Patent Publication Number: US-2022232444-A1

Title: Base station device, system, computer-readable storage medium, flying object, method, management device, and management method

Description:
The contents of the following Japanese patent application(s) are incorporated herein by reference: 
     NO. 2019-200297 filed in JP on Nov. 1, 2019 
     NO. PCT/JP2020/031355 filed in WO on Aug. 19, 2020 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a base station device, a system, a computer-readable storage medium, a flying object, a method, a management device, and a management method. 
     2. Related Art 
     Technology for providing a wireless communication service by a cell formed by a wireless base station is known (for example, see Patent document 1). 
     PRIOR ART DOCUMENTS 
     Patent Document 
     Patent document 1: Japanese Patent Application Publication No. 2019-075717 
     TECHNICAL PROBLEM 
     It is desirable to provide a technology that can appropriately reduce a load of a wireless base station. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically illustrating an example of a wireless base station  100 . 
         FIG. 2  is a diagram schematically illustrating an example of a wireless base station  100 . 
         FIG. 3  is a diagram schematically illustrating an example of a system  10 . 
         FIG. 4  is a diagram schematically illustrating an example of a flow of processing performed by the system  10 . 
         FIG. 5  is a diagram schematically illustrating an example of a functional configuration of an NMS  200 . 
         FIG. 6  is a diagram schematically illustrating an example of a cumulative distribution graph  222 . 
         FIG. 7  is a diagram schematically illustrating an example of a cumulative distribution graph  224 . 
         FIG. 8  is a diagram schematically illustrating an example of a functional configuration of a base station device  110 . 
         FIG. 9  is a diagram schematically illustrating an example of a flow of processing performed by the base station device  110 . 
         FIG. 10  is a diagram schematically illustrating an example of a flow of processing performed by the base station device  110 . 
         FIG. 11  is a diagram schematically illustrating an example of a HAPS  300 . 
         FIG. 12  is a diagram schematically illustrating an example of a hardware configuration of a computer  1200  serving as the base station device  110  or the NMS  200 . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to claims. In addition, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention. 
       FIG. 1  and  FIG. 2  are diagrams schematically illustrating an example of a wireless base station  100 . A plurality of wireless base stations are positioned around the wireless base station  100 , but in  FIG. 1  and  FIG. 2 , only one wireless base station  180  adjacent to the wireless base station  100  is illustrated. The wireless base station  100  may be an example of a base station device. A control device which is mounted on the wireless base station  100  to control an operation of the wireless base station  100  may be an example of the base station device. 
     The wireless base station  100  forms a cell  102  to provide a wireless communication service to a user terminal  30  within the cell  102 . A user terminal  30  may be any terminal as long as it is a communication terminal which can communicate with the wireless base station  100 . For example, the user terminal  30  is a mobile phone such as a smartphone. The user terminal  30  may be a tablet terminal, a PC (Personal Computer) and the like. The user terminal  30  may also be a so-called IoT (Internet of Thing) device. The user terminal  30  may include all things corresponding to a so-called IoE (Internet of Everything). 
     The user terminal  30  may assume a state in which it is existing within the cell  102  but not performing a wireless connection with the wireless base station  100 , and a state in which it is existing within the cell  102  and performing a wireless connection with the wireless base station  100  (the former may be described as an idle state, and the latter may be described as a connected state). In  FIG. 1  and  FIG. 2 , only the user terminal  30  existing in the wireless base station  100  is illustrated. 
     HO available area  104  schematically illustrates an area in which the user terminal  30  can be handed over from the cell  102  of the wireless base station  100  to a cell  182  of the wireless base station  180 . A size of the HO available area  104  is changed by changing a handover threshold (may be described as an HO threshold) which is set to the user terminal  30  by the wireless base station  100 . 
     For example, when an event type trigger A 2  is set as a timing for the user terminal  30  to transmit a Measurement Report (may be described as an MR) to the wireless base station  100 , the lower the HO threshold is, the narrower the HO available area  104  is. Also, when an event type trigger A 5  is set, the HO available area  104  becomes narrower as a threshold to be compared with the received radio wave intensity from the serving cell becomes lower and as a threshold to be compared with the received radio wave intensity from the neighbor cell becomes higher. 
     Also, when an event type trigger A 3  is set, the HO available area  104  becomes narrower as an HO threshold indicating an offset becomes higher. In the present embodiment, examples in which the event type trigger A 3  is employed as MR transmission timing will be mainly described. 
     The load of the wireless base station  100  increases by various factors, one of which is a control signal received from the user terminal  30 . For example, when the wireless base station  100  receives MRs from numerous user terminals  30 , the load for processing the numerous MRs increases. If the load of the wireless base station  100  increases, a situation where the handover of the user terminal  30  cannot be processed occurs, and a situation may occur where a user terminal  30  which cannot be handed over even though it cannot communicate due to an electric field that is really deteriorated and a user terminal  30  which can still communicate but is handed over are interspersed. 
     The wireless base station  100  according to the present embodiment changes the handover threshold which is set for the user terminal  30  that starts a wireless connection to the wireless base station  100  so that a handover from the wireless base station  100  of the user terminal  30  which establishes a wireless connection with the wireless base station  100  is suppressed when the load of the wireless base station  100  is increased. For example, when the load of the wireless base station  100  is increased, the wireless base station  100  increases the HO threshold for determining whether or not the received radio wave intensity from the neighbor cell is stronger than the received radio wave intensity from the serving cell by the HO threshold or more. 
     As a specific example, the wireless base station  100  changes the HO threshold to a first HO threshold which is higher than a default value when the load of the wireless base station  100  is increased. In this way, the first HO threshold which is higher than the default value can be set for the user terminal  30  that subsequently starts the wireless connection with the wireless base station  100 . The user terminal  30  that starts the wireless connection with the wireless base station  100  is, for example, a user terminal  30  which transits from an idle state to a connected state, a user terminal  30  which is handed over to the cell  102  of the wireless base station  100 , and the like. In this way, as illustrated in  FIG. 1  and  FIG. 2 , the HO available area  104  for the user terminal  30  that newly established the wireless connection with the wireless base station  100  can be narrowed, and the number of transmissions of MR to the wireless base station  100  can be reduced. By reducing the number of the MR received by the wireless base station  100 , the number of MR processing by the wireless base station  100  can be reduced, and the load of the wireless base station  100  can be reduced. In particular, a handover of a user terminal  30  with a good electric field among the user terminals  30  that reached an HO reference by increasing the HO threshold is suppressed, and the load of the wireless base station  100  can be reduced while allowing a handover of a user terminal  30  with a deteriorated electric field not to be suppressed. By causing targeted user terminals  30  with more deteriorated electric fields to perform the handover, a user terminal  30  which continues to switch between the same cells can be suppressed, and the number of HO perform signals can be significantly reduced. 
     The wireless base station  100  may reduce the HO threshold when the load of the wireless base station  100  is reduced after increasing the HO threshold. As a specific example, the wireless base station  100  changes the HO threshold to the default value. In this way, by limiting the handover of the user terminal  30  even though the load of the wireless base station  100  is not high, the occurrence of a situation where the user terminal  30  which normally should be handed over cannot be handed over can be suppressed. 
     The wireless base station  100  may gradually increase the HO threshold in accordance with the increase of the load of the wireless base station  100 . For example, the wireless base station  100  changes the HO threshold to the first HO threshold when the load of the wireless base station  100  becomes higher than the first load threshold, and changes the HO threshold to a second HO threshold which is higher than the first HO threshold when the load of the wireless base station  100  becomes higher than a second load threshold which is higher than the first load threshold. In this way, when the load of the wireless base station  100  is further increased for some reasons even though the number of MR receptions are reduced by changing the HO threshold to the first HO threshold, further reduction of the MR reception can contribute to the reduction of the load of the wireless base station  100 . The steps for increasing the HO threshold are not limited to two steps, but may be  3  steps or more. 
     The wireless base station  100  may determine whether the load of the wireless base station  100  is high or not, based on whether the load condition indicating that the load of the wireless base station  100  is high is satisfied or not. For example, the wireless base station  100  determines that the load of the wireless base station  100  is high when the load of the wireless base station  100  is higher than a predetermined load threshold, and determines that the load of the wireless base station  100  is low when the load of the wireless base station  100  is lower than the load threshold. As a specific example, the wireless base station  100  determines that the load of the wireless base station  100  is high when the CPU usage rate of the wireless base station  100  is higher than a predetermined usage rate threshold, and determines that the load of the wireless base station  100  is low when the CPU usage rate of the wireless base station  100  is lower than the usage rate threshold. These thresholds may be set arbitrarily, for example, by an administrator who manages the wireless base station  100 . 
     The wireless base station  100  may pre-store a value of the HO threshold set for the user terminal  30 . For example, the wireless base station  100  pre-stores the default value, the first HO threshold and the second HO threshold. These values may be set arbitrarily, for example, by an administrator who manages the wireless base station  100 . Also, these values may be determined by a network management system (may be described as NMS (Network Management System)) for managing the wireless base station  100 , and notified to the wireless base station  100 . The NMS may be an example of a management device. 
       FIG. 3  is a diagram schematically illustrating an example of a system  10 . The system  10  includes a plurality of wireless base stations  100  and an NMS  200 . 
     The plurality of wireless base stations  100  and the NMS  200  are communicating via a network  20 . The network  20  includes a mobile communication network. The mobile communication network may comply with any of 3G (3 rd  Generation) communication scheme, LTE (Long Term Evolution) communication scheme, 5G (5 th  Generation) communication scheme and a communication scheme after 6G (6 th  Generation) communication scheme. The network  20  may include the Internet. 
     Each of the plurality of wireless base stations  100  reports the MR which is a handover trigger (may be described as an HO trigger) of the existing user terminal  30  to the NMS  200 . The NMS  200  produces a distribution of the offset value based on the MR which is reported from the wireless base station  100  for each cell. The NMS  200  may compute the offset value based on a cumulative distribution for each cell. The NMS  200  may set HO thresholds at a high load gradually for each cell based on the computed offset value for the wireless base station  100 . 
     When the load of the wireless base station  100  is increased, the wireless base station  100  may set an HO threshold set from the NMS  200  as a HO threshold set for the user terminal  30  that starts the wireless connection to the wireless base station  100 . The wireless base station  100  may gradually change the HO threshold according to a load situation of the wireless base station  100 , and may continue the change of the HO threshold until the load falls below a reference load. The wireless base station  100  may return the HO threshold to the default value when the load of the wireless base station  100  falls below the reference load. 
     The NMS  200  may periodically perform an update of the HO threshold. The NMS  200  performs the update of the HO threshold for each predetermined period of time such as on a weekly basis, daily basis, or per hour basis, for example. For example, for each of the plurality of wireless base stations  100 , the NMS  200  derives the HO threshold based on the MR received during each period and sets the derived HO threshold. 
     The NMS  200  may reduce a frequency of the update of the HO threshold if the same tendency is found in continuous periods of time based on past statistics. In this way, the load of the NMS  200  and the wireless base station  100  required for the update can be reduced. 
       FIG. 4  is a diagram schematically illustrating an example of a flow of a processing performed by the system  10 . Herein, a flow of a processing which starts from establishing a wireless connection with a wireless base station  100  by one user terminal  30  and ends by a handover to a wireless base station  180  which is a neighbor cell of the wireless base station  100  is schematically illustrated. 
     In step (the step may be described as S for short)  102 , the user terminal  30  and the wireless base station  100  establish a connection. 
     In S 104 , the wireless base station  100  performs various settings for the user terminal  30 . For example, the wireless base station  100  transmits an RRC connection reconfiguration to the user terminal  30 , and the user terminal  30  transmits an RRC connection reconfiguration complete to the wireless base station  100 . 
     The wireless base station  100  may cause the user terminal  30  to set the transmission trigger and the HO threshold of the MR by the RRC connection reconfiguration. The wireless base station  100  causes the user terminal  30  to set the transmission trigger of the MR as an event type trigger A 3  and set the HO threshold as a default value, for example. 
     In S 106 , the user terminal  30  transmits the MR to the wireless base station  100  in accordance with the fact that a difference between received radio wave intensity from the wireless base station  100  and received radio wave intensity from the wireless base station  180  exceeds the HO threshold. The MR may include the received radio wave intensity of the wireless base station  100  and the received radio wave intensity of the wireless base station  180 . The wireless base station  100  determines whether to handover the user terminal  30  or not based on the received MR. Herein, the description continues assuming that no handover is determined to be performed. 
     In S 108 , the user terminal  30  transmits the MR to the wireless base station  100  in accordance with the fact that a difference between the received radio wave intensity from the wireless base station  100  and the received radio wave intensity from the wireless base station  180  exceeds the HO threshold. In S 110 , the wireless base station  100  determines to handover the user terminal  30  to the wireless base station  180  based on the MR received in S 108 . 
     In S 112 , the wireless base station  100  transmits, to the wireless base station  180 , an HO request for handing over the user terminal  30  to the wireless base station  180 . In S 114 , the wireless base station  100  transmits an HO instruction to the user terminal  30  instructing that it will be handed over to the wireless base station  180 . It should be noted that, the case where an X2 handover is performed is illustrated herein, but the wireless base station  100  may perform another handover such as an S1 handover. 
     In S 116 , the wireless base station  100  transmits, to the NMS  200 , the MR received from the user terminal  30  in S 108 , wherein the MR is the HO trigger of the user terminal  30 . In S 118 , an HO processing is performed between the user terminal  30  and the wireless base station  180 , and the user terminal  30  is handed over to the wireless base station  180 . 
     By transmitting the MR which is the HO trigger to the NMS  200  each time the wireless base station  100  causes the user terminal  30  to be handed over, the NMS  200  can collect a plurality of MRs. The NMS  200  may derive the HO threshold based on the plurality of MRs that are collected. 
       FIG. 5  is a diagram schematically illustrating an example of a functional configuration of an NMS  200 . The NMS  200  includes a measurement report receiving unit  202 , a measurement report storing unit  204 , an HO threshold deriving unit  206 , and an HO threshold transmitting unit  208 . 
     The measurement report receiving unit  202  receives, from the wireless base station  100 , an MR in the case where it is determined that the wireless base station  100  causes the user terminal  30  to be handed over based on the MR from the user terminal  30  existing in the wireless base station  100  (the MR which is the HO trigger). 
     The measurement report storing unit  204  stores, in association with base station identification information of the wireless base station  100 , the MR that the measurement report receiving unit  202  received from the wireless base station  100 . The measurement report storing unit  204  stores, in association with base station identification information of each of the plurality of wireless base station  100 , the MR that the measurement report receiving unit  202  received from each of the plurality of wireless base station  100 . 
     The HO threshold deriving unit  206  derives, for each of the plurality of wireless base stations  100 , an HO threshold based on the plurality of MRs corresponding to the wireless base stations  100  which are stored in the measurement report storing unit  204 . 
     The HO threshold deriving unit  206  may derive the HO threshold for each transmission trigger of the MRs. For example, when an event type trigger A 3  is employed, the HO threshold deriving unit  206  derives the HO threshold based on the received radio wave intensity from the serving cell and the received radio wave intensity from the neighbor cell included in the MRs. The HO threshold deriving unit  206  may derive the HO threshold based on a differential between the received radio wave intensity from the serving cell and the received radio wave intensity from the neighbor cell. The HO threshold deriving unit  206  derives the HO threshold based on a cumulative distribution of a plurality of differentials acquired from the plurality of MRs, for example. 
     The HO threshold deriving unit  206  may derive a value of a differential among the plurality of differentials, in which the cumulative distribution exceeds a predetermined first percentage, as a first HO threshold, and derive a value of a differential among the plurality of differentials, in which the cumulative distribution exceeds a second percentage, as a second HO threshold, for example. The second percentage is greater than the first percentage. The first percentage and the second percentage may be set arbitrarily, for example, by an administrator and the like of the NMS  200 . 
     Also, for example, when an event type trigger A 2  is employed, the HO threshold deriving unit  206  derives the HO threshold based on the received radio wave intensity from the serving cell included in the MRs. The HO threshold deriving unit  206  derives the HO threshold based on a cumulative distribution of the received radio wave intensity from the serving cell included in the plurality of MRs, for example. The HO threshold deriving unit  206  may derive a value of received radio wave intensity among the plurality of received radio wave intensities, in which the cumulative distribution exceeds a predetermined first percentage, as a first HO threshold, and derive a value of received radio wave intensity among the plurality of received radio wave intensities, in which the cumulative distribution exceeds a second percentage which is greater than the first percentage, as a second HO threshold, for example. 
     Also, for example, when an event type trigger A 5  is employed, the HO threshold deriving unit  206  derives an HO threshold for the serving cell and an HO threshold for the neighbor cell based on the received radio wave intensity from the serving cell and the received radio wave intensity from the neighbor cell included in the MR. The HO threshold deriving unit  206  derives an HO threshold for the serving cell and an HO threshold for the neighbor cell based on the cumulative distribution of the received radio wave intensity from the serving cell included in the plurality of MRs and a cumulative distribution of received radio wave intensity from the neighbor cell included in the plurality of MRs, for example. 
     The HO threshold deriving unit  206  may intermittently derive the HO threshold according to a predetermined timing. The HO threshold deriving unit  206  periodically derives the HO threshold according to a predetermined period, for example. The HO threshold deriving unit  206  performs the derivation of the HO threshold for each predetermined period of time such as on a weekly basis, daily basis, or per hour basis, for example. The HO threshold deriving unit  206  derives the HO threshold based on the MR received during each period, for example. 
     The HO threshold deriving unit  206  may reduce a frequency of the derivation of the HO threshold if the same tendency is found in continuous periods of time based on past statistics. For example, the HO threshold deriving unit  206  changes a derivation timing of the HO threshold from a daily basis to a weekday basis and Saturday, Sunday and National holiday basis, in the case in which the HO threshold is derived on a daily basis and in which a difference between the HO thresholds derived on weekdays are within a predetermined range, a difference between the HO thresholds derived on Saturday, Sunday and National holiday are within a predetermined range, and a difference between the HO thresholds derived on weekdays and the HO thresholds derived on Saturday, Sunday and National holiday exceeds a predetermined range. In this way, the load of the NMS  200  and the wireless base station  100  required for the update can be appropriately reduced. 
     The HO threshold transmitting unit  208  transmits the HO threshold derived by the HO threshold deriving unit  206  to the wireless base station  100 . The HO threshold transmitting unit  208  transmits, to each of the plurality of wireless base stations  100 , the HO threshold derived by the HO threshold deriving unit  206  for each of the plurality of wireless base stations  100 . 
       FIG. 6  is a diagram schematically illustrating an example of a cumulative distribution graph  222 . Herein, examples in which the event type trigger A 3  is employed as a transmission trigger of the MR will be described. The horizontal axis represents an offset value indicating a differential between the received radio wave intensity from the serving cell and the received radio wave intensity from the neighbor cell included in the MR. The vertical axis represents a percentage of each of the plurality of offset values relative to the total. 
     In the example indicated in  FIG. 6 , the NMS  200  may assume  5 dB that is an offset value for which the cumulative distribution exceeds X% as a first HO threshold, and assume  9 dB that is an offset value whose cumulative distribution exceeds Y% as a second HO threshold. The values of X and Y may be set arbitrarily, for example, by an administrator and the like of the NMS  200 . 
       FIG. 7  is a diagram schematically illustrating an example of a cumulative distribution graph  224 . The cumulative distribution graph  224  corresponds to a cell different from the cumulative distribution graph  222 . 
     In the example indicated in  FIG. 7 , the NMS  200  assumes  6 dB that is an offset value whose cumulative distribution exceeds X% as a first HO threshold, and assume  8 dB that is an offset value whose cumulative distribution exceeds Y% as a second HO threshold. As illustrated in  FIG. 6  and  FIG. 7 , since the distribution of the MR is different for each cell, different HO thresholds may be derived for each cell. 
       FIG. 8  is a diagram schematically illustrating an example of a functional configuration of a base station device  110 . The base station device  110  is mounted on the wireless base station  100 . The base station device  110  includes an HO threshold storing unit  111 , a terminal control unit  112 , a measurement report receiving unit  114 , an HO determining unit  116 , a measurement report storing unit  118 , a measurement report transmitting unit  120 , an HO threshold receiving unit  122 , an HO threshold deriving unit  126 , a load determining unit  128 , and an HO threshold change unit  130 . It should be noted that it is not always necessary for the base station device  110  to include all these components. 
     The HO threshold storing unit  111  stores the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110 . The HO threshold storing unit  111  may store the plurality of HO thresholds which corresponds to the height of the load of the base station device  110 . 
     The HO threshold storing unit  111  may store the HO threshold for each transmission trigger of the MRs. The HO threshold storing unit  111  stores, for example, an HO threshold for an event type trigger A 3 , an HO threshold for an event type trigger A 2 , an HO threshold for an event type trigger A 5 . 
     The terminal control unit  112  performs various controls with the user terminal  30 . The terminal control unit  112  establishes a communication connection with the user terminal  30 , for example. Also, the terminal control unit  112  performs various settings for the user terminal  30 , for example. The terminal control unit  112  may set a transmission trigger of the MR for the user terminal  30 . Also, the terminal control unit  112  may set the HO threshold for the user terminal  30 . The terminal control unit  112  transmits, for example to the user terminal  30  that starts a wireless connection to the base station device  110 , a transmission trigger of a preset MR, and an HO threshold to be set for the user terminal  30  that starts a wireless connection to the base station device  110 , the HO threshold being stored in the HO threshold storing unit  111 , and then sets the HO threshold for the user terminal  30 . 
     The measurement report receiving unit  114  receives the MR from the user terminal  30  existing in the wireless base station  100 . The measurement report receiving unit  114  receives the MR transmitted by the user terminal  30 , in accordance with the transmission trigger which is set by the terminal control unit  112 . 
     The HO determining unit  116  determines, when the measurement report receiving unit  114  receives the MR, whether or not to handover the user terminal  30  which has transmitted the MR, based on the MR. The HO determining unit  116  may determine whether or not to handover the user terminal  30  based on the MR as with the existing wireless base station. 
     When the HO determining unit  116  determines to handover the user terminal  30 , the terminal control unit  112  performs control to handover the user terminal  30 . The terminal control unit  112  may be an example of a handover control unit. 
     A handover manner may be similar to the existing manner. For example, when performing an X2 handover, the terminal control unit  112  transmits an HO request to the wireless base station  100  which is a handover destination, and transmits an HO instruction to the user terminal  30 . The terminal control unit  112  transmits the HO request to an MME (Mobility Management Entity) when performing an S1 handover, for example. 
     The measurement report storing unit  118  stores the MR in the case where the HO determining unit  116  is determined to handover the user terminal  30 . The measurement report transmitting unit  120  transmits the MR which is stored in the measurement report storing unit  118  to the NMS  200 . 
     The measurement report transmitting unit  120  may transmit the MR to the NMS  200  according to a preset timing. The measurement report transmitting unit  120  transmits the MR to the NMS  200  every time the measurement report storing unit  118  stores the MR, for example. Also, for example, for each predetermined period of time, the measurement report transmitting unit  120  transmits, to the NMS  200 , the MR which is stored by the measurement report storing unit  118  during each period. 
     It should be noted that the measurement report storing unit  118  may store all the MRs received by the measurement report receiving unit  114  and the measurement report transmitting unit  120  may transmit only MRs that are the HO triggers to the NMS  200 , among the MRs stored in the measurement report storing unit  118 . 
     The HO threshold receiving unit  122  receives, from the NMS  200 , the HO threshold derived by the NMS  200  based on the MR which is transmitted by the measurement report transmitting unit  120 . The NMS  200  may derive the HO threshold for each transmission trigger of the MR and transmit it to the base station device  110 . 
     The HO threshold deriving unit  126  derives the HO threshold based on the MR stored in the measurement report storing unit  118 . The HO threshold deriving unit  126  may derive the HO threshold using a similar method as the NMS  200 . 
     The load determining unit  128  determines whether a load condition indicating that a load of the base station device  110  is high is satisfied or not. The load determining unit  128  determines that the load condition is satisfied when the load of the base station device  110  is higher than a predetermined load threshold, and determines that the load condition is not satisfied when the load of the base station device  110  is lower than the load threshold, for example. The load determining unit  128  may determine that the load condition is satisfied when a CPU usage rate of the base station device  110  is higher than a predetermined usage rate threshold, and determine that the load condition is not satisfied when the CPU usage rate of the base station device  110  is lower than the usage rate threshold. 
     When the load determining unit  128  determines that the load condition is satisfied, the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110 , which is stored in the HO threshold storing unit  111 , such that a handover from the base station device  110  of the user terminal  30  which establishes the wireless connection between the base station device  110  is suppressed. 
     The HO threshold change unit  130  may gradually change the HO threshold until the load of the base station device  110  becomes lower than a predetermined load threshold when the load of the base station device  110  is higher than the predetermined load threshold. In this way, the load of the base station device  110  can be appropriately reduced to the predetermined load without excessively suppressing the handover of the user terminal  30 . 
     The HO threshold change unit  130  may change the HO threshold to the HO threshold which corresponds to the height of the load of the base station device  110 . In this way, the appropriate HO threshold can be set for the user terminal  30 , the appropriate HO threshold corresponding to a situation of the load of the base station device  110 . 
     When an event type trigger A 3  is employed as the transmission trigger of the MR, the HO threshold change unit  130  increases the HO threshold for determining whether or not received radio wave intensity from a neighbor cell is stronger than received radio wave intensity from a serving cell by the HO threshold or more. The HO threshold change unit  130  may change the HO threshold from a default value to a first HO threshold which is higher than the default value. The HO threshold change unit  130  uses a first HO threshold which is preset by an administrator and the like of the wireless base station  100 , for example. Also, the HO threshold change unit  130  may use a first HO threshold that the HO threshold receiving unit  122  received from the NMS  200 . Also, the HO threshold change unit  130  may use a first HO threshold derived from the HO threshold deriving unit  126 . The HO threshold change unit  130  may change the HO threshold to the default value when the load determining unit  128  determines that the load condition is not satisfied after the HO threshold is changed to the first HO threshold. The HO threshold change unit  130  may change the HO threshold into the first HO threshold when the load of the base station device  110  is higher than a first load threshold and lower than a second load threshold, and the HO threshold change unit  130  may change the HO threshold to a second HO threshold which is higher than the first HO threshold when the load of the base station device  110  is higher than the second load threshold. The HO threshold change unit  130  uses a second HO threshold which is preset by an administrator and the like of the wireless base station  100 , for example. Also, the HO threshold change unit  130  may use a second HO threshold that the HO threshold receiving unit  122  received from the NMS  200 . Also, the HO threshold change unit  130  may use a second HO threshold derived from the HO threshold deriving unit  126 . 
     When an event type trigger A 2  is employed as the transmission trigger of the MR, the HO threshold change unit  130  reduces the HO threshold for determining whether or not received radio wave intensity from the serving cell is lower than the HO threshold. The HO threshold change unit  130  may change the HO threshold from a default value to a first HO threshold which is lower than the default value. The HO threshold change unit  130  uses a first HO threshold which is preset by an administrator and the like of the wireless base station  100 , for example. Also, the HO threshold change unit  130  may use a first HO threshold that the HO threshold receiving unit  122  received from the NMS  200 . Also, the HO threshold change unit  130  may use a first HO threshold derived from the HO threshold deriving unit  126 . The HO threshold change unit  130  may change the HO threshold to the default value when the load determining unit  128  determines that the load condition is not satisfied after the HO threshold is changed to the first HO threshold. The HO threshold change unit  130  may change the HO threshold into the first HO threshold when the load of the base station device  110  is higher than a first load threshold and lower than a second load threshold, and the HO threshold change unit  130  may change the HO threshold to a second HO threshold which is higher than the first HO threshold when the load of the base station device  110  is lower than the second load threshold. The HO threshold change unit  130  uses a second HO threshold which is preset by an administrator and the like of the wireless base station  100 , for example. Also, the HO threshold change unit  130  may use a second HO threshold that the HO threshold receiving unit  122  received from the NMS  200 . Also, the HO threshold change unit  130  may use a second HO threshold derived from the HO threshold deriving unit  126 . 
     When an event type trigger A 5  is employed as the transmission trigger of the MR, the terminal control unit  112  reduces a serving cell HO threshold for determining whether the received radio wave intensity from a serving cell is lower than the serving cell HO threshold or not, and increases a neighbor cell HO threshold for determining whether received radio wave intensity from a neighbor cell is higher than the neighbor cell HO threshold or not. The terminal control unit  112  may change the serving cell HO threshold from the default value to a first serving cell HO threshold which is lower than the default value, and change the neighbor cell HO threshold from the default value to a first neighbor cell HO threshold which is higher than the default value. The HO threshold change unit  130  uses the first serving cell HO threshold and the first neighbor cell HO threshold which are preset by an administrator and the like of the wireless base station  100 , for example. Also, the HO threshold change unit  130  may use the first serving cell HO threshold and the first neighbor cell HO threshold that the HO threshold receiving unit  122  received from the NMS  200 . Also, the HO threshold change unit  130  may use the first serving cell HO threshold and the first neighbor cell HO threshold derived by the HO threshold deriving unit  126 . The HO threshold change unit  130  may change the serving cell HO threshold to the default value and change the neighbor cell HO threshold to the default value when the load determining unit  128  determines that the load condition is not satisfied after transmitting a changing instruction. The HO threshold change unit  130  may change the serving cell HO threshold to the first serving cell HO threshold when the load of the base station device  110  is higher than the first load threshold and lower than the second load threshold, change the neighbor cell HO threshold to the first neighbor cell HO threshold, change the serving cell HO threshold to a second serving cell HO threshold which is lower than the first serving cell HO threshold when the load of the base station device  110  is higher than the second load threshold, and change the neighbor cell HO threshold to a second neighbor cell HO threshold which is higher than the first neighbor cell HO threshold. The HO threshold change unit  130  uses the second serving cell HO threshold and the second neighbor cell HO threshold which are preset by an administrator and the like of the wireless base station  100 , for example. Also, the HO threshold change unit  130  may use the second serving cell HO threshold and the second neighbor cell HO threshold that the HO threshold receiving unit  122  received from the NMS  200 . Also, the HO threshold change unit  130  may use the second serving cell HO threshold and the second neighbor cell HO threshold derived by the HO threshold deriving unit  126 . 
       FIG. 9  is a diagram schematically illustrating an example of a flow of processing performed by the base station device  110 . Herein, a state in which a plurality of user terminals  30  are existing in the base station device  110 , an event type trigger A 3  is employed as the transmission trigger of the MR, and an HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  is set as a default value is described as an initialized state. 
     In S 202 , the load determining unit  128  determines whether a CPU usage rate of the base station device  110  is higher than a threshold or not. If the CPU usage rate of the base station device  110  is higher than a threshold is determined to be higher, the process proceeds to S 204 . 
     In S 204 , the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  to a value higher than the default value. After the change, the HO threshold is set for the user terminal  30  to be a value higher than the default value that starts a wireless connection to the base station device  110 , and the transmission of the MR from the user terminal  30  which newly established a wireless connection with the base station device  110  is suppressed. 
     In S 206 , the load determining unit  128  determines whether a CPU usage rate of the base station device  110  is lower than a threshold or not. If the CPU usage rate of the base station device  110  is lower than a threshold is determined to be higher, the process proceeds to S 208 . 
     In S 208 , the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  to the default value. The process returns to S 202 . The base station device  110  may terminate the process indicated in  FIG. 9  according to an instruction by an administrator of the base station device  110 , for example. 
       FIG. 10  is a diagram schematically illustrating an example of a flow of processing performed by the base station device  110 . Herein, a state in which a plurality of user terminals  30  are existing in the base station device  110 , an event type trigger A 3  is employed as the transmission trigger of the MR, and an HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  is set as a default value is described as an initialized state. 
     In S 302 , the load determining unit  128  determines whether a CPU usage rate of the base station device  110  is higher than a first threshold or not. If the CPU usage rate of the base station device  110  is higher than a threshold is determined to be higher, the process proceeds to S 304 . 
     In S 304 , the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  to a first HO threshold higher than the default value. 
     In S 306 , the load determining unit  128  determines whether a CPU usage rate of the base station device  110  is higher than a second threshold which is higher than the first threshold or not. If the CPU usage rate of the base station device  110  is determined to be higher than the second threshold, the process proceeds to S 308 . If the CPU usage rate of the base station device  110  is not determined to be higher than the second threshold, the process proceeds to S 312 . In S 308 , the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  to a second HO threshold higher than the first HO threshold. 
     In S 310 , the load determining unit  128  determines whether a CPU usage rate of the base station device  110  is lower than the second threshold or not. If the CPU usage rate of the base station device  110  is lower than a threshold is determined to be higher, the process proceeds to S 312 . In S 312 , the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  to the first HO threshold. 
     In S 314 , the load determining unit  128  determines whether a CPU usage rate of the base station device  110  is lower than the first threshold or not. If the CPU usage rate of the base station device  110  is determined to be lower than the first threshold, the process proceeds to S 316 . If the CPU usage rate of the base station device  110  is not determined to be lower than the first threshold, the process returns to S 306 . In S 316 , the HO threshold change unit  130  changes the HO threshold set for the user terminal  30  that starts a wireless connection to the base station device  110  to the default value. The process returns to S 302 . The base station device  110  may terminate the process indicated in  FIG. 10  according to an instruction by an administrator of the base station device  110 , for example. 
       FIG. 11  is a diagram schematically illustrating HAPS (High Altitude Platform Station)  300 . The HAPS  300  may be an example of a flying object. The HAPS  300  includes a vehicle  310 , a central part  320 , a propeller  330 , a pod  340 , and a solar panel  350 . The central part  320  has a flight control device and a base station device  110  which are not shown. 
     An electrical power generated by the solar panel  350  is stored in one or more batteries positioned in at least any of the vehicle  310 , the central part  320 , and the pod  340 . The electrical power stored in the battery is utilized by each component included in the HAPS  300 . 
     The flight control device controls the flight of the HAPS  300 . The flight control device controls the flight of the HAPS  300  by controlling the rotation of the propeller  330 , for example. Also, the flight control device may control the flight of the HAPS  300  by changing the angle of the flap or the elevator which are not shown. The flight control device may include various sensors such as a positioning sensor for example a GPS sensor and the like, a gyrosensor, and an acceleration sensor and the like, to manage the position, the moving direction, and the moving speed of the HAPS  300 . 
     The base station device  110  provides a wireless communication service to the user terminal  30  on the ground by using an FL (Feeder Link) antenna  322 , and an SL (Service Link) antenna  324 . The FL antenna  322  is an antenna for a feeder link. The base station device  110  forms a feeder link between itself and a terrestrial gateway  40  by the FL antenna  322 . 
     The SL antenna  324  is an antenna for a service link. The SL antenna  324  may be an antenna with lower directivity than the FL antenna  322 . The base station device  110  forms a cell  102  on the ground by the SL antenna  324 . 
     The base station device  110  establishes a feeder link between itself and each gateway  40  positioned at each location on the ground and then communicates with a network  20  on the ground via the gateway  40 , for example. The base station device  110  may communicate with an NMS  200  via the gateway  40  and the network  20 . The HAPS  300  covers a terrestrial area by the cell  102  while performing circular flight along a circular flight path over the terrestrial area to be covered and adjusting a beam direction determined by the FL antenna  322  and the SL antenna  324 , for example. Besides of precise circles and ovals and the like, the flight path may be shaped like a number 8 and the like. The adjustment of the beam direction may be performed by at least any of a physical orientation change of the antenna and beamforming. 
     In the case of the HAPS  300 , since a range of the terrestrial area covered by the cell  102  is broader compared to a terrestrial wireless base station, and an electric field variation in the terrestrial area becomes intense by a vehicle oscillation due to the flight, more control signals is generated compared to the terrestrial wireless base station. Therefore, the effect of changing, by the base station device  110 , the HO threshold in accordance with the load of the base station device  110  is more significant. 
     Also, in the case of the HAPS  300 , the appropriate HO threshold is likely to vary for each HAPS  300 , depending on positioning conditions of the cell in the covering target area, wind conditions in the flight area, performance errors of the vehicle, communication traffic tendency in the covering target area, seasonal variations, or the like. In contrast, in the present embodiment, since the HO threshold is derived for each HAPS  300 , the HO threshold suitable for each HAPS  300  can be applied and the load reduction can be appropriately realized. 
     Also, in the case of the HAPS  300 , it is predicted that the value distribution of offset values in the MR which is the HO trigger will become wider. Accordingly, a configuration with good time efficiency can be realized compared to the case in which the HO threshold is gradually adjusted, by aggregating the distribution of the offset values in the MR which is the HO trigger, derive the HO threshold based on the cumulative distribution in advance, and applying, according to the load of the base station device  110 , the HO threshold which is derived in advance. 
     Also, in the case of the HAPS  300 , computing resources are limited and the available electrical power is limited compared to the terrestrial wireless base station, but the message exchange between the base station device  110  and the NMS  200  can be reduced and a countermeasure at a high load is immediately performed while reducing the load of the base station device  110 , by performing the HO threshold derivation with the NMS  200  and performing the high load determination by the base station device  110 . 
       FIG. 12  is a diagram schematically illustrating an example of a hardware configuration of a computer  1200  serving as the base station device  110  or the NMS  200 . a program installed in the computer  1200  can cause the computer  1200  to function as one or more “units” of the device according to the above embodiment, or can cause the computer  1200  to perform operations or one or more “units” associated with the device according to the above embodiment, and/or can cause the computer  1200  to perform a process or steps of the process according to the above embodiment. Such a program may be executed by a CPU  1212  so as to cause the computer  1200  to perform specific operations associated with some or all of the blocks in the flowcharts and block diagrams described in the present specification. 
     The computer  1200  according to the present embodiment includes the CPU  1212 , a RAM  1214 , and a graphics controller  1216  which are mutually connected by a host controller  1210 . Also, the computer  1200  includes input/output units such as a communication interface  1222 , a storage device  1224 , a DVD drive and an IC card drive, which are connected to the host controller  1210  via an input/output controller  1220 . The storage device  1224  may be a hard disk drive, a solid state drive and the like. The computer  1200  also includes a legacy input/output unit such as a ROM  1230  and a keyboard, which are connected to the input/output controller  1220  via an input/output chip  1240 . 
     The CPU  1212  operates according to the program stored in the ROM  1230  and the RAM  1214 , thereby controlling each unit. The graphics controller  1216  is configured to acquire image data generated by the CPU  1212  in a frame buffer or the like provided in the RAM  1214  or in itself, and cause the image data to be displayed on a display device  1218 . 
     The communication interface  1222  communicates with other devices via a network. The storage device  1224  stores programs and data used by the CPU  1212  in the computer  1200 . The IC card drive reads programs and data from an IC card, and/or writes programs and data into the IC card. 
     The ROM  1230  stores therein boot programs or the like executed by the computer  1200  at the time of activation, and/or stores programs depending on the hardware of the computer  1200 . The input/output chip  1240  may also connect various input/output units to the input/output controller  1220  via a USB port, a parallel port, a serial port, a keyboard port, a mouse port or the like. 
     A program is provided by a computer-readable storage medium such as the DVD-ROM or the IC card. The program is read from the computer-readable storage medium, installed in the storage device  1224 , the RAM  1214 , or the ROM  1230 , which are also examples of the computer-readable storage medium, and is executed by the CPU  1212 . Information processing written in these programs is read by the computer  1200 , and provides cooperation between a program and the above-mentioned various types of hardware resources. An apparatus or a method may be configured by realizing the operation or processing of the information according to the usage of the computer  1200 . 
     For example, when communication is performed between the computer  1200  and an external device, the CPU  1212  may execute a communication program loaded in the RAM  1214 , and instruct the communication interface  1222  to execute communication processing based on processing written in the communication program. The communication interface  1222 , under control of the CPU  1212 , reads transmission data stored on a transmission buffer region provided in a recording medium such as the RAM  1214 , the storage device  1224 , the DVD-ROM, or the IC card, and transmits the read transmission data to a network or writes reception data received from a network to a reception buffer region or the like provided on the recording medium. 
     In addition, the CPU  1212  may cause all or a necessary portion of a file or a database to be read into the RAM  1214 , the file or the database having been stored in an external recording medium such as the storage device  1224 , the DVD drive (DVD-ROM), the IC card, etc., and perform various types of processing on the data on the RAM  1214 . Next, the CPU  1212  may write back the processed data into the external recording medium. 
     Various types of information, such as various types of programs, data, tables, and databases, may be stored in the recording medium, and subjected to information processing. The CPU  1212  may execute various types of processing on the data read from the RAM  1214  to write back a result to the RAM  1214 , the processing being described throughout the present disclosure, specified by instruction sequences of the programs, and including various types of operations, information processing, conditional determinations, conditional branching, unconditional branching, information retrievals/replacements, or the like. In addition, the CPU  1212  may search for information in the file, the database, or the like in the recording medium. For example, when a plurality of entries each having an attribute value of a first attribute associated with an attribute value of a second attribute are stored in the recording medium, the CPU  1212  may search, from the plurality of entries, for an entry that matches a condition in which the attribute value of the first attribute is specified, and read the attribute value of the second attribute stored in the entry, and thereby acquiring the attribute value of the second attribute associated with the first attribute that satisfies a predetermined condition. 
     The above-described program or software module may be stored on the computer  1200  or in a computer-readable storage medium near the computer  1200 . Also, a recording medium such as a hard disk or a RAM provided in a server system connected to a dedicated communication network or the Internet can be used as a computer-readable storage medium, thereby providing the program to the computer  1200  via the network. 
     In the flowcharts and the block diagrams in the present embodiment, the blocks may represent “units” of an apparatus having a role to perform steps of the process for performing operations or to perform the operations. A specific step or “unit” may be implemented by a dedicated circuit, a programmable circuit provided along with computer-readable instructions stored on a computer-readable storage medium, and/or a processor provided along with the computer-readable instructions stored on the computer-readable storage medium. The dedicated circuit may include a digital and/or analog hardware circuit, or may include an integrated circuit (IC) and/or a discrete circuit. The programmable circuit may include a reconfigurable hardware circuit, such as a field-programmable gate array (FPGA) and a programmable logic array (PLA), for example, including logical AND, logical OR, logical XOR, logical NAND, logical NOR, and other logical operations, flip-flops, registers, and memory elements. 
     The computer-readable storage medium may include any tangible device that can store instructions to be executed by a suitable device, so that the computer-readable storage medium having instructions stored thereon comprises a product including instructions that can be executed to configure means for performing operations specified in the flowcharts or block diagrams. Examples of the computer-readable storage medium may include an electronic storage medium, a magnetic storage medium, an optical storage medium, an electromagnetic storage medium, a semiconductor storage medium, etc. More specific examples of computer-readable storage media may include a floppy (registered trademark) disk, a diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an electrically erasable programmable read-only memory (EEPROM), a static random access memory (SRAM), a compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a BLU-RAY(registered trademark) disc, a memory stick, an integrated circuit card, etc. 
     The computer-readable instructions may include assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcodes, firmware instructions, state-setting data, or any of source codes or object codes described in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk (registered trademark), JAVA (registered trademark), or C++, and conventional procedural programming languages, such as “c” programming languages or similar programming languages. 
     The computer-readable instructions may be provided to a processor of a general-purpose computer, a special purpose computer or other programmable data processing apparatuses, or a programmable circuit, locally or via the local area network (LAN) or the wide area network (WAN) such as the Internet, so that the processor of the general-purpose computer, the special purpose computer or other programmable data processing apparatuses, or the programmable circuit executes the computer-readable instructions to generate means for performing the operations specified in the flowcharts or block diagrams. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, etc. 
     The above-described embodiment includes the NMS  200  as an example of the management device, but not limited thereto. The system  10  may include the management device aside from the NMS  200 . The management device may be connected to the network  20 , and include a measurement report receiving unit  202 , a measurement report storing unit  204 , an HO threshold deriving unit  206 , and an HO threshold transmitting unit  208 . 
     While the embodiments of the present invention have been described, the technical scope of the invention is not limited to the above-described embodiments. It is apparent to persons skilled in the art that various alterations and improvements can be added to the above-described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the invention. 
     The operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by “prior to,” “before,” or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as “first” or “next” in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order. 
     EXPLANATION OF REFERENCES 
       10 : system 
       20 : network 
       30 : user terminal 
       40 : gateway 
       100 : wireless base station 
       102 : cell 
       104 : HO available area 
       110 : base station device 
       111 : HO threshold storing unit 
       112 : terminal control unit 
       114 : measurement report receiving unit 
       116 : HO determining unit 
       118 : measurement report storing unit 
       120 : measurement report transmitting unit 
       122 : HO threshold receiving unit 
       126 : HO threshold deriving unit 
       128 : load determining unit 
       130 : HO threshold change unit 
       180 : wireless base station 
       200 : NMS 
       202 : measurement report receiving unit 
       204 : measurement report storing unit 
       206 : HO threshold deriving unit 
       208 : HO threshold transmitting unit 
       222 : cumulative distribution graph 
       224 : cumulative distribution graph 
       300 : HAPS 
       310 : vehicle 
       320 : central part 
       322 : FL antenna 
       324 : SL antenna 
       330 : propeller 
       340 : pod 
       350 : solar panel 
       1200 : computer 
       1210 : host controller 
       1212 : CPU 
       1214 : RAM 
       1216 : graphics controller 
       1218 : display device 
       1220 : input/output controller 
       1222 : communication interface 
       1224 : storage device 
       1230 : ROM 
       1240 : input/output chip