Wireless communication system

Abstract

To provide a wireless communication system capable of achieving in a short time with low power consumption, rec-connection of a once-disconnected mobile terminal to a wireless communication network.SOLUTION: In a wireless communication system 1 having nodes 3-1, 3-2 for establishing a wireless communication link with an approaching mobile terminal 4; a node for transmitting a beacon before starting wireless communication; and a mobile terminal for establishing a wireless communication link with an originating node of the received beacon. The nodes make frequencies of beacon transmission different from each other chronologically in accordance with chronological locations of the mobile terminals brought closer to or separated from each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wireless communication system having two or more devices and performing wireless communication with each of the mobile terminals that come close to each other, and in particular to a wireless communication system that enables a mobile terminal that has once left the wireless communication network to reconnect in a short time and with low power consumption. [Background technology]

[0002] Compared to wired communication systems, wireless communication systems have the advantage of reducing the space required for cables and allowing mobile devices such as smartphones, tablet devices, and notebook personal computers (notebook PCs) to connect to communication networks without compromising their portability. In addition, wireless communication itself has become faster and cheaper, accelerating the practical application of wireless communication. Against this background, the Institute of Electrical and Electronics Engineering (IEEE) is working on standardization of wireless communication.

[0003] Among them, the IEEE802.15.4 standard is a standard that enables small, inexpensive, and power-saving wireless communication in wireless communication networks, and communication devices that comply with this standard are used. In wireless communication networks that comply with the IEEE802.15.4 standard, various topologies are adopted that are composed of a collection control station (CS) and one or more nodes (see, for example, Non-Patent Document 1). In this communication topology, a lower node transmits data to a higher node or CS as necessary. In addition, various control signals are sent from the higher node or CS to the lower node. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] IEEE802-15.10, “IEEE Recommended Practice for Routing Packets in IEEE 802.15.4 Dynamically Changing Wireless Network,” 2017. Summary of the Invention [Problem to be solved by the invention]

[0005] In such a communication topology including the technology disclosed in Non-Patent Document 1, when a mobile terminal constituting each node, or a mobile terminal capable of wireless communication with each node, moves far away or when the mobile terminal itself turns off, it may leave the wireless communication network once. When such a mobile terminal that has left re-enters the wireless communication network and communicates with each node, it will reconnect the wireless communication link. When performing such reconnection, the mobile terminal will establish a wireless communication link after receiving a beacon transmitted from each node, but if it takes a long time for the mobile terminal to reconnect the wireless communication link, it will lead to a decrease in the operating performance of the wireless communication network. For this reason, there has been a strong demand for shortening the time until such a mobile terminal reconnects. In addition, in the process of reconnection, each node will periodically transmit a beacon until a wireless communication link with the mobile terminal is established, and the power consumption of each node will increase accordingly. For this reason, a system capable of reducing the power consumption of each node until a wireless communication link is established in response to the reconnection of the mobile terminal has been desired.

[0006] The present invention has been devised in consideration of the above-mentioned problems, and its object is to provide a wireless communication system that enables a mobile terminal that has once left the wireless communication network to reconnect to the wireless communication network in a short time and with low power consumption. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the inventors invented a wireless communication system in which, when transmitting a beacon before wireless communication begins, one device transmits a beacon with different frequencies from other devices, so that a mobile terminal that has once left the network can reconnect to the wireless communication network in a short time and with low power consumption, and the mobile terminal establishes a wireless communication link with the device that transmitted the received beacon.

[0008] The wireless communication system according to the first invention is a wireless communication system having a device that establishes a wireless communication link with a mobile terminal that has come close, the system comprising a device that transmits a beacon before wireless communication begins, and a mobile terminal that establishes a wireless communication link with the device that has transmitted the received beacon, the devices being characterized in that they vary the frequency of beacon transmission chronologically from each other depending on the chronological position of the mobile terminal that is approaching or moving away.

[0009] A wireless communication system according to a second aspect of the present invention has two or more devices, each of which establishes a wireless communication link with a mobile terminal that has approached, and the system includes each device that transmits a beacon before wireless communication begins, and a mobile terminal that establishes a wireless communication link with the device that transmitted the received beacon, and the one device makes the frequency of beacon transmission differ chronologically between the other devices depending on the chronological position of the mobile terminal that is approaching or moving away.

[0010] The wireless communication system according to the third invention is characterized in that, in the first or second invention, it further comprises a location information acquisition means for acquiring location information of the mobile terminal, and each of the devices controls the frequency of transmitting the beacon in accordance with the location information of the mobile terminal acquired by the location information acquisition means.

[0011] The wireless communication system of the fourth invention is characterized in that, in the third invention, each of the devices controls, based on the location information, the frequency of beacon transmission to increase as the locations of the mobile terminals approach each other, and controls the frequency of beacon transmission to decrease as the locations of the mobile terminals move away from each other.

[0012] The wireless communication system of the fifth invention is characterized in that, in the first invention, each of the devices adjusts the frequency of beacon transmission so that it becomes more frequent as the positions of the mobile terminals become closer, and so that it becomes less frequent as the positions of the mobile terminals become farther apart, based on the previously acquired moving route and moving timing of the mobile terminals.

[0013] The wireless communication system according to the sixth invention is characterized in that, in the first to fifth inventions, the mobile terminal, after terminating the desired data communication through the established wireless communication link, leaves the wireless communication link, and reconnects to the wireless communication link by receiving the beacon from the device at the start of the next wireless communication. Effect of the Invention

[0014] As described above, the wireless communication system to which the present invention is applied includes a device that transmits a beacon before wireless communication starts, and a mobile terminal that establishes a wireless communication link with the device that is the source of the received beacon, and the devices make the beacon transmission frequency different from each other in a time series according to the chronological positions of the mobile terminals that are close or far away. Also, the system includes each device that transmits a beacon before wireless communication starts, and a mobile terminal that establishes a wireless communication link with the device that is the source of the received beacon, and one device makes the beacon transmission frequency different from each other with other devices. At this time, the beacon transmission frequency is controlled to be higher as the mobile terminals are closer to each other, and the beacon transmission frequency is controlled to be lower as the mobile terminals are farther away from each other.

[0015] As a result, according to the present invention, the mobile terminal can increase the possibility of receiving a beacon from the node closest to the current location. Moreover, since the frequency of receiving beacons per unit time increases, it is possible to establish a wireless communication link in a shorter time. Even if a beacon cannot be received from a node farther away from the current location of the mobile terminal, if a beacon can be received from a closer node, a wireless communication link can be established between the node and the mobile terminal. Even if a node farther away from the current location of the mobile terminal transmits a beacon less frequently, there is no particular effect on establishing a wireless communication link. In addition, by reducing the frequency of transmitting a beacon from a node farther away from the current location of the mobile terminal, the power consumption of the node can be reduced accordingly, and it is possible to reduce the power consumption of the entire wireless communication system.

[0016] In addition, according to the present invention, the device further comprises a location information acquisition means for acquiring location information of the mobile terminal, and each device controls the frequency of transmitting a beacon in accordance with the location information of the mobile terminal acquired by the location information acquisition means.

[0017] As a result, even if the moving route or moving timing of the mobile terminal is unknown, it is possible to obtain the location information of the mobile terminal each time and control the frequency of beacon transmission based on this information.

[0018] Furthermore, according to the present invention, each device adjusts the beacon transmission frequency to be higher as the mobile terminals get closer to each other and to be lower as the mobile terminals get farther away, based on the previously acquired moving route and moving timing of the mobile terminals. In other words, when the moving route and moving timing of the mobile terminals are known, it is possible to control the beacon transmission frequency based on these. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram showing an example of a wireless communication system according to the present invention; [Diagram 2] FIG. 13 is a diagram showing an example of a time chart in the case where each node transmits a beacon B. [Diagram 3] 13 is a diagram showing another example of the time chart when each node transmits a beacon B. FIG. [Figure 4] FIG. 13 is a diagram showing an example in which, even if the moving route and moving timing of a mobile terminal are unknown, position information of the mobile terminal is acquired each time and the frequency of beacon transmission is controlled based on this. [Diagram 5] 11A and 11B are diagrams showing the results of verification for confirming the effects of the wireless communication system to which the present invention is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A wireless communication method according to a first embodiment of the present invention will now be described in detail.

[0021] 1 is a schematic diagram showing an example of a wireless communication system 1 according to the present embodiment. The wireless communication system 1 includes, as wireless communication terminals, nodes 3-1 and 3-2 with a collection control station (hereinafter referred to as CS) 2 as the root, and a mobile terminal 4 corresponding to a lower node, and employs a so-called tree topology. In this wireless communication system 1, the mobile terminal 4 corresponding to a lower node performs upstream data communication toward the higher node 3 and CS2. Also, in the wireless communication system 1, the higher node 3 and CS2 perform downstream data communication toward the lower node 3.

[0022] The CS2 is the highest-level master device, and collects data transmitted by upstream data communication from each of the nodes 3-1 to 3-2 and the mobile terminal 4. The CS2 also serves as a central control unit for controlling the entire wireless communication system 1, and transmits control data to a specific node 3 as downstream data communication.

[0023] The node 3 is a generic name for a device capable of transmitting and receiving data, including transmitting and relaying data, and is, for example, a communication device conforming to the IEEE802.15.4 standard. The node 3 will be described as a so-called fixedly installed base station, but is not limited thereto, and may be embodied as a terminal device capable of wireless communication, such as a mobile phone, a smartphone, a tablet terminal, a wearable terminal, or a notebook personal computer (PC). The node 3 may also include a control system such as an actuator, or may be configured as a device that controls a robot or various vehicles. In such a case, various control operations are executed based on control data transmitted as downstream data from the CS2 via other nodes 3.

[0024] In this embodiment, as shown in the wireless communication system 1 in Fig. 1, a case is described in which nodes 3-1 and 3-2 are arranged as fixed base stations under the CS2, and a mobile terminal 4 capable of wireless communication with the nodes 3-1 and 3-2 is formed, but the present invention is not limited to this. In other words, the nodes 3 arranged on the lower links of the CS2 may have a tree structure consisting of any branching pattern, and may be composed of any number of nodes 3 greater than or equal to one, as long as they allow the CS2 to collect data.

[0025] The mobile terminal 4 is a mobile communication device conforming to the IEEE802.15.4 standard, like the node 3. The mobile terminal 4 may be embodied as a terminal device capable of wireless communication, such as a mobile phone, a smartphone, a tablet terminal, a wearable terminal, or a notebook personal computer (PC). The mobile terminal 4 may also be configured as an electronic device capable of wireless communication mounted on a vehicle or the like. When the mobile terminal 4 approaches the vicinity of the node 3-1, it establishes a wireless communication link with the node 3-1 and performs wireless communication. When the mobile terminal 4 moves away from the node 3-1 and approaches the node 3-2, it releases the wireless communication link with the node 3-1 and establishes a new wireless communication link with the node 3-2.

[0026] When such a mobile terminal 4 moves away from both of these nodes 3-1 and 3-2, or when the power of the mobile terminal 4 itself is turned off, the mobile terminal 4 leaves the wireless communication network for a time. When the mobile terminal 4 that has left the network re-enters the wireless communication network and resumes wireless communication with each of the nodes 3-1 and 3-2, it will reconnect the wireless communication link. When reconnecting in this way, the mobile terminal 4 will establish a wireless communication link after receiving a beacon transmitted from each of the nodes 3-1 and 3-2.

[0027] In such a case, as shown in FIG. 1, the beacon transmission frequency is made different between the nodes 3-1 and 3-2. That is, the number of beacons transmitted per unit time is made different between the nodes 3-1 and 3-2. In such a case, the beacon transmission frequency of the different nodes 3-1 and 3-2 may be made different depending on the position of the mobile terminal 4. That is, the node 3-1 makes the beacon transmission frequency between the node 3-1 and the node 3-2 different in time series depending on the time-series position of the mobile terminal 4 that is close to or far from the node 3-2. In this case, when focusing on one of the nodes 3-1 and 3-2, the beacon transmission frequency is made different in time series.

[0028] For example, as shown in Fig. 1(a), when the mobile terminal 4 is closer to node 3-1 and farther from node 3-2, the beacon transmission frequency of node 3-1 is controlled to be higher, and the beacon transmission frequency of node 3-2 is controlled to be lower. On the other hand, as shown in Fig. 1(b), when the mobile terminal 4 is farther from node 3-1 and closer to node 3-2, the beacon transmission frequency of node 3-2 is controlled to be higher, and the beacon transmission frequency of node 3-1 is controlled to be lower. When viewed from the node 3 side, the closer the position of the mobile terminal 4 is, the higher the beacon transmission frequency is, and the farther the position of the mobile terminal 4 is, the lower the beacon transmission frequency is.

[0029] The time chart in Fig. 2 shows an example of a time chart in which node 3-1 and node 3-2 each transmit a beacon B. In the example in Fig. 2, during communication period T1a, the mobile terminal 4 is closer to node 3-1 and farther away from node 3-2. Therefore, during communication period T1a, the frequency of transmission of beacon B from node 3-1 is increased and the frequency of transmission of beacon B from node 3-2 is decreased.

[0030] 3, the mobile terminal 4 is farther away from the node 3-1 and closer to the node 3-2 during the communication period T2b. Therefore, during the communication period T2b, the frequency of beacon transmission from the node 3-1 is reduced and the frequency of beacon B transmission from the node 3-2 is increased. Of course, instead of reducing the frequency of transmission, a non-transmission period in which no beacon is transmitted at all within a unit time may be provided.

[0031] In other words, when focusing on one of the nodes 3-1 and 3-2, the frequency of beacon transmission is made to differ chronologically depending on the chronological position of the nearby or distant mobile terminal 4.

[0032] This allows the mobile terminal 4 to increase the possibility of receiving the beacon B from the node 3 closest to the current location. Moreover, since the frequency of receiving the beacon B per unit time increases, it is possible to establish a wireless communication link in a shorter time. Even if the beacon B cannot be received from a node 3 farther away from the current location of the mobile terminal 4, if the beacon B can be received from the closest node 3, a wireless communication link can be established between the node 3. Even if the node 3 farther away from the current location of the mobile terminal 4 transmits a beacon less frequently, there is no particular effect on establishing a wireless communication link. In addition, by reducing the frequency of transmitting a beacon from a node 3 farther away from the current location of the mobile terminal 4, the power consumption of the node 3 can be reduced accordingly, and it is possible to reduce the power consumption of the entire wireless communication system 1.

[0033] As shown in Fig. 2, the transmission frequency of the beacon B may be set uniformly in each communication period T1a, T1b, but is not limited to this. As shown in Fig. 3, the transmission frequency of the beacon B may be gradually increased or decreased in the nodes 3-1, 3-2. The mobile terminal 4 is closest to the node 3-1 in the communication period T2a, and closest to the node 3-2 in the communication period T2b. In such a case, the transmission frequency of the beacon B in the node 3-1 is set to the highest in the communication period T2a when the mobile terminal 4 is closest, and the transmission frequency of the beacon B is gradually decreased from the communication period T2c after the communication period T2a and before the communication period T2b. In addition, the node 3-2 lowers the transmission frequency of the beacon B in the communication period T2a, gradually increases the transmission frequency of the beacon B in the communication period T2c, and further increases the transmission frequency of the beacon B to the highest in the communication period T2b. As a result, the frequency of beacon reception is gradually increased as the mobile terminal 4 approaches each node 3, so that a wireless communication link can be established earlier, and the frequency of beacon transmission is gradually decreased as the mobile terminal 4 moves away from the node 3, so that the power consumption of the node 3 can be reduced accordingly. When focusing on one of the nodes 3-1 and 3-2, the frequency of beacon transmission is gradually increased as the chronological position of the mobile terminal 4 gradually approaches, and the frequency of beacon transmission is gradually decreased as the chronological position of the mobile terminal 4 gradually moves away. This makes it possible to reduce the power consumption of the entire wireless communication system 1.

[0034] When the moving route and the moving timing of the mobile terminal 4 are known, the time period when the mobile terminal 4 is closest to each of the nodes 3-1 and 3-2 can be known according to the known moving route and the moving timing. In such a case, it becomes possible to adjust the beacon transmission frequency in advance on the system side according to the known moving route and the moving timing of the mobile terminal 4. Specifically, based on the known moving route and the moving timing of the mobile terminal 4, each node 3 adjusts the beacon transmission frequency to be higher in the time period when the mobile terminal 4 is close to the node 3, and adjusts the beacon transmission frequency to be lower in the time period when the mobile terminal 4 is far from the node 3.

[0035] Also, the location information of the mobile terminal 4 may be acquired at any time, and the frequency of transmission of the beacon of each node 3 may be controlled based on the acquired location information. In such a case, the wireless communication system 1 is newly provided with a location information acquisition unit 16 for acquiring the location information of the mobile terminal 4, as shown in FIG. 4. This location information acquisition unit 16 is connected to the CS 2 and the node 3, and is configured to be capable of wired or wireless communication with them. Also, the location information acquisition unit 16 acquires the current location information of the mobile terminal 4 in real time. The location information of the mobile terminal 4 may be acquired using, for example, a Global Positioning System (GPS), but is not limited thereto, and may be acquired through various sensors. As an example of the various sensors, it may be configured with an infrared sensor capable of measuring the approach distance of the mobile terminal 4 to the node 3, and may be installed for each node 3. The approach distance of the mobile terminal 4 may be measured through this infrared sensor, and the frequency of transmission of the beacon may be controlled according to the degree of proximity of the mobile terminal 4 to the node 3.

[0036] In the above embodiment, the CS2 and each node 3, which are communication devices conforming to the IEEE802.15.4 standard, are used as an example, but the present invention is not limited to this. In other words, any device that performs wireless communication other than the IEEE802.15.4 standard may be applied to the above-mentioned CS2 and node 3, and the same processing operation may be executed.

[0037] In addition, in the above-described embodiment, an example has been described in which a mobile terminal 4 that has once left a wireless communication network reconnects to a node 3, but this is not limited to this, and it is of course also applicable to a case in which a mobile terminal 4 newly connects to a node 3.

[0038] The present invention is not limited to the above-mentioned embodiment. After the mobile terminal 4 has finished the desired data communication through the established wireless communication link, the mobile terminal 4 may once leave the wireless communication link. That is, the end of the desired data communication is used as a trigger to leave the wireless communication link. Then, at the start of the next wireless communication, the mobile terminal 4 reconnects to the wireless communication link by receiving a beacon from the node 3. By the mobile terminal 4 once leaving the wireless communication link as a trigger to end the desired data communication, it is possible to easily realize reconnection to the node 3 at the start of the next wireless communication. If the mobile terminal 4 was close to the node 3-1 when the previous wireless communication link was established, but is close to the node 3-2 at the start of the next wireless communication, if the previous wireless communication link remains established, it will be difficult to reconnect the wireless communication link to the node 3-2. For this reason, if reconnection is considered, it is desirable to leave the wireless communication link at the end of the desired data communication. EXAMPLES

[0039] In order to confirm the operational effect of the wireless communication system 1 to which the present invention is applied, the following verification was carried out. In this verification, a beacon was transmitted from a communication device which was regarded as a node 3, and the synchronization signal frequency (times / min) relative to the synchronization signal interval (sec) was measured as shown in Fig. 5. The synchronization signal interval here refers to the beacon transmission interval, and the synchronization signal frequency refers to the beacon transmission frequency.

[0040] The horizontal x-axis in FIG. 5 represents the synchronization signal interval (sec), the vertical y-axis (left side) represents the reconnection success rate, and the vertical y-axis (right side) represents the synchronization signal frequency.

[0041] The reconnection success rate is expressed as a fractional probability that the mobile terminal 4 successfully reconnects based on a beacon transmitted from a communication device represented as the node 3. As shown in FIG. 5, the smaller the synchronization signal interval, the higher the synchronization signal frequency and the higher the reconnection success rate.

[0042] Here, it is assumed that the range in which a beacon can be received from node 3 is 1 / 20 of the total area in which mobile terminal 4 can move. In this case, the comparative example continues to transmit beacons at the same synchronization signal interval and synchronization signal frequency while mobile unit 4 is in the entire area, regardless of whether mobile unit 4 is in a range in which a beacon can be received from node 3. In contrast, the example of the present invention transmits a beacon only when mobile unit 4 is within a range in which a beacon can be received from node 3, and does not transmit a beacon when mobile unit 4 departs from the range.

[0043] Figure 5 shows the results of simulating the reconnection success rate and synchronization signal frequency for each synchronization signal interval for the example of the present invention and the comparative example. When the synchronization signal interval is the same for the comparative example and the example of the present invention, the synchronization signal frequency for the example of the present invention is about 1 / 20 of that for the comparative example, which is almost the same as the ratio of the beacon transmission areas mentioned above. In addition, since the synchronization signal frequency is lower in total for the example of the present invention than for the comparative example, it is possible to reduce the power consumption at the node by that amount, which shows that it is possible to reduce the power consumption of the entire wireless communication system. [Explanation of symbols]

[0044] 1. Wireless communication systems 2. Collection Control Station 3 Node 4 Mobile terminals 16 Location information acquisition section

Claims

1. A wireless communication system having a device for establishing a wireless communication link with a mobile terminal that has come close to the device, A device that transmits a beacon before starting wireless communication; a mobile terminal that establishes a wireless communication link with the device that is the source of the received beacon; The device causes the frequency of beacon transmission to vary in a time series according to the time series positions of the mobile terminals adjacent to or separated from each other. A wireless communication system comprising:

2. In a wireless communication system having two or more devices, each of which establishes a wireless communication link with a mobile terminal that has come close to the other device, Each device transmits a beacon before starting wireless communication; a mobile terminal that establishes a wireless communication link with the device that is the source of the received beacon; The one device makes the frequency of beacon transmission between the one device and the other device different in time series according to the time series positions of the mobile terminals close to or far from each other. A wireless communication system comprising:

3. Further comprising a location information acquiring means for acquiring location information of the mobile terminal, Each of the devices controls the frequency of transmission of the beacon in response to the location information of the mobile terminal acquired by the location information acquisition means.

3. The wireless communication system according to claim 1, wherein:

4. Each of the devices controls the frequency of beacon transmission so that it increases as the positions of the mobile terminals approach each other and decreases as the positions of the mobile terminals move away from each other based on the position information.

4. The wireless communication system according to claim 3,

5. Each of the devices adjusts the frequency of beacon transmission so that it becomes higher as the positions of the mobile terminals become closer to each other and becomes lower as the positions of the mobile terminals become farther apart, based on the previously acquired moving route and moving timing of the mobile terminals.

2. The wireless communication system according to claim 1,

6. the mobile terminal terminates the desired data communication through the established wireless communication link, and then leaves the wireless communication link; At the next start of wireless communication, reconnecting to the wireless communication link by receiving the beacon from the device.

6. The wireless communication system according to claim 1, wherein:

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