Terminal device, aggregation device, control circuit, storage medium, and communication quality control method

Abstract

A terminal device (40) that transmits data to an aggregation device in a smart meter system includes a storage unit (45) that stores a communication quality information table (45a) in which, for each wireless link capable of wireless communication in the terminal device (40), a reception strength, a number of consecutive receptions of arrival confirmations from the aggregation device or other terminal devices, a number of consecutive times when arrival confirmations have not been received, and a modulation / coding scheme value that is a combination of a modulation scheme and a coding rate are recorded; and a table management unit that, when adjusting the modulation / coding scheme value based on the number of consecutive receptions of arrival confirmations or the number of consecutive times when arrival confirmations have not been received, corrects an upper limit value of the modulation / coding scheme value before determining whether the modulation / coding scheme value is to increase and corrects a lower limit value of the modulation / coding scheme value before determining whether the modulation / coding scheme value is to decrease, based on the reception strength at the time of adjustment.

Description

[Technical field]

[0001] The present disclosure relates to a terminal device, an aggregation device, a control circuit, a storage medium, and a communication quality control method used in a smart meter system. [Background technology]

[0002] The next-generation smart meter system to be introduced from 2025 will perform various communications such as environmental value trading and collection of power waveform data in addition to conventional automatic meter reading, and an increase in traffic is expected. In order to deal with the increase in traffic, in addition to the conventional 920MHz band multi-hop communication using Gaussian Frequency Shift Keying (GFSK), the introduction of 920MHz band multi-hop communication using Orthogonal Frequency Division Multiplexing (OFDM), which supports multiple MCS (Modulation and Coding Schemes) including high rates, is being considered. Since the communication quality of the wireless links between an aggregation device and a terminal device and between two terminal devices differs depending on the installation location, it is necessary to select an appropriate MCS for each wireless link in order to maximize the communication capacity of the entire system.

[0003] In response to such a problem, Patent Document 1 discloses a technique in which a wireless communication device selects an appropriate transmission power and modulation multi-level number according to the state of the propagation path between the wireless communication device and the opposite device. When the wireless communication device of Patent Document 1 determines that there is a high possibility that the modulation multi-level number should be increased based on the reception level of the device itself or the opposite device, the wireless communication device reduces the transmission power of the device itself, and then determines whether or not the modulation multi-level number should actually be increased according to the CNR (Carrier to Noise Ratio) of the device itself or the opposite device. The wireless communication device of Patent Document 1 also performs a similar determination when decreasing the modulation multi-level number. Moreover, the wireless communication device of Patent Document 1 increases the upper limit of the selection range of the modulation multi-level number as the reception level becomes higher, and performs control to lower the transmission power of the device itself, while decreasing the upper limit of the selection range of the modulation multi-level number as the reception level becomes lower. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-188808 A Summary of the Invention [Problem to be solved by the invention]

[0005] In smart meter systems, because transmission opportunities are limited due to the transmission time restrictions of the 920 MHz band, it is necessary to reduce the number of adjustments required to converge to an appropriate MCS as much as possible. However, the above conventional technology maintains an appropriate modulation level by making frequent adjustments. Therefore, there is a problem that the above conventional technology cannot be applied to smart meter systems with limited transmission opportunities.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a terminal device that can select an appropriate modulation and coding scheme value while suppressing an increase in the number of adjustments in wireless communication in a smart meter system. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a terminal device that transmits data to an aggregation device in a smart meter system. The terminal device is characterized by comprising: a storage unit that stores a communication quality information table in which, for each wireless link capable of wireless communication in the terminal device, a reception strength, a number of consecutive receptions of arrival confirmations from the aggregation device or other terminal devices, a number of consecutive non-receptions of arrival confirmations, and a modulation and coding scheme value that is a combination of a modulation scheme and a coding rate are recorded; and a table management unit that, when adjusting the modulation and coding scheme value based on the number of consecutive receptions of arrival confirmations or the number of consecutive non-receptions of arrival confirmations, corrects an upper limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is to be increased and corrects a lower limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is to be decreased, based on the reception strength at the time of adjustment. Effect of the Invention

[0008] The terminal device according to the present disclosure has an effect of being able to select an appropriate modulation and coding scheme value while suppressing an increase in the number of adjustments in wireless communication in a smart meter system. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration example of a smart meter system according to a first embodiment; [Diagram 2] FIG. 1 is a block diagram showing a configuration example of an aggregation device according to a first embodiment; [Diagram 3] FIG. 1 is a block diagram showing a configuration example of a terminal device according to a first embodiment; [Figure 4] FIG. 13 is a diagram showing an example of a communication quality information table stored in a storage unit of a terminal device and an example of a communication quality information table stored in a storage unit of an aggregation device according to the first embodiment; [Diagram 5] A flowchart showing the operation of a data transmission process of a terminal device and an aggregation device according to the first embodiment. [Figure 6] A flowchart showing the operation of the terminal device and the aggregation device for determining MCS increase according to the first embodiment. [Figure 7] A flowchart showing the operation of the terminal device and the aggregation device for determining MCS drop according to the first embodiment. [Figure 8] A flowchart showing the operation of a data reception process of a terminal device and an aggregation device according to the first embodiment. [Figure 9] A flowchart showing the operation of calculating an average RSSI (Received Signal Strength Indicator) of received frames by a terminal device and an aggregation device according to the first embodiment. [Figure 10] FIG. 1 is a diagram showing an example of the configuration of a processing circuit that realizes a terminal device according to a first embodiment when the processing circuit is configured with a processor and a memory; [Figure 11] FIG. 1 is a diagram showing an example of a processing circuit for implementing a terminal device according to a first embodiment when the processing circuit is configured with dedicated hardware; [Figure 12]A flowchart showing the operation of a data reception process of a terminal device according to a second embodiment. [Figure 13] A flowchart showing the operation of a data transmission process of a terminal device and an aggregation device according to a second embodiment. [Figure 14] A flowchart showing an operation of adjusting parameters of communication quality information of an aggregation device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A terminal device, an aggregation device, a control circuit, a storage medium, and a communication quality control method according to embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

[0011] Embodiment 1 FIG. 1 is a diagram showing a configuration example of a smart meter system 10 according to the first embodiment. The smart meter system 10 includes a server device 20, an aggregation device 30, and terminal devices 40-1 to 40-3. The terminal devices 40-1 to 40-3 have the same configuration, and are referred to as terminal devices 40 when there is no need to distinguish between the terminal devices 40-1 to 40-3. In the smart meter system 10, the terminal device 40 measures the amount of power usage and transmits data including the measured value of the amount of power usage to the aggregation device 30 via wireless communication. The aggregation device 30 aggregates data from the multiple terminal devices 40 and transmits the aggregated data to the server device 20 via wired communication. The aggregation device 30 also transmits control data to the terminal device 40 via wireless communication. The server device 20 accumulates and manages the data received from the aggregation device 30. The smart meter system 10 is assumed to perform wired communication between the server device 20 and the aggregation device 30, wireless communication between the aggregation device 30 and the terminal device 40, and wireless communication between the terminal devices 40 themselves; however, the system may also be configured such that the server device 20 and the aggregation device 30 perform wireless communication.

[0012] In the example of FIG. 1, the smart meter system 10 includes one aggregation device 30 and three terminal devices 40, but it is also possible to include two or more aggregation devices 30 and four or more terminal devices 40. In the smart meter system 10, when the aggregation device 30 and the terminal device 40 of the communication target cannot directly communicate with each other by wireless communication, another terminal device 40 on the path between the aggregation device 30 and the terminal device 40 of the communication target relays data transmission between the aggregation device 30 and the terminal device 40 of the communication target. In the example of FIG. 1, if the terminal device 40-3 is the terminal device 40 of the communication target, the terminal device 40-2 is the other terminal device 40. The path between the aggregation device 30 and the terminal device 40 of the communication target may be determined by the aggregation device 30 or may be determined autonomously between the terminal devices 40.

[0013] In the smart meter system 10, when a terminal device 40 transmits data, another terminal device 40 or an aggregation device 30 that receives the data transmits an ACK to the terminal device 40 that transmitted the data. Similarly, when an aggregation device 30 transmits data, the terminal device 40 that receives the data transmits an ACK to the aggregation device 30 that transmitted the data. In the following description, the ACK may be referred to as an arrival confirmation.

[0014] The following describes the configuration of the aggregation device 30. Fig. 2 is a block diagram showing an example of the configuration of the aggregation device 30 according to the first embodiment. The aggregation device 30 includes a wireless communication unit 31, a wireless communication control unit 32, a data processing unit 33, a table management unit 34, a storage unit 35 that stores a communication quality information table 35a, a server communication control unit 36, and a server communication unit 37.

[0015] When the wireless communication unit 31 receives data from the terminal device 40, it converts information included in the data into a format readable by the wireless communication control unit 32 and transmits the converted information to the wireless communication control unit 32. In addition, the wireless communication unit 31 converts information obtained from the wireless communication control unit 32 into a format readable by the terminal device 40 and transmits data including the converted information to the terminal device 40.

[0016] The wireless communication control unit 32 converts the information acquired from the wireless communication unit 31 into a format readable by the data processing unit 33, and transmits the information to the data processing unit 33. The wireless communication control unit 32 also converts the information acquired from the data processing unit 33 into a format readable by the wireless communication unit 31, and transmits the information to the wireless communication unit 31.

[0017] The data processing unit 33 extracts information required by the table management unit 34 or the server communication control unit 36 ​​from the information acquired from the wireless communication control unit 32. The data processing unit 33 converts information required by the table management unit 34 into a format readable by the table management unit 34 and transmits it to the table management unit 34, and converts information required by the server communication control unit 36 ​​into a format readable by the server communication control unit 36 ​​and transmits it to the server communication control unit 36. The data processing unit 33 also extracts information required by the wireless communication control unit 32 from the information acquired from the table management unit 34 or the server communication control unit 36, converts it into a format readable by the wireless communication control unit 32, and transmits it to the wireless communication control unit 32.

[0018] The table management unit 34 generates communication quality information based on the information acquired from the data processing unit 33, and records the generated communication quality information in a communication quality information table 35a stored in the storage unit 35. Furthermore, when the data processing unit 33 requests the table management unit 34 to read communication quality information about a specific wireless link, the table management unit 34 acquires the communication quality information of the specific wireless link from the communication quality information table 35a, converts it into a format readable by the data processing unit 33, and transmits it to the data processing unit 33.

[0019] The storage unit 35 stores a communication quality information table 35a. The communication quality information table 35a records communication quality information for each wireless link in response to an operation from the table management unit 34. In the communication quality information table 35a, communication quality information is written, read, and the like in response to an operation from the table management unit 34.

[0020] The server communication control unit 36 ​​converts the information acquired from the data processing unit 33 into a format readable by the server communication unit 37, and transmits it to the server communication unit 37. The server communication control unit 36 ​​also converts the information acquired from the server communication unit 37 into a format readable by the data processing unit 33, and transmits it to the data processing unit 33.

[0021] The server communication unit 37 converts the information acquired from the server communication control unit 36 ​​into a format readable by the server device 20, and transmits the information to the server device 20. The server communication unit 37 also converts the information acquired from the server device 20 into a format readable by the server communication control unit 36, and transmits the information to the server communication control unit 36.

[0022] Next, a description will be given of the configuration of the terminal device 40. Fig. 3 is a block diagram showing an example of the configuration of the terminal device 40 according to the embodiment 1. The terminal device 40 includes a wireless communication unit 41, a wireless communication control unit 42, a data processing unit 43, a table management unit 44, and a storage unit 45 that stores a communication quality information table 45a.

[0023] When the wireless communication unit 41 receives data from the aggregation device 30 or the terminal device 40, it converts information included in the data into a format readable by the wireless communication control unit 42 and transmits the converted information to the wireless communication control unit 42. In addition, the wireless communication unit 41 converts information acquired from the wireless communication control unit 42 into a format readable by the aggregation device 30 or the terminal device 40 and transmits data including the converted information to the aggregation device 30 or the terminal device 40.

[0024] The wireless communication control unit 42 converts the information acquired from the wireless communication unit 41 into a format readable by the data processing unit 43, and transmits the information to the data processing unit 43. The wireless communication control unit 42 also converts the information acquired from the data processing unit 43 into a format readable by the wireless communication unit 41, and transmits the information to the wireless communication unit 41.

[0025] The data processing unit 43 converts the information acquired from the wireless communication control unit 42 into a format readable by the table management unit 44, and transmits it to the table management unit 44. The data processing unit 43 also converts the information acquired from the table management unit 44 into a format readable by the wireless communication control unit 42, and transmits it to the wireless communication control unit 42.

[0026] The table management unit 44 generates communication quality information based on the information acquired from the data processing unit 43, and records the generated communication quality information in a communication quality information table 45a stored in the storage unit 45. Furthermore, when the data processing unit 43 requests the table management unit 44 to read communication quality information about a specific wireless link, the table management unit 44 acquires the communication quality information of the specific wireless link from the communication quality information table 45a, converts it into a format readable by the data processing unit 43, and transmits it to the data processing unit 43.

[0027] The storage unit 45 stores a communication quality information table 45a. The communication quality information table 45a records communication quality information for each wireless link in response to an operation from the table management unit 44. In the communication quality information table 45a, communication quality information is written, read, and the like in response to an operation from the table management unit 44.

[0028] Next, the operation of transmitting data from the terminal device 40 to the aggregation device 30, that is, the operation of the upstream communication of the terminal device 40 will be described. A certain terminal device 40 transmits data from itself to the aggregation device 30. When a certain terminal device 40 and the aggregation device 30 cannot wirelessly communicate with each other, another terminal device 40 on the path relays the data transmission from the certain terminal device 40 to the aggregation device 30. At this time, the path for relaying may be determined by the aggregation device 30 or may be determined autonomously between the terminal devices 40. In the following description, both the case where the terminal device 40 transmits data to the aggregation device 30 and the case where another terminal device 40 relays data from a certain terminal device 40 to the aggregation device 30 will be collectively treated as "data transmission processing".

[0029] Prior to the description of the data transmission process, the contents of the communication quality information table 45a will be described. FIG. 4 is a diagram showing an example of the communication quality information table 45a stored in the storage unit 45 of the terminal device 40 and the communication quality information table 35a stored in the storage unit 35 of the aggregation device 30 in the first embodiment. The communication quality information table 45a and the communication quality information table 35a have the same configuration, but will be described here as the communication quality information table 45a. The communication quality information table 45a is created independently in each terminal device 40, and holds a record for each wireless link that can wirelessly communicate with the terminal device 40, that is, for each aggregation device 30 or terminal device 40 that can wirelessly communicate. Each record of the communication quality information table 45a preferably includes, that is, records, for the corresponding wireless link identified by the number or MAC (Media Access Control) address, an average RSSI which is the reception strength of frames received in the past, an update time of the average RSSI which is the reception strength, the number of consecutive ACK receptions for data transmission on the corresponding wireless link, the number of consecutive ACK non-receptions for data transmission on the corresponding wireless link, and an MCS selection value used for transmission on the corresponding wireless link. Here, the ACK is transmitted from the aggregation device 30 or another terminal device 40. In the following description, the MCS selection value may be simply referred to as MCS, and the MCS may be referred to as a modulation and coding scheme value. The modulation and coding scheme value is a combination of a modulation scheme and a coding rate.

[0030] The terminal device 40 updates the initial MCS value, the upper limit MCS value, the lower limit MCS value, the threshold for the number of consecutive ACK receptions, and the threshold for the number of consecutive ACK non-receptions based on the average RSSI in the communication quality information table 45a at a specified timing in the data transmission process described later. It is assumed that the terminal device 40 has separately acquired the correspondence relationship between the average RSSI and the initial MCS value, the upper limit MCS value, the lower limit MCS value, the threshold for the number of consecutive ACK receptions, and the threshold for the number of consecutive ACK non-receptions before or during operation.

[0031] The operation of the data transmission process of the terminal device 40 will be described using a flowchart. FIG. 5 is a flowchart showing the operation of the data transmission process of the terminal device 40 and the aggregation device 30 according to the first embodiment. The operations of the data transmission process of the terminal device 40 and the aggregation device 30 are similar, but here, the operation of the data transmission process of the terminal device 40 will be described. In the terminal device 40, the table management unit 44 checks whether or not the MCS selection value of the wireless link to be used is in the communication quality information table 45a (step S11). In FIG. 5, for the sake of simplicity, the communication quality information table 45a is written as a table. The same applies hereinafter. If the MCS selection value of the wireless link to be used is not in the communication quality information table 45a (step S11: No), the table management unit 44 of the terminal device 40 refers to the communication quality information table 45a to read the average RSSI of frames previously received through the wireless link (step S12), and records the MCS initial value corresponding to the average RSSI in the communication quality information table 45a as the MCS selection value (step S13). That is, when there is no past record of MCS at the time of adjusting MCS, the table management unit 44 of the terminal device 40 determines the initial value of MCS based on the average RSSI, which is the reception strength.

[0032] If the MCS selection value of the wireless link to be used is in the communication quality information table 45a (step S11: Yes), the table management unit 44 of the terminal device 40 checks whether the number of consecutive ACK receptions in the communication quality information table 45a exceeds the threshold (step S14). If the number of consecutive ACK receptions in the communication quality information table 45a exceeds the threshold (step S14: Yes), the table management unit 44 of the terminal device 40 proceeds to an MCS increase determination (step S15). If the number of consecutive ACK receptions in the communication quality information table 45a does not exceed the threshold (step S14: No), the table management unit 44 of the terminal device 40 checks whether the number of consecutive ACK non-receptions in the communication quality information table 45a exceeds the threshold (step S16). If the number of consecutive ACK non-receptions in the communication quality information table 45a exceeds the threshold (step S16: Yes), the table management unit 44 of the terminal device 40 proceeds to an MCS decrease determination (step S17).

[0033] If the number of consecutive ACK receptions in the communication quality information table 45a does not exceed the threshold (step S14: No) and if the number of consecutive ACK non-receptions in the communication quality information table 45a does not exceed the threshold (step S16: No), the table management unit 44 of the terminal device 40 does not update the MCS selection value in the communication quality information table 45a. After the operation of step S13, or after the operation of step S15, or if the number of consecutive ACK non-receptions in the communication quality information table 45a does not exceed the threshold (step S16: No), or after the operation of step S17, the terminal device 40 transmits data with the MCS selection value in the communication quality information table 45a (step S18).

[0034] When adjusting the MCS based on, for example, the number of consecutive ACK receptions or the number of consecutive non-receptions of an ACK as a specified timing in the aforementioned data transmission process, the table management unit 44 of the terminal device 40 may correct the upper limit value of the MCS before determining whether the MCS is to be increased, and may correct the lower limit value of the MCS before determining whether the MCS is to be decreased, based on the average RSSI, which is the reception strength at the time of adjustment.

[0035] Note that the terminal device 40 may check the type of data to be transmitted and select either GFSK or OFDM prior to the operation of step S11 in the flowchart shown in Fig. 5. Furthermore, when the terminal device 40 selects OFDM, it may check the type of data to be transmitted and select either fixed MCS or variable MCS. When the terminal device 40 selects fixed MCS, it updates the MCS selection value in the communication quality information table 45a to the MCS value determined before or during operation.

[0036] The MCS increase determination in step S15 of the flowchart shown in Fig. 5 will be described in detail. Fig. 6 is a flowchart showing the operation of the MCS increase determination of the terminal device 40 and the aggregation device 30 according to the first embodiment. The MCS increase determination operations of the terminal device 40 and the aggregation device 30 are similar, but here, the MCS increase determination operation of the terminal device 40 will be described. In the terminal device 40, the table management unit 44 refers to the communication quality information table 45a and reads out the average RSSI of frames previously received on the relevant wireless link (step S21). The table management unit 44 of the terminal device 40 checks whether the MCS selection value in the communication quality information table 45a is equal to or greater than the MCS upper limit value corresponding to the average RSSI (step S22). If the MCS selection value in the communication quality information table 45a is equal to or greater than the MCS upper limit value corresponding to the average RSSI (step S22: Yes), the table management unit 44 of the terminal device 40 does not update the MCS selection value and ends the operation of the MCS increase determination.

[0037] If the MCS selection value in the communication quality information table 45a is smaller than the MCS upper limit value corresponding to the average RSSI (step S22: No), the table management unit 44 of the terminal device 40 increases the MCS selection value in the communication quality information table 45a by 1 (step S23). The table management unit 44 of the terminal device 40 resets the number of consecutive ACK receptions in the communication quality information table 45a (step S24), and updates the threshold value of the number of consecutive ACK receptions and the threshold value of the number of consecutive non-receptions of ACK in the communication quality information table 45a to values ​​corresponding to the average RSSI in the communication quality information table 45a (step S25). Note that, although the example of step S23 in the flowchart shown in FIG. 6 has been described as an example in which the MCS selection value is increased by 1, the table management unit 44 of the terminal device 40 may also check the conditions for increasing the MCS selection value to a higher value and increase the MCS selection value by 2 or more at a time.

[0038] The MCS down determination in step S17 of the flowchart shown in FIG. 5 will be described in detail. FIG. 7 is a flowchart showing the operation of the MCS down determination of the terminal device 40 and the aggregation device 30 according to the first embodiment. The MCS down determination operations of the terminal device 40 and the aggregation device 30 are similar, but here, the MCS up determination operation of the terminal device 40 will be described. In the terminal device 40, the table management unit 44 refers to the communication quality information table 45a and reads out the average RSSI of frames previously received on the relevant wireless link (step S31). The table management unit 44 of the terminal device 40 checks whether the MCS selection value in the communication quality information table 45a is equal to or lower than the MCS lower limit value corresponding to the average RSSI (step S32). If the MCS selection value in the communication quality information table 45a is equal to or lower than the MCS lower limit value corresponding to the average RSSI (step S32: Yes), the table management unit 44 of the terminal device 40 does not update the MCS selection value and ends the MCS down determination operation.

[0039] If the MCS selection value in the communication quality information table 45a is greater than the MCS lower limit value corresponding to the average RSSI (step S32: No), the table management unit 44 of the terminal device 40 decreases the MCS selection value in the communication quality information table 45a by 1 (step S33). The table management unit 44 of the terminal device 40 resets the number of consecutive ACK not received in the communication quality information table 45a (step S34), and updates the threshold value of the number of consecutive ACK not received in the communication quality information table 45a and the threshold value of the number of consecutive ACK not received in the communication quality information table 45a to values ​​corresponding to the average RSSI in the communication quality information table 45a (step S35). Note that, although the example of step S33 in the flowchart shown in FIG. 7 has been described as decreasing the MCS selection value by 1, the table management unit 44 of the terminal device 40 may also check the conditions for decreasing the MCS selection value to a higher value and decrease the MCS selection value by 2 or more in one go.

[0040] In the data transmission process shown in Fig. 5, the MCS increase determination shown in Fig. 6, and the MCS decrease determination shown in Fig. 7, if the average RSSI of the frame received through the corresponding wireless link is not present in the communication quality information table 45a, the table management unit 44 of the terminal device 40 may update the initial value of MCS, the upper limit value of MCS, the lower limit value of MCS, the threshold value of the number of consecutive ACK receptions, and the threshold value of the number of consecutive ACK non-receptions, assuming that the average RSSI is a reference value determined before or during operation. The reference value of the average RSSI determined before or during operation is, for example, the minimum value of the average RSSI assumed in the smart meter system 10. In addition, when the table management unit 44 of the terminal device 40 adjusts the MCS, the reference value for adjusting the MCS may be corrected based on the average RSSI, which is the reception strength.

[0041] Next, the operation of the data reception process of the terminal device 40 will be described using a flowchart. FIG. 8 is a flowchart showing the operation of the data reception process of the terminal device 40 and the aggregation device 30 according to the first embodiment. The operations of the data reception process of the terminal device 40 and the aggregation device 30 are similar, but here, the operation of the data reception process of the terminal device 40 will be described. In the terminal device 40, the table management unit 44 checks whether the wireless communication unit 41 is waiting to receive an ACK (step S41). If the wireless communication unit 41 is waiting to receive an ACK (step S41: Yes), the table management unit 44 of the terminal device 40 checks whether the wireless communication unit 41 has received an ACK within a specified time (step S42). If the wireless communication unit 41 has received an ACK within a specified time (step S42: Yes), the table management unit 44 of the terminal device 40 calculates the average RSSI of the received frame using the received ACK as the received frame (step S46). If the wireless communication unit 41 does not receive an ACK within the specified time (step S42: No), the table management unit 44 of the terminal device 40 does not calculate the average RSSI of the received frames, and ends the operation of the data reception process.

[0042] When the wireless communication unit 41 is not waiting for an ACK (step S41: No), if the wireless communication unit 41 receives a data frame from another terminal device 40 (step S43), the table management unit 44 of the terminal device 40 judges whether or not an ACK needs to be transmitted based on the frame type (step S44). When the table management unit 44 of the terminal device 40 judges that an ACK needs to be transmitted (step S44: Yes), it causes the wireless communication unit 41 to transmit an ACK (step S45). When the table management unit 44 of the terminal device 40 judges that an ACK does not need to be transmitted (step S44: No), it does not cause the wireless communication unit 41 to transmit an ACK. After the operation of step S45 or when step S44: No, that is, regardless of whether an ACK has been transmitted or not, the table management unit 44 of the terminal device 40 calculates the average RSSI of the received frame as the data frame received from the other terminal device 40 (step S46).

[0043] If the wireless communication unit 41 receives an ACK within the time period specified in step S42 (step S42: Yes), the table management unit 44 of the terminal device 40 increments the number of consecutive ACK receptions in the communication quality information table 45a by 1 and resets the number of consecutive ACK non-receptions in the communication quality information table 45a. If the wireless communication unit 41 does not receive an ACK within the time period specified in step S42 (step S42: No), the table management unit 44 of the terminal device 40 increments the number of consecutive ACK non-receptions in the communication quality information table 45a by 1 and resets the number of consecutive ACK receptions in the communication quality information table 45a.

[0044] The calculation of the average RSSI of the received frame in step S46 of the flowchart shown in FIG. 8 will be described in detail. FIG. 9 is a flowchart showing the operation of calculating the average RSSI of the received frame of the terminal device 40 and the aggregation device 30 according to the first embodiment. The operation of calculating the average RSSI of the received frame of the terminal device 40 and the aggregation device 30 is similar, but here it will be described as the operation of the data reception process of the terminal device 40. In the terminal device 40, when the table management unit 44 acquires the RSSI of the received frame received by the wireless communication unit 41 from the data processing unit 43 (step S51), it updates the average RSSI for the corresponding wireless link in the communication quality information table 45a using the acquired RSSI of the received frame (step S52). The table management unit 44 of the terminal device 40 records the update time of the average RSSI for the corresponding wireless link in the communication quality information table 45a (step S53). The table management unit 44 of the terminal device 40 sets a valid time for the average RSSI, and deletes the corresponding record when the valid time or more has elapsed since the update time of the record in the communication quality information table 45a. The valid time of the average RSSI may be common to all terminal devices 40, or may be set individually for each terminal device 40 according to the priority, operation conditions, and the like.

[0045] Next, the operation of transmitting data from the aggregation device 30 to the terminal device 40, that is, the downstream communication of the aggregation device 30 will be described. The aggregation device 30 transmits data to a certain terminal device 40. When the aggregation device 30 and a certain terminal device 40 cannot wirelessly communicate with each other, another terminal device 40 on the path relays the data transmission from the aggregation device 30 to the certain terminal device 40. At this time, the path for relaying may be determined by the aggregation device 30 or may be determined autonomously between the terminal devices 40. In the following description, both the case where the aggregation device 30 transmits data to the terminal device 40 and the case where another terminal device 40 relays data from the aggregation device 30 to the certain terminal device 40 are treated as "data transmission processing".

[0046] The configuration of the communication quality information table 35a stored in the storage unit 35 by the aggregation device 30 is the same as the configuration of the communication quality information table 45a stored in the storage unit 45 by the terminal device 40 shown in FIG. 4, as described above. The communication quality information table 35a is created independently by the aggregation device 30, and holds a record for each wireless link that can perform wireless communication with the aggregation device 30, that is, for each terminal device 40 that can perform wireless communication. Each record of the communication quality information table 35a preferably includes, for a corresponding wireless link identified by a number or MAC address, an average RSSI, which is the reception strength of frames received in the past, an update time of the average RSSI, which is the reception strength, the number of consecutive ACK receptions for transmissions on the corresponding wireless link, the number of consecutive ACK non-receptions for transmissions on the corresponding wireless link, and an MCS selection value used for transmissions on the corresponding wireless link. Here, the ACK is transmitted from the terminal device 40. The terminal device 40 also uses the communication quality information table 45a shown in FIG. 4 in the data transmission process of the downstream communication.

[0047] The aggregation device 30 updates the initial MCS value, the upper limit MCS value, the lower limit MCS value, the threshold for the number of consecutive ACK receptions, and the threshold for the number of consecutive ACK non-receptions based on the average RSSI in the communication quality information table 35a at a specified timing in the data transmission process described later. It is assumed that the aggregation device 30 has separately acquired the correspondence relationship between the average RSSI and the initial MCS value, the upper limit MCS value, the lower limit MCS value, the threshold for the number of consecutive ACK receptions, and the threshold for the number of consecutive ACK non-receptions before or during operation.

[0048] The operation of the data transmission process of the aggregation device 30 will be described using a flowchart. FIG. 5 is a flowchart showing the operation of the data transmission process of the terminal device 40 and the aggregation device 30 according to the first embodiment. As described above, the operations of the data transmission process of the terminal device 40 and the aggregation device 30 are similar, but here, the operation of the data transmission process of the aggregation device 30 will be described. Note that the terminal device 40 performs the same data transmission process operation in the case of downstream communication as in the case of upstream communication described above. In the aggregation device 30, the table management unit 34 checks whether or not the MCS selection value of the wireless link to be used is in the communication quality information table 35a (step S11). Note that in FIG. 5, the communication quality information table 35a is written as a table for the sake of simplicity. The same applies hereinafter. If the MCS selection value of the wireless link to be used is not in the communication quality information table 35a (step S11: No), the table management unit 34 of the aggregation device 30 refers to the communication quality information table 35a, reads the average RSSI of frames previously received on the wireless link (step S12), and records the MCS initial value corresponding to the average RSSI as the MCS selection value in the communication quality information table 35a (step S13). That is, if there is no past record of MCS when adjusting MCS, the table management unit 34 of the aggregation device 30 determines the initial value of MCS based on the average RSSI, which is the reception strength.

[0049] If the MCS selection value of the wireless link to be used is in the communication quality information table 35a (step S11: Yes), the table management unit 34 of the aggregation device 30 checks whether the number of consecutive ACK receptions in the communication quality information table 35a exceeds the threshold (step S14). If the number of consecutive ACK receptions in the communication quality information table 35a exceeds the threshold (step S14: Yes), the table management unit 34 of the aggregation device 30 proceeds to MCS increase determination (step S15). If the number of consecutive ACK receptions in the communication quality information table 35a does not exceed the threshold (step S14: No), the table management unit 34 of the aggregation device 30 checks whether the number of consecutive ACK non-receptions in the communication quality information table 35a exceeds the threshold (step S16). If the number of consecutive ACK non-receptions in the communication quality information table 35a exceeds the threshold (step S16: Yes), the table management unit 34 of the aggregation device 30 proceeds to MCS decrease determination (step S17).

[0050] If the number of consecutive ACK receptions in the communication quality information table 35a does not exceed the threshold (step S14: No) and if the number of consecutive ACK non-receptions in the communication quality information table 35a does not exceed the threshold (step S16: No), the table management unit 34 of the aggregation device 30 does not update the MCS selection value in the communication quality information table 35a. After the operation of step S13, or after the operation of step S15, or if the number of consecutive ACK non-receptions in the communication quality information table 35a does not exceed the threshold (step S16: No), or after the operation of step S17, the aggregation device 30 transmits data with the MCS selection value in the communication quality information table 35a (step S18).

[0051] When adjusting the MCS based on, for example, the number of consecutive ACK receptions or the number of consecutive non-receptions of an ACK as a specified timing in the aforementioned data transmission process, the table management unit 34 of the aggregation device 30 may correct the upper limit value of the MCS before determining whether the MCS is to increase, and may correct the lower limit value of the MCS before determining whether the MCS is to decrease, based on the average RSSI, which is the reception strength at the time of adjustment.

[0052] Prior to the operation of step S11 in the flowchart shown in Fig. 5, the aggregation device 30 may check the type of data to be transmitted and select either GFSK or OFDM. If the aggregation device 30 selects OFDM, the aggregation device 30 may check the type of data to be transmitted and select either fixed MCS or variable MCS. If the aggregation device 30 selects fixed MCS, the aggregation device 30 updates the selected MCS value in the communication quality information table 35a to the MCS value determined before or during operation.

[0053] The MCS increase determination in step S15 of the flowchart shown in Fig. 5 will be described in detail. Fig. 6 is a flowchart showing the operation of the MCS increase determination of the terminal device 40 and the aggregation device 30 according to the first embodiment. The MCS increase determination operations of the terminal device 40 and the aggregation device 30 are similar, but here, the MCS increase determination operation of the aggregation device 30 will be described. Note that the terminal device 40 performs the MCS increase determination operation in the case of downlink communication as in the case of uplink communication described above. In the aggregation device 30, the table management unit 34 refers to the communication quality information table 35a and reads out the average RSSI of frames previously received on the wireless link (step S21). The table management unit 34 of the aggregation device 30 checks whether the MCS selection value in the communication quality information table 35a is equal to or greater than the MCS upper limit value corresponding to the average RSSI (step S22). If the MCS selection value in the communication quality information table 35a is equal to or greater than the MCS upper limit value corresponding to the average RSSI (step S22: Yes), the table management unit 34 of the aggregation device 30 does not update the MCS selection value and ends the operation of determining an MCS increase.

[0054] If the MCS selection value in the communication quality information table 35a is smaller than the MCS upper limit value corresponding to the average RSSI (step S22: No), the table management unit 34 of the aggregation device 30 increases the MCS selection value in the communication quality information table 35a by 1 (step S23). The table management unit 34 of the aggregation device 30 resets the number of consecutive ACK receptions in the communication quality information table 35a (step S24), and updates the threshold value of the number of consecutive ACK receptions and the threshold value of the number of consecutive ACK non-receptions in the communication quality information table 35a to values ​​corresponding to the average RSSI in the communication quality information table 45a (step S25). Note that, although the example of step S23 in the flowchart shown in FIG. 6 has been described as an example in which the MCS selection value is increased by 1, the table management unit 34 of the aggregation device 30 may also check the conditions for increasing the MCS selection value to a higher value and increase the MCS selection value by 2 or more at a time.

[0055] The MCS down determination in step S17 of the flowchart shown in Fig. 5 will be described in detail. Fig. 7 is a flowchart showing the operation of the MCS down determination of the terminal device 40 and the aggregation device 30 according to the first embodiment. The MCS down determination operations of the terminal device 40 and the aggregation device 30 are similar, but here, the MCS up determination operation of the aggregation device 30 will be described. Note that the terminal device 40 performs the MCS down determination operation in the case of downlink communication as in the case of uplink communication described above. In the aggregation device 30, the table management unit 34 refers to the communication quality information table 35a and reads out the average RSSI of frames previously received on the wireless link (step S31). The table management unit 34 of the aggregation device 30 checks whether the MCS selection value in the communication quality information table 35a is equal to or lower than the MCS lower limit value corresponding to the average RSSI (step S32). If the MCS selection value in the communication quality information table 35a is equal to or lower than the MCS lower limit value corresponding to the average RSSI (step S32: Yes), the table management unit 34 of the aggregation device 30 does not update the MCS selection value and ends the operation of the MCS drop determination.

[0056] If the MCS selection value in the communication quality information table 35a is greater than the MCS lower limit value corresponding to the average RSSI (step S32: No), the table management unit 34 of the aggregation device 30 decreases the MCS selection value in the communication quality information table 35a by 1 (step S33). The table management unit 34 of the aggregation device 30 resets the number of consecutive ACK not received in the communication quality information table 35a (step S34), and updates the threshold value of the number of consecutive ACK not received in the communication quality information table 35a and the threshold value of the number of consecutive ACK not received in the communication quality information table 35a to values ​​corresponding to the average RSSI in the communication quality information table 35a (step S35). Note that, although the example of step S33 in the flowchart shown in FIG. 7 has been described as decreasing the MCS selection value by 1, the table management unit 34 of the aggregation device 30 may also check the conditions for decreasing the MCS selection value to a higher value and decrease the MCS selection value by 2 or more in one go.

[0057] In the data transmission process shown in Fig. 5, the MCS increase determination shown in Fig. 6, and the MCS decrease determination shown in Fig. 7, if the average RSSI of the frame received through the corresponding wireless link does not exist in the communication quality information table 35a, the table management unit 34 of the aggregation device 30 may update the initial value of MCS, the upper limit value of MCS, the lower limit value of MCS, the threshold value of the number of consecutive ACK receptions, and the threshold value of the number of consecutive ACK non-receptions, assuming that the average RSSI is a reference value determined before or during operation. The reference value of the average RSSI determined before or during operation is, for example, the minimum value of the average RSSI assumed in the smart meter system 10. Furthermore, when the table management unit 34 of the aggregation device 30 adjusts the MCS, the reference value for adjusting the MCS may be corrected based on the average RSSI, which is the reception strength.

[0058] Next, the operation of the data reception process of the aggregation device 30 will be described using a flowchart. FIG. 8 is a flowchart showing the operation of the data reception process of the terminal device 40 and the aggregation device 30 according to the first embodiment. The operations of the data reception process of the terminal device 40 and the aggregation device 30 are similar, but here, the operation of the data reception process of the aggregation device 30 will be described. Note that the terminal device 40 performs the same data reception process operation in the case of downstream communication as in the case of upstream communication described above. In the aggregation device 30, the table management unit 34 checks whether the wireless communication unit 31 is waiting to receive an ACK (step S41). If the wireless communication unit 31 is waiting to receive an ACK (step S41: Yes), the table management unit 34 of the aggregation device 30 checks whether the wireless communication unit 31 has received an ACK within a specified time (step S42). If the wireless communication unit 31 has received an ACK within a specified time (step S42: Yes), the table management unit 34 of the aggregation device 30 calculates the average RSSI of the received frame using the received ACK as the received frame (step S46). If the wireless communication unit 31 does not receive an ACK within the specified time (step S42: No), the table management unit 34 of the aggregation device 30 does not calculate the average RSSI of the received frame, and ends the operation of the data reception process.

[0059] When the wireless communication unit 31 is not waiting for ACK (step S41: No), the table management unit 34 of the aggregation device 30 judges whether or not ACK transmission is necessary based on the frame type when the wireless communication unit 31 receives a data frame from the terminal device 40 (step S43) (step S44). When the table management unit 34 of the aggregation device 30 judges that ACK transmission is necessary (step S44: Yes), it causes the wireless communication unit 31 to transmit ACK (step S45). When the table management unit 34 of the aggregation device 30 judges that ACK transmission is unnecessary (step S44: No), it does not cause the wireless communication unit 31 to transmit ACK. After the operation of step S45 or when step S44: No, that is, regardless of the presence or absence of ACK transmission, the table management unit 34 of the aggregation device 30 calculates the average RSSI of the received frame as the data frame received from the terminal device 40 (step S46).

[0060] If the wireless communication unit 31 receives an ACK within the time specified in step S42 (step S42: Yes), the table management unit 34 of the aggregation device 30 increments the number of consecutive ACK receptions in the communication quality information table 35a by 1 and resets the number of consecutive ACK non-receptions in the communication quality information table 35a. If the wireless communication unit 31 does not receive an ACK within the time specified in step S42 (step S42: No), the table management unit 34 of the aggregation device 30 increments the number of consecutive ACK non-receptions in the communication quality information table 35a by 1 and resets the number of consecutive ACK receptions in the communication quality information table 35a.

[0061] The calculation of the average RSSI of the received frame in step S46 of the flowchart shown in FIG. 8 will be described in detail. FIG. 9 is a flowchart showing the operation of calculating the average RSSI of the received frame of the terminal device 40 and the aggregation device 30 according to the first embodiment. Although the calculation of the average RSSI of the received frame of the terminal device 40 and the aggregation device 30 is similar, the operation of calculating the average RSSI of the received frame of the aggregation device 30 will be described here. Note that the terminal device 40 performs the operation of calculating the average RSSI in the case of the downlink communication as in the case of the uplink communication described above. In the aggregation device 30, when the table management unit 34 acquires the RSSI of the received frame received by the wireless communication unit 31 from the data processing unit 33 (step S51), it updates the average RSSI for the corresponding wireless link in the communication quality information table 35a using the acquired RSSI of the received frame (step S52). The table management unit 34 of the aggregation device 30 records the update time of the average RSSI for the corresponding wireless link in the communication quality information table 35a (step S53). The table management unit 34 of the aggregation device 30 sets a validity period for the average RSSI, and deletes a record in the communication quality information table 35a when the validity period has elapsed since the update time. The validity period for the average RSSI may be common to the terminal device 40, or may be set individually depending on the priority and operation conditions of the aggregation device 30 and the terminal device 40.

[0062] Next, the hardware configuration of the terminal device 40 will be described. In the terminal device 40, the wireless communication unit 41 is a communication interface capable of wireless communication. The storage unit 45 is a memory. The wireless communication control unit 42, the data processing unit 43, and the table management unit 44 are realized by processing circuits. The processing circuit may be a processor and memory that executes a program stored in the memory, or may be dedicated hardware. The processing circuit is also called a control circuit.

[0063] FIG. 10 is a diagram showing a configuration example of the processing circuit 90 in the case where the processing circuit for realizing the terminal device 40 according to the first embodiment is configured by a processor 91 and a memory 92. The processing circuit 90 shown in FIG. 10 is a control circuit and includes a processor 91 and a memory 92. When the processing circuit 90 is configured by the processor 91 and the memory 92, each function of the processing circuit 90 is realized by software, firmware, or a combination of software and firmware. The software or firmware is described as a program and stored in the memory 92. In the processing circuit 90, each function is realized by the processor 91 reading and executing the program stored in the memory 92. That is, the processing circuit 90 includes a memory 92 for storing a program that results in the processing of the terminal device 40 being executed. This program can also be said to be a program for causing the terminal device 40 to execute each function realized by the processing circuit 90. This program may be provided by a storage medium in which the program is stored, or may be provided by other means such as a communication medium.

[0064] The above program can also be said to be a program that causes the terminal device 40 to execute a data management step in which, when the table management unit 34 adjusts the modulation and coding scheme value, which is a combination of a modulation scheme and a coding rate, based on the number of consecutive times that an arrival confirmation has been received or the number of consecutive times that an arrival confirmation has not been received, the table management unit 34 corrects, based on the reception intensity at the time of adjustment, an upper limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value has increased, and corrects a lower limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value has decreased.

[0065] Here, the processor 91 is, for example, a CPU (Central Processing Unit), a processing device, an arithmetic device, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor), etc. Also, the memory 92 is, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), an EEPROM (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc), etc.

[0066] FIG. 11 is a diagram showing an example of a processing circuit 93 in the case where the processing circuit for realizing the terminal device 40 according to the first embodiment is configured with dedicated hardware. The processing circuit 93 shown in FIG. 11 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination of these. The processing circuit may be partially realized with dedicated hardware and partially realized with software or firmware. In this way, the processing circuit can realize each of the above-mentioned functions by dedicated hardware, software, firmware, or a combination of these.

[0067] The hardware configuration of the terminal device 40 has been described, but the aggregation device 30 has a similar hardware configuration. In the aggregation device 30, the wireless communication unit 31 is a communication interface capable of wireless communication. The server communication unit 37 is a communication interface capable of wired communication. The storage unit 35 is a memory. The wireless communication control unit 32, the data processing unit 33, the table management unit 34, and the server communication control unit 36 ​​are realized by processing circuits. The processing circuit may be a processor and memory that executes a program stored in the memory, or may be dedicated hardware.

[0068] As described above, according to this embodiment, when adjusting MCS according to the reception status of arrival confirmation, the aggregation device 30 and the terminal device 40 correct the initial MCS value when the communication quality information table does not include an MCS selection value, the upper limit of MCS when MCS is determined to increase, and the lower limit of MCS when MCS is determined to decrease, by the average RSSI. That is, when adjusting MCS according to the reception status of ACK, the aggregation device 30 and the terminal device 40 correct the initial MCS value, the upper limit of MCS, the lower limit of MCS, and the like, at an appropriate timing by the average RSSI. This allows the aggregation device 30 and the terminal device 40 to quickly reflect the wireless quality in the MCS.

[0069] Furthermore, when adjusting MCS by ACK, the aggregation device 30 and the terminal device 40 correct the MCS adjustment standard by the average RSSI when MCS increase is completed and when MCS decrease is completed. That is, when adjusting MCS by ACK, the aggregation device 30 and the terminal device 40 correct the MCS adjustment standard at an appropriate timing according to the reception strength. This allows the aggregation device 30 and the terminal device 40 to control so as not to change MCS excessively in response to instantaneous fluctuations in wireless quality. The aggregation device 30 and the terminal device 40 can select an appropriate MCS while suppressing an increase in the number of adjustments in wireless communication of the smart meter system 10.

[0070] Embodiment 2 In the first embodiment, a case has been described in which MCSs are selected separately for upstream communication and downstream communication on the premise that there is a certain amount or more of each of the upstream communication and downstream communication in the smart meter system 10. In the second embodiment, a method of dealing with a case in which the amount of downstream communication is smaller than the amount of upstream communication in the smart meter system 10 and an appropriate MCS cannot be selected for the downstream communication alone will be described.

[0071] In the second embodiment, the configurations of the smart meter system 10, the aggregation device 30, and the terminal device 40 are similar to the configurations of the smart meter system 10, the aggregation device 30, and the terminal device 40 in the first embodiment shown in FIGS.

[0072] A description will be given of an operation of uplink communication in which the terminal device 40 transmits data to the aggregation device 30. The operations of the terminal device 40 in the data transmission process, MCS increase determination, and MCS decrease determination are similar to those in the first embodiment.

[0073] The operation of the data reception process of the terminal device 40 will be described using a flowchart. FIG. 12 is a flowchart showing the operation of the data reception process of the terminal device 40 according to the second embodiment. In the terminal device 40, the table management unit 44 checks whether the wireless communication unit 41 is waiting to receive an ACK (step S61). If the wireless communication unit 41 is waiting to receive an ACK (step S61: Yes), the table management unit 44 of the terminal device 40 checks whether the wireless communication unit 41 has received an ACK within a specified time (step S62). If the wireless communication unit 41 has received an ACK within a specified time (step S62: Yes), the table management unit 44 of the terminal device 40 calculates the average RSSI of the received frame using the received ACK as the received frame (step S67). If the wireless communication unit 41 has not received an ACK within a specified time (step S62: No), the table management unit 44 of the terminal device 40 does not calculate the average RSSI of the received frame and ends the operation of the data reception process.

[0074] When the wireless communication unit 41 is not waiting to receive an ACK (step S61: No), if the wireless communication unit 41 receives a data frame from another terminal device 40 (step S63), the table management unit 44 of the terminal device 40 determines whether or not it is necessary to transmit an ACK based on the frame type (step S64). If the table management unit 44 of the terminal device 40 determines that it is necessary to transmit an ACK (step S64: Yes), it causes the wireless communication unit 41 to transmit an ACK (step S65). If the table management unit 44 of the terminal device 40 determines that it is not necessary to transmit an ACK (step S64: No), it does not cause the wireless communication unit 41 to transmit an ACK. After the operation of step S65, or if step S64: No, i.e., regardless of the presence or absence of ACK transmission, the table management unit 44 of the terminal device 40 checks the MCS of the data frame received by the wireless communication unit 41 from the other terminal device 40, and records the MCS of the data frame from the other terminal device 40 in the communication quality information table 45a as the MCS selection value of the corresponding wireless link (step S66). The table management unit 44 of the terminal device 40 calculates the average RSSI of the received frame, taking the data frame received from the other terminal device 40 as the received frame (step S67).

[0075] The operation of calculating the average RSSI of the received frames in step S67 of the flowchart shown in FIG. 12 is similar to the operation of calculating the average RSSI of the received frames in step S46 of the flowchart shown in FIG. 8, and is similar to the operation of the flowchart shown in FIG.

[0076] Next, the operation of transmitting data from the aggregation device 30 to the terminal device 40, that is, the operation of downstream communication between the aggregation device 30 and the terminal device 40 will be described.

[0077] FIG. 13 is a flowchart showing the operation of the data transmission process of the terminal device 40 and the aggregation device 30 according to the second embodiment. The operation of the data transmission process of the terminal device 40 and the aggregation device 30 is similar, but here, the operation of the data transmission process of the aggregation device 30 will be described. In the aggregation device 30, the table management unit 34 checks whether the MCS selection value of the wireless link to be used is in the communication quality information table 35a (step S71). If the MCS selection value of the wireless link to be used is not in the communication quality information table 35a (step S71: No), the table management unit 34 of the aggregation device 30 refers to the communication quality information table 35a to read the average RSSI of frames previously received in the corresponding wireless link (step S72), and records the MCS initial value corresponding to the average RSSI as the MCS selection value in the communication quality information table 35a (step S73). If the MCS selection value of the wireless link to be used is in the communication quality information table 35a (step S71: Yes), the table management unit 34 of the aggregation device 30 does not update the MCS selection value in the communication quality information table 35a. The aggregation device 30 transmits data using the MCS selection value in the communication quality information table 35a (step S74). Although the flow chart shown in Fig. 13 has been described as the operation of the aggregation device 30, the terminal device 40 also performs the same operation.

[0078] In the second embodiment, the data reception processing operation and the average RSSI calculation operation of the aggregation device 30 and the terminal device 40 are similar to the data reception processing operation and the average RSSI calculation operation of the aggregation device 30 and the terminal device 40 in the first embodiment. However, since the aggregation device 30 and the terminal device 40 do not adjust the MCS according to an ACK for downlink communication in the second embodiment, it is not necessary to record the number of consecutive ACK receptions and the number of consecutive non-receptions of ACK in the communication quality information table.

[0079] In this way, the table management unit 34 of the terminal device 40 adjusts the MCS for upstream communication from the terminal device 40 to the aggregation device 30 based on the number of consecutive ACK receptions or the number of consecutive non-receptions of ACK received from other terminal devices 40, and records and uses the MCS received in the upstream communication from other terminal devices 40 in the communication quality information table 45a for downstream communication from the aggregation device 30 to the terminal device 40. Also, the table management unit 34 of the aggregation device 30 adjusts the MCS for upstream communication from the terminal device 40 to the aggregation device 30 based on the number of consecutive ACK receptions or the number of consecutive non-receptions of ACK received from the terminal device 40, and records and uses the MCS received in the upstream communication from the terminal device 40 in the communication quality information table 35a for downstream communication from the aggregation device 30 to the terminal device 40.

[0080] As described above, according to this embodiment, the aggregation device 30 and the terminal device 40 apply the MCS adjusted in the upstream communication to the downstream communication. This allows the aggregation device 30 and the terminal device 40 to select an appropriate MCS even in an environment where the downstream communication is less than the upstream communication. Note that, in the second embodiment, a case where the downstream communication is less than the upstream communication has been described as an example, but this is not limiting. The aggregation device 30 and the terminal device 40 can select an appropriate MCS even in an environment where the upstream communication is less than the downstream communication by switching the operation of the upstream communication and the downstream communication.

[0081] Embodiment 3 In the first and second embodiments, the aggregation device 30 and the terminal device 40 independently select MCS. In the third embodiment, the aggregation device 30 periodically collects communication quality information from the terminal device 40, and updates the correspondence between the average RSSI and the initial value of MCS, the upper limit value of MCS, the lower limit value of MCS, the threshold value of the number of consecutive ACK receptions, and the threshold value of the number of consecutive non-receptions of ACK.

[0082] In the third embodiment, the configurations of the smart meter system 10, the aggregation device 30, and the terminal device 40 are similar to the configurations of the smart meter system 10, the aggregation device 30, and the terminal device 40 in the first embodiment shown in FIGS.

[0083] The operation of the uplink communication in which the terminal device 40 transmits data to the aggregation device 30 will be described. The operation of the terminal device 40 in the data transmission process, MCS increase determination, and MCS decrease determination is the same as that in the first embodiment. However, in the third embodiment, the terminal device 40 transmits communication quality information in its own device to the aggregation device 30. The terminal device 40 may transmit the communication quality information to the aggregation device 30 in all or part of the above-mentioned data transmission, or may transmit the information separately from the above-mentioned data transmission. In addition, the communication quality information transmitted by the terminal device 40 may be the entire communication quality information table 45a, or each record or part of each record included in the communication quality information table 45a.

[0084] In the third embodiment, the data reception processing and average RSSI calculation operations of the aggregation device 30 and the terminal device 40 are similar to those of the aggregation device 30 and the terminal device 40 in the first embodiment.

[0085] The following describes the operation of transmitting data from the aggregation device 30 to the terminal device 40, that is, the downstream communication of the aggregation device 30 and the terminal device 40. In the third embodiment, the operations of the data transmission process, MCS increase determination, and MCS decrease determination from the aggregation device 30 to the terminal device 40 are similar to those of the data transmission process, MCS increase determination, and MCS decrease determination from the aggregation device 30 to the terminal device 40 in the first embodiment. However, in the third embodiment, the aggregation device 30 performs the operation of adjusting parameters of communication quality information shown in the flowchart of FIG. 14 at a specified time interval.

[0086] FIG. 14 is a flowchart showing an operation of adjusting parameters of communication quality information of the aggregation device 30 according to the third embodiment. In the aggregation device 30, the table management unit 34 checks the communication quality information from the terminal device 40 received by the wireless communication unit 31 (step S81). The table management unit 34 of the aggregation device 30 updates the correspondence relationship between the average RSSI and the initial value of MCS (step S82). The table management unit 34 of the aggregation device 30 updates the correspondence relationship between the average RSSI and the upper limit value of MCS and the lower limit value of MCS (step S83). The table management unit 34 of the aggregation device 30 updates the correspondence relationship between the average RSSI and the threshold value of the number of consecutive ACK receptions and the threshold value of the number of consecutive ACK non-receptions (step S84). The table management unit 34 of the aggregation device 30 transmits the contents of the communication quality information updated in steps S82 to S84 to all the terminal devices 40 via the data processing unit 33, the wireless communication control unit 32, and the wireless communication unit 31 (step S85). The aggregation device 30 may transmit the contents of the updated communication quality information to the terminal device 40 according to the above-mentioned data transmission process, or may transmit the contents of the updated communication quality information according to a method different from the above-mentioned data transmission process.

[0087] The operations of the data reception process in which the aggregation device 30 receives communication quality information from the terminal device 40, the operations of the data reception process in which the terminal device 40 receives the contents of the updated communication quality information from the aggregation device 30, and the operations of calculating the average RSSI of the aggregation device 30 and the terminal device 40 are similar to the respective operations in embodiment 1.

[0088] In this way, the table management unit 44 of the terminal device 40 controls transmission of the communication quality information recorded in the communication quality information table 45a to the aggregation device 30, and updates the correspondence between the average RSSI, which is reception strength, and the initial value of MCS, the upper limit of MCS, the lower limit of MCS, the threshold value of the number of consecutive ACK receptions, and the threshold value of the number of consecutive ACK non-receptions, based on the update information of the correspondence acquired from the aggregation device 30. In addition, the table management unit 34 of the aggregation device 30 acquires communication quality information of the terminal device 40 for the same items as those recorded in the communication quality information table 35a from the terminal device 40, and updates the correspondence between the average RSSI, which is reception strength, and the initial value of MCS, the upper limit of MCS, the lower limit of MCS, the threshold value of the number of consecutive ACK receptions, and the threshold value of the number of consecutive ACK non-receptions, based on the communication quality information acquired from the terminal device 40.

[0089] As described above, according to the present embodiment, the aggregation device 30 updates the correspondence between the average RSSI and the initial value of MCS, the upper limit of MCS, and the lower limit of MCS based on the communication quality information collected from the terminal device 40, and transmits the contents of the updated communication quality information to the terminal device 40. This allows the aggregation device 30 and the terminal device 40 to quickly reflect the wireless quality in the MCS. Also, the aggregation device 30 updates the correspondence between the average RSSI and the threshold of the number of consecutive ACK receptions and the threshold of the number of consecutive ACK non-receptions based on the communication quality information collected from the terminal device 40, and transmits the contents of the updated communication quality information to the terminal device 40. This allows the aggregation device 30 and the terminal device 40 to control so as not to change the MCS excessively in response to an instantaneous change in wireless quality.

[0090] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0091] 10 smart meter system, 20 server device, 30 aggregation device, 31, 41 wireless communication unit, 32, 42 wireless communication control unit, 33, 43 data processing unit, 34, 44 table management unit, 35, 45 storage unit, 35a, 45a communication quality information table, 36 server communication control unit, 37 server communication unit, 40, 40-1 to 40-3 terminal device, 90, 93 processing circuit, 91 processor, 92 memory.

Claims

1. A terminal device that transmits data to an aggregation device in a smart meter system, a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the terminal device, a reception strength, a number of consecutive receptions of arrival confirmations from the aggregation device or other terminal devices, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; a table management unit that, when adjusting the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation, corrects an upper limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is increasing and corrects a lower limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is decreasing, based on the reception intensity during the adjustment; A terminal device comprising:

2. the table management unit determines an initial value of the modulation and coding scheme value based on the reception strength when there is no past record of the modulation and coding scheme value at the time of the adjustment.

2. The terminal device according to claim 1 .

3. When the modulation and coding scheme value is adjusted, the table management unit corrects a criterion for adjusting the modulation and coding scheme value based on the reception strength.

2. The terminal device according to claim 1 .

4. the table management unit adjusts the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmations received from the other terminal devices or the number of consecutive non-receptions of the arrival confirmations for upstream communication from the terminal device to the aggregation device, and records the modulation and coding scheme value received in the upstream communication from the other terminal devices in the communication quality information table and uses it for downstream communication from the aggregation device to the terminal device.

2. The terminal device according to claim 1 .

5. the table management unit controls transmission of the communication quality information recorded in the communication quality information table to the aggregation device, and updates a correspondence relationship between the reception strength and an initial value of the modulation and coding method value, an upper limit value of the modulation and coding method value, a lower limit value of the modulation and coding method value, a threshold value of the number of consecutive receptions of the arrival confirmation, and a threshold value of the number of consecutive non-receptions of the arrival confirmation, based on update information of the correspondence relationship acquired from the aggregation device.

5. The terminal device according to claim 1, wherein the terminal device is a terminal for receiving a signal from the external device.

6. An aggregation device that aggregates data from terminal devices in a smart meter system, a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the aggregation device, a reception strength, a number of consecutive receptions of arrival confirmations from the terminal device, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; a table management unit that, when adjusting the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation, corrects an upper limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is increasing and corrects a lower limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is decreasing, based on the reception intensity during the adjustment; An aggregation device comprising:

7. the table management unit determines an initial value of the modulation and coding scheme value based on the reception strength when there is no past record of the modulation and coding scheme value at the time of the adjustment. The aggregation device according to claim 6 .

8. When the modulation and coding scheme value is adjusted, the table management unit corrects a criterion for adjusting the modulation and coding scheme value based on the reception strength. The aggregation device according to claim 6 .

9. the table management unit adjusts the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation received from the terminal device or the number of consecutive non-receptions of the arrival confirmation received from the terminal device for upstream communication from the terminal device to the aggregation device, and records the modulation and coding scheme value received in the upstream communication from the terminal device in the communication quality information table for downstream communication from the aggregation device to the terminal device. The aggregation device according to claim 6 .

10. the table management unit acquires, from the terminal device, communication quality information of the terminal device for the same items as those recorded in the communication quality information table, and updates, based on the communication quality information acquired from the terminal device, correspondence relationships between the reception strength and an initial value of the modulation and coding scheme value, an upper limit value of the modulation and coding scheme value, a lower limit value of the modulation and coding scheme value, a threshold value for the number of consecutive receptions of the arrival confirmation, and a threshold value for the number of consecutive non-receptions of the arrival confirmation. The aggregation device according to any one of claims 6 to 9.

11. A control circuit for controlling a terminal device that transmits data to an aggregation device in a smart meter system, The terminal device a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the terminal device, a reception strength, a number of consecutive receptions of arrival confirmations from the aggregation device or other terminal devices, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; Equipped with when adjusting the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation, correcting an upper limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is increasing, and correcting a lower limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is decreasing, based on the reception intensity during the adjustment; A control circuit for causing the terminal device to execute the above.

12. A control circuit for controlling an aggregation device that aggregates data from terminal devices in a smart meter system, The aggregation device includes: a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the aggregation device, a reception strength, a number of consecutive receptions of arrival confirmations from the terminal device, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; Equipped with when adjusting the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation, correcting an upper limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is increasing, and correcting a lower limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is decreasing, based on the reception intensity during the adjustment; A control circuit that causes the aggregation device to execute the above.

13. A storage medium storing a program for controlling a terminal device that transmits data to an aggregation device in a smart meter system, The terminal device a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the terminal device, a reception strength, a number of consecutive receptions of arrival confirmations from the aggregation device or other terminal devices, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; Equipped with The program is when adjusting the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation, correcting an upper limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is increasing, and correcting a lower limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is decreasing, based on the reception intensity during the adjustment; A storage medium for causing the terminal device to execute the above.

14. A storage medium storing a program for controlling an aggregation device that aggregates data from terminal devices in a smart meter system, The aggregation device includes: a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the aggregation device, a reception strength, a number of consecutive receptions of arrival confirmations from the terminal device, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; Equipped with The program is when adjusting the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation, correcting an upper limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is increasing, and correcting a lower limit value of the modulation and coding scheme value before determining that the modulation and coding scheme value is decreasing, based on the reception intensity during the adjustment; A storage medium that causes the aggregation device to execute the above.

15. A communication quality control method for a terminal device that transmits data to an aggregation device in a smart meter system, comprising: The terminal device a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the terminal device, a reception strength, a number of consecutive receptions of arrival confirmations from the aggregation device or other terminal devices, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; Equipped with a data management step of correcting an upper limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is increasing and correcting a lower limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is decreasing, based on the reception intensity at the time of the adjustment, when the table management unit adjusts the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation; A communication quality control method comprising:

16. A method for controlling communication quality of an aggregation device that aggregates data from terminal devices in a smart meter system, comprising: The aggregation device includes: a storage unit in which a communication quality information table is stored in which, for each wireless link capable of wireless communication in the aggregation device, a reception strength, a number of consecutive receptions of arrival confirmations from the terminal device, a number of consecutive non-receptions of the arrival confirmations, and a modulation and coding scheme value which is a combination of a modulation scheme and a coding rate are recorded; Equipped with a data management step of correcting an upper limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is increasing and correcting a lower limit value of the modulation and coding scheme value before determining whether the modulation and coding scheme value is decreasing, based on the reception intensity at the time of the adjustment, when the table management unit adjusts the modulation and coding scheme value based on the number of consecutive receptions of the arrival confirmation or the number of consecutive non-receptions of the arrival confirmation; A communication quality control method comprising:

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