Communication method, aerial user equipment, and network node

Abstract

This communication method is executed by aerial user equipment in a mobile communication system, and includes: receiving cell reselection-related information which is broadcast from a network node and is used exclusively for the aerial user equipment; and in a radio resource control (RRC) idle state or an RRC inactive state, performing a cell reselection operation for prioritizing a cell which provides sky coverage, on the basis of the cell reselection-related information.

Description

Communication method, aerial user equipment, and network node

[0001] The present disclosure relates to a communication method, an aerial user equipment, and a network node used in a mobile communication system.

[0002] In 3GPP (3rd Generation Partnership Project) (registered trademark; the same applies hereinafter), the technical specifications of NR (New Radio), which is a 5th generation (5G) radio access technology, are defined. The 3GPP mobile communication system supports an aerial UE (Aerial User Equipment), which is a user equipment (UE) capable of aerial communication. The aerial UE 100 may be an Unmanned Aircraft Vehicle (UAV) such as a drone.

[0003] 3GPP technical specification "3GPP TS 38.300 V18.2.0 (2024-06)"

[0004] The present disclosure provides a technology for improving the cell reselection operation performed by an aerial user equipment in the radio resource control (RRC) idle state or the RRC inactive state.

[0005] The communication method according to the first aspect of the present disclosure is a communication method performed by an aerial user equipment in a mobile communication system, including receiving cell reselection related information broadcast from a network node and dedicatedly used by the aerial user equipment, and performing a cell reselection operation that prioritizes cells providing aerial coverage based on the cell reselection related information in the radio resource control (RRC) idle state or the RRC inactive state.

[0006] The aerial user equipment according to the second aspect of the present disclosure is an aerial user equipment used in a mobile communication system, including a receiving unit that receives cell reselection related information broadcast from a network node and dedicatedly used by the aerial user equipment, and a control unit that performs a cell reselection operation that prioritizes cells providing aerial coverage based on the cell reselection related information in the radio resource control (RRC) idle state or the RRC inactive state.

[0007] A network node according to a third aspect of this disclosure is a network node used in a mobile communication system and has a transmitting unit that broadcasts cell reselection-related information used exclusively for an aerial user device. The cell reselection-related information is information used by the aerial user device in a radio resource control (RRC) idle state or RRC inactive state to perform a cell reselection operation that prioritizes cells that provide airborne coverage.

[0008] This is a diagram illustrating an example configuration of a mobile communication system according to an embodiment. This is a diagram illustrating an example configuration of a UE (User Equipment) according to an embodiment. This is a diagram illustrating an example configuration of a gNB (Network Node) according to an embodiment. This is a diagram illustrating the configuration of the protocol stack of the wireless interface of the user plane that handles data. This is a diagram illustrating the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals). This is a diagram illustrating an overview of SSB, beam sweeping, and cell search according to an embodiment. This is a diagram illustrating an overview of SSB, beam sweeping, and cell search according to an embodiment. This is a diagram illustrating an aerial UE according to an embodiment. This is a diagram illustrating a cell reselection operation performed by an aerial UE in an RRC idle state or RRC inactive state according to an embodiment. This is a diagram illustrating an example configuration of an SIB related to the first operation pattern of the cell reselection operation according to an embodiment. This is a diagram illustrating an example operation of a mobile communication system related to the first operation pattern of the cell reselection operation according to an embodiment. This is a diagram illustrating an example configuration of an MIB related to the second operation pattern of the cell reselection operation according to an embodiment. This is a diagram illustrating an example operation of a mobile communication system related to the second operation pattern of the cell reselection operation according to an embodiment. This is a diagram illustrating a first configuration example of an SIB related to the third operation pattern of the cell reselection operation according to an embodiment. This figure shows a second configuration example of the SIB related to the third operation pattern of the cell reselection operation according to the embodiment. This figure shows an example of operation of the mobile communication system related to the third operation pattern of the cell reselection operation according to the embodiment. This figure shows an example of the SIB configuration related to the fourth operation pattern of the cell reselection operation according to the embodiment. This figure shows an example of operation of the mobile communication system related to the fourth operation pattern of the cell reselection operation according to the embodiment. This figure shows the RA operation performed by the aviation UE in the RRC idle state or RRC inactive state according to the embodiment. This figure shows an example of operation of the mobile communication system related to the first operation pattern of the random access operation according to the embodiment. This figure shows an example of operation of the mobile communication system related to the second operation pattern of the random access operation according to the embodiment.

[0009] A mobile communication system according to an embodiment will be described with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals.

[0010] (1) The mobile communication system configuration diagram 1 is a diagram showing an example of the configuration of the mobile communication system 1 according to this embodiment. The mobile communication system 1 conforms to the 5th generation system (5GS: 5th Generation System) of the 3GPP standard. In the following description, 5GS will be used as an example, but the mobile communication system may also have an LTE (Long Term Evolution) system applied to it at least partially. The mobile communication system may also have a 6th generation (6G) system applied to it at least partially.

[0011] The mobile communication system 1 comprises a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, NG-RAN 10 may be simply referred to as RAN 10, and 5GC 20 may be simply referred to as the core network (CN) 20. RAN 10 and CN 20 constitute the network 5 of the mobile communication system 1.

[0012] UE100 is a mobile wireless communication device. UE100 can be any device used by a user. For example, UE100 can be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device attached to a sensor, a vehicle or a device attached to a vehicle (Vehicle UE), or an aircraft or a device attached to an aircraft (Aerial UE). The link from UE100 to network 5 in the transmission direction is called the uplink (UL), and the link from network 5 to UE100 in the transmission direction is called the downlink (DL).

[0013] NG-RAN10 includes a base station (referred to as "gNB" in the 5G system) 200, which is a type of network node. The gNBs 200 are interconnected via the Xn interface, which is an inter-base station interface. The gNBs 200 manage one or more cells. The gNBs 200 perform wireless communication with UEs 100 that have established a connection with their own cell. The gNBs 200 have radio resource management (RRM) functions, user data (hereinafter simply referred to as "data") routing functions, measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to indicate the smallest unit of a wireless communication area. "Cell" is also used as a term to indicate a function or resource that performs wireless communication with a UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] Furthermore, gNBs can also connect to the EPC (Evolved Packet Core), which is the core network of LTE. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0015] 5GC20 includes AMF (Access and Mobility Management Function) and UPF (User Plane Function) 300. The AMF performs various mobility controls for UE100. The AMF manages the mobility of UE100 by communicating with UE100 using NAS (Non-Access Stratum) signaling. The UPF controls data transfer. The AMF and UPF are connected to gNB200 via the NG interface, which is the base station-core network interface.

[0016] Figure 2 shows an example configuration of UE100 (user device) according to this embodiment. UE100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit 140 that performs wireless communication with gNB200.

[0017] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0018] The transmitting unit 120 performs various types of transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 130 into a wireless signal and transmits it from the antenna.

[0019] The control unit 130 performs various control and processing operations in the UE 100. Such processing includes processing in each layer described later. The operation of the UE 100 described above and later may be controlled by the control unit 130. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing operations.

[0020] Figure 3 shows an example configuration of a gNB200 (network node) according to this embodiment. The gNB200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and a network communication unit 240. The transmitting unit 210 and the receiving unit 220 constitute a wireless communication unit 250 that performs wireless communication with the UE100. The network communication unit 240 includes a transmitting unit 241 that performs transmission and a receiving unit 242 that performs reception.

[0021] The transmitting unit 210 performs various types of transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a wireless signal and transmits it from the antenna.

[0022] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 230.

[0023] The control unit 230 performs various control and processing operations on the gNB 200. Such processing includes processing of each layer described later. The operation of the gNB 200 described above and later may also be controlled by the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, decoding, etc., of the baseband signal. The CPU executes programs stored in memory and performs various processing operations.

[0024] The network communication unit 240 is connected to an adjacent base station via the Xn interface, which is an inter-base station interface. The network communication unit 240 is connected to the AMF / UPF 300 via the NG interface, which is an inter-base station-core network interface. The gNB 200 may consist of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally separated), and the two units may be connected by the F1 interface, which is a front-haul interface.

[0025] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0026] The user plane radio interface protocol comprises a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0027] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on the physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from gNB200 has a CRC (Cyclic Redundancy Code) parity bit added, which is scrambled by the RNTI.

[0028] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ: Hybrid Automatic Repeat reQuest), and random access procedures. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via the transport channel. The MAC layer of gNB200 includes a scheduler. The scheduler determines the transport format for the up and down links (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0029] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of UE100 and the RLC layer of gNB200 via a logical channel.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0031] The SDAP layer maps IP flows, which are the units under which the core network performs QoS (Quality of Service) control, to wireless bearers, which are the units under which the AS (Access Stratum) performs QoS control. Note that if the RAN is connected to the EPC, the SDAP is not required.

[0032] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

[0033] The protocol stack of the control plane's wireless interface includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer, instead of the SDAP layer shown in Figure 4.

[0034] RRC signaling for various settings is transmitted between the RRC layer of the UE100 and the RRC layer of the gNB200. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. If there is a connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC idle state. If the connection between the RRC of the UE100 and the RRC of the gNB200 is suspended, the UE100 is in the RRC inactive state.

[0035] The NAS layer (also simply referred to as "NAS"), located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the NAS layer of the UE100 and the NAS layer of the AMF300. The UE100 also has an application layer in addition to the wireless interface protocol. Furthermore, the layer below the NAS layer is called the AS layer (also simply referred to as "AS").

[0036] (2) Overview of SSB The technical specifications for 5G / NR (New Radio) allow the use of higher frequency bands for wireless communication compared to 4G / LTE. Because propagation loss is greater in higher frequency bands, beamforming, which narrows the direction in which radio waves are transmitted, is used in wireless communication, and the propagation loss is compensated for by beam gain.

[0037] The gNB200, which manages the cells, transmits a synchronization signal block (SSB: Synchronization Signal / Physical Broadcast Channel Block) used for cell searching performed by the UE100 via beamforming. Cell searching is a procedure in which the UE100 obtains time and frequency synchronization with the cell and detects the cell ID of that cell. The UE100 performs cell searching based on the primary synchronization signal (PSS), secondary synchronization signal (SSS), and demodulation reference signal (DMRS) of the PBCH in the SSB.

[0038] The gNB200 performs beam sweeping, which switches the transmission beam direction of the SSB (also called the "beamforming pattern") at predetermined time intervals, in order to transmit SSB throughout the entire coverage area of ​​the cell. For example, the gNB200 transmits an SS burst (also called an "SS burst set" or "synchronous signal burst") consisting of multiple SSBs arranged in the time direction at a period of 20 [ms]. Here, the gNB200 transmits each SSB within the SS burst in a time-division multiplexed manner with a different transmission beam direction by beam sweeping. This allows the SSB to spread throughout the entire coverage area of ​​the cell within the SS burst, even when transmitting SSB using beamforming. Note that the SS burst is specified to be set within a predetermined time length (specifically, the time of a half frame).

[0039] As the frequency band increases, beamforming techniques that can form sharper beams are utilized, and therefore the number of SSBs within an SS burst tends to increase. For example, in FR (Frequency Range) 1, which corresponds to the Sub6 band, a maximum of 8 SSBs (i.e., up to 8 SSB beamforming patterns) can be used within an SS burst, and in FR2, which corresponds to the millimeter-wave band, a maximum of 64 SSBs (i.e., up to 64 SSB beamforming patterns) can be used within an SS burst.

[0040] Figures 6 and 7 are diagrams illustrating the overview of the SSB, beam sweeping, and cell search according to this embodiment.

[0041] As shown in Figure 6, in the frame structure used for 5G / NR wireless communication, one frame (wireless frame) is 10 ms in the time axis direction. Each frame is composed of 10 subframes, each 1 ms long. Each subframe is composed of a number of slots corresponding to the waveform configuration (also called "numerology"), such as the subcarrier spacing. Specifically, as the subcarrier spacing increases, the length of the slots in the time axis direction decreases. The number of symbols in one slot is 14 in the case of a normal CP (Cyc Prefix). On the other hand, in the frequency axis direction, one resource block (RB) is composed of 12 subcarriers. Also, one resource element (RE) is composed of one symbol and one subcarrier.

[0042] gNB 200 that manages cells transmits an SSB (SS / PBCH block) used for cell search performed by UE 100. Each SSB is composed of four symbols in the time axis direction and 240 consecutive subcarriers (i.e., 20 RBs) in the frequency axis direction. These subcarriers are numbered in ascending order from 0 to 239 within the SSB from the low frequency side to the high frequency side. The subcarrier on the lowest frequency side within the SSB is also referred to as subcarrier 0. Note that each of the PSS and SSS consists of one symbol and 127 subcarriers. The PBCH consists of three symbols and 240 subcarriers.

[0043] Each SSB includes a synchronization signal (SS) and a physical broadcast channel (PBCH). The SS includes a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). The PSS and SSS are used at least for synchronization in the time axis direction. Also, the combination of each signal sequence of the PSS and SSS indicates the cell ID (PCI: Physical Cell ID) of the transmitting cell. The PBCH includes a master information block (MIB) and a demodulation reference signal (DMRS). The MIB includes parameters for decoding the system information block type 1 (SIB1). The DMRS is a reference signal for decoding the PBCH. Note that the SIB1 is also referred to as RMSI (Remaining Minimum System Information). The SSB associated with the SIB1 (RMSI) is referred to as a cell definition SSB (CD-SSB). Hereinafter, the SSB refers to the CD-SSB.

[0044] The SSBs are arranged continuously in the time direction at specific frequencies within the cell's band. Specifically, in the current 3GPP technical specifications, the SSBs are arranged at a single frequency determined in advance on the gNB 200 side, and the SSBs are repeatedly transmitted in the time axis direction. The position of the SSB on the frequency axis can be notified from the gNB 200 to the UE 100 by RRC signaling.

[0045] The gNB200 periodically transmits SS bursts (also called "SS burst sets" or "synchronous signal bursts") consisting of multiple SSBs arranged in the time direction. The transmission period of the SS burst can be selected from 5 [ms], 10 [ms], 20 [ms], 40 [ms], 80 [ms], and 160 [ms], but 20 [ms] is the most common. The maximum number of SSBs in a single SS burst, i.e., the maximum number of consecutive SSBs, is 8 for FR1, which corresponds to the Sub6 band, and 64 for FR2, which corresponds to the millimeter wave band. In the illustrated example, the transmission period of the SS burst is 20 [ms], and the number of SSBs in the SS burst is 8. Note that the SS burst is specified to be set within the time of a half frame (5 [ms]). The time positions in which SSBs can be placed within a half frame are determined according to the subcarrier interval. On the other hand, the transmission period of the SS burst (i.e., the periodicity of the half-frames in which SSB is transmitted) is set by the gNB200.

[0046] In the example in Figure 6, all SSBs in the SS burst are shown being transmitted, but the gNB200 does not necessarily have to transmit all SSBs in the SS burst. The gNB200 can selectively transmit only some of the SSBs in the SS burst, depending on the requirements of network 5. In addition, the gNB200 can notify the UE100 via RRC signaling which SSBs are transmitted and which are not within the SS burst. Specifically, this transmission pattern is notified to the UE100 by an RRC information element (IE) called ssb-PositionInBurst.

[0047] gNB 200 assigns an SSB index, which is an identifier of the SSB, to each SSB within the SS burst. In the example of FIG. 6, "#1" to "#8" represent the SSB index. This number is reset to 1 in the next SS burst. The SSB index may be a unique number starting from 0 and incrementing by 1. When the SSB index starts from 0, the SSB index is reset to 0 in the next SS burst. gNB 200 notifies the UE 100 of the SSB index in the PBCH within the SSB. The UE 100 that has received the SSB can identify the SSB index of the received SSB based on the PBCH in the received SSB.

[0048] As shown in FIG. 7, in order to transmit the SSB over the entire coverage area of the cell, gNB 200 performs beam sweeping that switches the transmission beam direction of the SSB (also referred to as "beamforming pattern (BF pattern)") at a predetermined time interval within the period of each SS burst (SS burst period). That is, gNB 200 time-division transmits each SSB within the SS burst in a different transmission beam direction by beam sweeping. Therefore, within a half-frame, different SSBs are transmitted in different spatial directions (i.e., different transmission beam directions) so as to span the coverage area of the cell. Thereby, even when transmitting the SSB using beamforming, the SSB can be spread over the entire coverage area (cell coverage) of the cell within the SS burst.

[0049] UE100 performs a cell search based on SSBs (specifically, PSS, SSS, and DMRS within the SSBs). A cell search is a procedure in which UE100 obtains time and frequency synchronization with a cell and detects the cell ID of that cell. UE100 performs a scan (cell search) of SSBs against a synchronization raster, which is the position on the frequency axis where SSBs may be placed. UE100 measures the reception quality of each received SSB and identifies the appropriate beam by identifying the SSB Index of SSBs whose reception quality satisfies predetermined conditions. Here, reception quality may be RSRP (Reference Signal Received Power) in the SSB. The predetermined condition may be that the reception quality exceeds a threshold. The predetermined condition may also be that the reception quality is the highest among the SSBs received within a predetermined period (e.g., an SS burst period).

[0050] UE100 performs random access (RA) for initial access to gNB200. Specifically, UE100 transmits an RA preamble to gNB200 in order to perform RA. There are as many RA occasions as there are transmit beams of gNB200 (i.e., the number of SSBs in the SS burst), which are the timings in which an RA preamble can be transmitted. UE100 transmits an RA preamble to gNB200 at the RA occasion corresponding to an SSB (SSB Index) whose received quality meets predetermined conditions. Upon receiving the RA preamble, gNB200 can determine the preferred transmit beam for UE100 (i.e., the direction in which UE100 is located) based on the correspondence between the beam (SSB Index) and the RA occasion.

[0051] Furthermore, RA (Radio Absorption) occasions are notified to the UE100 in the System Information (SIB) provided by the gNB200. Specifically, the gNB200 notifies the UE100 of the time and frequency resources for the RA occasion. There is a one-to-one relationship between SSB (Standard Subband) and RA occasions. When the gNB200 directs its transmit beam in a certain direction, it receives the SSB during the corresponding RA occasion using a receive beam directed in the same direction as the transmit beam.

[0052] (3) Overview of Cell Reselection Operation When UE100 is in an RRC idle state or RRC inactive state, it performs a cell reselection operation to move from the current serving cell to an adjacent cell (non-serving cell) as it moves. Specifically, UE100 identifies the adjacent cell to which it should camp on through the cell reselection operation and reselects the identified adjacent cell. When the current serving cell and the adjacent cell have the same frequency (carrier frequency), it is called intra-frequency, and when the current serving cell and the adjacent cell have different frequencies (carrier frequencies), it is called inter-frequency. There are two types of cell reselection operations: intra-frequency cell reselection and inter-frequency cell reselection.

[0053] In the intra-frequency cell reselection operation, cells are reselected based on their ranking. For example, the following processes are performed during the intra-frequency cell reselection operation:

[0054] Firstly, the UE100 performs a measurement process to measure the wireless quality for both the serving cell and the adjacent cell. Specifically, the UE100 measures the RSRP and RSRQ of the CD-SSB (Cell Defining-Synchronization Signal and PBCH block) for both the serving cell and the adjacent cell.

[0055] Secondly, UE100 calculates a ranking criterion (Rs) for the serving cell and a ranking criterion (Rn) for adjacent cells for all cells that satisfy the cell selection criterion S. The cell selection criterion S is the criterion for selecting cells in which RSRP exceeds the minimum RSRP requirement level and RSRQ exceeds the minimum RSRQ requirement level. In UE100, the highest-ranked cell is basically re-selected from the two ranking criteria Rs and Rn.

[0056] On the other hand, inter-frequency cell reselection operation is performed based on absolute frequency priority. Frequency priority is provided from gNB200 to UE100 via broadcast signaling (e.g., system information block) or dedicated signaling (e.g., RRC release message). The frequency priority that can be set in UE100 in this way is also called network configuration priority.

[0057] During inter-frequency cell reselection, the following processes are performed, for example:

[0058] Firstly, the UE100 performs a measurement process to measure the radio quality for both the serving cell and adjacent cells. Specifically, the UE100 always measures the radio quality for frequencies with a higher priority than the current serving cell's frequency priority. Furthermore, for frequencies with the same or lower priority as the current serving cell's frequency priority, the UE100 measures the radio quality of those frequencies only if the current serving cell's radio quality falls below a predetermined quality.

[0059] Secondly, UE100 performs a cell reselection process to reselect the cell (serving cell) to which it will camp on based on the measurement results. Specifically, UE100 may reselect a cell to an adjacent cell if the frequency priority of an adjacent cell is higher than the priority of the current serving cell, and the adjacent cell meets a predetermined quality standard (i.e., the minimum required quality standard) for a predetermined period. If the frequency priority of an adjacent cell is the same as the priority of the current serving cell, UE100 may rank the wireless quality of the adjacent cell and reselect a cell to an adjacent cell that has a higher rank than the current serving cell for a predetermined period. If the frequency priority of an adjacent cell is lower than the priority of the current serving cell, and the wireless quality of the current serving cell is lower than a wireless quality threshold, and the wireless quality of the adjacent cell remains higher than another wireless quality threshold for a predetermined period, UE100 may reselect a cell to an adjacent cell.

[0060] (4) Aerial User Equipment The mobile communication system 1 according to this embodiment supports Aerial UE. Figure 8 is a diagram illustrating Aerial UE 100 according to this embodiment. Aerial UE 100 is a UE capable of aerial communication. Aerial UE 100 may be an Unmanned Aircraft Vehicle (UAV) such as a drone.

[0061] In the illustrated example, gNB200a manages cell a, and gNB200b manages cell b. Cell a is a serving cell of UE100, and cell b is a non-serving cell of UE100. gNB200a forms cell a facing upwards to provide aerial coverage. gNB200b forms cell b facing downwards to provide terrestrial coverage. However, cells a and b may be managed and formed by a single gNB200.

[0062] In the mobile communication system 1, cells for upper-air coverage and cells for ground coverage may be mixed. In the cells for upper-air coverage, one or more beams for upper-air coverage are formed. In the beams for upper-air coverage, the main lobe may be pointed upwards while the side lobes are pointed towards the ground. In the cells for ground coverage, one or more beams for ground coverage are formed. In the beams for ground coverage, the main lobe may be pointed towards the ground while the side lobes are pointed upwards. Each beam may be identified by SSB.

[0063] The Aerial UE100 can communicate wirelessly with the gNB200 in the airspace while flying. However, it is assumed that the Aerial UE100 will not perform continuous high-capacity data transmission. Under these assumptions, the Aerial UE100 does not necessarily need to maintain the RRC connected state; it may transition to the RRC idle state after data transmission is complete, or to the RRC inactive state for small data transmission.

[0064] (5) Operation of the aircraft user device in the RRC idle state or RRC inactive state The operation of the aircraft UE100 in the RRC idle state or RRC inactive state according to this embodiment will be described.

[0065] (5.1) Cell re-selection operation by aircraft user equipment When an aircraft UE 100 is in an RRC idle or RRC inactive state and is in flight, it is desirable that it be able to re-select (camp on) a cell that provides airspace coverage. However, conventional cell re-selection operations (cell re-selection operations) are based on the assumption that the UE 100 is mainly performing ground communications and have the problem of not being optimized for an aircraft UE 100 in flight. The following embodiments provide a technology for improving the cell re-selection operation performed by an aircraft UE 100 in an RRC idle or RRC inactive state.

[0066] Figure 9 shows the cell reselection operation performed by the aircraft UE 100 in the RRC idle state or RRC inactive state according to this embodiment.

[0067] In step S11, the aviation UE 100 in the RRC idle or RRC inactive state receives cell reselection-related information broadcast from the gNB 200 and used exclusively for the aviation UE 100. The cell reselection-related information is included in the system information block (SIB) or master information block (MIB) broadcast by the gNB 200. The SIB and MIB are information that the aviation UE 100 in the RRC idle or RRC inactive state can receive.

[0068] In step S12, an aviation UE 100 in an RRC idle or RRC inactive state performs a cell reselection operation that prioritizes cells that provide upper-air coverage, based on the cell reselection-related information received in step S11. Prioritizing cells that provide upper-air coverage may mean that the cell reselection priority for the cell that provides upper-air coverage (which may be an SSB within that cell) or the frequency to which that cell (SSB) belongs is higher than that for other cells or other frequencies. Prioritizing cells that provide upper-air coverage may also mean that the cell that provides upper-air coverage (which may be an SSB within that cell) or the frequency to which that cell (SSB) belongs is considered the highest priority for cell reselection. Prioritizing cells that provide upper-air coverage may also mean that a cell that does not provide upper-air coverage (which may be an SSB within that cell) or the frequency to which that cell (SSB) belongs is considered the lowest priority for cell reselection.

[0069] This operation makes it easier for an airborne UE100 in an RRC idle or RRC inactive state to re-select (camp on) a cell that provides airborne coverage, by performing a cell re-selection operation that prioritizes cells that provide airborne coverage based on cell re-selection-related information broadcast from the gNB200.

[0070] The aerial UE 100 performing this operation includes a receiving unit 110 that receives cell reselection-related information broadcast from the gNB 200 and used exclusively for the aerial UE 100, and a control unit 130 that, in the RRC idle state or RRC inactive state, performs cell reselection operations that prioritize cells that provide upper-air coverage based on the cell reselection-related information (see Figure 2). On the other hand, the gNB 200 has a transmitting unit 210 that broadcasts cell reselection-related information used exclusively for the aerial UE 100 (see Figure 3). The cell reselection-related information is information used by the aerial UE 100 in the RRC idle state or RRC inactive state to perform cell reselection operations that prioritize cells that provide upper-air coverage.

[0071] (5.1.1) First operation pattern of cell reselection operation by aviation user device The first operation pattern of cell reselection operation according to this embodiment will be described.

[0072] In the first operation pattern, the cell reselection-related information broadcast from the gNB 200 is altitude-based measurement SSB information that includes information indicating the SSB pattern for each altitude range. This allows the aviation UE 100 to receive and measure the appropriate SSB according to its altitude based on the altitude-based measurement SSB information. For example, an aviation UE 100 in flight can receive and measure the SSB for upper-air coverage and camp on to a cell broadcasting the SSB for upper-air coverage. The gNB 200 transmits an SIB containing the altitude-based measurement SSB information. This SIB may be an SIB used to provide cell reselection-related parameters. The altitude range includes an altitude (threshold) that sets the lower limit of the range. The altitude range may also include an altitude (threshold) that sets the upper limit of the range.

[0073] Here, the SSB pattern may be an SSB pattern that UE100 expects to be transmitted within a half-frame. The information indicating the SSB pattern may be a bitmap in which each bit is associated with an index of an SSB that can be transmitted within a half-frame. The aviation UE100 may assume that for bits set to "1" in the bitmap, the corresponding SSB may be transmitted. The aviation UE100 may assume that for bits set to "0" in the bitmap, the corresponding SSB will not be transmitted.

[0074] Figure 10 shows an example of the configuration of the SIB related to the first operation pattern of the cell reselection operation. In the illustrated example, the SIB includes altitude-based measurement SSB information (list of SSBs to be measured). The altitude-based measurement SSB information includes multiple measurement SSB information (measurement SSB information 1, measurement SSB information 2, ...). Each of the multiple measurement SSB information includes information indicating the altitude range and information indicating the SSB pattern.

[0075] Upon receiving altitude-based measurement SSB information from gNB200, the aerial UE100 compares its own altitude and altitude range information based on the received altitude-based measurement SSB information to identify the SSB pattern associated with the altitude range to which the aerial UE100's altitude belongs, and performs a cell reselection operation, including SSB measurement, based on the identified SSB pattern.

[0076] Figure 11 shows an example of the operation of the mobile communication system 1 related to the first operation pattern of cell reselection. The aviation UE 100 is assumed to be in an RRC idle state or RRC inactive state in the cell of gNB 200.

[0077] In step S101, the gNB 200 broadcasts an SIB containing altitude-based measurement SSB information within its cell. The aviation UE 100 receives the SIB. The SIB may be a system information block type 1 (SIB1) or a cell reselection-related SIB. SIB1 is an SIB that includes information used by the UE 100 for initial access and scheduling information for other SIBs. A cell reselection-related SIB may be a system information block type 2 (SIB2). SIB2 is an SIB that includes cell reselection information common to intra-frequency, inter-frequency, and / or inter-RAT cell reselection, and intra-frequency cell reselection information other than adjacent cell-related information.

[0078] The gNB200 may further broadcast an altitude threshold for determining whether the aircraft UE100 is in flight (at high altitude). The gNB200 may broadcast this altitude threshold, for example, in the SIB of step S101 or in another SIB.

[0079] In step S102, the aerial UE 100 may determine whether or not it is in flight (i.e., in flight). If the aerial UE 100 determines that it is in flight (step S102: YES), it may proceed to the subsequent processing. Generally, the aerial UE 100 has a GNSS (Global Navigation Satellite System) receiver and is capable of determining its own latitude, longitude, and altitude. The aerial UE 100 may determine whether or not it is in flight based on positioning information. The aerial UE 100 may also determine whether or not it is in flight based on information from its application layer, etc.

[0080] In step S103, the aircraft UE 100 identifies an SSB pattern associated with the altitude range to which the altitude of the aircraft UE 100 belongs, based on the altitude-based measurement SSB information received in step S101.

[0081] In step S104, the aircraft UE100 attempts to receive (and measure) each SSB indicated by the identified SSB pattern.

[0082] In step S105, the aerial UE 100 considers the cell or frequency that provides the SSB successfully received (and measured) in step S104 as the highest priority for cell reselection. Alternatively, or in addition, the aerial UE 100 may consider the cell or frequency that does not provide the SSB successfully received (and measured) in step S104 (i.e., a cell or frequency that does not provide airborne SSB or airborne coverage) as the lowest priority for cell reselection.

[0083] In step S106, the aircraft UE100 may perform cell reselection to camp on the cell or frequency that was deemed to have the highest priority in step S105.

[0084] The operation related to the first operation pattern (and the operation related to the second and third operation patterns described below) may be expressed in any of the following ways: • If the altitude of the aerial UE 100 is within the altitude range broadcast for SSB, the aerial UE 100 always considers the cell providing this SSB as having the highest priority (i.e., higher than other network setting priorities); • If the altitude of the aerial UE 100 exceeds the altitude threshold broadcast for SSB, the aerial UE 100 always considers the cell providing this SSB as having the highest priority (i.e., higher than other network setting priorities); • If the aerial UE 100 is in flight, the aerial UE 100 always considers the cell providing SSB for upper-air coverage as having the highest priority (i.e., higher than other network setting priorities); • If the aerial UE 100 is in flight, the aerial UE 100 always considers the cell providing upper-air coverage as having the highest priority (i.e., higher than other network setting priorities); - If the altitude of Aerial UE100 is within the altitude range broadcast for SSB, Aerial UE100 will always consider cells that do not provide this SSB as the lowest priority (i.e., lower than other network configuration priorities); - If the altitude of Aerial UE100 exceeds the altitude threshold broadcast for SSB, Aerial UE100 will always consider cells that do not provide this SSB as the lowest priority (i.e., lower than other network configuration priorities); - If Aerial UE100 is in flight, Aerial UE100 will always consider cells that do not provide SSB for upper-air coverage as the lowest priority (i.e., lower than other network configuration priorities); - If Aerial UE100 is in flight, Aerial UE100 will always consider cells that do not provide upper-air coverage as the lowest priority (i.e., lower than other network configuration priorities).

[0085] In addition, while the above examples described how a cell can be considered as having the highest or lowest priority, the frequency to which the cell belongs can also be considered as having the highest or lowest priority.

[0086] (5.1.2) Second Operation Pattern for Cell Reselection Operation by Aircraft User Device The second operation pattern for cell reselection operation according to this embodiment will be described. The second operation pattern may be performed in combination with the first operation pattern described above.

[0087] In the second operation pattern, the cell reselection-related information broadcast from the gNB200 is included in the SSB for upper-air coverage and is identification information (also referred to as "upper-air coverage identification information") indicating that the SSB is for upper-air coverage. The gNB200 broadcasts an identifier (e.g., 1-bit information) in the MIB for each SSB to indicate that the SSB is an upper-air SSB.

[0088] As a result, the aviation UE100 that receives the SSB can identify the received SSB as an SSB for airspace coverage based on the identification information contained in the received SSB (information in the MIB) and can camp on to the cell broadcasting the SSB for airspace coverage.

[0089] Figure 12 shows an example of the configuration of the MIB related to the second operation pattern of cell reselection operation. In the illustrated example, the SSB includes the MIB, and the MIB includes airborne coverage identification information when the SSB is for airborne coverage.

[0090] Figure 13 shows an example of the operation of the mobile communication system 1 related to the second operation pattern of cell reselection. The aviation UE 100 is assumed to be in an RRC idle state or RRC inactive state in the cell of gNB 200. Explanations of operations similar to the first operation pattern described above will be omitted to avoid repetition.

[0091] In step S201, the aircraft UE 100 may determine whether or not it is in flight (i.e., in flight). If the aircraft UE 100 determines that it is in flight (step S201: YES), it may proceed to the subsequent processing.

[0092] In step S202, the gNB200 transmits the airborne coverage identification information to the MIB included in each SSB for airborne coverage. The gNB200 does not need to include the airborne coverage identification information in the MIB included in each SSB for ground coverage.

[0093] The airspace coverage identification information may also be information indicating the altitude range covered by the corresponding SSB. For example, if the airspace coverage identification information is 2 bits, four altitude ranges can be represented. The correspondence between the airspace coverage identification information and the altitude range may be notified to the airborne UE 100 by the gNB 200 broadcasting via SIB. This correspondence may be predetermined in the technical specifications of the mobile communication system 1.

[0094] In step S203, the aviation UE 100, which received the SSB in step S202, determines whether the received SSB contains airspace coverage identification information. If the airspace coverage identification information is multi-bit information, the aviation UE 100 determines whether its own altitude is included in the altitude range indicated by the airspace coverage identification information included in the received SSB, and if it determines that its own altitude is included, it may proceed to step S204.

[0095] If the received SSB includes airspace coverage identification information (step S203: YES), in step S204, the aviation UE 100 considers the cell or frequency that provides the SSB received in step S202 as the highest priority for cell reselection. Alternatively, or in addition to this, the aviation UE 100 may consider the cell or frequency that does not provide the SSB received in step S202 (i.e., a cell or frequency that does not provide airspace SSB or airspace coverage) as the lowest priority for cell reselection.

[0096] In step S205, the aircraft UE100 may perform cell reselection to camp on to the cell or frequency that was deemed to have the highest priority in step S204.

[0097] (5.1.3) Third Operation Pattern for Cell Reselection Operation by Aircraft User Device The third operation pattern for cell reselection operation according to this embodiment will be described. The third operation pattern may be performed in combination with the first operation pattern and / or the second operation pattern described above.

[0098] In the third operation pattern, the aviation UE 100 receives cell reselection-related information from the serving cell (gNB 200), and the cell reselection-related information broadcast by the serving cell is information regarding SSB for upper-air coverage in the non-serving cell (adjacent cell). Here, the information regarding SSB for upper-air coverage in the non-serving cell (adjacent cell) may be altitude-based measurement SSB information of the non-serving cell (adjacent cell) at intra-frequency or inter-frequency. This information may also indicate whether the non-serving cell (adjacent cell) at intra-frequency or inter-frequency provides SSB for upper-air coverage.

[0099] This makes it easier for the aviation UE100 to receive and measure SSB for airspace coverage in non-serving cells (adjacent cells) and to camp on to cells (adjacent cells) that broadcast SSB for airspace coverage.

[0100] Figure 14 shows a first configuration example of an SIB related to the third operation pattern of cell reselection. In the illustrated example, the SIB includes a list of adjacent cell information. The adjacent cell information in the list includes the cell ID and / or frequency ID of the adjacent cell and the altitude-based measurement SSB information of the adjacent cell. The configuration of the altitude-based measurement SSB information is the same as that of the first operation pattern described above. According to this configuration example, the aircraft UE 100 in flight can grasp the SSB corresponding to its own altitude for adjacent cells and appropriately receive the SSB of the adjacent cells.

[0101] Figure 15 shows a second configuration example of the SIB related to the third operation pattern of cell reselection operation. In the illustrated example, the SIB includes a list of adjacent cell information. The adjacent cell information in the list includes the cell ID and / or frequency ID of the adjacent cell, and information indicating whether the adjacent cell provides SSB for airspace coverage. According to this configuration example, the aircraft UE 100 in flight can identify adjacent cells that provide SSB for airspace coverage and appropriately receive the SSB from those adjacent cells.

[0102] Figure 16 shows an example of the operation of the mobile communication system 1 related to the third operation pattern of cell reselection. The aviation UE 100 is assumed to be in an RRC idle state or RRC inactive state in the cell of gNB 200. Explanations of operations similar to the first and / or second operation patterns described above will be omitted to avoid repetition.

[0103] In step S301, the gNB 200 broadcasts an SIB containing adjacent cell information within its own cell. The aviation UE 100 receives the SIB. The SIB may be a cell reselection-related SIB. A cell reselection-related SIB may be a system information block type 3 (SIB3) or a system information block type 4 (SIB4). SIB3 is an SIB that contains information related only to intra-frequency cell reselection. SIB4 is an SIB that contains information related only to inter-frequency cell reselection. This includes cell reselection parameters common to the frequency and cell-specific reselection parameters.

[0104] The gNB200 may further broadcast an altitude threshold for determining whether the aircraft UE100 is in flight (at high altitude). The gNB200 may broadcast this altitude threshold, for example, in the SIB of step S301 or in another SIB.

[0105] In step S302, the aircraft UE 100 may determine whether or not it is in flight (i.e., in flight). If the aircraft UE 100 determines that it is in flight (step S302: YES), it may proceed to the subsequent processing.

[0106] In step S303, the aviation UE 100 identifies an adjacent cell that provides SSB for upper-air coverage based on the adjacent cell information received in step S301, and receives the SSB of the adjacent cell. The aviation UE 100 may also receive the SSB of the adjacent cell based on the SSB pattern of the adjacent cell associated with the altitude range to which the altitude of the aviation UE 100 belongs.

[0107] In step S304, the aviation UE 100 considers the cell or frequency that provides the SSB received in step S303 as the highest priority for cell reselection. Alternatively, or in addition, the aviation UE 100 may consider the cell or frequency that does not provide the SSB received in step S303 (i.e., a cell or frequency that does not provide airborne SSB or airborne coverage) as the lowest priority for cell reselection.

[0108] In step S305, the aircraft UE100 may perform cell reselection to camp on to the cell or frequency that was deemed to have the highest priority in step S304.

[0109] (5.1.4) Fourth Operation Pattern for Cell Reselection Operation by Aircraft User Device The fourth operation pattern for cell reselection operation according to this embodiment will be described. The fourth operation pattern may be performed in combination with the first operation pattern, the second operation pattern, and / or the third operation pattern described above.

[0110] In the first to third operating patterns described above, the aerial UE100 considered the cell or frequency providing SSB for airspace coverage as having the highest priority. In the fourth operating pattern, instead of such autonomous cell reselection priority control, the priority (absolute priority; network setting priority) of the frequency or cell providing SSB for airspace coverage is set from network 5 (gNB200) to the UE100.

[0111] In the fourth operation pattern, the cell reselection-related information broadcast by the gNB200 is altitude-based priority information that includes information indicating the frequency priority or cell priority in cell reselection for each altitude range. Based on the altitude-based priority information, the aviation UE100 identifies the priority (frequency priority or cell priority) associated with the altitude range to which the aviation UE100's altitude belongs, and performs cell reselection based on the identified priority.

[0112] Figure 17 shows an example of the configuration of the SIB related to the fourth operation pattern of the cell reselection operation. In the illustrated example, the SIB includes altitude-based priority information. The altitude-based priority information includes multiple priority information (priority information 1, priority information 2, ...). Each of the multiple priority information includes information indicating the altitude range and priority information for each frequency or cell. The priority information for each frequency may be multiple sets of frequency ID and priority value. The priority information for each cell may be multiple sets of cell ID and priority value.

[0113] Figure 18 shows an example of the operation of the mobile communication system 1 related to the fourth operation pattern of cell reselection. The aviation UE 100 is assumed to be in an RRC idle state or RRC inactive state in the cell of gNB 200. Explanations of operations similar to the first to third operation patterns described above will be omitted to avoid repetition.

[0114] In step S401, the gNB200 broadcasts an SIB containing altitude-based priority information within its cell. The aviation UE100 receives the SIB. This SIB may be a cell reselection-related SIB.

[0115] Altitude-based priority information is altitude-based frequency priority information, and frequency priorities (i.e., priority for each frequency) may be set for each altitude range (lower altitude limit, upper altitude limit). This frequency priority may be associated with identification information indicating that it is for use in the air.

[0116] Altitude-based priority information is information on altitude-based cell priorities, and cell priorities (i.e., priority for each cell) may be set for each altitude range (lower altitude limit, upper altitude limit). Cell priority may also be information that designates the corresponding cell as having the highest priority. Such cell priority may also be a cell-specific offset (an offset value to improve the cell measurement result or cell ranking).

[0117] The gNB200 may further broadcast an altitude threshold for determining whether the aircraft UE100 is in flight (at high altitude). The gNB200 may broadcast this altitude threshold, for example, in the SIB of step S401 or in another SIB.

[0118] In step S402, the aircraft UE 100 may determine whether or not it is in flight (i.e., in flight). If the aircraft UE 100 determines that it is in flight (step S402: YES), it may proceed to the subsequent processing.

[0119] In step S403, the aviation UE 100 identifies priority information associated with the altitude range to which the aviation UE 100's altitude belongs, based on the altitude-based priority information received in step S401, and applies the identified priority information. Specifically, the aviation UE 100 applies the frequency priority or cell priority associated with the altitude range to which the aviation UE 100's altitude belongs.

[0120] In step S404, the aviation UE100 may perform cell reselection based on the priority applied in step S403.

[0121] In this operation pattern, an example was described in which the gNB200 includes altitude-based priority information in the SIB and broadcasts it. However, the gNB200 may also include altitude-based priority information in the RRC Release message and send it to the UE100. The RRC Release message is an RRC message (a dedicated RRC message for the UE) that causes the UE100 to transition from the RRC Connected state to the RRC Idle state or the RRC Inactive state. The UE100 in the RRC Idle state or the RRC Inactive state may perform the above operations based on the altitude-based priority information set in the RRC Release message.

[0122] (5.2) Random access operation by the aircraft user device The random access operation according to this embodiment will be described.

[0123] As described above, the aviation UE 100 performs random access (RA) for initial access to the gNB 200. Specifically, the aviation UE 100 sends an RA preamble to the gNB 200 in order to perform RA. Such an RA procedure may be CBRA (Containment Based Random Access). There are as many RA occasions as there are transmit beams of the gNB 200 (i.e., the number of SSBs in the SS burst), which are the timings in which the RA preamble can be sent. The aviation UE 100 sends an RA preamble to the gNB 200 in the RA occasion corresponding to an SSB (SSB Index) whose received quality meets predetermined conditions. Upon receiving the RA preamble, the gNB200 can determine the preferred transmit beam for the aerial UE100 (i.e., the direction in which the aerial UE100 is located) based on the correspondence between the beam (SSB Index) and the RA occasion.

[0124] Furthermore, RA (Radio Absorption) occasions are notified to the Aeronautical UE 100 in the System Information (SIB) provided by the gNB 200. Specifically, the gNB 200 notifies the Aeronautical UE 100 of the time and frequency resources for the RA occasions. There is a one-to-one relationship between SSB (Standard Subband) and RA occasions. When the gNB 200 directs its transmit beam in a certain direction, it receives the SSB during the corresponding RA occasion using a receive beam directed in the same direction as the transmit beam.

[0125] According to the cell reselection operation of the embodiment described above, the aerial UE 100 can camp in a cell that provides airborne coverage. However, it is also important that the aerial UE 100 selects an SSB for airborne coverage when performing random access. For example, if the cell where the aerial UE 100 is camped provides both an airborne SSB and a ground SSB, the aerial UE 100 does not necessarily select an airborne SSB, but an aerial UE 100 in flight should select an airborne SSB. The following embodiment provides techniques for improving random access (RA) operations performed by an aerial UE 100 in an RRC idle or RRC inactive state.

[0126] Figure 19 shows the RA operation performed by the aircraft UE100 in the RRC idle state or RRC inactive state according to this embodiment.

[0127] In step S21, the aircraft UE 100 in RRC idle or RRC inactive state receives SSB-related information broadcast from the gNB 200 and used exclusively for the aircraft UE 100. The SSB-related information may be the altitude-based measurement SSB information described in the first operation pattern above and / or the airspace coverage identification information described in the second operation pattern above. The SSB-related information is included in the SIB or MIB broadcast by the gNB 200. The SIB and MIB are information that the aircraft UE 100 in RRC idle or RRC inactive state can receive.

[0128] In step S22, when an aircraft UE 100 in an RRC idle or RRC inactive state performs the RA procedure, it selects an SSB for upper-air coverage based on the SSB-related information received in step S21.

[0129] In step S23, the aviation UE 100, which is in an RRC idle or RRC inactive state, transmits an RA preamble to the gNB 200 using the RA resource associated with the upper-air coverage SSB selected in step S22. Specifically, the aviation UE 100 transmits an RA preamble to the gNB 200 in the RA occasion corresponding to the upper-air coverage SSB (SSB Index).

[0130] With this operation, an aviation UE100 in an RRC idle or RRC inactive state can transmit an RA preamble using an appropriate RA resource (RA occasion) corresponding to airborne SSB, based on SSB-related information broadcast from the gNB200.

[0131] The aerial UE 100 performing this operation includes a receiving unit 110 that receives SSB-related information broadcast from the gNB 200 and used exclusively by the aerial UE 100, a control unit 130 that selects an SSB for upper-air coverage based on the SSB-related information when performing an RA procedure in an RRC idle or RRC inactive state, and a transmitting unit 120 that transmits an RA preamble to the gNB 200 using the RA resource associated with the selected upper-air coverage SSB (see Figure 2). On the other hand, the gNB 200 has a transmitting unit 210 that broadcasts SSB-related information used exclusively by the aerial UE 100. The SSB-related information is information used by the aerial UE 100 in a Radio Resource Control (RRC) idle or RRC inactive state to select an SSB for upper-air coverage when performing an RA procedure (see Figure 3).

[0132] (5.2.1) First Operation Pattern of Random Access Operation by Aircraft User Device The first operation pattern of random access operation according to this embodiment will be explained, mainly in terms of the differences from the first operation pattern of cell reselection operation described above.

[0133] In the first operation pattern of random access operation, the SSB-related information broadcast from gNB200 in step S21 is altitude-based measurement SSB information that includes information indicating the SSB pattern for each altitude range. An aircraft UE100 in an RRC idle or RRC inactive state identifies the SSB pattern associated with the altitude range to which the altitude of the aircraft UE100 belongs based on the altitude-based measurement SSB information, and selects an upper-air coverage SSB based on the identified SSB pattern (step S22). The configuration of the altitude-based measurement SSB information (SIB) is the same as in the first operation pattern of cell reselection operation described above.

[0134] Figure 20 shows an example of the operation of the mobile communication system 1 related to the first operation pattern of random access operation. The aviation UE 100 is assumed to be in an RRC idle state or RRC inactive state in the cell of the gNB 200.

[0135] In step S501, the aviation UE 100 decides to start the RA procedure. For example, the aviation UE 100 decides to start the RA procedure in response to the generation of uplink data to be transmitted to network 5.

[0136] In step S502, the gNB200 broadcasts an SIB containing altitude-based measurement SSB information within its own cell. The aviation UE100 receives the SIB. This SIB may be SIB1 or an SIB related to cell reselection.

[0137] The gNB200 may further broadcast an altitude threshold for determining whether the aircraft UE100 is in flight (at high altitude). The gNB200 may broadcast this altitude threshold, for example, in the SIB of step S501 or in another SIB.

[0138] In step S503, the aircraft UE 100 may determine whether or not it is in flight (i.e., in flight). If the aircraft UE 100 determines that it is in flight (step S503: YES), it may proceed to the subsequent processing.

[0139] In step S504, the aircraft UE 100 identifies an SSB pattern associated with the altitude range to which the altitude of the aircraft UE 100 belongs, based on the altitude-based measurement SSB information received in step S502.

[0140] In step S505, the aircraft UE100 attempts to receive (and measure) each SSB indicated by the identified SSB pattern.

[0141] In step S506, the aviation UE 100 may determine whether the reception quality of the SSB selected and received in step S504 is higher than a threshold, and if the reception quality of the received SSB is higher than a threshold, it may proceed to the subsequent processing.

[0142] In step S507, the aviation UE 100 selects an RA resource (RA occasion) associated with the upper-air coverage SSB selected and received in step S505.

[0143] In step S508, the aviation UE 100 sends an RA preamble to the gNB 200 using the RA resource (RA occasion) selected in step S507. The gNB 200 receives the RA preamble. Subsequently, the aviation UE 100 may transition to the RRC connected state by a random access procedure.

[0144] (5.2.2) Second Operation Pattern of Random Access Operation by Aircraft User Device The second operation pattern of random access operation according to this embodiment will be explained mainly in terms of the differences from the second operation pattern of cell reselection operation described above.

[0145] In the second operation pattern of random access operation, the SSB-related information broadcast from gNB200 in step S21 is identification information (upper air coverage identification information) indicating that it is for upper air coverage. The upper air coverage identification information is included in the upper air coverage SSB. An air UE100 in an RRC idle or RRC inactive state selects an SSB that includes the upper air coverage identification information in its MIB as the upper air coverage SSB (step S22). The configuration of the upper air coverage identification information (MIB) is the same as in the first operation pattern of cell re-selection operation described above.

[0146] Figure 21 shows an example of the operation of the mobile communication system 1 related to the second operation pattern of random access operation. The aviation UE 100 is assumed to be in an RRC idle state or RRC inactive state in the gNB 200 cell. Repeated explanations of operations similar to those described above will be omitted.

[0147] In step S601, the aviation UE100 decides to initiate the RA procedure.

[0148] In step S602, the aircraft UE 100 may determine whether or not it is in flight (i.e., in flight). If the aircraft UE 100 determines that it is in flight (step S602: YES), it may proceed to the subsequent processing.

[0149] In step S603, the gNB200 transmits the airborne coverage identification information to the MIB included in each SSB for airborne coverage. The gNB200 does not need to include the airborne coverage identification information in the MIB included in each SSB for ground coverage.

[0150] In step S604, the aviation UE 100, which received the SSB in step S602, determines whether the received SSB contains airspace coverage identification information. If the airspace coverage identification information is multi-bit information, the aviation UE 100 determines whether its own altitude is included in the altitude range indicated by the airspace coverage identification information included in the received SSB, and may proceed to the subsequent processing if it determines that its own altitude is included.

[0151] In step S605, the aviation UE 100 may determine whether the reception quality of the SSB selected and received in step S603 is higher than a threshold, and if the reception quality of the received SSB is higher than a threshold, it may proceed to the subsequent processing.

[0152] In step S606, the aviation UE 100 selects an RA resource (RA occasion) associated with the upper-air coverage SSB selected and received in step S603.

[0153] In step S607, the aviation UE 100 sends an RA preamble to the gNB 200 using the RA resource (RA occasion) selected in step S606. The gNB 200 receives the RA preamble. Subsequently, the aviation UE 100 may transition to the RRC connected state by a random access procedure.

[0154] (6) Other Embodiments The operation according to the above embodiment may be applied to a normal UE 100 that is not an aerial UE 100. That is, the operation according to the above embodiment is not limited to an aerial UE 100, but may be applied to a normal UE 100.

[0155] The above-described operation flows can be performed not only independently, but also in combination of two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow. It is not necessary to execute all steps in each flow; only some steps may be executed. Furthermore, the order of steps in each flow may be changed as appropriate.

[0156] In the embodiments and examples described above, an example in which the base station is an NR base station (gNB) was described, but the base station may also be an LTE base station (eNB) or a 6G base station. Furthermore, the base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of an IAB node. Furthermore, UE100 may be an MT (Mobile Termination) of an IAB node. That is, UE100 may be a terminal function unit (a type of communication module) for the base station to control a relay device that performs signal relay. Such a terminal function unit is referred to as an MT. Examples of multi-transmission architectures (MTs) include IAB-MT, NCR (Network Controlled Repeater)-MT, and RIS (Reconfigurable Intelligent Surface)-MT.

[0157] Furthermore, the term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). Additionally, a network node may consist of a combination of at least a part of the core network device and at least a part of a base station.

[0158] A program may be provided that causes a computer to execute each process performed by the UE100 or gNB200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM and / or DVD-ROM. Alternatively, the circuits that execute each process performed by the UE100 or gNB200 may be integrated, and at least a part of the UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip).

[0159] The functions realized by UE100 or gNB200 may be implemented in a circuit or processing circuit, including a general-purpose processor, application processor, integrated circuit, ASICs (Application Specific Integrated Circuits), CPU (a Central Processing Unit), conventional circuitry, and / or a combination thereof, programmed to realize the described functions. A processor, including transistors and / or other circuitry, is considered a circuit or processing circuit. A processor may be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, and means are hardware programmed to realize or execute the described functions. The hardware may be any hardware disclosed herein, or any hardware known to be programmed to perform or execute the functions described herein. If the hardware is a processor that is considered to be of the type of circuit, the circuit, means, or unit is a combination of hardware and software used to constitute the hardware and / or processor.

[0160] The phrases “based on” and “depending on / in response to” as used in this disclosure do not mean “based solely on” or “in response solely” unless otherwise specified. “Based on” means both “based solely on” and “at least partially on.” Similarly, “depending” means both “at least partially on” and “at least partially on.” The terms “include,” “comprise,” and variations thereof do not mean that they include only the listed items, but may include only the listed items or may include additional items in addition to the listed items. Furthermore, the term “or” as used in this disclosure is not intended to mean exclusive OR. Additionally, any reference to elements using designations such as “first,” “second,” etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient way to distinguish between two or more elements. Therefore, references to the first and second elements do not imply that only two elements may be adopted therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated from the context that they are not.

[0161] Although the embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes can be made without departing from the gist of the invention.

[0162] This application claims priority to Japanese Patent Application No. 2024-172747 (filed on October 1, 2024), the entirety of which is incorporated into the specification of this application.

[0163] (7) Additional notes: Features of the above-described embodiments are noted below.

[0164] - Appendix 1 A communication method to be performed by an aerial user device in a mobile communication system, comprising: receiving cell reselection-related information broadcast from a network node and used exclusively by the aerial user device; and, in a radio resource control (RRC) idle state or RRC inactive state, performing a cell reselection operation that prioritizes cells that provide airspace coverage based on the cell reselection-related information.

[0165] - Appendix 2 The communication method described in Appendix 1, wherein the broadcast cell reselection-related information includes altitude-based measurement SSB information, which includes information indicating a synchronization signal block (SSB) pattern for each altitude range.

[0166] - Appendix 3 The communication method described in Appendix 2, wherein the aircraft user device identifies the SSB pattern associated with the altitude range to which the altitude of the aircraft user device belongs, based on the altitude-based measurement SSB information, and performs the cell reselection operation based on the identified SSB pattern.

[0167] - Appendix 4 The communication method according to any one of Appendix 1 to 3, wherein the broadcast cell reselection-related information is included in the synchronization signal block (SSB) for air coverage, and the SSB includes identification information indicating that it is for air coverage.

[0168] - Appendix 5 The communication method according to any one of Appendix 1 to 4, wherein the aerial user device receives the cell reselection-related information from the serving cell, and the broadcasted cell reselection-related information includes information relating to the synchronization signal block (SSB) for air coverage in the non-serving cell.

[0169] - Appendix 6 The cell reselection-related information is a communication method according to any one of the appendices 1 to 5, which includes altitude-based priority information that includes information indicating the frequency priority or cell priority in cell reselection for each altitude range.

[0170] - Appendix 7 The communication method described in Appendix 6, wherein the aircraft user device identifies the priority associated with the altitude range to which the altitude of the aircraft user device belongs, based on the altitude-based priority information, and performs the cell reselection operation based on the identified priority.

[0171] - Appendix 8 An aerial user device for use in a mobile communication system, comprising: a receiving unit that receives cell reselection-related information broadcast from a network node and used exclusively for the aerial user device; and a control unit that, in a radio resource control (RRC) idle state or RRC inactive state, performs a cell reselection operation that prioritizes cells that provide airspace coverage based on the cell reselection-related information.

[0172] - Appendix 9 A network node used in a mobile communication system, having a transmitting unit that broadcasts cell reselection-related information exclusively for use with an aerial user device, wherein the cell reselection-related information is information used by the aerial user device in a radio resource control (RRC) idle state or RRC inactive state to perform a cell reselection operation that prioritizes cells that provide airborne coverage.

[0173] 1: Mobile communication system 5: Network 10: RAN 20: CN 100: UE (Aeronautical UE) 110: Receiving unit 120: Transmitting unit 130: Control unit 140: Wireless communication unit 200: gNB 210: Transmitting unit 220: Receiving unit 230: Control unit 240: Network communication unit 241: Transmitting unit 242: Receiving unit 250: Wireless communication unit 300: AMF / UPF

Claims

1. A communication method performed by an aerial user device in a mobile communication system, comprising: receiving cell reselection-related information broadcast from a network node and used exclusively by the aerial user device; and, in a radio resource control (RRC) idle state or RRC inactive state, performing a cell reselection operation that prioritizes cells providing airspace coverage based on the cell reselection-related information.

2. The communication method according to claim 1, wherein the broadcast cell reselection-related information includes altitude-based measurement SSB information, which includes information indicating a synchronization signal block (SSB) pattern for each altitude range.

3. The communication method according to claim 2, wherein the aircraft user device identifies the SSB pattern associated with the altitude range to which the altitude of the aircraft user device belongs, based on the altitude-based measurement SSB information, and performs the cell reselection operation based on the identified SSB pattern.

4. The communication method according to claim 1, wherein the broadcast cell reselection-related information is included in a synchronization signal block (SSB) for air coverage, and includes identification information indicating that the SSB is for air coverage.

5. The communication method according to claim 1, wherein the aerial user device receives the cell reselection-related information from the serving cell, and the broadcasted cell reselection-related information includes information relating to a synchronous signal block (SSB) for airspace coverage in a non-serving cell.

6. The communication method according to claim 1, wherein the cell reselection-related information includes altitude-based priority information that includes information indicating frequency priority or cell priority in cell reselection for each altitude range.

7. The communication method according to claim 6, wherein the aircraft user device identifies the priority associated with the altitude range to which the altitude of the aircraft user device belongs, based on the altitude-based priority information, and performs the cell reselection operation based on the identified priority.

8. Air user device for use in a mobile communication system, comprising: a receiving unit that receives cell reselection-related information broadcast from a network node and used exclusively for the air user device; and a control unit that, in a radio resource control (RRC) idle state or RRC inactive state, performs a cell reselection operation that prioritizes cells that provide airspace coverage based on the cell reselection-related information.

9. A network node used in a mobile communication system, having a transmitting unit that broadcasts cell reselection-related information exclusively for use with an aerial user device, wherein the cell reselection-related information is information used by the aerial user device in a radio resource control (RRC) idle state or RRC inactive state to perform a cell reselection operation that prioritizes cells that provide airborne coverage.

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