JP2008306657A - Wireless node and wireless network system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems in the conventional art in which efficient power saving could not be attained because a synchronization signal had to be received each time for synchronization with a plurality of wireless nodes and because of a power control system being common to all the wireless nodes, and a correct synchronization signal could not be transmitted with respect to overlapping areas because of the same wireless channels being used for the synchronization signal and for data communication. <P>SOLUTION: A wireless node includes a built-in time keeper having a correct clock, and the time keeper is initialized with a synchronization signal received at the start of operation to determine timing for change to a power saving mode and timing for return to a normal mode using the built-in clock. A wireless channel available for a synchronization signal and a wireless channel available for data transmission/reception are different channels. Since the synchronization signal does not need to be received each time, a power saving period can be prolonged and power saving control can be performed according to the wireless node. In addition, even if radio wave reaching areas overlap, a correct synchronization signal can be transmitted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radio node capable of reducing power consumption of a radio node by controlling a power saving function on the radio node side, and a radio network system using the radio node.

  In a wireless network system using a wireless node (wireless terminal) driven by a battery, the power consumption of the wireless node must be reduced in order to extend the life of the battery. IEEE 802.15.4 defines a synchronization method that can reduce the power consumption of a wireless node. This synchronization method will be described with reference to FIGS.

  FIG. 8 is a diagram showing the configuration of a PAN (Personal Area Network) used in a mesh network. In FIG. 8, reference numeral 10 denotes a host, and only one is installed within a range where radio waves can reach one PAN. A synchronization signal transmission unit 11 is disposed in the host 10. Reference numerals 20a to 20n denote wireless nodes (wireless terminals) that communicate with the host 10, respectively. The host 10 periodically transmits a synchronization signal (dotted line) to the wireless nodes 20a to 20n using the synchronization signal transmission unit 11, and performs data transmission / reception (solid line). Note that data may be transmitted and received between the wireless nodes 20a to 20n without going through the host 10.

  The wireless nodes 20a to 20n consume more power when transmitting / receiving radio waves or when an internal CPU or the like operates. Therefore, power consumption can be reduced by shortening the transmission / reception period. For this reason, after synchronizing with the synchronization signal, each wireless node maintains a normal mode for operating the wireless node for a certain period, and then stops all functions except the necessary minimum function until immediately before receiving the next synchronization signal. Transition to power saving mode.

  FIG. 9 is a diagram showing the state of the wireless node. In FIG. 9, reference numeral 21 denotes a synchronization signal transmitted by the synchronization signal transmission unit 11, which is transmitted at a time interval of Tp. When the wireless nodes 20a to 20n receive this synchronization signal, they enter the normal mode for Ta time. The wireless nodes 20a to 20n transmit / receive data to / from the host 10 or the wireless nodes 20a to 20n. When the Ta time elapses, the mode shifts to the Ts (= Tp−Ta) time power saving mode, and the operation of returning to the normal mode immediately before the next synchronization signal is repeated. Since the wireless nodes 20a to 20n enter the power saving mode at a rate of Ts / (Ta + Ts), power consumption can be reduced.

  Since information related to synchronization such as the period of the synchronization signal is included in the synchronization signal, the wireless nodes 20a to 20n can predict the time when the synchronization signal is transmitted next. The radio channel used for transmitting the synchronization signal is the same channel as the radio channel used for data transmission / reception.

Patent Document 1 describes an invention of an intermittent reception control method capable of reliably performing data transmission / reception between a host and a wireless node by making the following improvements on the premise of such a wireless network. Yes.
(1) When data is transmitted from the wireless node to the host, data is transmitted in order from the data with the highest priority.
(2) When transmitting a large amount of data from the host, it notifies the wireless node to that effect. The wireless node does not enter the power saving mode until all data is received.
(3) When the data notified in advance cannot be received, the normal mode is maintained for a predetermined time.
(4) The period of the synchronization signal can be changed according to the amount of data exchanged with the wireless node.

  Patent Document 2 describes an invention in which a call signal is transmitted from a host only when it is necessary to call a wireless node, and when the wireless node determines that there is no call signal, the reception is immediately interrupted to shift to a power saving mode. Has been. Since the power saving mode time can be lengthened, the power consumption of the wireless node can be further reduced.

Patent Document 3 describes an invention in which a receiving terminal is operated at an interval of (a time shorter than the transmission interval of the transmitting terminal × the number of receiving terminals) in a network having the transmitting terminal and a plurality of receiving terminals. It can be received by any receiving terminal, and the non-operation time of the receiving terminal can be increased.
Japanese Patent Laid-Open No. 09-162798 JP-A-11-136181 JP 2003-304185 A

  However, since such a wireless network and wireless node are configured to alternately switch between the normal mode and the power saving mode in synchronization with the synchronization signal, each time the synchronization signal is transmitted regardless of whether data is transmitted or received. Must switch to normal mode. Since the cycle of the synchronization signal is as short as a maximum of about 4 minutes, there is a problem that the power saving mode cannot be maintained for a long time, and that significant power saving cannot be performed.

  Even if a wireless node operating on a battery is a node operating on the same PAN, an optimum power saving method varies depending on the type of data to be transmitted, the characteristics of the application, and the remaining battery level. For example, it may be advantageous to change the optimal transmission timing according to the configuration of the wireless node, the remaining battery level, etc., and not to perform reception itself. However, since it is necessary to return to the normal mode every time the synchronization signal is transmitted, it is difficult to introduce a detailed power control mechanism according to the configuration of the wireless node.

  The invention described in Patent Document 1 is an invention that can transmit and receive a large amount of data without dividing it, and is not necessarily an invention aimed at power saving. Moreover, although the invention described in Patent Document 2 can shorten the time for receiving the synchronization signal, the synchronization signal must be received every time, and there is a limit to power saving. Furthermore, the invention described in Patent Document 3 is an invention that can be applied to a network in which N receiving terminals are operated as one set, and is difficult to apply to a general network.

  Conventionally, the same channel is used for the wireless channel for transmitting the synchronization signal and the wireless channel for transmitting and receiving data. For this reason, there is a problem in that the synchronization signal is compressed in the wireless band for transmitting and receiving data, and the efficiency of data transmission and reception is reduced. This problem becomes more prominent as the interval between the synchronization signals is shorter.

  If the same channel is used for the wireless channel that transmits the synchronization signal and the wireless channel that transmits and receives data, in order to avoid radio wave interference, only one host that transmits the synchronization signal can be placed in the reachable range of the radio wave. Absent. This is because if there are a plurality of synchronization signal transmission sources within the radio wave reach, the transmission of one synchronization signal is affected by the transmission of the other synchronization signal, and the synchronization signal cannot be transmitted with accurate timing.

  The limitation that only one synchronization signal transmission source can be placed within the radio wave reach is not a problem in a star network. However, in a network with a data relay mechanism such as a tree type or mesh type, there are cases where a plurality of synchronization signal transmission sources are placed within the radio wave reach. In such a case, the wireless node receives the synchronization signal. There is also a problem that the entire network cannot be synchronized.

  Accordingly, an object of the present invention is to provide a wireless node and a wireless network system capable of reducing power consumption by reducing the number of times a synchronization signal is received by performing accurate time management on the wireless node side.

In order to solve such a problem, the invention according to claim 1 of the present invention,
In a wireless node that has a built-in battery and exchanges data with other devices using wireless communication,
A wireless transmission / reception unit for transmitting data to other devices using wireless and receiving data transmitted by other devices;
A time management unit that incorporates a clock, activates and / or corrects the clock according to a synchronization signal received by the wireless transmission / reception unit, and outputs a power saving mode transition notification and a normal mode return notification based on the clock;
A control unit that receives the power saving mode transition notification and the normal mode return notification, shifts to the power saving mode when the power saving mode transition notification is input, and returns to the normal mode when the normal mode recovery notification is input. When,
Is provided. Since it is not necessary to receive the synchronization signal every time, the power saving period can be extended.

The invention according to claim 2 is the invention according to claim 1,
The control unit is configured to stop the operation of the wireless transmission / reception unit when a power saving mode transition notification is input and to start the operation of the wireless transmission / reception unit when a normal mode return notification is input. is there. Power can be saved easily and effectively.

The invention according to claim 3 is the invention according to claim 1 or claim 2,
The synchronization signal includes a sequence number having a predetermined period and a value that changes with a constant change, and the time management unit notifies the transition to the power saving mode at a time when the sequence number becomes the first value. The normal mode return notification is output at a time when the second value different from the first value is output. The power saving timings of a plurality of wireless nodes can be synchronized.

The invention according to claim 4
A synchronization signal transmitter for outputting a synchronization signal;
A plurality of wireless nodes according to any one of claims 1 to 3,
Is provided. Power saving is possible and the power saving timing can be synchronized.

The invention according to claim 5 is the invention according to claim 4,
A radio channel used for the synchronization signal transmitting apparatus to output a synchronization signal is different from a radio channel used for the wireless node to transmit and receive data. The transmission / reception of the synchronization signal does not interfere with the data transmission / reception.

The invention according to claim 6 is the invention according to claim 4 or 5,
The plurality of wireless nodes are divided into a plurality of groups, and the timing for shifting to the power saving mode and the timing for returning to the normal mode are made different for each group. It is always possible for at least one set of wireless nodes to be able to transmit and receive.

The invention according to claim 7 is the invention according to any one of claims 4 to 6,
At least two synchronization signal transmission devices are provided, and these synchronization signal transmission devices use different radio channels for synchronization signal transmission. Adjacent area sync signals do not interfere.

As is apparent from the above description, the present invention has the following effects.
According to the first, second, third, fourth, fifth, sixth and seventh aspects of the present invention, a time management unit including a clock is arranged in the wireless node, and the clock is activated / corrected by a synchronization signal. Based on this, a power saving mode transition notification and a normal mode return notification are output, and the transition to the power saving mode and the return to the normal mode are performed based on these notifications. In addition, a wireless network system is configured by the wireless node and the synchronization signal transmitting apparatus.

  Even without receiving a synchronization signal every time, the transition to power saving mode and the return to normal mode can be synchronized between multiple wireless nodes, so the power saving period can be extended and power consumption can be reduced. There is an effect that can be done.

  In addition, there is an effect that it is possible to perform a power saving operation according to the characteristics of the wireless node, for example, a wireless node to which power is supplied from others such as a relay node does not perform a power saving operation. Furthermore, it is possible to change the operation timing of all wireless nodes belonging to the same network at the same time only by changing the timing data of the transition to the power saving mode and the return to the normal mode sent together with the synchronization signal. There is also.

  In addition, by making the wireless channel used for transmission of the synchronization signal different from the wireless channel used for data transmission / reception, there is an effect that a wireless network system in which the synchronization signal does not impose data transmission / reception can be realized. Furthermore, there is an effect that interference between the synchronization signals can be eliminated by changing the radio channel used for the synchronization signal transmission in the adjacent area.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a wireless node according to the present invention. In FIG. 1, reference numeral 30 denotes a wireless node, which includes a control unit 31, a wireless transmission / reception unit 32, a time management unit 33, a sensor unit 34, and a power source 35. The wireless node 30 is a wireless node having a function of measuring a physical quantity by the sensor unit 34 and transmitting the measured value to the outside.

  The control unit 31 includes a microprocessor and a memory, and controls the wireless transmission / reception unit 32 and the sensor unit 34 based on a program stored in the memory, and controls the entire wireless node 30 such as setting the time management unit 33. . The time management unit 33 determines the timing for entering the normal mode or the power saving mode.

  The wireless transmission / reception unit 32 receives the synchronization signal transmitted from the synchronization signal transmission device, and exchanges data with other wireless nodes. The synchronization signal received by the wireless transmission / reception unit 32 and data from other wireless nodes are output to the control unit 31 and data to be transmitted from the control unit 31 is input.

  The sensor unit 34 measures physical quantities such as pressure and flow rate, converts them into electrical signals, and outputs them to the control unit 31. The control unit 31 transmits this physical quantity to another wireless node via the wireless transmission / reception unit 32. The power source 35 incorporates a battery and supplies power to the control unit 31, the wireless transmission / reception unit 32, the time management unit 33, and the sensor unit 34. In FIG. 1, description of the power supply line to each element is omitted.

  In this embodiment, the wireless node is a wireless node that measures a physical quantity and transmits the measured value, but is not limited to this embodiment, and may be another wireless node.

  FIG. 2 shows the configuration of the wireless network system. FIG. 2 shows only the configuration of one PAN, but an actual network constitutes a mesh type or tree type network in which a plurality of PANs are arranged in a mesh shape. The synchronization signal and data are transmitted and received using radio.

  The tree-type network is a network in which nodes are connected in a tree shape with one concentrator (host) as a center. A mesh network is a network in which nodes are connected like a network. The basic unit is a tree network, a star network in which nodes are arranged in a star shape with a current collector as the center, and one network. A bus type network in which a plurality of nodes are connected to this bus is used.

  In FIG. 2, reference numerals 30a to 30n denote wireless nodes, which have the same configuration as the wireless node 30 of FIG. Reference numeral 40 denotes a synchronization signal transmission device that transmits a synchronization signal to the wireless nodes 30a to 30n at a predetermined cycle. This synchronization signal is transmitted using a broadcast address. Therefore, the wireless nodes 30a to 30n can simultaneously receive the synchronization signal.

  The wireless nodes 30a to 30n transmit / receive data to / from each other. The synchronization signal transmitter 40 transmits a synchronization signal to the radio nodes 30a to 30n using a radio channel different from the radio channel used by the radio nodes 30a to 30n for data transmission / reception. In this embodiment, the synchronization signal transmission device 40 is an independent device, but any one of the wireless nodes 30a to 30n may also function as the synchronization signal transmission device 40.

  FIG. 3 shows an operation sequence of the wireless node 30. The same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted. Time shall flow from top to bottom. The normal mode means that the wireless transmission / reception unit 32 is turned on, and the power saving mode means that it is turned off. The wireless node 30 can receive the synchronization signal only in the normal mode.

  In FIG. 3, when the wireless node 30 is activated, the control unit 31 sets a wireless channel for receiving the synchronization signal transmitted from the synchronization signal transmitting device 40. In wireless communication, a plurality of wireless channels divided by frequency or code can be used. If the same wireless channel is used, only one wireless node can be transmitted within the radio wave reach. However, if the wireless channels are different, a plurality of wireless nodes can transmit data simultaneously.

  When the synchronization signal is transmitted from the synchronization signal transmitting device 40 at time T1, the wireless transmission / reception unit 32 outputs a notification that the synchronization signal has been received to the control unit 31. The control unit 31 outputs this notification to the time management unit 33. When receiving the notification, the time management unit 33 sets and starts a timer arranged therein. Then, the control unit 31 sets the data channel so that the synchronization channel used when receiving the synchronization signal and the data channel used when transmitting / receiving data are not the same.

  The vertical line at the bottom of the wireless transmission / reception unit 32 indicates that the synchronization channel and the data channel may be the same, but the synchronization channel and the data channel differ depending on the data channel setting. Set to use the channel.

  Since the wireless transmission / reception unit 32 is turned on, the control unit 31 controls the wireless transmission / reception unit 32 to communicate with other wireless nodes to transmit / receive data. The time management unit 33 uses an internal timer to autonomously monitor the time when the wireless transmission / reception unit 32 is on (in the normal mode) and the time off (in the power saving mode).

  When the duration of the normal mode reaches a predetermined time at time T2, the time management unit 33 notifies the control unit 31 that the mode is shifted to the power saving mode. Upon receiving this power saving mode transition notification, the control unit 31 turns off the wireless transmission / reception unit 32 and shifts to the power saving mode. As a result, the power consumption of the wireless node 30 is significantly reduced. Note that the dotted line portion of the lower vertical line of the wireless transmission / reception unit 32 indicates that the wireless transmission / reception unit 32 is turned off.

  The time management unit 33 measures the time during which the power saving mode is continued, and outputs a normal mode return notification for returning to the normal mode to the control unit 31 when this time reaches a predetermined value at time T3. Upon receiving this notification, the control unit 31 turns on the wireless transmission / reception unit 32 and returns to the normal mode. Thereby, wireless communication becomes possible. The control unit 31 controls the wireless transmission / reception unit 32 to communicate with other wireless nodes and perform data transmission / reception.

  Similarly, the time management unit 33 outputs a power saving mode transition notification and a normal mode return notification to the control unit 31 at regular time intervals. When these notifications are input, the control unit 31 turns the wireless transmission / reception unit 32 on and off. When the wireless transmission / reception unit 32 is turned off, communication with other wireless nodes is not possible. However, if the frequency of data transmission / reception is not high, the operation is not hindered.

  If the accuracy of the time managed by the time management unit 33 is high, the timing of shifting to the power saving mode and returning to the normal mode can be synchronized with the synchronization signal without receiving the synchronization signal every time. If the period of the synchronization signal and the internal clock of the time management unit 33 are almost the same, only the synchronization signal is received at the time of activation, and the transition to the power saving mode or the normal mode is performed without receiving the synchronization signal thereafter. Can be synchronized with the synchronization signal.

  Even if there is a discrepancy between the cycle of the sync signal and the internal clock of the time management unit 33, the sync signal may be received at a frequency corresponding to the discrepancy to correct the internal clock. Recently, a highly stable crystal oscillator can be obtained at a low price, so that the number of times of receiving a synchronization signal can be greatly reduced. As can be seen from FIG. 3, the synchronization signal cannot be received when the wireless node 30 is in the power saving mode, but this does not cause a problem. Even in the normal mode, the synchronization signal can be ignored when correction is not necessary.

  The timing of the transition of each wireless node to the power saving mode and the return to the normal mode can be determined in advance, but can also be determined dynamically. Hereinafter, a mechanism for dynamically determining the on / off timing of the wireless transmission / reception unit 32 will be described.

  FIG. 4 shows an example of timing information for the time management unit 33 to determine the timing of shifting to the power saving mode and returning to the normal mode. This timing information is simultaneously transmitted to all wireless nodes by a broadcast address together with a synchronization signal. The control unit 31 in each wireless node receives this timing information from the synchronization signal received when it is activated or corrects the clock of the time management unit 33, and sets the time management unit 33 based on this timing information.

  In FIG. 4, the sequence number starts from 0 and increases by 1 for each synchronization signal. This number has an upper limit, and when it reaches this upper limit, it returns to zero. For example, if the upper limit is 9, the sequence number changes in the order of 0 → 1 → 2... 9 → 0. This sequence number has 10 cycles.

  The number of synchronization signals in one cycle represents the number of synchronization signals per cycle. In the above example, it is 10. The sequence number for returning to the normal mode represents the sequence number for returning from the power saving mode to the normal mode. When the sequence number becomes “sequence number for returning to the normal mode”, the time management unit 33 outputs a normal mode return notification to the control unit 31, and when the sequence number returns to 0, the “power saving mode shift notification” is output. Is output. The synchronization signal transmission interval represents a cycle in which the synchronization signal is output. For example, if the synchronization signal is output every second, the synchronization signal transmission interval is 1 second.

Next, the state switching of the wireless node will be described with reference to FIG. The timing information
Number of synchronization signals in one cycle = 10
Sequence number for normal mode = 5
The synchronization signal transmission interval is 1 second.

  In FIG. 5, an arrow 50 is a synchronization signal transmission timing, and 51 is a sequence number. The sequence number is a number starting from 0 and increasing by 1 with 9 as the upper limit. Since the sequence number in the normal mode is 5, the wireless node 30 is in the power saving mode when the sequence number is 0 to 4, and is in the normal mode at 5-9.

  Assume that the wireless node is activated between the sequence numbers 2 and 3. This wireless node first receives the synchronization signal of sequence number = 3, and based on the timing information, it is currently in the power saving mode, maintains the normal mode for 5 seconds after 2 seconds, and then enters the power saving mode for 5 seconds. Know to repeat the action.

  For this reason, the time management unit 33 that has completed the initial setting outputs a power saving mode transition notification to the control unit 31 and outputs a normal mode return notification after 2 seconds. Thereafter, a power saving mode transition notification and a normal mode return notification are alternately output every 5 seconds. When receiving the power saving mode transition notification, the control unit 31 turns off the wireless transmission / reception unit 32, and when receiving the normal mode return notification, the control unit 31 turns on the wireless transmission / reception unit 32. In this way, the period during which each wireless node is in the normal mode overlaps, so that the communication partner does not become unable to communicate because of the power saving mode.

  In this embodiment, the power saving mode is set when the sequence number is small, and the normal mode is set when the sequence number is equal to or higher than the normal mode. However, the normal mode is set when the sequence number is small, and the power saving is set when the sequence number is large. You may make it become a mode. The transition timing to the power saving mode, the normal mode, the sequence number period, and the change amount can be arbitrarily determined.

  In this embodiment, the timing information is taken in at the time of start-up, but the timing information can be updated during operation to change the ratio between the power saving mode period and the normal mode period. For example, if the number of wireless nodes in the network increases, the transmission / reception of relay packets and data search packets increases, and the frequency of data transmission / reception increases. Convenient to. Each wireless node may acquire new timing information when correcting the clock of the time management unit 33, and change the setting of the time management unit 33 based on this timing information. In this way, it is possible to change the settings of all the wireless nodes simply by changing the timing information output by the synchronization signal transmitting device 40.

  In addition, since power is always supplied to a relay node, a wireless node that specializes in data transfer to other wireless nodes, and the like, the power saving requirement is not large. Even if such a wireless node receives timing information, the wireless node does not shift to the power saving mode, and can always perform control optimal to the state of the wireless node, such as being always in the normal mode.

  In this embodiment, only on / off of the wireless transmission / reception unit 32 is controlled. However, not only the wireless transmission / reception unit 32 but also other elements except the time management unit 33 in the power saving mode, for example, a sensor unit If the operation of a part of the control unit 34 or the control unit 31 is stopped, the power consumption can be further reduced. Further, the radio transmission / reception unit 32 may stop and start the operation instead of turning the power on and off. Since the operation is naturally stopped when the power is turned off, the stop and start of the operation include turning the power on and off.

  Furthermore, in this embodiment, all the wireless nodes are simultaneously set to the normal mode and the power saving mode based on the timing information. However, each wireless node has a ratio of the normal mode period to the power saving mode period. You may make it change to. In this way, when the remaining amount of the battery is low, the power saving mode period can be lengthened to extend the battery life. In this case, it is only necessary to notify other wireless nodes of this by data communication so that no trouble occurs in data transmission / reception.

  FIG. 6 shows another embodiment of the wireless network system according to the present invention. This embodiment realizes a network system in which a wireless node can transmit power at any time by shifting the phase of a power saving mode period and a normal mode period by a wireless node, and a wireless node that wants to transmit information can transmit at any time. It is a thing. In this embodiment, the wireless nodes are divided into two groups so that one of the wireless nodes is always in the normal mode.

  In FIG. 6, (A) is a diagram showing the arrangement of wireless nodes. Here, 60 (□ mark) is a transmission source wireless node, 61 (Δ mark) is a reception destination wireless node, 62 (● mark) is a wireless node belonging to one set, and 63 (■ mark) belongs to the other set. It is a wireless node.

  FIG. 5B is a diagram showing the normal mode period of each wireless node, and the horizontal bar represents the normal mode period. The wireless node 62 enters the normal mode in the period A, and the wireless node 63 enters the normal mode in the period B. That is, one of the wireless nodes 62 and 63 is always in the normal mode.

  When data is transmitted from the transmission source wireless node 60 to the reception destination wireless node 61 in such a network, the data is transmitted via the wireless node in the normal mode. That is, when data is transmitted in the period A, the data is transmitted via the wireless node 62 marked with ■ as indicated by the solid line 64. Further, when transmitting in the period B, data is transmitted via the wireless node 63 marked with ● as indicated by a dotted line 65. In this way, it is possible to construct a network that can transmit and receive data at any time even when half of the wireless nodes are in the power saving mode. This is particularly effective when emergency data that cannot be waited until the normal mode is entered must be transmitted.

  In addition, what radio node is to be in the normal mode may be determined in advance. For example, the wireless node 62 marked with ■ is in the normal mode when the sequence number is smaller than the “sequence number for returning to the normal mode”, and the wireless node 63 marked with ● is the sequence number for returning to the normal mode. When it is larger, the normal mode may be set. By giving this information to the transmission source wireless node, it is possible to know which wireless node should be relayed. It may be divided into three or more.

  FIG. 7 shows another embodiment. This embodiment is an example of a network including a plurality of synchronization signal transmission devices. In FIG. 7, reference numerals 70 to 72 denote synchronization signal transmission apparatuses, reference numerals 73 to 75 denote radio wave arrival ranges of the synchronization signal transmission apparatuses 70 to 72, and black circles 76 denote wireless nodes. The synchronization signal transmitters 70 to 72 are connected to each other by a cable (not shown) or by another type of radio (for example, WiFi or a radio timepiece), and are accurately synchronized. Therefore, the synchronization signals output by the synchronization signal transmission devices 70 to 72 are output at exactly the same time.

  The radio wave reachable ranges 73 to 75 have overlapping portions. Conventionally, the synchronization signal transmitters 70 to 72 transmit the synchronization signal using the same radio channel. In an area where the radio wave coverage overlaps, two or more synchronization signals interfere with each other, and thus a synchronization signal that is accurately synchronized cannot be output. Further, since the synchronization signal radio channel and the data transmission / reception radio channel are the same in the past, changing the radio channel of the synchronization signal transmission devices 70 to 72 also changes the channel used for data transmission / reception, resulting in different radio wave arrival areas. There was a problem that data transmission / reception could not be performed between the wireless nodes to which the terminal belongs.

  In this embodiment, since the radio channel for transmitting the synchronization signal and the radio channel for transmitting the data are different from each other, the synchronization signal transmission devices 70 to 72 are different without changing the data transmission / reception channel. Wireless channels can be assigned. Therefore, even if there are overlapping areas, it is possible to output a synchronization signal that is accurately synchronized.

  Note that wireless nodes in overlapping areas can receive two or more different synchronization signals. Each wireless node may determine which synchronization signal output from which synchronization signal transmission device is a reference, but basically any synchronization signal can be selected and synchronized to the network without any problem.

It is a block diagram which shows one Example of the radio | wireless node which concerns on this invention. 1 is a configuration diagram showing an embodiment of a wireless network system according to the present invention. It is a sequence diagram for demonstrating operation | movement of a radio | wireless node. It is a block diagram of timing information. It is a figure for demonstrating the state switching of a radio | wireless node. It is a block diagram which shows the other Example of the radio | wireless network system which concerns on this invention. It is a block diagram which shows the other Example of the radio | wireless network system which concerns on this invention. It is a block diagram of the conventional wireless network. It is a figure for demonstrating the mode transition of the conventional radio | wireless node.

Explanation of symbols

30, 30a-30n, 62, 63, 76 Wireless node 31 Control unit 32 Wireless transmission / reception unit 33 Time management unit 34 Sensor unit 35 Power supply 40, 70-72 Synchronization signal transmission device 50 Synchronization signal timing 51 Sequence number 60 Transmission source node 61 Receiving node 64, 65 Relay route 73-75 Radio wave reach

Claims (7)

In a wireless node that has a built-in battery and exchanges data with other devices using wireless communication,
A wireless transmission / reception unit for transmitting data to other devices using wireless and receiving data transmitted by other devices;
A time management unit that incorporates a clock, activates and / or corrects the clock according to a synchronization signal received by the wireless transmission / reception unit, and outputs a power saving mode transition notification and a normal mode return notification based on the clock;
A control unit that receives the power saving mode transition notification and the normal mode return notification, shifts to the power saving mode when the power saving mode transition notification is input, and returns to the normal mode when the normal mode recovery notification is input. When,
A wireless node characterized by comprising:   The control unit stops the operation of the wireless transmission / reception unit when a power saving mode transition notification is input, and starts the operation of the wireless transmission / reception unit when a normal mode return notification is input. The wireless node according to claim 1, wherein:   The synchronization signal includes a sequence number having a predetermined period and a value that changes with a constant change, and the time management unit notifies the transition to the power saving mode at a time when the sequence number becomes the first value. 3. The wireless node according to claim 1, wherein a normal mode return notification is output at a time that is output and becomes a second value different from the first value. A synchronization signal transmitter for outputting a synchronization signal;
A plurality of wireless nodes according to any one of claims 1 to 3,
A wireless network system comprising:   5. The radio network system according to claim 4, wherein a radio channel used for outputting the sync signal by the sync signal transmitting apparatus is different from a radio channel used by the radio node for transmitting and receiving data. .   5. The method according to claim 4, wherein the plurality of wireless nodes are divided into a plurality of groups, and the timing for shifting to the power saving mode and the timing for returning to the normal mode are different for each group. 5. The wireless network system according to 5.   The radio according to any one of claims 4 to 6, comprising at least two synchronization signal transmission devices, wherein the synchronization signal transmission devices use different radio channels for synchronization signal transmission. Network system.

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