JP2022172686A - Relay device, control method, and program for making handover processing of radio relay station sophisticated - Google Patents

Abstract

To enable a flexible and effective handover in a wireless communication system that performs relay transmission by IAB.SOLUTION: In a wireless communication system in which a plurality of relay stations are wirelessly connected in series from a control device to form a communication path, a relay device included in the plurality of relay stations determines to perform a handover from a device connected to the control device side when viewed from the relay device in the communication path to another connection destination device. When it is determined to perform the handover, the relay device transmits a notification of the handover to the other connection destination device and including information on the other connection destination device to another relay device connected to the opposite side of the control device when viewed from the relay device in the communication path, determines whether the other relay device maintains connection with the relay device, and when determining to perform the handover, performs handover processing corresponding to a result of the determination.SELECTED DRAWING: Figure 5

Description

The present invention relates to advanced technology for handover processing in radio relay stations.

In the 3rd Generation Partnership Project (3GPP), IAB (Integrated Access and Backhaul) for relay transmission is standardized by applying a method of terminal device access to a network to a backhaul link. In the IAB, an IAB node that operates as a relay device establishes a wireless access link with an IAB donor that is connectable to the core network and controls relay transmission, using the function of a terminal device. Note that multiple IAB nodes can be directly connected to one IAB donor. Also, after an IAB node establishes a connection with an IAB donor, it can establish a connection with another IAB node acting as a terminal device. That is, multiple IAB nodes can be connected in series to one IAB donor. In the following, when viewed from the IAB node, the side of the IAB donor is called upstream, and the opposite side is called downstream. That is, in a configuration in which an IAB donor and IAB node A are directly connected, IAB node B is directly connected to IAB node A, and IAB node C is directly connected to IAB node B, from the perspective of IAB node B, IAB node A and IAB node A are directly connected. The IAB donor is the upstream device and IAB node C is the downstream device. An IAB donor can perform a handover to switch destination IAB donors or IAB nodes. This allows the IAB node to perform relay transmission with an IAB donor or IAB node having better radio quality as an upstream device.

In handover, after the communication quality of the wireless link being connected to the terminal equipment deteriorates, processing such as preparation for handover on the core network side is started, and an instruction message is normally sent from the base station equipment to the terminal equipment. method. However, with this method, it takes time to process from when the communication quality actually deteriorates to when the handover instruction is transmitted, so the time during which communication is not possible or the communication quality is insufficient may be prolonged. On the other hand, a method of executing this preparation process in advance and switching the connection destination cell without receiving an instruction message from the base station apparatus when a predetermined condition is satisfied in the terminal apparatus. is defined (see Non-Patent Document 1). The predetermined condition is, for example, when the wireless quality of the adjacent cell is better than the wireless quality of the connected cell by a predetermined level or more, or when the wireless quality of the connected cell is equal to or lower than a predetermined value. include. According to this method, preparations for handover on the core network side are completed before the deterioration of communication quality that should be executed by handover occurs, so the time during which communication is not possible or communication quality is insufficient can be greatly reduced. be able to. Such a handover is called conditional handover (CHO). Non-Patent Document 2 describes that this conditional handover is applied to the handover in the terminal function of the IAB node.

3GPP TR38.874, V16.0.0, December 2018 3GPP contribution, R3-210001, January 2021

As noted above, multiple IAB nodes may be connected in series. In this case, when a handover is performed, it is assumed that the second IAB node downstream from the first IAB node performing the handover switches the destination IAB donor together with the first IAB node. However, after the handover, the first IAB node is capable of communication that satisfies requirements such as delay, but the second IAB node may not be able to perform communication that satisfies the requirements. In addition, considering the IAB nodes connected downstream, the IAB node may significantly limit the degree of freedom of handover.

The present invention provides a technology that enables flexible and effective handover in a wireless communication system that performs relay transmission by IAB.

A relay device according to an aspect of the present invention is a relay device included in a plurality of relay stations in a wireless communication system in which a communication path is formed by wirelessly connecting a plurality of relay stations in series from a control device, determining means for determining to execute handover from a device connected to the control device side viewed from the relay device in the communication path to another connection destination device; A notification of handover to the another connection destination device, the notification including information of the another connection destination device is connected to the opposite side of the control device as seen from the relay device in the communication path. transmitting means for transmitting data to another relay device that is connected to the relay device; determining means for determining whether or not the other relay device maintains connection with the relay device; and an executing means for executing a handover process corresponding to the result of.

Another relay device according to an aspect of the present invention is a relay device included in the plurality of relay stations in a wireless communication system in which a plurality of relay stations are wirelessly connected in series from a control device to form a communication path. is a notification that another relay device connected to the control device side as viewed from the relay device in the communication path performs handover from the currently connected device to another connection destination device, Receiving means for receiving the notification containing information of another connection destination device from the other relay device; and determining means for determining whether to maintain the connection with the other relay device based on the notification. and executing means for executing handover processing for connecting to the control device or another control device without going through the other relay device when it is determined not to maintain the connection with the other relay device. and have

According to the present invention, flexible and effective handover in a wireless communication system that performs relay transmission by IAB becomes possible.

It is a figure which shows the structural example of a radio|wireless communications system. It is a figure which shows the hardware structural example of an IAB node. FIG. 4 is a diagram showing an example of the functional configuration of an IAB node that executes handover; It is a figure which shows the functional structural example of the IAB node of a downstream side. FIG. 3 is a diagram illustrating an example of the flow of processing performed in a wireless communication system;

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined arbitrarily. Also, the same or similar configurations are denoted by the same reference numerals, and redundant explanations are omitted.

(System configuration)
FIG. 1 shows a configuration example of a wireless communication system according to this embodiment. This radio communication system is a radio relay transmission system using IAB (Integrated Access and Backhaul) defined by the 3GPP standards. A wireless relay transmission system using IAB includes IAB donors (IAB donors X to Z) and IAB nodes (IAB nodes A to F). The IAB donor has a function (Central Unit, CU) as a control device that controls relay transmission and a function (Distributed Unit, DU) as a base station device that performs processing for transmission and reception of radio signals. On the other hand, an IAB node has a function (Mobile Termination, MT) and DU to operate as a terminal device, and wirelessly connects to any IAB donor by MT, either directly or via another IAB node. The IAB node then operates to relay communications between User Equipment (UE) and the IAB donor, performing relay transmissions under the control of the connected IAB donor's CU.

In the example of FIG. 1, the IAB donor X is directly connected to the IAB node A by radio. IAB node A relays communications between IAB donor X and its directly connected UEs under the control of IAB donor X's CU. The IAB node A establishes a connection with the MT of the IAB node E in a state in which the relay transmission of the IAB donor X can be executed, in the same procedure as the connection procedure with the UE, and the IAB node E establishes the connection with the IAB donor X. A communication path with relay transmission is established by executing the settings related to relay transmission between them. Similarly, IAB node F is connected to IAB node E to establish a communication path involving relay transmission. In this manner, a communication path is established by wirelessly connecting a plurality of relay stations (IAB nodes) in series. Note that this is an example, for example, IAB node F is directly connected to IAB node A, and a first communication path of IAB donor X-IAB node A-IAB node E and IAB donor X-IAB node A-IAB node F and a second communication path may be formed in parallel. However, when focusing on each communication path, it can be said that a communication path is formed in which one or more relay stations are wirelessly connected in series from the IAB donor to the terminal IAB node. .

In the example of FIG. 1, in addition to the communication path including IAB node A and IAB nodes E to F under IAB donor X as described above, IAB donor Y and IAB nodes B to C are formed. Communication paths and communication paths formed by IAB donor Z and IAB node D are shown.

IAB nodes can connect with DUs of IAB donors or other IAB nodes using MTs that function as terminal equipment as described above. An IAB MT can perform a handover to switch the destination IAB donor/IAB node in the same way as a normal UE. As described above, handover includes a conventional first method in which a terminal device switches connection destinations in accordance with an instruction from the network side, and a method in which a terminal device switches connection destinations from the network side when a predetermined condition is satisfied in the terminal device. There is a second way to perform a handover without receiving an indication message. This second approach is called "conditional handover (CHO)".

In CHO, a terminal device to be handed over measures the surrounding radio quality and notifies it to the base station device. Based on the notified radio quality, the base station apparatus determines another base station apparatus as a candidate for handover of the terminal apparatus, and requests handover of the terminal apparatus to the other base station apparatus. Another base station apparatus executes settings for establishing connection with the terminal apparatus before handover is actually performed, generates setting information, and transmits the setting information to the base station apparatus to which the terminal apparatus is connected. Upon receiving the setting information, the base station apparatus notifies the terminal apparatus of the setting information and predetermined conditions for executing handover. Here, the setting information can include, for example, a physical cell identifier that enables designation of the handover destination. Note that the predetermined condition may differ, for example, for each handover destination base station apparatus. As an example of the predetermined condition, for example, in the terminal device, the radio quality of the adjacent cell is better than the radio quality of the cell being connected to by a predetermined level or more, or the radio quality of the cell being connected is less than or equal to a predetermined value. can be determined to be satisfied if When the terminal device determines that the notified predetermined condition is satisfied, the terminal device disconnects the connection with the base station device without receiving an instruction message from the connected base station device, and performs preliminary handover. establishes a connection with another base station apparatus whose setting information is notified to. After that, the handover source base station apparatus receives a handover success notification from another handover destination base station apparatus to which connection with the terminal apparatus has been established, and another handover candidate set in advance as a handover candidate. The base station apparatus can be notified of the cancellation of the handover and cleared of the preset information. According to the above processing, when the terminal apparatus establishes a connection with another base station apparatus to which handover is to be performed, the post-handover setting information is held between the terminal apparatus and the other base station apparatus. Communication can start immediately. Therefore, it is possible to prevent the disconnection of communication caused by handover.

In this embodiment, the IAB node E is connected to the IAB donor X via the IAB node A, and the IAB node C is connected to the IAB donor Y (relay transmission is performed under the control of the IAB donor Y). state). In this case, it can be assumed that the IAB node F under the control of the IAB node E maintains the connection with the IAB node E and hands over together with the IAB node E to the control of the IAB donor Y. However, in this example, the IAB node E requires 2 hops to reach the IAB donor before the handover, whereas it requires 3 hops after the handover. The IAB node E can select the IAB node C as a connection destination with which communication can be performed within the allowable delay range as the handover destination. Communication may become impossible. In addition, the amount of resources (frequency/time resources and computational resources) available for relay transmission on the communication path from IAB donor Y to IAB node C decreases after IAB node E handover. Therefore, resources available for communication of the IAB node F may not be secured. In such a case, the IAB node F should handover to another connected device, for example. However, if the IAB node F performs handover after the IAB node E performs handover and attempts communication on the line after the handover, the IAB node F cannot communicate for a long period of time.

In this embodiment, in view of such circumstances, when an IAB node such as IAB node F where another IAB node exists between the IAB donor that controls the relay transmission, the other IAB node is handed over In addition, a technology is provided that enables handover to be flexibly connected to any IAB node without going through another IAB node as required. In this embodiment, as an example, the IAB node E connects to the IAB node C by handover, and the IAB node F does not maintain the connection with the IAB node E in the handover, and uses the IAB node D as the connection destination. , handover to another IAB donor Z. However, this is only an example, and IAB nodes E and F may be handed over to one of the IAB donors via another destination device. Also, in handover, it is sufficient to switch the directly connected device, and the connected IAB donor does not have to be changed. For example, IAB node F may handover to IAB node A when IAB node E changes the connected device to IAB node C due to handover. In this case, the IAB donor under IAB node F remains unchanged from IAB donor X before and after the handover. Further, when the IAB node E changes the connection destination device to the IAB node C by handover, the IAB node F may also handover to the IAB node C as the connection destination. In this case, IAB nodes E and F are connected to IAB node C in parallel. Alternatively, the IAB node F may be connected to the IAB node B. Also, the IAB node E can perform handover without changing the final connection destination IAB donor, such as switching the connection destination from the IAB node A to the IAB donor X, for example. In this way, IAB nodes E and F can connect to another device in various topologies by handover.

In this embodiment, IAB nodes E and F shall perform a conditional handover (CHO). For this purpose, the IAB nodes E and F measure the surrounding radio environment and notify the IAB donor X of the measurement results prior to the CHO. Then, IAB donor X determines handover destination candidate devices (direct connection destination devices) for each of IAB nodes E and F, and sends IAB nodes E and F to IAB donors who have the candidate devices under their control. send a message requesting a handover of Note that, for example, when the IAB donor X determines that the IAB node E satisfies the handover condition for CHO, the IAB node F connected downstream does not satisfy the condition, even if the IAB node F does not satisfy the condition. F also sends a handover request for CHO. That is, when starting preparations for CHO for one IAB node, preparations for CHO are also started for other IAB nodes connected downstream. It should be noted that the connection destination candidate devices at the time of handover between the IAB nodes E and F may differ from each other. For example, IAB node E includes IAB node C and IAB node B as connection destination candidate devices, and IAB node F includes IAB node A, IAB node C, and IAB node D as connection destination candidate devices. can contain The message requesting handover (for example, HANDOVER REQUEST message) may be the same as the message sent during CHO of a normal terminal device, and in one example, the relay as an IAB node is performed after handover It may contain information necessary for the settings for

The IAB donors (eg, IAB donors Y and Z) that host candidate handover devices for IAB node E or F receive the message requesting the handover. Then, the IAB donor determines, for example, whether handover can be accepted or not, and communication parameters after handover, for nodes that may be handed over under its own control of IAB nodes E and F, Information indicating the outcome of the decision is communicated to the source IAB donor. This notification can be made, for example, by a response message to a message requesting handover (eg, a HANDOVER REQUEST ACKNOWLEDGE message). At this point, the handover destination IAB donor determines the number of relays (the number of hops) from the IAB node to the IAB node to which IAB node E or F is connected, the transmission delay, and the number of relay transmissions. Information indicating the amount of available resources, the frequency and transmission power used for relay transmission, information on the functions of the relay device used for relay transmission (available frequencies, maximum transmission power, presence or absence of coverage extension function), congestion degree, etc. can be notified. If the handover source IAB donor knows such information in advance, for example, when information is exchanged periodically, this notification may be omitted. Also, the handover destination IAB donor may notify the handover source IAB donor of parameters for the IAB node E or F to perform relay transmission as a subordinate IAB node after handover.

Then, the handover source IAB donor (IAB donor X) sends information such as post-handover communication parameters related to each of the connection destination candidates and handover identification information corresponding to the handover destination to each of the IAB nodes E and F. to be notified. This notification can be made, for example, by a radio resource control (RRC) message (eg, RRCReconfiguration message). As an example, the IAB donor X notifies the IAB node E of the information of the IAB nodes B and C as connection destination candidate information, and the IAB donor X notifies the IAB node F of the connection destination candidate information of the IAB Nodes A, C and D information may be advertised. This completes the preparation for CHO.

After that, IAB node E satisfies the conditions for executing CHO, for example, when the radio quality of the signal from IAB node C exceeds the value obtained by adding a predetermined offset to the radio quality of the signal from IAB node A. and In this case, IAB node E disconnects from IAB node A and performs a random access procedure with IAB node C in order to connect to IAB node C. Here, in this embodiment, when the IAB node E decides to execute CHO to the IAB node C, the IAB node E notifies the IAB node F of the handover from the IAB node E to the IAB node C. I do. This notification is performed using, for example, an RRC message (eg, RRC Reconfiguration message) or a relay transmission control message (eg, BAP (Backhaul Adaptation Protocol) control PDU (Protocol Data Unit)). IAB node F may decide whether to maintain connection with IAB node E based on this notification. That is, IAB node F maintains a connection with IAB node E to form a communication path of IAB donor Y--IAB node B--IAB node C--IAB node E--IAB node F; Determines whether to connect to another handover destination candidate without maintaining the connection.

For example, IAB node F specifies the number of hops from itself to the IAB donor when maintaining connection with IAB node E, and does not maintain connection with IAB node E if the number of hops exceeds a predetermined number. can decide. In addition, the IAB node F estimates the delay time from itself to the IAB donor when maintaining the connection with the IAB node E, and maintains the connection with the IAB node E when the estimated delay time exceeds a predetermined value. can decide not to. In these cases, the IAB node F selects another connection destination device whose number of hops is equal to or less than a predetermined number or whose estimated delay time is equal to or less than a predetermined value, and executes handover to that device. can be done. According to these, the IAB node F prevents the IAB node F from maintaining the connection with the IAB node E even though the predetermined request cannot be satisfied for the delay time when the communication is actually performed. It is possible to handover to a connected device that can satisfy the request. Also, IAB node F may decide not to maintain a connection with IAB node E if the congestion of the communication path from the device to which IAB node E is connected to the IAB donor exceeds a predetermined level. In this case, the IAB node F can, for example, select another destination device whose congestion level is below a predetermined level, and execute handover to that device. According to this, it is possible to prevent the IAB node F from being unable to perform satisfactory communication due to the congestion of the communication path due to the handover of the IAB node E. In addition, IAB node F ensures the stability of communication based on information on the frequency and transmission power used in the communication path from the device to which IAB node E is connected to the IAB donor, and the function of the relay device used for relay transmission. If it can determine that it cannot, it may decide not to maintain the connection with IAB node E. In this case, the IAB node F selects another connection destination device that uses a frequency sufficient to ensure communication stability (for example, a frequency of 6 GHz or less) for the communication path, and performs handover to that device. be able to. Handover to another connection device that uses a repeater with a higher maximum transmission power for the medium-term route or that realizes relay transmission by a repeater that has a function to improve communication stability (e.g., coverage extension function) can also be executed. According to this, it is possible to prevent the IAB node F from losing communication stability due to the IAB node E's handover.

Information indicating a candidate device to which the IAB node E is connected, the number of hops from the connection destination device to the IAB donor that has the device under its control, and the IAB that has the device under its control from the connection destination device Information such as at least one of the delay time to the donor and the congestion degree of the communication path to the device to which it is connected and to the IAB donor who has the device under its control is included in the message for setting CHO from the IAB donor , to the IAB node E. Similarly, information indicating a candidate device to which the IAB node F is connected, the number of hops from the connection destination device to the IAB donor that has the device under its control, and the device from the connection destination to the IAB donor that has the device under its control. Information such as at least one of the delay time to the IAB donor and the degree of congestion of the communication path to the device to which it is connected and to the IAB donor who has the device under its control is a message for setting CHO from the IAB donor , the IAB node F is notified. Then, for example, when the IAB node E decides to perform a handover, the IAB node E notifies the IAB node F of information indicating the device to be connected by the handover, as well as information such as the number of hops, delay time, or degree of congestion. sell. As a result, the IAB node F can compare information such as the number of hops, delay time, or congestion level of the candidate device to which the IAB node F is to handover, with the information of the device to which the IAB node E is to handover. It becomes possible.

In addition, for IAB node F, information indicating a candidate device for connecting to IAB node E, the number of hops from the connecting device to the IAB donor that has the device under its control, and from the connecting device Even if information such as at least one of the delay time to the IAB donor who has the device under control and the congestion degree of the communication path to the device at the connection destination and the IAB donor who has the device under control is notified in advance good. That is, when an IAB node is the target of handover, the connection destination after the handover of the IAB node that is the target of handover is sent to another IAB node connected downstream of the IAB node in the current communication path. Information indicating a candidate device for , and information such as the number of hops, delay time, or degree of congestion when connecting to the device can be notified in advance. When the IAB node E decides to execute the handover, the IAB node E notifies the IAB node F of information indicating the connected device selected as the handover destination. In this case, since the IAB node F can acquire in advance information such as the number of hops, the delay time, or the degree of congestion for each of the candidate devices to which the IAB node E connects, the device selected by the IAB node E By notifying only the indicated information, the IAB node F can specify other information. Note that handover identification information can be set by the IAB donor for each candidate device to which the IAB node E is connected. Thus, the IAB node E may inform the IAB node F of the handover identification information corresponding to the selected destination device. Note that this is just an example, and any information that can identify the selected connection destination device between IAB node E and IAB node F may be used.

Also, the IAB node F, for example, determines that the quality of the radio signal from the connection destination candidate device set as its own CHO information is a value obtained by adding an offset to the radio signal quality of the signal from the IAB node E. Even if the IAB node E does not perform handover, such as when exceeding the number of devices, the connection with the IAB node E may be disconnected and the handover may be performed to another destination device. At this time, the IAB node F, for example, determines to execute the handover from the IAB node E based on information such as the number of hops, delay time, or congestion degree for each connection destination candidate device. good. As a result, regardless of the status of the IAB node E, the IAB node F can connect to the appropriate connection destination device when there is an appropriate connection destination device.

Note that, for example, when the IAB node F receives information indicating a connection destination device due to the handover of the IAB node E, the radio quality of the signal from the connection destination candidate device due to its own handover does not reach a predetermined value. , it may decide to maintain the connection with the IAB node E regardless of conditions such as the number of hops, delay time, congestion level, etc., if the conditions for handover are not met. That is, the IAB node F may decide to maintain the connection with the IAB node E regardless of other conditions, such as when the communication status deteriorates when the connection with the IAB node E is cut.

IAB node F may, for example, send a predetermined message to IAB node E indicating whether or not to maintain the connection with IAB node E. The predetermined message can be, for example, an RRC message (eg, RRCReconfigurationComplete message). In one example, IAB node F may send this predetermined message to IAB node E before it performs a handover. Also, the IAB node F may transmit this predetermined message to the IAB node E when disconnecting from the IAB node E. FIG. Based on this predetermined message, IAB node E may determine whether IAB node F maintains a connection with (through) itself. Note that this is just an example. For example, the IAB node E determines whether the IAB node F maintains the connection based on whether or not it has detected that the IAB node F has performed processing for disconnection from the IAB donor X. It may be determined whether In addition, the IAB node E, in response to the fact that the IAB node F did not perform processing for disconnection from the IAB node E within a predetermined period after transmitting the handover notification to the IAB node F, the IAB node E Node F determines that it maintains the connection.

IAB node E performs a handover such that a communication path with relay transmissions including IAB node F is established if IAB node F maintains the connection. In one example, IAB node E performs a process to connect IAB node F to the IAB donor that will have IAB node E after handover if IAB node F maintains the connection. Also, the IAB node E can perform handover processing including notifying the handover destination IAB donor that a communication path by relay transmission to the IAB node F should be established. On the other hand, IAB node E performs handover processing, including notifying the destination IAB donor that a communication path terminating at IAB node E should be established if IAB node F does not maintain the connection. sell. In this way, the IAB node E performs handover processing corresponding to the determination result of whether or not the IAB node F maintains the connection.

In the above example, the handover processing in the relationship between the IAB node E to be handed over and the IAB node F directly connected to the IAB node E has been described, but the present invention is not limited to this. That is, when a plurality of IAB nodes are connected downstream of IAB node E, IAB nodes that are not directly connected to IAB node E, but are connected downstream of IAB node E, such as IAB node F described above, can work. In this case, each of the plurality of IAB nodes on the downstream side is notified of the information of the device to be connected by the handover of the IAB node E, and each of the plurality of IAB nodes establishes a connection under the control of the IAB node E. You can decide whether to keep For example, when IAB node G is connected downstream of IAB node F in FIG. can be notified of the information of the device to be connected by handover for both IAB nodes E and F.

As described above, the IAB nodes can flexibly execute handover, and each IAB node can connect to a connection destination suitable for the situation and execute relay transmission.

(Equipment configuration)
Next, a hardware configuration example of the IAB node as described above will be described with reference to FIG. The IAB node, in one example, includes a processor 201 , a ROM 202 , a RAM 203 , a storage device 204 and a communication circuit 205 . The processor 201 is a computer including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) and ASIC (Application Specific Integrated Circuit). By reading and executing the program stored in the device, the overall processing of the device and each of the above-described processings are executed. A ROM 202 is a read-only memory that stores information such as programs and various parameters related to processing executed by the apparatus. A RAM 203 is a random access memory that functions as a work space when the processor 201 executes programs and stores temporary information. The storage device 204 is configured by, for example, a detachable external storage device or the like. The communication circuit 205 is configured by, for example, a circuit for 5G wireless communication. Although one communication circuit 205 is illustrated in FIG. 2, an IAB node may have multiple communication circuits, such as a wireless communication circuit for 5G and a wired communication circuit for wired communication. Note that the IAB node may have separate communication circuits 205 for each of a plurality of available frequency bands, or may have a common communication circuit 205 for at least some of those frequency bands. good.

FIG. 3 shows a functional configuration example of an IAB node (IAB node E in FIG. 1) to be handed over according to this embodiment. The IAB node to be handed over has, for example, a handover information acquisition unit 301, a handover necessity determination unit 302, a handover destination notification unit 303, a connection maintenance determination unit 304, and a handover execution unit 305, as an example of its functional configuration. . In addition, FIG. 3 shows only the part related to the description of this embodiment among the functions of the IAB node that is the target of handover, and the IAB node is a general IAB node MT and DU It has functions of course. Also, the IAB node may have functions other than the functions shown in FIG. 3 and the general functions of the IAB node. Furthermore, the functional configuration example in FIG. 3 is the function possessed by the IAB node that is the target of handover, but the IAB node can also be used as an IAB node that is connected downstream of the IAB node that is the target of handover as described later. can function. Therefore, the IAB node may also have the functional configuration of FIG. 4, which will be described later. Note that the functional blocks in FIG. 3 are shown schematically, and each functional block may be realized by being integrated, or may be further subdivided. Each function in FIG. 3 may be realized by, for example, the processor 201 executing a program stored in the ROM 202 or the storage device 204, or for example, a processor existing inside the communication circuit 205 may execute predetermined software. It may be realized by executing It should be noted that although each processing unit can take variations as described above, only some of them will be described here, and exhaustive description will be omitted.

Handover information acquisition section 301 acquires information for its own handover. This information includes, for example, information on connection destination candidate devices other than the currently connected device that is a handover destination candidate. Here, for each connection destination candidate device, as information for executing CHO, handover identification information corresponding to the connection destination candidate device, conditions under which handover should be executed, and information to be used after handover. Communication parameters are obtained. The handover information acquisition unit 301 can also acquire information for handover-related processing. For example, setting information for operating as a relay device can be obtained after handover.

The handover necessity determining unit 302 determines whether the condition for starting the process of connecting to one of the connection destination candidate devices by handover is satisfied, based on the handover condition information acquired by the handover information acquiring unit 301, for example. determine whether or not For example, the handover necessity determining unit 302 measures the radio quality of the signal transmitted from the connection destination candidate device, and the radio quality determines the handover condition defined for the corresponding connection destination candidate device. It can be determined whether or not it is satisfied. Then, when a predetermined condition for executing handover is satisfied, the handover necessity determining unit 302 performs handover processing for connecting to a connection destination candidate device associated with the predetermined condition. Decide to run.

The handover destination notification unit 303 notifies another IAB node connected downstream from itself in the currently formed communication path of information indicating the device determined as the connection destination by the handover necessity determination unit 302. do. Note that this notification may be done, for example, before the IAB node actually performs the handover. According to this, the IAB node can perform handover processing for itself after another downstream IAB node performs CHO using the information set at this time. If the IAB node performs the handover first, it may not be possible to use the CHO configuration of the downstream IAB node, so in this way the handover can be performed effectively. becomes possible.

The connection maintenance determination unit 304 determines whether or not the downstream IAB node maintains the connection with itself. For example, the connection maintenance determination unit 304 may perform this determination by receiving a predetermined message containing information indicating whether or not to maintain the connection from another downstream IAB node. For example, the connection maintenance determination unit 304 determines whether the other IAB node on the downstream side is currently It may be determined whether or not the connection is maintained based on whether or not the process for disconnecting the existing connection is started.

Handover executing section 305 executes processing for handover by a method corresponding to the determination result of connection maintenance determining section 304 . That is, when the connection is maintained, the handover process is executed so that the IAB donor to be connected after the handover is also connected to the IAB node on the downstream side. On the other hand, when it is determined that the IAB node on the downstream side does not maintain the connection, the handover execution unit 305 assigns the IAB node on the downstream side in the current communication path under the control of the IAB donor of the connection destination after the handover. Perform a handover that does not connect. For example, the handover execution unit 305 can start the handover process after the downstream IAB node that does not maintain the connection is disconnected. Also, the handover execution unit 305 performs setting processing for relay transmission, for example, as part of handover processing. When the downstream IAB node maintains the connection, the handover execution unit 305 performs processing so that a communication path from the handover destination IAB donor to the downstream IAB node is set, and the downstream IAB node is connected. is not maintained, setting processing for relay transmission can be performed so that the communication path terminates itself.

FIG. 4 shows a functional configuration example of an IAB node (IAB node F in FIG. 1) connected downstream of another IAB node to be handed over according to this embodiment. This IAB node has, for example, a handover information acquisition unit 401, a handover destination notification reception unit 402, a connection maintenance necessity determination unit 403, a connection maintenance necessity notification unit 404, and a handover execution unit 405 as an example of its functional configuration. . In addition, FIG. 4 shows only the part related to the description of this embodiment among the functions of the IAB node connected downstream of the other IAB node to be handed over, and the IAB node It naturally has the functions of MT and DU of a general IAB node. Also, the IAB node may have functions other than the functions shown in FIG. 4 and the general functions of the IAB node. Additionally, the IAB node may also act as the IAB node to be handed over as described above. Thus, an IAB node may also have the functional configuration of FIG. 3 above. Note that the functional blocks in FIG. 4 are shown schematically, and each functional block may be realized by being integrated, or may be further subdivided. Each function in FIG. 4 may be implemented by, for example, the processor 201 executing a program stored in the ROM 202 or the storage device 204, or for example, a processor existing inside the communication circuit 205 may execute predetermined software. It may be realized by executing It should be noted that although each processing unit can take variations as described above, only some of them will be described here, and exhaustive description will be omitted.

Handover information acquisition section 401 acquires information for its own handover. This information includes, for example, information on connection destination candidate devices other than the currently connected device that is a handover destination candidate. Here, for each connection destination candidate device, as information for executing CHO, handover identification information corresponding to the connection destination candidate device, conditions under which handover should be executed, and information to be used after handover. Communication parameters are obtained. The handover information acquisition unit 401 can also acquire information for handover-related processing. For example, setting information for operating as a relay device can be obtained after handover. Note that the handover information acquisition unit 401, for example, for each connection destination candidate device, determines the number of hops and communication delay time between the device and the IAB donor who has the device under its control, or the IAB donor and the device. Information such as the degree of congestion of the communication path to the device can also be acquired.

The handover destination notification receiving unit 402, when the upstream IAB node in the currently formed communication path decides to perform handover, sends a notification indicating the information of the device to which the upstream IAB node establishes connection by handover. receive. The handover destination notification receiving unit 402 receives, for example, information indicating the device to which the upstream IAB node is connected, the number of hops and the communication delay time between the device and the IAB donor who has the device to be connected to, Alternatively, information such as the degree of congestion of the communication path between the IAB donor and the device may be received through the notification. Note that the handover destination notification receiving unit 402 can acquire information on candidate devices to be connected to by the handover of the upstream IAB node before it is determined that the handover will be performed. In this case, when the upstream IAB node decides to perform handover, the handover destination notification receiving unit 402 only includes information specifying which of the connection destination candidate devices is to be the connection destination device. can receive

Based on the information acquired by the handover information acquisition unit 401 and the information received by the handover destination notification reception unit 402, the connection maintenance necessity determination unit 403 determines whether to maintain the connection with the IAB node targeted for handover. determine whether or not For example, it is determined whether or not to maintain the connection depending on whether or not the requirements such as the request for communication delay and the degree of congestion are satisfied even if the connection is maintained. The connection maintenance necessity notification unit 404 notifies the result of the determination by the connection maintenance necessity determination unit 403 to the IAB node to be handed over. When the connection maintenance necessity determination unit 403 determines that the connection with the upstream IAB node is not to be maintained, the handover execution unit 405 uses the information acquired by the handover information acquisition unit 401 to determine the connection destination device. switch. By executing handover by the handover processing unit 405 and disconnecting the connection with the upstream IAB node, it is possible to implicitly notify the upstream IAB node that the connection will not be maintained. In this case, the connection maintenance necessity notification unit 404 may be omitted.

(Processing flow)
Next, an example of the flow of processing will be outlined with reference to FIG. Since the details of each process are as described above, only the outline of the process will be described here. In this example of processing, in the configuration as shown in FIG. , and IAB node D as a connection destination device.

First, it is assumed that IAB node E is connected to IAB donor X via IAB node A (not shown in FIG. 5). It is also assumed that the IAB node F is connected to the IAB node E. Then, a communication path is formed from the IAB node F to the IAB donor X, and communication for the terminal device is relayed through the communication path (S501). In this state, IAB nodes E and F measure the quality of radio signals from surrounding devices, e.g. designated by IAB donor X, e.g. , and inform IAB donor X of the measurement results. Then, based on the notification, IAB donor X determines whether or not IAB nodes E and F make CHO ready (S502). Assume here that IAB donor X decides to start preparing CHO for IAB node E. In this case, since the IAB node F on the downstream side of the IAB node E is connected, the IAB donor X starts preparing CHO for the IAB node F as well.

Here, IAB donor X selects IAB nodes B and C as candidate devices for connecting to IAB node E, and selects IAB nodes A, C, and D as candidate devices for connecting to IAB node F. shall be In this case, IAB donor X uses a HANDOVER REQUEST message to request settings for CHO of IAB node E from IAB donor Y, which has IAB nodes B and C under its control (S503). Similarly, IAB donor X uses a HANDOVER REQUEST message to request settings for CHO of IAB node F to IAB donors Y and Z, which have connection destination candidate devices under their control (S503). . When each of the IAB donors Y and Z receives a request for CHO setting/preparation, etc., it determines whether or not to accept the handover for the IAB nodes E and F, which are the target of the CHO. Information such as communication parameters to be used after handover is generated (S504). If the IAB donors Y and Z have a plurality of devices under their control that can be connected to the IAB node E or F, the IAB donors Y and Z generate information such as communication parameters for each device. Note that handover identification information specified by IAB donor X or determined by IAB donors Y and Z may be associated with each of the candidate devices to connect to. Then, the setting information such as communication parameters and the handover identification information are associated with each other and notified to the IAB donor X (S505). Note that this notification can be made by a HANDOVER REQUEST ACKNOWLEDGE message. In this notification, information such as the number of hops to the IAB donor, communication delay information, and the degree of congestion in the corresponding communication path can be transmitted for each connection destination candidate device. Setting information for relay communication may also be generated together and notified to IAB donor X.

The IAB donor X transmits to the IAB node E, among the notified information, the information regarding the candidate device for the connection destination of the IAB node E (S506). This information may also be communicated to the IAB node F. In addition, the IAB donor X transmits to the IAB node F, among the notified information, the information on the candidate device for the connection destination of the IAB node F (S507). Here, the information notified in S506 and S507 includes information such as the number of hops to the IAB donor, communication delay information, and the degree of congestion in the corresponding communication path for each connection destination candidate device. After that, the IAB node E determines the handover condition specified for the IAB node C in the information acquired in S506 (for example, the radio quality of the signal from the IAB node C is higher than that of the signal from the currently connected IAB node A). It is assumed that it is detected that a condition such as significantly exceeding the radio quality) is satisfied (S508). Then, the IAB node E notifies the IAB node F on the downstream side that handover will be executed with the IAB node C as the connection destination (S509). In the example of FIG. 5, in S506, the IAB node F is notified of information for determining whether or not to maintain the connection, such as the number of hops, communication delay, and degree of congestion in the connection destination candidate device. Therefore, in S509, it is sufficient to notify the IAB node F of only the information specifying the connection destination device (IAB node C). On the other hand, in S506, if the information of the connection destination candidate is not notified to the IAB node F, the information can be notified in S509.

When the IAB node F receives the notification of S509, the reception quality of the signal from each of the candidate devices of its connection destination, and the number of hops, communication delay, congestion degree, etc. in each of these devices Based on information such as , and the IAB node E (S510). IAB node F, by connecting under the control of IAB donor Y through IAB node E and IAB node C, can meet the requirements such as the number of hops, communication delay, and degree of congestion, and from each of the candidate devices for its own connection destination may decide to maintain the connection with the IAB node E, such as when the received quality of the signals from the node E is insufficient. On the other hand, if IAB node F connects to IAB donor Y through IAB node C, it may not be able to meet the requirements for the number of hops, communication delay, congestion level, etc. It may decide not to maintain a connection with the IAB node E, such as when the signal reception quality is very good, and switch the connection to one of its candidate devices to connect to. In the example of FIG. 5, it is assumed that the IAB node F has decided to execute handover with the IAB node D as the connection destination device.

The IAB node F notifies the IAB node E of the determination result of S510 using, for example, the RRCReconfigurationComplete message (S511). This allows IAB node E to know that IAB node F has decided not to maintain a connection with it. The IAB node F then performs a random access procedure with the IAB node D (S512), and the IAB node E performs a random access procedure with the IAB node C (S513). Note that the order of S512 and S513 may be reversed, or may be performed simultaneously.

In this embodiment, in this way, when handover of an IAB node occurs, another IAB node connected downstream of the IAB node is unconditionally not changed even after the handover. Instead, allow that other IAB node to connect to yet another IAB node. According to this, when the handover of the upstream IAB node makes the communication of the downstream IAB node unable to meet the requirements, the downstream IAB node can be transferred to another device that can meet the requirements. You will be able to connect quickly. As a result, it is possible to flexibly and effectively form and operate a communication path involving relay transmission.

The invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the invention.

Claims (14)

A relay device included in a plurality of relay stations in a wireless communication system in which a communication path is formed by wirelessly connecting a plurality of relay stations in series from a control device,
determination means for determining execution of handover from a device connected to the control device side viewed from the relay device in the communication path to another connection destination device;
When a handover is determined to be executed, a notification of handover to the another connection destination device, the notification including information of the another connection destination device, is viewed from the relay device on the communication path. transmitting means for transmitting to another relay device connected to the opposite side of the control device;
determining means for determining whether or not the other relay device maintains connection with the relay device;
execution means for executing handover processing corresponding to the determination result when it is determined to execute handover;
A relay device characterized by comprising: The transmitting means notifies the other relay device of information of connection destination candidate devices when the relay device executes handover, and transmits one of the candidate devices to the other relay device. When the determining means determines that handover is to be executed as a connection destination device, information indicating to which of the candidate devices the connection is to be made is sent as a notification including information on the other connection destination device. send to a relay device,
2. The relay device according to claim 1, wherein: When the other relay device maintains connection with the relay device, the execution means executes processing for connecting the other relay device to a control device having the another connection destination device under control. ,
3. The relay device according to claim 1 or 2, characterized in that: The determination means determines whether or not the other relay device maintains connection with the relay device based on a predetermined message received from the other relay device.
4. The relay device according to any one of claims 1 to 3, characterized in that: The information indicating the another connection destination device includes the number of hops from the another connection destination device to a control device that has the another connection destination device under its control, and the number of hops from the another connection destination device to the other The delay time to the control device under control of the connection destination device, the frequency related to the relay path from the other connection destination device to the control device under the control of the other connection destination device, and the other Information on the function of a relay device that constitutes a relay path from a connection destination device to a control device that has the other connection destination device under its control, and from the other connection destination device to the other connection destination device Including information indicating at least one of the degree of congestion of the communication route to the control device under the
5. The relay device according to any one of claims 1 to 4, characterized in that: A relay device included in a plurality of relay stations in a wireless communication system in which a communication path is formed by wirelessly connecting a plurality of relay stations in series from a control device,
A notification that another relay device connected to the control device side as seen from the relay device in the communication path will handover from the currently connected device to another connection destination device, Receiving means for receiving the notification containing the information of the connection destination device from the other relay device;
determining means for determining whether to maintain the connection with the other relay device based on the notification;
execution means for executing a handover process for connecting to the control device or another control device without going through the other relay device when it is determined not to maintain the connection with the other relay device;
A relay device characterized by comprising: The receiving means
Before the other relay device executes handover, receiving information about a candidate device for connection in the handover;
When the other relay device executes handover, the other relay device transmits the notification including information indicating which of the candidate devices to connect as the another connection destination device by the other relay device. received from the device,
7. The relay device according to claim 6, characterized by: further comprising transmitting means for transmitting a predetermined message indicating whether or not to maintain connection with the other relay device to the other relay device;
8. The relay device according to claim 6 or 7, characterized by: further comprising acquisition means for acquiring information of a candidate for a connection destination of the relay device when connecting to the control device or to a subordinate of another control device without going through the other relay device;
The judging means maintains the connection with the other relay device based on the information of the connection destination candidate of the relay device and the information of the another connection destination device to which the other relay device is handed over. determine whether
9. The relay device according to any one of claims 6 to 8, characterized in that: The information indicating the another connection destination device includes the number of hops from the another connection destination device to a control device that has the another connection destination device under its control, and the number of hops from the another connection destination device to the other The delay time to the control device under control of the connection destination device, the frequency related to the relay path from the other connection destination device to the control device under the control of the other connection destination device, and the other Information on the function of a relay device that constitutes a relay path from a connection destination device to a control device that has the other connection destination device under its control, and from the other connection destination device to the other connection destination device Including information indicating at least one of the degree of congestion of the communication route to the control device under the
10. The relay device according to any one of claims 6 to 9, characterized in that: A control method executed by a relay device included in a plurality of relay stations in a wireless communication system in which a communication path is formed by wirelessly connecting a plurality of relay stations in series from a control device,
determining to execute a handover from a device connected to the control device side viewed from the relay device in the communication path to another connection destination device;
When a handover is determined to be executed, a notification of handover to the another connection destination device, the notification including information of the another connection destination device, is viewed from the relay device on the communication path. to another relay device connected to the other side of the control device;
Determining whether the other relay device maintains connection with the relay device;
executing handover processing corresponding to the result of the determination when it is determined to execute handover;
A control method comprising: A control method executed by a relay device included in a plurality of relay stations in a wireless communication system in which a communication path is formed by wirelessly connecting a plurality of relay stations in series from a control device,
A notification that another relay device connected to the control device side as seen from the relay device in the communication path will handover from the currently connected device to another connection destination device, Receiving the notification containing information of the connection destination device from the other relay device;
Determining whether to maintain the connection with the other relay device based on the notification;
When it is determined that the connection with the other relay device is not to be maintained, executing a handover process for connecting to the control device or another control device without going through the other relay device;
A control method comprising: In a wireless communication system in which a plurality of relay stations are wirelessly connected in series from a control device to form a communication path, a computer provided in a relay device included in the plurality of relay stations,
deciding to execute a handover from a device connected to the control device side viewed from the relay device in the communication path to another connection destination device;
When a handover is determined to be executed, a notification of handover to the another connection destination device, the notification including information of the another connection destination device, is viewed from the relay device on the communication path. to transmit to another relay device connected to the other side of the control device,
cause the other relay device to determine whether or not to maintain connection with the relay device;
When it is determined to execute handover, executing handover processing corresponding to the result of the determination;
program for. In a wireless communication system in which a plurality of relay stations are wirelessly connected in series from a control device to form a communication path, a computer provided in a relay device included in the plurality of relay stations,
A notification that another relay device connected to the control device side as seen from the relay device in the communication path will handover from the currently connected device to another connection destination device, receiving the notification containing the information of the connection destination device from the other relay device;
determining whether to maintain the connection with the other relay device based on the notification;
When it is determined that the connection with the other relay device is not to be maintained, a handover process for connecting to the control device or another control device without the other relay device is executed.
program for.

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