WO2018009020A1 - Method for managing power in wireless lan system and wireless terminal using same - Google Patents

Abstract

A method for managing power in a wireless LAN system, according to one embodiment of the present specification, comprises the steps of: a first wireless terminal receiving, from a second wireless terminal, a beacon frame including target transmission time information which indicates the transmission time of a trigger frame for an OFDMA-based random access process; the first wireless terminal transitioning from an awake state to a doze state after receiving the beacon frame; the first wireless terminal transitioning from the doze state to the awake state based on the target transmission time information; and the first wireless terminal receiving the trigger frame in the awake state.

Description

Method for power management in wireless LAN system and wireless terminal using same

The present disclosure relates to wireless communication, and more particularly, to a method for power management in a WLAN system and a wireless terminal using the same.

In next-generation WLANs, 1) enhancements to the Institute of Electronics and Electronics Engineers (IEEE) 802.11 physical physical access (PHY) and medium access control (MAC) layers in the 2.4 GHz and 5 GHz bands, and 2) spectral efficiency and area throughput. aims to improve performance in real indoor and outdoor environments, such as in environments where interference sources exist, dense heterogeneous network environments, and high user loads.

The environment mainly considered in the next-generation WLAN is a dense environment having many access points (APs) and a station (STA), and improvements in spectral efficiency and area throughput are discussed in such a dense environment. In addition, in the next generation WLAN, there is an interest in improving practical performance not only in an indoor environment but also in an outdoor environment, which is not much considered in a conventional WLAN.

Specifically, scenarios such as a wireless office, a smarthome, a stadium, and a hotspot are of interest in the next generation WLAN. On the basis of this scenario, a discussion of performance improvement of a WLAN system in an environment in which APs and STAs are concentrated is in progress.

An object of the present specification is to provide a method for power management and a wireless terminal using the same in a WLAN system having improved performance.

The present specification relates to a method for power management in a WLAN system. In a method for power management in a WLAN system according to an embodiment of the present invention, a target transmission point in which a first wireless terminal indicates a transmission point of a trigger frame for an orthogonal frequency division multiple access (OFDMA) based random access procedure Receiving a beacon frame including Transmission Time) information from the second wireless terminal; Switching, from the awake state to the sleep state, after reception of the beacon frame by the first wireless terminal; Switching, by the first wireless terminal, from the sleep state to the awake state based on the target transmission time information; And receiving, by the first wireless terminal, a trigger frame in an awake state.

According to an embodiment of the present disclosure, a method for power management in a WLAN system having improved performance and a wireless terminal using the same are provided.

1 is a conceptual diagram illustrating a structure of a WLAN system.

2 is a diagram illustrating an example of a PPDU used in the IEEE standard.

3 is a diagram illustrating an example of a HE PPDU.

4 is a diagram illustrating an arrangement of resource units used on a 20 MHz band.

5 is a diagram illustrating an arrangement of resource units used on a 40 MHz band.

6 is a diagram illustrating an arrangement of resource units used on an 80 MHz band.

7 is a diagram illustrating another example of the HE-PPDU.

8 is a block diagram illustrating an example of HE-SIG-B according to the present embodiment.

9 shows an example of a trigger frame in this embodiment.

10 shows an example of a common information field in this embodiment.

11 shows an example of a subfield included in an individual user information field in this embodiment.

12 is a diagram for a method for power management in a wireless LAN system according to the present embodiment.

FIG. 13 illustrates an example of an element including information for OFDMA-based random access according to the present embodiment.

14 is a diagram for a method for power management in a WLAN system according to another embodiment.

15 illustrates an example of an element including information for OFDMA-based random access according to another embodiment.

16 is a diagram for a method for power management in a WLAN system according to another embodiment.

FIG. 17 is a diagram illustrating an example of an element including information for OFDMA-based random access according to another embodiment.

18 is a diagram for a method for power management in a WLAN system according to an extension of another embodiment.

19 illustrates an example of an element including information for OFDMA-based random access according to an extension of another embodiment.

20 is a flowchart illustrating a method for power management in a WLAN system according to an exemplary embodiment.

21 is a block diagram illustrating a wireless terminal to which an embodiment of the present specification can be applied.

The above-described features and the following detailed description are all exemplary for ease of description and understanding of the present specification. That is, the present specification is not limited to this embodiment and may be embodied in other forms. The following embodiments are merely examples to fully disclose the present specification, and are descriptions to convey the present specification to those skilled in the art. Thus, where there are several methods for implementing the components of the present disclosure, it is necessary to clarify that any of these methods may be implemented in any of the specific or equivalent thereof.

In the present specification, when there is a statement that a configuration includes specific elements, or when a process includes specific steps, it means that other elements or other steps may be further included. That is, the terms used in the present specification are only for describing specific embodiments and are not intended to limit the concept of the present specification. Furthermore, the described examples to aid the understanding of the invention also include their complementary embodiments.

The terminology used herein has the meaning commonly understood by one of ordinary skill in the art to which this specification belongs. Terms commonly used should be interpreted in a consistent sense in the context of the present specification. In addition, terms used in the present specification should not be interpreted in an idealistic or formal sense unless the meaning is clearly defined. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

1 is a conceptual diagram illustrating a structure of a WLAN system. FIG. 1A shows the structure of an infrastructure network of the Institute of Electrical and Electronic Engineers (IEEE) 802.11.

Referring to FIG. 1A, the WLAN system 10 of FIG. 1A may include at least one basic service set (hereinafter, referred to as 'BSS', 100, 105). The BSS is a set of access points (APs) and stations (STAs) that can successfully synchronize and communicate with each other, and is not a concept indicating a specific area.

For example, the first BSS 100 may include a first AP 110 and one first STA 100-1 coupled with the first AP 110. The second BSS 105 may include a second AP 130 and one or more STAs 105-1 and 105-2 coupled with the second AP 130.

The infrastructure BSS (100, 105) may include at least one STA, AP (110, 130) providing a distribution service (Distribution Service) and a distribution system (DS, 120) connecting a plurality of APs. have.

The distributed system 110 may connect the plurality of BSSs 100 and 105 to implement an extended service set 140 which is an extended service set. The ESS 140 may be used as a term indicating one network to which at least one AP 110 or 130 is connected through the distributed system 120. At least one AP included in one ESS 140 may have the same service set identification (hereinafter, referred to as SSID).

The portal 150 may serve as a bridge for connecting the WLAN network (IEEE 802.11) with another network (for example, 802.X).

In a WLAN having a structure as shown in FIG. 1A, a network between APs 110 and 130 and a network between APs 110 and 130 and STAs 100-1, 105-1, and 105-2 may be implemented. Can be.

1B is a conceptual diagram illustrating an independent BSS. Referring to FIG. 1B, the WLAN system 15 of FIG. 1B performs communication by setting a network between STAs without the APs 110 and 130, unlike FIG. 1A. It may be possible to. A network that performs communication by establishing a network even between STAs without the APs 110 and 130 is defined as an ad-hoc network or an independent basic service set (BSS).

Referring to FIG. 1B, the IBSS 15 is a BSS operating in an ad-hoc mode. Since IBSS does not contain an AP, there is no centralized management entity. Thus, in the IBSS 15, the STAs 150-1, 150-2, 150-3, 155-4, and 155-5 are managed in a distributed manner.

All STAs 150-1, 150-2, 150-3, 155-4, and 155-5 of the IBSS may be mobile STAs, and access to a distributed system is not allowed. All STAs of the IBSS form a self-contained network.

The STA referred to herein includes a medium access control (MAC) conforming to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface to a wireless medium. As any functional medium, it can broadly be used to mean both an AP and a non-AP Non-AP Station (STA).

The STA referred to herein includes a mobile terminal, a wireless device, a wireless transmit / receive unit (WTRU), a user equipment (UE), and a mobile station (MS). It may also be called various names such as a mobile subscriber unit or simply a user.

2 is a diagram illustrating an example of a PPDU used in the IEEE standard.

As shown, various types of PHY protocol data units (PPDUs) have been used in the IEEE a / g / n / ac standard. Specifically, the LTF and STF fields included training signals, the SIG-A and SIG-B included control information for the receiving station, and the data fields included user data corresponding to the PSDU.

This embodiment proposes an improved technique for the signal (or control information field) used for the data field of the PPDU. The signal proposed in this embodiment may be applied on a high efficiency PPDU (HE PPDU) according to the IEEE 802.11ax standard. That is, the signals to be improved in the present embodiment may be HE-SIG-A and / or HE-SIG-B included in the HE PPDU. Each of HE-SIG-A and HE-SIG-B may also be represented as SIG-A or SIG-B. However, the improved signal proposed by this embodiment is not necessarily limited to the HE-SIG-A and / or HE-SIG-B standard, and controls / control of various names including control information in a wireless communication system for transmitting user data. Applicable to data fields.

3 is a diagram illustrating an example of a HE PPDU.

The control information field proposed in this embodiment may be HE-SIG-B included in the HE PPDU as shown in FIG. 3. The HE PPDU according to FIG. 3 is an example of a PPDU for multiple users. The HE-SIG-B may be included only for the multi-user, and the HE-SIG-B may be omitted in the PPDU for the single user.

As shown, a HE-PPDU for a multiple user (MU) includes a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal (L-SIG), High efficiency-signal A (HE-SIG-A), high efficiency-signal-B (HE-SIG-B), high efficiency-short training field (HE-STF), high efficiency-long training field (HE-LTF) It may include a data field (or MAC payload) and a PE (Packet Extension) field. Each field may be transmitted during the time period shown (ie, 4 or 8 ms, etc.). Detailed description of each field of FIG. 3 will be described later.

4 is a diagram illustrating an arrangement of resource units (RUs) used on a 20 MHz band. As shown in FIG. 4, resource units (RUs) corresponding to different numbers of tones (ie, subcarriers) may be used to configure some fields of the HE-PPDU. For example, resources may be allocated in units of RUs shown for HE-STF, HE-LTF, and data fields.

As shown at the top of FIG. 4, 26-units (ie, units corresponding to 26 tones) may be arranged. Six tones may be used as the guard band in the leftmost band of the 20 MHz band, and five tones may be used as the guard band in the rightmost band of the 20 MHz band. In addition, seven DC tones are inserted into the center band, that is, the DC band, and 26-units corresponding to each of the 13 tones may exist to the left and right of the DC band. In addition, other bands may be allocated 26-unit, 52-unit, 106-unit. Each unit can be assigned for a receiving station, i. E. A user.

On the other hand, the RU arrangement of FIG. 4 is utilized not only for the situation for a plurality of users (MU), but also for the situation for a single user (SU), in which case one 242-unit is shown as shown at the bottom of FIG. It is possible to use and in this case three DC tones can be inserted.

In the example of FIG. 4, various sizes of RUs have been proposed, that is, 26-RU, 52-RU, 106-RU, 242-RU, and the like. Since the specific sizes of these RUs can be expanded or increased, the present embodiment Is not limited to the specific size of each RU (ie, the number of corresponding tones).

5 is a diagram illustrating an arrangement of resource units (RUs) used on a 40 MHz band.

Just as RUs of various sizes are used in the example of FIG. 4, the example of FIG. 5 may also use 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the like. In addition, five DC tones can be inserted at the center frequency, 12 tones are used as the guard band in the leftmost band of the 40 MHz band, and 11 tones are in the rightmost band of the 40 MHz band. This guard band can be used.

Also, as shown, the 484-RU may be used when used for a single user. Meanwhile, the specific number of RUs may be changed as in the example of FIG. 4.

6 is a diagram illustrating an arrangement of resource units (RUs) used on an 80 MHz band.

Just as RUs of various sizes are used in the example of FIGS. 4 and 5, the example of FIG. 6 may also use 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, 996-RU, and the like. have. In addition, seven or five DC tones can be inserted at the center frequency, and 12 tones are used as the guard band in the leftmost band of the 80 MHz band, and in the rightmost band of the 80 MHz band. Eleven tones can be used as guard bands. Also available is a 26-RU with 13 tones each located to the left and right of the DC band.

Also, as shown, 996-RU may be used when used for a single user. Meanwhile, the specific number of RUs may be changed as in the example of FIGS. 4 and 5.

7 is a diagram illustrating another example of the HE-PPDU.

7 is another example illustrating the HE-PPDU block of FIG. 3 in terms of frequency.

The illustrated L-STF 700 may include a short training orthogonal frequency division multiplexing symbol. The L-STF 700 may be used for frame detection, automatic gain control (AGC), diversity detection, and coarse frequency / time synchronization.

The L-LTF 710 may include a long training orthogonal frequency division multiplexing symbol. The L-LTF 710 may be used for fine frequency / time synchronization and channel prediction.

L-SIG 720 may be used to transmit control information. The L-SIG 720 may include information about a data rate and a data length. In addition, the L-SIG 720 may be repeatedly transmitted. That is, the L-SIG 720 may be configured in a repeating format (for example, may be referred to as an R-LSIG).

The HE-SIG-A 730 may include control information common to the receiving station.

Specifically, the HE-SIG-A 730 may include 1) a DL / UL indicator, 2) a BSS color field which is an identifier of a BSS, 3) a field indicating a remaining time of a current TXOP interval, 4) 20, Bandwidth field indicating 40, 80, 160, 80 + 80 Mhz, 5) Field indicating MCS scheme applied to HE-SIG-B, 6) HE-SIB-B is dual subcarrier modulation for MCS ( field indicating whether it is modulated by dual subcarrier modulation), 7) field indicating the number of symbols used for HE-SIG-B, and 8) indicating whether HE-SIG-B is generated over the entire band. Field, 9) field indicating the number of symbols of the HE-LTF, 10) field indicating the length and CP length of the HE-LTF, 11) field indicating whether additional OFDM symbols exist for LDPC coding, 12) It may include information on a field indicating control information on the PE (Packet Extension), 13) a field indicating information on the CRC field of the HE-SIG-A, and the like. The. Specific fields of the HE-SIG-A may be added or omitted. In addition, some fields may be added or omitted in other environments where the HE-SIG-A is not a multi-user (MU) environment.

The HE-SIG-B 740 may be included only when it is a PPDU for a multi-user (MU) as described above. Basically, the HE-SIG-A 730 or the HE-SIG-B 740 may include resource allocation information (or virtual resource allocation information) for at least one receiving STA. The HE-SIG-B 740 is described in more detail with reference to FIG. 8 described below.

The previous field of the HE-SIG-B 740 on the MU PPDU may be transmitted in duplicated form. In the case of the HE-SIG-B 740, the HE-SIG-B 740 transmitted in a part of the frequency band (for example, the fourth frequency band) is the frequency band (ie, the fourth frequency band) of the Control information for a data field and a data field of another frequency band (eg, the second frequency band) except for the corresponding frequency band may be included. In addition, the HE-SIG-B 740 of a specific frequency band (eg, the second frequency band) duplicates the HE-SIG-B 740 of another frequency band (eg, the fourth frequency band). It can be one format. Alternatively, the HE-SIG-B 740 may be transmitted in an encoded form on all transmission resources. The field after the HE-SIG-B 740 may include individual information for each receiving STA that receives the PPDU.

The HE-STF 750 may be used to improve automatic gain control estimation in a multiple input multiple output (MIMO) environment or an orthogonal frequency-division multiple access (OFDMA) environment.

The HE-LTF 760 may be used to estimate a channel in a MIMO environment or an OFDMA environment.

The size of the FFT / IFFT applied to the field after the HE-STF 750 and the HE-STF 750 may be different from the size of the FFT / IFFT applied to the field before the HE-STF 750. For example, the size of the FFT / IFFT applied to the fields after the HE-STF 750 and the HE-STF 750 may be four times larger than the size of the IFFT applied to the field before the HE-STF 750. .

For example, at least one of L-STF 700, L-LTF 710, L-SIG 720, HE-SIG-A 730, HE-SIG-B 740 on the PPDU of FIG. When a field of s is called a first field, at least one of the data field 770, the HE-STF 750, and the HE-LTF 760 may be referred to as a second field. The first field may include a field related to a legacy system, and the second field may include a field related to a HE system. In this case, the FFT (Fast Fourier Transform) size / IFFT (Inverse Fast Fourier Transform) size is N times the FFT / IFFT size used in the existing WLAN system (N is a natural number, for example, N = 1, 2, 4) can be defined. That is, an FFT / IFFT of N (= 4) times size may be applied to the second field of the HE PPDU compared to the first field of the HE PPDU. For example, 256 FFT / IFFT is applied for a bandwidth of 20 MHz, 512 FFT / IFFT is applied for a bandwidth of 40 MHz, 1024 FFT / IFFT is applied for a bandwidth of 80 MHz, and 2048 FFT for a bandwidth of 160 MHz continuous or discontinuous 160 MHz. / IFFT can be applied.

In other words, the subcarrier spacing / subcarrier spacing is 1 / N times the size of the subcarrier space used in the conventional WLAN system (N is a natural number, for example, 78.125 kHz when N = 4). Can be. That is, spacing may be applied to a subcarrier having a size of 312.5 kHz, which is a conventional subcarrier spacing, and space may be applied to a subcarrier having a size of 78.125 kHz, as a second field of the HE PPDU.

Alternatively, the IDFT / DFT period applied to each symbol of the first field may be expressed as N (= 4) times shorter than the IDFT / DFT period applied to each data symbol of the second field. . That is, the IDFT / DFT length applied for each symbol in the first field of the HE PPDU is 3.2 μs, and the IDFT / DFT length applied for each symbol in the second field of the HE PPDU is 3.2 μs * 4 (= 12.8 μs Can be expressed as The length of an OFDM symbol may be a value obtained by adding a length of a guard interval (GI) to an IDFT / DFT length. The length of the GI can be various values such as 0.4 μs, 0.8 μs, 1.6 μs, 2.4 μs, 3.2 μs.

For convenience of description, although the frequency band used by the first field and the frequency band used by the second field are represented in FIG. 7, they may not exactly coincide with each other. For example, the main band of the first field (L-STF, L-LTF, L-SIG, HE-SIG-A, HE-SIG-B) corresponding to the first frequency band is the second field (HE-STF). , HE-LTF, Data) is the same as the main band, but in each frequency band, the interface may be inconsistent. 4 to 6, since a plurality of null subcarriers, DC tones, guard tones, etc. are inserted in the process of arranging the RU, it may be difficult to accurately match the interface.

The user, that is, the receiving station, may receive the HE-SIG-A 730 and may be instructed to receive the downlink PPDU based on the HE-SIG-A 730. In this case, the STA may perform decoding based on the changed FFT size from the field after the HE-STF 750 and the HE-STF 750. On the contrary, if the STA is not instructed to receive the downlink PPDU based on the HE-SIG-A 730, the STA may stop decoding and configure a network allocation vector (NAV). The cyclic prefix (CP) of the HE-STF 750 may have a larger size than the CP of another field, and during this CP period, the STA may perform decoding on the downlink PPDU by changing the FFT size.

Hereinafter, in the present embodiment, data (or frame) transmitted from the AP to the STA is called downlink data (or downlink frame), and data (or frame) transmitted from the STA to the AP is called uplink data (or uplink frame). Can be expressed in terms. In addition, the transmission from the AP to the STA may be expressed in terms of downlink transmission, and the transmission from the STA to the AP may be expressed as uplink transmission.

In addition, each of the PHY protocol data units (PPDUs), frames, and data transmitted through downlink transmission may be expressed in terms of a downlink PPDU, a downlink frame, and downlink data. The PPDU may be a data unit including a PPDU header and a physical layer service data unit (PSDU) (or MAC protocol data unit (MPDU)). The PPDU header may include a PHY header and a PHY preamble, and the PSDU (or MPDU) may be a data unit including a frame (or an information unit of a MAC layer) or indicating a frame. The PHY header may be referred to as a physical layer convergence protocol (PLCP) header in another term, and the PHY preamble may be expressed as a PLCP preamble in another term.

In addition, each of the PPDUs, frames, and data transmitted through uplink transmission may be represented by the term uplink PPDU, uplink frame, and uplink data.

In a WLAN system to which the present embodiment is applied, the entire bandwidth may be used for downlink transmission to one STA and uplink transmission of one STA based on single (or single) -orthogonal frequency division multiplexing (SUDM) transmission. Do. In addition, in the WLAN system to which the present embodiment is applied, the AP may perform downlink (DL) multi-user (MU) transmission based on MU MIMO (multiple input multiple output), and such transmission is DL MU MIMO transmission. It can be expressed as.

In addition, in the WLAN system according to the present embodiment, orthogonal frequency division multiple access (OFDMA) based transmission method is preferably supported for uplink transmission and downlink transmission. That is, uplink / downlink communication may be performed by allocating data units (eg, RUs) corresponding to different frequency resources to the user. Specifically, in the WLAN system according to the present embodiment, the AP performs OFDMA. DL MU transmission may be performed based on the above, and such transmission may be expressed in terms of DL MU OFDMA transmission. When DL MU OFDMA transmission is performed, the AP may transmit downlink data (or downlink frame, downlink PPDU) to each of the plurality of STAs through the plurality of frequency resources on the overlapped time resources. The plurality of frequency resources may be a plurality of subbands (or subchannels) or a plurality of resource units (RUs). DL MU OFDMA transmission can be used with DL MU MIMO transmission. For example, DL MU MIMO transmission based on a plurality of space-time streams (or spatial streams) is performed on a specific subband (or subchannel) allocated for DL MU OFDMA transmission. Can be.

In addition, in the WLAN system according to the present embodiment, UL MU transmission (uplink multi-user transmission) may be supported that a plurality of STAs transmit data to the AP on the same time resource. Uplink transmission on the overlapped time resource by each of the plurality of STAs may be performed in the frequency domain or the spatial domain.

When uplink transmission by each of the plurality of STAs is performed in the frequency domain, different frequency resources may be allocated as uplink transmission resources for each of the plurality of STAs based on OFDMA. The different frequency resources may be different subbands (or subchannels) or different resource units (RUs). Each of the plurality of STAs may transmit uplink data to the AP through different allocated frequency resources. The transmission method through these different frequency resources may be represented by the term UL MU OFDMA transmission method.

When uplink transmission by each of the plurality of STAs is performed in the spatial domain, different space-time streams (or spatial streams) are allocated to each of the plurality of STAs, and each of the plurality of STAs transmits uplink data through different space-time streams. Can transmit to the AP. The transmission method through these different spatial streams may be represented by the term UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be performed together. For example, UL MU MIMO transmission based on a plurality of space-time streams (or spatial streams) may be performed on a specific subband (or subchannel) allocated for UL MU OFDMA transmission.

In a conventional WLAN system that did not support MU OFDMA transmission, a multi-channel allocation method was used to allocate a wider bandwidth (for example, a bandwidth exceeding 20 MHz) to one UE. The multi-channel may include a plurality of 20 MHz channels when one channel unit is 20 MHz. In the multi-channel allocation method, a primary channel rule is used to allocate a wide bandwidth to the terminal. If the primary channel rule is used, there is a constraint for allocating a wide bandwidth to the terminal. Specifically, according to the primary channel rule, when a secondary channel adjacent to the primary channel is used in an overlapped BSS (OBSS) and 'busy', the STA may use the remaining channels except the primary channel. Can't. Therefore, the STA can transmit the frame only through the primary channel, thereby being limited to the transmission of the frame through the multi-channel. That is, the primary channel rule used for multi-channel allocation in the existing WLAN system may be a big limitation in obtaining high throughput by operating a wide bandwidth in the current WLAN environment where there are not many OBSS.

In the present embodiment to solve this problem is disclosed a WLAN system supporting the OFDMA technology. That is, the above-described OFDMA technique is applicable to at least one of downlink and uplink. In addition, the above-described MU-MIMO technique may be additionally applied to at least one of downlink and uplink. When OFDMA technology is used, a plurality of terminals may be used simultaneously instead of one terminal without using a primary channel rule. Therefore, wide bandwidth operation is possible, and the efficiency of the operation of radio resources can be improved.

As described above, when uplink transmission by each of a plurality of STAs (eg, non-AP STAs) is performed in the frequency domain, the AP has different frequency resources for each of the plurality of STAs based on OFDMA. It may be allocated as a link transmission resource. In addition, as described above, different frequency resources may be different subbands (or subchannels) or different resource units (RUs).

Different frequency resources for each of the plurality of STAs may be indicated through a trigger frame.

8 is a block diagram illustrating an example of HE-SIG-B.

As shown, the HE-SIG-B field includes a common field at the beginning, and the common field can be encoded separately from the following field. That is, as shown in FIG. 8, the HE-SIG-B field may include a common field including common control information and a user-specific field including user-specific control information. In this case, the common field may include a corresponding CRC field and may be coded into one BCC block. Subsequent user-specific fields may be coded into one BCC block, including a "user-specific field" for two users (2 users), a CRC field corresponding thereto, and the like, as shown.

9 shows an example of a trigger frame. The trigger frame of FIG. 9 allocates resources for uplink multiple-user transmission and can be transmitted from the AP. The trigger frame may consist of a MAC frame and may be included in a PPDU. For example, it may be transmitted through the PPDU shown in FIG. 3, through the legacy PPDU shown in FIG. 2, or through a PPDU specifically designed for the trigger frame. If transmitted through the PPDU of FIG. 3, the trigger frame may be included in the illustrated data field.

Each field shown in FIG. 9 may be partially omitted, and another field may be added. In addition, the length of each field may be varied as shown.

The frame control field 910 of FIG. 9 includes information about the version of the MAC protocol and other additional control information, and the duration field 920 includes time information or terminal for setting the NAV described below. Information about an identifier of (eg, AID) may be included.

In addition, the RA field 930 includes address information of the receiving STA of the corresponding trigger frame and may be omitted as necessary. The TA field 940 includes address information of an STA (for example, an AP) that transmits a corresponding trigger frame, and the common information field 950 is common to be applied to a receiving STA that receives the corresponding trigger frame. Contains control information

It is preferable to include per user information fields 960 # 1 to 960 # N corresponding to the number of receiving STAs receiving the trigger frame of FIG. 9. The individual user information field may be referred to as a "RU assignment field."

In addition, the trigger frame of FIG. 9 may include a padding field 970 and a frame check sequence field 980.

Each of the per user information fields 960 # 1 to 960 # N shown in FIG. 9 preferably includes a plurality of subfields.

10 shows an example of a common information field. Some of the subfields of FIG. 10 may be omitted, and other subfields may be added. In addition, the length of each illustrated subfield may be modified.

The illustrated length field 1010 has the same value as the length field of the L-SIG field of the uplink PPDU transmitted corresponding to the trigger frame, and the length field of the L-SIG field of the uplink PPDU indicates the length of the uplink PPDU. As a result, the length field 1010 of the trigger frame may be used to indicate the length of the corresponding uplink PPDU.

In addition, the cascade indicator field 1020 indicates whether a cascade operation is performed. The cascade operation means that downlink MU transmission and uplink MU transmission are performed together in the same TXOP. That is, after downlink MU transmission is performed, it means that uplink MU transmission is performed after a predetermined time (eg, SIFS). During the casecade operation, only one transmitting device (eg, AP) for downlink communication may exist, and a plurality of transmitting devices (eg, non-AP) for uplink communication may exist.

The CS request field 1030 indicates whether the state of the radio medium, the NAV, or the like should be considered in a situation in which the receiving apparatus receiving the trigger frame transmits the corresponding uplink PPDU.

The HE-SIG-A information field 1040 may include information for controlling the content of the SIG-A field (ie, the HE-SIG-A field) of the uplink PPDU transmitted in response to the corresponding trigger frame.

The CP and LTF type field 1050 may include information about the length of the LTF and the CP length of the uplink PPDU transmitted in response to the corresponding trigger frame. The trigger type field 1060 may indicate the purpose for which the corresponding trigger frame is used, for example, normal triggering, triggering for beamforming, a request for Block ACK / NACK, and the like.

11 illustrates an example of subfields included in an individual user information field. Some of the subfields of FIG. 11 may be omitted, and other subfields may be added. In addition, the length of each illustrated subfield may be modified.

The user identifier field 1110 of FIG. 11 indicates an identifier of an STA (ie, a receiving STA) to which per user information corresponds. An example of the identifier may be all or part of an AID. have.

In addition, the RU Allocation field 1120 may be included. That is, when the receiving STA identified by the user identifier field 1110 transmits an uplink PPDU in response to the trigger frame of FIG. 9, the corresponding uplink PPDU through the RU indicated by the RU Allocation field 1120. Send. In this case, the RU indicated by the RU Allocation field 1120 preferably indicates the RUs shown in FIGS. 4, 5, and 6.

The subfield of FIG. 11 may include a coding type field 1130. The coding type field 1130 may indicate a coding type of an uplink PPDU transmitted in response to the trigger frame of FIG. 9. For example, when BCC coding is applied to the uplink PPDU, the coding type field 1130 is set to '1', and when LDPC coding is applied, the coding type field 1130 is set to '0'. Can be.

In addition, the subfield of FIG. 11 may include an MCS field 1140. The MCS field 1140 may indicate an MCS scheme applied to an uplink PPDU transmitted in response to the trigger frame of FIG. 9. For example, when BCC coding is applied to the uplink PPDU, the coding type field 1130 is set to '1', and when LDPC coding is applied, the coding type field 1130 is set to '0'. Can be.

12 is a diagram for a method for power management in a wireless LAN system according to the present embodiment.

1 to 12, the horizontal axis of the AP 1200 may represent a time t of the AP 1200. The vertical axis of the AP 1200 may be associated with the presence of a frame transmitted by the AP 1200.

The horizontal axis of the first STA 1210 may represent the time t1 of the first STA 1210. The vertical axis of the first STA 1210 may be associated with the presence of a frame transmitted by the first STA 1210.

 The horizontal axis of the second STA 1220 may represent the time t2 of the second STA 1220. The vertical axis of the second STA 1220 may be associated with the presence of a frame transmitted by the second STA 1220.

The first STA 1210 and the second STA 1220 according to the present embodiment may be terminals that operate in a power save mode. Accordingly, the first STA 1210 and the second STA 1220 may switch from the active state to the doze state or from the sleep state to the active state for power management of the terminal.

For example, the active state may be a state in which a frame may be transmitted or received by the terminal. The sleep state may be a state in which transmission or reception of a frame by the terminal is impossible.

A plurality of OFDMA backoff counters (hereinafter, referred to as 'OBO counters') corresponding to a plurality of STAs performing an orthogonal frequency-division multiple access (OFDMA) based random access procedure may be individually defined for each STA.

For example, a first OBO counter for the first STA 1210 may be defined. In addition, a second OBO counter for the second STA 1220 may be defined.

The AP 1200 may transmit a first beacon frame BF1 including information on an OFDMA Contention Window (“OCW”) indicating a range of initial values to be set in each OBO counter.

In the first period T1 to T2, the first and second STAs 1210 and 1220 may individually set initial values to the first and second OBO counters according to the received information about the OCW. Information on the information about the OCW according to the present embodiment will be described in more detail with reference to the accompanying drawings.

For example, the information on the OCW included in the first beacon frame BF1 may include an OCWmin value. The first STA 1210 performing the OFDMA-based random access procedure may set an initial value for the first OBO counter to a randomly selected value in the interval [0, OCWmin].

Similarly, the second STA 1220 performing the OFDMA-based random access procedure may set an initial value (OBI2) for the second OBO counter to a randomly selected value in the interval [0, OCWmin].

Specifically, it is assumed that information (ie, OCWmin) about the OCW included in the first beacon frame BF1 is '7'.

The first STA 1210 may set an integer value v1 arbitrarily selected in [0, CWmin] as a first initial value (OBO1) for the first OBO counter. For example, the first STA 1210 may set '1' selected in [0, 7] as a first initial value (OBO1) for the first OBO counter.

The second STA 1220 may set the integer value v2 arbitrarily selected in [0, CWmin] as a second initial value (OBO2) for the second OBO counter. For example, the second STA 1220 may set '3' selected in [0, 7] as a second initial value (OBO2) for the second OBO counter.

According to the conventional operation, the STA that receives the beacon frame including the parameter information for the OFDMA based random access procedure (for example, the information about the OCW) is a trigger frame for the OFDMA based random access procedure (hereinafter, referred to as a random trigger frame, The awake state is maintained in an unnecessary section for the reception of the TFR).

The AP 1200 according to the present embodiment may transmit the first beacon frame BF1 further including target transmission time (TTT) information indicating a transmission time of the random trigger frame (TFR). Can be. The first and second STAs 1210 and 1220 receiving the target transmission time (TTT) information may switch from the awake state to the sleep state.

In the second period T2 to T3, the first and second STAs 1210 and 1220 may maintain a sleep state.

When entering the third section T3 to T4, the first and second STAs 1210 and 1220 may switch from the sleep state to the awake state based on the target transmission time point (TTT) information.

For example, the target transmission time point (TTT) information may be set to a value corresponding to the third time point T3. Alternatively, the target transmission time point (TTT) information may be set to a value corresponding to the second period (T2 ~ T3).

In the third period T3 to T4, the AP 1200 may transmit a random trigger frame (TFR). The first and second STAs 1210 and 1220 may maintain an awake state for the third period T3 to T4.

The random trigger frame (TFR) may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1200. For example, the allocation information may indicate two resource units RU1 and RU2. The random trigger frame TFR may be a frame having the frame format of FIGS. 9 to 11 described above.

A first association identifier (hereinafter, referred to as “1” in FIG. 11) included in the first user identifier field (eg, 1110 in FIG. 11) of the first user-specific field (eg, 960 # 1 in FIG. 9) of the random trigger frame TFR. AID ') may be set to a value corresponding to' 0 '. In addition, the first RU allocation field (eg, 1120 of FIG. 11) of the first user-specific field may be set to indicate the first resource unit RU1.

The second combined identifier (AID) included in the second user identifier field (eg, 1110 of FIG. 11) of the second user-specific field of the random trigger frame (TFR) (eg, 960 # 2 of FIG. 9) is' 0. It can be set to a value corresponding to '. In addition, the second RU allocation field (eg, 1120 of FIG. 11) of the second user-specific field may be set to indicate the second resource unit RU2.

Each STA 1210 and 1220 that receives the random trigger frame TFR may determine the first and second resource units RU1 and RU2 as resource units allocated for the OFDMA based random access procedure.

The first STA 1210 may perform an individual first countdown operation. The first STA 1210 may decrease the first initial value v1 set in the first OBO counter by the number '2' of the first and second resource units RU1 and RU2. According to the foregoing assumption, the first count value v1 'updated to the first OBO count becomes' 0'. Accordingly, the first countdown operation may be completed.

The second STA 1220 may perform an individual second countdown operation. The second STA 1220 may update the value v2 'of the second OBO counter to' 1 'by decreasing the second initial value v2 set in the second OBO counter.

After completing the first countdown operation, the first STA 1210 may select one of the RU sets RU1 and RU2 allocated to the random trigger frame TFR as a random resource unit. For example, the first STA 1210 may select the second resource unit RU2 as a random resource unit for transmitting an uplink frame.

In the fourth period T4 to T5, the first STA 1210 uses a random resource unit RU2 after a short inter-frame space (SIFS) from a reception time of the random trigger frame (TFR), and uses an uplink frame (UL). Frame) may be transmitted to the AP 1200. The first STA 1210 may maintain an awake state for the fourth period T4 to T5.

When entering the fourth section T4 to T5, the second STA 1220 may switch from the awake state to the sleep state. The second STA 1220 may maintain a sleep state for the fourth period T4 to T5.

The AP 1200 may transmit an ACK frame for notifying successful reception of an uplink frame (UL frame) after SIFS from a time point of receiving an uplink frame (UL frame).

In the fifth period T5 to T6, the AP 1200 may transmit the second beacon frame BF2. Hereinafter, the time intervals T1 to T5 between the first beacon frame BF1 and the second beacon frame BF2 may be referred to as beacon intervals. For example, the beacon interval may be 100 ms. The operation after the second beacon frame BF2 may be understood through the contents mentioned in the above-described first sections T1 to T2 to four sections T4 to T5.

In the example of FIG. 12, an operation for power management between an AP and two STAs will be described, but the present disclosure is not limited thereto. That is, it will be understood that the present specification may be extended to be applied between an AP and two or more STAs.

In addition, in the example of FIG. 12, two resource units allocated for the OFDMA random access procedure are illustrated, but the present specification is not limited thereto. That is, it will be understood that the present specification may also be extended by applying a random trigger frame including two or more resource units.

FIG. 13 illustrates an example of an element including information for OFDMA-based random access according to the present embodiment. 12 and 13, an element including information for the present OFDMA-based random access may be referred to as a random access information (RAI) element 1300.

The RAI element 1300 may be included in a beacon frame periodically transmitted by the AP. The RAI element 1300 may include a plurality of fields 1310, 1320, 1330, 1340, 1350.

The element ID field 1310 may be set to a value for indicating the RAI element 1300 among at least one element information included in the beacon frame. For example, one octet may be allocated for the element ID field 1310.

The length field 1320 may be set to a value indicating the total number of bits allocated for the RAI element 1300. For example, one octet may be allocated for the length field 1320.

One octet may be allocated for the target transmission time indication field 1330. The target transmission time indication field 1330 may include target transmission time (TTT) information of FIG. 12 indicating a transmission time of the random trigger frame (TFR).

The OCWmin field 1340 may be assigned an OCWmin value, which is information about the OCW for the OBO counter. For example, the initial value set in the OBO counter may be set based on the OCWmin value. For example, one octet may be allocated for the OCWmin field 1340.

The OCWmax field 1350 may be assigned an OCWmax value, which is information about the OCW for the OBO counter. The OCWmax value may be used to limit the number of retransmissions of a frame transmitted via an OFDMA based random access procedure. For example, one octet may be allocated for the OCWmax field 1350.

14 is a diagram for a method for power management in a WLAN system according to another embodiment.

12 to 14, the AP 1400, the first STA 1410, and the second STA 1420 of FIG. 14 may include the AP 1200, the first STA 1210, and the second STA (FIG. 12) of FIG. 12. 1220).

Referring to FIG. 14, in the first period T1 to T2, the AP 1400 may transmit the first beacon frame BF1.

The first beacon frame BF1 of FIG. 14 may include information on the OCW described above. The first beacon frame BF1 according to another embodiment may further include information about the transmission period of the random trigger frame TFR and information about the number of the random trigger frames TFR.

Specifically, the information on the transmission period of the random trigger frame (TFR) may indicate the time interval between the plurality of random trigger frame (TFR) periodically transmitted by the AP 1400 in the beacon interval (T1 ~ T9). have. For example, the information on the transmission period of the random trigger frame (TFR) may be set to 20ms.

The information on the number of random trigger frames TFR may indicate the number of random trigger frames TFR periodically transmitted by the AP 1400 in the beacon intervals T1 to T9. For example, information about the number of random trigger frames (TFR) may be set to three.

That is, the first and second STAs 1410 and 1420 are configured for the time intervals for maintaining the awake state and the time intervals for maintaining the sleep state in the beacon intervals T1 to T9 based on the first beacon frame BF1. Information can be obtained in advance.

The first and second STAs 1410 and 1420 that have received the information on the transmission period of the random trigger frame (TFR) and the information on the number of the random trigger frame (TFR) may switch from the awake state to the sleep state. .

In the second period T2 to T3, the first and second STAs 1410 and 1420 may maintain a sleep state. For example, the time length of the second section T2 to T3 may be 20 ms.

When entering the third section T3 to T4, the first and second STAs 1410 and 1420 may switch from the sleep state to the awake state.

In the third period T3 to T4, the AP 1400 may transmit the first random trigger frame TFR1. The first and second STAs 1410 and 1420 may maintain an awake state for the third period T3 to T4.

The first random trigger frame TFR1 may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1400. For example, the allocation information may indicate two resource units RU1 and RU2. The first random trigger frame TFR1 may be a frame having the frame format of FIGS. 9 to 11 described above.

Each STA 1410 or 1420 that receives the first random trigger frame TFR1 may determine the first and second resource units RU1 and RU2 as resource units allocated for the OFDMA-based random access procedure. have.

In the third period T3 to T4, each STA 1410 and 1420 may perform an individual countdown operation. For the sake of brevity, in the third period T3 to T4, the first STA 1410 completes the countdown operation, and selects one of the first and second resource units RU1 and RU2 in a random resource unit (eg, , RU2).

In the fourth period T4 to T5, the first STA 1410 may transmit the first uplink frame UL # 1 to the AP 1400 using the selected random resource unit (eg, RU2). The first STA 1410 may maintain an awake state for the fourth period T4 to T5.

When entering the fourth section T4 to T5, the second STA 1420 may switch from the awake state to the sleep state. The second STA 1420 may maintain a sleep state for the fourth period T4 to T5. For example, the time length of the fourth section T4 to T5 may be 20 ms.

In the fourth period T4 to T5, the AP 1400 may transmit an ACK frame (not shown) to inform the successful reception of the first uplink frame UL # 1.

For reference, when an ACK frame (not shown) is received from the AP 1400, the first STA 1410 may set an initial value for the first OBO counter again. The second STA 1420 may maintain a value obtained by subtracting the number of resource units allocated for the OFDMA-based random access procedure from the initial value for the second OBO counter.

In the fifth period T5 to T6, the AP 1400 may transmit a second random trigger frame TFR2. The first and second STAs 1410 and 1420 may maintain an awake state for the fifth period T5 to T6.

The second random trigger frame TFR2 may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1400. For example, the allocation information may indicate two resource units RU3 and RU4.

Each STA 1410 or 1420 that receives the second random trigger frame TFR2 may determine the third and fourth resource units RU3 and RU4 as resource units allocated for an OFDMA-based random access procedure. have.

In the fifth period T5 to T6, each STA 1410 and 1420 may perform an individual countdown operation. For the sake of brevity, in the fifth section T5 to T6, the second STA 1420 completes the countdown operation and selects one of the third and fourth resource units RU3 and RU4 from the random resource unit (eg, , RU3).

For reference, the second second STA 1420 may be a terminal updating the value of the second OBO counter to '0' by resuming the second countdown operation based on the value maintained in the second OBO counter.

In the sixth period T6 to T7, the second STA 1420 may transmit the second uplink frame UL # 2 to the AP 1400 using the selected random resource unit (eg, RU3). The second STA 1420 may maintain an awake state for the sixth periods T6 to T7.

When entering the sixth period T6 to T7, the first STA 1410 may switch from the awake state to the sleep state. The first STA 1410 may maintain a sleep state for the sixth period T6 to T7. For example, the time length of the sixth section T6 to T7 may be 20 ms.

In the sixth period (T6 ˜ T7), the AP 1400 may transmit an ACK frame (not shown) to inform the successful reception of the second uplink frame UL # 2.

For reference, when an ACK frame (not shown) is received from the AP 1400, the second STA 1420 may set an initial value for the second OBO counter again.

In the seventh period T7 to T8, the AP 1400 may transmit a third random trigger frame TFR3. The first and second STAs 1410 and 1420 may maintain an awake state during the seventh periods T7 to T8.

The third random trigger frame TFR3 may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1400. For example, the allocation information may indicate two resource units RU5 and RU6.

Each STA 1410 or 1420 that receives the third random trigger frame TFR3 may determine the fifth and sixth resource units RU5 and RU6 as resource units allocated for an OFDMA based random access procedure. have.

In the seventh periods T7 to T8, each STA 1410 and 1420 may perform an individual countdown operation. For the sake of brevity, it is assumed that in the seventh periods T7 to T8, the first and second STAs 1410 and 1420 do not complete separate countdown operations.

After reception of the third random trigger frame TFR3, each STA 1410 and 1420 may know in advance that subsequent random trigger frames are not transmitted for the remaining time T8 to T9 of the beacon intervals T1 to T9. Accordingly, each of the STAs 1410 and 1420 may maintain a sleep state for the eighth periods T8 to T9.

15 illustrates an example of an element including information for OFDMA-based random access according to another embodiment. 13 to 15, an element including information for the present OFDMA based random access may be referred to as a random access information (RAI) element 1500.

One octet may be allocated for the target transmission time indication field 1530. The target transmission time indication field 1530 may include a period subfield 1531 and a subfield 1532 for the number of scheduled random trigger frames.

The period subfield 1153 may include information on a transmission period of the random trigger frame (TFR) mentioned in FIG. 14. For example, the period subfield 1531 may be allocated 5 bits.

The subfield 1532 for the number of scheduled random trigger frames may include information on the number of the plurality of random trigger frames (TFRs) mentioned in FIG. 14. For example, three bits may be allocated to the subfield 1532 for the number of scheduled random trigger frames. The remaining fields 1510, 1520, 1540, and 1550 may be understood based on the description of FIG. 14.

16 is a diagram for a method for power management in a WLAN system according to another embodiment.

12 to 16, the AP 1600, the first STA 1610, and the second STA 1620 of FIG. 16 may include the AP 1200, the first STA 1210, and the second STA (FIG. 12) of FIG. 12. 1220).

Referring to FIG. 16, in the first period T1 to T2, the AP 1600 may transmit the first beacon frame BF1.

The first beacon frame BF1 of FIG. 16 may include information on the above-described OCW, information on a transmission period of the random trigger frame (TFR), and information on the number of random trigger frames (TFR).

Specifically, the information on the transmission period of the random trigger frame (TFR) may indicate the time interval between the plurality of random trigger frame (TFR) periodically transmitted by the AP 1600 in the beacon interval (T1 ~ T10). have. For example, the information on the transmission period of the random trigger frame (TFR) may be set to 20ms.

The information on the number of random trigger frames TFR may indicate the number of random trigger frames TFR periodically transmitted by the AP 1600 in the beacon intervals T1 to T10. For example, information about the number of random trigger frames (TFR) may be set to three.

The first beacon frame BF1 according to another embodiment may further include immediate sleep indication (ISI) information. One bit may be allocated for immediate sleep indication (ISI) information.

Immediate sleep indication (ISI) information according to another embodiment may indicate whether the STA maintains an awake state or switches to a sleep state after reception of the beacon frame.

For example, when the immediate sleep instruction (ISI) information is set to '0', the first and second STAs 1610 and 1620 that receive the first beacon frame BF1 are in a sleep state unlike the case of FIG. 14. The awake state can be maintained without switching to.

In the second period T2 to T3, the AP 1600 may immediately transmit a random trigger frame TFR_I. The first and second STAs 1610 and 1620 awake during the second period T2 to T3 to receive the immediate random trigger frame TFR_I received after the first beacon frame according to the immediate sleep indication (ISI) information. State can be maintained.

Unlike FIG. 16, a time interval may exist between the first sections T1 to T2 and the second sections T2 to T3.

The immediate random trigger frame TFR_I may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1600. For example, the allocation information may indicate two resource units RU1 and RU2.

The first and second STAs 1610 and 1620 that receive the immediate random trigger frame TFR_I transfer the first and second resource units RU1 and RU2 to resource units allocated for the OFDMA based random access procedure. You can judge.

In the second period T2 to T3, the first and second STAs 1610 and 1620 may perform separate countdown operations. For the sake of brevity, in the second periods T2 to T3, the first STA 1610 completes the countdown operation, and selects one of the first and second resource units RU1 and RU2 in a random resource unit (eg, , RU2).

In the third period T3 to T4, the first STA 1610 may transmit the first uplink frame UL # 1 to the AP 1600 using the selected random resource unit (eg, RU2). The first STA 1610 may maintain an awake state for the third period T3 to T4.

When entering the third section T3 to T4, the second STA 1620 may switch from the awake state to the sleep state. The second STA 1620 may maintain a sleep state for the third period T3 to T4. For example, the time length of the third section T3 to T4 may be 20 ms.

In the third period T3 to T4, the AP 1600 may transmit an ACK frame (not shown) to inform the successful reception of the first uplink frame UL # 1.

For reference, the first STA 1610 may be a terminal that updates the value of the first OBO counter to '0' by performing a first countdown operation based on an initial value set in the first OBO counter. After receiving the ACK frame (not shown), the first STA 1610 may reset the initial value for the first OBO counter.

The second STA 1620 maintains a value obtained by subtracting the initial value for the second OBO counter from the initial value for the second OBO counter by the number (2) of resource units allocated for the OFDMA-based random access procedure in the immediate random trigger frame (TFR_I). Can be.

In the fourth period T4 to T5, the AP 1600 may transmit the first random trigger frame TFR1. The first and second STAs 1610 and 1620 may maintain an awake state during the fourth periods T4 to T5.

The first random trigger frame TFR1 may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1600. For example, the allocation information may indicate two resource units RU3 and RU4.

The first and second STAs 1610 and 1620 that receive the first random trigger frame TFR1 allocate the third and fourth resource units RU3 and RU4 to an OFDMA based random access procedure. Judging by

In the fourth period T4 to T5, the first and second STAs 1610 and 1620 may perform separate countdown operations. For the sake of brevity, in the fourth period T4 to T5, the second STA 1620 completes the countdown operation and selects one of the third and fourth resource units RU3 and RU4 from the random resource unit (eg, , RU3).

In the fifth period T5 to T6, the second STA 1620 may transmit the second uplink frame UL # 2 to the AP 1600 using the selected random resource unit (eg, RU3). The second STA 1620 may maintain an awake state for the fifth period T5 to T6.

When entering the fifth section T5 to T6, the first STA 1610 may switch from the awake state to the sleep state. The first STA 1610 may maintain a sleep state for the fifth period T5 to T6. For example, the time length of the fifth section T5 to T6 may be 20 ms.

In the fifth period T5 to T6, the AP 1600 may transmit an ACK frame (not shown) to inform the successful reception of the second uplink frame UL # 2.

For reference, the second STA 1620 may be a terminal updating the value of the second OBO counter to '0' by resuming the second countdown operation based on the value maintained in the second OBO counter. After receiving the ACK frame (not shown), the second STA 1620 may reset the initial value for the second OBO counter.

In the sixth period T6 to T7, the AP 1600 may transmit a second random trigger frame TFR2. The first and second STAs 1610 and 1620 may maintain an awake state during the sixth periods T6 to T7.

The second random trigger frame TFR2 may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1600. For example, the allocation information may indicate two resource units RU5 and RU6.

The first and second STAs 1610 and 1620 that receive the second random trigger frame TFR2 allocate the fifth and sixth resource units RU5 and RU6 for an OFDMA based random access procedure. Judging by

In the sixth periods T6 to T7, the first and second STAs 1610 and 1620 may perform separate countdown operations. For the sake of brevity, it is assumed that in the sixth periods T6 to T7, the first and second STAs 1610 and 1620 do not complete separate countdown operations.

In the seventh periods T7 to T8, the first and second STAs 1610 and 1620 may maintain a sleep state. For example, the time length of the seventh periods T7 to T8 may be 20 ms.

In the eighth period T8 ˜ T9, the AP 1600 may transmit a third random trigger frame TFR3. The first and second STAs 1610 and 1620 may maintain an awake state for the eighth period T8 to T9.

The third random trigger frame TFR3 may include resource allocation information indicating a plurality of resource units (RUs) allocated by the AP 1600. For example, the allocation information may indicate two resource units RU7 and RU8.

The first and second STAs 1610 and 1620 that receive the third random trigger frame TFR3 allocate the seventh and eighth resource units RU7 and RU8 to the OFDMA based random access procedure. Judging by

In the eighth periods T8 to T9, the first and second STAs 1610 and 1620 may perform separate countdown operations. For the sake of brevity, it is assumed that in the eighth periods T8 to T9, the first and second STAs 1610 and 1620 do not complete separate countdown operations.

After reception of the third random trigger frame TFR3, each STA 1610 and 1620 may know in advance that subsequent random trigger frames are not transmitted for the remaining time T9 to T10 of the beacon intervals T1 to T10. Accordingly, each of the STAs 1610 and 1620 may maintain a sleep state during the ninth periods T8 to T10.

According to an embodiment different from FIG. 16, when the immediate sleep indication (ISI) information is set to '1', it may be understood based on FIG.

FIG. 17 is a diagram illustrating an example of an element including information for OFDMA-based random access according to another embodiment. 13 to 17, an element including information for the present OFDMA based random access may be referred to as a random access information (RAI) element 1700.

One octet may be allocated for the target transmission time indication field 1730. The target transmission time indication field 1730 may include a period subfield 1731, a subfield 1732 for the number of scheduled random trigger frames, and an immediate sleep indicator 1733.

The immediate sleep indicator 1733 may correspond to the immediate sleep indication (ISI) information of FIG. 16. For example, one bit may be allocated for the sleep indicator 1733.

The remaining fields 1710, 1720, 1731, 1732, 1740, and 1750 may be understood based on the description of FIG. 15.

18 is a diagram for a method for power management in a WLAN system according to an extension of another embodiment. 1 to 18, the AP 1800, the first STA 1810, and the second STA 1820 of FIG. 18 may include the AP 1600, the first STA 1610, and the second STA (FIG. 16) of FIG. 16. 1620).

Referring to FIGS. 16 and 18, the operation of the WLAN system (ie, 1800, 1810, 1820) in the first period T1 to T2 to the tenth period T10 to T11 of FIG. 18 is the first operation of FIG. The operation of the WLAN system (ie, 1600, 1610, 1620) in the sections T1 to T2 to the tenth section T10 to T11 may be understood.

Referring to FIG. 18, in the first period T1 to T2, the AP 1800 further includes information on time information for an immediate random trigger frame TFR_I (hereinafter, 'TFR_I time information'). The frame BF1 can be transmitted.

The TFR_I time information indicates an active period T3 ˜ T3 ′ in which the first STA 1810 that completed the countdown operation to successfully transmit the first uplink frame UL # 1 maintains an awake state. It may be information indicating.

For example, in the active period T3 ˜ T3 ′, the AP 1600 may transmit an ACK frame (not shown) to inform the successful reception of the first uplink frame UL # 1. For example, the TFR_I time information for the active periods T3 to T3 'may be set to a value corresponding to 10 ms.

After the active period T3 ′, the first STA 1810 may switch from the awake state to the sleep state. Subsequently, the first STA 1810 may maintain a sleep state until the reception of the first random trigger frame TFR1 (T3 ′ to T4).

19 illustrates an example of an element including information for OFDMA-based random access according to an extension of another embodiment. 13 to 19, an element including information for the present OFDMA based random access may be referred to as a random access information (RAI) element 1900.

The time information for the immediate random trigger frame TFR_I of FIG. 18 may be included in the target time field 1960 for the first TFR. One octet may be allocated for the target time field 1960 for the first TFR.

The remaining fields 1910, 1920, 1930, 1732, 1940, and 1950 may be understood based on the description of FIG. 17.

Although not shown in FIG. 19, the method of setting a time for which the STA that receives the beacon frame maintains an awake state may include an example of another method. In detail, one bit added to the random access information (RAI) element 1900 may be used as a scale factor (“SF”).

For example, the scale factor SF set to '0' may correspond to 5 ms, and the scale factor SF set to '1' may correspond to 10 ms. The STA receiving the beacon frame may switch to the awake operation after maintaining the sleep state for a time corresponding to the scale factor SF.

As another example, the scale factor SF set to '0' may correspond to a preset time, and the scale factor SF set to '1' may correspond to a time multiplied by a predetermined multiple of the preset time. The STA receiving the beacon frame may switch to the awake operation after maintaining the sleep state for a time corresponding to the scale factor SF.

As another example, information on the time at which the STA receiving the beacon frame maintains an awake state may be included in an element (eg, HE capabilities element or HE operation element) other than the random access information (RAI) element 1900. have.

As another example, the information on the time at which the STA that receives the beacon frame maintains the awake state may be included in the association request frame or the association response frame exchanged between the AP and the STA in the association step.

20 is a flowchart illustrating a method for power management in a WLAN system according to an exemplary embodiment.

1 to 20, in step S2010, a target transmission time point indicating a transmission time of a trigger frame for an orthogonal frequency division multiple access (OFDMA) based random access procedure by a first wireless terminal (ie, a user STA) A beacon frame including Target Transmission Time) information may be received from the second wireless terminal (ie, AP).

The beacon frame according to the present embodiment may further include window information for an OCW (OFDMA Counter Window) indicating a range of initial values set in the backoff counter of the first wireless terminal.

The first wireless terminal according to the present embodiment may set an initial value to the backoff counter based on the window information for the OCW for the OFDMA-based random access procedure.

In operation S2020, the first wireless terminal may switch from the awake state to the sleep state after receiving the beacon frame.

In step S2030, the first wireless terminal may switch from the sleep state to the awake state based on the target transmission time information.

In operation S2040, the first wireless terminal may receive a trigger frame for an OFDMA-based random access procedure in an awake state.

For example, the trigger frame for the OFDMA based random access procedure includes resource information indicating a plurality of resource units allocated for the OFDMA based random access procedure and a plurality of association identifiers corresponding to the plurality of resource units. can do. In addition, the plurality of association identifiers may be set to a value corresponding to '0'.

According to the present embodiment, a user STA receiving a beacon frame including an element associated with an OFDMA based random access procedure may maintain a sleep state for a time indicated by target transmission time information.

Accordingly, power consumed unnecessarily by the terminal can be reduced. Therefore, according to the present specification, a WLAN system having improved performance may be provided.

Further details of the OFDMA based random access procedure referred to herein may be understood with reference to section 27.5.2.6 of the standard document IEEE P802.11ax / D1.0 disclosed in November 2016.

21 is a block diagram illustrating a wireless terminal to which an embodiment of the present specification can be applied.

Referring to FIG. 21, a wireless terminal may be an STA capable of implementing the above-described embodiment and may be an AP or a non-AP STA. The wireless terminal may correspond to the above-described user or may correspond to a transmitting terminal for transmitting a signal to the user.

The AP 2100 includes a processor 2110, a memory 2120, and an RF unit 2130.

The RF unit 2130 may be connected to the processor 2110 to transmit / receive a radio signal.

The processor 2110 may implement the functions, processes, and / or methods proposed herein. For example, the processor 1910 may perform an operation according to the present embodiment described above. The processor 2110 may perform an operation of the AP disclosed in the present embodiment of FIGS. 1 to 20.

The non-AP STA 2150 includes a processor 2160, a memory 2170, and an RF unit 2180.

The RF unit 2180 may be connected to the processor 2160 to transmit / receive a radio signal.

The processor 2160 may implement the functions, processes, and / or methods proposed in the present embodiment. For example, the processor 2160 may be implemented to perform the non-AP STA operation according to the present embodiment described above. The processor 2160 may perform an operation of the non-AP STA disclosed in the present embodiment of FIGS. 1 to 20.

Processors 2110 and 2160 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices, and / or converters that convert baseband signals and wireless signals to and from each other. The memories 2120 and 2170 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit 1930 and 1980 may include one or more antennas for transmitting and / or receiving a radio signal.

When the embodiment of the present specification is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in the memories 2120 and 2170 and executed by the processors 2110 and 2160. The memories 2120 and 2170 may be inside or outside the processors 2110 and 2160, and may be connected to the processors 2110 and 2160 by various well-known means.

In the detailed description of the present specification, specific embodiments have been described, but various modifications are possible without departing from the scope of the present specification. Therefore, the scope of the present specification should not be limited to the above-described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims of the present invention.

Claims (10)

1. In the method for power management in a wireless LAN system,

   The first wireless terminal receives a beacon frame including target transmission time (Target Transmission Time) information indicating the transmission time of the trigger frame for the Orthogonal Frequency Division Multiple Access (OFDMA) based random access procedure step;

   Switching, by the first wireless terminal, from the awake state to the sleep state after receiving the beacon frame;

   Switching, by the first wireless terminal, from the sleep state to an awake state based on the target transmission time information; And

   Receiving, by the first wireless terminal, the trigger frame in the awake state.
2. According to claim 1,

   The beacon frame further includes window information for an OCW (OFDMA Counter Window) indicating a range of initial values set in a backoff counter of the first wireless terminal.
3. The method of claim 2,

   The trigger frame includes resource information indicating a plurality of resource units allocated for the OFDMA-based random access procedure and a plurality of association identifiers corresponding to the plurality of resource units.
4. The method of claim 3, wherein

   And setting, by the first wireless terminal, the initial value to the backoff counter based on the window information for the OCW for the OFDMA based random access procedure.
5. The method of claim 4, wherein

   Updating, by the first wireless terminal, the backoff counter to a value reduced by the number of the plurality of resource units from the initial value when the trigger frame is received; And

   If the backoff counter is updated to '0', the first wireless terminal further performing uplink transmission using any one of the plurality of resource units.
6. The method of claim 3, wherein

   And wherein the plurality of association identifiers is set to a value corresponding to '0'.
7. According to claim 1,

   The first wireless terminal is a user station operating in a power save mode,

   And the second wireless terminal is an access point (AP) station.
8. In a first wireless terminal using a method for power management in a wireless LAN system, the first wireless terminal,

   A transceiver for transmitting and receiving a radio signal; And

   A processor coupled to the transceiver, wherein the processor includes:

   Is configured to receive a beacon frame including target transmission time information indicating a transmission time of a trigger frame for an orthogonal frequency division multiple access (OFDMA) based random access procedure from a second wireless terminal,

   Is configured to switch from an awake state to a sleep state after reception of the beacon frame,

   It is implemented to switch from the sleep state to the awake state based on the target transmission time information,

   Wireless terminal configured to receive the trigger frame in the awake state.
9. The method of claim 8,

   The beacon frame further includes window information for an OCW (OFDMA Counter Window) indicating a range of initial values set in a backoff counter of the first wireless terminal.
10. The method of claim 9,

    The trigger frame includes a resource information indicating a plurality of resource units allocated for the OFDMA-based random access procedure and a plurality of association identifiers corresponding to the plurality of resource units. .

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