Patent Publication Number: US-11038663-B2

Title: Apparatus for communicating using a frequency band with priority

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/305,580, filed on Oct. 20, 2016, which is based on PCT filing PCT/JP2015/056408, filed on Mar. 4, 2015, and claims priority to JP 2014-115794, filed on Jun. 4, 2014, and JP 2014-234732, filed on Nov. 19, 2014, the entire contents of each are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an apparatus. 
     BACKGROUND ART 
     3G mobile telephone services called the third generation have been launched in Japan from 2002. At first, small-size packets were transmitted and received for voice calls, transmission of e-mails, and the like. Due to the introduction of High Speed Downlink Packet Access (HSDPA), however, larger-size packets have been transmitted and received for downloading music files, streaming of dynamic images, and the like. 
     According to the increase in packet volumes as described above, Long Term Evolution (LTE) which uses Orthogonal Frequency Division Multiple Access (OFDMA) in downlink has also been put in service for expanding radio network sides. Furthermore, 4G services are expected to start around 2015. Thus, a maximum of 1 Gbps (bit per second) can be realized in a semi-fixed environment, and a maximum of 100 Mbps can also be realized in a mobile environment. In addition, the use of small cells, for example, is under discussion in order to deal with hot spots in which traffic is regionally concentrated and to enhance use efficiency of frequency resources. Furthermore, introduction of a frequency sharing technology for causing a frequency band that is not temporally and regionally used and is called a white space to be shared by systems according to rules has been discussed. In addition, the introduction of a frequency sharing technology called a Spectrum Access System (SAS) has been discussed in North America in order to cause a frequency band that is not temporally or regionally used to be shared by systems according to rules. 
     For example, Patent Literature 1 discloses a technology in which, according to a traffic load of each of two or more access points (or the number of terminal apparatuses accessing them), bands are allocated to the two or more access points. Patent Literature 2 discloses, for example, a technology in which two evolved Node Bs (eNBs) share Radio Access Network (RAN) resources to realize load balancing. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: US Patent Application Publication No. 2009/0034457 
     Patent Literature 2: US Patent Application Publication No. 2013/0303114 
     SUMMARY OF INVENTION 
     Technical Problem 
     The technologies disclosed in Patent Literatures 1 and 2 mentioned above, however, are based on the premise that nodes having the same priority level of (or the same right of) use of a frequency band share the frequency band. Thus, for example, there is a possibility of the frequency band not being efficiently used if there is no node having the same priority level on the frequency band. 
     Therefore, it is desirable to provide a mechanism which enables a frequency band to be used with higher efficiency. 
     Solution to Problem 
     According to the present disclosure, there is provided an apparatus including: an acquisition unit configured to acquire information regarding a second base station that is a second base station having a coverage area that overlaps a coverage area of a first base station capable of using a frequency band with priority, and is incapable of using the frequency band with priority; and a control unit configured to request the second base station to transmit data destined for a terminal apparatus that accesses the first base station to the terminal apparatus. 
     According to the present disclosure, there is provided an apparatus including: an acquisition unit configured to acquire data destined for a terminal apparatus that accesses a first base station capable of using a frequency band with priority when a second base station that is a second base station having a coverage area which overlaps a coverage area of the first base station, and is incapable of using the frequency band with priority receives a request to transmit the data to the terminal apparatus; and a control unit configured to control radio communication of the second base station so that the second base station transmits the data to the terminal apparatus. 
     Advantageous Effects of Invention 
     According to the present disclosure described above, it is possible to use a frequency band with higher efficiency. Note that the effects described above are not necessarily limitative. With or in 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 illustrative diagram showing an example of a schematic configuration of a system according to an embodiment of the present disclosure. 
         FIG. 2  is an illustrative diagram for describing a first example of prioritized use of a frequency band. 
         FIG. 3  is an illustrative diagram for describing an example of another frequency band. 
         FIG. 4  is an illustrative diagram for describing a second example of prioritized use of a frequency band. 
         FIG. 5  is an illustrative diagram for describing an example of another frequency band. 
         FIG. 6  is an illustrative diagram for describing a third example of prioritized use of a frequency band. 
         FIG. 7  is an illustrative diagram for describing an example of another frequency band. 
         FIG. 8  is a block diagram showing an example of a configuration of a first base station according to the embodiment. 
         FIG. 9  is a block diagram showing an example of a configuration of a second base station according to the embodiment. 
         FIG. 10  is a sequence diagram showing an example of a schematic flow of a process according to the embodiment. 
         FIG. 11  is an illustrative diagram for describing seven existing TDD configurations. 
         FIG. 12  is an illustrative diagram for describing a downlink-dedicated configuration. 
         FIG. 13  is a sequence diagram showing an example of a schematic flow of a process according to another embodiment. 
         FIG. 14  is a block diagram showing an example of a schematic configuration of a server. 
         FIG. 15  is a block diagram showing a first example of a schematic configuration of an eNB. 
         FIG. 16  is a block diagram showing a second example of a schematic configuration of an eNB. 
         FIG. 17  is a block diagram showing an example of a schematic configuration of a smartphone. 
         FIG. 18  is a block diagram showing 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 appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation of these structural elements is omitted. 
     Note that description will be provided in the following order. 
     1. Introduction 
     2. Schematic configuration of system 
     3. Configuration of first base station 
     4. Configuration of second base station 
     5. Three cases with regard to use of frequency bands
         5.1. First case   5.2. Second case   5.3. Third case       

     6. Consideration of another radio communication system having higher priority level 
     7. Process flow 
     8. Modified examples
         8.1. First modified example   8.2. Second modified example       

     9. Other embodiment 
     10. Application examples
         10.1. Application example regarding other network node   10.2. Application example regarding base station   10.3. Application example regarding terminal device       

     11. Conclusion 
     1. INTRODUCTION 
     First, a frequency sharing technology called Spectrum Access System (SAS) will be described. 
     A “Notice of Proposed Rulemaking and Order” that was issued by the Federal Communications Commission (FCC) in December 2012 proposes creation of a new citizens&#39; broadband service in a 3.5 GHz band in North America. The 3.5 GHz band has been in use for application to non-federal fixed-satellite services and radars of the Department of Defense (i.e., “Incumbent Use”). Thus, a dynamic sharing model using the SAS has been introduced to start preparing for a framework for also using a frequency band for the “Incumbent Use” in the new citizens&#39; broadband service. 
     In a “three-tiered licensing proposal” of the “Notice of Proposed Rulemaking and Order” described above, respective users of the frequency band are classified into one of three groups. Each of these groups is called a “tier.” The three groups are called “Incumbent Access,” “Priority Access,” and “General Authorized Access (GAA).” In use of the frequency band, a priority level of “Incumbent Access” is the highest, a priority level of “Priority Access” is the second highest, and a priority level of “General Authorized Access” is the lowest. 
     “Incumbent Access” is a user group that includes users who uses the frequency band for “Incumbent Use.” “Incumbent Access” is not required to avoid or suppress interference with “Priority Access” and “General Authorized Access” that have lower priority levels than it. In addition, “Incumbent Access” is protected from being interfered with by “Priority Access” and “General Authorized Access.” That is, users of “Incumbent Access” use the frequency band without considering the presence of other groups. 
     “Priority Access” is required to avoid or suppress interference with “Incumbent Access” that has a higher priority level, but is not required to avoid or suppress interference with “General Authorized Access” that has the lower priority level. In addition, “Priority Access” is not protected from interference of the “Incumbent Access” that has a higher priority level, but is protected from interference of “General Authorized Access” that has the lower priority level. 
     “General Authorized Access” is required to avoid or suppress interference with “Incumbent Access” and “Priority Access” that have higher priority levels. In addition, “General Authorized Access” is not protected from interference of “Incumbent Access” and “Priority Access” that have higher priority levels. That is, users of “General Authorized Access” are in a “tier” that is only allowed opportunistic use. 
     2. SCHEMATIC CONFIGURATION OF SYSTEM 
     Next, a schematic configuration of a system  1  according to an embodiment of the present disclosure will be described with reference to  FIGS. 1 to 7 .  FIG. 1  is an illustrative diagram showing an example of a schematic configuration of the system  1  according to the embodiment of the present disclosure. With reference to  FIG. 1 , the system  1  includes a first base station  100  and a second base station  200 . 
     (First Base Station  100 ) 
     The first base station  100  performs radio communication with terminal apparatuses. The first base station  100 , for example, performs radio communication with terminal apparatuses positioned in a coverage area  10  of the first base station  100 . The first base station  100 , for example, transmits data and/or control information to terminal apparatuses and receives data and/or control information from the terminal apparatuses. 
     The first base station  100  communicates with other network nodes. For example, the first base station  100  communicates with the second base station  200 . 
     (Second Base Station  200 ) 
     The second base station  200  performs radio communication with terminal apparatuses. For example, the second base station  200  has a coverage area  20  that overlaps the coverage area  10  of the first base station  100 , and performs radio communication with terminal apparatuses positioned in the coverage area  20 . For example, the second base station  200  transmits data and/or control information to terminal apparatuses and receives data and/or control information from the terminal apparatuses. Note that only a part of the coverage area  20  may overlap the coverage area  10 , or the whole of the coverage area  20  may overlap the coverage area  10 . 
     The second base station  200  communicates with, for example, other network nodes. For example, the second base station communicates with the first base station  100 . 
     (Relationship Between First Base Station  100  and Second Base Station  200 ) 
     The first base station  100  is, for example, a base station of a macrocell, and the second base station  200  is a base station of a small cell that overlaps the macrocell. In other words, the coverage area  10  is a macrocell, and the coverage area  20  is a small cell. 
     The first base station  100  is, for example, a base station of a first radio communication system, and the second base station  200  is a base station of a second radio communication system that is different from the first radio communication system. 
     The first base station  100  is, for example, a base station operated by a first service provider, and the second base station  200  is a base station operated by a second service provider that is different from the first service provider. As an example, the first base station  100  may be a base station operated by a first mobile network operator (MNO), and the second base station  200  may be a base station operated by a second MNO. As another example, the first base station  100  may be a base station operated by an MNO, and the second base station  200  may be a base station operated by a mobile virtual network operator (MVNO). 
     Note that the second base station  200  may be a terminal apparatus which may operate as a base station. Specifically, for example, the second base station  200  may be a terminal apparatus that is a master node of a localized network, a terminal apparatus that performs tethering, a mobile router, or the like. 
     The first base station  100  (or the first radio communication system) and the second base station  200  (or the second radio communication system) perform, for example, radio communication according to the same communication scheme. As an example, the same communication scheme is LTE or LTE-Advanced. Alternatively, the same communication scheme may be Wideband Code Division Multiple Access (W-CDMA) that includes High Speed Downlink Packet Access (HSPA), Worldwide Interoperability for Microwave Access (WiMAX), IEEE 802.11, or the like. Note that the first base station  100  (or the first radio communication system) and the second base station  200  (or the second radio communication system) may perform radio communication according to different communication schemes. 
     (Use of Frequency Band) 
     In the embodiment of the present disclosure, the first base station  100  can use a frequency band with priority. For example, the first radio communication system that includes the first base station  100  can use the frequency band with priority. As an example, the first base station  100  (or the first radio communication system) is a user of “Priority Access” in the frequency band in the SAS. 
     Furthermore, the second base station  200  is incapable of using the frequency band with priority in the embodiment of the present disclosure. For example, the second radio communication system that includes the second base station  200  is incapable of using the frequency band with priority. As an example, the second base station  200  (or the second radio communication system) is a user of “General Authorized Access (GAA)” in the frequency band in the SAS. 
     (a) First Example 
     As a first example, the second base station  200  can use the frequency band under the condition that interference with a radio communication system which can use the frequency band with priority be avoided or suppressed. The radio communication system is, for example, the first radio communication system that includes the first base station  100 . Thus, the radio communication system can use the frequency band, for example, regardless of the presence of the second base station  200 . 
     The second base station  200  can use, for example, a part or the whole of the frequency band in a period in which the radio communication system does not use the part or the whole of the frequency band. Thus, the second base station  200 , for example, avoids interference with the radio communication system (for example, the first base station  100 ). 
     The first base station  100  (for example, a control unit  153  to be described below), for example, notifies the second base station  200  of the period. Thus, the second base station  200 , for example, can use the frequency band during the period. Note that another network node (for example, a frequency management system that manages the frequency band) may notify the second base station  200  of the period in place of the first base station  100 . 
     An example of use of a frequency band with priority will be described below with reference to  FIG. 2 . 
       FIG. 2  is an illustrative diagram for describing the first example of use of a frequency band with priority. Referring to  FIG. 2 , a frequency band  31  is shown. The first base station  100  can use the frequency band  31  with priority. On the other hand, the second base station  200  can use the frequency band  31  under the condition that interference with a radio communication system which can use the frequency band  31  with priority (for example, the first radio communication system that includes the first base station  100 ) be avoided or suppressed. Specifically, the frequency band  31  is, for example, a band for both “Priority Access” and “General Authorized Access (GAA)” in the SAS, the first base station  100  is a user of “Priority Access” in the frequency band  31 , and the second base station  200  is a user of “General Authorized Access” in the frequency band  31 . 
     Note that the second base station  200  may be capable of using another frequency band different from the frequency band. A specific example of this point will be described below with reference to  FIG. 3 . 
       FIG. 3  is an illustrative diagram for describing an example of another frequency band. Referring to  FIG. 3 , the frequency band  31  and a frequency band  33  are shown. The second base station  200  can use the frequency band  33 . Specifically, the frequency band  33  is, for example, a band for “General Authorized Access (GAA)” in the SAS, and the second base station  200  is a user of “General Authorized Access” in the frequency band  33 . 
     (b) Second Example 
     As a second example, the second base station  200  may be incapable of using the frequency band without permission. Thus, the first base station  100  can use the frequency band, for example, regardless of the presence of the second base station  200  in principle. 
     The permission is, for example, permission granted by the first base station  100 . Note that the permission may be permission granted by another node (as an example, a frequency management system that manages frequency bands). 
     An example of use of a frequency band with priority will be described below with reference to  FIG. 4 . 
       FIG. 4  is an illustrative diagram for describing a second example of use of a frequency band with priority. Referring to  FIG. 4 , the frequency band  31  is shown. The first base station  100  can use the frequency band  31  with priority. On the other hand, the second base station  200  is incapable of using the frequency band  31  without permission. Specifically, the frequency band  31  is, for example, a band for “Priority Access” in the SAS, the first base station  100  is a user of “Priority Access” in the frequency band  31 , and the second base station  200  is not a user of “Priority Access” in the frequency band  31 . 
     Note that the second base station  200  may be capable of using another frequency band different from the frequency band. A specific example of this point will be described below with reference to  FIG. 5 . 
       FIG. 5  is an illustrative diagram for describing an example of another frequency band. Referring to  FIG. 5 , the frequency band  31  and the frequency band  33  are shown. The base station  200  can use the frequency band  33 . Specifically, the frequency band  33  is, for example, a band for “General Authorized Access (GAA)” in the SAS, and the second base station  200  is a user of “General Authorized Access” in the frequency band  33 . 
     (c) Third Example 
     The first and the second examples described above may be combined. An example of use of a frequency band with priority with regard to this point will be described with reference to  FIG. 6 . 
       FIG. 6  is an illustrative diagram for describing a third example of use of a frequency band with priority. Referring to  FIG. 6 , a frequency band  31 A and a frequency band  31 B are shown. The first base station  100  can use the frequency band  31 A and the frequency band  31 B with priority. On the other hand, the second base station  200  is incapable of using the frequency band  31 A without permission, but can use the frequency band  31 B under the condition that interference with a radio communication system which can use the frequency band  31 B with priority be avoided or suppressed. Specifically, the frequency band  31 A is, for example, a band for “Priority Access” in the SAS, and the frequency band  31 B is a band for both “Priority Access” and “General Authorized Access (GAA)” in the SAS. Thus, the first base station  100  is a user of “Priority Access” in the frequency band  31 A and the frequency band  31 B, and the second base station  200  is a user of “General Authorized Access” in the frequency band  31 B. 
     Note that the second base station  200  may also be capable of using another frequency band that is different from the frequency bands. A specific example of this point will be described below with reference to  FIG. 7 . 
       FIG. 7  is an illustrative diagram for describing an example of another frequency band. Referring to  FIG. 7 , the frequency band  31 A, the frequency band  31 B and the frequency band  33  are shown. The base station  200  can use the frequency band  33 . Specifically, the frequency band  33  is, for example, a band for “General Authorized Access (GAA)” in the SAS, and the second base station  200  is a user of “General Authorized Access” in the frequency band  33 . 
     The frequency bands that the first base station  100  can use with priority have been described above. Note that there may of course be two or more frequency bands that the first base station  100  can use with priority. 
     (Another Radio Communication System Having a Higher Priority Level) 
     The above-described frequency band is, for example, a band used by another radio communication system (which will be referred to as a “third radio communication system” below) with priority over the radio communication system (i.e., the first radio communication system) that includes the first base station  100 . In this case, the first base station  100  can use the frequency band under the condition that interference with the third radio communication system be avoided or suppressed. 
     As an example, the third radio communication system is a user of “Incumbent Access” in the frequency band in the SAS. Furthermore, the first base station  100  (or the first radio communication system that includes the first base station  100 ) is a user of “Priority Access” in the SAS. In addition, the second base station  200  (or the second radio communication system that includes the second base station  200 ) is a user of “General Authorized Access” in the SAS. 
     Note that the frequency band may be a part of a band used by the third radio communication system. For example, referring to the examples of  FIGS. 3, 5, and 7  again, the band used by the third radio communication system may further include the frequency band  33  in addition to the frequency bands  31 . Alternatively, the frequency band may be the whole of a band used by the third radio communication system. Referring to the examples of  FIGS. 2, 4, and 6  again, the band used by the third radio communication system may be the frequency bands  31  only. 
     A way in which the first base station  100  can use the frequency band will be described below in detail. 
     3. CONFIGURATION OF FIRST BASE STATION 
     An example of a configuration of the first base station  100  according to the embodiment of the present disclosure will be described with reference to  FIG. 8 .  FIG. 8  is a block diagram showing the example of the configuration of the first base station  100  according to the embodiment of the present disclosure. Referring to  FIG. 8 , the first base station  100  has an antenna unit  110 , a radio communication unit  120 , a network communication unit  130 , a storage unit  140 , and a processing unit  150 . 
     (Antenna Unit  110 ) 
     The antenna unit  110  emits signals output by the radio communication unit  120  as radio waves to a space. In addition, the antenna unit  110  converts radio waves from the space into signals, and outputs the signals to the radio communication unit  120 . 
     (Radio Communication Unit  120 ) 
     The radio communication unit  120  transmits and receives signals. For example, the radio communication unit  120  transmits downlink signals to terminal apparatuses positioned in the coverage area  10  and receives uplink signals from terminal apparatuses positioned in the coverage area  10 . 
     (Network Communication Unit  130 ) 
     The network communication unit  130  transmits and receives information. For example, the network communication unit  130  transmits information to other network nodes and receives information from other network nodes. The other network nodes include, for example, the second base station  200 . 
     (Storage Unit  140 ) 
     The storage unit  140  temporarily or permanently stores programs and data for operations of the first base station  100 . 
     (Processing Unit  150 ) 
     The processing unit  150  provides various functions of the first base station  100 . The processing unit  150  includes an information acquisition unit  151  and a control unit  153 . Note that the processing unit  150  can further include another constituent element in addition to these constituent elements. In other words, the processing unit  150  can perform operations in addition to operations of these constituent elements. 
     (Information Acquisition Unit  151 ) 
     The information acquisition unit  151  acquires information with regard to the second base station  200 . As described above, the second base station  200  has the coverage area  20  that overlaps the coverage area  10  of the first base station  100 , and is incapable of using the frequency band with priority that is available to the first base station  100  with priority. 
     The information with regard to the second base station  200  includes, for example, identification information of the second base station  200  (for example, a cell ID), an address of the second base station  200  (for example, an IP address), position information indicating a position of the second base station  200 , and/or a measurement result on the second base station  200  obtained by a terminal apparatus. 
     The information with regard to the second base station  200  is, for example, stored in the storage unit  140 , and the information acquisition unit  151  acquires the information from the storage unit  140 . 
     (Control Unit  153 ) 
     The control unit  153  requests that the second base station  200  transmit data destined for a terminal apparatus that accesses the first base station  100  to the terminal apparatus. 
     (a) Terminal Apparatus 
     The terminal apparatus is, for example, a terminal apparatus positioned close to the second base station  200 . Specifically, the terminal apparatus is, for example, a terminal apparatus positioned in the coverage area  20  of the second base station  200 . 
     As an example, the control unit  153  determines that the terminal apparatus is positioned close to the second base station  200  based on a position of the terminal apparatus or a measurement result on the second base station  200  obtained by the terminal apparatus. For example, the control unit  153  may set a measurement gap and instruct the terminal apparatus to measure reception quality of a reference signal transmitted by the second base station  200  in the measurement gap. 
     (b) Specific Process 
     The control unit  153 , for example, transmits, to the second base station  200 , control information (for example, a message, a command, or the like) for requesting transmission of the above-described data to the terminal apparatus via the network communication unit  130 . In addition, the control unit  153 , for example, forwards the data to the second base station  200  via the network communication unit  130 . 
     (c) Trigger 
     As an example, when a traffic amount or a traffic load of the first base station  100  is equal to or greater than a threshold value, the control unit  153  requests that the data be transmitted from the second base station  200  to the terminal apparatus. 
     As another example, when the terminal apparatus is determined to be positioned close to the second base station  200 , the control unit  153  can request that the data be transmitted from the second base station  200  to the terminal apparatus. 
     Note that a trigger of the request is not limited to the above examples, and various kinds of triggers can be applied to the embodiment of the present disclosure. 
     As described above, the control unit  153  requests that the second base station  200  transmit data destined for the terminal apparatus that accesses the first base station  100  to the terminal apparatus. Thereby, for example, the second base station  200  transmits the data to the terminal apparatus. As a result, for example, a frequency band can be used with higher efficiency. More specifically, for example, even when there is no other base station (for example, a base station of a small cell) of the radio communication system that includes the first base station  100  around the first base station  100 , the second base station closer to the terminal apparatus, for example, can transmit the data to the terminal apparatus instead of the first base station  100 . As a result, the data can be transmitted to the terminal apparatus using fewer radio resources due to the effect of link adaptation. Alternatively, the data can be transmitted to the terminal apparatus with higher reliability using the same amount of radio resources. In other words, traffic off-loading can be realized. In this way, the frequency band can be used with higher efficiency. 
     Note that the control unit  153  performs other operations entailed by the request that the data be transmitted. The other operations will be described below in detail. 
     4. CONFIGURATION OF SECOND BASE STATION 
     An example of a configuration of the second base station  200  according to the embodiment of the present disclosure will be described with reference to  FIG. 9 .  FIG. 9  is a block diagram showing the example of the configuration of the second base station  200  according to the embodiment of the present disclosure. Referring to  FIG. 9 , the second base station  200  has an antenna unit  210 , a radio communication unit  220 , a network communication unit  230 , a storage unit  240 , and a processing unit  250 . 
     (Antenna Unit  210 ) 
     The antenna unit  210  emits signals output by the radio communication unit  220  as radio waves to a space. In addition, the antenna unit  210  converts radio waves from the space into signals, and the signals are output to the radio communication unit  220 . 
     (Radio Communication Unit  220 ) 
     The radio communication unit  220  transmits and receives signals. For example, the radio communication unit  220  transmits downlink signals to terminal apparatuses positioned in the coverage area  20  and receives uplink signals from terminal apparatuses positioned in the coverage area  20 . 
     (Network Communication Unit  230 ) 
     The network communication unit  230  transmits and receives information. For example, the network communication unit  230  transmits information to other network nodes and receives information from other network nodes. The other network nodes include, for example, the first base station  100 . 
     (Storage Unit  240 ) 
     The storage unit  240  temporarily or permanently stores programs and data for operations of the second base station  200 . 
     (Processing Unit  250 ) 
     The processing unit  250  provides various functions of the second base station  200 . The processing unit  250  includes the information acquisition unit  251  and the control unit  253 . Note that the processing unit  250  can further include another constituent element in addition to these constituent elements. In other words, the processing unit  250  can perform operations in addition to operations of these constituent elements. 
     (Information Acquisition Unit  251 ) 
     When it is requested to the second base station  200  that the second base station  200  transmit data destined for a terminal apparatus that accesses the first base station  100  to the terminal apparatus, the information acquisition unit  251  acquires the data. Here, the terminal apparatus that accesses the first base station  100  may at least have accessed the first base station  100  to transmit and receive control information (a C-plane). 
     As described above, the first base station  100  requests that the second base station  200  transmit data destined for a terminal apparatus that accesses the first base station  100  to the terminal apparatus. More specifically, the first base station  100  transmits, for example, control information (for example, a message, a command, or the like) for requesting that the data be transmitted to the second base station  200 . In addition, the first base station  100 , for example, forwards the data to the second base station  200 . Then, the data is stored in the storage unit  240 . At any timing thereafter, the information acquisition unit  251  acquires the data from the storage unit  240 . 
     (Control Unit  253 ) 
     The control unit  253  controls radio communication of the second base station  200  so that the second base station  200  transmits the data to the terminal apparatus. 
     For example, the control unit  253  performs scheduling of transmission of the data. In other words, the control unit  253  allocates radio resources of a band to be used for transmitting the data to a signal of the data. Then, the control unit  253  maps the signal of the data to the allocated radio resources. In other words, the storage unit  240  serves as a buffer in control of transmission of the data. 
     Note that the control unit  253  performs other operations entailed by the transmission of the data. The other operations will be described below in detail. Note that the control unit  253  may not only control the second base station  200  to transmit the data to the terminal apparatus, but also control the second base station  200  to receive data from the terminal apparatus. Here, the control for reception includes, for example, instructing the terminal apparatus to map a signal of the data to allocated radio resources. 
     5. THREE CASES WITH REGARD TO USE OF FREQUENCY BANDS 
     Next, three cases with regard to use of frequency bands for transmission of the data will be described. The three cases are summarized as follows. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Frequency band used for transmission of data 
               
            
           
           
               
               
               
            
               
                   
                 Frequency band that first base 
                 Other frequency band that 
               
               
                 Cases 
                 station can use with priority 
                 second base station can use 
               
               
                   
               
               
                 First case 
                 ◯ 
                   
               
               
                 Second case 
                   
                 ◯ 
               
               
                 Third case 
                 ◯ 
                 ◯ 
               
               
                   
                 (When selected) 
                 (When selected) 
               
               
                   
               
            
           
         
       
     
     5.1. First Case 
     In a first case, the second base station  200  uses a frequency band (i.e., a frequency band that the second base station  200  is incapable of using with priority) that is available to the first base station  100  with priority to transmit the data destined for the terminal apparatus that accesses the first base station  100  to the terminal apparatus. 
     (Operations of First Base Station  100 ) 
     (a) Request for Transmission of Data 
     The first base station  100  (the control unit  153 ), for example, requests that the second base station  200  transmit the data to the terminal apparatus using the frequency band. 
     (b) Permission to Use Frequency Band 
     The first base station  100  (the control unit  153 ), for example, permits the second base station  200  to use the frequency band. 
     Permitted Use 
     The first base station  100  (the control unit  153 ), for example, permits the second base station  200  to use a part or the whole of the frequency band in a period in which the first base station  100  does not use the part or the whole of the frequency band. 
     Referring to  FIGS. 2 to 7  again, the first base station  100  (the control unit  153 ), for example, permits the second base station  200  to use the frequency band  31  in a period in which the first base station  100  does not use the whole of the frequency band  31 . Alternatively, the first base station  100  (the control unit  153 ) permits the second base station  200  to use a part of the frequency band  31  in the period in which the first base station  100  does not use the part of the frequency band  31 . 
     Accordingly, for example, it is possible to avoid interference of the second base station  200  with the first base station  100 . 
     Note that the period may be one or more radio frames or one or more subframes, and may be a period indicated as times (for example, a start time and an end time, or a start time and a length of a period). 
     Specific Process 
     Decision 
     The first base station  100  (the control unit  153 ), for example, decides a period in which the first base station  100  does not use a part or the whole of the frequency band  31 . In addition, the first base station  100  (the control unit  153 ) also decides a part of the frequency band to permit use of the part of the frequency band. 
     Notification to Terminal Apparatus 
     The first base station  100  (the control unit  153 ), for example, notifies the second base station  200  of the period. In addition, when use of a part of the frequency band is permitted for use, the first base station  100  (the control unit  153 ), for example, also notifies the second base station  200  of the part of the frequency band. 
     When requesting that the second base station  200  transmit the data to the terminal apparatus, for example, the first base station  100  notifies the second base station  200  of the period (and the part of the frequency band). Specifically, the first base station  100 , for example, generates control information (for example, a message, a command, or the like) that is control information for requesting that the data be transmitted to the terminal apparatus indicating the period (and the part of the frequency band), and transmits the control information to the second base station  200 . 
     Note that the transmission of the information indicating the period to the second base station  200  can be considered as being equivalent to permitting use of the frequency band. In addition, the transmission of the information indicating the period (and the part of the frequency band) to the second base station  200  can be considered as being equivalent to requesting that the data be transmitted. 
     Non-Use 
     The first base station  100 , for example, does not use the part or the whole of the frequency band in the period. 
     The control unit  153  of the first base station  100 , for example, controls radio communication of the first base station  100  so that the first base station  100  does not use the part or the whole of the frequency band. Specifically, the control unit  153 , for example, does not map a signal to radio resources of the part or the whole of the frequency band in the period. 
     Note that, when the second base station  200  uses the part of the frequency band, a guard band may be provided between the band of the part and the remaining band. In addition, the part of the frequency band may be decided by taking the guard band into consideration. 
     Cancellation of Permission 
     The first base station  100  (the control unit  153 ) may cancel permission for the second base station to use the frequency band. 
     The first base station  100  (the control unit  153 ) may decide to cancel permission to use the frequency band, and may instruct the second base station  200  to stop using the frequency band. Note that the second base station  200  may notify the first base station  100  of the fact that the use of the frequency band has stopped, and the first base station  100  may start using the frequency band after the notification from the second base station  200 . 
     Accordingly, the first base station  100  can more flexibly use the frequency band. 
     As described above, the first base station  100  (the control unit  153 ), for example, permits the second base station  200  to use the frequency band. Accordingly, the second base station  200 , for example, can use the frequency band with priority, like the first base station  100 . 
     Note that, when the second base station  200  can use the frequency band albeit no priority provided, as described with reference to  FIG. 2  and the like, for example, the first base station  100  (the control unit  153 ) may not permit the second base station  200  to use the frequency band. In this case, the second base station  200  may use the frequency band, albeit no priority provided, to transmit the data to the terminal apparatus. 
     (c) Instruction of Use of SCC 
     The first base station  100  (the control unit  153 ), for example, instructs the terminal apparatus to use a band which is used by the second base station  200  to transmit the data as a secondary component carrier (SCC) accompanied by a primary component carrier (PCC) used by the first base station  100 . 
     More specifically, the control unit  153 , for example, activates the band as an SCC accompanied by a PCC (a PCC for the terminal apparatus) used by the first base station  100 . As an example, the control unit  153  transmits a Radio Resource Control (RRC) connection reconfiguration message for activating the band as an SCC to the terminal apparatus via the antenna unit  110  and the radio communication unit  120 . As another example, the control unit  153  may transmit a Media Access Control (MAC) control element for activating the band as an SCC via the antenna unit  110  and the radio communication unit  120 . 
     Accordingly, for example, the second base station  200  can transmit the data to the terminal apparatus without handover of the terminal apparatus. 
     Note that, in the first case, the band used by the second base station  200  to transmit the data is the frequency band that is available to the first base station  100  with priority. 
     (d) Transmission of Scheduling Information 
     The first base station  100  (the control unit  153 ), for example, transmits scheduling information indicating a result of scheduling the transmission of the data by the second base station  200  to the terminal apparatus. 
     Specifically, for example, the second base station  200  performs the scheduling and transmits the scheduling information to the first base station  100  as will be described below. Then, the first base station  100  (the control unit  153 ) transmits the scheduling information to the terminal apparatus. The first base station  100  transmits the scheduling information to the terminal apparatus using, for example, the frequency band or another frequency band (for example, a PCC of the terminal apparatus) that the first base station  100  uses for radio communication with the terminal apparatus. The first base station  100  transmits the scheduling information to the terminal apparatus on, for example, a control channel (for example, a Physical Downlink Control Channel (PDCCH)). 
     Note that the first base station  100  may perform the scheduling instead of the second base station  200  performing the scheduling. In addition, the second base station  200  may transmit the scheduling information to the terminal apparatus instead of the first base station  100  transmitting the scheduling information to the terminal apparatus. 
     (Operation of Second Base Station  200 ) 
     (a) Transmission of Data 
     The second base station  200  transmits the data to the terminal apparatus using the frequency band. For example, the control unit  253  of the second base station  200  controls radio communication of the second base station  200  so that the second base station  200  uses the frequency band to transmit the data to the terminal apparatus. 
     Transmission with Permission 
     The first base station  100 , for example, permits the second base station  200  to use a part or the whole of the frequency band in a period in which the first base station  100  does not use the part or the whole of the frequency band. Then, the second base station  200  uses the part or the whole of the frequency band to transmit the data to the terminal apparatus. For example, the control unit  253  of the second base station  200  controls radio communication of the second base station  200  so that the second base station  200  transmits the data to the terminal apparatus using the part or the whole of the frequency band. 
     Note that, the first base station  100  notifies the second base station  200  of the period (and the part of the frequency band) as described above. 
     Specific Process 
     The control unit  253 , for example, performs scheduling for transmitting the data. That is, the control unit  253  allocates radio resources of the part or the whole of the frequency band to a signal of the data. Then, the control unit  253  maps the signal of the data to the allocated radio resources. 
     Note that the first base station  100  may perform the scheduling instead of the second base station  200  performing the scheduling. 
     (b) Use of Frequency Band as SCC 
     The second base station  200 , for example, uses the band used to transmit the data as an SCC accompanied by a PCC used by the first base station  100 . For example, the control unit  253  controls radio communication of the second base station  200  so that the second base station  200  uses the band as the SCC. 
     Accordingly, the second base station  200  can transmit the data to the terminal apparatus, for example, without handover of the terminal apparatus. 
     Note that, in the first case, the band used by the second base station  200  to transmit the data is the frequency band that is available to the first base station  100  with priority. 
     (c) Transmission of Scheduling Information 
     The second base station  200  (the control unit  253 ), for example, transmits scheduling information indicating a result of the scheduling to the first base station  100 . Then, the first base station  100  transmits the scheduling information to the terminal apparatus. 
     Note that the second base station  200  (the control unit  253 ) may transmit the scheduling information to the terminal apparatus instead of the first base station  100  transmitting the scheduling information to the terminal apparatus. The second base station  200  may transmit the scheduling information to the terminal apparatus on, for example, a control channel (for example, a PDCCH). 
     (d) Additional Transmission of Data 
     When an amount of radio resources that is available to the second base station  200  among radio resources of the frequency band is greater than that of radio resources used to transmit the data to the terminal apparatus, the second base station  200  may use the extra radio resources to transmit other data to the terminal apparatus or another terminal apparatus. Accordingly, the radio resources of the frequency band, for example, are more effectively used. 
     (Synchronization of the First Base Station  100  and the Second Base Station  200 ) 
     The first base station  100  and the second base station  200 , for example, are synchronized with each other. 
     The first base station  100  and the second base station  200  are synchronized with each other for, for example, the frequency band. The first base station  100  and the second base station  200  are synchronized with each other for, for example, the frequency band in a time direction and/or a frequency direction. 
     As an example, the second base station  200  may be synchronized with the first base station  100  based on a synchronization signal transmitted by the first base station  100 . As another example, the second base station  200  may be provided with information for synchronizing with the first base station  100  from another network node (for example, the first base station  100  or a core network node) and thus be synchronized with the first base station  100  based on the information. 
     As described above in the first case, the second base station  200 , for example, transmits data destined for a terminal apparatus that accesses the first base station  100  to the terminal apparatus using the frequency band that is available to the first base station  100  with priority (i.e., the frequency band that the second base station  200  is incapable of using with priority). Accordingly, the second base station  200  can transmit the data to the terminal apparatus, for example, without a burden of radio resources. 
     5.2. Second Case 
     In a second case, the second base station  200  transmits data destined for the terminal apparatus that accesses the first base station  100  to the terminal apparatus using another frequency band that is available to the second base station  200 . The other frequency band is a band different from the frequency band that is available to the first base station  100  with priority. 
     (Operation of First Base Station  100 ) 
     (a) Request for Transmission of Data 
     The first base station  100  (the control unit  153 ), for example, requests that the second base station  200  transmit the data to the terminal apparatus using another frequency band available to the second base station  200 . 
     Referring to  FIGS. 3, 5, and 7  again, the other frequency band is the frequency band  33  as an example. That is, the second base station  200  uses the frequency band  33  to transmit the data to the terminal apparatus. Note that the other frequency band is not limited thereto, and can be another arbitrary frequency band available to the second base station  200 . 
     (b) Permission to Use Frequency Band 
     In the second case, the first base station  100  (the control unit  153 ) may not permit the second base station  200  to use the frequency band that is available to the first base station  100  with priority. 
     (c) Instruction on Use of SCC 
     The first base station  100  (the control unit  153 ), for example, instructs the terminal apparatus to use a band used by the second base station  200  for the transmission of the data as an SCC accompanied by a PCC used by the first base station  100 . There is no difference in description of the specific process thereof between the above-described first case and the second case. Thus, overlapping description will be omitted here. 
     Accordingly, the second base station  200  can transmit the data to the terminal apparatus, for example, without handover of the terminal apparatus. 
     Note that, in the second case, the band used by the second base station  200  for the transmission of the data is the other frequency band available to the second base station  200 . The first base station  100  may have known the other frequency band, or the second base station  200  may notify the first base station  100  of it. 
     (d) Transmission of Scheduling Information 
     The first base station  100  (the control unit  153 ), for example, transmits scheduling information indicating a result of scheduling for transmission of the data by the second base station  200  to the terminal apparatus. 
     Specifically, the second base station  200 , for example, performs the scheduling to transmit the scheduling information to the first base station  100  as will be described below. Then, the first base station  100  (the control unit  153 ) transmits the scheduling information to the terminal apparatus. The first base station  100 , for example, uses the frequency band that the first base station  100  uses (for example, a PCC of the terminal apparatus) for radio communication with the terminal apparatus to transmit the scheduling information to the terminal apparatus. The first base station  100  transmits the scheduling information to the terminal apparatus on, for example, a control channel (for example, a PDCCH). 
     Note that the first base station  100  may perform the scheduling instead of the second base station  200  performing the scheduling. In addition, the second base station  200  may transmit the scheduling information to the terminal apparatus instead of the first base station  100  transmitting the scheduling information to the terminal apparatus. 
     (Operation of Second Base Station  200 ) 
     (a) Transmission of Data 
     The second base station  200  uses the other frequency band available to the second base station  200  to transmit the data to the terminal apparatus. For example, the control unit  253  of the second base station  200  controls radio communication of the second base station  200  so that the second base station  200  transmits the data to the terminal apparatus using the other frequency band. 
     Specific Process 
     The control unit  253 , for example, performs scheduling for transmitting the data. That is, the control unit  253  allocates radio resources of the other frequency band to a signal of the data. Then, the control unit  253  maps the signal of the data to the allocated radio resources. 
     Note that the first base station  100  may perform the scheduling instead of the second base station  200  performing the scheduling. 
     (b) Use of Frequency Band as SCC 
     The second base station  200 , for example, uses a band for transmission of the data as an SCC accompanied by a PCC used by the first base station  100 . For example, the control unit  253  controls radio communication of the second base station  200  so that the second base station  200  uses the band as the SCC. 
     Accordingly, the second base station  200  can transmit the data to the terminal apparatus, for example, without handover of the terminal apparatus. 
     Note that, in the second case, the band used by the second base station  200  for transmission of the data is the other frequency band available to the second base station  200 . 
     (c) Transmission of Scheduling Information 
     The second base station  200  (the control unit  253 ), for example, transmits scheduling information indicating a result of the scheduling to the first base station  100 . Then, the first base station  100  transmits the scheduling information to the terminal apparatus. 
     Note that the second base station  200  (the control unit  253 ) may transmit the scheduling information to the terminal apparatus instead of the first base station  100  transmitting the scheduling information to the terminal apparatus. The second base station  200  may transmit the scheduling information to the terminal apparatus on, for example, a control channel (for example, a PDCCH). 
     (Synchronization of First Base Station  100  and Second Base Station  200 ) 
     The first base station  100  and the second base station  200  may or may not be synchronized with each other. 
     As described above in the second case, the second base station  200 , for example, uses another frequency band available to the second base station  200  to transmit data destined for the terminal apparatus that accesses the first base station  100  to the terminal apparatus. Accordingly, for example, the frequency band available to the first base station  100  with priority can be secured for the first base station  100 . That is, a reduction of the band available to the first base station  100  is avoided. In addition, the second base station  200  can transmit the data to the terminal apparatus, regardless of a situation in which the first base station  100  uses the frequency band available to the first base station  100  with priority. 
     5.4. Third Case 
     In a third case, the second base station  200  transmits the data to the terminal apparatus using at least one selected from the frequency band available to the first base station  100  with priority and another frequency band available to the second base station  200 . 
     (Operation of First Base Station  100 ) 
     The first base station  100  (the control unit  153 ), for example, requests that the second base station  200  transmit the data to the terminal apparatus using at least one selected from the frequency band available to the first base station  100  with priority and another frequency band available to the second base station  200 . 
     When the frequency band available to the first base station  100  with priority is selected, the first base station  100  operates as in the above-described first case. 
     When the other frequency band available to the second base station  200  is selected, the first base station  100  operates as in the above-described second case. 
     When both the frequency band and the other frequency band are selected, the first base station  100  performs both the operation of the above-described first case and the above-described second operation. Note that the operation of the above-described first case and the above-described second operation may be performed separately, or may be appropriately performed in an integrated manner. 
     Note that the first base station  100  (the control unit  153 ), for example, selects at least one of the frequency band and the other frequency band. 
     (Operation of Second Base Station  200 ) 
     The second base station  200  transmits the data to the terminal apparatus using at least one selected from the frequency band and the other frequency band. For example, the control unit  253  of the second base station  200  controls radio communication of the second base station  200  so that the second base station transmits the data to the terminal apparatus using the selected one. 
     When the frequency band available to the first base station  100  with priority is selected, the second base station  200  operates as in the above-described first case. 
     When the other frequency band available to the second base station  200  is selected, the second base station  200  operates as in the above-described second case. 
     When both the frequency band and the other frequency band are selected, the second base station  200  performs both the operation of the above-described first case and the above-described second operation. Note that the operation of the above-described first case and the above-described second operation may be performed separately, or may be appropriately performed in an integrated manner. 
     (Synchronization of First Base Station  100  and Second Base Station  200 ) 
     The first base station  100  and the second base station  200  are, for example, synchronized with each other. There is no difference in this point between the above-described first case and third case. Thus, overlapping description will be omitted here. 
     (Selection of at Least One Band) 
     An example in which at least one is selected from the frequency band (i.e., the frequency band available to the first base station  100  with priority) and the other frequency band (i.e., the other frequency band available to the second base station  200 ) will be described. 
     (First Example) 
     As a first example, when there is another frequency band available to the second base station  200 , the other frequency band is selected, and when there is no other frequency band, the foregoing frequency band is selected. 
     When there is the frequency band  33  as in the example shown in  FIGS. 3, 5 , and  7 , for example, the other frequency band is selected. The other frequency band is of course not limited to the example, and can be another arbitrary frequency band available to the second base station  200 . 
     Note that, when there is the other frequency band, the foregoing frequency band may also be selected in addition to the other frequency band. 
     Accordingly, for example, it is possible to secure the frequency band available to the first base station  100  with priority for the first base station  100  as much as possible. That is, a reduction of the band available to the first base station  100  is avoided as much as possible. 
     (Second Example) 
     As a second example, at least one selected from the frequency band and the other frequency band may be selected based on an amount or a ratio of radio resources (which is referred to as “remaining resources” below) available to the second base station  200  for transmission of the data among radio resources of the other frequency band. 
     When, for example, the amount or the ratio of the remaining resources is great (for example, the amount or the ratio of the remaining resources is equal to or greater than a first threshold value), the other frequency band is selected and the frequency band is not selected. 
     In addition, when the amount or the ratio of the remaining resources is small (for example, the amount or the ratio of the remaining resources is smaller than the first threshold value), for example, both the frequency band and the other frequency band are selected. 
     Note that, when the amount or the ratio of the remaining resources is small (for example, the amount or the ratio of the remaining resources is smaller than the first threshold value), only the foregoing frequency band may be selected. Alternatively, when the amount or the ratio of the remaining resources is very small (for example, the amount or the ratio of the remaining resources is smaller than a second threshold value (a threshold value smaller than the first threshold value)), only the foregoing frequency band may be selected. 
     Accordingly, for example, it is possible to secure the frequency band available to the first base station  100  with priority for the first base station  100  as much as possible. That is, a reduction of the band available to the first base station  100  is avoided as much as possible. 
     Furthermore, when at least the frequency band is selected, an amount of radio resources used by the second base station  200  among radio resources of the frequency band (for example, a period or a band) may be decided based on the amount or the ratio of the remaining resources. When the amount is larger or the ratio is greater, for example, the amount of the radio resources used by the second base station  200  among the radio resources of the frequency band may be smaller (for example, the period may be shorter or the band may be narrower). When the amount is less or the ratio is smaller, for example, the amount of the radio resources used by the second base station  200  among the radio resources of the frequency band may be larger (for example, the period may be longer or the band may be wider). Accordingly, for example, a reduction of interference and leveling of traffic are expected. 
     Note that the amount or the ratio of the remaining resources may be computed by the second base station  200  (the control unit  253 ), and the second base station  200  (the control unit  253 ) may notify the first base station  100  of it. Alternatively, the amount or the ratio of the remaining resources may be computed by the first base station  100  (the control unit  153 ) based on information provided by the second base station  200  (for example, scheduling information with regard to the other frequency band). 
     6. CONSIDERATION OF ANOTHER RADIO COMMUNICATION SYSTEM HAVING HIGHER PRIORITY LEVEL 
     Next, an operation of the first base station  100  and the second base station  200  taking another radio communication system having a higher priority level (i.e., the third radio communication system) into consideration will be described. 
     As described above, the frequency band is, for example, a band used by another radio communication system (i.e., the third radio communication system) with higher priority than the radio communication system that includes the first base station  100  (i.e., the first radio communication system). In this case, the first base station  100  can use the frequency band under the condition that interference with the third radio communication system be avoided or suppressed. 
     (Use of Frequency Band by First Base Station) 
     (a) First Example 
     As a first example, the first base station  100  can use the frequency band when reception power of the first base station  100  with respect to a signal transmitted from the third radio communication system using the frequency band is equal to or lower than a threshold value. 
     The first base station  100  (for example, the processing unit  150 ), for example, measures reception power with respect to the signal transmitted from the third radio communication system using the frequency band. Then, the processing unit  150  (for example, the control unit  153 ) determines whether the reception power is equal to or lower than the threshold value. Then, when the reception power is equal to or lower than the threshold value, the control unit  153  controls radio communication of the first base station  100  so that the first base station  100  transmits a signal using the frequency band. 
     Accordingly, for example, interference in the third radio communication system is suppressed. 
     (b) Second Example 
     As a second example, the first base station  100  may be capable of using the frequency band when the first base station  100  is positioned at a place at which the first base station  100  can suppress interference with the third radio communication system to a tolerable level. 
     When the first base station  100  is positioned outside an exclusive zone of the third radio communication system, for example, the first base station  100  may be capable of using the frequency band. The exclusive zone is an area in which there is a possibility of a signal transmitted with arbitrary transmission power interfering with the third radio communication system to an extent exceeding the tolerable level. 
     Specifically, for example, a frequency management system that manages use of a frequency band acquires position information indicating a position of the first base station  100  and determines whether the position is included in the exclusive zone. Then, the frequency management system notifies the first base station  100  of the result of the determination. Then, when the position is not included in the exclusive zone, the control unit  153  controls radio communication of the first base station  100  so that the first base station  100  transmits signals using the frequency band. Note that, in place of the frequency management system, the first base station  100  may determine whether the position of the first base station  100  is included in the exclusive zone by itself. In addition, when the position is not included in the exclusive zone, the frequency management system may transmit information regarding an available frequency band to the first base station  100  instead of notifying the first base station  100  of the result of the determination. The information regarding an available frequency band may include information indicating the frequency band, information indicating maximum transmission power of the frequency band, information indicating a period in which the frequency band is available, and the like. 
     Accordingly, interference in the third radio communication system, for example, is suppressed. 
     (c) Third Example 
     As a third example, the first base station  100  may be capable of using the frequency band in a period in which the third radio communication system does not use the frequency band. As described above, the frequency band may be a part of a band used by the third radio communication system or the whole of a band used by the third radio communication system. 
     A frequency management system that manages the frequency band or the third radio communication system, for example, may notify the first base station  100  of the period. Then, the control unit  153  may control radio communication of the first base station  100  so that the first base station  100  transmits a signal using the frequency band in the period. 
     (Use of Frequency Band by Second Base Station) 
     (a) Frequency Band Available to First Base Station  100  with Priority 
     The second base station  200 , for example, can use, albeit no priority provided, the frequency band available to the first base station  100  with priority. In this case, the second base station  200  can use the frequency band under the condition that, for example, interference with the first base station  100  (or the first radio communication system) and the third radio communication system be avoided or suppressed. 
     The second base station  200 , for example, can use a part or the whole of the frequency band in a period in which both the first base station  100  (or the first radio communication system) and the third radio communication system do not use the part or the whole of the frequency band. 
     For example, the first base station  100  or another network node (for example, a frequency management system that manages the frequency band) notifies the second base station  200  of the period. Then, the second base station  200  uses the part or the whole of the frequency band in the period to transmit or receive signals. 
     (b) Other Frequency Band Available to Second Base Station  200   
     Note that another frequency band available to the second base station  200  may be a band used by the third radio communication system with priority. In this case, the second base station  200  can use the other frequency band under the condition that interference with the third radio communication system be avoided or suppressed, like the first base station  100 . 
     Note that there is no difference in description regarding techniques for avoiding or suppressing interference in the third radio communication system between the technique of the above-described first base station  100  (the control unit  153 ) and the technique of the second base station  200  (the control unit  253 ) except for the difference in the target bands. 
     (Permission for First Base Station to Use Frequency Band) 
     When requesting that the second base station  200  transmit the data destined for the terminal apparatus to the terminal apparatus using the frequency band, for example, the first base station  100  (the control unit  153 ) permits the second base station  200  to use the frequency band as described above. 
     In addition, the second base station  200 , for example, may be incapable of using the frequency band without permission as described above. In this case, the first base station  100  (the control unit  153 ) may permit the second base station  200  to use a part or the whole of the frequency band. 
     The control unit  153  of the first base station  100 , for example, permits the second base station  200  to use the frequency band within a range within which the first base station  100  can use the frequency band. As an example, the control unit  153  permits the second base station  200  to use a part or the whole of the frequency band in a period in which the first base station  100  can use the frequency band. 
     Accordingly, for example, interference of the second base station  200  with the third radio communication system is avoided or suppressed. 
     7. PROCESS FLOW 
     Next, an example of a process according to the embodiment of the present disclosure will be described with reference to  FIG. 10 .  FIG. 10  is a sequence diagram showing an example of a schematic flow of the process according to the embodiment of the present disclosure. 
     The first base station  100  acquires information regarding the second base station  200 , and requests that the second base station  200  transmit data destined for a terminal apparatus that accesses the first base station  100  to the terminal apparatus (S 401 ). 
     In addition, the first base station  100  forwards the data destined for the terminal apparatus to the second base station  200  (S 403 ). 
     In addition, the first base station  100  transmits control information for activating an SCC (for example, an RRC connection configuration message, or an MAC control element) to the terminal apparatus (S 405 ). 
     The second base station  200  performs scheduling for transmission of the data and transmits scheduling information indicating the result of the scheduling to the first base station  100  (S 407 ). 
     The first base station  100  transmits the scheduling information to the terminal apparatus (S 409 ). Then, the second base station  200  transmits the data to the terminal apparatus (S 411 ). 
     8. MODIFIED EXAMPLES 
     Next, a first modified example and a second modified example of the embodiment of the present disclosure will be described. 
     8.1. First Modified Example 
     In a first modified example of the embodiment of the present disclosure, the first base station  100  (the control unit  153 ) gives an instruction to the second base station  200  with regard to a link direction for a band used by the second base station  200  to transmit the data to the terminal apparatus that accesses the first base station  100  (which will be referred to as a “link direction-related instruction” hereinbelow). 
     On the other hand, the second base station  200  performs radio communication using the band according to the link direction-related instruction. The control unit  253  of the second base station  200  controls radio communication of the second base station  200  according to the link direction-related instruction. 
     (Band) 
     The band is, for example, the frequency band available to the first base station  100  with priority (i.e., the band that the second base station  200  is incapable of using with priority). Note that the band may be the other frequency band available to the second base station  200 . 
     Note that, when the band is the frequency band available to the first base station  100  with priority, the link direction-related instruction is given, for example, with activation of the frequency band as an SCC. 
     (Link Direction-Related Instruction) 
     (a) Instruction of Duplex Scheme 
     The link direction-related instruction includes, for example, an instruction on a duplex scheme applied to the band. That is, the first base station  100  gives the instruction on the duplex scheme applied to the band, and the second base station  200  performs radio communication using the band according to the duplex scheme. 
     The duplex scheme is, for example, time division duplex (TDD) or frequency division duplex (FDD). 
     Accordingly, the first base station  100 , for example, can cause the second base station  200  to change a duplex scheme to be used when necessary. 
     (b) TDD: Instruction of TDD Configuration 
     A duplex scheme applied to the band is, for example, TDD. In this case, the link direction-related instruction includes, for example, an instruction of a TDD configuration applied to the band. That is, the first base station  100  gives the instruction of the TDD configuration applied to the band, and the second base station  200  performs radio communication using the band according to the TDD configuration. 
     The TDD configuration indicates a link direction in units of subframes of a radio frame. In other words, the TDD configuration indicates whether each subframe included in the radio frame is a downlink subframe, an uplink subframe, or a special subframe. Note that the TDD configuration is also called an uplink-downlink configuration or a TDD uplink-downlink configuration. 
     Note that, when the second base station  200  performs radio communication using a plurality of frequency bands (for example, when the base station performs radio communication using a plurality of component carriers (CCs)), different duplex schemes may be applied to at least two frequency bands of the plurality of frequency bands. For example, TDD may be applied to one frequency band and FDD to the other frequency band. 
     (b-1) Instruction of Existing TDD Configuration 
     The TDD configuration applied to the band is, for example, one of 7 existing TDD configurations. With regard to the 7 existing TDD configurations, the 7 existing TDD configurations defined in the technical standard of the 3 rd  Generation Partnership Project (3GPP) (TS 36.211 Table 4.2-2: Uplink-downlink Configuration) will be described with reference to  FIG. 11 . 
       FIG. 11  is an illustrative diagram for describing the 7 existing TDD configurations. Referring to  FIG. 11 , the 7 existing TDD configurations are shown. In the TDD configurations, each subframe is one among a downlink frame that is a subframe for downlink, an uplink frame that is a subframe for uplink, and a special subframe. A special subframe is provided when a downlink subframe and an uplink subframe are switched in order to consider a delay of propagation from a base station to a terminal apparatus. 
     Note that the first base station  100  (the control unit  153 ) may give an instruction of a TDD configuration to be applied to the band by giving a notification of the configuration number (0 to 6) of the TDD configuration. 
     Accordingly, when TDD is employed, for example, it is possible to change a ratio of uplink subframes and downlink subframes as necessary. For example, more radio resources can be allocated to transmit signals in downlink. 
     (b-2) Instruction of New TDD Configuration 
     The TDD configuration may be a TDD configuration other than the existing TDD configurations shown in  FIG. 11 . The TDD configuration may be, for example, a TDD configuration in which all subframes are downlink subframes (which will be referred to as a “downlink-dedicated configuration” below). That is, the link direction-related instruction may include an instruction of a downlink-dedicated configuration. The TDD configuration will be described below with reference to  FIG. 12 . 
       FIG. 12  is an illustrative diagram for describing the downlink-dedicated configuration. Referring to  FIG. 12 , the downlink-dedicated TDD configuration is shown. As shown in  FIG. 12 , all subframes in the downlink-dedicated TDD configuration are downlink subframes. 
     Accordingly, even when TDD is employed, for example, all radio resources can be used for transmission of a signal in downlink. In addition, this downlink-dedicated TDD configuration may be applied to a downlink SCC accompanied by a PCC used by the first base station  100  that operates in FDD. 
     Note that, when the second base station  200  performs radio communication using a plurality of frequency bands (for example, a plurality of CCs), different TDD configurations may be applied to at least two frequency bands of the plurality of frequency bands. 
     (c) FDD: Instruction of Link Direction of Frequency Band 
     The duplex scheme applied to the band is, for example, FDD. In this case, the link direction-related instruction includes, for example, an instruction of use of the band as a downlink band. That is, the first base station  100  gives the instruction of use of the band as a downlink band, and the second base station  200  performs radio communication using the band serving as a downlink band. 
     Note that the link direction-related instruction may include an instruction of use of the band as an uplink band instead of the instruction of use of the band as a downlink band. That is, the first base station  100  may give the instruction of use of the band as an uplink band, and the second base station  200  may perform radio communication using the band serving as an uplink band. 
     (Specific Process) 
     (a) Link Direction-Related Instruction 
     The first base station  100  (the control unit  153 ) transmits control information for giving the link direction-related instruction (for example, a message, a command, or the like) to the second base station  200 . Then, the second base station  200  (the control unit  253 ) performs radio communication using the band according to the control information. 
     Note that, when the first base station  100  requests that the second base station  200  transmit the data destined for the terminal apparatus that accesses the first base station  100  to the terminal apparatus, the control information may be control information for giving the link direction-related instruction, and may be control information for requesting that the data be transmitted to the terminal apparatus. 
     (b) Transmission of Data 
     When TDD is applied, for example, the control unit  253  of the second base station  200  allocates radio resources of downlink subframes to a signal of the data destined for the terminal apparatus and maps the signal to the radio resources. 
     When FDD is applied, for example, the control unit  253  of the second base station  200  allocates radio resources of a downlink band to the signal of the data destined for the terminal apparatus and maps the signal to the radio resources. 
     8.2. Second Modified Example 
     In the examples described above according to the embodiment of the present disclosure, the first base station  100  makes a request (i.e., request that the data destined for the terminal apparatus be transmitted) and permits use of a frequency band with respect to the second base station  200 . 
     In a second modified example of the embodiment of the present disclosure, for example, another network node, instead of the first base station  100 , may make a request (i.e., a request that the data destined for a terminal apparatus be transmitted) and permit use of a frequency band with respect to the second base station  200 . As an example, the other network node may be a frequency management system that manages frequency bands. 
     More specifically, at least one of the information acquisition unit  151  and the control unit  153  may be provided in the other network node. In addition, the rest of the information acquisition unit  151  and the control unit  153  may be provided in the first base station  100 . 
     9. OTHER EMBODIMENT 
     Next, another embodiment of the present disclosure will be described. 
     (Technical Problem) 
     For off-loading of traffic, for example, a radio communication apparatus that is not connected to wired backhaul (for example, a terminal apparatus which can operate as a base station, a base station simply not connected to wired backhaul, or the like) can operate as a base station (for example, a base station of a small cell). In this case, the radio communication apparatus can use radio backhaul between the radio communication apparatus and another base station (for example, a base station of a macrocell). 
     However, if it is not possible to secure a frequency band to be used for radio backhaul, it is not possible to transmit and receive data via the radio backhaul from the beginning. In addition, if it is not possible to secure a sufficient frequency band to be used for radio backhaul, there is a possibility of a delay occurring in the radio backhaul, and as a result, a communication speed in the coverage of the radio communication apparatus can be lowered. 
     Thus, it is desirable to provide a mechanism which enables transmission and reception of data via radio backhaul with satisfactory efficiency. 
     (Technical Features) 
     The first base station  100  (the information acquisition unit  151 ), for example, acquires information regarding the second base station  200  having a coverage area that overlaps a coverage area of the first base station  100 . Then, the first base station  100  (the control unit  153 ) requests that the second base station  200  transmit or receive data transmitted and received between the second base station  200  and a terminal apparatus that accesses the second base station  200  via radio backhaul that is radio backhaul between the first base station  100  and the second base station  200  and that uses a frequency band available to the second base station  200 . 
     (a) Second Base Station  200   
     Base Station Not Connected to Radio Backhaul 
     The second base station  200  is, for example, a base station that is not connected to radio backhaul. The second base station  200  may be a terminal apparatus operable as a base station, or just a base station that is not connected to wired backhaul. 
     Information Regarding Second Base Station  200   
     The information regarding the second base station  200  includes, for example, identification information of the second base station  200  (for example, a cell ID), an address of the second base station  200  (for example, an IP address), position information indicating a position of the second base station  200 , and/or a measurement result on the second base station  200  obtained by a terminal apparatus. 
     The information regarding the second base station  200  is, for example, stored in the storage unit  140 , and the information acquisition unit  151  acquires the information from the storage unit  140 . 
     (b) Radio Backhaul 
     As described above, the radio backhaul between the first base station  100  and the second base station  200  is radio backhaul that uses the frequency band available to the second base station  200 . 
     Frequency Band 
     Specific Example 
     The frequency band available to the second base station  200  is, for example, “another frequency band” according to the embodiment described before the other embodiment. More specifically, the frequency band available to the second base station  200  is, for example, the frequency band  33  shown in  FIG. 3, 5 , or  7 . 
     Permission 
     The frequency band is, for example, a frequency band of which use for the radio backhaul is permitted. The frequency band may be a frequency band that is already permitted before a request, or may be a frequency band permitted after a request. 
     The second base station  200  permits the frequency band to be used for the radio backhaul. 
     The frequency band is permitted to be used for the radio backhaul in a period in which the second base station  200  does not use the frequency band for communication with a terminal apparatus. 
     Additional Frequency Band 
     The radio backhaul may be radio backhaul that uses an additional frequency band as well as the frequency band. The additional frequency band may be a frequency band available to the first base station  100 . More specifically, the additional frequency band may be the frequency band  31  shown in one of  FIGS. 2 to 7 . In addition, when the first base station  100  is managed by a communication service provider assigned with a licensed frequency band, the additional frequency band may be the licensed frequency band. 
     (c) Specific Process 
     The control unit  153 , for example, transmits control information for a request to the second base station  200  (for example, a message, a command, or the like) to the second base station  200  via the radio communication unit  120 . 
     Note that the control unit  153 , for example, transmits the data to the second base station  200  and receives the data from the second base station  200  via the radio communication unit  120 . 
     (Process Flow) 
       FIG. 13  is a sequence diagram showing an example of a schematic flow of a process according to another embodiment of the present disclosure. 
     The first base station  100  acquires information regarding the second base station  200 . Then, the first base station  100  requests that the second base station  200  transmit or receive data transmitted and received between the second base station  200  and a terminal apparatus that accesses the second base station  200  via radio backhaul that is radio backhaul between the first base station  100  and the second base station  200  and uses a frequency band available to the second base station  200  (S 421 ). The frequency band may have already been permitted to be used for the radio backhaul, or may be permitted to be used for the radio backhaul after this request. 
     Then, the second base station  200  responds to the first base station  100  (S 423 ). 
     Then, upon receiving data destined for the terminal apparatus that accesses the second base station  200  from a network, the first base station  100  forwards the data to the second base station  200  via the radio backhaul (S 425 ). Then, the second base station  200  transmits the data to the terminal apparatus (S 427 ). 
     In addition, the terminal apparatus that accesses the second base station  200  transmits data to the second base station  200  (S 429 ), and the second base station  200  transmits the data to the first base station  100  via the radio backhaul (S 423 ). Note that the first base station  100  forwards the data to the network. 
     (Modified Example) 
     In the example described above, the first base station  100  requests the second base station  200  to transmit or receive the data via the radio backhaul. However, the other embodiment is not limited thereto. 
     As a first modified example, a network node (an information acquisition unit) different from the first base station  100  and the second base station  200  may acquire information regarding the second base station  200 . Then, the network node (a control unit) may request one of or both the first base station  100  and the second base station  200  to transmit or receive the data via the radio backhaul. As a result, the first base station  100  and the second base station  200  may transmit and receive the data via the radio backhaul. 
     As a second modified example, the second base station  200  (the information acquisition unit  251 ) may acquire information regarding the second base station  200 . Then, the second base station  200  (the control unit  253 ) may request the first base station  100  to transmit or receive the data via the radio backhaul. As a result, the first base station  100  and the second base station  200  may transmit and receive the data via the radio backhaul. 
     10. APPLICATION EXAMPLES 
     The technology of the present disclosure is applicable to various products. For example, a base station according to an embodiment of the present disclosure (for example, the first base station  100  and the second base station  200 ) may be realized as any type of evolved Node B (eNB) such as a macro eNB, and a small eNB. A small eNB may be an eNB that covers a cell smaller than a macrocell, such as a pico eNB, a micro eNB, or a home (femto) eNB. Instead, the base station may be realized as another type of base station such as a NodeB or a base transceiver station (BTS). The base station may include a main body (that is also referred to as a base station apparatus) configured to control radio communication, and one or more remote radio heads (RRH) disposed in a different place from the main body. Additionally, various types of terminals to be described below may also operate as the base station by temporarily or semi-permanently executing a base station function. Furthermore, at least a part of constituent elements of the base station may be realized in a base station apparatus or a module for a base station apparatus. 
     In addition, the other network node according to the second modified example may be realized as any type of server, for example, a tower server, a rack server, or a blade server. In addition, at least a part of constituent elements of the other network node may be realized in a module (for example, an integrated circuit module configured in one die, or a card or a blade inserted into a slot of a blade server) mounted in a server. 
     For example, the second base station  200  may be realized as a mobile terminal such as a smartphone, a tablet personal computer (PC), a notebook PC, a portable game terminal, a portable/dongle type mobile router, and a digital camera, or an in-vehicle terminal such as a car navigation apparatus. The second base station  200  may also be realized as a terminal (that is also referred to as a machine type communication (MTC) terminal) that performs machine-to-machine (M2M) communication. Furthermore, at least a part of constituent elements of the second base station  200  may be realized in a module (such as an integrated circuit module configured in one die) mounted on each of the terminals. 
     10.1. Application Example Regarding Other Network Node 
       FIG. 14  is a block diagram showing an example of a schematic configuration of a server  700  to which the technology of 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 functions of the server  700 . The memory  702  includes a random access memory (RAM) and a read only memory (ROM), and stores a program that is executed by the processor  701  and data. The storage  703  may include a storage medium such as a semiconductor memory and a hard disk. 
     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 an Evolved Packet Core (EPC), 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 (such as a high speed bus and a low speed bus) each of which has different speed. 
     At least a part of constituent elements (for example, the information acquisition unit  151  and/or the control unit  153 ) included in the processing unit  150  described with reference to  FIG. 8  may be implemented by the processor  701  of the server  700  shown in  FIG. 14 . As an example, a program for causing the processor to function as the at least part (i.e., a program for causing the processor to execute operations of the at least part) may be installed in the server  700 , and the processor  701  may execute the program. As another example, the server  700  may have a module that includes the processor  701  and the memory  702  to implement the at least part in the module. In this case, the module may store a program for causing the processor to function as the at least part in the memory  702 , and the processor  701  may execute the program. As described above, the server  700  or the module may be provided as an apparatus that includes the at least part, or the program for causing the processor to function as the at least part may be provided. In addition, a readable recording medium on which the program is recorded may be provided. 
     10.2. Application Examples Regarding First Base Station and Second Base Station 
     (First Application Example) 
       FIG. 15  is a block diagram showing a first example of a schematic configuration of an eNB to which the technology of the present disclosure may be applied. The 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 multiple antenna elements (such as multiple antenna elements included in a MIMO antenna), and is used for the base station apparatus  820  to transmit and receive radio signals. The eNB  800  may include the multiple antennas  810 , as illustrated in  FIG. 15 . For example, the multiple antennas  810  may be compatible with multiple frequency bands used by the eNB  800 . Although  FIG. 15  illustrates the example in which the eNB  800  includes the multiple antennas  810 , the eNB  800  may also include a single antenna  810 . 
     The base station apparatus  820  includes a controller  821 , a memory  822 , a network interface  823 , and a radio communication interface  825 . 
     The controller  821  may be, for example, a CPU or a DSP, and operates various functions of a higher layer of the base station apparatus  820 . For example, the controller  821  generates a data packet from data in signals processed by the radio communication interface  825 , and transfers the generated packet via the network interface  823 . The controller  821  may bundle data from multiple baseband processors to generate the bundled packet, and transfer the generated bundled packet. The controller  821  may have logical functions of performing control such as radio resource control, radio bearer control, mobility management, admission control, and scheduling. The control may be performed in corporation with an eNB or a core network node in the vicinity. The memory  822  includes a RAM and a ROM, and stores a program that is executed by the controller  821 , and various types of control data (such as a terminal list, transmission power data, and scheduling data). 
     The network interface  823  is a communication interface for connecting the base station apparatus  820  to a core network  824 . The controller  821  may communicate with a core network node or another eNB via the network interface  823 . In that case, the eNB  800 , and the core network node or the other eNB may be connected to each other through a logical interface (such as an Si interface and an X2 interface). The network interface  823  may also be a wired communication interface or a radio communication interface for radio backhaul. If the network interface  823  is a radio communication interface, the network interface  823  may use a higher frequency band for radio communication than a frequency band used by the radio communication interface  825 . 
     The radio communication interface  825  supports any cellular communication scheme such as Long Term Evolution (LTE) and LTE-Advanced, and provides wireless connection to a terminal positioned in a cell of the eNB  800  via the antenna  810 . The radio communication interface  825  may typically include, for example, a baseband (BB) processor  826  and an RF circuit  827 . The BB processor  826  may perform, for example, encoding/decoding, modulating/demodulating, and multiplexing/demultiplexing, and performs various types of signal processing of layers (such as L1, medium access control (MAC), radio link control (RLC), and a packet data convergence protocol (PDCP)). The BB processor  826  may have a part or all of the above-described logical functions instead of the controller  821 . The BB processor  826  may be a memory that stores a communication control program, or a module that includes a processor and a related circuit configured to execute the program. Updating the program may allow the functions of the BB processor  826  to be changed. The module may be a card or a blade that is inserted into a slot of the base station apparatus  820 . Alternatively, the module may also be a chip that is mounted on the card or the blade. Meanwhile, the RF circuit  827  may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna  810 . 
     The radio communication interface  825  may include the multiple BB processors  826 , as illustrated in  FIG. 15 . For example, the multiple BB processors  826  may be compatible with multiple frequency bands used by the eNB  800 . The radio communication interface  825  may include the multiple RF circuits  827 , as illustrated in  FIG. 15 . For example, the multiple RF circuits  827  may be compatible with multiple antenna elements. Although  FIG. 15  illustrates the example in which the radio communication interface  825  includes the multiple BB processors  826  and the multiple RF circuits  827 , the radio communication interface  825  may also include a single BB processor  826  or a single RF circuit  827 . 
     At least a part of the constituent elements included in the processing unit  150  (for example, the information acquisition unit  151  and/or the control unit  153 ) described with reference to  FIG. 8  may be implemented by the radio communication interface  825  of the eNB  800  shown in  FIG. 15 . Alternatively, the at least part of the elements may be implemented by the controller  821 . As an example, the eNB  800  may have a module that includes a part or all of the radio communication interface  825  (for example, the BB processors  826 ) and/or the controller  821 , and the at least part may be implemented by the module. In this case, the module may store a program for causing a processor to function as the at least part (in other words, a program for causing a processor to execute operations of the at least part) and execute the program. As another example, a program for causing a processor to function as the at least part may be installed in the eNB  800  and the radio communication interface  825  (for example, the BB processors  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 that includes the at least part, or a program for causing a processor to function as the at least part may be provided. In addition, a readable recording medium in which the program is recorded may be provided. With regard to these points, at least a part of the constituent elements included in the processing unit  250  (for example, the information acquisition unit  251  and/or the control unit  253 ) described with reference to  FIG. 9  are similar to the at least part of the constituent elements included in the processing unit  150 . 
     Furthermore, the radio communication unit  120  described with reference to  FIG. 8  may be implemented by the radio communication interface  825  (for example, the RF circuit  827 ) in the eNB  800  shown in  FIG. 15 . In addition, the antenna unit  110  may be implemented by the antenna  810 . Furthermore, the network communication unit  130  may be implemented by the controller  821  and/or the network interface  823 . With regard to this points, the antenna unit  210 , the radio communication unit  220 , and the network communication unit  230  described with reference to  FIG. 9  are similar to the antenna unit  110 , the radio communication unit  120 , and the network communication unit  130 . 
     (Second Application Example) 
       FIG. 16  is a block diagram showing a second example of a schematic configuration of an eNB to which the technology of 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 antenna  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 via a high speed line such as an optical fiber cable. 
     Each of the antennas  840  includes a single or multiple antenna elements (such as multiple antenna elements included in a MIMO antenna), and is used for the RRH  860  to transmit and receive radio signals. The eNB  830  may include the multiple antennas  840 , as illustrated in  FIG. 16 . For example, the multiple antennas  840  may be compatible with multiple frequency bands used by the eNB  830 . Although  FIG. 16  shows the example in which the eNB  830  includes the multiple antennas  840 , the eNB  830  may also include a single antenna  840 . 
     The base station apparatus  850  includes a controller  851 , a memory  852 , a network interface  853 , a radio 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. 15 . 
     The radio communication interface  855  supports any cellular communication scheme such as LTE and LTE-Advanced, and provides radio communication to a terminal positioned in a sector corresponding to the RRH  860  via the RRH  860  and the antenna  840 . The radio communication interface  855  may typically include, for example, a BB processor  856 . The BB processor  856  is the same as the BB processors  826  described with reference to  FIG. 15 , except the BB processors  856  are connected to RF circuits  864  of the RRH  860  via the connection interface  857 . The radio communication interface  855  may include the multiple BB processors  856 , as shown in  FIG. 16 . For example, the multiple BB processors  856  may be compatible with multiple frequency bands used by the eNB  830 . Although  FIG. 16  shows the example in which the radio communication interface  855  includes the multiple BB processors  856 , the radio communication interface  855  may also include a single BB processor  856 . 
     The connection interface  857  is an interface for connecting the base station apparatus  850  the (radio communication interface  855 ) to the RRH  860 . The connection interface  857  may also be a communication module for communication in the above-described high speed line that connects the base station apparatus  850  (the radio communication interface  855 ) to the RRH  860 . 
     The RRH  860  includes a connection interface  861  and a radio communication interface  863 . 
     The connection interface  861  is an interface for connecting the RRH  860  (the radio communication interface  863 ) to the base station apparatus  850 . The connection interface  861  may also be a communication module for communication in the above-described high speed line. 
     The radio communication interface  863  transmits and receives radio signals via the antenna  840 . The radio communication interface  863  may typically include, for example, the RF circuit  864 . The RF circuit  864  may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna  840 . The radio communication interface  863  may include multiple RF circuits  864 , as shown in  FIG. 16 . For example, the multiple RF circuits  864  may support multiple antenna elements. Although  FIG. 16  illustrates the example in which the radio communication interface  863  includes the multiple RF circuits  864 , the radio communication interface  863  may also include a single RF circuit  864 . 
     At least a part of the constituent elements included in the processing unit  150  (for example, the information acquisition unit  151  and/or the control unit  153 ) described with reference to  FIG. 8  may be implemented by the radio communication interface  855  and/or the radio communication interface  863  of the eNB  830  shown in  FIG. 16 . Alternatively, the at least part of the elements may be implemented by the controller  851 . As an example, the eNB  830  may have a module that includes a part or all of the radio communication interface  855  (for example, the BB processors  856 ) and/or the controller  851 , and the at least part may be implemented by the module. In this case, the module may store a program for causing a processor to function as the at least part (in other words, a program for causing a processor to execute operations of the at least part) and execute the program. As another example, a program for causing a processor to function as the at least part may be installed in the eNB  830  and the radio communication interface  855  (for example, the BB processors  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 that includes the at least part, or a program for causing a processor to function as the at least part may be provided. In addition, a readable recording medium in which the program is recorded may be provided. With regard to these points, at least a part of the constituent elements included in the processing unit  250  (for example, the information acquisition unit  251  and/or the control unit  253 ) described with reference to  FIG. 9  are similar to the at least part of the constituent elements included in the processing unit  150 . 
     Furthermore, the radio communication unit  120  described, for example, with reference to  FIG. 8  may be implemented by the radio communication interface  863  (for example, the RF circuit  864 ) in the eNB  830  shown in  FIG. 16 . In addition, the antenna unit  110  may be implemented by the antenna  840 . Furthermore, the network communication unit  130  may be implemented by the controller  851  and/or the network interface  853 . With regard to this points, the antenna unit  210 , the radio communication unit  220 , and the network communication unit  230  described with reference to  FIG. 9  are similar to the antenna unit  110 , the radio communication unit  120 , and the network communication unit  130 . 
     10.3. Application Examples Regarding Second Base Station 
     (First Application Example) 
       FIG. 17  is a block diagram showing an example of a schematic configuration of a smartphone  900  to which the technology of 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 radio communication interface  912 , one or more antenna switches  915 , one or more antennas  916 , a bus  917 , a battery  918 , and an auxiliary controller  919 . 
     The processor  901  may be, for example, a CPU or a system-on-a-chip (SoC), and controls functions of an application layer and another layer of the smartphone  900 . The memory  902  includes a RAM and a ROM, and stores a program that is executed by the processor  901 , and data. The storage  903  may include a storage medium such as a semiconductor memory and a hard disk. The external connection interface  904  is an interface for connecting an external device such as a memory card and a Universal Serial Bus (USB) device to the smartphone  900 . 
     The camera  906  includes an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and generates a captured image. The sensor  907  may include a group of sensors such as a measurement sensor, a gyro sensor, a geomagnetic sensor, and an acceleration sensor. The microphone  908  converts sounds that are input to the smartphone  900  to audio signals. The input device  909  includes, for example, a touch sensor configured to detect touch onto a screen of the display device  910 , a keypad, a keyboard, a button, or a switch, and receives an operation or an information input from a user. The display device  910  includes a screen such as a liquid crystal display (LCD) and an organic light-emitting diode (OLED) display, and displays an output image of the smartphone  900 . The speaker  911  converts audio signals that are output from the smartphone  900  to sounds. 
     The radio communication interface  912  supports any cellular communication scheme such as LTE and LTE-Advanced, and performs radio communication. The radio communication interface  912  may typically include, for example, a BB processor  913  and an RF circuit  914 . The BB processor  913  may perform, for example, encoding/decoding, modulating/demodulating, and multiplexing/demultiplexing, and performs various types of signal processing for radio communication. Meanwhile, the RF circuit  914  may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna  916 . The radio communication interface  912  may also be a one chip module that has the BB processor  913  and the RF circuit  914  integrated thereon. The radio communication interface  912  may include the multiple BB processors  913  and the multiple RF circuits  914 , as shown in  FIG. 17 . Although  FIG. 17  shows the example in which the radio communication interface  912  includes the multiple BB processors  913  and the multiple RF circuits  914 , the radio communication interface  912  may also include a single BB processor  913  or a single RF circuit  914 . 
     Furthermore, in addition to a cellular communication scheme, the radio communication interface  912  may support another type of radio communication scheme such as a short-distance radio communication scheme, a near field communication scheme, and a radio local area network (LAN) scheme. In that case, the radio communication interface  912  may include the BB processor  913  and the RF circuit  914  for each radio communication scheme. 
     Each of the antenna switches  915  switches connection destinations of the antennas  916  among multiple circuits (such as circuits for different radio communication schemes) included in the radio communication interface  912 . 
     Each of the antennas  916  includes a single or multiple antenna elements (such as multiple antenna elements included in a MIMO antenna), and is used for the radio communication interface  912  to transmit and receive radio signals. The smartphone  900  may include the multiple antennas  916 , as shown in  FIG. 17 . Although  FIG. 17  shows the example in which the smartphone  900  includes the multiple antennas  916 , the smartphone  900  may also include a single antenna  916 . 
     Furthermore, the smartphone  900  may include the antenna  916  for each radio communication scheme. In that case, the antenna switches  915  may be omitted from the 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 radio communication interface  912 , and the auxiliary controller  919  to each other. The battery  918  supplies power to blocks of the smartphone  900  illustrated in  FIG. 17  via feeder lines, which are partially shown as dashed lines in the figure. The auxiliary controller  919  operates a minimum necessary function of the smartphone  900 , for example, in a sleep mode. 
     At least a part of the constituent elements included in the processing unit  250  (for example, the information acquisition unit  251  and/or the control unit  253 ) described with reference to  FIG. 9  may be implemented by the radio communication interface  912  of the smartphone  900  shown in  FIG. 17 . Alternatively, the at least part of the constituent elements may be implemented by the processor  901  or the auxiliary controller  919 . As an example, the smartphone  900  may have a module that includes a part or all of the radio communication interface  912  (for example, the BB processor  913 ), the processor  901 , and/or the auxiliary controller  919 , and the constituent elements may be implemented by the module. In this case, the module may store a program for causing a processor to function as the constituent elements (in other words, a program for causing a processor to execute operations of the constituent elements) and execute the program. As another example, a program for causing a processor to function as the constituent elements may be installed in the smartphone  900  and the radio communication interface  912  (for example, the BB processors  913 ), the processor  901 , and/or the auxiliary controller  919  may execute the program. As described above, the smartphone  900  or the module may be provided as an apparatus that includes the constituent elements, or a program for causing a processor to function as the constituent elements may be provided. In addition, a readable recording medium in which the program is recorded may be provided. 
     Furthermore, the radio communication unit  220  described with reference to  FIG. 9  may be implemented by, for example, the radio communication interface  912  (for example, the RF circuits  914 ) in the smartphone  900  shown in  FIG. 17 . In addition, the antenna unit  210  may be implemented by the antennas  916 . 
     (Second Application Example) 
       FIG. 18  is a block diagram showing an example of a schematic configuration of a car navigation apparatus  920  to which the technology of the present disclosure may be applied. The car navigation apparatus  920  includes a processor  921 , a memory  922 , a Global Positioning System (GPS) module  294 , 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 radio 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 a navigation function and another function of the car navigation apparatus  920 . The memory  922  includes a RAM and a ROM, and stores a program that is executed by the processor  921 , and data. 
     The GPS module  294  uses GPS signals received from a GPS satellite to measure a position (such as latitude, longitude, and altitude) of the car navigation apparatus  920 . The sensor  925  may include a group of sensors such as a gyro sensor, a geomagnetic sensor, and a barometric sensor. The data interface  926  is connected to, for example, an in-vehicle network  941  via a terminal that is not shown, and acquires data generated by the vehicle, such as vehicle speed data. 
     The content player  927  reproduces content stored in a storage medium (such as a CD and a DVD) that is inserted into the storage medium interface  928 . The input device  929  includes, for example, a touch sensor configured to detect touch onto a screen of the display device  930 , a button, or a switch, and receives an operation or an information input from a user. The display device  930  includes a screen such as a LCD or an OLED display, and displays an image of the navigation function or content that is reproduced. The speaker  931  outputs sounds of the navigation function or the content that is reproduced. 
     The radio communication interface  933  supports any cellular communication scheme such as LET and LTE-Advanced, and performs radio communication. The radio communication interface  933  may typically include, for example, a BB processor  934  and an RF circuit  935 . The BB processor  934  may perform, for example, encoding/decoding, modulating/demodulating, and multiplexing/demultiplexing, and performs various types of signal processing for radio communication. Meanwhile, the RF circuit  935  may include, for example, a mixer, a filter, and an amplifier, and transmits and receives radio signals via the antenna  937 . The radio communication interface  933  may be a one chip module having the BB processor  934  and the RF circuit  935  integrated thereon. The radio communication interface  933  may include the multiple BB processors  934  and the multiple RF circuits  935 , as shown in  FIG. 18 . Although  FIG. 18  shows the example in which the radio communication interface  933  includes the multiple BB processors  934  and the multiple RF circuits  935 , the radio communication interface  933  may also include a single BB processor  934  or a single RF circuit  935 . 
     Furthermore, in addition to a cellular communication scheme, the radio communication interface  933  may support another type of radio communication scheme such as a short-distance radio communication scheme, a near field communication scheme, and a radio LAN scheme. In that case, the radio communication interface  933  may include the BB processor  934  and the RF circuit  935  for each radio communication scheme. 
     Each of the antenna switches  936  switches connection destinations of the antennas  937  among multiple circuits (such as circuits for different radio communication schemes) included in the radio communication interface  933 . 
     Each of the antennas  937  includes a single or multiple antenna elements (such as multiple antenna elements included in a MIMO antenna), and is used for the radio communication interface  933  to transmit and receive radio signals. The car navigation apparatus  920  may include the multiple antennas  937 , as shown in  FIG. 18 . Although  FIG. 18  shows the example in which the car navigation apparatus  920  includes the multiple antennas  937 , the car navigation apparatus  920  may also include a single antenna  937 . 
     Furthermore, the car navigation apparatus  920  may include the antenna  937  for each radio communication scheme. In that case, the antenna switches  936  may be omitted from the configuration of the car navigation apparatus  920 . 
     The battery  938  supplies power to blocks of the car navigation apparatus  920  shown in  FIG. 18  via feeder lines that are partially shown as dashed lines in the figure. The battery  938  accumulates power supplied form the vehicle. 
     The constituent elements included in the processing unit  250  (for example, the information acquisition unit  251  and/or the control unit  253 ) described with reference to  FIG. 9  may be implemented by the radio communication interface  933  of the car navigation apparatus  920  shown in  FIG. 18 . Alternatively, at least a part of the constituent elements may be implemented by the processor  921 . As an example, the car navigation apparatus  920  may have a module that includes a part or all of the radio communication interface  933  (for example, the BB processor  934 ) and/or the processor  921 , and the constituent elements may be implemented by the module. In this case, the module may store a program for causing a processor to function as the constituent elements (in other words, a program for causing a processor to execute operations of the constituent elements) and execute the program. As another example, a program for causing a processor to function as the constituent elements may be installed in the car navigation apparatus  920  and the radio communication interface  933  (for example, the BB processors  934 ), and/or the processor  921  may execute the program. As described above, the car navigation apparatus  920  or a program for causing a processor to function as the constituent elements may be provided. In addition, a readable recording medium in which the program is recorded may be provided. 
     Furthermore, the radio communication unit  220  described with reference to  FIG. 9  may be implemented by, for example, the radio communication interface  933  (for example, the RF circuits  935 ) in the car navigation apparatus  920  shown in  FIG. 18 . In addition, the antenna unit  210  may be implemented by the antennas  937 . 
     The technology of the present disclosure may also be realized as an in-vehicle system (or a vehicle)  940  including one or more blocks of the car navigation apparatus  920 , the in-vehicle network  941 , and a vehicle module  942 . That is, the in-vehicle system (or the vehicle)  940  may be provided as an apparatus that includes the constituent elements (for example, the information acquisition unit  251  and/or the control unit  253 ). The vehicle module  942  generates vehicle data such as vehicle speed, engine speed, and trouble information, and outputs the generated data to the in-vehicle network  941 . 
     11. CONCLUSION 
     Apparatuses and processes according to the embodiments of the present disclosure have been described so far with reference to  FIGS. 1 to 18 . 
     According to the embodiments of the present disclosure, the first base station  100  (or another network node) includes the information acquisition unit  151  that acquires information with regard to the second base station  200  that is the second base station  200  having the coverage area  20  that overlaps the coverage area  10  of the first base station  100  that can use a frequency band with priority and is incapable of using the frequency band with priority, and the control unit  153  that requests the second base station  200  to transmit data destined for a terminal apparatus that accesses the first base station  100  to the terminal apparatus. 
     In addition, according to the embodiments of the present disclosure, the second base station  200  is the second base station  200  having the coverage area  20  that overlaps the coverage area  10  of the first base station  100  which can use a frequency band with priority, and includes the information acquisition unit  251  that acquires data destined for a terminal apparatus that accesses the first base station  100  when the second base station  200  that is incapable of using the frequency band with priority receives a request to transmit the data to the terminal apparatus, and the control unit  253  that controls radio communication of the second base station  200 . 
     Thus, for example, the frequency band can be used with higher efficiency. 
     Although exemplary embodiments of the present disclosure have been described above with reference to the accompanied by drawings, it is needless to say that the present disclosure is not limited to thereto. It is obvious that a person skilled in the art can conceive various modified examples or altered examples with the scope described in the claims, they are of course understood as coming under the technical scope of the present disclosure. 
     For example, although the example in which the third radio communication system having a higher priority level than the first base station (or the first radio communication system that includes the first base station) is present has been described, the present disclosure is not limited thereto. For example, the third radio communication system may not be present. That is, users of a frequency band may be divided into two groups (for example, two “tiers”), rather than three groups (for example, three “tiers”). 
     Further, it is not necessary to chronologically execute the processing steps in the processing in the present specification 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, a CPU and a DSP) provided at apparatuses (for example, a base station, a base station apparatus for the base station, or a module for the base station or the base station apparatus, or another network node or a module for the other network node) in the present specification function as the components (for example, an information acquiring unit or the control unit) of 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 the components (for example, an information acquiring unit 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)   

     An apparatus including: 
     an acquisition unit configured to acquire information regarding a second base station that is a second base station having a coverage area that overlaps a coverage area of a first base station capable of using a frequency band with priority, and is incapable of using the frequency band with priority; and 
     a control unit configured to request the second base station to transmit data destined for a terminal apparatus that accesses the first base station to the terminal apparatus.
     (2)   

     The apparatus according to (1), wherein the control unit requests the second base station to transmit the data to the terminal apparatus using the frequency band.
     (3)   

     The apparatus according to (2), wherein the control unit permits the second base station to use the frequency band.
     (4)   

     The apparatus according to (3), wherein the control unit permits the second base station to use a part or a whole of the frequency band in a period in which the first base station does not use the part or the whole of the frequency band.
     (5)   

     The apparatus according to (3) or (4), wherein the control unit cancels the permission for the second base station to use the frequency band.
     (6)   

     The apparatus according to any one of (2) to (5), wherein the first base station and the second base station are synchronized with each other.
     (7)   

     The apparatus according to any one of (1) to (6), wherein the control unit requests the second base station to transmit the data to the terminal apparatus using another frequency band available to the second base station.
     (8)   

     The apparatus according to any one of (1) to (7), wherein the control unit requests the second base station to transmit the data to the terminal apparatus using at least one selected from the frequency band and another frequency band available to the second base station.
     (9)   

     The apparatus according to (8), wherein the at least one selected from the frequency band and the other frequency band is a band selected based on an amount or a ratio of radio resources available to the second base station for transmission of the data among radio resources of the other frequency band.
     (10)   

     The apparatus according to any one of (1) to (9), wherein the second base station is capable of using the frequency band under a condition that interference with a radio communication system capable of using the frequency band with priority be avoided or suppressed.
     (11)   

     The apparatus according to (10), wherein the second base station can use a part or a whole of the frequency band in a period in which the radio communication system does not use the part or the whole of the frequency band.
     (12)   

     The apparatus according to (11), wherein the control unit notifies the second base station of the period.
     (13)   

     The apparatus according to any one of (1) to (9), wherein the second base station is incapable of using the frequency band without permission.
     (14)   

     The apparatus according to any one of (1) to (13), wherein the control unit instructs the terminal apparatus to use a band used by the second base station for transmission of the data as a secondary component carrier accompanied by a primary component carrier used by the first base station.
     (15)   

     The apparatus according to any one of (1) to (14), wherein the control unit gives an instruction to the second base station with regard to a link direction of a band used by the second base station for transmission of the data.
     (16)   

     The apparatus according to (15), wherein the instruction includes an instruction on duplex scheme to be applied to the band.
     (17)   

     The apparatus according to (15) or (16), wherein the instruction includes an instruction of a Time Division Duplex (TDD) configuration applied to the band.
     (18)   

     The apparatus according to (17), wherein the TDD configuration is a TDD configuration in which all subframes are downlink subframes.
     (19)   

     The apparatus according to (15) or (16), wherein the instruction includes an instruction of use of the band as a downlink band.
     (20)   

     The apparatus according to any one of (1) to (19), 
     wherein the frequency band is a band that is used by another radio communication system with priority over a radio communication system that includes the first base station, and 
     the first base station is capable of using the frequency band under a condition that interference with the other radio communication system be avoided or suppressed.
     (21)   

     The apparatus according to (20), 
     wherein the control unit requests the second base station to transmit the data to the terminal apparatus using the frequency band, and 
     the control unit permits the second base station for use of the frequency band within a range within which the first base station is capable of using the frequency band.
     (22)   

     The apparatus according to any one of (1) to (21), wherein the apparatus is the first base station, a base station apparatus for the first base station, or a module for the first base station or the base station apparatus, or another network node or a module for the other network node.
     (23)   

     An apparatus including: 
     an acquisition unit configured to acquire data destined for a terminal apparatus that accesses a first base station capable of using a frequency band with priority when a second base station that is a second base station having a coverage area which overlaps a coverage area of the first base station, and is incapable of using the frequency band with priority receives a request to transmit the data to the terminal apparatus; and 
     a control unit configured to control radio communication of the second base station so that the second base station transmits the data to the terminal apparatus.
     (24)   

     The apparatus according to (23), wherein the control unit controls the radio communication so that the second base station transmits the data to the terminal apparatus using the frequency band.
     (25)   

     The apparatus according to (23) or (24), wherein the control unit controls the radio communication so that the second base station transmits the data to the terminal apparatus using another frequency band available to the second base station.
     (26)   

     The apparatus according to any one of (23) to (25), wherein the control unit controls the radio communication so that the second base station uses a band used for transmission of the data as a secondary component carrier accompanied by a primary component carrier used by the first base station.
     (27)   

     The apparatus according to any one of (23) to (26), wherein the control unit controls the radio communication according to an instruction to the second base station with regard to a link direction of a band used by the second base station for transmission of the data.
     (28)   

     The apparatus according to any one of (23) to (27), wherein the apparatus is the second base station, a base station apparatus for the second base station, or a module for the second base station or the base station apparatus.
     (29)   

     The apparatus according to any one of (1) to (28), 
     wherein the first base station is a base station of a macrocell, and 
     the second base station is a base station of a small cell that overlaps the macrocell.
     (30)   

     The apparatus according to any one of (1) to (29), 
     wherein the first base station is a base station operated by a first service provider, and 
     the second base station is a base station operated by a second service provider that is different from the first service provider.
     (31)   

     The apparatus according to any one of (1) to (28), wherein the second base station is a terminal apparatus operable as a base station.
     (32)   

     A method including: 
     acquiring information regarding a second base station that is a second base station having a coverage area that overlaps a coverage area of a first base station capable of using a frequency band with priority, and is incapable of using the frequency band with priority; and 
     requesting, by a processor, the second base station to transmit data destined for a terminal apparatus that accesses the first base station to the terminal apparatus.
     (33)   

     A program for causing a processor to execute: 
     acquiring information regarding a second base station that is a second base station having a coverage area that overlaps a coverage area of a first base station capable of using a frequency band with priority, and is incapable of using the frequency band with priority; and 
     requesting the second base station to transmit data destined for a terminal apparatus that accesses the first base station to the terminal apparatus.
     (34)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     acquiring information regarding a second base station that is a second base station having a coverage area that overlaps a coverage area of a first base station capable of using a frequency band with priority, and is incapable of using the frequency band with priority; and 
     requesting the second base station to transmit data destined for a terminal apparatus that accesses the first base station to the terminal apparatus.
     (35)   

     A method including: 
     acquiring data destined for a terminal apparatus that accesses a first base station capable of using a frequency band with priority when a second base station that is a second base station having a coverage area which overlaps a coverage area of the first base station, and is incapable of using the frequency band with priority receives a request to transmit the data to the terminal apparatus; and 
     controlling, by a processor, radio communication of the second base station so that the second base station transmits the data to the terminal apparatus.
     (36)   

     A program for causing a processor to execute: 
     acquiring data destined for a terminal apparatus that accesses a first base station capable of using a frequency band with priority when a second base station that is a second base station having a coverage area which overlaps a coverage area of the first base station, and is incapable of using the frequency band with priority receives a request to transmit the data to the terminal apparatus; and 
     controlling radio communication of the second base station so that the second base station transmits the data to the terminal apparatus.
     (37)   

     A readable recording medium having a program recorded thereon, the program causing a processor to execute: 
     acquiring data destined for a terminal apparatus that accesses a first base station capable of using a frequency band with priority when a second base station that is a second base station having a coverage area which overlaps a coverage area of the first base station, and is incapable of using the frequency band with priority receives a request to transmit the data to the terminal apparatus; and 
     controlling radio communication of the second base station so that the second base station transmits the data to the terminal apparatus.
     (N1)   

     An apparatus including: 
     an acquisition unit configured to acquire information regarding a second base station having a coverage area that overlaps a coverage area of a first base station; and 
     a control unit configured to request the first base station or the second base station to transmit or receive data transmitted and received between the second base station and a terminal apparatus that access the second base station via a radio backhaul that is the radio backhaul between the first base station and the second base station and uses a frequency band available to the second base station.
     (N2)   

     The apparatus according to (N1), wherein the frequency band is a frequency band permitted to be used for the radio backhaul.
     (N3)   

     The apparatus according to (N2), wherein the frequency band is a frequency band permitted by the second base station to be used for the radio backhaul.
     (N4)   

     The apparatus according to (N2) or (N3), wherein the frequency band is a frequency band permitted to be used for the radio backhaul in a period in which the second base station does not use the frequency band for communication with a terminal apparatus.
     (N5)   

     The apparatus according to any one of (N1) to (N4), 
     wherein the apparatus is the first base station, a base station apparatus for the first base station, or a module for the base station apparatus, and 
     the control unit requests the second base station to transmit or receive the data via the radio backhaul.
     (N6)   

     The apparatus according to any one of (N1) to (N4), 
     wherein the apparatus is a network node different from the first base station and the second base station, or a module for the network node, and 
     the control unit requests one of or both the first base station and the second base station to transmit or receive the data via the radio backhaul.
     (N7)   

     The apparatus according to any one of (N1) to (N4), 
     wherein the apparatus is the second base station, a base station apparatus for the second base station, or a module for the base station apparatus, and 
     the control unit requests the first base station to transmit or receive the data via the radio backhaul. 
     REFERENCE SIGNS LIST 
     
         
           1  system 
           10 ,  20  coverage area 
           31 ,  33  frequency band 
           100  first base station 
           151  information acquisition unit 
           153  control unit 
           200  second base station 
           251  information acquisition unit 
           253  control unit