Communication control method, user terminal, and processor

A communication control method is a method for performing offload to transfer a traffic load of a cellular base station to an access point. The communication control method comprises a step of maintaining without releasing the first connection, by a user terminal that have established a first connection with the cellular base station, even when the offload is started after establishing a second connection with the access point; and a determining step of determining, by the user terminal, whether the offload is continued or canceled after the offload is started.

TECHNICAL FIELD

The present invention relates to a communication control method, a user terminal, and a processor, used in cellular communication system allowed to cooperate with a wireless LAN system (a WLAN system).

BACKGROUND ART

In recent years, a user terminal (so-called dual terminal) comprising a cellular communication unit and a wireless LAN communication unit is becoming widely used. Further, the number of wireless LAN access points (hereinafter called “access points”) managed by an operator of a cellular communication system increases.

Therefore, in 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a cellular communication system, it is expected to consider a technology capable of enhancing cooperation between a cellular communication system and a wireless LAN system (see Non Patent Document 1).

One purpose of such technology is that balance of load level in a cellular base station and an access point is taken by improving usage rate of access point.

For example, it is possible to transfer (offload) traffic load of a cellular base station to an access point by switch such that traffic transmitted and received between the cellular base station and a user terminal is transmitted and received between the access point and the user terminal.

PRIOR ART DOCUMENT

SUMMARY OF THE INVENTION

By the way, the user terminal generally releases a connection with a cellular base station in a case where a user terminal establishes a connection with an access point. Thus, the user terminal becomes an idle state of the cellular communication during performing the above offload.

However, an inefficient operation (so-called ping-pong phenomenon) that the connection between the user terminal and the cellular base station is anew established may occur in such cases where communication status between the user terminal and the access point deteriorates after establishing the connection between the user terminal and the access point.

Therefore, an object of the present invention is to effectively control the offload to transfer the traffic load of a cellular base station to an access point.

A communication control method according to an embodiment is a method for performing offload to transfer a traffic load of a cellular base station to an access point. The communication control method comprises a step of maintaining without releasing the first connection, by a user terminal that have established a first connection with the cellular base station, even when the offload is started after establishing a second connection with the access point; and a determining step of determining, by the user terminal, whether the offload is continued or canceled after the offload is started.

A user terminal according to an embodiment comprises: a controller configured to establish a second connection with an access point which is included in a wireless local area network (WLAN) and start offload to transfer a traffic of a mobile communication network to the WLAN, when the user terminal has established the first connection with a base station which is included in the mobile communication network. The controller maintains the first connection even after the offload is started. The controller determines whether to continue the offload or not.

A processor according to a processor for controlling a user terminal. The processor comprises: a step of establishing a second connection with an access point which is included in a wireless local area network (WLAN) and starting offload to transfer a traffic of a mobile communication network to the WLAN, when the user terminal has established the first connection with a base station which is included in the mobile communication network; a step of maintaining the first connection even after the offload is started, and a step of determining whether to continue the offload or not.

DESCRIPTION OF THE EMBODIMENT

Overview of Embodiment

A communication control method according to the first embodiment and the second embodiment is a method for performing offload to transfer a traffic load of a cellular base station to an access point. The communication control method comprises a step of maintaining without releasing the first connection, by a user terminal that have established a first connection with the cellular base station, even when the offload is started after establishing a second connection with the access point; and a determining step of determining, by the user terminal, whether the offload is continued or canceled after the offload is started.

In the first embodiment and the second embodiment, in the determining step, the user terminal carries out the determination on the basis of a communication status with the access point.

In the operation pattern1according to the first embodiment, the communication control method further comprises: a step of receiving from the cellular base station, before the first connection is released, by the user terminal, configuration information for configuration of an operation of the user terminal after the first connection is released.

In the operation pattern1according to the first embodiment, the communication control method further comprises: a step of transmitting, by the user terminal, a notification indicating that the offload is continued, to the cellular base station, when it is determined in the determining step that the offload is continued; and a step of releasing, by the user terminal, the first connection after the notification is transmitted.

In the operation pattern1according to the first embodiment, the communication control method further comprises: a step of canceling the offload and discarding the configuration information, by the user terminal, when it is determined in the determining step that the offload is canceled.

In the operation pattern2according to the first embodiment, the communication control method further comprises a step of transmitting, to the cellular base station, by the user terminal, a transmission stop request for requesting to stop transmitting a release instruction of the first connection, before the offload is started.

In the operation pattern2according to the first embodiment, the communication control method further comprises: a step of transmitting, to the cellular base station, by the user terminal, a transmission request to request to transmit the release instruction when it is determined in the determining step that the offload is continued; and a step of receiving, by the user terminal, the release instruction from the cellular base station. The release instruction includes configuration information for configuration of an operation of the user terminal, after the first connection is released.

In the first embodiment and the second embodiment, the user terminal comprises a terminal-side timer that regulates a connection maintaining period during which the first connection should be maintained after the offload is started. The communication control method further comprises: a step of activating, by the user terminal, the terminal-side timer when the offload is started; and a maintaining step of maintaining, by the user terminal, the first connection until the terminal-side timer expires.

In the operation pattern1according to the second embodiment, the cellular base station comprises a base station-side timer that regulates a connection maintaining period during which the first connection should be maintained after transmission and reception of traffic with the user terminal is stopped. The connection maintaining period set to the terminal-side timer is equal to or shorter than the connection maintaining period set to the base station-side timer.

In the operation pattern2according to the second embodiment, the cellular base station comprises a base station-side timer that regulates a connection maintaining period during which the first connection should be maintained after transmission and reception of traffic with the user terminal is stopped. In the maintaining step, the user terminal transmits and receives the traffic with the access point and transmits and receives the traffic with the cellular base station for stopping the base station-side timer.

In the operation pattern3according to the second embodiment, the cellular base station comprises a base station-side timer that regulates a connection maintaining period during which the first connection should be maintained after transmission and reception of traffic with the user terminal is stopped. The communication control method further comprises a step of inquiring the user terminal from the cellular base station of whether it is possible to release the first connection in a case where the release request for the first connection is not received from the user terminal when the base station-side timer expires in the cellular base station.

In the operation pattern4according to the second embodiment, the cellular base station comprises a base station-side timer that regulates a connection maintaining period during which the first connection should be maintained after transmission and reception of traffic with the user terminal is stopped. The communication control method further comprises a control step of controlling, by the cellular base station, the base station-side timer in order to prevent the base station-side timer from expiring before the terminal-side timer expires.

In the operation pattern4-1according to the second embodiment, the base station-side timer includes a first base station-side timer used for a purpose of other than the offload and a second base station-side timer used for a purpose of the offload. The connection maintaining period set to the second base station-side timer is longer than the connection maintaining period set to the first base station-side timer. In the control step, the cellular base station selects the second base station-side timer and then activates the second base station-side timer, in response to a start of the offload.

In the operation pattern4-2according to the second embodiment, the communication control method further comprises a step of notifying, by the cellular base station, the user terminal of the connection maintaining period that should be set to the terminal-side timer. In the control step, the cellular base station sets the connection maintaining period equal to or longer than the connection maintaining period notified to the user terminal, to the base station-side timer.

In the operation pattern4-3according to the second embodiment, in the control step, the cellular base station cancels the activation of the base station-side timer in response to the start of the offload.

A user terminal according to the third embodiment comprises a cellular communication unit and a WLAN communication unit. The user terminal comprises: a controller configured to measure a movement speed of the user terminal when the WLAN communication unit is in an on state. The controller restricts a start of connection by the WLAN communication unit with an access point when detecting a rapid decrease in the movement speed.

In the third embodiment, the controller cancels the restriction of the start of the connection when detecting a rapid increase in the movement speed after detecting the rapid decrease in the movement speed.

In the modification of the third embodiment, it further comprises: a storage configured to store a list of the access points that should be subject to the connection restriction. The controller restricts a start of connection with the access point included in the list.

In the third embodiment, the cellular communication unit receives the list from a cellular base station. The storage stores the list received from the cellular base station.

A user terminal according to the fourth embodiment comprises a cellular communication unit and a WLAN communication unit. The user terminal comprises: a controller configured to measure a reception level from an access point when the WLAN communication unit is in an on state. The controller restricts a start of connection by the WLAN communication unit with the access point when detecting a rapid increase in the reception level.

In the fourth embodiment, the controller cancels the restriction of the start of the connection when detecting a rapid decrease in the reception level after detecting the rapid increase in the reception level.

In the modification of the fourth embodiment, it further comprises: a storage configured to store a list of the access points that should be subject to the connection restriction. The controller restricts the start of connection with the access point included in the list.

In the modification of the fourth embodiment, the cellular communication unit receives the list from a cellular base station. The storage stores the list received from the cellular base station.

A user terminal according to the fifth embodiment comprises: a cellular communication unit configured to transmit and receive a cellular radio signal with a cellular base station; a WLAN communication unit configured to transmit and receive a WLAN radio signal with an access point; and a controller configured to switch the WLAN communication unit to an on state, when the WLAN communication unit is in an off state and when the cellular communication unit receives, from the cellular base station, a WLAN on request for switching the WLAN communication unit to the on state. The WLAN on request includes scan control information for controlling a WLAN scan that is an operation in which reception of the WLAN radio signal is attempted by the WLAN communication unit for each WLAN channel. The controller controls the WLAN scan in accordance with the scan control information included in the WLAN on request after switching the WLAN communication unit to the on state.

In the fifth embodiment, the controller notifies, before receiving the WLAN on request, the cellular base station of at least one of information indicating a WLAN communication capability of the user terminal and information indicating that the WLAN communication unit is in an off state.

In the fifth embodiment, the scan control information includes at least one of channel information for designating a WLAN channel subject to the WLAN scan or a WLAN channel not subject to the WLAN scan, and frequency band information for designating a WLAN frequency band subject to the WLAN scan or a WLAN frequency band not subject to the WLAN scan.

In the fifth embodiment, the scan control information includes priority information for designating a WLAN channel or a WLAN frequency band where reception of the WLAN radio signal should be preferentially attempted in the WLAN scan.

In the fifth embodiment, the scan control information includes at least one of period information for designating a period during which the WLAN scan should be continued, and timing information for designating a timing at which the WLAN scan should be performed.

In the fifth embodiment, the user terminal further comprises: a GNSS receiver configured to receive a GNSS (Global Navigation Satellite System) signal. The controller notifies the cellular base station of information on a reception level of the GNSS signal prior to reception of the WLAN on request.

In the fifth embodiment, the controller ignores the WLAN on request when the WLAN communication unit is in an on state and when the cellular communication unit receives, from the cellular base station, the WLAN on request.

A communication control method according to the sixth embodiment is a communication control method for allowing a cellular communication system to cooperate with a wireless LAN system, and comprises: a determination step of determining whether or not a connection between a wireless LAN access point directly connected to a small cell base station and a user terminal connected to the wireless LAN access point becomes difficult; a connection step of connecting, by the user terminal, to a cell managed by another base station, when it is determined that the connection between the user terminal and the wireless LAN access point becomes difficult; and a transfer step of transferring, by the wireless LAN access point, user data on the user terminal owned by the wireless LAN access point by way of the small cell base station to the another base station when it is determined that the connection between the user terminal and the wireless LAN access point becomes difficult.

The communication control method according to the sixth embodiment further comprises: a request step of making, by the user terminal, a request to transfer the user data to the another base station when it is determined in the determination step that the connection between the user terminal and the wireless LAN access point becomes difficult, wherein in the transfer step, the wireless LAN access point transfers, resulting from the request in the request step, the user data to the another base station by way of the small cell base station.

In the communication control method according to the sixth embodiment, in the determination step, the user terminal determines that the connection with the wireless LAN access point becomes difficult, even if a signal intensity received from the wireless LAN access point is equal to or more than a predetermined value that is a value by which it is possible to ensure communication quality, when the wireless LAN access point is of collocated type in which the wireless LAN access point is disposed at the same place as the small cell base station, and a signal intensity received from the small cell base station is less than a predetermined value.

The communication control method according to the sixth embodiment further comprises: a first transfer request step of requesting, when receiving the request in the request step, by the another base station, the small cell base station to transfer the user data to the another base station from the wireless LAN access point by way of the small cell base station; and a second transfer request step of requesting, when receiving the request in the first transfer request step, by the small cell base station, the wireless LAN access point to transfer the user data to the small cell base station, wherein in the transfer step, when receiving the request in the second transfer request step, the wireless LAN access point receives transfers the user data to the another base station by way of the small cell base station.

In the communication control method according to the sixth embodiment, in the transfer step, when the small cell base station is a home base station that manages a specific cell to which only a specific user terminal having an access right is connectable, and even when the user terminal is not the specific user terminal, the small cell base station transfers the user data transferred from the wireless LAN access point to the another base station.

The communication control method according to the sixth embodiment further comprises: a negative acknowledgment step of sending a negative acknowledgment, by the another base station, to the request in the request step, when it is not possible to satisfy the request in the request step; and a re-request step of re-making, by the user terminal, a request in the request step, when receiving the negative acknowledgment.

In the communication control method according to the sixth embodiment, in the re-request step, the user terminal repeats the request in the request step until the number of times that the negative acknowledgment is received reaches a predetermined value.

In the communication control method according to another embodiment, in the determination step, the wireless LAN access point determines that the connection between the user terminal and the wireless LAN access point becomes difficult, when a signal intensity received from the user terminal is less than a predetermined value.

A communication control method according to the seventh embodiment is a communication control method for allowing a cellular communication system to cooperate with a wireless LAN system, and comprises: a determination step of determining whether or not a connection between a wireless LAN access point directly connected to a small cell base station and a user terminal connected to the wireless LAN access point becomes difficult; a connection step of connecting, by the user terminal, to a small cell managed by the small cell base station, when it is determined that the connection between the user terminal and the wireless LAN access point becomes difficult; and a transfer step of transferring, by the wireless LAN access point, user data on the user terminal owned by the wireless LAN access point to the small cell base station when it is determined that the connection between the user terminal and the wireless LAN access point becomes difficult.

The communication control method according to the seventh embodiment further comprises: a request step of requesting, by the user terminal, to transfer the user data to the small base station when it is determined in the determination step that the connection between the user terminal and the wireless LAN access point becomes difficult, wherein in the transfer step, the wireless LAN access point transfers, on the basis of the request in the request step, the user data to the small cell base station.

In the communication control method according to the seventh embodiment, in the determination step, the user terminal determines that the connection with the wireless LAN access point becomes difficult, when the wireless LAN access point is of collocated type in which the wireless LAN access point is disposed at the same place as the small cell base station, and before a signal intensity received from the small cell base station is less than a predetermined value that is a value by which it is possible to ensure a communication quality, when the signal intensity received from the wireless LAN access point is less than a predetermined value.

In the communication control method according to the seventh embodiment, in the determination step, the wireless LAN access point determines that the connection between the user terminal and the wireless LAN access point becomes difficult, when a signal intensity received from the user terminal is less than a predetermined value.

The communication control method according to the seventh embodiment, further comprises: a handover request step of making, to another base station adjacent to a small cell base station, a handover request requesting the user data transferred from the wireless LAN access point and a handover to a cell immediately after the small cell and the user terminal are connected, when the small cell base station is a home base station configured to manage a specific cell to which only a specific user terminal having an access right is connectable and when the user terminal is not the specific user terminal.

Next, a first embodiment to a seventh embodiment will be described. It is noted that in each of the embodiments, a description proceeds with a focus on a difference from another embodiment, and a like part will not be described where appropriate.

First Embodiment

Hereinafter, with reference to the drawing, an embodiment will be described in which a cellular communication system (an LTE system) configured in compliance with the 3GPP standards is allowed to cooperate with a wireless LAN (WLAN) system.

FIG. 1is a system configuration diagram according to the first embodiment. As shown inFIG. 1, the cellular communication system includes a plurality of UEs (User Equipments)100, E-UTRAN (Evolved Universal Terrestrial Radio Access Network)10, and EPC (Evolved Packet Core)20. The E-UTRAN10corresponds to a radio access network. The EPC20corresponds to a core network.

The UE100is a mobile radio communication device and performs radio communication with a cell with which a connection is established. The UE100corresponds to the user terminal. The UE100is a terminal (dual terminal) that supports both cellular communication scheme and WLAN communication scheme.

The E-UTRAN10includes a plurality of eNBs200(evolved Node-Bs). The eNB200corresponds to a cellular base station. The eNB200manages one or a plurality of cells and performs radio communication with the UE100which establishes a connection with the cell of the eNB200. It is noted that the “cell” is used as a term indicating a minimum unit of a radio communication area, and is also used as a term indicating a function of performing radio communication with the UE100. Further, the eNB200, for instance, has a radio resource management (RRM) function, a routing function of user data, and a measurement control function for mobility control and scheduling.

The eNBs200are connected mutually via an X2 interface. Further, the eNB200is connected to MME/S-GW500included in the EPC20via an S1 interface.

The EPC20includes a plurality of MMEs (Mobility Management Entities)/S-GWs (Serving-Gateways)500. The MME is a network node for performing various mobility controls, etc., for the UE100and corresponds to a controller. The S-GW is a network node that performs transfer control of user data and corresponds to a mobile switching center.

The WLAN system includes WLAN access point (hereinafter, called “AP”)300. The WLAN system is configured to be in compliance with some IEEE 802.11 standards, for example. The AP300communicates with the UE100in a frequency band (WLAN frequency band) different from a cellular frequency band. The AP300is connected to the EPC20via a router, etc.

It is noted that there may be one WLAN frequency band; there may be a plurality of WLAN frequency bands (for example, 2.4 GHz band and 5 GHz band). A plurality of WLAN channels may be included in one WLAN frequency band.

Further, it is not limited to the case where the eNB200and the AP300are separately disposed. The eNB200and the AP300may be disposed in the same place (Collocated). The eNB200and the AP300are directly connected by arbitrary interface of an operator as one embodiment of Collocated.

Subsequently, a configuration of the UE100, the eNB200, and the AP300will be described.

FIG. 2is a block diagram of the UE100. As shown inFIG. 2, the UE100includes: antennas101and102; a cellular communication unit (a cellular transceiver)111; a WLAN communication unit (a WLAN transceiver)112; a user interface120; a GNSS (Global Navigation Satellite System) receiver130; a battery140; a memory150; and a processor160. The memory150and the processor160configure a controller. Alternatively, the memory150configures a storage and the processor160configures a controller. The UE100may not have the GNSS receiver130. Furthermore, the memory150may be integrally formed with the processor160, and this set (that is, a chipset) may be called a processor160′ configuring a controller (and a storage).

The antenna101and the cellular communication unit111are used for transmitting and receiving a cellular radio signal. The cellular communication unit111converts a baseband signal output from the processor160into the cellular radio signal, and transmits the same from the antenna101. Further, the cellular communication unit111converts the cellular radio signal received by the antenna101into the baseband signal, and outputs the same to the processor160.

The antenna102and the WLAN communication unit112are used for transmitting and receiving a WLAN radio signal. The WLAN communication unit112converts the baseband signal output from the processor160into a WLAN radio signal, and transmits the same from the antenna102. Further, the WLAN communication unit112converts the WLAN radio signal received by the antenna102into a baseband signal, and outputs the same to the processor160.

The user interface120is an interface with a user carrying the UE100, and includes, for example, a display, a microphone, a speaker, and various buttons. Upon receipt of the input from a user, the user interface120outputs a signal indicating a content of the input to the processor160. The GNSS receiver130receives a GNSS signal in order to obtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor160. The battery140accumulates a power to be supplied to each block of the UE100.

The memory150stores a program to be executed by the processor160and information to be used for a process by the processor160. The processor160includes the baseband processor that performs modulation and demodulation, and encoding and decoding on the baseband signal and a CPU that performs various processes by executing the program stored in the memory150. The processor160may further include a codec that performs encoding and decoding on sound and video signals. The processor160executes various processes and various communication protocols described later.

FIG. 3is a block diagram of the eNB200. As shown inFIG. 3, the eNB200includes an antenna201, a cellular communication unit (a cellular transceiver)210, a network interface220, a memory230, and a processor240. The memory230and the processor240configure a controller. Furthermore, the memory230may be integrally formed with the processor240, and this set (that is, a chipset) may be called a processor configuring a controller.

The antenna201and the cellular communication unit210are used for transmitting and receiving a cellular radio signal. The cellular communication unit210converts the baseband signal output from the processor240into the cellular radio signal, and transmits the same from the antenna201. Furthermore, the cellular communication unit210converts the cellular radio signal received by the antenna201into the baseband signal, and outputs the same to the processor240.

The network interface220is connected to the neighboring eNB200via an X2 interface and is connected to the MME/S-GW500via the S1 interface. Further, the network interface220is used for communication with the AP300via the EPC20.

The memory230stores a program to be executed by the processor240and information to be used for a process by the processor240. The processor240includes the baseband processor that performs modulation and demodulation, encoding and decoding and the like on the baseband signal and a CPU that performs various processes by executing the program stored in the memory230. The processor240implements various processes and various communication protocols described later.

FIG. 4is a block diagram of the AP300. As shown inFIG. 4, the AP300includes an antenna301, a WLAN communication unit (a WLAN transceiver)311, a network interface320, a memory330, and a processor340. The memory330and the processor340configure a controller. Furthermore, the memory330may be integrally formed with the processor340, and this set (that is, a chipset) may be called a processor configuring a controller.

The antenna301and the WLAN communication unit311are used for transmitting and receiving the WLAN radio signal. The WLAN communication unit311converts the baseband signal output from the processor340into the WLAN radio signal and transmits the same from the antenna301. Further, the WLAN communication unit311converts the WLAN radio signal received by the antenna301into the baseband signal and outputs the same to the processor340.

The network interface320is connected to the EPC20via a router, etc. Further, the network interface320is used for communication with the eNB200via the EPC20.

The memory330stores a program executed by the processor340and information used for a process by the processor340. The processor340includes the baseband processor that performs modulation and demodulation, and encoding and decoding on the baseband signal and a CPU that performs various processes by executing the program stored in the memory330.

FIG. 5is a protocol stack diagram of a radio interface in the cellular communication system. As shown inFIG. 5, the radio interface protocol is classified into a layer 1 to a layer 3 of an OSI reference model, wherein the layer 1 is a physical (PHY) layer. The layer 2 includes a MAC (Media Access Control) layer, an RLC (Radio Link Control) layer, and a PDCP (Packet Data Convergence Protocol) layer. The layer 3 includes an RRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation and demodulation, antenna mapping and demapping, and resource mapping and demapping. Between the PHY layer of the UE100and the PHY layer of the eNB200, data is transmitted via the physical channel.

The MAC layer performs priority control of data, and a retransmission process and the like by hybrid ARQ (HARQ). Between the MAC layer of the UE100and the MAC layer of the eNB200, data is transmitted via a transport channel. The MAC layer of the eNB200includes a scheduler for selecting a transport format (a transport block size, a modulation and coding scheme and the like) of an uplink and a downlink, and an assigned resource block.

The RLC layer transmits data to an RLC layer of a reception side by using the functions of the MAC layer and the PHY layer. Between the RLC layer of the UE100and the RLC layer of the eNB200, data is transmitted via a logical channel.

The RRC layer is defined only in a control plane. Between the RRC layer of the UE100and the RRC layer of the eNB200, a control message (an RRC message) for various types of setting is transmitted. The RRC layer controls the logical channel, the transport channel, and the physical channel in response to establishment, re-establishment, and release of a radio bearer. When there is a connection (RRC connection) between the RRC of the UE100and the RRC of the eNB200, the UE100is in a connected state (RRC connected state); otherwise, the UE100is in an idle state (RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performs session management or mobility management, for example.

FIG. 6is a configuration diagram of a radio frame used in the LTE system. In the LTE system, OFDMA (Orthogonal Frequency Division Multiplexing Access) is applied to a downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is applied to an uplink, respectively.

As shown inFIG. 6, the radio frame is configured by 10 subframes arranged in a time direction, wherein each subframe is configured by two slots arranged in the time direction. Each subframe has a length of 1 ms and each slot has a length of 0.5 ms. Each subframe includes a plurality of resource blocks (RBs) in a frequency direction, and a plurality of symbols in the time direction. The resource block includes a plurality of subcarriers in the frequency direction.

Among radio resources assigned to the UE100, a frequency resource can be designated by a resource block and a time resource can be designated by a subframe (or slot).

In the downlink, an interval of several symbols at the head of each subframe is a control region mainly used as a physical downlink control channel (PDCCH). Furthermore, the remaining interval of each subframe is a region that can be mainly used as a physical downlink shared channel (PDSCH). Furthermore, in the downlink, reference signals such as cell-specific reference signals are distributed and arranged in each subframe.

In the uplink, both ends, in the frequency direction, of each subframe are control regions mainly used as a physical uplink control channel (PUCCH). Furthermore, the center portion, in the frequency direction, of each subframe is a region that can be mainly used as a physical uplink shared channel (PUSCH).

Operation According to First Embodiment

Next, an operation according to the first embodiment will be described.

(1) Operation Environment

FIG. 7is a diagram for describing operation environment according to the first embodiment. As shown inFIG. 7, the AP300is provided in coverage of the eNB200. The AP400is an AP (an Operator controlled AP) managed by an operator.

Further, a plurality of UEs100is located within the coverage of the eNB200and within coverage of the AP300. The UE100establishes a connection with the eNB200and performs cellular communication with the eNB200. Specifically, the UE100transmits and receives cellular radio signal including traffic (user data) with the eNB200. Alternatively, some UEs100may not establish the connection with the eNB200.

A load level of the eNB200becomes high when the eNB200establishes connections with a large number of UEs100. The load level means congestion degree of the eNB200such as traffic load of the eNB200or radio resource usage rate of the eNB200.

The traffic load of the eNB200can be transferred (offloaded) to the AP300by switching so that traffic transmitted and received between the eNB200and the UE100is transmitted and received between the AP300and the UE100.

However, the UE100becomes the idle state of cellular communication during performing the offload because of releasing the connection with the eNB200when the UE100generally establishes the connection with the AP300.

Thus, an inefficient operation (so-called ping-pong phenomenon) that the connection between the UE100and the eNB200is anew established may occur in such a case that communication status between the UE100and the AP300deteriorates after establishing the connection between the UE100and the AP300.

Hereinafter, an operation according to the first embodiment for resolving this defect will be described

(2) Operation Pattern1According to the First Embodiment

FIG. 8is a sequence diagram of an operation pattern1according to the first embodiment. In an initial state of the present sequence, the UE100is in a state in which the UE100has established a RRC connection (a first connection) with the eNB200.

As shown inFIG. 8, in step S101, when the UE100decides on starting of the offload, the UE100transmits an offload notification to that effect to the eNB200.

In step S102, the eNB200transmits an acknowledgment (an Ack) to the UE100in response to a receipt of the offload notification from the UE100. The eNB200transmits configuration information (hereinafter called “idle time configuration information”) for configuration of an operation (that is, an operation in the idle state) of the UE100after the RRC connection is released, to the UE100along with the Ack. When the UE100receives the idle time configuration information along with the Ack, the UE100stores the received idle time configuration information. The idle time configuration information is information similar to information included in a RRC release message (a RRC Connection Release) and information (such as freqPriorityList, idleModeMobilityControlInfo) for providing priority of cell reselection (Refer to 3GPP technical specification “TS 36.300”).

In step S103, the UE100establishes a connection (a second connection) with the AP300in response to a receipt of the Ack from the eNB200, and then the offload is started. Specifically, the UE100switches the traffic transmitted and received with the eNB200so as to be transmitted and received with the AP300.

The UE100and the eNB200maintain without releasing the RRC connection even when the offload is started. Thus, the UE100maintains the connection state of the cellular communication without transition to the idle state of the cellular communication even when the offload is started.

In step S104, the UE100activates a timer for measuring a predetermined time.

When the timer expires in step S105, the UE100determines whether the offload is continued or not in step S106. In other words, the UE100determines whether the UE100switches the traffic transmitted and received with the AP300so as to be transmitted and received with the eNB200. The UE100carries out the determination on the basis of a communication status with the AP300. The communication status with the AP300is radio link status between the UE100and the AP300and/or network status relevant to the AP300. The radio link status between the UE100and the AP300is signal intensity of beacon signal, radio link stability degree and the like. The network status relevant to the AP300is load level of the AP300and the like. For example, when the communication status between the UE100and the AP300is good, the UE100determines that the offload is continued, and otherwise the UE100determines that the offload is cancelled.

When it is determined that the offload is cancelled (in step S106: No), the UE100cancels the offload in step S107. In other words, the UE100switches the traffic transmitted and received with the AP300so as to be transmitted and received with the eNB200. Further, in step S108, the UE100discards the idle time configuration information stored in step S102. Also, the UE100may release the connection of the AP300.

On the other hand, when it is determined that the offload is continued (in step S106: Yes), the UE100transmits notification indicating that the offload is continued to the eNB200in step S109. As a result, the UE100and the eNB200release the RRC connection. Further, the UE100transits from the connection state of the cellular communication to the idle state.

In step S110, the UE100applies the idle time configuration information stored in step S102. Then, in step S111, the UE100performs an operation in the idle state on the basis of the idle time configuration information.

(3) Operation Pattern2According to the First Embodiment

FIG. 9is a sequence diagram of an operation pattern2according to the first embodiment. In an initial state of the present sequence, the UE100is in a state in which the UE100has established the RRC connection (the first connection) with the eNB200.

As shown inFIG. 9, in step S201, when the UE100decides on starting of the offload, the UE100transmits an offload notification to that effect to the eNB200. The UE100transmits transmission stop request for requesting to stop transmitting a release instruction (a RRC release message) of the RRC connection along with the offload notification. The eNB200sets a stopping transmitting the RRC release message to the UE100in the response to a receipt of the transmission stop request.

In step S202, the eNB200transmits an acknowledgment (an Ack) to the UE100in the response to a receipt of the offload notification from the UE100.

In step S203, the UE100establishes the connection (the second connection) with the AP300on the basis of the Ack from the eNB200, and then the offload is started. Specifically, the UE100switches the traffic transmitted and received with the eNB200so as to be transmitted and received with the AP300.

The UE100and the eNB200maintain without releasing the RRC connection even when the offload is started. Thus, the UE100maintains the connection state of the cellular communication without transition to the idle state of the cellular communication even when the offload is started.

In step S204, the UE100activates a timer for measuring a predetermined time.

In step S205, the UE100determines whether the offload is continued or not. A method of determination is the same as that of the operation pattern1.

When it is determined that the offload is cancelled (in step S205: No), the UE100cancels the offload in step S206. In other words, the UE100switches the traffic transmitted and received with the AP300so as to be transmitted and received with the eNB200. Also, the UE100may release the connection of the AP300.

On the other hand, when it is determined that the offload is continued (in step S205: Yes) and when the timer expires (in step S207), the UE100transmits a transmission request to request to transmit the RRC release message to the eNB200in step S208.

In step S209, the eNB200transmits the RRC release message to the UE100in a response to a receipt of the transmission request of the RRC release message. The RRC release message includes the idle time configuration information for configuration of an operation of the UE100after the RRC connection is released. As a result, the UE100and the eNB200release the RRC connection. Further, the UE100transits from the connection state of the cellular communication to the idle state. Then in step S210, the UE100performs an operation in the idle state on the basis of the idle time configuration information.

Conclusion of the First Embodiment

In the first embodiment, the UE100that have established the RRC connection with the eNB200maintains without releasing the RRC connection even when the offload is started after establishing the connection with the AP300. Further, the UE100determines whether the offload is continued or canceled after the offload is started. Thus, the above ping-pong phenomenon can be avoided by maintaining without releasing the RRC connection even when the offload is started.

In the first embodiment, the UE100carries out the determination on the basis of the communication status with the AP300. Thus, the UE100can respond to change in the communication status with the AP300after the offload.

In the operation pattern1, the UE100receives from the eNB200, before the RRC connection is released, the idle time configuration information for configuration of the operation of the UE100after the RRC connection is released. Thereby, the UE100can performs the proper operation after the RRC connection is released (that is, in the idle state).

In the operation pattern1, the UE100transmits the notification indicating that the offload is continued, to the eNB200, when it is determined that the offload is continued. Then, the UE100releases the RRC connection after the notification is transmitted. Thereby, the UE100can voluntarily release the RRC connection in a case where there is no problem releasing the RRC connection. In addition, cellular resource is saved by releasing the RRC connection.

In the operation pattern1, the UE100cancels the offload and discards the idle time configuration information when it is determined that the offload is canceled. Thereby, memory can be saved by discarding unnecessary idle time configuration information.

In the operation pattern2, the UE100transmits, to the eNB200, the transmission stop request for requesting to stop transmitting the RRC release message before the offload is started. Thereby, the UE100can prevent the eNB200from releasing the RRC connection.

In the operation pattern2, the UE100transmits to the eNB200the transmission request to request to transmit the RRC release message when it is determined that the offload is continued, and the UE100receives the RRC release message from the eNB200. Thereby, the UE100can voluntarily release the RRC connection in a case where there is no problem releasing the RRC connection. Also, the RRC release message includes the idle time configuration information. Thus, the UE100can performs the proper operation after the RRC connection is released (that is, in the idle state).

Second Embodiment

The second embodiment will be described while focusing on the difference from the first embodiment. Operation environment according to the second embodiment is similar to that of the first embodiment.

Operation According to Second Embodiment

In the above first embodiment, the timer comprised by each of the UE100and the eNB200is not described in detail. The second embodiment is an embodiment in which these timers are focused. As described above, the UE100comprises a terminal-side timer (hereinafter called an “UE timer”) that regulates a connection maintaining period during which the RRC connection should be maintained after the offload is started. The UE100activates the terminal-side timer when the offload is started (refer to step S104inFIG. 8and step S204inFIG. 9). Then, the UE100maintains the RRC connection until the UE timer expires.

On the other hand, the eNB200comprises a base station-side timer (hereinafter called an “eNB timer”) that regulates a connection maintaining period during which the RRC connection should be maintained after transmission and reception of traffic with the UE100is stopped. This eNB timer may be called an Inactivity timer. The eNB200activates the eNB timer when transmission and reception of traffic with the UE100is stopped. Further, the eNB200maintains the RRC connection until the eNB timer expires, transmits the RRC release message to the UE100when the eNB timer expires, and then releases the RRC connection.

Here, there is a possibility that competition occurs between the UE timer and the eNB timer. Specifically, in a case where the connection maintaining period set to the eNB timer is shorter than the connection maintaining period set to the UE timer, the eNB timer expires before the UE timer expires, and then the eNB200releases the RRC connection. Hereinafter, operation according to the second embodiment for resolving this defect will be described.

(1) Operation Pattern1According to the Second Embodiment

The operation pattern1according to the second embodiment is a pattern in which a suitable connection maintaining period is preliminarily set to the UE timer. Specifically, the connection maintaining period set to the UE timer is equal to or shorter than the connection maintaining period set to the eNB timer. In other words, the connection maintaining period set to the eNB timer is equal to or longer than the connection maintaining period set to the UE timer. Thus, the eNB timer can be prevented from expiring before the UE timer expires.

(2) Operation Pattern2According to the Second Embodiment

The operation pattern2according to the second embodiment is a pattern in which the UE transmits and receives the traffic with the AP300and transmits and receives the traffic with the eNB200to prevent the eNB timer from expiring (or to stop the eNB timer) after the offload is started.

For example, “the UE transmits and receives the traffic with the eNB200to prevent the eNB timer from expiring” means an operation in which a part of traffic (bearers) is left for the eNB200. This operation can basically apply in a case where the UE100uses a plurality of services via the eNB200. However, the connection state may be maintained by generating dummy traffic (keep arrive message) and periodically transmitting the dummy traffic to the eNB200even when the UE100uses only one service. The keep arrive message may be a message of upper layer (for example, a message transmitted to a server owned by an operator) or a message of lower layer (for example, a message exchanged among the MAC layer).

FIG. 10is a sequence diagram of the operation pattern2according to the second embodiment. In the present sequence, an operation in which a part of traffic is left for the eNB200will be described as an example. In an initial state of the present sequence, the UE100is in a state in which the UE100has established the RRC connection (the first connection) with the eNB200(in step S301).

As shownFIG. 10, in step S302, when the UE100decides that the offload is started, the UE100selects traffic which is left for the eNB200. A selection criterion is QoS type or service type and the like. For example, the UE100may determine that operator-unique service (service unique to an operator line that cannot be provided via the WLAN) is preferentially left for the eNB200.

In step S303, the UE100establishes a connection (a second connection) with the AP300and then the offload is started. Specifically, the UE100switches traffic other than traffic which is left for the eNB200from traffics transmitted and received with the eNB200so as to be transmitted and received with the AP300.

The UE100and the eNB200maintain without releasing the RRC connection even when the offload is started. Thus, the UE100maintains the connection state of the cellular communication without transition to the idle state of the cellular communication even when the offload is started.

In step S304, the UE100activates the UE timer in response to the start of the offload.

In step S305, the UE100determines whether the offload is continued or not. A method of determination is the same as that of the first embodiment.

When it is determined that the offload is canceled (in step S305: No), the UE100cancels the offload in step S306. In other words, the UE100switches the traffic transmitted and received with the AP300so as to be transmitted and received with the eNB200. Also, the UE100may release the connection of the AP300.

On the other hand, in a case where it is determined that the offload is continued (in step S305: Yes) and when the UE timer expires (in step S307), the UE100switches the traffic which is left for the eNB200so as to be transmitted and received with the AP300in step S308.

The eNB200activates the eNB timer in response to the traffic of the UE100having been lost, and then the eNB timer expires.

In step S309, the eNB200transmits the RRC release message to the UE100. The RRC release message includes the idle time configuration information for configuration of an operation of the UE100after the RRC connection is released. As a result, the UE100and the eNB200release the RRC connection. Further, the UE100transits from the connection state of the cellular communication to the idle state (in step S310). Then, the UE100performs an operation in the idle state on the basis of the idle time configuration information.

(3) Operation Pattern3According to the Second Embodiment

The operation pattern3according to the second embodiment is a pattern in which the eNB200inquires the UE100of whether it is possible to release the RRC connection in a case where the release request for the RRC connection is not received from the UE100when the eNB timer expires in the eNB200. In other words, the eNB200cannot release the RRC connection until an approval is gained from the UE100.

FIG. 11is a sequence diagram of the operation pattern3according to the second embodiment. In an initial state of the present sequence, the UE100is in a state in which the UE100has established the RRC connection (the first connection) with the eNB200.

As shownFIG. 11, in step S401, when the UE100decides on starting of the offload, the UE100transmits an offload notification to that effect to the eNB200.

In step S402, the eNB200transmits an acknowledgment (an Ack) to the UE100in response to a receipt of the offload notification from the UE100.

In step S403, the UE100establishes a connection (a second connection) with the AP300in response to a receipt of the Ack from the eNB200, and then the UE100starts the offload. Specifically, the UE100switches the traffic transmitted and received with the eNB200so as to be transmitted and received with the AP300. In addition, the UE100activates the UE timer in a response to the start of the offload.

The UE100and the eNB200maintain without releasing the RRC connection even when the offload is started. Thus, the UE100maintains the connection state of the cellular communication without transition to the idle state of the cellular communication even when the offload is started.

In step S404, the eNB200activates the eNB timer in response to the traffic of the UE100having been lost.

In step S405, the eNB timer expires. In step S406, the eNB200transmits release request for the RRC connection to the UE100when the eNB timer expires. The release request corresponds to an inquiring of whether it is possible to release the RRC connection. Also, the release request can be regarded as a notification indicating that the eNB timer expires.

In step S407, the UE100determines whether the release request for the RRC connection received from the eNB200. Since, during the UE timer running, the UE100carries out the determination whether the offload is continued or not, the UE100determines that the RRC release request is rejected when the UE100receives the release request for the RRC connection from the eNB200during the UE timer running. On the other hand, UE100determines that the RRC release request is accepted when the UE100receives the release request for the RRC connection from the eNB200after the UE timer expires.

In step S408, the UE100transmits, to the eNB200, a determination result of whether the release request for the RRC connection is accepted or rejected. The UE100transmits an Ack to the eNB200in a case where the release request for the RRC connection is accepted, and transmits a Nack to the eNB200in a case where the release request for the RRC connection is rejected.

In step S409, the eNB200verifies whether the Ack has been received or the Nack has been received from the UE100.

When the Ack has been received from the UE100(in step S409: Yes), the eNB200transmits the RRC release message to the UE100in step S410.

On the other hand, when the Nack has been received from the UE100(in step S409: No), the eNB200restarts the eNB timer in step S411. The connection maintaining period set to the eNB timer in the restart may be the same as the initial connection maintaining period, or may be different from the initial connection maintaining period (for instance, a connection maintaining period shorter than the initial connection maintaining period).

(4) Operation Pattern4According to the Second Embodiment

The operation pattern4according to the second embodiment is a pattern in which the eNB200controls the eNB timer in order to prevent the eNB timer from expiring before the UE timer expires. There are the following three methods (operation patterns4-1to4-3) as a method of controlling the eNB timer.

In the operation pattern4-1according to the second embodiment, the eNB timer includes a general eNB timer (a first eNB timer) used for a purpose of other than the offload and an offload eNB timer (a second eNB timer) used for a purpose of the offload. A connection maintaining period set to the offload eNB timer is equal to or longer than the connection maintaining period notified to the UE100. The eNB200selects the offload eNB timer and then activates the offload eNB timer in response to the start of the offload.

In the operation pattern4-2according to the second embodiment, the eNB200notifies the UE100of the connection maintaining period that should be set to the UE timer. It is preferable that this notification is a notification by broadcasting (for example, a notification by the SIB). However, this notification may be a notification by unicasting. The eNB200sets a connection maintaining period equal to or longer than the connection maintaining period notified to the UE100, to the eNB timer.

In the operation pattern4-3according to the second embodiment, the eNB200cancels the activation of the eNB200timer in response to the start of the offload. In this case, the eNB200may set the connection maintaining period equal to or longer than the connection maintaining period set to the UE timer, to the eNB timer in a case where the eNB200knows the connection maintaining period set to the UE timer. Alternatively, as described in the first embodiment, the release processing of the RRC connection may be performed at the initiative of the UE.

Also, in the operation patterns4-2and4-3according to the second embodiment, the eNB200may acquire information indicating the connection maintaining period set to the UE timer from the UE100. In this case, for example, the UE100may include information indicating the connection maintaining period set to the UE timer in the UE Capability message, for instance, and transmit the information to the eNB200.

FIG. 12is a sequence diagram of the operation pattern4according to the second embodiment. The operation pattern4-2is mainly assumed here. In an initial state of the present sequence, the UE100is in a state in which the UE100has established the RRC connection (the first connection) with the eNB200.

As shown inFIG. 12, in step S501, the eNB200transmits the information indicating the connection maintaining period that should be set to the UE timer to the UE100by broadcasting. The UE100sets the connection maintaining period indicated by the information received from the eNB200to the UE timer.

In step S502, when the UE100decides on starting of the offload, the UE100transmits an offload notification to that effect to the eNB200.

In step S503, the eNB200transmits an acknowledgment (an Ack) to the UE100in response to a receipt of the offload notification from the UE100.

In step S504, the eNB200sets the connection maintaining period equal to or longer than the connection maintaining period set to the UE timer to the eNB timer. Also, step S504may be between step S501and step S502or between step S502and step S503.

In step S505, the UE100establishes the connection (the second connection) with the AP300in response to a receipt of the Ack from the eNB200, and then the offload is started. Specifically, the UE100switches the traffic transmitted and received with the eNB200so as to be transmitted and received with the AP300.

The UE100and the eNB200maintain without releasing the RRC connection even when the offload is started. Thus, the UE100maintains the connection state of the cellular communication without transition to the idle state of the cellular communication even when the offload is started.

In step S506, the UE100activates the UE timer in response to the start of the offload.

In step S507, the eNB200activates the eNB timer in response to the traffic of the UE100having been lost.

In step S508, during the UE timer running, the UE100carries out the determination whether the offload is continued or not. A method of determination is the same as that of the first embodiment.

When it is determined that the offload is canceled (in step S508: No), the UE100cancels the offload in step S509. In other words, the UE100switches the traffic transmitted and received with the AP300so as to be transmitted and received with the eNB200. Also, the UE100may release the connection of the AP300.

In step S510, the UE timer expires.

In step S511, the eNB timer expires. Timing of the eNB timer expiring is later than timing of the UE timer expiring.

In step S512, the eNB200transmits the RRC release message to the UE100in a response to the expiration of the eNB timer. The RRC release message includes the idle time configuration information for configuration of an operation of the UE100after the RRC connection is released. As a result, the UE100and the eNB200release the RRC connection. Further, the UE100transits from the connection state of the cellular communication to the idle state (in step S513). Then, the UE100performs an operation in the idle state on the basis of the idle time configuration information.

Conclusion of the Second Embodiment

In the operation pattern1according to the second embodiment, the connection maintaining period set to the UE timer is equal to or shorter than the connection maintaining period set to the eNB timer. Thus, the eNB timer is prevented from expiring before the UE timer expires without modifying the existing eNB timer.

In the operation pattern2according to the second embodiment, the UE100transmits and receives the traffic with the AP300and transmits and receives the traffic with the eNB200to prevent the eNB timer from expiring (or to stop the eNB timer) after the offload is started. Thus, the eNB timer is prevented from expiring before the UE timer expires without modifying the existing eNB timer.

In the operation pattern3according to the second embodiment, the eNB200inquires the UE100of whether it is possible to release the RRC connection in a case where the release request for the RRC connection is not received from the UE100when the eNB timer expires in the eNB200. Thus, the RRC connection is prevented from being unexpectedly released because even though the eNB timer expires before the UE timer expires, the RRC connection is not released until the approval is gained from the UE100.

In the operation pattern4according to the second embodiment, the eNB200controls the eNB timer in order to prevent the eNB timer from expiring before the UE timer expires. Thus, the eNB timer is prevented from expiring before the UE timer expires.

Third Embodiment

Next, a third embodiment will be described.

A case is assumed where the communication state of each of the eNB200and the AP300is compared by the UE100so that the UE100itself is capable of selecting the connection target from the eNB200and the AP300.

In this case, the plurality of UEs100may select the same AP300as a connection target, and may simultaneously start a connection process on the AP300. Therefore, due to the conflict from the connection process, some UEs100may not establish a connection with the AP300.

Further, even when all of these UEs100are capable of establishing a connection with the AP300, there are problems that as a result of an increase in load level of the AP300, it is not possible to ensure a sufficient throughput and too many unused resources of the eNB200occur.

Thus, an object of the third embodiment is to resolve a problem caused due to simultaneous connection by the plurality of UEs100to the AP300.

Operation According to Third Embodiment

An operation according to the third embodiment will be described.

(1) Operation Environment

FIG. 13is a diagram for describing an operation environment according to the third embodiment.

As shown inFIG. 13, there are a plurality of UEs100in a coverage of the eNB200and in a transport T such as a train or a bus. The transport T moves along a predetermined route (a railway or a road).

The UE100has established a connection with the eNB200, and performs cellular communication with the eNB200. Specifically, the UE100transmits and receives a cellular radio signal including a traffic (user data) with the eNB200. Alternatively, some UEs100may not establish a connection with the eNB200.

Further, the AP300is provided in a coverage of the eNB200. The AP300is an AP (Operator controlled AP) managed by an operator. Specifically, the AP300is provided at a stop point (a station or a stop, etc.) at which the transport T stops.

It is noted that in the third embodiment, a case is assumed where the communication state of each of the eNB200and the AP300is compared by the UE100so that the UE100itself is capable of selecting the connection target from the eNB200and the AP300.

In such an operation environment, when the transport T moves into the coverage of the AP300(movement1), the plurality of UEs100in the transport T start a connection process to the AP300. The UE100that has established the connection with the AP300releases the connection with the eNB200.

Further, the transport T moves out of the coverage of the AP300(movement2) after stopping at the stop point. At that time, the plurality of UEs100in the transport T release the connection with the AP300and establish the connection with the eNB200.

Thus, in an operation environment where the AP300is provided at the stop point (a station or a stop, etc.) at which the transport T stops, when the UE100itself is capable of selecting the connection target from the eNB200and the AP300, there may occur an ineffective operation in which the UE100switches the connection from the eNB200to the AP300, and thereafter, the UE100switches the connection from the AP300to the eNB200. Further, when the plurality of UEs100simultaneously perform the connection process, there may be a conflict from the connection process.

An operation for resolving such a problem will be described, below.

(2) UE Operation Flow

FIG. 14is an operation flow diagram of the UE100according to the third embodiment. Here, a case is assumed where the WLAN communication unit112of the UE100is in an on state. In the third embodiment, when the WLAN communication unit112is in an on state, the processor160of the UE100measures a movement speed (hereinafter, “UE movement speed”) of the UE100, on the basis of the location information evaluated from the GNSS receiver130, for example. It is noted that when an acceleration sensor is provided in the UE100, the UE movement speed (acceleration) may be measured by the acceleration sensor.

As shown inFIG. 14, in step S601, the processor160determines whether or not the UE movement speed rapidly decreases. The “UE movement speed rapidly decreasing” means that an amount of decrease in UE movement speed per unit time exceeds a constant amount.

It is noted that the processor160executes a process in step S601when it is detected that the UE movement speed is high speed, and otherwise, may not execute the process in step S601. This is because the UE100being located in the transport T is a prerequisite of step S601.

When the UE movement speed rapidly decreases (step S601: Yes), in step S602, the processor160activates a timer that regulates a period of an AP connection restriction in which the connection by the WLAN communication unit112with the AP300is restricted (hereinafter, “AP connection restriction timer”). It is noted that the period of an AP connection restriction (that is, a timer value of the AP connection restriction timer) may be previously stored in the memory150, and may be designated by the eNB200to the UE100.

In the period of an AP connection restriction, the processor160switches the WLAN communication unit112to an off state. Alternatively, the processor160may cancel decoding the beacon signal of the AP300or transmitting to the AP300while maintaining the WLAN communication unit112in an on state.

In step S603, the processor160determines whether or not the UE movement speed rapidly increases. The “UE movement speed rapidly increasing” means that an amount of increase in UE movement speed per unit time exceeds a constant amount.

When the UE movement speed rapidly increases (step S603: Yes), in step S605, the processor160cancels the AP connection restriction. That is, it is made possible to connect with the AP300.

On the other hand, when the UE movement speed does not rapidly increase (step S603: No), in step S604, the processor160confirms whether or not the AP connection restriction timer expires. When the AP connection restriction timer expires (step S604: Yes), in step S605, the processor160cancels the AP connection restriction. On the other hand, when the AP connection restriction timer does not expire (step S604: No), the processor160returns the process to step S603.

Summary of Third Embodiment

The UE100according to the third embodiment measures the UE movement speed when the WLAN communication unit112is in an on state. Upon detection of a rapid decrease in UE movement speed, the UE100restricts the start of connection by the WLAN communication unit112with the AP300. As a result, in an operation environment as shown inFIG. 13, it is possible to avoid an ineffective operation in which the UE100switches the communication from the eNB200to the AP300, thereafter, the UE100switches the connection from the AP300to the eNB200. Further, it is possible to avoid the conflict from the connection process caused when the plurality of UEs100simultaneously perform the connection process.

In the third embodiment, when detecting a rapid increase in UE movement speed after detecting a rapid decrease in UE movement speed, the UE100cancels the restriction of a start of connection by the WLAN communication unit112with the AP300. As a result, it is possible to return to a normal operation from a state of the AP connection restriction.

Modification of Third Embodiment

FIG. 15is a sequence diagram according to a modification of the third embodiment.

As shown inFIG. 15, the processor240of the eNB200transmits, to the UE100, a list of APs300that should be subject to a connection restriction (hereinafter, “AP blacklist”). The AP blacklist includes an identifier of the AP300provided at a stop point (a station or a stop, etc.) at which the transport T stops, for example. The identifier of the AP300(AP identifier) is an SSID (Service Set Identifier) or a BSSID (Basic Service Set Identifier).

From a viewpoint of a usage efficiency of a radio resource, the processor240may transmit the AP blacklist to the UE100by broadcast. Further, the processor240may periodically transmit the AP blacklist. Alternatively, the eNB200may receive, from the UE100, information indicating whether the WLAN communication unit112is in an on state, and may transmit the AP blacklist by unicast to the UE100in which the WLAN communication unit112is in an on state.

The cellular communication unit111of the UE100receives the AP blacklist from the eNB200. The memory150stores the AP blacklist. When an AP identifier included in the beacon signal received by the WLAN communication unit112from the AP300matches an AP identifier in the AP blacklist, the processor160restricts the start of connection with the AP300.

However, it is necessary that such a method is not applied to the UE100other than the UE100located in the transport T. Therefore, the processor160may enable the AP blacklist in the memory150when detecting that the UE movement speed rapidly decreases, and otherwise, disable the AP blacklist.

Alternatively, when an AP identifier included in the beacon signal received by the WLAN communication unit112from the AP300matches an AP identifier in the AP blacklist, the processor160restricts a start of connection with the AP300during a constant period, and after the constant period passes, may cancel the connection restriction. Such a constant period may be regulated on the basis of an average time period during which the transport T stops at the stop point (a station or a stop, etc.).

Fourth Embodiment

Description about a fourth embodiment proceeds with a focus on a difference from the above-described third embodiment.

In the fourth embodiment, an operation flow of the UE100is different from that in the third embodiment. It is noted that a system configuration and an operation environment in the fourth embodiment are in much the same way as in the third embodiment.

FIG. 16is an operation flow diagram of the UE100according to the fourth embodiment. Here, a case is assumed where the WLAN communication unit112of the UE100is in an on state. In the fourth embodiment, when the WLAN communication unit112is in an on state, the processor160of the UE100measures the reception level of the beacon signal received by the WLAN communication unit112from the AP300(hereinafter, “AP reception level”).

As shown inFIG. 16, in step S701, the processor160determines whether or not the AP reception level rapidly increases. The “AP reception level rapidly increasing” means that an amount of increase in AP reception level per unit time exceeds a constant amount.

When the AP reception level rapidly increases (step S701: Yes), in step S702, the processor160activates the AP connection restriction timer. As described above, the period of an AP connection restriction (that is, a timer value of the AP connection restriction timer) may be previously stored in the memory150, and may be designated by the eNB200to the UE100.

In the fourth embodiment, in the period of an AP connection restriction, the processor160may cancel decoding the beacon signal of the AP300or transmitting the beacon signal to the AP300while maintaining the WLAN communication unit112in an on state. That is, although it is not possible to connect with the AP300, it is made possible to measure the AP reception level.

In step S703, the processor160determines whether or not the AP reception level rapidly decreases. The “AP reception level rapidly decreasing” means that an amount of decrease in AP reception level per unit time exceeds a constant amount.

When the AP reception level rapidly decreases (step S703: Yes), in step S705, the processor160cancels the AP connection restriction. That is, it is made possible to connect with the AP300.

On the other hand, when the AP reception level does not rapidly decrease (step S703: No), in step S704, the processor160confirms whether or not the AP connection restriction timer expires. When the AP connection restriction timer expires (step S704: Yes), in step S705, the processor160cancels the AP connection restriction. On the other hand, when the AP connection restriction timer does not expire (step S704: No), the processor160returns the process to step S703.

Summary of Fourth Embodiment

The UE100according to the fourth embodiment measures the AP reception level when the WLAN communication unit112is in an on state. When detecting a rapid increase in AP reception level, the UE100restricts the start of connection by the WLAN communication unit112with the AP300. As a result, in an operation environment as shown inFIG. 13, it is possible to avoid an ineffective operation in which the UE100switches the communication from the eNB200to the AP300, thereafter, the UE100switches the connection from the AP300to the eNB200. Further, it is possible to avoid the conflict from the connection process caused when the plurality of UEs100simultaneously perform the connection process.

In the fourth embodiment, when detecting a rapid decrease in AP reception level after detecting a rapid increase in AP reception level, the UE100cancels the restriction of a start of connection by the WLAN communication unit112with the AP300. As a result, it is possible to return to a normal operation from a state of the AP connection restriction.

Modification of Fourth Embodiment

In the fourth embodiment also, the AP blacklist may be applied in much the same way as in the above-described third embodiment. However, it is necessary that the AP blacklist is not applied to the UE100other than the UE100located in the transport T. Therefore, when detecting a rapid increase in AP reception level, the processor160may enable the AP blacklist in the memory150, and otherwise, disable the AP blacklist.

Alternatively, as described above, when an AP identifier included in the beacon signal received by the WLAN communication unit112from the AP300matches an AP identifier in the AP blacklist, the processor160restricts the start of connection with the AP300during a constant period, and after the constant period passes, may cancel the connection restriction.

Fifth Embodiment

Next, a fifth embodiment will be described.

Generally, the UE100performs a WLAN scan in order to discover a connectable AP300. The WLAN scan is an operation in which reception of a WLAN radio signal (for example, a beacon signal) is attempted by the WLAN communication unit112for each WLAN channel.

The UE100continues the WLAN scan while switching the WLAN channels until it is completed to attempt all the WLAN channels or until it is successful to receive the WLAN radio signal. Thus, the power consumption of the UE100(in particular, the power consumption of the WLAN communication unit112) increases.

Therefore, there is a problem that in an offload, the power consumption of the UE100increases resulting from the WLAN scan.

Therefore, an object of the fifth embodiment is to enable realization of an offload of the eNB200while restraining an increase in power consumption resulting from the WLAN scan.

FIG. 17is a system configuration diagram according to the fifth embodiment.

As shown inFIG. 17, the EPC20includes an E-SMLC (Evolved Serving Mobile Location Centre)600that is a serve device that provides location information indicating a geographical location of the UE100. The E-SMLC600collects a result of a radio measurement in the UE100and/or the eNB200to calculate location information indicating a geographical location of the UE100. For details of a mechanism for calculating the location information, refer to 3GPP technical specification “TS 36.305”.

Operation According to Fifth Embodiment

Next, an operation according to the fifth embodiment will be described.

(1) Operation Environment

FIG. 18is a diagram for describing an operation environment according to the fifth embodiment. As shown inFIG. 18, the AP300is provided in a coverage of the eNB200. The AP300is an AP (Operator controlled AP) managed by an operator.

Further, the UE100is located in the coverage of the eNB200and in the coverage of the AP300. The UE100has established a connection with the eNB200, and performs cellular communication with the eNB200. Specifically, the UE100transmits and receives a cellular radio signal including a traffic (user data) with the eNB200. It is noted that inFIG. 18, there shows only one UE100that have established the connection with the eNB200; in a real environment, a large number of UEs100may have established the connection with the eNB200.

When the eNB200establishes a connection with a large number of UEs100, a load level of the eNB200increases. The “load level” means the degree of congestion in the eNB200such as a traffic load of the eNB200or usage of radio resources of the eNB200. Here, at least a part of traffic transmitted and received between the UE100and the eNB200is allowed to transfer to the WLAN system, so that it is possible to disperse a traffic load of the eNB200, in the WLAN system.

Description will be provided for an operation for transferring (offloading) the traffic transmitted and received between the UE100and the eNB200, to the WLAN system below. It is noted that the offload includes not only a case where all the traffics transmitted and received between the UE100and the eNB200are transferred to the WLAN system but also a case where at least a part of the traffic is transferred to the WLAN system while maintaining a connection between the UE100and the eNB200.

Prior to description of the offload operation, a general WLAN scan will be described.

The UE100performs a WLAN scan in order to discover a connectable AP300. The WLAN scan is an operation in which reception of a WLAN radio signal from the AP300is attempted by the WLAN communication unit112for each WLAN channel. The WLAN scan includes a passive scan scheme and an active scan scheme; in the fifth embodiment, either scheme may be selected.

The passive scan scheme is a scheme in which the UE100attempts to receive the beacon signal periodically transmitted in the WLAN channel employed by the AP300. The beacon signal includes information on the AP300, such as an identifier of the AP300. The identifier of the AP300is an SSID (Service Set Identifier) or a BSSID (Basic Service Set Identifier). The UE100attempts to receive the beacon signal over a predetermined time equal to or longer than a transmission period of the beacon signal, for each WLAN channel. When a predetermined time passes or when it is not successful to receive the beacon signal within a predetermined time, the UE100switches to a next WLAN channel, and then, attempts to receive the beacon signal again.

The active scan scheme is a scheme in which the UE100transmits a probe request in the WLAN channel, the AP300that is employing the WLAN channel transmits a probe response in response to the probe request, and the UE100attempts to receive the probe response. Information included in the probe response is similar to the information included in the beacon signal. Therefore, it is possible to regard the probe response as one type of the beacon signal. The UE100attempts to receive the probe response over a predetermined time since transmitting the probe request, for each WLAN channel. When a predetermined time passes or when it is not successful to receive the probe response within a predetermined time, the UE100switches to a next WLAN channel, and transmits the probe request again, and then, attempts to receive the probe response.

Thus, the UE100continues the WLAN scan while switching the WLAN channels until it is successful to receive at least the beacon signal (or the probe response), and thus, the power consumption of the UE100(in particular, the power consumption of the WLAN communication unit112) increases. Therefore, in the offload operation according to the fifth embodiment, when the WLAN scan is made efficient, the power consumption in the WLAN scan is reduced.

FIG. 19is a sequence diagram of the offload operation according to the fifth embodiment. In an initial state of the present sequence, the UE100has established the connection with the eNB200, and brings the WLAN communication unit112into an off state (a state where it is not possible to transmit and receive the WLAN radio signal). Further, it is assumed that the load level of the eNB200is high and a preferable situation is realized to perform the offload, for example.

As shown inFIG. 19, in step S801, the processor160of the UE100notifies the eNB200by the cellular communication unit111of information indicating a WLAN communication capability (hereinafter, “WLAN capability information”) of the UE100. The WLAN capability information is information indicating whether or not the UE100supports the WLAN communication. When the UE100supports the WLAN communication, the WLAN capability information may include information indicating a function of the supported WLAN communication (hereinafter, “WLAN function information”). Examples of the function of the supported WLAN communication include a standard of the supported WLAN communication (IEEE 802.11a/b/g/n), a supported QoS function (WMM: Wi-Fi MultiMedia, etc.), and a support WLAN frequency band (2.4 GHz band, 5 GHz band, etc.).

It is noted that the UE100may autonomously notify the eNB200of the WLAN capability information during connection with the eNB200, and may notify the eNB200of the WLAN capability information in response to a request from the eNB200after connection with the eNB200.

When the cellular communication unit210receives the WLAN capability information, the processor240of the eNB200determines, on the basis of the received WLAN capability information, whether or not the UE100is an offloadable UE100(that is, the UE100that supports the WLAN communication). Further, the processor240may determine that the UE100is not possible to offload when there is no AP300that matches the WLAN function information, out of the APs300in the coverage of the eNB200. In this case, description is provided on the assumption that it is determined that the UE100is possible to offload.

In step S802, the processor160of the UE100notifies the eNB200, by the cellular communication unit111, of information indicating that the WLAN communication unit112is in an off state (hereinafter, “WLAN off information”). The processor160may notify the eNB200of the WLAN off information when bringing the WLAN communication unit112into an off state, and may notify the eNB200of the WLAN off information in response to an inquiry from the eNB200. Alternatively, the processor160may periodically notify the eNB200whether the WLAN communication unit112is in an off state or an on state.

In step S803, the processor240of the eNB200acquires information indicating an operation status of the AP300(hereinafter, “AP operation information”), by the network interface220, from the AP300. The AP operation information includes information indicating a WLAN channel operating in the AP300and information indicating a WLAN frequency band including the WLAN channel. Further, the AP operation information may include information indicating a timing (period) at which the AP300transmits the beacon signal. The AP300may periodically notify the eNB200of the AP operation information, and may notify the eNB200of the AP operation information in response to a request from the eNB200. The notification may be performed by way of a core network.

In step S804, the processor240of the eNB200acquires information indicating a geographical location of the UE100(hereinafter, “UE location information”), by the network interface220, from the E-SMLC600. Alternatively, when the UE100has the GNSS receiver130and the GNSS receiver130is in an on state, the processor240may acquire, by the cellular communication unit111, the UE location information generated by using the GNSS receiver130, from the UE100.

It is noted that step S801to step S804may be performed in any order as well as in this order.

In step S805, the processor240of the eNB200compares the UE location information and information indicating a geographical location of the AP300(hereinafter, “AP location information”) to determine whether or not the UE100comes close to the AP300. Specifically, the processor240determines whether or not the UE100is located in the coverage of the AP300. It is noted that the AP location information may be previously stored in the memory230of the eNB200and may be notified to the eNB200from the AP300. In this case, description is provided on the assumption that it is determined that the UE100comes close to the AP300.

The processor240of the eNB200determines the UE100as the UE100subject to offload because the UE100that supports the WLAN communication brings the WLAN communication unit112in an off state and comes close to the AP300. Then, the processor240generates scan control information for controlling the WLAN scan by the UE100, on the basis of the AP operation information. It is noted that when the scan control information is generated, the WLAN capability information, in addition to the AP operation information, may be taken into consideration.

The scan control information includes at least one of information on a scan frequency and information on a scan time. Further, the scan control information may include information on a priority (priority information).

The information on the scan frequency includes channel information for designating a WLAN channel subject to the WLAN scan or a WLAN channel not subject to the WLAN scan. The WLAN channel subject to the WLAN scan is a WLAN channel operating in the AP300near the UE100. The WLAN channel not subject to the WLAN scan is a WLAN channel not operating in the AP300near the UE100.

Further, the information on the scan frequency includes frequency band information for designating a WLAN frequency band subject to the WLAN scan or a WLAN frequency band not subject to the WLAN scan. The WLAN frequency band subject to the WLAN scan is a WLAN frequency band operating in the AP300near the UE100. The WLAN frequency band not subject to the WLAN scan is a WLAN frequency band not operating in the AP300near the UE100.

The priority information is information for designating a WLAN channel and/or a WLAN frequency band where reception of the WLAN radio signal (beacon signal, etc.) should be preferentially attempted in the WLAN scan. It is preferable to set the priority information so that the WLAN channel operating in the AP300near the UE100and/or the operating WLAN frequency band is preferentially scanned.

The information on the scan time includes period information for designating a period during which the WLAN scan should be continued (that is, a period during which the WLAN should be maintained in an on state).

Further, the information on the scan time includes timing information for designating a timing at which the WLAN scan should be performed. The timing information preferably is information indicating a timing (period) at which the AP300near the UE100transmits the beacon signal.

In step S806, the processor240of the eNB200transmits, by the cellular communication unit210, a WLAN on request for switching the WLAN communication unit112to an on state, to the UE100. The processor240transmits the scan control information to be included in the WLAN on request. The cellular communication unit111of the UE100receives the WLAN on request.

In step S807, the processor160of the UE100switches the WLAN communication unit112to an on state, in response to reception of the WLAN on request. Then, after switching the WLAN communication unit112to an on state, the processor160controls the WLAN scan in accordance with the scan control information included in the WLAN on request.

Specifically, the processor160performs the WLAN scan only on the WLAN channel subject to the WLAN scan, on the basis of the channel information, and performs the WLAN scan only on the WLAN frequency band subject to the WLAN scan, on the basis of the frequency band information. Further, on the basis of the priority information, the processor160preferentially attempts to receive the WLAN radio signal (beacon signal, etc.) in a WLAN channel and/or a WLAN frequency band having a high priority. Further, the processor160activates a timer for timing a period during which the WLAN scan should be continued, on the basis of the period information. The processor160performs the WLAN scan only at a timing at which the WLAN scan should be performed, on the basis of the timing information. It is noted that when there is no period information, the processor160may scan only once (one shot scan) by using reception of the WLAN on request as a trigger.

It is noted that even when the processor160switches the WLAN communication unit112to an on state in response to the WLAN on request, it is preferable for the processor160not to display the switching on the user interface120. This is to prevent a user from recognizing that an automatic WLAN on is a malfunction, which is different from a case where a user performs the operation to switch the WLAN communication unit112to an on state.

In step S808, the WLAN communication unit112of the UE100receives the beacon signal from the AP300. When the WLAN scan is performed in the corresponding WLAN channel and timing, the processor160detects the beacon signal from the AP300to discover the connectable AP300.

In step S809, the processor160determines whether or not a timer indicating a period during which the WLAN scan should be continued expires. When the timer expires without the connectable AP300not being discovered, the processor160switches the WLAN communication unit112to an off state. Here, description is provided on the assumption that the connectable AP300is discovered during the timer running (step S810).

In step S811, the processor160of the UE100transmits a connection request to the AP300, by the WLAN communication unit112, to the AP300. As a result, the connection between the UE100and the AP300is established.

Summary of Fifth Embodiment

The eNB200according to the fifth embodiment transmits the WLAN on request to the UE100. The WLAN on request includes the scan control information for controlling the WLAN scan. After switching the WLAN communication unit112to an on state in response to reception of the WLAN on request, the UE100controls the WLAN scan in accordance with the scan control information included in the WLAN on request. Therefore, when the WLAN communication unit112is switched by the eNB200to an on state, it is possible to establish a state where it is possible to offload the eNB200. Further, it is possible to efficiently perform the WLAN scan in accordance with the scan control information from the eNB200, and thus, the UE100is capable of reducing the power consumption in the WLAN scan.

In the fifth embodiment, the eNB200acquires at least one of the UE location information indicating the geographical location of the UE100and the AP operation information indicating the operation status of the AP300. Then, the eNB200controls to transmit the WLAN on request on the basis of the acquired information. As a result, the eNB200is capable of appropriately determining whether or not to transmit the WLAN on request to the UE100. Further, it is possible to appropriately set a content of the scan control information to be included in the WLAN on request.

In the fifth embodiment, prior to reception of the WLAN on request, the UE100notifies the eNB200of at least one of the WLAN capability information indicating the WLAN communication capability of the UE100and the WLAN off information indicating that the WLAN communication unit112is in an off state. The eNB200controls to transmit the WLAN on request on the basis of the information received from the UE100. As a result, the eNB200is capable of appropriately determining whether or not to transmit the WLAN on request to the UE100.

In the fifth embodiment, the scan control information includes at least one of the channel information for designating a WLAN channel subject to the WLAN scan or a WLAN channel not subject to the WLAN scan, and the frequency band information for designating a WLAN frequency band subject to the WLAN scan or a WLAN frequency band not subject to the WLAN scan. As a result, the UE100is capable of limiting the WLAN channel and/or the WLAN frequency band subject to the WLAN scan, and thus, it is possible to reduce the power consumption in the WLAN scan.

In the fifth embodiment, the scan control information includes the priority information for designating a WLAN channel and/or a WLAN frequency band where reception of the WLAN radio signal should be preferentially attempted in the WLAN scan. As a result, in the WLAN scan, the UE100is capable of discovering early the available WLAN channel, and thus, it is possible to reduce the power consumption in the WLAN scan.

In the fifth embodiment, the scan control information includes at least one of the period information for designating a period during which the WLAN scan should be continued, and the timing information for designating a timing at which the WLAN scan should be performed. As a result, the UE100is capable of limiting the period during which and/or the timing at which the WLAN scan is performed, and thus, it is possible to reduce the power consumption in the WLAN scan.

First Modification of Fifth Embodiment

Description is provided with a case where in the above-described operation sequence, the WLAN communication unit112of the UE100is in an off state, and the WLAN off information to that effect is notified from the UE100to the eNB200. However, the eNB200may transmit the WLAN on request to the UE100irrespective of the WLAN off information. When the WLAN communication unit112is in an on state and the WLAN on request is received from the eNB200, the processor160of the UE100ignores the WLAN on request.

Further, description is provided with a case where in the above-described operation sequence, the UE100supports the WLAN communication and the WLAN capability information to that effect is notified from the UE100to the eNB200. However, the eNB200may transmit the WLAN on request to the UE100irrespective of the WLAN capability information. The UE100that does not support the WLAN communication ignores the WLAN on request even when the cellular communication unit111receives the WLAN on request from the eNB200.

Second Modification of Fifth Embodiment

Prior to receiving the WLAN on request, the UE100may notify the eNB200of information on the reception level of the GNSS signal. When the reception level of the GNSS signal is low, it is possible to estimate that the UE100is located indoors, and otherwise, it is possible to estimate that the UE100is located outdoors. Further, there are some WLAN frequency bands that are prohibited from being used outdoors. Therefore, when it is possible to estimate that the UE100is located outdoors, the eNB200preferably generates the WLAN frequency band information so that a WLAN frequency band that is prohibited from being used outdoors is not subject to the WLAN scan.

Sixth Embodiment

Next, a sixth embodiment will be described.

A case is assumed where the UE100is not connected to a cell managed by the eNB200and performs data communication with the AP300in a wireless LAN system. In this case, there is a problem that when the UE100is off the coverage of the AP300, data communication is interrupted until the UE100is connected to the cell of the eNB200.

Therefore, an object of the sixth embodiment is to seamlessly transfer from data communication in a wireless LAN system to data communication in a cellular communication system.

FIG. 20is a system configuration diagram according to the sixth embodiment.

As shown inFIG. 20, in the sixth embodiment, the E-UTRAN10includes the eNB200(evolved Node-B) and a HeNB400(Home evolved Node-B). The eNB200corresponds to a cellular base station.

The HeNB400manages a specific cell (small cell/femto cell) having a narrower cover range than a cell managed by the eNB200(large cell: macro cell) (seeFIG. 22). The HeNB performs radio communication with the UE that has established a connection (RRC connection) with the specific cell.

The specific cell is called a “CSG cell”, a “hybrid cell”, or an “open cell” according to a set access mode.

The CSG cell is a cell accessible only by a UE100(called a “member UE”) having an access right, and broadcasts a CSG ID. The UE100holds a list (whitelist) of a CSG ID of an CSG cell for which the UE100has an access right, and determines the presence or absence of access right on the basis of the whitelist and the CSG ID broadcast by the CSG cell.

The hybrid cell is a cell in which the member UE is more advantageously treated as compared with the non-member UE, and broadcasts information indicating that the hybrid cell is a cell released also to the non-member UE, in addition to the CSG ID. The UE100determines the presence or absence of access right on the basis of the whitelist and the CSG ID broadcast by the hybrid cell.

The open cell is a cell in which the UE100is equivalently treated regardless of whether the UE100is a member, and does not broadcast the CSG ID. In view of the UE100, the open cell is equal to a cell.

It is noted that the MME/S-GW500verifies the UE100for access right to the CSG cell.

Further, the HeNB400and the AP300are directly connected to each other through an arbitrary interface of an operator. Therefore, the HeNB400has data directly transferred from the AP300.

The HeNB400and the AP300may be disposed in the same location (Collocated). That is, the HeNB400may be of collocated type. For example, as the HeNB400of collocated type, the HeNB400and the AP300may be of integrated type in which the HeNB400and the AP300are disposed in the same housing. In this case, the HeNB400and the AP300may share a controller.

Next, the configuration of the HeNB400will be described.

FIG. 21is a block diagram of the HeNB400. As shown inFIG. 21, the HeNB400includes an antenna401, a cellular communication unit410, a network interface420, a memory430, and a processor440. The memory430and the processor440configure a controller. It is noted that the memory430is integrated with the processor440, and this set (that is, a chipset) may be a processor configuring a controller.

The antenna401and the cellular communication unit410are used for transmitting and receiving a cellular radio signal. The cellular communication unit410converts a baseband signal output from the processor440into the cellular radio signal, and transmits the same from the antenna401. Further, the cellular communication unit410converts the cellular radio signal received by the antenna401into the baseband signal, and outputs the same to the processor440. In the present embodiment, the cellular communication unit410forms a CSG cell.

The network interface420is connected to the neighboring eNB200or the neighboring HeNB400via the X2 interface and is connected to the MME/S-GW500via the S1 interface. Further, the network interface420is connected to the AP300via an interface that directly connects the AP300and the HeNB400(hereinafter, “specific interface” where appropriate). The specific interface is used for communication with the AP300. For example, user data is transferred via the specific interface from the AP300.

The memory430stores a program to be executed by the processor440and information to be used for a process by the processor440. The processor440includes a baseband processor that performs modulation and demodulation, encoding and decoding, etc., on the baseband signal and a CPU that performs various processes by executing the program stored in the memory430. The processor440executes various types of processes and various types of communication protocols described later.

It is noted that in the present embodiment, the network interface320in the AP300is connected to the HeNB400via a specific interface that directly connects the AP300and the HeNB400. The specific interface in the AP300is used for communication with the HeNB400. For example, user data is transferred to the HeNB400via the specific interface.

In the present embodiment, the UE100has a collocated AP list. The UE100and the eNB200share the collocated AP list.

The collocated AP list is of collocated type located at the same place as the AP300, and includes a cell ID of a small cell managed by the HeNB400of collocated type connected directly to the AP300, and location information of the HeNB400. The collocated AP list may include information indicating an identifier of the AP300connected directly to the HeNB400.

The UE100acquires the collocated AP list from the eNB200. For example, the UE100receives the collocated AP list from the eNB200, during establishment of a connection, during execution of a handover, or at a timing at which a paging area is changed.

The eNB200may transmit the collocated AP list to the UE100on the basis of capability information indicating that the UE100supports communication methods of both the cellular communication and the WLAN communication.

Operation According to Sixth Embodiment

Next, an operation according to the sixth embodiment will be described with reference fromFIG. 22toFIG. 24.FIG. 22is a diagram showing a positional relation among the UE100, the eNB200, the AP300, and the HeNB400according to the sixth embodiment.FIG. 23andFIG. 24are a sequence diagram for describing an operation according to the sixth embodiment.

As shown inFIG. 22, the UE100exists in a large cell managed by the eNB200. Further, the HeNB400and the AP300are disposed in the same location, and the HeNB400and the AP300are directly connected. Specifically, the AP300is an AP (collocated-type AP) integrated with the HeNB400.

A coverage of a small cell managed by the HeNB400and a coverage of the AP300at least partially overlap. In the present embodiment, the coverage of the AP300and the coverage of the small cell are the same, or the coverage of the AP300is larger than the coverage of the small cell. Further, the coverage of the small cell and the coverage of the AP300are contained in the coverage of the large cell.

Further, in the present embodiment, description proceeds with an assumption that the UE100moves in a direction leaving the HeNB400to be off the coverage of the small cell. Further, description proceeds with an assumption that the UE100has an access right to the HeNB400. That is, the UE is a CSG member, and the small cell is a hybrid cell or an open cell.

As shown inFIG. 23, the UE100recognizes that the UE100is being connected to the AP300and the connected AP300is an AP300integrated with the HeNB400. For example, when receiving from the AP300that the AP300is of integrated type or receiving broadcast information from the HeNB400that the AP300is of integrated type, the UE100recognizes that the AP300is of integrated type. Alternatively, the UE100may recognize that the connected AP300is an integrated-type AP300on the basis of the collocated AP list. Specifically, the UE100recognizes that the connected AP300is the integrated-type AP300when an identifier of the connected AP300and an identifier of the AP300included in the collocated AP list match.

Further, as shown inFIG. 23, the UE100receives a reference signal from the HeNB400and a reference signal from the eNB200. The UE100measures a signal intensity of each reference signal. Further, the UE100is connected to the AP300(Offloading) and in an idle state (IDLE). That is, the UE100is not connected to the eNB200and the HeNB400.

As shown inFIG. 23, in step S901, the UE100detects deterioration of the signal intensity of the reference signal from the HeNB400.

The UE100moves in a direction leaving the HeNB400, and thus, the signal intensity of the reference signal gradually weakens. The UE100detects the deterioration of the signal intensity when the signal intensity of the reference signal from the HeNB400becomes less than a predetermined value that is a value by which it is possible to ensure the communication quality. As a result, the UE100determines on the basis of the deterioration of the signal intensity from the HeNB400that the connection with the AP300becomes difficult.

It is noted that in the present embodiment, the AP300is an AP integrated with the HeNB400, and thus, when the signal intensity of the reference signal from the HeNB400weakens, it is possible to estimate that the UE100comes close to the coverage end of the AP300, as a result of which even when the signal intensity of the beacon signal from the AP300is equal to or more than a predetermined value that is a value by which it is possible to ensure the communication quality, the UE100determines that the connection with the AP300becomes difficult when the signal intensity from the HeNB400is less than a predetermined value that is a value by which the connection with the AP300becomes difficult.

It is noted that the UE100exists in the large cell, and thus, the signal intensity from the eNB200is equal to or more than a predetermined value by which it is possible to ensure the communication quality.

In step S902, the UE100makes an RRC connection request including a transfer request, to the eNB200. The eNB200receives the RRC connection request.

The transfer request is a request to transfer user data about the UE100owned by the AP300connected to the UE100, via the HeNB400to the eNB200.

In step S903, the eNB200transmits ACK/NACK that responds to the RRC connection request, to the UE100. The UE100receives the ACK/NACK that responds to the RRC connection request.

In the present embodiment, description proceeds with an assumption that the eNB200transmits the ACK (acknowledgment) to the UE100.

In step S904, Connection Procedure is performed.

In step S905, the UE100transmits, to the eNB200, a Connection complete message indicating that the Connection Procedure is completed. In the present embodiment, in the Connection complete message, information on a transfer cancellation timer is included.

The transfer cancellation timer is used for canceling a process of transferring user data from the AP300to the eNB200. When the transfer cancellation timer expires, the eNB200cancels the process of transferring the user data from the AP300to the eNB200.

In step S906, each of the UE100and the eNB200activates the transfer cancellation timer.

In step S907, the eNB200transmits, to the HeNB400, a message confirming whether or not the HeNB400is capable of transferring the user data. Specifically, the eNB200performs a Buffer borrowing request to request temporary borrowing of a buffer of the HeNB400to transfer the user data. The HeNB400receives the Buffer borrowing request.

In step S908, the HeNB400transmits ACK/NACK that responds to the Buffer borrowing request, to the eNB200.

It is noted that the HeNB400may transmit the ACK to the eNB200even when the UE100does not have the access right to the HeNB400. Further, even when the UE100is not a CSG member (that is, the UE100does not have the access right to the HeNB400), the HeNB400may determine whether to accept the transfer request of the eNB200only when receiving the Buffer borrowing request. Alternatively, the transfer request may be accepted only to the transfer request of the eNB200to which the ACK that responds to the Buffer borrowing request is transmitted after receiving the Buffer borrowing request.

Further, the HeNB400transmits the NACK (negative acknowledgment) when a buffer capacity is equal to or more than a predetermined value and there is not a sufficient free space. Further, the HeNB400may transmit the NACK (negative acknowledgment) when the UE100does not have the access right to the HeNB400.

In the present embodiment, description proceeds with an assumption that the HeNB400transmits the ACK (acknowledgment) to the eNB200. It is noted that a case where the HeNB400transmits the NACK (negative acknowledgment) to the eNB200will be described later.

In step S909, the eNB200makes a transfer request (Forwarding Request) to the HeNB400. The HeNB400receives the transfer request.

In step S910, on the basis of the transfer request from the eNB200, the HeNB400makes a transfer request (Forwarding Request) to transfer the user data of the UE100to the AP300.

It is noted that in the present embodiment, the UE100is a CSG member, and thus, it is possible to use a resource of the HeNB400. Generally, the UE100which is not a CSG member is not capable of using the resource of the HeNB400. However, even for the UE100which is not a CSG member, the HeNB400may make, on the basis of the transfer request from the eNB200, a transfer request to transfer the user data of the UE100to the AP300.

In step S911, the AP300transfers, to the HeNB400, the user data of the UE100on the basis of the transfer request from the HeNB400. Here, the AP300is directly connected to the HeNB400via a specific interface, and thus, the transfer from the AP300to the HeNB400is rapidly performed.

In step S912, the HeNB400transfers, to the eNB200, the user data transferred from the AP300. Specifically, the HeNB400transfers the user data to the eNB200via the X2 interface. As a result, the user data is transferred from the AP300by way of the HeNB400to the eNB200.

In step S913, the UE100and the eNB200use the transferred user data to perform data communication.

When the UE100is connected with the AP300, the connection with the AP300may be ended.

Next, a case where the HeNB400transmits the NACK (negative acknowledgment) to the eNB200will be described by usingFIG. 24.

As shown inFIG. 24, in step S1009, the eNB200determines whether the NACK is received in response to the Buffer borrowing request. When the ACK is received, the eNB200performs a process in step S909inFIG. 23.

On the other hand, when the NACK is received, in step S1010, in response to the transfer request from the UE100, the eNB200transmits a response (NACK) indicating that the user data is not transferred from the AP300. The UE100receives the response (NACK) of the transfer request.

In step S1011, when receiving the response (NACK) of the transfer request, the UE100increments a transfer failure counter (Forwarding trial Counter), by one, provided in the UE100.

In step S1012, the UE100determines whether or not to perform once again step S1002(that is, whether or not to perform the transfer request in step S902. When the UE100determines to perform the transfer request (in a case of Yes), the UE100makes once again the transfer request to the eNB200. For example, when the transfer failure counter does not reach a predetermined value, the UE100makes once again the transfer request to the eNB200. Therefore, the UE100repeats the transfer request to the eNB200until the transfer failure counter reaches a predetermined value. The eNB200that has received the transfer request starts a process in step S1007(that is, step S907). It is noted that when information on a transfer cancellation timer is included in the transfer request, the eNB200starts a process in step S1006(that is, step S906). When the transfer cancellation timer is being activated, the eNB200resets the activated transfer cancellation timer, and activates the transfer cancellation timer on the basis of the information on the transfer cancellation timer.

On the other hand, when the transfer failure counter reaches a predetermined value, the UE100determines to not make the transfer request. In this case, the UE100performs a process as usual. For example, the UE100may transmit the RRC connection request to the eNB200or/and the HeNB400by reselection. In this case, the UE100may transmit the RRC connection request while being connected to the AP300.

Summary of Sixth Embodiment

In the present embodiment, when it is determined that the connection between the UE100and the AP300directly connected to the HeNB400becomes difficult, the UE100is connected to the eNB200, and the AP300transfers the user data of the UE100by way of the HeNB400to the eNB200. As a result, the AP300is capable of transferring the user data to the HeNB400via a specific interface, and thus, the eNB200is capable of rapidly acquiring the user data of the UE100owned by the AP300. This restrains stoppage of a user data flow, resulting in a seamless data communication.

In the present embodiment, when determining that the connection with the AP300becomes difficult and that it is possible to connect with a large cell, the UE100makes the RRC connection request and the transfer request for transferring the user data owned by the AP300to the eNB200, to the eNB200. Further, the AP300transfers the user data to the eNB200, resulting from the transfer request from the UE100. Thus, the UE100, which determines by itself that the connection with the AP300becomes difficult, is capable of making an appropriate determination on the basis of an actual radio situation of the UE100, resulting in a seamless data communication.

In the present embodiment, when the UE100is of collocated type in which the AP300is located at the same place as the HeNB400, even when the signal intensity of the beacon signal from the AP300is equal to or more than a predetermined value that is a value by which it is possible to ensure the communication quality, if the signal intensity from the HeNB400is less than a predetermined value that is a value by which it is possible to ensure the communication quality, then it may be possible to determine that the connection with the AP300becomes difficult. Thus, the AP300is of collocated type, and therefore, when the signal intensity from the HeNB400is less than a predetermined value, it is possible to estimate that the UE100exists near the coverage of the AP300, and as a result, when the transfer request is made in advance, a seamless data communication is further enabled.

In the present embodiment, the eNB200transmits the transfer request to the HeNB400when receiving the transfer request from the UE100, the HeNB400transmits the transfer request to the AP300when receiving the transfer request from the eNB200, and the AP300transfers the user data by way of the HeNB400to the eNB200when receiving the transfer request from the HeNB400. Thus, the HeNB400and the AP300are directly connected, and therefore, the eNB200is capable of more rapidly making the transfer request than making the transfer request by way of the core network, to the AP300. As a result, it is possible to further enable a seamless data communication.

In the present embodiment, even when the UE100is not a CSG member, the HeNB400transfers the user data transferred from the AP300, to the eNB200. As a result, even when the UE100is not a CSG member, the eNB200is capable of rapidly acquiring the user data of the UE100owned by the AP300, and thus, it is possible to further enable a seamless data communication.

In the present embodiment, when receiving the NACK from the eNB200that responds to the transfer request from the UE100, the UE100makes the transfer request once again. As a consequence, even if the transfer request is not accepted first, when a buffer capacity of the HeNB400is reduced as a result of the transfer request being made once again by making the transfer request once again, the transfer request is accepted, and thus, a seamless data communication is enabled.

In the present embodiment, the UE100repeatedly makes the transfer request until the number of times that NACK is received reaches a predetermined value. Thus, the UE100is capable of performing a seamless data communication when the transfer request is accepted as a result of the transfer request being repeated. On the other hand, when the transfer request is not accepted even when the transfer request is sent a predetermined number of times, the UE100is capable of restraining a meaningless transfer request transmission by canceling the transfer request.

Seventh Embodiment

Operation According to Seventh Embodiment

Next, an operation according to a seventh embodiment will be described by usingFIG. 25andFIG. 26.FIG. 25is a diagram showing a positional relation among the UE100, the eNB200, the HeNB400, and the AP300according to the seventh embodiment.FIG. 26is a sequence diagram for describing an operation according to the seventh embodiment. It is noted that a description will be provided while focusing on a portion different from the above-described embodiment, and a description of a similar portion will be omitted.

It is noted that in the seventh embodiment, in much the same way as in the sixth embodiment, the UE100recognizes that the UE100is being connected to the AP300and the connected AP300is an AP300integrated with the HeNB400.

In the above-described sixth embodiment, the coverage of the AP300is larger than the coverage of the small cell. In the present embodiment, the coverage of the AP300and the coverage of the small cell are the same, or as shown inFIG. 25, the coverage of the small cell is larger than the coverage of the AP300.

As shown inFIG. 26, in step S1101, the UE100detects deterioration of the signal intensity of the beacon signal from the AP300.

The UE100moves in a direction leaving the HeNB400, and thus, the signal intensity of the beacon signal gradually weakens. The UE100detects the deterioration of the signal intensity when the signal intensity of the beacon signal from the AP300becomes less than a predetermined value. As a result, the UE100determines on the basis of the deterioration of the signal intensity from the AP300that the connection with the AP300becomes difficult. In the present embodiment, the UE100determines that the connection with the AP300becomes difficult when the signal intensity of the beacon signal from the AP300becomes less than a predetermined value before the signal intensity received from the HeNB400becomes less than a predetermined value that is a value by which it is possible to ensure the communication quality.

It is noted that the UE100exists in the small cell, and thus, the signal intensity from the HeNB400is equal to or more than a predetermined value.

In step S1102, the UE100makes an RRC connection request including a transfer request, to the HeNB400. The HeNB400receives the RRC connection request.

When the signal intensity of the reference signal from the HeNB400is equal to or more than a predetermined value, the UE100makes the connection request to the HeNB400.

It is noted that when the signal intensity of the reference signal from the HeNB400is less than a predetermined value, the UE100makes the connection request to the eNB200.

In step S1103, the HeNB400transmits ACK/NACK that responds to the RRC connection request, to the UE100. The UE100receives the ACK/NACK that responds to the RRC connection request.

In the present embodiment, description proceeds with an assumption that the HeNB400transmits the ACK (acknowledgment) to the UE100.

In step S1104, Connection Procedure is performed.

In step S1105, the HeNB400transmits, to the AP300, the transfer request to transfer the user data from the AP300to the HeNB400, on the basis of the transfer request from the UE100. The AP300receives the transfer request.

In step S1106, the AP300transfers the user data to the HeNB400.

In step S1107, the HeNB400transmits a handover request (H.O. Request Ack) to the eNB200when the user data is transferred. The eNB200receives the handover request.

When receiving the measurement report indicating that the signal intensity from the HeNB400received by the UE100is less than a predetermined value, the HeNB400may transmit the handover request to the eNB200.

Further, when the UE100is not a CSG member, the HeNB400is not capable of using the resource (a resources for control signals and a buffer of the HeNB400) of the HeNB400, for the UE which is not a CSG member. However, when the UE100is not a CSG member, the HeNB400may permit the UE100to use the resources of the HeNB400on condition that the handover request is immediately transmitted to the eNB200when the user data is transferred to the HeNB400and when the CSG cell of the HeNB400and the UE100are connected.

In step S1108, a handover request response (H. O. Request Response) that responds to the handover request is transmitted to the HeNB400.

In step S1109, a handover procedure (H. O. Procedure) is performed.

In step S1110, the UE100and the eNB200use the transferred user data to perform data communication.

Summary of Seventh Embodiment

In the present embodiment, when determining that the connection with the AP300becomes difficult and that it is possible to connect with a small cell, the UE100makes to the HeNB400the RRC connection request and the transfer request for transferring the user data owned by the AP300to the HeNB400. Further, the AP300transfers the user data to the HeNB400, on the basis of the transfer request from the UE100. As a result, the HeNB400is capable of rapidly acquiring the user data of the UE100owned by the AP300, and thus, it is possible to restrain a flow of the user data from stopping and possible to further enable a seamless data communication.

In the present embodiment, the UE100determines that the connection with the AP300becomes difficult when the signal intensity of the beacon signal from the AP300becomes less than a predetermined value before the signal intensity received from the HeNB400becomes less than a predetermined value that is a value by which it is possible to ensure the communication quality. As a result, the UE100is capable of appropriately selecting the HeNB400as a target to which the transfer request is sent.

In the present embodiment, when the UE100is not a CSG member, the HeNB400may immediately transmit the handover request to the eNB200when the user data is transferred and when the CSG cell of the HeNB400and the UE100are connected. As a result, even the UE100which is not a CSG member is capable of a seamless data communication by using the HeNB400.

Other Embodiments

In the operation sequences according to the above-described first and second embodiments, the operation performed by the eNB200(base station) may be performed by another network device such as an upper device (for example, RNC) of the eNB200instead of the eNB200.

In the above-described third embodiment and fourth embodiments, no consideration is given to the operation environment where a movable AP (such as a mobile router) exists in the transport T. However, it is possible to apply the present invention to such an operation environment. For example, when being connected to the AP (movable AP) by the WLAN communication unit112and detecting that the UE movement speed rapidly decreases, the processor160of the UE100may restrict a start of connection with another AP (AP300) while maintaining the connection with that AP (movable AP).

In the modification of the third embodiment and the modification of the fourth embodiment, an example is described where the AP blacklist is provided from the eNB200. However, the UE100may previously hold the AP blacklist.

In the above-described fifth embodiment, the information transmitted and received between the UE100and the eNB200may be an RRC message or information element thereof.

In the above-described fifth embodiment, a case is assumed where the eNB200is a macro cell base station having a broad coverage; however, the eNB200may be a small cell base station having a coverage comparable to that of the AP300. Further, when the eNB200is a small cell base station and the AP300is collocated with the eNB200, it may be possible to omit the determination (step S805) whether or not the UE100comes close to the AP300.

The second modification of the above-described fifth embodiment may be applied to a process closed by the UE100. Specifically, when it is possible to estimate on the basis of the reception level of the GNSS signal that the UE100is located outdoors, the UE100regards the WLAN frequency band prohibited to be used outdoors not subject to the WLAN scan.

In the above-described sixth and seventh embodiments, the UE100determines whether or not the connection between the UE100and the AP300becomes difficult; however this is not limiting. The AP300may determine whether or not the connection between the UE100and the AP300becomes difficult.

Specifically, when the AP300measures the signal intensity received from the UE100and the signal intensity received from the UE100is less than a predetermined value that is a value by which it is possible to ensure the communication quality, the AP300determines that the connection between the UE100and the AP300becomes difficult.

When the AP300determines that the connection between the UE100and the AP300becomes difficult, the user data is transferred based on (A) the initiative of the UE or (B) the initiative of the AP300, as shown below.

(A) The Initiative of the UE100

When determining that the connection between the UE100and the AP300becomes difficult, the AP300notifies the UE100that the connection between the UE100and the AP300becomes difficult. When receiving the notification, the UE100measures the signal intensity of each reference signal of the eNB200and the HeNB400.

The UE100makes the RRC connection request including the transfer request to the eNB200or the HeNB400having a signal intensity being equal to or more than a predetermined value, out of the reference signals of the eNB200and the HeNB400. The processes after this are performed in much the same way as in the sixth or seventh embodiment.

When such a process is performed, the UE100does not need to perform a determination process that the connection between the UE100and the AP300becomes difficult, and thus, it is possible to restrain a process load in the UE100.

(B) The Initiative of the AP300

When the AP300determines that the connection between the UE100and the AP300becomes difficult, the AP300makes a request the eNB200or the HeNB400adjacent to the AP300so that the eNB200or the HeNB400adjacent to the AP300is connected to the UE100. When making the connection request to the eNB200, the AP300requests the eNB200by way of the HeNB400. Description proceeds with an assumption that the AP300requests the HeNB400to be connected to the UE100, below.

When receiving the connection request from the AP300, the HeNB400transmits, by paging, for example, to the UE100a notification indicating that the HeNB400is connected to the UE100. The UE100is connected to the HeNB400on the basis of the notification.

When the connection with the UE100is completed, the HeNB400transmits a connection complete notification to the AP300. When receiving the connection complete notification, the AP300starts transferring the user data to the HeNB400.

It is noted that when making the connection request to the eNB200, the AP300receives the connection complete notification from the eNB200to the AP300by way of the HeNB400.

When such a process is performed, it is possible to restrain a process load of the UE100because the UE100does not need to transmit the transfer request.

It is noted that when the connection with the eNB200or the HeNB400is completed, the UE100may perform a process for ending the connection between the UE100and the AP300.

Further, in the above-described sixth and seventh embodiments, when determining that the connection with the AP300becomes difficult, the UE100is connected to the HeNB400directly connected to the AP300with which the UE100is connected or the eNB200that manages the large cell enveloping the coverage of the AP; this is not limiting. For example, the UE100may be connected to the HeNB400adjacent to the HeNB400directly connected to the AP300with which the UE100is connected. In this case, the HeNB400directly connected to the AP300with which the UE100is connected transfers the user data to the adjacent HeNB400via the X2 interface.

Further, in the above-described sixth and seventh embodiments, the coverage of the small cell and the coverage of the AP300are enveloped in the coverage of the large cell; however, this is not limiting. The coverage of the small cell and the coverage of the AP300may partially overlap the coverage of the large cell.

Further, in the above-described sixth and seventh embodiments, as the small cell base station, the HeNB400is described as an example; however, this is not limiting. For example, a small cell base station may be a femto cell or a pico cell that manages the small cell.

Further, in the above-described sixth embodiment, the eNB200makes the Buffer borrowing request; however, this is not limiting. The eNB200may make the transfer request to the HeNB400without making the Buffer borrowing request.

It is noted that when the reference signal from the HeNB400and the beacon signal from the AP300are less than a predetermined value at the same time, or when the beacon signal from the AP300is less than a predetermined value before a predetermined time passes since the reference signal from the HeNB400is less than a predetermined value, the UE100may make the RRC connection request including the transfer request to the eNB200.

It is noted that in the above-described sixth and seventh embodiments, the UE100is in an idle state; however, when the UE100is in a state of being connected to the HeNB400, the UE100implements a normal handover to the eNB200.

In addition, in each above-described embodiment, the LTE system is described as one example of the cellular communication system; however, this is not limited to the LTE system, and the present invention may be applied to a cellular communication system other than the LTE system.

In addition, the entire content of Japanese Patent Application No. 2013-100600 (filed on May 10, 2013), Japanese Patent Application No. 2013-100777 (filed on May 10, 2013), Japanese Patent Application No. 2013-100779 (filed on May 10, 2013), Japanese Patent Application No. 2013-100780 (filed on May 10, 2013), and U.S. Provisional Application No. 61/864,250 (filed on Aug. 9, 2013) is incorporated in the present specification by reference.

INDUSTRIAL APPLICABILITY

As described above, the communication control method and the user terminal according to the present invention is useful for a mobile communication field.