WO2017213391A1 - Method for updating network allocation vector in wireless lan system, and device therefor - Google Patents

Abstract

A method for updating a network allocation vector (NAV) timer by a station (STA) in a wireless LAN system according to an embodiment of the present invention may comprise the steps of: detecting a first frame including a transmission opportunity (TXOP) duration field; updating an NAV timer maintained by the STA in order to protect a TXOP of another STA, on the basis of the TXOP duration field of the first frame; and when the NAV timer indicates zero, performing channel access for frame transmission of the STA, wherein, in updating the NAV timer, when the TXOP duration field has a specific value that does not belong to a valid TXOP duration, the STA resets the NAV timer to zero and performs the channel access on the basis of an extended inter-frame space (EIFS) operation, on an assumption that the first frame is a last frame transmitted within the TXOP of the another STA.

Description

Method for updating network allocation vector in WLAN system and apparatus therefor

The present invention relates to a method and apparatus for updating a network allocation vector (NAV) in a WLAN system, and more particularly, to a method and apparatus for updating a NAV based on a frame including a TXOP period field. It is about.

The standard for WLAN technology is being developed as an Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11a and b are described in 2.4. Using unlicensed band at GHz or 5 GHz, IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g applies orthogonal frequency-division multiplexing (OFDM) at 2.4 GHz to provide a transmission rate of 54 Mbps. IEEE 802.11n applies multiple input multiple output OFDM (MIMO-OFDM) to provide a transmission rate of 300 Mbps for four spatial streams. IEEE 802.11n supports channel bandwidths up to 40 MHz, in this case providing a transmission rate of 600 Mbps.

The WLAN standard uses a maximum of 160MHz bandwidth, supports eight spatial streams, and supports IEEE 802.11ax standard through an IEEE 802.11ac standard supporting a speed of up to 1Gbit / s.

An object of the present invention is to provide a method and apparatus for updating NAV more accurately and efficiently based on a transmission opportunity (TXOP) period included in a signaling field of a frame.

The present invention is not limited to the above-described technical problem and other technical problems can be inferred from the embodiments of the present invention.

In the WLAN system according to an aspect of the present invention for achieving the above-described technical problem, a method for updating a network allocation vector (NAV) timer by a station (STA), the first frame including a TXOP duration (TXmission duration) field Detecting; Updating a NAV timer maintained by the STA based on the TXOP period field of the first frame to protect a TXOP of another STA; And performing channel access for frame transmission of the STA when the NAV timer is 0. When updating the NAV timer, when the TXOP period field is a specific value that is not a valid TXOP period, the STA Under the assumption that the first frame is the last frame transmitted in the TXOP of the other STA, the NAV timer may be reset to 0 and the channel access may be performed based on an extended inter-frame space (EIFS) operation.

An STA for performing the above-described NAV timer update method includes a transmitter; receiving set; And detecting a first frame including a transmission opportunity duration field through the receiver, and based on the TXOP duration field of the first frame, the NAV timer maintained by the STA to protect the TXOP of another STA. And performing a channel access through the transmitter for frame transmission of the STA when the NAV timer is 0. In updating the NAV timer, the TXOP period field is not a valid TXOP period. If the specified value, the processor resets the NAV timer to 0 under the assumption that the first frame is the last frame transmitted in the TXOP of the other STA, and accesses the channel based on an extended inter-frame space (EIFS) operation. Can be performed.

If the TXOP period field is the specific value, the STA may reset the NAV timer to 0 after waiting for the EIFS period.

If the TXOP period field is the specific value, the STA may transmit the frame of the STA after confirming that the channel is idle for a period in which the EIFS period and the backoff period are combined after resetting the NAV.

The TXOP period field may correspond to 7-bits included in the signal field of the first frame, and the specific value may correspond to a value in which all 7-bits are filled with 0 or decimal 126.

If the TXOP period field of the first frame indicates the valid TXOP period in units of 128 us, and the previous update of the NAV timer is performed in units of 128 us, only when the current value of the NAV timer is smaller than the valid TXOP period. The NAV update may be performed. If the TXOP period field of the first frame indicates the valid TXOP period in units of 8 us, and a previous update of the NAV timer is performed in units of 128 us, the TXOP period field may be used as the valid TXOP period regardless of the current value of the NAV timer. NAV update can be performed.

In the WLAN system according to another aspect of the present invention for achieving the above-described technical problem, a method for transmitting a frame by a station (STA), to protect itself in the first TXOP duration (transmission opportunity duration) field of the first frame Setting a TXOP period value; Transmitting the first frame; And transmitting a second frame including a second TXOP period field, wherein if the second frame is the last frame transmitted within the TXOP of the STA, the STA may validate the second TXOP period field. The remaining TXOP is truncated by setting to a specific value other than the TXOP period, and the specific value may be a value for invoking an extended inter-frame space (EIFS) operation of a third party STA. have.

An STA that performs the above-described frame transmission method includes: a processor configured to set a TXOP period value to be protected by a first transmission opportunity duration field of a first frame; And a transmitter for transmitting the first frame under the control of the processor and transmitting a second frame including a second TXOP period field, wherein the second frame is the last frame transmitted in the TXOP of the STA. In this case, the processor truncates the remaining TXOP by setting the second TXOP period field to a specific value that is not a valid TXOP period, and the specific value is an EIFS (extended) of a third party STA. It may be a value for invoking an inter-frame space operation.

If the second TXOP period field is the specific value, the remaining TXOP may be truncated after the EIFS period.

When the second TXOP period field is the specific value, the third STA may transmit a frame after confirming that the channel is idle for a period of adding up the EIFS period and the backoff period after the remaining TXOP is truncated. Can be.

The second TXOP period field may correspond to 7-bits included in the signal field of the second frame, and the specific value may correspond to a value in which all of the 7-bits are filled with 0 or decimal 126.

When the second frame is a frame immediately before the last frame transmitted in the TXOP of the STA, the STA is configured to perform the second TXOP period based on a second time unit smaller than the first time unit used in the first frame. Field may be set to the valid TXOP period.

According to an embodiment of the present invention, if the TXOP period field of the received frame is a special value, the TXOP truncates the TXOP, that is, resets the NAV and performs channel access based on the EIFS operation, thereby solving the TXOP transient protection problem. have.

In addition to the above-described technical effects, other technical effects can be inferred from the embodiments of the present invention.

1 is a diagram illustrating an example of a configuration of a WLAN system.

2 is a diagram illustrating another example of a configuration of a WLAN system.

3 is a diagram illustrating a general link setup process.

4 is a diagram for describing a backoff process.

5 is a diagram for explaining hidden nodes and exposed nodes.

6 is a diagram for explaining an RTS and a CTS.

7 to 9 are diagrams for explaining the operation of the STA receiving the TIM.

10 is a diagram for explaining an example of a frame structure used in an IEEE 802.11 system.

11 illustrates a content free (CF) -END frame.

12-15 illustrate HE PPDUs.

16 is a diagram for explaining uplink multi-user transmission.

17 shows an example of a trigger frame format.

18 shows an example of NAV settings.

19 shows an example of TXOP truncation.

20 shows an example of SU PPDU transmission and MU PPDU transmission.

21 shows an example of UL MU transmission.

22 illustrates TXOP transient protection occurring in the cascade procedure and TXOP truncation to resolve it.

23 shows an SU procedure and a DL MU procedure for exchanging multiple frames.

24 illustrates a NAV update scheme in the UL MU procedure.

25 illustrates an example of over-protection of TXOP duration.

26 illustrates TXOP truncation according to an embodiment of the present invention.

27 illustrates TXOP truncation according to another embodiment of the present invention.

28 illustrates TXOP truncation according to another embodiment of the present invention.

29 shows an example of TXOP truncation using the TXOP duration field.

30 shows another example of TXOP truncation.

31 shows another example of over-protection of TXOP duration.

32 illustrates a NAV update method according to an embodiment of the present invention.

33 illustrates NAV extensions that may occur in multiple frame exchanges.

34 illustrates TXOP duration value settings according to an embodiment of the present invention.

35 illustrates an NAV update method based on an Intra-BSS HE PPDU according to an embodiment of the present invention.

36 is a view illustrating an NAV update method based on Intra-BSS HE PPDU according to another embodiment of the present invention.

37 illustrates a NAV timer update method according to an embodiment of the present invention.

38 illustrates a method of setting a TXOP duration field according to an embodiment of the present invention.

39 is a view for explaining an apparatus according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention.

As described above, the following description relates to a method and an apparatus therefor for efficiently utilizing a channel having a wide band in a WLAN system. To this end, first, a WLAN system to which the present invention is applied will be described in detail.

1 is a diagram illustrating an example of a configuration of a WLAN system.

As shown in FIG. 1, the WLAN system includes one or more basic service sets (BSSs). A BSS is a set of stations (STAs) that can successfully synchronize and communicate with each other.

An STA is a logical entity that includes a medium access control (MAC) and a physical layer interface to a wireless medium. The STA is an access point (AP) and a non-AP STA (Non-AP Station). Include. The portable terminal operated by the user among the STAs is a non-AP STA, and when referred to simply as an STA, it may also refer to a non-AP STA. A non-AP STA is a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, or a mobile subscriber. It may also be called another name such as a mobile subscriber unit.

The AP is an entity that provides an associated station (STA) coupled to the AP to access a distribution system (DS) through a wireless medium. The AP may be called a centralized controller, a base station (BS), a Node-B, a base transceiver system (BTS), or a site controller.

BSS can be divided into infrastructure BSS and Independent BSS (IBSS).

The BBS shown in FIG. 1 is an IBSS. The IBSS means a BSS that does not include an AP. Since the IBSS does not include an AP, access to the DS is not allowed, thereby forming a self-contained network.

2 is a diagram illustrating another example of a configuration of a WLAN system.

The BSS shown in FIG. 2 is an infrastructure BSS. Infrastructure BSS includes one or more STAs and APs. In the infrastructure BSS, communication between non-AP STAs is performed via an AP. However, when a direct link is established between non-AP STAs, direct communication between non-AP STAs is also possible.

As shown in FIG. 2, a plurality of infrastructure BSSs may be interconnected through a DS. A plurality of BSSs connected through a DS is called an extended service set (ESS). STAs included in the ESS may communicate with each other, and a non-AP STA may move from one BSS to another BSS while seamlessly communicating within the same ESS.

The DS is a mechanism for connecting a plurality of APs. The DS is not necessarily a network, and there is no limitation on the form if it can provide a predetermined distribution service. For example, the DS may be a wireless network such as a mesh network or a physical structure that connects APs to each other.

Hierarchy

The operation of the STA operating in the WLAN system may be described in terms of a layer structure. In terms of device configuration the hierarchy may be implemented by a processor. The STA may have a plurality of hierarchical structures. For example, the hierarchical structure covered by the 802.11 standard document is mainly the MAC sublayer and physical (PHY) layer on the DLL (Data Link Layer). The PHY may include a Physical Layer Convergence Procedure (PLCP) entity, a Physical Medium Dependent (PMD) entity, and the like. The MAC sublayer and PHY conceptually contain management entities called MAC sublayer management entities (MLMEs) and physical layer management entities (PLMEs), respectively.These entities provide a layer management service interface on which layer management functions operate. .

In order to provide correct MAC operation, a Station Management Entity (SME) is present in each STA. An SME is a layer-independent entity that can appear to be in a separate management plane or appear to be off to the side. While the exact features of the SME are not described in detail in this document, they generally do not include the ability to collect layer-dependent states from various Layer Management Entities (LMEs), and to set similar values for layer-specific parameters. You may seem to be in charge. SMEs can generally perform these functions on behalf of general system management entities and implement standard management protocols.

The aforementioned entities interact in a variety of ways. For example, entities can interact by exchanging GET / SET primitives. A primitive means a set of elements or parameters related to a particular purpose. The XX-GET.request primitive is used to request the value of a given MIB attribute (management information based attribute information). The XX-GET.confirm primitive is used to return the appropriate MIB attribute information value if the Status is "Success", otherwise it is used to return an error indication in the Status field. The XX-SET.request primitive is used to request that the indicated MIB attribute be set to a given value. If the MIB attribute means a specific operation, this is to request that the operation be performed. And, the XX-SET.confirm primitive confirms that the indicated MIB attribute is set to the requested value when status is "success", otherwise it is used to return an error condition in the status field. If the MIB attribute means a specific operation, this confirms that the operation has been performed.

In addition, the MLME and SME may exchange various MLME_GET / SET primitives through a MLME_SAP (Service Access Point). In addition, various PLME_GET / SET primitives may be exchanged between PLME and SME through PLME_SAP and may be exchanged between MLME and PLME through MLME-PLME_SAP.

link set up  process

3 is a diagram illustrating a general link setup process.

In order for an STA to set up a link and transmit / receive data with respect to a network, an STA first discovers the network, performs authentication, establishes an association, and authenticates for security. It must go through the back. The link setup process may also be referred to as session initiation process and session setup process. In addition, a process of discovery, authentication, association, and security establishment of a link setup process may be collectively referred to as association process.

An exemplary link setup process will be described with reference to FIG. 3.

In step S510, the STA may perform a network discovery operation. The network discovery operation may include a scanning operation of the STA. That is, in order for the STA to access the network, the STA must find a network that can participate. The STA must identify a compatible network before joining the wireless network. A network identification process existing in a specific area is called scanning.

There are two types of scanning methods, active scanning and passive scanning.

3 exemplarily illustrates a network discovery operation including an active scanning process. In active scanning, the STA performing scanning transmits a probe request frame and waits for a response to discover which AP exists in the vicinity while moving channels. The responder transmits a probe response frame to the STA that transmits the probe request frame in response to the probe request frame. Here, the responder may be an STA that last transmitted a beacon frame in the BSS of the channel being scanned. In the BSS, the AP transmits a beacon frame, so the AP becomes a responder. In the IBSS, since the STAs in the IBSS rotate and transmit a beacon frame, the responder is not constant. For example, an STA that transmits a probe request frame on channel 1 and receives a probe response frame on channel 1 stores the BSS-related information included in the received probe response frame and stores the next channel (eg, number 2). Channel) to perform scanning (i.e., probe request / response transmission and reception on channel 2) in the same manner.

Although not shown in FIG. 3, the scanning operation may be performed by a passive scanning method. In passive scanning, the STA performing scanning waits for a beacon frame while moving channels. The beacon frame is one of management frames in IEEE 802.11. The beacon frame is notified of the existence of a wireless network and is periodically transmitted to allow the STA performing scanning to find the wireless network and participate in the wireless network. In the BSS, the AP periodically transmits a beacon frame, and in the IBSS, STAs in the IBSS rotate and transmit a beacon frame. When the STA that performs the scanning receives the beacon frame, the STA stores the information on the BSS included in the beacon frame and records beacon frame information in each channel while moving to another channel. Upon receiving the beacon frame, the STA may store BSS related information included in the received beacon frame, move to the next channel, and perform scanning on the next channel in the same manner.

Comparing active and passive scanning, active scanning has the advantage of less delay and power consumption than passive scanning.

After the STA discovers the network, an authentication process may be performed in step S520. This authentication process may be referred to as a first authentication process in order to clearly distinguish from the security setup operation of step S540 described later.

The authentication process includes a process in which the STA transmits an authentication request frame to the AP, and in response thereto, the AP transmits an authentication response frame to the STA. An authentication frame used for authentication request / response corresponds to a 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, and 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, and may be replaced with other information or further include additional information.

The STA may send an authentication request frame to the AP. The AP may determine whether to allow authentication for the corresponding STA based on the information included in the received authentication request frame. The AP may provide a result of the authentication process to the STA through an authentication response frame.

After the STA is successfully authenticated, the association process may be performed in step S530. The association process includes a process in which the STA transmits an association request frame to the AP, and in response thereto, the AP transmits an association response frame to the STA.

For example, the association request frame may include information related to various capabilities, beacon listening interval, service set identifier (SSID), supported rates, supported channels, RSN, mobility domain. Information about supported operating classes, TIM Broadcast Indication Map Broadcast request, interworking service capability, and the like.

For example, an association response frame may include information related to various capabilities, status codes, association IDs (AIDs), support rates, Enhanced Distributed Channel Access (EDCA) parameter sets, Received Channel Power Indicators (RCPI), Received Signal to Noise Information, such as an indicator, a mobility domain, a timeout interval (association comeback time), an overlapping BSS scan parameter, a TIM broadcast response, and a QoS map.

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

After the STA is successfully associated with the network, a security setup process may be performed at step S540. The security setup process of step S540 may be referred to as an authentication process through a Robust Security Network Association (RSNA) request / response. The authentication process of step S520 is called a first authentication process, and the security setup process of step S540 is performed. It may also be referred to simply as the authentication process.

The security setup process of step S540 may include, for example, performing a private key setup through 4-way handshaking through an Extensible Authentication Protocol over LAN (EAPOL) frame. . In addition, the security setup process may be performed according to a security scheme not defined in the IEEE 802.11 standard.

Media access mechanism

In a WLAN system according to IEEE 802.11, a basic access mechanism of MAC (Medium Access Control) is a carrier sense multiple access with collision avoidance (CSMA / CA) mechanism. The CSMA / CA mechanism is also called the Distributed Coordination Function (DCF) of the IEEE 802.11 MAC. It basically employs a "listen before talk" access mechanism. According to this type of access mechanism, the AP and / or STA may sense a radio channel or medium during a predetermined time period (e.g., during a DCF Inter-Frame Space (DIFS), before starting transmission. When the medium determines that the medium is in an idle state, the frame transmission is started through the medium, while the medium is occupied. If it is detected that the AP and / or STA does not start its own transmission, it waits by setting a delay period (for example, a random backoff period) for medium access and attempting frame transmission. By applying a random backoff period, since several STAs are expected to attempt frame transmission after waiting for different times, collisions can be minimized.

In addition, the IEEE 802.11 MAC protocol provides a hybrid coordination function (HCF). HCF is based on the DCF and the Point Coordination Function (PCF). The PCF refers to a polling-based synchronous access scheme in which polling is performed periodically so that all receiving APs and / or STAs can receive data frames. In addition, the HCF has an Enhanced Distributed Channel Access (EDCA) and an HCF Controlled Channel Access (HCCA). EDCA is a competition based approach for providers to provide data frames to multiple users, and HCCA uses a non-competition based channel access scheme using a polling mechanism. In addition, the HCF includes a media access mechanism for improving the quality of service (QoS) of the WLAN, and can transmit QoS data in both a contention period (CP) and a contention free period (CFP).

4 is a diagram for describing a backoff process.

An operation based on an arbitrary backoff period will be described with reference to FIG. 4. When a medium that is occupy 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, STAs may select a random backoff count and wait for the corresponding slot time, respectively, before attempting transmission. The random backoff count has a packet number value and may be determined as one of values ranging from 0 to CW. Here, CW is a contention window parameter value. The CW parameter is given CWmin as an initial value, but may take a double value in case of transmission failure (eg, when an ACK for a transmitted frame is not received). When the CW parameter value is CWmax, data transmission can be attempted while maintaining the CWmax value until the data transmission is successful. If the data transmission is successful, the CW parameter value is reset to the CWmin value. The CW, CWmin and CWmax values are preferably set to 2 ⁿ -1 (n = 0, 1, 2, ...).

Once the random backoff process begins, the STA continues to monitor the medium while counting down the backoff slots according to the determined backoff count value. If the medium is monitored as occupied, the countdown stops and waits; if the medium is idle, it resumes the remaining countdown.

In the example of FIG. 4, when a packet to be transmitted to the MAC of the STA3 arrives, the STA3 may confirm that the medium is idle as much as DIFS and transmit the frame immediately. Meanwhile, the remaining STAs monitor and wait for the medium to be busy. In the meantime, data may also be transmitted in each of STA1, STA2, and STA5, and each STA waits for DIFS when the medium is monitored idle, and then counts down the backoff slot according to a random backoff count value selected by the STA. Can be performed. In the example of FIG. 4, STA2 selects the smallest backoff count value, and STA1 selects the largest backoff count value. In other words, 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. STA1 and STA5 stop counting for a while and wait for STA2 to occupy the medium. When the occupation of the STA2 ends and the medium becomes idle again, the STA1 and the STA5 resume the stopped backoff count after waiting for DIFS. 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 the STA5 is shorter than that of the STA1, the STA5 starts frame transmission. Meanwhile, while STA2 occupies the medium, data to be transmitted may also occur in STA4. At this time, when the medium is in an idle state, the STA4 waits for DIFS, performs a countdown according to a random backoff count value selected by the STA4, and starts frame transmission. In the example of FIG. 6, the remaining backoff time of STA5 coincides with an arbitrary backoff count value of STA4. In this case, a collision may occur between STA4 and STA5. If a collision occurs, neither STA4 nor STA5 receive an ACK, and thus data transmission fails. In this case, STA4 and STA5 may double the CW value, select a random backoff count value, and perform a countdown. Meanwhile, the STA1 waits while the medium is occupied due to transmission of the STA4 and STA5, waits for DIFS when the medium is idle, and starts frame transmission after the remaining backoff time passes.

Of STA Sensing  action

As described above, the CSMA / CA mechanism includes virtual carrier sensing in addition to physical carrier sensing in which the AP and / or STA directly sense the medium. Virtual carrier sensing is intended to compensate for problems that may occur in media access, such as a hidden node problem. For virtual carrier sensing, the MAC of the WLAN system may use a network allocation vector (NAV). The NAV is a value in which an AP and / or STA currently using or authorized to use a medium instructs another AP and / or STA how long to remain until the medium becomes available. Therefore, the value set to NAV corresponds to a period in which the medium is scheduled to be used by the AP and / or STA transmitting the corresponding frame, and the STA receiving the NAV value is prohibited from accessing the medium during the period. The NAV may be set, for example, according to the value of the "duration" field of the MAC header of the frame.

In addition, a robust collision detect mechanism has been introduced to reduce the possibility of collision. This will be described with reference to FIGS. 5 and 7. Although the actual carrier sensing range and transmission range may not be the same, it is assumed to be the same for convenience of description.

5 is a diagram for explaining hidden nodes and exposed nodes.

5A illustrates an example of a hidden node, in which STA A and STA B are in communication and STA C has information to transmit. In more detail, although STA A is transmitting information to STA B, it may be determined that the medium is idle when STA C performs carrier sensing before sending data to STA B. This is because transmission of STA A (ie, media occupation) may not be sensed at the location of STA C. In this case, since STA B receives the information of STA A and STA C at the same time, a collision occurs. At this time, STA A may be referred to as a hidden node of STA C.

FIG. 5B is an example of an exposed node, and STA B is a case in which STA C has information to be transmitted from STA D while transmitting data to STA A. FIG. In this case, when STA C performs carrier sensing, it may be determined that the medium is occupied by the transmission of STA B. Accordingly, since STA C is sensed as a medium occupancy state even if there is information to be transmitted to STA D, it must wait until the medium becomes idle. However, since STA A is actually outside the transmission range of STA C, transmission from STA C and transmission from STA B may not collide with STA A's point of view, so STA C is unnecessary until STA B stops transmitting. To wait. At this time, STA C may be referred to as an exposed node of STA B.

6 is a diagram for explaining an RTS and a CTS.

In order to efficiently use a collision avoidance mechanism in an exemplary situation as shown in FIG. 5, a short signaling packet such as a request to send (RTS) and a clear to send (CTS) may be 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, when an STA to transmit data transmits an RTS frame to an STA receiving the data, the STA receiving the data may inform the neighboring STAs that they will receive the data by transmitting the CTS frame.

FIG. 6A illustrates an example of a method for solving a hidden node problem, and assumes that both STA A and STA C try to transmit data to STA B. FIG. When STA A sends the RTS to STA B, STA B transmits the CTS to both STA A and STA C around it. As a result, STA C waits until data transmission between STA A and STA B is completed, thereby avoiding collision.

FIG. 6 (b) illustrates an example of a method for solving an exposed node problem, and STA C overhears RTS / CTS transmission between STA A and STA B so that STA C may use another STA (eg, STA). It may be determined that no collision will occur even if data is transmitted to D). That is, STA B transmits the RTS to all neighboring STAs, and only STA A having the data to actually transmit the CTS. Since STA C receives only RTS and not STA A's CTS, it can be seen that STA A is out of STC C's carrier sensing.

Power management

As described above, in the WLAN system, channel sensing must be performed before the STA performs transmission and reception, and always sensing the channel causes continuous power consumption of the STA. The power consumption in the receive state is not significantly different from the power consumption in the transmit state, and maintaining the receive state is also a great burden for the power limited STA (ie, operated by a battery). Therefore, if the STA maintains a reception standby state in order to continuously sense the channel, it inefficiently consumes power without any particular advantage in terms of WLAN throughput. In order to solve this problem, the WLAN system supports a power management (PM) mode of the STA.

The power management mode of the STA is divided into an active mode and a power save (PS) mode. The STA basically operates in the active mode. The STA operating in the active mode maintains an awake state. The awake state is a state in which normal operation such as frame transmission and reception or channel scanning is possible. On the other hand, the STA operating in the PS mode operates by switching between a sleep state (or a doze state) and an awake state. The STA operating in the sleep state operates at the minimum power, and does not perform frame scanning as well as channel scanning.

As the STA operates in the sleep state for as long as possible, power consumption is reduced, so the STA has an increased operation period. However, it is impossible to operate unconditionally long because frame transmission and reception are impossible in the sleep state. If there is a frame to be transmitted to the AP, the STA operating in the sleep state may transmit the frame by switching to the awake state. On the other hand, when the AP has a frame to transmit to the STA, the STA in the sleep state may not receive it and may not know that there is a frame to receive. Accordingly, the STA may need to switch to the awake state according to a specific period in order to know whether or not the frame to be transmitted to (or, if there is, receive it) exists.

The AP may transmit a beacon frame to STAs in the BSS at regular intervals. The beacon frame may include a traffic indication map (TIM) information element. The TIM information element may include information indicating that the AP has buffered traffic for STAs associated with the AP and transmits a frame. The TIM element includes a TIM used to inform unicast frames and a delivery traffic indication map (DTIM) used to inform multicast or broadcast frames.

7 to 9 are diagrams for explaining in detail the operation of the STA receiving the TIM.

Referring to FIG. 7, the STA may switch from the sleep state to the awake state to receive a beacon frame including the TIM from the AP, interpret the received TIM element, and know that there is buffered traffic to be transmitted to the AP. . After contending with other STAs for medium access for PS-Poll frame transmission, the STA may transmit a PS-Poll frame to request an AP to transmit a data frame. After receiving the PS-Poll frame transmitted by the STA, the AP may transmit the frame to the STA. The STA may receive a data frame and transmit an acknowledgment (ACK) frame thereto to the AP. The STA may then go back to sleep.

As shown in FIG. 7, the AP may operate according to an immediate response method of transmitting a data frame after a predetermined time (for example, a short inter-frame space (SIFS)) after receiving a PS-Poll frame from an STA. Can be. Meanwhile, when the AP fails to prepare a data frame to be transmitted to the STA during the SIFS time after receiving the PS-Poll frame, the AP may operate according to a deferred response method, which will be described with reference to FIG. 8.

In the example of FIG. 8, the STA switches from the sleep state to the awake state to receive the TIM from the AP and transmits the PS-Poll frame to the AP through contention as in the example of FIG. 7. If the AP does not prepare a data frame during SIFS even after receiving the PS-Poll frame, the AP may transmit an ACK frame to the STA instead of transmitting the data frame. When the data frame is prepared after transmitting the ACK frame, the AP may transmit the data frame to the STA after performing contention. The STA may transmit an ACK frame indicating that the data frame was successfully received to the AP and go to sleep.

9 illustrates an example in which the AP transmits a DTIM. STAs may transition from a sleep state to an awake state to receive a beacon frame containing a DTIM element from the AP. STAs may know that a multicast / broadcast frame will be transmitted through the received DTIM. The AP may transmit data (ie, multicast / broadcast frame) immediately after the beacon frame including the DTIM without transmitting and receiving the PS-Poll frame. The STAs may receive data while continuously awake after receiving the beacon frame including the DTIM, and may switch back to the sleep state after the data reception is completed.

Frame structure general

10 is a diagram for explaining an example of a frame structure used in an IEEE 802.11 system.

The Physical Layer Protocol Data Unit (PPDU) frame format may include a Short Training Field (STF), a Long Training Field (LTF), a SIG (SIGNAL) field, and a Data field. The most basic (eg, non-HT) PPDU frame format may include only a legacy-STF (L-STF), a legacy-LTF (L-LTF), a SIG field, and a data field.

The STF is a signal for signal detection, automatic gain control (AGC), diversity selection, precise time synchronization, etc. The LTF is a signal for channel estimation, frequency error estimation, and the like. The STF and LTF may be referred to as a PLCP preamble, and the PLCP preamble may be referred to as a signal for synchronization and channel estimation of an OFDM physical layer.

The SIG field may include a RATE field and a LENGTH field. The RATE field may include information about modulation and coding rate of data. The LENGTH field may include information about the length of data. In addition, 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 of the SERVICE field may be used for synchronization of the descrambler at the receiving end. The PSDU corresponds to an MPDU (MAC Protocol Data Unit) 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 zero. The padding bit may be used to adjust the length of the data field in a predetermined unit.

The MPDU 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 may be composed of MPDUs and may be transmitted / received through the PSDU of the data portion 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 include control information required for frame transmission / reception. The duration / ID field may be set to a time for transmitting the corresponding frame.

The duration / ID field included in the MAC header may be set to 16 bits long (e.b., B0 to B15). The content included in the period / ID field may vary depending on the frame type and subtype, whether the content is transmitted during the CFP (contention free period), the QoS capability of the transmitting STA, and the like. (i) In the control frame of which the subtype is PS-Poll, the duration / ID field may include the AID of the transmitting STA (e.g., via 14 LSB bits) and the 2 MSB bits may be set to one. (ii) In frames transmitted during CFP by a point coordinator (PC) or a non-QoS STA, the period / ID field may be set to a fixed value (e.g., 32768). (iii) In other frames transmitted by the non-QoS STA or control frames transmitted by the QoS STA, the duration / ID field may include a duration value defined for each frame type. In a data frame or management frame transmitted by the QoS STA, the duration / ID field may include a duration value defined for each frame type. For example, when B15 = 0 of the duration / ID field indicates that the duration / ID field is used to indicate TXOP Duration, B0 to B14 may be used to indicate actual TXOP Duration. The actual TXOP Duration indicated by B0 to B14 may be any one of 0 to 32767, and its unit may be microseconds (us). However, when the duration / ID field indicates a fixed TXOP Duration value (e.g., 32768), B15 = 1 and B0 to B14 = 0 may be set. In addition, when B14 = 1 and B15 = 1, the period / ID field is used to indicate an AID, and B0 to B13 indicate one AID of 1 to 2007. For details of the Sequence Control, QoS Control, and HT Control subfields of the MAC header, refer to the IEEE 802.11 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 content of each subfield of the frame control field may refer to an IEEE 802.11 standard document.

11 illustrates a content free (CF) -END frame.

For convenience of explanation, it is assumed that a CF-END frame is transmitted by a non-directional multi-gigabit (11ad) STA. The CF-END frame may be sent to truncate the TXOP duration. Therefore, the duration field in the CF-END frame is set to zero. The RA (Receiver Address) field may be set to a broadcast group address. The BSSID field may be set to the address of the STA included in the AP. However, in the case of the CF-END frame of the non-HT or non-HT duplicate format transmitted by the VHT STA to the VHT AP, the Individual / Group bit of the BSSID field may be set to 1.

HE PPDU  Structure example

Hereinafter, examples of HE PPDU (High Efficiency Physical layer Protocol Data Unit) format in a WLAN system supporting 11ax will be described.

12-15 illustrate HE PPDUs.

The HE-SIG A field is located after the L-Part (e.g., L-STF, L-LTF, L-SIG) and, like the L-Part, is repeated in units of 20 MHz. HE-SIG A may be included in all HE PPDUs, while HE-SIG B may be omitted from SU PPDUs and UL trigger-based PPDUs (e.g., UL PPDUs transmitted based on trigger frames).

HE-SIG A includes common control information (e.g., BW, GI length, BSS Color, CRC, Tail, etc.) for STAs. The HE-SIG A field contains information for interpreting the HE PPDU, so the information contained in the HE-SIG A field may vary depending on the format of the HE PPDU (eg, SU PPDU, MU PPDU, or trigger-based PPDU). Can be.

For example, (i) in the HE SU PPDU format, the HE-SIG A field may include a DL / UL indicator, a HE PPDU format indicator, BSS Color, TXOP Duration, BW (bandwidth), MCS, CP + LTF length, coding information, stream It may include at least one of the number, STBC (eg, STBC use), transmission beamforming (TxBF) information, CRC, and Tail. In the case of the HE SU PPDU format, the HE-SIG B field may be omitted. (ii) In the HE MU PPDU format, the HE-SIG A field may include a DL / UL indicator, a BSS Color, a TXOP Duration, a bandwidth (BW), MCS information of the SIG B field, a symbol number of the SIG B field, and a HE LTF symbol number. It may include at least one of the full-band MU-MIMO use indicator, CP + LTF length, transmission beamforming (TxBF) information, CRC and Tail. (iii) In the HE trigger based PPDU format, the HE-SIG A field may include at least one of a format indicator (eg, SU PPDU or trigger based PPDU), BSS Color, TXOP Duration, BW, CRC, and Tail. have.

In addition to the above common control information, the HE-SIG A may include at least one of user allocation information, for example, an STA identifier such as a PAID or a GID, allocated resource information, and the number of streams (Nsts). have.

Meanwhile, the DL / UL indicator may be referred to as a UL flag for convenience. In more detail, the DL / UL indicator may correspond to the name of the subfield included in the HE-SIG-A field. The transmitter sets a DL / UL indicator included in the HE-SIG-A field using the TXVECTOR parameter UL FLAG, which is a physical layer parameter. For example, when the TXVECTOR parameter UL FLAG is a value (e.g., 0) corresponding to the DL, the transmitting STA / AP sets the DL / UL indicator to a value (e.g., 0) corresponding to the DL. If the TXVECTOR parameter UL FLAG is a value corresponding to UL (e.g., 1), the transmitting STA / AP sets the DL / UL indicator to a value corresponding to UL (e.g., 1). Meanwhile, the receiving STA receives the DL / UL indicator included in the HE-SIG-A field, and sets the RXVECTOR parameter UL FLAG based on this. If the DL / UL indicator included in the received frame corresponds to a DL value (e.g., 0), the receiving STA / AP sets the RXVECTOR parameter UL FLAG to a value corresponding to the DL (e.g., 0). If the DL / UL indicator included in the received frame has a value corresponding to UL (e.g., 1), the receiving STA / AP sets the RXVECTOR parameter UL FLAG to a value corresponding to UL (e.g., 1).

Similar to the TX or RXVECTOR parameter UL FLAG, there is also a TX or RXVECTOR parameter BSS Color and TXOP duration corresponding to the BSS Color and TXOP duration of the HE-SIG A field.

12 and 14 correspond to the SU format, and there is a difference in the length of the HE-SIG A field. The HE SU PPDU of FIG. 12 is 8 us, whereas the HE-SIG A field has a length of 16 us when referring to the HE ER (extended range) SU PPDU of FIG. 14. That is, it may be understood that the HE-SIG A field is repeated in the HE ER SU PPDU.

The BSS color information included in the HE-SIG A field is information for identifying the BSS and has a shorter length than the BSSID. For example, the BSSID has a length of 48 bits, whereas the BSS color information may have a length of 6 bits. The STA may determine whether it is an intra-BSS frame using BSS color information. That is, even if the STA decodes only the HE-SIG A field without having to decode the entire HE PPDU, the STA may distinguish between the intra BSS PPDU and the inter BSS PPDU through BSS color information.

HE-SIG B may be independently encoded for each 20MHz channel unit. The HE-SIG B encoded every 20 MHz channel units may be referred to as an HE-SIG-B content channel.

According to an embodiment, when the bandwidth is not greater than 20 MHz, one HE-SIG B content channel may be transmitted. If the bandwidth is greater than 20 MHz, the 20 MHz-sized channels may be the first HE-SIG B content channel (hereinafter referred to as HE-SIG B [1]) or the second HE-SIG B content channel (hereinafter referred to as HE-SIG B [ 2]) can be transmitted. For example, the HE-SIG B [1] and the HE-SIG B [2] may be alternately transmitted. The odd 20 MHz channel may transmit HE-SIG B [1] and the even 20 MHz channel may transmit HE-SIG B [2]. More specifically, for 40 MHz bandwidth, HE-SIG B [1] is transmitted on the first 20 MHz channel and HE-SIG B [2] is transmitted on the second 20 MHz channel. For 80 MHz bandwidth, HE-SIG B [1] is transmitted on the first 20 MHz channel, HE-SIG B [2] is transmitted on the second 20 MHz channel, and the same HE-SIG B [1] is transmitted on the third Repeated transmission on the 20 MHz channel, the same HE-SIG B [2] is repeated on the fourth 20 MHz channel. Similar transmission in the 160 MHz bandwidth.

Meanwhile, contents of the HE-SIG B [1] and the HE-SIG B [2] may be different. However, the HE-SIG-Bs [1] all have the same content. Likewise, HE-SIG B [2] all have the same content.

The HE-SIG B may include a common field and a user specific field. The common field may precede the user specific field. The common field and the user specific field may be distinguished in bit units, not in OFDM symbol units.

The common field of the HE-SIG B includes information on all of the STAs designated to receive the PPDU in the corresponding bandwidth. The common field may include resource unit (RU) allocation information. For example, when dividing four 20 MHz channels constituting 80 MHz into [LL, LR, RL, RR], a common block for LL and RL is included in a common field of HE-SIG B [1], and HE- A common block for LR and RR may be included in a common field of SIG B [2].

The user specific field of the HE-SIG B may include a plurality of user fields, and each user field may include information specific to an individual STA designated to receive a PPDU. For example, the user field may include, but is not limited to, at least one of a station ID, an MCS for each STA, a stream number (Nsts), a coding (e.g., an indication for using an LDPC), a DCM indicator, and transmission beamforming information.

UL MU transmission

16 illustrates an uplink multi-user transmission situation according to an embodiment of the present invention.

As described above, in the 802.11ax system, a UL MU transmission scheme may be used, which means that the AP transmits a trigger frame to a plurality of STAs (eg, STA 1 to STA 4) as illustrated in FIG. 16. Can be started by. The trigger frame may include UL MU allocation information. The UL MU allocation information may include, for example, at least one of resource location and size, STA IDs or receiving STA addresses, MCS, and MU type (MIMO, OFDMA, etc.). In more detail, the trigger frame may include at least one of (i) a duration for the UL MU frame, (ii) the number of allocations (N), and (iii) information of each allocation. The information of each allocation may include per user information. The information of each allocation is, for example, AID (in addition, in the case of MU, additionally included by the number of STAs), power adjustment, resource (or tone) allocation information (eg, bitmap), MCS, number of streams (Nsts), It may include at least one of information on STBC, coding, and transmission beamforming.

Meanwhile, as illustrated in FIG. 16, the AP may acquire a TXOP for transmitting a trigger frame through a competition process to access a medium. In this regard, the STAs may transmit the UL data frame in the format indicated by the AP after SIFS of the trigger frame. Correspondingly, it is assumed that an AP according to an embodiment of the present invention performs an acknowledgment on a UL MU data frame through a block ACK (BA) frame.

17 illustrates a trigger frame format according to an embodiment.

Referring to FIG. 17, a trigger frame includes a frame control field, a duration field, a recipient STA address field, a transmitting STA address field, a common information field, and one or two. It may include at least one of the above Per User Info fields and the Frame Check Sum (FCS). The RA field indicates an address or ID of a receiving STA and may be omitted according to an embodiment. The TA field indicates the address of the transmitting STA.

The common information field may include a length subfield, a cascade indication, a HE-SIG A information subfield, a CP / LTF type subfield, a trigger type subfield, and a trigger-dependent common information. Common Info) may include at least one of the subfields. The length subfield indicates the L-SIG length of the UL MU PPDU. The cascade indicator indicates whether there is a transmission of a subsequent trigger frame after the current trigger frame. The HE-SIG A information subfield indicates content included in HE-SIG A of the UL MU PPDU. The CP / LTF type subfield indicates the CP and the HE LTF type included in the UL MU PPDU. The trigger type subfield indicates the type of trigger frame. The trigger frame may include type-specific common information and type-specific individual user information (Per User Info). The trigger type may include, for example, a basic trigger type (eg, type 0), a beamforming report poll trigger type (eg, type 1), and a multi-user block ack request (MU-BAR) type (eg, Type 2) or multi-user ready to send (MU-RTS) type (eg, type 3) may be set, but is not limited thereto. When the trigger type is MU-BAR, the trigger dependent common information subfield may include a GCR (Groupcast with Retries) indicator and a GCR address.

The Per User Info field includes a user identifier subfield, a resource unit (RU) allocation subfield, a coding type subfield, an MCS field, a dual sub-carrier modulation (DCM) subfield, and a spatial stream (SS) assignment. It may include at least one of a subfield and a trigger dependent per user info subfield. The user identifier subfield indicates the AID of the STA that will use the corresponding resource unit in order to transmit the MPDU of the UL MU PPDU. The RU allocation subfield indicates a resource unit for transmitting the UL MU PPDU by the corresponding STA. The coding type subfield indicates the coding type of the UL MU PPDU transmitted by the corresponding STA. The MCS subfield indicates the MCS of the UL MU PPDU transmitted by the corresponding STA. The DCM subfield indicates information about dual carrier modulation of the UL MU PPDU transmitted by the corresponding STA. The SS assignment subfield indicates information about spatial streams of the UL MU PPDU transmitted by the corresponding STA. If the trigger type is MU-BAR, the trigger dependent individual user information subfield may include BAR control and BAR information.

HT Control field

The MAC header includes an HT Control field. The HT Control field may be set in various formats. For example, it may be set to one of the HT variant, the VHT variant, and the HE variant. Table 1 shows the settings of the HT Control field for each format.

TABLE 1

The VHT Control Middle subfield included in the VHT Variant HT Control field may include MRQ, MSI / STBC, MFSI / GID-L, MFB, GID-H, Coding Type, FB Tx Type, and Unsolicited MFB.

The Aggregated Control subfield included in the HE Variant HT Control field may include a plurality of control subfields and padding bits. Each control subfield includes a 4-bit control ID and control information. The control ID indicates the type of information included in the control information and the length of the control information.

Control ID = 0 means UL MU response scheduling. If control ID = 0 is set, the control information includes scheduling information for the HE trigger based PPDU carrying an immediate acknowledgment. Here, the immediate response may be transmitted as a response to the requesting A-MPDU (A-MPDU). In addition, the control information may include UL PPDU length and RU allocation information.

Control ID = 1 means Receive operation mode indication. In this case, the control information includes control information regarding the reception operation mode of the STA transmitting the frame including the information. The control information may include a maximum number of spatial streams that the STA can receive and operating channel width information supported by the STA in reception.

Control ID = 2 means HE link adaptation. At this time, the control information may include information on the number of preferred spatial streams and MCS index for link adaptation.

NAV (network allocation vector)

The NAV may be understood as a kind of timer for protecting a transmitting STA (e.g., TXOP holder) TXOP. The STA may protect the TXOP of another STA by not performing channel access while the NAV configured for the STA is valid.

Currently, a non-DMG STA supports one NAV. Receiving a valid frame, the STA may update the NAV through a duration field (e.g., a duration field of the MAC header) of the PSDU. However, if the RA field of the received frame matches the MAC address of the STA, the STA does not update the NAV. If the duration indicated by the duration field of the received frame is greater than the current NAV value of the STA, the STA updates the NAV through the duration of the received frame.

18 shows an example of NAV settings.

Referring to FIG. 18, a source STA transmits an RTS frame and a destination transmits a CTS frame. As described above, the destination STA designated as the receiver through the RTS frame does not set the NAV. Some of the remaining STAs may receive the RTS frame to set up the NAV, and others may receive the CTS frame to set up the NAV.

If the CTS frame (eg, PHY-RXSTART.indication primitive) is not received within a certain period from the time when the RTS frame is received (eg, when the MAC receives the PHY-RXEND.indication primitive corresponding to the RTS frame), the RTS STAs that set or update the NAV through the frame may reset (eg, 0) the NAV. The period of time may be (2 * aSIFSTime + CTS_Time + aRxPHYStartDelay + 2 * aSlotTime). The CTS_Time may be calculated based on the length and data rate of the CTS frame indicated by the RTS frame.

In FIG. 18, for convenience, the NAV is set or updated through an RTS frame or a CTS frame. However, the NAV setting / resetting / update is performed by other various frames such as non-HT PPDU, HT PPDU, VHT PPDU, or HE PPDU. It may be performed based on a duration field (eg, a duration field in the MAC header of the MAC frame). For example, if the RA field in the received MAC frame does not match its address (e.g., MAC address), the STA may set / reset / update the NAV.

19 shows an example of TXOP truncation.

The TXOP holder STA may truncate the TXOP by transmitting a CF-END frame. The STA receiving the CF-END frame or the CF-END + CF-ACK frame may reset (e.g., 0) the NAV.

When the STA, which has obtained channel access through the EDCA, has emptied its transmission queue, it may transmit a CF-END frame. The STA may explicitly indicate the completion of its TXOP through the transmission of the CF-END frame. The CF-END frame can be transmitted by the TXOP holder. Non-AP STAs other than the TXOP holder cannot transmit CF-END frames. The STA receiving the CF-END frame resets the NAV at the end of the PPDU including the CF-END frame.

Referring to FIG. 19, an STA accessing a medium through EDCA transmits a sequence (e.g., RTS / CTS, etc.) for NAV configuration.

After SIFS, the TXOP holder (or TXOP initiator) and the TXOP responder send and receive PPDUs (e.g., initiator sequence). The TXOP holder truncates the TXOP by sending a CF-END frame when there is no more data to transmit within the TXOP limit.

Upon receiving the CF-END frame, the STAs can reset their NAV and start contending for media access without further delay.

As described above, in the current WLAN system, the TXOP duration is set through the Duration field of the MAC header. That is, the TXOP holder (e.g., Tx STA) and the TXOP Responder (e.g., Rx STA) transmit all the TXOP information necessary for the transmission and reception of frames in the Duration field of frames transmitted and received therebetween. Third party STAs (ie, third party STAs) that are not TXOP holders or TXOP Responders check the Duration field of frames exchanged between the TXOP holder and the TXOP Responder and defer channel usage until the NAV period by setting / updating the NAV. .

TXOP Duration of HE-SIG A

In an 11ax system supporting HE PPDU, if the UL MU PPDU does not include the HE-SIG B, the third STAs cannot decode the MPDU included in the UL MU PPDU even if the UL MU PPDU is received. If the third STAs cannot decode the MPDU, the third STAs cannot obtain TXOP Duration information (e.g., Duration field) included in the MAC header of the MPDU. Therefore, there is a problem that NAV setting / update is difficult to be performed correctly.

Even if the HE PPDU frame including the HE-SIG B is received, if the HE-SIG B structure is coded differently for each STA, and the HE-SIG B structure is designed such that the STAs can read only the HE-SIG B contents allocated thereto, The third STAs cannot decode MAC frames transmitted and received by other STAs (eg, MPDUs of other STAs in the HE PPDU). Therefore, even in this case, there is a problem that the third STAs cannot obtain TXOP information.

In order to solve such a problem, a method for transmitting an STA by including TXOP duration information in the HE-SIG A is proposed. As described above, 15 bits (e.g., B0 to 14) of the duration field of the MAC header may indicate duration information and may indicate a maximum of about 32.7 ms (0 to 32767 us). If the 15-bit duration information included in the duration field of the MAC header is transmitted to HE-SIG A as it is, the 11ax third party STA may correctly set / update NAV, but signaling over HE-SIG A There is a problem that the head is excessively increased. Although 15 bits are relatively small in the MPDU for payload transmission in the MAC layer, 15 bits in HE-SIG A are used because HE-SIG A is a compactly designed field for transmitting common control information in the physical layer. The increase of corresponds to a relatively large signaling overhead.

Therefore, an efficient indication method of TXOP duration that minimizes the overhead of HE-SIG A is proposed. In addition, a frame transmission / reception operation based on a newly defined TXOP duration in HE-SIG A is proposed. Hereinafter, the included duration field of the MAC header may be referred to as MAC duration for convenience.

The value set in the NAV of the third STA may be interpreted as the TXOP Duration for the TXOP holder / Responder. For example, the Duration field value means TXOP for frame transmission / reception from the viewpoint of the TXOP holder / Responder, or NAV value from the viewpoint of the third STA. Therefore, since the operation of setting / updating the NAV by the third STAs sets the NAV as much as the TXOP of the TXOP holder / Responder, the operation of setting / updating the NAV by the third STAs is referred to as setting / updating the TXOP for convenience. May be Further, the term TXOP Duration may be referred to simply as Duration or may be referred to simply as TXOP. TXOP Duration may optionally be used to refer to a field (e.g., TXOP Duration field in HE-SIG A) within a frame or may refer to an actual TXOP Duration value.

The TXOP duration field is a total of 7 bits (B0 to B6), and B0 to B6 are interpreted as follows.

If the TXOP duration field is 127 (i.e., B0 to B6 are all 1s), the TXOP duration field does not indicate a valid duration value, and therefore the TXOP duration field is not used for NAV update. The TXOP duration value 127 may be referred to as "UNSPECIFIED" because it does not specify a duration.

If the TXOP duration field is not 127, B0 in the TXOP duration field indicates whether the granularity of the duration is 8 us or 128 us. That is, 8 us or 128 us greater than 1 us is used to represent the duration in bits (i.e., 7 bits) less than the MAC duration of 15 bits and 1 us granularity. If B0 = 0, then duration = 8 us * (value of B1 ~ B6) us. If B0 = 1, then duration = 512 + 128 us * (value of B1 ~ B6) us. The maximum TXOP duration value that can be represented by the TXOP duration field may be limited to 8 ms.

NAV update and TXOP Truncation

First, the advantage of using two granularities 8 us and 128 us is explained in comparison with the case where 64 us is used as one granularity.

20 shows an example of SU PPDU transmission and MU PPDU transmission. In FIG. 20, (a) corresponds to SU PPDU transmission, and (b) corresponds to MU PPDU transmission. For convenience of description, a case where 64 us is supported as one granularity is referred to as Option 1, and a case where 8 and 128 us are supported as two granularities is referred to as Option 2.

Referring to FIG. 20, it can be seen that less TXOP over protection occurs in Option 2 than in Option 1. FIG. Therefore, using the smallest possible particle size for the SU / DL MU procedure is more efficient than using the larger particle size.

21 shows an example of UL MU transmission. As in FIG. 20, less TXOP transient protection occurs in option 2 than in option 1. FIG. Therefore, even in the UL MU procedure, using the smallest possible granularity for small packets is more efficient than using the larger granularity.

FIG. 22 is a diagram for explaining TXOP transient protection occurring in a cascade procedure and TXOP truncation for solving the TXOP transient.

Referring to FIG. 22A, when the AP transmits a DL MU PPDU including a trigger frame, the STAs transmit data through the UL MU PPDU in response. Thereafter, the AP transmits a DL MU BA for data reception. At this time, although there is a difference in length between option 1/2, both option 1/2 causes TXOP transient protection.

Referring to (b) of FIG. 22, when the AP transmits DL MU BA, which is the last PPDU in the TXOP, the AP sets the TXOP duration to a special value (e.g., 0). In this case, the special value is a value for cutting the remaining TXOP duration, and the 3rd party STA sets the NAV to zero. By default, NAV update is performed when the TXOP duration value is greater than the current NAV value, except when TXOP duration = 0, the NAV is reset to zero regardless of the current NAV value.

Through this, the problem of TXOP transient protection can be solved.

23 shows an SU procedure and a DL MU procedure for exchanging multiple frames. In FIG. 23, the SU procedure and the MU procedure are shown together for convenience. Those skilled in the art will appreciate that SU PPDU and ACK BA are used in the SU procedure, and DL MU PPDU and UL MU BA are used in the DL MU procedure.

FIG. 23A illustrates a case in which the TXOP duration value of the last frame is set to 0, as described above, and FIG. 23B illustrates the TXOP duration value of the last frame as 0, and the 3rd party STA is set to 0. FIG. The case where the granularity of the last NAV update is taken into account when updating the NAV is shown.

According to an embodiment of the present invention, when the previous NAV is updated to a TXOP duration based on a particle size of 128 us, and the granularity of the TXOP duration of the currently received frame is 8 us, the 3rd party STA may transmit the TXOP duration of the currently received frame. Even if the value is smaller than the NAV value, the NAV is updated with the TXOP duration value of the currently received frame. That is, since the TXOP duration value represented by 8 us is more accurate than the TXOP duration represented by 128 us, the STA updates the NAV through the corresponding TXOP duration when a TXOP duration value having a smaller particle size is detected.

Meanwhile, according to the 11ax system, an HE STA (e.g., non-AP STA or AP STA) may maintain two NAV timers. In virtual carrier sensing (CS), it is determined that the medium is idle when both NAV timers are zero. That is, if any NAV timer is a non-zero value, it is determined that the medium is busy.

Two NAVs may include intra-BSS NAV and basic NAV. The primary NAV may be referred to as regular NAV, OBSS NAV or inter-BSS NAV. The third party STA updates the intra-BSS NAV when it wants to update the NAV through an intra BSS PPDU, that is, a PPDU received from the same BSS as the BSS to which it belongs. Here, the update is not limited to updating to increase the NAV value, and may include initial setting or reset of the NAV.

When the 3rd party STA receives a PPDU that cannot be determined as an overlapping BSS (OBSS) PPDU or an intra-BSS PPDU, the base NAV is updated.

In order to determine whether the corresponding PPDU is an intra-BSS PPDU, BSS Color information of the PPDU may be used.

When both the TXOP duration of the HE-SIG A and the duration of the MAC header are obtained, the duration value of the MAC header with higher accuracy is used for updating the NAV. That is, it can be understood that the MAC duration has a high priority in the TXOP duration coverage of HE-SIG A. On the other hand, when the TXOP duration is all 1, NAV update is not performed with the corresponding 127 value.

When the above-described NAV update rule is applied, a method of updating two NAVs is described as follows.

The intra-BSS NAV is valid (ie, the NAV value is greater than 0), the intra-BSS NAV is updated based on a large unit (ie, 128 us), and the unit of the TXOP duration of the received intra-BSS PPDU is small ( ie, 8 us), the STA updates the intra-BSS NAV with the TXOP duration value of the received intra-BSS PPDU.

The regular NAV is valid (ie, the NAV value is greater than 0), the regular NAV is updated based on a large unit (ie, 128 us), and the unit has a small TXOP duration of the received inter-BSS PPDU (ie, 8 us). ), The STA updates the regular NAV with the TXOP duration value of the received inter-BSS PPDU. The same regular NAV update rule may be applied to a PPDU that cannot be determined as an intra BSS PPDU.

The NAV update scheme described in FIG. 23 may be equally applied to the UL MU procedure. 24 illustrates a NAV update scheme in the UL MU procedure. In FIG. 24 (a), the NAV is updated only with the 128 us based TXOP duration. Referring to FIG. 24 (b), the NAV is updated with the 8us based TXOP duration even if the 8us based TXOP duration is smaller than the NAV value. .

25 illustrates an example of over-protection of TXOP duration.

Referring to FIG. 25, an AP (e.g., TXOP holder) transmits a DL MU PPDU frame. The HE-SIG A field of the DL MU PPDU frame includes a TXOP field, and the MAC header field of the DL MU PPDU frame includes a Duration field. STAs designated as recipients of the DL MU PPDU frame (e.g., TXOP responder) transmit the UL MU BA frame within the TXOP duration as a response to receiving the DL MU PPDU frame. Thereafter, it is assumed that there is no additional frame transmission between the AP (e.g., TXOP holder) and the STAs (e.g., TXOP responder) (e.g., TXOP termination).

The third party STA cannot decode the MAC header and therefore configures / updates the NAV through the TXOP Duration field of the HE-SIG A field. The third party STA configures NAV as the TXOP Duration field value of the HE-SIG A field included in the DL MU PPDU frame transmitted by the AP. Here, since the NAV value set by the TXOP Duration field of the HE-SIG A field is larger than the MAC duration, over protection is generated by the difference between the two. The third party STA cannot access the channel during the time corresponding to over protection.

To solve this problem, information for truncation of the TXOP may be transmitted.

26 illustrates TXOP truncation according to an embodiment of the present invention. For example, FIG. 26 is a method for solving the over protection problem illustrated in FIG. 25, and a description overlapping with FIG. 25 will be omitted.

According to this example, when the STA receives a PPDU in which the TXOP duration of the HE-SIG A field is set to a specific value (e.g., 0), the STA resets the corresponding NAV. In this case, the corresponding NAV may be an Intra-BSS NAV or an Inter-BSS NAV according to the BSS color of the received PPDU. For example, when an Intra-BSS PPDU having a TXOP duration of a specific value is received, the STA resets the Intra-BSS NAV. Unlike this, when the STA receives an OBSS PPDU having a TXOP duration of a specific value or a PPDU that cannot identify whether it is an Intra-BSS PPDU or an OBSS PPDU, the Inter-BSS NAV is reset.

Referring to FIG. 26, TXOP duration = 0 of a HE-SIG A field of an UL MU BA frame (e.g., the last frame transmitted in TXOP) is set. TXOP duration = 0 may mean truncation of the corresponding TXOP.

The third party STA obtains the value of the TXOP duration field by decoding the HE-SIG A field of the UL MU BA frame. The third party STA determines that TXOP duration = 0, and resets the currently set NAV (e.g., set through the DL MU PPDU frame) (e.g., sets NAV to 0).

According to the existing NAV management operation, the STA does not perform NAV update or reset when the currently set NAV is equal to or greater than the received TXOP duration value. However, according to the present embodiment, when TXOP duration = 0, the STA resets the NAV even if the currently set NAV is greater than zero. Thus, the time corresponding to transient protection can be efficiently removed from the TXOP duration.

In FIG. 26, it is assumed that the TXOP duration of HE-SIG A is set to a value calculated by the MAC duration. For example, if the MAC duration is zero, the STA / AP sets the TXOP duration to zero. In addition, the STA / AP may set the TXOP duration to 0 even when the MAC duration is less than the threshold (e.g., TXOP truncation threshold). The TXOP truncation threshold may be, for example, IFS (e.g., AIFS, DIFS, PIFS, etc.) or may be an estimated length of time for a CF-END frame transmitted using MCS 0, but is not limited thereto.

27 illustrates TXOP truncation according to another embodiment of the present invention.

Referring to FIG. 27, when the AP transmits a trigger frame, the third party STA configures NAV based on the trigger frame.

Thereafter, the STA allocated the resource through the trigger frame transmits a UL MU PPDU. In this case, it is assumed that the TXOP duration of the UL MU PPDU is x and the TXOP duration is greater than the MAC duration.

The third party STA updates the NAV with the TXOP duration value x included in the UL MU PPDU.

When the AP receives the UL MU PPDU, the AP transmits an OFDMA Block Ack / M-BA frame. At this time, when transmitting a BA / M-BA based on the OFDMA PPDU, the AP may set the TXOP duration value of the HE-SIG A field of the corresponding PPDU to 0 in order to cut the remaining TXOP duration.

The third party STA that receives the BA / M-BA frame resets the NAV.

28 illustrates TXOP truncation according to another embodiment of the present invention.

Referring to FIG. 28 centering on a difference from FIG. 27, the AP may indicate TXOP truncation using a CF-END frame instead of a BA / M-BA frame. The AP may truncation the remaining TXOP by transmitting the CF-END frame immediately after transmitting the BA / M-BA frame. The third party STA may receive the CF-END frame and reset the corresponding NAV.

Meanwhile, in addition to the TXOP truncation method using the TXOP duration field of the HE-SIG A field, the TXOP truncation method using the MAC duration value of the MAC frame may be used. For example, the HE STA may reset the corresponding NAV when receiving a MAC frame having a Duration value set to 0. That is, if a MAC frame having a Duration value set to 0 is received and the frame is an intra-BSS frame (i.e., BSSID matches the RA or TA field of the MAC header), the STA resets the intra-BSS NAV. If a MAC frame with a Duration value set to 0 is received and the frame is an inter-BSS frame (i.e., BSSID does not match the RA or TA field of the MAC header), the STA resets the inter-BSS NAV.

29 shows an example of TXOP truncation using the TXOP duration field. Descriptions overlapping with the above are omitted.

Referring to FIG. 29, the TXOP duration of the DL MU PPDU is set to 128 us which is a large unit, and the TXOP duration of the UL MU PPDU is set to 8 us which is a small unit. The TXOP duration of the DL MU BA is set to a special value (e.g., 0 or 127) indicating that the corresponding PPDU is the last PPDU in the TXOP.

The 3rd party STA resets the NAV based on the TXOP duration indicating that the corresponding PPDU is the last PPDU in the TXOP.

Meanwhile, the information indicating the TXOP truncation may indicate causing / invoking an EIFS operation of a 3rd party STA. Information indicating that causing TXOP truncation and EIFS operations may be included in the HE-SIG A field. A new field may be defined in the HE-SIG A field to indicate TXOP truncation and EIFS behavior, or special values (eg, 0 (all 0s), 127 (all 1s), or 126, etc.) in the TXOP duration field. You may.

For example, if the TXOP duration (or MAC duration) of the HE-SIG A field is set to a special value, the 3rd party STA may truncate (i.e., reset the corresponding NAV) the TXOP after a certain period. The period of time may be EIFS. EIFS = aSIFSTime + AckTxTime + DIFS (or AIFS [AC]).

As another example, when the TXOP duration (or MAC duration) of the HE-SIG A field is set to a special value, the 3rd party STA may truncate the TXOP (i.e., reset the corresponding NAV) and perform an EIFS operation. Accordingly, the 3rd party STA may transmit the frame if the channel is idle during the EIFS and backoff periods.

If the intended STA receives a frame in which the TXOP duration (or MAC duration) of HE-SIG A is set to a special value (eg, 0, 126, or 127, etc.), the STA is currently present for TXOP truncation. And TXOP of HE-SIG A of the last PPDU to a special value (eg, 0).

30 shows another example of TXOP truncation.

Referring to FIG. 30, the TXOP of the soliciting HE PPDU requesting the last PPDU is set to a special value (e.g., 126 or other possible special value). This is advantageous for including an ACK frame (e.g., ACK / BA / M-MA, etc.) in the last PPDU.

When the HE PPDU including the TXOP set to the special value is received, the third party STA starts the EIFS operation after truncating the TXOP.

When a HE PPDU containing a TXOP set to a special value is received, an intended STA (e.g., a STA whose RA or TA matches its address) sets the TXOP of the last PPDU to a special value to cause TXOP truncation.

31 shows another example of over-protection of TXOP duration. In the case of FIG. 25, the AP corresponds to a procedure for transmitting a DL MU PPDU. In FIG. 31, the AP corresponds to a procedure for scheduling transmission of a UL MU PPDU through a trigger frame.

Referring to FIG. 31, a trigger frame for allocating a resource for transmitting a UL MU PPDU is transmitted. The third party STA updates the NAV using the MAC duration indicated by the trigger frame.

Thereafter, the STA allocated the resource through the trigger frame transmits a UL MU PPDU.

In this case, the TXOP duration indicated in the HE-SIG A field of the UL MU PPDU may be set larger than the MAC duration indicated in the trigger frame. Therefore, when the third party STA updates the NAV using the TXOP duration indicated in the HE-SIG A field of the UL MU PPDU, a transient protection problem occurs.

32 illustrates a NAV update method according to an embodiment of the present invention. 32 corresponds to an example for solving the transient protection problem illustrated in FIG. 31. The overlapping description with that described in FIG. 31 is omitted.

Referring to FIG. 32, if the current NAV is updated by the MAC duration of intra-BSS frame 1, the STA does not acquire the MAC duration of the currently received intra-BSS frame 2 and the TXOP duration of the HE-SIG A field If only a value is obtained, the STA does not update the NAV to the TXOP duration of intra-BSS frame 2 even if the TXOP duration of intra-BSS frame 2 is greater than the current NAV value.

33 illustrates NAV extensions that may occur in multiple frame exchanges.

In the existing NAV updating scheme, the NAV is updated when the duration (i.e., MAC duration) indicated by the received frame is larger than the current NAV value.

On the other hand, as shown in Figure 33, if the TXOP duration of the frame except the first frame in the multi-frame exchange is calculated using the TXOP duration of the previous frame, the use of granularity greater than 1 us causes NAV extension (extension) do.

For example, the TXOP duration of the HE-SIG A field in the first frame MU PPDU 1 is calculated using the MAC duration. The STA receiving the MU PPDU 1 transmits the M-BA 1, and the STA uses the TXOP duration field of the HE-SIG A field of the MU PPDU 1 to indicate the TXOP duration (M) to be set in the HE-SIG A field of the M-BA 1. eg, residual TXOP). At this time, the granularity used in the TXOP duration field is larger than 1 us, and a value larger than the actual TXOP may be set in the TXOP duration field of the HE-SIG A field of M-BA 1 according to the constraint of granularity. A similar process can be repeated several times in multiple frame exchanges, causing unwanted NAV extensions.

34 is a view illustrating setting a TXOP duration value according to an embodiment of the present invention.

The scheme of FIG. 34 may be used to solve the NAV extension problem of FIG.

According to the scheme of FIG. 34, when a MAC duration is included in the current frame, the STA calculates / sets a TXOP duration value of the current frame using the MAC duration of the current frame.

If the current frame does not include the MAC duration (eg, PS-Poll frame, etc.), and the previous frame received before SIFS from the present includes the MAC duration, the STA uses the MAC duration of the previous frame to present the current frame. Calculate / set the TXOP duration value of a frame.

According to this approach, the NAV extension occurs with less than 1 granularity. For example, if a granularity of 256 us is used in the TXOP duration field of the HE-SIG A field, the length of the extended NAV occurs within 256 us.

If the current frame does not include the MAC duration, and the previous frame received before SIFS also does not include the MAC duration, if the previous frame includes the TXOP duration of the HE-SIG A field, the STA transmits the TXOP of the previous frame. Calculate / set the TXOP duration value of the current frame using the duration.

35 illustrates an NAV update method based on an Intra-BSS HE PPDU according to an embodiment of the present invention.

According to this example, if (i) the current NAV is updated by the TXOP duration of the Intra-BSS HE PPDU or the current Intra-BSS NAV is valid (ie, the NAV value is greater than zero), ii) when an STA receives an unintended Intra-BSS HE PPDU (eg, an Intra-BSS HE PPDU whose RA does not match the STA's MAC address), and (iii) the TXOP duration value of the received Intra-BSS HE PPDU. If the STA is smaller than the current NAV value (eg, Intra-BSS NAV), the STA updates the NAV (eg, Intra-BSS NAV) using the TXOP duration value of the received Intra-BSS HE PPDU.

Referring to FIG. 35, the AP sequentially transmits N MU PPDUs. At this time, the TXOP duration indicated by the i-th MU PPDU is set to be shorter than the TXOP duration indicated by the i-1 th MU PPDU.

The third party STA first sets the NAV to the first TXOP duration value indicated by the 1st MU PPDU, after which the third party STA receives the 2nd MU PPDU and sets the NAV to the second TXOP duration value indicated by the 2nd MU PPDU. Update. By repeating a similar process, the third party STA updates the NAV with the Nth TXOP duration value indicated by the Nth MU PPDU. Therefore, the size of the NAV set in the third party STA gradually decreases.

36 is a view illustrating an NAV update method based on Intra-BSS HE PPDU according to another embodiment of the present invention.

According to this example, if (i) the current NAV is updated by the TXOP duration of the Intra-BSS HE PPDU or the current Intra-BSS NAV is valid (ie, the NAV value is greater than zero), ii) when an STA receives an unintended Intra-BSS HE PPDU (eg, an Intra-BSS HE PPDU whose RA does not match the STA's MAC address), and (iii) the TXOP duration value of the received Intra-BSS HE PPDU. And when the granularity is smaller than the current NAV value of the STA (eg, Intra-BSS NAV) and the granularity of the NAV, the STA uses the TXOP duration value of the received Intra-BSS HE PPDU to determine the NAV (eg, Intra-BSS NAV). Update

Referring to FIG. 36, similar to FIG. 35, the AP sequentially transmits N MU PPDUs. At this time, the TXOP duration indicated by the i-th MU PPDU is set to be shorter than the TXOP duration indicated by the i-1 th MU PPDU. However, it is assumed that the granularity of the TXOP duration of the 2 to N-1 th MU PPDUs is not smaller than the granularity of the TXOP duration of the 1st MU PPDU. In addition, it is assumed that the granularity of the TXOP duration of the N-th MU PPDU is smaller than the granularity of the TXOP duration of the 1st MU PPDU.

The third party STA first sets the NAV to the first TXOP duration value indicated by the 1st MU PPDU, after which the third party STA receives the 2 to N-1 th MU PPDUs, but the granularity is not smaller than the granularity of the current NAV. Do not update the NAV. Thereafter, the third party STA updates the NAV with an Nth TXOP duration value indicated by the Nth MU PPDU. Therefore, the size of the NAV set in the third party STA can be shortened by receiving the last MU PPDU.

The above-described NAV update method may be applied to NAV update by inter-BSS HE PPDU.

For example, if (i) the current NAV is updated by the TXOP duration of the Inter-BSS HE PPDU or the current Inter-BSS NAV is valid (ie, the NAV value is greater than zero), and (ii) When an unintended Inter-BSS HE PPDU is received at the STA, and (iii) if the TXOP duration value of the received Inter-BSS HE PPDU is smaller than the current NAV value of the STA (eg, Inter-BSS NAV), the STA is received. The NAV (eg, Inter-BSS NAV) is updated using the TXOP duration value of the Inter-BSS HE PPDU.

In another example, if (i) the current NAV is updated by the TXOP duration of the Inter-BSS HE PPDU or the current Inter-BSS NAV is valid (ie, the NAV value is greater than zero), and (ii) When an unintended Inter-BSS HE PPDU is received at the STA, (iii) the TXOP duration value and granularity of the received Inter-BSS HE PPDU are respectively greater than the STA's current NAV value (eg, Inter-BSS NAV) and granularity of NAV. If small, the STA updates the NAV (eg, Inter-BSS NAV) using the TXOP duration value of the received Inter-BSS HE PPDU.

Meanwhile, if the MAC Duration information is received after the NAV is updated by the TXOP duration field of HE-SIG A, the 3rd party STA updates the NAV with the received MAC Duration information, even if the received MAC Duration is smaller than the current NAV. You may. Specifically, the STA maintaining the Two NAVs updates the Intra-BSS NAV when receiving the MAC duration of the Intra-BSS PPDU. When the STA receives the MAC Duration of the Inter-BSS PPDU, the Regular NAV may be updated by the Inter-BSS PPDU, and may be updated to the MAC Duration information only when the BSS information matches.

37 and 38 are diagrams for explaining a NAV update method and a TXOP duration setting, respectively, according to an embodiment of the present invention. FIG. 37 is described from the perspective of the 3rd party STA updating the NAV timer, and FIG. 38 is described from the perspective of the TXOP holder or responder STA setting the TXOP duration field. 37 and 38 are separately shown for convenience of description, it will be understood by those skilled in the art that both are related to transmitting and receiving the same frame. In FIG. 37 and / or FIG. 38, the STA is not necessarily limited to the non-AP STA and may be implemented as an AP STA. Descriptions overlapping with the above are omitted.

Referring to FIG. 37, an STA corresponding to a 3rd party detects a first frame including a transmission opportunity duration field (3705).

The STA updates the NAV timer it maintains based on the TXOP period field of the first frame to protect the TXOP of another STA. Thereafter, when the NAV timer is 0, the STA performs channel access for frame transmission of the STA.

Looking at the NAV timer update process of the STA in more detail, the STA determines whether the TXOP period field of the first frame is a special value (e.g., 0 or 126, etc.) (3710). For example, the TXOP period field may correspond to 7-bits included in the signal field of the first frame, and the special value may correspond to a value in which all 7-bits are filled with zeros or may correspond to decimal 126.

If the TXOP period field of the first frame is a special value, the STA resets the NAV timer (3730). If the TXOP period field is a special value, the STA resets the NAV timer to 0 under the assumption that the first frame is the last frame transmitted in the TXOP of another STA, and performs the channel access based on an extended inter-frame space (EIFS) operation. Can be done. For example, if the TXOP period field is a special value, the STA may reset the NAV timer to 0 after waiting for the EIFS period. Or, if the TXOP period field is a specific value, after resetting the NAV, the STA may confirm that the channel is idle for the sum of the EIFS period and the backoff period and transmit its frame.

Meanwhile, when the TXOP period field of the first frame indicates a valid TXOP period instead of a special value, the STA compares the time unit used in the TXOP period field with the time unit used in the last NAV update (3715).

If the TXOP period field of the first frame indicates a valid TXOP period in units of 128 us (3715), and a previous update of the NAV timer is performed in units of 128 us, the current value of the NAV timer is smaller than the indicated valid TXOP period. NAV update may only be performed (3720, 3735).

In contrast, if the TXOP period field of the first frame indicates the valid TXOP period in 8 us units (3715), and if a previous update of the NAV timer was performed in 128 us units, the indicated valid value is independent of the current value of the NAV timer. The NAV update may be performed in the TXOP period (3735).

Next, referring to FIG. 38, the STA corresponding to the TXOP holder / responder sets a TXOP period value to be protected in the first TXOP duration field of the first frame (3805).

The STA transmits a first frame (3810).

The STA determines whether the second frame is the last frame (3815), and sets the second TXOP period field to be included in the second frame (3820, 3830) according to the result.

If the second frame is the last frame transmitted in the TXOP of the STA, the STA truncates the remaining TXOP by setting the second TXOP period field to a special value instead of a valid TXOP period (3820).

The special value may be a value for invoking an extended inter-frame space (EIFS) operation of a third party STA.

The second TXOP period field may correspond to 7-bits included in the signal field of the second frame, and the special value may correspond to a value in which all 7-bits are filled with 0 or decimal 126.

For example, when the second TXOP period field is a special value, the remaining TXOP may be truncated after the EIFS period. As another example, when the second TXOP period field is a special value, the third STA may transmit a frame after confirming that the channel is idle for a period of adding up the EIFS period and the backoff period after the remaining TXOP is truncated. have.

Thereafter, the STA transmits a second frame including the second TXOP period field (3825).

On the other hand, if the second frame is not the last frame, the STA sets the second TXOP period field of the second frame to a valid TXOP period value (3830). For example, when the second frame is a frame immediately before the last frame transmitted within the TXOP of the STA, the STA may include a second time unit (eg, 128 us) smaller than the first time unit (eg, 128 us) used in the first frame. 8 us), the second TXOP period field may be set as a valid TXOP period.

39 is a view for explaining an apparatus for implementing the method as described above.

The wireless device 800 of FIG. 39 may correspond to a specific STA of the above description, and the wireless device 850 may correspond to an AP of the above-described description.

The STA 800 may include a processor 810, a memory 820, a transceiver 830, and the AP 850 may include a processor 860, a memory 870, and a transceiver 880. The transceivers 830 and 880 may transmit / receive wireless signals and may be executed at a physical layer, such as IEEE 802.11 / 3GPP. Processors 810 and 860 run at the physical and / or MAC layers and are coupled to transceivers 830 and 880. Processors 810 and 860 may perform the aforementioned UL MU scheduling procedure.

Processors 810 and 860 and / or transceivers 830 and 880 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits and / or data processors. The memories 820 and 870 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media and / or other storage units. When an embodiment is executed by software, the method described above can be executed as a module (eg, process, function) that performs the functions described above. The module may be stored in the memory 820, 870 and executed by the processors 810, 860. The memories 820 and 870 may be disposed inside or outside the processes 810 and 860 and may be connected to the processes 810 and 860 by well-known means.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will understand that the present invention can be variously modified and changed from the above description. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention can be applied to various wireless communication systems including IEEE 802.11.

Claims (12)

1. A method for updating a network allocation vector (NAV) timer by a station (STA) in a WLAN system,

   Detecting a first frame comprising a TXOP duration field;

   Updating a NAV timer maintained by the STA based on the TXOP period field of the first frame to protect a TXOP of another STA; And

   If the NAV timer is 0, performing channel access for frame transmission of the STA;

   In updating the NAV timer, if the TXOP period field is a specific value that is not a valid TXOP period, the STA assumes that the NAV timer is zero under the assumption that the first frame is the last frame transmitted in the TXOP of the other STA. Reset and perform the channel access based on an extended inter-frame space (EIFS) operation.
2. The method of claim 1,

   If the TXOP period field is the specific value, the STA resets the NAV timer to zero after waiting for an EIFS period.
3. The method of claim 1,

   And when the TXOP period field is the specific value, the STA confirms that the channel is idle for a sum of an EIFS period and a backoff period after resetting the NAV, and transmits the frame of the STA.
4. The method of claim 1,

   The TXOP period field corresponds to 7-bits included in the signal field of the first frame,

   Wherein the particular value is a value filled with all zeros of the 7-bits or corresponds to decimal 126.
5. The method of claim 1,

   If the TXOP period field of the first frame indicates the valid TXOP period in units of 128 us, and the previous update of the NAV timer is performed in units of 128 us, only when the current value of the NAV timer is smaller than the valid TXOP period. The NAV update is performed,

   If the TXOP period field of the first frame indicates the valid TXOP period in units of 8 us, and a previous update of the NAV timer is performed in units of 128 us, the TXOP period field may be used as the valid TXOP period regardless of the current value of the NAV timer. How NAV update is performed.
6. In a station (STA) for updating a network allocation vector (NAV) timer in a WLAN system,

   transmitter;

   receiving set; And

   Detecting a first frame including a transmission opportunity duration field through the receiver and based on the TXOP duration field of the first frame a NAV timer maintained by the STA to protect the TXOP of another STA. A processor for updating, and performing channel access through the transmitter for frame transmission of the STA when the NAV timer is 0,

   In updating the NAV timer, when the TXOP period field is a specific value other than a valid TXOP period, the processor sets the NAV timer to 0 on the assumption that the first frame is the last frame transmitted in the TXOP of the other STA. And perform the channel access based on an extended inter-frame space (EIFS) operation.
7. In a method for transmitting a frame by a station (STA) in a WLAN system,

   Setting a TXOP duration value to which the user wants to be protected in a first transmission opportunity duration field of the first frame;

   Transmitting the first frame; And

   Transmitting a second frame including a second TXOP period field,

   If the second frame is the last frame transmitted in the TXOP of the STA, the STA truncates the remaining TXOP by setting the second TXOP period field to a specific value rather than a valid TXOP period,

   The specific value is a value that invokes an extended inter-frame space (EIFS) operation of a third party STA.
8. The method of claim 7, wherein

   If the second TXOP period field is the specific value, the remaining TXOP is truncated after an EIFS period.
9. The method of claim 7, wherein

   If the second TXOP period field is the specific value, the third STA confirms that the channel is idle for the sum of the EIFS period and the backoff period after the remaining TXOP is truncated and transmits a frame. , Way.
10. The method of claim 7, wherein

    The second TXOP period field corresponds to 7-bits included in the signal field of the second frame.

    Wherein the particular value is a value filled with all zeros of the 7-bits or corresponds to decimal 126.
11. The method of claim 7, wherein

    When the second frame is a frame immediately before the last frame transmitted in the TXOP of the STA, the STA is configured to perform the second TXOP period based on a second time unit smaller than the first time unit used in the first frame. Setting a field to the valid TXOP period.
12. In the station (STA) for transmitting a frame in a WLAN system,

    A processor configured to set a TXOP duration value to be protected by the first transmission opportunity duration field of the first frame; And

    Under the control of the processor, a transmitter for transmitting the first frame and transmitting a second frame including a second TXOP period field;

    If the second frame is the last frame transmitted within the TXOP of the STA, the processor truncates the remaining TXOP by setting the second TXOP period field to a specific value rather than a valid TXOP period,

    The specific value is a station that invokes an extended inter-frame space (EIFS) operation of a third party STA.

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