KR20080049958A - Apparatus and method for managing sleep mode in wideband wireless access system - Google Patents

Abstract

An apparatus for managing a sleep mode in a wideband radio access system and a method thereof are provided to change a sleep period and a listening period according to the characteristic of downlink traffic, thereby preventing a subscriber terminal from being entering a wake-up mode unnecessarily to improve power saving effect. A method for managing a sleep mode comprises the following steps of: determining whether the characteristic of downlink traffic changes if the downlink traffic occurs in correspondence to a terminal(10) operating in the sleep mode(S26,S30,S35); setting the listening period of the terminal differently in correspondence to the characteristic of the changed downlink traffic when the characteristic of downlink traffic changes(S25,S29,S33,S36); and transmitting information corresponding to the set listening period to the terminal.

Description

Apparatus and method for managing sleep mode in wideband wireless access system

1 is a signal flow diagram illustrating a sleep mode management operation in a typical broadband wireless access system.

FIG. 2A shows a sleep period and a listening period of power saving class 1 belonging to the power saving class type I in one subscriber station operating in the sleep mode.

FIG. 2B illustrates a sleep period and a listening period of power saving class 2 belonging to power saving class type II in one subscriber station operating in the sleep mode.

3 is a signal flowchart illustrating a sleep mode management operation in a broadband wireless access system according to an exemplary embodiment of the present invention.

4 is a flowchart illustrating a method for managing a sleep mode of a subscriber station by a base station according to an exemplary embodiment of the present invention.

5 is a flowchart illustrating a sleep mode management method of a subscriber station according to an exemplary embodiment of the present invention.

6 is a structural diagram illustrating a sleep mode management apparatus of a broadband wireless access system according to an exemplary embodiment of the present invention.

7 is a diagram illustrating a sleep mode manager according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power saving method of a wideband radio access system. More particularly, the present invention relates to a power saving mode or a sleep mode (hereinafter, sleep) in a broadband wireless access system. The power saving method).

The broadband wireless access system refers to a next-generation communication method that further supports mobility to a short-range data communication method using a fixed access point like a conventional wireless LAN.

Various standards have been proposed for such a broadband wireless access system, and international standardization of a broadband wireless access system is actively underway in IEEE 802.16e.

The conventional wireless LAN method such as IEEE 802.11 provides a data communication method capable of wireless communication within a short distance around a fixed access point, but this does not provide mobility of a subscriber station, but only wireless rather than wired. It had a limitation in supporting data communication.

On the other hand, a broadband wireless access system such as IEEE 802.16e ensures mobility even when a subscriber station moves from a cell currently managed by a base station to another cell managed by another base station, thereby providing data communication services that are not interrupted.

Accordingly, in the broadband wireless access system described above, the battery is mainly used as a power supply means of the subscriber station. Therefore, the battery usage time of the subscriber station in the broadband wireless access system described above is a large limiting factor of the service usage time.

Therefore, in the broadband wireless access system, in order to minimize power consumption of the terminal, all devices in the terminal support a sleep mode in which there is no operation to save power when there is no up and down traffic.

Meanwhile, in a broadband wireless access system, the quality of service (hereinafter referred to as "QoS") of a wireless channel set between a terminal and a base station varies according to traffic characteristics of each wireless channel. Accordingly, the IEEE 802.16e standard introduces a power saving class for efficient sleep mode management and separately manages sleep periods for each power saving class. For example, the radio channel where data is generated every 2 seconds and the radio channel where data is generated every 3 seconds correspond to different power saving classes so that each radio channel has a listening period at different periods during sleep mode to determine whether data is generated. do.

In the IEEE 802.16e standard, power saving classes are classified into three types according to the required QoS, and the method of updating the listening period and the sleeping period according to the power saving class type differs from the data receiving operation in the listening period.

The power saving class type I is for the best effort traffic (BE), which is the characteristic of existing Internet traffic, or the non-real-time variable rate (nrt-VR), which is a non-real-time traffic whose transmission rate is changed. Parameters defining power saving class type I include the initial sleep window, the final sleep window base, the final sleep window exponent, and the listening window. ) And the start frame number for sleep window.

The power saving class type II is for real-time variable rate (rt-VR), which is VoIP or real-time traffic with varying transmission rates.The parameters that define the power saving class type II are the initial sleep window and listening window. And the first frame number of the sleep window.

Power-saving class type III delivers a management message or multicast to which UEs in sleep mode should be periodically transmitted, such as Downlink Channel Descriptor / Uplink Channel Descriptor (DCD / UCD) and Mobile Neighbor Base-station Advertisement (MOB_NBR-ADV). For the data that should be intended, the parameters that define the power saving class Type III include the last sleep window basis, the last sleep window index, and the first frame number of the sleep window.

The wireless channels in the subscriber station can be defined as several power saving classes, where all power saving classes must belong to one of the three power saving types described above.

The following describes a sleep mode management method of a subscriber station in a broadband wireless access system according to the prior art, and a sleep period management method in power saving class type I and power saving class type II.

The case of power saving class type III is a special case, and thus description of power saving class type III will be omitted below.

1 is a signal flow diagram illustrating a sleep mode management operation in a typical broadband wireless access system.

The subscriber station 10 operating in the awake mode needs to be approved by the base station 20 to enter the sleep mode. The subscriber station 10 to enter the sleep mode transmits a sleep mode request message (SLP-REQ) to the base station 20 and performs a sleep mode request (S10).

If there is a sleep mode request as described above, the base station 20 transmits a sleep mode response message (SLP-RSP) to the subscriber station 10 to approve the sleep mode (S11).

If the sleep mode approval is received from the base station 20, the subscriber station 10 enters the sleep mode that does not receive data from the sleep mode entry time (S12). When the initial sleep period elapses, the subscriber station 10 switches to the listening mode and checks whether there is data waiting to be transmitted during the sleep period from the base station 20 (S13).

Here, the sleep period refers to a section in which the subscriber station 10 operates in the sleep mode, and the listening period refers to a section in which the subscriber station 10 operates in the listening mode.

At this time, if there is no data waiting to be transmitted during the initial sleep period, the base station 20 sets a message indicating the presence of data traffic to 0 and transmits it to the subscriber station 10 (S14).

After confirming that there is no data traffic transmitted during the listening mode, the subscriber station 10 enters the sleep mode again (S15). In this case, the sleep period may be equal to or larger than the initial sleep period according to the setting, and may vary according to the above-described power saving class.

Meanwhile, if there is downlink data waiting to be transmitted to the subscriber station 10 during the second sleep period, the base station 20 may buffer the downlink data (S17). The buffered data is notified of its existence when the subscriber station 10 is operating in the listening mode (S18).

In the listening mode step S16, when the subscriber station 10 determines that there is downlink data to be transmitted to the subscriber station 10, the subscriber station 10 ends the sleep mode, enters the awake mode, and is buffered. The downlink data is received, and then data communication is performed with the base station 20.

As described above, when there is no downlink data to be transmitted to the terminal, the subscriber station maintains the sleep mode to prevent unnecessary power consumption.

On the other hand, another sleep mode management method in the broadband wireless access system, if the downlink data buffered while the terminal is operating in the sleep mode, whether or not to complete the transmission of the buffered downlink data within the listening period of the terminal. To judge. Accordingly, if it is determined that transmission is possible within the listening period, transmission of the downlink data is terminated within the listening period and the sleep mode of the subscriber station is maintained.

In order to perform the transmission of the downlink data even during the listening mode, a special appointment must be made between the base station and the subscriber station, which is used to trigger traffic of the sleep mode request message (SLP-REQ) and the sleep mode response message (SLP-RSP). This is done by setting the wake flag (traffic_triggered_wakening_flag).

2A and 2B illustrate sleep periods and listening periods of power saving class 1 belonging to power saving class type I and power saving class 2 belonging to power saving class type II in one subscriber station operating in the sleep mode. It is.

Referring to FIG. 2A, when the subscriber station maintains the sleep mode, the power saving class 1 continuously increases the sleep period by an exponential power of 2, and determines that data transmission is required in the listening mode or data transmission in the listening period is impossible. If it is ordered to exit the sleep mode immediately. On the other hand, as shown in Fig. 2B, the power saving class 2 is composed of a fixed length listening period and a sleep period irrespective of data transmission and reception within the listening period.

As described above, when managing the sleep mode, in the power saving class Type II, by maintaining a fixed length of listening period and sleep period, it is possible to continuously transmit a fixed pattern of data traffic and periodically transmitted data traffic. However, if the data traffic pattern to be transmitted to the terminal is changed or the data traffic period is changed, if the terminal enters the sleep mode, the terminal should wait until the terminal enters the wake mode or the terminal enters the next listening section. It happens. In such a case, a problem arises in that the required QoS cannot be guaranteed due to delayed transmission of data traffic.

An object of the present invention is to provide a sleep mode management method and apparatus capable of continuously maintaining a quality of data by reducing a transmission delay time of data traffic in a broadband wireless access system, particularly an IEEE 802.16e system.

In a broadband wireless access system supporting a sleep mode for power saving of a terminal according to a feature of the present invention for solving the above problems, the base station manages the sleep mode,

a) determining whether a characteristic of the downlink traffic is changed when downlink traffic corresponding to the terminal operating in the sleep mode occurs; b) when the characteristic of the downlink traffic is changed, differently setting a listening period of the terminal in response to the changed characteristic of the downlink traffic; And c) transmitting information corresponding to the set listening period to the terminal.

In addition, a method for managing a sleep mode by a terminal in a broadband wireless access system supporting a sleep mode for power saving of the terminal according to another aspect of the present invention,

a) receiving downlink data corresponding to the first listening period of fixed length; b) receiving a message including information corresponding to the second listening period from the base station; And c) receiving downlink data in response to the second listening period.

In addition, a sleep mode management apparatus for managing a sleep mode in a broadband wireless access system supporting a sleep mode to save power of the terminal according to another aspect of the present invention,

A sleep mode manager configured to output a different listening period in response to the changed characteristic when the characteristic of the downlink traffic corresponding to the terminal operating in the sleep mode is changed; A sleep mode message transmitter configured to transmit a message including the listening period received from the sleep mode manager to the terminal; And a traffic transmission manager for transmitting the downlink data to the terminal in response to the listening period received from the sleep mode manager.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

Hereinafter, a sleep mode management method of a broadband wireless access system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In particular, a description will be given of a sleep mode management method in a broadband wireless access system serving downlink traffic corresponding to power saving class type II.

In the following description, an operation of waking up from the subscriber station in the sleep mode due to generation of uplink data to be transmitted to the base station while the subscriber station is operating in the sleep mode will be omitted. Since the sleep mode operation method in such a case is already well known, a detailed description thereof will be readily understood by those skilled in the art even if the detailed description thereof is omitted.

3 is a signal flowchart illustrating a sleep mode management operation in a broadband wireless access system according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the subscriber station 10 needs the approval of the base station 20 to enter the sleep mode. The subscriber station 10 to enter the sleep mode transmits a sleep mode request message (SLP-REQ) to the base station 20 and performs a sleep mode request (S20).

When the subscriber station 10 requests the sleep mode as described above, the base station 20 transmits a sleep mode response message (SLP-RSP) to grant the sleep mode to the subscriber station 10 (S21).

If the sleep mode is approved, the subscriber station 10 enters a sleep mode state in which data is not received from the sleep mode entry time (S22).

In this case, the power saving class, which belongs to the power saving class type II, includes a sleep period of the subscriber station 10 through an initial sleep window, a listening window, and an initial frame number of the sleep window included in the sleep mode request and sleep mode response messages. Set the listening period. In addition, the terminal controls periods S23 and S27 in the sleep mode and sections S25 and S29 in the listening mode according to the sleep period and the listening period.

On the other hand, when the subscriber station 10 does not request the sleep mode, but the base station 20 induces the sleep mode entry of the subscriber station 10, in the above-described sleep mode entry process of the subscriber station 10, The sleep mode request (S20) process of the subscriber station 10 is omitted, and the subscriber station 10 may enter the sleep mode only by the sleep mode response S21 of the base station.

When the downlink traffic for the subscriber station 10 is generated while the subscriber station 10 is operating in the sleep mode, the base station 20 buffers the traffic (S24) and the corresponding downlink data for the next listening period (S25). It is determined whether the transmission can be completed in the

If it is determined that transmission of the downlink data can be completed within the listening period of the subscriber station 10, the base station 20 transmits the corresponding downlink data to the subscriber station 10 when the subscriber station 10 enters a listening mode. After transmitting (S26) and receiving the corresponding downlink data from the base station 20, the subscriber station 10 enters the sleep mode again after the listening section (S27).

At this time, the listening mode and the sleep mode of the subscriber station 10 are managed corresponding to the first listening period and the first sleeping period set in the initial sleep mode request and response process.

On the other hand, when downlink traffic with a changed pattern or period occurs, the base station 20 buffers it (S28), and in response to the changed pattern or period, a new listening period (listening period 2) and a sleeping period (second sleep period) Calculate.

Then, when the subscriber station 10 is switched to the listening mode in the sleep mode (S27) (S29), the base station 20 transmits the buffered downlink data (S30), the sleep including the changed listening period and sleep period The mode response message is transmitted to the subscriber station 10.

At this time, even if the buffered downlink data is not completed transmission within the listening period of the subscriber station, the base station 20 controls to receive the subscriber station 10 in the next listening period (S33) without switching to the wake-up mode.

Thereafter, the subscriber station 10 manages the sleep modes S32 and S36 and the listening mode S33 in response to the sleep period and the listening period calculated by receiving the sleep mode response message.

4 is a flowchart illustrating a method for managing a sleep mode of a subscriber station by a base station 20 according to an exemplary embodiment of the present invention.

As shown in FIG. 4, when downlink traffic to be transmitted to the subscriber station 10 occurs (S100), the base station 20 determines whether there is a change in the period or pattern of the downlink traffic (S110).

If the characteristic of the downlink traffic is changed, the base station 20 calculates a new listening period and a sleeping period of the subscriber station 10 in response to the change of the pattern or the period of the downlink traffic (S120).

As described above, when the subscriber station 10 switches to the listening mode, the base station 20 having calculated the new listening period and the sleep period transmits a sleep mode response message including information on the corresponding listening period and the sleep period to the subscriber station. (S130).

Thereafter, when the downlink data to be transmitted to the subscriber station 10 is generated, the base station 20 transmits the downlink data to the subscriber station 10 in response to the changed listening period and sleep period.

5 is a flowchart illustrating a sleep mode management method of the subscriber station 10 according to an exemplary embodiment of the present invention.

As shown in FIG. 5, when the subscriber station receives the sleep mode response message from the base station 20 while operating in the listening mode (S200) (S210), the subscriber station calculates the changed sleep period and listening period in the sleep mode response message. (S220). In this case, the sleep mode response message includes an initial sleep window corresponding to the sleep period and a listening window corresponding to the listening period.

Thereafter, the subscriber station 10 manages the sleep mode in response to the changed listening period and the sleeping period (S230).

Now, a sleep mode management apparatus 200 of a broadband wireless access system according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

6 is a sleep mode management apparatus 200 of the base station 20 of the broadband wireless access system according to an embodiment of the present invention.

The sleep mode management apparatus 200 may be implemented in a base station managing subscriber stations, and may utilize a component for operating a sleep mode of an existing broadband wireless access system.

The sleep mode management apparatus 200 may include a sleep mode message receiver 210, a message analyzer 220, a subscriber station identifier 230, a sleep mode manager 240, a traffic receiver 250, a memory 260, and traffic. And a transmission manager 270 and a sleep mode message transmitter 280.

The sleep mode message receiver 210 receives a sleep mode request message (SLP-REQ) from a subscriber station. The sleep mode request message (SLP-REQ) includes a subscriber station identifier and sleep mode definition parameters for setting a sleep period and a listening period of the corresponding terminal.

The message analyzer 220 analyzes the sleep request message SLP-REQ received from the sleep mode message receiver 210, extracts the subscriber station identifier and the sleep mode definition parameter, and identifies the sleep mode manager 240 and the subscriber station. It sends to the unit 230.

The subscriber station identification unit 230 analyzes the received subscriber station identifier and transmits identification information corresponding to the subscriber station to the sleep mode manager 240.

The sleep mode manager 240 receives the subscriber station identifier and sleep mode definition parameters from the message analyzer 220, sets a sleep mode entry time of the corresponding terminal, and transmits the sleep mode message transmission unit to the sleep mode message transmitter 280.

That is, when the subscriber station enters the sleep mode by the sleep mode manager 240, the sleep mode manager 240 notifies the sleep mode message transmitter 280, and the sleep mode message transmitter 280 enters the sleep mode. Control to transmit a sleep mode response message to the subscriber station. Accordingly, the sleep mode message transmitter 280 responds to the sleep mode request by transmitting a MAC message (eg, an SLP-RSP message) including a sleep mode definition parameter and a sleep mode entry time point to the subscriber station.

In addition, the sleep mode manager 240 classifies the sleep mode definition parameters for each power saving class in the terminal and stores them in the memory 260 to manage them. Subsequently, the sleep mode manager 240 may determine the sleep mode definition parameter corresponding to the listening period and the sleep period that are optimal for the pattern or period when the downlink traffic having the pattern or the generation period changed in the characteristics of the previously received downlink traffic occurs. Change them. The changed sleep mode definition parameter is included in the sleep mode response message and transmitted within the listening interval of the subscriber station 10.

In addition, the traffic transmission management unit 270 also transmits downlink data to the subscriber station 10 in response to the changed listening period and sleep period.

Meanwhile, the traffic receiver 250 receives downlink data through a network, identifies a subscriber station to which data is to be transmitted, and transmits downlink data and terminal identification information to the traffic transmission manager 270.

The traffic transmission manager 270 transmits downlink data to the terminal in response to the listening period and the sleep period. That is, the traffic transmission management unit 270 temporarily stores the downlink data in the buffer when the terminal enters the sleep period, and transmits the stored downlink data to the corresponding terminal when entering the listening period or when the terminal enters the wake mode. .

7 is a diagram illustrating a sleep mode manager 240 according to an exemplary embodiment of the present invention.

As illustrated in FIG. 7, the sleep mode manager 240 includes a determiner 241 and a period changer 242.

When the downlink traffic occurs, the determination unit 241 determines whether a characteristic such as a period, a pattern, or the like has changed in response to the downlink traffic previously generated. When it is determined that the characteristics of the downlink traffic are changed and it is necessary to change the listening period and the sleep period of the subscriber station 10 to receive the corresponding traffic, the determination unit 241 outputs a control signal to notify the change unit 242 of this. do.

The change unit 242 changes the listening period and the sleep period of the subscriber station 10 in response to the control signal output from the determination unit 241. In this case, the changer 242 may increase the amount of data generated in the downlink traffic or increase the generation period of the downlink traffic so as to set the listening period of the subscriber station 10 to be longer, thereby preventing the subscriber station 10 from waking up unnecessarily and in the sleep period. QoS can be maintained by reducing the transmission delay of downlink data. On the other hand, if the amount of downlink traffic generated data is increased or the data generation period is long, the listening period of the subscriber station 10 is set to be short and the sleep period is set to reduce unnecessary power consumption.

The sleep mode management method and apparatus can prevent the terminal from entering the wake mode unnecessarily by adaptively changing the listening period and the sleep period of the subscriber station in response to a change in the pattern or the period of the downlink traffic. It is possible to maintain service quality while maximizing consumption.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

The sleep mode management method and apparatus for managing a sleep mode of a subscriber station by changing a sleep period and a listening period according to a characteristic (pattern or period) of downlink traffic according to an embodiment of the present invention, the subscriber station does not need a wake-up mode There is an advantage to increase the power saving effect by preventing the conversion to.

In addition, by preventing the transmission delay of the downlink data that may occur due to unnecessary sleep period, there is an effect of preventing the degradation of service quality.

Claims (18)

In a method for managing a sleep mode by a base station in a broadband wireless access system supporting a sleep mode for power saving of the terminal, a) determining whether a characteristic of the downlink traffic is changed when downlink traffic corresponding to the terminal operating in the sleep mode occurs; b) when the characteristic of the downlink traffic is changed, differently setting a listening period of the terminal in response to the changed characteristic of the downlink traffic; And c) transmitting information corresponding to the set listening period to the terminal; Sleep mode management method comprising a. The method of claim 1, d) transmitting downlink data to the terminal in response to the listening period; Sleep mode management method further comprising. The method of claim 1, In step c), Sleep information management method, characterized in that the information corresponding to the listening period is included in the sleep mode response message and transmitted to the terminal. The method of claim 3, wherein B), Setting different sleep periods of the terminal in response to the changed downlink traffic characteristics; Including, The sleep mode response message includes information corresponding to the sleep period. The method of claim 1, And the downlink traffic is downlink traffic included in power saving class type II among power saving class types classified according to quality of service. The method of claim 1, In step b), If the pattern of the downstream traffic is changed, And the listening period is increased when the amount of downlink traffic data increases due to the change of the pattern, and the listening period is decreased when the amount of downlink traffic data decreases. The method of claim 1, In step b), When the generation period of the downlink traffic is changed, Sleeping period management method characterized in that to increase the listening period when the generation period is faster, and to decrease the listening period when the generation period is slowed. The method of claim 2, In step b), If the pattern of the downstream traffic is changed, The sleep mode management method characterized in that the sleep period is reduced when the amount of downlink traffic data increases due to the change of the pattern, and the sleep period is increased when the data amount of the downlink traffic decreases. The method of claim 2, In step b), When the generation period of the downlink traffic is changed, The sleep mode management method characterized in that to reduce the sleep period when the generation cycle is faster, and to increase the sleep period when the generation cycle is slow. In the broadband wireless access system that supports the sleep mode for power saving of the terminal, the terminal manages the sleep mode, a) receiving downlink data corresponding to the first listening period of fixed length; b) receiving a message including information corresponding to the second listening period from the base station; And c) receiving downlink data in response to the second listening period Sleep mode management method comprising a. The method of claim 10, Step a) is Maintaining a sleep mode corresponding to the first sleep period of a fixed length Including, In step b), The message includes information corresponding to the second sleep period, C), Maintaining a sleep mode corresponding to the second sleep period Sleep mode management method further comprising. The method of claim 11, The message is a sleep mode response message, characterized in that the sleep mode response message. A sleep mode management apparatus for managing a sleep mode in a broadband wireless access system supporting sleep mode for power saving of a terminal, A sleep mode manager configured to output a different listening period in response to the changed characteristic when the characteristic of the downlink traffic corresponding to the terminal operating in the sleep mode is changed; A sleep mode message transmitter configured to transmit a message including the listening period received from the sleep mode manager to the terminal; And A traffic transmission manager for transmitting the downlink data to the terminal in response to the listening period received from the sleep mode manager. Sleep mode management device comprising a. The method of claim 13, The sleep mode manager sets different sleep periods in response to the changed characteristics, The sleep mode message transmission unit transmits the message including the sleep period, The traffic transmission management unit sleep mode management apparatus, characterized in that for buffering the downlink traffic in response to the sleep period. The method of claim 14, Sleep mode management unit, A determination unit for determining whether a characteristic has been changed in response to previously generated downlink traffic and outputting a control message including the change information when the downlink traffic occurs; And A change unit for calculating the listening period in response to the control message received from the determination unit Sleep mode management apparatus comprising a. The method of claim 14, The sleep mode management unit, If the amount of data of the downlink traffic is greater than before, the listening period is increased, and if the amount of data of the downlink traffic is less than before, the listening period is decreased, The sleep mode management apparatus, characterized in that to reduce the sleep period when the generation period of the downlink traffic is faster than before, and to increase the sleep period when the generation period is slower than before. The method of claim 15, The sleep mode management unit, If the amount of downlink traffic data is greater than before, the sleep period is reduced; if the amount of downlink traffic data is less than before, the sleep period is increased, The sleep mode management apparatus, characterized in that to reduce the sleep period when the generation period of the downlink traffic is faster than before, and to increase the sleep period when the generation period is slower than before. The method of claim 15, The sleep mode message transmitter, And sleep mode response message as the message.

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