JP5366920B2 - Wireless communication system, wireless communication method, and wireless communication program - Google Patents

Description

  The present invention relates to a technique for avoiding control signal collision in a multi-hop wireless communication system.

  In recent years, there is a communication network using ZigBee (“ZigBee” in the present specification and drawings is a registered trademark) as a system that is expected to be used and spread in sensor networks and the like (Non-Patent Documents 1 and 2). ). One of the features of this communication network is that multi-hop networks are supported as standard. A router having a relay function performs relay transmission one after another from a parent to a child and from a child to a grandchild, so that an end-to-end communication distance can be dramatically increased. Here, the relay function refers to a function that includes a routing table and performs data transfer based on the routing table.

  ZigBee adopts a CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) method as a method for accessing a wireless medium. In this method, each node transmits after confirming that the signal is not transmitted to the radio channel by carrier sense before transmission, and each node can transmit to other nodes even when it does not transmit the signal. Since it is necessary to always receive a signal from the receiver, the power consumption during standby cannot be ignored.

  On the other hand, in Zigbee, a beacon mode using a super frame configuration is prepared. In the beacon mode, a superframe is defined between a beacon transmitted by the coordinator and the next beacon (beacon period), and the superframe is divided into an active period and the other is divided into an inactive period. While the signal is transmitted during the active period, the signal is not transmitted during the inactive period. Accordingly, since the network is in a dormant state during the inactive period, each node can significantly reduce power consumption.

  FIG. 10 shows a superframe configuration in ZigBee. A superframe is initiated by a beacon. The beacon includes control information such as the network ID and the length of the active (active) period. The beacon is forcibly transmitted at a constant cycle without carrier sense. In the active period after the beacon, a signal is transmitted between the coordinator and the node. The active period is followed by an inactive period, followed by the beginning of the next superframe (beacon). The Active period is divided into 16 time slots, and each time slot is divided into a CAP period (required) and a CFP period (optional). In the CFP period, a GTS (Guaranteed Time Slot) in which the number of communicable nodes is limited to one is provided. The maximum number of GTS is 7. The CAP period is multiple access based on slotted-CSMA / CA, and each node performs carrier sense to check availability and perform transmission / reception. On the other hand, in the GTS period, one or a plurality of dedicated time slots are allocated in advance to a specific node, and there is no need for carrier sense because no collision occurs. Using this superframe configuration, vertical two-way communication (parent to child, child to parent) is performed in each time slot.

  For example, when the communication network configuration shown in FIG. 11 is assumed, it is configured by one coordinator 100 and three nodes (corresponding to routers or end devices) 111, 112, and 113. The super frame starts when the coordinator 100 transmits a beacon. This beacon is received by each node 111, 112, 113. Each node 111, 112, 113 acquires information such as a superframe length, and transmits a signal using the slotted CSMA / CA access method in the subsequent active period.

IEEE Std 802.15.4 Tatsumi Tsuji "ZigBee Development Handbook", Rick Telecom, February 2006

  However, when applying the beacon mode to a multi-hop network, the beacon transmitted by a coordinator or a plurality of routers having coordinator capabilities collides with other beacon signals and data signals, so that superframe control is performed at each node. There is a problem that information is not received normally. That is, a multi-hop network is constructed by connecting a plurality of coordinators to each other in a PtoP type. When each coordinator attempts to operate in a beacon mode for the purpose of power saving of a communication network, each transmits a beacon. There is a need. Here, for example, when coordinators connected in a PtoP manner try to configure their own superframe in synchronization with one superframe, beacons transmitted at the head of the superframe collide. This is a problem that occurs because a beacon is automatically transmitted periodically without performing CSMA, unlike a data signal. Since the beacon includes control information for forming a superframe, if this beacon is lost due to a collision, a node connected to each coordinator cannot transmit a signal, and the communication network fails. As a result, in the conventional technology, there is a problem that the beacon mode cannot be used except in a topology other than the star type.

  On the other hand, since the number of nodes connected to each router is not uniform, if the number of nodes increases, competition in the CAP period becomes intense and packet collisions are likely to occur. It is preferable that flexible access control according to the number can be performed.

  The present invention has been made in view of such circumstances, and each coordinator operates in the beacon mode while shifting the beacon transmission timing, and reduces the probability of packet collision that occurs when there are many connected nodes. It is an object of the present invention to provide a wireless communication system, a wireless communication method, and a wireless communication program that can realize a coordinator.

The present invention is a wireless communication system including a parent wireless terminal that is a basis of a tree topology and a child wireless terminal that is directly connected to the parent wireless terminal, and the parent wireless terminal constitutes the wireless communication system means for obtaining the number of all wireless terminals, on the basis of the number of radio terminals, means for calculating for all child wireless terminal, the total number of slots to be allocated in one superframe, the slot Means for determining the length of the slot from the total number and the beacon transmission period of the first beacon transmitted by the parent wireless terminal; the number of slots to be allocated to each of the child wireless terminals; and the child wireless terminal Means for determining a position of a slot allocated to the child radio terminal so that a slot allocated to the radio terminal does not overlap with another radio terminal;
Means for notifying the length of the slot and the position of the slot allocated to the child radio terminal by the first beacon, wherein the child radio terminal is notified of the slot notified by the first beacon. And a means for transmitting the second beacon by determining a timing for transmitting the second beacon transmitted by the terminal based on the length of the slot and the position of the slot.

The present invention includes a parent wireless terminal that is a basis of a tree topology, a first child wireless terminal that is connected to the parent wireless terminal, and a second child wireless terminal that is connected to the first child wireless terminal. The number of radio terminals that are directly or indirectly connected to each of the subordinate first and second child radio terminals by a tree topology. And the number of slots allocated in one superframe to each of the first child wireless terminal and the second child wireless terminal based on the means for obtaining Means for determining the length of the slot from a total number of the slots and a beacon transmission period of a first beacon transmitted by the parent wireless terminal; and Means for determining the number of lots, the position of the slot assigned to the child radio terminal so that the slot assigned to the child radio terminal does not overlap with other radio terminals, and the length of the slot by the first beacon. Means for notifying a position of a slot to be allocated to the child radio terminal, wherein the first child radio terminal is configured to notify the length of the slot notified by the received first beacon and the parent radio terminal. And the timing of the transmission of the second beacon based on the position of the slot assigned to the self , and the timing of the transmission of the determined second beacon and the length of the slot and the self and its subordinates. Means for transmitting a second beacon including a slot location assigned to a wireless terminal, wherein the second child wireless terminal receives Based on the position on the length of the the position of the second said notified by the beacon of the first child wireless terminal and slot allocated to the self-slot, the timing of transmitting a third beacon by itself to send And a means for transmitting the third beacon at a timing of transmitting the determined third beacon.

  In the present invention, the second child radio terminal starts from the slot assigned to the first child radio terminal from the first slot among slots assigned to the first child radio terminal. The third beacon is transmitted when a time corresponding to a difference in slot positions allocated to the terminal has elapsed.

  The present invention is characterized in that the active slots including the beacons have the same slot length.

The present invention is a wireless communication method in a wireless communication system including a parent wireless terminal that is a basis of a tree topology and a child wireless terminal that is directly connected to the parent wireless terminal, the parent wireless terminal including the wireless communication Obtaining the number of all wireless terminals constituting the system; calculating the total number of slots to be allocated in one superframe for all of the child wireless terminals based on the number of wireless terminals; Determining the length of the slot from the total number of slots and the beacon transmission period of the first beacon transmitted by the parent wireless terminal; the number of slots to be allocated to each of the child wireless terminals; A step of determining the position of the slot allocated to the child radio terminal so that the slot allocated to the child radio terminal does not overlap with other radio terminals. And a step of notifying the length of the slot and the position of the slot to be allocated to the child radio terminal by the first beacon, wherein the child radio terminal is notified by the first beacon. And determining the timing for transmitting the second beacon transmitted by the terminal based on the length of the slot and the position of the slot, and transmitting the second beacon.

The present invention includes a parent wireless terminal that is a basis of a tree topology, a first child wireless terminal that is connected to the parent wireless terminal, and a second child wireless terminal that is connected to the first child wireless terminal. The parent wireless terminal is connected directly or indirectly to each of the subordinate first child wireless terminal and the second child wireless terminal by a tree topology . The step of acquiring the number of wireless terminals, and the slots allocated in one superframe to each of the first child wireless terminal and the second child wireless terminal based on the acquired number of wireless terminals. Calculating the number of slots, determining the length of the slot from the total number of slots and the beacon transmission period of the first beacon transmitted by the parent wireless terminal; Determining the number of slots to be allocated to the child radio terminal, the position of the slot allocated to the child radio terminal so that the slot allocated to the child radio terminal does not overlap with other radio terminals, and the first beacon To notify the length of the slot and the position of the slot to be allocated to the child radio terminal, wherein the first child radio terminal is notified by the received first beacon . Based on the length of the slot and the position of the parent wireless terminal and the slot assigned to itself, it determines the timing at which the terminal transmits a second beacon, and at the timing at which the determined second beacon is transmitted, The second beacon that transmits the second beacon including the length and the position of the slot allocated to the self and subordinate child radio terminals. Tsu has a flop, the second sub wireless terminals located in the length of position and the slot of said received second said notified by the beacon of the first child wireless terminal and slots allocated to self And determining the timing for transmitting the third beacon transmitted by the terminal, and transmitting the third beacon at the timing for transmitting the determined third beacon.

  In the present invention, the second child radio terminal starts from the slot assigned to the first child radio terminal from the first slot among slots assigned to the first child radio terminal. The third beacon is transmitted when a time corresponding to a difference in slot positions allocated to the terminal has elapsed.

  The present invention is characterized in that the active slots including the beacons have the same slot length.

The present invention provides wireless communication that causes a computer on the parent wireless terminal to perform wireless communication processing in a wireless communication system that includes a parent wireless terminal that is a basis of a tree topology and a child wireless terminal that is directly connected to the parent wireless terminal. A program that obtains the number of all wireless terminals constituting the wireless communication system, and should be allocated in one superframe to all of the child wireless terminals based on the number of wireless terminals calculating a total number of slots, the total number of the slots, determining the length of the slot the parent wireless terminal and a beacon transmission period of the first beacon to be transmitted, to each of the child wireless terminal The number of slots to be allocated and the child radio terminal so that the slot allocated to the child radio terminal does not overlap with other radio terminals Determining the position of the slot allocated to the terminal, and notifying the length of the slot and the position of the slot allocated to the child radio terminal by the first beacon. Features.

  According to the present invention, in a multi-hop network having a function in which each node (wireless terminal) having a router function transmits a beacon signal, the entire superframe synchronized with the beacon signal of the parent node is Since the beacon signal position that is the starting point is set to be different, it is possible to perform communication using the beacon mode in a multi-hop topology without using a plurality of frequency channels. . In addition, beacon transmission and payload transmission can be performed without causing interference among a plurality of nodes in the same network. In addition, it is not necessary to share information for making a multi-beacon in the network, and a multi-beacon multi-hop network can be constructed in an autonomous and distributed manner.

It is a block diagram which shows the structure of one Embodiment of this invention. It is a flowchart which shows the processing operation of the coordinator shown in FIG. It is explanatory drawing which shows an example of the connection node number management table hold | maintained in the coordinator shown in FIG. It is a flowchart which shows the processing operation of the router shown in FIG. It is explanatory drawing which shows an example of a communication network structure. It is a figure which shows the beacon transmission operation | movement of each router in the communication network structure shown in FIG. It is explanatory drawing which shows an example of a communication network structure. It is a figure which shows the beacon transmission operation | movement of each router in the communication network structure shown in FIG. It is a figure which shows the beacon transmission operation | movement of each router in the communication network structure shown in FIG. It is a block diagram which shows the structure of the communication network by a prior art. It is explanatory drawing which shows the structure of a super frame.

  Hereinafter, a wireless communication system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. FIG. 1 is a diagram showing a communication network having a maximum depth of 3, a maximum number of child nodes of 4, and a maximum number of child routers of 4. The maximum depth is the number of routers that can be connected in series with respect to the parent coordinator 1 on which the tree topology is based. The maximum number of child nodes is the maximum number of child nodes that can be connected to one router, and the maximum number of child routers is the number of child routers that can be connected to one router. In FIG. 1, reference numeral 1 denotes a coordinator that supervises the processing operation of the router in the communication network shown in FIG. 1, and itself has a router function. The coordinator 1 is given a network address 0 in advance.

  Reference numerals 21, 22, and 23 are routers having a depth of 1 with respect to the coordinator 1, and are connected to the coordinator 1 through a wireless communication transmission path. The routers 21, 22, and 23 are previously assigned network addresses 1, 22, and 43, respectively. Reference numerals 31, 32, and 33 are routers having a depth of 2 with respect to the coordinator 1, and are connected to the router 21 through a wireless communication transmission path. The routers 31, 32, and 33 are previously assigned network addresses 2, 7, and 12, respectively. In the communication network shown in FIG. 1, end devices having a sensor function for measuring temperature and the like are connected to the subordinates of the routers 22 and 23 and the subordinates of the routers 31, 32, and 33 through a wireless communication transmission line as necessary. .

  Reference numeral 11 denotes a control unit that performs overall control of the processing operation of the coordinator 1. Reference numeral 12 denotes a data processing unit that executes predetermined processing on the transmitted and received data. Reference numeral 13 denotes a reception processing unit that receives information from the routers directly below (here, routers 21, 22, and 23). Reference numeral 14 denotes a transmission processing unit that transmits information to the routers directly below (here, routers 21, 22, and 23). Reference numeral 15 denotes a beacon generation unit that generates and assigns a beacon to information to be transmitted from the transmission processing unit 14. Reference numeral 16 denotes a beacon generation timing calculation unit that calculates the generation timing of a beacon generated by the beacon generation unit 15. Reference numeral 17 denotes a switch for switching whether information reception or information transmission is performed by the reception processing unit 13 or the transmission processing unit 14.

  The routers 21 to 23 and 31 to 33 illustrated in FIG. 1 have the same configuration as the coordinator 1 illustrated in FIG. 1, but the router does not necessarily include the beacon generation timing calculation unit 16. Since the configuration of the end device is known, a detailed description thereof is omitted here. Further, the communication network configuration shown in FIG. 1 will be described as configuring a ZigBee network. In the following description, the relationship between the parent and the child will be described as a relative relationship viewed from a certain router. That is, the parent of the router 21 is the coordinator 1, and the children are the three routers 31, 32, and 33. The children of the coordinator 1 are routers 21, 22, and 23, and the grandchildren are routers 31, 32, and 33 and end devices. In the following description, the coordinator 1, routers 21 to 23, 31 to 33, and end devices constituting the communication network are referred to as “nodes” when they are not distinguished from each other. Further, when individual routers are not distinguished, they are simply referred to as routers. The node corresponds to a wireless terminal referred to in the claims.

  Next, the processing operation of the coordinator 1 shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a flowchart showing an operation in which the coordinator 1 shown in FIG. 1 transmits a beacon. First, the beacon generation timing calculation unit 16 of the coordinator 1 calculates the total number of offset slots that need to be allocated in the superframe following the beacon before the beacon generation unit 15 generates the beacon and transmits the generated beacon. The offset slot length is calculated from the total number of offset slots (step S1). An offset slot is a slot of one unit when the beacon period is divided by the number of routing nodes (Rtotal) that can exist under the communication network by ZigBee. In other words, in a single superframe, all subordinate routers transmit beacons (including that data and control signals from other nodes are not transmitted at the same time as beacons) without overlapping each other, and each router is connected. The necessary number of offset slots is calculated so that a CAP period of time corresponding to the number of routers and nodes can be set. Here, the control unit 11 refers to the connection node number management table held therein and acquires the total number of assigned offset slots.

  FIG. 3 shows a table structure of the connection node number management table. In the connection node number management table, the number of nodes connected immediately below and the number of assigned offset slots, which is the number of offset slots to be assigned, are related to the network address of each node (coordinator or router). As a general rule, the number of assigned offset slots is a value obtained by adding 1 to the number of nodes connected to each router. For example, coordinator 1 (network address 0) having 3 connected nodes has 4 assigned offset slots. The router 22 (network address 22) having the number of connection nodes of 0 has an allocation offset slot number of 1. Therefore, in the case of the communication network shown in FIG. 1, the total number of assigned offset slots is 13. Thereby, the coordinator 1 determines that 13 offset slots are necessary in one superframe.

  Next, the beacon generation timing calculation unit 16 of the coordinator 1 calculates the offset slot length Tu by equally dividing one superframe (that is, the beacon interval) into 13 offset slots. In this way, the beacon interval is equally divided by the required number of offset slots and assigned as the active period of each router, thereby avoiding that the active period of each router overlaps. In other words, the offset slots are allocated so that the active period following the beacon does not overlap with other active periods in units of offset slots, and the end of the active period following the beacon matches the end of the offset slot. Subsequently, the beacon generation timing calculation unit 16 calculates the number of offset slots assigned to each router (step S2). As a general rule, the number of offset slots assigned to each router is obtained by adding 1 to the number of connection nodes of the target router. When the number of connection nodes is 0, the number is 1. As a general rule, 1 is added to the number of nodes connected to the router, because an offset slot is allocated according to the number of connected nodes, so that a CAP period in a superframe formed by this router can be increased. This is because it can. Also, when the number of connected nodes is 0, an offset slot is not assigned, and at least one offset slot is assigned in order to prevent the router from transmitting a beacon.

  In order to update the connection node count management table shown in FIG. 3, each router indicates connection / disconnection to the coordinator 1 when an end device or router is connected / disconnected to itself. The information is notified, and the coordinator 1 updates the connection node number management table based on the notified information.

  Next, the beacon generation timing calculation unit 16 calculates the offset value of each router (step S3). Here, the offset value is for determining the timing at which the router transmits a beacon, and indicates how many offset slots after which the coordinator 1 transmits a beacon and its own router should transmit the beacon. Is. The offset value is obtained from the network address of each router and the number of offset slots assigned to each router, and in order from the coordinator 1, an offset value having a smaller number is given as it is positioned higher in the network.

  Further, when a plurality of offset slots are assigned to the router with the previous offset value, the offset value becomes a skipped value. For example, since 4 offset slots are assigned to the coordinator 1 that is the network address 0 and the router 21 that is the network address 1, the offset values for the router 21 that is the network address 1 and the router 22 that is the network address 22 are skipped. The offset value of the subsequent router is assigned a large value one by one.

  Next, the beacon generation timing calculation unit 16 notifies the beacon generation unit 15 of (1) the offset slot length, (2) the number of offset slots assigned to each router, and (3) the offset value of each router. In response to this, the beacon generation unit 15 generates a beacon including (1) the offset slot length, (2) the number of offset slots assigned to each router, and (3) the offset value of each router, and transmits the generated beacon. It transmits via the processing unit 14 (step S4). This beacon includes the offset values and the number of assigned offset slots for all the subordinate routers. Each router relays the offset value and the number of assigned offset slots by a beacon for the subordinate routers.

Next, a processing operation in which each router other than the coordinator 1 performs beacon transmission will be described with reference to FIG. FIG. 4 is a flowchart showing the processing operation of the router shown in FIG. First, the router acquires (1) the offset slot length, (2) the number of offset slots assigned to each router, and (3) the offset value of each router from the beacon received from the parent (step S11). These are all values calculated by the beacon generation timing calculation unit 16 of the coordinator 1. Subsequently, the router performs the following calculation to obtain its beacon timing (step S12).
Beacon timing = (Self offset value-Parent offset value) x Offset slot length

  That is, the relative value of its own offset value is calculated based on the parent offset value, and the time obtained by multiplying this by the offset slot length is the time elapsed after the parent beacon is transmitted. Is the timing for transmitting a beacon. In the ZigBee network, although the parent beacon can be received in most cases, it is not guaranteed whether the beacon of another router can be received. Therefore, not all routers can receive the coordinator 1 beacon. Therefore, it is necessary that the beacon timing of the child can be calculated based on the beacon transmitted by the parent. As described above, each router can transmit beacons in an autonomous decentralized manner by adopting an address system that can recognize the timing at which the beacon can be transmitted based on the offset value between the parent and the self.

  Next, the router generates a beacon including (1) an offset slot length, (2) an assigned offset slot length of each subordinate router, and (3) an offset value of each subordinate router (step S13). Then, the router transmits the previously generated beacon at the calculated beacon timing (step S14). That is, only information related to the subordinate routers is extracted and notified by a beacon in the same manner as the coordinator 1.

  Each router constitutes a CAP period and GTS in the superframe following the beacon. Since the routers connected by a plurality of nodes are assigned the number of offset slots corresponding to the number, more A long superframe length (active period) is assigned. Thus, by grasping its own offset value by the relative value from the offset value of the coordinator 1, each router can always grasp the timing of transmitting its own beacon (even when the beacon of the coordinator 1 does not arrive). In addition, since all routers transmit beacons according to the router offset value notified by the coordinator 1, it is guaranteed that beacons transmitted by all routers do not overlap.

  In addition, since the length of the active period of each superframe is calculated based on the number of offset slots required in one superframe, the active periods in the superframes of all routers do not overlap. As a result, a situation where a beacon cannot be received due to an interference signal from another node can be avoided. Also, since each router can be assigned an offset slot according to the number of nodes (routers and end devices) connected to itself, more offset slots can be set as a CAP period accordingly. The probability of packet collision will be reduced.

  Next, a beacon transmission operation will be described with a specific example. FIG. 5 shows the configuration of the entire communication network. In FIG. 5, each circle indicates a node, and the highest node corresponds to the coordinator 1. A straight line between the nodes represents a wireless communication transmission path, and a value in each circle indicates a network address. In the example shown in FIG. 5, four routers are connected to the highest node (corresponding to coordinator 1), and the node (router or end device) with network address 23 is connected to the router with network address 22. Has been. Similarly, two nodes are connected to the router having the network address 64, and a node (router or end device) having the network address 76 is connected to the router having the network address 75.

  A beacon transmission operation in the communication network shown in FIG. 5 will be described with reference to FIG. In FIG. 6, a period indicated by hatching indicates an inactive period (inactive period), and a period without hatching indicates an active period (active period) to which a beacon is assigned. As shown in FIG. 5, the offset value of the node of the network address 1 is 1, the offset value of the node of the network address 22 is 2, the offset value of the node of the network address 43 is 4, and the offset value of the node of the network address 64 is 5. The offset value of the node of the network address 75 is 7, the offset value of the node of the network address 80 is 8, and the beacon transmitted from each node and the active period are arranged so as to deviate from each other. Overlap can be prevented.

  Also, a long usable time is allocated to a router having a large number of child nodes. Thus, by shifting the start timing of beacon transmission, it is possible to avoid interference between beacon signals and data signals of routing nodes that use the same frequency. In addition, since the most significant node (corresponding to the coordinator 1) manages the allocation of the active period length and the offset value in an integrated manner, the management considering the load balance of the entire communication network can be realized.

  Next, the beacon transmission operation when the communication network configuration is different will be described. FIG. 7 is a diagram showing the communication network configuration when the communication network configuration is different. As shown in FIG. 7, three nodes having a depth of 1 are connected to the highest node (network address 0), and a node having a depth of 2 is connected to the node having the network address 1.

A beacon transmission operation in the communication network shown in FIG. 7 will be described with reference to FIG. As shown in FIG. 8, the router with the network address 1 can control the total available time given to the subordinate node group for each child node (nodes with the network addresses 2, 3, and 12). Thereby, adaptive time resource allocation according to routing and network load can be performed. In addition, the depth N router needs to manage the usable time and the frame offset amount with respect to the depth N + 1 router, and provide a signal format for communicating with each routing device. The end device does not require any modification . Further, network entry may be performed for a parent node having a beacon with the highest reception level, and various control information is completely concealed, so that the utilization efficiency of radio resources can be improved.

  It should be noted that guard times (Tg1, Tg2) may be provided before and after each offset slot in consideration of low time synchronization accuracy between the routers or considering propagation delays in the antenna. In this case, as the active period Tactive in the superframe of each router, as shown in FIG. 9, Tactive satisfying (Tg1 + Tactive + Tg2) <(Tb / Rtotal) may be set. When each node detects multiple parent nodes when connecting to the parent node, it measures the received power of the beacon signal transmitted by each parent and transmits the beacon signal with the highest reception level. It is only necessary to connect to the parent node.

In addition, the beacon period (active time + inactive time) is Tb, the maximum number of routing nodes that can exist in the communication network is Rtotal, the active time length of the Active router i is BSD × 2 ^{SO (i)} , where i = 1, 2, ..., Ni (Ni <= Rtotal), the guard time of Active router i is Tg1, Tg2, the number of offset slots occupied by Active router i is Si, and Tg1 + BSD × 2SO ⁽ⁱ⁾ + Tg2 <Tb / Rtotal) × Si As a constraint condition, the number of offset slots Si to be assigned to the Active router i may be adaptively determined according to the number of child nodes under the Active router or the total transmission rate requested by the Active router. At this time, a combination of Si that maximizes ΣSi (maximum time efficiency) may be determined.

  In this way, in a multi-hop network having a function in which each node having a router function transmits a beacon signal, the entire superframe synchronized with the beacon signal of the parent node is the beacon signal that is the starting point of the superframe for each node. Since the positions are set to be different, it is possible to perform communication using the beacon mode in a multi-hop topology without using a plurality of frequency channels. In addition, beacon transmission and payload transmission can be performed without causing interference among a plurality of nodes in the same network. In addition, it is not necessary to share information for making a multi-beacon in the network, and a multi-beacon multi-hop network can be constructed in an autonomous and distributed manner.

  As described above, in conventional ZigBee, since access control is performed based on CSMA / CA, in order to perform a power saving operation, an active period in which data communication is performed and an inactive period in which the power saving operation is performed. The super frame comprised by this was formed. Here, the super frame is started by a beacon signal. When a network in which each of a plurality of wireless terminals other than the star type (for example, a tree type) needs to form a super frame is constructed, the beacon signal is used. There is a problem that control information cannot be acquired due to collision. Therefore, in a superframe having a period corresponding to a cycle in which a parent node transmits a beacon for a tree topology (configured by nodes such as a parent wireless terminal, a child wireless terminal, and a grandchild wireless terminal), this superframe Is divided into equal offset slots based on the number of nodes connected to this topology, and each offset slot is assigned to each node (router) according to the number of connected terminals. Thereby, the offset slot allocated to each node does not overlap between nodes, and it is possible to avoid collision of beacon signals. Since each node can obtain the number of offset slots according to the number of nodes connected to itself, it reduces the probability of packet collision caused by offset slot contention when the number of nodes under one node is large. be able to.

  Here, since each node (for example, grandchild node) does not necessarily receive the beacon of the parent node, each node is connected to the node to which it is connected (for example, a child node). The offset slot assigned to itself is notified, and a beacon is transmitted based on the relative position between the offset slot assigned to itself and the offset slot assigned to the parent node. That is, a beacon is transmitted after the offset slot assigned to the parent node for a time corresponding to the difference between the position of the offset slot assigned to itself and the position of the offset slot assigned to the parent node. . With this configuration, each node can accurately know the timing at which the node should transmit a beacon.

  The program for realizing the function of the processing unit in FIG. 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into the computer system and executed to calculate the beacon generation timing. Processing may be performed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, what is called a difference file (difference program) may be sufficient.

  When beacon mode is applied to a multi-hop network, it is applied to applications where it is indispensable to solve the problem that superframe control information is not normally received at each node due to collision of beacons sent by multiple coordinators. it can.

  DESCRIPTION OF SYMBOLS 1 ... Coordinator, 11 ... Control part, 12 ... Data processing part, 13 ... Reception processing part, 14 ... Transmission processing part, 15 ... Beacon generation part, 16 ... Beacon Generation timing calculation unit, 17... Switch, 21, 22, 23... Router, 31, 32, 33.

Claims (9)

A wireless communication system including a parent wireless terminal that is a basis of a tree topology and a child wireless terminal that is directly connected to the parent wireless terminal,
The parent wireless terminal is
Means for obtaining the number of all wireless terminals constituting the wireless communication system;
Means for calculating the total number of slots to be allocated in one superframe for all of the child radio terminals based on the number of radio terminals;
Means for determining the length of the slot from the total number of slots and a beacon transmission period of a first beacon transmitted by the parent wireless terminal;
Means for determining the number of slots to be allocated to each of the child radio terminals and the position of the slot allocated to the child radio terminals so that the slots allocated to the child radio terminals do not overlap with other radio terminals;
Means for notifying the length of the slot and the position of the slot to be allocated to the child radio terminal by the first beacon;
The child radio terminal is
Means for determining the timing for transmitting a second beacon transmitted by itself based on the length of the slot and the position of the slot notified by the first beacon, and transmitting the second beacon. A wireless communication system. A wireless communication system including a parent wireless terminal that is a basis of a tree topology, a first child wireless terminal that is connected to the parent wireless terminal, and a second child wireless terminal that is connected to the first child wireless terminal And the parent wireless terminal is
Means for acquiring the number of wireless terminals directly or indirectly connected to each of the subordinate first and second child wireless terminals by a tree topology ;
Means for calculating the number of slots to be allocated in one superframe for each of the first child wireless terminal and the second child wireless terminal based on the acquired number of wireless terminals;
Means for determining the length of the slot from the total number of slots and a beacon transmission period of a first beacon transmitted by the parent wireless terminal;
Means for determining the number of slots to be allocated to the child radio terminal and the position of the slot allocated to the child radio terminal so that the slot allocated to the child radio terminal does not overlap with other radio terminals;
Means for notifying the length of the slot and the position of the slot to be allocated to the child radio terminal by the first beacon;
The first child radio terminal is
Based on the length of the slot notified by the received first beacon and the position of the parent wireless terminal and the slot allocated to the self , the timing for the self to transmit the second beacon is determined, and the determined Means for transmitting a second beacon including the length of the slot at the timing of transmitting the second beacon and the position of the slot assigned to the self and subordinate child radio terminals;
The second child radio terminal is
Based on the position of the first child radio terminal notified by the received second beacon and the slot allocated to itself and the length of the slot, a third beacon transmitted by itself is transmitted. A wireless communication system comprising: means for determining a timing and transmitting the third beacon at a timing for transmitting the determined third beacon. The second child radio terminal is
Of the slots assigned to the first child radio terminal, the difference from the position of the slot assigned to the first child radio terminal to the position of the slot assigned to the first child radio terminal is calculated from the first slot. The wireless communication system according to claim 2, wherein the third beacon is transmitted when time has elapsed. The wireless communication system according to claim 1, item 1 to any of the 3, characterized in that the end of the active period subsequent to the beacon, the end of the slot match. A wireless communication method in a wireless communication system including a parent wireless terminal that is a basis of a tree topology and a child wireless terminal that is directly connected to the parent wireless terminal,
The parent wireless terminal is
Obtaining the number of all wireless terminals constituting the wireless communication system;
Calculating the total number of slots to be allocated in one superframe for all of the child wireless terminals based on the number of wireless terminals;
Determining the length of the slot from the total number of slots and the beacon transmission period of the first beacon transmitted by the parent wireless terminal;
Determining the number of slots to be assigned to each of the child wireless terminals, and the position of the slot assigned to the child wireless terminals so that the slots assigned to the child wireless terminals do not overlap with other wireless terminals;
Notifying the length of the slot and the position of the slot to be assigned to the child radio terminal by the first beacon;
The child radio terminal is
Determining the timing for transmitting the second beacon transmitted by the terminal based on the length of the slot and the position of the slot notified by the first beacon, and transmitting the second beacon. A wireless communication method. A wireless communication system including a parent wireless terminal that is a basis of a tree topology, a first child wireless terminal that is connected to the parent wireless terminal, and a second child wireless terminal that is connected to the first child wireless terminal A wireless communication method in
The parent wireless terminal is
Obtaining the number of wireless terminals directly or indirectly connected to each of the subordinate first child wireless terminal and the second child wireless terminal by a tree topology ;
Calculating the number of slots to be allocated in one superframe for each of the first child wireless terminal and the second child wireless terminal based on the acquired number of wireless terminals;
Determining the length of the slot from the total number of slots and the beacon transmission period of the first beacon transmitted by the parent wireless terminal;
Determining the number of slots to be allocated to the child radio terminal and the position of the slot allocated to the child radio terminal so that the slot allocated to the child radio terminal does not overlap with other radio terminals;
Notifying the length of the slot and the position of the slot to be assigned to the child radio terminal by the first beacon;
The first child radio terminal is
Based on the length of the slot notified by the received first beacon and the position of the parent wireless terminal and the slot allocated to the self , the timing for the self to transmit the second beacon is determined, and the determined Transmitting a second beacon including the length of the slot and the position of the slot assigned to the self and subordinate child radio terminals at the timing of transmitting the second beacon;
The second child radio terminal is
Based on the position of the first child radio terminal notified by the received second beacon and the slot allocated to itself and the length of the slot, a third beacon transmitted by itself is transmitted. A wireless communication method comprising: determining a timing, and transmitting the third beacon at a timing for transmitting the determined third beacon. The second child radio terminal is
Of the slots assigned to the first child radio terminal, the difference from the position of the slot assigned to the first child radio terminal to the position of the slot assigned to the first child radio terminal is calculated from the first slot. The wireless communication method according to claim 6, wherein the third beacon is transmitted when time has elapsed. And end of the active period subsequent to the beacon, the radio communication method according to any one of claims 5 7, characterized in that the end of the slots that match. A wireless communication program that causes a computer on the parent wireless terminal to perform wireless communication processing in a wireless communication system including a parent wireless terminal that is a basis of a tree topology and a child wireless terminal that is directly connected to the parent wireless terminal. ,
Obtaining the number of all wireless terminals constituting the wireless communication system;
Calculating the total number of slots to be allocated in one superframe for all of the child wireless terminals based on the number of wireless terminals;
Determining the length of the slot from the total number of slots and the beacon transmission period of the first beacon transmitted by the parent wireless terminal;
Determining the number of slots to be assigned to each of the child wireless terminals, and the position of the slot assigned to the child wireless terminals so that the slots assigned to the child wireless terminals do not overlap with other wireless terminals;
A wireless communication program causing the computer to perform a step of notifying the length of the slot and the position of the slot to be assigned to the child wireless terminal by the first beacon.

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