WO2018016784A1 - Method for channel access in wireless lan system, and wireless terminal using same - Google Patents

Abstract

A method for channel access in a wireless LAN system according to one embodiment of the present description, comprises the steps of: allowing a first wireless terminal to perform a first countdown operation on the basis of a back-off counter, which is set according to a first parameter set; allowing the first wireless terminal to transmit, to a second wireless terminal, operation mode indication information for requesting approval of an uplink operation mode for a multi-user when the first countdown operation is completed; and allowing the first wireless terminal to receive an ACK frame for approving the uplink operation mode from the second wireless terminal, wherein the back-off counter is reset according to a second parameter set for the uplink operation mode and the second parameter set is valid during a preset time interval.

Description

      Method for channel access in wireless LAN system and wireless terminal using same

The present disclosure relates to wireless communication, and more particularly, to a method for channel access 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 channel access in a WLAN system having an improved performance and a wireless terminal using the same.

The present disclosure relates to a method for channel access in a WLAN system. According to an embodiment of the present invention, a method for channel access in a WLAN system includes: performing, by a first wireless terminal, a first countdown operation based on a backoff counter set according to a first parameter set; When the first wireless terminal completes the first countdown operation, transmitting operating mode indication information for requesting approval of an uplink operation mode for a multi-user to the second wireless terminal. step; And the first wireless terminal receives an acknowledgment (ACK) frame acknowledging an uplink operating mode from the second wireless terminal, and the backoff counter is reset according to a second set of parameters for the uplink operating mode, The second set of parameters includes steps that are valid for a preset time period.

According to one embodiment of the present specification, a method for channel access 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.

9 shows an example of a trigger frame.

10 shows an example of a common information field.

11 shows an example of subfields included in individual user information fields.

12 illustrates an EDCA-based channel access method in a WLAN system.

13 is a conceptual diagram illustrating a backoff procedure according to EDCA.

14 is a view for explaining a frame transmission procedure in a WLAN system.

15 illustrates a method for channel access in a WLAN system according to an embodiment of the present invention.

16 is a diagram illustrating a method for channel access in a WLAN system according to another embodiment.

17 and 18 are diagrams illustrating a format of an element for MU EDCA aggregation information according to the present embodiment.

19 to 21 illustrate a format for an OMI frame according to the present embodiment.

22 is a flowchart illustrating a method for channel access in a WLAN system according to an embodiment.

FIG. 23 is a diagram illustrating a method for a wireless terminal to perform an individual TWT operation and an MU EDCA timer operation according to another exemplary embodiment.

24 is a diagram illustrating a TWT element including an EDCA request indicator or an EDCA command indicator according to another embodiment.

25 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 illustrates an EDCA-based channel access method in a WLAN system. An STA (or AP) performing enhanced distributed channel access (EDCA) in a WLAN system may perform channel access according to a plurality of user priorities defined for traffic data.

Specifically, to transmit quality of service (QoS) data frames based on a plurality of user priorities, four access categories (AC) (AC_BK (background), AC_BE (best effort), AC_VI (video), AC_VO (voice) may be defined.

The STA may receive traffic data (eg, MAC service data unit (MSDU)) with differential user priority from a logical link control (LLC) layer. User priority of traffic data arriving from the LLC layer to the medium access control (MAC) layer may be mapped as shown in Table 1 below.

Referring to Table 1, traffic data having a user priority of '1' or '2' may be buffered into the transmission queue 1250 of the AC_BK type. Traffic data having a user priority of '0' or '3' may be buffered into the transmission queue 1240 of the AC_BE type. Traffic data having a user priority of '4' or '5' may be buffered into a transmission queue 1230 of type AC_VI. Traffic data having a user priority of '6' or '7' may be buffered into the transmission queue 1220 of the AC_VO type.

Instead of DIFS (DCFS interframe space), CWmin, CWmax, which are parameters for the backoff procedure based on the existing distributed coordination function (DCF), an ARCA (arbitration interframe), which is an EDCA parameter set, for the backoff procedure of an STA that performs EDCA space) [AC], CWmin [AC], CWmax [AC] and TXOP limit [AC] can be used.

The difference in transmission priority between ACs may be implemented based on the differential EDCA parameter set. The default value of the EDCA parameter set (ie, AIFS [AC], CWmin [AC], CWmax [AC], TXOP limit [AC]) corresponding to each AC is shown in Table 2 below.

The EDCA parameter set for each AC may be set to a default value or carried in a beacon frame from the AP to each STA. The smaller the value of AIFS [AC] and CWmin [AC], the higher the priority. Therefore, the shorter the channel access delay, the more bandwidth can be used in a given traffic environment.

The EDCA parameter set may include information about channel access parameters (eg, AIFS [AC], CWmin [AC], CWmax [AC]) for each AC.

The backoff procedure for EDCA may be performed based on an EDCA parameter set individually set to four ACs included in each STA. Appropriate setting of EDCA parameter values, which define different channel access parameters for each AC, can optimize network performance and increase the transmission effect due to traffic priority.

Therefore, the AP of the WLAN system must perform overall management and coordination functions for the EDCA parameters to ensure fair access to all STAs participating in the network.

Referring to FIG. 12, one STA (or AP) 1200 may include a virtual mapper 1210, a plurality of transmission queues 1220-1250, and a virtual collision processor 1260. The virtual mapper 1210 of FIG. 12 may serve to map an MSDU received from a logical link control (LLC) layer to a transmission queue corresponding to each AC according to Table 1 above.

The plurality of transmission queues 1220-1250 of FIG. 12 may serve as individual EDCA competition entities for wireless medium access within one STA (or AP). For example, the transmission queue 1220 of the AC VO type of FIG. 12 may include one frame 1221 for a second STA (not shown).

 The transmission queue 1230 of the AC VI type may include three frames 1231 to 1233 for the first STA (not shown) and one frame 1234 for the third STA according to the order to be transmitted to the physical layer. Can be.

The transmission queue 1240 of the AC BE type of FIG. 12 includes one frame 1241 for the second STA (not shown) and one frame for the third STA (not shown) according to the order to be transmitted to the physical layer. 1242 and one frame 1243 for a second STA (not shown).

In exemplary embodiments, the transmission queue 1250 of the AC BE type of FIG. 12 may not include a frame to be transmitted to the physical layer.

If there is more than one AC that has been backed off at the same time, collisions between the ACs may be adjusted according to the functions included in the virtual collision handler 1260 (EDCA function, EDCAF).

Specifically, the collision problem in the STA may be solved by first transmitting a frame included in the AC having the highest priority among the collided ACs. In this case, the other AC may increase the contention window and update the backoff counter with the backoff value again selected based on the increased contention window.

Transmission opportunity (TXOP) can be initiated when the channel is accessed according to EDCA rules. If more than two frames are accumulated in one AC, if EDCA TXOP is obtained, the AC of the EDCA MAC layer may attempt to transmit several frames. If the STA has already transmitted one frame and can receive the transmission of the next frame and the ACK for the same frame within the remaining TXOP time, the STA may attempt to transmit the frame after an SIFS time interval.

The TXOP limit value may be set as a default value for the AP and the STA, or a frame associated with the TXOP limit value may be transferred from the AP to the STA.

If the size of the data frame to be transmitted exceeds the TXOP limit, the AP may fragment the frame into several smaller frames. Subsequently, the divided frames may be transmitted in a range not exceeding the TXOP limit.

13 is a conceptual diagram illustrating a backoff procedure according to EDCA.

Each STA may share a wireless medium based on a contention coordination function, a distributed coordination function (hereinafter, referred to as 'DCF'). DCF is an access protocol for coordinating collisions between STAs, and may use carrier sense multiple access / collision avoidance (CSMA / CA).

If the DCF determines that the wireless medium is not used during the DCF inter frame space (DIFS) (that is, the wireless medium is in the idle state), the STA may acquire a transmission right for transmitting an internally determined MPDU through the wireless medium. .

If the DCF determines that the wireless medium is used by another STA in DIFS (ie, the wireless medium is busy), the STA may wait until the wireless medium is idle to obtain transmission rights. Subsequently, the STA may wait as much as the contention window (hereinafter referred to as "CW") set in the backoff counter after deferring by DIFS based on the time when the wireless medium is switched to the idle state.

In order to perform the backoff procedure according to the EDCA, each STA may set a randomly selected backoff value in the contention window (CW) to the backoff counter. In the present specification, a time indicating a backoff value selected by each STA in slot time units may be understood as the backoff window of FIG. 13.

Each STA may perform a countdown operation of decreasing the backoff window set in the backoff counter in slot time units. An STA having a relatively shortest backoff window among a plurality of STAs may acquire a transmission opportunity (TXOP), which is a right to occupy a wireless medium.

During the time interval for the transmission opportunity (TXOP), the remaining STA may stop the countdown operation. The remaining STA may wait until the time interval for the transmission opportunity (TXOP) ends. After the time interval for the transmission opportunity (TXOP) ends, the remaining STA may resume the suspended countdown operation to occupy the wireless medium.

According to the DCF-based transmission method, a collision phenomenon that may occur when a plurality of STAs simultaneously transmit a frame may be prevented. However, the channel access scheme using DCF has no concept of transmission priority (ie, user priority). That is, when DCF is used, the quality of service (QoS) of traffic to be transmitted by the STA cannot be guaranteed.

In order to solve this problem, a new coordination function (hybrid coordination function, hereinafter 'HCF') is defined in 802.11e. The newly defined HCF has improved performance over the channel access performance of the existing DCF. HCF can use two channel access techniques, HCCA controlled channel access (HCCA) and polling-based enhanced distributed channel access (EDCA), for improving QoS.

Referring to FIG. 13, it is assumed that the STA performs EDCA for transmission of buffered traffic data to the STA. Referring to Table 1, the user priority set for each traffic data may be differentiated into eight levels.

Each STA may include output queues of four types (AC_BK, AC_BE, AC_VI, and AC_VO) mapped with the user priority of step 8 of Table 1.

The STA according to the present embodiment may transmit traffic data based on the Arbitration Interframe Space (AIFS) corresponding to the user priority instead of the previously used DCF Interframe Space (DIFS).

Hereinafter, in an embodiment of the present disclosure, the terminal may be a device capable of supporting both a WLAN system and a cellular system. That is, the terminal may be interpreted as a UE supporting the cellular system or an STA supporting the WLAN system.

Inter-frame spacing referred to in 802.11 is described for the sake of clarity herein. For example, the Interframe Interval (IFS) can be reduced interframe space (RIFS), short interframe space (SIFS), PCF interframe space (PIFS), DCF frame interval (DIFS). It may be a DCF interframe space, an arbitration interframe space (AIFS), or an extended interframe space (EIFS).

The interframe interval (IFS) may be determined according to an attribute specified by the physical layer of the STA regardless of the bit rate of the STA. The rest of the interframe intervals (IFS) except for AIFS may be understood as fixed values for each physical layer.

AIFS can be set to values corresponding to four types of transmission queues mapped to user priorities, as shown in Table 2.

SIFS has the shortest time gap among the above mentioned IFS. Accordingly, the STA occupying the wireless medium may be used when it is necessary to maintain the occupancy of the medium without interference by other STAs in the section in which the frame exchange sequence is performed.

That is, by using the smallest gap between transmissions in the frame exchange sequence, priority may be given to the completion of the ongoing frame exchange sequence. In addition, an STA accessing a wireless medium using SIFS may start transmission directly at the SIFS boundary without determining whether the medium is busy.

The duration of SIFS for a specific physical (PHY) layer may be defined by the aSIFSTime parameter. For example, in the physical layer (PHY) of the IEEE 802.11a, IEEE 802.11g, IEEE 802.11n and IEEE 802.11ac standards, the SIFS value is 16 μs.

PIFS can be used to provide the STA with the next highest priority after SIFS. In other words, PIFS can be used to obtain priority for accessing a wireless medium.

DIFS may be used by an STA to transmit a data frame (MPDU) and a management frame (Mac Protocol Data Unit (MPDU)) based on the DCF. If the medium is determined to be idle through a carrier sense (CS) mechanism after the received frame and the backoff time expire, the STA may transmit the frame.

14 is a view for explaining a frame transmission procedure in a WLAN system.

13 and 14, each STA 1410, 1420, 1430, 1440, and 1450 of the WLAN system may individually select a backoff value for channel access.

Each STA 1410, 1420, 1430, 1440, and 1450 may attempt transmission after waiting for the selected backoff value for a time indicated by a slot time (that is, the backoff window of FIG. 13).

In addition, each STA 1410, 1420, 1430, 1440, and 1450 may reduce the backoff window in slot time units through a countdown operation. The countdown operation for channel access to the wireless medium may be performed separately by each STA.

Each STA may individually set a backoff time (Tb [i]) for the backoff window to the backoff counter of each STA. Specifically, the backoff time Tb [i] is a pseudo-random integer value and may be calculated based on Equation 1 below.

Random (i) of Equation 1 is a function that uses a uniform distribution and generates a random integer between 0 and CW [i]. CW [i] may be understood as the contention window selected between the minimum contention window CWmin [i] and the maximum contention window CWmax [i].

For example, the minimum contention window CWmin [i] and the maximum contention window CWmax [i] may correspond to the default values CWmin [AC] and CWmax [AC] of Table 2, respectively.

For initial channel access, the STA may set CW [i] to CWmin [i] and use Random (i) to select a random integer between O and CWmin [i]. In this case, any integer selected can be referred to as a backoff value.

It can be understood that i in Equation 1 corresponds to the user priority in Table 1. That is, the traffic buffered in the STA may be understood to correspond to any one of AC_VO, AC_VI, AC_BE, or AC_BK of Table 1 based on the value set in i of Equation 1.

SlotTime of Equation 1 may be used to provide sufficient time for the preamble of the transmitting STA to be detected by the neighbor STA. Slot Time of Equation 1 may be used to define the aforementioned PIFS and DIFS. As an example. Slot time may be 9 μs.

For example, if the user priority i is '7', the initial backoff time Tb [7] for the transmission queue of type AC_VO slots the backoff value selected between 0 and CWmin [AC_VO]. It may be a time expressed in units of slot time.

When collision between STAs occurs according to the backoff procedure (or when ACK frame for the transmitted frame is not received), the STA increases the backoff time Tb [i] 'based on Equation 2 below. Can be newly calculated.

Referring to Equation 2, the new contention window CW _new [i] may be calculated based on the previous window CW _old [i]. The PF value of Equation 2 may be calculated according to the procedure defined in the IEEE 802.11e standard. For example, the PF value of Equation 2 may be set to '2'.

In this embodiment, when the increased back-off time (Tb [i] '), refer to any integer value (equation (2) is selected between 0 and the new contention window (CW _new [i]), the new contention window (CW _new [i]) may be calculated based on the previous window CW _old [i] The PF value of Equation 2 may be calculated according to a procedure defined in the IEEE 802.11e standard. The PF value of may be set to '2'.

In the present embodiment, the increased backoff time Tb [i] 'is equal to the slot time of any integer selected between 0 and the new contention window CW _new [i]. It can be understood as time expressed in units.

CWmin [i], CWmax [i], AIFS [i], and PF values mentioned in FIG. 14 may be signaled from the AP through a QoS parameter set element, which is a management frame. The CWmin [i], CWmax [i], AIFS [i] and PF values may be preset values by the AP and the STA.

Referring to FIG. 14, the horizontal axes t1 to t5 for the first to fifth STAs 1410 to 1450 may represent time axes. In addition, the vertical axis for the first to fifth STAs 1410 to 1450 may indicate a backoff time transmitted.

13 and 14, when a specific medium is changed from occupy or busy to idle, a plurality of STAs may attempt data (or frame) transmission.

At this time, in order to minimize the collision between STAs, each STA selects the backoff time (Tb [i]) of Equation 1 and waits for the corresponding slot time (slot time) before transmitting. You can try

When the backoff procedure is initiated, each STA may count down the individually selected backoff counter time in slot time units. Each STA may continue to monitor the medium while counting down.

If the wireless medium is monitored as occupied, the STA may stop counting down and wait. If the wireless medium is monitored in an idle state, the STA can resume counting down.

Referring to FIG. 14, when the frame for the third STA 1430 reaches the MAC layer of the third STA 1430, the third STA 1430 may check whether the medium is idle during DIFS. Subsequently, when the medium is determined to be idle during DIFS, the third STA 1430 may transmit a frame to an AP (not shown). However, although the inter frame space (IFS) of FIG. 14 is illustrated as DIFS, it will be understood that the present specification is not limited thereto.

While the frame is transmitted from the third STA 1430, the remaining STA may check the occupation state of the medium and wait for the transmission period of the frame. A frame may reach the MAC layer of each of the first STA 1410, the second STA 1420, and the fifth STA 1450. If the medium is identified as idle, each STA may wait for DIFS and then count down the individual backoff time selected by each STA.

Referring to FIG. 14, the second STA 1420 selects the smallest backoff time and the first STA 1410 selects the largest backoff time. The remaining backoff time of the fifth STA 1450 is the remaining back of the first STA 1410 at the time T1 after completing the backoff procedure for the backoff time selected by the second STA 1420 and starting the frame transmission. A case shorter than the off time is shown.

When the medium is occupied by the second STA 1420, the first STA 1410 and the fifth STA 1450 may suspend and wait for the backoff procedure. Subsequently, when the media occupation of the second STA 1420 ends (that is, the medium is idle again), the first STA 1410 and the fifth STA 1450 may wait as long as DIFS.

Subsequently, the first STA 1410 and the fifth STA 1450 may resume the backoff procedure based on the remaining remaining backoff time. In this case, since the remaining backoff time of the fifth STA 1450 is shorter than the remaining backoff time of the first STA 1410, the fifth STA 1450 may complete the backoff procedure before the first STA 1410. Can be.

Meanwhile, referring to FIG. 14, when a medium is occupied by the second STA 1420, a frame for the fourth STA 1440 may reach the MAC layer of the fourth STA 1440. When the medium is in the idle state, the fourth STA 1440 may wait as much as DIFS. Subsequently, the fourth STA 1440 may count down the backoff time selected by the fourth STA 1440.

Referring to FIG. 14, the remaining backoff time of the fifth STA 1450 may coincide with the backoff time of the fourth STA 1440. In this case, a collision may occur between the fourth STA 1440 and the fifth STA 1450. When a collision occurs between STAs, neither the fourth STA 1440 nor the fifth STA 1450 may receive an ACK, and may fail to transmit data.

Accordingly, the fourth STA 1440 and the fifth STA 1450 may separately calculate a new contention window CW _new [i] according to Equation 2 above. Subsequently, the fourth STA 1440 and the fifth STA 1450 may separately perform countdowns for the newly calculated backoff time according to Equation 2 above.

Meanwhile, when the medium is occupied due to transmission of the fourth STA 1440 and the fifth STA 1450, the first STA 1410 may wait. Subsequently, when the medium is idle, the first STA 1410 may resume backoff counting after waiting for DIFS. When the remaining backoff time of the first STA 1410 elapses, the first STA 1410 may transmit a frame.

The CSMA / CA mechanism may include virtual carrier sensing in addition to physical carrier sensing in which the AP and / or STA directly sense the medium.

Virtual carrier sensing is intended to compensate for problems that may occur in media access, such as a hidden node problem. For virtual carrier sensing, the MAC of the WLAN system uses a Network Allocation Vector (NAV). The NAV is a value that indicates to the other AP and / or STA how long the AP and / or STA currently using or authorized to use the medium remain until the medium becomes available.

Therefore, the value set to NAV corresponds to a period in which the medium is scheduled to be used by the AP and / or STA transmitting the frame, and the STA receiving the NAV value is prohibited from accessing the medium during the period. For example, the NAV may be set according to a value of a duration field of the MAC header of the frame.

15 illustrates a method for channel access in a WLAN system according to an embodiment of the present invention.

1 to 15, the horizontal axis of the AP 1500 represents time t, and the vertical axis of the AP 1500 may be associated with the presence of a frame transmitted by the AP 1500. The horizontal axis of the STA 1510 may represent time t1 and the vertical axis of the STA 1510 may be associated with the presence of a frame transmitted by the STA 1510.

Referring to FIG. 15, in the first period T1 to T2, the AP 1500 may transmit a beacon frame (hereinafter, referred to as 'BF'). For example, the transmission period of the beacon frame (BF) may be 100ms.

The beacon frame (BF) may include information about the EDCA parameter set corresponding to each AC shown in Table 2 above. Referring to Table 2 above, information on the EDCA parameter set includes AIFS [AC], CWmin [AC], CWmax [AC], and TXOP limit [AC] corresponding to each AC (AC_BK, AC_BE, AC_VI, AC_VO). can do.

In this specification, the information on the EDCA parameter set may be referred to as legacy EDCA set information for a first uplink operation mode of a single-user (hereinafter, referred to as 'SU').

In addition, the beacon frame BF may include MU EDCA aggregation information for a second uplink operation mode of a multi-user (hereinafter, referred to as 'MU').

For example, in the second uplink operation mode for a multi-user (MU), the MU EDCA set information may correspond to MU CWmin [AC], corresponding to each AC (AC_BK, AC_BE, AC_VI, AC_VO), as shown in Table 3 below. It may include values corresponding to MU CWmax [AC], MU AIFS [AC], and MU Timer [AC].

As an example, Table 3 shows that the values for MU CWmin [AC], MU CWmax [AC], and MU AIFS [AC] are twice the values for CWmin [AC], CWmax [AC], and AIFS [AC] in Table 2. Can be set to a large value.

It is to be understood that the value of Table 3 is set only twice as large as the set value of Table 2, and may be set to have a larger multiple. In addition, according to an embodiment, the drainage may be set differently for each AC.

By setting the EDCA parameter set as shown in Table 3, a penalty for lowering the transmission priority of the EDCA channel access performed by the STA that is likely to receive a trigger frame for uplink transmission from the AP may be granted.

The backoff counter for channel access of FIG. 15 may be defined individually for each STA. Each STA may set a random backoff time (RBT) calculated based on Equation 1 to the backoff counter.

For the sake of brevity, the unit of slot time in Equation 1 is assumed to be one slot. For example, if '10' is selected by the random function Random (i) of Equation 1, the random backoff time RBT set in the backoff counter may be represented by 10 slots.

Each STA may perform a countdown operation by counting down the random backoff time set in the backoff counter in a slot time unit.

For example, when the backoff counter of the STA is set to 10 slots, the STA may perform a countdown operation from 9 slots to reverse 0 slots. An STA that is slotted 0 before other STAs may be understood as an STA that has obtained channel access to the wireless medium.

The random function Random (i) of Equation 1 may be a function of selecting a random integer value between 0 and the contention window CW [i]. For example, by the random function Random (i), a value corresponding to CWmin [AC] may be set in the contention window CW [i].

The STA according to the present embodiment has a value corresponding to the contention window CW [i] based on legacy EDCA set information corresponding to Table 2 or MU EDCA set information corresponding to Table 3 according to the uplink operation mode of the STA. Can be set. In addition, if a collision occurs between STAs, the STA may recalculate the contention window CW [i] according to Equation 2 mentioned above.

In the second period T2 to T3, the STA 1510 may be a wireless terminal operating in a first uplink operation mode according to legacy EDCA set information included in the beacon frame BF.

Although the beacon frame BF of FIG. 15 is shown to include legacy EDCA aggregation information, it will be understood that embodiments according to the present disclosure may include embodiments when legacy EDCA aggregation information is preset in each STA. .

At the second time point T2, the STA 1510 may set a backoff counter based on the legacy EDCA set information corresponding to Table 2.

For example, if the data to be transmitted by the STA 1510 is of type AC_VI, the value corresponding to CWmin [AC_VI] is '15' and the value corresponding to CWmax [AC_VI] according to Table 2 may be '31'. have. Accordingly, '15' corresponding to CWmin [AC_VI] may be set in the contention window CW [i] for the STA 1510.

The random function random (i) of the STA 1510 may randomly select an integer value between '0' and '15'. For example, the random function random (i) of the STA 1510 may set the random value to '2'. Accordingly, the random backoff time (RBT) set in the backoff counter of the STA 1510 may be 2 slots.

In the second period T2 to T3, the STA 1510 may complete the countdown operation. The STA 1510 that has completed the countdown operation may be understood as a terminal obtaining channel access between the AP 1500 and another STA (not shown).

In the third period T3 to T4, the STA 1510 includes a frame including operating mode indication information for requesting approval of a second uplink operation mode for a multi-user (hereinafter, referred to as “station”). , OMI frame) may be transmitted to the AP 1500.

That is, the OMI frame transmitted by the AP 1500 in the third period T3 to T4 may be understood as a frame indicating that the STA 1510 may support UL operation mode for multiple users (UL MU enable). have.

For example, the OMI frame transmitted in the third period T3 to T4 may be a QoS data frame including a MAC header and a payload. In this case, an operation for requesting the approval of the second uplink operation mode for the multi-user (that is, informing the UE from the viewpoint of the uplink operation mode for the multi-user (UL MU enable) is notified) Mode indication (OMI) information may be included in the MAC header of the OMI frame.

In addition, the AC_VI type data according to the foregoing assumption may be included in the payload of the OMI frame. The OMI frame will be described in more detail with reference to the accompanying drawings.

The STA 1510 may receive an ACK frame in response to the OMI frame. The STA 1510 may receive an acknowledgment (ACK) frame that approves the second uplink operation mode of the STA 1510 from the AP 1500.

At the fourth time point T4, if an ACK frame is received in response to the OMI frame, the STA 1510 resets the backoff counter of the STA 1510 based on the MU EDCA set information corresponding to Table 3 below. can do.

For example, if the data to be transmitted by the STA 1510 is of type AC_VI, the value corresponding to MU CWmin [AC_VI] is '30' and the value corresponding to MU CWmax [AC_VI] is '62' according to Table 3 below. Can be. Accordingly, '30' may be set in the contention window CW [i] for the STA 1510 in the MU CWmin [AC_VI].

The random function Random (i) of the STA 1510 may randomly select an integer value between '0' and '30'. For example, the random function Random (i) of the STA 1510 of FIG. 15 may set the random value to '25'. Accordingly, the random backoff time (RBT) set in the backoff counter of the STA 1510 may be 25 slots.

Specifically, when the ACK frame is received in response to the OMI frame at the fourth time point T4, the STA 1510 based on the MU Timer [AC] corresponding to each AC among the MU EDCA set information corresponding to Table 3. The MU timer operation can be performed for a preset time.

If the data to be transmitted by the STA 1510 according to the present embodiment is an AC_BK type, the STA 1510 performing the MU timer operation may determine MU CWmin [AC_BK] and MU CWmax [AC_BK] corresponding to the AC_BK types in Table 3. It can be effectively used during the time period tm1 corresponding to the MU Timer [AC_BK].

As an example, if the data to be transmitted by the STA 1510 according to the present embodiment is of the AC_BE type, the STA 1510 performing the MU timer operation may use the MU CWmin [AC_BE] and the MU CWmax [corresponding to the AC_BE types of Table 3; AC_BE] can be effectively used during the time period tm2 corresponding to the MU Timer [AC_BE].

As an example, if the data to be transmitted by the STA 1510 according to the present embodiment is an AC_VI type, the STA 1510 performing the MU timer operation may use the MU CWmin [AC_VI] and the MU CWmax [corresponding to the AC_VI types in Table 3. AC_VI] can be effectively used during the time period tm3 corresponding to the MU Timer [AC_VI].

As an example, if the data to be transmitted by the STA 1510 according to the present embodiment is an AC_VO type, the STA 1510 performing the MU timer operation may use the MU CWmin [AC_VO] and the MU CWmax [corresponding to the AC_VO types shown in Table 3 below. AC_VO] can be effectively used during the time period tm4 corresponding to the MU Timer [AC_VO].

For the sake of brevity of FIG. 15, in a subsequent section, it is assumed that data to be transmitted by the STA 1510 is of type AC_VI.

The STA 1510 of FIG. 15 corresponds to the MU CWmin [AC_VI] from the fourth time point T4 to the eleventh time point T11 based on the first MU timer MU Timer # 1 corresponding to the MU Timer [AC_VI]. And a value corresponding to MU CWmax [AC_VI] may be used as a valid value for the backoff counter.

For example, the time section tm3 according to the first MU timer MU Timer # 1 may be understood as a section corresponding to T4 to T11 of FIG. 15.

When the time interval corresponding to the MU Timer [AC] elapses, the STA may perform channel access after setting the backoff counter again based on the legacy EDCA set information corresponding to Table 2.

In the fourth period T4 to T5, the STA 1510 may perform a countdown operation until the reception time T5 of the trigger frame (hereinafter, referred to as 'TF'). For example, the STA 1510 may reduce the slot '4' from the preset '25' slot until the reception time T5 of the trigger frame TF.

In the fifth period T5 to tT6, the STA 1510 may receive a trigger frame for individually allocating a plurality of uplink radio resources for multiple users (ie, a plurality of user terminals).

The uplink radio resource mentioned in the present specification may be understood as a resource unit (RU) referred to through FIGS. 4 to 6.

The trigger frame TF of FIG. 15 may be understood through the foregoing FIGS. 9 to 11. The trigger type field 1060 of the trigger frame TF of FIG. 15 may be set to indicate a trigger frame of a basic type.

When the trigger frame is received, the STA 1510 according to the present embodiment may stop the countdown operation. According to the present embodiment, the MU timer of the STA 1510 may be updated whenever a new trigger frame is received in a time interval set according to the MU timer.

At the sixth time point T6, when the basic type trigger frame TF is received, the STA 1510 resets the backoff counter of the STA 1510 again based on the MU EDCA set information corresponding to Table 3. )can do.

For example, if the data to be transmitted by the STA 1510 is an AC_VI type, the MU CWmin [AC_VI] may be '30' and the MU CWmax [AC_VI] may be '62' according to Table 3 below. Accordingly, '30' corresponding to the MU CWmin [AC_VI] may be set in the contention window CW [i] for the STA 1510.

The random function Random (i) of the STA 1510 may randomly select an integer value between '0' and '30'. For example, the random function Random (i) of the STA 1510 of FIG. 15 may set the random value to '28'. Accordingly, the random backoff time (RBT) set in the backoff counter of the STA 1510 may be 28 slots.

At the sixth time point T6, when the basic type trigger frame TF is received, the STA 1510 is preset based on the MU Timer [AC] corresponding to each AC among the MU EDCA set information corresponding to Table 3. You can perform the MU timer operation for a time.

At the sixth time point T6, when the trigger frame TF is received, the first MU timer MU Timer # 1 of the STA 1510 may be updated with a new second MU timer MU Timer # 2.

For example, the second MU timer MU Timer # 2 may correspond to the MU Timer [AC_VI] like the first MU timer MU Timer # 1. That is, the time section tm3 according to the second MU timer MU Timer # 2 may be understood as a section corresponding to T6 to T12 of FIG. 15.

Accordingly, the STA 1510 corresponds to the MU CWmin [AC_VI] and the MU CWmax [AC_VI] until the twelfth time point T12 based on the second MU timer MU Timer # 2 corresponding to the MU Timer [AC_VI]. The value can be used as a valid value for the backoff counter. For example, the time lengths of T6 to T12 of FIG. 15 and the time lengths of T4 to T11 of FIG. 15 may be the same.

For example, the STA 1510 according to the present embodiment slots '28' from the time point T6 at which the trigger frame TF is received to the time point T12 of the updated second MU timer MU Timer # 2. Can be reduced by '17' slots.

The sixth section T6 to T7 may be understood as a short inter-frame space (SIFS).

In the seventh period T7 to T8, the STA 1510 may transmit a trigger-based uplink frame (Trigger-based PPDU) in response to the trigger frame TF.

The trigger-based PPDU may be transmitted through an uplink radio resource individually allocated to the STA 1510 among a plurality of uplink radio resources allocated through the trigger frame TF.

The trigger-based uplink frame (Trigger-based PPDU) may include data of type AC_VI to be transmitted by the STA 1510. However, the trigger-based uplink frame (Trigger-based PPDU) does not include the data of the AC_VI type to be transmitted by the STA 1510, and may include data of other AC types (AC_VO, AC_BE, AC_BK).

The eighth section T8 to T9 may be understood as SIFS.

In the ninth period T9 ˜ T10, the AP 1500 may transmit a block ACK (BA) frame to inform successful reception of a trigger-based PPDU from the STA 1510.

Although not shown through FIG. 15, the BA frame successfully receives another trigger based uplink frame (not shown) received via an uplink radio resource allocated to another STA (not shown) at a time overlapping with the STA 1510. It can be used to inform.

At a twelfth time T12 when the second MU timer MU Timer # 2 expires, the STA 1510 may reset the backoff counter based on the legacy EDCA set information corresponding to Table 2.

For example, if the data to be transmitted by the STA 1510 is an AC_VI type, CWmin [AC_VI] may be '15' and CWmax [AC_VI] may be '31' according to Table 2. According to the foregoing assumption, '15' corresponding to CWmin [AC_VI] may be set in the competition window CW [i].

The random function random (i) of the STA 1510 may randomly select an integer value between '0' and '15'. For example, the STA 1510 of FIG. 15 may set the random value to '11'. That is, the random backoff time (RBT) set in the backoff counter of the STA 1510 may be 11 slots.

Thereafter, the STA 1510 may again perform a countdown operation based on 11 slots set in the backoff counter for channel access to the wireless medium.

The STA according to the present embodiment accesses a channel based on a backoff counter set according to the MU EDCA set information from a time point T4 when an ACK frame is received from the AP in response to the OMI information to a time point T5 before reception of the trigger frame. Can be performed.

Accordingly, according to the present embodiment, a WLAN system having improved performance in terms of fairness of channel access to a wireless medium performed by a plurality of terminals may be provided.

16 is a diagram illustrating a method for channel access in a WLAN system according to another embodiment.

1 through 16, the horizontal axis of the AP 1600 represents time t, and the vertical axis of the AP 1600 may be associated with the presence of a frame transmitted by the AP 1600.

The horizontal axis of the first STA 1610 may represent time t1, and the vertical axis of the first STA 1610 may be associated with the presence of a frame transmitted by the STA 1610. The horizontal axis of the second STA 1620 may represent time t2, and the vertical axis of the second STA 1620 may be associated with the presence of a frame transmitted by the second STA 1620.

In the first period T1 to T2 of FIG. 16, the beacon frame BF transmitted by the AP 1600 may be understood as a description of the beacon frame BF of FIG. 15. In a subsequent time interval, data to be transmitted by the first STA 1610 and the second STA 1610 may be assumed to be an AC_VI type.

Although the beacon frame BF of FIG. 16 is shown to include legacy EDCA aggregation information, it will be understood that another embodiment according to the present disclosure may include an embodiment in which legacy EDCA aggregation information is previously set in each STA. will be.

In the second period T2 to T3 of FIG. 16, the first STA 1610 may set the random backoff time 9 based on the legacy EDCA set information included in the beacon frame BF of the first STA 1610. Can be set on the backoff counter.

The first STA 1610 may reduce the number of slots by 6 slots until the reception time T3 of the trigger frame TF by performing a countdown operation based on the backoff counter in which the '9' slot is set.

The second STA 1620 may set the random backoff time 14 to the backoff counter of the second STA 1620 based on the legacy EDCA set information included in the beacon frame BF.

The second STA 1620 may reduce the number of slots by 6 slots until the reception time T3 of the trigger frame TF by performing a countdown operation based on the backoff counter in which the '14' slot is set.

In the third period (T3 ~ T4), the first STA 1610 and the second STA 1620 are a plurality of uplink radio resources (ie, resource unit (RU)) for multiple users (ie, a plurality of user terminals) ) Can receive a trigger frame (TF) to individually assign. In this case, the trigger frame TF may be understood through the foregoing FIGS. 9 to 11.

In addition, the trigger type field 1060 of the trigger frame TF according to the present embodiment may be set to indicate a trigger frame of a basic type.

When the trigger frame TF is received, the first STA 1610 according to the present embodiment may stop the countdown operation according to the legacy EDCA set information.

When the trigger frame TF is received, the second STA 1620 according to another embodiment may stop the countdown operation according to the legacy EDCA set information.

At the fourth time point T4, when a basic type trigger frame TF is received, the first STA 1610 determines a backoff counter of the first STA 1610 based on the MU EDCA aggregation information corresponding to Table 3. You can reset it again.

For example, if the data to be transmitted by the first STA 1610 is of type AC_VI, the value corresponding to MU CWmin [AC_VI] is' 30 'according to Table 3, and the value corresponding to MU CWmax [AC_VI] is' 62 '. Accordingly, '30' corresponding to the MU CWmin [AC_VI] may be set in the contention window CW [i] for the first STA 1610.

The random function Random (i) of the first STA 1610 may randomly select an integer value between '0' and '30'. For example, the random function Random (i) of the first STA 1610 may set the random value to '25'. Accordingly, the random backoff time (RBT) set in the backoff counter of the first STA 1610 may be 25 slots.

According to another exemplary embodiment, the first STA 1610 performs a backoff of the '25' slot from the time point T4 when the trigger frame TF is received to the time point T9 of the first MU timer MU Timer # 1. The counter can be decremented by the '19' slot.

 At the fourth time point T4, when the basic type trigger frame TF is received, the second STA 1620 may perform a backoff counter of the second STA 1620 based on the MU EDCA aggregation information corresponding to Table 3. You can reset it again.

For example, if the data to be transmitted by the second STA 1620 is of type AC_VI, the value corresponding to MU CWmin [AC_VI] is' 30 'according to Table 3, and the value corresponding to MU CWmax [AC_VI] is' 62 '. Accordingly, '30' corresponding to the MU CWmin [AC_VI] may be set in the contention window CW [i] for the second STA 1620.

The random function Random (i) of the second STA 1520 may randomly select an integer value between '0' and '30'. For example, the random function Random (i) of the second STA 1620 may set the random value to '30'. Accordingly, the random backoff time (RBT) set in the backoff counter of the second STA 1620 may be 30 slots.

For example, the second STA 1620 according to another embodiment of the present disclosure may perform a '30' from the time point T4 when the trigger frame TF is received to the time point T9 of the second MU timer MU Timer # 2. The backoff counter of the slot can be decremented by the '19' slot.

When the trigger frame TF is received, the first STA 1610 may start the first MU timer MU Timer # 1 from the fourth time point T4. Referring to Table 3, when the data frame to be transmitted by the first STA 1610 is an AC_VI type, the time interval t3 corresponding to the first MU timer MU Timer # 1 may be set from the fourth time point to the fourth time point in FIG. 16. It may be understood as the ninth time points T4 to T9.

Similarly, when the trigger frame TF is received, the second STA 1620 may start the second MU timer MU Timer # 2 from the fourth time point T4. Referring to Table 3, when the data frame to be transmitted by the second STA 1620 is of type AC_VI, the time interval t3 corresponding to the second MU timer MU Timer # 2 is determined from the fourth time point to the fourth time point in FIG. 16. It may be understood as the ninth time points T4 to T9.

The above example assumes that the first STA 1610 and the second STA 1620 transmit the same type of data frame, but it is to be understood that the present specification is not limited thereto.

In other words, when the data frame to be transmitted by the first STA 1610 is AC_BK, the time period tm1 corresponding to the first MU timer MU Timer # 1 may have a different time length. When the data frame to be transmitted by the second STA 1620 is AC_BE, the time period tm1 corresponding to the second MU timer MU Timer # 2 may have a different time length.

When the trigger frame TF is received, each STA 1610 and 1620 sets the parameter set for the contention window CW [i] of the backoff counter to the MU corresponding to Table 3 in the legacy EDCA set information corresponding to Table 2. Can be replaced with EDCA aggregation information.

That is, when the trigger frame TF is received, each STA 1610 and 1620 may determine the initial value of the backoff counter based on the contention window CW [i] set according to the MU EDCA set information.

The fourth section T4 to T5 may be understood as a short inter-frame space (SIFS).

In the fifth period T5 to T6, the first STA 1610 may transmit a first trigger-based uplink frame (Trigger-based PPDU # 1) in response to the trigger frame TF.

The first trigger-based uplink frame (Trigger-based PPDU # 1) is transmitted through an uplink radio resource individually allocated to the first STA 1610 among a plurality of uplink radio resources allocated through the trigger frame TF. Can be.

The second STA 1620 may transmit a second trigger-based uplink frame (Trigger-based PPDU # 2) in response to the trigger frame (TF).

The second trigger-based uplink frame (Trigger-based PPDU # 2) is transmitted through an uplink radio resource individually allocated to the second STA 1620 among a plurality of uplink radio resources allocated through the trigger frame (TF). Can be.

The first trigger-based uplink frame (Trigger-based PPDU # 1) and the second trigger-based uplink frame (Trigger-based PPDU # 2) are uplink frames transmitted to the AP through overlapping time intervals T5 to T6. It can be understood as.

The sixth section T6 to T7 may be understood as SIFS.

In the seventh period (T7 to T8), the AP 1600 is the first and second trigger-based uplink frame (Trigger-based PPDU # 1, Trigger-based) from the first STA (1610) and the second STA (1620) A Block ACK (BA) frame may be transmitted to indicate successful reception of PPDU # 2).

That is, the BA frame is the first and second trigger-based uplink frames (Trigger-based PPDU # 1, Trigger) received through the uplink radio resources individually allocated to the first STA 1610 and the second STA 1620. -based PPDU # 2) may be used to signal successful reception.

For reference, it will be understood that the AP may inform successful reception of two or more terminals simultaneously through a BA frame.

In the eighth period T8 to T9, the first STA 1610 and the second STA 1620 may continue to perform separate countdown operations.

At a ninth time point T9, the first MU timer MU Timer # 1 and the second MU timer MU Timer # 2 may expire. Accordingly, each STA 1610 and 1620 replaces the parameter set for the contention window CW [i] of the backoff counter with the legacy EDCA set information corresponding to Table 2 in the MU EDCA set information corresponding to Table 3. Can be.

That is, when the MU timer expires, each STA 1610, 1620 may re-determine an initial value of the backoff counter based on the contention window CW [i] set according to the legacy EDCA set information.

At the ninth time point T9, each STA 1610 and 1620 may resume the backoff counter according to the legacy EDCA aggregation information suspended at the third time point T3.

For example, the first STA 1610 may resume the '3' slot which is the value of the backoff counter according to the legacy EDCA set information suspended at the third time point T3. The second STA 1620 may resume the '8' slot which is the value of the backoff counter according to the legacy EDCA set information suspended at the third time point T3.

17 and 18 are diagrams illustrating a format of an element for MU EDCA aggregation information according to the present embodiment.

1 to 17, an element including MU EDCA aggregation information may be referred to as MU EDCA element 1700. The MU EDCA element 1700 may be included in a beacon frame transmitted periodically by the AP. The MU EDCA element 1700 may include a plurality of fields 1710, 1720, 1730, 1740, 1750, 1760, 1770, 1780.

The element ID field 1710 may be set to a value for indicating the MU EDCA element 1700 among at least one element information included in the beacon frame. For example, one octet may be allocated for the element ID field 1710.

The length field 1720 may be set to a value to indicate the total number of bits allocated for the MU EDCA element 1700. For example, one octet may be allocated for the length field 1720.

The element ID extension field 1730 may include additional information for the element ID field 1710. For example, one octet may be allocated for the element ID extension field 1730.

The MU QoS information field 1740 may include information for determining whether to change the MU EDCA set information. For example, one octet may be allocated for the MU QoS information field 1740.

The MU AC_BE parameter record field 1750, the MU AC_BK parameter record field 1760, the MU AC_VI parameter record field 1770, and the MU AC_VO parameter record field 1780 may include MU EDCA parameters corresponding to each AC.

Each of the MU AC_BE parameter recording field 1750, the MU AC_BK parameter recording field 1760, the MU AC_VI parameter recording field 1770, and the MU AC_VO parameter recording field 1780 has a structure of a subfield of FIG. 18 described below.

1 to 18, the plurality of subfields 1810, 1820, and 1830 of FIG. 18 may be included in the MU AC_BE parameter recording field 1750. The plurality of subfields 1810, 1820, and 1830 of FIG. 18 may be included in the MU AC_BK parameter recording field 1760.

The plurality of subfields 1810, 1820, and 1830 of FIG. 18 may be included in the MU AC_VI parameter recording field 1770. The plurality of subfields 1810, 1820, and 1830 of FIG. 18 may be included in the MU AC_VO parameter recording field 1780.

Hereinafter, for the sake of brevity, the description will be made based on the plurality of subfields 1810, 1820, and 1830 included in the MU AC_VI parameter recording field 1770.

The ACI / AIFSN subfield 1810 may include a value corresponding to MU AIFS [AC_VI] of Table 3 above. The ECWmin / ECWmax subfield 1820 may include values corresponding to MU CWmin [AC_VI] and MU CWmax [AC_VI] in Table 3 above. The MU EDCA timer subfield 1830 may include a value corresponding to the MU Timer [AC_VI] of Table 3 above.

For reference, more details on the MU EDCA element are referred to in section 9.4.2.221 of the standard document IEEE Draft P802.11ax ™ / D1.0, disclosed in November 2016.

19 to 21 illustrate a format for an OMI frame according to the present embodiment.

1 to 19, a MAC frame 1900 including operating mode indication (OMI) information for the present embodiment may include a plurality of fields 1911 to 1919 constituting a MAC header and payload. It may include a frame body field 1920 including a payload and having a variable length, and an FCS field 1930 used to confirm the integrity of the corresponding MAC frame. The MAC frame 1900 including the operation mode indication information may be understood as the OMI frame of FIG. 15.

The frame control field 1911, the duration / ID field 1912, the first address field 1913, and the last field of the MAC frame among the plurality of fields 1911 to 1919 included in the MAC header are all. Type may be included in the MAC frame.

In contrast, the second address field 1914, the third address field 1915, the sequence control field 1916, the fourth address field 1917, the quality of service (QoS) control field 1918, and the HT control field 1919 ) And frame body field 1920 may optionally be included in a particular type of MAC frame.

For the sake of brevity and clarity herein, it is assumed that the MAC frame 1900 of FIG. 19 is a QoS data frame or a QoS null frame. In addition, according to a specific value set in the frame control field 1911 of the MAC frame 1900 of FIG.

It is assumed that the HT control field (1919).

For reference, more details on QoS data frames or QoS null frames are referred to through section 9.3.2.1 of the standard document IEEE Draft P802.11-REVmc ™ / D8.0, which was published in August 2016.

1 to 20, the A-Control field 2010 of FIG. 20 represents a plurality of subfields included in the HT control field 1919 of FIG. 19.

Specifically, when the first bit and the second bit Bit 0-1 of the HT control field 1919 of FIG. 19 including 4 octets (32 bits) are set to '11', the HT control field ( The remaining bits Bit2-31 of 1919 may be allocated for the A-Control subfield 2010 of FIG. 20.

The A-Control field 2010 may include a sequence of at least one control information subfield (Control 1, ..., Control N). For example, the N-th control subfield 2020 may include a control ID subfield 2030 having a length of 4 bits and a control information subfield 2040 having a variable length. For example, the first control information subfield Control 1 may be the first subfield of the A-Control field 2010.

The control ID subfield 2030 may indicate the type of information included in the control information subfield 2040. The control information subfield 2040 related to the value of the control ID subfield 2030 may be defined as shown in Table 4 below.

Referring to Table 4, when the control ID subfield 2030 is set to '1', 12 bits of the control information subfield 2040 indicate a change in the operating mode of the STA transmitting the frame. May be assigned to indicate information to request.

Specifically, the information for requesting the change of the operation mode may indicate information for requesting the approval of the uplink operation mode for the multi-user.

In other words, as described above with reference to FIG. 15, the STA in the first uplink operation mode for a single user (SU) changes to a second uplink operation mode for a multi-user (MU) to the AP by transmitting an OMI frame. You can request

1 to 21, in order to change the operation mode mentioned in FIG. 20, the control information subfield 2100 includes all or part of the plurality of subfields 2110, 2120, 2130, 2140, and 2150. can do.

In addition, the control information subfield 2100 may further include a subfield not shown in FIG. 14 or may include only a part of the subfields shown in FIG. 21.

The Rx NSS subfield 2110 of FIG. 21 is a spatial stream used by a STA (eg, a non-AP STA) transmitting the control information subfield 2100 to receive a signal (eg, a PPDU). ) May be indicated. The Rx NSS subfield 2110 may include 3 bits.

The Rx NSS subfield 2110 may indicate the number of spatial streams that the STA uses for receiving the downlink PPDU. That is, the AP may configure a downlink PPDU for a specific user STA with reference to the corresponding subfield 2110.

The channel width subfield 2120 may indicate an operating channel width supported by an STA (eg, a non-AP STA) transmitting the control information subfield 2100.

For example, if the value set in the Channel Width subfield 2120 is '0', the width of the operating channel is 20 MHz, and if the width is '1', the width of the operating channel is 40 MHz, and the width of the operating channel is 80 MHz and '3'. ', The width of the operating channel can indicate 160MHz or 80 + 80MHz.

The UL MU Disable subfield 2130 may indicate whether a STA (eg, a non-AP STA) transmitting the control information subfield 2100 participates in UL MU MIMO transmission.

For example, if the STA determines not to participate in the UL MU MIMO transmission (ie, when the UL MU operation is suspended), a specific value (for example, '1') in the UL MU Disable subfield 2130 is determined. ) May be indicated.

As another example, when the STA determines to participate in the UL MU MIMO transmission (ie, when the UL MU operation is resumed), a specific value (eg, '0') in the UL MU Disable subfield 2130 is determined. This can be indicated.

According to the present embodiment, the STA in the first uplink operation mode for a single user (SU) transmits an OMI frame to the AP to request a change of the operation mode to the second uplink operation mode for a multi-user (MU). Can be. In this case, the OMI frame may be set to a specific value (eg, '0') in the UL MU Disable subfield 2130.

In order to indicate that the UL operation mode for the multi-user can be supported (UL MU enable), the STA may transmit an OMI frame assigned a specific value (eg, '0') to the UL MU Disable subfield 2130. Can be.

The Tx NSS subfield 2140 of FIG. 21 is a spatial stream used for transmission of a signal (eg, PPDU) by an STA (eg, a non-AP STA) transmitting the control information subfield 2100. number of streams). The reserved field 2150 of FIG. 21 may include 3 bits.

21 is an example in which the Rx NSS 2110 and Tx NSS 2140 subfields are separately configured, but it will be understood that the subfields may be modified.

For example, Rx NSS (ie, number of spatial streams used for PPDU reception at a specific STA) and Tx NSS (ie, number of spatial streams used for PPDU transmission at a specific STA) through one NSS subfield. It may be possible to indicate in common.

As an additional example, after transmission of an OMI frame in which a specific value (for example, '0') is assigned to the UL MU Disable subfield 2130, an STA that has not received a trigger frame of a basic type for a predetermined time again sets a legacy EDCA set. Channel access is performed based on the information.

The STA that transmits an OMI frame to which a specific value (for example, '0') is allocated in the UL MU Disable subfield 2130 may directly use the MU EDCA aggregation information instead of the legacy EDCA aggregation information.

In addition, an STA that transmits an OMI frame assigned a specific value (for example, '0') in the UL MU Disable subfield 2130 may perform legacy information on a relatively high transmission priority data frame such as an AC_VI and an AC_VO type. EDCA aggregation information can be used as it is.

However, an STA that transmits an OMI frame assigned a specific value (for example, '0') in the UL MU Disable subfield 2130 may perform an MU for a data frame having a relatively low transmission priority such as an AC_BE and an AC_BK type. EDCA aggregation information can be used directly.

As an additional embodiment, a bit is added to some bits (eg, 1 bit) of the HE operation element included in the conventional beacon frame without a separate frame, thereby changing to a second uplink operation mode for a multi-user (MU). You can request

Alternatively, by adding some bits of the HE capabilities element included in the conventional beacon frame, it may request a change to the second uplink operation mode for the multi-user (MU). Alternatively, by adding some bits to the MU EDCA parameter element included in the conventional beacon frame, a change may be requested to the second uplink operation mode for the multi-user (MU).

22 is a flowchart illustrating a method for channel access in a WLAN system according to an embodiment.

1 to 22, in operation S2210, a first wireless terminal (ie, a user STA) requests an operation mode indication for requesting approval of an uplink operation mode for a multi-user. Hereinafter, 'OMI' information may be transmitted to the second wireless terminal (ie, AP).

The operation mode indication (OMI) information may be information included in a medium access control (MAC) header of a quality of service (QoS) data frame or a MAC header of a QoS null frame.

In step S2210, for the channel access to the wireless medium, the first wireless terminal may be understood as a terminal that has completed the countdown operation based on the backoff counter set according to the legacy EDCA set information of Table 2.

In operation S2220, an ACK frame for notifying successful reception of an uplink frame including operation mode indication (OMI) information may be received from the second wireless terminal.

The first wireless terminal receiving the ACK frame may determine that the uplink operation mode for the multi-user (MU) requested by the first wireless terminal is approved by the second wireless terminal.

In step S2230, the first wireless terminal may reset the backoff counter for channel access according to the MU EDCA set information of Table 3. In this case, the MU EDCA set information may be effectively used for a preset time interval according to the MU timer information included in the MU EDCA set information.

For channel access to the wireless medium, the first wireless terminal may perform a second countdown operation based on the reset backoff counter. For example, the second countdown operation may be performed before reception of a trigger frame for individually allocating a plurality of uplink radio resources for uplink transmission from the second wireless terminal.

When a preset period passes without receiving the trigger frame, the first wireless terminal may reset the backoff counter based on the legacy EDCA set information of Table 2.

In the present specification, the trigger frame is a trigger frame of a basic type, and may be understood as a frame received within a preset time interval.

The first wireless terminal may transmit the trigger-based uplink frame to the second wireless terminal through a radio resource allocated to the first wireless terminal among the plurality of wireless resources in response to the trigger frame.

The legacy EDCA aggregation information of Table 2 and the MU EDCA aggregation information of Table 3 may be information included in the most recently received beacon frame among the beacon frames transmitted periodically from the second wireless terminal.

FIG. 23 is a diagram illustrating a method for a wireless terminal to perform an individual TWT operation and an MU EDCA timer operation according to another exemplary embodiment.

 1 to 23, the horizontal axis of the AP 2300 represents time t, and the vertical axis of the AP 2300 may be associated with the presence of a frame transmitted by the AP 2300.

In addition, the horizontal axis of the STA 2310 may represent time t1, and the vertical axis of the STA 2310 may be associated with the existence of a frame transmitted by the STA 2310.

The STA 2310 may be understood as a wireless terminal operating in a power save (PS) mode. The STA 2310 in the power save mode PS may switch from the awake state to the sleep state. The STA 2310 in the power save mode PS may switch from the sleep state to the awake state.

For example, the STA 2310 in the power save mode PS may operate in an awake state in which a frame can receive or transmit a frame. Alternatively, the STA 2310 in the power save mode PS may operate in a doze state in which a frame cannot be received or transmitted.

Referring to FIG. 23, in the first period T1 to T2, the AP 2300 and the STA 2310 may perform individual negotiation. The STA 2310 may transmit a target wake time (TWT) request frame to the AP 2300.

For example, the TWT request frame may be a frame for requesting information on a reception time of the beacon frame and interval information of the beacon frame.

In the first period T1 to T2, the AP 2300 may transmit a TWT response frame in response to the TWT request frame. The TWT response frame may include information on a reception time of the beacon frame and interval information of the beacon frame.

That is, through the received TWT response frame, the STA 2310 may obtain information about a reception time (eg, T3) of the beacon frame and interval information (eg, T3 to T7) of the beacon frame.

In the second period T2 to T3, the STA 2310 may switch to the sleep state according to the information on the reception time T3 of the beacon frame. The STA 2310 may maintain the switched sleep state for the second period T2 to T3.

At the third time point T3, the STA 2310 may switch from the sleep state to the awake state for receiving the first beacon frame BF # 1 according to the information on the reception time T3 of the beacon frame. .

In the third period T3 to T4, the STA 2310 may receive the first beacon frame BF # 1 transmitted from the AP 2300.

For example, the first beacon frame BF # 1 may include start time information of the first TWT service section TWT SP # 1 and duration information of the first TWT service section TWT SP # 1.

In addition, the first beacon frame (BF # 1) may include information on the transmission time of the trigger frame (TF) including a plurality of resource units for uplink transmission in the first TWT service interval (TWT SP # 1). Can be.

That is, through the received first beacon frame (BF # 1), STA 2310, the first beacon frame (BF # 1) is the start time information of the first TWT service interval (TWT SP # 1) (for example, T5 ) And duration information (eg, T5 to T6) of the first TWT service period (TWT SP # 1).

Also, through the received first beacon frame BF # 1, the STA 2310 may acquire information about a transmission time point T5_1 of the trigger frame TF in the first TWT service period TWT SP # 1. Can be.

In the fourth section T4 to T5, the STA 2310 may switch to the sleep state according to the start time information of the first TWT service section TWT SP # 1. The STA 2310 may maintain the switched sleep state for the fourth period T4 to T5.

At the fifth time point T5, the STA 2310 may switch from the sleep state to the awake state according to the start time information of the first TWT service period TWT SP # 1.

In the fifth section T5 to T6, the STA 2310 may maintain an awake state according to the duration information of the first TWT service section TWT SP # 1.

The STA 2310 may receive the trigger frame at a specific time point T5_1 according to the information on the transmission time point of the trigger frame TF. In addition, the STA 2310 may start an MU timer operation for MU EDCA set information from a time point T5_2 when reception of the trigger frame TF is completed.

MU EDCA aggregation information may be understood as information corresponding to Table 3 above. The MU EDCA aggregation information may be used for the backoff value set in the backoff counter of the channel access operation performed by the STA.

The MU timer operation may be performed by the STA 2310 during a time period in which the STA may effectively use the MU EDCA set information corresponding to Table 3 for channel access.

According to another embodiment, the MU timer operation may be performed from the start time T5_2 to the completion time T6 of the first TWT service section TWT SP # 1. The MU timer operation may be stopped in a section outside the first TWT service section (TWT SP # 1).

At the sixth time point T6, the STA 2310 may switch to the sleep state according to the duration information of the first TWT service period TWT SP # 1. The STA 2310 may maintain a sleep state for the sixth period T6 to T7 according to interval information of the beacon frame.

Since the sixth section T6 to T7 is not a TWT service section (TWT SP), the MU timer operation according to the present embodiment may be stopped during the sixth section T6 to T7.

At the seventh time point T7, the STA 2310 may switch from the sleep state to the awake state for receiving the second beacon frame BF # 2 according to the interval information of the beacon frame.

In the seventh period T7 to T8, the STA 2310 may receive a second beacon frame BF # 2 transmitted from the AP 2300.

For example, the second beacon frame BF # 2 may include start time information of the second TWT service section TWT SP # 2 and duration information of the second TWT service section TWT SP # 2.

That is, through the received second beacon frame (BF # 2), STA 2310, the second beacon frame (BF # 2) is the start time information of the second TWT service interval (TWT SP # 2) (for example, T9 ) And duration information (eg, T9 to T10) of the second TWT service interval (TWT SP # 2).

At the eighth time point T8, the STA 2310 may switch to the sleep state according to the start time point information of the second TWT service section TWT SP # 2. The STA 2310 may maintain the switched sleep state for the eighth period T8 to T9.

At the ninth time point T9, the STA 2310 may switch from the sleep state to the awake state according to the start time information of the second TWT service interval TWT SP # 2. The STA 2310 may maintain an awake state for the ninth periods T9 to T10 according to the duration information of the second TWT service period TWT SP # 2.

Since the ninth section T9 to T10 is a TWT service section (TWT SP), the MU timer operation according to another embodiment may be resumed during the ninth section T9 to T10.

Referring to FIG. 23, the MU timer operation may be completed at a specific time point T9_1 of the ninth periods T9 to T10.

In the remaining periods T9 to 1 to T10, the STA 2310 may replace the MU EDCA set information with the legacy EDCA set information corresponding to Table 3. Legacy EDCA aggregation information may be used for the backoff value set in the backoff counter of the channel access operation performed by the STA.

According to another embodiment of FIG. 23, an STA of a WLAN system may perform an MU timer operation only in a TWT service interval. According to another embodiment of the present disclosure, the operation of transmitting a data frame by waking up by the EDCA operation in the section where the STA is in the sleep state can be prevented. Accordingly, a WLAN system using power more efficiently may be provided.

Although not shown in FIG. 23, in another embodiment, when a trigger frame is not received in a specific number of TWT service intervals without consideration for the MU timer, the STA may perform channel access based on the legacy EDCA aggregation information.

Alternatively, if the trigger state reporting polling type trigger frame is not received in the TWT service interval of a certain number of times, the STA may determine that the MU timer expires by itself.

Although not shown in FIG. 23, as another embodiment, a new MU timer value used in the TWT service period may be defined by considering the TWT service interval or the TWT service period in the TWT service period. That is, the STA may perform the MU timer operation based on the new MU timer value in the TWT service interval.

Referring to FIG. 23, in an individual TWT operation, an STA may transmit a TWT request frame and receive a TWT response frame in response thereto.

For example, the TWT request frame may include an EDCA request indicator for requesting channel access according to any one of legacy EDCA set information corresponding to Table 2 and MU EDCA set information corresponding to Table 3.

As another example, the TWT response frame may include an EDCA command indicator for instructing channel access according to any one of legacy EDCA set information corresponding to Table 2 and MU EDCA set information corresponding to Table 3.

24 is a diagram illustrating a TWT element including an EDCA request indicator or an EDCA command indicator according to another embodiment.

1 to 24, a TWT element 2400 according to another embodiment may be included in a TWT request frame transmitted by an STA or a TWT response frame transmitted by an AP. According to another exemplary embodiment, the TWT element 2400 may include a plurality of fields 2410-2430 and 2441-2448.

One octet may be allocated for the Element ID field 2410. The Element ID field 2410 may be set to a value for indicating the TWT element 2400 among at least one element information included in the beacon frame.

One octet may be allocated for the length field 2420. The length field 2420 may be set to a value indicating the total number of bits allocated for the TWT element 2400.

One octet may be allocated for the Control field 2430. The control field 2430 may include an indicator indicating whether the TWT service interval (TWT SP) according to the TWT element 2400 is a broadcast TWT interval for a plurality of STAs.

Hereinafter, to indicate an individual TWT interval, it is assumed that the control field 2430 does not include an indicator indicating a broadcast TWT interval.

Two octets may be allocated for the Request field 2441. Information on the TWT FID Identifier may be included in the eighth to tenth bits B7-B9 and 2449 of the request field 2441. The request field 2441 may include information on a TWT flow identifier shown in Table 5 below.

Referring to Table 5, an allowance group may be classified into three groups according to a TWT flow identifier (TWT FID).

The first grant group is a case where the TWT flow identifier (TWT FID) is '0'. For example, when the STA receives a beacon frame having a TWT FID of '0', the STA may transmit all types of frames without limiting the frames that can be transmitted in the TWT service interval.

The second allowed group is a case where the TWT flow identifier (TWT FID) is '1'. For example, when the STA receives a beacon frame having a TWT FID of '1', the STA may transmit a power-save poll frame, a quality of service null frame, A frame associated with sounding feedback and a management frame may be transmitted.

If the TWT FID is set to '1', the AP may not transmit a trigger frame including at least one resource unit for random access for a random access procedure.

That is, the STA that receives the beacon frame in which the TWT FID is set to '1' cannot transmit a frame associated with random access. Further details of the random access procedure are disclosed in section 27.5.2.6.2 of the standard document IEEE 802.11ax / D1.0.

The third allowed group is a case where the TWT flow identifier (TWT FID) is '2'. For example, when the STA receives a beacon frame having a TWT FID of '2', the STA may transmit a power-save poll frame, a QoS null frame, a QoS null frame in the TWT service interval, A frame associated with sounding feedback and a management frame may be transmitted.

If the TWT flow identifier (TWT FID) is set to '2', the AP may transmit a trigger frame including at least one resource unit for random access for a random access procedure. That is, the STA that receives the beacon frame in which the TWT FID is set to '2' may transmit a frame associated with random access.

According to another embodiment of the present disclosure, the EDCA request indicator or EDCA command indicator mentioned through FIG. 23 may be included based on some values of '3' to '7' which are reserved values of the TWT flow identifier (TWT FID).

More details on the TWT element can be understood with reference to section 9.4.2.200 of the standard document IEEE P802.11ax / D1.0, disclosed in November 2016.

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

Referring to FIG. 25, the wireless terminal may be an AP or a non-AP station (STA) that may implement the above-described embodiment. 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 2500 includes a processor 2510, a memory 2520, and an RF unit 2530.

The RF unit 2530 may be connected to the processor 2510 to transmit / receive a radio signal.

The processor 2510 may implement the functions, processes, and / or methods proposed herein. For example, the processor 2510 may perform an operation according to the above-described exemplary embodiment. The processor 2510 may perform an operation of the AP disclosed in the present embodiment of FIGS. 1 to 24.

The non-AP STA 2550 includes a processor 2560, a memory 2570, and an RF unit 2580.

The RF unit 2580 may be connected to the processor 2560 to transmit / receive a radio signal.

The processor 2560 may implement the functions, processes, and / or methods proposed in the present embodiment. For example, the processor 2560 may be implemented to perform the non-AP STA operation according to the present embodiment described above. The processor 2560 may perform an operation of the non-AP STA disclosed in the present embodiment of FIGS. 1 to 24.

Processors 2510 and 2560 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices, and / or converters for interconverting baseband signals and wireless signals. The memories 2520 and 2570 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit 2530 and 2580 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 2520 and 2570 and executed by the processors 2510 and 2560. The memories 2520 and 2570 may be inside or outside the processors 2510 and 2560, and may be connected to the processors 2510 and 2560 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 (11)

1. In the method for channel access in a WLAN system,

   Performing, by the first wireless terminal, a first countdown operation based on a backoff counter set according to the first parameter set;

   When the first wireless terminal completes the first countdown operation, operating mode indication information for requesting approval of an uplink operation mode for a multi-user is transmitted to the second wireless terminal. Transmitting; And

   The first wireless terminal receives an Acknowledgment (ACK) frame acknowledging the uplink operation mode from the second wireless terminal, and the backoff counter is reset according to a second set of parameters for the uplink operation mode. and the second set of parameters is valid for a preset time period.
2. According to claim 1,

   The first wireless terminal receives a trigger frame for individually allocating a plurality of uplink radio resources from the second wireless terminal, wherein the reset backoff counter is received by the first wireless terminal until the trigger frame is received. Decreasing in accordance with a second countdown operation performed.
3. The method of claim 2,

   And when the preset time interval elapses, the first wireless terminal resetting the backoff counter according to the first parameter set.
4. The method of claim 2,

   The first wireless terminal transmits a trigger-based uplink frame through a radio resource allocated to a first wireless terminal among the plurality of uplink radio resources in response to the trigger frame, wherein the backoff is performed. The counter is reset again according to the second set of parameters upon receipt of the trigger frame; And

   And performing, by the first wireless terminal, a third countdown operation based on the reset backoff counter.
5. The method of claim 4, wherein

   Decrementing, by the first wireless terminal, the reset backoff counter according to the third countdown operation during the preset time period; And

   Resetting the reset backoff counter, which is decreased according to the third countdown operation, based on the first parameter set, when the first wireless terminal has elapsed. .
6. The method of claim 2,

   The trigger frame is a trigger frame of a basic type,

   The trigger frame is a frame received within the preset time interval.
7. The method of claim 2,

   And the first wireless terminal effectively uses the second parameter set for the preset time interval from the time of receipt of the trigger frame.
8. The method of claim 2,

   For the first countdown operation, the first parameter set includes first to fourth CWmin values and first to fourth CWmax values individually set to first to fourth access categories,

   And for the second countdown operation, the second set of parameters includes first to fourth MU CWmin values and first to MU CWmax values individually set to the first to fourth access categories.
9. The method of claim 8,

   Wherein the first CWmin value is set smaller than the first MU CWmin value and the first CWmax value is set smaller than the first MU CWmax value.
10. According to claim 1,

    And the first parameter set and the second parameter set are information included in the most recently received beacon frame from the second wireless terminal.
11. In a first wireless terminal using a method for channel access in a WLAN 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 implemented to perform a first countdown operation based on a backoff counter set according to the first parameter set,

    When the first countdown operation is completed, operating mode indication information for requesting approval of an uplink operation mode for a multi-user is transmitted to the second wireless terminal.

    And receive an acknowledgment (ACK) frame acknowledging the uplink operation mode from the second wireless terminal, wherein the backoff counter is reset according to a second set of parameters for the uplink operation mode, And the second parameter set is valid for a preset time period.

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