WO2016163641A1

WO2016163641A1 - Channel access method of sta for ul mu transmission and sta for performing same

Info

Publication number: WO2016163641A1
Application number: PCT/KR2016/001721
Authority: WO
Inventors: 김서욱; 류기선; 김정기; 조한규; 최혜영
Original assignee: 엘지전자 주식회사
Priority date: 2015-04-08
Filing date: 2016-02-22
Publication date: 2016-10-13

Abstract

A channel access method of an STA for UL MU transmission and an STA for performing the same are disclosed. The channel access method of the STA for the UL MU transmission may comprise the steps of: determining an access category of an uplink frame to be transmitted on the basis of UL MU OFDMA transmission by an STA; performing a channel access on the basis of a channel access parameter and resource unit configured according to the access category by the STA; and transmitting the uplink frame on a time resource, which overlaps with another uplink frame, to an AP on the basis of the UL MU OFDMA transmission by the STA, wherein the channel access parameter may include a CWmin value and a CWmax value for determining a size of a contention window for a channel access, and the resource unit may be a size of a frequency resource for the UL MU OFDMA transmission of the uplink frame.

Description

Channel access method of STA for UL MU transmission and STA performing such method

The present invention relates to wireless communication, and more particularly, to a channel access method of a station (STA) for UL uplink multi-user (MU) transmission and a STA that performs the method.

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 next-generation WLANs, we are interested in scenarios such as wireless office, smart home, stadium, hotspot, and building / apartment. There is a discussion about improving system performance in a dense environment with many APs and STAs.

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 invention is to provide a channel access method of an STA for UL MU transmission.

It is still another object of the present invention to provide an STA that performs a channel access method for UL MU transmission.

According to an aspect of the present invention for achieving the above object of the present invention, a channel access method of a station (STA) for uplink multi-user (UL) transmission in the STA transmits UL orthogonal frequency division multiple access (MU OFDMA) Determining an access category of an uplink frame to be transmitted, based on a channel access parameter and a resource unit set according to the access category, and the STA based on the UL MU OFDMA transmission The method may include transmitting the uplink frame to an access point (AP) on a time resource overlapped with another uplink frame, wherein the channel access parameter is used to determine the size of the contention window for the channel access. And a contention window minimum (CWmin) value and a contention window maximum (CWmax) value, wherein the resource unit is the uplink It may be the size of the frequency resource for the UL MU OFDMA transmission of the large frame.

In accordance with another aspect of the present invention, a station (STA) performing a channel access method for uplink multi-user (UL) transmission according to another aspect of the present invention transmits and receives a radio signal (RF). Unit and a processor operatively coupled to the RF unit, the processor to determine an access category of an uplink frame to be transmitted based on UL MU orthogonal frequency division multiple access (OFDM) transmission, Perform channel access based on channel access parameters and resource units set according to categories, and transmit the uplink frame to an access point (AP) on a time resource overlapped with another uplink frame based on the UL MU OFDMA transmission The channel access parameter may be implemented to determine the size of the contention window for the channel access. CWmin include (contention window minimum) value and the (maximum contention window) CWmax values, the resource unit may be a size of frequency resources for the UL MU OFDMA transmission of the uplink frame.

By performing channel access according to an access category of an uplink frame and transmitting an uplink frame through UL MU transmission, waste of unnecessary radio resources can be reduced and an uplink frame can be transmitted according to the priority of the uplink frame.

1 is a conceptual diagram illustrating a structure of a wireless local area network (WLAN).

2 is a conceptual diagram illustrating a scanning method in a WLAN.

3 is a conceptual diagram illustrating an authentication procedure and a combined procedure performed after a scanning procedure of an AP and an STA.

4 is a conceptual diagram illustrating a beacon frame-based power save method.

5 is a conceptual diagram illustrating a beacon frame-based power save method.

6 is a conceptual diagram illustrating a channel access process based on DCF.

7 is a conceptual diagram illustrating a backoff procedure of a plurality of STAs.

8 is a conceptual diagram illustrating a trigger method of an AP for UL MU transmission according to an embodiment of the present invention.

9 is a conceptual diagram illustrating a triggering method of an AP for UL MU transmission according to an embodiment of the present invention.

10 is a conceptual diagram illustrating a structure of a trigger frame according to an embodiment of the present invention.

11 is a conceptual diagram illustrating a trigger frame transmission method according to an embodiment of the present invention.

12 is a conceptual diagram illustrating an uplink frame transmission method based on a trigger frame according to an embodiment of the present invention.

13 is a conceptual diagram illustrating a method for transmitting an uplink frame based on a trigger frame according to an embodiment of the present invention.

14 is a conceptual diagram illustrating a method for transmitting an uplink frame based on a trigger frame according to an embodiment of the present invention.

15 is a conceptual diagram illustrating a random access method for transmitting an uplink frame according to an embodiment of the present invention.

16 is a conceptual diagram illustrating a random access method for transmitting an uplink frame according to an embodiment of the present invention.

17 is a conceptual diagram illustrating a DL MU PPDU format according to an embodiment of the present invention.

18 is a conceptual diagram illustrating transmission of an UL MU PPDU according to an embodiment of the present invention.

19 is a block diagram illustrating a wireless device to which an embodiment of the present invention can be applied.

1 shows the structure of the infrastructure basic service set (BSS) of the Institute of Electrical and Electronic Engineers (IEEE) 802.11.

Referring to the top of FIG. 1, the WLAN system may include one or more infrastructure BSSs 100 and 105 (hereinafter, BSS). The BSSs 100 and 105 are a set of APs and STAs such as an access point 125 and a STA1 (station 100-1) capable of successfully synchronizing and communicating with each other, and do not indicate a specific area. The BSS 105 may include one or more joinable STAs 105-1 and 105-2 to one AP 130.

The BSS may include at least one STA, APs 125 and 130 for providing a distribution service, and a distribution system (DS) 110 for connecting a plurality of APs.

The distributed system 110 may connect several BSSs 100 and 105 to implement an extended service set (ESS) 140 which is an extended service set. The ESS 140 may be used as a term indicating one network in which one or several APs 125 and 230 are connected through the distributed system 110. APs included in one ESS 140 may have the same service set identification (SSID).

The portal 120 may serve as a bridge for connecting the WLAN network (IEEE 802.11) with another network (for example, 802.X).

In the BSS as shown in the upper part of FIG. 1, a network between the APs 125 and 130 and a network between the APs 125 and 130 and the STAs 100-1, 105-1 and 105-2 may be implemented. However, it may be possible to perform communication by setting up a network even between STAs without the APs 125 and 130. A network that performs communication by establishing a network even between STAs without APs 125 and 130 is defined as an ad-hoc network or an independent basic service set (BSS).

1 is a conceptual diagram illustrating an IBSS.

Referring to the bottom of FIG. 1, the IBSS is a BSS operating in an ad-hoc mode. Since IBSS does not contain an AP, there is no centralized management entity. That is, in the IBSS, the STAs 150-1, 150-2, 150-3, 155-4, and 155-5 are managed in a distributed manner. In the IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may be mobile STAs, and access to a distributed system is not allowed, thus making a self-contained network. network).

A STA is any functional medium that includes 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. May be used to mean both an AP and a non-AP STA (Non-AP Station).

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

2 is a conceptual diagram illustrating a scanning method in a WLAN.

Referring to FIG. 2, a scanning method may be classified into passive scanning 200 and active scanning 250.

Referring to the left side of FIG. 2, the passive scanning 200 may be performed by the beacon frame 230 periodically broadcasted by the AP 200. The AP 200 of the WLAN broadcasts the beacon frame 230 to the non-AP STA 240 every specific period (for example, 100 msec). The beacon frame 230 may include information about the current network. The non-AP STA 240 receives the beacon frame 230 that is periodically broadcast to receive the network information to perform scanning for the AP 210 and the channel to perform the authentication / association (authentication / association) process Can be.

The passive scanning method 200 only needs to receive the beacon frame 230 transmitted from the AP 210 without requiring the non-AP STA 240 to transmit the frame. Thus, passive scanning 200 has the advantage that the overall overhead incurred by the transmission / reception of data in the network is small. However, since scanning can be performed manually in proportion to the period of the beacon frame 230, the time taken to perform scanning is relatively increased compared to the active scanning method. For a detailed description of the beacon frame, see IEEE Draft P802.11-REVmb ™ / D12, November 2011, 'IEEE Standard for Information Technology Telecommunications and information exchange between systems--Local and metropolitan area networks--Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (hereinafter referred to as IEEE 802.11) 'are described in 8.3.3.2 beacon frame. IEEE 802.11 ai may additionally use other formats of beacon frames, and these beacon frames may be referred to as fast initial link setup (FILS) beacon frames. In addition, a measurement pilot frame may be used in a scanning procedure as a frame including only some information of a beacon frame. Measurement pilot frames are disclosed in the IEEE 802.11 8.5.8.3 measurement pilot format.

In addition, a FILS discovery frame may be defined. The FILS discovery frame is a frame transmitted between transmission periods of a beacon frame at each AP and may be a frame transmitted with a shorter period than the beacon frame. That is, the FILS discovery frame is a frame transmitted with a period smaller than the transmission period of the beacon frame. The FILS discovery frame may include identifier information (SSID, BSSID) of the AP transmitting the detection frame. The FILS discovery frame may be transmitted before the beacon frame is transmitted to the STA to allow the STA to detect in advance that the AP exists in the corresponding channel. The interval at which a FILS discovery frame is transmitted from one AP is called a FILS discovery frame transmission interval. The FILS discovery frame may include part of information included in the beacon frame and be transmitted.

Referring to the right side of FIG. 2, in the active scanning 250, the non-AP STA 290 may transmit the probe request frame 270 to the AP 260 to proactively perform scanning.

After receiving the probe request frame 270 from the non-AP STA 290, the AP 260 waits for a random time to prevent frame collision, and then includes network information in the probe response frame 280. may transmit to the non-AP STA 290. The non-AP STA 290 may obtain network information based on the received probe response frame 280 and stop the scanning process.

In the case of the active scanning 250, since the non-AP STA 290 performs the scanning, the time used for scanning is short. However, since the non-AP STA 290 must transmit the probe request frame 270, there is a disadvantage in that network overhead for frame transmission and reception is increased. The probe request frame 270 is disclosed in IEEE 802.11 8.3.3.9 and the probe response frame 280 is disclosed in IEEE 802.11 8.3.3.10.

After scanning, the AP and the non-AP STA may perform an authentication procedure and an association procedure.

Referring to FIG. 3, after performing passive / active scanning, an authentication procedure and a combining procedure with one of the scanned APs may be performed.

Authentication and association procedures can be performed, for example, via two-way handshaking. The left side of FIG. 3 is a conceptual diagram illustrating an authentication and combining procedure after passive scanning, and the right side of FIG. 3 is a conceptual diagram showing an authentication and combining procedure after active scanning.

The authentication procedure and the association procedure are based on an authentication request frame 310 / authentication response frame 320 and an association request frame 330 regardless of whether active scanning method or passive scanning is used. ) / Association response frame 340 may be equally performed by exchanging an association response frame 340 between the

AP

300, 350 and the

non-AP STA

305, 355.

In the authentication procedure, the

non-AP STAs

305 and 355 may transmit the authentication request frame 310 to the

APs

300 and 350. The

AP

300 or 350 may transmit the authentication response frame 320 to the

non-AP STAs

305 and 355 in response to the authentication request frame 310. Authentication frame format is disclosed in IEEE 802.11 8.3.3.11.

In the association procedure, the

non-AP STAs

305 and 355 may transmit an association request frame 330 to the

APs

300 and 305. In response to the association request frame 330, the

APs

305 and 355 may transmit the association response frame 340 to the

non-AP STAs

300 and 350. The association request frame 330 transmitted to the AP includes information on the capabilities of the

non-AP STAs

305 and 355. Based on the performance information of the

non-AP STAs

305 and 355, the

APs

300 and 350 may determine whether support for the

non-AP STAs

305 and 355 is possible. When the support for the

non-AP STAs

305 and 355 is possible, the

APs

300 and 350 may transmit the combined response frame 340 to the

non-AP STAs

305 and 355. The association response frame 340 may include whether or not to accept the association request frame 340, and the capability information that can be supported by the association response frame 340. Association frame format is disclosed in IEEE 802.11 8.3.3.5/8.3.3.6.

After the association procedure is performed between the AP and the non-AP STA, normal data transmission and reception may be performed between the AP and the non-AP STA. If the association procedure between the AP and the non-AP STA fails, the association procedure with the AP may be performed again or the association procedure with another AP may be performed again based on the reason for the association failure.

When the STA is associated with the AP, the STA may be assigned an association identifier (AID) from the AP. The AID assigned to the STA may be a unique value within one BSS, and the current AID may be one of 1 to 2007. 14bit is allocated for AID and can be used as the value of AID up to 16383. However, the value of 2008 ~ 16383 is reserved.

In the IEEE 802.11 standard, a power save mechanism is provided to increase the lifespan of a STA of a WLAN.

For power saving, the STA can operate based on two modes (or states): active mode (awake state) and sleep mode (doze state). have. The STA may operate in a power save mode based on the awake state or the doze state.

The STA in the active mode (or awake state) may perform normal operations such as transmission or reception of a frame and channel scanning. In contrast, the STA in the sleep mode (or the doze state) does not perform transmission or reception of a frame and does not perform channel scanning to reduce power consumption. The STA operating in the power save mode may be kept in the doze state and, if necessary, may be switched to (or transitioned to) an awake state to communicate with the AP.

As the retention time of the doze state of the STA increases, the power consumption of the STA may decrease and the lifetime of the STA may also increase. However, in the doze state, transmission or reception of the frame of the STA is impossible. If there is an uplink frame pending in the STA, the STA may switch from the doze state to the active state and transmit the uplink frame to the AP. On the contrary, if there is a pending frame to be transmitted to the STA in the doze state, the AP cannot transmit the frame to the STA until the STA switches to the awake mode.

Accordingly, the STA may occasionally switch from the doze state to the awake state and receive information on whether there is a frame pending for the STA from the AP. The AP may transmit information on the existence of downlink data pending for the STA to the STA in consideration of the transition time of the STA to the awake state.

In more detail, the STA may periodically switch from the doze state to the awake state to receive a beacon frame in order to receive information on whether there is a frame pending for the STA. The beacon frame is a frame used for passive scanning of the STA and may include information on the capability of the AP. The AP may transmit a beacon frame to the STA periodically (eg, 100 msec).

4 is a conceptual diagram illustrating a beacon frame-based power save method.

Referring to FIG. 4, the AP may periodically transmit a beacon frame, and the STA may periodically switch from the doze state to the awake state to receive the beacon frame in consideration of the transmission timing of the beacon frame.

The beacon frame may include a traffic indication map element (TIM element). The TIM element may be used to transmit information on downlink data for the STA pending to the AP. For example, the TIM element may transmit information about a frame pending to the STA based on a bitmap.

The TIM element may be divided into a TIM or a delivery TIM (DTIM). The TIM may indicate the presence of pending downlink data to be transmitted to the STA on unicast basis. The DTIM may indicate the presence of pending downlink data to be transmitted on a broadcast / multicast basis.

The upper part of FIG. 4 discloses a method in which an AP transmits a downlink frame based on an immediate response to a power saving (poll) -poll frame.

Referring to the upper part of FIG. 4, the STA may receive information on the existence of downlink data pending for the STA from the AP based on the TIM of the beacon frame 400. The STA may transmit the PS-poll frame 410 to the AP. The AP may receive the PS-poll frame 410 from the STA and transmit the downlink frame 420 to the STA in an immediate response to the PS-poll frame 410. The immediate response to the PS-poll frame of the AP may be performed after receiving the PS-poll frame and short interframe space (SIFS).

The STA may transmit the ACK frame 430 in response to the downlink frame. When the transmission of the downlink data pending for the STA of the AP is terminated, the STA may be switched back (or transitioned) to the doze state.

4 shows a method of transmitting a downlink frame of an AP based on a deferred response to a PS-poll frame.

Referring to the bottom of FIG. 4, the STA may receive information about the existence of downlink data pending for the STA from the AP based on the TIM of the beacon frame 440. The STA may transmit the PS-poll frame 450 to the AP. The AP may receive the PS-poll frame 450 from the STA and transmit the ACK frame 460 to the STA in response to the PS-poll frame 450. The AP may transmit a downlink frame 470 including the pending downlink data to the STA after transmission of the ACK frame 460. The STA may monitor the downlink frame 470 transmitted by the AP to the STA after receiving the ACK frame 460.

Similarly, when transmission of the downlink data pending for the STA of the AP is terminated, the STA may be switched (or transitioned) from the awake state to the doze state again.

5 is a conceptual diagram illustrating a beacon frame-based power save method.

In FIG. 5, a case in which a delivery traffic indication map (DTIM) is transmitted through a beacon frame 500 is disclosed. Beacon frame 500 may include a DTIM. As described above, the DTIM may indicate the presence of pending downlink data to be transmitted on a broadcast / multicast basis.

Referring to FIG. 5, the AP may transmit a beacon frame 500 including the DTIM to the STA. After receiving the beacon frame 500 including the DTIM, the STA may maintain the awake state without transmitting the PS-poll frame and monitor the transmission of the downlink frame 520. The AP may transmit the downlink frame 520 to the STA through a multicast method or a broadcast method.

6 is a conceptual diagram illustrating a channel access process based on DCF.

First, in a channel coordination function (DCF) based channel access, the STA may determine whether to use the medium through a carrier sensing mechanism. If the medium is not in use for more than a DCF inter frame symbol (DIFS) period (that is, when the channel is idle), the STA may transmit a MAC protocol data unit (MPDU) that is about to be transmitted.

On the contrary, when the medium is in use during the DIFS period (ie, when the channel is busy), the STA may set the backoff time by a random backoff algorithm.

The backoff time is a time that the channel waits for a predetermined time (for example, DIFS) before transmitting a frame, and the backoff time may be defined as in the following equation.

BackoffTime = Random () x aSlotTime

Random () is a function that produces a pseudo-random integer (or random value) that is selected as an even distribution in the interval [0, CW]. CW may be selected from an integer greater than or equal to aCWMin and less than or equal to aCWmax. aCWMin and aCWmax may be determined according to PHY characteristics. aSlotTime may be a time unit defined according to PHY characteristics. If the STA fails to access the channel, CWmin may increase exponentially and CWmin may increase up to CWmax. That is, a STA that fails to access a channel may select a pseudo-random integer (or random value) within a range set based on a relatively larger CWmin value.

The STA may determine whether the channel is idle, and if the channel is idle, the backoff time may be reduced in units of SlotTime. Before the backoff time is reduced in units of SlotTime, the STA may again determine whether the channel is idle during the period corresponding to the DIFS. If the backoff time becomes zero, the STA may perform channel access. In other words, the random value is reduced by 1 in units of SlotTime, so that the backoff count may be set. When the backoff count becomes 0, the STA may perform channel access.

Referring to FIG. 7, the backoff time (or the size of the contention window (CW)) may be reduced after the medium is determined to be idle for the DIFS period. If the activity of the medium is not detected, the STA may reduce the backoff time in SlotTime units. If it is determined that the medium is in use during the backoff slot, the STA may postpone the reduction of the backoff time. The frame transmission of the STA may be started whenever the set backoff timer becomes zero. In other words, the STA may transmit a frame when the random value decreases to 0 by decreasing the random value.

After the frame transmission of the STA A 710, the backoff time set by each of the STA B 720, the STA C 730, and the STA D 740 may be reduced. Among the STA B 720, the STA C 730, and the STA D 740, the STA C 730 having the earliest backoff time reduced to 0 may transmit a frame through the medium. When STA C 730 transmits the frame, the reduction in backoff time of STA B 720 and STA D 740 may be delayed.

In addition, the DCF transmission scheme includes an RTS / CTS access mode in which control frames (request to send (RTS) and clear to send (CTS)) are exchanged and occupy channels in advance before data frames are transmitted. This method can reduce the waste of the channel by replacing the collision that may occur during the transmission of the data frame with the collision by a relatively short control frame.

A point coordination function (PCF) may be defined as another method for sharing a wireless medium by a plurality of STAs in the MAC layer. In the case of the above-described DCF, channel access based on carrier sense multiple access with collision avoidance (CSMA / CA). Therefore, real time transmission of data transmitted between the STA and the AP cannot be guaranteed. In contrast, PCF may be used as a method for providing a quality of service (QoS) for real time data transmission. PCF, unlike DCF, is a non-competitive transport service. The PCF does not exclusively use the entire transmission period of the medium, but may alternate with a DCF-based contention-based service. In the PCF, a point coordinator implemented in an AP of a BSS may control a right for each STA to occupy a medium using a polling scheme. PIFS, an inter-frame space (IFS) in the PCF, can be set to a smaller value than DIFS, the IFS of DCF. By using this method, the STA accessing the medium based on the PCF may have priority over the STA accessing the channel based on the DCF. IFS represents the interval between frames and may be used to set the priority for the STA to access the medium. IFS may be specifically defined as follows.

The STA may determine whether a channel is used during a time interval of an inter frame space (IFS) defined by a standard using a carrier detection method. The MAC layer using DCF defines a plurality of IFSs. Priority of the STA occupying the wireless medium may be determined by the IFS. The interval between frames according to IFS type is as follows.

(1) SIFS (short inter frame symbol): Used to transmit RTS / CTS, ACK frame. Highest priority

(2) PIFS (PCF IFS): used when transmitting a frame of an STA operating on a PCF basis

(3) DIFS (DCF IFS): used for frame transmission of STAs operating on the basis of DCF

(4) EIFS (extended IFS): used only when frame transmission error occurs, not fixed interval

Hereinafter, in the embodiment of the present invention, the data (or frame) transmitted from the AP to the STA is downlink data (or downlink frame), and the data (or frame) transmitted from the STA to the AP is uplink data (or uplink frame). It can be expressed by the term). 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. 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.

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 the existing WLAN system, the entire bandwidth is used for downlink transmission to one STA and uplink transmission of one STA based on single-orthogonal frequency division multiplexing (SUDM) transmission. In addition, in the conventional WLAN system, the AP may perform DL (downlink) multi-user (MU) transmission based on MU MIMO (multiple input multiple output), and such transmission may be expressed by the term DL MU MIMO transmission. Can be.

In a conventional WLAN system that did not support MU OFDMA (orthogonal frequency division multiple access) 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 has a large limitation in obtaining high throughput by operating a wide bandwidth in the current WLAN environment in which there is no overlapped basic service set (OBSS). Can be.

In order to solve this problem, an embodiment of the present invention discloses a WLAN system supporting MU OFDMA (orthogonal frequency division multiple access) technology. 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 thus the efficiency of radio resource management can be improved.

In more detail, in the WLAN system according to the embodiment of the present invention, the AP may perform DL MU transmission based on OFDMA, and such transmission may be expressed by the term 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) (eg, a basic tone unit (BTU), a small tone unit (STU)). DL MU OFDMA transmission can be used with DL MU MIMO transmission. For example, DL MU MIMO based on a plurality of space-time streams (or spatial streams) on a specific subband (or subchannel) or resource unit allocated for DL MU OFDMA transmission. The transfer can be performed.

The BTU illustrated as a resource unit above may be a larger size resource unit than a STU. For example, the BTU may be defined as a size of 52 tons, 56 tons, 114 tons, and the like. The BTU may be defined as the same size regardless of the amount of available bandwidth (eg, 20 MHz, 40 MHz, 80 MHz, 160 MHz, etc.) or may be defined as a size that varies depending on the amount of available bandwidth. For example, the size of the BTU may be defined as a relatively large value as the size of the available bandwidth increases. Tone may be interpreted as having the same meaning as a subcarrier. The STU may be a smaller size resource unit than the BTU. For example, the STU may be defined as a size of 26 tons.

In addition, in a WLAN system according to an embodiment of the present invention, UL MU transmission (uplink multi-user transmission) in which a plurality of STAs transmit data to an AP on the same time resource may be supported. 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) (eg, basic tone units (BTUs) and small tone units (STUs)). 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 may be performed based on a plurality of spatiotemporal streams (or spatial streams) on a specific subband (or subchannel) or resource unit allocated for UL MU OFDMA transmission.

In the present invention, a time-frequency structure assumed in a WLAN system according to an embodiment may be as follows.

The fast fourier transform (FFT) size / inverse fast fourier transform (IFFT) size may be defined as N times (N is a natural number, for example, N = 4) of the FFT / IFFT size used in a conventional WLAN system. . 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.

The subcarrier spacing may be 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).

The IDFT / DFT length (or effective symbol length) based on inverse discrete fourier transform (IDFT) / discrete fourier transform (DFT) (or FFT / IFFT) may be N times the IDFT / DFT length in the existing WLAN system. . For example, when the IDFT / DFT length is 3.2μs and N = 4 in the existing WLAN system, the IDFT / DFT length is 3.2μs * 4 (= 12.8μs) in the WLAN system according to an embodiment of the present invention Can be.

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.

Hereinafter, in the embodiment of the present invention, a triggering method of an AP for UL MU transmission is disclosed.

In FIG. 8, a method of transmitting an uplink frame of a plurality of STAs based on a trigger frame is disclosed.

Referring to FIG. 8, an AP may transmit a trigger frame 800 for triggering UL MU transmission of a plurality of STAs to a plurality of STAs.

The plurality of STAs receive the trigger frame 800, extract a random value based on the value of CWmin (or a minimum contention window) defined by the trigger frame 800, and then perform a contention based on backoff. You can access the channel with.

The random value determined by each of the plurality of STAs is a backoff count and may be reduced according to the number of transmitable resource units (or frequency units) or trigger frames transmitted to the STAs.

For example, when the number of resource units that can be allocated to each of the plurality of STAs is a specific number, only a STA having a random value having a value equal to or less than a number corresponding to a specific number of the plurality of STAs is included in the trigger frame 800. In response, the data frame may be transmitted. For another example, if the number of transmissions of the trigger frame transmitted afterwards corresponds to the number of transmission of the counted trigger frame and a random value, the STA may transmit an uplink data frame in response to the trigger frame.

As a specific example, when the value of CWmin set by the trigger frame 800 is 7, the STA that receives the trigger frame may select one integer from 0 to 7. If the STA selects 5, the STA may transmit an uplink frame on a fifth resource unit (or a sixth resource unit) of the plurality of available resource units. That is, if the random value selected by the STA is less than or equal to the number of available resource units (or the number of available resource units-1), the STA may perform an uplink data frame on a specific resource unit among the available resource units based on the random value. Can transmit

If the number of available resource units is smaller than the size of the selected random value, the STA may be restricted from transmitting uplink frames on the available resource units. For example, if the number of available resource units is 4 (RU1 810, RU2 820, RU3 830, RU4 840) and the random value selected by the STA is 5, the STA is It may not be able to transmit an uplink frame. If the number of available resource units is 4, the STA responds to the trigger frame 800 through at least one resource unit of the plurality of available resource units only when the random value selected by the STA is 0 to 3. The uplink frame can be transmitted.

If the random value selected by the STA (or random value + 1) is greater than the number of available resource units, the STA cannot transmit an uplink frame in response to the currently transmitted trigger frame 800. The STA may reduce the random value by the number of available resource units and attempt channel access based on the reduced random value when the next trigger frame is transmitted.

Alternatively, the STA counts the number of transmissions of the trigger frame transmitted after the currently transmitted trigger frame 800 and counts one frequency resource among one of a plurality of frequency resources available in response to the nth transmitted trigger frame corresponding to the random value. The uplink frame can be transmitted through the S-PDU.

The AP may receive a plurality of uplink frames through a plurality of resource units available from the plurality of STAs. The AP may transmit a plurality of BA frames to the plurality of STAs in response to the received plurality of uplink frames.

If the STA fails to transmit, then, the CWmin value of the STA for channel access may be set to increase exponentially based on the CWmin value set by the trigger frame. If the CWmin value increased by the STA due to the transmission failure is increased to CWmax, the STA may no longer increase the CWmin value.

In the method for transmitting an uplink frame based on the trigger frame 800 according to an embodiment of the present invention, the STA receives the trigger frame 800 from the AP, and the STA accesses the channel access parameter included in the trigger frame 800. When the random value is selected based on the information and the backoff count set based on the random value is reduced to become a specific value, the STA may be performed based on the step of transmitting an uplink frame. The channel access parameter information includes a CWmin value for determining the size of the minimum contention window for the backoff procedure, and a random value may be determined based on the CWmin value.

The backoff count is reduced based on the number of available resource units for transmission of the uplink frame, and the uplink frame is transmitted through at least one resource unit among the available resource units based on a random value. Can be.

Alternatively, the backoff count may be reduced based on the number of transmissions of other trigger frames transmitted after the trigger frame.

9 illustrates a method of transmitting an uplink frame of a plurality of STAs based on a trigger frame.

Referring to FIG. 9, the AP may transmit a trigger frame for triggering UL MU transmission of a plurality of STAs to the plurality of STAs.

The trigger frame may include information on available uplink transmission resources (or available uplink resource units / transmittable frequency units). The plurality of STAs may receive a trigger frame and perform channel access for transmission of uplink data in consideration of available uplink transmission resources indicated by the trigger frame.

The AP may allocate the entire uplink resource unit to the unspecified terminal or only some of the uplink resource units in the entire uplink resource unit according to the channel situation.

For example, the AP may set only RU1 910 and RU3 930 as available uplink resource units among all resource units (RU1 910, RU2 920, RU3 930, and RU4 940). In addition, information about the RU1 910 and the RU3 930 set in the available uplink resource unit may be transmitted through the trigger frame 1 900. The plurality of STAs may receive the trigger frame 1 900 and perform channel access through the RU1 910 and the RU3 930.

In addition, the AP may set only RU3 930 and RU4 940 as available uplink resource units among all resource units RU1 910, RU2 920, RU3 930, and RU4 940. Information about the RU3 930 and the RU4 940 set in the available uplink resource unit may be transmitted through the trigger frame 2 950. The plurality of STAs may receive trigger frame 2 950 and perform channel access through RU3 930 and RU4 940.

The procedure for transmitting an uplink frame based on a trigger frame according to an embodiment of the present invention mainly includes a probe request frame, an authentication request frame, an association request frame, and a buffer state. It may be used for transmission of an uplink frame such as a report status (buffer status report frame), PS-poll frame (PS-Poll frame). The AP may not know information about the STA transmitting the uplink frame.

Since the probe request frame, the authentication request frame, and the association request frame among the uplink frames as described above are transmitted in the pre-association step, an association identifier (AID) that is identification information of the STA allocated to the STA by the association procedure is not allocated to the STA. Therefore, it may be difficult to control the operation of the STA of the AP. In addition, the length of the probe request frame, the authentication request frame, and the combined request frame is generally 100 bytes or more.

In contrast, the buffer status report frame and the PS-poll frame may be uplink frames transmitted by the STA after the combining procedure. Accordingly, a buffer status report frame and a PS-poll frame may be transmitted based on the AID of the STA, and the operation of the STA by the AP may be controlled. The buffer status report frame and the PS-poll frame may be as short as several tens of bytes or less.

The AP may not know which STA transmits which uplink frame. Therefore, information for controlling the transmission of the uplink frame may be transmitted to the STA through the trigger frame. In addition, since the characteristics of the frame vary according to the type of the frame, the AP may provide an opportunity to transmit the frame to the STA by reflecting the type (or characteristic information of the frame) of the frame.

In an embodiment of the present invention, a method of allocating a transmission opportunity to an STA in consideration of characteristic information of a frame is disclosed. According to an embodiment of the present invention, the AP may perform channel access by setting different channel access parameters through a trigger frame.

As described above, the probe request frame, the authentication request frame, and the association request frame have a length of an uplink frame longer than 100 bytes, and it is difficult to predict a terminal to transmit the uplink frame. On the other hand, the buffer status report frame and the PS-poll frame have a relatively short frame length and can predict the terminal to which the frame will be transmitted. Accordingly, the AP may divide the frame type into two and perform channel access based on different channel access parameters (for example, CWmin and CWmax).

Since the probe request frame, the authentication request frame, and the association request frame have a long frame length, the size of the frequency resource (or resource unit) for transmitting the frame may be relatively large. When the size of the frequency resource is set to a large size, the possibility of resource waste due to collision between frames may be relatively increased. Therefore, the CWmin value and the CWmax value can be set relatively large. When the CWmin value and the CWmax value are set relatively large, contention between STAs accessing the channel may be further reduced. When the value of CWmin increases, the number of STAs that select the same random value may be reduced. In addition, when the value of CWmax increases, since the selection range of the random value by the STA that fails to transmit is increased, the number of STAs that select the same random value may be reduced. The CWmin value and the CWmax value may be adjusted by the AP according to the resource situation and the collision situation.

Since the buffer status report frame and the PS-poll frame have a short frame length, the size of the frequency unit (or resource unit) for transmitting the frame may be set relatively small. Therefore, the size of the padding bit required to match the length of the PPDU carrying the uplink frame transmitted by each STA can be reduced.

In addition, the AP may infer some extent of the STA to transmit the buffer status report frame and the PS-poll frame. For example, the AP may infer that the STA indicated by the AP based on the positive indication of the TIM element of the beacon frame will transmit the PS-poll frame. The positive indicator of the TIM element may indicate the presence of downlink data for the STA buffered in the AP. In addition, the AP may infer that the buffer status report frame is to be transmitted by the STA buffered with uplink data among the STAs coupled to the AP.

Accordingly, the AP may adaptively adjust CWmin and CWmax in consideration of the number of STAs coupled to the STAs and / or the number of STAs indicated by the presence of a buffered downlink based on the TIM element of the beacon frame. If the number of STAs currently coupled to the AP is small or the number of STAs indicated based on the positive indicator of the TIM element of the beacon frame is small, the values of CWmin and CWmax may be set relatively small.

Alternatively, if the number of STAs combined is very large and most STAs are in active mode (or awake state) or the number of STAs indicated based on the positive indicator of the TIM element is large, the CWmin and CWmax values may be set relatively large. Can

That is, channel access parameters (e.g., CWmin value, CWmax value) and radio resources (e.g., CWmin value) for transmission of a frame of a first frame type (e.g., probe request frame, authentication request frame, combined request frame) , The size of the resource unit) and the channel access parameter (for example, CWmin value, CWmax value) for transmission of the frame of the second frame type (buffer status report frame, PS-poll frame), and the radio resource (for example, The size of the resource unit) may be different.

Table 1 below discloses the CWmin value, CWmax value, and resource unit size according to the frame type.

	CWminCWmin	CWmaxCWmax	자원 크기(Resource Size)Resource Size

프레임 타입1(Frame Type 1)프로브 요청 프레임, 인증 요청 프레임, 결합 요청 프레임(Probe Request Frame, Authentication Request Frame, Association Request Frame)Frame Type 1 Probe Request Frame, Authentication Request Frame, Association Request Frame	1515	3131	22
프레임 타입2(Frame Type 2)버퍼 상태 리포트 프레임, PS-poll 프레임(Buffer Status Report Frame, PS-Poll Frame) Frame Type 2 Buffer Status Report Frame, PS-poll Frame (Buffer Status Report Frame, PS-Poll Frame)	77	1515	1One

Information on the CWmin value, the CWmax value, and the resource unit according to the above frame type may be transmitted through the trigger frame.

The distinction between frame type 1 and frame type 2 disclosed in the present invention may be exemplary. The frame included in each of the frame type 1 and the frame type 1 may be another frame as well as the illustrated frame. The AP may classify the frame into a specific frame type in consideration of information on the size of the frame / whether the frame is transmitted before combining, and determine the size of a channel access parameter for transmitting the frame and a size of a resource unit for transmitting the frame. .

In FIG. 10, channel access parameter information and resource unit size information according to a frame type transmitted through a trigger frame are disclosed.

Referring to FIG. 10, an MU random access information format may be defined in a trigger frame.

The MU random access information format (or MU random access information element) may include an element ID field 1000, a length field 1010, and an information field 1020 for each frame type.

The element ID 1000 field may include information indicating that an information element is an MU random access information element.

The length field 1010 may include information about the length of the MU random access information element.

The frame type information field 1020 may include information on a channel access parameter for each frame type and information on the size of a resource unit for each frame type.

If the frame type is divided into frame type 1 and frame type 2, the information field for each frame type includes information on CWmin value (CWmin for frame type1), CWmax value (CWmax for frame type1), and resource unit size for frame type1. (RU size for frame type1), CWmin value for frame type2 (CWmin for frame type2), CWmax value (CWmin for frame type2), and resource unit size information (RU size for frame type2). The frame type of the frame may be previously classified.

As described above, the CWmin value, the CWmax value, and the resource unit size depend on the number of STAs coupled to the STA, the number of STAs indicating the existence of a buffered downlink based on the TIM element of the beacon frame, and / or the size of the frame. Can change.

In FIG. 11, a method in which an STA is allocated a resource unit based on a trigger frame and transmits an uplink frame on a plurality of available resource units is disclosed. The trigger frame may include an MU random access information element. In addition, the trigger frame may include information on allocation of uplink transmission resources. Resource units of different sizes may be allocated to uplink transmission resources of the plurality of STAs by the trigger frame.

The trigger frame 1100 may allocate RU1 1110, RU2 1120, RU3 1130, and RU4 1140 as uplink transmission resources. The RU1 1110 may be a size 2 resource unit, the RU2 1120 may be a size 1 resource unit, the RU3 1130 may be a size 1 resource unit, and the RU4 1140 may be a size 2 resource unit.

An STA that receives the trigger frame 1100 and transmits a frame of frame type 1 may perform channel access based on CWmin and CWmax configured for frame type 1 through RU1 1110 and RU4 1140. An STA that receives a trigger frame and transmits a frame of frame type 2 may perform channel access based on CWmin and CWmax configured for frame type 2 through RU2 1120 and RU3 1130.

For example, each of STA1 and STA4 may transmit a probe request frame of frame type 1 through each of RU1 1110 and RU4 1140, and each of STA2 and STA3 may transmit a PS-poll frame of frame type 2 to RU2 (1120). ) And RU3 1130, respectively.

Frames of frame type 1 or frame type 2 transmitted in each RU may be delivered through a UL MU PPDU. The transmission start point of the UL MU PPDU may be determined based on the transmission (or reception) timing of the trigger frame, and the transmission termination timing of the plurality of UL MU PPDUs may be adjusted to the termination timing of the longest UL MU PPDU. Padding bits may be added to meet transmission termination points of a plurality of UL MU PPDUs, and a larger resource unit may be allocated for transmission of a relatively large frame type 1 to reduce the size of the padding bits. .

An AP receiving each of a plurality of UL MU PPDUs including each of a plurality of frames of frame type 1 from each of the plurality of STAs and a plurality of UL MU PPDUs including each of a plurality of frames of frame type 2 from each of the plurality of STAs A block acknowledgment (BA) frame may be transmitted to a plurality of STAs.

In FIG. 12, a method of transmitting an MU random access information element through a trigger frame is disclosed.

Referring to FIG. 12, a plurality of STAs may receive a trigger frame and transmit a plurality of uplink frames based on the trigger frame. The trigger frame may include the aforementioned MU random access information element.

Among the STAs, the STA that fails to transmit an uplink frame based on the trigger frame 1 1200 may receive the trigger frame 2 1250.

The STA that fails to access the channel may set the CWmin set by the trigger frame 2 1250 again as a new CWmin value without increasing the CWmin value set by the trigger frame 1 1200 by itself. The STA may newly set only the CWmin value and maintain a backoff procedure based on an existing selected random value. That is, the STA may perform channel access when the existing backoff count is maintained and the backoff count becomes zero. The STA performs a backoff procedure by newly selecting a random value based on a new CWmin value newly set by trigger frame 2 (1250) when channel access fails through a backoff procedure based on a selected random value of a zone. can do.

Alternatively, the STA may operate according to the MU random access information element of the first received trigger frame and may not consider the MU random access information element set by the subsequent received trigger frame.

In FIG. 13, a method of transmitting an MU random access information element via a beacon frame is disclosed.

Referring to FIG. 13, the MU random access information element may be transmitted through the beacon frame 1300 instead of the trigger frame.

The STA may receive channel access parameters and resource unit information for transmitting an uplink frame in response to a trigger frame during a transmission period of the beacon frame 1300 (interval between target beacon transmission times (TBTTs)) based on the beacon frame. Can be.

That is, the STA may perform channel access after receiving the trigger frame based on the channel access parameter and the resource unit set by the beacon frame 1300 during the transmission period of the beacon frame 1300.

The MU random access information element of the beacon frame 1300 may include information about CWmin, CWmax, resource unit (RU), and the like. When a trigger frame is transmitted, the MU random access information element transmitted by the beacon frame may be utilized. The beacon frame may further include information about a trigger frame to be transmitted after the beacon frame.

The trigger frame may include information on a scheduled transmission time of the trigger frame to be transmitted on the beacon interval and information on a frequency unit (RU) to be allocated by the trigger frame (eg, information on the position and the total number of RUs).

In FIG. 14, when the STA has already transmitted the frame through MU random access, but fails to transmit the frame due to a collision with a frame transmitted by another STA, the STA may attempt to retransmit the frame.

According to an embodiment of the present invention, an uplink resource for retransmission may be allocated based on another trigger frame 1450. If an uplink resource for retransmission is allocated, a channel access delay for retransmission of the STA can be reduced. Alternatively, if the channel environment of the retransmitting STA is considered to be bad, the first transmitting STA may have a separate protection effect and the overall performance may be improved.

The AP may inform, via the ACK frame, that the transmission of the trigger frame 1450 for retransmission is transmitted after the ACK frame.

The AP may receive a plurality of frames transmitted based on the MU random access, and if an error occurs in a specific frame among the plurality of frames, the AP may determine that a collision between frames occurs in the corresponding RU.

The AP may inform the transmission of the trigger frame 1450 for retransmission through an ACK frame, and then retransmit the trigger frame for retransmission.

The STA that fails to transmit the frame may retransmit the frame in response to the trigger frame 1450 for retransmission. The AP may configure resource units for retransmission (RU1 for ReTX, RU2 for ReTX, RU3 for ReTX) based on the trigger frame 1450 for retransmission. The trigger frame 1450 for retransmission may include information on a resource unit for retransmission.

The AP may include additional MU random access information when transmitting the trigger frame 1450 for retransmission. The MU random access information of the trigger frame 1450 for retransmission may include an adjusted CWmin value and an adjusted CWmax value. Since there may be many STAs around STAs retransmitted due to collision between frames, it is possible to set relatively large CWmin and CWmax values.

		CWminCWmin	CWmaxCWmax	자원 단위의 크기Resource SizeResource size
재전송(Retransmission)Retransmission	프레임 타입1(프로브 요청 프레임, 인증 요청 프레임, 결합 요청 프레임)Frame Type 1(Probe Request Frame, Authentication Request Frame, Association Request Frame)Frame Type 1 (Probe Request Frame, Authentication Request Frame, Association Request Frame)	3131	6363	22
재전송(Retransmission)Retransmission	프레임 타입2(버퍼 상태 리포트 프레임, PS-poll 프레임)Frame Type 2(Buffer Status Report Frame, PS-Poll Frame)Frame Type 2 (Buffer Status Report Frame, PS-Poll Frame)	1515	3131	1One
초기 전송(Initial Transmission)Initial Transmission	프레임 타입1(프로브 요청 프레임, 인증 요청 프레임, 결합 요청 프레임)Frame Type 1(Probe Request Frame, Authentication Request Frame, Association Request Frame)Frame Type 1 (Probe Request Frame, Authentication Request Frame, Association Request Frame)	1515	3131	22
초기 전송(Initial Transmission)Initial Transmission	프레임 타입2(버퍼 상태 리포트 프레임, PS-poll 프레임)Frame Type 2(Buffer Status Report Frame, PS-Poll Frame)Frame Type 2 (Buffer Status Report Frame, PS-Poll Frame)	77	1515	1One

Referring to Table 2, a CWmin value and a CWmax value that are relatively larger than the initial transmission may be set during retransmission.

In FIG. 15, random access for UL MU transmission of a frame according to an access category of the frame may be performed.

For example, the access category of a frame may be access category (AC) _VO (voice), AC_VI (video), AC_BE (best effort) or AC_BK (background). For convenience of description, it may be expressed as AC_VO, AC_VI, AC_BE, or AC_BK, but may also be expressed as terms of a first access category, a second access category, a third access category, and a fourth access category.

According to an embodiment of the present invention, the channel access parameter (e.g., CWmin, CWmax) and the size of the resource unit are increased so that the frame is transmitted to the AP through the medium with high priority in the order of AC_VO, AC_VI, AC_BE, AC_BK. Can be set. That is, channel access priority of an STA to transmit a frame using UL MU transmission may be determined based on an access category corresponding to a frame to be transmitted by the STA. In order to differentiate the channel access priority of the STA according to the access category of the frame to be transmitted, different sizes of the contention window may be defined according to the access category of the frame to be transmitted based on the UL MU transmission.

Referring to FIG. 15, for example, a frame such as a probe request frame, an authentication request frame, and a combination request frame transmitted by an STA to combine with an AP is important to reduce transmission delay. Accordingly, in order to set a high transmission priority for the frame, the access categories of the probe request frame, authentication request frame, and join request frame may be set to AC_VO, and transmission of the probe request frame, authentication request frame, and join request frame may be performed. The random access may be performed based on random access parameters CWmin and CWmax and resource units corresponding to AC_VO.

On the other hand, the access category of the PS-Poll frame transmitted by the STA after combining the STA and the AP may be set to AC_BE. Random access for transmission of the PS-poll frame may be performed based on random access parameters CWmin and CWmax and resource units corresponding to AC_BE.

In relation to the buffer status report frame, the access category of the buffer status report frame may change according to a queue of access categories to be reported through the buffer status report frame. For example, when the buffer status report frame reports information on the status of the STA's AC_VI queue, the access category of the buffer status report frame may be set to AC_VI to perform random access for transmission of the buffer status report frame. . For another example, when the buffer status report frame reports information on the status of the AC_VO queue, the access category of the buffer status report frame may be set to AC_VO to perform random access for transmission of the buffer status report frame.

Table 3 below discloses information on random access parameters (CWmim, CWmax) and resource size corresponding to the frame-by-frame access category and the frame-by-frame access category.

	CWminCWmin	CWmaxCWmax	자원 사이즈(Resource Size)Resource Size
AC_VO프로브 요청 프레임(probe request frame)인증 요청 프레임(authentication request frame)결합 요청 프레임(association request frame)AC_VO 큐의 상태 정보를 리포트하는 버퍼 상태 리포트 프레임(Buffer Status Report of AC_VO queue))AC_VO probe request frame authentication request frame association request frame Buffer Status Report of AC_VO queue.	33	33	1/21/2
AC_VIAC_VI 큐의 상태 정보를 리포트하는 버퍼 상태 리포트 프레임(Buffer Status Report of AC_VI queue))Buffer Status Report frame that reports the status information of the AC_VIAC_VI queue.	77	77	1One
AC_BEPS-poll 프레임 AC_BE 큐의 상태 정보를 리포트하는 버퍼 상태 리포트 프레임(Buffer Status Report of AC_VI queue)AC_BEPS-poll Frame Buffer Status Report Frame that reports the status information of the AC_BE queue.	77	1515	1One
AC_BKAC_BK 큐의 상태 정보를 리포트하는 버퍼 상태 리포트 프레임(Buffer Status Report of AC_BK queue)Buffer Status Report frame for reporting the status information of the AC_BKAC_BK queue	1515	3131	1One

Referring to Table 3, information on a random access parameter and a resource unit for UL MU random access for each access category is disclosed. The AP may include MU random access information in a trigger frame or beacon frame and transmit the same. The MU random access information may include information about a random access parameter and a resource unit for UL MU random access, as disclosed in Table 4.

Alternatively, in the combining step, the STA may previously receive and store MU random access information to be used in a basic service set (BSS) from the AP. The STA may determine an access category of an uplink frame to be transmitted to the AP based on UL MU transmission and perform random access for transmission of an uplink frame based on MU random access information.

Referring to FIG. 16, a random access method for transmission of an uplink frame may be performed based on a multi-user transmission opportunity (MU TXOP) sharing method.

That is, buffer status information corresponding to two access categories may be transmitted through one buffer status report frame based on the MU TXOP sharing method.

In more detail, one buffer status report frame may transmit not only the buffer status information for the primary access category (AC) but also the buffer status information for the secondary access category (AC).

The primary AC may be an AC that has obtained a TXOP through competition for the acquisition of the medium. The secondary AC may be an AC that has not obtained the TXOP through the competition for the acquisition of the medium.

In more detail, one STA may have a queue corresponding to each of the access categories AC_VO, AC_VI, AC_BE, and AC_BK, and data corresponding to each of the access categories may be stored in the queue of each of the access categories. Each of the plurality of access categories may perform contention-based channel access based on different random access parameters, and one access category may be selected in the contention to obtain a TXOP. The STA may transmit data corresponding to one access category selected in the competition to the AP through a frame.

According to the embodiment of the present invention, the buffer status information frame may transmit not only the buffer status information of the primary AC that has won the TXOP in a competition but also the buffer status information of the secondary AC that has gone in the competition. In this case, the buffer status report frame may be transmitted through UL MU transmission based on a random access value and a resource unit corresponding to the primary AC.

If retransmission of the buffer status information is performed due to the transmission failure of the buffer status information frame, by adjusting the CWmax value, the contention window size for the primary AC is increased and the contention window size for the secondary AC is increased. May increase and perform retransmission for the buffer status information frame by performing a backoff procedure.

FIG. 17 illustrates a DL MU PPDU format transmitted based on OFDMA by an AP according to an embodiment of the present invention.

Referring to FIG. 17, a PPDU header of a DL MU PPDU includes a legacy short training field (L-STF), a legacy long training field (L-LTF), a legacy-signal (L-SIG), and a HE-SIG A (high). efficiency-signal A), high efficiency-signal-B (HE-SIG B), high efficiency-short training field (HE-STF), high efficiency-long training field (HE-LTF), data field (or MAC payload ) May be included. From the PHY header to the L-SIG may be divided into a legacy part and a high efficiency (HE) part after the L-SIG.

The L-STF 1700 may include a short training orthogonal frequency division multiplexing symbol. The L-STF 1700 may be used for frame detection, automatic gain control (AGC), diversity detection, and coarse frequency / time synchronization.

The L-LTF 1710 may include a long training orthogonal frequency division multiplexing symbol. The L-LTF 1710 may be used for fine frequency / time synchronization and channel prediction.

The L-SIG 1720 may be used to transmit control information. The L-SIG 1720 may include information about a data rate and a data length.

The HE-SIG A 1730 may include information for indicating an STA to receive the DL MU PPDU. For example, the HE-SIG A 530 may be an indicator indicating whether a transmitted PPDU is DL transmission or UL transmission, an identifier of a specific STA (or AP) to receive the PPDU, and information for indicating a group of the specific STA. It may include. In addition, when the DL MU PPDU is transmitted based on OFDMA or MIMO, the HE-SIG A 530 may also include resource allocation information for receiving the DL MU PPDU of the STA.

In addition, the HE-SIG A 1730 may include color bit information, bandwidth information, transmission opportunity (TXOP) duration information, tail bits, CRC bits, and HE-SIG for BSS identification information. It may include modulation and coding scheme (MCS) information for the B 1740, symbol number information for the HE-SIG B 1740, and cyclic prefix (CP) (or guard interval (GI)) length information.

In addition, the HE-SIG A 1730 may have a repetitive mode for extending the transmission range. If a repetitive mode is used in the HE-SIG A 1730, use of the repetitive mode may be indicated prior to the HE-SIG A 1730. In the repeat mode, the HE-SIG A 1730 may be repeated once. The bit interleaver may be bypassed in repeated HE-SIG A symbols.

The HE-SIG B 1740 may include information about a length MCS of a physical layer service data unit (PSDU) for each STA, tail bits, and the like. In addition, the HE-SIG B 1740 may include information on the STA to receive the PPDU, OFDMA-based resource allocation information (or MU-MIMO information). If the HE-SIG B 1740 includes OFDMA-based resource allocation information (or MU-MIMO related information), the HE-SIG A 1730 may not include resource allocation information.

The previous field of the HE-SIG B 1740 on the DL MU PPDU may be transmitted in duplicated form in each of different transmission resources. In the case of the HE-SIG B 1740, the HE-SIG B 1740 transmitted in some resource units (eg, resource unit 1 and resource unit 2) is an independent field including individual information, and the remaining resources. The HE-SIG B 1740 transmitted in a unit (eg, resource unit 3 and resource unit 4) is an HE-SIG B 1740 transmitted in another resource unit (eg, resource unit 1, resource unit 2). ) May be in a format duplicated.

In more detail, the HE-SIG B 1740 may include a common block and a plurality of user blocks. The general block may include information on resource allocation, and the user block may include STA-specific information (or user specific information). A separate CRC may be defined for the general block, and a separate CRC may be defined for each of the set number of user blocks. For example, the HE-SIG B 1740 includes one common block and five user blocks (user blocks 1 to 5), and user blocks in units of two user blocks. It may be assumed that a CRC for is defined. In this case, the CRC1 for the general block, the CRC2 for the user block 1 and the user block 2, the CRC3 for the user block 3 and the user block 4, and the CRC4 for the user block 5 may be included in the HE-SIG B.

Each of the plurality of user blocks included in the HE-SIG B 1740 transmitted in one resource unit may include information about the plurality of users. For example, the user block 1 may include user specific information about STA1 and STA2, and the user block 2 may include user specific information about STA3 and STA4.

HE SIG B1 transmitted in resource unit 1 and HE SIG B2 transmitted in resource unit 2 may be HE SIG B including different information. For example, HE SIG B1 transmitted in resource unit 1 may include a general block and a user block for STA 1 and STA2, and HE SIG B2 transmitted in resource unit 2 may include a general block for STA 3 and STA4 and It may include a user block. As described above, the HE SIG B1 transmitted in the resource unit 3 may be generated by duplication of the HE SIG B1 transmitted in the resource unit 1, and the HE SIG B2 transmitted in the resource unit 4 may be the HE SIG transmitted in the resource unit 1. It can be generated by duplication of B2.

The HE-STF 1750 may be used to improve automatic gain control estimation in a multiple input multiple output (MIMO) environment or an OFDMA environment.

Specifically, the STA1 may receive the HE-STF1 transmitted through the resource unit 1 from the AP, and decode the data field 1 (or frame 1) by performing synchronization, channel tracking / prediction, and AGC. Similarly, the STA2 may receive the HE-STF2 transmitted through the resource unit 2 from the AP, and decode the data field 2 (or frame 2) by performing synchronization, channel tracking / prediction, and AGC. The STA3 may receive the HE-STF3 transmitted through the resource unit 3 from the AP, and decode the data field 3 (or frame 3) by performing synchronization, channel tracking / prediction, and AGC. The STA4 may receive the HE-STF4 transmitted through the resource unit 4 from the AP, and decode the data field 4 (or frame 4) by performing synchronization, channel tracking / prediction, and AGC.

The HE-LTF 1760 may be used to estimate a channel in a MIMO environment or an OFDMA environment.

The size of the IFFT applied to the fields after the HE-STF 1750 and the HE-STF 1750 and the size of the IFFT applied to the field before the HE-STF 1750 may be different. For example, the size of the IFFT applied to the fields after the HE-STF 1750 and the HE-STF 1750 may be four times larger than the size of the IFFT applied to the field before the HE-STF 1750. The STA may receive the HE-SIG A 1730 and may be instructed to receive the downlink PPDU based on the HE-SIG A 1730. In this case, the STA may perform decoding based on the FFT size changed from the field after the HE-STF 1750 and the HE-STF 1750. In contrast, when the STA is not instructed to receive the downlink PPDU based on the HE-SIG A 1730, the STA may stop decoding and configure a network allocation vector (NAV). The cyclic prefix (CP) of the HE-STF 1750 may have a larger size than the CP of another field, and during such CP period, the STA may perform decoding on the downlink PPDU by changing the FFT size.

An access point (AP) allocates each of a plurality of resource units for each of a plurality of STAs over the entire bandwidth, and each of the individual data fields (or downlinks) for each of the plurality of STAs through each of the plurality of resource units to the plurality of STAs Link frame) can be transmitted. Information about the allocation of each of the plurality of resource units for each of the plurality of STAs may be included in the HE-SIG A 1750 or the HE-SIG B 1760 as described above.

In FIG. 18, a UL MU PPDU format for UL MU transmission of an STA is disclosed as described above.

Referring to FIG. 18, a plurality of STAs may transmit UL MU PPDUs to the AP based on UL MU OFDMA. The data field 1870 of the UL MU PPDU may include uplink data (or uplink frame) triggered by a trigger frame. The AP may receive a plurality of UL frames transmitted by a plurality of STAs through a plurality of UL MU PPDUs transmitted on overlapping time resources.

The L-STF 1800, the L-LTF 1810, the L-SIG 1820, the HE-SIG A 1830, and the HE-SIG B 1840 may perform the roles disclosed in FIG. 17. Information included in the signal field L-SIG 1820, HE-SIG A 1830, and HE-SIG B 1840 may be generated based on the information included in the signal field of the received DL MU PPDU. .

The STA1 may perform uplink transmission through the entire bandwidth up to the HE-SIG B 1840 and uplink transmission through the allocated bandwidth after the HE-STF 1850. The STA1 may transmit an uplink frame based on the UL MU PPDU through the allocated bandwidth (eg, resource unit 1).

The uplink frame may be the above-described probe request frame, authentication request frame, combining request frame, buffer status report frame, PS-poll frame and the like.

The AP may allocate uplink resources of each of the plurality of STAs based on a DL MU PPDU (eg, HE-SIG A / B) (eg, a PPDU including the above-described trigger frame). Each STA may be allocated an uplink resource and transmit a UL MU PPDU.

Referring to FIG. 19, the wireless device 1900 may be an STA that may implement the above-described embodiments and may be an AP 1900 or a non-AP station (or STA) 1950.

The AP 1900 includes a processor 1910, a memory 1720, and a radio frequency unit 1730.

The RF unit 1930 may be connected to the processor 1910 to transmit / receive a radio signal.

The processor 1910 may implement the functions, processes, and / or methods proposed in the present invention. For example, the processor 1910 may be implemented to perform the operation of the AP according to the above-described embodiment of the present invention. The processor may perform the operation of the AP disclosed in the embodiment of FIGS. 1 to 18.

For example, the processor 1910 may be implemented to transmit multiple user (MU) random access information to the STA. In this case, the MU random access information may include information about a channel access parameter and a resource unit for each of the plurality of access categories.

The STA 1950 includes a processor 1960, a memory 1970, and a radio frequency unit 1980.

The RF unit 1980 may be connected to the processor 1960 to transmit / receive a radio signal.

The processor 1960 may implement the functions, processes, and / or methods proposed in the present invention. For example, the processor 1960 may be implemented to perform the operation of the STA according to the above-described embodiment of the present invention. The processor may perform an operation of the STA in the embodiment of FIGS. 1 to 18.

For example, the processor 1960 determines an access category of an uplink frame to be transmitted based on UL MU OFDMA transmission, performs channel access based on channel access parameters and resource units set according to the access category, and UL MU OFDMA. The uplink frame may be implemented to be transmitted to the AP on a time resource overlapped with another uplink frame based on the transmission.

In this case, the channel access parameter includes a contention window minimum (CWmin) value and a contention window maximum (CWmax) value for determining a contention window size for channel access, and the resource unit performs UL MU OFDMA transmission of an uplink frame. It may be the size of the frequency resource for.

In addition, the processor 1960 may be implemented to receive multiple user (MU) random access information from the AP, and the MU random access information may include information about a channel access parameter and a resource unit for each of a plurality of access categories. Can be.

The processor 1960 may determine an access category as follows. When the uplink frame to be transmitted is a probe request frame, an authentication request frame, or a combination request frame, the processor 1960 may determine an access category of the uplink frame as a first access category (eg, AC_VO). In addition, when the uplink frame to be transmitted is a power save (PS) -poll frame, the processor 1960 may determine the access category as the second access category AC_BE.

In this case, when the frame is the first access category, when the channel access parameters are the first CWmin and the first CWmax, and when the frame is the second access category, it is assumed that the channel access parameter is the second CWmin and the second CWmax, One CWmin may be a value smaller than the second CWmin, and the first CWmax may be a value smaller than the second CWmax.

In addition, the access category of the processor 1960 may be determined as follows. If the uplink frame is a buffer status report frame and buffer status information of the first access category (eg, AC_VO) is transmitted through the buffer status report frame, the processor 1960 may determine the access category as the first access category. have.

In addition, when the uplink frame is a buffer status report frame and buffer status information of a second access category (eg, AC_VI) is transmitted through the buffer status report frame, the processor 1960 may assign the access category to the second access category ( For example, AC_VI).

In addition, when the uplink frame is a buffer status report frame and buffer status information of a third access category (eg, AC_BE) is transmitted through the buffer status report frame, the processor 1960 may assign the access category to the third access category ( For example, it may be determined by AC_BE.

In addition, when the uplink frame is a buffer status report frame and buffer status information of the fourth access category (eg, AC_BK) is transmitted through the buffer status report frame, the processor 1960 accesses the access category to the fourth access category. This may be determined by a category (eg AC_BK).

In addition, the processor 1960 is a buffer status report frame and may transmit first buffer status information associated with the primary access category and second buffer status information associated with the secondary access category through the buffer status report frame. The access category of the buffer status report frame may be a primary access category.

Processors

1910 and 1960 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

memory

1920, 1970 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The

RF unit

1930 and 1980 may include one or more antennas for transmitting and / or receiving a radio signal.

When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. Modules may be stored in

memory

1920, 1970 and executed by

processors

1910, 1960. The

memories

1920 and 1970 may be internal or external to the

processors

1910 and 1960, and may be connected to the

processors

1910 and 1960 by various well-known means.

Claims

In a channel access method of a station (STA) for UL uplink multi-user (MU) transmission,

Determining, by the STA, an access category of an uplink frame to be transmitted based on UL MU orthogonal frequency division multiple access (OFDMA) transmission;

Performing channel access by the STA based on a channel access parameter and a resource unit set according to the access category; And

The STA transmitting the uplink frame to an access point (AP) on a time resource overlapped with another uplink frame based on the UL MU OFDMA transmission;

The channel access parameter includes a value of a contention window minimum (CWmin) and a contention window maximum (CWmax) for determining the size of the contention window for the channel access,

The resource unit is characterized in that the size of the frequency resource for the UL MU OFDMA transmission of the uplink frame.
The method of claim 1,

Wherein the STA further comprises receiving multiple user (MU) random access information from the AP,

The MU random access information includes the channel access parameter and the resource unit information for the access category.
The method of claim 2, wherein determining the access category comprises:

If the uplink frame is a probe request frame, an authentication request frame, or a combination request frame, determining the access category as a first access category; And

If the uplink frame is a power save (PS) -poll frame, the access category is determined as a second access category,

When the access category is the first access category, the CWmin is a first CWmin, the CWmax is a first CWmax,

When the access category is the second access category, the CWmin is a second CWmin, the CWmax is a second CWmax,

The first CWmin is less than the second CWmin,

Wherein the first CWmax is less than the second CWmax.
The method of claim 1, wherein determining the access category comprises:

If the uplink frame is a buffer status report frame and buffer status information of a first access category is transmitted through the buffer status report frame, determining the access category as the first access category;

When the uplink frame is the buffer status report frame and buffer status information of a second access category is transmitted through the buffer status report frame, determining the access category as the second access category;

If the uplink frame is the buffer status report frame and buffer status information of a third access category is transmitted through the buffer status report frame, determining the access category as a third access category; And

And if the uplink frame is the buffer status report frame and buffer status information of a fourth access category is transmitted through the buffer status report frame, determining the access category as a fourth access category.

And a higher priority in channel access in order of the first access category, the second access category, the third access category, and the fourth access category.
The method of claim 1,

If the uplink frame is a buffer status report frame and the first buffer status information associated with the primary access category and the second buffer status information associated with the secondary access category are transmitted through the buffer status report frame, the access category is primary. Including the steps determined by the access category,

The primary access category is an access category that has obtained transmission opportunity (TXOP) through competition,

And the secondary access category is an access category for which the TXOP is not obtained through the competition.
STA (station) performing a channel access method for UL uplink multi-user (MU) transmission,

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

A processor operatively coupled with the RF unit,

The processor determines an access category of an uplink frame to be transmitted based on UL MU orthogonal frequency division multiple access (OFDMA) transmission,

Perform channel access based on the channel access parameter and the resource unit set according to the access category,

On the basis of the UL MU OFDMA transmission is implemented to transmit the uplink frame to the AP (access point) on a time resource overlapped with another uplink frame,

The channel access parameter includes a value of a contention window minimum (CWmin) and a contention window maximum (CWmax) for determining the size of the contention window for the channel access,

The resource unit is a STA, characterized in that the size of the frequency resource for the UL MU OFDMA transmission of the uplink frame.
The method of claim 6,

Wherein the processor is configured to receive multiple user (MU) random access information from the AP,

The MU random access information includes the channel access parameter for the access category and information on the resource unit.
The method of claim 7, wherein the processor,

If the uplink frame is a probe request frame, an authentication request frame, or a combination request frame, determine the access category as a first access category,

If the uplink frame is a power save (PS) -poll frame, it is implemented to determine the access category as a second access category,

When the access category is the first access category, the CWmin is a first CWmin, the CWmax is a first CWmax,

When the access category is the second access category, the CWmin is a second CWmin, the CWmax is a second CWmax,

The first CWmin is less than the second CWmin,

The first CWmax is less than the second CWmax characterized in that the STA.
The method of claim 6, wherein the processor,

When the uplink frame is a buffer status report frame and buffer status information of a first access category is transmitted through the buffer status report frame, the access category is determined as the first access category,

If the uplink frame is the buffer status report frame and the buffer status information of the second access category is transmitted through the buffer status report frame, the access category is determined as the second access category,

When the uplink frame is the buffer status report frame and buffer status information of a third access category is transmitted through the buffer status report frame, the access category is determined as a third access category,

When the uplink frame is the buffer status report frame and the buffer status information of the fourth access category is transmitted through the buffer status report frame, the access category is configured to determine the fourth access category.

And a higher priority in channel access in the order of the first access category, the second access category, the third access category, and the fourth access category.
The method of claim 6,

If the uplink frame is a buffer status report frame and the first buffer status information associated with the primary access category and the second buffer status information associated with the secondary access category are transmitted through the buffer status report frame, the access category Is determined to be the primary access category,

The primary access category is an access category that has obtained transmission opportunity (TXOP) through competition,

And the secondary access category is an access category for which the TXOP has not been obtained through the competition.