JP7797335B2 - Wireless device, network system, and control method - Google Patents

Description

The present invention relates to the field of ad hoc networks, which communicate via multiple wireless devices.

In recent years, ad hoc networks have been attracting attention. In ad hoc networks, multiple wireless devices are scattered within an area, and when wireless devices located too far apart to communicate directly with each other, they communicate via other wireless devices. This type of network is called a multi-hop network.
Typical communication methods in a multi-hop network include a routing method and a flooding method.

When the routing method is adopted, for example, a routing table is provided in each wireless device, and a communication path is determined according to the routing table to carry out communication.
However, in the routing method, the wireless devices that are relayed when a message packet is sent are determined in advance, making it difficult to add a new wireless device or change the transfer route when a wireless device fails.

Therefore, a more flexible communication method is desired.
In Patent Document 1 below, a method is proposed in which broadcast communication is switched to unicast communication every time a packet is transmitted, and a forwarding table is updated every time communication is performed.

JP 2017-060034 A

However, the forwarding table used in Patent Document 1 generates a record for each combination of source address (the address of the wireless device that initially sent the information) and destination device address (the address of the device that is the final destination), so the data size increases as the number of devices and wireless devices increases, resulting in larger memory and wireless devices.

On the other hand, wireless devices are being placed in a variety of locations due to the diversification of their uses, so there is a demand for them to be miniaturized.

The present invention was developed in consideration of these problems, and aims to enable flexible communication while reducing memory usage.

The wireless device of the present invention is a wireless device that constitutes a wireless mesh network to which message packets are forwarded, and is equipped with a communication control unit that controls communication, a transmitting unit that transmits packets that are determined to be either the message packets or search packets, a receiving unit that receives the packets, and a memory unit that stores information about the radio wave strength of other wireless devices to which the message packets are to be sent as a forwarding table that is information that is not linked to the wireless device that is the final destination of the message packets, and the communication control unit uses the forwarding table to forward all of the received message packets that have been decided to be forwarded to other wireless devices using unicast communication in order of radio wave strength , regardless of the wireless device that is the final destination of the message packets .
Therefore, instead of a routing method in which a forwarding route is determined in advance using a routing table or the like when a message packet is sent, the message packet is sent and forwarded in accordance with the communication situation at the time using information from a forwarding table stored in a memory unit.

The network system of the present invention is a network system composed of a plurality of wireless devices, each of which is equipped with a communication control unit that controls communication, a transmitting unit that transmits packets that are either message packets or search packets, a receiving unit that receives the packets , and a memory unit that stores information about the radio wave strength of other wireless devices to which the message packet is to be sent as a forwarding table that is information that is not linked to the wireless device that is the final destination of the message packet , and the communication control unit uses the forwarding table to forward all of the received message packets that have been decided to be forwarded to other wireless devices , regardless of the wireless device that is the final destination of the message packet, in order of radio wave strength using unicast communication.

The control method of the present invention is a control method for a wireless device that includes a communication control unit that performs communication control, a transmitting unit that transmits packets that are either message packets or search packets, a receiving unit that receives the packets , and a memory unit that stores information about the radio wave strength of other wireless devices to which the message packets are to be sent as a forwarding table that is information that is not linked to the wireless device that is the final destination of the message packets.For all of the received message packets that have been decided to be forwarded to other wireless devices , the message packets are forwarded using unicast communication in order of radio wave strength, using the forwarding table, regardless of the wireless device that is the final destination of the message packets .
Such a network system and control method can also provide the above-mentioned effects.

This invention enables flexible communication while minimizing memory usage.

FIG. 1 is a diagram showing an overview of a wireless mesh network. FIG. 1 is a block diagram of a wireless device. FIG. 2 is a diagram illustrating main items included in a message packet. FIG. 10 illustrates an example of a forwarding table. FIG. 10 is a diagram illustrating an example of a received packet history. 10 is a flowchart illustrating an example of a process executed when a wireless device is added. 10 is a flowchart illustrating an example of a forwarding table update process. 10 is a flowchart illustrating an example of a process executed when a search packet is received. 10 is a flowchart illustrating an example of a process executed when a message packet is generated and transmitted. 10 is a flowchart illustrating an example of a process executed when a message packet is received.

The embodiments will be described below in the following order.
1. Configuration of wireless device
<2. Packet Structure>
<2-1. Message packet>
<2-2. Acknowledgment packet>
<2-3. Search packet>
3. Data stored in the storage unit
<3-1. Forwarding table>
<3-2. Received packet history>
<3-3. Setting data>
<4. Flowchart>
<4-1. Adding wireless devices>
<4-2. Receiving a search packet>
<4-3. Sending message packets>
<4-4. Message packet transfer>
5. Modified Examples
<6. Summary>

1. Configuration of wireless device
Hereinafter, a wireless device according to an embodiment will be described with reference to the drawings.
FIG. 1 is a diagram illustrating the concept of a wireless mesh network.
The wireless mesh network in Fig. 1 is composed of eight wireless devices, A to H. Each of the wireless devices A to H can directly communicate with other wireless devices located within its communication distance (hereinafter referred to as "communication range"). The communication distance of the wireless devices A to H is, for example, several tens of meters (m) or several hundred meters.

When information is sent from one wireless device to another wireless device located outside the communication range, the information is transmitted via several wireless devices. For example, in Figure 1, when information is sent from wireless device A to wireless device H, the information is transmitted via wireless devices D and F. At this time, wireless devices D and F perform a transfer process to forward the received data to the other wireless devices.

Note that the number of wireless devices that make up the wireless mesh network is not limited to eight. In the following explanation, examples are shown in which the wireless devices are fixed in their respective locations, but some or all of the wireless devices may be mobile.

Frequency bands used in wireless mesh networks are, for example, around 429 MHz (megahertz), 920 MHz, 1.2 GHz (gigahertz), 2.4 GHz, 5 GHz, and 6 GHz.

2 is a block diagram of the wireless device 100. Each of the wireless devices A to H in FIG. 1 has the configuration shown in FIG.
The wireless device 100 includes a communication control unit 100a, a transmitting unit 100b, a receiving unit 100c, a storage unit 100d, an interface unit 100e, a power supply unit 100f, and an antenna unit 100g.
The communication control unit 100a is configured to have, for example, a central processing unit, and performs processes such as creating message packets, reading the headers of received message packets and forwarding them according to the situation, generating (or updating) a forwarding table, etc. In other words, the communication control unit 100a performs overall control of the wireless device 100.

The transmitter 100b and the receiver 100c are configured, for example, as an integrated circuit (IC). The transmitter 100b and the receiver 100c may be configured as a single IC. In this case, the IC is configured to integrate a modulation unit, a power amplifier unit, a high-frequency amplifier unit, and a demodulator unit.
The transmitting unit 100b executes a process of transmitting the message packet passed from the communication control unit 100a to the other wireless device 100.
The receiving unit 100c receives message packets transmitted from other wireless devices 100 and passes them to the communication control unit 100a.

The memory unit 100d is configured to include a ROM (Read Only Memory) and a RAM (Random Access Memory), and stores various programs and setting data executed by the communication control unit 100a, as well as a forwarding table that the communication control unit 100a uses to determine the forwarding destination of message packets.
The storage unit 100d also stores message packets received from other wireless devices 100 as received packet history.
The forwarding table and received packet history will be described later.

The memory unit 100d also functions as a work area when the communication control unit 100a executes various processes.

The interface unit 100e receives information from external devices, such as sensor devices, to be transmitted to other wireless devices. The interface unit 100e uses, for example, asynchronous serial communication (RS232C). Note that the interface unit is not limited to wired connections and may also support short-range wireless communication.

The power supply unit 100f supplies power to each unit of the wireless device 100 (e.g., the communication control unit 100a, the transmitting unit 100b, the receiving unit 100c, the memory unit 100d, the interface unit 100e, the antenna unit 100g, etc.). The power supply unit 100f is, for example, a lithium-ion battery or a dry cell battery.

In the embodiment described below, an example will be described in which device 1 is wired to wireless device A. Device 1 is a device that does not have a wireless function, such as a measuring device such as a thermometer, pressure gauge, or flow meter, or a control device that produces some kind of output.
Similar to wireless device A, wireless device B is wired to device 2, wireless device C is wired to device 3, wireless device D is wired to device 4, and wireless device E is wired to device 5. Other wireless devices are also wired to some other device.
The wireless mesh network may be configured to include a wireless device that is not connected to any device and only performs forwarding, or a wireless device that is connected to two or more devices by wire.

<2. Packet Structure>
Next, packets flowing on the wireless mesh network in this embodiment will be described with reference to FIG.
The acknowledgement packet will be referred to as an ACK (Acknowledgement) packet hereinafter.

<2-1. Message packet>
The structure of a message packet is shown in Figure 3. Note that Figure 3 only shows the main parts of the structure of a message packet, and an actual message packet is structured to include a preamble area, a synchronization code area, a control data area, etc. in addition to the areas shown in Figure 3.

A message packet has various fields, including a message field (information the user wants to send), and is repeatedly sent and forwarded from the source wireless device until it reaches a destination device (such as a wireless device 100 connected to a measuring device). In the following explanation, the wireless device 100 that generates and initially sends a message packet will be referred to as the "source wireless device 100." The wireless device 100 that is the final destination will be referred to as the "destination wireless device 100." Furthermore, the wireless device 100 that receives the message packet and forwards it to another wireless device 100 will be referred to as the "source wireless device 100," and the wireless device 100 to which the message packet is forwarded will be referred to as the "destination wireless device 100."

The source address field stores a unique value (hereafter referred to as the "device address") for identifying the source wireless device 100. This value is, for example, any value between 0 and 239, with a different value assigned to each wireless device 100.

In this embodiment, in areas other than the message area in the message packet, each decimal digit is represented by 1 byte. For example, for the decimal number "239", the "2" is represented by 1 byte of binary notation, the "3" is represented by 1 byte of binary notation, and the "9" is represented by 1 byte of binary notation, resulting in "000000100000001100001001" being stored in the source address area.

By representing each decimal digit as a binary number with 1 byte in this way, it is possible to simplify the display of message packet data using terminal software, etc.

The destination address field stores a device address for identifying the wireless device 100 that is the final destination.
Although it is assumed here that a device address is assigned to the wireless device 100, device addresses may be assigned not only to the wireless device 100 but also to devices connected to the wireless device 100 by wire.

The source address field stores a device address for identifying the wireless device 100 that is the source of the transfer. When a wireless device transfers a received message packet to another wireless device, the device address of the wireless device itself is stored in the source address field. The source address field is not required in a message packet and may not be provided.

The destination address field stores a device address for identifying the destination wireless device 100. When performing unicast communication with a specified destination, the device address of the destination wireless device 100 is stored in the destination address field. When performing broadcast communication without specifying a destination, the destination address field stores information indicating that the transfer is not intended for a specific wireless device 100 (for example, "255" in decimal notation).

The TTL (Time To Live) field stores a value that determines the upper limit of the number of wireless devices 100 that can be relayed when delivering data from the source wireless device 100 to the destination wireless device 100.

The value stored in the TTL field is decremented by 1 each time a transfer is repeated, and eventually becomes 0. When wireless device 100 receives a message packet with 0 stored in the TTL field, it discards the message packet without transferring it.
This avoids or suppresses message packet congestion.

The sequential number field stores a serial number (sequential number) assigned to each message packet generated by the source wireless device 100. Specifically, the sequential number field of the first message packet generated by wireless device A stores "1." The sequential number field of the next message packet generated by wireless device A stores "2."

The sequential number increments, for example, from 1 to 256, and then returns to 1.

The message byte count field stores a value that represents the amount of data stored in the message field in bytes.

The message area is an area where user data is stored, such as sensor values obtained by sensor devices.

The CRC (Cyclic Redundancy Check) area stores a redundant code for detecting errors in data other than the CRC area. Note that the CRC area may store a redundant code for detecting errors only in user data.
Furthermore, the CRC area may store an error check code other than the CRC, such as a BCC (Block Check Character), etc. In other words, any error check (error correction) method may be used.

<2-2. Acknowledgment packet>
An ACK packet is a packet that a wireless device 100 that has received a forwarded message packet or the like sends to the wireless device 100 that forwarded it, and notifies the wireless device 100 that it has received the forwarded message packet.

The ACK packet has a structure in which, for example, the message area in Fig. 3 is omitted from the message packet.

<2-3. Search packet>
The search packet is a packet that is transmitted from the installation location of a new wireless device 100 when the new wireless device 100 is added to the wireless mesh network. The search packet is transmitted to surrounding wireless devices 100 using broadcast communication.

The structure of a search packet is the same as the message packet shown in Figure 3. The destination address field stores "255," indicating broadcast communication. The message field stores data in which each character of "SEARCH" is expressed in 1-byte character code, indicating that the packet is a search packet, and the message byte count field stores "6."

The surrounding wireless devices 100 that receive the search packet return an ACK packet and also add the wireless device 100 to a forwarding table (described later) as appropriate depending on the radio wave strength at the time of receiving the search packet.
This allows message packets to be transmitted via the newly added wireless device 100.

3. Data stored in the storage unit
<3-1. Forwarding table>
The forwarding table stored in storage unit 100d of wireless device 100 will be described with reference to FIG.
The forwarding table stores a device address for identifying the nearby wireless device 100 to which the packet is to be forwarded, and the radio wave strength (RSSI (Received Signal Strength Indicator) value) measured when a packet is received from the nearby wireless device 100, in association with each other.

As an example, Figure 4 shows the forwarding table stored in memory unit 100d of wireless device D shown in Figure 1.

The forwarding table can register up to five nearby wireless devices 100. Furthermore, data is stored in the forwarding table in descending order of RSSI value, i.e., in descending order of radio wave strength.

In the example shown in Figure 4, the wireless device 100 with the strongest radio wave intensity in communication with wireless device D is wireless device B (device address = 002), and its RSSI value is -75 dBm.

The wireless device 100 with the second strongest radio wave intensity is wireless device A (device address = 001), and its RSSI value is -77 dBm.

Furthermore, the wireless device 100 with the third strongest radio wave is wireless device E (device address = 005) and its RSSI value is -82 dBm, the wireless device 100 with the fourth strongest radio wave is wireless device F (device address = 006) and its RSSI value is -83 dBm, and the wireless device 100 with the fifth strongest radio wave is wireless device C (device address = 003) and its RSSI value is -89 dBm.

Note that the maximum number of wireless devices 100 is not necessarily registered in the forwarding table. For example, this may be the case if there are only three nearby wireless devices 100. Furthermore, wireless devices 100 with RSSI values below a threshold (e.g., -90 dBm) are not registered in the forwarding table because they are unlikely to be able to provide good wireless communication.

When a wireless device 100 forwards a message packet, it uses unicast communication to forward the packet to all wireless devices 100 stored in the forwarding table. The forwarding process is performed in order, starting with the wireless device 100 with the highest RSSI value.

In the example shown in Figure 4, if wireless device D receives a message packet that is not addressed to itself, it first forwards the message packet to wireless device B via unicast communication.

Next, wireless device D forwards a message packet to wireless device A via unicast communication, and then forwards a message packet to wireless device E via unicast communication.

In this way, transfer processing using unicast communication is also performed for wireless device F and wireless device C.

<3-2. Received packet history>
The storage unit 100d of the wireless device 100 stores a history of received message packets to avoid or suppress congestion.

The received packet history may store the entire message packet. In this embodiment, to reduce the storage capacity of the memory unit 100d, only the source address and sequential number of the message packet are stored.

The number of message packets stored as received packet history is preferably determined from the perspective of both the storage capacity of memory unit 100d and avoiding congestion. Here, the number of message packets stored in memory unit 100d is set to 10.

An example of the received packet history stored in the memory unit 100d of wireless device D is shown in Figure 5.

The table shown in Figure 5 is a history of message packets received by wireless device D, with data at the top of the table indicating older message packets. Message packets stored in the received packet history are message packets that have already been forwarded by wireless device D. Wireless device D compares a newly received message packet with the information in the received packet history to determine whether the newly received message packet can be forwarded.

When we look at message packets sent from wireless device A, whose device address is "001," as the source wireless device 100, four records are stored in the received packet history shown in Figure 5.

Wireless device D receives a message packet generated by wireless device A with sequential number "254", then receives message packets with sequential numbers "255" and "256", and then receives a message packet with sequential number "001".

In this way, the sequential number returns to "001" after "256".

By setting the maximum value of the sequential number to a relatively large number, it takes time for the sequential numbers to go through a cycle, reducing the possibility of different message packets being mistakenly determined to be the same and discarded.

<3-3. Setting data>
The storage unit 100d of the wireless device 100 also stores setting data for optimal communication using the wireless mesh network.

Here, we will explain the station address, number of retransmissions, search packet transmission interval, RSSI threshold, and TTL value as part of the configuration data.

The local station address setting data is assigned a different value for each wireless device 100 and is synonymous with the device address described above.

The retransmission count setting data specifies the number of times to retransmit a message packet if an ACK packet sent from the destination wireless device 100 cannot be confirmed when the message packet is sent using unicast communication. The retransmission count is used not only when retransmitting a message packet, but also when forwarding a received message packet.

By setting the number of retransmissions to a value greater than or equal to 1, the likelihood that the message packet will reach the destination wireless device 100 can be increased. It is also possible to configure the number of retransmissions to be one more than the value set as the configuration data for the number of retransmissions. This means that even if "0" is set, one retransmission will still be performed, thereby improving the likelihood that the message packet will reach the destination wireless device 100.

The search packet transmission interval setting data is a setting for the periodic transmission of search packets. For example, if the unit of the setting data is "hours" and "1" is set, a search packet will be transmitted via broadcast communication to surrounding wireless devices 100 every hour.

Note that if "0" is set as the search packet transmission interval, it is treated as a setting that does not require periodic transmission of search packets. In other words, the setting data for the search packet transmission interval is also used to set whether or not to transmit search packets periodically.

The RSSI threshold setting data sets the threshold for whether or not to register surrounding wireless devices 100 in the forwarding table.

The TTL value setting data is set to a numerical value to be stored in the TTL field of a message packet. The TTL value can be set to any value each time a message packet is generated, but by using this setting data, the user can avoid the trouble of setting the TTL value each time a message packet is generated.

The range of values that can be set as the TTL value is, for example, a maximum of 15, taking into consideration congestion suppression. Of course, if the size of the wireless mesh network is large and the physical area in which wireless devices 100 are installed is wide, the upper limit of the value that can be set as the TTL value may be set to 16 or more.

The setting data stored in the storage unit 100d also includes various other data such as setting values for channels used in wireless communication.

<4. Flowchart>
<4-1. Adding wireless devices>
The process executed by a wireless device 100 that is newly added to a wireless mesh network or a restarted wireless device 100 will be described with reference to Fig. 6. That is, the process shown in Fig. 6 is the process executed by the wireless device 100 after startup.

After powering on, the communication control unit 100a of the wireless device 100 transmits a search packet using broadcast communication in step S101.

This search packet is received by other wireless devices 100 located within a specified distance, and an ACK packet is sent back as appropriate. Details will be described later.

In step S102, the communication control unit 100a determines whether an ACK packet has been received. If it is determined that an ACK packet has been received, the communication control unit 100a performs a forwarding table update process in step S103. This forwarding table update process is executed upon reception of an ACK packet, and the process content differs depending on the radio wave strength at the time the ACK packet is received.
The wireless device 100 that is the source of the ACK packet and is the target of the determination of whether or not to register it in the forwarding table is referred to as the "target wireless device 100."

This will be explained in detail with reference to Figure 7.

In the forwarding table update process, in step S201, the communications control unit 100a determines whether the RSSI value at the time of packet reception is greater than or equal to a threshold value (-90 dBm in the example described above).

If it is determined that the RSSI value is equal to or greater than the threshold, the communication control unit 100a compares the RSSI values in step S202 to determine whether the RSSI value for the wireless device 100 being processed is within the top five RSSI values stored in the forwarding table.

If it is determined that the wireless device 100 is in the top five in the forwarding table, the communication control unit 100a decides to register the wireless device 100 being processed in the forwarding table.

When it is decided to register the wireless device 100 to be processed in the forwarding table, the communication control unit 100a determines in step S203 whether the wireless device 100 to be processed has already been registered in the forwarding table.

If it is determined that registration has been completed, the communication control unit 100a updates the record for the wireless device 100 being processed by updating the RSSI value in step S204, and then ends the forwarding table update process.

On the other hand, if it is determined in step S203 that the wireless device 100 being processed is not registered in the forwarding table, the communication control unit 100a registers the wireless device 100 being processed in the forwarding table in step S205 and ends the forwarding table update process.

In the registration process of step S205, if the number of records already registered in the forwarding table is four or less, the wireless device 100 to be processed is newly added to the forwarding table. If the number of registered records is the upper limit of five, the record of the wireless device 100 with the lowest RSSI value is deleted and the wireless device 100 to be processed is registered. At this time, the five records including the wireless device 100 to be processed are appropriately sorted in descending order of RSSI value.

If it is determined in step S202 that the RSSI value is not within the top five in the forwarding table, the communication control unit 100a determines in step S206 whether the wireless device 100 to be processed is already registered in the forwarding table.

If it is determined that the record has been registered, the communication control unit 100a deletes the record for the wireless device 100 being processed from the forwarding table in step S207, and ends the forwarding table update process.
By performing this deletion process, only wireless devices 100 that can always guarantee a certain level of communication quality are registered in the forwarding table.

If it is determined in step S206 that the wireless device 100 to be processed is not registered in the forwarding table, the communication control unit 100a terminates the forwarding table update process shown in Figure 7.

Also, if it is determined in step S201 that the RSSI value at the time of packet reception is less than the threshold, the determination process of step S206 is executed, and the deletion process of step S207 is executed as appropriate depending on the determination result.

Returning to the description of FIG.
After completing the forwarding table update process, the communication control unit 100a returns to step S102 and determines whether an ACK packet has been received from another wireless device 100.

The processing of steps S102 and S103 can be repeated as many times as there are wireless devices 100 within the range of the search packet transmitted from the wireless device 100 (within the communication range described above). Finally, the top five wireless devices 100 with the highest RSSI values among the surrounding wireless devices 100 are registered in the forwarding table.

Of course, if there are few wireless devices 100 within the communication range, the number of wireless devices registered in the forwarding table will be fewer.

If it is determined in step S102 that an ACK packet has not been received, the communication control unit 100a proceeds to step S104 and waits until a predetermined time has elapsed. Here, the predetermined waiting time is based on the value of the transmission interval of the search packet, which is one of the setting data stored in the memory unit 100d. Specifically, it is set to one hour, 24 hours, etc.

If it is determined that the predetermined time has elapsed, the communication control unit 100a returns to step S101 and transmits the search packet again. Note that the forwarding table may be cleared before transmitting the search packet. This prevents information about an inappropriate wireless device 100 as a forwarding destination from remaining in the forwarding table.

If it is determined that the predetermined time has not elapsed, the communication control unit 100a repeats the process of step S104.
If the value of the search packet transmission interval is set to "0", the determination result in step S104 is always "No".

<4-2. Receiving a search packet>
An example of the process executed by the communication control unit 100a when the wireless device 100 receives a search packet is shown in Fig. 8. Note that the same steps as those in Figs. 6 and 7 are given the same step numbers, and descriptions thereof will be omitted where appropriate.

In step S301, the communication control unit 100a of the wireless device 100 determines whether a search packet has been received. If it is determined that a search packet has not been received, the wireless device 100 executes the process of step S301 again.

On the other hand, if it is determined that a search packet has been received, the communication control unit 100a performs processing from step S201 onwards that is substantially the same as the forwarding table update processing shown in Figure 7. The difference from the forwarding table update processing is that an ACK packet is returned depending on the conditions.

Specifically, in step S201, the communication control unit 100a determines whether the RSSI value at the time the search packet is received is greater than or equal to a threshold value.

If it is determined that the RSSI value is equal to or greater than the threshold, the communication control unit 100a returns an ACK packet in step S302. In response, the wireless device 100 that transmitted the search packet executes the processing from step S102 onwards in Figure 6.

Next, in step S202, the communication control unit 100a determines whether the RSSI value is within the top five in the forwarding table, and if it determines that it is within the top five, it executes the processes of steps S203 to S205, and if it determines that it is not within the top five, it executes the processes of steps S206 to S207.
This causes the forwarding table to be updated.

Furthermore, if it is determined in step S201 that the RSSI value is less than the threshold, the processes of steps S206 and S207 are executed, and the corresponding record is deleted from the forwarding table as appropriate.

After performing each process, the communication control unit 100a returns to step S301.

8, when wireless device 100 receives a search packet, it does not transmit an ACK packet if the RSSI value is less than the threshold. By not transmitting an ACK packet, the search packet is not registered in the forwarding table of wireless device 100 that is the sender of the search packet.
If a wireless device 100 that cannot perform good wireless communication is registered in the forwarding table, the number of retransmissions of message packets will increase, resulting in a waste of communication bandwidth. This can be prevented by not returning an ACK packet when the RSSI value is below the threshold.

<4-3. Sending message packets>
An example of the processing executed by the communication control unit 100a when the wireless device 100 transmits a message packet is shown in Fig. 9. Note that the same steps as those in Figs. 6 and 7 are given the same step numbers, and descriptions thereof will be omitted where appropriate.

In step S401, the communication control unit 100a of the wireless device 100 determines whether an opportunity to transmit a message packet has arrived. For example, it determines that a transmission opportunity has arrived when a user performs an operation to transmit a message packet, or when a predetermined time has arrived to acquire and transmit a sensor value from a sensor device. If it determines that a transmission opportunity has not arrived, the communication control unit 100a repeats the processing of step S401.

On the other hand, if it is determined that a transmission opportunity has arrived, the communication control unit 100a performs processing to generate and transmit a message packet in step S402. This transmission processing uses unicast communication targeted at the wireless device 100 with the highest RSSI value in the forwarding table.

Next, in step S102, the communications control unit 100a determines whether an ACK packet has been received.

If it is determined that an ACK packet has been received, the communication control unit 100a performs forwarding table update processing in step S103.

On the other hand, if it is determined that an ACK packet has not been received, the communication control unit 100a determines in step S404 whether the number of retransmissions is less than the threshold. If it is determined that the number of retransmissions has not reached the threshold, the communication control unit 100a returns to step S402 and retransmits the message packet.

If it is determined that the number of retransmissions has reached the threshold, it is highly likely that the message packet, even if transmitted a predetermined number of times, did not reach the destination wireless device 100. If such a wireless device 100 is registered in the forwarding table, unnecessary wireless communication will occur thereafter.
Therefore, in step S207, the communication control unit 100a performs processing to delete the record of the wireless device 100 from the forwarding table.

After processing in step S207, or after the forwarding table update processing in step S103, the communication control unit 100a checks in step S403 whether there are any unselected transmission targets, i.e., records in the forwarding table that have not been selected as the destination of the message packet.

If it is determined that there is an unselected destination, the communication control unit 100a returns to step S402 and transmits the message packet to the next destination wireless device 100.

On the other hand, if it is determined that there are no unselected transmission targets, i.e., if it is determined that message packets have been sent to all wireless devices 100 stored in the forwarding table, the communication control unit 100a returns to step S401 and waits until the next opportunity to send a message packet arrives.

In the example shown in Figure 9, message packets are first transmitted to the wireless device 100 with the highest RSSI value in the forwarding table until an ACK packet can be received or the number of retransmissions reaches a threshold. Then, the wireless device 100 with the next highest RSSI value is selected as the new transmission target, and message packets are transmitted to the wireless device 100 until an ACK packet can be received or the number of retransmissions reaches a threshold.

In other words, the process is completed for each wireless device 100 to which transmission is to be made, but other methods may also be used.

For example, a message packet is sent once to each of the multiple wireless devices 100 stored in the forwarding table. Then, a second message packet is sent only to those wireless devices 100 that did not receive an ACK packet.

By adopting such a processing order, the first message packet can be sent to each wireless device 100 quickly, thereby speeding up the timing at which the message packet reaches the final destination wireless device 100.

<4-4. Message packet transfer>
An example of the processing executed by the communication control unit 100a when the wireless device 100 receives a message packet is shown in Fig. 10. Note that the same steps as those in Figs. 6, 7, 8, and 9 are given the same step numbers, and descriptions thereof will be omitted where appropriate.

In step S501, the communication control unit 100a of the wireless device 100 determines whether a message packet has been received. If it determines that a message packet has not been received, the communication control unit 100a repeats the processing of step S501.

On the other hand, if it is determined that a message packet has been received, the communication control unit 100a first returns an ACK packet to the wireless device 100 that sent the message packet in step S302.

Next, the communication control unit 100a performs forwarding table update processing in step S103, and then determines in the following step S502 whether the destination of the received message packet is its own station.

If the destination of the message packet is the local station, the communication control unit 100a captures the received message packet in step S503 and performs the appropriate processing.

On the other hand, if the destination of the message packet is not the local station, i.e., if the final destination address is not the local station address, the communication control unit 100a performs processing from step S504 onwards to check for duplication of the received message packet.

Duplicate confirmation is a process that checks whether a message packet identical to the one received this time has already been received. For example, wireless device D shown in Figure 1 may receive the same message packet not only from wireless device A, but also from wireless device B, wireless device C, etc.

Forwarding the same message packet every time it is received would increase unnecessary communication and cause congestion. Therefore, a duplicate check is performed to check whether the received message packet has already been received.

When checking for duplication, first, in step S504, it is determined whether there is a received packet history with a matching source address. The received packet history may contain, for example, around 10 histories, and it is determined whether each history matches the source address of the message packet received this time (for example, the wireless device 100 that generated the message packet).

If it is determined that a received packet history with a matching source address exists, the communications control unit 100a proceeds to step S505, where it further determines whether a received packet history with a matching sequential number exists. In other words, it determines whether a received packet history with a matching source address and sequential number exists.

If a matching history exists, the message packet received this time has already been forwarded, so the communication control unit 100a discards the message packet received this time in step S506 and returns to step S501.

If it is determined in step S504 that there is no received packet history with a matching source address, or if it is determined in step S505 that there is no received packet history with a matching sequential number, the communications control unit 100a determines in step S507 whether the TTL value of the currently received message packet is 0.

If the TTL value is determined to be 0, the message packet is discarded in step S506.

On the other hand, if it is determined that the TTL value is 1 or greater, the communications control unit 100a subtracts the TTL value in step S508, and then in the following step S509, stores the source address and sequential number of the currently received message packet as received packet history.

Note that if step S507 determines that the TTL value is 0, the received packet history is not stored. This is because the message packet received this time has not been forwarded. In other words, if the same message packet is received subsequently and the TTL value of that message packet is 1 or greater, the forwarding process will be carried out normally.

Furthermore, in the duplication check in steps S504 to S509, a process is executed to check whether a message packet with matching source address and sequential number has been received in the past, but it may also be determined whether the destination address matches, thereby reducing the possibility of erroneously determining that different message packets are the same.
When determining whether or not the destination addresses match, the destination address item is also stored as the received packet history in addition to the source address and sequential number shown in FIG.

After completing the process of registering the received packet in the received packet history in step S509, the communication control unit 100a forwards the message packet in step S510. The wireless device 100 selected as the forwarding destination here is the wireless device 100 with the highest RSSI value in the forwarding table. However, the wireless device 100 that was the sender (forwarder) when the current message packet was received is excluded from the selection of forwarding destination. In other words, there is no point in returning the message packet that was sent as is.

Next, in step S102, the communication control unit 100a determines whether an ACK packet has been received. The subsequent processing is substantially the same as the example shown in Figure 9, so the explanation will be simplified.

If it is determined that an ACK packet has been received, the communication control unit 100a performs forwarding table update processing in step S103.

On the other hand, if it is determined that an ACK packet has not been received, the communication control unit 100a determines in step S404 whether the number of retransmissions is less than the threshold value, and if the number of retransmissions has not reached the threshold value, the process returns to step S510 and the message packet is transferred again.

If it is determined that the number of retransmissions has reached the threshold, the communication control unit 100a performs processing to delete the record of the wireless device 100 that is the forwarding destination from the forwarding table in step S207.

After processing step S207 or step S103, the communication control unit 100a checks in step S511 whether there are any unselected forwarding targets. If there are, the process returns to step S510, where it selects a wireless device 100 as the next forwarding destination and forwards the message packet. However, even in the processing of step S511, the wireless device 100 that was the sender (forwarder) when the current message packet was received is excluded from the selection of forwarding destinations.

If it is determined in step S511 that there are no unselected forwarding targets, i.e., if it is determined that the message packet has been forwarded to all wireless devices 100 stored in the forwarding table, the communication control unit 100a returns to step S501 and waits until the next message packet is received.

10, similarly to FIG. 9, a message packet may be transferred to each wireless device 100 for the first time, and then retransferred to each wireless device 100 as appropriate.

5. Modified Examples
In the message packet forwarding process shown in FIG. 10, the wireless communication channel to be used may be changed each time a message packet is retransmitted to the same wireless device 100.
For example, when there are three channels in use in a wireless mesh network, it may be possible that the channel available for reception by the destination wireless device 100 is unknown. In preparation for such a case, the channel to be used can be changed each time a message packet is retransferred, thereby increasing the likelihood that the transferred message packet will be received by the destination wireless device 100.

Similarly, when sending message packets as shown in Figure 9, the channel may be changed each time a retransmission is made.

Each record stored in the received packet history may be configured to be deleted from the received packet history after a predetermined time (e.g., several days or one week) has elapsed since it was stored. This reduces the possibility of erroneously determining that different message packets are the same message packet. Alternatively, the maximum number of records stored in the received packet history may be set to a large number (e.g., 100). This makes it possible to appropriately check for duplication even when many message packets are received in a short period of time.

<6. Summary>
As explained in the above examples, the wireless devices 100 (A, B, C, D, E, F, G, H) are wireless devices 100 that constitute a wireless mesh network to which message packets are forwarded, and include a communication control unit 100a that controls communication, a transmitting unit 100b that transmits message packets, a receiving unit 100c that receives message packets, and a memory unit 100d that stores information about the radio wave strength of other wireless devices 100 to which the message packets are to be sent as a forwarding table, and the communication control unit 100a forwards the received message packet to other wireless devices 100 using unicast communication in order of radio wave strength (RSSI value) first.
In other words, instead of a routing method in which a forwarding path is determined in advance using a routing table or the like when a message packet is sent, the message packet is sent and forwarded in accordance with the communication situation at the time using the information in the forwarding table stored in memory unit 100d.
Therefore, even if radio interference occurs in part of the wireless mesh network, the forwarding table is rewritten to take into account the radio interference as message packets are sent and received, allowing message packets to be sent via an appropriate route. In other words, good fault tolerance can be achieved.
Such a configuration is suitable for a system that collects data once a day or once every few hours, for example.
Furthermore, since the transfer is performed in order from the wireless device 100 with the strongest radio wave, priority is given to good wireless communication, and the data can be delivered to the target wireless device 100 quickly.
Furthermore, since users do not need to create routing tables themselves, convenience can be improved.
The data stored in the storage unit 100d for performing such transfer processing is the transfer table shown in Fig. 4. The transfer table is approximately 30 bytes at most for five wireless devices 100. Therefore, appropriate transfer processing can be performed while suppressing the storage capacity of the storage unit 100d.

The forwarding table stored in the storage unit 100d may also store information about wireless devices 100 whose radio field strength (RSSI value) is equal to or greater than a threshold.
By appropriately setting the threshold, only information about wireless devices 100 that can forward messages is stored in the forwarding table. Therefore, unnecessary forwarding processing of message packets can be reduced, and bandwidth pressure in the communication environment can be avoided. Furthermore, by suppressing unnecessary forwarding of message packets, the power consumption of the wireless device 100 can be reduced. This is effective when the wireless device 100 is battery-powered.

Furthermore, the forwarding table stored in the storage unit 100d may store information about a predetermined number of wireless devices 100.
By limiting the amount of information stored in the forwarding table, it is possible to reduce the number of forwarding operations when forwarding to all wireless devices 100 stored in the forwarding table, thereby avoiding bandwidth pressure in the communication environment.

When the communication control unit 100a of the wireless device 100 obtains information on the radio wave strength (RSSI value) of another wireless device 100 that is not stored in the forwarding table, the communication control unit 100a performs a process of comparing the radio wave strength with the radio wave strength of another wireless device 100 that is already stored in the forwarding table, and may manage the forwarding table so that the other wireless device 100 with the lowest radio wave strength as a result of the comparison process is not stored in the forwarding table.
For example, each time a message packet is forwarded, information on the radio wave strength of other wireless devices 100 that are not stored in the forwarding table can be obtained. Then, the forwarding table can be managed (records can be swapped) so that information on wireless devices 100 that are more appropriate as forwarding destinations is stored in the forwarding table. This allows message packets to be sent to appropriate wireless devices 100, reducing the possibility of packet loss, whereby a message packet does not reach the intended wireless device 100.

The communication control unit 100a of the wireless device 100 may delete information about another wireless device 100 that is the target of unicast communication from the forwarding table if it is unable to receive an acknowledgement packet (ACK packet) from the other wireless device 100.
This allows a wireless device 100 or the like that is unable to send or receive message packets due to a malfunction or the like to be deleted from the forwarding table, thereby preventing unnecessary forwarding processing from being executed.

The memory unit 100d of the wireless device 100 stores the message packet received by the receiving unit 100c as a received packet history, and the communication control unit 100a determines whether the received message packet can be forwarded when the receiving unit 100c receives the message packet.In determining whether the message packet can be forwarded, if the received packet history contains information that identifies another wireless device 100 that is the sender of the received message packet and the sequential number of the message packet matches, it may be determined that the message packet cannot be forwarded.
The sequential number is, for example, a serial number assigned to a message packet generated by wireless device 100, and is assigned independently for each wireless device 100. Since it takes a fairly long time for the sequential numbers to go through one cycle, in a situation where the received packet history is updated appropriately, if a message packet whose sender (generator) wireless device 100 and sequential number both match is stored in the received packet history, it is highly likely that the message packet has already been forwarded. Therefore, by canceling the forwarding process for the currently received message packet, unnecessary forwarding processes can be reduced, and bandwidth pressure in the communication environment can be avoided.
Furthermore, if only the source address and sequential number are recorded as the received packet history, the amount of data stored in the storage unit 100d for the received packet history will be approximately 60 bytes at most, even if 10 message packets are recorded. This makes it possible to effectively suppress unnecessary transfer processing while suppressing the amount of data used by the storage unit 100d.

The communication control unit 100a of the wireless device 100 may transmit a search packet using broadcast communication at startup and update the forwarding table based on an acknowledgement packet (ACK packet) received from another wireless device 100 in response to the search packet.
As a result, a wireless device 100 newly added to the wireless mesh network is registered appropriately in the forwarding tables of other surrounding wireless devices 100 by transmitting a search packet after startup. Therefore, the newly added wireless device 100 can transmit and forward message packets thereafter without any problems.
In other words, a new wireless device 100 can be easily incorporated into a wireless mesh network without performing complicated initial setting processing.

The communication control unit 100a of the wireless device 100 may periodically transmit a search packet.
The radio wave strength between wireless devices 100 can change from moment to moment due to changes in the communication environment, malfunctions or maintenance of wireless devices 100, etc. Therefore, by having the communication control unit 100a periodically send search packets (every hour, every few hours, or every day, etc.), the forwarding table can be periodically updated to the latest state. Therefore, message packets can be appropriately forwarded even if the communication environment, etc. changes.

The wireless device 100 may be configured to not periodically transmit search packets.
In situations where changes in the communication environment are unlikely to occur, the transmission of search packets may cause bandwidth congestion in the communication environment. With this configuration, it is possible to set whether or not to periodically transmit search packets, so by setting an appropriate setting depending on the environment, it is possible to prevent unnecessary packet transmission.
For example, if wireless device 100 is operated so that no data is sent or received at night, the setting can be switched to one that does not send search packets in the evening before, and then switched back to one that sends search packets the next morning, thereby suppressing the sending and receiving of search packets and reducing the power consumption of wireless device 100.

A network system comprising multiple wireless devices 100 includes a communication control unit 100a for controlling communications in each wireless device 100, a transmission unit 100b for transmitting message packets, a reception unit 100c for receiving message packets, and a storage unit 100d for storing information on the radio wave strength of other wireless devices 100 to which message packets are to be sent as a forwarding table. When forwarding a received message packet to other wireless devices 100, the communication control unit 100a of each wireless device 100 uses unicast communication to forward the packet in descending order of radio wave strength (RSSI value) to the wireless device 100.

The control method executed by the wireless device 100, which is equipped with a communication control unit 100a that controls communication, a transmitting unit 100b that transmits message packets, a receiving unit 100c that receives the message packets, and a memory unit 100d that stores information about the radio wave strength of other wireless devices 100 to which the message packets are to be sent as a forwarding table, is a control method in which, when forwarding a received message packet to other wireless devices 100, the message packet is forwarded using unicast communication in order of radio wave strength (RSSI value) to the wireless device 100.
A program for implementing such a control method in wireless device 100 can be pre-recorded on a hard disk drive (HDD) or a ROM in a microcomputer having a central processing unit (CPU) as a recording medium built into a computer or other device. Alternatively, the program can be temporarily or permanently stored (recorded) on a removable recording medium such as a flexible disk, a CD-ROM (Compact Disk Read Only Memory), a Magneto Optical (MO) disk, a Digital Versatile Disc (DVD), a Blu-ray Disc (registered trademark), a magnetic disk, a semiconductor memory, or a memory card. Such removable recording media can be provided as a so-called package software.
Such a program can be installed onto a personal computer or the like from a removable recording medium, or can be downloaded from a download site via a network such as a LAN (Local Area Network) or the Internet.

Such a network system, control method, and program can also achieve the various effects described above.

The above examples can be combined in any way, and even when various combinations are used, the various effects described above can be achieved.

100 Wireless devices A to H Wireless device 100a Communication control unit 100b Transmitting unit 100c Receiving unit 100d Storage unit

Claims (11)

A wireless device constituting a wireless mesh network in which message packets are transferred,
a communication control unit that controls communication;
a transmitting unit that transmits a packet determined to be either the message packet or the search packet;
a receiving unit that receives the packet;
a storage unit in which information about the radio wave strength of other wireless devices to which the message packet is to be transmitted is stored as a forwarding table , the information being information not associated with the wireless device that is the final destination of the message packet ;
The communication control unit uses the forwarding table to forward all of the received message packets that have been decided to be forwarded to other wireless devices using unicast communication in order of radio wave strength, regardless of the wireless device that is the final destination of the message packets . The wireless device according to claim 1 , wherein the forwarding table stores information about wireless devices whose radio wave strength is equal to or greater than a threshold. The wireless device of claim 2 , wherein the forwarding table stores information for a predetermined number of wireless devices. The communication control unit
When obtaining information on the radio wave strength of another wireless device that is not stored in the forwarding table, a process of comparing the information with the radio wave strength of another wireless device that is stored in the forwarding table is performed;
The wireless device according to claim 3 , wherein the forwarding table is managed so that the other wireless device with the lowest radio wave intensity as a result of the comparison process is not stored in the forwarding table. The wireless device according to claim 1 , wherein the communication control unit deletes information about another wireless device that is a target of the unicast communication from the forwarding table when an acknowledgement packet is not received from the other wireless device. the storage unit stores the message packets received by the receiving unit as a received packet history;
the communication control unit determines whether or not the received message packet can be forwarded when the receiving unit receives the message packet;
The wireless device according to claim 1, wherein in determining whether or not the message packet can be forwarded, if the received packet history contains information that identifies another wireless device that is the sender of the received message packet and information in which the sequential number of the message packet matches, the wireless device determines that the message packet cannot be forwarded. the communication control unit transmits the search packet using broadcast communication at startup;
The wireless device according to claim 1 , wherein the forwarding table is updated based on an acknowledgement packet received from another wireless device in response to the search packet. The wireless device according to claim 7 , wherein the communication control unit periodically transmits the search packet. The wireless device according to claim 8 , wherein the wireless device can be configured to not periodically transmit the search packets. A network system configured by a plurality of wireless devices,
Each wireless device
a communication control unit that controls communication;
a transmitter for transmitting a packet determined to be either a message packet or a search packet;
a receiving unit that receives the packet;
a storage unit in which information about the radio wave strength of other wireless devices to which the message packet is to be transmitted is stored as a forwarding table , the information being information not associated with the wireless device that is the final destination of the message packet ;
The communication control unit uses the forwarding table to forward all received message packets that have been decided to be forwarded to other wireless devices using unicast communication in order of radio wave strength, regardless of the wireless device that is the final destination of the message packet . a communication control unit that controls communication;
a transmitter for transmitting a packet determined to be either a message packet or a search packet;
a receiving unit that receives the packet ;
a storage unit that stores information about radio wave strength of other wireless devices that are the transmission destinations of the message packet as a forwarding table that is not linked to the wireless device that is the final destination of the message packet ,
A control method in which, for all of the received message packets that have been decided to be forwarded to other wireless devices , the message packets are forwarded using unicast communication in order of radio wave strength using the forwarding table, regardless of the wireless device that is the final destination of the message packets .