Communication device, wireless communication system, control circuit, storage medium, and link re-selection recommendation method

Abstract

The purpose of the present invention is to obtain a communication device (3) which makes it possible to shorten a message non-delivery time by reducing a link switching time when re-selecting a link. The communication device (3) comprises: a reception unit (32) that receives data transferred from a preceding-stage communication device; a transfer unit (31) that transfers the data received by the reception unit (32) to a subsequent-stage communication device; and a control unit (33) that controls data relay, which uses the reception unit (32) and the transfer unit (31), in a multi-hop transmission, and when it is predicted that link quality among communication devices on a currently-used path will not satisfy required link quality in a wireless communication system allowing multi-hop transmission using a plurality of paths, performs control to cause the transfer unit (31) to transfer, to a communication device serving as the source of data transfer in the multi-hop transmission, a link re-selection recommendation message for recommending link re-selection in the multi-hop transmission.

Description

Recommended methods for communication devices, wireless communication systems, control circuits, storage media, and link reselection.

[0001] This disclosure relates to a communication device, wireless communication system, control circuit, storage medium, and link reselection recommendation method for multi-hop transmission.

[0002] Traditionally, multi-hop transmission in wireless communication systems has the advantage of extending the communication range by transmitting data via relay stations. Wireless communication networks that utilize multi-hop transmission are known as mobile ad-hoc networks (MANET) and mesh networks. Representative standardization standards include IEEE (Institute of Electrical and Electronics Engineers) 802.11s and Wi-SUN (Wireless Smart Utility Network).

[0003] In mobile ad-hoc networks and mesh networks, dynamic routing control that switches routes in response to changes in link quality due to environmental changes, terminal movement, etc., is crucial. Routing protocols that utilize topology information include the proactive routing protocol OLSR (Optimized Link State Routing) and the reactive routing protocol AODV (Ad hoc On-Demand Distance Vector routing). For example, IEEE 802.11s employs HWMP (Hybrid Wireless Mesh Protocol), which adds a route pre-configuration function to RM-AODV (Radio Metic AODV), an improved version of AODV.

[0004] In the 3GPP (Registered Trademark) (3rd Generation Partnership Project), which is a standardization standard for cellular communication systems, studies on multi-hop transmission have also been conducted. As a relay transmission method that utilizes direct communication between terminals called sidelink, UE (User Equipment)-to-Network Relay, UE-to-UE Relay, etc. are defined. In conventional UE-to-Network Relay, UE-to-UE Relay, etc., as Relay reselection, a method for changing the relay station has been proposed using Link Modification Request message and Link Modification Accept message. Also, in the method for changing the relay station in conventional UE-to-UE Relay, a method for the source UE to change the relay station has been proposed based on the link quality between the relay station and the target UE (for example, Patent Document 1).

[0005] These methods are premised on multi-hop transmission limited to two hops, that is, one relay, and cannot support multi-hop transmission of three hops or more. In 3GPP, studies are being conducted on multi-hop transmission of three hops or more in UE-to-Network Relay. Also, studies are being conducted on routing control in a mobile ad hoc network using sidelink.

[0006] Japanese Patent Publication No. 2023-527610

[0007] However, according to the above conventional technology, link reselection in a mobile ad hoc network using sidelink requests link switching to the previous transmission station or relay station at the timing when the link quality of its own transmission link fails to meet the required link quality, for example, when the link is disconnected, when the transmission delay of the link fails to meet the required delay, etc. Therefore, there is a problem that the time required from when the link quality fails to meet the required link quality until the link switching is completed becomes long.

[0008] This disclosure is made in view of the above, and aims to provide a communication device that can reduce the link switching time during link re-selection and shorten the message delivery time.

[0009] To solve the above-mentioned problems and achieve the objective, the communication device of this disclosure is characterized by comprising: a receiving unit that receives data transmitted from a preceding communication device; a transmitting unit that transmits the data received by the receiving unit to a subsequent communication device; and a control unit that controls the relaying of data using the receiving unit and the transmitting unit in multi-hop transmission, and, in a wireless communication system capable of multi-hop transmission via multiple paths, when it is predicted that the link quality between communication devices on the currently used path will no longer meet the required link quality, controls the transmitting unit to send a link reselection recommendation message to the source communication device of the data transmitted via multi-hop transmission, recommending reselection of the link in the multi-hop transmission.

[0010] The communication device disclosed herein has the effect of reducing the link switching time during link reselection and shortening the message delivery time.

[0011] Figures showing an example configuration of a wireless communication system including a communication device according to Embodiment 1. Figures showing an example configuration of a communication device that is a relay station according to Embodiment 1. Figures showing an example arrangement of each communication device when the wireless communication system according to Embodiment 1 performs multi-hop transmission. Sequence diagram showing the operation of the communication device according to Embodiment 1 when it performs link reselection in multi-hop transmission. Figures showing an example configuration of a processing circuit when the processing circuit realizing the communication device according to Embodiment 1 is realized with a processor and memory. Figures showing an example of a processing circuit when the processing circuit realizing the communication device according to Embodiment 1 is configured with dedicated hardware. Figures showing an example configuration of a communication device that is a relay station according to Embodiment 2. Sequence diagram showing the operation of the communication device according to Embodiment 2 when it performs link reselection in multi-hop transmission based on internal information. Figure 3 shows an example of the configuration of a communication device. Sequence diagram showing the operation when the communication device according to Embodiment 3 performs link reselection in multi-hop transmission based on information obtained from an external device. Figure 4 shows an example of the configuration of a wireless communication system including the communication device according to Embodiment 4. Sequence diagram showing the operation when the communication device according to Embodiment 4 performs link reselection in multi-hop transmission based on a link reselection recommendation message from the communication device which is the parent relay station. Figure 5 shows an example of the configuration of a wireless communication system including the communication device according to Embodiment 4 and a base station. Sequence diagram showing the operation when the communication device according to Embodiment 5 transmits a link reselection recommendation message in multi-hop transmission via multi-hop transmission. Sequence diagram showing the operation when the communication device according to Embodiment 6 performs acknowledgment of receipt after transmitting a link reselection recommendation message in multi-hop transmission.

[0012] The following describes in detail, with reference to the drawings, a communication device, a wireless communication system, a control circuit, a storage medium, and a link reselection recommendation method according to embodiments of the present disclosure.

[0013] Embodiment 1. Figure 1 is a diagram showing an example configuration of a wireless communication system 7 including communication devices 3-1 to 3-4 according to Embodiment 1. The wireless communication system 7 is a system capable of multi-hop transmission of data via multiple paths. In the wireless communication system 7, communication device 1 is a transmitting station and is both the source and origin of the data. Communication device 2 is a receiving station and is the destination of the data from communication device 1, which is the transmitting station, and receives the data from communication device 1, which is the transmitting station. Communication devices 3-1 to 3-4 are relay stations that relay the data transmitted from communication device 1, which is the transmitting station, and transmit it to communication device 2, which is the receiving station. In the following description, communication devices 3-1 to 3-4 may be referred to as communication device 3 when not distinguished. In Figure 1, the number of communication devices 3, which are relay stations, is shown as four as an example, but the number of communication devices 3, which are relay stations, is not particularly limited as long as multiple multi-hop transmission paths can be established.

[0014] Figure 2 shows an example configuration of a communication device 3 which is a relay station according to Embodiment 1. The communication device 3 which is a relay station comprises a transmitting unit 31, a receiving unit 32, and a control unit 33. The transmitting unit 31 transmits desired data to other communication devices. The transmitting unit 31 also transmits the data received by the receiving unit 32 to a subsequent communication device. The subsequent communication device may be the communication device 3 which is a relay station, or the communication device 2 which is a receiving station. The receiving unit 32 receives data transmitted from the preceding communication device, i.e., other communication devices. The preceding communication device, i.e., other communication devices, may be the communication device 3 which is a relay station, or the communication device 1 which is a transmitting station. The control unit 33 controls the transmitting unit 31 and the receiving unit 32 to perform data relay, transmission and reception link management, etc.

[0015] Figure 3 is a diagram showing an example of the arrangement of each communication device when the wireless communication system 7 according to Embodiment 1 performs multi-hop transmission. Figure 3 also shows the configuration of each communication device. As shown in Figure 3, the communication device 1, which is the transmitting station, comprises a transmitting unit 11, a receiving unit 12, and a control unit 13. The transmitting unit 11 transmits the desired data to other communication devices. The receiving unit 12 receives the data transmitted from other communication devices. In the communication device 1, which is the transmitting station, the other communication devices may be a communication device 3, which is a relay station, or a communication device 2, which is a receiving station. The control unit 13 controls the transmitting unit 11 and the receiving unit 12 to perform data transmission and reception, management of transmission and reception links, etc. Also, as shown in Figure 3, the communication device 2, which is the receiving station, comprises a transmitting unit 21, a receiving unit 22, and a control unit 23. The transmitting unit 21 transmits the desired data to other communication devices. The receiving unit 22 receives the data transmitted from other communication devices. In the receiving station, communication device 2, other communication devices may be a relay station, communication device 3, or a transmitting station, communication device 1. The control unit 23 controls the transmitting unit 21 and the receiving unit 22 to perform tasks such as sending and receiving data and managing the transmission and reception links.

[0016] When the wireless communication system 7 includes five or more communication devices 3, the communication devices 3 may be located between communication device 1 and communication device 3-1, between communication device 3-4 and communication device 2, in parallel with communication devices 3-2 and 3-3 between communication device 3-1 and communication device 3-4, or before or after each of the communication devices 3-2 and 3-3. Furthermore, when the wireless communication system 7 includes two communication devices 3, namely communication devices 3-2 and 3-3, it is possible for communication device 1, which is the transmitting station, to be connected to communication devices 3-2 and 3-3, and for communication device 2, which is the receiving station, to be connected to communication devices 3-2 and 3-3, and for communication device 1, which is the transmitting station, to transmit data to communication device 2, which is the receiving station, via communication device 3-2 or communication device 3-3.

[0017] Figure 4 is a sequence diagram showing the operation of the communication device 3 according to Embodiment 1 when it performs link reselection in multi-hop transmission. Figure 4 shows the portion of the wireless communication system 7 shown in Figure 3 that consists of communication devices 3-1 to 3-4. Specifically, the operation in which communication device 3-3 sends a link reselection recommendation message recommending link reselection in multi-hop transmission will be described. Communication device 1, which is the transmitting station, transmits the desired data to communication device 2, which is the receiving station, via relay stations, communication devices 3-1, 3-3, and 3-4, using multi-hop transmission. Communication devices 1, 2, and 3-1 to 3-4 each use a transmitting unit and a receiving unit to check the link status between communication devices, and these are managed by a control unit. Based on the required link quality and the link status between communication devices managed by each control unit, routing from communication device 1 to communication device 2 is determined.

[0018] Methods for checking the link status between communication devices include, for example, communication confirmation using periodically transmitted and received heartbeat signals, HELLO messages, etc., detection of degradation in transmission and reception performance using pilot signals, reference signals (Reference Signals), etc., Channel State Information measured using SINR (Signal-to-Interference-plus-Noise Ratio), RSRP (Reference Signal Received Power), RSSI (Received Signal Strength Indicator), etc. The method for checking the link status between communication devices may also be performed using event-driven signals, messages, etc., caused by data transmission timing, changes in the surrounding environment, etc., and any method may be used in this embodiment.

[0019] Furthermore, the required link quality may include, for example, error rate, transmission delay, transmission jitter, and throughput, and may also be QoS (Quality of Service) as defined in standardization specifications. The required link quality may be pre-configured, or it may be configured externally, and in this embodiment, any configuration method is acceptable. In the following description, as an example, it will be assumed that the routing from communication device 1 to communication device 2 is set to the path: communication device 1 → communication device 3-1 → communication device 3-3 → communication device 3-4 → communication device 2.

[0020] Communication device 1 transmits the desired data from the transmitting unit 11. Communication device 3-1 receives the data transmitted from communication device 1 using the receiving unit 32. Since communication device 3-1 is a relay station, it retransmits the received data from the transmitting unit 31 under the control of the control unit 33. Communication device 3-3 receives the data transmitted from communication device 3-1 using the receiving unit 32. Since communication device 3-3 is a relay station, it retransmits the received data from the transmitting unit 31 under the control of the control unit 33. Communication device 3-4 receives the data transmitted from communication device 3-3 using the receiving unit 32. Since communication device 3-4 is a relay station, it retransmits the received data from the transmitting unit 31 under the control of the control unit 33. Communication device 2 receives the data transmitted from communication device 3-4 using the receiving unit 22. Through this series of operations, data is transmitted in a multi-hop manner from communication device 1 to communication device 2 via communication devices 3-1, 3-3, and 3-4 (step S101).

[0021] The control unit 33 of the relay station communication device 3-3 checks the link status (step S102). If the control unit 33 of the relay station communication device 3-3 predicts, or detects, that the link quality of the transmission link to communication device 3-4 will not meet the required link quality in the future, it causes the transmission unit 31 to send a link reselection recommendation message (step S103). The link reselection recommendation message indicates to communication devices using communication device 3-3 as a relay station, i.e., a destination in multi-hop transmission, that the link quality of the transmission link of communication device 3-3, i.e., the quality of the transmission path after communication device 3-3 in multi-hop transmission, will deteriorate in the future, and therefore recommends link reselection, i.e., reselection of the path in multi-hop transmission, so that communication device 3-3 is not used as a relay station, i.e., a destination in multi-hop transmission. The link reselection recommendation message only needs to be received by communication devices using communication device 3-3 as a relay station. Therefore, communication device 3-3 may broadcast the link reselection recommendation message, or it may send it as a unicast message to a communication device that uses communication device 3-3 as a relay station, or it may send it as a multicast message that includes a communication device that uses communication device 3-3 as a relay station as a destination.

[0022] Since communication device 3-1 uses communication device 3-3 as a relay station, the receiving unit 32 receives the link reselection recommendation message transmitted from communication device 3-3. The link reselection recommendation message is a recommendation, not a request, for link reselection. Therefore, the decision on whether to reselect the link rests with communication device 3-1, which received the link reselection recommendation message, not with communication device 3-3, which sent the message. Accordingly, the control unit 33 of communication device 3-1 decides whether or not to perform link reselection.

[0023] When the control unit 33 determines that link reselection is necessary, the communication device 3-1 performs link reselection processing using the transmitting unit 31 and the receiving unit 32 (step S104). For example, if the link quality of the transmission link is good and there is a communication device 3-2 that maintains a link to communication device 3-4, the communication device 3-1 uses the transmitting unit 31 and the receiving unit 32 to perform link reselection arbitration processing by sending and receiving messages between the transmitting unit 31 and the receiving unit 32 of communication device 3-2 and the transmitting unit 31 and the receiving unit 32 of communication device 3-4, and switches the routing to go through communication device 3-2. The method of link reselection can be any method that allows routing to be established for communication device 2. For example, if the communication devices are connected via a PC5 interface in 3GPP, link reselection may be performed using the Relay Reselection flow described in 3GPP TS 23.304 V19.0.0 (2024-06) Proxy-based Services (ProSe) in the 5G System (5GS) (Release 19).

[0024] As a result, in the wireless communication system 7, data is transmitted via multi-hop transmission through a path from communication device 1 to communication device 2 via communication devices 3-1, 3-2, and 3-4 (step S105).

[0025] By performing the above-mentioned link reselection before the link quality of the transmission link of communication device 3-3 deteriorates, communication device 3-1 can switch links in advance in a shorter time compared to performing link reselection after the link quality deteriorates, thereby reducing the data delivery time in multi-hop transmission from communication device 1 to communication device 2. Furthermore, by recommending rather than requesting link reselection, communication device 3-1 can self-determine the timing and conditions of link switching in link reselection, thereby increasing the degree of flexibility in the link reselection process.

[0026] In this manner, the control unit 33 of the communication device 3 controls the relaying of data using the receiving unit 32 and the transmitting unit 31 in multi-hop transmission. Furthermore, in the wireless communication system 7, which is capable of multi-hop transmission via multiple paths, if it is predicted that the link quality between communication devices on the currently used path will no longer meet the required link quality, the control unit 33 controls the transmission of a link reselection recommendation message from the transmitting unit 31 to the communication device that is the source of the data transmitted via multi-hop transmission, recommending that the link be reselected in the multi-hop transmission. In this embodiment, the control unit 33 of the communication device 3 predicts the link quality based on the data transmission status of the transmitting unit 31.

[0027] In the example shown in Figure 4, the case where the link reselection recommendation message transmitted from the relay station communication device 3-3 is received by the same relay station communication device 3-1 is described, but the system is not limited to this. For example, if the transmitting station communication device 1 is located at the same position as the communication device 3-1 shown in Figures 3 and 4, when the transmitting station communication device 1 receives the link reselection recommendation message, as with the aforementioned communication device 3-1, it will decide whether or not to perform link reselection. If it decides to perform link reselection, it will use the transmitting unit 11 and the receiving unit 12 to perform the link reselection process.

[0028] In the following description, a communication device 3 that transmits a link reselection recommendation message, such as communication device 3-3, may be referred to as the first communication device. A communication device 3 that receives a link reselection recommendation message, such as communication device 3-1, may be referred to as the second communication device. In Embodiment 1, the first communication device transmits a link reselection recommendation message recommending link reselection in multi-hop transmission when it is predicted that the link quality between communication devices on the currently used path in the wireless communication system 7 will no longer meet the required link quality. The second communication device, upon receiving the link reselection recommendation message, performs link reselection. In Embodiment 1, an example of the first communication device is communication device 3-3 on the path where multi-hop transmission is taking place.

[0029] Next, the hardware configuration of the communication device 3, which is a relay station, will be described. In the communication device 3, the transmitting unit 31 and the receiving unit 32 are communication devices capable of wireless communication. The control unit 33 is implemented by a processing circuit. The processing circuit may be a processor and memory that execute a program stored in memory, or it may be dedicated hardware. The processing circuit is also called a control circuit.

[0030] Figure 5 is a diagram showing an example configuration of a processing circuit 90 when the processing circuit for realizing the communication device 3 according to Embodiment 1 is realized by a processor 91 and a memory 92. The processing circuit 90 shown in Figure 5 is a control circuit and comprises a processor 91 and a memory 92. When the processing circuit 90 is composed of a processor 91 and a memory 92, each function of the processing circuit 90 is realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 92. In the processing circuit 90, each function is realized by the processor 91 reading and executing the program stored in the memory 92. That is, the processing circuit 90 includes a memory 92 for storing a program that will ultimately be executed as processing for the communication device 3. This program can also be said to be a program that causes the communication device 3 to execute each function realized by the processing circuit 90. This program may be provided by a storage medium on which the program is stored, or by other means such as a communication medium.

[0031] The above program can also be described as a program that causes the communication device 3 to execute a receiving step in which the receiving unit 32 receives data transmitted from the preceding communication device, a transmitting step in which the transmitting unit 31 transmits the data received by the receiving unit 32 to the subsequent communication device, and a control step in which the control unit 33 controls the relaying of data using the receiving unit 32 and the transmitting unit 31 in multi-hop transmission, and, if it is predicted that the link quality between communication devices on the currently used path in the wireless communication system 7, which is capable of multi-hop transmission via multiple paths, will no longer meet the required link quality, the control unit 33 controls the transmission of a link reselection recommendation message to the source communication device of the data transmitted via multi-hop transmission, recommending that the link be reselected in the multi-hop transmission.

[0032] Here, the processor 91 is, for example, a CPU (Central Processing Unit), processing unit, arithmetic unit, microprocessor, microcomputer, or DSP (Digital Signal Processor). The memory 92 is, for example, a non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), EEPROM® (Electrically EPROM), magnetic disk, flexible disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0033] Figure 6 shows an example of a processing circuit 93 when the processing circuit for realizing the communication device 3 according to Embodiment 1 is configured with dedicated hardware. The processing circuit 93 shown in Figure 6 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The processing circuit may be partially implemented with dedicated hardware and partially implemented with software or firmware. In this way, the processing circuit can realize each of the above functions with dedicated hardware, software, firmware, or a combination thereof.

[0034] Furthermore, the hardware configuration of the transmitting station (communication device 1) and the receiving station (communication device 2) is the same as that of the relay station (communication device 3). In communication device 1, the transmitting unit 11 and the receiving unit 12 are communication devices capable of wireless communication. The control unit 13 is implemented by a processing circuit. Similarly, in communication device 2, the transmitting unit 21 and the receiving unit 22 are communication devices capable of wireless communication. The control unit 23 is implemented by a processing circuit. The processing circuit may be a processor and memory that execute a program stored in memory, or it may be dedicated hardware.

[0035] As described above, according to this embodiment, in the wireless communication system 7, the communication device 3, which is a relay station, predicts the link quality of the path through which data is being transmitted by ad-hoc transmission. If it is predicted that the link quality will no longer meet the required link quality, it sends a link reselection recommendation message to the communication device 1, which is a transmitting station, or the communication device 3, which is a relay station, that is further ahead of its own communication device, recommending that the link be reselected. Upon receiving the link reselection recommendation message, the communication device 1, which is a transmitting station, or the communication device 3, which is a relay station, decides whether or not to perform link reselection. If it decides to perform link reselection, it performs the link reselection process. As a result, the wireless communication system 7 can perform the link reselection process before the link quality actually deteriorates, thereby reducing the link switching time during link reselection and shortening the message delivery time.

[0036] Embodiment 2. In Embodiment 1, communication device 3-3, which is a relay station, sent a link reselection recommendation message based on the results of checking the link status between communication device 3-3 and communication device 3-4. Embodiment 2 describes a case in which communication device 3a, which is a relay station, sends a link reselection recommendation message based on information obtained internally by its own communication device. Components having the same function as in Embodiment 1 are given the same reference numerals, and detailed explanations are omitted.

[0037] Figure 7 shows an example configuration of a communication device 3a which is a relay station according to Embodiment 2. The communication device 3a which is a relay station comprises a transmitting unit 31, a receiving unit 32, a control unit 33a, and an internal information management unit 34. The internal information management unit 34 manages internal information, which is information obtained inside the communication device 3a on which it is installed. The internal information management unit 34 outputs the obtained internal information to the control unit 33a. The control unit 33a can operate in the same way as the control unit 33 described in Embodiment 1, and can also predict link quality based on the internal information obtained from the internal information management unit 34.

[0038] Figure 8 is a sequence diagram showing the operation of the communication device 3a according to Embodiment 2 when it performs link reselection in multi-hop transmission based on internal information. Although not shown in the diagram, the configuration of the wireless communication system in Embodiment 2 is the same as that of the wireless communication system 7 of Embodiment 1 shown in Figure 3, but with the relay station communication devices 3-1 to 3-4 replaced by relay station communication devices 3a-1 to 3a-4. The configuration of communication devices 3a-1 to 3a-4 is the same as that of communication device 3a shown in Figure 7. Specifically, the operation when communication device 3a-3 transmits a link reselection recommendation message recommending link reselection in multi-hop transmission based on internal information will be described.

[0039] The relay station communication device 3a-3 not only performs message transmission and reception between communication device 3a-3 and communication device 3a-4, as described in the link status confirmation method in Embodiment 1, but also predicts future link quality to communication device 3a-4 by having the internal information management unit 34, which manages the internal information of communication device 3a-3, provide internal information to the control unit 33a.

[0040] For example, in 3GPP sidelink communication, SPS (Semi-Persistent Scheduling) is used as a resource scheduling method in LTE (Long Term Evolution) Mode 4 and NR (New Radio) Mode 2. In SPS, a resource with the same cycle is used for a specified number of times, and the number of times it has been used is counted by the Resource Selection Counter. When the Resource Selection Counter becomes 0, resource re-selection is performed according to a probability determined by the Resource Selection Probability. If re-selection occurs, sensing-based resource selection is performed; otherwise, the same resource is used continuously. When resource reselection occurs, depending on the timing of the reselected resource, transmission delays may increase or decrease due to scheduling waits, potentially failing to meet the required link quality.

[0041] Therefore, values ​​such as the Selection Counter and Resource Selection Probability can be used to predict whether future resource reselection will occur, that is, whether the required link quality will no longer be met. The control unit 33a of the communication device 3a-3 obtains the above-mentioned internal information from the internal information management unit 34, and can then trigger the transmission unit 31 to send a link reselection recommendation message upon obtaining the internal information.

[0042] Furthermore, in sidelink communications within 3GPP, techniques for performing decentralized congestion control (DEC), as defined by ETSI (European Telecommunications Standards Institute) and SAE (Society of Automotive Engineers), are widely used, based on CBR (Channel Bus Ratio) and CR (Channel Occurrence Ratio) calculated from CBR. When congestion control is performed, communication equipment takes measures such as reducing transmission power and changing the MCS (Modulation and Coding Scheme), which can lead to increased error rates, decreased throughput, and potentially fail to meet the required link quality. Since CBR is internal information of the communication equipment that can be calculated by monitoring the RSSI in the communication equipment, the possibility of future congestion control can be inferred from fluctuations in CBR. Therefore, the control unit 33a of communication equipment 3a-3 can obtain the above-mentioned internal information from the internal information management unit 34, and trigger the transmission unit 31 to send a link reselection recommendation message upon acquisition of the internal information.

[0043] Furthermore, the communication device 3a-3 can observe the number of retransmissions during normal data transmission and predict a decrease in link quality from an increase in the number of retransmissions. Therefore, the control unit 33a of the communication device 3a-3 can obtain the above-mentioned internal information from the internal information management unit 34, and trigger the transmission unit 31 to send a link reselection recommendation message upon acquisition of the internal information.

[0044] Also, as internal information of the communication device 3a-3, for example, when the communication device 3a-3 is driven by a battery, it is possible to predict the possibility of becoming unable to transmit and receive due to a decrease in the remaining battery level. In addition, factors that cause performance degradation of the transmission unit 31, reception unit 32, and control unit 33a of the communication device 3a-3, such as the computing resources of the communication device 3a-3, the state of the process, external environmental factors such as temperature, humidity, and atmospheric pressure, the device startup time, and the startup count, are observed by the internal information management unit 34, so that a future decrease in link quality can be predicted. Therefore, the control unit 33a of the communication device 3a-3 can cause the transmission unit 31 to transmit a link reselection recommendation message upon obtaining the internal information as described above by obtaining the internal information from the internal information management unit 34.

[0045] Thus, in a situation where data is multi-hop transmitted from the communication device 1 to the communication device 2 via the communication devices 3a-1, 3a-3, 3a-4 (step S101), the communication device 3a-3 checks the internal information of the communication device 3a-3 as described above (step S201). When the control unit 33a of the communication device 3a-3 predicts, that is, detects, as a result of checking the internal information, that the link quality of the transmission link to the communication device 3a-4 will not meet the required link quality in the future, it causes the transmission unit 31 to transmit a link reselection recommendation message (step S103). The operations of the subsequent sequence diagrams shown in FIG. 8 are the same as the operations of the sequence diagram shown in FIG. 4. In the example of FIG. 8, in step S105, data is multi-hop transmitted from the communication device 1 to the communication device 2 via the communication devices 3a-1, 3a-2, 3a-4.

[0046] The hardware configuration of the communication device 3a will be described. In the communication device 3a, the internal information management unit 34 is implemented by a processing circuit. The processing circuit may be a processor and a memory that execute a program stored in the memory, or may be dedicated hardware.

[0047] As described above, according to this embodiment, the communication device 3a, which is a relay station, predicts the link quality of the path through which data is transmitted by ad hoc transmission based on the internal information obtained inside the communication device 3a, and when it is predicted that the link quality will not satisfy the required link quality, a link reselection recommendation message for recommending link reselection is transmitted to the communication device 1 that is a transmission station before the own communication device or the communication device 3a that is a relay station. Even in this case, the same effects as those in the first embodiment can be obtained.

[0048] Although the case where the communication device 3a predicts the link quality of the path through which data is transmitted by ad hoc transmission based on the internal information and transmits a link reselection recommendation message when it is predicted that the link quality will not satisfy the required link quality has been described, the present invention is not limited to this. The communication device 3a may predict the link quality of the path through which data is transmitted by ad hoc transmission using the two pieces of information, i.e., the confirmation result of the link state between the communication devices 3a-3 and 3a-4 and the internal information, and transmit a link reselection recommendation message when it is predicted that the link quality will not satisfy the required link quality.

[0049] Embodiment 3. In the second embodiment, the link reselection recommendation message was transmitted based on the internal information obtained inside the communication device 3a. In the third embodiment, the case where the communication device 3b, which is a relay station, transmits a link reselection recommendation message based on the information obtained outside the own communication device will be described. Configurations having the same functions as those in the first embodiment are given the same reference numerals, and detailed descriptions thereof are omitted.

[0050] Figure 9 shows an example configuration of a communication device 3b which is a relay station according to Embodiment 3. The communication device 3b which is a relay station comprises a transmitting unit 31, a receiving unit 32, and a control unit 33b. The control unit 33b is connected to an external device 4. When the external device 4 detects the possibility that the link quality will no longer meet the required link quality, it transmits link reselection supplementary information to the control unit 33b of the communication device 3b indicating that it has detected the possibility that the link quality will no longer meet the required link quality. The control unit 33b can operate in the same way as the control unit 33 described in Embodiment 1, and can also determine whether or not to have the transmitting unit 31 transmit a link reselection recommendation message based on the link reselection supplementary information obtained from the external device 4.

[0051] Figure 10 is a sequence diagram showing the operation of the communication device 3b according to Embodiment 3 when it performs link reselection in multi-hop transmission based on information obtained from the external device 4. Although not shown in the diagram, the configuration of the wireless communication system in Embodiment 3 is the same as that of the wireless communication system 7 of Embodiment 1 shown in Figure 3, but with the relay station communication devices 3-1 to 3-4 replaced by relay station communication devices 3b-1 to 3b-4. The configuration of communication devices 3b-1 to 3b-4 is the same as that of communication device 3b shown in Figure 9. Specifically, the operation when communication device 3b-3 transmits a link reselection recommendation message recommending link reselection in multi-hop transmission based on information obtained from the external device 4 will be described.

[0052] In a situation where data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3b-1, 3b-3, and 3b-4 (step S101), if external device 4 detects the possibility that the link quality between communication device 3b-3 and communication device 3b-4 will no longer meet the required link quality, it transmits link reselection supplementary information to the control unit 33b of communication device 3b-3 (step S301). Upon receiving the link reselection supplementary information, the control unit 33b of communication device 3b-3 determines whether or not to have the transmission unit 31 send a link reselection recommendation message. If it determines that the transmission unit 31 should send the link reselection recommendation message, it has the transmission unit 31 send the link reselection recommendation message (step S103). The operation of the sequence diagrams from Figure 10 onward is the same as the operation of the sequence diagram shown in Figure 4. In the example of Figure 10, in step S105, data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3b-1, 3b-2, and 3b-4.

[0053] External device 4 is a device that can acquire information such as the position, speed, acceleration, and direction of a device on which communication device 3b is installed. It can acquire and manage information such as positioning information acquisition results using GNSS (Global Navigation Satellite System), positioning or distance measurement results from odometer, LiDAR (Light Detection and Ranging), infrared radar, etc., and self-position estimation results using SLAM (Simultaneous Localization and Mapping) based on these results. Generally, from information such as speed and acceleration, an increase in Doppler frequency can be predicted, and a deterioration of signal quality can be predicted. Also, from information such as position and direction, changes in the propagation environment such as shielding and reflection can be predicted, and a deterioration of signal quality can be predicted. External device 4 transmits this information to the control unit 33b of communication device 3b-3 as link reselection supplementary information. Based on the acquired link reselection supplementary information, the control unit 33b of communication device 3b-3 determines whether or not to send a link reselection recommendation message, and if it determines that it is necessary, it has the transmission unit 31 send the link reselection recommendation message.

[0054] Furthermore, the external device 4 may be, for example, a device capable of acquiring routing information of the equipment on which the communication device 3b-3 is installed. From the routing information, the external device 4 can infer, for example, that the distance between the communication device 3b-3 and the communication device 3b-4 will increase in the future, that the propagation environment between the communication device 3b-3 and the communication device 3b-4 will change, and thus predict a future deterioration in link quality. Therefore, the external device 4 can transmit this information to the control unit 33b of the communication device 3b-3 as link reselection supplementary information. The control unit 33b of the communication device 3b-3 determines whether or not to send a link reselection recommendation message based on the acquired link reselection supplementary information, and if it determines that it is necessary, it has the transmission unit 31 send the link reselection recommendation message.

[0055] Furthermore, the external device 4 may observe and acquire other information, such as battery level, the computing resources or process status of the communication device 3b-3, external environmental factors such as temperature, humidity, and atmospheric pressure, and factors that cause performance degradation of the transmission unit 31, reception unit 32, and control unit 33b of the communication device 3b-3, such as device startup time and number of startups. If possible, this information may be transmitted to the control unit 33b of the communication device 3b-3 as link reselection supplementary information. The control unit 33b of the communication device 3b-3 determines whether or not to send a link reselection recommendation message based on the acquired link reselection supplementary information, and if it determines that it is necessary, it causes the transmission unit 31 to send the link reselection recommendation message.

[0056] The hardware configuration of the communication device 3b will now be described. In the communication device 3b, the control unit 33b is implemented by a processing circuit. The processing circuit may be a processor and memory that execute a program stored in memory, or it may be dedicated hardware.

[0057] As described above, according to this embodiment, the communication device 3b, which is a relay station, determines whether or not to send a link reselection recommendation message based on the link reselection supplementary information from the external device 4 obtained outside the communication device 3b, and sends the link reselection recommendation message if it determines that it is necessary. In this case as well, the same effects as in Embodiment 1 can be obtained. Furthermore, by utilizing the information obtained from the external device 4 connected to the communication device 3b, the communication device 3b becomes able to select a link that takes into account the influence of disturbances on the communication link.

[0058] While communication device 3b has determined whether or not to send a link reselection recommendation message based on the link reselection supplementary information from external device 4, it is not limited to this. For example, external device 4 may send link reselection supplementary information to communication device 3b only if it determines that it is necessary to send a link reselection recommendation message from communication device 3b. In this case, upon receiving the link reselection supplementary information from external device 4, communication device 3b can send a link reselection recommendation message without determining whether or not to send such a message.

[0059] Furthermore, while we have described a case in which the communication device 3b determines whether or not to send a link reselection recommendation message based on the link reselection supplementary information obtained from the external device 4, and sends the link reselection recommendation message if it decides to send it, it is not limited to this. The communication device 3b may also predict the link quality of the path where data is being transmitted by ad-hoc transmission using the link status confirmation result between the communication device 3b-3 and the communication device 3b-4, and the link reselection supplementary information obtained from the external device 4, and send a link reselection recommendation message if it is predicted that the link quality will no longer meet the required link quality.

[0060] Furthermore, while the case of applying Embodiment 3 to Embodiment 1 has been described, it is not limited to this. Embodiment 3 can also be applied to Embodiment 2. Although not shown in the figures, the control unit of the communication device may acquire internal information from the internal information management unit 34 inside the communication device and further acquire link reselection supplementary information from the external device 4. In this case, the communication device may use two or more of the link status confirmation results between its own communication device and the downstream communication device, the internal information from the internal information management unit 34, and the link reselection supplementary information obtained from the external device 4 to predict the link quality of the path where data is being transmitted by ad-hoc transmission, and may send a link reselection recommendation message if it is predicted that the link quality will no longer meet the required link quality.

[0061] Embodiment 4. In Embodiment 1, a link reselection recommendation message was transmitted to the communication device 3-1 by the communication device 3-3 associated with the link. Embodiment 4 describes the case in which a link reselection recommendation message is transmitted from a communication device not associated with the multi-hop transmission link. Components having the same function as in Embodiment 1 are given the same reference numerals, and detailed explanations are omitted.

[0062] Figure 11 shows an example configuration of a wireless communication system 7c including communication devices 3c-1 to 3c-5 according to Embodiment 4. The wireless communication system 7c is a system in which communication device 3c-5, which is not related to the link of multi-hop transmission, sends a link reselection recommendation message. In the following description, when communication devices 3c-1 to 3c-5 are not distinguished, they may be referred to as communication device 3c.

[0063] Communication devices 3c-1 to 3c-5 are relay stations, and one or more communication devices 3c relay data transmitted from the transmitting station, communication device 1, to the receiving station, communication device 2. Communication devices 3c-1 to 3c-5 constitute a relay station group 6c. Of the communication devices 3c-1 to 3c-5, communication devices 3c-1 to 3c-4 are child relay stations, and communication device 3c-5 is the parent relay station. Communication device 3c-5, being the parent relay station, corresponds to the parent node of the relay station group 6c. Communication devices 3c-1 to 3c-4, being child relay stations, correspond to child nodes of the relay station group 6c and are relay stations managed by communication device 3c-5, being the parent relay station. In Figure 11, the number of communication devices 3c, which are relay stations, is shown as five as an example, but the number of communication devices 3c, which are relay stations, is not particularly limited as long as multiple multi-hop transmission paths can be established.

[0064] Figure 12 is a sequence diagram showing the operation of the communication device 3c according to Embodiment 4 when link reselection in multi-hop transmission is performed by a link reselection recommendation message from the parent relay station, communication device 3c-5. In Figure 12, as in Figure 11, communication devices 3c-1 to 3c-4 are child relay stations, and communication device 3c-5 is the parent relay station. Specifically, the case in which communication device 3c-5, which is not related to the link in multi-hop transmission, sends a link reselection recommendation message will be described.

[0065] In a situation where data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3c-1, 3c-3, and 3c-4 (step S101), communication device 3c-5, which is the parent relay station, checks the link status between communication devices 3c-3 and 3c-4, which are child relay stations (step S401). The method for checking the link status can be, for example, by communication device 3c-5, which is the parent relay station, overhearing the transmission and reception of signals between communication devices 3c-3 and 3c-4, which are child relay stations, or by communication devices 3c-3 and 3c-4, which are child relay stations, reporting the link status to communication device 3c-5, which is the parent relay station, at a specified interval. However, any method is acceptable for communication device 3c-5, which is the parent relay station, to check the link status.

[0066] If the parent relay station, communication device 3c-5, which has checked the link status, predicts, i.e., detects that the link quality between the child relay stations, communication devices 3c-3 and 3c-4, will no longer meet the required link quality, it sends a link reselection recommendation message to the child relay station, communication device 3c-1 (step S402). The operation of the sequence diagram from Figure 12 onward is the same as the operation of the sequence diagram shown in Figure 4. In the example of Figure 12, in step S105, data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3c-1, 3c-2, and 3c-4.

[0067] Regarding the configuration of the parent relay station communication device 3c-5 and the child relay stations communication devices 3c-1 to 3c-4, any configuration is acceptable as long as the parent relay station communication device 3c-5 can check the link status between the child relay station communication devices 3c-1 to 3c-4. For example, the configuration of communication devices 3c-1 to 3c-5 is the same as the configuration of communication device 3 in Embodiment 1 shown in Figure 2.

[0068] The communication device installed, i.e., the self-communication device, is assumed to be a parent relay station communication device 3c-5 that checks the link quality of the child relay stations communication devices 3c-1 to 3c-4 in a relay station group 6c that includes a parent relay station communication device 3c-5 and multiple child relay stations communication devices 3c-1 to 3c-4. In this case, if the control unit 33 of the communication device 3c-5 predicts that the link quality of the child relay stations communication devices 3c-1 to 3c-4 performing multi-hop transmission will no longer meet the required link quality, it controls the transmission unit 31 to send a link reselection recommendation message to the source communication device 3c of the data transmission via multi-hop transmission, recommending reselection of the link in the multi-hop transmission. In this embodiment, the parent relay station communication device 3c-5 is a communication device that is not on the multi-hop transmission path before the link reselection.

[0069] As described above, according to this embodiment, the parent relay station communication device 3c-5 checks the link status between each of the child relay station communication devices 3c-1 to 3c-4, and if it detects that the link quality between the communication devices no longer meets the required link quality, it sends a link reselection recommendation message to the child relay station communication device 3c. In this case as well, the same effects as in Embodiment 1 can be obtained. Furthermore, by having the parent relay station communication device 3c-5, which is not involved in the links of multi-hop transmission, send the link reselection recommendation message, it is possible to unify and centralize link management, such as when reselection is performed on multiple links simultaneously.

[0070] In this embodiment, the parent relay station communication device 3c-5 sent a link reselection recommendation message to the child relay station communication device 3c, but this is not limited to this. For example, the role of the parent relay station communication device 3c-5 may be performed by a base station, access point, etc., capable of accommodating communication devices 3c-1 to 3c-4. Figure 13 is a diagram showing an example configuration of a wireless communication system 7d including communication devices 3c-1 to 3c-4 and a base station 5 according to Embodiment 4. A detailed explanation of the operation is omitted, but in Figure 13, the base station 5 performs the same operation as the parent relay station communication device 3c-5 shown in Figures 11 and 12. In the example of Figure 13, the base station 5 is included in the relay station group 6d, but the base station 5 may be located outside the relay station group 6d.

[0071] In this embodiment, the first communication device described in Embodiment 1 is a communication device 3c-5 that is a parent relay station and confirms the link quality of the child relay stations, communication devices 3c-1 to 3c-4, in a relay station group 6c that includes a parent relay station, communication device 3c-5, and a plurality of child relay stations, communication devices 3c-1 to 3c-4, and is a communication device that is not on a path where multi-hop transmission is taking place. Alternatively, the first communication device is a base station 5 that can accommodate the child relay stations, communication devices 3c-1 to 3c-4, i.e., the second communication device.

[0072] Furthermore, while the case of applying Embodiment 4 to Embodiment 1 has been described, it is not limited to this. Embodiment 4 can also be applied to Embodiments 2 and 3. Although not shown in the figures, the communication device of Embodiment 4 may be configured to include an internal information management unit 34, or it may be configured to be connected to an external device 4.

[0073] Embodiment 5. In Embodiment 1, the communication device 3-3 transmitted the link reselection recommendation message via one hop, i.e., directly. Embodiment 5 describes the case where the communication device transmits the link reselection recommendation message via multiple hops. Components having the same function as in Embodiment 1 are given the same reference numerals, and detailed explanations are omitted.

[0074] Although not shown in the diagram, the configuration of the wireless communication system in Embodiment 5 is the same as the configuration of the wireless communication system 7 of Embodiment 1 shown in Figure 3, but with the relay station communication devices 3-1 to 3-4 replaced by relay station communication devices 3e-1 to 3e-4. In the following description, when communication devices 3e-1 to 3e-4 are not distinguished, they may be referred to as communication device 3e. Figure 14 is a sequence diagram showing the operation of communication device 3e according to Embodiment 5 when it transmits a link reselection recommendation message in multi-hop transmission. Specifically, the operation when communication device 3e-3 transmits a link reselection recommendation message in multi-hop transmission will be described.

[0075] In a situation where data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3e-1, 3e-3, and 3e-4 (step S101), communication device 3e-3 checks the link status between communication device 3e-3 and communication device 3e-4 (step S102). If communication device 3e-3, having checked the link status, detects that the link quality between communication device 3e-3 and communication device 3e-4 no longer meets the required link quality, it sends a link reselection recommendation message to communication device 3e-2 (step S501). At this time, the destination of the link reselection recommendation message is assumed to be communication device 3e-1. When communication device 3e-2 receives the link reselection recommendation message, it sends the received link reselection recommendation message to communication device 3e-1 (step S502). The operation of the sequence diagrams from Figure 14 onward is the same as the operation of the sequence diagrams shown in Figure 4. In the example shown in Figure 14, in step S105, data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3e-1, 3e-2, and 3e-4.

[0076] Regarding the configuration of communication devices 3e-1 to 3e-4, any configuration is acceptable as long as it can transmit the link re-selection recommendation message via multi-hop. For example, the configuration of communication devices 3e-1 to 3e-4 is the same as the configuration of communication device 3 in Embodiment 1 shown in Figure 2.

[0077] In this manner, the control unit 33 of the communication device 3e-3, the source of the link reselection recommendation message, controls the transmission unit 31 to send the link reselection recommendation message via multi-hop transmission to the communication device 3e-1, the source of the data. Furthermore, the control unit 33 of the communication device 3e-2, which is not the destination of the link reselection recommendation message, controls the transmission unit 31 to send the link reselection recommendation message received by the receiving unit 32 if the receiving unit 32 receives a link reselection recommendation message that is not addressed to its own communication device.

[0078] Furthermore, the link reselection recommendation message in step S501, transmitted from communication device 3e-3, is destined for communication device 3e-1, and therefore may reach communication device 3e-1 directly. For this reason, when communication device 3e-1 receives both the link reselection recommendation message in step S501 transmitted from communication device 3e-3 and the link reselection recommendation message in step S502 transmitted from communication device 3e-2, it performs processing according to predetermined rules. These predetermined rules include, for example, adopting only the message with the earliest reception time and excluding subsequent messages, but are not limited to these rules.

[0079] Furthermore, while Figure 14 illustrates the case where the link re-selection recommendation message takes one hop, it is not limited to this. The link re-selection recommendation message may take two or more hops.

[0080] As described above, according to this embodiment, the communication device 3e, which is a relay station, transmits the link reselection recommendation message via multi-hop transmission. As a result, even if the communication device 3e that is the destination of the link reselection recommendation message cannot directly receive the link reselection recommendation message sent from the communication device 3e that is the source of the link reselection recommendation message, it can still receive the link reselection recommendation message that has been transmitted via multi-hop. In this way, the reliability of sending and receiving the link reselection recommendation message can be improved by transmitting the link reselection recommendation message via multi-hop transmission.

[0081] Although the description of Embodiment 5 has focused on its application to Embodiment 1, it is not limited to this. Embodiment 5 can also be applied to Embodiments 2 through 4. Although not shown in the figures, the communication device of Embodiment 5 may be configured to include an internal information management unit 34, or it may be configured to be connected to an external device 4.

[0082] Embodiment 6. In Embodiment 1, acknowledgment (ACK) or NACK (Negative ACKnowledgment) confirmation of receipt of link reselection recommendation messages was not performed between communication devices. Embodiment 6 describes a case in which acknowledgment of receipt of link reselection recommendation messages is performed between communication devices using ACK or NACK. Components having the same function as in Embodiment 1 are given the same reference numerals, and detailed explanations are omitted.

[0083] Although not shown in the diagram, the configuration of the wireless communication system in Embodiment 6 is the same as the configuration of the wireless communication system 7 of Embodiment 1 shown in Figure 3, but with the relay station communication devices 3-1 to 3-4 replaced by relay station communication devices 3f-1 to 3f-4. In the following description, when communication devices 3f-1 to 3f-4 are not distinguished, they may be referred to as communication device 3f. Figure 15 is a sequence diagram showing the operation when communication device 3f according to Embodiment 6 performs an acknowledgment of receipt when it transmits a link reselection recommendation message in multi-hop transmission. Specifically, the operation when communication device 3f-3 transmits a link reselection recommendation message in multi-hop transmission and performs an acknowledgment of receipt with communication device 3f-1, which is the destination of the link reselection recommendation message, will be described.

[0084] In a situation where data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3f-1, 3f-3, and 3f-4 (step S101), communication device 3f-3 checks the link status between communication device 3f-3 and communication device 3f-4 (step S102). If communication device 3f-3, having checked the link status, predicts, i.e., detects that the link quality between communication device 3f-3 and communication device 3f-4 will no longer meet the required link quality, it sends a link reselection recommendation message to communication device 3f-1 (step S103).

[0085] If communication device 3f-1 fails to successfully receive the link reselection recommendation message, it sends a NACK link reselection recommendation response message to communication device 3f-3 indicating that the link reselection recommendation message was not successfully received (step S601). Upon receiving the NACK link reselection recommendation response message, communication device 3f-3 retransmits the link reselection recommendation message to communication device 3f-1 (step S602). If communication device 3f-3 does not receive an ACK or NACK link reselection recommendation response message from communication device 3f-1 within a specified period after sending the link reselection recommendation message in step S103, it may retransmit the link reselection recommendation message to communication device 3f-1. If communication device 3f-1 successfully receives the link reselection recommendation message, it sends an ACK link reselection recommendation response message to communication device 3f-3 indicating that the link reselection recommendation message was successfully received (step S603). Through the sending and receiving of the above messages, in embodiment 6, link reselection is performed after the successful receipt of the link reselection recommendation message is confirmed. The operation of the sequence diagrams shown in Figure 15 and beyond is the same as the operation of the sequence diagram shown in Figure 4. In the example in Figure 15, in step S105, data is transmitted via multi-hop from communication device 1 to communication device 2 via communication devices 3f-1, 3f-2, and 3f-4.

[0086] If the communication device 3f-3 receives a NACK link reselection recommendation response message from the communication device 3f-1 regarding the link reselection recommendation message retransmitted in step S602, or if it does not receive an ACK or NACK link reselection recommendation response message from the communication device 3f-1 within a specified period, it may retransmit the link reselection recommendation message to the communication device 3f-1 again. If the communication device 3f-3 receives a NACK link reselection recommendation response message from the communication device 3f-1, or if it does not receive an ACK or NACK link reselection recommendation response message from the communication device 3f-1 within a specified period, it may send the link reselection recommendation message a predetermined number of times or within a predetermined period.

[0087] Furthermore, if the link quality between communication device 3f-3 and communication device 3f-4 no longer meets the required link quality, it becomes necessary to "request" link reselection, rendering the message "recommended" for link reselection ineffective. Therefore, communication device 3f-3 may terminate the process of sending the link reselection recommendation message and confirming the link reselection recommendation response message at the moment the link quality between communication device 3f-3 and communication device 3f-4 actually no longer meets the required link quality.

[0088] Regarding the configuration of communication devices 3f-1 to 3f-4, any configuration is acceptable as long as it can send and receive link reselection recommendation messages and link reselection recommendation response messages. For example, the configuration of communication devices 3f-1 to 3f-4 is the same as the configuration of communication device 3 in Embodiment 1 shown in Figure 2.

[0089] Thus, if the control unit 33 of the communication device 3f-3 fails to receive a link reselection recommendation response message from the destination communication device 3f-1 indicating that the link reselection recommendation message was successfully received, or if it receives a link reselection recommendation response message from the destination communication device 3f-1 indicating that the link reselection recommendation message was not successfully received, it controls the transmission unit 31 to resend the link reselection recommendation message. Furthermore, if the control unit 33 of the communication device 3f-1 receives a link reselection recommendation message from its own communication device to the destination communication device to the receiving unit 32, it controls the transmission unit 31 to send a link reselection recommendation response message indicating that the link reselection recommendation message was successfully received if the link reselection recommendation message was successfully received, and controls the transmission unit 31 to send a link reselection recommendation response message indicating that the link reselection recommendation message was not successfully received if the link reselection recommendation message was not successfully received.

[0090] As described above, according to this embodiment, the communication device 3f, which is a relay station, confirms receipt of the link reselection recommendation message and performs link reselection only after confirming that the link reselection recommendation message has been correctly received by the destination communication device 3f. This improves the reliability of the transmission and reception of the link reselection recommendation message for the communication device 3f.

[0091] Although the description of Embodiment 6 has focused on its application to Embodiment 1, it is not limited to this. Embodiment 6 can also be applied to Embodiments 2 through 5. Although not shown in the figures, the communication device of Embodiment 6 may be configured to include an internal information management unit 34, or it may be configured to be connected to an external device 4.

[0092] The configurations shown in the above embodiments are examples only, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention.

[0093] 1, 2, 3, 3-1 to 3-4, 3a, 3a-1 to 3a-4, 3b, 3b-1 to 3b-4, 3c-1 to 3c-5, 3e-1 to 3e-4, 3f-1 to 3f-4 Communication equipment, 4 External equipment, 5 Base station, 6c, 6d Relay station group, 7, 7c, 7d Wireless communication system, 11, 21, 31 Transmitting unit, 12, 22, 32 Receiving unit, 13, 23, 33, 33a, 33b Control unit, 34 Internal information management unit, 90, 93 Processing circuit, 91 Processor, 92 Memory.

Claims

1. A communication device comprising: a receiving unit that receives data transmitted from a preceding communication device; a transmitting unit that transmits the data received by the receiving unit to a subsequent communication device; and a control unit that controls the relaying of the data using the receiving unit and the transmitting unit in multi-hop transmission, and, in a wireless communication system capable of multi-hop transmission via multiple paths, when it is predicted that the link quality between communication devices on the currently used path will no longer meet the required link quality, controls the transmitting unit to send a link reselection recommendation message to the source communication device of the data transmitted via multi-hop transmission, recommending reselection of the link in the multi-hop transmission.

2. The communication device according to claim 1, characterized in that the control unit predicts the link quality based on the data transmission status of the transmission unit.

3. The communication device according to claim 1 or 2, comprising an internal information management unit for managing information obtained within the installed communication device, wherein the control unit predicts the link quality based on the internal information obtained from the internal information management unit.

4. A communication device according to any one of claims 1 to 3, characterized in that it is connected to an external device that transmits link reselection supplementary information when it detects the possibility that the link quality may no longer meet the required link quality, and the control unit determines whether or not to have the transmission unit transmit the link reselection recommendation message based on the link reselection supplementary information obtained from the external device.

5. The communication device is a parent relay station that checks the link quality of a communication device that is a child relay station in a relay station group including a parent relay station and a plurality of child relay stations, and the control unit predicts that the link quality of the child relay station that is performing the multi-hop transmission will no longer meet the required link quality, and controls the transmission unit to send a link reselection recommendation message to the source communication device of the data transmitted by the multi-hop transmission, recommending that the link be reselected in the multi-hop transmission, as described in any one of claims 1 to 4.

6. The communication device according to claim 5, characterized in that the communication device that is the parent relay station is a communication device that is not on the multi-hop transmission path before the re-selection of the link.

7. The communication device according to any one of claims 1 to 6, characterized in that the control unit controls the transmission unit to send the link reselection recommendation message via multi-hop transmission to the communication device that is the source of the data.

8. The communication device according to any one of claims 1 to 6, characterized in that, when the receiving unit receives a link reselection recommendation message that is not addressed to the local communication device, the receiving unit controls the transmitting unit to transmit the link reselection recommendation message that is not addressed to the local communication device that was received by the receiving unit.

9. The communication device according to any one of claims 1 to 8, characterized in that the control unit controls the transmission unit to resend the link reselection recommendation message if it fails to receive a link reselection recommendation response message from the destination communication device indicating that the link reselection recommendation message was successfully received, or if it receives a link reselection recommendation response message from the destination communication device indicating that the link reselection recommendation message was not successfully received.

10. The communication device according to any one of claims 1 to 8, characterized in that, when the receiving unit receives a link reselection recommendation message to which the local communication device is the destination communication device, the control unit controls the transmission unit to send a link reselection recommendation response message indicating that the link reselection recommendation message was received successfully if the link reselection recommendation message was received successfully, and when the link reselection recommendation message was not received successfully, the control unit controls the transmission unit to send a link reselection recommendation response message indicating that the link reselection recommendation message was not received successfully.

11. A wireless communication system capable of multi-hop transmission of data via multiple paths, comprising: a first communication device that sends a link reselection recommendation message recommending reselection of a link in multi-hop transmission when it is predicted that the link quality between communication devices on the currently used path will no longer meet the required link quality; and a second communication device that, upon receiving the link reselection recommendation message, performs the link reselection.

12. The wireless communication system according to claim 11, characterized in that the first communication device is a communication device on the path where the multi-hop transmission is performed.

13. The wireless communication system according to claim 11, characterized in that the first communication device is a communication device that is a parent relay station in a relay station group including a parent relay station and a plurality of child relay stations, which checks the link quality of the communication devices that are child relay stations, and is not a communication device that is on the path in which the multi-hop transmission is being performed.

14. The wireless communication system according to claim 11, characterized in that the first communication device is a base station capable of accommodating the second communication device.

15. A control circuit for controlling a communication device, characterized in that it causes the communication device to perform the following actions: receiving data transmitted from a preceding communication device, transmitting the received data to a subsequent communication device, controlling the relaying of the data in multi-hop transmission, and, in a wireless communication system capable of multi-hop transmission via multiple paths, if it is predicted that the link quality between communication devices on the currently used path will no longer meet the required link quality, it causes the communication device to send a link reselection recommendation message to the source communication device of the data transmitted via multi-hop transmission, recommending that the link be reselected in the multi-hop transmission.

16. A storage medium storing a program for controlling a communication device, wherein the program controls the following actions of the communication device: receiving data transmitted from a preceding communication device, transmitting the received data to a subsequent communication device, controlling the relaying of the data in multi-hop transmission, and, in a wireless communication system capable of multi-hop transmission via multiple paths, if it is predicted that the link quality between communication devices on the currently used path will no longer meet the required link quality, the storage medium causes the communication device to send a link reselection recommendation message to the source communication device of the data transmitted via multi-hop transmission, recommending the reselection of the link in the multi-hop transmission.

17. A link reselection recommendation method comprising: a receiving step in which a receiving unit receives data transmitted from a preceding communication device; a transmitting step in which a transmitting unit transmits the data received by the receiving unit to a subsequent communication device; and a control step in which a control unit controls the relaying of the data using the receiving unit and the transmitting unit in multi-hop transmission, and, when it is predicted that the link quality between communication devices on the currently used path in a wireless communication system capable of multi-hop transmission via multiple paths will no longer meet the required link quality, controls the transmitting unit to send a link reselection recommendation message to the source communication device of the data transmitted via multi-hop transmission, recommending reselection of the link in the multi-hop transmission.

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