Patent Publication Number: US-11388658-B2

Title: Information processing device, information processing method, and a program for information processing for performing measurement of first and second frequency bands based on first and second discovery reference signals within first and second periods respectively

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/233,149, filed Dec. 27, 2018, which is a continuation of U.S. application Ser. No. 16/019,272, filed Jun. 26, 2018 (now U.S. Pat. No. 10,200,942), which is a continuation of U.S. application Ser. No. 15/307,561, filed Oct. 28, 2016, which is based on PCT filing PCT/JP2015/054271, filed Feb. 17, 2015, which claims priority to JP 2014-097822, filed May 9, 2014, the entire contents of each are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a device. 
     BACKGROUND ART 
     In cellular systems according to communication standards such as Long Term Evolution (LTE), a terminal device performs measurement based on a reference signal for cell selection/cell reselection and a handover. For example, measurement of a frequency band that the terminal device does not use is referred to as inter-frequency measurement and is performed in a measurement gap. 
     Various technologies for measurement performed by a terminal device are proposed. For example, Patent Literature 1 discloses a technology in which a measurement gap is assigned to more component carriers as channel quality decreases. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1 JP 2014-53971A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when more frequency bands (for example, component carriers) are assigned to a system, for example, more measurements are necessary. For example, more inter-frequency measurements are necessary. In this case, for example, a terminal device performs inter-frequency measurement at a higher frequency. As a result, power consumption of the terminal device increases and system throughput may decrease or inter-frequency measurement may consume much time. 
     Therefore, it is preferable to provide a mechanism through which measurement performed by a terminal device can be improved. 
     Solution to Problem 
     According to the present disclosure, there is provided a device including: a measurement unit configured to perform measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by a terminal device. The measurement unit does not perform measurement of each of remaining frequency bands among the plurality of frequency bands or performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     According to the present disclosure, there is provided a device including: an acquiring unit configured to acquire information about a plurality of frequency bands that are not used by a terminal device; and a control unit configured to instruct the terminal device to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, and not to perform measurement of each of remaining frequency bands among the plurality of frequency bands or to perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     According to the present disclosure, there is provided a device including: a measurement unit configured to perform measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap and perform measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. 
     According to the present disclosure, there is provided a device including: an acquiring unit configured to acquire information indicating a first frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap; and a control unit configured to notify a terminal device of the first frequency band and the measurement gap. 
     According to the present disclosure, there is provided a device including: an acquiring unit configured to acquire information about a first frequency band in which a discovery reference signal is transmitted; and a control unit configured to decide an extended measurement gap including at least a part of a transmission period in which a discovery reference signal is transmitted in the first frequency band. 
     According to the present disclosure, there is provided a device including: an acquiring unit configured to acquire information about two or more frequency bands in which a discovery reference signal is transmitted; and a control unit configured to decide a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands. The first frequency band is a frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap, and the second frequency band is a frequency band in which a discovery reference signal is transmitted within at least a second period included in the measurement gap. 
     According to the present disclosure, there is provided a device including: a measurement unit configured to perform first measurement of each of a plurality of frequency bands and perform second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands. The first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length, and the second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length. 
     Advantageous Effects of Invention 
     As described above, according to the present disclosure, it is possible to improve measurement performed by a terminal device. Note that the effects described above are not necessarily limitative. With or in the place of the above effects, there may be achieved any one of the effects described in this specification or other effects that may be grasped from this specification. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram for describing an example of a small cell. 
         FIG. 2  is an explanatory diagram for describing an example of a small cell cluster. 
         FIG. 3  is a sequence diagram illustrating an example of a schematic flow of an on/off process of a small cell. 
         FIG. 4  is a sequence diagram illustrating an example of a schematic flow of an on/off process of a small cell when a DRS is used. 
         FIG. 5  is an explanatory diagram for describing an example of a measurement gap. 
         FIG. 6  is an explanatory diagram for describing a first scenario of carrier aggregation (CA). 
         FIG. 7  is an explanatory diagram for describing a second scenario of carrier aggregation (CA). 
         FIG. 8  is an explanatory diagram for describing a third scenario of carrier aggregation (CA). 
         FIG. 9  is a first explanatory diagram for describing an example of measurement in a small cell on/off environment. 
         FIG. 10  is a second explanatory diagram for describing an example of measurement in a small cell on/off environment. 
         FIG. 11  is an explanatory diagram illustrating an example of a schematic configuration of a communication system according to an embodiment of the present disclosure. 
         FIG. 12  is a block diagram illustrating an example of a configuration of a terminal device according to a first embodiment. 
         FIG. 13  is an explanatory diagram for describing a first example of measurement according to the first embodiment. 
         FIG. 14  is an explanatory diagram for describing a second example of measurement according to the first embodiment. 
         FIG. 15  is an explanatory diagram for describing a third example of measurement according to the first embodiment. 
         FIG. 16  is a block diagram illustrating an example of a configuration of a base station according to the first embodiment. 
         FIG. 17  is a sequence diagram illustrating a first example of a schematic flow of a process according to the first embodiment. 
         FIG. 18  is a sequence diagram illustrating a second example of a schematic flow of a process according to the first embodiment. 
         FIG. 19  is an explanatory diagram for describing a first example of measurement according to a modification example of the first embodiment. 
         FIG. 20  is an explanatory diagram for describing a second example of measurement according to a modification example of the first embodiment. 
         FIG. 21  is an explanatory diagram for describing a third example of measurement according to a modification example of the first embodiment. 
         FIG. 22  is a block diagram illustrating an example of a configuration of a terminal device according to a second embodiment. 
         FIG. 23  is an explanatory diagram for describing a first example of measurement according to the second embodiment. 
         FIG. 24  is an explanatory diagram for describing a second example of measurement according to the second embodiment. 
         FIG. 25  is an explanatory diagram for describing a third example of measurement according to the second embodiment. 
         FIG. 26  is a block diagram illustrating an example of a configuration of a base station according to the second embodiment. 
         FIG. 27  is a block diagram illustrating an example of a configuration of a control entity according to the second embodiment. 
         FIG. 28  is a sequence diagram illustrating an example of a schematic flow of a process according to the second embodiment. 
         FIG. 29  is a sequence diagram illustrating a first example of a schematic flow of a frequency group decision process according to the second embodiment. 
         FIG. 30  is a sequence diagram illustrating a second example of a schematic flow of a frequency group decision process according to the second embodiment. 
         FIG. 31  is a block diagram illustrating an example of a configuration of a terminal device according to a third embodiment. 
         FIG. 32  is an explanatory diagram for describing a first example of measurement according to the third embodiment. 
         FIG. 33  is an explanatory diagram for describing a second example of measurement according to the third embodiment. 
         FIG. 34  is an explanatory diagram for describing a third example of measurement according to the third embodiment. 
         FIG. 35  is an explanatory diagram for describing a fourth example of measurement according to the third embodiment. 
         FIG. 36  is a block diagram illustrating an example of a configuration of a base station according to the third embodiment. 
         FIG. 37  is a block diagram illustrating an example of a configuration of a control entity according to the third embodiment. 
         FIG. 38  is a sequence diagram illustrating an example of a schematic flow of a process according to the third embodiment. 
         FIG. 39  is a sequence diagram illustrating a first example of a schematic flow of an extended measurement gap decision process according to the third embodiment. 
         FIG. 40  is a sequence diagram illustrating a second example of a schematic flow of an extended measurement gap decision process according to the third embodiment. 
         FIG. 41  is a block diagram illustrating an example of a configuration of a terminal device according to the second embodiment. 
         FIG. 42  is an explanatory diagram for describing an example of frequency bands that are targets of first measurement and second measurement according to a fourth embodiment. 
         FIG. 43  is a flowchart illustrating an example of a schematic flow of a process according to the fourth embodiment. 
         FIG. 44  is a block diagram illustrating an example of a schematic configuration of a server. 
         FIG. 45  is a block diagram illustrating a first example of a schematic configuration of an eNB. 
         FIG. 46  is a block diagram illustrating a second example of the schematic configuration of the eNB. 
         FIG. 47  is a block diagram illustrating an example of a schematic configuration of a smartphone. 
         FIG. 48  is a block diagram illustrating an example of a schematic configuration of a car navigation apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENT(S) 
     Hereinafter, (a) preferred embodiment(s) of the present disclosure will be described in detail with reference to the appended drawings. In this specification and the drawings, elements that have substantially the same function and structure are denoted with the same reference signs, and repeated explanation is omitted. 
     In this specification and the drawings, there are cases in which components having substantially the same functional configuration are distinguished by adding different alphabets to the end of the same reference numeral. For example, a plurality of components having substantially the same functional configuration are distinguished like small base stations  15 A,  15 B, and  15 C as necessary. However, when a plurality of components having substantially the same functional configuration need not be particularly distinguished, only the same reference numeral is added. For example, when the small base stations  15 A,  15 B, and  15 C need not be particularly distinguished, they are referred to simply as a “small base stations  15 .” 
     The description will proceed in the following order.
     1. Introduction   1.1. Related technology   1.2. Problems related to measurement   2. Schematic configuration of communication system   3. First embodiment   3.1. Configuration of terminal device   3.2. Configuration of base station   3.3. Process flow   3.4. Modification example   4. Second embodiment   4.1. Configuration of terminal device   4.2. Configuration of base station   4.3. Configuration of control entity   4.4. Process flow   4.5. First modification example   4.6. Second modification example   5. Third embodiment   5.1. Configuration of terminal device   5.2. Configuration of base station   5.3. Configuration of control entity   5.4. Process flow   5.5. First modification example   5.6. Second modification example   6. Third embodiment   6.1. Configuration of terminal device   6.2. Process flow   7. Application examples   7.1. Application examples for control entity   7.2. Application examples for base station   7.3. Application examples for terminal device   8. Conclusion   

     1. Introduction 
     First, a technology related to an embodiment of the present disclosure and problems related to an embodiment of the present disclosure will be described with reference to  FIG. 1  to  FIG. 10 . 
     &lt;1.1. Related Technology&gt; 
     A technology related to an embodiment of the present disclosure will be described with reference to  FIG. 1  to  FIG. 8 . Specifically, a small cell, a measurement and carrier aggregation will be described. 
     (Small Cell) 
     (a) Small Cell 
     A small cell is a cell smaller than a macro cell. For example, the small cell partially or entirely overlaps the macro cell. Hereinafter, an example of the small cell will be described with reference to  FIG. 1 . 
       FIG. 1  is an explanatory diagram for describing an example of a small cell. Referring to  FIG. 1 , a macro base station  11 , a macro cell  13 , a small base station  15  and a small cell  17  are shown. The macro base station  11  is a base station of the macro cell  13 . The small base station  15  is a base station of the small cell  17 . In other words, the macro cell  13  is a coverage area of the macro base station  11  (that is, a communication area), and the small cell  17  is a coverage area of the small base station  15  (that is, a communication area). 
     A base station of LTE is referred to as an evolved node B (eNB). Here, a macro base station of LTE is referred to as a macro eNB, and a small base station of LTE is referred to as a small eNB. In addition, a terminal device of LTE is referred to as user equipment (UE). 
     (b) Small Cell Cluster 
     Small cells arranged at a high density form a small cell cluster. Hereinafter, an example of the small cell cluster will be described with reference to  FIG. 2 . 
       FIG. 2  is an explanatory diagram for describing an example of a small cell cluster. Referring to  FIG. 2 , the macro base station  11 , the macro cell  13  and the small cell  17  are shown. For example, small cells  17  arranged at a high density form a small cell cluster  19 . 
     (c) Small Cell On/Off 
     In a case in which small cells are arranged at a high density, inter-cell interference causes a serious problem. In general, the small base station transmits a cell-specific reference signal (CRS) regardless of the presence or absence of traffic of the small cell. In the case in which small cells are arranged at a high density, it is known that a CRS causes large interference in a neighbor cell. Therefore, various technologies for reducing interference are being studied. 
     As a technology for reducing such inter-cell interference, a small cell on/off technology has currently been focused on. In the small cell on/off technology, an on/off state of a small cell is adaptively switched, and thus it is possible to suppress interference in a surrounding cell of the small cell. While a trigger for switching an on/off state of the small cell has not yet been specifically decided, a trigger for switching based on, for example, a traffic amount, association of a terminal device, or arrival of a packet is being studied. Hereinafter, an example of a small cell on/off procedure will be described with reference to  FIG. 3 . 
       FIG. 3  is a sequence diagram illustrating an example of a schematic flow of a small cell on/off process. The small cell on/off process is a process that is disclosed in R1-134318 of the Third Generation Partnership Project (3GPP). When data to be transmitted is generated, the UE transmits an uplink signal to a macro eNB of a macro cell that is a serving cell (S 1001 ). Then, the macro eNB searches for a small eNB in an off state that is positioned around the UE, and instructs the appropriate small eNB to switch to an on state when there is an appropriate small eNB (S 1003 ). Then, the small eNB performs switching from the off state to the on state (S 1005 ). Then, the small eNB transmits downlink signals such as a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a cell-specific reference signal (CRS) and a physical broadcast channel (PBCH) signal (S 1007 ). In addition, the UE performs a cell search and RRM measurement (S 1009 ), and performs measurement reporting to the macro eNB (S 1011 ). Then, a handover of the UE from the macro cell to the small cell is performed (S 1013 ). Then, the UE and the small eNB perform an access procedure (S 1015 ) and perform data transmission (S 1017 ). 
     According to the procedure shown in  FIG. 3 , it is possible to switch an on/off state of a small cell. However, according to the procedure, a transition time may become relatively longer. That is, according to the procedure, a time from when a terminal device attempts to transmit data until the terminal device actually transmits the data may become relatively longer. Therefore, large improvement of throughput is difficult. In order to improve the transition time, while the small cell is in the off state, a measurement process that serves as a main delay factor is preferably performed by the terminal device. 
     (d) Discovery Reference Signal 
     Introduction of a discovery reference signal (DRS) is being studied in order to reduce the transition time. The DRS enables measurement of a small cell in the off state. The DRS is also referred to as a discovery signal (DS). A small base station (for example, a small eNB) transmits a DRS while a small cell (or a small base station) is in the off state, and a terminal device (for example, UE) performs measurement based on a DRS. Hereinafter, an example of a small cell on/off procedure when a DRS is used will be described with reference to  FIG. 4 . 
       FIG. 4  is a sequence diagram illustrating an example of a schematic flow of a small cell on/off process when a DRS is used. The small cell on/off process is a process that is disclosed in R1-134318 of the 3GPP. A macro eNB instructs a small eNB to transmit a DS (S 1031 ), and the small eNB transmits the DS in downlink (S 1033 ). The UE performs measurement based on the DS (S 1035 ) and reports a result of the measurement to the macro eNB (that is, an eNB of a macro cell that is a serving cell) (S 1037 ). The UE and the small eNB perform data transmission through subsequent procedures (S 1041  to S 1049 ) (S 1051 ). 
     According to the procedure shown in  FIG. 4 , while the small cell is in the off state, the terminal device can perform measurement. Therefore, the transition time is removed and throughput may be improved. 
     As various technologies for reducing interference, enhancement on a transmission side and a reception side such as muting, multiple instance and interference cancellation is also being studied. 
     (Measurement) 
     (a) CRS Measurement 
     In LTE, a terminal device performs measurement based on a CRS transmitted by a base station. Specifically, the terminal device receives a CRS transmitted by a base station and thus performs measurement of quality of a propagation path between the base station and the terminal device. The measurement is referred to as “radio resource management (RRM) measurement,” or is simply referred to as “measurement.” 
     A result of the measurement is used to select a cell for a terminal device. As a specific example, the result of the measurement is used for cell selection/cell reselection by a terminal device that is in a radio resource control (RRC) idle (RRC Idle) state. In addition, for example, the result of the measurement is reported to a base station by a terminal device that is in an RRC connected state and is used for a handover decision by the base station. 
     (b) RSRP and RSRQ 
     In LTE, CRS measurement is measurement of reference signal received power (RSRP) and/or reference signal received quality (RSRQ). In other words, a terminal device acquires RSRP and/or RSRQ as a result of the measurement of the CRS. The RSRQ is calculated from the RSRP and a received signal strength indicator (RSSI). 
     The RSRP is reception power of a CRS for each single resource element. That is, the RSRP is an average value of reception power of the CRS. The reception power of the CRS is obtained by detecting a correlation between a reception signal in a resource element of the CRS and a known signal CRS. The RSRP corresponds to a desired signal “Signal (S).” 
     The RSSI is total power of signals for each Orthogonal Frequency Division Multiple Access (OFDMA) symbol. Therefore, the RSSI includes a desired signal, an interference signal and noise. That is, the RSSI corresponds to “Signal (S)+Interference (I)+Noise (N).” 
     The RSRQ is RSRP/(RSRI/N). N denotes the number of resource blocks used for calculating an RSSI. The resource blocks are resource blocks that are arranged in a frequency direction. Therefore, the RSRQ is a value that is obtained by dividing the RSRP using the RSRI for each resource block. That is, the RSRQ corresponds to a signal-to-interference-plus-noise ratio (SINR). 
     As described above, according to the measurement of the CRS, reception power (that is, RSRP) and reception quality (that is, RSRQ) such as an SINR are obtained. 
     (c) Measurement Timing 
     Measurement of a frequency band that a terminal device uses is referred to as intra-frequency measurement. Conversely, measurement of a frequency band that a terminal device does not use is referred to as inter-frequency measurement. 
     The terminal device can receive a CRS transmitted in a frequency band that is used without switching a frequency of a radio frequency (RF) circuit. That is, it is unnecessary to switch a frequency of the RF circuit for intra-frequency measurement. 
     Conversely, in order for the terminal device to receive a CRS transmitted in a frequency band that is not used, it is necessary to switch a frequency of a radio frequency (RF) circuit. That is, it is necessary to switch a frequency of the RF circuit for inter-frequency measurement. Therefore, a period called a measurement gap is used for inter-frequency measurement. 
     During the measurement gap, the base station does not transmit a downlink signal addressed to a terminal device. In addition, the measurement gap is shared between the base station and the terminal device. For example, the base station transmits a message (for example, an RRC connection reconfiguration message) including information indicating a measurement gap to the terminal device. For example, the measurement gap is indicated by a measurement gap length (MGL), a measurement gap repetition period (MGRP) and a gap offset. In addition, a combination of the MGL and the MGRP is determined as, for example, a gap pattern. Hereinafter, an example of the measurement gap will be described with reference to  FIG. 5 . 
       FIG. 5  is an explanatory diagram for describing an example of a measurement gap.  FIG. 5  shows a matrix including columns of radio frames whose SFNs are 0 to 9 and rows of 10 subframes (subframes whose subframe numbers are 0 to 9) included in radio frames. In this example, the MGL is 6 milliseconds (ms), the MGRP is 40 ms, and the gap offset is 0. Therefore, the measurement gap has a length of 6 ms and appears every 40 ms. More specifically, for example, six subframes whose subframe numbers are 0 to 5 among radio frames whose SFNs are 0, 4 and 8 are the measurement gap. Inter-frequency measurement is performed during the measurement gap. 
     (d) Measurement Reporting 
     The terminal device reports a measurement result to the base station. The reporting is referred to as measurement reporting. 
     The measurement reporting is periodic reporting or event-triggered reporting. The periodic reporting is reporting that is performed at set periods. Conversely, the event-triggered reporting is reporting that is performed when a reporting event is generated. Reporting events A1 to A5 are events associated with a handover within a system, and reporting events B1 to B2 are events associated with a handover between systems. 
                         TABLE 1               Event           Type   Description                  Event A1   Serving becomes better than threshold       Event A2   Serving becomes worse than threshold       Event A3   Neighbour becomes offset better than serving       Event A4   Neighbour becomes better than threshold       Event A5   Serving becomes worse than threshold1 and            neighbour becomes better than threshold2       Event B1   Inter RAT neighbour becomes better than threshold       Event B2   Serving becomes worse than threshold1 and inter            RAT neighbour becomes better than threshold2                    
(Carrier Aggregation)
 
     Carrier aggregation (CA) is a technology through which communication is performed using a plurality of component carriers (CCs) at the same time. The component carrier is a frequency band having a maximum of a 20 MHz bandwidth. The carrier aggregation includes three scenarios. Hereinafter, three scenarios of the carrier aggregation will be described with reference to  FIG. 6  to  FIG. 8 . 
       FIG. 6  to  FIG. 8  are explanatory diagrams for describing first to third scenarios of carrier aggregation (CA). As illustrated in  FIG. 6 , in the first scenario (intra-band contiguous) of CA, the terminal device uses CCs adjacent in the same operating. As illustrated in  FIG. 7 , in the second scenario (intra-band non-contiguous) of CA, the terminal device uses CCs that are not adjacent in the same operating. As illustrated in  FIG. 8 , in the third scenario (inter-band non-contiguous) of CA, the terminal device uses CCs that are not adjacent in different operating. 
     &lt;1.2. Problems Related to Measurement&gt; 
     (Problem Caused when Plurality of Frequency Bands are Used) 
     When more frequency bands (for example, component carriers) are assigned to a system, for example, more measurements are necessary. For example, more inter-frequency measurements are necessary. In this case, for example, the terminal device performs inter-frequency measurement at a higher frequency. As a result, power consumption of the terminal device increases and system throughput may decrease or inter-frequency measurement may consume much time. 
     Accordingly, in the embodiment of the present disclosure, for example, it is possible to improve measurement performed by the terminal device. 
     (Problem Caused in Small Cell On/Off Environment) 
     In addition, in current standards of 3GPP, inter-frequency measurements are performed at periods of 40 ms or 80 ms. That is, the inter-frequency measurement is frequently performed. Conversely, in the current RAN2/RAN4, improvement of inter-frequency measurement is being studied. For example, when a measurement period increases, a measurement frequency decreases. As a result, throughput and power consumption may be improved. The measurement is referred to as relax measurement. However, when relax measurement is introduced into an environment in which an on/off state of a small cell is switched (hereinafter referred to as a “small cell on/off environment”), for example, a discovery of a small cell in the off state is delayed. This is because a base station of a small cell (that is, a small base station) in the off state periodically transmits a DRS. 
     —Measurement in Current Cellular System 
     In a current cellular system, a terminal device generally performs measurement based on a CRS transmitted in each subframe. For example, the terminal device can perform intra-frequency measurement based on a CRS transmitted in any subframe. In addition, for example, the terminal device can perform inter-frequency measurement based on a CRS transmitted in a measurement gap. 
     —Measurement in Small Cell On/Off Environment 
     As described above, transmission of a DRS in a small cell on/off environment is being studied. A case in which a DRS is transmitted for a relatively long period (for example, a period of several tens to several hundreds of ms) in a small cell in the off state is assumed. In addition, a case in which a DRS is transmitted not only in a small cell in the off state but also in a small cell in the on state is being studied. That is, in the small cell on/off environment, only a DRS is transmitted in the small cell in the off state and, conversely, a CRS and a DRS or only a CRS is transmitted in the small cell in the on state. 
     The above-described measurements are summarized as follows. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Transmission 
                 Measurement 
               
               
                 Scenario 
                 Reference Signal 
                 Period 
                 Period 
               
               
                   
               
             
            
               
                 Existing 
                 CRS 
                 Always 
                 40 ms or 
               
               
                   
                   
                   
                 80 ms 
               
               
                 Small cell 
                 (on)DRS + CRS or  
                 CRS: Always 
                 not yet 
               
               
                 On/Off 
                 CRS only 
                 DRS: per dozens/ 
                 determined 
               
               
                   
                 (off)DRS 
                 hundreds of 
                   
               
               
                   
                   
                 millisecond 
               
               
                   
               
            
           
         
       
     
     Specific Example 
     Hereinafter, an example of measurement in a small cell on/off environment will be described with reference to  FIG. 9  and  FIG. 10 . 
       FIG. 9  is a first explanatory diagram for describing an example of measurement in a small cell on/off environment. Referring to  FIG. 9 , the macro base station  11 , the macro cell  13 , the small base station  15 , the small cell  17  and a terminal device  21  are shown. A small cell  17 A and a small cell  17 B are included in a small cell cluster  19 A. A small cell  17 C and a small cell  17 D are included in a small cell cluster  19 B. The terminal device  21  is connected to the macro base station  11 . 
     In the macro cell  13 , a CC0 is used by the macro base station  11 . Therefore, a CRS is transmitted by the macro base station  11  in the CC0. 
     The small cell  17 A is in the on state. A CC1 is used by the small base station  15 A in the small cell  17 A. Therefore, in the CC1, a CRS is transmitted by the small base station  15 A. 
     The small cell  17 B is in the off state and a CC2 is used by the small base station  15 B in the small cell  17 B. Therefore, a DRS is transmitted by the small base station  15 B in the CC2. 
     The small cell  17 C is in the on state and a CC3 is used by the small base station  15 C in the small cell  17 C. Further, the small cell  17 D is in the off state and a CC3 is used by the small base station  15 D in the small cell  17 D. Therefore, in the CC3, a CRS is transmitted by the small base station  15 C and a DRS is transmitted by the small base station  15 D. 
       FIG. 10  is a second explanatory diagram for describing an example of measurement in a small cell on/off environment. Referring to  FIG. 10 , a CRS is transmitted in a CC0, a CRS is transmitted in a CC1, a DRS is transmitted in a CC2 and a CRS and a DRS are transmitted in a CC3 identically to those described with reference to  FIG. 9 . The terminal device  21  performs intra-frequency measurement of the CC0. In addition, the terminal device  21  performs inter-frequency measurement of the CC1, CC2 and the CC3 using a measurement gap having a period of 40 ms or 80 ms. 
     As shown in the example, an inter-frequency measurement frequency may increase when the number of CCs increases. In addition, since a DRS is transmitted even when a small cell is in the off state in the small cell on/off environment, an inter-frequency measurement frequency may increase regardless of an on/off state of the small cell. Alternatively, an inter-frequency measurement frequency is maintained and, as a result, inter-frequency measurement may consume much time. 
     In addition, it is necessary for the terminal device  21  to perform inter-frequency measurement in consideration of a timing at which a DRS is transmitted. Therefore, since inter-frequency measurement based on a DRS whose transmission period is long has a limited opportunity, the inter-frequency measurement based on a DRS may consume much time. 
     In the embodiment of the present disclosure, it is possible to improve inter-frequency measurement based on a DRS. 
     2. Schematic Configuration of Communication System 
     Next, a schematic configuration of a communication system  1  according to an embodiment of the present disclosure will be described with reference to  FIG. 11 .  FIG. 11  is an explanatory diagram illustrating an example of a schematic configuration of the communication system  1  according to an embodiment of the present disclosure. As illustrated in  FIG. 11 , the communication system  1  includes a terminal device  100 , a base station  200  and a control entity  300 . The communication system  1  is a system supporting, for example, LTE, LTE-Advanced or a communication standard equivalent thereto. 
     The terminal device  100  wirelessly communicates with the base station  200 . In addition, the terminal device  100  performs measurement of each frequency band that is used by the base station. In addition, the terminal device  100  reports a result of the measurement to the base station  200 . 
     The base station  200  wirelessly communicates with one or more terminal devices including the terminal device  100 . The base station  200  may be a base station of a macro cell (that is, a macro base station) or a base station of a small cell (that is, a small base station). 
     The control entity  300  performs control according to each embodiment of the present disclosure. The control entity  300  is, for example, an existing or new core network node. Alternatively, when the base station  200  is a small base station, the control entity  300  may be a macro base station. 
     3. First Embodiment 
     Next, a first embodiment of the present disclosure will be described with reference to  FIG. 12  to  FIG. 21 . 
     A terminal device  100 - 1  according to the first embodiment performs measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by the terminal device  100 - 1 . Specifically, according to the first embodiment, the terminal device  100 - 1  does not perform measurement of each of the remaining frequency bands among the plurality of frequency bands or performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 1 . As a specific example, a measurement load on the terminal device  100 - 1  may be reduced. 
     &lt;3.1. Configuration of Terminal Device&gt; 
     First, an example of a configuration of the terminal device  100 - 1  according to the first embodiment will be described with reference to  FIG. 12  to  FIG. 15 .  FIG. 12  is a block diagram illustrating an example of a configuration of the terminal device  100 - 1  according to the first embodiment. As illustrated in  FIG. 12 , the terminal device  100 - 1  includes an antenna unit  110 , a wireless communication unit  120 , a storage unit  130  and a processing unit  140 . 
     (Antenna Unit  110 ) 
     The antenna unit  110  emits a signal output by the wireless communication unit  120  into space as radio waves. In addition, the antenna unit  110  converts spatial radio waves into a signal and outputs the signal to the wireless communication unit  120 . 
     (Wireless Communication Unit  120 ) 
     The wireless communication unit  120  transmits and receives signals. For example, the wireless communication unit  120  receives a downlink signal from a base station and transmits an uplink signal to the base station. 
     (Storage Unit  130 ) 
     The storage unit  130  temporarily or permanently stores programs and data for operations of the terminal device  100 - 1 . 
     (Processing Unit  140 ) 
     The processing unit  140  provides various functions of the terminal device  100 - 1 . The processing unit  140  includes an information acquiring unit  141 , a measurement unit  143  and a reporting unit  145 . Alternatively, the processing unit  140  may further include a component other than these components. That is, the processing unit  140  may also perform an operation other than operations of these components. 
     (Information Acquiring Unit  141 ) 
     The information acquiring unit  141  acquires information about a frequency band. 
     For example, the information acquiring unit  141  acquires a measurement configuration of a frequency band. For example, a base station  200 - 1  transmits an RRC connection reconfiguration message including the measurement configuration to the terminal device  100 - 1 , and the information acquiring unit  141  acquires the measurement configuration. The measurement configuration includes information such as measurement objects, reporting configurations, measurement identities (measurement IDs) and measurement gaps. 
     For example, the information acquiring unit  141  acquires a neighboring cell list (NCL). For example, the information acquiring unit  141  acquires an intra-frequency NCL and an inter-frequency NCL. For example, the base station  200 - 1  informs the information acquiring unit  141  of an intra-frequency NCL within a system information block (SIB) 4, and the information acquiring unit  141  acquires the intra-frequency NCL. In addition, for example, the base station  200 - 1  informs the information acquiring unit  141  of an inter-frequency NCL within an SIB5, and the information acquiring unit  141  acquires the inter-frequency NCL. 
     (Measurement Unit  143 ) 
     The measurement unit  143  performs measurement of a frequency band. 
     In the first embodiment, the measurement unit  143  performs measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by the terminal device  100 - 1 . Conversely, the measurement unit  143  does not perform measurement of each of the remaining frequency bands among the plurality of frequency bands or performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 1 . 
     (a) Frequency Band 
     —Component Carrier (CC) 
     For example, each of the plurality of frequency bands is a component carrier (CC) of carrier aggregation. 
     —The Same Operating Band 
     For example, the remaining frequency bands are frequency bands included in the same operating band as the one or more frequency bands. That is, the plurality of frequency bands are included in a single operating band. 
     Accordingly, for example, general measurement of a representative frequency band among a plurality of frequency bands that are assumed to have similar characteristics (that is, a plurality of frequency bands in a single operating band) is performed. Therefore, for example, when there is a frequency band through which favorable communication quality can be provided to the terminal device  100 - 1 , the terminal device  100 - 1  can use the frequency band with a high probability while reducing a measurement load. 
     Further, for example, each of the remaining frequency bands is a frequency band adjacent to any frequency band included in the one or more frequency bands. 
     Accordingly, for example, general measurement of a representative frequency band between two frequency bands that are assumed to have fairly similar characteristics (that is, two adjacent frequency bands) is performed. Therefore, for example, when there is a frequency band through which favorable communication quality can be provided to the terminal device  100 - 1 , the terminal device  100 - 1  can use the frequency band with a fairly high probability while reducing a measurement load. 
     —Frequency Band of Small Cell 
     For example, each of the plurality of frequency bands is a frequency band that is used by a base station of a small cell. 
     Accordingly, for example, in an environment in which small cells are arranged, it is possible to reduce a measurement load. 
     The plurality of frequency bands have been described above. The first embodiment is not limited thereto. For example, the plurality of frequency bands may include frequency bands included in a different operating band. In addition, the plurality of frequency bands may include a frequency band that is used only by a macro base station. 
     (b) Measurement 
     (b-1) Measurement Based on Reference Signal 
     For example, the measurement of each of the one or more frequency bands is measurement based on a reference signal transmitted in each of the one or more frequency bands. In addition, the measurement of each of the remaining frequency bands is measurement based on a reference signal transmitted in each of the remaining frequency bands. 
     For example, the reference signal is a cell-specific reference signal (CRS). Accordingly, for example, it is possible to reduce a measurement load regarding a small cell in the on state. A measurement load regarding a macro cell may also be reduced. 
     The measurement of each of the one or more frequency bands is RRM measurement. For example, the measurement of each of the one or more frequency bands is measurement of reception power or reception quality. More specifically, for example, the measurement of each of the one or more frequency bands is measurement of RSRP or RSRQ. In addition, for example, the measurement of each of the one or more frequency bands is performed for each cell in which each of the one or more frequency bands is used (that is, a base station that uses each of the one or more frequency bands). 
     (b-2) Measurement of Remaining Frequency Bands 
     —First Example (Without Measurement) 
     As a first example, the measurement unit  143  does not perform the measurement of each of the remaining frequency bands. Hereinafter, this will be described with reference to a specific example of  FIG. 13 . 
       FIG. 13  is an explanatory diagram for describing a first example of measurement according to the first embodiment. As illustrated in  FIG. 13 , a CRS is transmitted in a CC0 and a CC1. In this example, the terminal device  100 - 1  performs inter-frequency measurement of the CC0. Conversely, inter-frequency measurement of the CC1 is not performed. 
     Accordingly, for example, a frequency band that is a measurement (that is, inter-frequency measurement) target is limited. Therefore, it is possible to further decrease a frequency of measurements performed by the terminal device  100 - 1 . As a result, a load of measurements performed by the terminal device  100 - 1  may be reduced. In addition, power consumption of the terminal device  100 - 1  may decrease and throughput may be improved. Alternatively, measurement of a specific frequency band can be intensively performed for a short period. As a result, measurement of the specific frequency band may be performed more quickly. 
     —Second Example (Measurement at Low Frequency) 
     As a second example, the measurement unit  143  performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     More specifically, for example, the measurement unit  143  performs the measurement of each of the remaining frequency bands using fewer measurement gaps than measurement gaps used for the measurement of each of the one or more frequency bands. 
     As an example, the measurement unit  143  skips a part of the measurement gaps assigned to each of the remaining frequency bands without measurement. Hereinafter, this will be described with reference to a specific example of  FIG. 14 . 
       FIG. 14  is an explanatory diagram for describing a second example of measurement according to the first embodiment. As illustrated in  FIG. 14 , a CRS is transmitted in a CC0 and a CC1. In this example, the same number of measurement gaps is assigned to the CC0 and CC1. The terminal device  100 - 1  performs measurement of the CC0 using all measurement gaps assigned to the CC0. Conversely, the terminal device  100 - 1  skips a part of all measurement gaps assigned to the CC1 without measurement of the CC1, and performs measurement of the CC1 using the rest of the all measurement gaps assigned to the CC1. 
     Accordingly, for example, a frequency of measurements performed by the terminal device  100 - 1  (that is, inter-frequency measurement) decreases. As a result, a load of measurements performed by the terminal device  100 - 1  may be reduced. In addition, power consumption of the terminal device  100 - 1  may decrease and throughput may be improved. 
     As another example, measurement gaps assigned to each of the remaining frequency bands may be fewer than measurement gaps assigned to each of the one or more frequency bands. Hereinafter, this will be described with reference to a specific example of  FIG. 15 . 
       FIG. 15  is an explanatory diagram for describing a third example of measurement according to the first embodiment. As illustrated in  FIG. 15 , a CRS is transmitted in a CC0 and a CC1. In this example, more measurement gaps are assigned to the CC0 and fewer measurement gaps are assigned to the CC1. The terminal device  100 - 1  performs measurement of the CC0 using the more measurement gaps assigned to the CC0, and performs measurement of the CC1 using the fewer measurement gaps assigned to the CC1. 
     Accordingly, for example, measurement of a specific frequency band can be intensively performed for a short period. As a result, measurement of the specific frequency band may be performed more quickly. 
     The measurement of each of the remaining frequency bands is RRM measurement. For example, the measurement of each of the remaining frequency bands is measurement of reception power or reception quality. More specifically, for example, the measurement of each of the remaining frequency bands is measurement of RSRP or RSRQ. In addition, for example, the measurement of each of the remaining frequency bands is performed for each cell in which each of the remaining frequency bands is used (that is, a base station that uses each of the remaining frequency bands). 
     (c) Measurement Control 
     For example, the measurement by the measurement unit  143  is performed according to an instruction from the base station  200 - 1 . That is, the terminal device  100 - 1  performs the measurement by the measurement unit  143  according to an instruction from the base station  200 - 1 . 
     The measurement by the measurement unit  143  may be voluntarily performed. That is, the terminal device  100 - 1  may voluntarily perform the measurement by the measurement unit  143 . In this case, the base station  200 - 1  may not perform some or all of operations which will be described. 
     (Reporting Unit  145 ) 
     The reporting unit  145  reports a result of the measurement of a frequency band to the base station  200 - 1 . 
     (a) Reporting of Result of Measurement of One or More Frequency Bands 
     The reporting unit  145  reports a result of the measurement of each of the one or more frequency bands to the base station  200 - 1 . 
     (b) Reporting of Result of Measurement of Remaining Frequency Bands 
     —First Example (Without Measurement) 
     As described above, as a first example, the measurement unit  143  does not perform the measurement of each of the remaining frequency bands. In this case, the reporting unit  145  does not report a result of the measurement of each of the remaining frequency bands to the base station  200 - 1 . 
     The reporting unit  145  may substitute a result of measurement of a first frequency band included in the one or more frequency bands with a result of measurement of a second frequency band included in the remaining frequency bands, and thus may report the result of the measurement of the second frequency band to the base station  200 - 1 . Accordingly, for example, a frequency band that is not actually measured may be selected as a frequency band that is used by the terminal device  100 - 1 . 
     —Second Example (Measurement at Low Frequency) 
     As described above, as the second example, the measurement unit  143  performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. In this case, the reporting unit  145  reports a result of the measurement of each of the remaining frequency bands to the base station  200 - 1 . 
     (c) Reporting Method 
     For example, the reporting unit  145  reports a result of measurement to the base station  200 - 1  according to a reporting configuration included in the measurement configuration from the base station  200 - 1 . 
     For example, the reporting unit  145  reports the result of the measurement to the base station  200 - 1  through the antenna unit  110  and the wireless communication unit  120 . 
     &lt;3.2. Configuration of Base Station&gt; 
     Next, an example of a configuration of the base station  200 - 1  according to the first embodiment will be described with reference to  FIG. 16 .  FIG. 16  is a block diagram illustrating an example of a configuration of the base station  200 - 1  according to the first embodiment. Referring to  FIG. 16 , the base station  200 - 1  includes an antenna unit  210 , a wireless communication unit  220 , a network communication unit  230 , a storage unit  240 , and a processing unit  250 . 
     (Antenna Unit  210 ) 
     The antenna unit  210  radiates a signal output from the wireless communication unit  220  into the air as radio waves. The antenna unit  210  converts the radio waves in the air into a signal, and outputs the signal to the wireless communication unit  220 . 
     (Wireless Communication Unit  220 ) 
     The wireless communication unit  220  transmits or receives a signal. For example, the wireless communication unit  220  transmits the downlink signal to the terminal device, and receives the uplink signal from the terminal device. 
     (Network Communication Unit  230 ) 
     The network communication unit  230  communicates with other nodes. For example, the network communication unit  230  communicates with a core network node and other base stations. For example, the network communication unit  230  communicates with a control entity  300 - 1 . 
     (Storage Unit  240 ) 
     The storage unit  240  temporarily or permanently stores a program and data for an operation of the base station  200 - 1 . 
     (Processing Unit  250 ) 
     The processing unit  250  provides various functions of the base station  200 - 1 . The processing unit  250  includes an information acquiring unit  251  and a control unit  253 . The processing unit  250  may further include any other component in addition to the above-mentioned components. In other words, the processing unit  250  may also perform an operation other than operations of the above-mentioned components. 
     (Information Acquiring Unit  251 ) 
     The information acquiring unit  251  acquires information about a plurality of frequency bands that are not used by the terminal device  100 - 1 . 
     Descriptions of the plurality of frequency bands are the same as those described above in the measurement unit  143  of the terminal device  100 - 1 . Therefore, redundant descriptions will be omitted here. 
     The information about the plurality of frequency bands includes information indicating each of the plurality of frequency bands (for example, a downlink carrier frequency or identification information). 
     (Control Unit  253 ) 
     The control unit  253  instructs the terminal device  100 - 1  to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, and not to perform measurement of each of the remaining frequency bands among the plurality of frequency bands or perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     (a) Frequency Band 
     For example, the control unit  253  selects the one or more frequency bands from among the plurality of frequency bands. Alternatively, the control unit  253  may select the remaining frequency bands other than the one or more frequency bands from among the plurality of frequency bands. 
     Descriptions of the one or more frequency bands and the remaining frequency bands are the same as those described above in the measurement unit  143  of the terminal device  100 - 1 . Therefore, redundant descriptions will be omitted here. 
     (b) Measurement of Remaining Frequency Bands 
     (b-1) First Example (Without Measurement) 
     As a first example, the control unit  253  instructs the terminal device  100 - 1  to perform the measurement of each of the one or more frequency bands and not to perform measurement of each of the remaining frequency bands among the plurality of frequency bands. 
     The control unit  253  may substitute a result of measurement of a first frequency band included in the one or more frequency bands with a result of measurement of a second frequency band included in the remaining frequency bands. For example, the control unit  253  substitutes a result of measurement of the first frequency band with a result of measurement of the second frequency band and thus may perform a handover decision. As an example, the second frequency band may be a frequency band that is adjacent to the first frequency band. Accordingly, for example, a frequency band that is not actually measured may be selected as a frequency band that is used by the terminal device  100 - 1 . 
     (b-2) Second Example (Measurement at Low Frequency) 
     As a second example, the control unit  253  instructs the terminal device  100 - 1  to perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     As a specific example, the control unit  253  instructs the terminal device  100 - 1  to perform the measurement of each of the remaining frequency bands using fewer measurement gaps than measurement gaps used for the measurement of each of the one or more frequency bands. 
     As an example, the control unit  253  instructs the terminal device  100 - 1  to skip a part of measurement gaps assigned to each of the remaining frequency bands without measurement. 
     As another example, the control unit  253  may instruct the terminal device  100 - 1  to assign fewer measurement gaps to each of the remaining frequency bands than to each of the one or more frequency bands. Alternatively, the control unit  253  may decide measurement gap assignment such that the measurement gaps assigned to each of the remaining frequency bands are fewer than measurement gaps assigned to each of the one or more frequency bands. Thus, the control unit  253  may instruct the terminal device  100 - 1  to perform the decided assignment. 
     (c) Specific Process 
     For example, the control unit  253  performs an instruction according to individual signaling to the terminal device  100 - 1 . For example, the individual signaling is RRC signaling. 
     As an example, the control unit  253  may transmit an RRC connection reconfiguration message including a measurement configuration through the antenna unit  210  and the wireless communication unit  220 , and thus may perform the instruction. 
     &lt;3.3. Process Flow&gt; 
     Next, examples of processes according to the first embodiment will be described with reference to  FIG. 17  and  FIG. 18 . 
     (First Example: Without Measurement) 
       FIG. 17  is a sequence diagram illustrating a first example of a schematic flow of a process according to the first embodiment. 
     The base station  200 - 1  (the information acquiring unit  251 ) acquires information about a plurality of frequency bands that are not used by the terminal device  100 - 1  (S 401 ). 
     Then, the base station  200 - 1  (the control unit  253 ) instructs the terminal device  100 - 1  to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands and not to perform measurement of each of the remaining frequency bands among the plurality of frequency bands (S 403 ). 
     Then, the terminal device  100 - 1  (the measurement unit  143 ) performs measurement of each of the one or more frequency bands (S 405 ). The terminal device  100 - 1  (the measurement unit  143 ) does not perform measurement of each of the remaining frequency bands. 
     Then, the terminal device  100 - 1  (the reporting unit  145 ) reports a result of the measurement to the base station  200 - 1  (S 407 ). 
     (Second Example: Measurement at Low Frequency) 
       FIG. 18  is a sequence diagram illustrating a second example of a schematic flow of a process according to the first embodiment. 
     The base station  200 - 1  (the information acquiring unit  251 ) acquires information about a plurality of frequency bands that are not used by the terminal device  100 - 1  (S 411 ). 
     Then, the base station  200 - 1  (the control unit  253 ) instructs the terminal device  100 - 1  to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands and perform measurement of each of the remaining frequency bands among the plurality of frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands (S 413 ). 
     Then, the terminal device  100 - 1  (the measurement unit  143 ) performs measurement of each of the one or more frequency bands, and performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands (S 415 ). 
     Then, the terminal device  100 - 1  (the reporting unit  145 ) reports a result of the measurement to the base station  200 - 1  (S 417 ). 
     &lt;3.4. Modification Example&gt; 
     Next, a modification example of the first embodiment will be described with reference to  FIG. 19  to  FIG. 21 . 
     As described above, for example, the measurement of each of the one or more frequency bands is measurement based on a reference signal transmitted in each of the one or more frequency bands. In addition, the measurement of each of the remaining frequency bands is measurement based on a reference signal transmitted in each of the remaining frequency bands. In addition, in the above-described example of the first embodiment, the reference signal is a CRS. Conversely, in the modification example of the first embodiment, the reference signal is a discovery reference signal (DRS). 
     (Terminal Device  100 - 1 : Measurement Unit  143 ) 
     (b) Measurement 
     (b-1) Measurement Based on Reference Signal 
     As described above, for example, the measurement of each of the one or more frequency bands is measurement based on a reference signal transmitted in each of the one or more frequency bands. In addition, the measurement of each of the remaining frequency bands is measurement based on a reference signal transmitted in each of the remaining frequency bands. 
     Specifically, in the modification example of the first embodiment, the reference signal is a discovery reference signal (DRS). Accordingly, for example, it is possible to reduce a measurement load regarding a small cell in the off state. 
     The DRS is a reference signal that is transmitted by a base station of the small cell in an off state. The DRS may also be referred to as a discovery signal (DR). 
     (b-2) Measurement of Remaining Frequency Bands 
     —First Example (Without Measurement) 
     As a first example, the measurement unit  143  does not perform the measurement of each of the remaining frequency bands. Hereinafter, this will be described with reference to a specific example of  FIG. 19 . 
       FIG. 19  is an explanatory diagram for describing a first example of measurement according to a modification example of the first embodiment. As illustrated in  FIG. 19 , a DRS is transmitted in a CC0 and a CC1. In this example, in the terminal device  100 - 1 , inter-frequency measurement of the CC0 is performed. Conversely, inter-frequency measurement of the CC1 is not performed. 
     —Second Example (Measurement at Low Frequency) 
     As a second example, the measurement unit  143  performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     As an example, the measurement unit  143  skips a part of measurement gaps assigned to each of the remaining frequency bands without measurement. Hereinafter, this will be described with reference to a specific example of  FIG. 20 . 
       FIG. 20  is an explanatory diagram for describing a second example of measurement according to a modification example of the first embodiment. As illustrated in  FIG. 20 , a DRS is transmitted in a CC0 and a CC1. In this example, the same number of measurement gaps is assigned to the CC0 and the CC1. The terminal device  100 - 1  performs measurement of the CC0 using all measurement gaps assigned to the CC0. Conversely, the terminal device  100 - 1  skips a part of all measurement gaps assigned to the CC1 without measurement of the CC1 and performs measurement of the CC1 using the rest of the all measurement gaps assigned to the CC1. 
     As another example, measurement gaps assigned to each of the remaining frequency bands may be fewer than measurement gaps assigned to each of the one or more frequency bands. Hereinafter, this will be described with reference to a specific example of  FIG. 21 . 
       FIG. 21  is an explanatory diagram for describing a third example of measurement according to a modification example of the first embodiment. As illustrated in  FIG. 21 , a DRS is transmitted in a CC0 and a CC1. In this example, more measurement gaps are assigned to the CC0 and fewer measurement gaps are assigned to the CC1. The terminal device  100 - 1  performs measurement of the CC0 using the more measurement gaps assigned to the CC0, and performs measurement of the CC1 using the fewer measurement gaps assigned to the CC1. 
     4. Second Embodiment 
     Next, a second embodiment of the present disclosure will be described with reference to  FIG. 22  to  FIG. 30 . 
     A terminal device  100 - 2  according to the second embodiment performs measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap, and performs measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. Specifically, in the second embodiment, the reference signal transmitted in the second frequency band is a DRS. That is, in the second embodiment, the terminal device  100 - 2  performs measurement of a frequency group including the first frequency band and the second frequency band using the measurement gap. Accordingly, for example, it is possible to improve measurement performed by a terminal device  100 - 3 . 
     &lt;4.1. Configuration of Terminal Device&gt; 
     First, an example of a configuration of the terminal device  100 - 2  according to the second embodiment will be described with reference to  FIG. 22  to  FIG. 25 .  FIG. 22  is a block diagram illustrating an example of a configuration of the terminal device  100 - 2  according to the second embodiment. As illustrated in  FIG. 22 , the terminal device  100 - 2  includes the antenna unit  110 , the wireless communication unit  120 , the storage unit  130  and a processing unit  150 . 
     There is no difference in descriptions of the antenna unit  110 , the wireless communication unit  120  and the storage unit  130  between the first embodiment and the second embodiment except for different reference numerals. Therefore, redundant descriptions will be omitted here, and only the processing unit  150  will be described. 
     (Processing Unit  150 ) 
     The processing unit  150  provides various functions of the terminal device  100 - 2 . The processing unit  150  includes an information acquiring unit  151 , a measurement unit  153  and a reporting unit  155 . The processing unit  150  may further include a component other than these components. That is, the processing unit  150  may also perform an operation other than operations of these components. 
     (Information Acquiring Unit  151 ) 
     The information acquiring unit  151  acquires information indicating a first frequency band in which a DRS is transmitted within at least a first period included in a measurement gap. Specifically, in the second embodiment, the information acquiring unit  151  acquires information indicating a frequency group including the first frequency band and a second frequency band. For example, the second frequency band is a frequency band in which a DRS is transmitted within at least a second period included in the measurement gap. 
     In addition, the information acquiring unit  151  acquires information indicating the measurement gap. 
     For example, a base station  200 - 2  notifies the terminal device  100 - 2  of the frequency group and the measurement gap. As a specific example, the base station  200 - 2  transmits information indicating the frequency group and information indicating the measurement gap to the terminal device  100 - 2 . As an example, the base station  200 - 2  transmits an RRC connection reconfiguration message including a measurement configuration including the information indicating the frequency group and the information indicating the measurement gap to the terminal device  100 - 2 . Then, the information acquiring unit  151  acquires the information indicating the frequency group and the information indicating the measurement gap. 
     (Measurement Unit  153 ) 
     The measurement unit  153  performs measurement of a frequency band. 
     In the second embodiment, the measurement unit  153  performs measurement of a first frequency band based on a DRS transmitted in the first frequency band within a first period included in a measurement gap. In addition, the measurement unit  153  performs measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 3 . 
     (a) Frequency Band 
     Component Carrier (CC) 
     For example, the first frequency band and the second frequency band each are component carriers (CCs) of carrier aggregation. 
     —Frequency Band of Small Cell 
     For example, each of the first frequency band and the second frequency band is a frequency band that is used by a base station of a small cell. 
     —Frequency Band that is Not Used 
     For example, each of the first frequency band and the second frequency band is a frequency band that is not used by the terminal device  100 - 2 . 
     In view of the above points, for example, each of the first frequency band and the second frequency band is a CC that is used by a base station of a small cell, and the CC is not used by the terminal device  100 - 2 . 
     (b) Measurement 
     The measurement of the first frequency band and the measurement of the second frequency band are RRM measurements, for example, measurements of reception power or reception quality. As a specific example, the measurement of the first frequency band and the measurement of the second frequency band are measurements of RSRP or RSRQ. 
     In addition, for example, measurement is performed in units of a combination of a frequency band and a cell (a base station). For example, the measurement of the first frequency band is performed for each cell in which the first frequency band is used (that is, a base station that uses the first frequency band). In addition, for example, the measurement of the second frequency band is performed for each cell in which the second frequency band is used (that is, a base station that uses the second frequency band). 
     (c) Reference Signal 
     Specifically, in the second embodiment, the reference signal transmitted in the second frequency band is a DRS. That is, the measurement unit  153  performs measurement of the first frequency band and the second frequency band in which a DRS is transmitted using the measurement gap. 
     The DRS is a reference signal that is transmitted by a base station of a small cell in the off state. The DRS may also be referred to as a discovery signal (DR). 
     (d) Measurement Gap 
     For example, the measurement gap is a period having a length of 6 milliseconds. That is, the measurement gap is a general measurement gap. 
     For example, each of the first period and the second period is a period shorter than 6 milliseconds. That is, a shorter period is used for measurement based on a DRS than general measurement based on a CRS. 
     (e) Specific Example of Measurement 
     Hereinafter, a first example of measurement according to the second embodiment will be described with reference to  FIG. 23 . 
       FIG. 23  is an explanatory diagram for describing a first example of measurement according to the second embodiment. Referring to  FIG. 23 , a measurement gap having a length of 6 subframes is shown. In this example, the measurement unit  153  performs measurement of a CC1 based on a DRS transmitted in the CC1 (a first frequency band) within a period (a first period) from a 1st subframe to a 3rd subframe within the measurement gap. In addition, the measurement unit  153  performs measurement of a CC2 based on a DRS transmitted in the CC2 (a second frequency band) within a period (a second period) from a 4th subframe to a 6th subframe within the measurement gap. 
     When measurement of the first frequency band and measurement of the second frequency band are collectively performed using the measurement gap, for example, it is possible to perform measurement of the first frequency band and measurement of the second frequency band using fewer measurement gaps. Therefore, measurement based on a DRS (that is, inter-frequency measurement of a frequency band that is used by a base station of a small cell) may be efficiently performed. As a specific example, measurement based on a DRS may be performed more quickly. 
     In addition, as described above, when measurement based on a DRS is performed using a short period, it is possible to actually perform measurement of two frequency bands (or two or more frequency bands) using the same measurement gap. 
     (f) Measurement of Additional Frequency Band 
     The measurement gap may include an additional period. The measurement unit  153  may perform measurement of an additional frequency band based on a DRS transmitted in the additional frequency band within the additional period. Hereinafter, this will be described with reference to a specific example of  FIG. 24 . 
       FIG. 24  is an explanatory diagram for describing a second example of measurement according to the second embodiment. Referring to  FIG. 24 , a measurement gap having a length of 6 subframes is shown. In this example, the measurement unit  153  performs measurement of a CC1 based on a DRS transmitted in the CC1 (a first frequency band) within a period (a first period) including a 1st subframe and a 2nd subframe within the measurement gap. In addition, the measurement unit  153  performs measurement of a CC2 based on a DRS transmitted in the CC2 (a second frequency band) within a period (a second period) including a 3rd subframe and a 4th subframe within the measurement gap. Further, the measurement unit  153  performs measurement of a CC3 based on a DRS transmitted in the CC3 (an additional frequency band) within a period (an additional period) including a 5th subframe and a 6th subframe within the measurement gap. 
     Accordingly, measurement based on a DRS (that is, inter-frequency measurement) may be further efficiently performed. 
     While an example in which the measurement gap includes one additional period and the measurement unit  153  performs measurement of one additional frequency band has been described, it should be understood that the second embodiment is not limited thereto. The measurement gap may include two or more additional periods and the measurement unit  153  may perform measurement of two or more additional frequency bands. 
     (g) Measurement Based on CRS and DRS 
     The measurement unit  153  may perform the measurement of the first frequency band that is used by the same base station based on a DRS and a CRS transmitted by the same base station in the first frequency band within the first period. Additionally or alternatively, the measurement unit  153  may perform the measurement of the second frequency band that is used by the same base station based on a DRS and a CRS transmitted by the same base station in the second frequency band within the second period. In this case, the first period may be a period shorter than 6 milliseconds. 
     As a specific example, a base station of a small cell in the on state transmits both a DRS and a CRS in the first frequency band. In this case, the measurement unit  153  may perform measurement of the first frequency band that is used by the base station based on the DRS and the CRS transmitted by the base station in the first frequency band within the first period. Hereinafter, hereinafter, this will be described with reference to a specific example of  FIG. 25 . 
       FIG. 25  is an explanatory diagram for describing a third example of measurement according to the second embodiment. Referring to  FIG. 25 , a measurement gap having a length of 6 subframes is shown. In this example, the measurement unit  153  performs measurement of a CC1 based on a DRS and a CRS transmitted by the same base station using the CC1 (a first frequency band) within a period (a first period) from a 1st subframe to a 4th subframe within the measurement gap. In addition, the measurement unit  153  performs measurement of a CC2 based on a DRS transmitted in the CC2 (a second frequency band) within a period (a second period) including a 5th subframe and a 6th subframe within the measurement gap. 
     Accordingly, for example, measurement of the first frequency band or the second frequency band (that is, inter-frequency measurement) is performed based on more reference signals. Therefore, the measurement of the first frequency band or the second frequency band used by the base station may be performed using a shorter period than when it is performed based on only a CRS. Therefore, measurement of the first frequency band and measurement of the second frequency band (that is, measurement of a frequency band that is used by a base station of a small cell in the on state and measurement of a frequency band that is used by a base station of another small cell) may be performed using the same measurement gap. 
     (h) Priority 
     —Measurement Based on Priority 
     For example, the measurement unit  153  performs measurement of a frequency group and measurement of one or more other frequency bands or measurement of one or more other frequency groups based on a priority of the frequency group including the first frequency band and the second frequency band and a priority of the one or more other frequency bands or a priority of the one or more other frequency groups. 
     As a specific example, a frequency group or a frequency band having a higher priority is sequentially selected from among the frequency group including the first frequency band and the second frequency band, the one or more other frequency bands, and the one or more other frequency groups. Then, the measurement unit  153  performs measurement of the selected frequency group or frequency band. 
     As an example, the priority of the frequency band is a priority included in an inter-frequency NCL contained in the SIB5. As another example, the priority of the frequency band may be a priority that is decided by the terminal device  100 - 2 . 
     The priority of the frequency group (and/or a priority of each of the one or more other frequency groups) may be decided in consideration of power consumption and/or a communication request of the terminal device  100 - 2 . As an example, when suppression of power consumption is requested, the priority of the frequency group may be higher. This is because, when the priority of the frequency group is high, measurement of more frequency bands is performed using a measurement gap. As another example, when high throughput is requested, the priority of the frequency group may be lower. This is because, when the priority of the frequency group is low, measurement of a frequency band that is used by a base station of a cell in the on state is preferentially performed, and, as a result, a handover is preferentially performed without a transition time. 
     —Measurement in Consideration of Transmission Period of DRS 
     For example, the measurement unit  153  performs the measurement of the frequency group, and the measurement of the one or more other frequency bands or the measurement of the one or more other frequency groups in consideration of a transmission period in which a DRS is transmitted in the first frequency band. As a specific example, the measurement unit  153  performs measurement of another frequency band or another frequency group whose priority is lower than the frequency group before the measurement of the frequency group outside of the transmission period. 
     Accordingly, for example, measurement may be performed more smoothly without wasting the measurement gap. 
     (Reporting Unit  155 ) 
     The reporting unit  155  reports a result of measurement of the frequency band to the base station  200 - 2 . 
     For example, the reporting unit  155  reports a result of measurement of the first frequency band to the base station  200 - 2 . In addition, for example, the reporting unit  155  reports a result of measurement of the second frequency band to the base station  200 - 2 . In addition, the frequency group may include an additional frequency band, and the reporting unit  155  may report a result of measurement of the additional frequency band to the base station  200 - 2 . 
     &lt;4.2. Configuration of Base Station&gt; 
     Next, an example of a configuration of the base station  200 - 2  according to the second embodiment will be described with reference to  FIG. 26 .  FIG. 26  is a block diagram illustrating an example of a configuration of the base station  200 - 2  according to the second embodiment. Referring to  FIG. 26 , the base station  200 - 2  includes an antenna unit  210 , a wireless communication unit  220 , a network communication unit  230 , a storage unit  240 , and a processing unit  260 . 
     There is no difference in descriptions of the antenna unit  210 , the wireless communication unit  220 , the network communication unit  230  and the storage unit  240  between the first embodiment and the second embodiment except for different reference numerals. Therefore, redundant descriptions will be omitted here, and only the processing unit  260  will be described. 
     (Processing Unit  260 ) 
     The processing unit  260  provides various functions of the base station  200 - 2 . The processing unit  260  includes an information acquiring unit  261  and a control unit  263 . The processing unit  260  may further include any other component in addition to the above-mentioned components. In other words, the processing unit  260  may also perform an operation other than operations of the above-mentioned components. 
     (Information Acquiring Unit  261 ) 
     (a) Frequency Group 
     The information acquiring unit  261  acquires information indicating a first frequency band in which a DRS is transmitted within at least a first period included in a measurement gap. 
     For example, the measurement gap further includes a second period in which a reference signal is transmitted in a second frequency band. 
     Specifically, in the second embodiment, the information acquiring unit  261  acquires information indicating the frequency group including the first frequency band and the second frequency band. The second frequency band is a frequency band in which a DRS is transmitted within at least a second period included in the measurement gap. 
     More specifically, for example, a control entity  300 - 2  decides the frequency group and notifies the base station  200 - 2  of the frequency group. Then, the information indicating the frequency group is stored in the storage unit  240 . The information acquiring unit  261  acquires the information indicating the frequency group at any time thereafter. 
     (b) Measurement Gap 
     Further, for example, the information acquiring unit  261  acquires information indicating the measurement gap. 
     More specifically, for example, the control entity  300 - 2  decides the measurement gap and notifies the base station  200 - 2  of the measurement gap. Then, information indicating the measurement gap is stored in the storage unit  240 . The information acquiring unit  261  acquires the information indicating the measurement gap at any time thereafter. 
     Alternatively, the measurement gap is decided by a device other than the control entity  300 - 2  and the base station  200 - 2  may be notified thereof. Alternatively, the measurement gap is decided by the base station  200 - 2 , and may be stored in the storage unit  240 . 
     (Control Unit  263 ) 
     (a) Notification of Frequency Group and Measurement Gap 
     The control unit  263  notifies the terminal device  100 - 2  of the first frequency band and the measurement gap. Specifically, in the second embodiment, the control unit  263  notifies the terminal device  100 - 2  of the frequency group including the first frequency band and the second frequency band and the measurement gap. 
     As a specific example, the control unit  263  transmits information indicating the frequency group and information indicating the measurement gap to the terminal device  100 - 2  through the antenna unit  210  and the wireless communication unit  220 . As an example, the control unit  263  transmits an RRC connection reconfiguration message including a measurement configuration including the information indicating the frequency group and the information indicating the measurement gap to the terminal device  100 - 2  through the antenna unit  210  and the wireless communication unit  220 . 
     (b) Priority Notification 
     For example, the control unit  263  notifies the terminal device  100 - 2  of a priority of the frequency group and a priority of one or more other frequency bands or a priority of one or more other frequency groups. 
     As a specific example, the control unit  263  transmits information indicating the priority of the frequency group and the priority of one or more other frequency bands or the priority of one or more other frequency groups to the terminal device  100 - 2  through the antenna unit  210  and the wireless communication unit  220 . As an example, the information is included in the inter-frequency NCL within the SIB5, and the control unit  263  informs the terminal device  100 - 2  of the SIB5 including the inter-frequency NCL through the antenna unit  210  and the wireless communication unit  220 . 
     &lt;4.3. Configuration of Control Entity&gt; 
     Next, an example of a configuration of the control entity  300 - 2  according to the second embodiment will be described with reference to  FIG. 27 .  FIG. 27  is a block diagram illustrating an example of a configuration of the control entity  300 - 2  according to the second embodiment. Referring to  FIG. 27 , the control entity  300 - 2  includes a communication unit  310 , a storage unit  320 , and a processing unit  330 . 
     (Communication Unit  310 ) 
     The communication unit  310  communicates with other nodes. For example, the communication unit  310  communicates with a core network node and a base station. For example, the communication unit  310  communicates with the base station  200 - 2 . 
     (Storage Unit  320 ) 
     The storage unit  320  temporarily or permanently stores a program and data for an operation of the control entity  300 - 2 . 
     (Processing Unit  330 ) 
     The processing unit  330  provides various functions of the control entity  300 - 2 . The processing unit  330  includes an information acquiring unit  331  and a control unit  333 . The processing unit  330  may further include any other component in addition to the above-mentioned components. In other words, the processing unit  330  may also perform an operation other than operations of the above-mentioned components. 
     (Information Acquiring Unit  331 ) 
     The information acquiring unit  331  acquires information about two or more frequency bands in which a DRS is transmitted. 
     Each of the two or more frequency bands is a frequency band that is used by a base station of a small cell. When a base station of a small cell in the off state transmits a DRS and a base station of a small cell in the on state does not transmit a DRS, each of the two or more frequency bands is a frequency band that is used by the base station of the small cell in the off state. Conversely, when a base station of a small cell transmits a DRS regardless of an on/off state, each of the two or more frequency bands is a frequency band that is used by the base station of the small cell. 
     (Control Unit  333 ) 
     (a) Decision of Frequency Group 
     The control unit  333  decides a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands. 
     The first frequency band is a frequency band in which a DRS is transmitted within at least a first period included in a measurement gap. In addition, the second frequency band is a frequency band in which a DRS is transmitted within at least a second period included in the measurement gap. 
     In addition, for example, the control unit  333  decides the measurement gap. 
     (a-1) First Method 
     For example, as a first method, the control unit  333  controls a transmission period in which a DRS is transmitted in a first frequency band such that the DRS is transmitted in the first frequency band within at least the first period or controls a transmission period in which a DRS is transmitted in a second frequency band such that the DRS is transmitted in the second frequency band within at least the second period. 
     More specifically, for example, the control unit  333  decides a frequency group including at least the first frequency band and the second frequency band among the two or more frequency bands. For example, the frequency group is any frequency band among the two or more frequency bands and the number thereof is equal to or less than a predetermined maximum number. For example, when a measurement gap has a length of M subframes (for example, 6 subframes) and a period used for measurement based on a DRS is N subframes (for example, 3 subframes), the predetermined maximum number is M/N (for example, 2). Further, the control unit  333  decides the measurement gap. Then, the control unit  333  instructs a base station that transmits a DRS in each of the frequency bands included in the frequency group to transmit the DRS during the measurement gap. For example, the control unit  333  instructs a base station that transmits a DRS in the first frequency band and a base station that transmits a DRS in the second frequency band to transmit the DRSs during the measurement gap. 
     Accordingly, for example, it is possible to more reliably perform measurement of two or more frequency bands using the same measurement gap. 
     (a-2) Second Method 
     As a second method, the information about the two or more frequency bands (that is, information acquired by the information acquiring unit  331 ) may include information indicating a transmission period in which a DRS is transmitted in each of the two or more frequency bands. Then, the control unit  333  may decide the frequency group based on the transmission period. 
     More specifically, for example, based on the information indicating a transmission period in which a DRS is transmitted in each of the two or more frequency bands, the control unit  333  decides at least two frequency bands whose transmission periods of the DRSs are the same (or similar) among the two or more frequency bands as a frequency group. The control unit  333  decides frequency bands whose number is equal to or less than a predetermined maximum number as a frequency group. In addition, the control unit  333  decides a measurement gap that overlaps the transmission period of the DRS. 
     Accordingly, for example, it is possible to perform measurement of each of the two or more frequency bands using the same measurement gap without the control entity  300 - 2  instructing a base station. 
     (b) Provide Notification to Base Station  200 - 2   
     For example, the control unit  333  notifies the base station  200 - 2  of the frequency group. In addition, for example, the control unit  333  notifies the base station  200 - 2  of the measurement gap. 
     As a specific example, the control unit  333  transmits a message including information indicating the frequency group and information indicating the measurement gap to the base station  200 - 2  through the communication unit  310 . 
     &lt;4.4. Process Flow&gt; 
     Next, examples of processes according to the second embodiment will be described with reference to  FIG. 28  to  FIG. 30 . 
     (Overall Process Flow) 
       FIG. 28  is a sequence diagram illustrating an example of a schematic flow of a process according to the second embodiment. 
     The control entity  300 - 2  performs a frequency group decision process (S 430 ). That is, the control entity  300 - 2  (the control unit  333 ) decides a frequency group including at least a first frequency band and a second frequency band among two or more frequency bands in which a DRS is transmitted. In addition, for example, the control entity  300 - 2  decides a measurement gap that is used for measurement of the frequency group. 
     Then, the control entity  300 - 2  notifies the base station  200 - 2  of the frequency group and the measurement gap (S 451 ). 
     Further, the base station  200 - 2  notifies the terminal device  100 - 2  of the frequency group and the measurement gap (S 453 ). 
     Then, the terminal device  100 - 2  (the measurement unit  153 ) performs measurement of the frequency group (S 455 ). Specifically, the measurement unit  153  performs measurement of the first frequency band based on a DRS transmitted in the first frequency band within a first period included in the measurement gap. In addition, the measurement unit  153  performs measurement of the second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. 
     Then, the terminal device  100 - 2  (the reporting unit  155 ) reports a result of measurement of the frequency band to the base station  200 - 2  (S 457 ). 
     (Frequency Group Decision Process) 
     (a) First Example 
       FIG. 29  is a sequence diagram illustrating a first example of a schematic flow of a frequency group decision process according to the second embodiment. 
     The processing unit  330  determines whether two or more frequency bands in which a DRS is transmitted exist (S 431 ). When two or more frequency bands do not exist (NO in S 431 ), the process ends. 
     When two or more frequency bands in which a DRS is transmitted exist (YES in S 431 ), the information acquiring unit  331  acquires information about the two or more frequency bands in which a DRS is transmitted (S 433 ). 
     Then, the control unit  333  decides a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands (S 435 ). 
     In addition, the control unit  333  decides a measurement gap (S 437 ). 
     Then, the control unit  333  controls a transmission period in which a DRS is transmitted in the first frequency band such that the DRS is transmitted in the first frequency band within at least a first period included in the measurement gap (S 438 ). For example, the control unit  333  instructs a base station that transmits a DRS in the first frequency band to transmit the DRS during the measurement gap. 
     In addition, the control unit  333  controls a transmission period in which a DRS is transmitted in the second frequency band such that the DRS is transmitted in the second frequency band within at least a second period included in the measurement gap (S 439 ). For example, the control unit  333  instructs a base station that transmits a DRS in the second frequency band to transmit the DRS during the measurement gap. Then, the process ends. 
     (b) Second Example 
       FIG. 30  is a sequence diagram illustrating a second example of a schematic flow of a frequency group decision process according to the second embodiment. 
     The processing unit  330  determines whether two or more frequency bands in which a DRS is transmitted exist (S 441 ). When two or more frequency bands do not exist (NO in S 441 ), the process ends. 
     When two or more frequency bands in which a DRS is transmitted exist (YES in S 441 ), the information acquiring unit  331  acquires information about the two or more frequency bands in which a DRS is transmitted (S 443 ). The information about the two or more frequency bands includes information indicating a transmission period in which a DRS is transmitted in each of the two or more frequency bands. 
     Then, the control unit  333  determines whether at least two frequency bands whose transmission periods of a DRS are the same (or similar) are included in the two or more frequency bands (S 445 ). When the at least two frequency bands are not included (NO in S 445 ), the process ends. 
     When the at least two frequency bands are included (YES in S 445 ), the control unit  333  decides a frequency group including at least two frequency bands (at least a first frequency band and a second frequency band) whose transmission periods of a DRS are the same (or similar) among the two or more frequency bands (S 447 ). 
     In addition, the control unit  333  decides a measurement gap that overlaps the transmission period of the DRS (S 449 ). Then, the process ends. 
     &lt;4.5. First Modification Example&gt; 
     Next, a first modification example of the second embodiment will be described. 
     In the first modification example of the second embodiment, the base station  200 - 2  decides the frequency group (and the measurement gap) instead of the control entity  300 - 2 . Then, the base station  200 - 2  notifies the terminal device  100 - 2  of the frequency group (and the measurement gap) it decided. 
     For example, in the first modification example of the second embodiment, the processing unit  260  of the base station  200 - 2  further includes the information acquiring unit  331  and the control unit  333 . 
     &lt;4.6. Second Modification Example&gt; 
     Next, a second modification example of the second embodiment will be described. 
     In the first modification example of the second embodiment, the terminal device  100 - 2  decides the frequency group (and the measurement gap) instead of the control entity  300 - 2 . Then, the base station  200 - 2  performs measurement of the frequency group it decided. 
     (Terminal Device  100 - 2 : Processing Unit  150 ) 
     In the second modification example of the second embodiment, the processing unit  150  decides a frequency group including at least a first frequency band and a second frequency band among two or more frequency bands in which a DRS is transmitted. In addition, for example, the processing unit  150  decides a measurement gap that is used for measurement of the frequency group. 
     As a specific example, the base station  200 - 2  notifies the terminal device  100 - 2  of two or more frequency bands in which a DRS is transmitted. For example, the base station  200 - 2  informs of the inter-frequency NCL (SIB5) including information indicating whether a DRS is transmitted for each frequency band and a transmission period of a DRS. For example, the processing unit  150  decides at least two frequency bands whose transmission periods of a DRS are the same (or similar) among the two or more frequency bands as a frequency group based on information about the transmission period. The processing unit  150  decides frequency bands whose number is equal to or less than a predetermined maximum number as a frequency group. In addition, the processing unit  150  decides a measurement gap that overlaps the same transmission period. 
     (Terminal Device  100 - 2 : Information Acquiring Unit  151 ) 
     As described above, the information acquiring unit  151  acquires information indicating the frequency group including the first frequency band and the second frequency band. In addition, the information acquiring unit  151  acquires information indicating the measurement gap. 
     In the second modification example of the second embodiment, for example, as described above, the processing unit  150  decides the frequency group and the measurement gap. Then, the information acquiring unit  151  acquires information indicating the decided frequency group and information indicating the decided measurement gap. 
     5. Third Embodiment 
     Next, a third embodiment of the present disclosure will be described with reference to  FIG. 31  to  FIG. 40 . 
     The terminal device  100 - 3  according to the third embodiment performs measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap, and performs measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. Specifically, in the third embodiment, the measurement gap is an extended measurement gap. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 3 . 
     &lt;5.1. Configuration of Terminal Device&gt; 
     First, examples of configurations of the terminal device  100 - 3  according to the third embodiment will be described with reference to  FIG. 31  to  FIG. 35 .  FIG. 31  is a block diagram illustrating an example of a configuration of the terminal device  100 - 3  according to the third embodiment. As illustrated in  FIG. 31 , the terminal device  100 - 3  includes the antenna unit  110 , the wireless communication unit  120 , the storage unit  130  and a processing unit  160 . 
     There is no difference in descriptions of the antenna unit  110 , the wireless communication unit  120  and the storage unit  130  between the first embodiment and the third embodiment except for different reference numerals. Therefore, redundant descriptions will be omitted here, and only the processing unit  160  will be described. 
     (Processing Unit  160 ) 
     The processing unit  160  provides various functions of the terminal device  100 - 3 . The processing unit  160  includes an information acquiring unit  161 , a measurement unit  163  and a reporting unit  165 . The processing unit  160  may further include a component other than these components. That is, the processing unit  160  may also perform an operation other than operations of these components. 
     (Information Acquiring Unit  161 ) 
     The information acquiring unit  161  acquires information indicating a first frequency band in which a DRS is transmitted within at least a first period included in a measurement gap. For example, the information acquiring unit  161  acquires information indicating a frequency group including the first frequency band and a second frequency band. Specifically, in the third embodiment, the measurement gap is an extended measurement gap. In addition, for example, the second frequency band is a frequency band in which a reference signal is transmitted within at least a second period included in the measurement gap (that is, the extended measurement gap). 
     In addition, the information acquiring unit  161  acquires information indicating the measurement gap. The measurement gap (that is, the extended measurement gap) will be described below in detail. 
     For example, a base station  200 - 3  notifies the terminal device  100 - 3  of the first frequency band (or the frequency group) and the measurement gap. As a specific example, the base station  200 - 3  transmits information indicating the first frequency band (or the frequency group) and information indicating the measurement gap to the terminal device  100 - 3 . As an example, the base station  200 - 3  transmits an RRC connection reconfiguration message including a measurement configuration including the information indicating the first frequency band (or the frequency group) and the information indicating the measurement gap to the terminal device  100 - 3 . Then, the information acquiring unit  161  acquires the information indicating the first frequency band (or the frequency group) and the information indicating the measurement gap. 
     (Measurement Unit  163 ) 
     The measurement unit  163  performs measurement of a frequency band. 
     In the third embodiment, the measurement unit  163  performs measurement of a first frequency band based on a DRS transmitted in the first frequency band within a first period included in a measurement gap. In addition, the measurement unit  163  performs measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 3 . 
     (a) Frequency Band 
     —Component Carrier (CC) 
     For example, each of the first frequency band and the second frequency band is a component carrier (CC) of carrier aggregation. 
     —Frequency Band of Small Cell 
     For example, each of the first frequency band and the second frequency band is a frequency band that is used by a base station of a small cell. 
     —Frequency Band that is Not Used 
     For example, each of the first frequency band and the second frequency band is a frequency band that is not used by the terminal device  100 - 3 . 
     In view of the above points, for example, each of the first frequency band and the second frequency band is a CC that is used by a base station of a small cell, and the CC is not used by the terminal device  100 - 3 . 
     (b) Measurement 
     The measurement of the first frequency band and the measurement of the second frequency band are RRM measurement, for example, measurement of reception power or reception quality. As a specific example, the measurement of the first frequency band and the measurement of the second frequency band are measurement of RSRP or RSRQ. 
     In addition, for example, measurement is performed in units of a combination of a frequency band and a cell (a base station). For example, the measurement of the first frequency band is performed for each cell in which the first frequency band is used (that is, a base station that uses the first frequency band). In addition, for example, the measurement of the second frequency band is performed for each cell in which the second frequency band is used (that is, a base station that uses the second frequency band). 
     (c) Reference Signal 
     For example, the reference signal transmitted in the second frequency band is a CRS. That is, the measurement unit  163  performs measurement of the first frequency band in which a DRS is transmitted and measurement of the second frequency band in which a CRS is transmitted using the measurement gap. 
     Alternatively, the reference signal transmitted in the second frequency band may be a DRS. 
     The DRS is a reference signal that is transmitted by a base station of the small cell in the off state. The DRS may also be referred to as a discovery signal (DR). 
     (d) Measurement Gap 
     Specifically, in the third embodiment, the measurement gap is an extended measurement gap. More specifically, for example, the extended measurement gap is a period longer than 6 milliseconds (ms). For example, a general measurement gap (that is, a measurement gap that is not extended) is a period having a length of 6 ms. 
     Further, for example, the first period is a period shorter than the second period. As described above, for example, since the reference signal transmitted in the second frequency band within the second period is a CRS, a shorter period is used for measurement of the first frequency band based on a DRS than measurement of the second frequency band based on a CRS. 
     (e) Specific Example of Measurement 
     Hereinafter, examples of measurement according to the third embodiment will be described with reference to  FIG. 32  and  FIG. 33 . 
       FIG. 32  is an explanatory diagram for describing a first example of measurement according to the third embodiment. Referring to  FIG. 32 , an extended measurement gap having a length of 8 subframes is shown. In this example, the measurement unit  163  performs measurement of a CC2 based on a CRS transmitted in the CC2 (a second frequency band) within a period (a second period) from a 1st subframe to a 6th subframe within the extended measurement gap. In addition, the measurement unit  163  performs measurement of a CC1 based on a DRS transmitted in the CC1 (a first frequency band) within a period (a first period) including a 7th subframe and an 8th subframe within the extended measurement gap. 
       FIG. 33  is an explanatory diagram for describing a second example of measurement according to the third embodiment. Referring to  FIG. 33 , an extended measurement gap having a length of 8 subframes is shown. In this example, the measurement unit  163  performs measurement of a CC1 based on a DRS transmitted in the CC1 (a first frequency band) within a period (a first period) including a 1st subframe and a 2nd subframe within the extended measurement gap. In addition, the measurement unit  163  performs measurement of a CC2 based on a CRS transmitted in the CC2 (a second frequency band) within a period (a second period) from a 3rd subframe to an 8th subframe within the extended measurement gap. 
     When measurement of the first frequency band and measurement of the second frequency band are collectively performed using the extended measurement gap, for example, it is possible to perform measurement of the first frequency band and measurement of the second frequency band using fewer measurement gaps. For example, the terminal device  100 - 3  can perform measurement of the first frequency band based on a DRS while performing measurement of the second frequency band based on a CRS. Alternatively, the terminal device  100 - 3  can perform measurement of the second frequency band based on a CRS while performing measurement of the first frequency band based on a DRS. Therefore, measurement based on the DRS (that is, inter-frequency measurement of a frequency band that is used by a base station of a small cell) may be efficiently performed. As a specific example, measurement based on the DRS may be performed more quickly. 
     In addition, as described above, when measurement based on a DRS is performed using a short period, the extended measurement gap may be shortened. That is, a period in which transmission of a signal from the terminal device  100 - 3  and transmission of a signal to the terminal device  100 - 3  are not continuous may be shortened. 
     (f) Measurement of Additional Frequency band 
     The measurement gap (that is, the extended measurement gap) may include an additional period. The measurement unit  163  may perform measurement of an additional frequency band based on a DRS transmitted in the additional frequency band within the additional period. Hereinafter, this will be described with reference to a specific example of  FIG. 34 . 
       FIG. 34  is an explanatory diagram for describing a third example of measurement according to the third embodiment. Referring to  FIG. 34 , an extended measurement gap having a length of 10 subframes is shown. In this example, the measurement unit  163  performs measurement of a CC2 based on a CRS transmitted in the CC2 (a second frequency band) within a period (a second period) from a 1st subframe to a 6th subframe within the extended measurement gap. In addition, the measurement unit  163  performs measurement of a CC1 based on a DRS transmitted in the CC1 (a first frequency band) within a period (a first period) including a 7th subframe and an 8th subframe within the extended measurement gap. Further, the measurement unit  163  performs measurement of a CC3 based on a DRS transmitted in the CC3 (an additional frequency band) within a period (an additional period) including a 9th subframe and a 10th subframe within the extended measurement gap. 
     Accordingly, measurement based on a DRS (that is, inter-frequency measurement) may be further efficiently performed. 
     While an example in which the measurement gap (that is, the extended measurement gap) includes one additional period and the measurement unit  163  performs measurement of one additional frequency band has been described, it should be understood that the third embodiment is not limited thereto. The measurement gap may include two or more additional periods, and the measurement unit  163  may perform measurement of two or more additional frequency bands. 
     (g) Measurement Based on CRS and DRS 
     The measurement unit  163  may perform the measurement of the first frequency band that is used by the same base station based on a DRS and a CRS transmitted by the same base station in the first frequency band within the first period. Additionally or alternatively, the measurement unit  163  may perform the measurement of the second frequency band that is used by the same base station based on a DRS and a CRS transmitted by the same base station in the second frequency band within the second period. In this case, the first period may be a period shorter than 6 milliseconds. 
     As a specific example, a base station of a small cell in the on state transmits both a DRS and a CRS in the second frequency band. In this case, the measurement unit  163  may perform measurement of the second frequency band that is used by the base station based on the DRS and the CRS transmitted by the base station in the second frequency band within the second period. Hereinafter, hereinafter, this will be described with reference to a specific example of  FIG. 35 . 
       FIG. 35  is an explanatory diagram for describing a fourth example of measurement according to the third embodiment. Referring to  FIG. 35 , an extended measurement gap having a length of 8 subframes is shown. In this example, the measurement unit  163  performs measurement of a CC2 based on a DRS and a CRS transmitted by the same base station using the CC2 (a second frequency band) within a period (a second period) from a 1st subframe to a 4th subframe within the extended measurement gap. In addition, the measurement unit  163  performs measurement of a CC1 based on a DRS transmitted in the CC1 (a first frequency band) within a period (a first period) including a 5th subframe and a 6th subframe within the measurement gap. Further, the measurement unit  163  performs measurement of a CC3 based on a DRS transmitted in the CC3 (an additional frequency band) within a period (an additional period) including a 7th subframe and an 8th subframe within the extended measurement gap. 
     Accordingly, for example, measurement of the first frequency band or the second frequency band (that is, inter-frequency measurement) is performed based on more reference signals. Therefore, the measurement of the first frequency band or the second frequency band used by the base station may be performed using a shorter period than when it is performed based on only a CRS. Therefore, the extended measurement gap may be shortened. 
     (h) Priority 
     For example, the measurement unit  163  performs measurement of a frequency group and measurement of one or more other frequency bands or measurement of one or more other frequency groups based on a priority of the frequency group including the first frequency band and the second frequency band and a priority of the one or more other frequency bands or a priority of the one or more other frequency groups. 
     As a specific example, a frequency group or a frequency band having a higher priority is sequentially selected from among the frequency group including the first frequency band and the second frequency band, the one or more other frequency bands and the one or more other frequency groups. Then, the measurement unit  163  performs measurement of the selected frequency group or frequency band. 
     As an example, the priority of the frequency band is a priority included in an inter-frequency NCL contained in the SIB5. As another example, the priority of the frequency band may be a priority that is decided by the terminal device  100 - 3 . 
     The priority of the frequency group (and/or a priority of each of the one or more other frequency groups) may be decided in consideration of power consumption and/or a communication request of the terminal device  100 - 3 . As an example, when suppression of power consumption is requested, the priority of the frequency group may be higher. This is because, when the priority of the frequency group is high, measurement of more frequency bands using a measurement gap is performed. As another example, when high throughput is requested, the priority of the frequency group may be lower. This is because, when the priority of the frequency group is low, measurement of a frequency band that is used by a base station of a cell in the on state is preferentially performed, and, as a result, a handover is preferentially performed without a transition time. 
     —Measurement in Consideration of Transmission Period of DRS 
     For example, the measurement unit  163  performs the measurement of the frequency group, the measurement of the one or more other frequency bands or the measurement of the one or more other frequency groups in consideration of a transmission period in which a DRS is transmitted in the first frequency band. As a specific example, the measurement unit  163  performs measurement of another frequency band or another frequency group whose priority is lower than the frequency group before the measurement of the frequency group outside of the transmission period. 
     Accordingly, for example, measurement may be performed more smoothly without wasting the measurement gap. 
     (Reporting Unit  165 ) 
     The reporting unit  165  reports a result of measurement of the frequency band to the base station  200 - 3 . 
     For example, the reporting unit  165  reports a result of measurement of the frequency band to the base station  200 - 3 . In addition, for example, the reporting unit  165  reports a result of measurement of the second frequency band to the base station  200 - 3 . In addition, the frequency group may include an additional frequency band, and the reporting unit  165  may report a result of measurement of the additional frequency band to the base station  200 - 3 . 
     &lt;5.2. Configuration of Base Station&gt; 
     Next, an example of a configuration of the base station  200 - 3  according to the third embodiment will be described with reference to  FIG. 36 .  FIG. 36  is a block diagram illustrating an example of a configuration of the base station  200 - 3  according to the third embodiment. Referring to  FIG. 36 , the base station  200 - 3  includes an antenna unit  210 , a wireless communication unit  220 , a network communication unit  230 , a storage unit  240 , and a processing unit  270 . 
     There is no difference in descriptions of the antenna unit  210 , the wireless communication unit  220 , the network communication unit  230  and the storage unit  240  between the first embodiment and the third embodiment except for different reference numerals. Therefore, redundant descriptions will be omitted here, and only the processing unit  270  will be described. 
     (Processing Unit  270 ) 
     The processing unit  270  provides various functions of the base station  200 - 3 . The processing unit  270  includes an information acquiring unit  271  and a control unit  273 . The processing unit  270  may further include any other component in addition to the above-mentioned components. In other words, the processing unit  270  may also perform an operation other than operations of the above-mentioned components. 
     (Information Acquiring Unit  271 ) 
     (a) Frequency Group 
     The information acquiring unit  271  acquires information indicating a first frequency band in which a DRS is transmitted within at least a first period included in a measurement gap. 
     Specifically, in the third embodiment, the measurement gap is an extended measurement gap. For example, the measurement gap further includes a second period in which a reference signal is transmitted in a second frequency band. More specifically, for example, the measurement gap includes a second period in which a CRS is transmitted in the second frequency band. 
     For example, the information acquiring unit  271  acquires information indicating a frequency group including the first frequency band and the second frequency band. The second frequency band is a frequency band in which a DRS is transmitted within at least a second period included in the measurement gap. 
     More specifically, for example, a control entity  300 - 3  decides the frequency group and notifies the base station  200 - 3  of the frequency group. Then, the information indicating the frequency group is stored in the storage unit  240 . The information acquiring unit  271  acquires the information indicating the frequency group at any time thereafter. 
     (b) Measurement Gap 
     Further, for example, the information acquiring unit  271  acquires information indicating the measurement gap. As described above, the measurement gap is an extended measurement gap. 
     More specifically, for example, the control entity  300 - 3  decides an extended measurement gap and notifies the base station  200 - 3  of the extended measurement gap. Then, the information indicating the extended measurement gap is stored in the storage unit  240 . The information acquiring unit  271  acquires the information indicating the extended measurement gap at any time thereafter. 
     Alternatively, the measurement gap is decided by a device other than the control entity  300 - 3 , and the base station  200 - 3  may be notified thereof. Alternatively, the measurement gap is decided by the base station  200 - 3  and may be stored in the storage unit  240 . 
     (Control Unit  263 ) 
     (a) Notification of First Frequency Band and Measurement Gap 
     The control unit  273  notifies the terminal device  100 - 3  of the first frequency band and the measurement gap. Specifically, in the third embodiment, the measurement gap is an extended measurement gap. 
     For example, the control unit  273  notifies the terminal device  100 - 3  of the frequency group including the first frequency band and the second frequency band and the measurement gap. 
     As a specific example, the control unit  273  transmits information indicating the frequency group and information indicating the measurement gap (that is, the extended measurement gap) to the terminal device  100 - 3  through the antenna unit  210  and the wireless communication unit  220 . As an example, the control unit  273  transmits an RRC connection reconfiguration message including a measurement configuration including the information indicating the frequency group and the information indicating the measurement gap to the terminal device  100 - 3  through the antenna unit  210  and the wireless communication unit  220 . 
     (b) Priority Notification 
     For example, the control unit  273  notifies the terminal device  100 - 3  of a priority of the frequency group and a priority of one or more other frequency bands or a priority of one or more other frequency groups. 
     As a specific example, the control unit  273  transmits information indicating the priority of the frequency group and the priority of one or more other frequency bands or the priority of one or more other frequency groups to the terminal device  100 - 3  through the antenna unit  210  and the wireless communication unit  220 . As an example, the information is included in the inter-frequency NCL within the SIB5 and the control unit  273  informs the terminal device  100 - 3  of the SIB5 including the inter-frequency NCL through the antenna unit  210  and the wireless communication unit  220 . 
     &lt;5.3. Configuration of Control Entity&gt; 
     First, an example of a configuration of the control entity  300 - 3  according to the third embodiment will be described with reference to  FIG. 37 .  FIG. 37  is a block diagram illustrating an example of a configuration of the control entity  300 - 3  according to the third embodiment. Referring to  FIG. 37 , the control entity  300 - 3  includes a communication unit  310 , a storage unit  320 , and a processing unit  340 . 
     There is no difference in descriptions of the communication unit  310  and the storage unit  320  between the second embodiment and the third embodiment except for different reference numerals. Therefore, redundant descriptions will be omitted here, and only the processing unit  340  will be described. 
     (Processing Unit  340 ) 
     The processing unit  340  provides various functions of the control entity  300 - 3 . The processing unit  340  includes an information acquiring unit  341  and a control unit  343 . The processing unit  340  may further include any other component in addition to the above-mentioned components. In other words, the processing unit  340  may also perform an operation other than operations of the above-mentioned components. 
     (Information Acquiring Unit  341 ) 
     The information acquiring unit  341  acquires information about a first frequency band in which a DRS is transmitted. 
     The first frequency band is a frequency band that is used by a base station of a small cell. When a base station of a small cell in the off state transmits a DRS and a base station of a small cell in the on state does not transmit a DRS, the first frequency band is a frequency band that is used by the base station of the small cell in the off state. Conversely, when a base station of a small cell transmits a DRS regardless of an on/off state, the first frequency band is a frequency band that is used by the base station of the small cell. 
     (Control Unit  343 ) 
     (a) Decision of Extended Measurement Gap 
     The control unit  343  decides an extended measurement gap including at least a part of a transmission period in which a DRS is transmitted in the first frequency band. 
     (a-1) First Method 
     For example, as a first method, the control unit  343  controls the transmission period such that at least a part of the transmission period is included in the extended measurement gap. 
     More specifically, for example, the control unit  343  decides an extended measurement gap. Then, the control unit  343  instructs a base station that transmits a DRS in the first frequency band to transmit a DRS during the extended measurement gap. 
     Accordingly, for example, it is possible to more reliably perform measurement of the first frequency band using the extended measurement gap. 
     (a-2) Second Method 
     As a second method, the information about the first frequency band (that is, information acquired by the information acquiring unit  341 ) may include information indicating the transmission period. Then, the control unit  343  may decide the extended measurement gap based on the transmission period (that is, a period in which a DRS is transmitted in the first frequency band). 
     As an example, the transmission period and the extended measurement gap are periods having the same length, and the control unit  343  decides the extended measurement gap such that the extended measurement gap matches the transmission period. As another example, the transmission period may be a period longer than the extended measurement gap, and the control unit  343  may decide the extended measurement gap such that the extended measurement gap is included in the transmission period. As still another example, the transmission period may be a period shorter than the extended measurement gap, and the control unit  343  may decide the extended measurement gap such that the extended measurement gap includes the entire transmission period. 
     Accordingly, for example, it is possible to perform measurement of each of the first frequency band and the second frequency band using the extended measurement gap without the control entity  300 - 3  instructing a base station. 
     (b) Decision of Frequency Group 
     For example, the control unit  343  decides a frequency group including at least the first frequency band and the second frequency band. 
     The first frequency band is a frequency band in which a DRS is transmitted within at least a first period included in the measurement gap. In addition, the second frequency band is a frequency band in which a reference signal is transmitted within at least a second period included in the measurement gap. For example, the reference signal is a CRS. 
     For example, the control unit  343  selects any frequency band in which a CRS is transmitted (for example, a frequency band used by a base station of a macro cell or a frequency band used by a base station of a small in the on state) as the second frequency band. Then, the control unit  343  decides a frequency group including the first frequency band and the second frequency band. 
     Alternatively, the reference signal transmitted in the second frequency band may be a DRS. In this case, the control unit  343  may decide the frequency group in the same manner as in the control unit  333  according to the second embodiment. 
     (c) Provide Notification to Base Station  200 - 3   
     For example, the control unit  343  notifies the base station  200 - 3  of the extended measurement gap. 
     For example, the control unit  343  notifies the base station  200 - 3  of the first frequency band. For example, the control unit  343  notifies the base station  200 - 3  of the frequency group including the first frequency band and the second frequency band. 
     As a specific example, the control unit  343  transmits a message including information indicating the frequency group and information indicating the extended measurement gap to the base station  200 - 3  through the communication unit  310 . 
     &lt;5.4. Process Flow&gt; 
     Next, examples of processes according to the third embodiment will be described with reference to  FIG. 38  to  FIG. 40 . 
     (Overall Process Flow) 
       FIG. 38  is a sequence diagram illustrating an example of a schematic flow of a process according to the third embodiment. 
     The control entity  300 - 3  performs an extended measurement gap decision process (S 470 ). That is, the control unit  343  decides an extended measurement gap including at least a part of a transmission period in which a DRS is transmitted in a first frequency band. 
     In addition, the control entity  300 - 3  decides a frequency group including at least the first frequency band and a second frequency band (S 491 ). 
     Then, the control entity  300 - 3  notifies the base station  200 - 3  of the frequency group and the extended measurement gap (S 493 ). 
     Further, the base station  200 - 3  notifies the terminal device  100 - 3  of the frequency group and the extended measurement gap (S 495 ). 
     Then, the terminal device  100 - 3  (the measurement unit  163 ) performs measurement of the frequency group (S 497 ). As a specific example, the measurement unit  163  performs measurement of the first frequency band based on a DRS transmitted in the first frequency band within a first period included in the extended measurement gap. In addition, for example, the measurement unit  163  performs measurement of the second frequency band based on a reference signal (for example, a CRS) transmitted in the second frequency band within a second period included in the extended measurement gap. 
     Then, the terminal device  100 - 3  (the reporting unit  165 ) reports a result of measurement of the frequency band to the base station  200 - 3  (S 499 ). 
     (Extended Measurement Gap Decision Process) 
     (a) First Example 
       FIG. 39  is a sequence diagram illustrating a first example of a schematic flow of an extended measurement gap decision process according to the third embodiment. 
     The information acquiring unit  341  acquires information about a first frequency band in which a DRS is transmitted (S 471 ). 
     Then, the control unit  343  decides an extended measurement gap (S 473 ). 
     Further, the control unit  343  controls a transmission period in which a DRS is transmitted in the first frequency band such that the DRS is transmitted in the first frequency band within at least a first period included in the extended measurement gap (S 475 ). For example, the control unit  343  instructs a base station that transmits a DRS in the first frequency band to transmit the DRS during the extended measurement gap. Then, the process ends. 
     (b) Second Example 
       FIG. 40  is a sequence diagram illustrating a second example of a schematic flow of an extended measurement gap decision process according to the third embodiment. 
     The information acquiring unit  341  acquires information about a first frequency band in which a DRS is transmitted (S 481 ). The information includes information indicating a transmission period in which a DRS is transmitted in the first frequency band. 
     Then, the control unit  343  decides an extended measurement gap based on the transmission period (that is, a period in which a DRS is transmitted in the first frequency band) (S 483 ). Then, the process ends. 
     &lt;5.5. First Modification Example&gt; 
     Next, a first modification example of the third embodiment will be described. 
     In the first modification example of the third embodiment, the base station  200 - 3  decides the extended measurement gap instead of the control entity  300 - 3 . In addition, for example, the base station  200 - 3  decides the frequency group. Then, the base station  200 - 3  notifies the terminal device  100 - 3  of the extended measurement gap and the frequency group it decided. 
     For example, in the first modification example of the third embodiment, the processing unit  270  of the base station  200 - 3  further includes, for example, the information acquiring unit  341  and the control unit  343 . 
     &lt;5.6. Second Modification Example&gt; 
     Next, a second modification example of the third embodiment will be described. 
     In the second modification example of the third embodiment, the terminal device  100 - 3  decides the extended measurement gap instead of the control entity  300 - 3 . In addition, for example, the terminal device  100 - 3  decides the frequency group. Then, the base station  200 - 3  performs measurement of the frequency group it decided by using the extended measurement gap it decided. 
     (Terminal Device  100 - 3 : Processing Unit  160 ) 
     In the second modification example of the third embodiment, the processing unit  160  decides the extended measurement gap. In addition, for example, the processing unit  160  decides a frequency group including at least a first frequency band in which a DRS is transmitted and a second frequency band in which a reference signal (for example, a CRS) is transmitted. 
     As a specific example, the base station  200 - 3  notifies the terminal device  100 - 3  of information about a first frequency band in which a DRS is transmitted. For example, the base station  200 - 3  informs of the inter-frequency NCL (SIB5) including information indicating whether a DRS is transmitted for each frequency band and a transmission period of a DRS. Then, the processing unit  160  decides an extended measurement gap including at least a part of the transmission period in which a DRS is transmitted in the first frequency band. In addition, the processing unit  160  decides a frequency group including at least the first frequency band and the second frequency band. The processing unit  160  decides frequency bands whose number is equal to or less than a predetermined maximum number as a frequency group. 
     (Terminal Device  100 - 3 : Information Acquiring Unit  161 ) 
     As described above, the information acquiring unit  161  acquires information indicating the first frequency band (or the frequency group). In addition, as described above, the information acquiring unit  161  acquires information indicating the extended measurement gap. 
     For example, as described above, the processing unit  160  decides the frequency group and the extended measurement gap. Then, the information acquiring unit  161  acquires information indicating the decided frequency group and information indicating the decided extended measurement gap. 
     6. Fourth Embodiment 
     Next, a fourth embodiment of the present disclosure will be described with reference to  FIG. 41  to  FIG. 43 . 
     A terminal device  100 - 4  according to the fourth embodiment performs first measurement of each of a plurality of frequency bands and second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands. The first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length. The second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length. That is, in the fourth embodiment, the terminal device  100 - 4  performs rough measurement of more frequency bands and performs more accurate measurement of fewer frequency bands that are a part of the more frequency bands. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 4 . 
     &lt;6.1. Configuration of Terminal Device&gt; 
     First, an example of a configuration of the terminal device  100 - 4  according to the fourth embodiment will be described with reference to  FIG. 41  and  FIG. 42 .  FIG. 41  is a block diagram illustrating an example of a configuration of the terminal device  100 - 4  according to the fourth embodiment. As illustrated in  FIG. 41 , the terminal device  100 - 4  includes the antenna unit  110 , the wireless communication unit  120 , the storage unit  130  and a processing unit  170 . 
     There is no difference in descriptions of the antenna unit  110 , the wireless communication unit  120  and the storage unit  130  between the first embodiment and the fourth embodiment except for different reference numerals. Therefore, redundant descriptions will be omitted here, and only the processing unit  170  will be described. 
     (Processing Unit  170 ) 
     The processing unit  170  provides various functions of the terminal device  100 - 4 . The processing unit  170  includes an information acquiring unit  171 , a measurement unit  173  and a reporting unit  175 . The processing unit  170  may further include a component other than these components. That is, the processing unit  170  may also perform an operation other than operations of these components. 
     (Information Acquiring Unit  171 ) 
     The information acquiring unit  171  acquires information about a frequency band. 
     For example, the information acquiring unit  171  acquires a neighbor cell list. For example, the information acquiring unit  171  acquires an intra-frequency NCL and an inter-frequency NCL. For example, a base station  200 - 4  informs the information acquiring unit  171  of an intra-frequency NCL within an SIB4, and the information acquiring unit  171  acquires the intra-frequency NCL. In addition, for example, the base station  200 - 4  informs the information acquiring unit  171  of an inter-frequency NCL within an SIB5 and the information acquiring unit  171  acquires the inter-frequency NCL. 
     For example, the information acquiring unit  171  acquires a measurement configuration of a frequency band. For example, the base station  200 - 4  transmits an RRC connection reconfiguration message including a measurement configuration to the terminal device  100 - 4 , and the information acquiring unit  171  acquires the measurement configuration. The measurement configuration includes information such as measurement objects, reporting configurations, measurement IDs and measurement gaps. 
     (Measurement Unit  173 ) 
     The measurement unit  173  performs measurement of a frequency band. 
     In the fourth embodiment, the measurement unit  173  performs first measurement of each of a plurality of frequency bands and second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands. The first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length. The second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length. That is, the measurement unit  173  performs rough measurement of more frequency bands (that is, the plurality of frequency bands) and performs more accurate measurement of fewer frequency bands (that is, the one or more frequency bands) that are a part of the more frequency bands. Accordingly, for example, it is possible to improve measurement performed by the terminal device  100 - 4 . For example, measurement of the frequency band may be performed more efficiently. 
     (a) First Measurement of Each of Plurality of Frequency Bands 
     (a-1) Plurality of Frequency Bands 
     —Component Carrier (CC) 
     For example, each of the plurality of frequency bands is a component carrier (CC) of carrier aggregation. 
     —Frequency Band of Small Cell 
     For example, each of the plurality of frequency bands is a frequency band that is used by a base station of a small cell. Accordingly, for example, measurement of the frequency band used in the small cell may be performed more efficiently. 
     —Frequency Band that is Not Used 
     For example, each of the plurality of frequency bands is a frequency band that is not used by the terminal device  100 - 4 . Accordingly, for example, inter-frequency measurement may be performed more efficiently. 
     In view of the above points, for example, each of the plurality of frequency bands is a CC that is used by a base station of a small cell, and the CC is not used by the terminal device  100 - 4 . 
     The plurality of frequency bands have been described above. The fourth embodiment is not limited thereto. For example, the plurality of frequency bands may include a frequency band that is used by only a macro base station. 
     (a-2) First Measurement 
     As described above, the first measurement (that is, the measurement of each of the plurality of frequency bands) is measurement that is performed based on a reference signal transmitted within a period having the first length. 
     —Period having First Length 
     For example, the period having the first length is a period including a measurement gap of a first number. That is, the measurement unit  173  performs measurement of each of the plurality of frequency bands based on a reference signal transmitted within the period including the measurement gap of the first number. 
     —Reference Signal 
     For example, the reference signal is a CRS. Accordingly, for example, measurement regarding a small cell in the on state may be performed more efficiently. In addition, a measurement load regarding a macro cell may be reduced. 
     Alternatively, the reference signal may be a DRS. Accordingly, for example, measurement regarding a small cell in the off state may be performed more efficiently. 
     RRM Measurement 
     The first measurement is RRM measurement, for example, measurement of reception power or reception quality. As a specific example, the first measurement is measurement of RSRP or RSRQ. In addition, the first measurement is performed for each cell (that is, a base station that uses each of the plurality of frequency bands) in which each of the plurality of frequency bands is used. 
     (b) Second Measurement of One or More Frequency Bands 
     (b-1) One or More Frequency Bands 
     For example, the one or more frequency bands are frequency bands that are selected from among the plurality of frequency bands based on a result of the first measurement of each of the plurality of frequency bands. 
     More specifically, for example, the one or more frequency bands are frequency bands the first measurement of which has a more favorable result. As an example, for example, the one or more frequency bands are frequency bands having higher RSRP (or RSRQ). Hereinafter, this will be described with reference to a specific example of  FIG. 42 . 
       FIG. 42  is an explanatory diagram for describing an example of frequency bands that are targets of first measurement and second measurement according to the fourth embodiment. Referring to  FIG. 42 , five CCs in one operating band are shown. For example, the measurement unit  173  performs first measurement of each of the five CCs. Then, two CCs having higher RSRP (or RSRQ) among the five CCs are selected as targets of the second measurement, and the measurement unit  173  performs the second measurement of the two CCs. 
     Accordingly, for example, rough measurement of more frequency bands is performed. Accurate measurement of fewer frequency bands favorable for the terminal device  100 - 4  among the more frequency bands is performed. That is, a frequency band favorable for the terminal device  100 - 4  may be found quickly from among the more frequency bands. 
     (b-2) Second Measurement 
     As described above, the first measurement is measurement that is performed based on a reference signal transmitted within a period having the first length. The second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length. 
     —Period having Second Length 
     As described above, for example, the period having the first length is a period including a measurement gap of a first number. Conversely, for example, the period having the second length is a period including a measurement gap of a second number that is greater than the first number. That is, the measurement unit  173  performs measurement of each of the one or more frequency bands based on a reference signal transmitted within a period including the measurement gap of the second number that is greater than the first number. 
     —Reference Signal 
     For example, the reference signal is a CRS. Alternatively, the reference signal may be a DRS. 
     —RRM Measurement 
     The second measurement is RRM measurement, for example, measurement of reception power or reception quality. As a specific example, the second measurement is measurement of RSRP or RSRQ. In addition, the second measurement is performed for each cell in which each of the one or more frequency bands is used (that is, a base station that uses each of the one or more frequency bands). 
     (Reporting Unit  175 ) 
     The reporting unit  175  reports a result of measurement of the frequency band to the base station  200 - 4 . 
     For example, the reporting unit  175  reports a result of measurement of each of the one or more frequency bands to the base station  200 - 4 . 
     &lt;6.2. Process Flow&gt; 
     Next, an example of a process according to the fourth embodiment will be described with reference to  FIG. 42 .  FIG. 42  is a flowchart illustrating an example of a schematic flow of a process according to the fourth embodiment. 
     The measurement unit  173  performs first measurement of each of a plurality of frequency bands (S 511 ). 
     Then, the processing unit  170  (for example, the measurement unit  173 ) selects one or more frequency bands that are a part of the plurality of frequency bands based on a result of the first measurement of each of the plurality of frequency bands (S 513 ). 
     Then, the measurement unit  173  performs second measurement of each of the one or more frequency bands (S 515 ). Then, the process ends. 
     7. Application Examples 
     The technology according to the present disclosure is applicable to a variety of products. The control entity  300  may be implemented as any type of server such as tower servers, rack servers, and blade servers. At least a part of components of the control entity  300  may be implemented in a module (e.g. integrated circuit module that includes a single die, or card or blade that is inserted into a slot of a blade server) mounted on a server. In addition, the control entity  300  may be implemented as any of various base stations which will be described. 
     The base station  200  may also be implemented, for example, as any type of evolved Node B (eNB) such as macro eNBs and small eNBs. Small eNBs may cover smaller cells than the macrocells of pico eNBs, micro eNBs, or home (femt) eNBs. Instead, the base station  200  may be implemented as another type of base station such as Nodes B or base transceiver stations (BTSs). The base station  200  may include the main apparatus (which is also referred to as base station apparatus) that controls wireless communication and one or more remote radio heads (RRHs) that are disposed at different locations from that of the main apparatus. Further, various types of terminals as will be discussed later may temporarily or semi-persistently execute the base station function to operate as the base station  200 . Further, at least part of components of the base station  200  may be implemented in a base station device or a module for the base station device. 
     The terminal device  100  may be implemented as a mobile terminal such as smartphones, tablet personal computers (PCs), notebook PCs, portable game terminals, portable/dongle mobile routers, and digital cameras, or an in-vehicle terminal such as car navigation apparatuses. The terminal device  100  may also be implemented as a terminal (which is also referred to as machine type communication (MTC) terminal) that performs machine to machine (M2M) communication. Furthermore, at least part of components of the terminal device  100  may be implemented as a module (e.g. integrated circuit module constituted with a single die) that is mounted on these terminals. 
     &lt;7.1. Application Examples for Control Entity&gt; 
       FIG. 44  is a block diagram illustrating an example of a schematic configuration of a server  700  to which the technology according to the present disclosure may be applied. The server  700  includes a processor  701 , a memory  702 , a storage  703 , a network interface  704 , and a bus  706 . 
     The processor  701  may be, for example, a central processing unit (CPU) or a digital signal processor (DSP), and controls various functions of the server  700 . The memory  702  includes a random access memory (RAM) and a read only memory (ROM), and stores a program executed by the processor  701  and data. The storage  703  can include a storage medium such as semiconductor memories and hard disks. 
     The network interface  704  is a wired communication interface for connecting the server  700  to a wired communication network  705 . The wired communication network  705  may be a core network such as evolved packet cores (EPCs), or a packet data network (PDN) such as the Internet. 
     The bus  706  connects the processor  701 , the memory  702 , the storage  703 , and the network interface  704  to each other. The bus  706  may include two or more buses each having different speed (e.g. high speed bus and low speed bus). 
     In the server  700  illustrated in  FIG. 44 , one or more components (the information acquiring unit  331  and/or the control unit  333 ) included in the processing unit  330  described above with reference to  FIG. 27  may be mounted in the processor  701 . As an example, a program causing the processor to function as one or more of the components above (that is, a program causing the processor to perform the operation of one or more of the components above) may be installed in the server  700 , and the processor  701  may execute the program. As another example, the server  700  may include a module including the processor  701  and the memory  702 , and one or more of the components above may be mounted in the module. In this case, the module may store the program causing the processor to function as one or more of the components above in the memory  702 , and the program may be executed by the processor  701 . As described above, the server  700  or the module may be provided as an apparatus including one or more of the components above, and the program causing the processor to function as one or more of the components above may be provided. A readable recording medium in which the program is recorded may be provided. For these points, one or more components included in the processing unit  340  described above with reference to  FIG. 37  (the information acquiring unit  341  and/or the control unit  343 ) are the same as one or more of the components above included in the processing unit  330 . 
     &lt;7.2. Application Examples for Base Station&gt; 
     (First Application Example) 
       FIG. 45  is a block diagram illustrating a first example of a schematic configuration of an eNB to which the technology according to the present disclosure may be applied. An eNB  800  includes one or more antennas  810  and a base station apparatus  820 . Each antenna  810  and the base station apparatus  820  may be connected to each other via an RF cable. 
     Each of the antennas  810  includes a single or a plurality of antenna elements (e.g. a plurality of antenna elements constituting a MIMO antenna) and is used for the base station apparatus  820  to transmit and receive a wireless signal. The eNB  800  may include the plurality of the antennas  810  as illustrated in  FIG. 45 , and the plurality of antennas  810  may, for example, correspond to a plurality of frequency bands used by the eNB  800 . It should be noted that while  FIG. 45  illustrates an example in which the eNB  800  includes the plurality of antennas  810 , the eNB  800  may include the single antenna  810 . 
     The base station apparatus  820  includes a controller  821 , a memory  822 , a network interface  823 , and a wireless communication interface  825 . 
     The controller  821  may be, for example, a CPU or a DSP, and operates various functions of an upper layer of the base station apparatus  820 . For example, the controller  821  generates a data packet from data in a signal processed by the wireless communication interface  825 , and transfers the generated packet via the network interface  823 . The controller  821  may generate a bundled packet by bundling data from a plurality of base band processors to transfer the generated bundled packet. The controller  821  may also have a logical function of performing control such as radio resource control, radio bearer control, mobility management, admission control, and scheduling. The control may be performed in cooperation with a surrounding eNB or a core network. The memory  822  includes a RAM and a ROM, and stores a program executed by the controller  821  and a variety of control data (such as, for example, terminal list, transmission power data, and scheduling data). 
     The network interface  823  is a communication interface for connecting the base station apparatus  820  to the core network  824 . The controller  821  may communicate with a core network node or another eNB via the network interface  823 . In this case, the controller  821  may be mutually connected to the eNB  800  and a core network node or another eNB through a logical interface (e.g. S1 interface or X2 interface). The network interface  823  may be a wired communication interface or a wireless communication interface for wireless backhaul. When the network interface  823  is a wireless communication interface, the network interface  823  may use a higher frequency band for wireless communication than a frequency band used by the wireless communication interface  825 . 
     The wireless communication interface  825  supports a cellular communication system such as long term evolution (LTE) or LTE-Advanced, and provides wireless connection to a terminal located within the cell of the eNB  800  via the antenna  810 . The wireless communication interface  825  may typically include a base band (BB) processor  826  and an RF circuit  827 . The BB processor  826  may, for example, perform encoding/decoding, modulation/demodulation, multiplexing/demultiplexing, and the like, and performs a variety of signal processing on each layer (e.g. L1, medium access control (MAC), radio link control (RLC), and packet data convergence protocol (PDCP)). The BB processor  826  may have part or all of the logical functions as discussed above instead of the controller  821 . The BB processor  826  may be a module including a memory having a communication control program stored therein, a processor to execute the program, and a related circuit, and the function of the BB processor  826  may be changeable by updating the program. The module may be a card or blade to be inserted into a slot of the base station apparatus  820 , or a chip mounted on the card or the blade. Meanwhile, the RF circuit  827  may include a mixer, a filter, an amplifier, and the like, and transmits and receives a wireless signal via the antenna  810 . 
     The wireless communication interface  825  may include a plurality of the BB processors  826  as illustrated in  FIG. 45 , and the plurality of BB processors  826  may, for example, correspond to a plurality of frequency bands used by the eNB  800 . The wireless communication interface  825  may also include a plurality of the RF circuits  827 , as illustrated in  FIG. 45 , and the plurality of RF circuits  827  may, for example, correspond to a plurality of antenna elements.  FIG. 45  illustrates an example in which the wireless communication interface  825  includes the plurality of BB processors  826  and the plurality of RF circuits  827 , but the wireless communication interface  825  may include the single BB processor  826  or the single RF circuit  827 . 
     In the eNB  800  illustrated in  FIG. 45 , one or more components included in the processing unit  250  described above with reference to  FIG. 16  (the information acquiring unit  251  and/or the control unit  253 ) may be mounted in the wireless communication interface  825 . Alternatively, at least some of the components may be mounted in the controller  821 . As an example, the eNB  800  may be equipped with a module including some or all components of the wireless communication interface  825  (for example, the BB processor  826 ) and/or the controller  821 , and one or more of the components above may be mounted in the module. In this case, the module may store a program causing the processor to function as one or more of the components above (that is, a program causing the processor to perform the operation of one or more of the components above) and execute the program. As another example, the program causing the processor to function as one or more of the components above may be installed in the eNB  800 , and the wireless communication interface  825  (for example, the BB processor  826 ) and/or the controller  821  may execute the program. As described above, the eNB  800 , the base station apparatus  820 , or the module may be provided as an apparatus including one or more of the components above, and the program causing the processor to function as one or more of the components above may be provided. A readable recording medium in which the program is recorded may be provided. For these points, one or more components included in the processing unit  260  described above with reference to  FIG. 26  (the information acquiring unit  261  and/or the control unit  263 ), and one or more components included in the processing unit  270  described above with reference to  FIG. 36  (the information acquiring unit  271  and/or the control unit  273 ) are the same as one or more of the components above included in the processing unit  250 . 
     In the eNB  800  illustrated in  FIG. 45 , the wireless communication unit  220  described above with reference to  FIG. 16  may be mounted in the wireless communication interface  825  (for example, the RF circuit  827 ). The antenna unit  210  may be mounted in the antenna  810 . The network communication unit  230  may be mounted in the controller  821  and/or the network interface  823 . 
     (Second Application Example) 
       FIG. 46  is a block diagram illustrating a second example of a schematic configuration of an eNB to which the technology according to the present disclosure may be applied. An eNB  830  includes one or more antennas  840 , a base station apparatus  850 , and an RRH  860 . Each of the antennas  840  and the RRH  860  may be connected to each other via an RF cable. The base station apparatus  850  and the RRH  860  may be connected to each other by a high speed line such as optical fiber cables. 
     Each of the antennas  840  includes a single or a plurality of antenna elements (e.g. antenna elements constituting a MIMO antenna), and is used for the RRH  860  to transmit and receive a wireless signal. The eNB  830  may include a plurality of the antennas  840  as illustrated in  FIG. 46 , and the plurality of antennas  840  may, for example, correspond to a plurality of frequency bands used by the eNB  830 .  FIG. 46  illustrates an example in which the eNB  830  includes the plurality of antennas  840 , but the eNB  830  may include the single antenna  840 . 
     The base station apparatus  850  includes a controller  851 , a memory  852 , a network interface  853 , a wireless communication interface  855 , and a connection interface  857 . The controller  851 , the memory  852 , and the network interface  853  are the same as the controller  821 , the memory  822 , and the network interface  823  described with reference to  FIG. 45 . 
     The wireless communication interface  855  supports a cellular communication system such as LTE and LTE-Advanced, and provides wireless connection to a terminal located in a sector corresponding to the RRH  860  via the RRH  860  and the antenna  840 . The wireless communication interface  855  may typically include a BB processor  856 . The BB processor  856  is the same as the BB processor  826  described with reference to  FIG. 45  except that the BB processor  856  is connected to an RF circuit  864  of the RRH  860  via the connection interface  857 . The wireless communication interface  855  may include a plurality of the BB processors  856 , as illustrated in  FIG. 46 , and the plurality of BB processors  856  may, for example, correspond to a plurality of frequency bands used by the eNB  830  respectively.  FIG. 46  illustrates an example in which the wireless communication interface  855  includes the plurality of BB processors  856 , but the wireless communication interface  855  may include the single BB processor  856 . 
     The connection interface  857  is an interface for connecting the base station apparatus  850  (wireless communication interface  855 ) to the RRH  860 . The connection interface  857  may be a communication module for communication on the high speed line which connects the base station apparatus  850  (wireless communication interface  855 ) to the RRH  860 . 
     The RRH  860  includes a connection interface  861  and a wireless communication interface  863 . 
     The connection interface  861  is an interface for connecting the RRH  860  (wireless communication interface  863 ) to the base station apparatus  850 . The connection interface  861  may be a communication module for communication on the high speed line. 
     The wireless communication interface  863  transmits and receives a wireless signal via the antenna  840 . The wireless communication interface  863  may typically include the RF circuit  864 . The RF circuit  864  may include a mixer, a filter, an amplifier and the like, and transmits and receives a wireless signal via the antenna  840 . The wireless communication interface  863  may include a plurality of the RF circuits  864  as illustrated in  FIG. 46 , and the plurality of RF circuits  864  may, for example, correspond to a plurality of antenna elements.  FIG. 46  illustrates an example in which the wireless communication interface  863  includes the plurality of RF circuits  864 , but the wireless communication interface  863  may include the single RF circuit  864 . 
     In the eNB  830  illustrated in  FIG. 46 , one or more components included in the processing unit  250  described above with reference to  FIG. 16  (the information acquiring unit  251  and/or the control unit  253 ) may be mounted in the wireless communication interface  855  and/or the wireless communication interface  863 . Alternatively, at least some of the components may be mounted in the controller  851 . As an example, the eNB  830  may be equipped with a module including some or all components of the wireless communication interface  855  (for example, the BB processor  856 ) and/or the controller  851 , and one or more of the components above may be mounted in the module. In this case, the module may store a program causing the processor to function as one or more of the components above (that is, a program causing the processor to perform the operation of one or more of the components above) and execute the program. As another example, the program causing the processor to function as one or more of the components above may be installed in the eNB  830 , and the wireless communication interface  855  (for example, the BB processor  856 ) and/or the controller  851  may execute the program. As described above, the eNB  830 , the base station apparatus  850 , or the module may be provided as an apparatus including one or more of the components above, and the program causing the processor to function as one or more of the components above may be provided. A readable recording medium in which the program is recorded may be provided. In these points, one or more components included in the processing unit  260  described above with reference to  FIG. 26  (the information acquiring unit  261  and/or the control unit  263 ), and one or more components included in the processing unit  270  described above with reference to  FIG. 36  (the information acquiring unit  271  and/or the control unit  273 ) are the same as one or more of the components above included in the processing unit  250 . 
     In the eNB  830  illustrated in  FIG. 46 , the wireless communication unit  220  described above with reference to  FIG. 16  may be mounted in the wireless communication interface  863  (for example, the RF circuit  864 ). The antenna unit  210  may be mounted in the antenna  840 . The network communication unit  230  may be mounted in the controller  851  and/or the network interface  853 . 
     &lt;7.3. Application Examples for Terminal Device&gt; 
     (First Application Example) 
       FIG. 47  is a block diagram illustrating an example of a schematic configuration of a smartphone  900  to which the technology according to the present disclosure may be applied. The smartphone  900  includes a processor  901 , a memory  902 , a storage  903 , an external connection interface  904 , a camera  906 , a sensor  907 , a microphone  908 , an input device  909 , a display device  910 , a speaker  911 , a wireless communication interface  912 , one or more antenna switches  915 , one or more antennas  916 , a bus  917 , a battery  918 , and a secondary controller  919 . 
     The processor  901  may be, for example, a CPU or a system on chip (SoC), and controls the functions of an application layer and other layers of the smartphone  900 . The memory  902  includes a RAM and a ROM, and stores a program executed by the processor  901  and data. The storage  903  may include a storage medium such as semiconductor memories and hard disks. The external connection interface  904  is an interface for connecting the smartphone  900  to an externally attached device such as memory cards and universal serial bus (USB) devices. 
     The camera  906  includes an image sensor such as charge coupled devices (CCDs) and complementary metal oxide semiconductor (CMOS), and generates a captured image. The sensor  907  may include a sensor group including, for example, a positioning sensor, a gyro sensor, a geomagnetic sensor, and an acceleration sensor. The microphone  908  converts a sound that is input into the smartphone  900  to an audio signal. The input device  909  includes, for example, a touch sensor which detects that a screen of the display device  910  is touched, a key pad, a keyboard, a button, or a switch, and accepts an operation or an information input from a user. The display device  910  includes a screen such as liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays, and displays an output image of the smartphone  900 . The speaker  911  converts the audio signal that is output from the smartphone  900  to a sound. 
     The wireless communication interface  912  supports a cellular communication system such as LTE or LTE-Advanced, and performs wireless communication. The wireless communication interface  912  may typically include the BB processor  913 , the RF circuit  914 , and the like. The BB processor  913  may, for example, perform encoding/decoding, modulation/demodulation, multiplexing/demultiplexing, and the like, and performs a variety of types of signal processing for wireless communication. On the other hand, the RF circuit  914  may include a mixer, a filter, an amplifier, and the like, and transmits and receives a wireless signal via the antenna  916 . The wireless communication interface  912  may be a one-chip module in which the BB processor  913  and the RF circuit  914  are integrated. The wireless communication interface  912  may include a plurality of BB processors  913  and a plurality of RF circuits  914  as illustrated in  FIG. 47 .  FIG. 47  illustrates an example in which the wireless communication interface  912  includes a plurality of BB processors  913  and a plurality of RF circuits  914 , but the wireless communication interface  912  may include a single BB processor  913  or a single RF circuit  914 . 
     Further, the wireless communication interface  912  may support other types of wireless communication system such as a short range wireless communication system, a near field communication system, and a wireless local area network (LAN) system in addition to the cellular communication system, and in this case, the wireless communication interface  912  may include the BB processor  913  and the RF circuit  914  for each wireless communication system. 
     Each antenna switch  915  switches a connection destination of the antenna  916  among a plurality of circuits (for example, circuits for different wireless communication systems) included in the wireless communication interface  912 . 
     Each of the antennas  916  includes one or more antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna) and is used for transmission and reception of the wireless signal by the wireless communication interface  912 . The smartphone  900  may include a plurality of antennas  916  as illustrated in  FIG. 47 .  FIG. 47  illustrates an example in which the smartphone  900  includes a plurality of antennas  916 , but the smartphone  900  may include a single antenna  916 . 
     Further, the smartphone  900  may include the antenna  916  for each wireless communication system. In this case, the antenna switch  915  may be omitted from a configuration of the smartphone  900 . 
     The bus  917  connects the processor  901 , the memory  902 , the storage  903 , the external connection interface  904 , the camera  906 , the sensor  907 , the microphone  908 , the input device  909 , the display device  910 , the speaker  911 , the wireless communication interface  912 , and the secondary controller  919  to each other. The battery  918  supplies electric power to each block of the smartphone  900  illustrated in  FIG. 47  via a feeder line that is partially illustrated in the figure as a dashed line. The secondary controller  919 , for example, operates a minimally necessary function of the smartphone  900  in a sleep mode. 
     In the smartphone  900  illustrated in  FIG. 47 , one or more components included in the processing unit  140  described above with reference to  FIG. 12  (the information acquiring unit  141 , the measurement unit  143 , and/or the reporting unit  145 ) may be mounted in the wireless communication interface  912 . Alternatively, at least some of the components may be mounted in the processor  901  or the secondary controller  919 . As an example, the smartphone  900  may be equipped with a module including some or all components of the wireless communication interface  912  (for example, the BB processor  913 ), the processor  901 , and/or the secondary controller  919 , and one or more of the components above may be mounted in the module. In this case, the module may store a program causing the processor to function as one or more of the components above (that is, a program causing the processor to perform the operation of one or more of the components above) and execute the program. As another example, the program causing the processor to function as one or more of the components above may be installed in the smartphone  900 , and the wireless communication interface  912  (for example, the BB processor  913 ), the processor  901 , and/or the secondary controller  919  may execute the program. As described above, the smartphone  900  or the module may be provided as an apparatus including one or more of the components above, and the program causing the processor to function as one or more of the components above may be provided. A readable recording medium in which the program is recorded may be provided. For these points, one or more components included in the processing unit  150  described above with reference to  FIG. 22  (the information acquiring unit  151 , the measurement unit  153 , and/or the reporting unit  155 ), one or more components included in the processing unit  160  described above with reference to  FIG. 31  (the information acquiring unit  161 , the measurement unit  163 , and/or the reporting unit  165 ), and one or more components included in the processing unit  170  described above with reference to  FIG. 41  (the information acquiring unit  171 , the measurement unit  173 , and/or the reporting unit  175 ) are the same as one or more of the components above included in the processing unit  140 . 
     In the smartphone  900  illustrated in  FIG. 47 , for example, the wireless communication unit  120  described above with reference to  FIG. 12  may be mounted in the wireless communication interface  912  (for example, the RF circuit  914 ). The antenna unit  110  may be mounted in the antenna  916 . 
     (Second Application Example) 
       FIG. 48  is a block diagram illustrating an example of a schematic configuration of a car navigation apparatus  920  to which the technology according to the present disclosure may be applied. The car navigation apparatus  920  includes a processor  921 , a memory  922 , a global positioning system (GPS) module  924 , a sensor  925 , a data interface  926 , a content player  927 , a storage medium interface  928 , an input device  929 , a display device  930 , a speaker  931 , a wireless communication interface  933 , one or more antenna switches  936 , one or more antennas  937 , and a battery  938 . 
     The processor  921  may be, for example, a CPU or an SoC, and controls the navigation function and the other functions of the car navigation apparatus  920 . The memory  922  includes a RAM and a ROM, and stores a program executed by the processor  921  and data. 
     The GPS module  924  uses a GPS signal received from a GPS satellite to measure the position (e.g. latitude, longitude, and altitude) of the car navigation apparatus  920 . The sensor  925  may include a sensor group including, for example, a gyro sensor, a geomagnetic sensor, and an air pressure sensor. The data interface  926  is, for example, connected to an in-vehicle network  941  via a terminal that is not illustrated, and acquires data such as vehicle speed data generated on the vehicle side. 
     The content player  927  reproduces content stored in a storage medium (e.g. CD or DVD) inserted into the storage medium interface  928 . The input device  929  includes, for example, a touch sensor which detects that a screen of the display device  930  is touched, a button, or a switch, and accepts operation or information input from a user. The display device  930  includes a screen such as LCDs and OLED displays, and displays an image of the navigation function or the reproduced content. The speaker  931  outputs a sound of the navigation function or the reproduced content. 
     The wireless communication interface  933  supports a cellular communication system such as LTE or LTE-Advanced, and performs wireless communication. The wireless communication interface  933  may typically include the BB processor  934 , the RF circuit  935 , and the like. The BB processor  934  may, for example, perform encoding/decoding, modulation/demodulation, multiplexing/demultiplexing, and the like, and performs a variety of types of signal processing for wireless communication. On the other hand, the RF circuit  935  may include a mixer, a filter, an amplifier, and the like, and transmits and receives a wireless signal via the antenna  937 . The wireless communication interface  933  may be a one-chip module in which the BB processor  934  and the RF circuit  935  are integrated. The wireless communication interface  933  may include a plurality of BB processors  934  and a plurality of RF circuits  935  as illustrated in  FIG. 48 .  FIG. 48  illustrates an example in which the wireless communication interface  933  includes a plurality of BB processors  934  and a plurality of RF circuits  935 , but the wireless communication interface  933  may be a single BB processor  934  or a single RF circuit  935 . 
     Further, the wireless communication interface  933  may support other types of wireless communication system such as a short range wireless communication system, a near field communication system, and a wireless LAN system in addition to the cellular communication system, and in this case, the wireless communication interface  933  may include the BB processor  934  and the RF circuit  935  for each wireless communication system. 
     Each antenna switch  936  switches a connection destination of the antenna  937  among a plurality of circuits (for example, circuits for different wireless communication systems) included in the wireless communication interface  933 . 
     Each of the antennas  937  includes one or more antenna elements (for example, a plurality of antenna elements constituting a MIMO antenna) and is used for transmission and reception of the wireless signal by the wireless communication interface  933 . The car navigation apparatus  920  includes a plurality of antennas  937  as illustrated in  FIG. 48 .  FIG. 48  illustrates an example in which the car navigation apparatus  920  includes a plurality of antennas  937 , but the car navigation apparatus  920  may include a single antenna  937 . 
     Further, the smartphone  920  may include the antenna  937  for each wireless communication system. In this case, the antenna switch  936  may be omitted from a configuration of the car navigation apparatus  920 . 
     The battery  950  supplies electric power to each block of the car navigation apparatus  930  illustrated in  FIG. 48  via a feeder line that is partially illustrated in the figure as a dashed line. The battery  950  accumulates the electric power supplied from the vehicle. 
     In the car navigation apparatus  920  illustrated in  FIG. 48 , one or more components included in the processing unit  140  described above with reference to  FIG. 12  (the information acquiring unit  141 , the measurement unit  143 , and/or the reporting unit  145 ) may be mounted in the wireless communication interface  933 . Alternatively, at least some of the components may be mounted in the processor  921 . As an example, the car navigation apparatus  920  may be equipped with a module including some or all components of the wireless communication interface  933  (for example, the BB processor  934 ), and/or the processor  921 , and one or more of the components above may be mounted in the module. In this case, the module may store a program causing the processor to function as one or more of the components above (that is, a program causing the processor to perform the operation of one or more of the components above) and execute the program. As another example, the program causing the processor to function as one or more of the components above may be installed in the car navigation apparatus  920 , and the wireless communication interface  933  (for example, the BB processor  934 ), and/or the processor  921  may execute the program. As described above, the car navigation apparatus  920  or the module may be provided as an apparatus including one or more of the components above, and the program causing the processor to function as one or more of the components above may be provided. A readable recording medium in which the program is recorded may be provided. For these points, one or more components included in the processing unit  150  described above with reference to  FIG. 22  (the information acquiring unit  151 , the measurement unit  153 , and/or the reporting unit  155 ), one or more components included in the processing unit  160  described above with reference to  FIG. 31  (the information acquiring unit  161 , the measurement unit  163 , and/or the reporting unit  165 ), and one or more components included in the processing unit  170  described above with reference to  FIG. 41  (the information acquiring unit  171 , the measurement unit  173 , and/or the reporting unit  175 ) are the same as one or more of the components above included in the processing unit  140 . 
     In the car navigation apparatus  920  illustrated in  FIG. 48 , for example, the wireless communication unit  120  described above with reference to  FIG. 12  may be mounted in the wireless communication interface  933  (for example, the RF circuit  935 ). The antenna unit  110  may be mounted in the antenna  937 . 
     Further, the technique according to the present disclosure may be implemented as an in-vehicle system (or a vehicle)  940  including one or more blocks of the above-described car navigation apparatus  920 , an in-vehicle network  941  and a vehicle side module  942 . That is, the in-vehicle system (or the vehicle)  940  may be provided as an apparatus including one more of the components above included in the processing unit  140  (or the processing unit  150 , the processing unit  160  or the processing unit  170 ). The vehicle side module  942  generates vehicle side data such as vehicle speed, engine speed and failure information and outputs the generated data to the in-vehicle network  961 . 
     8. Conclusion 
     The communication apparatuses and each process according to the embodiments of the present disclosure have been described above with reference to  FIGS. 9 to 48 . 
     According to the first embodiment, measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by the terminal device  100 - 1  is performed. The terminal device  100 - 1  does not perform measurement of each of the remaining frequency bands among the plurality of frequency bands or performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands. 
     According to the second embodiment and the third embodiment, the terminal device  100 - 2  performs measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap, and performs measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap. Specifically, in the second embodiment, the reference signal transmitted in the second frequency band is a DRS. Conversely, specifically, in the third embodiment, the measurement gap is an extended measurement gap. 
     According to the fourth embodiment, the terminal device  100 - 4  performs first measurement of each of a plurality of frequency bands and performs second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands. The first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length. The second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length. 
     According to each of the first to fourth embodiments, it is possible to improve measurement performed by the terminal device  100 . 
     The preferred embodiment of the present disclosure has been described above with reference to the accompanying drawings, whilst the present disclosure is not limited to the above examples. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present disclosure. 
     For example, while an example in which a communication system supports LTE or LTE-A has been described in embodiments of the present disclosure, the present disclosure is not limited thereto. For example, the communication system may be a system that supports another communication standard. 
     Further, it is not always necessary to execute the processing steps in the processing in the present specification in chronological order in order described in the flowcharts or the sequence diagrams. For example, the processing steps in the above-described processing may be executed in order different from the order described in the flowcharts or the sequence diagrams or may be executed in parallel. 
     Further, it is also possible to create a computer program for making a processor (such as, for example, a CPU and a DSP) provided at apparatuses (such as, for example, the terminal device, the base station or the control entity, or the modules thereof) in the present specification function as the above-described apparatuses (in other words, a computer program for making the processor execute operation of the components of the above-described apparatuses). Further, it is also possible to provide a recording medium having the above-described computer program recorded therein. Further, it is also possible to provide an apparatus (such as, for example, a finished product and a module (such as parts, processing circuits and chips) for the finished product) including a memory having the above-described computer program stored therein and one or more processors which can execute the above-described computer program. Further, a method including the operation of one or more of the components (for example, a measurement unit and/or a reporting unit, or an information acquiring unit and/or the control unit) of the above-described apparatuses is included in the technique according to the present disclosure. 
     In addition, the effects described in the present specification are merely illustrative and demonstrative, and not limitative. In other words, the technology according to the present disclosure can exhibit other effects that are evident to those skilled in the art along with or instead of the effects based on the present specification. 
     Additionally, the present technology may also be configured as below.
     (1)   

     A device including: 
     a measurement unit configured to perform measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by a terminal device, 
     wherein the measurement unit does not perform measurement of each of remaining frequency bands among the plurality of frequency bands or performs the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (2)   

     The device according to (1), 
     wherein the measurement unit does not perform the measurement of each of the remaining frequency bands.
     (3)   

     The device according to (2), further including: 
     a reporting unit configured to report a result of the measurement of each of the one or more frequency bands to a base station, 
     wherein the reporting unit substitutes a result of measurement of a first frequency band included in the one or more frequency bands with a result of measurement of a second frequency band included in the remaining frequency bands, and thus reports the result of the measurement of the second frequency band to the base station.
     (4)   

     The device according to (1), 
     wherein the measurement unit performs the measurement of each of the remaining frequency bands at a frequency lower than the frequency of the measurements of each of the one or more frequency bands.
     (5)   

     The device according to (4), 
     wherein the measurement unit performs the measurement of each of the remaining frequency bands using fewer measurement gaps than measurement gaps used for the measurement of each of the one or more frequency bands.
     (6)   

     The device according to (5), 
     wherein the measurement unit skips a part of measurement gaps assigned to each of the remaining frequency bands without measurement.
     (7)   

     The device according to (5), 
     wherein measurement gaps assigned to each of the remaining frequency bands are fewer than measurement gaps assigned to each of the one or more frequency bands.
     (8)   

     The device according to any one of (1) to (7), 
     wherein the measurement of each of the one or more frequency bands is measurement based on a reference signal transmitted in each of the one or more frequency bands, and 
     the measurement of each of the remaining frequency bands is measurement based on a reference signal transmitted in each of the remaining frequency bands.
     (9)   

     The device according to (8), 
     wherein the reference signal is a cell-specific reference signal.
     (10)   

     The device according to (8), 
     wherein the reference signal is a discovery reference signal.
     (11)   

     The device according to any one of (1) to (10), 
     wherein the remaining frequency bands are frequency bands included in the same operating band as the one or more frequency bands.
     (12)   

     The device according to (11), 
     wherein each of the remaining frequency bands is a frequency band that is adjacent to any frequency band included in the one or more frequency bands.
     (13)   

     The device according to any one of (1) to (12), 
     wherein each of the plurality of frequency bands is a frequency band that is used by a base station of a small cell.
     (14)   

     A device including: 
     an acquiring unit configured to acquire information about a plurality of frequency bands that are not used by a terminal device; and 
     a control unit configured to instruct the terminal device to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, and not to perform measurement of each of remaining frequency bands among the plurality of frequency bands or to perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (15)   

     The device according to (14), 
     wherein the control unit instructs the terminal device to perform the measurement of each of the one or more frequency bands and not to perform the measurement of each of the remaining frequency bands, 
     the control unit substitutes a result of measurement of a first frequency band included in the one or more frequency bands with a result of measurement of a second frequency band included in the remaining frequency bands.
     (16)   

     The device according to (14) or (15), 
     wherein the control unit instructs the terminal device to skip a part of measurement gaps assigned to each of the remaining frequency bands without measurement.
     (17)   

     A device including: 
     a measurement unit configured to perform measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap and perform measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap.
     (18)   

     The device according to (17), 
     wherein the measurement gap is an extended measurement gap.
     (19)   

     The device according to (18), 
     wherein the extended measurement gap is a period longer than 6 milliseconds.
     (20)   

     The device according to (18) or (19), 
     wherein the reference signal transmitted in the second frequency band is a cell-specific reference signal.
     (21)   

     The device according to (20), 
     wherein the first period is a period shorter than the second period.
     (22)   

     The device according to (17), 
     wherein the reference signal transmitted in the second frequency band is a discovery reference signal.
     (23)   

     The device according to (22), 
     wherein the measurement gap is a period having a length of 6 milliseconds.
     (24)   

     The device according to any one of (17) to (23), 
     wherein the measurement unit performs the measurement of the first frequency band that is used by the same base station based on a discovery reference signal and a cell-specific reference signal transmitted by the same base station in the first frequency band within the first period or performs the measurement of the second frequency band that is used by the same base station based on a discovery reference signal and a cell-specific reference signal transmitted by the same base station in the second frequency band within the second period.
     (25)   

     The device according to (24), 
     wherein at least one of the first period and the second period is a period shorter than 6 milliseconds.
     (26)   

     The device according to any one of (17) to (25), 
     wherein the measurement unit performs measurement of a frequency group and measurement of one or more other frequency bands or measurement of one or more other frequency groups based on a priority of the frequency group including the first frequency band and the second frequency band and a priority of the one or more other frequency bands or a priority of the one or more other frequency groups.
     (27)   

     The device according to (26), 
     wherein the measurement unit performs the measurement of the frequency group and the measurement of the one or more other frequency bands or the measurement of the one or more other frequency groups in consideration of a transmission period in which a discovery reference signal is transmitted in the first frequency band.
     (28)   

     The device according to (27), 
     wherein the measurement unit performs measurement of another frequency band or another frequency group whose priority is lower than the frequency group before the measurement of the frequency group outside of the transmission period.
     (29)   

     The device according to any one of (17) to (18), 
     wherein the measurement gap includes an additional period, and the measurement unit performs measurement of an additional frequency band based on a discovery reference signal transmitted in the additional frequency band within the additional period.
     (30)   

     A device including: 
     an acquiring unit configured to acquire information indicating a first frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap; and 
     a control unit configured to notify a terminal device of the first frequency band and the measurement gap.
     (31)   

     The device according to (30), 
     wherein the measurement gap further includes a second period in which a reference signal is transmitted in a second frequency band.
     (32)   

     The device according to (30) or (31), 
     wherein the measurement gap is an extended measurement gap.
     (33)   

     The device according to (32), 
     wherein the measurement gap includes a second period in which a cell-specific reference signal is transmitted in a second frequency band.
     (34)   

     The device according to any one of (30) to (32), 
     wherein the acquiring unit acquires information indicating a frequency group including the first frequency band and a second frequency band, and 
     the control unit notifies a terminal device of the frequency group and the measurement gap.
     (35)   

     The device according to (34), 
     wherein the second frequency band is a frequency band in which a discovery reference signal is transmitted within at least a second period included in the measurement gap.
     (36)   

     The device according to (34) or (35), 
     wherein the control unit notifies a terminal device of a priority of the frequency group and a priority of one or more other frequency bands or a priority of one or more other frequency groups.
     (37)   

     A device including: 
     an acquiring unit configured to acquire information about a first frequency band in which a discovery reference signal is transmitted; and 
     a control unit configured to decide an extended measurement gap including at least a part of a transmission period in which a discovery reference signal is transmitted in the first frequency band.
     (38)   

     The device according to (37), 
     wherein the control unit controls the transmission period such that at least a part of the transmission period is included in the extended measurement gap.
     (39)   

     The device according to (37), 
     wherein the information about the first frequency band includes information indicating the transmission period, and 
     the control unit decides the extended measurement gap based on the transmission period.
     (40)   

     A device including: 
     an acquiring unit configured to acquire information about two or more frequency bands in which a discovery reference signal is transmitted; and 
     a control unit configured to decide a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands, 
     wherein the first frequency band is a frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap, and 
     the second frequency band is a frequency band in which a discovery reference signal is transmitted within at least a second period included in the measurement gap.
     (41)   

     The device according to (40), 
     wherein the control unit controls a transmission period in which a discovery reference signal is transmitted in the first frequency band such that the discovery reference signal is transmitted in the first frequency band within at least the first period, or controls a transmission period in which a discovery reference signal is transmitted in the second frequency band such that the discovery reference signal is transmitted in the second frequency band within at least the second period.
     (42)   

     The device according to (40), 
     wherein the information about the two or more frequency bands includes information indicating a transmission period in which a discovery reference signal is transmitted in each of the two or more frequency bands, and 
     the control unit decides the frequency group based on the transmission period.
     (43)   

     A device including: 
     a measurement unit configured to perform first measurement of each of a plurality of frequency bands and perform second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, 
     wherein the first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length, and 
     the second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length.
     (44)   

     The device according to (43), 
     wherein the one or more frequency bands are frequency bands that are selected from among the plurality of frequency bands based on a result of the first measurement.
     (45)   

     The device according to (44), 
     wherein the one or more frequency bands are frequency bands the first measurement of which has a more favorable result.
     (46)   

     The device according to any one of (43) to (45), 
     wherein the device is a terminal device or a module for the terminal device, and 
     each of the plurality of frequency bands is a frequency band that is not used by the terminal device.
     (47)   

     The device according to (46), 
     wherein the period having the first length is a period including a measurement gap of a first number, and 
     the period having the second length is a period including a measurement gap of a second number that is greater than the first number.
     (48)   

     The device according to any one of (43) to (47), 
     wherein each of the plurality of frequency bands is a frequency band that is used by a base station of a small cell.
     (49)   

     The device according to (48), 
     wherein the reference signal is a discovery reference signal.
     (50)   

     The device according to any one of (43) to (48), 
     wherein the reference signal is a cell-specific reference signal.
     (51)   

     The device according to any one of (1) to (13), 
     wherein the device is the terminal device or a module for the terminal device.
     (52)   

     A method including: 
     performing, by a processor, measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by a terminal device; and 
     not performing, by a processor, measurement of each of remaining frequency bands among the plurality of frequency bands or performing the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (53)   

     A program for causing a processor to execute: 
     performing measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by a terminal device; and 
     not performing measurement of each of remaining frequency bands among the plurality of frequency bands or performing the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (54)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     performing measurement of each of one or more frequency bands that are a part of a plurality of frequency bands that are not used by a terminal device; and 
     not performing measurement of each of remaining frequency bands among the plurality of frequency bands or performing the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (55)   

     The device according to any one of (14) to (16), 
     wherein the device is a base station, a base station device for the base station or a module for the base station device.
     (56)   

     A method including: 
     acquiring information about a plurality of frequency bands that are not used by a terminal device; and 
     instructing, by a processor, the terminal device to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, and not to perform measurement of each of remaining frequency bands among the plurality of frequency bands or to perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (57)   

     A program for causing a processor to execute: 
     acquiring information about a plurality of frequency bands that are not used by a terminal device; and 
     instructing the terminal device to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, and not to perform measurement of each of remaining frequency bands among the plurality of frequency bands or to perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (58)   

     A readable medium having a program recorded thereon, the program causing a processor to execute: 
     acquiring information about a plurality of frequency bands that are not used by a terminal device; and 
     instructing the terminal device to perform measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, and not to perform measurement of each of remaining frequency bands among the plurality of frequency bands or to perform the measurement of each of the remaining frequency bands at a frequency lower than a frequency of the measurements of each of the one or more frequency bands.
     (59)   

     The device according to any one of (17) to (29), 
     wherein the device is a terminal device or a module for the terminal device.
     (60)   

     A method including: 
     performing, by a processor, measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap; and 
     performing, by a processor, measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap.
     (61)   

     A program for causing a processor to execute: 
     performing measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap; and 
     performing measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap.
     (62)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     performing measurement of a first frequency band based on a discovery reference signal transmitted in the first frequency band within a first period included in a measurement gap; and 
     performing measurement of a second frequency band based on a reference signal transmitted in the second frequency band within a second period included in the measurement gap.
     (63)   

     The device according to any one of (30) to (36), 
     wherein the device is a base station, a base station device for the base station or a module for the base station device.
     (64)   

     A method including: 
     acquiring information indicating a first frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap; and 
     notifying, by a processor, a terminal device of the first frequency band and the measurement gap.
     (65)   

     A program for causing a processor to execute: 
     acquiring information indicating a first frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap; and 
     notifying a terminal device of the first frequency band and the measurement gap.
     (66)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     acquiring information indicating a first frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap; and 
     notifying a terminal device of the first frequency band and the measurement gap.
     (67)   

     The device according to any one of (37) to (39), 
     wherein the device is a server, a module for the server, a base station, a base station device for the base station, or a module for the base station device.
     (68)   

     A method including: 
     acquiring information about a first frequency band in which a discovery reference signal is transmitted; and 
     deciding, by a processor, an extended measurement gap including at least a part of a transmission period in which a discovery reference signal is transmitted in the first frequency band.
     (69)   

     A program for causing a processor to execute: 
     acquiring information about a first frequency band in which a discovery reference signal is transmitted; and 
     deciding an extended measurement gap including at least a part of a transmission period in which a discovery reference signal is transmitted in the first frequency band.
     (70)   

     A readable recording medium having a program recorded thereon, the program for causing a processor to execute: 
     acquiring information about a first frequency band in which a discovery reference signal is transmitted; and 
     deciding an extended measurement gap including at least a part of a transmission period in which a discovery reference signal is transmitted in the first frequency band.
     (71)   

     The device according to any one of (40) to (42), 
     wherein the device is a server, a module for the server, a base station, a base station device for the base station, or a module for the base station device.
     (72)   

     A method including: 
     acquiring information about two or more frequency bands in which a discovery reference signal is transmitted; and 
     deciding, by a processor, a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands, 
     wherein the first frequency band is a frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap, and 
     the second frequency band is a frequency band in which a discovery reference signal is transmitted within at least a second period included in the measurement gap.
     (73)   

     A program for causing a processor to execute: 
     acquiring information about two or more frequency bands in which a discovery reference signal is transmitted; and 
     deciding a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands, 
     wherein the first frequency band is a frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap, and 
     the second frequency band is a frequency band in which a discovery reference signal is transmitted within at least a second period included in the measurement gap.
     (74)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     acquiring information about two or more frequency bands in which a discovery reference signal is transmitted; and 
     deciding a frequency group including at least a first frequency band and a second frequency band among the two or more frequency bands, 
     wherein the first frequency band is a frequency band in which a discovery reference signal is transmitted within at least a first period included in a measurement gap, and 
     the second frequency band is a frequency band in which a discovery reference signal is transmitted within at least a second period included in the measurement gap.
     (75)   

     The device according to any one of (43) to (50), 
     wherein the device is a terminal device or a module for the terminal device.
     (76)   

     A method including: 
     performing, by a processor, first measurement of each of a plurality of frequency bands; and 
     performing, by a processor, second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, 
     wherein the first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length, and 
     the second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length.
     (77)   

     A program for causing a processor to execute: 
     performing first measurement of each of a plurality of frequency bands; and 
     performing second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, 
     wherein the first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length, and 
     the second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length.
     (78)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     performing first measurement of each of a plurality of frequency bands; and 
     performing second measurement of each of one or more frequency bands that are a part of the plurality of frequency bands, 
     wherein the first measurement is measurement that is performed based on a reference signal transmitted within a period having a first length, and 
     the second measurement is measurement that is performed based on a reference signal transmitted within a period having a second length that is greater than the first length. 
     REFERENCE SIGNS LIST 
     
         
           1  communication system 
           100  terminal device 
           143 ,  153 ,  163 ,  173  measurement unit 
           145 ,  155 ,  165 ,  175  reporting unit 
           200  base station 
           251 ,  261 ,  271  information acquiring unit 
           253 ,  263 ,  273  control unit 
           300  control entity 
           331 ,  341  information acquiring unit 
           333 ,  343  control unit