JP2009296215A - Wireless multihop communication device, and communication control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish synchronization among adjacent nodes operating intermittently in a wireless multihop network. <P>SOLUTION: A wireless multihop communication device and a communication control method therefor have an active state and a sleep state. The active state in which communication with an adjacent node is possible, continues for an active period determined by given conditions from a return time determined based on a relative return time of an adjacent node in response to the reception of synchronized packet including the relative return time from a synchronized packet transmission time to its return time of the adjacent node, from the adjacent node included in the wireless multihop network wherein a maximum sleep time is set. The sleep state in which communication with an adjacent node is impossible, starts from a start of resting period starting after the active period elapses. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a node (wireless multihop communication apparatus) that relays a packet and a communication control method thereof in a wireless multihop network, and more particularly to a synchronization technique for communicating with an adjacent node.

In a wireless network, there is an ad hoc network technology that dynamically configures a wireless multi-hop network between nodes. In an ad hoc network, each node has a packet relay function, and performs multi-hop communication by transmitting / forwarding packets according to the routing table of each node. In an ad hoc network, it is possible to build a wireless network without performing wiring work by arranging battery-driven relay nodes. However, the wireless communication area becomes narrower and communication is impossible due to the battery of the relay node running out. It becomes. In order to use the wireless network for a long time, it is desirable to save power in the relay node. In a wireless multi-hop network, there is a technique described in Patent Document 1 as a technique for reducing the power consumption of a relay node. In the power saving technique described in Patent Document 1, the time of the relay node is adjusted to the time of the base station (time synchronization), and the relay node sleeps and returns at a predetermined time to perform an intermittent operation. Further, there is a technique described in Patent Document 2 that performs an intermittent operation without performing time synchronization of relay nodes.

Japanese Unexamined Patent Publication No. 2007-116408 JP 2007-318676

With the technique described in Patent Document 1, it is possible to return and sleep at a time at which the relay nodes constituting the wireless multi-hop network can communicate, but a base station for performing time synchronization is required. However, when a battery-driven relay node is arranged and a wireless network is immediately constructed, there is not always a base station that performs time synchronization, and it is not possible to synchronize intermittent operations without time synchronization. There is.

  In addition, the technology described in Patent Document 2 enables communication in intermittent operation without performing time synchronization between relay nodes, but a communication path (communication partner) is determined in advance, and a predetermined period after response transmission / reception is performed. The synchronization is maintained by the suspension, and it is not considered that a relay node is arranged to dynamically construct a communication path or newly establish synchronization.

The wireless multi-hop communication device and the communication control method thereof according to the present invention provide a relative return time of an adjacent node (time from a synchronous packet transmission time to a return time) from an adjacent node included in the wireless multi-hop network in which a maximum sleep time is set. In response to the reception of the synchronization packet including), the active state that can be communicated with the adjacent node from the return time determined based on the relative return time of the adjacent node for the active time determined from the given condition; And a sleep state in which communication with an adjacent node is impossible from the suspension time after the active time has elapsed.

  In another desirable aspect of the present invention, the given condition is one of a condition relating to power saving and an active time of an adjacent node included in the synchronization packet.

  According to still another desirable aspect of the present invention, the sleep state is at most the time obtained by subtracting the active time from the maximum sleep time.

  According to still another preferred aspect of the present invention, in response to receiving one of a routing packet and a data packet for establishing a communication path from another adjacent node included in the wireless multi-hop network, When in the active state, the packet is transmitted to the adjacent node.

  According to still another desirable aspect of the present invention, when a packet is received and in a sleep state where communication with the adjacent node is impossible, the transmission of the packet to the adjacent node is waited until the active state is reached.

  Another aspect of the present invention is the reception of a synchronization packet including the relative return time (time from the synchronization packet transmission time to the return time) of the adjacent node from the adjacent node included in the wireless multi-hop network in which the maximum sleep time is set. Active state in which communication is possible with an adjacent node for an active time determined from a given condition from a return time determined based on a relative return time of the adjacent node included in the synchronization packet received by the wireless communication unit And a timer for controlling a sleep time during which a sleep state in which communication with an adjacent node is impossible from the suspension time after the active time elapses continues.

  In another desirable aspect of the present invention, the CPU executes a sleep command for shifting to a sleep state in which power consumption other than that required for returning to the active state is suppressed as much as possible at the pause time.

  In another desirable aspect of the present invention, at the end of the sleep time, the timer outputs a return signal to the CPU, and the CPU shifts from the sleep state to the active state in response to the input of the return signal.

  According to still another desirable aspect of the present invention, the wireless communication unit receives one of a routing packet and a data packet for establishing a communication path from another adjacent node included in the wireless multi-hop network. Then, the CPU controls the wireless communication unit so as to transmit the received packet to the adjacent node when in the active state.

  Still another desirable aspect of the present invention includes a memory for storing a routing packet when the packet is received and in a sleep state where communication with an adjacent node is impossible.

According to the present invention, it is possible to synchronize the return timing of the intermittent operation without providing time synchronization between adjacent nodes (providing a communication time zone).

Embodiments of the present invention will be described below. In the present specification, terms are used as follows. A node (wireless multi-hop communication device) that relays packets in a wireless multi-hop network is called a relay node. Although referred to as a relay node, the node itself may be the entity that transmits and receives information. An adjacent relay node is called an adjacent node. Adjacent means that packets can be directly transmitted and received. The relay node has a communicable state and a communicable state, and the former is called an active state and the latter is called a sleep state. The change (transition) of the relay node from the sleep state to the active state is called (returned), and the change (transition) from the active state to the sleep state is called pause (perform). These state change times are referred to as return time and pause time, respectively, and the duration of the state is referred to as active time and sleep time. Other terms will be described as necessary.

  FIG. 1 is a diagram illustrating an example of the topology of a wireless multi-hop network in the present embodiment. In FIG. 1, reference numerals 101 to 109 denote relay nodes, which can communicate between adjacent relay nodes. In FIG. 1, the state of being adjacent to each other is represented by a branch connecting the nodes. For example, the relay node 101 is adjacent to and can communicate with the relay node 102 and the relay node 106. Relay node 102 is adjacent to and can communicate with relay node 101 and relay node 103, respectively. The relay nodes 103 to 109 are as illustrated.

  FIG. 2 is a diagram illustrating a configuration example of the relay node 1. The relay node 1 has a configuration in which a CPU 3, a wireless communication unit 4, a memory 5, and a timer 6 are connected to each other, and the antenna 2 is connected to the wireless communication unit 4. The battery 7 supplies power to each part of the relay node 1. The relay node 1 has an active state and a sleep state as described above, and each part of the relay node 1 shifts from the active state to the sleep state by the execution of the sleep command by the CPU 3. In the sleep state, the relay node 1 is in the power saving state. The power saving state is a state in which power consumption other than power necessary for each unit of the relay node 1 to return from the sleep state to the active state is suppressed as much as possible. On the other hand, when the sleep time for continuing the sleep state is set in the timer 6 when the CPU 3 enters the sleep state, the timer 6 sends a return signal (wake-up signal) to the CPU 3 after the sleep time elapses, and the CPU 3 responds to the return signal. Shifts relay node 1 to the active state.

  A maximum sleep time (Ts) is set for each of the relay nodes 101 to 109 in FIG. Each relay node controls so that there is a time during which communication with all adjacent nodes in the network is possible at least once during the maximum sleep time (Ts). Each relay node can communicate with the adjacent node by returning to the active time of the adjacent node. The return time is the time at which the relay node returns to the active state as described above, but the time of each relay node is synchronized (the time of the timer 6 of each relay node is the same (clock is set). The elapsed time from the start time of each relay node is set as the absolute time for each relay node.

  In this embodiment, it is not necessary for all relay nodes in the network to return at the same time, and each relay node only needs to obtain a common time zone in each active time with an adjacent node. Even if there are multiple adjacent nodes in a certain relay node and the common time zone between the adjacent nodes is different during the active time, the common time in the active time with each adjacent node It is possible to communicate with the band. In this way, a relay node having a common time zone in its active time with an adjacent node is called synchronization between adjacent nodes.

FIG. 3 shows an example of establishing synchronization between adjacent nodes. FIG. 5 is an example in which the relay nodes 101 to 106 and the relay node 109 are synchronized in the topology shown in FIG. This represents a temporal change between an active state (hatched portion) and a sleep state (white portion) of a relay node (represented by (number) in the figure). In order to make the explanation easy to understand, time is exemplified as necessary. Illustrative times are as follows. Corresponding to the passage of time in the figure, time t ₀ is −500 ms, time t ₁ is −250 ms, time t ₂ is 0 ms, time t ₃ is 500 ms, time t ₄ is 1250 ms, time t ₅ is 1500 ms, time t ₆ is 2000 ms, and time t ₇ is 2250 ms. The maximum sleep time (Ts) is 2000 ms.

At the time t ₀ (the absolute time 0 ms of the relay node 102), the relay nodes 105 to 109 have already established synchronization between adjacent nodes. The relay node 102 at time t _0, the relay node 103 at time t _1, the relay node 101 time t _2, the relay node 104 at time t _3, a launch (power is turned on, the operation start) is. Synchronization packet 31 from the relay node 106 at time t ₄ is the time t ₅ the sync packet 32 from the relay node 102 is transmitted.

  Processing for establishing synchronization between adjacent nodes will be described according to the synchronization flowchart between adjacent nodes shown in FIG. 4 using the example of the relay node 101 in FIG. The relay node 101 checks whether or not a certain time has elapsed after startup (step 405). The fixed time is set to a time longer than the maximum sleep time (Ts) (Ts ≦ fixed time). This is because each relay node is controlled so that there is a time during which communication can be performed with all adjacent nodes in the network at least once during the maximum sleep time (Ts). If the fixed time has not elapsed, the process proceeds to step 410, and if the fixed time has elapsed, the process proceeds to step 420.

  The reception of the synchronization packet is checked (step 410). If a synchronization packet is received, the process proceeds to step 413. If no synchronization packet is received, the process returns to step 405.

  A format example of the payload portion 50 of the synchronization packet is shown in FIG. In the payload portion 50 of the synchronization packet, the own node ID 51, the relative return time 52, and the active time 53 are stored. For the own node ID 51, an identifier for identifying a relay node such as an IP address or a node number is used. The relative return time 52 stores the time from the transmission time to the return time at the relay node that is the synchronization packet transmission source. The active time 53 stores the time during which the active state continues after the relay node that is the source of the synchronization packet is restored.

  If a synchronization packet transmitted from an adjacent node has been received, a communicable time management table is created based on the received synchronization packet (step 415), and the process returns to step 405.

3, the relay node 101 starts to time t _2, the receive synchronization packet 31 at time t ₄ from the relay node 106, and receives a synchronization packet 32 from the relay node 102 at time 514 t _5. The synchronization packet 31 from the relay node 106 stores 106 in its own node ID 51, 0 at the relative return time 52, and T _6A (500 ms) at the active time 53, and the synchronization packet 32 from the relay node 102 has its own node Assume that ID 51 is stored, T _2S (750 ms) is stored at relative return time 52, and T _2A (500 ms) is stored at active time 303.

In FIG. 6 (a), showing an example of neighbor nodes communicable time management table 60 at time t ₄ of the relay node 101. In the adjacent node ID 62, the own node ID 51 stored in the received synchronization packet 31 is stored. A column 61 of the adjacent node communicable time management table 60 is information on the adjacent node ID 62 of “106”.

The return time 63 represents the return time of the source relay node of the synchronization packet as an absolute time at the relay node that received the synchronization packet, and is based on the sum of the relative return time 52 stored in the received synchronization packet and the current time. Find and store. For example, the absolute time t ₄ −t ₂ (1250 ms) of the relay node 101 is the current time, the return time 63 when the adjacent node ID 62 is “106” is the time t ₄ (1250 ms), and this is the absolute time of the relay node 101. Is represented by t ₄ −t ₂ (1250 ms), and the sum of the absolute time and the relative return time “0” in the synchronization packet 31 is t ₄ −t ₂ (1250 ms). Therefore, the active time of the adjacent node 106 is from now.

In the active time 64, the active time 53 stored in the received synchronization packet is stored. For example, the active time 64 when the adjacent node ID 62 is “106” is T _6A (500 ms). The pause time 65 stores the time when the adjacent node pauses, that is, the time when the active state ends. The pause time 65 is an absolute time and stores the sum of the return time 63 and the active time 53 of the synchronization packet. For example, the pause time 65 when the adjacent node ID 62 is “106” is t ₄ −t ₂ + T _6A (1750 ms), and is in the active state from the return time t ₄ −t ₂ (1250 ms) to T _6A (500 ms). It shows that there is.

The recording time 66 stores the time when the information in the column of the adjacent node communicable time management table 60 is recorded. The recording time 66 when the adjacent node ID 62 is “106” is the absolute time t ₄ −t ₂ (1250 ms).

Returning to FIG. Until the fixed time has elapsed (step 405), the process of checking the synchronization packet reception (step 410) and creating the adjacent node communicable time management table 60 when the synchronization packet is received (step 415) are repeated. This iterative process, with respect to synchronization packets 32 received at time t _4, the neighboring node communicatively time management table 60 of relay node 101, as shown in FIG. 6 (b), the column 67 is added.

  It is checked whether a synchronization packet has been received within a certain time (step 420). If no synchronization packet has been received, the process proceeds to step 435. If received, the adjacent node communication time management table 60 is updated (step 425). The update target is a return time 63, a pause time 65, and a recording time 66.

  FIG. 7 shows a flowchart of the update process of the adjacent node communicable time management table 60. The current time is compared with the return time (step 705). If the return time is in the past (return time <current time), the return time 63 is updated (step 710) and the pause time 65 is updated (step 715). . The result of adding the maximum sleep time (Ts) to the return time 63 is set as the next return time 63. The time when the active time 64 has elapsed from the next return time 63 is defined as the next pause time 65. The current time when the adjacent node communication time management table 60 is updated is set as a recording time 66 (step 720).

FIG. 6C shows the result of the relay node 101 updating the adjacent node communicable time management table 60 at time t ₆ (2000 ms). The return time 63 when the adjacent node ID 62 is “106” is t ₄ −t ₂ + Ts (3250 ms), and the return time 63 when the adjacent node ID 62 is “102” is t ₇ −t ₂ (2250 ms). The pause time 65 when the adjacent node ID 62 is “106” is t ₄ −t ₂ + Ts + T _6A (3750 ms), and the pause time 65 when the adjacent node ID 62 is “102” is t ₇ −t ₂ + T _2A (2750 ms). The recording time 66 is the current time t ₆ −t ₂ , t ₆ −t ₂ (2000 ms) is stored in the recording time 66 of the adjacent node ID 62 “106”, and the adjacent node ID 62 is “102”. Store t ₆ −t ₂ (2000 ms) at recording time 66.

  Returning to FIG. The return time and active time of the relay node are set (step 430). The return time and the active time of the relay node are obtained by the union of the times in the active state expressed by Equation (1).

l _n ≦ x ≦ m _n (1)
Here, x is the time in the active state, l _n is the return time 63 in column n of the adjacent node communicable time management table 60, and _mn is the suspension time.

  In each column of the adjacent node communicable time management table 60, the time x in the active state represented by the expression (1) is obtained, and the union of x in all the columns becomes the time when the relay node is in the active state. . x may be divided into several sections within the maximum sleep time (Ts). The start time of each section is set as the return time, and the end time of the section is set as the pause time. Ask for time.

  The time during which the relay node may be in the active state during the maximum sleep time (Ts) is defined as the active time, and the time x in the active state is applied when the active time is not defined. In order to maintain the battery of the relay node longer, an active time is set in advance in the relay node. The active time of the relay node does not have to be the same for all the relay nodes, and may be obtained from the battery capacity installed in the relay node and the desired operation time of the relay node.

  When the active time is set, the time x in the active state may have a section length exceeding the active time. At this time, it is necessary to keep the length of the section of time x in the active state within the active time. FIG. 8 shows a flowchart of the process for obtaining the active time when the active time is set.

  The number of adjacent node IDs (number of columns in the table) n is obtained from the adjacent node communicable management table 60 (step 805). When there are a plurality of columns having the same adjacent node ID and different return times 63, etc., they are counted multiple times.

Tn is determined by Tn = T ÷ n, where Tn is the recoverable time per adjacent node and T is the recoverable time (step 810). If there is a column in the adjacent node communicable management table 60 for which the time x in the active state is not obtained (step 815), it is checked whether m _n > l _n + Tn (step 820). If m _n > l _n + Tn, the relay node is in an active state after the suspension time of the adjacent node. Therefore, if m _n > l _n + Tn, in order to suppress battery consumption, l _n ≦ x ≦ l _n + Tn is set (step 825). If m _n > l _n + Tn, l _n ≦ x ≤ m _n (step 830). A union of the obtained x is obtained (step 835).

  Although Tn = T ÷ n, the active possible time per adjacent node in the adjacent node communication management table 60 is Tn, and the sum ΣTn only needs to satisfy ΣTn ≦ T. Each active possible time Tn may be determined.

  X obtained when the active possible time is set according to the above flow may be divided into several sections in the maximum sleep time (Ts), and the start time of each section is set as the return time and the end of the section. By setting the time as the pause time, the return time and active time of the relay node can be obtained.

  The obtained return time and active time are stored in the return time management table. An example of the return time management table 90 of the relay node 101 is shown in FIG. The return time 93 is the return time of the relay node and is stored as an absolute time. The column 91 is a description relating to the return time 93 being 3250 ms, and the column 92 is a description relating to the return time 93 being 2250 ms.

The active time 94 stores the time during which the active state is continued. For example, when the time when this table is created is t ₆ (2000 ms) and the returnable time of the relay node 101 is set to 500 ms, Tn = T ÷ n = 500 ms ÷ 2 = 250 ms and the return time 93 The active time 94 of 3250 ms is 250 ms, and the active time 94 of the return time 93 of 2250 ms is 250 ms. The suspension time 95 stores the time for ending the active state. For example, the pause time 95 when the return time 93 is 3250 ms is 3500 ms, and the pause time 95 when the return time 93 is 2250 ms is 2500 ms. The recording time 96 is the time when the table is created or updated, and stores the absolute time from the start of the relay node.

  When the communicable time of the relay node 101 is not set, the return time 63 of the adjacent node communicable time management table 60 (FIG. 6 (c)) is 3250ms and 2250ms, and the active time is 500ms. When 500 ms is set, the return time 93 as shown in FIG. 9 is the same time (3250 ms and 2250 ms) as described above, but the active time is 250 ms. The above is the process for setting the return time and the active time in step 430. Next, the process proceeds to step 440.

  If the synchronization packet has not been received (step 420), the process proceeds to step 435. The return time and active time are set, but the adjacent node is not found (the synchronization packet has not been received), so the return time is set using a random value or a fixed value (step 435). The active time is set as a recoverable time if a recoverable time is set, and a random value or a fixed value is set if the recoverable time is not set. The value set here is stored in the return time management table 90.

  A synchronization packet is transmitted (step 440). The synchronization packet is transmitted by broadcast or multicast in order to reach a communicable adjacent node. The format of the synchronization packet is shown in FIG. 5. The relative return time 52 stores the difference between the value of the return time 93 in the return time management table 90 and the current time, and the active time 53 stores the active time 94 in the return time management table 90. Stores the value of. A plurality of return times and active times may be stored in the format.

The relay node continues to sleep until the next return time (step 445). For example, the next return time of the relay node 101 is the earliest return time 93 of the return time management table 90 is a 2250ms, because the current time (creation time of the return time management table) is 2000ms, until time t ₇ after 250ms Sleep.

  The relay node returns when the return time comes. FIG. 10 shows a return processing flowchart of the relay node at the time of return.

  When the relay node returns, it transmits a synchronization packet (step 1005). The synchronization packet transmission process is the same as that of step 440 in FIG. The return time 93 and the suspension time 95 corresponding to the current time in the return time management table 90 are updated (step 1010). The return time 93 and the rest time 95 are the times after the maximum sleep time (Ts) has elapsed. If the pause time has not elapsed (step 1015), and if the pause time has not elapsed, a reception check of the synchronization packet is performed (step 1020). If no synchronization packet has been received, the process returns to step 1015. If the synchronization packet has been received, processing for updating the adjacent node communicable time management table 60 is performed (step 1025). The adjacent node communicable time management table 60 is updated by deleting the column corresponding to the transmission source node ID of the synchronization packet of the adjacent node ID 62 and then performing the same process as step 425 in FIG. When the update of the adjacent node communicable time management table 60 is completed, the process returns to step 1015. If the pause time has elapsed in step 1015, the sleep state is entered until the next return time (step 1030).

  As described above, after the relay node is activated, it returns according to the return time of the adjacent node, thereby realizing synchronization between adjacent nodes.

  Next, a communication path construction method will be described. In an ad hoc network, communication routes are constructed dynamically by using a routing protocol that is being discussed by the Internet Engineering Task Force (IETF) MANET (Mobile Ad-hoc Networks) WG. Can do. In a routing protocol in an ad hoc network, detection of a radio link between adjacent nodes is performed by exchanging routing packets. For example, RFC 3626 (T. Clausen, P. Jacquet, “Optimized Link State Routing Protocol (OLSR)” 2003/10, http://www.ietf.org, a technical document published by the Internet Engineering Task Force (IETF). /rfc/rfc3626.txt) grasps neighboring nodes by exchanging routing packets called HELLO messages and grasps network topology by exchanging routing packets called TC messages. Each message is transmitted periodically.

  However, the above routing protocol does not consider the intermittent operation of nodes that exchange messages. As described above, if all return times are not the same between adjacent relay nodes, the adjacent node may not be in the return state even if the routing packet is transmitted, and the adjacent node may not receive the routing packet. . In this case, routing packets are lost, and there is a problem that detection of a wireless link between adjacent nodes fails and a communication path cannot be constructed.

  A method for constructing a communication path will be described with respect to this problem. The OLSR will be described as an example of the routing protocol. In OLSR, adjacent nodes are detected by periodically exchanging HELLO messages. Detection of a radio link with an adjacent node is performed by checking whether a HELLO message is received at a HELLO message transmission interval called a HELLO interval. In addition, TC messages are exchanged to understand the topology. The relay node transmits a TC message at a TC message transmission interval called a TC interval. Not all relay nodes need to send TC messages, but which relay node sends TC messages is defined by the OLSR. According to OLSR, at least a relay node called MPR (Multi Point Relay) needs to transmit a TC message.

  Routing packets such as HELLO messages and TC messages are broadcasted when the routing packet transmission time is reached by a program executing a routing protocol on the relay node. At this time, the conventional routing packet only broadcasts the routing packet once at the time of transmission. However, in order to enable the routing packet to be transmitted to all adjacent nodes during the maximum sleep time, The routing packet is transmitted once or a plurality of times according to a certain time.

  FIG. 11 shows a transmission flowchart of an OLSR routing packet for establishing a communication path between relay nodes that perform intermittent operation. When the routing packet transmission time is reached, the following transmission flow is executed. The following flows can use the same flow regardless of the type of routing packet (HELLO message, TC message and other messages defined by OLSR). It is checked whether the maximum sleep time (Ts) has elapsed (step 1105). If the maximum sleep time (Ts) has elapsed, the process proceeds to step 1130.

  It is checked from the adjacent node communicable time management table 60 whether the current time is between the return time 63 and the suspension time 65 of the adjacent node (step 1110). If the current time is not between the return time 63 of the adjacent node and the pause time 65, the process returns to step 1105.

In the adjacent node communicable time management table 60, it is checked whether or not the routing packet has been transmitted to all of the adjacent nodes stored in the adjacent node ID 62 in one or more columns that match the condition checked in step 1110 (step 1115). ). If there is no adjacent node ID 62 that has not yet been transmitted, the process returns to step 1105. Although illustration is omitted,
The management of the transmitted adjacent node ID is performed by the transmitted adjacent node management list 120 of the routing packet shown in FIG. In columns 121 and 122, 106 and 102 are stored as examples of transmitted adjacent nodes. If all the adjacent node IDs 62 that match the condition checked in step 1110 are stored in the transmitted adjacent node management list 120, it is not necessary to send the transmission of the routing packet, and the process returns to step 1105. A routing packet is transmitted (step 1120). The contents of the routing packet are not changed in accordance with OLSR. Although not shown, the routing packet is stored in the memory 5 while there is an adjacent node that has not yet transmitted the routing packet.

  After transmitting the routing packet, add the adjacent node IDs not registered in the transmitted adjacent node management list 120 among the adjacent node IDs stored in the adjacent node ID 62 that matches the condition checked in step 1110 (step 1125). Return to 1105.

  When the maximum sleep time (Ts) elapses in step 1105, the transmitted adjacent node management list 120 is cleared (step 1130), and the process ends.

  According to the above flow, the routing packet may be received shorter than the predetermined transmission interval, but this does not cause a problem in establishing a communication path in OLSR. As described above, exchange of routing packets is realized between relay nodes that perform intermittent operation, and a communication path is constructed.

  FIG. 13 shows an example of a route construction result (routing table) 130 by OLSR according to the above in the network topology of FIG. Dst131 indicates a destination node, and Next132 indicates an adjacent node serving as a gateway for the destination node 131. Further, since the adjacent node 132 does not exist for the destination node 131 capable of direct communication, “*” indicates that direct communication is possible.

  If a data packet is transmitted from the relay node 101 to the relay node 109 according to the routing table of FIG. 13, the relay node 106 cannot relay the data packet at the time when the relay node 106 has not returned, and the packet loss. And cannot communicate. Even if the relay node 106 is in the active state, if there is a relay node that is not in the active state on the route from the relay node 106 to the relay node 109, communication cannot be performed due to packet loss.

  Next, a data packet transfer method for solving this new problem will be described.

  When, for example, OLSR is used as a routing protocol and a communication path is constructed, the routing table 130 of the destination node and the adjacent node shown in FIG. 13 can be constructed. Here, an adjacent node serving as a gateway to the destination node of the data packet or a destination node when direct communication is possible is referred to as a transfer destination adjacent node. As a packet transfer method, when the transfer destination adjacent node has not recovered, the data packet to be transferred is stored in the memory 5 of the relay node 1, and the data packet is transferred when the transfer destination adjacent node is in the active state. Transfer using the store-and-forward method. Whether or not the transfer destination adjacent node is in an active state at the time of transfer can be determined from the adjacent node communicable time management table 60.

  FIG. 14 shows a process flowchart of the store-and-forward method. By checking whether the communication possible time of the transfer destination adjacent node is known at the time of packet transfer, whether there is a column in which the ID of the transfer destination adjacent node and the adjacent node ID 62 match in the adjacent node communication time management table 60 Check (step 1405). If the communication possible time of the transfer destination adjacent node is not grasped, the data packet is discarded (step 1425). When the communicable time of the transfer destination adjacent node is known, it is checked whether the transfer destination adjacent node can communicate at the current time (step 1410). This check can be performed by checking whether the current time is between the return time and the suspension time of the transfer destination adjacent node. If the current time is between the return time and the pause time of the transfer destination adjacent node, the transfer destination adjacent node is communicable, so the communication control unit 4 is controlled to transfer the data packet (step 1415). In step 1410, if the current time is not between the return time and the pause time of the transfer destination adjacent node, the transfer destination adjacent node is assumed to be in a time zone in which communication is possible, The data packet is stored in the memory (step 1420). It is checked whether there are any data packets stored in the memory (step 1430). If there are any data packets, the process returns to step 1405. If no packets remain, the process is terminated.

  With the above processing, even when a transfer request for a data packet occurs at a time when the transfer destination adjacent node is not in an active state, the packet can be transferred without loss.

  According to the present embodiment, it is possible to synchronize the relative time of the return of the intermittent operation without providing time synchronization between adjacent nodes (providing a communicable time zone).

  Further, according to the present embodiment, it is possible to dynamically construct a communication path between relay nodes that perform intermittent operation.

  According to the present embodiment, it is possible to determine the return time and active time of the relay node, and return to the time when communication with the adjacent node is possible.

  In addition, according to the present embodiment, it is possible to prevent a packet from being transferred to an adjacent node that is not in an active state when a routing packet or a data packet is transferred, and to reduce packet loss.

It is an example of a network topology. 2 is a configuration example of a relay node 1. It is an example which establishes synchronization between adjacent nodes. It is a synchronization flowchart between adjacent nodes. It is a format example of the payload part 50 of a synchronous packet. It is an example of an adjacent node communication possible time management table. It is an update process flowchart of an adjacent node communication possible time management table. It is a process flowchart which calculates | requires active time. It is an example of a return time management table. It is a return process flowchart of a relay node. It is a transmission flowchart of a routing packet. It is an example of the transmitted adjacent node management list. It is an example of a routing table. It is a process flowchart of a store and forward system.

Explanation of symbols

101 to 109: relay node, 1: relay node, 2: antenna, 3: CPU, 4: wireless communication unit, 5: memory, 6: timer, 7: battery.

Claims (19)

In response to receiving the synchronization packet including the relative return time from the synchronization packet transmission time to the return time of the adjacent node from the adjacent node included in the wireless multi-hop network in which the maximum sleep time is set, An active state communicable with the adjacent node that continues for an active time determined from a given condition from a return time determined based on a relative return time;
A wireless multi-hop communication device having a sleep state incapable of communicating with the adjacent node from a pause time after the active time has elapsed. 2. The wireless multi-hop communication apparatus according to claim 1, wherein the given condition is one of a condition relating to power saving and an active time of the adjacent node included in the synchronization packet. 3. The wireless multi-hop communication apparatus according to claim 2, wherein the sleep state is a time obtained by subtracting the active time from the maximum sleep time. When a plurality of the relative return times of the adjacent nodes are included in the synchronization packet, the state change between the active state and the sleep state is repeated a number of times corresponding to the plurality during the maximum sleep time. 4. The wireless multi-hop communication device according to claim 3. When the plurality of synchronization packets from a plurality of adjacent nodes are received, the return time of the own node is determined according to each relative return time included in the plurality of synchronization packets. Item 4. The wireless multi-hop communication device according to Item 3. In response to receiving one of a routing packet and a data packet for establishing a communication path from another adjacent node included in the wireless multi-hop network, when in the active state, 4. The wireless multi-hop communication device according to claim 3, wherein the packet is transmitted to the adjacent node. 7. The radio according to claim 6, wherein when the packet is received and in a sleep state incapable of communicating with the adjacent node, the wireless communication device waits for the packet to be transmitted to the adjacent node until the active state is reached. Multi-hop communication device. A wireless communication unit that receives the synchronization packet including a relative return time from a synchronization packet transmission time of the adjacent node to a return time from an adjacent node included in the wireless multi-hop network in which a maximum sleep time is set;
During an active time determined from a given condition from a return time determined based on a relative return time of the adjacent node included in the synchronization packet received by the wireless communication unit, an active state capable of communicating with the adjacent node is set. A wireless multi-hop communication apparatus, comprising: a CPU that continues and a timer that controls a sleep time during which a sleep state incapable of communicating with the adjacent node from a pause time after the active time elapses is continued. 9. The wireless multi-hop communication device according to claim 8, wherein the given condition is one of a condition relating to power saving and an active time of the adjacent node included in the synchronization packet. 10. The wireless multi-hop communication device according to claim 9, wherein the sleep state is a time obtained by subtracting the active time from the maximum sleep time. The CPU executes a sleep command for shifting to the sleep state in which power consumption other than power necessary for returning to the active state is suppressed as much as possible at the pause time. 10. The wireless multi-hop communication device according to 10. 11. The timer outputs a return signal to the CPU at the end of the sleep time, and the CPU shifts from the sleep state to the active state in response to the input of the return signal. Wireless multi-hop communication device. The wireless communication unit receives one of a routing packet and a data packet for establishing a communication path from another adjacent node included in the wireless multi-hop network, and is in the active state 11. The wireless multi-hop communication device according to claim 10, wherein the CPU controls the wireless communication unit so that the wireless communication unit transmits the packet to the adjacent node. 14. The wireless multi-hop communication device according to claim 13, further comprising a memory for storing the packet when the packet is received and in a sleep state where communication with the adjacent node is impossible. The wireless multi-hop communication device included in the wireless multi-hop network in which the maximum sleep time is set receives the synchronization packet including the relative return time from the synchronization packet transmission time of the adjacent node to the return time from the adjacent node, Determine a return time based on the relative return time of the adjacent node,
Determining an active time for continuing an active state capable of communicating with the adjacent node from a given condition;
The wireless multi-hop communication control method, wherein a time after the active time has elapsed is set as a pause time for transitioning to a sleep state where communication with the adjacent node is impossible. 16. The wireless multi-hop communication control method according to claim 15, wherein the given condition is one of a condition relating to power saving and an active time of the adjacent node included in the synchronization packet. 17. The wireless multi-hop communication control method according to claim 16, wherein the sleep state is a time obtained by subtracting the active time from the maximum sleep time. The wireless multi-hop communication device receives a packet from one of a routing packet and a data packet for establishing a communication path from another adjacent node included in the wireless multi-hop network,
18. The wireless multi-hop communication control method according to claim 17, wherein when the packet is in the active state, the packet is transmitted to the adjacent node. 19. The radio according to claim 18, wherein when the packet is received and in a sleep state incapable of communicating with the adjacent node, the wireless communication device waits for the packet to be transmitted to the adjacent node until the active state is reached. Multi-hop communication control method.

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