Abstract:
A user terminal, method, and apparatus receive an offload command instructing an offload from a cellular base station, the offload steering traffic from the cellular base station to a wireless local area network (WLAN) access point being while maintaining a connection between the user terminal and cellular base station. An attempt is made to connect to the WLAN access point in response to receiving the offload command, and in response to the attempt failing, determine whether a reason for the failure of connection to the WLAN access point is a first reason being an issue of a radio link between the user terminal and the WLAN access point or a second reason being an internal issue of the user terminal. A failure indication is transmitted to the base station in response to a connection failure indicates connection failure and indicates whether the reason is the first or second reason.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation Application of U.S. patent application Ser. No. 15/197,837 filed Jun. 30, 2016, which is a Continuation Application of U.S. patent application Ser. No. 14/906,760 filed Jan. 21, 2016 which is the U.S. National Phase Application of International Patent Application No. PCT/JP2014/070530 filed Aug. 4, 2014, which claims benefit of Japanese Patent Application No. 2013-164056 filed Aug. 7, 2013 the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a user terminal used in a cellular communication system capable of cooperating with a wireless LAN system, a cellular base station therefor, and a processor therefor. 
       BACKGROUND ART 
       [0003]    In recent years, the use of a user terminal including a cellular communication unit and a wireless LAN communication unit (so-called dual terminal) is widely spread. Further, the number of wireless LAN access points managed by an operator of a cellular communication system increases. 
         [0004]    Therefore, in 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a cellular communication system, consideration is given to a technology capable of strengthening cooperation between a cellular communication system and a wireless LAN system. 
         [0005]    For example, when traffic transmitted and received between a user terminal and a cellular base station is transitioned to a wireless LAN system, it is possible to reduce the traffic load of the cellular base station (offload). 
         [0006]    As a method of performing such an offload, there is proposed a method in which the cellular base station sets a WLAN measurement to a user terminal subject to offload, the user terminal reports a WLAN measurement result to the cellular base station, and then the cellular base station transmits an offload command to the user terminal on the basis of the report (see Non Patent Literature 1). 
       CITATION LIST 
     Non Patent Literature 
       [0007]    [NPL 1] 3GPP technical report “TR 37.834 V0.3.0” May, 2013 
       SUMMARY 
       [0008]    From the viewpoint of the cellular base station, as a method of selecting a user terminal subject to offload, it may be possible to consider a method in which a user terminal having a large amount of radio resources used is selected. 
         [0009]    However, from the viewpoint of the user terminal, when a user terminal subject to offload is selected on the basis only on such a selection criterion, a preferable selection may be not performed. The offload should not be performed on a user terminal such as a user terminal around which no wireless LAN access point is present, a user terminal which is moving, or a user terminal whose battery remaining amount is small. 
         [0010]    Therefore, the present disclosure provides a user terminal, method thereof, and apparatus thereof with which it is possible to properly select a user terminal subject to offload. 
         [0011]    A user terminal according to the disclosure comprises a controller including at least one processor and at least one memory configured to receive an offload command from a cellular base station. The offload command instructs an offload, the offload being an operation in which the user terminal steers traffic from the cellular base station to a wireless local area network (WLAN) access point while maintaining a connection between the user terminal and the cellular base station. The at least one processor and at least one memory are configured to attempt to connect to the WLAN access point in response to receiving the offload command, and in response to failing in connecting to the WLAN access point, determine whether a reason for the failure of connection to the WLAN access point is a first reason or a second reason. The first reason is an issue of a radio link between the user terminal and the WLAN access point, and the second reason is an internal issue of the user terminal. The at least one processor and at least one memory are configured to transmit a failure indication to the cellular base station in response to failing in connecting to the WLAN access point. The failure indication indicating that the user terminal fails in connecting to the WLAN access point and includes information indicating whether the reason is the first reason or the second reason. 
         [0012]    A method according to the disclosure for performing at a user terminal comprises receiving an offload command from a cellular base station, the offload command instructing an offload, the offload being an operation in which the user terminal steers traffic from the cellular base station to a wireless local area network (WLAN) access point while maintaining a connection between the user terminal and the cellular base station. The method comprises attempting to connect to the WLAN access point in response to receiving the offload command, and in response to failing in connecting to the WLAN access point, determining whether a reason for the failure of connection to the WLAN access point is a first reason or a second reason. The first reason is an issue of a radio link between the user terminal and the WLAN access point, and the second reason is an internal issue of the user terminal. The method comprises transmitting a failure indication to the cellular base station in response to failing in connecting to the WLAN access point, where the failure indication indicates that the user terminal fails in connecting to the WLAN access point. The failure indication includes information indicating whether the reason is the first reason or the second reason. 
         [0013]    An apparatus according to the disclosure for controlling a user terminal comprises at least one processor and at least one memory configured to receive an offload command from a cellular base station, the offload command instructing an offload, the offload being an operation in which the user terminal steers traffic from the cellular base station to a wireless local area network (WLAN) access point while maintaining a connection between the user terminal and the cellular base station. The at least one processor and at least one memory are configured to attempt to connect to the WLAN access point in response to receiving the offload command, and in response to failing in connecting to the WLAN access point, determine whether a reason for the failure of connection to the WLAN access point is a first reason or a second reason. The first reason is an issue of a radio link between the user terminal and the WLAN access point, and the second reason is an internal issue of the user terminal. The at least one processor and at least one memory are configured to transmit a failure indication to the cellular base station in response to failing in connecting to the WLAN access point, the failure indication indicating that the user terminal fails in connecting to the WLAN access point. The failure indication includes information indicating whether the reason is the first reason or the second reason. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a system configuration diagram according to a first embodiment and a second embodiment. 
           [0015]      FIG. 2  is a block diagram of a UE (user terminal) according to the first embodiment and the second embodiment. 
           [0016]      FIG. 3  is a block diagram of an eNB (cellular base station) according to the first embodiment and the second embodiment. 
           [0017]      FIG. 4  is a block diagram of an AP (wireless LAN access point) according to the first embodiment and the second embodiment. 
           [0018]      FIG. 5  is a protocol stack diagram of a radio interface in an LTE system. 
           [0019]      FIG. 6  is a configuration diagram of a radio frame used in the LTE system. 
           [0020]      FIG. 7  is a sequence diagram illustrating a basic operation according to the first embodiment. 
           [0021]      FIG. 8  is a sequence diagram of an operation pattern  1  according to the first embodiment. 
           [0022]      FIG. 9  is a sequence diagram of an operation pattern  2  according to the first embodiment. 
           [0023]      FIG. 10  is a sequence diagram of an operation pattern  3  according to the first embodiment. 
           [0024]      FIG. 11  is a sequence diagram according to the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Overview of Embodiments 
       [0025]    A user terminal according to a first embodiment and a second embodiment transmits and receives traffic to and from a cellular base station in a cellular communication system capable of cooperating with a wireless LAN system. The user terminal comprises a controller configured to determine, on the basis of a determination parameter related to a situation of the user terminal, whether or not an offload in which the traffic is transitioned to the wireless LAN system should be performed, when the user terminal is selected as a target terminal subject to the offload. The controller transmits, to the cellular base station, a rejection notification that related to rejection to the offload when the controller determines that the offload should not be performed. 
         [0026]    In the first embodiment, the determination parameter is information indicating whether or not a wireless LAN access point is present around the user terminal. The controller determines that the offload should not be performed when no wireless LAN access point is present around the user terminal. 
         [0027]    In the first embodiment, the determination parameter is information indicating whether or not the user terminal is moving. The controller determines that the offload should not be performed when the user terminal is moving. 
         [0028]    In the first embodiment, the determination parameter is information indicating a battery remaining amount of the user terminal. The controller determines that the offload should not be performed when the battery remaining amount falls below a threshold value. 
         [0029]    In the first embodiment, the determination parameter is information indicating a power consumption level of the user terminal. The controller determines that the offload should not be performed when the power consumption level exceeds a threshold value. 
         [0030]    In an operation pattern  1  according to the first embodiment, the user terminal further comprises a receiver configured to receive, from the cellular base station, a wireless LAN measurement command indicating that the user terminal is selected as a target terminal subject to the offload. The controller transmits the rejection notification to the cellular base station as a response to the wireless LAN measurement command when the controller determines that the offload should not be performed. 
         [0031]    In an operation pattern  2  according to the first embodiment, the user terminal further comprises a receiver configured to receive, from the cellular base station, a wireless LAN measurement command indicating that the user terminal is selected as a target terminal subject to the offload. The controller transmits, to the cellular base station, the rejection notification together with a wireless LAN measurement report to report a result of the wireless LAN measurement when the controller determines that the offload should not be performed. 
         [0032]    In an operation pattern  3  according to the first embodiment, the user terminal further comprises a receiver configured to receive an offload command, that instructs an execution of the offload, from the cellular base station. The controller transmits, to the cellular base station, the rejection notification as a response to the offload command when it is determined that the offload should not be performed. 
         [0033]    In the first embodiment, the controller includes rejection reason information indicating a reason for rejection in the rejection notification when the rejection notification is transmitted to the cellular base station. 
         [0034]    In the second embodiment, the user terminal further comprises a transmitter configured to transmit, to the cellular base station, a terminal information notification including the determination parameter before the user terminal is selected as a target terminal subject to the offload. 
         [0035]    A cellular base station according to the first embodiment and the second embodiment transmits and receives traffic to and from a user terminal in a cellular communication system capable of cooperating with a wireless LAN system. The cellular base station comprises a controller configured to exclude the user terminal from a target terminal subject to offload in which the traffic is transitioned to the wireless LAN system, when the user terminal is selected as a target terminal subject to the offload and when the controller receives a rejection notification related to rejection to the offload from the user terminal. 
         [0036]    In the second embodiment, the cellular base further comprises a receiver configured to receive, from the user terminal, a terminal information notification including a determination parameter related to a situation of the user terminal before the user terminal is selected as a target terminal subject to the offload. The controller selects a user terminal subject to the offload on the basis of the determination parameter. 
         [0037]    In the second embodiment, the determination parameter is information indicating whether or not a wireless LAN access point is present around the user terminal. The controller excludes a user terminal, around which no wireless LAN access point is present, from a target terminal subject to the offload. 
         [0038]    In the second embodiment, the determination parameter is information indicating whether or not the user terminal is moving. The controller excludes a user terminal which is moving, from a target terminal subject to the offload. 
         [0039]    In the second embodiment, the determination parameter is information indicating a battery remaining amount of the user terminal. The controller excludes a user terminal in which the battery remaining amount falls below a threshold value from a target terminal subject to the offload. 
         [0040]    In the second embodiment, the determination parameter is information indicating a power consumption level of the user terminal. The controller excludes a user terminal in which a power consumption level exceeds a threshold value, from a target terminal subject to the offload. 
         [0041]    A processor according to the first embodiment and the second embodiment provided in a user terminal that transmits and receives traffic to and from a cellular base station in a cellular communication system capable of cooperating with a wireless LAN system. The processor executes a process of determining, on the basis of a determination parameter related to a situation of the user terminal, whether or not an offload in which the traffic is transitioned to the wireless LAN system should be performed, when the user terminal is selected as a target terminal subject to the offload; and a process of transmitting, to the cellular base station, a rejection notification related to rejection to the offload when it is determined that the offload should not be performed. 
       First Embodiment 
       [0042]    Hereinafter, with reference to the drawing, embodiments will be described in which a cellular communication system (LTE system) configured to comply with the 3GPP standards is cooperated with a wireless LAN (WLAN) system. 
         [0043]    (System Configuration) 
         [0044]      FIG. 1  is a system configuration diagram according to first embodiment. As shown in  FIG. 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-UTRAN  10  corresponds to a radio access network. The EPC  20  corresponds to a core network. 
         [0045]    The UE  100  is a mobile radio communication device and performs radio communication with a cell with which a connection is established. The UE  100  corresponds to the user terminal. The UE  100  is a terminal (dual terminal) that supports both cellular communication scheme and WLAN communication scheme. 
         [0046]    The E-UTRAN  10  includes a plurality of eNBs  200  (evolved Node-Bs). The eNB  200  corresponds to a base station. The eNB  200  manages one or a plurality of cells and performs radio communication with the UE  100  which establishes a connection with the cell of the eNB  200 . 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 UE  100 . Further, the eNB  200  has a radio resource management (RRM) function, a routing function of user data, and a measurement control function for mobility control and scheduling. 
         [0047]    The eNBs  200  are connected mutually via an X2 interface. Further, the eNB  200  is connected to MME/S-GW  500  included in the EPC  20  via an S1 interface. 
         [0048]    The EPC  20  includes a plurality of MMES (Mobility Management Entities)/S-GWs (Serving-Gateways)  500 . The MME is a network node for performing various mobility controls, for example, for the UE  100 , and 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. 
         [0049]    The WLAN system includes a WLAN access point (WLAN AP)  300 . The WLAN system is configured to be in compliance with the IEEE 802.11 standards, for example. The WLAN AP  300  performs communication with the UE  100  in a frequency band different from a cellular frequency band (WLAN frequency band). The WLAN AP  300  is connected to the EPC  20  via a router, and the like. 
         [0050]    Further, it may be also possible that the eNB  200  and the WLAN AP  300  are located individually, and it may be possible that the eNB  200  and the WLAN AP  300  are located at a same place (Collocated). As one mode of the “Collocated”, the eNB  200  and the WLAN AP  300  may be directly connected with each other through any interface of an operator. 
         [0051]    Next, configurations of the UE  100 , the eNB  200 , and the WLAN AP  300  will be described. 
         [0052]      FIG. 2  is a block diagram of the UE  100 . As shown in  FIG. 2 , the UE  100  includes: antennas  101  and  102 ; a cellular transceiver (cellular communication unit)  111 ; a WLAN transceiver (WLAN communication unit)  112 ; a user interface  120 ; a GNSS (Global Navigation Satellite System) receiver  130 ; a battery  140 ; a memory  150 ; and a processor  160 . The memory  150  and the processor  160  configure a control unit. The UE  100  may not have the GNSS receiver  130 . It is noted that the memory  150  may be integrally formed with the processor  160 , and this set (that is, a chipset) may be called a processor  160 ′. 
         [0053]    The antennas  101  and the cellular transceiver  111  are used for transmitting and receiving a cellular radio signal. The cellular transceiver  111  converts a baseband signal output from the processor  160  into the cellular radio signal, and transmits the same from the antenna  101 . Further, the cellular transceiver  111  converts the cellular radio signal received by the antenna  101  into the baseband signal, and outputs the same to the processor  160 . 
         [0054]    The antennas  102  and the WLAN transceiver  112  are used for transmitting and receiving a WLAN radio signal. The WLAN transceiver  112  converts the baseband signal output from the processor  160  into a WLAN radio signal, and transmits the same from the antenna  102 . Further, the WLAN transceiver  112  converts the WLAN radio signal received by the antenna  102  into a baseband signal, and outputs the same to the processor  160 . 
         [0055]    The user interface  120  is an interface with a user carrying the UE  100 , and includes, for example, a display, a microphone, a speaker, and various buttons. Upon receipt of the input from a user, the user interface  120  outputs a signal indicating a content of the input to the processor  160 . The GNSS receiver  130  receives a GNSS signal in order to obtain location information indicating a geographical location of the UE  100 , and outputs the received signal to the processor  160 . The battery  140  accumulates a power to be supplied to each block of the UE  100 . 
         [0056]    The memory  150  stores a program to be executed by the processor  160  and information to be used for a process by the processor  160 . The processor  160  includes 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 memory  150 . The processor  160  may further include a codec that performs encoding and decoding on sound and video signals. The processor  160  executes various processes and various communication protocols described later. 
         [0057]      FIG. 3  is a block diagram of the eNB  200 . As shown in  FIG. 3 , the eNB  200  includes antennas  201 , a cellular transceiver  210 , a network interface  220 , a memory  230 , and a processor  240 . The memory  230  and the processor  240  configure a control unit. 
         [0058]    The antennas  201  and the cellular transceiver  210  are used for transmitting and receiving a cellular radio signal. The cellular transceiver  210  converts the baseband signal output from the processor  240  into the cellular radio signal, and transmits the same from the antenna  201 . Furthermore, the cellular transceiver  210  converts the cellular radio signal received by the antenna  201  into the baseband signal, and outputs the same to the processor  240 . 
         [0059]    The network interface  220  is connected to the neighboring eNB  200  via an X2 interface and is connected to the MME/S-GW  500  via the S1 interface. The network interface  220  may be used for communication with the AP  300  via the EPC  20 . 
         [0060]    The memory  230  stores a program to be executed by the processor  240  and information to be used for a process by the processor  240 . The processor  240  includes 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 memory  230 . The processor  240  implements various processes and various communication protocols described later. 
         [0061]      FIG. 4  is a block diagram of the WLAN AP  300 . As shown in  FIG. 4 , the WLAN AP  300  includes antennas  301 , a WLAN communication unit  311 , a network interface  320 , a memory  330 , and a processor  340 . 
         [0062]    The antennas  301  and the WLAN communication unit  311  are used for transmitting and receiving a WLAN radio signal. The WLAN communication unit  311  converts a baseband signal output from the processor  340  into a WLAN radio signal and transmits the same from the antenna  301 . Further, the WLAN communication unit  311  converts a WLAN radio signal received by the antenna  301  into a baseband signal and outputs the same to the processor  340 . 
         [0063]    The network interface  320  is connected to the EPC  20  via a router, and the like. Further, the network interface  320  is used for communication with the eNB  200  via the EPC  20 . 
         [0064]    The memory  330  stores a program executed by the processor  340  and information used for a process by the processor  340 . The processor  340  includes a baseband processor that performs modulation and demodulation, encoding and decoding, and the like on a baseband signal and a CPU that performs various processes by executing a program stored in the memory  330 . 
         [0065]      FIG. 5  is a protocol stack diagram of a radio interface in the cellular system. As shown in  FIG. 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. 
         [0066]    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 UE  100  and the PHY layer of the eNB  200 , data is transmitted via the physical channel. 
         [0067]    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 UE  100  and the MAC layer of the eNB  200 , data is transmitted via a transport channel. The MAC layer of the eNB  200  includes a scheduler for determining a transport format (a transport block size, a modulation and coding scheme and the like) of an uplink and a downlink, and an allocated resource block. 
         [0068]    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 UE  100  and the RLC layer of the eNB  200 , data is transmitted via a logical channel. 
         [0069]    The PDCP layer performs header compression and decompression, and encryption and decryption. 
         [0070]    The RRC layer is defined only in a control plane. Between the RRC layer of the UE  100  and the RRC layer of the eNB  200 , 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 UE  100  and the RRC of the eNB  200 , the UE  100  is in a connected state (RRC connected state), otherwise, the UE  100  is in an idle state (RRC idle state). 
         [0071]    A NAS (Non-Access Stratum) layer positioned above the RRC layer performs session management or mobility management, for example. 
         [0072]      FIG. 6  is a configuration diagram of a radio frame used in the LTE system. In the LTE system, OFDMA (Orthogonal Frequency Division Multiple Access) is applied to a downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is applied to an uplink, respectively. 
         [0073]    As shown in  FIG. 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. 
         [0074]    Among radio resources allocated to the UE  100 , a frequency resource can be designated by a resource block and a time resource can be designated by a subframe (or slot). 
         [0075]    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. 
         [0076]    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 
       [0077]    Next, an operation according to the first embodiment will be described. 
         [0078]    (1) Operation Overview 
         [0079]    In the first embodiment, an operation environment is assumed in which the WLAN AP  300  is provided in the coverage area of the eNB  200 . The WLAN AP  300  is an AP managed by an operator (Operator controlled AP). When the eNB  200  establishes a connection with a large number of UEs  100 , the traffic load of the eNB  200  increases. Thus, it is possible to reduce the traffic load of the eNB  200  when traffic (user data) transmitted and received between the UE  100  and the eNB  200  is transitioned to the WLAN system (offload). 
         [0080]    In the first embodiment, in order to perform such an offload, the eNB  200  sets a WLAN measurement to the UE  100  subject to offload, the UE  100  reports a WLAN measurement result to the eNB  200 , and the eNB  200  transmits an offload command to the UE  100  on the basis of the report. 
         [0081]      FIG. 7  is a sequence diagram illustrating a basic operation according to the first embodiment. In an initial state of the sequence, the UE  100  is in a state where an RRC connection is established with the eNB  200  (in a connected state). 
         [0082]    As shown in  FIG. 7 , in step S 1 , the eNB  200  transmits, to the UE  100  subject to offload, a WLAN measurement command to control a WLAN measurement. The WLAN measurement command includes an identifier of the WLAN AP  300  (WLAN identifier) to be measured by the UE  100 . Further, the WLAN measurement command includes trigger information indicating a trigger by which a WLAN measurement report for reporting a result of the WLAN measurement is transmitted to the eNB  200 . 
         [0083]    The UE  100  that receives the WLAN measurement command performs the WLAN measurement in accordance with the WLAN measurement command. For example, the UE  100  measures a received power of a beacon signal from the WLAN AP  300 , and the like, for the WLAN identifier included in the WLAN measurement command. 
         [0084]    In step S 2 , the UE  100  detects an event as a transmission trigger for the WLAN measurement report, on the basis of the trigger information included in the WLAN measurement command. Here, when the UE  100  is transitioned to an idle state, the UE  100  establishes again an RRC connection with the eNB  200  in order to transmit the WLAN measurement report to the eNB  200  (step S 3 ). 
         [0085]    In step S 4 , the UE  100  transmits the WLAN measurement report to report a result of the WLAN measurement, to the eNB  200 . The WLAN measurement report includes a WLAN identifier and a WLAN measurement result (received power of a beacon signal, and the like), for example. 
         [0086]    In step S 5 , the eNB  200  that receives the WLAN measurement report transmits, to the UE  100 , a Steering command (offload command) to instruct the execution of the offload, on the basis of the WLAN measurement report, the load of RAN, and the like. It is noted that the Steering command may be a command to instruct a traffic transition (offload cancellation) from the WLAN to the eNB  200 , in addition to a command to instruct a traffic transition (offload) from the eNB  200  to the WLAN. 
         [0087]    In step S 6 , the UE  100  that receives the offload command executes an offload. That is, the UE  100  switches so that the traffic to be transmitted and received to and from the eNB  200  is passed on to the WLAN AP  300 . It is noted that when the UE  100  does not establish connection with the WLAN AP  300  when the offload command is received, the UE  100  establishes connection with the WLAN AP  300  prior to the offload. 
         [0088]    In step S 7 , the UE  100  transmits, to the eNB  200 , a response responding to the offload command. 
         [0089]    In such a sequence, when the eNB  200  selects a UE  100  subject to offload, the selection of the UE  100  subject to offload may be inappropriate. The offload should not be performed for a UE  100  such as a UE  100  around which no WLAN AP  300  is present, a UE  100  which is moving, or a UE  100  whose battery remaining amount is low. 
         [0090]    In the first embodiment, when the UE  100  is selected as a target terminal subject to offload in which traffic is transitioned to the WLAN system, the UE  100  determines on the basis of a determination parameter related to the situation of the UE  100  whether or not the offload should be performed. Detail of the determination parameter (a determination parameter  1  to a determination parameter  4 ) will be described later. 
         [0091]    When the UE  100  determines on the basis of the determination parameter that the offload should not be performed, the UE  100  transmits a rejection notification, to the eNB  200 , related to rejection to the offload. A timing to transmit the rejection notification to the eNB  200  (an operation pattern  1  to an operation pattern  3 ) will be described later. 
         [0092]    The eNB  200  excludes the UE  100  from a target terminal subject to offload, when the UE  100  is selected as a target terminal subject to offload in which traffic is transitioned to the WLAN system, and when the eNB  200  receives a rejection notification related to rejection to the offload from the UE  100 . Accordingly, it is possible to properly select a UE  100  subject to offload. 
         [0093]    (2) Determination Parameter 
         [0094]    It is possible to use at least one of the determination parameter  1  to the determination parameter  4  below as the determination parameter described above. 
         [0095]    The determination parameter  1  is information indicating whether or not a WLAN AP  300  is present around the UE  100 . For example, if the UE  100  receives a beacon signal from a WLAN AP  300 , then it may be considered that the WLAN AP  300  is present around the UE  100 . Alternatively, when the UE  100  holds location information of a WLAN AP  300  (AP location information), if difference between GNSS location information and AP location information of the UE  100  (that is, distance) is small, then it may be possible to consider that the WLAN AP  300  is present around the UE  100 . The UE  100  determines on the basis of the determination parameter  1  that the offload should not be performed, and transmits a rejection notification when no WLAN AP  300  is present around the UE  100 . Thus, it is possible to avoid a UE  100  in a state where it is impossible to be offloaded from being selected as a UE  100  subject to offload. 
         [0096]    The determination parameter  2  is information indicating whether or not the UE  100  is moving. For example, if a change of GNSS location information of the UE  100  per unit time is larger than a predetermined amount, then it may be considered that the UE  100  is moving. Alternatively, if a handover frequency or a cell reselection frequency per unit time of the UE  100  is larger than a predetermined frequency, then it may be possible to consider that the UE  100  is moving. The UE  100  determines on the basis of the determination parameter  2  that the offload should not be performed and transmits a rejection notification when the UE  100  is moving. The UE  100  that is moving passes through the coverage area of the AP  300  in a short time. Accordingly, when the UE  100  that is moving is excludable from a target subject to offload, it is possible to avoid an inefficient offload from being performed. 
         [0097]    The determination parameter  3  is information indicating a battery remaining amount of the UE  100 . Information indicating a battery remaining amount may be the voltage value of the battery  140  or an index indicating the voltage level of the battery  140 . The UE  100  determines on the basis of the determination parameter  3  that the offload should not be performed and transmits a rejection notification when the battery remaining amount falls below the threshold value. When an offload is performed, the power consumption of the UE  100  increases, so that there occur problems that the UE  100  runs out of its battery, or that an outgoing call (including an emergency call) becomes impossible, and the like. Accordingly, when the UE  100  whose battery remaining amount is small is excludable from a target subject to offload, it is possible to avoid such problems. 
         [0098]    The determination parameter  4  is information indicating the power consumption level of the UE  100 . For example, when the UE  100  is set to a power saving mode, the power consumption level of the UE  100  is small. When the UE  100  is set to a high performance mode, the power consumption level of the UE  100  is large. The UE  100  determines on the basis of the determination parameter  4  that the offload should not be performed and transmits a rejection notification when the power consumption level exceeds the threshold value. When the offload is performed, the power consumption of the UE  100  increases, so that there are problems on the UE  100  whose power consumption level is high that the power consumption exceeds an allowance because of the offload, and the like. Accordingly, when the UE  100  whose power consumption level is high is excludable from a target subject to offload, it is possible to avoid such problems. 
         [0099]    (3) Operation Pattern  1   
         [0100]      FIG. 8  is sequence diagram of an operation pattern  1  according to the first embodiment. Here, differences from a basic operation described above will be mainly described. 
         [0101]    As shown in  FIG. 8 , in step S 1 , the UE  100  receives a WLAN measurement command indicating that the UE  100  is selected as a target terminal subject to offload, from the eNB  200 . 
         [0102]    In step S 10 , the UE  100  determines on the basis of the determination parameter whether or not an offload should be performed. 
         [0103]    When the UE  100  determines that an offload should not be performed (step S 10 : No), in step S 11 , the UE  100  transmits a rejection notification to the eNB  200  as a response to the WLAN measurement command. The UE  100  may include rejection reason information indicating a reason for the rejection into the rejection notification. Examples of the reason for the rejection include “no WLAN AP  300  is present in its neighborhood”, “the UE  100  is moving”, “the battery remaining amount is small”, and “power consumption level is high”. The eNB  200  which receives the rejection notification excludes the UE  100  from a target terminal subject to offload. 
         [0104]    On the other hand, when the UE  100  determines that an offload should be performed (step S 10 : Yes), the UE  100  detects an event to be a transmission trigger for a WLAN measurement report, on the basis of trigger information included in the WLAN measurement command in step S 2 . The subsequent operations are similar to the basic operation described above. 
         [0105]    (4) Operation Pattern  2   
         [0106]      FIG. 9  is a sequence diagram of an operation pattern  2  according to the first embodiment. Here, differences from a basic operation described above will be mainly described. 
         [0107]    As shown in  FIG. 9 , steps S 1  to S 3  are similar to the basic operation described above. 
         [0108]    In step S 20 , the UE  100  determines on the basis of the determination parameter whether or not an offload should be performed. 
         [0109]    When the UE  100  determines that an offload should not be performed (step S 20 : No), in step S 4 ′, the UE  100  transmits, to the eNB  200 , a rejection notification together with the WLAN measurement report to report a result of the WLAN measurement. The UE  100  may transmit the rejection notification included into the WLAN measurement report, and may transmit the WLAN measurement report and the rejection notification by an individual message. The UE  100  may include rejection reason information into the rejection notification. The eNB  200  which receives the rejection notification excludes the UE  100  from a target terminal subject to offload. 
         [0110]    On the other hand, when the UE  100  determines that an offload should be performed, the UE  100  transmits the WLAN measurement report to the eNB  200 , without transmitting the rejection notification. The subsequent operations are similar to the basic operation described above. 
         [0111]    (5) Operation Pattern  3   
         [0112]      FIG. 10  is a sequence diagram of an operation pattern  3  according to the first embodiment. Here, differences from a basic operation described above will be mainly described. 
         [0113]    As shown in  FIG. 10 , steps S 1  to S 5  are similar to the basic operation described above. Specifically, in step S 5 , the UE  100  receives an offload command to instruct the execution of an offload from the eNB  200 . 
         [0114]    In step S 30 , the UE  100  determines on the basis of the determination parameter whether or not an offload should be performed. 
         [0115]    When it is determined that an offload should not be performed (step S 30 : No), in step S 31 , the UE  100  transmits a rejection notification to the eNB  200  as a response to the offload command. It is noted that, the UE  100  may include rejection reason information into the rejection notification. The eNB  200  which receives the rejection notification excludes the UE  100  from a target terminal subject to offload. 
         [0116]    On the other hand, when it is determined that an offload should be performed (step S 30 : Yes), in step S 6 , the UE  100  executes the offload. The subsequent operations are similar to the basic operation described above. 
       Summary of First Embodiment 
       [0117]    As described above, when the UE  100  is selected as a target terminal subject to offload, the UE  100  determines on the basis of the determination parameter related to a situation of the UE  100  whether or not an offload should be performed. When the UE  100  determines on the basis of the determination parameter that the offload should not be performed, the UE  100  transmits a rejection notification, to the eNB  200 , related to rejection to the offload. The eNB  200  excludes the UE  100  from a target terminal subject to offload when the UE  100  is selected as a target terminal subject to offload, and when the eNB  200  receives a rejection notification related to rejection to the offload from the UE  100 . Accordingly, it is possible to properly select a UE  100  subject to offload. 
         [0118]    In the operation pattern  1  according to the first embodiment, it is possible to reduce the process load of the UE  100  and to reduce an amount of consumption of the radio resource involved in the WLAN measurement report because the rejection notification is transmitted to the eNB  200  without transmitting the WLAN measurement report to the eNB  200 . On the other hand, in the operation pattern  3  according to the first embodiment, because the UE  100  makes determination immediately before a timing when the offload should be performed, it is possible to properly make the determination on the basis of the latest situation of the UE  100 . The operation pattern  2  according to the first embodiment has a property intermediate that of the operation pattern  1  and that of the operation pattern  3 . 
       Second Embodiment 
       [0119]    A second embodiment will be described while focusing on the differences from the first embodiment. A system configuration and a basic operation according to the second embodiment are similar to those in the first embodiment. 
       Operation According to Second Embodiment 
       [0120]    An operation according to the second embodiment is performed prior to the basic operations described above. Specifically, the UE  100  transmits, to the eNB  200 , a terminal information notification including the determination parameter described above (at least one of the determination parameter  1  to the determination parameter  4 ) before the UE  100  is selected as a target terminal subject to offload. The terminal information notification may be “UE Capability Information” that is one of RRC messages. 
         [0121]    The eNB  200  receives the terminal information notification including the determination parameter from the UE  100  before the UE  100  is selected as a target terminal subject to offload. And, the eNB  200  selects the UE  100  subject to offload on the basis of the determination parameter. For example, the eNB  200  excludes a UE  100 , around which no WLAN AP  300  is present, from a target terminal subject to offload, on the basis of the determination parameter  1 . The eNB  200  excludes a UE  100  which is moving from a target terminal subject to offload, on the basis of the determination parameter  2 . The eNB  200  excludes a UE  100  whose battery remaining amount falls below the threshold value from a target terminal subject to offload, on the basis of the determination parameter  3 . The eNB  200  excludes a UE  100  whose power consumption level exceeds the threshold value from a target terminal subject to offload, on the basis of the determination parameter  3 . 
         [0122]      FIG. 11  is a sequence diagram according to the second embodiment. 
         [0123]    As shown in  FIG. 11 , in step  5101 , the eNB  200  transmits, to the UE  100 , a UE Capability Enquiry to request to transmit a terminal information notification (UE Capability Information). 
         [0124]    In step  5102 , the UE  100  which receives the UE Capability Enquiry, transmits, to the eNB  200 , the terminal information notification including the determination parameter (UE Capability Information). 
       Summary of Second Embodiment 
       [0125]    As described above, the UE  100  transmits, to the eNB  200 , the terminal information notification including the determination parameter before the UE  100  is selected as a target terminal subject to offload. The eNB  200  receives the terminal information notification including the determination parameter from the UE  100  before the UE  100  is selected as a target terminal subject to offload. The eNB  200  selects a UE  100  subject to offload on the basis of the determination parameter. Thus, it is possible to properly select a UE  100  subject to offload. 
       Other Embodiments 
       [0126]    In the second embodiment described above, the eNB  200  selects a UE  100  subject to offload, on the basis of the determination parameter received from the UE  100 . However, the eNB  200  may select a UE  100  subject to offload without relying on the determination parameter received from the UE  100 . For example, the eNB  200  measures an elapsed time after a UE  100  handovers to a cell of the eNB  200 , excludes a UE  100  in which the elapsed time is shorter than a fixed time from a target terminal subject to offload. Thus, it is possible to include a UE  100  which is in a cell of the eNB  200  in the long term as a target terminal subject to offload, and to exclude a UE  100  which only temporarily passes through the a cell of the eNB  200  from a target terminal subject to offload. 
         [0127]    The second embodiment described above is assumed to be used together with the first embodiment. However, the second embodiment may be executed separately from the first embodiment, and the second embodiment may be executed independently. 
         [0128]    In each of the embodiments described above, as one example of the cellular communication system, the LTE system is described, however, the present disclosure is not limiting to the LTE system, and the present disclosure may be applied to systems other than the LTE system. 
         [0129]    In each operation sequence described above, an operation performed by the eNB  200  (base station) may be operated by another network device (for example, an RNC) instead of the base station. 
       INDUSTRIAL APPLICABILITY 
       [0130]    According to the present disclosure, it is possible to provide a user terminal with which it is possible to properly select a user terminal subject to offload, a cellular base station therefor, and a processor therefor.