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 the wireless device and another device. [Background technology]

[0002] Research and development is currently underway on a sensor network system 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. In some sensor network systems, the sensors are mounted in slave station devices, and the slave station devices wirelessly transmit the values ​​detected by the sensors to the master station device.

[0003] In a sensor network system, power-saving communication is performed. In power-saving communication, the slave station equipment is in an on state intermittently. That is, the slave station equipment is in an on state for a predetermined period of time at a predetermined cycle, and in a sleep state during other periods. In the sleep state, power is supplied only to electronic circuits that determine the operation timing of the slave station equipment, such as a 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 necessary for wireless communication with the master station equipment. Power-saving communication reduces power consumption in the slave station equipment, and allows the batteries installed in the slave station equipment to be made smaller.

[0004] The master station equipment recognizes the on-time periods during which the slave station equipment is intermittently on through past communications with the slave station equipment. The master station equipment communicates with the slave station equipment during the on-time periods to start up the slave station equipment, and acquires the sensor detection values ​​through communications with the slave station equipment after the equipment has been started up.

[0005] The following Patent Document 1 and Non-Patent Document 1 disclose power-saving communication conforming to Coordinated Sampled Listening (CSL). In power-saving communication conforming to CSL, a master station transmits multiple wake-up signals that are successive on a time axis. A slave station 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 in response to the wake-up signal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-86240 A [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 bring the operation timing of the master station equipment closer to or coincide with that of the slave station equipment, the master station equipment may transmit multiple wake-up signals that are consecutive on the time axis, which may result in longer preliminary communication times or more complex preliminary communication.

[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 the master station device. [Means for solving the problem]

[0010] The wireless device of the present invention comprises a wireless unit that communicates with other devices and a control unit that controls the wireless unit, wherein the other device receives a signal at a receive window timing according to the other device time, and the control unit estimates the receive window timing based on information obtained by previous communication with the other device and the device time, transmits a wake-up signal according to the estimated receive window timing, and performs, together with the wireless unit, a process of communicating with the other device after a predetermined communication startup time has elapsed since transmitting the wake-up signal.

[0011] In addition, a wireless device of 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 receive window timing according to the other device time, and the control unit estimates the receive window timing based on information obtained by previous communication with the other device and its own device time, transmits a wake-up signal according to the estimated receive window timing, receives a reply signal 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, 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, estimates the receive window timing based on the timing difference and the own device time, and performs a process together with the wireless unit to transmit the next wake-up signal according to the estimated receive window timing.

[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] In addition, a wireless device of the present invention comprises a wireless unit that communicates with other devices, and a control unit that controls the wireless unit, and the control unit, together with the wireless unit, performs the following processes: receiving a signal transmitted from the other device according to the other device time at a receive window timing according to the own device time, and when receiving a wake-up signal transmitted from the other device, transmitting a reply signal to the other device after a predetermined fixed time has elapsed from the window time of the receive window timing; and the other device calculates a timing difference between the other device time and the own device time based on the timing at which the wake-up signal was transmitted and the timing at which the reply signal was received, estimates the receive window timing based on the timing difference and the other device time, and transmits the next wake-up signal according to the estimated receive window timing.

[0015] Preferably, the control unit executes communication with the other device together with the wireless unit after a predetermined communication startup time has elapsed since receiving the wake-up signal.

[0016] Preferably, the reply signal is a signal for transmitting information from the wireless device to the other device.

[0017] In addition, a wireless device of the present invention comprises a wireless unit that communicates with other devices, and a control unit that controls the wireless unit, and the control unit performs, together with the wireless unit, a process of receiving a signal transmitted from the other device according to the other device time at a receive window timing according to the own device time, and a process of calculating a timing difference between the own device time and the other device time 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 a wake-up signal transmitted from the other device is received, the other device receives a signal at a reference window timing that follows the other device time, the control unit estimates the reference window timing based on the timing difference and the own device time, and transmits an uplink wake-up signal according to the estimated reference window timing, and performs communication with the other device together with the wireless unit after a predetermined communication startup time has elapsed since transmitting the uplink wake-up signal.

[0018] Preferably, when the other device receives the uplink wakeup signal, it executes a process of transmitting a reply signal to the wireless device after a predetermined fixed time has elapsed from the window time of the reference window timing, and the control unit, together with the wireless unit, newly calculates the timing difference based on the timing at which the uplink wakeup signal is transmitted and the timing at which the reply signal is received, estimates the reference window timing based on the newly calculated timing difference and the own device time, and transmits 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. Effect 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 another device that communicates with the wireless device. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a sensor network system. [Diagram 2] 1 is a sequence chart of a basic process. [Diagram 3] 13 is a sequence chart of a timing correction process. [Figure 4] 6 is a sequence chart of a process in which the master station device determines a time correction coefficient. [Diagram 5] 11 is a sequence chart of a timing correction process when a slave station device operates as a start-up device and a master station device operates as a power-saving device. [Figure 6] 5 is a sequence chart of a process in which a slave station device determines 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 PREFERRED EMBODIMENTS

[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 are designated by the same reference numerals to simplify the description thereof.

[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 detection values ​​of 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 according to the timing of 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 according to the timing of 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-division manner with a predetermined time allocation. In this case, the local clock 16 included in each of the multiple slave station devices 14 defines the local time for each slave station device 14 with an accuracy such that wireless communications performed by the multiple slave station devices 14 do not interfere with each other.

[0026] In the following, wireless communication performed between the master station device 10 and one of the multiple slave station devices 14 will be described.

[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 executed by the master station device 10, and the lower part shows processing executed by the slave station device 14. The horizontal axis in the upper part shows the reference time, and the horizontal axis in the lower part shows the 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. Since the reference clock 12 and the local clock 16 are not synchronized, the intervals on the drawing of the scale of the reference time axis and the intervals on the drawing of the scale of the local time axis are different.

[0028] The slave station device 14 is in an on state for an on time Ton every time a period Tb elapses from the 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 the slave station device 14 is in an on state for the on time Ton and then in a sleep state for the sleep time (Tb-Ton), which constitutes one cycle. When the sleep mode is released, the operation mode of the slave station device 14 becomes a normal mode in which the slave station device 14 is maintained in an 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 at the receive window timing 24 when the slave station device 14 is in the on-state.

[0030] In order to change the operation mode of the slave station device 14 from the sleep mode to the normal mode, the master station device 10 transmits a wake-up signal group 20 when a wake-up instruction time Tc has elapsed since the start time T0. The wake-up instruction time Tc is counted by the reference clock 12 of the master station device 10. Here, the wake-up signal group 20 includes a plurality of wake-up signals 22 that are connected on the time axis. Each wake-up 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 countdown values ​​CN of "k", "k-1", . . . "i", "i-1", . . . are included in the wake-up signal 22 that is transmitted earliest. In this basic process, the countdown value CN has the significance of switching the operation mode from the sleep mode to the normal mode after a communication start-up time TT=CN·P+B has elapsed since the start of reception of the wake-up signal 22. Here, P and B are predetermined constants for determining the communication start-up 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 a sleep state to an on state and receives a wake-up signal 22 including "i" as a countdown value. When a 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 operation mode from the sleep mode to the normal mode and performs normal communication with the master station device 10.

[0032] Since 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 during which the wake-up signal group 20 is transmitted. In this basic technology, the wake-up signal group 20 includes a plurality of wake-up signals 22 that are consecutive 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 plurality of wake-up signals 22 is transmitted at the reception 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 between the master station device 10 and the slave station device 14. In the normal communication, a detection value of a sensor included in the slave station device 14 may be transmitted from the slave station device 14 to the master station device 10.

[0035] The wake-up command time Tc from the 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 the operation of the master station device 10 becoming complicated and the power consumption of the master station device 10 increasing may occur.

[0036] Therefore, in the embodiment of the present invention, the master station device 10 transmits one wake-up signal 22 by a 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 a timing correction process according to an embodiment of the present invention. The upper part of Fig. 3 shows the process executed by the master station device 10, and the lower part shows the process 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, when the wake-up instruction time Tc(j) has elapsed after the reference time has reached start time Ts(j), the master station device 10 transmits a wake-up signal 22. The wake-up instruction time Tc(j) is a time counted by the reference clock 12, and is calculated by multiplying a time period n times the specified period Ta by a time correction coefficient R(j), which will be described later. Then, the slave station device 14 receives the wake-up signal 22 at a receive window timing 24 that appears when a time period m times the period Tb has been counted by the local clock 16 after the local time has reached 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 prescribed period Ta is a fixed value in terms of 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, which is counted by the local clock 16.

[0040] In the timing correction process, normal communication is performed multiple times. As described later, in the j-th normal communication C(j) that was previously performed, the master station device 10 determines the time correction coefficient R(j). Here, the time correction coefficient R(j) is a coefficient that indicates how much the time indicated by the local clock 16 advances per certain time period relative to the time indicated by the reference clock 12. In this embodiment, the time correction coefficient R(j) is defined as the ratio of the count value of the local clock 16 over a certain length of time to the count value of the reference clock 12 over the same length 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 a wake-up instruction time Tc(j) has elapsed since the j-th start time Ts(j). When a 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 in which the master station device 10 determines the time correction coefficient R(j). This diagram shows the process immediately before the j-th normal communication C(j) is started. 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-1-th wake-up instruction time Tc(j-1) is known. When the wake-up instruction time Tc(j-1) has not been obtained, 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 from the j-1-th 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 a sleep state to an 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 in the slave station device 14 appears.

[0047] The slave station device 14 receives the wake-up signal 22, and when the communication startup 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 C(j) with the master station device 10.

[0048] The slave station device 14 obtains 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 obtains 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 start of reception of 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 for calculation. When the window time Ws(j-1) is ahead of the start of reception of 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 start of reception of 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 obtains the elapsed time from the start time T0(j) by subtracting the start time T0(j) from the local time. The slave station device 14 may set the time when a predetermined fixed time has elapsed from 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 obtains the elapsed time from the start time Ts(j) by subtracting the start time Ts(j) from the reference time. The master station device 10 may set the time when a predetermined fixed time has elapsed from 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 when it starts receiving the reply signal 26 from the time when a fixed time τ has elapsed since the time tr when 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 correction coefficient R(j) to execute the timing correction process shown in the sequence chart of FIG.

[0054] In this way, the master station device 10 and the slave station device 14 execute the following process. That is, the slave station device 14 receives a signal at a receive window timing 24 according to the local time. The master station device 10 obtains a time correction coefficient R(j-1) and further a wake-up command time Tc(j-1) based on information such as a timing difference Δ(j-1) obtained by 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 according to the estimated receive window timing 24, and receives a reply signal 26 transmitted from the slave station device 14 after a predetermined processing time τb according to the local time has elapsed since the slave station device 14 received the wake-up signal 22. The master station device 10 executes a process of obtaining a timing difference Δ(j) between the reference time and the local time based on the timing of transmitting the wake-up signal 22 and the timing of receiving the reply signal 26. 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. In addition, the master station device 10 executes 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 inform the master station device 10 of the operation timing. The reply signal 26 may be a signal having both a function as a control signal and a function as 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 from 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 one 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 which wake-up signal is the number in the forward or backward direction from the reference wake-up signal 22. The slave station device 14 includes this identification information in the reply signal 26, etc., to allow 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 one 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) including 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 the sleep mode to the normal mode, and a process may be executed in which normal communication is performed between the slave station device 14 and the master station device 10.

[0059] Fig. 5 shows a sequence chart of the timing correction process 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 the process executed by the master station device 10, and the third and bottom rows show the process executed by the slave station device 14. The horizontal axes of the top and second rows from the top indicate the reference time, and the horizontal axes of the third and bottom rows indicate the 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 command 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 command time Td(j) is counted by the local clock 16. In addition, 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) that 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 from 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, the upstream normal communication refers to communication in which the slave station device 14 performs a process similar to the process performed by the master station device 10 in the normal communication in the sequence charts of FIG. 3 and FIG. 4, and the master station device 10 performs a process similar to the process performed by the slave station device 14 in the normal communication in the sequence charts of FIG. 3 and FIG. 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 an upstream wakeup signal 30, and when a communication startup time TT has elapsed since starting to receive 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.

[0066] After the upstream normal communication in the timing correction process shown in Fig. 5 is performed, the process of performing the next and subsequent upstream normal communications is similar to the normal communications shown in Fig. 3 and Fig. 4. That is, the operation of the slave station device 14 operating as a start-up device according to the sequence chart in Fig. 5 is similar to the operation of the master station device 10 operating as a start-up device according to the sequence chart in 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 in Fig. 5 is similar to the operation of the slave station device 14 operating as a power-saving device according to the sequence chart in 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 correction process when performing upstream 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] 6 shows a sequence chart of the process in which the slave station device 14 operating as a start-up device determines 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 indicates the reference time, and the horizontal axis in the lower part indicates the local time. This figure shows the process immediately before the start of the k-th upstream normal communication D(k). However, for ease of explanation, the reference window timing 32 is shown stretched in the time axis direction. Here, the k-1-th wake-up instruction time Td(k-1) will be explained as having been determined in advance.

[0069] The slave station device 14 transmits one upstream wakeup signal 30 when the wakeup instruction time Td(k-1) has elapsed from 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 passed from the k-1th start time Ts(k-1), the master station device 10 switches from a sleep state to an on state for an on time Ton. In other words, when a time period m times the period Tb counted by the reference clock 12 has passed from the k-1th start time Ts(k-1), the reference window timing 32 in the master station device 10 appears.

[0071] The master station device 10 receives the upstream wakeup signal 30, and when a communication startup time TT has elapsed since starting to receive the upstream wakeup signal 30, the master station device 10 switches its operation mode from the sleep mode to the normal mode and performs upstream normal communication with the slave station device 14.

[0072] The master station device 10 obtains a 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 obtains 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 constant for calculation. 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 the transmission of the reply signal 36 is started as the start time Ts(k). The master station device 10 obtains the elapsed time from the start time Ts(k) by subtracting the start time Ts(k) from the reference time. The master station device 10 may set the time when a predetermined fixed time has elapsed from 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 the reception of the reply signal 36 is started as the start time T0(k). The slave station device 14 obtains the elapsed time from the start time T0(k) by subtracting the start time T0(k) from the local time. The slave station device 14 may set the time when a predetermined fixed time has elapsed from 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 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 from the wake-up command time Td(k) and transmits the upstream wake-up signal 30 at the reference window timing 32.

[0078] As described above, in each embodiment of the present invention, when the parent station device 10 is a wireless device and the child station device 14 is another device, the following processes (1) to (4) are executed. In the following, the own 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 according to the other device 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 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 a receive window timing 24 based on information obtained by previous communication with another device and its own device time. The wireless device transmits a wake-up signal 22 according to the estimated receive window timing 24, and receives a reply signal 26 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 22. The wireless device determines a timing difference between its own device time and the other 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 wireless device estimates a receive window timing 24 based on the timing difference and its own device time, and transmits the next wake-up signal 22 according to 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 parent station device 10 may be the other device, and the child 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. In the following, 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.

[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, the wireless device 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 determines 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 for transmitting 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 the own device time. When the wireless device receives a wakeup signal 22 transmitted from the other device, the wireless device calculates a timing difference between the own device time and the other device time based on the difference between the timing at which the wakeup signal 22 was received and the window time of the receive window timing 24. The other device receives a 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 the own device time. The wireless device transmits an upstream wakeup 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 upstream wakeup 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 from the window time of the reference window timing 32. The wireless device calculates a new timing difference based on the timing of transmitting the uplink wakeup signal 30 and the timing of receiving 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 above processes (5) to (10), the slave station device 14 may be the other device, and the master station device 10 may be the wireless device. 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 hardware of a wireless device used as the master station device 10. The master station device 10 includes a wireless unit 40, a control unit 42, a reference clock 12, a memory 44, and a battery 46. The wireless unit 40 transmits the transmission information output from the control unit 42 by including it in a wireless signal. The wireless unit 40 also receives the wireless signal, extracts the reception information from the wireless signal, and outputs it to the control unit 42. The reference clock 12 outputs a signal indicating the reference time to the control unit 42. The control unit 42 operates together with the wireless 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. The control unit 42 executes the program to execute the process executed by the master station device 10, among the processes shown in FIG. 3 to FIG. 6, together with the wireless unit 40. The battery 46 supplies power to necessary electric circuits constituting the wireless unit 40, the control unit 42, the reference clock 12, and the memory 44, according to the control by 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, each of the hardware for performing normal communication and the hardware for performing uplink normal communication may be configured to be able to switch between a sleep mode and a normal mode individually.

[0094] FIG. 8 shows an example of hardware of a wireless device used as the slave station device 14. The slave station device 14 includes a wireless unit 50, a control unit 52, a local clock 16, a memory 54, a sensor 56, and a battery 58. The wireless unit 50 transmits the transmission information output from the control unit 52 by including it in a wireless signal. The wireless unit 50 also receives the wireless signal, extracts the reception information from the wireless signal, and outputs it 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 wireless 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 detection value to the control unit 52. The control unit 52 executes the program to execute the process executed by the slave station device 14 among the processes shown in FIG. 3 to FIG. 6 together with the wireless unit 50. Battery 58 supplies power to necessary parts of the electric 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, each of the hardware for performing normal communication and the hardware for performing uplink normal communication may be configured to be able to switch between a sleep mode and a 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 start-up device. [Explanation of symbols]

[0097] 10 parent station device, 12 reference clock, 14 child 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 unit for communicating with other devices; A control unit that controls the radio unit, the other device receives a signal at a reception window timing according to the other device time; The control unit is estimating the receiving window timing based on information obtained by a previous communication with the other device and a time of the own device; Transmitting a wake-up signal in accordance with the estimated receive window timing; A wireless device, comprising: a wireless section that, after a predetermined communication startup time has elapsed since transmitting the wake-up signal, executes, together with the wireless section, a process for communicating with the other device.

2. A wireless unit for communicating with other devices; A control unit that controls the radio unit, the other device receives a signal at a reception window timing according to the other device time; The control unit is estimating the receiving window timing based on information obtained by a previous communication with the other device and a time of the own device; Transmitting a wake-up signal in accordance with the estimated receive window timing; receiving a response 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; determining a timing difference between the local device time and the other device time based on a timing of transmitting the wake-up signal and a timing of receiving the reply signal; A wireless device characterized by: estimating the receive window timing based on the timing difference and the device time; and performing, together with the wireless unit, a process of transmitting the next wake-up signal in accordance with the estimated receive window timing.

3. 3. A wireless device according to claim 2, The control unit is A wireless device, comprising: a wireless section that performs communication with the other device after a predetermined communication startup time has elapsed since the transmission of the wake-up signal;

4. A wireless device according to claim 2 or 3, 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.

5. A wireless unit for communicating with other devices; A control unit that controls the radio unit, The control unit is receiving a signal transmitted from the other device according to the other device time at a receiving window timing according to the own device time; and when receiving a wake-up signal transmitted from the other device, transmitting a reply signal to the other device after a predetermined fixed time has elapsed from a window time of the reception window timing, together with the wireless unit; The wireless device is characterized in that the other device calculates a timing difference between the other device time and the own device time based on the timing of transmitting the wake-up signal and the timing of receiving the reply signal, estimates the receive window timing based on the timing difference and the other device time, and transmits the next wake-up signal according to the estimated receive window timing.

6. 6. A wireless device according to claim 5, The control unit is A wireless device, comprising: a wireless section that performs communication with the other device after a predetermined communication startup time has elapsed since receiving the wake-up signal;

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

8. A wireless unit for communicating with other devices; A control unit that controls the radio unit, The control unit is receiving a signal transmitted from the other 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, executes, together with the wireless unit, a process of calculating a timing difference between a time of the own device and a time of the other device based on a difference between a timing of receiving the wake-up signal and a window time of the reception window timing; the other device receives a signal at a reference window timing according to the other device time; The control unit is estimating the reference window timing based on the timing difference and the local device time; Transmitting an upstream wake-up signal in accordance with the estimated reference window timing; A wireless device, comprising: a wireless section that performs communication with the other device after a predetermined communication startup time has elapsed since the transmission of the upstream wakeup signal;

9. 9. A wireless device according to claim 8, The other device is when receiving the upstream wakeup signal, a process of transmitting a reply signal to the wireless device after a predetermined fixed time has elapsed from a window time of the reference window timing; The control unit is A wireless device characterized by executing, together with the wireless unit, a process of newly calculating the timing difference based on the timing of transmitting the uplink wakeup signal and the timing of receiving the reply signal, estimating the reference window timing based on the newly calculated timing difference and the device's own time, and transmitting the next uplink wakeup signal in accordance with the estimated reference window timing.

10. 10. A wireless device according to claim 9, 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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