Optical transmission device control apparatus, base station control apparatus, optical transmission device, control method, and optical path switching method

Abstract

Provided is an optical transmission device control apparatus in a signal transfer system including: a plurality of base stations each accommodating one or more wireless terminals; a plurality of optical transmission devices each connected to at least any one of the plurality of base stations; the optical transmission device control apparatus that controls the plurality of optical transmission devices; and a base station control apparatus that controls the plurality of base stations. The optical transmission device control apparatus includes an optical control instruction unit that, on the basis of wireless control information, which is information related to wireless communication between the base stations and the wireless terminals and acquired from the base station control apparatus or from the plurality of base stations, issues an instruction to switch an optical path for each of the optical transmission devices to be subjected to the optical path switching, in conjunction with the timing at which the base station control apparatus executes a connection change with the one or more wireless terminals.　

Description

Optical Transmission Device Control Device, Base Station Control Device, Optical Transmission Device, Control Method, and Optical Path Switching Method

[0001] The present invention relates to an optical transmission device control device, a base station control device, an optical transmission device, a control method, and an optical path switching method.

[0002] In a conventional mobile communication network, as shown in FIG. 8, an optical path is generated between a base station and a core node that is the connection destination of the base station. Then, communication is performed between the base station and the core node via the generated optical path. FIG. 8 is a diagram showing a configuration example of a conventional signal transfer system. As shown in FIG. 8, the signal transfer system includes a core node, an optical transmission device, an optical transmission device controller, a base station controller, and a base station.

[0003] The core node communicates with a wireless terminal via an optical transmission device and a base station. The optical transmission device is a device that transfers signals exchanged between the core node and the wireless terminal. The optical transmission device controller is a device that controls the optical transmission device. The base station controller is a device that controls the base station. The base station is wirelessly connected to the wireless terminal, transmits the signal transferred from the optical transmission device to the wireless terminal, and transfers the signal received from the wireless terminal to the optical transmission device.

[0004] Unlike a conventional packet network, research has been underway on an all-photonic network (APN: All-Photonic Network) that provides a large-capacity, low-latency line by allocating dedicated resources of one wavelength to one user or one traffic flow using wavelength multiplexing (see, for example, Non-Patent Document 1). In order to be able to provide the dedicated resources of one wavelength in the all-photonic network to the wireless terminals in the mobile communication network as well, it is necessary for the optical path of the dedicated wavelength allocated for each wireless terminal or traffic flow to be switched in accordance with the handover due to the movement of the wireless terminal (see, for example, 9.2.3 of Non-Patent Document 2). Such standards in the mobile communication network are defined by 3GPP (Third Generation Partnership Project) (3GPP is a registered trademark).

[0005] “Open All-Photonic Network Functional Architecture”, IOWN Global Forum, 2023. “3GPP TS38.300 V18.2.0”, 3GPP, 2024. “O-RAN.WG1.Use-Cases-Detailed-Specification-R003-v13.00”, O-RAN Alliance, 2024. “3GPP TS 23.501 V19.0.0”, 3GPP, 2024. “O-RAN.WG3.Y1GAP-R003-v01.00”, O-RAN Alliance, 2024.

[0006] Unlike packet networks where routing can be changed by changing the destination address, mobile communication networks using all-photonic networks cannot switch the optical path between the base station and core node at the appropriate timing in conjunction with handover. As a result, there was a problem where packet loss occurred, such as packets that should have been sent to the source base station or core node being mistakenly sent to the destination base station or core node.

[0007] In view of the above circumstances, the present invention aims to provide a technology that enables switching of a specific optical path related to a wireless terminal in response to the movement of the wireless terminal, while suppressing packet loss.

[0008] One aspect of the present invention is an optical transmission device control device in a signal transfer system comprising: a plurality of base stations accommodating one or more wireless terminals; a plurality of optical transmission devices connected to at least one of the plurality of base stations; an optical transmission device control device for controlling the plurality of optical transmission devices; and a base station control device for controlling the plurality of base stations, wherein the optical transmission device control device includes an optical control instruction unit that, based on the base station control device or wireless control information which is information relating to wireless communication between the base station and the wireless terminal obtained from the plurality of base stations, instructs each optical transmission device subject to optical path switching to switch the optical path in conjunction with the timing of the execution of connection change with the one or more wireless terminal by the base station control device.

[0009] One aspect of the present invention is a base station control device in a signal transfer system comprising: a plurality of base stations accommodating one or more wireless terminals; a plurality of optical transmission devices connected to at least one of the plurality of base stations; an optical transmission device control device for controlling the plurality of optical transmission devices; and a base station control device for controlling the plurality of base stations, wherein the base station control device comprises a wireless control instruction unit that transmits a handover instruction to each base station subject to handover when a change in connection with the one or more wireless terminals is required, based on wireless control information which is information relating to wireless communication between the base station and the wireless terminal, obtained from the plurality of base stations or the optical transmission device control device.

[0010] One aspect of the present invention is an optical transmission device in a signal transfer system comprising a plurality of base stations accommodating one or more wireless terminals and a plurality of optical transmission devices connected to at least one of the plurality of base stations, the optical transmission device comprising: an optical control instruction unit that instructs switching of optical paths in conjunction with the timing of execution of connection changes with the one or more wireless terminals that have moved at each base station subject to handover, based on wireless control information which is information relating to wireless communication between the base station and the wireless terminals, obtained from the pre-mobile base station to which the one or more wireless terminals were connected before moving; and an optical control unit that executes the switching of optical paths in accordance with the instructions of the optical control instruction unit.

[0011] One aspect of the present invention is a control method performed by an optical transmission device control device in a signal transfer system comprising a plurality of base stations accommodating one or more wireless terminals, a plurality of optical transmission devices connected to at least one of the plurality of base stations, an optical transmission device control device for controlling the plurality of optical transmission devices, and a base station control device for controlling the plurality of base stations, wherein the control method acquires wireless control information, which is information relating to wireless communication between the base station and the wireless terminal, from the base station control device or the plurality of base stations, and based on the acquired wireless control information, instructs each optical transmission device subject to optical path switching to switch the optical path in conjunction with the timing of connection change execution with the one or more wireless terminal by the base station control device.

[0012] One aspect of the present invention is a control method performed by a base station control device in a signal transfer system comprising a plurality of base stations accommodating one or more wireless terminals, a plurality of optical transmission devices connected to at least one of the plurality of base stations, an optical transmission device control device for controlling the plurality of optical transmission devices, and a base station control device for controlling the plurality of base stations, wherein the control method acquires wireless control information, which is information relating to wireless communication between the base station and the wireless terminal, from the plurality of base stations or the optical transmission device control device, and based on the acquired wireless control information, transmits a handover instruction to each base station subject to handover when a change in connection with the one or more wireless terminal is necessary.

[0013] One aspect of the present invention is an optical path switching method performed by an optical transmission device in a signal transfer system comprising a plurality of base stations accommodating one or more wireless terminals and a plurality of optical transmission devices connected to at least one of the plurality of base stations, wherein the optical transmission device obtains radio control information, which is information relating to wireless communication between the base station and the wireless terminal, from the base station to which the one or more wireless terminals were connected before moving, and based on the obtained radio control information, it instructs each base station subject to handover to switch the optical path in conjunction with the timing of the execution of a connection change with the one or more wireless terminals that have moved, and executes the optical path switching in accordance with the instruction.

[0014] The present invention makes it possible to switch specific optical paths related to a wireless terminal in response to the movement of the wireless terminal, while suppressing packet loss.

[0015] This figure shows an example configuration of the signal transfer system in the first embodiment. This is a sequence diagram showing the processing flow of the signal transfer system in the first embodiment. This figure shows an example configuration of the signal transfer system in the second embodiment. This figure shows an example configuration of the signal transfer system in the third embodiment. This figure shows an example configuration of the signal transfer system in the fourth embodiment. This is a sequence diagram showing the processing flow of the signal transfer system in the fourth embodiment. This figure shows an example configuration of the signal transfer system in the fifth embodiment. This figure shows an example configuration of a conventional signal transfer system.

[0016] One embodiment of the present invention will be described below with reference to the drawings.

[0017] (First Embodiment) Figure 1 shows an example of the configuration of the signal transfer system 100 in the first embodiment. The signal transfer system 100 is a system that transfers signals from one communication device to another. The signal transfer system 100 includes, for example, a core node 10, an optical transmission device 20, an optical transmission device 25, an optical transmission device controller 30, a base station 40, and a base station controller 50. One or more wireless terminals 60 are wirelessly connected to the base station 40. In the following description, the direction from the core node 10 toward the wireless terminal 60 is described as the downlink direction, and the direction from the wireless terminal 60 toward the core node 10 is described as the uplink direction.

[0018] Figure 1 shows a configuration in which the signal transmission system 100 comprises one optical transmission device 20, two optical transmission devices 25-1 to 25-2, and two base stations 40-1 to 40-2. Note that the number of optical transmission devices 25 and base stations 40 is not limited as long as there are two or more, and the number of optical transmission devices 20 is not limited as long as there is one or more.

[0019] The core node 10 and the optical transmission device 20, the optical transmission device 20 and the optical transmission device 25, and the optical transmission device 25 and the base station 40 are connected by, for example, an optical transmission path. The optical transmission path is a path for transmitting optical signals, and is, for example, an optical fiber. The optical transmission path may include an optical amplifier for amplifying the optical signals.

[0020] Furthermore, the optical transmission device controller 30 and the base station controller 50, the optical transmission device controller 30 and the optical transmission device 20, the optical transmission device controller 30 and the optical transmission device 25, and the base station controller 50 and the base station 40 are connected, for example, by control lines that transmit control signals.

[0021] In describing the first embodiment, we assume that the initial state is that the wireless terminal 60 is connected to base station 40-1 and then to core node 10 via optical transmission device 25-1 and optical transmission device 20. Then, we assume that when the wireless terminal 60 moves and a handover becomes necessary, the wireless terminal 60 connects to base station 40-2 and then to core node 10 via optical transmission device 25-2 and optical transmission device 20. Note that base station 40-1 may also be referred to as the source base station and base station 40-2 as the destination base station.

[0022] The core node 10 is a device that communicates with each of the one or more wireless terminals 60 that are wirelessly connected to each base station 40. For example, the core node 10 receives uplink signals transmitted from the wireless terminals 60 and transmits downlink signals to the wireless terminals 60. The core node 10 is one form of a higher-level device.

[0023] Optical transmission devices 20 and 25 are devices that transfer signals exchanged between the core node 10 and one or more wireless terminals 60. Optical transmission device 20, for example, receives an uplink signal transmitted from a wireless terminal 60 from optical transmission device 25 and transfers it to the core node 10. Optical transmission device 20, for example, transfers a downlink signal transmitted from the core node 10 to the optical transmission device 25 to which the destination wireless terminal 60 is connected.

[0024] The optical transmission device 25, for example, receives an uplink signal transmitted from the wireless terminal 60 from the connected base station 40 and forwards it to the optical transmission device 20. The optical transmission device 25, for example, forwards a downlink signal forwarded from the optical transmission device 20 to the connected base station 40.

[0025] Furthermore, the optical transmission devices 20 and 25 perform dedicated optical path switching processing in response to optical path switching control instructions transmitted from the optical transmission device controller 30. The optical path switching control instructions are instructions to cause the optical transmission devices 20 and 25 to switch optical paths. A dedicated optical path is an optical path with a different wavelength from the basic optical path that is normally used, and is, for example, an optical path with a dedicated wavelength assigned to each wireless terminal 60 or traffic flow. In this way, a dedicated optical path is set up to transmit a specific traffic flow of a specific wireless terminal 60. The dedicated optical path switching processing is the process of switching the connection destination of the dedicated optical path in the section from the core node 10 to the base station 40.

[0026] When communication takes place between the wireless terminal 60 and the core node 10, the optical transmission devices 20 and 25 generate an optical path for transferring optical signals in the section from the core node 10 to the base station 40. This optical path is the basic optical path normally used to exchange all signals transmitted and received by each wireless terminal 60 connected to the same base station 40 with the core node 10. In the basic optical path, as described above, multiple traffic flows from each wireless terminal 60 connected to the same base station 40 will be mixed together. In contrast, a dedicated optical path is an optical path set up to transmit a specific traffic flow, so other traffic flows will not be mixed in.

[0027] In response to an optical path switching control instruction transmitted from the optical path switching controller 30, the optical transmission device 20 switches the dedicated optical path that corresponds to the wireless terminal 60 whose connection destination has been switched due to handover, and which is formed between the core node 10 and the optical transmission device 25. The optical transmission device 20 may, for example, delete the dedicated optical path formed with optical transmission device 25-1 and form a new dedicated optical path with optical transmission device 25-2. Alternatively, instead of deleting and forming a dedicated optical path, the optical transmission device 20 may change the input / output port of the signal for the dedicated optical path from a port for optical transmission device 25-1 to a port for optical transmission device 25-2.

[0028] The optical transmission device 25 switches the dedicated optical path it has formed with the optical transmission device 20, corresponding to the wireless terminal 60 whose connection destination has been switched due to a handover, in response to an optical path switching control instruction transmitted from the optical transmission device controller 30. The optical transmission device 25-1 deletes, for example, the dedicated optical path formed between the optical transmission device 20 and the base station 40-1. The optical transmission device 25-2 forms a new dedicated optical path between, for example, the optical transmission device 20 and the base station 40-2.

[0029] The optical transmission device controller 30 is a control device that controls the optical transmission devices 20 and 25. Here, the control of the optical transmission devices 20 and 25 refers to the control of switching optical paths in the optical transmission devices 20 and 25. The optical transmission device controller 30 acquires information regarding wireless communication between the base station 40 and the wireless terminal 60 (hereinafter referred to as "wireless control information") from the base station controller 50 for each traffic flow.

[0030] The wireless control information includes wireless bandwidth information for each traffic flow, information indicating priority for each traffic flow, and wireless quality information. The wireless bandwidth information for each traffic flow is, for example, the PDCP (Packet Data Convergence Protocol) throughput for each traffic flow (see, for example, Non-Patent Document 3). The wireless bandwidth information for each traffic flow may also be the PDCP SDU Data Volume and PDCP PDU size for each Scheduling Request, Uplink Grant, Buffer Status Report, QFI (QoS Flow Indicator). The information indicating priority for each traffic flow is the QCI (QoS Class Indicator), 5QI (5G QoS Indicator), etc. (see, for example, Non-Patent Document 4). Wireless quality information includes RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), RSSI (Received Signal Strength Indicator), etc., for each wireless terminal 60.

[0031] Furthermore, the interface for exchanging wireless control information between the optical transmission device controller 30 and the base station controller 50 may be, for example, the Y1 interface of a Near-Real-time RIC (RAN Intelligent Controller) (see, for example, Non-Patent Document 5).

[0032] The optical transmission device controller 30 analyzes the acquired wireless control information for each traffic flow to detect when a handover of the wireless terminal 60 is performed. When the optical transmission device controller 30 determines that a handover of the wireless terminal 60 is to be performed, it decides to switch the optical path. That is, when a handover of the wireless terminal 60 is necessary, the optical transmission device controller 30 sends an optical path switching control instruction to the optical transmission devices 20 and 25. The optical transmission device controller 30 also takes into account the delay time based on pre-held delay information when sending the optical path switching control instruction to the optical transmission devices 20 and 25.

[0033] The delay information is information regarding the signal transmission delay that occurs between the core node 10 and the base stations 40, and includes, for example, the distance between the core node 10 and each base station 40, processing delays by the optical transmission devices 20 and 25 (e.g., transmission delay, delay from receiving an instruction to switch optical paths until the optical path switching is performed, etc.), or control delays from the optical transmission device controller 30 to the optical transmission devices 20 and 25 (e.g., the distance from the optical transmission device controller 30 to the optical transmission devices 20 and 25).

[0034] When switching optical paths, if the optical path switching is not performed at the appropriate timing in conjunction with the path switching associated with the handover sequence between the core node 10 and the base station 40, packet loss may occur because packets that should be sent to the source base station are sent to the destination base station instead. To prevent this packet loss, the optical transmission device controller 30 adjusts the timing of the instruction to the optical transmission devices 20 and 25 for optical path switching control. Here, adjusting the instruction timing means delaying the instruction timing for optical path switching control by taking delay information into account, or conversely, advancing the instruction timing for optical path switching control. In this example, for example, the optical transmission device controller 30 takes into account the delay due to the distance between the base station 40 and the core node 10, and the time difference from receiving the optical path switching control instruction until the optical path switching is activated, and adjusts the transmission timing of the optical path switching control so that the optical path switching is activated just before the core node 10 starts sending downlink signals to the destination base station.

[0035] The base station 40 is a device that communicates with each of the one or more wireless terminals 60. The base station 40 transmits signals transferred from the optical transmission device 25 to the wireless terminals 60 wirelessly, and converts signals received from the wireless terminals 60 into optical signals and transfers them to the optical transmission device 25. When a handover process becomes necessary due to the movement of a wireless terminal 60, the base station 40 performs the handover process in accordance with instructions from the base station controller 50.

[0036] The base station 40 may be, for example, a Wi-Fi® access point. Therefore, the signal transfer system 100 may be applied to wireless communication systems other than mobile communication systems. This is also true in the embodiments shown below.

[0037] The base station controller 50 is a device that controls each base station 40. Here, controlling the base station 40 means switching the connection with the wireless terminal 60 in response to a handover execution instruction. The base station controller 50 receives wireless control information notified from each base station 40. The base station controller 50 forwards the received wireless control information to its internal functional unit and also forwards it to the optical transmission device controller 30. Here, the wireless control information to be forwarded may be the information received from the base station 40 itself, or it may be future information predicted using, for example, machine learning. The base station controller 50 analyzes the wireless control information in its internal functional unit and determines whether a handover of the wireless terminal 60 is necessary. If the base station controller 50 determines that a handover of the wireless terminal 60 is necessary, it issues a handover instruction to each base station 40.

[0038] The wireless terminal 60 is a user terminal operated by a user. The wireless terminal 60 has one or more traffic flows. The wireless terminal 60 communicates wirelessly with the base station 40. For example, the wireless terminal 60 receives downlink signals transmitted from the core node 10 via the base station 40. For example, the wireless terminal 60 transmits uplink signals destined for the core node 10 to the base station 40.

[0039] [Device Configuration] Next, we will describe the specific configuration of each device.

[0040] The optical transmission device 20 includes an optical control unit 21. The optical control unit 21 switches optical paths according to optical path switching control instructions transmitted from the optical transmission device controller 30. For example, when the optical control unit 21 receives an optical path switching control instruction, it deletes the dedicated optical path formed between the core node 10 and the optical transmission device 25-1 and forms a new dedicated optical path between the core node 10 and the optical transmission device 25-2. Alternatively, instead of deleting and forming a dedicated optical path, the optical control unit 21 may change the input / output port of the optical signal transmitted through the dedicated optical path of the optical transmission device 20 from a port for optical transmission device 25-1 to a port for optical transmission device 25-2.

[0041] In this way, the optical control unit 21, in response to receiving an optical path switching control instruction, switches the optical path so that signals can be sent and received between the moving wireless terminal 60 and the core node 10 by forming a new dedicated optical path between the core node 10 and the optical transmission device 25-2.

[0042] The optical transmission device 25 includes an optical control unit 26. The optical control unit 26 switches optical paths according to an optical path switching control instruction transmitted from the optical transmission device controller 30. The optical control unit 26-1 of the optical transmission device 25-1 deletes the dedicated optical path formed between the optical transmission device 20 and the base station 40-1 when it receives an optical path switching control instruction. The optical control unit 26-2 of the optical transmission device 25-2 forms a new dedicated optical path between the optical transmission device 20 and the base station 40-2 when it receives an optical path switching control instruction.

[0043] In this way, the optical control unit 26, in response to receiving an optical path switching control instruction, switches the optical path so that signals can be sent and received between the mobile wireless terminal 60 and the core node 10 by forming a new dedicated optical path between the optical transmission device 20 and the base station 40-2.

[0044] The base station 40 includes an information acquisition unit 41 and a radio control unit 42. The information acquisition unit 41 acquires radio control information for each traffic flow exchanged between the wireless terminal 60 and the core node 10. Note that the information acquisition unit 41 may acquire external information such as the movement information of an automobile or the trajectory of a drone as radio control information. In the following description, as an example, the case where the information acquisition unit 41 acquires radio control information for each traffic flow from the wireless terminal 60 to the core node 10 will be described. The information acquisition unit 41 notifies the base station controller 50 of the acquired radio control information.

[0045] The radio control unit 42 performs a handover between the base stations 40-1 and 40-2 in response to an instruction from the base station controller 50.

[0046] The base station controller 50 includes an information transfer unit 51, an information analysis unit 52, and a radio control instruction unit 53. The information transfer unit 51 acquires the radio control information acquired by the information acquisition unit 41 of each base station 40. The information transfer unit 51 transfers the acquired radio control information to the information analysis unit 52 and the optical transmission device controller 30. As described above, the information transfer unit 51 may transfer the acquired radio control information as it is to the information analysis unit 52 and the optical transmission device controller 30, or may transfer the future information predicted using machine learning to the information analysis unit 52 and the optical transmission device controller 30.

[0047] The information analysis unit 52 determines whether a handover of the wireless terminal 60 is necessary based on the acquired radio control information. The method for determining whether a handover is necessary is performed based on a predetermined common algorithm or threshold determination held between the optical transmission device controller 30 and the base station controller 50, as will be described later. When the information analysis unit 52 determines that a handover of the wireless terminal 60 is necessary, it instructs the radio control instruction unit 53 to send a handover instruction.

[0048] The radio control instruction unit 53 sends a handover instruction to each of the base stations 40-1 and 40-2 that are the targets of the handover in accordance with the instruction from the information analysis unit 52.

[0049] The optical transmission device controller 30 includes a transfer information analysis unit 31 and an optical control instruction unit 32. The transfer information analysis unit 31 receives wireless control information transferred from the base station controller 50. The transfer information analysis unit 31 analyzes the received wireless control information and determines whether a handover of the wireless terminal 60 is necessary. If the transfer information analysis unit 31 determines that a handover of the wireless terminal 60 is necessary, it determines an optical path switch corresponding to the handover. An optical path switch corresponding to a handover means switching the optical path so that at least the destination base station, which will be the new connection destination of the wireless terminal 60 due to the handover, can communicate with the core node 10. Note that an optical path switch corresponding to a handover also includes switching the optical path between the source base station and the optical transmission device 25.

[0050] Here, the information analysis unit 52 of the base station controller 50 and the transfer information analysis unit 31 of the optical transmission device controller 30 make decisions regarding handover and optical path switching using predetermined common algorithms and threshold judgments, in order to ensure that optical path switching is performed without packet loss by linking the control of the base station controller 50 (handover control) and the control of the optical transmission device controller 30.

[0051] These algorithms and thresholds may, for example, be held as design values ​​from the beginning by the optical transmission device controller 30 and the base station controller 50, or an external storage medium such as a database containing information on algorithms and thresholds may be prepared, and the optical transmission device controller 30 and the base station controller 50 may acquire the information from the storage medium. Furthermore, the optical transmission device controller 30 takes into account the delay due to the distance between the base station 40 and the core node 10, and the time difference from receiving the optical path switching control instruction until the optical path switching is activated, and adjusts the transmission timing of the optical path switching control so that the optical path switching is activated just before the core node 10 starts sending the downlink signal to the destination base station.

[0052] When the optical control instruction unit 32 determines that an optical path switch is to be switched by the transfer information analysis unit 31, it sends an optical path switching control instruction to the optical transmission devices 20 and 25. The timing of sending the optical path switching control instruction is determined by taking into account the delay information, as described above.

[0053] [Operation] Figure 2 is a sequence diagram showing the processing flow of the signal transfer system 100 in the first embodiment. In Figure 1, the optical transmission devices 20 and 25 are collectively referred to as the optical transmission device (group). At the start of processing in Figure 1, it is assumed that the wireless terminal 60 is connected to the base station 40-1, which is the mobile base station. Therefore, the user signal transmitted from the wireless terminal 60 is transferred to the core node 10 via the base station 40-1.

[0054] The wireless terminal 60 transmits measurement information to each base station 40-1 and 40-2 (steps S101 and S102). Now, suppose the wireless terminal 60 moves closer to base station 40-2 in response to the user of the wireless terminal 60 moving. The information acquisition units 41-1 and 41-2 of each base station 40-1 and 40-2 acquire the measurement information transmitted from the wireless terminal 60. The information acquisition units 41-1 and 41-2 notify the base station controller 50 of the acquired measurement information as wireless control information (steps S103 and S104).

[0055] The information transfer unit 51 of the base station controller 50 receives wireless control information notified from each base station 40-1, 40-2. The information transfer unit 51 transfers the received wireless control information to the information analysis unit 52 and the optical transmission device controller 30 (step S105). The information analysis unit 52 of the base station controller 50 analyzes the wireless control information transferred from the information transfer unit 51 to determine whether a handover is necessary (step S106). At this time, the information analysis unit 52 determines whether a handover is necessary based on an algorithm and threshold judgment common to the optical transmission device controller 30. Here, it is determined that a handover is necessary.

[0056] Furthermore, the transfer information analysis unit 31 of the optical transmission device controller 30 receives wireless control information transferred from the information transfer unit 51 of the base station controller 50. The transfer information analysis unit 31 analyzes the received wireless control information to determine whether or not to perform optical path switching (step S107). At this time, the transfer information analysis unit 31 determines whether or not to perform optical path switching based on algorithms and threshold judgments common to the base station controller 50.

[0057] If a handover of the wireless terminal 60 is required, the base station 40 to which the wireless terminal 60 is connected will be changed. In this case, an optical path needs to be formed between the optical transmission devices 20 and 25 connected to the base station 40 to which the moved wireless terminal 60 is connected (for example, base station 40-2). Therefore, the transfer information analysis unit 31 may decide to perform an optical path switch when it determines that a handover of the wireless terminal 60 is required based on an algorithm or threshold judgment common to the base station controller 50. Here, let's assume that it has been determined that an optical path switch is required.

[0058] If the forwarding information analysis unit 31 determines that it is necessary to perform an optical path switch, it needs to send an optical path switch control instruction to each optical transmission device 20, 25 in order to perform the optical path switch. However, if the optical path switch is performed immediately, packet loss may occur. Therefore, the forwarding information analysis unit 31 adjusts the timing of the transmission of the optical path switch control instruction, taking into account a delay corresponding to the distance between the base station 40 and the core node 10, or the time difference from the time the optical transmission devices 20, 25 receive the optical path switch control instruction until they actually perform the optical path switch, so that the optical path switch is performed just before the core node 10 starts transmitting the downlink signal to the destination base station.

[0059] The wireless control instruction unit 53 of the base station controller 50 transmits a handover instruction to each base station 40-1, 40-2 that is subject to handover, in accordance with the judgment of the information analysis unit 52 (steps S108, S109). Base stations 40-1, 40-2 switch their connection with the wireless terminal 60 in accordance with the handover instruction from the base station controller 50 (step S110). As a result, for example, the base station 40 to which the wireless terminal 60 is connected is switched from base station 40-1 to base station 40-2. Once the connection switch is complete, base station 40-2, which is the destination base station, transmits a route change request to the core node 10 (step S111).

[0060] The core node 10 receives a route change request transmitted from the base station 40-2. The core node 10 processes the route change in response to the received route change request (step S112). Specifically, when the core node 10 transmits a signal to the wireless terminal 60, it changes the route so that it passes through the optical transmission device 25-2.

[0061] When the optical control instruction unit 32 of the optical transmission device controller 30 reaches the timing for transmitting optical path switching control, it transmits an optical path switching control instruction to the optical transmission devices 20 and 25 (step S113). The optical control units 21 and 26 of the optical transmission devices 20 and 25 switch the dedicated optical paths according to the optical path switching control instruction from the optical transmission device controller 30 (step S114). Specifically, the optical control unit 26-1 of optical transmission device 25-1 deletes the dedicated optical path with optical transmission device 20. The optical control unit 26-2 of optical transmission device 25-2 creates a dedicated optical path with optical transmission device 20. The optical control unit 21 of optical transmission device 20 switches to form a dedicated optical path with optical transmission device 25.

[0062] Through the above process, the user signal transmitted from the wireless terminal 60 is transferred to the core node 10 via the base station 40-2 (destination base station). Here, the deletion of the dedicated optical path between the optical transmission device 25-1 and the optical transmission device 20, as described earlier, may be performed when the process in step S112 is completed and the path between the optical transmission device 25-1 and the optical transmission device 20 is no longer needed.

[0063] When the core node 10 completes the route change process, it sends a route change response to the base station 40-2 indicating that the route change process is complete (step S115). The base station 40-2 receives the route change response sent from the core node 10. In response to the received route change response, the base station 40-2 causes the mobile base station 40-1 to release the connection of the wireless terminal 60 (step S116).

[0064] According to the signal transfer system 100 configured as described above, the optical transmission device controller 30 includes an optical control instruction unit 32 that, based on wireless control information acquired from the base station controller 50, instructs each optical transmission device 20, 25 that is subject to optical path switching to switch optical paths in conjunction with the timing of the handover performed by the base station controller 50.

[0065] With this configuration, when a handover becomes necessary due to the movement of the wireless terminal 60, the optical paths of the optical transmission devices 20 and 25 can be switched in conjunction with the change in connection to the destination base station to which the wireless terminal 60 is connected after the move. As described above, if the switching timing of the optical paths of the optical transmission devices 20 and 25 is too early, packets may be lost because signals that should be forwarded to the source base station are forwarded to the destination base station instead. In contrast, the optical transmission device controller 30 in this embodiment switches the optical paths in conjunction with the change in connection to the destination base station to which the wireless terminal 60 is connected after the move. Therefore, it becomes possible to switch specific optical paths related to the wireless terminal in response to the movement of the wireless terminal 60 while suppressing packet loss.

[0066] The wireless control information is the same information used by the optical transmission device controller 30 to determine whether or not an optical path switch is necessary. Therefore, the optical transmission device controller 30 can understand that the base station controller 50 will perform a handover if it determines that a handover is necessary. Furthermore, the optical transmission device controller 30 can also determine which base station 40 is the target of the handover based on the wireless control information, and can perform the optical path switch at the destination base station. At this time, the optical transmission device controller 30 adjusts the optical path switch timing based on the delay required for the optical path switch of the optical transmission devices 20 and 25 connected to the destination base station, and the distance between the destination base station and the core node 10. Therefore, the optical transmission device controller 30 can perform the optical path switch in conjunction with the handover switch timing by the base station controller 50. As a result, it becomes possible to perform a specific optical path switch for the wireless terminal 60 in response to the movement of the wireless terminal 60 while suppressing packet loss.

[0067] Furthermore, the signal transfer system 100 includes a wireless control instruction unit 53 in which the base station controller 50 transmits a handover instruction to each base station 40 that is subject to handover when a handover is necessary, based on wireless control information acquired from multiple base stations 40.

[0068] The wireless control information is the same information used by the optical transmission device controller 30 to determine whether or not to switch optical paths. The optical transmission device controller 30 and the base station controller 50 then determine whether or not to perform a handover or switch optical paths based on a predetermined common algorithm and threshold judgment. Therefore, the optical transmission device controller 30 can understand that the base station 40 to which the wireless terminal 60 is connected will switch due to a handover. As a result, the base station controller 50 sends a handover instruction to each base station 40 that is subject to the handover, and in response to the change in the base station 40 to which the wireless terminal 60 is connected, the optical paths in the optical transmission devices 20 and 25 are also switched in conjunction. Therefore, it becomes possible to switch specific optical paths related to the wireless terminal in response to the movement of the wireless terminal 60 while suppressing packet loss.

[0069] (Second Embodiment) In the first embodiment, a configuration was shown in which a base station controller receives wireless control information notified from a base station and forwards it to an optical transmission device controller. In the second embodiment, a configuration will be described in which an optical transmission device controller receives wireless control information notified from a base station and forwards it to a base station controller.

[0070] Figure 3 shows an example configuration of the signal transfer system 100a in the second embodiment. The signal transfer system 100a is a system that transfers signals from one communication device to another. The signal transfer system 100a includes, for example, a core node 10, an optical transmission device 20, an optical transmission device 25, an optical transmission device controller 30a, a base station 40, and a base station controller 50a. The signal transfer system 100a differs from the signal transfer system 100 in that it includes an optical transmission device controller 30a and a base station controller 50a instead of the optical transmission device controller 30 and base station controller 50. The differences from the signal transfer system 100 will be explained below.

[0071] Figure 3 shows a configuration in which the signal transmission system 100a comprises one optical transmission device 20, two optical transmission devices 25-1 to 25-2, and two base stations 40-1 to 40-2. Note that the number of optical transmission devices 25 and base stations 40 is not limited as long as there are two or more, and the number of optical transmission devices 20 is not limited as long as there is one or more.

[0072] The core node 10 and the optical transmission device 20, the optical transmission device 20 and the optical transmission device 25, and the optical transmission device 25 and the base station 40 are connected, for example, by an optical transmission path. In addition, the optical transmission device controller 30a and the base station controller 50a, the optical transmission device controller 30a and the optical transmission device 20, the optical transmission device controller 30a and the optical transmission device 25, and the base station controller 50a and the base station 40 are connected, for example, by a control line that transmits control signals.

[0073] The optical transmission device controller 30a is a control device that controls the optical transmission devices 20 and 25. The optical transmission device controller 30a receives wireless control information notified from each base station 40. The optical transmission device controller 30a transfers the received wireless control information to its internal functional unit and also to the base station controller 50a. Here, the wireless control information to be transferred may be the information received from the base station 40 itself, or it may be future information predicted using, for example, machine learning. The optical transmission device controller 30a analyzes the wireless control information in its internal functional unit and detects the implementation of a handover of the wireless terminal 60 in the same manner as in the first embodiment. When the optical transmission device controller 30a determines that a handover of the wireless terminal 60 is to be implemented, it decides to switch the optical path. That is, when a handover of the wireless terminal 60 is necessary, the optical transmission device controller 30a sends an optical path switching control instruction to the optical transmission devices 20 and 25. Furthermore, the optical transmission device controller 30a transmits optical path switching control instructions to the optical transmission devices 20 and 25, taking into account the delay time based on the delay information held in advance.

[0074] Furthermore, the interface for exchanging wireless control information between the optical transmission device controller 30a and the base station controller 50a may be, for example, the Y1 interface of a Near-Real-time RIC (see, for example, Non-Patent Document 5).

[0075] The base station 40 acquires wireless control information for each traffic flow exchanged between the wireless terminal 60 and the core node 10, and notifies the optical transmission device controller 30a of the acquired wireless control information.

[0076] The base station controller 50a is a device that controls each base station 40. The base station controller 50a receives wireless control information transferred from the optical transmission device controller 30a. The base station controller 50a transfers the received wireless control information to its internal functional unit. Similar to the first embodiment, the base station controller 50a analyzes the wireless control information in its internal functional unit to determine whether a handover of the wireless terminal 60 is necessary. If the base station controller 50a determines that a handover of the wireless terminal 60 is necessary, it issues a handover instruction to each base station 40.

[0077] [Device Configuration] The optical transmission device controller 30a comprises an optical control instruction unit 32, an information transfer unit 33a, and an information analysis unit 34a. The information transfer unit 33a acquires wireless control information acquired by the information acquisition unit 41 of each base station 40. The information transfer unit 33a transfers the acquired wireless control information to the information analysis unit 34a and the base station controller 50a. As described above, the information transfer unit 33a may transfer the acquired wireless control information directly to the information analysis unit 34a and the base station controller 50a, or it may transfer future information predicted using machine learning to the information analysis unit 34a and the base station controller 50a.

[0078] The information analysis unit 34a analyzes the acquired wireless control information to determine whether a handover of the wireless terminal 60 is necessary. If the information analysis unit 34a determines that a handover of the wireless terminal 60 is necessary, it decides to switch the optical path. Here, the transfer information analysis unit 54a of the base station controller 50a and the information analysis unit 34a of the optical transmission device controller 30a make decisions on handover and optical path switching using predetermined common algorithms and threshold judgments, so that the optical path switching is performed without packet loss by linking the control of the base station controller 50a (handover control) and the control of the optical transmission device controller 30a (optical path switching control).

[0079] These algorithms and thresholds may, for example, be held as design values ​​from the beginning by the optical transmission device controller 30a and the base station controller 50a, or an external storage medium such as a database containing information on algorithms and thresholds may be prepared, and the optical transmission device controller 30a and the base station controller 50a may acquire the information from the storage medium. Furthermore, the optical transmission device controller 30a takes into account the delay due to the distance between the base station 40 and the core node 10, and the time difference from receiving the optical path switching control instruction until the optical path switching is activated, and adjusts the transmission timing of the optical path switching control so that the optical path switching is activated just before the core node 10 starts sending the downlink signal to the destination base station.

[0080] When the optical control instruction unit 32 determines that an optical path switch is to be switched by the information analysis unit 34a, it transmits an optical path switching control instruction to the optical transmission devices 20 and 25. The timing of transmitting the optical path switching control instruction is determined by taking into account the delay information, as described above.

[0081] The base station controller 50a includes a wireless control instruction unit 53a and a transfer information analysis unit 54a. The transfer information analysis unit 54a receives wireless control information transferred from the optical transmission device controller 30a. Based on the received wireless control information, the transfer information analysis unit 54a determines whether a handover of the wireless terminal 60 is necessary. The method by which the transfer information analysis unit 54a determines whether a handover of the wireless terminal 60 is necessary is the same as in the first embodiment. If the transfer information analysis unit 54a determines that a handover of the wireless terminal 60 is necessary, it instructs the wireless control instruction unit 53a to transmit a handover instruction.

[0082] The wireless control instruction unit 53a transmits a handover instruction to each base station 40-1, 40-2 that is subject to handover, in accordance with the instructions of the transfer information analysis unit 54a.

[0083] [Operation] Next, the processing flow of the signal transfer system 100a in the second embodiment will be described. The wireless terminal 60 transmits measurement information to each base station 40-1, 40-2. Here, let's assume that the wireless terminal 60 moves closer to base station 40-2 in response to the user of the wireless terminal 60 moving. The information acquisition units 41-1, 41-2 of each base station 40-1, 40-2 acquire the measurement information transmitted from the wireless terminal 60. The information acquisition units 41-1, 41-2 notify the optical transmission device controller 30a of the acquired measurement information as wireless control information.

[0084] The information transfer unit 33a of the optical transmission device controller 30a receives wireless control information notified from each base station 40-1, 40-2. The information transfer unit 33a transfers the received wireless control information to the information analysis unit 34a and the base station controller 50a. The information transfer analysis unit 54a of the base station controller 50a analyzes the wireless control information transferred from the information transfer unit 33a of the optical transmission device controller 30a to determine whether a handover is necessary. At this time, the information transfer analysis unit 54a determines whether a handover is necessary based on an algorithm and threshold judgment common to the optical transmission device controller 30a. Here, it is determined that a handover is necessary.

[0085] Furthermore, the information analysis unit 34a of the optical transmission device controller 30a receives wireless control information transferred from the information transfer unit 33a. The information analysis unit 34a analyzes the received wireless control information to determine whether or not to perform optical path switching. At this time, the information analysis unit 34a determines whether or not to perform optical path switching based on algorithms and threshold judgments common to the base station controller 50a.

[0086] If a handover of the wireless terminal 60 is required, the base station 40 to which the wireless terminal 60 is connected will be changed. In this case, an optical path needs to be formed between the optical transmission devices 20 and 25 connected to the base station 40 to which the moved wireless terminal 60 is connected (for example, base station 40-2). Therefore, the information analysis unit 34a may decide to perform an optical path switch when it determines that a handover of the wireless terminal 60 is required based on an algorithm or threshold judgment common to the base station controller 50a. Here, let's assume that it has been determined that an optical path switch is required.

[0087] When the information analysis unit 34a determines that it is necessary to perform an optical path switch, it needs to send an optical path switch control instruction to each optical transmission device 20, 25 in order to perform the optical path switch. However, if the optical path switch is performed immediately, packet loss may occur. Therefore, the information analysis unit 34a adjusts the timing of the transmission of the optical path switch control instruction, taking into account a delay corresponding to the distance between the base station 40 and the core node 10, or the time difference from the time when the optical transmission devices 20, 25 receive the optical path switch control instruction until they actually perform the optical path switch, so that the optical path switch is performed just before the core node 10 starts transmitting the downlink signal to the destination base station.

[0088] The wireless control instruction unit 53a of the base station controller 50a transmits a handover instruction to each base station 40-1 and 40-2 subject to the handover, according to the judgment of the transfer information analysis unit 54a. Base stations 40-1 and 40-2 switch their connection with the wireless terminal 60 in response to the handover instruction from the base station controller 50a. As a result, for example, the base station 40 to which the wireless terminal 60 is connected is switched from base station 40-1 to base station 40-2. Once the connection switch is complete, base station 40-2, which is the destination base station, transmits a route change request to the core node 10.

[0089] The core node 10 receives a route change request transmitted from the base station 40-2. The core node 10 processes the route change in response to the received route change request. Specifically, when the core node 10 transmits a signal destined for the wireless terminal 60, it changes the route so that it passes through the optical transmission device 25-2.

[0090] The optical control instruction unit 32 of the optical transmission device controller 30a transmits an optical path switching control instruction to the optical transmission devices 20 and 25 when it is time to transmit the optical path switching control. The optical control units 21 and 26 of the optical transmission devices 20 and 25 switch the dedicated optical paths according to the optical path switching control instruction from the optical transmission device controller 30a. Specifically, the optical control unit 26-1 of optical transmission device 25-1 deletes the dedicated optical path with optical transmission device 20. The optical control unit 26-2 of optical transmission device 25-2 creates a dedicated optical path with optical transmission device 20. The optical control unit 21 of optical transmission device 20 switches to form a dedicated optical path with optical transmission device 25. After that, the processes of steps S115 and S116 shown in Figure 2 are executed.

[0091] With the signal transfer system 100a configured as described above, the optical transmission device controller 30a transfers the wireless control information acquired from each of the base stations 40 to the base station controller 50a. Then, based on the same wireless control information transferred to the base station controller 50a, the optical transmission device controller 30a instructs each optical transmission device 20, 25 that is subject to optical path switching to switch optical paths, in conjunction with the timing of the handover execution by the base station controller 50. As a result, the same effects as in the first embodiment can be obtained.

[0092] (Third Embodiment) The first embodiment showed a configuration in which a base station controller receives wireless control information notified from a base station and forwards it to an optical transmission device controller. The second embodiment showed a configuration in which an optical transmission device controller receives wireless control information notified from a base station and forwards it to a base station controller. In contrast, the third embodiment describes a configuration in which the base station notifies both the optical transmission device controller and the base station controller of wireless control information.

[0093] Figure 4 shows an example configuration of the signal transfer system 100b in the third embodiment. The signal transfer system 100b is a system that transfers signals from one communication device to another. The signal transfer system 100b includes, for example, a core node 10, an optical transmission device 20, an optical transmission device 25, an optical transmission device controller 30, a base station 40b, and a base station controller 50. The signal transfer system 100b differs from the signal transfer system 100 in that it includes a base station 40b instead of a base station 40. The differences from the signal transfer system 100 will be explained below.

[0094] Figure 4 shows a configuration in which the signal transmission system 100b comprises one optical transmission device 20, two optical transmission devices 25-1 to 25-2, and two base stations 40b-1 to 40b-2. The number of optical transmission devices 25 and base stations 40b is not particularly limited as long as there are two or more, and the number of optical transmission devices 20 is not particularly limited as long as there is one or more.

[0095] The core node 10 and the optical transmission device 20, the optical transmission device 20 and the optical transmission device 25, and the optical transmission device 25 and the base station 40b are connected, for example, by an optical transmission path. In addition, the optical transmission device controller 30 and the base station controller 50, the optical transmission device controller 30 and the optical transmission device 20, the optical transmission device controller 30 and the optical transmission device 25, and the base station controller 50 and the base station 40b are connected, for example, by a control line that transmits control signals.

[0096] The base station 40b is a device that communicates with each of the one or more wireless terminals 60. The base station 40b transmits signals transferred from the optical transmission device 25 to the wireless terminals 60 wirelessly, and converts signals received from the wireless terminals 60 into optical signals and transfers them to the optical transmission device 25. The base station 40b notifies the optical transmission device controller 30 and the base station 40 of wireless control information. When a handover process becomes necessary due to the movement of a wireless terminal 60, the base station 40b performs the handover process according to instructions from the base station controller 50.

[0097] The base station 40b may be, for example, a Wi-Fi® access point. Therefore, the signal transfer system 100b may be applied to wireless communication systems other than mobile communication systems. This is also true in the embodiments described below.

[0098] The optical transmission device controller 30 is a control device that controls the optical transmission devices 20 and 25. The optical transmission device controller 30 acquires wireless control information from the base station 40b for each traffic flow. The processing after the optical transmission device controller 30 acquires the wireless control information is the same as in the first embodiment.

[0099] The base station controller 50 is a device that controls each base station 40b. The base station controller 50 receives wireless control information notified from each base station 40b. The base station controller 50 transfers the received wireless control information to its internal functional unit. The base station controller 50 in the third embodiment is the same as in the first embodiment, except that it does not transfer the received wireless control information to the optical transmission device controller 30. That is, in the base station controller 50 in the third embodiment, wireless control information is not transferred from the information transfer unit 51 to the optical transmission device controller 30.

[0100] With the signal transfer system 100b configured as described above, each base station 40b notifies the optical transmission device controller 30 and the base station controller 50 of wireless control information. This allows the optical transmission device controller 30 and the base station controller 50 to obtain common wireless control information. The optical transmission device controller 30 then instructs each optical transmission device 20, 25 that is subject to optical path switching to switch optical paths, in conjunction with the timing of the handover execution by the base station controller 50, based on the same wireless control information obtained by the base station controller 50. Similarly, the base station controller 50 transmits a handover instruction to the base station 40 that is subject to handover when a handover is necessary, based on the same wireless control information obtained by the optical transmission device controller 30. Therefore, the same effects as in the first embodiment can be obtained.

[0101] (Fourth Embodiment) In the fourth embodiment, the signal transmission system does not include a base station controller and an optical transmission device controller, and the base station determines whether a handover is necessary, and each optical transmission device determines whether an optical path switch is necessary.

[0102] Figure 5 shows an example configuration of the signal transfer system 100c in the fourth embodiment. The signal transfer system 100c is a system that transfers signals from one communication device to another. The signal transfer system 100c includes, for example, a core node 10, an optical transmission device 20c, an optical transmission device 25c, and a base station 40c. One or more wireless terminals 60 are wirelessly connected to the base station 40c. The signal transfer system 100c differs from the signal transfer system 100 in that it does not include an optical transmission device controller 30 and a base station controller 50, and instead of optical transmission devices 20, 25 and base station 40, it includes optical transmission devices 20c, 25c and base station 40c. The differences from the signal transfer system 100 will be explained below.

[0103] Figure 5 shows a configuration in which the signal transmission system 100c comprises one optical transmission device 20c, two optical transmission devices 25c-1 to 25c-2, and two base stations 40c-1 to 40c-2. Note that the number of optical transmission devices 25c and base stations 40c is not limited as long as there are two or more, and the number of optical transmission devices 20c is not limited as long as there is one or more.

[0104] The core node 10 and the optical transmission device 20c, the optical transmission device 20c and the optical transmission device 25c, and the optical transmission device 25c and the base station 40c are connected, for example, by optical transmission lines. Furthermore, each optical transmission device 20c, 25c and the base station 40c are connected by control lines that transmit control signals.

[0105] In describing the fourth embodiment, we assume that the initial state is that the wireless terminal 60 is connected to base station 40c-1 and then to the core node 10 via optical transmission device 25c-1 and optical transmission device 20c. Then, we assume that when the wireless terminal 60 moves and a handover becomes necessary, the wireless terminal 60 connects to base station 40c-2 and then to the core node 10 via optical transmission device 25c-2 and optical transmission device 20c. Note that base station 40c-1 may also be referred to as the source base station and base station 40c-2 as the destination base station.

[0106] Optical transmission devices 20c and 25c are devices that transfer signals exchanged between the core node 10 and one or more wireless terminals 60. Optical transmission device 20c, for example, receives an uplink signal transmitted from a wireless terminal 60 from optical transmission device 25c and transfers it to the core node 10. Optical transmission device 20c, for example, transfers a downlink signal transmitted from the core node 10 to the optical transmission device 25c to which the destination wireless terminal 60 is connected.

[0107] The optical transmission device 25c, for example, receives an uplink signal transmitted from the wireless terminal 60 from the connected base station 40c and forwards it to the optical transmission device 20c. The optical transmission device 25c, for example, forwards a downlink signal forwarded from the optical transmission device 20c to the connected base station 40c.

[0108] Furthermore, the optical transmission devices 20c and 25c acquire wireless control information from the mobile base station for each traffic flow. The optical transmission devices 20c and 25c analyze the acquired wireless control information for each traffic flow to detect when a handover of the wireless terminal 60 is performed. When the optical transmission devices 20c and 25c determine that a handover of the wireless terminal 60 is to be performed, they decide to switch the optical path according to that handover. In other words, when a handover of the wireless terminal 60 is necessary, the optical transmission devices 20c and 25c perform an optical path switch within their own devices according to that handover.

[0109] In this embodiment, not only are the control of the optical transmission devices 20c and 25c (control of optical path switching) and the control of the base station 40c (control of handover) linked, but the optical path switching between multiple optical transmission devices 20c and 25c is also linked so that optical path switching is performed without packet loss. Each optical transmission device 20c and 25c and the base station 40c make decisions on handover and optical path switching using a predetermined common algorithm or threshold judgment.

[0110] These algorithms and thresholds may, for example, be held as design values ​​from the outset by each optical transmission device 20c, 25c and the base station 40c, or an external storage medium such as a database containing information on algorithms and thresholds may be prepared, and each optical transmission device 20c, 25c and the base station 40c may acquire the information from the storage medium. Furthermore, each optical transmission device 20c, 25c takes into account the delay due to the distance between the base station 40c and the core node 10, and the time difference from receiving the optical path switching control instruction until the optical path switching is activated, and adjusts the transmission timing of the optical path switching control so that the optical path switching is activated just before the core node 10 starts sending the downlink signal to the destination base station.

[0111] The optical transmission devices 20c and 25c perform optical path switching within their own devices, taking into account the delay time based on pre-held delay information. That is, the optical transmission devices 20c and 25c may adjust the transmission timing of the optical path switching control, similar to the optical transmission device controller 30 in the first embodiment. When the transmission timing for the optical path switching control is reached, the optical transmission devices 20c and 25c perform the dedicated optical path switching process.

[0112] When it is time to transmit optical path switching control, the optical transmission device 20c switches the dedicated optical path that corresponds to the wireless terminal 60 whose connection destination has been switched due to handover, and which is formed between the core node 10 and the optical transmission device 25c. The optical transmission device 20c deletes the dedicated optical path formed with, for example, the optical transmission device 25c-1 and forms a new dedicated optical path with the optical transmission device 25c-2. Alternatively, instead of deleting and forming a dedicated optical path, the optical transmission device 20c may change the input / output port of the dedicated optical path signal from the port for optical transmission device 25c-1 to the port for optical transmission device 25c-2.

[0113] When it is time to transmit optical path switching control, the optical transmission device 25c switches the dedicated optical path that corresponds to the wireless terminal 60 whose connection destination has been switched due to handover, and which is the dedicated optical path formed with the optical transmission device 20c. The optical transmission device 25c-1 deletes, for example, the dedicated optical path formed between the optical transmission device 20c and the base station 40c-1. The optical transmission device 25c-2 forms a new dedicated optical path, for example, between the optical transmission device 20c and the base station 40c-2.

[0114] The base station 40c is a device that communicates with each of the one or more wireless terminals 60. The base station 40c transmits signals transferred from the optical transmission device 25c to the wireless terminals 60 wirelessly, and converts signals received from the wireless terminals 60 into optical signals and transfers them to the optical transmission device 25c. The base station 40c acquires wireless control information, transfers the acquired wireless control information to its internal functional unit, and also transfers it to each of the optical transmission devices 20c and 25c.

[0115] Based on the acquired radio control information, the base station 40c determines whether a handover of the radio terminal 60 is necessary. If the base station 40c determines that a handover process is necessary due to the movement of the radio terminal 60, it instructs its internal functional unit to perform the handover and transmits a handover instruction to the destination base station. As a result, the handover process is performed between the source base station and the destination base station.

[0116] The base station 40c may be, for example, a Wi-Fi® access point. Therefore, the signal transfer system 100c may be applied to wireless communication systems other than mobile communication systems. This is also true in the embodiments described below.

[0117] [Device Configuration] Next, we will describe the specific configuration of each device.

[0118] The optical transmission device 20c comprises an optical control unit 21, a transfer information analysis unit 22c, and an optical control instruction unit 23c. The transfer information analysis unit 22c receives wireless control information transferred from the mobile base station. The transfer information analysis unit 22c analyzes the received wireless control information and determines whether a handover of the wireless terminal 60 is necessary. If the transfer information analysis unit 22c determines that a handover of the wireless terminal 60 is necessary, it determines an optical path switch corresponding to that handover.

[0119] Here, as described above, the control of each optical transmission device 20c, 25c (control of optical path switching) and the control of the base station 40c (control of handover) are linked to ensure that optical path switching is performed without packet loss. The transfer information analysis unit 22c of each optical transmission device 20c, the transfer information analysis unit 27c of the optical transmission device 25c, and the information analysis unit 43c-1 of the mobile base station make decisions regarding handover and optical path switching using predetermined common algorithms and threshold judgments.

[0120] When the optical control instruction unit 23c determines that an optical path switch is to be switched by the transfer information analysis unit 22c, it transmits an optical path switching control instruction to the optical control unit 21. The timing of transmitting the optical path switching control instruction is determined by taking into account the delay information, as described above.

[0121] The optical control unit 21 switches optical paths according to the optical path switching control instruction transmitted from the optical control instruction unit 23c. The optical control unit 21 of the optical transmission device 20c-1, for example, deletes the dedicated optical path formed between the core node 10 and the optical transmission device 25-1 and forms a new dedicated optical path between the core node 10 and the optical transmission device 25-2 when it receives the optical path switching control instruction. Alternatively, instead of deleting and forming a dedicated optical path, the optical control unit 21 may change the input / output port of the optical signal transmitted on the dedicated optical path of the optical transmission device 20 from a port for optical transmission device 25-1 to a port for optical transmission device 25-2.

[0122] In this way, the optical control unit 21, in response to receiving an optical path switching control instruction, switches the optical path so that signals can be sent and received between the moving wireless terminal 60 and the core node 10 by forming a new dedicated optical path between the core node 10 and the optical transmission device 25c-2.

[0123] The optical transmission device 25c comprises an optical control unit 26, a transfer information analysis unit 27c, and an optical control instruction unit 28c. The transfer information analysis unit 27c receives wireless control information transferred from the mobile base station. The transfer information analysis unit 27c analyzes the received wireless control information and determines whether a handover of the wireless terminal 60 is necessary. If the transfer information analysis unit 27c determines that a handover of the wireless terminal 60 is necessary, it determines an optical path switch corresponding to that handover.

[0124] When the optical control instruction unit 28c determines that an optical path switch is to be switched by the transfer information analysis unit 27c, it transmits an optical path switching control instruction to the optical control unit 26. The timing of transmitting the optical path switching control instruction is determined by taking into account the delay information, as described above.

[0125] The optical control unit 26 switches the optical path according to the optical path switching control instruction transmitted from the optical control instruction unit 28c-1. The optical control unit 26-1 of the optical transmission device 25c-1 deletes the dedicated optical path formed between the optical transmission device 20c and the base station 40c-1 when it receives the optical path switching control instruction. The optical control unit 26-2 of the optical transmission device 25c-2 forms a new dedicated optical path between the optical transmission device 20c and the base station 40c-2 when it receives the optical path switching control instruction.

[0126] In this way, the optical control unit 26, in response to receiving an optical path switching control instruction, switches the optical path so that signals can be sent and received between the mobile wireless terminal 60 and the core node 10 by forming a new dedicated optical path between the optical transmission device 20c and the base station 40c-2.

[0127] The mobile base station (base station 40c-1) comprises an information acquisition unit 41-1, a radio control unit 42-1, an information analysis unit 43c-1, and a radio control instruction unit 44c-1. The information acquisition unit 41-1 acquires radio control information for each traffic flow exchanged between the radio terminal 60 and the core node 10. In the following description, as an example, the case in which the information acquisition unit 41-1 acquires radio control information for each traffic flow from the radio terminal 60 to the core node 10 will be described. The information acquisition unit 41-1 notifies the information analysis unit 43c-1 and each optical transmission device 20c, 25c of the acquired radio control information.

[0128] The information analysis unit 43c-1 determines whether a handover of the wireless terminal 60 is necessary based on the acquired wireless control information. The method for determining whether a handover is necessary is based on a predetermined common algorithm and threshold judgment maintained between each optical transmission device 20c, 25 and the base station 40c. If the information analysis unit 43c-1 determines that a handover of the wireless terminal 60 is necessary, it instructs the wireless control instruction unit 44c-1 to transmit a handover instruction.

[0129] The wireless control instruction unit 44c-1 transmits a handover instruction to the wireless control unit 42-1 and the destination base station in accordance with the instructions of the information analysis unit 43c-1.

[0130] The wireless control unit 42-1 performs a handover between the base station 40c-1 and the destination base station (for example, base station 40c-2) in response to instructions from the wireless control instruction unit 44c-1.

[0131] The destination base station (base station 40c-2) is equipped with a radio control unit 42-2. The radio control unit 42-2 performs a handover with the source base station in response to instructions transmitted from the source base station.

[0132] [Operation] Figure 6 is a sequence diagram showing the processing flow of the signal transfer system 100c in the fourth embodiment. In Figure 6, each optical transmission device 20c, 25c is collectively referred to as the optical transmission device (group). At the start of processing in Figure 6, it is assumed that the wireless terminal 60 is connected to the base station 40c-1, which is the mobile base station. Therefore, the user signal transmitted from the wireless terminal 60 is transferred to the core node 10 via the base station 40c-1.

[0133] The wireless terminal 60 transmits measurement information to each base station 40c-1 and 40c-2 (steps S201 and S202). Here, let's assume that the wireless terminal 60 moves closer to base station 40c-2 in response to the user of the wireless terminal 60 moving. The information acquisition unit 41-1 of each base station 40c-1 acquires the measurement information transmitted from the wireless terminal 60. The information acquisition unit 41-1 notifies the information analysis unit 43c-1 and each optical transmission device 20c and 25c of the acquired measurement information as wireless control information (step S203).

[0134] The forwarding information analysis units 22c and 27c of each optical transmission device 20c and 25c analyze the wireless control information notified from the mobile base station to determine whether a handover is necessary and to decide on an optical path switch (step S204). Here, it is determined that a handover is necessary and that an optical path switch corresponding to that handover is decided. When an optical path switch is decided, the forwarding information analysis units 22c and 27c need to send an optical path switch control instruction to the optical control units 21 and 26 of each optical transmission device 20c and 25c in order to perform the optical path switch. However, if the optical path switch is performed immediately, packet loss may occur. Therefore, the transfer information analysis units 22c and 27c take into account a delay corresponding to the distance between the base station 40c and the core node 10, or the time difference from the moment the optical transmission devices 20c and 25c receive the optical path switching control instruction until they actually perform the optical path switching, and adjust the transmission timing of the optical path switching control so that the optical path switching is performed just before the core node 10 starts transmitting the downlink signal to the destination base station.

[0135] The information analysis unit 43c-1 of the mobile base station acquires wireless control information from the information acquisition unit 41-1. The information analysis unit 43c-1 analyzes the acquired wireless control information to determine whether a handover is necessary (step S205). At this time, the information analysis unit 43c-1 determines whether a handover is necessary based on an algorithm and threshold judgment common to each optical transmission device 20c, 25c. Here, it is determined that a handover is necessary.

[0136] If the information analysis unit 43c-1 determines that a handover is necessary, it instructs the radio control instruction unit 44c-1 to send a handover instruction. In response to the instruction from the information analysis unit 43c-1, the radio control instruction unit 44c-1 sends the handover instruction to the radio control unit 42-1 and the destination base station (for example, base station 40c-2) (step S206). The radio control unit 42-2 of base station 40c-2 receives the handover instruction sent from base station 40c-1. Subsequently, base stations 40c-1 and 40c-2 switch their connections with the radio terminal 60 (step S207). As a result, for example, the base station 40c to which the radio terminal 60 is connected is switched from base station 40c-1 to base station 40c-2. Once the connection switchover is complete, base station 40c-2, which is the destination base station, sends a route change request to the core node 10 (step S208).

[0137] The core node 10 receives a route change request transmitted from the base station 40c-2. The core node 10 processes the route change in response to the received route change request (step S209). Specifically, when the core node 10 transmits a signal destined for the wireless terminal 60, it changes the route so that it passes through the optical transmission device 25c-2.

[0138] The optical control instruction units 23c and 28c of the optical transmission devices 20c and 25c transmit an optical path switching control instruction to the optical control units 21 and 26 when it is time to transmit the optical path switching control (step S210). For example, the optical control instruction unit 23c of the optical transmission device 20c transmits the optical path switching control instruction to the optical control unit 21 of its own device, and the optical control instruction unit 28c of the optical transmission device 25c transmits the optical path switching control instruction to the optical control unit 26 of its own device. The optical control units 21 and 26 of the optical transmission devices 20c and 25c switch the dedicated optical path according to the optical path switching control instruction from the optical control instruction units 23c and 28c (step S211).

[0139] Specifically, the optical control unit 26-1 of the optical transmission device 25c-1 deletes the dedicated optical path with the optical transmission device 20c. The optical control unit 26-2 of the optical transmission device 25c-2 creates a dedicated optical path with the optical transmission device 20c. The optical control unit 21 of the optical transmission device 20c switches to form a dedicated optical path with the optical transmission device 25c.

[0140] Through the above process, the user signal transmitted from the wireless terminal 60 is transferred to the core node 10 via the base station 40c-2 (destination base station). Here, the deletion of the dedicated optical path between the optical transmission device 25c-1 and the optical transmission device 20c, as described earlier, may be performed when the process in step S209 is completed and the path between the optical transmission device 25c-1 and the optical transmission device 20 is no longer needed.

[0141] When the core node 10 completes the route change process, it sends a route change response to the base station 40c-2 indicating that the route change process is complete (step S212). The base station 40c-2 receives the route change response sent from the core node 10. In response to the received route change response, the base station 40-2 releases the connection of the wireless terminal 60 to the source base station 40c-1 (step S213).

[0142] With the signal transfer system 100c configured as described above, the same effects as in the first embodiment can be obtained even in a configuration that does not include an optical transmission device controller 30 and a base station controller 50.

[0143] (Fifth Embodiment) In the fourth embodiment, a configuration was shown in which the mobile base station notifies not only optical transmission devices connected via an optical path, but also optical transmission devices not connected via an optical path, of wireless control information. In contrast, the fifth embodiment describes a configuration in which the mobile base station notifies only optical transmission devices connected via an optical path of wireless control information.

[0144] Figure 7 shows an example configuration of the signal transfer system 100d in the fifth embodiment. The signal transfer system 100d is a system that transfers signals from one communication device to another. The signal transfer system 100d includes, for example, a core node 10, an optical transmission device 20d, an optical transmission device 25d, and a base station 40c. One or more wireless terminals 60 are wirelessly connected to the base station 40c. The signal transfer system 100d differs from the signal transfer system 100c in that it includes one optical transmission device 25d, and both the source base station 40c-1 and the destination base station 40c-2 are connected to the optical transmission device 25d. The differences from the signal transfer system 100c will be explained below.

[0145] Figure 7 shows a configuration in which the signal transmission system 100d includes two base stations 40c-1 to 40c-2. While there is no particular limit to the number of base stations 40c (as long as there are two or more), the source base station and the destination base station must be connected to the optical transmission device 25d.

[0146] The core node 10 and the optical transmission device 20d, the optical transmission device 20d and the optical transmission device 25d, and the optical transmission device 25d and the base station 40c are connected, for example, by an optical transmission path. Furthermore, the optical transmission device 25d and the mobile base station are connected by a control line that transmits control signals.

[0147] In describing the fifth embodiment, we assume that the initial state is that the wireless terminal 60 is connected to base station 40c-1 and connected to core node 10 via optical transmission device 25d and optical transmission device 20d. Then, we assume that when the wireless terminal 60 moves and a handover becomes necessary, the wireless terminal 60 is connected to base station 40c-2 and connected to core node 10 via optical transmission device 25d and optical transmission device 20d.

[0148] Optical transmission devices 20d and 25d are devices that transfer signals exchanged between the core node 10 and one or more wireless terminals 60. Optical transmission device 20d, for example, receives an uplink signal transmitted from a wireless terminal 60 from optical transmission device 25d and transfers it to the core node 10. Optical transmission device 20d, for example, transfers a downlink signal transmitted from the core node 10 to the optical transmission device 25d to which the destination wireless terminal 60 is connected.

[0149] The optical transmission device 25d, for example, receives an uplink signal transmitted from the wireless terminal 60 from the connected base station 40c and forwards it to the optical transmission device 20d. The optical transmission device 25d, for example, forwards a downlink signal forwarded from the optical transmission device 20d to the connected base station 40c.

[0150] Furthermore, the optical transmission device 25d to which the mobile base station is connected acquires radio control information from the mobile base station for each traffic flow. The optical transmission device 25d analyzes the acquired radio control information for each traffic flow to detect when a handover of the wireless terminal 60 is performed. If the optical transmission device 25d determines that a handover of the wireless terminal 60 is to be performed, it decides to switch the optical path according to that handover. In other words, when a handover of the wireless terminal 60 is necessary, the optical transmission device 25d performs an optical path switch within its own device according to that handover.

[0151] In this embodiment, the control of the optical transmission device 25d (control of optical path switching) and the control of the base station 40c (control of handover) are linked to ensure that optical path switching is performed without packet loss. The optical transmission device 25d and the base station 40c make decisions regarding handover and optical path switching using predetermined common algorithms and threshold judgments.

[0152] These algorithms and thresholds may, for example, be held as design values ​​by the optical transmission device 25d and the base station 40c from the beginning, or an external storage medium such as a database containing information on algorithms and thresholds may be prepared, and the optical transmission device 25d and the base station 40c may acquire the information from the storage medium. Furthermore, the optical transmission device 25d takes into account the delay due to the distance between the base station 40c and the core node 10, and the time difference from receiving the optical path switching control instruction until the optical path switching is activated, and adjusts the transmission timing of the optical path switching control so that the optical path switching is activated just before the core node 10 starts sending the downlink signal to the destination base station.

[0153] The optical transmission device 25d performs optical path switching within its own device, taking into account a delay time based on pre-held delay information. That is, the optical transmission device 25d may adjust the transmission timing of the optical path switching control, similar to the optical transmission device controller 30 in the first embodiment. When the transmission timing for the optical path switching control arrives, the optical transmission device 25d performs the dedicated optical path switching process.

[0154] When it is time to transmit optical path switching control, the optical transmission device 25d switches the dedicated optical path that corresponds to the wireless terminal 60 whose connection destination has been switched due to handover, and which is the dedicated optical path formed with the base station 40c. The optical transmission device 25d deletes the dedicated optical path formed with, for example, base station 40c-1. The optical transmission device 25d forms a new dedicated optical path with, for example, base station 40c-2. Alternatively, instead of deleting and forming a dedicated optical path, the optical transmission device 20d may change the input / output port of the dedicated optical path signal from the port for base station 40c-1 to the port for base station 40c-2.

[0155] The base station 40c is a device that communicates with each of the one or more wireless terminals 60. The base station 40c transmits signals transferred from the optical transmission device 25d to the wireless terminals 60 wirelessly, and converts signals received from the wireless terminals 60 into optical signals and transfers them to the optical transmission device 25d. The base station 40c acquires wireless control information, transfers the acquired wireless control information to its internal functional unit, and also transfers it only to the optical transmission device 25d connected via an optical path. The processing of the base station 40c is the same as in the fourth embodiment, except that it transfers the acquired wireless control information only to the optical transmission device 25d connected via an optical path.

[0156] [Device Configuration] Next, we will describe the specific configuration of each device.

[0157] The optical transmission device 25d comprises an optical control unit 26d, a transfer information analysis unit 27d, and an optical control instruction unit 28d. The transfer information analysis unit 27d receives wireless control information transferred from the mobile base station. The transfer information analysis unit 27d analyzes the received wireless control information and determines whether a handover of the wireless terminal 60 is necessary. If the transfer information analysis unit 27d determines that a handover of the wireless terminal 60 is necessary, it determines an optical path switch corresponding to that handover.

[0158] When the optical control instruction unit 28d determines that an optical path switch is to be switched by the transfer information analysis unit 27d, it transmits an optical path switching control instruction to the optical control unit 26d. The timing of transmitting the optical path switching control instruction is the same as in the fourth embodiment.

[0159] The optical control unit 26d switches optical paths according to the optical path switching control instruction transmitted from the optical control instruction unit 28d. For example, when the optical control unit 26d receives the optical path switching control instruction, it deletes the dedicated optical path formed with base station 40c-1. For example, when the optical control unit 26d receives the optical path switching control instruction, it forms a new dedicated optical path with base station 40c-2.

[0160] Thus, a single optical transmission device 25d is connected to both the source base station and the destination base station. In response to receiving an optical path switching control instruction, the optical control unit 26d switches the optical paths so that signals can be transmitted and received between the mobile wireless terminal 60 and the core node 10 by deleting the optical path between it and the source base station (base station 40c-1) and forming a new dedicated optical path between it and the destination base station (base station 40c-2).

[0161] With the signal transfer system 100d configured as described above, the same effects as in the first embodiment can be obtained even when the source base station and the destination base station are connected to the same optical transmission device 25d.

[0162] (Modification 1 common to the first to fifth embodiments) The base stations 40, 40b, and 40c in each of the embodiments described above may be distributed central stations and distributed stations. In this configuration, the core node 10 in each embodiment can be replaced with a central station, and the base stations 40, 40b, and 40c can be replaced with distributed stations. The central station may be considered as a CU (Central Unit) in a mobile communication system, and the distributed stations as DUs (Distributed Units) in a mobile communication system, and the present invention may be applied to a network between CUs and DUs called an MMH (Mobile Midhaul). In this case, the section between CUs and DUs where optical transmission devices 20, 20c, 20d, 25, 25c, and 25d are installed is the MMH. Alternatively, the central station in a mobile communication system may be considered as a DU in a mobile communication system, and the distributed stations as RUs (Radio Units), and the present invention may be applied to a network between DUs and RUs called an MFH (Mobile Fronthaul). In this case, the section between the DU-RU where the optical transmission devices 20, 20c, 20d, 25, 25c, and 25d are installed is the MFH. The central station may be a Wi-Fi controller, and the distributed stations may be Wi-Fi access points.

[0163] (Modification 2 common to the first to fifth embodiments) In the embodiments described above, the case in which there is one core node 10 is shown, but 100, 100a, 100b, 100c, and 100d may have multiple core nodes 10. In this configuration, the present invention may be applied to optical path switching when the core node 10 to which the wireless terminal 60 is connected is changed in conjunction with a change in the base stations 40, 40b, and 40c to which the wireless terminal 60 is connected.

[0164] The optical transmission devices 20, 20c, 20d, optical transmission devices 25, 25c, 25d, optical transmission device controllers 30, 30a, base stations 40, 40b, 40c, and base station controllers 50, 50a, which are included in the signal transmission systems 100, 100a, 100b, 100c, 100d, are configured using, for example, a processor such as a CPU (Central Processing Unit), memory, and a communication interface. Each of the optical transmission devices 20, 20c, 20d, optical transmission devices 25, 25c, 25d, optical transmission device controllers 30, 30a, base stations 40, 40b, 40c, and base station controllers 50, 50a functions as a communication device equipped with a functional unit that performs specific processing by having the processor execute a program.

[0165] The above program provides functions for enabling the communication device to function as either optical transmission devices 20, 20c, 20d, optical transmission devices 25, 25c, 25d, optical transmission device controllers 30, 30a, base stations 40, 40b, 40c, or base station controllers 50, 50a. Note that all or part of these functions may be implemented using hardware including electronic circuits (or circuits) such as LSIs (Large Scale Integrated Circuits), ASICs (Application Specific Integrated Circuits), PLDs (Programmable Logic Devices), or FPGAs (Field Programmable Gate Arrays).

[0166] The above program may be recorded on a computer-readable non-temporary recording medium. Computer-readable non-temporary recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), CD-ROMs (Compact Disc Read Only Memory), and storage devices such as hard disks built into computer systems.

[0167] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0168] The present invention can be applied to a communication system and a communication control method for accommodating wireless terminals.

[0169] 10...Core node, 20, 20d, 25, 25-1 to 25-2, 25d...Optical transmission device, 21, 26, 26d, 26-1 to 26-2...Optical control unit, 22c, 27c, 27c-1 to 27c-2, 27d, 31, 54a...Transfer information analysis unit, 23c, 28c-1, 28c-1 to 28c-2, 28d, 32...Optical control instruction unit, 30, 30a...Optical transmission device controller, 33a, 51...Information transfer unit, 34a, 43c-1, 52...Information analysis unit, 40, 40-1 to 40-2, 40b, 40b-1 to 40b-2, 40c, 40c-1 to 40c-2...Base station, 41, 41-1 to 41-2...Information acquisition unit, 42, 42-1 to 42-2... Wireless control unit, 44c-1, 53, 53a... Wireless control instruction unit, 50, 50a... Base station controller, 60... Wireless terminal, 100, 100a, 100b, 100c, 100d... Signal transfer system

Claims

1. An optical transmission device control device in a signal transfer system comprising: a plurality of base stations accommodating one or more wireless terminals; a plurality of optical transmission devices connected to at least one of the plurality of base stations; an optical transmission device control device for controlling the plurality of optical transmission devices; and a base station control device for controlling the plurality of base stations, wherein the optical transmission device control device comprises: an optical control instruction unit that, based on wireless control information which is information relating to wireless communication between the base station and the wireless terminal obtained from the base station control device or the plurality of base stations, instructs each optical transmission device subject to optical path switching to switch the optical path in conjunction with the timing of connection change with the one or more wireless terminals by the base station control device.

2. An optical transmission device control device according to claim 1, further comprising: an information transfer unit that transfers the wireless control information obtained from the plurality of base stations as is, or information obtained by processing based on the wireless control information, to the base station control device as the wireless control information, wherein the optical control instruction unit, based on the wireless control information transferred by the information transfer unit to the base station control device, instructs each optical transmission device subject to optical path switching to switch the optical path in conjunction with the timing of the base station control device's execution of the connection change with the one or more wireless terminals, when switching of the optical path is necessary under conditions common to the conditions used by the base station control device to determine whether or not to perform a connection change with the one or more wireless terminals, 3. A base station control device in a signal transfer system comprising: a plurality of base stations accommodating one or more wireless terminals; a plurality of optical transmission devices connected to at least one of the plurality of base stations; an optical transmission device control device for controlling the plurality of optical transmission devices; and a base station control device for controlling the plurality of base stations, the base station control device comprising: a wireless control instruction unit that transmits a handover instruction to each base station subject to handover when a change in connection with one or more wireless terminals is required, based on wireless control information which is information relating to wireless communication between the base station and the wireless terminal, obtained from the plurality of base stations or the optical transmission device control device.

4. The base station control device according to claim 3, further comprising: an information transfer unit that transfers the wireless control information obtained from the plurality of base stations as is, or information obtained by processing based on the wireless control information, to the optical transmission device control device as the wireless control information, wherein the wireless control instruction unit transmits a handover instruction to each base station subject to handover when a change in connection with one or more wireless terminals is required based on the wireless control information transferred by the information transfer unit to the base station control device.

5. An optical transmission device in a signal transfer system comprising a plurality of base stations accommodating one or more wireless terminals and a plurality of optical transmission devices connected to at least one of the plurality of base stations, comprising: an optical control instruction unit that instructs the switching of an optical path in conjunction with the timing of the execution of a connection change with the one or more wireless terminals that have moved at each base station subject to handover, based on wireless control information which is information relating to wireless communication between the base station and the wireless terminals, obtained from the pre-movement base station to which the one or more wireless terminals were connected before moving; and an optical control unit that executes the switching of the optical path in accordance with the instruction of the optical control instruction unit.

6. A control method performed by an optical transmission device control device in a signal transfer system comprising: a plurality of base stations accommodating one or more wireless terminals; a plurality of optical transmission devices connected to at least one of the plurality of base stations; an optical transmission device control device for controlling the plurality of optical transmission devices; and a base station control device for controlling the plurality of base stations, the control method comprising: acquiring wireless control information, which is information relating to wireless communication between a base station and a wireless terminal, from the base station control device or the plurality of base stations; and, based on the acquired wireless control information, instructing each optical transmission device subject to optical path switching to switch the optical path in conjunction with the timing of connection change with the one or more wireless terminals performed by the base station control device.

7. A control method performed by a base station control device in a signal transfer system comprising: a plurality of base stations accommodating one or more wireless terminals; a plurality of optical transmission devices connected to at least one of the plurality of base stations; an optical transmission device control device for controlling the plurality of optical transmission devices; and a base station control device for controlling the plurality of base stations, the control method comprising: acquiring wireless control information, which is information relating to wireless communication between the base station and the wireless terminal, from the plurality of base stations or the optical transmission device control device; and, based on the acquired wireless control information, transmitting a handover instruction to each base station subject to handover when a change in connection with the one or more wireless terminal is required.

8. An optical path switching method performed by an optical transmission device in a signal transfer system comprising a plurality of base stations accommodating one or more wireless terminals and a plurality of optical transmission devices connected to at least one of the plurality of base stations, wherein the optical transmission device obtains radio control information, which is information relating to wireless communication between the base station and the wireless terminal, from the base station to which the one or more wireless terminals were connected before moving, and based on the obtained radio control information, instructs each base station subject to handover to switch the optical path in conjunction with the timing of the execution of a connection change with the one or more wireless terminals that have moved, and executes the optical path switching in accordance with the instruction.

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