JP7549851B2 - COMMUNICATION SYSTEM, COMMUNICATION METHOD, AND NODE - Google Patents

Description

The present disclosure relates to a communication system, a communication method, and a node.

In existing cellular communication systems, base stations that provide wireless access lines for user devices are often connected to a backbone network (sometimes called a core network) via a wired backhaul (BH) network.

On the other hand, as one form of realizing a new generation of mobile communications, a system or network that connects multiple wireless nodes (e.g., base stations or access points) that provide wireless communication areas with a radius of several tens of meters using wireless multi-hop is being considered.

JP 2005-143046 A International Publication No. 2011/105371

Multi-stage relay wireless backhaul technology for wireless LAN access points RF World No.33, pp89-105, February 2016; Hiroshi Furukawa

There is room for consideration regarding rescue control in the event that some wireless links in a wireless BH network become unavailable.

A communication system according to one embodiment includes a plurality of nodes, a first node of the plurality of nodes includes a transmitter that transmits a control signal including information specifying at least one first link among a plurality of links established between the plurality of nodes, and a second node of the plurality of nodes includes a receiver that receives the control signal, a controller that determines a second link that constitutes an alternative second route to the first route of data communication using the first link among the remaining links excluding the first link specified by the information of the received control signal based on an index related to the propagation quality of one or more links through which the control signal passes, and a storage unit that stores information related to the second link in association with the first link, and when it is detected that the deterioration amount of the line quality of the first link is equal to or greater than a threshold value, the controller switches the route used for the data communication from the first route to the second route based on the information related to the second link in the storage unit.

In one aspect of the communication method, a first node among a plurality of nodes transmits a control signal including information specifying at least one first link among a plurality of links established between the plurality of nodes, and a second node among the plurality of nodes receives the control signal, and determines a second link that constitutes an alternative second route to the first route of data communication using the first link among the remaining links excluding the first link specified by the information of the received control signal based on an index related to the propagation quality of one or more links through which the control signal passes, stores information related to the second link in association with the first link, and when it is detected that the amount of degradation in the line quality of the first link is equal to or greater than a threshold, switches the route used for the data communication from the first route to the second route based on the stored information related to the second link.

The node according to one embodiment is one of a plurality of nodes, and includes a receiver that receives a control signal including information specifying at least one first link among a plurality of links established between the plurality of nodes, a controller that determines a second link that constitutes an alternative second route to the first route of data communication using the first link among the remaining links excluding the first link specified by the information of the received control signal, based on an index related to the propagation quality of one or more links through which the control signal passes, and a memory that stores information related to the second link in association with the first link, and when it is detected that the deterioration amount of the line quality of the first link is equal to or greater than a threshold, the controller switches the route used for the data communication from the first route to the second route based on the information related to the second link in the memory.

According to a non-limiting aspect of the present disclosure, rescue control can be realized when some wireless links become unavailable in a wireless BH network.

1 is a block diagram showing an example of a configuration of a wireless communication system according to an embodiment; FIG. 2 is a diagram illustrating a protocol stack of a wireless node according to one embodiment. FIG. 2 is a block diagram showing an example of a hardware configuration of a wireless node according to an embodiment. FIG. 1 is a conceptual diagram of upstream data transfer between hop links to which BF transmission according to an embodiment is applied; FIG. 13 is a conceptual diagram of downstream data transfer between hop links to which BF transmission according to an embodiment is applied. FIG. 13 is a diagram illustrating an example of BF control according to an embodiment. 2 is a block diagram showing an example of a functional configuration of a control unit of a wireless node according to an embodiment; 10 is a flowchart illustrating an example of the operation of a core node (CN) according to an embodiment. 11 is a flowchart illustrating an example of the operation of a slave node (SN) according to an embodiment. 11 is a flowchart illustrating an example of the operation of a slave node (SN) according to an embodiment. FIG. 13 is a diagram illustrating an example of a route construction packet according to an embodiment. FIG. 2 is a diagram illustrating an example of a routing table stored in a wireless node according to an embodiment. 12 is a diagram showing an example of an alternative relay route shown in the routing table shown in FIG. 11 .

Below, the embodiments will be described with reference to the drawings as appropriate. The same elements throughout this specification are given the same reference numerals unless otherwise specified. The matters described below together with the attached drawings are intended to explain exemplary embodiments and are not intended to represent the only embodiments. For example, when an order of operations is indicated in an embodiment, the order of operations may be changed as appropriate within the scope of no inconsistency in the overall operation.

When multiple embodiments and/or variants are given as examples, some configurations, functions and/or operations in one embodiment and/or variant may be included in other embodiments and/or variants to the extent that no inconsistency arises, or may be replaced with the corresponding configurations, functions and/or operations in other embodiments and/or variants.

In addition, in the embodiments, more detailed explanations than necessary may be omitted. For example, detailed explanations of publicly known or well-known technical matters may be omitted in order to avoid unnecessarily lengthy explanations and/or ambiguity in technical matters or concepts, and to facilitate understanding by those skilled in the art. Furthermore, duplicate explanations of substantially identical configurations, functions, and/or operations may be omitted.

The accompanying drawings and the following description are provided to aid in understanding the embodiments, and are not intended to limit the subject matter described in the claims. Furthermore, the terms used in the following description may be appropriately replaced with other terms to aid in the understanding of those skilled in the art.

<Findings that led to this disclosure>
By making the BH network, which is one of the infrastructures of mobile communication, wireless by wireless multi-hop, it is possible to eliminate the need to lay wired cables and reduce the installation costs required for introducing a mobile communication system. Therefore, for example, when introducing a mobile communication system temporarily (or provisionally), it is effective to make the BH network wireless by wireless multi-hop.

For example, when installing a large number of small cell base stations (wireless nodes) in the service area of a mobile communication system to cover the service area, it is effective to make the BH network wireless by wireless multi-hop, and this has already been widely introduced, mainly in wireless LAN (e.g., Wi-Fi (registered trademark)) systems.

Furthermore, the fifth generation mobile communication system (5G), for which commercial services are expected to begin worldwide around 2019 or 2020, will use radio waves in the high frequency band. High frequency bands include, for example, the centimeter wave band (3 GHz to 30 GHz, sometimes called Super High Frequency (SHF)) and the millimeter wave band (30 GHz to 300 GHz, sometimes called Extreme High Frequency (EHF)). In high frequency bands, radio wave propagation loss is large, so the application of beamforming (BF) technology is being considered to compensate for radio wave propagation loss.

For example, even when BF technology is applied to high-frequency band access lines, the cell radius is 100 to several hundred meters, so the cell size is small (small cells). This requires a huge number of base stations, making it difficult to lay wired cables for the BH network. Making the BH network wireless eliminates the need to lay wired cables, so it is also effective when applying BF technology in high-frequency bands.

For example, in the method described in Non-Patent Document 1 (sometimes referred to as "wireless backhaul engine (BE)"), a wireless multi-hop relay route is constructed in advance, and when a communication session occurs (data transfer occurs), data frames are transferred between wireless nodes along the constructed relay route. This method is a wireless backhaul technology that separates the "route control" that constructs the relay route from the "frame transfer (sometimes referred to as "relay transfer")" of data.

In this embodiment, one example is the application of the wireless beamforming technology described in Non-Patent Document 1 to wireless standards that use beamforming (BF) in high frequency bands, such as next-generation Wi-Fi (IEEE802.11ax and/or IEEE802.11ay) and the fifth generation mobile communication system (5G).

In order for each node to perform relay forwarding using BF (transmission and reception of data along a relay route), "route control" is performed to construct a relay route before transmitting and receiving data. Route control may include establishment of a hop link including BF control processing, and construction of a relay route based on the established hop link. Each node can improve the efficiency of relay forwarding by knowing the constructed relay route in advance. Here, the BF control processing may include transmission weight control or transmission directivity control of the transmitting antenna at each node, and reception weight control or reception directivity control of the receiving antenna at each node. In addition, a hop link may correspond to a mesh link between a certain node and N surrounding nodes (N is an integer equal to or greater than 1).

Although it is possible to execute the BF control process when a communication session occurs in a node and relay transfer of data is performed, the time required for relay transfer may increase. This may result in a decrease in the throughput of the BH line. Here, the occurrence of a communication session may correspond to, for example, a state in which a packet to be relayed in a node is on standby and the node has obtained a wireless channel (wireless resources) in Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA).

In addition, in the method described in Non-Patent Document 1, each node measures the received power of the route control packet (e.g., measures the received signal strength indicator (RSSI)) for the route control packet that is broadcast, and determines the quality of the hop link of each node (e.g., the assigned metric). By each node determining the quality of the hop link, route control for relay forwarding is performed efficiently.

For example, when BF is applied to relaying data, even during the route control stage, each node may determine the quality of each hop link based on the transmission and reception of route control packets in unicast to which BF is applied, instead of broadcast route control packets. By determining the quality of each hop link based on the transmission and reception of route control packets in unicast to which BF is applied, a route for relaying data to which BF is applied can be more appropriately selected.

On the other hand, when BF is applied to relaying data, communication is possible using two or more beams with directivities in different directions, so each node can communicate with two or more nodes at the same frequency and at the same time. In other words, when BF is applied to relaying data, spatial reuse of frequencies is possible. For example, a root node branching out in a relay path can receive data transmitted by multiple nearby transmitting nodes at the same time and frequency. In this case, it is desirable for each node to process data from multiple nodes in parallel at the same time, or to process it in a time-division manner at high speed.

Furthermore, in the high frequency band, radio waves tend to travel in a straight line, so if there is an obstruction (or obstacle) between the transmitting point and the receiving point, such as a building, tree, person, or vehicle, the loss of radio wave propagation from the transmitting point to the receiving point is likely to increase. This makes it easy for the line quality of the wireless link to deteriorate, and in the worst case scenario, the wireless link may be disconnected.

Therefore, the inventors of the present application adapted the method described in Non-Patent Document 1 to the case where BF technology is applied in high frequency bands, and developed a wireless BH network technology with higher throughput that takes advantage of the wider bandwidth of high frequency bands than the bandwidth of existing systems such as LTE.

Below, we will explain a non-limiting example of wireless BH technology that applies BF to a BH link, which can achieve high throughput by taking advantage of the wide bandwidth of high frequency bands and compensate for radio wave propagation loss in high frequency bands.

<System configuration example>
Fig. 1 is a block diagram showing an example of the configuration of a wireless communication system according to an embodiment. The wireless communication system 1 shown in Fig. 1 illustratively includes a plurality of nodes 3. In Fig. 1, eight nodes 3 are illustrated as a non-limiting example, and are indicated by node numbers #0 to #7. The number of nodes 3 may be two or more and less than eight, or may be nine or more.

Each node 3 is an example of a wireless device capable of wireless communication. Therefore, each node 3 may be referred to as a "wireless node 3."

Each node 3 forms an area in which wireless communication is possible. The "area in which wireless communication is possible" may be called a "wireless communication area," "wireless area," "communication area," "service area," "coverage area," "cover area," or the like. A wireless communication area formed by nodes 3 that conform to or are based on wireless LAN-related standards may be considered to correspond to a "cell," a term used in cellular communication. For example, a wireless communication area formed by individual nodes 3 may be considered to correspond to a "femtocell," which is classified as a "small cell."

When each node 3 is located in the service area of another node 3, it is capable of wireless communication with the other node 3. A plurality of nodes 3 form, for example, a wireless backhaul (BH) network that wirelessly relays communication between a backbone network 5 and a terminal device 7. A "wireless BH network" may be referred to as a "BH network" by omitting "wireless."

The "BH network" may be referred to as a "relay network." Individual nodes 3 that are entities of the BH network may be referred to as "relay nodes."

The backbone network 5 is, for example, a large-scale communication network such as the Internet. The "backbone network" may also be referred to as a "core network" or a "global network", etc.

The path or section through which a wireless signal is transmitted in a BH network may be interchangeably referred to as a "wireless BH communication path," "wireless BH transmission path," "wireless BH line," "wireless BH connection," "wireless BH channel," "wireless link," or "hop link." In these terms, "wireless" may be omitted, and "BH" may be interchangeably referred to as "relay."

In contrast, for example, the section where wireless signals are transmitted between the terminal device 7 and the BH network may be called a "wireless access line" or a "wireless access channel." In these terms, "wireless" may be omitted.

In the following description, the term "signal" may be interpreted as a term that refers to a unit of a signal divided over time, such as "frame" or "packet."

The wireless base station line and the wireless access line may be assigned different frequencies (channels).

Some of the multiple nodes 3 may be wired to the backbone network 5. FIG. 1 illustrates an example in which one node #0 is wired to the backbone network 5. For example, a LAN cable or an optical fiber cable may be used for the wired connection.

Node #0, which is connected by wire to the backbone network 5, may be referred to as a "core node (CN)." Of the multiple nodes 3 forming the BH network, each node 3, except for CN #0, may be referred to as a "slave node (SN)." For example, in FIG. 1, nodes #1 to #7 are all SNs. The number of CNs may be two or more, and the number of SNs may be less than seven or eight or more.

Note that in FIG. 1, #0 to #7 assigned to each node 3 are an example of information used to identify each node 3 (hereinafter sometimes abbreviated as "node identification information"). Node identification information may be any information that can uniquely identify each node 3 in the same BH network, and may be, for example, a node number, a device identifier, or address information. A non-limiting example of address information is a MAC (Media Access Control) address.

The BH network may have one or more tree structures (which may be referred to as "tree topologies") with one CN3 (#0) as the root node. Note that the structure of the BH network is not limited to a tree structure.

In a tree topology, an SN3 that has no child nodes may be referred to as a "leaf node," and an SN3 that has child nodes may be referred to as an "internal node." For example, in FIG. 1, SNs #2, #6, and #7 all correspond to "leaf nodes." Also, SNs #1, #3, #4, and #5 all correspond to "internal nodes."

The wireless BH line may include a "downlink" in the direction from the core node 3 to the leaf node 3, and an "uplink" in the direction from the leaf node 3 to the core node 3. The "downlink" and "uplink" may be referred to as "downlink (DL)" and "uplink (UL)", respectively, following the names used in cellular communications.

The flow of signals (downstream signals) on the "downstream line" may be referred to as "downstream," and the flow of signals (upstream signals) on the "upstream line" may be referred to as "upstream." Each of the "downstream signals" and "upstream signals" may include control signals and data signals. "Control signals" may include signals that do not fall under the category of "data signals."

Note that a "child node" may be considered to correspond to a node (downstream node) connected downstream of a certain node by a wireless link when focusing on the "downstream line." A node connected upstream of a certain node by a wireless link when focusing on the downstream line may be called a "parent node" or "upstream node." When focusing on the "upstream line," the relationship between a "child node" (downstream node) and a "parent node" (upstream node) is reversed.

Also, when focusing on the "downlink", a "core node" may be called an "start node" or "origin node", and a "leaf node" may be called an "end node" or "edge node". An "internal node" may be called an "intermediate node" or "relay node".

The tree-structured route (tree topology) in the BH network may be constructed, for example, based on the metric of the route from CN3 to a specific SN3 (hereinafter sometimes abbreviated as "route metric"). The route metric may be an index indicating the quality or performance of radio wave propagation in the wireless section from CN3 to a specific SN3 (hereinafter referred to as "propagation quality index").

Non-limiting examples of propagation quality indicators include the received power or strength of a wireless signal (e.g., Received Signal Strength Indicator (RSSI)), radio wave propagation loss, and propagation delay. "Radio wave propagation loss" may be read as "path loss."

The propagation quality index may be one or a combination of two or more selected from the above index candidates. Note that in this embodiment, the propagation quality index does not need to use an index related to the distance of the route, such as the number of hops.

For example, by transmitting a signal (e.g., a control signal) starting from CN3, the radio wave propagation loss of each wireless section between the transmitting node 3 and the receiving node 3 of the control signal can be calculated at the receiving node 3.

Then, each receiving node 3 transmits the obtained radio wave propagation loss information together with the control signal, so that information on the cumulative radio wave propagation loss (in other words, the cumulative value) of the wireless section through which the control signal has propagated can be transmitted between nodes 3.

Each node 3, for example, calculates a route metric based on the cumulative radio wave propagation loss for each upstream node candidate that is the source of the control signal, and selects one node 3 from among the upstream node candidates that has, for example, the smallest route metric. This allows a tree-structured route with the smallest radio wave propagation loss to be constructed.

The tree-structured route (hereinafter sometimes referred to as the "tree route") can be dynamically or adaptively updated by sending control signals periodically or irregularly starting from CN3.

Hereinafter, the processing or control involved in constructing and updating such tree routes may be referred to as "route control" for convenience.

In addition, at least one of the downlink and uplink of the BH line may include a wired line. If at least one of the downlink and uplink of the BH line includes a wired line, the route metric of the wired section may be calculated using a predetermined value (e.g., a minimum value) that is smaller than the propagation loss expected in the wireless section.

When the terminal device 7 is located in the service area of any of the SNs 3, it connects to any of the multiple SNs 3 forming the BH network via a wireless access line, and communicates with the backbone network 5 via the BH line. The terminal device 7 may also be connected to any of the SNs 3 (SN#3 as an example in FIG. 1) via a wired line (wired IF). As a non-limiting example, the terminal device 7 may be a mobile terminal such as a mobile phone, smartphone, or tablet terminal.

For example, any of the following may be applied to the wireless access line: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), and Single Carrier Frequency Division Multiple Access (SC-FDMA). OFDMA may be implemented by wireless technologies such as IEEE802.11, IEEE802.16, Long Term Evolution (LTE), and LTE-Advanced.

MIMO (Multiple Input Multiple Output) technology using an antenna array having multiple antenna elements may be applied to all or part of the downlink and/or uplink in the wireless base station line and/or wireless access line.

For example, beamforming using an antenna array may be performed on the downlink and/or uplink of one or more sections between CN3 and SN3, between SN3 and SN3, and between SN3 and terminal device 7. Beamforming using an antenna array will be described later.

In the following, the term "transmission" of a signal may be read as other terms such as "relay," "transfer," "propagation," "conveyance," "routing," or "forwarding" of a signal. "Relay" of a signal may be read as "bridging" of a signal.

The term "transmission" of a signal may include the meaning of "flooding," "broadcasting," "multicasting," or "unicasting" of a signal. The term "connection" of a line may be taken to mean a state in which a wired and/or wireless communication link is "established" or "linked up."

The term "apparatus" may be interchangeably read as "circuit," "device," "unit," or "module." The term "interface (IF)" may be interchangeably read as "adapter," "board," "card," "module," or "chip."

The node 3 and/or the terminal device 7 may be an IoT (Internet of Things) device. With the IoT, various "things" can be equipped with wireless communication functions. Various "things" equipped with wireless communication functions can connect to the backbone network 5 via wireless access lines and/or wireless BH lines to communicate.

For example, IoT devices may include sensor devices and meters (measuring instruments) equipped with wireless communication functions. Devices with sensing and/or monitoring functions, such as surveillance cameras and/or fire alarms equipped with sensor devices and/or meters, may correspond to the nodes 3 and/or terminal devices 7. Therefore, the BH network may correspond to, for example, a sensor network and/or a monitoring network. Note that wireless communication by IoT devices is sometimes referred to as MTC (Machine Type Communications). Therefore, IoT devices are sometimes referred to as "MTC devices."

Below, an example of a protocol stack and an example of a hardware configuration of node 3 that constitutes wireless communication system 1 will be described.

<An example of a protocol stack for node 3>
2 is a diagram showing a protocol stack of a wireless node according to an embodiment of the present invention, as shown in FIG 2. Layer 2.5 is positioned between Layer 2 and Layer 3, and controls wireless multi-hop transmission of the BH link.

Layer 1 may be referred to as the PHY layer. In Layer 1, wireless transmission with BF functionality is performed, for example. For example, Layer 1 complies with IEEE 802.11ay and/or 5G (NR) wireless standards.

In layer 2.5, "mesh link establishment" and "route control" are separated and independent.

In "mesh link establishment," each node scans for neighboring nodes, links up mesh links in the backhaul network, and stores information (node information) about the neighboring nodes that have been linked up. Here, the neighboring nodes of a certain node 3 may correspond to nodes that are located in positions that can receive signals (e.g., beacon signals) transmitted by the certain node 3, for example.

In "routing control", multi-hop routes between each slave node and the core node are dynamically constructed. In the two-layer hierarchy of layer 2.5, "mesh link establishment" is positioned in the lower layer of layer 2.5, and "routing control" is positioned in the upper layer of layer 2.5.

The Layer 2.5 hierarchy allows the sending node to know in advance which node the data should be forwarded to when it forwards a frame of data, enabling data transfer with minimal latency.

When applying high-frequency band BF transmission to wireless multi-hop transmission over a BH line, the following three processes are executed in the protocol stack of wireless node 3, which includes layer 2.5, for example.

(1) In the process of establishing a mesh link, each node stores information about surrounding nodes (node information) and performs BF control for BF transmission between nodes. BF control will be described later.

(2) In the process of routing control, the routing control packets that are the subject of RSSI measurements to evaluate the propagation quality between nodes are unicast using the BF between the nodes instead of being broadcast. Each node receives the unicast routing control packets and performs RSSI measurements.

When data is transmitted and received using BFs between nodes, even in the route control process that determines a multi-hop route, evaluating the propagation quality by transmitting and receiving route control packets by unicast using BFs can build a more accurate multi-hop route than transmitting and receiving route control packets that are broadcast.

However, in the process of route control, the evaluation of the propagation quality between nodes may be performed by broadcasting route control packets. When the evaluation of the propagation quality between nodes is performed by broadcasting route control packets, the number of times route control packets are sent can be reduced, and therefore the execution time of route control can be shortened. Furthermore, even when the propagation quality between nodes is evaluated by broadcasting route control packets, it is possible to perform an accurate evaluation to a certain extent.

(3) In the process of route control, a relay route is determined in advance when some of the wireless links between the nodes included in the mesh link are excluded (in other words, are not used). The relay route determined in route control in a state in which some of the wireless links are excluded may be called an "alternative relay route." Then, when the line quality of the wireless link between the nodes deteriorates, a relay route is determined that is switched to an alternative relay route that does not include the deteriorated wireless link.

In high frequency bands, such as the millimeter wave band, radio waves tend to travel in a straight line, and when there is an obstruction between the transmission point and the reception point, such as a building, tree, person, or vehicle, the loss of radio wave propagation from the transmission point to the reception point becomes extremely large. Therefore, when the line quality of the wireless link between the wireless node that is the transmission point and the wireless node that is the reception point deteriorates significantly, a relay transmission route is selected by the route control process along a multi-hop route that does not include the deteriorated wireless link, and relay transmission is performed along that route.

<Example of Hardware Configuration of Node 3>
Fig. 3 is a block diagram showing an example of a hardware configuration of a wireless node 3 according to an embodiment. The example configuration shown in Fig. 3 may be common to the CN 3 and the SN 3. As shown in Fig. 3, the node 3 may include, for example, a processor 31, a memory 32, a storage 33, an input/output (I/O) device 34, wireless IFs 35 and 36, a wired IF 37, a wired IF 39, and a bus 38.

In addition, in the example hardware configuration shown in FIG. 3, the amount of hardware may be increased or decreased as appropriate. For example, any hardware block may be added, removed, divided, or integrated in any combination, and bus 38 may be added or removed as appropriate.

The processor 31, memory 32, storage 33, input/output (I/O) device 34, wireless IFs 35 and 36, and wired IFs 37 and 39 can be connected to, for example, a bus 38 to communicate with each other. The number of buses 38 may be one or more.

A plurality of processors 31 may be provided in the node 3. Furthermore, the processing in the node 3 may be executed by one processor 31 or by multiple processors 31. In one or multiple processors 31, multiple processes may be executed simultaneously, in parallel, or sequentially, or may be executed by other methods. The processor 31 may be a single-core processor or a multi-core processor. The processor 31 may be implemented using one or more chips.

One or more functions possessed by node 3 are realized, for example, by loading specific software into hardware such as processor 31 and memory 32. Note that "software" may be interchangeably interpreted as other terms such as "program," "application," "engine," or "software module."

For example, the processor 31 reads and executes a program by controlling one or both of reading and writing data stored in one or both of the memory 32 and the storage 33. Note that the program may be provided to the node 3 by communication via a telecommunication line using at least one of the wireless IF 35, the wireless IF 36, and the wired IF 37, for example.

The program may be a program that causes a computer to execute all or part of the processing in node 3. One or more functions of node 3 are realized in response to execution of program code contained in the program. All or part of the program code may be stored in memory 32 or storage 33, or may be written as part of the operating system (OS).

The processor 31 is an example of a processing unit, and for example, operates an OS to control the entire computer. The processor 31 may be configured using a central processing unit (CPU) that includes an interface with peripheral devices, a control device, an arithmetic unit, a register, etc.

The processor 31 also reads, for example, one or both of programs and data from the storage 33 to the memory 32 and executes various processes.

The memory 32 is an example of a computer-readable recording medium, and may be configured using at least one of, for example, a ROM, an EPROM, an EEPROM, a RAM, an SSD, etc. Note that "ROM" is an abbreviation for "Read Only Memory", and "EPROM" is an abbreviation for "Erasable Programmable ROM". "EEPROM" is an abbreviation for "Electrically Erasable Programmable ROM", "RAM" is an abbreviation for "Random Access Memory", and "SSD" is an abbreviation for "Solid State Drive".

Memory 32 may also be called a register, cache, main memory, work memory, or primary storage device.

Storage 33 is an example of a computer-readable recording medium, and may be configured using at least one of an optical disk such as a CD-ROM (Compact Disc ROM), a hard disk drive (HDD), a flexible disk, a magneto-optical disk (e.g., a compact disk, a digital versatile disk, a Blu-ray (registered trademark) disk), a smart card, a flash memory (e.g., a card, a stick, a key drive), a flexible disk, a magnetic strip, etc. Storage 33 may also be referred to as an auxiliary storage device. The above-mentioned recording medium may be, for example, a database, a server, or other suitable medium that includes one or both of memory 32 and storage 33.

The input/output (I/O) device 34 is an example of an input device that accepts input of a signal from outside the node 3, and an output device that outputs a signal from the node 3 to the outside. The input device may include, for example, one or more of a keyboard, a mouse, a microphone, a switch, a button, and a sensor. The output device may include, for example, one or more of a display, a speaker, and a light-emitting device such as an LED (Light Emitting Diode).

The buttons may include, for example, a power button and/or a reset button. The power button is operated, for example, to start up and shut down the node 3. The reset (or reroute) button is operated, for example, to indicate an intentional reset and/or restructuring (or reroute) of the tree path.

The input/output (I/O) device 34 may be configured with separate input and output. Also, the input/output (I/O) device 34 may be configured with an integrated input and output, such as a touch panel display.

The wireless IF 35, for example, transmits and receives wireless signals over an access line between the terminal device 7. The wireless IF 35 may include, for example, one or more antennas 350, a baseband (BB) signal processing circuit, a MAC processing circuit, an up-converter, a down-converter, and an amplifier (not shown).

The BB signal processing circuit of the wireless IF 35 may, for example, include an encoding circuit and a modulation circuit for encoding and modulating the transmission signal, and a demodulation circuit and a decoding circuit for demodulating and decoding the received signal.

The antenna 350 may be, for example, an m-multiplexed MIMO antenna that multiplexes m signals. For example, m may be 8, or m may be a positive integer other than 8.

The wireless IF 36, for example, transmits and receives wireless signals over the BH line with other SNs 3. An example of the internal configuration of the wireless IF 36 will be described later.

Wireless IF 35 and wireless IF 36 may be referred to as wireless communication unit 35 and wireless communication unit 36, respectively.

The wired IF 37, for example, transmits and receives signals via a wired connection between the backbone network 5 and/or the upstream node 3. The wired IF 39, for example, transmits and receives signals via a wired connection between the terminal device 7 and/or the downstream node 3. For the wired IFs 37 and 39, for example, a network interface conforming to the Ethernet (registered trademark) standard may be used. Note that the wired IFs 37 and 39 only need to be provided in at least the CN 3, and do not have to be provided in the SN 3 (in other words, they may be optional for the SN 3). However, if part of the BH line is connected via a wired connection, the wired IFs 37 and 39 may be used for the wired connection.

Node 3 may be configured to include hardware such as a microprocessor, DSP, ASIC, PLD, FPGA, etc. For example, processor 31 may be implemented to include at least one of these pieces of hardware. The hardware may realize some or all of the functional blocks described later in FIG. 5.

Note that "DSP" is an abbreviation for "Digital Signal Processor," and "ASIC" is an abbreviation for "Application Specific Integrated Circuit." "PLD" is an abbreviation for "Programmable Logic Device," and "FPGA" is an abbreviation for "Field Programmable Gate Array."

The following describes the wireless IF 36 (wireless communication unit 36).

For example, input data from the input/output (I/O) device 34 is divided into n series of transmission data #1 to transmission data #n (n is an integer equal to or greater than 1) and input to the wireless IF 36. Here, n represents the maximum number of directional directions in which the node 3 can transmit simultaneously. For example, when n is 1, the node 3 transmits data in one direction (e.g., to one destination node). When n is 2 or greater, the node 3 transmits data in multiple directions (e.g., to multiple destination nodes) simultaneously.

The transmission digital BF control unit 361 performs, for example, encoding and modulation processing on each of the n series of transmission data to generate n series of data signals. The transmission digital BF control unit 361 performs, for example, weighting of the signals (multiplication by a transmission weight) to form a beam in the direction of the transmission directivity of each of the n series.

A digital to analog converter (DAC) 362 and an RF transmitter 363 are provided corresponding to each of the n data signal series, for example.

For example, each of the n series of weighted data signals is input to the DAC 362. For example, the DAC 362 converts the input data signals from digital signals to analog signals and outputs them to the RF transmission unit 363.

The RF transmitter 363 converts, for example, the baseband analog signal input from the DAC 362 into an analog signal in the carrier frequency band.

The output of the RF transmission unit 363 is converted, for example, in the transmission analog BF control unit 364 into an analog signal that is supplied to each antenna element of the antenna (subarray) 360, which is composed of antenna elements that transmit radio waves. The transmission analog BF control unit 364 may include, for example, a power distributor, a phase shifter, and an amplifier. The transmission analog BF control unit 364 may output a number of analog signals according to the configuration of the antenna 360, which will be described later. For example, if the antenna 360 has n subarrays, each of which has 256 antenna elements, the transmission analog BF control unit 364 may output n x 256 analog signals.

The duplexer 365, for example, separates a transmission signal from a reception signal. For example, the analog signal output from the analog BF control unit 364 is supplied to the antenna 360 through the duplexer 365.

The antenna 360 has, for example, n subarrays. Each subarray has, for example, 256 antenna elements. For example, n may be 4 or a positive integer other than 4. The number of antenna elements in each subarray may be 256 or a number other than 256. The number of antenna elements may differ for each subarray. The more antenna elements there are per subarray, the narrower and sharper the directivity of the subarray becomes.

For example, if n is 4, the signals supplied through the duplexer 365 are sent from four subarrays, each with its own directivity in four directions.

A signal received by antenna 360 having n subarrays is input to reception analog BF control unit 366, for example, through duplexer 365. A number of analog signals according to the configuration of antenna 360 may be input to reception analog BF control unit 366. For example, if antenna 360 has n subarrays, each of which has 256 antenna elements, n x 256 analog signals may be input to reception analog BF control unit 366.

The reception analog BF control unit 366 has, for example, a low noise amplifier (LNA) and a phase shifter. The reception analog BF control unit 366 performs control (adjustment) to align the phase of the reception signal according to the reception directivity to be formed. The reception analog BF control unit 366 divides the processed reception signal into a series of n signals according to the received subarray, and outputs them to the RF reception unit 367.

The RF receiver 367 and analog to digital converter (ADC) 368 are provided, for example, corresponding to each of the n signal series.

The RF receiver 367 converts, for example, an analog signal in the carrier frequency band input from the receive analog BF control unit 366 into a baseband analog signal.

The ADC 368 converts, for example, a baseband analog signal input from the RF receiver 367 into a digital signal.

The reception digital BF control unit 369, for example, weights the signals (multiplies the reception weights) associated with the reception directivity directions of each of the n digital signal series, and separates the n digital signal series. The reception digital BF control unit 369, for example, performs demodulation and decoding processes on each of the n series of signals, generates n series of reception data, and outputs the n series of reception data to the input/output (I/O) device 34.

In the BF control (determination of BF directivity) described later in FIG. 6, a process called sector sweep is performed to determine the transmission directivity direction (transmission directivity direction of the transmitting wireless node) and reception directivity direction (reception directivity direction of the receiving wireless node) in order to determine the optimal combination of transmission and reception directivities. In this process, for example, a unique data pattern for power measurement is used for the transmission data.

The configuration of the wireless node 3 including the processor 31, memory 32, storage 33, etc. may be referred to as the control unit 40. The control unit 40 controls, for example, the data transmission/reception operation including layer 2.5 processing of the wireless communication unit 36, the data transmission/reception operation of the wireless communication unit 35, and the data transmission/reception operation via the wired IFs 37 and 38. The configuration of the control unit 40 will be described later.

Next, an example of data transfer using BF by the wireless node 3 in the wireless communication system 1 shown in FIG. 1 will be described with reference to FIG. 4 and FIG. 5.

Figure 4 is an image diagram of upstream data transfer between hop links using BF transmission according to one embodiment. Figure 4 shows the backbone network 5, CN#0, and SN#1 to SN#5 in the wireless communication system 1 shown in Figure 1. Figure 4 also shows an example of the transmission directivity of SN#1 to SN#5 when a signal is transmitted in the upstream direction (from the leaf node to CN#0).

In this disclosure, an example is the application of wireless BH technology, which is a method of separating "route control" for constructing a relay route from "frame forwarding" of data, to a wireless standard that uses BF in a high frequency band. In FIG. 4, as a result of route control, each wireless node knows the wireless node that is the transmission destination of data. Also, in this embodiment, as a result of route control, each wireless node knows the wireless node that is the transmission destination of data in the alternative relay route. More specifically, the storage 33 mounted on each node may store information indicating to which node data should be transmitted in the upstream data transmission (for example, information on the transmission destination (which may also be referred to as the destination, forwarding destination, or transmission destination)) and parameter information that can be transmitted by BF to that node. For example, the parameter information includes information for realizing a drive current to be supplied to each antenna element that constitutes the antenna array. When each node receives data to be transmitted in the upstream direction, it realizes BF transmission by calling up the information stored in the storage 33.

Each transmitting node that has data to transmit checks whether or not there is an available channel prior to transmission in order to acquire a wireless channel (wireless resource) for transmission. For example, the check for an available channel is performed by means of Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) or the like. The transmitting node that has acquired an available channel transmits data using BF over a wireless link that has been established in advance at layer 2.5 with the receiving node. For convenience, "layer 2.5" or "a layer belonging to layer 2.5" may be referred to as a "mesh layer." In this embodiment, the MAC layer process, which is the process of acquiring a wireless channel, may follow CSMA/CA or the like as is.

In FIG. 4, BF transmission is performed in the wireless link from SN#4 to SN#3, the wireless link from SN#3 to SN#1, the wireless link from SN#2 to CN#0, the wireless link from SN#1 to CN, and the wireless link from SN#5 to SN#1. The wireless link to which BF is applied may be called a wireless beam link. In the wireless beam link, the wireless node on the transmitting side forms a transmission beam, and the wireless node on the receiving side forms a reception beam to perform data communication (transmission and reception of data). In the wireless beam link, at least one of the wireless nodes on the transmitting side and the receiving side may form a beam to perform data communication. These BF transmissions may be performed at different times. Alternatively, some or all of these BF transmissions may be performed at the same time. Alternatively, some or all of these BF transmissions may be performed at times that overlap on the time axis. In other words, FIG. 4 is merely an image diagram of data transfer. For example, the transmission beams (transmission directivity) shown in FIG. 4 do not have to be formed simultaneously. For example, a situation may be assumed in which, at the same time that upstream data transfer is occurring between SN#5 and SN#1, downstream data transfer is occurring between SN#3 and SN#4.

When BF transmission is applied, the transmission distance of the wireless link can be extended compared to when BF transmission is not applied. For example, BF transmission from SN#2 to CN#0 in FIG. 3 can be achieved by extending the transmission distance.

By applying BF transmission, radio waves transmitted from the source wireless node (source node) have a sharp directivity in the direction (destination direction) of the destination wireless node (destination node). In addition, the energy of radio waves sent in a direction different from the desired direction is suppressed. In addition, by applying BF reception, the energy of received radio waves arriving from a direction different from the desired direction is suppressed at the receiving destination node. Received radio waves arriving from a direction different from the desired direction may be regarded as interference waves at the destination node.

Therefore, in data transfer using BF transmission, the probability that the same frequency can be used for data transmission in the same time (the same time or the time span including the same timing) in the vicinity is higher than when BF transmission is not applied. For example, in FIG. 4, data transmission from SN#2 to CN#0 and data transmission from SN#1 to CN#0 can be performed at the same frequency and at the same time. In this case, CN#0 can receive data transmitted from SN#2 and data transmitted from SN#1 at the same frequency and at the same time. Also, data transmission from SN#3 to SN#1 and data transmission from SN#5 to SN#1 can be performed at the same frequency and at the same time. In this case, SN#1 can receive data from SN#3 to SN#1 and data from SN#5 to SN#1 at the same frequency and at the same time.

In this case, the wireless nodes (e.g., CN#0 and SN#1) may receive data of multiple different series (at least two series in the example of FIG. 4) at the same time. For example, the example hardware configuration of the wireless node described in FIG. 3 can receive data of multiple different series (n series).

The ability to use the same frequency in the same neighborhood at the same time leads to a significant increase in the frequency utilization efficiency of wireless base station circuits, thereby increasing the system capacity of wireless communication systems.

When determining an available channel using CSMA/CA, a wireless node may apply Request to Send/Clear to Send (RTS/CTS) to determine one transmitting node that will acquire the right to transmit. In this case, even if the wireless node is configured not to receive multiple different series of data at the same time, the probability of multiple data transfers colliding at the receiving node can be minimized. For example, in this embodiment, each node transfers data using BF, so that each node not involved in the transfer does not receive unnecessary radio waves, or even if it does, the radio waves are very weak. Therefore, interference is reduced for each node not included in the relay route while no data transfer is being performed through that node, and it becomes possible to perform other data transfers or training, which will be described later, at the same time.

In this embodiment, if degradation of the line quality of a hop link is detected during relay forwarding and/or in the process of monitoring the line quality of the hop link, each wireless node switches the frame forwarding path to an alternative relay path. The process of monitoring the line quality of the hop link may be referred to as a self-healing process. Information regarding the alternative relay path is updated at a predetermined interval and stored by each wireless node.

The switching of an alternative relay path for upstream data transfer will be explained using an example in which degradation of line quality is detected in the hop link (uplink) from SN#3 to SN#1 in Figure 4.

Note that below, a hop link from node #j to node #k may be written as L(j, k). j and k are identifiers that identify the nodes, and are, for example, integers equal to or greater than 0. For example, in FIG. 4, a hop link from SN#3 to SN#1 is written as L(3, 1).

A relay route may also be represented using L(j, k). For example, if a relay route includes a hop link from node #j to node #k, the relay route may be represented as including L(j, k).

In FIG. 4, when SN#3 detects a deterioration in the line quality of L(3,1), SN#3 switches the route used for frame forwarding before the detection to an alternative relay route corresponding to L(3,1). Here, the alternative relay route corresponding to L(3,1) is, for example, the optimal route determined under the condition that L(3,1) is excluded.

For example, in FIG. 4, if the alternative relay route corresponding to L(3,1) includes L(3,5), SN#3 switches the data forwarding destination from SN#1, which is the forwarding destination on the route used for frame forwarding before detection, to SN#5, which is the forwarding destination on the alternative relay route corresponding to L(3,1).

For example, a wireless node may determine the degradation of line quality based on an ACK/NACK response from a destination wireless node in response to a data transfer to the destination node. For example, a wireless node may determine that the line quality of a hop link with a destination node has deteriorated if an ACK is not returned. Also, for example, a wireless node may determine that the line quality of a hop link with a destination node has deteriorated if an ACK is not returned consecutively a predetermined number of times (e.g., three times) or more. Note that a case where an ACK is not returned may include a case where a NACK is returned.

When a wireless node determines that the line quality of a hop link has deteriorated if an ACK is not returned a predetermined number of times (e.g., three times) or more in succession, it can determine whether the deterioration in line quality of the hop link has continued for a predetermined period of time or more. This makes it possible to avoid switching to an alternative relay route even if the deterioration in line quality of the hop link is momentary (e.g., less than a predetermined period of time).

Figure 5 is an image diagram of downstream data transfer between hop links using BF transmission according to one embodiment. Like Figure 4, Figure 5 shows the backbone network 5, CN#0, and SN#1 to SN#5 in the wireless communication system 1 shown in Figure 1. Figure 5 also shows an example of the transmission directivity of CN#0 and SN#1 to SN#5 when a signal is transmitted downstream (from CN#0 to the leaf node).

In FIG. 5, as in FIG. 4, as a result of route control, each wireless node knows the wireless node that is the data transmission destination. In addition, in this embodiment, as a result of route control, each wireless node knows the wireless node that is the data transmission destination on the alternative relay route. The difference from the upstream data transfer in FIG. 4 is that, unlike the upstream data transfer in which data is transferred toward CN#0, the downstream data transfer has a different leaf node as the transfer destination. Note that, although the same route is illustrated in FIG. 4 and FIG. 5, the present disclosure is not limited to this. The route for downstream data transfer and the route for upstream data transfer may be different from each other. For example, in a radio wave situation that changes from moment to moment, the data transfer route may also change from moment to moment.

Each transmitting node that has data to transmit checks whether or not there is an available channel prior to transmission in order to acquire a wireless channel (wireless resource) for transmission. For example, the check for an available channel is performed by a means such as CSMA/CA. The transmitting node that has acquired an available channel transmits data using BF over a wireless link that has been established in advance with the receiving node at layer 2.5 (e.g., mesh layer). In this embodiment, the MAC layer process, which is the process of acquiring a wireless channel, may follow a method such as CSMA/CA.

Figure 5 shows that BF transmissions are performed in the wireless link from CN#0 to SN#2, the wireless link from CN#0 to SN#1, the wireless link from SN#1 to SN#3, the wireless link from SN#1 to SN#5, and the wireless link from SN#3 to SN#4. These BF transmissions may be performed at different times. Alternatively, some or all of these BF transmissions may be performed at the same time. Alternatively, some or all of these BF transmissions may be performed at times that overlap on the time axis.

When BF transmission is applied, the transmission distance of the wireless link can be extended compared to when BF transmission is not applied. For example, BF transmission from CN#0 to SN#2 in FIG. 5 can be achieved by extending the transmission distance.

As in Figure 4, by applying BF transmission, radio waves transmitted from the source node have a sharp directivity in the direction of the destination node (the desired direction). In addition, the energy of radio waves sent in a direction different from the desired direction is suppressed. Furthermore, at the receiving destination node, by applying BF reception, the energy of received radio waves arriving from a direction different from the desired direction is suppressed. Received radio waves arriving from a direction different from the desired direction can be considered as interference waves at the destination node.

For this reason, in data transfers that use BF transmission, the probability that the same frequency can be used for nearby data transmission at the same time is higher than when BF transmission is not applied. For example, in FIG. 5, CN#0 can transmit data to SN#2 and SN#1 at the same time and frequency. Also, SN#1 can transmit data to SN#3 and SN#5 at the same time and frequency.

In this case, the wireless nodes (e.g., CN#0 and SN#1) may transmit data in multiple different series (at least two series in the example of FIG. 5) at the same time. For example, the example hardware configuration of the wireless node described in FIG. 3 can transmit data in multiple different series (n series).

As with the upstream data transfer in Figure 4, the downstream data transfer in Figure 5 allows the same frequency to be used in the same vicinity at the same time, which leads to a significant increase in the frequency utilization efficiency of the wireless backhaul line. This allows the system capacity of the wireless communication system to be increased.

In this embodiment, as described above, when degradation of the line quality of a hop link is detected during relay forwarding and/or self-healing processing, each wireless node switches the frame forwarding route to an alternative relay route. Information regarding the alternative relay route is updated at a predetermined interval and stored by each wireless node.

The switching of the alternative downstream data transfer relay path will be explained using an example in which degradation of the line quality of the hop link (downlink) (L(1,3)) from SN#1 to SN#3 in Figure 5 is detected.

In FIG. 5, when SN#1 detects a deterioration in the line quality of L(1,3), SN#1 switches the route used for frame forwarding before the detection to an alternative relay route corresponding to L(1,3). Here, the alternative relay route corresponding to L(1,3) is, for example, the optimal route determined under the condition that L(1,3) is excluded.

For example, in FIG. 5, if the alternative relay route corresponding to L(1,3) includes L(1,5) and L(5,3), SN#1 switches the data forwarding destination from SN#3, which is the forwarding destination on the route used for frame forwarding before detection, to SN#5, which is the forwarding destination on the alternative relay route corresponding to L(1,3). In other words, SN#1 sets SN#3 and SN#5 as forwarding destinations on the route used for frame forwarding before detection, but SN#3 is excluded from the forwarding destination on the alternative relay route corresponding to L(1,3).

In addition, SN#5, which corresponds to a leaf node in the route used for frame forwarding before detection, switches to a relay node in which SN#3 is set as the data forwarding destination in the alternative relay route corresponding to L(1,3).

For example, a wireless node may determine the degradation of line quality based on an ACK/NACK response from a destination wireless node (destination node) in response to a data transfer to the destination wireless node. For example, a wireless node may determine that the line quality of a hop link with a destination node has deteriorated if an ACK is not returned. Also, for example, a wireless node may determine that the line quality of a hop link with a destination node has deteriorated if an ACK is not returned consecutively a predetermined number of times (e.g., three times) or more. Note that a case where an ACK is not returned may include a case where a NACK is returned.

When a wireless node determines that the line quality of a hop link has deteriorated if an ACK is not returned a predetermined number of times (e.g., three times) or more in succession, it can determine whether the deterioration in line quality of the hop link has continued for a predetermined period of time or more. This makes it possible to avoid switching to an alternative relay route even if the deterioration in line quality of the hop link is momentary (e.g., less than a predetermined period of time).

<Example of BF control>
Next, an example of the above-mentioned BF control will be described. Fig. 6 is a diagram showing an example of the BF control according to an embodiment. In the BF control, a wireless node determines the directivity of the BF. The BF control shown in Fig. 6 is an example of control for executing training related to the BF. Note that the BF control shown in Fig. 6 may be executed by, for example, control of the control unit 40 of the wireless node 3.

For example, in BF control, a wireless node determines a transmission beam suitable for transmitting a signal to a wireless node with which it is communicating from among multiple beams having directivities in different directions. Also, in BF control, a wireless node determines a reception beam suitable for receiving a signal transmitted from a wireless node with which it is communicating from among multiple reception beams having directivities in different directions.

For example, FIG. 6 shows signals transmitted and received between a transmission initiation node (which may be called an Initiator) that initiates transmission and a destination node (which may be called a Responder) that is the destination of the signal transmitted by the transmission initiation node.

For example, in the example of FIG. 6, a transmission beam (transmission directivity) having directivity in 64 different directions and a reception beam (reception directivity) having directivity in 64 different directions are prepared. Then, the wireless node determines one transmission beam and one reception beam with the optimal direction from each of the 64 directions. In the example of FIG. 6, the determination process is executed in four steps, STEP 1 to STEP 4. Note that FIG. 6 describes an example in which the beam with the optimal direction (optimum beam) is the beam that can obtain the maximum received power on the receiving side among the beams with directivity in 64 different directions.

In STEP 1, the transmission start node switches the directivity in 64 pre-prepared directions in a time-division (e.g., sequential) and transmits a signal. This process may be called a sector sweep. The signal transmitted by the transmission start node may include, for example, a data pattern sequence for which the received power is to be measured. The destination node waits for reception of a signal with the maximum beam width, and receives the signal transmitted by the sector sweep of the transmission start node with the maximum beam width. Note that reception with the maximum beam width may be, for example, reception of a beam with no directivity or reception of a beam with omni-directivity. The destination node then measures the received power for the 64 directivities and stores the measurement results. The measurement results stored may be all of the received power for the 64 directivities, or a part of it, for example, information on the directivity with the highest received power (for example, one of the index numbers (e.g., #i) assigned to each beam).

In STEP 2, the transmitting side and receiving side of the signal in STEP 1 are swapped, and the same process as in STEP 1 is performed. For example, the destination node switches the directivity in 64 directions prepared in advance in a time-division manner and transmits a signal. The signal transmitted by the destination node may include, for example, a data pattern sequence for measuring the received power. Alternatively, the signal transmitted by the destination node may include the measurement result of the destination node in STEP 1 (for example, the index number #i of the beam having the directivity with the highest received power). The transmission start node waits for the reception of a signal with the maximum beam width, and receives the transmission signal by the sector sweep of the destination node with the maximum beam width. Then, the transmission start node measures the received power for the 64 directivities and stores the measurement result. The measurement result to be stored may be all of the received power for the 64 directivities, or information on the directivity with the highest received power (for example, one of the index numbers (for example, #r) assigned to each beam. The transmission start node also stores the measurement result of the destination node in STEP 1 included in the received signal.

In STEP 3, the start node forms a transmission beam based on the measurement results reported in STEP 2, and transmits a signal to the destination node. For example, the start node transmits a signal using beam #i with an index number corresponding to the transmission directivity that is the directivity with the highest received power in STEP 1. The signal transmitted by the start node may include the measurement results of the start node in STEP 2 (for example, index number #r of the beam with the directivity with the highest received power). The destination node receives the signal transmitted by the start node with the maximum beam width. The destination node stores the measurement results of the start node in STEP 2 that are included in the received signal.

In STEP 4, the destination node uses directivity #r to return a response (Acknowledgement (ACK)) to the initiating node to confirm that the BF control process (i.e., the process of determining directivity #i and directivity #r) has been completed successfully. The initiating node receives the ACK on beam #i and confirms the completion of the BF control process.

In the BF control process shown in FIG. 6, an optimal transmission beam is determined by executing a sector sweep (transmission sector sweep) in signal transmission. Then, a reception beam having a directivity corresponding to the optimal transmission beam is determined to be the optimal reception beam.

This embodiment is not limited to the BF control process shown in FIG. 6. For example, each node may determine a receiving beam separately from determining a transmitting beam. For example, an optimal receiving beam may be determined by executing a sector sweep (receiving sector sweep) in signal reception. For example, in a receiving sector sweep, the destination node switches directivity in a time-division manner to 64 directions prepared in advance, and receives a signal transmitted by the transmission start node using the maximum beam width. Then, the destination node may determine the beam having the directivity with the highest received power as the optimal receiving beam. Then, in a receiving sector sweep, the destination node and the transmission start node may switch the transmission and reception of signals, and the transmission start node may determine the beam having the directivity with the highest received power as the optimal receiving beam.

The BF control process illustrated in FIG. 6 may be executed between a node and a terminal when BF transmission is applied to an access line. In this case, the BF control process may be executed before data transmission/reception (or while data transmission/reception is not taking place) each time data transmission/reception occurs between the node and the terminal.

On the other hand, in this embodiment, BF transmission is applied in the BH line. In this case, link-up of the hop link including the BF control process may be performed at a predetermined time interval (predetermined frequency) independently of the data transfer. The BF control process corresponds to a process of determining (or confirming) the information of the beam directivity #i and directivity #r between each wireless node. The determined information of the beam directivity #i and directivity #r may be referred to as BF control information. Also, link-up refers to a state in which, when data transfer is to be performed, the information used for the data transfer (e.g., BF control information) is known in each wireless node and preparation for the data transfer is completed.

The BF control information can be updated by performing link-up of the hop link including the BF control process at a predetermined time interval (predetermined frequency).

In this way, the process of performing link-up of a hop link and updating information used for data transfer including BF control information may be referred to as mesh link establishment. In this embodiment, by including BF control processing in this mesh establishment, when data transfer between wireless nodes occurs, data transfer using BF transmission can be performed immediately. Mesh link establishment may also be considered as the establishment of a wireless beam link with a surrounding node.

Next, we will explain an example of the configuration of the control unit 40 of the wireless node 3.

Figure 7 is a block diagram showing an example of the functional configuration of the control unit 40 of the wireless node 3 according to one embodiment. The functions of the control unit 40 are configured from a scan processing unit 401, a node management unit 402, a frame forwarding processing unit 403, a route control unit 404, a mesh link establishment unit 405, and an IPT (Interminent Periodic Transmission) control unit 406.

The scan processing unit 401 scans surrounding nodes and performs processing to link up mesh links in the BH network. In this embodiment, in order to apply BF to data transmission and reception between wireless nodes, the scan processing unit 401 cooperates with the mesh link establishment unit 405 described below to perform scanning including BF control processing.

The node management unit 402 stores information about the surrounding nodes identified by the wireless node 3 as a result of processing by the scan processing unit 401.

The node management unit 402 also stores a routing table that stores the node number of the destination node when relay data is forwarded. For example, the node management unit 402 updates the routing table when there is a relay route update in the route control. The routing table includes an upstream direction routing table that stores the destination node on the route heading in the direction toward the core node (uplink route), and a downstream direction routing table that stores the destination node on the route heading in the opposite direction from the core node (downlink route).

The mesh link establishment unit 405 provides the scan processing unit 401 with a BF control processing function for executing link-up of a mesh link by applying the BF control described in FIG. 6 during the scanning process of the surrounding nodes executed by the scan processing unit 401. The mesh link establishment unit 405 and the scan processing unit 401 cooperate to execute link-up of a mesh link at a predetermined frequency (period).

The mesh link establishment unit 405 has a BF control processing unit 4051 and a BF parameter storage unit 4052.

The BF control processing unit 4051 provides the scan processing unit 401 with a BF control processing function for performing link-up of a mesh link by applying BF control.

The BF parameter storage unit 4052 stores parameters obtained by applying BF control to perform link-up of a mesh link. For convenience, the parameters may be referred to as "BF parameters" or "mesh link parameters." The mesh link parameters may include, for example, control information regarding a transmitting BF and control information regarding a receiving BF. The mesh link parameters may also include, for example, an index of an optimal transmitting beam and an index of an optimal receiving beam for each of the surrounding nodes.

By being able to update the mesh link parameters to the latest ones while the radio wave environment is constantly changing, accurate BF transmission can be performed when transferring frames between wireless nodes. In addition, the route control packets sent and received in the route control process performed by the route control unit 404 described below can also be sent and received by unicast, which applies BF transmission and reception between surrounding wireless nodes, instead of broadcast. This allows for more accurate route construction.

The route control unit 404 controls the construction and updating of routes on the mesh link by transmitting route control packets in the mesh link. The construction and updating of routes may be performed, for example, by selecting (or deselecting) information on wireless links to be registered in (or excluded from) the route from among multiple wireless links that form the mesh link, as described below.

The route control unit 404 determines dynamic routes in mesh links based on an index that indicates the quality of a route, called a route metric. Below, an example is described in which a smaller route metric value indicates better line quality of the route. For example, the route control unit 404 evaluates line quality between nodes by measuring the RSSI of route control packets sent by surrounding wireless nodes. The route control packets include the cumulative route metric up to the surrounding nodes.

The route control packet generator 4041 of the route control unit 404 generates a route control packet. A route control packet is an example of a control signal that is generated in CN3 and propagated from CN3 to each node 3 in the BH network.

The route metric calculation unit 4042 of the route control unit 404 determines the route metric of the hop link between the local node and the surrounding nodes obtained by the RSSI measurement. The route metric calculation unit 4042 calculates the cumulative route metric up to the local wireless node based on the cumulative route metric included in the route control packet and the route metric between the local node and the surrounding nodes.

The route update unit 4043 of the route control unit 404 compares the route metric calculated by the route metric calculation unit 4042 with the route metric stored in the route update unit 4043, and determines whether to update the route. If the calculated route metric is smaller than the stored route metric, the route update unit 4043 determines to update the route. If the calculated route metric is smaller than the stored route metric, this means that the route corresponding to the calculated route metric is configured with multi-hop wireless links with better line quality than the route corresponding to the stored route metric.

This route control procedure can follow, for example, the route control method described in Non-Patent Document 1. However, when the target is to transmit and receive using BF in a high frequency band on a BH line, the route control unit 404 may have, for example, the following two functions.

(1) When sending and receiving route control packets, BF transmission is applied using BF control information determined by the BF control described in Figure 6.

In route control, by sending and receiving route control packets between neighboring nodes using unicast with BF applied instead of broadcast, more accurate route construction can be achieved.

(2) In the process of route control, if the line quality of the wireless link between nodes deteriorates, a multi-hop route that does not include the deteriorated wireless link is determined as the relay transmission route.

In the high frequency band, radio waves have a strong tendency to travel in a straight line, and when there is an obstruction between the transmission point and the reception point, such as a building, a tree, a person, or a vehicle, the loss of radio wave propagation from the transmission point to the reception point is likely to increase. Therefore, in preparation for the case where the line quality of the wireless link between the transmission point and the reception point deteriorates and the wireless link is disconnected, for example, the route update unit 4043 included in the route control unit 404 updates the route. In this embodiment, the millimeter wave band has been mainly described as an example, but this band is not limited to this. For example, in the millimeter wave band or even higher frequency band, a short-term interruption of radio waves at a certain point of the wireless network may cause a situation in which communication of the wireless network is interrupted. According to this embodiment, the optimal tree route is updated periodically or non-periodically, so it is suitable for application in a communication environment of the millimeter wave band or a higher frequency band. For example, when a communication environment is realized, even if communication is normally good, the communication environment may deteriorate due to a vehicle stopped by a traffic light, or the communication environment may deteriorate while a passerby crosses a route to which BF is applied. In the case of such a temporary deterioration of the communication environment, in an environment using a lower frequency band such as the microwave band, the communication speed will be temporarily reduced, but in the millimeter wave band, communication may be interrupted. Therefore, it is preferable to apply this embodiment to a communication environment using the millimeter wave band or a higher frequency band.

The determination and update of the relay route and the alternative relay route are performed by the core node transmitting a route control packet at a predetermined period, as will be described in detail later in FIG. 8 and subsequent figures. The predetermined period may be set arbitrarily. However, as described above, in the millimeter wave band or a higher frequency band in which radio wave propagation loss is large, when BF transmission and reception is applied to compensate for radio wave propagation loss and ensure the required transmission distance, the deterioration of line quality due to the insertion of an obstacle between the transmitting node and the receiving node is extremely large, and may lead to communication interruption. From this perspective, it is desirable to eliminate the influence of this deterioration of line quality as quickly as possible. For example, it is desirable to quickly construct a new optimal relay route under conditions in which a wireless link with deteriorated line quality exists. Therefore, it is better to have a short route control period (for example, a transmission period of a route control packet in a core node). However, an increase in the number of transmissions and receptions of route control packets may increase the traffic load and cause deterioration of the performance of the wireless communication system. In order to suppress deterioration of the performance of the wireless communication system, it is better to have a long route control period. Therefore, the above-mentioned predetermined period is not limited to an example in which it is set to a uniform value (for example, a uniform optimal value). For example, the period of route control may be determined for each wireless communication system, taking into consideration the frequency of occurrence of factors that induce failures, such as the insertion of a shield, in the environment in which the wireless node is installed, and the degree of impact of deterioration of line quality on the QoS of the wireless communication system. According to this embodiment in which an alternative relay route assuming a wireless link with deteriorated line quality is determined in advance, even if unexpected deterioration of line quality occurs, relay forwarding can be continued by switching to the alternative relay route. Therefore, it is possible to avoid setting a short route control period, or to reduce the number of route control operations, and it is possible to deal with unexpected deterioration of line quality without performing route control processing at an excessively short period.

For example, when the line quality of a wireless link deteriorates, in order to avoid a decrease in the throughput of the BH network or a stop of the BH network and to suppress the delay time related to the update of the route of the BH network, the relay route may be switched to an alternative relay route that excludes the wireless link with deteriorated line quality. Also, when the line quality of a wireless link deteriorates, in order to avoid a decrease in the throughput of the BH network or a stop of the BH network and to suppress the delay time related to the update of the route of the BH network, the transmission period of the route control packet transmitted by the core node may be controlled. In other words, switching to an alternative relay route and control of the transmission period of the route control packet may be used in combination. For example, when the line quality of a wireless link deteriorates, switching to an alternative relay route may be performed and the transmission period of the route control packet may be set to be short.

For example, the transmission period of the route control packets may be controlled by a core node. Alternatively, the transmission period of the route control packets may be instructed from the backbone network.

For example, a core node may set a short transmission period for route control packets sent by the core node.

Alternatively, instead of uniformly shortening the transmission period of route control packets in wireless BH lines using high frequency bands, the transmission period of route control packets may be controlled based on certain conditions. For example, the core node may count the number of times per hour that the line quality of the wireless link significantly deteriorates (e.g., deteriorates to a predetermined quality or lower), and the more times this occurs, the shorter the transmission period of the route control packets may be controlled to be. In other words, the transmission period of the route control packets may be variably controlled in response to fluctuations in the line quality of the wireless link.

Alternatively, the core node may control the transmission period of the route control packets based on a request from an application provided in the wireless communication system. For example, when the Quality of Service (QoS) required by the application, which indicates the degree of requirement for suppressing temporary line disconnection time and/or delay time associated with line disconnection time, is high, the transmission period of the route control packets may be set to be shorter. For example, QoS is high for applications that perform real-time data transmission such as voice calls and video distribution.

Since route update processing is performed by sending and receiving route control packets over a wireless link, by variably controlling the transmission period of route control packets, the frequency of route update processing can be adaptively reduced, thereby preventing a decrease in throughput of the BH line.

In addition, in the route update process, the above-mentioned alternative relay route may be determined and updated. Each wireless node 3 has a function of determining and storing in advance an alternative relay route that does not use a wireless link with degraded line quality. The alternative relay route may be considered to be the optimal relay route under conditions that exclude wireless links with degraded line quality. This makes it possible to avoid setting the transmission period of route control packets to an excessively short period, and allows relay transmission of the BH line to continue smoothly.

The process of constructing (determining) the relay route and the alternative relay route may be performed independently of the data transfer process, such as during a time period when no data transfer is occurring. Since the process of constructing (determining) the relay route and the alternative relay route can be performed less frequently, the impact on the reduction in throughput of the BH line can be suppressed.

As will be described later in FIG. 9, by providing commonality between the processing methods for constructing a normal relay route and constructing an alternative relay route, this function can be easily added and removed from the software configuration of layer 2.5. Here, the normal relay route may correspond to a relay route determined in a state in which each of the linked-up mesh links is not excluded. In this embodiment, the "relay route" may refer to the normal relay route, as distinguished from the "alternative relay route."

In addition, in order to avoid switching to an alternative relay path when the deterioration of the line quality of the hop link is momentary, the wireless node may determine that the line quality of the hop link has deteriorated when frame forwarding has failed a predetermined number of times (e.g., three times) in succession, instead of determining that the line quality has deteriorated when frame forwarding has failed once. The failure of frame forwarding may correspond, for example, to the failure to return an ACK from the receiving node.

The IPT control unit 406 controls the timing of packet transmission by the wireless communication unit for the BH line, for example, according to a transmission period corresponding to the frequency reuse interval.

The frame forwarding processing unit 403 performs processing to prepare the forwarding data coming down from the upper layers (layer 3 or higher) to layer 2.5 by adding a layer 2.5 control information header to prepare a frame to be forwarded at the lower layers (layer 2 or lower).

(Example of CN operation)
Next, an example of the operation of the CN will be described. Fig. 8 is a flowchart showing an example of the operation of the core node (CN) according to one embodiment. The flowchart in Fig. 8 may be considered to be executed in the control unit 40 of the CN, for example.

The control unit 40 sets the transmission period for route control packets (S101).

The transmission period when the route control packets are periodically transmitted may be constant, or may be changed according to the number of times the flowchart in FIG. 8 is executed, since the route constructed in this embodiment is asymptotically stable. The predetermined time may be set to a "specific timing", or may be set by a user of the wireless communication system. The control unit 40 may also control the transmission period of the route control packets based on certain conditions. For example, the control unit 40 may count the frequency of line quality degradation (such as line disconnection) of the hop link, and variably control the transmission period of the route control packets according to the counted frequency. For example, the control unit 40 sets the transmission period of the route control packets to be shorter as the frequency of line quality degradation increases. For example, the frequency of line quality degradation of the hop link may be counted in the self-healing process described later.

The count may be performed by a self-healing process (corresponding to S105), which is a process in which the core node checks whether each slave node is operating normally. In addition, variable control may be applied to shorten the period of sending route control packets when the quality of service (QoS), which indicates the degree of requirement for minimizing temporary line disconnection time and the associated delay time, is high for an application provided in a wireless communication system.

The control unit 40 monitors, for example, whether a specific event has been detected (S102). A "specific event" may include, for example, the CN being started, the reset button being operated, and the arrival of a specific timing. An example of a "specific timing" is, for example, a transmission timing set for transmitting a route control packet on a regular or irregular basis.

If no specific event is detected (NO in S102), processing in S104 is executed.

When a specific event is detected (YES in S102), the control unit of the CN generates a route control packet and transmits the route control packet to a neighboring SN identified based on the neighboring node information, for example, via a wireless communication unit (S103). The route control packet may be broadcast or unicast using BF transmission.

For example, when the start of a CN is detected and when the timing to send a route construction packet is detected, a route construction packet is sent to the surrounding SN. When the operation of a reset button is detected and when the timing to send a reset packet is detected, a reset packet is sent to the surrounding SN.

Next, the control unit 40 determines whether it is time to execute a self-healing process (S104). A self-healing process is a process in which a core node checks whether a slave node is operating normally. For example, in a self-healing process, the core node sends a self-healing packet (which may be called a hello packet) to the slave node, and checks whether the slave node is operating normally based on the response from the slave node.

If it is not time to execute the self-healing process (NO in S104), the process of S107 is executed.

If it is time to execute the self-healing process (YES in S104), the control unit 40 executes self-healing (S105). Then, based on the result of self-healing, the control unit 40 detects the frequency (number of times) of degradation of the line quality of the hop link (S106).

Next, the control unit 40 determines whether the self-healing execution period has elapsed (timed out) (S107).

If the self-healing execution period has not elapsed (timed out) (NO in S107), the process of S104 is executed.

If the self-healing execution period has elapsed (timed out) (YES in S107), the control unit 40 determines whether a specific event was detected in S102 (S108). In other words, the control unit 40 determines whether a route control packet was sent.

If a specific event has not been detected in S102 (NO in S108), the process of S101 is executed. If a specific event has been detected in S102 (YES in S108), the control unit 40 determines whether the execution period of the route control process has elapsed (timed out) (S109).

If the execution period for the route control process has not elapsed (timeout) (NO in S109), the process of S101 is executed.

When the execution period of the route control process has elapsed (timed out) (YES in S109), the control unit 40 sets a relay route (S110). For example, the control unit 40 sets a normal relay route while it does not detect any degradation in the line quality of the adjacent current hop links on the upstream and downstream sides. Also, for example, when the control unit 40 detects degradation in the line quality of the adjacent current hop links on the upstream and downstream sides, it sets an alternative relay route that excludes the hop links with degraded line quality.

Then, the control unit 40 may start processing the data packet (data relay transfer) (S111). When the execution period of the route control process has elapsed (timeout), the data relay route between the core node and the slave node is updated to the latest state. Note that as a result of the route control process, the data relay route does not need to change before and after the route control process.

Next, the control unit 40 detects the deterioration of the line quality of the hop link (e.g., the frequency (number of times) of the deterioration) (S112). For example, the control unit 40 may detect the frequency of the deterioration of the line quality based on the response from the slave node in the self-healing process.

If no deterioration in the line quality of the hop link is detected (NO in S112), the flow ends. If deterioration in the line quality of the hop link is detected (YES in S112), the control unit 40 updates the frequency of deterioration in the hop link line quality (S113). Then, the flow ends.

As described above, the core node propagates a route control packet to each of the slave nodes that make up the BH network by transmitting the route control packet (e.g., unicasting via BF transmission) to each of the multiple wireless links that have been linked up with the surrounding nodes.

The process of determining a relay route may also be applied to determining an alternative relay route. An alternative relay route is a relay route that does not use a specific hop link. In this embodiment, an example in which there is one specific hop link is described as an example, but the present disclosure is not limited to this. The specific hop link may be a combination of two or more hop links. Even if the specific hop link is a combination of two or more hop links, an alternative relay route can be determined by the same process as in the example in which there is one specific hop link.

By determining and/or updating the alternative relay route in advance, when degradation of the line quality of the hop link is detected during the relay forwarding process and/or the self-healing process, each wireless node switches the frame forwarding destination based on the alternative relay route. This switching allows relay transmission of the BH line to continue smoothly.

As with normal relay routes, alternative relay routes may be determined by transmitting and receiving route control packets that contain route metric information that reflects a propagation quality index (called a link metric) measured by, for example, RSSI measurement for each hop link. The route control packets are propagated from the core node side to the downstream wireless node side.

In the case of an alternative relay route, unlike a normal relay route, the link metric for the excluded hop link is set (replaced) to a specified value that corresponds to extremely low line quality. For example, if the lower the line quality, the larger the link metric value, the specified value may be an extremely large value, for example, mathematically infinity (∞) or the upper limit of the possible values for the link metric. By setting (replacing) the link metric in this way, the alternative relay route propagates route control packets in the same way as a normal relay route, and is determined to be a relay route that does not include the hop link to be excluded.

In other words, the process of determining an alternative relay route can be performed in the same way as the process of determining a normal relay route, except for the link metric setting (link metric replacement) described above.

Whether to determine an alternative relay route or a normal relay route may be determined by, for example, the core node based on an event that occurred in S102 described above. Information (flag) indicating whether to determine an alternative relay route or a normal relay route may be included in the route control packet transmitted by the core node in S103 described above. For example, since the determination of an alternative relay route corresponds to determining an alternative relay route assuming that a certain wireless link has been disconnected, in the following, as an example, information indicating that the determination of an alternative relay route will be performed may be described as "disconnection assumed." In other words, the information (flag) indicating whether to determine an alternative relay route or a normal relay route indicates either "disconnection assumed" or "normal."

In addition, when the route control packet includes information indicating that an alternative relay route is to be determined, the route control packet may include information indicating hop links to be excluded in the alternative relay route. The hop links to be excluded in the alternative relay route may be referred to as "hop links to be disconnected." The configuration of the route control packet will be described later.

Non-limiting examples of the propagation quality index (link metric) include the received power or strength of the wireless signal (e.g., RSSI; Received Signal Strength Indicator), radio wave propagation loss, and propagation delay. In addition, for example, when the transmission technology specifications applied to each hop link are different, instead of using the RSSI to calculate the link metric (an index reflecting the line quality of the hop link), the link throughput associated with the RSSI and the transmission technology specification may be used to calculate the link metric. Examples of transmission technology specifications that determine the link throughput include wireless standards (802.11n, 802.11ac, 802.11ax, 5GNR (5th generation mobile communication specification; 5G New Radio)), the number of MIMO streams, adaptive modulation method, etc. For example, even if the RSSI is the same between two hop links, if the wireless standards are different between the two hop links, the link throughput will be different between the two hop links. In such a case, the reliability of the line quality of the route to be constructed can be improved by using the link throughput to calculate the link metric. Note that an example in which the link throughput is used to calculate the link metric may correspond to an example in which the lower the line quality, the smaller the link metric value.

When link throughput is used as the link metric in the process of determining an alternative relay route, the link metric for the hop link to be excluded may be set (replaced) with a value equivalent to 0 bps. By setting (replacing) the link metric in this way, the hop link to be excluded can be reliably excluded from the alternative relay route.

It is also possible that wired transmission such as wired LAN cables or Power Line Communication (PLC) is applied to the transmission technology of some hop links in addition to or instead of wireless transmission. In this way, when the transmission technology specifications applied to each hop link are different, a more accurate indicator of line quality can be calculated by using link throughput to calculate the link metric or the route metric, which is a comprehensive indicator of the link metrics for multiple hop links included in the relay route. By using more accurate line quality, it may be possible to build a route with better line quality than, for example, when link throughput is not used.

For example, by transmitting a signal (e.g., a control signal) originating from the CN, the radio wave propagation loss of each wireless section between the transmitting node and the receiving node of the control signal can be calculated at the receiving node.

Then, each receiving node transmits the calculated radio wave propagation loss information together with the control signal, so that information on the cumulative radio wave propagation loss (in other words, the cumulative value) for the wireless section through which the control signal propagates can be transmitted between nodes.

Each node calculates a route metric based on the cumulative radio wave propagation loss for each upstream node candidate that is the source of the control signal, and selects one node from the upstream node candidates that has the smallest route metric, for example. This allows a tree-structured route with the smallest radio wave propagation loss to be constructed. Each node may write either the selected destination node information or parameter information for BF transmission in the tree-structured relay route, or both, to at least one of the memory 32 and the storage 33. Here, for example, if the destination node information or parameter information is stored in a server, a time lag occurs when each node reads information from the server to use the tree-structured relay route. In order to instantly configure the tree-structured relay route without a time lag, it is desirable that the destination node information and/or parameter information be stored using a storage medium possessed by each node. The information stored by each node does not need to be limited to the destination node information and/or parameter information.

(SN operation example)
Fig. 9 is a flowchart showing an example of the operation of a slave node (SN) according to an embodiment. An example of the operation of the SN will be described with reference to Fig. 9. The flowchart in Fig. 9 may be considered to be executed in the control unit 40 of the SN.

The SN determines whether or not a self-healing hello packet is received, for example, in the wireless communication unit 36 of the BH line (S201).

If a self-healing hello packet is not received (NO in S201), processing in S203 is executed.

If a self-healing hello packet is received (YES in S201), the control unit 40 of the SN reports the results of self-healing to the CN (S202).

Next, the control unit 40 determines whether or not a route control packet is received, for example, in the wireless communication unit 36 of the BH line (S203).

If a route control packet has not been received (NO in S203), the process of S201 is executed. If a route control packet has been received (YES in S203), the control unit 40 of the SN checks the type of the route control packet. For example, the control unit 40 checks whether the received route control packet is a reset packet (S204).

If the received route control packet is a reset packet (YES in S204), the control unit 40 performs an initialization process (S205). The initialization process may include, for example, the following processes.
Deselecting links that are selected as valid tree routes in the neighboring node information Initializing the stored route metric to an initial value (e.g., the maximum value)

After the initialization process, the control unit 40, for example, transmits the received reset packet to the neighboring SNs (S206). Then, the process of S201 is executed. The reset packet may include an identifier (ID). Each node may store the ID included in the received reset packet. The reset packet may be transmitted by unicast or multicast.

If the ID of the received reset packet matches a stored ID, in other words, if it indicates that the reset packet was previously sent (forwarded), each node will not further transmit the reset packet. This makes it possible to prevent the reset packet from looping in the BH network.

On the other hand, if the received route control packet is not a reset packet (NO in S204), the control unit 40 checks whether the route control packet is a route construction packet (S207).

If the received route control packet is not a route construction packet (NO in S207), the process of S201 is executed. If the received route control packet is a route construction packet (YES in S207), the control unit 40 refers to the surrounding node information (S208).

Then, the control unit 40 checks whether the flag in the received route control packet indicates "disconnection expected" (S209).

If the flag in the received route control packet does not indicate "disconnection expected" (NO in S209), the control unit 40 executes the process of S212.

If the flag in the received route control packet indicates "disconnection assumed" (YES in S209), the control unit 40 refers to the information on the hop link assumed to be disconnected (e.g., L(j, k)) contained in the route control packet and determines whether the local node is node #k (S210).

In addition to determining whether the own node is node #k in S210, it may also be determined whether the source node of the received route control packet is node #j. In this case, "NO at S210" described below may correspond to the case where the own node is not node #k and/or the source node is not node #j. Also, "YES at S210" described below may correspond to the case where the own node is node #k and the source node is node #j.

If the own node is not node #k (NO at S210), the control unit 40 executes the process of S212.

If the own node is node #k (YES in S210), the control unit 40 replaces the propagation quality index (link metric) (S211). For example, the propagation quality index may be replaced with a value (e.g., infinity) that corresponds to L(j, k) being disconnected (or the line quality being extremely low). Then, the control unit 40 executes the process of S213.

The control unit 40 calculates the propagation quality index (e.g., radio wave propagation loss) of the link through which the route construction packet was received (S212).

In other words, if the flag of the received route control packet is "disconnection assumed" and the local wireless node 3 is the receiving side of the hop link that is assumed to be disconnected, the radio wave quality index is replaced with a propagation quality index that corresponds to the hop link being disconnected. The control unit 40 refers to the surrounding node information and performs a process of replacing the propagation quality index instead of calculating the propagation quality index (e.g., radio wave propagation loss) of the link that received the route construction packet.

Then, the control unit 40 calculates the route metric (S213). For example, the control unit 40 calculates the cumulative radio wave propagation loss as the new route metric by adding the calculated radio wave propagation loss or the replaced propagation quality index to the propagation quality index included in the received route construction packet.

Then, the control unit 40 compares the new route metric with the old route metric that was stored before the new route metric was calculated, and determines whether the route metric needs to be updated (S214).

For example, if the new route metric is smaller than the old route metric, the control unit 40 determines to update the old route metric to the new route metric (YES in S214). Note that if it is determined not to update (NO in S214), the control unit 40 may execute the process of S201.

Then, the control unit 40 checks whether the flag in the received route control packet indicates "disconnection expected" (S215).

If the flag in the received route control packet does not indicate "disconnection expected" (NO in S215), the control unit 40 selects the upstream wireless link that corresponds to the new route metric in the surrounding node information as a valid route (updates the selected link) (S217).

The selected link update process is performed when the flag in the route construction packet is "normal," but is not performed when the flag in the route construction packet is "disconnected."

If the flag of the received route control packet indicates "disconnection expected" (YES at S215), the control unit 40 determines the upstream wireless link corresponding to the alternative relay route in the surrounding node information as a valid route and stores it in the alternative relay route information (S216).

After updating the selected link or storing the alternative relay route information, the control unit 40 transmits, for example, a route construction packet including the new route metric to the neighboring SNs identified in the neighboring node information (S218). For example, the route construction packet may be transmitted by multicast or by unicast with BF transmission.

Then, the control unit 40 monitors whether a certain period of time has elapsed (timeout) (S219). If a timeout is not detected (NO in S219), the process of S201 is executed.

If a timeout is detected (YES in S219), the control unit 40 sets a relay route (S220). For example, the control unit 40 sets a normal relay route while it does not detect any degradation in the line quality of the adjacent current hop links on the upstream and downstream sides. Also, for example, if the control unit 40 detects degradation in the line quality of the adjacent current hop links on the upstream and downstream sides, it sets an alternative relay route that excludes the hop links with degraded line quality.

Then, the control unit 40 may start the transmission process (relay forwarding) of the data packet (S221). The transmission process of the data packet may be, for example, a data packet forwarding process to a destination node. The transmission process of the data packet is executed according to the relay route in the routing table that stores the node number of the forwarding destination (destination) when relay forwarding is performed. The routing table may include a downstream direction routing table and an upstream direction routing table. Each wireless node 3 stores the adjacent hop links of the alternative relay route in the routing table when the deterioration of the line quality of the current adjacent hop links on the upstream and downstream sides is detected. Then, in the relay forwarding process or the self-healing process, when it is detected that the line quality of the above-mentioned current adjacent hop link has deteriorated, each wireless node 3 switches the destination of the frame forwarding based on the alternative relay route that has been updated and determined in advance. This allows the relay transmission of the BH line to be continued without interruption. In route control, until a new relay route is determined and information about the new relay route is stored and updated in memory 32 or storage 33, each node may, as a temporary measure, read out the destination node information and parameter information for BF transmission between the destination node and the node from memory 32 or storage 33 and perform relay transmission.

Next, the control unit 40 detects the deterioration of the line quality of the hop link (e.g., the frequency (number of times) of the deterioration) (S222). For example, the control unit 40 may detect the frequency of the deterioration of the line quality based on the response from the slave node in the self-healing process.

If no deterioration in the line quality of the hop link is detected (NO in S222), the flow ends. If deterioration in the line quality of the hop link is detected (YES in S222), the control unit 40 updates the frequency of deterioration in the hop link line quality (S223). Then, the flow ends.

If the received route control packet is neither a reset packet nor a route construction packet, the control unit 40 may transition to a route control packet reception monitoring process.

In addition, if the calculated new route metric is greater than or equal to the old route metric and it is determined that updating the selected link is not necessary, the control unit 40 may transition to the process of monitoring the reception of route control packets.

As described above, in response to receiving a route construction packet, the SN selects one of the multiple wireless links that are linked up with the surrounding nodes based on the route metric. This allows a tree route based on the route metric to be constructed and updated in the BH network where the mesh links are linked up.

When the flag in the route construction packet indicates "disconnection expected," the SN selects one of the multiple wireless links linked up with the surrounding node based on the route metric. As a result, an alternative relay route based on the route metric is constructed and updated in the BH network where the mesh link is linked up. The alternative relay route constructed and updated here does not include a hop link expected to be disconnected (a hop link to be excluded).

In other words, by processing similar to that for constructing a normal relay route, the SN can determine one of the multiple linked-up wireless links based on the route metric under conditions that exclude the hop link that is assumed to be disconnected, in response to receiving a route construction packet in which the "normal/assumed disconnection" flag is set to "assumed disconnection." This allows for switching to an alternative relay route tree route without delay even if the line quality of some hop links in a BH network in which mesh links are linked up suddenly deteriorates (for example, an extremely large reduction or disconnection). This makes it possible to provide a wireless BH network technology that can continue to operate stably by quickly switching the relay route, even when the radio wave propagation loss from the transmission point to the reception point is extremely large in high-frequency bands with high directivity and the line quality of the wireless link deteriorates significantly.

Next, an example of the configuration of a route control packet (route construction packet) will be described with reference to FIG. 10. FIG. 10 is a diagram showing an example of a route construction packet according to one embodiment.

The route construction packet contains a flag indicating "normal or expected to be disconnected," information on the wireless link expected to be disconnected, the source node number, the destination node number, the route metric, and a data series for the propagation quality measurement target (for example, the RSSI measurement target).

When the flag indicating "normal or assumed disconnection" is "normal," this indicates that the route construction packet is for dynamically constructing and updating a normal relay route, as described in Figures 8 and 9.

When the flag indicating "normal or expected disconnection" is "expected disconnection," it indicates that the packet is a route construction packet for constructing and dynamically updating an alternative relay route, as described in Figures 8 and 9. For example, an alternative relay route is constructed and updated in preparation for a situation in which the line quality of part of the wireless link deteriorates in the future and the link should not be included in the relay route.

The information on the wireless link that is expected to be disconnected includes information on the hop link that is excluded in the alternative relay route. For example, if the hop link from wireless node #j to wireless node #k is excluded, the information on the wireless link that is expected to be disconnected includes information representing L(j, k).

The source node number is a number that identifies the node that sent the route control packet. For example, in a route control packet sent by wireless node #m to wireless node #n, the source node number may be set to #m.

The destination node number is a number that identifies the node to which the route control packet is addressed. For example, in a route control packet that wireless node #m sends to wireless node #n, the destination node number may be set to #n.

Next, examples of alternative relay routes will be described with reference to Figs. 11 and 12. Fig. 11 is a diagram showing an example of a routing table stored in a wireless node in one embodiment. Fig. 12 is a diagram showing an example of an alternative relay route shown in the routing table shown in Fig. 11.

The routing table in FIG. 11 is stored, for example, by SN#3 (node#3) of the BH network shown in FIG. 12. In the routing table in FIG. 11, an "exclusion hop link", an "upstream node of node#3", and a "downstream node of node#3" are associated. Note that the "exclusion hop link" may correspond, for example, to the "wireless link assumed to be disconnected" shown in FIG. 10.

Here, the absence of an "exclusion hop link" represents a normal relay route. The example in Figure 11 shows that when there is no "exclusion hop link", the "upstream node of node #3" is node #2, and the "downstream node of node #3" is nodes #4 and #5. For example, node #3 performs relay forwarding based on this routing table. Figure 12 (a) shows a normal relay route corresponding to the absence of an "exclusion hop link".

When the "exclusion hop link" is "L(1,2)," this represents an alternative relay route in a state where L(1,2) is excluded. In this case, in the example of FIG. 11, the "upstream node of node #3" is node #1, and the "downstream nodes of node #3" are nodes #2, #4, and #5. For example, FIG. 12(b) shows an alternative relay route in which the "exclusion hop link" corresponds to "L(1,2)."

When the "exclusion hop link" is "L(3,5)", this represents an alternative relay route in a state where L(3,5) is excluded. In this case, in the example of FIG. 11, the "upstream node of node #3" is node #2, and the "downstream node of node #3" is node #4. For example, FIG. 12(c) shows an alternative relay route in which the "exclusion hop link" corresponds to "L(3,5)".

As shown in FIG. 11, the wireless node 3 stores the upstream node and downstream node for each excluded hop link. In other words, the wireless node 3 stores information on multiple alternative relay routes each having a different excluded hop link.

The wireless node 3 may store information on each of the alternative relay routes in which each wireless link of the linked-up mesh link becomes an excluded hop link. Alternatively, the wireless node 3 may store information on the alternative relay route in which a hop link that is disconnected at a frequency equal to or higher than a predetermined frequency becomes an excluded hop link.

In the embodiment described above, one of the multiple wireless nodes constituting the backhaul network (e.g., a core node) transmits a control signal (e.g., a route construction packet) including information designating at least one of the wireless links established between the multiple nodes as an excluded hop link (which may also be referred to as a link to be disconnected). Then, one of the multiple wireless nodes (e.g., a slave node) determines a wireless link that constitutes an alternative route to the route of data communication using the excluded hop link from among the remaining wireless links excluding the excluded hop link. For example, the determination is made based on an index related to the propagation quality of one or more wireless links via which the control signal has passed.

This configuration allows alternative routes to be constructed in advance in case some wireless links become unavailable, enabling rescue control to be realized in the case some wireless links become unavailable in the wireless BH network.

In addition, the wireless communication system according to this embodiment can transfer data between nodes in the high frequency band with sharp beamforming directionality, thereby improving the spatial reuse efficiency of frequencies. Even if there is a large radio wave propagation loss from the transmitting point to the receiving point, causing the line quality of the wireless link to deteriorate significantly and causing the wireless link to be disconnected, stable operation can be continued by quickly switching the relay path.

In the present embodiment, an example has been described in which each wireless node performs beamforming to transfer data, but the present disclosure is not limited to this. For example, each wireless node may transfer data without using beamforming.

In the above description, it is assumed that when the number of hop links where degradation of line quality occurs is one, an optimal alternative relay route under conditions excluding that hop link is constructed, updated, and stored in advance. The present disclosure is not limited to this, and may be extended to constructing, updating, and storing in advance alternative relay routes when multiple (e.g., two hop links) line qualities deteriorate at the same time.

In the above description, it is assumed that the flooding of route control packets in this embodiment is performed by unicast using BF transmission and reception, as an example. The present disclosure is not limited to this. The flooding of route control packets may be performed by broadcast. By performing the flooding by broadcast, the time required for the process of constructing the relay route and the alternative relay route can be reduced.

In addition, the alternative relay route is determined to be the one with the smallest route metric in calculations, but this does not necessarily mean that the alternative relay route has high throughput. By constructing an alternative relay route in advance, the probability that some functions of the wireless BH system will be degraded can be reduced. On the other hand, if the route metric of the alternative relay route is equal to or greater than a specified value, there may be a function to send an alarm to the wireless communication system operator to assist in reviewing the number and placement locations of wireless nodes.

In addition, in the construction and update of an alternative relay route, an example has been shown in which all hop links (hop links not expected to be included in the alternative relay route) or combinations of hop links that are assumed to be disconnected are covered, but the present disclosure is not limited to this. For example, in the construction and update of an alternative relay route, it is also possible to limit to some hop links or combinations of hop links. In that case, it is also possible to store which hop links frequently experience degradation in line quality (including disconnection) and reflect this in the above-mentioned limiting method.

In addition, each hop link of a wireless backhaul system does not have to apply the same wireless communication standard or the same wireless parameters (e.g., transmission power and/or number of MIMO streams). In a wireless backhaul system in which the same wireless communication standard and the same wireless parameters are applied between hop links, the link metric indicator uses an RSSI measurement value, and an appropriate link metric may be given in constructing a relay path when the link metric indicator is an RSSI measurement value. For example, in a wireless backhaul system in which different wireless communication standards and/or wireless parameters are mixed in a hop link, a link metric determined by associating the measured RSSI with the transmission speed (throughput, bps) of the wireless communication standard and/or wireless parameters of the hop link may be given as an example of a link metric indicator.

In addition, some of the hop links in the wireless backhaul system may include wired links. In that case, in a node connected to a wired link that cannot perform wireless flooding reception processing of route control packets, the route control packets may be received via a wired line, and the link metric may be replaced with the transmission speed of the wired link to perform route construction processing.

Furthermore, by using (adapting) the alternative relay route construction method of this embodiment, a hop link that is not to be included in the normal relay route construction may be specified, and a relay route that does not include that hop link may be constructed. For example, when it is expected that people or vehicles will travel between a certain wireless node and another wireless node, it may be possible to prevent the inclusion of a hop link between these wireless nodes in advance. Also, for example, when a moving wireless node wants to avoid forming a hop link with another specific wireless node, the hop link may be set as a wireless link expected to be disconnected in the route construction packet, and used for constructing a normal relay route.

In other words, this disclosure is not limited to cases where operation is performed in high frequency bands, but can construct relay routes that exclude specific hop links that are set according to various requirements and circumstances, thereby enabling the construction of an appropriate wireless BH network.

In addition, when a hop link between a wireless node and another wireless node is included in a relay path or an alternative relay path, the link metric of the hop link may be replaced with a link metric of a sufficiently small value instead of a link metric calculated from a measured RSSI, etc.

For example, two wireless nodes in the same train car (e.g., one at the front and one at the rear of the train) move at the same speed, so it is possible to construct a relay route that includes a fixed hop link between them. In this way, when a hop link between two wireless nodes in the same train car is to be included in a relay route, the "assumed disconnection" in the route construction packet of FIG. 10 may be expanded to "assumed hop link formation" instead of "assumed disconnection." Then, while the link metric for the assumed hop link is replaced with a sufficiently large value in the "assumed disconnection" case, it may be replaced with a sufficiently small value in the "assumed hop link formation" case. By replacing values in this way, a relay route that includes a specific hop link is constructed.

In other words, this disclosure is not limited to cases where operation is performed in high frequency bands, but can construct relay routes that include specific hop links that are set according to various requirements and circumstances, and can construct an appropriate wireless BH network.

In addition, in this embodiment, the wireless node has a control unit that performs training on beamforming with each of the multiple surrounding nodes that make up the backhaul network, and a communication unit that performs data communication using a wireless beam link corresponding to the surrounding node selected as the data communication path from among the multiple wireless beam links established with each of the surrounding nodes through training. With this configuration, it is possible to build an appropriate BH network using high-frequency wireless to which beamforming (BF) technology is applied to compensate for radio wave propagation loss.

In addition, according to this embodiment, even if the radio wave propagation loss from the transmission point to the reception point becomes large, the frequency of route construction (or update) can be increased to suppress a decrease in throughput in the wireless communication system.

In addition, according to this embodiment, when linking up a mesh link, a beamforming control process is executed and a beam suitable for communication between wireless nodes is determined. For example, the beamforming control before data transfer can be omitted, and a decrease in the throughput of the beamforming line can be suppressed.

In addition, according to this embodiment, in route control, the quality of each hop link is determined based on unicast transmission and reception using BF transmission, making it possible to select a more appropriate route.

Furthermore, according to this embodiment, in data transfer, a wireless node may be configured to transmit multiple series of data and/or receive multiple series of data in parallel at the same time. This configuration can improve the throughput in the wireless communication system.

REFERENCE SIGNS LIST 1 Wireless communication system 3 Wireless node 5 Backbone network 7 Terminal device 31 Processor 32 Memory 33 Storage 34 Input/output (I/O) device 35, 36 Wireless interface (IF)
37, 39 Wired Interface (IF)
38 Bus 40 Control unit 350, 360 Antenna 401 Scan processing unit 402 Node management unit 403 Frame forwarding processing unit 404 Route control unit 405 Mesh link establishment unit 406 IPT control unit 4041 Route control packet generation unit 4042 Route metric calculation unit 4043 Route update unit 4051 BF control processing unit 4052 BF parameter storage unit

Claims (6)

A plurality of nodes are provided.
A first node of the plurality of nodes comprises:
a transmitter that transmits a control signal including information specifying at least one first link among a plurality of links established between the plurality of nodes;
Equipped with
A second node of the plurality of nodes:
A receiving unit for receiving the control signal;
a control unit that determines, from among the remaining links excluding the first link designated by the information of the received control signal, a second link that constitutes an alternative second route to the first route of data communication using the first link, based on an index related to a propagation quality of one or more links through which the control signal has passed;
a storage unit that stores information about the second link in association with the first link;
Equipped with
when it is detected that a deterioration amount of line quality of the first link is equal to or greater than a threshold, the control unit switches a route used for the data communication from the first route to the second route based on information related to the second link in the storage unit;
Communication systems. the control unit, when the second node corresponds to a receiving side of the first link, replaces an index related to a propagation quality of the first link with a value indicating that the propagation quality of the first link is most deteriorated among possible values of the index;
The communication system according to claim 1 . the plurality of links includes at least one wireless link;
the first link is selected from the at least one wireless link.
The communication system according to claim 1 . the plurality of links includes at least one wired link;
the first link is not selected from the at least one wired link;
The communication system according to claim 3. A first node of the plurality of nodes
transmitting a control signal including information specifying at least one first link of a plurality of links established between the plurality of nodes;
A second node of the plurality of nodes:
receiving the control signal;
determining, from among the remaining links excluding the first link designated by the information of the received control signal, a second link constituting an alternative second route to the first route of data communication using the first link, based on an index related to a propagation quality of one or more links via which the control signal has passed;
storing information about the second link in association with the first link;
when it is detected that the deterioration amount of the line quality of the first link is equal to or greater than a threshold, switching a route used for the data communication from the first route to the second route based on the stored information about the second link;
Communication methods. One of the plurality of nodes,
a receiving unit that receives a control signal including information specifying at least one first link among a plurality of links established between the plurality of nodes;
a control unit that determines, from among the remaining links excluding the first link designated by the information of the received control signal, a second link that constitutes an alternative second route to the first route of data communication using the first link, based on an index related to a propagation quality of one or more links through which the control signal has passed;
a storage unit that stores information about the second link in association with the first link;
Equipped with
when it is detected that a deterioration amount of line quality of the first link is equal to or greater than a threshold, the control unit switches a route used for the data communication from the first route to the second route based on information related to the second link in the storage unit;
node.

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