JP2011176888A - Radio communication system, communication control method, and communication node - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve reduction in power consumption of each radio node, efficient access control and the like, in an electronic tag system or sensor network system for which power saving at radio nodes is important. <P>SOLUTION: A fixed period starting from a beacon transmitted from a gateway (GW) 100 is specified separately from an active period during which each radio node (P2P tag) transmits/receives a frame, and a sleep period during which a frame transmitting/receiving operation is halted. Further, the active period is divided by a plurality of fixed-length timeslots, such a period is divided and set such that each class of GW, fixed node (P2P-S tag) and mobile node (P2P-M tag) can perform frame transmission, respectively. Each P2P tag randomly selects a timeslot from the period for its own class and after waiting just for a random waiting time in the selected timeslot, a frame is transmitted which includes information specifying its own ID and the selected timeslot or the waiting time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wireless communication system, a communication control method, and a communication node, and more particularly, wireless communication for realizing low power consumption media access control (MAC) when a moving communication node exchanges data bidirectionally. The present invention relates to a system, a communication control method, and a communication node.

  Reduction of power consumption of wireless hardware in a wireless device is an important requirement. Examples of applications that particularly require a power saving mechanism in a wireless communication system include an active electronic tag system and a sensor network system. These active electronic tags and sensor nodes in sensor networks are required to be portable and easy to install / flexible, and are usually battery-powered nodes incorporating a small battery.

  Applications such as these active electronic tag systems and sensor network systems are characterized by low traffic. In the active electronic tag system, usually, small data including the ID (identification information) of the active electronic tag itself is transmitted. In sensor network systems as well, sensor nodes often perform intermittent transmission of small sensing data.

  In the active electronic tag system, information exchange is performed in such a way that a reader receives data transmission from the electronic tag. Normally, an active electronic tag does not have a relationship with other active electronic tags. Therefore, in order to receive information from an active electronic tag that is randomly transmitted, the reader must always activate the receiver. is there. Further, in the active electronic tag system, since each active electronic tag operates independently, a data collision may occur due to simultaneous data transmission of a plurality of active electronic tags. In such an active electronic tag system, one-way communication from the electronic tag to the reader is performed. Therefore, in order to simply perform bidirectional communication, it is assumed that a node having a single electronic tag and reader / writer is used. However, problems relating to power consumption and access control (collision avoidance control) remain.

  Reduction of power consumption in the wireless device as described above is an important requirement, and several solutions have been proposed. As an example of the above solution, for example, in a low-traffic network such as a sensor network, when there is no data transmission / reception and the wireless circuit (wireless communication function) is not used, the wireless circuit is turned off (sleep state). Can be mentioned. In such intermittent communication, when considering turning off the radio circuit on both the transmission side and the reception side, it is important how the transmission and reception timings are synchronized between the transmission node and the reception node. It becomes a problem.

  One solution in intermittent two-way communication is an approach in ZigBee (ZigBee: registered trademark) that uses the MAC layer defined in IEEE 802.15.4. In IEEE 802.15.4, when a synchronization mode called a beacon mode is used, each node is synchronized by a beacon transmitted from a coordinator serving as a control device. In ZigBee, an idle period can be defined by defining a super frame as shown in FIG. 9 and making the beacon interval larger than the super frame period. This allows all synchronized nodes to go to sleep during this idle period.

  However, in this method, it is necessary for each node to receive and synchronize the beacon of the control device. For example, when there are a plurality of beacon transmission nodes, between the star networks centering on the beacon transmission nodes. Since there is no transmission / reception timing adjustment, there is a problem that the network topology is limited to a star type.

Patent Document 1 below discloses a technique related to low power consumption in a beacon-less solution that does not perform system synchronization using a beacon (see FIG. 10). In the technique disclosed in Patent Document 1, each receiving node is activated for a certain period of time periodically when T _L << T _PL with respect to the monitoring period T _PL and the monitoring period T _L. Monitor the interface.

On the other hand, the transmission source node outputs a wake-up signal (WU) during this _TPL period, whereby all the receiving nodes transmit data corresponding to the wake-up signal during _TL , which is its own reception period. Grasp that. In addition, when the wakeup signal includes information (time pointer) regarding the transmission start time, it is possible to grasp the activation time (data transmission start time).

Furthermore, when the destination address is included in the wake-up signal as the information transmitted on the wake-up signal, only the corresponding node that has received this wake-up signal activates the receiving unit, so that the activation time of the other nodes is increased. It becomes possible to decrease. Furthermore, by exchanging the communication end time and the communication start time of the next monitoring period of the corresponding node every time communication is performed, the sampling schedule of each node is held as table information, and during the period of the monitoring cycle _TPL It is possible to shorten the necessary transmission time of the wakeup signal.

JP 2006-148906 A

However, in the technique disclosed in Patent Document 1 described above, a wake-up signal needs to be transmitted in the period of the monitoring period _TPL until the table information is obtained. As suggested in Patent Document 1, This period not only consumes the power of the source node, but also occupies the radio channel for a considerable time period, which prevents other nodes from transmitting other wake-up signals. Or collisions may occur in other ongoing transmissions.

  In particular, when a large number of unspecified wireless nodes perform communication while moving, it is considered that there will be more opportunities for long-term exchange using the wake-up signal WU until the first table configuration, and power is wasted. Will be consumed. Similarly, when transmission is performed to an unspecified number of nodes (broadcast or multicast), it is necessary to notify a wakeup signal during the monitoring period of each node, and power is wasted. In addition, in the method of notifying the information of the data to be transmitted by the wakeup signal before outputting the actual data and synchronizing the transmission / reception timing with the receiving node, when exchanging small data at a very low frequency, the wakeup signal is the data However, it is considered that communication becomes inefficient.

In the technique disclosed in Patent Document 1, when the sampling schedule of each node can be held as table information, the transmitting node transmits a wakeup signal only during the monitoring period of the receiving node that is the counterpart. Then, its own transmission start timing is notified. However, during the monitoring period T _PL, unlike when transmitting a wake-up signal, since the node recognizes data transmission period of the transmitting node is only receiving node serving as the destination, the other transmitting node Even if there is a possibility of transmitting data to other receiving nodes at the same time, this cannot be detected. For this reason, the possibility that the signals collide increases, and there arises a problem that access control (collision avoidance control) between the transmission nodes becomes difficult.

  In view of the above problems, the present invention is a wireless communication system including a small wireless node capable of bidirectional communication, and a reduction in power consumption when performing communication while a large number of moving small wireless nodes are moving, An object of the present invention is to provide a radio communication system, a communication control method, and a communication node for realizing efficient access control.

In order to achieve the above-mentioned object, it is composed of a plurality of wireless nodes and a reference node, and is composed of a plurality of fixed-length time slots in which the plurality of wireless nodes and the reference node can transmit and receive frames. The active period and the sleep period in which the transceiver unit of the wireless node is in a stopped state are repeated at a constant cycle, and when the reference node transmits a frame to the reference time slot of the fixed cycle that is repeated, A wireless communication system that matches a start timing of the active period with the reference node when the wireless node has not received a frame transmitted by the reference node;
Frame transmitting means for transmitting a frame in which a wireless node synchronized with the active period randomly selects the time slot at the time of data transmission and adds a slot number of the selected time slot as synchronization information Have
Based on the timing at which the wireless node that has received the frame with the synchronization information added receives the synchronization information and the frame in the frame, the start timing of the active period next to the active period in which the frame has been received And a synchronization means for performing a synchronization process for the active period.
With this configuration, another wireless node can be synchronized using a frame transmitted from a wireless node synchronized with a frame transmitted by the reference node, and wireless nodes that cannot communicate directly with the reference node are also sequentially Transmission and reception can be performed synchronously. This makes it possible to exchange data with a wireless node in a wide area, and it is not necessary to always start the transmitter / receiver, realizing efficient access control and reducing power consumption. Is possible.

Furthermore, in addition to the above configuration, a wireless communication system is provided in which the synchronization information further includes transmission timing information inside the time slot for transmitting the frame.
With this configuration, it is possible to improve the accuracy of the synchronization processing performed by frame reception.

  Further, according to the present invention, a communication control method and a communication node are also provided as in the case of a wireless communication system.

  According to the present invention, it is possible to control activation of a radio unit (transmission / reception unit) of each radio node so that power consumption is reduced, and it is possible to realize efficient access control in a transmission path. It has the effect. Further, according to the present invention, since a wireless node that has received this frame can synchronize with an active period by a frame transmitted by each synchronized wireless node, a wireless node that cannot directly receive a frame from a reference node can also perform the wireless communication. It is possible to synchronize in the system, and there is an effect that the wireless communication system can be applied and extended to a wider area.

The figure which shows an example of the communication system comprised by the various different wireless node in embodiment of this invention. The block diagram which shows an example of a structure of the P2P tag in embodiment of this invention The figure which shows an example of the time slot structure in embodiment of invention The figure which shows an example of the frame structure which each P2P tag in embodiment of this invention transmits The timing chart which shows an example of the frame transmission / reception timing of each node of the communication system in embodiment of this invention The timing chart which shows another example of the frame transmission / reception timing of each node of the communication system in embodiment of this invention The flowchart which shows an example of operation | movement of the P2P-S tag in embodiment of this invention 7 is a flowchart illustrating an example of the synchronization process in step S701 in FIG. 7A. The flowchart which shows an example of operation | movement of the P2P-M tag in embodiment of this invention. The figure explaining the time slot structure in the conventional synchronous system The figure explaining the transmission and reception timing processing in the conventional asynchronous system

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, with reference to FIG. 1, a communication system configured with various types of wireless nodes in the embodiment of the present invention will be described. FIG. 1 is a diagram illustrating an example of a communication system configured by various types of wireless nodes in the embodiment of the present invention.

  The communication system illustrated in FIG. 1 includes a gateway (GW) 100 and a plurality of wireless nodes (wireless tags) 110 to 114. The GW 100 is a communication node that is connected to an external network (for example, the Internet) 105 via wired / wireless communication and can communicate with the external network 105. Note that the GW 100 is preferably fixedly installed in a place where power supply necessary for operation can be received through predetermined wiring.

  On the other hand, the wireless tags 110 to 114 are small wireless tags (active electronic tags) driven by a battery, and are communication nodes capable of transmitting and receiving frames and exchanging data bidirectionally. Hereinafter, this wireless tag is referred to as a P2P tag. The P2P tag includes a P2P-S tag that is a P2P tag that does not assume movement after installation (that is, a P2P tag that is fixedly installed), and a P2P-M tag that is a P2P tag that is held and moved by a person, for example. There are two types.

  As shown in FIG. 1, each P2P tag exchanges its ID (identification information) with a P2P tag in its communicable range ad hoc. In this way, mutual contact histories are held by exchanging and accumulating IDs with each other by the moving P2P-M tag. As a result, a P2P-M tag contains a person's action history (a history of identification information of the P2P-S tag existing at the place where the P2P-M tag stopped), and a P2P-S tag contains a person's action history. The passage history (the history of identification information of the P2P-M tag that has passed through the communicable range of the P2P-S tag) is accumulated.

  1 includes three P2P-S tags (P2P-S tag 110 (identification information “# 0”), P2P-S tag 111 (identification information “# 1”), and P2P-S tag 112 (identification information). "# 2")) Two P2P-M tags (P2P-M tag 113 (identification information "# 3"), P2P-M tag 114 (identification information "# 4")) are shown. In FIG. 1, the P2P-M tag 113 (identification information “# 3”) communicates with the P2P-S tag 112 (identification information “# 2”) and the P2P-S tag 111 (identification information “# 1”). A state in which the possible range is moved and connected to the GW 100 is illustrated. Further, in FIG. 1, the P2P-M tag 114 (identification information “# 4”) communicates with the P2P-S tag 110 (identification information “# 0”) and the P2P-S tag 111 (identification information “# 1”). The movement of the possible range is illustrated.

  As a result, the P2P-S tag 110 has identification information “# 4”, the P2P-S tag 111 has identification information “# 3” and “# 4”, the P2P-S tag 112 has identification information “# 3”, Identification information “# 2” and “# 1” are recorded in the P2P-M tag 113, and identification information “# 0” and “# 1” are recorded in the P2P-M tag 114, respectively.

  As an example of a specific application of the communication system as illustrated in FIG. 1, human behavior in a city, acquisition of a contact history, and the like can be considered. In this case, the GW 100 is fixedly installed in a place where a power source can be secured, and a large number of P2P-S tags are arranged in other places, so that the behavior, contact history, etc. of the person with the P2P-M tag are acquired. It becomes possible. In the above-mentioned application in which the wireless node (P2P tag) simply exchanges its own ID and leaves a contact history, it is not necessary for the transmitting side of the information to specify the receiving side, and each P2P tag has its own The P2P tag that received the ID may accumulate the received ID.

  Next, the function of the P2P tag in the embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing an example of the configuration of the P2P tag in the embodiment of the present invention. In FIG. 2, each function of the P2P tag is illustrated by a block, but the function represented by each block can be realized by hardware and / or software.

  The P2P tag 200 illustrated in FIG. 2 includes a wireless unit 210 having a transmission unit 201 and a reception unit 202, a control unit 203, an ID storage unit 204, a clock 205, and a power supply unit 206.

  The transmitting unit 201 has a function of transmitting a frame including its own ID to the outside via wireless. As described above, ID transmission in the transmission unit 201 is performed by broadcasting. The receiving unit 202 has a function of receiving a frame including an ID transmitted by another P2P tag or GW in the same manner.

  The control unit 203 has a function of controlling the operation of the P2P tag 200. For example, the control unit 203 has a function of controlling the ID transmission timing in the transmission unit 201 based on a clock signal obtained from the clock 205. Further, the control unit 203 has a function of accumulating IDs of other P2P tags received by the receiving unit 202 in the ID accumulating unit 204. The control unit 203 also has a function of controlling operations illustrated in FIGS. 7A, 7B, and 8 to be described later.

  When the P2P tag 200 is a P2P-S tag, the control unit 203 basically controls to record only the frame received from the P2P-M tag. On the other hand, when the P2P tag 200 is a P2P-M tag, the control unit 203 basically controls to record the frames received from the GW, P2P-S, and P2P-M without discrimination.

  The ID storage unit 204 has a function of storing IDs of other P2P tags received by the receiving unit 202. When the ID is stored in the ID storage unit 204, for example, time information at that time may be recorded together with the ID.

  The clock 205 has a function of outputting a clock signal for grasping the timing of frame transmission in the transmission unit 201 and frame reception in the reception unit 202. The power feeding unit 206 is a power source built in the P2P tag 200 so that the P2P tag can be moved to an arbitrary place, for example, a battery mounted in a housing of the P2P tag 200.

  Next, a time slot configuration according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing an example of the time slot configuration in the embodiment of the present invention.

  In the embodiment of the present invention, as shown in FIG. 3, in order to reduce the power consumption, an active period (T_act) and a sleep period of the radio unit are defined, and this active period is a constant cycle. It is determined to be repeated at (beacon period: T_p).

  Further, the active period is composed of a plurality of time slots. In the present embodiment, the first time slot in the active period (described as being for GW in FIG. 3) is used as a reference time slot, and this reference time slot is used by the GW. The GW functions as a reference node, and a frame is always transmitted from the GW at the beginning of an active period of a fixed period, so that the P2P tag that has received this frame can synchronize with the active period. Note that, as described above, since the GW can operate in a state in which power can be reliably secured, a frame used as an index for synchronization is reliably transmitted from the GW in the first slot of the active period. The However, in the present invention, the frame used by the reference node only needs to be defined in the system, and is not necessarily the first time slot of the active period.

  The other time slots in the active period are a P2P-S tag frame transmission time slot (hereinafter also referred to as a P2P-S slot) and a P2P-M tag frame transmission time slot. (Hereinafter also referred to as a P2P-M slot). The time slot allocation method and the number of time slot allocations for each of the P2P-M tag and the P2P-S tag can be arbitrarily determined depending on the system configuration and settings.

  In FIG. 3, as an example, following the first time slot (reference time slot) of the active period, five time slots for P2P-S tag frame transmission (indicated as P2P-S in FIG. 3) are allocated. Further, a time slot for transmitting a frame of the P2P-M tag (denoted as being for P2P-M in FIG. 3) is assigned 10 slots. In the example of the time slot configuration shown in FIG. 3, it is assumed that each time slot has a fixed length and has a sufficient size (period) for transmitting a frame exchanged by each P2P tag. Further, a standby time {unit standby time × n (integer)} for determining a point for starting transmission of a frame in the corresponding slot is defined. In FIG. 3, four transmission points (random numerical values in which the standby time n is 0 to 3) are shown as an example. Which transmission point is used as a frame transmission point (how many standby times are used) can be determined randomly for each node to be transmitted for each slot. The maximum value of n and the unit standby time can be arbitrarily determined depending on the system configuration and settings.

  Next, the configuration of a frame transmitted by each P2P tag according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing an example of a frame configuration transmitted by each P2P tag in the embodiment of the present invention.

  As shown in FIG. 4, the frame transmitted by the P2P tag includes a slot number field 401 for storing the slot number transmitted by the P2P tag in addition to the ID field 404 for storing the ID of the P2P tag. A waiting time number field 402 for storing the waiting time number (the above-mentioned integer n) in each slot is included. From this waiting time number, it is possible to grasp at which timing of the corresponding time slot this frame is transmitted.

  A P2P tag that has received a frame having a format as shown in FIG. 4 synchronizes the active period based on the reception timing and the slot number and waiting time information included in the received frame. Is possible. That is, according to this frame configuration, it is possible to synchronize the active period based on data in an arbitrary frame received (a frame received from an arbitrary transmission source at an arbitrary timing). The frame further includes a type field 403. This type field 403 stores type information indicating the type of node that transmitted this frame. For example, GW, P2P-S tag, and P2P-M tag are distinguished from each other by type information.

  Next, a specific operation of the P2P-S tag will be described with reference to FIGS. 7A and 7B. FIG. 7A is a flowchart illustrating an example of the operation of the P2P-S tag according to the embodiment of the present invention, and FIG. 7B is a flowchart illustrating an example of the synchronization processing in step S701 in FIG. 7A.

  In FIG. 7A, when the P2P-S tag is activated, synchronization processing is first performed (step S701). Hereinafter, the detailed operation of the synchronization processing in step S701 will be described with reference to FIG. 7B.

  In FIG. 7B, the P2P-S tag first determines whether it is synchronized with the active period (step S7011). For example, the P2P-S tag is configured to indicate that it is in a synchronized state by a predetermined flag when synchronization is established. In step S7011, it is determined whether or not the predetermined state is referred to by referring to the predetermined flag. Is done.

  Naturally, since it is not synchronized immediately after the start, processing in asynchronous time is started. At this time, the P2P-S tag activates the wireless unit 210 for transmitting and receiving the frame itself (step S7012), and then starts scanning (step S7013). The present invention is not particularly limited with respect to the radio frequency and channel used for communication. In the embodiment of the present invention, in step S7013, the P2P-S tag scans a channel that is set to be used in the communication system.

  In step S7014 and S7015, if no frame is received from the start of scanning until the time T_p (one beacon period) elapses, at that time, the vicinity of the P2P-S tag (P2P- This means that there is no P2P tag and GW transmitting the frame in the area where the S tag can receive the frame. In this case, the P2P-S tag shifts to the sleep process A state (step S7016). In the sleep process A, for example, the P2P-S tag randomly calculates an integral multiple of the time (cycle T_p × integer) based on one beacon cycle T_p, and stops the operation of the radio unit 210 for the calculated time. To save power.

  On the other hand, in steps S7014 and S7015, when a frame is received before one beacon period T_p has elapsed from the start of scanning, the P2P-S tag immediately synchronizes the active period based on the information of the received frame (step S7017). ). The frame can be transmitted only by the GW and the synchronized P2P tag, and the P2P-S tag starts the active period from the slot number and the waiting time number of the corresponding frame when the frame is received. Timing) can be calculated. In addition, it is desirable that the P2P-S tag does not perform synchronization processing based on the frame received from the P2P-M tag. That is, the P2P-S tag refers to the type field 403 of the received frame, and only when this frame is a frame transmitted from the GW or P2P-S tag, the start timing of the active period based on this frame is calculated. It is desirable to do.

  As shown in FIG. 7A, the P2P-S tag that is in a state where the active period is synchronized (synchronized state) by the synchronization process in the above-described step S701 (the process of steps S7011 to S7017 shown in FIG. 7B), In synchronization with the active period, the wireless unit 210 is activated to transmit and receive a frame (step S702).

  Further, the P2P-S tag determines a time slot (frame transmission slot) for transmitting a frame at the same time (step S703). The determination of the frame transmission slot is simply to randomly select a time slot for frame transmission in the own node. However, at this time, for example, in the case of a P2P-S tag, each P2P tag has its P2P tag selected, such as selecting a slot for P2P-S (in the example of FIG. 3, five slots following the reference time slot of the active period). It is necessary to select a frame transmission slot from the time slots allocated to the type. Also, in step S703, the P2P-S tag determines the waiting time at random similarly to the selection of the frame transmission slot, and adjusts the transmission timing in the selected frame transmission slot.

  Thereafter, the P2P-S tag starts scanning from the reference time slot in the active period (step S704). At this time, the P2P-S tag activates the wireless unit 210 and performs normal scan processing until it becomes a time slot for transmitting a frame (steps S705 to S707).

  When a frame is received in this scan processing, the P2P-S tag performs processing of received data described later (step S708), and performs synchronization readjustment processing (step S709). In addition, when the P2P-S tag reaches the timing of the time slot for transmission, the P2P-S tag waits for the determined number of waiting times and then performs carrier sense to confirm that the time slot is unused (idle). After confirming, it actually transmits its own frame (step S710).

  The frame transmitted in step S710 includes the corresponding slot number (identification information of the time slot that performs frame transmission) and the number of standby times. Even in a time slot randomly selected at the time of frame transmission in this manner, a plurality of P2P tags are assigned the same time slot as a frame transmission slot in order to perform collision avoidance processing by carrier sense after shifting the transmission timing according to the standby time. Even if it is selected as, it is possible to prevent the destruction of the frame due to a useless collision. Further, since the frame transmission slot is not randomly determined and fixed for each active period, it is possible to flexibly cope with a change in the number of installed P2P-S tags.

  Note that the P2P-S tag performs synchronization in the active period by receiving a frame transmitted by each already synchronized P2P-S tag in addition to receiving a frame from the GW in step S7017 of FIG. 7B. Is possible. Strictly speaking, in the synchronization processing in step S7017, it is considered that a shift depending on the clock accuracy of each P2P-S tag occurs. However, frame transmission of each P2P-S tag (frame transmission processing in step S710 in FIG. 7A) is performed after the idle state of the transmission path is confirmed based on a check by carrier sense. In such CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance), in order to avoid transmission frame collision and to use the transmission path effectively, the transmission timing is random. Importantly, the deviation depending on the clock accuracy of each P2P-S tag described above has the effect of avoiding collisions after carrier sense that can occur in a fully synchronized system.

  Although not shown in FIG. 7A, as described later (P2P-S1 tag in FIG. 6), the P2P-S tag that can receive a frame from the GW in the reference time slot is a frame itself. It is possible to stop the operation of the radio unit 210 in other P2P-S slots excluding the time slot for transmitting.

  Next, the reception data processing in step S708 described above will be described. The P2P-S tag is basically configured to record only frames received from the P2P-M tag. That is, in the received data processing in the P2P-S tag, if the type field indicated in the received frame is not a P2P-M tag, the received data is not recorded, while the type field indicated in the received frame is In the case of a P2P-M tag, received data is recorded. However, when a frame is received again from the same P2P-M tag received during the previous active period, it is desirable that the P2P-S tag does not perform any processing for this received frame.

  The reason why the frame received from the GW or P2P-S tag is not recorded as described above is that there is no change due to movement in the GW or P2P-S tag that is fixedly installed. In this way, it is possible to prevent unnecessary memory consumption by not taking a movement history for a communication node (GW or P2P-S tag) that does not change. Also, for the same reason, it is possible to avoid wasteful power consumption and wasteful memory consumption by avoiding continuous recording of P2P-M tags that remain in the same place. You may do it.

  Next, the synchronization readjustment process in step S709 described above will be described. In the communication system according to the embodiment of the present invention, except for the P2P tag that can directly receive a frame from the GW, the P2P tag is based on the received frame from the P2P tag that is directly or indirectly synchronized with the GW. Synchronize with tags. For this reason, unless the readjustment of the synchronization of the active period is performed for a long time, the accuracy of synchronization of the P2P tag existing at a place away from the GW is lowered due to the deviation of the clock accuracy of each P2P tag. For this reason, it is desirable that each P2P tag performs synchronization readjustment as appropriate. For example, each P2P tag is configured to perform synchronization readjustment processing upon receipt of a frame.

  However, if each P2P tag can receive a frame in the reference time slot (that is, if it can receive a frame from the GW), it performs a synchronization readjustment process based on this received frame, and then receives the received frame in the subsequent time slot. It is desirable not to perform synchronization readjustment processing based on the above. In addition, when a frame is received in the P2P-S slot, each P2P tag performs synchronization readjustment processing based on the time slot that first received the frame, and synchronization based on the received frame in the subsequent time slot. It is desirable not to perform readjustment processing.

  In addition, when a frame cannot be received in the reference time slot and the P2P-S slot, each P2P tag is synchronized again based on the received frame even if the frame is received in the P2P-M slot. It is desirable not to perform processing. This is because, in the case of the P2P-M tag, it may have existed in a place where no frame can be received from any communication node due to movement, and therefore the P2P-M tag is used as a reference for the synchronization readjustment. Because it is not appropriate.

  Further, since the P2P-S tag records and holds only the information of the P2P-M tag, when the above-mentioned synchronization readjustment process is completed, until the timing of the next P2P-M slot (P2P-M slot) is reached. The operation of the radio unit 210 can be stopped in other P2P-S slots other than the time slot in which the frame itself is transmitted. When reception of the last slot for P2P-M ends and the active period ends, the P2P-S tag performs sleep processing B (step S711). In the sleep process B, the P2P-S tag turns off the wireless unit 210 for transmitting and receiving frames for the remaining time in one beacon period, thereby saving power consumption.

  Next, the processing of the P2P-M tag will be described with reference to FIG. FIG. 8 is a flowchart showing an example of the operation of the P2P-M tag in the embodiment of the present invention. The difference in processing between the P2P-M tag and the P2P-S tag is that the P2P-S tag does not move after installation, whereas the P2P-M tag moves. For this reason, once the P2P-S tag is synchronized, it can be kept synchronized by the synchronization readjustment process. However, in the case of the P2P-M tag, the P2P-S tag moves to a place where it cannot communicate with the GW or other P2P tags. There is a possibility that the synchronization readjustment process based on the received frame from the GW or another P2P tag cannot be performed. In this case, the P2P-M tag may cause a synchronization shift in the active period. For this reason, the P2P-M tag performs processing that is partially different from that of the P2P-S tag.

  In FIG. 8, when the P2P-M tag is activated, it is determined whether or not it is synchronized in the same manner as the P2P-S tag. If it is not synchronized, a synchronization process is performed (step S801). In the synchronization process in step S801, basically, the same process as the synchronization process illustrated in FIG. 7B is performed. That is, the P2P-M tag activates the wireless unit 210 when not synchronized yet, scans for the period of T_p which is the beacon period, and receives a frame during this period, Based on the synchronization process. Unlike the P2P-S tag, the P2P-M tag receives this frame when receiving a frame from another P2P-M tag even when no frame is received from the GW or P2P-S tag. The synchronization process is performed based on the above. This is because the P2P-M tag moves differently from the P2P-S tag, so even if it synchronizes with the P2P-M tag once, it receives further frames directly from the GW or P2P-S tag in the subsequent movement. This is because there is a possibility that synchronization processing based on this received frame can be performed.

  The P2P-M tag that is in a state in which the active period is synchronized (synchronized state) activates the wireless unit 210 to perform frame transmission / reception in synchronization with the active period, similarly to the P2P-S tag described above. (Step S802) At the same time, a slot for transmitting a frame is determined at the same time, and a standby time is also determined (Step S803). Thereafter, the reference time slot and the P2P-S slot in the active period are scanned (steps S804 and S805). When the P2P-M tag receives a frame in the P2P-S slot (step S806), the P2P-M tag performs reception data processing and synchronization readjustment processing similar to the above-described P2P-S tag (step S807, S808).

  When the P2P-S slot ends, the processing of the P2P-M tag is different depending on whether the frame is received or not (that is, in the reference time slot and the P2P-S slot). This is performed (step S809).

  When a frame is received in the P2P-S slot (and the reference time slot), the P2P-M tag does not perform reception processing for the subsequent P2P-M slots. When the transmission node (GW or P2P-S tag) of the corresponding reception frame includes a previously unreceived node, the P2P-M tag performs frame transmission processing in its own transmission slot determined in advance. (Step S810). Note that the frame transmission process is the same process as the P2P-S tag (for example, the same process as step S710 in FIG. 7A). In addition, when the node that has transmitted the received frame does not include a previously unreceived node or after the frame transmission processing in step S810, the P2P-M tag performs a sleep process that turns off the wireless unit 210 for transmitting and receiving the frame. The process proceeds to B (step S811).

  On the other hand, if the frame is not received before the end of the P2P-S slot, the P2P-M tag continues to perform the frame reception process also in the P2P-M slot (step S812). In the slot for P2P-M, when the P2P-M tag has a frame to be transmitted, when the P2P-M tag becomes a frame transmission slot selected for frame transmission by itself (step S813), frame transmission processing is performed. This is performed (step S815). When the P2P-M tag receives a frame in the P2P-M slot (step S814), the P2P-M tag performs reception data processing and synchronization readjustment processing (steps S816 and S817).

  When the P2P-M slot ends, all time slots in the active period have ended. The case where no frames are received in all the time slots in the active period means the following matters (1) and (2), or (1) and (3).

(1) The P2P-M tag exists in a place where reception from the GW and the P2P-S tag is not possible.
(2) The P2P-M tag is present at a place where a frame cannot be received from another P2P-M tag that detects reception of a previously unreceived P2P-S tag and transmits a frame.
Or
(3) Another P2P-M tag that exists in a place where it can communicate with an arbitrary P2P-S tag exists in its own communicable range, but this other P2P-M tag has not moved, for example. Therefore, since the P2P-S tag that has not been received last time is not detected, and the other P2P-M tag is not transmitting a frame, the P2P-M tag is separated from the other P2P-M tag. The frame cannot be received.

  As described above, even when another P2P-M tag exists in a communicable range (that is, in the case of (3)), the P2P-M tag does not receive a frame from another P2P-M tag. Cases can also occur. Therefore, even if the frame is not received by the end of the P2P-M slot in step S818, it is determined that synchronization has been lost immediately, and synchronization readjustment is not performed and synchronization readjustment is performed up to the specified number of times. Without performing, the process proceeds to the sleep process B as in the other cases (step S819).

  On the other hand, if the frames cannot be received continuously for the prescribed number of active periods, the P2P-M tag determines that the synchronization has been lost, and sets, for example, a flag indicating whether or not the synchronization is in an asynchronous state ( Step S820). As a result, the process returns to the synchronization process in step S801 again, where the active period is synchronized. As a result, by performing scanning for one beacon period, the P2P-M tag that has been out of synchronization and cannot receive frames transmitted during the active period can re-synchronize and return to normal operation. Become. When the active period ends, the process proceeds to sleep process B in step S811, and the P2P-M tag enters a sleep state during the period other than the active period.

  In the received data processing in the P2P-M tag, the P2P-M tag is basically configured to record the frames received from the GW, P2P-S, and P2P-M without discrimination. However, when frames are received from the same GW, P2P-S tag, and P2P-M tag received during the previous active period, the P2P-M tag does not perform any processing for this received frame.

  Next, the frame transmission / reception timing of each node in the communication system according to the embodiment of the present invention will be described with reference to FIG. FIG. 5 is a timing chart showing an example of frame transmission / reception timing of each node of the communication system according to the embodiment of the present invention. FIG. 5 shows the frame transmission / reception timings of two P2P-S tags (P2P-S1 tag and P2P-S2 tag) and one P2P-M tag (P2P-M1 tag).

  FIG. 5 illustrates the timing at which the P2P-S2 tag and the P2P-M1 tag that are not yet synchronized are synchronized with the P2P-S1 tag that has already undergone synchronization adjustment after receiving a frame from the GW, for example. Has been.

  Each of the P2P-S2 tag and the P2P-M1 tag performs scanning. The state in which this scan processing is performed corresponds to a case where the P2P-S2 tag is moved while being activated, and a case where the P2P-M1 tag is moved while being scanned for synchronization at the time of activation or asynchronously. The hatched portion shown in FIG. 5 indicates that each tag transmits a frame. In FIG. 5, only the frame transmission timing is indicated by hatching, and the frame reception timing is not shown. Both the P2P-S2 tag and the P2P-M1 tag stop scanning when the P2P-S1 tag frame is received, perform synchronization processing based on the received frame from the P2P-S1 tag, and synchronize with the next active period. Then, the wireless unit 210 is activated. In addition, since the scan can be stopped at the time of synchronization in this way, it is not always necessary to activate the wireless unit 210 for one beacon period.

  FIG. 6 is a timing chart showing another example of the frame transmission / reception timing of each node of the communication system in the embodiment of the present invention. FIG. 6 schematically shows frame transmission / reception operations between P2P tags after all P2P tags are synchronized in the above-described situation shown in FIG. In FIG. 6, the symbols “GW”, “S1”, “S2”, and “M1” attached to each slot are used by GW, P2P-S1, P2P-S2, and P2P-M1 for frame transmission, respectively. The frames “GW”, “S1”, “S2”, and “S2” indicate frames transmitted in each time slot. In addition, a portion surrounded by a thick line in each time slot in FIG. 6 is a period in which each P2P tag is turning on the wireless unit 210, while each P2P tag has a wireless unit 210 in other periods. It is turned off to save power.

  In FIG. 6, the P2P-S1 tag receives and synchronizes the frame “GW” from the GW, and the P2P-S2 tag receives and synchronizes the frame “S1” from the P2P-S1 tag. In addition, the P2P-M1 tag receives a frame of the P2P-S1 tag for the first time after moving, and is moving in the direction of the P2P-S2 tag.

  In FIG. 6, in the frame transmission / reception of each P2P tag in the first active period, only the P2P-S1 tag receives the frame “GW” in the first slot. This is because only the P2P-S1 tag can communicate with the GW. Since the P2P-S1 tag can perform synchronization readjustment processing based on the received frame from the GW, as shown in FIG. 6, in the subsequent P2P-S slots, Except when transmitting a frame, the radio unit 210 may be stopped to save power.

  The frame “S1” transmitted by the P2P-S1 tag is received by both the P2P-M1 tag and the P2P-S2 tag. Both the P2P-M1 tag and the P2P-S2 tag perform synchronization readjustment processing based on the frame “S1” of the P2P-S1 tag. On the other hand, the P2P-S2 tag transmits the frame “S2” at its own frame transmission timing. However, the frame “S2” transmitted from the P2P-S2 tag has not yet reached the P2P-M1 tag. Also, P2P-S1 does not receive the frame from the P2P-S2 tag because the wireless unit 210 is stopped after transmitting the frame “S1”.

  On the other hand, the P2P-M1 tag records the P2P-S1 tag because the frame “S1” is the first frame reception. In addition, after completing the frame reception in the P2P-S slot, the P2P-M1 tag performs a process of transmitting its own frame in the time slot selected by the P2P-M slot itself. Note that since the P2P-M1 tag receives the frame in the P2P-S slot, the P2P-M slot does not perform reception processing. When the P2P-M1 tag transmits the frame “M1” to the P2P-M slot selected by itself, the P2P-S1 tag existing in the communicable range receives this frame. At this time, the ID of the P2P-M1 tag is recorded in the P2P-S1 tag.

  Here, it is assumed that the P2P-M1 tag continues to exist in the same place without moving even in the next active period. In this case, the P2P-M1 tag receives the frame “S1” as in the previous active period, but has already received the frame “S1” from the P2P-S1 tag in the previous (previous) active period. The operation of the wireless unit 210 is stopped without performing its own frame transmission processing.

  Further, in the next active period, it is assumed that the P2P-M1 tag moves and can further communicate with the P2P-S2 tag. In this case, the P2P-M1 tag receives frames from both the P2P-S1 and P2P-S2 tags, and the received frame “S2” from P2P-S2 is received from a new P2P tag that has not been received during the previous active period. Therefore, the ID of the P2P-S2 tag that is the transmission source of the frame “S2” is recorded, and the transmission process of the frame “M1” is performed. The frame “M1” is received by both the P2P-S1 tag and the P2P-S2 tag existing in the communicable range, and the ID of the P2P-M1 tag is recorded by the P2P-S2 tag. At this time, in the P2P-S1 tag, for example, this frame reception may be additionally recorded together with the frame reception time, and since a reception frame from P2P-M1 has already been recorded, a certain time or more If it has not elapsed, recording of frame reception from the same P2P tag may not be performed.

  As described above, each of the P2P-S tag and the P2P-M tag can have a period during which the radio unit 210 is stopped even in the time slot in the active period, thereby further reducing power consumption. It is possible to plan. In this embodiment, the case where only one GW as a reference node is described has been described. However, in the present invention, it is not necessary to have one reference node in the same system. A plurality of reference nodes may be used in the same system if they are installed so that no nodes can communicate with the node at the same time, and these multiple reference nodes are synchronized other than by the method of the present invention. For example, as a method of synchronizing the reference node, synchronization using an external network to which the reference node is connected can be considered.

  The present invention can reduce power consumption of each wireless node in a wireless communication system and can realize efficient access control, and can be applied to a wireless network system, and in particular, power saving in each communication node. Is applicable to an electronic tag system or a sensor network system.

100 Gateway (GW)
105 External network 110, 111, 112 P2P-S tag (wireless tag, wireless node)
113, 114 P2P-M tag (wireless tag, wireless node)
200 P2P tag 201 Transmission unit 202 Reception unit 203 Control unit 204 ID storage unit 205 Clock 206 Power supply unit 210 Radio unit 401 Slot number field 402 Waiting time field 403 Type field 404 ID field

Claims (6)

An active period configured by a plurality of radio nodes and a reference node, and configured by a plurality of fixed-length time slots in which the plurality of radio nodes and the reference node can transmit and receive frames; and the radio node When the reference node transmits a frame to the repeated reference time slot of the fixed period, a sleep period in which the transmission / reception unit is stopped is repeated at a fixed period, and a frame transmitted by the reference node is transmitted. If the wireless node is not receiving, a wireless communication system that matches the start timing of the active period with the reference node,
Frame transmitting means for transmitting a frame in which a wireless node synchronized with the active period randomly selects the time slot at the time of data transmission and adds a slot number of the selected time slot as synchronization information Have
Based on the timing at which the wireless node that has received the frame with the synchronization information added receives the synchronization information and the frame in the frame, the start timing of the active period next to the active period in which the frame has been received A wireless communication system having synchronization means for calculating the synchronization period for the active period.   The wireless communication system according to claim 1, wherein the synchronization information further includes transmission timing information inside the time slot for transmitting the frame. An active period configured by a plurality of radio nodes and a reference node, and configured by a plurality of fixed-length time slots in which the plurality of radio nodes and the reference node can transmit and receive frames; and the radio node When the reference node transmits a frame to the repeated reference time slot of the fixed period, a sleep period in which the transmission / reception unit is stopped is repeated at a fixed period, and a frame transmitted by the reference node is transmitted. When the wireless node is not receiving, a communication control method in a wireless communication system that matches the start timing of the active period with the reference node,
A frame transmitting step in which a wireless node synchronized with the active period randomly selects the time slot at the time of data transmission and then transmits a frame with the slot number of the selected time slot added as synchronization information; ,
Based on the timing at which the wireless node that has received the frame with the synchronization information added receives the synchronization information and the frame in the frame, the start timing of the active period next to the active period in which the frame has been received And a synchronization step for performing a synchronization process for the active period,
A communication control method.   The communication control method according to claim 3, wherein the synchronization information further includes transmission timing information inside the time slot for transmitting the frame. The predetermined reference node has a transmission timing of a frame to be transmitted at a constant cycle, and performs communication in synchronization with an active period composed of a plurality of fixed-length time slots capable of transmitting and receiving the frame. A communication node that matches the start timing of the active period with the predetermined reference node when a frame transmitted by the predetermined reference node is not received;
When the communication node is synchronized with the active period, a frame transmission means for transmitting a frame with predetermined synchronization information after randomly selecting the time slot at the time of data transmission;
When the frame to which the synchronization information is added is received, the start timing of the active period next to the active period in which the frame is received is calculated based on the synchronization information in the frame, and the synchronization with respect to the active period is calculated. Synchronization means for processing,
Having communication nodes.   The communication node according to claim 5, wherein the communication node is configured to use a slot number of the selected time slot as the previous period synchronization information.