JP2013038542A - Base station device and sleep control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base station device and sleep control method for improving power saving effect.SOLUTION: A base station device comprises: a transmission buffer for storing transmission packets addressed to a terminal station; transmission means for transmitting the transmission packets stored in the transmission buffer; reception means for receiving the packets transmitted from the terminal station; recording means for recording a communication history showing transmission/reception of the transmission packets to/from the terminal station; first sleep control means for making the base station device be in a sleep state over a predetermined period; second sleep control means for repeatedly making the base station device be in an awake state and, when receiving no packets from the terminal station, be in a sleep state over a period shorter than that of the first sleep control means; and control means for selecting the first sleep control means when no transmission packets are in the transmission buffer and no communication history in a predetermined period is in the recording means, and selecting the second sleep control means, otherwise.

Description

  The present invention relates to a base station apparatus and a sleep control method for reducing power consumption in a base station constituting a radio access system.

  With the spread of the Internet in recent years, the use of the Internet in mobile environments centering on smartphones is increasing in addition to wired lines such as optical lines and ADSL. In the mobile environment, a third-generation mobile phone (3G) or a line such as LTE (Long Term Evolution) positioned as the next-generation mobile phone is used. These systems use a microwave band that is relatively easy to use among various frequency bands used for wireless access. By utilizing the characteristics of this frequency band, a single base station has a wide range. It is possible to make an area into a service area collectively.

  However, such a convenient microwave band is expected to be used in other systems, and has already faced the problem of depletion of frequency resources. In particular, as communication traffic increases rapidly due to an increase in broadband applications including moving pictures and the spread of smartphones, LTE and the like require a wider frequency band allocation. On the other hand, a plurality of businesses share the entire bandwidth, and the bandwidth allocated to one business is very limited at present.

  In order to solve this problem, a wireless system that bypasses these 3G and LTE lines is required. The most realistic system is WiFi using the 2.4 GHz band and the 5 GHz band. With WiFi compliant with the IEEE 802.11 standard (including all standards such as 802.11a, b, g, n, etc.), by using an access technology called CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance), Wireless access can be used efficiently and stably even in the presence of radio stations that are unplanned and turbulent using the same frequency channel. Furthermore, such systems as home networks in homes, portable game machines, notebook PCs, mobile phones, etc., have become explosively widespread. Already, base station devices (AP: also called access points) and The price of both terminal devices is very low.

  The CSMA / CA technology in WiFi can be operated without failure even if the station station design of the base station is not particularly conscious. In particular, by reducing the transmission power to make a microcell with a small service area radius, a predetermined throughput can be realized for each microcell, resulting in an increase in transmission capacity per unit area. In this way, it is possible to efficiently accommodate traffic overflowing from lines such as 3G and LTE via the WiFi network.

  However, if a detour from a 3G line with a wide communication area is assumed, at least a large number of base stations will be installed to cover a large area such as densely populated urban areas and residential areas. There is a need. Originally, WiFi is a wireless standard designed for indoor use, so it is difficult to cover a wide area with a single base station, and in order to increase the transmission capacity of the entire system, micro-cells can be used. As a result, the number of base stations that need to be installed becomes enormous. Thereby, even if the power consumption of the base station is not so large, the power consumption of the entire system becomes enormous, and it is necessary to reduce the load on the environment from the viewpoint of environmental problems.

  Use of renewable energy is expected to solve these problems. Solar power generation is expected to be the most powerful method because the amount of power that can be generated is relatively larger than other power generation technologies.

  Furthermore, if the base station can operate stably only by power supply using renewable energy, the connection between the base station and the commercial power supply becomes unnecessary, and the placement flexibility can be improved. If placement freedom increases, it can be used as a countermeasure against disasters such as earthquakes. For example, a communication network or a power network may be damaged in an area affected by a disaster, and restoration of the communication network or the power network may take several days to about one month. By introducing a base station device that is powered by a solar cell at that time, it is possible to provide a communication service as an alternative to the conventional communication system.

  As described above, power consumption reduction of various electronic devices has been widely promoted as a social approach in consideration of the environment. However, assuming the above-described base station device powered by solar cells, Power saving is an important issue. In the following, we introduce the power saving technology for base station equipment in the prior art.

  For example, the sleep control technology for base stations described in Non-Patent Document 1 is one of them. Usually, since the base station apparatus is connected to a commercial power source, it is not necessary to sleep, but in order to reduce power consumption or in a special base station equipped with a battery, the base station apparatus side also has a predetermined Power consumption is reduced by stopping one's own circuit in a cycle and entering a sleep state. However, if the terminal station itself is in the sleep state, the terminal station under its control (in some cases, the terminal that was turned off at the start of sleep of the base station will be turned on during the sleep operation of the base station. There is also a need to provide a mechanism that prohibits access via wireless links (including terminal stations with such possibilities).

FIG. 16 shows an outline of sleep control of a base station in the prior art.
In FIG. 16, 201 and 202 are beacon signals, 203 and 204 are sleep control packets, and indicate the states of the base station and the terminal station, respectively. For convenience of explanation, timings A, B,..., G are shown in the figure.

  In WiFi, the base station transmits beacon signals 201 and 202, which are broadcast control information, in a predetermined cycle. In the sleep control of the terminal station, the terminal station returns to the normal operation (sleep release) based on the cycle of the beacon signal, but the terminal station does not receive all the beacon signals. The beacon signals 201 and 202 contain information including a DTIM (Delivery Traffic Indication MAP) count, a DTIM period, and the like, and only a beacon having a DTIM count value of zero is received. Therefore, the base station sets this DTIM cycle to 1, sets the DTIM count values of all the beacon signals 201 and 202 to 0, and sleep control packets 203 and 204 for the base station to perform the sleep operation therein. Send. That is, in order to configure a timing at which all terminal stations can receive a packet transmitted from the base station, the DTIM counter value and the DTIM period of the beacon signal are set to the above values, and the sleep control packet is transmitted at the timing.

  In general, a wireless packet used in WiFi includes NAV (Network Allocation) in order to secure a bandwidth for a predetermined time in a certain wireless link (a combination of one base station and one terminal station that perform wireless communication with each other). A time called Vector) is set, and transmission of wireless terminals other than the link is prohibited. In the sleep control packets 203 and 204, this NAV is set to block the terminal from transmitting a signal, and during that time, its own power is turned off to reduce power consumption.

  For example, the NAV set by the sleep control packet 203 is the time C to D, and the interval during which no signal is transmitted, the time C to D, is the sleep time of the base station. Since the maximum NAV time that can be set by one sleep control packet 203, 204 is limited, the sleep control packet 204 is transmitted after the sleep control packet 203 in order to perform further sleep. Thus, it is possible to sleep from time E to time F, and this situation is shown as the state of the base station. Incidentally, as for the state of the terminal station, the terminal station recognizes the time C to E and the time E to F as NAV, and does not transmit a radio packet at this time. The sleep control packets 203 and 204 may be anything as long as the NAV can be set. Typically, a CTS (Clear to Send) packet is used, but a packet such as broadcast or multicast may be used. Depending on the setting at this time, the terminal station can also shift to sleep.

  Note that the number of transmissions of the sleep control packet is determined by the total sleep period set in advance in the base station. If the total sleep period is large, the number of times the sleep control packet is transmitted also increases.

  Similar sleep control can be realized using other control messages. For example, a field called “Quiet” is set in a beacon signal that is one of control signals in WiFi, and a wireless access prohibition period can be set in a beacon period using this field.

FIG. 17 shows an outline of an example of sleep control using a Quiet field.
In FIG. 17, 201 and 202 are beacon signals, which indicate the states of the base station and the terminal station, respectively. For convenience of explanation, timings A, B, and C are shown in the figure.

  In WiFi, available frequency bands include a band that is common to frequency bands used by various radars. In such a band, for example, it is necessary to periodically detect whether a base station has a station that transmits a radar wave around it. This is a control called DFS (Dynamic Frequency Selection), but radio access from the subordinate terminal stations must be prohibited during the radar wave detection operation. Therefore, a radar wave is detected using a predetermined period of time during which transmission from the terminal is prohibited (times A to B in the figure). Using this, the base station enters a sleep state at times A to B and enters an awake state at times B to C. In general terminal stations, since the operation during the transmission prohibition period is not defined, whether or not the time A to B can be sleep depends on the terminal, but there is a possibility that at least significant data may be transmitted and received during this time. Therefore, an operation similar to sleep is possible.

Ogawa et al., “Performance Evaluation of Power Saving Mode in Wireless LAN Access Points”, IEICE Technical Report MoMuC2009-13

  In the sleep control technology described in Non-Patent Document 1, if there is data in the buffer of the base station at the time of beacon transmission or if there is a history of traffic transmission / reception with the terminal station within a certain time, Thus, the base station is controlled so as not to enter the sleep mode. This is because there is a high possibility that traffic transmission / reception occurs within the beacon interval, so that the base station is prevented from shifting to the sleep mode in order not to deteriorate the communication quality such as the delay of the data.

  Here, whether or not the base station shifts to the sleep mode is determined only at the time of beacon transmission. Therefore, the base station maintains an unnecessary awake state even when there is no traffic to be transmitted / received after the base station completes transmission / reception of the data accumulated in the buffer within the beacon interval. In other words, this prior art is a means that can enter the sleep mode only when there is no terminal station connected to the base station or when no traffic is generated even if there is a terminal station. In such a case, since the base station cannot shift to the sleep mode, a large power saving effect cannot be expected.

  To solve this problem, the base station reduces unnecessary awake states, and determines whether to shift to the sleep mode in a short cycle as a means for shifting the base station to the sleep mode even when there is more than a certain amount of traffic. Means are conceivable. For example, it is a method of setting a short beacon period and determining the transition to the sleep mode at the beacon transmission timing. Since it is possible to determine sleep transition in a short cycle, the time for maintaining an unnecessary awake state after completing transmission of accumulated traffic is shortened. Thus, by shortening the beacon period, the base station can shift to the sleep mode even when there is constant traffic.

  However, the following three problems can be considered in shortening the beacon period. First, since the beacon transmission frequency increases, the power consumption required for beacon transmission increases. Second, since the base station frequently recovers during the awake period, the total time during which the base station shifts to the sleep mode is shortened. Thirdly, many base station apparatuses that stop power supply during sleep take a long time to restart once the circuit is stopped. For example, a clock supplied to a baseband signal processing circuit, a local oscillator for frequency conversion between a radio frequency and a baseband, and the like take a relatively long time to stabilize to a desired frequency error after power-on. Such a circuit that takes a long time to function stably cannot stop power supply in the sleep mode for a short time, and cannot efficiently reduce power consumption in the sleep mode.

  In the present invention, when the base station has a means for shifting to the sleep mode for a long time in order to improve the power saving effect by the sleep control technology, even if there is traffic, the base station is not allowed to shift to the sleep mode. An object of the present invention is to provide a base station apparatus and a sleep control method that can reduce the necessary awake state and improve the power saving effect.

  In a base station apparatus that performs wireless communication with a terminal station, a first invention includes a transmission buffer that accumulates transmission packets addressed to the terminal station, a transmission unit that transmits transmission packets accumulated in the transmission buffer, and a terminal station Receiving means for receiving packets transmitted from the terminal, recording means for recording a communication history indicating transmission / reception of transmission packets with the terminal station, first sleep control means for entering a sleep state over a predetermined period, A second sleep control unit that repeats the awake state and a sleep state in a shorter period of time than the first sleep control unit when a packet is not received from the terminal station; Control means for selecting the first sleep control means when there is no communication history for the period, and for selecting the second sleep control means in other cases. .

  In the base station apparatus of the first invention, the second sleep control means is a period in which the terminal station waits to transmit a packet when there is no transmission packet in the transmission buffer and the terminal station does not receive the packet. When it is detected that the terminal station has continued beyond, transmission of the terminal station is prohibited and the base station is set in the sleep state.

  In the base station apparatus according to the first aspect of the invention, the number of components of the base station apparatus that the first sleep control unit puts to sleep is the number of components of the base station apparatus that the second sleep control means puts to sleep. More than that.

  In the base station apparatus of the first invention, when the base station is driven by power from a battery that stores the generated power of the power generation means, the remaining amount of power stored in the battery and the amount of power generated by the power generation means stabilize the base station. A stable operation condition determining means for determining whether or not the operation condition is sufficient for the operation of the first sleep control means, and shorter than the sleep state period of the first sleep control means and shorter than the sleep state period of the second sleep control means A third sleep control unit that repeats the awake state and a sleep state in a period equivalent to the sleep state of the second sleep control unit when a packet is not received from the terminal station after entering the sleep state for a long period; And the control means includes first sleep control means when there is no transmission packet in the transmission buffer and there is no communication history for a predetermined period in the recording means. Selected, otherwise if safe operational conditions of selecting the second sleep control means when sufficient, safe operating conditions to select the third sleep control means when not enough.

  In the base station apparatus of the first invention, the second sleep control unit and the third sleep control unit transmit a packet when the terminal station does not receive a packet from the terminal station when there is no transmission packet in the transmission buffer. When it is detected that the terminal has continued beyond the waiting period, transmission of the terminal station is prohibited and the base station is set in the sleep state.

  In the base station apparatus of the first invention, the repetition of the awake state and the sleep state shifts from the awake state to the sleep state without notifying the terminal station of the radio access prohibition period, and enters the awake state after the sleep state ends. This is a process for carrying out carrier sense and shifting to the sleep state again when the radio channel is not busy, and maintaining the awake state when the radio channel is busy and receiving the packet transmitted by the terminal station. The state time is set to a short time during which it is possible to determine whether or not the radio channel is busy by carrier sense, and the sleep time is set from the terminal station in the awake state after the radio channel is busy by carrier sense. Is set to a time when the re-sending packet can be received.

  According to a second aspect of the present invention, in the sleep control method for a base station that performs wireless communication with a terminal station, the base station transmits a transmission buffer that stores transmission packets addressed to the terminal station, and a transmission packet stored in the transmission buffer. Transmitting means, receiving means for receiving packets transmitted from the terminal station, recording means for recording a communication history indicating transmission / reception of transmission packets with the terminal station, and a sleep state over a predetermined period A first sleep control unit; an awake state; and a second sleep control unit that repeats a sleep state in a shorter period than the first sleep control unit when a packet is not received from the terminal station, and transmits to the transmission buffer The first sleep control means is selected when there is no packet and the recording means does not have a communication history for a predetermined period. Otherwise, the second sleep control is selected. To select the stage.

  In the sleep control method according to the second aspect of the present invention, when the base station is driven by power from the battery that stores the generated power of the power generation means, the remaining power of the battery and the power generation amount of the power generation means are A stable operation condition determining means for determining whether or not the station is sufficient for stable operation; a sleep state of the second sleep control means that is shorter than a sleep state period of the first sleep control means; After the sleep state has been set for a period longer than the period, the awake state, and when no packet is received from the terminal station, the sleep state is repeated in a period equivalent to the sleep state of the second sleep control means. A first sleep control when there is no transmission packet in the transmission buffer and there is no communication history for a predetermined period in the recording means. Select stage, otherwise if safe operational conditions of selecting the second sleep control means when sufficient, safe operating conditions to select the third sleep control means when not enough.

  According to the present invention, two sleep controls can be switched according to the traffic state between the base station and the terminal station, and further, three sleep controls can be switched according to the traffic state and the remaining battery charge level.

  The first sleep control means is a control method applied when there is no terminal station connected to the base station or when there is a terminal station connected to the base station but no traffic is generated. Since the mode can be shifted to the continuous sleep mode, the power saving effect can be enhanced.

  The second sleep control means is a control method applied when there is a terminal station connected to the base station and traffic has occurred recently, and traffic generation is expected in the beacon interval. In addition, since the base station can intermittently shift to the sleep mode while receiving packets from the terminal station, the power saving effect can be enhanced.

  The third sleep control means is a control in which the base station shifts to a long-time sleep mode when the remaining battery charge or power generation amount does not satisfy a predetermined stable operation condition even when traffic is expected between beacons. It is a method, and sleep operation can be performed with priority given to the power saving of the base station.

It is a time chart which shows the outline | summary of the sleep control of the base station in Example 1 of this invention. It is a figure which shows the structural example of the base station apparatus in Example 1 of this invention. It is a figure which shows the example of a sleep profile. It is a flowchart which shows the sleep control processing procedure in Example 1 of this invention. It is a flowchart which shows the process sequence of the sleep control 1 in Example 1 of this invention. It is a flowchart which shows the process sequence of the sleep control 2 in Example 1 of this invention. It is a time chart which shows the outline | summary of the sleep control of the base station in Example 2 of this invention. It is a figure which shows the structural example of the base station apparatus in Example 2 of this invention. It is a flowchart which shows the sleep control processing procedure in Example 2 of this invention. It is a flowchart which shows the process sequence of the sleep control 3 in Example 2 of this invention. It is a time chart which shows the outline | summary of the sleep control of the base station in Example 3 of this invention. It is a time chart which shows the outline | summary of the sleep control of the base station in Example 4 of this invention. It is a time chart which shows the outline | summary of the sleep control of the base station in Example 5 of this invention. It is a flowchart which shows the process sequence of the sleep control 6 in Example 5 of this invention. It is a time chart which shows the outline | summary of the sleep control of the base station in Example 6 of this invention. It is a time chart which shows the sleep control example (NAV utilization) of the base station in a prior art. It is a time chart which shows the sleep control example (Quiet IE utilization) of the base station in a prior art.

FIG. 1 shows an outline of sleep control of a base station in Embodiment 1 of the present invention.
In the first embodiment, the two sleep control methods are selectively used according to the traffic state, thereby improving the power saving effect. First, each sleep control method will be described.

  The sleep control 1 is a control method applied when there is no terminal station connected to the base station or when there is a terminal station connected to the base station but no traffic is generated. It is possible to enter a continuous sleep mode.

  As a specific means for performing the sleep control 1, for example, the base station notifies the terminal station of the wireless access prohibition period by the quiet duration of the quiet field of the beacon, and the base station shifts to the sleep mode during that period. In the standard specification, 18 bits are assigned to Quiet Duration, which is expressed in TU (Time Unit: 1024 μs). A sleep time of up to 33.55 s can be set, and since the mode can be shifted to the sleep mode continuously for a long time, a great power saving effect can be expected. Also, it is possible to notify a long-time wireless access prohibition period by other methods. For example, a method using PCF (Point Coordination Function: access control by centralized control based on polling) is also conceivable. The time zone controlled by the PCF is called CFP (Contention Free Period), and only the terminal station designated by polling of the base station is allowed to transmit traffic during this period. That is, for a terminal station not designated by the base station, this period is a radio access prohibition period. This CFP parameter can be set as an information element in the beacon.

  In the long sleep mode, if transmission traffic is generated in the terminal station, a large delay may occur. However, this sleep control 1 is a sleep mode that is applied when there is no terminal station connected to the base station, or there is a connected terminal station but no traffic occurs. Even if the delay is large, it is considered that the influence on the communication quality experienced by the user is small.

  The sleep control 2 is a control method applied when there is a terminal station connected to the base station and traffic has been generated most recently and traffic is expected to be generated in the beacon interval. In this case, considering the influence on the communication quality, it does not shift to the long continuous sleep mode like the sleep control 1. However, when the communication between the base station and the terminal station is completed, when there is no transmission packet in the buffer of the base station and the terminal station does not transmit the packet, the base station is in a short sleep mode even between beacons. It is controlled so that it can be transferred at any time.

  Specific means for performing the sleep control 2 can be realized by a technique in which the base station shifts to the sleep mode after transmitting a sleep control packet such as CTS and notifying the terminal station of the NAV, for example. In addition, although 16 bits are allocated in the duration of CTS, since it is expressed in units of 1 μs, the maximum NAV period is 32.77 ms.

FIG. 2 shows a configuration example of the base station apparatus according to the first embodiment of the present invention.
In FIG. 2, the base station apparatus 1 includes an antenna 2, a transmission / reception unit 3, a communication control unit 4, a buffer unit 5, an interface unit 6, a communication history storage unit 7, a terminal information storage unit 8, a sleep profile storage unit 9, a first The sleep control unit 10 and the second sleep control unit 11 are configured.

  The base station apparatus 1 receives a signal via a radio line by an antenna 2 and performs filtering of an out-of-band signal by a transmission / reception unit 3, signal amplification by a low noise amplifier, frequency conversion from an RF frequency to a baseband, and an analog signal Processing such as A / D conversion to a digital signal is performed. Further, the digitized baseband signal is subjected to a series of signal processing such as timing detection, termination of header information related to the physical layer, demodulation processing, and error correction. A signal subjected to demodulation processing or the like output from the transmission / reception unit 2 is input to the communication control unit 4. If the received signal is a data packet, the data packet is output to the interface unit 6 via the buffer unit 5. The interface unit 6 is an interface for inputting / outputting data packets between the base station apparatus and the outside. On the other hand, when a packet is output from the interface unit 6, the data packet is stored in the buffer unit 5. When this data packet is transmitted under the control of the communication control unit 4, the communication control unit 4 outputs the wireless packet to the transmission / reception unit 3, and performs various modulation processes in the transmission / reception unit 3 to generate a baseband signal. The digital signal is converted from an analog signal to D / A conversion, frequency conversion, out-of-band signal filtering, signal amplification, and the like, and transmitted from the antenna 2.

  The first sleep control unit 10 shifts the base station to the sleep mode by the sleep control 1 in FIG. 1, and the second sleep control unit 11 shifts the base station to the sleep mode by the sleep control 2 in FIG. The communication control unit 4 refers to information in the communication history storage unit 7, the terminal information storage unit 8, and the buffer unit 5 to determine which sleep control method the base station adopts. Packets to be transmitted by the base station are stored in the buffer unit 5, and the communication control unit 4 can determine whether there is a transmission packet by inquiring the buffer unit 5. The communication history storage unit 7 stores a past communication history, and the communication control unit 4 can determine whether or not a packet has been transmitted / received within a predetermined time with reference to the communication history. The terminal information storage unit 8 stores information on terminal stations connected to (associated with) the base station, and the communication control unit 4 refers to the information to determine whether there is a connected terminal station. You can get it.

  In the sleep profile storage unit 9, information of a base station circuit that stops power supply when the base station shifts to a sleep mode according to each sleep control method is shown as a sleep profile. An example of the sleep profile is shown in FIG. When the base station shifts to the sleep mode by the sleep control 1, the first sleep control unit 10 refers to the sleep profile storage unit 9 to determine a circuit that stops power supply during the sleep control 1. Similarly, when the base station shifts to the sleep mode by the sleep control 2, the second sleep control unit 11 refers to the sleep profile storage unit 9 to determine a circuit that stops power supply during the sleep control 2.

  In sleep control 1, power supply to many circuits (other than CLK) of the base station is stopped, and power consumption during sleep is set to be small. The power supply is also stopped for circuits that require time until the circuit function is stabilized after the power supply, but the sleep time in the sleep control 1 can be set to a larger value than the above-mentioned stable time. The impact on the On the other hand, in the sleep control 2, considering the influence on the communication quality, the sleep mode is shifted to the sleep mode in a shorter time than the sleep control 1. The maximum sleep time is about 32 ms. Therefore, in the sleep control 2, it is impossible to stop the power supply of the frequency synchronization circuit or the like that takes a long time until the circuit function is stabilized after the power is supplied. Therefore, the sleep control 2 is limited to the MAC unit and the RF power amplifier that operate stably at an early stage. Stop the power supply. Note that, in the sleep control 2, since there are fewer circuits that stop power supply than in the sleep control 1, power consumption in the sleep mode is larger than that in the sleep control 1. Note that the sleep profile shown in FIG. 3 is merely an example, and other profiles may be selected in consideration of the stabilization time from the start of power supply to each circuit and the sleep time.

  In addition, the communication history storage unit 7, the terminal information storage unit 8, the sleep profile storage unit 9, the first sleep control unit 10, and the second sleep control unit 11 have been described separately from the communication control unit 4. Can be regarded as one entire control unit.

FIG. 4 shows a sleep control processing procedure in Embodiment 1 of the present invention.
In FIG. 4, the sleep control processing procedure of the communication control unit 4 is performed every beacon interval. The communication control unit 4 starts determining whether to perform sleep control 1 or sleep control 2 in the next beacon interval for each beacon interval (S101). That is, it is determined whether there is no transmission packet in the base station buffer at the time of beacon transmission and whether there is no communication history between the base station and the terminal station within a predetermined period (S102). The predetermined period may be set to the awake period of the terminal in the beacon interval, or may be set to another time. That is, the predetermined period here is a time set for the purpose of determining the presence / absence of a terminal station connected to the base station and the presence / absence of communication traffic when there is a connected terminal station. It can be anything.

  When there is no transmission packet in the buffer and there is no communication history within a predetermined period (Yes in S102), the operation of sleep control 1 is performed (S103). When there is a transmission packet in the buffer, or when there is a communication history within a predetermined period (No in S102), the operation of sleep control 2 is performed (S104). The operation of the sleep control 1 or sleep control 2 continues until the beacon interval ends (S105), and repeats S102 to S105 again at the time of beacon transmission.

FIG. 5 shows a processing procedure of the sleep control 1 according to the first embodiment of the present invention.
In FIG. 5, when sleep control 1 is started (S201), a sleep period length is set (S202), and a beacon in which the sleep period length is set as a wireless access prohibition period is transmitted (S203). Along with the transmission of the beacon, the base station shifts to the sleep mode during the sleep period (S204). When the sleep period elapses, the base station shifts to the awake mode (S205). When the beacon interval ends (S206), the operation of the sleep control 1 ends (S207).

  In the sleep control 1, it is possible to set most of the beacon intervals to the sleep period. For example, when transmission traffic is generated in a terminal station in a certain beacon interval, an awake period of 2 to 3 ms is set so that the terminal station can transmit the traffic in the beacon interval, and all other times are set as sleep periods. Can be assigned. In this case, the delay of transmission traffic of the terminal station may be a problem, but the sleep control 1 is a sleep mode when there is no terminal station connected to the base station or there is no communication history even if there is a terminal station. Since this is a mode, the traffic transmitted during the awake period of sleep control 1 is traffic for initial connection. Therefore, even if a large delay occurs in this traffic, it is considered that there is little adverse effect on the user experience quality.

FIG. 6 shows a processing procedure of sleep control 2 in Embodiment 1 of the present invention.
In FIG. 6, when sleep control 2 is started (S301), a beacon that does not set a wireless access prohibition period is transmitted (S302). Subsequently, it is determined whether there is a transmission packet in the buffer of the base station (S303). If there is a transmission packet in the buffer (Yes in S303), carrier sense is performed (S304). If the wireless channel is not used for a predetermined time (Yes in S305), a downlink packet is transmitted (S306). . If the radio channel is in use (No in S305), an uplink packet transmitted using the radio channel is received (S307), and the presence / absence of a transmission packet in the buffer of the base station is determined again (S307). S303). The operation of S304 to S307 here is the same as the operation of a general wireless LAN, and the time for determining the channel usage status by carrier sense (predetermined time in S305) is the sum of the DIFS time and the backoff time ( (Indicated as DIFS and CW in FIG. 1). The backoff time is determined by a value randomly selected from the contention window range, and is set to a time obtained by multiplying the value by the slot time.

  On the other hand, if there is no transmission packet in the buffer of the base station (No in S303), carrier sense is performed (S308), and if the wireless channel is not used for a predetermined time (Yes in S309), the mode shifts to the sleep mode. To transmit the CTS, the terminal station is notified of the NAV by the duration of the CTS (S310). At the same time, the base station shifts to the sleep mode (S311), and shifts to the awake mode after the lapse of Duration (S312). This case assumes that there is no transmission packet in the base station buffer at the time of beacon transmission, but there is a communication history between the base station and the terminal station within a predetermined period, and the terminal station does not transmit a packet at this time This corresponds to the operation when the base station enters sleep based on the sleep control 2.

  If the wireless channel is in use (No in S309), the wireless packet transmitted using the wireless channel is received (S313), and the presence / absence of the transmission packet in the buffer of the base station is determined again (S313). S303).

  The operations of S303 to S313 are repeated until the end of the beacon interval (S314), and the process of the sleep control 2 is ended together with the beacon interval (S315). Note that since the maximum NAV that can be set in CTS is 32.77 ms, the sleep period in the sleep control 2 is shorter than that in the sleep control 1.

  Here, when the terminal station has a transmission packet, in order to prioritize the packet transmission from the terminal station over the packet transmission from the base station, the predetermined time (DIFS + CW) of the base station in S305 and S309 is the terminal station Set longer than that. For example, it is possible to set the contention window maximum value for each number of retransmissions (15 slots for the initial transmission of IEEE 802.11a). This is because the terminal station selects the contention window value as a random value from zero to the maximum value, so that the contention window value of the base station becomes larger. Thus, priority is given to packet transmission by the terminal station, and the base station transmits a transmission packet only when the terminal station has no transmission packet (S306), and shifts to the sleep mode if there is no transmission packet. (S310 to S311) becomes possible.

  The second embodiment is a sleep control method in consideration of the case where a base station including a power supply unit using a solar cell or the like and a battery is operated as a wireless communication infrastructure. The sleep control in the prior art is intended only for vague power saving, and is not a control that reflects the remaining battery charge. A base station that can be powered by a solar cell as a wireless communication infrastructure is the situation that should be avoided most due to exhaustion of the remaining battery charge. Therefore, in that case, it is necessary to forcibly secure a long sleep period and prolong the battery duration.

  In the sleep control 2 of the first embodiment, when detecting that there is no transmission packet in the buffer of the base station and no transmission packet from the terminal station at a predetermined time in a beacon interval in which communication between the base station and the terminal station is expected, It is possible to shift to the sleep mode in the short term. However, when there is a lot of traffic in the base station or terminal station, transmission / reception of such traffic is prioritized, so the base station cannot shift to the sleep mode and cannot save power consumption of the base station.

  Here, when considering a base station that can be powered by a solar cell as a wireless communication infrastructure, if the remaining battery charge is extremely low, for example, even if the base station or terminal station has a lot of traffic, the consumption of the base station In order to save power and avoid non-operation due to battery depletion, it is effective for the base station to forcibly shift to the long sleep mode regardless of traffic.

FIG. 7 shows an outline of sleep control of the base station in the second embodiment of the present invention.
The second embodiment is a method for newly enabling selection of the sleep control 3 in addition to the sleep control 1 and the sleep control 2 shown in the first embodiment. In the first embodiment, the sleep control 2 is selected when traffic generation is expected in the beacon interval. In the second embodiment, the sleep control 2 or the sleep control 3 is selected.

  Even if traffic generation between the beacons is expected, the sleep control 3 transmits a beacon in which a long wireless access prohibition time is set when the remaining battery charge and power generation amount do not satisfy predetermined stable operation conditions. The base station shifts to a long sleep mode. That is, when the base station shifts to the sleep mode for a long time, the amount of transmission delay in the terminal station increases, but the sleep operation is performed with priority given to the power saving of the base station. In addition, after the sleep period is completed, communication with the terminal station is enabled in the same manner as the sleep control 2. That is, the sleep control 3 is controlled by the sleep control 1 in the first half and the sleep control 2 in the second half.

  Here, the stable operation conditions for the remaining battery charge and the amount of power generation are conditions under which the base station can continue to operate stably without a significant decrease in the battery charge of the base station. For example, it is also possible to set a threshold value for the remaining amount of battery storage and make it a condition that it is equal to or greater than the threshold value. In addition, necessary conditions for stable operation may be derived from the predicted value of power generation and the planned value of power consumption. Specifically, it is as follows.

(About predicted power generation)
The prediction of the power generation amount of the solar cell (power supply amount from the solar cell to the battery) will be described.
The amount of power generated by solar cells increases and decreases every 24 hours. In addition, if the solar altitude and sunshine hours vary depending on the season, and if the clear sky rate during the rainy season is taken into account, the average amount of power generated by solar cells over a 24-hour average period Changes throughout the year. It is possible to obtain a predicted value of the future power generation amount by referring to such a database of fluctuations in the power generation amount by the solar cell. In addition, if external information such as weather forecast is acquired via a network, it is possible to predict with higher accuracy. The predicted value of the power generation amount predicted in this way is meaningful, and the design predicted value of the power generation amount after the elapse of time t from now is discussed as Cdes (t). The design predicted value Cdes (t) of the power generation amount is an amount that varies with time. However, since control on a certain period of time is assumed, the time-related argument t is continuous. It does not represent time, but is treated as a function that takes discrete values at certain time intervals Δt, such as 10-minute intervals, 30-minute intervals, and 1-hour intervals.

(About planned power consumption)
The prediction of power consumption will be described. The power consumption is determined by the amount of downlink and uplink traffic flowing through the network, the sleep time of the base station, and various operation parameter values.

  Among these, it is possible to predict temporal fluctuations in the amount of traffic flowing through the network from statistical data. Of course, the time variation method changes depending on the conditions of places such as public facilities such as stations, shopping streets, and residential areas, and also on conditions such as days of the week, holidays, and summer holidays, but in addition to the predicted value given by the initial setting on the device If a measure such as sequentially updating the predicted value in consideration of the learning data is taken, a highly accurate time fluctuation predicted value of the traffic amount can be obtained for each condition. If the predicted time fluctuation value of the traffic amount is obtained, it is possible to estimate the next time rate including the sleep time when the first embodiment is applied.

(a) During signal transmission: In addition to the baseband signal processing circuit, the clock, synthesizer, and transmission high-power amplifier operate (maximum power consumption)
(b) During signal reception: In addition to the baseband signal processing circuit, the clock, synthesizer, and reception low-noise amplifier operate (the power consumption of the low-noise amplifier is slightly smaller than the power consumption of the high-power amplifier)
(c) During reception standby: Although no significant signal is actually being received, the power consumption is approximately the same as (b) because it is monitoring the presence or absence of signal reception.
(d) Full sleep: Most of the baseband signal processing circuits (except for the interface circuit and some circuits for sleep management), all transmission / reception amplifier systems are stopped, clocks, synthesizers, etc. are also stopped (minimum power consumption) value)
(e) Incomplete sleep: Most of the baseband signal processing circuits (except for the interface circuit and some circuits for sleep management) and all transmission / reception amplifier systems are stopped, but the clock, synthesizer, etc. are stopped. Not
(f) Sleep wake-up preparation: The clock and synthesizer are also stopped in full sleep, but these circuits need to be turned on again about 50 to 100ms before actual wake-up to ensure frequency stability. In effect, the power consumption is effectively the same as (e).

With respect to the above states, the power consumption changes between the states of the following power values.
P ₁ : Maximum power consumption corresponding to the above (a) P ₂ : Power consumption corresponding to the above (b) and (c) P ₃ : Power consumption corresponding to the above (e) and (f) P _min : Above ( d) Minimum power consumption corresponding to

If the time ratios of these power consumption times t are R ₁ (t), R ₂ (t), R ₃ (t), and R ₄ (t) using various operation parameters of the base station, At this time, the total power consumption Pdes (t) at time t is obtained by the following equation (1). Here, R ₁ (t) + R ₂ (t) + R ₃ (t) + R ₄ (t) = 1.
_{Pdes (t) = P 1 R} 1 (t) + P 2 R 2 (t) + P 3 R 3 (t) + P min R 4 (t) ... (1)

(Requirements for stable operation)
Conditions for stable operation exist between the predicted power consumption design value Pdes (t) thus obtained and the predicted power supply design value Cdes (t). This is a condition for ensuring that the remaining battery level does not become zero during operation. Although management of this stable operation condition needs to be performed in a certain long period, in general, the difference in time fluctuation every 24 hours is smaller than the time fluctuation within 24 hours per day, so the management period is 24 An integer multiple of time is ideal. This control cycle is Tcont (for example, 24 hours, 3 days, etc.). Then, by considering that the remaining battery level does not decrease below the current battery level after the control period Tcont has elapsed, the following stable state is avoided by considering avoiding a steady discharge state. Set conditional expressions for operation.
∫ _t ^{t + Tcont} {Cdes (t ′) − Pdes (t ′)} dt ′ ≧ 0 (2)

  Although the above expression is expressed in an integral form, the control is actually performed at intervals of discrete time Δt, so it may be appropriate to express in the form of addition / summation for each time. Therefore, it will be described in integral form.

The power consumption plan value Pdes (t) is controlled so as to satisfy Expression (2) of the above conditions. If the above conditions for stable operation are not satisfied, the sleep time R ₄ (t) is set longer. That is, the sleep control 3 is applied instead of the sleep control 2.

FIG. 8 shows a configuration example of a base station apparatus in Embodiment 2 of the present invention.
In addition to the configuration of the first embodiment, a third sleep control unit 12 that performs the sleep control 3 and a stable operation condition determination unit 13 that is connected to the power generation means 15 via the battery 14 are provided. The third sleep control unit 12 executes control to shift the base station to the sleep mode by the sleep control 3 shown in FIG. The power generation means 15 is a power generation means using renewable energy such as sunlight or wind power. The energy generated here is output to the battery 14, and the battery 14 stores the input energy. The stable operation condition determination unit 13 includes a power consumption plan value acquisition unit, a power generation amount prediction value acquisition unit, and a storage power remaining amount acquisition unit. Judgment is made as to whether the amount and the amount of power generation satisfy a predetermined condition. The communication control unit 4 refers to the stable operation condition determination unit 13 in addition to the buffer unit 5, the communication history storage unit 7, the terminal information storage unit 8, and the sleep profile storage unit 9. Which sleep control is to be executed is determined.

FIG. 9 shows a sleep control processing procedure in the second embodiment of the present invention.
In FIG. 9, the sleep control processing procedure of the communication control unit 4 is performed at every beacon interval. The communication control unit 4 starts determining whether to perform sleep control 1, 2, or 3 in the next beacon interval for each beacon interval (S401). That is, it is determined whether there is no transmission packet in the base station buffer at the time of beacon transmission and whether there is no communication history between the base station and the terminal station within a predetermined period (S402). The predetermined period may be set to the awake period of the terminal in the beacon interval, or may be set to another time. That is, the predetermined period here is a time set for the purpose of determining the presence / absence of a terminal station connected to the base station and the presence / absence of communication traffic when there is a connected terminal station. It can be anything.

  When there is no transmission packet in the buffer and there is no communication history within a predetermined period (Yes in S402), the operation of sleep control 1 is performed (S403). When there is a transmission packet in the buffer, or when there is a communication history within a predetermined period (No in S402), it is determined whether or not the remaining battery charge and the amount of power generation satisfy the conditions for stable operation of the base station ( S403). If Yes in S403, the sleep control 2 is performed (S404). In the case of No in S405, the operation of sleep control 3 is performed (S406). The operations of the sleep controls 1, 2, and 3 are continued until the beacon interval ends (S407), and S402 to S407 are repeated again during beacon transmission.

  Since the processing procedures of the sleep control 1 and the sleep control 2 are the same as those in the first embodiment, the processing procedure of the sleep control 3 will be described below.

FIG. 10 shows a processing procedure of the sleep control 3 in the second embodiment of the present invention.
In FIG. 10, when sleep control 3 is started (S501), a sleep period length is set (S502), and a beacon in which the sleep period is set as a wireless access prohibition period is transmitted (S503). When the beacon is transmitted, the base station shifts to the sleep mode during the sleep period (S504), and shifts to the awake mode after the sleep period elapses (S505). The process so far is the same as the process of S201-S205 of the sleep control 1 of Example 1 shown in FIG. Next, it is determined whether there is a transmission packet in the buffer of the base station (S506). This S506 and the following processes are the same as the processes of S303 to S313 of the sleep control 2 of the first embodiment shown in FIG. 6, and this process is repeated until the end of the beacon interval (S314). The process ends.

FIG. 11 shows an outline of sleep control of the base station in the third embodiment of the present invention.
The third embodiment is a control technique in which the sleep control 2 of the first embodiment shown in FIG. In the sleep control 2, when it is determined that there is no transmission packet of the base station and no transmission packet of the terminal station, the base station shifts to the sleep mode, but prohibits packet transmission of the terminal station during the sleep mode. The base station notifies the NAV by CTS or the like and sets the access prohibition period. In the sleep control 4 of the third embodiment, when it is determined that there is no transmission packet of the base station and no transmission packet of the terminal station, the base station shifts to the sleep mode without notifying the CTS of the NAV. .

The configuration of the base station is replaced with a fourth sleep control unit in which the second sleep control unit 11 shown in FIG. In the processing procedure of the sleep control 4, the CTS transmission (S310) in the processing procedure of the sleep control 2 of the first embodiment shown in FIG. 6 is omitted, and the time for shifting from the sleep mode to the awake mode is uniquely set in the base station (S312). ).
As described above, the power consumption required for CTS transmission when shifting to the sleep mode is unnecessary in the third embodiment, and thus a higher power saving effect than that in the first embodiment can be realized. Since the base station determines whether or not the terminal station transmits traffic before shifting to the sleep mode, if the sleep mode is short, traffic is generated in the terminal station during that time, Is unlikely to be sent to. If the terminal station transmits a packet during the sleep mode, the terminal station only repeats retransmission.

FIG. 12 shows an outline of sleep control of a base station in Embodiment 4 of the present invention.
The fourth embodiment is a control technique in which the sleep control 2 of the second embodiment shown in FIG. 7 is replaced with the sleep control 4 and the sleep control 3 is replaced with the sleep control 5. The sleep control 4 of the fourth embodiment is the same as the sleep control 4 of the third embodiment, and the second half of the sleep control 5 is the same as the sleep control 4 in which the base station shifts to the sleep mode without notifying the CAV of the NAV. It is.

  The configuration of the base station is replaced with a fourth sleep control unit in which the second sleep control unit 11 shown in FIG. 8 performs the sleep control 4 and a third sleep control unit 12 in the third sleep control unit 12 that performs the sleep control 5. The processing procedure of the sleep control 5 omits the CTS transmission (S310) in the processing procedure of the sleep control 3 of the second embodiment shown in FIG. 10, and the base station uniquely sets the time for shifting from the sleep mode to the awake mode (S312). ). The operations of the sleep control 4 and the sleep control 5 are the same as in the third embodiment.

FIG. 13: shows the outline | summary of the sleep control of the base station in Example 5 of this invention.
The fifth embodiment is a control technique in which the sleep control 2 of the first embodiment shown in FIG. 1 or the sleep control 4 of the third embodiment shown in FIG. When the sleep control 6 determines that there is no transmission packet of the base station and no transmission packet of the terminal station as in the sleep control 4, the base station shifts to the sleep mode without notifying the NAV by the CTS. However, there is a difference in that the sleep mode and the awake mode are repeated in a short cycle and the carrier sense for a short time is performed in the awake mode.

  Based on the carrier sense, whether to shift to the sleep mode is determined depending on whether the wireless channel is busy. If the carrier sense execution result is idle, the base station again shifts to the sleep mode. If the carrier sense execution result is busy, the awake mode is maintained. When the terminal station is transmitting an uplink packet, the radio channel is busy, so the base station knows that the terminal station is trying to transmit the packet and keeps it in awake mode and retransmits it. Receive the packet.

  Thus, since the base station can grasp the packet transmission of the terminal station by repeating the awake mode in a short cycle, the number of packet retransmissions at the terminal station can be reduced, and the probability of discarding can be reduced. On the other hand, the base station can periodically enter the sleep mode and reduce power consumption without notifying the terminal station of the wireless access prohibition period by using a beacon, CTS, or the like.

  Although the base station recovers to the awake mode in a short cycle, the carrier sense in the awake mode in the sleep control 6 is not for the purpose of receiving a packet, but only for determining whether the radio channel is busy based on the carrier sense. Therefore, the awake time here can be significantly shorter than the awake time (DIFS + CW) of the sleep control 4. For example, the awake time can be set to one slot time (20 μsec in IEEE802.11b) defined by the IEEE802.16 standard. Alternatively, the awake time can be set to the minimum time required for signal detection by carrier sense. Therefore, the total awake time can be significantly reduced compared to the sleep control 4.

  From the viewpoint of delay in communication quality, it is desirable that packets can be received while the number of retransmissions of the terminal station is small. Considering this, the sleep time is set. For example, the data packet size of IEEE802.11b is at least 218 μsec (transmission rate 11 Mbps, payload 0 bit). Therefore, if the sleep time is set to 200 μsec, the base station detects it by carrier sense after the first sleep mode and stops the sleep mode by the first transmission of the packet by the terminal station. The station can receive.

  The configuration of the base station is replaced with a sixth sleep control unit in which the second sleep control unit 11 shown in FIG. The processing procedure of the sleep control 6 replaces the processing of the transition from the CTS transmission (S310) to the awake mode (S312) in the processing procedure of the sleep control 2 of the first embodiment shown in FIG. 6 with the processing shown in FIG.

  In FIG. 14, when the sleep control 6 is started (S601), a sleep time is set (S602). Subsequently, the power of the predetermined circuit is turned off in the set sleep time (S603). Here, referring to the sleep profile storage unit, it is possible to grasp the circuit for turning off the power from the set sleep time. If a transmission packet is generated in the buffer of the base station during the sleep time (Yes in S604), the sleep mode is immediately terminated (S608, S111). On the other hand, it immediately recovers from the sleep mode to the awake mode. If no sleep packet is generated (No in S603) and the sleep time elapses, the circuit is turned on and carrier sense is performed (S606). It is determined whether or not the wireless channel is busy based on the carrier sense. If the wireless channel is not busy (No in S607), the mode shifts to the sleep mode again (S602 to S605). If it is determined that it is busy (Yes in S607), the sleep mode is immediately terminated (S608).

FIG. 15 shows an outline of sleep control of a base station in Embodiment 6 of the present invention.
The sixth embodiment is a control technique in which the sleep control 4 in the fourth embodiment shown in FIG. 12 is replaced with the sleep control 6 and the sleep control 5 is replaced with the sleep control 7. The sleep control 6 of the sixth embodiment is the same as the sleep control 6 of the fifth embodiment, and the second half of the sleep control 7 is a method in which the base station shifts to the sleep mode without notifying the NAV by CTS in the same manner as the sleep control 6. It is.

  The configuration of the base station is replaced with a sixth sleep control unit in which the second sleep control unit 11 illustrated in FIG. 8 performs the sleep control 6 and a third sleep control unit 12 is replaced with a seventh sleep control unit in which the sleep control 7 is performed. The processing procedure of the sleep control 7 replaces the processing of the transition from the CTS transmission (S310) to the awake mode (S312) in the processing procedure of the sleep control 3 of the second embodiment shown in FIG. 10 with the processing shown in FIG.

DESCRIPTION OF SYMBOLS 1 Base station apparatus 2 Antenna 3 Transmission / reception part 4 Communication control part 5 Buffer part 6 Interface part 7 Communication history memory | storage part 8 Terminal information memory | storage part 9 Sleep profile memory | storage part 10 1st sleep control part 11 2nd sleep control part 12 3rd sleep Control unit 13 Stable operation condition determination unit 14 Battery 15 Power generation means

Claims (8)

In a base station device that performs wireless communication with a terminal station,
A transmission buffer for accumulating transmission packets addressed to the terminal station;
Transmitting means for transmitting transmission packets stored in the transmission buffer;
Receiving means for receiving a packet transmitted from the terminal station;
Recording means for recording a communication history indicating transmission / reception of the transmission packet with the terminal station;
First sleep control means for setting a sleep state for a predetermined period;
A second sleep control unit that repeats an awake state and a sleep state in a shorter period than the first sleep control unit when a packet is not received from the terminal station;
Control means for selecting the first sleep control means when there is no transmission packet in the transmission buffer and there is no communication history for a predetermined period in the recording means, and for selecting the second sleep control means in other cases And a base station apparatus comprising: The base station apparatus according to claim 1,
In the second sleep control means, when there is no transmission packet in the transmission buffer, a state in which no packet is received from the terminal station continues beyond a period in which the terminal station waits to transmit a packet. When it is detected that the terminal station is present, the transmission of the terminal station is prohibited and the base station is set in the sleep state. The base station apparatus according to claim 1,
The number of components of the base station apparatus that the first sleep control unit sets to the sleep state is greater than the number of components of the base station apparatus that the second sleep control unit sets to the sleep state. Base station apparatus. The base station apparatus according to claim 1,
Whether the base station is driven by power from the battery that stores the power generated by the power generation means, and whether or not the remaining power of the battery and the amount of power generated by the power generation means are sufficient to operate the base station stably. A stable operation condition determination means for determining a stable operation condition;
After entering the sleep state for a period shorter than the period of the sleep state of the first sleep control unit and longer than the period of the sleep state of the second sleep control unit, the awake state and a packet from the terminal station And third sleep control means for repeating the sleep state in a period equivalent to the sleep state of the second sleep control means when not receiving,
The control means selects the first sleep control means when there is no transmission packet in the transmission buffer and the recording means does not have the communication history for a predetermined period, and otherwise the safe operation condition is The base station apparatus, wherein the second sleep control unit is selected when sufficient, and the third sleep control unit is selected when the safe operation condition is not sufficient. In the base station apparatus according to claim 4,
The second sleep control unit and the third sleep control unit wait for the terminal station to transmit a packet when there is no transmission packet in the transmission buffer and the terminal station does not receive the packet. When it is detected that the terminal has continued beyond a period, transmission of the terminal station is prohibited and the base station is set in the sleep state. In the base station apparatus according to claim 1 or 4,
The repetition of the awake state and the sleep state is performed by transferring from the awake state to the sleep state without notifying the terminal station of a radio access prohibition period, and after the sleep state ends, the state is changed to the awake state. It is a process of performing carrier sense, transitioning to the sleep state again when the radio channel is not busy, and receiving a packet transmitted by the terminal station while maintaining the awake state when the radio channel is busy,
The time of the awake state is set to a short time during which it can be determined whether the radio channel is busy by the carrier sense,
The time in the sleep state is set to a time during which a retransmission packet can be received from the terminal station in the awake state after the radio channel becomes busy by the carrier sense. In a sleep control method of a base station that performs wireless communication with a terminal station,
The base station
A transmission buffer for accumulating transmission packets addressed to the terminal station;
Transmitting means for transmitting transmission packets stored in the transmission buffer;
Receiving means for receiving a packet transmitted from the terminal station;
Recording means for recording a communication history indicating transmission / reception of the transmission packet with the terminal station;
First sleep control means for setting a sleep state for a predetermined period;
An awake state, and a second sleep control unit that repeats a sleep state in a shorter period than the first sleep control unit when a packet is not received from the terminal station,
The first sleep control unit is selected when the transmission packet is not in the transmission buffer and the recording unit does not have the communication history for a predetermined period, and the second sleep control unit is selected otherwise. A sleep control method characterized by the above. In the sleep control method according to claim 7,
The base station
Whether the base station is driven by power from the battery that stores the power generated by the power generation means, and whether or not the remaining power of the battery and the amount of power generated by the power generation means are sufficient to operate the base station stably. A stable operation condition determination means for determining a stable operation condition;
After entering the sleep state for a period shorter than the period of the sleep state of the first sleep control unit and longer than the period of the sleep state of the second sleep control unit, the awake state and a packet from the terminal station And third sleep control means for repeating the sleep state in a period equivalent to the sleep state of the second sleep control means when not receiving,
The first sleep control unit is selected when the transmission packet is not in the transmission buffer and the recording unit does not have the communication history for a predetermined period, and the safety operation condition is sufficient in other cases. A sleep control method comprising: selecting a second sleep control unit, and selecting the third sleep control unit when the safe operation condition is not sufficient.

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