Base station, mobile station, communication method, and program

Abstract

The purpose of the present invention is to provide a base station capable of stabilizing connection status. A base station according to the present disclosure comprises: a communication unit for receiving a measurement report message from a mobile station; and a determination unit for determining, on the basis of the measurement report message, whether or not to execute a handover. When the mobile station satisfies a first condition for being handed over to another base station from the base station and a change amount in a reception radio wave intensity of a signal received by the mobile station from the base station is within a prescribed range, the determination unit sets an offset period after receiving the measurement report message, and executes a handover of the mobile station to the other base station after the offset period passes.

Description

Base station, mobile station, communication method and program

[0001] The present disclosure relates to a base station, a mobile station, a communication method, and a program.

[0002] A mobile station in a mobile communication system measures the received signal strength in the cell in which it is currently located and in surrounding cells, and periodically reports the results to a base station in a message called a Measurement Report. The base station uses the measurement information contained in the Measurement Report message reported by the mobile station to control the connection destination of the mobile station so that the mobile station can connect to a cell that can receive the strongest possible signal.

[0003] Patent Document 1 discloses a configuration in which a mobile device communicates with a fixed base station installed at a specific location via a mobile base station mounted on a train. Patent Document 1 also discloses the flow of a handover process for switching the fixed base station to which the mobile base station is connected.

[0004] Japanese Patent Application Laid-Open No. 2007-235541

[0005] Patent Document 1 discloses that a mobile device always communicates with a fixed base station via a mobile base station. Here, for example, when a user carrying the mobile device gets off a train, the mobile device needs to switch its connection from the mobile base station to the fixed base station. However, when a train equipped with a mobile base station stops at a station, the boundary between the cell formed by the fixed base station and the cell formed by the mobile base station changes. In this case, there is a problem that the connection state between the mobile device and the base station becomes unstable, such as handovers being frequently repeated at the cell boundary.

[0006] In view of the above-mentioned problems, an object of the present disclosure is to provide a base station, a mobile station, a communication method, and a program that can stabilize the connection state.

[0007] A base station according to the present disclosure includes a communication unit that receives a Measurement Report message from a mobile station, and a determination unit that determines whether to execute a handover based on the Measurement Report message, wherein the determination unit sets an offset period after receiving the Measurement Report message when a first condition for the mobile station to execute a handover from the base station to another base station is satisfied and a change in received radio wave strength of a signal received at the mobile station from the base station is within a predetermined range, and executes a handover of the mobile station to the other base station after the offset period has elapsed.

[0008] The mobile station according to the present disclosure is a mobile station that connects to a mobile base station installed in a vehicle, and includes a measurement unit that measures the received radio wave strength of signals received from the connected mobile base station and base stations surrounding the mobile base station, and a communication unit that transmits a Measurement Report message to the mobile base station when the received radio wave strength continues to satisfy a predetermined condition for a predetermined period of time, the predetermined period being longer than the period adopted when the mobile station is connected to a fixed base station installed at a predetermined location.

[0009] A communication method according to the present disclosure is a communication method executed in a base station, which receives a Measurement Report message from a mobile station, and determines whether to perform a handover based on the Measurement Report message. When determining whether to perform the handover, if the mobile station satisfies a first condition for handing over from the base station to another base station and a change in received radio wave intensity of a signal received at the mobile station from the base station is within a predetermined range, the communication method sets an offset period after receiving the Measurement Report message, and executes handover of the mobile station to the other base station after the offset period has elapsed.

[0010] A program according to the present disclosure is a program executed by a base station, which is a computer, to receive a Measurement Report message from a mobile station, determine whether to execute a handover based on the Measurement Report message, and, when determining whether to execute the handover, if the mobile station satisfies a first condition for handing over from the base station to another base station and a change in received radio wave intensity of a signal received at the mobile station from the base station is within a predetermined range, set an offset period after receiving the Measurement Report message, and execute a handover of the mobile station to the other base station after the offset period has elapsed.

[0011] The present disclosure makes it possible to provide a base station, a mobile station, a communication method, and a program that can stabilize the connection state.

[0012] FIG. 1 shows an example of the configuration of a base station. FIG. 2 shows the flow of communication processing executed in the base station. FIG. 3 shows an example of the configuration of a mobile station. FIG. 4 is a diagram showing the flow of communication processing executed in the mobile station. FIG. 5 shows the flow of handover processing in a communication system including a UE and an eNB. FIG. 6 shows the flow of handover processing when the eNB is a mobile base station. FIG. 7 shows the flow of handover processing when the eNB is a mobile base station. FIG. 8 shows the flow of handover processing when the eNB is a fixed base station. FIG. 9 shows the flow of handover processing when the eNB is a fixed base station. FIG. 10 shows an example of the configuration of a UE. FIG. 11 shows the flow of Measurement Report message transmission processing executed in the UE. FIG. 12 is a block diagram showing an example of the configuration of a base station. FIG. 13 is a block diagram showing example configurations of a mobile station and a UE.

[0013] (First Embodiment) Fig. 1 shows a configuration example of a base station 10. The base station 10 may be a computer device operated by a processor executing a program stored in a memory. The base station 10 may be a gNB (next generation NodeB) that supports 5G (5th Generation) defined as a wireless communication standard by 3GPP (3rd Generation Partnership Project) (registered trademark) or an eNB (evolved NodeB) that supports 4G (4th Generation). The base station 10 may also be an ng-eNB (next generation eNB) that supports 5G.

[0014] The base station 10 includes a communication unit 11 and a determination unit 12. The communication unit 11 and the determination unit 12 may be software or modules that are executed by a processor executing a program stored in a memory, or may be hardware such as a circuit or a chip.

[0015] The communication unit 11 receives a Measurement Report message from a mobile station. The mobile station may be User Equipment (UE), which is a general term for terminals in 3GPP. The mobile station may also be a smartphone terminal, a tablet terminal, an IoT (Internet of Things) terminal, or the like.

[0016] The Measurement Report message may include, for example, a measurement result of the received signal strength of a signal received in a cell to which the mobile station is currently connected. Connecting to a cell may be rephrased as connecting to a base station that forms the cell. The Measurement Report message may also include a measurement result of the received signal strength of a signal received from a cell surrounding the cell to which the mobile station is currently connected. The received signal strength may be referred to, for example, as RSRP (Reference Signal Received Power).

[0017] The communication unit 11 may receive a Measurement Report message from the mobile station periodically or periodically, or may receive a Measurement Report message from the mobile station when the communication unit 11 detects an event that triggers the mobile station to transmit a Measurement Report message.

[0018] The determination unit 12 determines whether to execute a handover based on the Measurement Report message. Handover is a process or function in which, when a mobile station communicating in a certain cell moves to another cell, the mobile station continues communication by switching base stations. For example, when the received radio wave strength in another cell is stronger than the received radio wave strength in the cell to which the mobile station is currently connected, the determination unit 12 may determine to handover the mobile station to the cell with the stronger received radio wave strength. In other words, the determination unit 12 may determine to execute handover processing for the mobile station. When the determination unit 12 determines to execute handover processing, the determination unit 12 may instruct the mobile station to execute handover via the communication unit 11. The handover processing may include the base station 10 transmitting a message instructing the mobile station to execute handover, and the base station 10 receiving a response message in response to the instruction message from the mobile station. The handover processing may also include the base station 10 transmitting a message requesting handover of the mobile station to the destination base station of the mobile station.

[0019] Regarding the received radio wave strength of the mobile station, the condition or criterion used for executing handover of the mobile station may be that the received radio wave strength in another cell is greater than that in the cell to which the mobile station is currently connected. Also, the determination unit 12 may determine the destination cell taking into consideration the load of the base station forming the destination cell, etc. In other words, the determination unit 12 may include, in the conditions used for executing handover of the mobile station, the load of the base station forming the destination cell being smaller than that of other base stations, etc.

[0020] The determination unit 12 further determines whether the amount of change in the received radio wave strength of a signal received by the mobile station from a base station is within a predetermined range. The determination unit 12 may identify the amount of change in the received radio wave strength by calculating the difference in the received radio wave strength included in Measurement Report messages received at different times. The determination unit 12 may calculate the difference in the received radio wave strength included in the latest Measurement Report message and the Measurement Report message immediately before the latest Measurement Report message. Alternatively, the determination unit 12 may determine a reference Measurement Report message and, each time a Measurement Report message is received, calculate the difference from the received radio wave strength included in the reference Measurement Report message.

[0021] The determination unit 12 sets the offset period when the conditions for executing a handover of the mobile station are satisfied and the change in the received radio wave strength of the signal received by the mobile station from the base station is within a predetermined range. The offset period may be set after receiving a Measurement Report message. Specifically, the offset period may be set after receiving the Measurement Report message used when the determination unit 12 determined that the conditions for executing a handover of the mobile station are satisfied.

[0022] The determining unit 12 executes handover of the mobile station to another base station after the offset period has elapsed.

[0023] FIG. 2 shows the flow of communication processing executed in the base station 10. First, the communication unit 11 receives a Measurement Report message from the mobile station (S11). Next, the determination unit 12 determines whether the conditions for handing over the mobile station from the currently connected base station to another base station are met (S12). If the determination unit 12 determines that the conditions for handing over the mobile station from the currently connected base station to another base station are met, the determination unit 12 determines whether the change in the received radio wave strength of the signal received by the mobile station from the currently connected base station is within a predetermined range (S13). If the determination unit 12 determines that the change in the received radio wave strength of the signal received by the mobile station from the currently connected base station is within the predetermined range, the determination unit 12 sets an offset period (S14). Next, the determination unit 12 executes handover of the mobile station to another base station after the offset period has elapsed (S15).

[0024] If the determination unit 12 determines in step S12 that the conditions for handing over the mobile station from the currently connected base station to another base station are not satisfied, the process of step S11 is repeated. If the determination unit 12 determines in step S13 that the change in the received radio wave intensity of the signal received at the mobile station from the currently connected base station is not within a predetermined range, the process of step S15 is executed.

[0025] As described above, even if the base station 10 determines that the conditions for executing a handover of the mobile station are satisfied, the base station 10 executes the handover after the offset period has elapsed. This makes it possible to prevent handovers from being frequently repeated at cell boundaries, and reduces the burden of handover processing on the mobile station and the base station.

[0026] In addition, if the change in the received radio wave intensity of the signal received by the mobile station from the base station 10 is not within a predetermined range, the communication quality between the mobile station and the base station 10 may not be maintained, and therefore the base station 10 may perform handover processing for the mobile station.

[0027] (Embodiment 2) Fig. 3 shows an example of the configuration of a mobile station 20. The mobile station 20 may be a computer device that operates when a processor executes a program stored in a memory. The mobile station 20 is assumed to be connected to a mobile base station installed in a vehicle. A base station installed in a predetermined location is called a fixed base station. The vehicle may be a car traveling on a road, a train, or the like. The mobile base station may also be a base station installed in an airplane or a ship, in addition to a vehicle.

[0028] The mobile station 20 has a measurement unit 21 and a communication unit 22. The measurement unit 21 and the communication unit 22 may be software or modules that are executed by a processor executing a program stored in a memory, or may be hardware such as a circuit or a chip.

[0029] The measurement unit 21 measures the received radio wave strength of signals received from the connected mobile base station and base stations in the vicinity of the mobile base station. The measurement unit 21 may store the measurement results in a memory or the like within the mobile station 20. "Storing" may also be interpreted as "storing," "recording," "memorizing," "managing," etc. Furthermore, the measurement unit 21 may identify the amount of change in the received radio wave strength using the measurement results at different measurement timings.

[0030] The communication unit 22 transmits a Measurement Report message to the mobile base station when the received radio wave intensity satisfies a predetermined condition for a predetermined period of time, which is longer than the period used as the timing for transmitting a Measurement Report message when the mobile station 20 is connected to a fixed base station.

[0031] 4 is a diagram showing the flow of communication processing executed in mobile station 20. First, measurement unit 21 measures the received radio wave strength of signals received from the connected mobile base station and base stations in the vicinity of the mobile base station (S21). Next, communication unit 22 transmits a Measurement Report message to the mobile base station if the received radio wave strength continues to satisfy a predetermined condition for a predetermined period of time (S22).

[0032] As described above, when the mobile station 20 is connected to a mobile base station, the timing of transmitting a Measurement Report message can be delayed compared to when the mobile station 20 is connected to a fixed base station. This allows the mobile base station that determines whether to perform a handover to delay the timing of performing a handover of the mobile station 20. This prevents the mobile station 20 from frequently repeating handovers at the cell boundary between the mobile base station and the fixed base station.

[0033] (Embodiment 3) Next, the flow of handover processing in a mobile network will be described. Fig. 5 shows the flow of handover processing in a communication system including a UE and an eNB. In Fig. 5, an example is described in which an eNB is used as a base station, but a gNB may be used instead of the eNB. Alternatively, the mobile network may include a mixture of eNBs and gNBs.

[0034] The eNB 40 is an eNB that forms a source cell of the UE 30, and the eNB 50 is an eNB that forms a destination cell of the UE 30. The source cell may be referred to as a pre-handover cell, and the destination cell may be referred to as a post-handover cell. The eNB 40 and the eNB 50 have the same configuration as the base station 10 in FIG. 1 .

[0035] First, UE 30 transmits a Measurement Report message to eNB 40. Assume that UE 30 is present in the cell formed by eNB 40. In other words, UE 30 is connected to the cell formed by eNB 40. Connecting to the cell formed by eNB 40 may be rephrased as connecting to eNB 40. Connecting to the cell formed by eNB 40 may also mean being in a state where communication with eNB 40 is possible. The cell to which UE 30 is connected may be referred to as a serving cell.

[0036] The UE 30 may periodically or periodically transmit a Measurement Report message to the eNB 40. Alternatively, the UE 30 may transmit the Measurement Report message to the eNB 40 when a predetermined event is triggered. The Measurement Report message may include, for example, a measurement result of received signal strength when an SS / PBCH (Synchronization Signals / Physical Broadcast channel) block related to synchronization information is received from the serving cell. Alternatively, the Measurement Report message may include a measurement result of received signal strength when an RS (Reference Signal), which is a reference signal, is received from the serving cell. Furthermore, the Measurement Report message may include a measurement result of received signal strength in cells surrounding the serving cell.

[0037] The predetermined event may be when the value of the received radio wave strength in the serving cell exceeds or matches a threshold. The value of the received radio wave strength exceeding the threshold indicates that the reception quality at the UE 30 is better than when the value of the received radio wave strength is below the threshold. The threshold may be predetermined.

[0038] Alternatively, the predetermined event may be the value of the received radio wave strength in the serving cell falling below a threshold or matching the threshold.

[0039] Alternatively, the predetermined event may be that the received radio wave strength in a cell surrounding the serving cell exceeds or matches the received radio wave strength in the serving cell. UE 30 receives signals not only from the serving cell but also from eNBs forming cells surrounding the serving cell. Therefore, UE 30 can measure the received radio wave strength in the cells surrounding the serving cell.

[0040] Alternatively, the predetermined event may be when the received signal strength in a cell surrounding the serving cell exceeds a value obtained by adding an offset value to the received signal strength in the serving cell.

[0041] Alternatively, the predetermined event may be when the received radio wave strength in a cell surrounding the serving cell exceeds or matches a threshold value.

[0042] Alternatively, the predetermined event may be when the received signal strength in the serving cell falls below threshold_1 and when the received signal strength in a cell surrounding the serving cell exceeds threshold_2. Threshold_1 may be greater than, less than, or the same as threshold_2.

[0043] Furthermore, a wireless communication method different from the wireless communication method applied to the serving cell may be applied to cells surrounding the serving cell. For example, the serving cell may use a wireless communication method called 4G, and the surrounding cells may use a wireless communication method called 5G. Alternatively, the surrounding cells may use a communication method different from the communication method defined in 3GPP, such as a wireless communication method called wireless LAN (Local Area Network).

[0044] Next, eNB40 determines to perform handover of UE30 based on the measurement result included in the Measurement Report message (S32). For example, eNB40 detects, in the measurement result included in the Measurement Report message periodically received, that the received radio wave strength in the cell formed by eNB50 is greater than the received radio wave strength in the cell formed by eNB40. In this case, eNB40 may determine to perform handover of UE30 from the cell formed by eNB40 to the cell formed by eNB50.

[0045] Alternatively, eNB 40 may receive a measurement result included in a Measurement Report message that is transmitted when UE 30 detects a predetermined event as a trigger. From the measurement result included in the Measurement Report message received in this manner, eNB 40 detects that the received radio wave strength in the cell formed by eNB 50 is greater than the received radio wave strength in the cell formed by eNB 40. In this case, eNB 40 may decide to perform a handover of UE 30 from the cell formed by eNB 40 to the cell formed by eNB 50.

[0046] Alternatively, the eNB 40 receives a Measurement Report message that is transmitted when the received radio wave strength in a cell surrounding the serving cell exceeds the received radio wave strength in the serving cell. Here, it is assumed that the cell surrounding the serving cell is formed by the eNB 50. When receiving such a Measurement Report message, the eNB 40 may decide to perform handover of the UE 30 from the cell formed by the eNB 40 to the cell formed by the eNB 50.

[0047] Alternatively, the eNB 40 receives a Measurement Report message that is triggered by the fact that the received radio wave strength in a cell surrounding the serving cell exceeds a value obtained by adding an offset value to the received radio wave strength in the serving cell. When receiving such a Measurement Report message, the eNB 40 may decide to perform handover of the UE 30 from the cell formed by the eNB 40 to the cell formed by the eNB 50.

[0048] Alternatively, the eNB 40 receives a Measurement Report message that is triggered by the fact that the received radio wave strength in the serving cell falls below threshold 1 and the received radio wave strength in a cell surrounding the serving cell exceeds threshold 2. When receiving such a Measurement Report message, the eNB 40 may decide to perform handover of the UE 30 from the cell formed by the eNB 40 to the cell formed by the eNB 50.

[0049] Next, after deciding to perform handover, the eNB 40 transmits a request signal requesting handover to the eNB 50 after or before the offset period has elapsed (S33). Next, the eNB 40 transmits an instruction signal instructing the eNB 50 to perform handover after or before the offset period has elapsed (S33). The instruction signal may include identification information indicating the cell to which handover is to be performed.

[0050] When the eNB 40 transmits an instruction signal to the UE 30, the UE 30 switches the cell to which it is connected to the cell formed by the eNB 50.

[0051] Here, a description will be given of the handover process in the eNB 40. Fig. 6 shows the flow of the handover process when the eNB 40 is a mobile base station.

[0052] First, the determination unit 12 determines to perform handover for the UE 30 (S41). Specifically, the determination unit 12 determines to perform handover of the UE 30 to a cell formed by the eNB 50 based on a Measurement Report message received from the UE 30. Performing handover may mean switching the cell.

[0053] Next, the determination unit 12 determines whether the amount of change in the received radio wave strength of the signal received by the UE 30 from the eNB 40 is within a predetermined range (S42). The received radio wave strength is, for example, RSRP, and is expressed using a numerical value in dBm units. The RSRP is expressed, for example, as -N dBm (N is a positive value), where the value of N increases as the received radio wave strength decreases.

[0054] The change in the received radio wave strength may be the difference between the received radio wave strength included in Measurement Report message M1 used when deciding to perform handover and Measurement Report message M2 received before Measurement Report message M1.

[0055] Measurement Report message M2 may be a message received at eNB 40 immediately before Measurement Report message M1, or may be a message received at eNB 40 a predetermined period before receiving Measurement Report message M1.

[0056] Alternatively, instead of the received signal strength included in Measurement Report message M2, the average of the received signal strengths included in multiple Measurement Report messages received at eNB 40 before Measurement Report message M1 may be used. That is, the amount of change in the received signal strength may be the difference between the received signal strength included in Measurement Report message M1 and the average of the received signal strengths included in the multiple Measurement Report messages. Instead of the average of the received signal strengths included in the multiple Measurement Report messages, the maximum, minimum, or median of the received signal strengths may be used, or other statistical values ​​may be used.

[0057] The fact that the amount of change in the received radio wave strength of a signal received by UE 30 from eNB 40 is within a predetermined range means that UE 30 can continue communication with eNB 40. Alternatively, the fact that the amount of change in the received radio wave strength of a signal received by UE 30 from eNB 40 is within a predetermined range means that UE 30 is maintaining communication quality that allows it to continue communication with eNB 40. Alternatively, the fact that the amount of change in the received radio wave strength of a signal received by UE 30 from eNB 40 is within a predetermined range means that UE 30 is maintaining communication quality that is equal to or higher than the minimum quality required to continue communication with eNB 40.

[0058] Next, when the determination unit 12 determines that the amount of change in the received radio wave strength of the signal received by the UE 30 from the eNB 40 is within a predetermined range, the determination unit 12 discards the Measurement Report message received within the set offset period (S43). The offset period may start, for example, from the time when the Measurement Report message M1 is received, or from the time when the decision to perform handover is made in step S41. Alternatively, the offset period may start from the time when the UE 30 determines that the amount of change in the received radio wave strength of the signal received by the UE 30 from the eNB 40 is within a predetermined range.

[0059] The offset period is a period used to delay the timing of actually executing handover after the eNB 40 decides to perform handover of the UE 30. Even during the offset period, the eNB 40 may periodically receive Measurement Report messages from the UE 30. Therefore, the eNB 40 discards the Measurement Report messages so as not to perform processing related to the Measurement Report messages received during the offset period.

[0060] Next, after the offset period has elapsed, the determination unit 12 transmits an instruction message to the UE 30 via the communication unit 11 to instruct the UE 30 to execute handover (S44).

[0061] In step S42, if the determination unit 12 determines that the amount of change in the received radio wave intensity of the signal received by the UE 30 from the eNB 40 is not within the predetermined range, the determination unit 12 executes the process of step S44.

[0062] Next, a description will be given of handover processing in the eNB 40 that differs from that in Fig. 6. Fig. 7 shows the flow of handover processing when the eNB 40 is a mobile base station.

[0063] Steps S51 and S52 are similar to steps S41 and S42 in FIG. 6, and therefore detailed description thereof will be omitted.

[0064] In step S53, the determination unit 12 discards the Measurement Report message a certain number of times. The period during which the Measurement Report message is received a certain number of times may correspond to the offset period.

[0065] Next, the determination unit 12 discards a certain number of Measurement Report messages, and then transmits an instruction message to the UE 30 via the communication unit 11 to instruct the UE 30 to execute a handover (S54).

[0066] Next, a description will be given of handover processing in the eNB 40 that differs from that in Figures 6 and 7. Figure 8 shows the flow of handover processing when the eNB 40 is a fixed base station.

[0067] Step S61 is the same as step S41 in FIG. 6 , and therefore a detailed description thereof will be omitted. Next, the determination unit 12 determines whether the eNB 50 that forms the destination cell of the UE 30 is a mobile base station (S62). If the determination unit 12 determines that the eNB 50 that forms the destination cell of the UE 30 is a mobile base station, it executes the processes of steps S63 to S65. The processes of steps S63 to S65 are the same as the processes of steps S42 to S44 in FIG. 6 , and therefore a detailed description thereof will be omitted. If the determination unit 12 determines in step S62 that the eNB 50 that forms the destination cell of the UE 30 is not a mobile base station, that is, is a fixed base station, it executes the process of step S65.

[0068] 8, when UE 30 performs handover from a fixed base station to a mobile base station, the processes from step S63 onward are executed. Therefore, when UE 30 performs handover from a fixed base station to a mobile base station, a process for delaying the timing of executing the handover is executed. In other words, when UE 30 performs handover from a fixed base station to a fixed base station, the process for delaying the timing of executing the handover does not need to be executed.

[0069] Next, a description will be given of handover processing in the eNB 40 that differs from that in Figures 6 to 8. Figure 9 shows the flow of handover processing when the eNB 40 is a fixed base station.

[0070] Steps S71 to S73 are the same as steps S61 to S63 in Fig. 8, and therefore detailed description thereof will be omitted. Also, steps S74 and S75 are the same as steps S53 and S54 in Fig. 7, and therefore detailed description thereof will be omitted.

[0071] As described above, when the eNB 40 operating as a mobile base station executes handover of the UE 30, it sets an offset period before actually executing the handover, depending on the received radio wave strength of the UE 30. This makes it possible to prevent the UE 30 from frequently repeating handover processing at cell boundaries.

[0072] Furthermore, when the eNB 40 operates as a fixed base station, when the UE 30 performs a handover to a mobile base station, an offset period is set depending on the received radio wave strength of the UE 30 before the handover is actually performed. In other words, when the UE 30 performs a handover from one fixed base station to another, the eNB 40 performs a normal handover process. Generally, a mobile base station is a base station that is assumed to be mobile. Therefore, the radio wave characteristics at the cell boundary between a cell formed by a mobile base station and a cell formed by a fixed base station are more likely to change than at the cell boundary between cells formed by two fixed base stations. In other words, when the UE 30 performs a handover to a cell formed by a mobile base station, the eNB 40 operating as a fixed base station sets an offset period depending on the received radio wave strength of the UE 30, thereby effectively avoiding the UE 30 from repeatedly performing handovers.

[0073] (Fourth Embodiment) Next, the operation of UE 60 connected to eNB 40, which is a mobile base station, will be described. Fig. 10 shows an example configuration of UE 60. UE 60 has a measurement unit 61, a determination unit 62, and a communication unit 63. Measurement unit 61, determination unit 62, and communication unit 63 may be software or modules whose processes are performed by a processor executing a program stored in a memory. Alternatively, measurement unit 61, determination unit 62, and communication unit 63 may be hardware such as a circuit or a chip.

[0074] The measurement unit 61 corresponds to the measurement unit 21 in the mobile station 20 in Fig. 3. The communication unit 63 corresponds to the communication unit 22 in the mobile station 20 in Fig. 3.

[0075] Here, the processing or operations of the measurement unit 61, the determination unit 62, and the communication unit 63 will be described with reference to Fig. 11. Fig. 11 shows the flow of the Measurement Report message transmission processing executed in the UE 60.

[0076] First, the measurement unit 61 measures the received radio wave intensity of signals received from the eNB 40 and the eNBs 50 present in the vicinity of the eNB 40 (S81).

[0077] Next, the determination unit 62 determines whether the eNB 40 is a mobile base station (S82). For example, the determination unit 62 may determine whether the eNB 40 is a mobile base station by using a cell ID that the eNB 40 periodically transmits within its cell.

[0078] For example, the range of cell ID values ​​used in the mobile base station and the range of cell ID values ​​used in the fixed base station may be separate. In this case, the determination unit 62 may store information indicating the range of cell ID values ​​used in the mobile base station and the range of cell ID values ​​used in the fixed base station in advance. The determination unit 62 may use the information stored in advance to determine whether the received cell ID falls within the range of cell ID values ​​used in the mobile base station or the range of cell ID values ​​used in the fixed base station.

[0079] Alternatively, the determination unit 62 may previously store a database in which cell IDs are associated with types of base stations. The type of base station may be, for example, information indicating a mobile base station or a fixed base station. Upon receiving a cell ID, the determination unit 62 may use the database to determine whether the received cell ID corresponds to a mobile base station or a fixed base station.

[0080] Alternatively, the eNB40 and the eNB50 may transmit information indicating the type of base station together with the cell ID. The determination unit 62 may determine whether the eNB40 and the eNB50 correspond to a mobile base station or a fixed base station based on the information indicating the type of base station.

[0081] Next, when the determining unit 62 determines that the eNB 40 is a mobile base station, the determining unit 62 determines whether or not a predetermined event has been detected (S83).

[0082] The predetermined event may be when the value of the received radio wave intensity of the signal received from the eNB 40 exceeds a threshold or matches a threshold.

[0083] Alternatively, the predetermined event may be the value of the received radio wave intensity of the signal received from the eNB 40 falling below a threshold or matching the threshold.

[0084] Alternatively, the predetermined event may be that the received radio wave strength of the signal received from eNB50 exceeds the received radio wave strength of the signal received from eNB40, or matches the received radio wave strength of the signal received from eNB40.

[0085] Alternatively, the predetermined event may be when the received radio wave strength of the signal received from eNB 50 exceeds a value obtained by adding an offset value to the received radio wave strength of the signal received from eNB 40 .

[0086] Alternatively, the predetermined event may be when the received radio wave strength of the signal received from the eNB 50 exceeds a threshold or matches a threshold.

[0087] Alternatively, the predetermined event may be when the received radio wave strength of the signal received from eNB 40 falls below threshold_1 and when the received radio wave strength of the signal received from eNB 50 exceeds threshold_2. Threshold_1 may be a value greater than, smaller than, or the same as threshold_2.

[0088] Next, when a predetermined event is detected, the determination unit 62 determines whether the duration of the detected event exceeds a predetermined period (S84). Here, the predetermined period is set to be longer than the predetermined period set when the UE 60 is connected to a fixed base station. In other words, the predetermined period set when the UE 60 is connected to a mobile base station is set to be longer than the predetermined period set when the UE 60 is connected to a fixed base station.

[0089] Next, if the determining unit 62 determines that the duration of the detected event exceeds the predetermined period, the communication unit 63 transmits a Measurement Report message to the eNB 40 (S85).

[0090] If the determination unit 62 determines in step S82 that the eNB 40 is not a mobile base station, the communication unit 63 transmits a Measurement Report message to the eNB 40 (S85). If the determination unit 62 determines in step S83 that a predetermined event has not been detected, the process from step S81 onward is repeated. If the determination unit 62 determines in step S84 that the duration of the detected event has not exceeded a predetermined period, the process from step S83 onward is repeated.

[0091] As described above, UE 60 does not transmit a Measurement Report message to eNB 40 when a predetermined event is detected as a trigger, but transmits a Measurement Report message to eNB 40 when the event continues for a predetermined period of time. This allows the eNB 40 to delay its decision on handover processing for UE 60.

[0092] For example, when a train equipped with a mobile base station stops at a station, many passengers may get off and on the train. In such a case, the mobile base station needs to perform a large number of handover processes. Here, when a UE 60 connected to the mobile base station moves to a cell formed by another mobile base station or a fixed base station, the UE 60 delays the timing of transmitting a Measurement Report message to the mobile base station. This makes it possible to avoid the concentration of handover processes at the mobile base station installed on the train.

[0093] Furthermore, by delaying the timing at which UE 60 transmits the Measurement Report message, it is possible to delay the decision on the handover process for UE 60 in eNB 40. As a result, it is possible to prevent UE 60 from frequently repeating the handover process at the cell boundary.

[0094] Furthermore, in FIG. 11, the predetermined period compared with the duration of the event that triggers the transmission of the Measurement Report message is adjusted, but the method of delaying the timing of transmitting the Measurement Report message is not limited to this.

[0095] For example, the threshold value used when the determination unit 62 determines whether a predetermined event has been detected may be different depending on whether the UE 60 is connected to a mobile base station or a fixed base station. In this case, the process of step S84 in FIG. 11 may be omitted.

[0096] Specifically, if the predetermined event is that the value of the received radio wave strength of the signal received from eNB 40 exceeds or matches a threshold, the threshold value may be set to a larger value when eNB 40 is a mobile base station than when eNB 40 is a fixed base station.

[0097] Alternatively, if the predetermined event is that the value of the received radio wave strength of the signal received from eNB 40 falls below or matches a threshold, the threshold value may be smaller when eNB 40 is a mobile base station than when eNB 40 is a fixed base station.

[0098] Alternatively, a case will be described in which the predetermined event is that the received radio wave strength of a signal received from eNB 50 exceeds a value obtained by adding an offset value to the received radio wave strength of a signal received from eNB 40. In this case, if eNB 40 is a mobile base station, the offset value may be larger than when eNB 40 is a fixed base station.

[0099] Alternatively, if the predetermined event is that the received radio wave strength of the signal received from eNB 50 exceeds or matches a threshold, the threshold value may be set to a larger value when eNB 40 is a mobile base station than when eNB 40 is a fixed base station.

[0100] Alternatively, a case will be described in which the predetermined event is that the received radio wave strength of a signal received from eNB 40 falls below threshold_1 and that the received radio wave strength of a signal received from eNB 50 exceeds threshold_2. In this case, when eNB 40 is a mobile base station, the value of threshold_1 may be made smaller or the value of threshold_2 may be made larger than when eNB 40 is a fixed base station. Alternatively, when eNB 40 is a mobile base station, the value of threshold_1 may be made smaller and the value of threshold_2 may be made larger than when eNB 40 is a fixed base station.

[0101] Regarding the predetermined period or threshold that uses different values ​​when UE 60 is connected to a mobile base station and when UE 60 is connected to a fixed base station, the predetermined period and threshold used in the mobile base station may be notified, for example, at the timing when UE 60 is connected to the mobile base station. Specifically, the predetermined period and threshold used in the mobile base station may be notified from the mobile base station to UE 60. Alternatively, the value used in the mobile base station and the value used in the fixed base station may be notified from the mobile base station or the fixed base station at the timing when UE 60 is started up.

[0102] FIG. 12 is a block diagram showing an example configuration of a base station 10. Referring to FIG. 12, the base station 10 includes an RF (Radio Frequency) transceiver 1001, a network interface 1003, a processor 1004, and a memory 1005. The RF transceiver 1001 performs analog RF signal processing for communication with UEs. The RF transceiver 1001 may include multiple transceivers. The RF transceiver 1001 is coupled to an antenna 1002 and a processor 1004. The RF transceiver 1001 receives modulation symbol data (or OFDM (Orthogonal Frequency Division Multiplexing) symbol data) from the processor 1004, generates a transmit RF signal, and provides the transmit RF signal to the antenna 1002. The RF transceiver 1001 also generates a baseband receive signal based on the receive RF signal received by the antenna 1002 and provides the baseband receive signal to the processor 1004.

[0103] The network interface 1003 is used to communicate with network nodes (e.g., other core network nodes) and may include, for example, a network interface card (NIC) compliant with the IEEE 802.3 series.

[0104] The processor 1004 performs data plane processing and control plane processing, including digital baseband signal processing for wireless communication.

[0105] The processor 1004 may include multiple processors. For example, the processor 1004 may include a modem processor (e.g., a Digital Signal Processor: DSP) that performs digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit: CPU or a Micro Processing Unit: MPU) that performs control plane processing.

[0106] The memory 1005 is configured by a combination of volatile memory and nonvolatile memory. The memory 1005 may include multiple physically independent memory devices. The volatile memory may be, for example, static random access memory (SRAM), dynamic RAM (DRAM), or a combination thereof. The nonvolatile memory may be mask read only memory (MROM), electrically erasable programmable ROM (EEPROM), flash memory, a hard disk drive, or any combination thereof. The memory 1005 may include storage located remotely from the processor 1004. In this case, the processor 1004 may access the memory 1005 via the network interface 1003 or an input / output (I / O) interface (not shown).

[0107] The memory 1005 may store software modules (computer programs) including instructions and data for performing processing by the base station 10. In some implementations, the processor 1004 may be configured to read and execute the software modules from the memory 1005 to perform processing by the base station 10.

[0108] FIG. 13 is a block diagram showing an example configuration of a mobile station 20 and a UE 60 (hereinafter referred to as the mobile station 20, etc.). A radio frequency (RF) transceiver 1101 performs analog RF signal processing to communicate with an eNB or a gNB. The analog RF signal processing performed by the RF transceiver 1101 includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver 1101 is coupled to an antenna 1102 and a baseband processor 1103. That is, the RF transceiver 1101 receives modulation symbol data (or OFDM symbol data) from the baseband processor 1103, generates a transmit RF signal, and supplies the transmit RF signal to the antenna 1102. The RF transceiver 1101 also generates a baseband receive signal based on the receive RF signal received by the antenna 1102 and supplies the baseband processor 1103.

[0109] The baseband processor 1103 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. Digital baseband signal processing includes (a) data compression / decompression, (b) data segmentation / concatenation, (c) transmission format (transmission frame) generation / decomposition, (d) transmission path coding / decoding, (e) modulation (symbol mapping) / demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using Inverse Fast Fourier Transform (IFFT). Meanwhile, control plane processing includes communication management for Layer 1, Layer 2, and Layer 3.

[0110] The baseband processor 1103 may include a modem processor (e.g., a Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit (CPU) or a Micro Processing Unit (MPU)) that performs control plane processing. In this case, the protocol stack processor that performs control plane processing may be shared with the application processor 1104, which will be described later.

[0111] The application processor 1104 is also referred to as a CPU, MPU, microprocessor, or processor core. The application processor 1104 may include multiple processors (multiple processor cores). The application processor 1104 executes a system software program (operating system (OS)) and various application programs (e.g., a call application, a web browser, a mailer, a camera operation application, and a music playback application) read from the memory 1106 or a memory not shown, thereby implementing various functions of the mobile station 20, etc.

[0112] In some implementations, the baseband processor 1103 and the application processor 1104 may be integrated on a single chip, as indicated by the dashed line (1105) in Figure 13. In other words, the baseband processor 1103 and the application processor 1104 may be implemented as a single System on Chip (SoC) device 1105. An SoC device may also be called a system Large Scale Integration (LSI) or chipset.

[0113] The memory 1106 is volatile memory, nonvolatile memory, or a combination thereof. The memory 1106 may include multiple physically independent memory devices. Volatile memory is, for example, static random access memory (SRAM), dynamic RAM (DRAM), or a combination thereof. Nonvolatile memory is, for example, mask read only memory (MROM), electrically erasable programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. For example, the memory 1106 may include an external memory device accessible from the baseband processor 1103, the application processor 1104, and the SoC 1105. The memory 1106 may also include an internal memory device integrated within the baseband processor 1103, the application processor 1104, or the SoC 1105. Furthermore, the memory 1106 may include memory within a Universal Integrated Circuit Card (UICC).

[0114] The memory 1106 may store software modules (computer programs) including instructions and data for performing processing by the mobile station 20, etc. In some implementations, the baseband processor 1103 or the application processor 1104 may be configured to read and execute the software modules from the memory 1106 to perform processing by the mobile station 20, etc.

[0115] In the above examples, the program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0116] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0117] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0118] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes. (Supplementary Note 1) A base station comprising: a communication unit that receives a Measurement Report message from a mobile station; and a determination unit that determines whether to execute a handover based on the Measurement Report message, wherein the determination unit sets an offset period after receiving the Measurement Report message when a first condition for the mobile station to execute a handover from the base station to another base station is satisfied and a change in received radio wave strength of a signal received at the mobile station from the base station is within a predetermined range, and executes a handover of the mobile station to the other base station after the offset period has elapsed. (Supplementary Note 2) The base station according to Supplementary Note 1, wherein the determination unit discards the Measurement Report message received during the offset period. (Supplementary Note 3) The base station according to Supplementary Note 1 or 2, wherein the determination unit determines the offset period based on the number of times the Measurement Report message is received. (Supplementary Note 4) The base station according to any one of Supplementary Notes 1 to 3, wherein the base station is a fixed base station installed at a predetermined position, and the determination unit, when a handover destination of the mobile station is a mobile base station installed in a vehicle, sets the offset period and executes handover of the mobile station to the mobile base station after the offset period has elapsed. (Supplementary Note 5) The base station according to Supplementary Note 4, wherein the determination unit, when identification information identifying a cell to which the mobile station is to be handover is a value within a range of identification information assigned to a cell formed by the mobile base station, determines that the handover destination of the mobile station is the mobile base station.(Supplementary Note 6) A mobile station connected to a mobile base station installed in a vehicle, comprising: a measurement unit that measures the received radio wave strength of signals received from the mobile base station currently connected and base stations surrounding the mobile base station, and a communication unit that transmits a Measurement Report message to the mobile base station when a state in which the received radio wave strength satisfies a predetermined condition continues for a predetermined period of time, the predetermined period being longer than a period adopted when the mobile station is connected to a fixed base station installed in a predetermined position. (Supplementary Note 7) A mobile station connected to a mobile base station installed in a vehicle, comprising: a measurement unit that measures the received radio wave strength of signals received from the mobile base station currently connected and base stations surrounding the mobile base station, and a communication unit that transmits a Measurement Report message to the mobile base station when a difference between a first received radio wave strength of signals received from the mobile station and a second received radio wave strength of signals received from the surrounding base stations exceeds a predetermined value, the predetermined value being greater than a value adopted when the mobile station is connected to a fixed base station installed in a predetermined position. (Supplementary Note 8) A communication method executed in a base station, comprising: receiving a Measurement Report message from a mobile station; determining whether to execute a handover based on the Measurement Report message; and, when determining whether to execute the handover, if the mobile station satisfies a first condition for handing over from the base station to another base station and an amount of change in received radio wave intensity of a signal received at the mobile station from the base station is within a predetermined range, setting an offset period after receiving the Measurement Report message; and, after the offset period has elapsed, executing handover of the mobile station to the other base station.(Supplementary Note 9) A communication method executed in a mobile station connected to a mobile base station installed in a vehicle, comprising: measuring the received radio wave strength of signals received from the mobile base station currently connected and base stations surrounding the mobile base station; and transmitting a Measurement Report message to the mobile base station when a state in which the received radio wave strength satisfies a predetermined condition continues for a predetermined period of time, the predetermined period being longer than a period adopted when the mobile station is connected to a fixed base station installed in a predetermined position. (Supplementary Note 10) A communication method executed in a mobile station connected to a mobile base station installed in a vehicle, comprising: measuring the received radio wave strength of signals received from the mobile base station currently connected and base stations surrounding the mobile base station; and transmitting a Measurement Report message to the mobile base station when a difference between a first received radio wave strength of signals received from the mobile station and a second received radio wave strength of signals received from the surrounding base stations exceeds a predetermined value, the predetermined value being greater than a value adopted when the mobile station is connected to a fixed base station installed in a predetermined position. (Supplementary Note 11) A program executed by a base station that is a computer, the program causing the computer to perform the following steps: receive a Measurement Report message from a mobile station; determine whether to execute a handover based on the Measurement Report message; and, when determining whether to execute the handover, if the mobile station satisfies a first condition for handing over from the base station to another base station and an amount of change in received radio wave strength of a signal received at the mobile station from the base station is within a predetermined range, set an offset period after receiving the Measurement Report message; and execute handover of the mobile station to the other base station after the offset period has elapsed.(Supplementary Note 12) A program to be executed by a mobile station, which is a computer connected to a mobile base station installed in a vehicle, comprising: measuring the received radio wave strength of signals received from the mobile base station currently connected and base stations in the vicinity of the mobile base station; and transmitting a Measurement Report message to the mobile base station when a state in which the received radio wave strength satisfies a predetermined condition continues for a predetermined period of time, the predetermined period being longer than a period adopted when the mobile station is connected to a fixed base station installed in a predetermined position. (Supplementary Note 13) A program to be executed by a mobile station, which is a computer connected to a mobile base station installed in a vehicle, comprising: measuring the received radio wave strength of signals received from the mobile base station currently connected and base stations in the vicinity of the mobile base station; and transmitting a Measurement Report message to the mobile base station when a difference between a first received radio wave strength of signals received from the mobile station and a second received radio wave strength of signals received from the surrounding base stations exceeds a predetermined value, the predetermined value being greater than a value adopted when the mobile station is connected to a fixed base station installed in a predetermined position.

[0119] Some or all of the elements (e.g., configurations and functions) described in Supplementary Notes 2 to 5 that are dependent on Supplementary Note 1 may also be dependent on Supplementary Notes 8 and 11 in the same dependency relationship as Supplementary Notes 2 to 5. Some or all of the elements described in any Supplementary Note may be applied to various hardware, software, recording means for recording software, systems, and methods.

[0120] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0121] This application claims priority based on Japanese Patent Application No. 2024-41392, filed March 15, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0122] 10 Base station 11 Communication unit 12 Determination unit 20 Mobile station 21 Measurement unit 22 Communication unit 30 UE 40 eNB 50 eNB 60 UE 61 Measurement unit 62 Determination unit 63 Communication unit 1001 Transceiver 1002 Antenna 1003 Network interface 1004 Processor 1005 Memory 1101 RF transceiver 1102 Antenna 1103 Baseband processor 1104 Application processor 1105 SoC 1106 Memory

Claims

1. A base station comprising: a communication means for receiving a Measurement Report message from a mobile station; and a judgment means for judging whether to execute a handover based on the Measurement Report message, wherein the judgment means sets an offset period after receiving the Measurement Report message when the mobile station satisfies a first condition for handing over from the base station to another base station and a change in the received radio wave strength of a signal received at the mobile station from the base station is within a predetermined range, and executes handover of the mobile station to the other base station after the offset period has elapsed.

2. The base station according to claim 1, wherein said determining means discards said Measurement Report message received during said offset period.

3. The base station according to claim 1 or 2, wherein the determining means determines the offset period based on the number of times the Measurement Report message is received.

4. A base station according to claim 1 or 2, wherein the base station is a fixed base station installed at a predetermined location, and the determination means, when the handover destination of the mobile station is a mobile base station installed in a vehicle, sets the offset period and executes handover of the mobile station to the mobile base station after the offset period has elapsed.

5. A base station according to claim 4, wherein the determination means determines that the mobile station is to be handed over to the mobile base station if identification information identifying the cell to which the mobile station is to be handed over is a value within the range of identification information assigned to cells formed by the mobile base station.

6. A mobile station connected to a mobile base station installed in a vehicle, comprising: a measuring means for measuring the received radio wave strength of signals received from the connected mobile base station and base stations surrounding the mobile base station; and a communication means for transmitting a Measurement Report message to the mobile base station when the received radio wave strength continues to satisfy a predetermined condition for a predetermined period of time, wherein the predetermined period is longer than the period adopted when the mobile station is connected to a fixed base station installed in a predetermined location.

7. A mobile station connected to a mobile base station installed in a vehicle, comprising: a measuring means for measuring the received radio wave strength of signals received from the connected mobile base station and from base stations surrounding the mobile base station; and a communication means for transmitting a Measurement Report message to the mobile base station when a difference between a first received radio wave strength of a signal received from the mobile station and a second received radio wave strength of a signal received from the surrounding base station exceeds a predetermined value, wherein the predetermined value is greater than the value adopted when the mobile station is connected to a fixed base station installed at a predetermined location.

8. A communication method executed in a base station, comprising: receiving a Measurement Report message from a mobile station; determining whether to execute a handover based on the Measurement Report message; and, when determining whether to execute the handover, if the mobile station satisfies a first condition for handing over from the base station to another base station and a change in the received radio wave strength of a signal received at the mobile station from the base station is within a predetermined range, setting an offset period after receiving the Measurement Report message; and, after the offset period has elapsed, executing a handover of the mobile station to the other base station.

9. A communication method executed in a mobile station connected to a mobile base station installed in a vehicle, the method measuring the received radio wave strength of signals received from the connected mobile base station and base stations surrounding the mobile base station, and transmitting a Measurement Report message to the mobile base station when the received radio wave strength continues to satisfy a predetermined condition for a predetermined period of time, the predetermined period being longer than the period used when the mobile station is connected to a fixed base station installed in a predetermined location.

10. A communication method executed in a mobile station connected to a mobile base station installed in a vehicle, comprising: measuring the received radio wave strength of signals received from the connected mobile base station and base stations surrounding the mobile base station; and transmitting a Measurement Report message to the mobile base station when a difference between a first received radio wave strength of a signal received from the mobile station and a second received radio wave strength of a signal received from the surrounding base station exceeds a predetermined value, wherein the predetermined value is greater than a value adopted when the mobile station is connected to a fixed base station installed at a predetermined location.

11. A program executed by a computer that is a base station, the program causing the computer to: receive a Measurement Report message from a mobile station; determine whether or not to execute a handover based on the Measurement Report message; and, when determining whether or not to execute the handover, if the mobile station satisfies a first condition for handing over from the base station to another base station and the amount of change in the received radio wave strength of a signal received at the mobile station from the base station is within a predetermined range, set an offset period after receiving the Measurement Report message; and execute handover of the mobile station to the other base station after the offset period has elapsed.

12. A program executed by a mobile station, which is a computer connected to a mobile base station installed in a vehicle, which measures the received radio wave strength of signals received from the connected mobile base station and base stations surrounding the mobile base station, and sends a Measurement Report message to the mobile base station when the received radio wave strength continues to satisfy a predetermined condition for a specified period of time, wherein the specified period is longer than the period used when the mobile station is connected to a fixed base station installed in a specified location.

13. A program executed by a mobile station, which is a computer connected to a mobile base station installed in a vehicle, comprising: measuring the received radio wave strength of signals received from the connected mobile base station and base stations surrounding the mobile base station; and transmitting a Measurement Report message to the mobile base station when the difference between a first received radio wave strength of signals received from the mobile station and a second received radio wave strength of signals received from the surrounding base stations exceeds a predetermined value; wherein the predetermined value is greater than the value adopted when the mobile station is connected to a fixed base station installed in a predetermined location.

Images