Figure 12] This is a simplified sequence diagram showing a procedure for reporting predicted cell departure / entry times in the context of a RACH-less conditional handover procedure, which may be used in the communication system shown in Figure 2. [Figure 13] This is a simplified sequence diagram showing the procedure for configuring the valid time window in the context of a RACH-less conditional handover procedure that may be used in the communication system shown in Figure 2. [Figure 14] This is a simplified sequence diagram showing a first simplified RACH-less procedure that may be used in the communication system shown in Figure 2. [Figure 15]This is a simplified diagram of a portion of the ASN.1 definition of the data structure of the system information block, which can be used in the procedure shown in Figure 14. [Figure 16] This is a simplified diagram of part of the ASN.1 definition of the data structure of an RRC reconstructed message, which can be used in the procedure shown in Figure 14. [Figure 17] This is a simplified sequence diagram showing a simplified first RACH-less procedure that may be used in the communication system shown in Figure 2. [Figure 18] Figure 2 is a simplified block diagram showing the main components of user equipment that may be used in the communication system. [Figure 19] Figure 2 is a simplified block diagram showing the main components of a base station / access network node that may be used in the communication system. [Modes for carrying out the invention]

[0093] overview Here, an exemplary communication system will be described using general terminology, with reference to Figures 2-6, merely as an example.

[0094] Figure 2 is a schematic diagram of a mobile ("cellular" or "wireless") communication system 1 to which exemplary embodiments of the present disclosure are applicable.

[0095] In network 1, user equipment (UE) 3 (3-1, 3-2, 3-3) (e.g., mobile phones and / or other portable devices) can communicate with each other via corresponding radio access networks (RAN) 5-1, 5-2 that operate according to one or more compatible radio access technologies (RATs). In the illustrated example, each RAN 5-1, 5-2 includes base stations 5A (5A-1, 5A-2) (e.g., NR / 5G base stations 5A (5A-1, 5A-2) such as gNB5A (5A-1, 5A-2)) that operate one or more associated cells 9 (9-1, 9-2).

[0096] As those skilled in the art will understand, three UE3s and two RAN5-1s and 5-2s are shown in Figure 2 for illustrative purposes, but in implementation, the system typically includes other RAN5s and UE3s.

[0097] Each RAN5-1, 5-2 directly controls one or more associated cells, or indirectly controls them through one or more other nodes (e.g., home base stations, relays, remote radio heads, distributed units, etc.). It will be understood that RAN5 can be configured to support both 4G and 5G, and / or any other 3GPP or non-3GPP communication protocols.

[0098] Each RAN5 base station has at least one distributed unit (DU) 5A (e.g., gNB-DU). DU And, (for example, gNB-CU) central unit (CU) 5A CU A distributed base station may also be provided with the following: In such a distributed base station, the CU uses a separate control plane and user plane, and therefore the CU itself is also divided into a control plane function (CU-CP) and a user plane function (CU-UP), which communicate with the DU via the F1-C logical interface and the F1-U logical interface (together forming the F1 interface (or "reference point")), and communicate with each other via the E1 logical interface. The DU provides the functionality of the lower part of the PHY layer and therefore may include the physical and virtual elements necessary to communicate with the UE3 via the air interface, but it will be understood that the base station may alternatively (or additionally) include one or more separate radio units (RUs) (e.g., providing this functionality of the lower part of the PHY layer). Nevertheless, it will be understood that the base station may be in a non-distributed form, for example, as an integrated gNB or eNB.

[0099] UE3 and their serving RAN5 are connected via appropriate air interfaces (e.g., so-called "Uu" interfaces and / or similar). Adjacent RAN5 base stations may be connected to each other via appropriate inter-base station interfaces (e.g., so-called "X2" interfaces, "Xn" interfaces and / or similar).

[0100] The core network 7 includes several logical nodes (or "functions") to support communication in the communication system 1. In this example, the core network 7 comprises a control plane function (CPF) 10 and one or more user plane functions (UPFs) 11. The CPF 10 includes one or more Access and Mobility Management Functions (AMFs) 10-1, one or more Session Management Functions (SMFs) 10-2, and several other functions 10n (e.g., an Authentication Server Function (AUSF) to facilitate the 5G security process, Unified Data Management (UDM) entities for managing user-specific data (e.g., access permissions, user registration, and data network profiles), a Policy Control Function (PCF), an Application Function (AF), etc.). It will be understood that nodes or functions may have different names in different systems.

[0101] RAN5 connects to the core network nodes via appropriate interfaces (or "reference points"), such as the N2 reference point between the RAN5 base station and AMF10-1 for control signaling communications, and the N3 reference point between the RAN5 base station and each UPF11 for user data communications. Each UE3 connects to AMF10-1 via a logical non-access stratum (NAS) connection on the N1 reference point (similar to the S1 reference point in LTE). It will be understood that N1 communications are routed transparently through RAN5.

[0102] One or more UPF11s are connected to an external data network (such as an IP network like the Internet) via a reference point N6 for user data communication.

[0103] The AMF10-1 performs mobility management-related functions, maintains NAS signaling connections with each UE3, and manages UE registration. The AMF10-1 also manages paging.

[0104] SMF10-2 is connected to AMF10-1 via the N11 reference point. SMF10-2 provides session management functionality (which forms part of the MME functionality in LTE) and also combines several control plane functions (provided by the serving gateway and packet data network gateway in LTE). SMF10-2 also assigns IP addresses to each UE3. SMF10-2 uses user information provided via AMF10-1 to determine the session manager best suited to the user. SMF10-2 can be effectively considered a gateway from the user plane to the network control plane. SMF10-2 also assigns IP addresses to each UE3.

[0105] RAN5 is also configured for receiving control information and user data via several downlink (DL) physical channels, and UE3 is configured for receiving control information and user data via several downlink (DL) physical channels and for transmitting several physical signals. DL physical channels correspond to resource elements (REs) that carry information emitted from higher layers, and DL physical signals are used in the physical layer and correspond to REs that do not carry information emitted from higher layers.

[0106] Physical channels may include, for example, a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), and a physical downlink control channel (PDCCH). The PDSCH carries data that shares its capacity on a time and frequency basis. The PDSCH can carry various data items, including, for example, user data, UE-specific upper-layer control messages mapped down from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) to support several functions, including scheduling downlink transmissions on the PDSCH and, similarly, uplink data transmissions on the physical uplink shared channel (PUSCH). The PBCH provides the Master Information Block (MIB) to the UE3. It also works in conjunction with the PDCCH to support time and frequency synchronization, which assists in cell acquisition, selection, and re-selection.

[0107] DL physical signals may include, for example, a reference signal (RS) and a synchronization signal (SS). The reference signal (sometimes called a pilot signal) is a signal with a predefined special waveform known to both UE3 and RAN5 base stations. Reference signals may include, for example, a cell-specific reference signal, a UE-specific reference signal (UE-RS), a downlink demodulation signal (DMRS), and a channel state information reference signal (CSI-RS).

[0108] Similarly, UE3 is configured to transmit control information and user data via several uplink (UL) physical channels corresponding to REs that carry information transmitted from higher layers, and to transmit UL physical signals used in the physical layer that do not carry information transmitted from higher layers, and the base station of RAN5 is configured to receive that control information and user data, and UL physical signals. Physical channels may include, for example, PUSCH, physical uplink control channel (PUCCH), and / or physical random-access channel (PRACH). UL physical signals may include, for example, demodulation reference signals (DMRS) for UL control / data signals, and / or sounding reference signals (SRS) used for UL channel measurements.

[0109] The UE3 and base station 5A of RAN5 of communication system 1 are configured with each other to execute a random access channel (RACH) procedure for UE3 to access the network. Specifically, upon detection and selection of a cell (and / or beam in the case of 5G), UE3 may attempt to access that cell and / or beam using an initial radio resource control (RRC) connection setup procedure that includes a random access procedure. Before attempting initial access, UE3 selects a random access resource (e.g., including a preamble) to use to initiate the RACH procedure. UE3 transmits the selected preamble (e.g., "Msg1") to the base station of RAN5 via a physical random access channel (PRACH) to initiate the process of achieving synchronization on the uplink (UL). The base station of RAN5 responds with a random access response (RAR) (or "Msg2"). The RAR includes a timing-alignment (TA) command to indicate the reception of the preamble and adjust the UE's transmission timing based on the timing of the received preamble, an uplink grant field indicating the resources to be used on the uplink for the physical uplink shared channel (PUSCH), a frequency hopping flag to indicate whether the UE transmits on PUSCH with or without frequency, an MCS field that allows the UE to determine the modulation and coding scheme (MCS) for the PUSCH transmission, and a transmit power control (TPC) command value to set the power for the PUSCH transmission. The UE3 then sends a third message ("Msg3") to the network on the physical uplink shared channel (PUSCH) based on the information in the RAR.The specific messages sent by the UE in this step, and the content of those messages, depend on the context in which the random access procedure is being used. However, in the example of an initial radio RRC connection setup, Msg3 contains an RRC setup request or similar message carrying a temporary, randomly generated UE identifier. The network responds with a fourth message ("Msg4") carrying the randomly generated UE identifier received in Msg3 for the purpose of resolving conflicts between different UEs using the same preamble sequence. If successful, Msg4 also transitions the UE to a connected state.

[0110] While a four-step conflict-based RACH procedure is described, it will be understood that the base station and UE3 of RAN5 in communication system 1 can also perform a non-conflict-based (or "no conflict") procedure in which a dedicated preamble is assigned to the UE by the base station of RAN5. Alternatively, UE3 and the base station of RAN5 in communication system 1 may perform a two-step RACH procedure (for example, as described in the introduction).

[0111] UE3 can trigger the initiation of the RACH procedure itself (for example, when UE3 needs to connect to the network), but it will be understood that the initiation of the RACH procedure may also be triggered by the network. For example, the RACH procedure may be initiated by a message sent via downlink control information (DCI) having an appropriate DCI format (e.g., 1_0) on the physical downlink control channel (PDCCH), such a message is generally known as a PDCCH order. The RACH procedure may also be initiated by a base station on RAN5 when a handover is requested (for example, using a handover command message).

[0112] NTN RAN In the exemplary communication system 1, each RAN5 may be implemented as a non-terrestrial network (NTN) RAN5.

[0113] Figure 3 schematically shows one such NTN RAN5 that may be used in the communication system shown in Figure 2.

[0114] As shown in Figure 3, NTN RAN5 comprises a base station or 5A operating one or more associated cells 9, a gateway 5B, and a non-terrestrial (space or air) platform 5C (e.g., including one or more satellites and / or airborne aircraft), which is sometimes commonly referred to as “satellite” 5C for simplification. Communications via NTN RAN5 are routed through the core network 7 and the external data network 20 (e.g., via the N6 interface / reference point).

[0115] NTN RAN5 controls the number of directional satellite beams that can be provided by the associated NTN cell 9. Specifically, each satellite beam has an associated footprint on the Earth's surface that forms an NTN cell or part of an NTN cell. Each NTN cell has associated Physical Cell Identity (PCI). The satellite beam footprint may move as satellite 5C moves along its orbit (for example, as indicated by arrow A in Figure 3). Alternatively, the satellite beam footprint may be fixed to the Earth, in which case the movement of satellite 5C can be compensated for using an appropriate satellite beam pointing mechanism (mechanical or electronic steering). In NTN, satellite beams and satellites are not considered to be visible from the perspective of the UE. However, this does not preclude the distinction between network types (e.g., NTN and terrestrial systems) at the public land mobile network (PLMN) level.

[0116] NTN RAN5 base station 5A is configured to provide ephemeris data from satellite 5C to UE3 to assist UE3 in performing measurements and cell selection / reselection and to support initial access. This ephemeris data may include information about orbital information, such as orbital plane-level or satellite-level information, and / or information (e.g., pointers or indices) that allows UE3 to retrieve more detailed ephemeris data stored in (e.g., a subscriber identity module: SIM). At least a portion of this ephemeris information may be provided, for example, in system information, and / or using UE-specific (dedicated) signaling, such as RRC signaling.

[0117] Specifically, base station 5A may provide satellite support information about the satellite as part of a dedicated system information block (SIB) broadcast to UE3 in the corresponding cell 9 of NTN RAN5 (in the case of 5G NTN, this may be, for example, SIB19, but in future generations, it may be provided in a different SIB or in a different way). The satellite support information may include information that identifies at least one relevant NTN configuration (for example, as part of NTN-Config IE, etc.). The NTN configuration includes parameters (for example, ephemeris data, common timing alignment parameters, scheduling (e.g., k_offset), validity period of uplink synchronization information, and epoch time (reference time for which the support information is valid)) to help UE3 access the network using NTN access.

[0118] Figure 4 shows, as a mere example, an abstract syntax notation one (ASN.1) definition of the data structure of NTN configuration information elements that may be used in the communication system shown in Figure 2.

[0119] Satellite-supported information may include, for example, an indication of the time when a cell provided via the NTN Quasi-Earth Fixed System (e.g., in t-Service IE) is about to cease service to the area it currently covers. This can be expressed, for example, as a time in multiples of 10 milliseconds after 00:00:00 on January 1, 1900 (midnight between Sunday, December 31, 1899 and Monday, January 1, 1900). The exact time of the cessation may be between the time indicated by the value in this field minus 1 and the time indicated by the value in this field.

[0120] With the help of this ephemeris data, UE3 can search for a first connectable NTN cell. After detecting the synchronization signal block (SSB) of cell 9 broadcast via satellite 5C, UE3 can read the initial system information of that cell, which may contain further ephemeris information about the cell's exact location (and / or about the satellite broadcasting the cell). This ephemeris information may be given, for example, in relation to information about the orbital plane that UE3 may have already obtained.

[0121] Because the accuracy of satellite orbit or satellite position predictions can decrease over time, the ephemeris data provided to UE3 is updated (a)periodically to help ensure accuracy.

[0122] The same PCI may be used for several satellite beams, or there may be one PCI per satellite beam. A satellite beam can consist of one or more SSB beams, and one cell (PCI) has up to L SSB beams, where L is typically 4, 8, or 64 depending on the bandwidth. During initial access, the UE3 performs cell discovery based on the SSBs, with each SSB transmitted on a different beam. Each SSB includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH). Since an SSB carries the synchronization signal (SS) / PBCH (SS / PBCH) transmission, it is sometimes called an SS / PBCH block.

[0123] As those skilled in the art will understand, although this disclosure is described in the context of NTN-based RAN / base stations, many of the technical features described are generally applicable to and can be implemented in any RAN / base station of more conventional (non-NTN) based communication systems.

[0124] NTN RAN Architecture Figures 5A to 5C show possible architectures for NTN RAN5 that can be used.

[0125] For the sake of explanation, NTN RAN5 will be described based on the architecture shown in Figure 5A when implemented in communication system 1. However, it should be understood that NTN RAN5 may potentially use one of the different architectures, and the entities of communication system 1 may be adapted accordingly.

[0126] The architecture of FIG. 5A is sometimes referred to as a "transparent satellite" - based RAN architecture. In this architecture, base station 5A is a terrestrial base station that transmits and receives communications destined for and originating from UE3 via a gateway 5B located on the ground and via a satellite 5C that does not have base station functionality. Satellite 5C relays these communications between UE3 within one or more cells operated by base station 5A and, if necessary, between satellite 5C and gateway 5B. The non - terrestrial platform 5C transparently relays these communications without on - board processing and effectively functions as a so - called "bent pipe". In this embodiment, the feeder link between gateway 5B and satellite 5C effectively functions as part of the NR - Uu interface (or reference point) between base station 5A and one or more UE3. Similarly, the service link between satellite 5C and one or more UE3 effectively functions as the other part of the NR - Uu interface (or reference point) between base station 5A and one or more UE3. The communication link of the base station with the core network 7 (for signaling via, for example, N1, N2, N3 interfaces / reference points, etc.) is provided only on the ground.

[0127] The architecture of FIG. 5B is sometimes referred to as a "regenerative relay satellite" - based RAN architecture (i.e., where the satellite performs on - board processing of the payload being communicated between UE3 and core network 7). In this architecture, base station 5A is a distributed base station 5A having a Central Unit (CU) 5A installed on the ground CU and a Distributed Unit (DU) 5A mounted on satellite 5C. DU The CU5A located on the ground CU performs part of the functions of base station 5A (typically the upper layers), while the non - terrestrial DU5A DU performs the other (typically lower layer) functions of base station 5A. The CU5A located on the ground CUThis includes Gateway 5B and Gateway 5B and DU5A DU The F1 interface, which is implemented via a satellite radio interface with satellite 5C, is provided for DU5A, which is not located on the ground. DU It communicates with [the other party].

[0128] Satellite 5C transmits and receives communications between it and Gateway 5B, as needed, to and from UE3s in one or more cells operated by Base Station 5A. However, in this implementation, the lower-layer processing of communications originating to or from one or more UE3s is handled by DU5A. DU The higher layer processing of communications sent to and from UE3, which are executed on satellite 5C, is handled by CU5A located on the ground. CU It is executed by [the specified method / system].

[0129] Therefore, in this implementation, the feeder link between gateway 5B and satellite 5C is connected to base station CU5A CU and DU5A DU It effectively functions as the F1 interface (or reference point) between it and the satellite 5C. On the other hand, the service link between satellite 5C and one or more UE3s effectively functions as the NR-Uu interface (or reference point) between base station 5A and one or more UE3s. The base station's communication link with the core network 7 (for signaling via, for example, N1, N2, N3 interfaces / reference points, etc.) is provided only on the ground.

[0130] The architecture in Figure 5C is sometimes referred to as a “regenerative relay satellite” based RAN architecture (i.e., the satellite performs onboard processing of payloads being communicated between UE3 and the core network 7). In this configuration, base station 5A is mounted on satellite 5C. Base station 5A, mounted on satellite 5C, performs, as needed, communication to and from UE3 in one or more cells operated by base station 5A, and communication to and from the core network 7 via gateway 5B. However, in this embodiment, the processing of communications destined for and from UE3 is performed on satellite 5C by base station 5A.

[0131] Therefore, in this implementation, the feeder link between gateway 5B and satellite 5C effectively functions as part of the N1 / N2 / N3 interface (or reference point) between base station 5A and core network 7. Thus, the base station's communication link with core network 7 (e.g., for signaling via N1, N2, N3 interface / reference point, etc.) is provided partly via the feeder link and partly on the ground. On the other hand, the service link between satellite 5C and one or more UE3 effectively functions as the NR-Uu interface (or reference point) between base station 5A and one or more UE3.

[0132] This allows base station 5A to control one or more associated cells via n satellites 5C. It will be understood that base station 5A may be configured to support both 4G and 5G, and / or any other 3GPP or non-3GPP communication protocols.

[0133] RACH-based conditional handover UE3 and RAN5 of communication system 1 are configured to perform RACH-based conditional handover (CHO) as needed.

[0134] Here, with reference to Figure 6, an exemplary RACH-based conditional handover (CHO) procedure that may be used in communication system 1 is described as merely an example.

[0135] Figure 6 is a simplified sequence diagram showing a RACH-based conditional handover procedure that may be implemented in communication system 1.

[0136] Referring to Figure 6, the CHO procedure in this case concerns the handover of UE3 between the source cell of source base station 5A-1 and the target cell (of potentially multiple candidate cells) of target base station 5A-2. Target base station 5A may be one of a number of candidate base stations (i.e., candidates that could become the handover base station 5A-2), each capable of operating one or more candidate cells (i.e., candidates that could be the target cell).

[0137] Before the CHO procedure is initiated, the source base station 5A-1 that serves and communicates with UE3 in S602 (i.e., the source base station 5A-1 of the CHO) typically remembers the UE context of UE3. This may include, for example, information regarding roaming and access restrictions provided when the connection between the UE and source base station 5A-1 was established or at the time of the last tracking area update.

[0138] Source base station 5A-1 configures the measurement procedure to be performed by UE3, and UE3 reports according to the measurement configuration (S612). At some point, source base station 5A-1 makes a decision to configure UE3 for CHO in order to hand over UE3, for example, based on the measurement results and / or radio resource management (RRM) information received in the measurement report (S614).

[0139] Therefore, in S616-x and / or S616-2, source base station 5A-1 proceeds to send a handover request and request CHO for each of the one or more candidate cells belonging to one or more candidate base stations 5A-x, 5A-2, including target base station 5A-2. A CHO request message is sent for each candidate cell.

[0140] Although not shown in the diagram, it will be understood that admission control may be performed by each candidate base station 5A-x, 5A-2. For example, if the corresponding slice information has been sent to that candidate base station 5A-x, 5A-2, slice-oriented admission control may be performed, and if a protocol data unit (PDU) session is associated with an unsupported slice, the candidate base station 5A-x, 5A-2 may reject such a PDU session.

[0141] Each candidate base station 5A-x, 5A-2 transmits its respective CHO response (e.g., a handover request acknowledgment message) for each CHO candidate cell to source base station 5A-1 (S618-x, S618-2). Each CHO response includes the configuration of the corresponding CHO candidate cell (e.g., an RRC reconfiguration message).

[0142] In S622, source base station 5A-1 sends an RRC reconfiguration message to UE3 (for example, an RRCReconfiguration message in a 5G system). The RRC reconfiguration message includes information indicating the configuration for each candidate CHO cell and information indicating the execution conditions for one or more CHOs determined by source base station 5A-1. Although not shown, it will be understood that other reconfiguration information from source base station 5A-1 may follow the CHO configuration for one or more candidate cells.

[0143] In S630, UE3 sends an appropriate RRC reconfiguration completion message (for example, an RRCReconfigurationCompletion message in a 5G system) to source base station 5A-1 (effectively confirming RRC reconfiguration).

[0144] In S624, after receiving the CHO configuration, UE3 maintains its connection with the source base station 5A-1 and begins evaluating the CHO execution conditions for one or more candidate cells (for example, based on measurements performed by UE3). If one or more measurement results for at least one CHO candidate cell satisfy the corresponding CHO execution conditions, UE3 detaches from the source base station 5A-1, applies the stored corresponding configuration to the selected candidate cell (which is the handover target cell), and synchronizes with that candidate (target) cell (S626).

[0145] In S638, UE3 performs a RACH-based initial access procedure with the candidate (i.e., target) base station 5A-2 that will operate the target cell. Specifically, UE3 sends a selected preamble (e.g., "Msg1") to the target base station 5A-2 via RACH to initiate the process for uplink (UL) synchronization. In response, the RAN5 base station responds with a RAR (or "Msg2"). The RAR indicates receipt of the preamble and includes a Timing-Alignment (TA) command to adjust UE3's transmission timing based on the timing of the received preamble, and an uplink grant field indicating the resources to be used by PUSCH (and other information as needed). Then, based on the information in the RAR, UE3 sends an RRC reconfiguration completion message (e.g., an RRCReconfiguration Completion message in a 5G system) as Msg3 to the network via PUSCH. This completes the RRC handover procedure. UE3 releases the stored CHO configuration after the RRC handover procedure has successfully completed.

[0146] Next, in S460, the target base station 5A-2 sends a message to the source base station 5A-1 indicating that the handover was successful (e.g., a handover success message) to notify the source base station 5A-1 that UE3 has successfully accessed the target cell. Then, if necessary, the source base station 5A-1 can send a message (e.g., a handover cancellation message) (in S642-x) to cancel the handover of any other candidate cell at the target base station 5A-2 and / or any other candidate base station 5A-x, thereby canceling the CHO of UE3 at that candidate base station 5A-x.

[0147] RACH-less conditional handover Beneficially, UE3 and RAN5 of communication system 1 are also configured to perform RACH-less conditional handover (CHO) as needed.

[0148] Specifically, as will be explained in more detail later, for example, UE3 and RAN5 of communication system 1 may be configured to perform a general RACH-less CHO procedure. In this procedure, RACH skip / RACH-less can be configured by one or more candidate base stations 5A-x / 5A-2 for one or more associated candidate cells (e.g., as an optional configuration of the corresponding CHO configuration). If RACH skip is configured by a candidate base station 5A-x / 5A-2, that candidate base station 5A-x / 5A-2 may also further configure one or more associated pre-allocated periodic uplink grants (e.g., as an optional configuration of the corresponding CHO configuration). When UE3 detaches from an old (source) cell, UE3 can perform downlink and uplink synchronization to a new (target) cell without using the RACH procedure. As will be described in more detail later, UE3 can send an initial RRC reconfiguration complete message using PUSCH configured according to one of several different options, including using a pre-configured CG (potentially affected by the "effective" time similar to that described below), using dynamic scheduling, and / or using a competition-based CG (as will be described in more detail later).

[0149] UE3 and RAN5 of communication system 1 are also configured to interact with each other to make several extensions and modifications to the CHO procedure, which may be used depending on the requirements.

[0150] For example, UE3 and RAN5 of communication system 1 are configured to perform RACH-less initial access using a competition-based PUSCH. The RACH-less initial access procedure using a competition-based PUSCH may be used by UE3 for initial access in a target cell after a CHO, or possibly for initial access procedures during other mobility / cell change procedures, including conventional handovers (HO) and / or L1 / L2 triggered mobility (LTM). Beneficially, a competition-based PUSCH may also provide benefits during the access procedure for forming an initial connection in a cell (e.g., RRC connection setup) and / or for resuming such a connection (e.g., RRC connection resumption). In this example, target base station 5-2A can configure a competition-based PUSCH in UE3 via broadcast system information and / or via dedicated signaling. The competition-based PUSCH may be, for example, a periodic CG (i.e., a CG that appears continuously in time). Furthermore, beneficially, multiple grants can potentially consist of the same time slot but at different frequency positions. Multiple grants can also potentially consist of (e.g., at different timings) within a single competition-based push period.

[0151] In another example, UE3 and RAN5 of communication system 1 are configured to perform a RACH-less CHO procedure in which, when one or more CHO execution conditions are met (or about to be met), the UE reports to the source (serving) base station 5A-1 in the source cell (current serving cell) that UE3 is about to perform a CHO to a selected target cell. The source base station 5A-1 then notifies the target base station 5A-2 (for example, in the case of an inter-base station CHO) of UE3's next CHO to the target cell. This is particularly useful for the target base station 5A-2 to know when to start dynamic scheduling of UE3 in the target cell (i.e., the (approximately) optimal time), and / or when the pre-configured / pre-assigned configuration grant will actually be used in real time. Therefore, in practice, by notifying the source base station 5A-1 of an impending CHO, UE3 provides an implicit indication of the approximate timing of the CHO, which may be used by the target base station 5A-2 to optimize the timing of downlink scheduling and / or PUSCH monitoring / reception.

[0152] In another example, UE3 and RAN5 of communication system 1 are configured to perform a RACH-less CHO procedure, and UE3 can calculate the predicted time to leave the current cell (i.e., the serving / source cell) and / or the predicted time to enter another cell (i.e., the adjacent / target cell), and report one or more predictions to the source (serving) base station 5A-1. The source base station 5A-1 then forwards the reported information to the target base station 5A-2 in the target cell. This prediction-related information can then be appropriately used by the base stations to appropriately preconfigure uplink grants (potentially having one or more associated "effective" time windows, similar to those described below with reference to Figure 13, for example), and / or determine the (approximately) optimal timing to initiate dynamic scheduling of UE3.

[0153] In another example, RAN5 of communication system 1 is configured to define an "effective" time window in relation to the relevant CHO (or possibly conventional handover) configuration (e.g., in an RRC reconfiguration message sent from candidate / target base stations 5A-x 5A-2 to source base station 5A-1). This may be, for example, an independent time window, or it may be linked to a time window defined by the configuration of a time-based CHO trigger event (e.g., a so-called "CondEvent T1") if the execution condition corresponds to that CHO trigger event. If UE3 receives a pre-configured uplink grant with an effective time window, the uplink grant is considered valid during the indicated window. Otherwise, the uplink grant is held or released. If the CHO execution condition is met but the timing of execution falls outside the effective time window, UE3 may need to fall back to a RACH-based CHO procedure, use an uplink resource configured for a scheduling request (SR), or release the corresponding CHO configuration. The effective time may be applicable to several scenarios. For example, the validity window may be used in the case of a quasi-earth-fixed cell, in which case a time parameter is typically configured that indicates the time at which the cell provided via the NTN quasi-earth-fixed system is about to cease providing service to the area it currently covers (e.g., the parameter called "t-service" mentioned above), and thus the handover time is predetermined. The validity window may also be used for earth-moving cells, in which case it is possible to predict approximately how long the UE3 will remain in the current cell before a handover occurs, and / or the validity time can be determined based on the observed handover frequency. The network can also use the validity window as a reference based on a network-side prediction of the timing of the next handover of the UE3, for example, using an appropriate artificial intelligence / machine learning (AI / ML) algorithm.

[0154] It will be understood that the exemplary features described above are not mutually exclusive. Nevertheless, these exemplary features are also independent of each other. Therefore, any combination of one, some, or all of these features can be implemented in communication system 1 to provide relevant benefits.

[0155] Satellite switching Figure 7 shows a typical service link / satellite switching scenario, where the service link / satellite serving the area where UE3 is located is changed from the first satellite (5C-1 to the second satellite 5C-2).

[0156] As shown in Figure 7, when a service link / satellite changes due to satellite relocation, and the feeder link of the new satellite 5C-2 providing the new service link passes through the same base station 5A and gateway 5B as the old satellite 5C-1, the physical RAN hardware (i.e., implementing the base station) and associated radio resources that cell 9-1 (when served via the first satellite 5C-1) and cell 9-2 (when served via the second satellite 5C-2) pass through remain unchanged. Therefore, except that they are served via different satellites 5C-1 and 5C-2, cell 9-1 (when served via the first satellite 5C-1) and cell 9-2 (when served via the second satellite 5C-2) are essentially the same serving cell 9.

[0157] Nevertheless, as explained above, it is possible for serving cell 9 to have different PCIs before and after the satellite switchover, but it is also possible for serving cell 9 to have the same PCI before and after the satellite switchover.

[0158] Beneficial, as will be explained in more detail, UE3 and RAN5 of communication system 1 are also configured to perform a simplified RACH-less procedure (i.e., without performing all the steps normally considered necessary for a Layer 3 (L3) handover procedure) in the event of a satellite switchover.

[0159] Advantageously, UE3 and RAN5 of communication system 1 may be configured for a first version of a simplified RACH-less procedure for scenarios where PCI changes. Advantageously, UE3 and RAN5 of communication system 1 may also be configured for a second version of a simplified RACH-less procedure for scenarios where PCI does not change.

[0160] Specifically, as will be explained in more detail later, in the first version of the simplified RACH-less procedure, when it indicates that the PCI and satellite 5C-1 of the serving cell have been replaced by another satellite 5C-2 and PCI at the indicated time (e.g., indicated by the t-Service parameter or some other parameter), or when some other “replacement” condition is met, UE3 does not perform the RACH procedure or L3 handover. UE3 simply detaches from the “old” cell 9-1 (identified by the old PCI) and synchronizes to the “new” / “replacement cell” (identified by the new PCI).

[0161] Furthermore, as will be explained in more detail later, in the second version of the simplified RACH-less procedure, if the serving cell's satellite 5C-1 is replaced by another satellite 5C-2, UE3 also does not perform either the RACH procedure or the L3 handover. UE3 simply (re)acquires the appropriate satellite support information for the new satellite 5C-2 and can recalculate the timing alignment based on the replacement satellite (and other necessary) information indicated by the NTN configuration corresponding to the newly (re)acquired satellite 5C-2. Thus, UE3 can obtain proper uplink synchronization.

[0162] RACH-less conditional handover (general procedure) As described above, UE3 and RAN5 of communication system 1 may be configured to perform a general RACH-less CHO procedure.

[0163] Here, we will describe a possible such procedure as a mere example, with reference to Figure 8, a simplified sequence diagram showing a typical RACH-less conditional handover procedure that may be used in communication system 1.

[0164] Referring to Figure 8, the CHO procedure in this case concerns the handover of UE3 between the source cell of source base station 5A-1 and the target cell (of potentially multiple candidate cells) of target base station 5A-2. Target base station 5A-2 may be one of a number of candidate base stations (i.e., candidates that could be the handover destination base station 5A-2) each capable of operating one or more candidate cells (i.e., candidates that could be the target cell).

[0165] Before the CHO procedure is initiated, in S802, the source base station 5A-1 that serves and communicates with UE3 (i.e., the source base station 5A-1 of the CHO) typically stores the UE context for UE3. This may include, for example, information regarding roaming and access restrictions provided when the connection between the UE and source base station 5A-1 is established or at the time of the last tracking area update.

[0166] Source base station 5A-1 configures the measurement procedure to be performed by UE3, and UE3 reports according to the measurement configuration (S812). At some point, source base station 5A-1 makes a decision to configure UE3 for CHO to hand over, for example, based on the measurement results and / or radio resource management (RRM) information received in the measurement report (S814).

[0167] Therefore, source base station 5A-1 proceeds to S816-x and / or S816-2 to send the respective handover request and request CHO to each of the one or more candidate cells belonging to one or more candidate base stations 5A-x, 5A-2, including target base station 5A-2. A CHO request message is sent for each candidate cell.

[0168] Although not shown in the diagram, it will be understood that admission control may be performed by each candidate base station 5A-x, 5A-2. For example, if the corresponding slice information has been sent to that candidate base station 5A-x, 5A-2, slice-oriented admission control may be performed, and if a protocol data unit (PDU) session is associated with an unsupported slice, the candidate base station 5A-x, 5A-2 may reject such a PDU session.

[0169] Each candidate base station 5A-x, 5A-2 transmits its respective CHO response (e.g., a handover request acknowledgment message) to source base station 5A-1 for each CHO candidate cell (S818-2 in S818-x). Each CHO response includes the configuration of the corresponding CHO candidate cell (e.g., an RRC reconfiguration message). Each candidate base station 5A-x, 5A-2 can configure a RACH skip / RACH-less based CHO for the corresponding candidate cell as part of the corresponding CHO configuration. The RRC reconfiguration message carrying the candidate cell's CHO configuration may, for example, be a RACH skip information element (IE) indicating that RACH should be skipped for any access to the candidate cell if the candidate cell is to be the target cell for the CHO. Candidate base stations 5A-x and 5A-2 that provide CHO configuration to candidate cells configured with RACH skip / RACH-less initial access may also optionally configure one or more pre-assigned periodic uplink grants (pre-configured CGs) that UE3 can use for PUSCH to carry the first uplink message (e.g., RRC reconfiguration complete) in that candidate cell when the candidate cell becomes the target cell for the CHO procedure.

[0170] In S822, source base station 5A-1 sends an RRC reconfiguration message to UE3 (for example, an RRCReconfiguration message in a 5G system). The RRC reconfiguration message includes information indicating the configuration of each CHO candidate cell—including (if applicable) that RACH skips are configured and any one or more pre-assigned periodic uplink grants—and information indicating one or more CHO execution conditions. Although not shown, it will be understood that other reconfiguration information from source base station 5A-1 may follow the CHO configuration of one or more candidate cells.

[0171] In S830-1, UE3 sends an appropriate RRC reconfiguration completion message (e.g., an RRCReconfigurationCompletion message in a 5G system) to source base station 5A-1 (effectively confirming RRC reconfiguration).

[0172] In S824, after receiving the CHO configuration, UE3 maintains its connection with source base station 5A-1 and begins evaluating the CHO execution conditions for one or more candidate cells (for example, based on measurements performed by UE3). If one or more measurement results for at least one CHO candidate cell satisfy the corresponding CHO execution conditions, UE3 detaches from source base station 5A-1, applies the stored corresponding configuration to the selected candidate cell (which is the handover target cell), and synchronizes with that candidate (target) cell (S826).

[0173] If the target base station 5A-2 knows (or can calculate) the timing at which one or more CHO conditions will be met (predicted), then, based on that timing, the target base station 5A-2 can begin to dynamically schedule a first / initial uplink grant to the UE3 moving towards the target cell (for example, via a PDCCH that transmits appropriate downlink control information (DCI)) in S828.

[0174] For example, if the service link / satellite changes (as shown in Figure 7, for example), the timing of the serving link change may be known by the target base station 5A-2, and therefore the CHO time and scheduling time may also be determined. Alternatively, the timing may be based on UE3 notifying source base station 5A-1 that UE3 is about to perform a CHO to the target cell, and then source base station 5A-1 notifying target base station 5A-2 (as described above, for example, and in more detail below with reference to Figure 11).

[0175] For example, if the service link / satellite changes (as shown in Figure 7), the timing of the serving link change may be known because it is known by the target base station 5A-2, and therefore the CHO time and scheduling time may also be determined.

[0176] The timing may also be based on a notification provided by UE3 to source base station 5A-1 (for example, as described above and in more detail below with reference to Figure 11) that UE3 is attempting to perform a CHO to the target cell and that this will subsequently be notified to target base station 5A-2 by source base station 5A-1.

[0177] The timing may also be based on the predicted time to leave the current cell (i.e., the serving / source cell) and / or the predicted time to enter another cell (i.e., the adjacent / target cell), which is reported by UE3 to source base station 5A-1 and forwarded by source base station 5A-1 to target base station 5A-2 (for example, as described above and in more detail below with reference to Figure 12).

[0178] If RACH skip / RACH-less initial access is configured for the candidate cell that will become the target cell, UE3 can perform the RACH-less initial access procedure with the target base station 5A-2, and UE3 can send an RRC reconfiguration completion message (in S830-2) using PUSCH with a configured uplink grant (CG) or a dynamically scheduled uplink grant (DG).

[0179] When a PUSCH with a configured uplink grant (CG) is used, the validity period can be configured (in advance) (for example, as described above and in more detail below with reference to Figure 13).

[0180] Alternatively, if PUSCH is configured (for example, as described above and in more detail below with reference to Figures 9 and 10), UE3 can use PUSCH in conjunction with competition-based PUSCH to send an RRC reconfiguration completion message (S830-2).

[0181] In the context of dynamic grants, it will be understood that any of the timings mentioned above may also be used by the target base station 5A-2 to determine when a pre-allocated / pre-configured uplink grant may be used.

[0182] Next, the target base station 5A-2 sends a message to the source base station 5A-1 in S840 indicating that the handover was successful (e.g., a handover success message) to notify the source base station 5A-1 that UE3 has successfully accessed the target cell. The source base station 5A-1 can then, if necessary, send a message (e.g., a handover cancellation message) in S842-x to cancel the handover of any other candidate cell at the target base station 5A-2 and / or any other candidate base station 5A-x, thereby canceling the CHO of UE3 at that candidate base station 5A-x.

[0183] RACH-less initial access using competition-based PUSCH As described above, UE3 and RAN5 of communication system 1 may be configured to perform RACH-less initial access using competition-based PUSCH.

[0184] While the RACH-less initial access procedure using competition-based PUSCH is primarily described in the context of initial access to a target cell after a CHO, it will be understood that a similar initial access procedure can be used in initial access procedures during other mobility / cell change procedures, including conventional handovers and / or L1 / L2 triggered mobility (LTM). Furthermore, competition-based PUSCH can also be usefully used during access procedures to form initial connections in a cell (e.g., RRC connection setup) and / or to resume such connections (e.g., RRC connection reactivation).

[0185] Here, the use of such a competition-based push for initial access will be illustrated with reference to Figures 9 and 10, as merely an example.

[0186] Figure 9 shows a simplified time-frequency diagram illustrating how uplink grants can be configured for a competition-based PUSCH.

[0187] As shown in Figure 9, the resources for the uplink grant of the competitive base PUSCH are defined / configured periodicity (T PUSCH ) can be configured as a periodic CG in which uplink resources are periodically available. Furthermore, as seen in Figure 9, multiple grants can be configured (optionally) at different frequency positions in the same one or more time slots (or symbols). It will also be recognized that multiple grants can potentially be configured, for example, at different associated timings, in a single competition-based PUSCH period (TPUSCH) (for example, using one or more different time slots or symbols for the start of each period).

[0188] The resources for a competition-based PUSCH uplink grant may be predefined (for example, implicitly based on parameters related to the target cell). However, the target base station 5-2A may be able to configure the resources for a competition-based PUSCH to UE3 using appropriate signaling. The target base station 5-2A may be able to configure the resources for a competition-based PUSCH uplink grant via broadcast system information, for example. The target base station 5-2A may, alternatively or additionally, be able to configure the resources for a competition-based PUSCH uplink grant using dedicated signaling. It will be recognized that the configuration of the resources for a competition-based PUSCH uplink grant may be included in the CHO configuration.

[0189] Figure 10 is a simplified sequence diagram showing a RACH-less initial access procedure using competition-based PUSCH, which may be used in the communication system shown in Figure 2.

[0190] As shown in Figure 10, if initial access to a cell is triggered in S1050 (for example, following a CHO, HO, or LTM procedure, or for initial RRC connection setup / restart), and UE3 has configured RACH skip / RACH-less initial access (for the cell on which initial access is being performed), UE3 makes a first attempt in S1052-1 to send the necessary uplink data / uplink messages over the selected conflict-based PUSCH. The uplink data may include, for example, the C-RNTI assigned to the target cell by the target base station 5A-2, or it may be sent using RRC reconfiguration completion messages (for example, to confirm CHO / HO completion), RRC setup requests, and RRC restart requests.

[0191] In S1052-2, if the UE3 does not receive a conflict resolution message within a first defined / configured time window (T1), it retransmits the uplink data / uplink message using a conflict-based periodic push, and then uses a random backoff timer (T) for retransmission S1052-3 in subsequent conflict-based periodic uplink grants. BackOff ) can be applied.

[0192] The target / new base station 5A-2 can send one or more dedicated uplink grants to UE3 if base station 5A-2 can detect a conflict on the conflict-based CG and can deduce which one or more UEs are transmitting data.

[0193] If UE3 receives a conflict resolution (for example, in S1054), the conflict resolution is considered to have completed successfully, and initial access to the CHO (or other procedure) is considered to have completed. A conflict resolution may be indicated, for example, by a (DL) conflict resolution MAC CE (which may include some or all of the content of uplink data / messages previously sent by UE3, i.e., sent in a conflict-based PUSCH). A conflict resolution may also be indicated, for example, by any DCI sent on the PDCCH addressed to a C-RNTI of UE3 (for example, a C-RNTI pre-configured for the target cell).

[0194] However, if UE3 does not receive a conflict resolution within the second defined / configured time window (T2), the three UEs may fall back to a RACH-based handover procedure or declare a handover failure.

[0195] RACH-less conditional handover (with CHO notification) As described above, UE3 and RAN5 of communication system 1 may be configured to perform a RACH-less CHO procedure, in which case, when one or more CHO execution conditions are met (or about to be met), the affected UE3 reports to source base station 5A-1 that UE3 is about to perform a CHO for the selected target cell, and source base station 5A-1 notifies target base station 5A-2 of the next CHO.

[0196] Here, we will describe a possible such procedure as a mere example, referring to Figure 11, a simplified sequence diagram showing another RACH-less conditional handover procedure that may be used in communication system 1. The procedure will be found to be largely similar to the procedure in Figure 8.

[0197] Referring to Figure 11, the CHO procedure in this case concerns the handover of UE3 between the source cell of source base station 5A-1 and the target cell (of potentially multiple candidate cells) of target base station 5A-2. Target base station 5A may be one of a number of candidate base stations (i.e., candidates that could become the handover base station 5A-2) each capable of operating one or more candidate cells (i.e., candidates that could be the target cell).

[0198] Before the CHO procedure is initiated, the source base station 5A-1 that serves and communicates with UE3 in S1102 (i.e., the source base station 5A-1 of the CHO) typically remembers the UE context of UE3. This may include, for example, information regarding roaming and access restrictions provided when the connection between the UE and source base station 5A-1 is established or at the time of the last tracking area update.

[0199] Source base station 5A-1 configures the measurement procedure to be performed by UE3, and UE3 reports according to the measurement configuration (S1112). At some point, source base station 5A-1 makes a decision to configure UE3 for CHO to hand over, for example, based on the measurement results and / or radio resource management (RRM) information received in the measurement report (S814).

[0200] Therefore, in S1116-x and / or S1116-2, source base station 5A-1 proceeds to hand over its respective requests and request CHO to each of the one or more candidate cells belonging to one or more candidate base stations 5A-x, 5A-2, including target base station 5A-2. A CHO request message is sent for each candidate cell.

[0201] Although not shown in the diagram, it will be understood that admission control may be performed by each candidate base station 5A-x, 5A-2. For example, if the corresponding slice information has been sent to that candidate base station 5A-x, 5A-2, slice-oriented admission control may be performed, and if a protocol data unit (PDU) session is associated with an unsupported slice, the candidate base station 5A-x, 5A-2 may reject such a PDU session.

[0202] Each candidate base station 5A-x, 5A-2 transmits its respective CHO response (e.g., a handover request acknowledgment message) for each CHO candidate cell to source base station 5A-1 (in S1118-x, S1118-2). Each CHO response includes the configuration of the corresponding CHO candidate cell (e.g., an RRC reconfiguration message). Although not explicitly shown, each candidate base station 5A-x, 5A-2 may configure a RACH skip / RACH-less based CHO for the corresponding candidate cell as part of the corresponding CHO configuration (as described with respect to Figure 8). The RRC reconfiguration message carrying any such CHO configuration for a candidate cell may, for example, be a RACH skip information element (IE) indicating that RACH should be skipped for any access to that candidate cell if the candidate cell is to be the target cell for the CHO. Candidate base stations 5A-x and 5A-2 that provide CHO configuration to candidate cells configured with RACH skip / RACH-less initial access may also optionally configure one or more pre-assigned periodic uplink grants (pre-configured CGs) that UE3 can use for PUSCH to carry the first uplink message (e.g., RRC reconfiguration complete) in that candidate cell when the candidate cell becomes the target cell for the CHO procedure.

[0203] In S1122, source base station 5A-1 sends an RRC reconfiguration message to UE3 (for example, an RRCReconfiguration message in a 5G system). The RRC reconfiguration message includes information indicating the configuration of each CHO candidate cell—including (if applicable) that RACH skips are configured and any one or more pre-assigned periodic uplink grants—and information indicating one or more CHO execution conditions. Although not shown, it will be understood that other reconfiguration information from source base station 5A-1 may follow the CHO configuration of one or more candidate cells.

[0204] In S1130-1, UE3 sends an appropriate RRC reconfiguration completion message (e.g., an RRCReconfigurationCompletion message in a 5G system) to source base station 5A-1 (effectively confirming RRC reconfiguration).

[0205] After receiving the CHO configuration, UE3 maintains its connection with source base station 5A-1 and, in S1124, begins evaluating the CHO execution conditions for one or more candidate cells (for example, based on measurements performed by UE3). If UE3 determines that one or more measurement results for at least one CHO candidate cell satisfy (or will satisfy) the corresponding CHO execution conditions, UE3 sends a message (for example, a CHO notification message) to source base station 5A-1 in S1125 to inform UE3 that it is about to perform a CHO on the target cell. Since this message identifies the target cell, source base station 5A-1 can then notify target base station 5A-2 (for example, using a handover notification message) that UE3 has an imminent CHO.

[0206] Next, UE3 detaches from source base station 5A-1, applies the stored corresponding configuration to the selected candidate cell (which is the handover target cell), and synchronizes with the candidate (target) cell (S1126).

[0207] Therefore, if the target base station 5A-2 knows that the CHO condition has been met (or will soon be met), it can, in S1128, dynamically begin scheduling a first / initial uplink grant to the UE3 as it moves to the target cell (e.g., via a PDCCH that transmits appropriate downlink control information (DCI)). If a pre-configured / pre-assigned CG has been configured for the UE3 for use in the target cell, the target base station 5A-2 also knows that the pre-configured / pre-assigned CG is about to be used.

[0208] If RACH skip / RACH-less initial access is configured for the candidate cell that will become the target cell, UE3 can perform the RACH-less initial access procedure with the target base station 5A-2. In this case, UE3 can send an RRC reconfiguration completion message (in S1130-2) using PUSCH with a configured uplink grant (CG) or a dynamically scheduled uplink grant (DG).

[0209] Next, in S1140, the target base station 5A-2 sends a message to the source base station 5A-1 indicating that the handover was successful (e.g., a handover success message) to notify the source base station 5A-1 that UE3 has successfully accessed the target cell. Then, if necessary, the source base station 5A-1 can cancel the CHO of UE3 at the target base station 5A-2 and / or any other candidate base station 5A-x by sending a message (e.g., a handover cancellation message) (in S1142-x) to cancel the handover of any other candidate cell.

[0210] RACH-less conditional handover (with display of CHO timing to the network) As described above, UE3 and RAN5 of communication system 1 may be configured to perform a RACH-less CHO procedure, in which UE3 can calculate the predicted time to leave the current cell (i.e., serving / source cell) and / or the predicted time to enter another cell (i.e., adjacent / target cell) and report one or more predictions to source base station 5A-1. Source base station 5A-1 can then forward the reported information to target base station 5A-2.

[0211] Here, with reference to Figure 12, a simplified sequence diagram showing a procedure for reporting predicted cell departure / entry times in the context of a RACH-less conditional handover procedure that may be used in communication system 1, a possible such procedure will be described as merely an example.

[0212] Referring to Figure 12, in S1260, UE3 calculates the predicted time for UE3 to leave the current serving cell and / or the predicted time for UE3 to enter an adjacent cell. In the case of NTN, the calculation may be based, for example, on ephemeris, orbit, and / or coverage information of the serving satellite and / or adjacent satellites. Then, in S1262, UE3 reports the predicted departure and / or entry times to the serving base station 5A-1. It will be understood that one or more predicted times may be reported as part of a measurement report message before CHO preparation begins (for example, before a CHO decision is made by source base station 5A-1). Alternatively or additionally, one or more predicted times may also be included in the RRC reconfiguration completion message used to confirm the CHO configuration. Alternatively or additionally, one or more predicted times may also be included in UE support information (for example, provided as part of the UE support information procedure defined in section 5.7.4 of 3GPP TS 38.331).

[0213] Next, in S1263, the serving base station 5A-1 forwards this information to the adjacent base station 5A-2 operating the adjacent cell to which this information relates. This information may also be provided, for example, to a candidate / target base station / cell for a CHO or LTM procedure, or to a target base station / cell for another handover procedure. This information may also be forwarded in a handover request (for example, if one or more predicted times are received earlier in a measurement report, etc.) and, as it will be understood, may be used to assist in the pre-configuration of the target cell's CG. If dynamic scheduling is used, this information may be forwarded later in the procedure.

[0214] The receiving base station 5A-2 can then pre-allocate / pre-configure one or more uplink grants and / or determine when to initiate any dynamic scheduling for UE3 (for example, as part of the CHO procedure described with reference to Figure 8). It will be recognized that one or more pre-allocated / pre-configured uplink grants may provide an "effective" time window based on one or more predicted times (similar to the "effective" time window described in more detail with reference to Figure 13, for example).

[0215] Therefore, UE3 can complete the RACH-less CHO / HO procedure with neighboring base station 5A-2 as target base station 5A-2 using a pre-configured UL grant or a dynamically scheduled grant for initial access as S1266, as more generally described with reference to Figure 8.

[0216] Validity period of pre-allocated UL grants As described above, the RAN5 of communication system 1 may be configured to configure an "effective" time window in relation to the associated CHO (or possibly conventional handover) configuration.

[0217] Here, with reference to Figure 13, a simplified sequence diagram showing the procedure for configuring an effective time window in the context of a RACH-less conditional handover procedure that may be used in communication system 1, a possible procedure for configuring such an effective time window will be described as a mere example.

[0218] Referring to Figure 13, in S1370, UE3 initiates a CHO (or other handover procedure) with the serving (source) base station 5A-1. In the case of a CHO, this procedure may be initiated in the manner described with reference to Figure 8 (and may also include other candidate base stations, as described in that procedure).

[0219] After the target base station 5A-2 receives a handover request (or a handover request for multiple cells) from the source base station 5A-1 (S1312), the target base station 5A-2 pre-allocates / pre-configures one or more associated uplink grants for one or more candidate / target cells (S1374), each candidate / target cell having an "effective" time window during which its uplink grant can be considered valid.

[0220] Next, the target base station 5A-2 sends a response to the source base station 5A-1 (e.g., a handover request acknowledgment message) that includes the corresponding RRC reconfiguration (S818). In this example, the RRC reconfiguration includes information defining one or more pre-allocated / pre-configured uplink grants in relation to information defining one or more associated valid windows. For CHOs, a separate response may be sent for each CHO candidate cell (e.g., an RRC reconfiguration message), including the configuration of the corresponding CHO candidate cell. The RRC reconfiguration may include, for example, an indication that a RACH skip / RACH-less based (C)HO is configured for the corresponding cell.

[0221] Source base station 5A-1 transmits one or more RRC reconfigurations to UE3 in S1322, which include information defining one or more pre-assigned / pre-configured uplink grants related to information defining one or more associated valid windows.

[0222] If one or more corresponding CHO execution conditions are met, UE3 uses a pre-configured UL grant in S1376, subject to use within the validity period window, as described more generally with reference to Figure 8.

[0223] If the conditions for executing a CHO are met but the timing of execution falls outside the valid time window, UE3 may need to fall back to a RACH-based (C)HO procedure (as seen in S1376), use the uplink resources configured for a scheduling request (SR), or release the corresponding CHO configuration.

[0224] The time window configured for a pre-allocated / pre-configured uplink grant can be, for example, an independent time window. Alternatively, the time window configured for a pre-allocated / pre-configured uplink grant can be, for example, a relative time window linked to a time window defined by the configuration of a time-based CHO trigger event, if the execution condition corresponds to its CHO trigger event. One such event is the so-called "CondEvent T1," which is triggered in UE3 when the measured time falls within a period from a threshold.

[0225] Specifically, for CondEvent T1, UE3 considers the entry condition to the event to be met when the first condition (T1-1) is met, and the exit condition to the event to be met when the second condition (T1-2) is met. The entry / first condition (T1-1) is defined by the inequality Mt > Threshold 1, and the exit / second condition (T1-2) is defined by the inequality Mt > Threshold 1 + Duration.

[0226] The variables in the inequality are, -Mt is the time measured in UE3 (which can be expressed in ms). -Threshold 1 is the threshold parameter for this event (this can be defined by the appropriate IE (e.g., t1 threshold IE) within the report configuration for this event (e.g., reportConfigNR for 5G)), -Duration is the duration parameter for this event (which can be defined by the appropriate IE (e.g., Duration IE) within the report configuration (e.g., reportConfigNR for 5G) for this event), as is defined. Thresh1 and Duration are expressed in the same units as Mt.

[0227] As mentioned above, this validity period may be applicable in several scenarios. For example, the validity period window may be used for quasi-earth-fixed cells, in which case the t-Service parameter is typically configured to indicate the time at which a cell provided via the NTN quasi-earth-fixed system is about to cease service to the area it currently covers, and thus the handover time is predetermined. The validity period window may also be used for earth-moving cells, in which case it is predictable how long the UE3 will remain in the current cell before a handover occurs, and / or the validity period may be determined based on the observed handover frequency. The network can also base the validity period window on network-side predictions of the timing of the next UE3 handover, for example, using an appropriate artificial intelligence / machine learning (AI / ML) algorithm.

[0228] Satellite switching (PCI change) As described above, UE3 and RAN5 of communication system 1 may also be configured to perform a simplified RACH-less procedure (i.e., not performing all steps that are normally considered necessary for a Layer 3 (L3) handover procedure) in the event of a satellite switchover.

[0229] Here, a possible procedure is described, merely as an example, with reference to Figures 14-16.

[0230] Figure 14 is a simplified sequence diagram showing a first simplified RACH-less procedure that can be used in communication system 1 when a satellite switchover occurs and the PCI is changed.

[0231] As shown in Figure 14, UE3 is initially located in the cell of serving base station 5A-1, which is provided via the first satellite (or other non-terrestrial platform) 5C-1, and has the first associated PCI (PCIA). In this cell, UE3 receives replacement cell information from serving base station 5A-1 in S1480, and this replacement cell information is ultimately used to replace the corresponding cell-related information of the cell where UE3 is located when the satellite / service link changes to the second satellite 5C-2. It will be understood that this replacement cell information may conceptually be thought of as information about the “replacement” cell on satellite switching (i.e., the cell that replaces the current cell), or as “replacement” information for the same serving cell on satellite switching (i.e., information that replaces the current information).

[0232] In this example, since the PCI changes during satellite switching, the replacement cell information includes at least the new PCI (PCIB) used for the serving cell after the satellite / service link is switched to the second satellite 5C-2. The replacement cell information may also include replacement satellite information (such as NTN configuration information regarding the second satellite 5C-2, as illustrated with reference to Figure 4). The replacement cell information may also include information defining the time and / or any other conditions that indicate when the replacement is thought to have occurred.

[0233] Replacement cell information may be provided, for example, as part of the broadcast information associated with the current satellite, as part of the system information (e.g., SIB19), or as part of the satellite support information for the current satellite. Figure 15 shows, as a mere example, an abstract syntax notation one (ASN.1) definition of the data structure of the system information block that may be used in the procedure of Figure 14. In this example, t-Service-r17 IE may be (re)used to indicate when the switchover occurs, and / or the format of ntn-Config IE-r17 may be (re)used for a new NTN configuration (e.g., ntn-Config-r18 IE) corresponding to the replacement satellite at the time of the switchover.

[0234] Replacement cell information may be provided, for example, via dedicated signaling, in an RRC reconfiguration message. Figure 16 shows, as a mere example, an abstract syntax notation one (ASN.1) definition of the data structure of an RRC reconfiguration message that may be used in the procedure of Figure 14. In this example, a new IE may be added to indicate the switching timing (e.g., t-r18). Nevertheless, the t-Service indicator (provided, for example, in SIB19) may be (re)used.

[0235] As seen in S1482, at the indicated time (or when any other defined condition is met), UE3 detaches from the serving cell as identified by the first PCI (PCIA). Almost simultaneously, a satellite switchover to the second satellite 5C-2 occurs, and the serving ("replacement") cell begins to be provided via the second satellite 5C-2.

[0236] Subsequently, in S1485, UE3 may consider that uplink synchronization has been lost and therefore may interrupt all uplink transmissions.

[0237] Subsequently, UE3 can search for a "new" cell in S1486 that is identified by a second PCI (PCI B) and perform downlink synchronization for it.

[0238] In S1488, UE3 can (re)acquire satellite support information (e.g., SIB19) in which NTN configuration information (e.g., NTN-config IE) corresponding to the replacement satellite and cell information should exist. This step is optional, but is particularly useful when the replacement satellite information is not configured together with the satellite information of the previous satellite, as in S1480.

[0239] UE3 can recalculate the timing alignment based on information about the replacement satellite 5C-2 and other necessary information indicated by the NTN configuration corresponding to the new satellite 5C-2. UE3 can then proceed assuming that uplink synchronization has been achieved.

[0240] Therefore, UE3 can continue with RRC connectivity using the same configuration as S1492, and advantageously, it does not require RACH or L3 mobility (including key changes).

[0241] If for any reason UE3 cannot detect the cell identified by PCI B, UE3 can fall back to the radio-link failure (RLF) / RRC re-establishment procedure.

[0242] It should be understood that this procedure is applicable to both hard switching (where the old cell disappears and then the new cell appears) and soft switching (where the old cell disappears after the new cell appears).

[0243] Satellite switching (unchanging PCI) As described above, UE3 and RAN5 of communication system 1 may also be configured to perform another simplified RACH-less procedure (i.e., without performing all the steps that are normally considered necessary for a Layer 3 (L3) handover procedure) in the event of a satellite switchover.

[0244] Here, a possible procedure is described with reference to Figure 17, merely as an example.

[0245] Figure 17 is a simplified sequence diagram showing a first simplified RACH-less procedure that can be used in communication system 1 when a satellite switchover occurs in which PCI does not change.

[0246] As shown in Figure 17, UE3 is initially located in the cell of serving base station 5A-1, which is provided via the first satellite (or other non-terrestrial platform) 5C-1, and has the associated PCI (PCIA). In this cell, UE3 receives information in S1780 that defines the time and / or any other conditions indicating when the replacement is thought to have occurred.

[0247] The information may be provided, for example, as part of broadcast information related to the current satellite, in system information (e.g., SIB19), or as part of satellite support information relating to the current satellite. The time indicated by t-Service IE may be (re)used in this procedure, for example, to define the time when satellite switching occurs. Nevertheless, replacement cell information may be provided via dedicated signaling, for example, in RRC reconfiguration messages.

[0248] As seen in S1782, at the indicated time (or when any other defined condition is met), a satellite switchover to the second satellite 5C-2 occurs, and the serving ("replacement") cell (also identified by PCIA in this example) begins to be served via the second satellite 5C-2.

[0249] In S1785, UE3 may consider uplink synchronization to be lost and therefore interrupt all uplink transmissions.

[0250] Next, in S1788, UE3 (re)acquires satellite support information (e.g., SIB19) in which NTN configuration information (e.g., NTN-config IE) corresponding to the replacement satellite and cell information should exist.

[0251] UE3 can recalculate the timing alignment based on information about the replacement satellite 5C-2 and other necessary information indicated by the NTN configuration corresponding to the new satellite 5C-2. UE3 may then proceed assuming that uplink synchronization has been achieved.

[0252] Therefore, UE3 can continue with the RRC connection using the same configuration, and advantageously, neither RACH nor L3 mobility (including key changes) is required.

[0253] User equipment Figure 18 is a simplified block diagram showing the main components of UE3 for implementation in the system shown in Figure 2.

[0254] As shown in the figure, UE3 includes a transceiver circuit 31 that can operate to transmit signals to RAN5 via the air interface 33 and one or more antennas, and to receive signals from RAN5.

[0255] UE3 has a controller 37 that controls the operation of UE3. The controller 37 is associated with memory 39 and coupled to transceiver circuit 31. UE3 may, of course, have all the usual features of a conventional UE3 (e.g., user interfaces 35 such as a touchscreen / keypad / microphone / speaker to enable direct user control and interaction), which may be provided by hardware, software, and firmware, one or any combination thereof, as needed.

[0256] In this example, the controller 37 is configured to control the overall operation of the UE3 by program instructions or software instructions stored in memory 39. The software may be pre-installed in memory 39 and / or downloaded, for example, via a communication system or from a removable data storage device (RMD). As shown in the figure, these software instructions include, among other things, an operating system 41 and a communication control module 43.

[0257] The communication control module 43 is operable to control communication between the UE3 and one or more serving RAN5 (and other communication devices connected to the RAN5, e.g., further UEs and / or core network nodes). The communication control module 43 is configured to handle uplink communication in general via associated uplink channels (e.g., via physical uplink control channel (PUCCH), random access channel (RACH), and / or physical uplink shared channel (PUSCH)), including both dynamic and quasi-static signaling (e.g., SRS). The communication control module 43 is also configured to handle the reception of downlink communication in general via associated downlink channels (e.g., via physical downlink control channel (PDCCH) and / or physical downlink shared channel (PDSCH)), including both dynamic and quasi-static signaling (e.g., CSI-RS, SSBs).

[0258] The communication control module 43 plays a role in controlling the parts handled by UE3 in procedures such as receiving measurement control / configuration information, receiving system information, RRC signaling, mobility procedures, and implementing appropriate timing advances to compensate for timing misalignments.

[0259] The communication control module 43 controls the role of the UE in executing, for example, initial access procedures (RACH and RACH-less) for connecting to base station 5A, as well as mobility procedures including conditional and other handover procedures, and other procedures that the serving cell modifies (or appears to modify).

[0260] It should be recognized that the communication control module 43 may include several sub-modules (or "layers") that support specific functions. For example, the communication control module 63 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an SDAP sub-module, an IP sub-module, an RRC sub-module, etc.

[0261] Base station FIG. 18 is a simplified block schematic diagram showing the main components of a base station 5A for implementation in the system of FIG. 2 (such as, for example, an NTN access network or other such RAN 5).

[0262] As shown in the figure, the base station 5A includes a transceiver circuit 51 operable to transmit signals to and receive signals from the UE 3 via an air interface 53 and one or more antennas (such as, for example, a gateway 9 or a non-terrestrial platform 11). The transceiver circuit 51 is also operable to transmit signals to and receive signals from the functions of the core network 7 and / or other base stations 5A via a network interface 55. The network interface typically includes N1, N2, and / or N3 interfaces for communicating with the core network and a base station-to-base station (such as, for example, Xn) interface for communicating with other base stations.

[0263] The base station 5A also includes a controller 57 that controls the operation of the transceiver circuit 51 according to software stored in a memory 59. The software may be pre-installed in the memory 59 and / or downloaded, for example, via a communication network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 61 and a communication control module 63.

[0264] The communication control module 63 is operable to control communication between the base station 5A and the UE3, and between the base station 5A and other network entities connected to the base station 5A. For example, the communication control module 63 controls the uplink and downlink user traffic flow, as well as the portion of the flow of control data transmitted to one or more UE3s served by the base station 5A, including control data for managing the operation of the base station 5A. The communication control module 63 is responsible for the overall processing of receiving and decoding uplink communications via uplink channels (e.g., via a physical uplink control channel (PUCCH), a random-access channel (RACH), and / or a physical uplink shared channel (PUSCH)), including both dynamic and quasi-static signaling (e.g., SRS). The communication control module 63 is also responsible for the overall processing of downlink communications transmissions via relevant downlink channels, including both dynamic and quasi-static signaling (e.g., CSI-RS, SSB, etc.) (e.g., via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)).

[0265] The communication control module 63 is responsible for controlling the parts of the process that are handled by the base station 5A, such as the communication of measurement control / configuration information, broadcasting of system information, RRC signaling, mobility procedures, and determining and signaling appropriate timing advances to compensate for timing misalignments.

[0266] The communication control module 63 is responsible for controlling the parts of the process that are handled by the base station 5A, such as the initial access procedures (RACH and RACH-less) for connecting to the UE3, mobility procedures including conditional and other handover procedures, and other procedures that the serving cell modifies (or appears to modify).

[0267] It will be recognized that the communication control module 63 may include several submodules (or "layers") that support specific functions. For example, the communication control module 63 may include a PHY submodule, a MAC submodule, an RLC submodule, a PDCP submodule, an SDAP submodule, an IP submodule, an RRC submodule, and so on.

[0268] Here, various methods that may be used in System 1 are described merely as examples.

[0269] Variations and alternative examples Detailed embodiments have been described above. As those skilled in the art will understand, several modifications and substitutions can be made to the exemplary embodiments described above, while still benefiting from the disclosure embodied therein.

[0270] It will be understood that the descriptions of base stations (or gNBs), NTN nodes, and UEs, and the actions they perform, may apply equally to base stations and UEs that communicate only on the ground plane (i.e., as part of the ground RAN without NTN RAN features such as gateways and space or airborne platforms) as to base stations that communicate via non-terrestrial planes.

[0271] Furthermore, the descriptions of the base station (or gNB) characteristics and the actions performed by the base station (or gNB) apply equally to both distributed and non-distributed base stations.

[0272] Furthermore, while we have described information elements with specific names, it should be understood that information elements with different names but serving similar purposes can also be used.

[0273] In the above description, the UE and base station are described as having several separate functional components or modules for the sake of ease of understanding. These modules may thus be provided in certain applications, for example, where an existing system is modified to implement the present disclosure, but in other applications, for example, systems designed from the outset with the features of the present invention in mind, these modules may be incorporated into the overall operating system or code, and therefore these modules may not be identified as separate entities.

[0274] In the exemplary embodiments described above, several software modules have been explained. As those skilled in the art will understand, software modules may be provided in compiled or uncompiled form and may be supplied to a UE or base station via a computer network or as signals on a recording medium. Furthermore, the functions performed by some or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred because it facilitates updates to update the functions of a UE or base station.

[0275] Each controller may include, but is not limited to, one or more hardware-implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (IO) circuits, internal memory / cache (programs and / or data), processing registers, communication buses (such as control buses, data buses, and / or address buses), direct memory access (DMA) functions, hardware or software-implemented counters, pointers, and / or timers, and any other suitable form of processing circuitry. Various other modifications will be obvious to those skilled in the art and will not be described in further detail here.

[0276] In this disclosure, user equipment (or "UE," "mobile station," "mobile device," or "wireless device") is an entity connected to a network via a wireless interface.

[0277] Please note that this disclosure is not limited to dedicated communication devices, but can be applied to any device having communication functions as described in the following paragraphs.

[0278] The terms “User Equipment” or “UE” (as used by 3GPP), “Mobile Station,” “Mobile Device,” and “Radio Device” are generally intended to be synonymous with each other and include standalone mobile stations such as terminals, cell phones, smartphones, tablets, cellular IoT devices, IoT devices, and machines. The terms “Mobile Station” and “Mobile Device” will be understood to also include devices that remain stationary for extended periods.

[0279] UE may be, for example, items of equipment for production or manufacturing and / or items of energy-related machinery (e.g., boilers, engines, turbines, solar panels, wind turbines, hydroelectric generators, thermal power generators, nuclear power generators, batteries, nuclear systems and / or related equipment, heavy electrical machinery, pumps including vacuum pumps, compressors, fans, blowers, hydraulic equipment, pneumatic equipment, metalworking machinery, manipulators, robots and / or their application systems, tools, molds or dies, rolls, conveying equipment, lifting equipment, material handling equipment, textile machinery, sewing machines, printing and / or related machinery, paper processing machinery, chemical machinery, mining and / or construction machinery and / or related equipment, machinery and / or equipment for agriculture, forestry and / or fisheries, safety and / or environmental protection equipment, tractors, precision bearings, chains, gears, power transmission equipment, lubrication equipment, valves, pipe fittings and / or application systems for any of the aforementioned equipment or machinery).

[0280] For example, UE may be an item of transport equipment (such as transport equipment such as railway cars, automobiles, motorcycles, bicycles, trains, buses, carts, rickshaws, ships and other vessels, aircraft, rockets, satellites, drones, balloons, etc.).

[0281] UE may be, for example, an item of information and communication equipment (such as electronic computers and related equipment, communication and related equipment, electronic components, etc.).

[0282] UE may include, for example, refrigerators, refrigerator applications, trading and / or service industry equipment items, vending machines, automated service machines, office machines or equipment, and household appliances and electronic devices (such as audio equipment, video equipment, loudspeakers, radios, televisions, microwave ovens, rice cookers, coffee machines, dishwashers, washing machines, dryers, electronic fans or related equipment, vacuum cleaners, etc.).

[0283] The UE may be, for example, an electrical application system or device (such as an electrical application system or device like an X-ray system, particle accelerator, radioisotope device, acoustic device, electromagnetic application device, power application device, etc.).

[0284] The UE may be, for example, an electronic lamp, lighting fixture, measuring instrument, analyzer, tester, or a surveying or detection device (such as a surveying or detection device like a smoke alarm, human alarm sensor, motion sensor, wireless tag, etc.), a wristwatch or clock, experimental equipment, optical device, medical device and / or system, weapon, cutting tool, hand tool, etc.

[0285] [[ID=Z]] The UE may be, for example, a personal digital assistant or related device of wireless equipment (such as a wireless card or module designed to be attached to or inserted into another electronic device (such as a personal computer, electrical measuring instrument, etc.)).

[0286] The UE may be part of a device or system that uses various wired and / or wireless communication technologies to provide the applications, services, and solutions described below with respect to the "Internet of Things (IoT)".

[0287] Internet of Things devices (or "things") may be equipped with appropriate electronic devices, software, sensors, network connections, etc. that enable these devices to collect and exchange data with each other and other communication devices. IoT devices may be equipped with automated devices that follow software instructions stored in internal memory. IoT devices may operate without the need for human supervision or interaction. IoT devices may also remain stationary and / or inactive for long periods of time. IoT devices may be implemented as part of a (generally) stationary device. IoT devices may also be incorporated into a non-stationary device (such as a vehicle), or attached to an animal or person to be monitored / tracked.

[0288] It will be understood that IoT technology can be implemented on any communication device that can connect to a communication network to send / receive data, regardless of whether such communication device is controlled by human input or by software instructions stored in memory.

[0289] It will be understood that IoT devices are sometimes called Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be understood that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in the table below. This list is not exhaustive and is intended to show some examples of machine-type communication applications. [Table 1]

[0290] Furthermore, the aforementioned UE categories are merely examples of applications of the technical concepts and exemplary embodiments described in this document. Needless to say, these technical concepts and exemplary embodiments are not limited to the UEs described above and are subject to various modifications.

[0291] Each feature disclosed herein (this term includes the claims) and / or shown in the drawings may be incorporated into this disclosure independently of (or in combination with) any other disclosed and / or illustrated features, where it is technically feasible to do so. In particular, but not limited to, any feature of a claim dependent on a particular independent claim may be introduced into that independent claim in any combination or individually, provided that doing so does not result in a technical incompatibility or result in something that does not make technical sense.

[0292] Various other examples of modifications will be obvious to those skilled in the art and will not be described in further detail here.

[0293] For example, all or part of the exemplary embodiments disclosed above may be described, but are not limited to, as follows: (Note 1) A method performed by a candidate access network node, To request user equipment (UE) to prepare for a conditional handover, the service includes receiving at least one message from the serving cell of the serving access network node to at least one candidate cell of the candidate access network node, where at least one candidate cell is a candidate to be the target cell for the conditional handover, and the candidate access network node is a candidate to be the target access network node for the conditional handover. The method includes sending at least one message to a serving access network node containing configuration information regarding a conditional handover to at least one candidate cell. Configuration information includes a method that includes information indicating that when a UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel. (Note 2) The access procedure must schedule at least one resource for uplink communication used by the UE, If the UE performs an access procedure to access at least one candidate cell, The method according to Appendix 1, further comprising receiving an uplink message from a UE that was sent using at least one resource for uplink communication scheduled by a candidate access network node. (Note 3) The uplink message indicates that a conditional handover to at least one candidate cell has been completed in the UE, as described in Appendix 2. (Note 4) The method according to Appendix 2 or 3, further comprising receiving a notification from a serving access network node that a conditional handover to at least one candidate cell has been initiated or will be initiated, and receiving an uplink message based on the notification. (Note 5) The method according to Appendix 4, wherein receiving based on notification includes dynamically scheduling at least one resource for uplink communication and using at least one resource for uplink communication to receive uplink messages. (Note 6) The method according to Appendix 4, further comprising pre-configuring at least one resource for uplink communication prior to receiving a notification, and receiving based on the notification comprising decoding an uplink message based on the notification. (Note 7) The method according to Appendix 2, Appendix 3, or Appendix 4, wherein the scheduling includes dynamic scheduling of at least one resource for uplink communication. (Note 8) The method according to Appendix 7, further comprising receiving time information from a serving access network node indicating the predicted time when a UE will leave a serving cell and / or the predicted time when a UE will enter at least one candidate cell, wherein the timing of dynamic scheduling is based on the time information. (Note 9) Scheduling is as described in Appendix 2, 3, or 4, which includes pre-configuring at least one resource for uplink communication as a configured grant. (Note 10) The configured grant is configured specifically to be used by the UE for uplink communication in the access procedure relating to conditional handover, as described in Appendix 9. (Note 11) The configured grant is configured for competition-based uplink communication, as described in Appendix 9. (Note 12) Configuration information for conditional handovers includes scheduling information for configuring the configured grants, as described in Appendix 9 or 10. (Note 13) Configuration information for a conditional handover is the method described in Appendix 12, including time information to constitute the period during which the configured grant is valid. (Note 14) The method according to Appendix 13, wherein the time information is configured to constitute a period during which the configured grant is valid for a further period of time-based conditions for triggering a conditional handover. (Note 15) The method according to Appendix 13 or 14, further comprising receiving additional time information from a serving access network node indicating the predicted time at which a UE will leave a serving cell and / or the predicted time at which a UE will enter at least one candidate cell, wherein the time information is based on the additional time information. (Note 16) A method performed by a serving access network node, To request user equipment (UE) to prepare for a conditional handover, the service includes sending at least one message from the serving cell of a serving access network node to at least one candidate cell of a candidate access network node, wherein at least one candidate cell is a candidate to become the target cell for the conditional handover, and at least one candidate access network node is a candidate to become the target access network node for the conditional handover. The method is, Receiving at least one message from the target access network node containing configuration information regarding a conditional handover to at least one candidate cell, This includes sending configuration information regarding conditional handover to the UE, Configuration information includes a method that includes information indicating that when a UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel. (Note 17) The method as described in Appendix 16, further comprising receiving a first notification from the UE that a conditional handover to at least one candidate cell has been initiated or will be initiated, and sending a second notification to a candidate access network node that a conditional handover to at least one candidate cell has been initiated or will be initiated. (Note 18) The method as described in Appendix 16 or 17, further comprising receiving time information from the UE indicating the predicted time for the UE to leave the serving cell and / or the predicted time for the UE to enter at least one candidate cell, and transmitting the time information to at least one candidate access network node. (Note 19) A method performed by user equipment (UE), The process includes receiving configuration information from the serving access network node regarding a conditional handover from the serving cell of the serving access network node to at least one candidate cell of at least one candidate access network node, wherein at least one candidate cell is a candidate to be the target cell of the conditional handover, and at least one candidate access network node is a candidate to be the target access network node of the conditional handover. Configuration information includes a method that includes information indicating that when a UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel. (Note 20) The method according to Appendix 17, further comprising performing an access procedure to access a specific candidate cell of a specific candidate access network node, the access procedure comprising sending an uplink message to the specific candidate access network node using at least one resource for uplink communication scheduled by the specific candidate access network node. (Note 21) The method as described in Appendix 17 or 18, further comprising sending a notification to a serving access network node that a conditional handover to at least one candidate cell has been initiated or will be initiated. (Note 22) The method according to Appendix 17, 18, or 19, further comprising transmitting time information to a serving access network node indicating the predicted time for the UE to leave a serving cell and / or the predicted time for the UE to enter at least one candidate cell. (Note 23) A method performed by user equipment (UE), As part of an initial access procedure that does not involve the use of random access channels, the procedure includes sending an initial uplink message to an access network node using at least one uplink resource, where at least one uplink resource is configured for contention-based uplink communication. The method is, If no conflict resolution indication is received from the access network node within the first period, resend the initial uplink message to the access network node using at least one uplink resource, If a conflict resolution indication is received from the access network node within the first period, the initial access procedure will be treated as having been successfully completed in further communication with the access network node, A method including treating the initial access procedure as not having completed successfully if no conflict resolution indication is received from the access network node within the second period. (Note 24) The method as described in Appendix 23, further comprising, if a conflict resolution indication is not received from the access network node within a first period and is still not received within a third period beginning from the end of the first period, repeating the retransmission of the initial uplink message to the access network node using at least one uplink resource. (Note 25) The method as described in Appendix 23 or 24, further comprising performing a fallback initial access procedure using a random access channel if a conflict resolution indication is not received from the access network node within a second period. (Note 26) If a conflict resolution notification is received from an access network node, the conflict resolution notification includes at least some of the information contained in the uplink message, as described in Appendix 23, 24, or 25. (Note 27) If a conflict resolution notice is received from an access network node, the conflict resolution notice is provided using a media access control (MAC) control element (CE) as described in any one of the appendices 23 to 26. (Note 28) When a conflict resolution notification is received from an access network node, the conflict resolution notification is provided using downlink control information (DCI) as described in any one of the appendices 23 to 26. (Note 29) The method described in Appendix 28, wherein the DCI is encoded using the radio network temporary identifier (RNTI) associated with the UE. (Note 30) A method performed by an access network node, As part of an initial access procedure that does not involve the use of random access channels, it includes receiving an initial uplink message from user equipment (UE) using at least one uplink resource, where at least one uplink resource is configured for contention-based uplink communication. The method is, Sending a conflict resolution notification to the UE, A method further including treating the initial access procedure as having been successfully completed in further communication with the UE. (Note 31) A method performed by user equipment (UE), Based on the connection configuration, communication with the access network node occurs in a first cell provided by the access network node via a first non-terrestrial platform. Receiving cell-related information from an access network node via the first non-terrestrial platform, which applies to the first cell when the first cell is provided by an access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or applies to the second cell provided by an access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform, Following the change of the non-terrestrial platform, preparations will be made for communication via the second non-terrestrial platform based on cell-related information, A method comprising continuing communication with an access network node based on a connection configuration in the first cell, or in the second cell if the second cell replaces the first cell. (Note 32) The method as described in Appendix 31, wherein cell-related information includes a new physical cell identifier (PCI) applicable to the second cell, provided by an access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform. (Note 33) The method as described in Appendix 32, further comprising (re)detecting the first cell based on a new PCI, or (re)detecting the second cell if the second cell has replaced the first cell, before continuing communication. (Note 34) The cell-related information is as described in Appendix 31 or 32, including information indicating the time when a change to a non-ground platform is made and / or other conditions that will be met at that time. (Note 35) Cell-related information is provided in the manner described in Appendix 31, 32, or 33, including supporting information for the second non-terrestrial platform. (Note 36) The method according to any one of the appendices 31 to 35, further comprising obtaining supporting information regarding the second non-terrestrial platform to be broadcast via the second non-terrestrial platform before continuing communication. (Note 37) The method described in any one of the appendices 31 to 36, further comprising temporarily suspending the uplink communication before continuing the communication. (Note 38) The method according to any one of the appendices 31 to 37, further comprising recalculating the timing alignment for communication via a second non-terrestrial platform before continuing communication. (Note 39) A method performed by an access network node, Based on the connection configuration, communication with user equipment (UE) in a first cell provided by an access network node via a first non-terrestrial platform, Sending cell-related information to the UE via the first non-terrestrial platform, which applies to the first cell when it is provided by the access network node via the second non-terrestrial platform following a change in the non-terrestrial platform, or which applies to the second cell when it is provided by the access network node via the second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform, A method comprising continuing communication with the UE in the first cell, or in the second cell if the second cell replaces the first cell, based on the connection configuration. (Note 40) Candidate access network node, A means for receiving at least one message from a serving cell of a serving access network node to at least one candidate cell of a candidate access network node, in order to request user equipment (UE) to prepare for a conditional handover, wherein at least one candidate cell is a candidate to be the target cell for the conditional handover, and the candidate access network node is a candidate to be the target access network node for the conditional handover. A means for sending at least one message to a serving access network node containing configuration information regarding a conditional handover to at least one candidate cell, The configuration information includes a candidate access network node that indicates that the access procedure should be performed without using a random access channel when the UE performs an access procedure to access at least one candidate cell. (Note 41) A serving access network node, A means for sending at least one message from a serving cell of a serving access network node to at least one candidate cell of a candidate access network node in order to request user equipment (UE) to prepare for a conditional handover, wherein at least one candidate cell is a candidate to be the target cell for the conditional handover, and at least one candidate access network node is a candidate to be the target access network node for the conditional handover. Means for receiving at least one message from a target access network node containing configuration information regarding a conditional handover to at least one candidate cell, The system includes means for sending configuration information regarding conditional handover to the UE, The configuration information includes a serving access network node that indicates that if the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel. (Note 42) User equipment (UE), A means for receiving configuration information relating to a conditional handover from a serving cell of a serving access network node to at least one candidate cell of at least one candidate access network node, wherein at least one candidate cell is a candidate to be the target cell of the conditional handover, and at least one candidate access network node is a candidate to be the target access network node of the conditional handover, the means comprising: The configuration information includes user equipment (UE) information indicating that when the UE performs an access procedure to access at least one candidate cell, the access procedure should be performed without using a random access channel. (Note 43) User equipment (UE), A means for sending an initial uplink message to an access network node using at least one uplink resource as part of an initial access procedure that does not involve the use of a random access channel, wherein at least one uplink resource is a resource configured for competition-based uplink communication; If no conflict resolution indication is received from the access network node within the first period, means for resending the initial uplink message to the access network node using at least one uplink resource, A means for treating the initial access procedure as having been successfully completed in further communication with the access network node when a conflict resolution indication is received from the access network node within the first period, User equipment (UE) includes means for treating the initial access procedure as not having been successfully completed if a conflict resolution indication is not received from the access network node within a second period. (Note 44) Access network node, A means for receiving an initial uplink message from user equipment (UE) using at least one uplink resource, as part of an initial access procedure that does not involve the use of a random access channel, wherein at least one uplink resource is a resource configured for contention-based uplink communication; A means of sending a conflict resolution notification to the UE, An access network node, including means for treating the initial access procedure as having been successfully completed in further communication with the UE. (Note 45) User equipment (UE), Based on the connection configuration, a means for communicating with an access network node in a first cell provided by an access network node via a first non-terrestrial platform, A means for receiving cell-related information from an access network node via a first non-terrestrial platform, which applies to the first cell when the first cell is provided by an access network node via a second non-terrestrial platform following a change in the non-terrestrial platform, or applies to the second cell provided by an access network node via a second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform, A means for preparing for communication via a second non-terrestrial platform based on cell-related information following a change in the non-terrestrial platform, User equipment (UE) comprising: means for continuing communication with an access network node based on the connection configuration in the first cell, or in the second cell if the second cell replaces the first cell. (Note 46) Access network node, Based on the connection configuration, means for communicating with user equipment (UE) in a first cell provided by an access network node via a first non-terrestrial platform, Means for transmitting cell-related information to a UE via the first non-terrestrial platform, which applies to the first cell when the first cell is provided by an access network node via the second non-terrestrial platform following a change in the non-terrestrial platform, or applies to the second cell when the first cell is provided by an access network node via the second non-terrestrial platform that replaces the first cell following a change in the non-terrestrial platform; An access network node comprising means for continuing communication with the UE in the first cell, or in the second cell if the second cell replaces the first cell, based on the connection configuration.

[0294] This application claims priority based on UK Patent Application No. 2305109.7, filed on 5 April 2023, the disclosure thereof being incorporated herein by reference in its entirety. [Explanation of Symbols]

[0295] 1. Communication System 3. User equipment 5 base station 5b Distributed Unit (DU) 5c Central Unit (CU) 7 Core Network 9 cells 10 Control Plane Functions 11. User Plane Functions 20 External data network 31 Transceiver Circuit 33 Antennas 35 User Interface 37 Controllers 39 memory 41 Operating Systems 43 Communication control module 51 Transceiver Circuit 53 Air Interface 55 Core Network Interfaces 57 Controllers 59 memory 61 Operating Systems 63 Communication control module

Claims

1. A method performed by user equipment (UE), A method that includes performing an initial access procedure with an access network node without using a random access channel at the configured time.

2. The aforementioned initial access procedure is performed using the resources configured by the access network node. The method according to claim 1.

3. The aforementioned resources are configured to be allocated periodically. The method according to claim 2.

4. Executing the aforementioned initial access procedure is performed using the aforementioned resources within the time window. The method according to claim 2.

5. The aforementioned time window is comprised of the access network nodes, The method according to claim 4.

6. The aforementioned time window is configured for each condition that triggers the execution of the initial access procedure, The method according to claim 4 or 5.

7. If the timing for executing the initial access procedure falls outside the time window, Executing the initial access procedure using a random access channel, or This further includes executing scheduling requests, The method according to any one of claims 4 to 6.

8. The aforementioned resources include competition-based, periodically configured grants. Performing the aforementioned initial access procedure includes sending data in the competition-based periodically configured grant, The aforementioned method, If the UE does not receive a conflict response when it transmits the data, To resend the aforementioned data, Executing the initial access procedure using a random access channel, or Including declaring a disability, The method according to any one of claims 2 to 5.

9. Further includes receiving a conflict resolution in response to the transmission of the aforementioned data, The aforementioned conflict resolution is, A Media Access Control (MAC) control element (CE) that includes at least a portion of the aforementioned data, or The physical downlink channel (PDCCH) corresponding to the UE's Radio Network Temporary Identifier (RNTI), Including at least one of the following: The method according to claim 8.

10. Information for constructing the aforementioned competition-based periodically configured grants, System information block, or Radio Resource Control (RRC) message, The method according to claim 8 or 9, further comprising receiving at [a specific location].

11. Performing the aforementioned initial access procedure means Information to be transferred to the aforementioned access network node, The conditions for a conditional handover from another access network node to the said access network node are met, or The timing at which the UE accesses a target cell operated by the other access network node, or the timing at which the UE leaves a serving cell operated by the access network node Information indicating at least one of the above is transmitted to the other access network node configured in the serving cell of the UE, In response to the transmission of the aforementioned information, information for allocating resources to the UE is received from the access network node, Accessing the access network node using the aforementioned resources, Executed by The method according to claim 1.

12. The aforementioned initial access procedure is: Conditional handover procedure, Handover procedure, Layer 1 or Layer 2 triggered mobility (LTM), Radio Resource Control (RRC), connection setup procedure, or RRC connection reactivation procedure, Including at least one of the following: The method according to any one of claims 1 to 11.

13. The configured timing is a method that includes the timing of switching of a non-terrestrial platform corresponding to the access network node, This includes receiving information from the access network node indicating a target cell operated by the access network node, The initial access procedure is performed by synchronizing with the target cell. The method according to claim 1.

14. From the aforementioned access network node, A new non-terrestrial platform corresponding to the aforementioned switching of the non-terrestrial platform, or The timing corresponding to the switching of the aforementioned non-ground platform, Receiving configuration information that indicates at least one of the following, The further includes recalculating the timing advance value of the target cell based on the aforementioned configuration information, The method according to claim 13.

15. If the UE cannot detect the target cell, the initial access procedure is further performed using a random access channel. The method according to claim 13 or 14.

16. The information indicating the target cell is, System information block, or Radio Resource Control (RRC) message, Included The method according to any one of claims 13 to 15.

17. The cell serving the aforementioned UE will be maintained throughout the aforementioned switching of the non-terrestrial platform. The method according to any one of claims 13 to 16.

18. A method performed by an access network node, A method that includes performing an initial access procedure with user equipment (UE) without using a random access channel at a configured time.

19. User equipment (UE), User equipment including means for performing initial access procedures with access network nodes without using random access channels at the configured time.

20. Access network node, An access network node that includes means for performing an initial access procedure with user equipment (UE) without using a random access channel at the time of configuration.

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