JP2010231566A - Wireless sensor terminal and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless sensor terminal to be used for automatic construction of a multihop wireless sensor network, which performs reception with high accuracy equal to that of a synchronous system while using a non-synchronous transmitting/receiving system with low facility cost, while reducing the power consumption. <P>SOLUTION: In the wireless sensor terminal, a built-in transmitting and receiving radio chip for radio relay is intermittently set to a receiving standby state RX at predetermined time intervals. When transmitting data, prior to transmission of a data signal therefor, the radio chip transmits a preamble signal continuing for a time longer than the receiving standby interval, and the data signal is transmitted successively. The preamble signal includes information on the time left from each point of time in the continuing period to the data signal. The radio chip is set to OFF state, upon receipt of the preamble signal transmitted from the other radio sensor terminal in the receiving standby state RX, until the data signal is transmitted based on the remaining time information at the time of receipt, and changed to the receiving state when the remaining time elapses, to receive the data signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an autonomous wireless sensor terminal having a wireless relay function used for automatic construction of a multi-hop wireless sensor network and a control method thereof.

  Conventionally, there is a demand for acquiring information on a remote place without helping a person. For example, it is a request for obtaining information such as the state of a store or building owned, the home during travel, the temperature of a vegetable garden, the looseness of the ground. In response to such demands, the Internet has been used so far. That is, such information acquisition is possible even today by connecting the sensor for information acquisition to a personal computer and always connecting to the Internet.

  However, the personal computer is large, and there are limits to increasing the number of observation points. Further, when the observation point moves, for example, when monitoring the health condition of a person remotely, a large personal computer has a problem in portability. Furthermore, there is a problem that the Internet connection needs to be set or the coverage area of the wireless LAN is narrow, which also makes it difficult to cope with an increase in the number of observation points and movement. One of the technologies recently developed under such circumstances is a wireless sensor network system using a small and autonomous wireless sensor terminal known as “MOTE” (registered trademark), for example (Patent Document 1). ).

  In this wireless sensor network, as shown in FIG. 5, a wireless sensor terminal 1 called a node is installed at a location where information is to be collected. The wireless sensor terminal 1 includes a data communication unit having a wireless transmission function for transmitting data and a wireless relay function for relaying data from other wireless sensor terminals 1 in addition to a sensor for collecting information. is doing. “M” in the wireless sensor terminal 1 is a main body of the MOTE, which represents a processor board on which a data communication unit or the like is mounted, and “S” represents a sensor board combined therewith.

  What is characteristic is a data communication unit having a wireless transmission function and a wireless relay function. This data communication unit is composed of a wireless chip that transmits and receives data and a control unit that controls the operation of the wireless chip. In addition to transmitting information from the sensor mounted on its own wireless sensor terminal, Receives and transmits information from sensors mounted on wireless sensor terminals. A plurality of wireless sensor terminals 1 automatically construct a large-scale wireless mesh network by such multihop of information by the wireless transmission function and the wireless relay function of the data communication unit.

  That is, even if the individual wireless sensor terminals 1 have low processing capabilities and low wireless capabilities, a system having a capability that far exceeds the individual capabilities is constructed by the above-described wireless relay function and multihop by this. For this reason, each wireless sensor terminal 1 is very small, inexpensive and has low power consumption, and can easily cope with an increase or movement of observation points. Because of this feature, a wireless network system using a plurality of wireless sensor terminals 1 has begun to be used for seabird ecology research and the like.

  The individual terminal information is sent to a base station such as a host computer via an interface 2 called a gateway, and is centrally managed. Further, when the base station is connected to a LAN or the Internet, this MOTE terminal information can be obtained virtually anywhere in the world.

  By the way, the wireless sensor terminal 1 having a wireless relay function is also called a relay node. As a power source for the relay node, dry batteries are frequently used because they are simpler and more economical than solar cells, fuel cells, and the like. However, when a dry battery is used as a power source, it is necessary to replace the battery. To reduce the frequency of replacement, it is important to reduce the power consumption of the relay node. The power consumption of the relay node is greatly related to the transmission / reception mode. Hereinafter, the transmission / reception mode of the relay node will be described, and the relationship with the power consumption will be clarified.

  The transmission / reception modes of the relay node are shown in FIGS. In the relay node, as shown in FIG. 6A, the transmission / reception wireless chip for wireless relay changes from the off state to the transmission state TX at predetermined time intervals. In the transmission state TX, sensor information from a sensor mounted on the relay node is transmitted. In addition, sensor information from other relay nodes is transmitted for relay. In order to perform this relay function, it is necessary to receive sensor information transmitted from other relay nodes. As a method for this reception, the transmission timing and the reception timing are generally synchronized between the relay nodes. This is because, according to this synchronization method, the wireless chip is turned on only at the time of transmission / reception, and the wireless chip can be turned off at other times, so that power consumption is greatly reduced. In addition, as long as accurate synchronization timing is maintained, reception errors due to a difference between transmission timing and reception timing do not occur.

  As another method, as shown in FIG. 6B, there is also a constant standby method in which a reception standby state RX is set between the transmission state TX and the next transmission state TX. According to this method, reception is possible at any time, but the power consumption in the reception standby state RX is not much different from the transmission state TX, and a current close to a steady current is always required. However, the accuracy of reception is high. Under such circumstances, the former synchronization method is mainly used as the transmission / reception mode in the relay node, and various improvements are being made in this direction.

  However, in the case of the synchronization method, there is a problem that the relay node requires a highly accurate time measuring device for the synchronization, and the circuit configuration becomes complicated and the device cost increases. When the number of relay nodes increases, there is a problem that transmission data and reception data interfere with each other. For this reason, an intermittent standby method that simplifies the always-on standby method (FIG. 6B) has also been developed.

  In the intermittent standby method, as shown in FIG. 6C, the wireless chip operates in an intermittent standby mode in which the wireless chip is intermittently switched from the off state to the reception standby state RX at predetermined time intervals. In this method, if there is a signal to be received in the reception standby state RX, the wireless chip rises to the reception state, performs packet reception, and returns to the off state. If there is no signal to be received in the reception standby state RX, the state returns to the off state. The activation interval to the reception standby state, that is, the reception standby interval T is, for example, 125 ms. As a result, although the power consumption is not as high as that of the synchronous method, the power consumption is remarkably reduced as compared with the always-on standby method which is the same asynchronous method.

  However, the power consumption here is in a relationship that is in conflict with the accuracy of reception. If the reception standby interval T is shortened, the reception accuracy increases, but the power consumption also increases, and conversely the reception standby interval T is increased. If so, the power consumption is reduced, but the accuracy of reception is also lowered.

JP 2007-14471 A

  An object of the present invention is a wireless sensor terminal that is capable of receiving data with high accuracy equivalent to that of a synchronous method while being an asynchronous method with low equipment cost, and that has low power consumption and excellent accuracy and economy. And providing a control method thereof.

  In order to achieve the above object, a wireless sensor terminal of the present invention is a wireless sensor terminal with a wireless relay function used for construction of a multi-hop wireless sensor network, and is used for transmission and reception for a built-in wireless relay. The wireless chip operates in an intermittent standby mode in which the wireless chip intermittently enters a reception standby state at predetermined time intervals. When transmitting a data signal to another wireless sensor terminal, the wireless chip prior to the transmission of the data signal And after transmitting a preamble signal including remaining time information from each time point in the continuous period until data signal transmission, and then transmitting a data signal, When a preamble signal transmitted from a wireless sensor terminal is received, a data signal is transmitted based on the remaining time information at the time of reception. The wireless chip is turned off, to adopt a configuration for receiving a data signal the Upon expiration of the remaining time wireless chip is a reception state until.

  The wireless sensor terminal control method of the present invention is a method for controlling a wireless sensor terminal with a wireless relay function used for construction of a multi-hop wireless sensor network, and is used for transmission / reception for a built-in wireless relay. The wireless chip is operated in an intermittent standby mode in which a reception standby state is intermittently set every predetermined time interval. On the other hand, when transmitting a data signal to another wireless sensor terminal, the reception standby interval is performed prior to the transmission of the data signal. After transmitting a preamble signal from the wireless chip that lasts for a longer period of time and includes remaining time information from each time point in the continuation period until the data signal transmission, the data signal is transmitted subsequently, and the other in the reception standby state When the preamble signal transmitted from the wireless sensor terminal is received, the data signal is based on the remaining time information at the time of reception. The wireless chip is turned off until the signal, to adopt a configuration for receiving a data signal as the reception state of the wireless chip Upon expiration of the remaining time.

  In the wireless sensor terminal and the control method thereof according to the present invention, the wireless chip is intermittently placed in a reception standby state at predetermined time intervals. That is, the intermittent standby method. On the other hand, at the time of data transmission, the wireless chip transmits a preamble signal that lasts longer than the reception standby interval prior to transmission of the data signal, and then transmits the data signal. The preamble signal is a dummy packet for a mark placed in front of the data signal. Since the duration of this preamble signal is longer than the reception standby interval, the reception signal is always in a reception standby state once during the preamble signal transmitted by another wireless sensor terminal. For this reason, the data signal which another wireless sensor terminal transmits can be received reliably.

  In addition, the preamble signal here includes remaining time information from each time point during the continuation period to the data signal transmission. When a preamble signal from another wireless sensor terminal is received, the wireless chip is temporarily turned off until the data signal is transmitted based on the remaining time information at the time of reception, and when the remaining time has elapsed. In the reception state, the data signal is received. Since the wireless sensor terminal only operates in the intermittent standby mode in which the reception standby state is intermittently repeated except during data reception, the power consumption is substantially equivalent to the above-described conventional general intermittent standby system.

  A configuration in which the wireless chip is returned to the intermittent standby mode again after the wireless chip is in a receiving state and receives a data signal is preferable. According to this configuration, the operation time of the wireless chip is shortened, and power saving is further promoted.

  As yet another configuration, it is preferable that the preamble signal includes transmission destination ID information, and that reception is rejected when the ID information in the preamble signal received from another wireless sensor terminal in a reception standby state is other than the terminal. According to this configuration, in a wireless sensor terminal that does not require relaying, the wireless chip is not in a receiving state, so that the operation time of the wireless chip is further shortened, and power saving is further promoted.

  The wireless sensor terminal and the control method thereof according to the present invention basically employs an intermittent standby method in which the wireless chip is intermittently placed in a reception standby state at predetermined time intervals. In the case of using a dry battery as a power source, the replacement frequency can be reduced, and the use of the dry battery becomes easy. When transmitting data, the wireless chip transmits a preamble signal that lasts longer than the reception standby interval before transmitting the data signal, and then transmits the data signal. When a signal is transmitted, the preamble signal can be reliably received, and high-accuracy data reception equivalent to the always-on standby method can be performed. Furthermore, the wireless chip includes the remaining time information from each time point during the duration to the data signal transmission until the data signal is transmitted based on the remaining time information at the time when the preamble signal is received. Since it is temporarily turned off, power consumption is further reduced.

It is a block diagram which shows the hardware of the wireless sensor terminal which shows one Embodiment of this invention. It is a flowchart which shows the subroutine about the information transmission of the same wireless sensor terminal. It is a flowchart which shows the subroutine about the information reception of the same wireless sensor terminal. It is a time chart which shows the concept about the information reception of the same wireless sensor terminal. It is a conceptual diagram of the wireless sensor network by multihop. It is a time chart which shows the general transmission / reception mode of a wireless sensor terminal.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present embodiment, the wireless sensor terminal is a terminal having a wireless transmission / reception function and a relay function, which is used as a relay node of the multi-hop wireless sensor network shown in FIG.

  As shown in FIG. 1, the wireless sensor terminal includes a sensor 3 for collecting various information such as temperature and humidity, an MPU 4 as a control unit for processing collected data and performing various arithmetic processes, A timer 5 that gives time data for arithmetic processing in the MPU 4, a wireless chip 6 that performs wireless transmission and reception in accordance with instructions from the MPU 4, a ROM 7 that stores arithmetic processing procedures in the MPU 4, and data for the arithmetic processing in the MPU 4 A RAM 8 and the like for sending and receiving are provided.

  The power source of this wireless sensor terminal is a replaceable dry battery. In order to reduce the replacement frequency, reduction of power consumption is a major technical issue. The wireless sensor terminal of this embodiment solves this technical problem by improving the transmission / reception mode.

  The basic mode related to transmission / reception of the wireless sensor terminal is an asynchronous method in which transmission is performed at regular intervals and reception is also performed intermittently for reception (see FIG. 6C). Here, the reception standby interval T is set to 125 ms. The transmission interval is considerably longer than this, for example, several minutes and several tens of minutes, and is appropriately selected according to the use environment.

  A processing procedure at the time of transmission / reception will be described below with reference to flowcharts of FIGS. 2 and 3 and a time chart of FIG. This processing procedure is stored in the ROM 7 and executed by the MPU 4.

  In the transmission mode, as shown in FIG. 2, the MPU 4 measures the elapsed time from the previous transmission state TX based on information from the timer 5 in step S11. In step S12, the MPU 4 determines whether or not the elapsed time has reached the transmission interval. If the elapsed time does not reach the transmission interval, the process returns to step S11. When the elapsed time reaches the transmission interval, the process proceeds to step S13, where the MPU 4 captures sensor data to be transmitted to another wireless sensor terminal. The sensor data is data obtained from the sensor 3 and / or sensor data from other wireless sensor terminals received by the wireless chip 6 for relaying and stored in the RAM 8 or the like.

  When the data capture in step S13 is completed, the process proceeds to step S14, and the MPU 4 creates a preamble signal. As shown in FIG. 4, the preamble signal is a dummy packet for a mark placed before the data signal in the transmission state TX. The transmission time of the preamble signal is set to, for example, 130 ms which is longer than the period of the reception standby state RX (reception standby interval T = 125 ms) in the wireless sensor terminal. This preamble signal is composed of a large number of subpackets that are parallel in time series, and the time of each subpacket is 20 ms here.

  In each subpacket, ID information (address information) of a relay node to be transmitted and information on remaining time until a data signal is transmitted are written. The remaining time information written in the first subpacket is (130-20) ms, and the remaining time information written in the second subpacket is (130-40) ms. Decreases by 20 ms.

  When the preamble signal is created in this way, the process proceeds to step S15, and the MPU 4 creates a data signal including information to be transmitted. In next step S16, the MPU 4 switches the wireless chip 6 from the off state to the transmission state TX, and transmits the created preamble signal and data signal.

  By repeating this, the wireless sensor terminal transmits data at predetermined time intervals.

  Next, the reception mode of the wireless sensor terminal in this embodiment will be described.

  In the reception mode, as shown in FIG. 3, the MPU 4 measures the elapsed time from the previous reception standby state RX based on the information from the timer 5 in step S21. In step S22, the MPU 4 determines whether or not the elapsed time has reached the reception standby interval T (125 ms in this case). If the elapsed time does not reach the reception standby interval T, the process returns to step S21. When the elapsed time reaches the reception standby interval T, the process proceeds to step S23, and the wireless chip 6 is switched from the off state to the reception standby state RX according to an instruction from the MPU 4.

  Next, the process proceeds to step S24, where the MPU 4 determines whether a preamble signal is received by the wireless chip 6. If the preamble signal has not been received, the process returns to step S21 and the elapsed time measurement is resumed. When the preamble signal is received, the MPU 4 that is the control unit analyzes the destination information included in the preamble signal, the remaining time information at the time of reception, and the like. Specifically, as shown in FIG. 4, the MPU 4 analyzes the destination information and remaining time information included in the subpacket at the time when the preamble signal is received.

  More specifically, the preamble signal transmitted by the wireless sensor terminal that is the relay node A is a wireless sensor terminal that is the relay node B, a wireless sensor terminal that is the relay node C, and a wireless sensor that is the relay node D. Suppose that it is received by the terminal. The preamble signal transmitted from the relay node A is composed of a large number of subpackets, and the duration of the preamble signal is longer than the reception waiting interval T in the relay nodes B, C, D, so at any timing during the transmission of the preamble signal. The relay nodes B, C and D receive the preamble signal.

  Assuming that the subpacket in the preamble signal at the time point when the relay node B receives the preamble signal is P1, P1 includes destination information and remaining time information from P1 to the data signal. The MPU 4 serving as the control unit first analyzes the information included in the subpacket P1 in step S25, and then determines whether the destination information includes the relay node B in the information in step S26. If the destination information does not include the relay node B, the process returns to step S21. If the destination information includes the relay node B, the remaining time information included in the subpacket P1 is read in step S27, the wireless chip 6 is temporarily turned off in step S28, and time measurement is started in step S29. In step S30, the MPU 4 determines whether or not the measurement time has reached the remaining time.

  If the measurement time reaches the remaining time, the process proceeds to step S31, and the wireless chip 4 is changed from the OFF state to the reception state according to an instruction from the MPU 4. As a result, a data signal following the preamble signal is received. If the measurement time does not reach the remaining time, step S30 is repeated. When the reception of the data signal is completed, the wireless chip 4 is turned off again according to an instruction from the MPU 4, and the process returns to step S21.

  Thus, in the relay node B, the wireless chip 4 enters the reception standby state RX at any timing during the transmission of the preamble signal, and the preamble signal is received. When the preamble signal is received, information in the preamble signal is read at the time of reception, and then the wireless chip 4 is temporarily turned off. Then, when the data signal arrives, the wireless chip 4 enters the receiving state, and the data signal is received.

  Similarly for the relay node C, the wireless chip 4 receives the subpacket P2 in the signal at any timing during transmission of the preamble signal, and the destination information stored in the subpacket P2 includes the relay node C. Then, the wireless chip 4 is temporarily turned off until the data signal arrives, and when the data signal arrives, the wireless chip 4 enters the reception state and receives the data signal.

  For relay node D, the destination information written in the preamble signal does not include relay node D. Although the wireless chip 4 receives the subpacket P0 in the signal at any timing during the transmission of the preamble signal, the relay node D is not included in the destination information, so the wireless signal is transmitted wirelessly even when the data signal is transmitted. Chip 4 is not in a receiving state and does not receive a data signal.

  Thus, in the wireless sensor terminal, between the reception standby state RX and the next reception standby state RX, although the wireless chip 4 adopts the reception mode of the intermittent standby system in which the wireless chip 4 is intermittently activated to the reception standby state RX. There is no danger of receiving errors. In addition, since the wireless chip 4 is temporarily turned off from the time when the preamble signal is received until the data signal arrives, power consumption can be further reduced.

1 Wireless sensor terminal (relay node)
2 Interface 3 Sensor 4 MPU
5 Timer 6 Wireless chip 7 ROM
8 RAM

Claims (4)

A wireless sensor terminal with a wireless relay function used to construct a multi-hop wireless sensor network,
The built-in wireless chip for wireless relay for wireless relay operates in an intermittent standby mode in which a reception standby state is intermittently set every predetermined time interval,
When transmitting a data signal to another wireless sensor terminal, the wireless chip continues for a time longer than the reception standby interval prior to the transmission of the data signal, and information on the remaining time from each point in the duration until the data signal transmission After transmitting the preamble signal including, the data signal is transmitted following this,
When a preamble signal transmitted from another wireless sensor terminal is received in the reception standby state, the wireless chip is turned off until a data signal is transmitted based on the remaining time information at the time of reception, and the remaining time A wireless sensor terminal that receives a data signal when the wireless chip is in a reception state when a time has elapsed.   The wireless sensor terminal according to claim 1, wherein the wireless chip returns to the intermittent standby mode again after the wireless chip is in a receiving state and receives a data signal. A method of controlling a wireless sensor terminal with a wireless relay function used for construction of a wireless sensor network by multi-hop,
While operating the built-in wireless chip for radio relay for wireless relay in the intermittent standby mode that intermittently enters the standby state at predetermined time intervals,
When transmitting a data signal to another wireless sensor terminal, a preamble signal including a remaining time information from each time point during the continuation period to the data signal transmission is continued prior to the transmission of the data signal and for a time longer than the reception standby interval. After transmitting from the wireless chip, subsequently transmit a data signal,
When a preamble signal transmitted from another wireless sensor terminal is received in the reception standby state, the wireless chip is turned off until a data signal is transmitted based on the remaining time information at the time of reception, and the remaining time A method of controlling a wireless sensor terminal, wherein a data signal is received with the wireless chip in a reception state when a time has elapsed.   4. The method of controlling a wireless sensor terminal according to claim 3, wherein after the wireless chip is in a reception state and receives a data signal, the wireless chip is returned to the intermittent standby mode again.

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