JP5654431B2 - Base station apparatus and sleep control method for the base station apparatus - Google Patents

Description

  The present invention relates to a base station apparatus and a sleep control method thereof, and more particularly to a technique for realizing power saving of a base station apparatus in a wireless communication system.

  In recent years, devices equipped with a wireless LAN communication function compliant with the IEEE 802.11 standard have become widespread. For example, wireless LAN communication functions are installed in terminal station devices such as notebook PCs, mobile phones, and game machines, and these terminal station devices can access the Internet via wireless LAN base station devices by wireless communication. It has become.

  In Non-Patent Document 1, a power saving mode of a terminal station apparatus driven by a battery as described above is defined as a standard. In this power saving mode, the terminal station apparatus notifies the base station apparatus that it will transition to the sleep state when no communication traffic of the terminal station is generated. The terminal station apparatus that shifts to the sleep state can save battery power consumption by suspending a part of the transmission / reception circuit in the terminal station apparatus. Further, the terminal station apparatus is controlled to transition from the sleep state to an awake state in which traffic can be transmitted and received at a constant cycle and to receive a beacon signal from the base station apparatus.

  Since the above-described beacon signal includes information regarding the presence / absence of communication data addressed to the terminal station device, the terminal station device can determine the presence / absence of communication data addressed to itself by receiving the beacon signal. When there is communication data addressed to itself, the terminal station device transmits Power Save-Poll (PS-poll) to the base station device and maintains the awake state until the communication with the base station device is completed. On the other hand, when the beacon is received and there is no communication data addressed to the own station, the terminal station device returns to the sleep state again to save power consumption.

  While the power saving mode of such a terminal station apparatus is defined by the standard, the power saving mode of the base station apparatus is not defined. This is because, unlike a battery-driven terminal station device, a general base station device is connected to an external power source by a cable or the like, and thus it has been considered that the demand for power saving is not high. However, in recent years, portable wireless LAN base station devices that are driven only by batteries are becoming popular. The portable wireless LAN base station device operates as the infrastructure mode and can perform data communication with the terminal station device, but the time during which communication is possible is limited depending on the remaining amount of power stored in the battery. Therefore, a power saving control method for extending the operation time of the battery-driven base station apparatus is required.

  Non-Patent Document 2 discloses a power saving control method for a wireless LAN base station apparatus. With reference to FIG. 7, an outline of the operation of this power saving control method will be described. When the base station apparatus (AP) transmits the beacon 201, it is confirmed whether there is downlink communication traffic in the transmission buffer. When there is no downlink communication traffic in the transmission buffer, the base station apparatus transmits a beacon 201, and then transmits a control signal 203 using a CTS-to-Self or broadcast signal, etc., and transmits a NAV (to the terminal station apparatus (STA). The transmission prohibition period is set by Network Allocation Vector. During the transmission prohibition period, even if traffic occurs in the terminal station apparatus, the traffic is not transmitted immediately, and uplink transmission is possible after the set transmission prohibition period ends. In FIG. 7, the transmission period of the terminal station apparatus is a period from time “A” to time “B” and a period from time “F” to time “G”.

  Since the maximum transmission prohibition period that can be set by the base station apparatus is limited in one transmission of the control signal, the base station apparatus sets the control signal multiple times in order to set the transmission prohibition period and perform sleep control. Need to send. In FIG. 7, the base station apparatus sets a transmission prohibition period with the control signal 203 for the terminal station apparatus, and then performs sleep control in a period from time “C” to time “D”. Thereafter, the base station apparatus sets a transmission prohibition period from time “E” to time “F” by the control signal 204 and performs sleep control again. The number of control signal transmissions is determined by the total sleep period set in advance in the base station apparatus. If the total sleep period is long when the transmission prohibition period is constant, the number of transmissions of the control signal also increases.

IEEE Standard 802.11, Wireless LAN medium access control (MAC) and Physical layer (PHY) specification, 12 June, 2007. "Performance evaluation of power saving mode in wireless LAN base station equipment" (Ogawa, et al.), IEICE technical report MoMoMuC2009-13.

  According to the sleep control technique described in Non-Patent Document 2 described above, when data is stored in the buffer of the base station device before beacon transmission, control is performed so that the base station device does not enter the sleep state. In this control, whether or not the base station apparatus shifts to the sleep state is determined only at the time of beacon transmission. Therefore, the base station apparatus may maintain an unnecessary awake state even when there is no traffic to be transmitted / received after the base station apparatus completes transmission / reception of the data accumulated in the buffer within the beacon interval. Further, according to this conventional technique, the base station device performs sleep control only when there is no terminal station device connected to the base station device or when no traffic in the network is generated, and traffic is transmitted and received. In this case, the base station device cannot shift to the sleep state, so that a large power saving effect cannot be expected.

  In order to alleviate the above problem, the base station apparatus can reduce unnecessary awake state and shift the base station apparatus to the sleep state in a short cycle even when there is more than a certain amount of traffic. A method of judging can be considered. 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. According to this method, it is possible to make a sleep transition determination in a short cycle. Therefore, the time for maintaining an unnecessary awake state after completing transmission of accumulated traffic is shortened, and the awake state can be reduced. In addition, even if communication traffic occurs in the base station apparatus or terminal station apparatus during sleep, the base station apparatus immediately returns to the awake state, so it is considered that there is little deterioration in communication quality.

However, shortening the beacon period may have the following problems. First, since the transmission frequency of sleep control packets such as CTS and beacons increases, the power consumption required for beacon transmission increases. Secondly, in order to perform sleep transition determination at each beacon transmission time, it is necessary to determine whether or not uplink transmission from the terminal station device is required, and a certain awake time (time of FIG. 7) before beacon transmission. The period from “F” to time “G” must be set. As a result, each time the beacon transmission frequency increases, the time for the awake state increases, so there is a limit to power consumption reduction by sleep control.
Therefore, in order to improve the power saving effect by the sleep control technology, a technology that enables the base station device to shift to the sleep state without setting the transmission prohibited section by CTS-to-self is necessary. It is.

  The present invention has been made in view of the above circumstances, and a base station apparatus that enables a terminal station apparatus to shift to a sleep state without setting a transmission prohibition section and a sleep control method for the base station apparatus The purpose is to provide.

In order to achieve the above object, a base station apparatus according to the present invention provides a base station apparatus that communicates with a terminal station apparatus via a radio channel while transitioning between an awake state and a sleep state. Transition from the awake state to the sleep state without notifying the transmission prohibition period, and transition to the awake state at the end of the sleep state to perform carrier sense, and as a result of the carrier sense, the wireless channel The control means for shifting to the sleep state again when the wireless channel is not busy and maintaining the awake state when the wireless channel is busy, and the total traffic amount and the minimum packet between the terminal station apparatus in the past fixed period Information acquisition means for acquiring a length, and the control means is configured such that the total amount of traffic is a threshold value. In the following case, the terminal station apparatus limits the transmission rate used when transmitting, and the sleep state based on the time required to transmit the minimum packet length data using the transmission rate. The base station apparatus has a configuration in which a period is set.
In the base station apparatus, for example, the control means determines a transmission rate used when the terminal station apparatus transmits to a transmission rate lower than a transmission rate of a packet received in the past.
In the base station apparatus, for example, the control means sets the period of the sleep state to be smaller than a time necessary for transmitting the data having the minimum packet length.
In the base station apparatus, for example, the control means refers to a time necessary for transmitting the data of the minimum packet length, and refers to a time period (TXOP, Transmission opportunity) in which the terminal station apparatus can continuously transmit. An upper limit value is set.

  Also, the sleep control method for a base station apparatus according to the present invention is a transmission control prohibited for the terminal station apparatus in the sleep control method for a base station apparatus that performs communication with the terminal station apparatus while transitioning between an awake state and a sleep state. When a transition is made from the awake state to the sleep state without notifying the period, and when the sleep state ends, the awake state is entered and carrier sense is performed. As a result of the carrier sense, the radio channel is not busy The control step for transitioning to the sleep state again and maintaining the awake state when the radio channel is busy, and the information acquisition for acquiring the total traffic amount and the minimum packet length with the terminal station device during a past fixed period And in the control step, the total traffic amount is If the value is equal to or less than the value, the terminal station apparatus limits the transmission rate used when transmitting, and the sleep state based on the time required to transmit the minimum packet length data using the transmission rate. The base station apparatus sleep control method is characterized in that the period of time is set.

  According to the present invention, the base station apparatus can shift to the sleep state without notifying the terminal station apparatus of the transmission prohibition period by a beacon signal, CTS, or the like, and can be connected to and communicated with the terminal station apparatus. The time for the awake state can be reduced as compared with the prior art while avoiding the influence on the quality. Therefore, it is possible to save power in the base station apparatus.

It is a figure for demonstrating the outline | summary of the sleep control technique of the base station apparatus by embodiment of this invention. It is a figure for demonstrating the sleep control subject (problem regarding the deterioration of connectivity with a terminal station apparatus) of the base station apparatus by embodiment of this invention. It is a figure for demonstrating the sleep control subject (the subject regarding reduction of the power-saving effect by the data packet with a long payload length) of the base station apparatus by embodiment of this invention. It is a functional block diagram of the base station apparatus by embodiment of this invention. It is a figure which shows an example of the setting procedure of the sleep period of the base station apparatus by embodiment of this invention. (A) is a figure which shows the structure of an IEEE802.11 standard EDCA parameter set element, (B) is a figure which shows the structure of an AC_BE, AC_BK, AC_VI, AC_VO parameter record field among EDCA parameter set elements. . It is a figure for demonstrating the outline | summary of the sleep control of the base station apparatus by a prior art.

<Overview>
In general, when the base station apparatus shifts to the sleep state without setting the transmission prohibition period in the terminal station apparatus by CTS-to-self or the like, there is a possibility that the packet loss of the terminal station apparatus occurs. That is, while the base station apparatus is in the sleep state, the terminal station apparatus may transmit uplink data, but since the base station apparatus is in the sleep state, it is not possible to transmit an ACK signal that is an arrival confirmation signal. Absent. In this case, since the terminal station apparatus does not receive the ACK signal, the terminal station apparatus retransmits the data. The terminal station apparatus repeats retransmission of the same data until an ACK signal is received or until the number of data transmission retransmissions reaches an upper limit. When the number of retransmissions by the terminal station device reaches the upper limit value, packet loss occurs. Therefore, in the present embodiment, the state of the wireless channel is monitored at a fixed period, it is determined whether to perform sleep control according to the state of the channel, and the sleep period is set with reference to the past communication history. This prevents the occurrence of packet loss while enabling the transition to the sleep state without setting the transmission prohibition period in the terminal station device.

FIG. 1 shows an outline of sleep control of a base station apparatus according to the present invention.
When the base station apparatus transitions to the sleep state, the base station apparatus transitions to the awake state at a constant cycle, and transitions between the awake state and the sleep state. In FIG. 1, for example, when shifting from the sleep state 103-1 to the awake state, the base station apparatus performs carrier sense 104-1. In the carrier sense 104-1, it is determined whether or not the reception strength of the radio signal is equal to or higher than a predetermined threshold. If it is equal to or higher than the threshold, it is determined that the radio channel is busy.

  When determining that the radio channel is busy, the base station apparatus interrupts sleep control and shifts to an awake state. When it is determined that the radio channel is not busy, that is, when no signal is detected from the radio channel, the base station apparatus transitions again to the sleep state 103-2, and then returns to the awake state again, and the carrier sense 104-2. To implement.

  In this way, the base station apparatus periodically performs carrier sense in the process of transitioning between the awake state and the sleep state, and repeats the sleep transition determination. In this case, the terminal station device may transmit data when the base station device is in the sleep state. In this case, if data transmission by the terminal station device can be detected by carrier sense by the base station device, The station apparatus immediately recovers to the awake mode, and can receive data retransmitted by the terminal station apparatus. Therefore, it is possible to improve the packet loss of the terminal station apparatus by repeating the carrier sense by the sleep control shown in FIG.

  In the sleep control described above, the base station apparatus returns from the sleep state to the awake state because it is necessary to perform carrier sense 104-1, etc., but carrier sense is not for receiving data, and continues sleep control. It is a judgment means of whether to do. For this reason, it is possible to set the carrier sense period short, for example, it can be set to 20 μsec, which is the length of one slot time of the 802.11b standard, thereby reducing the overall awake time including carrier sense. can do. Alternatively, if the minimum time required for signal detection by carrier sense is set, the power saving effect is further increased.

  In the sleep control, the power saving effect, the communication quality, and the connectivity with the terminal station apparatus are greatly affected by the length of the sleep period. For example, if the sleep period is lengthened, the entire awake time can be reduced, and the power saving effect can be improved. However, in this case, as shown in FIG. 2, communication quality and connectivity with the terminal station apparatus may be deteriorated. That is, when the sleep period length is long and the carrier sense frequency is low, and when the length of the data 105-1 to 105-3 transmitted by the terminal station apparatus is short, the timing of the carrier sense 104-1 to 104-3 is the terminal station. The probability of overlapping with the standby transmission time 109 by the device increases.

  When the timing of carrier senses 104-1 to 104-3 overlaps with the standby transmission time (109) by the terminal station apparatus, the base station apparatus does not determine that the radio channel is busy and repeats sleep. If this duplication continues, not only will packet delay increase, but packet loss will occur due to repeated retransmissions. Therefore, from the viewpoint of communication quality and connectivity with the terminal station apparatus, it is desirable that the packet can be received while the number of retransmissions of the terminal station apparatus is small. Considering this, a standard sleep period can be set. For example, the size of an IEEE802.11b data packet is at least 218 μsec (transmission rate 11 Mbps, payload 0 bit). Therefore, in this case, if the standard sleep period is set to 200 μsec, the base station apparatus determines that the radio channel is busy by the initial transmission of the packet by the terminal station apparatus, stops the sleep state, and transmits the first retransmission packet to the base station apparatus. Can be received.

  Here, if the transmission rate transmitted by the terminal station apparatus can be set low and the packet transmission time can be set long, the sleep period of the base station apparatus can be set long accordingly, and the communication quality and terminal The power saving effect can be effectively enhanced without harming both the connectivity with the station apparatus.

  However, since the payload length of the data packet varies depending on the terminal station apparatus, the application, and the like, if the transmission rate is set low, a data packet having a long payload length is generated unnecessarily, and there is a possibility of reducing the power saving effect. This will be described with reference to FIG. Here, the base station apparatus returns to the awake state from the sleep period 103 and grasps the occupied state of the radio channel by the carrier sense 104. In the example of FIG. 3, the data 105-1 is transmitted from the terminal station apparatus in the sleep period 103-2, and a part of the data 105-1 is detected by the carrier sense 104-2 after the sleep period 103-2. The Thereby, the base station determines that the radio channel is busy.

  The base station apparatus that determines that the radio channel is busy from the carrier sense 104-2 shifts to an awake state and waits for data retransmission. When the time 105-1 required for data transmission by the terminal station apparatus is large, the awake period 108 until the retransmission data 105-2 is received may be longer after the sleep period 103-2 in the base station apparatus. The awake period 108 corresponds to the sum of a part 106 of data transmission and a retransmission waiting time 107 of the terminal station apparatus. If there is such an unnecessary awake period, there is a possibility of reducing the power saving effect.

  Therefore, in addition to the transmission rate of the traffic transmitted by the terminal station device, the data transmission time from the terminal station device is controlled, and if the sleep period is set long, the power saving effect can be effectively improved. Become.

  Therefore, in the present embodiment, as described below, when the traffic transmitted by the terminal station apparatus is smaller than the threshold, the transmission rate used by the terminal station apparatus can be extended so that the sleep period of the base station apparatus can be extended. Is low. Then, when the transmission rate is used, the period during which the terminal station occupies the channel is calculated based on information such as the payload length of the data packet, and based on the channel occupancy period of the terminal station apparatus obtained by this calculation The sleep period of the base station device is set. The base station apparatus enters a sleep state according to the sleep period in the channel occupation period.

<Device configuration>
FIG. 4 shows an example of functional blocks of the base station apparatus 501 according to the embodiment of the present invention.
The base station apparatus 501 is a base station apparatus that communicates with a terminal station apparatus (not shown) via a wireless channel while changing between an awake state and a sleep state, and includes an antenna 502, a transmission / reception unit 503, and a communication control unit. 504, a buffer unit 505, an interface unit 506, a sleep control unit 507, a communication history information unit 508, and a power management unit 509.

  Here, the transmission / reception unit 503 performs signal processing for communication via a wireless channel (wireless line). The communication control unit 504 controls the overall operation related to data transmission / reception. The buffer unit 505 temporarily accumulates data during the transmission / reception process. The interface unit 506 is responsible for data packet input / output between the base station device 501 and the outside (wired LAN or the like). The sleep control unit 507 controls the sleep state of the base station device 501. The communication history information unit 508 stores information necessary for control by the sleep control unit 507. The power management unit 509 is responsible for power management for temporarily suspending the circuit of the base station apparatus 501 under the control of the sleep control unit 507.

  As will be described below, among the above components, the communication control unit 504 and the sleep control unit 507 shift from the awake state to the sleep state without notifying the terminal station device of the wireless access prohibition period, and the sleep state When the wireless channel is not busy, a transition is made to the sleep state when the wireless channel is not busy, and the awake state is maintained when the wireless channel is busy. Functioning as a control means (claim 1). Further, the communication control unit 504 functions as information acquisition means (claim 1 of the present application) that acquires the total amount of traffic with the terminal station device and the minimum packet length in a certain past period. Further, when the total traffic amount is equal to or less than the threshold, the sleep control unit 507 limits the transmission rate used when the terminal station device transmits, and transmits the data with the minimum packet length using the transmission rate. Therefore, it functions as a control means (the claim 1 of the present application) that sets the period of the sleep state based on the time required for the purpose.

<Device operation>
Next, the overall operation of the base station apparatus 501 will be described.
Base station apparatus 501 receives a signal via a radio channel by antenna 502 in an awake state. The transmission / reception unit 503 performs filtering of out-of-band signals, signal amplification by a low noise amplifier, frequency conversion from an RF frequency to a baseband, and A / D conversion from an analog signal to a digital signal with respect to a signal received by the antenna 502 Further, a series of signal processing such as timing detection, termination of header information related to the physical layer, demodulation processing, and error correction is performed on the digitized baseband signal. A signal subjected to demodulation processing or the like output from the transmission / reception unit 503 is input to the communication control unit 504. If the received signal is a data packet, the communication control unit 504 outputs the data packet to the interface unit 506 via the buffer unit 505. The interface unit 506 inputs and outputs data packets between the base station apparatus 501 and the outside.

  On the other hand, when a data packet is input from the external wired LAN or the like via the interface unit 506, the data packet is stored in the buffer unit 505. When this data packet is transmitted via a wireless channel under the control of the communication control unit 504, the communication control unit 504 outputs this data packet to the transmission / reception unit 503. The transmission / reception unit 503 generates a baseband signal by performing various modulation processes on the data packet to be transmitted, and performs D / A conversion, frequency conversion, band conversion for converting the baseband signal from a digital signal to an analog signal. After performing filtering of external signals, signal amplification, and the like, transmission is performed from the antenna 502.

  Here, when the base station apparatus 501 receives a data packet from a terminal station apparatus (not shown) through a radio channel by the above procedure, the communication control unit 504 includes information on the payload length included in the data packet, and The transmission rate used to transmit the data packet is acquired and output to communication history information section 508. Further, the communication control unit 504 also acquires information on the total amount of traffic communicated with the terminal station device during a past fixed period and outputs the information to the communication history information unit 508.

  The sleep control unit 507 acquires information on the total traffic amount and the data payload length for sleep control from the communication history information unit 508 periodically or at arbitrary timing. Further, the sleep control unit 507 determines a transmission rate for limiting communication with the terminal station apparatus from the transmission rate used for transmitting the data packet, and determines the sleep period from the transmission rate and the payload length of the data packet. Has a function to calculate. Details of the transmission rate determination method and the sleep period calculation will be described later.

  Parameters such as a sleep period and a transmission rate calculated by the sleep control unit 507 are output to the communication control unit 504. The sleep period calculated by the sleep control unit 507 is output to the power management unit 509. The power management unit 509 shifts the base station device 501 to the sleep state by pausing the circuit of the base station device 501 during the sleep period calculated by the sleep control unit 507, thereby reducing power consumption.

  Further, the power management unit 509 has a function of causing a circuit for performing carrier sense in the base station apparatus 501 to transition to an awake state before the sleep period ends. As an implementation result of this carrier sense, the communication control unit 504 notifies the sleep control unit 507 of the result of whether or not the radio channel is busy. When the wireless channel is busy, the sleep control unit 507 interrupts the sleep control and notifies the power management unit 509 of information indicating that the base station device 501 is maintained in the awake state. The power management unit 509 has a function of shifting all circuits in the base station device 501 to the awake state after receiving a notification that the sleep control is interrupted.

<How to set the sleep period>
Next, a method for acquiring communication history information used in sleep control by the sleep control unit 507 and a method for setting a sleep period in the base station apparatus 501 will be described. Note that the parameters used in the description conform to the IEEE 802.11b standard.

  The procedure for setting the sleep period of the base station apparatus 501 is shown in FIG. First, the sleep control unit 507 refers to the communication history stored in the communication history information unit 508 as described above, and as communication history information, the total amount of traffic in a past fixed period, the payload length of data received from the terminal station device, And the information of the transmission rate used by data transmission is acquired (S202). This fixed period in the past is a period that can be arbitrarily set, and may be set to one period or more of the beacon interval. Subsequently, the sleep control unit 507 calculates an average traffic amount per unit time (for example, 1 second) using the above-described total traffic amount (S203). The smaller this average traffic amount, the longer the period during which the base station apparatus can enter the sleep state. In this case, the power saving effect is increased by setting the sleep period to be large.

  Therefore, the sleep control unit 507 compares the average traffic amount with a threshold value and determines whether or not the average traffic amount is equal to or greater than the threshold value (S204). Here, the threshold value provides a criterion for determining whether or not to limit the transmission rate in the sleep control. The reason for determining the average traffic volume in this way is that if the transmission rate is limited according to the sleep control according to the present invention when the average traffic volume is large, the throughput of the terminal station apparatus is compressed and the data transmission by the terminal station apparatus is performed. This is because the time required for the base station apparatus to shift to sleep is reduced by occupying most of the beacon interval, and the power saving effect may be impaired.

  As the above threshold value selection method, for example, it is possible to set the threshold value along the maximum physical transmission rate supported by the base station apparatus. For example, when the maximum transmission rate is 11 Mbps, the threshold value of the average traffic amount is set. Set to 5.5Mbps, which is half of 11Mbps. Note that the threshold setting method is not limited to the above, and other reference values may be applied in order to obtain the maximum power saving effect of the present invention.

  When the average traffic volume is less than the threshold (S204; NO), the transmission rate of the physical layer that is used by the terminal station apparatus in the next sleep control period according to the transmission rate of the data packet received by the base station apparatus 501 in the past To decide. Here, the lower the transmission rate, the longer the time it takes for the terminal station device to transmit a single packet, and the base station device can extend the sleep period accordingly. large.

  Therefore, a transmission rate lower than the transmission rate used for past communication is selected. For example, when the transmission rate used for past communication with a certain terminal station apparatus is 11 Mbps, the transmission rate used for new communication with this terminal station apparatus is selected to be 5.5 Mbps or 2 Mbps, which is lower than 11 Mbps. (S205). Further, when there is a communication history with a plurality of terminal station apparatuses using different transmission rates, a transmission rate equal to or lower than the lowest rate is selected. In addition, when communication does not occur in the past fixed time and there is no information regarding the transmission rate, the lowest transmission rate may be selected from a plurality of transmission rates.

  In the present embodiment, the average traffic volume per unit time (for example, 1 second) is calculated from the total traffic volume, and the average traffic volume is compared with a threshold value. The total amount of traffic during the period may be compared with the threshold value. The threshold value in this case is set to a value corresponding to the length of the “predetermined period”, unlike the threshold value compared with the average traffic volume. In the present invention, the expression “the total amount of traffic is equal to or less than the threshold value” includes both a concept of comparing the threshold value with the total traffic amount for a certain period in the past and a concept of comparing the threshold value with the average traffic amount per unit time.

  Subsequently, the sleep control unit 507 refers to the communication history information and acquires the minimum value (minimum packet length) of the data payload length received from the terminal station device during the past fixed period. Based on the minimum value of the data payload and the transmission rate set in step S205, the minimum time required to transmit the packet is calculated (S206). In addition, when communication does not occur within a certain past time and there is no information on the data payload length, for example, the packet is transmitted from the packet length of the signal for initial connection such as a probe signal according to the standard. Calculate the minimum time required to If the sleep period is set to be smaller than the minimum time required for transmitting a packet, it is possible to prevent the problem of packet continuous transmission / retransmission failure shown in FIG.

  Subsequently, the sleep control unit 507 refers to the minimum time for transmitting the packet obtained in step S206, and the upper limit value of the sleep period and the period during which the terminal station apparatus can continuously transmit (TXOP, Transmission opportunity) Is set (S207). By setting TXOP for the terminal station device, the terminal station device fragments the length of the payload of the transmission packet so that it does not exceed TXOP when transmitting the packet. Therefore, after the sleep period shown in FIG. Therefore, it is possible to avoid an unnecessary increase in the awake period. Here, considering the carrier sense time after the sleep period, the sleep period is set to a value obtained by subtracting the carrier sense time from the minimum time for transmitting a packet. TXOP is set as the minimum time necessary for transmitting a packet.

  Finally, the base station apparatus 501 describes information on the upper limit of the transmission rate and TXOP in the fields of Supported Rates and EDCA parameter set of the beacon signal or probe response signal, and changes these parameters with the beacon signal or probe response signal. (S208). Using the Supported Rates field of the beacon signal or the probe response signal, it is possible to notify the transmission rate of the physical layer that can be used for communication to all the terminal station devices.

  FIG. 6A shows the configuration of the EDCA parameter set of the IEEE 802.11 standard. This EDCA parameter set includes parameters for performing communication quality control of traffic of four types of access categories (AC): best effort, background, voice and video. FIG. 6B shows the parameter description field. In the TXOP Limit field, a parameter relating to the maximum continuous transmission time of the AC is described. In step S208 above, TXOP Limit is set for all access categories (AC).

  The base station apparatus 501 executes steps S201 to S208 described above, and performs sleep control using the calculated length of the sleep period. After receiving a beacon or probe response signal, a terminal station device (not shown) changes communication parameters according to the described transmission rate and the upper limit value of TXOP. Thereafter, the terminal station apparatus communicates with the base station apparatus 501 using the changed parameters.

  In the following, an example of a sleep period setting method using IEEE 802.11b standard parameters will be described. For example, the average traffic volume is equal to or less than the threshold, and the received data payload lengths are three types, which are 200, 800, and 1500 bytes, respectively. The transmission rate used for past communication is 2 Mbps. The lower the transmission rate, the longer it takes to transmit data. In this case, the power saving effect is enhanced by setting the sleep period longer according to the time required for the data transmission by the base station apparatus. Therefore, the base station apparatus 501 designates the transmission rate as 1 Mbps. Next, using the minimum value 200 bytes of the data payload, the time required for transmission when the transmission rate is 1 Mbps is calculated.

  Data packet transmission time (200 bytes) = PHY header + MAC header + payload (200 bytes @ 1 Mbps) = 2.08 msec = 2080 μsec

The base station apparatus 501 sets the sleep period by subtracting the time required for carrier sense from this value. For example, when the carrier sense time is set to 20 μsec for one time slot according to the 802.11b standard, one sleep period is set to 2080−20 = 2060 μsec.
With this setting, the problem that the sleep period is longer than the data packet transmission time and data cannot be detected by carrier sense as shown in FIG. 2 can be avoided.

  The time for transmitting a data packet with payload = 1500 bytes is as follows.

  Data packet transmission time (1500 bytes) = PHY header + MAC header + payload (1500 bytes @ 1 Mbps) = 12.48 msec = 12480 μsec

  Since this numerical value is larger than the set sleep period = 2060 μsec, there may occur a problem that the awake period after the sleep period increases as shown in FIG. In order to avoid such a problem, the base station apparatus 501 changes the EDCA parameter and designates the upper limit value of the time TXOP that can be continuously transmitted as the above calculation result 2.08 msec. The standard stipulates that it is necessary to divide the payload of transmission data so that the terminal station device does not exceed the specified TXOP in one transmission. Therefore, a terminal station apparatus having a 1500-byte payload divides a long payload into short fragments before transmitting data. Since the upper limit of TXOP is not exceeded at the specified transmission rate, the maximum payload length that can be transmitted in one data packet is 200 bytes. The terminal station apparatus divides and transmits the data payload according to the maximum payload length.

  By controlling the transmission rate and data packet length of the terminal station device as described above, the sleep period of the base station device 501 can be set large while avoiding the problems shown in FIGS. .

  On the other hand, when the average traffic amount is equal to or greater than the threshold (S204: YES), since communication between the base station device 501 and the terminal station device is frequently occurring, the base station device 501 transmits the transmission rate of the terminal station device or the continuous rate. By limiting the transmission time (TXOP), the communication quality in the terminal station apparatus can be degraded. Here, the base station apparatus 501 sets the sleep period to the standard sleep period so as not to greatly deteriorate the communication quality (S210). This standard sleep period can be set according to the minimum physical layer and MAC layer header length necessary for data transmission according to the 802.11 standard. For example, in the 802.11b standard parameter, it is set according to the header length of one data packet of 218 μsec. However, the setting of the standard sleep period is not limited to the above, and may be set according to another method for obtaining the maximum power saving effect of the present invention.

  The base station apparatus 501 can appropriately control the sleep period by the above method. The timing for controlling the sleep period can be performed regularly or irregularly. For example, at intervals of 30 seconds, the base station apparatus 501 grasps communication traffic with the terminal station apparatus by the above control, and sets parameters such as a sleep period, a transmission rate with the terminal station apparatus, and a TXOP upper limit value of the terminal station apparatus. It is only necessary to update and notify the terminal station device of this change. In addition, when a new terminal station device is initially connected to the base station device 501, or when the terminal station device is disconnected from the base station device 501, the number of connected terminal station devices is increased or decreased in the same manner as described above. The sleep period may be controlled.

  501: Base station apparatus, 502: Antenna, 503: Transmission / reception unit, 504 ... Communication control unit, 505 ... Buffer unit, 506 ... Interface unit, 507 ... Sleep control unit, 508 ... Communication history information unit, 509 ... Power management unit, S202-S208, S210 ... step.

Claims (5)

In a base station device that communicates with a terminal station device via a wireless channel while transitioning between an awake state and a sleep state,
Transitioning from the awake state to the sleep state without notifying the terminal station device of a transmission prohibition period, transitioning to the awake state at the end of the sleep state, performing carrier sense, and performing the carrier sense As a result, when the wireless channel is not busy, the control unit shifts again to the sleep state, and maintains the awake state when the wireless channel is busy;
Comprising information acquisition means for acquiring a total traffic amount and a minimum packet length with the terminal station device in a past fixed period,
The control means includes
When the total amount of traffic is less than or equal to a threshold, the transmission rate used when the terminal station apparatus transmits is limited, and based on the time required to transmit the minimum packet length data using the transmission rate The base station apparatus characterized in that the period of the sleep state is set.   The base station according to claim 1, wherein the control means sets a transmission rate used when the terminal station apparatus transmits to a transmission rate lower than a transmission rate of a packet received in the past. apparatus.   The said control means sets the period of the said sleep state smaller than the time required in order to transmit the data of the said minimum packet length, It is any one of Claim 1 or 2 characterized by the above-mentioned. Base station equipment.   The control means refers to a time required to transmit the data with the minimum packet length, and sets an upper limit value of a period (TXOP, Transmission opportunity) in which the terminal station apparatus can continuously transmit The base station apparatus according to any one of claims 1 to 3. In the sleep control method of the base station apparatus that performs communication with the terminal station apparatus while transitioning between the awake state and the sleep state,
Transitioning from the awake state to the sleep state without notifying the terminal station device of a transmission prohibition period, transitioning to the awake state at the end of the sleep state, performing carrier sense, and performing the carrier sense As a result, when the radio channel is not busy, the control step shifts to the sleep state again, and maintains the awake state when the radio channel is busy;
An information acquisition step of acquiring a total traffic amount and a minimum packet length with the terminal station device in a past fixed period,
In the control step,
When the total amount of traffic is less than or equal to a threshold, the transmission rate used when the terminal station apparatus transmits is limited, and based on the time required to transmit the minimum packet length data using the transmission rate The sleep control method for the base station apparatus is characterized in that the period of the sleep state is set.

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