JP6967439B2 - Wireless communication protocol - Google Patents

Description

The invention disclosed herein relates to, for example, a wireless communication protocol for a sensor module.

Generally, in a wireless communication protocol, a transmission period during which packets can be continuously transmitted is limited, and after a predetermined transmission period (for example, a maximum of 50 ms) has elapsed, a predetermined pause period (for example, a minimum of 50 ms) is reached. It must wait for the packet to resume transmission (see, for example, ARIB STD-T108, which is one of the standards compliant with the Radio Law of Japan). Therefore, in the wireless communication period for transmitting data composed of a plurality of packets by the wireless communication unit, the above transmission period and the pause period are alternately repeated from the start to the end.

Japanese Unexamined Patent Publication No. 2013-191984

However, in the above-mentioned conventional wireless communication protocol, there is room for further improvement in reducing the power consumption of the wireless communication unit that performs wireless communication according to the protocol.

The invention disclosed in the present specification is to provide a novel wireless communication protocol capable of reducing the power consumption of the wireless communication unit in view of the above-mentioned problems found by the inventors of the present application. The purpose.

The wireless communication protocol disclosed in the present specification limits the transmission period during which the packet can be continuously transmitted in the wireless communication period for transmitting data composed of a plurality of packets by the wireless communication unit. After the predetermined transmission period has elapsed, the packet transmission restart must be waited for for a predetermined pause period, and the transmission period and the pause period are from the start to the end of the wireless communication period. It is repeated alternately, and the number of packets to be transmitted is fixed for each transmission period, the transmission operation is completed within the transmission period, and then the wireless communication unit is operated during the pause period. It is configured to shift from the normal mode to the power saving mode in which the power consumption is smaller than this (first configuration).

Further, the wireless communication circuit disclosed in the present specification includes a control unit and a wireless communication unit controlled by the control unit, and data is based on the wireless communication protocol having the first configuration. It is said that the configuration is such that wireless communication is performed (second configuration).

In the wireless communication circuit having the second configuration, the control unit outputs a power saving mode transition signal when a predetermined transition standby time has elapsed since the transmission request to the wireless communication unit was started. The wireless communication unit may be configured to shift from the normal mode to the power saving mode (third configuration) in response to the power saving mode transition signal.

Further, in the wireless communication circuit having the third configuration, the control unit outputs a normal mode return signal when a predetermined return standby time has elapsed after outputting the power saving mode transition signal, and outputs the normal mode return signal. The communication unit may be configured to return from the power saving mode to the normal mode (fourth configuration) in response to the normal mode return signal.

Further, in the wireless communication circuit having the second configuration, the control unit supplies power to the wireless communication unit when a predetermined transition standby time has elapsed since the transmission request to the wireless communication unit was started. The wireless communication unit may be configured to shift from the normal mode to the power saving mode (fifth configuration) by stopping the power supply.

Further, in the wireless communication circuit having the fifth configuration, the control unit supplies power to the wireless communication unit when a predetermined recovery standby time elapses after the power supply to the wireless communication unit is stopped. The wireless communication unit may be configured to return from the power saving mode to the normal mode (sixth configuration) by restarting the power supply.

Further, the sensor circuit disclosed in the present specification comprises a sensor unit that measures a predetermined measurement target and a configuration according to any one of the second to sixth, and wireless communication of the measurement result obtained by the sensor unit. It is a configuration (seventh configuration) having a wireless communication circuit for performing the above.

Further, the sensor module disclosed in the present specification comprises a power supply circuit including an energy harvesting unit and a power storage unit, and a sensor circuit that operates intermittently by receiving power supply from the power supply circuit having the above-mentioned seventh configuration. And, it is said to have a configuration (eighth configuration).

The sensor module having the eighth configuration further includes a voltage monitoring circuit that constantly monitors the input voltage stored in the power storage unit, and the sensor circuit performs measurement of the measurement target and wireless communication of the measurement result. The active state to be performed and the sleep state to suspend the operation are alternately repeated. In the sleep state, the output of the voltage monitoring circuit is confirmed at a predetermined cycle, and the input voltage is higher than the predetermined reference voltage. If it is high, the active state may be restored, and if the input voltage is lower than the reference voltage, the sleep state may be maintained (nineth configuration).

Further, the sensor network disclosed in the present specification has a configuration (10th) including a sensor module having the eighth or ninth configuration and a receiver that wirelessly receives the measurement result of the sensor module. The composition of).

According to the invention disclosed in the present specification, it is possible to provide a novel wireless communication protocol capable of reducing the power consumption of the wireless communication unit.

The figure which shows the 1st Embodiment of a sensor network. The figure which shows one configuration example of a sensor module Time chart showing a comparative example of intermittent operation (without voltage monitoring) Flowchart showing an example of intermittent operation (with voltage monitoring) Time chart showing an example of intermittent operation (with voltage monitoring) Time chart showing the periodicity of data acquisition timing The figure which shows the 1st Embodiment of a voltage monitoring circuit The figure which shows the 2nd Embodiment of a voltage monitoring circuit The figure which shows the 2nd Embodiment of a sensor network Time chart showing an example of collision avoidance method Figure showing an example of TSA [time slot assign] method The figure which shows the current profile in a general wireless communication protocol. The figure which shows the behavior of each part in a general wireless communication protocol Diagram showing challenges in common wireless communication protocols The figure which shows the behavior of each part in a new wireless communication protocol

<Sensor network (first embodiment)>
FIG. 1 is a diagram showing a first embodiment of a sensor network. The sensor network X of the present embodiment includes a sensor module 1, a receiver 2, and a server 3.

The sensor module 1 is, for example, a terminal that operates using self-generated electric power generated by energy harvesting, and measures a predetermined measurement target (= machine vibration, etc.). Further, the sensor module 1 has a one-way or two-way wireless communication function, and wirelessly transmits its own measurement result to the receiver 2.

The receiver 2 is a communication device that wirelessly receives the measurement result of the sensor module 1 and transfers it to the server 3 by wire or wirelessly.

The server 3 records and analyzes the measurement result of the sensor module 1 transferred from the receiver 2.

In the sensor network X of the present embodiment, since the power consumption of the sensor module 1 is covered by the energy harvesting, it is not necessary to lay the power supply wiring or replace the battery for the sensor module 1. Further, since wireless communication is performed between the sensor module 1 and the receiver 2, no signal wiring for connecting the two is required. Therefore, the sensor module 1 can be arranged at an arbitrary position.

For example, when monitoring the vibration and temperature of the vehicle using the sensor network X, it is possible to reduce the weight of the vehicle by omitting the power supply wiring and the signal wiring to the sensor module 1. Further, when monitoring the biological information of the patient using the sensor network X, the burden on the patient is reduced by embedding the sensor module 1 in the patient's body and reading the detection result by the receiver 2 outside the body. It is possible. Further, when monitoring the vibration or temperature of an air conditioner, a compressor, or the like in a factory or the like, it is possible to reduce disconnection due to a transport vehicle and accidents due to wiring.

<Sensor module>
FIG. 2 is a diagram showing a configuration example of the sensor module 1. The sensor module 1 of this configuration example includes a power supply circuit 10, a sensor circuit 20, and a voltage monitoring circuit 30.

The power supply circuit 10 is a means for supplying electric power to each part of the sensor module 1, and includes an energy harvesting unit 11, a power storage unit 12, and a power management unit 13.

The energy harvesting unit 11 is a means (so-called energy harvester) that receives energy (= vibration, light, heat, etc.) existing in the environment where the sensor module 1 is placed to generate power. When vibration is used as an energy source, a piezoelectric element such as a piezo element may be used as the power generation element. When sunlight or illumination light is used as an energy source, a silicon-based, compound-based, or organic-based photoelectric element may be used as the power generation element. When heat is used as an energy source, a thermoelectric element such as a Pelche element may be used as the power generation element. Further, if energy harvesting (or self-power generation) is considered in a broader sense, a CT type current sensor can also be used. The principle is that an alternating current (secondary current) according to the winding ratio flows in the winding on the secondary side so as to cancel the magnetic flux generated in the magnetic core due to the alternating current flowing in the measuring conductor (primary side). It is a thing. However, the above is just an example, and a power generation device based on another power generation principle may be used. For example, vibration power generation includes not only a piezoelectric type (a type using a piezo element) but also an electromagnetic induction type (a type using electromagnetic induction using a coil and a magnet) and an electrostatic type (a type using an electret).

The power storage unit 12 is a means for storing the self-generated power obtained by the energy harvesting unit 11 (however, when a CT type current sensor is used, it may be read as non-contact power supply power), and is, for example, a supercapacitor (= electricity). A general term for double layer capacitors) can be preferably used. The input voltage Vin (= charging voltage of the supercapacitor) stored in the power storage unit 12 is supplied to the power management unit 13, while being monitored by the voltage monitoring circuit 30.

The power management unit 13 generates a desired power supply voltage Vdd from the input voltage Vin and supplies it to the sensor circuit 20. As the power management unit 13, for example, a DC / DC converter can be preferably used.

The sensor circuit 20 includes a sensor unit 21, a wireless communication unit 22, and a control unit 23, and operates intermittently by receiving power supply from the power supply circuit 10.

The sensor unit 21 has a predetermined measurement target (magnetic, acceleration, angular velocity, pressure, strain, vibration, temperature, humidity, light, infrared rays, ultraviolet rays, electromagnetic waves, radiation, electric current, current, voltage, power, position, distance, displacement, It is a means for measuring flow velocity, flow rate, component, composition, concentration, sound, gas, odor, electrical conductivity, pH, water level, count, etc.). The sensor unit 21 may be an analog output or a digital output.

In the sensor module 1, it is preferable that the energy source of the energy harvesting unit 11 and the measurement target of the sensor unit 21 are common. As one example, there is a case where the energy harvesting unit 11 uses vibration as an energy source and the sensor unit 21 measures the above vibration. In this case, when the sensor unit 21 tries to measure the vibration, the energy harvesting unit 11 receives the vibration and generates electric power. Therefore, the sensor unit 21 is more reliably connected to the sensor unit 21 as compared with the case where the energy source is other than the vibration. It becomes possible to supply power.

The wireless communication unit 22 wirelessly transmits the measurement result obtained by the sensor unit 21 to the receiver 2 in response to an instruction from the control unit 23. The wireless communication unit 22 and the control unit 23 can be understood as one of the circuit elements constituting the wireless communication circuit, respectively.

The control unit 23 is a control main body of the sensor unit 21 and the wireless communication unit 22, and includes an interface circuit that receives the output signal of the sensor unit 21, a digital control circuit that performs various signal processing, and the like. As the control unit 23, an MCU [micro control unit] or the like is preferably used.

The voltage monitoring circuit 30 constantly monitors the input voltage Vin stored in the power storage unit 12, and sends the monitoring result to the control unit 23 as an output signal So.

The harvester capacity of the energy harvesting unit 11 is not necessarily large, and it is difficult to keep the sensor circuit 20 operating at all times. Therefore, the sensor circuit 20 is in an active state in which measurement of the measurement target and wireless communication of the measurement result are performed while checking the output signal So of the voltage monitoring circuit 30 in a predetermined cycle T, and a sleep in which the operation is temporarily suspended. Intermittent operation that repeats the state and the state alternately is performed. Hereinafter, the intermittent operation of the sensor circuit 20 will be described in detail.

<Intermittent operation>
First, prior to the description of the intermittent operation using the voltage monitoring circuit 30, as a comparative example, the intermittent operation without using the voltage monitoring circuit 30 will be briefly described with reference to FIG.

FIG. 3 is a time chart showing a comparative example of intermittent operation (without voltage monitoring), and shows the operating states (A: active state, S: sleep state) of the input voltage Vin and the sensor circuit 20 in order from the upper side. There is. The on-voltage Von is a voltage that the power management unit 13 turns on, and the off-voltage Voff is a voltage that the power management unit 13 turns off.

As shown in this figure, the sensor circuit 20 performs an intermittent operation in which an active state A (= measurement and wireless communication) and a sleep state S (= charging) are alternately repeated. In this figure, for convenience of illustration, the time for maintaining the active state A (for example, times t11 to t12) is depicted longer than it should be, but in reality, the time for maintaining the sleep state S (= intermittent operation). It is completed in an extremely short time as compared with the cycle T (for example, several minutes to several hours).

If the stored power in the sleep state S is larger than the power consumption in the active state A, once the input voltage Vin exceeds the on-voltage Von, it does not fall below the off-voltage Voff. Therefore, the sensor circuit 20 can perform intermittent operation while maintaining a constant period T.

On the other hand, as shown in this figure, when the stored power in the sleep state S is smaller than the power consumption in the active state A, the input voltage Vin gradually decreases each time the sleep state S returns to the active state A. Finally, it falls below the off voltage Voff. As a result, the power management unit 13 is turned off and the power supply to the sensor circuit 20 is stopped, so that the timer of the control unit 23 is cut off and the intermittent operation cannot be performed at a constant cycle T (time t12 to t13). And time t14 to t15 for comparison, T ≠ T'). In this way, if the period T of the intermittent operation fluctuates, it becomes impossible to acquire data having periodicity.

Further, if the input voltage Vin falls below the off voltage Voff in the middle of the active state A, measurement and wireless communication are interrupted, so that sufficient data cannot be acquired, or all data. Cannot be sent (see times t13 to t14).

The above-mentioned problem can be improved to some extent by adjusting the on-voltage Von and the off-voltage Voff of the power management unit 13, but cannot be fundamentally solved. In the following, the intermittent operation that can fundamentally solve the above-mentioned problems by using the voltage monitoring circuit 30 will be described in detail.

FIG. 4 is a flowchart showing an example of intermittent operation using the voltage monitoring circuit 30. When the power generation operation of the energy harvesting unit 11 is started by the activation of the sensor module 1, the input voltage Vin stored in the power storage unit 12 increases. Then, when the input voltage Vin reaches the on voltage Von in step S1, the power management unit 13 is turned on in the subsequent step S2.

As a result, the power supply to the sensor circuit 20 is started, so that the sensor circuit 20 is turned on in step S3. After that, in step S4, the measurement target is measured by the sensor unit 21, and further, in step S5, the wireless communication unit 22 wirelessly communicates the measurement result. It should be noted that these steps S3 to S5 correspond to the above-mentioned active state.

When the wireless communication in step S5 is completed, the sensor circuit 20 is turned off in the following step S6. That is, the sensor circuit 20 shifts from the active state to the sleep state. However, even after the transition to the sleep state, the circuit elements (timer of the control unit 23, etc.) required for returning to the active state continue to operate by receiving the minimum power supply from the power management unit 13. ..

After that, in step S7, the control unit 23 determines whether or not the period T has elapsed. Here, when a yes determination is made, the flow proceeds to step S8, and when a no determination is made, the flow is returned to step S7.

If a yes determination is made in step S7, in step S8, the control unit 23 confirms the output signal So of the voltage monitoring circuit 30, and determines whether or not the input voltage Vin is higher than the predetermined reference voltage Vref. Will be done. Although not specified in this flow, it is assumed that the voltage monitoring circuit 30 constantly monitors the input voltage Vin regardless of the operating state of the sensor circuit 20. Here, when the yes determination is made, the flow is returned to step S3, and the return from the sleep state to the active state is performed. On the other hand, when a no determination is made, the flow is returned to step S7, and the progress determination of the cycle T is repeated.

That is, in this flow, in the sleep state (steps S6 to S8), the output of the voltage monitoring circuit 30 is confirmed in the predetermined period T, and if the input voltage Vin is higher than the predetermined reference voltage Vref, the active state is activated. The loop is turned to wake up and stay asleep if the input voltage Vin is lower than the reference voltage Vref, in other words, to repeat the sleep state of period T until the input voltage Vin exceeds the reference voltage Vref. ing.

FIG. 5 is a time chart showing an example of intermittent operation using the voltage monitoring circuit 30, and as in FIG. 3 above, the input voltage Vin and the operating state of the sensor circuit 20 (A: active state, S) are in order from the upper side. : Sleep state) is shown.

The above-mentioned reference voltage Vref is at least the input voltage Vin in the active state A (see time t21 to t22, time t23 to t24, or time t26 to t27) with respect to the off voltage Voff of the power management unit 13. It is assumed that the voltage value (Vref ≧ Voff + Δ) is set higher by the assumed decrease value Δ of.

After the completion of the active state A (corresponding to steps S3 to S5 in FIG. 4) at times t21 to t22, the sensor circuit 20 shifts from the active state A to the sleep state S at time t22 (corresponding to step S6 in FIG. 4). .. Therefore, the input voltage Vin changes from a decrease to an increase.

After that, at time t23, as the cycle T elapses (corresponding to step S7 = Y in FIG. 4), the determination of returning from the sleep state S to the active state A (corresponding to step S8 in FIG. 4) is performed. In the example of this figure, since the input voltage Vin exceeds the reference voltage Vref at the time t23, the return from the sleep state S to the active state A is recognized (corresponding to step S8 = Y in FIG. 4). .. Therefore, the input voltage Vin changes from rising to falling.

Further, after the completion of the active state A (corresponding to steps S3 to S5 in FIG. 4) at times t23 to t24, the sensor circuit 20 again shifts from the active state A to the sleep state S at time t24 (step S6 in FIG. 4). Equivalent to). Therefore, the input voltage Vin changes from a decrease to an increase again.

After that, at time t25, as the cycle T elapses (corresponding to step S7 = Y in FIG. 4), the determination of returning from the sleep state S to the active state A (corresponding to step S8 in FIG. 4) is performed. However, in the example of this figure, since the input voltage Vin does not exceed the reference voltage Vref at the time t25, the return from the sleep state S to the active state A is not recognized, and the sleep state S is maintained (FIG. 4 corresponds to step S8 = N). Therefore, the input voltage Vin continues to rise without turning to a decline.

After the return to the active state A is postponed at the time t25, at the time t26, with the passage of the second cycle T (corresponding to step S7 = Y in FIG. 4), the sleep state S is changed to the active state A again. (Corresponding to step S8 in FIG. 4) is determined. In the example of this figure, since the input voltage Vin exceeds the reference voltage Vref at the time t26, the return from the sleep state S to the active state A is not recognized, and the sleep state S is changed to the active state A. Return is recognized (corresponding to step S8 = Y in FIG. 4). Therefore, the input voltage Vin changes from rising to falling.

After the time t26, the same operation as described above is repeated, so that the intermittent operation using the voltage monitoring circuit 30 is continued. According to such an operation algorithm, the sensor module 1 can always continue to operate in a safe voltage region (Vin> Voff).

Therefore, since the operation is not interrupted in the middle of the active state A, it is possible to prevent a problem that sufficient data cannot be acquired or all data cannot be transmitted. It becomes possible to do.

Further, according to the above operation algorithm, as shown in FIG. 6, the data acquisition interval is n times the period T (however, n is a natural number and is variable depending on the harvester capacity of the energy harvesting unit 11). Value). Therefore, it becomes possible to acquire data with periodicity, and it becomes possible to predict in advance the timing at which the data should be read by the receiver 2.

The ○ mark (= time t31, t32, t34, t37) in FIG. 6 indicates the timing at which the data acquisition was performed, and the × mark (= time t33, t35, t36) in FIG. 6 indicates the data acquisition. Indicates when was skipped. Therefore, the data acquisition intervals in this figure are T (= time t31 to t32), 2T (= time t32 to t34), and 3T (= time t34 to t37).

For example, when trying to measure the vibration of a motor at regular intervals, the cycle of intermittent operation itself varies when the harvester capacity of the energy harvesting unit 11 is low in the existing sensor network, so the timing to read the data is completely different. Unpredictable.

On the other hand, in the case of the sensor network X of this configuration example, even if the harvester capacity of the energy harvesting unit 11 is low, it is always determined whether or not data can be acquired at a constant cycle T (see steps S7 and S8 in FIG. 4). Is done. That is, the data acquisition interval is standardized to a length (= n × T) n times with respect to a predetermined period T as a reference. Therefore, if the data is read every cycle T, at least there is no risk of missing the data.

Further, in the case of the sensor module 1 of this configuration example, the above-mentioned intermittent operation can be realized by using its own voltage monitoring circuit 30. Therefore, unlike the conventional technique of Patent Document 1, the cycle T of the intermittent operation can be determined by itself without requiring a separate system manager, so that the sensor network X can be constructed more easily.

Further, in the sensor module 1 of this configuration example, the measurement of the measurement target (step S4 in FIG. 4) and the wireless communication of the measurement result (step S5 in FIG. 4) are set, and the sleep state S is changed to the active state A. Unless the input voltage Vin exceeds the reference voltage Vref at the time of recovery determination, both operations are skipped.

With such a configuration, when the harvester capacity of the energy harvesting unit 11 is insufficient, not only the wireless communication of the measurement result but also the measurement of the measurement target is skipped and the charging of the energy storage unit 12 is concentrated. be able to. Therefore, it is possible to further reduce the power consumption (and thus shorten the data acquisition interval n × T) as compared with the conventional technique of Patent Document 2. In Patent Document 2, the amount of stored electricity is confirmed before the data is transmitted, but the amount of stored power is not confirmed before the data is acquired or stored. Therefore, there is a risk that the energy will be insufficient during the acquisition and storage of data, resulting in inoperability. That is, in Patent Document 2, there is no guarantee that sufficient data can be acquired and all of them can be stored. Therefore, it can be said that the sensor module 1 of this configuration example has advantages not only in terms of power consumption reduction but also in terms of system stability.

Further, with the sensor module 1 of this configuration example, the sensor network X can be stably operated for a long time even when the harvester capacity of the energy harvesting unit 11 is relatively low. Become. Therefore, for example, it can be said that it is very suitable as a monitoring means for infrastructure equipment and FA [factory automation] equipment.

<Voltage monitoring circuit (first embodiment)>
FIG. 7 is a diagram showing a first embodiment of the voltage monitoring circuit 30. The voltage monitoring circuit 30 of this embodiment includes a reset IC 31 and a pull-up resistor 32.

The reset IC 31 is a semiconductor integrated circuit device that generates an output signal So (= reset signal) according to the comparison result between the input voltage Vin and the reference voltage Vref and sends it to the control unit 23, and is a comparator CMP and an N-channel type. MOS [metal oxide semiconductor] field effect transistor N1 is integrated.

The comparator CMP compares the input voltage Vin input to the inverting input terminal (−) with the reference voltage Vref input to the non-inverting input terminal (+) to generate a gate signal Vg. The gate signal Vg becomes a low level when the input voltage Vin is higher than the reference voltage Vref, and becomes a high level when the input voltage Vin is lower than the reference voltage Vref. Since the comparator CMP has hysteresis, the logic level of the gate signal Vg is unlikely to become unstable even if the input voltage Vin fluctuates in the vicinity of the reference voltage Vref.

The transistor N1 is a switch element that forms an open-drain type output stage, and is connected between the output end and the ground end of the output signal So. The transistor N1 is turned on when the gate signal Vg is at a high level and turned off when the gate signal Vg is at a low level. An open collector type output stage may be formed by using an npn type bipolar transistor as the transistor N1.

The pull-up resistor 32 is connected between the input end of the power supply voltage Vdd and the output end of the output signal So. Therefore, the output signal So is a binary signal driven by a pulse between the power supply voltage Vdd and the ground voltage GND according to the on / off of the transistor N1.

The control unit 23 confirms the logic level of the output signal So and determines whether or not the input voltage Vin is higher than the reference voltage Vref. More specifically, when the output signal So is at a high level (= Vdd), it is determined that the input voltage Vin is higher than the reference voltage Vref, and when the output signal So is at a low level (= GND), the input is input. It is determined that the signal Vin is lower than the reference voltage Vref.

As described above, if the reset IC 31 and the pull-up resistor 32 are used, the voltage monitoring circuit 30 having a small area can be realized with a small number of parts. Therefore, even if the voltage monitoring circuit 30 is mounted, the sensor module 1 is unnecessary. It does not have to be large.

In particular, if a reset IC 31 having an open-drain type output stage is used, the peak value of the output signal So can be obtained by simply attaching an external pull-up resistor 32 between the input end of the power supply voltage Vdd and the output end of the output signal So. (= Vdd-GND) can be accommodated within the input dynamic range of the control unit 23.

In addition, a large number of variations of the input dynamic range and the reference voltage of the commercially available reset IC are prepared. Therefore, it is possible to realize the voltage monitoring circuit 30 according to the harvester capacity of the energy harvesting unit 11 only by selecting an appropriate model as the reset IC 31 from the commercially available products. It can be said that such specifications are suitable for energy harvesting, which is constantly changing.

<Voltage monitoring circuit (second embodiment)>
FIG. 8 is a diagram showing a second embodiment of the voltage monitoring circuit 30. The voltage monitoring circuit 30 of this embodiment includes a resistor ladder 33 and a switch 34.

The resistor ladder 33 includes resistors 33a and 33b (resistance values R33a and R33b) connected in series between the input end and the ground end of the input voltage Vin, and the input voltage Vin from the connection node between the resistors 33a and 33b. This is a voltage divider circuit that outputs a voltage divider voltage Vdiv (= Vin × {R33b / (R33a + R33b)}). The voltage divider voltage Vdiv is sent to the control unit 23 as an output signal So of the voltage monitoring circuit 30.

The switch 34 is connected between the input end of the input voltage Vin and the resistance ladder 33, and is turned on / off according to an instruction from the control unit 23.

The control unit 23 includes an A / D [analog-to-digital] converter 23a that converts an analog output signal So into a digital signal, confirms the voltage value of the divided voltage Vdiv, and the input voltage Vin is from the reference voltage Vref. Is also high or not. Further, the control unit 23 turns on the switch 34 at the timing of reading the voltage value of the voltage dividing voltage Vdiv every cycle T, and turns off the switch 34 after reading the voltage value of the voltage dividing voltage Vdiv. By such control, the current does not continue to flow in the resistor ladder 33, so that unnecessary current consumption can be eliminated.

In the voltage monitoring circuit 30 of this embodiment, unlike the first embodiment (FIG. 7) above, even the reset IC 31 is not used, so that the area can be further reduced. Further, in the voltage monitoring circuit 30, it is sufficient to adjust the resistance values R33a and R33b so that the voltage dividing voltage Vdiv falls within the input dynamic range of the control unit 23 while suppressing the current consumption. It's easy.

Further, by using the voltage monitoring circuit 30 of this embodiment, not only the comparison result between the input voltage Vin and the reference voltage Vref can be obtained in the control unit 23, but also the voltage value itself of the input voltage Vin can be recognized. .. Therefore, for example, it is possible to acquire predictive information such as how much power is insufficient for returning to the active state, and how long the sleep state should be continued. If such prediction information is notified to the administrator of the sensor network X or the like, it is possible to know how many hours later the data should be read. Further, by reading the voltage divider voltage Vdiv for each cycle T, it is possible to know how much the voltage divider voltage Vdiv changes during the cycle T. Therefore, it is possible to grasp the current harvester capacity of the energy harvesting unit 11. When the amount of change in the voltage divider voltage Vdiv during the period T is smaller than the predetermined value, the timing of reading the voltage divider voltage Vdiv by the A / D converter 23a of the control unit 23 is determined according to the degree of the change. It is preferable to set it to T (where k is an integer of 2 or more). With such a configuration, it is not necessary to read the voltage dividing voltage Vdiv for each cycle T, so that it is possible to realize further reduction in power consumption.

<Sensor network (second embodiment)>
FIG. 9 is a diagram showing a second embodiment of the sensor network. The sensor network X of the present embodiment is constructed as a one-to-many wireless sensor network, and the receiver 2 is shared by a plurality of sensor modules 1.

Examples of applications of such sensor network X include medical / health fields (health management and safety confirmation), structure monitoring (wire disconnection and bolt loosening monitoring), plant monitoring (equipment abnormality monitoring), and Logistics management (monitoring of distribution status and quality) can be mentioned.

However, when constructing the sensor network X of the present embodiment, collisions between a plurality of sensor modules 1 provided for a single receiver 2 (= collision of radio signals and data loss associated therewith, etc.) Need to be avoided. In particular, when the number of sensor modules 1 is large, the collision occurrence rate becomes high, so measures for avoiding collisions are indispensable. Therefore, in the following, a collision avoidance method in the sensor network X will be specifically described.

FIG. 10 is a time chart showing an example of the collision avoidance method, in which the communication timings of the plurality of sensor modules 1 (1) to 1 (3) (three in this figure) are marked with a circle in order from the upper side of the paper. It is depicted.

As shown in this figure, the communication timings of the sensor modules 1 (1) to 1 (3) are staggered from each other in order to avoid collisions between the sensors modules 1 (1) to 1 (3). For example, the sensor modules 1 (1) to 1 (3) have different times t41 (1) to t41 (3), times t42 (1) to t42 (3), and times t43 (1) to t43 (3), respectively. Perform wireless communication in 3).

For example, each of the sensor modules 1 (1) to 1 (3) may adopt a collision avoidance method in which wireless communication is performed while shifting the timing based on the time of the built-in clock (RTC [real time clock] or the like). More specifically, each of the sensor modules 1 (1) to 1 (3) has a transmission / reception function, and while communicating with each other, the communication timing of each sensor module 1 (1) to 1 (3) is shifted based on the time of the built-in clock. You just have to leave it.

As described above, the data acquisition interval (and thus the wireless communication interval) of each of the sensor modules 1 (1) to 1 (3) is set to the period T. Therefore, the above-mentioned mutual communication does not necessarily have to be performed every time the communication timing arrives, and it is sufficient to perform at least the first communication timing. This is because if the first communication timings are staggered from each other, the second and subsequent communication timings that are visited each time the cycle T elapses are inevitably staggered as shown in this figure.

Further, for example, in the sensor modules 1 (1) to 1 (3), collision avoidance methods (so-called LBT [listen before talk]) in which the other sensor modules perform their own wireless communication after confirming that they are not in wireless communication. ] Method, for example, EnOcean communication protocol (ERP [enocean radio protocol] 2 in Japan, ERP1 in the United States and Europe) may be adopted. More specifically, sensor modules 1 (1) to 1 (3). ), Before starting the transmission of the wireless signal, confirms whether or not there is a terminal transmitting the wireless signal around itself by picking up the wireless signal by itself as a receiver, and is applicable. If there is a terminal, the configuration may be such that the terminal waits until the transmission of the wireless signal is completed, and then the terminal starts transmitting its own wireless signal.

Further, for example, each of the sensor modules 1 (1) to 1 (3) adopts a collision avoidance method (so-called TSA [time slot assign] method) in which wireless communication is performed only in a time slot specified by a separate system manager. You may. More specifically, as shown in FIG. 11, when (1) sufficient energy required for each sensor module to operate can be secured, a transmission request is sent to the receiver, and (2) reception is performed. The machine receives the transmission request and notifies the sensor module of the slot number, and (3) the sensor module receives the notification of the slot number and transmits data in the designated time slot.

<Battery installed>
Since there are many applications that cannot be supported by the energy harvesting unit 11, a battery (mobile battery or the like) may be provided in parallel with the energy harvesting unit 11 in order to cover this. The position of the battery is the same as that of the energy harvesting unit 11.

When a battery is used, power is supplied to the load while charging the power storage unit 12. The same applies to the energy harvesting unit 11. However, since the output current of the battery is quite small, the power supply source is only the power storage unit 12 as a whole. The energy harvesting unit 11 can be considered to be a battery having a considerably high output impedance.

The sleep operation described above does not depend on whether the energy harvesting unit 11 or the battery is used. The sleep operation is controlled by software. After the sleep state of the cycle T has elapsed, the input voltage Vin is checked, and if the voltage exceeds the reference voltage Vref, the active state is restored, and if the voltage falls below the reference voltage Vref, the sleep state of the cycle T is maintained again. Is performed in the same manner as when the environmental power generation unit 11 is used.

<General wireless communication protocol (comparative example)>
Next, an outline of a general wireless communication protocol in the wireless communication process of the sensor module 1 (= corresponding to step S5 in FIG. 4) will be described.

FIG. 12 is a diagram showing a current profile (= behavior of current consumption Ic flowing through the sensor circuit 20) when performing wireless communication according to a general wireless communication protocol.

As shown in this figure, during the sleep period T10 of the sensor module 1 (= corresponding to steps S6 to S8 in FIG. 4), the current consumption Ic of the sensor circuit 20 is almost 0 (to be exact, the sensing period T20 and wireless). Compared with the current consumption Ic in the communication period T30, it is almost 0).

On the other hand, during the sensing period T20 of the sensor module 1 (= corresponding to step S4 in FIG. 4, for example, 0.8 s), the current consumption Ic required for the measurement operation in the sensor unit 21 flows.

Further, in the wireless communication period T30 of the sensor module 1 (= corresponding to step S5 in FIG. 4, for example, 1.6 s), the current consumption Ic required for the wireless communication operation in the wireless communication unit 22 flows. During this wireless communication period T30, the measurement result (= data composed of a plurality of packets) obtained by the sensor unit 21 is transmitted from the wireless communication unit 22.

In a general wireless communication protocol, the transmission period T31 at which packets can be continuously transmitted is limited in the wireless communication period T30. That is, after the predetermined transmission period T31 (for example, the maximum of 50 ms) has elapsed, the packet transmission resumption must be waited for the predetermined pause period T32 (for example, the minimum of 50 ms).

Therefore, the transmission period T31 and the pause period T32 are alternately repeated from the start to the end of the wireless communication period T30. Therefore, the current consumption Ic flowing in the wireless communication period T30 includes a pulse-shaped current component.

However, as can be seen from this figure, the current consumption Ic in the wireless communication period T30 includes not only the pulsed current component but also the current component Icc that continues to flow steadily from the start to the end of the wireless communication period T30 (for example,). About 4mA) is included. This current component Icc is caused by the fact that the wireless communication unit 22 must continue to operate from the start to the end of the wireless communication period T30. The reason will be explained below.

FIG. 13 is a diagram showing the behavior of each part in a general wireless communication protocol, in order from the top, the packet transmission state of the wireless communication unit 22, the communication state between the wireless communication unit 22 and the control unit 23, and the sensor circuit. Twenty current consumption Ic is depicted.

As shown in this figure, the wireless communication unit 22 outputs a packet transmission command to a power amplifier for driving transmission (not shown) in response to a request signal S1 (= packet transmission request) input from the control unit 23. On the other hand, the response signal S2 (= notification of output completion of the packet transmission command) is returned to the control unit 23. After that, the wireless communication unit 22 transmits the packet S3 by the power amplifier in response to the previous packet transmission command. Along with such a packet transmission operation, a pulse-shaped current component appears in the current consumption Ic of the sensor circuit 20.

Of the wireless communication period T30 of the sensor module 1, the above series of packet transmission operations are repeated during the transmission period T31. Then, after the predetermined transmission period T31 (for example, the maximum of 50 ms) has elapsed, the resumption of transmission of the packet S3 is awaited for the predetermined pause period T32 (for example, the minimum of 50 ms). Regarding the alternate switching operation between the transmission period T31 and the pause period T32, the wireless communication unit 22 plays a central role in controlling the timing thereof.

By the way, one packet S3 is composed of a plurality of (for example, three) sub-telegrams. Therefore, depending on the output timing of the request signal S1, it may not be possible to finish transmitting all the sub-telegrams constituting the packet S3 within the transmission period T31.

For example, in this figure, since the request signal S1 is output well before the expiration timing of the transmission period T31, the packet transmission operation corresponding to the request signal S1 can be completed within the transmission period T31. There is.

On the other hand, in FIG. 14, since the request signal S1 is output immediately before the expiration timing of the transmission period T31a, the packet transmission operation corresponding to the request signal S1 cannot be completed within the transmission period T31a.

More specifically, in the transmission period T31a, only one sub-telegram among the three sub-telegrams constituting the packet S3x can be transmitted, and the remaining two sub-telegrams have the rest period T32. After waiting for the progress, the transmission is performed in the next transmission period T31b.

That is, the packet S3x is divided into transmission periods T31a and T31b before and after the pause period T32 and transmitted. In order to carry out such divided transmission of the packet S3x without any trouble, both the sub-telegram first transmitted in the transmission period T31a and the sub-telegram transmitted later in the transmission period T31b are the same packet. The wireless communication unit 22 must recognize that it constitutes S3x.

Therefore, not only in the transmission periods T31a and T31b, but also in the pause period T32, the wireless communication unit 22 is maintained in the normal mode (= all the functional units are operating) so as not to forget the transmission status immediately before that. This is the cause of the steady current component Icc (see also FIG. 12 above) included in the current consumption Ic.

In the following, we propose a novel wireless communication protocol that can reduce such current component Icc.

<New wireless communication protocol>
FIG. 15 is a diagram showing the behavior of each unit in the new wireless communication protocol, and as in FIGS. 13 and 14, the packet transmission state of the wireless communication unit 22 and the wireless communication unit 22 and the control unit 23 are shown in this order from the top. The communication state with and the current consumption Ic of the sensor circuit 20 are described.

The new wireless communication protocol proposed here is based on the above-mentioned general wireless communication protocol (see FIG. 13), and the number of packets S3 to be transmitted is fixed for each transmission period T31, and the transmission thereof is fixed. After completing the operation within the transmission period T31, the wireless communication unit 22 is characterized in that it shifts from the normal mode to the power saving mode in which the power consumption is smaller than this in the pause period T32.

More specifically, the control unit 23 has elapsed a predetermined transition standby time T41 (however, T41 <T31) after starting the packet transmission request (= output operation of the request signal S1) to the wireless communication unit 22. At that time, the power saving mode transition signal S4 is output. The transition standby time T41 may be set to an appropriate length in consideration of the time required until the predetermined number of packets S3 are transmitted.

On the other hand, the wireless communication unit 22 shifts from the normal mode to the power saving mode in response to the power saving mode transition signal S4 from the control unit 23, and the acknowledge signal S5 (= power saving mode transition signal S4) is transmitted to the control unit 23. Receipt confirmation notice) will be replied.

By shifting to the power saving mode, the wireless communication unit 22 maintains only the minimum necessary functional unit for returning to the normal mode (for example, a signal receiving unit for waiting for the normal mode return signal S6). All other functional units (for example, a power amplifier for transmitting the packet S3) are stopped. As a result, the steady current component Icc consumed in the normal mode disappears, so that the current consumption Ic of the sensor circuit 20 returns to 0 base.

After that, the wireless communication unit 22 switches to the pause period T32 as the transmission period T31 elapses. At this time, the wireless communication unit 22 has already shifted to the power saving mode. Therefore, in the pause period T32, unnecessary power is not wasted in the wireless communication unit 22.

Further, in the new wireless communication protocol, the transmission operation can be surely completed within the transmission period T31 by intentionally limiting the number of packets S3 to be transmitted for each transmission period T31. That is, the packet S3 is not divided and transmitted over the pause period T32. Therefore, even if the wireless communication unit 22 forgets the transmission status up to that point due to the shift to the power saving mode, the subsequent packet transmission operation will not be hindered.

After that, the control unit 23 outputs the normal mode return signal S6 (= interrupt signal as a start trigger) when the predetermined return standby time T42 has elapsed after the power saving mode transition signal S4 is output. The return waiting time T42 may be set to an appropriate length in consideration of the length of the rest period T32. For example, the return standby time T42 may be set so that the wireless communication unit 22 returns from the power saving mode to the normal mode before the pause period T32 expires.

On the other hand, the wireless communication unit 22 returns from the power saving mode to the normal mode in response to the normal mode return signal S6 from the control unit 23. Therefore, thereafter, the wireless communication unit 22 can perform a packet transmission operation in response to the request signal S1 from the control unit 23.

As described above, in the new wireless communication protocol, the wireless communication unit 22 shifts from the normal mode to the power saving mode in the pause period T32 in which the operation of the wireless communication unit 22 becomes unnecessary. Therefore, during the pause period T32, the current consumption Ic of the sensor circuit 20 can be returned to the 0 base, so that the power consumption of the entire sensor module 1 can be reduced.

More specifically, the new wireless communication protocol can reduce the power consumption of the sensor module 1 by 4 to 5% as compared with the general wireless communication protocol. In particular, the harvester capacity of the energy harvesting unit 11 is not necessarily large, so that the sensor module 1 is very effective.

However, since the total amount of data transmitted during the wireless communication period T30 does not change, it should be noted that the wireless communication period T30 is slightly longer in the new wireless communication protocol (for example, 1.6 ms → 2. 2ms).

Further, in FIG. 15, a configuration in which the mode switching control of the wireless communication unit 22 is performed by using the power saving mode transition signal S4 and the normal mode return signal S6 is given as an example. The present invention is not limited, and for example, instead of the mode switching control described above, a configuration may be used in which the power supply to the wireless communication unit 22 is turned on / off.

More specifically in line with FIG. 15, the control unit 23 starts a packet transmission request (= output operation of the request signal S1) to the wireless communication unit 22, and then has a predetermined transition standby time T41 (however, T41). When <T31) has elapsed, the power supply to the wireless communication unit 22 is stopped, and the wireless communication unit 23 shifts from the normal mode to the power saving mode by stopping the power supply. The power saving mode here is different from the content described above, and corresponds to a state in which all the functional units of the wireless communication unit 23 have stopped operating.

After that, the control unit 23 resumes the power supply to the wireless communication unit 22 when the predetermined recovery standby time T42 has elapsed since the power supply to the wireless communication unit 22 was stopped, and the wireless communication unit 23 resumes the power supply to the wireless communication unit 22. By restarting the power supply, the power saving mode is restored to the normal mode.

When the above-mentioned mode switching control method is adopted, the transition standby time T41 becomes the transmission period T31 itself, and the return standby time T42 becomes the pause period T32 itself. That is, the alternate switching control between the transmission period T41 and the pause period T32 is performed mainly by the control unit 23.

<Other variants>
In addition to the above-described embodiments, the various technical features disclosed in the present specification can be modified in various ways without departing from the spirit of the technical creation. That is, it should be considered that the above embodiment is exemplary in all respects and is not restrictive, and the technical scope of the present invention is not limited to the above embodiment and is claimed. It should be understood that the meaning of scope and equality and all changes belonging to the scope are included.

The sensor module or sensor network disclosed in the present specification can be suitably used as, for example, a monitoring means for infrastructure equipment and FA equipment.

1, 1 (1) -1 (3) Sensor module 2 Receiver 3 Server 10 Power supply circuit 11 Energy harvesting unit 12 Power storage unit 13 Power management unit 20 Sensor circuit 21 Sensor unit 22 Wireless communication unit 23 Control unit 23a A / D converter 30 Voltage monitoring circuit 31 Reset IC
32 Pull-up resistor 33 Resistance ladder 33a, 33b Resistance 34 Switch CMP comparator N1 N-channel type MOS field effect transistor X sensor network S1 request signal S2 response signal S3, S3x packet S4 power saving mode transition signal S5 acknowledgment signal S6 normal mode return signal

Claims (8)

Control unit and
The wireless communication unit controlled by the control unit and
Have,
A wireless communication circuit that performs wireless communication of data according to the wireless communication protocol for operating a computer.
The wireless communications protocol in a wireless communication periods for transmitting data comprising a plurality of packets by the wireless communication unit, the packet has a transmission period which can be continuously transmitted is limited to a predetermined transmission period After that, the packet transmission restart must be waited for a predetermined pause period, and the function is such that the transmission period and the pause period are alternately repeated from the start to the end of the wireless communication period. In addition, the number of packets to be transmitted is fixed for each transmission period, the transmission operation is completed within the transmission period, and then the wireless communication unit is changed from the normal mode to the rest period. Also functions to shift to a power saving mode with low power consumption.
The control unit outputs a power saving mode transition signal when a predetermined transition standby time has elapsed since the transmission request to the wireless communication unit was started.
The wireless communication unit is a wireless communication circuit that shifts from the normal mode to the power saving mode in response to the power saving mode transition signal . The control unit outputs a normal mode return signal when a predetermined return standby time has elapsed after outputting the power saving mode transition signal.
The wireless communication circuit according to claim 1 , wherein the wireless communication unit returns from the power saving mode to the normal mode in response to the normal mode return signal. Control unit and
The wireless communication unit controlled by the control unit and
Have,
A wireless communication circuit that performs wireless communication of data according to the wireless communication protocol for operating a computer.
The wireless communications protocol in a wireless communication periods for transmitting data comprising a plurality of packets by the wireless communication unit, the packet has a transmission period which can be continuously transmitted is limited to a predetermined transmission period After that, the packet transmission restart must be waited for a predetermined pause period, and the function is such that the transmission period and the pause period are alternately repeated from the start to the end of the wireless communication period. In addition, the number of packets to be transmitted is fixed for each transmission period, the transmission operation is completed within the transmission period, and then the wireless communication unit is changed from the normal mode to the rest period. Also functions to shift to a power saving mode with low power consumption.
The control unit stops the power supply to the wireless communication unit when a predetermined transition standby time has elapsed since the transmission request to the wireless communication unit was started.
The wireless communication unit is a wireless communication circuit that shifts from the normal mode to the power saving mode by stopping the power supply . The control unit resumes power supply to the wireless communication unit when a predetermined recovery standby time has elapsed after stopping the power supply to the wireless communication unit.
The wireless communication circuit according to claim 3 , wherein the wireless communication unit returns from the power saving mode to the normal mode by restarting the power supply. A sensor unit that measures a predetermined measurement target, and
The wireless communication circuit according to any one of claims 1 to 4 , which performs wireless communication of measurement results obtained by the sensor unit.
A sensor circuit characterized by having. A power supply circuit including an energy harvesting unit and a power storage unit,
The sensor circuit according to claim 5 , which operates intermittently by receiving power supply from the power supply circuit.
Has a sensor module. Further, it has a voltage monitoring circuit that constantly monitors the input voltage stored in the power storage unit.
The sensor circuit alternately repeats an active state in which measurement of a measurement target and wireless communication of measurement results are performed and a sleep state in which the operation is paused. In the sleep state, the voltage monitoring is performed at a predetermined cycle. The sixth aspect of claim 6, wherein the output of the circuit is confirmed, and if the input voltage is higher than a predetermined reference voltage, the active state is restored, and if the input voltage is lower than the reference voltage, the sleep state is maintained. Sensor module. The sensor module according to claim 6 or 7.
A receiver that wirelessly receives the measurement results of the sensor module,
A sensor network characterized by having.

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