JP7065505B2 - Wireless communication method and wireless communication system - Google Patents

Description

The present invention relates to a wireless communication method and a wireless communication system in a tree-type network that transmits / receives data between a plurality of devices including a collection control station and two or more nodes arranged with the collection control station as a root. Is.

In recent years, in wireless networks, communication devices compliant with the IEEE 802.15.4 standard, which are small in size, inexpensive, and capable of performing low-output digital wireless communication, have been used. In a network compliant with the IEEE 802.15.4 standard, for example, as shown in FIG. 11, a CS (Collection station) 71, which is a collection control station, and one or more nodes 72 (nodes 72-1 to 72-4 in FIG. 11). A tree-type topology consisting of multiple devices including) is adopted. In the tree-type topology, the lower node 72 transmits data to the higher node 72 or CS71 as needed (see, for example, Patent Documents 1 to 3).

FIG. 12 shows an example of a time chart in the case of transmitting data from lower nodes 72-3 and 72-4 to CS71. The CS71 and each node 72 are assigned an active period (communication period T1 (unit: time t)) and a sleep period T2 (unit: time t) within the basic interval T (unit: time t), respectively. In the communication period T1, wireless communication becomes possible, and in the sleep period T2, the receiving side shifts to the sleep state, so that wireless communication cannot be performed. By intentionally providing the sleep period T2 within the basic interval T, the power consumption can be reduced, and the power consumption of the entire system can be suppressed.

For example, when data is transmitted from the node 72-3 to the CS71, the route is transmitted from the node 72-3 to the CS71 via the node 72-1. In such a case, the upper node 72-1 is the master and the lower node 72-3 is the slave between the node 72-3 and the node 72-1 above the node 72-3. Similarly, between the nodes 72-1 and CS71, the CS71 as the upper node is the master and the lower node 72-1 is the slave. In such a relationship between the master and the slave, the higher master determines the timing of the communication period T1 at the basic interval T, and the lower slave determines the timing of the communication period T1 determined on the master side. Send the data.

Under such a rule, in FIG. 12, first, the node 72-3 transmits the data D81 generated at the timing t91 in accordance with the communication period T1 of the node 72-1 as the master starting at the timing t92. Upon receiving this data D81, the node 72-1 transmits the data D81 in accordance with the communication period T1 of the CS71 as the master starting at the timing t93. As a result, the CS71 can receive the data D81 within the communication period T1 set by itself.

Similarly, when data is transmitted from the node 72-4 to the CS71, the node 72-4 relays the node 72-1 and becomes the route of the CS71. The node 72-4 transmits the data D82 generated at the timing t94 in accordance with the communication period T1 of the node 72-1 as the master starting at the timing t95. Upon receiving the data D82, the node 72-1 transmits the data D82 in accordance with the communication period T1 of the CS71 as the master starting at the timing t96. As a result, the CS71 can receive the data D82 within the communication period T1 set by itself.

The CS71 can collect all the data from each node 72 in the tree-type network based on the above-mentioned wireless communication processing operation method. By adopting the route selection control assuming relay communication between such devices, it becomes possible to limit the service area due to the limit of the wireless communication distance.

Japanese Unexamined Patent Publication No. 2015-198333 Japanese Unexamined Patent Publication No. 2014-23085 Japanese Unexamined Patent Publication No. 2014-103580

By the way, in the conventional tree-type topology including the above-mentioned Patent Documents 1 to 3, communication delay between devices may be caused by the allocation of the sleep period T2. In particular, when it becomes difficult to maintain the synchronization state due to the movement of the node 72 or the like, the route selection information indispensable for the route selection control is not updated promptly, and there is a concern that the performance in the wireless network deteriorates.

Therefore, the present invention has been devised in view of the above-mentioned problems, and an object thereof is a wireless communication method and a wireless system capable of promptly updating route selection information indispensable for route selection control. It is to provide a communication system.

In order to solve the above-mentioned problems, the present inventors send and receive data between a plurality of devices including a collection control station and a node arranged over two or more with the collection control station as a root. We have developed a wireless communication method and a wireless communication system in a type network. In the wireless communication method, a synchronization signal is transmitted from a first device included in a plurality of devices to a plurality of lower devices including a first lower device that synchronizes as a lower level of the first device, and the first lower device sends a synchronization signal. When it is determined that it is difficult to receive, the first lower device sends a rescue signal to the first device to notify the state that reception is difficult, and based on the rescue signal, the first device sends a rescue signal to a plurality of lower devices. Relief for setting a new synchronization state Relief is sent to the first lower device from each of a plurality of lower devices different from the first lower device based on the instruction signal by transmitting an instruction signal prompting the transmission of the synchronization signal. It is characterized by transmitting a synchronization signal and maintaining a synchronization state between the rescue device that has transmitted the rescue synchronization signal received by the first lower device and the first lower device.

The wireless communication method according to claim 1 is a radio in a tree-type network that transmits / receives data between a plurality of devices including a collection control station and a node arranged over two or more with the collection control station as a root. In a communication method, a synchronization signal is transmitted from a first device included in a plurality of the devices to a plurality of lower devices including a first lower device to be synchronized as a lower layer of the first device, and the first lower device is transmitted. When the device determines that it is difficult to receive the synchronization signal, the first lower device transmits a rescue signal informing the first device of the state in which reception is difficult, and based on the rescue signal, the first device. The device transmits an instruction signal prompting the transmission of a rescue synchronization signal for setting a new synchronization state to the plurality of the lower devices, and based on the instruction signal, a plurality of the lower devices different from the first lower device. From each of the devices, the rescue synchronization signal is transmitted to the first lower device, and the synchronization state between the rescue device that has transmitted the rescue synchronization signal received by the first lower device and the first lower device is determined. It is characterized by maintaining.

According to the second aspect of the present invention, in the invention of the first aspect, the frequency of transmitting the instruction signal from the first device is higher than the frequency of transmitting the synchronization signal from the first device. It is a feature.

The wireless communication method according to claim 3 is the invention according to claim 1 or 2, wherein the rescue signal is transmitted to the first device and a higher device synchronized as a higher level of the first device. Alternatively, it is transmitted to the higher-level device via the first device, and based on the rescue signal, the higher-level device synchronizes with one or more second devices and the first device that synchronize as a lower level of the higher-level device. On the other hand, the instruction signal is transmitted, and based on the instruction signal, from each of the plurality of the lower devices different from the first lower device and one or more second lower devices synchronized as the lower devices of the second device. , The first lower device is characterized by transmitting the rescue synchronization signal.

The wireless communication method according to claim 4 is characterized in that, in the invention according to claim 3, the frequency of transmitting the instruction signal from the first device is higher than the frequency of transmitting the instruction signal from the higher-level device. And.

The wireless communication method according to claim 5 is the invention according to any one of claims 1 to 4, wherein the rescue signal is transmitted until the first lower device receives the rescue synchronization signal. It is characterized in that the reception state of the first lower device is continuously maintained.

The wireless communication system according to claim 6 is a radio in a tree-type network that transmits / receives data between a plurality of devices including a collection control station and a node arranged over two or more with the collection control station as a root. A communication signal transmission means for transmitting a synchronization signal from a first device included in a plurality of the devices to a plurality of lower devices including a first lower device to be synchronized as a lower level of the first device. When the first lower device determines that it is difficult to receive the synchronization signal, the first lower device transmits a rescue signal notifying the first device that reception is difficult. , An instruction signal transmitting means for transmitting an instruction signal for prompting transmission of a rescue synchronization signal for setting a new synchronization state from the first device to a plurality of the lower devices based on the rescue signal, and the instruction signal. Rescue synchronization signal transmission means for transmitting the rescue synchronization signal to the first lower device and the first lower device received from each of the plurality of lower devices different from the first lower device. It is characterized by comprising a rescue device that has transmitted the rescue synchronization signal and a resynchronization means that maintains a synchronization state with the first lower-level device.

According to the present invention having the above-described configuration, a rescue synchronization signal is transmitted to the first lower device from each of the plurality of lower devices different from the first lower device based on the instruction signal. Further, the synchronization state between the rescue device that transmitted the rescue synchronization signal received by the first lower device and the first lower device is maintained. That is, even when the synchronization state between the first lower device and the first device becomes difficult, the first lower device receives the rescue synchronization signal to obtain a new synchronization state between the first lower device and the rescue device. Establish. Therefore, the route selection information in the first lower-level device can be updated quickly. This makes it possible to suppress deterioration of performance in the wireless network.

Further, according to the present invention having the above-described configuration, the frequency of transmitting the instruction signal from the first device is higher than the frequency of transmitting the synchronization signal from the first device. Therefore, when the synchronization state between the first lower device and the first device becomes difficult, the instruction signal can be transmitted at a frequency higher than the frequency at which the synchronization signal is normally transmitted. This makes it possible to significantly reduce the time required to establish a new synchronization of the first inferior device.

Further, according to the present invention having the above-described configuration, the rescue signal is transmitted to the higher-level device or is transmitted to the higher-level device via the first device. Further, based on the rescue signal, an instruction signal is transmitted from the host device to one or more second devices and the first device. Therefore, the number of devices that transmit the rescue synchronization signal can be significantly increased. This makes it possible to further shorten the time for establishing a new synchronization of the first inferior device.

FIG. 1 is a schematic diagram showing an example of a wireless communication system to which the present invention is applied. FIG. 2 is a diagram showing a specific example of a control support terminal when one node is assigned as a controlled terminal. FIG. 3 is a time chart during uplink data communication between nodes other than the control support terminal. FIG. 4A is a diagram showing an example of a synchronization state between nodes in the first embodiment, and FIG. 4B is a diagram showing an example of a rescue signal transmitting means in the first embodiment. FIG. 5A is a diagram showing an example of an instruction signal transmitting means according to the first embodiment, and FIG. 5B is a diagram showing an example of a rescue synchronous signal transmitting means according to the first embodiment. FIG. 6 is a diagram showing an example of the resynchronization means in the first embodiment. FIG. 7 (a) is a diagram showing an example of a first period in which the synchronization signal in the first embodiment is transmitted, and FIG. 7 (b) is a diagram in FIG. 7 (b) is a second period in which the instruction signal in the first embodiment is transmitted. It is a figure which shows an example. FIG. 8 is a diagram showing an example of the range in which the node moves in the first embodiment. 9 (a) and 9 (b) are diagrams showing an example of the rescue signal transmitting means in the second embodiment. FIG. 10 is a diagram showing an example of the instruction signal transmitting means according to the second embodiment. FIG. 11 is a diagram showing an example of a network conforming to the standard of IEEE 802.15.4. FIG. 12 is a diagram for explaining the prior art.

(First Embodiment)
Hereinafter, the wireless communication system 1 as the first embodiment of the present invention will be described in detail. FIG. 1 is a schematic diagram showing an example of the wireless communication system 1 of the present embodiment. The wireless communication system 1 includes a collection station (Collection Station: hereinafter referred to as CS) 2 and nodes 3 (3-1, 3-2, ... 3) of wireless terminals arranged over two or more roots of CS2. It is equipped with a plurality of devices including −k (k is an integer)), and a so-called tree-type topology (tree-type network) is adopted. In this wireless communication system 1, a lower-level node 3 performs uplink data communication toward a higher-level node 3 or CS2. Further, in the wireless communication system 1, the higher-level node 3 and CS2 perform downlink data communication toward the lower-level node 3.

The CS2 is the highest-level master device, and collects data transmitted from each node 3 by uplink data communication. The CS2 also plays a role as a central control unit for controlling the entire wireless communication system 1, and performs downlink data communication of control system data to a specific node 3.

Node 3 is a general term for devices capable of transmitting and receiving data such as transmission and relay of data, and is, for example, a communication device conforming to the standard of IEEE 802.15.4. The node 3 is embodied as a sensor that senses predetermined data and transmits it wirelessly, and also, for example, a mobile phone, a smartphone, a tablet terminal, a wearable terminal, a notebook personal computer (PC), or the like. It may be embodied as a terminal device capable of wireless communication. Further, the node 3 may include a control system such as an actuator. In such a case, for example, in the field of agriculture and the like, it is embodied as a device capable of controlling to stop the valve, controlling the robot, and controlling to stop the gas. If the node 3 is embodied as an actuator including a control system, various control operations should be executed based on the control data transmitted from CS2 via the other node 3 for downlink data. It becomes.

In this embodiment, as shown in the wireless communication system 1 shown in FIG. 1, a plurality of nodes 3 (nodes 3-1, 3-2, 3-3, 3-4, 3- in FIG. 1) under CS2. An explanation will be given by taking the case where 5 and 3-6) are arranged as an example. The node 3 arranged in the lower link of the CS2 may have a tree structure composed of any branching pattern as long as the CS2 collects data, and any number of nodes 3 having one or more. It may be composed of.

In the wireless communication system 1 of the present embodiment, for example, the CS2 and the controlled terminal, and all the nodes 3 arranged on these paths may be specified as control support terminals. In the example shown in FIG. 2, when node 3-4 is assigned as a controlled terminal, CS2, node 3-1 and node 3-4 are specified as control support terminals. In the present embodiment, the communication method is common between the wireless communication between the control support terminals and the wireless communication between other routes, and for example, the communication methods may be different from each other.

FIG. 3 shows an example of a time chart in the case where data is transferred from node 3-5 to CS2 by relaying data between nodes 3 and data communication is performed. A communication period T1 and a sleep period T2 are assigned to the CS2 and each of the nodes 3-2 and 3-5 within the basic interval T, respectively. In the communication period T1, wireless communication becomes possible, and in the sleep period T2, the receiving side shifts to the sleep state, so that wireless communication cannot be performed. By intentionally providing the sleep period T2 within the basic interval T, the power consumption can be reduced, and the power consumption of the entire system can be suppressed.

When transmitting data from node 3-5 to CS71, between node 3-5 and node 3-2 above this, the upper node 3-2 is the master and the lower node 3 is. -5 is the slave relationship. Similarly, between the nodes 3-2 and CS2, CS2 as the upper node is the master and the lower node 3-2 is the slave. In such a relationship between the master and the slave, the higher master allocates the timing of the communication period T1 within the basic interval T, and the lower slave assigns the data according to the timing of the communication period T1 assigned on the master side. It will be sent.

Under such a rule, as shown in FIG. 3, first, the node 3-5 adjusts the data D21 generated at the timing t11 to the communication period T1 starting at the timing t12 of the node 3-2 as the master. Send. Upon receiving the data D21, the node 3-2 transmits the data D21 in accordance with the communication period T1 of the CS2 as the master starting at the timing t13. As a result, CS2 can receive the data D21 within the communication period T1 set by itself.

As shown in FIG. 4, for example, the wireless communication system 1 of the present embodiment has a plurality of lower nodes 31 (node 3- in FIG. 4) that are synchronized with the node 3-1 (first device) as lower portions of the node 3-1. 3, 3-4, 3-6, 3-7, 3-8, 3-9: lower device). The wireless communication system 1 of the present embodiment includes a synchronization signal transmission means, a rescue signal transmission means, an instruction signal transmission means, a rescue synchronization signal transmission means, and a resynchronization means.

The synchronization signal transmission means transmits the synchronization signal B1 (beacon) from the node 3-1 to the lower node 31. The synchronization signal B1 is transmitted within the communication period T1 assigned to each lower node 31.

For example, as shown in FIG. 4A, when the lower node 31 is arranged within the transmittable range R1 of the node 3-1 the lower node 31 receives the synchronization signal B1. Therefore, the lower node 31 can receive the synchronization signal B1. As a result, the synchronous state between the node 3-1 and the lower node 31 can be maintained. The solid line arrow in FIG. 4 indicates the synchronization state, and each lower node 31 (node 3-3, 3-4, 3-6, 3-7, 3-8, 3-9) is a node 3-1. Indicates that the synchronization state is maintained.

As shown in FIG. 4B, for example, when the rescue signal transmitting means determines that it is difficult for the node 3-3 (first lower device) to receive the synchronization signal B1, the rescue signal transmitting means changes from the node 3-3 to the node 3-1. In response, the rescue signal S1 is transmitted. The rescue signal S1 is a signal indicating that the node 3-3 is in a state where it is difficult to receive the synchronization signal B1.

The rescue signal transmission means is performed when, for example, the node 3-3 moves out of the transmittable range R1 of the node 3-1. For example, when the node 3-1 is arranged within the transmittable range R2 in the node 3-3, the node 3-1 receives the rescue signal S1 transmitted from the node 3-3. In addition to the movement of the node 3-3 described above, the rescue signal transmitting means predicts that the conventional wireless network will be disconnected or disconnected due to, for example, a change in the arrangement environment or a malfunction of the node 3-3. It may be done when it is done.

The rescue signal S1 is transmitted, for example, at the timing of the communication period T1 assigned to the node 3-3. That is, the rescue signal S1 is transmitted, for example, within the communication period T1. Therefore, the node 3-1 can perform wireless communication at the same timing as the synchronization state with the node 3-3. As a result, the node 3-1 can surely receive the rescue signal S1 transmitted from the node 3-3.

The instruction signal transmission means is performed after the rescue signal transmission means. As shown in FIG. 5A, for example, the instruction signal transmission means transmits the instruction signal S2 from the node 3-1 to the plurality of lower nodes 31 based on the rescue signal S1. The instruction signal S2 is a signal for prompting transmission of the rescue synchronization signal S3 for setting a new synchronization state. The instruction signal S2 is transmitted within the communication period T1.

The instruction signal transmission means is performed by, for example, the node 3-1 receiving the rescue signal S1. The node 3-1 temporarily transmits, for example, the instruction signal S2. Therefore, the instruction signal S2 can be set to be transmitted only in an emergency, and can be transmitted at a higher frequency than the synchronization signal B1. As a result, the instruction signal transmission means can be performed while maintaining the conventional suppression of power consumption as much as possible. The "frequency" of the above-mentioned transmission will be described later.

The rescue synchronization signal transmission means is performed after the instruction signal transmission means. As shown in FIG. 5B, for example, the rescue synchronization signal transmission means is based on the instruction signal S2, and the rescue synchronization signal is transmitted from each of the plurality of lower nodes 31 different from the node 3-3 to the node 3-3. S3 is transmitted. The rescue synchronization signal S3 is a signal for setting a synchronization state with each lower node 31, and may include information for setting a different synchronization state for each lower node 31, for example.

The rescue synchronization signal means is performed by, for example, the lower node 31 receiving the instruction signal S2. For example, when the node 3-3 is arranged within the transmittable range R3 in the node 3-4 (rescue device), the node 3-3 receives the rescue synchronization signal S3 transmitted from the node 3-4.

The lower node 31 temporarily transmits, for example, the rescue synchronization signal S3. The rescue synchronization signal S3 may be transmitted, for example, by each lower node 31 at a different cycle and frequency.

Note that the node 3-3 may continuously maintain the reception state from the transmission of the rescue signal S1 to the reception of the rescue synchronization signal S3, for example. In this case, even when the rescue synchronization signal S3 is transmitted at intervals independent of the basic interval T, the node 3-3 can easily receive the rescue synchronization signal S3.

The resynchronization means is performed after the rescue synchronization signal means. As shown in FIG. 6, for example, the resynchronization signal means maintains a synchronization state between the node 3-4 that has transmitted the rescue synchronization signal S3 received by the node 3-3 and the node 3-3. At this time, the node 3-3 does not maintain the synchronization state with the node 3-1.

As a result, the upper level of node 3-3 is changed from node 3-1 to node 3-4. In the resynchronization means, for example, the rescue synchronization signal S3 may be transmitted from node 3-4 to node 3-3 at arbitrary periods.

When each of the above-mentioned means is executed, the operation of the wireless communication system 1 of the present embodiment is completed. Further, by performing each of the above-mentioned means as a method, the wireless method of the present embodiment can be performed. This prevents the node 3-3 from dropping out of the wireless network.

According to the present embodiment, based on the instruction signal S2, the rescue synchronization signal S3 is directed to the node 3-3 from each of the plurality of lower nodes 31 (lower devices) different from the node 3-3 (first lower device). To send. Further, the synchronization state between the node 3-4 (rescue device) that transmitted the rescue synchronization signal S3 received by the node 3-3 and the node 3-3 is maintained. That is, even when the synchronization state between the node 3-3 and the node 3-1 (first device) becomes difficult, the node 3-3 receives the rescue synchronization signal S3, so that the node 3-3 and the node 3 Establish a new synchronization state with -4. Therefore, the route selection information in the node 3-3 can be updated quickly. This makes it possible to suppress deterioration of performance in the wireless network.

For example, as shown in FIG. 8, when the node 3-3 moves within the range P1, it stays within the transmittable range R1 of the node 3-1 and therefore the synchronization state with the node 3-1 is maintained. On the other hand, when the node 3-3 moves within the range P2, the range P3, or the range P4, it goes out of the transmittable range R1 of the node 3-1 and the synchronization state with the node 3-1 becomes difficult (conventional). System). At this time, by applying this embodiment, even when the node 3-3 moves within the range P2 or the range P3, it is newly added to the lower node 31 (for example, node 3-4 or node 3-9). It is possible to maintain a good synchronization state. That is, according to the present embodiment, it is possible to reduce the possibility of the wireless network dropping out when moving to the range P2 and the range P3, as compared with the conventional case. For example, when the range P2 = range P3 = 60 ° and the range P4 = 120 °, the dropout possibility of the wireless network in this embodiment is 50% ((60 ° + 60 °) / (60 ° + 60 ° + 120 °). )) Can be improved. This makes it possible to suppress deterioration of performance in the wireless network.

Here, the frequency of transmitting the synchronization signal B1 and the instruction signal S2 from the above-mentioned node 3-1 will be described. Here, the "frequency" indicates the number of times each signal B1 and S2 is transmitted in a certain period. For example, when the signals B1 and S2 are transmitted at predetermined intervals, the case where the period is short can be indicated as a high "frequency". Further, for example, when each signal B1 or S2 is randomly transmitted in a certain period, when the total number of transmissions is large, or when the average of the transmission cycles is short, it can be indicated as a high "frequency". Hereinafter, a case where the signals B1 and S2 are transmitted at predetermined intervals will be described with reference to FIG. 7.

For example, as shown in FIG. 7A, the synchronization signal transmission means transmits the synchronization signal B1 from the node 3-1 to the lower node 31 for each first period Tb1. The node 3-1 periodically transmits the synchronization signal B1 with a time of m times the basic interval T (m is an integer of 2 or more) as the first period Tb1 (in FIG. 7A, the basic interval T). Twice as much as). In this case, the frequency of transmitting the synchronization signal B1 is expressed as 0.5 times with respect to the basic interval T (fixed period).

For example, as shown in FIG. 7B, the instruction signal transmitting means transmits the instruction signal S2 from the node 3-1 to the plurality of lower nodes 31 for each second period Tb2. The node 3-1 periodically transmits the instruction signal S2 with a time n times the basic interval T (n is an integer of 1 or more) as the second period Tb2 (in FIG. 7B, the basic interval T). 1 times). In this case, the frequency of transmitting the instruction signal S2 is expressed once with respect to the basic interval T (fixed period).

As described above, according to the present embodiment, the frequency of transmitting the instruction signal S2 from the node 3-1 (first device) is higher than the frequency of transmitting the synchronization signal B1 from the node 3-1. Therefore, when the synchronization state between the node 3-3 and the node 3-1 becomes difficult, the instruction signal S2 can be transmitted at a higher frequency than the frequency at which the synchronization signal B1 is normally transmitted. This makes it possible to significantly reduce the time required to establish a new synchronization of node 3-3.

Even when at least one of the instruction signal S2 and the synchronization signal B1 is randomly transmitted from the node 3-1 for a certain period (for example, the basic interval T), the frequency of transmitting the instruction signal S2 is the synchronization signal B1. Can be sent more frequently than. Therefore, similarly to the above, it is possible to significantly shorten the time for establishing a new synchronization of the nodes 3-3.

Further, the rescue signal S1 and the rescue synchronization signal S3 may also be transmitted periodically, for example, at p times the basic interval T (p is an integer of 1 or more). The frequency at which the rescue signal S1 and the rescue synchronization signal S3 are transmitted can be higher than the frequency at which the synchronization signal B1 is transmitted. Therefore, similarly to the above, it is possible to significantly shorten the time for establishing a new synchronization of the nodes 3-3.

(Second Embodiment)
Next, the wireless communication system 1 as the second embodiment of the present invention will be described in detail. The difference between the above-described embodiment and the second embodiment is that the host device (CS2 in FIG. 9) of the node 3-1 receives the rescue signal S1. The description of the main configuration similar to the above-described embodiment will be omitted.

The wireless communication system 1 of the second embodiment includes, for example, a node 3-1 and a plurality of lower nodes 31 and a CS2 (upper device), as shown in FIG. 9, for example, one or more nodes 3-2. (In FIG. 9, node 3-2a, node 3-2b: second device) and one or more subordinate nodes 32 that synchronize as subordinates of node 3-2 (node 3-as subordinates of node 3-2a in FIG. 9). 5, 3-10, 3-11: second lower device) may be provided. That is, the wireless communication method of the second embodiment is executed not only with the above-described embodiment but also with the higher-level device of the node 3-1. In the following description, the higher-level device of node 3-1 will be described as CS2, but for example, any number of nodes 3 may be synchronized between node 3-1 and CS2, and node 3-1 may be used. On the other hand, it suffices to have at least one or more higher-level nodes.

As shown in FIG. 9A, for example, the rescue signal means transmits the rescue signal S1 from node 3-3 to node 3-1 and CS2 synchronized as a higher level of node 3-1. In this case, the rescue signal S1 may be transmitted at the timing of the communication period T1 assigned to the node 3-3, or may be transmitted at a timing different from the communication period T1 (for example, continuously or randomly). good. Thereby, for example, even when the communication period T1 of the CS2 is different from the communication period T1 assigned to the node 3-3, the rescue signal S1 can be received by the CS2 in a short period of time.

As the rescue signal means, for example, as shown in FIG. 9B, the rescue signal S1 may be transmitted from the node 3-3 to the CS2 via the node 3-1. In this case, the rescue signal S1 is transmitted to the CS2 at the timing of the communication period T1 assigned to the node 3-1 so that the CS2 can be reliably received via the node 3-1.

As shown in FIG. 10, for example, the instruction signal means transmits the instruction signal S5 from CS2 to the plurality of nodes 3-2 and 3-1 based on the rescue signal S1. The instruction signal S5 is a signal for prompting transmission of the rescue synchronization signal S3 for setting a new synchronization state, similarly to the instruction signal S2 described above. The CS2 temporarily transmits, for example, the instruction signal S5. Further, the instruction signal S5 is periodically transmitted every third period, or is transmitted at random, for example. The third period is, for example, q times the basic interval T (q is an integer of 1 or more), and is shorter than, for example, the first period Tb1.

After that, the instruction signals S51 and S52 are transmitted from the nodes 3-1 and 3-2 that have received the instruction signal S5 to the lower nodes 31 and 32, respectively. In addition, each node 3-1 and 3-2 may directly transmit the rescue synchronization signal S3 to the node 3-3 based on the received instruction signal S5, for example.

In the instruction signal means, for example, the node 3-1 transmits the instruction signal S51 to the lower node 31 based on the rescue signal S1 received from the node 3-3 and the instruction signal S5 received from the CS2. In this case, for example, the instruction signal S51 may be transmitted with priority given to the information of the instruction signal S5, or the instruction signal S2 may be transmitted with priority given to the information of the rescue signal S1, for example, as described above. For example, the node 3-1 may compare the cycle in which the instruction signal S5 is transmitted and the cycle in which the rescue signal S1 is transmitted, and select the type of the instruction signal S51.

For example, when the node 3-1 receives the rescue signal S1, the node 3-1 transmits the instruction signal S2 every second period, as in the above-described embodiment. Further, the node 3-1 receives the instruction signal S5 every third period. At this time, according to the second embodiment, the second period Tb2 can be shorter than the third period. That is, the frequency of transmitting the instruction signal S2 from the node 3-1 is higher than the frequency of transmitting the instruction signal S5 from CS2. In this case, the node 3-1 preferentially transmits the instruction signal S2. Therefore, it is possible to preferentially execute the condition that is likely to establish the synchronization state of the node 3-3 in a short time. This makes it possible to avoid or reduce the time for the node 3-3 to drop out of the wireless network.

For example, node 3-2a does not receive the rescue signal S1. Therefore, the node 3-2a transmits the instruction signal S52 to the lower node 32 based on the received instruction signal S5.

For example, node 3-2b does not receive the rescue signal S1 and is not synchronized with node 3 at the lower level. In this case, the node 3-2b may transmit the rescue synchronization signal S3 to the node 3-3 based on the instruction signal S5 in the rescue synchronization signal transmission means.

In the relief synchronization signal transmission means, the relief synchronization signal S3 is transmitted to the node 3-3 from each of the lower node 31 and the lower node 32 different from the node 3-3, as in the above-described embodiment. The rescue synchronization signal S3 is a signal for setting a synchronization state with each of the lower nodes 31 and 32, and may include information for setting a different synchronization state for each of the lower nodes 31 and 32, for example.

After that, the resynchronization means is performed in the same manner as in the above-described embodiment. By executing each of the above-mentioned means, the operation of the wireless communication system 1 of the second embodiment is completed. Further, by performing each of the above-mentioned means as a method, the wireless method of the second embodiment can be performed. This prevents the node 3-3 from dropping out of the wireless network.

According to the second embodiment, as in the above-described embodiment, from each of the plurality of lower nodes 31 (lower devices) different from the node 3-3 (first lower device), the node 3 is based on the instruction signal S2. The rescue synchronization signal S3 is transmitted to -3. Further, the synchronization state between the node 3-4 (rescue device) that transmitted the rescue synchronization signal S3 received by the node 3-3 and the node 3-3 is maintained. That is, even when the synchronization state between the node 3-3 and the node 3-1 (first device) becomes difficult, the node 3-3 receives the rescue synchronization signal S3, so that the node 3-3 and the node 3 Establish a new synchronization state with -4. Therefore, the route selection information in the node 3-3 can be updated quickly. This makes it possible to suppress deterioration of performance in the wireless network.

According to the second embodiment, the rescue signal S1 is transmitted to CS2 (upper device) or transmitted to CS2 via node 3-1. Further, based on the rescue signal S1, the CS2 transmits an instruction signal S5 to the plurality of nodes 3-2 and 3-1. Therefore, the number of nodes 3 (devices) that transmit the rescue synchronization signal S3 can be significantly increased. This makes it possible to further shorten the time for establishing a new synchronization of node 3-1 (first inferior device).

1 Wireless communication system 2,71 CS
3,72 Nodes 31, 32 Lower nodes B1 Synchronous communication D Data P1 to P4 Range R1 to R3 Transmittable range S1 Relief signal S2, S5 Instruction signal S3 Relief synchronization signal T Basic interval T1 Communication period T2 Sleep period Tb1 First period Tb2 Second period

Claims (6)

A wireless communication method in a tree-type network for transmitting and receiving data between a plurality of devices including a collection control station and a node arranged over two or more with the collection control station as a root.
A synchronization signal is transmitted from the first device included in the plurality of the devices to a plurality of lower devices including the first lower device to be synchronized as the lower devices of the first device.
When the first lower device determines that it is difficult to receive the synchronization signal, the first lower device transmits a rescue signal notifying the first device that reception is difficult.
Based on the rescue signal, the first device transmits an instruction signal prompting the plurality of lower devices to transmit a rescue synchronization signal for setting a new synchronization state.
Based on the instruction signal, the rescue synchronization signal is transmitted to the first lower device from each of the plurality of lower devices different from the first lower device.
A wireless communication method comprising maintaining a synchronized state between a rescue device that has transmitted the rescue synchronization signal received by the first lower device and the first lower device. The wireless communication method according to claim 1, wherein the frequency of transmitting the instruction signal from the first device is higher than the frequency of transmitting the synchronization signal from the first device. The rescue signal is transmitted to the first device and a higher device synchronized as a higher level of the first device, or is transmitted to the higher device via the first device.
Based on the rescue signal, the higher-level device transmits the instruction signal to one or more second devices and the first device that are synchronized as lower levels of the higher-level device.
Based on the instruction signal, from each of the plurality of lower devices different from the first lower device and one or more second lower devices synchronized as lower layers of the second device, the first lower device is referred to. The wireless communication method according to claim 1 or 2, wherein the rescue synchronization signal is transmitted. The wireless communication method according to claim 3, wherein the frequency of transmitting the instruction signal from the first device is higher than the frequency of transmitting the instruction signal from the higher-level device. Any of claims 1 to 4, wherein the reception state of the first lower device is continuously maintained from the transmission of the rescue signal to the reception of the rescue synchronization signal by the first lower device. The wireless communication method according to paragraph 1. A wireless communication system in a tree-type network that transmits / receives data between a plurality of devices including a collection control station and two or more nodes arranged with the collection control station as a root.
A synchronization signal transmission means for transmitting a synchronization signal from a first device included in the plurality of devices to a plurality of lower devices including a first lower device that synchronizes as a lower level of the first device.
When the first lower device determines that it is difficult to receive the synchronization signal, the first lower device transmits a rescue signal notifying the first device that reception is difficult, and a rescue signal transmission means.
An instruction signal transmission means for transmitting an instruction signal for prompting transmission of a rescue synchronization signal for setting a new synchronization state from the first device to a plurality of the lower devices based on the rescue signal.
A rescue synchronization signal transmission means for transmitting the rescue synchronization signal to the first lower device from each of the plurality of lower devices different from the first lower device based on the instruction signal.
A resynchronization means for maintaining a synchronization state between the rescue device that has transmitted the rescue synchronization signal received by the first lower device and the first lower device.
A wireless communication system characterized by being provided with.

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