JP7629335B2 - Communication system and wireless communication terminal - Google Patents

Description

The present invention relates to a communication system and a wireless communication terminal.

One type of wireless communication system is a telemetry system (see, for example, Patent Document 1). A telemetry system includes a parent unit and multiple child units. In the wireless telemetry system of Patent Document 1, when a child unit is unable to communicate with a predetermined communication partner, it selects another child unit located within its own communication range as a detour destination terminal (relay terminal), forms a detour route between the child unit and the detour destination terminal, and transmits a message to the detour destination terminal.

JP 2018-207250 A

However, the slave unit may be unable to communicate with the detouring terminal due to some reason (for example, an increase in traffic volume around the slave unit, or a malfunction). In this case, the slave unit cannot make a detouring. With the wireless telemetry system of Patent Document 1, it is not possible to know in advance which wireless communication terminal cannot be detouring when communication with a predetermined communication partner becomes impossible. Therefore, there is room for improvement in the wireless telemetry system of Patent Document 1.

The present invention has been made in consideration of the above problems, and its purpose is to provide a communication system and a wireless communication terminal that can identify in advance wireless communication terminals that cannot be bypassed when communication with a predetermined communication partner becomes impossible.

The communication system of the present invention includes a plurality of lower wireless communication terminals and an upper wireless communication terminal that communicates with the plurality of lower wireless communication terminals. Each of the plurality of lower wireless communication terminals broadcasts a response request signal, receives response information from other lower wireless communication terminals that are detour destination candidate terminals within the wireless communication range of the terminal, and transmits the received response information to the upper wireless communication terminal. The response information includes information unique to each of the other lower wireless communication terminals. The upper wireless communication terminal includes a storage unit and a processing unit. The storage unit stores the response information received from each of the plurality of lower wireless communication terminals. The processing unit identifies, from among the plurality of lower wireless communication terminals, a first lower wireless communication terminal that has not been able to receive the response information from each other based on the response information stored in the storage unit and the current response information received from each of the plurality of lower wireless communication terminals, and identifies, from among the identified first lower wireless communication terminals, a second lower wireless communication terminal that cannot communicate with the corresponding detour destination candidate terminal.

The wireless communication terminal of the present invention communicates with a plurality of lower wireless communication terminals. Each of the plurality of lower wireless communication terminals broadcasts a response request signal, receives response information from other lower wireless communication terminals that are detour destination candidate terminals within the wireless communication range of the terminal, and transmits the received response information to the wireless communication terminal. The response information includes information unique to each of the other lower wireless communication terminals. The wireless communication terminal includes a storage unit and a processing unit. The storage unit stores the response information received from each of the plurality of lower wireless communication terminals. The processing unit identifies, from among the plurality of lower wireless communication terminals, a first lower wireless communication terminal that has not been able to receive the response information from each other based on the response information stored in the storage unit and the current response information received from each of the plurality of lower wireless communication terminals, and identifies, from among the identified first lower wireless communication terminals, a second lower wireless communication terminal that cannot communicate with the corresponding detour destination candidate terminal.

The communication system and wireless communication terminal of the present invention make it possible to identify in advance wireless communication terminals that cannot be bypassed when communication with a predetermined communication partner becomes impossible.

1 is a diagram showing a communication system according to a first embodiment of the present invention; 2 is a block diagram showing a configuration of a slave unit included in the communication system according to the first embodiment of the present invention. FIG. 1 is a block diagram showing a configuration of a parent device according to a first embodiment of the present invention; 5 is a flowchart showing a process executed by a control unit of the parent device according to the first embodiment of the present invention. 6 is a flowchart showing a second determination process, a second notification process, a third determination process, and a third notification process executed by a control unit of the parent device according to the first embodiment of the present invention. 11 is a sequence diagram showing a beacon collection process executed by a control unit of a master device. FIG. 11 is a sequence diagram showing a detouring destination candidate search process executed by a control unit of the first handset; FIG. 11 is a sequence diagram showing a detouring destination candidate search process executed by a control unit of the second handset; FIG. 13 is a sequence diagram showing a detouring destination candidate search process executed by a control unit of the third handset; FIG. 13 is another sequence diagram showing the detouring destination candidate search process executed by the control unit of the second handset. FIG. 13 is another sequence diagram showing the detouring destination candidate search process executed by the control unit of the third handset. FIG. 13 is a diagram showing a previous beacon collection result stored in a storage unit of the parent device. FIG. 13 is a diagram showing beacon collection results currently received by the master unit from each of the first to third slave units. FIG. 6 is a sequence diagram showing a first determination process, a setting process, and a first notification process executed by a control unit of the parent device; FIG. 11 is a sequence diagram showing a second determination process and a second notification process executed by a control unit of the parent device. FIG. 13 is a sequence diagram showing a third determination process and a third notification process executed by a control unit of the parent device. FIG. FIG. 11 is a diagram showing a communication system according to a second embodiment of the present invention.

Below, an embodiment of the communication system and wireless communication terminal of the present invention will be described with reference to the drawings (Figs. 1 to 16). Note that where explanations overlap, they may be omitted as appropriate. Also, in the drawings, the same or equivalent parts will be given the same reference symbols and explanations will not be repeated.

[Embodiment 1]
A first embodiment of the present invention will be described below with reference to Figs. 1 to 15. First, a communication system 100 according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing the communication system 100 according to the present embodiment. In the present embodiment, the communication system 100 is a telemetry system. Hereinafter, the communication system 100 may be referred to as the "telemetry system 100". As shown in Fig. 1, the telemetry system 100 includes a master unit 21, a plurality of slave units 22, and a center device 11 that manages the master unit 21 and the plurality of slave units 22. The center device 11 is an example of a management device.

The center device 11 is communicatively connected to the wide area wireless network Ne via a center-side network control device 12. The center-side network control device 12 is communicatively connected to the base unit 21 via the wide area wireless network Ne. The center-side network control device 12 is provided, for example, in a public network of a telecommunications carrier. The center-side network control device 12 controls communication between the base unit 21 and the center device 11 via the wide area wireless network Ne.

The wide area wireless network Ne is, for example, a PHS (Personal Handy-phone System) network, a FOMA (Freedom Of Mobile Multimedia Access) network, an LTE (Long Term Evolution) network, a 4G (fourth generation mobile communication system) network, or a 5G (fifth generation mobile communication system) network.

In the telemetry system 100, communication between the parent unit 21 and the child unit 22, and between the child units 22, is performed using, for example, specific low-power radio (special low-power radio). The frequency band for communication using special low-power radio is, for example, the 920 MHz band. Hereinafter, communication using special low-power radio may be referred to as "special low-power radio communication."

The communication partner (wireless communication terminal) of the parent device 21 is determined in advance. Similarly, the communication partner (wireless communication terminal) of the child device 22 is determined in advance. Therefore, the communication route between the parent device 21 and the child device 22 is determined in advance.

Specifically, the parent device 21 and the child device 22 store adoption information that specifies the communication partner (wireless communication terminal) of the parent device 21. The parent device 21 communicates with the communication partner specified in the adoption information. Similarly, the child device 22 communicates with the communication partner specified in the adoption information. Hereinafter, the communication partner (wireless communication terminal) specified by the adoption information may be referred to as an "adoption terminal."

In the example shown in FIG. 1, the multiple handset 22 includes the first handset 22a to the third handset 22c. The parent unit 21 communicates with the first handset 22a to the third handset 22c. Thus, the adoption terminal of the parent unit 21 includes the first handset 22a to the third handset 22c. Each of the adoption terminals of the first handset 22a to the third handset 22c includes the parent unit 21. In this embodiment, the parent unit 21 is an example of a "higher wireless communication terminal", and the first handset 22a to the third handset 22c are examples of "multiple lower wireless communication terminals".

Next, the detour destination selection process executed by the child device 22 will be described. If the child device 22 is unable to communicate with the matching terminal due to some reason (for example, an increase in traffic volume around the child device 22 or a malfunction), the child device 22 executes the detour destination selection process to select a detour destination terminal. Then, the child device 22 communicates with the detour destination terminal. Hereinafter, the child device 22 that executes the detour destination selection process may be referred to as the "detour route forming terminal."

The detour route forming terminal (child unit 22) executes the detour destination selection process to select one of the wireless communication terminals installed within the communication distance range (wireless communication range) of the terminal as the detour destination terminal. A child unit 22 other than the matched terminal is selected as the detour destination terminal. Hereinafter, a child unit 22 other than the matched terminal among the wireless communication terminals installed within the communication distance range (wireless communication range) of the terminal may be referred to as a "detour destination candidate terminal". The detour destination selection process is a process of selecting one of the detour destination candidate terminals as the detour destination terminal. Note that the communication distance of special low-power wireless communication is 1 m or more and 1000 m or less.

In this embodiment, the detour route forming terminal (child device 22) selects the detour destination terminal by executing a beacon collection process. In detail, the detour route forming terminal executes a beacon collection process to collect beacon information Be from wireless communication terminals set within the wireless communication range of the detour route forming terminal. Hereinafter, the wireless communication terminals set within the wireless communication range of the detour route forming terminal may be referred to as "terminals within communication range."

Specifically, the detour route forming terminal broadcasts a beacon request signal ReB. As a result, the detour route forming terminal receives beacon information Be from terminals within the communication range. The beacon information Be includes address information, hop count information, and reception field strength information. The address information indicates the address of the wireless communication terminal. The hop count information indicates the number of hops of the wireless communication terminal. The reception field strength information indicates the reception field strength.

The address is information unique to each wireless communication terminal. In the following description, the unique information may be referred to as "unique information." The hop count indicates the tier from the parent device 21 where the wireless communication terminal is. Specifically, the parent device 21 is the 0th tier wireless communication terminal. Therefore, the hop count of the parent device 21 is "0." The first child device 22a to the third child device 22c are wireless communication terminals in the 1st tier. Therefore, the hop count of the first child device 22a to the third child device 22c is "1."

The received electric field strength indicates the electric field strength value of the radio wave (radio wave carrying the beacon request signal ReB) received by the terminal within the communication range from the detour route forming terminal. The electric field strength value is, for example, the RSSI (Received Signal Strength Indicator) value.

The detour route forming terminal selects a detour destination terminal based on the collected beacon information Be. For example, the detour route forming terminal may select the detour destination candidate terminal with the strongest received electric field strength as the detour destination terminal from among the detour destination candidate terminals with the same number of hops as the detour route forming terminal or those with a number of hops less than the detour route forming terminal.

In the example shown in FIG. 1, the wireless communication range of the parent device 21 includes the first child device 22a to the third child device 22c. The wireless communication range of the first child device 22a includes the parent device 21 and the second child device 22b. The wireless communication range of the second child device 22b includes the parent device 21, the first child device 22a, and the third child device 22c. The wireless communication range of the third child device 22c includes the parent device 21 and the second child device 22b. Therefore, the detour destination candidate terminal for the first child device 22a is the second child device 22b. The detour destination candidate terminals for the second child device 22b are the first child device 22a and the third child device 22c. The detour destination candidate terminal for the third child device 22c is the second child device 22b.

For example, if the second handset 22b collects beacon information Be and finds that the received electric field strength of the first handset 22a is greater than the received electric field strength of the third handset 22c, the second handset 22b selects the first handset 22a as the detouring terminal.

Next, the detour destination candidate search process executed by the adopted terminal (child unit 22) of the parent unit 21 will be described. The adopted terminal of the parent unit 21 executes the detour destination candidate search process to search for detour destination candidate terminals and transmit detour destination candidate information to the parent unit 21. The detour destination candidate information includes information unique to each of the detour destination candidate terminals (unique information). The detour destination candidate search process is repeatedly executed at a predetermined cycle. The predetermined cycle is, for example, a 45-day cycle. Hereinafter, the predetermined cycle may be referred to as the "first cycle."

In this embodiment, the parent device 21's adopting terminal (child device 22) executes a beacon collection process each time the first period elapses. That is, each time the first period elapses, a beacon request signal ReB is broadcast and beacon information Be is received (collected) from terminals within the communication range. Then, the collected beacon information Be is transmitted to the parent device 21 as detouring destination candidate information. Hereinafter, the collected beacon information Be may be referred to as "beacon collection result C." Note that the beacon request signal ReB is an example of a "response request signal," and the address information (unique information) included in the beacon information Be is an example of "response information."

Specifically, the first child device 22a transmits a beacon collection result C to the parent device 21 based on the beacon information Be received from each of the parent device 21 and the second child device 22b. Similarly, the second child device 22b transmits a beacon collection result C to the parent device 21 based on the beacon information Be received from each of the parent device 21, the first child device 22a, and the third child device 22c. The third child device 22c transmits a beacon collection result C to the parent device 21 based on the beacon information Be received from each of the parent device 21 and the second child device 22b.

The beacon collection result C includes beacon information Be of a child device 22 that has the same number of hops as the child device 22 that transmits the beacon collection result C, or a smaller number of hops. However, the beacon collection result C may further include beacon information Be of a child device 22 that has a larger number of hops than the child device 22 that transmits the beacon collection result C.

Next, the isolated terminal identification process executed by the parent device 21 will be described. The isolated terminal identification process is a process for searching for a child device 22 that cannot communicate with a detouring destination candidate terminal from among the parent device 21's associated terminals. Hereinafter, a child device 22 that cannot communicate with a detouring destination candidate terminal may be referred to as an "isolated terminal." An isolated terminal cannot communicate with a detouring destination terminal. Therefore, if an isolated terminal cannot communicate with the parent device 21, it cannot send a message addressed to the center device 11. An isolated terminal is an example of a "second lower wireless communication terminal."

In the example shown in FIG. 1, if the first handset 22a cannot communicate with the second handset 22b for some reason, it becomes an isolated terminal. If the second handset 22b cannot communicate with either the first handset 22a or the third handset 22c for some reason, it becomes an isolated terminal. If the third handset 22c cannot communicate with the second handset 22b for some reason, it becomes an isolated terminal.

As already explained, the parent device 21 receives the detour destination candidate information from its own adopted terminal. The parent device 21 stores the detour destination candidate information. The parent device 21 then compares the stored past detour destination candidate information with the received current detour destination candidate information, and identifies isolated terminals based on the comparison results. Specifically, the parent device 21 identifies child devices 22 from among its own adopted terminals that are unable to receive beacon information Be (response information) from each other, and identifies, from among the identified child devices 22, child devices 22 that are unable to communicate with the corresponding detour destination candidate terminal as isolated terminals.

For example, since the only detouring candidate terminal for the third handset 22c is the second handset 22b, if the second handset 22b and the third handset 22c are unable to receive beacon information Be from each other, the parent device 21 identifies the third handset 22c as an isolated terminal.

In this embodiment, after identifying an isolated terminal, the parent device 21 executes a first determination process to determine the wireless communication state with the isolated terminal. Then, if the wireless communication state does not match a predefined condition, the parent device 21 executes a first notification process. The first notification process is a process of transmitting first notification information Nt1 to the center device 11. The first notification information Nt1 indicates that the child device 22 identified as an isolated terminal cannot communicate with the corresponding detouring destination candidate terminal.

For example, the parent device 21 may determine the radio wave conditions between the parent device 21 and the isolated terminal by the first determination process. In detail, the parent device 21 may determine whether the electric field strength of the radio waves received by the isolated terminal from the parent device 21 is equal to or lower than a predetermined threshold. If the electric field strength of the radio waves received by the isolated terminal from the parent device 21 is equal to or lower than the predetermined threshold, the radio wave conditions between the parent device 21 and the isolated terminal are unstable, and communication between the parent device 21 and the isolated terminal may not be possible. If the electric field strength of the radio waves received by the isolated terminal from the parent device 21 is equal to or lower than the predetermined threshold, the parent device 21 transmits first notification information Nt1 addressed to the center device 11 to the center-side network control device 12. As a result, the center device 11 receives the first notification information Nt1.

The first determination process does not have to be executed. In this case, when the parent device 21 identifies an isolated terminal, it transmits the first notification information Nt1 to the center device 11.

Next, the configuration of the handset 22 will be described with reference to Figures 1 and 2. Figure 2 is a block diagram showing the configuration of the handset 22 included in the communication system 100 of this embodiment. As shown in Figure 2, the handset 22 includes a control unit 221, a storage unit 222, a communication unit 223, and a connection unit 224.

The communication unit 223 performs wireless communication with other wireless communication terminals. For example, as described with reference to FIG. 1, the communication unit 223 establishes a communication connection with an adoption terminal or a detouring terminal, and transmits and receives messages between the adoption terminal and the detouring terminal. Also, as described with reference to FIG. 1, the communication unit 223 broadcasts a beacon request signal ReB and receives beacon information Be from terminals within the communication range. Furthermore, as described with reference to FIG. 1, the communication unit 223 transmits a beacon collection result C to the parent device 21 as detouring destination candidate information. For example, the communication unit 223 includes a communication module having an RF-LSI for 920 MHz band communication.

Specifically, the communication unit 223 has an antenna (not shown). The communication unit 223 transmits and receives wireless signals (radio waves) via the antenna. The communication unit 223 converts (decodes) the received wireless signals into signals that can be processed by the control unit 221, and outputs the signals to the control unit 221. The communication unit 223 also converts signals output from the control unit 221 to the communication unit 223 into signals that comply with a predetermined wireless communication method (e.g., a special low-power radio communication method). This signal is output to the antenna. As a result, the wireless signals (radio waves) are transmitted from the antenna.

In this embodiment, the communication unit 223 measures the electric field strength value (received electric field strength) of the radio waves received by the antenna. The communication unit 223 outputs a signal indicating the measured electric field strength value to the control unit 221.

The connection unit 224 is connected to the electric wire PL which is connected to the meter 23. Therefore, the connection unit 224 is wired to the meter 23 via the electric wire PL. The meter 23 is installed for each consumer, such as a private home, a company, or various facilities. The meter 23 is a measuring device. The measurement target of the meter 23 is, for example, the usage of resources such as gas, water, or electricity. The meter 23 measures the usage of resources such as gas, water, or electricity, and outputs the measurement result to the electric wire PL.

The control unit 221 acquires the measurement results from the meter 23 via the electric wire PL and the connection unit 224, and stores data indicating the measurement results in the memory unit 222. The control unit 221 reads out the data indicating the measurement results from the memory unit 222, and creates a telegram addressed to the center indicating the measurement results. The telegram addressed to the center is transmitted to the center device 11. For example, the first child device 22a transmits the telegram addressed to the center to the parent device 21 via its own communication unit 223. As a result, the parent device 21 transmits the telegram addressed to the center to the center device 11 via the wide area wireless network Ne and the center-side network control device 12.

The control unit 221 controls each element of the device (child device 22). For example, the control unit 221 controls the memory unit 222 and the communication unit 223. The control unit 221 includes a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor controls each element of the device (child device 22) by executing a computer program stored in the memory unit 222. The control unit 221 and the memory unit 222 may form a microcomputer.

The control unit 221 executes various processes. For example, the control unit 221 executes the detour destination selection process and the detour destination candidate search process described with reference to FIG. 1. More specifically, the control unit 221 executes the beacon collection process.

The memory unit 222 stores various data. For example, the memory unit 222 stores the association information of the own device, the address information of the own device, the hop count information of the own device, the beacon information Be, and the measurement results. The memory unit 222 also stores information indicating the first period described with reference to FIG. 1. The memory unit 222 includes, for example, a semiconductor memory such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a flash memory.

The storage unit 222 stores various computer programs executed by the control unit 221 (processor). The various computer programs include, for example, a computer program for executing the detour destination selection process and the detour destination candidate search process described with reference to FIG. 1. In this embodiment, the computer program for executing the detour destination selection process and the detour destination candidate search process includes a computer program for executing the beacon collection process described with reference to FIG. 1.

The configuration of the parent unit 21 will now be described with reference to Figures 1 and 3. Figure 3 is a block diagram showing the configuration of the parent unit 21 of this embodiment. As shown in Figure 3, the parent unit 21 includes a control unit 211, a memory unit 212, a first communication unit 213, and a second communication unit 214. The control unit 211 is an example of a processing unit. The first communication unit 213 and the second communication unit 214 are examples of a transmission unit.

The first communication unit 213 is communicatively connected to the center device 11. Specifically, the first communication unit 213 communicates with the center-side network control device 12 via the wide-area wireless network Ne. Therefore, the first communication unit 213 is communicatively connected to the center device 11 via the wide-area wireless network Ne and the center-side network control device 12. The first communication unit 213 is a communication module capable of wide-area communication such as a PHS network, a FOMA network, an LTE network, a 4G network, and a 5G network. The first communication unit 213 transmits the measurement result to the center device 11. Also, the first communication unit 213 transmits the first notification information Nt1 to the center device 11 as described with reference to FIG. 1.

The second communication unit 214 performs wireless communication with the adoption terminal. The second communication unit 214 includes, for example, a communication module having an RF-LSI for 920 MHz band communication. The second communication unit 214 establishes a communication connection with the adoption terminal and transmits and receives messages with the adoption terminal. For example, the second communication unit 214 receives measurement results from the adoption terminal. The second communication unit 214 also broadcasts a beacon request signal ReB and receives beacon information Be from terminals within the communication range. Furthermore, the second communication unit 214 receives beacon collection results C from the adoption terminal as detour destination candidate information, as described with reference to FIG. 1.

The control unit 211 controls each element of the device (parent device 21). For example, the control unit 211 controls the memory unit 212, the first communication unit 213, and the second communication unit 214. The control unit 211 includes a processor such as a CPU or MPU. The processor controls each element of the device (parent device 21) by executing a computer program stored in the memory unit 212. Note that the control unit 211 and the memory unit 212 may form a microcomputer.

The control unit 211 executes various processes. For example, the control unit 211 executes a beacon collection process. The control unit 211 also executes an isolated terminal identification process and a first determination process described with reference to FIG. 1. Furthermore, the control unit 221 executes a first notification process as described with reference to FIG. 1, and transmits first notification information Nt1 to the center device 11.

The memory unit 212 stores various data. For example, the memory unit 212 stores the matchmaking information of the own device, the address information of the own device, and the hop count information of the own device. Furthermore, the memory unit 212 stores the beacon collection result C (detouring destination candidate information) described with reference to FIG. 1. The memory unit 212 includes, for example, a semiconductor memory such as a ROM, a RAM, and a flash memory.

The storage unit 212 stores various computer programs executed by the control unit 211 (processor). For example, the various computer programs include a computer program for executing a beacon collection process. The various computer programs also include a computer program for executing the isolated terminal identification process and the first determination process described with reference to FIG. 1. Furthermore, the various computer programs include a computer program for executing a first notification process.

Next, the process executed by the control unit 211 of the parent device 21 of this embodiment will be described with reference to Figures 1 to 4. Figure 4 is a flowchart showing the process executed by the control unit 211 of the parent device 21 of this embodiment. The process shown in Figure 4 begins when the parent device 21 receives a beacon collection result C from the adoption terminal.

When the control unit 211 receives the beacon collection result C transmitted from the adoption terminal via the second communication unit 214, it executes the isolated terminal identification process described with reference to FIG. 1. In this embodiment, the control unit 211 first determines whether the previous beacon collection result C stored in the memory unit 212 matches the currently received beacon collection result C (step S1). Note that the previous beacon collection result C is the beacon collection result C obtained when the adoption terminals of the parent device 21 do not include an isolated terminal.

If the control unit 211 determines that the previous beacon collection result C and the current beacon collection result C match (Yes in step S1), it ends the process shown in FIG. 4. If the control unit 211 determines that the previous beacon collection result C and the current beacon collection result C do not match (No in step S1), it identifies an isolated terminal (step S2).

Specifically, the control unit 211 compares the previous beacon collection result C with the current beacon collection result C to identify child devices 22 that are unable to receive beacon information Be from each other, and identifies, from among the identified child devices 22, child devices 22 that are unable to communicate with the corresponding detouring destination candidate terminal as isolated terminals. Hereinafter, child devices 22 that are unable to receive beacon information Be from each other may be referred to as "monitored terminals."

If the previous beacon collection result C and the current beacon collection result C do not match, the control unit 211 does not store the current beacon collection result C in the memory unit 212. Therefore, the memory unit 212 holds the previous beacon collection result C (the beacon collection result C obtained when the parent device 21's adopted terminals do not include an isolated terminal).

After identifying the isolated terminal, the control unit 211 executes the first determination process described with reference to FIG. 1. Specifically, the control unit 211 transmits a radio wave measurement request signal ReM to the isolated terminal. The radio wave measurement request signal ReM is a signal requesting received electric field strength information M. When the communication unit 223 of the isolated terminal (child unit 22) receives the radio wave measurement request signal ReM, it measures the electric field strength value of the radio wave carrying the radio wave measurement request signal ReM. Based on the radio wave measurement request signal ReM, the control unit 221 of the isolated terminal (child unit 22) transmits received electric field strength information M indicating the measured electric field strength value to the parent unit 21 via the communication unit 223. When the control unit 211 of the parent unit 21 acquires the received electric field strength information M via the second communication unit 214, it determines whether the electric field strength value is equal to or less than a threshold (step S3).

When the control unit 211 determines that the electric field strength value is not equal to or less than the threshold value (No in step S3), it ends the process shown in FIG. 4. When the control unit 211 determines that the electric field strength value is equal to or less than the threshold value (Yes in step S3), it executes the first notification process described with reference to FIGS. 1 and 2, and transmits first notification information Nt1 to the center device 11 (step S4). As a result, it is possible to notify the administrator of the center device 11 that the telemetry system 100 includes an isolated terminal, and that the radio wave environment of the isolated terminal is unstable.

In this embodiment, the control unit 211 executes a setting process after transmitting the first notification information Nt1 (step S5). The setting process is a process of changing the cycle in which the monitored terminal executes the detour destination candidate search process to a second cycle that is shorter than the first cycle. For example, if the first cycle is a 45-day cycle, the second cycle may be a 7-day cycle. After executing the setting process, the control unit 221 ends the process shown in FIG. 4.

In detail, the control unit 211 transmits a setting signal Set to the monitored terminal via the second communication unit 214. The setting signal Set indicates an instruction to change the first cycle to the second cycle and the number of executions N, which is the number of times to execute the detour destination candidate search process in the second cycle. The number of executions N is, for example, 4 or 5 times.

When the control unit 221 of the monitored terminal (child unit 22) receives the setting signal Set via the communication unit 223, it changes the period of the detour destination candidate search process from the first period to the second period based on the setting signal Set. Specifically, it stores the second period in the memory unit 222. Also, the control unit 221 of the monitored terminal (child unit 22) stores the number of executions N in the memory unit 222 based on the setting signal Set. As a result, the monitored terminal executes the detour destination candidate search process N times in the second period.

The setting process may be executed after the first notification process is executed.

Next, the second determination process, the second notification process, the third determination process, and the third notification process executed by the control unit 211 of the parent device 21 in this embodiment will be described with reference to Figures 1 to 3 and Figure 5. Figure 5 is a flowchart showing the second determination process, the second notification process, the third determination process, and the third notification process executed by the control unit 211 of the parent device 21 in this embodiment. The process shown in Figure 5 starts when the parent device 21 receives a beacon collection result C from the monitored terminal.

When the control unit 211 receives the beacon collection result C transmitted from the monitored terminal via the second communication unit 214, it determines whether the isolated terminal is now able to communicate with the detouring terminal candidate. Specifically, the control unit 211 determines whether the beacon collection result C of the monitored terminal stored in the memory unit 212 matches the current beacon collection result C acquired from the monitored terminal (step S11).

As described with reference to FIG. 4, the beacon collection result C stored in the memory unit 212 is the beacon collection result C obtained when the parent device 21 does not include an isolated terminal among its associated terminals.

When the control unit 211 determines that the beacon collection result C of the monitored terminal stored in the memory unit 212 matches the current beacon collection result C obtained from the monitored terminal (Yes in step S11), it executes a second determination process.

Specifically, the control unit 211 determines whether the number of consecutive matches between the beacon collection result C of the monitored terminal stored in the memory unit 212 and the current beacon collection result C acquired from the monitored terminal has reached N2 times (step S12). Here, N2 is an integer equal to or greater than 2, and is pre-stored in the memory unit 212. N2 times may indicate the same value as the number of executions N, or may indicate a value different from the number of executions N.

If it is determined that the number of consecutive matches between the beacon collection result C of the monitored terminal stored in the memory unit 212 and the current beacon collection result C obtained from the monitored terminal has not reached N2 times (No in step S12), the control unit 211 ends the processing shown in FIG. 5.

If it is determined that the number of consecutive matches between the beacon collection result C of the monitored terminal stored in the memory unit 212 and the current beacon collection result C obtained from the monitored terminal has reached N2 times (Yes in step S12), the control unit 211 executes a second notification process (step S13) and ends the process shown in FIG. 5.

The second notification process is a process of transmitting second notification information Nt2 to the center device 11. The second notification information Nt2 indicates that the isolated terminal is now able to communicate with the detouring destination candidate terminal. In other words, the second notification information Nt2 indicates that the isolated terminal has recovered from the isolated state.

On the other hand, if the control unit 211 determines that the beacon collection result C of the monitored terminal stored in the memory unit 212 does not match the current beacon collection result C obtained from the monitored terminal (No in step S11), it executes a third determination process.

Specifically, the control unit 211 determines whether the number of times that the beacon collection result C of the monitored terminal stored in the memory unit 212 does not match the current beacon collection result C acquired from the monitored terminal has reached N3 times (step S14). Here, N3 is an integer equal to or greater than 2, and is pre-stored in the memory unit 212. N3 times may indicate the same value as the number of executions N, or may indicate a value different from the number of executions N. Furthermore, N3 times may indicate the same value as N1 times, or may indicate a value different from N1 times.

If it is determined that the number of times that the beacon collection result C of the monitored terminal stored in the memory unit 212 does not match the current beacon collection result C obtained from the monitored terminal has not reached N3 (No in step S14), the control unit 211 ends the processing shown in FIG. 5.

If it is determined that the number of times that the beacon collection result C of the monitored terminal stored in the memory unit 212 does not match the current beacon collection result C obtained from the monitored terminal has reached N3 (Yes in step S14), the control unit 211 executes a third notification process (step S15) and ends the process shown in FIG. 5.

The third notification process is a process of transmitting third notification information Nt3 to the center device 11. The third notification information Nt3 indicates, for example, that the isolated terminal is malfunctioning. In other words, the control unit 211 may transmit a malfunction notification to the center device 11.

After the monitored terminal executes the detour destination candidate search process N times in the second cycle, the parent device 21 transmits a setting signal to the monitored terminal to change the cycle of the detour destination candidate search process back to the first cycle from the second cycle.

Next, an example of the operation of the parent unit 21 and the first to third child units 22a to 22c will be described with reference to Figures 1 to 15. First, an example of the operation of the parent unit 21 and the first to third child units 22a to 22c will be described with reference to Figures 6 to 9.

Figure 6 is a sequence diagram showing the beacon collection process executed by the control unit 211 of the parent device 21. As shown in Figure 6, the control unit 211 of the parent device 21 broadcasts a beacon request signal ReB via the second communication unit 214. As a result, the control unit 211 of the parent device 21 receives beacon information Be from each of the first child device 22a to the third child device 22c via the second communication unit 214. The control unit 211 of the parent device 21 stores the beacon collection result C of the parent device 21 in the memory unit 212.

The beacon collection result C of the parent device 21 indicates that the parent device 21 can communicate with the first child device 22a to the third child device 22c. Specifically, the beacon collection result C of the parent device 21 includes unique information (address information) of each of the first child device 22a to the third child device 22c.

Figure 7 is a sequence diagram showing the detour destination candidate search process executed by the control unit 221 of the first handset 22a. As shown in Figure 7, the control unit 221 of the first handset 22a broadcasts a beacon request signal ReB via the communication unit 223. As a result, the control unit 221 of the first handset 22a receives beacon information Be from each of the parent unit 21 and the second handset 22b via the communication unit 223.

When the control unit 221 of the first child device 22a receives the beacon information Be, it transmits the beacon collection result C to the parent device 21. The control unit 211 of the parent device 21 stores the beacon collection result C of the first child device 22a in the memory unit 212.

The beacon collection result C of the first child device 22a indicates that the first child device 22a can communicate with the parent device 21 and the second child device 22b. Specifically, the beacon collection result C of the first child device 22a includes unique information (address information) of each of the parent device 21 and the second child device 22b.

Figure 8 is a sequence diagram showing the detour destination candidate search process executed by the control unit 221 of the second handset 22b. As shown in Figure 8, the control unit 221 of the second handset 22b broadcasts a beacon request signal ReB via the communication unit 223. As a result, the control unit 221 of the second handset 22b receives beacon information Be from each of the parent unit 21, the first handset 22a, and the third handset 22c via the communication unit 223.

When the control unit 221 of the second child device 22b receives the beacon information Be, it transmits the beacon collection result C to the parent device 21. The control unit 211 of the parent device 21 stores the beacon collection result C of the second child device 22b in the memory unit 212.

The beacon collection result C of the second handset 22b indicates that the second handset 22b can communicate with the parent unit 21, the first handset 22a, and the third handset 22c. Specifically, the beacon collection result C of the second handset 22b includes unique information (address information) of each of the parent unit 21, the first handset 22a, and the third handset 22c.

Figure 9 is a sequence diagram showing the detour destination candidate search process executed by the control unit 221 of the third handset 22c. As shown in Figure 9, the control unit 221 of the third handset 22c broadcasts a beacon request signal ReB via the communication unit 223. As a result, the control unit 221 of the third handset 22c receives beacon information Be from each of the parent unit 21 and the second handset 22b via the communication unit 223.

When the control unit 221 of the third child device 22c receives the beacon information Be, it transmits the beacon collection result C to the parent device 21. The control unit 211 of the parent device 21 stores the beacon collection result C of the third child device 22c in the memory unit 212.

The beacon collection result C of the third handset 22c indicates that the third handset 22c can communicate with the parent device 21 and the second handset 22b. Specifically, the beacon collection result C of the third handset 22c includes unique information (address information) of each of the parent device 21 and the second handset 22b.

Next, with reference to Figures 10 and 11, we will explain the operations of the parent device 21, the second device 22b, and the third device 22c when communication cannot be performed between the second device 22b and the third device 22c for some reason.

Figure 10 is another sequence diagram showing the detour destination candidate search process executed by the control unit 221 of the second handset 22b. As shown in Figure 10, the control unit 221 of the second handset 22b broadcasts a beacon request signal ReB via the communication unit 223. If communication cannot be performed between the second handset 22b and the third handset 22c for some reason, the communication unit 223 of the second handset 22b does not receive beacon information Be from the third handset 22c. Therefore, the control unit 221 of the second handset 22b receives beacon information Be from each of the parent unit 21 and the first handset 22a via the communication unit 223.

When the control unit 221 of the second child device 22b receives the beacon information Be, it transmits the beacon collection result C to the parent device 21. The control unit 211 of the parent device 21 stores the beacon collection result C of the second child device 22b in the memory unit 212.

If communication cannot be performed between the second handset 22b and the third handset 22c for some reason, the beacon collection result C of the second handset 22b indicates that the second handset 22b can communicate with the parent unit 21 and the first handset 22a. Specifically, the beacon collection result C of the second handset 22b includes the unique information (address information) of each of the parent unit 21 and the first handset 22a.

Figure 11 is another sequence diagram showing the detour destination candidate search process executed by the control unit 221 of the third handset 22c. As shown in Figure 11, the control unit 221 of the third handset 22c broadcasts a beacon request signal ReB via the communication unit 223. If communication cannot be performed between the second handset 22b and the third handset 22c for some reason, the communication unit 223 of the third handset 22c does not receive beacon information Be from the second handset 22b. Therefore, the control unit 221 of the third handset 22c receives beacon information Be from the parent unit 21 via the communication unit 223.

When the control unit 221 of the third child device 22c receives the beacon information Be, it transmits the beacon collection result C to the parent device 21. The control unit 211 of the parent device 21 stores the beacon collection result C of the third child device 22c in the memory unit 212.

If communication cannot be performed between the second handset 22b and the third handset 22c for some reason, the beacon collection result C of the third handset 22c indicates that the third handset 22c can communicate with the parent device 21. Specifically, the beacon collection result C of the third handset 22c includes unique information (address information) of the parent device 21.

Next, the isolated terminal identification process executed by the control unit 211 of the parent device 21 will be described with reference to Figures 12A and 12B. Figure 12A is a diagram showing the previous beacon collection result C stored in the memory unit 212 of the parent device 21. Figure 12B is a diagram showing the beacon collection result C currently received by the parent device 21 from each of the first child device 22a to the third child device 22c. In detail, Figure 12A shows the beacon collection result C acquired by the parent device 21 when the parent device 21's adopted terminals do not include an isolated terminal. Figure 12B shows the beacon collection result C acquired by the parent device 21 when communication cannot be performed between the second child device 22b and the third child device 22c for some reason.

As shown in Figures 12A and 12B, if communication cannot be performed between the second handset 22b and the third handset 22c for some reason, the unique information of the third handset 22c disappears from the beacon collection result C of the second handset 22b, and the unique information of the second handset 22b disappears from the beacon collection result C of the third handset 22c. Therefore, the control unit 221 of the parent unit 21 compares the previous beacon collection result C stored in the memory unit 212 with the beacon collection result C received this time, thereby identifying the second handset 22b and the third handset 22c as the handset 22 that could not receive beacon information Be (response information) from each other.

As shown in FIG. 12B, the second child device 22b is not an isolated terminal because it can communicate with the first child device 22a. On the other hand, the third child device 22c cannot communicate with other child devices 22 that have the same hop count or a hop count smaller than that of the third child device 22c. Therefore, the control unit 211 of the parent device 21 identifies the third child device 22c as an isolated terminal based on the beacon collection result C received this time.

Next, the first determination process, the setting process, and the first notification process executed by the control unit 211 of the parent device 21 will be described with reference to FIG. 13. FIG. 13 is a sequence diagram showing the first determination process, the setting process, and the first notification process executed by the control unit 211 of the parent device 21.

As shown in FIG. 13, when the control unit 211 of the parent device 21 identifies the third handset 22c as an isolated terminal, it transmits a radio wave measurement request signal ReM to the third handset 22c. As a result, the control unit 211 of the parent device 21 receives the reception field strength information M from the third handset 22c via the second communication unit 214.

When the control unit 211 of the parent device 21 receives the received electric field strength information M, it determines whether the electric field strength value is equal to or less than the threshold value. If the control unit 211 of the parent device 21 determines that the electric field strength value is equal to or less than the threshold value, it transmits a setting signal Set to the second handset 22b and the third handset 22c, which are the terminals to be monitored. As a result, the period during which the second handset 22b and the third handset 22c execute the detour destination candidate search process is changed from the first period to the second period. In addition, the number of times that the second handset 22b and the third handset 22c execute the detour destination candidate search process in the second period is set to N times.

In the example shown in FIG. 13, the control unit 211 of the parent device 21 executes the setting process, then executes the first notification process, and transmits the first notification information Nt1 to the center device 11.

Next, the second determination process and the second notification process executed by the control unit 211 of the parent device 21 will be described with reference to FIG. 14. FIG. 14 is a sequence diagram showing the second determination process and the second notification process executed by the control unit 211 of the parent device 21.

In the example shown in FIG. 14, N2 times is 2 times. As shown in FIG. 14, when the number of consecutive matches between the beacon collection result C (see FIG. 12A) of the monitored terminal (second handset 22b and third handset 22c) stored in the memory unit 212 of the parent device 21 and the current beacon collection result C obtained from the monitored terminal reaches 2 times (N2 times), the control unit 211 of the parent device 21 executes a second notification process and transmits second notification information Nt2 to the center device 11.

Next, the third determination process and the third notification process executed by the control unit 211 of the parent device 21 will be described with reference to FIG. 15. FIG. 15 is a sequence diagram showing the third determination process and the third notification process executed by the control unit 211 of the parent device 21.

In the example shown in FIG. 15, N3 times is N times. As shown in FIG. 15, when the number of times that the beacon collection result C (see FIG. 12A) of the monitored terminal (second handset 22b and third handset 22c) stored in the memory unit 212 of the parent device 21 does not match the current beacon collection result C obtained from the monitored terminal reaches N times (N3 times), the control unit 211 of the parent device 21 executes a third notification process and transmits third notification information Nt3 to the center device 11.

The first embodiment of the present invention has been described above with reference to Figs. 1 to 15. According to this embodiment, it is possible to identify in advance child devices 22 (isolated terminals) that cannot be bypassed when communication with a related terminal becomes impossible for some reason.

In addition, according to this embodiment, the first determination process makes it possible to identify in advance isolated terminals that are more likely to be unable to communicate with compatible terminals.

In addition, according to this embodiment, the setting process can temporarily shorten the cycle of the detour destination candidate search process by the monitored terminal. This makes it possible to check earlier whether the deterioration of the radio wave environment is temporary.

In this embodiment, in the first determination process, the parent device 21 determines the radio wave conditions between the parent device 21 and the isolated terminal based on the received electric field strength of the isolated terminal. However, the radio wave conditions between the parent device 21 and the isolated terminal may be determined based on the electric field strength of the radio waves received by the parent device 21 from the isolated terminal.

In addition, in this embodiment, the parent unit 21 executes the setting process once, but the parent unit 21 may execute the setting process multiple times to gradually bring the period of the detour destination candidate search process closer to the first period from the second period. For example, the parent unit 21 may set a third period that is shorter than the first period and longer than the second period after the monitored terminal executes the detour destination candidate search process N times in the second period. For example, if the first period is a 45-day period and the second period is a 7-day period, the third period may be a 15-day period.

In addition, in this embodiment, the parent device 21 executes the second determination process and the third determination process, but both or one of the second determination process and the third determination process may be omitted.

In this embodiment, the parent device 21 executes the second notification process when the number of consecutive matches between the beacon collection result C of the monitored terminal stored in the storage unit 212 of the parent device 21 and the current beacon collection result C acquired from the monitored terminal reaches N2 times. However, the parent device 21 may determine whether the current beacon collection result C acquired from the isolated terminal includes a child device 22 other than the wireless communication terminal included in the beacon collection result C of the isolated terminal stored in the storage unit 212. In this case, the parent device 21 executes the second notification process when the number of times it is determined that the current beacon collection result C acquired from the isolated terminal includes a child device 22 other than the wireless communication terminal included in the beacon collection result C of the isolated terminal stored in the storage unit 212 reaches N2 times. For example, if the third child device 22c is an isolated terminal, the parent device 21 determines whether the beacon collection result C acquired from the third child device 22c includes a child device 22 other than the parent device 21 and the second child device 22b. Here, the handset 22 that is different from the parent unit 21 and the second handset 22b is, for example, a handset 22 that is newly installed within the wireless communication range of the third handset 22c.

In addition, in this embodiment, the parent device 21 executes the third notification process when the number of times that the beacon collection result C of the monitored terminal stored in the memory unit 212 of the parent device 21 does not match the current beacon collection result C acquired from the monitored terminal reaches N3 times, but the parent device 21 may execute the third notification process when the number of times that the parent device 21 determines that the current beacon collection result C acquired from the isolated terminal does not include a child device 22 other than the wireless communication terminal included in the beacon collection result C of the isolated terminal stored in the memory unit 212 reaches N3 times.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to Fig. 16. However, only differences from the first embodiment will be described, and a description of the same matters as in the first embodiment will be omitted. The second embodiment differs from the first embodiment in that the slave unit 22 executes the isolated terminal identification process.

Figure 16 is a diagram showing a communication system 100 of this embodiment. As shown in Figure 16, the communication system 100 (telemetry system) includes a master unit 21, multiple slave units 22, and a center device 11.

In the example shown in FIG. 16, the multiple child devices 22 include a first child device 22d, a second child device 22d1, a third child device 22d2, and a fourth child device 22d3. The parent device 21 communicates with the first child device 22d. Thus, the adoption terminal of the parent device 21 includes the first child device 22d. Each of the adoption terminals of the second child device 22d1 to the fourth child device 22d3 includes the first child device 22d. In this embodiment, the first child device 22d is an example of a "higher wireless communication terminal", and the second child device 22d1 to the fourth child device 22d3 are examples of "multiple lower wireless communication terminals".

Each of the second handset 22d1 to the fourth handset 22d3 executes a detour destination candidate search process and transmits detour destination candidate information to the first handset 22d. In this embodiment, the detour destination candidate information is the beacon collection result C.

The first handset 22d executes an isolated terminal identification process. Therefore, the first handset 22d identifies an isolated terminal from among the second handset 22d1 to the fourth handset 22d3 based on the beacon collection result C (detouring destination candidate information) received from each of the second handset 22d1 to the fourth handset 22d3.

When the first handset 22d identifies an isolated terminal, it executes a first determination process. Then, if the wireless communication state between the first handset 22d and the isolated terminal does not meet a predefined condition, it executes a first notification process and transmits first notification information Nt1 addressed to the center device 11 to the parent device 21. As a result, the center device 11 receives the first notification information Nt1.

The first slave unit 22d further executes a setting process to change the period during which the monitored terminal executes the detour destination candidate search process to a second period that is shorter than the first period. The first slave unit 22d then determines whether the isolated terminal is now able to communicate with the detour destination candidate terminal.

When the isolated terminal is able to communicate with the detouring destination candidate terminal, the first child device 22d executes the second notification process and transmits the second notification information Nt2 addressed to the center device 11 to the parent device 21. On the other hand, when the isolated terminal is not able to communicate with the detouring destination candidate terminal, the first child device 22d executes the third notification process and transmits the third notification information Nt3 addressed to the center device 11 to the parent device 21.

The second embodiment of the present invention has been described above with reference to FIG. 16. According to this embodiment, it is possible to identify in advance child devices 22 (isolated terminals) that cannot be bypassed when communication with a related terminal becomes impossible for some reason.

The above describes embodiments of the present invention with reference to the drawings (Figs. 1 to 16). However, the present invention is not limited to the above embodiments, and can be implemented in various aspects without departing from the gist of the present invention. In addition, the components disclosed in the above embodiments can be modified as appropriate. For example, a component among all the components shown in one embodiment may be added to a component of another embodiment, or some of all the components shown in one embodiment may be deleted from the embodiment.

The drawings are primarily schematic illustrations of each component to facilitate understanding of the invention, and the thickness, length, number, spacing, etc., of each component shown may differ from the actual configuration due to the convenience of creating the drawings. Furthermore, the configuration of each component shown in the above embodiment is merely an example and is not particularly limited, and it goes without saying that various modifications are possible within a range that does not substantially deviate from the effects of the present invention.

For example, in the embodiment described with reference to Figures 1 to 16, the meter 23 was not connected to the parent unit 21, but the meter 23 may be connected to the parent unit 21.

In the embodiment described with reference to Figures 1 to 16, the slave unit 22 and the meter 23 are connected by wire PL, but the slave unit 22 and the meter 23 may be connected wirelessly. Similarly, the master unit 21 and the meter 23 may be connected wirelessly.

The present invention provides a communication system and a wireless communication terminal, and has industrial applicability.

11: Center device 21: Parent device 22: Child device 100: Communication system (telemetry system)
211: Control unit 212: Memory unit Be: Beacon information C: Beacon collection result M: Reception field strength information N: Number of executions Nt1: First notification information Nt2: Second notification information Nt3: Third notification information ReB: Beacon request signal ReM: Radio wave measurement request signal Set: Setting signal

Claims (8)

A communication system including a plurality of lower wireless communication terminals and an upper wireless communication terminal that communicates with the plurality of lower wireless communication terminals,
each of the plurality of lower wireless communication terminals broadcasts a response request signal, receives response information from other lower wireless communication terminals that are detouring destination candidate terminals within a wireless communication range of the terminal, and transmits the received response information to the upper wireless communication terminal, the response information including information unique to each of the other lower wireless communication terminals;
The upper wireless communication terminal includes:
a storage unit that stores the response information received from each of the plurality of lower-level wireless communication terminals;
a processing unit that identifies, from among the plurality of lower wireless communication terminals, a first lower wireless communication terminal from which the response information cannot be received based on the response information stored in the memory unit and the current response information received from each of the plurality of lower wireless communication terminals, and identifies, from among the identified first lower wireless communication terminals, a second lower wireless communication terminal that cannot communicate with the corresponding detouring destination candidate terminal. a management device for managing the upper wireless communication terminal and the plurality of lower wireless communication terminals,
2. The communication system according to claim 1, wherein the upper wireless communication terminal further comprises a transmission unit that transmits, to the management device, information indicating that communication cannot be performed between the second lower wireless communication terminal and the corresponding detouring destination candidate terminal. The communication system according to claim 2, wherein the processing unit determines whether the second lower wireless communication terminal has been able to communicate with the corresponding detouring destination candidate terminal based on the response information stored in the storage unit and the current response information received from each of the first lower wireless communication terminals, and when the second lower wireless communication terminal has been able to communicate with the corresponding detouring destination candidate terminal, transmits information indicating that the second lower wireless communication terminal can communicate with the corresponding detouring destination candidate terminal via the transmission unit to the management device. The communication system according to claim 2 or 3, wherein the processing unit determines a wireless communication state with the second lower wireless communication terminal, and when the wireless communication state does not match a predefined condition, transmits, via the transmission unit, information indicating that the second lower wireless communication terminal cannot communicate with the corresponding detouring destination candidate terminal to the management device. each of the plurality of lower-level wireless communication terminals transmits the response request signal in a first period that is defined in advance;
5. The communication system according to claim 4, wherein when the wireless communication state does not match the condition, the processing unit transmits, via the transmitting unit, a signal to the first lower wireless communication terminal, which sets a period for transmitting the response request signal to a second period shorter than the first period. The communication system according to claim 5, wherein the first lower-level wireless communication terminal transmits the response request signal in the second period a predetermined number of times. The communication system according to claim 6, wherein the processing unit transmits a signal to the first lower-level wireless communication terminal via the transmission unit, after the first lower-level wireless communication terminal transmits the response request signal in the second period the predetermined number of times, to set the period for transmitting the response request signal to a third period longer than the second period and shorter than the first period. A wireless communication terminal that communicates with a plurality of lower-level wireless communication terminals,
each of the plurality of lower wireless communication terminals broadcasts a response request signal, receives response information from other lower wireless communication terminals that are detouring destination candidate terminals within a wireless communication range of the terminal, and transmits the received response information to the wireless communication terminal, the response information including information unique to each of the other lower wireless communication terminals;
The wireless communication terminal includes:
a storage unit that stores the response information received from each of the plurality of lower-level wireless communication terminals;
a processing unit that identifies, from among the plurality of lower wireless communication terminals, a first lower wireless communication terminal from which the response information cannot be received based on the response information stored in the memory unit and the current response information received from each of the plurality of lower wireless communication terminals, and identifies, from among the identified first lower wireless communication terminals, a second lower wireless communication terminal that cannot communicate with the corresponding detouring destination candidate terminal.

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