JP5868506B2 - Time synchronization method in wireless network system - Google Patents

Description

  The present invention relates to time synchronization in wireless multi-hop communication.

  In recent years, the use of wireless communication for automatic meter reading systems and plant systems for power consumption has been promoted taking advantage of the reduction of operation and facility costs and the convenience of wireless communication. In these wireless communications, all the terminals belonging to the wireless network are synchronized with the common time information for the purpose of suppressing interference with a plurality of wireless terminals or other systems and guaranteeing the communication band, A time division multiplexing method is used in which the transmission time of each wireless terminal is managed by time division. In this case, each terminal has accurate time information such as a GPS receiver, so that time synchronization of all terminals in the wireless network can be realized, but the cost is increased and the place is blocked indoors or with a metal door, etc. There is also a possibility that the time of the terminal installed in cannot be synchronized. Therefore, the wireless terminal uses the wireless communication by multicast transmission of the time information held by the own terminal at a predetermined cycle, and updates when the surrounding terminals receiving the information are newer than the time information held by the own terminal. Thus, there is a method for realizing time synchronization (Patent Document 1). Also, periodically or in response to an instruction from the management terminal, the wireless terminal (slave) transmits a time request packet to the terminal (master) that wants time synchronization, and receives a time synchronization response packet from the terminal. Thus, there is a method for realizing time synchronization (Patent Document 2). In addition, there is a method of realizing synchronization by using a transmission / reception delay error of normal upper direction and lower direction data communication without using time synchronization information (Patent Document 3).

JP 2011-35699 A JP 2011-223419 A JP 2003-50289 A

  However, when these technologies are applied to a large-scale wireless multi-hop network, there are the following problems. For example, when receiving time information packets periodically as in Patent Document 1, if packet loss occurs in wireless communication, time synchronization cannot be adjusted, so it is difficult to match the synchronization accuracy in the entire wireless system. . Further, as in Patent Document 2, when request / response communication between master and slave is adopted for time synchronization, communication traffic is increased for time synchronization. A failure may occur. Due to a communication failure, the time synchronization packet cannot be received, and it is difficult to match the synchronization accuracy of the entire wireless system as in Patent Document 1. In addition, as in Patent Document 3, when data communication is used, the timing for performing time synchronization adjustment depends on the number of data communications, so the number of times wireless multihop transfer processing is performed, that is, data communications performed by each terminal. Since the number of times is not uniform throughout the system, it is difficult to match the synchronization accuracy of the entire wireless system.

  An object of the present invention is to achieve keeping the synchronization accuracy of each wireless terminal constant throughout the system in a data collection system that collects terminal information in a network by wireless communication.

In order to solve the above problems, the present invention has the following configuration.
In a wireless multi-hop network, all wireless terminals are time synchronized by wireless communication. For the time synchronization, a data communication response confirmation packet or a time synchronization information request packet and its response packet are used appropriately and used to synchronize with the parent terminal of the terminal itself. Specifically, time synchronization is performed with a data communication response confirmation packet at a place where constant data communication traffic occurs (between terminals), and time synchronization communication is performed at a place where constant data communication traffic does not occur. Generate traffic and synchronize time between terminals. By appropriately using the time synchronization method in this way, it is possible to maintain the synchronization accuracy of the wireless terminals in the wireless network constant throughout the system.

  Furthermore, by increasing or decreasing the transmission interval of the time synchronization request packet in stages according to the past data traffic volume in the vicinity, the synchronization accuracy of the wireless terminal can be maintained with higher accuracy.

  In the wireless network system, it is possible to keep the synchronization accuracy of each wireless terminal constant.

Overall configuration diagram of wireless communication system Hardware configuration diagram of radio terminal and radio relay terminal constituting radio communication system Hardware configuration diagram of wireless gateway configuring wireless communication system Packet configuration example (data communication packet) Packet configuration example (data acknowledgment packet) Packet configuration example (time synchronization information request packet) Packet configuration example (time synchronization information distribution packet) Time synchronization packet flow diagram (unicast acknowledgment) Data transfer flow diagram Configuration diagram of time request transmission wait time Transmission timing management processing of time synchronization information request of each terminal Processing when each terminal receives wireless packets Processing when receiving time synchronization information of each terminal (time synchronization information distribution packet) Processing when receiving time synchronization information of each terminal (data confirmation response packet) Time synchronization information distribution packet reception and transmission request timing change sequence Time synchronization information request packet reception and transmission request timing change sequence Time synchronization packet flow diagram in embodiment 2

  Hereinafter, the first embodiment 1 will be described with reference to FIGS. Next, a second embodiment will be described with reference to FIG.

  A wireless communication system configuration and a wireless packet configuration will be described with reference to FIGS. Next, an outline of the operation of the time synchronization process in the wireless communication system will be described with reference to FIGS.

  FIG. 1 is an overall configuration diagram of a radio communication system according to the present embodiment. The wireless network 100 includes a gateway 101, a wireless relay terminal (Node A) 102, a wireless relay terminal (Node B) 103, a wireless relay terminal (Node C) 104, a wireless terminal (Node D) 105, and a wireless relay terminal (Node E). 106, wireless relay terminal (node F) 107, wireless terminal (node H) 108, wireless terminal (node I) 109, wireless terminal (node J) 110, wireless terminal (node (K)) 111, wireless terminal (node G) 112). A dotted line connecting each wireless terminal in the wireless network 101 indicates a communication path capable of wireless communication.

  FIG. 2 is a hardware configuration diagram of a radio terminal and a radio relay terminal that configure the radio communication system according to the present embodiment. Here, the wireless relay terminal and the wireless terminal are the same hardware. These are determined by the network topology in the wireless multi-hop network. For convenience, when there is another node below the own node, it is called a wireless relay terminal, and when the own node is a terminal, it is called a wireless terminal.

  The wireless terminal / wireless relay terminal 201 is an embedded device having a wireless communication function with the wireless terminal gateway, and includes a microcomputer 202, a clock generation circuit 209, a power supply circuit 210, and an RF peripheral circuit 211. The microcomputer 202 includes a ROM 203 and a RAM 208, and is connected to a power supply circuit 210, a clock generation circuit 209, and an RF peripheral circuit 211. The ROM 203 is a storage device composed of a read-only semiconductor memory or the like, and is composed of a central control unit 204, a time synchronization control unit 205, a path management unit 206, and a wireless communication processing unit 207, and is connected to the RAM 208. . The central control unit 204 controls execution of a program in the ROM, and is connected to the time synchronization control unit 205, the wireless communication processing unit 207, and the route management unit 206. The time synchronization control unit 205 realizes a function to synchronize with the time transmitted from the wireless terminal gateway which is a time base station, and adjusts the progress of the clock using the received synchronization time information, The timing for requesting information is determined. The route management unit 206 manages routes in multi-hop communication between terminals in the network.

  The wireless communication processing unit 207 implements transmission / reception processing in wireless communication. Specifically, packet assembly processing such as designation of the transmission destination and hop number when transmitting, and packet analysis processing such as determination of whether or not the packet is a self-destination packet when receiving are performed. A frame storage unit 212 is connected. A RAM 208 is a storage device such as a rewritable semiconductor memory element, is used as a transmission / reception buffer in wireless communication, and is connected to the ROM 203. The clock generation circuit 209 is a circuit that generates a clock used in the microcomputer and the RF peripheral circuit, and is connected to the power supply circuit 210, the microcomputer 202, and the RF peripheral circuit 211. The power supply circuit 210 supplies power to the wireless terminal / wireless relay terminal itself, and is connected to the clock generation circuit 209, the microcomputer 202, and the RF peripheral circuit 211. The RF peripheral circuit 211 is a circuit that transmits and receives radio signals, and is connected to the power supply circuit 210, the clock generation circuit 209, and the microcomputer 202. Note that the wireless terminal / wireless relay terminal 201 may be an independent device instead of an embedded device.

  FIG. 3 is a hardware configuration diagram of a wireless gateway constituting the wireless communication system according to the present embodiment.

  The gateway wireless terminal 301 is a device that communicates with a wireless communication function with a wireless terminal / wireless relay terminal and a device connected to an external network and realizes a connection between the wireless network and the external network. In addition to the hardware configuration similar to that of the wireless relay terminal, the device includes an external network connection circuit 312. The external network connection circuit 312 is a circuit that realizes a function for using an external network such as Ethernet (registered trademark), WiFi (registered trademark), an optical line, and a telephone network.

  FIG. 4A to FIG. 4D are wireless packet configuration diagrams according to the present embodiment. These packets are a data communication packet 401, a data confirmation response packet 402, a time synchronization information request packet 403, and a time synchronization information distribution packet 404, respectively. Here, the data communication packet 401 is a packet for transmitting data from a certain wireless terminal / wireless relay terminal to another wireless terminal / wireless relay terminal in response to a request for application or the like. The data confirmation response packet 402 is a packet for confirming that the wireless terminal / wireless relay terminal that has received the data communication packet 401 has received the packet to the wireless terminal / wireless relay terminal that has transmitted the packet. The time synchronization information request packet 403 is a packet when a certain wireless terminal / wireless relay terminal requests time information from another wireless terminal / wireless relay terminal. The time synchronization information distribution packet 404 is transmitted when the wireless terminal / wireless relay terminal that has received the time synchronization information request packet transmits the time information that the terminal itself has to the wireless terminal / wireless relay terminal that has transmitted the packet, This is a packet for broadcasting time information including other wireless terminals / wireless relay terminals.

  FIG. 4A shows a data communication packet. The data communication packet 401 includes a transmission destination ID 405, a transmission source ID 406, a sequence number 407, a packet length 408, and a data communication payload area 409. The transmission destination ID 405 stores information for identifying a transmission destination of a wireless packet, such as a MAC address of a terminal serving as a destination when the terminal itself transmits. The transmission source ID 406 stores information for identifying the transmission source of the wireless packet such as the MAC address of the own terminal. The sequence number indicates the order of the data communication packet 401 transmitted by the wireless terminal specified by the transmission source ID, and is used to correspond to the data confirmation response packet.

  The packet length 408 is information indicating the length of the data communication packet 401. The payload area for data communication stores application data to be transmitted, data for wireless multi-hop route control, and the like.

  FIG. 4B shows a data confirmation response packet. The data confirmation response packet 402 includes a transmission destination ID 405, a transmission source ID 406, a sequence number 407, a packet length 408, and time synchronization information 410. The sequence number 407 stores a sequence number included in the received data communication packet 401. The time synchronization information 410 is common time information for synchronizing wireless networks, and stores time information immediately before the data confirmation response packet is transmitted.

  FIG. 4C shows a time synchronization information request packet. The time synchronization information request packet 403 includes a transmission destination ID 405, a transmission source ID 406, a sequence number 407, a packet length 408, a time synchronization information request 411, and a time information requester ID 412. The transmission destination ID 406 stores information specifying a terminal that makes a time synchronization information request. In particular, in the case of a wireless multi-hop network having a tree structure such as the wireless network 101, information specifying a parent terminal close to the gateway wireless terminal 101 is stored. The time synchronization information request flag 411 stores information for identifying a time synchronization information request packet. The time information requester ID 412 stores information for identifying the transmission source of the time synchronization information request packet, and may be the same information as the transmission source ID 406.

  FIG. 4D shows a time synchronization information distribution packet. The time synchronization information distribution packet 404 includes a transmission destination ID 405, a transmission source ID 406, a sequence number 407, a packet length 408, time synchronization information 410, and a time information requester ID 412. The time information requester ID stores a time information requester ID 412 corresponding to the received time synchronization information request packet 403.

  Next, an outline of the operation of the time synchronization process in the wireless communication system will be described with reference to FIGS.

  FIG. 5 is a time synchronization packet flow diagram (unicast confirmation response) between wireless terminals according to the present embodiment. First, an example using a time synchronization information request packet will be described. In the wireless network 100, in the wireless relay terminal (F) 107, the wireless terminal (H) 108, and the wireless terminal (K) 109, the wireless terminal (H) 108 sends time information to the wireless relay terminal (F) 107 that is the parent terminal. The request packet 403 is transmitted, and the wireless relay terminal (F) 107 broadcasts the time synchronization information distribution packet 404. The time synchronization control unit 205 of the wireless terminal (H) 108 and the wireless terminal (K) 109 adjusts the time synchronization deviation according to the time synchronization information 410 of the time synchronization information packet 404, and the time synchronization ends.

  Next, an example using a data communication packet will be described. The wireless terminal (K) 109 or the wireless terminal (H) 108 stores application data or the like in the data communication packet 401 and transmits it to the wireless relay terminal (F) (in FIG. 5, transmitted from the wireless terminal (K) 109. Explain what to do). At this time, the data confirmation response packet 402 corresponding to each data communication packet is transmitted to the wireless terminal (K) 109 by unicast (if transmitted from the wireless terminal (H) 108, it is transmitted to the wireless terminal (H) 108. ) The individual terminal that has received the data confirmation response packet 402 from the parent terminal adjusts the time synchronization deviation according to the time synchronization information 410 of the data confirmation response packet 402. As described above, when each wireless terminal receives the time synchronization information distribution packet broadcast-transmitted from the parent terminal and the data confirmation response packet corresponding to the data communication packet transmitted by the own terminal, the time synchronization information is received. Use to adjust the time. This makes it possible for all the wireless terminals in the wireless network 101 to synchronize time using wireless communication.

  FIG. 6 is a data transfer flowchart in the wireless multi-hop communication according to the present embodiment. When collecting information of each wireless terminal in a server or the like outside the wireless network, such as automatic power meter reading or a sensor network, data is collected via a gateway. In the case of a wireless multi-hop network, if the wireless relay terminal determines that the packet is addressed to the GW, the wireless relay terminal that has received the packet transfers the data communication packet to a parent terminal that is higher than itself. When the wireless relay terminal (A) 102 receives the data communication packet 401 from the wireless relay terminal (C) 104, the wireless relay terminal (A) 102 determines in the wireless packet reception processing 601 that the final destination of the wireless network is the GW 101. To the gateway wireless terminal GW101. As described above, in a wireless multi-hop network, application data from a wireless terminal or a wireless relay terminal may be transmitted to the gateway wireless terminal GW by a plurality of times of unicast communication. The number of synchronization adjustments is not the same for all terminals belonging to the wireless network 100, but is determined by the network topology. Specifically, the number of packet transmissions increases by becoming higher.

  FIG. 7 is a diagram illustrating the time request transmission waiting time of each wireless terminal. The time request transmission waiting time 701 includes a fixed part (T1) 702 and a traffic-dependent part (T2) 703. The time request transmission waiting time 701 indicates a waiting time from when the previous time synchronization processing is performed to when the next time synchronization information request packet is transmitted.

  The minimum value is the shortest interval at which the synchronization error adjustment process is performed, and is a fixed amount (T1) 702. The maximum value is determined based on the synchronization error and clock performance in the wireless system, and is the longest period of time for performing the synchronization error adjustment processing to keep the synchronization accuracy in the wireless system constant. The fixed part (T1) 702 is a value determined by the system. The traffic dependence (T2) 703 is a value determined depending on neighboring communication traffic, and is determined by the traffic volume of the time synchronization information request packet 403 and the time synchronization information distribution packet 404 in the neighboring terminal. Here, the neighboring terminal refers to a terminal that belongs to the same parent terminal.

  This is because, when the time synchronization information distribution packet 404 is received from the parent terminal even though the time synchronization information request packet 403 is not transmitted by itself, neighboring terminals belonging to the same parent terminal The next time synchronization information request packet 403 is left to the neighboring terminal, and the time synchronization control unit extends the time request transmission waiting time to twice a fixed amount. Thereby, the possibility that a plurality of time synchronization information request packets 403 are simultaneously transmitted from child terminals belonging to the same parent terminal is reduced, and an increase in traffic volume due to the time information synchronization request packet 403 can be reduced. . In addition, as the traffic dependence, the extended time interval is twice the fixed amount, but it does not necessarily have to be twice.

  FIG. 8 shows an operation process of transmission timing management of the time synchronization information request of each terminal.

  Step 801 is processing in which the wireless terminal starts managing the transmission timing of the time synchronization information request packet 403.

  Step 802 is processing for confirming whether or not there is a transmission reservation of the time synchronization information request packet 403. In this step, it is confirmed that the transmission timing management of the same time information request is started. If no transmission reservation has been made, the process proceeds to step 803, and if transmission reservation has already been made, the process proceeds to step 804.

  Step 803 is a step for making a transmission reservation for the time synchronization information request packet 403. This step is the first setting, and the transmission after the fixed time (T1) 702 is set as the request transmission waiting time.

  Step 804 is processing for determining whether the time managed in the own terminal exceeds the transmission reservation time of the time synchronization information request packet 403. If the reserved time has been exceeded, the process proceeds to step 805, and if not, the process proceeds to step 802.

  Step 805 is transmission processing of the time synchronization information request packet 403. In this step, a time synchronization information request packet 403 is transmitted to the parent terminal of the own terminal.

  Step 806 is processing for confirming the set time for the request transmission waiting time. In this step, if the request transmission waiting time is set longer than the fixed time (T1) 702, the process proceeds to step 807, and if the fixed time (T1) 702 is longer than the transmission waiting time, the step Go to 802. When there is another child terminal belonging to the same parent terminal and the time synchronization information distribution packet 404 can be received by transmission of the time synchronization information request packet 403 performed by the child terminal, the request transmission time is Since there is no need to send a synchronization information request packet, it is extended. However, if this step is performed (YES in S806), it means that it has transmitted a time synchronization information request packet, so it is determined that there are no child terminals belonging to the same parent terminal around, It returns to the fixed time (T1) 702 which is the shortest frequency of the transmission interval of the synchronization information request packet. As a result, the time synchronization information distribution packet 404 can be received at regular intervals, and the time synchronization accuracy can be maintained.

  FIG. 9 shows an operation process when each terminal receives a radio packet. Step 901 is processing for starting reception of a wireless packet.

  Step 902 is processing for determining whether or not the received packet is the time synchronization information request packet 403. If it is the time synchronization information request packet 403, the process proceeds to step 906, and if it is any other packet, the process proceeds to step 903.

  Step 903 is processing for determining whether or not the received packet is the time synchronization information distribution packet 404. If it is the time synchronization information distribution packet 404, the process proceeds to step 907, and if it is any other packet, the process proceeds to step 904.

  Step 904 is processing for determining whether or not the received packet is the data confirmation response packet 402. If it is the data confirmation response packet 402, the process proceeds to step 910, and if it is any other packet, the process proceeds to step 905.

  Step 905 is processing for determining whether or not the received packet is the data communication packet 401. If it is a data communication packet 402, the process proceeds to step 910, and if it is any other packet, the process proceeds to step 905.

  Step 906 is processing for transmitting the time synchronization information distribution packet 404. In this step, the time synchronization information distribution packet 404 is transmitted to the transmission source terminal of the time synchronization information request packet 403 received in step 901.

  Step 907 is a process for receiving time synchronization information. In this step, a time synchronization adjustment process using the time synchronization information 410 of the time synchronization information distribution packet 404 received by broadcast communication is performed.

  Step 908 is processing for determining whether there is processing to be performed other than processing related to the time synchronization processing for the packet received in step 901. Processing other than time synchronization processing includes application processing, path control processing, network address resolution processing, and the like. If there is a process to be performed, the process proceeds to step 909, and if not, the radio packet reception process is terminated.

  Step 909 is packet reception processing other than processing related to the time synchronization processing for the packet received in step 901.

  Step 910 performs time synchronization information reception processing. This step is a time synchronization adjustment process using the time synchronization information 410 of the data confirmation response packet 402 received by unicast communication.

  Step 911 is processing for performing an acknowledgment of the data communication packet received in step 901. In this step, a data confirmation response packet storing time information immediately before the transmission of the data confirmation response packet is transmitted to the transmission source terminal of the data communication packet.

  FIG. 10 is a diagram for explaining in detail the processing in step 907 in FIG. 9, that is, the operation processing when the time synchronization information 410 of the time synchronization information distribution packet 404 received by each terminal is received.

  Step 1001 is processing for confirming the transmission source of the received time synchronization information distribution packet 404. If the transmission source is the parent terminal, the process proceeds to step 1002; otherwise, the process ends.

  Step 1002 is a process of confirming whether or not the time information request ID 412 in the received time synchronization information distribution packet 404 is the own terminal. If the time information request ID is the local terminal, the process proceeds to step 1003. If the time information request ID is not the local terminal, the process proceeds to step 1005.

  Step 1003 is a time synchronization adjustment process using the time synchronization information 410 of the received time synchronization information distribution packet 404.

  Step 1004 is processing for setting the transmission time of the next time synchronization information request packet 403. The next transmission time is a time obtained by adding the request transmission waiting time to the current free time.

  Step 1005 is processing for confirming the length of the request transmission waiting time. If the request transmission waiting time is the prescribed maximum time, the process proceeds to step 1003, and if not, the process proceeds to step 1006.

  Step 1006 is processing for extending the length of the request transmission waiting time. In this step, by extending the length of the traffic dependence (T2) 703, the interval until the next request transmission waiting time is extended. The method of extending the length of the traffic dependent portion (T2) 703 adds a fixed time (T1) 702 minutes to the current traffic dependent portion (T2) 703. Note that the method for extending the traffic dependence (T2) 703 is not limited to this as long as the value is increased.

  FIG. 11 shows the processing in step 910 of FIG. 9, that is, the operation processing when receiving the time synchronization information 410 of the data confirmation response packet 402 received by each terminal.

  Step 1101 is processing for confirming the transmission source of the received data confirmation response packet 402. If the transmission source is the parent terminal, the process proceeds to step 1003. Otherwise, the process ends. The processing of steps 1003 and 1004 is the same as the processing of the same step number in FIG.

  FIG. 12 shows a sequence for changing the reception timing of the time synchronization information distribution packet 404 and the transmission timing of the time synchronization information request packet 403.

  The wireless terminal (H) 108 reserves the first time synchronization information request packet 403 transmission at time t11201, and reserves the second time at time t21202 when the fixed time (T1) 702 has passed. The wireless terminal (K) 109 reserves the first time synchronization information request packet 403 transmission at time t31203, and reserves the second time at time t41204 when the fixed time (T1) 702 has passed. The wireless terminal (K) 108 transmits the time synchronization information request packet 403 to the wireless relay terminal (F) 107 at time t1, and receives the packet in accordance with the operation processing of the transmission timing management of the time synchronization information request of each terminal in FIG. The wireless relay terminal (F) 107 broadcast-transmits the time synchronization information distribution packet 404, and the wireless terminal (K) 108 and the wireless terminal (F) 109 receive them. In this case, the wireless terminal (K) 108 and the wireless terminal (F) 109 set the transmission time of the next time synchronization information request packet in accordance with the operation processing at the time of reception of the wireless packet of each terminal in FIG. Since the wireless terminal (K) 108 requested the same time information itself, the transmission time of the next time synchronization information request packet 403 is not changed from the time t21202 when the fixed time (T1) 702 has passed. On the other hand, since the wireless terminal (K) does not request the same time information itself, the transmission waiting time (T) is reserved at time t51205 to which a fixed time (T1) 702 is further added as a traffic-dependent portion, and time t31203 And the reservation at time t41204 is canceled. As described above, it is possible to keep the time synchronization error constant while reducing the traffic of the time synchronization information request packet 403 transmitted from the child terminal to the parent terminal using the time synchronization information request packet 403 of the peripheral terminal. Become.

  FIG. 13 shows a sequence for receiving the data confirmation response packet 402 and the time synchronization information distribution packet 404 and changing the transmission timing of the time synchronization information request packet 403.

  13 shows a transmission timing change sequence of the time synchronization information request packet 403 when a data communication packet from the wireless terminal (H) 108 to the wireless relay terminal (F) 107 is generated in addition to the communication traffic of FIG.

The wireless terminal (H) 108 transmits a data communication packet to the wireless relay terminal (F) 107 at time t61301, and the wireless relay terminal (F) 107 transmits a data confirmation response packet 402 to the wireless terminal (H) 108. The wireless terminal (H) 108 that has received the data confirmation response packet 402 cancels the transmission reservation at time t2 in accordance with the operation processing when receiving the time synchronization information 410 of the data confirmation response packet 402 in FIG. The request packet 403 is reserved at time t71302 when the fixed time (T1) 702 has elapsed.
As described above, a wireless terminal and a wireless relay terminal that frequently perform data communication can perform time synchronization adjustment processing using a data confirmation response packet. Therefore, unnecessary time synchronization information request packet 403 traffic can be reduced while keeping the time synchronization error constant.

  In the first embodiment, the transmission interval of the time synchronization information request packet is adjusted according to the communication traffic around the terminal itself, in particular, the traffic volume of the time synchronization information distribution packet 404, and data communication occurs periodically. By delaying the transmission interval of the time synchronization information request packet transmitted by the wireless terminal, it is possible to reduce the time synchronization information request packet and keep the time synchronization accuracy in the wireless network at a certain level or more. This is an embodiment of the present invention in the case where a wireless network is constructed using a wireless communication method that confirms both the transmission destination ID 405 and the transmission source ID 406 when a data confirmation response packet is received.

  In the second embodiment, an embodiment of the present invention will be described in the case where a wireless network is constructed using a wireless communication method in which only the transmission source ID 406 is confirmed when a data confirmation response packet is received.

  First, the outline | summary of the operation | movement of the time synchronization process in a radio | wireless communications system structure, a radio | wireless packet structure, and a radio | wireless communications system concerning a present Example is demonstrated.

Wireless communication system according to the present embodiment (FIG. 1), terminal hardware configuration (FIGS. 2 and 3), wireless packet configuration (FIG. 4), time request transmission waiting time configuration (FIG. 7),
Each terminal's time synchronization information request transmission timing management processing (FIG. 8), each terminal's wireless packet reception procedure (FIG. 9), each terminal's time synchronization information reception procedure 1 (FIG. 10), Processing procedure 2 (FIG. 11) when receiving time synchronization information of the terminal is the same as in the first embodiment.

  FIG. 14 is a time synchronization packet flow diagram between wireless terminals according to the present embodiment. In the wireless network 100, in the wireless relay terminal (F) 107, the wireless terminal (H) 108, and the wireless terminal (K) 109, the wireless terminal (H) 108 sends time information to the wireless relay terminal (F) 107 that is the parent terminal. The request packet 403 is transmitted, and the wireless relay terminal (F) 107 broadcasts the time synchronization information distribution packet 404. The wireless terminal (H) 108 and the wireless terminal (K) 109 adjust the time synchronization deviation according to the time synchronization information 410 of the time synchronization information packet 404. Next, the wireless terminal (K) 109 and the wireless terminal (H) 108 store application data and the like in the data communication packet 401 and transmit them to the wireless relay terminal (F). At this time, the data confirmation response packet 402 corresponding to each data communication packet is transmitted to the wireless terminal (K) 109 and the wireless terminal (H) 108 by unicast. Even in the case of unicast communication or broadcast communication, there is a high possibility that the radio wave will arrive in the same way. In this embodiment, when the transmission source ID 406 is the parent terminal of the own terminal, each terminal receives a radio packet. The time synchronization deviation is adjusted according to the processing procedure (FIG. 9) of FIG. 9 and the processing procedure 2 (FIG. 11) when receiving the time synchronization information of each terminal. This makes it possible for all the wireless terminals in the wireless network 101 to synchronize time using wireless communication.

  As described above, when configuring a wireless network topology in which a wireless terminal that frequently performs data communication and a wireless relay terminal are connected to the same parent terminal, time synchronization adjustment processing by a data confirmation response packet can be performed. It is possible to reduce the traffic of the unnecessary time synchronization information request packet 403 while keeping the time synchronization error constant.

  In addition, according to the present invention, the communication traffic necessary for time synchronization in the wireless network is reduced, so that the communication traffic of the entire network can be suppressed, and a sensor network that automatically generates a certain amount of data communication traffic or power automatic In the meter-reading network, the number of wireless terminals existing under one gateway can be increased, which is effective in reducing the cost of the entire system.

  In addition, according to the present invention, the time synchronization information distribution packet can be actively requested instead of being periodically and passively received. Since the time synchronization error in the wireless network can be kept constant, it is not necessary to require high clock accuracy, which is effective for reducing the cost of the wireless terminal.

DESCRIPTION OF SYMBOLS 100 ... Wireless network, 101 ... Gateway wireless terminal (GW), 102 ... Wireless relay terminal (A), 103 ... Wireless relay terminal (B), 104 ... Wireless relay terminal (C), 105 ... Wireless terminal (D), 106 ... wireless relay terminal (E), 107 ... wireless relay terminal (F), 108 ... wireless terminal (H), 109 ... wireless terminal (I), 110 ... wireless terminal (J), 111 ... wireless terminal (K), 112 ... Wireless terminal (G), 202 ... Microcomputer, 203 ... ROM, 204 ... Central control unit, 205 ... Time synchronization control unit, 206 ... Path management unit, 207 ... Wireless communication processing unit, 208 ... RAM, 209 ... Clock generation circuit 210 ... Power supply circuit, 211 ... RF peripheral circuit, 301 ... Gateway wireless terminal, 312 ... External network connection circuit, 401 ... Data communication packet, 402 ... Data confirmation response packet, 403 ... Time synchronization information request packet, 404 ... Time synchronization Information distribution packet, 405 ... transmission destination ID, 406 ... transmission source ID, 407 ... sequence 408 ... packet length, 409 ... payload area for data communication, 409 ... time synchronization information, 410 ... time synchronization information request flag, 410 ... time synchronization information requester ID, 601 ... radio packet reception processing, 701 ... time request Transmission waiting time (T), 702 ... fixed part (T1), 702 ... traffic dependent part (T2), 1201 ... time (t1), 1202 ... time (t2), 1204 ... time (t3), 1204 ... time (t4) ), 1205 ... time (t5), 1301 ... time (t6), 1302 ... time (t7).

Claims (7)

In a wireless terminal that communicates wireless packets between multiple wireless terminals,
A communication unit that communicates wireless packets with other wireless terminals;
A time synchronization control unit that synchronizes time with other wireless terminals,
The time synchronization control unit dynamically extends or shortens the transmission interval of packets requesting time synchronization information according to the communication traffic around the terminal ,
A wireless communication device that, when receiving the time synchronization information from the other wireless terminal without a request from the own terminal, extends a transmission interval of a packet for requesting the time synchronization information by a predetermined interval. Terminal. The wireless terminal according to claim 1 ,
The time synchronization control unit
When the packet transmission interval elapses after the previous time synchronization processing, and when the time synchronization information is received from the own terminal and the time synchronization information is received, the packet transmission interval requesting the time synchronization information A wireless terminal characterized by shortening to the shortest interval. In the wireless terminal according to claim 1 or 2 ,
The time synchronization control unit
Receiving time information in a data communication confirmation response from the other wireless terminal, adjusting a time synchronization error, and extending a transmission time of a packet requesting time synchronization information from the own terminal; Wireless terminal. Wireless network system comprising a wireless terminal according to any one of claims 1 to 3, and a gateway that allows connection to an external network. In a communication method for communicating wireless packets between a plurality of wireless terminals,
A communication step of communicating wireless packets with other wireless terminals;
A time synchronization step for synchronizing time with other wireless terminals,
The time synchronization step dynamically extends or shortens the transmission interval of packets requesting time synchronization information according to the communication traffic around the terminal ,
A communication method characterized by extending a transmission interval of packets requesting the time synchronization information when the time synchronization information is received from the other wireless terminal without a request from the own terminal. The communication method according to claim 5 , wherein
The time synchronization step includes:
When the packet transmission interval elapses after the previous time synchronization processing, and when the time synchronization information is received from the own terminal and the time synchronization information is received, the packet transmission interval requesting the time synchronization information Is shortened to the shortest interval. The communication method according to any one of claims 5 and 6 ,
The time synchronization step receives time information in the data communication confirmation response from the other wireless terminal, adjusts the time synchronization error, and extends the transmission time of the packet requesting the time synchronization information from the own terminal. A communication method characterized by:

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