Base station, terminal, communication system, control method, and program

Abstract

To contribute to reducing power consumption of an entire communications system.SOLUTION: A base station 10 that wirelessly communicates with a terminal 20 includes: a communication interface 11 that communicates wirelessly; a control unit 12 that calculates a sleep time length, which is the length of time during which the communication interface 11 maintains a sleep state; and a generation unit 13 that generates a beacon signal including the sleep time length calculated by the control unit 12, transmits the generated beacon signal to the terminal 20 via the communication interface 11, and thereby maintains a communication interface 21 of the terminal 20 that receives the beacon signal in the sleep state for the sleep time length. The control unit 12 further controls the communication interface 11 to be maintained in the sleep state for the sleep time length when the generation unit 13 transmits the beacon signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a base station, a terminal, a communication system, a control method, and a program.

Background Art

[0002] There is a communication standard for wireless communication using the 920 MHz band. One of the communication standards is the IEEE802.11ah standard.

[0003] In the 920 MHz band, the total transmission time of a communication device is regulated by the Radio Law. One of the purposes is to fairly use the radio wave band. Therefore, when a communication device performs continuous data transmission or transmission of a large amount of data, etc., it may be necessary to stop the transmission even during the data transmission.

[0004] Patent Document 1 describes a technique in which a wireless transmission device with an upper limit on the total transmission time performs transmission without delay and reduces power consumption.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 mentions the effect of reducing the power consumption of a wireless communication device on the transmission side while complying with the restrictions based on the Radio Law. However, the above technique does not mention reducing the power consumption of a wireless communication device on the reception side.

[0007] An object of the present invention is to provide a base station, a terminal, etc. that contribute to reducing the power consumption of the entire communication system including wireless communication devices on the transmission side and the reception side.

Means for Solving the Problem

[0008] Hereinafter, the invention obtained from the disclosure of this specification will be exemplified, and the effects and the like obtained from the invention will be described.

[0009] (1) A base station that performs wireless communication with a terminal, comprising: a first communication interface for performing the wireless communication; a control unit that calculates a sleep time length which is the time length for the first communication interface to maintain a sleep state; a generation unit that generates a beacon signal including the sleep time length calculated by the control unit and transmits the generated beacon signal to the terminal through the first communication interface, so as to maintain the second communication interface of the terminal that has received the beacon signal in a sleep state during the sleep time length, wherein the control unit further controls to maintain the first communication interface in a sleep state during the sleep time length when the generation unit transmits the beacon signal.

[0010] According to the above aspect, the base station can suppress the occurrence of losses or delays in the communication between the base station and the terminal by maintaining the communication interfaces of the base station and the terminal in a sleep state at substantially the same timing during the calculated sleep time length. For example, when one of the base station and the terminal maintains a sleep state and the other maintains an awake state, losses or delays in the communication from the other to the one may occur. However, by maintaining the communication interfaces of the terminal and the base station in a sleep state at substantially the same timing, the occurrence of the above losses or delays can be suppressed. In addition, the base station contributes to reducing the power consumption of the entire communication system by maintaining the communication interfaces of the base station and the terminal in a sleep state. In other words, the power consumption can be significantly reduced compared to the case where only one of the communication interfaces of the base station or the terminal is maintained in a sleep state. Thus, the base station contributes to reducing the power consumption of the entire communication system.

[0011] (2) The first communication interface performs the wireless communication in a wireless communication band with a limit value of the total transmission time per unit time defined, and when the transmission amount of the total transmission time in the most recent unit time becomes equal to or more than a predetermined ratio with respect to the limit value due to the first communication interface performing the wireless communication, the control unit calculates the sleep time length and performs the control to maintain the first communication interface in the sleep state. When the control unit calculates the sleep time length, the generation unit generates the beacon signal and transmits it to the terminal. The base station according to (1).

[0012] According to the above aspect, when the base station performs wireless communication in a wireless communication band with a limit value of the total transmission time per unit time defined, when it is expected that the total transmission time will exceed the limit value, the communication interfaces of the terminal and the base station are maintained in the sleep state at substantially the same timing. Thereby, the base station suppresses the total transmission time per unit time from exceeding the limit value, suppresses the occurrence of loss or delay in the communication between the base station and the terminal, and contributes to the reduction of power consumption during the period when the transmission is restricted.

[0013] (3) The sleep time length calculated by the control unit is a time length equal to or longer than the time length from the first time point to the second time point. The first time point is the time point when the beacon signal is transmitted, and the second time point is the time point that has advanced in the direction in which time elapses from the first time point and is the first time point when the total transmission time of the unit time with the second time point as the end period becomes smaller than the reference value. The base station according to (2).

[0014] According to the above aspect, as time passes, at least until the total transmission time in the most recent unit time falls outside the duty window and decreases to be less than the reference value, the base station maintains the communication interfaces of the terminal and the base station in the sleep state at substantially the same timing, and secures a certain amount of time as the transmission available time after waking up. Thereby, as time passes, the power consumption during the period until the total transmission time in the most recent unit time becomes less than the reference value can be reduced. Therefore, the base station can more appropriately contribute to reducing the power consumption of the entire communication system.

[0015] (4) When the first communication interface is in the awake state, the control unit updates the history information including the transmission available time of the first communication interface in each time interval and the information necessary for calculating the transmission available time of the time interval a predetermined time after the time interval, and when the first communication interface is in the sleep state, limits the update of the history information, and when the first communication interface transitions from the sleep state to the awake state, collectively updates the history information during the period in which the first communication interface maintained the sleep state. The base station according to any one of (1) to (3).

[0016] According to the above aspect, the base station can acquire history information including the period in which the first communication interface is in the sleep state, more appropriately calculate the sleep time length using the history information, and maintain the communication interfaces of the base station and the terminal in the sleep state at substantially the same timing. Therefore, the base station can more appropriately contribute to reducing the power consumption of the entire communication system.

[0017] (5) When the communication time point at which the first communication interface will perform the wireless communication in the future can be specified, the control unit specifies the communication time point, calculates the time length from the current time point to the communication time point as the sleep time length, and performs the control to maintain the first communication interface in the sleep state. When the control unit calculates the sleep time length, the generation unit generates the beacon signal and transmits it to the terminal. The base station according to (1).

[0018] According to the above aspect, when the base station can identify the time point for future wireless communication, the base station causes the communication interfaces of the terminal and the base station to be maintained in the sleep state at substantially the same timing during the period until that time point. Thereby, the base station suppresses the occurrence of losses or delays in the communication between the base station and the terminal, and contributes to reducing the power consumption during the time band in the sleep state.

[0019] (6) A terminal that performs wireless communication with a base station, the terminal comprising: a second communication interface for performing the wireless communication; and a control unit that, when receiving a beacon signal including a sleep time length, which is the time length for which a first communication interface included in the base station maintains a sleep state, from the base station, controls to maintain the second communication interface in the sleep state for the sleep time length.

[0020] According to the above aspect, the terminal transitions the communication interface to the sleep state during the sleep time length included in the beacon signal received from the base station. At this time, the communication interface of the base station is also maintained in the sleep state. Therefore, by maintaining the communication interfaces of the base station and the terminal in the sleep state at substantially the same timing, the occurrence of losses or delays in the communication between the base station and the terminal can be suppressed. For example, if one of the base station and the terminal maintains the sleep state and the other maintains the awake state, losses or delays in the communication from the other to the one may occur. However, by maintaining the communication interfaces of the terminal and the base station in the sleep state at substantially the same timing, the occurrence of the above losses or delays can be suppressed. In addition, the terminal contributes to reducing the power consumption of the entire communication system. In other words, the power consumption can be reduced more significantly than when maintaining the communication interface of only one of the base station or the terminal in the sleep state. Thus, the terminal contributes to reducing the power consumption of the entire communication system.

[0021] (7) When the communication interface maintains the sleep state based on the control, the control unit maintains the connection state with the base station even when the beacon signal from the base station is not received for a predetermined time or more. The terminal according to (6).

[0022] According to the above aspect, since the terminal maintains the connection state with the base station without performing the connection process with the base station after the communication interface transitions to the awake state, the terminal is in a state where communication with the base station is possible, and when frame transmission is required, communication can be performed without delay. Therefore, the terminal can contribute to reducing the power consumption of the entire communication system while performing communication without delay.

[0023] (8) A communication system including the base station according to (1) and the terminal according to (6) that wirelessly receives the beacon signal including the sleep time length transmitted by the base station.

[0024] According to the above aspect, the communication system has the same effects as the above base station and the above terminal.

[0025] (9) A control method executed by a base station that performs wireless communication with a terminal, the method including: calculating a sleep time length that is the time length for which a first communication interface that performs the wireless communication maintains a sleep state; generating a beacon signal including the calculated sleep time length, and transmitting the generated beacon signal to the terminal through the first communication interface to maintain the second communication interface of the terminal that has received the beacon signal in a sleep state for the sleep time length; and when the beacon signal is transmitted, performing control to maintain the first communication interface in a sleep state for the sleep time length.

[0026] According to the above aspect, the same effects as the above base station are achieved.

[0027] (10) A control method executed by a terminal that performs wireless communication with a base station, the method including: a step in which a communication interface for the wireless communication receives a beacon signal including a sleep time length; and a step of controlling to maintain the communication interface in a sleep state for the sleep time length.

[0028] According to the above aspect, the same effect as that of the above terminal is achieved.

[0029] (11) A control method for a system including a base station and a terminal, the method including: the base station executing the control method described in (9); and the terminal executing the control method described in (10).

[0030] According to the above aspect, the same effect as that of the above communication system is achieved.

[0031] (12) A program for causing a computer to execute the control method described in (9).

[0032] According to the above aspect, the same effect as that of the above base station is achieved.

[0033] Note that the present invention can be realized not only as an apparatus, but also as a method having processing means constituting the apparatus as steps, as a program for causing a computer to execute those steps, as a recording medium such as a computer-readable CD-ROM recording the program, or as information, data, or signals indicating the program. And those programs, information, data, and signals may be distributed via a communication network such as the Internet.

Effects of the Invention

[0034] According to the present invention, the base station contributes to reducing the power consumption of the entire communication system.

Brief Description of the Drawings

[0035]

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[0036] Hereinafter, the embodiment will be specifically described with reference to the drawings.

[0037] The embodiments described below all show preferred specific examples of the present invention. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. In addition, among the components in the following embodiments, the components not described in the independent claims indicating the highest concept of the present invention are described as optional components constituting a more preferred form. Note that the same components may be denoted by the same reference numerals, and the description may be omitted in some cases.

[0038] (Embodiment) In the present embodiment, a base station, a terminal, etc. that contribute to reducing the power consumption of the entire communication system will be described. In the present embodiment, a base station, a terminal, etc. that contribute to reducing the power consumption of the entire communication system in a communication system that communicates in a communication band in which the total transmission time per unit time of a communication device is limited will be described.

[0039] FIG. 1 is a schematic diagram showing the configuration of a communication system 1 according to the present embodiment.

[0040] As shown in FIG. 1, the communication system 1 includes a base station 10 and terminals 20. Note that there may be a plurality of terminals 20.

[0041] The base station 10 is a base station device that performs wireless communication and is generally also referred to as an AP (Access Point). The base station 10 establishes a communication link for wireless communication with the terminal 20 and transmits and receives a communication frame (simply also referred to as a frame) through the communication link.

[0042] The base station 10 receives frames from the terminal 20. When a plurality of terminals 20 are connected to the base station 10, the frames received from one terminal 20 can be relayed to other terminals 20. When the base station 10 is connected to a communication network (not shown) outside the communication system 1, the frames exchanged between the terminal 20 and the communication network can be relayed. The external communication network may include, for example, a local area network such as an office or a factory, or the Internet. The state in which the base station 10 has established a communication link with the terminal 20 is also referred to as a connected state.

[0043] The terminal 20 is a terminal device that performs wireless communication and is generally also referred to as an STA (Station). The terminal 20 establishes a communication link for wireless communication with the base station 10 and transmits and receives frames through the communication link. The terminal 20 can transmit frames addressed to the base station 10. When a plurality of terminals 20 are connected to the base station 10, the terminal 20 can transmit and receive frames with other terminals 20 via relay by the base station 10. When the base station 10 is connected to a communication network (not shown) outside the communication system 1, frames can be transmitted and received with the communication network. The state in which the terminal 20 has established a communication link with the base station 10 is also referred to as a connected state.

[0044] The wireless communication between the base station 10 and the terminal 20 is performed in a communication band in which a limit value of the total transmission time per unit time is defined, for example, in the 920 MHz band. More specifically, the wireless communication between the base station 10 and the terminal 20 is communication compliant with the IEEE802.11ah standard. Note that the limitation on the time for transmitting frames as described above is based on, for example, regulations (such as regulations of the Radio Law) for the purpose of fair use of radio waves by a plurality of applications or a plurality of communication devices.

[0045] Specifically, the limit value for wireless communication in the 920 MHz band is 10% of the entire communication band. Also, the unit time can be set to 1 hour. In this case, the total transmission time that one communication device can transmit frames within 1 hour is 6 minutes. Note that the ratio of the total transmission time to the entire communication band is also referred to as the duty ratio. Also, the period for determining that the total transmission time of the communication device is below the limit value is also referred to as the duty window.

[0046] The total transmission time of the communication device is required to comply with the restrictions regarding the duty ratio, that is, to be below the limit value within any duty window. For example, if a communication device has transmitted for 6 minutes during a 1-hour period (also referred to as the most recent 1 hour in the past) with the current time as the end time, that communication device cannot transmit frames at that point in time. In this case, as time passes, the communication device will be able to transmit frames when the total transmission time during the most recent 1-hour period in the past is less than 6 minutes.

[0047] Hereinafter, the base station 10 and the terminal 20 will be described in detail. Hereinafter, the case where the time width of the duty window (also referred to as the duty window time or DW time) is 1 minute will be described as an example, but it is not limited to this.

[0048] The base station 10 includes a communication interface 11, a control unit 12, and a generation unit 13. Note that the control unit 12 and the generation unit 13 can be realized by a processor (such as a CPU (Central Processing Unit), etc.) provided in the base station 10 executing a predetermined program using a memory.

[0049] The communication interface 11 is a communication interface for wireless communication, and includes an antenna and a transmission / reception circuit for wireless communication signals, etc. The communication interface 11 can be connected to the terminal 20 and perform wireless communication with the terminal 20. The communication standard of the communication interface 11 is, for example, the IEEE802.11ah standard. The communication interface 11 transmits a frame such that the total transmission time in any duty window is below a limit value. In other words, the communication interface 11 transmits a frame while restricting so that the total transmission time in any duty window does not exceed the limit value. The restriction on the transmission of the frame is made by the control unit 12.

[0050] The communication interface 11 counts the total transmission time within the duty window with the current time as the end time, and calculates the available transmission time at the current time using the total transmission time. The available transmission time at the current time is the remaining time obtained by subtracting the total transmission time from the limit value. The available transmission time at the current time means the longest time for which frames can be continuously transmitted if frames are transmitted continuously from the current time.

[0051] The control unit 12 controls the transmission of the communication interface 11 and the sleep state of the communication interface 11.

[0052] The control unit 12 acquires the available transmission time from the communication interface 11 and updates the history information of the available transmission time. More specifically, when the communication interface 11 is in the awake state, the control unit 12 repeatedly acquires the available transmission time from the communication interface 11, and each time it is acquired, the acquired available transmission time is added to the history information. Further, the control unit 12 calculates information necessary for calculating the available transmission time in the future (specifically, the "recovery amount of the available transmission time after DW time" described later) and stores it in the history information. Also, when the communication interface 11 transitions from the sleep state to the awake state, the control unit 12 collectively updates the history information during the period in which the sleep state was maintained by a complement processing. The complement processing will be described later.

[0053] The time interval at which the control unit 12 acquires the transmission available time is shorter than the duty window time (for example, 1 second or less). Here, the history information is retained by being successively stored and erased in the memory provided in the base station 12.

[0054] Thereby, the control unit 12 updates the history information so that the transmission available time within the duty window with the current time as the end period is included in the history information. Then, the control unit 12 performs control to limit the transmission of frames in an amount exceeding the limit value by using the history information of the transmission available time. Note that when updating the history information, the control unit 12 may delete the transmission available time prior to the duty window with the current time as the end period from the history information.

[0055] Also, the control unit 12 performs control to transition the communication interface 11 to the sleep state or maintain it. Specifically, the control unit 12 calculates the sleep time length which is the length of time for which the communication interface 11 maintains the sleep state. Then, the control unit 12 performs control to maintain the communication interface 11 in the sleep state for the sleep time length. The control unit 12 executes the above control to maintain the communication interface 11 in the sleep state when the generation unit 13 transmits a sleep beacon (described later).

[0056] The control for the control unit 12 to transition the communication interface 11 to the sleep state is executed at a point slightly before the transmission of the communication interface 11 is restricted. Specifically, when the total transmission time within the duty window with the current time as the end period becomes equal to or more than a predetermined ratio (for example, about 97% to 99%) (also referred to as the first ratio) with respect to the limit value due to the communication interface 11 performing wireless communication, the control unit 12 calculates the sleep time length and performs control to maintain the communication interface 11 in the sleep state for the sleep time length. Also, in the above case, the control unit 12 can control the generation unit 13 to generate a sleep beacon and transmit it to the terminal 20. The method for calculating the sleep time length will be described in detail later.

[0057] The generation unit 13 generates a beacon signal (also referred to as a sleep beacon) including the sleep time length, and transmits the generated sleep beacon to the terminal 20 through the communication interface 11. By transmitting the sleep beacon to the terminal 20, the generation unit 13 causes the communication interface 21 of the terminal 20 that has received the sleep beacon to be maintained in the sleep state during the sleep time length. The generation unit 13 acquires the sleep time length calculated by the control unit 12, and generates a sleep beacon including the sleep time length.

[0058] For example, when the total transmission time within the most recent unit time exceeds a predetermined ratio with respect to the limit value due to the communication interface 11 performing wireless communication, the generation unit 13 generates a sleep beacon and transmits it to the terminal 20. Under the control of the control unit 12, the generation unit 13 can generate and transmit a sleep beacon.

[0059] In this case, the sleep time length included in the sleep beacon generated by the generation unit 13 is the time length from the first time point to the second time point. Here, the first time point is the time point when the sleep beacon is transmitted. The second time point is the time point that has advanced in the direction in which time elapses from the first time point, and is the first time point at which the total transmission time within the unit time (i.e., the duty window) with the second time point as the end period becomes smaller than the limit value (in other words, the transmission available time recovers from zero). If the sleep time length is set as the time length from the first time point to the second time point, the communication interface 11 can maximize the transmission amount while observing the restrictions regarding the duty ratio. Note that the sleep time length may be longer than the time length from the first time point to the second time point. When the sleep time length is longer than the time length from the first time point to the second time point, the time during which the communication interface 11 does not transmit is extended (i.e., the total transmission time within the duty window is decreased), and thus, transmission is not newly restricted. In the above case, by increasing the time during which the communication interface 11 and the communication interface 21 are maintained in the sleep state, the power consumption can be further reduced.

[0060] The terminal 20 includes a communication interface 21 and a control unit 22. Note that the control unit 22 can be realized by a processor included in the terminal 20 executing a predetermined program using a memory.

[0061] The communication interface 21 is a communication interface for wireless communication and includes an antenna and a transmission / reception circuit for wireless communication signals, etc. The communication interface 21 can be connected to the base station 10 and perform wireless communication with the base station 10. The communication standard of the communication interface 21 is, for example, the IEEE802.11ah standard.

[0062] The control unit 22 controls the sleep state of the communication interface 21. Specifically, when the communication interface 21 receives a beacon signal (i.e., a sleep beacon) including a sleep time length, the control unit 22 controls to maintain the communication interface 21 in the sleep state for the sleep time length.

[0063] Also, when the communication interface 21 is maintaining the sleep state based on the above control, the control unit 22 maintains the connection state with the base station 10 even if it does not receive a beacon signal from the base station 10 for a predetermined time or more. In general communication between the base station 10 and the terminal 20, when the terminal 20 does not receive a beacon signal periodically transmitted by the base station 10 (for example, every 100 milliseconds) for a predetermined time (for example, 1 second) or more, the terminal 20 disconnects the communication link with the base station 10 to release the connection state. However, when the communication interface 21 is maintaining the sleep state based on the above control, although the communication interface 21 does not receive a beacon signal, it maintains the connection state even if it does not receive a beacon signal for a predetermined time or more. In other words, it suppresses releasing the connection state based on not receiving a beacon signal for a predetermined time or more, so that it is not necessary for the base station 10 and the terminal 20 to perform unnecessary communication to re-establish the communication link.

[0064] FIG. 2 is an explanatory diagram showing the communication state and the transmittable time of the wireless communication of the base station 10 according to the present embodiment.

[0065] The horizontal axis of the graph shown in FIG. 2 represents the elapsed time, and the vertical axis represents the transmitable time at the point in time of the elapsed time. Also, the communication state of the radio communication of the base station 10 at the point in time of the elapsed time is shown at the upper part of the graph.

[0066] Here, as an example, the communication state and the transmitable time of the base station 10 when the base station 10 transmits frames to the terminal 20 in the section of the elapsed time from 20 seconds to 26 seconds and in the section of the elapsed time from 100 seconds to 103 seconds will be described.

[0067] The section of the elapsed time from 0 seconds to 20 seconds shown in FIG. 2 is shown to be a state where the communication interface 11 is not communicating (also referred to as a non-communication state). In the section of the elapsed time from 0 seconds to 20 seconds, no frame is transmitted, and the transmitable time is 6 seconds.

[0068] The section of the elapsed time from 20 seconds to 26 seconds is shown to be a state where the communication interface 11 is transmitting a frame (also referred to as a transmission state). In the section of the elapsed time from 20 seconds to 26 seconds, the transmitable time linearly decreases, and at the point in time of the elapsed time of 26 seconds, the transmitable time becomes 0 seconds. Based on the fact that the transmitable time becomes 0 seconds, the control unit 12 starts restricting the transmission of the communication interface 11.

[0069] The section of the elapsed time from 26 seconds to 80 seconds is shown to be a state where the communication interface 11 cannot communicate due to the communication band restriction (also referred to as a non-communicable state). In the section of the elapsed time from 26 seconds to 80 seconds, the transmitable time maintains 0 seconds, and the control unit 12 maintains the restriction of the transmission of the communication interface 11.

[0070] The interval of elapsed time from 80 seconds to 100 seconds indicates that the communication interface 11 was in a state where it was not communicating (also referred to as a non-communication state). Also, in the interval of elapsed time from 80 seconds to 86 seconds within the above interval, the transmit available time increased linearly, and at the point in time of 86 seconds of elapsed time, the transmit available time became 6 seconds. The fact that the transmit available time increases linearly in the interval of elapsed time from 80 seconds to 86 seconds is due to the communication performance in the interval of elapsed time from 20 seconds to 26 seconds deviating from the duty window. When the transmit available time becomes greater than 0 seconds at the point in time of 80 seconds of elapsed time, the control unit 12 releases the restriction on the transmission of the communication interface 11.

[0071] The interval of elapsed time from 100 seconds to 103 seconds indicates that the communication interface 11 was in a state where it was transmitting (also referred to as a transmit state). In the interval of elapsed time from 100 seconds to 103 seconds, the transmit available time decreased linearly, and at the point in time of 103 seconds of elapsed time, the transmit available time became 3 seconds.

[0072] The interval of elapsed time from 103 seconds to 180 seconds indicates that the communication interface 11 was in a state where it was not communicating (also referred to as a non-communication state). Also, in the interval of elapsed time from 160 seconds to 163 seconds within the above interval, the transmit available time increased linearly, and at the point in time of 163 seconds of elapsed time, the transmit available time became 6 seconds.

[0073] In this way, the base station 10 can communicate while observing the restrictions regarding the duty ratio using the transmit available time.

[0074] FIG. 3 is an explanatory diagram showing a sleep beacon 31 which is a beacon signal according to the present embodiment.

[0075] As shown in FIG. 3, the sleep beacon 31 includes control information 33 and a sleep time length 34.

[0076] The control information 33 is information indicating that the beacon signal is the sleep beacon 31. For example, the control information 33 may be assigned to a predetermined bit in the beacon signal. In that case, it can be said that when the bit that is the control information 33 is 1, it indicates that the beacon signal is the sleep beacon 31.

[0077] The sleep time length 34 is the time length calculated by the control unit 12 and included in the sleep beacon 31. The sleep time length 34 is the time length for which the communication interface 11 of the base station 10 maintains the sleep state, and is also the time length for which the communication interface 21 of the terminal 20 that has received the sleep beacon 31 maintains the sleep state.

[0078] The control information 33 and the sleep time length 34 can be stored in a predetermined field (for example, the Vender Specific IE (Information Element) field) included in the beacon signal defined by the wireless communication standard.

[0079] The processing of the base station 10 and the terminal 20 configured as described above will be described.

[0080] FIG. 4 is a flowchart showing the processing of the base station 10 according to the present embodiment. FIG. 5 is a flowchart showing the detailed processing of the base station 10 according to the present embodiment. FIG. 6 is an explanatory diagram showing the history information according to the present embodiment. FIG. 7 is an explanatory diagram showing the information used for calculating the sleep time length of the base station 10 according to the present embodiment. FIG. 8 is an explanatory diagram showing the complementary processing of the history information of the base station 10 according to the present embodiment. The processing of the base station 10 will be described with reference to FIGS. 4 to 8.

[0081] Note that the series of processes shown in FIGS. 4 and 5 are repeatedly executed for each section (also simply referred to as a section) corresponding to a predetermined time. Hereinafter, the above-mentioned "predetermined time" is, for example, 1 second, and this case will be described as an example, but it is not limited thereto.

[0082] In step S101, the control unit 12 acquires the transmission available time from the communication interface 11, and updates the history information by adding the acquired transmission available time to the history information. Further, using the acquired transmission available time, the control unit 12 calculates the recovery amount of the transmission available time after the DW time (the "recovery amount of the transmission available time" is also simply referred to as the recovery amount) from the current time and stores it in the history information. The control unit 12 can calculate the recovery amount after the DW time by subtracting the acquired transmission available time from the sum of the transmission available time in the immediately preceding section and the oldest recovery amount in the history information. The acquired transmission available time is a value obtained by adding the recovery amount in the acquired section to the transmission available time in the immediately preceding section and subtracting the transmission amount. Since the recovery amount after the DW time is the same as the transmission amount in the acquired section, it is necessary to calculate the recovery amount after the DW time including the recovery amount in the acquired section.

[0083] Here, the reason why the recovery amount after the DW time is the same as the transmission amount in the acquired section is clear from the fact that, as described in FIG. 2 above, during the elapsed time of the communication-free state, the transmission amount before the DW time deviates from the DW time width, and the transmission available time increases (recovers) by that amount. Specifically, in FIG. 2, the transmission available time increases linearly (in the section from the elapsed time of 80 seconds to 86 seconds), is equal to the transmission time before the DW time (60 seconds), and the transmission available time becomes 6 seconds (at the elapsed time of 86 seconds). The oldest recovery amount included in the history information immediately before adding the newly acquired information indicates the recovery amount in the section where the transmission available time was acquired. By subtracting the acquired transmission available time from the sum of this value and the transmission available time in the immediately preceding section, the recovery amount after the DW time can be calculated.

[0084] An example of the history information is shown in FIG. 6. In FIG. 6, the transmission available time (in microseconds) acquired by the control unit 12 in each section and the recovery amount (in microseconds) in the time section after the DW time in the corresponding section are shown.

[0085] In addition, in FIG. 6, the latest transmission available time and the recovery amount after the DW time are shown in section #10. When the control unit 12 acquires a new transmission available time, it shifts the transmission available time and the recovery amount after the DW time in sections #2 to #10 upward (in other words, in the direction of going back in time) by one section each, and stores the acquired new transmission available time and the calculated new recovery amount in section #10.

[0086] For example, FIG. 6(a) shows the history information at the time when no frame has been transmitted in the last 10 seconds. In all the sections shown in FIG. 6(a), the transmission available time is 1,000,000 microseconds. Since the acquired transmission available time is equal to the transmission available time in the immediately preceding section, the control unit 12 calculates the recovery amount after the DW time as 0 microseconds.

[0087] FIG. 6(b) shows the history information at the time when 5 sections have passed since the time in FIG. 6(a). #10 in FIG. 6(a) corresponds to #5 in FIG. 6(b). It is shown that the communication interface 11 transmitted for 200,000 microseconds in the section immediately after the time in FIG. 6(a) (corresponding to #6 in FIG. 6(b)), and starting from 2 sections later, the communication interface 11 transmitted for 100,000 microseconds continuously for 3 sections, one section at a time. The transmission available time changed by the above transmissions is shown as the transmission available time in each of sections #6 to #10 in FIG. 6(b). Also, the control unit 12 calculates the recovery amount after the DW time for each time section from #6 to #10 by using the acquired transmission available time, the sum of the transmission available time in the immediately preceding section, and the recovery amount of the oldest transmission amount in the history information.

[0088] Further, (c) of FIG. 6 shows the history information at the time when four intervals have elapsed from the time of (b) of FIG. 6. #10 in (b) of FIG. 6 corresponds to #6 in (c) of FIG. 6. It is shown that in the interval immediately after the time of (b) of FIG. 6 (corresponding to #7 in (c) of FIG. 6), the communication interface 11 transmitted for 300,000 microseconds, and in the interval three intervals later, the communication interface 11 transmitted for 100,000 microseconds. The transmitable time changed by the above transmission is shown as the transmitable time for each of the intervals #7 to #10 in (c) of FIG. 6. Further, the control unit 12 uses the acquired transmitable time, the transmitable time of the immediately preceding interval, and the sum of the recovery amounts of the oldest transmission amounts in the history information to calculate the recovery amounts after the DW time for each of the time intervals #7 to #10.

[0089] Returning to FIG. 4, in step S102, the control unit 12 determines whether the transmitable time acquired in step S101 is less than the first reference value. If it is determined that the transmitable time is less than the first reference value (Yes in step S102), the process proceeds to step S103; otherwise (No in step S102), the series of processes shown in FIG. 4 ends. Here, the first reference value is a value of the transmitable time at which, when the transmitable time becomes less than the first reference value, the control unit 12 calculates the sleep time length and controls the sleep. The first reference value is a predetermined ratio (for example, about 1% to 3%) (also referred to as the second ratio) to the limit value, and is a value obtained by subtracting the first ratio from 1.

[0090] In step S103, the control unit 12 calculates the sleep time length. The detailed processing included in step S103 will be described with reference to FIG. 5.

[0091] In step S111, the control unit 12 acquires the recovery amount of the future transmission amount. Specifically, the control unit 12 acquires the recovery amount n seconds after the current time with n being each integer value from 1 to DW. DW is a numerical value indicating the DW time in seconds.

[0092] At the time of (c) in FIG. 6, the recovery amount n seconds after that time calculated by the control unit 12 is shown in FIG. 7. The recovery amount n seconds after that time is equal to the recovery amount after the DW time of each section included in the history information. Therefore, the control unit 12 can obtain the recovery amount after the DW time of each section shown in (c) of FIG. 6 as the recovery amount n seconds after that time.

[0093] In step S112, the control unit 12 calculates the future transmitable time. Specifically, the control unit 12 calculates the transmitable time n seconds after that time with n being each integer value from 1 to DW.

[0094] At the time of (c) in FIG. 6, the transmitable time n seconds after that time calculated by the control unit 12 is shown in FIG. 7. The transmitable time n seconds after that time can be calculated by adding the recovery amount n seconds after that time to the transmitable time at that time. Specifically, the control unit 12 can calculate the transmitable time 1 second after (that is, 100,000 microseconds) by adding the recovery amount 1 second after (that is, 0 microseconds) to the transmitable time of 100,000 microseconds, which is the transmitable time of section #10 shown in (c) of FIG. 6. The control unit 12 can calculate the transmitable time 2 seconds after (that is, 300,000 microseconds) by adding the recovery amount 2 seconds after (that is, 200,000 microseconds) to the transmitable time of 100,000 microseconds, which is the transmitable time of section #10 shown in (c) of FIG. 6. The same applies to subsequent seconds.

[0095] In step S113, the control unit 12 identifies the first point in time among the transmission available times n seconds after the current time calculated in step S112 (where n is each integer value from 1 to DW) at which the transmission available time becomes equal to or greater than the second reference value (also simply referred to as the reference value). Here, the second reference value is the value of the transmission available time at which the control unit 12 releases the transmission restriction of the communication interface 11 when the transmission available time becomes equal to or greater than the second reference value. The second reference value can be, for example, 300,000 microseconds (30% of the DW time), 500,000 microseconds (50% of the DW time), or 1,000,000 microseconds (100% of the DW time), etc.

[0096] As is clear from FIG. 7, when the second reference value is 300,000 microseconds, the control unit 12 identifies the point in time 2 seconds later as the first point in time among the transmission available times n seconds after the current time at which the transmission available time becomes equal to or greater than the second reference value. This is because the transmission available time of 100,000 microseconds, which is the transmission available time 1 second later, is less than 300,000 microseconds, and the transmission available time becomes equal to or greater than the second reference value (300,000 microseconds) 2 seconds later.

[0097] Similarly, for each case where the second reference value is 500,000 microseconds or 1,000,000 microseconds, the control unit 12 identifies the point in time 5 seconds later or 10 seconds later as the first point in time among the transmission available times n seconds after the current time at which the transmission available time becomes equal to or greater than the second reference value.

[0098] In step S114 of FIG. 5, the control unit 12 calculates the time length from the current time to the point in time identified in step S113 as the sleep time length. When the control unit 12 identifies the point in time 2 seconds later, 5 seconds later, or 10 seconds later in step S113, it calculates 2 seconds, 5 seconds, or 10 seconds as the sleep time length, respectively.

[0099] Returning to FIG. 4, in step S104, the generation unit 13 generates a sleep beacon including the sleep time length calculated in step S103. Further, the generation unit 13 transmits the generated sleep beacon to the terminal 20 through the communication interface 11. More specifically, the generation unit 13 transmits the sleep beacon by broadcast, and the terminal 20 receives the transmitted sleep beacon. Since the sleep beacon is transmitted by broadcast, when a plurality of terminals 20 are connected to the base station 10, the sleep beacon transmitted once by the base station 10 is received by the plurality of terminals 20. In other words, since it is not necessary for the base station 10 to transmit the sleep beacon for the number of the plurality of terminals 20, there are effects of reducing the processing load of the information processing of the base station 10 and reducing the power consumption, and there is also an effect of avoiding excessive transmission of radio waves related to communication.

[0100] Immediately after the broadcast transmission of the sleep beacon, in step S105, the control unit 12 sets a timer for the sleep time length calculated in step S103. Further, the control unit 12 transitions the communication interface 11 to the sleep state. When the time corresponding to the sleep time length has elapsed since the timer was set, a timer interrupt occurs in the processor. When the timer interrupt occurs, the control unit 12 executes the process of step S106.

[0101] In step S106, the control unit 12 releases the sleep state of the communication interface 11 and transitions it to the awake state in response to the occurrence of the timer interrupt.

[0102] In step S107, the control unit 12 updates the history information. Specifically, the control unit 12 updates the history information by complementing the information during the period in which the communication interface 11 maintains the sleep state (also referred to as the sleep period).

[0103] More specifically, as described with reference to FIG. 6, the control unit 12 shifts the transmission available time and the recovery amount included in the history information upward by the time length of the sleep period. At this time, the control unit 12 may delete the transmission available time and the recovery amount that are prior to the duty window with the current time as the end time. Then, the control unit 12 stores appropriate transmission available time and recovery amount described below in the portion vacated by the above shift.

[0104] That is, as the transmission available time for each section, the control unit 12 stores a time obtained by adding the "recovery amount after DW time" of the section DW time before the current section to the transmission available time of the section immediately preceding the current section.

[0105] Also, during the sleep period, the control unit 12 stores "0 microseconds" as the "recovery amount after DW time" for each section. This is because during the sleep period, the communication interface 11 does not perform transmission, so the transmission available time does not decrease from that of the immediately preceding section.

[0106] An example of the history information complement is shown in FIG. 8.

[0107] FIG. 8(a) shows the history information immediately after the sleep period has elapsed. The history information shown in FIG. 8(a) is the same as the history information immediately before sleep (see FIG. 6(c)), and the sleep period has not been complemented yet.

[0108] FIG. 8(b) shows the history information after complement when the sleep period is 2 seconds. The transmission available time and the recovery amount in the sections #1 to #8 in FIG. 8(b) are the transmission available time and the recovery amount in the sections #3 to #10 in FIG. 8(a) shifted upward by two sections, and their contents are the same.

[0109] The control unit 12 calculates the transmission available time of the #9 section in FIG. 8(b) by complementation as follows. That is, the control unit 12 calculates the transmission available time of the #9 section in FIG. 8(b) as the time obtained by adding the "recovery amount after DW time" (i.e., 0 microseconds) of the section before the DW time from the #9 section (i.e., the #1 section in FIG. 8(a)) to the transmission available time of the #8 section (i.e., 100,000 microseconds), and calculates it as 100,000 microseconds.

[0110] Further, the control unit 12 stores, as the transmission available time of the #10 section in FIG. 8(b), the transmission available time acquired from the communication interface 11 immediately after the sleep period has elapsed.

[0111] FIG. 8(c) shows the history information after complementation when the sleep period is 5 seconds. The transmission available time and the recovery amount of the #1 to #5 sections in FIG. 8(c) are the transmission available time and the recovery amount of the #6 to #10 sections in FIG. 8(a) shifted upward by five sections, and their contents are the same.

[0112] The control unit 12 calculates the transmission available time of the #6 section in FIG. 8(c) by the same process as when calculating the transmission available time of the #9 section in FIG. 8(b) above. Further, the control unit 12 calculates the transmission available time of the #7 to #9 sections in FIG. 8(c) by the same process as above. Specific descriptions are omitted. Also, the control unit 12 stores, as the transmission available time of the #10 section in FIG. 8(c), by the same process as when storing the transmission available time of the #10 section in FIG. 8(b) above.

[0113] FIG. 8(d) shows the history information after complementation when the sleep period is 10 seconds.

[0114] The transmission available time and the recovery amount shown in FIG. 8(d) do not include the transmission available time and the recovery amount shown in FIG. 8(a). This is because, as a result of shifting the transmission available time and the recovery amount of each section in FIG. 8(a) upward by ten sections, the transmission available time and the recovery amount of each section in FIG. 8(a) do not remain.

[0115] The control unit 12 calculates the transmission available time of the section #1 in FIG. 8(d) by the same process as that for calculating the transmission available time of the section #9 in FIG. 8(b) above. Further, the control unit 12 calculates the transmission available times of the sections #2 to #9 in FIG. 8(d) by the same process as above. Specific description is omitted. Further, the control unit 12 stores, as the transmission available time of the section #10 in FIG. 8(d), by the same process as that for storing the transmission available time of the section #10 in FIG. 8(b) above.

[0116] FIG. 9 is a flowchart showing the processing of the terminal 20 according to the present embodiment.

[0117] In step S201, the control unit 22 determines whether or not it has received a sleep beacon including a sleep time length via the communication interface 21. The sleep beacon that the control unit 22 can receive may be the sleep beacon transmitted by the base station 10 in step S104 (see FIG. 4). If it is determined that a sleep beacon including a sleep time length has been received (Yes in step S201), the process proceeds to step S202; otherwise (No in step S201), step S201 is executed again. That is, the control unit 22 waits in step S201 until it is determined that a sleep beacon including a sleep time length has been received.

[0118] In step S202, the control unit 22 sets a timer for the sleep time length included in the sleep beacon received in step S201. Further, the control unit 22 transitions the communication interface 21 to the sleep state. When the time corresponding to the sleep time length has elapsed since the timer was set, a timer interrupt occurs in the processor. When the timer interrupt occurs, the control unit 22 executes the process of step S203.

[0119] In step S203, the control unit 22 releases the sleep state of the communication interface 21 and transitions it to the awake state in response to the occurrence of the timer interrupt. After the process of step S203 is completed, step S201 is executed again.

[0120] Note that the terminal 20 maintains the connection state with the base station 10 without interruption during the execution of the above series of processes. In particular, during the period from when the communication interface 21 transitions to the sleep state (step S202) until it transitions to the awake state (step S203) (also referred to as the sleep period), the beacon signal is not received from the base station 10, but even in this case, the connection state with the base station 10 is maintained without interruption. By doing so, after the communication interface 21 transitions to the awake state, the communication with the base station 10 can be established immediately without performing the connection process with the base station 10, and there is an effect that communication can be performed without delay when frame transmission is required.

[0121] FIG. 10 is an explanatory diagram showing the power consumption of the base station 10 and the terminal 20 according to the present embodiment.

[0122] In FIG. 10, the power consumption of the base station 10 according to the present embodiment is indicated by a solid line, and the power consumption of the base station according to the comparative example is indicated by a broken line. The comparative example is a base station and a terminal that do not transition to the sleep state.

[0123] The horizontal axis of the graph shown in FIG. 10 indicates the elapsed time, and the vertical axis indicates the power consumption at the time point of the elapsed time. The power consumption is shown in arbitrary units with the power consumption when the base station is not performing communication in the awake state being 1. The elapsed time on the horizontal axis is common to the elapsed time on the horizontal axis shown in FIG. 2. Note that since the power consumption of the terminal 20 is the same as that of the base station 10 shown in FIG. 10, the illustration is omitted.

[0124] Here, similar to FIG. 2, the case where the base station 10 transmits frames to the terminal 20 in the section of elapsed time from 20 seconds to 26 seconds and the section of elapsed time from 100 seconds to 103 seconds will be described as an example. Also, as an example, the first reference value is 99% of the limit value.

[0125] As shown in FIG. 10, in the time period from 0 seconds to 20 seconds of the elapsed time, since the communication interface 11 and the terminal 20 are not communicating, the power consumption is 1 respectively.

[0126] In the time period from 20 seconds to 26 seconds of the elapsed time, since the base station 10 was transmitting a frame to the terminal 20, the power consumption was greater than 1. Immediately before the point in time of 26 seconds of the elapsed time, that is, when the total transmission time within the duty window with the current point in time as the end period reached the first reference value, the base station 10 transmitted a sleep beacon to the terminal 20 and transitioned to the sleep state. The sleep time length is calculated as approximately 54 seconds from the point in time immediately before the point in time of 26 seconds of the elapsed time to the point in time of 80 seconds of the elapsed time. Also, the terminal 20 transitions to the sleep state when it receives the sleep beacon.

[0127] In the time period from 26 seconds to 80 seconds of the elapsed time, since the base station 10 and the terminal 20 are maintaining the sleep state, the power consumption is less than 1 respectively.

[0128] At the point in time of 80 seconds of the elapsed time, the communication interface 11 of the base station 10 transitions to the awake state. However, thereafter, in the time period from 80 seconds to 100 seconds of the elapsed time, since the base station 10 and the terminal 20 are not communicating, the power consumption is 1 respectively.

[0129] In the time period from 100 seconds to 103 seconds of the elapsed time, since the base station 10 and the terminal 20 were transmitting a frame, the power consumption was greater than 1 respectively.

[0130] In the time period from 103 seconds to 180 seconds of the elapsed time, since the base station 10 and the terminal 20 are not communicating, the power consumption is 1 respectively.

[0131] Since the base station and the terminal according to the comparative example do not transition to the sleep state, the power consumption of the base station and the terminal according to the comparative example is 1 respectively in the time period from 26 seconds to 80 seconds of the elapsed time, and is the same as that of the base station 10 and the terminal 20 according to the present embodiment in other time periods.

[0132] As described above, when comparing overall, the power consumption of the base station 10 and the terminal 20 according to the present embodiment is smaller than the power consumption of the base station and the terminal according to the comparative example, respectively. Further, the periods during which the base station 10 and the terminal 20 according to the present embodiment maintain the sleep state are the periods during which transmission is restricted due to bandwidth restriction even for the base station and the terminal according to the comparative example. Therefore, from the viewpoint of communication, the base station 10 and the terminal 20 according to the present embodiment are equivalent to the base station and the terminal according to the comparative example. In other words, there is no delay in communication. Nor is it the case that the communication delay of the base station 10 and the terminal 20 according to the present embodiment is greater than the communication delay of the base station and the terminal according to the comparative example.

[0133] Thus, when the base station 10 and the terminal 20 according to the present embodiment perform wireless communication in a wireless communication band in which a limit value of the total transmission time per unit time is defined, by maintaining the communication interfaces of the terminal 20 and the base station 10 in the sleep state at substantially the same timing, it is possible to suppress the occurrence of losses or delays in the communication between the base station 10 and the terminal 20. Further, the base station 10 and the terminal 20 contribute to reducing the power consumption of the entire communication system 1 by maintaining the communication interfaces in the sleep state. In other words, the power consumption can be reduced more significantly than when maintaining the communication interface of either the base station 10 or the terminal 20 in the sleep state. Thus, the base station 10 contributes to reducing the power consumption of the entire communication system 1.

[0134] (Embodiment 2) In the present embodiment, a base station, a terminal, etc. that contribute to reducing the power consumption of the entire communication system will be described. In the present embodiment, a base station, a terminal, etc. that contribute to reducing the power consumption of the entire communication system in a communication system that performs communication at predetermined time intervals will be described.

[0135] The configuration of the communication system of the present embodiment is the same as the configuration of the communication system 1 of Embodiment 1 (see FIG. 1).

[0136] In this embodiment, a case where the terminal 20 transmits information to the base station 10 at predetermined time intervals will be described as an example. In this case, the base station 10 can identify the time point (also referred to as the communication time point) when the communication interface 11 will perform wireless communication in the future.

[0137] For example, when the terminal 20 is equipped with a temperature sensor, and the terminal 20 periodically measures the temperature with the temperature sensor and transmits temperature information indicating the measured temperature to the base station 10, the communication system 1 can be used. Note that, as in the first embodiment, there may be a plurality of terminals 20. The predetermined time interval is, for example, 5 minutes. The time point when the base station 10 transmits information is the communication time point when the communication interface 11 will perform wireless communication in the future, and can be specified as the time point that arrives every 5 minutes from the reference time point shared in advance between the base station 10 and the terminal 20.

[0138] In this case, the control unit 12 of the base station 10 identifies the next time point (corresponding to the communication time point) when the base station 10 and the terminal 20 communicate, calculates the time length from the current time point to the communication time point as the sleep time length, and controls to maintain the communication interface 11 in the sleep state during the sleep time length. Further, in the above case, the control unit 12 can control the generation unit 13 to generate a sleep beacon and transmit it to the terminal 20.

[0139] For example, when the above communication time point is identified, the generation unit 13 generates a sleep beacon and transmits it to the terminal 20. The generation unit 13 can generate and transmit the above sleep beacon under the control of the control unit 12.

[0140] FIG. 11 is an explanatory diagram showing the communication volume of the base station 10 and the terminal 20 according to this embodiment.

[0141] The horizontal axis of the graph shown in FIG. 11 indicates the elapsed time, and the vertical axis indicates the communication volume at the time point of the elapsed time. The communication volume indicates, in arbitrary units, the communication volume related to the communication of information from the terminal 20 to the base station 10. Here, the time interval at which the terminal 20 transmits information is set to 5 minutes.

[0142] In FIG. 11, the time point at which the base station 10 and the terminal 20 should perform the first communication is set as 0 minutes. In this case, the time point at which the second communication should be performed is 5 minutes, and the time point at which the third communication should be performed is 10 minutes. Thereafter, the time points at which communication should be performed come at 5-minute intervals.

[0143] After the base station 10 and the terminal 20 perform one communication, they do not perform communication until the time point at which the next communication should be performed. When the base station 10 performs one communication, it generates a sleep beacon with the time until the next communication should be performed as the sleep time length and transmits it to the terminal 20, and maintains the communication interface 11 of the base station 10 in a sleep state for the sleep time length. When the terminal 20 receives the transmitted sleep beacon, it maintains the communication interface 21 of the terminal 20 in a sleep state for the sleep time length. Thereby, the communication system 1 contributes to reducing power consumption.

[0144] FIG. 12 is a flowchart showing the processing of the base station 10 according to the present embodiment.

[0145] In step S301, the control unit 12 initializes the terminal list. The terminal list is a list in which the terminal 20 that has transmitted temperature information to the base station 10 is recorded. Initializing the terminal list means setting the terminal list to a state where temperature information has not been transmitted from any terminal 20.

[0146] In step S302, when the control unit 12 receives temperature information from the terminal 20, it updates the terminal list. The control unit 12 updates the terminal list by adding the terminal 20 that has transmitted the received temperature information to the terminal list.

[0147] In step S303, the control unit 12 determines whether it has received temperature information from all the terminals 20. When all the terminals 20 are recorded in the terminal list, the control unit 12 can determine that it has received temperature information from all the terminals 20. If it is determined that temperature information has been received from all the terminals 20 (Yes in step S303), the process proceeds to step S304; otherwise (No in step S303), step S302 is executed again.

[0148] In step S304, the control unit 12 calculates the sleep time length. First, the control unit 12 identifies the communication time point that first arrives after the current time point among the communication time points that arrive every five minutes from the reference time point. Further, the control unit 12 calculates the time at the identified communication time point from the current time point as the sleep time length.

[0149] In step S305, the generation unit 13 generates a sleep beacon including the sleep time length calculated in step S304. Further, the generation unit 13 transmits the generated sleep beacon to the terminal 20 through the communication interface 11. The process of step S305 is the same as step S104 (see FIG. 4) of Embodiment 1.

[0150] In step S306, the control unit 12 sets a timer for the sleep time length calculated in step S304. Further, the control unit 12 transitions the communication interface 11 to the sleep state. When the time corresponding to the sleep time length has elapsed since the timer was set, a timer interrupt occurs in the processor. When the timer interrupt occurs, the control unit 12 executes the process of step S307.

[0151] In step S307, the control unit 12 releases the sleep state of the communication interface 11 and transitions it to the awake state in response to the occurrence of the timer interrupt.

[0152] FIG. 13 is an explanatory diagram showing the power consumption of the base station 10 and the terminal 20 according to the present embodiment.

[0153] In FIG. 13, the power consumption of the base station 10 according to the present embodiment is shown by a solid line, and the power consumption of the base station according to the comparative example is shown by a broken line. The comparative example is a base station and a terminal that do not transition to the sleep state.

[0154] The horizontal axis of the graph shown in FIG. 13 represents the elapsed time, and the vertical axis represents the power consumption at the time of the elapsed time. The power consumption is shown in arbitrary units with the power consumption when the base station is not performing communication in the awake state being 1. The elapsed time on the horizontal axis is common to the elapsed time on the horizontal axis shown in FIG. 11. Note that since the power consumption of the terminal 20 is the same as that of the base station 10 shown in FIG. 13, illustration thereof is omitted.

[0155] Here, similar to FIG. 11, the case where the terminal 20 transmits a frame to the base station 10 at the time when the elapsed time is 0 minutes, 5 minutes, and 10 minutes will be described as an example.

[0156] As shown in FIG. 13, at the time when the elapsed time is 0 minutes, since the terminal 20 was transmitting a frame to the base station 10, the power consumption is greater than 1. From the time when the above communication ended until the time when the elapsed time is 5 minutes, since the base station 10 and the terminal 20 maintain the sleep state, the power consumption of each is less than 1.

[0157] At the time when the elapsed time is 5 minutes and 10 minutes, similar to the above, since the terminal 20 was transmitting a frame to the base station 10, the power consumption is greater than 1. From the time when the above communication ended until the next communication should be performed, since the base station 10 and the terminal 20 maintain the sleep state, the power consumption of each is less than 1.

[0158] Since the base station and the terminal according to the comparative example do not transition to the sleep state, the power consumptions of the base station and the terminal according to the comparative example are each 1 between the end of communication at the time of elapsed time 0 minutes and the time of elapsed time 5 minutes, between the end of communication at the time of elapsed time 5 minutes and the time of elapsed time 10 minutes, and between the end of communication at the time of elapsed time 10 minutes and the time when the next communication should be performed, and are the same as those of the base station 10 and the terminal 20 according to the present embodiment in other sections.

[0159] From the above, when comparing as a whole, the power consumptions of the base station 10 and the terminal 20 according to the present embodiment are each smaller than the power consumptions of the base station and the terminal according to the comparative example. Also, the periods during which the base station 10 and the terminal 20 according to the present embodiment maintain the sleep state are the periods during which transmission is restricted due to bandwidth restriction even for the base station and the terminal according to the comparative example. Therefore, from the viewpoint of communication, the base station 10 and the terminal 20 according to the present embodiment are equivalent to the base station and the terminal according to the comparative example. In other words, there is no delay in communication. It is also not the case that the communication delay of the base station 10 and the terminal 20 according to the present embodiment is greater than the communication delay of the base station and the terminal according to the comparative example. Furthermore, if the connection state between the base station 10 and the terminal 20 is maintained even during the sleep state in the present embodiment, there is also no problem of communication delay due to reconnection processing when returning to the awake state.

[0160] As described above, when the base station 10 and the terminal 20 according to the present embodiment perform communication at predetermined time intervals, by maintaining the communication interfaces of the terminal 20 and the base station 10 in the sleep state at substantially the same timing, it is possible to suppress the occurrence of losses or delays in the communication between the base station 10 and the terminal 20. Also, the base station 10 and the terminal 20 contribute to reducing the power consumption of the entire communication system 1 by maintaining the communication interfaces in the sleep state. In other words, the power consumption can be reduced more significantly than when maintaining the communication interface of only one of the base station 10 or the terminal 20 in the sleep state. Thus, the base station 10 contributes to reducing the power consumption of the entire communication system 1.

[0161] Note that this embodiment is applicable to a system that communicates at predetermined time intervals. The transmission for transitioning to the sleep state does not necessarily have to be performed by the base station, and it may be transmitted from any terminal.

[0162] Note that the present invention can be realized not only as an apparatus, but also as a method having the processing means constituting the apparatus as steps, or as a program for causing a computer to execute those steps, or as a recording medium such as a computer-readable CD-ROM recording the program, or as information, data, or a signal indicating the program. And those programs, information, data, and signals may be distributed via a communication network such as the Internet.

[0163] As described above, the base station and the like of the present invention have been described based on the embodiments. However, the present invention is not limited to these embodiments. As long as the gist of the present invention is not deviated from, various modifications conceived by those skilled in the art applied to these embodiments, or forms constructed by combining the constituent elements in different embodiments are also included in the scope of the present invention.

Industrial Applicability

[0164] The present invention can be applied to a communication system, a base station, a terminal, and the like that perform wireless communication.

Explanation of Signs

[0165] 1 Communication system 10 Base station 11, 21 Communication interface 12, 22 Control unit 13 Generation unit 20 Terminal 31 Sleep beacon 33 Control information 34 Sleep time length

Claims

1. A base station that performs wireless communication with a terminal, a first communication interface for performing the wireless communication, a control unit that calculates a sleep time length which is the length of time for which the first communication interface maintains a sleep state, a generation unit that generates a beacon signal including the sleep time length calculated by the control unit, and transmits the generated beacon signal to the terminal through the first communication interface, thereby maintaining the second communication interface of the terminal that has received the beacon signal in a sleep state for the sleep time length, The control unit further performs control to maintain the first communication interface in a sleep state for the sleep time length when the generation unit transmits the beacon signal. Base station.

2. The first communication interface performs the wireless communication in a wireless communication band in which a limit value of the total transmission time per unit time is defined, when the total transmission time of the most recent unit time becomes equal to or more than a predetermined ratio with respect to the limit value due to the first communication interface performing the wireless communication, the control unit calculates the sleep time length and performs the control to maintain the first communication interface in the sleep state, when the control unit calculates the sleep time length, the generation unit generates the beacon signal and transmits it to the terminal. The base station according to Claim 1.

3. The sleep time length calculated by the control unit is a time length equal to or longer than the time length from a first time point to a second time point, the first time point is the time point when the beacon signal is transmitted, the second time point is a time point that has advanced in the direction in which time elapses from the first time point, and is the first time point at which the total transmission time of the unit time having the second time point as the end becomes smaller than a reference value. The base station according to Claim 2.

4. The control unit when the first communication interface is in an awake state, updates, for each time interval, history information including the transmission available time of the first communication interface for the time interval and information necessary for calculating the transmission available time of the time interval a predetermined time after the time interval, when the first communication interface is in a sleep state, restricts the update of the history information, when the first communication interface transitions from the sleep state to the awake state, collectively updates the history information during the period in which the first communication interface maintained the sleep state. The base station according to any one of claims 1 to 3.

5. The first communication interface can identify the communication time point for future wireless communication, the control unit identifies the communication time point, calculates the time length from the current time point to the communication time point as the sleep time length, and performs the control to maintain the first communication interface in the sleep state, when the control unit calculates the sleep time length, the generation unit generates the beacon signal and transmits it to the terminal The base station according to claim 1.

6. A terminal that performs wireless communication with a base station, a second communication interface for performing the wireless communication, and a control unit that, when receiving a beacon signal including a sleep time length, which is the time length for which the first communication interface provided in the base station maintains the sleep state, from the base station, performs control to maintain the second communication interface in the sleep state for the sleep time length Terminal.

7. When the second communication interface maintains the sleep state based on the control, the control unit maintains the connection state with the base station even when the beacon signal from the base station is not received for a predetermined time or more. The terminal according to claim 6.

8. The base station according to claim 1, and the terminal according to claim 6, which receives the beacon signal including the sleep time length transmitted by the base station by wireless communication Communication system.

9. A control method executed by a base station that performs wireless communication with a terminal, including the step of calculating a sleep time length, which is the time length for which the first communication interface for performing the wireless communication maintains the sleep state, generating a beacon signal including the calculated sleep time length, and transmitting the generated beacon signal to the terminal through the first communication interface, thereby maintaining the second communication interface of the terminal that has received the beacon signal in the sleep state for the sleep time length, and the step of performing control to maintain the first communication interface in the sleep state for the sleep time length when the beacon signal is transmitted Control method.

10. A control method executed by a terminal that performs wireless communication with a base station, including the step of receiving a beacon signal including a sleep time length by the communication interface for performing the wireless communication Controlling to maintain the communication interface in a sleep state during the sleep time period Control method. **Claim 11** A control method for a communication system including a base station and a terminal, wherein the base station executes the control method according to Claim 9, and the terminal executes the control method according to Claim 10 Control method. **Claim 12** A program for causing a computer to execute the control method according to Claim 9.

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