Communication control system

Abstract

A communication control system according to the present invention has at least three wireless base station devices and a communication control device that controls the switching of communication connections between the wireless base station devices and terminal devices. The communication control device has: a detection unit that detects that a terminal device that is communicatively connected to a first wireless base station device and a second wireless base station device and is moving away from the first wireless base station device while approaching a third wireless base station device has entered a prescribed range that is within 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 has been detected that the terminal device has entered the prescribed range, performs control that establishes a communication connection between the terminal device and the third wireless base station and then ends the communication connection between the terminal device and the first wireless base station device. The prescribed range is set on the basis of the communication environment between the first wireless base station device and another device in the vicinity of a movement path and the communication environment between the third wireless base station device and the other device in the vicinity of the movement path.

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, because the above-described conventional handover is triggered by a drop in radio wave strength, the throughput temporarily drops while the link is being switched, which means that 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 communication disconnection when switching links.

[0008] One aspect of the present invention is 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 terminal devices, wherein the communication control device includes 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, has entered a predetermined range within an overlapping area in which it can communicate with both the first wireless base station device and the third wireless base station device, and the terminal device is connected to a first wireless base station device and a second wireless base station device, and the terminal device is moving in a direction away from the first wireless base station device and in a direction toward a third wireless base station device, and a detection unit that detects that the terminal device has entered a predetermined range within an overlapping area in which it can communicate with both the first wireless base station device and the third wireless base station device, and a switching control unit that, when it is detected that the terminal device has entered a 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, wherein the specified range is a range set based on first information indicating the respective communication environments between the first radio base station device and multiple other devices present in the vicinity of the movement path of the terminal device, and second information indicating the respective communication environments between the third radio base station device and multiple other devices present in the vicinity of the movement path of the terminal device.

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

[0010] FIG. 1 is a diagram for explaining a link switching procedure that is a premise in a wireless communication system according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 3 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 4 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 5 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 6 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 7 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 8 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1 according to a first embodiment of the present invention. FIG. 1 is a block diagram showing a functional configuration of a communication control device 10 in a first embodiment of the present invention. FIG. 2 is a flowchart showing an operation of the communication control device 10 in the first embodiment of the present invention. FIG. 3 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1a in a second embodiment of the present invention. FIG. 4 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1a in a second embodiment of the present invention. FIG. 5 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1a in a second embodiment of the present invention. FIG. 6 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1a in a second embodiment of the present invention.10 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1b in a modified example of the second embodiment of the present invention. FIG. 11 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1b in a modified example of the second embodiment of the present invention. FIG. 12 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1b in a modified example of the second embodiment of the present invention. FIG. 13 is a diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1b in a modified example of the second embodiment of the present invention. FIG. 14 is a diagram for explaining a procedure for specifying a position of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. FIG. 15 is a diagram for explaining a procedure for specifying a position of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. FIG. 16 is a diagram for explaining a procedure for specifying a position of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. FIG. 17 is a diagram for explaining a procedure for specifying a position of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. 10 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in the third embodiment of the present invention. FIG. 11 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in the third embodiment of the present invention. FIG. 12 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in the third embodiment of the present invention. FIG. 13 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in the third embodiment of the present invention. FIG. 14 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in the third embodiment of the present invention. FIG. 15 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in the third embodiment of the present invention.10 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. FIG. 11 is a diagram for explaining a procedure for specifying the position of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. FIG. 12 is a diagram showing characteristics for each positional relationship of a plurality of base stations BS with respect to the movement route of a terminal MT. FIG. 13 is an angle θ accompanying the movement of a terminal MT in the case of Case 1+. １ and angle θ ２ 10 is a graph showing the change in angle θ accompanying the movement of the terminal MT in case 3+. FIG. 11 is a diagram for explaining the procedure for specifying the position of the terminal MT by the wireless communication system 1c in the third embodiment of the present invention. FIG. 12 is a diagram for explaining the procedure for specifying the position of the terminal MT by the wireless communication system 1c in the third embodiment of the present invention. １ and angle θ ２ 10 is a graph showing changes in . A diagram for explaining a procedure for specifying the location of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. A diagram for explaining a procedure for specifying the location of a terminal MT by a wireless communication system 1c in a third embodiment of the present invention. A diagram for explaining a procedure for setting a switching start range r by a wireless communication system 1d in a fourth ...

[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] In each embodiment of the present invention, it is assumed that the movement route of the terminal MT is predetermined and that a plurality of base stations BS are installed along the movement route of the terminal MT.

[0026] Examples of such situations include a case where a terminal MT carried by a user on a moving train is connected to a base station BS installed on the roof or wall of a building along the railroad tracks (i.e., the path of movement of the terminal MT). Another example is a case where a terminal MT carried by a user in a car traveling on a highway is connected to a base station BS installed on the roof or wall of a building along the highway (i.e., the path of movement of the terminal MT). Another example is a case where a terminal MT carried by a user traveling on an indoor moving walkway is connected to a base station BS installed on an interior wall or ceiling along the moving walkway (i.e., the path of movement of the terminal MT). In either case, the base station BS connected to the terminal MT is switched as the terminal MT moves.

[0027] [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.

[0028] 2 to 7 are diagrams illustrating the procedure for identifying the location of a terminal MT by the wireless communication system 1 according to the first embodiment of the present invention. In this embodiment, it is assumed that the terminal MT moves in a straight line. In FIGS. 2 to 7, the terminal MT moves in a straight line from left to right in each diagram. In the following description, the right side of the direction of movement (direction of travel) of the terminal MT will be referred to as the "right side of the movement path," and the left side of the direction of movement (direction of travel) of the terminal MT will be referred to as the "left side of the movement path."

[0029] 2 and 3 show a case where base stations BS1, BS2, and BS3 are all located on the right side of the movement path of terminal MT. In other words, all base stations BS are located on one side of the movement path of terminal MT. Hereinafter, this case will be referred to as "Case 1."

[0030] Fig. 2 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 3 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0031] In the wireless communication system 1 according to the present embodiment, a predetermined direction is set as a reference direction when identifying the position of the terminal MT. In Fig. 2 and Fig. 3, as an example, the direction of movement of the terminal MT (i.e., the direction from left to right in each figure) is set as the reference direction.

[0032] 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 This angle θ' １ and angle 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. 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.

[0033] 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 angle θ １and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0034] In addition, the angle θ' １ and angle θ' ２ and a method for identifying the position of the terminal MT from the value of the angle θ １ and angle θ ２ As a method for identifying the location of the terminal MT from the value of (a) and (b), for example, AoA (Angle of Arrival) technology can be used. The AoA technology is an existing technology based on triangulation, and is a technology for identifying the location of the 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 with multiple antennas, and identifies the location of the terminal by calculating the phase difference of the reception angles for each antenna.

[0035] 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.

[0036] As described above, in each embodiment of the present invention, it is assumed that the movement route of the terminal MT is known. Therefore, in order to identify the position of the terminal MT, it is not necessary to know the direction (angle θ') of the terminal MT at the positions of multiple base stations BS. １ and angle θ' ２ , or angle θ １ and angle θ ２ ) does not need to be specified based on the movement path of the terminal MT and the direction (one direction) of the terminal MT at the position of any one base station BS (more specifically, the movement path of the terminal MT and the angle θ'１ or angle θ' ２ or based on the value of the movement path of the terminal MT and the angle θ １ or angle θ ２ However, by specifying the directions of the terminal MT at the positions of a plurality of base stations BS, the accuracy of estimating the position of the terminal MT can be further improved.

[0037] 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.

[0038] The wireless communication system 1 in this embodiment, for example, sets the direction of the beam selected by this beam forming (beam angle) in the direction where the terminal MT of the communication partner is located (the above angle θ' １ , angle θ' ２ , or angle θ １ , angle θ ２ ) is used for calculation. This allows the wireless communication system 1 to identify the position of the terminal MT by using the existing beamforming configuration, without requiring a new configuration for detecting the direction of the terminal MT.

[0039] As mentioned above, the angle θ １ and angle θ ２ Since the position of the terminal MT has already been identified from the movement route of the terminal MT, the direction of the terminal MT at the position of the base station BS3 to which communication is newly connected (angle θ ３) can also be easily identified. Therefore, when link switching is initiated and the base station BS3 starts a communication connection with the terminal MT, the beam sweep operation can be omitted. The beam sweep operation is a beamforming operation in which the base station BS detects the direction of the terminal MT and aligns the beam formation direction with the detected direction of the terminal MT. By omitting the beam sweep operation, it becomes possible to more quickly establish a communication connection between the base station BS3 and the terminal MT.

[0040] The state before link switching has been described above with reference to Figure 2, and the state at the start of link switching execution has been described with reference to Figure 3. As shown in Figures 2 and 3, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multilink) via multiple (at least two) links. To realize such multilink, for example, the multihoming technology implemented by the aforementioned MPTCP (Multipath TCP) can be used.

[0041] 4 and 5 show a case where base station BS1 is located on the left side of the movement path of terminal MT, and base stations BS2 and BS3 are located on the right side of the movement path of terminal MT. In other words, base station BS1, which is disconnected by link switching, is located on the opposite side of the movement path of terminal MT from base station BS2, which remains connected, and base station BS3, which is newly connected by link switching. Hereinafter, this case will be referred to as "Case 3."

[0042] Fig. 4 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 5 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0043] The wireless communication system 1 of this embodiment sets a predetermined direction as a reference direction when identifying the position of the terminal MT. In Figures 4 and 5, as an example, the direction of movement of the terminal MT is set as the reference direction.

[0044] As shown in FIG. 4, 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 4, 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 This angle θ' １ and angle 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. 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.

[0045] Similarly, as shown in FIG. 5, 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 5, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0046] 6 and 7 show a case where base station BS2 is located on the left side of the movement path of terminal MT, and base stations BS1 and BS3 are located on the right side of the movement path of terminal MT. In other words, the base station BS2 that continues to be connected is located on the opposite side of the movement path of terminal MT from the base station BS1 that is disconnected by link switching and the base station BS3 that is newly connected by link switching. Hereinafter, this case will be referred to as "Case 0."

[0047] Fig. 6 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 7 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0048] The wireless communication system 1 of this embodiment sets a predetermined direction as a reference direction when identifying the position of the terminal MT. In Figures 6 and 7, as an example, the direction of movement of the terminal MT is set as the reference direction.

[0049] As shown in FIG. 6, 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 6, 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 This angle θ' １ and angle 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. 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.

[0050] Similarly, as shown in FIG. 7, 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 １7, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0051] Furthermore, although not shown, there may be a case where, for example, base station BS3 is located on the left side of the movement path of terminal MT, and base stations BS1 and BS2 are located on the right side of the movement path of terminal MT. In other words, there may be a case where base station BS3, which is newly connected by link switching, is located on the opposite side of the movement path of terminal MT from base station BS1, which is disconnected by link switching, and base station BS2, which remains connected. Hereinafter, this case will be referred to as "Case 2."

[0052] As described above, the wireless communication system 1 in this embodiment uses the direction (angle θ １ ) and the direction of the terminal MT at the position of the base station BS2 (angle θ ２ In this configuration, the location of the terminal MT is identified by focusing on the value of (value of) . In this case 2, base station BS1 and base station BS2 are on the same side (for example, both are on the right side) of the direction of movement (direction of travel) of the terminal MT. In other words, case 2 is common to case 1 in that the two base stations BS connected to the terminal MT before the link switching are on the same side of the movement path of the terminal MT. For this reason, it can be said that the characteristics of case 2 in identifying the location of the terminal MT are substantially the same as the characteristics of case 1. For this reason, illustration of case 2 is omitted here.

[0053] The characteristics of the above cases 0 to 3 are summarized in a table as shown in Figure 8. Figure 8 is a diagram showing the characteristics for each positional relationship of multiple base stations BS with respect to the movement route of the terminal MT. Figure 8 shows the trends in the changes in the values ​​of five parameters for each case. As shown in Figure 8, the five parameters are categorized into "reception level" and "angle."

[0054] The reception level parameter is "R ＢＳ１ " and "R ＢＳ２ " is included. ＢＳ１ is the reception level of the signal transmitted from the terminal MT at the base station BS1. ＢＳ２ is the reception level at base station BS2 of the signal transmitted from terminal MT.

[0055] The angle parameter is "θ １ " and "θ ２ " and "θ ３ As shown in FIGS. 3, 5, and 7, the angle θ １ , angle θ ２ , and angle θ ３ are the angle between the reference direction and the direction of terminal MT at the position of base station BS1, the angle between the reference direction and the direction of terminal MT at the position of base station BS2, and the angle between the reference direction and the direction of terminal MT at the position of base station BS3, respectively.

[0056] In the table shown in FIG. 8, the reception level R ＢＳ１ In the parameter column, a downward arrow is shown for all cases from case 0 to case 3. This is because the reception level R ＢＳ１ This shows that the value of the reception level R tends to decrease. This is because in all cases from Case 0 to Case 3, the terminal MT moves away from the base station BS1. Therefore, basically, the reception level R ＢＳ１ The value of tends to decrease monotonically.

[0057] In addition, in the table shown in FIG. ＢＳ２In the parameter column, an upward arrow is shown for all cases from case 0 to case 3. This indicates that the reception level R ＢＳ２ This shows that the value of R tends to increase. This is because in all cases from Case 0 to Case 3, the terminal MT moves closer to the base station BS2. Therefore, basically, the value of R increases as the terminal MT moves. ＢＳ２ The value of tends to increase monotonically.

[0058] In addition, in the table shown in FIG. １ In the parameter column, a downward arrow is shown for all cases from Case 0 to Case 3. This is because the angle θ １ As can be seen from FIGS. 2 to 7, in all of Cases 0 to 3, the value of θ' tends to decrease. １ >θ １ and the angle θ １ The value of tends to decrease.

[0059] In addition, in the table shown in FIG. ２ In the parameter column, a downward arrow is shown for all cases from Case 0 to Case 3. This is because the angle θ ２ As can be seen from FIGS. 2 to 7, in all of Cases 0 to 3, the value of θ' tends to decrease. ２ >θ ２ and the angle θ ２ The value of tends to decrease.

[0060] As shown in FIG. 8, the angle θ ３ The values ​​of the parameters are unknown until measurements are made after the terminal MT has moved into the switching start range r. Therefore, in the table shown in FIG. 8, the angle θ ３ The trend of change in the value of is not shown.

[0061] In this way, the angle θ １ and the angle θ２ The value of the angle θ tends to decrease as the terminal MT moves. １ and the angle θ ２ By focusing on the change in the value of , it becomes possible to identify the timing at which the terminal MT enters the switching start range r. This makes it possible to start link switching at the timing at which the terminal MT enters the switching start range r.

[0062] [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.

[0063] 9 to 12 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 9 to 12 show the time-series changes in the communication connection state when switching links.

[0064] 9 to 12 respectively show base station BS1, base station BS2, base station BS3, and terminal MT. Also, in Fig. 9 to 12, 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. 9 to 12, 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.

[0065] 9 to 12, 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.

[0066] 9 to 12, the switching start range r is shown as a (shaded) oval. As shown in Fig. 9 to 12, the switching start range r is set at a position within the overlapping area d, closer to the base station BS1 side. The reason why the switching start range r is set at such a position will be explained below.

[0067] 1 (1) to (4), Figures 9 to 12 show terminal MT moving from a position closer to base station BS1 (left side of the figure), passing through 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.

[0068] 9 shows a 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 FIGS. 9 to 12, 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.

[0069] Figure 10 shows the state in Figure 9 where terminal MT enters within switching start range r, initiating link switching from base station BS1 to base station BS3. In Figure 10, 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 10 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 9 and 10, 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 9) until the execution of link switching begins (Figure 10).

[0070] 11 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, terminal MT is still located within overlap area d, so the link between base station BS1 and terminal MT is also still established. That is, in FIG. 11, terminal MT is able to communicate with all of base stations BS1, BS2, and BS3 (i.e., with three base stations BS).

[0071] 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. 11, 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.

[0072] 12 shows a state in which the link between base station BS1 and terminal MT is disconnected. As shown in FIG. 12, terminal MT soon moves to a position where it will soon leave overlap area d (the right edge of overlap area d).

[0073] 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.

[0074] 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.

[0075] 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.

[0076] [Overall Configuration of Wireless Communication System] The following describes the overall configuration of the wireless communication system 1. Fig. 13 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. 13, 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).

[0077] 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.

[0078] 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. 13). The base station BS relays communications between a higher-level device (not shown in FIG. 13) 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.

[0079] [Configuration of communication control device] The following describes the configuration of the communication control device 10. Fig. 14 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. 14, the communication control device 10 includes a detection unit 11, a storage unit 12, and an execution control unit 13.

[0080] 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. 14, 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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 angle θ １ , angle θ ２ , angle θ' １ , angle θ' ２ Identify the following:

[0085] 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 specified above (for example, the above-mentioned angle θ １ and angle θ ２ , or angle θ' １ and angle θ' ２ etc.), the location of the terminal MT is calculated using, for example, the AoA technology described above.

[0086] Alternatively, the terminal position calculation unit 112 acquires reference direction information stored in advance in the storage unit 12. The movement route information here is information indicating a predetermined movement route of the terminal MT. The terminal position calculation unit 112 calculates the movement route of the terminal MT and the angle formed between the reference direction and the direction of the terminal MT at the position of one base station BS (for example, angle θ １ , angle θ ２ , angle θ' １ , angle θ' ２ The position of the terminal MT is calculated based on the above.

[0087] 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.

[0088] 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.

[0089] 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, in this case, 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 base stations BS to be controlled so as to disconnect one of the links established between this terminal MT and each of the multiple base stations BS.

[0090] As described above, the decision as to which base station BS to establish a new link with and which base station BS to disconnect among the multiple existing links is made based on the switching start range r that includes the position of the terminal MT. That is, since the switching start range r is set in advance for each combination of two base stations BS as shown in Figures 9 to 12, the switching execution decision unit 113 can uniquely identify which base station BS to establish a new link with and which base station BS to disconnect among the multiple existing links.

[0091] For example, the switching start range r shown in Figures 9 to 12 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 9 to 12, 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.

[0092] 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 into consideration. For example, in the situation illustrated in Figures 9 to 12, 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 base station BS1 to a position closer to base station BS3 and detects that the terminal MT has entered a switching start range r.

[0093] If the location of the terminal MT is not included in the switching start range r, the switching execution determination unit 113 determines not to execute link switching.

[0094] When the switching execution decision unit 113 decides to execute link switching, it outputs to the execution control unit 13 information identifying the base station BS (i.e., base station BS1) that will cut off the link, information identifying the base station BS (i.e., base station BS3) that will newly establish a link, information identifying the terminal MT, and the like.

[0095] The storage unit 12 stores various data and programs. For example, the storage unit 12 stores the above-mentioned reference direction information, movement route information, and switching start range information in advance. The storage unit 12 may also store various programs for operating each functional unit of the communication control device 10.

[0096] As shown in FIG. 14, 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 .

[0097] The link connection instruction unit 131 acquires information identifying the base station BS (i.e., base station BS3) with 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 with which a link is to be newly established, instructing it to establish a link with the terminal MT.

[0098] For example, in the situation illustrated in Figures 9 to 12, the link connection instruction unit 131 sends 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 9 to 11).

[0099] The connection completion report receiving unit 132 receives a connection completion report indicating that a link with the terminal MT has been established from the base station BS that will newly establish a link. For example, in the situations illustrated in Figures 9 to 12, the connection completion report receiving unit 132 receives a connection completion report from base station BS3. When the connection completion report receiving unit 132 receives the connection completion report, it notifies the link disconnection instruction unit 133.

[0100] The link disconnection instruction unit 133 acquires information identifying the base station BS (i.e., base station BS1) that is to have the link disconnected and information identifying the terminal MT, which are output from the switching execution determination unit 113 of the detection unit 11. Furthermore, the link disconnection instruction unit 133 receives a notification indicating that a connection completion report has been received from the connection completion report receiving unit 132. When receiving this notification, the link disconnection instruction unit 133 transmits link disconnection instruction information to the base station BS that is to have the link disconnected, the link disconnection instruction information instructing the base station BS that is to have the link disconnected to disconnect the link with the terminal MT.

[0101] For example, in the situation illustrated in Figures 9 to 12, 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 12).

[0102] 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.

[0103] 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.

[0104] [Operation of communication control device] An example of the operation of the communication control device 10 will be described below. Fig. 15 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. 15 is periodically started at a predetermined interval (for example, every 1 to 10 seconds).

[0105] 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.

[0106] 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).

[0107] 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 angle θ １ and angle θ ２ , or angle θ' １ and angle θ' ２ etc.) are identified (step S003).

[0108] 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.

[0109] Alternatively, the terminal position calculation unit 112 may calculate the angle between the reference direction and the direction of the terminal MT at the position of one base station BS (for example, the above-mentioned angle θ １ , angle θ ２ , angle θ' １ , angle θ' ２ In addition, the terminal position calculation unit 112 acquires travel route information stored in advance in the storage unit 12, for example.

[0110] Next, the terminal position calculation unit 112 calculates the position of the terminal MT based on the movement route of the terminal MT indicated by the movement route information and the angle formed between the reference direction and the direction of the terminal MT at the position of one base station BS specified 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.

[0111] 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).

[0112] Next, the switching execution determination unit 113 determines whether the location of the terminal MT based on the acquired location information is included in the switching start range r based on the switching start range information (step S006). If the location of the terminal MT is not included in 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. 15.

[0113] 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, to the execution control unit 13, information identifying the base station BS to disconnect the link (i.e., base station BS1), information identifying the base station BS to newly establish a link (i.e., base station BS3), information identifying the terminal MT, and the like.

[0114] The link connection instruction unit 131 acquires information identifying the base station BS with 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 with which a link is to be newly established (i.e., base station BS3), instructing it to establish a link with the terminal MT (step S007).

[0115] 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.

[0116] The link disconnection instruction unit 133 acquires information identifying the base station BS whose link is to be disconnected and information identifying the terminal MT, output from the switching execution determination unit 113 of the detection unit 11. The link disconnection instruction unit 133 receives a notification indicating that a connection completion report has been received from the connection completion report receiving unit 132. Upon receiving this notification, the link disconnection instruction unit 133 transmits link disconnection instruction information to the base station BS whose link is to be disconnected (i.e., base station BS1) instructing it to disconnect the link with the terminal MT (step S009). This completes the operation of the communication control device 10 shown in the flowchart of FIG. 15.

[0117] 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 controls and executes 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. 2 to 7) and a second base station (e.g., base station BS2 illustrated in FIGS. 2 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. 2 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.

[0118] Alternatively, 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 Figures 2 to 7) and a second base station (e.g., base station BS2 illustrated in Figures 2 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 2 to 7) based on a predetermined movement path of the terminal MT and the direction of the terminal MT as seen from the first base station or the direction of the terminal MT as seen from the second base station (i.e., the direction of the terminal MT as seen from one base station BS).

[0119] 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.

[0120] 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 MT can communicate with the base station BS via multiple links (multi-link), including when link switching is being performed. As a result, the wireless communication system 1 can suppress communication disconnections, even when an unexpected communication failure or the like occurs, including when link switching is being performed.

[0121] 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.

[0122] 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.

[0123] In the first embodiment described above, the switching start range r is set based on an overlapping area d, which is an area where the range of the cell of base station BS1, which will be disconnected from the terminal MT, overlaps with the range of the cell of base station BS3, which will be newly connected to the terminal MT (a link will be established). More specifically, as shown in Figures 9 to 12, the switching start range r is set at a position within the overlapping area d, closer to the base station BS1.

[0124] In this way, in order to prevent a decrease in throughput and communication disconnection during link switching, the wireless communication system 1 in the first embodiment described above sets the switching start range r to a range within which communication is possible with both the base station BS1 whose communication connection is being disconnected and the base station BS3 that will newly connect to the terminal MT. That is, in the first embodiment described above, link switching is initiated simply based on the fact that the location of the terminal MT is within the ranges of the cells of both of the two base stations BS (within a predetermined range of the overlapping area d).

[0125] However, in many actual communication environments, there may be many other terminals MT in the vicinity of the movement route of the terminal MT. If information about the communication environment can be obtained from such other terminals MT, it may be possible to set a more appropriate switching start range r. The information about the communication environment here refers to, for example, information indicating the communication status, such as the received signal strength indicator (RSSI) of the signal received at the terminal MT from the base station BS.

[0126] A wireless communication system 1a in a second embodiment described below is configured to acquire information about the communication environment from multiple other terminals MT present in the vicinity of the movement route of a terminal MT, and generate a propagation map of radio waves from a base station BS. The wireless communication system 1a sets a switching start range r based on the generated propagation map.

[0127] [Switching Start Range Setting Procedure] The following describes the procedure by which the wireless communication system 1a of this embodiment sets the switching start range r. Figures 16 to 19 are diagrams for explaining the procedure by which the wireless communication system 1 of the second embodiment of the present invention sets the switching start range r. Note that this embodiment assumes that the terminal MT moves in a straight line. In Figures 16 to 19, the terminal MT moves in a straight line from the left to the right in each figure.

[0128] 16 to 19, the case where base station BS2 is located on the left side of the movement path of terminal MT and base stations BS1 and BS3 are located on the right side of the movement path of terminal MT will be described as an example. That is, the case where base station BS2, which continues to be connected, is located on the opposite side of the movement path of terminal MT from base station BS1, which is disconnected by link switching, and base station BS3, which is newly connected by link switching, will be described as the above-mentioned "Case 0."

[0129] As shown in FIG. 16, there are n other terminals (terminals MT, １ ~ Terminal MT ｎA communication control device in the second embodiment (hereinafter referred to as "communication control device 10a") collects information about the communication environment between the terminal MT and the base station BS from each of a plurality of other terminals MT present in the vicinity of the movement route of the terminal MT.

[0130] More specifically, the communication control device 10a collects, for example, from each of a plurality of other terminals MT present in the vicinity of the movement path of the terminal MT, a measurement value of the received signal strength (RSSI) of the signal received from base station BS1. The communication control device 10a also collects, for example, from each of a plurality of other terminals MT present in the vicinity of the movement path of the terminal MT, a measurement value of the received signal strength (RSSI) of the signal received from base station BS3.

[0131] The communication control device 10a then generates a propagation map of radio waves transmitted from base station BS1 using the collected measured values ​​of received signal strength indicator (RSSI) of signals received from base station BS1. The communication control device 10a also generates a propagation map of radio waves transmitted from base station BS3 using the collected measured values ​​of received signal strength indicator (RSSI) of signals received from base station BS3. The communication control device 10a sets an appropriate switching start range r based on the two generated propagation maps.

[0132] Fig. 17 is a diagram showing an example of a propagation map of radio waves transmitted from base station BS1, generated by the communication control device 10a. In contrast to Fig. 16, Fig. 17 adds seven additional curves, labeled (a) to (g). These curves are lines connecting positions where the received signal strength indicator (RSSI) values ​​of the received signal from base station BS1 are estimated to be the same.

[0133] 17, (a) is the curve closest to base station BS1, and (g) is the curve farthest from base station BS1. Therefore, among (a) to (g), the position where curve (a) passes through has the strongest received signal strength (RSSI), and the positions where curves (b) and on pass through have the weakest received signal strength (RSSI), and the position where curve (g) passes through has the weakest received signal strength (RSSI).

[0134] 18 is a diagram showing an example of a propagation map of radio waves transmitted from base station BS3, generated by the communication control device 10a. In comparison with the aforementioned FIG. 16, seven additional curves labeled (a) to (g) are added in FIG. 18. These curves are lines connecting positions where the received signal strength indicator (RSSI) values ​​of the received signal from base station BS3 are estimated to be the same.

[0135] 18, (a) is the curve closest to base station BS3, and (g) is the curve farthest from base station BS3. Therefore, among (a) to (g), the position where curve (a) passes through has the strongest received signal strength (RSSI), and the positions where curves (b) and on pass through have the weakest received signal strength (RSSI), with the position where curve (g) passes having the weakest received signal strength (RSSI).

[0136] The communication control device 10a sets an appropriate switching start range r based on the two propagation maps shown in Figures 17 and 18. Here, the appropriate switching start range r is, for example, an area on the movement path of the terminal MT where the smaller of the received signal strength indicator (RSSI) values ​​of the radio waves from base station BS1 and the received signal strength indicator (RSSI) values ​​of the radio waves from base station BS3 is maximized. By setting the switching start range r in this manner, the terminal MT can receive signals from both base station BS1 and base station BS3 with a relatively strong received signal strength (RSSI) when switching links. This makes it possible to suppress a decrease in throughput and the occurrence of communication disconnections when switching links.

[0137] Fig. 19 is a diagram showing a switching start range r set based on the two generated propagation maps. Fig. 19 shows, as an example, a case where the switching start range r is set to a range around the movement path of the terminal MT and surrounded by the curve (e) of the propagation map shown in Fig. 17 and the curve (e) of the propagation map shown in Fig. 18.

[0138] More specifically, as shown in Fig. 19, the switching start range r is shown as a (shaded) oval located closer to base station BS1 within the area surrounded by the curve (e) of the propagation map shown in Fig. 17 and the curve (e) of the propagation map shown in Fig. 18 (hereinafter referred to as the "overlap area at curve (e)"). The reason why the switching start range r is set at such a position is the same as the reason why the switching start range r is set at a position closer to base station BS1 within the overlap area d, as explained in the first embodiment with reference to Figs. 9 to 12.

[0139] That is, the reason why the switching start range r is set closer to base station BS1 within the overlapping area of ​​curve (e) is that in order to perform link switching in the order of establishing a link between base station BS3 and terminal MT and then disconnecting the link between base station BS1 and terminal MT, it is desirable for the wireless communication system 1a to carry out link switching from start to completion while the moving terminal MT is still within the overlapping area of ​​curve (e).

[0140] By setting the switching start range r closer to base station BS1 within the overlapping area of ​​the curve (e), link switching begins as soon as the terminal MT enters the overlapping area of ​​the curve (e). Furthermore, by setting the switching start range r closer to base station BS1 within the overlapping area of ​​the curve (e), even if the terminal MT is moving closer to base station BS3, the time that the terminal MT remains within the overlapping area of ​​the curve (e) can be ensured to be longer. This allows the wireless communication system 1a 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.

[0141] The switching start range r may be the same range as the overlapping region of the curve (e). In that 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 (for example, in real time) and a mechanism for transmitting control signals for controlling link switching without delay are required.

[0142] As an example, the information about the communication environment collected by the communication control device 10a from multiple other terminals MT present in the vicinity of the movement path of the terminal MT is assumed to be a measured value of received signal strength indicator (RSSI). However, the information about the communication environment collected by the communication control device 10a is not limited to this. For example, instead of the measured value of received signal strength indicator (RSSI), the information about the communication environment collected by the communication control device 10a may be other information representing the communication state, such as a signal-to-noise ratio (S / N ratio), reliability (Throughput), a bit error rate (BER), a packet error rate (PER), or a symbol error rate (SER).

[0143] The information about the communication environment that the communication control device 10a collects from multiple other terminals MT that exist in the vicinity of the movement route of the terminal MT is not limited to information collected in real time, but may be information collected in the past. For example, if the communication environment changes periodically, information about the communication environment may be collected at an appropriate timing according to the period.

[0144] For example, if the communication environment changes every day, the communication control device 10a may generate a propagation map based on information about the communication environment collected during the same time period on a previous day. For example, when generating a radio wave propagation map at 10:00 a.m., the communication control device 10a may collect information such as received signal strength indicator (RSSI) measured around 10:00 a.m. on a previous day to generate the propagation map.

[0145] Alternatively, for example, if the communication environment changes every year, the communication control device 10a may generate a propagation map based on information about the communication environment collected on the same day (or in the same season) of a previous year. For example, when generating a radio wave propagation map for August, the communication control device 10a may collect information such as received signal strength indicator (RSSI) measured in August of a previous year to generate the propagation map. Note that a configuration for generating a propagation map based on information about the communication environment collected in the past will also be described in a fourth embodiment, which will be described later.

[0146] In addition, for example, when there is no periodicity in the changes in the communication environment, it is desirable to generate a propagation map based on the most recently collected information on the communication environment. For example, in a case where a terminal MT carried by a user in a car traveling on a highway is connected to a base station BS installed on the roof or wall of a building along the highway (i.e., the travel path of the terminal MT), the propagation map may be generated based on information collected from the terminals MT carried by users in other cars traveling up to several cars ahead in the same lane.

[0147] As described above, the wireless communication system 1a according to the second embodiment of the present invention acquires information about the communication environment from multiple other terminals MT present in the vicinity of the movement route of the terminal MT, and generates a propagation map of radio waves from the base station BS. The wireless communication system 1a then sets the switching start range r based on the generated propagation map. With this configuration, the wireless communication system 1a according to the second embodiment can set an appropriate switching start range r that makes it less likely for communication disconnections to occur.

[0148] Similarly to the wireless communication system 1 in the first embodiment, the wireless communication system 1a in the second embodiment of the present invention includes at least three base stations BS and a communication control device 10a that executes and controls link switching between each of these base stations BS and a terminal MT. The communication control device 10a identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1) and a second base station (e.g., base station BS2) and is moving away from the first base station and approaching a third base station (e.g., base station BS3) 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.

[0149] Alternatively, the communication control device 10a identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1) and a second base station (e.g., base station BS2) and is moving away from the first base station and approaching a third base station (e.g., base station BS3) based on a predetermined movement path of the terminal MT and the direction of the terminal MT as seen from the first base station or the direction of the terminal MT as seen from the second base station (i.e., the direction of the terminal MT as seen from one base station BS).

[0150] 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 of the first base station and the connectable range of the third base station, the communication control device 10a starts control of link switching. First, the communication control device 10a 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 10a disconnects the existing link between the terminal MT and the first base station, which are moving away from each other.

[0151] 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. That is, the wireless communication system 1a according to the second 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 (multi-link), including when link switching is being performed. As a result, the wireless communication system 1a can suppress communication disconnections, even when an unexpected communication failure occurs, including when link switching is being performed.

[0152] 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.

[0153] (Modification of Second Embodiment) A wireless communication system 1b according to a modification of the second embodiment of the present invention will be described below. The wireless communication system 1b described below is an example of a communication control system of the present invention.

[0154] In many actual communication environments, there may be obstacles that block radio waves or radio waves of the same frequency that cause interference in the vicinity. In this case, even if the terminal MT is within the range of both the cell of the base station BS1 whose communication connection is being cut off and the cell of the base station BS3 that will newly connect to the terminal MT, there is a possibility that throughput will decrease and communication will be cut off during link switching due to radio wave blockage or interference. In the following modified example of the second embodiment, a method for setting an appropriate switching start range r even in a communication environment where radio wave blockage or interference occurs will be described.

[0155] [Switching Start Range Setting Procedure] The following describes the procedure by which the wireless communication system 1b of this modified example sets the switching start range r. Figures 20 to 23 are diagrams for explaining the procedure by which the wireless communication system 1b of this modified example sets the switching start range r in the wireless communication system 1 of the modified example of the second embodiment of the present invention. Note that this modified example also assumes that the terminal MT moves in a straight line. In Figures 20 to 23, the terminal MT moves in a straight line from the left side to the right side of each figure.

[0156] 20 to 23, the case where base station BS2 is located on the left side of the movement path of terminal MT and base stations BS1 and BS3 are located on the right side of the movement path of terminal MT will be described as an example. That is, the case where base station BS2, which continues to be connected, is located on the opposite side of the movement path of terminal MT from base station BS1, which is disconnected by link switching, and base station BS3, which is newly connected by link switching, will be described as the above-mentioned "Case 0."

[0157] As shown in FIG. 20, there are n other terminals (terminals MT, １ ~ Terminal MT ｎ A communication control device in a modified example of the second embodiment (hereinafter referred to as "communication control device 10b") collects information about the communication environment between the terminal MT and the base station BS from each of a plurality of other terminals MT present in the vicinity of the movement route of the terminal MT.

[0158] More specifically, the communication control device 10b collects, for example, from each of a plurality of other terminals MT present in the vicinity of the movement path of the terminal MT, a measurement value of the received signal strength (RSSI) of the signal received from base station BS1. The communication control device 10b also collects, for example, from each of a plurality of other terminals MT present in the vicinity of the movement path of the terminal MT, a measurement value of the received signal strength (RSSI) of the signal received from base station BS3.

[0159] Then, the communication control device 10b generates a propagation map of radio waves transmitted from base station BS1 using the collected measured values ​​of received signal strength indicator (RSSI) of signals received from base station BS1. The communication control device 10b also generates a propagation map of radio waves transmitted from base station BS3 using the collected measured values ​​of received signal strength indicator (RSSI) of signals received from base station BS3. The communication control device 10b sets an appropriate switching start range r based on the two generated propagation maps.

[0160] This modification also assumes the presence of an obstacle blocking radio waves near the movement path of terminal MT. As shown in FIGS. 20 to 23, an obstacle s is present on the right side of the movement path of terminal MT. The communication control device 10b in this modification sets an appropriate switching start range r, taking into account the blocking of radio waves by the obstacle s. Note that, while a case where radio waves are blocked by the obstacle s will be described as an example here, the basic concept is the same even in a communication environment where radio wave interference occurs due to the presence of radio waves of the same frequency in the vicinity.

[0161] Figure 21 is a diagram showing an example of a propagation map of radio waves transmitted from base station BS1, generated by the communication control device 10b. In comparison with Figure 20, Figure 21 adds seven additional curves, labeled (a) to (g). These curves are lines connecting positions where the received signal strength indicator (RSSI) values ​​of the received signal from base station BS1 are estimated to be the same.

[0162] 21, (a) is the curve closest to base station BS1, and (g) is the curve farthest from base station BS1. Therefore, among (a) to (g), the position where curve (a) passes through has the strongest received signal strength (RSSI), and the positions where curves (b) and on pass through have the weakest received signal strength (RSSI), and the position where curve (g) passes through has the weakest received signal strength (RSSI).

[0163] However, as can be seen by comparing the propagation map with that of the second embodiment shown in Figure 17 described above, in the propagation map of this modified example shown in Figure 21, the area shaded by obstacle s is an area where the received signal strength is extremely weak because radio waves are blocked by obstacle s.

[0164] 22 is a diagram showing an example of a propagation map of radio waves transmitted from base station BS3, generated by the communication control device 10b. In addition to the aforementioned FIG. 20, seven additional curves labeled (a) to (g) are added in FIG. 22. These curves are lines connecting positions where the received signal strength indicator (RSSI) values ​​of the received signal from base station BS3 are estimated to be the same.

[0165] 22, (a) is the curve closest to base station BS3, and (g) is the curve farthest from base station BS3. Therefore, among (a) to (g), the position where curve (a) passes through has the strongest received signal strength (RSSI), and the positions where curves (b) and on pass through have the weakest received signal strength (RSSI), with the position where curve (g) passes having the weakest received signal strength (RSSI).

[0166] However, as can be seen by comparing the propagation map with that of the second embodiment shown in Figure 18 described above, in the propagation map of this modified example shown in Figure 22, the area shaded by obstacle s is an area where the received signal strength is extremely weak because radio waves are blocked by obstacle s.

[0167] The communication control device 10b sets an appropriate switching start range r based on the two propagation maps shown in Figures 21 and 22. Here, as described above, the appropriate switching start range r is, for example, a region on the movement path of the terminal MT where the smaller of the received signal strength indicator (RSSI) values ​​of the radio waves from base station BS1 and the received signal strength indicator (RSSI) values ​​of the radio waves from base station BS3 is maximized. By setting the switching start range r in this manner, the terminal MT can receive signals from both base station BS1 and base station BS3 with a relatively strong received signal strength (RSSI) when switching links. This makes it possible to suppress a decrease in throughput and communication interruptions when switching links.

[0168] Fig. 23 is a diagram showing a switching start range r set based on the two generated propagation maps. Fig. 23 shows, as an example, a case where a range that is a periphery of the movement path of terminal MT and is surrounded by the curve (e) of the propagation map in Fig. 21 and the curve (e) of the propagation map in Fig. 22 is set as the switching start range r.

[0169] More specifically, as shown in Fig. 23, the switching start range r is shown as a (shaded) oval located closer to base station BS1 within the "overlap area at curve (e)," which is the area surrounded by the curve (e) on the propagation map shown in Fig. 21 and the curve (e) on the propagation map shown in Fig. 23. The reason why the switching start range r is set at such a position is the same as the reason why the switching start range r is set at a position closer to base station BS1 within the overlap area d, which was described in the first embodiment with reference to Figs. 9 to 12.

[0170] That is, the reason why the switching start range r is set closer to base station BS1 within the overlapping area of ​​curve (e) is that in order to perform link switching in the order of establishing a link between base station BS3 and terminal MT and then disconnecting the link between base station BS1 and terminal MT, it is desirable for the wireless communication system 1b to carry out link switching from start to completion while the moving terminal MT is still within the overlapping area of ​​curve (e).

[0171] By setting the switching start range r closer to base station BS1 within the overlapping area of ​​the curve (e), link switching begins as soon as the terminal MT enters the overlapping area of ​​the curve (e). Furthermore, by setting the switching start range r closer to base station BS1 within the overlapping area of ​​the curve (e), even if the terminal MT is moving closer to base station BS3, the time that the terminal MT remains within the overlapping area of ​​the curve (e) can be ensured to be longer. This allows the wireless communication system 1b in this modified example to prevent the terminal MT from falling into an unstable state in which only one link (with base station BS2) is established.

[0172] The switching start range r may be the same range as the overlapping region of the curve (e). In that 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 (for example, in real time) and a mechanism for transmitting control signals for controlling link switching without delay are required.

[0173] However, the switching start range r set by the communication control device 10b in this modified example takes into account the possibility of radio wave blocking by obstacles s, and therefore is in a different position from the switching start range r set in the second embodiment shown in Figure 19 above.

[0174] As an example, the information about the communication environment collected by the communication control device 10b from multiple other terminals MT present in the vicinity of the movement path of the terminal MT is assumed to be a measured value of received signal strength indicator (RSSI). However, the information about the communication environment collected by the communication control device 10b is not limited to this. For example, instead of a measured value of received signal strength indicator (RSSI), the information about the communication environment collected by the communication control device 10b may be other information representing the communication state, such as a signal-to-noise ratio (S / N ratio), reliability (Throughput), bit error rate (BER), packet error rate (PER), or symbol error rate (SER).

[0175] The information about the communication environment that the communication control device 10b collects from multiple other terminals MT that exist in the vicinity of the movement route of the terminal MT is not limited to information collected in real time, but may be information collected in the past. For example, if the communication environment changes periodically, information about the communication environment may be collected at an appropriate timing according to the period.

[0176] For example, if the communication environment changes every day, the communication control device 10b may generate a propagation map based on information about the communication environment collected during the same time period on a previous day. Alternatively, if the communication environment changes every year, the communication control device 10b may generate a propagation map based on information about the communication environment collected on the same day (or in the same season) on a previous year. Note that, for example, if the communication environment does not change periodically, it is desirable to generate a propagation map based on information about the communication environment collected more recently.

[0177] Third Embodiment A wireless communication system 1c according to a third embodiment of the present invention will be described below. The wireless communication system 1c described below is an example of a communication control system according to the present invention.

[0178] In the first and second embodiments described above, it is assumed that the terminal MT moves in a straight line (i.e., the movement path of the terminal MT is straight). However, in reality, the movement path of the terminal MT is not always straight, and is often a curved path. In the third embodiment described below, it is assumed that the movement path of the terminal MT is curved.

[0179] [Procedure for Identifying Terminal Location] As in the above-described embodiments, in this embodiment, 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 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 location of the terminal MT will be described.

[0180] 24 to 39 are diagrams illustrating the procedure for identifying the location of a terminal MT by a wireless communication system 1c according to a third embodiment of the present invention. As described above, this embodiment assumes that the terminal MT moves along a curved path. In FIGS. 24 to 39, the terminal MT moves along the path from left to right in each diagram. As in the previous sections, in the following description, the right side of the direction of movement (direction of travel) of the terminal MT will be referred to as the "right side of the path of travel," and the left side of the direction of movement (direction of travel) of the terminal MT will be referred to as the "left side of the path of travel."

[0181] Figures 24 and 25 show a case where base station BS1, base station BS2, and base station BS3 are all located on the right side of the movement path of terminal MT. In other words, this is a case where all base stations BS are located on one side of the movement path of terminal MT. Figures 24 and 25 also show a case where the side where all base stations BS are located is the valley side of the curved movement path of terminal MT. In other words, this is a case where all base stations BS are located on the valley side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 1+".

[0182] Fig. 24 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 25 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0183] In the first embodiment, the second embodiment, and the modified examples thereof, the wireless communication systems 1, 1a, and 1b are configured to set a predetermined direction as a reference direction when identifying the position of the terminal MT. More specifically, in the first embodiment, the second embodiment, and the modified examples thereof, the reference direction is, for example, the direction of movement of the terminal MT (i.e., the direction from left to right in each drawing).

[0184] On the other hand, in a wireless communication system 1c according to a third embodiment described below, when identifying the position of a terminal MT, the direction of a base station BS (i.e., base station BS3) that will newly establish a communication connection is set as the reference direction. More specifically, when identifying the direction of the terminal MT at base station BS1, the direction of the terminal MT is identified by setting the direction of base station BS3 at base station BS1 as an angle relative to the reference direction. Furthermore, when identifying the direction of the terminal MT at base station BS2, the direction of the terminal MT is identified by setting the direction of base station BS3 at base station BS2 as an angle relative to the reference direction.

[0185] In this embodiment, the reason why the direction of the new base station BS (i.e., base station BS3) is set as the reference direction is because the moving path of the terminal MT is curved. Specifically, because the moving path of the terminal MT is curved, the moving direction of the terminal MT changes over time and the moving direction of the terminal MT cannot be uniquely determined, so the moving direction of the MT cannot be set as the reference direction.

[0186] Therefore, in this embodiment, from the viewpoint of switching the link from base station BS1 to base station BS3, the direction of base station BS3 in base station BS1 is set as the reference direction until the link switching is performed. Also, since it is assumed that the terminal MT moves along a movement path that moves away from the base station BS (i.e., base station BS1) whose communication connection is cut off and approaches the base station BS (i.e., base station BS3) with which the terminal MT will newly connect, the reference direction determined in this way is a direction that roughly follows the movement direction of the terminal MT.

[0187] It is assumed here that the positions of all base stations BS, including base station BS1 and base station BS3, are known, and therefore the reference direction can be easily identified.

[0188] In this way, when determining the position of terminal MT, the advantages of using a method of setting the direction of the new base station BS (i.e., base station BS3) that will establish a communication connection with terminal MT as the reference direction include the fact that even if the movement path of terminal MT is curved, a certain degree of similarity between the movement direction of terminal MT and the reference direction is maintained, and the fact that the reference direction can be easily determined.

[0189] As shown in FIG. 24, 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 θ′. １ 24, 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 This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0190] As shown in FIG. 24, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ'. ３１ 24, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0191] Similarly, as shown in FIG. 25, 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 25, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0192] As shown in FIG. 25, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 25, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0193] In FIG. 24, which shows an example, the angles are θ′ １ = 61°, θ' ２ = 127°, θ' ３１ =-12°, θ' ３２ In addition, in FIG. 25 shown as an example, the angles are θ １ = 38°, θ ２= 95°, θ ３１ =-22°, θ ３２ =-37°.

[0194] In addition, the angle θ' １ and angle θ' ２ and a method for identifying the position of the terminal MT from the value of the angle θ １ and angle θ ２ As a method for identifying the location of the terminal MT from the value of , for example, the AoA technology described above can be used. Note 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 location of the terminal MT more accurately. 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 the location of the terminal MT may be identified using any other technology.

[0195] As described above, in each embodiment of the present invention, it is assumed that the movement route of the terminal MT is known. Therefore, in identifying the position of the terminal MT, it is not necessary to know the direction (angle θ') of the terminal MT at the positions of multiple base stations BS. １ and angle θ' ２ , or angle θ １ and angle θ ２ ) does not need to be specified based on the movement path of the terminal MT and the direction (one direction) of the terminal MT at the position of any one base station BS (more specifically, the movement path of the terminal MT and the angle θ' １ or angle θ' ２ or based on the value of the movement path of the terminal MT and the angle θ １ or angle θ ２ However, by specifying the directions of the terminal MT at the positions of a plurality of base stations BS, the accuracy of estimating the position of the terminal MT can be further improved.

[0196] 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.

[0197] The wireless communication system 1c in this embodiment, for example, sets the direction of the beam selected by this beam forming (beam angle) in the direction where the terminal MT of the communication partner is located (the above angle θ' １ , angle θ' ２ , or angle θ １ , angle θ ２ ) is used for calculation. This allows the wireless communication system 1 to identify the position of the terminal MT by using the existing beamforming configuration, without requiring a new configuration for detecting the direction of the terminal MT.

[0198] As mentioned above, the angle θ １ and angle θ ２ Since the position of the terminal MT has already been identified from the movement route of the terminal MT, the direction of the terminal MT at the position of the base station BS3 to which communication is newly connected (angle θ ３ ) can also be easily identified. Therefore, when link switching is initiated and the base station BS3 starts a communication connection with the terminal MT, the beam sweep operation can be omitted. The beam sweep operation is a beamforming operation in which the base station BS detects the direction of the terminal MT and aligns the beam formation direction with the detected direction of the terminal MT. By omitting the beam sweep operation, it becomes possible to more quickly establish a communication connection between the base station BS3 and the terminal MT.

[0199] The state before link switching has been described above with reference to Figure 24, and the state at the start of link switching has been described with reference to Figure 25. As shown in Figures 24 and 25, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0200] Figures 26 and 27 show a case where base station BS1, base station BS2, and base station BS3 are all located on the right side of the movement route of terminal MT. In other words, this is a case where all base stations BS are located on one side of the movement route of terminal MT. Figures 26 and 27 also show a case where the side where all base stations BS are located is the mountain side of the curved movement route of terminal MT. In other words, this is a case where all base stations BS are located on the mountain side of the curved movement route of terminal MT. Hereinafter, this case will be referred to as "Case 1-".

[0201] Fig. 26 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 27 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0202] As shown in FIG. 26, 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 θ′. １ 26, 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 This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0203] As shown in FIG. 26, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ′. ３１ 26, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0204] Similarly, as shown in FIG. 27, 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 27, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0205] As shown in FIG. 27, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 27, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0206] In FIG. 26, which shows an example, the angles are θ′ １ = 66°, θ' ２ = 122°, θ' ３１ =-14°, θ' ３２ In addition, in FIG. 27 shown as an example, the angles are θ １ = 19°, θ ２= 105°, θ ３１ =-11°, θ ３２ =-25°.

[0207] The state before link switching has been described above with reference to Figure 26, and the state at the start of link switching execution has been described with reference to Figure 27. As shown in Figures 26 and 27, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0208] Figures 28 and 29 show a case where base station BS1 is located on the left side of the movement path of terminal MT, and base stations BS2 and BS3 are located on the right side of the movement path of terminal MT. In other words, base station BS1, which is disconnected by link switching, is located on the opposite side of the movement path of terminal MT from base station BS2, which remains connected, and base station BS3, which is newly connected by link switching. Also, Figures 28 and 29 show a case where the side where base station BS1 is located is on the mountain side of the curved movement path of terminal MT. In other words, this is a case where the base station BS, whose communication connection is disconnected, is located on the mountain side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 3+."

[0209] Fig. 28 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 29 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0210] As shown in FIG. 28, 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 θ′. １ 28, 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'. ２This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0211] As shown in FIG. 28, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ'. ３１ 28, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0212] Similarly, as shown in FIG. 29, 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 29, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0213] As shown in FIG. 29, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 29, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0214] In FIG. 28, which is shown as an example, the angles are θ′ １ =-37°, θ' ２ = 140°, θ' ３１ = 6°, θ' ３２ In addition, in FIG. 29 shown as an example, the angles are θ １ = 11°, θ ２ = 105°, θ ３１ =-5°, θ ３２ =-30°.

[0215] The state before link switching has been described above with reference to Figure 28, and the state at the start of link switching execution has been described with reference to Figure 29. As shown in Figures 28 and 29, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0216] Figures 30 and 31 show a case where base station BS1 is located on the left side of the movement path of terminal MT, and base stations BS2 and BS3 are located on the right side of the movement path of terminal MT. In other words, base station BS1, which is disconnected by link switching, is located on the opposite side of the movement path of terminal MT from base station BS2, which remains connected, and base station BS3, which is newly connected by link switching. Also, Figures 30 and 31 show a case where the side where base station BS1 is located is on the valley side of the curved movement path of terminal MT. In other words, this is a case where the base station BS, which is disconnected by link switching, is located on the valley side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 3-".

[0217] Fig. 30 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 31 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0218] As shown in FIG. 30, 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 30, 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 This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0219] As shown in FIG. 30, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ′. ３１ 30, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0220] Similarly, as shown in FIG. 31, 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 31, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0221] As shown in FIG. 31, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 31, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0222] In FIG. 30, which shows an example, the angles are θ′ １ =-38°, θ' ２ = 141°, θ' ３１ = 6°, θ' ３２ In addition, in FIG. 31 shown as an example, the angles are θ １ =-19°, θ ２ = 130°, θ ３１ = 12°, θ ３２ =-14°.

[0223] The state before link switching has been described above with reference to Figure 30, and the state at the start of link switching execution has been described with reference to Figure 31. As shown in Figures 30 and 31, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0224] Figures 32 and 33 show a case where base station BS2 is located on the left side of the movement path of terminal MT, and base stations BS1 and BS3 are located on the right side of the movement path of terminal MT. In other words, the continuously connected base station BS2 is located on the opposite side of the movement path of terminal MT from the base station BS1 that is disconnected by link switching and the base station BS3 that is newly connected by link switching. Also, Figures 32 and 33 show a case where the side where base station BS2 is located is on the mountain side of the curved movement path of terminal MT. In other words, this is a case where the continuously connected base station BS is located on the mountain side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 0+."

[0225] Fig. 32 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 33 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0226] As shown in FIG. 32, 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 θ′. １ 32, 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 This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0227] As shown in FIG. 32, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ'. ３１32, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0228] Similarly, as shown in FIG. 33, 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 33, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0229] As shown in FIG. 33, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 33, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0230] In FIG. 32, which shows an example, the angles are θ′ １ = 63°, θ' ２ =-113°, θ' ３１ = 12°, θ' ３２ In addition, in FIG. 33 shown as an example, the angles are θ １ = 38°, θ ２ =-103°, θ ３１ = 23°, θ ３２ =-16°.

[0231] The state before link switching has been described above with reference to Figure 32, and the state at the start of link switching execution has been described with reference to Figure 33. As shown in Figures 32 and 33, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0232] Figures 34 and 35 show a case where base station BS2 is located on the left side of the movement path of terminal MT, and base stations BS1 and BS3 are located on the right side of the movement path of terminal MT. In other words, the continuously connected base station BS2 is located on the opposite side of the movement path of terminal MT from the base station BS1 that is disconnected by link switching and the base station BS3 that is newly connected by link switching. Also, Figures 34 and 35 show a case where the side where base station BS2 is located is on the valley side of the curved movement path of terminal MT. In other words, this is a case where the continuously connected base station BS is located on the valley side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 0-".

[0233] Fig. 34 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 35 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0234] As shown in FIG. 34, 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 θ′. １ 34, 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 This angle θ' １ and angle θ' ２Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0235] As shown in FIG. 34, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ'. ３１ 34, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0236] Similarly, as shown in FIG. 35, 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 35, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0237] As shown in FIG. 35, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 35, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0238] In FIG. 34, which shows an example, the angles are θ′ １= 68°, θ' ２ =-119°, θ' ３１ =-15°, θ' ３２ In addition, in FIG. 35 shown as an example, the angles are θ １ = 22°, θ ２ =-85°, θ ３１ =-10°, θ ３２ = 29°.

[0239] The state before link switching has been described above with reference to Figure 34, and the state at the start of link switching execution has been described with reference to Figure 35. As shown in Figures 34 and 35, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0240] Figures 36 and 37 show a case where base station BS3 is located on the left side of the movement path of terminal MT, and base stations BS1 and BS2 are located on the right side of the movement path of terminal MT. In other words, the base station BS3 to be newly connected to is located on the opposite side of the movement path of terminal MT from base station BS1, which is disconnected by link switching, and base station BS2, which remains connected to the movement path of terminal MT. Also, Figures 36 and 37 show a case where the side where base station BS3 is located is on the mountain side of the curved movement path of terminal MT. In other words, the base station BS to be newly connected to the movement path of terminal MT is located on the mountain side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 2+."

[0241] Fig. 36 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 37 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0242] As shown in FIG. 36, 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 θ′. １ 36, 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 This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0243] As shown in FIG. 36, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ'. ３１ 36, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0244] Similarly, as shown in FIG. 37, 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 37, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0245] As shown in FIG. 37, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 37, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0246] In FIG. 36, which shows an example, the angles are θ′ １ = 34°, θ' ２ = 109°, θ' ３１ =-6°, θ' ３２ In addition, in FIG. 37 shown as an example, the angles are θ １ = 14°, θ ２ =-74°, θ ３１ =-9°, θ ３２ =-31°.

[0247] The state before link switching has been described above with reference to Figure 36, and the state at the start of link switching execution has been described with reference to Figure 37. As shown in Figures 36 and 37, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0248] 38 and 39 show a case where base station BS3 is located on the left side of the movement path of terminal MT, and base stations BS1 and BS2 are located on the right side of the movement path of terminal MT. In other words, the base station BS3 to be newly connected to is located on the opposite side of the movement path of terminal MT from the base station BS1 that is disconnected by link switching and the base station BS2 that continues to be connected to the movement path of terminal MT. These figures show a case where the side on which base station BS3 is located is on the valley side of the curved movement path of terminal MT. In other words, this is a case where the base station BS to be newly connected to is located on the valley side of the curved movement path of terminal MT. Hereinafter, this case will be referred to as "Case 2-".

[0249] Fig. 38 shows an example of the positional relationship of each device when the terminal MT is not located within the switching start range r, while Fig. 39 shows an example of the positional relationship of each device when the terminal MT is located within the switching start range r.

[0250] As shown in FIG. 38, 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 θ′. １ 38, 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 This angle θ' １ and angle θ' ２ Based on the values ​​of r and r, the wireless communication system 1c in this embodiment can identify the location of the terminal MT. Then, it is determined that the identified location of the terminal MT is not within the range of the preset switching start range r.

[0251] As shown in FIG. 38, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ′. ３１ 38, when the position of the terminal MT is not within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is defined as θ'. ３２ Let's say.

[0252] Similarly, as shown in FIG. 39, 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 39, 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 angle θ １ and angle 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 identified to be within a preset switching start range r. When it is identified that the location of the terminal MT is within the switching start range r, execution of link switching is initiated.

[0253] As shown in FIG. 39, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS1 and the direction of the terminal MT at the position of the base station BS3 is θ. ３１ 39, when the position of the terminal MT is within the switching start range r, the angle formed between the direction of the base station BS2 and the direction of the terminal MT at the position of the base station BS3 is θ ３２ Let's say.

[0254] In FIG. 38, which is shown as an example, the angles are θ′ １ = 44°, θ' ２ = 104°, θ' ３１ =-9°, θ' ３２ In addition, in FIG. 39 shown as an example, the angles are θ １ =-8°, θ ２ = 83°, θ ３１ = 6°, θ ３２ =-17°.

[0255] The state before link switching has been described above with reference to Figure 38, and the state at the start of link switching execution has been described with reference to Figure 39. As shown in Figures 38 and 39, in the state before link switching, the terminal MT is communicatively connected to the base station BS via two links, and in the state at the start of link switching execution, the terminal MT is communicatively connected to the base station BS via at least two links (maximum three). In other words, in either state, the base station BS and the terminal MT maintain a communicatively connected state (multi-link) via multiple (at least two) links.

[0256] The characteristics of the above cases 0± to 3± (i.e., the characteristics when the movement path of the terminal MT is curved) can be summarized in a table as shown in Figure 40. Note that Figure 40 also lists the characteristics of cases 0 to 3 shown in Figure 8 (i.e., the characteristics when the movement path of the terminal MT is straight).

[0257] Similar to Fig. 8, Fig. 40 is a diagram showing the characteristics of each positional relationship of multiple base stations BS with respect to the moving route of the terminal MT. Fig. 40 shows the tendency of change in the values ​​of six parameters for each case. As shown in Fig. 40, the six parameters are classified into "reception level" and "angle."

[0258] The reception level parameter is "R ＢＳ１ " and "R ＢＳ２ " is included. ＢＳ１ is the reception level of the signal transmitted from the terminal MT at the base station BS1. ＢＳ２ is the reception level at base station BS2 of the signal transmitted from terminal MT.

[0259] The angle parameter is "θ １ " and "θ ２ " and "θ ３１ " and "θ ３２ As shown in Figures 25, 27, 29, 31, 33, 35, 37, and 39, θ １ , θ ２ , θ ３１ and θ ３２are respectively the angle formed between the reference direction and the direction of terminal MT at the position of base station BS1, the angle formed between the reference direction and the direction of terminal MT at the position of base station BS2, the angle formed between the opposite direction of the reference direction (the direction of base station BS1) and the direction of terminal MT at the position of base station BS3, and the angle formed between the opposite direction of the reference direction (the direction of base station BS2) and the direction of terminal MT at the position of base station BS3.

[0260] In the table shown in FIG. 40, the reception level R ＢＳ１ In the parameter column, a downward arrow is shown for all cases from Case 0± to Case 3± (and all cases from Case 0 to Case 3). This indicates that the reception level R ＢＳ１ This shows that the value of R tends to decrease. This is because in all of Case 0± to Case 3± (and Case 0 to Case 3), the terminal MT moves away from the base station BS1. Therefore, basically, the value of R decreases as the terminal MT moves. ＢＳ１ The value of tends to decrease monotonically.

[0261] In addition, in the table shown in FIG. ＢＳ２ In the parameter column, an upward arrow is shown for all cases from Case 0± to Case 3± (and all cases from Case 0 to Case 3). This indicates that the reception level R ＢＳ２ This shows that the value of R tends to increase. This is because in all of the cases 0± to 3± (and cases 0 to 3), the terminal MT moves closer to the base station BS2. Therefore, basically, the value of R increases as the terminal MT moves. ＢＳ２ The value of tends to increase monotonically.

[0262] In addition, in the table shown in FIG. １ In the parameter column, a downward arrow is shown in all cases except for case 3+ (i.e., almost all cases). This indicates that in all cases except for case 3+ (i.e., almost all cases), the angle θ １As can be seen from FIGS. 24 to 39, in all cases except for Case 3+ (i.e., almost all cases), the value of θ' tends to decrease. １ >θ １ and the angle θ １ The value of tends to decrease.

[0263] In addition, in the table shown in FIG. ２ In the parameter column, a downward arrow is shown for all cases from Case 0± to Case 3± (and all cases from Case 0 to Case 3). This indicates that the angle θ ２ As can be seen from FIGS. 24 to 39, in any of Case 0± to Case 3± (and Case 0 to Case 3), the value of θ' tends to decrease. ２ >θ ２ and the angle θ ２ The value of tends to decrease.

[0264] In this way, the angle θ １ and the angle θ ２ In almost all cases, the value of tends to decrease as the terminal MT moves. As mentioned above, the movement path of the terminal MT is known, so the angle θ １ and the angle θ ２ By focusing on the change in the value of , it becomes possible to identify the timing at which the terminal MT enters the switching start range r. This makes it possible to start link switching at the timing at which the terminal MT enters the switching start range r.

[0265] FIG. 41 shows the angle θ associated with the movement of the terminal MT in the case of the above-mentioned Case 1+. １ and angle θ ２ The graph shown in Fig. 41 has two line graphs, one above the other, and the lower line graph shows the change in the direction of the terminal MT at the base station BS1 (i.e., the angle θ １ On the other hand, the upper line graph represents the change in the direction of the terminal MT at the base station BS2 (i.e., the angle θ ２) represents a change in

[0266] As shown in the graph of FIG. 41, as the terminal MT moves, the angle θ １ The value of θ' １ = 61°, θ'' １ = 51°, θ''' １ = 44°, θ １ 41, the angle θ decreases monotonically as the terminal MT moves. ２ The value of θ' ２ = 127°, θ′′ ２ = 118°, θ′′′ ２ = 108°, θ ２ = 95° and decreases monotonically.

[0267] In addition, the angle θ' １ and angle θ' ２ The diagram corresponding to the case of the angle θ １ and angle θ ２ The figure corresponding to the case of is the aforementioned FIG. 25. And, the angle θ'' １ and angle θ'' ２ The diagram corresponding to the case of angle θ''' is shown in FIG. １ and angle θ′′′ ２ The diagrams corresponding to the cases (a) and (b) are shown in FIG.

[0268] FIG. 44 shows the angle θ associated with the movement of the terminal MT in the case of the above-mentioned Case 3+. １ and angle θ ２ The graph shown in FIG. 44 includes two line graphs, one above the other, and the lower line graph shows the change in the direction of the terminal MT at the base station BS1 (i.e., the angle θ １ On the other hand, the upper line graph represents the change in the direction of the terminal MT at the base station BS2 (i.e., the angle θ ２ ) represents a change in

[0269] As shown in the graph of FIG. 44, as the terminal MT moves, the angle θ １ The value of θ' １ = -37°, θ'' １ =-13°, θ'''１ = 5°, θ １ 44, the angle θ ２ The value of θ' ２ = 140°, θ′′ ２ = 130°, θ′′′ ２ = 117°, θ ２ = 105° and decreases monotonically.

[0270] In addition, the angle θ' １ and angle θ' ２ The diagram corresponding to the case of the angle θ １ and angle θ ２ The figure corresponding to the case of is the above-mentioned FIG. 29. And, the angle θ'' １ and angle θ'' ２ The diagram corresponding to the case of angle θ''' is shown in FIG. １ and angle θ′′′ ２ The diagrams corresponding to the cases (a) and (b) are shown in FIG.

[0271] As described above, the wireless communication system 1c according to the third embodiment of the present invention sets the direction of the new base station BS (i.e., base station BS3) as the reference direction when determining the location of the terminal MT. More specifically, when determining the direction of the terminal MT at base station BS1, the direction of base station BS3 at base station BS1 is set as the angle relative to the reference direction, and the direction of the terminal MT is determined. Furthermore, when determining the direction of the terminal MT at base station BS2, the direction of base station BS3 at base station BS2 is set as the angle relative to the reference direction, and the direction of the terminal MT is determined. With this configuration, the wireless communication system 1c according to the third embodiment can set an appropriate switching start range r even when the movement path of the terminal MT is curved.

[0272] Similarly to the wireless communication system 1 in the first embodiment, a wireless communication system 1c in the third embodiment of the present invention includes at least three base stations BS and a communication control device 10c that executes and 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) and a second base station (e.g., base station BS2) and is moving away from the first base station and approaching a third base station (e.g., base station BS3) 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.

[0273] Alternatively, 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) and a second base station (e.g., base station BS2) and is moving away from the first base station and approaching a third base station (e.g., base station BS3) based on a predetermined movement path of the terminal MT and the direction of the terminal MT as seen from the first base station or the direction of the terminal MT as seen from the second base station (i.e., the direction of the terminal MT as seen from one base station BS).

[0274] When the communication control device 10c detects that the moving terminal MT has entered a switching start range r that is predetermined based on the connectable range of the first base station and the connectable range of the third base station, the communication control device 10c starts control of link switching. First, the communication control device 10c 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 10c disconnects the existing link between the terminal MT and the first base station, which are moving away from each other.

[0275] With this configuration, the wireless communication system 1c according to the third 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 1c according to the third 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 (multi-link), including when link switching is being performed. As a result, the wireless communication system 1c can suppress communication disconnections, even when an unexpected communication failure occurs, including when link switching is being performed.

[0276] Furthermore, the wireless communication system 1c 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 1c 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 1c according to the third embodiment can ensure communication reliability at all times, including when link switching is being performed.

[0277] Fourth Embodiment A wireless communication system 1d according to a fourth embodiment of the present invention will now be described. The wireless communication system 1d described below is an example of a communication control system according to the present invention.

[0278] As briefly mentioned in the description of the second embodiment, the information about the communication environment collected by the communication control device from multiple other terminals MT present in the vicinity of the movement route of the terminal MT may be information collected in the past. In particular, if the communication environment changes periodically, information about the communication environment collected at an appropriate timing according to the period may be used. Furthermore, if the change in the communication environment is not periodic, information about the communication environment may be collected from other terminals MT that have recently traveled the same movement route.

[0279] The following describes a case where information about the communication environment is collected from another terminal MT that has traveled the same route in the past. In the following description, time t represents the timing (time) at which terminal MT reaches the switching start range r. Time t-Δt represents a timing (time) earlier than t.

[0280] As an example, consider a commuter train that runs through an urban area and has tens of thousands of passengers boarding and alighting every day. In this case, assume that the time t is, for example, a certain time during rush hour, when the commuter train is running on a gently curving rail. In this case, the time Δt is the time interval between the commuter trains during rush hour (i.e., the time interval between the previous commuter train) or several times that time interval (i.e., the time interval between the previous commuter trains).

[0281] If each commuter train is carrying a passenger with a terminal MT, different terminals MT will be traveling one after another along the same route at intervals of several minutes or several tens of minutes. In such cases, it becomes possible to collect information about the communication environment (e.g., measured values ​​such as received signal strength indicator (RSSI)) from other terminals MT that have recently traveled along the same route, and initiate link switching at an appropriate timing.

[0282] As another example, consider a route bus traveling along a road lined with broad-leaved trees that regularly exist as roadside trees in urban areas, residential areas, etc. In this case, it is assumed that the above-mentioned time t is, for example, a seasonal operating time and is the timing at which the route bus travels along a straight or curved road lined with broad-leaved trees on its route.

[0283] If each commuter train is equipped with passengers and a driver each carrying a terminal MT, different terminals MT will be traveling one after another along the same route at intervals of several minutes or several tens of minutes. In such cases, it becomes possible to collect information about the communication environment (e.g., measured values ​​such as received signal strength indicator (RSSI)) from other terminals MT that have recently traveled along the same route, and initiate link switching at an appropriate timing.

[0284] The density of broad-leaved trees between the terminal MT and the base station BS changes depending on the season. When high-frequency radio waves are used for wireless communication, the communication environment also changes depending on the density of broad-leaved trees. For example, in the summer months of July and August, broad-leaved trees are denser, which has a greater impact on radio wave propagation obstruction, while in the winter months of January and February, broad-leaved trees are less dense, which has a greater impact on radio wave propagation obstruction.

[0285] In such a case, the time Δt is an annual interval that varies depending on the season of each year. However, data for roughly the same time period for route bus operation must be used for each season. For example, in the summer, data collected during the 10:00 AM time period in July and August each year is used. For example, in the winter, data collected during the 2:00 PM time period in January and February each year is used.

[0286] A wireless communication system 1d in a fourth embodiment described below is configured to acquire information about the communication environment (e.g., measured values ​​of received signal strength indicator (RSSI)) from multiple other terminals MT that have recently traveled the same travel route as the terminal MT, and generate a propagation map of radio waves from the base station BS. The wireless communication system 1d sets a switching start range r based on the generated propagation map.

[0287] [Switching Start Range Setting Procedure] The following describes the procedure for setting the switching start range r by the wireless communication system 1d of this embodiment. Figures 47 to 50 are diagrams for explaining the procedure for setting the switching start range r by the wireless communication system 1d in the fourth embodiment of the present invention. Note that this embodiment assumes that the terminal MT moves along a curved movement path. In Figures 47 to 50, the terminal MT moves along a movement path that curves from left to right in each figure.

[0288] 47 to 50, the case where base station BS2 is located on the left side of the movement path of terminal MT and base stations BS1 and BS3 are located on the right side of the movement path of terminal MT will be described as an example. That is, the case where base station BS2, which continues to be connected, is located on the opposite side of the movement path of terminal MT from base station BS1, which is disconnected by link switching, and base station BS3, which is newly connected by link switching, will be described as the above-mentioned "Case 0."

[0289] As shown in FIG. 47, there are at least n other terminals MT (terminals MT １＋ ~ Terminal MT ｎ＋ A communication control device in the fourth embodiment (hereinafter referred to as "communication control device 10d") collects information on the communication environment between the terminal MT and the base station BS from each of a plurality of other terminals MT that are present on the same (or similar) moving route as the terminal MT.

[0290] More specifically, the communication control device 10d collects, for example, from each of a plurality of other terminals MT moving in front of the terminal MT on the moving route, a measurement value of the received signal strength indicator (RSSI) of the signal received from the base station BS1. The communication control device 10d also collects, for example, from each of a plurality of other terminals MT moving in front of the terminal MT on the moving route, a measurement value of the received signal strength indicator (RSSI) of the signal received from the base station BS3.

[0291] Then, the communication control device 10d generates a propagation map of radio waves transmitted from base station BS1 using the collected measured values ​​of received signal strength indicator (RSSI) of signals received from base station BS1. The communication control device 10d also generates a propagation map of radio waves transmitted from base station BS3 using the collected measured values ​​of received signal strength indicator (RSSI) of signals received from base station BS3. The communication control device 10d sets an appropriate switching start range r based on the two generated propagation maps.

[0292] Figure 48 is a diagram showing an example of a propagation map of radio waves transmitted from base station BS1, generated by the communication control device 10d. In comparison with Figure 47, Figure 48 adds seven additional curves, labeled (a) to (g). These curves are lines connecting positions where the received signal strength indicator (RSSI) values ​​of the received signal from base station BS1 are estimated to be the same.

[0293] As shown in Fig. 48, (a) is the curve closest to base station BS1, and (g) is the curve farthest from base station BS1. Therefore, among (a) to (g), the position where curve (a) passes through has the strongest received signal strength (RSSI), and the positions where curves (b) and on pass through have the weakest received signal strength (RSSI), with the position where curve (g) passes having the weakest received signal strength (RSSI).

[0294] 49 is a diagram showing an example of a propagation map of radio waves transmitted from base station BS3, generated by the communication control device 10d. In comparison with the aforementioned FIG. 47, seven additional curves labeled (a) to (g) are added in FIG. 49. These curves are lines connecting positions where the received signal strength indicator (RSSI) values ​​of the received signal from base station BS3 are estimated to be the same.

[0295] As shown in Fig. 49, (a) is the curve closest to base station BS3, and (g) is the curve farthest from base station BS3. Therefore, among (a) to (g), the position where curve (a) passes through has the strongest received signal strength (RSSI), and the positions where curves (b) and on pass through have the weakest received signal strength (RSSI), with the position where curve (g) passes having the weakest received signal strength (RSSI).

[0296] The communication control device 10d sets an appropriate switching start range r based on the two propagation maps shown in Figures 48 and 49. Here, the appropriate switching start range r is, for example, an area on the movement path of the terminal MT where the smaller of the received signal strength indicator (RSSI) values ​​of the radio waves from base station BS1 and the received signal strength indicator (RSSI) values ​​of the radio waves from base station BS3 is maximized. By setting the switching start range r in this manner, the terminal MT can receive signals from both base station BS1 and base station BS3 with a relatively strong received signal strength (RSSI) when switching links. This makes it possible to suppress a decrease in throughput and communication interruptions when switching links.

[0297] Fig. 50 is a diagram showing a switching start range r set based on the two generated propagation maps. Fig. 50 shows, as an example, a case where a range that is a periphery of the movement path of terminal MT and is surrounded by the curve (e) of the propagation map in Fig. 48 and the curve (e) of the propagation map in Fig. 49 is set as the switching start range r.

[0298] More specifically, as shown in Fig. 50, the switching start range r is shown as a (shaded) oval located closer to base station BS1 within the "overlap area at curve (e)," which is the area surrounded by the curve (e) on the propagation map shown in Fig. 48 and the curve (e) on the propagation map shown in Fig. 49. The reason why the switching start range r is set at such a position is the same as the reason why the switching start range r is set at a position closer to base station BS1 within the overlap area d, as explained in the first embodiment with reference to Figs. 9 to 12.

[0299] That is, the reason why the switching start range r is set closer to base station BS1 within the overlapping area of ​​curve (e) is that in order to perform link switching in the order of establishing a link between base station BS3 and terminal MT and then disconnecting the link between base station BS1 and terminal MT, it is desirable for the wireless communication system 1d to carry out link switching from start to completion while the moving terminal MT is still within the overlapping area of ​​curve (e).

[0300] By setting the switching start range r closer to base station BS1 within the overlapping area of ​​the curve (e), link switching begins as soon as the terminal MT enters the overlapping area of ​​the curve (e). Furthermore, by setting the switching start range r closer to base station BS1 within the overlapping area of ​​the curve (e), even if the terminal MT is moving closer to base station BS3, the time that the terminal MT remains within the overlapping area of ​​the curve (e) can be ensured to be longer. This allows the wireless communication system 1d 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.

[0301] The switching start range r may be the same range as the overlapping region of the curve (e). In that 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 (for example, in real time) and a mechanism for transmitting control signals for controlling link switching without delay are required.

[0302] As an example, the information about the communication environment collected by the communication control device 10d from each of multiple other terminals MT that are on the same (or similar) moving route as the terminal MT is assumed to be a measured value of received signal strength indicator (RSSI). However, the information about the communication environment collected by the communication control device 10d is not limited to this. For example, instead of the measured value of received signal strength indicator (RSSI), the information about the communication environment collected by the communication control device 10d may be other information about the communication state, such as a signal-to-noise ratio (S / N ratio), reliability (Throughput), bit error rate (BER), packet error rate (PER), or symbol error rate (SER).

[0303] As described above, the wireless communication system 1d in the fourth embodiment of the present invention acquires information about the communication environment (e.g., measured values ​​of received signal strength indicator (RSSI)) from multiple other terminals MT that have recently traveled the same travel route as the terminal MT, and generates a propagation map of radio waves from the base station BS. Alternatively, the wireless communication system 1d may acquire information about the communication environment (e.g., measured values ​​of received signal strength indicator (RSSI)) from multiple other terminals MT that have traveled the same travel route as the terminal MT in the past during seasons with the same environmental conditions, and generate a propagation map of radio waves from the base station BS.

[0304] Then, the wireless communication system 1d sets the switching start range r based on the generated propagation map. With this configuration, the wireless communication system 1d according to the fourth embodiment can set an appropriate switching start range r that makes communication disconnection less likely to occur even when the communication environment does not change periodically.

[0305] Similarly to the wireless communication system 1 in the first embodiment, a wireless communication system 1d in the fourth embodiment of the present invention includes at least three base stations BS and a communication control device 10d that executes and controls link switching between each of these base stations BS and a terminal MT. The communication control device 10d identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1) and a second base station (e.g., base station BS2) and is moving away from the first base station and approaching a third base station (e.g., base station BS3) 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.

[0306] Alternatively, the communication control device 10d identifies the position of a terminal MT that has a link established between a first base station (e.g., base station BS1) and a second base station (e.g., base station BS2) and is moving away from the first base station and approaching a third base station (e.g., base station BS3) based on a predetermined movement path of the terminal MT and the direction of the terminal MT as seen from the first base station or the direction of the terminal MT as seen from the second base station (i.e., the direction of the terminal MT as seen from one base station BS).

[0307] When the communication control device 10d detects that the moving terminal MT has entered a switching start range r that is predetermined based on the connectable range of the first base station and the connectable range of the third base station, the communication control device 10d starts control of link switching. First, the communication control device 10d establishes a new link between the terminal MT and the third base station that are approaching each other. Then, after the link between the third base station and the terminal MT is established, the communication control device 10d disconnects the existing link between the terminal MT and the first base station that are moving away from each other.

[0308] With this configuration, the wireless communication system 1d 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. That is, the wireless communication system 1d 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 (multi-link), including when link switching is being performed. As a result, the wireless communication system 1d can suppress communication disconnections, even when, for example, an unexpected communication failure occurs, including when link switching is being performed.

[0309] Furthermore, the wireless communication system 1d according to the fourth 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 1d 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 1d according to the fourth embodiment can ensure communication reliability at all times, including when link switching is being performed.

[0310] 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 wireless communication system 1 and wireless communication systems 1a to 1d in the embodiments, the wireless base station devices are base station BS and base station BS1 to base station BS3 in the embodiments, and the communication control devices are communication control device 10 and communication control device 10a to 10d in the embodiments. The communication control device controls switching of communication connections between the wireless base station devices and terminal devices. For example, the terminal device is terminal MT in the embodiments, and switching of communication connections is link switching in the embodiments.

[0311] The communication control device includes a detection unit and a control unit. For example, the detection unit corresponds to the detection unit 11 in the embodiment, and the switching control unit corresponds to the execution control unit 13 in the embodiment.

[0312] 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 area, which is an area in which the terminal device can communicate with both the first wireless base station device and the third wireless base station device. 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 area is overlapping area d in the embodiment, and the predetermined range is switching start range r in the embodiment.

[0313] 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.

[0314] The predetermined range is a range set based on first information indicating the respective communication environments between a first wireless base station device and a plurality of other devices present in the vicinity of the movement path of the terminal device, and second information indicating the respective communication environments between a third wireless base station device and a plurality of other devices present in the vicinity of the movement path of the terminal device. For example, the other devices are the terminal MT in the embodiment. １ ~ Terminal MT ｎ and terminal MT １＋ ~ Terminal MT ｎ＋ The first information is information relating to the communication environment between the terminal MT and the base station BS1 in the embodiment, and the second information is information relating to the communication environment between the terminal MT and the base station BS3 in the embodiment.

[0315] The first information may be information indicating a communication environment between the first wireless base station device and a plurality of other devices that have traveled the same or a similar route as the movement route of the terminal device. The second information may be information indicating a communication environment between the third wireless base station device and a plurality of other devices that have traveled the same or a similar route as the movement route of the terminal device. For example, the information indicating the communication environment may be a measured value of received signal strength indicator (RSSI) in the embodiment.

[0316] The communication control device may further include an acquisition unit and a calculation unit. The acquisition unit is the beam selection information acquisition unit 111 in the embodiment, and the calculation unit is the terminal position calculation unit 112 in the embodiment. The acquisition unit acquires information indicating a first direction, which is the direction of the terminal device as seen from a first wireless base station device, or information indicating a second direction, which is the direction of the terminal device as seen from a second wireless base station device. The calculation unit calculates the position of the terminal device based on the angle formed between the first direction and the moving direction of the terminal device and the moving route, or based on the angle formed between the second direction and the moving direction of the terminal device and the moving route. For example, the angle formed between the first direction and the moving direction of the terminal device is angle θ in the embodiment. １ or angle θ' １ and 、 The angle between the second direction and the direction of movement of the terminal device is the angle θ ２ or angle θ' ２ is.

[0317] The communication control device may further include an acquisition unit and a calculation unit. The acquisition unit corresponds to the beam selection information acquisition unit 111 in the embodiment, and the calculation unit corresponds to the terminal position calculation unit 112 in the embodiment. The acquisition unit acquires information indicating a first direction, which is the direction of the terminal device as seen from the first wireless base station device, and information indicating a third direction, which is the direction of the third wireless base station device as seen from the first wireless base station device, or information indicating a second direction, which is the direction of the previous wireless base station device as seen from the second wireless base station device, and information indicating a fourth direction, which is the direction of the third wireless base station device as seen from the second wireless base station device. The calculation unit calculates the position of the terminal device based on the angle formed between the first direction and the third direction and the movement route, or based on the angle formed between the second direction and the fourth direction and the movement route. For example, the angle formed between the first direction and the third direction is angle θ in the embodiment. １ or angle θ' １ and the angle formed by the second direction and the fourth direction is the angle θ ２ or angle θ' ２ is.

[0318] The server device (communication control devices 10, 10a to 10d) 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.

[0319] Some or all of the configuration of the communication control devices 10, 10a to 10d 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 media that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks such as the Internet or over communication lines such as telephone lines, or media 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 a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0320] 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.

[0321] DESCRIPTION OF SYMBOLS 1, 1a to 1d... Wireless communication system 10, 10a to 10d... Communication control device 11... Detection unit 12... Storage unit 13... Execution control unit 111... Beam selection information acquisition unit 112... Terminal position calculation unit 113... Switching execution determination unit 131... Link connection instruction unit 132... Connection completion report receiving unit 133... Link disconnection instruction unit BS, BS1 to BS3... Base station 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 that 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. A communication control system in which the specified range is set based on first information indicating the respective communication environments between the first radio base station device and multiple other devices located in the vicinity of the movement path of the terminal device, and second information indicating the respective communication environments between the third radio base station device and multiple other devices located in the vicinity of the movement path of the terminal device.

2. The communication control system of claim 1, wherein the first information is information indicating the communication environment between the first wireless base station device and a plurality of other devices that have traveled along a route that is the same as or similar to the movement route of the terminal device, and the second information is information indicating the communication environment between the third wireless base station device and a plurality of other devices that have traveled along a route that is the same as or similar to the movement route of the terminal device.

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

4. The communication control device of claim 1 or 2 further comprises: an acquisition unit that acquires information indicating a first direction, which is the direction of the terminal device as seen from the first wireless base station device, and information indicating a third direction, which is the direction of the third wireless base station device as seen from the first wireless base station device, or information indicating a second direction, which is the direction of the terminal device as seen from the second wireless base station device, and information indicating a fourth direction, which is the direction of the third wireless base station device as seen from the second wireless base station device; and a calculation unit that calculates the position of the terminal device based on the angle formed between the first direction and the third direction and the movement route, or based on the angle formed between the second direction and the fourth direction and the movement route.

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