CELL RESELECTION METHOD AND USER EQUIPMENT

In a first aspect, a cell reselection method is performed in a mobile communication system. The cell reselection method includes transmitting, by a base station, mapping information between a first slice group and a second slice group when the second slice group includes at least some of network slices included in the first slice group, the first slice group being available in a region of the base station, and the second slice group being available in a neighboring region adjacent to the region. The cell reselection method includes performing, by a user equipment, slice-specific cell reselection by using the mapping information.

TECHNICAL FIELD

The present disclosure relates to a cell reselection method in a mobile communication system.

BACKGROUND

In specifications of the Third Generation Partnership Project (3GPP), which is a standardization project for mobile communication systems, Network Slicing has been defined (for example, see Non-Patent Document 1). Network slicing is a technique for configuring a network slice that is a virtual network by logically dividing a physical network constructed by a telecommunications carrier.

CITATION LIST

SUMMARY

In a first aspect, a cell reselection method is performed in a mobile communication system. The cell reselection method includes transmitting, by a base station, mapping information between a first slice group and a second slice group when the second slice group includes at least some of network slices included in the first slice group, the first slice group being available in a region of the base station, and the second slice group being available in a neighboring region adjacent to the region. The cell reselection method includes performing, by a user equipment, slice-specific cell reselection by using the mapping information.

DESCRIPTION OF EMBODIMENTS

A user equipment in a Radio Resource Control (RRC) idle state or an RRC inactive state performs a cell reselection procedure. In the 3GPP, slice-specific cell reselection that is a network slice-dependent cell reselection procedure is under study.

An aspect aims at cell reselection being appropriately performed by the user equipment. An aspect aims at improving transmission efficiency in a base station. An aspect aims at mitigating a security problem.

A mobile communication system according to an embodiment is 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 signs.

First Embodiment

Configuration of Mobile Communication System

FIG.1is a diagram illustrating a configuration of a mobile communication system according to a first embodiment. The mobile communication system1complies with the 5th Generation System (5GS) of the 3GPP standard. The description below takes the 5GS as an example, but Long Term Evolution (LTE) system may be at least partially applied to the mobile communication system. A sixth generation (6G) system may be at least partially applied to the mobile communication system.

The mobile communication system1includes a User Equipment (UE)100, a 5G radio access network (Next Generation Radio Access Network (NG-RAN))10, and a 5G Core Network (5GC)20. The NG-RAN10may be hereinafter simply referred to as a RAN10. The 5GC20may be simply referred to as a core network (CN)20.

The UE100is a mobile wireless communication apparatus. The UE100may be any apparatus as long as the UE100is used by a user. Examples of the UE100include a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or an apparatus provided on a sensor, a vehicle or an apparatus provided on a vehicle (Vehicle UE), and a flying object or an apparatus provided on a flying object (Aerial UE).

The NG-RAN10includes base stations (referred to as “gNBs” in the 5G system)200. The gNBs200are interconnected via an Xn interface which is an inter-base station interface. Each gNB200manages one or more cells. The gNB200performs wireless communication with the UE100that has established a connection to the cell of the gNB200. The gNB200has a radio resource management (RRM) function, a function of routing user data (hereinafter simply referred to as “data”), a measurement control function for mobility control and scheduling, and the like. The “cell” is used as a term representing a minimum unit of a wireless communication area. The “cell” is also used as a term representing a function or a resource for performing wireless communication with the UE100. One cell belongs to one carrier frequency (hereinafter simply referred to as one “frequency”).

Note that the gNB can be connected to an Evolved Packet Core (EPC) corresponding to a core network of LTE. An LTE base station can also be connected to the 5GC. The LTE base station and the gNB can be connected via an inter-base station interface.

The 5GC20includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF)300. The AMF300performs various types of mobility controls and the like for the UE100. The AMF300manages mobility of the UE100by communicating with the UE100by using Non-Access Stratum (NAS) signaling. The UPF controls data transfer. The AMF and UPF300are connected to the gNB200via an NG interface which is an interface between a base station and the core network.

FIG.2is a diagram illustrating a configuration of the UE100(user equipment) according to the first embodiment. The UE100includes a receiver110, a transmitter120, and a controller130. The receiver110and the transmitter120constitute a wireless communicator that performs wireless communication with the gNB200.

The receiver110performs various types of reception under control of the controller130. The receiver110includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (a reception signal) and outputs the resulting signal to the controller130.

The transmitter120performs various types of transmission under control of the controller130. The transmitter120includes an antenna and a transmission device. The transmission device converts a baseband signal (a transmission signal) output by the controller130into a radio signal and transmits the resulting signal through the antenna.

The controller130performs various types of control and processing in the UE100. Such processing includes processing of respective layers to be described later. The controller130includes at least one processor and at least one memory. The memory stores a program to be executed by the processor and information to be used for processing by the processor. The processor may include a baseband processor and a Central Processing Unit (CPU). The baseband processor performs modulation and demodulation, coding and decoding, and the like of a baseband signal. The CPU executes the program stored in the memory to thereby perform various types of processing.

FIG.3is a diagram illustrating a configuration of the gNB200(base station) according to the first embodiment. The gNB200includes a transmitter210, a receiver220, a controller230, and a backhaul communicator240. The transmitter210and the receiver220constitute a wireless communicator that performs wireless communication with the UE100. The backhaul communicator240constitutes a network communicator that performs communication with the CN20.

The transmitter210performs various types of transmission under control of the controller230. The transmitter210includes an antenna and a transmission device. The transmission device converts a baseband signal (a transmission signal) output by the controller230into a radio signal and transmits the resulting signal through the antenna.

The receiver220performs various types of reception under control of the controller230. The receiver220includes an antenna and a reception device. The reception device converts a radio signal received through the antenna into a baseband signal (a reception signal) and outputs the resulting signal to the controller230.

The controller230performs various types of control and processing in the gNB200. Such processing includes processing of respective layers to be described later. The controller230includes at least one processor and at least one memory. The memory stores a program to be executed by the processor and information to be used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation and demodulation, coding and decoding, and the like of a baseband signal. The CPU executes the program stored in the memory to thereby perform various types of processing.

The backhaul communicator240is connected to a neighboring base station via an Xn interface which is an inter-base station interface. The backhaul communicator240is connected to the AMF/UPF300via a NG interface between a base station and the core network. Note that the gNB200may include a Central Unit (CU) and a Distributed Unit (DU) (i.e., functions are divided), and the two units may be connected via an F1 interface, which is a fronthaul interface.

FIG.4is a diagram illustrating a configuration of a protocol stack of a radio interface of a user plane handling data.

A radio interface protocol of the user plane 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.

The PHY layer performs coding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Data and control information are transmitted between the PHY layer of the UE100and the PHY layer of the gNB200via a physical channel. Note that the PHY layer of the UE100receives downlink control information (DCI) transmitted from the gNB200over a physical downlink control channel (PDCCH). Specifically, the UE100blind decodes the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE100. The DCI transmitted from the gNB200is appended with CRC parity bits scrambled by the RNTI.

The MAC layer performs priority control of data, retransmission processing through hybrid ARQ (HARQ: Hybrid Automatic Repeat reQuest), a random access procedure, and the like. Data and control information are transmitted between the MAC layer of the UE100and the MAC layer of the gNB200via a transport channel. The MAC layer of the gNB200includes a scheduler. The scheduler decides transport formats (transport block sizes, Modulation and Coding Schemes (MCSs)) in the uplink and the downlink and resource blocks to be allocated to the UE100.

The RLC layer transmits data to the RLC layer on the reception side by using functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE100and the RLC layer of the gNB200via a logical channel.

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

The SDAP layer performs mapping between an IP flow as the unit of Quality of Service (QOS) control performed by a core network and a radio bearer as the unit of QoS control performed by an Access Stratum (AS). Note that, when the RAN is connected to the EPC, the SDAP need not be provided.

FIG.5is a diagram illustrating a configuration of a protocol stack of a radio interface of a control plane handling signaling (a control signal).

The protocol stack of the radio interface of the control plane includes a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer illustrated inFIG.4.

RRC signaling for various configurations is transmitted between the RRC layer of the UE100and the RRC layer of the gNB200. The RRC layer controls a logical channel, a transport channel, and a physical channel according to establishment, re-establishment, and release of a radio bearer. When a connection (RRC connection) between the RRC of the UE100and the RRC of the gNB200is present, the UE100is in an RRC connected state. When no connection (RRC connection) between the RRC of the UE100and the RRC of the gNB200is present, the UE100is in an RRC idle state. When the connection between the RRC of the UE100and the RRC of the gNB200is suspended, the UE100is in an RRC inactive state.

The NAS which is positioned upper than the RRC layer performs session management, mobility management, and the like. NAS signaling is transmitted between the NAS of the UE100and the NAS of the AMF300. Note that the UE100includes an application layer other than the protocol of the radio interface. A layer lower than the NAS is referred to as Access Stratum (AS).

Overview of Cell Reselection Procedure

FIG.6is a diagram illustrating an overview of a cell reselection procedure.

The UE100in the RRC idle state or the RRC inactive state performs the cell reselection procedure with moving to migrate from a current serving cell (cell #1) to a neighboring cell (any one of cells #2 to #4). To be more specific, the UE100specifies a neighboring cell to be camped by the UE100through the cell reselection procedure and reselects the specified neighboring cell. When the frequency (carrier frequency) is the same between the current serving cell and the neighboring cell, it is referred to as an intra-frequency, and when the frequency (carrier frequency) is different between the current serving cell and the neighboring cell, it is referred to as an inter-frequency. The current serving cell and the neighboring cell may be managed by the same gNB200. The current serving cell and the neighboring cell may be managed by the gNBs200different from each other.

FIG.7is a flowchart illustrating a schematic flow of a typical (or legacy) cell reselection procedure.

In step S11, the UE100performs frequency priority handling processing based on frequency-specific priorities (also referred to as “absolute priorities”) specified by the gNB200, for example, by way of a system information block or an RRC release message. To be more specific, the UE100manages the frequency priority designated by the gNB200for each frequency.

In step S12, the UE100performs measurement processing of measuring radio qualities of the serving cell and each of the neighboring cells. The UE100measures reception powers and reception qualities of reference signals transmitted by the serving cell and each of the neighboring cells, to be more specific, cell defining-synchronization signal and PBCH block (CD-SSB). For example, the UE100always measures the radio quality for frequencies having a higher priority than the frequency of the current serving cell, and for frequencies having a priority equal to or lower than the priority of the frequency of the current serving cell, the UE100measures the radio quality of the frequency having the priority equal to or lower than the priority of the frequency of the current serving cell when the radio quality of the current serving cell is below a predetermined quality.

In step S13, the UE100performs the cell reselection processing of reselecting a cell on which the UE100camps based on the measurement result in step S20. For example, the UE100may perform cell reselection to a neighboring cell when a priority of a frequency of the neighboring cell is higher than the priority of the current serving cell and when the neighboring cell satisfies a predetermined quality standard (i.e., a minimal quality standard) for a predetermined period of time. When the priories of the frequencies of the neighboring cells are the same as the priority of the current serving cell, the UE100may rank the radio qualities of the neighboring cells to perform cell reselection to the neighboring cell ranked higher than a rank of the current serving cell for a predetermined period of time. When the frequency of the neighboring cell has a lower priority than the frequency of the current serving cell, the radio quality of the current serving cell is lower than a certain threshold value, and the radio quality of the neighboring cell is continuously higher than another threshold value for the predetermined period of time, the UE100may perform cell reselection to reselect the neighboring cell.

Overview of Network Slicing

The network slicing is a technique for virtually dividing a physical network (for example, a network including the NG-RAN10and the 5GC20) constructed by an operator to create a plurality of virtual networks. Each virtual network is referred to as a network slice. Hereinafter, the “network slice” may be simply referred to as a “slice”.

The network slicing allows a communication carrier to create slices according to service requirements of different service types, such as enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communications (URLLC), and massive Machine Type Communications (mMTC), for example, to optimize network resources.

FIG.8is a diagram illustrating an example of the network slicing.

Three slices (slices #1 to #3) are configured on a network50including the NG-RAN10and the 5GC20. The slice #1 is associated with a service type of eMBB, the slice #2 is associated with a service type of URLLC, and the slice #3 is associated with a service type of mMTC. Note that three or more slices may be configured on the network50. One service type may be associated with a plurality slices.

Each slice is provided with a slice identifier for identifying the slice. Examples of the slice identifier include a Single Network Slicing Selection Assistance Information (S-NSSAI). The S-NSSAI includes an 8-bit slice/service type (SST). The S-NSSAI may further include a 24-bit slice differentiator (SD). The SST is information indicating a service type with which a slice is associated. The SD is information for differentiating a plurality of slices associated with the same service type. The information including a plurality of pieces of S-NSSAI is referred to as a Network Slice Selection Assistance Information (NSSAI).

One or more slices may be grouped to configure a slice group. The 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 the core network (for example, the AMF300), or may be configured by the radio access network (for example, the gNB200). The UE100may be notified of the configured slice group.

Hereinafter, the term “network slice (slice)” may refer to S-NSSAI that is an identifier of a single slice or NSSAI that is a collection of pieces of S-NSSAI. The term “network slice (slice)” may refer to a slice group that is a group of one or more pieces of S-NSSAI or NSSAI.

The UE100also determines an intended slice that the UE100desires to use. A desired slice may be referred to as an “intended slice”. In the first embodiment, the UE100determines a slice priority for each network slice (desired slice). For example, the NAS of the UE100determines the slice priority based on an operation status of an application in the UE100and/or a user operation/setting, and notifies the AS of slice priority information indicating the determined slice priority.

Overview of Slice-Specific Cell Reselection Procedure

FIG.9is a diagram illustrating an overview of a slice-specific cell reselection procedure.

In the slice-specific cell reselection procedure, the UE100performs cell reselection processing based on slice frequency information provided from the network50. The slice frequency information may be provided from the gNB200to the UE100through broadcast signaling (for example, a system information block) or dedicated signaling (for example, an RRC release message).

The slice frequency information is information indicating mapping between network slices, frequencies, and frequency priorities. For example, the slice frequency information indicates, for each slice (or slice group), a frequency (one or more frequencies) that supports the slice and a frequency priority assigned to each frequency.FIG.10illustrates an example of the slice frequency information.

In the example illustrated inFIG.10, three frequencies F1, F2, and F4 are associated with the slice #1 as frequencies that support the slice #1. Among these three frequencies, the frequency priority of F1 is “6”, the frequency priority of F2 is “4”, and the frequency priority of F4 is “2”. In the example ofFIG.10, the larger the number of the frequency priority, the higher the priority is, but a case in which the smaller the number, the higher the priority is may also be possible.

Three frequencies F1, F2, and F3 are associated with the slice #2 as frequencies that support the slice #2. Among these three frequencies, the frequency priority of F1 is “0”, the frequency priority of F2 is “5”, and the frequency priority of F3 is “7”.

Three frequencies F1, F3, and F4 are associated with the slice #3 as frequencies that support the slice #3. Among these three frequencies, the frequency priority of F1 is “3”, the frequency priority of F3 is “7”, and the frequency priority of F4 is “2”.

Hereinafter, the frequency priority indicated in the slice frequency information may be referred to as a “slice-specific frequency priority” in order to be distinguished from the absolute priority in the conventional cell reselection procedure.

As illustrated inFIG.9, the UE100may perform the cell reselection processing further based on slice support information provided from the network50. The slice support information may be information indicating mapping between a cell (for example, a serving cell and each neighboring cell) and a network slice that is not provided or provided by the cell. For example, a cell may temporarily fail to provide some or all network slices due to congestion or the like. That is, even for a slice support frequency capable of providing a network slice, some cells within the frequency may not provide the network slice. Based on the slice support information, the UE100may grasp which network slice is not provided by each cell. The slice support information like this may be provided from the gNB200to the UE100through broadcast signaling (for example, a system information block) or dedicated signaling (for example, an RRC release message).

FIG.11is a flowchart illustrating a basic flow of the slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, the UE100is assumed to be in the RRC idle state or the RRC inactive state, and to receive and retain the above-mentioned slice frequency information. The “slice-specific cell reselection procedure” describes the procedure of the “slice-specific cell reselection”. However, in the following description, the “slice-specific cell reselection” and the “slice-specific cell reselection procedure” may be used with the same meaning.

In step S0, the NAS of UE100determines the slice identifiers of the desired slices for the UE100and the slice priorities of the desired slices, and notifies the AS of the UE100of slice priority information including the determined slice priorities. The “desired slice” is an “Intended slice”, and includes a slice that is likely to be used, a candidate slice, a wanted slice, a slice with which communication is desired, a requested slice, an allowed slice, or an intended slice. For example, the slice priority of the slice #1 is determined to be “3”, the slice priority of the slice #2 is determined to be “2”, and the slice priority of the slice #3 is determined to be “1”. The larger the number of the slice priority, the higher the priority is, but a case in which the smaller the number, the higher the priority is may also be possible.

In step S1, the AS of the UE100rearranges the slices (slice identifiers), of which the AS is notified by the NAS in step S0, in descending order of slice priority. A list of the slices arranged in this manner is referred to as a “slice list”.

In step S2, the AS of the UE100selects one network slice in descending order of slice priority. The network slice selected in this manner is referred to as a “selected network slice”.

In step S3, the AS of the UE100assigns, for the selected network slice, a frequency priority to each of the frequencies associated with that network slice. To be more specific, the AS of the UE100specifies frequencies associated with the slice based on the slice frequency information and assigns frequency priorities to the specified frequencies. For example, when the selected network slice selected in step S2is the slice #1, the AS of the UE100assigns the frequency priority “6” to the frequency F1, the frequency priority “4” to the frequency F2, and the frequency priority “2” to the frequency F4 according to the slice frequency information (for example, the information inFIG.10). The AS of the UE100refers to a list of frequencies arranged in descending order of frequency priority as a “frequency list”.

In step S4, the AS of the UE100selects one of the frequencies in descending order of frequency priority for the selected network slice selected in step S2, and performs the measurement processing on the selected frequency. The frequency selected in this manner is referred to as a “selected frequency”. The AS of the UE100may rank the cells measured within the selected frequency in descending order of radio quality. Among the cells measured within the selected frequency, those cells that satisfy a predetermined quality standard (i.e., a minimal quality standard) are referred to as “candidate cells”.

In step S5, the AS of the UE100specifies a highest ranked cell based on the result of the measurement processing in step S4, and determines whether the cell provides the selected network slice based on the slice support information. When determining that the highest ranked cell provides the selected network slice (step S5: YES), the AS of the UE100reselects the highest ranked cell and camps on that cell in step S5a.

On the other hand, when determining that the highest ranked cell does not provide the selected network slice (step S5: NO), the AS of UE100determines in step S6whether a frequency not measured is present in the frequency list created in step S3. In other words, the AS of the UE100determines whether a frequency to which the frequency priorities have been assigned in step S3other than the selected frequency is present in the selected network slice. When determining that a frequency not measured is present (step S6: YES), the AS of the UE100resumes the processing for the frequency having the next highest frequency priority, and performs the measurement processing by use of that frequency as selected frequency (returns the processing to step S4).

When determining that a frequency not measured is not present in the frequency list created in step S3(step S6: NO), the AS of the UE100may determine in step S7whether an unselected slice is present in the slice list created in step S1. In other words, the AS of the UE100may determine whether a network slice other than the selected network slice is contained in the slice list. When determined that an unselected slice is present (step S7: YES), the AS of the UE100resumes the processing for the network slice having the next highest slice priority, and selects that network slice as the selected network slice (returns the processing to step S2). Note that in the basic flow illustrated inFIG.11, the process in step S7may be omitted.

When determining that an unselected slice is not present (step S7: NO), the AS of the UE100performs conventional cell reselection processing in step S8. The conventional cell reselection processing may mean an entirety of a typical (or legacy) cell reselection procedure illustrated inFIG.7. The conventional cell reselection processing may also mean only cell reselection processing (step S30) illustrated inFIG.7. In the latter case, the UE100may use the measurement result in step S4without measuring the radio qualities of the cells again.

Cell Reselection Method according to First Embodiment

As described above, in the slice-specific cell reselection (which may be slice aware cell reselection), the UE100selects the desired slice for processing. At this time, the UE100may select a slice group as the selected slice. For example, the UE100selects a slice group #1 that includes the slice #1, which is the desired slice. In this case, the UE100may reselect a cell supporting the corresponding slice group #1 in the slice-specific cell reselection.

The slice group includes one or more network slices. The 3GPP has agreed that slice groups should be homogeneous within the same Registration Area (RA). That is, in the same RA, all the network slices included in a slice group should be the same.

Note that the RA includes one or a plurality of cells, and is defined as a set of Tracking Areas (TAs). Since the RA includes a plurality of TAs, the RA enables a reduction in the number of transmissions of the registration update signaling compared to per TA transmission of the registration update signaling.

On the other hand, in a different RA, the slice group may include different network slices.

FIG.12is a diagram illustrating an example of mapping relationships between slice groups and network slices according to the first embodiment.FIG.12illustrates an example in which the boundary between the cell range of a gNB200-1and the cell range of a gNB200-2is the boundary between RAs. That is, the cell of the gNB200-1belongs to an RA #1, and the cell of the gNB200-2belongs to an RA #2. The RA #1 including the cell of the gNB200-1includes the slice #1 and the slice #2 as the slice group #1. In the RA #2 including the cell of the gNB200-2, the slice group #1 includes the slice #3 and the slice #4. Between the RA #1 and the RA #2, even the same slice group #1 includes different network slices.

In such an example, the following case is considered. That is, in the RA #1, the UE100camps on the cell supporting the slice group #1 by cell reselection according to the slice-specific cell reselection procedure.

Subsequently, the UE100moves and performs cell reselection again according to the slice-specific cell reselection procedure. At this time, the UE100is assumed to have moved to an area where the UE100can communicate with the cell of the gNB200-2(that is, the cell of the RA #2). In this case, since the desired slice is the slice #1, the UE100may select the slice group #1 in the RA #2 and perform the slice-specific cell reselection procedure. The UE100attempts to camp on the cell supporting the slice group #1 in the RA #2.

However, the slice group #1 in the RA #2 does not support the slice #1, which is the desired slice. Therefore, in such a case, selecting, by the UE100, the slice group #1 in the RA #2 means selecting a wrong cell group. In such a case, the UE100performs no appropriate cell reselection.

Thus, such a problem may be solved by using a SIB to broadcast, by the gNB200, the slice groups supported in the neighboring cell. For example, in the case ofFIG.12, the gNB200-1broadcasts identification information of the slice group #1 and identification information of each of the slice #3 and the slice #4 as the information of the slice group #1 supported in the neighboring cell (i.e., the RA #2). Since the UE100can recognize the mapping relationship between the slice group #1 and slices (the slice #3 and the slice #4) in the RA #2, the UE100can refrain from selecting the slice group #1 in the RA #2 at the time of slice-specific cell reselection.

However, the broadcast of the slice group by the gNB200may pose the following problem.

First, 32 bits are present for the identification information of the network slice. The identification information of the network slice has a large data size compared to the information of the slice group, which is simply a number. Accordingly, transmission of the identification information of the network slice by the gNB200during transmission of the slice group is not necessarily more efficient than transmission of the identification information of the slice group.

Second, the transmission of the identification information of the network slice by the gNB200may pose a problem in terms of security. For example, an operator other than the operator managing the gNB200may be able to acquire the identification information of the network slice.

Thus, an object of the first embodiment is to perform appropriate cell reselection in the UE100. Another object of the first embodiment is to improve the transmission efficiency in the gNB200. Yet another object of the first embodiment is to mitigate the security problem.

Thus, in the first embodiment, the gNB200-1transmits mapping information indicating the mapping relationships between the slice groups in the RA #1 and the slice groups in the RA #2 without transmitting the identification information of the network slice.

Specifically, first, the base station (e.g., the gNB200-1) transmits the mapping information between a first slice group (e.g., a cell group #1) and a second slice group (e.g., a cell group #2) when the second slice group includes at least some of network slices included in the first slice group, the first slice group being available in a region (e.g., the RA #1) of the base station, and the second slice group being available in a neighboring region (e.g., the RA #2) adjacent to the region. Second, the user equipment (e.g., the UE100) performs slice-specific cell reselection using the mapping information.

Thus, the UE100can acquire information of the slice group including the desired slice in the RA #2 from the mapping information received from the gNB200-1. Therefore, even upon moving to the boundary between the RAs, the UE100can mitigate a wrong selection of a slice group by reselecting a cell supporting the desired slice. Therefore, the UE100can perform appropriate cell reselection.

The mapping information includes no identification information of the network slice. Therefore, the transmission of the mapping information can improve the transmission efficiency of the gNB200compared with the transmission of the identification information of the network slice. Since the identification information of the network slice is not transmitted, the security problem can be mitigated.

Specific examples of the mapping information include the following.

First, some of the network slices included in a first slice group in a first RA may be included in a second slice group in a second RA.

FIG.13is a diagram illustrating an example of mapping relationships between slice groups and network slices according to the first embodiment. InFIG.13, both the slice group #1 in the RA #1 and the slice group #2 in the RA #2 include the same slice #1. Therefore, the slice group #1 in the RA #1 and the slice group #2 in the RA #2 can be mapped as the mapping information. Specifically, the identification information of the RA #1 and the identification information of the slice group #1 may be mapped to each other, the identification information of the RA #2 and the identification information of the slice group #2 may be mapped to each other, and information obtained by mapping these pieces of information may be included in the mapping information. Note that the identification information of the RA may be represented by a list of TAs included in the RA (the list refers to a Tracking Area Identity (TAI) list). The same applies to the description below. Note that the mapping information may include information indicating a “partial match” as a type of mapping information. The mapping information may also include the number of network slices included in each slice group. For example, in the example ofFIG.13, the mapping information may include “2” for the slice group #1 in the RA #1 (the slice #1 and the slice #2) and “2” for the slice group #2 in the RA #2 (the slice #1 and the slice #5).

Second, all of the network slices included in the first slice group in the first RA may be included in the second slice group in the second RA.

FIG.14is a diagram illustrating an example of mapping relationships between slice groups and network slices according to the first embodiment. InFIG.14, the network slices (the slice #3 and the slice #4) included in the slice group #2 in the RA #1 are all the same as the network slices (the slice #3 and the slice #4) included in the slice group #1 in the RA #2. In this case, in the mapping information, the identification information of the RA #1 and the identification information of the slice group #2 are mapped to each other, the identification information of the RA #2 and the identification information of the slice group #1 are mapped to each other, and information obtained by mapping these pieces of information may be included in the mapping information. Note that the mapping information may include information indicating a “complete match” as a type of mapping information. The mapping information may also include the number of network slices included in each slice group. For example, in the example ofFIG.14, the mapping information includes information indicating “2” for the slice group #2 in the RA #1 (the slice #3 and the slice #4) and “2” for the slice group #1 in the RA #2 (the slice #3 and the slice #4).

Third, one network slice included in the first slice group in the first RA may be the same as one network slice included in the second slice group in the second RA.

FIG.15is a diagram illustrating an example of mapping relationships between slice groups and network slices according to the first embodiment. InFIG.15, one network slice (the slice #6) included in the slice group #3 in the RA #1 is the same as one network slice (the slice #6) included in the slice group #3 in the RA #2. In this case, in the mapping information, the identification information of the RA #1 and the identification information of the slice group #3 may be mapped to each other, the identification information of the RA #2 and the identification information of the slice group #3 may be mapped to each other, and information obtained by mapping these pieces of information may be included in the mapping information. The mapping information in this case is more effective when one slice group includes only one network slice. Note that the mapping information may include information indicating a “complete match” as a type of mapping information. The mapping information may also include the number of network slices included in the slice group. For example, in the example ofFIG.15, the mapping information may include information indicating “1” for the slice group #3 in the RA #1 (the slice #6) and “1” for the slice group #3 in the RA #2 (the slice #6).

The above three types of mapping information may be combined. In the example shown inFIG.14, the slice group #1 in the RA #1 and the slice group #2 in the RA #2 may be mapped to each other, the slice group #2 in the RA #1 and the slice group #1 in the RA #2 may be mapped to each other, and two mapping relationships may be included in one piece of mapping information. In the example illustrated inFIG.15, the slice group #1 in the RA #1 and the slice group #2 in the RA #2 may be mapped to each other, the slice group #2 in the RA #1 and the slice group #1 in the RA #2 may be mapped to each other, the slice group #3 in the RA #1 and the slice group #3 in the RA #2 may be mapped to each other, and three mapping relationships may be included in one piece of mapping information. Note that the mapping information may include information indicating the type of each mapping relationship (a “partial match” or a “complete match”). The mapping information may include information indicating the number of network slices included in each slice group.

In the examples described above, the network slices included in the slice group vary from RA to RA, but the present invention is not limited to this. For example, the network slices included in the slice group may vary from TA to TA. For example, inFIG.15, by replacing the portion labeled “RA #1” with “TA #1” and replacing the portion labeled “RA #2” with “TA #2”, the present embodiment can be implemented as is the case with the RAs.

That is, any region may be used as long as the mapping relationships between the slice groups and the network slices are homogeneous in the regions. When the mapping relationships between the slice groups and the network slices may change between such regions, the present embodiment can be implemented at the boundary between such regions. The above-described examples indicate that the region may be either an RA or a TA. The region may be a RAN-based Notification Area (RNA) or may be a Public Land Mobile Network (PLMN). The region may include a plurality of cells. The region may include a plurality of RAs, may include a plurality of TAs, or may include a plurality of RNAs. The region may be a combination of a TA, an RA, an RNA, a PLMN, and a plurality of cells. For example, the gNB200arranged in the TA #1 may transmit the mapping information of the RA #2 adjacent to TA #1.

Operation Example according to First Embodiment

FIG.16is a flowchart illustrating an operation example according to the first embodiment. In the following description, the regions are RAs (or TAs) as an example.

As illustrated inFIG.16, in step S20, the gNB200acquires the mapping relationships between the slice groups and the network slices in the neighboring RA (or the neighboring TA). The gNB200-1may acquire the information representing the mapping relationships between the slice groups and the network slices from the neighboring gNB200-2arranged in the neighboring RA (or the neighboring TA). In this case, the gNB200-1may acquire the information by receiving an Xn message including the information. The gNB200-1may acquire the information by receiving, from the AMF300, an NG message including the information.

In step S21, the gNB200generates mapping information based on the mapping relationships between the slice groups and the network slices in the local RA (or the local TA) and the mapping relationships between the slice groups and the network slices in the neighboring RA (or the neighboring TA). In the example ofFIG.13, the gNB200manages the mapping relationship between the slice group #1 and the slices (the slice #1 and the slice #2) in the local RA (the RA #1). The gNB200is assumed to have acquired, from the neighboring RA, the mapping relationships between the slice groups and the network slices (the mapping relationship between the slice group #1 and the slices (the slice #3 and the slice #4) and the mapping relationship between the slice group #2 and the slices (the slice #1 and the slice #5)). In this case, since the slice group #1 in the RA #1 and the slice group #2 in the RA #2 both include the slice #1, the gNB200generates mapping information in which the slice group #1 in the RA #1 and the slice group #2 in the RA #2 are mapped to each other.

Note that the gNB200may acquire the mapping information from the AMF300, while generating no mapping information by itself. In this case, the gNB200may acquire the mapping information by receiving the NG message including the mapping information. The gNB200may acquire the mapping information from the neighboring gNB, while generating no mapping information by itself. In this case, the gNB200may acquire the mapping information by receiving the Xn message including the mapping information.

Referring back toFIG.16, in Step S22, the gNB200transmits the mapping information. The gNB200may broadcast the mapping information through broadcast signaling (e.g., the SIB). The gNB200may transmit the mapping information through dedicated signaling (e.g., RRC release (RRCRelease) message). In this case, the gNB200may include, in the mapping information, the mapping relationships between the slice groups and the network slices in the neighboring RA (or the neighboring TA). For example, in the example ofFIG.13, the gNB200-1may transmit mapping information including the mapping relationship between the slice group #1 and the slices (the slice #3 and the slice #4) in the RA #2 and the mapping relationship between the slice group #2 and the slices (the slice #1 and the slice #5) in the RA #2. This is because concern about security is mitigated in the RRC message. However, regardless of the RRC message, even in the case of broadcast transmission, the gNB200may transmit, in a predetermined case, the mapping relationships between the slice groups and the network slices in the neighboring RA (or neighboring TA). The predetermined case is, for example, the case of only a “partial match” with the neighboring RA (or the neighboring TA) and/or the case of the boundary between the RAs (or the TAs). This is based on the idea that the concern for security is not regarded as a problem under a limited condition involving the predetermined case.

Note that the mapping information may include a Tracking Area Code (TAC) and/or a Physical Cell ID (PCI).

Note that the AMF300may transmit the mapping information to the UE100. In this case, the AMF300may transmit, to the NAS of the UE100, a NAS message including the mapping information, and the NAS of the UE100may notify the AS of the UE100of the mapping information. In this case, upon generating mapping information, the gNB200may transmit, to the AMF300, the NG message including the mapping information.

Subsequently, in step S23, the UE100performs the slice-specific cell reselection procedure using the mapping information. For example, as illustrated inFIG.13, a case is considered in which the UE100moves to the vicinity of the cell of the gNB200-2arranged in the neighboring RA (or the neighboring TA) and performs the slice-specific cell reselection procedure. Even in this case, the UE100can select the slice group #2 in the RA #2 as a selected slice using the mapping information, and can reselect the cell supporting the slice group #2 in the RA #2.

Note that the transmission of the mapping information (step S22) and the execution of the slice-specific cell reselection procedure (step S23) may be performed at predetermined timings. For example, at the stage where the field strength of the serving cell in the UE100(e.g., the serving cell of the gNB200-1) does not require cell reselection, the gNB200transmits the mapping information (step S22). Then, at the stage where the field strength requires cell reselection, the UE100may perform the slice-specific cell reselection procedure (step S23).

OTHER EMBODIMENTS

A program causing a computer to execute each of the processing performed by the UE100or the gNB200may be provided. The program may be recorded in a computer readable medium. Use of the computer readable medium enables the program to 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.

Circuits for executing processing performed by the UE100or the gNB200may be integrated, and at least a part of the UE100or the gNB200may be implemented as a semiconductor integrated circuit (chipset, system on a chip (SoC)).

The phrases “based on” and “depending on” used in the present disclosure do not mean “based only on” and “only depending on,” unless specifically stated otherwise. The phrase “based on” means both “based only on” and “based at least in part on”. The phrase “depending on” means both “only depending on” and “at least partially depending on”. The terms “include”, “comprise” and variations thereof do not mean “include only items stated” but instead mean “may include only items stated” or “may include not only the items stated but also other items.” The term “or” used in the present disclosure is not intended to be “exclusive or”. Any references to elements using designations such as “first” and “second” as used in the present disclosure do 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 first and second elements does not mean that only two elements may be employed there or that the first element needs to precede the second element in some manner. For example, when the English articles such as “a,” “an,” and “the” are added in the present disclosure through translation, these articles include the plural unless clearly indicated otherwise in context.

Embodiments have been described above in detail with reference to the drawings, but specific configurations are not limited to those described above, and various design variations can be made without departing from the gist of the present disclosure. All or some of the embodiments, operations, processes, and steps may be combined without being inconsistent.

Supplementary Note

Features relating to the embodiments described above are described below as supplements.

A cell reselection method in a mobile communication system, the cell reselection method including:transmitting, by a base station, mapping information between a first slice group and a second slice group when the second slice group includes at least some of network slices included in the first slice group, the first slice group being available in a region of the base station, and the second slice group being available in a neighboring region adjacent to the region; andperforming, by a user equipment, slice-specific cell reselection by using the mapping information.
(2)

The cell reselection method according to (1) recited above, wherein the region is a Tracking Area (TA), and the neighboring region is a neighboring TA adjacent to the TA, orthe region is a Registration Area (RA), and the neighboring region is a neighboring RA adjacent to the RA.
(3)

The cell reselection method according to (1) or (2) recited above, whereinthe mapping information includes identification information of the first slice group andidentification information of the second slice group.

REFERENCE SIGNS