Mesh network system and mobile node

Abstract

To provide a mesh network system that can suppress reduction in throughput due to the hidden terminal problem.SOLUTION: A mesh network system according to an example includes a flying mobile node 301 connected to a wireless network, and a plurality of fixed nodes 311 to 314 that constitute the wireless network and are also connected to a wired network, and each of the plurality of fixed nodes 311 to 314 uses an antenna pattern with suppressed horizontal gain such that a carrier cannot be detected between the adjacent fixed nodes.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a mesh network system having an airborne mobile node connected to a wireless network and a plurality of fixed nodes that constitute the wireless network and are also connected to a wired network. [Background technology]

[0002] Recent advances in robotics technology have been remarkable, and robots are increasingly being used to solve various social issues. Many of these robots are unmanned mobile objects, such as unmanned aerial vehicles and autonomous vehicles. Unmanned mobile objects must be equipped with a communication system to transmit control command data for remote control and autonomous control, as well as video data captured by cameras mounted on the unmanned mobile object. In this case, if the unmanned mobile object is not a machine that moves along a predetermined path such as a rail, wireless communication suitable for movement is often used.

[0003] For example, Patent Document 1 discloses an invention in which a mobile base station and a terminal station are equipped with a long-distance communication function for preparing for short-distance communication and a short-distance communication function for data transmission, and the timing of short-distance communication is scheduled by communication using the long-distance communication function. Also, Patent Document 2 discloses an invention in a relay system using an unmanned aerial vehicle, in which the relay position of the unmanned aerial vehicle is searched for based on the communication quality of the relay, the scheduled relay time, and the power supply status of the unmanned aerial vehicle (available power supply amount). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 018021 [Patent Document 2] Japanese Patent Application Publication No. 2019-169848 Summary of the Invention [Problem to be solved by the invention]

[0005] One type of communication network that can be used to communicate with unmanned vehicles is a mesh network. A mesh network is made up of multiple nodes, and by connecting adjacent nodes that can communicate with each other, the entire network is formed into a mesh-like structure. In particular, when the connections between nodes are made wirelessly, it is called a wireless mesh network, and data is transferred wirelessly between multiple nodes in a bucket brigade style.

[0006] Mesh networks typically have multiple paths, and if one path becomes unavailable, they can switch to an alternative path, making them more resilient to failures than other network topologies. However, the existence of multiple paths also means that the network may have loop-like paths. When broadcasting IP packets in such a network, a spanning tree protocol is generally used to prevent the IP packet from repeating the broadcast even after it has circumnavigated the looped path, causing a broadcast storm.

[0007] The spanning tree protocol uses a spanning tree algorithm to automatically block communication between specific nodes, thereby preventing loops. In addition, when a failure occurs, the blocking state can be released, allowing communication to continue via an alternative route.

[0008] However, such mesh networks are less efficient than centralized control methods because all nodes decide routes on an equal footing, rather than through centralized control by specific high-priority nodes. This may make it impossible to adopt a highly fault-tolerant mesh network, particularly in cases where high throughput and low latency are required.

[0009] One use case that requires high throughput and low latency in addition to fault tolerance is a wireless communication system that transmits video related to the remote control of an unmanned aerial vehicle (UAV). Figure 1 shows a configuration example of a conventional example 1 of such a wireless communication system. For example, when the UAV is flying beyond visual line of sight, this system transfers video captured from the UAV of the surrounding environment to a server, allowing the pilot to check the video in real time.

[0010] In the wireless mesh network of Conventional Example 1 shown in Figure 1, a first fixed node 111, a second fixed node 112, a third fixed node 113, and an n-th fixed node 114 are placed on the ground along the flight path of a mobile node 101 including a UAV body. A server 121 is also connected to the first fixed node 111 by wire. In the following explanation, the number of hops is defined as the number of nodes that communicated minus one, such that wireless communication between two nodes, whether mobile or fixed nodes, is one hop, and wireless communication between three consecutive nodes is two hops.

[0011] When the mobile node 101 is flying above the first fixed node 111, one-hop communication takes place between the mobile node 101 and the first fixed node 111, and data is transferred to the server 121 via the shortest route. Next, when the mobile node 101 moves above the second fixed node 112 and is no longer able to communicate directly with the first fixed node 111, two-hop communication takes place from the mobile node 101 to the first fixed node 111 via the second fixed node 112. Similarly, when the mobile node 101 moves above the third fixed node 113, the communication becomes three-hop communication, and when the mobile node 101 moves above the nth fixed node 114, the communication becomes n-hop communication. As the number of hops increases, throughput decreases and delay time also increases.

[0012] Furthermore, for example, if the first fixed node 111 and the third fixed node 113, which are located on either side of the second fixed node 112, cannot detect each other's carrier, there is a risk that a packet transmitted by the first fixed node 111 and a packet transmitted by the third fixed node 113 will collide at the second fixed node 112. In this way, when multiple nodes that cannot detect each other's communications transmit signals simultaneously to the same node, the signals may collide (the so-called hidden terminal problem), which can further reduce throughput.

[0013] Fig. 2 shows an example of the configuration of a wired and wireless mesh network (hereinafter referred to as a "wired / wireless mesh network") as Conventional Example 2. In the system of Fig. 2, similar to the system of Fig. 1, a first fixed node 211, a second fixed node 212, a third fixed node 213, and an nth fixed node 214 are placed on the ground along the flight path of a mobile node 201 including a UAV body, and a server 221 is further connected to all the fixed nodes by wire. However, wireless communication between the fixed nodes is prohibited.

[0014] Specifically, the MAC addresses of the second fixed node 212, the third fixed node 213, and the nth fixed node 214 are specified for the first fixed node 211, and connection with these fixed nodes is prohibited by MAC address filtering. This allows the first fixed node 211 to wirelessly connect only with the mobile node 201. Similar settings are made for the other fixed nodes.

[0015] 2 also differs from Conventional Example 1 in that the maximum number of hops is set to 1. This can be achieved by setting the TTL (Time To Live) in the IP header of a packet to be transmitted to 1. When a packet is transferred from wireless node to wireless node, 1 is subtracted from the TTL, immediately making it 0, and if the packet has not reached the destination node at this point, the packet is discarded, resulting in a wireless network with a maximum number of hops of 1. In other words, since the route indicated by the dashed line in FIG. 2 can be traversed only once, no loop is formed even if the wireless network and wired network are connected by multiple nodes, and no blocking occurs between a specific fixed node and server 221.

[0016] In this way, if the wireless network exceeds a predetermined number of hops, packets are forcibly discarded to prevent the formation of a loop, thereby preventing blocking on the wired network. Furthermore, by setting a route that always ensures that the wired network can be reached within a predetermined number of hops from the wireless network, communication is always carried out via the shortest route regardless of which fixed node the mobile node 201 is connected to. This makes it possible to build a network that achieves high throughput and low latency.

[0017] However, for example, if there is an external communication device that can detect the carrier between second fixed node 212 but cannot detect the carrier between mobile node 201, there is a risk that a packet transmitted by mobile node 201 will collide with a packet transmitted by the external communication device at second fixed node 212. In other words, even in the system of Conventional Example 2 shown in Figure 2, a decrease in throughput may occur due to the hidden terminal problem.

[0018] The present invention has been made in view of the above-mentioned conventional circumstances, and has an object to provide a mesh network system that can suppress a decrease in throughput due to the hidden terminal problem. [Means for solving the problem]

[0019] In order to achieve the above object, a mesh network system according to one aspect of the present invention is configured as follows. That is, in a mesh network system having an airborne mobile node connected to a wireless network and a plurality of fixed nodes that form the wireless network and are also connected to a wired network, each of the plurality of fixed nodes is characterized by using an antenna pattern with reduced horizontal gain so that carriers cannot be detected between adjacent fixed nodes.

[0020] Here, in the mesh network system according to the present invention, each of the multiple fixed nodes may use an antenna pattern in which the gain in the sky direction is higher than the gain in the horizontal direction.

[0021] In addition, in the mesh network system according to the present invention, the mobile node may use an antenna pattern in which the gain in the ground direction is higher than the gain in the horizontal direction.

[0022] Furthermore, a mobile node according to another aspect of the present invention is configured as follows. That is, in an airborne mobile node connected to a wireless network consisting of multiple fixed nodes connected to a wired network, the mobile node has a first antenna pattern in which the horizontal gain is higher than the ground gain, and a second antenna pattern in which the horizontal gain is lower than the first antenna pattern but the ground gain is higher, and is characterized by switching to use the first antenna pattern when the flight altitude is below a predetermined threshold, and the second antenna pattern when the flight altitude is equal to or higher than the threshold. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a mesh network system that can suppress a decrease in throughput due to the hidden terminal problem. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless mesh network according to a first conventional example. [Figure 2] FIG. 10 is a diagram illustrating a configuration example of a wired / wireless mesh network according to Conventional Example 2. [Figure 3] 1 is a diagram illustrating an example of the configuration of a wired / wireless mesh network according to an embodiment of the present invention. [Figure 4] FIG. 10 is a diagram illustrating an example of the configuration of a mobile node according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows an example of the configuration of a wired / wireless mesh network according to an embodiment of the present invention. The wired / wireless mesh network of this example includes a mobile node 301, a first fixed node 311, a second fixed node 312, a third fixed node 313, an nth fixed node 314, and a server 321. The mobile node 301 is mounted on an unmanned UAV (unmanned aerial vehicle) or the like. The fixed nodes 311-314 are placed on the ground, for example, along the flight path of the UAV. The mobile node 301 and the fixed nodes 311-314 are wireless nodes capable of wireless communication with each other. However, wireless communication between the fixed nodes is prohibited. All of the fixed nodes 311-314 are connected to the server 321 via a wired network.

[0026] The mobile node 301 uses an antenna pattern with a high gain in the direction toward the ground. Here, the mobile node 301 uses an antenna pattern with a higher gain in the direction toward the ground than in the horizontal direction.

[0027] Furthermore, each of the fixed nodes 311 to 314 uses an antenna pattern with high gain in the sky direction and low gain in the horizontal direction. Here, the fixed nodes 311 to 314 use an antenna pattern in which the gain in the horizontal direction is higher than the gain in the sky direction, suppressing the gain in the horizontal direction so that the carrier cannot be detected between adjacent fixed nodes.

[0028] The antenna patterns of the mobile node 301 and the fixed nodes 311-314 can be realized by providing each node with a dedicated antenna according to its role. Alternatively, each node may be provided with a mechanism capable of controlling the antenna pattern to be used. As an example, each node may be provided with a first antenna having a higher gain in the horizontal direction than in the vertical direction and a second antenna having a higher gain in the vertical direction than in the horizontal direction, and the desired antenna pattern may be used by switching the antenna depending on the node's role. As another example, each node may be provided with either the first antenna or the second antenna described above, and the desired antenna pattern may be used by changing the orientation of that antenna. As yet another example, each node may be provided with an antenna unit capable of controlling antenna directivity, and the desired antenna pattern may be used by adjusting the orientation and width of the transmitting and receiving beams to change the antenna directivity.

[0029] The operation of the wired / wireless mesh network of this example will be described below with reference to Figure 3. As shown in Figure 3, all fixed nodes 311-314 are not only arranged along the flight path of the UAV, but are also positioned so that their antenna patterns with high gain in the sky overlap in the sky, allowing the mobile node 301 to communicate with at least one or more fixed nodes along the flight path of the UAV. On the other hand, the antenna patterns of all fixed nodes 311-314 have low gain in the horizontal direction, and are positioned so that adjacent fixed nodes cannot detect carriers between each other.

[0030] In addition, in the wired / wireless mesh network of this example, the maximum number of hops is set to 1. This can be achieved by setting the TTL (Time to Live) in the IP header of the packet to be sent to 1. In this case, when a packet is transferred from one wireless node to another, 1 is subtracted from the TTL, immediately making it 0, and if the packet has not reached the destination node at this point, it is discarded, resulting in a wireless network with a maximum number of hops of 1.

[0031] Furthermore, in the wired / wireless mesh network of this example, the fixed nodes 311-314 connected to both the wireless network and the wired network are equipped with a MAC address filtering function to prevent loops from forming between the wireless network and the wired network. Specifically, when a packet having a source address belonging to the wireless network is received from the wired network, the packet is discarded, thereby avoiding a broadcast storm without blocking the route on the wired network side.

[0032] For example, when a packet transmitted from mobile node 301 belonging to a wireless network reaches second fixed node 312 and then reaches other fixed nodes 311, 313, and 314 via the wired network, the packet is discarded. In contrast, when a packet transmitted from server 321 belonging to a wired network reaches second fixed node 312 and then reaches mobile node 301 via the wireless network, the packet is not forwarded to other fixed nodes because the wireless network has a maximum hop count of 1. It is assumed that fixed nodes connected to both a wireless network and a wired network have different MAC addresses on the wireless and wired sides.

[0033] Here, it is assumed that mobile node 301 is flying above first fixed node 311, and that only first fixed node 311 is wirelessly connected to mobile node 301. In this state, when mobile node 301 sends data such as video information to server 321 for the first time, the IP address of server 321 is usually known, but the MAC address of server 321 is unknown, so an ARP request packet is broadcast. The ARP request packet reaches server 321 only via the route via first fixed node 311, and server 321 completes address resolution by returning its own MAC address in an ARP response packet to mobile node 301. On the other hand, ARP request packets that reach other fixed nodes 312, 313, and 314 from first fixed node 311 via the wired network are discarded by the MAC address filtering function.

[0034] After address resolution, data from mobile node 301 is transmitted wirelessly in one hop to first fixed node 311, and then transferred via wire to server 321. Incidentally, Figure 3 shows that there is a house near first fixed node 311, and interference waves of the same frequency are leaking from the windows of this house. Note that first fixed node 311 has an antenna pattern with low gain in the horizontal direction, so that packets from mobile node 301 and packets from the house are less likely to collide at first fixed node 311.

[0035] Similarly, collisions between packets from the mobile node 301 and packets from the second fixed node 312 are unlikely to occur at the first fixed node 311. Furthermore, because the interference waves leaking from the windows of the houses have a low level of radiation into the sky, if the flying altitude of the mobile node 301 is sufficiently high, collisions between packets from the first fixed node 311 and packets from the houses are unlikely to occur at the mobile node 301. Although not shown in Figure 3, interference waves from nearby houses may exist at other fixed nodes, just like the first fixed node 311. However, because all fixed nodes have antenna patterns with low gain in the horizontal direction, it is expected that packet collisions will be suppressed, just like the first fixed node 311.

[0036] Next, as the mobile node 301 approaches the sky above the second fixed node 312, a wireless connection is established between the mobile node 301 and the second fixed node 312, and the mobile node 301 becomes connected to the first fixed node 311 and the second fixed node 312. After that, when the mobile node 301 moves further and is no longer able to communicate with the first fixed node 311, the mobile node 301 broadcasts an ARP request packet again to the server 321. This ARP request packet reaches the server 321 via a route that passes through the second fixed node 312, and the server 321 returns an ARP response packet, and address resolution is performed again.

[0037] Similarly, as the mobile node 301 approaches the sky above the third fixed node 313, a wireless connection is established between the mobile node 301 and the third fixed node 313. After that, when the mobile node 301 moves further and is no longer able to communicate with the second fixed node 312, the mobile node 301 broadcasts an ARP request packet again to the server 321. This ARP request packet reaches the server 321 via the third fixed node 313, and the server 321 returns an ARP response packet, and address resolution is performed again. In this way, similar route switching control is performed until mobile node 301 reaches nth fixed node 314 located near the final destination.

[0038] As described above, the mesh network system of this example includes an airborne mobile node 301 connected to a wireless network, and multiple fixed nodes 311-314 that form the wireless network and are also connected to a wired network. Each of the multiple fixed nodes 311-314 uses an antenna pattern with reduced horizontal gain so that adjacent fixed nodes cannot detect carriers. This prevents packet collisions between fixed nodes, thereby minimizing throughput degradation due to the hidden terminal problem. Furthermore, reducing horizontal gain also makes it possible to suppress interference from surrounding residential areas.

[0039] In addition, in the mesh network system of this example, each of the multiple fixed nodes 311 to 314 uses an antenna pattern in which the gain in the sky direction is higher than the gain in the horizontal direction, which enables each of the fixed nodes 311 to 314 to perform stable communication with the mobile node 301 flying above.

[0040] In addition, in the mesh network system of this example, the mobile node 301 uses an antenna pattern in which the gain in the direction toward the ground is higher than the gain in the horizontal direction, which enables the mobile node 301 to maintain a flight altitude that minimizes the effects of interference from residential areas, while maintaining stable communication with the fixed nodes 311-314 on the ground.

[0041] Furthermore, in this mesh network system, the wired network side blocking is prevented by preventing loop formation through the setting of the maximum hop count on the wireless network side and the setting of MAC address filtering on the wired network side, which makes it possible to build a network that is resilient to failures while maintaining high throughput and low latency.

[0042] 4 shows an example of the configuration of a mobile node according to another embodiment of the present invention. Mobile node 401 in this example is a wireless node mounted on an unmanned UAV (unmanned aerial vehicle) or the like, and can be used in place of mobile node 301 described above. Mobile node 401 includes first antenna 411, second antenna 412, antenna switch 413, wireless processing unit 414, and altimeter 415.

[0043] The first antenna 411 is an antenna having a first antenna pattern in which the gain in the horizontal direction is higher than the gain in the ground direction. The second antenna 412 is an antenna having a second antenna pattern in which the gain in the horizontal direction is lower than that of the first antenna pattern, while the gain in the ground direction is higher (for example, an antenna pattern in which the gain in the ground direction is higher than the gain in the horizontal direction). The radio processing unit 414 performs processing related to radio communication using the first antenna 411 or the second antenna 412. The altimeter 415 is a sensor that measures the flight altitude of the mobile node 401.

[0044] Antenna switch 413 switches the antenna to be used for wireless communication based on the flight altitude measured by altimeter 415. In this example, when the flight altitude is below a predetermined threshold, first antenna 411 is connected to wireless processing unit 414. In other words, when the flight altitude is low, a first antenna pattern in which the gain in the horizontal direction is higher than the gain in the direction toward the ground is used for wireless communication. On the other hand, when the flight altitude is equal to or higher than the predetermined threshold, second antenna 411 is connected to wireless processing unit 414. In other words, when the flight altitude becomes high to a certain extent, antenna switching is performed so that a second antenna pattern in which the gain in the horizontal direction is lower than that of the first antenna pattern but the gain in the direction toward the ground is used for wireless communication.

[0045] In this way, by switching antennas taking into account changes in the positional relationship with the fixed node according to the flight altitude of the mobile node, wireless communication with the fixed node can be performed more stably. Note that, although the example in Figure 4 is configured to switch between two antennas, three or more antennas may be provided in a switchable manner. Also, instead of switching between multiple physically different antennas, an antenna whose antenna directivity can be dynamically changed (for example, an array antenna) may be used.

[0046] Although the embodiments of the present invention have been described above, the above embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the present invention. These embodiments and modifications are included in the scope and spirit of the invention described in this specification, etc., and are included in the invention described in the claims and their equivalents.

[0047] Furthermore, the present invention can be provided not only as devices such as those described above or as systems composed of these devices, but also as methods executed by these devices, programs for realizing the functions of these devices using a processor, and storage media for storing such programs in a computer-readable manner. [Industrial Applicability]

[0048] The present invention can be used in a mesh network system having airborne mobile nodes connected to a wireless network and a plurality of fixed nodes that form the wireless network and are also connected to a wired network. [Explanation of symbols]

[0049] 101, 201, 301, 401: mobile nodes, 111, 211, 311: first fixed node, 112, 212, 312: second fixed node, 113, 213, 313: third fixed node, 114, 214, 314: nth fixed node, 121, 221, 321: server, 411: first antenna, 412: second antenna, 413: antenna switch, 414: radio processing unit, 415: altimeter

Claims

1. A mesh network system having a mobile node mounted on an unmanned flying vehicle and connected to a wireless network, and a plurality of fixed nodes that constitute the wireless network and are also connected to a wired network, the maximum hop count of the wireless network is 1; each of the plurality of fixed nodes has a MAC address filtering function for discarding a packet when the fixed node receives a packet having a source address belonging to the wireless network from the wired network side; Furthermore, the mesh network system is characterized in that each of the multiple fixed nodes uses an antenna pattern that reduces horizontal gain regardless of whether or not the external communication equipment is present, so that carriers are not detected between adjacent fixed nodes and so that packets from the mobile node and packets from external communication equipment located at a position lower than the flight path of the unmanned mobile body do not collide at the fixed node.

2. 2. The mesh network system according to claim 1, A mesh network system characterized in that each of the plurality of fixed nodes uses an antenna pattern in which gain in the sky direction is higher than gain in the horizontal direction.

3. 3. The mesh network system according to claim 1, A mesh network system characterized in that the mobile node uses an antenna pattern in which the gain in the ground direction is higher than the gain in the horizontal direction.

4. In the mesh network system according to claim 1 or claim 2, The mobile node: a first antenna pattern having a horizontal gain higher than a ground gain; a second antenna pattern that has a lower gain in the horizontal direction and a higher gain in the ground direction than the first antenna pattern, A mesh network system characterized by switching to use a first antenna pattern when the flight altitude is below a predetermined threshold, and to use a second antenna pattern when the flight altitude is above the threshold.

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