WO2017074025A1 - Method for receiving data in wireless lan system, and terminal using same - Google Patents

Abstract

A method for receiving data in a wireless LAN system according to an embodiment of the present specification comprises: a step in which an access point sets TXOP duration information for a plurality of uplink data units to be received from a plurality of stations via wireless resources which are individually set in an overlapped time period, wherein the TXOP duration information indicates a transmission opportunity period including a time period; a step in which the access point obtains TXOP limit information which indicates an allocable limit period for the plurality of stations; a step in which the access point determines whether the transmission opportunity period is included in the limit period on the basis of the TXOP duration information and the TXOP limit information; a step in which the access point transmits, to the plurality of stations, a trigger frame which requests transmission of the plurality of uplink data units on the basis of whether the transmission opportunity period is included in the limit period; and a step in which the access point receives the plurality of uplink data units from the plurality of stations in the transmission opportunity period.

Description

Method for receiving data in WLAN system and terminal using same

The present disclosure relates to a technique for receiving data in wireless communication. More specifically, an access point (AP) receives uplink data or a station (STA) downlinks from an AP in a wireless LAN system. It relates to a method for receiving data and a terminal using the same.

Discussion is underway for the next generation wireless local area network (WLAN). 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, in the next generation WLAN, there is a great interest in scenarios such as wireless office, smarthome, stadium, hotspot, building, or apartment, and many APs and STAs are concentrated based on the scenario. There is a discussion on improving system performance in an environment.

In addition, in the next-generation WLAN, there will be more discussion about improving system performance in outdoor overlapping basic service set (OBSS) environment, improving outdoor environment performance, and cellular offloading, rather than improving single link performance in one basic service set (BSS). It is expected. The directionality of these next-generation WLANs means that next-generation WLANs will increasingly have a technology range similar to that of mobile communications. Considering the recent situation in which mobile communication and WLAN technology are discussed together in the small cell and direct-to-direct (D2D) communication area, the technical and business convergence of next-generation WLAN and mobile communication is expected to become more active.

An object of the present specification is to provide a method for receiving data with improved performance in a WLAN system and a terminal using the same.

The present specification relates to a method for receiving data in a WLAN system and a terminal using the same. In a method for receiving data in a WLAN system according to an embodiment of the present disclosure, TXOP duration information for a plurality of uplink data units to be received through a radio resource that is individually set in a time interval in which an access point overlaps from a plurality of stations Wherein, TXOP duration information is a step of indicating a transmission opportunity period including a time interval, obtaining an TXOP limit information indicating a limit period (allocable) limit period for the plurality of stations (access point), Determining whether the access point is included in the limit section based on the TXOP duration information and the TXOP limit information; and a plurality of uplink data units based on whether the access point is included in the limit section. Transmits a trigger frame requesting transmission to a plurality of stations Phase and the access point includes receiving a plurality of uplink data units from a plurality of stations at the transmission opportunity period.

According to an embodiment of the present disclosure, a method for receiving data with improved performance in a WLAN system and a 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 (RUs) used on a 20 MHz band.

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

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

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

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

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 is a view showing an EDCA-based channel access method in a wireless LAN system of the present disclosure.

13 is a conceptual diagram illustrating a backoff procedure of the EDCA of the present specification.

14 is a view for explaining a backoff period and a frame transmission procedure in a wireless communication system of the present specification.

15 and 16 are diagrams for describing the TXOP sharing of the present specification.

17 is a diagram for explaining a transmission opportunity section and TXOP sharing of the present specification.

18 is a diagram illustrating a parameter set including TXOP limit information for a multi-user according to an embodiment of the present specification.

FIG. 18 is a diagram illustrating a parameter set including TXOP limit information for a multi-user according to another embodiment of the present specification.

19 is a diagram illustrating a parameter set including TXOP limit information for a multi-user according to another embodiment of the present specification.

20 is a conceptual diagram illustrating a relationship between a TXOP limit section and a transmission opportunity section according to an embodiment of the present specification.

21 is a flowchart illustrating a downlink operation for multiple users according to an embodiment of the present disclosure.

22 illustrates an uplink operation for multiple users according to an embodiment of the present disclosure.

23 is a flowchart illustrating an uplink operation for multiple users according to an embodiment of the present disclosure.

24 is a flowchart illustrating a cascade operation for multiple users according to an embodiment of the present disclosure.

25 is a block diagram illustrating a wireless terminal to which an embodiment 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. The second BSS 105 may include a second AP 130 and one or more STAs 105-1, 105-2.

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 120 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), a mobile station (MS). It may also be called various names such as a mobile subscriber unit or simply a user.

2 is a conceptual diagram of a layer architecture of a WLAN system supported by IEEE 802.11. Referring to FIG. 2, a hierarchical architecture of a WLAN system includes a physical medium dependent (PMD) sublayer 200, a physical layer convergence procedure (PLCP) sublayer ( 210 and a medium access control (MAC) sublayer 220.

The PMD sublayer 200 may serve as a transmission interface for transmitting and receiving data between a plurality of STAs. The PLCP sublayer 210 is implemented such that the MAC sublayer 220 can operate with a minimum dependency on the PMD sublayer 200.

The PMD sublayer 200, the PLCP sublayer 210, and the MAC sublayer 220 may conceptually include management entities. For example, the management unit of the MAC sublayer 220 is referred to as a MAC Layer Management Entity (MLME) 225. The management unit of the physical layer is referred to as a PHY Layer Management Entity (PLME) 215.

Such management units may provide an interface for performing a layer management operation. For example, the PLME 215 may be connected to the MLME 225 to perform management operations of the PLCP sublayer 210 and the PMD sublayer 200. The MLME 225 may be connected to the PLME 215 to perform a management operation of the MAC sublayer 220.

In order for the correct MAC layer operation to be performed, a STA management entity (hereinafter, referred to as “SME”, 250) may exist. The SME 250 may operate as an independent component in each layer. The PLME 215, the MLME 225, and the SME 250 may transmit and receive information from each other based on primitives.

The operation of each sub-layer is briefly described as follows. For example, the PLCP sublayer 110 may include a MAC protocol data unit (MAC protocol data unit) received from the MAC sublayer 220 according to an indication of the MAC layer between the MAC sublayer 220 and the PMD sublayer 200. Hereinafter, the MPDU is transmitted to the PMD sublayer 200 or the frame coming from the PMD sublayer 200 is transferred to the MAC sublayer 220.

The PMD sublayer 200 may be a PLCP lower layer to perform data transmission and reception between a plurality of STAs over a wireless medium. The MPDU delivered by the MAC sublayer 220 is referred to as a physical service data unit (hereinafter, referred to as a PSDU) in the PLCP sublayer 210. The MPDU is similar to the PSDU. However, when an aggregated MPDU (AMPDU) that aggregates a plurality of MPDUs is delivered, individual MPDUs and PSDUs may be different from each other.

The PLCP sublayer 210 adds an additional field including information required by the transceiver of the physical layer in the process of receiving the PSDU from the MAC sublayer 220 and transmitting the PSDU to the PMD sublayer 200. In this case, the added field may be a PLCP preamble, a PLCP header, tail bits required to return the convolutional encoder to a zero state in the PSDU.

The PLCP sublayer 210 adds the above-described fields to the PSDU to generate a PPCP (PLCP Protocol Data Unit), which is then transmitted to the receiving station via the PMD sublayer 200, and the receiving station receives the PPDU to receive the PLCP preamble and PLCP. Obtain and restore information necessary for data restoration from the header.

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, 3) 20, Bandwidth field indicating 40, 80, 160, 80 + 80 Mhz, 4) Field indicating MCS scheme applied to HE-SIG-B, 5) HE-SIB-B is dual subcarrier modulation for MCS ( field indicating whether the modulation is performed using a dual subcarrier modulation), 6) a field indicating the number of symbols used for the HE-SIG-B, and 7) a field indicating whether the HE-SIG-B is generated over the entire band. Field, 8) field indicating the number of symbols in the HE-LTF, 8) field indicating the length and CP length of the HE-LTF, 9) field indicating whether additional OFDM symbols exist for LDPC coding, 10) 11) field indicating the control information on the PE (packet extension), 11) field indicating the information on the CRC field of the HE-SIG-A, etc. may be included. All. 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 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 (that is, 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 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 fast fourier transform (FFT) size / inverse fast fourier transform (IFFT) size is N times the FFT / IFFT size used in the conventional 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 to each symbol of the first field of the HE PPDU is 3.2 μs, and the IDFT / DFT length applied to each symbol of 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 in terms of 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 not. 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 are indicated through a trigger frame.

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

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-feature field" for two users and a corresponding CRC field, 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 changed differently than 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 for setting the NAV described below. Information about an identifier (eg, AID) of the terminal 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.

The trigger frame of FIG. 9 may include per user information fields 960 # 1 to 960 # N corresponding to the number of receiving STAs receiving the trigger frame. 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 preset time (eg, SIFS). During the casecade operation, only one transmitting device (eg, AP) for downlink communication may exist, and a plurality of transmitting devices (eg, non-AP) for uplink communication may exist.

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

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

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

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

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

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

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

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

12 is a view showing an EDCA-based channel access method in a wireless LAN system of the present disclosure. In a WLAN system, an STA (or AP) performing channel access based on enhanced distributed channel access (EDCA) may perform channel access by defining a plurality of user priorities with respect to traffic data.

For the transmission of quality of service (QoS) data frames based on multiple user priorities, EDCA provides four access categories (AC): AC_BK (background), AC_BE (best effort), AC_VI (video), and AC_VO ( voice)). In EDCA, traffic data such as MAC service data unit (MSDU) is mapped as shown in Table 1 below as an example of arriving from a logical link control (LLC) layer to a medium access control (MAC) layer with different user priorities. can do.

Table 1 is an exemplary table showing the mapping between user priority and AC.

Table 1

For each AC, transmission queues and AC parameters can be defined. The difference in transmission priority between ACs may be implemented based on different AC parameter values. EDCA uses the AIFS (arbitration interframe space) instead of DIFS (DCF interframe space), CWmin, CWmax, which are parameters for the backoff procedure based on the distributed coordination function (DCF) in the backoff procedure for transmitting a frame belonging to AC. ) [AC], CWmin [AC], CWmax [AC] can be used.

The EDCA parameter used for the backoff procedure 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 element may include information about channel access parameters for each AC (eg, AIFS [AC], CWmin [AC], CWmax [AC]).

If a collision occurs between STAs while the STAs transmit frames, the backoff procedure of EDCA, which generates a new backoff count, is similar to the backoff procedure of the existing DCF. However, the differentiated backoff procedure for each AC of the EDCA may be performed based on the EDCA parameters individually set for each AC. EDCA parameters are an important means used to differentiate channel access of various user priority traffic.

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 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 includes one frame 1221 for a second STA (not shown). The transmission queue 1230 of the AC VI type includes 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. .

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).

For example, the transmission queue 1250 of the AC BE type of FIG. 12 does 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). That is, the frame at the highest priority AC is transmitted first, and the other ACs increase the contention window value to update the backoff count again.

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 attempts to transmit the frame after the 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 STA may split the frame into several smaller frames. Subsequently, the divided frames may be transmitted within a range not exceeding the TXOP limit.

13 is a conceptual diagram illustrating a backoff procedure of the EDCA of the present specification.

12 and 13, each traffic data transmitted from the STA has a priority and may perform a backoff procedure based on a competing EDCA scheme. For example, the priority given to each traffic may be divided into eight.

As described above, within one STA (or AP), different output queues have different priorities, and each output queue operates according to the rules of the EDCA. Each output queue may transmit traffic data using different Arbitration Interframe Space (AIFS) according to each priority instead of the previously used DCF Interframe Space (DIFS).

In addition, when the STA (or AP) needs to transmit traffic having different priorities at the same time, the collision in the STA (or AP) is prevented by transmitting the traffic having a higher priority.

The backoff procedure may occur in the following situations. For example, when a frame is transmitted from an STA (or an AP), a transmission collision occurs and is used when retransmission is required. To start the backoff procedure, each STA (or AP) sets a random backoff time (Tb [i]) to the backoff timer. The random backoff time Tb [i] may be calculated using the following Equation 1 as a pseudo-random integer value.

Equation 1

Where Random (i) is a function that generates a random integer between 0 and CW [i] using a uniform distribution. CW [i] is the contention window between the minimum contention window CWmin [i] and the maximum contention window CWmax [i], where i represents the traffic priority. Each time a collision occurs, a new competition window CW _new [i] is calculated using Equation 2 below using the previous window CW _old [i].

Equation 2

Here, the PF can be calculated according to the procedure defined in the IEEE 802.11e standard. The EDCA parameters CWmin [i], AIFS [i], and PF values are set to default values for each STA (or AP) or are controlled by the QoS parameter set element (QoS parameter set element), which is a management frame. Can be sent.

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.

Based on Equation 1 and Equation 2 above, when the backoff procedure of the transmit queue 1230 of the AC VI type of FIG. 14 is terminated first, the transmit queue 1230 of the AC VI type may access a medium. Transmission opportunity (TXOP) can be obtained.

The AP 1200 of FIG. 12 may determine the transmission queue 1230 of the AC VI type as the primary AC, and the remaining transmission queues 1220, 1240, and 1250 may be determined as the secondary AC.

As described above, a process of determining the transmission queue in which the backoff procedure is completed first as the primary AC by performing the backoff procedure on the plurality of transmission queues 1220 to 1250 may be referred to as a primary AC rule. Can be.

A transmission opportunity period according to a transmission opportunity (TXOP) may be determined based on the primary AC determined by the primary AC rule. In addition, frames included in the secondary AC may be transmitted together in a transmission opportunity period determined based on the primary AC. This is described with reference to FIG. 15 described below when referred to as TXOP sharing.

14 is a view for explaining a backoff period and a frame transmission procedure in a wireless communication system of the present specification.

13 and 14, when a specific medium is changed from occupy or busy to idle, several STAs may attempt to transmit data (or frames). At this time, as a method for minimizing the collision between STAs, each of the STAs may select a random backoff time and wait for a slot time corresponding thereto to attempt transmission.

When the random backoff process starts, the STA may count down the determined backoff count time in slot time units and continue to monitor the medium while counting down. If the medium is monitored as occupied, the STA stops counting down and waits. If the medium is monitored idle, the STA resumes counting down.

Referring to FIG. 14, when a packet for STA 3 reaches the MAC layer of STA 3, STA 3 may determine that the medium is idle as much as DIFS and transmit a frame immediately. The inter frame space (IFS) of FIG. 14 is illustrated as DIFS, but it is to be understood that the present disclosure is not limited thereto.

Meanwhile, the remaining STAs may monitor and wait that the medium is busy. Meanwhile, data to be transmitted in each of STA 1, STA 2, and STA 5 may occur. After each STA waits for DIFS if the medium is monitored idle, each STA can count down the individual random backoff time selected by each STA.

Referring to FIG. 14, it is shown that STA 2 selects the smallest backoff time and STA 1 selects the largest backoff count value. FIG. 14 illustrates a case in which the remaining backoff time of STA 5 is shorter than the remaining backoff time of STA 1 at the time when STA 2 finishes backoff counting for the selected random backoff time and starts frame transmission.

STA 1 and STA 5 then stop and wait for the countdown while STA 2 occupies the medium. When the media occupancy of the STA 2 ends and the medium becomes idle again, the STA 1 and the STA 5 resume counting down the remaining backoff time after waiting for DIFS. In this case, since the remaining backoff time of the STA 5 is shorter than that of the STA 1, the STA 5 may transmit a frame before the STA 1.

Meanwhile, data to be transmitted by STA 4 may reach the MAC layer of STA 4 while STA 2 occupies the medium. In this case, when the medium is idle, the STA 4 may wait as long as DIFS and count down the random backoff time selected by the STA 4.

FIG. 14 illustrates a case in which the remaining backoff time of STA 5 coincides with the random backoff time of STA 4, in which case a collision may occur between STA 4 and STA 5. If a collision occurs between STAs, neither STA 4 nor STA 5 can receive an ACK, and thus fail to transmit data.

In this case, each of STA 4 and STA 5 may calculate a new contention window CW _new [i] according to Equation 2 above. Subsequently, each of STA 4 and STA 5 may perform a countdown on the newly calculated random backoff time according to Equation 1 above.

Meanwhile, the STA 1 may wait while the medium is occupied due to the transmission of the STA 4 and the STA 5. Subsequently, when the medium is in the idle state, the STA 1 waits for DIFS and resumes backoff counting to transmit a frame when the remaining backoff time elapses.

The CSMA / CA mechanism also includes 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 and 16 are diagrams for describing the TXOP sharing of the present specification.

Referring to FIG. 15, the operation of DL SU-MIMO is performed by the AP acquiring a wireless channel (Obtaining an Enhanced Distributed Channel Access Transmission Opportunity) (S1510) and a frame transmission through multiple radio channels (EDCA TXOP). Step S1520 may be included.

12 to 16, the operation of the DL MU-MIMO is to share the TXOP between the frame transmission step (S1630) as well as the radio channel acquisition (right to transmit the frame during TXOP) step (S1610) (EDCA TXOP Sharing) It may further comprise a step (S1620).

As described in the preceding figures, the DL MU-MIMO allows the AP to acquire a radio channel using the IEEE 802.11e EDCA scheme (S1610). Frames (audio, video, data, and background) accessing Wi-Fi may be stored in different buffers (access categories) according to the EDCA method. Subsequently, each buffer (AC) can implement service differentiation by accessing a wireless channel independently and mutually competitively, and imposing a difference on channel accessibility for each AC.

In the TXOP sharing step (S1620) of FIG. 16, a secondary AC (primary AC) that acquires a wireless channel does not acquire a wireless channel to simultaneously transmit a plurality of frames through a plurality of channels in the same frequency band. Sharing the TXOP with AC). The standard IEEE 802.11ac DL MU-MIMO shares TXOP in a priority manner.

The frame transmitting step (S1630), which is the last step of the DL MU-MIMO of FIG. 16, transmits frames determined in the TXOP sharing step. TXOP is a period in which a plurality of frames can be transmitted to synchronize with the transmission of the frame for each channel. In this case, the synchronized frames may be transmitted through a simultaneous transmission group (MU-transmission group) including one or more frames of the primary AC. The WLAN system may detect a channel error or an inter-frame collision that occurs after transmitting a frame through an acknowledgment message received every time one MU-transmission group is sent.

17 is a diagram for explaining a transmission opportunity section and TXOP sharing of the present specification. Referring to FIG. 17, the MU-MIMO operation of FIG. 17 is defined in downlink from an AP to a client (ie, a non-AP STA).

Multi-user frames are sent simultaneously to multiple receivers, but acknowledgments are sent individually on the uplink.

In addition, as shown in FIG. 17, a block ACK (BA) may be transmitted from a multi-user in response to a block ACK request (BAR) frame by the AP rather than an immediate response to the multi-user frame.

The horizontal axis t of the AP of FIG. 17 and the horizontal axes t1, t2, and t3 of each of the plurality of STAs STA1, STA2, and STA3 indicate time. In addition, the vertical axis of the AP of FIG. 17 and the vertical axis of each of the plurality of STAs (STA1, STA2, and STA3) indicate the existence of a frame.

For example, an AP may receive a MU PPDU (i.e.,

Preamble and data). MU PPDU of FIG. 17 is transmitted to each STA

It may include an A-MPDU. After receiving the MU PPDU from the AP of FIG. 17, the STA 1 may transmit a block acknowledgment (BA) frame to the AP after SIFS.

Subsequently, the AP receiving the BA frame from STA 1 may transmit a block acknowledgment request (BAR) frame to STA 2 after SIFS. Subsequently, the STA 2 may transmit a BA frame to the AP after SIFS.

The AP, which receives the BA frame from STA 2, may transmit a BAR frame to STA 3 after SIFS. Subsequently, STA 3 transmits a BA frame to the AP after SIFS. If this process is performed for all STAs, the AP may transmit the next MU PPDU to all STAs.

12 to 17, the AP includes first to third frames 1231 for one STA (eg, STA1) included in the transmission queue 1230 of the AC VI type selected as primary AC in FIG. 12. The transmission opportunity period (TXOP_P) may be determined based on ~ 1233).

The AP transmits the data frames 1221, 1241-1243 buffered in the transmission queues 1220, 1240, 1250 of the AP corresponding to the secondary AC according to the aforementioned TXOP sharing, during the transmission time interval TXOP_P. , STA2, and STA3).

In addition, the AP may transmit a fourth frame 1234 for another STA (eg, STA3) together with the first frame 1231 for the first STA to the transmission queue 1230 of the AC VI type.

FIG. 18 is a diagram illustrating a parameter set including TXOP limit information for a multi-user according to an embodiment of the present specification. Referring to FIG. 18, existing EDCA parameter values CWmin, CWmax, AIFS, and TXOP limit according to the type of an access category AC are shown. The value set in the existing EDCA parameters CWmin, CWmax, AIFS, and TXOP limit according to the type of the access category AC of FIG. 18 is for frame transmission for a conventional single user (hereinafter, referred to as 'SU'). The parameter has also been conventionally used for frame transmission for multi-users (hereinafter referred to as 'MU').

The EDCA parameter values CWmin, CWmax, AIFS, and TXOP limit may be set to defaults by the AP or the STA, or may be values broadcast by the AP to the STAs.

For example, the TXOP limit value (hereinafter referred to as 'TXOP limit') of the AC VI type AC among the existing parameters of FIG. 18 is 3.008 ms, and the TXOP limit value of the AC VO type AC is 1.504 ms. The TXOP limit value for AC of AC BK and AC BE type is set to '0'. The TXOP limit value set to '0' may mean that only one MAC service data unit (MSDU) or only one management frame is transmitted during the obtained TXOP.

The new parameter according to the present specification is not only the existing EDCA parameters (CWmin, CWmax, AIFS, TXOP limit) but also TXOP limit information (hereinafter, referred to as' MU TXOP limit) for multi-user (MU) frame transmission. It may further include a field for '). In this case, it will be understood that the TXOP limit section may be determined according to the value set in the MU TXOP limit field.

The value set in the MU TXOP limit field may be applied to downlink operation for multiple users, uplink operation for multiple users, or cascade operation for multiple users. An example where the MU TXOP limit is applied for the three situations mentioned is described.

For example, in downlink (DL) operation, the AP determines a transmission opportunity period according to a primary AC rule. It will be appreciated that the description of the primary AC rule may be replaced by the previous figures.

However, DL. In operation, according to the primary AC rule, the queue length included in the downlink queue (not shown) corresponding to each access class (AC VO. AC VI, AC BE, AC BK) included in the AP is Not considered. As a result, when one downlink queue selected as the primary AC includes fewer PPDUs than the downlink queue corresponding to the secondary AC, the PPDU included in the secondary AC is sufficiently transmitted within one TXOP. There can be cases when it cannot.

Accordingly, when the AP transmits DL frames (eg, DL data frames) to a plurality of STAs in a DL MU operation according to an embodiment of the present disclosure, without considering the conventional primary AC rule, the AP may perform the MU of FIG. 18. Based on the value set in the TXOP limit field, a transmission time interval for transmitting a DL frame may be set. That is, the AP may set the transmission opportunity period not to exceed the limit period indicated by the value set in the MU TXOP limit field.

In the DL situation, the value set in the MU TXOP limit field may be determined in consideration of the TXOP limit defined for each AC in the existing EDCA. The value set in the MU TXOP limit field used for the multi-user (MU) in the DL situation may be determined in consideration of the network situation including the AP and the STA.

In the case of FIG. 18, the value set in the MU TXOP limit field is shown as 16 ms, but it will be understood that this is only an example and is not limited thereto. As another example, the value set in the MU TXOP limit field may be 8 ms. An example in which a value set in the MU TXOP limit field is applied in the DL operation will be described in more detail with reference to the following drawings.

As another example, in an uplink (UL) operation, the AP may receive buffer status information (BSI) of STAs from a plurality of STAs. The frame including the BSI may be referred to as a buffer status report frame (hereinafter, referred to as a 'BSR frame'). For example, the BSR frame may include QoS (QoS) information of a frame to be transmitted by each STA and the total number of frames pending to the STA.

The AP may determine a time interval for a plurality of UL data units to be transmitted from the plurality of STAs based on the received BSR frame. In this specification, a time interval for an uplink data unit (UL data unit) may be referred to as a TXOP duration.

Also, the transmission opportunity section may include a section for preamble, a section for transmitting data (TXOP duration), and a section for receiving an ACK frame.

In 802.11 ax, an aggregation MAC protocol data unit (A-MPDU) may include a plurality of traffic identifiers (hereinafter, 'multiple TIDs'). In other words, this means that the primary AC rule mentioned in the DL MU operation may not be defined separately in the UL MU operation.

Accordingly, in the UL MU operation according to another embodiment of the present specification, regardless of the conventional primary AC rule, the AP may determine the UL frame (eg, the UL data frame) based on the value set in the MU TXOP limit field of FIG. 18. Interval for transmission can be set. That is, the AP may set the transmission opportunity interval so as not to exceed the interval indicated by the value set in the MU TXOP limit field.

In the UL situation, the value set in the MU TXOP limit field may be determined in consideration of the value set in the TXOP limit field defined for each AC in the existing EDCA. The value set in the MU TXOP limit field used for the multi-user (MU) in the UL context may be determined in consideration of a network situation including the AP and the STA.

In the case of FIG. 18, the value set in the MU TXOP limit field is shown as 16 ms, but it will be understood that this is only an example and is not limited thereto. As another example, the value set in the MU TXOP limit may be 8 ms. An example in which the value set in the MU TXOP limit field is applied in the UL operation will be described in more detail with reference to the following drawings.

As another example, the MU TXOP limit may be applied to a cascade operation for a multi-user (MU). In the cascade operation, the PPDU for the DL MU is transmitted, and when a predetermined interval (xIFS) elapses, the PPDU for the UL MU is transmitted.

If a value set in the TXOP limit field of the EDCA parameter configured for the conventional SU is used, a sufficient time interval for cascade operation may not be allocated. Accordingly, when a frame is transmitted in a cascade operation according to another embodiment of the present disclosure, regardless of the conventional primary AC rule, the AP or each STA may select a frame based on a value set in the MU TXOP limit field of FIG. 18. Can send and receive

19 is a diagram illustrating a parameter set including TXOP limit information for a multi-user according to another embodiment of the present specification. 18 and 19, a field for MU TXOP limit for the multi-user of FIG. 19 may be set for each access category.

For example, the first threshold time T1 may be set in the AC of the AC_BK type of the MU TXOP limit field. A second threshold time T2 may be set in the AC of the AC_BE type in the MU TXOP limit field. A third threshold time T3 may be set to AC of type AC_VI in the MU TXOP limit field. A fourth threshold time T4 may be set in an AC of type AC_VO in the MU TXOP limit field.

In this case, the first to fourth threshold time T4 set in the MU TXOP limit field of FIG. 19 may have a differential value according to a user priority according to quality of service (QoS) information. .

For example, the first threshold time T1 set in the AC_BK type AC having the lowest priority may indicate the longest time. The fourth threshold time T4 set in the AC of the AC_VO type having the highest priority may indicate the shortest time.

In addition, the second threshold time T2 set in the AC_BE type AC may indicate a time shorter than the first threshold time T1 and longer than a fourth threshold time T4. The third threshold time T3 set in the AC_VI type AC may indicate a time shorter than the second threshold time T2 and longer than a fourth threshold time T4. The above description of the first to fourth threshold times T1 to T4 is merely an example, and it will be understood that the present specification is not limited thereto.

The value set individually in the MU TXOP limit field for each AC may be applied to downlink operation for multiple users, uplink operation for multiple users, or cascade operation for multiple users. An example is described in which the values individually set in the MU TXOP limit field are applied for the three situations mentioned.

For example, in a downlink (DL) operation, the AP may determine a TXOP period according to a primary AC rule. It will be appreciated that the description of the primary AC rule may be replaced by the previous figures.

For example, when the AP transmits DL frames (eg, DL data frames) to a plurality of STAs in a DL MU operation, the AP multiplexes DL frames based on a value set in the MU TXOP limit field corresponding to the primary AC. May be transmitted to the STA. That is, the AP may set a TXOP period so as not to exceed the limit period indicated by the value set in the MU TXOP limit field.

In the DL situation, a value set individually in the MU TXOP limit field for each AC may be determined in consideration of the TXOP limit defined for each AC in the existing EDCA. A value individually set for each AC of the MU TXOP limit field used for the multi-user (MU) in the DL situation may be determined in consideration of a network situation including the AP and the STA.

As another example, in an uplink (UL) operation, the AP may determine a time interval for a plurality of UL data units to be transmitted from a plurality of STAs based on the received BSR frame. . In this specification, a time period for an uplink data unit (UL data unit) may be referred to as a TXOP period.

In the UL MU operation according to another embodiment of the present disclosure, regardless of the conventional primary AC rule, the AP may perform an UL frame (eg, UL data) based on a value individually set in the MU TXOP limit field for each AC of FIG. 19. TXOP period for the transmission of the frame) can be set. That is, the AP may set a TXOP period so as not to exceed the limit period indicated by the value set in the MU TXOP limit field.

For example, the AP may use a value indicating the longest critical section among values individually set in the MU TXOP limit field for each AC of FIG. 19. Alternatively, the AP may use a value of the MU TXOP limit field corresponding to an access category (AC) set as a default for transmission of the trigger frame.

In addition, when there is an AC defined by the primary AC, a value of the MU TXOP limit field corresponding to the primary AC may be used. That is, it will be understood that the method of using a value individually set in the MU TXOP limit field for each AC is not limited to a specific embodiment.

In the UL situation, the value individually set in the MU TXOP limit field for each AC may be determined in consideration of the value set in the TXOP limit field defined for each AC in the existing EDCA. A value individually set for each AC of the MU TXOP limit field used for the multi-user (MU) in the UL context may be determined in consideration of the network situation including the AP and the STA.

As another example, the MU TXOP limit may be applied to a cascade operation for a multi-user (MU). In the cascade operation, the PPDU for the DL MU is transmitted, and when a predetermined interval (xIFS) elapses, the PPDU for the UL MU is transmitted.

When a frame is transmitted in a cascade operation according to another embodiment of the present disclosure, regardless of the conventional primary AC rule, the AP or each STA is based on a value individually set according to each AC in the MU TXOP limit field of FIG. 19. Frame can be transmitted and received.

For example, the AP may use a value indicating the longest critical section among values individually set in the MU TXOP limit field for each AC of FIG. 19 for a cascade operation. Alternatively, the AP may use a value of the MU TXOP limit field corresponding to an access category (AC) set as a default for transmission of the trigger frame.

20 is a conceptual diagram illustrating a relationship between a TXOP limit section and a transmission opportunity section according to an embodiment of the present specification.

18 to 20, the TXOP limit period 2010 of FIG. 20 may be determined based on a value set in the MU TXOP limit field mentioned in FIGS. 18 and 19.

That is, the AP may set the transmission opportunity period 2020 to be included in the TXOP limit period 2010 when setting the transmission opportunity period 2020 (TXOP period).

The transmission opportunity period 2020 of FIG. 20 may be determined by the primary AC rule in the DL operation. In addition, the transmission opportunity period 2020 of FIG. 20 may be determined by the AP based on the BSR frame in the UL operation. The length of the transmission opportunity period 2020 may be variable.

In an operation for a multi-user (MU), the AP sometimes allocates a transmission opportunity period exceeding the TXOP limit period. This is due to the fact that the conventional TXOP limit period is based on a single user SU.

According to an embodiment of the present disclosure, a new multi-user TXOP limit period for multi-user (MU) operation may be provided.

A longer time (eg, 8 ms or 16 ms) than the TXOP limit period of the conventional EDCA parameter may be allocated to the new TXOP limit period proposed in the present specification. Accordingly, the AP may set the transmission opportunity period so that the transmission opportunity period is included in the TXOP limit interval in the DL operation or the UL operation. This prevents a situation in which a specific STA occupies a medium exclusively for an unnecessarily long time in a multi-user (MU) operation.

21 is a flowchart illustrating a downlink operation for multiple users according to an embodiment of the present disclosure.

12 to 21, in step S2110, the AP corresponds to a downlink buffer corresponding to an access category in which backoff counting is terminated first among a plurality of downlink buffers of the AP according to a primary AC rule. Can be determined as primary AC.

As described above with reference to FIGS. 16 and 17, the AP may set a transmission opportunity period based on the amount of data frames present in the downlink buffer determined as primary AC. In this case, the transmission opportunity period may be a variable time interval set by the AP according to the amount of frames present in the downlink buffer.

In operation S2120, the AP may determine whether the transmission opportunity interval set in operation S2110 is less than or equal to the TXOP limit interval according to the value set in the MU TXOP limit field of FIG. 18. For example, the value set in the MU TXOP limit field may be a value obtained by the AP based on a preset parameter.

Step S2130 may be performed if the transmission opportunity period does not exceed the TXOP limit interval. In detail, the AP may transmit a plurality of downlink data units to the plurality of STAs in a transmission opportunity section.

If it is determined in step S2130 that the transmission opportunity section exceeds the TXOP limit section, the procedure is terminated. Although not shown in FIG. 21, the AP may divide a transmission opportunity section exceeding the TXOP limit section into at least two time sections not exceeding the TXOP limit section. Subsequently, downlink data may be transmitted in at least two divided time intervals.

22 illustrates an uplink operation for multiple users according to an embodiment of the present disclosure. 12 to 22, the AP of FIG. 22 may transmit a trigger frame for requesting transmission of a plurality of uplink data units to be received from a plurality of STAs to a plurality of STAs. The trigger frame is described in more detail with reference to the accompanying drawings.

For example, the AP of FIG. 22 may be received through a radio resource individually set by the AP in a time interval T_O overlapped by the first to fourth STAs after SIFS from the period T_R in which the trigger frame is transmitted. The first to fourth uplink data units UL_D1 to UL_D4 may be received.

Subsequently, the AP of FIG. 22 may transmit a block ACK frame to inform the first to fourth STAs of reception of the first to fourth uplink data units UL_D1 to UL_D4.

The transmission opportunity period TXOP_P of FIG. 22 is a period T_R for transmitting a trigger frame, a period in which preambles for the first to fourth uplink data units UL_D1 to UL_D4 are received, and the first to second beams. An overlapping time interval T_O in which the fourth uplink data units UL_D1 to UL_D4 are received and a section T_A for transmitting a BA frame for the first to fourth uplink data units UL_D1 to UL_D4. can do.

However, the transmission opportunity section TXOP_P is not limited to the embodiment of FIG. 22, and may mean only a section in which uplink data is received, and may include various embodiments.

23 is a flowchart illustrating an uplink operation for multiple users according to an embodiment of the present disclosure. 12 to 23, in step S2310 of FIG. 23, an AP may set a transmission opportunity period (corresponding to TXOP_P of FIG. 22) to receive a plurality of uplink data units from a plurality of STAs. In detail, the transmission opportunity period (TXOP_P of FIG. 22) may be determined according to a value set in the TXOP duration information of the AP.

In addition, the AP may acquire TXOP limit information indicating an allowable limit period for the plurality of stations in order to receive the plurality of uplink data units. For example, a time length of a limit period may be determined according to TXOP limit information.

TXOP limit information may be a value preset in the AP or STA. TXOP limit information may be a value calculated by the AP.

In step S2320, the AP may compare a limit period according to the transmission opportunity period and TXOP limit information set in step S2320.

In step S2320, if the AP determines that the transmission opportunity period is included in the limit period, the procedure proceeds to step S2330.

In contrast, in step S2320, if the AP determines that the transmission opportunity period is not included in the limit period, the procedure ends.

Also, when the transmission opportunity period is not included in the limit period, although not shown in FIG. 21, the AP divides the transmission opportunity period exceeding the TXOP limit period into at least two time periods not exceeding the TXOP limit period. Can be. Subsequently, TXOP duration information corresponding to the two divided time intervals may be reset. Subsequently, the AP may generate a trigger frame including the reset TXOP duration information.

For reference, the trigger frame referred to in this specification includes STA identifier (STA ID) information of a multi-user (MU), information on individually set radio resources (for example, subcarrier information for OFDMA and stream index information for MIMO). And MCS (modulation and coding scheme) information configured for each STA.

In step S2330, the AP may generate a trigger frame including information (eg, TXOP duration information) associated with the transmission opportunity period set in step S2310 and transmit the generated trigger frame to the plurality of STAs.

For example, the trigger frame generated in step S2330 may include overlapping time intervals (T_0 in FIG. 22) and radio resources (eg, for a plurality of uplink data units (UL_D1 to UL_D4 in FIG. 22) to be received from the plurality of STAs. RU allocation information) may be further included.

In operation S2340, the AP may receive a plurality of uplink data units from the plurality of STAs in response to the trigger frame.

As described above, rather than using the value set in the TXOP limit field of the SU-based EDCA parameter, the uplink operation or the downlink operation is performed based on the value set in the MU TXOP limit field for the MU according to the present specification. It may be guaranteed to set the transmission opportunity section TXOP_P within the limit section according to the value set in the MU TXOP limit field. Accordingly, a situation in which a medium is occupied by a specific AP or a specific STA can be prevented and the overall performance of the WLAN system can be improved.

24 is a flowchart illustrating a cascade operation for multiple users according to an embodiment of the present disclosure. 16 to 24, the transmission opportunity section TXOP_P of FIG. 24 includes a multi-user downlink transmission section T_DL in which a DL MU frame is transmitted, and a multi-user uplink transmission section T_UL in which an UL MU frame is transmitted. And an interframe interval (xIFS) between the multi-user downlink transmission interval (T_DL) and the multi-user uplink transmission interval (T_UL) through which the UL MU frame is transmitted.

When the AP sets the transmission opportunity period TXOP_P for the MU cascade operation, the AP may set the transmission opportunity period TXOP_P to be included in a limit period according to a value set in the MU TXOP limit field of FIG. 18. .

25 is a block diagram illustrating a wireless terminal to which an embodiment 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 2160 may implement the functions, processes, and / or methods proposed in the present embodiment. For example, the processor 2160 may be implemented to perform the non-AP STA operation according to the present embodiment described above. The processor 2160 may perform the 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 present embodiment 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 (8)

1. In the method for receiving data in a WLAN system,

   Set TXOP (transmission opportunity) duration information for a plurality of uplink data units to be received through radio resources individually set in a time interval in which an access point overlaps from a plurality of stations, TXOP duration information indicating a TXOP period including the time period;

   Obtaining TXOP limit information indicating, by the access point, an allowable limit period for the plurality of stations;

   Determining, by the access point, whether the transmission opportunity section is included in the limit section based on the TXOP duration information and the TXOP limit information;

   Transmitting, by the access point, a trigger frame for requesting transmission of the plurality of uplink data units to the plurality of stations based on whether the transmission opportunity section is included in the limit section; And

   Receiving, by the access point, the plurality of uplink data units transmitted in response to the trigger frame from the plurality of stations in the transmission period.
2. The method of claim 1,

   Transmitting the trigger frame to the plurality of stations,

   If the transmission opportunity period is equal to or included in the limit period, the access point comprising generating the trigger frame including the set TXOP duration information.
3. The method of claim 1,

   Transmitting the trigger frame to the plurality of stations,

   If the transmission opportunity section is not included in the limit section, the access point dividing the transmission opportunity section into at least two division sections included in the limit section;

   Updating, by the access point, the TXOP duration information according to the at least two division periods; And

   The access point comprising generating the trigger frame including the updated TXOP duration information.
4. The method of claim 1,

   The TXOP limit information is a first access category of an access category (AC) voice type having the highest priority and an AC BK having the lowest priority according to the quality of service (QoS) information of the access point. A second access category of type), a third access category of type AC VI having a lower priority than the AC VO type, an AC best effort (BE) having a priority lower than the AC VI and higher than the AC BK. Individually set to the fourth access category of the type.
5. The method of claim 4, wherein

   The shortest first limit time is set in the first access category, the longest second limit time is set in the second access category, and is longer than the first limit time and shorter than the second limit time. And a third limit time is set in the third access category, and a fourth limit time shorter than the second limit time and longer than the third limit time is set in the fourth access category.
6. The method of claim 1,

   The TXOP duration information is set based on buffer status information previously received from the plurality of STAs.
7. The method of claim 1,

   The length of time is 8 milliseconds or 16 milliseconds.
8. In a first terminal for receiving data in a WLAN system, the first terminal,

   RF (radio frequency) unit for transmitting a radio signal; And

   A processor operatively connected with the RF unit,

   The processor may be configured to set transmission opportunity (TXOP) duration information for a plurality of uplink data units to be received through radio resources individually set in overlapping time intervals from a plurality of second terminals. TXOP duration information indicates a transmission opportunity section including the time interval,

   It is implemented to obtain TXOP limit information (limit information) indicating the limit period (allocable) limit period for the plurality of second terminal,

   And determining whether the transmission opportunity section is included in the limit section based on the TXOP duration information and the TXOP limit information.

   And transmitting a trigger frame for requesting transmission of the plurality of uplink data units to the plurality of second terminals based on whether the transmission opportunity section is included in the limit section.

   And a terminal configured to receive the plurality of uplink data data units transmitted from the plurality of second terminals in the transmission opportunity section in response to the trigger frame.

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