Method, user equipment and access network node for tn-to-ntn mobility

Abstract

An example of the object of the present disclosure is to provide a method, a user equipment and an access network node capable of reducing user equipment (UE) power consumption. In one example aspect, a method performed by a user equipment (UE) is configured to communicate via a non-terrestrial network (NTN). The method includes: receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and determining whether to perform measurements for the NTN-TN mobility based on the information.

Description

METHOD, USER EQUIPMENT AND ACCESS NETWORK NODE FOR TN-TO-NTN MOBILITY

[0001] The present disclosure relates to a method, a user equipment and an access network node.

[0002] Under the 3rd Generation Partnership Project (3GPP) standards, a NodeB (or an eNB in LTE, and gNB in 5G) is the radio access network (RAN) node (or simply 'access node', 'access network node' or 'base station') via which communication devices (user equipments or 'UEs') connect to a core network and communicate with other communication devices or remote servers.

[0003] NPL 1: the Next Generation Mobile Networks (NGMN) Alliance, 'NGMN 5G White Paper', February 17th, 2015, V1.0, <URL: https: / / www.ngmn.org / 5g-white-paper.html> NPL 2: 3GPP TR 38.811 V15.4.0

[0004] A UE maintains connection with its source RAN node while it evaluates one or more conditional handover (CHO) execution conditions for the CHO target RAN nodes. If at least one CHO execution condition is satisfied for a CHO candidate cell, the UE detaches from the source RAN node, applies the corresponding stored configuration for the target RAN node that operates that candidate cell and synchronises to that target RAN node. The UE accesses the target RAN node and completes the handover procedure.

[0005] However, irrespective of whether conventional or conditional handover procedures are used, when handing over between a terrestrial network (TN) RAN and non-terrestrial network (NTN) RAN (e.g., when a UE leaves an area covered by a TN RAN an enters an area covered by an NTN RAN), undesirable delays and excessive UE power consumption can occur because typically, TN RAN coverage is prioritised for a UE over NTN RAN coverage.

[0006] An example of the object of the present disclosure is to provide a method, a user equipment and an access network node capable of reducing user equipment (UE) power consumption.

[0007] In a first example aspect, a method performed by a user equipment (UE) is configured to communicate via a non-terrestrial network (NTN), the method including: 　　receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and 　　determining whether to perform measurements for the NTN-TN mobility based on the information.

[0008] In a second example aspect, a method is performed by an access network node, the method including: 　　transmitting, to a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), information indicating coverage of a terrestrial network (TN) for NTN-TN mobility, wherein 　　the information is used by the UE to determine whether to perform measurements for the NTN-TN mobility based on the information.

[0009] In a third example aspect, a user equipment (UE) is configured to communicate via a non-terrestrial network (NTN), the UE including: 　　means for receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and 　　means for determining whether to perform measurements for the NTN-TN mobility based on the information.

[0010] In a fourth example aspect, an access network node includes: 　　means for transmitting, to a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), information indicating coverage of a terrestrial network (TN) for NTN-TN mobility, wherein 　　the information is used by the UE to determine whether to perform measurements for the NTN-TN mobility based on the information.

[0011] According to the present disclosure, it is possible to provide a method, a user equipment and an access network node capable of reducing UE power consumption.

[0012] Examples of apparatus and methods will now be described, by way of example, with reference to the accompanying drawings in which:Fig. 1 illustrates schematically an exemplary mobile (cellular or wireless) communication system;Fig. 2 illustrates schematically a non-terrestrial network (NTN) radio access network that may be used in the communication system of Fig. 1;Fig. 3A illustrates a possible architecture of an NTN RAN;Fig. 3B illustrates a possible architecture of an NTN RAN;Fig. 3C illustrates a possible architecture of an NTN RAN;Fig. 4 is a simplified sequence diagram illustrating a UE-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 5 is a simplified sequence diagram illustrating another UE-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 6 is a simplified sequence diagram illustrating another UE-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 7 is a simplified sequence diagram illustrating a network-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 8 is a simplified sequence diagram illustrating a network-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 9 is a simplified sequence diagram illustrating a network-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 10 is a simplified sequence diagram illustrating a network-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1;Fig. 11 is a simplified block schematic illustrating the main components of a user equipment that may be used in the communication system of Fig. 1; andFig. 12 is a simplified block schematic illustrating the main components of a base station / access network node that may be used in the communication system of Fig. 1.

[0013] The present disclosure relates to a communication system and to parts thereof. The disclosure has particular but not exclusive relevance to wireless communication systems and devices thereof operating according to the 3rd Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof (including LTE-Advanced, Next Generation or 5G networks, future generations, and beyond). The disclosure has particular but not exclusive relevance to improvements relating to mobility scenarios such as terrestrial network (TN) to non-terrestrial network (NTN) mobility procedures.

[0014] Each of the drawings or figures is merely an example to illustrate one or more example embodiments. Each figure may not be associated with only one particular example embodiment, but may be associated with one or more other example embodiments. As those of ordinary skill in the art will understand, various features or steps described with reference to any one of the figures can be combined with features or steps illustrated in one or more other figures, for example, to produce example embodiments that are not explicitly illustrated or described. Not all of the features or steps illustrated in any one of the figures to describe an example embodiment are necessarily essential, and some features or steps may be omitted. The order of the steps described in any of the figures may be changed as appropriate.

[0015] (Related Arts) 　　Earlier developments of the 3GPP standards were referred to as the Long-Term Evolution (LTE) of Evolved Packet Core (EPC) network and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), also commonly referred as '4G'. More recently, the term '5G' and 'new radio' (NR) is used to refer to an evolving communication technology that supports a variety of applications and services. Various details of 5G networks are described in, for example, the 'NGMN 5G White Paper' V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, which document is available from https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G by way of the so-called 3GPP Next Generation (NextGen) radio access network (RAN) and the 3GPP NextGen core network.

[0016] Under the 3GPP standards, a NodeB (or an eNB in LTE, and gNB in 5G) is the radio access network (RAN) node (or simply 'access node', 'access network node' or 'base station') via which communication devices (user equipments or 'UEs') connect to a core network and communicate with other communication devices or remote servers. For simplicity, the present application will use the term access network node, RAN node (or simply RAN) or base station to refer to any such access nodes.

[0017] For simplicity, the present application will use the term mobile device, user device, or UE to refer to any communication device that is able to connect to the core network via one or more base stations. Although the present application may refer to mobile devices in the description, it will be appreciated that the technology described can be implemented on any communication devices (mobile and / or generally stationary) that can connect to a communications network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0018] In the current 5G architecture, the base station structure may be split into two or more parts. In some RAN implementations there are two parts, known as the Central Unit (CU or gNB-CU) - sometimes referred to as a 'control unit' - and the Distributed Unit (DU or gNB-DU), connected by an F1 interface. This enables the use of a 'split' architecture in which the typically 'higher' CU layers (for example, but not necessarily or exclusively, Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers) and the, 'lower' DU layers (for example, but not necessarily or exclusively, Radio Link Control (RLC), Media (sometimes referred to as 'Medium') Access Control (MAC), and Physical (PHY) layers) are separated between a particular CU, and one or more DUs that are connected to and controlled by that CU via the F1 interface. Thus, for example, the higher layer CU functionality for a number of base stations may be implemented centrally (for example, by a single processing unit, or in a cloud-based or virtualised system), whilst retaining the lower layer DU functionality locally separately for each base station.

[0019] In 5G, core network entities comprise logical nodes (or 'functions') including control plane functions (CPFs) and one or more user plane functions (UPFs). The CPFs include, amongst other things, one or more Access and Mobility Management Functions (AMFs), a session management function (SMF), and one or more location management functions (LMFs). The AMF generally corresponds to the MME in 4G and performs many of the functions performed by the MME. Each UPF combines functionality of both the S-GW and P-GW - specifically user plane functionality of the S-GW (SGW-U) and user plane functionality of the P-GW (PGW-U). The SMF provides session management functionality (that formed part of MME functionality in 4G). The SMF also combines the some of the functionality provided by the S-GW and P-GW - specifically control plane functionality of the S-GW (SGW-C) and control plane functionality of the P-GW (PGW-C). The SMF also allocates IP addresses to each UE.

[0020] 3GPP is also working with the satellite communication industry to specify an integrated satellite and terrestrial network infrastructure in the context of 5G. This is referred to as non-terrestrial networks (NTN) which term refers to networks, or segments of networks, using an airborne or spaceborne vehicle for transmission of data and control signalling. Satellites refer to spaceborne vehicles in Low Earth Orbits (LEO), Medium Earth Orbits (MEO), Geostationary Earth Orbit (GEO) or in Highly Elliptical Orbits (HEO). Airborne vehicles refer to High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) - including tethered UAS, Lighter than Air UAS and Heavier than Air UAS - all operating quasi-stationary at an altitude typically between 8 and 50 km.

[0021] 3GPP Technical Report (TR) 38.811 is a study on New Radio to support such on-terrestrial networks. The study includes, amongst other things, NTN deployment scenarios and related system parameters (such as architecture, altitude, orbit etc.) and a description of adaptation of the 3GPP channel models for non-terrestrial networks (propagation conditions, mobility, etc.). Non-terrestrial networks are expected to: - help foster the 5G service roll out in un-served or underserved areas to upgrade the performance of terrestrial networks; - reinforce service reliability by providing service continuity for user equipment or for moving platforms (e.g. passenger vehicles - aircraft, ships, high speed trains, buses); - increase service availability everywhere; especially for critical communications, future railway / maritime / aeronautical communications; and - enable 5G network scalability through the provision of efficient multicast / broadcast resources for data delivery towards the network edges or even directly to the user equipment.

[0022] Non-Terrestrial Network access typically features the following elements (amongst others): - NTN Terminal: This may refer to the 3GPP UE or to a UE specific to the satellite system in the case that the satellite does not serve directly 3GPP UEs; - A service link which refers to the radio link between the user equipment and the space / airborne platform (which may be in addition to a radio link with a terrestrial based RAN); - A space or an airborne platform (e.g., a satellite or the like); - Gateways that connect the satellite or aerial access network to the core network. It will be appreciated that gateways will mostly likely be collocated with a base station (e.g. a gNB); - Feeder links which refer to the radio links between the Gateways and the space / airborne platform.

[0023] Satellite or aerial vehicles typically generate several satellite beams over a given area. The beams have a typically elliptic footprint on the surface of the earth. The beam footprint may be moving over the earth with the satellite or the aerial vehicle motion on its orbit. Alternatively, the beam footprint may be earth fixed (albeit temporarily), in such case some beam pointing mechanisms (mechanical or electronic steering feature) may be used to compensate for the satellite or the aerial vehicle motion. There are different options for beam identification purposes. In one option multiple (nearby / neighbouring) satellite beams may have the same associated physical cell ID (PCI) and hence the PCI can remain unchanged as a UE moves from beam-to-beam of the set of beams sharing a PCI. Alternatively, there may be a one-to-one relationship between the PCIs and the satellite beams (at least within a particular satellite's coverage area comprising multiple beams).

[0024] The coverage in 5G is primarily beam-based rather than cell based. There is no cell-level reference channel from where the coverage of the cell could be measured. Instead, each cell has one or more so-called synchronization signal / physical broadcast channel (PBCH) block (SSB) beams (which are different to satellite or NTN beams). SSB beams form a matrix of beams covering an entire cell area. Each SSB beam carries an SSB comprising a primary synchronization signal (PSS), secondary synchronization signal (SSS), and physical broadcast channel (PBCH).

[0025] The UE searches for and performs measurements on the SSB beams (e.g. of the synchronization signal reference signal received power, 'SS-RSRP', synchronization signal reference signal received quality, 'SS-RSRQ', and / or the synchronization signal to noise or interference ratio, 'SS-SINR'). The UE maintains a set of candidate beams which may contain beams from multiple cells. A PCI and beam ID (or SSB index) thus distinguish the SSB beams from each other. Effectively, therefore, the SSB beams are like mini cells which may be within a larger cell. Once a UE has detected and selected a cell (and / or an SSB beam in the case of 5G) it may attempt to access that cell and / or SSB beam using an initial RRC connection setup procedure comprising a random access procedure.

[0026] For example, once a UE has detected and selected a cell (and / or a beam in the case of 5G) it may attempt to access that cell and / or beam using an initial radio resource control (RRC) connection setup procedure comprising a random access (RACH) procedure that typically involves four distinct steps. Alternatively, the UE may attempt to access that cell and / or beam using a so-called two-step RACH procedure. Both the four step and two step RACH procedures are well known to those skilled in the art.

[0027] As those skilled in the art will appreciate, while a contention based PRACH procedure is described, a non-contention based (or 'contention free') procedure may also be used in which a dedicated preamble is assigned by the base station to the UE.

[0028] Random access procedures such as those described may also be used in other contexts including, for example, handover, connection reestablishment, requesting UL scheduling where no dedicated resource for a scheduling-request has been configured for the UE, etc.

[0029] Nevertheless, whilst a RACH procedure may be used to access a target cell of a target RAN node during handover, the UE may attempt to access that cell and / or beam using a so called 'RACH-less' based handover which provides reductions in the data connectivity interruption time at each handover as it removes the need for performing random access when first accessing the target cell, and hence reduces overall handover execution time.

[0030] In conventional handover procedures (including RACH-less handover procedures) a source base station may initially decide to initiate a handover based on measurement reporting by the UE (e.g., a measurement report triggered by a particular measurement reporting event, or periodically, or the like). In response, the source RAN node initiates preparation of a target RAN node for handover by sending a handover request message to the target RAN node.

[0031] Assuming the target RAN node decides to allow the handover request (e.g., based on appropriate admission control), the target RAN node then prepares handover and sends a handover request acknowledgement message to the source RAN node. This handover request acknowledgement message includes an RRC message generated by the target RAN node for instructing modification / reconfiguration of the UE's RRC connection for the purposes of handover.

[0032] The source RAN node then initiates a handover execution phase by sending the RRC reconfiguration message (including the mobility control information) to the UE. The UE receives the RRC reconfiguration message and is thus commanded by the source RAN node to perform the handover. The UE derives target RAN node specific keys and configures the selected security algorithms to be used in the target cell. After receiving the RRC Reconfiguration message, the UE will attempt to access a primary cell (PCell) of the target RAN node at the first available physical uplink shared channel (PUSCH) occasion.

[0033] To confirm the handover the UE may send an RRC reconfiguration complete message to the target RAN node. The RRC reconfiguration complete message includes a cell radio network temporary identifier (C-RNTI), e.g., along with an uplink buffer status report, and / or uplink data, whenever possible. The target RAN node verifies the C-RNTI sent in the RRC reconfiguration complete message. The target RAN node can then begin sending data to the UE after scheduling appropriate downlink resources using the PDCCH.

[0034] The handover procedure is completed for the UE when the UE receives a UE contention resolution identity MAC control element (MAC CE) from the target RAN node or the UE receives a PDCCH addressed to its C-RNTI from the target RAN node after sending the initial uplink transmission.

[0035] (Problem of Related Arts) 　　In conditional handover (CHO), the handover is not executed until the UE being handed over (rather than the network) determines that one or more handover execution conditions have been met. As in conventional handover, in CHO, a source RAN node may make the initial handover decision based on measurement reporting by the UE (e.g., a measurement report triggered by a particular measurement reporting event, or periodically, or the like). However, the UE 3 makes the ultimate decision of when to commence handover, e.g., when one or more handover execution conditions have been met. In response to the measurement reports, the source RAN node decides to use CHO for handover and requests a CHO with one or more 'candidate' target RAN nodes by sending each target RAN node a respective CHO request message. In response to a CHO request message, a target RAN node typically sends a CHO response including a configuration of CHO candidate target RAN nodes to the source RAN node.

[0036] The source RAN node then sends a RRC configuration message to the UE, which contains the configurations of the CHO target RAN nodes and of one or more CHO execution conditions. The source RAN node decides on the CHO conditions for the execution of CHO and adds information for configuring the conditions to the RRC message sent to the UE. In response, the UE sends an RRC message to the source RAN node to confirm the RRC configuration at the UE.

[0037] The UE maintains connection with its source RAN node while it evaluates one or more CHO execution conditions for the CHO target RAN nodes. If at least one CHO execution condition is satisfied for a CHO candidate cell, the UE detaches from the source RAN node, applies the corresponding stored configuration for the target RAN node that operates that candidate cell and synchronises to that target RAN node. The UE accesses the target RAN node and completes the handover procedure.

[0038] However, irrespective of whether conventional or conditional handover procedures are used, when handing over between a TN RAN and NTN RAN (e.g., when a UE leaves an area covered by a TN RAN an enters an area covered by an NTN RAN), undesirable delays and excessive UE power consumption can occur because typically, TN RAN coverage is prioritised for a UE over NTN RAN coverage.

[0039] TN RAN coverage is preferred over NTN RAN coverage because typically radio links between UEs and NTN RANs are generally of poorer quality than similar radio links between UEs and TN RANs. However, as TN RAN coverage is preferred, UEs are not typically expected to continuously perform measurements for NTN cell (re)selection procedures and may not even be aware when they are leaving (or about to leave) TN coverage. As such the UEs may be ill-prepared for a mobility procedure for their handover from a TN base station (and corresponding cell) to an NTN base station (and corresponding cell). Consequently, coverage may be temporarily lost during handover and / or the handover process may be slow. Furthermore, in the absence of prior knowledge of NTN coverage (e.g., a time where a satellite will be present and their ephemeris, and the frequency used), transition between an TN RAN and an NTN RAN that occurs when the UE leaves TN coverage can be excessively slow and result in excessive UE power consumption as the UE attempts to obtain sufficient information to allow the handover.

[0040] One possible solution to the above issue would be to provide the UE with NTN information in advance of any possible transition to the NTN RAN. For example, the TN RAN to which the UE is connected could provide the UE with information about proximal NTN RANs to which it could switch. Given the poorer quality of radio links with NTN RANs, the prior provisioning of information about the NTN RAN by the TN RAN has benefits, however to provide the UE with NTN information in advance of any possible transition to the NTN RAN the UE will typically need to continuously perform measurements to detect signals from the TN RAN containing NTN RAN information as the UE will not know in advance when the TN RAN will send such signals. Thus, while in the above solution the speed of the transition by the UE between the TN RAN and the NTN RAN may be improved, the UE will end up consuming excessive amounts of power as it continuously scans for NTN information being broadcast by the TN RAN. There is thus a need for cell (re)selection enhancements for UEs to reduce UE power consumption, especially in the context of cell (re)selection for transition from a TN RAN to an NTN RAN.

[0041] The disclosure aims to provide one or more apparatus and / or one or more associated methods that at least partially addresses or contributes to addressing one or more of the above issues.

[0042] In the following disclosure 'satellite' based NTN will generally be referred to but it will be appreciated that the principles and methods described are more widely applicable to other space (or air) borne platforms used for implementing NTNs.

[0043] The various functional means described below that are part of the UE may be provided by a memory and one or more processors that execute instructions stored in the memory. Similarly, the various functional means described below that are part of the access network node may be provided by a memory and one or more processors that execute instructions stored in the memory.

[0044] Various example described below may be implemented by means of a computer program product comprising computer implementable instructions for causing a programmable computer to carry out the any of the methods described below. The computer implementable instructions may be provided as a signal or on a tangible computer readable medium.

[0045] (Overview) 　　An exemplary communication system will now be described in general terms, by way of example only, with reference to Figs. 1 to 3.

[0046] Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') communication system (e.g., communication system 1) to which the examples described herein are applicable. In the communication system 1 user equipment (UEs) 3 (3-1, 3-2, 3-3) (e.g. mobile telephones and / or other mobile devices) can communicate with each other via a corresponding radio access network (RAN) 5-1, 5-2 that operates according to one or more compatible radio access technologies (RATs). In the illustrated example, each RAN 5-1, 5-2 includes a base station 5A-1, 5A-2 (e.g., a base station such as a gNB) that respectively operates one or more associated cells 9 (9-1, 9-2).

[0047] As those skilled in the art will appreciate, whilst three UEs 3, and two RANs 5-1, 5-2 are shown in Fig. 1 for illustration purposes, the system, when implemented, will typically include other RANs 5 and UEs 3.

[0048] In the illustrated example, one of the RANs 5-1 is a non-terrestrial network (NTN) RAN 5 and one of the RANs 5-1 is a terrestrial network (TN) RAN. In the exemplary communication system 1, either of the RANs 5 may also be configured to support operation in one or more network energy saving (NES) modes.

[0049] Each RAN 5 controls one or more associated cells 9-1, 9-2 either directly, or indirectly via one or more other nodes (such as home base stations, relays, remote radio heads, distributed units, and / or the like). It will be appreciated that each RAN 5 may be configured to support 4G, 5G, 6G and / or later generations, and / or any other 3GPP or non-3GPP communication protocols.

[0050] The base station 5A of each RAN 5 may be a distributed base station comprising at least one distributed unit (DU) (e.g., a gNB-DU or the like), and a central unit (CU) (e.g., a gNB-CU or the like). In such a distributed base station, the CU employs a separated control plane and user plane and so is, itself, split between a control plane function (CU-CP) and a user plane function (CU-UP) which respectively communicate, with the DU via an appropriate interface (e.g. an F1-C interface) and an appropriate interface (e.g. an F1-U interface (together forming an F1 interface (or 'reference point'))), and with one another via an appropriate interface (e.g. an E1 interface). It will be appreciated that while the DU may include the physical and virtual elements required to provide the functionality of the lower parts of the PHY layer and hence communicate with the UEs 3 over the air interface, the base station 5A may alternatively (or additionally) include one or more separate radio units (RUs) (e.g., providing this functionality of the lower parts of the PHY layer). It will, nevertheless, be appreciated that the base station 5A may be in a non-distributed form, for example as an integrated base station.

[0051] The UEs 3 and their serving RAN 5 are connected via an appropriate air interface (for example the so-called 'Uu' interface and / or the like). Base stations 5A of neighbouring RANs 5 may be connected to each other via an appropriate base station to base station interface (such as the so-called 'X2' interface, 'Xn' interface and / or the like - not shown in Fig. 1).

[0052] The core network 7 includes a number of logical nodes (or 'functions') for supporting communication in the communication system 1. In this example, the core network 7 comprises control plane functions (CPFs) 10 and one or more network node entities for the communication of user data (e.g. user plane functions (UPFs) 11). The CPFs 10 include one or more network node entities for the communication of control signalling (e.g. Access and Mobility Management Functions (AMFs) 10-1), one or more network node entities for session management (e.g. Session Management Functions (SMFs) 10-2) and a number of other functions 10-n (such as, for example, an Authentication Server Function (AUSF) which facilitates security processes, a Unified Data Management (UDM) entity for managing user specific data (e.g., for access authorization, user registration, and data network profiles), a Policy Control Function (PCF), an Application Function (AF), and / or the like). It will be appreciated that the nodes or functions may have different names in different systems.

[0053] The RAN 5 is connected to the core network nodes via appropriate interfaces (or 'reference points') such as an N2 reference point between the base station 5A of the RAN 5 and the AMF 10-1 for the communication of control signalling, and an N3 reference point between the base station 5A of the RAN 5 and each UPF 11 for the communication of user data. The UEs 3 are each connected to the AMF 10-1 via a non-access stratum (NAS) connection over an appropriate interface (e.g. an N1 reference point (analogous to the S1 reference point in LTE)). It will be appreciated, that N1 communications are routed transparently via the RAN 5.

[0054] One or more UPFs 11 are connected to an external data network (e.g. an IP network such as the internet) via an appropriate interface (e.g. an N6 reference point) for communication of the user data.

[0055] The AMF 10-1 performs mobility management related functions, maintains the NAS connection with each UE 3 and manages UE registration. The AMF 10-1 is also responsible for managing paging.

[0056] The SMF 10-2 is connected to the AMF 10-1 via an appropriate interface (e.g. an N11 reference point). The SMF 10-2 provides session management functionality (that formed part of MME functionality in LTE) and additionally combines some control plane functions (provided by the serving gateway and packet data network gateway in LTE). The SMF 10-2 also allocates IP addresses to each UE 3. The SMF 10-2 uses user information provided via the AMF 10-1 to determine what session manager would be best assigned to the user. The SMF 10-2 may be considered effectively to be a gateway from the user plane to the control plane of the network. The SMF 10-2 also allocates IP addresses to each UE 3.

[0057] Each base station 5A is also configured for transmission of, and the UEs 3 are configured for the reception of, control information and user data via a number of downlink (DL) physical channels and for transmission of a number of physical signals. The DL physical channels correspond to resource elements (REs) carrying information originated from a higher layer, and the DL physical signals are used in the physical layer and correspond to REs which do not carry information originated from a higher layer.

[0058] The 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 sharing the PDSCH's capacity on a time and frequency basis. The PDSCH can carry a variety of items of data including, for example, user data, UE-specific higher layer control messages mapped down from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) for supporting a number of functions including, for example, scheduling the downlink transmissions on the PDSCH and also the uplink data transmissions on a physical uplink shared channel (PUSCH). The PBCH provides UEs 3 with the Master Information Block (MIB). It also, in conjunction with the PDCCH, supports the synchronisation of time and frequency, which aids cell acquisition, selection and re-selection.

[0059] Specifically, the PBCH is sent by the base station 5A via a Synchronisation Signal / Physical Broadcast Channel (PBCH) Block (SSB), which is also sometimes referred to as an SS / PBCH block, together with a primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS). On reception of the SSB, the UE 3 may assume that the PBCH, PSS and SSS are in consecutive symbols forming the SSB. The base station 5A may transmit a number of such SSBs corresponding to different DL beams (referred to as 'SSB' beams).

[0060] The DL physical signals may include, for example, reference signals (RSs) and synchronization signals (SSs). A reference signal (sometimes known as a pilot signal) is a signal with a predefined special waveform known to both the UE 3 and the base station 5A of the RAN 5. The reference signals may include, for example, cell specific reference signals, UE-specific reference signal (UE-RS), downlink demodulation signals (DMRS), and channel state information reference signal (CSI-RS).

[0061] Similarly, the UEs 3 are configured for transmission of, and the base station 5A of the RAN 5 is configured for the reception of, control information and user data via a number of uplink (UL) physical channels corresponding to REs carrying information originated from a higher layer, and UL physical signals which are used in the physical layer and correspond to REs which do not carry information originated from a higher layer. The physical channels may include, for example, the PUSCH, a physical uplink control channel (PUCCH), and / or a physical random-access channel (PRACH). The UL physical signals may include, for example, demodulation reference signals (DMRS) for a UL control / data signal, and / or sounding reference signals (SRS) used for UL channel measurement.

[0062] (Synchronisation and Initial Access) 　　In order to initially synchronise, in the downlink, with the network, the UE 3 is configured to search for, and perform measurements of the SSB beams (e.g., of the synchronisation signal reference signal received power, 'SS-RSRP', synchronisation signal reference signal received quality, 'SS-RSRQ', and / or the synchronisation signal to noise or interference ratio, 'SS-SINR'). The UE 3 may maintain a set of candidate beams which may contain beams from multiple cells (with a PCI and beam ID (or SSB index) distinguishing the SSB beams from one another). The UE 3 is configured to select an SSB beam (e.g., the best beam) based on the measurements, and to synchronise its reception to the selected SSB beam based on the synchronisation signals in that SSB (e.g., by estimating and correcting frequency and time offsets appropriately). The UE 3 decodes the corresponding PSS and SSS, detects the associated cell identity, and then decodes the PBCH and the MIB carried by the PBCH. The UE 3 also detects DMRSs transmitted via the selected beam. Hence, the UE 3 can detect and decode other system information carried in other SIBs (e.g., including cell access related information caried by SIB1).

[0063] Once downlink synchronisation has been completed, the UE 3 may then attempt to access the cell 9 via the SSB beam using an initial RRC connection setup procedure comprising an appropriate random access procedure which will be described in more detail below.

[0064] (Random access channel (RACH) procedure) 　　The UEs 3 and base station 5A of the RAN 5 of the communication system 1 are mutually configured for performing RACH procedure for the UE 3 to access the network. Specifically, on detection and selection of a cell (and / or a beam) the UE 3 is able to attempt access to that cell and / or beam using an initial radio resource control (RRC) connection setup procedure comprising a random access procedure. Prior to attempting initial access the UE 3 chooses random access resources (including, for example, a preamble) to use to initiate the RACH procedure. The UE 3 sends the selected preamble (e.g., in 'Msg1') to the base station 5A of the RAN 5 over a physical random access channel (PRACH) for initiating the process to obtain synchronization in the uplink (UL). In response, the base station 5A of the RAN 5 responds with a random access response (RAR) (or 'Msg2'). The RAR indicates reception of the preamble and includes: a timing-alignment (TA) command for adjusting the transmission timing of the UE 3 based on the timing of the received preamble; an uplink grant field indicating the resources to be used in the uplink for a physical uplink shared channel (PUSCH); a frequency hopping flag to indicate whether the UE 3 is to transmit on the PUSCH with or without frequency; a modulation and coding scheme (MCS) field from which the UE 3 can determine the MCS for the PUSCH transmission; and a transmit power control (TPC) command value for setting the power of the PUSCH transmission. The UE 3 then sends a third message ('Msg3') to the network over a physical uplink shared channel (PUSCH) based on the information in the RAR. The specific message sent by the UE 3 in this step, and the content of the message, depends on the context in which the random access procedure is being used. In the example of initial radio RRC connection setup, however, Msg3 typically comprises an RRC Setup request or similar message carrying a temporary randomly generated UE identifier. The network responds with a fourth message ('Msg4') which carries the randomly generated UE identifier received in Msg3 for contention purposes to resolve any collisions between different UEs 3 using the same preamble sequence. When successful, Msg4 also transfers the UE 3 to a connected state.

[0065] While a four-step contention-based RACH procedure is described it will be appreciated that a UE 3 and the base station 5A of either RAN 5 of the communication system 1 may also perform a non-contention based (or 'contention free') procedure in which a dedicated preamble is assigned by the base station 5A of the RAN 5 to the UE 3. Moreover, a UE 3 and the base station 5A of the RAN 5 of the communication system 1 may perform a two-step RACH procedure (e.g., as described in the introduction).

[0066] It will be appreciated that while the UE 3 can trigger initiation of the RACH procedure itself (e.g., when the UE 3 needs to connect to the network), initiation of the RACH procedure may be by the network. For example, a RACH procedure may be initiated via a message sent via downlink control information (DCI) with an appropriate DCI format (e.g. 1_0) in a physical downlink control channel (PDCCH) - such a message id commonly known as a PDCCH order. A RACH procedure may be also initiated by the base station 5A of the RAN 5 when handover is required (e.g., using a handover command message).

[0067] (NTN RAN) 　　As indicated above, in the exemplary communication system 1, one of the RANs 5-1 is implemented as a non-terrestrial network (NTN) RAN 5-1.

[0068] Fig. 2 illustrates schematically one such NTN RAN 5-1 that may be used in the communication system 1 of Fig. 1.

[0069] As seen in Fig. 2, the NTN RAN 5-1 comprises a base station 5A-1 operating one or more associated cells 9, a gateway 5B-1, and a non-terrestrial space (or air) borne platform 5C-1 (e.g. comprising one or more satellites and / or airborne vehicles), which may be referred to generally as a 'satellite' for simplicity. Communication via the NTN RAN 5-1 is routed through the core network 7 and external data network 20 (e.g. via the N6 interface / reference point).

[0070] The NTN RAN 5-1 controls a number of directional satellite beams via which associated NTN cells 9 may be provided. Specifically, each satellite beam has an associated footprint on the surface of the Earth which forms an NTN cell 9, or part of an NTN cell 9. Each NTN cell 9 has an associated Physical Cell Identity (PCI). The satellite beam footprints may be moving as the non-terrestrial space (or air) borne platform (e.g. satellite) 5C-1 is travelling along its orbit (e.g. as illustrated by the arrows A in Fig. 2). Alternatively, the satellite beam footprint may be earth fixed, in which case an appropriate satellite beam pointing mechanism (mechanical or electronic steering) may be used to compensate for the movement of the non-terrestrial space (or air) borne platform 5C-1. Satellite beams and satellites are not considered visible from a UE perspective in NTN. This does not, however, preclude differentiating at the public land mobile network (PLMN) level the type of network (e.g. NTN vs. terrestrial).

[0071] The base station 5A-1 of the NTN RAN 5-1 is configured to provide ephemeris data for the non-terrestrial space (or air) borne platform 5C-1, to the UEs 3, to help UEs 3 perform measurement and cell selection / reselection and for supporting initial access. This ephemeris data may comprise information on orbital information such as information on orbital plane level or on satellite level and / or information (e.g., a pointer or index) from which more detailed ephemeris data stored in the UE 3 (e.g. in a universal subscriber identity module, 'USIM') may be obtained. At least some of this ephemeris information may, for example, be provided in system information and / or may be provided using UE specific (dedicated) signalling such as RRC signalling.

[0072] Specifically, the base station 5A-1 is able to provide satellite assistance information for the satellite as part of a dedicated system information block (SIB) that is broadcast to UEs 3 in a corresponding cell 9 of the NTN RAN 5-1 (for 5G NTN this may, for example, be SIB19 but for future generations it may be provided in another SIB or in a different way). The satellite assistance information may include, for example, information identifying at least one associated NTN configuration (e.g., as part of an NTN-Config IE or the like). The NTN configuration includes parameters for assisting the UE 3 to access the network using NTN access (e.g., ephemeris data, common timing alignment parameters, a scheduling (e.g., koffset), validity duration for uplink synchronisation information, and an epoch time (a reference time for which assistance information is valid)).

[0073] The satellite assistance information may include, for example, an indication of a time information on when a cell provided via NTN quasi-Earth fixed system is going to stop serving the area it is currently covering (e.g., in a t-Service IE). This may be indicated, for example, as a time in multiples of 10ms after 00:00:00 on a Gregorian calendar date of 1 January 1900 (midnight between Sunday, December 31, 1899, and Monday, January 1, 1900). The exact stop time may be between the time indicated by the value of this field minus 1 and the time indicated by the value of this field.

[0074] With the help of this ephemeris data, a UE 3 may search for the first NTN cell 9 it can connect to. After detecting a synchronization signal / physical broadcast channel (PBCH) block (SSB) of a cell 9 broadcasted via a non-terrestrial space (or air) borne platform 5C-1, the UE 3 may be able to read initial system information of that cell which may contain further ephemeris information relating to the exact location of the cell (and / or to the satellite broadcasting the cell). This ephemeris information may be given relative to information relating, for example, to the orbital plane that the UE 3 may already have obtained.

[0075] The accuracy of the prediction of a satellite orbit or the satellite position can decrease with time and so, to help ensure accuracy, the ephemeris data provided to the UE 3 is updated periodically or aperiodically.

[0076] 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 with one cell (PCI) having a maximum of L SSB beams, where L can typically be 4, 8 or 64 depending on the band. During initial access, the UEs 3 perform cell search based on SSBs where each SSB is transmitted in a different respective beam. Each SSB comprises a primary synchronization signal (PSS), secondary synchronization signal (SSS), and physical broadcast channel (PBCH). As the SSB carries synchronization signals (SSs) / PBCH (SS / PBCH) transmissions it is sometimes referred to as an SS / PBCH block.

[0077] As those skilled in the art will understand, while the disclosure is described in the context of an NTN based RAN 5-1 / base station 5A-1, many of the technical features described are generally applicable to, and can be implemented in, any RAN / base station of a more conventional (non-NTN) based communication system.

[0078] (NTN RAN Architecture) 　　Figs. 3A to 3C each respectively illustrate a possible architecture of an NTN RAN 5 that may be used.

[0079] For the purposes of description, when implemented in the communication system 1, the NTN RAN 5 will be described in terms of the architecture illustrated in Fig. 3A. It will be appreciated, however, that the NTN RAN 5 could potentially use a different one of the architectures and the entities of the communication system 1 could be adapted accordingly.

[0080] The architecture of Fig. 3A may be referred to as a 'transparent satellite' based RAN architecture. In this architecture, the base station 5A-1 is a terrestrially located base station that sends and receives communications respectively destined for and originating from the UEs 3 via a (terrestrially located) gateway 5B-1 and via a non-terrestrial space (or air) borne platform 5C-1 that has no base station functionality. The non-terrestrial space (or air) borne platform 5C-1 relays these communications to and from the UEs 3 in one or more cells operated by the base station 5A-1, and from and to the gateway 5B-1 as required. The non-terrestrial space (or air) borne platform 5C-1 relays these communications transparently without on-board processing them in effect acting as a so-called 'bent-pipe'. In this implementation, the feeder link between the gateway 5B-1 and the non-terrestrial space (or air) borne platform 5C-1 effectively acts as part of the NR-Uu interface (or reference point) between the base station 5A-1 and one or more UEs 3. Similarly, the service link between the non-terrestrial space (or air) borne platform 5C-1 and one or more UEs 3 effectively acts as another part of the NR-Uu interface (or reference point) between the base station 5A-1 and one or more UEs 3. The base station's communication link with the core network 7 (e.g. for signalling over the N2, N3 interface / reference point etc.) is provided solely terrestrially.

[0081] The architecture of Fig. 3B may be referred to as a 'regenerative satellite' based RAN architecture (i.e., in which the satellite performs on board processing of the payload being communicated between the UE 3 and the core network 7). In this architecture, the base station 5A-1 is a base station 5A-1 of a distributed type having a terrestrially located central unit (CU) 5ACU-1 and a distributed unit (DU) 5ADU-1 provided on-board the non-terrestrial space (or air) borne platform 5C-1. The terrestrially located CU 5ACU-1 performs some of the (typically higher layer) functionality of the base station 5A-1 whereas the non-terrestrially located DU 5ADU-1 performs other (typically lower layer) functionality of the base station 5A-1. The terrestrially located CU 5ACU-1 communicates with the non-terrestrially located DU 5ADU-1 via the gateway 5B-1 and an F1 interface implemented via a satellite radio interface between the gateway 5B-1 and the non-terrestrial space (or air) borne platform 5C-1 in which the DU 5ADU-1 is provided.

[0082] The non-terrestrial space (or air) borne platform 5C-1 transmits communications destined for and originating from the UEs 3 in one or more cells operated by the base station 5A-1, and from and to the gateway 5B-1 as required. However, in this implementation lower layer processing of communication respectively destined for and originating from the UEs 3 is performed on-board the non-terrestrial space (or air) borne platform 5C-1 by the DU 5ADU-1 and higher layer processing of that communication respectively destined for and originating from the UEs 3 is performed by the terrestrially located CU 5ACU-1.

[0083] Accordingly, in this implementation, the feeder link between the gateway 5B-1 and the non-terrestrial space (or air) borne platform 5C-1 effectively acts as the F1 interface (or reference point) between the CU 5ACU-1 and DU 5ADU-1 of the base station 5A-1. The service link between the non-terrestrial space (or air) borne platform 5C-1 and one or more UEs 3, on the other hand, effectively acts as the NR-Uu interface (or reference point) between the base station 5A-1 and one or more UEs 3. The base station's communication link with the core network 7 (e.g. for signalling over the N2, N3 interface / reference point etc.) is provided solely terrestrially.

[0084] The architecture of Fig. 3C may also be referred to as a 'regenerative satellite' based RAN architecture (i.e., in which the satellite performs on board processing of the payload being communicated between the UE 3 and the core network 7). In this architecture, the base station 5A-1 is provided on-board the non-terrestrial space (or air) borne platform 5C-1. The base station 5A-1 on board the non-terrestrial space (or air) borne platform 5C-1 transmits communications destined for and originating from the UEs 3 in one or more cells operated by the base station 5A-1, and from and to the core network 7 via the gateway 5B-1 as required. However, in this implementation, processing of communication respectively destined for and originating from the UEs 3 is performed on-board the non-terrestrial space (or air) borne platform 5C-1 by the base station 5A-1.

[0085] Accordingly, in this implementation, the feeder link between the gateway 5B-1 and the non-terrestrial space (or air) borne platform 5C-1 effectively acts as part of the N2 / N3 interfaces (or reference points) between the base station 5A-1 and the core network 7. The base station's communication link with the core network 7 (e.g., for signalling over the N2, N3 interface / reference point etc.) is thus provided partly via the feeder link and partly terrestrially. The service link between the non-terrestrial space (or air) borne platform 5C-1 and one or more UEs 3, on the other hand, effectively acts as the NR-Uu interface (or reference point) between the base station 5A-1 and one or more UEs 3.

[0086] The base station 5A-1 thus controls one or more associated cells via the non-terrestrial space (or air) borne platform 5C-1. It will be appreciated that the base station 5A-1 may be configured to support 4G, 5G, 6G and / or later generations, and / or any other 3GPP or non-3GPP communication protocols.

[0087] (TN-NTN Mobility) 　　As already described above, undesirable delays and excessive UE power consumption can occur in mobility procedures between a TN RAN 5 and NTN RAN 5 (e.g., when a UE 3 leaves an area covered by a TN RAN 5 an enters an area covered by an NTN RAN 5). Such excessive UE power consumption however may be addressed by providing NTN information to the UE 3 prior to the mobility procedure. Such NTN information may be provided to the UE 3 via pre-existing signalling procedures. For example, where the NTN information is contained in an NTN configuration specific information element (IE) (e.g., an NTN-Config IE or the like), then the information may be provided to the UE 3 via a SIB such as SIB19. SIB19 is a SIB that was introduced to provide system information to UEs 3 accessing new radio (NR) via NTN access e.g., NTN-specific parameters for serving cell and / or neighbour cells, satellite assistance information, ephemeris data, common timing advance parameters, koffset, validity duration for UL synchronization epoch time, cell reference location, cell stop time, and the like. Such NTN configuration information contained in the SIB19 typically contains sufficient information to facilitate synchronisation signal (SS) / physical broadcast channel (PBCH) block measurement timing configuration (SMTC) adjustments, and to perform NTN neighbour cell measurements. Accordingly, NTN information such as NTN-Config helps UEs 3 look for NTN cells in available frequencies, thus making the cell (re)selection process faster and more energy efficient.

[0088] Where the NTN information consists of an NTN configuration information indicated by SIB19, that information may beneficially be signalled to the UE 3 during an initial synchronisation procedure, periodically in additional SIB19 transmissions to the UE 3, and / or on-demand via on-demand SIB transmissions requested by the UE 3. Such SIB19 transmissions are transmitted in the broadcast control channel (BCCH) logical channel, which are carried on the downlink shared channel (DL-SCH) and transmitted on the PDSCH. It will be appreciated however that where the NTN information consists of more than just an NTN configuration specific IE, or does not include an NTN configuration specific IE, the information may be transmitted via a different mechanism and via a different channel as is appropriate to help UEs 3 look for NTN cells in available frequencies, thus making the cell (re)selection process faster and more energy efficient.

[0089] Beneficially as described in more detail below, the communication system 1, is configured to implement one or more mechanisms that take into consideration at least some issues that might otherwise arise if NTN information is to be provided to the UE 3 prior to the handover to the NTN RAN 5, especially if UE energy and time transition efficiency is to be achieved. For example, the communication system 1 is configured to avoid a TN RAN 5 continuously providing NTN signaling as this would represent additional power consumption both for the TN RAN 5 continuously signaling the NTN information, and the UE 3 that has to continuously scan / measure such signaling. Beneficially, therefore, the NTN base station 5A and UEs 3 are mutually configured to ensure UEs 3 acquire NTN information as shortly before leaving TN coverage as reasonably possible to allow / trigger NTN measurements and facilitate a smooth transition between the TN to the NTN.

[0090] Furthermore, in addition to the NTN information providing sufficient information to facilitate SMTC adjustments, and to perform NTN neighbour cell measurements, the NTN base station 5A is beneficially configured to provide, in the NTN information, enhanced information including information indicating how a UE 3 connected to the TN may behave.

[0091] For example, the enhanced information may indicate TN / NTN frequency priorities, and / or whether to acquire NTN measurements prior to a handover. For example, despite being situated in an edge cell (e.g., a last TN cell before there are only NTN cells remaining), not all the UEs 3 in the edge cell may need to acquire NTN measurements, even if NTN information is broadcast to all UEs and, so providing the enhanced information can help to avoid unnecessary measurements by UEs 3 that will not ultimately need to perform a handover.

[0092] Furthermore, in the communication system 1, the NTN base station 5A and UEs 3 are mutually configured to help ensure that even where a UE 3 should perform NTN measurements prior to handover, the UE 3, only does so at an appropriate time (e.g., when the UE 3 is near the edge of available terrestrial cell coverage). The enhanced information may also be used to indicate to NTN-capable UEs 3 how to behave shortly before their transition to an NTN RAN 5 in order to improve energy and transition / handover efficiency.

[0093] (UE-based TN-NTN Mobility) 　　Fig. 4 is a simplified sequence diagram illustrating a UE-based TN-NTN mobility procedure that may be used in the communication system 1 of Fig. 1.

[0094] As shown in Fig. 4 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 may be in an RRC_CONNECTED mode with the TN base station 5ATN, or alternatively it may be in an RRC_IDLE mode. As shown in Fig. 4, there is also an NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which may be an NTN cell, to maintain communication with the core network 7.

[0095] When in RRC_CONNECTED mode the UE 3, following completion of a RRC setup procedure, is allocated a cell radio network temporary identifiers (C-RNTIs) used to address the UE 3 when making resource allocations. The UE 3 is also configured with at least one signalling radio bearer (SRB) and at least one data radio bearer (DRB) to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively.

[0096] When in the RRC_CONNECTED mode the UE 3 is also able to monitor downlink control information (DCI) on the physical downlink control channel (PDCCH). Additionally, the UE 3 may also receive other downlink information from the TN base station 5ATNto help the UE 3 understand if it is about to leave the TN coverage area of the TN base station 5ATNto which it is connected (step S402) i.e., information relevant to the edge of the TN coverage. That information may comprise of a specific indication from the TN base station 5ATNindicating that the UE 3 is in one of the edge cells of the TN. Alternatively, that information may comprise signalling information (such as signal strength information), and the like, from which the UE 3 can infer that it is currently in an edge cell of the TN operated by base station 5ATN. By way of example only, some of the downlink information that can help the UE 3 understand if it is about to leave the TN coverage area may include sets of parameters such as reference signal receive power (RSRP) thresholds, beam profiles, geographical locations / borders, and the like. It will be appreciated that where the downlink information includes geographical locations / borders the TN base station 5ATNand / or UE 3 may have global navigation satellite system (GNSS) capabilities to provide base station / UE based geographical location information respectively.

[0097] The information relating to the edge of the TN coverage sent to the UE 3 may be sent in the form of a broadcast signal (i.e., that is sent to any UE 3 in the vicinity of the TN base station 5ATN), or alternatively it may be in the form of dedicated signalling (to a specific UE 3 or set / group of UEs 3), and not arbitrarily to all UEs 3 within a specific distance from the TN base station 5ATN.

[0098] At step S404, the TN base station 5ATNmay (blindly) provide NTN information to the UE 3. For example, the TN base station 5ATNmay broadcast NTN information. That NTN information may include, by way of example only, NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like. It will be appreciated that as such NTN information is broadcast by the TN base station 5ATNthe NTN information is received by all UEs 3 within the signalling range of the TN base station 5ATN.

[0099] At step S406 the UE 3 determines whether it is at the edge of the TN coverage area. The UE 3 may perform that determination upon receipt of the NTN information as depicted in the flow diagram of Fig. 4. However, in this example, it will be appreciated that determining of whether the UE 3 is at the edge of the TN coverage area is based on the information received by the UE at step S402, and thus the UE 3 may determine that it is at the edge of the TN coverage area earlier in the procedure (e.g., prior to step S404).

[0100] It will be appreciated that determining that the UE 3 is at the edge of the coverage area may simply require the UE 3 to decode the information sent at step S402 (e.g., if the information includes an explicit indication that the UE 3 is in an edge cell of the TN. If however the information sent at S402 consists of information from which the UE 3 needs to infer whether it is in an edge cell (e.g., signal powers) then the UE 3 may determine whether the UE 3 is at the edge of the coverage area based on rules for the UE behaviour hardcoded at the UE 3. For example, the UE 3 may determine that it is at the edge of the coverage area when a RSRP is below a hardcoded threshold, and the like.

[0101] Alternatively, or additionally, the information received from the TN base station 5ATNat step S402 may signal network controlled rules to the UE 3 that it may apply to determine whether it is at the edge of the coverage area. For example, the information may indicate signal strength / power thresholds, indications that the UE's 3 current camping / connected cell is the last / only suitable TN cell, or the like, that the UE 3 is to apply to any incoming signals from the TN base station 5ATNto determine whether it is at the edge of the TN coverage area.

[0102] Alternatively or additionally, at least some rules that the UE 3 may apply to the information from the TN base station 5ATNto determine that the UE 3 is at the edge of the TN coverage area may not be hardcoded at the UE 3, or sent at step S402, but instead be provided to the UE 3 by the TN base station 5ATNat another time. Those rules may be signalled, for example, to the UE 3 by the TN base station 5ATNwhen the UE 3 first joins a cell of the TN base station 5ATNduring a RRC procedure. Those rules may then be stored at the UE 3 and maintained even when the UE 3 goes RRC_IDLE.

[0103] If the UE 3, as result of processing the information relevant to the edge of the TN coverage (i.e., the edge cell), ascertains that the UE 3 is at the edge of the TN coverage area, then the UE 3 subsequently may use the information to decide whether to perform NTN measurements in preparation for a TN-NTN mobility procedure (e.g., a conventional or conditional handover procedure, or the like) to an NTN base station 5ANTN, and if such measurements are to be performed, when such measurements are to be performed.

[0104] It will be appreciated that the UE's 3 decision whether to perform NTN measurements and when to trigger such measurements may depend not just on whether the UE 3 is at the edge of the TN coverage area, but may also depend on a current situation of the UE 3. For example, whether to trigger the NTN measurements may be dependent on a current direction, velocity, acceleration, or general movement of the UE 3 at the moment that it is determined that it is at the edge of the coverage area. For example, if the UE 3 is moving in a direction into the coverage area, then despite the UE 3 being currently at the edge of the coverage area, a handover to an NTN coverage area will not be necessary. As other example, depending on whether the UE 3 is located on an aeroplane, boat, train, or in a car, will drastically impact the velocity / acceleration at which the UE 3 is moving and thus when it is appropriate to handover to an NTN base station 5ANTNmay differ between the different scenarios. As a further example, if the UE 3 is on a person hiking up a mountain, and thus a change in altitude of the UE 3 is detected, it may be determined to be more appropriate to switch to an NTN coverage area as TN coverage areas may become weaker as the hiker climbs the mountain. If, on the other hand, the UE 3 determines that it is not at the edge of the TN coverage (i.e., in the edge cell of the TN) it may decide that it is not necessary to make NTN measurements and thus such NTN measurements will not be triggered. As a further example, if it is determined based on GNSS information that the UE 3 is stationary for hours / days, then despite being in an edge cell of the TN, the UE 3 may decide that there is no need to handover to an NTN base station 5ANTNto maintain coverage.

[0105] If the UE 3 ascertains that the UE 3 is at the edge of the coverage area (i.e., in the edge cell of the TN base station 5ATN), and the UE 3 also decides to perform NTN measurements in preparation for a possible TN-NTN mobility procedure (e.g., a handover from the TN base station 5ATNto an NTN base station 5ANTN), then at step S406, the UE 3 triggers NTN measurements, and NTN measurements are carried out (step S408). Such NTN measurements may include, for example, primary / secondary synchronization signal (PSS / SSS) measurements of target (NTN) cells, and the like.

[0106] Following those NTN measurements, the UE 3, at step S410, in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, may perform a TN-NTN mobility procedure. For example, a (conditional) handover procedure may be performed to handover the UE 3 from the TN to the NTN.

[0107] Beneficially, by providing UE 3 with information at step S402 to allow the UE 3 to determine whether it is in the edge cell of the TN base station 5ATNprior to the UE 3 performing the NTN measurements, the UE 3 may avoid performing NTN measurements unnecessarily, for example when it is determined that the UE 3 is not leaving the TN coverage. Furthermore, by allowing the UE 3 to determine whether it is in the edge cell as described above, the UE 3 may be prevented from performing NTN measurement too early (e.g., no satellite has arrived in case of discontinuous coverage), or too late (e.g., after TN RLF).

[0108] It will be appreciated that while the above description of Fig. 4 related to a scenario where the UE 3 was in an RRC_CONNECTED mode, the UE-based TN-NTN mobility procedure may also be performed when the UE 3 is in an RRC_IDLE mode. When in RRC_IDLE mode the UE 3 may read information such as system information (SI) transmitted on a broadcast control channel (BCCH) to provide the UE 3 with all the necessary information required to access the network and complete cell (re)selection i.e., to complete all necessary RACH and RRC connection setup procedures.

[0109] Fig. 5 is a simplified sequence diagram illustrating another UE-based TN-NTN mobility procedure that may be used in the communication system 1 of Fig. 1.

[0110] As shown in Fig. 5 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 and TN base station 5ATNmay be in an RRC_CONNECTED mode, or alternatively they may be in an RRC_IDLE mode. As shown in Fig. 5, there is also an NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which may be an NTN cell to maintain communication with the core network 7.

[0111] When in RRC_CONNECTED mode the UE 3, following completion of a RRC setup procedure, is allocated a cell radio network temporary identifiers (C-RNTIs) used to address the UE 3 when making resource allocations. The UE 3 is also configured with at least one signalling radio bearer (SRB) and at least one data radio bearer (DRB) to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively.

[0112] When in the RRC_CONNECTED mode the UE 3 is also able to monitor downlink control information (DCI) on the physical downlink control channel (PDCCH). Additionally, the UE 3 may also receive other downlink information from the TN base station 5ATNto help the UE 3 understand if it is about to leave the TN coverage area of the TN base station 5ATNto which it is connected (step S502) i.e., information relevant to the edge of the TN coverage. That information may comprise of a specific indication from the TN base station 5ATNindicating that the UE 3 is in one of the edge cells of the TN. Alternatively, that information may comprise signalling information (such as signal strength information), and the like, from which the UE 3 can infer that it is currently in an edge cell of the TN operated by TN base station 5ATN. By way of example only, some of the downlink information that can help the UE 3 understand if it is about to leave the TN coverage area may include sets of parameters such as reference signal receive power (RSRP) thresholds, beam profiles, geographical locations / borders, and the like. It will be appreciated that where the downlink information includes geographical locations / borders the TN base station 5ATNand / or UE 3 may have GNSS capabilities to provide base station / UE based geographical location information respectively.

[0113] The information relating to the edge of the TN coverage sent to the UE 3 may be sent in the form of a broadcast signal (i.e., that is sent to any UE 3 in the vicinity of the TN base station 5ATN), or alternatively it may be in the form of dedicated signalling, ( to a specific UE 3 or set / group of UEs 3), and not arbitrarily to all UEs 3 within a specific distance from the TN base station 5ATN.

[0114] At step S504 the UE 3 determines whether it is at the edge of the coverage of the TN base station 5ATNi.e., whether the UE 3 is in the edge cell of the TN base station 5ATN, as described previously with reference to S506. If the UE 3 determines that it is in the edge cell, then the UE 3 sends, at S505, a request message to the TN base station 5ATNto request NTN information such as NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like. In response to receipt of the request message, the TN base station 5ATNmay return an acknowledgement message (not shown).

[0115] In response to receipt of the request message, the TN base station 5ATNbroadcasts the requested NTN information at step S506. For example, the TN base station 5ATNmay broadcast NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like. It will be appreciated that as such NTN information is received by all UEs 3 within the signalling range of the TN base station 5ATN.

[0116] In response to receiving the NTN information, the UE 3 may subsequently use the information to decide whether to perform NTN measurements in preparation for a TN-NTN mobility procedure (e.g., a conventional or conditional handover procedure, or the like), and if such measurements are to be performed, when such measurements are to be performed. It will be appreciated that the UE's 3 decision whether to perform NTN measurements and thus whether to trigger such measurements may be based on both whether the UE 3 is at the edge of the coverage area of the TN, and on a current situation of the UE 3. By way of example only, whether to trigger the NTN measurements may be based on a current direction, velocity, acceleration, or general movement of the UE 3 at the moment that it is determined that it is at the edge of the coverage area. Examples of how the current velocity, acceleration, or general movement of the UE 3 may impact its decision to perform NTN measurements are outlined above.

[0117] If the UE 3 ascertains that the UE 3 is to perform NTN measurements in preparation for a possible TN-NTN mobility procedure (e.g., a handover from the TN base station 5ATNto an NTN base station 5ANTN), then at step S508, the UE 3 triggers NTN measurements, and NTN measurements are carried out (step S510). Such NTN measurements may include, for example, primary / secondary synchronization signal (PSS / SSS) measurements of target (NTN) cells, and the like.

[0118] Following those NTN measurements, the UE 3, at step S512, in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, may perform a TN-NTN mobility procedure. For example, a (conditional) handover procedure may be performed to handover the UE 3 from the TN to the NTN.

[0119] As with the sequence shown in Fig. 4, beneficially by providing UE 3 with information at step S502 to allow the UE 3 to determine whether it is at the edge of the cell coverage of the TN, prior to the UE 3 performing the NTN measurements, the UE 3 may avoid performing NTN measurements unnecessarily, for example when it is determined that the UE 3 is not leaving the TN coverage. Furthermore, by allowing the UE 3 to determine whether it is at the edge of the TN cell coverage supported by the TN base station 5ATNas described above, the UE 3 may be prevented from performing NTN measurement too early (e.g., no satellite has arrived in case of discontinuous coverage), or too late (e.g., after TN RLF).

[0120] It will be appreciated that while the above description of Fig. 5 related to a scenario where the UE 3 was in an RRC_CONNECTED mode, the UE-based TN-NTN mobility procedure may also be performed when the UE 3 is in an RRC_IDLE mode (in which case the request sent at S505 may be achieved by initiating a random access procedure using a dedicated PRACH configuration for requesting an 'on demand' SIB or the like that includes the requested information). When in RRC_IDLE mode the UE 3 may read information such as system information (SI) transmitted on a broadcast control channel (BCCH) to provide the UE 3 with all the necessary information required to access the network and complete cell (re)selection i.e., to complete all necessary RACH and RRC connection setup procedures.

[0121] Fig. 6 is a simplified sequence diagram illustrating another UE-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1.

[0122] As shown in Fig. 6 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 and TN base station 5ATNmay be in an RRC_CONNECTED mode. As shown in Fig. 6, there is also an NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which will be an NTN cell, to maintain communication with the core network 7.

[0123] When in RRC_CONNECTED mode the UE 3, following completion of a RRC setup procedure, is allocated a cell radio network temporary identifiers (C-RNTIs) used to address the UE 3 when making resource allocations. The UE 3 is also configured with at least one signalling radio bearer (SRB) and at least one data radio bearer (DRB) to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively. Once in the RRC_CONNECTED mode the UE 3 is also able to monitor downlink control information (DCI) on the physical downlink control channel (PDCCH).

[0124] When in the RRC_CONNECTED mode the UE 3 is also able to monitor downlink control information (DCI) on the physical downlink control channel (PDCCH). Additionally, the UE 3 may also receive other downlink information from the TN base station 5ATNto help the UE 3 understand if it is about to leave the TN coverage area of the TN base station 5ATNto which it is connected (step S602) i.e., information relevant to the edge of the TN coverage. That information may comprise of a specific indication from the TN base station 5ATNindicating that the UE 3 is in one the edge cells of the TN. Alternatively, that information may comprise signalling information (such as signal strength information), and the like, from which the UE 3 can infer that it is currently in an edge cell of the TN base station 5ATN. By way of example only, some of the downlink information that can help the UE 3 understand if it is about to leave the TN coverage area may include sets of parameters such as reference signal receive power (RSRP) thresholds, beam profiles, geographical locations / borders, and the like. It will be appreciated that where the downlink information includes geographical locations / borders the TN base station 5ATNand / or UE 3 may have GNSS capabilities to provide base station / UE based geographical location information respectively.

[0125] The information relating to the edge of the TN coverage sent to the UE 3 may be sent in the form of a broadcast signal (i.e., that is sent to any UE 3 in the vicinity of the TN base station 5ATN), or alternatively it may be in the form of dedicated signalling(to a specific UE 3 or set / group of UEs 3, and not arbitrarily to all UEs 3 within a specific distance from the TN base station 5ATN.

[0126] At step S604 the UE 3 determines whether it is at the edge of the coverage of the TN base station 5ATNi.e., whether the UE 3 is in an edge cell of the TN, as described previously. If the UE 3 determines that it is in an edge cell, then the UE 3 sends a request message at step S606 to the TN base station 5ATNto request NTN information such as NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like. In response to receipt of the request message the TN base station 5ATNmay return an acknowledgement message (not shown).

[0127] In response to receipt of the request message sent at S606, the TN base station 5ATNtransmits, to the UE 3, dedicated NTN information at step S608. For example, the TN base station 5ATNmay send NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like, However, unlike in Figs. 4 and 5 where the NTN information is broadcast to all UEs 3 in the vicinity of the TN base station 5ATN, in the mobility process of Fig. 6, the NTN information may be sent specifically to the UE 3 i.e., it is dedicated NTN information for UE 3.

[0128] As the NTN information sent at S608 is dedicated NTN information for UE 3, the information may include more information (instead of, or on top of NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like) that is specific to the UE 3 that requested the NTN information. For example, the dedicated NTN information may include information such as more precise TN / NTN coverage information in the area of the UE 3 (or an intended path of the UE 3) for optimized cell (re)selection, or other such information to enhance TN-NTN service continuity.

[0129] In response to receiving the dedicated NTN information, the UE 3 may subsequently use the information to decide whether to perform NTN measurements in preparation for a TN-NTN mobility procedure (e.g., a conventional or conditional handover procedure, or the like), and if such measurements are to be performed, when such measurements are to be performed. It will be appreciated that the UE's decision whether to perform NTN measurements and thus whether to trigger such measurements may be based on both whether the UE 3 is at the edge of the coverage area of the TN, and also on the current situation of the UE 3. By way of example only, whether to trigger the NTN measurements may be based on a current direction, velocity, acceleration, or general movement of the UE 3 at the moment that it is determined that it is at the edge of the coverage area of the TN. Examples of how the current direction velocity, acceleration, or general movement of the UE 3 may impact its decision to perform NTN measurements are outlined above.

[0130] If the UE 3 ascertains that the UE 3 is to perform NTN measurements in preparation for a possible TN-NTN mobility procedure (e.g., a handover from the TN base station 5ATNto an NTN base station 5ANTN), then at step S609, the UE 3 triggers NTN measurements, and NTN measurements are carried out (step S610). Such NTN measurements may include, for example, primary / secondary synchronization signal (PSS / SSS) measurements of target (NTN) cells, and the like.

[0131] Following those NTN measurements, the UE 3, at step S612, in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, may perform a TN-NTN mobility procedure. For example, a (conditional) handover procedure may be performed to handover the UE 3 from the TN to the NTN.

[0132] As with the sequence shown in Figs. 4 and 5, beneficially by providing UE 3 with information at step S602 to allow the UE 3 to determine whether it is at the edge of the cell coverage (i.e., in the edge cell of the TN base station 5ATN) supported by the TN base station 5ATN, prior to the UE 3 performing the NTN measurements, the UE 3 may avoid performing NTN measurements unnecessarily, for example when it is determined that the UE 3 is not leaving the TN coverage. Furthermore, by allowing the UE 3 to determine whether it is at the edge of the cell coverage supported by the TN base station 5ATNas described above, the UE 3 may be prevented from performing NTN measurement too early (e.g., no satellite has arrived in case of discontinuous coverage), or too late (e.g., after TN RLF).

[0133] Also beneficially, by allowing UE 3 to request dedicated NTN information from the TN base station 5ATNin response to determining that the UE 3 is at the edge of the cell coverage of the TN to allow the UE 3 to perform subsequent NTN measurements, the UE 3 does not have to continuously receive and decode broadcast NTN information that is not relevant to the UE 3 thereby saving power and processing time. Furthermore, by allowing the provision of dedicated NTN information to the UE 3 rather than broadcasting generic NTN information, the dedicated signaling may include more information (instead of, or on top of NTN configuration information) that is specific to the UE 3 and its current situation. Furthermore, other UEs 3 in the area do not receive unsolicited NTN information which it must process, thereby improving the efficiency of those UEs 3 as unnecessary processing of unsolicited NTN information is avoided. This also advantageously prevents other UEs 3 from accidently being triggered to perform unnecessary NTN measurements.

[0134] It will be appreciated that the UE-based TN-NTN mobility procedure described above with reference to Fig. 6 may only be performed when the UE 3 is in RRC_CONNECTED mode, and that unlike in the scenarios shown in Figs. 4 and 5 it may not be performed when the UE 3 is in an RRC_IDLE mode. This is because the process shown in Fig. 6 involves UE-specific information (e.g., the dedicated NTN information) being requested and transmitted and thus the UE 3 must be in the RRC_CONNECTED mode to make such requests.

[0135] (Network-based TN-NTN Mobility) 　　Fig. 7 is a simplified sequence diagram illustrating a network-based TN-NTN handover procedure that may be used in the communication system 1 of Fig. 1.

[0136] As shown in Fig. 7 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 and TN base station 5ATNmay be in an RRC_CONNECTED mode, or alternatively they may be in an RRC_IDLE mode. As shown in Fig. 7, there is also an NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which will be an NTN cell to maintain communication with the core network 7.

[0137] When in RRC_CONNECTED mode, the UE 3, following completion of a RRC setup procedure, is allocated a C-RNTIs used to address the UE 3 when making resource allocations. The UE 3 is also configured with at least one SRB and at least one DRB to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively. Once in the RRC_CONNECTED mode the UE 3 is also able to monitor DCI on the PDCCH.

[0138] At step S702, the TN base station 5ATNmay broadcast NTN information to UEs 3 (including UE 3) in the vicinity of the TN base station 5ATN. Such NTN information may include NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like. As that NTN information is broadcast to all UEs 3 in the vicinity rather than specifically to UE 3, UE 3 may choose not to decode it or may choose not to actively perform NTN measurements even though it has decoded the NTN information. In either case, the broadcast NTN information may be stored at the UE 3 for a period of time for some future use, and may be updated either periodically (e.g., in response to a timer running out), or in response to determining a change in the broadcast NTN information being broadcast to the UE 3.

[0139] At step S704 the TN base station 5ATNdetermines whether the UE 3 is at the edge of the coverage of the TN i.e., whether the UE 3 is in an edge cell of the TN supported by the TN base station 5ATN. If the TN base station 5ATNdetermines that the UE 3 is in an edge cell, then the TN base station 5ATNsends an indication to the UE 3 (step S706) to indicate that the UE 3 should i) decode and use the NTN information it has already received, and / or ii) use NTN information that it is to receive at some future point e.g., at step S708.

[0140] At step S708 the TN base station 5ATNmay broadcast NTN information to UEs 3 (including UE 3) in the vicinity of the TN base station 5ATNvia a PBCH. That broadcast of NTN information may be the first time that the UEs 3 (including UE 3) receive such broadcasted NTN information, or may be in addition to, or alternatively to the NTN information broadcast at step S702. As with the broadcasted NTN information at step S702, the NTN information broadcasted at S708 may include NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like. It will be appreciated that as the NTN information can be broadcast by the TN base station 5ATN, the NTN information may beneficially be targeted at groups of UEs 3 where it is determined that there are a number of UEs 3 at the edge of the coverage of the TN base station 5ATN.

[0141] In response to the UE 3 decoding NTN information received by and stored at the UE 3 (step S702) and / or decoding NTN information being transmitted to the UE 3 (S708), the UE 3 determines whether to perform NTN measurements in preparation for a TN-NTN mobility procedure (e.g., a conventional or conditional handover procedure, or the like), and if such measurements are to be performed, when such measurements are to be performed. It will be appreciated that the UE's decision whether to perform NTN measurements and thus whether to trigger such measurements may be based on the UE 3 determining that it is at the edge of the coverage area of the TN, as well as on a current situation of the UE 3. By way of example only, whether to trigger the NTN measurements may be dependent on a current direction, velocity, acceleration, or general movement of the UE 3 at the moment that it is determined that it is at the edge of the coverage area. Examples of how the current velocity, acceleration, or general movement of the UE 3 may impact its decision to perform NTN measurements are outlined above.

[0142] If the UE 3 determines that it is to perform NTN measurements in preparation for a possible TN-NTN mobility procedure (e.g., a handover from the TN base station 5ATNto an NTN base station 5ANTN), then at step S710, the UE 3 triggers NTN measurements, and NTN measurements are carried out (step S712).

[0143] Following those NTN measurements, the UE 3, at step S714, in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, may perform a TN-NTN mobility procedure. For example, a (conditional) handover procedure may be performed to handover the UE 3 from the TN to the NTN.

[0144] Beneficially, by the TN base station 5ATNdetermining that the UE 3 is at the edge of the coverage area of the TN base station 5ATNand then indicating to the UE 3 that it is to decode NTN information previously broadcasted to the UE 3 and / or NTN information broadcasted to the UE 3 at some future time, a power saving is achieved at the UE 3. Specifically, as the UE 3 does not have to decode broadcasted NTN information until it is specifically instructed to do so by the TN base station 5ATN, the UE 3 does not have to continuously decode the NTN information broadcasted to it. Furthermore, it will be appreciated that dedicated signaling to indicate that a UE 3 is to decode the NTN information is also beneficial for other UEs 3 in the vicinity of the TN base station 5ATN. Specifically, despite all UEs 3 in the vicinity of the TN base station 5ATNreceiving the broadcast NTN information, not all UEs 3 must decode the information unless it is relevant to that UE 3. Accordingly, energy and processing efficiencies are also achieved for other UEs 3 in the vicinity of the TN base station 5ATNbut which do not require to undertake NTN measurements.

[0145] Further beneficially, it will be appreciated that although the scenario above only discuses one UE 3, UE 3, as the NTN information can be broadcast by the TN base station 5ATN, the NTN information may be targeted at groups of UEs 3 where it is determined that there are several UEs 3 at the edge of the coverage of the TN base station 5ATN, e.g., a group of UEs 3 on a boat, train or aeroplane.

[0146] It will be appreciated that while the above description of Fig. 7 related to a scenario where the UE 3 was in an RRC_CONNECTED mode, the network-based TN-NTN mobility procedure may also be performed when the UE 3 is in an RRC_INACTIVE mode. When in RRC_INACTIVE mode the UE 3 is provided with a full and a short inactive radio network temporary identifier (I-RNTI). The full I-RNTI may be used by the network to address the UE 3 within RRC paging messages, while the short I-RNTI may be used within a RRC Resume Request message when attempting to re-enter RRC_CONNECTED mode. While in RRC_INACTIVE mode the UE 3 may monitor for short messages (e.g., paging messages) transmitted with a paging radio network temporary identifier (P-RNTI) over DCI and other small data transmissions (SDTs) which are a transmission of a short data burst in a connectionless state where a device does not need to establish connections when small amounts of data need to be sent. For example, the UE 3 may perform SDT procedures to monitor control channels associated with the shared data channels to determine if data is scheduled for it. The UE 3 may also be able to perform neighbouring cell measurements and cell (re)selection and acquires system information, while SDT procedures are not ongoing, and the like.

[0147] Fig. 8 is a simplified sequence diagram illustrating a network-based TN-NTN handover procedure that may be used in the communication system 1 of Fig. 1.

[0148] As shown in Fig. 8 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 and TN base station 5ATNmay be in an RRC_CONNECTED mode, or alternatively they may be in an RRC_IDLE mode. As shown in Fig. 8, there is also a NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which may be an NTN cell to maintain communication with the core network 7.

[0149] When in RRC_CONNECTED mode the UE 3, following completion of a RRC setup procedure, is allocated a C-RNTI used to address the UE 3 when making resource allocations. The UE 3 is also configured with at least one SRB and at least one DRB to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively. Once in the RRC_CONNECTED mode the UE 3 is also able to monitor DCI on the PDCCH.

[0150] At step S802 the TN base station 5ATNdetermines whether the UE 3 is at the edge of the coverage of the TN supported by the TN base station 5ATNi.e., whether the UE 3 is in an edge cell of the TN supported by the TN base station 5ATN. If the TN base station 5ATNdetermines that the UE 3 is in the edge cell, then the TN base station 5ATNbegins transmitting dedicated NTN information to the UE 3 at step S804. For example, the dedicated NTN information may include UE-specific NTN information additionally or alternatively to the information contained in the broadcast NTN information previously described (e.g., NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like, in addition to UE-specific NTN information, for example UE-specific satellite preferences).

[0151] Beneficially, the dedicated NTN information is sent by the TN base station 5ATNspecifically to the UE 3 and does not broadcast to other UEs 3 in the vicinity the TN base station 5ATN. Thus other UEs 3 in the area do not receive unsolicited NTN information which it must process, thereby improving the efficiency of those UEs 3 as unnecessary processing of unsolicited NTN information is avoided. This also advantageously prevents other UEs 3 from accidently being triggered to perform unnecessary NTN measurements. Such NTN measurements may include, for example, primary / secondary synchronization signal (PSS / SSS) measurements of target (NTN) cells, and the like.

[0152] Following receipt of the dedicated NTN information at step S804, the UE 3 decides to perform NTN measurements in preparation for a possible TN-NTN mobility procedure (e.g., a handover from the TN base station 5ATNto an NTN base station 5ANTN) and the UE 3 triggers NTN measurements at step S806, and NTN measurements are carried out (step S808).

[0153] Following those NTN measurements, the UE 3, at step S810, in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, may perform a TN-NTN mobility procedure. For example, a (conditional) handover procedure may be performed to handover the UE 3 from the TN to the NTN.

[0154] It will be appreciated that while the above description of Fig. 8 related to a scenario where the UE 3 was in an RRC_CONNECTED mode, the network-based TN-NTN mobility procedure may also be performed when the UE 3 is in an RRC_INACTIVE mode. When in RRC_INACTIVE mode the UE 3 is provided with a full and a short inactive radio network temporary identifier (I-RNTI). The full I-RNTI may be used by the network to address the UE 3 within RRC paging messages, while the short I-RNTI may be used within a RRC Resume Request message when attempting to re-enter RRC_CONNECTED mode. While in RRC_INACTIVE mode the UE 3 may monitor for short messages (e.g., paging messages) transmitted with a paging radio network temporary identifier (P-RNTI) over DCI and other small data transmissions (SDTs) which are a transmission of a short data burst in a connectionless state where a device does not need to establish connections when small amounts of data need to be sent. For example, the UE 3 may perform SDT procedures to monitors control channels associated with the shared data channels to determine if data is scheduled for it. The UE 3 may also be able to perform neighbouring cell measurements and cell (re)selection and acquires system information, while SDT procedures are not ongoing, and the like. As such, when in RRC_INACTIVE mode the UE 3 may acquire on-demand SIBs, thus enabling the UE 3 to obtain NTN information even when in an idle mode.

[0155] Fig. 9 is a simplified sequence diagram illustrating a network-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1.

[0156] As shown in Fig. 9 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 and TN base station 5ATNmay be in an RRC_CONNECTED mode, or alternatively they may be in an RRC_IDLE mode. As shown in Fig. 9, there is also an NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which may be an NTN cell to maintain communication with the core network 7.

[0157] When in RRC_CONNECTED mode the UE 3, following completion of a RRC setup procedure, is allocated a C-RNTIs used to address the UE when making resource allocations. The UE 3 is also configured with at least one SRB and at least one DRB to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively. Once in the RRC_CONNECTED mode the UE 3 is also able to monitor DCI on the PDCCH.

[0158] At step S902 the TN base station 5ATNdetermines whether the UE 3 is at the edge of the coverage of the TN i.e., whether the UE 3 is in an edge cell of the TN supported by TN base station 5ATN. If the TN base station 5ATNdetermines that the UE 3 is in an edge cell, then the TN base station 5ATNtriggers an TN-NTN handover procedure at step S904, which will now be described in more detail.

[0159] The TN-NTN handover procedure at step S904 is typically a conventional handover (HO) procedure, although it will be appreciated that the handover procedure may be a conditional handover (CHO) procedure. In conventional HO procedures (including RACH-less handover procedures) the TN base station 5ATNmay initially decide to initiate a handover based on measurement reporting or the triggering of an event such as determining that UE 3 is at the edge of the TN (as at step S902). In response, TN base station 5ATNmay initiate preparation of a target RAN node (e.g., NTN base station 5ANTN) for handover by sending a handover request message to NTN base station 5ANTN(not shown in Fig. 9).

[0160] Assuming NTN base station 5ANTNdecides to allow the handover request (e.g., based on appropriate admission control), NTN base station 5ANTNmay then prepare handover and typically sends a handover request acknowledgement message to the source RAN node (e.g., TN base station 5ATN). This handover request acknowledgement message typically includes an RRC message generated by the NTN base station 5ANTNfor instructing modification / reconfiguration of the UE's RRC connection for the purposes of handover (not shown in Fig. 9).

[0161] TN base station 5ATNthen initiates a handover execution phase by sending a handover command to the UE 3 at step S906. That handover command may include, for example, a RRC (re)configuration message (including mobility control information). The UE 3 receives the RRC reconfiguration message and is thus commanded by the TN base station 5ATNto perform the handover.

[0162] In the scenario shown in Fig. 9, that handover command sent at step S906 also includes dedicated NTN information that is sent by the TN base station 5ATNto the UE 3. For example, the dedicated NTN information may include UE-specific NTN information (for example UE-specific satellite preferences) additionally or alternatively to NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like.

[0163] Following receipt of the dedicated NTN information at step S906, the UE 3 decides to perform NTN measurements as part of the handover procedure from the TN base station 5ATNto the NTN base station 5ANTN, and the UE 3 triggers NTN measurements at step S908, and NTN measurements are carried out (step S910).

[0164] Following those NTN measurements, the UE 3, at step S912, in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, continues the handover procedure. For example, the UE 3 may derive NTN base station 5ANTNspecific keys and configure security algorithms to be used in a target cell of the NTN supported by the NTN base station 5ANTN. After receiving the RRC Reconfiguration message, the UE 3 will attempt to access a target cell at the first available physical uplink shared channel (PUSCH) occasion.

[0165] To confirm the handover the UE 3 may send an RRC reconfiguration complete message to the NTN base station 5ANTN. The RRC reconfiguration complete message includes a cell radio network temporary identifier (C-RNTI), along with an uplink buffer status report, and / or uplink data, whenever possible. The NTN base station 5ANTNmay verify the C-RNTI sent in the RRC reconfiguration complete message. The NTN base station 5ANTNcan then begin sending data to the UE 3 after scheduling appropriate downlink resources using the PDCCH. The handover procedure is completed for the UE 3 when the UE 3 receives a UE contention resolution identity MAC control element (MAC CE) from the NTN base station 5ANTNor the UE 3 receives a PDCCH addressed to its C-RNTI from the NTN base station 5ANTNafter sending the initial uplink transmission.

[0166] Conventional handover procedures are known by the skilled person in the art, as such it will be appreciated that other steps not here described, but which are common to conventional handover procedures, may be included in the TN-NTN handover procedure S904 described above.

[0167] Beneficially, by signalling dedicated NTN information from the TN base station 5ATNin response to the TN base station 5ATNdetermining that the UE 3 is at the edge of the cell coverage of the TN to allow the UE 3 to perform subsequent NTN measurements, the UE 3 does not have to continuously receive and decode broadcast NTN information that is not relevant to the UE 3 thereby saving power and processing time. Furthermore, by allowing the provision of dedicated NTN information to the UE 3 rather than broadcasting generic NTN information, the dedicated signaling may include more information (instead of, or on top of NTN configuration information). For example, the dedicated NTN information may include information that is specific to the UE 3 and its current situation. Furthermore, other UEs 3 in the area do not receive unsolicited NTN information which it must process, thereby improving the efficiency of those UEs 3 as unnecessary processing of unsolicited NTN information is avoided. This also advantageously prevents other UEs 3 from accidently being triggered to perform unnecessary NTN measurements.

[0168] Furthermore, beneficially by signalling dedicated NTN information in the handover command as part of the TN-NTN handover procedure, the amount of overall signaling required to facilitate the TN-NTN handover procedure is reduced, thereby improving the overall efficiency of the procedure. For example, separate distinct NTN information signaling is not required but instead is subsumed into pre-existing signaling in the TN-NTN handover procedure.

[0169] It will be appreciated that while the above description of Fig. 7 related to a scenario where the UE 3 was in an RRC_CONNECTED mode, the network-based TN-NTN mobility procedure may also be performed when the UE 3 is in an RRC_INACTIVE mode. When in RRC_INACTIVE mode the UE 3 is provided with a full and a short inactive radio network temporary identifier (I-RNTI). The full I-RNTI may be used by the network to address the UE 3 within RRC paging messages, while the short I-RNTI may be used within a RRC Resume Request message when attempting to re-enter RRC_CONNECTED mode. While in RRC_INACTIVE mode the UE 3 may monitor for short messages (e.g., paging messages) transmitted with a paging radio network temporary identifier (P-RNTI) over DCI and other small data transmissions (SDTs) which are a transmission of a short data burst in a connectionless state where a device does not need to establish connections when small amounts of data need to be sent. For example, the UE 3 may perform SDT procedures to monitors control channels associated with the shared data channels to determine if data is scheduled for it. The UE 3 may also be able to perform neighbouring cell measurements and cell (re)selection and acquires system information, while SDT procedures are not ongoing, and the like. As such, when in RRC_INACTIVE mode the UE 3 may acquire on-demand SIBs, thus enabling the UE 3 to obtain NTN information even when in an idle mode.

[0170] Fig. 10 is a simplified sequence diagram illustrating a network-based TN-NTN mobility procedure that may be used in the communication system of Fig. 1.

[0171] As shown in Fig. 10 there is a UE 3 in communication with a TN base station 5ATNwhich provides a certain cell coverage and connection to the core network 7. The UE 3 and TN base station 5ATNmay be in an RRC_CONNECTED mode, or alternatively they may be in an RRC_IDLE mode. As shown in Fig. 8, there is also an NTN base station 5ANTNwhich provides a different cell coverage to that the of the TN base station 5ATN. The cell coverage provided by the TN base station 5ATNand the cell coverage provided by the NTN base station 5ANTNmay be in close proximity to one another such that when in a TN edge cell (e.g., a cell at the edge of a TN coverage area), the UE 3 may be handed over to the next available cell, which will be an NTN cell to maintain communication with the core network 7.

[0172] When in RRC_CONNECTED mode the UE 3, following completion of a RRC setup procedure, is allocated a C-RNTIs used to address the UE 3 when making resource allocations. The UE 3 is also configured with at least one SRB and at least one DRB to allow the transfer of signalling and application data between the UE 3 and the TN base station 5ATN, respectively. Once in the RRC_CONNECTED mode the UE 3 is also able to monitor DCI on the PDCCH.

[0173] At step S1002 the TN base station 5ATNdetermines whether the UE 3 is at the edge of the coverage of the TN i.e., whether the UE 3 is in an edge cell of the TN supported by the TN base station 5ATN. If the TN base station 5ATNdetermines that the UE 3 is in an edge cell, then the TN base station 5ATNprepares for a CHO procedure (step S1002). Once prepared the CHO procedure is triggered at step S1004. The CHO procedure will now be described in more detail.

[0174] In CHO procedures, the handover is not executed until the UE 3 being handed over (rather than the network) determines that one or more handover execution conditions have been met. As in conventional handover, in CHO, TN base station 5ATNmay make the initial handover decision based on measurement reporting, a trigger event or the like, such as the determination that the UE 3 is at the edge of TN at step S1002. However, the UE 3 makes the ultimate decision of when to commence handover, e.g., when one or more handover execution conditions have been met.

[0175] In response determining that the UE 3 is at the edge of the TN, TN base station 5ATNmay request a CHO with one (or more) 'candidate' target RAN nodes (e.g., NTN base station 5ANTN) by sending each target RAN node a respective CHO request message (i.e., the TN base station 5ATNprepares for a CHO). In response to the CHO request message, NTN base station 5ANTNmay typically send a CHO response including a configuration of CHO candidate NTN base station 5ANTNto the TN base station 5ATN(not shown in Fig. 10).

[0176] TN base station 5ATNthen sends a handover command to the UE 3 at step S1006. That handover command may include, for example, a RRC (re)configuration message. which contains the configurations of the NTN base station 5ANTNand one or more CHO execution conditions, which may typically set by the TN base station 5ATN. In the scenario shown in Fig. 10, that handover command sent at step S1006 also includes dedicated NTN information that is sent by the TN base station 5ATNto the UE 3. For example, the dedicated NTN information may include UE-specific NTN information (for example UE-specific satellite preferences) additionally or alternatively to NTN configuration information, available NTN cell frequencies, TN / NTN frequency priorities, when and / or whether to acquire NTN measurements, and the like.

[0177] It will be appreciated that as further studies and developments are made to NT-NTN mobility procedures that utilize CHO there may be a desire or need to transmit additional new triggers or new trigger conditions to the UE 3 for the trigger of NTN measurements and / or CHO. Such new triggers and / or trigger conditions may be included in the signaling used for transmitting dedicated NTN information to the UE 3, or alternatively the new triggers and / or trigger conditions may be signaled to the UE 3 via a new signaling scheme / mechanism.

[0178] Upon receipt of the handover command, the UE 3 will maintain connection with TN base station 5ATNwhile it evaluates one or more CHO execution conditions for the NTN base station 5ANTN. If at least one CHO execution condition is satisfied, then the UE 3 proceeds at step S1008 to trigger NTN measurements, which are performed at step S1010.

[0179] Following those NTN measurements, the UE 3 (at step S1012) in conjunction with the TN base station 5ATNand the NTN base station 5ANTN, continue the handover procedure. For example, the UE 3 may derive NTN base station 5ANTNspecific keys and configure security algorithms to be used in a target cell of the NTN base station 5ANTN. After receiving the RRC Reconfiguration message, the UE 3 will attempt to access the target cell of the NTN base station 5ANTNat the first available physical uplink shared channel (PUSCH) occasion.

[0180] To confirm the handover the UE 3 may send an RRC reconfiguration complete message to the NTN base station 5ANTN. The RRC reconfiguration complete message includes a cell radio network temporary identifier (C-RNTI), e.g., along with an uplink buffer status report, and / or uplink data, whenever possible. The target RAN node verifies the C-RNTI sent in the RRC reconfiguration complete message. The NTN base station 5ANTNcan then begin sending data to the UE 3 after scheduling appropriate downlink resources using the PDCCH.

[0181] The handover procedure is completed for the UE 3 when the UE 3 receives a UE contention resolution identity MAC control element (MAC CE) from the target RAN node or the UE 3 receives a PDCCH addressed to its C-RNTI from the NTN base station 5ANTNafter sending the initial uplink transmission.

[0182] Beneficially, by signalling dedicated NTN information from the TN base station 5ATNin response to the TN base station 5ATNdetermining that the UE 3 is at the edge of the cell coverage of the TN supported by the TN base station 5ATNto allow the UE 3 to perform subsequent NTN measurements, the UE 3 does not have to continuously receive and decode broadcast NTN information that is not relevant to the UE 3 thereby saving power and processing time. Furthermore, by allowing the provision of dedicated NTN information to the UE 3 rather than broadcasting generic NTN information, the dedicated signaling may include more information (instead of, or on top of NTN configuration information) that is specific to the UE 3 and its current situation. Furthermore, other UEs 3 in the area do not receive unsolicited NTN information which it must process, thereby improving the efficiency of those UEs 3 as unnecessary processing of unsolicited NTN information is avoided. This also advantageously prevents other UEs 3 from accidently being triggered to perform unnecessary NTN measurements.

[0183] Furthermore, beneficially by signalling dedicated NTN information in the handover command as part of the TN-NTN handover procedure the amount of overall signaling required to facilitate the TN-NTN handover procedure is reduced, thereby improving the overall efficiency of the procedure. For example, separate distinct NTN information signaling is not required but instead is subsumed into pre-existing signaling in the TN-NTN handover procedure.

[0184] It will be appreciated that while the above description of Fig. 7 related to a scenario where the UE 3 was in an RRC_CONNECTED mode, the network-based TN-NTN mobility procedure may also be performed when the UE 3 is in an RRC_INACTIVE mode. When in RRC_INACTIVE mode the UE 3 is provided with a full and a short inactive radio network temporary identifier (I-RNTI). The full I-RNTI may be used by the network to address the UE 3 within RRC paging messages, while the short I-RNTI may be used within a RRC Resume Request message when attempting to re-enter RRC_CONNECTED mode. While in RRC_INACTIVE mode the UE 3 may monitor for short messages (e.g., paging messages) transmitted with a paging radio network temporary identifier (P-RNTI) over DCI and other small data transmissions (SDTs) which are a transmission of a short data burst in a connectionless state where a device does not need to establish connections when small amounts of data need to be sent. For example, the UE 3 may perform SDT procedures to monitors control channels associated with the shared data channels to determine if data is scheduled for it. The UE 3 may also be able to perform neighbouring cell measurements and cell (re)selection and acquires system information, while SDT procedures are not ongoing, and the like. As such, when in RRC_INACTIVE mode the UE 3 may acquire on-demand SIBs, thus enabling the UE 3 to obtain NTN information even when in an idle mode.

[0185] (User Equipment) 　　Fig. 11 is a simplified block schematic illustrating the main components of a UE 3 for implementation in the communication system 1 of Fig. 1.

[0186] As shown, the UE 3 has a transceiver circuit 31 that is operable to transmit signals to and to receive signals from a base station 5A via one or more antenna 33 (e.g., comprising one or more antenna elements). The UE 3 has a controller 37 to control the operation of the UE 3. The controller 37 is associated with a memory 39 and is coupled to the transceiver circuit 31. Although not necessarily required for its operation, the UE 3 might, of course, have all the usual functionality of a conventional UE 3 (e.g., a user interface 35, such as a touch screen / keypad / microphone / speaker and / or the like for, allowing direct control by and interaction with a user) and this may be provided by any one or any combination of hardware, software, and firmware, as appropriate. Software may be pre-installed in the memory 39 and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example.

[0187] The controller 37 is configured to control overall operation of the UE 3 by, in this example, program instructions or software instructions stored within memory 39. As shown, these software instructions include, among other things, an operating system 41, and a communications control module 43.

[0188] The communications control module 43 is operable to control the communication between the UE 3 and its serving base station or base stations 5A (and other communication devices connected to the base station 5A, such as further UEs 3 and / or core network nodes). The communications control module 43 is configured for the overall handling of uplink communications via associated uplink channels (e.g., via a physical uplink control channel (PUCCH), random access channel (RACH), and / or a physical uplink shared channel (PUSCH)) including both dynamic and semi-static signalling (e.g., SRS). The communications control module 43 is also configured for the overall handling of receipt of downlink communications via associated downlink channels (e.g., of DCI via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)) including both dynamic and semi-persistent scheduling (e.g., SPS). The communications control module 43 is responsible, for example: for determining where to monitor for downlink control information; for determining the resources to be used by the UE 3 for transmission / reception of UL / DL communications (including interleaved resources and resources subject to frequency hopping); for managing frequency hopping at the UE side; for determining how slots / symbols are configured (e.g., for UL, DL or full duplex communication, or the like); for determining which bandwidth parts are configured for the UE 3; for determining how uplink transmissions should be encoded and the like.

[0189] It will be appreciated that the communications control module 43 may include a number of sub-modules ('layers' or 'entities') to support specific functionalities. For example, the communications control module 43 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an RRC sub-module, etc.

[0190] The communications control module 43 is configured, in particular, to control the UE's communications, in accordance with any of the methods described herein.

[0191] (Base Station) 　　Fig. 12 is a simplified block schematic illustrating the main components of a base station 5A for implementation in the communication system 1 of Fig. 1 (e.g., in an NTN access network or other such RAN 5).

[0192] As shown, the base station 5A has a transceiver circuit 51 for transmitting signals to and for receiving signals from the communication devices (such as UEs 3) via one or more antenna 53 (e.g., a single or multi-panel antenna array / massive antenna), and a core network interface 55 for transmitting signals to and for receiving signals from network nodes in the core network 7. Although not shown, the base station 5A may also be coupled to other base stations via an appropriate interface (e.g., the so-called 'X2' interface in LTE or the 'Xn' interface in NR). The base station 5A has a controller 57 to control the operation of the base station 5A. The controller 57 is associated with a memory 59. Software may be pre-installed in the memory 59 and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example. The controller 57 is configured to control the overall operation of the base station 5A by, in this example, program instructions or software instructions stored within memory 59.

[0193] As shown, these software instructions include, among other things, an operating system 61, and a communications control module 63.

[0194] The communications control module 63 is operable to control the communication between the base station 5A and UEs 3 and other network entities (e.g., core network nodes) that communicate with the base station 5A. The communications control module 63 is configured for the overall control of the reception and decoding of uplink communications, via associated 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 semi-static signalling (e.g., SRS). The communications control module 63 is also configured for the overall control of the transmission of downlink communications via associated downlink channels (e.g., via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)) including both dynamic and semi-persistent scheduling (e.g., SPS). The communications control module 63 is responsible, for example: for determining where to configure the UE 3 to monitor for downlink control information (e.g., the location of search spaces, CORESETs, and associated PDCCH candidates to monitor); for determining the resources to be scheduled for UE transmission / reception of UL / DL communications (including interleaved resources and resources subject to frequency hopping); for managing frequency hopping at the base station side; for configuring slots / symbols appropriately (e.g., for UL, DL or full duplex communication, or the like); for configuring bandwidth parts for the UE 3; for providing related configuration signalling to the UE 3; and the like.

[0195] It will be appreciated that the communications control module 63 may include a number of sub-modules ('layers' or 'entities') to support specific functionalities. For example, the communications control module 63 may include, for communicating with a UE 3, a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an RRC sub-module, etc. Moreover, the communications control module 63 may include, for communicating with a core network entity such as an MME (or similar node such as an AMF 10-1), an S1 application protocol (S1-AP) sub-module, a stream control transmission protocol (SCTP) sub-module, an IP sub-module, a layer 1 (L1) sub-module, a layer 2 (L2) sub-module, etc (or corresponding sub-modules for communicating with an AMF 10-1).

[0196] The communications control module 63 is configured in particular, to control the base station's communications, in accordance with any of the methods described herein.

[0197] (Modifications and Alternatives) 　　Detailed examples been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above examples whilst still benefiting from the enhancements embodied therein.

[0198] It will be appreciated that description of features of and actions performed by a base station (or eNB or gNB), NTN nodes, and UEs may be applied equally to base stations and UEs that communicate in the terrestrial plane only (i.e. as part of a terrestrial RAN without features of an NTN RAN such as a gateway and space or airborne platform) as to base stations that communicate via a non-terrestrial plane.

[0199] Moreover, description of features of and actions performed by a base station (or eNB or gNB), apply equally to distributed type base stations as to non-distributed type base stations.

[0200] It will also be appreciated that whilst information elements having specific names have been described differently named information elements but having a similar purpose may be used.

[0201] In the above description the UE and the base station are described for ease of understanding as having a number of discrete functional components or modules. Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the disclosed enhancements, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities.

[0202] In the above examples, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the UE or base station as a signal over a computer network, or on a recording medium. Further, the functionality performed by part, or all, of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the UE or the base station in order to update their functionalities.

[0203] Each controller may comprise any suitable form of processing circuitry including (but not limited to), for example: one or more hardware implemented computer processors; microprocessors; central processing units (CPUs); arithmetic logic units (ALUs); input / output (IO) circuits; internal memories / caches (program and / or data); processing registers; communication buses (e.g. control, data and / or address buses); direct memory access (DMA) functions; hardware or software implemented counters, pointers and / or timers; and / or the like. Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0204] The memories shown above may be formed by a non-transitory computer readable medium or a tangible storage medium. However, the memories may be formed by a combination of a non-transitory computer readable medium and a tangible storage medium.

[0205] A program includes instructions (or software codes) that, when loaded into a computer, cause the computer to perform one or more of the functions described in the example embodiments. The program may be stored in a non-transitory computer readable medium or a tangible storage medium. By way of example, and not limitation, non-transitory computer readable media or tangible storage media can include a random-access memory (RAM), a read-only memory (ROM), a flash memory, a solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disk (DVD), Blu-ray disc ((R): Registered trademark) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted on a transitory computer readable medium or a communication medium. By way of example, and not limitation, transitory computer readable media or communication media can include electrical, optical, acoustical, or other form of propagated signals.

[0206] The User Equipment (or "UE", "mobile station", "mobile device" or "wireless device") in the present disclosure is an entity connected to a network via a wireless interface.

[0207] It should be noted that the present disclosure is not limited to a dedicated communication device and can be applied to any device having a communication function as explained in the following paragraphs.

[0208] The terms "User Equipment" or "UE" (as the term is used by 3GPP), "mobile station", "mobile device", and "wireless device" are generally intended to be synonymous with one another, and include standalone mobile stations, such as terminals, cell phones, smart phones, tablets, cellular IoT devices, IoT devices, and machinery. It will be appreciated that the terms "mobile station" and "mobile device" also encompass devices that remain stationary for an extended period of time.

[0209] A UE may, for example, be an item of equipment for production or manufacture and / or an item of energy related machinery (for example equipment or machinery such as: boilers; engines; turbines; solar panels; wind turbines; hydroelectric generators; thermal power generators; nuclear electricity generators; batteries; nuclear systems and / or associated equipment; heavy electrical machinery; pumps including vacuum pumps; compressors; fans; blowers; oil hydraulic equipment; pneumatic equipment; metal working machinery; manipulators; robots and / or their application systems; tools; moulds or dies; rolls; conveying equipment; elevating equipment; materials handling equipment; textile machinery; sewing machines; printing and / or related machinery; paper converting machinery; chemical machinery; mining and / or construction machinery and / or related equipment; machinery and / or implements for agriculture, forestry and / or fisheries; safety and / or environment preservation equipment; tractors; precision bearings; chains; gears; power transmission equipment; lubricating equipment; valves; pipe fittings; and / or application systems for any of the previously mentioned equipment or machinery etc.).

[0210] A UE may, for example, be an item of transport equipment (for example transport equipment such as: rolling stocks; motor vehicles; motorcycles; bicycles; trains; buses; carts; rickshaws; ships and other watercraft; aircraft; rockets; satellites; drones; balloons etc.).

[0211] A UE may, for example, be an item of information and communication equipment (for example information and communication equipment such as: electronic computer and related equipment; communication and related equipment; electronic components etc.).

[0212] A UE may, for example, be a refrigerating machine, a refrigerating machine applied product, an item of trade and / or service industry equipment, a vending machine, an automatic service machine, an office machine or equipment, a consumer electronic and electronic appliance (for example a consumer electronic appliance such as: audio equipment; video equipment; a loud speaker; a radio; a television; a microwave oven; a rice cooker; a coffee machine; a dishwasher; a washing machine; a dryer; an electronic fan or related appliance; a cleaner etc.).

[0213] A UE may, for example, be an electrical application system or equipment (for example an electrical application system or equipment such as: an x-ray system; a particle accelerator; radio isotope equipment; sonic equipment; electromagnetic application equipment; electronic power application equipment etc.).

[0214] A UE may, for example, be an electronic lamp, a luminaire, a measuring instrument, an analyser, a tester, or a surveying or sensing instrument (for example a surveying or sensing instrument such as: a smoke alarm; a human alarm sensor; a motion sensor; a wireless tag etc.), a watch or clock, a laboratory instrument, optical apparatus, medical equipment and / or system, a weapon, an item of cutlery, a hand tool, or the like.

[0215] A UE may, for example, be a wireless-equipped personal digital assistant or related equipment (such as a wireless card or module designed for attachment to or for insertion into another electronic device (for example a personal computer, electrical measuring machine)).

[0216] A UE may be a device or a part of a system that provides applications, services, and solutions described below, as to "internet of things (IoT)", using a variety of wired and / or wireless communication technologies.

[0217] Internet of Things devices (or "things") may be equipped with appropriate electronics, software, sensors, network connectivity, and / or the like, which enable these devices to collect and exchange data with each other and with other communication devices. IoT devices may comprise automated equipment that follow software instructions stored in an internal memory. IoT devices may operate without requiring human supervision or interaction. IoT devices might also remain stationary and / or inactive for an extended period of time. IoT devices may be implemented as a part of a (generally) stationary apparatus. IoT devices may also be embedded in non-stationary apparatus (e.g. vehicles) or attached to animals or persons to be monitored / tracked.

[0218] It will be appreciated that IoT technology can be implemented on any communication devices that can connect to a communications network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0219] It will be appreciated that IoT devices are sometimes also referred to as Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be appreciated that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in the following table. This list is not exhaustive and is intended to be indicative of some examples of machine type communication applications.

[0220] Further, the above-described UE categories are merely examples of applications of the technical ideas and exemplary examples described in the present document. Needless to say, these technical ideas and examples are not limited to the above-described UE and various modifications can be made thereto. Further, each example embodiment can be appropriately combined with at least one of example embodiments.

[0221] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0222] Part of or all the foregoing aspects can be described as in the following appendixes, but the present disclosure is not limited thereto. Some or all of elements specified in any of Supplementary Notes may be applied to various types of hardware, software, and recording means for recording software, systems, and methods. 　　(Supplementary Note 1) 　　A method performed by a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), the method comprising: 　　receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and 　　determining whether to perform measurements for the NTN-TN mobility based on the information. 　　(Supplementary Note 2) 　　The method according to Supplementary Note 1, wherein 　　the information is received via a system information block or a dedicated signaling. 　　(Supplementary Note 3) 　　The method according to Supplementary Note 1 or 2, wherein 　　the information includes at least one of: 　　　　information related to coverage areas of the TN, or 　　　　information related to a location for the coverage areas of the TN. 　　(Supplementary Note 4) 　　The method according to any one of Supplementary Notes 1 to 3, further comprising: 　　skipping the measurements for the NTN-TN mobility based on the determining. 　　(Supplementary Note 5) 　　The method according to any one of Supplementary Notes 1 to 4, further comprising: 　　transmitting, to the access network node, a request for the information, and wherein 　　the receiving the information is performed upon the transmitting the request. 　　(Supplementary Note 6) 　　The method according to any one of Supplementary Notes 1 to 4, wherein 　　the receiving the information is performed in a case where the access network node determines that the UE is required to perform the NTN-TN mobility. 　　(Supplementary Note 7) 　　The method according to any one of Supplementary Notes 1 to 6, further comprising: 　　initiating a conditional handover procedure as the NTN-TN mobility. 　　(Supplementary Note 8) 　　The method according to Supplementary Note 7, further comprising: 　　receiving, from the access network node, information indicating a condition for initiating the conditional handover procedure, wherein 　　the condition is related to at least one of: 　　　　coverage areas of the TN, or 　　　　a location for the coverage areas of the TN. 　　(Supplementary Note 9) 　　A method performed by an access network node, the method comprising: 　　transmitting, to a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), information indicating coverage of a terrestrial network (TN) for NTN-TN mobility, wherein 　　the information is used by the UE to determine whether to perform measurements for the NTN-TN mobility based on the information. 　　(Supplementary Note 10) 　　A user equipment (UE) configured to communicate via a non-terrestrial network (NTN), the UE comprising: 　　means for receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and 　　means for determining whether to perform measurements for the NTN-TN mobility based on the information. 　　(Supplementary Note 11) 　　An access network node comprising: 　　means for transmitting, to a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), information indicating coverage of a terrestrial network (TN) for NTN-TN mobility, wherein 　　the information is used by the UE to determine whether to perform measurements for the NTN-TN mobility based on the information.

[0223] Some or all of elements (e.g., structures and functions) specified in Supplementary Notes 2 to 8 dependent on Supplementary Note 1 may also be dependent on Supplementary Note 9, Supplementary Note 10 and Supplementary Note 11 in dependency similar to that of Supplementary Notes 2 to 8 on Supplementary Note 1. Some or all of elements specified in any of Supplementary Notes may be applied to various types of hardware, software, and recording means for recording software, systems, and methods.

[0224] This application is based upon and claims the benefit of priority from United Kingdom Patent Application No. 2316824.8, filed on November 2, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0225] 1　　COMMUNICATION SYSTEM 3, 3-1, 3-2, 3-3　　USER EQUIPMENT 5, 5-1, 5-2　　(R)AN NODE 5A, 5A-1, 5A-2　　BASE STATION 5B-1　　GATEWAY 5C-1　　SPACE (OR AIR) BORNE PLATFORM 7　　CORE NETWORK 9, 9-1, 9-2　　CELL 10　　CONTROL PLANE FUNCTION 10-1　　ACCESS AND MOBILITY MANAGEMENT FUNCTION 10-2　　SESSION MANAGEMENT FUNCTION 10-n　　OTHER FUNCTION 11　　USER PLANE FUNCTION 20　　EXTERNAL DATA NETWORK 31　　TRANSCEIVER CIRCUIT 33　　ANTENNA 35　　USER INTERFACE 37　　CONTROLLER 39　　MEMORY 41　　OPERATING SYSTEM 43　　COMMUNICATIONS CONTROL MODULE 51　　TRANSCEIVER CIRCUIT 53　　ANTENNA 55　　CORE NETWORK INTERFACE 57　　CONTROLLER 59　　MEMORY 61　　OPERATING SYSTEM 63　　COMMUNICATIONS CONTROL MODULE

Claims

1. A method performed by a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), the method comprising: 　　receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and 　　determining whether to perform measurements for the NTN-TN mobility based on the information.

2. The method according to claim 1, wherein 　　the information is received via a system information block or a dedicated signaling.

3. The method according to claim 1 or 2, wherein 　　the information includes at least one of: 　　　　information related to coverage areas of the TN, or 　　　　information related to a location for the coverage areas of the TN.

4. The method according to any one of claims 1 to 3, further comprising: 　　skipping the measurements for the NTN-TN mobility based on the determining.

5. The method according to any one of claims 1 to 4, further comprising: 　　transmitting, to the access network node, a request for the information, and wherein 　　the receiving the information is performed upon the transmitting the request.

6. The method according to any one of claims 1 to 4, wherein 　　the receiving the information is performed in a case where the access network node determines that the UE is required to perform the NTN-TN mobility.

7. The method according to any one of claims 1 to 6, further comprising: 　　initiating a conditional handover procedure as the NTN-TN mobility.

8. The method according to claim 7, further comprising: 　　receiving, from the access network node, information indicating a condition for initiating the conditional handover procedure, wherein 　　the condition is related to at least one of: 　　　　coverage areas of the TN, or 　　　　a location for the coverage areas of the TN.

9. A method performed by an access network node, the method comprising: 　　transmitting, to a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), information indicating coverage of a terrestrial network (TN) for NTN-TN mobility, wherein 　　the information is used by the UE to determine whether to perform measurements for the NTN-TN mobility based on the information.

10. A user equipment (UE) configured to communicate via a non-terrestrial network (NTN), the UE comprising: 　　means for receiving, from an access network node, information indicating coverage of a terrestrial network (TN) for NTN-TN mobility; and 　　means for determining whether to perform measurements for the NTN-TN mobility based on the information.

11. An access network node comprising: 　　means for transmitting, to a user equipment (UE) configured to communicate via a non-terrestrial network (NTN), information indicating coverage of a terrestrial network (TN) for NTN-TN mobility, wherein 　　the information is used by the UE to determine whether to perform measurements for the NTN-TN mobility based on the information.

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