Radio communication system, base station, mobile station, communication control method, and non-transitory computer readable medium

A first base station (1) that operates a first cell (10) is configured to receive, from a mobile station (4) through a signaling radio bearer in the first cell (10), a signal containing a NAS message that causes a setup of a data bearer in a data transfer apparatus (7) within a core network (5). The first base station (1) is also configured to send, when forwarding the NAS message received from the mobile station (4) to the mobility management apparatus (6) within the core network (5), a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus (6). It is thus, for example, possible to contribute to a simple establishment of a U-Plane bearer in a dual-connectivity scenario.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of International Application No. PCT/JP2013/007156 entitled “Radio Communication System, Base Station, Mobile Station, Communication Control Method, and Non-Transitory Computer Readable Medium” filed on Dec. 5, 2013, which claims priority to Japanese Application No. 2013-004435 filed on Jan. 15, 2013, the disclosures of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a radio communication system, and more particularly, to network architecture in a small cell enhancement scenario.

BACKGROUND ART

In the Long Term Evolution (LTE) Release 12 according to the 3rd Generation Partnership Project (3GPP), “local area enhancement” or “small cell enhancement” for accommodation of a large amount of local traffic, improvement in throughput, and efficient use of a high-frequency band has become one of the subjects for discussion (see Non-patent literature 1). In the local area enhancement or the small cell enhancement, a low-power node (LPN) that forms a small cell is used.

Further, a dual-connectivity scenario has been proposed regarding the small cell enhancement (see Non-Patent literature 2). In one example of the dual connectivity, it is assumed that a macro cell provides a control plane (e.g., Radio Resource Control (RRC) connection and Non-Access Stratum (NAS) message forwarding) for a mobile station (User Equipment (UE)) and a small cell provides a user plane for the UE. This example of the dual connectivity may be referred to as a C/U-plane split. In one specific example of the dual-connectivity scenario, for the Control plane (C-plane), the macro cell can keep a good connection with the UE by a wide coverage using a low frequency band and to support mobility of the UE. Meanwhile, for the user plane (U-plane), the small cell can provide a local high throughput for the UE by using a wide bandwidth in a high frequency band.

In the dual-connectivity scenario, a case in which a small cell does not require transmission of existing cell specific signals/channels (e.g., Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), Cell-specific Reference Signal (CRS), Master Information Block (MIB), and System Information Block (SIB)) is also assumed. Such a new small cell may be referred to as a phantom cell. Further, a base station (eNB) or an LPN that provides a small cell may be referred to as a Phantom eNodeB (PhNB).

CITATION LIST

Non Patent Literature

SUMMARY OF INVENTION

Technical Problem

As described above, the dual-connectivity scenario in which the C-plane is provided for UEs in a cell controlled by the MeNB and the U-plane is provided for the UEs in a cell controlled by the LPN has been proposed. In the following description, a cell that provides the C-Plane in the dual-connectivity scenario is referred to as a primary cell (PCell) and a cell that provides the U-Plane in the dual-connectivity scenario is referred to as a secondary cell (SCell).

The present inventors have studied about processing for establishing a U-Plane bearer in the SCell in the dual-connectivity scenario and have found various problems therewith. For example, in the LTE, a mobility management apparatus (i.e., Mobility Management Entity (MME)) in a core network executes a procedure for establishing the U-Plane bearer (i.e., E-RAB and S5/S8 bearer) in response to receiving a NAS message (e.g., Attach Request or Service Request) transmitted from the UE. Considering the dual-connectivity scenario, the MME need to set a data bearer that passes through an LPN (SCell), which is different from the MeNB (PCell), in response to the NAS message received through the MeNB (PCell). However, since the MME does not know to which LPN the U-Plane bearer should be set, it is impossible to set up the U-Plane bearer that passes through an appropriate LPN.

Accordingly, one object of the present invention is to provide a radio communication system, a base station, a mobile station, a communication control method, and a program that contribute to a simple establishment of a U-Plane bearer in the dual-connectivity scenario.

Solution to Problem

In a first aspect, a radio communication system includes: a first base station that operates a first cell; at least one second base station, each of which operates a second cell; a core network that includes a mobility management apparatus and a data transfer apparatus; and a mobile station. The mobile station has a capability to establish a data radio bearer in the second cell when the mobile station has established a signaling radio bearer in the first cell. The first base station is configured to receive, from the mobile station through the signaling radio bearer, a signal containing a NAS message that causes a setup of a data bearer in the data transfer apparatus. The first base station is further configured to send, when forwarding the NAS message to the mobility management apparatus, a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus.

In a second aspect, a first base station includes: a radio communication unit that operates a first cell; and a controller. The controller is configured to receive, from a mobile station through a signaling radio bearer in the first cell, a signal containing a NAS message that causes a setup of a data bearer in a data transfer apparatus within a core network. The mobile station has a capability to establish a data radio bearer in a second cell of a second base station when the mobile station has established the signaling radio bearer in the first cell. The controller is further configured to send, when forwarding the NAS message to a mobility management apparatus within the core network, a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus.

In a third aspect, a mobile station is used in combination with the radio communication system according to the first aspect stated above, and includes a radio communication unit and a controller. The controller is configured to control the radio communication unit to receive configuration information regarding the data radio bearer from the first base station and receive or transmit user data through the second cell.

In a fourth aspect, a communication control method in a first base station that operates a first cell includes:

(a) receiving, from a mobile station through a signaling radio bearer in the first cell, a signal containing a NAS message that causes a setup of a data bearer in a data transfer apparatus within a core network, the mobile station having a capability to establish a data radio bearer in a second cell of a second base station when the mobile station has established a signaling radio bearer in the first cell; and

(b) sending, when forwarding the NAS message to a mobility management apparatus within the core network, a control message that causes a suspension of the setup of the data bearer to the mobility management apparatus.

In a fifth aspect, a program includes instructions for causing a computer to perform the communication control method according to the above fourth aspect.

Advantageous Effects of Invention

According to the above aspects, it is possible to provide a radio communication system, a base station, a mobile station, a communication control method, and a program that contribute to a simple establishment of a U-Plane bearer in the dual-connectivity scenario.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to the drawings, specific embodiments will be described in detail. Throughout the drawings, identical or corresponding components are denoted by the same reference symbols, and overlapping descriptions will be omitted as appropriate for the sake of clarification of description.

First Embodiment

FIG. 1shows a configuration example of a radio communication system according to this embodiment. The radio communication system according to this embodiment includes a first base station1, a second base station2, a mobile station4, and a core network5. The base stations1and2operate a first cell10and a second cell20, respectively. The core network5includes a mobility management apparatus6and a data transfer apparatus7. In the following description, for the sake of simplification of the description, a case in which the radio communication system according to this embodiment is an LTE system will be described as an example. Accordingly, the first base station1corresponds to an MeNB, the second base station2corresponds to an LPN, the mobile station4corresponds to a UE, the core network5corresponds to an Evolved Packet Core (EPC), the mobility management apparatus6corresponds to a Mobility Management Entity (MME), and the data transfer apparatus7corresponds to a Serving Gateway (S-GW).

The radio communication system according to this embodiment applies the dual connectivity to the cells10and20. That is, the UE4supports the dual connectivity. In other words, the UE4has a capability to establish a data radio bearer (DRB) in the cell20when the UE4has established a signaling radio bearer (SRB) in the cell10. The LPN2provides U-Plane services for the UE4in the cell20. In other words, the LPN2establishes the DRB with the UE4in the cell20and transfers user data of the UE4. The MeNB1provides C-plane services in the cell10for the UE4, which establishes the DRB with the LPN2. In other words, the MeNB1establishes the SRB with the UE4in the cell10and provides RRC signaling, for example, to establish and modify the DRB in the cell20of the LPN2, and NAS message transfer between the EPC5and the UE4. The MeNB1may transmit, on a downlink channel of the cell10(e.g., Physical Broadcast Channel (PBCH) or Physical Downlink Shared Channel (PDSCH)), master information (e.g., system bandwidth and the number of transmission antennas) and system information (e.g., parameters regarding the DRB in the cell20) regarding the cell20of the LPN2.

The MeNB1may not provide all the C-plane services regarding the UE4. For example, the LPN2may control a layer 1 (physical layer) and a layer 2 (Media Access Control (MAC) sublayer and Radio Link Control (RLC) sublayer) regarding the data radio bearer that is established for the LPN2. Specifically, the LPN2may receive layer 1/layer 2 control signals (e.g., Hybrid Automatic Repeat Request (H-ARQ) ACK, Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), and Rank Indicator (RI)) using an uplink control channel (e.g., Physical Uplink Control Channel (PUCCH)) or an uplink data channel (e.g., Physical Uplink Shared Channel (PUSCH)). The LPN2may transmit downlink scheduling information, ACK/NACK for uplink transmission and the like to the UE4using a downlink control channel (e.g., Physical Downlink Control Channel (PDCCH)).

The EPC5is a core network that is generally managed by an operator that provides mobile communication services. The EPC5has control plane (C-plane) functions including mobility management (e.g., location registration and location update) and bearer management (e.g., bearer establishment, bearer modification, and bearer release) of the UE4, and user plane (U-plane) functions including transferring user data of the UE4between the MeNB1and an external network (not shown) and between the LPN2and the external network. The MME6contributes to the C-plane functions in the EPC. The S-GW7contributes to the U-plane functions in the EPC. The S-GW7is arranged at a boundary between the EPC5and a radio access network (RAN) including the MeNB1and the LPN2.

FIG. 1shows only one LPN2arranged in the cell10of the MeNB1. However, a plurality of LPNs2and a plurality of second cells20may be arranged in the cell10of the MeNB1. The MeNB1selects a selected LPN that establishes the U-Plane bearer for the UE4from at least one LPN2.

Next, a procedure for establishing the U-Plane bearer for the UE4according to this embodiment will be described further in detail. The MeNB1according to this embodiment is configured to receive, from the UE4through the SRB in the cell10, an RRC message (RRC signal) containing an initial NAS message that causes a setup of the U-Plane bearer (i.e., S1 bearer, E-RAB, or EPS bearer) in the S-GW7. The NAS message that causes the setup of the U-Plane bearer is, for example, Attach Request, Service Request, or Tracking Area Update (TAU) Request.

Further, the MeNB1is configured to send, when forwarding the NAS message from the UE4that supports the dual connectivity to the MME6, a control message that causes a suspension of the setup of the U-Plane bearer (i.e., an S1 bearer, an E-RAB, or an EPS bearer) to the MME6. The control message that causes the suspension of the setup of the data bearer is hereinafter referred to as a “bearer setup suspension request”. The bearer setup suspension request requests the MME6to suspend the establishment of the U-Plane bearer. The bearer setup suspension request may indicate that a LPN2that terminates the S1 bearer (hereinafter referred to as a selected LPN) has not yet been determined. The selected LPN is selected from at least one LPN2and terminates the S1 bearer for the UE4.

The MME6receives the bearer setup suspension request from the MeNB1. Accordingly, the MME6can change the operation for setting up the U-Plane bearer according to whether the bearer setup suspension request has been received. In other words, the MME6can change the operation for setting up the U-Plane bearer according to whether the UE, which has originated the initial NAS message, supports the dual connectivity. That is, in some implementations, when the MME6has received the NAS message but has not received the bearer setup suspension request, the MME6initiates the setup of the U-Plane bearer that passes through the MeNB1in accordance with the normal bearer setup procedure in the LTE. On the other hand, when the MME6has received both of the NAS message and the bearer setup suspension request, the MME6performs a connection procedure for connecting the UE4to the core network5or a location update procedure regarding the UE4without performing the U-Plane bearer setup procedure.

In one example, the MeNB1may send the bearer setup suspension request together with the NAS message that causes a setup of the U-Plane bearer. In this case, the MeNB1may include the bearer setup suspension request into an “S1-AP: INITIAL UE MESSAGE” that is used to forward the NAS message to the MME6.

After sending the bearer setup suspension request, the MeNB1may determine the selected LPN and send to the MME6a bearer setup request for setting up the U-Plane bearer. The bearer setup request may include LPN information indicating the selected LPN. The LPN information includes identification information that can specify the selected LPN (e.g., an address). The LPN information indicates, for example, a base station address of the selected LPN, a cell ID of the selected LPN, or a tunnel endpoint ID (TEID) of the selected LPN, or a combination thereof. In this case, the MME6receives the LPN information. Accordingly, the MME6can know an appropriate LPN2(i.e., the selected LPN) that should establish the S1 bearer and can set up the S1 bearer between the S-GW7and the appropriate selected LPN.

In the following description, with reference toFIGS. 2 and 3, the bearer architecture according to this embodiment will be described.FIG. 2shows a first example of the bearer architecture related to the user data transfer in the cell20. The radio bearer has already been described above. That is, the MeNB1establishes the SRB with the UE4, and provides, in the cell10, C-plane services including RRC signaling, for example, to establish and modify the DRB in the cell20and NAS message transfer between the EPC5and the UE4. Meanwhile, the LPN2establishes the DRB with the UE4and transmits and receives the user data of the UE4on the cell20.

Next, bearers between the EPC5and the MeNB1and between the EPC5and the LPN2will be described. A signaling bearer with the EPC5(i.e., S1 signaling bearer using an S1-MME interface) is established between the MME6and the MeNB1. The MeNB1establishes the S1 signaling bearer with the MME6and sends and receives S1 Application Protocol (S1-AP) messages to and from the MME6. Meanwhile, a data bearer with the EPC5(i.e., S1 bearer using an S1-U interface) is established between the S-GW7and the LPN2. The LPN2establishes the S1 bearer with the S-GW7and sends and receives user data of the UE4to and from the S-GW7.

Further, the MeNB1establishes a signaling bearer with the LPN2. The signaling bearer between the MeNB1and the LPN2is established using, for example, an X2 interface. The X2 interface is an interface between eNBs. A case in which the LPN2is defined as a new node and a new interface different from the X2 interface is defined between the eNB and the LPN may be considered. In this case, the signaling bearer between the MeNB1and the LPN2may be established using this new interface. In this specification, this new interface is provisionally referred to as an X3 interface. The MeNB1is configured to send, to the LPN2via an X2/X3 signaling bearer, the bearer context (hereinafter referred to as E-UTRAN Radio Access Bearer (E-RAB) configuration information) that is necessary to establish the S1 bearer with the S-GW7and the DRB with the UE4in the LPN2. The E-RAB is a radio access bearer including the DRB and the S1 bearer.

According to the bearer architecture shown inFIG. 2, the LPN2does not require the S1 signaling bearer with the MME6and can set up the DRB and the S1 bearer based on E-RAB configuration information supplied from the MeNB1. In addition, in the above-mentioned bearer architecture, a termination point of the S1 bearer (S1-U bearer) is different from a termination point of the S1 signaling bearer. That is, the LPN2, not the MeNB1, terminates the S1 bearer. That is, in the architecture shown inFIG. 2, the C/U planes are separated not only with regard to the signaling in the RAN but also with regard to the interfaces between the EPC5and the RAN. As a result of this, the MeNB1is only required to perform signaling to establish the S1 bearer and the DRB necessary for the UE4to transmit and receive user data via the cell20and the LPN2. In other words, in one example, the MeNB1needs not to terminate the S1 bearer (i.e., GPRS Tunneling Protocol (GTP) tunnel) for the communication of the UE4via the cell20, and also needs not to perform forwarding of user data packets between the S1 bearer and the DRB. These processing are performed by the LPN2. Accordingly, in one example, it is possible to reduce the processing load on the MeNB1.

The S1 bearer is a GTP tunnel and the user data (data packet) is encapsulated in GTP tunnel packets to be transferred between the S-GW7and the LPN2. For example, the GTP tunnel packets that encapsulate downlink user data arrive at the LPN2by being subjected to routing and forwarding by routers arranged between the S-GW7and the LPN2. Accordingly, in the bearer architecture shown inFIG. 2, typically, the GTP tunnel packets are transferred without passing through the MeNB1. In this case, the MeNB1need not carry out processing for terminating the S1 bearer and thus it is possible to reduce the processing load on the MeNB1. Further, since the GTP tunnel packets do not flow through the X2/X3 interface between the MeNB1and the LPN2, performance requirements on the capacity, the delay and the like of the X2/X3 interface are relaxed. It is possible, for example, to use a non-optical fiber line (e.g., wireless communication path) for the X2/X3 interface.

However, in some implementations, the GTP tunnel packets that encapsulate the user data may be transferred between the S-GW7and the LPN2via the MeNB1. In this case, the MeNB1may function as a router (e.g., Internet Protocol (IP) router) and may perform routing and forwarding of the GTP tunnel packets. The routing of the GTP tunnel packets that pass through the MeNB1can be achieved by setting up routing tables included in the S-GW7, the LPN2, and the MeNB1.

FIG. 3shows a second example of the bearer architecture. In the example shown inFIG. 3, the MeNB1performs routing and forwarding of the GTP tunnel packets. The MeNB1may have a proxy function to convert the IP addresses of the GTP tunnel packets. Specifically, the MeNB1and the LPN2set up a tunnel80(e.g., GTP Tunnel) via the X2/X3 interface. The MeNB1further encapsulates the GTP tunnel packets, which encapsulate the user data on the S1 bearer between the S-GW7and the LPN2, and forwards the encapsulated GTP tunnel packets using the tunnel80. The tunnel80may be omitted. That is, the MeNB1may directly forward the GTP tunnel packets without performing further encapsulation of the GTP tunnel packets.

One notable point in the example shown inFIG. 3is that the MeNB1need not terminate the S1 bearer. The MeNB1is only required to operate as a router that forwards the GTP tunnel packets and need not perform decapsulation processing to retrieve user packets. Accordingly, an increased processing load on the MeNB1which is due to the GTP tunnel termination does not occur.

Another notable point in the example shown inFIG. 3is that the MeNB1can monitor the GTP tunnel packets. The MeNB1can monitor, for example, the traffic amount of the GTP tunnel packets to be forwarded. By monitoring the traffic amount of the GTP tunnel packets, the MeNB1can autonomously estimate the load on the cell20or the load on the LPN2. Accordingly, the MeNB1according to this embodiment can determine deactivation of the cell20or the E-RAB that passes through the LPN2, based on the traffic amount of the GTP tunnel packets monitored by the MeNB1.

In the following description, configuration examples of the MeNB1, the LPN2, the UE4, the MME6, and the S-GW7according to this embodiment will be described.FIG. 4is a block diagram showing a configuration example of the MeNB1. A radio communication unit11receives an uplink signal transmitted from the UE4via an antenna. A reception data processing unit13restores the received uplink signal. The resultant received data is forwarded to another network node (e.g., the MME6or the S-GW7) via a communication unit14. For example, uplink user data received from the UE4in the cell10is forwarded to the S-GW7. Further, NAS data among control data received from the UE4is forwarded to the MME6. Further, the reception data processing unit13receives from a controller15the control data to be transmitted to the LPN2or the MME6and sends the control data to the LPN2or the MME6via the communication unit14.

A transmission data processing unit12obtains user data destined for the UE4from the communication unit14, and generates a transport channel by performing error correction coding, rate matching, interleaving and the like on the user data. The transmission data processing unit12then generates a transmission symbol sequence by adding control information to the data sequence of the transport channel. The radio communication unit11generates a downlink signal by performing processing such as carrier wave modulation based on the transmission symbol sequence, frequency conversion, and signal amplification, and transmits the generated downlink signal to the UE4. Furthermore, the transmission data processing unit12receives the control data to be transmitted to the UE4from the controller15and transmits the control data to the UE4via the radio communication unit11.

The controller15performs signaling with the MME6, the LPN2, and the UE4via the signaling bearers in order to enable the UE4to receive or transmit the user data through the cell20operated by the LPN2. Specifically, the controller15sends, to the MME6via the S1 signaling bearer, the NAS message (e.g., Attach Request, Service Request, or TAU Request) that causes a setup of the U-Plane bearer. The controller15sends, to the LPN2via the X2/X3 signaling bearer, the E-RAB configuration information that is necessary to establish the S1 bearer and the DRB in the LPN2. The controller15sends, to the UE4via the SRB in the cell10, the DRB configuration information that is necessary to establish the DRB in the cell20in the UE4. Further, as already described above, when forwarding to the MME6the NAS message from the UE4that supports the dual connectivity, the controller15sends the bearer setup suspension request to the MME6.

The controller15may be configured to receive measurement information regarding at least one LPN2(hereinafter referred to as LPN measurement information) from the UE4and select the selected LPN from at least one LPN2. The LPN measurement information includes, for example, measurement results regarding the radio quality in the UE4(e.g., Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRQ)). The LPN measurement information may further include a list of the LPNs2detected by the UE4(e.g., a list of base station IDs or a list of cell IDs). The controller15may select, as the selected LPN, a LPN2of which the radio quality measured by the UE4is the highest based on the LPN measurement information. In one example, after forwarding to the MME6the initial NAS message (e.g., Attach Request, Service Request, or TAU Request) from the UE that supports the dual connectivity and sending the bearer setup suspension request to the MME6, the controller15may receive the LPN measurement information from the UE4and then determine the selected LPN. After that, the controller15may send to the MME6the bearer setup request containing the LPN information indicating the selected LPN.

FIG. 5is a block diagram showing a configuration example of the LPN2. The functions and the operations of a radio communication unit21, a transmission data processing unit22, a reception data processing unit23, and a communication unit24shown inFIG. 5are similar to those of the corresponding elements of the base station1shown inFIG. 4(i.e., the radio communication unit11, the transmission data processing unit12, the reception data processing unit13, and the communication unit14).

A controller25of the LPN2receives the E-RAB configuration information from the MeNB1(controller15) via the X2/X3 signaling bearer, and sets up the S1 bearer with the S-GW7and the SRB with the UE4in accordance with the E-RAB configuration information.

FIG. 6is a block diagram showing a configuration example of the UE4. A radio communication unit41can communicate with both the cell10and the cell20. In addition, the radio communication unit41may support carrier aggregation of a plurality of cells operated by different eNBs. In this case, the radio communication unit41can simultaneously use the plurality of cells10and20to transmit or receive user data. The radio communication unit41receives downlink signals from one or both of the eNB1and the LPN2via an antenna. A reception data processing unit42restores received data from the received downlink signal, and sends the received data to a data controller43. The data controller43uses the received data according to the purpose thereof. A transmission data processing unit44and the radio communication unit41generate an uplink signal using transmission data supplied from the data controller43, and transmit the uplink signal to one or both of the eNB1and the LPN2.

A controller45of the UE4controls the radio communication unit41to establish the SRB with the MeNB1on the cell10. The controller45then receives from the MeNB1the DBB configuration information to establish the DRB with the LPN2and controls the radio communication unit41to transmit or receive the user data through the cell20. Accordingly, the UE4can communicate with the LPN2via the DRB based on the signaling with the MeNB1.

Further, the controller45may measure downlink signals from at least one LPN2and transmit the LPN measurement information to the MeNB1. As already stated above, the LPN measurement information is used by the MeNB1to determine the selected LPN.

FIG. 7is a block diagram showing a configuration example of the MME6. A communication unit61communicates with the MeNB1and the S-GW7. A bearer setup controller62communicates with the MeNB1and the S-GW7via the communication unit51, and controls the setup of the data bearer (E-RAB or S1 bearer) or the signaling bearer (S1 signaling bearer) in these apparatuses. Specifically, in response to receiving the initial NAS message (e.g., Attach Request, Service Request, or TAU Request) from the UE4via the MeNB1, the bearer setup controller62requests the S-GW7to set up the S1 bearer and sends to the MeNB1the bearer configuration information regarding the E-RAB (i.e., E-RAB configuration information).

Further, the bearer setup controller62receives the bearer setup suspension request from the MeNB1when receiving the initial NAS message from the UE4that supports the dual connectivity. Accordingly, the bearer setup controller62can change the operation for setting up the U-Plane bearer according to whether the UE, which has originated the initial NAS message, supports the dual connectivity. That is, in some implementations, when the bearer setup controller62has received the NAS message but has not received the bearer setup suspension request, the bearer setup controller62initiates the setup of the U-Plane bearer that passes through the MeNB1in accordance with the normal bearer setup procedure in the LTE. On the other hand, when the MME6has received both of the NAS message and the bearer setup suspension request, the MME6performs a connection procedure for connecting the UE4to the core network5or a location update procedure regarding the UE4without executing the U-Plane bearer setup procedure.

FIG. 8is a block diagram showing a configuration example of the S-GW7. A communication unit71establishes the S1 bearer with the LPN2and transmits or receives user data to or from the LPN2through the S1 bearer. The communication unit71may establish the S1 bearer with the MeNB1to enable the UE4to receive or transmit the user data through the cell. A communication unit74sets up the S5/S8 bearer with a Packet Data Network Gateway (P-GW) in the EPC5and transmits and receives the user data to and from another data transfer apparatus.

A transmission data processing unit72receives downlink user data destined for the UE4from the communication unit74, and forwards the downlink user data to the S1 bearer based on mapping between the upstream side S5/S8 bearer and the downstream side S1 bearer. A reception data processing unit73receives uplink user data from the communication unit71and forwards the uplink user data to the S5/S8 bearer based on the mapping between the S5/S8 bearer and the S1 bearer.

In the following description, a specific example of a procedure for establishing the U-Plane bearer in the SCell will be described.FIG. 9is a flowchart showing an operation example of the MeNB1regarding the establishment of the U-Plane bearer in the SCell. In Step S101, the MeNB1(controller15) receives the RRC message containing the initial NAS message (e.g., Attach Request, Service Request, or TAU Request) from the UE4, which supports the dual connectivity. In Step S102, the MeNB1forwards the NAS message received from the UE4to the MME6and sends the U-Plane bearer setup suspension request to the MME6.

FIG. 10is a flowchart showing an operation example of the MME6regarding the establishment of the U-Plane bearer in the SCell. In Step S201, the MME6(bearer setup controller62) determines whether a NAS message that causes a setup of the U-Plane bearer has been received from the MeNB1. When the NAS message has been received (YES in Step S201), the MME6determines whether the bearer setup suspension request that accompanies the NAS message has been received. When the bearer setup suspension request has been received (YES in Step S202), the MME6performs the connection process for connecting the UE4to the core network5or the location update process regarding the UE4without performing the bearer setup procedure (Step S203). On the other hand, when the bearer setup suspension request has not been received (NO in Step S202), the MME6performs the normal bearer setup procedure in the LTE (Steps S204and S205). In Step S206, the MME6sends a response message to the MeNB1.

FIG. 11is a sequence diagram showing a first example of the procedure for establishing the U-Plane bearer in the SCell. In the example shown inFIG. 11, the MeNB1determines the selected LPN in response to receiving the RRC message containing the NAS message from the UE4and sends the LPN information indicating the selected LPN to the MME6together with the bearer setup request. In Step S301, the MeNB1and the UE4establish an RRC connection. In Step S302, the UE4sends the NAS message (e.g., Attach Request, Service Request, or TAU Request) that requests for setting up the U-Plane bearer. The establishment of the RRC connection in the LTE includes establishment of the signaling radio bearer (i.e., SRB1) and transfer of an initial uplink NAS message. That is, the NAS message transmitted in Step S302is contained in an RRC Connection Setup Complete message transmitted to the MeNB1from the UE4at the last stage of the RRC connection establishment procedure (Step S301).

In Step S303, the MeNB1forwards the NAS message to the MME6and also sends the bearer setup suspension request to the MME6. In one example, the MeNB1may include the bearer setup suspension request into the “S1-AP: INITIAL UE MESSAGE” that is used to forward the NAS message. In Step S304, the MME6performs the connection process for connecting the UE4to the core network5or the location update process regarding the UE4without performing the bearer setup procedure. The MME6sends a response message (S1-AP message) containing the NAS message (e.g., Attach Accept) to the MeNB1. In Step S305, the MeNB1forwards the NAS message received from the MME6to the UE4. For example, the MeNB1may send the NAS message using an RRC Connection Reconfiguration message.

In Step S306, the MeNB1determines the selected LPN from at least one LPN2. In one example, the MeNB1may receive the LPN measurement information from the UE4and determine the LPN2of high reception quality at the UE4as the selected LPN. In Step S307, the MeNB1sends the bearer setup request in order to request the MME6to establish the U-Plane bearer for the UE4. The MeNB1also sends the LPN information indicating the selected LPN to the MME6together with the bearer setup request. The MeNB1may include the LPN information into the S1-AP message that is used to forward the NAS message.

In Step S308, the MME6and the S-GW7perform the procedure for setting up the bearer for the UE4. That is, the MME6sends a Create Session Request message to the S-GW7. The S-GW7receives the Create Session Request message, generates a new entry in an EPS bearer context table, communicates with a P-GW (not shown) to configure a bearer context of the S5/S8 bearer, and configures the S-GW7side endpoint of the S1 bearer. The S-GW7sends a response (i.e., Create Session Response message) including an S1 bearer context to the MME6. The S1 bearer context includes, for example, a tunnel endpoint identifier (TEID) and an address of the S-GW7in the U-plane. The TEID indicates the S-GW7side endpoint of the GTP tunnel as the S1 bearer. In Step S206, the MME6sends an INITIAL CONTEXT SETUP REQUEST message to the MeNB1. The INITIAL CONTEXT SETUP REQUEST message includes an E-RAB bearer context (E-RAB configuration information).

In Step S310, the MeNB1sends the E-RAB configuration information to the LPN2(in this example, selected LPN) via the X2/X3 signaling bearer. The E-RAB configuration information includes S1 bearer configuration information and DRB configuration information. The LPN2sets up the S1 bearer and the DRB in accordance with the E-RAB configuration information. The S1 bearer configuration information includes information that is necessary to establish the S1 bearer with the S-GW7. The S1 bearer configuration information includes, for example, at least one of the E-RAB ID, a Quality Class Indicator (QCI), the IP address of the S-GW7, the S-GW7side TEID of a GTP tunnel (S1 bearer), a security key, and a Temporary Mobile Subscriber Identity (TMSI) allocated to the UE4. Further, the DRB configuration information includes configuration information that is necessary to establish the DRB with the UE4. The DRB configuration information includes, for example, the E-RAB ID, a Quality Class Indicator (QCI), and configuration information of the physical layer and the MAC sublayer.

In Step S311, the MeNB1transmits, to the UE4through the SRB in the cell10, the DRB configuration information regarding the DRB in the cell20. The DRB configuration information is transmitted using an RRC Connection Reconfiguration message. The UE4sets up the DRB in accordance with the DRB configuration information.

In Step S312, the MeNB1sends a message indicating E-RAB setup completion (i.e., INITIAL CONTEXT SETUP RESPONSE message) to the MME6. This message includes LPN2side configuration information regarding the S1 bearer (e.g., the address and the TEID of the selected LPN). In Step S210, the MME6and the S-GW7modify the EPS bearer context based on the INITIAL CONTEXT SETUP RESPONSE message. That is, the MME6sends to the S-GW7a message (i.e., MODIFY BEARER REQUEST message) containing the TEID and the address of the selected LPN. The S-GW7updates the S1 bearer configuration with the TEID and the address of the LPN2received from the MME6.

According to the above processing of Steps S302to S313, the E-RAB that passes through the LPN2has been configured between the UE4and the S-GW7. In Step S314, the UE4receives or transmits user data via the cell20and the LPN2.

Next, a modified example of the U-Plane bearer establishment procedure will be described.FIG. 12is a sequence diagram showing a second example of the procedure for establishing the U-Plane bearer in the SCell. In the example shown inFIG. 12, the MeNB1receives, after sending the bearer setup request (Step S407) to the MME6, the bearer context regarding the S1 bearer from the MME6(Step S409), sends the bearer context to the selected LPN (Step S410), and then sends the LPN information to the MME6after the S1 bearer has been configured in the selected LPN (Step S412). Specifically, the MeNB1includes the LPN information into the S1-AP: INITIAL CONTEXT SETUP COMPLETE MESSAGE” that is used to notify the MME6of the completion of the bearer setup.

The processing in Steps S401to S406inFIG. 12is similar to the processing in Steps S301to S306shown inFIG. 11. In Step S407, the MeNB1sends the bearer setup request to the MME6but does not send the LPN information. The processing in Steps S408to S411is similar to the processing in Steps S308to S311shown inFIG. 11. Specifically, in Step S408, the MME6and the S-GW7perform the EPS bearer setup procedure. In Step S409, the MME6sends the INITIAL CONTEXT SETUP REQUEST message to the MeNB1. The INITIAL CONTEXT SETUP REQUEST message contains the E-RAB bearer context (E-RAB configuration information). In Step S410, the MeNB1sends the E-RAB configuration information to the selected LPN via the X2/X3 signaling bearer. In Step S411, the MeNB1transmits, to the UE4through the SRB in the cell10, the DRB configuration information regarding the DRB in the cell20.

In Step S412, the MeNB1sends a message indicating the E-RAB setup completion (i.e., INITIAL CONTEXT SETUP RESPONSE message) to the MME6. This INITIAL CONTEXT SETUP RESPONSE message contains the LPN information indicating the selected LPN. In this case, the LPN information may be LPN2side configuration information regarding the S1 bearer (e.g., the address and the TEID of the selected LPN). In Step S413, the MME6and the S-GW7modify the EPS bearer context based on the INITIAL CONTEXT SETUP RESPONSE message. That is, the MME6sends a message (i.e., MODIFY BEARER REQUEST message) containing the address and the TEID of the selected LPN to the S-GW7. The S-GW7updates the S1 bearer configuration with the address and the TEID of the LPN2received from the MME6.

According to the above processing of Steps S402to S413, the E-RAB that passes through the LPN2has been configured between the UE4and the S-GW7. In Step S414, the UE4receives or transmits user data via the cell20and the LPN2.

Note that, in Step S306shown inFIG. 11and Step S406shown inFIG. 12, the MeNB1may select the MeNB1itself when there is no appropriate LPN2. In one example, the MeNB1may configure the U-Plane bearer for the UE4in the cell10of the MeNB1when any LPN reception quality measured by the UE4is below a reference value.

Second Embodiment

In this embodiment, a specific example of the procedure for determining the selected LPN using the LPN measurement information from the UE4will be described. A configuration example of a radio communication system according to this embodiment is similar to that shown inFIG. 1. The MeNB1according to this embodiment receives the LPN measurement information from the UE4and then determines the selected LPN based on the LPN measurement information.

FIG. 13is a sequence diagram showing a specific example of the U-Plane bearer establishment procedure according to this embodiment. The processing in Steps S501to S505is similar to the processing in Steps S301to S305shown inFIG. 11(or Steps S401to S405shown inFIG. 12). In Step S506, the UE4transmits the LPN measurement information to the MeNB1. The UE4may transmit the LPN measurement information using a Measurement Report message. In Step S507, the MeNB1determines the selected LPN based on the LPN measurement information. The processing in Steps S508to S515is similar to the processing in Steps S307to S314shown inFIG. 11(or Steps S407to S414inFIG. 12).

FIG. 14is a flowchart showing an operation example of the MeNB1according to this embodiment. The processing in Steps S601and S602is similar to the processing in Steps S101and S102shown inFIG. 9. In Step S603, the MeNB1(controller15) receives from the MME6a response to the NAS message. In Step S604, the MeNB1receives the LPN measurement information from the UE4. In Step S605, the MeNB1determines the selected LPN that terminates the data bearer (S1 bearer) for the UE4based on the LPN measurement information. In Step S606, the MeNB1requests the MME6to set up a bearer regarding the selected LPN. Specifically, the MeNB1sends to the MME6the LPN information, which indicates the selected LPN, and the bearer setup request. As described in the first embodiment, the MeNB1may send the LPN information to the MME6when sending to the MME6a bearer setup response (i.e., INITIAL CONTEXT SETUP RESPONSE message) after the setup of the U-Plane bearer (E-RAB) in the selected LPN has been completed.

FIG. 15is a flowchart showing an operation example of the UE4according to this embodiment. In Step S701, the UE4(controller45) sends the initial NAS message (e.g., Attach Request, Service Request, or TAU Request) that causes a setup of the U-Plane bearer. In Steps S6702and S703, the UE4transmits the LPN measurement information to the MeNB1in response to receiving the LPN measurement request from the MeNB1. The UE4may measure downlink signals from LPNs2in response to the instruction from the MeNB1(Step S702). The UE4may send to the MeNB1, as the LPN measurement information, a measurement log that has been obtained in advance by the UE4during an idle mode.

Third Embodiment

This embodiment shows first to third examples of the procedure for detecting the UE that supports the dual connectivity. The procedure for detecting the UE that supports the dual connectivity described in this embodiment can be combined with any of the first and second embodiments stated above. A configuration example of a radio communication system according to this embodiment is similar to that shown inFIG. 1.

FIG. 16is a sequence diagram showing the first detection procedure. In the first detection procedure, the UE4sends dual-connectivity support information to the MeNB1(Step S801). The UE4may notify the MeNB1that the UE4supports (or does not support) the dual connectivity. The MeNB1receives the dual-connectivity support information from the UE4and determines whether the UE4supports the dual connectivity (Step S802).

For example, the UE4may indicate the support of the dual connectivity using an RRC connection request message or RRC Connection Setup Complete message transmitted during the RRC connection establishment procedure. For example, the UE4may indicate the support of the dual connectivity using an establishment cause contained in the RRC connection request message. The UE4may indicate the support of the dual connectivity using an attach type or request type contained in an Attach Request message as the initial NAS message.

In the second detection procedure, the MeNB1operates a special cell that can be accessed only by dual-connectivity-supporting UEs. The MeNB1determines that the UE4which has accessed this special cell as a dual-connectivity-supporting UE. In one example, the special cell, which can be accessed only by dual-connectivity-supporting UEs, may be a cell which has an assignment of reference signals (RSs) different from that of a legacy cell that can be accessed by UEs (legacy UEs) that do not support the dual connectivity. Alternatively, the special cell, which can be accessed only by dual-connectivity-supporting UEs, may be a cell that uses a special frequency band that cannot be used by the legacy UEs.

FIG. 17is a sequence diagram showing the third detection procedure. In the third detection procedure, the MeNB1obtains identification information (e.g., TMSI) of a dual-connectivity-supporting UE (Steps S901and S902). The MeNB1receives the identification information of the UE4when the UE4connects to a network. In the example shown inFIG. 17, the MeNB1receives an RRC Connection Request message containing the identification information of the UE4(e.g., TMSI) (Step S903). The MeNB1then determines whether the UE4is a dual-connectivity-supporting UE or not, according to whether the identification information of the UE4coincides with the identification information of dual-connectivity-supporting UEs (Step S904).

According to this embodiment, the MeNB1can determine whether the UE4supports the dual connectivity. Accordingly, the MeNB1can easily determine whether to set up the U-Plane bearer for the UE4to the MeNB1or to the LPN2according to whether the UE4supports the dual connectivity.

Other Embodiments

The above-described first to third embodiments may be appropriately combined.

All the communication control methods in the dual-connectivity scenario performed by the MeNB1, the LPN2, the UE4, the MME6, and the S-GW7described in the first to third embodiments may be implemented by using a semiconductor processing device including an Application Specific Integrated Circuit (ASIC). Alternatively, these methods may be implemented by causing a computer system including at least one processor (e.g., microprocessor, Micro Processing Unit (MPU), Digital Signal Processor (DSP)) to execute a program. Specifically, one or more programs including instructions to cause a computer system to perform the algorithms shown in the flowcharts and the sequence diagrams may be created and these programs may be supplied to a computer.

In the above first to third embodiments, the LTE system has been mainly described. However, these embodiments may be applied to radio communication systems other than the LTE system, for example, a 3GPP Universal Mobile Telecommunications System (UMTS), a 3GPP2 CDMA2000 system (1×RTT, High Rate Packet Data (HRPD)), a Global System for Mobile Communications (GSM) system, or a WiMAX system.

Further, the above embodiments are merely examples of applications of technical ideas obtained by the present inventors. Needless to say, these technical ideas are not limited to the above embodiments and may be changed in various ways.

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-004435, filed on Jan. 15, 2013, the disclosure of which is incorporated herein in its entirety by reference.

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