JP2014204253A - Radio communication system, radio terminal, and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a radio terminal consuming a lot of power in the prior art technique because each radio terminal (slave unit) has to regularly measure a reception level and notify a management device (master unit) of it.SOLUTION: A slave unit transmits a transmission message and receives a reply message transmitted by a master unit, increases transmission output of a next transmission message when the reception electric field strength of the reply message is at or lower than an electric field strength threshold value at least once, and decreases transmission output of a next transmission message when the reception electric field strength of the reply message is larger than an electric field strength threshold value at least once.

Description

  The present invention relates to a wireless communication system, a wireless terminal, and a communication method that can be used in a wireless communication system including one or more parent devices and a child device.

In a wireless communication system having a base unit such as a base station and a wireless terminal (hereinafter referred to as a slave unit) that is driven by a battery and communicates with the master unit, the slave unit is generally used to reduce power consumption of the slave unit. Intermittent reception.
In a wireless communication system in which a child device performs intermittent reception, the parent device periodically transmits a beacon signal, and the child device periodically receives the beacon signal. Based on the received beacon signal, the slave unit sets its own clock (or counter, clock, etc.) to the master unit clock (or counter, clock, etc.) and transmits it from the master unit at a predetermined timing. Received data. The above reception method is called a synchronization method and is effective for power saving of the slave unit.
In a synchronous radio communication system, when direct communication is not possible between a master unit and a slave unit, a relay radio terminal (hereinafter referred to as a repeater) that relays a radio signal from the master unit to the slave unit is used. In a relay communication system that relays radio signals, a method for managing a communication route between a parent device and a child device is important. As an example of a communication route management method in the relay communication system, a method disclosed in Patent Document 1 can be cited.
According to Patent Literature 1, there is a management device that manages a communication route between wireless terminals, and each wireless terminal determines a communication route based on a communication route table created by the management device. Further, the route management method disclosed in Patent Document 1 will be described in detail. Each wireless terminal periodically transmits a measurement signal for measuring electric field strength and receives a measurement signal transmitted from another wireless terminal. Each wireless terminal measures the reception level based on the received measurement signal, and transmits information on the measured reception level to the management device. The management device creates or updates a communication route table based on the reception level information transmitted from each wireless terminal, and each wireless terminal communicates with the communication partner based on the communication route table created by the management device. Determine the communication route.

JP-A-11-168526

However, in the conventional technique described in Patent Document 1, each wireless terminal must periodically measure the reception level and notify the management device in order to create or update the communication route table by the management device. . Therefore, the wireless terminal has a problem of consuming a lot of power.
An object of the present invention is to provide a wireless terminal, a wireless communication system, and a communication method capable of suppressing power consumption of a wireless terminal driven by a battery in order to solve the problems in the conventional technology.

A wireless communication system including one or more parent devices and a child device, wherein the child device transmits a transmission message, receives a return power transmission message transmitted from the parent device, and returns the return message. When the received electric field strength of the message is at least once below the electric field strength threshold, increase the transmission output of the next transmission message, and when the received electric field strength of the return transmission message is greater than the electric field strength threshold at least once, The wireless communication system is configured to reduce a transmission output of a next transmission message, and the parent device receives a transmission message transmitted from the child device and transmits the return transmission message to the child device.

According to the present invention, power consumption of a wireless terminal driven by a battery can be suppressed.

The figure which shows an example of the communication area structure of the radio | wireless communications system in this invention The figure which shows an example of the communication sequence of the subunit | mobile_unit and parent | base_unit in this invention Basic configuration diagram of a wireless terminal as a slave in the present invention The block diagram of the subunit | mobile_unit in 1st embodiment of this invention Block diagram of the master unit in the second embodiment of the present invention The block diagram of the subunit | mobile_unit in 3rd embodiment of this invention

  1st invention is a radio | wireless communications system containing 1 or 2 or more main | base stations, and a subunit | mobile_unit, Comprising: A subunit | mobile_unit transmits a transmission telegram and receives the return power transmission sentence transmitted from the main | base station. When the received electric field strength of the return transmission text is at least once below the electric field strength threshold, the transmission output of the next transmission message is increased, and the received electric field strength of the return transmission text is at least once higher than the electric field strength threshold. This is a wireless communication system in which the transmission output of the next transmission message is reduced, and the parent device receives the transmission message transmitted from the child device and transmits the returned power transmission message to the child device.

  According to the first invention, the power consumption of the slave unit can be suppressed by reducing the transmission output of the slave unit. Further, interference or interference with other wireless terminals can be suppressed. Furthermore, stable communication with the parent device can be ensured by increasing the transmission output of the child device.

  According to a second aspect of the present invention, when the reception electric field strength of the return power transmission sentence continuously falls below the threshold value of the electric field strength for a predetermined number of times, the slave unit increases the transmission output of the next transmission message, This is a wireless communication system that reduces the transmission output of the next transmission telegram when the electric field intensity threshold value is continuously increased a predetermined number of times.

  According to the second invention, by performing the determination of the received electric field strength of the return power transmission sentence a plurality of times, the reliability of the determination of changing the transmission output is improved, the communication quality is stabilized, and the power consumption of the slave unit is suppressed. In addition, interference or interference can be suppressed.

  According to a third aspect of the present invention, when the slave unit has a ratio of the number of times that the received electric field strength of the return power transmission text is equal to or less than the threshold value of the electric field strength with respect to the total stored number of received electric field strengths of the return power transmission text in a predetermined period Increase the transmission output of the next transmission message, and the ratio of the number of times the reception electric field strength of the return transmission text is greater than the threshold value for the total number of received field strengths of the return transmission text in the predetermined period exceeds the predetermined ratio. This is a wireless communication system that reduces the transmission output of the next transmission message.

  According to the third invention, by performing the determination of the reception electric field strength of the return power transmission sentence a plurality of times, the reliability of the determination of changing the transmission output is improved, the communication quality is stabilized, and the power consumption of the slave unit is suppressed. In addition, interference or interference can be suppressed.

According to a fourth aspect of the present invention, when the received electric field strength of the received transmission message is less than the electric field strength threshold at least once, the master unit increases the transmission output of the returned transmission message, and the received electric field strength of the received transmission message is at least This is a wireless communication system that reduces the transmission output of the returned power transmission text when the electric field strength threshold value is once exceeded.

  According to the fourth invention, by changing the transmission output of the master unit, the power consumption of the slave unit is suppressed and the interference or the suppression is performed while the interference or the interference to other wireless terminals by the master unit is suppressed. Stable communication can be realized.

According to a fifth aspect of the present invention, when the received electric field strength of the transmission message continuously falls below the electric field strength threshold for a predetermined number of times, the master unit increases the transmission output of the return transmission message, and the received electric field strength of the transmission message continues. The wireless communication system reduces the transmission output of the returned power transmission text when the electric field strength threshold value exceeds a predetermined number of times.
According to the fifth aspect of the present invention, the reception electric field strength of the transmission message is determined a plurality of times, so that the reliability of the determination of changing the transmission output of the parent device is improved, the communication quality is stabilized, and the consumption of the child device is increased. In addition to suppressing power, interference or interference can be suppressed.

According to a sixth aspect of the present invention, when the ratio of the number of times that the received electric field strength of the transmitted message is equal to or less than the electric field strength threshold to the total number of received electric field strengths of the transmitted message in a predetermined period exceeds the predetermined ratio. When the transmission power of the return message is increased and the ratio of the number of times the received electric field strength of the transmitted message exceeds the electric field strength threshold with respect to the total stored number of received electric field strengths of the transmitted message in the predetermined period exceeds the predetermined ratio This is a wireless communication system for reducing the transmission output of the returned power transmission text.
According to the sixth aspect of the present invention, the reception electric field strength of the transmission message is determined a plurality of times, so that the reliability of the determination of changing the transmission output of the parent device is improved, the communication quality is stabilized, and the consumption of the child device is improved. In addition to suppressing power, interference or interference can be suppressed.

  In a seventh aspect of the invention, the transmission message transmitted from the child device includes information on the transmission output of the transmission message, and the parent device that has received the transmission message transmits the return transmission message with the same transmission output as the transmission output of the transmission message. A wireless communication system for transmission to a machine.

  According to the seventh aspect of the invention, since the master unit varies the transmission output according to the transmission output notified from the slave unit, the configuration of the master unit can be simplified, and the power consumption of the slave unit can be suppressed and interference or interference can be suppressed. It can be performed.

  An eighth aspect of the invention is a wireless communication system in which when a slave unit detects an alarm, the slave unit transmits a transmission telegram including alarm information with a maximum transmission output or a transmission output larger than the electric field strength threshold.

  According to the eighth aspect, by increasing the transmission output regardless of the electric field strength threshold, it is possible to reliably transmit an important notification requiring an emergency to the parent device.

  The ninth invention is a transmitter / receiver that transmits a transmission message and receives a return power transmission message transmitted from the parent device, and a next transmission message when the reception field strength of the return power transmission text is at least once below the field strength threshold. And an output variable unit that decreases the transmission output of the next transmission message when the reception electric field strength of the return transmission message becomes greater than the electric field strength threshold at least once.

  According to the ninth aspect, the power consumption of the slave unit can be suppressed by reducing the transmission output of the slave unit. Further, interference or interference with other wireless terminals can be suppressed. Furthermore, stable communication with the parent device can be ensured by increasing the transmission output of the child device.

The tenth aspect of the invention further includes an alarm detection unit that detects an alarm. When the alarm is detected, the transmission / reception unit transmits a transmission message including alarm information with a maximum transmission output or a transmission output larger than the electric field strength threshold. A wireless terminal.

According to the tenth aspect, by increasing the transmission output regardless of the electric field strength threshold, it is possible to reliably transmit an important notification requiring an emergency to the parent device.
The eleventh aspect of the invention transmits a transmission message, receives a return transmission message, and increases the transmission output of the next transmission message when the received electric field strength of the return transmission message becomes equal to or less than the electric field strength threshold at least once. This is a communication method for reducing the transmission output of the next transmission message when the received electric field strength becomes greater than the electric field strength threshold at least once.

  According to the eleventh aspect, by reducing the transmission output, it is possible to suppress power consumption and suppress interference or interference between other wireless terminals. Furthermore, stable communication between wireless terminals can be ensured by increasing the transmission output.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited by this embodiment, and those skilled in the art can easily understand that it can be expressed using similar terms or similar descriptions in the same field. I will.
(Embodiment 1)
FIG. 1 is a diagram illustrating an example of a communication area configuration of a wireless communication system according to the present invention. The configuration of the communication area will be described below with reference to FIG.

In FIG. 1, 101, 201, 301, 401 are parent devices, and 102, 202, 302, 303, 402 are child devices.
Area S-1 indicates an area where the parent device 101 and another parent device or child device can communicate with each other with a predetermined communication quality. That is, in the range of area S-1, the reception level of the radio wave from the parent device is equal to or higher than the first predetermined value. Note that the first predetermined value is, for example, −90 dBm.
Here, the radio wave varies depending on the surrounding environment. This is a phenomenon called fading, and generally it may drop instantaneously about 10 to 20 dB. Therefore, if the reception limit of the wireless device is −110 dB, if a 20 dB margin is ensured with respect to this −110 dBm, −90 dBm becomes a radio wave intensity that allows stable communication.
Similarly, areas S-2, S-3, and S-4 indicate areas where the parent devices 201, 301, and 401 can communicate with other parent devices or child devices with predetermined communication quality. That is, in the range of areas S-2, S-3, and S-4, the reception level of the radio wave from each parent device is equal to or higher than the first predetermined value.

  The child device 102 belongs to the communication area S-1 of the parent device 101, the communication area S-2 of the parent device 201, and the communication area S-3 of the parent device 301. That is, the slave unit 102 can communicate with the master units 101, 201, and 301 at a first predetermined level or higher. And since the subunit | mobile_unit 102 is the closest to the main | base station 201, the reception level of the electromagnetic wave (signal) from the main | base station 201 is usually the highest.

  Similarly, the slave units 202 and 302 belong to a plurality of communication areas. Since the handset 202 is closest to the base unit 301, the reception level of the radio wave (signal) from the base unit 301 is the highest. Since the child device 302 is closest to the parent device 401, the reception level of the radio wave (signal) from the parent device 401 is the highest.

  On the other hand, since the communication area to which the child device 402 belongs is only the communication area S-4 of the parent device 401, the reception level of the radio wave (signal) from the parent device 401 is the highest.

Next, a communication method between the parent device and the child device in the wireless communication system of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing an example of a communication sequence between the slave unit and the master unit in the present invention.

The master unit is installed in a place with a good view, for example, on the roof of a building, and functions as a base station. The master unit is driven by an AC power source and is used in a state where radio communication is always possible. In FIG. 2, the base unit is always in a receiving state during a time zone during which no signal (telegram) is transmitted. On the other hand, the slave unit is installed, for example, in a gas meter in each home or attached externally, and periodically transmits a meter reading value to the master unit. The transmitted meter reading value is sent to the center of the gas company through the master unit. The power source of the slave unit is a battery, and maintenance-free for a long period (for example, 10 years, 15 years, 20 years) is required.
Therefore, in order to reduce power consumption, the slave unit cannot always maintain a state in which wireless communication is possible. That is, as shown in FIG. 2, after transmitting the meter reading value at a specific timing, the slave unit waits for a return from the master unit at a predetermined timing (time zone), and at other timings, the slave unit Stop the communication circuit. By performing such intermittent reception, the power consumption of the slave unit is suppressed.
Here, since the master unit plays a role like a base station, it is required to accommodate (cover) several thousand to several tens of thousands of slave units in one master unit. For this reason, the communication area (cover area) of the base unit needs to be several hundred meters to several kilometers. Therefore, the transmission output of the parent device and the child device needs about several hundred mW to 1 W. In this case, the power consumed during transmission increases.
Here, the case of a gas meter has been described as an example, but the same applies to an automatic meter reading system such as a water meter. In any meter, the installation location and mounting method of the slave unit built in the meter cannot be changed for a long period of time (or need not be changed) from the time of installation. In other words, the slave unit is a fixed station whose installation location is fixed.
In addition, even with a slave unit installed externally to the meter, it is possible to change the installation method somewhat after the start of operation, but basically the installation method is extensive (based on the installation location and surrounding environment). It is difficult to change to a stick). Therefore, as in the case where the slave unit is built in, a stable operation as a fixed station is required for a long time after it is once installed.
On the other hand, the base unit is basically not supposed to change the installation location after it is installed in a place with good visibility such as the rooftop of a building. In order to change the installation location, a person has to go to the installation location, and labor costs and work man-hours are generated. The same applies to the slave unit. Therefore, in a long-term maintenance-free wireless communication system, both the master unit and the slave unit are required to have long-term stable communication quality as a fixed station.
FIG. 3 shows a basic configuration diagram of a wireless terminal as a slave in the present invention. The wireless terminal transmits a transmission message, receives the return power transmission message transmitted from the base unit, and when the received electric field strength of the return power transmission message becomes equal to or less than the electric field strength threshold at least once, the next transmission message And an output variable unit 3 that reduces the transmission output of the next transmission message when the transmission output is increased and the reception field strength of the return transmission message becomes greater than the electric field strength threshold at least once. With this configuration, power consumption of the wireless terminal can be suppressed.
Next, a specific operation of the slave unit will be described with reference to the block diagram of FIG.
As shown in FIG. 4, the slave unit includes an antenna 1, a transmission / reception unit 2, an output variable unit 3, a measurement unit 4, a control unit 5, and a storage unit 6.
Here, a specific operation will be described by taking the slave unit 102 in FIG. 1 as an example. The subunit | mobile_unit 102 has an output variable function which varies a transmission output. When the slave unit 102 is installed at the site and starts operating, the control unit 5 creates a transmission message and outputs the transmission message to the transmission / reception unit 2. The transmission / reception unit 2 transmits the transmission message output from the control unit 5 via the antenna 1.
The transmission output (transmission power) at this time is the maximum output (maximum power) that the slave unit 102 can transmit. The transmission output is adjusted by the output variable unit 3. After transmitting the transmission message, handset 102 waits for a return power transmission message from the parent device at a predetermined timing (time zone).
A transmission message transmitted from the child device 102 is received by the parent device 101, the parent device 201, and the parent device 301. Then, any one of the parent device 101, the parent device 201, and the parent device 301 transmits a return power transmission statement to the child device 102. Here, base unit 201 closest to handset 102 transmits a return power transmission statement.
Of the parent device 101, the parent device 201, and the parent device 301, which parent device transmits the return power transmission statement is related to the location relationship between each parent device and the child device 102, the child device in each parent device. For example, the center of the gas company may determine based on the number of accommodations (number of covers) and instruct each parent machine in advance.
The transmission / reception unit 2 receives the return power transmission text from the parent device 201 via the antenna 1. And the measurement part 4 measures the received electric field strength of the received return power transmission sentence.
On the other hand, a predetermined electric field strength threshold value is stored in the storage unit 6 of the child device 102. This electric field strength threshold is a predetermined level at which the parent device and the child device can stably communicate, and is, for example, −90 dBm as described above.
When the received electric field strength of the return power transmission message transmitted from the parent device 201 is greater than the electric field strength threshold stored in the storage unit 6 (or more than the electric field strength threshold), the slave device 102 transmits the transmission output of the next transmission message. (Transmission power) is set lower than the previous transmission output.
More specifically, the control unit 5 compares the received electric field strength of the returned power transmission text output from the measurement unit 4 with the electric field strength threshold stored in the storage unit 6, and outputs the comparison result to the output variable unit 3. The output variable unit 3 changes the transmission output of the transmission message transmitted from the transmission / reception unit 2 based on the comparison result. That is, if the output variable unit 3 determines that the received electric field strength of the return power transmission text is greater than the electric field strength threshold (or more than the electric field strength threshold) from the comparison result, the transmission output of the next transmission telegram is greater than the previous transmission power. The transmission / reception unit 2 is instructed to decrease by a predetermined amount. The transmission / reception unit 2 transmits the transmission message created by the control unit 5 in accordance with an instruction from the output variable unit 3.
Note that the amount of decrease for reducing the transmission output (in other words, the difference between the previous transmission output and the next transmission output) may be a predetermined value, or stored in the storage unit 6 and the received electric field strength of the return transmission text. You may adjust from the difference with the measured electric field strength threshold value. For example, if the difference between the received electric field strength and the electric field strength threshold is 5 dBm, the transmission output is reduced by an amount corresponding to 5 dBm at the next transmission. Alternatively, as the difference between the received field strength and the field strength threshold is larger, the amount of decrease is increased and the transmission output is decreased.

  In this way, the slave unit 102 transmits the next transmission message with a transmission output smaller than the previous transmission power, based on the received power intensity of the return transmission message from the parent unit. And the main | base station 201 which received the transmission message | telegram from a subunit | mobile_unit transmits a returned power transmission sentence. After receiving the power transmission message from the parent device again, handset 102 measures the received field strength, compares the stored field strength threshold with the measured received field strength, and transmits the transmission output of the next transmitted message. To decide.

  The subunit | mobile_unit 102 repeats said communication sequence until the received electric field strength of the received return power transmission sentence becomes equal to an electric field strength threshold value. Then, when the received electric field strength of the received return power transmission message becomes equal to the electric field strength threshold, the slave unit 102 transmits the transmission message while maintaining the transmission output at that time.

On the other hand, when the received electric field strength of the return power transmission message transmitted from the parent device 201 is equal to or less than the electric field strength threshold (or smaller than the electric field strength threshold), the slave device 102 sets the transmission output (transmission power) of the next transmission message. Transmit larger than the previous transmission output.
More specifically, the control unit 5 compares the received electric field strength of the returned power transmission text output from the measurement unit 4 with the electric field strength threshold stored in the storage unit 6, and outputs the comparison result to the output variable unit 3. The output variable unit 3 changes the transmission output of the transmission message transmitted from the transmission / reception unit 2 based on the comparison result. That is, when the output variable unit 3 determines that the received electric field strength of the return transmission text is equal to or lower than the electric field strength threshold (or smaller than the electric field strength threshold) from the comparison result, the transmission output of the next transmission message is set to be lower than the previous transmission power. The transmitter / receiver 2 is instructed to increase it by a predetermined amount. The transmission / reception unit 2 transmits the transmission message created by the control unit 5 in accordance with an instruction from the output variable unit 3.
Note that the amount of increase for increasing the transmission output (in other words, the difference between the previous transmission output and the next transmission output) may be a predetermined value, or stored in the storage unit 6 and the received electric field strength of the returned power transmission text. You may adjust from the difference with the measured electric field strength threshold value. For example, if the difference between the received electric field strength and the electric field strength threshold is 5 dBm, the transmission output is increased by the amount corresponding to 5 dBm at the next transmission. Alternatively, as the difference between the received electric field strength and the electric field strength threshold is larger, the amount of increase is increased and the transmission output is increased.
Thereafter, the slave unit 102 repeats the same operation, and when the received electric field strength of the received return transmission text is larger than the electric field strength threshold stored in the storage unit 6, the transmission output is reduced, and the received electric field of the received return transmission text is received. When the intensity is equal to or less than the electric field intensity threshold stored in the storage unit 6, the transmission output is increased and the transmission message is transmitted. Note that these operations of the slave unit 102 are controlled by the control unit 5.

The above movement will be described with reference to FIG. Base units 101, 201, 301, and 401 each have four service areas capable of stable communication, areas S-1, S-2, S-3, and S-4. 90 dBm is the standard. The reference value −90 dBm is the same as the electric field strength threshold value stored in the storage unit 6 of FIG. That is, when the base unit 201 is used as a reference, the line on the service area S-2 can be regarded as an electric field strength of −90 dBm.
Here, as shown in FIG. 1, the slave unit 102 is disposed inside the reference of the service area S-2 of the master unit 201 (that is, the line of the service area S-2). That is, the distance from the base unit 201 is closer than the limit (boundary) of the service area S-2. This is presumed that the received electric field strength of the radio wave received by the slave unit 102 from the master unit 201 (in other words, the return power transmission text received from the master unit 201) is greater than -90 dBm. In this case, the slave unit 102 often repeatedly transmits a transmission message to the master unit 201 with a transmission power smaller than the maximum transmission power (or field strength threshold).

The magnitude of transmission power is directly linked to the magnitude of current consumption used during transmission. In particular, in the case of a wireless terminal that requires a high output of about several hundred mW to 1 W as in the communication system of the present invention, the transmission current also increases.
Therefore, being able to repeat transmission with a reduced transmission output is a great advantage as a reduction in power consumption of the slave unit. Of course, since the electric field strength threshold (for example, −90 dBm) in the service area capable of stable communication is secured, communication reliability is not impaired. However, if the received electric field strength temporarily decreases due to environmental changes, noise, or interference, it operates to temporarily increase the transmission output at the next transmission, so stable communication is possible. Recovery can also be realized.

  Next, a case where the slave unit 102 cannot receive the return power transmission text from the master unit 201 will be described. When the handset 102 cannot receive the return power transmission text for some reason, the measuring unit 4 cannot measure the received electric field strength. In this case, the output variable unit 3 transmits the transmission message to be transmitted next time with a larger transmission output. Slave unit 102 repeats the same operation thereafter until it can receive the return power transmission text from master unit 201.

  Here, when the master unit 201 fails for some reason, or a stationary obstacle is installed on the radio wave propagation path between the master unit 201 and the slave unit 102, communication becomes impossible or the electric field strength is remarkably reduced. Is assumed. In these cases, even if the child device 102 increases the transmission output of the transmission message, the return power transmission message from the parent device 201 cannot be received, and therefore communication between the parent device 201 and the child device 102 may not be recovered. That is, since the transmission message from the child device 102 does not reach the parent device 201 regardless of the magnitude of the transmission power, the parent device 201 does not transmit the return transmission message.

Such a situation can be detected or recognized at the center of a gas company, for example.
If the transmission message from the slave unit 102 is not notified to the gas company center via the master unit 201, the gas company center detects a communication abnormality between the slave unit 102 and the master unit 201. can do. Alternatively, when a high-rise building or the like is constructed on the radio wave propagation path between the parent device 201 and the child device 102, the center of the gas company can recognize the cause beyond communication by a field survey or the like.
For example, if the gas company center determines that the communication abnormality between the child device 102 and the parent device 201 is not solved due to the construction of a high-rise building or the like, the gas company center An instruction is given to another parent device different from the parent device 201 to change from the parent device 201 to another parent device as a parent device communicating with the child device 102.
Upon receiving this instruction, the other parent device transmits an instruction message including instruction information for changing from the parent device 201 to another parent device as a parent device that communicates with the child device 102.
On the other hand, the parent device 201 that has received this instruction stops waiting for transmission from the child device 102. Further, the base unit 201 may transmit a return power transmission sentence including instruction information for changing from the base unit 201 to another base unit as a base unit that communicates with the slave unit 102. . In this case, the transmission power of the return transmission text may be larger than the service area reference value (for example, −90 dBm) as the emergency transmission power.
The transmission / reception unit 2 receives a return power transmission message from the parent device 201 or an instruction message from another parent device via the antenna 1. When the instruction information for changing the parent device 201 to another parent device is detected as a parent device for communication, the control unit 5 creates a transmission message for transmission to another parent device, and transmits and receives A transmission message is output to unit 2. The transmission / reception unit 2 transmits a transmission message for transmission to another parent device output from the control unit 5 via the antenna 1.
Even when the transmission message transmitted from the child device 102 does not reach the parent device 201, there is a possibility that it will reach another parent device (for example, the parent device 301). In this case, the parent device 301 does not transmit a return power transmission message to the child device 102, but notifies the transmission company message transmitted from the child device 102 to the center of the gas company.
After such a state continues, the gas company center determines that the radio wave environment between the slave unit 102 and the master unit 201 is bad, and transmits a return power transmission message to the transmission message transmitted from the slave unit 102. It is also possible to instruct the master unit 301.
By doing this, even when a communication abnormality between the child device 102 and the parent device 201 is not resolved, another communication route is established and communication between the other parent device and the child device 102 is continued. Can do.
On the other hand, since the slave unit 102 cannot receive the return power transmission message from the master unit 201, the slave unit 102 transmits the transmission message while gradually increasing the transmission output. Then, the transmission message transmitted from the child device 102 may be received by the parent device 101 or the parent device 301 in FIG.
That is, when the child device 102 continues stable communication with the parent device 201, the child device 102 sets the transmission power of the transmission message so as not to exceed the threshold (for example, -90 dBm) of the service area S-2. The transmission was narrowed down (in other words, the operation was performed in accordance with a communication sequence that could not exceed the electric field strength threshold).
For this reason, the transmission message transmitted from the child device 102 does not reach the parent device 101 or the parent device 301 whose distance from the child device 102 is farther than that of the parent device 201. However, when the slave unit 102 increases the transmission output in accordance with the above-described operation, the transmission message transmitted from the slave unit 102 with the transmission power exceeding the electric field strength threshold reaches the master unit 101 or the master unit 301. .

Here, since it is determined that the base unit 201 transmits the return power transmission message to the transmission message transmitted from the slave unit 102, the master unit 101 or the master unit 301 receives the transmission message transmitted by the slave unit 102. Even if it is possible, the parent device 101 or the parent device 301 does not transmit a return power transmission message.
However, it is assumed that the parent device 101 or the parent device 301 sends data included in the transmission message transmitted by the child device 102 to the server of the gas company. In other words, in this case, the data from the slave unit 102 does not reach the server (or center) of the gas company via the master unit 201 but arrives via the master unit 101 or the master unit 301.

Based on these circumstances, the center of the gas company responds to the transmission message of the child device 102 when the transmission message from the child device 102 or the data included in the transmission message arrives via another parent device different from the parent device 101. The parent device that transmits the returned power transmission text is switched from the parent device 201 to another parent device.
For example, in the case of the location shown in FIG. 1, the center of the gas company designates the parent device 301 whose distance to the child device 102 is the second shortest after the parent device 201 as the parent device that transmits a return power transmission statement on behalf of the parent device 201. To do. That is, the center of the gas company returns a transmission message to the transmission message of the child device 102 when the transmission message from the child device 102 or the data included in the transmission message arrives via a plurality of other parent devices different from the parent device 101. As a parent device that transmits a message, the other parent device having the shortest distance from the parent device 201 after the parent device 201 is selected from among a plurality of other parent devices, and the parent device 201 is switched to another selected parent device. .

When the base unit 301 selected as the base unit that transmits the return power transmission message receives a transmission message from the slave unit 102 after being selected from the center of the gas company, for example, the base unit 301 transmits the return power transmission statement to the slave unit 102. Thereafter, the slave unit 102 and the master unit 301 communicate according to the same communication sequence as described above, and the slave unit 102 secures the electric field strength threshold value (for example, −90 dBm) of the service area S-3 of the master unit 301. The transmission output is gradually reduced.
From the above, even when a communication failure occurs, communication on other communication routes is established, and by changing the transmission output of the slave unit on the established communication, power consumption is maintained while maintaining stable communication quality. Can be suppressed.

In the present embodiment, a case has been described in which the parent device 201 transmits a returned power transmission message every time in response to a transmission message transmitted from the child device 102. However, the parent device 201 does not necessarily need to transmit a returned power transmission message every time. Absent. For example, the master unit 201 may transmit a return power transmission message once when a transmission message from the child device 102 is received a predetermined number of times (for example, three times). Alternatively, the parent device 201 may transmit a returned power transmission message once a day when a transmission message from the child device 102 is received.
In this case, in a situation where the return power transmission text is not received from the base unit 201, if the timing at which the return power transmission text is not received is different from the return timing defined in advance, the slave unit 102 is normal even if the return power transmission text is not received. The transmission message is transmitted with the transmission output determined based on the comparison result between the received electric field strength of the return transmission message received last time and the electric field strength threshold. On the other hand, the transmission output of the next transmission message is increased only when the return transmission message is not received at a predetermined return timing.

The above method in which the parent device does not transmit the return power transmission statement every time is also advantageous in that the communication traffic of the wireless communication system is reduced. The timing at which the slave unit transmits a transmission message is basically the timing at which a meter reading value such as a gas meter is acquired and transmitted to a server (or center) such as a gas company via the master unit.
For example, when the gas company wants to acquire the meter reading value every hour in almost real time, the slave unit needs to transmit the meter reading value every hour. Here, when hundreds to thousands of slave units transmit every hour, a huge amount of traffic occurs. Furthermore, the traffic further increases when the master unit transmits a return power transmission message to the transmission message that transmits the meter reading value.

  Therefore, for example, in response to the transmission of the meter reading value for each hour of the slave unit, the master unit does not transmit the return power transmission text. In this case, according to the above method, even if the slave unit cannot receive the return power transmission message, the slave unit does not retransmit the transmission message and does not increase the transmission output.

In order to suppress the clock deviation between the parent device and the child device, the child device needs to periodically set its own clock to the parent device clock. For example, when the slave unit sets its own clock to the master unit once a day, the master unit needs to transmit clock data to the slave unit once a day.
In this case, the master unit transmits clock data (or a return power transmission message including clock data) as a return power transmission message once a day to the meter reading value data as a transmission message transmitted by the slave unit. Then, the slave unit adjusts the clock included in the slave unit based on the clock data.
By doing so, it is possible to reduce communication traffic and accurately transmit and receive meter reading values in real time.

Further, by reducing the transmission output of the slave unit, it is possible to suppress interference or interference with surrounding wireless terminals. That is, if the transmission output of the transmission message transmitted from the slave unit 102 is reduced, the influence on other wireless communication systems is also reduced.
In another wireless communication system, a transmission message transmitted from the slave unit 102 becomes an interference signal or an interference signal, which hinders transmission / reception of communication signals in the other wireless communication system. Therefore, by reducing the transmission output of handset 102, the range of influence on other wireless communication systems can be reduced, and as a result, interference or interference can be suppressed.
The same applies to a communication system including a slave unit. That is, as shown in FIG. 1, the wireless communication system of the present invention is composed of a plurality of master units and a plurality of slave units, each performing transmission and reception at a unique timing.
Therefore, the transmission message transmitted from the child device 102 becomes an interference signal or an interference signal in communication by other child devices on the same wireless communication system. For example, in FIG. 1, when the slave unit 202 is waiting to receive a return power transmission message from the master unit 301 and the transmission message of the slave unit 102 interferes or interferes with the slave unit 202, the slave unit 202 There is a possibility that the return transmission message cannot be received.
However, in the present embodiment, since the handset 102 can transmit a transmission message with a transmission output as necessary (in some cases, the minimum necessary), it can be transmitted to other wireless terminals in the same wireless communication system. Thus, the influence of interference or interference can be suppressed.

In the present embodiment, each time the slave unit 102 measures the received electric field strength of the returned power transmission text from the master unit and compares the measurement result with a predetermined threshold value, It was explained that the transmission output of was adjusted.
However, for example, the received electric field strength of the return power transmission sentence from the base unit 201 is continuously a predetermined number of times with respect to the electric field strength threshold (for example, −90 dBm) of the service area S-2 stored in the storage unit 6. When the value is below (that is, below the field strength threshold (or smaller than the field strength threshold)), the transmission output of the slave unit is increased, or continuously exceeds the predetermined number of times (that is, the field strength threshold) It is also possible to adopt a configuration in which the transmission output of the slave unit is reduced when it is larger (or when the electric field strength threshold is exceeded).
Since the received electric field strength varies instantaneously due to changes in the surrounding environment, etc., it may be difficult to ensure stable communication if the transmission output is changed for each threshold determination. Therefore, threshold determination is continuously performed a predetermined number of times, and transmission output is adjusted based on the determination result, thereby stabilizing communication quality, reducing power consumption of the slave unit, and suppressing interference or interference. It can be performed.

Further, the received electric field strength of the returned power transmission text is continuously stored in the storage unit 6 for a predetermined period, and the ratio of the number of times (period) the electric field intensity threshold is reduced during the predetermined period or the number of times (period) the electric field intensity threshold is exceeded It is also possible to adjust the transmission power of the handset when the ratio exceeds a predetermined ratio.
That is, when the ratio of the number of times the received electric field strength falls below the electric field strength threshold (or smaller than the electric field strength threshold) with respect to the total number of received electric field strength stored in a predetermined period exceeds the predetermined ratio, the transmission power of the transmission message If the ratio of the number of times the received electric field strength is greater than the electric field strength threshold (or more than the electric field strength threshold) to the total stored number of received electric field strengths in a predetermined period exceeds the predetermined ratio, the transmission message Reduce transmission power.

  In this embodiment, only the operation between the parent device and the child device has been described. However, the same method can be applied to a system in which a repeater is introduced. That is, the slave unit receives the return power transmission text from the base unit or the repeater, and has the same effect by controlling the transmission output (transmission power) of the next transmission message according to the received electric field strength of the received return power transmission text. be able to.

The operation when a new master unit or repeater is introduced in a state where the system is already in operation will be described.
As shown in FIG. 1, as a state where the system has already been operated, the slave unit 102 is set in advance by the center of the gas company so as to receive a return power transmission message from the master unit 201. It is assumed that a parent device 501 (not shown) or a repeater is newly introduced there.
Here, when the installation environment of the parent device 501 (or the repeater) is superior to that of the parent device 201 for the child device 102, the transmission message transmitted from the child device 102 is the newly installed parent device. It should reach 501 as well.
Therefore, the center of the gas company can receive the transmission message transmitted from the child device 102 via the parent device 201 and the newly installed parent device 501. As a result, by comparing the reception electric field strength result of the transmission message transmitted from the child device 102 in the parent device 501 with the reception electric field strength result of the transmission message transmitted from the child device 102 in the parent device 201, the center of the gas company Determines whether the parent device 201 can be left as the parent device that transmits the returned power transmission text to the child device 102 or is switched to the newly installed parent device 501.

On the other hand, when the installation environment of the parent device 501 (or repeater) is inferior to that of the parent device 201 for the child device 102, the transmission message transmitted from the child device 102 is transmitted to the newly installed parent device 501. May not reach.
When the transmission message transmitted from the child device 102 does not reach the parent device 501, the center of the gas company can receive the transmission message transmitted from the child device 102 only via the parent device 201.
Of course, since the center of the gas company knows the installation location relationship of the newly installed parent device 501, the child device 102, and the parent device 201, the return power transmission message to the child device 102 is based on the installation location relationship. It is also possible to re-select the parent device that transmits. However, it is not known whether the transmission message actually transmitted from the child device 102 does not reach the parent device 501 due to the installation location.

In consideration of such a situation, the slave unit 102 transmits a transmission output (or higher than the electric field strength threshold) (or, regardless of the determination with the electric field strength threshold value stored in the storage unit 6 once every plural times (for example, 10 times)). The transmission message may be transmitted at the maximum transmission output).
In this case, even if the installation environment of the parent device 501 is inferior to that of the parent device 201, the parent device 501 may be able to receive a transmission message transmitted from the child device 102. Information can be communicated to the gas company center. As a result, the center of the gas company can receive the transmission message transmitted from the slave unit 102 via the newly installed master unit 501.
Then, the center of the gas company can be left as the master unit 201 or newly installed as a master unit that transmits a return power transmission message from the installation location to the slave unit 102 received from the master unit 501. It is determined whether to switch to the parent device 501. By doing so, it is possible to increase the accuracy of route selection corresponding to the newly installed master unit or repeater while minimizing the increase in the transmission output of the slave unit.
(Embodiment 2)
A second embodiment of the present invention will be described below. Note that in the second embodiment, description of the same matters as in the first embodiment will be omitted.

In the second embodiment, the operation of the slave unit is the same as that of the first embodiment. The communication operation of the master unit will be described with reference to the block diagram of FIG.
As shown in FIG. 5, the parent device includes an antenna 11, a transmission / reception unit 12, an output variable unit 13, a measurement unit 14, a control unit 15, and a storage unit 16.

  Here, a specific operation will be described with reference to the base unit 201 in FIG. Base unit 201 has an output variable function for changing the transmission output. In the parent device 201, the transmission / reception unit 12 receives a transmission message from the child device 102 via the antenna 11. And the measurement part 14 measures the received electric field strength of the received transmission message.

On the other hand, a predetermined electric field strength threshold value is stored in the storage unit 16 of the parent device 201. This electric field strength threshold is a predetermined level at which the parent device and the child device can stably communicate, and is, for example, −90 dBm as in the first embodiment.
When the received electric field strength of the transmission message transmitted from the child device 102 is larger than the electric field strength threshold stored in the storage unit 16 (or greater than or equal to the electric field strength threshold), the parent device 201 transmits the transmission output (transmission) of the returned power transmission message. (Power) is reduced so as to be about the electric field strength threshold stored in the storage unit 16 and transmitted.
More specifically, the control unit 15 compares the received electric field strength of the transmission message output from the measurement unit 14 with the electric field strength threshold stored in the storage unit 16 and outputs the comparison result to the output variable unit 13. The output variable unit 13 changes the transmission output of the returned power transmission text transmitted from the transmission / reception unit 12 based on the comparison result.
That is, if the output variable unit 13 determines that the received electric field strength of the transmission message is greater than the electric field strength threshold (or greater than or equal to the electric field strength threshold) from the comparison result, the output variable unit 13 reduces the transmission output of the return transmission message to about the electric field strength threshold. The transmitter / receiver 12 is instructed. The transmission / reception unit 12 transmits the return power transmission text created by the control unit 15 in accordance with an instruction from the output variable unit 13.

  As described above, the base unit 201 transmits the return power transmission text with the same transmission output as the electric field strength threshold. Then, every time the master unit 201 receives a transmission message transmitted from the slave unit 102, the master unit 201 measures the received electric field strength, and compares the stored electric field strength threshold with the measured received electric field strength. The transmission output of the return power transmission statement is determined.

  Master device 201 repeats the above communication sequence until the received electric field strength of the transmitted message from slave device 102 becomes equal to the electric field strength threshold. When the received electric field strength of the transmitted message from the child device 102 becomes equal to the electric field strength threshold, the parent device 201 transmits a return power transmission message while maintaining the transmission output at that time.

On the other hand, when the received electric field strength of the transmitted message from the child device 102 is equal to or less than the electric field strength threshold (or smaller than the electric field strength threshold), the parent device 201 stores the transmission output (transmission power) of the returned power transmission message in the storage unit. The signal is transmitted so as to be about the threshold value of the electric field strength described in FIG.
More specifically, the control unit 15 compares the received electric field strength of the transmission message output from the measurement unit 14 with the electric field strength threshold stored in the storage unit 6, and outputs the comparison result to the output variable unit 13. The output variable unit 13 changes the transmission output of the returned power transmission text transmitted from the transmission / reception unit 12 based on the comparison result.
That is, the output variable unit 13 increases the transmission output of the return power transmission text to about the field strength threshold when it is determined from the comparison result that the received field strength of the transmission text is equal to or less than the field strength threshold (or smaller than the field strength threshold). The transmitter / receiver 12 is instructed. The transmission / reception unit 12 transmits the return power transmission text created by the control unit 15 in accordance with an instruction from the output variable unit 13.
Thereafter, the base unit 201 repeats the same operation, and when the received electric field strength of the transmitted message from the slave unit 102 is larger than the electric field strength threshold stored in the storage unit 16, the transmission output is reduced and received. When the received electric field strength of the transmission message from the slave unit 102 is equal to or less than the electric field strength threshold stored in the storage unit 16, the transmission output is increased and the return transmission message is transmitted. Note that these operations of the parent device 201 are controlled by the control unit 15.
In the present embodiment, as in the case of the slave unit in the first embodiment, for example, the received field strength of the transmission message from the slave unit 102 is the electric field strength threshold value stored in the storage unit 6. On the other hand, when the number of times continuously falls below a predetermined number of times (that is, below the field strength threshold (or smaller than the field strength threshold)), the transmission output of the return transmission text is increased or continuously It is also possible to adopt a configuration in which the transmission output of the returned power transmission text is reduced when the number of times exceeds the number of times (that is, greater than the field strength threshold (or greater than the field strength threshold)).
In addition, the reception electric field strength of the transmission message is continuously stored in the storage unit 6 for a predetermined period, and the ratio of the number of times (period) when the electric field intensity threshold is exceeded during the predetermined period or the number of times (period) when the electric field strength threshold is exceeded. It is also possible to adjust the transmission power of the return power transmission sentence when the ratio exceeds the predetermined ratio.
In other words, when the ratio of the number of times the received electric field strength is less than or equal to the electric field strength threshold (or smaller than the electric field strength threshold) to the total stored number of received electric field strengths of the transmitted message in a predetermined period exceeds the predetermined ratio. If the ratio of the number of times that the received electric field strength exceeds the electric field strength threshold (or exceeds the electric field strength threshold) with respect to the total number of times of storage exceeds the predetermined ratio, the transmission power of the return transmission text is reduced. .

When the first embodiment and the second embodiment are combined, both the child device 102 and the parent device 201 control their transmission outputs. If there is no change in the distance between wireless terminals and the surrounding environment due to the characteristics of wireless communication, the received electric field strength when the other side receives a signal transmitted from one side is the same as that received by the transmitting side (one side). Even if the side (the other side) is replaced, the same is true. If the frequency is different, the transmission side (one side) and the receiving side (the other side) are different.
Therefore, by changing the transmission output of both the child device 102 and the parent device 201, it is possible to communicate with a more appropriate transmission output while ensuring the quality of mutual communication without depending on the frequency to be used. . In particular, for slave units that are required to reduce power consumption due to battery operation, the transmission output of the return message is adjusted even in the master unit, which improves the setting accuracy of the transmission output of the slave unit's transmission message, and reduces power consumption. It can suppress more efficiently.

  In addition, by changing the transmission output of the master unit, it is possible to suppress the influence of interference or interference that the master unit has on other surrounding systems and / or its own system. In addition, since it is necessary for the main | base station to transmit a returned power transmission sentence with respect to several subunit | mobile_unit, it is necessary to adjust transmission output for every subunit | mobile_unit.

Furthermore, the adjustment of the transmission output in the parent device is not based on the electric field strength threshold of the parent device itself, but may be performed according to the transmission power information in the child device included in the transmission message transmitted from the child device. Good.
That is, the control unit 5 includes transmission output information in the transmission message. The master unit that has received the transmission message transmitted from the slave unit analyzes the message and extracts the transmission output information of the slave unit, and returns the return transmission message with the same transmission output as the transmission output of the transmission message transmitted from the slave unit. Send to the slave unit.
In this method, when there is no change in the distance between radios and the surrounding environment due to the characteristics of wireless communication, the received electric field strength when the other receives a signal transmitted from one is ) And the receiving side (the other side) are used in the same manner.

In the case of this method, the master unit does not need to include the measurement unit 14 and the storage unit 16 that stores the electric field strength threshold. In addition, the parent device needs to change the transmission output of the return power transmission message for each child device, but does not need to store the electric field strength threshold value for each child device, and is included in the transmission message transmitted from each child device. Based on the above, it is possible to determine the transmission output of the return power transmission text to be transmitted to each slave unit.
(Embodiment 3)
A third embodiment of the present invention will be described below. Note that in the third embodiment, descriptions of the same matters as in the first embodiment and the second embodiment are omitted.

  The operation of the slave unit in the third embodiment will be described with reference to the block diagram of FIG. In FIG. 6, the antenna 1, the transmission / reception unit 2, the output variable unit, the measurement unit 4, the control unit 5, and the storage unit 6 operate in the same manner as in the first embodiment. Further, the slave shown in FIG. 6 includes an alarm detection unit 7.

The subunit | mobile_unit 102 has various alarm functions, for example, in order to drive with the battery installed in the gas meter internally or externally. For example, alarms such as excessive gas maximum flow (or abnormal flow value), removal of a slave due to mischief, gas leak detection, low battery level, and the like can be considered.
Here, when these alarms occur, it is necessary to reliably notify the gas company center. This is because the contents (type) of the alarm may cause a dangerous situation for the user's life or may prevent the collection of a reliable gas fee based on the meter reading value. This is because a quick response by the company is required.
The alarm detection unit 7 detects these alarms. Then, when an alarm is detected, the slave unit 102 transmits a telegram that is notified by the control unit 5 to notify the center of the gas company via the master unit. More specifically, the alarm detection unit 7 outputs a detection result to the control unit 5 when detecting an alarm. The control unit 5 generates alarm detection information based on the detection result output from the alarm detection unit 7.
At this time, in the slave unit 102, even if the transmission output of the transmission message is suppressed as in the first embodiment, the output variable unit 3 maximizes the transmission output with respect to the transmission / reception unit 2. Alternatively, the transmission / reception unit 2 transmits a message (or transmission message including alarm information) for notifying an alarm via the antenna 1 in accordance with an instruction from the output variable unit 3. Do.

The above operation will be described with reference to FIG. Normally, the child device 102 transmits a transmission message with a minimum transmission output that can ensure stable communication with the parent device 201. However, when information such as alarm notification must be sent to the gas company center via the master unit without fail, not only the master unit 201 but also the surrounding master unit 101 and / or the master unit 301 may arrive. Send alarm information with send output.
As a result, even if the parent device 201 fails to receive a message that is more important than a normal transmission message, an important message (for example, alarm information) is transmitted to the gas company via the parent device 101 and / or the parent device 301. The possibility of being sent increases, and important information can be surely notified.
Since alarms do not occur frequently, even if the transmission output is increased compared to the normal transmission telegram, the battery life of the slave unit 102 is not greatly affected, and the peripheral system or wireless terminal is not affected. The effects of interference or interference on the stool are not serious.
Although cases have been described with the above embodiment as examples where the present invention is configured by hardware, the present invention can also be realized by software.
Each functional block used in the description of each of the above embodiments is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.
Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.
Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied.

  As described above, the wireless terminal, the wireless communication system, and the communication method according to the present invention are useful in a wireless terminal that continues to operate with battery operation for a long period of 10 years or more and a wireless communication system including the wireless terminal. .

DESCRIPTION OF SYMBOLS 1, 11 Antenna 2, 12 Transmission / reception part 3, 13 Output variable part 4, 14 Measurement part 5, 15 Control part 6, 16 Storage part 7 Alarm detection part 101, 201, 301, 401, 501 Base unit 102, 202, 302 , 303, 402

Claims (11)

A wireless communication system including one or more parent devices and a child device,
The slave is
Send a send message,
Receive the return power transmission text sent from the base unit,
When the received electric field strength of the return transmission text has become below the electric field strength threshold at least once, the transmission output of the next transmission message is increased, and the received electric field strength of the return transmission text is greater than the electric field strength threshold at least once. At the next time, reduce the transmission output of the next transmission message,
The base unit is
Receive a transmission message sent from the slave,
Sending the return power transmission statement to the slave unit;
Wireless communication system. The slave unit increases the transmission power of the next transmission message when the reception electric field strength of the return transmission text continuously falls below the electric field strength threshold a predetermined number of times, and the reception electric field strength of the return transmission text continues. When the electric field strength threshold value exceeds a predetermined number of times, the transmission output of the next transmission message is reduced.
The wireless communication system according to claim 1. When the ratio of the number of times the received electric field strength of the return power transmission text becomes equal to or less than the electric field strength threshold with respect to the total stored number of received electric field strengths of the return power transmission text in a predetermined period exceeds a predetermined ratio, The ratio of the number of times the received electric field strength of the returned power transmission text becomes greater than the electric field strength threshold to the total stored number of received electric field strengths of the returned power transmission text in the predetermined period is a predetermined ratio When exceeding, reduce the transmission output of the next transmission message,
The wireless communication system according to claim 1. The base unit is
When the received field strength of the received transmission message is at least once below the field strength threshold, the transmission power of the return transmission message is increased, and the received field strength of the received transmission message is greater than the field strength threshold at least once. When it becomes, reduce the transmission output of the return transmission sentence,
The wireless communication system according to claim 1. The base unit increases the transmission power of the return power transmission message when the reception field strength of the transmission message continuously falls below the field strength threshold a predetermined number of times, and the reception field strength of the transmission message continuously When the electric field strength threshold is greater than a predetermined number of times, the transmission output of the return transmission text is reduced.
The wireless communication system according to claim 4. When the ratio of the number of times that the reception electric field strength of the transmission message is equal to or less than the electric field strength threshold with respect to the total number of reception electric field strengths of the transmission message in a predetermined period exceeds a predetermined ratio, The transmission power of the return message is increased, and the ratio of the number of times the received electric field strength of the transmitted message is larger than the electric field strength threshold to the total stored number of received electric field strengths of the transmitted message in the predetermined period is a predetermined ratio. When it exceeds, reduce the transmission output of the return power transmission statement.
The wireless communication system according to claim 4. The transmission message transmitted from the slave unit includes information on the transmission output of the transmission message,
The master unit that has received the transmission message transmits the return power transmission message to the slave unit with the same transmission output as the transmission output of the transmission message.
The wireless communication system according to claim 1. When the slave detects an alarm, the slave transmits a transmission message including the alarm information with a maximum transmission output or a transmission output larger than the electric field strength threshold.
The wireless communication system according to claim 1. A transmission / reception unit that transmits a transmission message and receives a return transmission message transmitted from the parent device;
When the received electric field strength of the return power transmission sentence becomes at least the electric field strength threshold value at least once, the transmission power of the next transmission power message is increased, and the received electric field strength of the return power transmission sentence becomes at least once greater than the electric field strength threshold value. Output variable unit to reduce the transmission output of the next transmission message,
A wireless terminal comprising: An alarm detection unit for detecting an alarm;
When the alarm is detected, the transmission / reception unit transmits a transmission message including the alarm information with a maximum transmission output or a transmission output larger than the electric field strength threshold.
The wireless terminal according to claim 9. Send a send message,
Receive the return power transmission statement,
When the received electric field strength of the return power transmission sentence becomes at least the electric field strength threshold value at least once, the transmission power of the next transmission power message is increased, and the received electric field strength of the return power transmission sentence becomes at least once greater than the electric field strength threshold value. To reduce the transmission output of the next transmission message,
Communication method.

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