KR20170062719A - Method and apparatus for channel access for supporting uplink multiple user transmission in high efficiency wireless lan - Google Patents

Abstract

The present invention relates to a method and apparatus for channel access for supporting uplink multi-user transmission in a high-efficiency WLAN system. According to an aspect of the present invention, a method may be provided in which an access point performs channel access in a wireless LAN. The method includes: obtaining a transmission opportunity (TXOP) that includes UL MU transmission of a plurality of stations (STAs); Transmitting a frame containing trigger information to the plurality of STAs within the TXOP; And receiving a UL MU PPDU (Physical Layer Protocol Data Unit) transmitted based on the trigger information from the plurality of STAs in the TXOP. The TXOP acquisition step may comprise determining based on at least one of UL traffic access category (AC) information associated with the UL MU transmission or DL traffic AC information associated with a downlink multi-user (DL MU) transmission transmitted with the trigger information (CCA) operation that is performed based on the channel access parameters being received.

Description

TECHNICAL FIELD [0001] The present invention relates to a channel access method and apparatus for supporting uplink multi-user transmission in a high-efficiency wireless LAN, and a channel access method and apparatus for supporting uplink multi-

The present invention relates to a wireless LAN system, and more particularly, to a recording medium storing a method, apparatus, software, or software for channel access for supporting uplink multi-user transmission in a high-efficiency wireless LAN system.

Recently, as the number of devices supporting a wireless LAN (WLAN) such as a smart phone increases, more access points (APs) are deployed to support this. In addition, although the use of wireless LAN devices supporting the IEEE 802.11ac standard, which provides high performance compared to a wireless LAN device supporting the conventional IEEE 802.11g / n standard, is increasing, As the consumption of high capacity content such as super high definition video by users of devices is increasing, a wireless LAN system supporting higher performance is required. Although the conventional wireless LAN system aims at increasing the bandwidth and improving the peak transmission rate, there is a problem in that the actual user experience is not high.

A task group named IEEE 802.11ax is discussing a high efficiency WLAN standard. A high-efficiency wireless LAN aims at enhancing a user's sense of performance requiring a high capacity and a high rate service while supporting the simultaneous access of many terminals in an environment where a large number of APs are concentrated and an AP coverage is overlapped.

For example, in a high-efficiency wireless LAN, OFDMA (Orthogonal Frequency-Division Multiple Access), improved Multiple Input Multiple Output (MIMO) and beamforming, cooperation between APs and Overlapping Basic Service Set (OBSS) We are discussing technologies to support performance enhancement, dense user performance improvement, and outdoor environmental performance enhancement.

However, up to now, there is no concrete method for channel access to support uplink multi-user transmission.

The present invention provides a channel access scheme for supporting uplink multi-user transmission.

The present invention provides a channel access method for acquiring a transmission opportunity including uplink multi-user transmission.

The present invention provides a carrier sense, a clear channel assessment (CCA), or a listen-before-talk (LBT) operation scheme performed by an access point to obtain a transmission opportunity including a trigger frame, As a technical task.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

According to an aspect of the present invention, a method may be provided in which an access point performs channel access in a wireless LAN. The method includes: obtaining a transmission opportunity (TXOP) that includes UL MU transmission of a plurality of stations (STAs); Transmitting a frame containing trigger information to the plurality of STAs within the TXOP; And receiving a UL MU PPDU (Physical Layer Protocol Data Unit) transmitted based on the trigger information from the plurality of STAs in the TXOP. The TXOP acquisition step may comprise determining based on at least one of UL traffic access category (AC) information associated with the UL MU transmission or DL traffic AC information associated with a downlink multi-user (DL MU) transmission transmitted with the trigger information (CCA) operation that is performed based on the channel access parameters being received.

According to another aspect of the present invention, a method may be provided in which a station (STA) performs uplink multi-user (UL MU) transmission in a wireless LAN. The method includes receiving a frame including trigger information from an access point (AP); And transmitting a UL MU Physical Layer Protocol Data Unit (PPDU) concurrently with one or more other STAs based on the trigger information. The reception of the frame containing the trigger information and the transmission of the UL MU PPDU may be performed in a TXOP obtained by the AP. Wherein the TXOP is a channel determined based on at least one of UL traffic access category (AC) information associated with the UL MU transmission or DL traffic AC information associated with a downlink multi-user (DL MU) transmission transmitted with the trigger information May be determined through the Clear Channel Assessment (CCA) operation of the AP based on the access parameters.

In various aspects of the present invention, when the frame including the trigger information does not include the DL MU transmission, the channel access parameter may include parameters corresponding to any one of the UL traffic AC information of the plurality of STAs .

If the frame containing the trigger information includes the DL MU transmission, the channel access parameter corresponds to any one of the UL traffic AC information of the plurality of STAs and the DL traffic AC information of the plurality of STAs Parameters.

When the frame including the trigger information includes the DL MU transmission, the channel access parameter may include parameters corresponding to any one of the DL traffic AC information for the plurality of STAs.

The UL traffic AC information of the plurality of STAs may be received from the plurality of STAs prior to the TXOP acquisition step.

The UL traffic AC information of the plurality of STAs may be included in a buffer status report frame transmitted from the plurality of STAs.

The channel access parameter may include Enhanced Distributed Channel Access (EDCA) access parameters.

The EDCA access parameter may include one or more of a contention window minimum value (CWmin), a contention window maximum value (CWmax), an Arbitration Inter-Frame Space Number (AIFSN), or a TXOP limit.

And transmitting an ACK / BA (Acknowledgment / Block Acknowledgment) frame in response to the UL MU PPDU in the TXOP.

The features briefly summarized above for the present invention are only illustrative aspects of the detailed description of the invention which are described below and do not limit the scope of the invention.

According to the present invention, a method for channel access for supporting uplink multi-user transmission can be provided.

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention, illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention.
1 is a diagram showing a configuration of a wireless device according to the present invention.
2 is a conceptual diagram showing an embodiment of a configuration of a WLAN system.
3 is a diagram for explaining a link setup process in a wireless LAN.
4 is a diagram for explaining a medium access mechanism in a wireless LAN.
5 and 6 are diagrams for explaining the sensing operation of the STA in the wireless LAN.
7 and 8 are diagrams for explaining RTS and CTS.
9 is a diagram for explaining an example of a frame structure used in the wireless LAN system.
10 is a diagram for explaining the configuration of the A-MPDU.
11 is a diagram for explaining an uplink multiple user (MU) transmission.
12 to 15 are diagrams illustrating various UL MU transmission modes.
16 and 17 illustrate examples of CCA operations of an AP according to the present invention.
18 is a flow chart illustrating an exemplary method according to the present invention.
19 is a diagram for explaining a configuration of a processor according to the present invention.

Hereinafter, the contents related to the present invention will be described in detail with reference to exemplary drawings and embodiments. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

Throughout the specification, a station (STA) refers to any functional medium including a medium access control (MAC) and a physical layer interface to a wireless medium. A station (STA) can be divided into a station (STA) which is an access point (AP) and a station (STA) which is a non-AP. A station (STA), which is an access point (AP), may be referred to simply as an access point (AP), and a station (STA) that is a non-AP may be simply referred to as a terminal.

An access point (AP) may refer to a centralized controller, a base station (BS), a node-B, an eNode-B, a base transceiver system (BTS), a site controller, May include some or all of the functions of the < / RTI >

A terminal may be a wireless transmit / receive unit (WTRU), a user equipment (UE), a user terminal (UT), an access terminal (AT), a mobile station May refer to a mobile terminal, a subscriber unit, a subscriber station (SS), a wireless device, or a mobile subscriber unit, Or all functions.

Here, a desktop computer, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smart phone, an e- a book reader, a portable multimedia player (PMP), a portable game machine, a navigation device, a digital camera, a digital multimedia broadcasting (DMB) player, a digital audio recorder, a digital audio player A digital picture recorder, a digital picture player, a digital video recorder, a digital video player, or the like can be used.

1 is a diagram showing a configuration of a wireless device according to the present invention.

1 illustrates a terminal apparatus 100 corresponding to an example of a downlink receiving apparatus or an uplink transmitting apparatus and an AP apparatus 200 corresponding to an example of a downlink transmitting apparatus or an uplink receiving apparatus.

The terminal device 100 may include a processor 110, an antenna unit 120, a transceiver 130,

The processor 110 performs baseband related signal processing and may include an upper layer processing unit 111 and a physical layer processing unit 112. [ The upper layer processing unit 111 may process an operation of a MAC (Medium Access Control) layer or higher layers. The physical layer processing unit 112 can process the operation of the physical (PHY) layer (e.g., uplink transmission signal processing, downlink reception signal processing). The processor 110 may control the overall operation of the terminal device 100, in addition to performing baseband-related signal processing.

The antenna unit 120 may include one or more physical antennas, and may support MIMO transmission / reception when the antenna unit 120 includes a plurality of antennas. The transceiver 130 may include a radio frequency (RF) transmitter and an RF receiver. The memory 140 may store information processed by the processor 110, software related to the operation of the terminal device 100, an operating system, applications, and the like, and may include components such as buffers.

The AP apparatus 200 may include a processor 210, an antenna unit 220, a transceiver 230, and a memory 240.

The processor 210 performs baseband-related signal processing, and may include an upper layer processing unit 211 and a physical layer processing unit 212. [ The upper layer processing unit 211 can process the operation of the MAC layer or higher layers. The physical layer processing unit 212 can process the operation of the PHY layer (e.g., downlink transmission signal processing, uplink reception signal processing). In addition to performing baseband-related signal processing, the processor 210 may also control the operation of the entire AP apparatus 200.

The antenna unit 220 may include one or more physical antennas, and may support MIMO transmission / reception when the antenna unit 220 includes a plurality of antennas. The transceiver 230 may include an RF transmitter and an RF receiver. The memory 240 may store arithmetic processed information of the processor 210, software related to the operation of the AP apparatus 200, an operating system, an application, and the like, and may include components such as buffers.

The operation of the STA operating in the wireless LAN system can be described in terms of the layer structure. In terms of device configuration, the hierarchy can be implemented by a processor. An STA may have a plurality of hierarchical structures. For example, the hierarchical structure covered in the 802.11 standard document is mainly a MAC layer and a PHY layer. The PHY may include a Physical Layer Convergence Procedure (PLCP) entity, a PMD (Physical Medium Dependent) entity, and the like. The MAC and PHY conceptually include management entities called MLME (Media Management Entity) and PLME (Physical Layer Management Entity), respectively. These entities can provide a layer management service interface in which a layer management function operates .

In order to provide accurate MAC operation, a Station Management Entity (SME) may exist within each STA. An SME is a layer-independent entity and can generally take on functions such as collecting layer-dependent states from various Layer Management Entities (LMEs) and similarly setting the values of layer-specific parameters.

The entities described above may interact in various ways. For example, interactions can be made between entities by exchanging primitives. A primitive is an element, a set of parameters, or a set of instructions related to a particular purpose.

2 is a conceptual diagram showing an embodiment of a configuration of a WLAN system.

Referring to FIG. 2, the WLAN system includes at least one Basic Service Set (BSS). A BSS is a set of stations (STA 1, STA 2 (AP 1), STA 3, STA 4, STA 5 (AP 2)) that are able to successfully communicate and communicate with each other, no.

The BSS can be divided into an infrastructure BSS (infrastructure BSS) and an independent BSS (independent BSS), and BSS 1 and BSS 2 correspond to an infrastructure BSS. The BSS 1 includes a terminal STA 1, an access point STA 2 (AP 1) providing a distribution service, and a plurality of access points STA 2 (AP 1) and STA 5 (AP 2) And a distribution system (DS) for connecting the system. In BSS 1, the access point (STA 2 (AP 1)) manages the terminal (STA 1).

The BSS 2 is connected to a plurality of access points (STA 3 and STA 4), an access point (STA 5 (AP 2)) and a plurality of access points (STA 2 (AP 1) and STA 5 Distribution system. In BSS 2, the access point (STA 5 (AP 2)) manages the terminals STA 3 and STA 4.

Meanwhile, the independent BSS is a BSS operating in an ad-hoc mode. Since an independent BSS does not include an access point, there is no centralized management entity in the center. That is, terminals in an independent BSS are managed in a distributed manner. In an independent BSS, all terminals can be made as mobile terminals and a self-contained network is formed because connection is not permitted to the distribution system (DS).

The access points STA 2 (AP 1) and STA 5 (AP 2) provide a connection to the distribution system (DS) over the wireless medium for the terminal (STA 1, STA 3, STA 4) . The communication between the terminals STA 1, STA 3 and STA 4 in the BSS 1 or BSS 2 is generally performed through the access points STA 2 (AP 1) and STA 5 (AP 2) link is established, direct communication between the terminals STA 1, STA 3 and STA 4 is possible.

A plurality of infrastructure BSSs may be interconnected via a distribution system (DS). A plurality of BSSs connected through a distribution system (DS) is referred to as an extended service set (ESS). The stations included in the ESS can communicate with each other, and within the same ESS, the UE can move from one BSS to another while seamlessly communicating.

The distribution system DS is a mechanism by which one access point communicates with another access point. According to this, the access point transmits a frame for terminals connected to the BSS that it manages, or moves to another BSS A frame can be transmitted for an arbitrary terminal. The access point can also transmit and receive frames to and from an external network, such as a wired network. Such a distribution system (DS) is not necessarily a network, and there is no restriction on its form. For example, the distribution system may be a wireless network, such as a mesh network, or may be a physical structure that connects the access points to each other.

Although the operation of the AP and the STA in the infrastructure BSS network structure is described as a main example, the present invention can be applied to a device corresponding to a group owner and a group client Examples of the present invention can also be applied to the operation of a device corresponding to a group client.

3 is a diagram for explaining a link setup process in a wireless LAN.

In order for the STA to set up a link to the network and transmit and receive data, the STA first discovers the network, performs authentication, establishes an association, establishes an authentication procedure for security, . The link setup process may be referred to as a session initiation process or a session setup process. Also, the process of searching for a link setup process, authentication, combining, and security setting may collectively be referred to as a combining process.

In step S310, the STA may perform a network search operation. The network search operation may include a scanning operation of the STA. In other words, in order for the STA to access the network, it must find a network that can participate. The STA must identify a compatible network before joining the wireless network. The process of identifying a network in a specific area is called scanning.

The scanning methods include active scanning and passive scanning.

FIG. 3 illustrates a network search operation including an exemplary active scanning process. The STA performing the scanning in the active scanning transmits the probe request frame and waits for a response in order to search for the existence of an AP in the surroundings while moving the channels. The responder sends a probe response frame in response to the probe request frame to the STA that transmitted the probe request frame. Here, the responder may be the STA that last transmitted the beacon frame in the BSS of the channel being scanned. In the BSS, the AP transmits the beacon frame, so the AP becomes the responder. In the independent BSS, the STAs in the independent BSS transmit the beacon frame while the beacon frame is transmitted. For example, the STA that transmits the probe request frame on channel 1 and receives the probe response frame on channel 1 stores the BSS-related information included in the received probe response frame and transmits the next channel (for example, Channel) and perform scanning in the same manner (i.e., transmitting / receiving a probe request / response on the second channel).

Although not shown in Fig. 3, the scanning operation may be performed in a passive scanning manner. In passive scanning, the STA performing the scanning waits for the beacon frame while moving the channels. The beacon frame is one of the management frames defined in the IEEE 802.11 standard. The beacon frame is transmitted periodically to notify the presence of the wireless network and allow the STA performing the scanning to find the wireless network and participate in the wireless network. In the BSS, the AP periodically transmits the beacon frame, and in the independent BSS, the beacon frame is transmitted while the STAs in the independent BSS rotate. Upon receiving the beacon frame, the scanning STA stores information on the BSS included in the beacon frame and records beacon frame information on each channel while moving to another channel. The STA receiving the beacon frame stores the BSS-related information included in the received beacon frame, moves to the next channel, and performs scanning in the next channel in the same manner.

After the STA has searched the network, the authentication process may be performed in step S320. This authentication process can be referred to as a first authentication process in order to clearly distinguish from the security setup operation in step S340 described later.

The authentication process includes an STA transmitting an authentication request frame to the AP, and an AP transmitting an authentication response frame to the STA in response to the authentication request frame. The authentication frame used for the authentication request / response corresponds to the management frame.

The authentication frame includes an authentication algorithm number, an authentication transaction sequence number, a status code, a challenge text, a robust security network (RSN), a finite cyclic group Group), and the like. This corresponds to some examples of information that may be included in the authentication request / response frame, may be replaced by other information, or may include additional information.

The STA may send an authentication request frame to the AP. Based on the information included in the received authentication request frame, the AP can determine whether or not to allow authentication for the STA. The AP can provide the result of the authentication process to the STA through the authentication response frame.

After the STA has been successfully authenticated, a binding procedure may be performed at step S330. The combining process includes an STA transmitting an association request frame to the AP, and an AP transmitting an association response frame to the STA in response to the association request frame.

For example, the association request frame may include information related to various capabilities, a listen interval, a service set identifier (SSID), supported rates, supported channels, an RSN, Domain, supported operating classes, TIM (Traffic Indication Map Broadcast request), interworking service capability, and the like.

For example, the association response frame may include information related to various capabilities, status codes, Association IDs, support rates, Enhanced Distributed Channel Access (EDCA) parameter sets, Received Channel Power Indicator (RCPI) A timeout interval (association comeback time), a overlapping BSS scan parameter, a TIM broadcast response, a Quality of Service (QoS) map, and the like.

This corresponds to some examples of information that may be included in the association request / response frame, may be replaced by other information, or may include additional information.

After the STA is successfully coupled to the network, the security setup process may be performed at step S340. The security setup process in step S340 may be referred to as an authentication process through a Robust Security Network Association (RSNA) request / response, and the authentication process in step S320 may be referred to as a first authentication process. In step S340, May also be referred to simply as an authentication process.

The security setup process of step S340 may include a private key setup through a 4-way handshaking over an Extensible Authentication Protocol over LAN (EAPOL) frame, for example . In addition, the security setup process may be performed according to various security procedures not defined in the IEEE 802.11 standard.

4 is a diagram for explaining a medium access mechanism in a wireless LAN.

In a wireless LAN system, the basic access mechanism of a MAC is a CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism. The CSMA / CA mechanism is also referred to as the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC and basically adopts a "listen before talk (LBT)" access mechanism. That is, the AP or the STA can perform a clear channel assessment (CCA) for sensing a radio channel or a medium for a predetermined time period called IFS (Inter-Frame Space) before starting transmission have.

For example, sensing for a wireless channel or medium may determine that the channel or medium is idle state if energy below a predetermined energy threshold is detected, When energy exceeding the energy threshold is detected, it can be determined that the channel or medium is occupied state or busy state.

As a result of sensing, if it is determined that the medium is in an idle state, frame transmission is started through the medium. On the other hand, if it is detected that the medium is in an occupied state, the AP or the STA may set a Defer Period for media access without attempting to start its own transmission, and then wait for a frame transmission after waiting. That is, if an AP or STA detects that the medium is in an idle state for a predetermined IFS (e.g., DIFS (Distributed Coordination Function IFS) or AIFS (Arbitration IFS) if the medium is changed from an occupied state to an idle state, If the channel is idle even after waiting for a predetermined delay period (e.g., a random backoff period), the transmission can be performed. [0050] With the application of the random backoff period, several STAs wait for different time periods, , It is possible to minimize the collision.

In addition, the IEEE 802.11 MAC protocol provides HCF (Hybrid Coordination Function). The HCF is based on the DCF and the PCF (Point Coordination Function). The PCF is a polling-based, synchronous access scheme that refers to periodically polling all receiving APs and / or STAs to receive data frames. In addition, HCF has EDCA (Enhanced Distributed Channel Access) and HCCA (HCF Controlled Channel Access). EDCA is a contention-based access method for a provider to provide data frames to a large number of users, and HCCA uses a contention-based channel access method using a polling mechanism. In addition, the HCF includes a medium access mechanism for improving the quality of service (QoS) of a WLAN, and can transmit QoS data in both a contention period (CP) and a contention free period (CFP).

If the medium that is occupied or busy is changed to an idle state, several STAs may attempt to transmit data (or frames). At this time, as a method for minimizing the collision, each of the STAs may select a random backoff count and wait for a slot time corresponding thereto, and then try transmission. The random backoff count has a packet number value and can be determined to be one of the values in the range of 0 to CW. Here, CW is a contention window parameter value. The CW parameter is given an initial value of CWmin, but can take a value of two times in the case of a transmission failure (for example, if ACK for the transmitted frame is not received or NACK (Negative ACK) is received) have. If the ACK is not received, the CW parameter value is exponentially increased to continuously attempt data transmission. If the CW parameter value is CWmax, the CWmax value is maintained until the data transmission is successful. If the data transfer is successful, it is reset to the CWmin value. CW, CWmin, and CWmax values can be set to 2 ⁿ -1 (n = 0, 1, 2, ...).

When the random backoff process is started, the STA continuously monitors the medium while counting down the backoff slot according to the determined backoff count value. That is, when the medium is judged to be in the idle state for a predetermined time (for example, CCA slot time (for example, 9 占 퐏)) during the random backoff, counting down is performed. When the medium is monitored in the occupied state, the countdown is stopped and waited, and the remaining countdown is resumed after a certain delay time (e.g., DIFS or AIFS) when the medium becomes idle.

More specifically, in the case of a data frame, a data frame may be transmitted after the DIFS has elapsed since the medium became idle, or after the AIFS elapsed in the case of QoS-based data transmission, after the backoff has been performed.

In the case of a management frame (e.g., a beacon frame, a probe request / response frame, a combined request / response frame, etc.), after the IFS such as DIFS or Point coordination function IFS (PIFS) Frames can be transmitted.

In the case of a control frame (for example, a Request-To-Send (RTS) frame, a Clear-To-Send (CTS) frame, an Acknowledgment Otherwise, it may be transmitted after performing the backoff after the elapse of the DIFS, and may be transmitted without performing the backoff after elapse of the SIFS (short IFS) in the case of the response frame of another frame.

In the case of a Quality of Service (STA), an Arbitration IFS (AIFS [i], where i is a value determined by AC) determined by an access category (AC) Later, after performing the backoff, the frame can be transmitted. At this time, the frame in which AIFS [i] may be used may be a data frame, a management frame, or a control frame other than a response frame.

Here, the SIFS is determined in consideration of the delay time in the PHY and the processing time in the MAC, and may have a value of 16 mu s, for example.

PIFS is a time interval for providing high channel access priority next to SIFS, and is defined as PIFS = aSIFSTime + aSlotTime. Here, aSIFSTime corresponds to the length of the SIFS time interval, aSlotTime is determined to provide sufficient time to decode the preamble transmitted by the transmitting node, and may have a value of 9 mu s, for example.

DIFS is defined as DIFS = aSIFSTime + 2 * aSlotTime, which is a time interval unit used when a STA operating on a DCF basis accesses a channel.

AIFS is a unit of time interval used when performing channel access for QoS data transmission, and is defined as AIFS [i] = aSIFSTime + AIFSN [i] * aSlotTime. Here, i is a value determined by AC. The AIFSN (Arbitration IFS Number) corresponds to the length of the time interval corresponding to the number of slots determined according to the i value.

The random backoff operation in the wireless LAN system will be described with reference to the example of FIG.

In the example of FIG. 4, when a packet (or data) to be transmitted in the STA3 occurs, the STA3 can confirm that the medium is in the idle state by DIFS (AIFS [i] in case of the QoS STA) and transmit the frame immediately. Meanwhile, the remaining STAs monitor and wait for the medium to be in a busy state. In the meantime, data to be transmitted may be generated in each of STA1, STA2 and STA5. Each STA waits for DIFS (AIFS [i] in case of QoS STA) when the medium is monitored in the idle state, It is possible to perform the countdown of the backoff slot according to the backoff count value.

In the example of FIG. 4, STA2 selects the smallest backoff count value, and STA1 selects the largest backoff count value. That is, the case where the remaining backoff time of the STA5 is shorter than the remaining backoff time of the STA1 at the time when the STA2 finishes the backoff count and starts the frame transmission is illustrated. STA1 and STA5 stop countdown and wait for a while while STA2 occupies the medium.

When the occupation of the STA2 is ended and the medium is again in the idle state, STA1 and STA5 wait for DIFS (AIFS [i] in case of QoS STA) and then resume the stopped backoff count. That is, the frame transmission can be started after counting down the remaining backoff slots by the remaining backoff time. Since the remaining backoff time of STA5 is shorter than STA1, STA5 starts frame transmission.

On the other hand, data to be transmitted may also occur in the STA 4 while the STA 2 occupies the medium. At this time, in the STA4, if the medium becomes an idle state, it waits for DIFS (AIFS [i] in case of QoS STA), then counts down according to the random backoff count value selected by itself and starts frame transmission .

In the example of FIG. 4, it is assumed that the remaining backoff time of the STA5 coincides with the random backoff count value of the STA4. In this case, a collision may occur between the STA4 and the STA5. When a collision occurs, neither STA4 nor STA5 receives an ACK for data transmission, and thus data transmission fails. In this case, STA4 and STA5 can double the CW value and then select a random backoff count value and perform a countdown.

On the other hand, STA1 waits while the medium is occupied due to the transmission of STA4 and STA5, waits for DIFS (AIFS [i] in case of QoS STA) when the medium becomes idle, The frame transmission can be started.

5 and 6 are diagrams for explaining the sensing operation of the STA in the wireless LAN.

As described above, the CSMA / CA mechanism also includes physical carrier sensing and virtual carrier sensing in which the AP or STA directly senses the medium. Virtual carrier sensing is intended to compensate for problems that may occur in media access, such as hidden node problems. For the virtual carrier sensing, the MAC of the wireless LAN system may use a network allocation vector (NAV). The NAV is a value that informs another AP or STA of the time remaining until the AP or STA that is currently using or authorized to use the medium becomes available. Therefore, the value set to NAV corresponds to the period during which the medium is scheduled to be used by the AP or the STA that transmits the frame, and the STA receiving the NAV value is prohibited from accessing the medium during the corresponding period. The NAV may be set according to the value of the Duration field of the MAC header of the frame, for example.

Further, a robust collision detection mechanism can be applied to reduce the possibility of collision, which will be described with reference to Figs. 5 and 6. Fig. In the examples of FIGS. 5 and 6, the carrier sensing range of the STA and the transmission range of the STA may not actually be the same, but they are assumed to be the same for convenience of explanation.

In the example of FIG. 5, it is assumed that STA A and STA B are in communication and STA C has information to be transmitted. Specifically, STA A is transmitting information to STA B, but when STA C performs carrier sensing before sending data to STA B, STA C can determine that the medium is idle. This is because the STA A transmission (ie, media occupancy) may not be sensed at the STA C location. In this case, STA B receives information of STA A and STA C at the same time, so that collision occurs. In this case, STA A is a hidden node of STA C.

FIG. 6 is an example of an exposed node, and STA B has data to be transmitted to STA A, and STA C has information to be transmitted to STA D. FIG. In this case, if the STA C carries out the carrier sensing, it can be determined that the medium is occupied due to the transmission of the STA B. Accordingly, even if STA C has information to be transmitted to STA D, it is sensed that the media is occupied, and therefore, it is necessary to wait until the medium becomes idle. However, since the STA A is actually out of the transmission range of the STA C, the transmission from the STA C and the transmission from the STA B may not collide with each other in the STA A. Therefore, the STA C is not necessary until the STA B stops transmitting It is to wait. In this case, STA C can be regarded as an exposed node of STA B.

7 and 8 are diagrams for explaining RTS and CTS.

In order to efficiently utilize the collision avoidance mechanism in the exemplary situation shown in FIGS. 5 and 6, a short signaling packet such as RTS (request to send) and CTS (clear to send) is used . The RTS / CTS between the two STAs may allow the surrounding STA (s) to overhear, allowing the surrounding STA (s) to consider whether to transmit information between the two STAs. For example, if the STA to which data is to be transmitted transmits an RTS frame to the STA receiving the data, the STA receiving the data can notify that it will receive the data by transmitting the CTS frame to surrounding STAs.

FIG. 7 is an illustration of a method for solving a hidden node problem, assuming that both STA A and STA C attempt to transmit data to STA B. FIG. When STA A sends RTS to STA B, STA B transmits CTS to both STA A and STA C around it. As a result, STA C waits until the data transmission of STA A and STA B is completed, thereby avoiding collision.

FIG. 8 is an illustration of a method for solving the exposed node problem, in which STA C overrides the RTS / CTS transmission between STA A and STA B, so that STA C sends itself to another STA (e.g., STA D) It can be determined that collision does not occur even if data is transmitted. That is, STA B transmits RTS to all surrounding STAs, and only STA A having data to be transmitted transmits CTS. Since STA C only receives RTS and does not receive the CTS of STA A, STA C knows that STA A is outside its carrier sensing range.

9 is a diagram for explaining an example of a frame structure used in the wireless LAN system.

The PHY can prepare a MAC PDU (Protocol Data Unit) to be transmitted by the MAC command (or primitive). For example, when the PHY receives a command requesting the start of transmission of the PHY from the MAC, the PHY switches to the transmission mode and transmits information (for example, data) provided from the MAC in the form of a frame.

Further, when the PHY detects a valid preamble of a received frame, the PHY monitors the header of the preamble and can transmit a command to the MAC to notify the start of reception of the PHY.

In this way, information transmission and reception in the wireless LAN system is performed in the form of a frame, and a physical layer protocol data unit (PPDU) frame format is defined for this purpose.

The PPDU frame may include Short Training Field (STF), Long Training Field (LTF), SIGN (SIGNAL) field, and Data field. The most basic (e.g., non-HT (High Throughput)) PPDU frame format is a combination of L-STF (Legacy-STF), L-LTF (Legacy-LTF), L- Lt; / RTI > Further, depending on the kind of the PPDU frame format (for example, the HT-mixed format PPDU, the HT-greenfield format PPDU, the VHT (Very High Throughput) PPDU, STF, LTF, and SIG fields of < / RTI >

STF is a signal for signal detection, AGC (Automatic Gain Control), diversity selection, precise time synchronization, etc., and LTF is a signal for channel estimation and frequency error estimation. The STF and LTF are signals for synchronization and channel estimation of OFDM (Orthogonal Frequency-Division Multiplexing) physical layer.

The SIG field may include a RATE field and a LENGTH field. The RATE field may contain information on the modulation and coding rate of the data. The LENGTH field may contain information on the length of the data. Additionally, the SIG field may include a parity bit, a SIG TAIL bit, and the like.

The DATA field may include a SERVICE field, a Physical Layer Service Data Unit (PSDU), a PPDU TAIL bit, and may also include a padding bit if necessary. Some bits in the SERVICE field may be used for synchronization of the descrambler at the receiving end. The PSDU corresponds to an MAC PDU (MPDU) defined in the MAC layer, and may include data generated / used in an upper layer. The PPDU TAIL bit can be used to return the encoder to the 0 state. The padding bits may be used to match the length of the data field to a predetermined unit.

The MAC PDU is defined according to various MAC frame formats, and the basic MAC frame is composed of a MAC header, a frame body, and a frame check sequence (FCS). The MAC frame is composed of MAC PDUs and can be transmitted / received via the PSDU of the data part of the PPDU frame format.

The MAC header includes a Frame Control field, a Duration / ID field, an Address field, and the like. The frame control field may contain control information necessary for frame transmission / reception. The duration / ID field may be set to a time for transmitting the frame or the like. The specific contents of the Sequence Control, QoS Control, and HT Control subfields of the MAC header can refer to the IEEE 802.11-2012 standard document.

The frame control field of the MAC header may include Protocol Version, Type, Subtype, To DS, From DS, More Fragment, Retry, Power Management, More Data, Protected Frame, Order subfields. The contents of each subfield of the frame control field may refer to the IEEE 802.11-2012 standard document.

On the other hand, a null-data packet (NDP) frame format means a frame format that does not include a data packet. That is, the NDP frame refers to a frame format that includes only the physical layer convergence procedure (PLCP) header portion (i.e., STF, LTF, and SIG fields) in the general PPDU frame format and does not include the remaining portion do. The NDP frame may also be referred to as a short frame format.

10 is a diagram for explaining the configuration of the A-MPDU.

In order to transmit a plurality of MPDUs in one PPDU frame, a plurality of MPDUs may be aggregated. As shown in FIG. 10, in the MAC layer, a short MPDU delimiter is appended to each MPDU so that a plurality of MPDUs are logically concatenated to form an A-MPDU. In the PHY layer, one PPDU can be constructed by configuring one A-MPDU as one PSDU and attaching a preamble (for example, STF, LTF, SIG field) to the front.

In addition, one MPDU may include one MSDU or A-MSDU (i.e., a concatenation of a plurality of MSDUs), and may be configured by attaching an MPDU header and an FCS (i.e., CRC) to MSDU / A- .

11 is a diagram for explaining an uplink multiple user (MU) transmission.

In the high-efficiency WLAN standard being prepared through the IEEE 802.11ax task group, uplink multi-user (UL MU) transmission technology is discussed. UL MU transmission means that a plurality of STAs simultaneously perform transmission to the AP, and may include UL MU-MIMO transmission and / or UL OFDMA transmission.

In order to support UL MU transmission, frames transmitted by a plurality of STAs must be received within the CP (Cyclic Prefix) size at the AP, so that it is necessary to align the timing of UL transmissions of a plurality of STAs. It is also possible for a plurality of STAs to be able to receive certain frequency domain resources (e.g., subchannels, resource units (RU), tones, or subcarriers) or spatial domain resources (e.g., Time stream) must be used, UL transmission from a plurality of STAs can be performed without collision.

In this way, for UL MU transmission, the AP can inform scheduling information for UL MU transmission to a plurality of STAs, and a frame including this information can be referred to as a trigger frame.

Information for scheduling the UL MU transmission may be included in the MPDU of the trigger frame or may be included in the preamble of the PPDU (e.g., a SIG field). The information provided through the trigger frame may include time synchronization information between STAs participating in the MU transmission (e.g., MU-MIMO transmission and / or OFDMA transmission) (e.g., end of the trigger frame ), Frequency offset correction information, duration of UL MU transmission (or length of PPDU) information, identification information of STAs participating in MU transmission, frequency resources (for example, , Tone, or RU) allocation information, spatial resource (e.g., stream) allocation information, or power control (PC) information.

When a plurality of STAs receives the trigger frame from the AP, the UL MU PPDU frame can be transmitted using the predetermined timing and the allocated resources. An AP receiving an UL MU PPDU from a plurality of STAs can transmit an ACK frame to the plurality of STAs.

12 to 15 are diagrams illustrating various UL MU transmission modes.

The example of FIG. 12 shows an UL MU transmission mode that includes a standalone trigger frame in a TXOP within one TXOP. Specifically, when the AP acquires the TXOP, it can transmit a frame including trigger information (i.e., information that elicits UL MU transmission) on the downlink (DL). A plurality of STAs receiving the trigger information can transmit UL MU PPDUs, and in response, the AP can transmit an ACK / BA frame.

The example of FIG. 13 shows a UL MU transmission mode including a DL / UL cascading TXOP structure (DL / UL cascading TXOP structure). Specifically, when the AP obtains the TXOP, the frame including the trigger information and the DL MU data can be transmitted. A plurality of STAs that have received the trigger information can transmit UL MU PPDUs (UL MU PPDUs can include UL MU data and additionally can further include ACK / BA information for DL MU PPDUs) The AP can transmit an ACK / BA frame.

The example of FIG. 14 shows an UL MU transmission mode that includes multiple trigger frames in a TXOP in one TXOP. Specifically, when the AP acquires the TXOP, it can transmit a frame including the first trigger information. A plurality of STAs receiving the first trigger information may transmit a first UL MU PPDU, and in response, the AP may transmit a first ACK / BA frame. In the TXOP, the AP transmits a frame including the second trigger information, and a plurality of STAs receiving the second trigger information can transmit a second UL MU PPDU, and in response, the AP transmits a second ACK / Lt; / RTI >

The example of FIG. 15 shows a UL MU transmission mode that includes a standalone trigger frame and a short MAC control frame in one TXOP. Specifically, when the AP is allowed to perform channel assignment (or transmission) during the TXOP by performing the CCA operation (or LBT) described above, a buffer state (BS) report from a plurality of STAs, a beamforming , Or a Power Save (PS) -Poll) frame, and the STAs receiving the trigger frame may transmit a trigger frame that includes a BS, BF, or PS-Poll frame UL MU PPDU, and in response, the AP can transmit an ACK / BA frame.

That is, in the example of FIG. 15, the STAs receiving the trigger frame from the AP include BS information, channel state information for the BF, or STA that has been released in the PS mode (i.e., STA converted from the doze or sleep state to the awake state) It may transmit information to the AP that desires to receive DL data from this AP (or informs it that it is ready to receive DL data). As described above, the trigger frame may be transmitted from the AP to a plurality of STAs for the purpose of receiving control information from a plurality of STAs, instead of triggering UL traffic transmission of a plurality of STAs. This allows a plurality of STAs to simultaneously transmit control information to the AP in an UL MU transmission scheme (e.g., in a UL OFDMA or UL MU-MIMO scheme).

Hereinafter, examples of the present invention for a new channel sensing (e.g., CCA performing) or LBT operation for UL MU transmission will be described. Specifically, examples of the present invention for the operation of the AP to perform the CCA for UL MU transmission will be described. More specifically, the AP transmits a frame that triggers UL OFDMA transmission, receives an uplink frame (e.g., a data frame or a control frame) associated with the trigger frame, and transmits an acknowledgment frame for the uplink frame Examples of the present invention regarding the CCA operation for transmission will be described.

In a contention-based channel access scheme, basically, an STA in which a frame to be transmitted occurs can perform a backoff process to acquire a TXOP (i.e., to allow channel occupancy during a TXOP). A TXOP means a time interval in which a particular QoS STA succeeding in contention for a channel has the right to initiate a frame exchange sequence on the wireless medium and can be defined by a start time and a maximum duration.

In a wireless LAN system prior to the HEW, it was defined that a subject to transmit a frame would attempt to acquire a TXOP according to a contention-based channel access scheme (e.g., EDCA). That is, the subject that transmits the frame is the same as the subject that obtains the TXOP. For example, when the AP transmits the DL data in the QoS-based channel access method, the channel access parameter (AC) determined according to the access category (AC) or the traffic category (TC) of the DL data included in the DL PPDU For example, EDCA access parameters), the AP may perform a CCA operation to obtain a TXOP. Similarly, when the STA transmits the UL data in the QoS-based channel access method, the STA transmits the UL data based on the channel access parameters (for example, EDCA access parameters) determined according to the AC or TC of the UL data included in the UL PPDU The STA may perform the CCA operation to obtain the TXOP (i.e., be allowed to occupy the channel during the TXOP).

The EDCA access parameters for a particular AC can be defined as shown in Table 1 or Table 2 below.

In Table 1, EDCA access parameters for each of AC_BK (Background), AC_BE (Best Effort), AC_VI (Video) and AC_VO (Voice) are exemplarily shown. Table 2 provides an exemplary EDCA access parameter for AC_Control in addition to Table 1.

The CWmin and CWmax values represent the minimum and maximum values for the size of the contention window (CW), and provide the range of CW that the node performing the CCA can have. For example, a node may start a CCA operation with a CWmin value with a CW value, and may have a maximum CWmax value by exponentially increasing the CW value according to channel state or ACK information. Once the CW value is determined, the node can use a random backoff counter value by selecting a random value between [0 ~ CW] values. Thus, the CWmin and CWmax values given for a particular AC can affect the probability or frequency with which a node attempting to transmit the traffic of that AC will succeed in channel access.

AIFSN is a factor that determines the minimum time that a CCA performing node must wait before occupying a channel. That is, before the CCA performing node performs the backoff process, it confirms whether the channel is idle for AIFS [i] (AIFS [i] = aSIFSTime + AIFSN [i] * aSlotTime) AIFSN is used as an argument. An AIFSN value may be set differently depending on whether it is delay sensitive traffic or not. Thus, AIFSN, like the CWmin and CWmax values, can affect the probability or frequency with which a node attempting to transmit a particular AC traffic will succeed in channel access.

The TXOP limit indicates a limit value for a time when a node acquiring a channel in the EDCA scheme can occupy the channel. For example, if TXOP limit = 0, the TXOP time can be determined according to the duration of one PPDU. If the TXOP limit is given a specific value (for example, a TXOP limit of 3.008 ms corresponding to AC_VI), the size of the TXOP can be up to 3.008 ms.

The AC_Control in Table 2 is not limited by the name AC_Control and may include a shorter delay period or a smaller contention window than the EDCA access parameters corresponding to ACs of data transmission (e.g., AC_BK, AC_BE, AC_VI, AC_VO) Means a new AC corresponding to an EDCA access parameter having a probability of having a size. For example, AC_Control may mean AC of control information transmission, but is not limited thereto. Accordingly, when the CCA is performed based on the EDCA access parameter corresponding to the new AC, it is possible to acquire the channel with a higher probability and perform the transmission faster as compared with the data transmission.

On the other hand, in the trigger-based UL frame transmission (see the example of FIGS. 12 to 15) introduced in the new WLAN system, the STA is the subject of transmitting the UL frame, while the TXOP is obtained , The channel is allowed to occupy during the TXOP). That is, the frame transmitting entity and the TXOP receiving entity are different from each other.

Therefore, in the CCA operation performed by the AP to obtain the TXOP for the UL frame transmission of the STAs, the existing CCA operation (for example, the CCA operation performed by the AP to acquire the TXOP for DL frame transmission) Can not be applied, and a new CCA operation is required.

An example of the present invention for the UL MU transmission mode including a standalone trigger frame within one TXOP as shown in FIG. 12 will be described.

The AP can receive buffer state information from the STAs in advance before transmitting the trigger frame to know which STAs have a request for UL PPDU transmission. Based on this, the AP may send a trigger frame to the particular STAs causing the UL MU transmission from the specific STAs. For example, the AP may determine a resource to be allocated for UL transmission of each STA based on buffer state information of a plurality of STAs, and may provide the determined resource allocation information to a plurality of STAs by including the determined resource allocation information in a trigger frame .

The STA can transmit buffer status information to the AP in a solicited or unsolicited manner. For example, if the AP explicitly requests buffer status information from the STA (e.g., the AP sends a trigger frame to the STA causing the buffer status information transmission of the STA), each STA responds to the buffer status Information may be transmitted to the AP. Alternatively, the STA may implicitly provide buffer state information to the AP through any frame it transmits to the AP, without the request by the AP.

Additionally, the AC information for the UL traffic that each STA is to transmit may be provided by the STA to the AP in advance. For example, each STA may provide its AP with the AC information of its traffic along with its buffer status information. Specifically, a frame for transmitting buffer status information may be used for STAs to transmit AC information determined according to UL traffic to an AP.

More specifically, the STA may use the frame containing the QoS control field for buffer status reporting and may implicitly convey the AC of the UL traffic to the AP using a specific bit of the QoS control field.

Table 3 below shows an exemplary format of the QoS control field.

The QoS control field may be composed of a 16-bit size field, and a sub-field allocated to each bit may be determined according to the applicable frame type (or sub-type). For example, in a nonmesh BSS, a TPU (Tunneled Direct-Link Setup) Peer U-APSD (Unscheduled-Automatic Power Save Delivery) is transmitted by non-AP STAs that are not sleep STAs or TPU buffer STAs. In the case of the QoS data frame and the QoS data and the Contention Free (ACK) frame, the bits 0-3 of the QoS control field are TID (Traffic Identifier), the bits 5-6 are the Ack policy, and the Bit 7 is the A-MSDU Bits 8-15 may be assigned to the TXOP duration request subfield if bit 4 is 0 and to the queue size subfield if bit 4 is 1. [ In the case of QoS null frames transmitted by non-AP STAs other than the TPU sleep STA or the TPU buffer STA in the non-mesh BSS, the bits 0-3 of the QoS control field are the TID, and the bits 5-6 are the Ack policy Bit 7 is reserved, bits 8 to 15 are allocated to the TXOP duration request subfield when bit 4 is 0, and when the value of Bit 4 is 1, the bits are allocated to the queue size subfield Can be assigned.

For example, a frame containing a QoS control field including a TXOP Duration Requested subfield may be used as a frame for a buffer status report (BSR).

In addition, AC of the UL traffic can be implicitly transmitted to the AP using a specific bit in the QoS control field. For example, the mapping relationship between the TID value of the QoS control field and AC is predetermined, and the AP that receives the frame including the QoS control field transmitted by the STA transmits the frame to the corresponding STA based on the TID value of the QoS control field Related AC information can be obtained.

The mapping relationship between the TID value and the AC value can be defined as shown in Table 4 or Table 5 below.

As shown in Table 4, when the 4-bit TID value is 0000, 0001, or 0010, the AP can determine that the AC of the UL traffic to be transmitted by the STA is AC_BK. If the TID value is 0100, 0101, or 0110, the AP may determine that the AC of the UL traffic to be transmitted by the STA is AC_BE. If the TID value is 1000, 1001, or 1010, the AP may determine that the AC of the UL traffic to be transmitted by the STA is AC_VI. When the TID value is 1100, 1101, 1110, or 1111, the AP may determine that the AC of the UL traffic to be transmitted by the STA is AC_VO. This is merely an example, and the scope of the present invention is not limited thereto.

Alternatively, as shown in Table 5, if the 4-bit TID value is 0000, 0001, or 0010, the AP may determine that the AC of the UL traffic to be transmitted by the STA is AC_BK. If the TID value is 0011, 0100, or 0101, the AP may determine that the AC of the UL traffic to be transmitted by the STA is AC_BE. If the TID value is 0110, 0111, or 1000, the AP can determine that the AC of the UL traffic that the STA is to transmit is AC_VI. If the TID value is 1001, 1010, or 1011, or 1111, the AP may determine that the AC of the UL traffic that the STA is to transmit is AC_VO. If the TID value is 1100, 1101, 1110, or 1111, the AP may determine that the STA is to transmit a short MAC control frame (i.e., the AC of the UL traffic to be transmitted by the STA is AC_Control).

Alternatively, in the case of a short MAC control frame, instead of informing the AP that the STA should transmit a short MAC control frame before the AP sends the trigger, the AP may collect the control information A trigger frame that causes BS, BF, and PS-Poll frames of a plurality of STAs may be transmitted.

Alternatively, the STA may provide AC information to the AP using other fields of the frame used for the BSR. For example, the STA may explicitly convey AC information to the AP using the other bits in the QoS control field of the frame used for the BSR. Alternatively, the STA may explicitly or implicitly convey AC information to the AP using fields other than the QoS control field of the frame used for the BSR.

Alternatively, the STA may provide AC information to the AP through frames other than those used for BSR.

The AP can determine whether to transmit UL traffic of each STA and AC of the corresponding UL traffic based on the BSR and AC information acquired from the STAs, determine STAs to participate in the UL MU transmission, and include resource allocation information Trigger frames can be transmitted. The AP may determine the EDCA access parameters needed to perform the CCA to obtain the TXOP required for the exchange of the trigger frame, the UL MU PPDU, and the ACK frame before transmitting the trigger frame.

The UL MU transmission includes transmission of UL traffic from multiple STAs at the same time. When the AC of the UL traffic of a plurality of STAs to be simultaneously transmitted is the same, the EDCA access parameter is determined according to the criteria shown in Table 1 or Table 2 based on the AC, and the CCA is performed based on the determined EDCA access parameter .

If the ACs of the UL traffic of a plurality of STAs to be simultaneously transmitted are not equal to each other, the EDCA access parameters can be determined based on the specific AC among them. Where the specific AC may be determined based on the priority of the ACs among the plurality of ACs. In the example of Table 1, it can be assumed that the priorities of the ACs have a relationship of AC_BK <AC_BE <AC_VI <AC_VO. Or, in the example of Table 2, it can be assumed that the priorities of the ACs have a relation of AC_BK <AC_BE <AC_VI <AC_VO <AC_Control. In this case, the specific AC may be determined as AC having the lowest priority (for example, AC_BK) or AC having the highest priority (for example, AC_VO or AC_Control) among a plurality of ACs.

For example, the AP may determine that STA1, STA2, and STA3 participate in the UL MU PPDU based on the BSR from the plurality of STAs. Here, it is assumed that the ACs reported by STA1, STA2, and STA3 to the AP are AC_BK, AC_BE, and AC_VO, respectively. If the AP determines the EDCA access parameter based on the lowest priority AC, the EDCA access parameters (e.g., CWmin = 31, CWmax = 1023, AIFSN = 7, TXOP limit = 0). In this case, the Defer Period may be determined as AIFS [AC_BK]. For example, AIFS [AC_BK] = aSIFSTime + AIFSN [AC_BK] * aSlotTime = 16 [mu] s + 7 * 9 [mu] s = 79 [mu] s. Thus, the AP can perform the CCA and obtain the TXOP (i.e., determine the TXOP value) based on the determined EDCA access parameters.

Alternatively, in the above example, the AP may determine the EDCA access parameters based on the highest priority AC and obtain a TXOP (i.e., be allowed to occupy the channel during the TXOP), thereby providing more fair channel access Lt; RTI ID = 0.0 &gt; and / or &lt; / RTI &gt; For example, the AP may trigger the STAs to transmit data corresponding to AC_BK and AC_BE on the MU basis, based on AC_VO corresponding to the highest priority.

16 and 17 illustrate examples of CCA operations of an AP according to the present invention.

16 and 17, the AP acquires AC information for UL transmissions from a plurality of STAs, determines an EDCA access parameter based on the obtained AC information, and performs a CCA operation based on the determined EDCA access parameter . &Lt; / RTI &gt;

In the example of FIG. 16, the AP transmits an EDCA access message, which is used for the CCA operation for acquiring the TXOP for exchanging the trigger frame, the UL MU PPDU, and the ACK / BA frame based on the AC information on the UL transmission acquired in advance from the STAs Parameters can be determined.

In the example of FIG. 16, while another AP or STA (AP / STA) operating on the same channel as the 11ax AP or 11ax STA (11ax AP / STA) occupies (Tx) the channel, 11ax AP / State and may not perform the transmission. When the channel occupation of another AP / STA is terminated and the channel becomes an idle state, the 11ax AP can perform a random backoff process when the channel is idle for a predetermined delay period.

Here, the delay period of FIG. 16 can be determined based on the EDCA access parameter (for example, AIFSN) corresponding to any one of the AC information for the UL transmission of a plurality of STAs previously acquired by the 11ax AP. The contention window size and the like of the random backoff process of FIG. 16 are the same as the EDCA access parameters (for example, CWmin and CWmax) corresponding to any one of the AC information for the UL transmission of a plurality of STAs acquired by the 11ax AP, . &Lt; / RTI &gt; The TXOP including the exchange of the trigger frame, the UL MU PPDU, and the ACK / BA frame is also transmitted to the 11ax AP through the EDCA access parameter (for example, , TXOP limit).

11ax APs that have acquired the channel access through the random backoff process transmit DL trigger frames, and a plurality of 11ax STAs transmit UL MU PPDUs using resources indicated by trigger information, and 11ax APs transmit a plurality of 11ax And may transmit an ACK / BA frame in response to the UL MU PPDU from the STA. During a TXOP that includes a sequence of frame exchanges between 11ax and 11ax STAs, another AP / STA operating on the same channel may determine that the channel state is busy and not perform the transmission.

16 is a stand-alone trigger frame UL MU transmission mode in one TXOP of FIG. 12, an UL MU transmission mode including a plurality of trigger frames in one TXOP in FIG. 14, one TXOP in FIG. 15, Lt; RTI ID = 0.0 &gt; UL &lt; / RTI &gt; MU transmission mode including a standalone trigger frame and a short MAC control frame.

In a case where UL data transmission from some 11ax STAs in a plurality of 11ax STAs and control information from 11ax STAs different from one another are multiplexed and transmitted simultaneously in one UL MU PPDU, Determines an EDCA access parameter based on any one of the AC information (data or control information) (e.g., highest priority or lowest priority) ACC, and based on the determined EDCA access parameter, Can be performed.

In the example of FIG. 17, the 11ax AP transmits trigger information and DL MU data (FIG. 17) based on the AC information for the UL transmission acquired in advance from the STAs and / or AC for the DL MU data, DL Trigger / Data), UL MU PPDU, and TXOP for exchanging ACK / BA frames.

In the example of Figure 17, while another AP or STA (AP / STA) operating on the same channel as the 11ax AP or the 11ax STA (11ax AP / STA) occupies (Tx) the channel, the 11ax AP / State and may not perform the transmission. When the channel occupation of another AP / STA is terminated and the channel becomes an idle state, the 11ax AP can perform a random backoff process when the channel is idle for a predetermined delay period.

The delay period of FIG. 17, the contention window size of the random backoff process, the TXOP, and the like can be determined based on the EDCA access parameters (for example, AIFSN, CWmin, CWmax, TXOP limit) determined by the 11ax AP.

Here, the EDCA access parameters determined by the 11ax AP can be determined based on only the AC corresponding to the DL MU data that the 11ax AP transmits to the 11ax STAs, irrespective of ACs previously transmitted by the 11ax STAs. If the 11 ax APs are different from the ACs (DL_AC1, DL_AC2, ...) of the DL data to be transmitted to the plurality of 11ax STAs, any of the ACs (e.g., the highest priority AC , Max (DL_AC1, DL_AC2, ...)) or the lowest priority AC (i.e., Min (DL_AC1, DL_AC2, ...)).

Alternatively, the EDCA access parameters determined by the 11ax AP may be determined in consideration of both the AC information previously transmitted by the 11ax STAs and the AC corresponding to the DL MU data to be transmitted to the 11ax STAs by the 11ax AP. For example, ACs (DL_AC1, DL_AC2, ...) corresponding to the DL MU data to be transmitted by the 11ax AP and ACs (UL_AC1, UL_AC2, ...) corresponding to the UL MU data / ...), the 11ax AP can determine the EDCA access parameters. Specifically, the AC (s) corresponding to the DL MU data to be transmitted by the 11ax AP and the AC (s) having the lowest priority among the AC (s) corresponding to the UL MU data / control information previously announced by the plurality of 11ax STAs (DL_AC1, DL_AC2, ..., UL_AC1, UL_AC2, ...)) of the highest priority (DL_AC1, DL_AC2, ..., UL_AC1, UL_AC2, , The 11ax AP can determine the EDCA access parameters.

Alternatively, if the UL MU PPDUs transmitted by the plurality of 11ax STAs include only MAC control frames, the EDCA access parameters determined by the 11ax AP are the AC parameters corresponding to the DL MU data to be transmitted to the 11ax STAs by the 11ax AP, Can be determined on the basis of &quot; only &quot; If the 11 ax APs are different from the ACs (DL_AC1, DL_AC2, ...) of the DL data to be transmitted to the plurality of 11ax STAs, any of the ACs (e.g., the highest priority AC , Max (DL_AC1, DL_AC2, ...)) or the lowest priority AC (i.e., Min (DL_AC1, DL_AC2, ...)).

Alternatively, the EDCA access parameters determined by the 11ax AP may be any one of the ACs previously transmitted by the plurality of 11ax STAs and the AC corresponding to the DL MU data to be transmitted to the 11ax STAs by the 11ax AP May be determined.

For example, an AC (i.e., Max (DL_AC1, DL_AC2, ...)) having the highest priority among the ACs corresponding to the DL MU data to be transmitted by the 11ax AP and the UL MU Max (DL_AC1, DL_AC2, ...) among ACs corresponding to the data / control information among the ACs having the highest priority among the ACs corresponding to the data / , ...), Max (DL_AC1, DL_AC2, ...)}, the 11ax AP can determine the EDCA access parameters.

(I.e., Min (DL_AC1, DL_AC2, ...)) having the lowest priority among the ACs corresponding to the DL MU data to be transmitted by the 11ax AP and the UL MU data / Min (DL_AC1, DL_AC2, ...) among the ACs corresponding to the control information among the ACs having the lowest priority (i.e., Min (DL_AC1, DL_AC2, ...)) among the ACs corresponding to the control information. ...), Min (DL_AC1, DL_AC2, ...)}), the 11ax AP can determine the EDCA access parameters.

(I.e., Min (DL_AC1, DL_AC2, ...)) having the lowest priority among the ACs corresponding to the DL MU data to be transmitted by the 11ax AP and the UL MU data / (DL_AC1, DL_AC2,...) Having the lowest priority among the ACs corresponding to the control information (e.g., Min (DL_AC1, DL_AC2, ...)) among the ACs corresponding to the control information. ...), Min (DL_AC1, DL_AC2, ...)}), the 11ax AP can determine the EDCA access parameters.

(I.e., Max (DL_AC1, DL_AC2, ...)) having the highest priority among the ACs corresponding to the DL MU data to be transmitted by the 11ax AP and the UL MU data / (I.e., Max (DL_AC1, DL_AC2, ...) among the ACs corresponding to the control information among the ACs having the highest priority among the ACs corresponding to the control information. ..., Max (DL_AC1, DL_AC2, ...)}), the 11ax AP can determine the EDCA access parameters.

The 11ax AP that has acquired the channel access through the random backoff process transmits a DL PPDU (DL Trigger / Data) including trigger information and DL MU data, and a plurality of 11ax STAs transmit resources using the resources indicated by the trigger information And the 11ax AP may transmit an ACK / BA frame in response to the UL MU PPDU from the plurality of 11ax STAs. During a TXOP that includes a sequence of frame exchanges between 11ax and 11ax STAs, another AP / STA operating on the same channel may determine that the channel state is busy and not perform the transmission.

The example of FIG. 17 can be applied to the UL MU transmission mode including the DL / UL cascading TXOP structure of FIG. 13 described above.

18 is a flow chart illustrating an exemplary method according to the present invention.

In step S1810, the AP may receive AC information for UL traffic from the STA group including a plurality of STAs. In addition to the AC information for UL traffic, the BSR of each of a plurality of STAs belonging to the STA group can also be received. For example, some STA's AC information may be included in the BSR. AC information or BSRs from a plurality of STAs belonging to the STA group may be simultaneously received by the AP or received at another point in time.

In step S1820, the AP may determine whether to transmit trigger information that causes UL MU PPDU transmission from the STA group with DL MU data. If it is determined that only the standalone trigger frame is to be transmitted without the DL MU data, the process can proceed to step S1831, and if it is determined to transmit the DL MU PPDU including the trigger information and the DL MU data, the process can proceed to step S1841.

In step S1831, the AP can determine the EDCA access parameter based on the UL traffic AC information. For example, the EDCA access parameters may be determined based on any one of the ACs for UL traffic (data and / or control information). A detailed description thereof is the same as the examples of the present invention described with reference to FIG.

In step S1832, the AP may perform the CCA operation based on the contention window, the TXOP, and the like of the delay period determined based on the determined EDCA access parameters (e.g., CWmin, CWmax, AIFSN, TXOP limit). In steps S1833, S1834, and S1835, the AP may transmit the trigger frame to the STA group, receive the UL MU PPDU from the STA group, and transmit the ACK / BA frame in response thereto.

On the other hand, in step S1841, the AP can determine the EDCA access parameter based on the DL data AC information and / or the UL traffic AC information. For example, the EDCA access parameters may be determined based on any one of the DL data ACs or based on either the DL data AC information and the ACs for UL traffic (data and / or control information). A detailed description thereof is the same as the examples of the present invention described with reference to FIG.

In step S1842, the AP may perform the CCA operation based on the contention window, the TXOP, and the like of the delay period determined based on the determined EDCA access parameters (e.g., CWmin, CWmax, AIFSN, TXOP limit). In steps S1843, S1844, and S1845, the AP may transmit the trigger frame to the STA group, receive the UL MU PPDU from the STA group, and transmit the ACK / BA frame in response thereto.

Although the above-described exemplary methods are represented by a series of acts for clarity of explanation, they are not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously or in a different order. In addition, not all illustrated steps are necessary to implement the method according to the present invention.

The foregoing embodiments include examples of various aspects of the present invention. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

The scope of the present invention includes devices that process or implement operations in accordance with various embodiments of the present invention (e.g., the wireless device and its components described with reference to FIG. 1).

19 is a diagram for explaining a configuration of a processor according to the present invention.

The UL MU transmission operation described in various examples of the present invention can be handled by the upper layer processing unit 111 and the physical layer processing unit 112 of the processor 110 of the terminal device 100. [

The upper layer processing unit 111 may include a UL transmission control information generating unit 1910 for generating buffer status information, UL traffic AC information, and the like. The UL transmission control information generation unit 1910 can transmit buffer status information, UL traffic AC information, and the like to the AP apparatus 200 through the physical layer processing unit 112.

The upper layer processing unit 111 receives the trigger information received from the AC device 200 through the physical layer processing unit 112 and generates UL traffic for UL MU PPDU transmission based on the trigger information (1920). &Lt; / RTI &gt; The UL traffic generation unit 1920 can transmit the generated UL traffic to the AP apparatus 200 through the physical layer processing unit 112 on the resource indicated by the trigger information.

On the other hand, a channel access operation supporting the UL MU transmission described in various examples of the present invention can be handled by the upper layer processing unit 211 and the physical layer processing unit 212 of the processor 210 of the AP apparatus 200 have.

The upper layer processing unit 211 receives UL transmission control information received from the plurality of STA apparatuses 100 through the physical layer processing unit 212 and transmits UL transmission control information (e.g., buffer status information, UL traffic AC And / or an EDCA access parameter determination unit 1960 that determines EDCA access parameters based on DL traffic AC information. The CCA operation of the AP apparatus 200 can be performed based on the parameters determined by the EDCA access parameter determination unit 1960. [

The upper layer processing unit 211 includes a trigger information generating unit 1970 that generates trigger information for causing UL MU transmission from a plurality of STA apparatuses 100, And a DL traffic generation unit (1980). Trigger information generated by the trigger information generating unit 1970 may be transmitted to the plurality of STA apparatuses 100 via the physical layer processing unit 212 together with the DL MU data generated in the DL traffic generating unit 1980, Lt; / RTI &gt;

The operation of the processor 110 of the terminal device 100 or the processor 210 of the AP device 200 described above may be implemented by software processing or hardware processing or may be implemented by software and hardware processing.

The scope of the present invention includes software (or an operating system, application, firmware, program, etc.) that enables an operation according to various embodiments of the present invention to be performed on a device or computer, It includes a possible medium.

Although various embodiments of the present invention have been described with reference to an IEEE 802.11 wireless LAN system, the present invention can be applied to various mobile communication systems.

Claims (10)

A method for an access point performing channel access in a wireless LAN,
Obtaining a transmission opportunity (TXOP) comprising uplink multi-user (UL MU) transmission of a plurality of stations (STAs);
Transmitting a frame containing trigger information to the plurality of STAs within the TXOP; And
Receiving a UL MU PPDU (Physical Layer Protocol Data Unit) transmitted based on the trigger information from the plurality of STAs in the TXOP,
The TXOP acquisition step may comprise determining based on at least one of UL traffic access category (AC) information associated with the UL MU transmission or DL traffic AC information associated with a downlink multi-user (DL MU) transmission transmitted with the trigger information And performing a Clear Channel Assessment (CCA) operation based on a channel access parameter to be transmitted. The method according to claim 1,
Wherein if the frame containing the trigger information does not include the DL MU transmission, the channel access parameter comprises parameters corresponding to any one of the UL traffic AC information of the plurality of STAs. The method according to claim 1,
If the frame containing the trigger information includes the DL MU transmission, the channel access parameter corresponds to any one of the UL traffic AC information of the plurality of STAs and the DL traffic AC information of the plurality of STAs &Lt; / RTI &gt; The method according to claim 1,
Wherein if the frame containing the trigger information comprises the DL MU transmission, then the channel access parameter comprises parameters corresponding to any of the DL traffic AC information for the plurality of STAs. The method according to claim 1,
Wherein the UL traffic AC information of the plurality of STAs is received from the plurality of STAs prior to the TXOP acquisition step. The method according to claim 1,
Wherein the UL traffic AC information of the plurality of STAs is included in a buffer status report frame transmitted from the plurality of STAs. The method according to claim 1,
Wherein the channel access parameter comprises an EDCA (Enhanced Distributed Channel Access) access parameter. 8. The method of claim 7,
Wherein the EDCA access parameter comprises at least one of a contention window minimum value (CWmin), a contention window maximum value (CWmax), an Arbitration Inter-Frame Space Number (AIFSN), or a TXOP limit. The method according to claim 1,
Further comprising transmitting an ACK / BA (Acknowledgment / Block Acknowledgment) frame in response to the UL MU PPDU in the TXOP. A method for performing uplink multi-user (UL MU) transmission in a wireless local area network (STA)
Receiving a frame including trigger information from an access point (AP); And
And transmitting a UL MU PPDU (Physical Layer Protocol Data Unit) at the same time as one or more other STAs based on the trigger information,
The reception of the frame containing the trigger information and the transmission of the UL MU PPDU are performed in a TXOP obtained by the AP,
Wherein the TXOP is a channel determined based on at least one of UL traffic access category (AC) information associated with the UL MU transmission or DL traffic AC information associated with a downlink multi-user (DL MU) transmission transmitted with the trigger information And determining through the Clear Channel Assessment (CCA) operation of the AP based on the access parameter.

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