Relay devices, control methods, and storage media for relay communication

Abstract

A relay device relays communication between a base station device and a terminal device wirelessly. The relay device performs the following steps: when the destination device of the wireless connection in the relay path is changed during the connection with a first base station device via the relay path, it determines whether the base station device connected via the changed destination device is the first base station device or a second base station device different from the first base station device; and if the base station device connected via the changed destination device is the second base station device, it executes a first setting related to the changed relay path, and if the base station device connected via the changed destination device is the first base station device, it executes a second setting different from the first setting, that is, a second setting related to the changed relay path.

Description

Technical Field

[0001] This invention relates to a relay device, a control method, and a storage medium, and more specifically, to path setting technology in relay communication. Background Technology

[0002] In the 3rd Generation Partnership Project (3GPP), a technology has been explored in which a method is applied to backhaul links available in 5G wireless communication networks, in which terminal devices access the network (see Non-Patent Document 1). This technology is called Integrated Access and Backhaul (IAB). For example, a relay device called an IAB node establishes a connection with a 5G base station device (IAB donor: IAB host node) using a wireless link. At this time, the IAB node can be directly connected to the IAB host node by establishing a wireless link, or indirectly connected to the IAB host node by establishing a wireless link with another IAB node that is directly or indirectly connected to the IAB host node. In this system, each relay path formed via each IAB node in the IAB host node is added with an identifier to identify that relay path. The target signal is transmitted by including an identifier called BAP routing ID corresponding to one of the relay paths as information indicating the path through which the relay signal should be transmitted. Additionally, BAP stands for Backhaul Adaptation Protocol. Furthermore, the signal includes destination information indicating the terminal node in the relay path (e.g., a node that has already established a direct wireless link with a terminal device in the downlink). Each IAB node stores the identifier of each relay path and information about the IAB node indicating the next forwarding destination of the signal in each relay path in a mutually correlated manner. Upon receiving a signal, the IAB node determines whether its own device is a terminal node in the signal's relay path. If its own device is a terminal node in the relay path, the IAB node sends the signal to the terminal device connected to its own device, without forwarding the signal to another IAB node. On the other hand, if its own device is not a terminal node in the relay path, the IAB node recognizes the relay path identifier included in the signal and, based on that identifier, identifies another IAB node stored in its own device. The IAB node then forwards the signal to the designated other IAB node. This allows the base station device to provide communication services to terminal devices over a wide area.

[0003] Existing technical documents

[0004] Non-patent literature

[0005] Non-patent literature 1: 3GPP, TR38.874, V16.0.0, December 2018 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] This invention provides a technique that enables communication using relay paths to be applied in various situations.

[0008] means for solving problems

[0009] According to one aspect of the present invention, a relay device relays communication between a base station device and a terminal device wirelessly. The relay device includes: a determination mechanism that, when the destination device of the wireless connection in the relay path is changed during a connection with a first base station device via a relay path, determines whether the base station device connected via the changed destination device is the first base station device or a second base station device different from the first base station device; and a setting mechanism that, if the base station device connected via the changed destination device is the second base station device, performs a first setting related to the changed relay path, and if the base station device connected via the changed destination device is the first base station device, performs a second setting different from the first setting, i.e., a second setting related to the changed relay path.

[0010] Beneficial effects of the invention

[0011] According to the present invention, communication using relay paths can be applied to various situations.

[0012] Other features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings. Furthermore, in the drawings, the same reference numerals denote the same or similar configurations. Attached Figure Description

[0013] The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the invention and, together with the textual description, serve to explain the principles of the invention.

[0014] Figure 1 This is a block diagram illustrating an example of the structure of a wireless communication system;

[0015] Figure 2 This is a block diagram illustrating an example of the hardware layout of a relay device;

[0016] Figure 3 This is a block diagram illustrating an example of the functional arrangement of a relay device; and

[0017] Figure 4 This is a flowchart illustrating an example of the processing steps performed by a relay device. Detailed Implementation

[0018] The embodiments will now be described in detail with reference to the accompanying drawings. Furthermore, the following embodiments are not intended to limit the invention as defined in the claims, nor do they limit the invention to combinations of all features described in the claimed embodiments. Two or more of the multiple features described in the embodiments may be suitably combined. Additionally, the same reference numerals are assigned to the same or similar configurations, and repeated descriptions thereof are omitted.

[0019] (System Configuration)

[0020] Figure 1 This illustrates an example of the structure of a wireless communication system according to an embodiment. As described above, the wireless communication system of this embodiment performs relay transmission including a base station device (IAB host node) and a relay device (IAB node). Furthermore, for the sake of simplicity, Figure 1 Only the IAB host node and IAB nodes are shown, but terminal devices that can establish wireless links with each of these devices for communication are of course possible. Furthermore, the IAB host node includes a central unit (CU) that performs various control operations and a distributed unit (DU) that has the same functions as other nodes; the IAB node includes a DU. Control messages from the CU of the IAB host node are passed to another IAB node via the DU of the IAB host node, and control messages from the IAB node are passed to the CU of the IAB host node via the DU of the IAB host node. Additionally, for simplicity, the IAB host node will be described without distinguishing between CU and DU unless it is necessary to differentiate them. Furthermore, for simplicity, Figure 1 The diagram illustrates one IAB host node and five IAB nodes, but multiple IAB host nodes can exist, and the number of IAB nodes connected to each IAB host node can be four or less or six or more. For example, an IAB host node can send signals to or receive signals from terminal devices connected to it, and can also send signals to or receive signals from terminal devices that have already established a wireless connection with at least one IAB node via one or more IAB nodes. Furthermore, the IAB host node will sometimes be simply referred to as the host node, and the IAB node will sometimes be referred to as a relay node or node.

[0021] Each relay node establishes a connection to the host node, either directly or via one of other relay nodes already connected to the host node, when it is not currently connected to the host node. During connection establishment, the relay node acts as the endpoint. Additionally, a relay node can actually establish a connection with another relay node. Similarly, in this case, a relay node can establish a connection with the host node when other relay nodes relay signals between the host node and the relay node.

[0022] When a relay node establishes an RRC (Radio Resource Control) connection with a host node, the host node configures the relay node's address (BAP address) and the identifier of the relay path associated with the relay node (BAP routing ID) in the relay node's BAP. Additionally, when configuring the relay path identifier, the next forwarding destination for the signal within that relay path is also specified. For example, refer to... Figure 1 When node 106 establishes a connection with host node 101 via node 105, host node 101 sets the BAP address of node 106 and notifies the host node 101 of the BAP route ID of the relay path when node 106 sends a signal to host node 101 in the uplink. Host node 101 notifies node 106 of node 105's BAP address as information about the next forwarding destination in the relay path. Node 106 maintains its own device's BAP address and also associates the BAP route ID and the information about the next forwarding destination (node ​​105's BAP address) with each other. Additionally, in this case, node 105 stores its BAP route ID and information about the next forwarding destination (node ​​104's BAP address). Similarly, node 104 also stores its BAP route ID and information about the next forwarding destination (host node 101's BAP address). Node 104 or node 105 can obtain this information during the process of host node 101 transmitting a message to notify node 106 of the BAP route ID, or it can obtain this information through additional notifications received from the host node. Additionally, host node 101 uses, for example, an RRC Reconfiguration message to notify node 106 of the above configuration information.

[0023] Similarly, for the relay path in the downlink to node 106, host node 101 sets the identifier of the relay path. In this case, host node 101, for example, notifies node 105 of the BAP route ID of the relay path where node 106 is the next forwarding destination. Likewise, host node 101 notifies node 104 of the BAP route ID and the information of the next forwarding destination (the BAP address of node 105). Alternatively, host node 101 can use a BH routing configuration message to make this notification.

[0024] Subsequently, node 106 sends a request message to host node 101 to configure the F1 interface using the relay path in the uplink configured as described above. This request message is, for example, an F1 SETUP REQUEST message. Upon receiving this message, host node 101 sends an F1 SETUP RESPONSE message to establish the F1 interface. The F1 interface is the interface established between the IAB host node and the IAB nodes, but another interface can be configured.

[0025] As described above, the relay path between host node 101 and node 106 can be used for both uplink and downlink. When a signal is sent to host node 101, node 106 includes the BAP route ID and information about host node 101 in the signal as destination information, and sends the signal to node 105, which stores the signal in its own device as the next forwarding destination corresponding to the BAP route ID. Node 105 sends the received signal to node 104 based on the BAP route ID included in the signal, and node 104 stores the signal in its own device as the next forwarding destination corresponding to the BAP route ID. Similarly, node 104 passes the signal to host node 101. This allows the signal sent by node 106 to reach host node 101. Likewise, in the downlink, host node 101 includes the BAP route ID and information about node 106 in the signal as destination information and passes the signal to node 104 as the next forwarding destination corresponding to the BAP route ID. Then, node 104 passes the signal to node 105, which stores it as the next forwarding destination corresponding to the BAP route ID included in the signal. Similarly, node 105 also passes the signal to node 106, which stores it as the next forwarding destination corresponding to the BAP route ID included in the signal. This allows signals sent by host node 101 to reach node 106. As described above, when a new connection is established with a relay node, host node 101 sets an identifier in the relay path that includes the relay node and stores the identifier and next forwarding destination information in association between each node, thereby making the relay path available. Alternatively, relay paths can be set individually for each frequency band or for each cell deployed by the host node or node. If, for example, a wireless link is established between host node 101 and node 104 using a first frequency band and a second frequency band, then a first relay path using the first frequency band between host node 101 and node 104 and a second relay path using the second frequency band between host node 101 and node 104 can be set as a relay path between host node 101 and node 106.

[0026] The aforementioned relay transmission can be used by the host node 101 to provide communication services outside its range, where the radio waves emitted from the host node 101 within that range are powerful enough to provide communication services, or where there are terminal devices within that range capable of emitting radio waves that reach the host node 101 with sufficient power. That is, relay transmission can be used to extend the communicable range of the host node 101 to the periphery of nodes 102-106. As an example, when a node is positioned at a predetermined location (a location where it can communicate with the host node), such as next to a window in a room, it can provide sufficiently high-quality communication services to terminal devices present in the room.

[0027] For example, when a node is deployed on a moving object such as a train or bus carrying multiple terminal devices, it can provide stable communication services to the multiple terminal devices moving with the moving object. Additionally, in this case, the node may need to switch its connection to a destination node as it moves. Similarly, even a fixed node may need to switch its connection to a destination node based on changes in the wireless environment. In this case, the node is reconnected to a host node or node located on the periphery. However, for the path including the wireless link between the node and the destination, the BAP route ID is not configured, and therefore the path cannot be used as a valid relay path. Therefore, after the switch, the host node re-executes the aforementioned relay path configuration. This enables communication to be performed using the relay path after the switch.

[0028] Furthermore, a node that has already performed a handover can, for example, delete the settings associated with the relay path before the handover by sending a message indicating that a portion of the relay path has been sent from the host node to this node and deleting the settings. Since this releases the BAP route IDs for unusable relay paths, the limited range of BAP route IDs can be used effectively. On the other hand, there are situations where a node cannot receive messages from the host node, such as when the wireless link is unexpectedly disconnected. In this case, the node cannot delete the relay path settings and may unnecessarily maintain the settings information for unusable relay paths. It is possible to configure relay path identification information individually for each host node. That is, it allows two different host nodes to use the same identifier for available relay paths. Therefore, if a node connects directly to a second host node different from the first host node in the path before the handover without deleting the relay path settings, a signal that should not actually be transmitted may be transmitted, or the signal may be transmitted to an incorrect forwarding destination, based on the undeleted settings. Therefore, in the simplest form, the node is configured to reset (delete) the relay path settings when the radio link is lost (e.g., a radio link failure) or the connection destination changes. However, in this step, the relay path settings are not reset unnecessarily when the connection destination is changed without changing the host node. As a result, for example, if a relay path is configured in the node via multiple other nodes, the entire relay path settings can be deleted when the connection destination is changed only for one of those other nodes. Furthermore, if the host node before the connection destination change is different from the host node after the connection destination change, the node needs to reset the F1 interface. On the other hand, if the host node before the connection destination change is the same as the host node after the connection destination change, the node does not need to reset the F1 interface.

[0029] In this embodiment, considering the above situation, when switching connection destinations, the node determines whether the host node has changed, and changes the processing to be performed based on the determination result.

[0030] For example, if the host node changes when switching connection destinations, the node performs a first process including setting the F1 interface (e.g., sending an F1 setup response message to the changed host node). Furthermore, the first process may include, for example, resetting information stored in the node related to the relay path settings. In this case, the node can remove the host node information in the relay path along with the relay path settings. Alternatively, the node may store the stored relay path settings associated with each host node. In this case, the first process may include reading and setting the relay path settings associated with the changed host node. Additionally, the node may perform an F1 interface reset process regardless of whether there is a change in the host node. That is, the first process does not need to include F1 interface settings.

[0031] On the other hand, if the host node does not change when switching connection destinations, the node can perform a second process, such as configuring the relay path, while maintaining the settings of the FL interface. In this case, when, for example, an RRC connection is established with the switched connection destination, the node waits for a message from the host node to process the relay path configuration. Then, in response to this message, the node performs a process, such as storing the BAP route ID of the relay path in the uplink in association with the BAP address of the next forwarding destination (the switched connection destination). Additionally, if the configuration information of the relay path, including the switched connection destination as the next forwarding destination, is already maintained, the node can use this configuration information. Furthermore, the node can remove the relay path configuration information related to the connection destination before the switch, or it can keep the configuration information unchanged unless the host node sends an explicit deletion command.

[0032] To perform the above processing, the node needs to determine whether the host node changes with the change of connection destination. At this time, the node receives a handover instruction (RRC reconfiguration message) including the physical cell identifier (physCellId) corresponding to the CU of the host node. Therefore, it is assumed that when the host node changes, the physical cell identifier changes from the physical cell identifier before the handover. On the other hand, there are cases where the same host node corresponds to multiple physical cell identifiers, and even if the physical cell identifier changes, the node cannot always determine that the host node has changed. That is, the host node cannot be identified solely by the physical cell identifier. Therefore, in one example according to this embodiment, the host node notifies the relay device of an identifier different from the physical cell identifier and can identify the host node. For example, the cell identity (CellIdentity) different from the physical cell identifier is notified to the relay device. Furthermore, the cell identity is just one example, and other information can be notified to the relay device. The host node can include such an identifier in, for example, the RRC reconfiguration message, thereby sending notification of the host node's identifier to the node that first connected to the host node or the node switching connection destination. Alternatively, information indicating the correspondence between the CU and the physical cell identifier can be notified to each relay device in advance. For example, the host node and its connected nodes can broadcast the physical cell identifier (PCI) of the host node's CU. Furthermore, the host node and its connected nodes can notify newly connected nodes of the host node's PCI. Additionally, they can also send notifications of the PCIs of other nearby host nodes. Therefore, when the connection destination changes, in response to receiving the host node's PCI after a connection switch, a node can determine whether the host node has changed along with the connection destination.

[0033] The following describes an example of the arrangement of nodes to perform the above processing and the steps to be performed.

[0034] (Installation)

[0035] Figure 2This section illustrates an example of the hardware arrangement of a relay device (IAB node) according to this embodiment. In one example, the relay device is configured by including a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer configured by including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) and an ASIC (Application-Specific Integrated Circuit), and performs the overall processing of the relay device or each of the aforementioned processes by reading and executing a program stored in the ROM 202 or the storage device 204. The ROM 202 is a read-only memory that stores programs related to the processing performed by the relay device and information such as various parameters. The RAM 203 is a random access memory that serves as a workspace when the processor 201 executes the program and stores temporary information. The storage device 204 is, for example, a removable external storage device. The communication circuit 205 is, for example, a wireless communication circuit. The relay device is configured by including an antenna and baseband circuitry, RF circuitry, etc., for cellular communication as the communication circuit 205 for communicating with other devices. Furthermore, Figure 2 A communication circuit 205 is shown, but a relay device can include multiple communication circuits. For example, in addition to a wireless communication circuit for communicating with a terminal device, the relay device may also include a wireless communication circuit for communicating with a base station device (IAB host node) or another relay device. For example, the relay device may include wireless communication circuits for each frequency band, and may use wireless communication circuits for relatively high frequency bands to communicate with the base station device or another relay device, and use wireless communication circuits for relatively low frequency bands to communicate with the terminal device.

[0036] Figure 3 This illustrates an example of the functional arrangement of a relay device according to this embodiment. The relay device includes a communication unit 301, a change determination unit 302, and a setting control unit 303 as functional components. Furthermore, these functional components can be implemented, for example, when the processor 201 executes a program stored in the ROM 202 or the storage device 204. However, the invention is not limited thereto, and for example, dedicated hardware can be prepared in which at least one of these functions is implemented.

[0037] In addition to wireless communication with the terminal device, the communication unit 301 also controls wireless communication with the base station device (IAB host node) or another relay device (IAB node). That is, the communication unit 301 performs various communication control operations for relaying communication between the base station device and the terminal device. For example, if the other relay device or the base station device connected to the destination changes, the change determination unit 302 determines whether the base station device (IAB host node) connected to the destination has changed before and after the change. For example, as described above, the change determination unit 302 can indicate information such as cell identity that can identify the base station device (IAB host node) through the message when the destination is changed, and determine whether the base station device has changed based on the indicated information. In addition, the change determination unit 302 can obtain and maintain information for associating the base station device with the physical cell identifier in advance, identify the base station device through the physical cell identifier notified when receiving the RRC message, and determine whether the base station device has changed based on the identification result.

[0038] The setting control unit 303 makes various settings, such as communication settings in the communication unit 301 and settings related to the relay path used for relay transmission. For example, in response to detecting a nearby base station device or another relay device, the setting control unit 303 establishes a connection with one of these devices by performing a random access step, and then performs the relay path setting process as described above. For example, the setting control unit 303 obtains the BAP route ID corresponding to the relay path and the BAP address of the next forwarding destination of the signal in the relay path from the message received from the base station device (IAB host node), and maintains them. The setting control unit 303 also maintains the BAP address of its own device. This enables relay transmission. Furthermore, when the connection destination changes, the setting control unit 303 causes the change determination unit 302 to perform the above-described determination process, and performs setting control processing corresponding to the determination result.

[0039] If a base station device changes in response to a change in the connection destination, the setting control unit 303 performs F1 interface setting processing with the changed base station device as the first process. In the first process, all setting information of the relay path set for the base station device before the change can be reset. For example, the setting information of the relay path can be saved for each base station device. In this case, the setting information of the relay path used before the base station device change is not deleted, and can be stored in the storage device 204, etc., along with information that can identify the base station device (e.g., cell identity). At this time, if the setting information of the relay path associated with the changed base station device is stored, the setting control unit 303 can read the setting information from the storage device 204, etc., as the setting information to be used.

[0040] If the base station device does not change its settings in response to the change in the connection destination, the setting control unit 303 maintains the F1 interface as a second process. That is, in the second process, the execution of the F1 interface setting process can be prevented. In this case, although the F1 interface is maintained, settings related to the relay path via the new connection destination are made. Alternatively, for example, in response to an instruction from the base station device, the setting information of the relay path used before the change in the connection destination can be removed.

[0041] (Processing steps)

[0042] Figure 4 This section illustrates examples of processing steps performed by a relay device (IAB node) according to this embodiment. Details of each process are as described above. Therefore, an overview of the processing steps will be provided, and their detailed descriptions will be omitted. This embodiment assumes that the relay device is connected directly or via another relay device to a base station device (IAB host node), and that the relay path setup and F1 interface establishment are complete. In this state, for example, based on the degradation of the wireless quality of the wireless connection established with the base station device or other relay device, the relay device switches the wireless connection to a connection with another device (S401). In response to the switch of the wireless connection, the relay device determines whether the base station device (host node) of the connection destination has changed (S402). For example, as described above, the relay device can perform the determination process in step S402 based on information that identifies the base station device, such as a cell identity different from the physical cell identifier. Alternatively, for example, the relay device can obtain information indicating the correspondence between the physical cell identifier and the base station device in advance, and perform the determination process in step S402, for example, based on the physical cell identifier obtained via the RRC message during the connection processing in step S401.

[0043] Then, if the relay device determines that the base station device has changed ("Yes" in step S402), it performs the F1 interface establishment process and, for example, deletes the settings maintained related to the relay path (BAP route ID, next forwarding destination of the signal, BAP address, etc.) in the first setting process (S403). Additionally, if, for example, the setting information of the relay path connected to the base station device is maintained along with information that can identify the base station device, the relay device can disable the setting information of the relay path associated with the base station device before the change. If the setting information of the relay path associated with the changed base station device is maintained, the relay device can enable that setting information. On the other hand, if the relay device determines that the base station device has not changed ("No" in step S402), it performs the second setting process, for example, deleting or disabling the settings related to the relay path used by the wireless connection before the change (BAP route ID, next forwarding destination of the signal, BAP address, etc.), while maintaining the F1 interface (S404). In this case, the relay device can maintain the setting information related to the relay path used before the wireless connection change without deleting or disabling it. Additionally, if, for example, no configuration information related to the changed relay path is held in advance, the relay device performs relay path configuration processing. For example, the relay device holds information about the BAP route ID and the next forwarding destination of the signal (as well as the BAP address, if necessary) specified by the base station device in the changed relay path, and uses them thereafter in relay transmission.

[0044] In the above steps, the relay path is flexibly configured to make various changes, thereby enabling relay transmission to be performed appropriately between the base station device and the terminal device.

[0045] The present invention is not limited to the foregoing embodiments, and various changes or modifications can be made within the spirit of the present invention.

Claims

1. A relay device that relays communication between a base station device and a terminal device wirelessly, the relay device comprising: The determining mechanism, when the connection destination device of the wireless connection in the relay path is changed during the connection with the first base station device via the relay path, determines whether the base station device connected via the changed connection destination device is the first base station device or a second base station device different from the first base station device; and The setting mechanism performs a first setting related to the changed relay path when the base station device connected via the changed connection destination device is the second base station device, and performs a second setting different from the first setting when the base station device connected via the changed connection destination device is the first base station device. in, The setting mechanism does not remove the relay path setting between the first base station device during the connection with the second base station device, but maintains it.

2. The relay device according to claim 1, wherein, The setting mechanism performs settings related to the changed relay path while maintaining the F1 interface established with the first base station device, as the second setting.

3. The relay device according to claim 1, wherein, The setting mechanism performs the process of establishing an F1 interface with the second base station device, as the first setting.

4. The relay device according to claim 3, wherein, The setting mechanism sends an F1 setting request to the second base station device as the first setting.

5. The relay device according to claim 1, wherein, The setting mechanism removes the relay path setting between itself and the first base station device, and uses this as the first setting.

6. The relay device according to claim 1, wherein, The settings associated with the relay path include storing the relay path identifier and information indicating the next forwarding destination of the signal in the relay path.

7. The relay device according to claim 1, wherein, The settings associated with the relay path include storing information about the relay device used in the relay transmission.

8. The relay device according to claim 1, wherein, The determining mechanism determines, based on the identifier received via the modified connection destination device, whether the base station device connected via the modified connection destination device is the first base station device or the second base station device.

9. The relay device according to claim 8, wherein, The identifier is the cell identity.

10. The relay device according to claim 8, wherein, The relay device further includes an acquisition mechanism, which pre-acquires information that associates the base station device with the physical cell identifier. The identifier is the physical cell identifier.

11. A control method executed by a relay device that wirelessly relays communication between a base station device and a terminal device, the control method comprising the following steps: If the destination device of the wireless connection in the relay path is changed during the connection with the first base station device via the relay path, it is determined whether the base station device connected via the changed destination device is the first base station device or a second base station device different from the first base station device. If the base station device connected via the changed destination device is the second base station device, a first setting related to the changed relay path is executed. If the base station device connected via the changed destination device is the first base station device, a second setting different from the first setting, i.e., a second setting related to the changed relay path, is executed. in, During the connection with the second base station device, the relay path setting between the first base station device is not removed but maintained.

12. A computer-readable storage medium storing a program that causes a computer in a relay device that relays communication wirelessly between a base station device and a terminal device to perform the following steps: If the destination device of the wireless connection in the relay path is changed during the connection with the first base station device via the relay path, it is determined whether the base station device connected via the changed destination device is the first base station device or a second base station device different from the first base station device. If the base station device connected via the changed destination device is the second base station device, a first setting related to the changed relay path is executed. If the base station device connected via the changed destination device is the first base station device, a second setting different from the first setting, i.e., a second setting related to the changed relay path, is executed. in, During the connection with the second base station device, the relay path setting between the first base station device is not removed but maintained.

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