CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2018/002041, filed Jan. 24, 2018, claiming priority to Japanese Patent Application No. 2017-118095, filed Jun. 15, 2017, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a radio communication system and, in particular, to communication in which a radio terminal simultaneously uses a plurality of cells of different Radio Access Technologies (RATs) operated by different radio stations (multi-connectivity operation).

BACKGROUND ART

The 3rd Generation Partnership Project (3GPP) has been conducting the standardization for the fifth generation mobile communication system (5G) to make it a commercial reality in 2020 or later. 5G is expected to be realized by continuous enhancement/evolution of LTE and LTE-Advanced and an innovative enhancement/evolution by an introduction of a new 5G air interface (i.e., a new Radio Access Technology (RAT)). The new RAT supports, for example, frequency bands higher than the frequency bands (e.g., 6 GHz or lower) supported by LTE/LTE-Advanced and its continuous evolution. For example, the new RAT supports centimeter-wave bands (10 GHz or higher) and millimeter-wave bands (30 GHz or higher).

In this specification, the fifth generation mobile communication system is referred to as a 5G System or a Next Generation (NextGen) System (NG System). The new RAT for the 5G System is referred to as a New Radio (NR), a 5G RAT, or a NG RAT. A new Radio Access Network (RAN) for the 5G System is referred to as a 5G-RAN or a NextGen RAN (NG RAN). A new base station in the 5G-RAN is referred to as a NR NodeB (NR NB) or a gNodeB (gNB). A new core network for the 5G System is referred to as a 5G Core Network (5G-CN or 5GC) or a NextGen Core (NG Core). A radio terminal (i.e., User Equipment (UE)) capable of being connected to the 5G System is referred to as 5G UE or NextGen UE (NG UE), or simply referred to as UE. The official names of the RAT, UE, radio access network, core network, network entities (nodes), protocol layers and the like for the 5G System will be determined in the future as standardization work progresses.

The term “LTE” used in this specification includes enhancement/evolution of LTE and LTE-Advanced to provide interworking with the 5G System, unless otherwise specified. The enhancement/evolution of LTE and LTE-Advanced for the interworking with the 5G System is referred to as LTE-Advanced Pro, LTE+, or enhanced LTE (eLTE). Further, terms related to LTE networks and logical entities used in this specification, such as “Evolved Packet Core (EPC)”, “Mobility Management Entity (MME)”, “Serving Gateway (S-GW)”, and “Packet Data Network (PDN) Gateway (P-GW))”, include their enhancement/evolution to provide interworking with the 5G System, unless otherwise specified. Enhanced EPC, enhanced MME, enhanced S-GW, and enhanced P-GW are referred to, for example, as enhanced EPC (eEPC), enhanced MME (eMME), enhanced S-GW (eS-GW), and enhanced P-GW (eP-GW), respectively.

In LTE and LTE-Advanced, for achieving Quality of Service (QoS) and packet routing, a bearer per QoS class and per PDN connection is used in both a RAN (i.e., an Evolved Universal Terrestrial RAN (E-UTRAN)) and a core network (i.e., EPC). That is, in the Bearer-based QoS (or per-bearer QoS) concept, one or more Evolved Packet System (EPS) bearers are configured between a UE and a P-GW in an EPC, and a plurality of Service Data Flows (SDFs) having the same QoS class are transferred through one EPS bearer satisfying this QoS. An SDF is one or more packet flows that match an SDF template (i.e., packet filters) based on a Policy and Charging Control (PCC) rule. In order to achieve packet routing, each packet to be transferred through an EPS bearer contains information for identifying which bearer (i.e., General Packet Radio Service (GPRS) Tunneling Protocol (GTP) tunnel) the packet is associated with.

In contrast, with regard to the 5G System, it is discussed that although radio bearers may be used in the NG-RAN, no bearers are used in the 5GC or in the interface between the 5GC and the NG-RAN (see Non-Patent Literature 1). Specifically, PDU flows are defined instead of an EPS bearer, and one or more SDFs are mapped to one or more PDU flows. A PDU flow between a 5G UE and a user-plane terminating entity in an NG Core (i.e., an entity corresponding to a P-GW in the EPC) corresponds to an EPS bearer in the EPS Bearer-based QoS concept. The PDU flow corresponds to the finest granularity of the packet forwarding and treatment in the 5G system. That is, the 5G System adopts the Flow-based QoS (or per-flow QoS) concept instead of the Bearer-based QoS concept. In the Flow-based QoS concept, QoS is handled per PDU flow. In the QoS framework of the 5G system, a PDU flow is identified by a PDU flow ID contained in a header encapsulating a Service Data Unit of a tunnel of a NG3 interface. The NG3 interface is a user plane interface between the 5GC and the gNB (i.e., NG-RAN). Association between a 5G UE and a data network is referred to as a “PDU session”. The term “PDU session” corresponds to the term “PDN connection” in LTE and LTE-Advanced. A plurality of PDU flows can be configured in one PDU session.

The PDU flow is also referred to as a “QoS flow”. The QoS flow is the finest granularity in QoS treatment in the 5G system. User plane traffic having the same NG3 marking value in a PDU session corresponds to a QoS flow. The NG3 marking corresponds to the above-described PDU flow ID, and it is also referred to as a QoS flow ID or a Flow Identification Indicator (FII).

FIG. 1shows a basic architecture of the 5G system. A UE establishes one or more Signalling Radio Bearers (SRBs) and one or more Data Radio Bearers (DRBs) with a gNB. The 5GC and the gNB establish a control plane interface and a user plane interface for the UE. The control plane interface between the 5GC and the gNB (i.e., RAN) is referred to as an NG2 interface or an NG-c interface and is used for transfer of Non-Access Stratum (NAS) information and for transfer of control information (e.g., NG2 AP Information Element) between the 5GC and the gNB. The user plane interface between the 5GC and the gNB (i.e., RAN) is referred to as an NG3 interface or an NG-u interface and is used for transfer of packets of one or more PDU flows in a PDU session of the UE.

Note that the architecture shown inFIG. 1is merely one of the 5G architecture options (or deployment scenarios). The architecture shown inFIG. 1is referred to as “Standalone NR (in NextGen System)” or “Option 2”. The 3GPP further discusses several network architectures for multi-connectivity operations using the E-UTRA and NR radio access technologies. The multi-connectivity operation using the E-UTRA and NR radio access technologies is referred to as Multi-RAT Dual Connectivity (MR-DC). The MR-DC is dual connectivity between E-UTRA and NR nodes.

In the MR-DC, one of the E-UTRA node (i.e., eNB) and the NR node (i.e., gNB) operates as a Master node (MN) and the other one operates as a Secondary node (SN), and at least the MN is connected to the core network. The MN provides one or more Master Cell Group (MCG) cells to the UE, while the SN provides one or more Secondary Cell Group (SCG) cells to the UE. The MR-DC includes “MRDC with the EPC” and “MRDC with the 5GC”.

The MRDC with the EPC includes E-UTRA-NR Dual Connectivity (EN-DC). In the EN-DC, the UE is connected to an eNB operating as the MN and a gNB operating as the SN. Further, the eNB (i.e., Master eNB) is connected to the EPC, while the gNB (i.e. Secondary gNB) is connected to the Master eNB through the X2 interface.

The MRDC with the 5GC includes NR-E-UTRA Dual Connectivity (NE-DC) and E-UTRA-NR Dual Connectivity (NG-EN-DC). In the NE-DC, the UE is connected to a gNB operating as the MN and an eNB operating as the SN, the gNB (i.e., Master gNB) is connected to the 5GC, and the eNB (i.e. Secondary eNB) is connected to the Master gNB through the Xn interface. On the other hand, in the NG-EN-DC, the UE is connected to an eNB operating as the MN and a gNB operating as the SN, the eNB (i.e., Master eNB) is connected to the 5GC, and the gNB (i.e. Secondary gNB) is connected to the Master eNB through the Xn interface.

FIGS. 2, 3, and 4show network configurations of the above-described three DC types, i.e., EN-DC, NE-DC, and NG-EN-DC, respectively.FIG. 5shows SRBs and DRBs supported by these three DC types. Not that,FIG. 5shows bearer types to be supported in 3GPP Release 15 that is currently under discussion in the 3GPP. Accordingly, the bearer types supported by the three DC types may be different from those shown inFIG. 5.

The MCG SRB is an SRB established between the UE and the MN. Radio Resource Control Protocol Data Units (RRC PDUs) generated by the SN can be transported to the UE via the MN and the MCG SRB. Alternatively, the UE is able to establish an SRB (SCG SRB) with the SN in order to transport RRC PDUs for the SN directly between the UE and the SN. The MCG split SRB enables duplication of RRC PDUs generated by the MN.

The MCG bearer is a user plane bearer whose radio protocols are only located in the MCG. The MCG split bearer is a user plane bearer whose radio protocols are split at the MN and belong to both the MCG and the SCG. The SCG bearer is a user plane bearer whose radio protocols are only located in the SCG. The SCG split bearer is a user plane bearer whose radio protocols are split at the SN and belong to both the SCG and the MCG.

Note that, the layer 2 functionality of the gNB (NR) is not the same as the layer 2 functionality of the eNB (LTE). For example, the layer 2 of the gNB (NR) includes four sublayers, i.e., a Service Data Adaptation Protocol (SDAP) sublayer, a Packet Data Convergence Protocol (PDCP) sublayer, a Radio Link Control (RLC) sublayer, and a Medium Access Control (MAC) sublayer. In the NR PDCP sublayer, the size of the PDCP Sequence Number (SN) for DRBs is 12 bits or 18 bits, which is a subset of the possible values for the size of LTE PDCP SN (i.e., 7 bits, 12 bits, 15 bits, or 18 bits). However, when the eNB (LTE) is connected to the 5GC, the layer 2 of the eNB (LTE) includes an SDAP sublayer.

The 3GPP is also discussing an introduction of a unified split bearer. The purpose of the introduction of the unified split bearer is to use the same protocols, configurations, and procedures for both the MCG and SCG split bearers as much as possible, thereby simplifying the specification and UE implementation. As specific means for this introduction, a common (single) PDCP layer has been proposed (see Non-Patent Literature 1). The common PDCP layer supports both the MCG and SCG split bearers. For example, the common PDCP layer may be the same as a PDCP layer (NR PDCP layer) used for the NR standalone operation.

Non-Patent Literature 1 proposes that it should be possible to switch between split and no-split bearers without re-establishing PDCP in cases where the PDCP termination point is not moved. Non-Patent Literature 1 further proposes that it should be possible to configure the same PDCP version as used for split bearers already when the UE operates in LTE only, to allow switching to and from split bearers without PDCP re-establishment due to protocol change.

CITATION LIST

Non Patent Literature

[Non-Patent Literature 1] 3GPP Tdoc R2-1704414, Ericsson, “On the different bearer options”, 3GPP TSG-RAN WG2 Meeting #98, May 2017

SUMMARY OF INVENTION

Technical Problem

As described above, Non-Patent Literature 1 proposes a common (single) PDCP layer that supports both the MCG and SCG split bearers. The common PDCP layer may be referred to as a unified PDCP layer. However, it is not clear how the common (or unified) PDCP layer should be implemented in a radio communication network (e.g., 3GPP network).

One of the objects to be attained by embodiments disclosed herein is to provide an apparatus, a method, and a program that assist in implementation of a common (or unified) PDCP layer in a radio communication network. It should be noted that this object is merely one of the objects to be attained by the embodiments disclosed herein. Other objects or problems and novel features will be made apparent from the following description and the accompanying drawings.

Solution to Problem

In a first aspect, a master RAN node associated with a master RAT includes a memory and at least one processor coupled to the memory. The at least one processor is configured to communicate with a secondary RAN node associated with a secondary RAT and provide a radio terminal with dual connectivity that uses the master RAT and the secondary RAT. The at least one processor is further configured to, in response to receiving, from the radio terminal or a core network, terminal capability information indicating that the radio terminal supports a split bearer, use a Packet Data Convergence Protocol (PDCP) entity, which provides unified PDCP functionalities, for a master cell group split bearer for the radio terminal. The unified PDCP functionalities are used for both the master cell group split bearer and a secondary cell group split bearer. The master cell group split bearer is a user plane bearer whose radio protocols are split at the master RAN node and belong to both a master cell group provided by the master RAN node and a secondary cell group provided by the secondary RAN node. The secondary cell group split bearer is a user plane bearer whose radio protocols are split at the secondary RAN node and belong to both the secondary cell group and the master cell group.

In a second aspect, a secondary RAN node configured to support a secondary RAT includes a memory and at least one processor coupled to the memory. The at least one processor is configured to communicate with a master RAN node that supports a master RAT and provide a radio terminal with dual connectivity that uses the master RAT and the secondary RAT. The at least one processor is further configured to, if the master RAN node receives, from the radio terminal or a core network, terminal capability information indicating that the radio terminal supports a split bearer, use a Packet Data Convergence Protocol (PDCP) entity, which provides unified PDCP functionalities, for a secondary cell group split bearer for the radio terminal.

In a third aspect, a radio terminal includes at least one wireless transceiver and at least one processor. The at least one wireless transceiver is configured to communicate with both a master radio access network (RAN) node associated with a master radio access technology (RAT) and a secondary RAN node associated with a secondary RAT. The at least one processor is configured to perform, via the at least one wireless transceiver, dual connectivity that uses the master RAT and the secondary RAT. The at least one processor is further configured to, if the radio terminal supports a split bearer, transmit, to the master RAN node, terminal capability information indicating that the radio terminal supports a split bearer. Furthermore, the at least one processor is configured to, if the radio terminal supports a split bearer, use a Packet Data Convergence Protocol (PDCP) entity, which provides unified PDCP functionalities, for a master cell group split bearer for the radio terminal.

In a fourth aspect, a method for a master RAN node associated with a master RAT includes:

(a) communicating with a secondary RAN node associated with a secondary RAT and providing a radio terminal with dual connectivity that uses the master RAT and the secondary RAT; and

(b) in response to receiving, from the radio terminal or a core network, terminal capability information indicating that the radio terminal supports a split bearer, using a Packet Data Convergence Protocol (PDCP) entity for a master cell group split bearer for the radio terminal, the PDCP entity providing unified PDCP functionalities.

In a fifth aspect, a method for a secondary RAN node configured to support a secondary RAT includes:

(a) communicating with a master RAN node that supports a master RAT and providing a radio terminal with dual connectivity that uses the master RAT and the secondary RAT; and

(b) if the master RAN node receives, from the radio terminal or a core network, terminal capability information indicating that the radio terminal supports a split bearer, using a Packet Data Convergence Protocol (PDCP) entity for a secondary cell group split bearer for the radio terminal, the PDCP entity providing unified PDCP functionalities.

In a sixth aspect, a method for a radio terminal includes:

(a) performing dual connectivity that uses a master radio access technology (RAT) and a secondary RAT via a wireless transceiver configured to communicate with both a master radio access network (RAN) node associated with the master RAT and a secondary RAN node associated with the secondary RAT;

(b) if the radio terminal supports a split bearer, transmitting, to the master RAN node, terminal capability information indicating that the radio terminal supports a split bearer; and

(c) if the radio terminal supports a split bearer, using a Packet Data Convergence Protocol (PDCP) entity for a master cell group split bearer for the radio terminal, the PDCP entity providing unified PDCP functionalities.

In a seventh aspect, a master RAN node associated with a master RAT includes a memory and at least one processor coupled to the memory. The at least one processor is configured to communicate with a secondary RAN node associated with a secondary RAT and provide a radio terminal with dual connectivity that uses the master RAT and the secondary RAT. The at least one processor is further configured to, if the radio terminal does not support a split bearer, use, for a master cell group bearer for the radio terminal, a PDCP entity that provides first Packet Data Convergence Protocol (PDCP) functionalities corresponding to the master RAT. Furthermore, the at least one processor is configured to, if the radio terminal supports the split bearer, use, for the master cell group bearer for the radio terminal, a PDCP entity that provides unified PDCP functionalities, regardless of whether the dual connectivity is started for the radio terminal. The master cell group bearer is a user plane bearer whose radio protocols are only located in the master cell group.

In an eighth aspect, a radio terminal includes at least one wireless transceiver and at least one processor. The at least one wireless transceiver is configured to communicate with both a master radio access network (RAN) node associated with a master radio access technology (RAT) and a secondary RAN node associated with a secondary RAT. The at least one processor is configured to perform, via the at least one wireless transceiver, dual connectivity that uses the master RAT and the secondary RAT. The at least one processor is further configured to, if the radio terminal does not support a split bearer, use, for a master cell group bearer for the radio terminal, a PDCP entity that provides first Packet Data Convergence Protocol (PDCP) functionalities corresponding to the master RAT. Furthermore, the at least one processor is configured to use, if the radio terminal supports the split bearer, use, for the master cell group bearer for the radio terminal, a PDCP entity that provides unified PDCP functionalities, regardless of whether the dual connectivity is started for the radio terminal.

In a ninth aspect, a method for a master RAN node associated with a master RAT includes:

(a) communicating with a secondary RAN node associated with a secondary RAT and providing a radio terminal with dual connectivity that uses the master RAT and the secondary RAT;

(b) if the radio terminal does not support a split bearer, using, for a master cell group bearer for the radio terminal, a PDCP entity that provides first Packet Data Convergence Protocol (PDCP) functionalities corresponding to the master RAT; and

(c) if the radio terminal supports the split bearer, using, for the master cell group bearer for the radio terminal, a PDCP entity that provides unified PDCP functionalities, regardless of whether the dual connectivity is started for the radio terminal.

In a tenth aspect, a method for a radio terminal comprises:

(a) performing dual connectivity that uses a master radio access technology (RAT) and a secondary RAT via a wireless transceiver configured to communicate with both a master radio access network (RAN) node associated with the master RAT and a secondary RAN node associated with the secondary RAT;

(b) if the radio terminal does not support a split bearer, using, for a master cell group bearer for the radio terminal, a PDCP entity that provides first Packet Data Convergence Protocol (PDCP) functionalities corresponding to the master RAT; and

(c) if the radio terminal supports the split bearer, using, for the master cell group bearer for the radio terminal, a PDCP entity that provides unified PDCP functionalities, regardless of whether the dual connectivity is started for the radio terminal.

In an eleventh aspect, a program includes instructions (software codes) that, when loaded into a computer, cause the computer to perform the method according to the above-described fourth, fifth, sixth, ninth, or tenth aspect.

Advantageous Effects of Invention

According to the above-deceived aspects, it is possible to provide an apparatus, a method, and a program that assist in implementation of a common (or unified) PDCP layer in a radio communication network.

