Wireless Device and Wireless Communication System

Abstract

To simplify the coordination of the operation timing of each of a wireless device and other devices that communicate with it.SOLUTION: A slave station device 14 receives a signal at a receiving window timing 24 that follows a local time. A master station device 10 estimates the receiving window timing 24 based on a reference time and based on information obtained by communication performed previously with the slave station device 14, and transmits a wake-up signal 22 in accordance with the estimated receiving window timing 24. The master station device 10 communicates with the slave station device 14 after a predetermined communication startup time has elapsed since transmitting the wake-up signal 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wireless device, and more particularly to a technique for adjusting the timing of communications between wireless devices and other devices. [Background technology]

[0002] Research and development is underway on sensor network systems in which sensors such as temperature sensors and illuminance sensors are placed at multiple locations and the values detected by the sensors are collected via wireless communication. Some sensor network systems have sensors mounted in slave station devices that wirelessly transmit the sensor values to a master station device.

[0003] Sensor network systems employ power-saving communication. In power-saving communication, the slave station devices are intermittently turned on. That is, the slave station devices are turned on for a predetermined period of time at a predetermined cycle, and are in a sleep state during other periods. In the sleep state, power is supplied only to electronic circuits that determine their own operation timing, such as the clock oscillator, and power is not supplied to other electronic circuits. On the other hand, in the on state, power is supplied to electronic circuits required for wireless communication with the master station device. Power-saving communication reduces power consumption in the slave station devices and allows for the size of the batteries installed in the slave station devices to be reduced.

[0004] The master station device recognizes the on-time periods during which the slave station devices are intermittently on through past communications with the slave station devices. The master station device communicates with the slave station devices to activate them during the on-time periods, and acquires the sensor detection values through communications with the slave station devices after activation.

[0005] The following Patent Document 1 and Non-Patent Document 1 describe power-saving communication that conforms to Coordinated Sampled Listening (CSL). In power-saving communication that conforms to CSL, a master station device transmits multiple wake-up signals that are successive on a time axis. A slave station device turns on when one of the multiple wake-up signals is transmitted, receives one of the wake-up signals, and communicates with the master station device in response to that wake-up signal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-86240 [Non-patent literature]

[0007] [Non-Patent Document 1] Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs) Amendment 1: MAC sublayer, IEEE Std 802.15.4e, IEEE Computer Society, 2012 Summary of the Invention [Problem to be solved by the invention]

[0008] In low-power communication as specified in the CSL, in order to make the operation timing of the master station device closer to or coincide with the operation timing of the slave station devices, the master station device may transmit multiple wake-up signals that are connected on the time axis, which may result in longer or more complex preliminary communication times.

[0009] An object of the present invention is to simplify the adjustment of the operation timing of wireless devices, such as the master station device and slave station device, and other devices that communicate with them. [Means for solving the problem]

[0010] The present invention Related technologies The wireless device according to the present invention comprises a wireless unit that communicates with another device and a control unit that controls the wireless unit, wherein the other device receives a signal at a receiving window timing that conforms to the other device's time, the control unit estimates the receiving window timing based on information obtained by a previous communication with the other device and the device's own time, transmits a wake-up signal in accordance with the estimated receiving window timing, and executes, together with the wireless unit, a process of communicating with the other device after a predetermined communication startup time has elapsed since the wake-up signal was transmitted.

[0011] Furthermore, the present invention Related technologies The wireless device according to the present invention includes a wireless unit that communicates with another device and a control unit that controls the wireless unit, wherein the other device receives a signal at a receive window timing according to another device time, the control unit executes a process of estimating the receive window timing based on information obtained by a previous communication with the other device and the device time, transmits a wake-up signal according to the estimated receive window timing, and executes, together with the wireless unit, a process of receiving a reply signal transmitted from the other device after a predetermined processing time according to the other device time has elapsed since the other device received the wake-up signal, and The timing difference between the time of the local device and the time of the other device is calculated based on the timing of transmitting the wake-up signal and the timing of receiving the reply signal, and a time correction coefficient is determined based on the timing difference and a predetermined pre-correction wake-up instruction time, the time correction coefficient indicating the difference in speed between the rate at which the time of the local device advances and the rate at which the time of the other device advances, the pre-correction wake-up instruction time, and the time of the local device, and the process of transmitting the next wake-up signal according to the estimated receive window timing is performed together with the wireless unit.

[0012] Preferably, the control unit executes communication with the other device together with the wireless unit after a predetermined communication startup time has elapsed since transmitting the wake-up signal.

[0013] Preferably, the reply signal is a signal that conveys information from the other device to the wireless device.

[0014] Preferably, the control unit, together with the wireless unit, performs a process of transmitting a plurality of the wake-up signals at different times according to the receive window timing estimated by a previous communication with the other device, and receiving the reply signal transmitted from the other device after a predetermined processing time according to the other device time has elapsed since the other device received one of the plurality of the wake-up signals, the reply signal including identification information indicating which of the plurality of the wake-up signals was received by the other device, and performs a process of determining the timing difference based on the timing of transmitting one of the plurality of the wake-up signals recognized by the identification information and the timing of receiving the reply signal. do.

[0015] Further, a wireless communication system according to the present invention is a wireless communication system including a wireless device and another device, wherein when the other device receives a signal at a receive window timing according to another device time, the wireless device transmits a wake-up signal to the other device according to the receive window timing estimated based on information obtained by a previous communication between the wireless device and the other device and its own device time, the other device transmits a reply signal to the wireless device after a predetermined processing time according to the other device time has elapsed since receiving the wake-up signal, the wireless device calculates a timing difference between the own device time and the other device time based on the timing at which the wake-up signal was transmitted and the timing at which the reply signal was received, and the other device calculates the timing difference based on the difference between the timing at which the wake-up signal was received and the window time of the receive window timing. When the wireless device receives a signal at a reference receive window timing according to the device's own time, the other device estimates the reference receive window timing based on the timing difference and the other device time, transmits an uplink wakeup signal according to the estimated reference receive window timing, and performs communication with the wireless device after a predetermined communication startup time has elapsed since transmitting the uplink wakeup signal, and the wireless device performs communication with the other device after a predetermined communication startup time has elapsed since receiving the uplink wakeup signal. It is characterized by:

[0016] Preferably, the wireless device estimates the receive window timing based on the timing difference and the local device time, and transmits the next wake-up signal in accordance with the estimated receive window timing. teeth, After a predetermined communication startup time has elapsed since the wake-up signal was transmitted, communication with the other device is performed, and the other device communicates with the wireless device after a predetermined communication startup time has elapsed since the wake-up signal was received.

[0017] A wireless device according to the present invention includes a wireless unit that communicates with other devices and a control unit that controls the wireless unit, When the wireless device operates as a power saving device, The control unit Acts as a boot device A signal transmitted from the other device according to the other device's time is received at a receiving window timing according to the device's own time. Faith , Acts as a boot device When a wake-up signal transmitted from the other device is received, a timing difference between the time of the own device and the time of the other device is calculated based on a difference between a timing at which the wake-up signal was received and a window time of the reception window timing. Reason , executing together with the radio unit; Acts as a starter device and then as a power saver the other device receives a signal at a reference window timing according to the other device time; When the wireless device acts as an initiator, The control unit estimates the reference window timing based on the timing difference and the local device time. Execute the process and transmitting an upstream wake-up signal in accordance with the estimated reference window timing, and starting communication with the other device after a predetermined communication startup time has elapsed since transmitting the upstream wake-up signal. The process to be performed , which is characterized by being executed together with the radio unit.

[0018] Preferably, Acts as a power saver When the other device receives the upstream wakeup signal, the other device process After the time has elapsed, a reply signal is sent to the wireless device. Faith , When the wireless device acts as an initiator, The control unit newly calculates the timing difference based on the timing at which the upstream wakeup signal is transmitted and the timing at which the reply signal is received, and estimates the reference window timing based on the newly calculated timing difference and the host device time. Execute the process The wireless communication unit then executes, together with the radio unit, a process of transmitting the next uplink wakeup signal in accordance with the estimated reference window timing.

[0019] Preferably, the reply signal is a signal that conveys information from the other device to the wireless device. Preferably, when the wireless device operates as a startup device, the control unit estimates the receive window timing based on a time correction coefficient determined based on the timing difference and the wake-up instruction time before correction, which indicates the difference between the rate at which the time of the local device advances and the rate at which the time of the other device advances, the wake-up instruction time before correction, and the time of the local device. [Effects of the Invention]

[0020] According to the present invention, it is possible to simplify the adjustment of the operation timing of a wireless device and other devices that communicate with it. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a sensor network system. [Figure 2] 1 is a sequence chart of a basic process. [Figure 3] 10 is a sequence chart of a timing correction process. [Figure 4] 10 is a sequence chart of a process in which the master station device determines a time correction coefficient. [Figure 5] 10 is a sequence chart of a timing correction process when a slave station device operates as a starter device and a master station device operates as a power-saving device. [Figure 6] 10 is a sequence chart of a process in which a slave station device calculates a time correction coefficient. [Figure 7] FIG. 2 is a diagram illustrating an example of hardware of a master station device. [Figure 8] FIG. 2 is a diagram illustrating an example of hardware of a slave station device. DETAILED DESCRIPTION OF THE INVENTION

[0022] The related art and embodiments of the present invention will be described with reference to the drawings. The same components shown in multiple drawings will be assigned the same reference numerals to simplify the description.

[0023] 1 shows the configuration of a sensor network system 100 according to an embodiment of the present invention. The sensor network system 100 includes a master station device 10 and multiple slave station devices 14. Each slave station device 14 is equipped with sensors (not shown), such as a temperature sensor and an illuminance sensor. Each slave station device 14 communicates wirelessly with the master station device 10 and transmits detected values from its own sensors to the master station device 10.

[0024] The master station device 10 is equipped with a reference clock 12 that outputs a signal indicating a reference time, and operates in accordance with the reference time. Each slave station device 14 is equipped with a local clock 16 that outputs a signal indicating a local time, and operates in accordance with the local time.

[0025] In the sensor network system 100 according to this embodiment, the reference clock 12 and the local clock 16 are not synchronized. Each slave station device 14 may operate in a time-sharing manner according to a predetermined time allocation. In this case, the local clock 16 provided in each of the multiple slave station devices 14 defines the local time for each slave station device 14 with an accuracy sufficient to prevent mutual interference between wireless communications performed by the multiple slave station devices 14.

[0026] The following describes wireless communication performed between the master station device 10 and one of the slave station devices 14.

[0027] FIG. 2 shows a sequence chart of basic processing related to the present invention. This basic processing complies with the CSL. The upper part of FIG. 2 shows processing performed by the master station device 10, and the lower part shows processing performed by the slave station device 14. The horizontal axis in the upper part indicates reference time, and the horizontal axis in the lower part indicates local time. In FIG. 2, the fact that the length on the reference time axis and the length on the local time axis are equal on the drawing means that the actual time lengths are equal. Because the reference clock 12 and the local clock 16 are not synchronized, the intervals between the scales on the reference time axis and the scales on the local time axis are different on the drawing.

[0028] The slave station device 14 is in an on state for an on time Ton each time a period Tb elapses from start time T0 according to the local time indicated by its own local clock 16, and is in a sleep state during other time periods. That is, the slave station device 14 operates in a sleep mode in which one cycle of operation is repeated, with the slave station device 14 being in an on state for the on time Ton and then in a sleep state for the sleep time (Tb-Ton). When the sleep mode is released, the operating mode of the slave station device 14 becomes a normal mode in which the slave station device 14 is maintained in the on state.

[0029] In the sleep mode, a receive window timing 24 of an on-time Ton is set with a cycle Tb for the slave station device 14. That is, in the sleep mode, the slave station device 14 receives a signal during the receive window timing 24 when the slave station device 14 is in the on state.

[0030] To change the operating mode of the slave station device 14 from sleep mode to normal mode, the master station device 10 transmits a wakeup signal group 20 when a wakeup instruction time Tc has elapsed since the start time T0. The wakeup instruction time Tc is counted by the reference clock 12 of the master station device 10. The wakeup signal group 20 includes multiple wakeup signals 22 connected on a time axis. Each wakeup signal 22 includes a countdown value. The countdown value may be, for example, a numerical value that specifies the time until the slave station device 14 is started. In the example shown in FIG. 2 , the wakeup signal 22 transmitted earliest includes countdown values CN of “k,” “k−1,” . . . , “i,” “i−1,” . . . . In this basic process, the countdown value CN indicates that the operating mode is switched from sleep mode to normal mode after a communication startup time TT = CN·P + B has elapsed since the start of reception of the wakeup signal 22. Here, P and B are predetermined constants used to determine the communication startup time TT.

[0031] When a time period m times the period Tb counted by the local clock 16 of the slave station device 14 has elapsed, the slave station device 14 switches from the sleep state to the on state and receives the wake-up signal 22 that includes "i" as the countdown value. When the communication startup time TT = i·P + B has elapsed since the slave station device 14 started receiving the wake-up signal 22, the slave station device 14 switches its operating mode from the sleep mode to the normal mode and performs normal communication with the master station device 10.

[0032] Because the reference clock 12 included in the master station device 10 and the local clock 16 included in the slave station device 14 are not synchronized, the time m times the period Tb counted by the local clock 16 varies within the time period during which the wake-up signal group 20 is transmitted. In this basic technology, the wake-up signal group 20 includes multiple wake-up signals 22 that are successive on the time axis, and the time length of the wake-up signal group 20 is longer than the period Tb counted by the local clock 16. Therefore, even if the difference between the real time (actual time) m times the period Tb counted by the local clock 16 and the real time of the wake-up instruction time Tc counted by the reference clock 12 is not constant, any one of the multiple wake-up signals 22 is transmitted within the receive window timing 24, and one wake-up signal 22 is received by the slave station device 14.

[0033] When the communication start-up time TT has elapsed since the slave station device 14 started receiving the wake-up signal 22, the slave station device 14 switches its operation mode from the sleep mode to the normal mode and performs normal communication with the master station device 10.

[0034] 2, as long as a receive window timing 24 appears between the transmission of the first wake-up signal 22 and the transmission of the last wake-up signal 22, the operation of the slave station device 14 is switched from the sleep mode to the normal mode. This allows normal communication to be performed between the master station device 10 and the slave station device 14. In normal communication, the slave station device 14 may transmit a detection value of a sensor included in the slave station device 14 to the master station device 10.

[0035] The wake-up command time Tc, which is the time from start time T0 until the master station device 10 starts transmitting the wake-up signal 22, is determined by the reference time, and the receive window timing 24 is determined by the local time. Therefore, if the time length of the wake-up signal group 20 is longer than the period Tb counted by the local clock 16, normal communication will start even if there is a difference between the reference time and the local time. However, if the wake-up signal group 20 includes many wake-up signals 22 and the time length is increased, problems such as complex operation of the master station device 10 and increased power consumption by the master station device 10 may arise.

[0036] Therefore, in the embodiment of the present invention, the master station device 10 transmits one wake-up signal 22 by the timing correction process described below. This simplifies the process executed by the master station device 10 and reduces the power consumption of the master station device 10.

[0037] Fig. 3 shows a sequence chart of timing correction processing according to an embodiment of the present invention. The upper part of Fig. 3 shows processing executed by the master station device 10, and the lower part shows processing executed by the slave station device 14. The horizontal axis of the upper part indicates the reference time, and the horizontal axis of the lower part indicates the local time.

[0038] 3, the master station device 10 transmits a wake-up signal 22 when a wake-up instruction time Tc(j) has elapsed after the reference time reaches start time Ts(j). The wake-up instruction time Tc(j) is a time counted by the reference clock 12, and is calculated by multiplying n times the specified period Ta by a time correction coefficient R(j), which will be described later. The slave station device 14 receives the wake-up signal 22 at a receive window timing 24 that appears when the local clock 16 has counted m times the period Tb after the local time reaches start time T0(j).

[0039] Here, n is a predetermined natural number. m is a natural number used for convenience in explaining the operation and is an unknown natural number. The specified period Ta is a fixed value by design, and in this embodiment is a period counted by the reference clock 12. The period Tb is a period at which the receive window timing 24 appears, counted by the local clock 16.

[0040] In the timing adjustment process, normal communication is performed multiple times. As will be described later, the master station device 10 determines the time adjustment coefficient R(j) during the jth normal communication C(j) that was previously performed. Here, the time adjustment coefficient R(j) is a coefficient that indicates how much the time indicated by the local clock 16 advances per fixed period of time relative to the time indicated by the reference clock 12. In this embodiment, the time adjustment coefficient R(j) is defined as the ratio of the count value of the local clock 16 over a certain period of time to the count value of the reference clock 12 over the same period of time. The master station device 10 determines the wake-up instruction time Tc(j) according to Equation 1.

[0041] (Equation 1) Tc(j)=R(j)·n·Ta

[0042] The master station device 10 transmits one wake-up signal 22 when the wake-up instruction time Tc(j) has elapsed since the j-th start time Ts(j). When the communication startup time TT has elapsed since the master station device 10 started transmitting the wake-up signal 22, the master station device 10 becomes capable of normal communication with the slave station device 14.

[0043] When the communication start-up time TT has elapsed since the slave station device 14 started receiving the wake-up signal 22, the slave station device 14 switches its operation mode from the sleep mode to the normal mode and performs normal communication with the master station device 10.

[0044] 4 shows a sequence chart of the process by which the master station device 10 determines the time correction coefficient R(j). This diagram shows the process immediately before the jth normal communication C(j) begins. However, for ease of explanation, the receive window timing 24 is shown stretched in the time axis direction. Here, the explanation will be given assuming that the j-1th wake-up instruction time Tc(j-1) is known. If the wake-up instruction time Tc(j-1) has not been determined, a predetermined constant is set to the wake-up instruction time Tc(j-1).

[0045] The master station device 10 transmits one wake-up signal 22 when the wake-up instruction time Tc(j-1) has elapsed since the j-1th start time Ts(j-1).

[0046] When a time period m times the period Tb counted by the local clock 16 has elapsed from the j-1-th start time T0(j-1), the slave station device 14 switches from the sleep state to the on state for the on time Ton. In other words, when a time period m times the period Tb counted by the local clock 16 has elapsed from the j-1-th start time T0(j-1), the receive window timing 24 appears in the slave station device 14.

[0047] The slave station device 14 receives the wake-up signal 22, and when the communication startup time TT has elapsed since the start of reception of the wake-up signal 22, the slave station device 14 switches its operation mode from the sleep mode to the normal mode and performs normal communication C(j) with the master station device 10.

[0048] The slave station device 14 calculates the timing difference Δ(j) from the window time Ws(j-1) of the receive window timing 24 to the time when reception of the wake-up signal 22 begins. That is, the slave station device 14 calculates the timing difference Δ(j) by subtracting the time when reception of the wake-up signal 22 begins from the window time Ws(j-1) of the receive window timing 24. Here, the window time Ws(j-1) is a nominal time determined on the local time axis with respect to the receive window timing 24. The window time Ws(j-1) may be, for example, the center time of the receive window timing 24.

[0049] The slave station device 14 further transmits a reply signal 26 to the master station device 10 when a processing time τb has elapsed since the slave station device 14 started receiving the wake-up signal 22. Here, the processing time τb is a time obtained by subtracting the timing difference Δ(j) from the fixed time τ, which is a constant used for calculation. When the window time Ws(j-1) is ahead of the time when the slave station device 14 started receiving the wake-up signal 22, the timing difference Δ(j) is positive, and the processing time τb is shorter than the fixed time τ. When the window time Ws(j-1) is behind the time when the slave station device 14 started receiving the wake-up signal 22, the timing difference Δ(j) is negative, and the processing time τb is longer than the fixed time τ. In the example shown in FIG. 4, the timing difference Δ(j) is a positive value, and the processing time τb is shorter than the fixed time τ.

[0050] The slave station device 14 stores the local time when it starts transmitting the reply signal 26 as the start time T0(j). The slave station device 14 subtracts the start time T0(j) from the local time to determine the elapsed time from the start time T0(j). The slave station device 14 may set the time when a predetermined fixed time has elapsed since the start time T0(j) as the time when the next receive window timing 24 appears. The master station device 10 receives the reply signal 26 and stores the reference time when it starts receiving the reply signal 26 as the start time Ts(j). The master station device 10 subtracts the start time Ts(j) from the reference time to determine the elapsed time from the start time Ts(j). The master station device 10 may set the time when a predetermined fixed time has elapsed since the start time Ts(j) as the time when the next receive window timing 24 appears.

[0051] The master station device 10 also calculates the timing difference Δ(j) by subtracting the time at which it starts receiving the reply signal 26 from the time a fixed time τ has elapsed since the time tr at which it started transmitting the wake-up signal 22. The master station device 10 calculates the time correction coefficient R(j) according to the following equation (2).

[0052] (Math 2) R(j)=[n·Ta+τ-Δ(j)] / (n·Ta+τ)

[0053] The master station device 10 uses the time adjustment coefficient R(j) to execute the timing adjustment process shown in the sequence chart of FIG.

[0054] In this way, the master station device 10 and the slave station device 14 perform the following process. Specifically, the slave station device 14 receives a signal at a receive window timing 24 based on local time. The master station device 10 calculates a time correction coefficient R(j-1) and a wake-up command time Tc(j-1) based on information such as the timing difference Δ(j-1) obtained in a previous communication with the slave station device 14, and estimates the receive window timing 24 based on the reference time. The master station device 10 transmits a wake-up signal 22 in accordance with the estimated receive window timing 24, and receives a reply signal 26 from the slave station device 14 a predetermined processing time τb based on local time after the slave station device 14 receives the wake-up signal 22. The master station device 10 performs a process to calculate the timing difference Δ(j) between the reference time and local time based on the timing at which the wake-up signal 22 is transmitted and the timing at which the reply signal 26 is received. That is, the master station device 10 estimates the receive window timing 24 based on the timing difference Δ(j−1) and the reference time, and transmits a wake-up signal 22 in accordance with the estimated receive window timing 24. Furthermore, the master station device 10 starts communication with the slave station device 14 after a predetermined communication start-up time TT has elapsed since transmitting the wake-up signal 22.

[0055] The reply signal 26 is a control signal intended for the slave station device 14 to notify the master station device 10 of the operation timing. The reply signal 26 may be a signal that has both the function of a control signal and the function of an information transmission signal for transmitting information from the slave station device 14 to the master station device 10 in normal communication.

[0056] In the above example, the master station device 10 transmits one wake-up signal 22 when the wake-up instruction time Tc(j-1) has elapsed since the start time Ts(j-1). The master station device 10 may transmit one or more additional wake-up signals either before or after this single wake-up signal 22, or both. This increases the likelihood that the wake-up signal will be received by the slave station device 14, even if there is a large fluctuation in the difference between the reference time and the local time.

[0057] In this case, for example, each of the multiple wake-up signals includes identification information indicating the number of the wake-up signal in relation to the reference wake-up signal 22. The slave station device 14 includes this identification information in the reply signal 26 or the like, thereby allowing the master station device 10 to recognize which wake-up signal has been received by the slave station device 14. Based on the received wake-up signal, the slave station device 14 performs processing equivalent to that performed when the reference wake-up signal 22 has been received. Based on the wake-up signal recognized as the wake-up signal received by the slave station device 14, the master station device 10 performs processing equivalent to that performed when a single wake-up signal 22 has been transmitted.

[0058] In the above embodiment, the master station device 10 operates as a start-up device that transmits a wake-up signal 22, and the slave station device 14 operates as a power-saving device that is released from a sleep state by the wake-up signal 22. In a wireless communication system (second embodiment) configured with two devices, the master station device 10 and the slave station device 14, the slave station device 14 may operate as a start-up device, and the master station device 10 may operate as a power-saving device. That is, a wake-up signal may be transmitted from the slave station device 14, and the operation mode of the master station device 10 that has received the wake-up signal may be switched from sleep mode to normal mode, and normal communication may be performed between the slave station device 14 and the master station device 10.

[0059] 5 shows a sequence chart of timing correction processing when the slave station device 14 operates as a start-up device and the master station device 10 operates as a power-saving device after normal communication C(j) is executed. The top and second rows from the top of Fig. 5 show processing executed by the master station device 10, and the third and bottom rows show processing executed by the slave station device 14. The horizontal axes in the top and second rows from the top indicate reference time, and the horizontal axes in the third and bottom rows indicate local time.

[0060] In the timing correction process shown in Fig. 5, the slave station device 14 executes the process that the master station device 10 executed in the timing correction process shown in Fig. 3, and the master station device 10 executes the process that the slave station device 14 executed. In the timing correction process shown in Fig. 5, the slave station device 14 calculates the wake-up instruction time Td(j) according to (Equation 2) and (Equation 3).

[0061] (Equation 3) Td(j)= n Ta / R(j)

[0062] After the local time reaches start time T0(j), the slave station device 14 transmits an upstream wakeup signal 30 when the wakeup instruction time Td(j) is counted by the local clock 16. Furthermore, after the reference time reaches start time Ts(j), the master station device 10 receives the upstream wakeup signal 30 at reference window timing 32 (corresponding to the receive window timing 24 of the slave station device 14) which appears when the reference clock 12 counts a time n times the period Tb.

[0063] The slave station device 14 transmits one upstream wakeup signal 30 to the master station device 10 when an upstream wakeup instruction time Td(j) has elapsed since the start time T0(j). The slave station device 14 becomes capable of performing upstream normal communication with the master station device 10 when a communication startup time TT has elapsed since the slave station device 14 started transmitting the upstream wakeup signal 30. Here, upstream normal communication refers to communication in which the slave station device 14 performs the same processing as the processing performed by the master station device 10 in the normal communication in the sequence charts of FIGS. 3 and 4, and the master station device 10 performs the same processing as the processing performed by the slave station device 14 in the normal communication in the sequence charts of FIGS. 3 and 4. The upstream normal communication may be performed in a frequency band different from the frequency band in which the above-mentioned normal communication is performed.

[0064] When a time period m times the period Tb counted by the reference clock 12 has elapsed from the start time Ts(j), the master station device 10 switches from the sleep state to the on state for the on time Ton. In other words, when a time period m times the period Tb counted by the reference clock 12 has elapsed from the j-th start time Ts(j), the reference window timing 32 in the master station device 10 appears.

[0065] The parent station device 10 receives the upstream wake-up signal 30, and when a communication startup time TT has elapsed since the start of reception of the upstream wake-up signal 30, the parent station device 10 switches the operation mode from a sleep mode to a normal mode and performs upstream normal communication with the child station device 14.

[0066] After the upstream normal communication in the timing correction process shown in Fig. 5 is performed, the process for performing subsequent upstream normal communication is the same as the normal communication shown in Fig. 3 and Fig. 4. That is, the operation of the slave station device 14 operating as a starter device according to the sequence chart of Fig. 5 is the same as the operation of the master station device 10 operating as a starter device according to the sequence chart of Fig. 3 and Fig. 4. Also, the operation of the master station device 10 operating as a power-saving device according to the sequence chart of Fig. 5 is the same as the operation of the slave station device 14 operating as a power-saving device according to the sequence chart of Fig. 3 and Fig. 4.

[0067] 5, the timing difference Δ(j) calculated by the slave station device 14 in the previous normal communication C(j) is used in the timing adjustment process when performing uplink normal communication. This simplifies the process when performing both wireless communication in which the master station device 10 is the activating device and the slave station device 14 is the power-saving device and wireless communication in which the master station device 10 is the power-saving device and the slave station device 14 is the activating device.

[0068] FIG. 6 shows a sequence chart of the process by which the slave station device 14 operating as a start-up device calculates the time correction coefficient Q(k). The upper part of FIG. 6 shows the process executed by the master station device 10 as a power-saving device, and the lower part shows the process executed by the slave station device 14 as a start-up device. The horizontal axis in the upper part represents the reference time, and the horizontal axis in the lower part represents the local time. This diagram shows the process immediately before the start of the kth uplink normal communication D(k). However, for ease of explanation, the reference window timing 32 is shown stretched along the time axis. Here, the explanation will be given assuming that the k-1th wake-up instruction time Td(k-1) has been calculated in advance.

[0069] The slave station device 14 transmits one upstream wakeup signal 30 when the wakeup instruction time Td(k-1) has elapsed since the (k-1)th start time T0(k-1).

[0070] When a time period m times the period Tb counted by the reference clock 12 has elapsed from the k-1th start time Ts(k-1), the master station device 10 switches from the sleep state to the on state for the on time Ton. In other words, when a time period m times the period Tb counted by the reference clock 12 has elapsed from the k-1th start time Ts(k-1), the reference window timing 32 in the master station device 10 appears.

[0071] The parent station device 10 receives the upstream wakeup signal 30, and when a communication startup time TT has elapsed since the parent station device 10 started receiving the upstream wakeup signal 30, the parent station device 10 switches the operation mode from a sleep mode to a normal mode and performs upstream normal communication with the child station device 14.

[0072] The master station device 10 calculates the timing difference Δ(k) from the window time Wss(k-1) of the reference window timing 32 to the time when reception of the upstream wakeup signal 30 begins. That is, the master station device 10 calculates the timing difference Δ(k) by subtracting the time when reception of the upstream wakeup signal 30 begins from the window time Wss(k-1) of the reference window timing 32. Here, the window time Wss(k-1) is a nominal time determined on the reference time axis with respect to the reference window timing 32. The window time Wss(k-1) may be, for example, the center time of the reference window timing 32.

[0073] The master station device 10 further transmits a reply signal 36 to the slave station device 14 when a processing time τb has elapsed since the start of reception of the upstream wakeup signal 30. Here, the processing time τb is a time obtained by subtracting the timing difference Δ(k) from the fixed time τ, which is a calculation constant. When the window time Wss(k-1) is ahead of the start of reception of the upstream wakeup signal 30, the timing difference Δ(k) is positive, and the processing time τb is shorter than the fixed time τ. When the window time Wss(k-1) is behind the start of reception of the upstream wakeup signal 30, the timing difference Δ(k) is negative, and the processing time τb is longer than the fixed time τ. In the example shown in FIG. 6, the timing difference Δ(k) is a negative value, and the processing time τb is longer than the fixed time τ.

[0074] The master station device 10 stores the reference time when it starts transmitting the reply signal 36 as the start time Ts(k). The master station device 10 subtracts the start time Ts(k) from the reference time to determine the elapsed time from the start time Ts(k). The master station device 10 may set the time when a predetermined fixed time has elapsed since the start time Ts(k) as the time when the next reference window timing 32 appears. The slave station device 14 receives the reply signal 36 and stores the local time when it starts receiving the reply signal 36 as the start time T0(k). The slave station device 14 subtracts the start time T0(k) from the local time to determine the elapsed time from the start time T0(k). The slave station device 14 may set the time when a predetermined fixed time has elapsed since the start time T0(k) as the time when the next reference window timing 32 appears.

[0075] The slave station device 14 also calculates the timing difference Δ(k) by subtracting the time at which it starts receiving the reply signal 36 from the time when a fixed time τ has elapsed since the time tr at which it started transmitting the upstream wakeup signal 30. The slave station device 14 calculates the time correction coefficient Q(k) according to the following equation (4).

[0076] (Math. 4) Q(k)=[n·Ta+τ-Δ(k)] / (n·Ta+τ)

[0077] The slave station device 14 uses the time correction coefficient Q(k) to calculate the next wake-up command time Td(k) according to Td(k)=Q(k)·n·Ta. The slave station device 14 calculates the next reference window timing 32 using the wake-up command time Td(k), and transmits the upstream wake-up signal 30 at that reference window timing 32.

[0078] As described above, in each embodiment of the present invention, when the master station device 10 is a wireless device and the slave station device 14 is another device, the following processes (1) to (4) are executed. The following self-device time is the reference time indicated by the reference clock 12, and the other-device time is the local time indicated by the local clock 16.

[0079] (1) The other device receives a signal at a receive window timing 24 that conforms to the other device's time. The wireless device estimates the receive window timing 24 based on information obtained from a previous communication with the other device and its own device's time. The wireless device transmits a wake-up signal 22 in accordance with the estimated receive window timing 24, and executes communication with the other device after a predetermined communication startup time has elapsed since transmitting the wake-up signal 22.

[0080] (2) The wireless device estimates receive window timing 24 based on information obtained from a previous communication with another device and its own device time. The wireless device transmits a wake-up signal 22 in accordance with the estimated receive window timing 24, and receives a reply signal 26 from the other device after a predetermined processing time according to the other device time has elapsed since the other device received the wake-up signal 22. The wireless device calculates the timing difference between its own device time and the other device time based on the timing difference and its own device time, and transmits the next wake-up signal 22 in accordance with the estimated receive window timing 24.

[0081] (3) In the process of (2) above, the wireless device executes communication with another device after a predetermined communication startup time has elapsed since transmitting the wake-up signal 22.

[0082] (4) In the process of (3) above, the reply signal 26 may be a signal that conveys information from another device to the wireless device in communication with the other device.

[0083] In the above processes (1) to (4), the master station device 10 may be the other device, and the slave station device 14 may be the wireless device. In this case, the own device time is the local time indicated by the local clock 16, and the other device time is the reference time indicated by the reference clock 12.

[0084] In each embodiment of the present invention, when the slave station device 14 is a wireless device and the master station device 10 is another device, the following processes (5) to (10) are executed. The following self-device time is the local time indicated by the local clock 16, and the other-device time is the reference time indicated by the reference clock 12.

[0085] (5) The wireless device receives a signal transmitted from another device according to the other device time at a receive window timing 24 according to its own device time. When the wireless device receives a wake-up signal 22 transmitted from the other device, it transmits a reply signal 26 to the other device after a predetermined fixed time τ has elapsed from the window time of the receive window timing 24. The other device calculates the timing difference between the other device time and its own device time based on the timing at which it transmitted the wake-up signal 22 and the timing at which it received the reply signal 26. The other device estimates the receive window timing 24 based on the timing difference and the other device time, and transmits the next wake-up signal 22 according to the estimated receive window timing 24.

[0086] (6) In the process of (5) above, the wireless device executes communication with another device after a predetermined communication startup time has elapsed since receiving the wake-up signal 22.

[0087] (7) In the process of (6) above, the reply signal 26 may be a signal that transmits information from the wireless device to another device in communication with the other device.

[0088] (8) The wireless device receives a signal transmitted from another device according to the other device time at a receive window timing 24 according to its own device time. When the wireless device receives a wake-up signal 22 transmitted from the other device, it calculates the timing difference between its own device time and the other device time based on the difference between the timing at which the wake-up signal 22 was received and the window time of the receive window timing 24. The other device receives the signal at a reference window timing 32 according to the other device time. The wireless device estimates the reference window timing 32 based on the timing difference and its own device time. The wireless device transmits an uplink wake-up signal 30 according to the estimated reference window timing 32. The wireless device performs communication with the other device after a predetermined communication startup time has elapsed since transmitting the uplink wake-up signal 30.

[0089] (9) In the process of (8) above, when the other device receives the uplink wakeup signal 30, it transmits a reply signal 36 to the wireless device after a predetermined fixed time τ has elapsed since the window time of the reference window timing 32. The wireless device calculates a new timing difference based on the timing at which it transmitted the uplink wakeup signal 30 and the timing at which it received the reply signal 36, and estimates the reference window timing 32 based on the timing difference and its own device time. The wireless device transmits the next uplink wakeup signal 30 in accordance with the estimated reference window timing 32.

[0090] (10) In the process of (9) above, the reply signal 36 may be a signal that conveys information from another device to the wireless device in communication with the other device.

[0091] In the processes (5) to (10) above, the slave station device 14 may be the other device described above, and the master station device 10 may be the wireless device described above. In this case, the local device time is the reference time indicated by the reference clock 12, and the other device time is the local time indicated by the local clock 16.

[0092] FIG. 7 shows an example of the hardware of a wireless device used as the master station device 10. The master station device 10 includes a radio unit 40, a control unit 42, a reference clock 12, a memory 44, and a battery 46. The radio unit 40 transmits transmission information output from the control unit 42 by incorporating it into a radio signal. The radio unit 40 also receives the radio signal, extracts received information from the radio signal, and outputs the extracted information to the control unit 42. The reference clock 12 outputs a signal indicating a reference time to the control unit 42. The control unit 42 operates together with the radio unit 40 at a timing according to the reference time. The control unit 42 may include a processor that executes a program stored in the memory 44. By executing the program, the control unit 42, together with the radio unit 40, performs the processes performed by the master station device 10, among the processes shown in FIGS. 3 to 6. The battery 46 supplies power to necessary electrical circuits constituting the radio unit 40, the control unit 42, the reference clock 12, and the memory 44, under the control of the control unit 42. Instead of the battery 46, a power supply circuit that supplies power from a commercial power source may be used.

[0093] The wireless unit 40 may have separate hardware for performing normal communication and hardware for performing uplink normal communication. In this case, the hardware for performing normal communication and the hardware for performing uplink normal communication may be configured to be able to switch between sleep mode and normal mode individually.

[0094] FIG. 8 shows an example of hardware for a wireless device used as the slave station device 14. The slave station device 14 includes a radio unit 50, a control unit 52, a local clock 16, a memory 54, a sensor 56, and a battery 58. The radio unit 50 transmits transmission information output from the control unit 52 by incorporating it into a wireless signal. The radio unit 50 also receives the wireless signal, extracts received information from the wireless signal, and outputs the extracted information to the control unit 52. The local clock 16 outputs a signal indicating the local time to the control unit 52. The control unit 52 operates together with the radio unit 50 at a timing according to the local time. The control unit 52 may include a processor that executes a program stored in the memory 54. The sensor 56 may be a temperature sensor, a humidity sensor, a water level sensor, a gas sensor that detects the concentration of a specific gas, or the like. The sensor 56 outputs a detected value to the control unit 52. The control unit 52 executes the program to perform, together with the radio unit 50, the processing performed by the slave station device 14 among the processing shown in FIGS. 3 to 6. Battery 58 supplies power to necessary electrical circuits constituting radio unit 50, control unit 52, local clock 16, memory 54, and sensor 56 under the control of control unit 52. Note that instead of battery 58, a power supply circuit that supplies power from a commercial power source may be used.

[0095] The wireless unit 50 may have separate hardware for performing normal communication and hardware for performing uplink normal communication. In this case, the hardware for performing normal communication and the hardware for performing uplink normal communication may be configured to be able to switch between sleep mode and normal mode individually.

[0096] The above describes an embodiment in which the present invention is used in the sensor network system 100. The present invention may also be used in other systems such as a telemetering system. A telemetering system is a system in which a measuring unit such as a watt-hour meter or gas meter is connected to a power-saving device, and the power-saving device transmits the measured value of the measuring unit to a starting device. [Explanation of symbols]

[0097] 10 master station device, 12 reference clock, 14 slave station device, 16 local clock, 20 wake-up signal group, 22 wake-up signal, 24 receive window timing, 26, 36 reply signal, 30 upstream wake-up signal, 32 reference window timing, 40, 50 radio section, 42, 52 control section, 44, 54 memory, 46, 58 battery, 56 sensor.

Claims

1. A wireless communication system including a wireless device and another device, When the other device receives a signal at a reception window timing according to the other device time, The wireless device transmitting a wake-up signal to the other device in accordance with the reception window timing estimated based on information obtained by previous communication with the other device and a time of the device itself; The other device is transmitting a response signal to the wireless device after a predetermined processing time has elapsed according to the time of the other device since receiving the wake-up signal; The wireless device calculating a timing difference between the time of the own device and the time of the other device based on a timing of transmitting the wake-up signal and a timing of receiving the reply signal; The other device is determining the timing difference based on a difference between a timing at which the wake-up signal is received and a window time of the receive window timing; When the wireless device receives a signal at a reference reception window timing according to the device time, The other device is estimating the reference receive window timing based on the timing difference and the other device time, and transmitting an upstream wakeup signal in accordance with the estimated reference receive window timing; After a predetermined communication start-up time has elapsed since the upstream wake-up signal was transmitted, communication with the wireless device is performed; The wireless device A wireless communication system, characterized in that communication with the other device is performed after a predetermined communication startup time has elapsed since the upstream wake-up signal was received.

2. 2. The wireless communication system according to claim 1, The wireless device estimating the receive window timing based on the timing difference and the local device time; A wireless communication system, characterized in that the next wake-up signal is transmitted in accordance with the estimated reception window timing.

3. 3. The wireless communication system according to claim 1, The wireless device After a predetermined communication start time has elapsed since the wake-up signal was transmitted, communication with the other device is performed; The other device is a wireless communication system that performs communication with the wireless device after a predetermined communication startup time has elapsed since the wake-up signal was received;

4. A wireless device, a wireless unit for communicating with other devices; a control unit that controls the radio unit, When the wireless device operates as a power saving device, the control unit receiving a signal transmitted from the other device operating as a start-up device according to the other device time at a reception window timing according to the own device time; When receiving a wake-up signal transmitted from the other device operating as a start-up device, executes, together with the wireless unit, a process of determining a timing difference between the time of the own device and the time of the other device based on a difference between a timing at which the wake-up signal was received and a window time of the reception window timing; the other device that operates as a power-saving device after operating as a startup device receives a signal at a reference window timing according to the other device time; When the wireless device operates as a activating device, the control unit executing a process of estimating the reference window timing based on the timing difference and the host device time; transmitting an upstream wake-up signal in accordance with the estimated reference window timing; A wireless device characterized in that, after a predetermined communication startup time has elapsed since transmitting the upstream wakeup signal, the wireless device executes, together with the wireless section, a process for communicating with the other device.

5. 5. The wireless device according to claim 4, The other device that operates as a power saving device is When the upstream wakeup signal is received, a response signal is transmitted to the wireless device after a predetermined processing time has elapsed since the window time of the reference window timing; When the wireless device operates as a activating device, the control unit a timing difference based on the timing at which the uplink wakeup signal is transmitted and the timing at which the reply signal is received; a process of estimating the reference window timing based on the newly calculated timing difference and the device's own time; and a process of transmitting the next uplink wakeup signal according to the estimated reference window timing, performed together with the radio unit.

6. 6. The wireless device according to claim 5, The reply signal is A wireless device characterized in that the signal is a signal that transmits information from the other device to the wireless device.

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