JP5006815B2 - Multi-hop wireless network system - Google Patents

Description

  The present invention relates to a power saving technique for reducing the power consumption of a relay terminal in a network to which multi-hop radio is applied.

  A system in which battery-driven sensor terminals are arranged at multiple points and the terminals are interconnected by a wireless network to detect anomalies and monitor the environment is called a sensor network system. In such a sensor network system, there is a ZIGBEE (registered trademark) standard as a wireless communication standard for interconnecting sensor terminals.

  In this ZIGBEE (registered trademark) standard, there is a provision regarding multi-hop communication so that the system can be installed in a wide range, and even between terminals arranged at a distance where radio waves do not reach directly, relays arranged in between A method is adopted in which communication is possible by the terminal relaying the packet.

  In such a system, the sensor terminal is often configured by a terminal called an end device in the ZIGBEE (registered trademark) standard, and the communication function is enabled only when there is a communication request, otherwise communication is performed. In many cases, long-term operation by battery operation is realized by stopping the function.

  On the other hand, the relay terminal is called a router in the ZIGBEE (registered trademark) standard. A router is required to always have a wireless communication function enabled in order to relay a communication request from an end device that can occur asynchronously. Accordingly, the power source is very consumed in the battery, and it is necessary to supply power from the outside by a commercial power source or the like for long-time operation.

  However, the wireless sensor network may be installed in a place where infrastructure facilities are not prepared, such as outdoors. In such a case, if a terminal having a relay function can be supplied with a battery while saving power, there is no restriction on the location of the terminal having the relay function, and a system can be constructed at a low cost. It becomes.

As a conventional technique related to power saving of a relay terminal, for example, there is a technique using a time slot (Patent Document 1). This technique includes the step of waking up one node from the low power consumption mode in at least one corresponding slot period of a frame provided with a time slot.
JP 2004-33679 A

  However, with the method using time slots, the transmission side cannot communicate freely for transmission requests that occur asynchronously. For data transmission that requires relaying by many relay terminals, The transmitting terminal waits for the destination terminal to wake up and cannot perform multi-hop communication without delay.

  For the above reasons, a relay terminal having a relay function in a conventional wireless network capable of multi-hop communication cannot achieve sufficient power saving without communication delay.

  Therefore, in order to perform multi-hop communication without delay in a wireless network, it is necessary for a terminal having a relay function to supply power from the outside with a commercial power source or the like.

  In the present invention, each control sensor received by a control terminal serving as a collection station by transmitting a command packet describing a sleep mode duration to sensor terminals and relay terminals in a sensor network to all terminals in the network. The terminal and each relay terminal shift to the sleep mode, and return to the normal mode after the sleep mode duration described in the command packet.

  In addition, by describing the number of times of sensing in the command packet, each sensor terminal performs sensing between the transition to the sleep mode mode and the return to the normal mode, and transmits the sensing result after the return to the normal mode to the control terminal.

  In addition, the control terminal and the terminal that is continuing the sleep mode based on the command packet from the control terminal predetermine a packet (hereinafter referred to as an unreceived relief packet) that describes the contents of the command packet and the continuation status of the sleep mode up to the present time. By performing broadcast transmission that can reach only a terminal within one hop at every interval, a terminal operating in the normal mode in the vicinity is shifted to the sleep mode. At this time, the terminals other than the control terminal, which are the transmission sources, are in the sleep mode and thus transmit the unreceived relief packet by temporarily activating the transmission function for a very short time.

  The transmission timing of each terminal of the unreceived relief packet is distributed uniformly or nearly uniformly within a predetermined interval time.

  In the present invention, the command packet is transmitted from the control terminal to all the terminals, so that all the terminals are synchronously shifted to the sleep mode and the normal mode. Therefore, the sensing command (command packet) is transmitted from the control station or the sensor terminal. Multi-hop communication is possible when transmitting the sensing result from. In addition, by repeating the sleep mode and the normal mode in synchronism with all terminals, the communication protocol of the existing wireless network can be easily applied only in the normal mode, and the duration of the sleep mode is made longer than the duration of the normal mode. However, if it is sufficiently long, sufficient power saving of the sensor terminal and the relay terminal is possible.

  When there is a terminal operating in the normal mode because each terminal was reset for battery replacement or failed to receive a command packet from the control terminal and failed to enter the sleep mode while the terminal was in sleep mode By receiving and analyzing the unreceived relief packet transmitted by the terminal in the sleep mode at a predetermined interval, it is possible to shift to the sleep mode like other terminals in the network.

  In addition, in order to prevent the transmission timing of unreceived relief packets transmitted while each terminal is in the sleep mode from overlapping, it is distributed in a uniform or nearly uniform manner within a predetermined interval time. The expected value of the time until the operating terminal receives an unreceived relief packet is reduced.

The present invention provides a sleep mode in which a sensor terminal and a relay terminal constituting a wireless network capable of multi-hop communication as shown in FIG. 1 can temporarily stop a receiving circuit and a main clock for power saving. In the sensor network that has
The command packet transmitted from the control terminal to all the terminals in the network describes the time Ts during which the sleep mode is continued and the number of sensing times Ns performed during Ts, and each terminal that receives the command packet The normal mode is maintained for the maximum transmission time Td, and then the sleep mode is entered and the sleep mode is continued for (Ts−2Td−Tl). (Tl is a margin time taking into account the accuracy of the internal timer of the terminal. Td and Tl are sufficiently smaller than Ts.)

  During the sleep mode period, each sensor terminal performs sensing Ns times described in the command packet. The sensing timing is performed at intervals of (Ts / Ns) after receiving the command packet. Before the last sensing timing (Td + Tl), the mode is shifted from the sleep mode to the normal mode. After the last sensing is completed, the results sensed so far are transmitted to the control terminal. At this time, since all terminals in the network should have returned to the normal mode, multi-hop communication is possible between each sensor terminal and the control terminal.

  On the other hand, since each relay terminal is not equipped with a sensor, the normal mode is maintained for Td after receiving the command packet, and then the sleep mode is continued for (Ts−2Td−Tl) to return to the normal mode. .

  The control terminal waits for transmission of sensing results from all sensor terminals for (Ts + Tc) after transmitting the command packet. Tc is a time-out period for the control terminal to wait for the sensing result from the sensor terminal. When sensing results from all the sensor terminals can be received earlier than (Ts + Tc), the control terminal does not necessarily wait for (Ts + Tc).

  The sensor network system according to the present invention repeats transmission of a command packet by the control terminal, sleep mode of all terminals in the network excluding the control terminal, and collection of sensing results from the sensor terminals, and all sensor terminals in the network Enables power saving for all relay terminals. FIG. 2 shows the timing from the command packet transmission of the control terminal to the transmission of the sensing result to the control terminal through the continuation and sensing of the sleep mode of each sensor terminal in the example of the network configuration shown in FIG. Is.

  While each terminal continues in the sleep mode, a certain terminal in the network may be operating in the normal mode. For example, when the software that was running on the terminal is reset due to battery replacement etc. while the sleep mode is continued, and the normal mode is started, or the command packet sent from the control terminal is missed and the sleep mode is entered. It may be the case that failed. In order to prevent fatal battery consumption of these terminals operating in the normal mode, the terminal that is in the sleep mode does the following regardless of whether there is a terminal operating in the normal mode in the vicinity.

  Each terminal that continues the sleep mode temporarily activates the transmission function for a minute time during which one packet can be transmitted at a predetermined interval Tk, and can receive unreceived relief packets only to terminals within one hop. Broadcast transmission. In the unreceived relief packet, the contents Ts and Ns of the command packet received when shifting to the sleep mode, the elapsed time Tp since the command packet was received, and the like are described. The terminal that has finished transmitting the unreceived relief packet stops the transmission function and continues the operation in the sleep mode using the command packet. Also, in the control terminal within Ts after sending the command packet, the unreceived relief packet in which the contents of the command packet and the elapsed time Tp from the command packet transmission are described at the predetermined interval Tk is similarly sent to the terminal within one hop. Broadcast transmission that can only be reached.

  When the terminal operating in the normal mode receives the unreceived relief packet, the terminal shifts to the sleep mode. At that time, based on Ts, Ns, and Tp described in the unreceived relief packet, the time to continue the sleep mode from the current time and the time until the next sensing are calculated. By receiving the packet, an operation that is not different from other terminals that have continued in the sleep mode is performed. However, there are cases where some sensing timings have passed when the sensor terminal receives the unreceived relief packet (such as Tp> (Ts / Ns)). In such a case, when transmitting the sensing result after the end of the sleep mode duration period, the data indicating that the sensing is not performed is transmitted to the control terminal in the position corresponding to the sensing data missed timing in the transmission packet. And

  In addition, it is desirable that the timing at which each terminal transmits an unreceived relief packet is uniformly distributed within a predetermined interval Tk. By shifting the transmission timing of each terminal so as to be uniformly distributed within a predetermined interval Tk, the expected value of the time until the terminal in normal mode operation receives an unreceived relief packet is reduced, and the sleep mode The time to shift to can be advanced. For example, assuming that there are Na terminals that are in sleep mode in the vicinity of a terminal A that is operating in normal mode that failed to receive a command packet, the timing for transmitting unreceived relief packets from each terminal is uniformly distributed In this case, the expected value Ta of the time until the terminal A receives the unreceived relief packet is Ta = Tk / 2Na. On the other hand, if the timing of transmitting the unreceived relief packet of each terminal is the same timing, Ta = Tk / 2. In the example of the network configuration shown in FIG. 3, FIG. 4 shows the timing at which unreceived relief packets are broadcast from each terminal at a predetermined interval Tk. In the example of the network configuration shown in FIG. 3, FIG. 5 shows a sequence in which the sensor terminal 11 that has failed to receive the command packet receives the unreceived relief packet and shifts to the sleep mode.

  As described above, the present invention has the same sleep mode duration and communication timing for all terminals by the command packet from the control terminal, and the rescue processing by the unreceived rescue packet of the terminal out of the sleep mode. This enables high-performance power saving.

  According to the present invention, in a sensor network capable of multi-hop communication, it is possible to sufficiently save power of all terminals including terminals having a relay function in the network, and it is not necessary to supply power from the outside by a commercial power source or the like. Therefore, it is possible to construct a sensor network system for sensing in various places, both indoors and outdoors.

It is the figure which showed the example of the structure of the network in this invention. The line segment connecting the terminals connects terminals that can transmit data with one hop. It is the figure which showed the duration of sleep mode and the timing of communication in the example of FIG. It is the figure which showed the example of the structure of the network in this invention different from FIG. FIG. 4 is a diagram illustrating a transmission timing of an unreceived relief packet of each terminal in the example of FIG. 3. FIG. 4 is a diagram illustrating a sequence in which a sensor terminal that has failed to receive an instruction packet shifts to a sleep mode by receiving an unreceived relief packet in the example of FIG. 3.

Claims (7)

In a wireless sensor network system capable of multi-hop communication composed of a control terminal and two or more terminals ,
The terminal has a sleep mode that can temporarily stop the transmission and reception circuit and the main clock, and from the sleep mode by the interrupt function of the internal timer itself has a possible return to the communication is possible normal mode, a command packet transmitted from the control terminal to the addressed terminal in the network by receiving the respective terminal a command packet sleep mode duration has been described from the sleep mode transition to the normal mode return, the terminal There shifts to the sleep mode in synchronization, during the sleep mode duration described in the instruction packet, after continuing the sleep mode by the terminal returns to the normal mode in synchronization, a multi-hop in the network Maintaining the communication function and enabling power saving of the terminal ,
The terminal that is continuing the sleep mode enables the packet transmission function at a predetermined interval, and uses the broadcast transmission function that can reach only the other terminal within one hop, and the sleep mode duration time and A wireless sensor network system , wherein when there is the terminal operating in the normal mode by transmitting a relief packet including an elapsed time from the time of receiving the command packet , the wireless sensor network system shifts to a synchronized sleep mode . To the command packet sent from the control terminal to the addressed terminal in the network, describes a sensing times performed during the sleep mode, after the terminal that has received the command packet that has shifted to the sleep mode, the The wireless sensor network system according to claim 1 , wherein sensing is performed according to the number of sensing times, and the sensing result is transmitted to the control terminal after returning to the normal mode. The wireless sensor network system according to claim 1 or 2, wherein the two or more terminals include a terminal having a relay function and a sensor function . 2. The wireless sensor network system according to claim 1 , wherein the control terminal transmits a relief packet including the sleep mode duration time and an elapsed time since the command packet is transmitted at a predetermined interval. Wireless sensor network system according to any one of claims 1 to 4, characterized in that the terminal when to send the repair packets, Ru was distributed evenly or uniformly near form between the terminals . A system comprising the wireless sensor network system according to any one of claims 1 to 5 as a partial network system.   The wireless sensor network system according to any one of claims 1 to 5, further comprising a terminal that controls an external device.