JP2019105975A - Radio communication protocol - Google Patents

Abstract

To reduce the power consumption of a radio communication part.SOLUTION: In a radio communication protocol, a transmission period T31 when packets S3 can continuously be transmitted is limited in a radio communication period T30 for allowing a radio communication part to transmit data composed of a plurality of packets S3. Specifically, transmission resumption of the packets S3 must be waited over a prescribed pause period T32 after the prescribed transmission period T31 elapses. Then, the transmission period T31 and the pause period T32 are alternately repeated from a start of the radio communication period T30 to an end. Here, a new radio communication protocol fixes the number of packets S3 to be transmitted in each transmission period T31, and the radio communication part is shifted from a normal mode to a power-saving mode having power consumption smaller than in the normal mode in the pause period T32 after completing the transmission operation within the transmission period T31. Consequently, current consumption Ic in the pause period T32 becomes approximately zero.SELECTED DRAWING: Figure 15

Description

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

  Generally, in a wireless communication protocol, the transmission period in which packets can be transmitted continuously is limited, and after a predetermined transmission period (for example, 50 ms at maximum) has elapsed, a predetermined pause period (for example, 50 ms at minimum) Throughout the process, it is necessary to wait for transmission resumption of packet transmission (see, for example, ARIB STD-T 108, which is one of the standards based on the Japanese Radio Law). Therefore, in the wireless communication period for transmitting data composed of a plurality of packets by the wireless communication unit, the transmission period and the pause period are alternately repeated from the start to the end.

JP, 2013-191984, A

  However, in the above-described 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 this.

  In view of the above problems found by the inventors of the present invention, the invention disclosed herein provides a novel wireless communication protocol that can reduce the power consumption of a wireless communication unit. To aim.

  The wireless communication protocol disclosed in the present specification limits the transmission period in which the packets can be continuously transmitted during the wireless communication period for transmitting data consisting of a plurality of packets by the wireless communication unit. After the predetermined transmission period has passed, the transmission resumption of the packet must be waited 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. The number of packets to be transmitted is fixed every transmission period, and the transmission operation is completed within the transmission period, and then the wireless communication unit is used in the idle period. A configuration (first configuration) is to shift from the normal mode to a power saving mode with lower power consumption.

  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 the data according to the wireless communication protocol having the first configuration. The 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 start of a transmission request to the wireless communication unit. The wireless communication unit may be configured (third configuration) to shift from the normal mode to the power saving mode in response to the power saving mode transition signal.

  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 the power saving mode transition signal is output. The communication unit may be configured (fourth configuration) to return from the power saving mode to the normal mode 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 start of a transmission request to the wireless communication unit. The wireless communication unit may be configured (fifth configuration) to shift from the normal mode to the power saving mode by stopping the power supply.

  In the wireless communication circuit having the fifth configuration, the control unit may supply power to the wireless communication unit when a predetermined return standby time has elapsed since power supply to the wireless communication unit was stopped. The wireless communication unit may be configured (sixth configuration) to return from the power saving mode to the normal mode by resuming the power supply.

  In addition, the sensor circuit disclosed in the present specification includes a sensor unit that measures a predetermined measurement target, and the wireless communication of the measurement result obtained by the sensor unit, including the configuration of any of the second to sixth embodiments. And a wireless communication circuit for performing the above (a seventh configuration).

  Further, a sensor module disclosed in the present specification includes a power supply circuit including an environmental power generation unit and a storage unit, and a sensor circuit which comprises the seventh configuration and operates intermittently by receiving power supply from the power supply circuit. And a configuration (eighth configuration).

  Note that the sensor module having the eighth configuration further includes a voltage monitoring circuit that constantly monitors the input voltage stored in the storage unit, and the sensor circuit measures the measurement target and wirelessly communicates the measurement result. In the sleep state, the output of the voltage monitoring circuit is checked at a predetermined cycle, and the input voltage is higher than a predetermined reference voltage. It is preferable to return to the active state if high and to maintain the sleep state if the input voltage is lower than the reference voltage (ninth configuration).

  Further, a sensor network disclosed in the present specification includes a sensor module having the eighth or ninth configuration, and a receiver that wirelessly receives the measurement result of the sensor module (tenth configuration). Configuration).

  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.

A diagram showing a first embodiment of a sensor network A diagram showing an exemplary configuration of a sensor module Time chart showing a comparative example of intermittent operation (without voltage monitoring) Flow chart showing an example of intermittent operation (with voltage monitoring) Time chart showing an example of intermittent operation (with voltage monitoring) A time chart showing the periodicity of data acquisition timing A diagram showing a first embodiment of a voltage monitoring circuit A diagram showing a second embodiment of the voltage monitoring circuit A diagram showing a second embodiment of a sensor network Time chart showing an example of collision avoidance method Figure showing an example of TSA [time slot assign] method Diagram showing current profiles in common wireless communication protocols Diagram showing the behavior of each part in a common wireless communication protocol Diagram of the challenges in a typical wireless communication protocol Diagram showing the behavior of each part in the 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 power by environmental power generation, and measures a predetermined measurement target (= machine vibration or the like). Further, the sensor module 1 has a one-way or two-way wireless communication function, and wirelessly transmits its 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 the measurement result to the server 3 in a wired or wireless manner.

  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 environmental power generation, for the sensor module 1, the installation of the power supply wiring and the replacement of the battery become unnecessary. In addition, since wireless communication is performed between the sensor module 1 and the receiver 2, signal wiring for connecting between each other is also unnecessary. Therefore, it is possible to arrange the sensor module 1 at an arbitrary place.

  For example, when monitoring the vibration, temperature, and the like 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. In addition, when monitoring the patient's biological information using the sensor network X, the sensor module 1 is embedded in the patient's body, and the detection result is read by the external receiver 2 to reduce the burden on the patient. It is possible. Moreover, when monitoring vibration or temperature of an air conditioner, a compressor, etc. in a factory etc., it becomes possible to reduce the disconnection by a conveyance vehicle and the accident by wiring.

<Sensor module>
FIG. 2 is a view showing an example of the configuration 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 power to each part of the sensor module 1, and includes an environmental power generation unit 11, a power storage unit 12, and a power management unit 13.

  The environmental power generation unit 11 is a means (so-called energy harvester) which receives power (= 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 piezoelectric element may be used as the power generation element. In the case where sunlight or illumination light is used as an energy source, it is preferable to use a silicon-based, compound-based, or organic-based photoelectric element as the power generation element. When heat is used as an energy source, a thermoelectric element such as a Peltier element may be used as the power generation element. In addition, in the broader sense of environmental power generation (or self power generation), a CT type current sensor can also be used. The principle is that an alternating current (secondary current) flows according to the winding ratio in the secondary side winding so as to cancel the magnetic flux generated in the magnetic core by the alternating current flowing through the measurement conductor (primary side) It is a thing. However, the above is merely an example, and power generation devices based on other power generation principles may be used. For example, vibration power generation includes not only a piezoelectric type (using a piezo element) but also an electromagnetic induction type (by electromagnetic induction using a coil and a magnet), an electrostatic type (one using an electret), and the like.

  The storage unit 12 is a means for storing the self-generated power obtained by the environmental power generation unit 11 (however, it may be read as non-contact feed power when using a CT type current sensor), for example, a super capacitor (= electricity A generic term for double layer capacitors can be suitably used. The input voltage Vin (= charging voltage of the super capacitor) stored in the storage unit 12 is supplied to the power management unit 13 and is to be 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. In addition, as the power management unit 13, for example, a DC / DC converter can be suitably used.

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

  The sensor unit 21 is a predetermined measurement target (magnetic, acceleration, angular velocity, pressure, strain, vibration, temperature, humidity, light, infrared light, ultraviolet light, electromagnetic wave, radiation, electric field, current, voltage, power, position, distance, displacement, Flow rate, flow rate, component, composition, concentration, sound, gas, smell, 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 environmental power generation unit 11 and the measurement target of the sensor unit 21 be common. One example is a case where the energy generation 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 is generated by the environmental power generation unit 11 in response to the vibration. Therefore, compared to the case where the energy source other than the vibration is used as the energy source, Power supply can be performed.

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

  The control unit 23 is a control entity of the sensor unit 21 and the wireless communication unit 22, and includes an interface circuit that receives an 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 suitably used.

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

  The harvester ability of the environmental power generation unit 11 is not necessarily large, and it is difficult to keep the sensor circuit 20 operating at all times. Therefore, while the sensor circuit 20 checks the output signal So of the voltage monitoring circuit 30 at a predetermined period T, the sensor circuit 20 performs an active state in which wireless communication of the measurement target and the measurement result is performed, and a sleep that temporarily suspends its operation. Intermittent operation that alternately repeats the state and the state is performed. The intermittent operation of the sensor circuit 20 will be described in detail below.

<Intermittent operation>
First, prior to the description of the intermittent operation using the voltage monitoring circuit 30, the intermittent operation not using the voltage monitoring circuit 30 will be briefly described with reference to FIG. 3 as a comparative example.

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

  As shown in the figure, the sensor circuit 20 performs an intermittent operation in which the active state A (= measurement and wireless communication) and the sleep state S (= charge) are alternately repeated. In the drawing, for convenience of illustration, the time for maintaining the active state A (for example, time t11 to t12) is drawn longer than originally, but actually, the time for maintaining the sleep state S (= intermittent operation) In a very short time as compared with the period T (eg, 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, the input voltage Vin once exceeds the on voltage Von and thereafter does not fall below the off voltage Voff. Therefore, the sensor circuit 20 can perform the intermittent operation while maintaining the constant cycle T.

  On the other hand, as shown in the 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 every time the sleep state S returns to the active state A. And eventually 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 the timer of the control unit 23 runs out and the intermittent operation can not be performed in a fixed cycle T (time t12 to t13). And compare time t14 to t15, T ≠ T '). As described above, when the cycle T of the intermittent operation changes, it is impossible to acquire data having periodicity.

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

  Although the above problems can be somewhat improved by adjusting the on voltage Von and the off voltage Voff of the power management unit 13, they can not be fundamentally solved. In the following, the intermittent operation which can fundamentally solve the above problems by using the voltage monitoring circuit 30 will be described in detail.

  FIG. 4 is a flowchart showing an example of the intermittent operation using the voltage monitoring circuit 30. When the power generation operation of the environmental power generation unit 11 is started by the activation of the sensor module 1, the input voltage Vin stored in the storage unit 12 rises. 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, since power supply to the sensor circuit 20 is started, the sensor circuit 20 is turned on in step S3. Thereafter, in step S4, the measurement of the measurement target is performed by the sensor unit 21. Furthermore, in step S5, wireless communication of the measurement result by the wireless communication unit 22 is performed. These steps S3 to S5 correspond to the aforementioned active state.

  When the wireless communication in step S5 is completed, the sensor circuit 20 is turned off in the subsequent 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 necessary for return to the active state (such as the timer of the control unit 23) continue to operate with the minimum power supply from the power management unit 13. .

  Thereafter, in step S7, the control unit 23 determines whether the cycle T has elapsed. Here, when the determination is YES, the flow is advanced to step S8, and when the determination is NO, the flow is returned to step S7.

  When the determination in step S7 is YES, in step S8, the control unit 23 confirms the output signal So of the voltage monitoring circuit 30, and determines whether the input voltage Vin is higher than a predetermined reference voltage Vref. To be done. Although not shown in the present 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, if a yes determination is made, the flow is returned to step S3, and return from the sleep state to the active state is performed. On the other hand, when a negative determination is made, the flow is returned to step S7, and the determination of the elapse of period T is repeated.

  That is, in this flow, in the sleep state (steps S6 to S8), the output confirmation of the voltage monitoring circuit 30 is performed at a predetermined cycle T, and if the input voltage Vin is higher than a predetermined reference voltage Vref The loop is turned to return to the sleep state 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 the case of FIG. 3, the input voltage Vin and the operating state of the sensor circuit 20 (A: active state, S : Sleep state is shown.

  The reference voltage Vref described above is at least the input voltage Vin in the active state A (refer to 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 V Voff + Δ), which is higher by the assumed reduction value Δ of (1), is set.

  After completion of the active state A (corresponding to steps S3 to S5 in FIG. 4) at time 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 turns from rising to rising.

  Thereafter, at time t23, with the elapse of the cycle T (corresponding to step S7 = Y in FIG. 4), it is judged whether the sleep state S returns to the active state A (corresponding to step S8 in FIG. 4). In the example of this figure, since the input voltage Vin exceeds the reference voltage Vref at time t23, 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 turns from rising to falling.

  Further, after completion of the active state A (corresponding to steps S3 to S5 in FIG. 4) at time t23 to t24, the sensor circuit 20 transitions from the active state A to the sleep state S again at time t24 (step S6 in FIG. 4). Equivalent to Accordingly, the input voltage Vin is again turned from the decrease to the increase.

  Thereafter, at time t25, with the elapse of the cycle T (corresponding to step S7 = Y in FIG. 4), it is determined whether the sleep state S returns to the active state A (corresponding to step S8 in FIG. 4). However, in the example of this figure, since the input voltage Vin does not exceed the reference voltage Vref at time t25, return from the sleep state S to the active state A is not recognized, and the sleep state S is maintained (figure Step S8 = 4 (corresponding to N)). Therefore, the input voltage Vin continues to rise without falling.

  At time t25, after the return to the active state A is missed, at time t26, from the sleep state S to the active state A again with the elapse of the second cycle T (corresponding to step S7 = Y in FIG. 4). Is determined (corresponding to step S8 in FIG. 4). In the example of this figure, since the input voltage Vin exceeds the reference voltage Vref at time t26, return from the sleep state S to the active state A is not recognized, and the sleep state S to the active state A is not recognized. A return is recognized (corresponding to step S8 = Y in FIG. 4). Therefore, the input voltage Vin turns from rising to falling.

  By repeating the same operation as described above after time t26, the intermittent operation using the voltage monitoring circuit 30 is continued. According to such an operation algorithm, the sensor module 1 can always keep operating in a safe voltage range (Vin> Voff).

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

  Further, according to the above operation algorithm, as shown in FIG. 6, the data acquisition interval is n times the period T (where n is a natural number and variable depending on the harvester ability of the environmental power generation unit 11) Value). Therefore, periodical data acquisition can be performed, and the timing at which the receiver 2 should read data can be predicted in advance.

  The な お marks (= time t31, t32, t34, t37) in FIG. 6 indicate the timings at which data acquisition was performed, and the x marks (= time t33, t35, t36) in FIG. Indicates when it 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 it is intended to measure the vibration of the motor at regular intervals, the existing sensor network scatters the period of the intermittent operation itself when the harvester ability of the environmental power generation unit 11 is low. It can not be predicted.

  On the other hand, in the case of the sensor network X of this configuration example, whether or not data acquisition can always be performed at a constant period T even if the harvester capability of the environmental power generation unit 11 is low (see steps S7 and S8 in FIG. 4) Is done. That is, the data acquisition interval is normalized to a length n (= n × T) with reference to a predetermined cycle T. Therefore, if the data is read every cycle T, there is no risk of losing at least the data.

  Further, in the case of the sensor module 1 of this configuration example, the above-mentioned intermittent operation can be realized using the voltage monitoring circuit 30 of its own. Therefore, unlike the prior art of Patent Document 1, the period T of the intermittent operation can be determined by itself without requiring any additional 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 as a set. Both operations are skipped as long as the input voltage Vin does not exceed the reference voltage Vref at the time of return determination of

  With such a configuration, when the harvester capability of the environmental power generation 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 charge of the storage unit 12 is concentrated. be able to. Therefore, as compared with the prior art of Patent Document 2, it is possible to further reduce the power consumption (that is, shorten the data acquisition interval n × T). In Patent Document 2, although the storage amount is confirmed before transmitting data, confirmation of the storage capacity is not performed before data acquisition, storage, and the like. Therefore, energy may not be sufficient while acquiring or storing data, which may result in inoperability. That is, Patent Document 2 does not 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 an advantage in terms of not only the reduction in power consumption but also the stability of the system.

  Further, with the sensor module 1 of this configuration example, even if the harvester capability of the environmental power generation unit 11 is relatively low, the sensor network X can continue to operate stably for a long time. Become. Therefore, for example, it can be said that it is very suitable as a monitoring means of 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. As shown in FIG. The voltage monitoring circuit 30 of the present 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 of the input voltage Vin and the reference voltage Vref and sends it to the control unit 23. A 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 goes low when the input voltage Vin is higher than the reference voltage Vref, and goes high when the input voltage Vin is lower than the reference voltage Vref. Since the comparator CMP has a hysteresis, the logic level of the gate signal Vg is unlikely to be unstable even if the input voltage Vin fluctuates in the vicinity of the reference voltage Vref.

  The transistor N1 is a switch element forming an open drain type output stage, and is connected between the output end of the output signal So and the ground end. The transistor N1 turns on when the gate signal Vg is at high level, and turns off when the gate signal Vg is at low level. An open collector type output stage may be formed by using an npn 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 which is pulse-driven between the power supply voltage Vdd and the ground voltage GND according to the on / off of the transistor N1.

  The control unit 23 checks the logic level of the output signal So to determine whether 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 It is determined that the signal Vin is lower than the reference voltage Vref.

  As described above, the use of the reset IC 31 and the pull-up resistor 32 can realize the voltage monitoring circuit 30 of a small area with a small number of parts. Therefore, even if the voltage monitoring circuit 30 is mounted, the sensor module 1 is unnecessary. You do not need to get bigger.

  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 simply by externally connecting the pull-up resistor 32 between the input end of the power supply voltage Vdd and the output end of the output signal So. It becomes possible to fit (= Vdd-GND) within the input dynamic range of the control unit 23.

  In addition, in the commercially available reset IC, a large number of variations are prepared for the input dynamic range and the reference voltage. Therefore, it is possible to realize the voltage monitoring circuit 30 according to the harvester capability of the environmental power generation unit 11 only by selecting an appropriate model as the reset IC 31 from commercially available products. Such specifications are said to be suitable for constantly changing environmental power generation.

<Voltage Monitoring Circuit (Second Embodiment)>
FIG. 8 is a diagram showing a second embodiment of the voltage monitoring circuit 30. As shown in FIG. The voltage monitoring circuit 30 of the present embodiment includes a resistor ladder 33 and a switch 34.

  Resistor ladder 33 includes resistors 33a and 33b (resistance values R33a and R33b) connected in series between the input terminal of input voltage Vin and the ground terminal, and input voltage Vin from the connection node between resistors 33a and 33b. The divided voltage Vdiv (= Vin × {R33b / (R33a + R33b)}) is output. The divided 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 resistor 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 the analog output signal So into a digital signal, confirms the voltage value of the divided voltage Vdiv, and determines the input voltage Vin from the reference voltage Vref. Also determine whether it is high. Further, the control unit 23 turns on the switch 34 at the timing of reading the voltage value of the divided voltage Vdiv every cycle T, and turns off the switch 34 after reading the voltage value of the divided voltage Vdiv. By such control, since current does not continue to flow in the resistance ladder 33, wasteful current consumption can be eliminated.

  In the case of the voltage monitoring circuit 30 of this embodiment, unlike the first embodiment (FIG. 7), only the reset IC 31 is 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 divided voltage Vdiv falls within the input dynamic range of the control unit 23 while suppressing the current consumption, so the setting operation is It is easy.

  Further, using the voltage monitoring circuit 30 of this embodiment, the control unit 23 can not only obtain the comparison result of the input voltage Vin and the reference voltage Vref, but also recognize the voltage value itself of the input voltage Vin. . Therefore, for example, it is possible to obtain prediction information such as how much electric power is not enough or how long the sleep state should be continued to return to the active state. If such prediction information is reported to the administrator or the like of the sensor network X, it can be understood how many hours after which data should be read. Furthermore, if the divided voltage Vdiv is read for each cycle T, it can be known how much the divided voltage Vdiv changes during the cycle T. Therefore, it becomes possible to grasp the present harvester ability in the environmental power generation unit 11. Further, when the amount of change in divided voltage Vdiv during period T is smaller than a predetermined value, the timing at which divided voltage Vdiv is read next by A / D converter 23 a of control unit 23 is k × It is good to set to T (however, k is an integer greater than or equal to 2). With such a configuration, it is not necessary to read the divided voltage Vdiv every cycle T, so 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 this 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 application of such a sensor network X include medical and health fields (health management and safety confirmation), structure monitoring (monitoring of wire breakage and bolt loosening), plant monitoring (monitoring of equipment abnormality), and Physical distribution management (monitoring of distribution status and quality) can be mentioned.

  However, when constructing the sensor network X according to the present embodiment, collisions between sensor modules 1 provided in plural for a single receiver 2 (= collision of radio signals and data loss associated therewith) You need to avoid it. In particular, when the number of sensor modules 1 is large, the collision occurrence rate becomes large, so it is essential to take measures to avoid collisions. Therefore, the collision avoidance method in the sensor network X will be specifically described below.

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

  As shown in the figure, the communication timings of the sensor modules 1 (1) to 1 (3) are mutually offset in order to avoid collisions with one another. For example, the sensor modules 1 (1) to 1 (3) are different from time t41 (1) to t41 (3), time t42 (1) to t42 (3), and time t43 (1) to t43 ( Perform wireless communication in 3).

  For example, 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 an internal 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 one another, the respective communication timings are shifted based on the time of the built-in clock. You should keep it.

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

  Also, for example, in each of the sensor modules 1 (1) to 1 (3), a collision avoidance method (so-called LBT [listen before talk] in which its own wireless communication is performed after confirming that other sensor modules are not in wireless communication). For example, a communication protocol of EnOcean (ERP [enocean radio protocol] 2 in Japan, ERP 1 in the United States and Europe) may be adopted. More specifically, the sensor modules 1 (1) to 1 (3 ), Before starting to transmit a radio signal, check if there is a terminal transmitting a radio signal around itself by picking up the radio signal as a receiver by itself. If there is a terminal, it may be configured to wait until the terminal completes the transmission of the wireless signal and then starts to transmit its own wireless signal.

  Also, 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 time slots designated by a separate system manager. You may More specifically, as shown in FIG. 11, (1) when sufficient energy for operating each sensor module can be secured, a transmission request is issued to the receiver, and (2) reception The device receives the transmission request, notifies the sensor module of the slot number, and (3) receives the notification of the slot number and transmits data in the designated time slot.

<Battery mounted>
In addition, since there are many applications that can not be handled by the environmental power generation unit 11, a battery (such as a mobile battery) may be provided in parallel with the environmental power generation unit 11 in order to cover this. The positioning of the battery is the same as that of the environmental power generation unit 11.

  When using a battery, power is supplied to the load while charging the storage unit 12. About this, the environmental power generation part 11 is also the same. However, since the output current of the battery is quite small, the power supply source is only the storage unit 12 when viewed as a whole. The environmental power generation unit 11 may be considered to be a battery having a relatively high output impedance.

  The aforementioned sleep operation does not depend on which one of the energy harvesting unit 11 and the battery is used. The sleep operation is controlled by software. After the sleep state of period T has elapsed, the input voltage Vin is checked, and if it is higher than the reference voltage Vref, the active state is restored, and if it is lower, the sleep state of period 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 overview of a general wireless communication protocol in the wireless communication process (= corresponding to step S5 in FIG. 4) of the sensor module 1 will be described.

  FIG. 12 is a diagram showing a current profile (= the behavior of the consumed current Ic flowing through the sensor circuit 20) when performing wireless communication in accordance with a general wireless communication protocol.

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

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

  In addition, in the wireless communication period T30 of the sensor module 1 (= corresponding to step S5 in FIG. 4, for example, 1.6 s), the consumption current Ic necessary for the wireless communication operation in the wireless communication unit 22 flows. In the 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, a transmission period T31 in which packets can be transmitted continuously is limited in the wireless communication period T30. That is, after a predetermined transmission period T31 (for example, the longest 50 ms) has elapsed, it is necessary to wait for the transmission resumption of packet transmission for the predetermined pause period T32 (for example, the shortest 50 ms).

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

  However, as can be understood from this figure, the consumption current Ic in the wireless communication period T30 includes not only the pulse-like current component but also the current component Icc which constantly flows from the start to the end of the wireless communication period T30 (for example, 4 mA is included. The current component Icc is generated due to the fact that the radio communication unit 22 has to continue operating from the start to the end of the radio communication period T30. The reason will be described below.

  FIG. 13 is a diagram showing the behavior of each unit in a general wireless communication protocol, and 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 consumptions Ic are depicted.

  As shown in the figure, the wireless communication unit 22 outputs a packet transmission instruction to a transmission driving power amplifier (not shown) in response to the request signal S1 (= packet transmission request) input from the control unit 23. On the other hand, a response signal S2 (= output completion notification of a packet transmission instruction) is sent back to the control unit 23. Thereafter, in the wireless communication unit 22, transmission of the packet S3 by the power amplifier is performed according to the above-described packet transmission instruction. With such a packet transmission operation, a pulse-like current component appears in the consumption current Ic of the sensor circuit 20.

  In the transmission period T31 of the wireless communication period T30 of the sensor module 1, the series of packet transmission operations are repeated. Then, after the predetermined transmission period T31 (for example, the longest 50 ms) has elapsed, the transmission resumption of the transmission of the packet S3 is waited for the predetermined pause period T32 (for example, the shortest 50 ms). The radio communication unit 22 mainly controls the timing switching of the alternate switching operation of the transmission period T31 and the idle period T32.

  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 the figure, since the request signal S1 is output long before the expiration timing of the transmission period T31, the packet transmission operation according 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 according to the request signal S1 can not be completed within the transmission period T31a.

  More specifically, in the transmission period T31a, only one of the three subtelegrams constituting the packet S3x can be transmitted, and the remaining two subtelegrams have the idle period T32 After waiting for the passage, it is transmitted 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 divisional transmission of such a packet S3x without trouble, both the sub-telegram transmitted earlier in the transmission period T31a and the sub-telegram transmitted later in the transmission period T31 b are identical to each other. The wireless communication unit 22 must recognize that it is a component of S3x.

  Therefore, the wireless communication unit 22 is maintained in the normal mode (= the state where all the functional units are operating) so as not to forget the transmission state immediately before that in the transmission period T31a and T31b as well as in the idle period T32. It is necessary to keep in mind that this causes the generation of a steady-state current component Icc (see also FIG. 12 mentioned earlier) included in the consumption current Ic.

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

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

  The novel wireless communication protocol proposed here is based on the above-mentioned general wireless communication protocol (see FIG. 13), while fixing the number of packets S3 to be transmitted in each transmission period T31, and transmitting the packet S3. It is characterized in that after the operation is completed within the transmission period T31, the wireless communication unit 22 is shifted from the normal mode to the power saving mode with smaller power consumption in the idle period T32.

  More specifically, the control unit 23 starts a packet transmission request (= output operation of the request signal S1) to the wireless communication unit 22, and a predetermined transition standby time T41 (where T41 <T31) elapses. At this point, 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 required time until transmission of the predetermined number of packets S3 is completed.

  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 sends an acknowledge signal S5 (= power saving mode transition signal S4) to the control unit 23. Acknowledge receipt confirmation)

  Note that, upon transition 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, since the constant current component Icc consumed in the normal mode is eliminated, the consumption current Ic of the sensor circuit 20 returns to 0 base.

  Thereafter, the wireless communication unit 22 switches to the idle period T32 with the elapse of the transmission period T31. At this time, the wireless communication unit 22 has already shifted to the power saving mode. Therefore, unnecessary power is not wasted in the wireless communication unit 22 during the idle period T32.

  Further, in the novel wireless communication protocol, by intentionally limiting the number of packets S3 to be transmitted in each transmission period T31, the transmission operation can be surely completed within the transmission period T31. That is, the divided transmission of the packet S3 is not performed across the pause period T32. Therefore, even if the wireless communication unit 22 forgets the previous transmission status due to the transition to the power saving mode, subsequent packet transmission operations will not be disturbed.

  Thereafter, the control unit 23 outputs the normal mode return signal S6 (= an interrupt signal as a start trigger) when a predetermined return standby time T42 has elapsed since the output of the power saving mode transition signal S4. The return waiting time T42 may be set to an appropriate length in consideration of the length of the pause period T32. For example, the return waiting 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, in response to the normal mode return signal S6 from the control unit 23, the wireless communication unit 22 returns from the power saving mode to the normal mode. Therefore, after that, the wireless communication unit 22 can perform the packet transmission operation according to the request signal S1 from the control unit 23.

  As described above, in the new wireless communication protocol, the wireless communication unit 22 is shifted from the normal mode to the power saving mode in the idle period T32 in which the operation of the wireless communication unit 22 is unnecessary. Therefore, since the consumption current Ic of the sensor circuit 20 can be returned to the 0 base in the idle period T32, it is possible to realize low power consumption of the entire sensor module 1.

  More specifically, in the new wireless communication protocol, power consumption of the sensor module 1 can be cut by 4 to 5% as compared with a general wireless communication protocol. In particular, since the harvester capability of the environmental power generation unit 11 is not necessarily large, the sensor module 1 is very effective.

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

  Although FIG. 15 exemplifies a configuration in which mode switching control of the wireless communication unit 22 is performed using the power saving mode transition signal S4 and the normal mode return signal S6, the mode switching control method will be described. For example, instead of the mode switching control described above, power supply to the wireless communication unit 22 may be turned on / off.

  Specifically, referring to 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 waits for a predetermined transition standby time T41 (however, T41). When <T31> elapses, 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 due to the stop of the power supply. The power saving mode here is different from the contents described above, and corresponds to a state in which all the functional units of the wireless communication unit 23 have stopped operating.

  Thereafter, the control unit 23 resumes the power supply to the wireless communication unit 22 when the predetermined return waiting time T42 elapses after the power supply to the wireless communication unit 22 is stopped, and the wireless communication unit 23 The power saving mode is returned to the normal mode by resuming the power supply.

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

<Other Modifications>
In addition to the embodiments described above, various technical features disclosed in the present specification can be modified in various ways without departing from the scope of the technical creation. That is, the above embodiment should be considered as illustrative in all points and not restrictive, and the technical scope of the present invention is not limited to the above embodiment, and claims It is to be understood that the scope and equivalent meaning and all modifications that fall within the scope are included.

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

1, 1 (1) to 1 (3) Sensor Module 2 Receiver 3 Server 10 Power Supply Circuit 11 Environmental Power Generation 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 resistor ladder 33a, 33b resistor 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 acknowledge signal S6 normal mode return signal

Claims (10)

In a wireless communication period for transmitting data consisting of a plurality of packets by a wireless communication unit, a transmission period in which the packets can be transmitted continuously is limited, and a predetermined transmission period has elapsed. A wireless communication protocol, which must wait for resumption of transmission of the packet over an idle period, and in which the transmission period and the idle period are alternately repeated from the start to the end of the wireless communication period,
The number of packets to be transmitted is fixed for each transmission period, and the transmission operation is completed within the transmission period, and then the wireless communication unit consumes less power than in the normal mode during the idle period. A wireless communication protocol characterized by transitioning to a small power saving mode.   A wireless communication circuit comprising: a control unit; and a wireless communication unit controlled by the control unit, wherein wireless communication of data is performed in accordance with the wireless communication protocol according to claim 1. The control unit outputs a power saving mode transition signal when a predetermined transition standby time has elapsed since the start of the transmission request to the wireless communication unit.
The wireless communication circuit according to claim 2, wherein the wireless communication unit 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 the power saving mode transition signal is output.
The wireless communication circuit according to claim 3, wherein the wireless communication unit returns from the power saving mode to the normal mode in response to the normal mode return signal. The control unit stops power supply to the wireless communication unit when a predetermined transition standby time has elapsed since the start of a transmission request to the wireless communication unit.
The wireless communication circuit according to claim 2, wherein the wireless communication unit shifts from the normal mode to the power saving mode when the power supply is stopped. The control unit resumes the power supply to the wireless communication unit when a predetermined return waiting time has elapsed after stopping the power supply to the wireless communication unit.
6. The wireless communication circuit according to claim 5, wherein the wireless communication unit returns from the power saving mode to the normal mode by resuming the power supply. A sensor unit that measures a predetermined measurement target;
The wireless communication circuit according to any one of claims 2 to 6, wherein wireless communication of the measurement result obtained by the sensor unit is performed.
A sensor circuit characterized by having. A power supply circuit including an environmental power generation unit and a storage unit;
The sensor circuit according to claim 7, wherein the sensor circuit operates intermittently by receiving power supply from the power supply circuit.
Sensor module characterized by having. It further comprises a voltage monitoring circuit that constantly monitors the input voltage stored in the 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 suspended. In the sleep state, the voltage monitoring is performed at a predetermined cycle. The output confirmation of the circuit is performed, and the active state is recovered if the input voltage is higher than a predetermined reference voltage, and the sleep state is maintained if the input voltage is lower than the reference voltage. The sensor module according to 8. A sensor module according to claim 8 or 9;
A receiver that wirelessly receives the measurement result of the sensor module;
The sensor network characterized by having.