COMMUNICATION CONTROL METHOD, USER EQUIPMENT, CORE NETWORK NODE, AND ACCESS NETWORK NODE

Abstract

A communication control method according to one aspect is for a mobile communication system. The communication control method comprises a step for transmitting, to a base station, slice priority reception presence / absence information indicative of whether or not a user equipment has received, from a core network device, slice priority information indicative of the priority of a network slice.

Description

Communication Control Method

[0001] The present disclosure relates to a communication control method in a mobile communication system.

[0002] Network slicing is defined in the specifications of the Third Generation Partnership Project (3GPP), a standardization project for mobile communication systems. Network slicing is a technology that creates virtual networks, called network slices, by logically dividing a physical network built by a telecommunications carrier.

[0003] A user equipment in a radio resource control (RRC) idle state or an RRC inactive state can perform a cell reselection procedure. 3GPP is considering a network slice-dependent cell reselection procedure called slice specific cell reselection (also called slice aware cell reselection or slice based cell reselection) (see, for example, Non-Patent Document 1). By performing the slice specific cell reselection procedure, the user equipment can, for example, camp on a neighboring cell that supports a desired network slice.

[0004] 3GPP TS 38.300 V17.8.0 (2022-3)

[0005] According to one aspect, a communication control method is provided in a mobile communication system, the communication control method including a step of transmitting, to a base station, slice priority reception status information indicating whether slice priority information indicating a priority of a network slice has been received from a core network device by a user equipment.

[0006] According to another aspect, there is provided a communication control method in a mobile communication system, the communication control method including a step of transmitting, to a base station, slice priority transmission information indicating whether slice priority information indicating a priority of a network slice has been transmitted to a user device by a core network device.

[0007] Furthermore, a communication control method according to one aspect is a communication control method in a mobile communication system, the communication control method including a step of transmitting, by a base station, to a user equipment, an RRC release message including legacy frequency priority information representing a priority for each frequency, regardless of whether the user equipment has received slice priority information representing a priority of a network slice from a core network device.

[0008] Furthermore, a communication control method according to one aspect is a communication control method in a mobile communication system, the communication control method including a step of, when a user equipment does not receive slice priority information indicating a priority of a network slice from a core network device, transmitting an RRC message including information indicating that the slice priority information has not been received to a base station.

[0009] FIG. 1 is a diagram illustrating an example of the configuration of a mobile communication system according to the first embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a UE (user equipment) according to the first embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a gNB (base station) according to the first embodiment. FIG. 4 is a diagram illustrating an example of the configuration of a protocol stack related to a user plane according to the first embodiment. FIG. 5 is a diagram illustrating an example of the configuration of a protocol stack related to a control plane according to the first embodiment. FIG. 6 is a diagram for explaining an overview of a cell reselection procedure. FIG. 7 is a diagram illustrating a schematic flow of a general cell reselection procedure. FIG. 8 is a diagram illustrating an example of network slicing. FIG. 9 is a diagram illustrating an overview of a slice-specific cell reselection procedure. FIG. 10 is a diagram illustrating an example of slice frequency information. FIG. 11 is a diagram illustrating a basic flow of a slice-specific cell reselection procedure. FIG. 12 is a diagram illustrating an example of an operation according to the first embodiment. FIG. 13 is a diagram illustrating an example of an operation according to the second embodiment. FIG. 14 is a diagram illustrating an example of an operation according to the third embodiment. FIG. 15 is a diagram illustrating an example of an operation according to the fourth embodiment. FIG. 16 is a diagram illustrating a mismatch in signaling between an AMF and a gNB.

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] [First embodiment]

[0012] (Configuration of mobile communication system) Fig. 1 is a diagram showing the configuration of a mobile communication system according to the first embodiment. The mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. Although the following description will be given using 5GS as an example, the mobile communication system may be at least partially applied to an LTE (Long Term Evolution) system or at least partially applied to a 6th Generation (6G) system.

[0013] The mobile communication system 1 includes 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, the NG-RAN 10 may be simply referred to as the RAN 10. Furthermore, the 5GC 20 may be simply referred to as the core network (CN) 20.

[0014] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0015] The NG-RAN 10 includes a base station (called a "gNB" in a 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource for wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0016] In addition, the gNB200 can be connected to the Evolved Packet Core (EPC), which is the core network of LTE. The LTE base station can also be connected to the 5GC20. The LTE base station and the gNB200 can also be connected via an inter-base station interface.

[0017] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0018] 2 is a diagram showing the configuration of the UE 100 (user equipment) according to the first embodiment. The UE 100 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 that performs wireless communication with the gNB 200.

[0019] 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 a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0020] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0021] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. 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 the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 130 may perform each process or operation in the UE 100 in each of the embodiments described below.

[0022] 3 is a diagram showing the configuration of a gNB 200 (base station) according to the first embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0023] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0024] 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 a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0025] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer described below. 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 in the processes by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 230 may perform each process or operation in the gNB 200 in each of the embodiments described below.

[0026] The backhaul communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected by an F1 interface, which is a fronthaul interface.

[0027] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0028] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0029] 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 a 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 DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC parity bit scrambled by the RNTI added.

[0030] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the gNB 200 via a transport channel. The MAC layer of the gNB 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE 100.

[0031] 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 the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0032] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0033] The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0034] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0035] The protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) instead of the SDAP layer shown in FIG.

[0036] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0037] The NAS, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS of the UE 100 and the NAS of the AMF 300. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, the layer below the NAS is called an Access Stratum (AS).

[0038] (Outline of Cell Reselection Procedure) FIG. 6 is a diagram for explaining an outline of a cell reselection procedure.

[0039] A UE 100 in an RRC idle state or an RRC inactive state performs a cell reselection procedure to transition from a current serving cell (cell #1) to a neighboring cell (any of cells #2 to #4) as it moves. Specifically, the UE 100 identifies a neighboring cell on which it should camp by the cell reselection procedure and reselects the identified neighboring cell. When the frequency (carrier frequency) of the current serving cell and the neighboring cell is the same, this is called an intra-frequency, and when the frequency (carrier frequency) of the current serving cell and the neighboring cell is different, this is called an inter-frequency. The current serving cell and the neighboring cell may be managed by the same gNB 200 or may be managed by different gNBs 200.

[0040] FIG. 7 is a diagram illustrating the general flow of a typical (or legacy) cell reselection procedure.

[0041] In step S11, the UE 100 performs frequency prioritization processing based on the priority (also referred to as "absolute priority") for each frequency specified by the gNB 200, for example, via an RRC release message. Specifically, the UE 100 manages the frequency priority specified by the gNB 200 for each frequency.

[0042] In step S12, the UE 100 performs a measurement process to measure the radio quality of each of the serving cell and the neighboring cell. The UE 100 measures the received power and received quality of reference signals transmitted by each of the serving cell and the neighboring cell, specifically, CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, the UE 100 always measures the radio quality for a frequency having a higher priority than the frequency priority of the current serving cell, and for a frequency having a priority equal to or lower than the frequency priority of the current serving cell, when the radio quality of the current serving cell falls below a predetermined quality, measures the radio quality of the frequency having the same priority or lower priority.

[0043] In step S13, the UE 100 performs a cell reselection process to reselect a cell on which the UE 100 will camp based on the measurement result in step S12. For example, if the frequency priority of a neighboring cell is higher than the priority of the current serving cell and the neighboring cell satisfies a predetermined quality standard (i.e., a minimum required quality standard) for a predetermined period, the UE 100 may perform cell reselection to the neighboring cell. If the frequency priority of the neighboring cell is the same as the priority of the current serving cell, the UE 100 may rank the radio qualities of the neighboring cells and perform cell reselection to a neighboring cell having a higher rank than the rank of the current serving cell for a predetermined period. If the frequency priority of the neighboring cell is lower than the priority of the current serving cell and the radio quality of the current serving cell is lower than a certain threshold and the radio quality of the neighboring cell is higher than another threshold, the UE 100 may perform cell reselection to the neighboring cell.

[0044] (Outline of Network Slicing) Network slicing is a technology for creating multiple virtual networks by virtually dividing a physical network (for example, a network consisting of an NG-RAN 10 and a 5GC 20) constructed by a carrier. Each virtual network is called a network slice. Hereinafter, a network slice may be simply referred to as a "slice."

[0045] Network slicing allows telecommunications operators to create slices according to the service requirements of different service types, such as eMBB (enhanced Mobile Broadband), URLLC (Ultra-Reliable and Low Latency Communications), and mMTC (massive Machine Type Communications), thereby optimizing network resources.

[0046] FIG. 8 is a diagram illustrating an example of network slicing.

[0047] Three slices (slice #1 to slice #3) are configured on a network 50 configured with an NG-RAN 10 and a 5GC 20. Slice #1 is associated with a service type called eMBB, slice #2 is associated with a service type called URLLC, and slice #3 is associated with a service type called mMTC. Note that three or more slices may be configured on the network 50. One service type may be associated with multiple slices.

[0048] Each slice is provided with a slice identifier that identifies the slice. An example of a slice identifier is S-NSSAI (Single Network Slicing Selection Assistance Information). The S-NSSAI includes an 8-bit SST (slice / service type). The S-NSSAI may further include a 24-bit SD (slice differentiator). The SST is information indicating the service type to which the slice is associated. The SD is information for differentiating multiple slices associated with the same service type. Information including multiple S-NSSAIs is called NSSAI (Network Slice Selection Assistance Information).

[0049] Furthermore, one or more slices may be grouped to form a slice group. A slice group is a group including one or more slices, and a slice group identifier is assigned to the slice group. The slice group may be configured by a core network (e.g., the AMF 300) or a radio access network (e.g., the gNB 200). The configured slice group may be notified to the UE 100.

[0050] Hereinafter, the term "network slice (slice)" may refer to an S-NSSAI, which is an identifier of a single slice, or an NSSAI, which is a collection of S-NSSAIs. The term "network slice (slice)" may refer to a slice group, which is a group of one or more S-NSSAIs or NSSAIs. A slice group may be represented by an NSSAI. The slice group may be represented by an NSAG (Network Slice Access Stratum Group).

[0051] Furthermore, UE100 determines a desired slice that it desires to use. The desired slice may be called an "intended slice." In the first embodiment, UE100 determines a slice priority for each network slice (desired slice). For example, the NAS of UE100 determines the slice priority based on the operation status of an application in UE100 and / or user operation / settings, and notifies the AS of slice priority information indicating the determined slice priority. Note that the NAS of UE100 receives the slice priority information from AMF300. That is, AMF300 determines the slice priority for each slice. AMF300 transmits slice priority information indicating the slice priority to the NAS of UE100. The NAS of UE100 may determine the slice priority based on the slice priority information received from AMF300.

[0052] (Overview of Slice-Specific Cell Reselection Procedure) FIG. 9 is a diagram illustrating an overview of a slice-specific cell reselection (also referred to as slice-aware cell reselection or slice-based cell reselection) procedure.

[0053] In the slice-specific cell reselection procedure, the UE 100 performs a cell reselection process based on slice frequency information provided by the network 50. The slice frequency information may be provided to the UE 100 by dedicated signaling (e.g., an RRC release message) from the gNB 200.

[0054] The slice frequency information indicates the correspondence between network slices, frequencies, and frequency priorities. For example, for each slice (or slice group), the slice frequency information indicates the frequency (one or more frequencies) that supports the slice and the frequency priority assigned to each frequency. An example of the slice frequency information is shown in FIG. 10 .

[0055] In the example shown in Fig. 10 , three frequencies F1, F2, and F4 are associated with slice #1 as frequencies supporting slice #1. Of these three frequencies, F1 has a frequency priority of "6," F2 has a frequency priority of "4," and F4 has a frequency priority of "2." In the example of Fig. 10 , the larger the frequency priority number, the higher the priority; however, it may also be the case that the smaller the number, the higher the priority.

[0056] Furthermore, three frequencies F1, F2, and F3 are associated with slice #2 as frequencies supporting slice #2. Of these three frequencies, F1 has a frequency priority of "0," F2 has a frequency priority of "5," and F3 has a frequency priority of "7."

[0057] Furthermore, three frequencies, F1, F3, and F4, are associated with slice #3 as frequencies supporting slice #3. Of these three frequencies, F1 has a frequency priority of "3," F3 has a frequency priority of "7," and F4 has a frequency priority of "2."

[0058] Hereinafter, the frequency priority indicated in the slice frequency information may be referred to as a "slice-specific frequency priority" to distinguish it from the absolute priority in the conventional cell reselection procedure.

[0059] As shown in FIG. 9, the UE 100 may perform a cell reselection process based on slice support information provided by the network 50. The slice support information may be information indicating a correspondence between a cell (e.g., a serving cell and each neighboring cell) and a network slice that the cell does not provide or provides. For example, a cell may temporarily not provide some or all network slices due to congestion or other reasons. That is, even if a slice support frequency has the ability to provide a certain network slice, some cells within the frequency may not provide the network slice. The UE 100 can identify the network slices that each cell does not provide based on the slice support information. Such slice support information may be provided to the UE 100 by broadcast signaling (e.g., a system information block) or dedicated signaling (e.g., an RRC release message) from the gNB 200.

[0060] 11 is a diagram showing a basic flow of a slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, the UE 100 is in an RRC idle state or an RRC inactive state, and has received and stored the above-mentioned slice frequency information. Note that the procedure of "slice-specific cell reselection" is represented as a "slice-specific cell reselection procedure." However, hereinafter, "slice-specific cell reselection" and "slice-specific cell reselection procedure" may be used interchangeably.

[0061] In step S0, the NAS of UE 100 determines slice identifiers of desired slices of UE 100 and slice priorities of each desired slice, and notifies the AS of UE 100 of slice priority information including the determined slice priorities. A "desired slice" is an "intended slice" and includes a slice that is likely to be used, a candidate slice, a desired slice, a slice to be communicated, a requested slice, an allowed slice, or an intended slice. For example, the slice priority of slice #1 is determined to be "3," the slice priority of slice #2 is determined to be "2," and the slice priority of slice #3 is determined to be "1." A larger number for the slice priority indicates a higher priority, but a smaller number may also indicate a higher priority.

[0062] In step S1, the AS of the UE 100 sorts the slices (slice identifiers) notified from the NAS in step S0 in descending order of slice priority. The list of slices sorted in this manner is called a "slice list."

[0063] In step S2, the AS of the UE 100 selects one network slice in descending order of slice priority. The network slice selected in this manner is called a "selected network slice."

[0064] In step S3, the AS of UE100 assigns frequency priorities to each frequency associated with the selected network slice. Specifically, the AS of UE100 identifies a frequency associated with the slice based on slice frequency information, and assigns frequency priorities to the identified frequency. For example, if the selected network slice selected in step S2 is slice #1, the AS of UE100 assigns frequency priority "6" to frequency F1, frequency priority "4" to frequency F2, and frequency priority "2" to frequency F4 based on slice frequency information (e.g., the information of FIG. 10). The AS of UE100 calls the list of frequencies arranged in descending order of frequency priority a "frequency list."

[0065] In step S4, the AS of UE 100 selects one frequency in descending order of frequency priority for the selected network slice selected in step S2, and performs measurement processing on the selected frequency. The frequency selected in this manner is called a "selected frequency." The AS of UE 100 may rank each cell measured within the selected frequency in descending order of radio quality. Among the cells measured within the selected frequency, a cell that satisfies a predetermined quality standard (i.e., a required minimum quality standard) is called a "candidate cell."

[0066] In step S5, the AS of UE100 identifies the highest-ranked cell based on the result of the measurement process in step S4, and determines whether the cell provides the selected network slice based on the slice support information. If it is determined that the highest-ranked cell provides the selected network slice (step S5: YES), in step S5a, the AS of UE100 reselects the highest-ranked cell and camps on the cell.

[0067] On the other hand, if it is determined that the highest-ranked cell does not provide the selected network slice (step S5: NO), in step S6, the AS of UE100 determines whether there are any unmeasured frequencies in the frequency list created in step S3. In other words, the AS of UE100 determines whether there are any frequencies assigned in step S3 other than the selected frequency in the selected network slice. If it is determined that there are any unmeasured frequencies (step S6: YES), the AS of UE100 resumes processing on the frequency with the next highest frequency priority and performs measurement processing with that frequency as the selected frequency (returning to step S4).

[0068] If it is determined that there are no unmeasured frequencies in the frequency list created in step S3 (step S6: NO), in step S7, the AS of UE100 may determine whether or not there are any unselected slices in the slice list created in step S1. In other words, the AS of UE100 may determine whether or not there are any network slices other than the selected network slice in the slice list. If it is determined that there are any unselected slices (step S7: YES), the AS of UE100 resumes processing on the network slice with the next highest slice priority and selects that network slice as the selected network slice (returns processing to step S2). Note that in the basic flow shown in FIG. 11, the processing of step S7 may be omitted.

[0069] If it is determined that there is no unselected slice (step S7: NO), in step S8, the AS of the UE 100 performs a conventional cell reselection process. The conventional cell reselection process may mean the entire general (or legacy) cell reselection procedure shown in Fig. 7. The conventional cell reselection process may mean only the cell reselection process (step S13) shown in Fig. 7. In the latter case, the UE 100 may use the measurement result in step S4 without measuring the radio quality of the cell again.

[0070] (Communication control method according to the first embodiment) In 3GPP, the following specifications and agreements exist regarding the frequency priority used in the legacy cell reselection procedure (Figure 7) (hereinafter referred to as "legacy frequency priority") and the frequency priority used in the slice-specific cell reselection procedure (Figure 11) (hereinafter referred to as "slice-specific frequency priority").

[0071] (1) The RRC Release message may include legacy frequency priority and / or slice-specific frequency priority.

[0072] (2) If any frequency priority is included in the RRC release message, UE 100 ignores all frequency priorities (legacy frequency priorities and / or slice-specific frequency priorities) received in the system information (SIB).

[0073] (3) If UE100 does not receive slice priority from AMF300, it cannot perform a slice-specific cell reselection procedure.

[0074] For example, assume that UE100 receives an RRC release message from gNB200 that does not include legacy frequency priority but includes slice-specific frequency priority, and does not receive slice priority from AMF300. In such a case, UE100 receives slice frequency priority from gNB200, but does not receive slice priority from AMF300. Therefore, UE100 cannot perform the slice-specific cell reselection procedure according to (3) above.

[0075] Thus, although there are specifications and agreements according to (1) to (3) above, cases such as those described above exist, and therefore UE 100 may not be able to properly perform the cell reselection procedure.

[0076] Therefore, the first embodiment aims to enable the UE 100 to appropriately execute the cell reselection procedure.

[0077] In the following, a cell reselection procedure that does not use a network slice may be referred to as a "legacy cell reselection procedure." Figure 7 shows an example of a legacy cell reselection procedure. On the other hand, a cell reselection procedure that uses a network slice may be referred to as a "slice-specific cell reselection procedure." Figure 11 shows an example of a slice-specific cell reselection procedure. When there is no particular distinction between the legacy cell reselection procedure and the slice-specific cell reselection procedure, they may simply be referred to as a "cell reselection procedure."

[0078] In the following, the priority for each frequency used in the legacy cell reselection procedure (which may be referred to as "absolute priority") may be referred to as "legacy frequency priority" as described above. "Legacy frequency priority information" representing the legacy frequency priority is included in an RRC release message and / or an SIB and transmitted from the gNB 200 to the UE 100.

[0079] On the other hand, the priority for each network slice may be referred to as "slice priority" as described above. The slice priority is used in a slice-specific cell reselection procedure. "Slice priority information" representing the slice priority is included in a NAS message and transmitted from the AMF 300 to the UE 100.

[0080] Furthermore, the priority for each frequency supporting a network slice may be referred to as a "slice-specific frequency priority" as described above. The slice-specific frequency priority is also used in the slice-specific cell reselection procedure. "Slice-specific frequency priority information" representing the slice-specific frequency priority is included in an RRC release message and / or an SIB and transmitted from the gNB200 to the UE100. Note that the slice-specific frequency priority information may include the slice frequency information described above. Alternatively, the slice-specific frequency priority information may be slice frequency information.

[0081] When there is no particular distinction between legacy frequency priority and slice-specific frequency priority, they may simply be referred to as "frequency priority."

[0082] Furthermore, as described above, a slice may refer to a single slice, a slice group consisting of multiple slices, or multiple slice groups. A slice group may be represented by an NSAG.

[0083] In the first embodiment, the UE 100 transmits to the gNB 200 information indicating whether slice priority information has been received from the AMF 300. The information indicating whether slice priority information has been received from the AMF 300 may be referred to as "slice priority reception presence / absence information" hereinafter.

[0084] Specifically, a user device (e.g., UE100) transmits slice priority reception / non-reception information indicating whether slice priority information representing the priority of a network slice has been received from a core network device (e.g., AMF300) to a base station (e.g., gNB200).

[0085] As a result, for example, the gNB 200 can determine whether the UE 100 has received slice priority information based on the slice priority reception presence / absence information. When the gNB 200 determines that the UE 100 has not received the slice priority information, it can transmit an RRC release message including legacy frequency priority information without including slice-specific frequency priority. Therefore, the gNB 200 can avoid a situation in which the UE 100 transmits an RRC release message including slice-specific frequency priority information without including legacy frequency priority information to the UE 100 even though the UE 100 has not received the slice priority information. Furthermore, when the gNB 200 determines that the UE 100 has received slice priority information, it can transmit an RRC release message including slice-specific frequency priority information without including legacy frequency priority information. In this case, the UE 100 can perform a slice-specific cell reselection procedure using the slice priority information and the slice-specific frequency priority information.

[0086] Therefore, the UE 100 can appropriately perform the cell reselection procedure according to the frequency priority information (slice-specific frequency priority information or legacy frequency priority information) included in the RRC release message.

[0087] (Example of Operation According to First Embodiment) Next, an example of operation according to the first embodiment will be described.

[0088] FIG. 12 is a diagram illustrating an example of operation according to the first embodiment.

[0089] 12, in step S30, AMF 300 transmits a NAS message including slice priority information to UE 100. Alternatively, AMF 300 may not transmit a NAS message including slice priority information to UE 100. In the first embodiment, AMF 300 may or may not transmit slice priority information.

[0090] The slice priority information includes a priority for each slice for which a slice priority has been set. The slice priority information may include a slice number (or a slice group number) of the slice for which a slice priority has been set. Alternatively, the slice priority information may include the slice number and the priority of the slice.

[0091] In step S31, the gNB 200 may inquire of the UE 100 whether or not it has received slice priority information. Specifically, the gNB 200 may transmit an RRC message, a MAC Control Element (MAC CE), or Downlink Control Information (DCI) including information inquiring whether the UE 100 has received the slice priority information. The gNB 200 may make an inquiry to the UE 100 that has set (or transmitted) a slice-specific frequency priority without setting (or transmitting) a legacy frequency priority. The gNB 200 does not need to make an inquiry to the UE 100 that has set both the legacy frequency priority and the slice-specific frequency priority. This is because the UE 100 can perform a legacy cell reselection procedure based on the legacy frequency priority. Alternatively, gNB200 may make an inquiry to UE100 that has set (or transmitted) a slice-specific frequency priority only at the timing when it attempts to set (or transmit) a slice-specific frequency priority without setting (or transmitting) a legacy frequency priority.

[0092] In step S32, the UE 100 transmits to the gNB 200 slice priority reception presence / absence information indicating whether slice priority information has been received from the AMF 300. The UE 100 may transmit the slice priority reception presence / absence information to the gNB 200 in response to the inquiry in step S31. Alternatively, the UE 100 may transmit the slice priority reception presence / absence information to the gNB 200 without receiving the inquiry in step S31. The AS of the UE 100 may transmit the slice priority reception presence / absence information to the gNB 200 when the NAS of the UE 100 has received (notification of) a slice priority setting, (notification of) a slice priority setting change, or (notification of) a slice priority setting cancellation. The UE 100 may transmit an RRC message including the slice priority reception presence / absence information to the gNB 200.

[0093] First, the slice priority reception information may include the slice number of the slice for which the slice priority is set. The slice number may be a slice group number. There may be one slice number or multiple slice numbers. Alternatively, instead of the slice priority reception information, the slice number may be transmitted from the UE100 to the gNB200. In this case, the slice number may be included in the RRC message. The gNB200 may determine whether the UE100 has received the slice priority based on whether the slice number has been received. That is, if the gNB200 has received the slice number, it may determine that the UE100 has received the slice priority, and if the gNB200 has not received the slice number, it may determine that the UE100 has not received the slice priority.

[0094] Second, the slice priority reception information may include the slice number of the slice for which the slice priority is set and the slice priority. The slice number may be a slice group number. There may be one slice number and one slice priority, or there may be multiple slice numbers and slice priorities. Alternatively, instead of the slice priority reception information, the slice number and the slice priority may be transmitted from the UE100 to the gNB200. In this case, the slice number and the slice priority may be included in an RRC message. The gNB200 may determine whether the UE100 has received the slice priority based on whether the slice number and the slice priority have been received. That is, if the gNB200 has received the slice number and the slice priority, it may determine that the UE100 has received the slice priority. If the gNB200 has not received the slice number and the slice priority, it may determine that the UE100 has not received the slice priority.

[0095] In step S33, the gNB200 checks whether the UE100 has received the slice priority based on the slice priority reception information. In step S33, if the gNB200 checks that the UE100 has received the slice priority (YES in step S33), the process proceeds to step S34. On the other hand, in step S33, if the gNB200 checks that the UE100 has not received the slice priority (NO in step S33), the process proceeds to step S35.

[0096] In step S34, the gNB 200 transmits an RRC release message including slice-specific frequency priority information to the UE 100. Specifically, the gNB 200 may transmit an RRC release message including slice-specific frequency priority information without including legacy frequency priority information. The gNB 200 may transmit an RRC release message including both legacy frequency priority information and slice-specific frequency priority information.

[0097] On the other hand, in step S35, the gNB 200 transmits an RRC release message including legacy frequency priority information to the UE 100. Specifically, the gNB 200 may transmit an RRC release message including legacy frequency priority information without including slice-specific frequency priority information. The gNB 200 may transmit an RRC release message including both legacy frequency priority information and slice-specific frequency priority information.

[0098] Through steps S34 and S35, gNB200 transmits an RRC release message to UE100 including either legacy frequency priority information or slice-specific frequency priority information based on the slice priority transmission information.

[0099] In step S36, if the RRC release message includes slice-specific frequency priority information, the UE 100 performs a slice-specific cell reselection procedure using the slice-specific frequency priority information. Alternatively, if the RRC release message includes legacy frequency priority information, the UE 100 performs a legacy cell reselection procedure using the legacy frequency priority information.

[0100] Second Embodiment Next, a second embodiment will be described, focusing on the differences from the first embodiment.

[0101] In the second embodiment, an example will be described in which the AMF 300 transmits to the gNB 200 information indicating whether the AMF 300 has transmitted slice priority information to the UE 100. In the first embodiment, the UE 100 transmitted slice priority reception presence / absence information to the gNB 200, but in the second embodiment, an example is shown in which the AMF 300 transmits information indicating whether the slice priority information has been transmitted to the gNB 200. Information indicating whether the slice priority information has been transmitted may be referred to as "slice priority transmission presence / absence information." The slice priority transmission presence / absence information may be information indicating whether the AMF 300 has set the slice priority in a NAS message.

[0102] Specifically, a core network device (e.g., AMF 300) transmits slice priority transmission status information indicating whether slice priority information representing the priority of the network slice has been transmitted to a user device (e.g., UE 100) to a base station (e.g., gNB 200).

[0103] As a result, the gNB200 can determine whether the AMF300 has transmitted slice priority information based on the slice priority transmission presence / absence information. When the gNB200 determines that the AMF300 has not transmitted slice priority information, it is possible to transmit an RRC release message including legacy frequency priority to the UE100 without including slice-specific frequency priority. Therefore, the gNB200 can avoid a situation in which an RRC release message including slice-specific frequency priority information is transmitted to the UE100 even though the AMF300 has not transmitted slice priority information.

[0104] Therefore, the UE 100 can properly perform the cell reselection procedure.

[0105] (Example of Operation According to Second Embodiment) Next, an example of operation according to the second embodiment will be described.

[0106] 13 is a diagram illustrating an example of operation according to the second embodiment. Before the operation illustrated in FIG. 13 is started, the AMF 300 may or may not transmit a NAS message including slice priority information to the UE 100.

[0107] In step S40, the AMF 300 transmits slice priority transmission presence / absence information to the gNB 200. Specifically, the AMF 300 transmits an NG message including slice priority transmission presence / absence information to the gNB 200. The AMF 300 may transmit the slice priority transmission presence / absence information to the gNB 200 when the slice priority of the UE 100 is set, when the slice priority setting is changed, or when the slice priority setting is cancelled.

[0108] First, the slice priority transmission presence / absence information may include identification information (ID) of the UE 100 that transmitted the slice priority information. The ID may be an ID of an individual UE. The ID may be an ID of a UE group including the UE 100. There may be one ID. There may be multiple IDs. The ID may be an International Mobile Subscriber Identity (IMSI). The ID may be a value obtained by dividing the IMSI by "1024" (IMSI (mod 1024)). Alternatively, the ID may be a Cell Radio Network Temporary Identifier (C-RNTI). The ID may be a Group Radio Network Temporary Identifier (G-RNTI). The ID may be another Radio Network Temporary Identifier (RNTI). The C-RNTI is an RNTI used for identifying an RRC connection and for individual scheduling for the UE 100. The G-RNTI is an RNTI that represents a group of RNTIs.

[0109] Second, the slice priority transmission information may include the slice number of the slice for which the slice priority is set. The slice number may be a slice group number. There may be one slice number, or there may be multiple slice numbers. Alternatively, instead of the slice priority transmission information, the slice number may be transmitted from the AMF 300 to the gNB 200. In this case, the slice number may be transmitted by being included in an NG message. The gNB 200 may determine whether the AMF 300 has transmitted the slice priority (or whether the UE 100 has received the slice priority) based on whether the slice number has been received. That is, when the gNB 200 receives the slice number, the gNB 200 may determine that the AMF 300 has transmitted the slice priority (or that the UE 100 has received the slice priority), and when the gNB 200 does not receive the slice number, the gNB 200 may determine that the AMF 300 has not transmitted the slice priority (or that the UE 100 has not received the slice priority).

[0110] Third, the slice priority reception information may include the slice number of the slice for which the slice priority is set and the slice priority. The slice number may be a slice group number. There may be one slice number and one slice priority, or there may be multiple slice numbers and slice priorities. Alternatively, instead of the slice priority reception information, the slice number and the slice priority may be transmitted from the AMF 300 to the gNB 200. In this case, the slice number and the slice priority may be transmitted in an NG message. The gNB 200 may determine whether the AMF 300 has transmitted the slice priority (or whether the UE 100 has received the slice priority) based on whether the slice number and the slice priority have been received. That is, if gNB200 receives the slice number and the slice priority, it may determine that AMF300 has transmitted the slice priority (or UE100 has received the slice priority), and if it does not receive the slice number and the slice priority, it may determine that AMF300 has not transmitted the slice priority (or UE100 has not received the slice priority).

[0111] Note that instead of step S40, the gNB 200 may confirm with the AMF 300 whether or not the slice priority has been transmitted (step S41). Specifically, the gNB 200 may transmit to the AMF 300 an NG message including information indicating confirmation of whether or not the slice priority has been transmitted. Note that, with respect to step S41, the gNB 200 may confirm whether or not the slice priority has been transmitted to the AMF 300 only at the timing when the gNB 200 attempts to set a slice-specific frequency priority for the UE 100 without setting a legacy frequency priority. Note that, when the gNB 200 sets both the legacy frequency priority and the slice-specific frequency priority for the UE 100, the gNB 200 does not need to confirm with the AMF 300 whether or not the slice priority has been transmitted. This is because the UE 100 can execute a legacy cell selection procedure using the legacy frequency priority. The NG message may include identification information (ID) of the UE 100 in order to specify the UE 100 to be confirmed. The UE 100 to be confirmed may be a UE 100 for which the gNB 200 has set (or transmitted) a slice-specific frequency priority instead of a legacy frequency priority. The ID may be the ID of an individual UE. The ID may be the ID of a UE group including the individual UE. The ID may be an IMSI, IMSI (mod 1024), C-RNTI, G-RNTI, or NG-AP UE ID, for example.

[0112] Then, the AMF 300 may transmit slice priority transmission presence / absence information in response to confirmation from the gNB 200 (step S42). The slice priority transmission presence / absence information transmitted in step S42 may be the same as the slice priority transmission presence / absence information transmitted in step S40.

[0113] In step S43, gNB200 checks whether AMF300 has transmitted slice priority (or whether UE100 has received slice priority) based on the slice priority transmission presence / absence information. In step S43, if gNB200 checks that AMF has transmitted slice priority, the process proceeds to step S44. On the other hand, in step S43, if gNB200 checks that AMF300 has not transmitted slice priority, the process proceeds to step S45.

[0114] In step S44, the gNB 200 transmits an RRC release message including slice-specific frequency priority information to the UE 100. Specifically, the gNB 200 may transmit an RRC release message including slice-specific frequency priority information without including legacy frequency priority information. The gNB 200 may transmit an RRC release message including both legacy frequency priority information and slice-specific frequency priority information.

[0115] On the other hand, in step S45, the gNB 200 transmits an RRC release message including legacy frequency priority information to the UE 100. Specifically, the gNB 200 may transmit an RRC release message including legacy frequency priority information without including slice-specific frequency priority information. The gNB 200 may transmit an RRC release message including both legacy frequency priority information and slice-specific frequency priority information.

[0116] In this way, based on the slice priority transmission information, gNB200 transmits an RRC release message to UE100 that includes either legacy frequency priority information representing the priority for each frequency or slice-specific frequency priority information representing the priority for each frequency that supports the network slice (steps S44 and S45).

[0117] In step S46, if the RRC release message includes legacy frequency priority information, the UE 100 performs a legacy cell reselection procedure using the legacy frequency priority information. On the other hand, in step S46, if the RRC release message includes slice-specific frequency priority information, the UE 100 performs a slice-specific cell reselection procedure using the slice-specific frequency priority information.

[0118] Third Embodiment Next, a third embodiment will be described, focusing on the differences from the first embodiment.

[0119] In the third embodiment, an example is described in which gNB200 sends an RRC release message including legacy frequency priority to UE100 regardless of whether UE100 has received slice priority information from AMF300.

[0120] Specifically, a base station (e.g., gNB200) sends an RRC release message to a user equipment (e.g., UE100) including legacy frequency priority information representing the priority of each frequency, regardless of whether the user equipment (e.g., UE100) has received slice priority information representing the priority of the network slice from a core network device (e.g., AMF300).

[0121] For example, gNB200 sets legacy frequency priority as the default frequency priority in the RRC release message. Then, when gNB200 confirms that UE100 has received slice priority information, it can optionally set slice-specific frequency priority in the RRC release message.

[0122] This allows gNB200 to avoid a situation in which slice-specific frequency priority is set in the RRC release message when UE100 has not received slice priority information from AMF300. Even if UE100 has not received slice priority information from AMF300, it can perform a legacy cell reselection procedure by using at least the legacy frequency priority information included in the RRC release message. Therefore, UE100 can properly perform the cell reselection procedure.

[0123] (Example of Operation According to Third Embodiment) Next, an example of operation according to the third embodiment will be described.

[0124] FIG. 14 is a diagram illustrating an example of operation according to the third embodiment.

[0125] As shown in FIG. 14 , in step S50, AMF 300 may or may not transmit slice priority information to UE 100.

[0126] In step S51, gNB200 transmits an RRC release message including legacy frequency priority information to UE100, regardless of whether UE100 has received slice priority information. When gNB200 confirms that UE100 has received slice priority information based on either slice priority reception status information received from UE100 or slice priority transmission status information received from AMF300, gNB200 may transmit an RRC release message including legacy frequency priority information and slice-specific frequency priority information.

[0127] In addition, regardless of whether the UE 100 has received slice priority information, when the gNB 200 includes slice-specific frequency priority information in the RRC release message, the gNB 200 always includes legacy frequency priority information in the message and transmits it. In other words, legacy frequency priority information is usually an optional IE (which may or may not be included), but when slice-specific frequency priority information is included, it is a mandatory IE. When slice-specific frequency priority information is included in the message, the legacy frequency priority information becomes conditional mandatory.

[0128] In step S52, UE 100 performs a cell reselection procedure. If UE 100 has not received slice priority information from AMF 300, UE 100 performs a legacy cell reselection procedure using legacy frequency priority information included in the RRC release message. If slice-specific frequency priority information is included in the RRC release message, UE 100 may perform a slice-specific cell reselection procedure using the slice-specific frequency priority information, assuming that slice priority information has been received from AMF 300.

[0129] Fourth Embodiment Next, a fourth embodiment will be described, focusing on the differences from the first embodiment.

[0130] In the fourth embodiment, when UE100 does not receive slice priority information, an example is given in which UE100 uses a UE capability information (UECapabilityInformation) message to notify gNB200 that UE100 did not receive slice priority information.

[0131] Specifically, when a user equipment (e.g., UE100) does not receive slice priority information indicating the priority of a network slice from a core network device (e.g., AMF300), it transmits an RRC message (e.g., UE capability information message) including information indicating that slice priority information was not received to a base station (e.g., gNB200).

[0132] As a result, gNB200 can understand that UE100 has not received slice priority information from AMF300. Therefore, gNB200 can transmit an RRC release message including legacy frequency priority information to UE100 without including slice-specific frequency priority information. UE100 can perform a legacy cell reselection procedure using the legacy frequency priority information. Therefore, UE100 can perform the cell reselection procedure appropriately.

[0133] In the following, information indicating that slice priority information has not been received may be referred to as “no slice priority reception information.” The no slice priority reception information corresponds to, for example, information in the slice priority reception / non-reception information of the first embodiment when slice priority has not been received.

[0134] (Example of Operation According to Fourth Embodiment) Next, an example of operation according to the fourth embodiment will be described.

[0135] FIG. 15 is a diagram illustrating an example of operation according to the fourth embodiment.

[0136] As shown in FIG. 15 , in step S60, AMF 300 may or may not transmit slice priority information to UE 100.

[0137] In step S61, if the UE 100 does not receive slice priority information from the AMF 300, it transmits an RRC message including slice priority non-reception information to the gNB 200. Specifically, the UE 100 may set the UE-NR-Capability, which is an information element included in the UE capability information message, to "non-supported" (for example, "non supported"). For example, the UE 100 sets "sliceInfoforCellReselection" in the UE-NR-Capability to "non-supported". "sliceInfoforCellReselection" is an information element indicating whether the UE 100 supports slice information used in slice-specific cell reselection. Alternatively, the UE capability information message may include a new information element that can be set to indicate that slice priority was not received. The UE 100 may set slice priority reception non-information in the new information element.

[0138] The UE capability information message is an RRC message used by the UE 100 to notify the network of its radio access capability in response to a request (UECapabilityEnquiry) message from the network. UE-NR-Capability is an information element used to transmit parameters indicating the radio access capability of the UE 100.

[0139] In step S62, if gNB200 confirms based on the slice priority no reception information that UE100 has not received slice priority information, it sends an RRC release message including legacy frequency priority information to UE100.

[0140] In step S63, the UE 100 performs a legacy cell reselection procedure by using the legacy frequency priority information.

[0141] (Another Example of the Fourth Embodiment) In the fourth embodiment, an example (step S61) in which slice priority no-reception information is transmitted using a UE capability information message has been described, but this is not limited to this. For example, the UE 100 may set slice priority no-reception information in a UE assistance information (UEAssistanceInformation) message and transmit a UE assistance information message including the slice priority no-reception information.

[0142] By using the UE assistance information message, the UE 100 can notify the network that it is capable of performing a slice-specific cell reselection procedure as its own capability, but has not received slice priority information from the AMF 300. Specifically, the UE 100 may include UE-NR-Capability as an information element in the UE assistance information message. In this case, the UE 100 may transmit a UE assistance information message including UE-NR-Capability in which "sliceInfoforCellReselection" is set to "temporarily non-supported". Alternatively, a new information element in which slice priority reception non-information can be set may be included in the UE assistance information message. In this case, UE 100 may transmit slice priority no-reception information by setting slice priority no-reception information in the new information element and transmitting a UE assistance information message.

[0143] In addition, the slice priority no-reception information may be transmitted using an RRC message other than the UE capability information message or the UE assistance information message. In this case, the RRC message may include a new information element in which the slice priority no-reception information can be set. The UE 100 may transmit the slice priority no-reception information by setting the slice priority no-reception information in the new information element and transmitting the RRC message.

[0144] [Other embodiments] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the UE 100 or the gNB 200 may be integrated, and at least a portion of the UE 100 or the gNB 200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0145] As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." Furthermore, the terms "include" and "comprise" do not mean including only the listed items, but may mean including 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 an exclusive or. Furthermore, 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 method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0146] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made within the scope of the gist. Furthermore, it is also possible to combine all or part of each embodiment, each operation, each process, and each step within the scope of consistent combinations.

[0147] This application claims priority to U.S. Provisional Application No. 63 / 395,084 (filed August 4, 2022), the entire contents of which are incorporated herein by reference.

[0148] (Supplementary Note 1) (Supplementary Note 1) A communication control method in a mobile communication system, comprising a step in which a user device transmits slice priority reception / non-reception information indicating whether slice priority information indicating the priority of a network slice has been received from a core network device to a base station.

[0149] (Supplementary Note 2) The communication control method according to Supplementary Note 1, further comprising a step in which the base station transmits to the user equipment an RRC release message including either legacy frequency priority information representing a priority for each frequency or slice-specific frequency priority information representing a priority for each frequency that supports the network slice, based on the slice priority reception presence / absence information.

[0150] (Supplementary Note 3) A communication control method in a mobile communication system, comprising a step of a core network device transmitting to a base station slice priority transmission status information indicating whether slice priority information indicating the priority of a network slice has been transmitted to a user device.

[0151] (Supplementary Note 4) The communication control method according to Supplementary Note 3, further comprising a step in which the base station transmits to the user equipment an RRC release message including either legacy frequency priority information representing a priority for each frequency or slice-specific frequency priority information representing a priority for each frequency that supports the network slice, based on the slice priority transmission presence / absence information.

[0152] (Supplementary Note 5) The communication control method according to Supplementary Note 2 or Supplementary Note 4, further comprising a step in which the user equipment performs a legacy cell reselection procedure using the legacy frequency priority information included in the RRC release message, and performs a slice-specific cell reselection procedure using the slice-specific frequency priority information included in the RRC release message.

[0153] (Supplementary Note 6) A communication control method in a mobile communication system, comprising: a step in which a base station transmits an RRC release message to a user equipment, the RRC release message including legacy frequency priority information representing a priority for each frequency, regardless of whether the user equipment has received slice priority information representing a priority of a network slice from a core network device.

[0154] (Supplementary Note 7) The communication control method according to Supplementary Note 6, wherein the transmitting step includes a step in which the base station transmits the RRC release message including the legacy frequency priority information to the user equipment even if the user equipment has received the slice priority information from the core network device.

[0155] (Supplementary Note 8) A communication control method in a mobile communication system, comprising: when a user equipment does not receive slice priority information indicating a priority of a network slice from a core network device, transmitting an RRC message to a base station, the RRC message including information indicating that the slice priority information has not been received.

[0156] (Supplementary Note 9) The communication control method according to Supplementary Note 8, wherein the RRC message is a UE capability information message or a UE assistance information message.

[0157] (Supplementary Note 10) The communication control method according to Supplementary Note 8 or Supplementary Note 9, wherein the transmitting step includes a step in which the user equipment transmits to the base station the RRC message including the information indicating that the slice priority information has not been received from the core network device by setting UE-NR-Capability included in the RRC message to non-support.

[0158] (Supplementary Note 11) The communication control method according to any one of claims 8 to Supplementary Note 10, wherein the transmitting step includes a step of transmitting, to the base station, the RRC message including, as an information element, the information indicating that the user equipment has not received the slice priority information from the core network device.

[0159] (Addendum 2) 1. Introduction Based on the RAN2#118e meeting, the following agreement was reached on slice-specific cell reselection.

[0160] If the RRC release message contains any kind of cell reselection priority, the UE should only consider the cell reselection priority received in the RRC release and ignore any kind of cell reselection priority received in the SIB message.

[0161] The RRC release can include both legacy and slice-specific reselection priorities.

[0162] We have discovered some issues between these agreements and the SA2 specification, which we discuss in this appendix.

[0163] 2. Discussion 2.1 Problem Definition The previous RAN2 agreement, as outlined in TS 38.304, specifies the following:

[0164] 5.2.4 Cell Reselection Evaluation Process 5.2.4.1 Reselection Priority Operation The absolute priorities of different NR frequencies or inter-RAT frequencies may be provided to the UE in the system information, in an RRC release message, or by inheriting from another RAT during inter-RAT cell (re)selection. In the system information, an NR frequency or an inter-RAT frequency may be listed without providing a priority (i.e., there is no cellReselectionPriority field for that frequency). If a field with cellReselectionPriority or nsag-CellReselectionPriority is provided in dedicated signaling, the UE ignores the fields with cellReselectionPriority and nsag-CellReselectionPriority provided in the system information.

[0165] Based on the above specifications, the following observations are made:

[0166] Observation 1: If a UE receives a dedicated priority in the SIB, it must ignore the frequency priority.

[0167] On the other hand, TS23.501 has the following SA2 specifications:

[0168] 5.3.4.3.4 Network slice based cell reselection If one or more S-NSSAI(s) are associated with NSAG(s), the UE can perform network slice based cell reselection as described in TS 38.300, TS 38.304, TS 38.331, and TS 24.501.

[0169] When providing NSAG information to the UE, the AMF must also provide NSAG priority information for the NSAG provided in the NSAG information. The AMF determines the NSAG priority information based on the operator's policy. If the UE receives NSAG priority information from the AMF, the UE uses the NSAG priority information provided by the AMF for cell reselection, as described below. If the UE does not receive NSAG priority information from the AMF, the UE does not use network slice-based cell reselection at all.

[0170] Based on the above specifications, the following observations are made:

[0171] Observation 2: The UE does not perform slice-specific cell reselection if it has not received NSAG priority from the AMF.

[0172] There is a contradiction between these specifications. That is, if the UE does not receive NSAG priority from the AMF and only nsag-CellReselectionPriority is included in dedicated signaling (such as RRC release), the UE must ignore the cell reselection priority provided in the system information, and the UE cannot use the nsag-CellReselectionPriority included in the dedicated signaling, so the UE cannot apply any cell reselection priority to perform cell reselection. Therefore, RAN2 should specify a solution to this problem.

[0173] Proposal 1: RAN2 should specify a solution to this problem: if the UE does not receive NSAG priority information from the AMF and the dedicated signaling contains only nsag-CellReselectionPriority, the UE cannot apply any cell reselection priority to perform cell reselection.

[0174] Solutions are divided into those on the gNB side and those on the UE side.

[0175] 2.1.1 Response on the gNB side 2.1.1.1. When nsag-CellReselectionPriority is set, the gNB always sets both cellReselectionPriority and nsag-CellReselectionPriority in dedicated signaling.

[0176] The simplest solution is for the gNB to set both cellReselectionPriority and nsag-CellReselectionPriority in dedicated signaling whenever nsag-CellReselectionPriority is set.

[0177] This allows the UE to apply cellReselectionPriority even if it has not received NSAG priority from the AMF. However, this solution may be useless if the UE has received NSAG priority from the AMF.

[0178] Observation 3: As a response from the gNB side, when nsag-CellReselectionPriority is set, one solution is for the gNB to always set both cellReselectionPriority and nsag-CellReselectionPriority in dedicated signaling.

[0179] 2.1.1.2. If the UE does not receive NSAG priority from the AMF, the gNB sets cellReselectionPriority in dedicated signaling.

[0180] On the other hand, if the UE does not receive NSAG priority from the AMF, the gNB can set cellReselectionPriority in dedicated signaling. However, in this solution, the gNB needs to check in advance whether the UE has received NSAG priority from the AMF. Therefore, a signal is required from the AMF to the gNB or from the UE to the gNB indicating that the UE has received NSAG priority from the AMF.

[0181] Observation 4: As a solution on the gNB side, if the UE has not received the NSAG priority from the AMF, the gNB can set cellReselectionPriority to dedicated signaling. In this solution, the gNB needs to check in advance whether the UE has received the NSAG priority from the AMF. Therefore, a signal including the UE's receipt of the NSAG priority from the AMF is required from the AMF to the gNB or from the UE to the gNB.

[0182] 2.1.2 UE-side response As a UE-side response, if the UE does not receive NSAG priority from the AMF and only nsag-CellReselectionPriority is included in the dedicated signaling, the UE applies the cellReselectionPriority included in the SIB. However, this may waste radio resources and reduce the controllability of the NW side.

[0183] Observation 5: If the UE does not receive NSAG priority from the AMF and the dedicated signaling contains only nsag-CellReselectionPriority, the UE can apply the cellReselectionPriority included in the SIB.

[0184] 2.2 Proposal Based on the above discussion, when the UE does not receive NSAG priority from the AMF and the dedicated signaling contains only nsag-CellReselectionPriority, we will consider solutions on both the gNB and UE sides.

[0185] If the UE does not receive an NSAG priority from the AMF, it means that slice-specific cell reselection is not permitted from the AMF. Therefore, the dedicated signaling nsag-CellReselectionPriority does not apply. In this case, the UE may apply the cellReselectionPriority configured in the dedicated signaling or SIB.

[0186] Furthermore, it is not that the UE does not have the capability for slice-specific cell reselection, but rather that the UE is not permitted to use slice-specific cell reselection from the AMF, so RAN2 should specify this solution. Meanwhile, the gNB knows the UE's capability for slice-specific cell reselection by checking the UE capability signaling, but does not know whether the AMF has configured the UE with NSAG priority. Therefore, the gNB may only set nsag-CellReselectionPriority in dedicated signaling. If the UE does not receive NSAG priority from the AMF and only nsag-CellReselectionPriority is included in the dedicated signaling, the current specification may confuse the UE implementation.

[0187] This document has discussed three solutions (i.e., Finding 3 (O-3), Finding 4 (O-4), and Finding 5 (O-5)), but each solution has some problems.

[0188] O-4 was initially excluded from the scope of the study because it may affect RAN3 and RAN2 and data collection is currently underway.

[0189] Both solutions O-3 and O-5 waste signal resources. O-3 affects the operation of the gNB. O-5 may reduce controllability on the network side, affecting UE implementation.

[0190] For the time being, the problem where the UE does not receive the NSAG priority from the AMF and the dedicated signaling contains only nsag-CellReselectionPriority may be a rare case. Therefore, if O-5 is considered as the last fail-safe rule, O-5 has less impact on the whole. Therefore, O-5 is adopted.

[0191] In conclusion, as a fail-safe rule, the solution in "Observation 5" is preferable as it has the least impact on the specification and implementation.

[0192] Proposal 2: If the UE has not received NSAG priority from the AMF and the dedicated signaling only includes nsag-CellReselectionPriority, the UE should apply the legacy frequency priority included in the SIB.

[0193] 2.3. Proposed text If we agree with Proposal 2 above, we propose the following proposed text for TS38.304.

[0194] Proposal 3: RAN2 should agree to the proposed text of TS38.304 above.

[0195] 5.2.4 Cell Reselection Evaluation Process 5.2.4.1 Reselection Priority Operation The absolute priority of different NR frequencies or inter-RAT frequencies may be provided to the UE in the system information, in an RRC release message, or by inheriting from another RAT during inter-RAT cell (re)selection. In the case of system information, an NR frequency or an inter-RAT frequency may be listed without providing a priority (i.e., there is no cellReselectionPriority field for that frequency). If cellReselectionPriority or nsag-CellReselectionPriority is provided in dedicated signaling, or if nsag-CellReselectionPriority is provided in dedicated signaling and NSAG priority information is provided in NAS, the UE shall ignore the cellReselectionPriority and nsag-CellReselectionPriority fields provided in the system information.

[0196] When the UE is in normal camped state, if it supports slice-based cell reselection and has received the NSAG and its priority from the NAS, the UE shall derive the reselection priority according to clause 5.2.4.11.

Claims

1. A communication control method in a mobile communication system, comprising: The user equipment transmits slice priority reception information indicating whether slice priority information indicating a priority of a network slice is received from a core network node to an access network node. Communications control method.

2. The access network node further includes transmitting, to the user equipment, an RRC release message including either legacy frequency priority information representing a priority for each frequency or slice-specific frequency priority information representing a priority for each frequency supporting the network slice, based on the slice priority reception / non-reception information. The communication control method according to claim 1 .

3. A communication control method in a mobile communication system, comprising: The core network node transmits slice priority transmission information indicating whether slice priority information indicating a priority of a network slice has been transmitted to the user equipment to the access network node. Communications control method.

4. The access network node further transmits, to the user equipment, an RRC release message including either legacy frequency priority information representing a priority for each frequency or slice-specific frequency priority information representing a priority for each frequency supporting the network slice, based on the slice priority transmission presence / absence information. The communication control method according to claim 3.

5. The user equipment performs a legacy cell reselection procedure using the legacy frequency priority information included in the RRC release message, and performs a slice-specific cell reselection procedure using the slice-specific frequency priority information included in the RRC release message. The communication control method according to claim 2 or 4.

6. A communication control method in a mobile communication system, comprising: The access network node transmits an RRC release message to the user equipment, the RRC release message including legacy frequency priority information representing a priority for each frequency, regardless of whether the user equipment receives slice priority information representing a priority of the network slice from the core network node. Communications control method.

7. The transmitting step includes the access network node transmitting the RRC release message to the user equipment including the legacy frequency priority information even if the user equipment has received the slice priority information from the core network node. The communication control method according to claim 6.

8. A communication control method in a mobile communication system, comprising: When the user equipment does not receive slice priority information indicating a priority of a network slice from a core network node, the user equipment transmits an RRC message including information indicating that the slice priority information has not been received to the access network node. Communications control method.

9. The RRC message is a UE Capability Information message or a UE Assistance Information message. The communication control method according to claim 8.

10. The sending step includes sending the RRC message including the information indicating that the user equipment did not receive the slice priority information from the core network node to the access network node by setting the UE-NR-Capability included in the RRC message to non-support. The communication control method according to claim 8.

11. The transmitting step includes transmitting the RRC message to the access network node, the RRC message including the information indicating that the user equipment did not receive the slice priority information from the core network node as an information element. The communication control method according to claim 8.

12. A user device, comprising: A transmitter for transmitting slice priority reception information indicating whether slice priority information indicating the priority of a network slice has been received from a core network node to an access network node. User equipment.

13. A core network node, comprising: A transmitter for transmitting slice priority transmission information indicating whether slice priority information indicating a priority of a network slice has been transmitted to a user device to an access network node. Core network node.

14. An access network node, comprising: A transmitter that transmits an RRC release message including legacy frequency priority information representing a priority for each frequency to the user equipment, regardless of whether the user equipment has received slice priority information representing a priority of the network slice from a core network node. Access network node.

15. A user device comprising: A transmitter that, when slice priority information indicating a priority of a network slice is not received from a core network node, transmits an RRC message including information indicating that the slice priority information has not been received to an access network node. User equipment.