User equipment mobility between non-terrestrial and terrestrial networks

Abstract

Methods and apparatus in a wireless network spanning a terrestrial network, TN, region (502) and a non-terrestrial network, NTN, cell (124) provide a handover mechanism for a User Equipment, UE, (102) staying on the NTN cell (124) from the NTN cell (124) to a TN cell (127) of the TN region (502). While staying on the NTN cell (124), the UE (102) determines whether it is within or close to the TN area (502), and only at that time, the UE (102) measures parameters of a TN cell (127) associated with the TN area (502).

Description

[0001] This document generally relates to wireless communication and, more particularly, to a user equipment (UE) that supports connection to a non-terrestrial network (NTN) to perform inter-frequency measurements on terrestrial network (TN) frequencies. BACKGROUND OF THE INVENTION

[0002] This background description is provided for the purpose of generally presenting the context of embodiments described in the detailed description. The work of the currently named inventors (to the extent it is described in this background section) and aspects of the specification that may not otherwise qualify as prior art at the time of filing are neither expressly nor impliedly admitted as prior art against this document.

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

[0004] 5G technology mainly relies on traditional TNs (i.e., wireless networks described in technical specifications). However, the 3rd Generation Partnership Project (3GPP) organization has proposed extending 5G communication to NTN by leveraging 5G New Radio (NR) technology or by using Long-Term Evolution (LTE) technology customized for narrowband Internet of Things (NB-IoT) or enhanced machine type communication (eMTC) scenarios. In NTN, RF transceivers are installed on satellites, unmanned aerial vehicle systems (UAS) (also known as drones, balloons, airplanes), or other suitable devices. For simplicity, all such devices are referred to as satellites in the following discussion. In addition to satellites, NTN may include a satellite gateway (referred to as a "sat gateway" or "NTN gateway") that connects the NTN to a public data network, a feeder link between the sat gateway and the satellite, a service link between satellites, and an inter-satellite link (ISL) when the satellites form a constellation.

[0005] Based on altitude, orbit, and beam footprint size, satellites can belong to one of several types. These types include low Earth orbit (LEO) satellites, medium Earth orbit (MEO) satellites, geostationary orbit (GEO) satellites, UAS platforms (including high-altitude platform stations (HAPS)), and highly elliptical orbit (HEO) satellites. GEO satellites are also known as geosynchronous orbit (GSO) satellites, and LEO / MEO satellites are also known as non-GSO (NGSO) satellites.

[0006] GSO satellites can communicate with one or several satellite gateways deployed above the satellite target coverage area (e.g., a region or even a continent). Non-GSO satellites can communicate with one or several serving satellite gateways at different times. NTN is designed to ensure service and feeder link continuity between serving satellite gateways, while having sufficient duration for mobile anchoring and handover.

[0007] Satellites can transmit transparent or regenerative (with on-board processing) payloads, and typically generate several beams for a given service area defined by the field of view. The coverage area of the beam usually has an elliptical shape and depends on the on-board antenna configuration and elevation angle. For the transparent payload implementation, the satellite can apply RF filtering, frequency conversion, and amplification, and does not change the waveform signal. For the regenerative payload implementation, the satellite can apply RF filtering, frequency conversion, and amplification, demodulation and decoding, routing, and encoding / modulation. The satellite transmitting the payload in a regenerative manner is actually equivalent to implementing most of the functions of a base station (e.g., gNB).

[0008] In this and other cases, whenever possible, the UE connected via the NTN cell is preferably handed over to the TN cell to receive better and more economical services. The network configures the UE via the NTN cell to periodically measure the TN frequency, so that the UE can find and report at least one TN cell when the TN cell is available. However, since the NTN cell coverage area is usually much larger than the TN cell coverage area, and the NTN cell coverage area can overlap with several TN cell coverage areas, there may be many UEs measuring the TN frequency in the search for TN cells when there is actually no TN cell close to the UE, which results in power waste for these UEs. Summary of the Invention

[0009] The techniques described in one or more embodiments provide a method for a UE to selectively perform inter-frequency measurements when it is within an NTN cell. A UE wirelessly connected to the network via an NTN cell is configured to measure a signal having at least one TN frequency associated with at least one TN cell only when the UE is close to or within a TN region including the TN cell. The BS sends a list of TN regions and associated frequencies to the UE for measurement. When the UE determines its position relative to the TN region (i.e., within or close to the TN region) while in a connected state with the NTN cell, the UE performs inter-frequency measurements. Since the UE does not share its position with the network at this stage, the UE makes the determination stated above (instead of the network). When the UE determines that it is within a specific TN region, the UE performs measurements on at least one frequency associated with this specific TN region. Based on the UE measurement report, the network decides whether to hand over the UE to the TN cell detected by the UE.

[0010] In a variant of this method, the UE can receive a list of TN regions and associated frequencies while in the idle state and determine whether it is within or near a given TN region in the list only after transitioning to the connected state.

[0011] In another method, the UE receives a list of TN regions from the BS but does not receive their corresponding frequencies. Then, the UE determines whether it is within or near a TN region based on its own location. When the UE determines that it is within or near a TN region, the UE notifies the BS about the TN region, and the BS provides the UE with at least one frequency associated with the TN region. Then, the UE performs inter-frequency measurements on the indicated at least one frequency. In a variant of this method, the UE receives a list of TN regions while in the idle state and determines whether it is within or near a TN region only after transitioning to the connected state.

[0012] According to yet another method, the BS is configured to send a location indication of a TN region to a UE connected to an NTN cell. After the UE notifies the BS that the UE is within or near a given TN region, the BS sends the corresponding frequency of the TN region to the UE such that the UE can perform handover-related measurements on the TN frequency of the TN region.

[0013] In a variant of this method, the BS sends the corresponding frequency of the TN region and the location indication of the TN region. In yet another variant of this method, the BS sends location information in a radio resource control message and the frequency of the TN region in a system information message or a radio resource control message. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings incorporated in and constituting a part of this specification illustrate one or more embodiments and, together with the description, explain these embodiments.

[0015] Figure 1 is a block diagram of a wireless communication system including a UE, a base station (BS) of a non-terrestrial network (NTN), and a BS of a terrestrial network (TN);

[0016] Figure 2 is a block diagram of a base station having a centralized unit (CU) and a distributed unit (DU);

[0017] Figure 3 is a block diagram of an NTN node having a transparent payload implementation;

[0018] Figure 4 is a block diagram of an NTN node having a transparent payload implementation, where the base station is connected to multiple satellites via the same satellite gateway;

[0019] Figure 5 Illustrates a scenario where a connected UE is configured to suppress measuring TN frequencies / cells when the UE is in an NTN cell but far from a TN area including one or more TN cells.

[0020] Figure 6 Illustrates a scenario where a connected UE is configured to measure TN frequencies / cells when the UE is in an NTN cell and close to or within the TN area.

[0021] Figure 7 Is a messaging diagram showing how a UE in connected mode via an NTN cell makes measurements on a TN carrier frequency, where the UE may or may not be close to any TN cell operating on that TN carrier frequency.

[0022] Figure 8 Is a messaging diagram showing how a UE in connected mode via an NTN cell transmits a proximity indication to the network and makes measurements on a TN carrier frequency.

[0023] Figure 9 Is a messaging diagram showing how an idle UE receives area information in a system information broadcast, then enters connected mode via an NTN cell, and transmits a proximity indication to the network based on the area information.

[0024] Figure 10 Is a messaging diagram showing how an idle UE receives area information in a system information broadcast, then enters connected mode via an NTN cell, and makes measurements on a TN carrier frequency based on the area information.

[0025] Figure 11 Is a flowchart of a method performed by a UE in connected mode via an NTN cell for determining whether to make measurements on a TN carrier frequency.

[0026] Figure 12 Is a flowchart of a method performed by a UE in connected mode via an NTN cell for transmitting a proximity indication to the network and making measurements on a TN carrier frequency.

[0027] Figure 13 Is a flowchart of a method performed by an idle UE communicating with an NTN cell for transmitting a proximity indication to the network based on area information broadcast in system information.

[0028] Figure 14 Is a flowchart of a method performed by an idle UE communicating with an NTN cell for making measurements on a TN carrier frequency based on area information broadcast in system information.

[0029] Figure 15 It is a flowchart of a method executed by an NTN BS for configuring a UE with a measurement object including a TN carrier frequency to be measured and a region associated with the carrier frequency.

[0030] Figure 16 It is a flowchart of a method executed by an NTN BS for providing a proximity indication configuration to a UE and configuring the UE to measure a TN carrier frequency when a proximity indication is received from the UE.

[0031] Figure 17 It is a flowchart of a method executed by an NTN BS for broadcasting TN area information and receiving a proximity indication from a UE.

[0032] Figure 18 It is a flowchart of a method executed by an NTN BS for broadcasting a TN carrier frequency and TN area information and configuring a UE to measure the TN carrier frequency broadcast in system information. Detailed implementation

[0033] As discussed in more detail below, a UE and a communication network including NTN cells and TN cells can use the techniques of this document to manage the handover process of the UE from an NTN cell to a TN cell, while saving power at the UE and without having to disclose the location of the UE to the network.

[0034] Reference Figure 1 , the wireless communication system 100 includes a UE 102, a base station (BS) 104 that communicates with the UE 102 via a satellite (so the BS 104 is represented as a satellite icon in this figure, but the setup is shown in more detail in Figure 3 ), a BS 106, and a core network (CN) 110. The BSs 104 and 106 can operate in a RAN 105 connected to the CN 110. The CN 110 can be implemented as an evolved packet core (EPC) 111 or a fifth-generation (5G) core (5GC) 160 (both are shown in Figure 1 , but it is not required that both exist). The CN 110 can also include a sixth-generation (6G) core (not shown).

[0035] BS 104 can communicate with UE 102 via cell 124, and BS 106 can communicate with UE 102 via cells 127, 128, and / or 129. If BS 104 is a gNB, then cell 124 is an NR cell. If BS 104 is an ng-eNB or an eNB, then cell 124 is an evolved universal terrestrial radio access (E-UTRA) cell. Similarly, if BS 106 is a gNB, then cells 127 to 129 are NR cells, and if BS 106 is an ng-eNB or an eNB, then cells 127 to 129 are E-UTRA cells. Cells 124, 127, 128, and 129 can be in the same radio access network notification area (RNA) or different RNAs. Generally, RAN 105 can include any number of BSs, where each of the BSs is capable of communicating with the UE via one or more cells. UE 102 supports at least 5G NR (or simply referred to as "NR") or an E-UTRA air interface to communicate with BSs 104 and 106. Each of BSs 104, 106 can be connected to CN 110 via an interface (e.g., S1 or NG interface). BSs 104 and 106 can also be interconnected via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes.

[0036] Among other components, EPC 111 can include a serving gateway (SGW) 112, a mobility management entity (MME) 114, and a packet data network gateway (PGW) 116. SGW 112 is configured to transport user plane packets related to audio calls, video calls, Internet traffic, etc., and MME 114 is configured to manage authentication, registration, paging, and other related functions. PGW 116 provides the UE with connectivity to one or more external packet data networks such as the Internet and / or an Internet protocol (IP) multimedia subsystem (IMS) network.

[0037] 5GC 160 includes a user plane function (UPF) 162, an access and mobility management function (AMF) 164, and / or a session management function (SMF) 166. UPF 162 is configured to transport user plane packets related to audio calls, video calls, Internet traffic, etc., AMF 164 is configured to manage authentication, registration, paging, and other related functions, and SMF 166 is configured to manage packet data unit (PDU) sessions.

[0038] As Figure 1 shown, TN cells 127 and 128 and TN cells 128 and 129 partially overlap, such that UE 102 can select, reselect, or handover from one cell to another cell. Figure 1It is further shown that the TN cell overlaps with the NTN cell 124, such that selection, reselection, or handover from NTN to TN is also possible. To directly exchange messages or information, BS104 and BS 106 may support the X2 or Xn interface. In general, CN 110 may be connected to any suitable number of BSs that support new radio (NR) cells and / or E-UTRA cells. E-UTRA is typically associated with the 3GPP long term evolution (LTE) radio access technology (RAT), and NR is typically associated with the 5G RAT.

[0039] UE 102 and / or BS 104 and 106 may utilize the techniques described in this section when UE 102 operates in an inactive or idle state of the protocol (i.e., radio resource protocol, RRC) for controlling radio resources between UE 102 and the core network 110 (i.e., the RRC_INACTIVE or RRC_IDLE state of the RRC protocol), but may also utilize the techniques when UE 102 operates in a connected state, as discussed later.

[0040] BS 104 is equipped with processing hardware 130, which includes a processor 132 (but may include more than one general-purpose processor, such as a CPU), a transceiver 134, and a non-transitory computer-readable medium (CRM) 136 such as a memory. Additionally or alternatively, the processing hardware 130 may include a dedicated processing unit. The processor 132 is configured to process data transmitted by BS 104 to UE 102 in the downlink direction, and / or process data received by BS 104 from UE 102 in the uplink direction. The transceiver 134 may include a transmitter configured to transmit data in the downlink direction, and a receiver configured to receive data in the uplink direction. The CRM 136 stores executable instructions that the processor 132 executes to perform the various techniques described in this section. BS 106 includes components similar to those of BS 104. In other words, the components 140, 142, 144, and 146 of BS 106 are respectively similar to the components 130, 132, 134, and 136 of BS 104.

[0041] UE 102 is equipped with processing hardware 150, which includes at least one processor 152 (but it may include more than one general-purpose processor, such as a CPU, and / or a dedicated processing unit), a transceiver 154, and a non-transitory computer-readable medium (CRM) 156 such as a memory. The processor 152 is configured to process data transmitted by the UE 102 in the uplink direction and / or process data received by the UE 102 in the downlink direction. The transceiver 154 may include a transmitter configured to transmit data in the uplink direction and a receiver configured to receive data in the downlink direction. The CRM 156 stores executable instructions that the processor 152 executes to perform the various techniques described in this section.

[0042] Figure 2 is a block diagram of a distributed BS 170, which may operate as the BS 104 or 106 in the system shown in Figure 1 The BS 170 includes a central unit (CU) 172 and at least one distributed unit (DU) 174. Each CU and DU includes processing hardware, such as one or more general-purpose processors (e.g., CPUs) and / or dedicated processing units, a transceiver, and a CRM that stores machine-readable instructions executable by the processor. The DU or CU may operate as the BS 104 or 106 in the system shown in Figure 1 The CU may operate as a packet data convergence protocol (PDCP) controller, an RRC controller, and / or an RRC inactivity controller. The CU may also operate as an RLC controller configured to manage or control one or more radio link control (RLC) operations or procedures. The DU may operate as a MAC controller configured to manage or control one or more media access control (MAC) operations or procedures (e.g., random access procedures), an RLC controller configured to manage or control one or more RLC operations or procedures, and / or a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0043] In some embodiments, the RAN 105 supports integrated access and backhaul (IAB) functionality. In some implementations, the DU 174 operates as an IAB node, and the CU 172 operates as an IAB donor. In some embodiments, the RAN 105 supports NTN functionality.

[0044] The CU 172 may include a logical node CU-CP 172A that hosts the control plane part of the PDCP protocol of the CU 172. The CU 172 may also include a logical node CU-UP 172B that hosts the user plane part of the PDCP protocol and / or the Service Data Adaptation Protocol (SDAP) protocol of the CU 172. The CU-CP 172A may transmit control information (e.g., RRC messages, F1 application protocol messages), and the CU-UP 172B may transmit data packets (e.g., SDAP PDUs or Internet protocol packets). The CU-CP 172A may be connected to multiple CU-UPs (such as CU-UP 172B) via an E1 interface. The CU-CP 172A selects an appropriate CU-UP 172B for the requested service of the UE 102. In some implementations, a single CU-UP (such as CU-UP 172B) may be connected to multiple CU-CPs (such as CU-CP 172A) via an E1 interface. The CU-CP 172A may be connected to one or more DUs (such as DU 174) via an F1-C interface. The CU-UP 172B may be connected to one or more DUs (such as DU 174) via an F1-U interface under the control of the same CU-CP 172A. In some implementations, one DU (such as DU 174) may be connected to multiple CU-UPs 172B under the control of the same CU-CP 172A. In such implementations, the connectivity between the CU-UP and the DU is established by the CU-CP using a bearer context management function.

[0045] Figure 3 FIG. is a schematic illustration of an NTN network operating with a transparent payload architecture. The satellite (NTN) gateway 302 and the "transparent" satellite 304 extend the range of the Uu interface of the BS 104. The satellite 304 may use frequency conversion and radio frequency (RF) amplifiers in both the uplink and downlink directions. The satellite functions similarly to the function of an analog RF repeater. As a result, the satellite 304 relays the Uu radio interface signals transmitted via the feeder link (between the NTN gateway and the satellite) and then via the service link (between the satellite and the UE) in the downlink direction, and vice versa in the uplink direction. The satellite radio interface (SRI) of the feeder link is Uu, and the NTN gateway 302 supports all the necessary functions for forwarding the signals of the Uu interface. The NTN gateway 302 may be collocated with the BS (e.g., eNB, gNB) 104, or may be connected to the BS 104 via a wired link. It is also possible to have more than one NTN gateway connected to the BS. Different transparent satellites such as 304 may be connected to the same terrestrial BS via the same NTN gateway or via different NTN gateways. Figure 4Shows a situation where two different satellites (304 and 306) are connected to the same BS 104 via the same NTN gateway 302. These two satellites (304 and 306) beam towards the Earth's surface for two NTN cells with two different physical cell IDs (PCIs).

[0046] Figure 5 Is an example scenario showing how the network (i.e., BS 104 or a network entity of BS 104, or any other part of the network discussed above) configures the UE 102 to measure the TN frequency / cell when the UE is in the connected state and connected to the NTN cell 124. Note that the UE is in the "connected state" when it is actively communicating with the BS serving the NTN cell 124. When not actively communicating with the BS, the UE is in the "idle state". The idle state is typically associated with periods when the UE is not using data services, making calls, or sending / receiving messages. In this scenario, the UE 102 is within the coverage area of the NTN cell 124 and is connected to this NTN cell. Additionally, the NTN cell 124 includes three TN cells (TN cell 127, TN cell 128, and TN cell 129) that are close to each other and have a much smaller coverage area size than the NTN cell. In one application, these TN cells are operating in the same frequency band, which can be different from the frequency band of the NTN cell 124. In this scenario, if the UE is within the coverage area of the TN cell, the network will preferably connect the UE to the TN cell because the TN cell generally provides better throughput than the NTN cell. Therefore, if at least one TN cell is available, the network can configure the UE 102 to measure at the frequencies operated by these TN cells for performing handover.

[0047] To configure the UE 102 to measure on a frequency operated by at least one TN cell, a network entity (e.g., BS 104) may configure a measurement object (e.g., measObjectNR defined in the 3GPP technical specification) indicating the TN frequency to be measured (e.g., ssbFrequency defined in the 3GPP technical specification), and send the measurement object to the UE 102 via an RRCReconfiguration message (as defined in the 3GPP technical specification). Note that in the remainder of this document, terms defined in the 3GPP technical specification are written in italics or uppercase letters without further description of their origin, and they are illustrative rather than restrictive. In one embodiment, the network also includes the physical cell identifiers of TN cells 127, 128, and 129 in the allowed cell list in the measurement object. The network may also provide the UE 102 with a measurement gap configuration that aligns the NTN inactive period with the transmission timing of the synchronization signal and PBCH block (SSB) of the TN frequency, so that the UE 102 can periodically switch from the serving frequency (of the NTN cell) to the TN frequency (of the TN cell) for inter-frequency measurement.

[0048] Conventionally, after the UE 102 is configured with a measurement object indicating the TN frequency to be measured, when the serving cell measurement is below a certain threshold, the UE 102 must continuously measure on the indicated TN frequency regardless of where the UE 102 is currently located, i.e., far from any TN cell (as Figure 5 shown) or close to such a cell. As a result, when measuring on the TN frequency, the UE 102 may not be able to detect any TN cell most of the time. Eventually, if the UE is not close to any TN cell, the UE ultimately wastes power without effective results (i.e., no suitable TN cell is found to connect).

[0049] According to an embodiment, a "TN area" 502 is defined (see Figure 5 ) to avoid this problem. The TN area is associated with a combined area of one or more TN cells that can share the same TN frequency. Using this concept, the UE is configured to perform measurements on the TN frequency only when it is close to or within the TN area, thus saving energy when it is not within or close to the TN area. The TN area in this embodiment can be characterized by a central physical location and a distance parameter (e.g., radius). Additional parameters that can be used for the TN area will be discussed later. As Figure 6As shown, if the UE 102 is close to or within the TN area 502, the UE 102 is likely to be able to detect at least one TN cell within the TN area via measurement, and thus be able to trigger an NTN to TN handover after sending a corresponding measurement report to the network. Therefore, it would be advantageous if the technology configures the UE 102 to perform measurements on the TN frequency only when the UE 102 is near the TN area or within the TN area including TN cells. Alternatively, it would also be advantageous if the technology configures the UE 102 to determine whether the UE 102 is near the TN area or within the TN area including TN cells and measure the TN frequency only then. As long as the UE starts to perform measurements and can detect any TN cell in the TN area, cell measurements can be triggered, and reporting this measurement to the BS can lead to subsequent handover procedures.

[0050] The TN area can be defined as an area surrounded by a perimeter such as a circle, an ellipse, or a polygon (having n sides, where n is an integer equal to or greater than 3). Those skilled in the art will understand that one or more functions, i.e., parameterization, can also be used to define the perimeter of the TN area. Depending on the shape of the perimeter of the TN area, two or more parameters may be required to locate the TN area (i.e., its boundary) in space. For example, if the perimeter of the TN area is a circle, the center position of the circle (e.g., x, y, and z coordinates) and the radius (distance parameter) may be required to fully define and locate the TN area. If the perimeter of the TN area is a rectangle or an ellipse, the center position and two distances (two distance parameters, e.g., the distances from the center position to the short side and the long side of the rectangle or the semi - minor axis and the semi - major axis of the ellipse) may be required to fully define and locate the TN area. In other words, the number of parameters required to fully define the TN area depends on the shape of the perimeter of the TN area.

[0051] The TN area can include any number of TN cells. Although the TN area can also include only one TN cell, for this particular case, the TN area does not realize its full potential. If there are two or more TN cells in the TN area, the network reduces the overhead signaling between the BS and the UE because the BS can provide a single TN frequency for the entire TN area, and thus, the UE performs measurements on a single TN frequency to detect / evaluate any one of the TN cells in the TN area, rather than performing multiple measurements on multiple frequencies. In one embodiment, the physical area of the TN area is larger than the combined physical area of the TN cells located within the TN area.

[0052] When the UE is within the TN region or when the UE is "close" to the TN region, the embodiments discussed herein apply equally. In this regard, the coverage area of a TN cell (in 3G, 4G, LTE, or 5G) is defined by the geographical area that can be served by a particular cell or base station for reliable and high-quality wireless communication. However, if the UE is not within the coverage area of any TN cell in the TN region, the UE may still communicate with a TN cell in the TN region, but with a medium or low-quality wireless connection. This means that there is an envelope 604 of the TN region 502 that can support communication (even if not of high quality) between the UE 102 and one of the TN cells in the TN region 502, as Figure 6 schematically shown in. The envelope 604 can completely surround the TN region 502. Thus, in the following embodiments, when the UE is within the envelope 604, the UE 102 is "close" to the TN region 502. In one application, the shape of the envelope 604 mimics the shape of the corresponding TN region 502. The area of the envelope is always larger than the area of the corresponding TN region. In one application, the area of the envelope is at least 5% larger than the area of the corresponding TN region. The percentage can be larger or smaller, depending on the TN cells of the TN region. Although only one TN region is shown for simplicity, the NTN cell coverage area can encompass multiple non-overlapping or overlapping TN regions.

[0053] Next, reference is made to Figures 7 to 10 discuss several scenarios in which the UE and / or RAN and / or BS implement one or more of the above techniques to avoid wasting power for TN measurements. The term "network" is used in this document to refer to the RAN or BS or any part of the RAN or BS. When the UE is in the connected state, these techniques advantageously support NTN-to-TN mobility, resulting in enhanced UE power savings. When the UE is in the idle state and transitions to the connected state to determine when the UE is close to or within the TN region, these techniques also support NTN-to-TN mobility. Figures 7 to 10 Similar events in are labeled with similar reference numerals, with differences discussed below where appropriate. For example, event 710 is similar to event 810 and event 1010, and event 730 is similar to event 830, event 930, and event 1030. To simplify the following description, the term "inactive state" is used and the term "inactive state" can represent the RRC_INACTIVE or RRC_IDLE state, and the term "connected state" is used and the term "connected state" can represent the RRC_CONNECTED state.

[0054] Figure 7Message passing diagram 700 showing a scenario in which a connected UE (i.e., in a connected state) selectively measures on the TN carrier frequency of a TN cell in a TN region, where the UE may or may not be close to any TN cell operating at that carrier frequency. In Figure 7 UE 102 is initially connected via satellite 304 to BS 104 associated with NTN cell 124, where NTN cell 124 covers another TN cell 127 that is part of TN region 502. While remaining in the connected state with NTN cell 124, UE 102 receives at 710 an RRCReconfiguration message (commonly referred to as a "TN information message") that includes a measurement object configuration for the TN carrier frequency used by TN region 502 (and implicitly used by at least one TN cell; in this embodiment, by TN cell 127) and the TN region associated with that carrier frequency. Note that in step 710, the UE may receive one or more TN regions and associated frequencies. If the TN region is circular, information about each TN region may be provided in the format {reference position, radius}, where the reference position represents the center position of the TN region and the radius represents the radius of the TN region. If the TN region is not circular, as discussed above, other geometric features (e.g., angles, sides) may be provided to describe the position of the TN region and its extent in space. In one embodiment, information about the TN region may also include information about its envelope 604. For example, the envelope may be defined by a given range. If the TN region is circular, the UE is close to the TN region when the distance between the reference point of the TN region and the position of the UE is within that given range, which has a lower limit equal to the radius of the TN region and an upper limit equal to that radius plus a given distance.

[0055] In response to the RRCReconfiguration message, UE 102 applies the configuration and then transmits a 712 RRCReconfigurationComplete message to the NTN cell 124. Next, UE 102 determines 720 that it is not within or near any TN region associated with the TN carrier frequency received in step 710. If this is the case, the UE decides 722 not to perform measurements on the TN carrier frequency, thus saving power. In one implementation, UE 102 determines whether it is within the TN region by reading its GNSS coordinates from the GNSS module and checking whether the GNSS coordinates fall within the boundaries of the TN region. In this implementation or another implementation, UE 102 determines whether it is near the TN region (i.e., outside the TN region but close enough to communicate with a TN cell within the TN region) by reading its GNSS coordinates from the GNSS module and checking whether the GNSS coordinates fall within the envelope of the TN region (the envelope can have a radius greater than the radius of the TN region). To facilitate the UE's determination of whether it is near the TN region, the position and / or size of the envelope can be provided to the UE by the network via system information or via a dedicated RRC message, and then the UE uses the position and / or size of the envelope to check whether the distance between the reference position of the TN region and the GNSS coordinates of the UE has exceeded the size of the envelope (if the UE is outside the envelope, the UE is not near the TN region; otherwise the UE is near the TN region).

[0056] Later, UE 102 determines 730 that it has moved into one of the TN regions associated with the received TN carrier frequency. In response to this determination, UE 102 performs 740 inter-frequency measurements on the associated TN carrier frequency and then detects, for example, TN cell 127 in TN region 502 when performing the measurements. Note that the UE can detect any TN cell within the TN region. UE 102 reports this measurement to the network, which in turn can trigger a handover process that causes the network to hand over 750 UE 102 from NTN cell 124 to the found TN cell 127.

[0057] In one embodiment, UE receives 710 an RRCReconfiguration message that includes multiple measobjectNR information elements (IEs), where at least two IEs indicate or describe the same TN region. Since each measobjectNR supports one TN frequency, in this embodiment, the UE can receive multiple TN regions, where at least one TN region has a different TN frequency. For this case, the UE performs steps 720, 722, and 730 for each TN frequency of at least one TN region. This process can also be implemented in the embodiments discussed next.

[0058] Figure 8 Message diagram 800 shows another scenario where the connected UE transmits a proximity indication to the network when connected to an NTN cell and makes measurements on the TN carrier frequency. Figure 8 The message diagram in Figure 7 is similar to the message diagram in Figure 8 with the differences discussed below. In Figure 8 , after the UE 102 is connected to the BS 104 which is connected to the NTN cell 124 via the satellite 304, the UE 102 receives an 811 RRCReconfiguration message via the NTN cell 124, which includes a proximity indication configuration (i.e., ProximityIndConfig), and the proximity indication configuration includes a list of TN regions that overlap with the NTN cell 124. The proximity indication configuration may include location information about each TN region, for example, a reference position and a radius in the case where the TN region is circular. Note that in this embodiment, the message in step 811 does not include the frequency associated with the TN region. Therefore, at this stage, even if the UE is within or near the TN region, the UE cannot make any measurements on the TN cell associated with the TN region. In response to the RRCReconfiguration message, the UE 102 applies the proximity indication configuration, stores the list of TN regions, and transmits an 813 RRCReconfigurationComplete message to the NTN cell 124.

[0059] Later, the UE 102 determines 830 that it is near or has moved into one of the TN regions stored by the UE in the proximity indication configuration, and that TN region is the region where the TN cell 127 is located. As discussed above with respect to Figure 7 , the UE 102 determines whether it is within or near the TN region 502. In response to the location determination in step 830, the UE 102 transmits an 814 proximity indication message to the BS 104 to indicate that it is within or near the TN region 502, where the proximity indication message may be a specific UL MAC CE, and each bit sequentially represents each TN region stored by the UE (i.e., the first bit in the MAC CE represents the first TN region signaled in the RRCReconfiguration message, the second bit in the MAC CE represents the second TN region signaled in the RRCReconfiguration message, ……, and so on). Each bit in the proximity indication MAC CE may be '0' or '1', where '0' indicates that the UE is not within or near the represented TN region, and '1' indicates that the UE is within or near the represented TN region.

[0060] After receiving the proximity indication message from UE 102, BS 104 determines that UE 102 is close to TN area 502 and thus transmits an 810 RRCReconfiguration message to UE 102, which includes a measurement object configuration indicating the TN carrier frequency used by the TN cell in TN area 502. In response to the RRCReconfiguration message, UE 102 performs 740 inter-frequency measurements on the indicated TN carrier frequency and then detects TN cell 127 when performing the measurements (where cell 127 is chosen as an example and in fact UE can measure any cell within the TN area). UE 102 may send a measurement report to the network, which in turn may trigger a handover process that causes the network to handover 750 UE 102 from NTN cell 124 to TN cell 127 (or to other cells within TN area 502).

[0061] Although the embodiments discussed above with respect to Figure 7 and Figure 8 consider that UE 102 is in the connected state, the embodiments discussed next with respect to Figure 9 and Figure 10 consider that the UE is initially in the idle state and then UE 102 transitions to the connected state. More specifically, Figure 9 is a messaging diagram 900 showing a scenario where an idle UE becomes a connected UE and then transmits a proximity indication to the network based on the area information broadcast in the system information. Figure 9 The messaging diagram in Figure 8 is similar to the messaging diagram in Figure 9In it, the UE 102 initially stays 901 in the idle state and obtains 904 from the NTN cell 124 system information including a list of TN regions (i.e., tnArea), where each TN region can be provided in the format {reference location, radius}. As previously discussed, if the shape of the TN region is not circular, the radius can be replaced by one or more distance parameters describing the range of the area of the TN region. Note that in step 904, the UE does not obtain the TN frequency associated with the TN region. The UE 102 then internally stores the list of TN regions as the proximity indication configuration. Thereafter, the UE 102 performs the RRC connection setup procedure with the BS 104 and then transitions 702 to the connected state, where the RRC connection setup procedure involves the UE 102 sending 905 an RRCSetupRequest message to the BS 104, the BS 104 sending 906 an RRCSetup message to the UE 102, and the UE 102 sending 907 an RRCSetupComplete message to the BS 104. In one application, if the UE 102 is able to receive system information and communicate with the BS 104 simultaneously in the connected state, step 904 can be performed by the UE after the UE 102 has entered the connected state. In this case, after the UE 102 has established an RRC connection with the BS 104, the UE stores the list of TN regions.

[0062] After connecting to the BS 104, the UE 102 can move closer to the TN region 502 and thus determine 930 that it is close to or has moved into one of the TN regions stored by the UE in the proximity indication configuration. In response to this determination, the UE 102 transmits 814 a proximity indication message to the BS 104 to indicate that it is within or close to the TN region 502. Moving forward, the remainder of the process is the same as Figure 8 and for this reason, the same reference numerals are used for similar steps.

[0063] Figure 10 is a messaging diagram 1000 showing the scenario where an idle UE changes to a connected UE and then measures on the TN carrier frequency of the TN region information broadcast in the system information received by the UE while in the idle state. Figure 10 The messaging diagram in Figure 9 is similar to the messaging diagram in Figure 10In it, UE 102 initially stays 901 in the idle state and obtains 1004 system information, which includes a list of at least one TN area associated with the corresponding TN carrier frequency. For example, the list may include TN frequency 1 and associated TN area 1, TN frequency 2 and associated TN areas 2 and 3, and TN frequency 3 and associated TN area 1. Although this example list only includes three members, the list may have more or fewer members. Step 1004 is performed via NTN cell 124. Then, UE 102 internally stores the carrier frequencies and the list of TN areas associated with each of these carrier frequencies. Thereafter, UE 102 performs the RRC connection setup procedure (905, 906, and 907) with BS 104, and then transitions 702 to the connected state. In one application, if UE102 can receive system information and communicate with BS 104 in the connected state simultaneously, step 1004 can be performed by this UE after UE 102 has entered the connected state. In this case, after UE 102 has established an RRC connection with BS 104, this UE stores the list of TN frequencies (and associated TN areas).

[0064] When transitioning to the connected state, UE 102 receives 1010 an RRCReconfiguration message, which includes a measurement object configuration indicating the TN carrier frequency (i.e., ssbFrequency). This TN carrier frequency can be used by TN area 502, such as TN cell 127. Thereafter, when UE 102 determines 1020 that it is not within or near any TN area associated with that TN carrier frequency in the TN area, UE 102 further determines 1022 not to perform measurements on that TN carrier frequency.

[0065] UE 102 can then move closer to TN area 502, and thus determines 1030 that it is near or has moved into one of the TN areas associated with the TN carrier frequency. In response to this determination, UE 102 performs 740 inter-frequency measurements on the TN carrier frequency, and then detects TN cell 127 (or any other cell from the TN area) when performing the measurements. UE 102 can send a measurement report to the network, which in turn can trigger a handover process that causes the network to hand over 750 UE 102 from NTN cell 124 to TN cell 127.

[0066] Figure 11 is a flowchart of a method 1100 performed by a UE (e.g., UE 102 in the present disclosure) for determining whether to perform measurements on a TN carrier frequency when connected to an NTN cell. This method is related to Figure 7corresponds to the scenario shown in. Initially, the UE receives an RRC message from the BS at 1110 indicating the carrier frequency to be measured and the TN area associated with the carrier frequency. In one application, if multiple TN areas are provided, the UE may receive one carrier frequency for each TN area. In this or another embodiment, multiple TN frequencies may be provided for a given TN area. If multiple TN frequencies are provided for a given TN area, the UE is configured to perform step 720 or 1020 once for each TN frequency, even if these TN frequencies are associated with the same TN area. The UE determines at 1130 whether the UE is within or near any TN area associated with the carrier frequency in the TN area.

[0067] If the determination at 1130 is 'yes' (i.e., the UE is within or near any TN area associated with the carrier frequency in the TN area), the UE makes a measurement at 1140 on that carrier frequency. If multiple TN frequencies are provided for a given TN area, the UE is configured to perform step 720 or 1020 once for each TN frequency, even if these TN frequencies are associated with the same TN area.

[0068] Alternatively, if the determination at 1130 is 'no' (i.e., the UE is neither within any TN area in the TN area nor near any TN area in the TN area), the UE determines at 1122 not to make a measurement on the associated carrier frequency, and then the process returns to the decision step 1130. In this way, when no TN area is in range, the UE saves power by not performing measurements.

[0069] Figure 12 is a flowchart of method 1200 performed by a UE (e.g., UE 102 in the present disclosure) for transmitting a proximity indication to the network and making measurements on a TN carrier frequency when connected to an NTN cell. This method corresponds to Figure 8 the scenario shown in. The UE receives at 1211 an RRC message from the BS including a proximity indication configuration that includes a list of TN areas. Thereafter, the UE determines at 1230 whether the UE is within or near any TN area configured in the proximity indication configuration.

[0070] If it is determined that 1230 is 'Yes' (i.e., the UE is within any TN region in the TN area or close to any TN region in the TN area), the UE transmits to the BS 1214 a proximity indication MAC CE indicating in which (which) TN region or close to which (which) TN region the UE is. Thereafter, the UE receives from the BS 1210 an RRC message that includes a measurement configuration indicating the carrier frequencies to be measured. The UE performs 1240 measurements on the received carrier frequencies based on the measurement configuration provided in the RRC message. Alternatively, if it is determined that 1230 is 'No' (i.e., the UE is neither within any TN region in the TN area nor close to any TN region in the TN area), the process returns to the decision step 1230.

[0071] Figure 13 It is a flowchart of a method 1300 performed by a UE (e.g., UE 102 in the present disclosure) for transmitting a proximity indication to a network based on area information broadcast in system information. This method corresponds to Figure 9 the scenario shown in Figure 13 The flowchart in Figure 12 is similar to the flowchart in

[0072] with the differences discussed below. The UE receives from the BS 1304 system information that includes a list of TN regions. Thereafter, the UE transitions 1302 to the connected state. In one application, if the UE is able to receive system information and communicate with the BS simultaneously in the connected state, the order of steps 1304 and 1302 can be reversed. The UE determines 1330 whether the UE is within any TN region in the TN regions listed in the system information or close to any TN region in the TN area.

[0073] Figure 14It is a flowchart of method 1400 for performing measurements on a TN carrier frequency based on area information broadcast in system information, which is executed by a UE (e.g., UE 102 in this disclosure). The UE receives 1404 system information from the BS, which includes a list of carrier frequencies and TN areas (one or more TN areas) associated with each of the carrier frequencies. The UE then transitions 1302 to the connected state, and then receives 1410 an RRC message from the BS, which includes a measurement configuration indicating the carrier frequencies to be measured. In one application, if the UE is capable of receiving system information and communicating with the BS simultaneously in the connected state, the order of steps 1404 and 1302 can be reversed.

[0074] The UE determines 1430 whether it is within any of the TN areas listed in the system information and associated with the carrier frequency to be measured. If the determination 1430 is 'yes' (i.e., the UE is within or near any of the TN areas associated with the carrier frequency to be measured in the TN area), the UE performs 1140 measurements on that carrier frequency.

[0075] Alternatively, if the determination 1430 is 'no' (i.e., the UE is neither within nor near any of the TN areas associated with the carrier frequency to be measured in the TN area), the UE determines 1122 not to perform measurements on that carrier frequency, and then the process returns to the decision step 1430.

[0076] Regarding Figures 11 to 14 The above-described embodiments discussed describe the Figures 7 to 10 scenario shown from the perspective of the UE. The following figures describe the same scenario, but from the perspective of the NTN BS. Figure 15 It is a flowchart of method 1500 for configuring a UE with a measurement object including a TN carrier frequency to be measured and a TN area associated with the carrier frequency, which can be implemented by an NTN BS (e.g., BS 104 in this disclosure). This method corresponds to the Figure 7 scenario shown. The BS transmits 1510 an RRC message to the UE, which includes a measurement configuration indicating the carrier frequency to be measured and the TN area associated with the carrier frequency. Thereafter, the BS may receive 1542 a measurement report from the UE, which includes the measurement results of the carrier frequency to be measured. The measurement results may provide data on the UE neighboring TN cell 127 that can support handover. The network then optionally performs 1560 a handover process of the UE 102 to the TN cell 127 based on the measurement report received from the UE 102.

[0077] Figure 16It is a flowchart of method 1600 that can be implemented by an NTN BS (e.g., BS 104 in this disclosure) to initially provide proximity indication configuration to a UE and later configure the UE to measure the TN carrier frequency when a proximity indication is received from the UE. This method corresponds to Figure 8 the scenario shown in. The BS transmits an RRC message 1611 to the UE, and the RRC message includes a proximity indication configuration that includes a list of TN regions but no carrier frequencies for any of the TN regions in the TN region. Thereafter, the UE determines whether it is close to or within a TN region, and the BS may receive a proximity indication MAC CE 1614 from the UE indicating that TN region. Note that at this stage, the BS does not provide the UE with any TN frequencies associated with the TN region.

[0078] After receiving the proximity indication from the UE, the BS transmits an RRC message 1610 to the UE, and the RRC message includes a measurement configuration indicating the carrier frequency to be measured, where the carrier frequency to be measured is the TN carrier frequency used by one or more TN cells 127 located in the TN region indicated by the UE.

[0079] After transmitting the RRC message including the measurement configuration to the UE, the BS may receive a measurement report 1542 from the UE that includes the measurement results of the TN cell 127. The network then optionally performs a handover procedure 1560 of the UE 102 to the TN cell 127 based on the measurement report received from the UE 102.

[0080] Figure 17 It is a flowchart of method 1700 that can be implemented by an NTN BS (e.g., BS 104 in this disclosure) to broadcast TN region information and receive proximity indications from the UE. This method corresponds to Figure 9 the scenario shown in. When the UE is in the idle state in the NTN cell 124, the BS transmits system information 1704 including a list of TN regions 502 to the UE. After the UE transitions to the connected state, the BS may receive a proximity indication MAC CE 1614 from the connected UE indicating which (which) TN region the UE is close to or within. After receiving the proximity indication from the UE, the BS transmits an RRC message 1610 to the UE, and the RRC message includes a measurement configuration indicating the carrier frequency to be measured, where the carrier frequency to be measured is the TN carrier frequency used by one or more TN cells 127 located in the TN region 502 (in which or close to which the UE is located).

[0081] After transmitting an RRC message including a measurement configuration to the UE, the BS may receive a 1542 measurement report from the UE, the measurement report including measurement results regarding one or more TN cells 127 in the TN area 502. The network then optionally performs a handover procedure of the UE 102 to the TN cell 127 based on the measurement report received from the UE 102.

[0082] Figure 18 is a flowchart of a method 1800 that can be implemented by an NTN BS (e.g., BS 104 in the present disclosure) for broadcasting TN carrier frequency and TN area information and for configuring the UE to measure the TN carrier frequencies broadcast in the system information. This method corresponds to Figure 10 the scenario shown in. When the UE is in the idle state in the NTN cell 124, the BS transmits 1804 system information including a list of carrier frequencies and the TN area (one or more TN areas) associated with each of the carrier frequencies to the UE. After the UE transitions to the connected state with the NTN cell 124, the BS transmits 1810 an RRC message to the UE, the RRC message including a measurement configuration indicating the TN carrier frequencies to be measured. In one application, it may be possible that if multiple TN areas are sent in step 1804 and each TN area has its own carrier frequency different from other TN areas, step 1810 is repeated multiple times for each frequency of the TN areas.

[0083] Thereafter, the BS may receive a 1542 measurement report from the UE, the measurement report including measurement results for the TN carrier frequencies to be measured for a given TN area. The network then optionally performs a handover procedure of the UE102 to the TN cell 127 based on the measurement report received from the UE 102.

[0084] The concepts proposed in the present disclosure have wide applicability in a wide variety of ranges of telecommunication systems, network architectures, and communication standards. For example, consider 3GPP, i.e., the standards organization responsible for defining many wireless communication standards, especially those related to the evolved packet system (EPS) commonly referred to as the long term evolution (LTE) network. The evolved versions of LTE, such as the fifth generation (5G) network, can support a large number of services and applications, including but not limited to web browsing, video streaming, internet protocol voice (VoIP), mission-critical applications, multi-hop networks, real-time remote operations (e.g., remote surgery), etc.

[0085] Accordingly, the teachings presented herein can be implemented across a variety of network technologies, including but not limited to 6G, 5G, fourth generation (4G), third generation (3G), and diverse network architectures. Moreover, the techniques described herein can be applied to different types of links, whether it is a downlink, uplink, peer-to-peer link, or any other connection type.

[0086] The choice of a particular telecommunications standard, network architecture, or communication standard depends on the particular application and the overall system design constraints imposed. Although, for clarity, these disclosures may show certain aspects in the context of 6G, 5G, or LTE systems, those skilled in the art will recognize that these teachings are equally applicable to other technical frameworks, networks, components, signaling methods, etc.

[0087] In summary, the adaptability and versatility of the concepts discussed in this disclosure make them applicable to a wide variety of telecommunications scenarios, regardless of the specific terms or technologies involved.

[0088] The numerical adjectives "first", "second", and "third" used in the above embodiments do not imply any order (not ordinal), but are labels for distinguishing separate instances of similar elements. References to the singular (e.g., "a" or "an", "the") should include the plural unless otherwise expressly indicated.

[0089] Although the features and elements of this embodiment are described in a particular combination in the embodiments, each feature or element can be used alone without the other features and elements in the embodiments, or in various combinations with or without other features and elements disclosed herein. A method or flowchart can be implemented by a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a specially programmed computer or processor.

Claims

1. A wireless communication method (1100, 1200, 1300, 1400) performed by a user equipment UE (102), the method comprises: receiving (1110, 1211, 1304, 1404) from a non-terrestrial network (NTN) BS (104) a TN information message specifying at least one TN area (502) including at least one terrestrial network TN cell (127); and determining (1130, 1230, 1330, 1440) whether the UE (102) is within or near the at least one TN area (502).

2. The method according to claim 1, further comprises: transmitting a measurement report indicating measurement parameters of the at least one TN cell only when the UE is within or near the at least one TN area.

3. The method according to any one of claims 1 or 2, wherein the TN information message includes a reference point of the at least one TN area and a distance parameter of the at least one TN area, the distance parameter describing the range of the TN area relative to the reference point.

4. The method according to any one of claims 1 to 3, wherein the TN area includes two or more TN cells using the same TN frequency.

5. The method according to claim 4, wherein when the UE is outside the TN area and within an envelope surrounding the TN area, the UE is near the at least one TN area.

6. The method according to any one of claims 1 to 5, wherein when receiving the TN information message, the UE is in a connected state via the NTN cell.

7. The method according to any one of claims 1 to 6, wherein the TN information message further includes a carrier frequency for measuring the measurement parameters of the at least one TN cell.

8. The method according to any one of claims 1 to 6, wherein the TN information message includes only position information of the at least one TN area, and the method further comprises: receiving a reconfiguration message having a carrier frequency of the at least one TN cell for measuring the parameters.

9. The method according to claim 8, further comprises: transmitting a proximity indication identifying the at least one TN area.

10. The method according to any one of claims 1 to 5, wherein when receiving the TN information message, the UE is in an idle state within a coverage area of an NTN cell (124) of the NTN BS (104).

11. The method according to claim 10, furthercomprises: the UE switching from the idle state to a connected state; and when in the connected state, receiving a reconfiguration message including a carrier frequency associated with the at least one TN cell.

12. The method according to claim 11, furthercomprises: transmitting a proximity indication identifying the at least one TN area.

13. The method according to claim 10, wherein the TN information message further includes a carrier frequency. ​ ​ 14. The method according to any one of claims 1 to 13, wherein the TN information message is a radio resource control message or a system information message.

15. A wireless communication method (1500, 1600, 1700, 1800) performed by a base station (104) communicating with a user equipment (102) UE via a non-terrestrial network NTN cell (124), the method comprising: transmitting (1510, 1611, 1704, 1804) to the UE (102) a TN information message specifying at least one TN area (502) including at least one terrestrial network TN cell (127); and initiating (1560) a handover process of the UE (102) to the at least one TN cell (127) based on the received measurement report.

16. The method according to claim 15, wherein the TN information message further includes at least the carrier frequency of the at least one TN area.

17. The method according to claim 15, further comprising: receiving (1614) from the UE (102) a message indicating that the UE (102) is located within or near the TN area (502); transmitting (1610) to the UE (102) an additional TN message including the frequency of the at least one TN area (502); and receiving (1542) the measurement report from the UE (102).

18. The method according to any one of claims 15 to 17, further comprising: receiving a proximity indication from the UE, the proximity indication identifying a specific TN area among the at least one TN area.

19. The method according to claim 17, wherein the additional TN message is a radio resource control message.

20. The method according to any one of claims 15 to 19, wherein the TN information is sent via a radio resource control message or a system information message.

21. A wireless communication device (102, 104) comprising a transceiver (134, 154), a processor (132, 152) and a computer-readable storage medium (136, 156) storing executable instructions for the processor to use the transceiver to perform any of the methods according to claims 1 to 20.

Images