Patent Abstract:
[Problem] To provide a base station device and a handover control method capable of avoiding a situation in which the base station device of a cell becomes overloaded when the cell transitions from an inactive state to an active state. [Solution] A base station device ( 100 ) having: an adjacent base station information table ( 150 ) for storing adjacent base station information that includes handover suppression information correlated with an adjacent cell ( 200   a ) managed by an adjacent base station device ( 200 ), and also includes the processing capacity index of the adjacent base station device; and a handover control unit ( 130 ) for limiting the handover of a mobile terminal device ( 300 ) under control to an activated adjacent cell on the basis of the handover suppression information and the processing capacity index when the adjacent cell transitions from an inactive state to an active state.

Full Description:
TECHNICAL FIELD 
     The present invention relates to a wireless communication system and, more particularly, to a base station device and a handover control method, which perform handover control. 
     BACKGROUND ART 
     As one of measures to improve a system throughput in a cellular network, there is a technique of arranging a plurality of small base-station devices in a macrocell provided by a base station device. Because an area of a small cell provided by the small base-station device is small, a mobile terminal device is not necessarily present in the small cell. Accordingly, in a state in which no mobile terminal device is present in the small cell, electric power consumed by the small base-station device is wasted. Thus, in 3GPP (3rd Generation Partnership Project), Energy Saving function is proposed as one of SON (Self Organization Networks) functions (NPTL1). 
     A small base-station device having the Energy Saving function has an active state and an inactive state. In the active state, such device performs a normal operation as the small base-station device. In the inactive state, power saving of the entire network is realized by stopping radio transmission in a part or the whole of the cells. The state-transition of the active state/inactive state of the cell can be controlled according to a traffic amount. For example, based on statistical data of traffic change, the number of the small base-station devices in operation is increased in a time zone, such as a traffic peak time, in which the traffic amount is large. In a time zone, such as an off-peak time, in which the traffic amount is small, the number of the small base-station devices in operation is reduced. 
     However, the stopping of the radio transmission may have a large impact on the mobile terminal device and neighboring cells. Thus, when an own cell transfers to an inactive state, specification of a signal notifying the neighboring cell of the transition of the own cell to an inactive state is performed as specific processing for reducing the impact. In addition, a signal requesting an inactive cell to become active is specified (NPTL2). The notification and request messages are usually transmitted via an inter-base-station interface between the base station devices which control target cells. 
     Furthermore, in a mobile communication system having a plurality of base station devices like a cellular network, mobility control or handover control is performed, which switches base stations so that communication is continued when a mobile terminal device moves from a cell provided one of the base station devices to another cell provided by another of the base station devices. Handover of the mobile terminal device is controlled, based on a value measured and reported by the mobile terminal device, by the base station device providing a cell in which the mobile terminal device is located. Generally, the base station device controls the handover to select a better cell (or best cell) in respect of radio wave reception environment for the mobile terminal device and to hand over the mobile terminal to the selected cell. 
     Hereinafter, a general handover control procedure is briefly described with reference to  FIG. 1 . Incidentally, a cell in which a mobile terminal device is present is referred to as a serving cell. A base station device of a serving cell is referred to as a serving base station device. A handover destination cell is referred to as a target cell. A base station device of a target cell is referred to as a target base station device. 
     In  FIG. 1 , a serving base station device sets measurement conditions, measurement reporting conditions, and the like by transmitting a measurement setting message M 100  to a mobile terminal device. The mobile terminal device measures reference signal received power (RSRP: Reference Signal Received Power), reference signal received quality (RSRQ: Reference Signal Received Quality), or other parameters of each of the serving cell and the neighboring cell according to the measurement conditions set by the serving base station device (operation S 100 ). The parameters includes reference signal received power (RSRP: Reference Signal Received Power), reference signal received quality (RSRQ: Reference Signal Received Quality), or other parameters. Then, if a measurement result satisfies the measurement reporting conditions, a measurement reporting message M 101  is transmitted to the serving base station device. 
     The serving base station device performs handover execution determination, based on a measurement report received from the mobile terminal device (operation S 101 ). In the handover execution determination, a target cell is determined by judging whether handover execution is necessary. In the determination of a target cell, generally, a cell is selected, which is better in radio wave reception environment for the mobile terminal device. Subsequently, the serving base station device transmits, when the target cell is determined, a handover request message M 102  including information concerning the mobile terminal device to the target base station device. 
     The target base station device performs, upon the handover request received from the serving base station device, judging of acceptance of a mobile terminal device (operation S 102 ). The judging of acceptance is performed, based on access control rules such as access authority of the mobile terminal device and a load of the target base station device. If the mobile terminal device is determined to be acceptable, handover preparation such as securement of data resources for the mobile terminal device is executed. Then, if handover is determined to be acceptable, the target base station device transmits, to the serving base station device, a handover request response message M 103  including a handover instruction to the mobile terminal device. 
     Upon the handover request response, the serving base station device transmits, to the mobile terminal device, a handover instruction message M 104  received from the target base station device. In response to the handover instruction, the mobile terminal device transmits a handover instruction response to the target base station device. Thus, the handover control procedure is completed. 
     Incidentally, a method is proposed, which determines, when a target base station is determined, a preferential order by considering not only quality of the radio wave reception environment but capability of the neighboring base station (see PTL1). 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL1] Japanese Patent Application Laid-Open No. 2011-525759 
       
    
     Non-Patent Literatures 
     
         
         [NPTL1] 3GPP TS36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network; Overall description; Stage 2, V10.2.0 
         [NPTL2] 3GPP TS36.423, Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP), V9.2.0 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when a base station device makes an inactive cell of a small base-station device transfer to an active state, radio wave reception environment of the activated cell may be better for a mobile terminal device being present in vicinity of the activated cell than radio wave reception environment of the serving cell. When many such mobile terminal devices are present, many mobile terminal devices are simultaneously handed over to the small base-station device by the handover control. Generally, the small base-station device is low in processing capability, compared to the base station device. Thus, increase in local processing load has a high probability of causing a congestion state of the small base-station. Consequently, there is a problem that service quality is degraded due to a handover failure and a processing delay. 
     Accordingly, an object of the present invention is to provide a base station device and a handover control method capable of avoiding, when a cell transfers from an inactive state to an active state, a situation in which a base station device of the cell is overloaded. 
     Solution to Problem 
     A base station device according to the present invention is a base station device in a wireless communication system, which includes a neighboring base station information storage means that stores neighboring base station information including handover inhibition information associated with a neighboring cell managed by a neighboring base station device, and a processing capability index of the neighboring base station device, and a handover control means that limits that, when the neighboring cell transfers from an inactive state to an active state, a mobile terminal device hands over to the activated neighboring cell, based on the handover inhibition information and the processing capability index. 
     A handover control method according to the present invention is a handover control method in a wireless communication system, which includes storing neighboring base station information including handover inhibition information associated with a neighboring cell managed by a neighboring base station device, and a processing capability index of the neighboring base station device, and limiting that, when the neighboring cell transitions from an inactive state to an active state, a mobile terminal hands over to the activated neighboring cell, based on the handover inhibition information and the processing capability index. 
     Advantageous Effects of Invention 
     According to the present invention, when a neighboring cell is activated, handover of a mobile terminal device which communicates with a serving base station to the neighboring cell is limited. Thus, a situation can be avoided, in which a base station device of the neighboring cell is overloaded. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sequence diagram illustrating a general handover control procedure. 
         FIG. 2  is a schematic diagram illustrating a schematic configuration of a wireless communication system according to a first exemplary embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a configuration of a base station device according to the present exemplary embodiment. 
         FIG. 4  is a schematic diagram illustrating an example of a neighboring base station information table in the present exemplary embodiment. 
         FIG. 5  is a sequence diagram illustrating a handover control procedure according to the present exemplary embodiment. 
         FIG. 6  is a flowchart illustrating a handover control operation of a base station device according to the present exemplary embodiment. 
         FIG. 7  is a schematic diagram illustrating a schematic configuration of a wireless communication system according to a second exemplary embodiment of the present invention. 
         FIG. 8  is a sequence diagram illustrating a handover control procedure according to the present exemplary embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     According to exemplary embodiments of the present invention, a base station device acquires a processing capability index of a neighboring base station device by inter-base-station communication. When the base station device detects that a cell of the neighboring base station device transfers from an inactive state to an active state, the base station device inhibits handover of a mobile terminal device to the activated cell, based on the processing capability index of the neighboring base station device, for a specified period of time. Consequently, increase in processing-load of the neighboring base station can be suppressed. Even a small base-station device with low processing capability can avoid a congestion state due to overload. Hereinafter, exemplary embodiments of the present invention are described in detail with reference to the drawings. 
     1. First Exemplary Embodiment 
     1. 1) System Configuration 
     In  FIG. 2 , in order not to complicate description, it is assumed that a wireless communication system according to a first exemplary embodiment is configured by a base station device  100 , a small base-station device  200 , and a mobile terminal device  300 , and that the base station device  100  and the small base-station device  200  are connected via an inter-base-station interface to each other. Here, a cell configuration is illustrated, in which a small cell  200   a  of the small base-station device  200  is included in a macrocell  100   a  of the base station device  100 . However, the present exemplary embodiment is not limited thereto. Incidentally, the small cell  200   a  may be either a picocell or a microcell. Additionally, the base station device  100  and the small base-station device  200  may be connected to another base station device (not illustrated) via an inter-base-station interface. Hereinafter, a case where the base station device  100  makes an inactive cell of the small base-station device  200  transition to an active state is described as an example. 
     1. 2) Base Station Device 
     As illustrated in  FIG. 3 , the base station device  100  is configured by a wireless communication control unit  110 , an inter-base-station communication control unit  120 , a handover control unit  130 , an activation control unit  140 , and a neighboring base station device information table  150 . However, here, for simplicity of drawing, only a configuration relating to the present exemplary embodiment is illustrated. The base station device  100  has a control unit equivalent to a base station device used in a general mobile communication system. 
     The wireless communication control unit  110  is connected to a mobile terminal device via a wireless link, and performs data transmission and reception therewith. The inter-base-station communication control unit  120  establishes an inter-base-station interface with the neighboring base station device, and performs data transmission and reception with the neighboring base station device via the established inter-base-station interface. The handover control unit  130  executes handover execution determination and handover control, based on a measurement report from the mobile terminal device. 
     The activation control unit  140  determines whether to activate the inactive cell  200   a  of the small base-station device  200  under the macrocell  100   a  of the base station device  100 . Whether to activate the inactive cell  200   a  can be determined, based on statistical traffic information in the macrocell  100   a . For example, in a traffic-peak time, the inactive cell is controlled to transfer to an active cell. 
     As illustrated in  FIG. 4 , the neighboring base station information table  150  has a neighboring base station device ID concerning each of neighboring base station devices neighboring the base station device  100 , neighboring cell information concerning a cell of each of the neighboring base station devices, surrounding cell information concerning cells located around the cell of each of the neighboring base station devices, handover inhibition timer information associated with each neighboring cell, the number of times of executing handover to the neighboring cell during the handover inhibition timer is being activated, and information concerning a processing capability index of each of the neighboring base station devices. Information concerning a cell of the neighboring base station device, neighboring cell information concerning a cell of the neighboring base station device, and information concerning the processing capability index of the neighboring base station device are recorded, based on information received when the inter-base-station interface is established. 
     The handover timer information represents information indicating whether the handover inhibition timer is being activated (ON) or stopped (OFF), and an elapsed time if the timer is being activated. For example, in a cell C 1   a  of a neighboring base station BS 1  illustrated in  FIG. 4 , the handover inhibition timer is activated, and the elapsed time is T 1   a.    
     The processing capability index is the number of processable calls per second, or the like. Additionally, the number of times of executing handover represents the number of times of executing, during the handover inhibition timer is being activated, handover processing from the cell  100   a  of the base station device  100  to the neighboring cell (here, the cell  200   a ). 
     Incidentally, functions of the inter-base-station communication control unit  120 , the handover control unit  130 , and the activation control unit  140  can be implemented by executing programs stored in a memory (not illustrated) on a computer (CPU: Central Processing Unit). 
     1. 3) Handover Inhibition Control 
     In  FIG. 5 , first, the base station device  100  and the small base-station device  200  establish an inter-base-station interface by exchanging an inter-base-station interface establishment request message M 200  and a response message M 201  thereto. The inter-base-station interface establishment request message M 200  and the response message M 201  thereto include cell information concerning cells of the base station devices respectively transmitting these messages, neighboring cell information concerning cells of the neighboring base station devices respectively transmitting these messages, and information concerning a processing capability index of each of relevant neighboring base station devices. In the present exemplary embodiment, the base station device transmits the inter-base-station interface establishment request message M 200 , and the small base-station device transmits the response message M 201 . However, this may be vice versa. 
     The inter-base-station control unit  120  of the base station device  100  extracts the above information from the response message M 201  received from the small base-station device  200  and records the extracted information in a neighboring base station device information table  150  (operation S 200 ). Next, if it is determined (operation S 201 ) that an inactive cell of the small base-station device  200  is activated, the activation control unit  140  of the base station device  100  transmits a cell activation request message M 202  to the small base-station device  200 . 
     The small base-station device  200  activates a cell designated in the cell activation request message M 202  (operation S 202 ) and transmits a cell activation request response message M 203  to the base station device  100  after the cell is activated. Incidentally, in the present exemplary embodiment, the small base-station device  200  transmits the inter-base-station interface establishment response message M 201  in which the neighboring cell information concerning the cell of the small base-station device  200  and the processing capability index of the small base-station device  200  are included. However, the small base-station device  200  may transmit the cell activation request response message M 203  in which the neighboring cell information concerning the cell of the small base-station device  200  and the processing capability index of the small base-station device  200  are included. In this case, an operation S 200  of the base station device  100  is performed after the base station device  100  receives the cell activation request response message M 203 . 
     When the base station device  100  receives the cell activation request response message M 203 , the handover control unit  130  of the base station device  100  activates a handover inhibition timer associated with the activated designated-cell of the small base-station device  200  (operation S 203 ). When the handover inhibition timer is activated, the handover inhibition timer information in the neighboring base station device information table  150  is updated to ON. 
     If the handover inhibition timer is being activated, the handover control unit  130  inhibits the handover control conditionally, as is described below, even when receiving a measurement report message M 204  from the mobile terminal device  300  (operation S 204 ). Then, when the handover inhibition timer stops after elapse of a predetermined period of time, the handover control unit  130  updates the handover inhibition timer information in the relevant cell in the neighboring base station device information table  150  from ON to OFF, and initializes the number of times of executing handover (i.e., sets the number of times of executing handover to 0) (operation S 205 ). 
     Hereinafter, the handover inhibition control operation S 204  in the base station device  100  according to the present exemplary embodiment is described with reference to  FIG. 6 . 
     In  FIG. 6 , when the wireless communication control unit  110  of the base station device  100  receives the measurement report message M 204  from the mobile terminal device  300 , the handover control unit  130  determines, based on the received measurement report, a handover destination candidate cell (operation S 300 ). Handover destination candidate cell determination processing can select, e.g., all of neighboring cells, each of which is larger in reference signal received power than the serving cell, as the candidate cells. Hereinafter, the handover destination candidate cells are assumed to be determined, based on the reference signal received power. However, a technique of determining a handover destination cell according to a measurement report value other than the received power may be employed. 
     Next, the handover control unit  130  selects a cell (best cell), which is largest in reference signal received power, from the selected handover destination candidate cells and refers to the neighboring base station device information table  150 . Thus the handover control unit  130  determines whether the handover inhibition timer is being activated in the best cell (operation S 301 ). If the handover inhibition timer is being activated (operation S 301 ; YES), the handover control unit  130  acquires cell information concerning the best cell from the neighboring base station device information table  150  (operation S 302 ). The cell information includes the processing capability index of the neighboring base station device (here, the small base-station device  200 ) controlling the cell concerned, the number of neighboring cells, and the number of times of executing handover thereto. 
     Next, the handover control unit  130  determines whether a value (actual result value) obtained by dividing a number calculated by adding 1 to the number of times of executing handover included in the acquired cell information by a handover inhibition timer elapsed time is smaller than a value (capability threshold) obtained by dividing the processing capability index by the number of the neighboring cells (operation S 303 ). 
     If the actual result value is less than the capability threshold (operation S 303 ; YES), the handover control unit  130  can determine that the processing capability of the neighboring base station device has a margin. Therefore, the handover control unit  130  determines the best cell as a handover destination cell (operation S 304 ) and increments the number of times of executing handover of the best cell in the neighboring base station device information table  150  by 1. 
     If the actual result value is equal to or more than the capability threshold (operation S 303 ; NO), the processing capability of the neighboring base station device of the best cell has no margin. Thus, the handover control unit  130  determines whether there is still another cell among the selected handover destination candidate cells (operation S 305 ). If there is still another cell (operation S 305 ; YES), the handover control unit  130  excludes, from the handover destination candidate cells, the cell of the neighboring base station device concerned (operation S 306 ). Then, the handover control unit  130  returns to the above operation S 301 . If there are no other cells (operation S 305 ; NO), the handover control unit  130  inhibits handover to the mobile terminal device  300  to the best cell (operation S 307 ). 
     Incidentally, if the handover inhibition timer associated with the best cell is being stopped (operation S 301 ; NO), as normal, the handover control unit  130  determines the best cell as a handover destination cell (operation S 308 ). Thus, when the handover destination cell is determined, handover processing is executed as described with reference to  FIG. 1 . 
     1. 4) Advantageous Effects 
     As described above, according to the first exemplary embodiment of the present invention, when a cell of the neighboring small base-station device  200  transitions from an inactive state to an active state, handover of the mobile terminal device  300  to the activated cell  200   a  is inhibited, based on the processing capability index of the small base-station device  200 , for a certain period of time until the inhibition timer is timed out. Consequently, rapid increase in processing-load of the small base-station device  200  can be avoided. Degradation of service quality due to a handover failure and a processing delay can be reduced. 
     2. Second Exemplary Embodiment 
     2. 1) System Configuration 
     In  FIG. 7 , in order not to complicate description, it is assumed that a wireless communication system according to a second exemplary embodiment is configured by base station devices  100  and  101 , a small base-station device  200 , and mobile terminal devices  300  and  301 , and that each of the base station devices  100  and  101  is connected to the small base-station device  200  via an inter-base-station interface. Here, a cell configuration is illustrated, in which a small cell  200   a  of the small base-station device  200  is provided in a peripheral portion where a macrocell  100   a  of the base station device  100  overlaps a macrocell  101   a  of the base station device  101 . However, the present exemplary embodiment is not limited thereto. It is assumed that the mobile terminal device  300  is located in the cell  100   a  of the base station device  100 , and that the mobile terminal device  301  is located in the cell  101   a  of the base station device  101 . Hereinafter, a case where the base station device  100  makes an inactive cell of the small base-station device  200  transition to an active state is described as an example. 
     2. 2) Base Station Device 
     The base station devices  100  and  101  each have a configuration similar to the block configuration illustrated in  FIG. 3 . Therefore, description of the base station devices  100  and  101  is omitted. 
     2. 3) Handover Inhibition Control 
     In a sequence diagram illustrated in  FIG. 8 , a same operation as that in the handover inhibition control procedure according to the first exemplary embodiment illustrated in  FIG. 5  is designated with same reference numeral. Therefore, description of such an operation is omitted. Only different operations in the procedure are described. 
     As already described, similarly to the procedure in which the base station device  100  and the small base-station device  200  establish the inter-base-station interface, the base station device  101  and the small base-station device  200  establish the inter-base-station interface by exchanging an inter-base-station interface establishment request message M 200  and a response message M 201  thereto. Then, the base station devices  100  and  101  extract the above information from the response message M 201  received from the small base-station device  200  and records the extracted information on a neighboring base station device information table  150  (operation S 200 ). In addition, as described above, the inter-base-station interface establishment request message M 200  and the response message M 201  thereto include cell information concerning cells located under the transmitting-side base station devices, neighboring cell information concerning cells respectively the neighboring cells of the transmitting-side base station devices, and information concerning a processing capability index of each of relevant neighboring base station devices. As a specific processing capability index, the number of processable calls per second is set. 
     The small base-station device  200  activates a designated cell according to the cell activation request message M 202  received from the base station device  100  (operation S 202 ). After the activation of the cell, the small base-station device  200  transmits a cell activation request response message M 203  and a cell state change notification message M 205  to the base station devices  100  and  101 , respectively. Incidentally, even in the present exemplary embodiment, similarly to the first exemplary embodiment, the neighboring cell information, and information concerning the processing capability index may be transmitted by being included in each of the cell activation request response message M 203  and the cell state change notification message M 205 . In this case, the operation S 200  of each of the base station devices  100  and  101  is performed after an associated one of the cell activation request response message M 203  and the cell state change notification message M 205  is received. 
     When the base station devices  100  and  101  receive the cell activation request response message M 203  and the cell state change notification message M 205 , respectively, a handover inhibition timer associated with the designated cell activated by the small base-station device  200  is activated (operation S 203 ). When the handover inhibition timer is activated, handover inhibition timer information in a neighboring base station device information table  150  of each of the base station devices  100  and  101  is updated to ON. 
     If the handover inhibition timer is being activated, the base station device  100  inhibits the handover control conditionally, as already described, even when receiving a measurement report message M 204  from the mobile terminal device  300 . Similarly, the base station device  101  inhibits the handover control conditionally, even when receiving a measurement report message M 204  from the mobile terminal device  301  (operation S 204 ). Then, when the handover inhibition timer stops after elapse of a predetermined period of time, each of the base station devices  100  and  101  updates the handover inhibition timer information in the relevant cell in the neighboring base station device information table  150  from ON to OFF, and initializes the number (=0) of times of executing handover (operation S 205 ). The handover inhibition control operation S 204  of the base station device  101  is similar to that of the base station device  100  described with reference to  FIG. 6 . Therefore, description of the handover inhibition control operation S 204  of the base station device  101  is omitted. 
     3. Supplemental Notes 
     A part or all of the above exemplary embodiments can also be described as the following supplemental notes. However, the present invention is not limited thereto. 
     [Supplemental Note 1] 
     A base station device in a wireless communication system, including: 
     a neighboring base station information storage means which stores neighboring base station information including handover inhibition information associated with a neighboring cell managed by a neighboring base station device, and a processing capability index of the neighboring base station device; and 
     a handover control means which limits, when the neighboring cell transitions from an inactive state to an active state, handover to the activated neighboring cell of a subordinate mobile terminal device, based on the handover inhibition information and the processing capability index. 
     [Supplemental Note 2] 
     The base station device according to Supplemental Note 1, in which the handover inhibition information is a handover inhibition timer that is activated when the neighboring cell transitions from an inactive state to an active state, and that indicates a predetermined handover inhibition time, and in which the handover control means inhibits, during the handover inhibition time, handover of the mobile terminal device to the neighboring cell, based on the processing capability index. 
     [Supplemental Note 3] 
     The base station device according to Supplemental Note 2, in which the handover control means permits handover of the mobile terminal device to the neighboring cell only in a case where the processing capability of the neighboring base station device has a margin, if within the handover inhibition time. 
     [Supplemental Note 4] 
     The base station device according to Supplemental Note 3, in which the margin of the processing capability of the neighboring base station device is determined by the number of times of executing handover to the neighboring cell within the handover inhibition time, and by the processing capability index. 
     [Supplemental Note 5] 
     The base station device according to one of Supplemental Notes 1 to 4, in which the neighboring base station device is a small base-station device located under the base station device. 
     [Supplemental Note 6] 
     A handover control method for a base station device in a wireless communication system, including: 
     storing, in a neighboring base station information storage means, neighboring base station information including handover inhibition information associated with a neighboring cell managed by a neighboring base station device, and a processing capability index of the neighboring base station device; and 
     limiting, when the neighboring cell transitions from an inactive state to an active state, handover to the activated neighboring cell of a subordinate mobile terminal device, based on the handover inhibition information and the processing capability index. 
     [Supplemental Note 7] 
     The handover control method according to Supplemental Note 6, in which the handover inhibition information is a handover inhibition timer that is activated when the neighboring cell transitions from an inactive state to an active state, and that indicates a predetermined handover inhibition time, and in which, during the handover inhibition time, handover of the mobile terminal device to the neighboring cell is limited, based on the processing capability index. 
     [Supplemental Note 8] 
     The handover control method according to Supplemental Note 7, in which handover of the mobile terminal device to the neighboring cell is permitted only in a case where the processing capability of the neighboring base station device has a margin, if within the handover inhibition time. 
     [Supplemental Note 9] 
     The handover control method according to Supplemental Note 8, in which the margin of the processing capability of the neighboring base station device is determined by the number of times of executing handover to the neighboring cell during the handover inhibition time, and the processing capability index. 
     [Supplemental Note 10] 
     The handover control method according to one of Supplemental Notes 6 to 9, in which the neighboring base station device is a small base-station device located under the base station device. 
     [Supplemental Note 11] 
     A wireless communication system including a plurality of base station devices, one of the plurality of base station devices, including: 
     a neighboring base station information storage means which stores neighboring base station information including handover inhibition information associated with a neighboring cell managed by a neighboring base station device, and a processing capability index of the neighboring base station device; and 
     a handover control means which limits, when the neighboring cell transitions from an inactive state to an active state, handover to the activated neighboring cell of a subordinate mobile terminal device, based on the handover inhibition information and the processing capability index. 
     [Supplemental Note 12] 
     The wireless communication system according to Supplemental Note 11, in which the handover inhibition information is a handover inhibition timer that is activated when the neighboring cell transitions from an inactive state to an active state, and that indicates a predetermined handover inhibition time, and in which the handover control means inhibits, during the handover inhibition time, handover of the mobile terminal device to the neighboring cell, based on the processing capability index. 
     [Supplemental Note 13] 
     The wireless communication system according to Supplemental Note 12, in which the handover control means permits handover of the mobile terminal device to the neighboring cell only in a case where the processing capability of the neighboring base station device has a margin, if within the handover inhibition time. 
     [Supplemental Note 14] 
     The wireless communication system according to Supplemental Note 13, in which the margin of the processing capability of the neighboring base station device is determined by the number of times of executing handover to the neighboring cell within the handover inhibition time, and by the processing capability index. 
     [Supplemental Note 15] 
     The wireless communication system according to one of Supplemental Notes 11 to 14, in which the neighboring base station device is a small base-station device located under the base station device. 
     [Supplemental Note 16] 
     A program for implementing, in a computer, a handover control function of a base station device in a wireless communication system, the program implementing, in the computer: 
     a neighboring base station information storage function of storing neighboring base station information including handover inhibition information associated with a neighboring cell managed by a neighboring base station device, and a processing capability index of the neighboring base station device; and 
     a handover control function of limiting, when the neighboring cell transitions from an inactive state to an active state, handover to the activated neighboring cell of a subordinate mobile terminal device, based on the handover inhibition information and the processing capability index. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a power saving technique in a wireless communication system and, more particularly, to reduction of a load on a small base-station device. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  101  base station devices 
           100   a ,  101   a  base station device cells 
           200   a  small base-station cell 
           300 ,  301  mobile terminal devices 
           110  wireless communication control unit 
           120  inter-base-station communication control unit 
           130  handover control unit 
           140  activation control unit 
           150  neighboring base station device information table

Technology Classification (CPC): 8