Communication control method, user device, program, chipset, and mobile communication system

Abstract

This invention provides a communication control method, user device, program, chipset, and mobile communication system related to a network slice-dependent cell reselection procedure. [Solution] The communication control method includes step S32 in which, if the user device 100 receives an RRC release message from the base station 200 that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, without receiving slice priority information representing the priority of the network slice from the core network device 300 and without including legacy frequency priority information representing the priority for each frequency, the user device 100 ignores the slice-specific frequency priority information.

Description

Technical Field

[0001] The present disclosure relates to a communication control method, a user device, a program, a chipset, and a mobile communication system.

Background Art

[0002] In the specifications of 3GPP (The Third Generation Partnership Project), which is a standardization project for mobile communication systems, network slicing is defined. Network slicing is a technology for constructing network slices, which are virtual networks, by logically dividing the physical network built by a communication carrier.

[0003] A user device in the radio resource control (RRC) idle state or the RRC inactive state can execute a cell reselection procedure. 3GPP is considering a slice-specific cell reselection procedure, which is a network slice-dependent cell reselection procedure (see, for example, Non-Patent Document 1). By executing the slice-specific cell reselection procedure, a user device can camp on an adjacent cell that supports a desired network slice, for example.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

[0005] One embodiment of the communication control method is a communication control method in a mobile communication system. The communication control method includes a step in which, if a user device receives an RRC release message from a base station that includes slice-specific frequency priority information representing the priority of frequencies supporting the network slice without receiving slice priority information representing the priority of the network slice from a core network device, the user device ignores the slice-specific frequency priority information. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a diagram showing an example configuration of a mobile communication system according to the first embodiment. [Figure 2] Figure 2 is a diagram showing an example configuration of a UE (User Equipment) according to the first embodiment. [Figure 3] Figure 3 is a diagram showing an example configuration of a gNB (base station) according to the first embodiment. [Figure 4] Figure 4 is a diagram showing an example of the configuration of a protocol stack related to the user plane according to the first embodiment. [Figure 5] Figure 5 is a diagram showing an example of the configuration of a protocol stack related to the control plane according to the first embodiment. [Figure 6] Figure 6 is a diagram illustrating the overview of the cell reselection procedure. [Figure 7] Figure 7 is a diagram illustrating the general flow of a typical cell reselection procedure. [Figure 8] Figure 8 shows an example of network slicing. [Figure 9] Figure 9 is a diagram illustrating the overview of the slice-specific cell reselection procedure. [Figure 10] Figure 10 shows an example of slice frequency information. [Figure 11] Figure 11 is a diagram illustrating the basic flow of the slice-specific cell reselection procedure. [Figure 12]Figure 12 is a diagram illustrating an example of operation according to the first embodiment. [Figure 13] Figure 13 illustrates the signaling mismatch between AMF and gNB. [Modes for carrying out the invention]

[0007] 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.

[0008] [First Embodiment]

[0009] (Configuration of mobile communication systems) Figure 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. In the following explanation, 5GS will be used as an example, but the mobile communication system may also have at least a portion of an LTE (Long Term Evolution) system applied to it. The 6th Generation (6G) system may also have at least a portion of it applied to it.

[0010] The mobile communication system 1 comprises User Equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereafter, NG-RAN 10 may be simply referred to as RAN 10, and 5GC 20 may be simply referred to as core network (CN) 20.

[0011] 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 smartphones) and / or a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or device attached to a sensor, a vehicle or device attached to a vehicle (Vehicle UE), or an aircraft or device attached to an aircraft (Aerial UE).

[0012] NG-RAN10 includes base stations (referred to as "gNBs" in 5G systems) 200. The gNBs 200 are interconnected via the Xn interface, which is an inter-base station interface. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with UEs 100 that have established a connection with its own cell. The gNB 200 has radio resource management (RRM) functions, user data routing functions (hereinafter simply referred to as "data"), 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").

[0013] Furthermore, the gNB200 can also connect to the EPC (Evolved Packet Core), which is the core network of LTE. LTE base stations can also connect to the 5GC20. LTE base stations and the gNB200 can also be connected via an inter-base station interface.

[0014] 5GC20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE100. The AMF manages the mobility of the UE100 by communicating with the UE100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB200 via the NG interface, which is an interface between the base station and the core network.

[0015] Figure 2 is a diagram showing the configuration of the UE100 (user device) according to the first embodiment. The 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 that performs wireless communication with the gNB200.

[0016] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the wireless signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0017] 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 the baseband signal (transmitted signal) output by the control unit 130 into a wireless signal and transmits it from the antenna.

[0018] The control unit 130 performs various controls and processes in the UE 100. Such processes include the processes of each layer described later. 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 for the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals, etc. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 130 may perform each process or each operation in the UE 100 in each of the embodiments shown below.

[0019] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to the first embodiment. The gNB 200 includes a transmission unit 210, a reception unit 220, a control unit 230, and a backhaul communication unit 240. The transmission unit 210 and the reception unit 220 constitute a radio communication unit that performs radio communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0020] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0021] The reception unit 220 performs various receptions under the control of the control unit 230. The reception unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0022] The control unit 230 performs various control and processing in the gNB200. Such processing includes processing in each layer described later. 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. The control unit 230 may perform each processing or operation in the gNB200 in each of the embodiments shown below.

[0023] The backhaul communication unit 240 is connected to an adjacent base station via the Xn interface, which is an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF300 via the NG interface, which is an inter-base station-core network interface. The gNB200 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 fronthaul interface.

[0024] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0025] The user plane radio interface protocol consists of 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.

[0026] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the UE100's PHY layer and the gNB200's PHY layer via a physical channel. The UE100's PHY layer receives downlink control information (DCI) transmitted from the gNB200 over the physical downlink control channel (PDCCH). Specifically, the 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 the gNB200 has a CRC parity bit added, which is scrambled by the RNTI.

[0027] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat request (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of the UE100 and the MAC layer of the gNB200 via the transport channel. The MAC layer of the 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 the UE100.

[0028] 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 UE100's RLC layer and the gNB200's RLC layer via a logical channel.

[0029] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0030] 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.

[0031] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

[0032] The control plane's wireless interface protocol stack includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer, instead of the SDAP layer shown in Figure 4.

[0033] 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.

[0034] The NAS, located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the UE100's NAS and the AMF300's NAS. The UE100 also has application layers in addition to the wireless interface protocol. Layers below the NAS are called AS (Access Stratum).

[0035] (Overview of the cell reselection procedure) Figure 6 is a diagram illustrating the overview of the cell reselection procedure.

[0036] A UE100 in an RRC idle or RRC inactive state performs a cell reselection procedure to move from its current serving cell (cell #1) to an adjacent cell (one of cells #2 through #4) upon movement. Specifically, the UE100 identifies the adjacent cell to which it should camp on using the cell reselection procedure and reselects the identified adjacent cell. When the current serving cell and the adjacent cell have the same frequency (carrier frequency), it is called an intra-frequency, and when the current serving cell and the adjacent cell have different frequencies (carrier frequencies), it is called an inter-frequency. The current serving cell and the adjacent cell may be managed by the same gNB200. The current serving cell and the adjacent cell may be managed by different gNB200s.

[0037] Figure 7 is a schematic diagram illustrating a typical (or legacy) cell reselection procedure.

[0038] In step S11, UE100 performs frequency prioritization based on the frequency-specific priority (also called "absolute priority") specified by gNB200, for example, via an RRC release message. Specifically, UE100 manages the frequency priority specified by gNB200 for each frequency.

[0039] In step S12, the UE100 performs a measurement process to measure the radio quality for both the serving cell and the adjacent cell. The UE100 measures the received power and received quality of the reference signal transmitted by each of the serving cell and the adjacent cell, specifically the CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, the UE100 always measures the radio quality for frequencies with a higher priority than the current serving cell's frequency priority, and for frequencies with the same or lower priority as the current serving cell's frequency priority, it measures the radio quality of frequencies with the same or lower priority if the current serving cell's radio quality falls below a predetermined quality.

[0040] In step S13, UE100 performs a cell reselection process to reselect the cell to which it will camp on, based on the measurement results in step S12. For example, UE100 may reselect a cell to an adjacent cell if the frequency priority of the 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 the adjacent cell is the same as the priority of the current serving cell, UE100 may rank the radio 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 the adjacent cell is lower than the priority of the current serving cell, and the radio quality of the current serving cell remains below a certain threshold, and the radio quality of the adjacent cell remains above another threshold for a predetermined period, UE100 may reselect a cell to that adjacent cell.

[0041] (Overview of network slicing) Network slicing is a technique that creates multiple virtual networks by virtually dividing a physical network built by an operator (for example, a network consisting of NG-RAN10 and 5GC20). Each virtual network is called a network slice. In the following, a network slice may be simply referred to as a "slice."

[0042] Network slicing allows telecommunications carriers to create slices tailored 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.

[0043] Figure 8 shows an example of network slicing.

[0044] Three slices (slice #1 to slice #3) are configured on network 50, which consists of NG-RAN10 and 5GC20. Slice #1 is associated with the service type eMBB, slice #2 is associated with the service type URLLC, and slice #3 is associated with the service type mMTC. Note that more than three slices may be configured on network 50. A single service type may be associated with multiple slices.

[0045] Each slice is assigned a slice identifier to identify it. An example of a slice identifier is S-NSSAI (Single Network Slicing Selection Assistance Information). S-NSSAI includes an 8-bit SST (slice / service type). S-NSSAI may further include a 24-bit SD (slice differentiator). SST is information indicating the service type to which the slice is associated. SD is information used to differentiate multiple slices associated with the same service type. Information containing multiple S-NSSAIs is called NSSAI (Network Slice Selection Assistance Information).

[0046] Alternatively, one or more slices may be grouped together to form a slice group. A slice group is a group containing one or more slices, and a slice group identifier is assigned to such a slice group. A slice group may be configured by a core network (e.g., AMF300) or by a wireless access network (e.g., gNB200). The configured slice group may be notified to the UE100.

[0047] In the following, the term "network slice (slice)" may mean an S-NSSAI, which is the identifier of a single slice, or an NSSAI, which is a collection of S-NSSAIs. The term "network slice (slice)" may also mean a slice group, which is a group of one or more S-NSSAIs or NSSAIs. A slice group may be represented by an NSSAI. Such a slice group may be represented by an NSAG (Network Slice Access Stratum Group).

[0048] Furthermore, the UE100 determines the desired slice it wishes to use. The desired slice is sometimes called an "intended slice". In the first embodiment, the UE100 determines the slice priority for each network slice (desired slice). For example, the NAS of the UE100 determines the slice priority based on the operating status of applications within the UE100 and / or user operations / settings, and notifies the AS of the slice priority information indicating the determined slice priority. The NAS of the UE100 receives the slice priority information from the AMF300. That is, the AMF300 determines the slice priority for each slice. The AMF300 sends the slice priority information representing the slice priority to the NAS of the UE100. The NAS of the UE100 may determine the slice priority based on the slice priority information received from the AMF300.

[0049] (Overview of the slice-specific cell reselection procedure) Figure 9 is a diagram illustrating the procedure for slice-specific cell reselection (also known as slice-aware cell reselection or slice-based cell reselection).

[0050] In the slice-specific cell reselection procedure, UE100 performs cell reselection based on slice frequency information provided from network 50. The slice frequency information may also be provided to UE100 from gNB200 via dedicated signaling (e.g., RRC release message).

[0051] Slice frequency information is information that shows the correspondence between network slices, frequencies, and frequency priorities. For example, slice frequency information shows, for each slice (or slice group), the frequencies (one or more frequencies) that support that slice and the frequency priority assigned to each frequency. An example of slice frequency information is shown in Figure 10.

[0052] In the example shown in Figure 10, three frequencies, F1, F2, and F4, are associated with slice #1 as the frequencies that support 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 in Figure 10, a higher frequency priority number indicates a higher priority, but a lower number could also indicate a higher priority.

[0053] Furthermore, for slice #2, three frequencies, F1, F2, and F3, are associated as frequencies that support 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".

[0054] Furthermore, for slice #3, three frequencies, F1, F3, and F4, are associated as frequencies that support 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".

[0055] In the following, to distinguish it from the absolute priority in conventional cell reselection procedures, the frequency priority shown in the slice frequency information may be referred to as "slice intrinsic frequency priority."

[0056] As shown in Figure 9, UE100 may perform cell reselection processing based on slice support information provided from network 50. Slice support information may also be information indicating the correspondence between cells (e.g., serving cells and each adjacent cell) and network slices that the cell does not provide or does provide. For example, a cell may temporarily not provide some or all of the network slices due to congestion or other reasons. That is, even if a slice support frequency has the capability to provide a certain network slice, some cells within that frequency may not provide that network slice. Based on the slice support information, UE100 can identify the network slices that each cell does not provide. Such slice support information may be provided to UE100 from gNB200 via broadcast signaling (e.g., system information block) or dedicated signaling (e.g., RRC release message).

[0057] Figure 11 shows the basic flow of the slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, it is assumed that UE100 is in an RRC idle or RRC inactive state and has received and is holding the slice frequency information described above. The procedure for "slice-specific cell reselection" is referred to as the "slice-specific cell reselection procedure." However, in the following, "slice-specific cell reselection" and "slice-specific cell reselection procedure" may be used interchangeably.

[0058] In step S0, the NAS of UE100 determines the slice identifier of the desired slices of UE100 and the slice priority of each desired slice, and notifies the AS of UE100 of the slice priority information, including the determined slice priorities. "Desired slices" are "Intended slices" and include slices that are likely to be used, candidate slices, desired slices, slices to communicate, requested slices, allowed slices, or intended slices. For example, slice priority of slice #1 is determined to be "3", slice priority of slice #2 is determined to be "2", and slice priority of slice #3 is determined to be "1". A higher number indicates higher priority, although a lower number may also indicate higher priority.

[0059] In step S1, the AS of UE100 sorts the slices (slice identifiers) notified from the NAS in step S0 in order of slice priority. The list of slices sorted in this way is called the "slice list".

[0060] In step S2, the AS of UE100 selects one network slice in order of slice priority. The network slice selected in this way is called the "selected network slice".

[0061] In step S3, the AS of the UE100 assigns frequency priority to each frequency associated with the selected network slice. Specifically, the AS of the UE100 identifies the frequencies associated with the slice based on the slice frequency information and assigns frequency priority to the identified frequencies. For example, if the selected network slice selected in step S2 is slice #1, the AS of the UE100 assigns frequency priority "6" to frequency F1, frequency priority "4" to frequency F2, and frequency priority "2" to frequency F4 based on the slice frequency information (e.g., the information in Figure 10). The AS of the UE100 refers to the list of frequencies arranged in descending order of frequency priority as the "frequency list".

[0062] In step S4, the AS of UE100 selects one frequency from the selected network slice selected in step S2 in order of frequency priority, and performs measurement processing on the selected frequency. The frequency thus selected is called the "selected frequency". The AS of UE100 may also rank each cell measured within the selected frequency in order of wireless quality. Among the cells measured within the selected frequency, those that meet a predetermined quality standard (i.e., the minimum required quality standard) are called "candidate cells".

[0063] In step S5, the AS of UE100 identifies the highest-ranked cell based on the results of the measurement process in step S4 and determines, based on the slice support information, whether that cell provides the selected network slice. If it is determined that the highest-ranked cell provides the selected network slice (step S5: YES), in step S5a, the AS of UE100 re-selects the highest-ranked cell and camps on to that cell.

[0064] On the other hand, if it is determined that the highest-ranked cell does not provide a 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 in the selected network slice other than the selected frequencies that were assigned in step S3. If it is determined that there are unmeasured frequencies (step S6: YES), the AS of UE100 resumes processing targeting the next highest frequency priority and performs measurement processing on that frequency as the selected frequency (returning to step S4).

[0065] If it is determined that there are no unmeasured frequencies in the frequency list created in step S3 (step S6: NO), then 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 network slices other than the selected network slices in the slice list. If it is determined that there are unselected slices (step S7: YES), the AS of UE100 resumes processing targeting the next highest slice priority network slice and selects that network slice as the selected network slice (returning to step S2). Note that in the basic flow shown in Figure 11, the processing in step S7 may be omitted.

[0066] If it is determined that there are no unselected slices (step S7: NO), in step S8, the AS of UE100 performs the conventional cell reselection process. The conventional cell reselection process may refer to the entire general (or legacy) cell reselection procedure shown in Figure 7. Or, the conventional cell reselection process may refer only to the cell reselection process shown in Figure 7 (step S13). In the latter case, UE100 may reuse the measurement results from step S4 without measuring the wireless quality of the cell again.

[0067] (Communication control method according to the first embodiment) 3GPP has the following specifications and agreements 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").

[0068] (1) The RRC release (RRCRelease) message may include legacy frequency priority and / or slice intrinsic frequency priority.

[0069] (2) If any frequency priority is included in the RRC release message, UE100 ignores all frequency priorities (legacy frequency priority and / or slice-specific frequency priority) received in the System Information (SIB).

[0070] (3) If UE100 has not received a slice priority from AMF300, it cannot execute the slice-specific cell reselection procedure.

[0071] For example, suppose UE100 receives an RRC release message from gNB200 that includes slice-specific frequency priority but does not include legacy frequency priority, but does not receive slice priority from AMF300. In such a case, UE100 cannot execute the slice-specific cell reselection procedure as described in (3) above because it has received slice-specific frequency priority from gNB200 but not from AMF300.

[0072] Thus, although specifications and agreements exist as described in (1) to (3) above, there are cases like the one described above, and therefore UE100 may not be able to properly execute the cell reselection procedure.

[0073] Therefore, the objective of the first embodiment is to enable UE100 to properly execute the cell reselection procedure.

[0074] In the following, a cell reselection procedure that does not use network slices 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 network slices 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 legacy cell reselection procedures and slice-specific cell reselection procedures, they may simply be referred to as "cell reselection procedures."

[0075] Furthermore, in the following, the frequency-specific priority used in the legacy cell reselection procedure (sometimes referred to as "absolute priority") may be referred to as "legacy frequency priority" as described above. The "legacy frequency priority information" representing the legacy frequency priority is included in the RRC release message and / or SIB and sent from gNB200 to UE100.

[0076] On the other hand, the priority for each network slice is sometimes referred to as "slice priority," as described above. Slice priority is used in the slice-specific cell reselection procedure. "Slice priority information," which represents the slice priority, is included in the NAS message and sent from the AMF300 to the UE100.

[0077] Furthermore, the frequency-specific priority that supports network slices is sometimes referred to as "slice-specific frequency priority," as described above. Slice-specific frequency priority is also used in the slice-specific cell reselection procedure. The "slice-specific frequency priority information," which represents the slice-specific frequency priority, is included in the RRC release message and / or SIB and sent from gNB200 to 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.

[0078] When legacy frequency priority and slice intrinsic frequency priority are not specifically distinguished, the term "frequency priority" is sometimes used without further distinction.

[0079] Furthermore, as mentioned above, a slice may refer to a single slice. A slice may also refer to a group of slices. A slice group may also refer to multiple slice groups. A slice group may be represented by an NSAG.

[0080] In the first embodiment, an example is described in which UE100 ignores the slice intrinsic frequency priority when it receives an RRC release message containing the slice intrinsic frequency priority without receiving slice priority information.

[0081] Specifically, if a user device (e.g., UE100) receives an RRC release message from a base station (e.g., gNB200) that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, without receiving slice priority information representing the priority of the network slice from the core network device (e.g., AMF300), the slice-specific frequency priority information will be ignored.

[0082] This makes it possible to implement countermeasures for the UE100 (ignoring the slice-specific frequency priority) in cases where the UE100 receives an RRC release message containing the slice-specific frequency priority without including the legacy frequency priority, even though it has not received the slice priority from the AMF300.

[0083] In this case, UE100 ignores the slice-specific frequency priority information included in the RRC release message and therefore does not use that information to execute the slice-specific cell reselection procedure. This is consistent with the 3GPP agreement that UE100 should not use the slice-specific cell reselection procedure if it does not receive slice priority information.

[0084] When UE100 receives a System Information Block (SIB) containing legacy frequency priority information from gNB200, it uses that legacy frequency priority information to execute a legacy cell reselection procedure.

[0085] Therefore, UE100 can properly execute the cell reselection procedure.

[0086] (Example of operation according to the first embodiment) Next, an example of operation according to the first embodiment will be described.

[0087] Figure 12 is a diagram illustrating an example of operation according to the first embodiment.

[0088] As shown in Figure 12, in step S30, the AMF300 does not send slice priority information to the UE100. Therefore, the UE100 does not receive slice priority information.

[0089] In step S31, gNB200 sends an RRC release message that includes slice intrinsic frequency priority information but does not include legacy frequency priority information. UE100 receives the RRC release message.

[0090] In step S32, UE100 ignores the slice intrinsic frequency priority information contained in the RRC release message. Alternatively, AMF300 may send a NAS message to UE100 containing information instructing UE100 to perform the ignoring operation. UE100 may perform the ignoring operation upon receiving the NAS message. Alternatively, gNB200 may send an RRC message (such as an SIB or RRC release (RRCRelease) message) to UE100 containing information instructing UE100 to perform the ignoring operation. UE100 may perform the ignoring operation upon receiving the RRC message. Alternatively, the ignoring operation may be hardcoded within UE100. UE100 may send an RRC message to gNB200 containing information indicating that the slice intrinsic frequency priority information has been ignored.

[0091] In step S33, the gNB200 broadcasts a System Information Block (SIB) containing legacy frequency priority information. The UE100 receives the SIB.

[0092] In step S34, UE100 executes the legacy cell reselection procedure using the legacy frequency priority information contained in the SIB. Furthermore, even if UE100 receives the SIB before the T320 timer, which indicates the period during which the information contained in the RRC release message is valid, expires, UE100 will still execute the legacy cell reselection procedure using the legacy frequency priority information contained in the SIB.

[0093] [Other embodiments] 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 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).

[0094] The terms “based on” and “depending on” used in this disclosure do not mean “based solely on” or “depending solely on” unless otherwise specified. “Based on” means both “based solely on” and “at least partially on.” Similarly, “depending on” means both “at least partially on” and “at least partially on.” Furthermore, the terms “include,” “comprise,” and variations thereof do not mean that only the listed items are included; they may include only the listed items, or they may include additional items in addition to the listed items. Also, the term “or” used in this disclosure is not intended to mean exclusive OR. Moreover, any reference to elements using designations such as “first,” “second,” etc., 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 by the context that they are not.

[0095] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the gist of the work. Furthermore, it is possible to combine all or part of each embodiment, each operation, each process, and each step, as long as they do not contradict each other.

[0096] This application claims priority to U.S. Provisional Application No. 63 / 395091 (filed August 4, 2022), the entirety of which is incorporated into the specification of this application.

[0097] (First Appendix) The features of the above-described embodiment are noted below.

[0098] (Note 1) A communication control method in a mobile communication system, If a user device receives an RRC release message from a base station that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, without receiving slice priority information representing the priority of the network slice from the core network device, and without including legacy frequency priority information representing the priority of each frequency, the user device will ignore the slice-specific frequency priority information. Communication control method.

[0099] (Note 2) The aforementioned disregard includes, when the user device receives a system information block containing the legacy frequency priority information from the base station, executing a legacy cell reselection procedure using the legacy frequency priority information. The communication control method described in Appendix 1.

[0100] (Note 3) The user device further transmits an RRC message to the base station that includes information indicating that the slice intrinsic frequency priority information has been ignored. The communication control method described in Appendix 1 or 2.

[0101] (Second Addendum) 1. Introduction Based on the RAN2#118e meeting, the following agreement was reached regarding slice-specific cell reselection.

[0102] If the RRC release message contains any type of cell reselection priority, the UE should only consider the cell reselection priority received in the RRC release and ignore any other type of cell reselection priority received in the SIB message.

[0103] RRC release can include both legacy and slice-specific reselection priorities.

[0104] We discovered a problem between these agreements and the SA2 specification. This addendum discusses this issue.

[0105] 2. Discussion 2.1 Defining the Problem The previous RAN2 agreement was stipulated in TS38.304 as follows:

[0106] 5.2.4 Cell Reselection Evaluation Process 5.2.4.1 Priority operation for re-selection The absolute priority of different NR frequencies or inter-RAT frequencies may be provided to the UE through system information, RRC release messages, or inheritance from another RAT during inter-RAT cell (re)selection. In the case of system information, NR frequencies or inter-RAT frequencies may be listed without providing priority (i.e., there is no cellReselectionPriority field for that frequency). If a field with cellReselectionPriority or nsag-CellReselectionPriority is provided by dedicated signaling, the UE ignores the fields with cellReselectionPriority and nsag-CellReselectionPriority provided in the system information.

[0107] Based on the specifications described above, the following observations are made.

[0108] Finding 1: If a UE receives a dedicated priority within the SIB, it must ignore that frequency priority.

[0109] On the other hand, TS23.501 has the following SA2 specifications.

[0110] 5.3.4.3.4 Network slice-based cell reselection If one or more S-NSSAIs are associated with an NSAG, the UE can perform cell reselection based on network slices, as described in TS38.300, TS38.304, TS38.331, and TS24.501.

[0111] When providing NSAG information to the UE, the AMF must also provide NSAG priority information for the NSAGs 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 cell reselection based on network slices at all.

[0112] Based on the specifications described above, the following observations are made.

[0113] Finding 2: The UE does not perform slice-specific cell reselection if it has not received NSAG priority from the AMF.

[0114] There is a contradiction between these specifications. Specifically, if the UE does not receive NSAG priority from the AMF and only nsag-CellReselectionPriority is included in the dedicated signaling (such as RRC release), the UE must ignore the cell reselection priority provided in the system information, and since the UE cannot use nsag-CellReselectionPriority included in the dedicated signaling, the UE cannot perform cell reselection by applying an arbitrary cell reselection priority. Therefore, RAN2 should specify a solution to this problem.

[0115] Proposal 1: RAN2 should specify a solution to this problem. That is, if the UE has not received NSAG priority information from the AMF and its dedicated signaling only includes nsag-CellReselectionPriority, the UE cannot perform cell reselection by applying an arbitrary cell reselection priority.

[0116] The solutions are divided into those on the gNB side and those on the UE side.

[0117] 2.1.1 gNB-side support 2.1.1.1. When nsag-CellReselectionPriority is set, gNB always sets both cellReselectionPriority and nsag-CellReselectionPriority to dedicated signaling.

[0118] The simplest solution is for the gNB to set both cellReselectionPriority and nsag-CellReselectionPriority to dedicated signaling whenever nsag-CellReselectionPriority is set.

[0119] This allows the UE to apply cellReselectionPriority even if it has not received NSAG priority from AMF. However, if the UE has received NSAG priority from AMF, this solution may be redundant.

[0120] Finding 3: As for the gNB's response, if nsag-CellReselectionPriority is set, the gNB can always set both cellReselectionPriority and nsag-CellReselectionPriority to dedicated signaling.

[0121] 2.1.1.2. If the UE has not received an NSAG priority from the AMF, the gNB sets the cellReselectionPriority to dedicated signaling.

[0122] On the other hand, if the UE has not received NSAG priority from the AMF, another solution is for the gNB to set cellReselectionPriority in its dedicated signaling. However, in this solution, the gNB needs to check beforehand whether the UE has received NSAG priority from the AMF. Therefore, a signal is needed from the AMF to the gNB, or from the UE to the gNB, indicating that the UE has received NSAG priority from the AMF.

[0123] Finding 4: One solution for the gNB is to set cellReselectionPriority to a dedicated signaling if the UE has not received the NSAG priority from the AMF. In this solution, the gNB needs to check in advance whether the UE has received the NSAG priority from the AMF, so a signal is required from the AMF to the gNB, or from the UE to the gNB, indicating that the UE has received the NSAG priority from the AMF.

[0124] 2.1.2. UE-side response As a solution on the UE side, if the UE has not received NSAG priority from the AMF and its dedicated signaling only includes nsag-CellReselectionPriority, the UE can apply the cellReselectionPriority included in the SIB. However, this may waste radio resources and reduce network controllability.

[0125] Finding 5: If the UE has not received NSAG priority from the AMF and its dedicated signaling only includes nsag-CellReselectionPriority, one possible solution for the UE is to apply the cellReselectionPriority included in the SIB.

[0126] 2.2. Proposal Based on the above discussion, we will consider solutions on both the gNB and UE sides for the case where the UE does not receive NSAG priority from the AMF and only nsag-CellReselectionPriority is included in the dedicated signaling.

[0127] 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 nsag-CellReselectionPriority of the dedicated signaling is not applied. In this case, the UE can apply the cellReselectionPriority set in the dedicated signaling or SIB.

[0128] Furthermore, RAN2 should specify a solution not because the UE lacks slice-specific cell reselection capabilities, but because the UE is not permitted by AMF to use slice-specific cell reselection. On the other hand, gNBs know about the UE's capabilities for slice-specific cell reselection by checking the UEcapability signaling, but they do not know whether AMF has configured the UE with NSAG priority. Therefore, gNBs may only set nsag-CellReselectionPriority in their dedicated signaling. If the UE has not received NSAG priority from AMF and only nsag-CellReselectionPriority is included in its dedicated signaling, the current specification could lead to confusion in the UE implementation.

[0129] This document discussed three solutions (i.e., Finding 3 (O-3), Finding 4 (O-4), and Finding 5 (O-5)), but each of these solutions has some problem.

[0130] O-4 was initially excluded because it could potentially affect RAN3 and RAN2, and because it is currently being collected.

[0131] Both solutions O-3 and O-5 waste signal resources. O-3 affects the operation of the gNB. O-5 may reduce the controllability on the network side and affect the implementation of the UE.

[0132] The issue of the UE not receiving NSAG priority from AMF and the dedicated signaling only including nsag-CellReselectionPriority may be a rare case. Therefore, considering O-5 as the last fail-safe rule, it has less overall impact. Thus, we adopt O-5.

[0133] In conclusion, the solution described in "Observation 5," which has the least impact on the specifications and implementation, is preferable as a fail-safe rule.

[0134] Proposal 2: If the UE does not receive NSAG priority from the AMF and its dedicated signaling includes only nsag-CellReselectionPriority, the UE should apply the legacy frequency priority included in the SIB.

[0135] 2.3. Proposal text If you agree with proposal 2 above, I propose the following proposal for TS38.304.

[0136] Proposal 3: RAN2 should agree to the above proposal in TS38.304.

[0137] 5.2.4 Cell Reselection Evaluation Process 5.2.4.1 Priority operation for re-selection The absolute priority of different NR frequencies or inter-RAT frequencies may be provided to the UE by system information, RRC release messages, or by inheritance from another RAT during inter-RAT cell (re)selection. In the case of system information, NR frequencies or inter-RAT frequencies may be listed without providing priority (i.e., there is no cellReselectionPriority field for that frequency). If cellReselectionPriority or nsag-CellReselectionPriority is provided by dedicated signaling, or if nsag-CellReselectionPriority is provided by dedicated signaling and NSAG priority information is provided in the NAS, the UE shall ignore the cellReselectionPriority and nsag-CellReselectionPriority fields provided in the system information.

[0138] When the UE is in a normal camping state, and supports slice-based cell reselection, and receives the NSAG and its priority from the NAS, the UE must derive the reselection priority according to Section 5.2.4.11.

Claims

1. A communication control method performed by a user device in a mobile communication system, Receiving an RRC release message from a network node that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, without including legacy frequency priority information representing the priority of each frequency, This includes controlling whether or not the slice-specific cell reselection procedure is executed. Communication control method.

2. Receiving a system information block containing the legacy frequency priority information from the network node, The RRC release message further includes a timer indicating that the information contained in the RRC release message is valid, and even if the timer starts, the legacy cell reselection procedure is executed using the legacy frequency priority information contained in the system information block. The communication control method according to claim 1.

3. User device, A receiving unit that receives RRC release messages from network nodes, which include slice-specific frequency priority information representing the priority of frequencies supporting a network slice, but do not include legacy frequency priority information representing the priority of each frequency. The system includes a control unit that performs control to prevent the execution of the slice-specific cell reselection procedure. User device.

4. On the user device, The process involves receiving an RRC release message from a network node that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, but does not include legacy frequency priority information representing the priority of each frequency. This process controls whether the slice-specific cell reselection procedure is executed, and then executes the following: program.

5. A chipset for user equipment, The process involves receiving an RRC release message from a network node that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, but does not include legacy frequency priority information representing the priority of each frequency. The process of controlling whether or not the slice-specific cell reselection procedure is executed, and the process of executing Chipset.

6. A mobile communication system comprising network nodes and user equipment, The User device is The network node receives an RRC release message that includes slice-specific frequency priority information representing the priority of the frequencies supporting the network slice, without including legacy frequency priority information representing the priority of each frequency. This controls whether the slice-specific cell reselection procedure is executed. Mobile communication system.

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