JP5081874B2 - Data collection system - Google Patents

Description

  In the present invention, an integrated watt-hour meter or the like installed at each customer has a wireless communication function to form a large number of wireless communication terminals, and the wireless communication terminals constitute a network, for example, every time when meter reading data is predetermined ( The present invention relates to a system that realizes automatic meter reading and the like by transmitting to a host device by multi-hop wireless communication and collecting it at the time of occurrence of a predetermined event (timed meter reading) or a predetermined event (such as a power failure).

  Patent Document 1 discloses a typical prior art in which electricity, gas, water meter reading data, etc. are periodically taken up from the measuring instrument terminal to the host device by multi-hop wireless communication. In such a data collection system, it is necessary to perform meter reading when each terminal reaches a predetermined meter reading time, and to transmit the result to the host device at a notification time set in the own device. For this reason, it is necessary to set the clock of each terminal. Therefore, in Patent Document 2, when each terminal reaches a preset clock time set in its own device, it communicates with the host device to prevent interference even if there are many terminals in the area. , And a clock that is a reference for the above-mentioned regular notification.

JP 2000-187793 A Japanese Patent No. 3288162

  However, Patent Document 2 uses a PHS (Personal Handyphone System) transceiver mode, and each terminal A, B, C,... Is directly connected to a server device (host device) S as shown in FIG. One-to-one communication is performed. Specifically, each terminal A, B, C,... Transmits a time synchronization request at a predetermined timing, and in response to this, the server apparatus S transmits time information, so that clocks are sequentially set. Is done. Therefore, since the terminal on the terminal side (C in FIG. 6) passes through a large number of terminals A and B, the clock cannot be set due to a communication failure or the like on the way, and the accuracy of the clock may be lowered.

  Further, since each terminal A, B, C,... Sequentially communicates with the server device S, there is a problem that the network occupation time of such synchronous communication becomes long and the network throughput decreases (originally) Affects the collection of meter reading data). On the other hand, if the clock adjustment cycle is lengthened in order to suppress the decrease in throughput, the accuracy of the clock decreases. By the way, each terminal A, B, C,... Can be equipped with a device capable of acquiring accurate time information such as a GPS receiver, so that transmission / reception of such time information can be made unnecessary. In addition, the cost increases, and a terminal installed in an apartment house that is shielded by a metal door or the like may not be able to receive the GPS signal of one satellite.

  An object of the present invention is to provide a data collection system capable of improving the clock accuracy of each wireless communication terminal in a data collection system configured to collect control information of many wireless communication terminals by multi-hop wireless communication. It is.

  The data collection system of the present invention comprises a host device and a plurality of wireless communication terminals that transmit and receive control information to and from the host device by multi-hop wireless communication, and the host device is predetermined. A time generation unit that issues time information at a timing, wherein each of the wireless communication terminals includes a clock unit that holds the time information, a wireless communication unit that performs wireless communication of the control information, and a time of the clock unit An operation is performed based on the information, and the control information generated by itself is transmitted to the wireless communication unit, and the communication control unit is configured to transfer the received control information. When the wireless communication unit performs multicast transmission with the radio wave coverage as the distribution target and the information received by the wireless communication unit is time information, And a time correction unit that corrects the time of the clock unit with the time information when the received time information is later than the time of issue in the host device. .

  According to the above configuration, a plurality of wireless communication terminals form a network, and each wireless communication terminal transmits its control information to the host device by multi-hop wireless communication at a predetermined time or at a predetermined event occurrence time. In the system that realizes automatic meter reading and the like by transmitting and collecting the time information, the host device issues time information from the time generation unit at a predetermined timing and causes each wireless communication terminal to receive the time information. Then, the time information of the clock part is corrected.

  Therefore, each wireless communication terminal wirelessly communicates to the wireless communication unit based on time information of the wireless communication unit, the clock unit, and the clock unit that transmits the control information by 1: 1 multi-hop wireless communication. And a time adjustment unit that corrects the time information of the clock unit in response to the time information received by the wireless communication unit. It should be noted that this time correction unit causes the wireless communication unit to transmit the time information held by itself to the surrounding terminals by multicast transmission with the radio wave arrival range as a distribution target. When the wireless communication unit receives time information from surrounding terminals, the time correction unit compares it with time information held by itself, and the received time information is issued (generated) in the host device. When the time is late, the time of the clock unit is corrected with the time information. In addition, when the time correction unit receives the time information transmitted by the wireless communication unit in a state where the clock unit has a reception history of time information, the time information does not extend indefinitely. Even if it is received, it is not transferred to the surrounding terminals. That is, the multicast is limited to distribution to terminals that can receive transmitted radio waves, unlike broadcast that distributes to all terminals belonging to the same network.

  Therefore, many wireless communication terminals constituting the network usually correct their own clocks with time information from terminals on the higher side of the route to the host device. If the time information that exists in the surroundings and that the terminal has is newer and the time information can be received, the clock of its own device is set to that time. That is, each wireless communication terminal can synchronize the time regardless of the communication path to the host, as long as the time information transmitted from any terminal located in the vicinity can receive the radio wave that transmits the time information. .

  As a result, each wireless communication terminal is synchronized with newer time information, and the accuracy of the clock can be improved. For example, a communication failure on a route to a normal host device due to passage of a vehicle, etc. Resistance can be increased. In addition, it does not increase the number of times that time information is transmitted from the host device via a normal multi-hop route, so the network occupancy period due to the distribution of time information is suppressed, and the effect on the decrease in control information throughput and responsiveness is reduced. be able to.

  In the data collection system of the present invention, when the time correction unit receives the time information transmitted by the wireless communication unit in a state where the clock unit has no reception history of the time information, the time correction unit displays the time information. The wireless communication unit is retransmitted.

  According to the above configuration, the time correction unit of each wireless communication terminal, as described above, does not retransmit the time information multicast-transmitted from the adjacent terminal even if it is received. However, if the time information is received in a state where there is no reception history of the time information in the timepiece unit, the surrounding terminals may be connected at the beginning of power-on (start-up) or re-input after a power failure. Most of them do not have time information (no reception history). Therefore, in such a case, the retransmission is performed.

  Therefore, the clocks of the respective wireless communication terminals can be quickly adjusted at the beginning of the power-on (start-up) or at the time of re-turn-on after a long power failure.

  Furthermore, in the data collection system of the present invention, when the information received by the wireless communication unit is time information, the time correction unit is when the number of hops from the host device is greater than or equal to a predetermined reference value. Is characterized by being ignored.

  According to the above configuration, as described above, when the time information received by the wireless communication unit from the surrounding terminals is later than the time information held by the own device, When the correction unit corrects the time of the clock unit with the time information, if the number of hops from the host device is greater than or equal to a predetermined reference value, the correction is not performed and the received time information is ignored.

  Therefore, it is possible to prohibit the correction of the clock unit with time information that cannot be trusted via many routes only by the late time of generation (generation) in the host device.

  In the data collection system of the present invention, the wireless communication unit performs the multi-hop wireless communication and multicast communication according to a wireless LAN standard.

  According to the above configuration, even in a wireless LAN between channels with a wide channel interval, there is a possibility that a signal of another channel enters the frequency transition width and causes interference. Not much.

  Therefore, it is particularly effective to suppress the network occupation period due to the distribution of time information as described above.

  Furthermore, in the data collection system of the present invention, the wireless communication terminal is a measuring instrument terminal installed in each consumer, and the control information is meter reading data.

  According to the above configuration, the meter terminal installed in each consumer, for example, the integrated watt hour meter, has an enormous number of installations, and the data collection and time synchronization method of the present invention is particularly effective.

  In the data collection system of the present invention, as described above, a plurality of wireless communication terminals constitutes a network, and each wireless communication terminal transmits its control information at a predetermined time or when a predetermined event occurs. In a system that realizes automatic meter reading and the like by transmitting and collecting to the host device by communication, the host device issues time information from the time generating unit at a predetermined timing, and each wireless communication terminal The time correction unit normally corrects its own clock with the time information from the terminal on the higher side of the route to the host device. If the time information held is newer and the time information can be received, the clock of the own device is set to that time.

  Therefore, each wireless communication terminal is synchronized with newer time information, and the accuracy of the clock can be improved. For example, a communication failure in a route to a normal host device due to passage of a vehicle or the like can be obtained. Resistance can be increased. In addition, it does not increase the number of times that time information is transmitted from the host device via a normal multi-hop route, so the network occupancy period due to the distribution of time information is suppressed, and the effect on the decrease in control information throughput and responsiveness is reduced. be able to.

It is a block diagram which shows schematic structure of the meter-reading data collection system which concerns on one Embodiment of this invention. It is a front view which shows one structural example of the measuring instrument terminal in the said meter-reading data collection system. It is a block diagram which shows the example of 1 structure of a radio | wireless communication apparatus. It is a figure for demonstrating the time setting operation | movement of each measuring device terminal in the normal state in the said meter-reading data collection system. It is a figure for demonstrating the reception operation | movement of the time synchronous frame for the time setting of each measuring device terminal in the said meter-reading data collection system. It is a figure for demonstrating the transmission operation | movement of the time synchronous frame for the time setting of each meter terminal in the said meter-reading data collection system. It is a figure for demonstrating the time setting operation | movement of each measuring device terminal in the initial state in the said meter-reading data collection system. It is a figure for demonstrating the time setting operation | movement of each measuring device terminal in the typical meter-reading data collection system of a prior art.

  FIG. 1 is a block diagram showing a schematic configuration of a data collection system according to an embodiment of the present invention. This data collection system includes weighing terminals U1, U2,..., Which are wireless communication terminals installed at the respective consumers H1, H2,. When collectively referred to by the reference symbol U), the meter reading data is dynamically configured, that is, always overlooks the surroundings and autonomously switches to the route with the best transmission state to form a multi-hop wireless communication network. Is transmitted to the server device 1 as a host device and collected at predetermined time intervals or at a predetermined event occurrence time, thereby realizing automatic meter reading.

  The meter terminal U is realized as an integrated watt-hour meter in this embodiment, and performs communication according to the wireless LAN standard. Therefore, each measuring instrument terminal U performs 1: 1 wireless communication as indicated by reference numerals A1, A2, A3, and A4 in an ad hoc mode for wireless LAN terminal-to-terminal communication. When each measuring instrument terminal U is activated (turned on), it monitors the surrounding radio wave condition as described above, and the measuring instrument terminal having the best communication quality (hanging destination: measuring instrument terminal U1 in the example of FIG. 1). U2 for U3 and U4) for U3 to connect, that is, join the network, autonomously select the route to gateway 3 which is the end of the wireless communication network, and communicate in the ad hoc mode. Start.

  The gateway 3 connects a wireless communication network and a wired network 4 dedicated to a network operating company such as an electric power company. The server device 1 is connected to the wired network 4. This gateway 3 is provided in, for example, a main utility pole, and the number of accommodation terminals is about several hundreds. Further, the number of hops of each measuring instrument terminal U is several tens at the maximum, preferably 10 hops or less.

  Connected to the wired network 4 is an NTP (Network Time Protocol) server 1a, which is another host device and generates time information from its time generator. The NTP server 1a generates a time synchronization frame, which is time information, at a predetermined periodic timing such as once every 10 minutes for the gateway 3 connected by the wired network 4 such as an in-house optical fiber network, Alert. The gateway 3 that has received this performs time synchronization processing that will be described in detail later, that is, correction of the internal clock. After the processing is completed, the gateway 3 generates a time synchronization frame as will be described in detail later, and transmits it to each measuring instrument terminal U. Each measuring instrument terminal U that has received it also performs time synchronization processing, and maintains the timing of the scheduled meter reading and the transmission timing of the meter reading result with a predetermined accuracy.

  FIG. 2 is a front view showing a configuration example of the weighing instrument terminal U. This measuring instrument terminal U is configured by arranging a load switch 7, a watt hour meter 8, and a wireless communication device 5 from the terminal block 6 side to which each distribution line in the house is connected. The watt-hour meter 8 measures the accumulated power amount every predetermined period, for example, every 30 minutes, and the meter reading data is set at a timing preset by the wireless communication device 5 in the meter terminal U as will be described later. The data is transmitted to the gateway 3 to which the own device belongs and transferred to the server device 1. On the other hand, control data for performing opening / closing of the load switch 7, backup meter reading for resending non-delivery meter data, etc. is transmitted from the server device 1 via the gateway 3 to each wireless communication device 5 as necessary. Sent to These meter reading data and control data constitute control information.

  FIG. 3 is a block diagram showing a configuration example of the wireless communication device 5. The wireless communication device 5 includes a wireless communication unit 11 of the wireless LAN, a wireless communication control unit 12 that controls the communication, a clock unit 13, an interface 14 that receives meter reading data from the watt-hour meter 8, An interface 15 that transmits control information to the load switch 7, an in-machine communication control unit 16 that controls communication with the watt hour meter 8 and the load switch 7, and a memory 17 that stores the meter reading data in a backup manner. And a time correction unit 18 that corrects the time information (internal clock) of the clock unit 13 (performs the time synchronization process) as described later.

  The in-flight communication control unit 16 receives meter reading data from the watt hour meter 8 via the interface 14 at a predetermined meter reading time, for example, every minute, in response to the internal clock of the clock unit 13. Then, it is stored in the memory 17 as indicated by reference numeral 17a. In response to the internal clock, the wireless communication control unit 12 reads out the meter reading data and transmits it from the wireless communication unit 11 at a predetermined transmission time. In response to the internal clock, the wireless communication unit 11 determines the hop destination by looking around the surroundings as described above at a predetermined time, and transmits the meter reading data to the hop destination and receives the other The meter reading data from the measuring terminal U is also transferred.

  FIG. 4 is a diagram for explaining the time setting operation of each measuring instrument terminal U in the normal state in the meter-reading data collection system configured as described above. First, the gateway 3 is synchronized with the upper NTP server 1a by the NTP / SNTP client function at a predetermined cycle timing such as once every 10 minutes, and time synchronization is performed. Then, for example, the time synchronization frame is generated at a predetermined cycle timing such as once per hour, and multicast transmission is performed by using the NTP / SNTP function with the radio wave arrival range as a distribution target.

  Upon receiving this, the time correction unit 18 of each measuring instrument terminal U issues (generates) the time (NTP completion time) at the NTP server 1a of the time synchronization frame that is the basis of the internal clock of the clock unit 13 of its own device. ) When the received time synchronization frame is later than the time synchronization frame received in T1, the internal clock of the clock unit 13 is corrected with the time synchronization frame. At this time, if the number of hops from the gateway 3 of the received time synchronization frame is equal to or greater than the specified number of hops, the reliability of the time synchronization frame may be lowered via many paths. As such, the received time synchronization frame may be ignored without performing such correction.

  In addition, the time correction unit 18 refers to the clock unit 13 of its own device at the time of reporting set at a random timing, for example, once an hour, and performs time synchronization after the previous reporting timing. If not, the time synchronization frame is not transmitted to suppress traffic, and if time synchronization is performed, a time synchronization frame corresponding to the current internal clock is created and wireless communication control is performed. Multicast transmission from the unit 12. Note that a time synchronization frame may be transmitted regardless of whether or not time synchronization has been performed after the previous notification timing, and a terminal that could not be received in the surrounding area may be given a re-reception opportunity.

  Specifically, in the example of FIG. 4, terminals A, B, C, D, and E are arranged in series from the upstream side with gateway 3 as a reference. In the range of FIG. 4, communication is performed only with an adjacent terminal. Cannot be performed. That is, each gateway 3 and terminals A, B, C, D, and E can communicate with other terminals not shown in FIG. 4 (including terminals under other gateways). Assuming that time synchronization is appropriately performed via this, it is assumed that in the range of FIG. 4, communication that skips the arrangement order cannot be performed, and communication can be performed only with the front and rear terminals.

  In FIG. 4, the time synchronization frame creation times T1 held by the terminals A, B, C, D, and E in the initial state at time t0 are respectively 10:10:00, 10: 00: 00: 00, and 10:00. 0:00, 9:00: 00, 8:00: 00, and when the internal clock (current time) after synchronization with the time synchronization frame is UT, 10:20:00, 10:20:00 10:20:00, 10:20:05, 10:20:10. That is, the internal clocks UT of the terminals A, B, and C that have performed the synchronization process of the clock unit 13 with a relatively new time synchronization frame match, and the terminal D that has a synchronization process time one hour older than the internal clock UT. In the terminal E which is 5 seconds ahead and 2 hours old, the internal clock UT is advanced by 10 seconds. When the number of hops is Hop, the terminals A, B, C, D, and E are 1, 2, 3, 4, and 5 in order from the gateway 3 side.

  In this state, first, at time t1, it is assumed that the terminal C has reached the timing for issuing the random time synchronization frame once per hour. Therefore, the time correction unit 18 of the terminal C is based on the internal clock UT of the clock unit 13 corrected by the time synchronization frame created by the gateway 3 at T1 = 10: 00: 00, and the time T2 = 10: 21: A time synchronization frame to be transmitted at 00 is created and the multicast is transmitted. The terminals that can receive this are upstream B and downstream D. In this case, in the time correction unit 18 of the upstream terminal B, the creation time of the received time synchronization frame is T1 = This is the same as the time synchronization frame creation time T1 = 10: 00: 00: 00 held by the own device at 10:00, and the creation time is not newer (slower), so it is ignored. On the other hand, in FIG. 4, the terminal D on the downstream side has not received the time synchronization frame due to radio interference, and the time correction unit 18 does not perform the time synchronization process of the clock unit 13.

  Next, at time t2, it is assumed that terminal A has reached the notification timing. Therefore, the time correction unit 18 of the terminal A is based on the internal clock UT of the clock unit 13 corrected by the time synchronization frame created by the gateway 3 at T1 = 10: 10: 00, and the time T2 = 10: 30: A time synchronization frame to be transmitted at 00 is created and the multicast is transmitted. The terminal that can receive this is B on the downstream side. In this case, the time correction unit 18 of the terminal B has its own time synchronization frame creation time T1 = 10: 10: 00 Is later than the creation time T1 of the time synchronization frame held at 10:00 = 10:00: 00, the synchronization processing of the clock unit 13 is performed with the newly received time synchronization frame. The time synchronization process is performed by correcting the time required for the transmission / reception of the time synchronization frame at the terminal A in the preceding stage and the synchronization (correction) process of the clock unit 13. Further, terminal B that has received this time synchronization frame does not transfer (retransmit) the time synchronization frame as described above. On the other hand, at this time t2, the gateway 3 can also receive the time synchronization frame from the terminal A, but the gateway 3 only synchronizes with the NTP server 1a on the wired side, and the received time synchronization frame Is ignored.

  Thereafter, at time t3, the synchronization timing is once every 10 minutes. When the gateway 3 synchronizes with the NTP server 1a, immediately at the time T2 = 10: 50: 00, T1 = 10: 50: 00 The time synchronization frame is created and the multicast is transmitted. Since the terminal A that has received this is later than the time T1 creation time T1 = 10: 10: 00 of the time synchronization frame held by itself, this time synchronization frame of the clock unit 13 is received by this newly received time synchronization frame. Synchronize with.

  On the other hand, at the most downstream terminal E, at time t4, the time synchronization frame created at time T2 = 10: 25: 00 from the surrounding terminals (including terminals under different gateways as described above) Upon reception, the time correction unit 18 is based on the time synchronization frame based on the time T1 = 10: 20: 00, and is later than the time synchronization frame creation time T1 = 8: 00: 00 held by itself. Therefore, the clock unit 13 is synchronized with the newly received time synchronization frame.

  After that, at time t5, when the terminal E has reached the issue timing, it transmits a time synchronization frame of T2 = 10: 40: 00 created based on the time synchronization frame of T1 = 10: 20: 00. The terminal that can receive this is D on the upstream side, and the time adjustment unit 18 of the terminal D holds that the time T1 = 10: 20: 00 of the received time synchronization frame is held by itself. The clock unit 13 is synchronized with the newly received time synchronization frame because it is later than the creation time T1 = 9: 00 of the time synchronization frame.

  Further, at time t6, when the terminal D reaches the issue timing, it transmits a time synchronization frame of T2 = 10: 55: 00 created based on the time synchronization frame of T1 = 10: 20: 00. Terminals that can receive this are C on the upstream side and E on the downstream side, but the terminal C on the upstream side receives the creation time T1 = 10: 20: 00 of the received time synchronization frame, Since the time synchronization frame generation time T1 held is later than 10:00:00, the clock unit 13 is synchronized with the newly received time synchronization frame. However, in the downstream terminal E, the time synchronization frame creation time T1 = 10: 20: 00 received is the same as the time synchronization frame creation time T1 = 10: 20: 00 held by itself. Since the creation time is not newer (late), this time synchronization frame is ignored.

  After that, at time t7, when the terminal B comes to the final timing, the time synchronization of T2 = 11: 00: 0 created based on the time synchronization frame of T1 = 10: 10: 00 received at the time t2. Send a frame. However, the downstream side terminal C that has received this has already received the time synchronization frame of T1 = 10: 20: 00 from the downstream side terminal D at the time t6, and the newly received time synchronization frame is ignore. Similarly, the upstream terminal A has already received a time synchronization frame of T1 = 10: 50: 00 from the upstream gateway 3 at the time t3, and ignores the newly received time synchronization frame.

  FIG. 5 is a flowchart for explaining the reception operation of the time synchronization frame as described above of the time correction unit 18 in each measuring instrument terminal U. When the time synchronization frame is received, the process proceeds to step S1. First, the number of hops Hop required for the time synchronization frame to reach from the gateway 3 to the own apparatus is determined. Ignore and end processing. On the other hand, if the hop number Hop is less than 40, the process proceeds to step S2. In addition, this step S1 does not need to be provided especially as mentioned above.

  In step S2, the creation time T1 of the received time synchronization frame is compared with the creation time T1 of the time synchronization frame held by itself. If the held time synchronization frame is newer, this reception is performed. The process is terminated ignoring the time synchronization frame. On the other hand, if the received time synchronization frame is newer, the process proceeds to step S3, and the transmission time T2 of the received time synchronization frame is set (updated) in the internal clock UT of the own device, and the time synchronization frame is generated. The time T1 is updated and held, and the hop number Hop is also added and held.

  FIG. 6 is a flowchart for explaining the above-described time synchronization frame transmission operation of the time correction unit 18 in each measuring instrument terminal U. When the random issue time is reached, the process proceeds to step S11, where a new time synchronization frame is received from the previous transmission time of the time synchronization frame of the own device, it is determined whether or not it is synchronized, and is not synchronized. That is, if the clock of the own device has not been updated, the process is terminated, and if it has been updated, the process proceeds to step S12. Note that step S11 is not particularly required as described above. In step S12, a time synchronization frame from the own device is created based on the time synchronization frame held by the own device, and transmission is performed in step S13.

  On the other hand, FIG. 7 is a diagram for explaining the time setting operation of each measuring instrument terminal U in the initial state in the meter-reading data collection system. Such an operation is performed in a rare case such as when the operation is started by newly adding or moving the measuring terminal U or when recovering from a power failure. Therefore, the clock unit 13 of each terminal A, B, C, D, E does not have the internal clock UT in the time synchronization frame (indicated by an indefinite * in FIG. 7), and at time t11, the gateway 3 The time synchronization frame from the server 1a is received and time synchronization is performed. At time t12, the gateway 3 transmits the updated time synchronization frame. When the terminal A first receives the time synchronization unit 18, the time correction unit 18 uses the time synchronization frame. The internal clock UT of the clock unit 13 is corrected, and the time synchronization frame is immediately transferred (retransmitted) at time t13. As a result, the terminal B and the gateway 3 in the subsequent stage receive the same time synchronization frame, but the gateway 3 synchronizes only with the NTP server 1a, ignores it, and the terminal B modifies the clock unit 13. After that, at time t14, the time correction unit 18 of the terminal B immediately transfers (retransmits) the received time synchronization frame, the terminal A in the front stage ignores it, and the terminal C in the rear stage ignores the internal clock of the clock unit 13. Modify the UT. Thereafter, the same operation is repeated, and as a result, time synchronization is instantaneously performed in the form of broadcast transmission.

  Thus, in this embodiment, normally, the wireless communication control unit 12 causes the wireless communication unit 11 to transmit and receive meter reading data and control data by 1: 1 multi-hop wireless communication. When transmitting a time synchronization frame at a predetermined notification timing, the time correction unit 18 causes the wireless communication unit 11 to perform multicast transmission, and when the information received by the wireless communication unit 11 is a time synchronization frame, The time adjustment unit 18 compares the time synchronization frame held by the clock unit 13 of its own device with the received time synchronization frame when the notification (generation) time T1 in the NTP server 1a is later. The internal clock UT of the clock unit 13 is corrected with the time synchronization frame. In addition, when the time correction unit 18 receives the time synchronization frame transmitted by multicast in the wireless communication unit 11 in a state where the clock unit 13 has a reception history of the time synchronization frame, In order not to spread indefinitely, even if it is received, it is not transferred to surrounding terminals. That is, the multicast is limited to distribution to terminals that can receive transmitted radio waves, unlike broadcast that distributes to all terminals belonging to the same network. That is, many measuring instrument terminals U constituting the network normally synchronize time from terminals on the upper side of the route to the NTP server 1a as shown by reference numerals A2 → A1 and A4 → A3 in FIG. When a frame is used to correct its own clock, there are terminals that are out of its path, the time synchronization frame held by the terminal is newer, and the time synchronization frame is received. As shown by A10, set your watch to that position.

  As a result, each measuring instrument terminal U is synchronized with a newer time synchronization frame, so that the accuracy of the clock unit 13 can be improved and, for example, a route to the normal NTP server 1a due to passage of a vehicle or the like It is possible to increase resistance to communication failures. In addition, since the number of times the time synchronization frame is transmitted from the NTP server 1a through the normal multi-hop route is not increased, the network occupation period by the time synchronization frame is suppressed, and the influence on the decrease in the meter reading data throughput and responsiveness is small. Can be suppressed.

  In addition, in this way, in the wireless LAN used by the wireless communication unit 11, even if the channel interval is wide, it is possible to suppress the network occupation period due to the time synchronization frame. This is particularly effective because the signal may enter and cause interference, and the number of channels that can be used is not very large.

  Furthermore, the time correction unit 18 of each measuring instrument terminal U does not retransmit the time synchronization frame transmitted from the adjacent terminal even if it is received, so that this retransmission is endlessly expanded, and the traffic is increased indiscriminately. However, if a time synchronization frame is received in a state where there is no reception history of the time synchronization frame, many of the surrounding terminals are time-synchronized at the beginning of power-on (start-up) or re-input after a power failure. In such a case, it is determined that there is a high possibility that the frame is not held, and in this case, the time synchronization frame is immediately retransmitted.

  In the present embodiment, since the wireless communication terminal is a measuring instrument terminal U installed in each consumer H and transmits meter reading data, the measuring instrument terminal U such as an integrated watt hour meter The data collection and time synchronization method as in the present embodiment is particularly effective.

DESCRIPTION OF SYMBOLS 1 Server apparatus 1a NTP server 3 Gateway 4 Wired network 5 Wireless communication apparatus 6 Terminal block 7 Load switch 8 Electricity meter 11 Wireless communication part 12 Wireless communication control part 13 Clock part 14, 15 Interface 16 In-machine communication control part 17 Memory 18 Time correction unit H1, H2, ... Consumer U1, U2, ... Measuring terminal

Claims (5)

A host device and a plurality of wireless communication terminals configured to transmit and receive control information by multi-hop wireless communication between the host device and the host device;
The host device has a time generation unit that issues time information at a predetermined timing,
Each wireless communication terminal is
A clock unit holding the time information;
A wireless communication unit for performing wireless communication of the control information;
A communication control unit that performs an operation based on time information of the clock unit, causes the wireless communication unit to transmit the control information generated by itself, and transfers the received control information;
When the time information of the clock unit is transmitted from the wireless communication unit at a predetermined timing by multicast transmission with the radio wave coverage as the distribution target, and the information received by the wireless communication unit is time information, And a time correction unit that corrects the time of the clock unit with the time information when the received time information is later in the notification time in the host device. Data collection system. A host device and a plurality of wireless communication terminals configured to transmit and receive control information by multi-hop wireless communication between the host device and the host device;
The host device has a time generation unit that issues time information at a predetermined timing,
Each wireless communication terminal is
A clock unit holding the time information;
A wireless communication unit for performing wireless communication of the control information;
A communication control unit that performs an operation based on time information of the clock unit, causes the wireless communication unit to transmit the control information generated by itself, and transfers the received control information;
When the time information of the clock unit is transmitted from the wireless communication unit at a predetermined timing by multicast transmission with the radio wave coverage as the distribution target, and the information received by the wireless communication unit is time information, A time correction unit that corrects the time of the clock unit with the time information when the time of notification in the host device is later than the time information received.
When the time correction unit receives the time information that has been multicast-transmitted by the wireless communication unit in a state where the clock unit has no reception history of time information, the time correction unit causes the wireless communication unit to retransmit the time information. features and be Lud over data collection system. A host device and a plurality of wireless communication terminals configured to transmit and receive control information by multi-hop wireless communication between the host device and the host device;
The host device has a time generation unit that issues time information at a predetermined timing,
Each wireless communication terminal is
A clock unit holding the time information;
A wireless communication unit for performing wireless communication of the control information;
A communication control unit that performs an operation based on time information of the clock unit, causes the wireless communication unit to transmit the control information generated by itself, and transfers the received control information;
When the time information of the clock unit is transmitted from the wireless communication unit at a predetermined timing by multicast transmission with the radio wave coverage as the distribution target, and the information received by the wireless communication unit is time information, A time correction unit that corrects the time of the clock unit with the time information when the time of notification in the host device is later than the time information received.
The time adjustment unit, said time information received by the wireless communication unit is time information, features and to Lud over that number of hops from the host device is ignored if it is more than the reference value predetermined Data collection system.   The data collection system according to claim 1 or 2, wherein the wireless communication unit performs the multi-hop wireless communication and multicast communication according to a wireless LAN standard.   The data collection system according to any one of claims 1 to 4, wherein the wireless communication terminal is a measuring instrument terminal installed at each consumer, and the control information is meter reading data.

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