Communication control system

Abstract

The present invention pertains to a communication control system comprising three or more wireless base station devices and a communication control device for controlling switching of the communication connection between the wireless base station devices and a terminal device. The communication control device comprises: a detection unit that detects when a terminal device, which is communicably connected with a first wireless base station device and a second wireless base station device and which moves in a direction that separates from the first wireless base station device and approaches a third wireless base station device, has entered a prescribed range within an overlap region, which is a region in which communication with both the first wireless base station device and the third wireless base station device is possible; and a switching control unit that, if it is detected that the terminal device has entered the prescribed range, establishes a communication connection between the third wireless base station device and the terminal device, and thereafter performs a control for severing the communication connection between the first wireless base station device and the terminal device.

Description

Communication Control System

[0001] The present invention relates to a communication control system.

[0002] In mobile communications that use a cellular system, if the signal strength from a base station weakens due to a terminal moving to the cell boundary or for other reasons, communication becomes impossible. Therefore, when the signal strength decreases, a handover is performed to switch to a base station with stronger signal strength.

[0003] Conventionally, a technology for preventing temporary communication interruptions when a handover is performed includes, for example, MPTCP (Multipath TCP) (see, for example, Non-Patent Document 1). MPTCP allows a terminal to connect to one base station via at least two communication paths (hereinafter referred to as "links"). In MPTCP, handover is performed sequentially for each of the multiple links, so that even when one link is disconnected, the base station and the terminal can communicate via the other link that maintains communication connection. This makes it possible to prevent temporary communication interruptions.

[0004] Hayato Tsuchiya et al., "Verification of Wi-Fi Handover Using MPTCP," FIT2019 (18th Forum on Information Science and Technology), Vol. 4 CM-009, pp. 67-70, 2019

[0005] However, since the above-described conventional handover is triggered by a decrease in radio wave strength, the throughput temporarily decreases while the link is being switched. Therefore, the conventional technology has a problem in that it is not possible to ensure the reliability of communication while the link is being switched.

[0006] Furthermore, in the conventional handover described above, while the link is being switched, there is temporarily only one link between the base station and the terminal, so with the conventional technology, if the only link that is connected for communication while the link is being switched is cut off due to, for example, a failure, there is a problem that communication cannot be performed immediately.

[0007] In view of the above circumstances, an object of the present invention is to provide a technique that can prevent a decrease in throughput and the occurrence of communication disconnection when switching links.

[0008] One aspect of the present invention is a communication control system having three or more radio base station devices and a communication control device that controls switching of communication connections between the radio base station devices and a terminal device, wherein the communication control device is equipped with a detection unit that detects that the terminal device, which is communicatively connected to a first radio base station device and a second radio base station device, and is moving in a direction away from the first radio base station device and toward a third radio base station device, has entered a predetermined range within an overlapping area in which communication with both the first radio base station device and the third radio base station device is possible, and a switching control unit that, when it is detected that the terminal device has entered the predetermined range, establishes a communication connection between the third radio base station device and the terminal device, and then controls to disconnect the communication connection between the first radio base station device and the terminal device.

[0009] The present invention makes it possible to prevent a decrease in throughput and communication interruptions when switching links.

[0010] It is a diagram for explaining a link switching procedure assumed in the wireless communication system of the embodiment of the present invention. It is a diagram for explaining a procedure for specifying the position of the terminal MT by the wireless communication system 1 in the first embodiment of the present invention. It is a diagram for explaining a procedure for specifying the position of the terminal MT by the wireless communication system 1 in the first embodiment of the present invention. It is a diagram for explaining a procedure for setting a switching start range r by the wireless communication system 1 in the first embodiment of the present invention. It is a diagram for explaining a procedure for setting a switching start range r by the wireless communication system 1 in the first embodiment of the present invention. It is a diagram for explaining a procedure for setting a switching start range r by the wireless communication system 1 in the first embodiment of the present invention. It is a diagram for explaining a procedure for setting a switching start range r by the wireless communication system 1 in the first embodiment of the present invention. It is an overall configuration diagram of the wireless communication system 1 in the first embodiment of the present invention. It is a block diagram showing the functional configuration of the communication control device 10 in the first embodiment of the present invention. It is a flowchart showing the operation of the communication control device 10 in the first embodiment of the present invention. It is a diagram showing the constellation in each QAM scheme. It is a diagram for explaining a procedure for selecting a QAM scheme by the wireless communication system 1a in the second embodiment of the present invention. It is a diagram for explaining a procedure for selecting a QAM scheme by the wireless communication system 1a in the second embodiment of the present invention. It is a diagram for explaining a procedure for selecting a QAM scheme by the wireless communication system 1a in the second embodiment of the present invention. It is a diagram for explaining the addition of a link by the wireless communication system 1a in the second embodiment of the present invention. It is a diagram for explaining the addition of a link by the wireless communication system 1a in the second embodiment of the present invention. It is a block diagram showing the functional configuration of the communication control device 10a in the second embodiment of the present invention. It is a flowchart showing the operation of the communication control device 10a in the second embodiment of the present invention. It is a flowchart showing the operation of the communication control device 10a in the second embodiment of the present invention. It is a flowchart showing the operation of the communication control device 10a in the second embodiment of the present invention. It is a diagram for explaining link switching by the wireless communication system 1b in the third embodiment of the present invention.10a is a diagram for explaining link switching by the wireless communication system 1b in the third embodiment of the present invention. FIG. 10b is a diagram for explaining link switching by the wireless communication system 1b in the third embodiment of the present invention. FIG. 10c is a diagram for explaining link switching by the wireless communication system 1b in the third embodiment of the present invention. FIG. 10d is a diagram for explaining improvement in estimation accuracy of the terminal MT position by the wireless communication system 1b in the third embodiment of the present invention. FIG. 10b is a block diagram showing the functional configuration of a communication control device 10b in the third embodiment of the present invention. FIG. 10b is a flowchart showing the operation of the communication control device 10b in the third embodiment of the present invention. FIG. 10c is a diagram for explaining a procedure for specifying the position of a terminal MT by the wireless communication system 1c in the fourth embodiment of the present invention. FIG. 10c is a block diagram showing the functional configuration of a communication control device 10c in the fourth embodiment of the present invention. FIG. 10c is a flowchart showing the operation of the communication control device 10c in the fourth embodiment of the present invention.

[0011] Hereinafter, several embodiments of the communication control system of the present invention will be described in detail with reference to the drawings.

[0012] First Embodiment A wireless communication system 1 according to a first embodiment of the present invention will be described below. The wireless communication system 1 described below is an example of a communication control system according to the present invention.

[0013] [Link Switching Procedure as a Prerequisite] First, a link switching procedure as a prerequisite in the wireless communication system 1 of this embodiment will be described. Note that the link switching procedure described below is basically the same in each of the following embodiments.

[0014] 1 is a diagram illustrating a link switching procedure that is a prerequisite for a wireless communication system according to an embodiment of the present invention. (1) to (4) in FIG. 1 show the time-series changes in the communication connection state when the link is switched.

[0015] (1) to (4) in Figure 1 show base station BS1, base station BS2, base station BS3, and terminal MT, respectively. Base station BS1, base station BS2, and base station BS3 are wireless communication base station devices. Hereinafter, when it is not necessary to distinguish between the base stations, they will be simply referred to as "base station BS." Base station BS1, base station BS2, and base station BS3 are installed in locations separate from each other and form different cells (not shown). Here, it is assumed that at least a portion of each cell overlaps with the other cells.

[0016] The terminal MT is a mobile wireless terminal device (wireless mobile terminal). The arrows (1) to (4) in FIG. 1 indicate the direction of movement of the terminal MT. That is, (1) to (4) in FIG. 1 show the terminal MT moving from a position closer to base station BS1 (left side of the figure), passing a position closer to base station BS2, and moving toward a position closer to base station BS3 (right side of the figure). Note that, for simplicity of explanation, the terminal MT will be described as moving in a straight line.

[0017] As described above, in each embodiment described below, it is assumed that the wireless communication system has at least three or more base stations BS that communicate with one terminal MT. Furthermore, the wireless communication system also has a communication control device (not shown in FIG. 1 ) (described below). The communication control device is a server device that executes and controls link switching between the base station BS and the terminal MT. While in practice, the wireless communication system may communicate with multiple terminals MT, for simplicity, the following description will focus on link switching for one terminal MT.

[0018] (1) in Figure 1 shows a state in which terminal MT is located in a location that is closest to base station BS1 among the three base stations BS, and the next closest to base station BS2. At this time, terminal MT is connected to two base stations BS, base station BS1 and base station BS2. In Figure 1 (1) to (4), the solid line connecting the base station BS and terminal MT shows a state in which a link between the base station BS and terminal MT is established (a state in which communication is connected).

[0019] As terminal MT moves from the state shown in Figure 1(1) toward the right side of the figure, it reaches the state shown in Figure 1(2). Figure 1(2) shows a state in which terminal MT is located closest to base station BS2 among the three base stations BS, and next closest to base station BS1. In Figure 1(2), the range r enclosed by the dashed line frame represents the range (hereinafter referred to as the "switching start range") that satisfies the relay start condition (switching start condition) described below.

[0020] When it is detected that the moving terminal MT has entered the switching start range r, execution of link switching is initiated. That is, the fact that the terminal MT has entered the switching start range r triggers the start of execution of link switching. The switching start range r shown in (2) of FIG. 1 is the switching start range used as a trigger when switching one of the destinations of the link to which the terminal MT is connected from base station BS1 to base station BS3. Note that even while the link switching is being performed, the link between the terminal MT and base station BS2 remains established.

[0021] (3) in Fig. 1 shows the state in (2) in Fig. 1 where terminal MT has entered switching start range r and link switching from base station BS1 to base station BS3 has begun. In (3) in Fig. 1, the dashed line connecting base station BS3 and terminal MT indicates the state in which connection initiation processing for the link connecting the two is in progress (the state before a communication connection is established). In other words, (3) in Fig. 1 shows the state in which connection initiation processing for the link between base station BS3 and terminal MT is in progress.

[0022] The terminal MT continues to move during the link switching process. (4) in Fig. 1 shows the state after the link between the base station BS3 and the terminal MT is established. After the link between the base station BS3 and the terminal MT is established, the link between the base station BS1 and the terminal MT is disconnected. In this way, the link switching from the base station BS1 to the base station BS3 is performed.

[0023] By performing link switching according to the procedure described above, even during link switching, the terminal MT maintains a communication connection with base station BS2 and also maintains a communication connection with at least one of base stations BS1 and BS3. In other words, even during link switching, the terminal MT can always maintain a communication connection with two or more base stations BS. This makes it possible to prevent communication interruptions, for example, even when an unexpected communication failure occurs in one link.

[0024] In the link switching procedure described above, the decision to start link switching is made based on the location of the terminal MT. As such, the link switching procedure underlying the wireless communication system of the embodiment of the present invention, unlike conventional techniques in which link switching is initiated when a decrease in radio wave strength is detected, does not result in a state in which throughput is reduced even while link switching is being performed. As a result, the wireless communication system of the embodiment of the present invention can ensure communication reliability at all times, including during link switching.

[0025] [Procedure for Identifying Terminal Location] In the link switching procedure that is the premise of the above, it has been explained that the decision to start execution of link switching is made based on the location of the terminal MT (i.e., whether or not the terminal MT has entered the switching start range r). To achieve this, a configuration that can identify the location of the terminal MT is essential. Below, a procedure for the wireless communication system 1 of this embodiment to identify the location of the terminal MT will be described.

[0026] 2 and 3 are diagrams for explaining the procedure for identifying the location of the terminal MT by the wireless communication system 1 in the first embodiment of the present invention. Fig. 2 shows an example of the positional relationship of each device when the location of the terminal MT is not within the switching start range r. On the other hand, Fig. 3 shows an example of the positional relationship of each device when the location of the terminal MT is within the switching start range r.

[0027] In this embodiment, the procedure for identifying the location of the terminal MT uses AoA (Angle of Arrival) technology. AoA technology is an existing technology based on triangulation, and is a technology for identifying the location of a terminal that transmitted a signal based on the reception angles of the signal at multiple points. The AoA technology receives a signal transmitted from the terminal using multiple antennas and identifies the terminal's location by calculating the phase difference between the reception angles for each antenna.

[0028] It should be noted that by combining the terminal location estimation result obtained by the AoA technology with the measurement result of the received signal strength indicator (RSSI), it is possible to more accurately identify the location of the terminal MT. Note that in the present invention, the technology used to identify the location of the terminal MT is not limited to the AoA technology, and any other technology may be used to identify the location of the terminal MT.

[0029] In the wireless communication system 1 according to the present embodiment, a predetermined direction is set as a reference direction when identifying the location of the terminal MT. As an example, in Figures 2 and 3, the reference direction is set to a direction from bottom to top in the figure. In practice, the reference direction may be set to, for example, north.

[0030] As shown in FIG. 2, when the position of the terminal MT is not within the switching start range r, the angle formed between the reference direction and the direction of the terminal MT at the position of the base station BS1 is defined as θ′. １ 2, when the position of the terminal MT is not within the switching start range r, the angle formed between the reference direction and the direction of the terminal MT at the position of the base station BS2 is defined as θ'. ２ Let this θ' １ and θ' ２ Based on the values ​​of r and r, the wireless communication system 1 in this embodiment can identify the location of the terminal MT using AoA technology. Then, it is determined that the identified location of the terminal MT is not within a preset switching start range r. The procedure for setting the switching start range r in advance will be described later.

[0031] Similarly, as shown in FIG. 3, when the position of the terminal MT is within the switching start range r, the angle formed between the reference direction and the direction of the terminal MT at the position of the base station BS1 is θ １ 3, when the position of the terminal MT is within the switching start range r, the angle formed between the reference direction and the direction of the terminal MT at the position of the base station BS2 is θ ２ This θ １ and the value of θ ２ The location of the terminal MT can be identified based on the values ​​of r and r. The identified location of the terminal MT is then determined to be within a preset switching start range r. When it is determined that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0032] Recently, wireless communication systems have begun to utilize higher frequency bands. In wireless communication systems utilizing such higher frequency bands, base stations are generally equipped with directional antennas such as array antennas, and beamforming technology is used to appropriately select transmit and receive beams formed toward the communication partner terminal.

[0033] In the wireless communication system 1 of this embodiment, for example, the direction of the beam selected by this beam forming (beam angle) is determined based on the direction in which the terminal MT of the communication partner is located (the above-mentioned θ １ , θ ２ , θ' １ , θ' ２ As a result, the wireless communication system 1 does not require a new configuration for detecting the direction of the terminal MT, and can identify the position of the terminal MT using the AoA technology by utilizing the existing beamforming configuration.

[0034] [Procedure for Setting Switching Start Range] Hereinafter, a procedure for the wireless communication system 1 of this embodiment to set the switching start range r will be described.

[0035] 4 to 7 are diagrams illustrating the procedure for setting the switching start range r by the wireless communication system 1 according to the first embodiment of the present invention. Figures 4 to 7 show the time-series changes in the communication connection state when switching links.

[0036] 4 to 7 respectively show base station BS1, base station BS2, base station BS3, and terminal MT. Also, in Fig. 4 to 7, the boundary line indicating the range of the cell of base station BS1 is shown in the form of a two-dot chain arc centered at the position of base station BS1. Also, in Fig. 4 to 7, the boundary line indicating the range of the cell of base station BS3 is shown in the form of a one-dot chain arc centered at the position of base station BS3.

[0037] 4 to 7, an overlapping area d, which is an area where communication connection with both base station BS1 and base station BS3 is possible, is shown as a dashed oval. Strictly speaking, the area where communication connection with both base station BS1 and base station BS3 is possible is the area surrounded by the arc of a two-dot chain line indicating the boundary of the cell of base station BS1 and the arc of a one-dot chain line indicating the boundary of the cell of base station BS3. Therefore, the overlapping area d is not oval, but rather has a lens-like shape with pointed ends. However, for simplicity, the overlapping area d is shown as an oval here.

[0038] 4 to 7, the switching start range r is indicated by a solid oval. As shown in Fig. 4 to 7, the switching start range r is set at a position within the overlapping area d, closer to base station BS1. The reason why the switching start range r is set at such a position will be explained below.

[0039] 1 (1) to (4), Figures 4 to 7 show terminal MT moving from a position closer to base station BS1 (left side of the figure), passing a position closer to base station BS2, and moving toward a position closer to base station BS3 (right side of the figure). For ease of explanation, terminal MT will be described as moving in a straight line.

[0040] Figure 4 shows the state in which terminal MT has just entered the switching start range r from the left side of the figure. At this time, terminal MT is able to communicate with two base stations BS, base station BS1 and base station BS2. In Figures 4 to 7, the solid line connecting the base station BS and terminal MT indicates that a link between the base station BS and terminal MT has been established. Link switching begins when it is detected that the moving terminal MT has entered the switching start range r.

[0041] Figure 5 shows the state in Figure 4 where terminal MT enters within switching start range r, initiating link switching from base station BS1 to base station BS3. In Figure 5, the dashed line connecting base station BS3 and terminal MT indicates the state in which the link connection initiation process between base station BS3 and terminal MT is currently being executed (the state before the link is established). In other words, Figure 5 shows the state in which the link connection initiation process between base station BS3 and terminal MT is currently being executed. Note that, as can be seen by comparing Figures 4 and 5, terminal MT moves closer to base station BS3 (toward the right side of the figure) from the time terminal MT enters within switching start range r (Figure 4) until the execution of link switching begins (Figure 5).

[0042] 6 shows the state when a link between base station BS3 and terminal MT is established. At the time when the link between base station BS3 and terminal MT is established, the terminal MT is still located within overlapping area d, so the link between base station BS1 and terminal MT is also still established. That is, in FIG. 6, the terminal MT is able to communicate with all of base stations BS1, BS2, and BS3 (i.e., with three base stations BS).

[0043] After it is confirmed that the link between base station BS3 and terminal MT has been established, the link between base station BS1 and terminal MT is disconnected. Note that, as shown in Fig. 6, at the time when the link between base station BS3 and terminal MT is established, terminal MT may have already moved to a position outside the switching start range r.

[0044] 7 shows a state in which the link between base station BS1 and terminal MT is disconnected. As shown in FIG. 7, terminal MT soon moves to a position where it will soon leave overlap area d (the right edge of overlap area d).

[0045] The reason why the switching start range r is set to a position closer to base station BS1 within the overlapping area d is that in order to perform link switching in the order of establishing a link between base station BS3 and terminal MT and then severing the link between base station BS1 and terminal MT, the wireless communication system 1 needs to carry out the link switching from start to completion while the moving terminal MT is still within the overlapping area d.

[0046] By setting the switching start range r at a position closer to base station BS1 within the overlapping area d, link switching begins as soon as the terminal MT enters the overlapping area d. Furthermore, by setting the switching start range r at a position closer to base station BS1 within the overlapping area d, the terminal MT can remain within the overlapping area d for a longer period of time, even if the terminal MT is moving closer to base station BS3. This allows the wireless communication system 1 in this embodiment to prevent the terminal MT from falling into an unstable state in which only one link (with base station BS2) is established.

[0047] The switching start range r may be the same range as the overlapping area d. In this case, however, it is necessary to start and complete link switching immediately when the terminal MT enters the switching start range r. To achieve this, a mechanism for detecting the current location of the terminal MT more frequently (e.g., in real time) and a mechanism for transmitting control signals for controlling link switching without delay are required.

[0048] [Overall Configuration of Wireless Communication System] The following describes the overall configuration of the wireless communication system 1. Fig. 8 is a diagram showing the overall configuration of the wireless communication system 1 in the first embodiment of the present invention. As shown in Fig. 8, the wireless communication system 1 includes a communication control device 10 and base stations BS1 to BSn (n is an integer of 3 or more).

[0049] The communication control device 10 is a server device that controls multiple (three or more) base stations BS and controls link switching between each of the multiple base stations BS and the terminal MT. The communication control device 10 is configured to include an information processing device such as a general-purpose computer. The communication control device 10 and each of the multiple base stations BS are connected by a communication line that is either wired, wireless, or a combination thereof. In this embodiment, the communication control device 10 is an independently installed device, but this is not limited to this. For example, the communication control device 10 may be a device integrated with one of the multiple base stations BS.

[0050] The base station BS is a wireless communication base station device that serves as a wireless access point for multiple terminals MT (not shown in FIG. 8). The base station BS relays communications between a higher-level device (not shown in FIG. 8) and each of the multiple terminals MT. The base station BS and each of the multiple terminals MT are connected by a wireless communication line. In this embodiment, the base station BS communicates with the terminals MT using a directional antenna such as an array antenna. The base station BS and the higher-level device are connected by a wired, wireless, or combination of these communication lines.

[0051] [Configuration of communication control device] The following describes the configuration of the communication control device 10. Fig. 9 is a block diagram showing the functional configuration of the communication control device 10 in the first embodiment of the present invention. As shown in Fig. 9, the communication control device 10 includes a detection unit 11, a storage unit 12, and an execution control unit 13.

[0052] The detection unit 11 detects that a situation has arisen in which link switching should be performed. The detection unit 11 identifies the location of the terminal MT and determines whether or not link switching should be performed based on the identified location of the terminal MT and a predetermined switching start range r. As shown in Fig. 9, the detection unit 11 includes a beam selection information acquisition unit 111, a terminal position calculation unit 112, and a switching execution determination unit 113.

[0053] The beam selection information acquisition unit 111 collects beam selection information from each of the multiple base stations BS. The beam selection information here refers to information that identifies the beam selected for communication with the terminal MT in the beamforming performed by each of the multiple base stations BS. The beam selection information is information that can identify the direction of the terminal MT as seen from the base station BS. Because the terminal MT moves, the beam selection information acquisition unit 111 periodically collects beam selection information at predetermined intervals (for example, every 1 to 10 seconds). The beam selection information acquisition unit 111 outputs the collected beam selection information to the terminal position calculation unit 112.

[0054] The beam selection information may be information indicating the direction (bearing) of the beam selected for communication with the terminal MT in beamforming performed by each of the multiple base stations BS. In other words, the beam selection information may be information itself indicating the direction (bearing) of the terminal MT as seen from the base station BS, instead of information identifying the beam. The beam here may be a transmission beam, a reception beam, or both.

[0055] Although the present description focuses on one terminal MT for simplicity, in reality, a base station BS may be connected to multiple terminals MT for communication. In this case, the beam selection information acquisition unit 111 may collect beam selection information for each terminal MT from each of the multiple base stations BS.

[0056] The terminal position calculation unit 112 acquires beam selection information collected from each of the multiple base stations BS, output from the beam selection information acquisition unit 111. The terminal position calculation unit 112 also acquires reference direction information stored in advance in the storage unit 12. The reference direction information here is information indicating the above-mentioned reference direction. The reference direction is, for example, the north direction. Based on the acquired reference direction information and beam selection information, the terminal position calculation unit 112 calculates the angle formed between the reference direction and the direction of the terminal MT at the position of each of the multiple base stations BS (for example, the above-mentioned θ １ , θ ２ , θ' １ , θ' ２ Identify the angle of the object.

[0057] The terminal position calculation unit 112 calculates the position of the terminal MT using, for example, the above-mentioned AoA technology, based on the angle formed between the reference direction and the direction of the terminal MT at the positions of each of the multiple base stations BS identified above. The terminal position calculation unit 112 outputs position information indicating the calculated position of the terminal MT to the switching execution determination unit 113. Note that the position information indicating the position of the terminal MT may be coordinates in an arbitrary coordinate system, or may be position information expressed by latitude and longitude, etc.

[0058] The switching execution determination unit 113 acquires location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The switching execution determination unit 113 also acquires switching start range information previously stored in the storage unit 12. As described above, the switching start range information here is information indicating a range (switching start range r) that satisfies the relay start condition (switching start condition). The switching start range r may be a range expressed by coordinates in an arbitrary coordinate system, or may be a range expressed by latitude and longitude, etc.

[0059] The switching execution determination unit 113 determines whether the location of the terminal MT based on the acquired information is within the switching start range r. If the location of the terminal MT is within the switching start range r, the switching execution determination unit 113 determines to execute link switching. That is, the switching execution determination unit 113 determines to control each of the base stations BS to be controlled so as to establish a new link between the terminal MT and another base station BS and then disconnect one of the links established between the terminal MT and each of the multiple base stations BS.

[0060] As described above, the decision as to which base station BS to establish a new link with and which of the existing multiple links to disconnect is made based on the switching start range r that includes the position of the terminal MT. That is, the switching start range r is set in advance for each combination of two base stations BS as shown in Figures 4 to 7, and therefore can be uniquely identified.

[0061] For example, the switching start range r shown in Figures 4 to 7 is the switching start range set for the combination of base station BS1 and base station BS3. Therefore, when the switching execution determination unit 113 detects that the location of terminal MT is included in the switching start range r shown in Figures 4 to 7, it determines to establish a new link with base station BS3 for the target terminal MT and then to disconnect the link with base station BS1.

[0062] The switching execution determination unit 113 may estimate the moving direction of the terminal MT from the position of the terminal MT over time, and may determine whether to execute link switching by taking the estimated moving direction of the terminal MT into consideration. For example, in the situation illustrated in Figures 4 to 7, the switching execution determination unit 113 may determine to execute link switching when it estimates that the terminal MT is moving from a position closer to the base station BS1 to a position closer to the base station BS3 and detects that the terminal MT has entered the switching start range r.

[0063] If the location of the terminal MT is not included in the switching start range r, the switching execution decision unit 113 decides not to execute link switching.

[0064] When the switching execution decision unit 113 determines that link switching should be performed, it outputs to the execution control unit 13 information identifying the base station BS to which the link will be severed, information identifying the base station BS to which a new link will be established, and information identifying the terminal MT.

[0065] The storage unit 12 stores various data and programs. For example, the storage unit 12 pre-stores the reference direction information and switching start range information described above. The storage unit 12 may also store various programs for operating each functional unit of the communication control device 10.

[0066] As shown in FIG. 9, the execution control unit 13 includes a link connection instruction unit 131 , a connection completion report receiving unit 132 , and a link disconnection instruction unit 133 .

[0067] The link connection instruction unit 131 acquires information identifying the base station BS to disconnect the link and information identifying the terminal MT, which are output from the switching execution determination unit 113 of the detection unit 11. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly connected, instructing it to establish a link with the terminal MT.

[0068] For example, in the situation illustrated in Figures 4 to 7, the link connection instruction unit 131 transmits link connection instruction information to base station BS3 and establishes a new link between base station BS3 and terminal MT (corresponding to the situation in Figures 4 to 6).

[0069] The connection completion report receiving unit 132 receives a connection completion report from the base station BS to which the link is newly connected, the connection completion report indicating that a link with the terminal MT has been established. When the connection completion report receiving unit 132 receives the connection completion report, it notifies the link disconnection instruction unit 133.

[0070] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, the link disconnection instruction information instructing the base station BS that is to disconnect the link to the terminal MT.

[0071] For example, in the situation illustrated in Figures 4 to 7, the link disconnection instruction unit 133 transmits link disconnection instruction information to the base station BS1, and disconnects the link between the base station BS1 and the terminal MT (corresponding to the situation in Figure 7).

[0072] The detection unit 11 and the execution control unit 13 are configured to include a processor such as a CPU (Central Processing Unit). For example, the detection unit 11 and the execution control unit 13 realize the functions of the above-described functional units included in the detection unit 11 and the execution control unit 13 by reading and executing various programs stored in the storage unit 12.

[0073] The storage unit 12 is configured to include, for example, a semiconductor memory such as RAM (Random Access Memory) and EEPROM (Electrically Erasable Programmable Read-Only Memory), a flash memory such as SSD (Solid State Drive), a magnetic disk such as HDD (Hard Disk Drive), an optical disk, or other storage medium, or any combination of these storage media.

[0074] [Operation of communication control device] An example of the operation of the communication control device 10 will be described below. Fig. 10 is a flowchart showing the operation of the communication control device 10 in the first embodiment of the present invention. The operation of the communication control device 10 shown in the flowchart of Fig. 10 is periodically started at a predetermined interval (for example, every 1 to 10 seconds).

[0075] First, the beam selection information acquisition unit 111 collects beam selection information from each of the plurality of base stations BS (step S001). The beam selection information acquisition unit 111 outputs the collected beam selection information to the terminal position calculation unit 112.

[0076] Next, the terminal position calculation unit 112 acquires the beam selection information collected from each of the multiple base stations BS output from the beam selection information acquisition unit 111. The terminal position calculation unit 112 also acquires the reference direction information stored in advance in the storage unit 12 (step S002).

[0077] Next, the terminal position calculation unit 112 calculates the angle between the reference direction and the direction of the terminal MT at the position of each of the plurality of base stations BS (for example, the above-mentioned θ １ , θ ２ , θ' １ , θ' ２ The angle of the object is identified (step S003).

[0078] Next, the terminal position calculation unit 112 calculates the position of the terminal MT using, for example, the AoA technology described above, based on the angle formed between the reference direction and the direction of the terminal MT at the positions of each of the multiple base stations BS identified above (step S004). The terminal position calculation unit 112 outputs position information indicating the calculated position of the terminal MT to the switching execution determination unit 113.

[0079] Next, the switching execution determination unit 113 acquires the location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The switching execution determination unit 113 also acquires the switching start range information stored in advance in the storage unit 12 (step S005).

[0080] Next, the switching execution determination unit 113 determines whether the location of the terminal MT based on the acquired information is within the switching start range r (step S006). If the location of the terminal MT is not within the switching start range r (step S006: NO), the switching execution determination unit 113 determines not to execute link switching. This completes the operation of the communication control device 10 shown in the flowchart of FIG. 10.

[0081] On the other hand, if the position of the terminal MT is included in the switching start range r (step S006: YES), the switching execution determination unit 113 determines to execute link switching. When determining to execute link switching, the switching execution determination unit 113 outputs information identifying the base station BS to disconnect the link, information identifying the base station BS to newly establish a link, information identifying the terminal MT, etc. to the execution control unit 13.

[0082] The link connection instruction unit 131 acquires information identifying the base station BS to which a link is to be newly established and information identifying the terminal MT, which are output from the switching execution determination unit 113 of the detection unit 11. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly established, instructing it to establish a link with the terminal MT (step S007).

[0083] Next, the connection completion report receiving unit 132 waits for reception of a connection completion report from the base station BS to which the link is to be newly connected, indicating that a link with the terminal MT has been established (step S008). When the connection completion report receiving unit 132 receives the connection completion report (step S008, YES), it notifies the link disconnection instructing unit 133 to that effect.

[0084] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, instructing the base station BS that is to disconnect the link to the terminal MT (step S009). This completes the operation of the communication control device 10 shown in the flowchart of FIG. 10.

[0085] As described above, the wireless communication system 1 according to the first embodiment of the present invention includes at least three base stations BS and a communication control device 10 that executes and controls link switching between each of these base stations BS and a terminal MT. The communication control device 10 identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1 illustrated in FIGS. 4 to 7) and a second base station (e.g., base station BS2 illustrated in FIGS. 4 to 7) and is moving away from the first base station and approaching a third base station (e.g., base station BS3 illustrated in FIGS. 4 to 7) based on the direction of the terminal MT as seen from the first base station and the direction of the terminal MT as seen from the second base station.

[0086] When the communication control device 10 detects that the moving terminal MT has entered a switching start range r that is predetermined based on the connectable range with the first base station and the connectable range with the third base station, the communication control device 10 starts control of link switching execution. First, the communication control device 10 establishes a new link between the terminal MT and the third base station, which are approaching each other. Then, after the link between the third base station and the terminal MT is established, the communication control device 10 disconnects the existing link between the terminal MT and the first base station, which are moving away from each other.

[0087] With this configuration, the wireless communication system 1 according to the first embodiment of the present invention can always maintain a state in which a link is established between the terminal MT and at least two base stations BS (the second base station and at least one of the first base station and the third base station) even when link switching is being performed. That is, the wireless communication system 1 according to the first embodiment of the present invention can always maintain a state in which one terminal can communicate with the base station BS via multiple links, including when link switching is being performed. As a result, the wireless communication system 1 can suppress communication disconnections, for example, even when an unexpected communication failure occurs, including when link switching is being performed.

[0088] Furthermore, the wireless communication system 1 according to the first embodiment of the present invention determines whether to start link switching based on the location of the terminal MT. Therefore, unlike conventional wireless communication systems that start link switching when a decrease in radio wave strength is detected, the wireless communication system 1 according to the first embodiment does not experience a decrease in throughput even when link switching is being performed. This allows the wireless communication system 1 according to the first embodiment to ensure communication reliability at all times, including when link switching is being performed.

[0089] Second Embodiment A wireless communication system 1a according to a second embodiment of the present invention will be described below. The wireless communication system 1a described below is an example of a communication control system according to the present invention.

[0090] Generally, efficient modulation methods for wireless communication vary depending on the distance between communication devices. For example, quadrature amplitude modulation (QAM) is one of the highly efficient digital modulation methods widely used in digital wireless communication such as mobile phones, smartphones, wireless local area networks (LANs), and terrestrial digital broadcasting. There are multiple types of QAM methods, including 16QAM, 64QAM, and 256QAM.

[0091] Among these QAM systems, the larger the number, the larger the communication capacity, and therefore the larger the amount of information that can be transmitted in a given period of time. That is, among the 16QAM system, 64QAM system, and 256QAM system, the 256QAM system can transmit the largest amount of information in a given period of time. On the other hand, the larger the number, the shorter the distance between signal points, and therefore, when the average power is the same, symbol errors are more likely to occur due to noise and signal distortion in the transmission path. That is, among the 16QAM system, 64QAM system, and 256QAM system, when the average power is the same, the 256QAM system is most likely to cause symbol errors.

[0092] Figure 11 shows constellations for each QAM system. Figure 11(A) shows a constellation for the 256QAM system, Figure 11(B) shows a constellation for the 64QAM system, and Figure 11(C) shows a constellation for the 16QAM system. As shown in Figure 11, the larger the number of the QAM system, the shorter the distance between signal points.

[0093] As in the first embodiment, in the second embodiment, the terminal MT is a mobile wireless terminal device. Therefore, the distance between the terminal MT and each of the multiple base stations BS changes over time. Therefore, the wireless communication system 1a in the second embodiment described below, in addition to the configuration of the wireless communication system 1 in the first embodiment, further includes a configuration for selecting an appropriate QAM scheme depending on the distance between the base station BS and the terminal MT. The procedure for selecting an appropriate QAM scheme will be described below using a specific example.

[0094] 12 to 14 are diagrams illustrating the procedure for selecting a QAM scheme by the wireless communication system 1a according to the second embodiment of the present invention. Here, for example, it is assumed that the relative positions of the base station BS1, the base station BS2, and the terminal MT are as shown in FIG.

[0095] 12, terminal MT is shown moving from a position closer to base station BS1 (left side of the figure), passing through a position closer to base station BS2 (right side of the figure), and moving toward a position closer to base station BS3 (not shown) (right side outside the figure). For ease of explanation, terminal MT will be described as moving in a straight line.

[0096] (a), (b), and (c) in Figure 12 each show the position of the terminal MT at a certain point in time. Because the terminal MT moves from left to right in the figure, the order in chronological order is (a) → (b) → (c). As shown in Figure 12, among (a), (b), and (c), the distance between the terminal MT and the base station BS1 is shortest when the terminal MT is at the position (a) in Figure 12. Thereafter, as the terminal MT moves sequentially to the positions (b) and (c) in Figure 12, the distance between the terminal MT and the base station BS1 gradually increases.

[0097] Conversely, as shown in Figure 12, among (a), (b), and (c), the distance between terminal MT and base station BS3 is longest when terminal MT is in position (a) of Figure 12. Thereafter, as terminal MT moves sequentially to positions (b) and (c) of Figure 12, the distance between terminal MT and base station BS3 gradually becomes shorter.

[0098] As mentioned above, the 256QAM system has the advantage of being able to transmit a relatively large amount of information in a given period of time, but the disadvantage of being prone to symbol errors. On the other hand, the 16QAM system has the advantage of being less prone to symbol errors, but the advantage of being able to transmit a relatively small amount of information in a given period of time. In addition, the 64QAM system has characteristics intermediate between those of the 256QAM system and the 16QAM system.

[0099] From the above, since terminal MT is a wireless terminal device that is moving away from base station BS1, it is considered effective to switch the modulation method used in the link between terminal MT and base station BS1 as it moves, for example, from 256QAM to 64QAM to 16QAM. On the other hand, conversely, since terminal MT is a wireless terminal device that is approaching base station BS3, it is considered effective to switch the modulation method used in the link between terminal MT and base station BS2 as it moves, for example, from 16QAM to 64QAM to 256QAM.

[0100] Fig. 13 shows the modulation schemes selected at each of the positions of the terminal MT in (a), (b), and (c) of Fig. 12. In Fig. 13, the lengths of the solid and dashed horizontal lines represent the distance between the terminal MT and the base station BS (base station BS1 or base station BS2).

[0101] As shown in Figure 13, it can be seen that the modulation scheme used in the link between the terminal MT and base station BS1 is switched from 256QAM to 64QAM as the terminal MT moves from position (a) to position (b) in Figure 12. Also, as shown in Figure 13, it can be seen that the modulation scheme used in the link between the terminal MT and base station BS2 is switched from 16QAM to 64QAM as the terminal MT moves from position (b) to position (c) in Figure 12.

[0102] Fig. 14 shows criteria for switching modulation methods. The upper part of Fig. 14 is the same as Fig. 12 and shows an example of the relative positions of base station BS1, base station BS2, and terminal MT. The lower part of Fig. 14 shows the transition of the radio wave reception level for each position of terminal MT, which corresponds to the relative positions of the devices shown in the upper part.

[0103] In Fig. 14, the solid line R1 indicates the transition of the reception level at the terminal MT of radio waves transmitted from base station BS1. Therefore, as shown in Fig. 14, the reception level is highest at position P1, where terminal MT is closest to base station BS1. Also, in Fig. 14, the dashed line R2 indicates the transition of the reception level at the terminal MT of radio waves transmitted from base station BS2. Therefore, as shown in Fig. 14, the reception level is highest at position P2, where terminal MT is closest to base station BS2.

[0104] The criteria for determining whether to switch between modulation schemes are set in advance based on the reception level. As shown in Fig. 14, for example, the reception level that serves as the criterion for switching between the 16QAM scheme and the 64QAM scheme is L1 [dB]. Also, as shown in Fig. 14, for example, the reception level that serves as the criterion for switching between the 64QAM scheme and the 256QAM scheme is L2 [dB].

[0105] Therefore, first, when terminal MT moves to position P11, the reception level of radio waves from base station BS1 at terminal MT decreases from L2 [dB] or more to less than L2 [dB], so the modulation method is switched from 256QAM to 64QAM. Next, when terminal MT moves to position P12, the reception level of radio waves from base station BS2 at terminal MT increases from less than L1 [dB] to L1 [dB] or more, so the modulation method is switched from 16QAM to 64QAM.

[0106] Next, when terminal MT moves to position P13, the reception level of radio waves from base station BS1 at terminal MT decreases from L1 [dB] or more to less than L1 [dB], so the modulation method is switched from 64QAM to 16QAM. Next, when terminal MT moves to position P14, the reception level of radio waves from base station BS2 at terminal MT increases from less than L2 [dB] to L2 [dB] or more, so the modulation method is switched from 64QAM to 256QAM.

[0107] For simplicity of explanation, it is assumed here that the modulation method to be used is determined only by the distance between the terminal MT and the base station BS. However, in reality, the modulation method to be used also depends on, for example, the presence or absence of an obstruction between the terminal MT and the base station BS.

[0108] For example, if there are no obstructions between the terminal MT and the base station BS and the distance between the terminal MT and the base station BS is relatively short, resulting in a sufficiently high reception level at the terminal MT, then a high-order modulation scheme such as 256QAM can be used. Conversely, if the Fresnel zone formed between the terminal MT and the base station BS is partially obstructed or the distance between the terminal MT and the base station BS is relatively long, resulting in an insufficient reception level at the terminal MT, then only a low-order modulation scheme such as 16QAM can be used.

[0109] The communication speed (bps: bits per second) at each of the positions of the terminal MT in (a), (b), and (c) of Figure 12 can be estimated based on the symbol rate (sps: symbols per second) and the modulation method.

[0110] For example, the communication speed of the link shown in (a) of Figure 13, in which communication is carried out using the 256QAM method between terminal MT and base station BS1, and the link in which communication is carried out using the 16QAM method between terminal MT and base station BS2, can be calculated using the following equation (1).

[0111] bps=sps×(Log ２ 256+Log ２ 16) = sps × (8 + 4) = sps × 12 ... (1)

[0112] Furthermore, for example, the communication speed of the link shown in (b) of Figure 13, in which communication is carried out using the 64QAM method between terminal MT and base station BS1, and the link in which communication is carried out using the 16QAM method between terminal MT and base station BS2, can be calculated using the following equation (2).

[0113] bps=sps×(Log ２ 64+Log ２ 16) = sps × (6 + 4) = sps × 10 ... (2)

[0114] Furthermore, for example, the communication speed of the link shown in (c) of Figure 13, in which communication is carried out using the 64QAM method between terminal MT and base station BS1, and the link shown in (c) of Figure 13, in which communication is carried out using the 64QAM method between terminal MT and base station BS2, can be calculated using the following equation (3).

[0115] bps=sps×(Log ２ 64+Log ２ 64) = sps × (6 + 6) = sps × 12 ... (3)

[0116] In this way, in the case of the relative positions of base station BS1, base station BS2, and terminal MT illustrated in Figures 12 to 14, it can be seen that the communication speed (= sps x 10 < sps x 12) temporarily drops when terminal MT is in position (b) of Figure 12 compared to when terminal MT is in positions (a) and (c) of Figure 12. Therefore, in positions where the communication speed temporarily drops, it is desirable to take measures to increase the communication speed.

[0117] In contrast to this, the wireless communication system 1a according to the second embodiment further includes a configuration for increasing the communication speed at such a location where the communication speed temporarily drops.

[0118] Specifically, the wireless communication system 1a in the second embodiment determines whether the communication speed (bps) estimated based on the symbol rate (sps) and the modulation method, for example, as in the above equations (1) to (3), is less than a predetermined communication speed (less than a threshold value). If the estimated communication speed (bps) is less than the threshold value, the wireless communication system 1a adds another link that uses a modulation method that obtains the maximum communication capacity among the multiple links established between the terminal MT and multiple base stations BS.

[0119] As mentioned above, the modulation scheme that obtains a larger communication capacity is the modulation scheme used for the link with the shorter distance between the terminal MT and the plurality of base stations BS, so that the wireless communication system 1a ends up adding the link with the shortest distance among the plurality of links established between the terminal MT and the plurality of base stations BS.

[0120] 15 and 16 are diagrams illustrating the addition of a link by the wireless communication system 1a according to the second embodiment of the present invention. As described above, in the case of the relative positions of base station BS1, base station BS2, and terminal MT illustrated in FIGS. 12 to 14, when terminal MT is at the position shown in FIG. 12(b), the communication speed temporarily decreases compared to when terminal MT is at the positions shown in FIG. 12(a) and (c). Here, it is assumed that the expected communication speed when terminal MT is at the position shown in FIG. 12(b) is less than a predetermined communication speed (less than a threshold).

[0121] In such a case, the wireless communication system 1a further adds a link using the modulation scheme that provides the maximum communication capacity among the links established between the terminal MT and the plurality of base stations BS (base station BS1 and base station BS2). That is, when the terminal MT is located at the position shown in FIG. 12(b), the link between the terminal MT and base station BS1 is established using the 64QAM scheme, and the link between the terminal MT and base station BS2 is established using the 16QAM scheme. Therefore, the wireless communication system 1a further adds a link (the link between the terminal MT and base station BS1) using the 64QAM scheme, which is a modulation scheme with a larger communication capacity.

[0122] As shown in Figure 15, an additional link has been added between terminal MT and base station BS1, resulting in two links. Figure 16 shows the modulation schemes selected at each of the terminal MT positions shown in (a), (b), and (c) in Figure 12. As in Figure 13, the lengths of the solid and dashed horizontal lines in Figure 16 also represent the distance between terminal MT and base station BS (base station BS1 or base station BS2).

[0123] As shown in Figure 16, when the terminal MT is located at (b) in Figure 12, a shorter link (the link using the 64QAM method between the terminal MT and the base station BS1) is added, making two links. By adding this link, the communication capacity of the link between the terminal MT and the base station BS1 is doubled when the terminal MT is located at (b) in Figure 12.

[0124] When a link is added, the communication speed (bps) at the position of the terminal MT in Figure 12(b) can be calculated using the following formula (4): Note that the communication speed (bps) at each of the positions of the terminal MT in Figures 12(a) and 12(b) can be calculated using the above formulas (1) and (2).

[0125] bps=sps×(2×Log ２ 64+Log ２ 16) = sps × (2 × 6 + 4) = sps × 16 ... (4)

[0126] In this way, the communication speed (bps) at the location of terminal MT in Figure 12(b) when a link is added becomes sps x 16, which is a faster value than the communication speed (bps) at the location of terminal MT in Figure 12(b) when a link is not added, which is sps x 10. Also, the communication speed (bps) at the location of terminal MT in Figure 12(b) when a link is added becomes sps x 16, which is a value that exceeds the communication speed (bps) at the location of terminal MT in Figures 12(a) and 12(c), which is sps x 12.

[0127] In this way, the wireless communication system 1a in the second embodiment can increase the communication speed by adding links at locations where the communication speed temporarily drops, thereby preventing the communication speed from falling below a predetermined threshold.

[0128] [Overall configuration of wireless communication system] The overall configuration of the wireless communication system 1a in the second embodiment is basically the same as the overall configuration of the wireless communication system 1 in the first embodiment described above with reference to the overall configuration diagram of Figure 8, so a description thereof will be omitted.

[0129] The configuration of the wireless communication system 1a in the second embodiment is different from the configuration of the wireless communication system 1 in the first embodiment in the configuration of the communication control device. Hereinafter, the communication control device of the wireless communication system 1a in the second embodiment will be referred to as a "communication control device 10a."

[0130] [Configuration of communication control device] The configuration of the communication control device 10a will be described below. Fig. 17 is a block diagram showing the functional configuration of the communication control device 10a in the second embodiment of the present invention. As shown in Fig. 17, the communication control device 10 includes a detection unit 11, a storage unit 12a, an execution control unit 13, a modulation method switching control unit 14, and a link addition control unit 15.

[0131] The detection unit 11 detects that a situation has arisen in which link switching should be performed. The detection unit 11 identifies the location of the terminal MT and determines whether or not link switching should be performed based on the identified location of the terminal MT and a predetermined switching start range. As shown in Fig. 17 , the detection unit 11 includes a beam selection information acquisition unit 111, a terminal position calculation unit 112, and a switching execution determination unit 113.

[0132] The beam selection information acquisition unit 111 collects beam selection information from each of the multiple base stations BS. As described above, the beam selection information is information that identifies the beam selected for communication with the terminal MT in the beamforming performed by each of the multiple base stations BS. Because the terminal MT moves, the beam selection information acquisition unit 111 periodically collects the beam selection information at predetermined intervals (for example, every 1 to 10 seconds). The beam selection information acquisition unit 111 outputs the collected beam selection information to the terminal position calculation unit 112.

[0133] The beam selection information may be information indicating the direction (orientation) of the beam selected for communication with the terminal MT in beamforming performed by each of the base stations BS. The beam here may be a transmission beam, a reception beam, or both.

[0134] Although the present description focuses on one terminal MT for simplicity, in reality, the base station BS may be connected to multiple terminals MT for communication. In this case, the beam selection information acquisition unit 111 collects beam selection information for each terminal MT from each of the multiple base stations BS.

[0135] The terminal position calculation unit 112 acquires beam selection information collected from each of the multiple base stations BS, output from the beam selection information acquisition unit 111. The terminal position calculation unit 112 also acquires reference direction information stored in advance in the storage unit 12. As described above, the reference direction information is information indicating a reference direction. The reference direction is, for example, the north direction. Based on the acquired reference direction information and beam selection information, the terminal position calculation unit 112 calculates the angle formed between the reference direction and the direction of the terminal MT at the position of each of the multiple base stations BS (for example, the above-mentioned θ １ , θ ２ , θ' １ , θ' ２ Identify the angle of the object.

[0136] The terminal position calculation unit 112 calculates the position of the terminal MT using, for example, the above-mentioned AoA technology, based on the angle formed between the reference direction and the direction of the terminal MT at the position of each of the identified multiple base stations BS. The terminal position calculation unit 112 outputs position information indicating the calculated position of the terminal MT to the switching execution determination unit 113 and an inter-device distance calculation unit 141 of the modulation method switching control unit 14, which will be described later. Note that the position information indicating the position of the terminal MT may be coordinates in an arbitrary coordinate system, or may be position information expressed by latitude and longitude, etc.

[0137] The switching execution determination unit 113 acquires location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The switching execution determination unit 113 also acquires switching start range information previously stored in the storage unit 12. As described above, the switching start range information is information indicating a range (switching start range r) that satisfies the relay start condition (switching start condition). The switching start range r may be a range expressed by coordinates in an arbitrary coordinate system, or may be a range expressed by latitude and longitude, etc.

[0138] The switching execution determination unit 113 determines whether the location of the terminal MT based on the acquired information is within the switching start range r. If the location of the terminal MT is within the switching start range r, the switching execution determination unit 113 determines to execute link switching. That is, the switching execution determination unit 113 determines to establish a new link between this terminal MT and another base station BS, and then to control each of the target base stations BS to disconnect one of the links established between this terminal MT and each of the multiple base stations BS.

[0139] As described above, which base station BS to establish a new link with and which base station BS among the existing links to disconnect can be uniquely identified based on the switching start range r that includes the position of the terminal MT. That is, the switching start range r is set in advance for each combination of two base stations BS as shown in Figures 4 to 7, and therefore can be uniquely identified.

[0140] The switching execution determination unit 113 may determine whether to execute link switching by identifying the direction of movement of the terminal MT from the position of the terminal MT over time, and taking the direction of movement of the terminal MT into consideration. For example, in the situation illustrated in Figures 4 to 7, the switching execution determination unit 113 may determine to execute link switching when it detects that the terminal MT is moving from a position closer to the base station BS1 to a position closer to the base station BS3 and that the terminal MT has entered the switching start range r.

[0141] For example, the switching start range r shown in Figures 4 to 7 is a switching start range that is set to disconnect the link with base station BS1 and establish a new link with base station BS3. Therefore, when the switching execution determination unit 113 detects that the location of the terminal MT is included in the switching start range r shown in Figures 4 to 7, it determines to establish a new link with base station BS3 for the target terminal MT and to disconnect the link with base station BS1.

[0142] If the location of the terminal MT is not included in the switching start range r, the switching execution decision unit 113 decides not to execute link switching.

[0143] When the switching execution decision unit 113 determines that link switching should be performed, it outputs to the execution control unit 13 information identifying the base station BS to which the link will be severed, information identifying the base station BS to which a new link will be established, and information identifying the terminal MT.

[0144] The storage unit 12a stores various data and programs. For example, the storage unit 12a pre-stores the reference direction information and switching start range information described above. The storage unit 12a also pre-stores base station position information, reception level attenuation information, a modulation method switching threshold, and a link addition threshold, which will be described later. The storage unit 12a may also store various programs for operating each functional unit of the communication control device 10a.

[0145] As shown in FIG. 17, the execution control unit 13 includes a link connection instruction unit 131 , a connection completion report receiving unit 132 , and a link disconnection instruction unit 133 .

[0146] The link connection instruction unit 131 acquires information identifying the base station BS to disconnect the link and information identifying the terminal MT, which are output from the switching execution determination unit 113 of the detection unit 11. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly connected, instructing it to establish a link with the terminal MT.

[0147] For example, in the situation illustrated in Figures 4 to 7, the link connection instruction unit 131 transmits link connection instruction information to base station BS3 and establishes a new link between base station BS3 and terminal MT (corresponding to the situation in Figures 4 to 6).

[0148] The connection completion report receiving unit 132 receives a connection completion report from the base station BS to which the link is newly connected, the connection completion report indicating that a link with the terminal MT has been established. When the connection completion report receiving unit 132 receives the connection completion report, it notifies the link disconnection instruction unit 133.

[0149] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, the link disconnection instruction information instructing the base station BS that is to disconnect the link to the terminal MT.

[0150] For example, in the situation illustrated in Figures 4 to 7, the link disconnection instruction unit 133 transmits link disconnection instruction information to the base station BS1, and disconnects the link between the base station BS1 and the terminal MT (corresponding to the situation in Figure 7).

[0151] As shown in FIG. 17, the modulation method switching control unit 14 includes an inter-device distance calculation unit 141 , a reception level estimation unit 142 , a modulation method switching determination unit 143 , and a modulation method switching instruction unit 144 .

[0152] The device-to-device distance calculation unit 141 acquires location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The device-to-device distance calculation unit 141 also acquires base station location information stored in advance in the storage unit 12. The base station location information here refers to information indicating the location of each of a plurality of base stations BS.

[0153] The inter-device distance calculation unit 141 calculates the distance between the terminal MT and each of the multiple base stations BS based on the position of the terminal MT indicated by the acquired information and the positions of each of the multiple base stations BS. Note that any means can be used to calculate the distance from the position between the terminal MT and each of the multiple base stations BS. The inter-device distance calculation unit 141 outputs information indicating the calculated distance between the terminal MT and each of the multiple base stations BS to the reception level estimation unit 142.

[0154] The reception level estimation unit 142 acquires information indicating the distance between the terminal MT and the position of each of the plurality of base stations BS, output from the device-to-device distance calculation unit 141. The reception level estimation unit 142 also acquires reception level attenuation information pre-stored in the storage unit 12a. The reception level estimation unit 142 estimates the reception level of radio waves from each of the plurality of base stations BS at the terminal MT based on the distance between the terminal MT and each of the plurality of base stations BS indicated by the acquired information and the reception level attenuation information.

[0155] The reception level attenuation information here refers to information that associates the distance between the terminal MT and the base station BS with the reception level of the radio waves corresponding to that distance. For example, the reception level attenuation information is information that indicates the transition of the reception level at the terminal MT of the radio waves transmitted from base station BS1, as shown by the solid line R1 in Figure 14. Also, for example, the reception level attenuation information is information that indicates the transition of the reception level at the terminal MT of the radio waves transmitted from base station BS3, as shown by the dashed line R2 in Figure 14.

[0156] The reception level estimation unit 142 outputs information indicating the estimated reception levels of radio waves from each of the plurality of base stations BS at the terminal MT to the modulation method switching determination unit 143 .

[0157] The modulation method switching determination unit 143 acquires information indicating the reception level of radio waves from each of the plurality of base stations BS at the terminal MT, output from the reception level estimation unit 142. The modulation method switching determination unit 143 also acquires a modulation method switching threshold value stored in advance in the storage unit 12a.

[0158] The modulation method switching threshold here is a threshold used to determine whether to switch the modulation method between, for example, 16QAM, 64QAM, and 256QAM. For example, the modulation method switching threshold is the reception level values ​​L1 and L2 shown in Fig. 14. The storage unit 12a pre-stores, for example, a modulation method switching threshold (for example, the value of L1) for determining which modulation method, 16QAM or 64QAM, to use, and a modulation method switching threshold (for example, the value of L2) for determining which modulation method, 64QAM or 256QAM, to use.

[0159] The modulation method switching determination unit 143 identifies, for each link (each base station BS), an appropriate modulation method to be used in the link between the terminal MT and the base station BS, based on an estimated value of the reception level of radio waves from the base station BS at the terminal MT and a modulation method switching threshold.

[0160] Then, the modulation method switching determination unit 143 compares the identified appropriate modulation method with the modulation method actually used for each link (each base station BS). If there is a link in which the identified appropriate modulation method differs from the modulation method actually used, the modulation method switching determination unit 143 determines to switch the modulation method used for that link.

[0161] The modulation method switching determination unit 143 outputs information indicating the base station BS of the link for which the modulation method switching is to be performed and information indicating the modulation method after the switch to the modulation method switching instruction unit 144 and the communication speed estimation unit 151 of the link addition control unit 15 described later.

[0162] The modulation method switching instruction unit 144 acquires information indicating the base station BS of the link for which modulation method switching is to be performed and information indicating the modulation method after switching, which are output from the modulation method switching determination unit 143. The modulation method switching instruction unit 144 transmits modulation method switching instruction information to the base station BS of the link for which the modulation method indicated by the acquired information is to be switched to the modulation method indicated by the acquired information.

[0163] 14, when the terminal MT moves to the position P11, information indicating base station BS1 and information indicating the 64QAM method are output from the modulation method switching determination unit 143 to the modulation method switching instruction unit 144. The modulation method switching instruction unit 144 transmits modulation method switching instruction information to the base station BS1 to instruct the base station BS1 to switch to the 64QAM method.

[0164] 14, when the terminal MT moves to the position P12, information indicating base station BS2 and information indicating the 64QAM method are output from the modulation method switching determination unit 143 to the modulation method switching instruction unit 144. The modulation method switching instruction unit 144 transmits modulation method switching instruction information to the base station BS2 to instruct the base station BS2 to switch to the 64QAM method.

[0165] 14, when the terminal MT moves to position P13, information indicating base station BS1 and information indicating the 16QAM method are output from the modulation method switching determination unit 143 to the modulation method switching instruction unit 144. The modulation method switching instruction unit 144 transmits modulation method switching instruction information to the base station BS1 to instruct the base station BS1 to switch to the 16QAM method.

[0166] 14, when the terminal MT moves to position P14, information indicating base station BS2 and information indicating the 256QAM method are output from the modulation method switching determination unit 143 to the modulation method switching instruction unit 144. The modulation method switching instruction unit 144 transmits modulation method switching instruction information to the base station BS2, instructing it to switch to the 256QAM method.

[0167] As shown in FIG. 17, the link addition control unit 15 includes a communication speed estimation unit 151 , a link addition determination unit 152 , an additional link selection unit 153 , and a link addition instruction unit 154 .

[0168] The communication speed estimation unit 151 acquires information indicating the base station BS of the link for which modulation scheme switching is to be performed and information indicating the modulation scheme after switching, which are output from the modulation scheme switching determination unit 143. The communication speed estimation unit 151 estimates the communication speed (bps) based on the modulation scheme based on the acquired information and the symbol rate (sps). The communication speed estimation unit 151 outputs the estimated communication speed value to the link addition determination unit 152.

[0169] The link addition determination unit 152 acquires the value of the communication speed output from the communication speed estimation unit 151. The link addition determination unit 152 also acquires a link addition threshold pre-stored in the storage unit 12 a. The link addition threshold here is a predetermined communication speed (bps) value that serves as a criterion for determining whether or not to add a link.

[0170] The link addition determination unit 152 compares the acquired communication speed value with a link addition threshold. If the acquired communication speed value is less than the link addition threshold, the link addition determination unit 152 determines to add a link. If the link addition determination unit 152 determines to add a link, it outputs information indicating the terminal MT to which the link is to be added to the added link selection unit 153.

[0171] The additional link selection unit 153 acquires information indicating the terminal MT to which a link is to be added, output from the link addition determination unit 152. The additional link selection unit 153 selects a link that uses a modulation method that obtains the maximum communication capacity from among the links established between the terminal MT and each of the multiple base stations BS.

[0172] As mentioned above, the modulation scheme that obtains the greatest communication capacity is the modulation scheme used for the link with the shortest distance between the terminal MT and the multiple base stations BS. As a result, the additional link selection unit 153 will assume the link with the shortest distance among the multiple links established between the terminal MT and the multiple base stations BS.

[0173] The additional link selection unit 153 outputs information indicating the selected link to the link addition instruction unit 154 as a link to be newly added.

[0174] The link addition instruction unit 154 acquires information indicating the link to be added, which is output from the additional link selection unit 153. The link addition instruction unit 154 transmits link addition instruction information to the base station BS of the link based on the acquired information, instructing it to establish another additional link with the terminal MT.

[0175] The detection unit 11, the execution control unit 13, the modulation method switching control unit 14, and the link addition control unit 15 are configured to include a processor such as a CPU. For example, the detection unit 11, the execution control unit 13, the modulation method switching control unit 14, and the link addition control unit 15 realize the functions of the above-described functional units included in the detection unit 11, the execution control unit 13, the modulation method switching control unit 14, and the link addition control unit 15 by reading and executing various programs stored in the storage unit 12a.

[0176] The storage unit 12a is configured to include, for example, a storage medium such as a RAM, a semiconductor memory such as an EEPROM, a flash memory such as an SSD, a magnetic disk such as an HDD, an optical disk, or any combination of these storage media.

[0177] [Operation of communication control device] An example of the operation of the communication control device 10a will be described below. Figures 18 to 20 are flowcharts showing the operation of the communication control device 10a in the second embodiment of the present invention. The operation of the communication control device 10a shown in the flowcharts of Figures 18 to 20 is periodically started at a predetermined interval (for example, every 1 to 10 seconds).

[0178] First, the beam selection information acquisition unit 111 collects beam selection information from each of the plurality of base stations BS (step S101). The beam selection information acquisition unit 111 outputs the collected beam selection information to the terminal position calculation unit 112.

[0179] Next, the terminal position calculation unit 112 acquires the beam selection information collected from each of the multiple base stations BS output from the beam selection information acquisition unit 111. The terminal position calculation unit 112 also acquires the reference direction information stored in advance in the storage unit 12 (step S102).

[0180] Next, the terminal position calculation unit 112 calculates the angle between the reference direction and the direction of the terminal MT at the position of each of the plurality of base stations BS (for example, the above-mentioned θ １ , θ ２ , θ' １ , θ' ２ The angle of the object is identified (step S103).

[0181] Next, the terminal position calculation unit 112 calculates the position of the terminal MT based on the angle formed between the reference direction and the direction of the terminal MT at the positions of each of the specified base stations BS, for example, using the AoA technology described above (step S104). The terminal position calculation unit 112 outputs position information indicating the calculated position of the terminal MT to the switching execution determination unit 113 and the device-to-device distance calculation unit 141.

[0182] Next, the switching execution determination unit 113 acquires the location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The switching execution determination unit 113 also acquires the switching start range information stored in advance in the storage unit 12 (step S105).

[0183] Next, the switching execution determination unit 113 determines whether the location of the terminal MT based on the acquired information is within the switching start range (step S106). If the location of the terminal MT is not within the switching start range (step S106: NO), the switching execution determination unit 113 determines not to execute link switching. Then, the process proceeds to step S110 in FIG. 19.

[0184] On the other hand, if the position of the terminal MT is included in the switching start range (step S106, YES), the switching execution determination unit 113 determines to execute link switching. When determining to execute link switching, the switching execution determination unit 113 outputs information identifying the base station BS to which a new link is to be established, information identifying the base station BS to which the link is to be disconnected, information identifying the terminal MT, etc. to the execution control unit 13.

[0185] The link connection instruction unit 131 acquires information identifying the base station BS to which a link is to be newly established and information identifying the terminal MT, which are output from the switching execution determination unit 113 of the detection unit 11. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly established, instructing it to establish a link with the terminal MT (step S107).

[0186] Next, the connection completion report receiving unit 132 waits for reception of a connection completion report from the base station BS to which the link is to be newly connected, indicating that a link with the terminal MT has been established (step S108). When the connection completion report receiving unit 132 receives the connection completion report (step S108, YES), it notifies the link disconnection instructing unit 133.

[0187] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, instructing the base station BS that is to disconnect the link to the terminal MT (step S109). Then, the process proceeds to step S110 in FIG. 19 .

[0188] Next, the device-to-device distance calculation unit 141 acquires location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The device-to-device distance calculation unit 141 also acquires base station location information stored in advance in the storage unit 12. As described above, the base station location information is information indicating the location of each of the multiple base stations BS.

[0189] The inter-device distance calculation unit 141 calculates the distance between the terminal MT and each of the base stations BS based on the position of the terminal MT indicated by the acquired information and the positions of each of the base stations BS (step S110). The inter-device distance calculation unit 141 outputs information indicating the calculated distance between the terminal MT and each of the base stations BS to the reception level estimation unit 142.

[0190] The reception level estimator 142 acquires information indicating the distance between the terminal MT and each of the plurality of base stations BS output from the device-to-device distance calculator 141. The reception level estimator 142 also acquires reception level attenuation information pre-stored in the memory 12a. Based on the distance between the terminal MT and each of the plurality of base stations BS indicated by the acquired information and the reception level attenuation information, the reception level estimator 142 estimates the reception level of radio waves from each of the plurality of base stations BS at the terminal MT (i.e., the reception level of each link) (step S111).

[0191] As described above, the reception level attenuation information is information that associates the value of the distance between the terminal MT and the base station BS with the value of the reception level of the radio waves corresponding to that distance. The reception level estimation unit 142 outputs information that indicates the estimated reception level of the radio waves from each of the multiple base stations BS at the terminal MT to the modulation method switching determination unit 143.

[0192] Next, the modulation method switching determination unit 143 acquires information indicating the reception level of radio waves from each of the plurality of base stations BS at the terminal MT, output from the reception level estimation unit 142. The modulation method switching determination unit 143 also acquires a modulation method switching threshold value stored in advance in the storage unit 12a. As described above, the modulation method switching threshold value is a threshold value used to determine whether to switch the modulation method between, for example, 16QAM, 64QAM, and 256QAM.

[0193] The modulation scheme switching determination unit 143 identifies an appropriate modulation scheme to be used for the link between the terminal MT and the base station BS for each link (for each base station BS) based on an estimated value of the reception level of the radio wave from the base station BS at the terminal MT and the modulation scheme switching threshold. Then, the modulation scheme switching determination unit 143 compares the identified appropriate modulation scheme for each link (for each base station BS) with the modulation scheme actually used (step S112).

[0194] If there is a link in which the identified appropriate modulation method differs from the modulation method actually used (step S112, YES), the modulation method switching determination unit 143 determines to switch the modulation method used in that link. The modulation method switching determination unit 143 outputs information indicating the base station BS of the link for which modulation method switching is to be performed and information indicating the modulation method after switching to the modulation method switching instruction unit 144 and the communication speed estimation unit 151 of the link addition control unit 15, which will be described later.

[0195] Next, the modulation method switching instruction unit 144 acquires information indicating the base station BS of the link for which modulation method switching is to be performed and information indicating the modulation method after switching, which are output from the modulation method switching determination unit 143. The modulation method switching instruction unit 144 transmits modulation method switching instruction information to the base station BS of the link for which the modulation method indicated in the acquired information is to be switched to the modulation method indicated in the acquired information (step S113). Then, the process proceeds to step S114 in FIG. 20 .

[0196] Next, the communication speed estimation unit 151 acquires information indicating the base station BS of the link for which modulation scheme switching is to be performed and information indicating the modulation scheme after switching, which are output from the modulation scheme switching determination unit 143. The communication speed estimation unit 151 estimates the communication speed (bps) based on the modulation scheme and the symbol rate (sps) based on the acquired information (step S114). The communication speed estimation unit 151 outputs the estimated communication speed value to the link addition determination unit 152.

[0197] Next, the link addition determination unit 152 acquires the value of the communication speed output from the communication speed estimation unit 151. The link addition determination unit 152 also acquires the link addition threshold pre-stored in the storage unit 12 a. As described above, the link addition threshold is a predetermined communication speed (bps) value that serves as a criterion for determining whether or not to add a link.

[0198] The link addition determination unit 152 compares the acquired communication speed value with the link addition threshold. If the acquired communication speed value is less than the link addition threshold (YES in step S115), the link addition determination unit 152 determines to add a link. If the link addition determination unit 152 determines to add a link, it outputs information indicating the terminal MT to which the link is to be added to the added link selection unit 153.

[0199] Next, the additional link selection unit 153 acquires information indicating the terminal MT to which a link is to be added, output from the link addition determination unit 152. The additional link selection unit 153 selects, from among the links established between the terminal MT and each of the multiple base stations BS, a link that uses a modulation method that obtains the maximum communication capacity (step S116). The additional link selection unit 153 outputs information indicating the selected link to the link addition instruction unit 154, designating the selected link as a new link to be added.

[0200] Next, the link addition instruction unit 154 acquires information indicating the link to be added output from the additional link selection unit 153. The link addition instruction unit 154 transmits link addition instruction information to the base station BS of the link based on the acquired information, instructing it to establish another link with the terminal MT (step S117). This completes the operation of the communication control device 10a shown in the flowcharts of Figures 18 to 20.

[0201] As described above, the wireless communication system 1a according to the second embodiment of the present invention includes at least three base stations BS and a communication control device 10a that controls link switching between each of the base stations BS and the terminal MT. The communication control device 10a periodically calculates the distance between the moving terminal MT and each of the base stations BS. Based on the calculated distances, the communication control device 10a estimates the reception level of radio waves transmitted from each of the base stations BS at the terminal MT. Then, based on the estimated reception level and the modulation method switching threshold described above, the communication control device 10a switches the modulation method as necessary so that an appropriate modulation method is used for each link.

[0202] With this configuration, the wireless communication system 1a according to the second embodiment of the present invention can switch to a more efficient modulation scheme as needed in response to changes in the positional relationship between the terminal MT and the base stations BS. The more efficient modulation scheme here refers to, for example, a modulation scheme that can transmit more information while suppressing the occurrence of symbol errors.

[0203] As described above, the communication control device 10a of the wireless communication system 1a in the second embodiment of the present invention periodically calculates the communication speed (bps) of each link established between the mobile terminal MT and each of the multiple base stations BS based on the modulation method and symbol rate (sps) used in each link. If the calculated communication speed is below the link addition threshold, the communication control device 10a adds a new link. Here, the communication control device 10a further adds a link that uses a modulation method that achieves the maximum communication capacity among the multiple links established between the terminal MT and the multiple base stations BS.

[0204] By having such a configuration, the wireless communication system 1a in the second embodiment of the present invention can maintain a state in which the desired communication speed is always met by adding a new link, even if it is estimated that the desired communication speed will temporarily not be met due to a change in the positional relationship between the terminal MT and multiple base stations BS.

[0205] Furthermore, as described above, the communication control device 10a of the wireless communication system 1a in the second embodiment of the present invention identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1 illustrated in Figures 4 to 7) and a second base station (e.g., base station BS2 illustrated in Figures 4 to 7) and is moving away from the first base station and approaching a third base station (e.g., base station BS3 illustrated in Figures 4 to 7) based on the direction of the terminal MT as seen from the first base station and the direction of the terminal MT as seen from the third base station.

[0206] When the communication control device 10a detects that the moving terminal MT has entered a switching start range r that is predetermined based on the connectable range with the first base station and the connectable range with the third base station, the communication control device 10a starts control of link switching execution. The communication control device 10a establishes a new link between the terminal MT and the third base station that are approaching each other. After the link between the third base station and the terminal MT is established, the communication control device 10a disconnects the existing link between the terminal MT and the first base station that are moving away from each other.

[0207] With this configuration, the wireless communication system 1a according to the second embodiment of the present invention can always maintain a state in which a link is established between the terminal MT and at least two base stations BS (the second base station and at least one of the first base station and the third base station) even when link switching is being performed. In other words, the wireless communication system 1a according to the second embodiment of the present invention can always maintain a state in which one terminal can communicate with the base station BS via multiple links, including when link switching is being performed. This makes it possible to prevent communication interruptions, for example, even when an unexpected communication failure occurs.

[0208] Furthermore, the wireless communication system 1a according to the second embodiment of the present invention determines whether to start link switching based on the location of the terminal MT. Therefore, unlike conventional wireless communication systems that start link switching when a decrease in radio wave strength is detected, the wireless communication system 1a according to the second embodiment does not fall into a state in which throughput is reduced even when link switching is being performed. As a result, the wireless communication system 1a according to the second embodiment can ensure communication reliability at all times, including when link switching is being performed.

[0209] Third Embodiment A wireless communication system 1b according to a third embodiment of the present invention will now be described. The wireless communication system 1b described below is an example of a communication control system according to the present invention.

[0210] The wireless communication system 1 in the first embodiment and the wireless communication system 1a in the second embodiment described above were configured to assume link switching between the three base stations BS (base stations BS1 to BS3) and the terminal MT. Furthermore, the first and second embodiments described above assumed that the terminal MT would move linearly from near base station BS1 toward base station BS3. Therefore, the wireless communication system 1 in the first embodiment and the wireless communication system 1a in the second embodiment described above were configured to maintain the established link between the terminal MT and base station BS2, establish a new link between the terminal MT and base station BS3, and disconnect the link between the terminal MT and base station BS1 (i.e., switch the link between the terminal MT and base station BS1 to the link between the terminal MT and base station BS3).

[0211] However, in reality, various communication environments are possible, such as when the terminal MT needs to maintain links with three or more base stations BS at all times, including when switching links, or when there are multiple base stations BS that are candidates for link switching, etc. Furthermore, in reality, there may be cases where the terminal MT does not always move toward a specific base station BS.

[0212] In the third embodiment described below, it is assumed that a terminal MT always maintains links with three or more base stations BS, including during link switching, there are multiple base stations BS that are candidates for link switching, and the terminal MT moves in any direction. The wireless communication system 1b in the third embodiment has a configuration that can perform link switching while preventing a decrease in throughput and communication disconnection in such a communication environment.

[0213] 21 to 24 are diagrams illustrating link switching by a wireless communication system 1b according to a third embodiment of the present invention. As an example, FIGS. 21 to 24 show a wireless communication system 1b having seven base stations BS (base stations BS1 to BS7). The communication control device according to the third embodiment is omitted from FIGS. 21 to 24. The terminal MT is also omitted from FIGS. 21 to 24.

[0214] 21 to 24 show a state in which terminal MT has established links with base station BS1, base station BS2, base station BS6, and base station BS7, respectively. Also, in Fig. 21 to 24, three base stations BS (base stations BS3 to BS5) are shown as candidates for link switching destinations.

[0215] In Figure 21, the overlapping area d13, which is an area where communication connection with both base station BS1 and base station BS3 is possible, is shown as a dashed oval. Strictly speaking, the area where communication connection with both base station BS1 and base station BS3 is possible is the area surrounded by the arc of a two-dot chain line indicating the boundary of the cell of base station BS1 and the arc of a one-dot chain line indicating the boundary of the cell of base station BS3. Therefore, the overlapping area d13 is not oval, but rather has a lens-like shape with pointed ends. However, for simplicity, the overlapping area d13 is shown as an oval here. The overlapping areas d13 and d14 described below are also shown as ovals for the same reason.

[0216] 21, a switching start range r13 is indicated by a solid oval. When it is detected that a moving terminal MT has entered the switching start range r13, execution of link switching is initiated. In other words, the fact that the terminal MT has entered the switching start range r13 triggers the start of execution of link switching. The switching start range r13 is used to determine whether to switch the link between the terminal MT and base station BS1 to the link between the terminal MT and base station BS3.

[0217] As shown in Fig. 21, the switching start range r13 is set to a position closer to base station BS1 within the overlapping area d13, similar to the switching start range r shown in Figs. 4 to 7. The reason for this is as follows.

[0218] As with the switching start range r described above, the switching start range r13 is set to a position closer to base station BS1 within the overlapping area d13, so that link switching begins as soon as terminal MT enters the overlapping area d13. Furthermore, because the switching start range r13 is set to a position closer to base station BS1 within the overlapping area d13, even if terminal MT is moving in a direction closer to base station BS3, it is possible to ensure a longer period of time until terminal MT leaves the overlapping area d, and it is therefore possible to prevent terminal MT from falling into an unstable state in which only a link (only one link) is established with base station BS2.

[0219] The switching start range r13 may be the same range as the overlapping area d13. In that case, however, it is necessary to start and complete link switching immediately when terminal MT enters the switching start range r13. To achieve this, a mechanism for detecting the current location of terminal MT more frequently (for example, in real time) and a mechanism for transmitting control signals for controlling link switching without delay are required.

[0220] In Figure 22, an overlapping area d14, which is an area where communication connection with both base station BS1 and base station BS4 is possible, is shown as a dashed oval. Also in Figure 22, a switching start range r14 is shown as a solid oval. When a moving terminal MT is detected to have entered the switching start range r14, execution of link switching is initiated. That is, the fact that terminal MT has entered the switching start range r14 triggers the initiation of execution of link switching. The switching start range r14 is used to determine whether to switch the link between terminal MT and base station BS1 to the link between terminal MT and base station BS4. That is, the switching start range r14 is used when terminal MT moves from near base station BS1 toward base station BS4 (toward the upper right in the figure).

[0221] As shown in Fig. 22, the switching start range r14 is set at a position closer to base station BS1 within the overlapping area d14, similar to the switching start range r shown in Figs. 4 to 7. The reason for this is the same as in the case of the switching start range r13. Note that the switching start range r14 may be the same range as the overlapping area d14.

[0222] In Figure 23, an overlapping area d15, which is an area where communication connection with both base station BS1 and base station BS5 is possible, is shown as a dashed oval. Also in Figure 23, a switching start range r15 is shown as a solid oval. When a moving terminal MT is detected to have entered the switching start range r15, execution of link switching is initiated. That is, the fact that terminal MT has entered the switching start range r15 triggers the start of execution of link switching. The switching start range r15 is used to determine whether to switch the link between terminal MT and base station BS1 to the link between terminal MT and base station BS5. That is, the switching start range r15 is used when terminal MT moves from near base station BS1 toward base station BS5 (toward the lower right in the figure).

[0223] As shown in Fig. 23, the switching start range r15 is set at a position closer to base station BS1 within the overlapping area d15, similar to the switching start range r shown in Figs. 4 to 7. The reason for this is the same as in the case of the switching start range r13. Note that the switching start range r15 may be the same range as the overlapping area d15.

[0224] Figure 24 is a diagram that combines the above-mentioned Figures 21 to 23. The switching start ranges r13 to r15, which are the switching start ranges for each of base stations BS3 to BS5 that are candidates for link switching destinations, are areas as shown in Figure 24. The wireless communication system 1b in the third embodiment determines the new link (base station BS) to be established based on which switching start range the moving terminal MT enters.

[0225] For example, if the terminal MT moves from the vicinity of the base station BS1 toward the right side in Fig. 24, the terminal MT will enter the switching start range r13. Therefore, the wireless communication system 1b starts to execute link switching to switch the link between the terminal MT and the base station BS1 to the link between the terminal MT and the base station BS3.

[0226] 24, the terminal MT enters the switching start range r14, and the wireless communication system 1b starts to execute link switching to switch the link between the terminal MT and the base station BS1 to the link between the terminal MT and the base station BS4.

[0227] 24, the terminal MT enters the switching start range r15, and the wireless communication system 1b starts to execute link switching to switch the link between the terminal MT and the base station BS1 to the link between the terminal MT and the base station BS5.

[0228] Note that there may be cases where at least a portion of the switching start ranges overlap with each other. For example, in Fig. 24, a portion of the switching start range r13 overlaps with a portion of the switching start range r14. Also, in Fig. 24, a portion of the switching start range r13 overlaps with a portion of the switching start range r15.

[0229] If the area into which the moving terminal MT has entered is an area in which the switching start ranges overlap, the wireless communication system 1b may execute link switching corresponding to one of the switching start ranges according to any predetermined rule. For example, the wireless communication system 1b may select a base station BS to be the target of link switching based on the distance between the terminal MT and each of the base stations BS.

[0230] Specifically, for example, when a moving terminal MT enters an area where the switching start ranges r13 and r14 overlap, the wireless communication system 1b calculates the distance from the location of the terminal MT to base station BS3 and the distance from the location of the terminal MT to base station BS4. The distance calculation may use, for example, the AoA technology described above. The wireless communication system 1b may then select the base station BS that is closer to the base station BS3 or the base station BS4 as the base station BS to be subjected to link switching.

[0231] For example, the wireless communication system 1b may select a base station BS to be used for link switching based on the communication speed (bps) whose calculation method has been explained in the second embodiment.

[0232] Specifically, for example, when a moving terminal MT enters an area where switching start range r13 and switching start range r14 overlap, the wireless communication system 1b calculates the communication speed of a link established between the terminal MT and base station BS3 and the communication speed of a link established between the terminal MT and base station BS4. Then, the wireless communication system 1b may select, as the base station BS to be subjected to link switching, the base station BS that is estimated to have a faster link communication speed, out of base station BS1 and base station BS3.

[0233] In addition, as in the wireless communication system 1b of the third embodiment, by having multiple base stations BS to which links can be switched, it becomes possible to switch to the link with better conditions. For example, in reality, depending on the positional relationship between the terminal MT and the base station BS, there may be a case where an obstruction or the like is present between them. In such a situation, by having multiple base stations BS to which links can be switched, it becomes possible to control the link to be temporarily switched to another base station BS during a period when the positional relationship between the moving terminal MT and the base station BS is such that an obstruction is present between them.

[0234] As described above, in the wireless communication system 1b illustrated in Figures 21 to 24, a link is established between each of base stations BS1, BS2, BS6, and BS7 and the terminal MT. In this way, the accuracy of estimating the location of the terminal MT improves as the number of base stations BS that have established links with the terminal MT increases. The reason for this is explained below.

[0235] 25 is a diagram illustrating an improvement in the accuracy of estimating the location of a terminal MT by a wireless communication system 1b according to a third embodiment of the present invention. As described above, in wireless communication systems that utilize higher frequency bands, base stations are generally equipped with directional antennas, such as array antennas, and beamforming technology is used to appropriately select transmit and receive beams formed toward the direction of the terminal of the communication partner. In the present invention, for example, the direction of the beam selected by this beamforming (beam angle) is calculated as being the direction in which the terminal of the communication partner is located, thereby making it possible to identify the location of the terminal MT using the above-mentioned AoA technology.

[0236] As shown in Fig. 25, the beam formed by each antenna (not shown) of the base station BS has a width. The width becomes wider the farther away from the base station BS. For example, the beam formed by the base station BS1 is angled θ １ Similarly, the beam formed by base station BS2 has a certain width in the left and right directions with a center in the direction of θ ２ Similarly, the beam formed by base station BS6 has a certain width in the left and right directions with a center in the direction of θ ６ Similarly, the beam formed by base station BS7 has a certain width in the left and right directions with a center in the direction of θ ７ It has a certain width in the left and right directions centered on the degree direction.

[0237] 25, the area where these four beams, each having a certain width, overlap is darkly shaded. That is, the wireless communication system 1b in the third embodiment can estimate that the terminal MT is located in this darkly shaded area.

[0238] On the other hand, if the terminal MT has established links only with two base stations BS (base station BS1 and base station BS2), as in the wireless communication system 1 of the first embodiment, the location of the terminal MT can only be narrowed down to the area where the beam formed by base station BS1 and the beam formed by base station BS2 overlap. In Figure 25, the area where these two beams overlap, each having a certain width, is lightly shaded.

[0239] Furthermore, if terminal MT has established links only with two other base stations BS (base station BS6 and base station BS7), the location of terminal MT can only be narrowed down to the area where the beam formed by base station BS6 overlaps with the beam formed by base station BS7. In Figure 25, the area where these two beams, each with a certain width, overlap is the area surrounded by a dashed line.

[0240] In this way, the size of the overlapping area of ​​the beams formed by each of the multiple base stations BS varies depending on how the combination of multiple base stations BS is selected to establish a link with the terminal MT.

[0241] For example, as shown in the right diagram of Figure 25, the darkly shaded area is smaller than the lightly shaded area, and the darkly shaded area is also smaller than the area enclosed by the dashed line. In other words, a larger number of base stations BS that have established links with the terminal MT makes it possible to narrow down the estimated location of the terminal MT to a smaller range.

[0242] Although the accuracy of estimating the location of the terminal MT can be improved by increasing the number of base stations BS that have established links with the terminal MT, as described above, as long as there are at least two base stations BS that have established links with the terminal MT, as in the first embodiment described above, it is possible to estimate the location of the terminal MT. In reality, increasing the number of base stations BS that have established links with the terminal MT has disadvantages, such as an increase in the amount of calculation required to estimate the location of the terminal MT. Therefore, in practice, it is preferable to increase the number of base stations BS that have established links with the terminal MT, provided that the amount of calculation is kept within a predetermined range.

[0243] [Overall configuration of wireless communication system] The overall configuration of the wireless communication system 1b in the third embodiment is basically the same as the overall configuration of the wireless communication system 1 in the first embodiment described above with reference to the overall configuration diagram of Figure 8, so a description thereof will be omitted.

[0244] The configuration of the wireless communication system 1b in the third embodiment is different from the configuration of the wireless communication system 1 in the first embodiment described above in terms of the configuration of the communication control device. Hereinafter, the communication control device of the wireless communication system 1b in the third embodiment will be referred to as a "communication control device 10b."

[0245] [Configuration of communication control device] The configuration of the communication control device 10b will be described below. Fig. 26 is a block diagram showing the functional configuration of the communication control device 10b according to the third embodiment of the present invention. As shown in Fig. 26, the communication control device 10b includes a detection unit 11b, a storage unit 12b, and an execution control unit 13.

[0246] The detector 11b detects that a situation has arisen in which link switching should be performed. The detector 11b identifies the location of the terminal MT, and determines whether or not link switching should be performed based on the identified location of the terminal MT and a predetermined switching start range, and which base station BS should be the target of link switching. As shown in Fig. 26, the detector 11b includes a beam selection information acquirer 111, a terminal position calculator 112b, and a switching execution determiner 113b.

[0247] The beam selection information acquisition unit 111 collects beam selection information from each of the multiple base stations BS. As described above, the beam selection information is information that identifies the beam selected for communication with the terminal MT in the beamforming performed by each of the multiple base stations BS. The beam selection information acquisition unit 111 periodically collects the beam selection information at predetermined intervals (for example, every 1 to 10 seconds). The beam selection information acquisition unit 111 outputs the collected beam selection information to the terminal position calculation unit 112b.

[0248] The beam selection information may be information indicating the direction (orientation) of the beam selected for communication with the terminal MT in beamforming performed by each of the base stations BS. The beam here may be a transmission beam, a reception beam, or both.

[0249] Although the present description focuses on one terminal MT for simplicity, in reality, the base station BS may be connected to multiple terminals MT for communication. In this case, the beam selection information acquisition unit 111 collects beam selection information for each terminal MT from each of the multiple base stations BS.

[0250] The terminal position calculation unit 112b acquires beam selection information collected from each of the multiple base stations BS, output from the beam selection information acquisition unit 111. The terminal position calculation unit 112b also acquires reference direction information stored in advance in the storage unit 12b. As described above, the reference direction information is information indicating a reference direction. The reference direction is, for example, the north direction. Based on the acquired reference direction information and beam selection information, the terminal position calculation unit 112b calculates the angle formed between the reference direction and the direction of the terminal MT at the position of each of the multiple base stations BS (for example, the above-mentioned θ １ , θ ２ , θ ６ , θ ７ Identify the angle of the object.

[0251] The terminal position calculation unit 112b calculates the position of the terminal MT using, for example, the above-mentioned AoA technology, based on the angle formed between the reference direction and the direction of the terminal MT at the position of each of the identified multiple base stations BS. The terminal position calculation unit 112b outputs position information indicating the calculated position of the terminal MT to the switching execution determination unit 113b. Note that the position information indicating the position of the terminal MT may be coordinates in an arbitrary coordinate system, or may be position information expressed by latitude and longitude, etc.

[0252] The switching execution determination unit 113b acquires location information indicating the location of the terminal MT output from the terminal location calculation unit 112b. The switching execution determination unit 113b also acquires multiple pieces of switching start range information stored in advance in the storage unit 12b. As described above, the switching start range information is information indicating a range (switching start range) that satisfies a relay start condition (switching start condition). The switching start range may be a range expressed by coordinates in an arbitrary coordinate system, or may be a range expressed by latitude and longitude, etc.

[0253] The switching execution determination unit 113b determines whether the location of the terminal MT based on the acquired information is included in any of a plurality of switching start ranges. If the location of the terminal MT is included in any of the plurality of switching start ranges, the switching execution determination unit 113b determines to execute link switching. That is, the switching execution determination unit 113b determines to establish a new link between this terminal MT and another base station BS, and then to control each of the target base stations BS so as to disconnect one of the links established between this terminal MT and each of the plurality of base stations BS.

[0254] As described above, which base station BS to establish a new link with and which base station BS to disconnect from among the multiple existing links can be uniquely identified based on the switching start range that includes the position of the terminal MT. That is, the switching start range is set in advance for each combination of two base stations BS as shown in Figures 21 to 24, and therefore can be uniquely identified.

[0255] If the location of the terminal MT is not included in the switching start range, the switching execution determination unit 113b determines not to execute link switching. If the switching execution determination unit 113b determines to execute link switching, it outputs to the execution control unit 13 information identifying the base station BS to disconnect the link, information identifying the base station BS to newly establish a link, information identifying the terminal MT, and the like.

[0256] The storage unit 12b stores various data and programs. For example, the storage unit 12b pre-stores the above-mentioned reference direction information and multiple pieces of switching start range information. The storage unit 12b may also store various programs for operating each functional unit of the communication control device 10b.

[0257] As shown in FIG. 26, the execution control unit 13 includes a link connection instruction unit 131 , a connection completion report receiving unit 132 , and a link disconnection instruction unit 133 .

[0258] The link connection instruction unit 131 acquires information identifying the base station BS to disconnect the link and information identifying the terminal MT, which are output from the switching execution determination unit 113 of the detection unit 11. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly connected, instructing it to establish a link with the terminal MT.

[0259] The connection completion report receiving unit 132 receives a connection completion report from the base station BS to which the link is newly connected, the connection completion report indicating that a link with the terminal MT has been established. When the connection completion report receiving unit 132 receives the connection completion report, it notifies the link disconnection instruction unit 133.

[0260] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, the link disconnection instruction information instructing the base station BS that is to disconnect the link to the terminal MT.

[0261] The detection unit 11b and the execution control unit 13 are configured to include a processor such as a CPU. For example, the detection unit 11b and the execution control unit 13 realize the functions of the above-described functional units included in the detection unit 11b and the execution control unit 13 by reading and executing various programs stored in the storage unit 12b.

[0262] The storage unit 12b is configured to include, for example, a storage medium such as a RAM, a semiconductor memory such as an EEPROM, a flash memory such as an SSD, a magnetic disk such as an HDD, an optical disk, or any combination of these storage media.

[0263] [Operation of communication control device] An example of the operation of the communication control device 10b will be described below. Fig. 27 is a flowchart showing the operation of the communication control device 10b in the third embodiment of the present invention. The operation of the communication control device 10b shown in the flowchart of Fig. 27 is periodically started at a predetermined interval (for example, every 1 to 10 seconds).

[0264] First, the beam selection information acquisition unit 111 collects beam selection information from each of the plurality of base stations BS (step S201). The beam selection information acquisition unit 111 outputs the collected beam selection information to the terminal position calculation unit 112b.

[0265] Next, the terminal position calculation unit 112b acquires the beam selection information collected from each of the multiple base stations BS output from the beam selection information acquisition unit 111. The terminal position calculation unit 112b also acquires reference direction information stored in advance in the storage unit 12 (step S202).

[0266] Next, the terminal position calculation unit 112b calculates the angle between the reference direction and the direction of the terminal MT at the position of each of the plurality of base stations BS (for example, the above-mentioned θ １ , θ ２ , θ ６ , θ ７ The angle of the object is identified (step S203).

[0267] Next, the terminal position calculation unit 112b calculates the position of the terminal MT based on the angle between the reference direction and the direction of the terminal MT at the positions of each of the specified base stations BS, for example, using the AoA technology described above (step S204). The terminal position calculation unit 112b outputs position information indicating the calculated position of the terminal MT to the switching execution determination unit 113b.

[0268] Next, the switching execution determination unit 113b acquires the location information indicating the location of the terminal MT output from the terminal location calculation unit 112b. The switching execution determination unit 113b also acquires multiple pieces of switching start range information stored in advance in the storage unit 12 (step S205).

[0269] Next, the switching execution determination unit 113b determines whether the location of the terminal MT based on the acquired information is included in any of the multiple switching start ranges (step S206). If the location of the terminal MT is not included in any of the multiple switching start ranges (step S206: NO), the switching execution determination unit 113b determines that link switching will not be performed. This completes the operation of the communication control device 10b shown in the flowchart of Figure 27.

[0270] On the other hand, if the location of the terminal MT is included in any of the multiple switching start ranges (step S206, YES), the switching execution determination unit 113b determines to execute link switching. If the switching execution determination unit 113b determines to execute link switching, it identifies the base station BS to which a new link is to be established (i.e., identifies the link to be switched) based on the switching start range that includes the location of the terminal MT (step S207). The switching execution determination unit 113b outputs information identifying the base station BS to which the link is to be disconnected, information identifying the base station BS to which a new link is to be established, information identifying the terminal MT, etc. to the execution control unit 13.

[0271] The link connection instruction unit 131 acquires information identifying the base station BS to which a link is to be newly established and information identifying the terminal MT, which are output from the switching execution determination unit 113b of the detection unit 11b. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly established, instructing it to establish a link with the terminal MT (step S208).

[0272] Next, the connection completion report receiving unit 132 waits for reception of a connection completion report from the base station BS to which the link is to be newly connected, indicating that a link with the terminal MT has been established (step S209). When the connection completion report receiving unit 132 receives the connection completion report (step S209, YES), it notifies the link disconnection instructing unit 133.

[0273] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, instructing the base station BS that is to disconnect the link to the terminal MT (step S210). This completes the operation of the communication control device 10b shown in the flowchart of Figure 27.

[0274] As described above, the wireless communication system 1 according to the third embodiment of the present invention includes four or more base stations BS and a communication control device 10b that controls link switching between each of these base stations BS and a terminal MT. The communication control device 10b identifies the location of a terminal MT that has established links with multiple base stations (e.g., base stations BS1, BS2, BS6, and BS7 shown in FIGS. 21 to 24) and is moving away from a first base station and approaching an nth base station (e.g., any of base stations BS3 to BS5 shown in FIGS. 21 to 24) based on the direction of the terminal MT as seen from each of the multiple base stations with which the links are established and the direction of the terminal MT as seen from a base station that is a candidate for link switching.

[0275] When the communication control device 10b detects that the moving terminal MT has entered a predetermined switching start range based on the connectable range with the first base station and the connectable range with the base station to be switched, the communication control device 10b starts control of link switching execution. The communication control device 10 establishes a new link between the terminal MT and the base station to be switched, which are approaching each other. After the link between the base station to be switched and the terminal MT is established, the communication control device 10b disconnects the existing link between the terminal MT and the first base station, which are moving away from each other.

[0276] With this configuration, the wireless communication system 1b according to the third embodiment of the present invention can maintain a state in which each link is established between the terminal MT and three or more base stations BS, even when link switching is performed. That is, the wireless communication system 1b according to the third embodiment of the present invention can maintain a state in which one terminal can communicate with the base station BS via multiple links at all times, including when link switching is performed. This makes it possible to prevent communication interruptions, for example, even when an unexpected communication failure occurs.

[0277] Furthermore, the wireless communication system 1b according to the third embodiment of the present invention determines whether to start link switching based on the location of the terminal MT. Therefore, unlike conventional wireless communication systems that start link switching when a decrease in radio wave strength is detected, the wireless communication system 1b according to the third embodiment does not fall into a state in which throughput is reduced even when link switching is being performed. As a result, the wireless communication system 1b according to the third embodiment can ensure communication reliability at all times, including when link switching is being performed.

[0278] Fourth Embodiment A wireless communication system 1c according to a fourth embodiment of the present invention will be described below. The wireless communication system 1c described below is an example of a communication control system of the present invention.

[0279] The wireless communication system 1 in the first embodiment, the wireless communication system 1a in the second embodiment, and the wireless communication system 1b in the third embodiment are all configured assuming that the multiple base stations BS and the terminals MT are all on the same horizontal plane. However, in reality, the antennas of the base stations BS are often installed at higher positions, such as on the rooftops of buildings, to avoid radio wave blocking by obstructions. Furthermore, the installation heights of the antennas of the multiple base stations BS are different from one another.

[0280] On the other hand, moving terminals MT are relatively often at ground level, for example, when carried by a person walking on a sidewalk or a person driving a car on a roadway. However, terminals MT are not necessarily always at ground level. As such, in reality, multiple base stations BS and terminals MT do not all exist on the same two-dimensional plane. Therefore, in the wireless communication system 1 in the first embodiment, the wireless communication system 1a in the second embodiment, and the wireless communication system 1b in the third embodiment, the accuracy of estimating the location of the terminal MT may be low.

[0281] In contrast, a wireless communication system 1c in a fourth embodiment described below determines whether the position of the terminal MT is within the switching start range by taking into account the vertical position as well. More specifically, when calculating the position of the terminal MT based on the direction of the beams formed by the antennas of each of the multiple base stations BS, the wireless communication system 1c in the fourth embodiment, as in the above-mentioned embodiments, takes into account not only the horizontal beam direction but also the vertical beam direction.

[0282] The wireless communication system 1c then determines whether the calculated three-dimensional position of the terminal MT is within a preset switching start range. The switching start range set here is an ellipsoid in three-dimensional space, rather than an elliptical range on a two-dimensional plane as set in the above-described embodiments.

[0283] [Procedure for Identifying Terminal Location] In the link switching procedure described in the first embodiment with reference to Figures 2 and 3, it was explained that the decision to start execution of link switching is made based on the location of the terminal MT (i.e., whether or not the terminal MT has entered the switching start range). This also applies to the fourth embodiment described below. To achieve this, a configuration capable of identifying the location of the terminal MT is essential. Below, a procedure for the wireless communication system 1c of this embodiment to identify the three-dimensional location of the terminal MT will be described.

[0284] 28 and 29 are diagrams for explaining the procedure for identifying the position of a terminal MT by a wireless communication system 1c according to the fourth embodiment of the present invention. Fig. 28 shows an example of the positional relationship of each device when the three-dimensional position of the terminal MT is not within the three-dimensional switching start range rc. On the other hand, Fig. 29 shows an example of the positional relationship of each device when the three-dimensional position of the terminal MT is within the three-dimensional switching start range rc.

[0285] As shown in Figures 28 and 29, as an example, it is assumed that base station BS1, base station BS2, and base station BS3 are installed on the rooftops of different buildings, and that terminal MT is moving on a roadway on the ground.

[0286] The procedure for identifying the location of the terminal MT in the fourth embodiment uses AoA technology, as in the previous embodiments. However, the procedure for identifying the location of the terminal MT in the fourth embodiment differs from the procedure for identifying the location of the terminal MT in the previous embodiments in that the three-dimensional location of the terminal MT is calculated using not only the horizontal angle but also the vertical angle.

[0287] That is, the wireless communication system 1c in the fourth embodiment can determine the three-dimensional position of the terminal MT by determining the horizontal position of the terminal MT using the direction (angle) of the terminal MT on a horizontal plane as seen from the positions of each of the multiple base stations BS, and by determining the vertical position of the terminal MT using the direction (angle) of the terminal MT on a vertical plane as seen from the positions of each of the multiple base stations BS.

[0288] It should be noted that by combining the terminal location estimation result by the AoA technology with the measurement result of the received signal strength indicator (RSSI), it is possible to identify the terminal location more accurately. In the present invention, the technology used to identify the location of the terminal MT is not limited to the AoA technology, and any other technology may be used to identify the location of the terminal MT.

[0289] In the wireless communication system 1c of this embodiment, similar to the above-described embodiments, a predetermined direction is used as the reference direction when identifying the position of the terminal MT. In the examples shown in FIGS. 28 and 29, the reference direction is set to a direction from the lower right to the upper left of the figure. In practice, the reference direction may be set to, for example, north. That is, the upper left direction may be north in FIGS. 28 and 29.

[0290] As shown in FIG. 28, when the three-dimensional position of the terminal MT is not within the three-dimensional switching start range rc, the angle on the horizontal plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS1 is defined as θ′. １ 28, when the three-dimensional position of the terminal MT is not within the three-dimensional switching start range rc, the angle on the vertical plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS1 is defined as φ'. １ Let's say.

[0291] As shown in FIG. 28, when the three-dimensional position of the terminal MT is not within the three-dimensional switching start range rc, the angle on the horizontal plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS3 is defined as θ′. ２ 28, when the three-dimensional position of the terminal MT is not within the three-dimensional switching start range rc, the angle on the vertical plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS3 is defined as φ'. ２ Let's say.

[0292] This (θ' １ , φ' １ ) and (θ' ２ , φ' ２) the three-dimensional position of the terminal MT can be identified. Then, it is determined that the identified position is not within a preset three-dimensional switching start range rc. The setting of the three-dimensional switching start range rc will be described later.

[0293] Similarly, as shown in FIG. 29, when the three-dimensional position of the terminal MT is within the three-dimensional switching start range rc, the angle on the horizontal plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS1 is θ １ 29, when the three-dimensional position of the terminal MT is within the three-dimensional switching start range rc, the angle on the vertical plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS1 is φ. ２ Let's say.

[0294] As shown in FIG. 29, when the three-dimensional position of the terminal MT is within the three-dimensional switching start range rc, the angle on the horizontal plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS2 is θ ２ 29, when the position of the terminal MT is within the three-dimensional switching start range rc, the angle on the vertical plane formed by the reference direction and the direction of the terminal MT at the position of the base station BS2 is φ. ２ Let's say.

[0295] This (θ １ , φ １ ) and (θ ２ , φ ２ ) the three-dimensional position of the terminal MT can be identified. Then, it is determined that the identified position is within a preset three-dimensional switching start range rc. When it is determined that the three-dimensional position of the terminal MT is within the three-dimensional switching start range rc, execution of link switching is initiated.

[0296] As mentioned above, for example, the direction of the beam (beam angle) selected by beamforming in the base station BS is determined based on the direction in which the terminal MT of the communication partner is located (the above (θ １ , φ １ ), (θ ２ , φ ２), (θ' １ , φ' １ ), (θ' ２ , φ' ２ )) and perform calculations accordingly, it becomes possible to identify the location of the terminal MT using the AoA technology described above.

[0297] [Procedure for Setting Switching Start Range] Hereinafter, a procedure for the wireless communication system 1 of this embodiment to set the three-dimensional switching start range rc will be described.

[0298] 28 and 29 show a three-dimensional switching start range rc. The three-dimensional switching start range rc is set at a position closer to base station BS1 within the overlapping region (not shown) of the ellipsoids. The reason for setting such a three-dimensional switching start range rc will be explained below.

[0299] The overlapping area (not shown) in the fourth embodiment is an area where spheres each having a center at each of the positions of a plurality of base stations BS overlap each other. Therefore, strictly speaking, the overlapping area is not an ellipsoid but has a lens-like shape with pointed ends. However, for simplicity, the overlapping area is represented here as an ellipsoid.

[0300] 28 and 29 show terminal MT moving from a position closer to base station BS1 (lower left side of the figure), passing a position closer to base station BS2, and moving toward a position closer to base station BS3 (upper right side of the figure). For ease of explanation, terminal MT will be described as moving in a straight line.

[0301] 29 shows a state in which the terminal MT has just entered the three-dimensional switching start range rc from the lower left side of the figure. At this time, the terminal MT is in a state in which it can communicate with two base stations BS, base station BS1 and base station BS2. When it is detected that the moving terminal MT has entered the three-dimensional switching start range rc, link switching is initiated.

[0302] The reason why the three-dimensional switching start range rc is set at a position closer to base station BS1 within the overlapping area (not shown) is that, in order to perform link switching in the order of establishing a link between base station BS3 and terminal MT and then severing the link between base station BS1 and terminal MT, as in each of the above-mentioned embodiments, it is necessary to start and complete the link switching while the moving terminal MT is located within the overlapping area.

[0303] Because the three-dimensional switching start range rc is set at a position closer to base station BS1 within the overlapping area, link switching begins as soon as terminal MT enters overlapping area d. Furthermore, because the three-dimensional switching start range rc is set at a position closer to base station BS1 within overlapping area d, even if terminal MT is moving in a direction closer to base station BS3, it is possible to ensure a longer period of time until terminal MT leaves the overlapping area, thereby preventing terminal MT from falling into an unstable state in which only a link (only one link) is established with base station BS2.

[0304] The three-dimensional switching start range rc may be the same range as the overlapping area. In this case, however, it is necessary to start and complete link switching immediately when the terminal MT enters the three-dimensional switching start range rc. To achieve this, a mechanism for detecting the current position of the terminal MT more frequently (e.g., in real time) and a mechanism for transmitting control signals for controlling link switching without delay are required.

[0305] [Overall configuration of wireless communication system] The overall configuration of the wireless communication system 1c in the fourth embodiment is basically the same as the overall configuration of the wireless communication system 1 in the first embodiment described above with reference to the overall configuration diagram of Figure 8, so a description thereof will be omitted.

[0306] The configuration of the wireless communication system 1c in the fourth embodiment is different from the configuration of the wireless communication system 1 in the first embodiment in the configuration of the communication control device. Hereinafter, the communication control device of the wireless communication system 1c in the fourth embodiment will be referred to as a "communication control device 10c."

[0307] [Configuration of communication control device] The configuration of the communication control device 10c will be described below. Fig. 30 is a block diagram showing the functional configuration of the communication control device 10c according to the fourth embodiment of the present invention. As shown in Fig. 30, the communication control device 10c includes a detection unit 11c, a storage unit 12c, and an execution control unit 13.

[0308] The detection unit 11c detects that a situation has arisen in which link switching should be performed. The detection unit 11c identifies the three-dimensional position of the terminal MT and determines whether or not link switching should be performed based on the identified three-dimensional position of the terminal MT and a predetermined three-dimensional switching start range. As shown in Figure 30, the detection unit 11c is configured to include a beam selection information acquisition unit 111c, a three-dimensional terminal position calculation unit 112c, and a switching execution determination unit 113c.

[0309] The beam selection information acquisition unit 111c collects beam selection information from each of the multiple base stations BS. The beam selection information here refers to information that identifies the beam selected for communication with the terminal MT in the beamforming performed by each of the multiple base stations BS. The beam selection information acquisition unit 111c periodically collects the beam selection information at predetermined intervals (for example, every 1 to 10 seconds). The beam selection information acquisition unit 111c outputs the collected beam selection information to the terminal position calculation unit 112.

[0310] The beam selection information may be information indicating the three-dimensional forming direction (orientation) of the beam selected for communication with the terminal MT in beamforming performed by each of the base stations BS. The beam here may be a transmission beam, a reception beam, or both.

[0311] Although the present description focuses on one terminal MT for simplicity, in reality, the base station BS may be connected to multiple terminals MT for communication. In this case, the beam selection information acquisition unit 111c collects beam selection information for each terminal MT from each of the multiple base stations BS.

[0312] The three-dimensional terminal position calculation unit 112c acquires beam selection information collected from each of the multiple base stations BS, output from the beam selection information acquisition unit 111c. The three-dimensional terminal position calculation unit 112c also acquires reference direction information stored in advance in the storage unit 12c. The reference direction information here is information indicating the above-mentioned reference direction. The reference direction is, for example, north. Based on the acquired reference direction information and beam selection information, the three-dimensional terminal position calculation unit 112c calculates the angle on the horizontal plane and the angle on the vertical plane (for example, the above-mentioned (θ １ , φ １ ), (θ ２ , φ ２ ), (θ' １ , φ' １ ), (θ' ２ , φ' ２ ) angle, etc.

[0313] The three-dimensional terminal position calculation unit 112c calculates the horizontal position of the terminal MT using, for example, the AoA technology described above, based on the angle on the horizontal plane formed between the reference direction and the direction of the terminal MT at the specified positions of each of the multiple base stations BS. The three-dimensional terminal position calculation unit 112c also calculates the vertical position of the terminal MT using, for example, the AoA technology described above, based on the angle on the vertical plane formed between the reference direction and the direction of the terminal MT at the specified positions of each of the multiple base stations BS. This allows the three-dimensional position of the terminal MT to be determined.

[0314] The three-dimensional terminal position calculation unit 112c outputs position information indicating the calculated three-dimensional position of the terminal MT to the switching execution determination unit 113c. Note that the position information indicating the position of the terminal MT may be coordinates in an arbitrary three-dimensional coordinate system, or may be position information expressed by latitude, longitude, altitude, etc.

[0315] The switching execution determination unit 113c acquires location information indicating the location of the terminal MT output from the terminal location calculation unit 112. The switching execution determination unit 113c also acquires three-dimensional switching start range information stored in advance in the storage unit 12c. As described above, the three-dimensional switching start range information here is information indicating a three-dimensional range (switching start range) that satisfies the relay start condition (switching start condition). The switching start range may be a range expressed by coordinates in an arbitrary three-dimensional coordinate system, or may be a range expressed by latitude, longitude, altitude, etc.

[0316] The switching execution determination unit 113c determines whether the three-dimensional position of the terminal MT based on the acquired information is included in a three-dimensional switching start range. If the three-dimensional position of the terminal MT is included in the three-dimensional switching start range, the switching execution determination unit 113c determines to execute link switching. In other words, the switching execution determination unit 113c determines to establish a new link between this terminal MT and another base station BS, and then control each of the target base stations BS to disconnect one of the links established between this terminal MT and each of the multiple base stations BS.

[0317] As described above, which base station BS to establish a new link with and which of the existing multiple links to disconnect from is uniquely determined based on the three-dimensional switching start range that includes the three-dimensional position of the terminal MT. That is, the three-dimensional switching start range is set in advance for each combination of two base stations BS, as in the above-described embodiments, and therefore can be uniquely determined.

[0318] The switching execution determination unit 113c may determine whether to execute link switching by identifying the direction of movement of the terminal MT from the position of the terminal MT over time, and taking the direction of movement of the terminal MT into consideration. For example, the switching execution determination unit 113c may determine to execute link switching when it detects that the terminal MT is moving from a position closer to the base station BS1 to a position closer to the base station BS3 and that the terminal MT has entered the three-dimensional switching start range rc.

[0319] For example, the three-dimensional switching start range rc shown in Figures 28 and 29 is a switching start range that is set to disconnect the link with base station BS1 and establish a new link with base station BS3. Therefore, when the switching execution determination unit 113 detects that the position of terminal MT is included in the three-dimensional switching start range rc shown in Figures 28 and 29, it determines to establish a new link with base station BS3 for the target terminal MT and to disconnect the link with base station BS1.

[0320] If the location of the terminal MT is not included in the switching start range, the switching execution determining unit 113c determines not to execute link switching.

[0321] When the switching execution judgment unit 113c judges that link switching should be executed, it outputs to the execution control unit 13 information identifying the base station BS to which the link will be severed, information identifying the base station BS to which a new link will be established, and information identifying the terminal MT.

[0322] The storage unit 12c stores various data and programs. For example, the storage unit 12c pre-stores the aforementioned reference direction information and three-dimensional switching start range information. The storage unit 12c may also store various programs for operating each functional unit of the communication control device 10c.

[0323] As shown in FIG. 30, the execution control unit 13 includes a link connection instruction unit 131 , a connection completion report receiving unit 132 , and a link disconnection instruction unit 133 .

[0324] The link connection instruction unit 131 acquires information identifying the base station BS to disconnect the link and information identifying the terminal MT, which are output from the switching execution determination unit 113c of the detection unit 11c. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly connected, instructing it to establish a link with the terminal MT.

[0325] The connection completion report receiving unit 132 receives a connection completion report from the base station BS to which the link is newly connected, the connection completion report indicating that a link with the terminal MT has been established. When the connection completion report receiving unit 132 receives the connection completion report, it notifies the link disconnection instruction unit 133.

[0326] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, the link disconnection instruction information instructing the base station BS that is to disconnect the link to the terminal MT.

[0327] The detection unit 11c and the execution control unit 13 are configured to include a processor such as a CPU. For example, the detection unit 11c and the execution control unit 13 realize the functions of the above-described functional units included in the detection unit 11c and the execution control unit 13 by reading and executing various programs stored in the storage unit 12c.

[0328] The storage unit 12c is configured to include, for example, a storage medium such as a semiconductor memory such as a RAM and an EEPROM, a flash memory such as an SSD, a magnetic disk such as an HDD, an optical disk, or any combination of these storage media.

[0329] [Operation of communication control device] An example of the operation of the communication control device 10c will be described below. Fig. 31 is a flowchart showing the operation of the communication control device 10c in the fourth embodiment of the present invention. The operation of the communication control device 10c shown in the flowchart of Fig. 31 is periodically started at a predetermined interval (for example, every 1 to 10 seconds).

[0330] First, the beam selection information acquisition unit 111c collects beam selection information from each of the plurality of base stations BS (step S301). The beam selection information acquisition unit 111c outputs the collected beam selection information to the terminal position calculation unit 112.

[0331] Next, the three-dimensional terminal position calculation unit 112c acquires the beam selection information collected from each of the multiple base stations BS output from the beam selection information acquisition unit 111c. The three-dimensional terminal position calculation unit 112c also acquires the reference direction information stored in advance in the storage unit 12c (step S302).

[0332] Next, the three-dimensional terminal position calculation unit 112c calculates the angles formed between the reference direction and the directions of the terminal MT on the horizontal and vertical planes (for example, the above-mentioned (θ １ , φ １ ), (θ ２ , φ ２ ), (θ' １ , φ' １ ), (θ' ２ , φ' ２ ) and the angle of the target object (step S303).

[0333] Next, the three-dimensional terminal position calculation unit 112c calculates the three-dimensional position of the terminal MT using, for example, the above-mentioned AoA technology, based on the angles formed between the reference direction and the directions of the terminal MT on the horizontal and vertical planes at the positions of each of the specified base stations BS (step S304). The three-dimensional terminal position calculation unit 112c outputs position information indicating the calculated three-dimensional position of the terminal MT to the switching execution determination unit 113c.

[0334] Next, the switching execution determination unit 113c acquires the position information indicating the three-dimensional position of the terminal MT output from the three-dimensional terminal position calculation unit 112c. The switching execution determination unit 113c also acquires the three-dimensional switching start range information stored in advance in the storage unit 12c (step S305).

[0335] Next, the switching execution determination unit 113c determines whether the three-dimensional position of the terminal MT based on the acquired information is included in the three-dimensional switching start range (step S306). If the three-dimensional position of the terminal MT is not included in the three-dimensional switching start range (step S306, NO), the switching execution determination unit 113c determines that link switching will not be performed. This completes the operation of the communication control device 10c shown in the flowchart of FIG.

[0336] On the other hand, if the three-dimensional position of the terminal MT is included in the three-dimensional switching start range (step S306, YES), the switching execution determination unit 113c determines to execute link switching. When determining to execute link switching, the switching execution determination unit 113 outputs, to the execution control unit 13, information identifying the base station BS to disconnect the link, information identifying the base station BS to newly establish a link, information identifying the terminal MT, and the like.

[0337] The link connection instruction unit 131 acquires information identifying the base station BS to which a link is to be newly established and information identifying the terminal MT, which are output from the switching execution determination unit 113c of the detection unit 11c. The link connection instruction unit 131 transmits link connection instruction information to the base station BS to which the link is to be newly established, instructing it to establish a link with the terminal MT (step S307).

[0338] Next, the connection completion report receiving unit 132 waits for reception of a connection completion report from the base station BS to which the link is to be newly connected, indicating that a link with the terminal MT has been established (step S308). When the connection completion report receiving unit 132 receives the connection completion report (step S308, YES), it notifies the link disconnection instructing unit 133.

[0339] The link disconnection instruction unit 133 receives a notification indicating that the connection completion report has been received from the connection completion report receiving unit 132. When the link disconnection instruction unit 133 receives the notification, it transmits link disconnection instruction information to the base station BS that is to disconnect the link, instructing the base station BS that is to disconnect the link to the terminal MT (step S309). This completes the operation of the communication control device 10c shown in the flowchart of Figure 31.

[0340] As described above, the wireless communication system 1c according to the fourth embodiment of the present invention includes at least three base stations BS and a communication control device 10c that controls link switching between each of these base stations BS and a terminal MT. The communication control device 10c identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1 illustrated in FIGS. 28-29) and a second base station (e.g., base station BS2 illustrated in FIGS. 28-29) and is moving away from the first base station and approaching a third base station (e.g., base station BS3 illustrated in FIGS. 28-29) based on the horizontal and vertical directions of the terminal MT as seen from the first base station and the horizontal and vertical directions of the terminal MT as seen from the third base station.

[0341] When the communication control device 10c detects that the moving terminal MT has entered a three-dimensional switching start range rc that is predetermined based on the connectable range with the first base station and the connectable range with the third base station, the communication control device 10c starts control of link switching execution. The communication control device 10c establishes a new link between the terminal MT and the third base station that are approaching each other. After the link between the third base station and the terminal MT is established, the communication control device 10c disconnects the existing link between the terminal MT and the first base station that are moving away from each other.

[0342] With this configuration, the wireless communication system 1c according to the fourth embodiment of the present invention can always maintain a state in which a link is established between the terminal MT and at least two base stations BS (the second base station and at least one of the first base station and the third base station) even when link switching is being performed. In other words, the wireless communication system 1c according to the fourth embodiment of the present invention can always maintain a state in which one terminal MT can communicate with the base station BS via multiple links, including when link switching is being performed. This makes it possible to prevent communication interruptions, for example, even when an unexpected communication failure occurs.

[0343] Furthermore, the wireless communication system 1c according to the fourth embodiment of the present invention determines whether to start link switching based on the three-dimensional position of the terminal MT. Therefore, unlike conventional wireless communication systems that start link switching when a decrease in radio wave strength is detected, the wireless communication system 1c according to the fourth embodiment does not fall into a state in which throughput is reduced even when link switching is being performed. As a result, the wireless communication system 1c according to the fourth embodiment can ensure communication reliability at all times, including when link switching is being performed.

[0344] According to the above-described embodiment, the communication control system includes three or more wireless base station devices and a communication control device. For example, the communication control system is a wireless communication system 1, 1a to 1c in the embodiment, the wireless base station devices are base stations BS, BS1 to BSn in the embodiment, and the communication control devices are communication control devices 10, 10a to 10c in the embodiment. The communication control devices control switching of communication connections between the wireless base station devices and terminal devices. For example, the terminal devices are terminals MT in the embodiment, and the switching of communication connections is link switching in the embodiment.

[0345] The communication control device includes a detection unit and a switching control unit. For example, the detection unit corresponds to the detection units 11, 11b to 11c in the embodiment, and the switching control unit corresponds to the execution control unit 13 in the embodiment.

[0346] The detection unit detects that a terminal device, which is communicatively connected with a first wireless base station device and a second wireless base station device and is moving in a direction away from the first wireless base station device and in a direction toward a third wireless base station device, has entered a predetermined range within an overlapping region, which is a region in which communication with both the first wireless base station device and the third wireless base station device is possible. For example, the first wireless base station device is base station BS1 in the embodiment, the second wireless base station device is base station BS2 in the embodiment, and the third wireless base station device is base station BS3 in the embodiment, the overlapping region is overlapping region d in the embodiment, and the predetermined range is switching start ranges r, r13, r14, r15, and rc in the embodiment.

[0347] When the switching control unit detects that the terminal device has entered a specified range, it establishes a communication connection between the third wireless base station device and the terminal device, and then controls the communication connection between the first wireless base station device and the terminal device to be disconnected.

[0348] In the above communication control system, the predetermined range may be a range that is set in advance at a position relatively closer to the first wireless base station device within the overlapping area.

[0349] In the above communication control system, the communication control device may further include an acquisition unit and a calculation unit. For example, the acquisition unit is the beam selection information acquisition unit 111 or 111c in the embodiment, and the calculation unit is the terminal position calculation unit 112 or 112b and the three-dimensional terminal position calculation unit 112c in the embodiment.

[0350] The acquisition unit acquires, from the first wireless base station device, first direction information indicating the direction of the terminal device as seen from the first wireless base station device, and acquires, from the second wireless base station device, second direction information indicating the direction of the terminal device as seen from the second wireless base station device. For example, the first direction information may be an angle θ between a reference direction and the direction of the terminal MT at the position of the base station BS1 in the embodiment. １ , φ １ Alternatively, the second direction information is information for identifying a beam selected by beamforming performed by the base station BS1 for the terminal MT, and the second direction information is information for identifying an angle θ between the reference direction and the direction of the terminal MT at the position of the base station BS2 in the embodiment. ２ , φ ２ Or, it is information for identifying a beam selected by beamforming performed by the base station BS2 for the terminal MT. The calculation unit calculates the position of the terminal device based on the first direction information and the second direction information.

[0351] In the above communication control system, the first direction information and the second direction information may include information for identifying a beam selected by beamforming performed by the wireless base station device for the terminal device.

[0352] The server device (communication control device 10, 10a to 10c) of the communication control system of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0353] Some or all of the configuration of the communication control devices 10, 10a to 10c in the above-described embodiments may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer system that serves as the server or client. Furthermore, the program may be designed to implement some of the above-described functions, or may be capable of implementing the above-described functions in combination with programs already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0354] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope that do not deviate from the gist of the present invention.

[0355] DESCRIPTION OF SYMBOLS 1, 1a to 1c... Wireless communication system 10, 10a to 10c... Communication control device 11, 11b to 11c... Detection unit 12, 12a to 12c... Storage unit 13... Execution control unit 14... Modulation method switching control unit 15... Link addition control unit 111, 111c... Beam selection information acquisition unit 112, 112b... Terminal position calculation unit 112c... Three-dimensional terminal position calculation unit 113, 113b to 113c... Switching execution determination unit 131... Link connection instruction unit 132... Connection completion report receiving unit 133... Link disconnection instruction unit 141... Device-to-device distance calculation unit 142... Reception level estimation unit 143... Modulation method switching determination unit 144... Modulation method switching instruction unit 151... Communication speed estimation unit 152... Link addition determination unit 153... Additional link selection unit 154... Link addition instruction unit BS, BS1 to BSn... base stations MT... terminal

Claims

1. A communication control system having three or more wireless base station devices and a communication control device that controls switching of communication connections between the wireless base station devices and a terminal device, wherein the communication control device comprises: a detection unit that detects that the terminal device, which is connected to a first wireless base station device and a second wireless base station device and is moving in a direction away from the first wireless base station device and toward a third wireless base station device, has entered a predetermined range within an overlapping area, which is an area in which communication with both the first wireless base station device and the third wireless base station device is possible; and a switching control unit that, when it is detected that the terminal device has entered the predetermined range, establishes a communication connection between the third wireless base station device and the terminal device, and then controls to disconnect the communication connection between the first wireless base station device and the terminal device.

2. A communication control system according to claim 1, wherein the predetermined range is a range set in advance at a position relatively closer to the first wireless base station device within the overlapping area.

3. The communication control system of claim 1 or 2, further comprising: an acquisition unit that acquires first direction information indicating the direction of the terminal device as seen from the first wireless base station device from the first wireless base station device, and acquires second direction information indicating the direction of the terminal device as seen from the second wireless base station device from the second wireless base station device; and a calculation unit that calculates the position of the terminal device based on the first direction information and the second direction information.

4. A communication control system as described in claim 3, wherein the first direction information and the second direction information include information identifying a beam selected by beamforming performed by the radio base station device for the terminal device.

Images