JP4749282B2 - Wireless communication system, communication control method, and communication node - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve reduction of power consumption and efficient access control at each of wireless nodes in an electronic tag system and a sensor network system, etc. in which power saving of the wireless node is important. <P>SOLUTION: Each node in wireless communication is synchronized in a period of an AP (active period) for transmitting/receiving data and an iAP (inactive period) for stopping transmission/reception of the data. When a certain node transmits, for example, data with comparatively large data size, the data are transmitted in slots in a plurality of APs. At this time, when a packet is transmitted by a certain slot of a certain AP, information indicating that the data are transmitted also in the same slot of the next AP is inserted into a packet. In addition, the node performs CCA (Clear Channel Assessment) from the head (waiting time w0) of the slot to perform packet transmission only in a slot reserved in advance. <P>COPYRIGHT: (C)2008,JPO&amp;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 order to respond to the recent diversification of communication usage forms, it is important to provide bidirectional communication. However, in the active electronic tag system, since one-way communication from the electronic tag to the reader is performed, even if a node such as a single electronic tag and reader / writer is used for simple bidirectional communication, However, it is difficult to reduce power consumption because the receiver is always activated, and problems remain in terms of access control (collision avoidance control).

  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. At present, ZigBee (registered trademark) using a MAC layer defined in IEEE 802.15.4 has been proposed as such a solution.

  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, a superframe is defined as shown in FIG. 1, and an inactive period (inactive period) can be defined by making the beacon interval larger than the superframe period. This allows all synchronized nodes to go to sleep during this pause period. In this way, data is transmitted according to the synchronization schedule using the superframe, whereby the data is received at each node.

  In IEEE 802.15.4, as shown in FIG. 1, the superframe period is divided into 16 slots (time slots). When transmitting data, a node selects a slot and performs transmission using CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) inside the slot. Even when the number of nodes existing in the node increases, the opportunity of data transmission between the nodes can be kept as fair as possible.

  In the latter half of the superframe period, a GTS (Guaranteed Time Slot) is defined. This GTS is a period for guaranteeing that the coordinator preferentially uses a slot for a specific node. Therefore, communication in this GTS is not allowed for each node other than a specific node permitted to use by communication in GTS. As shown in FIG. 1, the length of the GTS is assigned by the node negotiating with the coordinator, and as a result, communication avoiding collision of transmission data is performed.

  However, in IEEE 802.15.4, the number of slots that can be used as GTSs in a superframe is limited, so when the number of nodes that request slot reservation increases, all the nodes that requested slot reservation have a single slot. It becomes difficult to receive GTS allocation within the superframe period. In this case, the node that has not received the slot reservation must wait until the next superframe period. Further, the network topology is limited to the star type as long as the GTS is assigned from the coordinator and the coordinator is notified that the GTS is assigned to a node existing in a range where radio waves reach. Since the star topology lacks flexibility in configuration, it has a drawback that it is not suitable for use as a topology assumption when a moving node performs communication.

  As described above, in order to implement slot reservation in IEEE 802.15.4, there is a limit to the number of slots that can be used for slot reservation within a single superframe period. IEEE 802.15.4 requires a coordinator to manage slot reservation, and as a result, there are restrictions on the network configuration (network topology restrictions).

Also, unlike ZigBee superframe communication, a technique related to low power consumption in a beaconless solution that does not perform system synchronization using beacons is disclosed in Patent Document 1 (see FIG. 2). In the technique disclosed in Patent Document 1, each receiving node is periodically activated for a fixed time 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 its own reception period _TL. 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 for each node for each communication, the sampling schedule of each node is held as table information, and a period of the monitoring cycle _TPL is required. It is possible to shorten the transmission time of the wakeup signal.

  Further, the system disclosed in Patent Document 1 has a mechanism for preferentially receiving transmitted data by matching the activation times of receivers of a plurality of nodes. Furthermore, by sending a wake-up signal, it is possible to designate the start time of data transmission as the time requested by the node, and there is a mechanism for priority control of data transmission.

However, in the system disclosed in Patent Document 1, it is necessary to transmit a wake-up signal during the period of the monitoring cycle _TPL until the table information is obtained. Does not only consume the power of the source node, but also occupies the radio channel for a considerable period of time, which prevents other nodes from transmitting other wake-up signals Or, collisions may occur in other ongoing transmissions. In particular, when communication is performed while a large number of unspecified wireless nodes move, it is considered that there are more opportunities for long-term exchange using a wake-up signal until the first table configuration.

Therefore, in the system disclosed in Patent Document 1 described above, in order to perform priority control of data transmission, a long channel occupation period and a long set time until the start of data transmission are required.
JP 2006-148906 A

  In order to realize power saving in a wireless communication system, for example, a data transmission method using periodic data transmission (RFID (Radio Frequency Identification), use of an active electronic tag, ALOHA (Aloha) using periodic broadcast) ) Communication) is effective as a simple data transmission means to a plurality of nodes in wireless short-range communication that does not specify a communication partner node (hereinafter referred to as CN: Correspondent Node). In particular, the data transmission method based on periodic data transmission is effective for communication between moving nodes (hereinafter referred to as MN: Mobile Node). Its effectiveness is to reduce the number of messages exchanged by communicating with a simple protocol, reduce the amount of data to be transmitted, shorten the data transmission / reception time, save power, and start and end data exchange processing. It is to realize high speed.

  When short data (small amount of data) is periodically transmitted, there is a limit to the amount of information that can be exchanged between two nodes by one data transmission / reception. At this time, it is possible to increase the amount of information transmitted by performing multiple times of data transmission / reception, but in this case, a mechanism for guaranteeing a wireless communication path without causing a data transmission collision Is required. However, the simple protocol does not have a mechanism for avoiding the possibility of a data transmission collision, and cannot secure a wireless communication path (reliable guarantee).

  In addition, IEEE 802.15.4 defines GTS slot guarantees within a superframe period as described above, but limits the number of slots that can be used for slot reservation within a single superframe period. There is a problem of (upper limit). In addition, since a coordinator for managing slot reservation is necessary, there is a problem that configuration restrictions occur in the network. The network topology restricted by IEEE802.15.4 is not suitable particularly when data transmission / reception is performed between MNs by P2P (Peer to Peer).

  Further, in the system disclosed in Patent Document 1, it is possible to realize guarantees for data transmission and reception by defining a wake-up signal and uniformly synchronizing the activation times of the receivers of the peripheral nodes. However, there is a problem that a channel occupation time (a period from transmission of a wakeup signal to transmission of data) in which a channel is occupied by a wakeup signal transmitted before a certain node starts data transmission is long. For this reason, when the number of transmission nodes increases, there are many opportunities for the channel to be occupied, and as a result, it is difficult to guarantee data transmission. Also, focusing on data transmission / reception between MNs, the period from the transmission of a wakeup signal to the transmission of data is long, so that propagation is possible while one MN occupies a channel with a wakeup signal to perform data transmission. In some cases, the MN moves outside the service area (that is, communication between MNs becomes impossible).

  In view of the above problems, the present invention is a wireless communication system including a small wireless node capable of bidirectional communication, and can reduce power consumption when a large number of small wireless nodes moving perform communication. An object of the present invention is to provide a radio communication system, a communication control method, and a communication node that guarantee a transmission opportunity to realize access control.

In order to achieve the above object, the wireless communication system of the present invention includes a plurality of wireless nodes, and includes a plurality of fixed-length time slots in which the plurality of wireless nodes can transmit and receive data. A wireless communication system in which an active period and a non-active period in which a transceiver of the wireless node is in a dormant state are repeated at a constant cycle,
When the wireless node transmits a packet in an arbitrary time slot in an arbitrary active period, the wireless node is configured to reserve a time slot in communication in the next active period.
With this configuration, in a wireless communication system including a small wireless node capable of two-way communication, in order to reduce power consumption and perform efficient access control when a large number of moving small wireless nodes perform communication. It is possible to guarantee transmission opportunities.

In addition to the above-described configuration, the wireless communication system of the present invention may have a next active period in the same position as a time slot in which the packet can be transmitted in an arbitrary time slot in the arbitrary active period. A time slot is configured to be reserved as a time slot in the communication during the next active period.
With this configuration, when data transmission is performed by the same radio node in a plurality of active periods, the same time slot is selected, and the relationship between a specific radio node and the data transmission time slot is clarified. Become.

In addition to the above configuration, the wireless communication system of the present invention is configured so that the wireless node that has made a reservation for the time slot transmits the packet from the beginning of the time slot in the communication during the next active period. It is configured to perform processing.
With this configuration, it is possible to preferentially perform communication by the wireless node that has reserved the time slot.

In addition to the above configuration, the wireless communication system according to the present invention may be configured such that when the wireless node receives a packet including a request for reservation of the time slot from another wireless node, the wireless node A time slot for data transmission is selected while avoiding the time slot in which a reservation request is made.
With this configuration, a packet declaring the reservation of a time slot is notified to other peripheral nodes, so that the node that has received the notification can refrain from using the reserved time slot.

In addition to the above configuration, the wireless communication system of the present invention may be configured such that when the wireless node does not receive a packet including a request for reservation of the time slot from another wireless node, the other wireless node It is configured to search for a time slot in which the data transmission is possible so that the node and the data transmission do not collide.
With this configuration, a wireless node that has not received a packet declaring time slot reservation can transmit data by searching for a time slot for its own data transmission.

  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.

  In view of the above problems, the present invention is a wireless communication system including a small wireless node capable of bidirectional communication, and can reduce power consumption when a large number of small wireless nodes moving perform communication. An object of the present invention is to provide a radio communication system, a communication control method, and a communication node that guarantee a transmission opportunity to realize access control. In particular, according to the present invention, when data exchange is performed between a large number of nodes in which the schedule of the operation period and the suspension period of the radio unit is synchronized, an opportunity to perform data transmission over a plurality of activation periods is provided. By securing in advance, it becomes possible to avoid transmission collision with other nodes over a plurality of operation periods regarding data transmission, and further, it is possible to secure a pause period of the radio unit and reduce power consumption. It becomes like this.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 schematically shows a wireless communication network including a plurality of nodes 1 to 4 according to the embodiment of the present invention. In FIG. 3, each of the plurality of nodes 1 to 4 is a wireless communication node capable of directly communicating with other nodes existing around each node 1 to 4 (within the wireless propagation range). Also, each node 1 to 4 can change its communicable node by moving. The nodes 1 to 4 may move or may be fixedly installed.

  The nodes 1 to 4 are nodes that perform wireless communication as described above, and each is a node that automatically activates and deactivates a receiver of a wireless unit (hereinafter also referred to as Rx). With respect to the activation and suspension schedules, each node can have the same schedule by synchronizing the nodes.

  Each of the nodes 1 to 4 in the embodiment of the present invention is a node configured not to simultaneously transmit and receive a packet when performing wireless communication processing. That is, each of the nodes 1 to 4 in the embodiment of the present invention indicates that the packet is not received while the packet is being transmitted, and the packet is not transmitted while the packet is being received. However, each of the nodes 1 to 4 is configured not to perform packet transmission and reception at the same time when performing wireless communication processing according to the present invention, and packet transmission and packet reception in wireless communication. You may have the function to perform simultaneously. In the present specification, a unit of information transmitted by each node in one transmission opportunity is referred to as a “packet”.

  FIG. 4 also shows a time slot configuration showing a specific example of the activation and suspension schedules of the receiver Rx of the radio unit used when the node according to the embodiment of the present invention performs radio communication using a communication channel. Is shown. In FIG. 4, the period in which Rx is activated is AP (Active Period), and the period in which Rx is paused is iAP (inActive Period). In the AP, the node activates Rx and receives all packets from the peripheral nodes existing around the node. On the other hand, in iAP, the node does not receive the packet from the peripheral node because the node is inactive Rx. In addition, by matching the AP start position between the nodes, it is possible to synchronize the Rx activation schedule of each node.

  Also, in this specification, an AP that performs communication at a specific time of interest is referred to as cAP (current AP), and an AP immediately before cAP is referred to as pAP (previous AP). Furthermore, an AP that visits after the cAP will be referred to as nAP (next AP).

  In addition, each node activates a transmitter of the wireless unit (hereinafter also referred to as Tx) in the AP and transmits a packet. The time that can be used for transmission of this packet is set in the form of a slot (time slot) in which the AP is divided into a plurality of periods. Each node selects a slot when transmitting a packet, and starts packet transmission in the selected slot. Further, the node according to the present invention has a function of reserving a slot once selected so that the same slot can be continuously used every time an AP comes. This function will be described later. In the embodiment of the present invention, as an example of the slot selection method, a method of randomly selecting a slot before packet transmission is described, but the slot selection method is not particularly limited. In FIG. 4, the AP is divided into 10 slots, but the number of divisions is not limited to a specific value.

  For example, CSMA / CA is used for packet transmission in the selected slot. In CSMA / CA, it is possible to avoid a collision with a timing at which another node transmits a packet by performing reception for a predetermined time before communication on a channel (frequency) to be used. This is called CCA (Clear Channel Assessment). If no radio wave is received on the same channel during CCA, it is determined that another node is not transmitting a packet on that channel. Also in the embodiment of the present invention, CCA is performed to detect the presence / absence of another node using a slot before packet transmission. When the CCA detects that the channel is not used, the node starts data transmission.

  When performing CCA, the position where CCA is started is shifted from the slot start position within the slot. When the position where CCA is started by each node is the same, even if the own node succeeds in CCA, if other nodes that have performed CCA at the same time also succeed in CCA, the use timing of the communication channel Will collide. In order to reduce the probability of this collision, it is desirable to be able to change the position where the CCA starts. Accordingly, even when a plurality of nodes select to use the same slot for packet transmission, it is possible to reduce the transmission timing collision probability by randomly changing the position where CCA is started. If a node that has started CCA at a relatively early position in a slot and has confirmed the availability of the channel is using a channel, the node that started CCA at a relatively late position in the same slot is used by this channel. Since it is possible to detect that the channel is being used, collision of channel use timing can be avoided.

  FIG. 4 shows a WP (Waiting Period for CCA) in which four slots w0 to w3 that can be selected as CCA start positions are defined. Each node selects a slot for transmitting a packet and then further selects a WP at random when performing packet transmission. For example, when a node that has selected w0 as a WP and a node that has selected w2 exist, the node that has selected w0 can transmit a packet preferentially. At this time, since the node that has selected w0 transmits a packet from the position where w0 has elapsed with reference to the slot start position, the node that has selected w2 starts CCA at the position of w2 and the channel is in use. Detect that. As a result, packets are not transmitted from the node that has selected w2 within the selected slot.

  However, when a plurality of nodes select w0, a packet transmission collision occurs. In order to avoid this situation, in the present invention, only a node that has issued a slot reservation request at a certain AP can select w0 at the nAP so that the channel of w0 at the nAP is used preferentially. become. In FIG. 4, the number of WPs is four, w0 to w3, but any number can be defined. Also, random selection can be adopted as an example of selection of WP from w1 to w3, but any other selection method may be used.

  FIG. 5 shows an example of a timing chart when each of the three nodes 1 to 3 transmits a packet without performing slot reservation based on the conventional technology. Here, it is assumed that the nodes 1 to 3 exist at a distance that allows wireless communication with each other.

  In the embodiment of the present invention, for the purpose of reducing the power consumption of a node, in order to make the AP, which is the effective operation time of the node, a short time, the slot for each node to transmit a packet is also a short time. Set to Therefore, there is a limit on the upper limit data amount that can be transmitted in a single slot. This is very similar to a communication path expressed as having a small MTU (Max Transfer Unit) in IP communication, for example.

  Each node can also transmit a packet using a plurality of slots of the AP. Use of multiple slots, for example, when transmitting data that cannot be transmitted in a single slot, or when improving the reliability of data propagation by transmitting the same data redundantly (overlapping) To be done.

  A request for such a transmission form is a request from a layer higher than the MAC handled by the present invention. For example, when a request for transmitting various attribute information (information handled by an upper layer such as position information, temperature information, hobby information, etc.) along with the node ID is received from the upper layer, the amount of data transmitted by the packet is simply reduced. When the amount of data is difficult to complete with only one slot, packet transmission using a plurality of slots is performed. At this time, a request from an upper layer can be satisfied by transmitting a packet using a plurality of slots.

  In FIG. 5, in the first AP (AP1), the node 1 uses the slot 1 to transmit a packet. Similarly, node 2 uses slot 4 and node 3 uses slot 8 to transmit packets.

  In the second AP (AP2), node 1 uses slot 9, node 2 uses slot 5, and node 3 uses slot 0 to transmit packets. In FIG. 5, the nodes 1 to 3 do not make slot reservations, and the same node may use different slots for each AP. Further, a node that performs slot reservation and a node that does not perform slot reservation may coexist in the same wireless communication system.

  As a result of randomly selecting a slot in the third AP (AP3), node 1 selected slot 1 and did not cause a transmission collision with other nodes, but node 2 and node 3 It is assumed that the packet transmissions from the two have been selected at the same time and have collided with each other.

  Such a transmission collision can occur when the same WP is selected in different nodes (node 2 and node 3), and the WP that starts the CCA implementation is finite (ie, the CCA waiting time). Thus, it is impossible to completely avoid such transmission collisions (selected from a finite WP slot). In addition, as the transmission opportunity of a single node increases and the number of nodes that perform packet transmission increases, the opportunity for such transmission collision increases. Note that the transmission collision occurs in the same manner regardless of whether the node performs packet transmission only once or multiple times. As described above, packet transmission collision between different nodes occurs because the recognition of the slot used in the AP cannot be shared between the nodes.

  FIG. 6 shows an example of a timing chart when each of the three nodes 1 to 3 performs slot reservation and transmits a packet in the embodiment of the present invention. It is assumed that the nodes 1 to 3 are at a distance that allows wireless communication with each other. Here, it is assumed that the nodes 1 to 3 exist at a distance that allows wireless communication with each other.

  In FIG. 6, in the first AP (AP1), the node 1 uses the slot 1 for packet transmission. At the time of packet transmission, channel availability is confirmed by performing CCA. A packet transmitted by node 1 in slot 1 is received by nodes 2 and 3. When the use of the channel is detected by the CCA, the node 1 gives up the packet transmission in the slot 1 and tries the packet transmission in another slot.

  Here, for example, it is assumed that the node 1 has transmission data that is not completed by packet transmission in a single slot, and has a request to continue packet transmission after nAP (next AP2). At this time, if the transmission method shown in FIG. 5 described above is attempted, there is a possibility of causing a transmission collision. Therefore, in the present invention, the slot reservation at AP2 is performed at the time of the first packet transmission at AP1, thereby causing the transmission collision. Try to avoid it.

  The slot reservation is performed for a slot in which packet transmission is successful without detecting channel use by the CCA. In order to make a slot reservation, the node transmits a packet request with the slot reservation indicator field 701 (described later) included in the packet format shown in FIG. It becomes possible to show to the node.

  In FIG. 6, the nodes 2 and 3 that have received the packet in which the slot reservation indicator is valid (the packet transmitted from the node 1 in the slot 1 of the AP 1) continue to use the slot 1 in the node 1. Detect that you have a request. Then, the node 2 and the node 3 do not use the slot 1 in the AP 2 so that the transmission collision related to the packet using the slot 1 by the node 1 does not occur.

  In addition, the node 1 that has transmitted the packet with the slot reservation indicator enabled in AP1 sets the WP for starting CCA at the time of packet transmission in the slot 1 of AP2 to w0. As a result, the node 1 can preferentially use the slot 1 in the AP 2.

  Further, when making a slot reservation at AP3, node 1 reserves the use of slot 1 of AP3 at AP2, and also starts a CCA at w0 of slot 1 at AP3 to transmit a packet. In this way, the node can continue to reserve the same slot until the transmission of data with a transmission request is completed. Further, when transmission of all data having a transmission request is completed in AP3, node 1 does not perform packet transmission in AP4 which is the next AP. Therefore, by disabling the slot reservation indicator of the packet transmitted by AP3, node 1 can notify other nodes that it does not reserve the use of slot 1 by AP4.

  FIG. 6 illustrates a case where node 1 preferentially uses slot 1 of AP2 and AP3 by reserving a slot (slot 1) of the same number of nAPs when transmitting a packet in cAP. However, similarly, the node 2 reserves the slot 4 and the node 3 reserves the slot 8 to transmit the packet, respectively.

  Next, an example of a packet format that enables slot reservation in FIG. 6 will be described. FIG. 7 shows an example of a packet format used when a node makes a slot reservation in the embodiment of the present invention. The packet format shown in FIG. 7 has a slot reservation indicator field 701, a transmission source node ID field 702, and a data field 703.

  In FIG. 7, a slot reservation indicator field 701 is a field for notifying other nodes that the same slot as that used for packet transmission is also used by the nAP. That is, the node performs slot reservation by inserting information indicating slot reservation in nAP into the slot reservation indicator field 701. The slot reservation indicator field 701 can be realized by, for example, a flag (valid / invalid) for instructing two types of information indicating whether to make a slot reservation or not to make a slot reservation. A slot number of a reserved slot may be inserted in the field 701.

The source node ID field 702 is a field in which the ID (identification information) of the node that transmitted the packet is described. The node that has received the packet can identify the node that has transmitted the packet by referring to the ID of the node in the transmission source node ID field 702.
A data field 703 is a field for inserting data having a request to be transmitted by the node. It is desirable that complete information such as node attribute information (for example, position information) is given to the data field in one packet. When a node that has received a plurality of packets assigned to the data field 703 of a plurality of packets by dividing the completed data into a plurality of data has a function of recombining the divided data as completed data, The data assigned to the data field 703 of one packet may not be completed.

  Next, an example of a data reception table held by each node in the embodiment of the present invention for managing the status of slot reservation performed by another node will be described. FIG. 8 is a diagram showing an example of a data reception table held by each node in the embodiment of the present invention for managing the status of slot reservation performed by other nodes.

  Each node holds a data reception table as shown in FIG. 8 in order to manage the status of slot reservation by other nodes. The data reception table shown in FIG. 8 includes the ID of the node that transmitted the received packet (node ID), the slot that received the packet (reception slot), and the slot number reserved by the node that transmitted the packet. (Reserved slot).

  The information held in the data reception table is information that can be acquired when a packet is received from an arbitrary node. In FIG. 8, in the embodiment of the present invention, a packet indicating that a slot in nAP is reserved from node 2 is received in slot 2, and a packet indicating that a slot in nAP is reserved from node 3 is slotted. 5 shows a data reception table constructed when a packet received at 5 and indicating that a slot at nAP is not reserved from node 4 is received at slot 8. In the embodiment of the present invention, it is allowed to mix a node that performs slot reservation (node 2 and node 3 in FIG. 8) and a node that does not perform slot reservation (node 4 in FIG. 8). In the table, there may be a reservation slot entry including nAP slot reservation information and a reservation slot entry including no nAP slot reservation information.

  Further, since the contents of the data reception table are configured by information relating to all packets received until the AP is terminated, the packet reception status at the pAP is included in the data reception table at the start of the AP. Each node is configured to select a slot for packet transmission with cAP using the contents of the data reception table when a packet is received with pAP.

  Further, FIG. 9 shows the transition of the data reception table in the node 1 when the communication of FIG. 6 is performed. At the time of starting AP1 in the communication of FIG. 6, since no packet is received by the AP before AP1, no information is held in the data reception table of each node. Therefore, when performing slot selection at AP1, each node performs slot selection without any information to be referred to at the time of slot selection. When information regarding slot reservation is held in the data reception table at the start of AP1, the slot itself uses it for packet transmission from slots other than slots reserved by other nodes (that is, slots not reserved). Select a slot for.

  At the start of subsequent AP2 and AP3, the data reception table holds the contents related to node 2 and node 3 from the packet reception status at AP1. The node 1 can grasp that the node 2 reserves the slot 4 and the node 3 reserves the slot 8 by referring to the data reception table at the start of the AP2 and AP3.

  In addition, since the packet received by the node 1 from the node 2 and the node 3 in the AP 3 indicates that the slot reservation is not performed, when the AP 4 starts, the entries related to the reserved slots of the node 2 and the node 3 are It becomes blank and it can be understood that no slot reservation is made. Although not shown, if no packet is transmitted / received at AP4, the data reception table of each node at the start of AP5 has no information similar to the data reception table at the start of AP1. Is not held.

  Next, the operation of the node in the embodiment of the present invention will be described. FIG. 10 is a flowchart illustrating an example of a packet transmission / reception operation according to the embodiment of the present invention. FIG. 11 is a flowchart showing an example of the operation of slot selection (reserved) in the embodiment of the present invention corresponding to the slot selection processing (reserved) of step S1003 of FIG. FIG. 12 is a flowchart showing an example of the operation of slot selection (no reservation) in the embodiment of the present invention corresponding to the slot selection process (no reservation) in step S1004 of FIG.

  First, the node checks whether a slot reservation has already been made (step S1001). As described above, when data transmission is performed over a plurality of slots, a node can make a reservation for a transmission slot in nAP. For example, the basic operation starts when new data transmission is performed. Specifically, slot reservation is not performed.

  If slot reservation is not performed, the node determines whether there is data to be transmitted and whether or not it is necessary to perform data transmission processing over a plurality of slots, and determines whether or not to perform slot reservation. Is determined (step S1002).

  If it is determined in step S1002 that slot reservation is necessary, slot selection processing (reserved) is performed (step S1003). On the other hand, if it is determined that slot reservation is not required, Slot selection processing (no reservation) is performed (step S1004).

  Here, with reference to FIGS. 11 and 12, the slot selection process (with reservation) in step S1003 and the slot selection process (without reservation) in step S1004 will be described.

  In the slot selection process (reserved) in step S1003, for example, the process illustrated in FIG. 11 is performed. In FIG. 11, first, the node checks whether or not data has been transmitted by pAP (step S1101). If data transmission is performed by pAP, the node selects a slot reserved by pAP (transmission slot in pAP) for packet transmission (step S1102), and further selects w0 as WP (step S1103). .

  On the other hand, if data transmission is not performed by pAP, it is confirmed whether data is received from another node by pAP (step S1104). The confirmation in step S1104 can be performed by referring to the data reception slot described above.

  When data is received by pAP, the node refers to the data reception table and avoids a slot reserved by pAP (that is, a reserved slot specified by each node) and uses it by cAP. A transmission slot is selected (step S1105), and WP is selected avoiding w0 in the selected slot (step S1106).

  On the other hand, when data is not received by pAP, the node randomly selects a transmission slot, for example (step S1107), and selects WP avoiding w0 in the selected slot (step S1108).

  Then, after the transmission slot and WP are selected in each case, the node determines whether to use the transmission slot in cAP also in nAP (step S1109). The determination in step S1109 is made based on, for example, the amount of transmission data passed from the upper layer. For example, when it is necessary to transmit a packet over a plurality of slots, the slot reservation indicator of the packet is validated and slot reservation in nAP is performed (step S1110). On the other hand, for example, when it is not necessary to transmit a packet over a plurality of slots, the slot reservation indicator of the packet is invalidated (step S1111).

  In the slot selection process (no reservation) in step S1004, for example, the process illustrated in FIG. 12 is performed. In FIG. 12, first, the node checks whether or not data has been received by pAP (step S1201).

  When data is received by pAP, the node refers to the data reception table and avoids a slot reserved by pAP (that is, a reserved slot specified by each node) and uses it by cAP. A transmission slot is selected (step S1202), and WP is selected avoiding w0 in the selected slot (step S1203).

  On the other hand, when data is not received by pAP, the node randomly selects a transmission slot, for example (step S1204), and selects WP avoiding w0 in the selected slot (step S1205).

  After the transmission slot and WP are selected in each case, the node indicates that slot reservation is not performed by invalidating the slot reservation indicator of the packet (step S1206).

  In FIG. 10, after performing the slot selection process (with reservation) in step S1003 or the slot selection process (without reservation) in step S1004, the node performs Rx at a timing according to the activation schedule (for example, the timing at which the AP is started). Is activated (step S1005), and an elapsed time since activation (for example, whether or not a predetermined time T1 has elapsed) is monitored (step S1006).

  If the predetermined time T1 has not elapsed since the activation of Rx, has the node reached the transmission slot selected in the slot selection process (reserved) in step S1003 or the slot selection process (no reservation) in step S1004? Whether or not is monitored (step S1007). If it is not a transmission slot, it is monitored whether a packet is sent from another node (step S1008). If no packet is received from another node, the process returns to step S1006 to continue the monitoring process. On the other hand, when a packet is received from another node, the node records the received packet information in the data reception table (step S1009), and then returns to step S1006 to continue the monitoring process.

  On the other hand, when the slot becomes a transmission slot, CCA is performed at the timing of the WP selected in the slot selection process (reserved) in step S1003 or the slot selection process (no reservation) in step S1004 (step S1010). It is confirmed whether or not it is free (step S1011). If it is confirmed in step S1012 that the channel is free, the node performs packet transmission processing (step S1012), and then returns to step S1006 to continue monitoring processing.

  On the other hand, if the channel is not free in step S1011, refer to the data reception table to avoid slots that are already reserved for other nodes at the time of pAP, and transmit slots in cAP from slots after CCA failure. Is selected (step S1013). Further, in the transmission slot selected by cAP, for example, WP is randomly selected avoiding w0 (step S1014).

  Further, the node determines whether or not to use the transmission slot in cAP also in nAP (step S1015). For example, when it is necessary to transmit a packet over a plurality of slots, the slot reservation indicator of the packet is validated and slot reservation in nAP is performed (step S1016). On the other hand, for example, when there is no need to transmit a packet over a plurality of slots, the slot reservation indicator of the packet is invalidated (step S1017). Then, after determining whether the slot reservation indicator of the packet is valid / invalid in step S1016 or S1017, the process returns to step S1006 to continue the monitoring process.

  In step S1006, when a predetermined time T1 has elapsed since activation of Rx, the node stops Rx (step S1018). Note that the stop of Rx is performed only for a predetermined time T2 in accordance with the activation schedule, for example, and then returns to the process starting from step S1001. As a result, activation of Rx is limited to a period required for packet transmission / reception, and power consumption of Rx can be suppressed.

  Next, the function of the node in the embodiment of the present invention will be described with reference to FIG. FIG. 13 is a block diagram showing an example of the configuration of a node in the embodiment of the present invention. In FIG. 13, each function of the node is illustrated by a block, but the function represented by each block can be realized by hardware and / or software.

  A node 1300 illustrated in FIG. 13 includes a wireless unit 1310 having a transmitter (Tx) 1301 and a receiver (Rx) 1302, a control unit 1303, an ID storage unit 1304, a data reception table holding unit 1305, a clock 1306, and a power supply. Part 1307.

  The transmitter 1301 has a function of transmitting a frame including its own ID to the outside via radio. As described above, ID transmission in the transmitter 1301 is performed by broadcasting. The receiver 1302 has a function of receiving a frame including an ID transmitted by another P2P tag or GW in the same manner.

  The control unit 1303 has a function of controlling the operation of the node 1300. The control unit 1303 has a function of controlling the ID transmission timing in the transmitter 1301 based on, for example, a clock signal obtained from the clock 1306. The control unit 1303 has a function of storing IDs of other P2P tags received by the receiver 1302 in the ID storage unit 1304. The control unit 1303 has a function of reading / writing information in the data reception table based on the content of the received packet, the slot number of the received packet, and the like. The control unit 1303 also has a function of controlling the operations illustrated in FIGS. 10 to 12 described above.

  The ID accumulation unit 1304 has a function of accumulating IDs of other P2P tags received by the receiver 1302. When the ID is stored in the ID storage unit 1304, for example, time information at that time may be recorded together with the ID. The data reception table holding unit 1305 has a function of holding the above-described data reception table (see FIGS. 8 and 9).

  The clock 1306 has a function of outputting a clock signal for grasping the timing of frame transmission in the transmitter 1301 and frame reception in the reception unit 1302. The power feeding unit 1307 is a power source built in the node 1300, for example, a battery mounted in the casing of the node 1300.

  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.

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 The figure which shows typically the radio | wireless communication network containing the some node in embodiment of this invention The time slot block diagram which shows the specific example of the start-up and suspension schedule of the receiver Rx of the radio | wireless part used when the node in embodiment of this invention performs radio | wireless communication using a communication channel In the prior art, a timing chart showing an example when each of three nodes transmits a packet without making a slot reservation In the embodiment of the present invention, a timing chart showing an example when each of the three nodes performs slot reservation and transmits a packet The figure which shows an example of the packet format in embodiment of this invention The figure which shows an example of the data reception table which each node in embodiment of this invention hold | maintains in order to manage the condition of the slot reservation performed by the other node The figure which shows the transition of the data reception table in the specific node at the time of communication of FIG. The flowchart which shows an example of the packet transmission / reception operation | movement in embodiment of this invention The flowchart which shows an example of the operation | movement of slot selection (with reservation) in embodiment of this invention The flowchart which shows an example of the operation | movement of slot selection (no reservation) in embodiment of this invention The block diagram which shows an example of a structure of the node in embodiment of this invention

Explanation of symbols

701 Slot reservation indicator field 702 Source node ID field 703 Data field 1300 Node 1301 Transmitter (Tx)
1302 Receiver (Rx)
1303 Control unit 1304 ID storage unit 1305 Data reception table holding unit 1306 Clock 1307 Power supply unit 1310 Wireless unit

Claims (15)

It is composed of a plurality of wireless nodes, and an active period composed of a plurality of fixed-length time slots in which the plurality of wireless nodes can transmit and receive data, and a transceiver unit of the wireless node is in a dormant state A wireless communication system in which a certain inactive period is repeated at a constant cycle,
A wireless communication system configured to reserve a time slot in communication in the next active period when the wireless node transmits a packet in an arbitrary time slot in an arbitrary active period.   The time slot of the next active period that exists at the same position as the time slot capable of transmitting the packet in the arbitrary time slot of the arbitrary active period is reserved as the time slot in the communication of the next active period. The wireless communication system according to claim 1, configured as described above.   2. The wireless communication according to claim 1, wherein the wireless node that has reserved the time slot is configured to perform processing for transmitting the packet from the beginning of the time slot in communication in the next active period. system.   When the wireless node receives a packet including a request for reservation of the time slot from another wireless node, data transmission is performed while avoiding the time slot in which the reservation request is made by the other wireless node. The wireless communication system of claim 1, wherein the wireless communication system is configured to select a time slot for.   When the wireless node does not receive a packet including a request for reservation of the time slot from another wireless node, the time slot capable of transmitting the data so that the data transmission does not collide with the other wireless node. The wireless communication system according to claim 4, wherein the wireless communication system is configured to search for. It is composed of a plurality of wireless nodes, and an active period composed of a plurality of fixed-length time slots in which the plurality of wireless nodes can transmit and receive data, and a transceiver unit of the wireless node is in a dormant state A communication control method in a wireless communication system in which a certain inactive period is repeated at a constant cycle,
A communication control method for reserving a time slot in communication in the next active period when the wireless node transmits a packet in an arbitrary time slot in an arbitrary active period.   The time slot of the next active period that exists at the same position as the time slot capable of transmitting the packet in the arbitrary time slot of the arbitrary active period is reserved as the time slot in the communication of the next active period. The communication control method according to claim 6.   The communication control method according to claim 6, wherein the wireless node that has made a reservation for the time slot performs a process for transmitting the packet from the head of the time slot in communication in the next active period.   When the wireless node receives a packet including a request for reservation of the time slot from another wireless node, data transmission is performed while avoiding the time slot in which the reservation request is made by the other wireless node. The communication control method according to claim 6, wherein a time slot for selecting is selected.   When the wireless node does not receive a packet including a request for reservation of the time slot from another wireless node, the time slot capable of transmitting the data so that the data transmission does not collide with the other wireless node. The communication control method according to claim 9, wherein a search is performed. A communication node that communicates in synchronization with an active period composed of a plurality of fixed-length time slots capable of transmitting and receiving data,
A communication node configured to reserve a time slot in communication of the next active period when transmitting a packet in an arbitrary time slot of an arbitrary active period.   The time slot of the next active period that exists at the same position as the time slot capable of transmitting the packet in the arbitrary time slot of the arbitrary active period is reserved as the time slot in the communication of the next active period. The communication node according to claim 11, configured to be configured as follows.   The communication node according to claim 11, configured to perform processing for transmitting the packet from the head of the time slot in communication in the next active period when the time slot is reserved.   When a packet including a request for reservation of the time slot is received from another radio node, the time slot for data transmission is avoided by avoiding the time slot for which the request for reservation is made by the other radio node. The communication node according to claim 11, configured to select. When a packet including a request for reservation of the time slot is not received from another radio node, the time slot capable of transmitting the data is searched so that the data transmission does not collide with the other radio node. The communication node according to claim 14, which is configured.

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