Radio communications system

Abstract

To provide a radio communications system for collecting data from a plurality of radio terminals, capable of reducing the power consumption in each radio terminal.SOLUTION: A radio communications system comprises a plurality of radio terminals and a management device. The management device generates a communication time table in which a radio terminal is allocated to part of time slots of a plurality of time slots in a data collection period one by one, and distributes them to each radio terminal. Each radio terminal uses each time slot to which each terminal is allocated in the communication time table to transmit the data. A first radio terminal transmits data by selecting a first time slot from unused time slots when the time slot to which the first radio terminal is allocated cannot be used. The communication time table held by each radio terminal is updated to a state where the first radio terminal is allocated to the first time slot.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a wireless communication system having a plurality of wireless terminals. [Background technology]

[0002] A wireless communication system in which a gateway node collects data from multiple nodes has been put to practical use. As an example, in a wireless communication system including multiple wireless terminals and a management device capable of communicating with the multiple wireless terminals, a configuration has been proposed in which the management device selects a transmission method for each wireless terminal to transmit data for each time period based on radio wave usage status data indicating the usage status of wireless channels around each wireless terminal (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-032254 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned configuration, in order to transmit data at an appropriate timing to avoid interference, it is necessary to update the radio wave usage status data at a relatively short period. However, in order to update the radio wave usage status data, continuous carrier sensing is required in each wireless terminal, which increases the power consumption of each wireless terminal. In a wireless communication system in which each wireless terminal operates on a battery, it is important to reduce the power consumption of each wireless terminal.

[0005] An object of one aspect of the present invention is to reduce the power consumption of each wireless terminal in a wireless communication system that collects data from a plurality of wireless terminals. [Means for solving the problem]

[0006] A wireless communication system according to one aspect of the present invention includes a plurality of wireless terminals and a management device that manages communication between the plurality of wireless terminals. The management device creates a communication time table in which the plurality of wireless terminals are each assigned once to some of a plurality of time slots obtained by dividing a predetermined period, and distributes the communication time table to the plurality of wireless terminals. Each of the plurality of wireless terminals transmits data to the management device using the time slot assigned to it in the communication time table. When a first wireless terminal of the plurality of wireless terminals cannot use the time slot assigned to it in the communication time table, the first wireless terminal selects a first time slot from among vacant time slots not assigned to any wireless terminal in the communication time table, and transmits data to the management device using the selected first time slot. The communication time table is updated to a state in which the first wireless terminal is assigned to the first time slot. Effect of the Invention

[0007] According to the above aspect, it is possible to reduce the power consumption of each wireless terminal in a wireless communication system that collects data from a plurality of wireless terminals. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of a wireless communication system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating an example of a functional configuration of a wireless slave device. [Diagram 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a wireless master device. [Figure 4] FIG. 2 illustrates an example of a hardware configuration of a server device. [Diagram 5] FIG. 11 is a diagram showing an example of a communication time table. [Figure 6] 13 is a diagram illustrating an example of updating the communication time table when a communication abnormality is detected. FIG. [Figure 7] 5 is a flowchart showing an example of an operation of the wireless slave device. [Figure 8] 11 is a diagram illustrating an example of a sequence in which a wireless master device collects data from each wireless slave device. [Figure 9] FIG. 11 is a diagram showing an example of a communication time table used in the second embodiment. [Figure 10] FIG. 13 is a diagram showing an example of a communication time table held by a wireless master device in the third embodiment. [Figure 11] 13 is a diagram illustrating an example of information held by a wireless slave device for controlling data transmission in the third embodiment. FIG. [Figure 12] FIG. 1 illustrates an example of a server device having a function of managing data transmission from a wireless slave device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 1 shows an example of a wireless communication system according to an embodiment of the present invention. The wireless communication system 100 according to the embodiment of the present invention includes a plurality of wireless slave devices 1 (1a to 1h), a wireless master device 2, and a server device 3. The number of wireless slave devices 1 included in the wireless communication system 100 is not particularly limited. Moreover, the wireless slave device 1 is an example of a wireless terminal.

[0010] The wireless slave device 1 has a function of transmitting data acquired at a node where the wireless slave device 1 is installed to the wireless master device 2. As an example, the wireless slave device 1 acquires sensor data and transmits it to the wireless master device 2. At this time, the wireless slave device 1 may transmit the data to the wireless master device 2 without going through other wireless slave devices 1, or may transmit the data to the wireless master device 2 via one or more other wireless slave devices 1. That is, the wireless communication system 100 may perform multi-hop communication.

[0011] The wireless communication system 100 assigns different transmission timings to each wireless slave device 1 (1a to 1h) so that wireless signals do not collide with each other. Then, the wireless slave device 1 transmits data at the transmission timing assigned to it. At this time, the wireless slave device 1 performs carrier sense to check whether or not there is jamming radio waves. As a result, if the received radio wave strength is lower than a predetermined threshold level, the wireless slave device 1 transmits data. On the other hand, if the received radio wave strength is higher than the threshold level, the wireless slave device 1 does not transmit data. For example, when another wireless device 51 that does not belong to the wireless communication system 100 is operating, the wireless slave device 1 may detect jamming radio waves. In this case, the wireless slave device 1 transmits data at different timings using a communication time table described later.

[0012] In the multi-hop communication, a route for transferring data from each wireless slave device 1 to the wireless master device 2 may be determined in advance. For example, a router may be set so that data transmitted from the wireless slave device 1f is transferred to the wireless master device 2 via the wireless slave device 1d and the wireless slave device 1b. In addition, in the multi-hop communication, the wireless slave device 1 operating as a relay node may transmit data received from other wireless slave devices 1 and data acquired at its own node to the wireless master device 2. For example, the wireless slave device 1d may receive data F from the wireless slave device 1f and transmit data F and data D to the wireless master device 2 when it acquires data D of its own node. In addition, the wireless slave device 1b may receive data F and data D from the wireless slave device 1d and transmit data F, data D, and data B to the wireless master device 2 when it acquires data B of its own node.

[0013] The wireless master device 2 is a wireless terminal having a gateway function, and is communicably connected to a higher-level device such as a server device 3 via a communication network such as the Internet or a LAN (Local Area Network). The wireless master device 2 is communicably connected to the above-mentioned multiple wireless slave devices 1 (1a to 1h) via wireless links. The wireless master device 2 receives data transmitted from each wireless slave device 1. That is, the wireless master device 2 collects data acquired by each wireless slave device 1. In this embodiment, the collected data is sent to the server device 3.

[0014] The server device 3 processes the data collected from each wireless slave device 1. For example, the server device 3 may perform statistical processing on the collected sensor data. Alternatively, the server device 3 may calculate fees based on the collected data. The server device 3 may also distribute control information, firmware, or the like to each wireless slave device 1 via the wireless master device 2.

[0015] In the wireless communication system 100 having the above configuration, the wireless master device 2 (or the server device 3) collects data from each wireless slave device 1 at a predetermined cycle. In this embodiment, the wireless master device 2 collects data from each wireless slave device 1 at a cycle of 30 minutes. However, the wireless master device 2 assigns different transmission timings to each wireless slave device 1 so that wireless signals transmitted from each wireless slave device 1 (1a to 1h) do not collide with each other. Then, each wireless slave device 1 (1a to 1h) transmits data to the wireless master device 2 at the transmission timing assigned to it. Thus, in this embodiment, the wireless master device 2 operates as a management device that manages data transmission from the multiple wireless slave devices 1a to 1h.

[0016] The wireless communication system 100 may be constructed using an ISM (Industry, Science, and Medical) band. The ISM band is a frequency band allocated for use in the fields of industry, science, and medicine, and the 920 MHz band has been used in wireless communication systems that perform remote meter reading using smart meters for electricity, gas, water, and the like. In recent years, the number of measuring instruments, sensors, and the like connected to networks has been increasing, and it is expected that the frequency band of the ISM band will become congested in the future, and wireless terminals will repeat carrier sense and data retransmission more frequently. On the other hand, in wireless communication systems for smart meters for electricity, gas, water, and the like, wireless terminals often operate on battery power. For this reason, if carrier sense and data retransmission are repeatedly performed, power consumption increases, and there is a risk that the available time will be shortened.

[0017] Fig. 2 shows an example of a functional configuration of the wireless slave device 1. In this embodiment, the wireless slave device 1 includes a sensor IF unit 11, a storage unit 12, a control unit 13, a wireless communication unit 14, and a power supply unit 15. Note that the wireless slave device 1 may further include other functions, circuits, or devices not shown in Fig. 2.

[0018] The sensor IF unit 11 provides an interface with the sensor 4. The sensor 4 is not particularly limited, but is, for example, a sensor that measures a physical quantity, such as a temperature sensor, a light sensor, a vibration sensor, a current sensor, or a voltage sensor. Alternatively, the sensor 4 may be a sensor that detects the usage status of an electricity meter, a gas meter, a water meter, or the like. The sensor IF unit 11 acquires the measured value or detected value of the sensor 4 and passes it to the control unit 13.

[0019] The storage unit 12 stores setting information and log information. The setting information includes control information for controlling communication of the wireless slave device 1 (for example, a communication time table described later). The log information represents communication contents of the wireless slave device 1 in chronological order. The storage unit 12 may further store various information not shown in FIG. 2.

[0020] The control unit 13 is realized by a microcomputer including a processor and a memory, and controls the operation of the wireless slave device 1. The control unit 13 also includes a communication control unit 13a, a communication monitoring unit 13b, and an information transmission unit 13c. The communication control unit 13a controls transmission and reception by the wireless communication unit 14 according to the setting information stored in the storage unit 12. The communication monitoring unit 13b monitors the radio wave conditions around the node based on the measurement by the wireless communication unit 14. The information transmission unit 13c creates information to be transmitted to the wireless master device 2 and passes it to the wireless communication unit 14. For example, the information transmission unit 13c creates information to be transmitted to the wireless master device 2 by adding time information to the data acquired by the sensor IF unit 11. Alternatively, the information transmission unit 13c may create information for updating the communication time table.

[0021] The wireless communication unit 14 includes a wireless transmission unit 14a, a wireless reception unit 14b, and a reception level measurement unit 14c. The wireless transmission unit 14a outputs a wireless signal via an antenna in response to an instruction from the control unit 13. The wireless reception unit 14b receives the wireless signal via the antenna. The reception level measurement unit 14c performs carrier sense when transmitting data. That is, the reception level measurement unit 14c measures the received radio wave intensity of the frequency band in which communication is performed.

[0022] The power supply unit 15 is a DC power supply such as a battery, and supplies power to the sensor IF unit 11, the storage unit 12, the control unit 13, and the wireless communication unit .

[0023] Fig. 3 shows an example of a functional configuration of the wireless master device 2. In this embodiment, the wireless master device 2 includes a communication IF unit 21, a storage unit 22, a control unit 23, and a wireless communication unit 24. However, the wireless master device 2 may further include other functions, circuits, or devices not shown in Fig. 3.

[0024] The communication IF unit 21 provides an interface with the server device 3. That is, the communication IF unit 21 transmits data collected from each wireless slave device 1 to the server device 3. In addition, the communication IF unit 21 passes instructions, data, and information transmitted from the server device 3 to the control unit 23.

[0025] The storage unit 22 stores setting information and log information. The setting information includes control information (such as a communication time table described later) for controlling communication between the wireless master device 2 and each wireless slave device 1. The log information represents the content of communication between the wireless master device 2 and each wireless slave device 1 in chronological order. The storage unit 22 may further store various information not shown in FIG. 3.

[0026] The control unit 23 is realized by a microcomputer including a processor and a memory, and controls the operation of the wireless master device 2. The control unit 23 also includes a communication control unit 23a, a communication monitoring unit 23b, and an information transmission unit 23c. The communication control unit 23a controls transmission and reception by the wireless communication unit 24 in accordance with the setting information stored in the storage unit 22. The communication monitoring unit 23b monitors the communication of the wireless communication system 100, and creates and updates a communication timetable, which will be described later. The information transmission unit 23c creates information to be transmitted to the wireless slave device 1, and passes it to the wireless communication unit 24.

[0027] The wireless communication unit 24 includes a wireless transmission unit 24a, a wireless reception unit 24b, and a reception level measurement unit 24c. The wireless transmission unit 24a outputs a wireless signal via an antenna in response to an instruction from the control unit 23. The wireless reception unit 24b receives the wireless signal via the antenna. The reception level measurement unit 24c performs carrier sense before transmitting the wireless signal to the wireless slave unit 1. That is, the reception level measurement unit 24c measures the received radio wave intensity of the frequency band in which communication is performed.

[0028] Fig. 4 shows an example of a hardware configuration of the server device 3. In this embodiment, the server device 3 includes a processor 31, a memory 32, a storage 33, a communication device 34, an input device 35, and an output device 36. However, the server device 3 may further include other functions, circuits, or devices not shown in Fig. 4.

[0029] The processor 31 is a computing device such as a CPU (Central Processing Unit) and provides the functions of the server device 3 by executing programs stored in the storage 33. The memory 32 is used as a working area for the processor 31. The storage 33 stores the programs executed by the processor 31 and various data / information.

[0030] The communication device 34 includes, for example, a NIC (Network Interface Card) for communicating with the wireless master device 2 via a communication network. The input device 35 includes input devices (for example, a keyboard, a touch panel, a pointing device, a microphone, a switch, a button, a sensor, etc.) that accept input from the outside. The output device 36 includes output devices (for example, a display, a speaker, etc.) that perform output to the outside. The bus 37 is commonly connected to the above-mentioned components 31 to 36, and transmits address signals, data signals, various control signals, etc.

[0031] In the wireless communication system 100 configured as above, the wireless master device 2 (or the server device 3) collects data from each wireless slave device 1 at 30-minute intervals. Therefore, the wireless master device 2 creates a communication time table with a 30-minute interval and distributes it to each wireless slave device 1. Each wireless slave device 1 transmits data to the wireless master device 2 according to the communication time table. At this time, each wireless slave device 1 refers to the communication time table based on a reference time set in the wireless communication system 100. The reference time is set at the same time interval as the interval at which the wireless master device 2 collects data from each wireless slave device 1. That is, the reference time is set at a 30-minute interval (for example, 9:00, 9:30, 10:00, etc.).

[0032] 5 shows an example of a communication time table. In the communication time table 5, a plurality of time slots are defined, which are obtained by dividing a period (i.e., 30 minutes) during which the wireless master device 2 collects data from each wireless slave device 1 into a plurality of periods. At this time, the data collection period is divided evenly. That is, the length of each time slot is the same as each other. In this embodiment, the length of the time slot is 10 seconds.

[0033] In the communication time table 5, the communication time and the transmitting slave are set. The communication time indicates the start time of each time slot. However, the communication time indicates a relative time with respect to the above-mentioned reference time. For example, when the reference time is 9:00, "communication time = 00:00:00" indicates 9:00:00 seconds, and "communication time = 00:00:10" indicates 9:00:10 seconds. Similarly, when the reference time is 9:30, "communication time = 00:00:00" indicates 9:30:00 seconds, and "communication time = 00:00:10" indicates 9:30:10 seconds.

[0034] The transmitting slave unit represents a wireless slave unit 1 assigned to a corresponding time slot. Here, each wireless slave unit 1 is assigned to one of the time slots. Moreover, multiple wireless slave units 1 are not assigned to one time slot. Furthermore, the total number of wireless slave units 1 assigned to the time slots is assumed to be less than the total number of time slots constituting the communication time table 5. In this embodiment, since the total number of time slots constituting the communication time table 5 is 180, the total number of wireless slave units 1 operating in the wireless communication system 100 is required to be less than 180. Therefore, multiple wireless slave units 1 are each assigned once to some of the time slots constituting the communication time table 5.

[0035] The multiple wireless slave devices 1 are assigned to corresponding consecutive time slots in the communication time table 5 in the order of the time slot with the earliest communication time. In the embodiment shown in Fig. 5, one wireless slave device 1 (slave devices a to n) is assigned to each of the 96 consecutive time slots between "communication time = 00:00:00" and "communication time = 00:15:50". Note that no wireless slave device 1 is assigned to any of the time slots between "communication time = 00:16:00" and "communication time = 00:29:50". In other words, each time slot within this period is an empty time slot (or an unused time slot).

[0036] The wireless master device 2 distributes the communication time table 5 created as described above to each wireless slave device 1. Then, each wireless slave device 1 transmits data according to this communication time table 5. For example, at "communication time=00:00:00", only slave device a transmits data, and at "communication time=00:00:10", only slave device b transmits data. Therefore, by each wireless slave device 1 transmitting data according to the communication time table 5, collisions between the wireless slave devices 1 are avoided.

[0037] However, the wireless communication system 100 may be affected by radio waves output from other electronic devices. In the example shown in Fig. 1, a radio signal output from another wireless device 51 may affect the communication of the wireless communication system 100 as jamming radio waves.

[0038] Therefore, when the wireless slave device 1 transmits data using its own time slot, it first performs carrier sense. Then, if the received radio wave strength is lower than a predetermined threshold level, the wireless slave device 1 transmits data using its own time slot. On the other hand, if the received radio wave strength is higher than the threshold level, the wireless slave device 1 does not transmit data, but refers to the communication time table 5 and selects one of the available time slots for data transmission. At this time, it is preferable that the wireless slave device 1 selects an available time slot corresponding to a time later than its own time slot from among the available time slots managed by the communication time table 5. It is also preferable that the wireless slave device 1 selects an available time slot corresponding to the earliest time from among the available time slots managed by the communication time table 5.

[0039] For example, in the embodiment shown in FIG. 6, assume that the slave c performs carrier sensing at "communication time=00:00:20" and as a result, the received radio wave strength is higher than a predetermined threshold level. In this case, the slave c selects a time slot corresponding to the earliest time among the available time slots. Here, at this point, the wireless slave units 1 are assigned to the time slots between "communication time=00:00:00" and "communication time=00:15:50". Therefore, the slave c selects "communication time=00:16:00". Then, the slave c transmits data at "communication time=00:16:00".

[0040] At this time, the slave device c updates the communication time table 5 held in its own node, and notifies the wireless master device 2 of the selected time slot. The wireless master device 2 then updates its own communication time table 5 in accordance with the notification, and distributes the updated communication time table 5 to each wireless slave device 1. Thereafter, each wireless slave device 1 transmits data in accordance with the updated communication time table 5.

[0041] 7 is a flowchart showing an example of the operation of the wireless slave device 1. The process of this flowchart is started, for example, at each reference time that is preset in the wireless communication system 100. In addition, it is assumed that the wireless slave device 1 has received a communication time table 5 from the wireless master device 2.

[0042] In S1, the wireless slave device 1 waits for the communication time corresponding to the time slot assigned to it. Then, when the communication time corresponding to the time slot assigned to it arrives, the wireless slave device 1 performs carrier sense in S2 to S3. As a result, if the received radio wave intensity is lower than a predetermined threshold level (S3: No), the wireless slave device 1 performs data transmission using its own time slot in S4.

[0043] When the received radio wave intensity is higher than a predetermined threshold level (S3: Yes), in S5, the wireless slave device 1 selects an available time slot by referring to the communication time table 5. In S6, the wireless slave device 1 updates the communication time table 5 that it holds based on the selection in S5. That is, the wireless slave device 1 assigns itself to the selected time slot. At this time, the time slot that was assigned to the wireless slave device 1 is updated in the communication time table 5 to a state that indicates an available time slot or an unavailable time slot.

[0044] In S7, the wireless slave device 1 waits for the communication time corresponding to the newly selected time slot. Then, when the communication time corresponding to the newly selected time slot arrives (S7: Yes), the wireless slave device 1 performs carrier sense in S8 to S9. As a result, if the received radio wave intensity is lower than a predetermined threshold level (S9: No), the wireless slave device 1 performs data transmission in S10 using the time slot newly selected in S5. At this time, the wireless slave device 1 notifies the wireless master device 2 of the time slot newly selected in S5.

[0045] When the received radio wave strength is higher than the predetermined threshold level (S9: Yes), the process of the wireless slave device 1 returns to S5. That is, a new free time slot is selected. Thereafter, the processes of S5 to S9 are repeatedly executed until a state in which jamming radio waves are sufficiently weak in the newly selected time slot is detected. Then, when a state in which jamming radio waves are sufficiently weak is detected, the wireless slave device 1 transmits data and notifies the newly selected time slot in S10 using the newly selected time slot. However, when a state in which jamming radio waves are sufficiently weak is not detected even after repeatedly executing the processes of S5 to S9 a predetermined number of times, the wireless slave device 1 may stop the data transmission and execute error processing.

[0046] In addition, in S3 or S9, the wireless slave device 1 may determine that jamming radio waves are present when a state in which the received radio wave strength is higher than a predetermined threshold level is repeatedly detected a predetermined number of times. In addition, in S10, the wireless slave device 1 may notify the wireless master device 2 and all other wireless slave devices 1 of the newly selected time slot by broadcast communication. Furthermore, in S10, the wireless slave device 1 may transmit a communication time table updated within the device to the wireless master device 2 (and other wireless slave devices 1) instead of notifying the wireless master device 2 (and other wireless slave devices 1) of the newly selected time slot.

[0047] 8 shows an example of a sequence in which the wireless master device collects data from each wireless slave device. In this embodiment, the wireless master device collects data from the wireless slave devices a to c. It is also assumed that a communication time table is distributed from the wireless master device to each of the wireless slave devices a to c. In this communication time table, it is assumed that the wireless slave devices a to c are assigned to time slots TS1 to TS3, respectively.

[0048] In time slot TS1, the wireless slave device a performs carrier sensing. In this embodiment, the received radio wave intensity is lower than the threshold level. In this case, the wireless slave device a transmits data to the wireless master device. In addition, the wireless master device transmits an ACK message to the wireless slave device a. The ACK message is an example of a confirmation message for receiving the data transmitted from the wireless slave device.

[0049] In time slot TS2, the wireless slave device b performs carrier sense. In this embodiment, the received radio wave strength is higher than the threshold level. In this case, the wireless slave device b does not transmit data in time slot TS2, but refers to the communication time table to select an available time slot. Here, since time slots TS1 to TS3 are in use, the wireless slave device b selects time slot TS4.

[0050] In time slot TS3, the wireless slave device c performs carrier sensing. In this embodiment, the received radio wave intensity is lower than the threshold level. In this case, the wireless slave device c transmits data to the wireless master device. In addition, the wireless master device transmits an ACK message to the wireless slave device c.

[0051] In time slot TS4, the wireless slave device b performs carrier sense. In this embodiment, the received radio wave strength is lower than the threshold level. In this case, the wireless slave device b transmits data to the wireless master device. At this time, the wireless slave device b transmits update information indicating the newly selected time slot together with the data to the wireless master device. Then, the wireless master device transmits an ACK message to the wireless slave device b.

[0052] The wireless master device updates the communication time table based on the update information received from the wireless slave device b. In this example, the communication time table is updated to a state in which the wireless slave device a, the wireless slave device c, and the wireless slave device b are assigned to the time slots TS1, TS3, and TS4, respectively.

[0053] After that, the wireless master device distributes the updated communication time table to each of the wireless slave devices a to c. Although the distribution method is not particularly limited, for example, in the next data collection period, the updated communication time table is transmitted to the wireless slave device together with an ACK message in response to the data reception.

[0054] In the embodiment shown in Fig. 8, in time slot TS1 of the next data collection period, the wireless slave device a transmits data to the wireless master device. Then, the wireless master device transmits an ACK message and the updated communication time table to the wireless slave device a. Similarly, the updated communication time table is transmitted to the other wireless slave devices. As a result, the updated communication time table is set in each of the wireless slave devices a to c. Thereafter, each of the wireless slave devices a to c transmits data according to the updated communication time table.

[0055] As described above, in the wireless communication system 100 according to the embodiment of the present invention, a communication time table is distributed to each wireless slave device 1, and the wireless slave device 1 transmits data using a time slot designated by the communication time table. When a jamming radio wave is detected by carrier sense during data transmission, the wireless slave device 1 refers to the communication time table to select an available time slot, and transmits data using the selected time slot. After this, the communication time tables of the wireless master device 2 and each wireless slave device 1 are updated. Therefore, each wireless slave device 1 does not need to perform continuous carrier sense to update the communication time table, and only needs to perform carrier sense in the time slot assigned to it. As a result, in the wireless communication system 100 according to the embodiment of the present invention, it is possible to avoid collisions between the wireless slave devices 1 while suppressing the power consumption of each wireless slave device 1.

[0056] <Second embodiment> In the embodiment shown in Figs. 5 to 8, the wireless master device 2 and each wireless slave device 1 hold the same communication time table 5. Here, as shown in Fig. 5, the communication time table 5 indicates which time slot each wireless slave device 1 is assigned to. However, the wireless slave device 1 does not necessarily need to recognize which time slot other wireless slave devices 1 are assigned to. Therefore, in the second embodiment of the present invention, in order to suppress the memory usage of the wireless slave device 1, the amount of information in the table held by each wireless slave device 1 is reduced. Note that wireless slave devices used in sensor networks and the like often have small memory capacities, so it is important to reduce the amount of information in the tables held.

[0057] Fig. 9 shows an example of a communication timetable used in the second embodiment. Fig. 9(a) shows an example of a communication timetable 5 held by the wireless master device 2, and Fig. 9(b) shows an example of an individual timetable 6 held by the wireless slave device 1. The communication timetable 5 held by the wireless master device 2 is substantially the same in the embodiments shown in Figs. 5 to 8 and the second embodiment shown in Fig. 9.

[0058] In the initial communication time table 5, one wireless slave device 1 is assigned to each time slot in order from the earliest communication time. In the embodiment shown in Fig. 9(a), each wireless slave device 1 (slave devices a to n) is assigned to each time slot between "communication time = 00:00:00" and "communication time = 00:15:50". Note that each time slot between "communication time = 00:16:00" and "communication time = 00:29:50" is an empty time slot (or an unused time slot).

[0059] The individual time table 6 held by the wireless slave device 1 indicates the data collection start time, data collection end time, and communication time. The data collection start time indicates the time when the first data transmission is performed in each data collection cycle. Therefore, the data collection start time is "00:00:00". The data collection start time is a fixed value. The data collection end time indicates the time when the last data transmission is performed in each data collection cycle. For example, according to the communication time table shown in FIG. 9(a), the end time of the time slot to which the slave device n that performs the last data transmission is assigned is "00:16:00". Therefore, in this case, the data collection end time is "00:16:00". The data collection end time is a value that can be updated. The data collection start time and data collection end time are the same for all wireless slave devices 1.

[0060] The communication time is set for each wireless slave 1 by the wireless master 2 in accordance with the communication time table 5. For example, when the wireless master 2 holds the communication time table 5 shown in Fig. 9(a), the communication time set in the individual time table for slave a is "00:00:00", and the communication time set in the individual time table for slave b is "00:00:10". Note that Fig. 9(b) shows the individual time table 6 held by slave c. Therefore, in this individual time table 6, "00:00:20" is set as the communication time.

[0061] Each wireless slave unit 1 transmits data according to its own individual time table. For example, slave unit c shown in Fig. 9(b) performs carrier sense at "00:00:20". As a result, if the received radio wave strength is lower than the threshold level, slave unit c transmits data.

[0062] On the other hand, when the received radio wave strength is higher than the threshold level, the slave c selects an available time slot without transmitting data. Here, the time at which data transmission from the wireless slave 1 to the wireless master 2 ends within each data collection period is recorded as the "data collection end time" in the individual time table 6. In other words, the time slots in the time period after the "data collection end time" within each data collection period are available time slots. Therefore, the slave c selects a time slot for data transmission from among the time slots in the time period after the "data collection end time". At this time, it is preferable to select the time slot immediately after the "data collection end time".

[0063] In this embodiment, slave c selects the time slot immediately following the "data collection end time." Then, slave c updates the "communication time" in the individual time table it holds to the time corresponding to the selected time slot, as shown in FIG. 9(b). Also, slave c updates the "data collection end time" to the time at which the selected time slot ends. As a result, the "communication time" is updated from "00:00:20" to "00:16:00," and the "data collection end time" is updated from "00:16:00" to "00:16:10."

[0064] Thereafter, the child device c transmits data using the selected time slot and notifies the wireless master device 2 of the update contents of the individual time table 6. The wireless master device 2 then updates the communication time table 5 in accordance with the notified update contents. In this example, as shown in Fig. 9(a), the child device c is assigned to "communication time = 00:16:00". At this time, the wireless master device 2 may record information indicating that the time slot to which the child device c was assigned (i.e., the time slot corresponding to "communication time = 00:00:20") is an empty time slot or an unavailable time slot in the communication time table 5.

[0065] Furthermore, the wireless master device 2 notifies each wireless slave device 1 that the "data collection end time" has been updated from "00:16:00" to "00:16:10". Then, each wireless slave device 1 updates the "data collection end time" in its own individual timetable in response to the notification from the wireless master device 2. Note that when the wireless slave device 1 changes the time slot for data transmission, it may update its own individual timetable and notify the wireless master device 2 and each wireless slave device 1 of the updated content by broadcast communication.

[0066] As described above, according to the second embodiment, each wireless slave device 1 transmits data using an individual time table indicating the data collection start time, data collection end time, and communication time. That is, the wireless slave device 1 does not need to hold the communication time table 5 shown in FIG. 5. Therefore, in the second embodiment, the size of the table held by each wireless slave device 1 can be made smaller than in the embodiment shown in FIGS. 5 to 8. Also, the time required to register information related to the timing of data transmission in each wireless slave device 1 is reduced.

[0067] 9, the data collection start time, data collection end time, and communication time are set in the individual timetable 6, but the second embodiment is not limited to this configuration. For example, the individual timetable 6 does not need to include the data collection start time.

[0068] <Third embodiment> FIG. 10 shows an example of a communication time table held by the wireless master device 2 in the third embodiment. The communication time table 7 held by the wireless master device 2 in the third embodiment manages the communication time and the state of the time slot for the slot number (1 to m) that identifies each time slot in a data collection period. The communication time indicates the time when data communication using the time slot is performed. The state of the time slot indicates whether the time slot is in use, available, or unavailable. "In use" indicates a state in which any wireless slave device 1 is assigned to the time slot. "Available" indicates a state in which no wireless slave device 1 is assigned to the time slot. "Unavailable" indicates that a communication abnormality has been detected in the time slot.

[0069] In the initial communication timetable 7, the wireless slave devices 1 are assigned one by one in the order of the time slots with the earliest communication times. In this embodiment, in the initial setting, the wireless slave devices 1 are assigned to the time slots 1 to n. Therefore, "status: in use" is set for the time slots 1 to n, and "status: free" is set for the time slots n+1 to m.

[0070] Fig. 11 shows an example of information held by the wireless slave device 1 for controlling data transmission in the third embodiment. Specifically, Fig. 11(a) shows an example of timing information 8 held by each wireless slave device 1. Fig. 11(b) shows an example of a communication time table 9 held by each wireless slave device 1.

[0071] The timing information 8 indicates a communication interval and a slot number. The communication interval corresponds to the length of a time slot, and is 10 seconds in this embodiment. The communication interval is the same for all wireless slave devices 1. The slot number indicates a number that identifies a time slot assigned to the wireless slave device 1 by the wireless master device 2, and is different for each wireless slave device 1.

[0072] The communication time table 9 is configured from information extracted from the communication time table 7 held by the wireless master device 2. Specifically, the communication time table 9 manages the state of each time slot.

[0073] Each wireless slave device 1 transmits data according to the timing information 8 that it holds. Specifically, the wireless slave device 1 calculates its own communication time by multiplying the "communication interval" by the "slot number." In the example shown in FIG. 11(a), 30 seconds is obtained. In this case, the wireless slave device 1 performs carrier sense when 30 seconds have elapsed from the reference time. As a result, if the received radio wave intensity is lower than the threshold level, the wireless slave device 1 transmits data.

[0074] When the received radio wave intensity is higher than the threshold level, the wireless slave device 1 refers to the communication time table 9 held by itself and selects an available time slot. In the example shown in FIG. 11(b), it is assumed that time slots n+1 to m are available time slots, and the wireless slave device 1 selects time slot n+1. In this case, the wireless slave device 1 updates the status of the selected time slot n+1 in the communication time table 9 from "available" to "in use", and updates the status of time slot 3 in which jamming radio waves have been detected from "in use" to "unusable". In addition, the wireless slave device 1 updates the slot number indicating the time slot in which data transmission is performed in the timing information 8 from "3" to "n+1".

[0075] Thereafter, the wireless slave device 1 transmits data using time slot n+1, and notifies the wireless master device 2 of the update contents of the communication time table 9. The wireless master device 2 then updates its own communication time table 7 in accordance with the notified update contents. In this example, as shown in Fig. 10, the status of time slot 3 is updated from "in use" to "unavailable", and the status of time slot n+1 is updated from "free" to "in use".

[0076] Furthermore, the wireless master device 2 notifies each wireless slave device 1 of the update contents of the communication time table 7. Then, each wireless slave device 1 updates its own communication time table 9 in response to the notification from the wireless master device 2. Note that a wireless slave device 1 that detects jamming radio waves may update its own communication time table 9 and notify the wireless master device 2 and each wireless slave device 1 of the update contents by broadcast communication.

[0077] Thus, according to the third embodiment, each wireless slave device 1 transmits data using the timing information 8 and the communication time table 9. Here, the timing information 8 is composed of information indicating a communication interval and one slot number, and therefore the amount of information is small. Furthermore, the communication time table 9 manages the state of each time slot, but the state of the time slot can be represented by, for example, two bits, and the amount of information is small. Therefore, compared with the embodiment shown in Figs. 5 to 8, the third embodiment can also reduce the size of the table held by each wireless slave device 1. Furthermore, the time required to register information related to the timing of data transmission in each wireless slave device 1 is reduced.

[0078] <Variations> In the above embodiment, the wireless master device 2 creates a communication time table to manage data transmission from each wireless slave device 1, but the embodiment of the present invention is not limited to this configuration. For example, the server device 3 shown in Fig. 1 may create a communication time table to manage data transmission from each wireless slave device 1. The server device 3 may also have the functions of the wireless master device 2.

[0079] Fig. 12 shows an example of a server device having a function of managing data transmission of wireless slave devices. That is, the server device 3 shown in Fig. 12 can manage data transmission of each wireless slave device 1 in addition to the function of collecting and processing data received from each wireless slave device 1. In this case, the server device 3 includes a communication IF unit 41, a data management unit 42, a table processing unit 43, a notification unit 44, and a storage unit 45, and operates as a management device that manages data transmission of a plurality of wireless slave devices 1a to 1h. Note that the server device 3 may further include other functions, circuits, or devices not shown in Fig. 12.

[0080] The communication IF unit 41 provides an interface with the wireless master device 2. That is, the communication IF unit 41 receives data and information transmitted from each wireless slave device 1 via the wireless master device 2. In addition, the communication IF unit 41 transmits instructions, data, and information to the wireless master device 2 and each wireless slave device 1.

[0081] The data management unit 42 stores and manages data transmitted from each wireless slave device 1 in the storage unit 45. In the embodiment shown in FIG. 12, sensor data transmitted from each wireless slave device 1 is stored in the storage unit 45. The table processing unit 43 creates and updates the above-mentioned communication timetable. The notification unit 44 notifies the wireless slave device 1 of the update contents of the communication timetable. Note that the data management unit 42, the table processing unit 43, and the notification unit 44 are realized, for example, by the processor 31 shown in FIG. 4 executing a software program.

[0082] The storage unit 45 stores terminal management information, sensor data, a communication time table, etc. The terminal management information includes information related to each wireless device (wireless master device 2 and wireless slave device 1) operating in the wireless communication system 100. The sensor data is data transmitted from each wireless slave device 1. The communication time table indicates the allocation of wireless slave devices to each time slot in a data collection period, as shown in FIG. 5 etc. [Explanation of symbols]

[0083] 1(1a~1h) Wireless adapter 2 Wireless router 3. Server equipment 4 Sensors 5, 7, 9 Communication Timetable 6 Individual Timetable 8 Timing Information 100 Wireless communication system

Claims

1. A wireless communication system including a plurality of wireless terminals and a management device for managing communications between the plurality of wireless terminals, The management device includes: creating a communication time table in which a portion of a plurality of time slots obtained by dividing a predetermined period is assigned to each of the plurality of wireless terminals once; Distributing the communication timetable to the plurality of wireless terminals; each of the plurality of wireless terminals transmits data to the management device using a time slot assigned to the wireless terminal in the communication time table; When a first wireless terminal of the plurality of wireless terminals cannot use the time slot assigned to it in the communication time table, the first wireless terminal selects a first time slot from among vacant time slots not assigned to any wireless terminal in the communication time table, and transmits data to the management device using the selected first time slot; The communication time table is updated to a state in which the first wireless terminal is assigned to the first time slot.

1. A wireless communication system comprising:

2. the first wireless terminal notifies the management device of the first time slot; The management device includes: updating the communication time table to indicate that the time slot to which the first wireless terminal was assigned is unused or unavailable and to indicate that the first wireless terminal is assigned to the first time slot; Distributing the updated communication timetable to the plurality of wireless terminals.

2. The wireless communication system according to claim 1 .

3. The management device transmits the updated communication time table to each of the plurality of wireless terminals together with a confirmation message for receipt of data transmitted from each of the plurality of wireless terminals.

3. The wireless communication system according to claim 2.

4. A wireless communication system including a plurality of wireless terminals and a management device for managing communications between the plurality of wireless terminals, The management device includes: creating a communication time table in which a plurality of time slots obtained by dividing a predetermined period are assigned to each of the plurality of wireless terminals once in order from the earliest time within the predetermined period; creating an individual timetable to be referenced by each of the plurality of wireless terminals based on the communication timetable, and distributing the individual timetable to each of the corresponding wireless terminals; the individual time table indicates an end time of a time period to which the plurality of wireless terminals are assigned in the communication time table and a time when a time slot to which the wireless terminals are assigned appears; each of the plurality of wireless terminals transmits data to the management device using a time slot assigned to the wireless terminal in an individual time table created for the wireless terminal; when a first wireless terminal among the plurality of wireless terminals is unable to use the time slot to which it is assigned in the individual time table, transmits data to the management device using a first time slot representing the time slot immediately following the end time within the predetermined period; The end time of each individual timetable distributed to the plurality of wireless terminals is updated to a time corresponding to the first time slot.

1. A wireless communication system comprising:

5. A wireless communication system including a plurality of wireless terminals and a management device for managing communications between the plurality of wireless terminals, The management device includes: allocating each of the plurality of wireless terminals once to a portion of a plurality of time slots obtained by dividing a predetermined period; creating a communication time table in which state information is set for each of the plurality of time slots, the state representing a busy state in which any of the plurality of wireless terminals is assigned, an unused state in which none of the plurality of wireless terminals is assigned, or an unavailable state in which communication is prohibited; Distributing the communication timetable to the plurality of wireless terminals; notifying each of the plurality of wireless terminals of a slot number representing a time slot to which the wireless terminal is assigned; each of the plurality of wireless terminals transmits data to the management device using a time slot identified by a slot number notified by the management device; When a first wireless terminal of the plurality of wireless terminals cannot use a time slot identified by a slot number notified by the management device, the first wireless terminal selects a first time slot from among time slots whose status information indicates an unused state in the communication time table, and transmits data to the management device using the selected first time slot; In the communication timetable, the status information of the time slot to which the first wireless terminal has been assigned is updated to an unavailable state, and the status information of the first time slot is updated to an in-use state.

1. A wireless communication system comprising:

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