Communication Systems

Abstract

To provide a communication system capable of transmitting large-capacity or variable-length data, that is, data of arbitrary data length, with low power consumption and high reliability.SOLUTION: In a communication system according to the present invention in which a sensor node that transmits local transmission data is arranged under a gateway and sensing data that is the result of sensing the state of the installation environment of the sensor node is aggregated to a host server via the gateway, the gateway includes a gateway server capable of communicating wide area transmission data with the host server, and a gateway device that collects the local transmission data and communicates with the gateway server as wide area communication data in the gateway by intermittent communication. The gateway device and the sensor node are driven by a battery or energy harvest technology.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a communication system To Regarding. [Background technology]

[0002] As IoT-related technologies continue to develop, there exists a data collection system as shown in FIG. 1 as a system for collecting data, for example, sensor data (see Patent Document 1).

[0003] Such a data collection system (sensor network) may be composed of a sensor node Z1 that senses the state of the installation environment, packetizes the sensing data, and then outputs it as local transmission data using, for example, a private communication system utilizing the 920 MHz band; a gateway Z2 that outputs the collected local transmission data as wide-area transmission data using, for example, a mobile communication service such as 3G / 4G / 5G; and a DB server A3 that stores the wide-area transmission data in a database (DB) and visualizes it. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-122310 A Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, if it is desired to drive the above-mentioned sensor node Z1 and gateway Z2 using batteries or energy harvesting technology, for example, the following measures are required.

[0006] First, the gateway side of the mobile communication system between the gateway Z2 and the DB server A3 is operated intermittently. Second, a low-power consumption communication protocol characterized by intermittent communication is adopted for the private communication system. Third, SRAM (Static Random Access Memory) is adopted instead of DRAM (Dynamic Random Access Memory) for the main memory of the sensor node Z1 and the gateway Z2.

[0007] However, taking the above measures gives rise to the following problems.

[0008] First, when SRAM is used as the main memory, SRAM has a smaller capacity per cost than DRAM and cannot store a lot of data. Therefore, it is difficult to transmit large-volume or variable-length data such as waveform data acquired at a high sampling rate, photographs taken with a camera, and data processed from these. A typical example of variable-length data is data compressed by entropy coding.

[0009] If a protocol that maintains a session, such as Message Queuing Telemetry Transport (MQTT), which is often used in the Internet of Things (IoT), is used to connect Gateway Z2 and DB Server A3, the gateway cannot be powered down in order to maintain the session, and a large solar panel, for example, would be required.If session maintenance were to be abandoned, packets sent from DB Server A3 to Gateway Z2 while the connection between Gateway Z2 and DB Server A3 was disconnected would be lost.

[0010] Therefore, a communication system capable of transmitting large-volume or variable-length data, i.e., data of any length, with low power consumption and high reliability is required. M It is desired. [Means for solving the problem]

[0011] BooksThe invention relates to a communication system in which a sensor node that transmits local transmission data is placed under a gateway, and the sensor data, which is a result of sensing the state of the installation environment of the sensor node, is aggregated in a host server via the gateway. The gateway has: (1) a gateway server that can communicate wide-area transmission data with the host server; and (2) a gateway device that collects the local transmission data and communicates it with the gateway server by intermittent communication as intra-GW wide-area communication data; and (3) the gateway device and the sensor node are powered by a battery or an energy storage device. - Powered by Harvest Technology (4) the sensor node has (4-1) a sensing data generation unit that senses the state of the installation environment and generates the sensing data, (4-2) a packetization unit that packetizes the sensing data and outputs it as a sensor packet, and (4-3) a sensor node transmission unit that transmits the sensor packet to the gateway device as the local transmission data, (4-4) the sensor packet can express one piece of the sensing data in one or more packets by a head flag, a tail flag, and a sequence number that are fields reserved in the sensor packet, and (4-5) the gateway server restores the sensing data based on the head flag, the tail flag, and the sequence number in the sensor packet, and transmits it to the upper server as the wide-area transmission data. It is characterized by: Effect of the Invention

[0016] According to the present invention, large-volume or variable-length data, that is, data of any length, can be transmitted with low power consumption and high reliability. [Brief description of the drawings]

[0017] [Figure 1] 1 is an overall configuration diagram showing the overall configuration of a data collection system (communication system) according to a first embodiment. [Diagram 2] FIG. 2 is an internal configuration diagram showing the internal configuration of a sensor node according to the first embodiment. [Diagram 3] FIG. 2 is an internal configuration diagram showing the internal configuration of a gateway according to the first embodiment. [Figure 4] 4 is an explanatory diagram illustrating an example of the configuration of a sensor packet generated by a packetizer according to the first embodiment; FIG. [Diagram 5] FIG. 2 is a sequence diagram showing the operation of the data collection system (sensor network) according to the first embodiment. [Figure 6] FIG. 11 is a diagram showing the internal configuration of a sensing data generating unit according to a second embodiment. [Figure 7] FIG. 11 is an internal configuration diagram showing the internal configuration of a gateway device according to a second embodiment. [Figure 8]FIG. 11 is an internal configuration diagram showing the internal configuration of a gateway server according to the second embodiment. [Figure 9] FIG. 11 is a sequence diagram showing the operation of the data collection system (sensor network) according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] (A) First embodiment In the following, the communication system according to the present invention will be described. M The first embodiment will be described in detail with reference to the drawings.

[0019] (A-1) Configuration of the First Embodiment FIG. 1 is a diagram showing the overall configuration of a data collection system (communication system) according to the first embodiment.

[0020] 1, the data collection system 1 according to the first embodiment includes a plurality of sensor nodes A1, a gateway A2, and the above-mentioned DB server A3. The following describes the sensor node A1 and the gateway A2, focusing on differences from the above-mentioned sensor node Z1 and gateway Z2.

[0021] [Sensor node] FIG. 2 is a diagram showing the internal configuration of the sensor node according to the first embodiment.

[0022] In FIG. 2, the sensor node A1 includes a sensing data generating unit B11, a packetizing unit B12, and a sensor node transmitting unit B13.

[0023] The sensor node of the first embodiment may be configured as hardware, such as a dedicated IC chip equipped with each component shown in FIG. 2, or may be configured as software, centered around a CPU and a program executed by the CPU, and functionally can be represented as shown in FIG. 2.

[0024] The sensing data generating unit B11 senses the state of the installation environment and generates sensing data. The generated sensing data is provided to a packetizing unit B12.

[0025] The packetizing unit B12 packetizes the sensing data and outputs the packetized data as sensor packets to the sensor node transmitting unit B13.

[0026] The sensor node transmitting unit B13 outputs (transmits) the sensor packet as local transmission data to the gateway A2, for example, by using a private communication system that utilizes the 920 MHz band.

[0027] [gateway] FIG. 3 is a diagram illustrating an internal configuration of the gateway according to the first embodiment.

[0028] In FIG. 3, the gateway A2 has a gateway device B21 that outputs local transmission data collected from the sensor node A1 as intra-GW wide-area transmission data using a mobile communication service such as 3G / 4G / 5G, and a gateway server B22 that outputs the intra-GW wide-area transmission data as wide-area transmission data.

[0029] The gateway of the first embodiment may be configured as hardware, such as a dedicated IC chip equipped with each component shown in FIG. 3, or may be configured as software centered around a CPU and a program executed by the CPU, and functionally, it can be represented as shown in FIG. 3.

[0030] When a predetermined transmission condition is satisfied (for example, when a number of packets equal to or greater than a predetermined threshold has accumulated inside through local transmission data), the gateway device B21 activates a communication function for intra-GW wide-area transmission data and transmits data intermittently (intermittent communication) to the gateway server B22. Furthermore, when a time equal to or greater than a predetermined threshold has elapsed since the last activation of the communication function for intra-GW wide-area transmission data, the gateway device B21 may activate the communication function for intra-GW wide-area transmission data even if the number of packets has not reached the threshold, and transmit data to the gateway server B22. Furthermore, intermittent communication may be performed based on time alone, without setting a threshold for the number of packets.

[0031] Generally, mobile communication services such as 3G / 4G / 5G consume a lot of power for communication, and once communication has started, power consumption does not immediately decrease even when the communication seen from the application layer is terminated, but there is a delay before power consumption decreases. In other words, since there is overhead in power consumption, power consumption is reduced by storing a sufficient number of packets and communicating them together. The property of having overhead in power consumption when communication starts is the same for communication modules of the low-power LPWA standard LTE Cat.M1, for example, so this function is effective to a certain extent even when these communication methods are adopted for communication of wide-area transmission data within GW.

[0032] The gateway server B22 may maintain a steady session with the DB server A3 on behalf of the gateway device B21, which requires energy saving, and may cache downstream packets such as communications and retransmission requests from the DB server A3, etc., and deliver the cached packets when a connection is established with the gateway device B21.

[0033] As a result, even when the gateway A2 and the DB server A3 communicate using a protocol that maintains a session, it is possible to distribute packets from the DB server A3 to the gateway A2 with low power consumption and without loss, without installing huge solar panels, etc. Also, since the gateway server B22 can take over the power consumption required for authentication, etc., every time a connection is re-established with the DB server A3, it has the effect of reducing the power consumption of the gateway device B21 compared to the conventional gateway Z2.

[0034] Furthermore, when the gateway A2 and the DB server A3 are connected by MQTT, MQTT has a function called "Persistent Session" as a mechanism for reliably delivering the output from the gateway A2, but to enable this function, it is necessary to hold a certain amount of transmitted data in memory, etc., and a sufficient storage area is required. As in this embodiment, the gateway A2 is composed of a gateway device B21 and a gateway server B22, and the gateway server B22 is responsible for the function called Persistent Session, so that the gateway A2 can guarantee the communication quality between the gateway A2 and the DB server A3 while maintaining the power saving performance of the gateway device B21.

[0035] [Details of the packetizer, sensor node transmitter, gateway server, etc.] Next, the packetizer B12, the sensor node transmitter B13, the gateway server B22, and other related parts will be described in detail.

[0036] The packetizer B12 is characterized in that one piece of sensing data is represented by one or more packets, and this characteristic enables transmission of large-volume or variable-length data, that is, data of any length.

[0037] FIG. 4 is an explanatory diagram illustrating an example of the configuration of a sensor packet generated by the packetizer according to the first embodiment.

[0038] In FIG. 4, a sensor packet 10 has a header section H in which a source, a destination, and the like are stored, and a payload section P in which sensing data is stored.

[0039] A feature of the sensor packet 10 of the first embodiment is that the header section H includes a head flag field F1 indicating a head flag, a tail flag field F2 indicating a tail flag, and a sequence number field F3 indicating a sequence number.

[0040] The head flag is a flag indicating that the packet is the first packet in a series of packets representing one piece of sensing data, and is active when the sensor packet 10 is the first. For example, when the head flag is active, the head flag field F1 stores "1," and when the head flag is inactive (negative), it stores "0." Hereinafter, a sensor packet 10 with an active head flag will be referred to as a "head packet."

[0041] On the other hand, the tail flag is a flag that indicates that the packet is the last packet in a series of packets, and is active when the sensor packet 10 is the last. For example, when the tail flag is active, a "1" is stored in the tail flag field F2, and when the tail flag is inactive (negative), a "0" is stored. Hereinafter, a sensor packet 10 with an active head flag will be referred to as a "tail packet."

[0042] Moreover, a sensor packet 10 (hereinafter referred to as an "intermediate packet") sandwiched between a head packet and a tail packet has both its head flag and tail flag set to negative, thereby indicating that the packet is an intermediate packet. The sequence number identifies which head packet and tail packet the intermediate packet is inserted between and in what order. Note that by raising (activating) both the head flag and the tail flag, it is possible to express a single packet that transmits sensing data that can be expressed in one packet.

[0043] The packetizer B12 may packetize the input data in a sequential streaming manner and output the packetized data as a sensor packet without waiting for all data representing one piece of sensing data to be input from the sensing data generator B11. It is assumed that, when packetizing the data in a sequential streaming manner, a predetermined byte pattern is inserted or a handshake is performed between the sensing data generator B11 and the packetizer B12 so that the packetizer B12 can identify the delimiters of the sensing data in the byte sequence constituting the sensing data. For example, if the upper limit of the number of bytes that can be stored in one packet is determined to be N bytes in the protocol of the communication network that transmits the adopted local transmission data, each time N bytes are input from the sensing data generator B11, the N bytes may be packetized and output as a sensor packet without waiting for the subsequent data.

[0044] As a method for expressing one piece of sensing data in multiple packets, rather than using a head flag, a tail flag, and a sequence number, it is also possible to calculate and transmit the number of divisions, i.e., the number of packets representing one piece of sensing data, in advance. However, in order to calculate the number of divisions, the packetization unit B12 needs to know in advance the total data length of the sensing data input from the sensing data generation unit B11.

[0045] However, in order to know the total data length, the packetizer B12 must buffer all of the data that will become one piece of sensing data, or the type of data coming up from the sensing data generator B11 must be specified in advance.

[0046] If the former is selected, depending on the data length of the sensing data, it may be difficult to adopt a low-capacity SRAM with low power consumption in the sensor node A1, making it difficult to drive the sensor node A1 using batteries or energy harvesting. On the other hand, if the latter is selected, the sensing data generation unit B11 and the packetization unit B12 are tightly coupled, making it impossible to ensure the arbitrariness of the sensing data, and in particular making it impossible to receive variable-length data.

[0047] As described above, the packetizer B12 divides packets using the head flag, tail flag, and sequence number, making it possible to handle sensing data of any length while reducing the amount of memory required by the sensor node. Reducing the amount of memory makes it possible to use SRAM in the sensor node A1, which in turn reduces power consumption, making it possible to operate the sensor node on batteries or through energy harvesting.

[0048] In response to the possibility that the packetization unit B12 may split packets, the gateway server B22 refers to the head flag, tail flag, and sequence number, and if necessary, concatenates the packets to restore the sensing data and outputs it as wide-area transmission data.

[0049] Specifically, the gateway server B22 arranges the received packets (sensor packets 10) in memory according to the sequence numbers, identifies one or more packets expressing one piece of sensing data by referring to the head flag and tail flag, and generates sensing data by combining packets from a head packet with an active head flag to a tail packet with an active tail flag when one piece of sensing data is divided into two or more packets. Note that when combining, the payload section P is concatenated at the byte level, not the header section H that contains various information such as the head flag, tail flag, and sequence number.

[0050] The process of combining the divided packets requires memory buffering, and in addition, since the gateway device B21 collects data from many sensor nodes A1, it requires memory for the number of divisions multiplied by the number of sensor nodes plus a margin that takes into account packet replacement. It is difficult to perform this type of processing in a device with a small amount of memory, but by having the gateway server B22 take on this function, the gateway A2 can handle large volumes or variable length data while maintaining the power saving properties of the gateway device B21.

[0051] The sensor node transmitter B13 may cache transmitted packets as much as memory allows, and the cached packets are used to respond to retransmission requests. The packet requesting retransmission is identified by its sequence number. Since the amount of memory available for caching is limited, packets are discarded, for example, starting with the oldest packet.

[0052] In response to the sensor node transmitter B13 being able to respond to a retransmission function, the gateway server B22 may, for example, detect missing sequence numbers by arranging received packets in memory according to sequence numbers, and output a retransmission request upon detecting a missing sequence number.

[0053] Up to this point, we have mainly explained upstream data transmission from the sensor node transmitter B13 to the gateway server B22, but there is also downstream data transmission from the gateway server B22 to the sensor node transmitter B13, such as a retransmission request.

[0054] To detect missing packets, memory for managing sequence numbers of already arrived packets is required at least for the number of sensor nodes, and furthermore, taking into consideration the possibility that packets may be divided or that packets may arrive in a different order due to retransmission requests as described above, sufficient memory capacity is required to hold multiple pieces of data (number of divisions x number of sensor nodes) to guarantee complete reconstruction of sensing data. It is difficult to perform such processing in a device with little memory, but by having the gateway server B22 take on this function, the gateway A2 can handle large volumes or variable length data while maintaining the power saving properties of the gateway device B21.

[0055] For example, the packetizer B12 may assign a "type ID" indicating the data type of the sensing data to the packet, select a type ID that can express the input sensing data with the minimum number of bytes, and secure a field of the data type indicated by the type ID in the packet and write a value therein, thereby generating a sensor packet with the minimum number of bytes required. For example, if the input sensing data is an integer value that falls within [0, 255], a type ID indicating that it is a 1-byte unsigned integer is assigned, and bytes are allocated to the sensing data in the packet. Also, if the input sensing data is an integer value that falls within [-32768, 32767], a type ID indicating that it is a 2-byte signed integer is assigned, and bytes are allocated to the sensing data in the packet.

[0056] The above examples are examples in which many cases can be expressed in a single packet, but there are also cases where the sensing data does not fit into a single packet, for example when it is composed of multiple values. Therefore, this function is effective even when the packet is divided.

[0057] When splitting packets, it is up to the designer whether to place the type ID in every packet or only in a representative packet such as the head packet. This function minimizes the data length, so it is possible to reduce the amount of memory occupied by packet data and therefore the power consumption that depends on the amount of memory, as well as the power consumption required for transmission.

[0058] In response to the packetization unit B12 assigning a type ID to the data and packetizing it, the gateway server B22 changes the interpretation method of the byte sequence according to the type ID, restores the sensing data, and outputs it as wide-area transmission data.

[0059] (A-2) Operation of the First Embodiment Next, the operation of the data collection system 1 according to the first embodiment will be described in detail with reference to the drawings.

[0060] FIG. 5 is a sequence diagram showing the operation of the data collection system (sensor network) according to the first embodiment.

[0061] The sensing data generating unit B11 of the sensor node A1 generates sensing data obtained by sensing the state of the installation environment with a predetermined sensor (not shown) (S101), and outputs the sensing data to the packetizing unit B12 (S102). Note that the sensing data generating unit B11 may sequentially output bytes that can be output from the byte sequence that constitutes the sensing data.

[0062] The packetizer B12 generates packets from the byte sequence of the input sensing data (S103), and outputs them as sensor packets (S104). As described above, the input data may be packetized in a sequential streaming manner, and may be output as the sensor packets 10 shown in Fig. 4, for example. By dividing the packets using the head flag, tail flag, and sequence number, sensing data of any data length can be handled.

[0063] The sensor node transmitting unit B13 transmits the input sensor packet to the gateway device B21 as local transmission data by using a private communication system that utilizes, for example, the 920 MHz band (S105).

[0064] The gateway device B21 sequentially collects the locally transmitted data transmitted from the sensor node A1 and stores it in a cache (S106).

[0065] The gateway device B21 checks whether the amount of accumulated data is equal to or greater than a predetermined threshold (S107). If the amount of accumulated data is equal to or greater than the threshold, the gateway device B21 executes the following process. On the other hand, if the amount of accumulated data is less than the threshold, the gateway device B21 waits until data is accumulated.

[0066] When the number of accumulated data is equal to or greater than the threshold, the gateway device B21 activates the communication function of intra-GW wide-area transmission data and transmits the accumulated data as intra-GW wide-area transmission data to the gateway server B22 (S108). Note that, when a time equal to or greater than a predetermined threshold has elapsed since the last activation of the communication function of intra-GW wide-area transmission data, the gateway device B21 may activate the communication function of intra-GW wide-area transmission data and transmit the data to the gateway server B22 even if the number of data does not reach the threshold.

[0067] The gateway server B22 refers to the head flag, tail flag, and sequence number of the received data (sensor packet), and restores the sensing data by concatenating the packets if necessary (S109). Here, as described above, for example, if the received packets are arranged in memory according to the sequence numbers, the following steps S110 to S112 can be executed.

[0068] The gateway server B 22 detects whether or not there is a missing sequence number in the sensor packets arranged in memory according to the sequence numbers (S110).

[0069] When the gateway server B22 detects a missing sequence number, it requests the sensor node A1 to retransmit the sensor packet related to the missing sequence number via the gateway device B21 (S111).

[0070] The sensor node A1 (sensor node transmitter B13) transmits the locally transmitted data (sensor packet related to the missing sequence number) present in the cache to the gateway server B22 via the gateway device B21 (S112).

[0071] If the gateway server B22 is able to restore the sensing data because there are no missing sequence numbers in the aforementioned step S110, or if the gateway server B22 is able to restore the sensing data by receiving a sensor packet related to the missing sequence number in the aforementioned step S112, the gateway server B22 transmits the restored sensing data to the DB server A3 as wide-area transmission data using a mobile communication service (S113).

[0072] In addition, the gateway server B22 may maintain a steady session with the DB server A3 in place of the gateway device B21 for which power saving is required, cache downstream packets such as packets from the DB server A3, and deliver the cached packets when a connection is established with the gateway device B21.

[0073] (A-3) Effects of the First Embodiment As described above, according to the first embodiment, large-capacity or variable-length data, i.e., data of any length, can be transmitted with low power consumption and high reliability, and the sensor nodes and gateways can be powered by batteries or energy harvesting technology.

[0074] (B) Second embodiment In the following, the communication system according to the present invention will be described. M The second embodiment will be described in detail with reference to the drawings.

[0075] (B-1) Configuration of the second embodiment The data collection system (communication system) according to the second embodiment has the same configuration as the data collection system 1 of the first embodiment shown in Fig. 1, and the second embodiment will also be described using Fig. 1. However, since the internal configuration of each device is partially different from that of the first embodiment, the following description will focus on the differences.

[0076] [Sensing data generation section] FIG. 6 is a diagram showing the internal configuration of a sensing data generating unit according to the second embodiment.

[0077] In FIG. 6, the sensing data generation unit B11 has a sensing data generation core unit C111, an attachment data generation unit C112, and a sensing data integration unit C113.

[0078] The sensing data generating unit B11 has the same functions as the sensing data generating unit B11 according to the above-described first embodiment, and outputs data obtained by sensing the state of the installation environment as main data.

[0079] The additional data generating unit C112 outputs additional data (additional data) a predetermined time after the sensing data generating core unit C111 outputs the main data. The additional data is, for example, low-volume data such as temperature and humidity data, or low-volume dummy data that has no particular meaning.

[0080] The sensing data integration unit C113 sequentially outputs the given main data and additional data as sensing data. The sensing data output to the packetization unit B12 is packetized in the same manner as in the first embodiment.

[0081] As described above, the gateway server B22 detects packet loss by detecting a missing sequence number. When one piece of sensing data is divided into multiple packets and a tail packet is lost, the loss cannot be detected until the next piece of sensing data is generated and transmitted to the gateway server B22. The sensor node A1 transmits the additional data a predetermined time after the main data, thereby making it possible to detect the loss earlier.

[0082] The reason why the grant data is transmitted after a predetermined time period following the main data is that packet loss occurs depending on the physical state of the wireless environment and the state of the repeater. Since these conditions change over time, the transmission timing of the main data and the grant data is intentionally shifted to transmit them under different conditions, that is, under different packet loss probabilities.

[0083] The assignment data generating unit C112 may include, as part of the assignment data, a command to request the gateway device B21 to start a communication function for intra-GW wide-area transmission data. Upon receiving the command, the gateway device B21 immediately starts the communication function for intra-GW wide-area transmission data and outputs the intra-GW wide-area transmission data.

[0084] As described above, in the data collection system 1, the gateway server B22 detects packet loss by detecting a missing sequence number, but since the sensing data is cached in the gateway device B21, packet loss is not detected until the communication function for intra-GW wide-area transmission data is activated. Since there are times when packet loss needs to be detected immediately, such as for emergency data, the delay until packet loss detection can be reduced by including a command to the gateway device B21 to activate the communication function for intra-GW wide-area transmission data as part of the attached data. However, if the communication function for intra-GW wide-area transmission data is activated every time all main data is transmitted, the power consumption of the gateway device B21 will increase significantly, so a setting is made to indicate the timing of including the command in advance, such as including a command to request activation of the communication function for intra-GW wide-area transmission data only at a set time or when the device is in emergency mode.

[0085] [Gateway device, gateway server] FIG. 7 is a diagram showing an internal configuration of a gateway device according to the second embodiment.

[0086] In FIG. 7, the gateway device B21 includes a gateway device packet interval control unit C211 and a gateway device core unit C212.

[0087] The gateway device core unit C212 has the same functions as the gateway device B21 according to the above-described first embodiment. The gateway device core unit C212 receives the GW device internal data from the gateway device packet interval control unit C211.

[0088] The gateway device packet interval control unit C211 controls the transmission interval of downstream packets from the gateway device core unit C212 to the sensor node transmission unit B13 so that it is equal to or longer than a predetermined time. In other words, if downstream packets arrive at the gateway device packet interval control unit C211 at an interval shorter than the predetermined time, a wait process is inserted for the predetermined time and the downstream packets are sequentially output to the sensor node transmission unit B13.

[0089] Since the amount of data that can be communicated in a wireless environment is limited, the probability of packet loss increases when multiple packets are transmitted and received at the same time. If the private communication system used for transmitting local transmission data is characterized by power saving, the probability of packet loss increases further due to the small buffer capacity in the communication module. In particular, if the private communication system described above is capable of communicating by relaying multiple communication modules and each communication module performs intermittent communication, there is a high probability of packet loss when transmitting and receiving simultaneously. Since the timing and amount of downstream packets generated depend on the occurrence status of packet loss and cannot be determined, the gateway device packet interval control unit C211 controls the transmission interval of downstream packets in order to prevent further congestion of the network due to downstream packets such as retransmission requests.

[0090] In particular, in this embodiment, the sensing data is cached in the gateway device B21, and data from multiple sensor nodes A1 is sent together at the timing of starting the communication function for intra-GW wide-area transmission data, so there is a possibility that multiple retransmission requests addressed to different sensor nodes A1 are generated together in the gateway server B22 that manages missing sequence numbers. Since packets generated together cause network congestion as described above, controlling the transmission interval of downstream packets, including retransmission requests, to be sufficiently large contributes to improving communication quality.

[0091] The predetermined transmission interval may be automatically determined as a value obtained by multiplying N+1 (the number of sensor nodes N generating upstream packets plus the number of gateways 1 generating downstream packets) by the packet transmission interval of the private communication system, with the number of sensor nodes A1 participating in the network, i.e., the number of sensor nodes A1 connected to the gateway A2, being known to the gateway apparatus packet interval control unit C211. As a method for the gateway apparatus packet interval control unit C211 to obtain the number of sensor nodes A1 participating in the network, various methods can be considered, such as a method of setting the number in advance, or a method of counting the number of events notifying that the sensor node A1 has participated in the network.

[0092] Although the above-mentioned FIG. 7 shows a configuration in which the transmission interval of downstream packets is controlled in the gateway device B21, a configuration in which the transmission interval of downstream packets is controlled in the gateway server B22 as shown in the following FIG. 8 may be adopted.

[0093] FIG. 8 is a diagram showing the internal configuration of the gateway server according to the second embodiment.

[0094] In FIG. 8, the gateway server B22 has a gateway server packet interval control section C221 and a gateway server core section C222.

[0095] The gateway server core unit C222 has the same functions as the gateway server B22 according to the above-described first embodiment, and receives data in the GW server from the gateway device B21.

[0096] The gateway server packet interval control unit C221 has the same function as the above-mentioned gateway apparatus packet interval control unit C211.

[0097] In addition, when the aforementioned predetermined transmission interval is automatically determined based on the number of sensor nodes participating in the aforementioned network, the number of sensor nodes A1 connected to the gateway A2, etc. is transmitted from the gateway device B21 to the gateway server B22.

[0098] Furthermore, when the gateway device B21 and the gateway server B22 control the packet interval, downstream packets such as communications from the DB server A3 and the like and the aforementioned retransmission requests are cached. At this time, it is effective for the gateway device packet interval control unit C211 and the gateway server packet interval control unit C221 to transmit the aforementioned retransmission request packets preferentially among the cached downstream packets. In order to distinguish between retransmission request packets and other packets, for example, a field indicating the packet type is prepared in each packet.

[0099] As described above, the sensor node A1 and the gateway device B21 do not have an abundant storage area, and the memory for backing up packets already sent for retransmission is smaller than that of a server computer. If a downstream packet requesting new sensing is delivered before a packet requesting retransmission, some of the packets already sent for retransmission (for example, an old packet in many cases) may be overwritten by a new packet due to the new sensing, which may result in a risk of retransmission failure. By prioritizing the transmission of the retransmission request packet among the cached downstream packets, this risk can be reduced, enabling more reliable communication.

[0100] Since the function of the sensing data generation unit B11, the function of the gateway device B21, and the function of the gateway server B22 are independent of each other, a certain effect can be achieved even if only one of them is applied to the data collection system 1. In particular, since the purpose of the gateway device B21 or the gateway server B22 is the same, a sufficient effect can be achieved by implementing either one of them.

[0101] However, controlling the packet transmission intervals in the gateway server B22 rather than in the gateway device B21 can reduce the amount of memory required in the gateway device B21, which in turn enables the use of low-power memory, and is expected to reduce power consumption.

[0102] (B-2) Operation of the Second Embodiment Next, the operation of the data collection system 1 according to the second embodiment will be described in detail with reference to the drawings.

[0103] Fig. 9 is a sequence diagram showing the operation of a data collection system (sensor network) according to the second embodiment. In Fig. 9, the same reference numerals are used to denote processes that are the same as or correspond to the characteristic operations in Fig. 5 according to the first embodiment. Detailed descriptions of the processes that are the same as or correspond to the characteristic operations in Fig. 5 according to the first embodiment will be omitted to avoid duplication.

[0104] The sensing data generation core unit C111 executes processing similar to that of step S101 described above (outputs the main data), and the attachment data generation unit C112 generates attachment data a predetermined period of time after the sensing data generation core unit C111 outputs the main data, and the sensing data integration unit C113 sequentially outputs the main data and the attachment data as sensing data (S201).

[0105] If there is a missing sequence number in the aforementioned step S110, the gateway server packet interval control unit C221 controls the transmission interval of downstream packets (here, retransmission requests of sensor packets related to the missing sequence number) to be equal to or longer than a predetermined time (S202).

[0106] If the transmission interval satisfies the condition in the above-mentioned step S202, the gateway server packet interval control unit C221 transmits a downstream packet to the sensor node A1 (the sensor node A1 via the gateway device B21) (S203).

[0107] When the gateway device packet interval control unit C211 receives a downstream packet (here, a retransmission request for the sensor packet related to the missing sequence number) from the gateway server B22, it controls the transmission interval in the same manner as in step S202 described above (S204).

[0108] If the transmission interval satisfies the condition in step S204, the gateway device packet interval control unit C211 transmits the downstream packet to the sensor node A1 (S205). The subsequent processing is the same as in the first embodiment, and therefore the description will be omitted.

[0109] In the above FIG. 9, a retransmission request has been described as an example of controlling the transmission interval of downstream packets. However, the transmission interval control of steps S202 to S205 described above is also performed for downstream packets such as commands from DB server A3 to sensor node A1 in the same manner.

[0110] As described above, the control of the transmission interval of downstream packets may be performed only by either the gateway server B22 (steps S202, S203) or the gateway device B21 (steps S204, S205).

[0111] (B-3) Effects of the Second Embodiment As described above, according to the second embodiment, in addition to the effects described in the first embodiment, it is possible to detect a retransmission request early even in a situation where intra-GW wide-area transmission data is communicated intermittently, and by providing a mechanism for preventing further network congestion due to the retransmission request, it is possible to transmit data of any length with low power consumption and high reliability. Furthermore, it is possible to drive the sensor node and the gateway by batteries or energy harvesting technology.

[0112] (C) Other embodiments The present invention is not limited to the above-described first and second embodiments, and may include modified embodiments such as those exemplified below.

[0113] (C-1) In the above first and second embodiments, the power supply configuration of the sensor node A1 and / or the gateway device B21 is not particularly limited, but the effects of the present invention are most pronounced when the sensor node A1 and / or the gateway device B21 are battery-powered or equipped with a power generation device using energy harvesting technology such as a solar panel. The problem to be solved by the present invention is to transmit data of any length with low power consumption and high reliability, and power saving is required especially when it is desired to operate the sensor node A1 and / or the gateway device B21 using battery power or a power generation device using energy harvesting technology such as a solar panel.

[0114] (C-2) In the above first and second embodiments, the sensor node A1 and the gateway device B21 are assumed to be physically separate devices. However, the gateway device B21 may contain software having the functions of the sensor node A1. In this case, communication will take place via a virtual private communication system.

[0115] (C-3) In the above first and second embodiments, the effects of the present invention are achieved whether the gateway server B22 and the DB server A3 operate on different devices (computers) or on the same device (computer).

[0116] (C-4) In the above first and second embodiments, a method may be adopted in which the gateway server B22 can wake up the gateway device B21 when there are packets even if the mobile communication system is a low-power-consumption system such as the energy-saving LPWA standard LTE Cat.M1. In this case, once communication is started, the power consumption does not immediately decrease even if the communication seen from the application layer is ended, but a delay occurs until the power consumption decreases, that is, there is overhead in the power consumption. Therefore, the gateway server B22 can store downstream packets and communicate them together, that is, the power consumption due to the overhead is consolidated, which has the effect of reducing power consumption. However, this is limited to downstream packets for which the transmission delay to the sensor node A1 is not a problem.

[0117] (C-5) In the first embodiment, when the head flag and tail flag are both negative, it is considered to be an intermediate packet, and when they are both positive, it is considered to be a single packet. However, as long as it is possible to distinguish between intermediate packets and single packets, it is also possible to consider when the head flag and tail flag are both positive, it is considered to be an intermediate packet, and when they are both negative, it is considered to be a single packet.

[0118] (C-6) In the second embodiment, the sensing data integration unit C113 sequentially outputs the main data and the additional data as sensing data to the packetization unit B12, but as a modified example, the main data and the additional data may be assigned a series of sequence numbers (sequence numbers in a numbering system different from the sequence numbers of the packetization unit B12) and output as sensing data. By assigning sequence numbers to the sensing data, the sensing data can be managed by sequence numbers in the same way as the above-mentioned sensor packets. [Explanation of symbols]

[0119] 1...data collection system, 10...sensor packet, A1...sensor node, A2...gateway, A3...DB server, B11...sensing data generation unit, B12...packetization unit, B13...sensor node transmission unit, B21...gateway device, B22...gateway server, C111...sensing data generation core unit, C112...attachment data generation unit, C113...sensing data integration unit, C211...gateway device packet interval control unit, C212...gateway device core unit, C221...gateway server packet interval control unit, C222...gateway server core unit, F1...head flag field, F2...tail flag field, F3...sequence number field, H...header unit, P...payload unit.

Claims

1. A communication system in which a sensor node that transmits local transmission data is placed under a gateway, and sensing data obtained by sensing the state of an installation environment of the sensor node is collected in a higher-level server via the gateway, The gateway, a gateway server capable of communicating wide area transmission data with the upper server; A gateway device that collects the local transmission data and communicates the data with the gateway server through intermittent communication as intra-GW wide area communication data; The gateway device and the sensor node are driven by a battery or an energy harvesting technology, The sensor node includes: a sensing data generating unit that senses a state of an installation environment and generates the sensing data; a packetizing unit that packetizes the sensing data and outputs the packetized data as a sensor packet; a sensor node transmitting unit that transmits the sensor packet to the gateway device as the local transmission data; The sensor packet can express one piece of sensing data in one or more packets by using a head flag, a tail flag, and a sequence number, which are fields reserved in the sensor packet, and The gateway server restores the sensing data based on the head flag, the tail flag, and the sequence number in the sensor packet, and transmits the restored sensing data to the upper server as the wide-area transmission data. A communication system comprising:

2. the sensor node transmitting unit caches the sensor packet transmitted as the local transmission data as a transmitted packet, and when a retransmission request is received using the designated sequence number, retransmits the corresponding transmitted packet; The gateway server detects a missing sequence number of the sensor packet received as the intra-GW wide area communication data, and for the sensor packet for which the missing sequence number has been detected, transmits a retransmission request specifying the sequence number as a downstream packet to the sensor node via the gateway device.

2. The communication system according to claim 1 .

3. the packetization unit assigns a type ID indicating a data type of the sensing data to the sensor packet, selects the type ID capable of expressing the sensing data input from the sensing data generation unit in a minimum number of bytes, and secures a field of the data type indicated by the type ID in the sensor packet and writes a value therein, thereby generating the sensor packet in the minimum number of bytes required; The gateway server changes the interpretation method of the byte sequence according to the type ID to restore the sensing data and outputs the restored data as the wide-area transmission data.

3. The communication system according to claim 2.

4. The sensing data generation unit a sensing data generation core unit that senses the state of the installation environment and generates main data; an additional data generating unit that outputs low-capacity additional data a predetermined time after the sensing data generating core unit outputs the main data; a sensing data integration unit that associates the main data with the additional data and sequentially outputs the associated data as the sensing data; 4. The communication system according to claim 2 or 3.

5. The grant data includes a command to request the gateway device to activate a communication function for the wide area communication data within the GW, Upon receiving the command, the gateway device immediately starts a communication function for the intra-GW wide-area communication data and outputs the intra-GW wide-area communication data.

5. The communication system according to claim 4.

6. The gateway device includes: A gateway device core unit that communicates the intra-GW wide area communication data with the gateway server through intermittent communication; a gateway device packet interval control unit that collects the local transmission data and communicates data within the gateway device with the gateway device core unit; The gateway device packet interval control unit controls communication so that the transmission interval of downstream packets is equal to or longer than a predetermined time.

6. The communication system according to claim 1, wherein the first and second communication devices are connected to each other.

7. 7. The communication system according to claim 6, wherein the gateway device packet interval control unit sets a transmission interval of downstream packets to a value obtained by multiplying the number of the sensor nodes connected to the gateway plus one gateway, by a packet transmission interval of a wireless system used for communicating the local transmission data.

8. 8. The communication system according to claim 6, wherein the gateway device packet interval control unit transmits, from among the cached downstream packets, packets requesting retransmission with priority.

9. The gateway server includes: a gateway server core unit capable of communicating the wide area transmission data with the upper server; a gateway server packet interval control unit for communicating intra-GW wide area communication data with the gateway device and for communicating intra-GW server data with the gateway server core unit; The gateway server packet interval control unit controls communication so that the transmission interval of downstream packets is equal to or longer than a predetermined time. A communication system according to any one of claims 1 to 8.

10. 10. The communication system according to claim 9, wherein the gateway server packet interval control unit sets a downstream packet transmission interval by a value obtained by multiplying the number of the sensor nodes connected to the gateway plus one gateway, by the packet transmission interval of a wireless system used for communicating the local transmission data.

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